AP402
     AIR POLLUTION
ENGINEERING  MANUAL
          SECOND EDITION

         Compiled and Edited
               by
          John A. Danielson


   AIR POLLUTION CONTROL DISTRICT
      COUNTY OF LOS ANGELES
    ENVIRONMENTAL PROTECTION AGENCY
      Office of Air and Water Programs
  Office of Air Quality Planning and Standards
     Research Triangle Park, NX.  27711

             May 1973

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The AP series of reports is published by the Technical Publications Branch of the
Information Services Division of the Office of Administration for the Office of Air
and  Water Programs,  Environmental Protection  Agency,  to report the results of
scientific and engineering studies,  and information  of  general interest in the  field
of air pollution. Information reported in this series includes coverage of intramural
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agencies, research institutes, and industrial organizations.   Copies  of AP reports
are available free of charge to Federal employees,  current contractors and grantees,
and nonprofit  organizations - as supplies permit  -  from the Air Pollution Technical
Information Center,  Environmental Protection  Agency, Research Triangle Park,
North Carolina 27711 or from the Superintendent of Documents.
                            '   Publication No. AP-40
                 For sale by the Superintendent of Documents, U S (lovernment Printing Office
                                   Washington, D (' 21)402
                                  Stock No 055-003-0(1051)-!)
                                         11

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                                     FOREWORD
As  concern for the quality of the atmosphere has grown, so also has the response to that
concern.   Federal, State, and local programs are assuming increasingly greater respon-
sibility in the development and practice of the many disciplines that contribute to under-
standing and resolution of the air pollution problem.

Rapid  program expansion imposes even greater demands for the dissemination of knowl-
edge in the field of air  pollution control.  Much work has been accomplished by compe-
tent scientists and engineers. However, in many instances, the experience gained has not
been transcribed and organized into a form readily accessible to those most in need of
information.

We are pleased,  therefore, to have the opportunity to make available this second edition
of the  Air Pollution Engineering  Manual.  Distilling as it does  the equivalent  of hundreds
of man-years of painstaking engineering innovation in the air pollution control field under
one cover, it has become a valuable—if not indispensable—tool.

The manual is an outgrowth of the practical knowledge gained by the technical personnel
of the  Los  Angeles County Air Pollution Control District,  long recognized as outstanding
in the  field.  District personnel  have worked closely with industry to develop emission
controls where none formerly existed.

It •will  be noted that there are categories of industrial emissions that are not discussed.
The reason is that engineering control applications are described for only those industries
located in Los Angeles  County.

Realizing the  value  of this manual to the field of air pollution, Mr. Robert L.  Chass, Air
Pollution Control Officer of Los Angeles County, has authorized the up-dating of the manual
into this  second edition.  The editorial and  technical content were developed  exclusively
by the  District.  The staff, in turn, was supervised during  the development of the manual
by Mr. Robert G.  Lunche, Chief Deputy Air Pollution Control Officer,  and Mr.  Eric
Lemke, Director of Engineering.  Mr.  John A. Danielson,  Senior Air Pollution Engineer,
has again served as editor.

The Environmental  Protection Agency, recognizing the need for such a manual, is pleased
to serve as publisher.

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                                      PREFACE
The first edition of the Air Pollution Engineering Manual was acknowledged by its readers
to be an  outstanding and practical manual on the control of air pollution.  It has been in
wide demand throughout the United States and in many other parts of the world.  Recog-
nizing the need for an up-dated version, Editor John A. Danielson and the engineers of
the Los Angeles County Air Pollution Control District have prepared this second edition.

The first edition  was  -written  in the early sixties.  Since that time, many changes have
occurred in the field of air pollution control, and this second edition reflects these changes.
The control  of photochemically reactive organic  solvent emissions is but one example,
and  a new chapter  is devoted to this subject. Reducing  the formation  of oxides  of nitrogen
in combustion processes by improved burner and furnace designs is another new innova-
tion. Improved versions of afterburner control devices are included.  This second edition
also contains  a comprehensive index to aid  the  reader in locating quickly the subject of
his choice.

The manual  deals  with the control  of  air  pollution at specific sources.  This approach
emphasizes  the practical engineering problems  of design  and operation associated with
the many sources  of  air  pollution.   These sources include metallurgical,  mechanical,
incineration, combustion,  petroleum, chemical, and organic-solvent-emitting  processes.

The manual  consists  of 12 chapters, each by different authors,  and 5 appendices.   The
first five chapters treat the history of air pollution in Los Angeles County,  the types of
contaminants,  and  the  design of air  pollution control devices.  The remaining chapters
discuss the control of air pollution from specific sources. A reader interested in control-
ling air pollutionfrom a specific source can gain the information needed by referring only
to the chapter of the manual dealing with that source.  If he  then desires more general
information  about  an  air  pollution control device, he can refer to other chapters.  It is
suggested that Chapter  1 be read since it cites Los Angeles County prohibitory rules  that
regulated the degree of control efficiency required when the manual was written in 1971.

It is  recognized that air pollution problems of one area can be quite different  from those
of another area.  The air pollution problems presented in this  manual originate in indus-
trial and commercial  sources in the Los Angeles area.  Consequently, some processes,
e.g. , the burning of coal in combustion equipment, are not mentioned.  Furthermore, the
degree  of air  pollution control strived  for in this manual corresponds to the degree of
control demanded by air pollution statutes of the Los Angeles County Air Pollution Control
District.   Many other  areas  require  less  stringent  control  and  permit less efficient
control devices.

Sole responsibility for the information is borne by the District, which presents this second
edition  of the  manual for the advancement of national understanding of the control of air
pollution from stationary sources.
                                              Robert L. Chass
                                              Air Pollution Control Officer
                                              County of Los Angeles

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                                ACKNOWLEDGMENT
Under  the  provisions of the California law creating the Los Angeles County Air Pollution
Control District, the Board of Supervisors is empowered to act as the Air Pollution Con -
trol Board. Responsible for  supervision  and policy determination for the District,  their
firm support of needed air pollution control measures has advanced engineering capability
in this field to a high degree.  The information gained in Los Angeles County is applicable
to the improvement of air quality wherever air pollution is experienced.  Without the sup-
port of this Board,  the information presented here would not have  been possible.
                           THE BOARD OF SUPERVISORS
                             OF LOS ANGELES COUNTY

                         PETER F. SCHABARUM,  Chairman
                                    First District


         KENNETH HAHN                                  JAMES A. HAYES
         Second District                                    Fourth District

         ERNEST E.  DEBS                                 BAXTER WARD
         Third District                                     Fifth District

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                         CHAPTER  1
                     INTRODUCTION
      JOHN A.  DANIELSON, Senior Air Pollution Engineer

       ROBERT L. CHASS,  Air Pollution Control Officer
ROBERT G. LUNCHE,  Chief Deputy Air Pollution Control Officer

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                                              CHAPTER 1
                                           INTRODUCTION
The past two decades have witnessed remarkable
progress  in  the development of reasonable engi-
neering solutions  for  controlling  industrial and
commercial sources of air pollution.  This man-
ual presents the practical technical  knowledge ac-
quired through more than 25 years of experience
by the Engineering Division of the Los Angeles
County Air  Pollution Control District.  With the
rich background of experience attained by govern-
ment  and industry,  this  engineering knowledge
can now be applied to solving specific community
air pollution problems throughout the world.


         THE LOS ANGELES BASIN

Los Angeles and its environs have special prob-
lems  peculiar  to  the area.   Los Angeles County
is the largest heavily industrialized, semitropical
area  in the world.   It comprises  4, 083 square
miles and contains  more than  75 incorporated
cities and large scattered unincorporated areas.
Its population has more than doubled since  1939,
and industry has  expanded  from  approximately
6,000 establishments  in  1939 to about  25,000  in
1970.

Topographical  and meteorological conditions ag-
gravate the effects of  the pollution produced by
this population and this industry in the Los Angeles
Basin,  The average  wind velocity there is less
than  6 miles per  hour.  The light winds that do
develop are  relatively  ineffective  in carrying off
the polluted  air because of the  temperature in-
versions  that prevail  approximately  260 days  of
the year.  The height  of the inversion base var-
ies from ground level to 3,  000 feet.  These in-
versions  have  been most  noticeable  during the
summer  months,  but in  the last  few years ex-
treme inversions have occurred in the  November-
Dec ember period as well. Their  effect is to limit
vertical distribution of atmospheric pollution while
local winds from the west are moving the air over
the area  during the day.

In Los Angeles  County, the complex mixture  of
smoke, dusts, fumes,  gases, and other  solid and
liquid particles is called "smog. " This smog may
produce a single effect or a combination of effects,
such  as  irritation of eyes,  irritation of throats,
reduction of visibility,  damage  to  vegetation,
cracking  of rubber,  local nuisances, and a host
of other effects, real and fancied.

Any community suffering  from  an air  pollution
problem  must  inevitably turn its attention to the
 operations  of industry,  because these operations
 have been most frequently associated with com-
 munity air pollution problems.   Accordingly,  the
 Los Angeles  County control program  was first
 directed to industrial operations.

 Although the exactyear when smogwas first rec-
 ognized in Los Angeles  is  not  known,  the first
 public demands for relief from air pollution appear
 to have been made immediately after World War II
 (Weisburd, 1962).  Newspapers,  in particular,
 began to expose the problem in the public interest.
 As a consequence, air pollution control groups
 were formed under  health department jurisdic-
 tion- first by  the  city of Los Angeles, and then
 by the county of Los Angeles in the unincorporated
 areas.   These  control  efforts  failed, however,
 because of the  multiplicity and inadequacy  of the
 control jurisdictions.  It was soon apparent that
 adequate  control could be  exercised  only by  a
 single  authority with jurisdiction over the entire
 pollution zone- the incorporated and unincorpo-
 rated areas of Los Angeles County.   As a result,
 Assembly  Bill  No. 1 was presented to the 1947
 session of the California Legislature.  This Bill
 proposedconsolidation of control measures.  The
 Legislature voted to add Chapter 2,  "Air Pollution.
 Control District, " to Division  20  of  the Health
 and Safety Code relating to the  control and sup-
 pression of air pollution.   Thus, the first state-
 wide air  pollution control statute was enacted.
 This statute,  The  California Act,  is an enabling
 type of legislation that legalizes the establishment
 of air pollution control districts  on a local option
 basis by the counties of California.


          RULES  AND  REGULATIONS
          IN LOS  ANGELES COUNTY

 Under authority of the Health and Safety Code,  the
 Board  of Supervisors of Los Angeles  County en-
 acted, on December 30,  1947, the first rules and
 regulations guiding the conduct of the Los Angeles
 County Air Pollution Control District.  Additional
 rules and  regulations were enacted  as the need
 arose.  The rules are contained in  eight  regula-
 tions,   as follows:  (I) "General Provisions, "  (II)
 "Permits,  " (III) "Fees," (IV) "Prohibitions,"  (V)
 "Procedure Before the Hearing Board, " (VI) "Or-
chard or Citrus Grove Heaters,"  (VII) "Emergen-
cies," (VIII) "Orders for Abatement. "

It is important that the reader realize that most of the
revisions of the  second edition of this manual were
 234-167 O - 77 - 3

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                                             INTRODUCTION
written in  1971.  The degree of air pollution control
achieved, therefore,  relates to 1971 rules and regu-
lations.  Since that  time,  there have  been many
changes, particularly to the prohibition rules.  For
example, Rule 50, which limited emissions to Number
2 on the Ringelmann Chart in 1971, now limits emis-
sions to Number  1.   The rules summarized in  this
chapter are those which were effective as of January
1, 1971. The current rules, i.e., those which were
effective January 1, 1973, are shown in Appendix A.
In using this manual, the reader  should be aware
of certain provisions of the 1971  rules.  Of most
importance are Regulations II  and IV, "Permits"
and "Prohibitions, "  respectively.

REGULATION II: PERMITS

The permit system of the Los Angeles County Air
Pollution Control District  is one of the most im-
portant features of  the air pollution control pro-
gram.  A  diagram of  the permit system and how
it operates is given in Figure  1.  In general,  the
system requires owners,  operators,  or lessees
to apply for permits to  construct and operate any
equipment  capable of  emitting air contaminants.
If the  applicant's plans,  specifications, and field
tests  show that the  equipment can  operate within
the limits  allowed by law, then a  permit is grant-
ed.  If the  equipment is capable  of emitting con-
taminants  that create a public nuisance or violate
any section of the State Health or Safety Code  or
the rules and regulations of the Air  Pollution Con-
trol District,  then a permit is denied.

 This permit system is  effective because it elimi-
 nates use  of  equipment  that emits excessive air
 contaminants or reduces emissions to within allow-
 able  limits by requiring  that  the  design of the
 equipment or of the process be modified or that
 adequate control  equipment  be used.  The con-
 struction  or operation of control equipment must
 also be authorized  by permit.   Thus, the permit
             system  is a  positive means  of  controlling  air
             pollution.
             In using  this regulation,  the members of the  En-
             gineering Division of the Air  Pollution Control
             District  have  reviewed the design and  approved
             or  denied the construction or  operation of thou-
             sands of industrial and  commercial  enterprises
             in Los Angeles County.   These  25 years  of ex-
             perience provide  the background  for much of the
             data in this manual.

             REGULATION IV:  PROHIBITIONS

             The  rules  in Regulation IV prohibit the emission
             of certain air contaminants and regulate certain
             types of  equipment.  Because these rules apply to
             engineering problems and  touch  upon many sci-
             ences, they require  extraordinary care for their
             framing.  The prohibitions that were in effect at
             the  time this  manual was written (1971) and that
             are pertinent to readers of this manual  will now
             be discussed.

             Rule  50:  The Ringelmann  Chart

             Rule  50 sets  standards  for reading densities and
             opacities  of visible emissions in  determining vi-
             olation of, or compliance with, the law.   It limits
             to 3 minutes in any hour  the discharge, from any
             single source,  of any air  contaminant that is (1)
             as dark as or darker than that designated as Num-
             ber  2 on the Ringelmann  Chart,   or  (2) of  such
             opacity  as to  obscure an  observer's  view to a
             degree equal to or greater than that to which smoke
             described in (1) does.

             Rule  51:  Nuisance
             According to Rule 51, whatever tends  to  endanger
             life  or property or whatever affects the health of
             the community is  a public nuisance. The nuisance
             must, however,  affect the community at large and
             not merely  one or a few  persons.   A  nuisance
                                                                                   Enforcement
                                             SUBMISSION OF CONSTRUCTION PLANS
                                             	I	
                          AUTHORITY TO CONSTRUCT ISSUED
                PERMIT TO OPERATE GRANTED
                INSPECTION OF EQUIPMENT
                A Continuing Process
                REVOCATION OF PERMIT
                Or action in criminal or civil
                court if inspection discloses
                defects or improper operation.
                                                   PERMIT TO OPERATE DENIED
APPEAL OF DENIAL
To hear i nq board .
                                                                              AUTHORITY TO CONSTRUCT DENIED
                                                                                   APPEAL OF DENIAL
                                                                                   To heart nq board  or
                                                                                   new plans submitted.
PETITION FOR VARIANCE
Submitted to hearing board to permit
operation for limited time while control
equipment is developed or installed.
    Figure  1.   The  permit  system  and  how  it  operates  when  industry  seeks  to  install  equipment  that  may
    pollute  the air.

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                                         Rules and Regulations
becomes  a crime if it contributes  seriously to the
discomfort of an area,

 Rule  52:  Particulate Matter

Rule 52 establishes the maximum allowable limits
for the discharge of particulate matter.  It limits
the discharge of this  contaminant from any source
to a maximum concentrationof 0. 3 grainper cubic
foot  of gas  at  standard conditions  of 60° F  and
 14. 7 psia.   This  rule does  not,  however,  apply
when the particulate matter is a combustion con-
taminant. *

 Rule  53:   Specific Contaminants

Rule 53 establishes the maximum allowable limits
for the discharge of  sulfur compounds and com-
bustion contaminants as follows:

   Rule 53a-.  Sulfur compounds calculated as sul-
   fur dioxide (SO2):   0. 2 percent,  by volume.
   Rule 53b:  Combustioncontaminants:  0. 3 grain
   per cubic foot of  gas calculated  to 12 percent
   of carbon dioxide (CC>2) at  standard conditions.
   Inmeasur ing the combustion contaminants from
   incinerators used to dispose of combustible ref-
   use by burning,  the CO2 produced by combus-
   tionof any liquid or gaseous fuels shall be ex-
   cluded from  the  calculation to 12  percent of
   CO2.

Rules 53.1,  53.2, and  53.3: Sulfur  Production
and  Sulfuric Acid Plants
These rules  set maximum allowable concentra-
tions of  sulfur dioxide in the effluent gases from
the sulfur production and sulfuric acid plants at
500 parts per million.  The standards further limit
the total  weight of sulfur  dioxide  emissions from
these plants  to no more than 200 pounds per hour.
In the case  of sulfuric production plants, a further
limitation in the maximum allowable concentra-
tions of hydrogen  sulfide  of 10 parts  per million.
was set.  Sulfur production plants must meet the
new emission standards by June  30, 1973.  Sulfuric
acid  plants  must  meet the  new   standards  by
December 31, 1973.

Rule  54:  Dust and Fumes

Rule 54  establishes the maximum allowable lim-
its for the discharge of dusts and fumes according
to the process weightsf of materials processed
-"Particulate matter is any material, except uncombined water,
 that exists in a finely divided form as a liquid or solid at
 standard conditions.  6 combustion contaminant is particulate
 matter discharged into the atmosphere from the burning of any
 kind of material containing carbon in a free or combined state.
TProcess weight is  the total weight of  all materials intro-
 duced into any specific process that is capable of causing
 any discharge into the atmosphere.  Solid fuels charged are
 considered part of the process weight, but liquid and gas-
 eous fuels and combustion air are not.  The "process weight
 per hour" is derived by dividing the  total process weight
 by the number of hours in one complete operation from the
 beginning of any given process to the  completion thereof, ex-
 cluding any time during which the equipment is idle.
per hour. The maximum allowable weight in pounds
per hour is graduated according to the weights of
materials processed per hour.   The maximum
emission allowed is 40  pounds per hour where
60,000or morepounds are processed in the equip-
ment in any given hour.


Rule 56:  Storage of Petroleum Products

Rule  56 sets  forth the  type of equipment that can
be  used for  the  control  of hydrocarbons arising
from, the storage of  gasoline and certain petrole-
um distillates.  Rule 56 provides that any tank of
more than 40,000-gallon capacity used for storing
gasoline or any petroleum distillate having a vapor
pressure of 1 -1 /Zpsia or  greater must be equipped
witha vapor loss control device suchas apontoon-
type or double-deck-type floating roof or a vapor
recovery system capable of collecting all emis-
sions.
Rules 57 and  58: Open Fires and  Incinerators

Rules 57 and 58 ban the  burning of combustible
refuse in open fires and single-chamber incinera-
tors in the Los Angeles Basin,
Rule 59: Oil-Effluent Water  Separators

Rule 59 regulates the type of equipment that can
be used for the control of hydrocarbons from oil-
water  separators.  It provides that this equipment
must either be covered,  or  provided with a float-
ing roof, or equipped with a vapor recovery sys-
tem, or fitted with other equipment  of equal effi-
ciency if the effluent handled by the separator con-
tains a. minimum of 200 or more gallons  of petro-
leum products per day.
Rule 61: Gasoline Loading into Tank Trucks

and Trailers

Rule 61 sets forth the type of  control equipment
that can  be used for the control of hydrocarbons
resulting from  the loading  of  gasoline  into tank
trucks.  It  provides  for the installation of vapor
collection and disposal systems on bulk gasoline-
loading facilities where more than 20, 000  gallons
of gasoline  are loaded per day and requires that
the loading facilities be  equippedwith a vapor col-
lection and disposal system.  The disposal system
employed must  have  a minimum  recovery effi-
ciency  of 90 percent or  a variable vapor space
tank compressor and fuel gas system of such capac-
ity  as  to handle all vapors and gases displaced
from the trucks  being loaded.

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                                           INTRODUCTION
Rules  62,  62.1, and 62.2:  Sulfur Content  of  Fuels

Rules 62, 62. 1, and 62.2 prohibit the burning in
the Los Angeles Basin of any gaseous fuel contain-
ing sulfur compounds in excess of 50 grains per
100 cubic feet of gaseous fuel (calculated as hydro-
gen sulfide  at standard conditions) or any liquid
or solid fuel having a sulfur  content in  excess of
0. 5 percent by weight.
Rule 63:  Gasoline Specifications

Rule 63 prohibits the sale and use of fuel for motor
vehicles having a degree of unsaturation exceeding
a bromine number of 30.
Rule 66.2:  Disposal and  Evaporation of Solvents

Rule 66. 2 prohibits the  disposal of more  than
1-1/2 gallons per day  of any photochemically re-
active  solvent by any means that will permit the
evaporation of such solvent into the atmosphere.
Rule 67:  Fuel-Burning Equipment

Rule  67  requires that  a person  shall not build,
erect, install, or expand any fuel-burning equip-
ment unless the discharge  of  contaminants will
not exceed 200 pounds per hour of sulfur dioxide,
or  140 pounds per  hour of nitrogen oxides,  or
10 pounds per hour of combustion contaminants.
Rule 64:  Reduction of Animal  Matter

Rule 64  requires  that malodors from all equip-
ment used for reduction of  animal matter either
be  incinerated at temperatures of not less than
1, 200° F for a period of not less than 0. 3 second
or  processed in an odor-free manner under con-
ditions stated in the rule.
Rule 65: Gasoline Loading into Tanks

Rule 65 prohibits the loading of gasoline into any
stationary tank with a capacity of 250 gallons  or
more  from  any tank  truck  or  trailer,   except
through a permanent submerged fill pipe,  unless
such tank is  equipped with a  vapor loss control
device as described in Rule 56, or is a pressure
tank as described in Rule 56.
Rule 68: Fuel-Burning Equipment - Oxides of
Nitrogen

Rule 68 requires that a person shall not discharge
into the atmosphere from any fuel-bearing equip-
ment  having a heat input of more than 1775 x 10"
Btu per  hour, flue  gas having a concentration of
nitrogen oxides at 3 percent oxygen in excess of
the following:
                         Effective date
Fuel
Gas, ppm
Liquid or
solid, ppm
December 31,
1971
225
325
December 31,
1974
125
225
ROLE  OF  THE  AIR  POLLUTION  ENGINEER
Rule 66: Organic Solvents

Rule 66 requires that photochemically  reactive
organic solvent emissions in excess of 40 pounds
per  day (or 15 pounds  per day from processes
involving  contact  with a flame or  baking,  heat-
curing  or  heat polymerizing, in the presence of
oxygen) shall not be emitted unless controlled by
incineration,  adsorption,  or in an equally effi-
cient manner.
Clearly, as  indicated by this impressive list of
prohibitions, the rules and regulations affect the
operation of nearly every industry in Los Angeles
County. Through their enforcement, controls have
been  applied to  such diverse sources and opera-
tions  as incinerators,  open fires, rendering cook-
ers, coffee roasters, petroleum refineries, chem-
ical plants,  rock crushers,  and asphalt plants.
From the  smelting of metals to the painting  of
manufactured goods, industrial and commercial
operations have  been  brought within the scope of
the control program. This control has been accom-
plished through the use of the permit system.
Rule 66.1:  Architectural Coatings

Rule 66.1  prohibits the sale of architectural coat-
ings containing photochemically reactive solvents
in containers larger than  1-quart  capacity.  It
also prohibits diluting any architectural coating
with a photochemically reactive solvent.
ACCOMPLISHMENTS OF THE PERMIT  SYSTEM

Under the permit system every source capable of
emitting air contaminants  and constructed since
February 1948 has  needed an authorization to be
constructed  and  a permit to be operated from the

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                                         Use of This Manual
Engineering  Division of the Air Pollution Control
District.  From April  1948  through April 1969,
109,332 permits were issued by District engineers.
The  estimated value of the  basic equipment was
$1, 363, 400, 000 and that of the control equipment
•was  an  additional $152,200,000.  During this same
period,  6, 045 applications for basic and control
equipment were denied.

This wealth of engineering experience is reflected
in the contents of this manual. Nearly all the  data
presented were  acquired through the  experience
and work of the District's Air Pollution engineers
and of engineers  in industry.   Their  pioneering
efforts to stay at least one pace ahead of the prob-
lem  have produced many engineering firsts in the
control  of air pollution.


             USE  OF  THIS  MANUAL

Users of this manual should remember  that the
degree  of air pollution control discussed herein is
based upon the  prohibitions  as set forth by the
rules and  regulations of the Los Angeles County
Air Pollution Control District in effect as of  Jan-
uary 1,  1971.  In many  areas, air pollution reg-
ulations are less  stringent,   and  control devices
of lower efficiency may  be permitted.
GENERAL DESIGN PROBLEMS

This manual consists of 12 chapters and 5 appen-
dixes.   Chapters 2 through 5 present general de-
sign problems confronting air pollution engineers
in the development  of air pollution control sys-
tems.  Specifically, chapter 2 describes the types
of air contaminants encountered and chapter 3 pre-
sents design problems of hoods and exhaust sys-
tems.  Types of control  devices,  and their gen-
eral design features are discussed in chapters 4
and 5.
SPECIFIC AIR POLLUTION  SOURCES
Chapters 6  through 12 discuss the control of air
pollution from specific sources.  Each solution of
an air pollution problem  represents a separate
sectionof the text.  Many processes are discussed:
metallurgical and mechanical processes, process-
es of incineration and combustion,  and processes
associated with petroleum, chemical equipment,
and organic solvents,  each in a separate  chapter
and in that order.  Usually the process  is des-
cribed and  then the  air pollution  problem asso-
ciated with  it is  discussed,  together with  the
characteristics  of the air  contaminants  and  the
unique design features of the  air pollution control
equipment.
By this arrangement, the reader can, if he wishes,
refer only to that section discussing the specific
process in which he is interested.  If he wants to
know more about the general design features of the
air pollution control device serving that process,
he can refer  to chapters 4 and 5 on control equip-
ment.

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                      CHAPTER 2
               AIR  CONTAMINANTS
JANET DICKINSON, Assistant Chief Air Pollution Analyst

   ROBERT L. CHASS,  Air Pollution Control Officer
     W. J. HAMMING, Chief Air Pollution Analyst

  JOHN A. DANIELSON, Senior Air Pollution Engineer

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                                              CHAPTER 2
                                       AIR  CONTAMINANTS
               INTRODUCTION

 The purpose of this chapter is to describe briefly
 the parameters of an air pollution problem, par-
 ticularly  the problem of Los Angeles County; the
 measures taken to eliminate the problem; and those
 still needed.  Other chapters will  delineate, in
 detail,  the  methods  and equipment successfully
 used  in the control of emissions of air contami-
 nants from  a variety of stationary sources.

 The control program in the County of Los Angeles
 during the past 25 years has been the most effec-
 tive ever attempted anywhere.   During the same
 period, however, the county has had a phenomenal
 population explosion that has caused the emissions
 from motor vehicles to  overtake and surpass the
 gains made by control  over stationary sources.
 The net effect has been the more frequent occur-
 rence of smog symptoms over an increasingly larg-
 er area.

 Since control over motor vehicle emissions is the
 responsibility  of the state and federal govern-
 ments rather than of the local agency, substantial
 improvement  in  the situation in Los Angeles will
 probably have to await the successful implementa-
 tion of their programs.  In the interim, however,
 the Air Pollution Control District of Los Angeles
 County will continue  its efforts to reduce emis-
 sions of air contaminants from stationary sources
 wherever possible within its jurisdiction.
FACTORS  IN  AIR  POLLUTION  PROBLEMS

Literally,  any substance not normally present in
the atmosphere, or measured there in greater than
normal concentrations,  should be considered an
air contaminant.  More practically, however, a
substance is not so labeled until its  presence and
concentration produce or contribute to the produc-
tion of some deleterious effect.

Manyforeign substances find their way into the at-
mosphere as the  result of some  human activity.
Under normal circumstances, they diffuse through-
out a rather large volume  of air and do not accu-
mulate  to potentially harmful  concentrations.
Under less favorable conditions, however,  the air
volume available for this diffusion becomes inade-
quate.  The  concentrations of  some foreign sub-
stances then may reach a level  at which  an air
pollution problem  is created.
Air pollution problems may exist over a  small
area as  a  result of just one emission source or
group of sources or they may be widespread and
cover a  whole  community or urban complex in-
volving a variety of sources. The effects thatcause
the situation to be regarded as a problem may be
limited in scope and associated with a  single kind
of contaminant or they may be the variable results
of complexatmospheric interaction of a number of
contaminants.

The factors that contribute to the creation of an
air pollution problem  are both natural and man
made.   The natural factors are primarily mete-
orological, sometimes geographical, and are gen-
erally beyond man's  sphere of control, whereas
the manmade factors involve the emission of air
contaminants in quantities sufficient  to produce
deleterious  effects and are within man's sphere
of control.  The natural factors that restrict the
normal dilution of contaminant emissions include:
temperature inversions, which  prevent diffusion
upwards; very low wind speeds,  which do little to
move emitted substances away from their points
of origin; and geographical terrain, which causes
the flow to follow certain patterns and carry from
one area to another whatever the air contains.  The
manmade factors  involve  the contaminant emis-
sions resulting from some human activity.

The predominant kind of air pollution problem in-
volves  simply  the overloading of the atmosphere
with harmful or unpleasant materials.  This is
the problem usually associated with an industrial
area, and  the  type that has been responsible for
all  the killer air  pollution incidents of the past.
Itis also the type of problem most readily solved,
if the need and desire to do so are great enough.
Contaminants frequently associated with this kind
of problem include:  Sulfur compounds (sulfur
oxides, sulfates, sulfides, mercaptans); fluorides;
metallic  oxides; odors; smoke; and all types of
dusts and fumes. The harmful effects may be such
as to cause illness and death to persons and ani-
mals, damage to vegetation, or just annoyance and
displeasure to persons in affected areas.

During the past 25 years, however, another kind
of air pollution problem  has  evolved--that pro-
duced by the photochemical  reaction  of organic
chemicals  and oxides of nitrogen in the presence
of sunlight.  The effects of this type of air pollu-
tion were first  noted  in the Los Angeles area in
the mid-1940's, butthe cause was not then known.
                                                 11

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12
                                      _AIR  CONTAMINANTS
nor was there any apparent relationship between
the initial effects and air pollution.

The effect first noted  was damage to vegetation.
This was followed by irritation of the eyes, marked
reduction in visibility not related to unusual quan-
tities of atmospheric moisture or dust, and later,
unexplained acceleration of the aging  of rubber
products as evidenced by cracking. Early research
demonstrated and additional research confirmed
that all these  effects  were produced by the reac-
tion in the  atmosphere  of organic compounds,
principally hydrocarbons,  and  nitrogen dioxide,
and  that  the  cracking  of  rubber  products was
caused specifically by one of the products of these
reactions,  ozone.

Initially,  only a relatively  small portion  of the
Los Angeles Basin was affected, but a tremendous
influx  of new  residents and new industrial growth
during the  past 20 years have caused a continuous
enlargement  of  the  affected area. Within  this
area,  certain local  problems  related  to single
sources and  groups of  sources also exist, but
they are  of  less  significance  than the  overall
problem of photochemical smog.


     TYPES  OF AIR  CONTAMINANTS

Substances  considered  air  contaminants in Los
Angeles Countyfall into three classes on the basis
of their chemical composition and physical state.
These  are  (1)  organic gases, (2) inorganic gases,
and (3) aerosols.  Each class may include many
different compounds, emanate  from several dif-
ferent  sources,  and  contribute to the production
of a number  of characteristic  smog effects.   A
brief summary of some  of the contaminants, their
principal sources, and  their significance is pre-
sented in Table  1.

ORGANIC GASES

The first group, organic  gases, consists entirely
of compounds of carbon and hydrogen  and their
derivatives.   These include all classes  of hydro-
carbons (olefins, paraffins, and aromatics)  and
the compounds formed when some of the hydrogen
in the original compounds  is replaced by oxygen,
halogens, nitro or other substituent groups.  The
latter  are the hydrocarbon  derivatives.

The principal origin of hydrocarbons is petroleum,
and the principal sources of emissions of hydro-
carbons and their derivatives are those related  to
the  processing  and  use of petroleum  and its
products.  Hydrocarbons are released to the atmo-
sphere during the  refining of petroleum, during
the transfer  and storage of petroleum products,
and during the use of products such as fuels, lu-
bricants,  and solvents.  Derivatives  of hydro-
carbons can also be released into the atmosphere
in connection with these processes and in connec-
tion  with  their manufacture and use.  They can
even be formed in the atmosphere as the result
of certain photochemical reactions.


Current Sources in  Los  Angeles  County

More specifically,  the principal current  sources
of organic gases in Los Angeles County are listed
in Table  1.
Hydrocarbons

The most  important source, by far,  of emission
of hydrocarbons is the use of gasoline for the oper-
ation of 4-1/4 million motor vehicles. This source
alone accounts for approximately  1,610 tons per
day, or 65  percent of the total emissions.  Of this
quantity, about 73 percent is attributed to exhaust
emissions;  5  percent,  to crankcase  emissions ;
and 22  percent,  to evaporation of fuel from car-
buretors and  gasoline  tanks.  Except for about 2
percent of the total, the balance of the hydrocarbon
emissions  are divided between the petroleum in-
dustry  and industrial  and  commercial uses  of
organic solvents.

Kinds of hydrocarbons contributed by these sources
vary considerably.  Auto exhaust, for example,  is
the principal  source of olefins  and  other photo-
chemically reactive  hydrocarbons, though other
sources connected  with  the operation of  motor
vehicles and with the processing  and handling of
gasoline contribute indirect proportion to the  ole-
fin content of the  gasoline  marketed  here.   All
these sources contribute paraffins  and aromatics,
and emissions of hydrocarbons from solvent usage
are composed almost entirely of these two classes.

Hydrocarbon derivatives

Of the 300 tons of hydrocarbon derivatives (or sub-
stituted hydrocarbons) emitted to the atmosphere
of Los Angeles County each day, about three-fourths
results from solvent uses such as surface coating,
degreasing, and dry cleaning, and other industrial
and commercial processes.  The balance is in-
cluded  in the products of combustion of various
petroleum fuels and of incineration of refuse.  The
substituted hydrocarbons emitted to the atmosphere
by industrial and commercial use of organic sol-
vents include oxygenates, such as aldehydes,  ke-
tones, and alcohols; organic acids; and chlorinated
hydrocarbons.  Most hydrocarbon derivatives as-
sociated with surface coating are oxygenates whose
presence canbe related either to the solvent itself
or to the products of the partial oxidation involved
in  the drying of the coated objects.   The hydro-
carbon derivatives associated with degreasing and
dry cleaning are mostly chlorinated hydrocarbons.
The derivatives associated with combustion, either

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                            Types of Contaminants
                                                                                      13
Table I.   AIR CONTAMINANTS IN LOS ANGELES COUNTY, THEIR PRINCIPAL
                SOURCES AND SIGNIFICANCE (JANUARY 1971)
Emitted contaminant
Organic gases
Hydrocarbons
Paraffins
Olefins
Aromatics
Others
Oxygenated hydrocarbons
(Aldehydes > ketones,
alcohols, acids)
Halogenated hydrocar-
bons (Carbon tetrachlo-
ride, trichloroethylene,
etc)
Inorganic gases
Oxides of nitrogen
(Nitric oxide, nitrogen
dioxide)
Oxides of sulfur
(Sulfur dioxide, sulfur
trioxide)
Carbon monoxide
Aerosols
Solid particles
Carbon or soot particles
Metal oxides and salts
Silicates and mineral
dusts
Metallic fumes
Liquid particles
Acid droplets
Oily or tarry droplets
Paints and surface
coatings
Principal sources

Processing and transfer of
petroleum products; use of
solvents; motor vehicles
Processing and transfer of
gasoline; motor vehicles
Same as for paraffins
Use of solvents; motor
vehicles
Use of solvents

Combustion of fuels; motor
vehicles
Combustion of fuels; chem-
ical industry
Motor vehicles; petroleum
refining; metals industry;
piston-driven aircraft
Combustion of fuels; motor
vehicles
Catalyst dusts from re-
fineries; motor vehicle
exhaust; combustion of
fuel oil; metals industry
Minerals industry; con-
struction
Metals industry
Combustion of fuels ;plating;
battery manufacture
Motor vehicles; asphalt
paving and roofing; asphalt
saturators; petroleum re-
fining
Various industries
Significant effects
Plant damage


X
X
(Atypical)



X
X
(Specific type)







Eye
irritation

X
X
X
X
X

X
X







Oxidant
formation

X
X
X
X
X

X








Visibility
reduction

X
X
X
X
X

X
X

X
X
X
X
X
X

Danger
to
health







X
X
X
X
(Under
special
circum-
stances)





Other



Odors

Odors









Property
damage

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14
                                        AIR CONTAMINANTS
of fuels or of refuse,  are products of incomplete
combustion and are almost entirely oxygenates.
Thus, the  composition of atmospheric emissions
of hydrocarbon derivatives is currently about one-
fourth to one-third chlorinated  hydrocarbons and
two-thirds to three-fourths oxygenates.

In addition to the hydrocarbon derivatives con-
tributed by direct emissions,  the atmosphere of
photochemical  smog contains similar compounds
formed there as a result of the reactions that pro-
duced the  smog.   These substituted hydrocarbons
include oxygenates,  such as aldehydes,  ketones,
alcohols,  and organic acids, and nitrogen-contain-
ing compounds, such  as  the  peroxyacyl nitrates
and, perhaps,  nitro olefins.   These compounds
are the products of partial oxidation of hydrocar-
bons and some  derivatives in the atmosphere and
of atmospheric reactions between oxides of nitro-
gen and organic  gases in sunlight, but not in the
dark.

Significance  in Air  Pollution Problem

Hydrocarbons and  their derivatives are important
factors in the air pollution problem in Los Angeles
County because of  their ability to participate in the
atmospheric reactions thatproduce effects associ-
ated with photochemical smog.  Not  all hydro-
carbons and their derivatives have the same  poten-
tial for smog formation.  The most reactive  group,
the  olefins (unsaturated hydrocarbons),  can react
with atomic oxygen, formed from the dissociation
of nitrogen dioxide  in sunlight, or with ozone to
produce plant damage, eye irritation,  visibility-
reducing aerosols, oxidants, and additional  ozone.
Branched paraffinic hydrocarbons can  also react
when nitrogen dioxide is present  in sunlight to
produce some oxidants or ozone, but the reaction
depends specifically upon the concentration ratio
of nitrogen oxides and paraffins.  In Los Angeles
this  ratio in the  atmosphere is not conducive  to
this formation for normal straight-chain paraffins.
Eye irritation and plant damage  are  not caused by
paraffinic hydrocarbons in general.

The second most important group of  hydrocarbons
is the aromatic hydrocarbons, particularly those
having various substituent groups.  These com-
pounds can also react with atomic oxygen formed
from the sunlight  dissociation of nitrogen dioxide
to produce all the same  types and kinds of smog
effects.  Sometimes,  however,  depending upon a
high ratio of nitrogen oxides to hydrocarbon, a
different kind of plant damage results from these
reactions.

The  hydrocarbon  derivatives,  particularly some
of the aldehydes and  ketones, and even some of the
chlorinated hydrocarbons, can also  react -with
nitrogen dioxide in the  atmosphere to produce eye
irritation, aerosols, and ozone.  Further, some
of the aldehydes and nitro derivatives are, them-
selves, lachrymators and some of the chlorinated
hydrocarbons are rather toxic.  Except  for  the
peroxyacyl  nitrates,  these compounds  are  not,
however,  generally associated with production of
plant damage.


The hydrocarbons are further indicted  because
photochemical reactions in which they participate
sometimes produce hydrocarbon derivatives such
as aldehydes, ketones, and nitro-substituted  or-
ganics, •which  can in  turn  react to increase the
production of smog effects.


INORGANIC GASES

Inorganic gases constitute the second major group
of air contaminants in Los Angeles County. They
include oxides of nitrogen,  oxides of sulfur,  car-
bon monoxide,  and much  smaller quantities of
ammonia, hydrogen sulfide, and chlorine.

The principal source of all the oxides listed above
is the combustion of fuel for industrial,  commer-
cial, and domestic uses; for  transportation; for
space heating; and for  generation of power.  Addi-
tionally,  small quantities  of  sulfur oxides  and
carbon monoxide, and the total of the minor con-
stituents, ammonia,  hydrogen sulfide,  and chlo-
rine, are  emitted in connection with certain indus-
trial processes.

Current Sources in Los Angeles County
The principal sources  currently responsible for
atmospheric emissions of  each of the  important
inorganic gaseous air contaminants will now be
discussed.


Oxides of nitrogen

A number  of  compounds must be  classified as
oxides of nitrogen, but only two, nitric oxide (NO)
and nitrogen dioxide (NOz), are important as air
contaminants.  The first, nitric oxide,  is formed
through the direct combination of nitrogen  and oxy-
gen from the air in the intense heat of any com-
bustion process.  Nitric oxide in the atmosphere
is then able, in the presence of sunlight,  to com-
bine with additional oxygen to form nitrogen dioxide.

Usually the  concentrations  of  nitric oxide in the
combustion effluents constitute 90 percent or more
of the  total nitrogen oxides.  Nonetheless, since
every mole  of nitric oxide emitted to the atmos-
phere has the potential to produce a mole of nitro-
gen dioxide, one  may  not be  considered -without
the other. In fact, measurement of their  concen-
trations often provides  only  a  sum of  the  two
reported as the dioxide.

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                                       Types of Contaminants
                                                                                                   15
Of the total quantities of these contaminants  cur-
rently being  emitted  each day  in  Los Angeles
County, approximately 70  percent,  or 740 tons,
must be attributed  to  the exhaust effluents from
gasoline-powered motor  vehicles.   Almost  the
entire balance is produced as the result of com-
bustion of fuel for  space heating and power gen-
eration.

Oxides of sulfur

Air  contaminants classified  as oxides  of sulfur
consist essentially of only two compounds, sulfur
dioxide (SO2) and sulfur trioxide  (803).  The pri-
mary  source of  both is the combination of atmo-
spheric  oxygen  with the  sulfur  in  certain fuels
during their combustion. The total emitted quan-
tities of these  substances are, therefore, directly
related to the sulfur content and total quantities  of
the principal fuels used in a community. Normally,
the dioxide is  emitted in much greater quantities
than  the  trioxide,  the latter being formed only
under rather unusual conditions.  In fact, the tri-
oxide  is normally a finely divided aerosol rather
than a gas.

In Los Angeles  County,  the  emissions of sulfur
oxides have shown  a marked decrease during the
•winter months with  the promulgation of Rule 62. 2.
This  rule  places a limitation  of 0.  5 percent, by
weight, on the sulfur  content of the liquid fuels.
Prior to the adoption of this rule, high-sulfur  oils,
often as high as  1. 6 percent sulfur,  were allowed
to be burned when natural gas was not available.

During the period November 15 to April  15, emis-
sions  of sulfur  oxides are 290 tons per  day,  of
which 85  tons per  day is from the combustion  of
fuels. Ninety tons per  day are from  sulfur recov-
ery plants and 25 tons per day occur from sulfuric
acid plants.  The remainder is from  petroleum
refining and metallurgical plants.

During the period April 15 to November  15, the
total emissions  of  sulfur  oxides is 220 tons per
day.   The  70-ton reduction is  mainly a result  of
burning natural  gas instead  of low-sulfur oil  in
steam power plants.

Carbon monoxide

Carbon monoxide (CO) is  a single  contaminant
formed during incomplete  oxidation of any carbo-
naceous fuel and currently has only one significant
source in  Los  Angeles  County—the  incomplete
combustion of gasoline in  motor vehicles.  Of a
total of 9,100 tons of this contaminant emitted per
day,  98 percent  is  attributable  to  this source.
About  1.5 percent is attributable to the emissions
from aircraft,  and the balance from dies el engines,
metallurgical processes, and petroleum refining
operations.
 Significance  in Air Pollution  Problem

 The importance of the  inorganic gases in an air
 pollution problem varies with the gas  in question.
 Each will, therefore, be discussed separately.
 Oxides of nitrogen

The oxides of nitrogen have far greater significance
in photochemical smog than any of the other inor-
ganic gaseous contaminants.  Research has dem-
onstrated  that  upon  absorbing  sunlight  energy
nitrogen  dioxide  undergoes  several  reactions,
depending upon the wavelength or frequency of the
light.  The near-ultraviolet  wavelengths are  the
most effective  in producing  atomic  oxygen from
the nitrogen dioxide, and this  oxygen reacts with
a number  of organic compounds to produce all the
effects associated with photochemical smog.   In
fact,  this  type  of air pollution was named photo-
chemical  smog because of the manner in which
it is generated.   The presence of the dioxide has
been shown to be a necessary  condition for these
reactions.  This does not,  however, diminish the
need for adequate consideration of nitric oxide as
air contaminant,  since this  is the form in -which
the oxides of nitrogen normally enter the atmos-
phere.

In  communities  not affected  by photochemical
smog,  the  oxides of nitrogen  still must be consid-
ered if only for their inherent ability to produce
deleterious effects by themselves. The only effect
that must seriously be considered in this regard
is their toxicity, though the reddish-brown color
of the dioxide and its sharp odor could cause prob-
lems in areas near a nylon plant, nitric acid plant,
or nitrate  fertilizer plant.  Nitric oxide is consid-
erably less toxic than the dioxide.  It acts as an
asphyxiant when in concentrations great enough to
reduce  the normal oxygen supply from the air.
Nitrogen dioxide, on the other hand, in concentra-
tions  ofl approximately 10 ppm for  8 hours, can
produce  lung  injury  and edema,  and  in greater
concentrations,  i. e. ,  20  to  30 ppm  for 8 hours
can produce fatal lung damage.

The dioxide, then, is  heavily  indicted as  an un-
desirable  constituent of the atmosphere, regard-
less of the type of air pollution problem under con-
sideration. Nitric oxide is indicted, too, because
of its ability to produce the dioxide by atmospheric
oxidation.
Oxides of sulfur

During the past few years,  information in the lit-
erature has indicated  that the presence of sulfur
dioxide  in the  photochemical-smog  reaction en-
hances the formation  of visibility-reducing aero-
sols.  The mechanism responsible for this effect

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16
                                       AIR CONTAMINANTS
has notbeen described, and it is not known whether
sulfur dioxide enters into the organic photochemical
reactions or  whether the  additional aerosols ob-
served  represent simply  a combination  of sulfur
dioxide and moisture.

Primarily,  gaseous oxides of sulfur in the atmo-
sphere  are significant because  of their  toxicity.
Both  the dioxide and trioxide are capable of pro-
ducing  illness and lung injury even at small con-
centrations, from 5 to 10 ppm.  Further, each can
combine with water  in the air to form toxic acid
aerosols that can cor rode metal surfaces,  fabrics,
and the leaves of plants.   Sulfur dioxide by itself
also produces a characteristic type of damage  to
vegetation whereby portions of the plants' leaves
are bleached in a specific pattern.  In concentra-
tions  as small as 5 ppm, sulfur dioxide is irri-
tating to the eyes  and respiratory system.

Both  the dioxide  and trioxide can  combine with
particles  of  soot and other aerosols to produce
contaminants  more  toxic than either alone.  The
combination of the dioxide and trioxide with their
acid aerosols has also been found to exert a syn-
ergistic effect on their individual toxicities.  These
mixtures were apparently responsible for the ill-
ness and death associated with the famous air pol-
lution incidents that occurred in the Meuse Valley,
Belgium; inDonora, Pennsylvania; and, more re-
cently,  in London, England.

Carbon  monoxide

Carbon monoxide plays no part in the formation  of
photochemical smog though it is almost invariably
emitted to the atmosphere along with the most po-
tent of  smog  formers--hydrocarbons and oxides
of nitrogen.   At concentrations  of 200 ppm  and
greater, itproduces illness and death by depriving
the blood of its oxygen-carrying  capacity.  It has
been detected in the  atmosphere  of various urban
centers  of the world at concentrations from 10  to
lOOppm.  Greater concentrations have occasion-
ally been measured  in confined spaces  such as
tunnels and large, poorly ventilated garages.  At-
mospheric concentrations have not yet been linked
to fatalities  but have sometimes  been implicated
in short-term illnesses of traffic officers.

Miscellaneous inorganic gases

A few additional  gases were listed among those
emitted to the atmosphere from various operations
in Los  Angeles County.   They include ammonia,
hydrogen  sulfide, chlorine,  and  fluorine or fluo-
rides. Although none has been detected in greater
than trace quantities in the Los Angeles atmosphere
and none is known to have any significance in the
formation of photochemical smog, these contami-
nants can be important in other types of air pollu-
tion problems. All are toxic in small to moderate
concentrations, and the first three have unpleasant
odors.  Hydrogen sulfide can cause discoloration
of certain kinds of paint; ammonia and chlorine
can discolor certain fabric dyes; fluorine and fluo-
rides, especially hydrogen  fluoride, are  highly
toxic, corrosive, and capable of causing damage
to vegetation,  and illness and injury to humans
and animals.

Many other inorganic gases maybe individually or
locally objectionable or toxic. These are of rela-
tivelyminor importance and will not be discussed
here.


AEROSOLS

Aerosols (also called particulate matter) present
in the atmosphere may be organic or inorganic in
composition, and in liquid or solid physical state.
By definition, they must be particles  of very small
size or they will not remain dispersed in the atmo-
sphere.  Among the most common are carbon or
soot particles;  metallic oxides and salts; oily or
tarry droplets; acid droplets;  silicates  and other
inorganic dusts; and metallic fumes.

The quantities of aerosols emitted in Los Angeles
County,  at present,  are relatively small but in-
clude atleast some amounts of all the types listed
above.  Particles of larger than aerosol size are
also  emitted but,  because of their weight,  do not
long  remain airborne.  Additionally, however,
vast  quantities  of aerosols are formed in the at-
mosphere as the result of photochemical reactions
among emitted contaminants.  Total quantities of
these aerosols may easily exceed those of emitted
aerosols, at least in terms of particle numbers.
Current Sources in Los Angeles  County

The most  important current sources  of aerosol
emissions in Los Angeles County, by type of aero-
sol, will now be discussed.
Carbon or soot particles

Probably the most commonly emitted kind of par-
ticle  anywhere  is  carbon.  Carbon particles are
nearly always present among the products of com-
bustion from all types of fuels,  even from opera-
tions in which the combustion is apparently complete.

In Los  Angeles County, the principal sources of
emissions containing carbon or soot particles are
the exhaust effluents from motor vehicles, and
the combustion of fuels for power generation and
space  heating,  though  not all the particulates
emitted from these sources are carbon.  Emis-
sions from the latter group of sources vary with
the Rule 62 period* since these particles  occur in
 •April 15 to November 15.

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                                       Types of Contaminants
                                             17
greater quantities  in the effluent from the burning
of fuel oil than in that from the burning of natural
gas.  During  Rule 62 periods,  then,  the combus-
tion of fuel for  space heating and generation of
power accounts for about one-fourth of the carbon
particles emitted to the atmosphere,   and during
non-Rule 62 periods,  about one-half.  The portion
contributed by auto  exhaust varies,  therefore ,
during comparable periods from one-half to three -
fourths of the total.

The actual total of emitted carbon particles cannot
be estimated with much accuracy, but they probably
represent about  one-third  to one-half of the total
aerosol emissions.

The only  other  sources from which significant
quantities of carbon particles might be emitted are
incineration of refuse, operation of piston-driven
aircraft,  and operation  of  ships and railroads.
Even the total of particulate emissions from these
sources  does not,  however, comprise 5 percent
of the total carbon emissions.
 probablythe emissions  associated with the opera-
 tion  of  motor vehicles, particularly crankcase
 emissions; exhaust emissions from gasoline- and
 diesel-powered vehicles; effluents from asphalt
 manufacturing,  saturating,  paving, and roofing
 operations; and effluents from inefficient combus-
 tionof fuels in stationary sources. Small amounts
 might also be found in the effluents from  aircraft,
 ships, and locomotives and from  incineration of
 refuse.  Oily or tarry particles also appear to be
 among the products of the photochemical reactions
 that produce smog.  Emitted quantities  of  these
 materials probably comprise 10 to 20 percent of
 the total particulate emissions.
 Although the composition of these materials is not
 well established, they appear to be predominantly
 organic.   They undoubtedly have relatively high
 molecular  weights and probably  contain at least
 some aromatics.  The polycyclic  hydrocarbons,
 which currently cause so much concern,  probably
 occur in a liquid phase in the atmosphere.
Metallic oxides and salts

Metallic oxides and  salts  can be found  in small
quantities  in  the  emissions  from many  sources.
These sources include catalyst dusts from  refinery
operations, emissions from the metals industry,
effluents from combustion  of fuel oil,  and even
exhaust from motor vehicles.  The total quantity
of these emissions is, however, small and  probably
does  not constitute more than 5 to 10 percent of
the total particulate emitted to the atmosphere.

The materials emitted as catalyst dusts are mostly
oxides.  Small quantities of metallic oxides may
also  result from  the combustion  of fuel oil and
perhaps  from metal-working operations.  These
oxides might include those of vanadium,  aluminum,
titanium,  molybdenum,  calcium,  iron,  barium ,
lead, mangenese, zinc, copper, nickle, magne-
sium, chromium,  and silver.
 Acid droplets

 Small droplets of acid, both organic and inorganic,
 are emitted from a number  of sources in Los
 Angeles County  under certain conditions.  These
 sources include stack effluents from power plants,
 especially during combustion of fuel  oil;  effluents
 from industrial operations such as  certain metal-
 working and plating operations, and storage bat-
 tery reclamation; effluents from waste rendering
 and incineration; and  even effluents from motor
 vehicle exhaust.  Under some circumstances, these
 acid droplets are also formed  in the  atmosphere.
 Like  the other kinds  of  particulate matter,  the
 total emitted quantities of these droplets are small,
 probably 5 to  10 percent of  the total particulate
 emissions. Even the quantities of these materials
 formed  in the atmosphere are small  relative to
 the total.
Metallic salts are emitted from  essentially  the
same sources - again,  in  small concentrations.
Most emissions of particulate lead in auto exhaust,
for example, are present  as  oxides  and complex
salts, usually chlorides, bromides, and sulfates.
Metallic oxides are  emitted from certain metals
operations,  and  small quantities  of  sulfates are
emitted from some industrial operations.
Oily or tarry droplets

Small droplets of oily or tarry materials are fre-
quently found in combustion effluents from many
types of sources. The  most common sources are
 The inorganic acids  emitted to  the  atmosphere
 include,  primarily, sulfuric and nitric acids; the
 organic acids include probably acetic, propionic,
 and butyric acids. The acids formed in the atmos -
 phere through  combination  of  gases with water
 include  sulfurous,  sulfuric, nitrous, and nitric
 acids.  Acid droplets formed through oxidation of
 organic emissions may not include  any but acetic
 acid, if that.

Silicates and other inorganic dusts

Emis sions of inorganic dusts in Los Angeles County
consist primarily of  silicates,  carbonates,  and

-------
18
                                       AIR CONTAMINANTS
oxides and are probably associated most commonly
with quarrying operations, sand and gravel plants,
and other phases of the minerals industry.   They
can also  result from highway construction and
landfill operations. Their quantity may represent
about 5 to 10 percent of the total particulate emissions.


Metallic fumes

The metals industry  is responsible for 8 percent
of the total aerosol emissions,  and metal fumes
probably  constitute less than half of this portion.
Metal fumes are generally considered to be minute
particles created by the condensation of metals
that have vaporized or sublimed from the molten
state.
 Significance in  Air  Pollution Problem

 The significance of aerosols, and of all airborne
 particulate matter, varies with the type of air pol-
 lution problem in which they are involved.  In most
 situations,  particulate emissions represent a
 major portion of the total quantity of air contami-
 nants and would be important for their soiling and
 and nuisance properties alone, if  for no  other.
 Even in air pollution problems of the type pro-
 duced by coal burning, which involves only carbon
 particles,  ash, and oxides of sulfur,  there are in-
 dications that the toxic effect of the  sulfur dioxide
 and trioxide is enhanced by the concomitant par-
 ticulate matter. This kind of effect has been noted
 in other cases involving aerosols and toxic gases
 or  liquids and has  given rise  to the theory that
 other contaminants can adsorb on  the surface  of
 the particles and thus come into  contact with inner
 surfaces  of the lungs and mucous membranes  in
 much greater concentrations than  would other-
 wise be possible.


 Particulate emissions are also associatedwith re-
 duction of visibility.  In some instances,  this  is
 the simple physical phenomenon of obscuration of
 visibility by  the quantity of interfering material.
 In  those instances associated with photochemical
 smog,  however,  the visibility reduction is  due  to
 refraction and scattering of light, and the number
 and size of the particles involved are much more
 important than their identities.   The smaller the
 particles (maximum reduction of visibility at 0. 7mi-
 cron) and the larger their number, the greater
 their collective effect on visibility.


 It has  also  been  suggested that the presence  of
 minute particles promotes the  photochemical re-
 actions that produce smog.  Furthermore, small
 aerosol particles are among the products of these
 reactions  and add to the visibility reduction pro-
 duced by the emitted contaminants.
       AIR POLLUTION CONTROLS

           ALREADY  IN EFFECT

When the air pollution problem in Los  Angeles
County  was recognized,  an agency was immedi-
ately provided to study the problem and try to  solve
it.   The first Air  Pollution Control District in
Californiawas formed and charged with responsi-
bility for the elimination or,  at least,significant
reduction of air pollution in Los Angeles County.

During its first 10 years, the District concentrated
its efforts on control of emissions from stationary
sources. Experience of other agencies in this field
had  shown that  certain kinds of industrial emis-
sions were most commonly responsible  for air
pollution problems.  Mobile  equipment was ex-
empted from  control and not  at that time  con-
sidered a serious source of contaminants.

Continuous  study and diligence have since led to
the promulgation of the most stringent and  com-
plete rules and regulations  in force anywhere in
the world and to the most effective control program
currently feasible.  Both are frequently copied and
studied. Table 2 concisely summarizes what has
been accomplished.  Other sections of this  man-
ual explain in detail the methods and equipment
used.

Perhaps the most graphic evidence of the success
of this  control effort is the almost complete ab-
sence of emissions from stacks and chimneys any-
where  in  the  Los Angeles Basin.  Any source of
visible  emissions immediately calls attention to
itself.


  CONTROL  MEASURES STILL  NEEDED

Despite an almost incredibly successful program
of control over stationary-source emissions, the
persistence of unpleasant effects of air pollution
and the concentrations of atmospheric contami-
nants still being measured did not properly reflect
these dramatic reductions.  A research program
undertaken concurrently with the programs of con-
trol and enforcementhad revealed that the air pol-
lution problem in the Los Angeles area was dif-
ferent from that usually encountered.  It had shown
also  that the hydrocarbons and oxides of nitrogen
primarily  responsible  for the effects associated
with  smog in Los Angeles were likely to be emitted
only in connectionwith the processing and handling
of petroleum and the  combustion of fuels.

As soon as hydrocarbons were recognized to  be of
great significance in this kind of air pollution prob-
lem,  measures  were undertaken to control the
emissions from their  principal stationary sources,
the refineries. Although these  measures failed to
eliminate smog effects  throughout the basin, they

-------
                                        Control Measures Needed
                                                                                                        19
  en
  W
  H
  O
  o
  o
  M  C^'
   O
o




X





x



XXX
XXX





x



X X X X X X
































Miscellaneous
Rendering (inedible)
Coffee roasting
Meat smokehouses
Feed and grain
Wood processing
Other






Tf ^J.
•o ^o"




X
X
x
X
x
0








c

o
o
r-

x

„

«

X

X
X
o
"
IT











°


in o

in

^ '
r~ S
' -Z
S
s

	
0



S
2


O


—"


o
-J3
fo
0
in
o


•D
S
Total contaminants redt
by APCD rules








Total ( Rounded)
I 1
« a

I £

2 3
: i
i 5

•3 c
234-767 O - 77 - 4

-------
20
AIR CONTAMINANTS
diminished  these  effects and reduced the atmo-
spheric hydrocarbon concentrations in the refinery
area  of the county.  At the same time, however,
damage to plants,  irritation of eyes, and reduc-
tion in visibility were more  widespread and in-
creasing in severity in suburban areas that had
previously been almost smog free.   Obviously,
some important source of the contaminants that
produce photochemical smog had not  been  ade-
quately taken into  account.   This source proved
to be the most prevalent consumer of petroleum
products, the gasoline-powered motor  vehicle.

Although no feasible  means  for  control of motor
vehicle emissions were yet known, assessment  of
the relative importance of this source of emissions
was clearly mandatory. Investigation  of exhaust
emissions revealed that,  although each individual
vehicle was negligible as a source, the vast number
of vehicles could have great significance. Further
study demonstrated how  the phenomenal postwar
growth of the Los Angeles area  had  so increased
the sources of air contaminants that the gains made
by  the  control of stationary sources had  been
almost nullified.  From 1945 to 1955, for example
the pollution of Los Angeles County  increased by
almost 50 percent; motor vehicle registration and
gasoline consumption increased about 100 percent;
and the number of industrial establishments in-
creased by  nearly 80 percent.   The district had
had to "run at great speed to stay in one place, "
and the picture of what the situation might have
be en without a control program was almost unimag-
inable.

Estimating  the total  quantities of air pollution  in
Los Angeles County, the district was able to de-
termine  that hydrocarbon emissions from motor
vehicles  as a  fraction of the total for the county
had probably increased from about one-eighth  in
1940  to one-third in  1950 and to one-half to two-
thirds in 1955.  Oxides of nitrogen emissions from
motor vehicles probably constituted about 50 per-
cent of the  total in 1940 and 1950,  and 50 to 60
percent in 1955. During the entire period, motor
vehicle emissions probably accounted for 85 to 95
percent of the total  of carbon monoxide emitted  to
the atmosphere.   These estimates represent the
net effect of both growth and control measures and
illustrate the change  in emphasis that has grad-
ually taken place.   Probably this would, however,
be  less true of areas that had little or no control
over emissions from stationary sources.

MOTOR VEHICLE EMISSIONS
For Los Angeles  County, this gradual change and
its effect on the solution of the air pollution prob-
lem had to be carefully evaluated, and the probable
necessity for control of motor vehicle  emissions,
prudently considered.  In 1957, though no controls
were available, appropriate  steps were taken  to
              enable  the  district to encourage the development
              of necessary control devices and require their use
              when they became available.   Additional  study,
              plus  the increasing occurrence of the effects of
              photochemical smog in other areas of California,
              suggested  that control of mobile  sources at the
              local, or district, level probably would not be ade-
              quate.  In  1959,  therefore, the state government
              formally occupied this particular field of air pol-
              lution control in California.  Although the Los
              Angeles County Air Pollution Control District con-
              tinued its  participation in research on vehicular
              emissions, its primary responsibility reverted to
              control of  emissions from stationary sources.


              ADDITIONAL CONTROLS OVER STATIONARY SOURCES
             The principal  areas in which additional controls
             will be needed involve reduction of emissions of
             organic gases  and oxides of nitrogen.  Present
             control measures have so far brought about only
             67  and 53 percent control, respectively, of these
             emissions from stationary  sources.  Obviously,
             control of these emissions  from motor vehicles
             also  is necessary,  but this is no longer the Dis-
             trict's responsibility.

             The State of California has adopted  strict ambient
             air quality standards for  specific  contaminants;
             these standards are exceeded on many days of the
             year  in Los Angeles County.  Because these stand-
             ards  are being exceeded, new rules must be adopt-
             ed to reduce these  contaminants.  Of  particular
             concern,  in addition to organic gases and oxides
             of nitrogen as mentioned above, are sulfur  dioxide
             and particulate matter.
              Organic Gases
              On a tonnage  basis,  only  67 percent control of
              organic  gases from stationary  sources has been
              achieved.  The full benefits from Rule 66 pertain-
              ing to organic  solvents have not yet been realized.
              Many of these organic solvent processes are now
              undergoing modifications; afterburners are being
              installed on existing  basic equipment,  and proc-
              esses are being revamped to substitute solvents
              that do not react photochemically.  A new  rule,
              to be effective September 1,  1974, also will pre-
              vent large users of non-photochemically-reactive
              solvents from discharging these contaminants into
              the atmosphere. In petroleum processes, asphalt
              air-blowing  and release of organic gases and va-
              pors  from vacuum-producing devices or systems
              (including hot  wells and accumulators) also will
              be controlled under new rules.   Other new rules
              will require that pumps and compressors be e-
              quipped with mechanical seals and that safety pres-

-------
                                      Control Measures Needed
                                                                                                   21
sure  relief valves be vented to a vapor recovery
or disposal system.

Oxides of  Nitrogen
Oxides  of  nitrogen from stationary sources will
be reduced significantly during the next 3 years
by the provisions  of Rule 68. Future single large
sources of oxides of nitrogen will no  longer  be
allowed in Los  Angeles  County  because  of the
limitations imposed by Rule 67, Most of the future
reduction in oxides of nitrogen will be achieved by
the electric power generating plants.  In anticipa-
tion  of Rule 68, -which was adopted early  in 1971,
much  work already  has been accomplished  and
measurable reductions were achieved in 1969 and
1970.  In fact, the design changes and operational
changes brought about during those  2  years re-
duced oxides  of nitrogen about one-half from the
power utilities.
 Other  Contaminants
If the  strict ambient air quality standards of the
State of California are to be met, additional  rules
must be adopted to further control sulfur dioxide
and particulate matter.  Recently adopted Rules
53.1,  53.2,  and 53. 3  will reduce substantially the
emissions of sulfur dioxide from sulfur scavenger
plants  and sulfuric acid plants.  Several new rules
are in effect to further reduce particulate emis-
sions.

Continued  surveillance  of all contaminant emis -
sions  will be  maintained.  If any emissions are
found  to have  increased to  the extent that more
stringent control is  necessary, or  if means are
discovered  to  make  certain additional controls
feasible, then  new rules will be adopted immedi-
ately.

-------
                                            CHAPTER 3
                           DESIGN  OF  LOCAL EXHAUST SYSTEMS
                                      FLUID FLOW FUNDAMENTALS
                          HERBERT SIMON,  Senior Air Pollution Engineer
                     JOHN L. McGINNITY, Intermediate Air Pollution Engineer*
                             JOHN L. SPINKS, Air Pollution Engineer

                                           HOOD DESIGN
                          HERBERT SIMON,  Senior Air Pollution Engineer
                     JOHN L. McGINNITY,  Intermediate Air Pollution Engineer*
                         JOHN L.  SPINKS,  Senior Air Pollution Engineer

                                           DUCT DESIGN
                      EDWIN J.  VINCENT,  Intermediate Air Pollution Engineer*

                                            FAN DESIGN
                      EDWIN J.  VINCENT,  Intermediate Air Pollution Engineer*
                             LEWIS K. SMITH, Air Pollution Engineert

                                        VAPOR COMPRESSORS
                          GEORGE THOMAS,  Senior Air Pollution Engineer

                                    CHECKING AN EXHAUST SYSTEM
                            JOSEPH D'IMPERIO, Air Pollution Engincert

                                    COOLING OF GASEOUS EFFLUENTS
                         GEORGE THOMAS, Senior Air Pollution Engineer
*Now with Environmental Protection Agency, Research Triangle Park, N.  C.
fNow deceased.

-------
                                               CHAPTER 3
                            DESIGN  OF  LOCAL EXHAUST  SYSTEMS
       FLUID  FLOW  FUNDAMENTALS

 Local exhaust systems are devices used to cap-
 ture  dusts and fumes or other contaminants  at
 their  source and prevent the discharge of these
 contaminants into the atmosphere.  Close-fitting
 hoods are used to capture the contaminants from
 one or more locations so that  the laden gases can
 by conveyed through a  system of ducts by one or
 more exhaust fans.  An air pollution  control de-
 vice can then be used  to collect the air contami-
 nants and discharge the cleansed air  into the at-
 mosphere.

 In designing a local exhaust system, sufficient air
 must be provided for essentially complete pickup
 of the contaminants.   Conversely, too  much air
 can  result in  excessive  construction and opera-
 tion costs.  It is, therefore, necessary for the de-
 signer  to  understand  certain physical principles
 that are useful in analyzing the ventilation needs
 and in selecting the hooding devices.

 The nature of flow of a real fluid is very complex.
 The basic  laws describing the complete  motion of
 a  iluid are, in general,  unknown.  Some simple
 cases of laminar flow,  however,  maybe  computed
 analytically.  For turbulent flow, on the other  hand,
 only  a partial  analysis can be made  by using  the
 principles of mechanics .  The flow  in exhaust sys-
 tems is always turbulent; therefore , the final solu-
 tion to these problems  depends upon experimental
 data.

 BERNOULLI'S EQUATION

 The  basic  energy equation of a f rictionlcs s,  in-
 compressible fluid for the case of steady flow along
 a single streamline is  given by Bernoulli as
             h +
T-  =  C
                                             (1)
where
   h = elevation above any arbitrary datum, ft

   p = pressure,  Ib/ft
   7 = specific weight, Ib/ft

   v = velocity,  ft/sec

   g = acceleration due to gravity, 32. 17 ft/sec

   C = a constant,  different for each streamline.
Each term in Bernoulli' s equation has the units foot-
pounds  per pound of fluid or feet of fluid.  These
terms are frequently referred to as elevation head,
pressure head, and velocity head.  They also rep-
resent the potential energy,  pressure energy, and
velocity energy,  respectively.


When Bernoulli's  equation is  applied to industrial
exhaust systems, the elevation term is usually
omitted, since only relatively small changes in el-
evation are involved.   Since all streamlines  orig-
inate froma reservoir of constant energy (the at-
mosphere), the constant is the same  for all
streamlines, and the restriction of the equation to
a single streamline can be removed.  Furthermore,
since the pressure  changes in nearly all exhaust
systems are at most only a few percent  of the ab-
solute pressure, the assumption of incompressi-
bility may be made with negligible error.  Although
steady-flow conditions do not always exist in ex-
haust systems, it is safe to make the assumption
of steady  flow if the worst possible case is con-
sidered.  Any error will then be on the safe side.
All real fluids  have a property called viscosity.
Viscosity accounts  for energy losses, which are
the result of shear stresses during flow.  The mag-
nitude of the losses must be determined experi-
mentally, but once established, the values can be
applied to dynamically similar configurations.
Bernoulli's equation may be applied to a real fluid
by  adding  an energy  loss term.   Letting 1_ be an
upstream point and 2_ a  downstream point, the
energy per unit weight at J_ is  equal to the energy
per unit weight at 2_ plus all energy losses between
point 1 and point 2.

PITOT TUBE FOR FLOW MEASUREMENT

The velocity of a fluid (liquid) flowing in an open
channel  may be  measured by means of a simple
pitottube, as  shown in Figure  2 (Streeter, 1951).
Although this instrument is simple, usually con-
sisting of a glass  tube with a right-angle bend, it
is  one of the most accurate means of measuring
velocity.   When the  tube opening is directed up-
stream,  the fluid flows into the tube until the  pres-
sure intensity builds up within the  tube sufficiently
to withstand the impact of  velocity against  it.  The
fluid at a point directly in front of the tube (stag-
nation point)  is then at rest.  The pressure  at the
stagnation point is  known from  the height  of the
liquid column in the tube.  The velocity of the fluid
                                                  25

-------
26
                               DESIGX OF LOCAL EXHAUST  SYSTEMS
           Figure  2.  Simple pi tot tube
           (Strgeter, 1951).

in the stream may be evaluated  by writing Ber-
noulli's equation between point j_ upstream of the
stagnation point  and point 2 the  stagnation  point.
Note that h] = h^ and V2 =  0.
                              Therefore
            _J_
            2g
£i
 7
P2
 7
Pl_
 Y
                                              (2)
solving for the velocity,
                                              (3)
will again indicate the total pressure,  but now the
portion of the Lotal head caused by velocity  cannot
be distinguished.  The static pres sure in this case
can be  measured by a piezometer or static tube,
as shown in Figure 3.  The total  pressure H con-
sists  of the  sum of the static pressure  hs and
the velocity pressure hv,  or

                 H = hs + hv                  (4)

The velocity can be determined,  therefore, from
the difference between  the total  and static heads.

In practice,   measurement of total pressure and
static  pressure  is combined into a  single instru-
ment (pitot-static tube,  Figure 4), which  permits
direct measurement  of velocity  head  since the
static  head is automatically subtracted from the
total head. An inclined manometer (Ellison guage)
is particularly useful when the  heads are small
as in  exhaust systems.   Use of this  device to
measure the  flow of a gas introduces, however,
an additional factor, which is the conversion of
readings in inches of manometer fluid into mean-
ingful velocity  terms.   This relationship,  when
water is used as the manometer  fluid to measure
the velocity of air,  is
A  simple pilot  tube measures  the  total head or
total pressure,  which is composed of two parts,
as shown inFigure 2.  These are the static pres-
sure  Rg  and the dynamic or  velocity pressure
hv.  In open-channel flow, hv  ig measured from
the free surface.   When the liquid  is in a pipe or
conduit in which it flows full, a simple pilot tube
     FLOW
  ' STREAMLINES
                                r
                                1
                     P I EZOMETER
                     OPENINGS
                                                                          4005
                                                                                                   (5)
                                                      where
                                                                 velocity pressure or head, inches of
                                                                 water
                                                       4005   =   1096.
                                                                           Volume in ft  of 1 Ib of air
                                                                           at 70°F and 14. 7 psia
                                                                 velocity of air,  fpm.
                                                                     • PIEZOWETER
                                                                       OPENINGS
     Figure 3.  Static tube (Streeter,  1951)
                                                        Figure 4.  Pitot-static tube  (Streeter,  1951).

-------
                                            Hood Design
                                                                                                  27
Correction Factors

The relationship expressed in equation 5 is exact
only for air at standard temperature and pressure,
70°F and 14. 7 psia, respectively.  A correction
must be applied for other than  standard  condi-
tions.  If the air in the duct departs from. 70 °F by
more than about  50°F, a correction is  required:
•where
                                             (6)
          the temperature of the air,  °F.
For  smaller temperature deviations, the error is
not significant and maybe neglected.  If the gas is
other than air,  a correction for the difference in
density may be applied:
            /  v
      hv ~  \4005/
  
-------
28
                              DESIGN OF LOCAL EXHAUST SYSTEMS
AIR FLOW INTO A DUCT

If a circular duct opening,  representing a simple
hood,  is  substituted for the imaginary point,  the
pattern of flow into the end of the duct, or hood,
will be modified as shown in Figure 5 because of
the interference from the  duct.  The velocity of
the air approaching a plain, circular opening along
the axis of the duct is given by Dalla Valle (1952)
as approximately
                           0. 1A
              100  - Y
                                           (10)
•where
   Y  =
   A  =
          the percent of the velocity at the open-
          ing found at a point x on the  axis

          the distance outward along the axis from
          the opening,  ft

          the area of the opening, ft .
The velocity at the opening is computed from the
continuity equation.

The actual  flow  pattern  is  found  to be as shown
in Figure 5 from studies by Dalla Valle and others.
The lines of constant velocity are called contour
lines,  -while those perpendicular  to  them are
streamlines, which represent the direction of  flow.
The addition of a flange improves the efficiency of
the duct as  a hood for a distance of about one di-
ameter from the duct face.  Beyond this point,
flanging the duct improves the efficiency only
slightly.  Figure 6 illustrates flow patterns for
several sizes of  square hoods.   Because  there is
little difference in the center line velocity of hoods
of equal air volume at  a distance of one or two
hood diameters from the hood face,  Hemeon (1955)
recommends using one  equation for all shapes --
square, circular, and rectangular up to about 3:1
length-to-width ratio.  He also does not distinguish
between flanged  and unflanged hoods, which ap-
pears justified when these hoods are used only at
distances of one  diameter or more from the  hood
face.  At close  distances,  flanged hoods are far
superior  at the  same volume.  By rearranging
terms in equation  10 and combining with equation
8, the following is obtained:
            V
                =  v  (lOx
                    X
(ID
where

   V

   v

   X
          the volume of air entering the hood, cfm

          the velocity at point x,  fpm

          the distance to any point x on the axis or
          center line of the hood measured from
          the hood face, ft
   A   =  the area of the- hood face,  ft .
           Analysis of equation 11 shows that at the hood face
           x = 0 and the equation becomes identical to equa-
           tion 8.  For large values of x, the Af term becomes
           less significant, as the evidence shows it should.
           To use  equation 11,  select a value of vx that is
           sufficient to  assure complete capture of the air
           contaminants at point x.  From the physical di-
           mensions and location  of  the hood,  Af and x are
           determined.  The volume  required  may then be
           calculated.

           While equation 11 applies to a freestanding or un-
           obstructed  hood, it can also be applied to a  rec-
           tangular hood bounded on one side by a. plane  sur-
           face, as shown in Figure 7.  The hood is considered
           to be twice its actual size,  the additional portion
           being the mirror image of the actual  hood and the
           bounding plane  being the bisector.  Equation 11
           then becomes
                                                                   V   =
                                                                    t
                                                                                lOx
                                                                                       2A_
                                                       (12)
•where the terms have the same meaning as before.

NULL POINT

Air contaminants  are often released into the at-
mosphere with considerable velocity at their point
of generation.  Because the mass is  essentially
small, however, the momentum is soon spent and
the particles  are then easily captured.  Hemeon
(1955) refers to a null point,  shown in Figure 8,
as the distance •within which the initial energy of
an emitted air contaminant has been dissipated or
nullified in overcoming air resistance.  If an ade-
quate velocity toward the hood is provided  at the
farthest null point from the hood,  all the air con-
taminants released from the process will be cap-
tured.  What  constitutes an adequate velocity to-
wards the hood depends upon drafts in the area and
cannot, therefore, be determined precisely.

Establishing the null point  in advance for  a new
process is not always easy or even pos sible.   For
existing  equipment,  however, direct observation
will usually establish a locus of null points.  Ob-
viously,  in the absence of external disturbances,
any positive velocity toward the hood at the farthest
null point will give assurance of complete capture.
When this is put into practice, however, the re-
sults are disappointing.  Even closed rooms have
drafts and thermal currents that destroy the hood's
effectiveness unless a substantial velocity toward
the hood is created at the farthest null point.  Ex-
perience  has  shown that  a  velocity of less than
100 fpm at  a null point can seldom,  if ever,  be
tolerated without a loss in the hood's effectiveness.

Draft velocities  in  industrial situations may al-
most  always be  expected to be 200 to  300 fpm

-------
                                  Hood Design
                                    29
                                    23456      7
                                           DISTANCE FROM OPENING,  inches
                 FLANGE
      CUCT  ."ALL
V
                                                                    \
                                                                          \
       CFNTEFL l'*r
                                          \
                                           3      4     5      f      7
                                            DISTANCE FROM OPENING,  inches
Figure 5.  Actual  flow contours and streamlines for flow  into  circular  openings.
Contours are  expressed as percentage  of  opening velocity  (Dalla  Valle,  1952).

-------
30
DESIGN OF LOCAL EXHAUST SYSTEMS
       \
                           5    6    7
                DISTANCE OUTHARD FBOM OPENING, inches
Figure 6.   Actual  velocities  for square openings
of different sizes.   Air  flow through each opening
is 500 cfm (Da!la  Valle,  1952).
  Figure  7.   Rectangular hood bounded by  a  plane
  surface  (Hemeon, 1955).
 or  more periodically, and draft velocities of 500
 to600fpmare not unusual in many cases.   Drafts
 such as these may prevent capture of air contami-
 nants by exterior hoods, as illustrated in Figure 9
 for the case of ahigh-canopy hood, unless adequate
 baffling is  provided or hood volume is increased
 to unreasonable values.  Baffling provides, in ef-
 fect, an enclosure that is almost always the most
 efficient  hooding.


 DESIGN OF HOODS FOR COLD PROCESSES

 A large body of recommended ventilation rates has
 be en built up over the years by various groups and
 organizations who are concerned with the control
 of air contaminants.  This type of data is illustrated
 in Table 3.  The use of these recommended values
                                                           Figure 8. Location of null point and x-distance
                                                           (Hemeon,  1955).
                           Figure 9.   Drafts  divert  the  rising
                           column of  air  and  prevent  its capture
                           by the hood  (Hemeon,  1955).
                    greatly simplifies hoodingdesignfor the control of
                    many  common air pollution problems.  Note that
                    almost all published recommendations have speci-
                    fied complete or nearly complete  enclosure.
                    These published data provide a reliable guide for
                    the design  engineer.  The recommended values
                    must,  however, be  adjusted to specific applica-
                    tions that depart from the assumed normal
                    conditions.

-------
                                 Hood Design
                                                                     31
     Table 3.  EXHAUST REQUIREMENTS FOR VARIOUS OPERATIONS
   Operation
Exhaust arrangement
                                                      Remarks
Abrasive blast
rooms


Abrasive blast
cabinets


Bagging machines


Belt conveyors
Bucket elevator
Foundry screens
Tight enclosures with
air inlets (generally
in roof)
Tight enclosure
Booth or enclosure

Hoods at transfer
points enclosed as
much as possible
Tight casing
Enclosure
Foundry shakeout Enclosure
Foundry shakeout Side hood (with side
                 shields when possible)
Grinders,  disc
and portable

Grinders and
crushers
Mixer
Packaging
machines
Paint spray

Rubber rolls
(calendars)
Welding (arc)
Downdraft grilles in
bench or floor

Enclosure

Enclosure
Booth
Downdraft
Enclosure

Booth


Enclosure


Booth
For 60 to 100 fpm downdraft or 100 fpm
crossdraft in room


For 500 fpm through all openings,  and
a minimum of 20 air changes per
minute

For 100 fpm through all openings for
paper bags; 200 fpm for cloth bags
For belt speeds less than 200 fpm,
V = 350 cfm/ft belt width with at least
150 fpm through openings.  For belt
speeds greater than 200 fpm, V =
500 cfm/ft belt width with at least
200 fpm through remaining  openings

For 100 cfm/ft  of elevator casing
cross-section (exhaust near elevator
top and also vent at bottom  if over
35 ft high)

Cylindrical--400 fpm through openings,
and not less  than 100 cfm/ft^ of cross-
section; flat deck--200 fpm through
openings, and not less than 25 cfm/ft
of screen area
For 200 fpm through all openings,  and
not less than 200 cfm/ft  of grate area
•with hot castings and 150 cfm/ft^ with
cool castings

For 400 to 500 cfm/ft2 grate area with
hot castings  and 350 to 400  cfm/ft2 with
cool castings
For 200 to 400 fpm through open face,
but at least 150 cfm/ft  of plan -working
area
For 200 fpm through openings

For 100 to 200 fpm through openings
For 50 to 100 fpm
For 75 to 150 fpm
For 100 to 400 fpm

For 100 to 200 fpm indraft,  depending
upon size of work,  depth of booth,  etc.

For 75 to 100 fpm through openings
For 100 fpm through openings

-------
32
                               DESIGN OF LOCAL EXHAUST SYSTEMS
Spray Booths

Spray booths of the open-face type are generally
designed  to  have  a face indraft velocity of 100 to
200 fpm.  This is usually adequate to assure com-
plete capture of all over spray, provided the spray-
ing is done  within the confines of the booth, and
the spray gun is always directed towards the in-
terior. It is a common practice, especially with
large'workpieces, toplace the work a short dis-
tance  in front of the booth face.   The over spray
deflected from the -workmay easily escape capture,
particularly with a careless  or inexperienced op-
erator. If this situation is anticipated, the equip-
ment designer can provide a velocity of 100 fpm
at the farthest  point to be controlled, as in the
following illustrative problem.
Example 1


Given:

A paint spray booth  10 feet -wide by 7 feet high.
Work may be  5 feet  in front of the booth face at
times.  Nearly draftless area requires  100 fpm
at point of spraying.


Problem:

Determine the exhaust rate required.

Solution:

From equation 12, volume required is
                 2
   V   =  v
    t      x
             / lOx  +  2Af \
             v      r     /
From equation 8,  face velocity is

          V
    f     Af

          19,500
                          ,
                          fpm
 When the spraying area is completely enclosed to
 form a paint spray room, the ventilation require-
 ments are not  greatly  reduced over those  for
 spraying inside an open-face booth.  This is nec-
 essary because a velocity of approximately 100
 fpm must be provided through the room for the
 comfort and health of the operator.
                                                     Abrasive Blasting

                                                     Abrasive  blasting booths  are similar to spray
                                                     booths except that a complete enclosure is always
                                                     required.  In addition, particularly for small booths
                                                     (benchtype), the ventilation rate must sometimes
                                                     be increased to accommodate the air used for blast-
                                                     ing.  The volume of blasting air can be determined
                                                     from the  manufacturer's  specifications.   For  a
                                                     small blasting booth, this -will usually be about 50
                                                     to 150 cfm.   The following  illustrative problem
                                                     shows how  the ventilation rate is calculated.
Example 2

Given:

A small abrasive blasting enclosure 4 feet wide by
3 feet high by 3 feet deep.  Total open area equals
1.3 ft2.

Problem:

Determine the exhaust rate required.

Solution:
From Table 3, ventilation required = 500 fpm
through all openings but not less than 20 air
changes per minute.
                                                     Volume at 500 fpm through all openings:

                                                        V  =   500 x 1. 3                  = 650 cfm

                                                     Volume required for 20 air changes per minute:
   V   =  20 x  volume of booth

   V   =  20x4x3x3
                                                                                           =  720 cfm
                                                     Open-Surface Tanks

                                                     Open-surface tanks may be controlled by canopy
                                                     hoods or by slothoods, as illustrated in Figure 10.
                                                     The latter are  more commonly  employed.  The
                                                     ventilation rates required for open-surface tanks
                                                     may be taken from Table 4, which is a modifica-
                                                     tion of the American Standards Association code
                                                     Z 9. 1.  These values shouldbe considered as min-
                                                     imum under conditions-where no significant drafts
                                                     will interfere with the operation  of the hood.  When
                                                     slot hoods are  employed the usual practice is to
                                                     provide a slot along each long side of the tank.  The
                                                     slots are  designed for  a velocity  of 2, 000 fpm
                                                     through the  slot face at the required ventilation
                                                     rate.  For a tank with two parallel slot hoods, the
                                                     ventilation rate required and the slot width bs may
                                                     be  taken  directly from Figure 11, which graphs
                                                     the American Standards  Association code Z 9. 1.

-------
                                              Hood Design
                                                                 33
SLOT v. IPTH D.
          Figure 10.  Slot hood for control
          of emissions from open-surface tanks
          (Adapted from Industrial Ventilation.
          1960).
Neither  the  code nor Figure  11 makes allowance
fordrafts.  The use of baffles is strongly recom-
mended wherever possible to minimize the effect
of drafts.  If baffles cannot be used or are not suf-
ficiently effective, the ventilation rate must be in-
creased.  The slot v/idth is also increased to hold
the slot face velocity in the range  of  1,800 to
2, 000 fpm.

The use of Figure 11 is illustrated in the follow-
ing problem:

Example  3

Given:

A chrome plating tank, 2 feet wide by 3 feet long,
to be  controlled by parallel slot hoods along each
of the 3-foot-long sides.

Problem:

Determine the total exhaust rate required and the
slot -width.

Solution:

From Figure 11,  the ventilation rate required is
390 cfm per foot of tank length.
   V   =  390 x  3
-  1, 170 cfm
From Figure 11,  the  slot width is  1— inches.
                                   8
If a slot hood is used on only one side of a tank to
capture  emissions,  and the opposite side of the
tank is bounded by a vertical wall, Figure  11  can
                   be used by assuming the tank to be half of a tank
                   twice as wide having slot hoods on both sides.  This
                   procedure is illustrated below.

                   Example 4

                   Given:

                   The same tank as in Example 3, but a slot hood
                   is to be installed along one side only.  The other
                   side is flush with a vertical -wall.

                   Problem:

                   Determine the total exhaust rate and slot width
                   required.

                   Solution:

                   The ventilation rate in  cfm per foot of tank length
                   is taken as half the rate for a tank twice as wide
                   from Figure 11.  Use width of 4 feet.
                      V
                             _880
                              2
= 440 cfm per foot
                    Total exhaust volume required
                      V  =  440  x 3
  1, 320 cfm
                   Slot width is read directly from Figure 11 for twice
                   the width bg =  2-5/8 inches.
1,000
"" 8CO


"" 6CO
o
e
£ 400
Z3
O
-z

•**,
1.
>
z
5 20C
•x.
z
150
—
—
—

	
—
i-
—
n_
~

E
~ A
t
~\ 1









>
f..

/

1 1 II








/
1^




Illl






/
/






Illl



.
/
/








Illllllll

x
y











iiiilini
j













I
3
2-1/2



1-3/4 ^
Q

^
<^
UJ
cc
1 t-
0
7,0 W
O
3/4 »-
o
%
5/3
1/2
                              15     20        30     40    50   6C
                                   WIDTH OF TANK (o),  inches

                          Figure 11.   Minimum ventilation  rates
                          requi red for tanks.

-------
34
DESIGN OF LOCAL EXHAUST SYSTEMS
                   Table 4.  VENTILATION RATES FOR OPEN-SURFACE  TANKS
                             (American Air  Filter Company, Inc., 1964)



Process




Plating
Chromium (chromic acid mist)
Arsenic (arsine)
Hydrogen cyanide
Cadmium
Anodizing
Metal cleaning (pickling)
Cold acid
Hot acid
Nitric and sulfuric acids
Nitric and hydrofluoric acids
Metal cleaning (degreasing)
Trichloro ethyl ene
Ethylene dichloride
Carbon tetrachloride
Metal cleaning (caustic or electrolytic)
Not boiling
Boiling
Bright dip (nitric acid)
Stripping
Concentrated nitric acid
Concentrated nitric and sulfuric acids
Salt baths (molten salt)
Salt solution (Parkerise.Bonderise, etc.]
Not boiling
Boiling
Hot water (if vent, desired)
Not boiling
Boiling
Vtinimum ventilation rate,
cfm per ft of
hood opening
Enclosing
hood
One
open
side

75
65
75
75
75

65
75
75
75

75
75
75

65
75
75

75
75
50

90
75

50
75
Two
open
sides

100
90
100
100
100

90
100
100
100

100
100
100

90
100
100

100
100
75

90
100

75
100
Canopy
hood
Three
open
sides

125
100
125
125
125

100
125
125
125

125
125
125

100
125
125

125
125
75

100
125

75
125
Four
open
sides

175
150
175
175
175

150
175
175
175

175
175
175

150
175
175

175
175
125

150
175

125
175
Minimum ventilation rate, a
cfm per ft of tank area.
Lateral exhaust
, tank width
W/L - • ratio
tank length
W/L
00 to 0. 24
A B

125 175
90 130
125 175
125 175
125 175

90 130
125 175
125 175
125 175

125 175
125 175
125 175

90 130
125 175
125 175

125 175
125 175
60 90

90 130
125 175

60 90
125 175
W/L
0. 25 to 0.49
A B

150 200
110 150
150 200
150 200
150 200

110 150
150 200
150 200
150 200

150 200
150 200
150 200

110 150
150 200
150 200

150 200
150 200
75 100

110 150
150 200

75 100
150 200
W/L
0.50 to 1.0
A B

175 225
130 170
175 225
175 225
175 225

130 170
175 225
175 225
175 225

175 225
175 225
175 225

130 170
175 225
175 225

175 225
175 225
90 110

130 170
175 225

90 110
175 225
  aColumn A refers to tank -with hood along one side or two parallel sides when one hood is against a
   wall or a baffle running length of tank and as high as tank is  wide; also to tanks with exhaust mani-
   fold along center line with W/2 becoming tank width in W/L  ratio.
   Column B refers to freestanding tank with hood along one side or two parallel sides.
 DESIGN  OF HOODS  FOR HOT PROCESSES

 Canopy Hoods

 Circular  high-canopy hoods

 Hoodingfor hot processes requires the application
 of different principles than that for cold processes
 because of the thermal effect.  When significant
 quantities of heataretransferred to the surround-
 ing air by conduction and convection,a thermal draft
 is created that may cause a rising  air current with
 velocities sometimes over 400 fpm.  The design
                    of the hood and the ventilation rate provided must
                    take this thermal draft into consideration.

                    As the heated air stream rising from a hot sur-
                    face moves upward,  it mixes turbulently with the
                    surrounding air.  The higher the air  column rises
                    the larger it becomes and the more diluted with
                    ambient air. Sutton(1950) investigated the turbu-
                    lent mixing  of a rising column of hot  air above a
                    heat source.   Using data  from, experiments by
                    Schmidt published in Germany,  and his own ex-
                    periments with military smoke generators, Sutton
                    developed equations that describe the velocity and

-------
                                              Hood Design
                                                                                    35
diameter of a hot rising jet at any height above a
hypothetical point source located a distance z be-
low the actual hot surface. H erne on adapted Button's
equations to the design of high-canopy hoods for
the control  of air contaminants from hot sources.
The rising air column illustrated  in Figure  12 ex-
pands approximately  according  to the empirical
formula
            D
=  0. 5
                           0.88
(13)
•where
  D   =  the diameter of the hot column of air at
          the level of the hood face, ft

  x    =  the distance from the hypothetical point
          source to the hood face, ft.

From Figure  12 it is apparent that xf is the sum
of y, the distance from hot source to the hood face,
and z the  distance below the hot source to the hy-
pothetical point source.   Values of z may be taken
from Figure 13.  According to Hemeon, the ve-
locity of  the  rising  column of air into the hood
may be calculated from








10





















/
/
/











,
/
/













f















/
















/















/
f\
I











/
/
/
/

- (2DS)U








J

r





38








                                                 1      2345     1C     ;03f
                                                   DIAMETER OF HOT SOURCE (Ds), feet

                                               Figure 13.   Value  of  z  for  use
                                               with high-canopy  hood equations.
                                                                             37
                                                                            0. 29
                                                                      ,1/3
                                                                                                   (14)
      HYPOTHETICAL
      POINT SOURCE
        Figure  12.   Dimensions used to
        design  high-canopy hoods for hot
        sources  (Hemeon,  1955).
                                                         v    =  the velocity of the hot air jet at the
                                                                level of the hood face, fpm

                                                         x    =  the height of the hood face above the
                                                                theoretical point source = y +  z,  ft
                                                         q    =  the rate at which heat is transferred
                                                          ^c
                                                                to the rising column of air,  Btu/min.

                                                      The rate at -which heat is absorbed by the rising
                                                      column may be calculated  from the appropriate
                                                      natural convection heat loss coefficient q  listed
                                                      in Table 5 and from  the relationship
                                                      where
                                        A
                                          s
                                         At
                                                                           60
                                                               A   At
                                                                s
                                                                                                   (15)
                    the total heat absorbed by the  rising air
                    column, Btu/min

                    the natural convection heat loss coeffi-
                    cient listed in Table 5, Btu/hr-ft2- °F
                    the area of the hot source, ft

                    the temperature difference between the hot
                    source and the ambient air, °F.
  234-767 O - 77 - 5

-------
36
         DESIGN OF LOCAL EXHAUST SYSTEMS
                       Table 5.  COEFFICIENTS FOR CALCULATING SENSIBLE
                       HEAT LOSS BY NATURAL CONVECTION (Hemeon, 1955)
Shape or disposition of heat surface
Vertical plates, over 2 ft high
Vertical plates, less than 2 ft high
(X = height in ft)
Horizontal plates, facing upward
Horizontal plates, facing down-
ward
Single horizontal cylinders
(where d is diameter in inches)
Vertical cylinders, over 2 ft high
(same as horizontal)
Natural convection
heat loss (qr) coefficient3-
0.3 (At)1/4
(^i_)1/4
0.38 (At)1/4
0.2 (At)1/4
d
At I/4
0.4 tf,
Vertical cylinders less than 2 ft
   high.  Multiply q^ from
   formula above by appropriate
   factor below:

               Height, ft
                                                               Factor
0.
0.
0.
0.
0.
1.
1
2
3
4
5
0
3.
2.
2.
1.
1.
1.
5
5
0
7
5
1
                       aHeat loss coefficient,  q  is related to q as follows:
                                               J-i               C
                                                "77T A   Ai
                                                60   s
Schmidt's experiments were conducted in a closed
laboratory environment designed to minimize drafts
and other disturbances.  Nevertheless, Sutton re-
ports that there was a considerable  amount  of
waver and fluctuation in the rising air column.  In
developing his equations, Sutton defined the hori-
zontal limits of the rising air column as the locus
of points having  a temperature difference  relative
to the ambient atmosphere equal to 10 percent of
that at the center of the column.

In view  of the facts  that this arbitrary definition
doesnottruly define the outer limits of the  rising
air  column and that  greater  effects of waver and
drafts may be expected in an industrial environ-
ment, a safety  factor should be applied in calcu-
lating the size of the hood required and the mini-
mum ventilation rate to assure complete capture
of the emissions.  Since high-canopy hoods usually
control  emissions arising from horizontal-plane
                              surfaces, a simplification can be derived by com-
                              bining equations  14 and 15 -with the heat transfer
                              coefficient for horizontal-plane surfaces and allow-
                              ing a 15 percent safety factor.
                                                                         (16)
                             Although the mean diameter of the rising air col-
                             umn  in  the  plane of  the hood face is determined
                             from equation 13, the hood must be made some-
                             what larger in order to assure complete capture
                             of the rising column of contaminated air as it wavers
                             back and forth and is  deflected by  drafts.  The
                             exact amount  of  allowance cannot be calculated
                             precisely, but factors that must be considered in-
                             clude the horizontal velocity of the air currents in
                             the  area,  the size and velocity of the rising air
                             jet,   and tne distance y of the hood above the hot

-------
                                              Hood Design
                                                                                  37
source.   Other factors being equal, it appears
most likely that the additional allowance for the
hood  size must be  a  function of the distance y.
Increasing the diameter of the hood by a factor of
0. 8 y has been recommended (Industrial Ventila-
tion, I960).   The total volume for the hood  can be
calculated from
          V   =
VfAc
                  v (A  - A )
                   r  f     c
(17)
                                     Diameter of rising air stream at the hood face
                                     from Equation 13:
                                                D   =  0. 5 xr
                                                 c          f
                                                             0.88
                                                D   =  0. 5 (21)
                                                              0.88
                                                                                 = 7.3 feet
                                                      Area of rising air stream at the hood face:
•where

  , V

   Vf
=  the total volume entering the hood.cfm

=  the velocity of the rising air column at
   the hood face, fpm

=  the area of the rising column of con-
   taminated air at the hood face,  ft

=  the required velocity through the  re-
   maining area of the hood,  A  - AC,  fpm

=  the total area of the hood face,  ft^.
 The value  of  vr  selected will depend upon the
 draftiness,  height  of the hood above the source,
 and the seriousness  of  permitting  some of the
 contaminated  air to escape capture.  The value
 of this velocity is  usually taken in the  range  of
 100 to 200 fpm.  It  is recommended that a value
 less  than 100 fpm  not be used except under ex-
 ceptional circumstances.  The following  problem
 illustrates the use of this method to design a high-
 canopy hood  to  control  the  emissions  from a
 metal-melting furnace.
 Example 5

 Given:

 A zinc-melting pot 4 feet in diameter with metal
 temperature 880°F.   A high-canopy hood is to
 be used to capture emissions.  Because of inter-
 ference, the hood must be located  10 feet  above
 the pot.  Ambient air temperature is 80°F.

 Problem:

 Determine the size of hood and exhaust rate
 required.

 Solution:

 z   =  11 feet from Figure 13 for 4-foot-diameter
 source
                                                A   =  (0.7854)(7.3)
                                                 c
                                                       - 42 square feet
                                                      Hood size required- -including increase to allowfor
                                                      waver of jet and effect of drafts:
                                                                D   =  D    +  0.8y
                                                                  f       c
                                                D   =  7.3  +   (0.8)(10) = 15.3

                                                Use  15-foot-4-inch-diameter hood

                                     Area of hood face:
                                                   =  7 "V2
                                               A  =  (0.7854)(15.33)

                                                      =  185 square feet

                                     Velocity of  rising air jet at hood face:
                                                              1/4
                                                           . 57)1/3(800)5/1Z
                                                             (21)
                                                      = 143 fpm
                                                                1/4
                                     Total volume required for hood:
                                               V
                                                          .  =  v A   +  100 (A  - A )
                                                          tic           f    c
                                               V  =  (143)(42)  +  (100)(185-42)
                                                       =  20, 300 cfm
           xf  =  z  +  y

           x  =  11  +  10
                   =  21 feet
                                              If the hood could be lowered, the volume required
                                              to capture the emissions -would be reduced sub-
                                              stantially as illustrated below:

-------
38
                         DESIGN OF LOCAL EXHAUST SYSTEMS
Example 6

Given:

The same furnace as in example problem No. 5,
but the hood is lowered to 6 feet above the pot.
                                                       (8)(12.57)1/3 (8QO)5712
                                                              (17)
                                                                  1/4
                                                                                 =  149 fpm
                                             Total volume required for hood:
Problem:

Determine the size of hood and exhaust rate
required.

Solution:

z  =  11 feet from Figure 13 for 4-foot-diameter
source
       xf  =  z  +  y
       x   =  11  +  6
                           =  17 feet
Diameter of rising air  stream at the hood face
from equation 13.
                                                    V   -  v A  +  100 (A.  -  A  )
                                                     t      f c          f     c
           =  (149)(29.2)
           =  10, 800  cfm
                                                                          (100)(93.7-29.2)
Rectangular high-canopy hoods

The control of emissions from sources -with other
than circular shape may best be handled by hoods
of appropriate shape.   Thus, a rectangular  source
would require a rectangular hood in order to min-
imize  the  ventilation  requirements.   A circular
hood used to control a rectangular source of emis-
sion would require  an excessive  volume.   The
method used to design  a hood for a rectangular
source is illustrated in example 7.
       D    =   0.5x°'88
         c         f

       D    =   0. 5  (17)°' 88   =  6. 1 feet
Area of the rising air stream at the hood face:


       A   =  f (D )2
         c     4    c

       A   =   (0.7854)(6. 1)    =  29. 2 square feet
         c

Hood size required:

       Df  =   D    +   0.8 y


       Df  =   (6. 1) + (0. 8)(6)   = 10.9 feet

       Use 10-foot-11-inch-diameter hood
                                             Example 7

                                             Given:

                                             A rectangular lead-melting furnace 2 feet 6 inches
                                             wide by 4 feet long.  Metal temperature 700°F. A
                                             high-canopy hood is to be used located  8 feet  .bove
                                             furnace.  Assume 80 °F  ambient air.


                                             Problem.:

                                             Determine the dimensions of the hood and the ex-
                                             haust rate required.

                                             Solution:

                                             z =  6. 2 from Figure 13 for 2. 5-foot  source
                                                    x   =  z + y =  6. 2 + 8     = 14. 2 feet
Area of the hood face:
                                             The "width of the  rising air jet at the hood may be
                                             calculated from
    f  =  (0.7854)(10.92)    = 93. 7 square feet
Velocity of rising air jet at hood face:
             8(A
vf -          174"
           xf
                                                             D   =  0.5 xr
                                                              c          f
                                                             D   =0.5 (14. 2)
                                                              c
                                                                      0. 88
                                                                                = 5. 2 feet
                                                      The length of the rising air jet may be assumed
                                                      to be increased over that of the source the same
                                                      amount as the width
                                                             D   =  (4)  -1-  (5.2 - 2.5)   =6.7 feet
                                                              c

-------
                                             Hood Design
                                                                            39
The area of the rising air jet is
       A  = (5.Z)(6.7)   =  35 square feet
         c
The hood must be larger than the rising air stream
to allow for waver and drafts.   By allowing 0. 8 y
for both width and length, the hood size is

        Width = (5.2)  +  (0.8)(8)   =  11. 6 feet

        Length =  (6. 7) +  (0. 8)(8)   =13.1 feet

        Use hood 11 feet 7 inches wide by  13 feet
        1 inch long


Area  of hood:


      Af =  (11.58M13. 083)   = 152  square feet


Velocity of rising air  jet:
             (8)(A
       Vf =
1/4
                       (620)
                           5/12
                                   =  130 fpm
important distinction  is that the hood  is close
enough  to the  source  that  very little mixing be-
tween the rising air column and the surrounding
atmosphere occurs.  The diameter of the air col-
umn may,  therefore,  be considered essentially
equal to the diameter of the hot source.  The hood
needbe larger by only a small amount than the hot
source to provide for the effects  of waver and de-
flection due to drafts.  When drafts are not a  seri-
ous problem,  extending the hood  6 inches  on all
sides should be  sufficient.  This means that the
hood face diameter must be taken  as  1 foot greater
than the diameter of the source.  For rectangular
sources,  a  rectangular hood  would be provided
•with dimensions 1 foot wider and 1 foot longer than
the source.  Under more severe conditions of draft
or toxic emissions, or  both,  a greater safety factor
is required,  which can be provided by increasing
the size  of the  hood  an additional foot or more  or
byproviding a complete enclosure.  A solution to
the problem of designing low-canopy hoods for hot
sources  has been proposed  by Hemeon (1955).

Although the hood is usually larger than the source,
little  error occurs  if they are considered equal.
The total volume for the hood may then  be deter-
mined from the following equation obtained by re-
arranging terms in Hemeon's equation and apply-
ing a 15  percent safety factor.
                                                                          (18)
Total volume required for hood:
       V  =  v A  + v  (A  - A )
         t     f  c    r  f    c
  V  =  (130)(35) +  (200)(152-35) =  28, 000 cfm
                               •where

                                  Vt
                                  °f
                                  At
          total volume ior the hood, cfm

          the diameter of the hood, ft
          the difference bet-ween the temperature
          of the hot source and the ambient at-
          mosphere,  °F.
Note that in this problem a velocity of 200 fpm was
used through the area of the hood in excess of the
area of the rising air column.  A larger value was
selected for this  case because lead fumes must
be captured completely to protect the health of the
•workers in the area.
                               A  graphical  solution to equation  18 is shown in
                               Figure 14.  To use this graph, select a hood size
                               1 or 2 feet larger than the source.  The total vol-
                               ume required for a hood Df feet in diameter may
                               then be  read  directly from the graph for the actual
                               temperature difference  At between the hot  source
                               and the  surrounding atmosphere.
Circular low-canopy hoods

The design of low-canopy hoods is somewhat dif-
ferent from  that for high-canopy hoods.  A hood
may be considered a low-canopy hood when the
distance between the hood and the hot source does
not exceed approximately the diameter of the
source, or 3 feet, whichever is smaller.  A rigid
distinction between low-canopy hoods and high-
canopy  hoods is not intended or necessary.  The
                               Example 8

                               Given:
                               A low-canopy hood is to be used to capture the
                               emissions during fluxing and slagging of brass
                               in a 20-inch-diameter ladle.  The metal tem-
                               perature during this operation will not exceed
                               2, 350°F.   The hood will be located 24 inches
                               above the metal surface.  Ambient temperature
                               may be assumed to be 80°F.

-------
40
                                DESIGN OF LOCAL EXHAUST SYSTEMS
Q
o
o
                  200
300
400   500
                                                    ,000
                                                                  2,000
                                                            3,000  4,000 5,000

                      TOTAL  VENTILATION RATE (Vt),  cfm
Figure  14.  Minimum ventilation rates required  for circular low-canopy  hooas.
                                                                                                   10,000
 Problem:

 Determine the size of hood and exhaust rate
 required.


 Solution:

 Temperature difference between hot source and
 ambient air:
        At  =  2,350
                        80
    =  2., 270°F
 Use a hood diameter 1 foot larger than the hot
 source:
        Df  =   1.67   +1.0     =  2.67 feet
Total exhaust rate required from Figure 14:


                  V          =  1, 150 cfm

Rectangular low-canopy hoods

In a similar manner, Hemeon's equations for
low-canopy hoods may be modified and simpli-
fied for application to rectangular hoods.  With
a 15 percent safety factor, the equation then
becomes
                                                                         ,  , ,4/3   5/12
                                                                      =  o. 2 b    At
                                                                     (19)
                                                     where

                                                        V
                                                         At  =
                              the total volume for a low-canopy rec-
                              tangular hood, cfm

                              the length of the rectangular hood (usu-
                              ally I to 2 feet larger than the source),
                              ft

                              -width of the rectangular hood (usually 1
                              to 2 feet larger than the source), ft

                              the temperature difference between the
                              hot source and the surrounding atmo-
                              sphere,  °F.
                                                      Figure 15 is a graphical solution of equation 19.
                                                      The use of this graph to design a low-canopy rec-
                                                      tangular hood for a rectangular source is illus-
                                                      trated in example 9.

                                                      Example  9

                                                      Given:

                                                      A zinc die-casting machine with a 2-foot-wide by
                                                      3-foot-long holding  pot for  the molten zinc.  A
                                                      low-canopy hood is to be provided 30 inches above
                                                      the pot.   The metal temperature is  820°F.  Am-
                                                      bient air temperature is 90°F.

-------
                                             Hood Design
                                                                       41
                     60
80   100      150    200      300    400   500  600    800  1,000
   MINIMUM VENTILATION RATE (VfL), dm ft of hood  length
                                  1,500
                Figure 15.  Minimum ventilation rates for  rectangular low-canopy hoods.
Problem:

Determine hood size and exhaust rate required.
                          Total exhaust rate required for hood:
                                                        V   =  430  x  4
                                                        =  1, YZO cfm
Solution:
Use a hood 1 foot wider and 1 foot longer than
the source.

   Hood size =  3 feet wide by 4 feet long.
Temperature difference between the hot source
and ambient air:
   At  =  820 - 90
   = 730T
Exhaust rate required per foot of hood length
from Figure 15:
                                430 cfm/ft
Enclosures

A low-canopy hood with baffles is essentially the
samea.s a complete enclosure.  The exhaust rate
for an enclosure around a hot source must, there-
fore, De based on the  same principles as that for
a low-canopy hood. Enclosures for hot processes
cannot, however, be designed in the same manner
as for  cold processes.  Here again,  the thermal
draft must  be accommodated by the hood.   Fail-
ure  to  do so will certainly  result in emissions
escaping from the hood  openings.  After deter-
mining the exhaust rate required to accommodate
the thermal draft,  calculate the hood face velocity
or indraft through all openings. The indraft through
all openings in the hood should not be less than  100
fpm under any circumstances.  When air contami-
nants are released with considerable force, a min-
imum indraft velocity of 200 fpm should be pro-
vided.  When the  air  contaminants are released
with extremely great force as, for example, in  a.

-------
                                 DESIGN OF LOCAL EXHAUST SYSTEMS
direct-arc electric steel-melting furnace,  an in-
draft of 500 to 800 fpm through all openings in the
hood is required.

Specific Problems

Steaming tanks

When the hot source is  a steaming tank of water,
Hemeon (1955) develops a special equation by as-
suming a latent heat of 1,000  Btu per pound of
water evaporated.  He derives the following equa-
tion for the total volume required for a low-canopy
hood venting a tank of steaming hot water.
        V
  -  290 (W  A, D )
           s  f  t
                             1/3
                                            (20)
where
   V   =  the total hood exhaust rate, cfm
    t
   W
     s

   Af


   D
the rate at which steam is released,
Ib/min
the area of the hood face,  assumed
approximately equal to the tank area,
ft2
the diameter for circular tanks or the
•width for  rectangular tanks, ft.
                                              A
       =  the rate at which heat is transferred
          to the air  in the  hood from the hot
          source,  Btu/min
       =  the area of the orifice,  ft
       =  the average  temperature of the air in-
          side the hood, °F.
                                                            11 feet
                                                           Figure  16.   Illustration of leakage  from
                                                           top of  hood  (Hemeon,  1955)
Preventing leakage

Hoods for hot processes must be airtight.   When
leaks or  openings in the hood above the level of
the hood  face occur,  as  illustrated in Figure 16,
they will  be a source of leakage owing to a chim-
ney effect, unless the volume vented from the hood
is  substantially  increased.   Since  openings may
sometimes  be unavoidable in the upper portions
of  an enclosure  or canopy hood, a means of de-
termining the  amount of the leakage and the in-
crease  in the  volume required to  eliminate the
leakage is necessary.  Hemeon (1955) has  devel-
oped an equation to determine the volume of leak-
age from a sharp-edge orifice in a hood at a point
above the hood face.
         v  = 200|
                       q
                      o c
                               ,1/3
                     (460 + t
                    o       m'
                                  (21)
•where
          the velocity of escape through orifices
          in the upper portions of a hood, fpm
          the vertical distance above the hood
          face to the location of the orifice, ft
A  small amount of leakage can often be tolerated;
however, if the emissions are toxic or malodorous,
the leakage must be prevented completely.  If all
the cracks or  openings in the upper portion of the
hood cannot be eliminated, the volume vented from
the hood  must be increased so that the minimum
indraft velocity through all  openings including the
hood lace is in excess of the escape velocity through
the orifice calculated by means of equation 21. The
value of qc may be determined by using the appro-
priate heat transfer coefficient from Table 5 to-
gether with equation 15 or by any other appropriate
means.   This method is illustrated in example 10.


Example 10

Given:

Several oil-fired crucible furnaces are hooded
and vented as illustrated in Figure 16.  The en-
closure is 20 feet long.  It  is not  possible to pre-
vent leakage  at the top of the enclosure.  Total
area of the leakage openings is 1  square foot. The
fuel rate is 30 gallons per hour and the heating
value is  140, 000 Btu per gallon.  Assume 80°F
ambient air and 150°F average temperature of
gases in the hood.

-------
                                              Hood Design
                                                                   43
 Problem:
                       HOOD CONSTRUCTION
 Determine the minimum face velocity and total
 exhaust rate required to prevent leakage of con-
 taminated air through the upper openings by as-
 suming all openings are sharp-edge orifices.

 Solution:

 The rate of heat generation:

                           Btu     1
    qc= du_.x 140,000—  x^

       = 70,000^
                mm
 Total open area:
    A   =  (20  x 7)  +  1       = 141 ft
     o
 The escape velocity through the leakage orifice:
                   (460  +  150)

 The required exhaust rate:
    V   =  v A
     t      e   o
    V   =  (420)(141)
                                     = 420 fpm
= 59, 000 cfm
 Check mean hood air temperature:
              q   =   V  p c At
               c      t   p
 where
     p  =  average density of mixture, 0. 075 Ib/ft
    c   =  average specific heat of mixture,  0. 24
     P     Btu/lb per °F

    At   =  average hood temperature minus ambient
           air temperature.

 Solving for At in the  equation:
   At   =
                 70,000
           (59, 000)(0.075)(0. 24)
                              ~  = 66°F
  At    =  80  +  66
    m
  = 146°F
This adequately approximates the original assump-
tion.
If air temperature and corrosion problems are not
severe,  hoods  are usually constructed of galva-
nized sheet metal.  As-with elbows and transitions,
the metal should be at least 2 gauges heavier than
the  connecting  duct.  Reinforcement with  angle
iron and other devices is required except for very
small  hoods.

High-Temperature  Materials

For elevated temperatures up to approximately
900 °F, black iron may be employed, the thickness
of  the metal  being increased in proportion  to the
temperature.   For temperatures in the range of
400 to 500°F, 10-gauge metal is  most commonly
used.   When the temperature  of the  hood is as
high as 900 °F,  the thickness of  the metal may
be  increased up to 1/4 inch.  Over 900°F, up to
about  1,600 to 1,800°F,  stainless steel must be
employed.  If the hood temperature periodically
exceeds  1,800°F or is in excess of  l,600°Ffor
a substantial  amount of the time,   refractory ma-
terials are required.

Corrosion-Resistant Materials

A variety of materials are available for corrosive
conditions. Plywood is  sometimes employed for
relatively light duty or for temporary installa-
tions.   A  rubber  or plastic coating may  some-
times  be  applied  on steel.  Some of these coat-
ings can be applied like ordinary paint.  If severe
corrosion problems  exist, hoods must be  con-
structed  of sheets of PVC (polyvinyl chloride),
glass fiber, or  transite.
 Design Proportions

 Although  the items of primary importance in de-
 signinghoods are the size,  shape,  and location of
 the hood  face, and the exhaust rate,  the depth of
 the hood and the transition to the connecting duct
 must also be considered.  A hood that is too shal-
 low  is nothing more than a flanged-duct opening.
 On the other hand,  excessive depth increases the
 cost without serving a useful purpose.


 Transition to Exhaust Duct

It is desirable  to have a transition piece between
the hood and the exhaust system ductwork that is
 cone shaped with an included angle of 60° or less.
 This can  often be made a part of the hood itself.
 The exact shape of the transition is the most im-
portant factor in determining the hood orifice
losses. Examples of good practice in this regard
are illustrated in Figure  17.

-------
44_
DESIGN OF LOCAL EXHAUST SYSTEMS
             POURING STATION FOR SMALL MOLDS
                                 TOP BAFFLE
TRANSITION
PIE

CE 	 ^/


^4-
y ^
	 r
H;
« 	 5/3 b 	 •
WIN


MOLD

;»'•'
jf


f LANCE

                                    MOLD

                                     CLEAPANCFX.
      V = 200(10X2 + A)
      where V = minimum ventilation  rate, cfm
           X = distance between hood and ladle, ft
           A = face area of hood,  ft2

              ENCLOSURE FOR FOUNDRY  SHAKEOUT
 TRANSITION
  PIECE 	
     Provide a minimum indraft of 200 cfm per square
     foot of opening but not less than 200 cfm per
     square foot of grate area for  hot castings.

    Figure  17.   Examples  of good  hood design.
    Note use of enclosure,  flanges, and transi-
    tions   (Industrial Ventilation,  1960)

               DUCT DESIGN

 The design of hoods and tht  determination of ex-
 haust volumes have been considered.  Now the de-
 sign of the ductwork required to conduct the  con-
 taminants to a collection device will be discussed.
 Calculations of pressure drop,  system resistance,
 system balance, and  duct construction  will be
 covered.
                      Whenlongrows of equipment must be served, the
                      main  header duct should be  located as near as
                      possible to the center of the group of  equipment in
                      order to equalize runs of branch duct.   Where nec-
                      essary, the equipment should be divided into  sub-
                      groups and subheaders located to provide good
                      distribution of airflow in the duct system, and
                      proper velocities at the hood and enclosure inlets.


                      Air flowing in ducts  encounters resistance due to
                      frictionand dynamic losses.  Friction losses oc-
                      cur from the rubbing of the air along the surface
                      of the duct, whereas dynamic losses occur from
                      air turbulence due to rapid changes in velocity or
                      direction.   From Bernoulli's theorem, the sum
                      of the static and  velocity pressure upstream is
                      equal to the sum of the static and velocity pres-
                      sure  plus the friction and dynamic losses down-
                      stream.   A fan is normally  required to provide
                      sufficient static pressure to overcome the resis-
                      tance of the system.


                      TYPES OF  LOSSES

                      The losses in an exhaust system may be expressed
                      as inertia losses,  orifice losses,  straight-duct
                      friction losses, elbow  and branch entry losses,
                      and contraction and expansion  losses.  In addition
                      to losses from the ductwork, there are also pres-
                      sure  losses through  the  air  pollution  collection
                      equipment.
                      Inertia Losses

                      Inertia losses  may  be defined as the energy re-
                      quired to accelerate the air from rest to the ve-
                      locity in the duct.  In effect,  they are the velocity
                      pressure.  Many  other losses are expressed in
                      terms of velocity pressure, but velocity pressure
                      itself represents the  energy of acceleration.   It is
                      calculated by equation 5,  set forth earlier.  By
                      this equation, values of velocity pressure versus
                      velocity have been calculated, as  shown in Table 6.


                      Orifice Losses
GENERAL LAYOUT  CONSIDERATIONS

Before designing and installing an exhaust system,
try to group together the equipment to be served
in order to make the system as small and com-
pact as possible and thereby reduce the resistance
load and power required.  Extending an exhaust
system to  reach an isolated hood or enclosure is
usually costly in regard to power consumption,  and
if the isolated hood cannot be located close to the
main exhaust system, the installation of a separate
system to care for the isolated equipment is prob-
ably preferable,  in terms  of operating economy.
                      The pressure or energy losses at the hood or duct
                      entrances vary widely depending on the shape of
                      the  entrance.   The  losses  are due mainly to the
                      vena contracta at the hood throat.  They are usu-
                      ally expressed as a percentage of the velocity pres-
                      sure corresponding  to the  velocity at  the hood
                      throat.  The losses vary from 1. 8 hv for a sharp-
                      edge orifice to nearly zero for a well-rounded bell-
                      mouth  entry.   Losses for common shapes of en-
                      tries are given in Figure 18.  Most complicated
                      entries can be broken down into two or more  sim-
                      ple  entries, and the total entry loss computed by
                      adding the individual losses.

-------
                                              Duct Design
                                              45
      Table 6.  TABLE  FOR CONVERSION
                OF VELOCITY (va)
          TO VELOCITY PRESSURE (hv)
va, fpm
400
500
600
700
800
900
1,000
1, 100
1,200
1, 300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
2, 100
2,200
2,300
2,400
2,500
2,600
2,700
2,800
2,900
3,000
3, 100
3,200
3,300
hv, in. WC
0.010
0. 016
0.022
0. 031
0. 040
0. 051
0. 062
0. 075
0. 090
0. 105
0. 122
0. 140
0. 160
0. 180
0. 202
0. 225
0.249
0. 275
0. 301
0. 329
0. 359
0. 389
0.421
0. 454
0. 489
0. 524
0. 561
0. 599
0. 638
0. 678
va, fpm
3, 400
3, 500
3, 600
3, 700
3, 800
3,900
4, 000
4, 100
4,200
4, 300
4, 400
4, 500
4, 600
4, 700
4, 800
4, 900
5, 000
5, 100
5, 200
5, 300
5, 400
5, 500
5, 600
5, 700
5, 800
5,900
6, 000
6, 100
6, 200

hv, in.WC
0. 720
0. 764
0.808
0.853
0. 900
0.948
0.998
1.049
1. 100
1. 152
1.208
1.262
1.319
1.377
1.435
1.496
1.558
1.621
1.685
1.751
1.817
1.886
1.955
2.026
2.098
2. 170
2.244
2.320
2.397

Straight-Duct Friction Losses

Many  charts have been developed  that  give  the
friction  losses in straight ducts.  Most of these
charts are based on new,   clean duct.  A resis-
tance chart in which  allowance has been made for
moderate roughness of the duct is shown in Figure 1 9.
Most exhaust  systems  collecting appreciable a-
mounts of air contaminants are believed to reach
at least  this degree  of  roughness in a relatively
short time after being placed in operation.   Fric-
tion loss in inches of water per  100 feet of  duct is
plotted in terms  of  duct diameter,  velocity,  and
volume.   If  any two  of these quantities are given,
the other two can be read from the chart.


Elbow and Branch Entry Losses

The simplest way to express resistance of elbows
and branch entries is  in equivalent feet of straight
duct of the  same diameter that will have the same
pressure loss as the fitting.  The equivalent lengths
are added to the actual lengths of straight duct,  and
the resistance for each run computed from Figure  19.
Equivalent lengths of elbows and entries are given
in Table 7.

Exhaust system  calculator

Most of the  charts,  tables,  and equations have
been  incorporated into a single  sliderule device,
as illustrated in Figure 20.  The  upper scales on
the front side will give friction losses just as in
Figure  19.   Velocity pressure can be read from
the same scales by setting 4, 000 on the velocity
scale opposite  1. 00 on the friction scale.  Then,
opposite any other velocity,  the friction  scale
will give the cor rect velocity pressure .   The lower
scales perform  volume  and velocity calculations
fora given duct diameter.   Temperature correc-
tion  scales  and  a duct condition correction scale
are provided.  On the reverse side (not shown in
Figure 20),  equivalent lengths for elbows,  branch
entries,  and weather caps  are given.  On the  low-
er portion of each side, hood entry  losses  are
given for all the usual entry shapes.
                                                        PLAIN DUCT
                                                           END
             FLANGED DUCT
                 END
TRAP OR SETTLING CHAMBER
                                                       STANDARD GRINDER HOOD
                                                                                              ORIFICE PLUS
                                                                                              FLANGED DUCT
                      HE  = ''8HV   HE = 1 .8HV ORIFICE
                                       + 0.5 H,, DUCT
 FLARED ENTRY        DIRECT BRANCH
                     BOOTH
                                    BELL-MOUTH ENTRY
                        Z2-
                                        = 0.025H,,
                   TAPERED HOODS

4-
i b
0
s
o
0
0
0
E
ROUND
0.15 H
0 .OB H
0 tj B H
0 08 H
0 1 S H
0.26 H
YTRY LOSS
RECTANGU
0 . 2 5 H
0 . 1 6 H
0.15 H
0 1 7 H
0-25 H
0,35 H

_AR






E N T
R 0 U
0 .
0 .
0 .
0 .
0 ,
0
R Y C 0 E F F
N D RECTA
0 . 6
0 . 9
0 . 9
0 . 9
0 . 6
0 ,8
C 1 EM T
N G U L A R






   Figure 18.   Hood entry losses (Adapted  from
   Industrial  Ventilation,  1956).

-------
46
      DESIGN OF LOCAL EXHAUST SYSTEMS
       100,000
           100
             0
               10
20   0.30 0.40 0.50   0.70   1
            FRICTION, inches
0          23

of water/I 00 feet
                                                     4   5  678910
                                    Figure  19.   Friction  loss  chart.

-------
                                            Duct Design
                                             47
         Table 7.   AIR FLOW RESISTANCE CAUSED BY ELBOWS AND BRANCH ENTRIES
                    EXPRESSED AS EQUIVALENT FEET OF STRAIGHT DUCT
                            (Adapted from Industrial Ventilation, 1956)




Diameter
of duct,
in.
3
4
5
6
7
8
9
10
11
12
14
16
18
20
22
24
26
28
30
36
40
48




90° Elbow
/
/

»D«

Throat radius (R)
1.0 D
5
7
9
11
12
14
17
20
23
25
30
36
41
46
53
59
64
71
75
92
105
130
1. 5 D
4
5
6
7
9
10
12
13
16
17
21
24
28
32
37
40
44
49
51
63
72
89
2. 0 D
3
4
5
6
7
8
10
11
13
14
17
20
23
26
30
33
36
40
42
52
59
73
























1





1

s^~
/


/^
/ R

e/


/
&/
^^

60° Elbow
Throat radius (R)
0 D
4
5
7
8
9
1
12
14
•
7
20
23
27
32
36
39
44
48
52
55
68
75
91
1. 5 D
3
4
5
5
6
7
9
10
12
13
16
18
22
24
27
30
33
35
38
46
51
62
2.0 D
2
3
4
4
5
6
7
8
10
11
13
15
18
20
22
25
27
29
31
38
42
51
45° Elbow
Throat radius (R)
1.0 D
2
4
5
6
7
8
9
10
11
12
14
17
20
23
27
30
32
35
37
46
52
64
T. 5 D
1
3
4
4
5
5
6
7
8
9
10
12
13
16
18
20
22
24
26
32
35
44
2. 0 D
1
2
3
3
4
4
5
6
6
7
8
10
11
13
15
16
18
20
21
26
29
36

(j




Branch entry
Angle of entry (9)
45°
3
5
6
7
9
11
12
14
15
18
21
25
28
32
36
40
44
47
51
-
-
-
30°
2
3,
4
5
6
7
8
9
10
11
13
15
18
20
23
25
28
30
32
-
-
-






















15°
1
1
2
2
3
3
4
4
5
5
6
8
9
10
11
13
14
15
16
-
-
-
Contraction  and Expansion Losses

When the cross -sectional area of a channel through
•which a gas  is flowing contracts, a pressure loss
is encountered.  The magnitude of  the loss de-
pends  upon  the abruptness of the contraction.
When the cross-sectional  area expands,  a portion
of the decrease in velocity pressure  may be con-
verted into static pressure.  The increase or de-
crease in pressure from expansion and contraction
can be calculated from the diagrams and formulas
given in Tables  8  and 9.  Losses  from small
changes in velocity can be neglected.
data,  resistances are usually estimated by com-
paring them with known values for similar equip-
ment.  In collectors such as cyclones and scrub-
bers -where the velocities are high, pressure varies
approximately with the square of the velocity.  If
the loss is known at one velocity,  the loss at any
other velocity is computed by multiplying by the
square of the ratio of the velocities.  In cloth fil-
ter dust collectors, however,  the flow is laminar,
and pressure drop varies  approximately as  the
first power of the velocity ratios.


DESIGN  PROCEDURES
Collection Equipment

Pressure through collection  equipment varies
widely. Most manufacturers supply data on pres-
sure drop for their equipment.  In the absence of
Methods of Calculation

The  first step in designing an exhaust system is
to determine  the  volume  of air required at each
hood or  enclosure to  ensure complete collection

-------
48
                                 DESIGN OF LOCAL EXHAUST SYSTEMS
                                           HOOD ENTRY LOSSES
                                Figure  20.   Exhaust system calculator.
of the air contaminants,  by using the principles
given previously.  The required conveying velocity
is then determined from  the  nature  of the con-
taminant.  Table  10 can  be used in determining
conveying velocities.

The  branch duct and  header diameters are then
calculated to give the minimum conveying velocity.
When the calculated diameter lies between  two
available diameters, the smaller diameter should
be chosen to ensure an adequate conveying velocity.
The duct layout is then completed, and the lengths
of ducts and number  and  kinds of fittings deter-
mined.  The  system resistance can then be com-
puted.  The calculations can be most easily accom-
plished by using a tabular form such as those  shown
later.
Methods  of  Design

In designing a system of ductwork with multiple
branches,  the resistance  of each branch must be
adjusted so that the static pressure balance, which
exists at the junction  of two branches, will give
the desired  volume in each  branch.  In general,
two methods of accomplishing this result are used:

1. The balanced-duct or static pressure balance
   method, in which  duct sizes are chosen so that
   the static-pressure balance at each junction -will
   achieve the  desired  air volume in each branch
   duct.

2. The blast gate adjustment method,  inwhichcal-
   culations begin at the branch of greatest resis-
   tance.   The other  branches are merely sized

-------
                                               Duct Design
                                               49
   to give the minimum  required velocity at the
   desired volume.   Blast gates are provided in
   eachbranch, and after construction, the gates
   are adjusted to give the desired volume in each
   branch duct.

   The balanced-duct system is less flexible and
   more  tedious to calculate, but it has no  blast
   gates that might collect deposits or be tampered
   withbyunauthorized persons.  Layout must be
   in complete detail and construction must follow
   layout exactly.

   The blast gate system has more flexibility for
   future changes and is easier to calculate; vol-
   umes  can be adjusted  within certain  ranges,
   and duct location is not so critical.
Calculation Procedures

The balanced-duct method:  The calculations for a
balanced-duct system start at the branch of greatest
resistance.  Using the duct size that will give the
required volume at the minimum  conveying ve-
locity, calculate the static pressure up to the junc-
tion with the next branch.  The  static pressure is
then calculated along this next branch to the same
junction.  If the two calculations agree -within 5 per-
cent, the branches may be considered in balance.
Table 8.  DUCTWORK DESIGN DATA SHOWING
  STATIC PRESSURE LOSSES AND REGAINS3-
 THROUGH ENLARGING DUCT TRANSITIONS
                                 1962)
                       e
Taper angle (6),
degrees
3-1/2
5
10
15
20
25
30
over 30
X
8.13
5.73
2.84
1.86
1.38
1.07
0.87

Regain factor (R)
0.78
0.72
0.56
0.42
0.28
0. H
0.00
0.00
Loss factor (L)
0.22
0.28
0.44
0.58
0.72
0.87
1.00
1.00
 aThe regain and loss factors are expressed as a fraction of
  the velocity pressure difference between points (1) and (2).
  In calculating the static pressure changes through an en-
  larging duct transition, select R from the table and sub-
  stitute in the equation
          SP_
                =  SP
 where
                        hv is (+)
         SP is  (+) in discharge duct from fan
         SP is  (-) in inlet duct to fan
                     Table 9.  DUCTWORK DESIGN DATA SHOWING  CONTRACTION
                   PRESSURE LOSSES THROUGH DECREASING DUCT TRANSITIONS
                                       (Industrial Ventilation,  1956)
Taperangle (6),
degrees
5
10
15
20
25
30
45
60
X
Dl-°2
5. 73
2.84
1.86
1. 38
1. 07
0. 87
0. 50
0.29
Loss fraction (L)
of hv. difference
0. 05
0. 06
0. 08
0. 10
0. 11
0. 13
0.20
0.30
For abrupt contraction (6 > 60°)
Ratio DZ/DI
0. 1
0.2
0.3
0.4
0.5
0.6
0. 7

Factor K
0.48
0.46
0.42
0.37
0.32
0.26
0.20

              SP change:
                  SP  =SP -(h   -h
                    2     1    v
-L(h  -h   )
     SP change:
         SP  =SP - (h
           2     1   v_

-------
 50
                                 DESIGN OF LOCAL EXHAUST SYSTEMS
                      Table 10.  RECOMMENDED MINIMUM DUCT VELOCITIES
                                            (Brandt,  1947)
                   Nature of contaminant
   Example s
Duct velocity, fpm
                 Gases,  vapors, smokes,
                 fumes,  and very light
                 dusts
                 Medium-density dry dust
                 Average industrial dust
                 Heavy dusts
All vapors,  gases,
and smokes; zinc
and aluminum ox-
ide fumes; wood,
flour,  and cotton
lint

Buffing lint;  saw-
dust; grain,   rub-
ber, and plastic
dust

Sandblast and
grinding dust,
•wood shavings,
cement dust

Lead,  and foundry
shakeout dusts;
metal turnings
      2,000
      3, 000
      4,000
      5,000
If  the  difference in static pressure is more than
20 percent, a  smaller  diameter  duct  normally
should be used for economy reasons in the branch
with the  lower pressure drop to increase its
resistance. Branch sizes smaller than 3 inches
in diameter should be avoided.  When the difference
in pressure loss in the two branches is between
5 and  20 percent,  balance  can be  obtained by
increasing the flow in the  branch with the lower
loss.    Since  pressure  losses increase -with the
square of  the volume, the  increased volume can
be readily calculated as:
                 A /hg larger
 Corrected cfm  = 1 /-	(Original cfm)  (22)
                  I/ h  lower     6
                  V  s

 The pressure loss in the header is then calculated
 to the next branch.  This branch is then sized to
 achieve a static pressure balance at this junction
 with the required volume (or slightly greater) in
 the branch duct.  This procedure is continued un-
 til the discharge point of the  system is reached.

 The blast gate  adjustment method:  The calcula-
 tions for a system to be balanced by blast gate ad-
 justment also start at the branch of greatest resis-
 tance and proceed to the header.  Pressure losses
 are then calculated only along the header.   Pres-
 sure drops in the remaining branches are not cal-
 culated except-when calculation is deemed advisable
 in order to check a branch to be sure its pressure
 drop  does not exceed  the  static pressure  at its
 junction •with the header.
         Fan Static  Pressure

         The preceding calculations are based on static
         pressure; that is, the balancing or governing pres-
         sures  at the duct junctions are static pressures.
         Most fan-rating  tables  are given in terms of fan
         static pressure.  The National Association of Fan
         Manufacturers defines the fan static pressure as
         the total pressure diminished by the velocity pres-
         sure at the fan outlet, or
            fan h   =   fan H   -  h  fan outlet         (23)
                 s               v
          On the absolute pressure scale,


               fan H  =  H outlet  -  H  inlet         (24)


          Combining the two equations
          fan h   = H outlet - H inlet - h  outlet
              s                       v
                 = h  outlet + h  outlet - (h  inlet + h  inlet)
                    S          V           S        V
                   - h  outlet
                     v
                 =  h  outlet  - h  inlet - h  inlet
                   s          s         v
                                 (25)
         Static pressures are nearly always measured rel-
         ative to atmospheric pressure, and static pressure
         at the fan inlet is negative.  In ordinary usage,
         only the numerical values are considered, in which
         case,  equation 25 becomes

-------
                                             Duct Design
                                             51
fan h  = h  outlet
     s    s
h  inlet  - h inlet     (26)
 s          v
In evaluating  the  performance of a fan,  examine
the tables to determine whether they are based on
fan static pressure or on total pressure.

Balanced-Duct  Calculations

A problem illustrating calculation by the balanced-
duct method is worked out as follows.  The given
operation involves the blending of dry powdered
materials.  A sketch of the equipment is given in
Figure 21.  The equipment and ventilation require-
ments are presented in Tables  11 and 12.

A minimum conveying velocity  of 3, 500 fpm is to
be maintained in all ducts.  Elbows have a throat
radius of 2 D.  The balanced-duct method is to be
used in the duct design.  The detailed calculations
are  shown  in Table  13.  Calculations  start at
branch A.  A 6-inch-diameter duct gives the near-
est velocity  to 3,  500 fpm at the required volume
of 750 cfm.  The  actual  velocity of 3, 800  fpm is
entered  in  column  5.  and  the  corresponding
velocity pressure, in column 6.   From Figure 18,
the entry loss  is 50 percent hv, which is entered
in column 7 left.   The length  of straight duct is
entered  in column 8.  The equivalent length for
the elbows  is  found  in Table 7, and the sum is
entered in column 9  right.   The total equivalent
length is then found by adding  column 8 and col-
umn 9 right and  entering the  sum in column 11.
The  resistance per  100  feet of duct is then read
from Figure 20 at  6-inch diameter and 3, 800 fpm,
and  is  entered in column 12.  The  resistance
pressure  (hr)  is   calculated by   multiplying
column 11 by column 12 and dividing by 100.  This
value is entered  in column 13.  The  static pres-
sure  is then the sum of the velocity pressure and
the hood loss  plus the resistance  pressure, col-
umn. 6 +  column 7  right + column 13.
In branch B,  a volume of 200 cfm is required.  A
3-1/2-inch duct would give a velocity of 3, 000 fpm,
-which  is below  the minimum.  Hence the branch
•was  calculated with a 3-inch duct at 4, 000 fpm.
The  resulting hg  (column 14 left) was more than
20 percent greater than that for branch A.  A 3-172-
inch duct must, therefore, be used and the volume
increased to 240 cfm to maintain the minimum ve-
locity.  At these conditions,  the hs values for the
two branches are -within 5 percent and may be  con-
sidered in balance.
In section C, a 7-inch duct will carry the  combined
volume from branches A and B at the  nearest ve-
locity above the minimum.  The onlypressure drop
     Figure 21.  SKetch of  exhaust system used
     in Table 11 showing duct design calcula-
     tions by the balanced-duct method.
                     Table 11.  EQUIPMENT AND VENTILATION REQUIREMENTS
                                      FOR SAMPLE PROBLEM
Equipment
Dump hopper (1),
2- by 3 -ft opening
Bucket elevator (2),
1 - by 2 -ft casing
Ribbon blender (3),
1- by 2 -ft opening
Drum -filling booth (4),
1- by 3 -ft opening
Cloth filter dust collector (5)
maximum resistance, 4 in.wg
Ventilation requirement
125-fpm indraft
through' opening
100 cfm per ft2
of casing area
150-fpm indraft
through opening
200-fpm indraft
through opening


Volume , cfm
750

200

300

600



234-767 O - 77 - 6

-------
52
DESIGN OF LOCAL EXHAUST SYSTEMS
   Table 12.  DUCT LENGTHS AND FITTINGS
       REQUIRED IN SAMPLE PROBLEM
Branch
A
B

C
D

E
F

G
H
Length, ft
14
4

7
6

3
11

12
8
Elbows, No.
and degree
2, 90
1, 90
1, 60

1, 90
1, 60

2, 90
1, 60
2, 90

Entries, No.
and degree

1, 30


1, 30


1, 30



is due to the friction in the 7 feet of straight duct.
This hr is added to the hs at the first junction.  In
branch D,  300 cfm is required,  and this volume
will give approximately 3, 450 fpm in a 4-inch duct.
The resulting hs  is, however,  about  20 percent
lower than  the hg at the  main.  The cfm  must,
therefore, be increased by the ratio of the square
roots of the static pressures,or from 300 to 350 cfm.

In main duct E, an 8-inch diameter duct will handle
a volume of 1, 340 cfm at a velocity of 3, 800 fpm.
An hr of 0. 10 inch  WC is  recorded in column 13,
giving an hs of 2. 87 inches WC to the  junction EF.

Calculation procedures for branch F  are similar
to those for branch E, and the required 600 cfm
for the drum-filling booth must be  increased to
640 cfm to obtain a static pressure balance at
junction EF.

The total volume of 1, 980 cfm gives  a velocity of
3,600 fpm in a 10-inch-diameter main duct G to
thebaghouse. This run of duct and two 90° elbows
have a resistance pressure of 0.88 inch WC, giv-
ing a total inlet  static pressure of 7.75 inches  WC,
after the given resistance of the baghouse is  added.
The outlet static pressure is calculated similarly
by calculating  the resistance of the  straight run
of  duct H.   This static pressure  of 0.21 inch WC
is added to the inlet static pressure.   The velocity
pressure of 0. 81 inch WC (one hv at a velocity of
3, 600 fpm  at the fan inlet) is subtracted from the
above total  static pressure to yield a fan static
pressure of 7.  15 inches WC.

Blast Gate  Method

The same system can be designed by the blast gate
adjustment method.  The calculations are shown
in  Table 14.   Branch A is calculated as before.
Branches B, D,  and F are calculated at or near
the minimum conveying velocity so  that the hg
drop in each does not exceed the hs at the junction
                     with the main.   No adjustments are made in the
                     volumes.  Blast gates will be installed in each of
                     these branches to provide the  required  increase
                     in resistance.
                     CHECKING  AN EXHAUST SYSTEM

                     The preceding example problem illustrates  the
                     calculations for designing an exhaust system.  In
                     checking plans for an exhaust system,  use similar
                     calculations but take a different approach.  A sys-
                     tem of ductwork with a specific exhauster is given
                     and the problem is to determine the flow conditions
                     that will exist.

                      The objectives of checking an exhaust system, are:

                      1.  To determine the exhaust volume and indraft
                         velocity at each  pickup point and evaluate the
                         adequacy of contaminant pickup;

                      2.  to determine the total exhaust volume and eval-
                         uate the size  and performance of the collector
                         or control device;

                      3.  to determine the system's static pressure and
                         evaluate the  fan  capacity,  speed, and horse-
                         power required;

                      4.  to determine the temperature at all points  in
                         the  system in order to evaluate the materials
                         of construction of the ductwork and the collector.
                      Illustrative Problem

                      To illustrate a method of checking an exhaust sys-
                      tem, another problem is -worked.  A line drawing
                      of the duct-work is given in Figure 22.  None of the
                      calculations  used  in  designing the  system  are
                      given.   Since no blast  gates are shown, assume
                      that the system-was designed by the balanced-duct
                      method.

                      Resistance calculations are  presented in Table 15.
                      This form -was designed for maximum facility in
                      checking an  exhaust  system.  Calculations  start
                      at hood A with an assumed velocity (or volume) of
                      3, 500 fpm. The static pressure drop is then com-
                      puted to junction_C_.  Branch B-C is then computed
                      •withan assumed velocity of  3, 500 fpm.   Since the
                      hs from this branch does  not match that from
                      branch A-C, the second velocity is corrected by
                      multiplying by the square root of hg A-C/hg B-C.
                      The corrected velocity is entered in column 14  and
                      is used to compute  the cfm, which is entered in
                      column 15.  The other branches are calculated in
                      the same manner,  that is, assume a velocity at
                      the hood and correct it by  the square root of the
                      hs ratio.  Thus, all  the calculations are related
                      to the original assumption  of velocity in the first
                      branch.

-------
Duct Design
53





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-------
54
DESIGN OF LOCAL EXHAUST SYSTEMS





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-------
Duct Design
                                                         55








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-------
56
DESIGN OF LOCAL EXHAUST SYSTEMS
0 [
B
4 in.

[


F
^J
H
ORIFICE LOSS = 0 65 hv
ELBOH THROAT RADIUS = 20
BRANCH ENTRIES = 30°
NO DAMPERS OR BLAST GATES USED
      Figure  22.  Layout of  ductwork used in
      example showing procedure  in checking
      an  exhaust system.
Since assumed values  of volume are used in the
calculations, the final result is the system's resis -
tance at a given total volume.  The system's resis-
tance will increase with increase in volume by the
square of the ratio of the increase in volume.  On
the other hand, the capacity of an exhauster de-
creases with increase in  resistance.   The one
point that satisfies both system and fan can best
be found by plotting the characteristic  curves of
the system and the fan.  The operating point is
the point of intersection of the two curves.  The
system's characteristic curve is that curve
established by the static pressure losses through
the exhaust system for various air volumes. It
is computed by starting -with the resistance  and
volume from Table 15 and calculating the  resis-
tance at other volumes by using the square of
the ratio of the volume change.  The curve for
the sample problem is  computed from  Table 16.
          Table 16.  CALCULATIONS
        FOR CHARACTERISTIC CURVE
Volume, cfm
1,600
1,800
2, 000
1,400
1,200
1, 000
500
Multiplying factor

(1, 800/1, 600)2 x 4. 84
(2, 000/1, 600)2 x 4.84
(1, 400/1, 600)2 x 4.84
(1,200/1,600)2 x 4.84
(1, 000/1, 600)2 x 4.84
(500/1, 600)2 x 4.84
New hg
4.84
6. 12
7.56
3. 71
2. 72
1.89
0.47
                                                     Fan hs is  used in computing this curve because
                                                     the fan,  a Chicago No. 25 Steel Plate Exhauster,
                                                     is rated by the methods of the National Associa-
                                                     tion of Fan Manufacturers  (NAFM).   The  fan
                                                     characteristic  curves are families  of  curves at
                                                     different fan speeds defining static pressures  de-
                                                     veloped for various volumes of air handled through
                                                     the fan.  These data are available from fan manu-
                                                     facturers.  Data for the single fan curve at  2, 600
                                                     rpmas specified by this example are obtained from
                                                     Chicago  Blower  Corporation Bulletin SPE-102.
                                                     Fan capacities at various static  pressures and at
                                                     the given speed nearest to 2, 600 rpm are tabulated
                                                     on the left in Table 17;  on the  right the figures  are
                                                     corrected to 2, 600 rpm by use of the fan laws, as
                                                     follows:
                                                                 cfm   =  cfm   x
                                                                       =  h     x
                                                                           si     LrpmiJ
                                 np?    =  hp,    x
                                                    rpm
                     A horsepower versus air volume curve can also
                     be plotted from Table 17.
                         Table 17.  FAN CAPACITY AT VARIOUS
                                   STATIC PRESSURES
From Chicago Bulletin
rpm
2,630
2,615
2, 605
2,625
2,620
cfm
2,470
2,240
2, 005
1,655
1, 065
hs
5
4
6
7
8
hp
4.44
3. 89
3. 44
3. 09
2. 54
Corrected to 2, 600 rpm
cfm
2, 440
2, 230
2, 000
1, 640
1, 050
hs
4.9
5. 4
6.0
6.9
7.8
hp
4. 3
3.8
3.4
3. 0
2.5
                                                     The  system  curve,  fan curve,  and horsepower
                                                     curve are plotted in Figure 23.   The fan and sys-
                                                     tem curves intersect at 1, 360 cfm and 6. 5 inches
                                                     hg.  The horsepower required is 3.2.
                                                     Since the volume obtained from the curves of Fig-
                                                     ure 23 is appreciably higher than the total volume
                                                     from  Table  15,  the volume at each hood must be
                                                     corrected.   The  correction factor is obtained by
                                                     dividing the volume from the curve by the total
                                                     volume from Table 15.  Corrections are made in
                                                     Table  18.

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                                  Duct Design
                                                   57
500
        1,000     1,500     2,000
                VOLUME, cfm
2,500
 Figure  23.   Characteristic curves  of an
 exhaust system.
           o
         3,000
                                                         Fan Curve Calculator

                                                         The calculations required to
                                                         produce a fan curve from catalog
                                                         data have been incorporated in a
                                                         slide rule-type calculator (Fig-
                                                         ure 24).  A calculator of this
                                                         type will reduce the time re-
                                                         quired to plot characteristic
                                                         curves such as shown in Figure
                                                         23.
CORRECTIONS FOR  TEMPERATURE
AND ELEVATION

Fan tables, resistance charts,
and exhaust volume require-
ments  are  based on standard
atmospheric conditions of 70°F
and average barometric pres-
sure at sea level.  Under these
conditions  the density of air is
0. 075 pound per cubic foot.
Where conditions vary appre-
ciably  from standard condi-
tions,  the change in air den-
sity must be considered.
                       Figure  24.   Fan curve calculator.

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 58
DESIGN OF LOCAL EXHAUST SYSTEMS
 Table  18.  CORRECTIONS FOR HOOD VOLUME
Hood
A
B
D
E
H
Volume from
Table 15, cfm
320
480
170
290
340
Correction
factor
1,860/1, 600
1,860/1, 600
1, 860/1, 600
1,860/1, 600
1, 860/1, 600
Corrected
volume, cfm
370
560
200
340
390
The  density of air varies inversely with absolute
temperature  and  directly with barometric pres-
sure.  Both  effects are  combined in the density
correction factors given in Table 19.

Velocity pressure,  static pressure,  and resis-
tance pressure vary directly with gas density.  In
calculating a  system,  if the temperatures in all
the ducts are approximately the same (within 25 °F),
compute the entire system's resistance as at  stan-
dard conditions and correct the final  system's
static pressure by multiplying by the density  cor-
rection factor. If the temperatures in the different
branches vary, the static pressure in each branch
must be corrected.
                    A centrifugal fan connected to a given system will
                    exhaust the same volume regardless of gas density.
                    Theweightof air exhausted will,  however, be di-
                    rectly proportional to the density, and so •will the
                    static pressure developed and the horsepower
                    consumed.
                                                      In selecting an exhauster from multirating tables
                                                      to move a given volume of air at a given static
                                                      pressure and at a given temperature and altitude,
                                                      proceed as f ollows :
                     1.  Read  the  density  correction  factor  from
                        Table 19.
                     2.  Multiply the given hs by the correction factor.
                     3.  Select the fan size andrpm based on the given
                        volume and the corrected static pressure.
                        Multiply the horsepower  (given  by the above
                        selection)  by the density correction factor to
                        obtain the  required horsepower.
                           Table 19.  DENSITY CORRECTION FACTORS2
                                     Altitude, ft above sea level
Temp,
°F
0
40
70
100
120
140
160
180
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1, 000
0
1. 15
1. 06
1. 00
0.96
0. 92
0.88
0.85
0.83
0.80
0. 75
0. 70
0.65
0.62
0. 58
0. 55
0.53
0.50
0.48
0.46
0. 44
0.42
0.40
0. 39
0. 38
0. 36
1, 000
1. 10
1. 02
0. 96
0. 91
0.88
0. 85
0. 82
0. 79
0. 77
0. 72
0. 67
0. 62
0.60
0.56
0. 53
0.51
0. 48
0. 46
0. 44
0.42
0.40
0.38
0. 37
0. 36
0.35
2, 000
1. 06
0. 98
0. 93
0.88
0. 85
0.82
0. 79
0. 77
0. 74
0.70
0. 65
0.60
0. 57
0. 54
0.51
0.49
0. 46
0. 44
0.43
0. 41
0. 39
0. 37
0.36
0.35
0. 33
3, 000
1.04
0.94
0.89
0. 84
0.81
0.79
0.76
0. 74
0.71
0.67
0.62
0.58
0.55
0.52
0.49
0.47
0. 45
0.43
0.41
0.39
0.37
0. 36
0.35
0.34
0.32
4, 000
0. 99
0. 91
0. 86
0. 81
0. 78
0. 76
0. 74
0. 71
0. 68
0. 64
0.60
0.56
0. 53
0. 50
0. 47
0. 45
0.43
0.41
0. 39
0. 38
0.36
0. 34
0.33
0.32
0.31
5, 000
0. 95
0.88
0. 83
0.78
0. 75
0.73
0.70
0.68
0.66
0.62
0.58
0.54
0.51
0.48
0.45
0. 44
0.41
0.40
0.38
0.36
0.35
0.33
0.32
0.31
0.30
6, 000
0.92
0.84
0. 80
0.75
0.72
0. 70
0.68
0.66
0.64
0.60
0. 56
0.52
0.49
0.46
0. 44
0.42
0.40
0.38
0.37
0.35
0.33
0. 32
0. 31
0.30
0.29
7, 000
0.88
0.81
0. 78
0. 72
0. 70
0. 68
0. 65
0.63
0. 61
0. 58
0. 54
0. 50
0.47
0. 44
0.42
0.40
0.38
0. 36
0. 35
0. 33
0. 32
0. 31
0. 30
0. 29
0.28
8, 000
0.85
0.79
0. 74
0. 70
0. 67
0. 65
0.63
0.61
0.59
0. 55
0.52
0.48
0.44
0.42
0.40
0. 38
0.36
0. 34
0..33
0. 32
0.31
0.30
0.29
0.28
0.27
               aDensity in lb/ft3 = 0.075  x density factor.

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                                              Duct Design
                                                                                                59
 The procedure for plotting the fan's characteristic
 curve at other than standard conditions is as follows:

 1.  Correct the values of cfm, hs, and hp from the
    tables to the given rpm.

 2.  Multiply the values of hg and hp by the density
    correction factor.

 3.  Plot values of hs and hp from Step 2 against
    values of cfm from Step 1.


 DUCT CONSTRUCTION

 Correct design and competent installation of sheet
 steel ducts andhoods are necessary for the proper
 functioning of an exhaust system. The following
 construction and installation practices are recom-
 mended (Industrial Ventilation,  1956):

 1.  All exhaust systems  should be constructed of
    new materials and installed in a permanent
    and workmanlike manner.  Interior of all ducts
    should be smooth  and free from obstructions,
    with joints either  welded or soldered airtight.

 2.  Ducts should be constructed of galvanized sheet
    steel riveted and soldered or black iron welded,
    except where corrosive gases or  mists or  other
    factors make, such materials impractical.  Gal-
    vanized  construction is not recommended for
    temperatures above 400 °F.   Welding of black
    iron of 18 gauge and lighter is not recommend-
    ed for field fabrication.

 3.  For  average exhaust on noncorrosive applica-
    tion,  the following gauges should  be used for
    straight duct:
                       U. S. Standard gage
                    Class I  Class II Class  III
24
22
20
18
22
20
18
16
20
18
16
14
Duct diameter

To 8 in.
8- to 18 in.
19 to 30 in.
Over 30  in.
Class I.   Includes nonabrasive applications, such
          as paint spraying, woodworking, food
          products, and discharge ducts from dust
          collectors,

Class II.  Includes nonabrasive material in large
          concentration, moderately abrasive ma-
          terial  in small to moderate concentra-
          tions, and highly abrasive material in
          small concentration.

Class III.  Includes all highly abrasive material in
          moderate to heavy concentrations  and
         moderately abrasive material in heavy
         concentration.

     Brown and Sharpe gage numbers are used
     to indicate thickness of aluminum sheet as
     compared with U. S.  Standard gages  for
     steel  sheet.   When aluminum duct is indi-
     cated,  the following  equivalent  B and S
     gages should be used:
     Steel - U.S.  Standard gage
     26  24  22  20  18  16   14

     Aluminum - B and S gage
     24  22  20  18  16  14   12

 4.   Elbows and angles should be a minimum of
     two gauges heavier than straight sections of
     the same diameter.

 5.   Longitudinal joints of the ducts should be lapped
     and riveted or spot-welded on 3-inch centers
     or less.

 6.   Girth joints of ducts  should be made with the
     lap in the  direction of airflow.  A 1-inch lap
     should be  used for ducts to 19-inch diameters
     and 1-1/4-inch laps for diameters over 19
     inches.

 7.   All bends  should have an inside or throat ra-
     dius of two pipe diameters whenever possible,
     but never  less than one  diameter.  Large ra-
     dii bends are recommended for heavy concen-
     trations of highly abrasive dust.   Ninety de-
      gree elbows not over 6 inches in diameter
     should be  constructed of at least five sections,
     and over 6-inch diameter of at least seven
     sections.

 8.   The duct should be connected to the fan inlet
     by means  of a split-sleeve drawband at least
     one pipe diameter long, but not less than 5
     inches.

 9.   Transition in main and  submains should be
     tapered,  with a taper of about 5  inches
     for each 1-inch change in diameter.

10. All branches should enter main at the large
    end of transition at an angle not to exceed
    45°, preferably 30° or less.  Branches should
    be connected only to the top or sides of main,
    never to the bottom.  Two branches should
    never enter a main at diametrically opposite
    points.

11. Dead-end caps should be provided on mains
    and  submains about 6 inches from the last
    branch.

12. Cleanout openings should be provided every
    10 or 12 feet and near each bend or duct
    junction.

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60
DESIGN OF LOCAL EXHAUST SYSTEMS
13.  The ducts should be supported sufficiently so
     that no load is ever placed on connecting e-
     quipment. Ducts  8 inches or smaller should
     be  supported  at least every 12 feet, and larg-
     er  ducts, at least every 20 feet.

14.  A minimum clearance of 6 inches should be
     provided between  the ducts and ceilings, -walls,
     or  floors.

15.  Blast gates used for adjusting a system should
     be  placed near the connection of branch to
     main,  and means  provided for locking them
     in place after the  system has been balanced.

16.  Round ducts should be used wherever possi-
     ble.  Where clearances prevent the use of
     round  ducts,  rectangular ducts as nearly
     square as possible may be used.
                 FAN  DESIGN

Fans are used to move air from one point to anoth-
er. In the control of air pollution, the fan,  blower,
or exhauster imparts movement to  an air mass
and conveys the air contaminants from the source
of generation to a control device in -which the air
contaminants are separated and collected, allow-
ing cleaned air to be exhausted to the atmosphere.

Fans  are  divided into  two  main classifications:
(1) radial-flow or centrifugal type,  in which the
airflow is at right angles to the axis of rotation of
the rotor,  and (2) axial-flow or propeller type, in
which the  airflow is  parallel to the axis of rota-
tion of the  rotor.
CENTRIFUGAL  FANS

A  centrifugal fan consists  of  a -wheel or rotor
mounted on a shaft that rotates  in a scroll-shaped
housing. Air enters at the eye of the rotor, makes
a right-angle turn, and is forced through the blades
of  the rotor by centrifugal force into the scroll-
shaped  housing.   The centrifugal force imparts
static pressure to the air.  The diverging shape
of the scroll also converts a portion of the velocity
pressure into static pressure.

Centrifugal fans  may be divided into three main
classifications as follows:

1.   Forward-curved-blade  type.  The rotor of the
    forward-curved-blade fan  is known as the
    squirrel-cage rotor.  A solid steel  backplate
    holds one end of  the blade, and a  shroud ring
    supports the other end.  The blades are  shal-
    low -with the  leading edge curved towards  the
    direction of rotation.  The usual number of
    blades is 20  to 64.
                    2.   Backward-curved -blade type.  In the back-
                         ward-curved-blade fan, the blades are in-
                         clined in a direction opposite to the direc-
                         tion of rotation,  and the blades are larger
                         than those of the forward-curved-blade fan.
                         The usual number of blades is 14 to 24, and
                         they are  supported by a solid steel backplate
                         and shroud ring.

                    3.   Straight-blade type.  The blades of the
                         straight-blade fan may be attached to the
                         rotor by a solid steel backplate or a spider
                         built up from the hub.  The rotors are of
                         comparatively large diameter.   The usual
                         number of blades is 5 to 12.  This classifi-
                         cation includes a number of modified  de-
                         signs whose  characteristics are, in part,
                         similar to those of the forward- and back-
                         ward-curved blade types.

                    AXIAL-FLOW FANS

                    Axial -flow fans  include all those -wherein the  air
                    flows through the impellers substantially parallel
                    with the shaft upon -which the  impeller  is mounted.
                    Axial-flow fans depend upon the action of the  re-
                    volving airfoil-type blades to pull the air in by the
                    leading edge  and discharge it from the  trailing
                    edge in a helical pattern of flow.  Stationary vanes
                    may be installed on the suction side or the dis-
                    charge side  of the rotor, or both.  These vanes
                    convert the centrifugal force  and the helical -flow
                    pattern to static  pressure.

                    Axial fans may be  divided into three main classi-
                    fications:

                    1.   Propeller type.  Propeller fans have large,
                         disc-like blades or narrow, airfoil-type
                         blades.   The number of blades is 2 to 16.
                         The propeller fan blades may be mounted on
                         a  large or small hub, depending upon the use
                         of the fan.  The propeller fan is distinguished
                         from the tube-axial and vane-axial fans in that
                         it is equipped  -with a mounting ring only.

                    2.   Tube-axial type.   The tube-axial fan  is simi-
                         lar to the propeller fan except it is mounted
                         in a tube or  cylinder.  It is more efficient than
                         the propeller fan and, depending upon the de-
                         sign of the rotor and hub, may develop medi-
                         um pressures. A two-stage,  tube-axial fan,
                         •with one  rotor revolving  clock-wise and the
                         second,  counter-clockwise, -will recover a
                         large portion of the centrifugal force as static
                         pressure, which -would otherwise be  lost  in
                         turbulence.  Two-stage,  tube-axial fans ap-
                         proach vane-axial fans in efficiency.

                    3.   Vane-axial type.   The vane-axial fan is simi-
                         lar in design to a tube-axial fan except that
                         air-straightening vanes are installed on the

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                                              Fan Design
                                             61
suction side or discharge side of the rotor.
Vane-axial fans are readily adaptable to mul-
tistaging,  and  fans have been designed that
will operate at a pressure of 16 inches water
column at  high volume and efficiency.
 FAN CHARACTERISTICS

 The performance of a fan is characterized by the
 volume of gas flow, the pressure at •which this flow
 is produced,  the  speed of rotation, the power re-
 quired,  and  the  efficiency.  The relationships of
 these quantities are measuredby the fan manufac-
 turer with testing methods sponsored by the Na-
 tional Association of  Fan Manufacturers or the
 American Society of Mechanical Engineers. Brief-
 ly,  the  method consists of mounting  a duct on the
 fan  outlet,  operating  the fan  -with  various sized
 orifices in  the  duct,  and measuring the  volume,
 pressure, velocity, and power  input.  About 10
 tests are run, with the duct opening varied from
 wide open to  completely closed.   The test results
 are then plotted against volume on the abscissa to
 provide the characteristic curves of the fan,  such
 as those shown in Figure 25.
  Figure 25.  Typical  fan  characteristic curves
  (Air Moving and Conditioning Assn., Inc.,1563).
From the volume and pressure, the air horsepower
is computed, either the real power based on total
pressure or the fictitious  static power based on
fan static pressure.  The efficiency based  on total
pressure is called mechanical efficiency.


INFLUENCE OF  BLADE SHAPE

The size,  shape,  and number of blades in a cen-
trifugal fan have  a considerable  influence on the
operating characteristics of the fan.  The  general
effects are indicated by the curves in Figure 26.
             FORWARD-CURVED-BLADE
                     VOLUME
            BACKWARD-CURVED-BLADE
                     VOLUME
                                                                          VOLUME

                                                             Figure  26.  Centrifugal fan typical
                                                             characteristic curves (Hicks,  1951).
These  curves are shown for comparison purposes
only; they are not applicable for fan selection but
do indicate variations in the operating character-
istics of a specific type of fan.
1.   Forward-Curved-Blade Fans.  This type of
    fan is normally referred to as a volume fan.
    In this fan,  the static pressure rises sharply
    from free delivery to a point at approximate
    maximum efficiency,  then drops to point a_
    shown in Figure 26, before rising to static
    pressure at no delivery.  Horsepower input
    rises rapidlyfromno delivery to free delivery.
    Sound level is least at maximum efficiency and
    greatest at  free delivery.  Forward-curved-
    blade fans are designed to handle large vol-
    umes of air at low pressures.  They rotate at
    relatively low speeds,  which results in quiet
    operation.   Initial cost of such a fan is low.

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62
DESIGN OF LOCAL EXHAUST SYSTEMS
     Resistance of a system to be served by this
     type of fan must be constant and must be deter-
     mined accurately in advance because of sharp-
     ly rising power demand. This type of fan should
     not be used for gases containing dusts or  fumes
     because deposits -will accumulate on the short
     curved Blades resulting in an unbalanced wheel
     and excessive maintenance.   The  pressure
     produced by a forward-curved-blade fan is
     not normally sufficient to meet the pressure
     requirements for the majority of air pollution
     control devices.   They are, however,  used
     extensively in heating, ventilating, and air
     conditioning -work.  Also, they are commonly
     used for  exhausting air from one  enclosed
     space to another without the use of ductwork.


2.   Backward-Curved-Blade Fans.  The static
     pressure of this  type fan rises sharply from
     free delivery almost to the point of no delivery.
     Maximum efficiencies occur at maximum
     horsepower input.   The horsepower require-
     ment is self-limiting; it rises to a maximum
     as the capacity increases and then decreases
     with additional capacity.  Thus, when the re-
     sistance of a complex exhaust system is fre-
     quently changed because of production demands,
     the self-limiting power requirements prevent
     overloading the motor.

     This type of fan develops higher pressure than
     the forward-curved-blade type.  Sound  level
     is least at maximum efficiency and  increases
     slightly  at free delivery.  The physical sizes
     of backward-curved-blade fans for given duties
     are large,  but for most industrial -work this
     may be unimportant.  The operating efficiency
     is high,  but initial cost is also high.  Blade
     shape is conducive to buildup of material and
     should not be used on gases containing dusts
     or fumes.

     The backward-curved-multiblade fan is used
     extensively in heating, ventilating, and air
     conditioning •work and for continuous service
     •where a large  volume of air is to be handled.
     It is commonly found on forced-draft combus-
     tion processes.  It may be used on some air
     pollution control devices, but must be installed
     on the clean air  discharge as an induced system.
                         This type fan is utilized for exhaust systems
                         handling gas streams that are contaminated
                         with dusts  and fumes.   Various  blades  and
                         scroll designs have been developed for specific
                         dust-handling and pneumatic -conveying prob-
                         lems.   This fan is too large for some  duties,
                         but for most industrial work this may be un-
                         important.   Initial cost of this type fan is less
                         than that of the backward-curved-blade type,
                         but efficiency is  also less.  Fan blades  may
                         be made of an abrasive resistant alloy or
                         covered  with rubber to prevent high  main-
                         tenance in systems handling abrasive or cor-
                         rosive materials.

                         A number of modified designs of straight-blade
                         fans have been specifically developed  for hand-
                         ling contaminated air or gas streams.


                         Axial Fans.  For this type fan,  the horsepower
                         curve may be essentially flat and self-limiting,
                         depending upon the design of the blades, or it
                         may fall from a maximum at no delivery as
                         capacity increases.   The type  of vanes in the
                         vane-axial tans measurably affects the horse-
                         power  curve and efficiency.  Maximum effi-
                         ciencies occur  at a higher percent delivery
                         than \vith the centrifugal-type fan.

                         Space requirements  for  a specific fan duty ar
                         exceptionally low.  Available fans can be in-
                         stalled directly in circular ducts  (vane-axial
                         or tube-axial type).  Initial cost of the fan is
                         low.

                         The axial-type  fan is best adapted for hand-
                         ling large  volumes of air against low resis-
                         tance.  The propeller type, which is equipped
                         only with a mounting ring, is commonly used
                         for ventilation and is mounted directly in a
                         wall.  Although the vane-axial  and tube-axial
                         fans can deliver large volumes  of air  at rela-
                         tively high resistances,  they are best suited for
                         handling clean  air only.   Any solid material
                         in the air being handled  causes rapid erosion
                         of impellers, guide vanes, hubs, and the inner
                         •wall of the cylindrical  fan housing.   This
                         results from the high tip speed of the fan and
                         the high air velocity through the fan housing.
3.   Straight-Blade Fans.   The static pressure of
     this type fan rises sharply from free delivery
     to a maximum point near no delivery, -where
     it falls off.  Maximum static efficiency occurs
     near maximum pressure.   Mechanical effi-
     ciency rises rapidly from no delivery to a
     maximum near maximum pressure,  then
     drops slowly as the fan capacity approaches
     free delivery.
                     Geometrically Similar  Fans

                     Fan manufacturers customarily produce a series
                     of fans characterized by constant ratios  of linear
                     dimensions and constant angles between various
                     fan parts.  These fans are said to be geometrically
                     similar or of a homologous series.   The drawings
                     of all the  fans in the series are identical in all
                     views except for scale.

-------
                                              Fan Design
                                                       63
It is usual for a manufacturer to produce homol-
ogous series of fans with diameters increasing by
afactor of about  1. 10.  Each is  designated by the
impeller diameter or by an arbitrary symbol, often
a number proportional to the diameter.


Multiroting Tables

The performance of each fan in  a homologous
series is usually given in a series of tables'called
multirating tables. Values of static pressure  are
usually arranged as headings of columns, which
contain the fan speed and horsepower required to
produce various volume flows. The point of maxi-
mum efficiency at each static pressure is usually
indicated.

FAN  LAWS

Certain relationships have been established among
the variables affecting the performance of fans of
a homologous series or a single fan operating at
varying speed in a constant system.  The quantity,
V^,and the power, p, are  controlled by four inde-
pendent variables:  (1) Fan size, wheel diameter,
D,   (2) fan  speed, N,   (3) gas  density, p,  and
(4) system resistance, hr.  Since all dimensions
of homologous fans are proportional, any dimen-
sion could be used to designate the size.  The wheel
diameter is, however, nearly always used.

In order to develop these  relationships, the effects
of system resistance must be  fixed by limiting the
comparisons to  the  same points of rating.   For
two fans of different size,  the  same  point of rating
is  obtained  when the respective volumes are the
same percentage of wide open volume,  and the
static pressure is the same percentage of shut-off
static pressure.  For the same fan,  the same point
of rating  is obtained when the system is  held con-
stant and the fan speed is varied.
          equating exponents for like terms,

              m:  0  =  c
              L:  3  =  a - 3c
              t  : -1  =  -b

          and solving the equations simultaneously

              a  =  3;b=l;c  =  0

          hence:
                         V  =  k D  N
(28)
          Repeating for the system resistance developed
          and noting that hr is fundamentally force per
          unit area  =  mass X acceleration per area,
                          h   =  kDaNbpC
                           r
                     ml/V2
              m   1  = c
              L  -1  = a - 3c
              t   -2  = -b

              a  =  2;  b  =  2;  c  =  1
                        h   =  kD2N2p
(29)
          And repeating again for the power required:
                        P  =  kDaNbpC
For homologous fans  (or the same fan) operating
at the same point of rating, the quantity (V^-) and
the power (P) will depend upon the fan size (D),
fan speed (N),  and gas  density (p).  The flow
through a fan is always in the turbulent region,
and the effect of viscosity  is ignored.  The form
of dependence can be derived from dimensional
analysis by the equation
               =  k
(27)
 By substituting fundamental dimensional units,
                           [ml/3]'
                   mL t"   =  k
              m   1  =  c
              L    2  =  a - 3c
              t  -3  =  -b

              a  =   5;   b  =  3;   c = 1
                                                                     P  -  kD5N3p
                                                     (30)
          Equations 28, 29, and 30 for Vt, hr>  and P define
          the relationships among all the variables,  within
          the limitations originally stated.   The equations
          can be simplified,  combined,  or modified to yield

-------
64
                                DESIGN OF LOCAL EXHAUST SYSTEMS
a large number of relationships.  The following
relationships derived from them are usually re-
ferred to as the Fan Laws.

1. Change in Fan Speed.

   Fan size,  gas density,  and system constant.

   a. V, varies as fan speed.

   b. h varies as fan speed squared.

   c. P varies as fan speed cubed.


2. Change in Fan Size.

   Fan speed and gas density constant,

   a. V varies as cube of wheel diameter.

   b. h varies as square  of wheel diameter.

   c. P varies as fifth power of wheel diameter.

   d. Tip speed varies as wheel diameter.


3. Change in Fan Size.

   Tip speed and gas density constant.

   a. V varies as square  of wheel diameter.

   b. h remains constant.
       r

   c. P varies as square of wheel diameter.

   d. rpm varies inversely as wheel diameter.


4. Change in Gas Density.

   System, fan speed, and fan  size constant.
   a.  V  is constant.

   b.  h  varies as density.

   c.  P varies as density.
5.  Change in Gas Density.

   Constant pressure and system, fixed fan size,
   and variable fan speed.

   a.  V varies inversely as square root of density.

   b.  Fan speed varies inversely as square root of
      density.

   c,  P varies inversely as square root of density.
6.  Change in Gas Density.

   Constant weight of gas, constant system, fixed
   fan size, and variable fan speed.

   a.  V  varies inversely as gas density.

   b.  h   varies inversely as gas density.

   c.  Fan speed varies inversely as gas density.

   d.  P varies inversely as square gas  density.

 The  fan laws enable a manufacturer to calculate
 the operating characteristics for all the fans in a
 homologous series from test data obtained from a
 single  fan in the series.  The laws also enable
 users of fans to make many  needed computations.
 A few of the more important cases are illustrated
 as follows.

 Example 11

 A fan operating  at 830 rpm delivers 8, 000  cfm at
 6 inches static pressure and requires 11.5 horse-
 power.  It is desired to increase the output to
 10, 000  cfm in the same system.  What should be
 the increased speed and what -will be the horse-
 power  required  and the new  static pressure?
 Solution:

 Use fan law la,  b ,   c :
    N'  =
h1   =    7
 r
P'  =  11.
'1.03?]'
  830 J
                                                                     830 J
                     =  1, 037 rpm
                         =  9. 35 in. WC
                         =  22.4hp
 Example  12

 A fan is exhausting  12, 000 cfm of air at 600°F.
 (density = 0. 0375 pound per cubic foot at 4 inches
 static pressure from a drier).  Speed is 630 rpm,
 and 13 horsepower is  required.   What -will be the
 required horsepower if air at  70°F (density 0. 075
 pound per cubic foot) is pulled through the system?


 Solution:

 Use fan law  4 c :
           13
                0. 075
                --

-------
                                             Fan Design
                                                                                          65
If a 15-horsepower motor were used in this in-
stallation,  it would be necessary to use a damper
when starting up cold to prevent overloading the
fan motor.

Example 13

A 30-inch-diameter fan operating at 1, 050  rpm
delivers 4,600 cfm at 5 inches static pressure.
What size fan of the same series would deliver
11, 000 cfm at the same static pressure?

Solution:
Use fan law 2 a .
   D1
 /ii,ooo\1/3
 \ 4,600 /
(30)  =  40. 0 in.
 Selecting a Fan From  Multirating Tables

 A typical multirating table is given in Table 20.
 The data in this table are for a paddle •wheel-type
 industrial exhauster.  In us ing multirating tables,
 use linear interpolation to find values  between
 those  given  in the table.  For instance, from
 Table 20 it is desired to find the fan speed that
 will deliver  6, 300 cfm at 6-1/2 inches static
 pressure.  The nearest capacities are 6, 040
 and 6, 550.
At 6 in.  h the speed is
          s
1^^1^
                     (1,095 -1.088), 1,092
At 7 in.  h the speed is
          S
The required speed at 6-1/2 inches static pres-
sure and 6, 300 cfm is half-way between 1, 092 and
1, 167 or 1, 129 rpm.


CONSTRUCTION  PROPERTIES

Special materials of construction must be used for
tans handling corrosive gases.  Certain alloys that
have been used  have  proved very satisfactory.
Bronze alloys are used for handling sulfuric acid
fumes  and other  sulfates,  halogen acids, various
organic gases, and  mercury compounds.  These
alloys are particularly applicable to low-tempera-
ture installations.   Stainless  steel is the most
commonly used metal for corrosion-resistant im-
pellers and fan housings.  It has proved satisfac-
tory for exhausting the furnes of many acids.  Pro-
tective  coatings  on standard fan housing and
impellers such as bisonite, cadmium plating, hot
galvanizing,  and rubber  covering have proved
satisfactory.  Cadmium plating and hot galvanizing
are often used in conjunction with a zinc chromate
primer,  with which they form a chemical bond.
The zinc chromate primer may then be covered
with various types of paints.   This combination
has proved favorable  in  atmospheres  near the
ocean.

The increasing use of  rubber for coating fan im-
pellers  and housings deserves special  mention.
Rubber  is one of  the least porous materials and,
when vulcanized to the  metal,  surrounds and pro-
tects  the metal from corrosive gases or fumes.
Depending upon the particular application, soft,
medium,  or firm  rubber is bonded to the metal.
A good bond -will  yield an adhesive strength of
700pounds per square inch.  When pure,  live rub-
ber is so bonded,  it is capable of withstanding the
high stresses set up in the fan and is sufficiently
flexible to resist cracking.  Rubber-covered fans
have proved exceptionally  durable and are found
throughout the chemical  industry.
                                Heat  Resistance

                                Standard construction fans with ball bearings can
                                •withstand temperatures up to 250°F.  Water-
                                cooled bearings, shaft coolers, and heat gaps per-
                                mit operation up to SOO°F.  A shaft cooler is a
                                separate,  small, centrifugal fan that is mounted
                                between the fan housing and the inner bearing and
                                that circulates cool air over the bearing and shaft.
                                A heat gap,  which  is merely a space of 1-1/2 to
                                2 inches between the bearing pedestal and fan housing,
                                reduces heat transfer to the bearings by conduction.

                                Certain types of stainless steel will •withstand the
                                high  temperatures  encountered  in the  induced-
                                draft fan from furnaces or combustion processes.
                                Stainless steel fans have been known to withstand
                                temperatures as high as 1, 100°F without excess
                                warping.

                                Explosive-Proof Fans  and Motors

                                When an exhaust system is handling  an explosive
                               mixture of air and gas  or powder,  a material to
                                be  used in  the construction of the fan must gen-
                                erally be specified  to  be one that  will not produce
                                a spark if accidentally struck by  another metal.
                                Normally, the fan impeller  and housing are con-
                                structed of bronze or aluminum alloys, which pre-
                                cludes spark formation.  Aluminum is frequently
                               used  on some of the  narrower or smaller fans,
                                especially those overhung  on the  motor  shaft.
                               Aluminum reduces the weight and vibration of the
                               motor shaft and protects the motor bearing from
                                excessive -wear.

-------
66
DESIGN OF  LOCAL EXHAUST  SYSTEMS
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-------
                                        Vapor Compressors
                                            67
Explosive-proof motors and fan -wheels are re-
quired by law for installation in places where
an explosive mixture  may be  encountered. Ex-
haust systems  such as those used in paint spray
booths usually  consist of an aluminum or bronze
tube-axial  fan  and an  explosive-proof motor that
drives the fan wheel by indirect drive.

Fan Drives

All types of fans may be obtained with either direct
drive or belt drive. Directly driven exhausters
offer  the advantage of  a more compact assembly
and ensure constant fan speed.  They are not trou-
bled by the belt slippage that  occurs when belt-
driven fan drives are  not  properly maintained.
Fan speeds are,  however, limited to the available
motor speeds,  -which  results in inflexibility ex-
cept in direct-current application. A quick change
in fan speed,  -which  is possible with belt-driven
fans,  is a definite advantage in many applications.


          VAPOR  COMPRESSORS

Compressors  are widely used in industry  to in-
crease the pressure of gases or  vapors for  a
variety of reasons.  They are used:

1. To provide the desired pressure for chemical
   and physical reactions;

2. to  control boiling points  of fluids, as in gas
   separation,  refrigeration,  and evaporation;
3.  to evacuate enclosed volumes;

4.  to transport gases or vapors;

5.  to store compressible fluids  as gases  or
   liquids under pressure and assist in recov-
   ering them from storage or tank  cars;

b.  to convert mechanical energy to  fluid energy for
   operating instruments,  air agitation, fluidiza-
   tion, solid  transport, blowcetses, air tools,  and
   motors.


Compressors  normally  take  suction near atmo-
spheric pressure and deliver fluids  at pressures
ranging upward to 40, 000 psig in commercial ap-
plications and even higher in experimental uses.
The capacity of commerically available compres-
sors ranges from low volumes up to  3 million cfm.

TYPES  OF  COMPRESSORS

Vapors or gases canbe compressed by either posi-
tive displacement or dynamic action.   The positive-
displacement  compressors produce pressure  by
physically reducing the gas  volume.  The dynamic
compressors  increase  pressure by accelerating
the gas and converting the  velocity into pressure
in a receiving chamber.  Positive-displacement
compressors are of reciprocating- or rotary-dis-
placement types.  The dynamic compressors are
centrifugal- or axial-flow  machines.  Figure 27
shows  general compressor applications, and
Table  21 gives general limits of compressors.
 I02
                    10
                                      I03                10*
                                        COMPRESSOR INLET CAPACITY, cfm
                   I05
                                     I06
                 Figure  27.  General  areas  of compressor applications (Des Jardms, 1956).
 234-767 O - 77 - 7

-------
68
DESIGN OF LOCAL EXHAUST SYSTEMS
 Table 21. GENERAL LIMITS OF COMPRESSORS
              (Des Jardins,  1956)
Compressor
type

Reciprocating
Centrifugal
Rotary displace-
ment
Axial flow
Approximate maximum limits
of commercially
available compressors
Discharge
pressure,
psLa
35, 000
4, 200
125

90
Compression
ratio per
stage
10
4
4

1.2
Inlet
capacity,
cfm
13, 000
18, 000
7, 000

*3,000, 000
Positive-Displacement  Compressors

A reciprocating compressor raises the pressure
of the air or gas by the forced reduction of its
volume through the movement of a piston -within
the confines of a cylinder.   These compressors
are commercially  designed for volumes  up to
15, 000 cfm and pressure sup to 40, OOOpsig.  They
are by far the most common type in use both for
process  systems and air  pollution control sys-
tems  (Cumiskey, 1956).

Rotary sliding-vane compressors have longitudinal
vanes that slide radially in a rotor mounted eccen-
trically in a cylinder.  The rotor is supported  at
each  end by antifriction bearings mounted in the
heads, which,  in turn,  are bolted and doweled to
the cylinder.   Figure 28 shows a cross-sectional
view of a sliding-vane compressor.

In a sliding-vane unit,  pressure is increased  by
reducing the size of the compression cell while  it
rotates from the suction to the discharge ports.
          SLIDING VANE
                            ROTOR
                                 CYLINDER
                      As the unit rotates, each compression cell reaches]
                      maximum size when it passes the inlet ports.  Fur
                      ther rotation of this cell reduces  its size, and com
                      pression is completed upon reaching the discharge
                      ports  (Bruce and Schubert, 195b).   In general,
                      single-stage,  rotary,  sliding-vane compressors
                      are suitable for pressures up to 50 psig.  Multi-
                      staged machines are designed for pressures up to
                      250 psig, and booster units are available for pres-
                      sure up to 400 psig.  These machines can delive:
                      up to 6, 000  cfm.

                      Rotary-lobe compressors have two mating, lobed
                      impellers that revolve within a cylinder.  Timing
                      gears, mounted outside the cylinder, prevent the
                      impellers from contacting each other. The lobes
                      are mounted on  shafts supported  by antifriction
                      bearings. Figure 29 shows a cross-sectional viev
                      of a rotary-lobe compressor. Flow through the
                      rotary-lobe compressor  is accomplished by the
                      lobes' pushing the air or gas from the suction to
                      the discharge.  Essentially, no compression take:
                      place  within the unit; rather,  compression takes
                      place  against system back pressure (Bruce and
                      Schubert, 1956). Rotary-lobe compressors are
                      available in sizes up to 50, 000 cfm and pressures
                      up to 30 psig.  Single-stage machines are usually
                      good for pressures up to  15 psig,  and vacuums t<
                      22 inches of mercury.
                            ROTARY LOBE
            Figure 28.   SI iding-vane
            compressor  (Bruce and
            Schubert,  1956).
                                  Figure 29.  Rotary-lobe
                                  compressor  (Bruce and
                                  Schubert, 1956).

                     Rotary liquid-piston  compressors use water or
                     other liquids, usually in a single rotating element
                     to displace the air or gas being handled.  A ro-
                     tating  element is mounted on  a shaft and supporte
                     at each end by antifriction bearings.  Figure 30
                     shows  a  cross-sectional view of a rotary liquid-
                     piston  compressor.  In the rotary liquid-piston
                     compressor,  flow of compressed air or gas is
                     discharged in a uniform,  nonpulsating stream.
                     Compression is obtained  in this machine by ro-
                     tating  a round, multiblade rotor freely in an ellip-

-------
                                            CONTENTS


                                      CHAPTER  1.  INTRODUCTION

THE LOS ANGELES BASIN	      3
RULES AND REGULATIONS IN LOS ANGELES COUNTY	      3
  Regulation II: Permits	      4
  Regulation IV: Prohibitions	      4
   Rule 50: The Ringelmann  Chart	      4
   Rule 51: Nuisance	      4
   Rule 52: Particulate Matter	      5
   Rule 53: Specific  Contaminants	      5
   Rules 53.1, 53.2, and 53.3:  Sulfur Production and Sulfuric Acid Plants	      5
   Rule 54: Dust and Fumes	      5
   Rule 56: Storage of Petroleum Products	      5
   Rules 57 and 58: Open Fires and Incinerators	      5
   Rule 59: Oil-Effluent Water Separators	      5
   Rule 61: Gasoline Loading Into Tank Trucks and Trailers	      5
   Rules 62, 62. 1, and 62.2:  Sulfur Content of Fuels	      5
   Rule 63: Gasoline Specifications	      6
   Rule 64: Reduction  of Animal Matter	      6
   Rule 65: Gasoline Loading Into Tanks	      6
   Rule 66: Organic Solvents	      6
   Rule 66. 1: Architectural Coatings	      6
   Rule 66. 2: Disposal and Evaporation of Solvents	      6
   Rule 67: Fuel-Burning Equipment	      6
   Rule 68: Fuel-Burning Equipment - Oxides  of Nitrogen	      6
ROLE OF  THE AIR POLLUTION ENGINEER	      6
  Accomplishments of the Permit System	      6
USE OF THIS MANUAL	      7
  General Design Problems	      7
  Specific Air Pollution Sources	      7

                                    CHAPTER 2.  AIR CONTAMINANTS
INTRODUCTION	     11
FACTORS  IN AIR POLLUTION PROBLEMS	     11
TYPES OF AIR  CONTAMINANTS	     12
  Organic Gases	     12
   Current Sources in Los Angeles County	     12
    Hydrocarbons  - 12 . . .  Hydrocarbon derivatives -  12
   Significance in Air Pollution Problem	     14
  Inorganic Gases	     14
   Current Sources in Los Angeles County	     14
    Oxides of nitrogen - 14 ...  Oxides of sulfur - 15 ... Carbon monoxide - 15
   Significance in Air Pollution Problem	     15
    Oxides of nitrogen - 15 ...  Oxides of sulfur - 15 . . . Carbon monoxide - 16 • • •
    Miscellaneous  inorganic gases - 16
  Aerosols	     16
   Current Sources in Los Angeles County	     16
    Carbon or soot particles  - 16 ... Metallic oxides and salts  - 17 ...  Oily or tarry drop-
    lets -  17 . . .  Acid droplets  - 17 ... Silicates and other inorganic dusts - 17 ...  Metallic
    fumes - 18
   Significance in Air Pollution Problem	     18
AIR POLLUTION CONTROLS ALREADY IN EFFECT	     18
CONTROL MEASURES  STILL NEEDED	     18
  Motor Vehicle  Emissions	     20
  Additional Controls  Over Stationary Sources	     20
   Organic Gases	     20
   Oxides of Nitrogen	     20
   Other Contaminants	     21

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                                            CONTENTS
                           CHAPTER 3.  DESIGN OF LOCAL  EXHAUST SYSTEMS

FLUID FLOW FUNDAMENTALS	     25
 Bernoulli's Equation	     25
 Pitot Tube for Flow Measurement	,	     25
   Correction Factors	     27
HOOD DESIGN	     27
 Continuity Equation	     27
 Air Flow Into a Duct	     28
 Null Point	     28
 Design of Hoods for Cold Processes	     30
   Spray Booths	     32
   Abrasive Blasting	     32
   Open-Surface Tanks	     32
 Design of Hoods for Hot Processes	     34
   Canopy Hoods	     34
    Circular high-canopy hoods - 34 ... Rectangular high-canopy hoods  - 38 . .  .
    Circular low-canopy hoods  - 39 .  .  . Rectangular low-canopy hoods -  40  .  . .
    Enclosures - 41
   Specific Problems	     42
    Steaming tanks - 42 .  . . Preventing leakage - 42
 Hood Construction	     43
   High-Temperature Materials	     43
   Corrosion-Resistant Materials	     43
   Design Proportions	     43
   Transition to Exhaust Duct	     43
DUCT DESIGN	     44
 General Layout Considerations	     44
 Types of Losses	     44
   Inertia Losses	     44
   Orifice Losses	     44
   Straight-Duct Friction Losses	     45
   Elbow and Branch Entry Losses	     45
    Exhaust system calculator - 45
   Contraction and Expansion Losses	     47
   Collection Equipment	     47
 Design Procedures	     47
   Methods  of Calculation	     47
   Methods  of Design	     48
   Calculation Procedures	     49
   Fan Static Pressure	     50
   Balanced-Duct Calculations	     51
   Blast Gate Method	     52
 Checking an Exhaust System	     52
   Illustrative Problem	     52
   Fan Curve Calculator	     57
 Corrections for Temperature and Elevation	     57
 Duct Construction	     59
FAN DESIGN	     60
 Centrifugal Fans	     60
 Axial-Flow Fans	     60
 Fan Characteristics	     61
 Influence of Blade Shape	     61
   Geometrically Similar Fans	     62
   Multirating Tables	     63
 Fan Laws	     63
   Selecting a Fan  From Multirating Tables	     65
 Construction Properties	     65
   Heat Resistance	     65
   Explosive-Proof Fans and Motors	     65
   Fan Drives	     67

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EDITORIAL REVIEW COMMITTEE

         Robert L.  Chass
        William B.  Krenz
          Eric E.  Lemke
        Robert G.  Lunche
       Robert J. Mac Knight
          John L. Mills


    TECHNICAL ASSISTANCE

          Ivan S.  Deckert
       William F.  Hammond
        John L. McGinnity
        Robert C.  Murray
        Arthur B.  Netzley
          Herbert Simon
         Robert T.  Walsh
        Sanford M.  Weiss
       John E. Williamson


     EDITORIAL ASSISTANCE

         Jerome D.  Beale
         Eugene Hochman
          George Thomas
         Edwin J.  Vincent
       Wayne E. Zwiacher

          GRAPHIC ART

          Lewis K.  Smith

         PHOTOGRAPHY

        John A. Daniels on

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                                             CONTENTS
   Polyurethane	    703
   Thermoplastic Resins	    703
   Polyvinyl Resins	    703
   Polystyrene	    704
   Petroleum and Coal Tar Resins	    704
  Re sin-Manufacturing Equipment	    704
  The Air Pollution Problem	    705
  Air  Pollution Control Equipment	    706
VARNISH COOKERS	    708
  Introduction	    708
  Definitions - Products and Processes	    708
  Major Types of Varnish Cooking Equipment	    709
  The Air Pollution Problem	    711
  Hooding and Ventilation Requirements	    711
  Air  Pollution Control Equipment	    712
   Scrubbers	    714
   Condensers	    715
   Afterburners	    715
SULFURIC ACID MANUFACTURING	    716
  Contact Process	    716
  The Air Pollution Problem	    718
  Air  Pollution Control Equipment	    719
   Sulfur Dioxide Removal	    719
   Acid Mist Removal	,	    720
    Electrical precipitators - 720 .  . . Packed-bed separators - 720 . . .
    Wire mesh mist eliminators - 721 .  .  . Ceramic filters - 722 .  . .
    Sonic agglomeration - 722 .  .  .  Miscellaneous devices - 722
SULFUR SCAVENGER PLANTS	    722
  Introduction	    722
  Sulfur in Crude Oil.	    722
  Removal of H2S From Refinery Waste Gases	    723
  The Air Pollution Problem	    726
  Air  Pollution Control Equipment	    726>
   Incineration Requirements	    727
   Stack Dilution Air	    732
   Incinerator Stack Height	    732
   Plant Operational Procedures	    733
   Tail Gas Treatment	    734
PHOSPHORIC ACID MANUFACTURING	    734
  Phosphoric Acid Process	    734
  The Air Pollution Problem	    735
  Hooding and Ventilation Requirements	    736
  Air  Pollution Control Equipment	    736
SOAP, FATTY ACID,  AND GLYCERINE MANUFACTURING EQUIPMENT	    737
  Introduction	    737
  Raw Materials	    738
  Fatty Acid Production	    739
  Glycerine Production	    740
  Soap Manufacturing	    743
  Soap Finishing	    744
  The Air Pollution Problem	    745
  Air  Pollution Control Equipment	    746
SYNTHETIC DETERGENT SURFACTANT MANUFACTURING EQUIPMENT	    749
  Introduction	    749
   Raw Materials	    749
   Processes	    750
  Oleum Sulfonation	    750
   The Air  Pollution Problem	    751
   Air Pollution Control Equipment	    751
  Oleum Sulfonation and Sulfation	    752
   Process	    752
   The Air  Pollution Problem	    752

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xxvi                                         CONTENTS
 Sulfur Trioxide Vapor Sulfonation	    753
   The Air Pollution Problem	    754
   Air Pollution Control Equipment	    755
 Sulfur Trioxide Liquid Sulfonation	    755
   The Air Pollution Problem	    755
   Air Pollution Control Equipment	    755
 Chlorosulfuric Acid Sulfation	    756
   The Air Pollution Problem	    756
   Air Pollution Control Equipment	    757
 Sulfoalkylation	    757
   The Air Pollution Problem	    759
   Air Pollution Control Equipment	    759
SYNTHETIC DETERGENT PRODUCT MANUFACTURING EQUIPMENT	    759
 Introduction	    759
   Raw Materials	    759
   Processes	    761
 Slurry Preparation	    761
   The Air Pollution Problem	    761
   Air Pollution Control Equipment	    761
 Spray Drying	    762
   The Air Pollution Problem	    762
   Air Pollution Control Equipment	    764
 Granule Handling	    764
   The Air Pollution Problem	    764
   Air Pollution Control Equipment	    765
GLASS MANUFACTURE	    765
 Types of Glass	    765
 Glass-Manufacturing  Process	,	    765
 Handling,  Mixing, and Storage Systems  for Raw Materials	    767
   The Air Pollution Problem	    767
   Hooding and Ventilation Requirements	    767
   Air Pollution Control Equipment	    768
 Continuous Soda-Lime Glass-Melting Furnaces	    769
   The Air Pollution Problem	    769
     Source  test data -  770 . . . Opacity of stack emissions - 771
   Hooding and Ventilation Requirements	    771
   Air Pollution Control Methods	    773
     Control of raw materials  - 775 .  .  .  Batch preparation - 775  . . .  Checkers - 777 . . .
     Preheaters - 777 .  .  . Refractories  and insulation  - 778 . .  .  Combustion of fuel - 778 .  .  .
     Electric melting - 779 .  .  •  Baghouses and centrifugal scrubbers -  779
 Glass-Forming Machines	    781
   The Air Pollution Problem	    781
   Air Pollution Control Methods	    781
FRIT SMELTERS	    782
 Introduction	    782
   Raw Materials	    782
   Types  of Smelters	    783
   Frit Manufacturing	    783
   Application, Firing,  and Uses of Enamels	    787
 The Air Pollution Problem	    787
 Hooding and Ventilation Requirements	    787
 Air Pollution Control Equipment	    788
FOOD PROCESSING EQUIPMENT	    788
 Coffee Processing	    791
   Batch Roasting	    791
   An Integrated Coffee Plant	    791
   The Air  Pollution Problem	    793
   Hooding  and Ventilation Requirements	    793
   Air Pollution  Control Equipment	    793
 Smokehouses	    794
   The Smoking Process	    794
   Atmospheric Smokehouses	,	    794

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                                             CONTENTS
 Hooding and Ventilation Requirements	    823
   Emission Rates From Cookers	    824
   Emission Rates From Driers	    825
 Air Pollution Control Equipment	    825
   Controlling High-Moisture Streams	    825
   Subcooling Condensate	    826
   Condenser Tube Materials	    826
   Interceptors in Cooker Vent Lines	    826
   Vapor Incinerator	,	    827
   Condensation-Incineration Systems	    827
   Carbon Adsorption of Odors	    828
   Odor  Scrubbers	    829
   Odor  Masking and Counteraction	    829
ELECTROPLATING	    829
 The Air Pollution Problem	    830
 Hooding and Ventilating Requirements	    831
 Air Pollution Control Equipment	    831
   Scrubbers	    831
   Mist Inhibitors	    831
INSECTICIDE MANUFACTURE	    832
 Methods of Production	    832
   Solid-Insecticide Production Methods	    833
   Liquid-Insecticide Production Methods	    835
 The Air Pollution Problem	    836
 Hooding and Ventilation Requirements	    836
 Air Pollution Control Equipment	    837
HAZARDOUS  RADIOACTIVE  MATERIAL	    838
 Hazards in the Handling of Radioisotopes	    838
 The Air Pollution Problem	    838
   Characteristics of Solid, Radioactive  Waste	    838
   Characteristics of Liquid,  Radioactive Waste	    838
   Problems in Control of Airborne,  Radioactive Waste.	    839
 Hooding and Ventilation Requirements	    839
   Hooding	    839
   Ventilation	    839
 Air Pollution Control Equipment	    840
   Reduction of Radioactive,  Particulate Matter at Source	    840
   Design of Suitable Air-Cleaning Equipment	    841
    Reverse-jet baghouse - 841 . . . Wet collectors -  841
    Electrical precipitators - 842 .  .  .  Glass fiber filters - 842 .  .  .  Paper filters - 843
   Disposal and Control of Solid, Radioactive Waste	    843
   Disposal and Control of Liquid, Radioactive Waste	    843
OIL AND SOLVENT RE-REFINING	    844
 Re-refining  Process for Oils	    844
 Re-refining  Process for Organic Solvents	    844
 The Air Pollution Problem	    845
   Air Pollution From Oil Re-refining	    845
   Air Pollution From Solvent Re-refining	    846
 Air Pollution Control Equipment	    846
   Oil Re-refining	    846
   Solvent Re-refining	    846
CHEMICAL MILLING	    846
 Description  of the Process	    846
 Etchant Solutions	    848
 The Air Pollution Problem	    849
   Mists	    849
   Vapors	    849
   Gases	    849
   Solvents	    849
 Hooding and VentilationsRequirements	    849
 Air Pollution Control Equipment	    849
   Corrosion  Problems	    850

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                                            CONTENTS
   Recirculating Smokehouses	    795
   Smoking by Immersion	,	,    795
   Smoking by Electrical Precipitation	    795
   The Air Pollution Problem	    796
   Hooding and Ventilation Requirements	 ,	    796
   Air Pollution Control Equipment	    796
    Afterburners - 796 .  . . Electrical precipitators - 79"
    Electrical precipitation versus incineration - 797
    Bypassing control devices during nonsmoking periods -  798
 Deep Fat Frying	,    799
   The Air Pollution Problem	    799
   Hooding and Ventilation Requirements	    800
   Air Pollution Control Equipment	    800
 Livestock Slaughtering	    801
   The Air Pollution Problem	    801
   Air Pollution Control Equipment	    801
 Edible-Lard and Tallow  Rendering	    802
   Dry Rendering	    803
    Batchwise rendering  - 803 .  . ,  Continuous low-temperature rendering - 803
   Wet Rendering	    803
   The Air Pollution Problem	    803
   Hooding and Ventilation Requirements	    803
   Air Pollution Control Equipment	    804
FISH CANNERIES AND FISH REDUCTION PLANTS	    804
 Wet-Fish Canning	    805
 Tuna Canning.	    805
 Cannery Byproducts	    806
 Fish Meal Production	    806
 Fish Solubles and  Fish Oil Production	    807
 Digestion Processes	    809
 The Air Pollution  Problem	    809
   Odors From Meal Driers	    809
   Smoke From Driers	    810
   Dust From Driers and Conveyors	    810
   Odors From Reduction Cookers	    811
   Odors From Digesters	    811
   Odors From Evaporators	    811
   Odors From Edibles Cookers	    811
 Hooding and Ventilation  Requirements	    811
 Air Pollution Control Equipment	    812
   Controlling Fish Meal  Driers	    812
   Incinerating Drier Gases	    812
   Chlorinating and Scrubbing Drier Gases	    812
   Controlling Reduction Cookers and Auxiliary Equipment	    813
   Controlling Digesters	    814
   Controlling Evaporators	    814
   Collecting Dust	    815
   Controlling Edible-Fish Cookers	    815
REDUCTION OF INEDIBLE ANIMAL MATTER	    815
 Batch-wise Dry Rendering	    816
 Continuous Dry Rendering	    817
 Wet Rendering	    818
 Refining Rendered Products	    819
 Drying Blood	    819
 Processing Feathers	    820
 Rotary Air Driers	    820
 The Air Pollution Problem	    820
   Cookers  as Prominent Odor Sources	    822
   Odors From Air Driers	    822
   Odors and Dust From Rendered-Product Systems	    822
   Grease-Processing Odors		    823
   Raw-Materials Odors	    823

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                                            CONTENTS
VAPOR COMPRESSORS	     67
 Types of Compressors	     67
   Positive-Displacement Compressors	     68
   Dynamic Compressors	     69
   Reciprocating Compressors	     69
 Use in Air Pollution Control	     72
CHECKING OF EXHAUST SYSTEM	     72
 Theory of Field Testing	     72
   Quantity Meters	     72
   Velocity Meters	     72
 Pitot Tubes	'.	     72
   Pitot Tube  Traversing Procedure	     73
   Altitude and Temperature Corrections for  Pitot Tubes	     73
 Swinging-Vane Velocity Meter	     73
   Calibrating the Velocity Meter	     74
   Uses of the Velocity Meter	     75
COOLING OF  GASEOUS  EFFLUENTS	     76
 Methods of Cooling Gases	     76
   Dilution With Ambient Air	     76
   Quenching With Water	     79
   Natural Convection and Radiation	     81
   Forced-Draft Cooling	     86
 Factors Determining Selection of Cooling Device	     86

               CHAPTER  4.  AIR POLLUTION CONTROL  EQUIPMENT  FOR  PARTICULATE MATTER
INERTIAL SEPARATORS	     91
 Single-Cyclone Separators	     91
   Theory of Operation	     92
   Separation  Efficiency	     93
   Pressure Drop	     93
 Other Types of Cyclone Separators	     94
   High-Efficiency Cyclone  Separators	     94
   Multiple-Cyclone Separators	     94
   Mechanical,  Centrifugal  Separators	     94
 Predicting Efficiency of Cyclones	     95
   Method of Solving a Problem	     97
WET COLLECTION  DEVICES	     99
 Theory of Collection	    100
 Mechanisms for Wetting the Particle	    100
 Types of Wet Collection Devices	    101
   Spray Chambers	    101
   Cyclone-Type Scrubbers	    101
   Orifice-Type Scrubbers	    101
   Mechanical Scrubbers	    102
   Mechanical,  Centrifugal  Collector With Water Sprays	    102
   High-Pressure Sprays 	    103
   Venturi Scrubbers	    104
   Packed Towers	    104
   Wet Filters	    105
 The Role of Wet Collection Devices	    105
BAGHOUSES	    106
 Filtration Process	    106
   Mechanisms	    106
     Direct interception - 108 . .  Impingement -  109  . .  Diffusion - 110 .  . Electrostatics - 110
   Baghouse Resistance	    110
     Clean cloth resistance - 110 .  . . Resistance of dust mat -  111 . .  .
     Effect of resistance on  design  - 115
   Filtering Velocity	    116
   Filtering Media	    118
   Fibers	    118
     Cotton - 118 . . . Wool - 118 . .  . Nylon -  118 . .  . Dynel  - 118 .  .  . Orion and Dacron -
     118 ...  Teflon - 119 ... Glass  - 119

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xii                                           CONTENTS
   Yarn	    119
    Filament yarns - 119 .  . . Staple yarns - 119
   Weave	    120
    Plain weave - 1ZO . . .  Twill weave  - 120 .  .  .  Satin weave  -  1ZO
   Finish	    120
   Size and Shape of Filters	    121
    Diameters of tubular filtering elements  -  121  . . .  Length of tubular bags - 121 .  .  .
    Length-to-diameter ratio - 121  .  . .  Multiple-tube bags - 122  .  . . Envelope  type - 122
  Installation of Filters	    122
   Arrangement	    122
   Bag Spacing	    123
   Bag Attachment	    123
    Bottom attachments - 123 . .  .  Top support - 123
  Cleaning  of Filters	    124
   Methods	    124
    Manual cleaning - 124 . . . Mechanical  shakers - 125 .  . . Pneumatic shakers  - 125 . .  .
    Bag  collapse -  127 .  .  .  Sonic cleaning  - 127 . .  .  Reverse airflow -  128 . . .
    Reverse-air jets  - 128
   Cleaning Cycles	    130
    Manually initiated cycles - 130 . . .  Semiautomatic cycles - 131 .  .  .
    Fully automatic cycles - 131 . .  .  Continuous cleaning -  131
  Disposal  of Collected Dust	    131
  Baghouse  Construction	    132
   Pushthrough versus Pullthrough	    132
   Structural Design	    132
   Hoppers	    132
    Size - 132 .  .  . Slope of hopper sides -  133  .  . . Gage of metal - 133 .  . .
    Use  of vibrators and rappers  -  133 .  .  . Discharge -  134
  Maintenance	    134
   Service	    134
   Bag Replacement	    134
   Precoating	    135
SINGLE-STAGE  ELECTRICAL PRECIPITATORS	    135
  History of Electrostatic Precipitation	    135
   Origins of  Electrostatic Principles	    135
   Early Experiments With Electrostatics on Air Contaminants	    137
   Development of the First Successful Precipitator	    137
   Improvements in Design, and Acceptance by Industry	    138
  Advantages and Disadvantages of Electrical Precipitation	    138
  Mechanisms Involved in Electrical Precipitation	    139
  Diverse Applications of Electrical Precipitation	    141
   Construction Details of Electrical Precipitators	    141
    Discharge electrodes -  141 .  .  . Collecting  electrodes -  141 .  .  .
    Tubular collecting electrodes -  141 . .  . Removal  of dust from collecting electrodes - 143 .  .
    Precipitator shells and hoppers - 144
   High Voltage for Successful  Operation	    145
    Tube-type rectifiers - 145 .  .  . Solid-state  rectifiers - 145
   Effects  of Wave  Form	    145
   Controlled Sparking Rate	    146
   Operating Voltage	    146
   Uniform Gas Distribution	    146
   Cost of Electrical Precipitator Installations	    146
   Theoretical Analysis of Precipitator Performance	    147
    Particle charging  - 147 .  . .  Particle migration -  148
   Theoretical Efficiency	    149
   Deficiencies  in  Theoretical Approach to Precipitator Efficiency	    150
   Effects  of Resistivity	    150
   Methods of Reducing Reentrainment	    152
   Practical Equations for Precipitator Design and Efficiency	    153
   Effects  of Nonuniform Gas Velocity	    154
   Important Factors  in the Design of a Precipitator	    156
  Summary and Conclusions	    156

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                                            CONTENTS                                         xiii
TWO-STAGE ELECTRICAL PRECIPITATORS	    156
 Theoretical Aspects	    158
   Theory of Dust Separation	    158
   Particle Charging	    159
   Drift Velocity	    159
   Efficiency	    160
 Design Factors	    160
   Electrical Requirements	    160
   Air Capacity	    161
   Air Distribution	    161
   Auxiliary Controls	    162
 Construction and Operation	    163
   Assembly	    163
   Maintenance	    163
   Safety	    163
 Application	    163
   Two-Stage Precipitators of Special Design	    165
   Equipment Selection	    165
OTHER PARTICULATE-COLLECTING DEVICES	    166
 Settling Chambers	    166
 Impingement Separators	    166
 Panel Filters	    167
 Precleaners	    168

                      CHAPTER 5.  CONTROL  EQUIPMENT  FOR  GASES AND VAPORS
AFTERBURNERS	    171
 Direct-Flame Afterburners	    171
 Design Principles	    171
 Afterburner Chamber	    172
 Gas Burners for Afterburners	    172
   Mixing-Plate Burners	    172
   Multi-Port Burners	    172
   Nozzle Mixing and Premixing Burners	    173
 Sources  of Combustion Air for Gas  Burners	    174
 Oil Firing of Afterburners	    174
 Afterburner Controls	    175
 Direct-Flame Afterburner Efficiency	    175
 Direct-Flame  Afterburner Design Problem	    176
 Catalytic Afterburners	    179
 Operation	    180
 Efficiency	    181
 Recovery of Heat From Afterburner Exhaust Gases	    181
 Preheating of Afterburner Inlet Gases	    182
BOILERS  USED AS AFTERBURNERS	    183
 Conditions for Use	    183
 Manner of Venting  Contaminated Gases	    185
 Adaptable Types of Equipment	'	    187
   Boilers and  Fired Heaters	    187
   Burners	    187
 Safety	    187
 Design Procedure	    187
 Test Data	    189
ADSORPTION EQUIPMENT	    189
 Types of Adsorbents	    191
 Use of Activated Carbon in Air Pollution Control	    191
   Saturation	    191
   Retentivity	    192
   Breakpoint	    192
   Adsorption of Mixed Vapors	    192
   Heat of Adsorption	    192
   Carbon Regeneration	    193
 Equipment Design	  193

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                                            CONTENTS
   Fixed-Bed Adsorber	    194
    Conical fixed-bed adsorber  - 196
   Continuous Adsorber	    197
   Pressure Drop	    197
 Operational Problems	    198
   Particulate Matter	    198
   Corrosion	    198
   Polar and Nonpolar  Compounds	    198
VAPOR CONDENSERS	    198
 Types of Condensers	    199
 ,  Surface and Contact Condensers	    199
 Typical Installations	    201
   Condensers in Control Systems	    201
   Subcooling Condensate	    202
 Contact Condensers	    203
   Sizing Contact Condensers	    203
 Surface Condensers 	    203
   Characteristics of Condensation	    203
   Design of Surface Condensers	    203
 Applications	    207
GAS ABSORPTION EQUIPMENT	    207
 General Types of Absorbers	    208
 Packed Tower Design	    208
   Packing  Materials	    209
   Liquid Distribution	    209
   Tower Capacity	    210
   Tower Diameter	    211
   Number  of Transfer  Units (NTU)	    213
   Height of a  Transfer Unit	    214
   Pressure Drop Through Packing	      216
   Illustrative Problem	    216
 Plate or Tray Towers	    220
   Types of Plates	    220
 Bubble Cap Plate Tower Design	    221
   Liquid Flow	    221
   Plate Design and  Efficiency	    221
   Flooding	    222
   Liquid Gradient on Plate	    223
   Plate Spacing	    224
   Tower Diameter	    224
   Number of Theoretical Plates	    225
   Illustrative Problem	    225
 Comparison of Packed and Plate Towers	    227
 Vessels for Dispersion of Gas  in Liquid	    228
 Spray Towers and Spray Chambers	    228
 Venturi Absorbers	    228
NOTATIONS	    229

                               CHAPTER 6.  METALLURGICAL EQUIPMENT
FURNACE  TYPES	    233
 Reverberatory Furnace	    233
 Cupola Furnace	    234
   Combustion Air	    234
   Methods of Charging	    235
   Preheating Combustion Air	    235
 Electric Furnace	    236
   Direct-Arc Furnace	    236
   Indirect-Arc Furnace	    236
   Induction Furnace	    237
   Resistance Furnace	    237
 Crucible Furnace	    237
   Tilting Furnace	    238

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                                             CONTENTS
   Pit Crucible	    238
   Stationary Crucible	    238
  Pot Furnace	    238
STEEL-MANUFACTURING PROCESSES	    239
  Open-Hearth Furnaces	    240
   The Air Pollution Problem	    241
   Hooding and Ventilation Requirements	    242
   Air Pollution Control Equipment	    244
  Electric-Arc Furnaces	    Z45
   The Air Pollution Problem	    246
   Hooding and Ventilation Requirements	    246
   Air Pollution Control Equipment	    252
     Baghouse dust collectors - 252 .  . Electrical precipitators - 25Z . . Water scrubbers - 253
  Electric-Induction Furnace	    254
   The Air Pollution Problem	    254
   Hooding and Ventilation Requirements	    255
   Air Pollution Control Equipment	    255
IRON CASTING	    256
  Cupola Fvirnaces	    256
   The Air Pollution Problem	    256
   Hooding and Ventilation Requirements	    258
   Air Pollution Control Equipment	    258
     Afterburners  - 259 . .  Baghouse dust collectors -  260 . .  Electrical precipitators - 260
   Illustrative Problem	    262
  Electric-Arc Furnaces	    266
   The Air Pollution Problem	    267
   Hooding and Ventilation Requirements	    267
   Air Pollution Control Equipment	    267
     Baghouse dust collectors - 267 .  . . Electrical precipitators -  267
  Induction Furnaces	    267
  Reverberatory Furnaces	    267
SECONDARY BRASS- AND  BRONZE-MELTING PROCESSES	    269
  Furnace Types	    269
   The Air Pollution Problem	    269
     Characteristics of emissions - 269 . . Factors causing large concentrations of zinc fumes - 270
     Crucible furnace--pit and tilt type - 272 .  .  Electric furnace--low-frequency induction type - 272
     Cupola furnace - 273
   Hooding and Ventilation Requirements	    273
     Reverberatory furnace--open-hearth type  - 273. .  Reverberatory furnace--cylindrical type  - 275
     Reverberatory furnace--tilting type - 275 .  . Reverberatory furnace--rotary tilting type - 275 . .
     Crucible-type furnaces - 278 . .  Low-frequency induction furnace - 278 . .  Cupola furnace - 279
   Air Pollution Control Equipment	    279
     Baghouses - 279 .  . . Electrical precipitators - 280 . . .  Scrubbers  - 282
SECONDARY ALUMINUM-MELTING PROCESSES	    283
  Types of  Process	    283
   Crucible Furnaces	    283
   Reverberatory  Furnaces	    284
   Fuel-Fired Furnaces	    284
   Electrically Heated Furnaces	    284
   Charging Practices	    284
   Pouring Practices	    285
   Fluxing	    285
     Cover fluxes - 286 .  .  . Solvent fluxes - 286 . .  .  Degassing fluxes - 286 .  .  .
     Magnesium-reducing fluxes - 286 . .  .  Magnesium reduction with chlorine - 287
  The Air Pollution Problem	    287
   Particle Size of Fumes From Fluxing	    288
  Hooding and Ventilation Requirements	    288
  Air Pollution Control Equipment	    289
SECONDARY ZINC-MELTING PROCESSES	    293
  Zinc Melting	    293
   The Air Pollution Problem	    293
  Zinc Vaporization	    293

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xvi                                          CONTENTS
  Reduction Retort Furnaces	    294
   Reduction in Belgian Retorts	    294
   The Air Pollution Problem	    295
   Hooding and Ventilation Requirements	    295
  Distillation Retort Furnaces	    295
   The Air Pollution Problem	    296
   Hooding and Ventilation Requirements	    296
  Muffle  Furnaces	    297
   The Air Pollution Problem	    297
   Hooding and Ventilation Requirements	    298
  Air Pollution Control Equipment	    299
LEAD REFINING	    299
  Reverberatory Furnaces	    300
   The Air Pollution Problem	    300
   Hooding and Ventilation Requirements	    301
   Air Pollution Control Equipment	  .    301
  Lead Blast Furnaces	    302
   The Air Pollution Problem	    302
   Hooding and Ventilation Requirements	    302
   Air Pollution Control Equipment	    302
  Pot-Type Furnaces	    303
   The Air Pollution Problem	    304
   Hooding and Ventilation Requirements	    304
   Air Pollution Control Equipment	    304
  Barton Process	    304
METAL  SEPARATION PROCESSES	    304
  Aluminum Sweating	    305
  Zinc, Lead,  Tin, Solder, and Low-Melting Alloy Sweating	    305
   The Air Pollution Problem	    306
     Contaminants from aluminum-separating processes -  306 . .  .
     Contaminants from low-temperature sweating - 306
   Hooding and Ventilation Requirements.	    306
   Air Pollution Control Equipment	    308
     Aluminum-separating processes - 308 . . .  Low-temperature sweating - 308
CORE OVENS	    308
  Types  of Ovens	    309
  Heating Core Ovens	    311
  Core Binders	    312
   The Air Pollution Problem	    314
   Hooding and Ventilation Requirements	    314
   Air Pollution Control Equipment	    315
FOUNDRY SAND-HANDLING EQUIPMENT	    315
  Types  of Equipment	    315
   The Air Pollution Problem	    316
   Hooding and Ventilation Requirements	    316
     Shakeout grates - 317 .  . . Other sand-handling equipment -  317
   Air Pollution Control Equipment	    317
HEAT TREATING SYSTEMS	    320
  Heat Treating  Equipment	    320
   The Air Pollution Problem	    320
   Hooding and Ventilation Requirements	    321
   Air Pollution Control Equipment	    321

                                  CHAPTER  7.  MECHANICAL EQUIPMENT
HOT-MIX ASPHALT PAVING BATCH PLANTS	    325
  Introduction	    325
   Raw Materials Used	    325
   Basic Equipment	    325
  Plant Operation	    325
  The Air Pollution Problem	    326
  Hooding and  Ventilation Requirements	    328
  Air Pollution Control Equipment	    328

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                                             CONTENTS    	        	         xvii
   Variables Affecting Scrubber Emissions	    330
   Collection Efficiencies Attained	    332
   Future Trends in Air Pollution Control Equipment	    333
CONCRETE-BATCHING PLANTS	    334
 Wet-Concrete-Batching Plants	    334
   The Air Pollution Problem	    334
   Air Pollution Control Equipment	    335
    Cement-receiving and storage system - 335 . .  .  Cement weigh hopper - 336 .  . .
    Gathering hoppers  - 336
 Dry-Concrete-Batching Plants	    336
   The Air Pollution Problem	    337
   Hooding and Ventilation Requirements	    337
   Air Pollution Control Equipment	    337
    Dust created by truck movement - 337
 Central Mix Plants	    337
   The Air Pollution Problem	    338
   Hooding and Ventilation Requirements	    339
   Air Pollution Control Equipment	    339
CEMENT-HANDLING EQUIPMENT	    339
 The Air Pollution Problem	    339
 Hooding and Ventilation Requirements	    339
   Receiving Hoppers	    339
   Storage and Receiving Bins	    339
   Elevators and Screw Conveyors	    340
   Hopper  Truck and Car Loading	    340
 Air  Pollution Control Equipment	    340
ROCK AND GRAVEL AGGREGATE PLANTS	    340
 The Air Pollution Problem	    341
 Hooding and Ventilation Requirements	    341
 Air  Pollution Control  Equipment	    341
MINERAL WOOL FURNACES	    342
 Introduction	    342
   Types and Uses of Mineral Wool Products	    342
   Mineral Wool  Production	    342
 The Air Pollution Problem	    343
 Hooding and Ventilation Requirements	    344
 Air  Pollution Control  Equipment	    347
   Baghouse Collection and Cupola Air Contaminants	    347
   Afterburner Control of  Curing Oven Air Contaminants	    347
   Reducing Blowchamber Emissions	    349
   Controlling Asphalt Fumes	    349
PERLITE-EXPAND ING FURNACES	    350
 Introduction	    350
   Uses	    350
   Mining Sites	    350
   Perlite  Expansion Plants	    350
   Expansion Furnaces	    350
   Gas and Product Cooling	    350
   Product Collectors and Classifiers	    350
 The Air Pollution Problem	    351
 Hooding and Ventilation Requirements	    351
 Air  Pollution Control  Equipment	    351
FEED AND GRAIN MILLS	    352
 Introduction	    352
   Receiving, Handling, and Storing  Operations	    353
   Feed-Manufacturing Processes	    354
 The Air Pollution Problem	    355
   Receiving, Handling, and Storing  Operations	    356
   Feed-Manufacturing Processes	    357
 Hooding and Ventilation Requirements	    357
   Receiving,  Handling, and Storing  Operations	    357
   Feed-Manufacturing Processes	    358

  234-767 O - 77 - 2

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                                             CONTENTS
 Air Pollution Control Equipment	    358
   Receiving, Handling, and Storing Operations	    359
   Feed-Manufacturing Processes	    359
   Filter Vents	    359
   Cyclones	    359
   Baghouses	    360
PNEUMATIC CONVEYING EQUIPMENT	    362
 Introduction	    362
   Types of Pneumatic Conveying Systems	    362
   Types of Air-Moving Used in Conveying	    363
   Preliminary Design Calculations	    365
 The Air Pollution Problem	    367
 Air Pollution Control Equipment	    367
DRIERS	    367
 Introduction	    367
   Rotary Driers	    367
   Flash Driers	    367
   Spray Driers	    369
   Other Types of Driers	    370
 The Air Pollution Problem	    371
 Hooding and Ventilation Requirements	    371
 Air Pollution Control Equipment	    371
   Dust Control	    371
   Drying With Solvent Recovery	    371
   Smoke and Odor Emissions	    372
WOODWORKING EQUIPMENT	    372
 Exhaust Systems	    372
   Construction of Exhaust Systems	    372
 The Air Pollution Problem	    373
 Hooding and Ventilation Requirements	    373
 Air Pollution Control Equipment	    373
   Disposal of Collected Wastes	    374
RUBBER-COMPOUNDING EQUIPMENT	    375
 Introduction	    375
   Additives Employed in Rubber Compounding	    375
 The Air Pollution Problem	    376
 Hooding and Ventilation Requirements	    377
 Air Pollution Control Equipment	    377
ASPHALT ROOFING FELT SATURATORS	    378
 Description and Operation	    378
   Asphalt Coating of Felt	    378
   Roof Capping Materials	    379
 The Air Pollution Problem	    381
 Hooding and Ventilation Requirements	    383
 Air Pollution Control Equipment	    384
   Afterburners	    384
   Scrubbers	    386
   Electrical Precipitators	    386
   Baghouses	    389
   Glass Fiber Mats	    390
PIPE COATING EQUIPMENT	    390
 Introduction	    390
 Methods of Application	    392
   Pipe Dipping	    392
   Pipe Spinning	    392
   Pipe Wrapping	    392
   Preparation ofEnamel	    392
 The Air Pollution Problem	 .    392
 Hooding and Ventilation Requirements	    394
 Air Pollution Control Equipment	    395
ABRASIVE BLAST CLEANING	    397
 Introduction	"  397

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                                             CONTENTS
   Abrasive Materials	    397
   Method of Propelling the Abrasive	    397
   Equipment Used to Confine the Blast	    398
  The Air Pollution Problem	    401
  Hooding and Ventilation Requirements	    401
  Air Pollution Control  Equipment	    401
ZINC-GALVANIZING EQUIPMENT	    402
  Introduction	    402
   Cleaning	    402
   Cover Fluxes	    402
   Foaming Agents	    403
   Dusting  Fluxes	    403
  The Air Pollution Problem	    403
   Physical and Chemical Composition of the Contaminants	    404
  Hooding and Ventilation Requirements	    404
  Air Pollution Control  Equipment	    406
   Baghouses	    406
   Electrical Precipitators	    409
TIRE BUFFING EQUIPMENT	    410
  Introduction	    410
  The Air Pollution Problem	    411
  Hooding and Ventilation Requirements	    411
  Air Pollution Control  Equipment	    412
   Cyclones	    412
   Cyclones With Afterburners	    413
   Cyclones With Dry Filters	    413
   Cyclones With Baghouses and Dry Filters	    413
  Other Tread Removal Methods	    413
   Cutting Type Detreader	    413
   Water Spray at Rasp	    414
  Cost of Pollution Control	    414
WOOD TREATING EQUIPMENT	    414
  Introduction	    414
  Methods of Treating Wood	    415
  The Air Pollution Problem	    418
  Hooding and Ventilation Requirements	    419
  Air Pollution Control  Equipment	    419
CERAMIC SPRAYING AND METAL DEPOSITION EQUIPMENT	    421
  Introduction	    421
  Ceramic Spraying	    422
   The Air Pollution Problem	    422
   Air Pollution Control Equipment	    423
  Metal Deposition	    429
   The Air Pollution Problem	    431
   Air Pollution Control Equipment	    432

                                      CHAPTER 8.  INCINERATION
DESIGN PRINCIPLES FOR MULTIPLE-CHAMBER INCINERATORS	    437
  Retort Type	    437
  In-Line Type	    437
  Description of the  Process	    439
  Design Types and Limitations	    440
   Comparison of Types	    440
  Principles of Combustion	    440
  Design Factors	    441
   Design Precepts	    441
GENERAL-REFUSE INCINERATORS	    443
  The Air Pollution Problem	    444
  Air Pollution Control  Equipment	    444
  Design Procedure	    445
   General Construction	    446
   Refractories	    447

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                                            CONTENTS
   Grates and Hearths	   447
   Air Inlets	   447
   Stack	   449
   Induced-Draft System	   450
   Operation	   450
   Illustrative Problem	   450
MOBILE MULTIPLE-CHAMBER INCINERATORS	   452
 Design Procedure	   452
   Stack Requirements	   452
   Induced-Draft Fan System	   452
 Standards of Construction	   454
   Refractories  	   454
   Grates	   454
   Air Inlets	   454
   Structure	   454
   Auxiliary Burners	   454
 Stack Emissions	   454
   Illustrative Problem	:	   455
MULTIPLE-CHAMBER INCINERATORS FOR BURNING WOOD WASTE	   460
 Introduction	   460
   Description of the Refuse	   460
 The Air Pollution Problem	   460
 Air  Pollution Control Equipment	   460
 Design Procedure	   460
   Incinerator Arrangements	   463
 Design Procedure for Mechanical Feed Systems	   465
   Surge Bin	   465
   Screw or Drag Conveying	   466
   Pneumatic  Conveying	   467
 Standards for Construction	   467
   Refractories	   468
   Grates	   468
   Exterior Walls	   468
   Air Ports	   468
 Operation of Incinerators	   469
   Illustrative Problem	   469
FLUE-FED APARTMENT INCINERATORS	   471
 Introduction	   471
   Description of Refuse	   472
 The Air Pollution Problem	   472
   Stack Emissions	   472
 Air  Pollution Control Equipment	   472
 Installation of Afterburner on a Roof	   473
   Design Procedure	   473
    Draft control -  473 .  .  . Chute door locks - 474 .  . . Design parameters - 474 . . .
    Limitations - 474 . . . Typical installations  - 475
   Standards for  Construction	   476
    Mounting  and supports  - 476 .  .  . Metals - 476 . .  . Castable refractories -  476 ...
    Firebrick - 476 . . . Insulating firebrick - 476 . .  . Burners - 476 . . .
    Draft control damper - 477 .  . . Chute door  locks - 477
   Stack Emissions	   477
   Operation	   477
 Basement Afterburner	   478
   Design Procedure	   478
    Design parameters - 478 .  . . Typical installation - 478
   Standards for  Construction	   479
    Hot-zone  refractory  - 479 .  .  . Draft control damper  - 479
   Stack Emissions	   479
   Operation	   479
 Multiple - Chamber Incinerator, Basement Installation	   479
   Design Procedure	   479
    Draft control -  480 .  .  . Typical installation - 480

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                                            CONTENTS                                         xxi
   Standards for Construction	    481
   Stack Emissions	    481
   Operation	    481
   Illustrative Problem	    481
PATHOLOGICAL-WASTE INCINERATORS	    484
  The Air Pollution Problem	    485
  Air  Pollution Control Equipment	    485
   Design Procedure	    486
    Ignition chamber - 487  . .  .  Secondary combustion zone - 488 . . .  Stack design - 489 .  . .
    Piping requirements - 489 •  •  • Crematory design - 489 • •  •
    Incinerator design configuration - 489
   Standards for Construction.	    492
   Stack Emissions	    493
   Operation	    493
   Illustrative Problem	    493
DEBONDING OF BRAKE SHOES AND RECLAMATION OF ELECTRICAL EQUIPMENT
WINDINGS	    496
  Debonding of Brake Shoes	    496
  Reclamation of Electrical  Equipment Winding	    497
  The Air Pollution Problem	    498
  Air  Pollution Control Equipment	    498
   Primary Ignition Chamber	    499
   Secondary Combustion Chamber	    499
   Stack	    499
   Emissions	    499
   Typical Reclamation Equipment	    499
   Standards for Construction	    501
   Illustrative Problem	    501
DRUM RECLAMATION  FURNACES	    506
  Introduction	    506
   Description of the Furnace Charge	    507
   Description of the Process	    507
  The Air Pollution Problem	    507
  Air  Pollution Control Equipment	    507
   Primary Ignition Chamber,  Batch Type	    507
   Primary Ignition Chamber,  Continuous Type	    508
   Afterburner (Secondary Combustion Chamber)	    511
   Draft	    511
   Standards for Construction	    511
   Operation	    512
   Illustrative Problem	    512
WIRE RECLAMATION	    520
  Description of the Process	    520
  Description of the Charge	    521
  The Air Pollution Problem	    521
  Air  Pollution Control Equipment	    521
   Primary Ignition Chamber	    522
   Secondary Combustion	    525
   Emissions	    525
   Draft	    526
   Equipment Arrangement	    526
   General Construction	    526
   Refractories	    527
   Charge  Door	    527
   Combustion Air Ports	    527
   Gas Burners	    527
   Operation	    527
   Illustrative Problem	    528

                                CHAPTER 9.   COMBUSTION  EQUIPMENT
GASEOUS AND LIQUID FUELS	    535
  Introduction	    535

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xxii                                         CONTENTS
   Gaseous Fuels	    535
   Oil Fuels	    536
  The Air Pollution Problem	    537
   Black Smoke	    537
   White Smoke	    537
   Particulate Emissions	    538
   Sulfur in Fuels	    539
   Sulfur Oxides	    539
   Oxides of Nitrogen	    539
  Air Pollution Control Methods	    540
   Prohibitions Against Sulfur Emissions	    540
   Removal of Sulfur and Ash From Fuels	    540
   Illustrative Problem.	    541
GAS AND OIL, BURNERS	    542
  Introduction	    542
   Draft Requirements	    542
   Gas Burners	    542
   Partially Aerated Burners	    543
   Multiple-Port Gas Burners	    544
   Forced-Draft Gas Burners	    544
   Gas Flow Rates	    545
   Oil Burners	    545
   Viscosity and Oil Preheaters	    549
  The Air Pollution Problem	    549
   Smoke and Unburned Contaminants	    549
   Ash and Sulfur  Oxides	    553
   Oxides of Nitrogen	    553
  Air Pollution Control Equipment	    553
BOILERS,  HEATERS,  AND STEAM GENERATORS	    553
  Introduction	    553
   Industrial Boilers and Water Heaters	    553
   Power Plant Steam Generators	    554
   Refinery Heaters	    556
   Hot Oil Heaters and Boilers	    556
   Fireboxes	    556
   Soot Blowing	    558
  The Air Pollution Problem	    560
   Solid Particulate Emission During Normal Oil Firing	    560
   Soot-Blowing Participates	    561
   Sulfur Dioxide	    562
   Sulfur  Trioxide	    562
   Excessive Visible Emissions	    563
   Oxides of Nitrogen	    564
   Estimating NOX Emissions	    567
  Air Pollution Control Methods	    567
   Combustible Particulates	    568
   Soot Collectors. .	    568
   Collection of Sulfur Oxides	    568
     Wet absorption - 569 . . •  Dry absorption - 569. . . Wet adsorption - 570 . . .
     Catalytic  oxidation  - 570 .  . . Other  processes  for -removing SO2  from stack gases - 570
   Controlling Oxides of Nitrogen	    570
     Reduction  of NOxby modification of boiler operation - 571.  .  . Removal of NOx by
     treatment of flue gas  -  576

                                 CHAPTER 10.  PETROLEUM  EQUIPMENT

GENERAL INTRODUCTION	,	    581
  Crude Oil Production	    581
  Refining	    581
   Flares and Slowdown Systems	    581
   Pressure Relief Valves	    581
   Storage Vessels	.	    581
   Bulk-Loading Facilities	    582
   Catalyst Regenerators	    582

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                                            CONTENTS                                        xxiii
   Effluent-Waste Disposal	    584
   Pumps and Compressors	    584
   Air-Blowing Operations	    584
   Pipeline Valves and Flanges, Blind Changing,  Process Drains	    584
   Cooling Towers	    584
   Vacuum Jets and Barometric Condensers	    584
  Effective Air Pollution Control Measures	    585
  Marketing	    585
WASTE-GAS DISPOSAL SYSTEMS	    585
  Introduction	    585
   Design of Pressure Relief System	    588
   Safety Valves	    589
   Rupture Discs	    590
    Sizing rupture discs - 592 . .  .  Sizing liquid safety valves - 593 . .  .
    Sizing vapor  and gas relief and safety valves - 594 . .  .
    Installing relief and safety valves  and rupture discs  - 595 .  .  . Knockout vessels - 596 . . .
    Sizing a blowdown line -  598
  The Air Pollution Problem	    604
   Smoke From Flares	    604
   Noise From Flares	    604
   Other Air Contaminants From Flares	    605
  Air  Pollution Control Equipment	    605
   Types of Flares	    605
    Elevated flares - 605 . .  . Ground level flares - 610 . . .  Effect of  steam injection - 613 .  .
    Design  of a smokeless flare - 614 .  . . Pilot ignition system  - 616 . . .
    Instrumentation and control of steam and gas  - 617 . . . Supply and  control of steam- 618. .
    Design  of water-injection-type ground flares  - 623 .  .  .
    Design  of venturi-type ground flares - 624 .  .  . Maintenance  of flares - 626
STORAGE VESSELS	    626
  Types of,Storage Vessels	    626
   Pressure Tanks and Fixed-Roof Tanks	    627
   Floating-Roof Tanks	    627
   Conservation Tanks	    628
   Open-Top Tanks,  Reservoirs, Pits, and Ponds	    631
  The Air Pollution Problem	    631
   Factors Affecting Hydrocarbon  Vapor Emissions	    631
   Hydrocarbon Emissions From Floating-Roof Tanks	    632
    Withdrawal emissions - 634 .  .  .  Application of results  - 634
   Hydrocarbon Emissions From Low-Pressure Tanks	    634
   Hydrocarbon Emissions From Fixed-Roof Tanks	    638
   Aerosol Emissions	    642
   Odors	    64Z
  Air  Pollution Control Equipment	    643
   Seals for Floating-Roof Tanks	    644
   Floating  Plastic Blankets	    644
   Plastic Microspheres	    645
   Vapor Balance Systems	    647
   Vapor Recovery Systems	    647
   Miscellaneous Control Measures	    648
   Masking  Agents	    649
   Costs of  Storage Vessels	    649
LOADING FACILITIES	    649
  Introduction	    649
   Loading Racks	    652
   Marine Terminals	    652
   Loading Arm Assemblies	    652
  The Air Pollution Problem	    653
  Air  Pollution Control Equipment	    655
   Types of Vapor Collection Devices for Overhead Loading	    655
   Collection of Vapors From Bottom Loading	    658
   Factors Affecting Design of Vapor Collection Apparatus	    659
   Methods  of Vapor Disposal	, . ,	    660

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                                            CONTENTS
CATALYST REGENERATION	    662
 Types of  Catalysts	    662
   Loss of Catalyst Activity	    664
 Regeneration Processes	    664
   FCC Catalyst Regenerators	    664
   TCC Catalyst Regenerators	    665
   Catalyst Regeneration in Catalytic Reformer Units	    665
 The Air Pollution Problem	    666
 Air  Pollution Control Equipment	    667
   Wet- and Dry-Type, Centrifugal Dust Collectors	    667
   Electrical Precipitators	    668
   Carbon  Monoxide Waste-Heat Boilers	    670
   Economic Considerations	    671
OIL-WATER EFFLUENT SYSTEMS	    672
 Functions of Systems	    672
   Handling of Crude-Oil Production Effluents	    672
   Handling of Refinery Effluents	    673
   Treatment of Effluents by Oil-Water Separators	    673
   Clarification of Final-Effluent Water Streams	    673
   Effluent Wastes From Marketing Operations	    674
 The Air Pollution Problem	    675
   Hydrocarbons From Oil-Water Separators	„	    675
   Treatment of Refinery Liquid Wastes at Their Source	    677
    Oil-in-water emulsions - 677 . .  .  Sulfur-bearing waters - 677 .  .  . Acid  sludge - 678 ,  .  .
    Spent caustic wastes - 679
PUMPS	    679
 Types of  Pumps	    679
   Positive-Displacement Pumps	    680
   Centrifugal Pumps	    680
 The Air Pollution Problem	    681
 Air  Pollution Control Equipment	    681
   Results of Study to  Measure Losses From Pumps	    684
AIRBLOWN ASPHALT	    685
 Recovery of Asphalt  From Crude Oil	    686
 Airblowing of Asphalt	    686
 The Air Pollution Problem	    687
 Air  Pollution Control Equipment	    687
VALVES	    689
 Types of Valves	    689
   Manual  and Automatic Flow Control Valves	    689
   Pressure Relief and Safety Valves	    690
 The Air Pollution Problem	    690
   Total Emissions  From  Valves	    691
 Air  Pollution Control Equipment	    691
COOLING  TOWERS	    692
 Characteristics of Cooling Tower Operation	    693
 The Air Pollution Problem	    694
 Air  Pollution Control Equipment	    695
MISCELLANEOUS SOURCES	    695
 Airblowing	    695
 Blind Changing	    695
 Equipment Turnarounds	    696
 Tank Cleaning	    697
 Use of Vacuum Jets	    697
 Use of Compressor Engine Exhausts	    697

                            CHAPTER 11.  CHEMICAL PROCESSING EQUIPMENT
RESIN KETTLES	    701
 Types of Resins	    701
   Phenolic Resins	    701
   Amino Resins	    702
   Polyester and Alkyd Resins	    702

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                                             CONTENTS                                        xxix
                          CHAPTER 12.  ORGANIC SOLVENT  EMITTING EQUIPMENT

SOLVENTS AND THEIR USES	    855
 Introduction	    855
 Rule 66	    855
   Limitations on the Use of Photochemlcally Reactive Solvents	    857
   Baking and Curing Operations	    857
 Air Pollution Control Measures	    857
SURFACE  COATING OPERATIONS	    858
 Introduction	    858
 Types of  Equipment	    858
   Spray Booths	    858
   Flowcoating Machines	    858
   Dip Tanks	    860
   Roller Coating Machines	    861
 The Air Pollution Problem	    861
   Air Contaminants From Paint Spray  Booths	    861
   Air Contaminants From Other Devices	    863
 Hooding and Ventilation Requirements	    863
   Requirements for Paint Spray Booths	    863
   Requirements for Other Devices	    863
 Air Pollution Control Equipment	    864
   Control of Paint Spray Booth Particulates	    864
   Control of Organic  Vapors From Surface Coating Operations	    865
PAINT BAKING OVENS AND OTHER SOLVENT-EMIT TING OVENS	    865
 Introduction	    865
 Bake Oven Equipment	    866
   Batch Type Ovens	    866
   Continuous Ovens	    866
   Heating of Ovens	    866
   Oven Circulating and Exhaust Systems	    867
   Air Seals	    867
 The Air Pollution Problem	    867
 Hooding and Ventilation Requirements	    868
 Air Pollution Control Equipment	    869
 Other Ovens Emitting Air Contaminants	    870
   Can Lithograph Oven	    870
   Printing System Ovens	    871
SOLVENT  DEGREASERS	    871
 Introduction	    871
   Design and Operation	    871
   Types of Solvent	    871
 The Air Pollution Problem	    872
 Hooding and Ventilation Requirements	.•	    872
 Air Pollution Control Methods	    873
   Methods of Minimizing Solvent Emissions	    873
   Tank Covers	    873
   Controlling Vaporized Solvent	    874
DRY CLEANING EQUIPMENT	    875
 Introduction	    875
   Wash Machines	    875
   Combination  Machines	    876
   Extractors	    876
   Tumblers	    876
   Filters	    878
   Stills	    878
   Muck Reclaimers	    879
 The Air Pollution Problem	    879
   Solvents	    879
   Lint	    881
 Hooding and Ventilation Requirements	    882
 Air Pollution Control Methods	    882

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XXX
                                            CONTENTS
   Adsorbers	    883
   Lint Traps	    884

                                            REFERENCES
REFERENCES	    885

                                            APPENDIXES

APPENDIX A:  RULES AND REGULATIONS OF THE AIR POLLUTION CONTROL DISTRICT,  . .    907
  COUNTY OF LOS ANGELES
APPENDIX B:  ODOR-TESTING TECHNIQUES	    931
  The Odor Panel	    931
  The Odor Evaluation Room	    931
  Sampling Techniques	    932
  Evaluation of Odor Samples	;	    933
  Determination of Odor Concentration	    934
APPENDK C:  HYPOTHETICAL AVAILABLE HEATS FROM NATURAL GAS	    935
APPENDIX D:  MISCELLANEOUS DATA	    937
APPENDIX E:  EMISSION SURVEYS,  INVENTORIES, AND FACTORS	    959
  Introduction	    959
  Values of Surveys	    959
  Need for Continuing Surveys	    959
  Conducting the Survey	    960
  Sources of Survey Information	    960
  Detailed Versus "Short-Cut" Surveys	    960
  Elements of a Survey	    961
   Developing a List of Surveyees	    961
   Developing Emission Factors	    962
   Determining and Phrasing Appropriate Questions	    962
   Designing Effective Questionnaires	    962
   Treating and Evaluating the Data,  Reporting Results, and Recommending Action	    966

                                           SUBJECT  INDEX
SUBJECT INDEX	    969

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                                        Vapor Compressors
                                             69
                  LIQUID RING
     I NLET PORT
                                   DISCHARGE PORT
 Dl SCHARGE PORT
                                    INLET PORT
    Figure 30.  Rotary liquid-piston compressor
    (Bruce and Schubert,  1956).
tical  casing  partially fillecTwith liquid.   The ro-
tating force  of  the multiblade  rotor  causes the
liquid to follow the inside contour of the elliptical
casing. As the liquid recedes from the rotor blades
at the inlet port, the  space between buckets fills
•with the air or gas.  As the liquid reaches the
narrow point of the  elliptical  casing, the air or
gas is compressed and forced out through the dis-
charge p.orts (Bruce and Schubert, 1956).   Rotary
liquid-piston compressors are  available  in sizes
up to approximately 5,000 cfm.   Standard single-
stage units are used for pressures to 35 psig,  and
special single-stage units, for pressures  up to 75
psig.  Units  are staged above 75 psig.
Dynamic Compressors

Centrifugal compressors are similar to centrifugal
pumps and  fans.  An impeller rotates in a case,
imparting a high velocity and  a centrifugal motion
to the gas being compressed.   The impeller is
mounted on a shaft supported by bearings in each
end of the case.  In multiple -stage compressors,
several impellers are mounted on a single shaft.
Passages conduct  the gas from one stage to the
next.  Guide vanes in the passages direct the gas
flow from one impeller to the next at the proper
angle for efficient operation.  Figure 31 shows a
cross-sectional view of  a typical four-stage
compressor.

Since the flow of gas to the  centrifugal compressor
is continuous,  the fundamental concepts of fluid
flow apply.  The gas  enters  at the eye of the im-
peller,  passes through the impeller, changing in
velocity and direction, and exits into the diffuser
or volute, -where the kinetic energy is converted  to
pressure  (Leonard, 1956).
 The centrifugal compressor generally handles
 a large volume of gas at relatively low pres-
 sures,  but some commercially used centrifugal
 compressors have discharge pressures of up
 to 4,200 psig.  These compressors are, of
 course, multistaged.  Generally,  the single-
 stage centrifugal compressor produces pres-
 sures up to 35 psig.

 The axial-flow compressor,  shown in Figure 32
 is another type of dynamic compressor.  It is  dis-
 tinguished by the multiplicity of its rotor and stator
 blades.  These are either forged, machined,  or
 precision cast into airfoil shapes.  The compres-
 sor casing is made of cast iron, or fabricated out
 of steel,  depending upon inlet volume, pressure
 ratio, and temperature conditions.  Stator blades
 are attached to the casing to direct the flow of gas
 through the case.

 The rotor is a drum -with blades mounted around
 its periphery.  The drum is mounted on the  shaft
 supported by bearings in each end of the case.  As
 the rotor turns, the blades' force air through the
 compressor in an action similar to that of the  pro-
 peller fan.  The stator blades control the direction
 of the air as it leaves the rotor blades.  Pressure
 is increased owing to the kinetic energy given to
 the gas,  and the action of  the  gas on the stator
 blades.  Axial-flow compressors are high-speed
 high-volume  machines.   The pressures attained
 are relatively low, withamaximum commercially
 used discharge pressure of 90 psig.  These  com-
 pressors are rarely used for inlet capacities be-
 low 5, 000 cfm (Claude,  1956).


 Reciprocating  Compressors

 Reciprocating compressors are positive-displace-
 mentmachines used to increase the pressure of a
 definite volume of gas by volume reduction (Case,
 1956).   Most reciprocating  compressors used in
 heavy industrial production and continuous chem-
 ical  processing are stationary,  -water-cooled,
 double-acting units (see Figure  33).  The basic
 running-gear mechanism is  of the crank-and-fly-
 wheel type  enclosed  in  a cast-iron frame.  The
 crosshead construction permits  complete separa-
 tion of the compression  cylinder from the crank-
 case, an ideal feature  for handling combustible,
 toxic, or corrosive gases.  Generally, the cylinder
 is double acting, that is, compression occurs al-
 ternately in the head and crank end of the cylinder.
 The cylinder and its heads are usually water cooled
 to reduce thermal stresses and dissipate part of
 the  heat developed during  compression.   Com-
 pression rings  on  the pistons seal  one end of the
 cylinder from the  other.  The piston rod is  sealed
 in the  cylinder by highly effective packing,  and
 any slight leakage may be collected in a vent gland
for return to suction or for venting to the atmosphere.

-------
70
DESIGN OF LOCAL EXHAUST SYSTEMS
Figure 31.   Cross-section of a typical  four-stage centrifugal  compressor  (Clark Bros. Co., Clean,  N.Y.
from'  Leonard, 1956).
Gas  being compressed  enters and leaves  the
cylinder through the voluntary valves, which are
actuated entirely by the difference in pressure be-
tween the interior of the cylinder and the outside
system. Upon entering the cylinder,  the gas may
be compressed from the initial to the  desired final
pressure in one continuous step,  that is,  single-
stage compression.  Alternatively, multistage com-
pression divides  the compression into a series of
steps or stages,  each occurring in an  individual
cylinder. Here the gas is usually cooled between
the various stages of  compression.

The  compression process is  fundamentally isen-
tropic  (perfectly reversible adiabatic),  with cer-
tain actual modifications  or losses that may be
                      considered as efficiencies related to the isentropic
                      base.  Thermal dynamic losses within the cylinde
                      including fluid friction losses through the valves,
                      heating of the gas on admission to the cylinder,
                      and irreversibility of the process, maybe grouped
                      under  the single  term  compression efficiency.
                      Mechanical friction losses  encountered in  the
                      piston rings,  rod packings, and frame bearings
                      are grouped under the term mechanical efficiency.
                      Thus, the overall efficiency of the compressor is
                      the product  of compression and mechanical
                      efficiency.

                      For given service,  the actual brake horsepower
                      requirement of the compressor is normally about
                      IS to 33 percent  greater than the calculated ideal

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                                        Vapor Compressors
71
Figure 32.   Axial-flow compressor  (AlIis-Chalmers  Manufacturing Company, Milwaukee, Wisconsin, from

Claude,  1956).


                                                                     V'<"' ^»*v\%
                                                             •   > ^ -^';*3rsfeJ
  Figure 33.  Four-cylinder, horizontal, balanced,  opposed,  synchronous-motor compressor  (Worthingtort
  Corporation, Harrison, N.J.,  from Case, 1956).

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72
                                  DESIGN OF LOCAL EXHAUST SYSTEMS
 isentropic horsepower.  Or, stated another way,
 the  overall efficiency of most  compressors is in
 the range of 75 to 85  percent.

 USE IN AIR POLLUTION CONTROL

 Compressors are used to transport vapors or gases
 from  their source and deliver them to a control
 device or system under  pressure.  In some cases,
 the vapors or gases can be pressurized directly to a
 holding vessel and then  a compressor is used to
 send the vapors to control equipment.

 The vapors  created  from the refining,  storing,
 and bulk loading of volatile petroleum products are
 being controlled by the use of compressors.  The
 compressors deliver the  vapors  under pressures
 ranging from 5 to 200 psig to plant fuel systems,
 process streams, or absorption  systems.

 Centrifugal,  reciprocating,  and rotary-lobe com-
 pressors  arc  being used for controlling air  con-
 taminants.  Single-stage  reciprocating machines
 are the most common.  Two-stage compressors
 developing pressures up to 200 psig are in  use.
    CHECKING  OF  EXHAUST  SYSTEM

Air  flow  measurements and test data are neces-
sary to determine  whether an exhaust system is
functioning  properly  and in  compliance with de-
sign  specifications.  Correct testing procedures
must be  established  to obtain measurements for
determining whether  an exhaust system has suf-
ficient capacity for  additional hoods, and also to
obtain operational data from existing installations
for designing future exhaust  systems.
Velocity Meters

Velocity meters are  more commonly used in the
field  for  determining air  velocities.   The most
accurate and widely accepted in engineering prac-
tices are the pitot tube and  the swinging-vane ve-
locity meter.

PITOT TUBES

For  determining air  velocity, the standard pitot
tube,  named for the man who discovered the prin-
ciple, is considered reliable and is generally ac-
cepted in engineering practice.   It is the most
widely used field method  for  determining air
velocity.

A  standard pitot tube (Figure 34) consists of two
concentric  tubes:  the inner  tube measures the
impact  pressure,  which is the sum of the static
and kinetic  pressures, while the outer tube mea-
sures only the static pressure.  When the two tubes
are connected across a U-tube manometer or other
suitable  pressure-measuring device, the  static
pressure  is nullified  automatically and only the
velocity pressure (kinetic pressure) is registered.
The velocity is correlated to the velocity pressure
by the equation
where
                  1096.5
         velocity, fpm
(31)
   h  =  velocity pressure (manometer reading),
    V    in.  WC

   p  =  density of air, Ib/ft  .
THEORY OF FIELD TESTING

For most purposes the most important factor is the
accurate measurement of air quantity. Most field
meters measure  velocity  rather  than  quantity.
This neces sitatcs equating velocity to quantity.  By
using equation 8 and  a velocity meter, the quantity
of air flowing through  an exhaust system can be
accurately measured.
Quantity Meters

Some examples of quantity meters are thin-plate
orifices, sharp-edged orifices ,  and venturi meters .
These meters  are used extensively in laboratory
studies, but infrequently in industrial exhaust
systems.
Clearly, below 1, 266 fpm, the velocity pressure
becomes extremely low and is,  therefore,  diffi-
cult to read accurately on a manometer.  With a
                       IMPACT PRESSURE CONNECTION
                           TUBING ADAPTER
         STAINLESS STEEL  TU Bl N G ' J- r'
                                    BELL REDUCERS
                                                                                      SFATIC PRESSURE CONNECTION
                                                           STATIC PRESSURE HOLES  STAINLESS STEEL PIPE NIPPLES
                                                           OUTER PIPE ONLY
   IMPACT PRESSURE OPENING

 Figure 34.  Standard pitot tube (Western
 Precipitation,  Division of Joy Manufacturing
 Co., Los Angeles,  Calif.,  from ASHRAE  Guide
 and Data Book,  1963).

-------
                                       Checking of Exhaust System
U-tube manometer, the accuracy is low for veloc-
ities  below 2,500 fpm.   With a carefully made,
accurately leveled, inclined manometer,  veloci-
ties  as low  as 600 fpm can be determined satis-
factorily,  but field  conditions  ordinarily make
this procedure difficult (ASHRAE Guide and Data_
Book, 1963).

Pitot  Tube  Traversing Procedure

Since the  velocity  in a  duct is  seldom uniform
across any cross section and since each pi tot tube
reading determines the  velocity at only one local-
ized point,  a traverse of the duct is necessary in
order to  compute the average velocity and thus
determine air flow accurately.   Suggested pitot
tube locations for traversing round and rectangu-
lar ducts are shown in Figure 35.

The velocity in a duct varies greatly.  It is gen-
erally lowest near  the  edges or  corners and
greatest in  the  central  portion.   Because of this
fluctuation,  a large number of readings  must be
taken to determine the true average velocity.  In
round ducts,  not  less than eight readings should
be  taken along two diameters at centers  of equal
annular areas.  Additional readings are necessary
when ducts are larger than  1 foot in diameter. In
rectangular ducts, the readings should be  taken in
the center  of equal areas  over the cross section of
the duct.   The number  of  spaces  should be taken
as depicted in Figure 35.   In determining the  av-
erage velocity in the  duct, the velocity  pressure
readings  are converted to  velocities; the veloci-
ties,  not the  velocity pressures,  arc averaged to
compute the average duct velocities.

Disturbed  flow will give  erroneous results; there-
fore,  whenever possible,  the pitot tube traverse
should be made at least 7. 5 duct diameters down-
stream from any major  air stream disturbances
such as a branch  entry,  fitting, or  supply open-
ing (ASHRAE Guide and Data Book,  1963).


Altitude and Temperature  Corrections for
Pitot Tubes
If the temperature of the air stream is more  than
30°  above  or below the  standard temperature of
70 °F, or  if the  altitude is  more than 1, 000 feet,
or if both conditions hold true,  make a correction
for density change as follows:

Corrected velocity pressure = measured  h  x — t
        p'  ~   relative density of air, at the
              sured condition,  Ib/ft .
      Cross section of a circular  stack  divided
      into three concentric, equal areas, showing
      location of traverse points.  The  location
      and number of these points for a stack of
      given diameter can be determined from Tables
      22 and 23.
   Cross  section of a  rec-tangular stack divided into  12
   equal  areas, with traverse points located  at the cen-
   ter of each area.   The minimum number of test points
   is shown i n Table 24.

   Figure  35.  Pitot  tube traverse for  round and
   rectangular ducts.
                                             (32)
where
   h  =  velocity pressure, as determined by
         pitot tube, in. WC
SWINGING-VANE VELOCITY METER

The factors that make the  swinging-vane velocity
meter an extensively used field instrument  are its
portability,  instantaneous  reading  featxires,  and

-------
74
DESIGN OF LOCAL EXHAUST SYSTEMS
       Table 22.  SUGGESTED NUMBER
               OF EQUAL AREAS
       FOR VELOCITY MEASUREMENT
            IN CIRCULAR STACKS
Stack diameter,
ft
1 or less
1 to 2
2 to 4
4 to 6
over 6
Number of
equal areas
2
3
4
5
6 or more
      Table 23.  PERCENT OF CIRCULAR
       STACK DIAMETER FROM INSIDE
         WALL TO TRAVERSE POINT
Point Number of areas selected
number 1 ^ I

i
2
3
4
5
6
7
8
9
10

11
12
6.7
25. 0
4
14
75. 0 29
93. 3 70
-- , 85
--
--
--




--
95
-
-
-
_

-
-
3 1 4
- I 	
. 4
. 7
. 5
3.
10.
19.
. 5 32.
. 3
. 6
-
67.
80.
89.
- 96.
-
_
--
	

-

- "
1 5
-T—
3 2.
5
8.
4:i4.
3 22.
7
34.
6 ! 65.
5 77.
7





85.
91.
97,


--
~P6
— i 	
5 ' 2. 1
2
6. 7
6 11.8
6 17. 7
2 • 25. 0
8 35. 5
4 64. 5
4
8
5



75.0
82. 3
88. 2

93.3
97. 9
         Table 24.  MINIMUM NUMBER
                OF TEST POINTS
          FOR RECTANGULAR DUCTS
Cross



sectional area,
ft2
< 2
2-25
> 25
Number of
test points
4
12
20
wide-range scale.  The instrument is fairly rug-
ged,  and its  accuracy  is suitable for most field
velocity determinations.

The meter consists of  a pivoted vane enclosed in
a case,  against which air exerts a pressure as it
passes through the instrument from an upstream
to a downstream opening; movement of the vane is
                       resisted by a hair  spring  and damping magnet.
                       The instrument gives instantaneous readings  of
                       directional velocities on the indicating scale.

                       Calibrating  the Velocity  Meter

                       Before using a meter, check the zero setting.  If the
                       pointer does not come to rest at the zero position,
                       turn the zero adjuster to make the necessary cor-
                       rections.  The meter with its fittings is calibrated
                       as a unit; therefore, fittings  cannot be interchanged
                       from one meter to another.   The serial number on
                       the fittings  and  on  the meter  must agree.   If a
                       meter  was  originally calibrated  for  a filter, it
                       must always be used.  Only connecting tubing of
                       the same length and  inside diameter as that orig-
                       inally supplied with the meter should be used,
                       since changes in  tubing affect the calibration of
                       the meter (Industrial Ventilation, 1956).

                       When the  temperature  of an air stream  varies
                       more than 30° from the standard temperature of
                       70CF, or the altitude is more than 1, 000 feet,  or
                       when both conditions are fulfilled, it is advisable
                       to  make a correction for temperature and pres-
                       sure.  Other correction factors,  as  shown  in
                       Table 25 should also be used (Industrial Ventila-
                       tion, 1956).
                                                         Table 25.  SOME CORRECTION FACTORS
                                                       FOR THE SWINGING-VANE VELOCITY METER
                                                                (Industrial Ventilation,  I960)
                                  Opening

                       Pressure openinga
                        Hold meter jet against grille
                        (use gross area) more than
                        4 in. wide and up to 600 in.
                        area, free opening 70% or
                        more of gross area.   Hold
                        meter jet against grille (use
                        free-open area)
                        Hold meter jet 1 inch in front
                        of grille (use gross area)
                                                      Suction opening
                                                        Square punched grille (use
                                                        free-open area)
                                                        Bar grille  (use gross area)
                                                        Strip grille (use gross  area)
                                                        Free op^n,  no  grille
                                                                                      Correction factor
0. 93
                                                                                             1. 00
                                                             0. 88
                                                             0. 78
                                                             0. 73
                                                             1. 00
                        For pressure openings,  it is advisable to use the
                        grille manufacturer's coefficient of discharge.
                        For suction openings, hold meter jet  perpendicu-
                        lar to the opening, with the tip in the  same plane
                        as (he opening.  This is  very important because
                        velocities are changing very rapidly in front of a
                        suction opening.

                      Note:  volume,  cfm =  area, ft  x air  velocity,
                                             fpm  x  correction factor.

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                                       Checking of Exhaust System
                                              75
Uses of the  Velocity Meter
Some uses of the mete r and fittings are illustrated
in Figure 36.   On  large (at least 3 ft )  supply
openings , where the instrument itself will not seri-
ously block the opening and where the velocities
are low, hold the instrument itself in the air stream,
the air impinging directly in the left-hand port.
When the  opening is smaller than 3 square feet,
or the  velocities are above the no-jet scale,  or
when both conditions hold true , appropriate fittings
mustbeused.  On modern air -conditioning grilles,
the meter or fitting should be held between 1 and
2 inches in front of the grille.

If the exhaust opening is large  (at least 3 ft^) and
the air velocities  are  low,  as in spray booths,
chemical hoods, andsoforth, the meter itself can
be held in the air stream.  The instrument should
be held so that the left-hand port of the meter  is
flush with the exhaust opening.   When the opening
is  smaller than 3 square feet,  or the velocities
are above the  no-jet scale, or when both conditions
hold true, appropriate fittings  must be used  (In-
dustrial Ventilation, 1956).
                   2220 OR  3920
              BLOWER
                            JET

                 SUPPLY SYSTEM
                   EXHAUST SYSTEM
                                        GRlNDER
                                                                     3930 JET
                                                                 PLATING TANK
      SPRAY BOOTH  (NO-JET  RANGE)
           Figure  36.   Some  swinging-vane velocity meter applications (Industrial  Ventilation
           I960)

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76
DESIGN OF LOCAL EXHAUST SYSTEMS
    COOLING  OF GASEOUS  EFFLUENTS

When designing an air pollution  control system,
the designer must know the temperatures of the
gases to be handled before he can specify the
materials  of construction for the system, the size
of ductwork, the size of the blower, and the type
of air pollution control device.  Often,  hot gases
must be cooled before being admitted to the  con-
trol device.  The cooling equipment will add to
the resistance of the flow of gases through the
exhaust system and may affect the volume and
composition of the gases.  Since the gases must
pass through the cooling device,  it must be de-
signed as an integral part of  the exhaust system.


METHODS OF COOLING GASES

Although there are several methods of cooling hot
gases, those most commonly used in air pollution
control systems are:  (1) Dilution with ambient air,
(2) quenching with water,  and (3) natural convec-
tion and radiation from ductwork.  In a few cases,
forced-draft heat exchangers , air cooled and water
cooled, have been used.

With the dilution method, the hot gaseous effluent
from the process equipment is  cooled by adding
sufficient  ambient air to  result  in a mixture of
gases  at the desired temperature.  Natural con-
vection and  radiation occur  whenever  there is a
temperature difference between the gases  inside a
duct and the atmosphere surrounding it.  Cooling
hot gases by this method requires only the pro-
vision of enough heat transfer area to obtain the
desired amount of cooling.  The water  quench
method uses the heat of vaporization of water to
cool the gases.  Water is sprayed into  the hot gas-
es under conditions conducive to evaporation,  the
heat in the gases evaporates the water, and this
cools the gases.  In forced-draft heat exchangers,
the hot gases are cooled by forcing cooling fluid
past the barrier separating the fluid from the hot
 Dilution With Ambient Air

 The cooling of gases by dilution with ambient air is
 the  most  simple method that  can be employed.
 Essentially  it involves the inixing of ambient air
 with a gas  of known volume and temperature to
 produce a low-temperature mixture that can be
 admitted to an air pollution  control device.  In de -
 signing such a system, first determine the volume
 and temperature of air necessary to capture and
 convey the air contaminants from a given source.
 Then calculate the amount of ambient air required
 to  provide a mixture of the desired temperature.
 The air pollution  control  device is then sized
 to handle the combined mixture.
                     Although little instrumentation is required, a gas
                     temperature  indicator with a  warning device, at
                     the very  least,  should be used  ahead of the air
                     pollution  control device to ensure that no damage
                     occurs owing to sudden,  unexpected surges of
                     temperature.  The instrumentation may be ex-
                     panded to control either the fuel input to the
                     process or the volume of ambient air to the ex-
                     haust  system.
                     This method of cooling hot gases is  used exten-
                     sively where the hot gases are discharged from
                     process equipment in such a way that an external
                     hood must be used to capture the air contaminants.
                     The amount of air needed to ensure  complete cap-
                     ture of the air contaminants is generally sufficient
                     to cool the gases  to approximately 500 °F, which
                     permits the use of high-temperature air pollution
                     control devices.  When the  volume of hot gases is
                     small,  this method may be  used economically even
                     when much more  air is needed to  achieve the de-
                     sired cooling than that needed for adequate capture
                     of air  contaminants.
                      When large volumes of hot gases require cooling,
                      the size of the exhaust system and control device
                      becomes  excessively large for dilution cooling.
                      In any case, compare the costs of installation and
                      operation of the various cooling methods before
                      deciding which method to use.
                     The following examples illustrate (1) a method of
                     determining the resultant temperature  of the mix-
                     ture of the hot furnace gases and the ambient air
                     induced at the furnace hood,  and  (2) a method of
                     determining the volume of air needed to cool the
                     hot furnace gases to a selected temperature.
                      Example 14

                      Given:

                      Yellow-brass-melting crucible furnace.  Fuel
                      burned:  1,750 cfh  natural gas with 20 percent
                      excess air.

                      Maximum gas temperature at furnace outlet:
                      2, 500°F.

                      Volume of dilution air drawn in at the furnace
                      hood:  4, 000  cfm.
                      Maximum temperature of dilution air:  100°F.

                      For this  problem, neglect the  heat losses due
                      to radiation and natural convection from the
                      hood and ductwork.  Assume complete combus-
                      tion of the fuel.

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                                      Cooling of Gaseous Effluents
                                             77
                               TO CONTROL CEVICE





PRODUCTS OF
COMBUST 1 ON
ATFMP - i
2,500 F
l| 1
\
CRUC 1 BLE
FURNACE

| HOOD

^y DILUTI ON Al R
4,000 cfm
FUEL
1,750 cfh
  Figure 37.  Problem: Determine the tempera-
  ture  of  the gases entering the control device.
Solution:

1.  Determine the weight (W) and heat (Q) above
   60 °F in the products of combustion (PC):
                  Q  =  2.-Q.
                           i
                  Q.  =  W. h
                   i       11
 vhere
   W.  =  weight of individual gas flowing, Ib/min

   h.  =  enthalpy above  60°F of each gas, Btu/lb
   Q.  =  heat above  60°F in each gas, Btu/min
                          i  "7 c r\
                                     29. 17 cfm
                                                       Convert fuel rate to cfm  —'-	
                                                                                   60
   Referring to the calculation data of Table
   26, Wi  =  29. 14 Ib/min and Qi = 21,470
   Btu/min
2.  Heat above 60°F in 4, 000 cfm of dilution air
   entering hood at 100°F:

   Density of air at 100°F = 0.0708 Ib/ft  (from
   Table Dl, Appendix D)

   Enthalpy of air  at  100°F =9.6  Btu/lb (from
   Table D3, Appendix D)

   Weight of dilution air = (4, 000)(0. 0703) =
   283. 2 Ib/min
   Heat above 60°F in dilution air  =  (9. 6)(283. 2)
   =  2, 720 Btu/min

3.  Enthalpy of mixture of PC and dilution air:

   Total  weight of  mixture = 29. 14 + 233. 2
   = 312.3 Ib/min
   Heat above 60 °F in mixture 21, 470 +  2, 720
   = 24,190
                          24 190
   Enthalpy of mixture =       -  = 77.4 Btu/lb
4. Temperature of mixture:

   To determine the  temperature of the mixture,
   determine the enthalpy of the mixture at two
   temperatures, preferably above and below the
   calculated enthalpy of 77. 4 Btu/lb.
                                   Table 26.   CONVERSION VALUES
                                     FOR  ITEM 1,  EXAMPLE 14
PC per cubic foot
of fuel
Component
C°2
H2°
N2
°2
Totals
Weight,
Ib/ft3
0. 132a
0. 099
0. 731
0. 037
PC from
furnace
Ib/min
3.85b
2.89
21.32
1.08
29. 14
Enthalpy
of
component
hi at 2, 500°F,
Btu/lb
690.2°
1, 318. 1
672.3
621.0
Heat above
60 °F in
component
Qi,
Btu/min
2,660d
3,810
14, 330
670
21, 470
                          From Table D7,  Appendix D.
                        bW. =  (0. 132 Ib/ft3)(29. 17 ft3/min) = 3.85 Ib/min
                        cFrom Table D3,  Appendix D.
                        dQ.  =  (3.85 Ib/min)(690. 2 Btu/lb)  =  2,660 Btu/min

-------
78
                                DESIGN OF  LOCAL EXHAUST SYSTEMS
   Then,  by interpolation, the temperature cor-
   responding to 77. 4 Btu/lb can be determined.
   Since the mixture contains mostly nitrogen,
   the enthalpies  should be close to those of ni-
   trogen.  From Table D3 it appears that the
   mixture temperature will be between 350°F
   and 400 °F.  The enthalpy of the mixture, H   ,
                Q
 ^here
   W
   Q
                W
      r. W.
          i
      >; w. h.
          i  i
                       at desired temperatures
 The C>2 and NT from the dilution air must be added
 to the O2 and N2 from the PC.

 Weight of dilution air = 283. 2 Ib/min

 O2 content = (283. 2)(0. 23)  =   65. 0 Ib/mm
 N2 content = (283. 2)(0. 77)  =  218 Ib/min

 Referring to the calculation  data of Table 27:

     at 350°F =  22'53° =  72. 1 Btu/lb
at 400°F =
                        =  83. 6 Btu/lb.
By interpolation the mixture temperature = 373 °F

Therefore, the exhaust system and control device
must be designed to handle gases at 373 °F.
Example 15

Problem:

Using the same given data in Problem No. ^de-
termine the amount of dilution air required to re-
duce the temperature of PC to 300 °F.

Solution:

1. Heat above  60 °F in PC at 2, 500 °F = 21, 470
   Btu/min (From Table 26)


2. Heat lost by PC in cooling from 2, 500°F to
   300°F:  From Table 26 obtain the  weight (W-)
   of each  component of PC discharged from  the
   furnace. From Table D3, obtain the enthalpy
   (h^ of each  component at 300°F.   Referring
   to the calculation data of Table 28: Heat to
   be lost = 21,470  - 1,847 = 19,623  Btu/min


3. Volume of air needed to cool PC to 300°F:

   Air inlet temperature = 100°F (given)
   Final air temperature = 300 °F

   h at 100°F  = 9.  6 Btu/lb (from Table D3)

   h.at 300°F  = 57.8 Btu/lb (from Table D3)

        Ah = 48. 2 Btu/lb
                                                    Weight of air needed =   '      = 408 Ib/min
                                  Table 27.  CONVERSION VALUES
                                     FOR ITEM 4, EXAMPLE  14
Component
C°2
N2
°2
Totals
Ib/min
3.85
2.89
245. 02a
60.58C
312. 3b
at 350°F,
Btu/lb
63. 1
131.3
73.3
64.8
at 4000F,
Btu/lb
74. 9
154. 3
84. 9
76.2
Qi - hiWi
at 350°F,
Btu/min
242. 9e
379. 2
17, 980. 0
3, 925. 0
22, 530
Qi = hiWi
at 400°F,
Btu/min
288.4
455.6
20, 800.0
4, 615.0
26, 150
                       Wi of N£ is sum of N£ from PC and dilution air.
                       Totals are rounded off to four significant figures.
                      CW- of Q£ is sum of ©2 from PC and dilution air.
                      dFrom Table D3, Appendix D.
                      eQ.  =  (3.85 Ib/min) (63. 1 Btu/lb)  =  242.9 Btu/min,

-------
                                     Cooling of Gaseous Effluents
                                                                          79
        Table 28.   CONVERSION VALUES
Gaseous
components
C02
HzO
N2
02
Totals
wif
Ib/min
3. 85
2.89
21. 32
1.08
29. 14
hi at 300° F,
Btu/lb
51. 3
108. 2
59. 8
53.4
Qi = hiWi, at
300° F Btu/min
197.7
312.5
1,279. 0
57.5
1, 846. 7
Total heat above 60°F in PC at 300° F = 1, 847 Btu/
min
   Volume of dilution air at 100°F

   p at 100°F  =  0. 0708 lb/ft3 (From Table Dl)
                   408
       Volume =
                 0.0708
= 5, 760 cfm
The exhaust system must be designed to handle
a sufficient volume of gases at 300°F to pro-
vide an indraft of dilution air of 5,760 cfm in ad-
dition to the products of combustion.

Quenching  With  Water

When a large volume of hot gas is to be cooled and
only a small quantity of dilution air is needed to
capture the air  contaminants, some methods of
cooling other than dilution with ambient air  should
be used.  Since the evaporation of water requires
a large amount  of heat, the gas can be cooled sim-
ply by spraying water into the hot gas.

For efficient evaporation  of water in a gas stream,
it has been determined that the gas velocity should
be from 500 to 700 fpm and the entire cross sec-
tion of the stream should  be covered with  a  fine
spray of water.  If, however, water  carryover is
undesirable,  as in a baghouse, satisfactory set-
tling of the water droplets must be attained; hence,
lower velocities are  employed.  Eliminator plates
are seldom used in installations where excessive
maintenance due to corrosion or fouling is expected.
To  reduce further the likelihood of water droplet
carryover, place the water spray chamber as far
from the baghouse as practical.

Water spray pressures generally range from 50
to 150 psig; however, to reduce the amount  of
moisture collected, some installations have em-
ployed pressures as high  as 400 psig.  Since the
moisture collected in spray chambers readily cor-
rodes steel, the chambers are frequently lined with
materials resistant to corrosion.
If the gases discharged from the basic equipment
.ire exceptionally hot, as  are those from the cupo-
la furnace,  the first portion of the duct should be
                            refractory lined or made from stainless steel.  In
                            some cases,  stainless steel ducts with water sprays
                            have been used between the furnace and the quench
                            chamber.

                            For controlling the gas  temperature leaving the
                            quench chamber, a temperature controller is
                            generally used to regulate  the amount of water
                            sprayed into the quench chamber.   For emergen-
                            cy conditions, a second temperature controller
                            can be used to divert excessively hot gases away
                            from the air pollution control device.

                            Cooling  hot gases with a water quench is  relative-
                            ly simple and requires very little  space.   Figure
                            38 shows a quench chamber used to cool the gas-
                                Figure  38.  A quench chamber in  a  baghouse
                                control system serving a cupola  furnace
                                (Harsell Engineer ing Company,  Inglewood,
                                Cal i fornia).

-------
80
                                 DESIGN OF LOCAL EXHAUST SYSTEMS
ecus effluent from a cupola furnace.   Quench cham-
bers are little more than enlarged portions of the
ductwork equipped with water sprays.  They are
easy to operate and, with automatic temperature
controls, only that amount of water is used that
is needed to maintain the desired temperature of
the gases at the discharge.   Their installation and
operating costs are generally considered to be less
than for other  cooling methods.  Quench chambers
should not be used when the gases to  be cooled  Con-
tain a large amount of gases or fumes that become
highly corrosive when wet.   This creates  addition-
al maintenance problems, not only in the quench
chamber, but in the remainder  of the ductwork,
the control  device,  and the blower.

The following example \vill illustrate some of the
factors that must be considered when designing a
quench  chamber to cool the  gaseous effluent from
a gray-iron-melting cupola.

Example 16

Given:

32-in.-I. D.  cupola.  Maximum  temperature of
gaseous effluent at cupola outlet - 2,  000 °F.
Weight  of gaseous effluent at cupola outlet ^
216 Ib/min.
Volume of gaseous effluent at cupola  outlet -
13,280  cfm at  2,000°F.  This volume of effluent
includes indraft air at the charging door of the cu-
pola.   The temperature of 2, 000 °F is a maximum
temperature.

Assume the  effluent gases have the same proper-
ties as  air.  Consideration  of the enthalpies of the
gaseous constituents in the  effluent gas stream will
show that this  is  a valid assumption.   Any correc-
tions  would introduce an insignificant refinement
to the calculations when considered with respect to
the accuracy of other design factors.

      TEMP - 2,000 f
      VOL  - 13, 280 cfm


             EVAPORATIVE
         COOL ING V ATER =
AATFF ^PPAY
COS'C I TIOMNC CHAMBFR
                               TO CONTROL
                               TE",'P = ??5
 CUPOLA
 FURNACE
    Figure  39.   Problem: Determine the water
    needed  to  cool the gaseous effluent to  225°F
    and  the  total volume of gases discharged
    from the  quench chamber.
                        Solution:

                        1. Cooling required:

                           Enthalpy of gas at 2, 000°F = 509. 5 Btu/lb
                           Enthalpy of gas at    225 °F =  39. 6 Btu/lb
                                                  Ah = 469. 9 Btu/lb

                                          (216)(469.  9) = 101, 300 Btu/min


                        2. Water to be evaporated:

                           Heat absorbed per Ib of water:

                           Q  =  h  (225°F, 14. 7 psig) - hf (60°F)


                              =-  1, 156. 3  -  28. 06 =  1, 123. 7 Btu/lb

                                             101, 300     „„ ,,  ,  .
                           Water required = -—-  -     =  90 Ib/min


                        3. Volume of water evaporated at 225°F:
                            79  /460 + 225\
                            13   V 460 + 60 I
                                              (90)  =  2,510  cfm
                        4. Total volume vented from spray chamber at
                           225°F:
   Cupola =  (13,280)
/   225  +  460\
\Z, 000  +  460/
                                                              =  3,700 cfm
   Water  =  2,510 cfm

   Total  =  6, 210 cfm

Problem Note'  In this example,  the calculated
amount of water required to cool the  gases, 90
Ib/min or 10. 3  gal/min, is only the water that
must be evaporated.   Since all the water sprayed
into  a  quench chamber does not evaporate,  the
pump and spray system should be sized to supply
more water than that  calculated.   The amount of
excess water needed will  depend  on factors such
as the  inlet temperature of the gases, the tem-
perature drop required,  the fineness of the water
spray,  and the arrangement of spray heads.  It
is not  uncommon to size the pump to give 200 per-
cent of the water needed for evaporation.  The ac-
tual  amount of -water used should be controlled by
the temperature of the gases discharged from the
quench chamber.

The  loss of heat by radiation and convection from
the ducts was neglected.  With long duct runs, how-
ever,  a considerable  temperature drop in the gas-

-------
                                      Cooling of Gaseous Effluents
                                                                                          81
eous effluent could occur,  especially if the quench
chamber was installed near the downstream end of
the ductwork.  If the quench chamber  is placed near
the control device,  adequate  water entrainment sep-
arators must be employed.


Natural Convection  and Radiation
                                             of the gas.  This term,  too, is fixed for a partic-
                                             ular process.  It is calculated as follows:
                                                      At
                                                               (t -t )  - (t  -t  )
                                                                la    2  a
                                                                log
                        (t.-t )
                          1   a
                       e (t -t )
                          2   a
                                              (35)
When a hot gas flows through a duct, the duct be-
comes hot and heats the surrounding air.  As the
air becomes heated, natural drafts are formed
carrying the heat away from the duct.  This phe-
nomenon is called natural convection.  Heat is also
discharged from the hot duct to its surrounding s by
radiant energy.

The rate of heat transfer is a function of the  resis-
tances to heat flow, the mean temperature differ-
ence between the hot gas and the air  surrounding
the duct, and the surface area  of the duct.  It may
be expressed as:
               Q
                     UA
                                   (33)
where

   Q
   U
  At
rate of heat transfer, Btu/hr

overall heat transfer coefficient, Btu/
hr-°F-ft2

heat transfer  area,  ft

log-mean temperature difference,  °F.
The rate of heat transfer is determined by the
amount of heat to be removed from the hot gas-
eous effluent entering the exhaust system.  For
any particular basic process, the weight of gas-
eous effluent and its maximum temperature are
fixed.   The cooling system must,  therefore,  be
designed to dissipate sufficient heat to lower  the
effluent temperature to the operating temperature
of the air pollution control device to be used.
where

   t   =  gas temperature of inlet, °F

   t   =  gas temperature at outlet, °F
   t   -  air temperature,  °F.


In many processes the temperature of the gaseous
effluent is not constant but varies during different
operational phases.  The atmospheric tempera-
tures also vary a great deal.  In such cases, the
cooling system  must be designed for the worst con-
ditions that prevail to ensure  adequate cooling at
all  times.   The inlet temperature (t, ) chosen must
be the maximum temperature of the gas entering
the system; t^ must be the maximum allowable
temperature of  the gas discharged from the cool-
ing system; and ta must be the maximum expected
atmospheric temperature.

The overall coefficient of heat transfer, U,  is the
reciprocal of the  overall resistance to heat flow.
It is a function of the individual  heat transfer coef-
ficients,  which  can be estimated by empirical equa-
tions.  U  must be based on either the inside or out-
side surface of  the duct.   For radiation-convection
cooling, it is generally based on the outside surface
and is denoted by Uo.   Uo is  defined by the following
equation (Kern,  1950):
                                                         U
                   h.  h
                     10  o
                   h.  +h
                     10   o
(36)
                                             where
The rate of heat transfer can be determined by the
enthalpy difference  of the gas  at the inlet and out-
let  of the cooling system.
                                               h.   =  inside film coefficient based on the out-
                                                       side surface area,  Btu/hr-°F-ft

                                               fi    =  outside film  coefficient, Btu/hr-°F-ft  .
where
            Q  =  WAh
                                  (34)
                                                       The inside film coefficient can be solved by the
                                                       formula  (Kern,  1950):
   W  =  weight of gas flowing,  Ib/hr

  Ah   =  enthalpy change between inlet and out-
          let,  Btu/lb.
The log-mean temperature difference is the dif-
ference in temperature between the air surround-
ing the duct, and the inlet and outlet temperature
                                                       •where
                                               JH
          hi   =  ^HD Vk,
                                                                                          (37)
          h.D
                                                                 -l/3
                                                                       and is plotted against

-------
                                DESIGN OF LOCAL EXHAUST SYSTEMS
        Reynolds number (Re) as shown in Fig-
        ure 40

k    =   thermal conductivity,  Btu/hr-ft-°F

D    =   inside diameter of duct, ft
C    =   heat capacity, Btu/lb-°F

(i    =   viscosity, Ib/hr-ft.

oc
00
CO
00
00






10
5
3
2

" at = FLOW
C = SPE
0 = INS
0 = MAS
h - INS
k - THE
L = LENC








— - 4i
\-ia^s
-~^£

"^^®-
•^Sif
•^*g£.




iREA THROUGH
FIC HEAT Btu
DE Dl iMETER 0
VELOC TY W/a
DE FILM COEFF
WAL CONDUCTI ¥
TH OF PATH (t
HT FLO* OF FLU






/
' //
//
if I
/ 1
1
J








W
t














TUBES f
/] b-°F
TU3ES
t "''"
CIENT
TY Btj
D 1 b 'h









4
j*
f








'


















.2
ft
-ft!
t, hr-ft2-°F
hr-ft-°F


>
S
s
t1

















_jT
^




















/






















/






















/






















/





















(




















jf
/
S

















     1,000  2,000   4,000   10,000  20,000   50,000 100,000 200,000

                    REYNOLDS NUMBER (Re),
                                   fl£
                                   M-
   Figure  40.   Tube-side heat-transfer curve
   (Adapted  from  Sieder and  Tate  in Kern, 1950)
The Reynolds number is a function of the duct di-
ameter,  the mass velocity,  and viscosity of the
gas.  It is calculated by the equation
                                                        seen that an increase in Re will increase the rate
                                                        of heat transfer.   Since the weight of gas flowing
                                                        is fixed,  Re can be increased only by increasing
                                                        the velocity of the gas.  It has already been shown
                                                        that an increase in velocity will increase the power
                                                        required to move the gases through the exhaust
                                                        system.  Consequently, the optimum velocity for
                                                        good heat transfer  at reasonable blower -operating
                                                        costs must be determined.   It is known that a sac-
                                                        rifice in heat transfer rate to obtain lower blower
                                                        horsepower results in the most  economical  cooling
                                                        system.  Owing to  the many variables involved, how
                                                        ever,  each system must be calculated on its own
                                                        merits.

                                                        The  outside film coefficient (ho) is the sum of the
                                                        coefficient  due  to natural convection (hc)  and the
                                                        coefficient  due  to radiation (hr).  An empirical
                                                        equation for hc for vertical pipes more than 1 foot
                                                        high and for horizontal pipes is  (McAdams,  1942):
                                                                      0. 27
                                                                           At
                                                                          D
                                                                                  0. 25
                                           (39)
                                                        wh ere
                                                           At
                                                               the temperature difference between the
                                                               outside duct wall and the  air, I   - t  ,
                                                                                              W   a
                                                               0 F
                                                          D   =  outside duct diameter, ft.
                                                            o
                                                        The radiation coefficient is  computed from
                                                        (McAdams,  1942):
                                                                VT2

                                                            = 0.173-* KTl/100)4 ^(Tz/lOoA    (4Q)
                                                     wh ere
where
               Re  =
                                           (33)
                            W           2
   G   =  mass velocity =  -  Ib/hr-ft  and
    p                       a
   a   =  flow area inside the duct =
    P

The  inside film coefficient is a measure of the flow
of heat through the inside film.   An increase in h^
will,  therefore,  increase the rate of heat trans-
ferred from the gas to the atmosphere.  It can be
e   =  emissivity of the duct surface, dimen-
       sionless

 cr   =  Stefan-Boltzmann constant,  0. 173 x


T   =  absolute temperature  of the duct sur-
       face,  °R
T   =  absolute temperature  of the air,  °R.
                                                     In Figure 41,  Tj is plotted against hr for several
                                                     air  temperatures; hr was calculated for an emis-
                                                     sivity equal to 1.0.   To obtain hr for a system,
                                                     multiply the hr found from Figure 41 by the emis-
                                                     sivity of the duct surface.  Since  the emissivity of

-------
                                      Cooling of Gaseous Effluents
                                              83
the surface is  a function of the surface condition,
and a black sur-face generally gives the highest
emissivity, the ductwork should be blackened.
   12
   10
             o m , [T|;ioo)"-(T2;ioo|»]
                  T, - T2
                  DUCT SURFACE TEMPERATURE. °f
      Figure 41.  Coefficient of  heat  transfer
      by  radiation for t = 1.0 (Adapted from
      McAdams,  1942).
 When calculating hQ,  assume the temperature of
 the duct wall (tw) and then check.   The assumed
 tw can then be checked with the following  equa-
 tion (Kern, 1950):
                                 (t  -t )       (41)
         w     m     h  + h.    v"m "a
where
   t    =  the average gas temperature,  °F.
 If t   is not the  same as assumed
 new tw and recalculate ho
 and calculated
                   estimate a
          When the assumed t...
                             W
are the same,  use the corre-
 spending h  to calculate Uo.

 The heat transfer area (A) can now be calculated.
 The length of duct needed to give the necessary
 area is then calculated by using the outside di-
 ameter used in determining the film coefficients.
 If the length of duct needed  is large, the ductwork
 will probably be arranged in vertical columns to
 conserve floor space.   Figure 42 shows  such an
 installation serving a lead blast furnace  and a lead
 reverberatory furnace .  The  columns require sev-
 eral 180° bends,  which will offer a large resis-
 tance to the flow  of gas.  To minimize these loss-
 es.  the gas velocity should be low, preferably
less than normal dust-conveying velocities.  By
joining the bottoms of the columns with hoppers,
any dust settling out as a result of low velocities
can be  collected without fouling the exhaust sys-
tem.  If the cooling area is such that a single loop
around the plant or across a roof is sufficient, avoid
sharp bends  and maintain carrying velocities.  When
gases are cooled through a large temperature range,
the volume will be reduced,  so that smaller di-
ameter ductwork may be needed as the gases pro-
ceed  through the cooling system.   With cooling
columns, the diameter  of the duct joining the last
column and the air pollution  control device must
be  sized properly to provide suitable conveying ve-
locities for the cooled  effluent.

For most convection-radiation cooling systems,
the only equipment used is sufficient ductwork to
provide the required heat transfer area and, of
course, a blower of sufficient capacity to move the
gaseous effluent through the  system.  Unless the
temperature of the gases discharged from the ba-
sic process is exceptionally  high,  or there are
corrosive gases or fumes  present,  black iron duct-
work is generally  satisfactory. The temperature
of the duct wall can be determined for any portion
of the ductwork by using the  method previously
described for determining tw. If tw proves to  be
greater than black iron can withstand,  either use
a more heat resistant material for that portion of
the system or  recirculate  a portion of the cooled
gas to lower the gas temperature  at the inlet to
the cooling system.
With this type of cooling,  flexibility in control-
ling the gas temperature is limited.  When either
the gas stream or air temperatures,  or both,  are
lower  than design values, the gases discharged
f j. om the  cooling device will be less than that cal-
culated,  and condensation of moisture from the
effluent within the control device might result.
Conversely,  when design temperatures are ex-
ceeded,  the temperature of the gases  discharged
from the  cooling system could become too high.
To  avoid  damage to the  air pollution control de-
vice,  install a quick-response temperature con-
troller to warn the operator of the  change in tem-
perature  so that proper adjustments can be made.

The radiation-convection cooling system is in
operation whenever hot  gases are being conduc-
ted through the exhaust  system.  The  gases  being
cooled are not diluted with any cooling fluid.  The
exhaust system blower and the air  pollution con-
trol device need not be sized for  an extra volume
of gases  due  to dilution.  Since no water is used,
there is no need for pumps, and corrosion prob-
lems are nonexistent.  On the other hand, these
cooling systems require considerable  space, and
blower horsepower requirements are high owing
to the additional resistance to gas flow.
234-767 O - 77 - I

-------
 84
                                  DESIGN OF LOCAL EXHAUST SYSTEMS
 Figure  42.   Radiation-convection cooling columns  in an air pollution system serving a lead blast furnace
 and  a  lead  reverberatory  furnace (Western Lead Products Company, City of Industry,  California).
The following example illustrates a method of de-
termining the heat transfer area needed to cool
the gaseous  effluent from the cupola of example 16
with a natural convection-radiation cooler.

Example 17

Given:
capacity of the gaseous constituents in the effluent
gas stream will  show that this is a valid assump-
tion.  Any correction would introduce an insignifi-
cant refinement  to the calculations when considered
with respect to the accuracy of other design factors.
32-in.-I. D.  cupola.

Gaseous effluent  = 12, 960 Ib/hr.

Maximum temperature of effluent = 2, 000"F,

Volume of effluent at  ?, 000°F  =  13, 280  cfm. This
volume of effluent includes  indraft air at the charg-
ing door of the  cupola.  The temperature of 2, 000
°F is a maximum.

The vertical cooling columns must  be located a
minimum of 60  feet from the cupola.

Assume the effluent gases have the same physical
properties as air.  Consideration of the enthalpy,
viscosity,  thermal conductivity,  density, andheat
                                                              TEMP  • 2,000C F
   r
A  A  A
                                    TO CONTROL DEV ICE
                                   TEK'P " 225 F
                      V  V  V
                     COOLING  COLUMNS
     Figure 43.  Problem: Determine the length
     of duct needed to cool the gases to 225°F
     by natural convection-radiation columns.

-------
                                     Cooling  of Gaseous Effluents
                                                                                                   85
Solution:



1. Heat (Q) to be transferred:



   Enthalpy of gas  (2, 000°F) = 509. 5 Btu/lb

   (from Table D3, Appendix D)


   Enthalpy of gas  (225°F)  =  39. 6


                       AH  =  469. 9


   Q = (469.9)(12,960)  = 6, 078, 000 Btu/hr
                                                           j    = (See Figure 40) = 215
                                                            H
                                                        (b) Obtain k,  C,  and -7^-  from Ta ie Dl
                                                                             K



                                                                    k  =  0.0297



                                                                    C  =  0.247




                                                                   C|JL  =  0.775

                                                                    k
2.  Determine logarithmic mean temperature dif-

   ference (At  ):
              m


   Gas inlet temperature (t )       = 2,000°F


   Gas outlet  temperature  (t?)      = 225°F


   Cooling air temperature (t  )     = 100°F
                            a
    At
                   - (vv
             log
                  (t -t )
                   1  a

                e  (t -t )
                   2  a
                                                         (c)  Substitute above data in formula, and
                                                             solve for h.:
                                                                        i
                                                                         X 775)1/3 =  2. 66 Btu/hr-ft2-°F
                                                     4. Convert h| to inside film coefficient

                                                        on outside surface area:
                                                                                                 based
 Use a  10-gage duct wall,  thickness = 0. 141

 inch
            (2,000-100) - (225-100)
                   log
                       1, 900

                     e   125
                                                        D  =(2.2)
                                                          o
                                                                          ?
                                                                          12
                                                                                 =2.224 ft
                                                        h.   = (2.66) ~~~   =  2.62 Btu/hr-ft2-°F
                                                         10          2.224
3. Determine inside film coefficient (h ):
                                      i
                            ,1/3
   (a)  Obtain j   from Figure 40:



                      DG

                Re  = 	£•




   Using a design velocity of 3, 500 fpm in the

   horizontal section at the cupola discharge:
           13,230 cfm            2
   Area =         	   =  3.79ft
           3,500 fpm
   Pipe diameter (D) = f (3'7J)(4)-j     =2.2
                                           ft
                         =  3,4201b/hr-ft
                                                     5.  Determine the outside film coefficient (h  ):
                                                                                               o


                                                                  h  = h   + h
                                                                   o    c     r
                                                        (a)  h  =  0.,
                                                                             0.25
                                                            Assume a duct wall temperature of 525 °F
                                                           h  = 0. 27
                                                            c
                                                                              0. 25
                                                                                  = 1. 00 Btu/hr-ft -°F
             3.79 ft
(b)  Obtain h  from Figure 41:



    h  =3.42 (Emissivity = 1.0)



    Use an emissivity of 0. 736 for rusted black

    iron duct



    h  =(3.42)(0.736) =  2. 52 Btu/hr-ft2-°F
    |j.    =  0.094 Ib/hr-ft (Table Dl, Appendix D)
                                                       (c)  h   =  h  + h
                                                            o     c    r
                                                               =  1.00 + 2.52   =  3. 52 Btu/hr-ft  -°F

-------
86
                                DESIGN OF LOCAL EXHAUST SYSTEMS
   (d)  Since t  was  assumed,  it must be checked
           i  w
       as shown:
       t   =t   - I     '     I (t   -  t ,
       w   m    I hQ + hio  /   m    a
                    "5
            100
t  =  1, 112  -
 w            \ 3
                         =      2.
                         = 100°F
                         3.5Z     \
                       .52 + 2. 62 /
             x (1, 112 - 100) =  530° F
       The assumed t,,. was 525°F, which che.cks
                     W
       closely with 530°F
6.  Determine the overall heat transfer coefficient
   (UQ) based on the outside  surface area:
      10  o

7. Determine heat transfer area (A):
A =
        Q
    U , A t
      od    m
            6,073,000
           (1.50)(653)-
8. Determine length of duct (L) required:
         L =
      _6, 210
      (2.224)(7r)
                        =  386 ft
The duct from the cupola to the vertical column
is  60 feet long.  The length of duct in the col-
umn section will,  therefore, be 886 - 60 = 826
feet.
Forced-Draft  Cooling

Heat transfer by convection is due to fluid motion.
Cold fluid adjacent to a hot surface receives heat,
which is imparted to the bulk of the fluid by mixing.
With natural convection, the heated fluid adjacent
to the hot surface rises and is replaced by colder
fluid.  By agitating the fluid,  mixing occurs at a
much higher rate than with natural currents, and
heat is taken away from the hot surface at a much
higher rate.  In most process applications,  the agi-
tation is induced by circulating the fluid at a rapid
rate past the hot surface.   This method of heat trans
fer is called forced convection.  Since forced con-
vection transfers heat much faster than natural con-
vection,  most process applications use forced-con-
vection heat exchangers.   Whenever possible,  heat
is exchanged between hot and cold streams to re-
duce the heat input to the process.  There are, how-
ever, many industrial applications -where it is  not
feasible  to exchange heat,  and so a cooling fluid sue?
as water or air is used,  and the heat removed from
the stream is dissipated to the atmosphere.  When
water is used,  the heat is  taken from the process
stream in a shell and tube cooler, and the heat
picked up by the  water is dissipated to the atmo-
sphere in a cooling tower.  When air is used as the
cooling medium in either shell and tube or fin tube
coolers, the heated air is  discharged to the atmo-
sphere and is not recirculated through the cooler.

With forced-convection cooling, the temperature
of the cooled stream can be controlled within nar-
row limits even with widely varying atmospheric
or -water temperatures.  Heat transfer area is
greatly reduced from that  needed with natural con-
vection.  Power  requirements to  force the process
stream through the cooler are generally less.  On
the other hand,  either a pump or  a blower is needed
to circulate the cooling fluid through the cooler.
With water cooling,  a  cooling tower may be needed
and additional maintenance is required to clean
scale from the tubes.
                                              FACTORS  DETERMINING SELECTION OF COOLING DEVICE
If columns are 50 feet high, then 826/50, or
16. 5 columns will be required.  Since the con-
necting ductwork between columns will con-
sist of at least 2 feet of duct between each col-
umn,  a total of 16 columns 50 feet high will be
required.

Problem Note: The example illustrates one meth-
od of determining the length of duct needed to cool
a given hot gaseous effluent.  To determine the op-
timum duct diameter, it is necessary to make simi-
lar calculations for other duct diameters, and then
determine the pressure drop through each system.
By comparing the construction costs with the oper-
ating costs, the optimum duct diameter can be found.
                                              Cooling by dilution air is commonly used where
                                              conveying air volumes are low or -where there is
                                              a large volume of dilution inherent  in the hoods
                                              required to capture the air contaminants.  If large
                                              gas volumes are necessary, and dilution air is not
                                              economical, then direct cooling with -water quench
                                              chambers is generally favored over other cooling
                                              devices.  This is probably due to the  small space
                                              requirements, ease of operation, and low instal-
                                              lation costs of the water  quench chambers.  When
                                              the characteristics  of the gaseous effluent and the
                                              contaminants are such that water cannot be used,
                                              natural convection-radiation cooling is  generally
                                              employed.   The ease of operation and low main-
                                              tenance costs make these cooling systems mor.e

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                                       Cooling of Gaseous Effluents	87
attractive than forced-convection coolers.  In fact,     it has been used where the heat of the cooling air
forced-convection equipment has  seldom been used     can be utilized,  for example as combustion air
in air pollution control installations. In some cases    in the basic process being controlled.

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                                           CHAPTER 4

          AIR  POLLUTION  CONTROL  EQUIPMENT FOR  PARTICULATE  MATTER



                                      INERTIAL SEPARATORS

                       HOWARD DEY, Intermediate Air Pollution Engineer
                           JOHN MALONEY, Air Pollution Engineer*
                          JOSEPH D'IMPERIO, Air Pollution Engineer!



                                     WET COLLECTION  DEVICES

                   EDWIN J.  VINCENT, Intermediate Air Pollution Engineer**



                                           BAGHOUSES

                        HERBERT SIMON, Senior Air Pollution Engineer



                              SINGLE-STAGE ELECTRICAL  PRECIPITATORS

                        HERBERT SIMON, Senior Air Pollution Engineer



                               TWO-STAGE ELECTRICAL  PRECIPITATORS

                    ROBERT  C. ADRIAN,  Intermediate Air Pollution Engineer f



                              OTHER  PARTICULATE-COLLECTING DEVICES

                   EDWIN J. VINCENT, Intermediate Air  Pollution Engineer**
 *Now with the Air Pollution Control District of Monterey County, California.
 TNow deceased.
 T Now with State of California, Air Resources Board, Sacramento, California.
';*Now with Environmental Protection Agency, Research Triangle Park, North Carolina.

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                                               CHAPTER 4
         AIR  POLLUTION  CONTROL  EQUIPMENT  FOR  PARTICULATE  MATTER
Air pollution control equipment may be classified
into two groups:  (1) Equipment controlling partic-
ulate  matter,  and  (2) equipment controlling  gas-
eous emissions.  From an air pollution viewpoint,
particulate matter  is any material that exists as
a solid  or liquid at standard conditions.  Some ex-
amples  of particulates  are smoke, dusts, fumes,
mists,  and sprays.
Devices for control of particulate matter are avail-
able in a wide variety of designs using various prin-
ciples of operation and having a wide latitude in col-
lection efficiency,  initial cost, operating and main-
tenance costs,  space, arrangement, and materials
of construction.  In selecting the optimum device
for a specific job,  it is necessary to consider many
factors.  Rose et al., (1958)  consider the following
factors  significant:

1.  Particulate characteristics, such as particle
   size range, particle shape,  particle density,
   and physico-chemical properties  such as  ag-
   glomeration tendencies, corrosiveness, hygro-
   scopic tendencies,  stickiness,  inflammability,
   toxicity,  electrical conductivity,  and so forth.

2.  Carrier gas characteristics, such as temper-
   ature, pressure, humidity,  density, viscosity,
   dew points of condensable components,  elec-
   trical conductivity, cor rosiveness, inflamma-
   bility, toxicity,  and so  forth.
3. Process factors, such as volumetric gas rate,
   particulate concentration,  variability of ma-
   terial flow rates, collection efficiency require-
   ments,  allowable pressure drop,  product qual-
   ity requirements,  and so forth.


4. Operational factors, including structural lim-
   itations such as head room,  floor space, and
   so forth, and equipment material limitations
   such as pressure, temperature, corrosion ser-
   vice  requirements, and  so forth.
In this chapter, devices for control of particulate
matter have been grouped into six classes:  (1)
Inertial separators,  (2) wet collection devices,
(3) baghouses,  (4) single-stage electrical precip-
itators,  (5) two-stage  electrical precipitators,
and (6) other particulate-collecting devices.
           INERTIAL  SEPARATORS

Inertial separators arc the most widely used de-
vices lor collecting medium- and coarse-sized
particulates.  The construction of inertial sep-
arators is  usually relatively simple,  and initial
costs and maintenance  costs are generally lower
than lor most other types  of dust collectors. Col-
lection efficiencies, however, are usually not high.
Although suitable for medium-sized particulates
(15 to 40 |J.),  ordinary inertial separators are gen-
erally unsuitable for  fine dusts or metallurgical
fumes.  Dusts with a particle  size ranging from
5 to 10 microns are normally  too fine to be collec-
ted efficiently.  In some cases,  however, small-
diameter,  high-efficiency cyclones can be effec-
tive in collecting particles in the 5-micron  range.

Incrtial separators operate by the principle of  im-
parting  centrifugal force to the particle to be re-
moved from the carrier gas stream.  This  force
is produced by directing the gas in a  circular path
or effecting an abrupt change in direction.
SINGLE-CYCLONE SEPARATORS

A cyclone,  which is an inertial separator without
moving parts, separates particulate matter from
a carrier gas by transforming the velocity of an
inlet stream into a double vortex confined within
the cyclone.  In the double vortex the  entering gas
spirals downward at the outside and spirals up-
ward at the inside of the cyclone outlet.  The par-
ticulates, because of their inertia, tend to move
toward the  outside wall,  from which they are led
to a receiver.

Cyclones can be designed to handle a wider  range
of chemical and physical conditions of operation
than most other types of collection equipment can
handle.  Any  conditions for which structural ma-
terials are  available can be met by a cyclone,  if
the degree  of collection falls within the operating
range of the cyclone,  and physical characteristics
of the particulates are such that no fouling  of the
cyclone or  excessive wall buildup occurs.

Because of  its versatility and low cost, the  single-
cyclone separator is probably the most widelyused
of the dry centrifugal separators.  These cyclones
are made in a wide variety of configurations.  Al-
though many design factors must be considered,
                                                  91

-------
92
AIR  POLLUTION CONTROL EQUIPMENT FOR  PARTICULATE MATTER
the degree of collection efficiency is most depen-
dent upon the horsepower expended.  Hence, cy-
clones with high inlet velocities,  small diameters,
and long cylinders are generally found most effi-
cient.  They are commonly called pencil cyclones
or high-efficiency cyclones.  Figure 44 shows  a
single high-efficiency cyclone,  with typical dimen-
sion ratios as follows:
                                     combined into a dimensionles s quantity called the
                                     separation factor:
Major cylinder diameter

Major cylinder length

Cone length



Gas outlet diameter



Gas outlet length


Gas inlet height



Gas inlet width


Dust outlet
                                       D
                 L    =   2 D
                  c         c
                 Z   =  2 D
                  c         c
                        D
                 D
            H  +  S   =  5/8 D
              c   c          c
                        D
                 H
                 B
                        D
                        D
In Figure 44, this cyclone consists  of a cylinder
with a tangential gas inlet, an axial gas outlet, and
a conical lower section with an axial dust outlet.
The gas inlet is a rectangular opening,  with the
height of the opening equal to twice  the width.  The
gas outlet is a tube approximately one half the di-
ameter of the major cylinder,  concentric with and
extending inside the major cylinder to slightly be-
low the lower edge  of the gas inlet.   The tangen-
tial, high-velocity gas entry imparts a circular
motion to the gas stream; the particulates, because
of their greater inertia, tend to concentrate on the
wall of the cyclone.  The inlet gas  follows a dou-
ble vortex path,  spiraling downward at the outside
and spiraling upward at the inside to the gas  out-
let.  Figure 45 illustrates the double-vortex  path
of the  gas stream.  The downward  spiral,  assis-
ted by gravity,  carries the particulates downward
to the  dust outlet where they drop into a  dusttight
bin, or are removed by a rotary valve or screw
conveyor.
Theory  of Operation

The centrifugal force applied to particulates varies
as the square of the inlet velocity and inversely as
the radius of the cyclone.  These factors have been
                                                       O   „
                                                            y
                                              (42)
where

   S  =
   V  =

   r  =

   g  =
separation factor
inlet velocity,  ft/sec

cyclone cylinder radius, ft

gravitational constant,  32. 2 ft/sec  .
It has not been possible to establish a definite cor-
relation between separation factor and collection
efficiency; yet,  for cyclones of similar design and
use, collection  efficiency generailly varies directly
as a function of the separation feictor.

Stern et al. (19^6) discuss the variation of collec-
tion efficiency with inlet velocity.  Several theo-
retical  formulas are presented in which critical
particle size is shown to vary as  1/V '  . Critical
particle size is defined as the largest sized par-
ticle not separated from the gas stream,  all lar-
ger particles being separated, and critical-sized
and all  smaller sizes being lost into the outlet duct.
The critical size varies inversely as the velocity,
and the greater the critioal size,  the less efficient
                                             Figure 44.  Single high-efficiency
                                             cyclone with typical  dimension
                                             ratios.

-------
                                          Inertial Separators
                                             93
           Figure 45.   Double-vortex path
           of the gas  stream  in  a cyclone
           (Montross,  1953).

is the cyclone collection.  The collection efficien-
cy, therefore, varies as the  inlet velocity.  There
are, however, limits  to the inlet velocity; if it is
too great,  turbulence  develops to such a degree at
the inlet that overall cyclone efficiency is reduced.
The velocity at which  excessive turbulence occurs
is dependent upon configuration of the  inlet, de-
sign of the cyclone, and the characteristics of the
carrier gas.
 Separation Efficiency

For high efficiency,  the separating forces should
be large and the dust removal effective so that
separated dust is not reentrained.  In general,  cy-
clone efficiency increases -with an increase in the
following:  (1) Density of the particulate matter,
(2)  inlet velocity into the cyclone,  (3) cyclone body
length,  (4) number of gas revolutions (experiments
indicate that the number of revolutions made  by the
gas stream in a typical simple cyclone ranges from
0. 5 to 3 and averages 1. 5 for cyclones of normal
configuration),   (5) ratio of  cyclone body diameter
to cyclone outlet diameter,   (6) particle diameter,
(7)  amount of dust entrained in carrier gas, and
(8)  smoothness  of inner cyclone wall.

An  increase in the following will  decrease the over-
all  efficiency:   (1) Carrier gas viscosity,  (2) cy-
clone diameter,   (3)  gas outlet diameter,  (4) gas
inlet duct width,  (5) inlet area,  and  (6) gas density.

A common cause of poor cyclone performance is
leakage of air into the dust outlet.  A small air leak
at this point can result in  an appreciable decrease
in collection efficiency,  particularly with fine dusts.
For continuous -withdrawal of collected dust a ro-
tary star valve,  a double-lock valve, or a screw
conveyor with a spring-loaded choke should be used.

Collection efficiency is noticeably reduced by the
installation of inlet vanes,  probably because of in-
terference with the normal flow pattern.  In gen-
eral, all sorts of guide vanes,  straightening vanes,
baffles,  and so forth placed inside an other-wise
well-designed cyclone have been found  of little  val-
ue or actually detrimental.  In some instances, for
poorly designed cyclones, these devices have im-
proved performance.  Baffles designed to reduce
leakage  of air into the dust outlet are sometimes
helpful.  These consist of a horizontal, circular
device installed on the cyclone axis  near  the dust
outlet.

In practice, extensive agglomeration may be ex-
pected for dust  concentrations greater  than 100
grains per cubic foot and may be present at much
smaller  concentrations, depending upon the phys-
ical properties  of the particulates being collected.
Fibrous  or tacky particles are especially apt to ag-
glomerate.  Agglomeration produces a larger ef-
fective particle size and thereby increases the  ef-
ficiency  of separation. Nevertheless,  extremely
sticky, hygroscopic, or similar material that could
possibly plug the dust outlet or accumulate on the
cyclone  walls adversely affect cyclone  operation.
In addition, the agglomeration effect is reduced
sharply  -when high inlet velocities are used.  In
some cases -where agglomeration was significant,
an increase in cyclone inlet velocity actually re-
duced the collection efficiency.   Conversely,  the
efficiency -was improved by reducing the inlet
velocity.


Pressure  Drop

A satisfactory method of determining the pressure
drop of a given  cyclone has not yet been developed.
Pressure drop, to be determined accurately, should
be determined experimentally on a geometrically
similar  prototype.   Lapple (1963) has suggested a
relationship that may be used to approximate the
pressure drop:
                 F  =
              KBH

              D2
                                             (43)
where
    F  =

    K  =

    B  =
    H  =
    D  =
cyclone friction loss, number of cyclone
inlet velocity heads,  dimensionles s

empirical proportionality constant, di-
mensionless
width of rectangular  cyclone inlet  duct, ft

height of rectangular cyclone inlet, ft
cyclone gas exit duct diameter,  ft.

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94
AIR  POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
In this equation,  K varies from 7. 5 to 18.4. Pres-
sure drop values, for a value of K =  13. 0,  have
been found to check with experimental data  within
30 percent.
The Industrial Hygiene Codes Committee (1938)
states that the resistance pressure across pull-
through cyclones is approximately three inlet ve-
locity heads.   For pushthrough cyclones venting
directly to the atmosphere,  the resistance pres-
sure  is approximately one and one-half velocity
heads.  These values are valid for simple cyclones,
but a considerable variation may be expected for cy-
clones of unusual design.
OTHER TYPES OF CYCLONE SEPARATORS
High-Efficiency Cyclone Separators

When collection of particulates in the 5- to  10-
micron range is desired, long, small-diameter,
high-efficiency cyclones may sometimes be used.
Operation is,  however, more expensive,  since
pressure drop increases with a decrease in cy-
clone diameter; the  greater the pressure drop,
the greater the power cost.


High-efficiency cyclones are made  more  effective
than simple cyclones by increasing the bodylength
and decreasing the diameter.  These two altera-
tions act both to increase retention time in the cy-
clone and exert greater centrifugal force on the par-
ticulates, -which results in  greater  separation.
                                             Figure  46.  Multiple-cyclone separa-
                                             tor  (Western Precipitation, Division
                                             of  Joy  Manufacturing Company,  Los
                                             Angeles,  Calif.).
Multiple-Cyclone Separators


A multiple-cyclone separator consists of a num-
ber of small-diameter cyclones operating in par-
allel, having a common gas inlet and outlet, as
shown in Figure 46.   The flow pattern differs from
that in a conventional cyclone in that the gas,in-
stead of entering at the side to initiate the swirling
action,  enters at the top of the collecting tube and
has a swirling action imparted to it by a station-
ary vane positioned in its path.  The diameters of
the collecting tubes usually range from 1 foot to as
small as 2 inches.  Properly designed units can be
constructed that have a collection efficiency as high
as 90 percent for particulates in the 5- to 10-mi-
cron range.

Mechanical, Centrifugal Separators

Several types of collectors are readily available
in which centrifugal force is supplied by a rotat-
                                        ing vane.   Figure 47 illustrates  this type  of
                                        collector,  in which  the  unit serves both as
                                        exhaust  fan and dust collector.   In operation,
                                        the rotating fan blade exertj a large  cen-
                                        trifugal  force  on the particulates,  ejecting
                                        them from the tip of the blades  to a  skim-
                                        mer bypass leading  into a  dust hopper.
                                        Efficiencies of mechanical,  centrifugal  sep-
                                        arators  are somewhat  higher  than those
                                        obtainable with simple  cyclones.  Mechanical,
                                        centrifugal separators  are compact and are
                                        particularly useful where  a large number  of
                                        individual collectors  are required.   These
                                        units cannot,  however,  be generally used  to
                                        collect particulates that cake  or tend to ac-
                                        cumulate on the rotor  blades  since these
                                        particulates cause  clogging  and unbalancing
                                        of the impellor blades  with resultant high
                                        maintenance costs  and  shutdowns.

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                                          Inertial Separators
                                              95
        Figure 47.  Mechanical,  centrifugal
        separator  (American Air  Filter Com-
        pany,  Inc., Louisville,  Kentucky).
 PREDICTING EFFICIENCY OF CYCLONES

 Many investigations attempt to correlate cyclone
 performance with various parameters.  Lapple
 (1951, 1963) treats the subject at length in sev-
 eral publications, introducing the concept of cut
 size (DpC), which is defined as the diameter of
 those particles collected with 50 percent efficien-
 cy.  Collection efficiency for particles larger than
 the cut size will be greater than  50 percent  while
 that for smaller particles will be less.  Another
 term used is the average particle size (Dp), which
 is simply the average of the size range.  For ex-
 ample, if the size range is  1 0 to 15 microns ,  D_ =
 12.5 microns.
A separation efficiency correlation for typical  cy-
clones of the type mentioned by Lapple is presen-
ted in Figure 48. Additional experimental data
have  been used to check Lapple's ratios of Dp/DpC.
All results compared favorably with  the original
curve of Lapple.  Manufacturers' efficiency curves
for cyclones and multiple cyclones converted to
Dp/Dpc curves had  slightly lower efficiencies than
Lapple's  correlation for Dp/DpC ratios greater
than 1.   The maximum  deviation noted was 5 per-
cent for the cyclone curve at Dp/Dpc of  1-1/2 and
12 percent for the multiple-cyclone curve at Dp/
DpC of 2 to 3.  Apparently,  Lapple's  correlation
is sufficiently accurate  for an engineering estima-
tion of many cyclone applications.  A size-efficien-
cy curve may be calculated from this  correlation
after  the actual size of the cut size particle is  es-
                                                        100
                                                       5 50
                                                       Z
                                                       LU
                                                       o «

                                                       £ 30
                                                       z
                                                       (=>

                                                       £ 20
                                                         10
                                                         0.3  0 4 0.5
                                                                                                     10
                                                                      PARTICLE SIZE RATIO, (Dp -Opc)
                                                          Figure  48.   Cyclone  efficiency versus particle
                                                          size ratio  (Lapple,  1951).
                                                       tablished.  Particle cut size may be calculated by
                                                       equation 44:
                                                             D
                                                               pc
                                                                              9p.b
 wh ere
                 2 N  V (p  - p )  -n
                    e   i   p    g
                                             (44)
 D     =  diameter cut size particle collected at
         50 percent  efficiency,  ft

    [j.  =  gas viscosity, Ib mass /sec-ft = centi-
         poise  x 0.672 x  10"3

    b  =  cyclone inlet width,  ft

  N   =  effective number of turns within cyclone,
    e
         The number of turns are about five for a
         high-efficiency cyclone but may vary from
         1/2 to 10 for other cyclones (Freidlander
         et al. ,  1952)

  V.   =  inlet gas velocity,  ft/sec

  p   -  true particle density,  Ib/ft
  p   -  gas density, Ib/ft  .
    &
 Figure 49  presents a graphical solution of this
 equation for typical cyclones having an inlet ve-
 locity of 50 fps,  gas viscosity of 0. 02 centipoise,
 effective number of turns equal to five, and cy-
 clone  inlet width  of Dc/4.  From these curves,
 the cut size may  be approximated from the cy-
 clone  diameter and the dust's true  specific grav-
 ity.  Corrections for viscosity, inlet gas velocity,
 effective number of turns,  and inlet width different
 from those assumed  in Figure 49 may be found
 graphically by using  Figure 50.

 The calculated particle cut size may be used in
 conjunction with the general cyclone efficiency
 curve  of Lapple   (1951, 1963) as shown in Fig-
ure 48  to  calculate a particle size  efficiency
 curve  for the cyclone in question,  A particle size
distribution of  the feed must also be known or cal-
 culable to  continue the final efficiency determina-

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96
AIR  POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
                                I    I   I
                  n - P J TT
       where^i = Viscosity  0 02 centipotse
            b = Inlet width  eye]one di a.  DC/I
           He = Number of tu rns  5
           V, = Inlet velocity  50 fps

           "" = ,Tbm3specif'c "e'qt" °f cartlculate
           p = Gas density  lb/ft3
          Dpc = Cut size  microns on ordinate

       See Figure 50 for correction factors for other
       viscosities  inlet widths  inlet, velocities
     •- and number of turns.
                                                                                              I 00
                        Figure 49.   Cyclone  diameter  versus  cut  size  (Lapple, 1951).
tion.  Size distribution data should be plotted on
logarithmic-probability paper to check for reli-
ability.  Drinker and Hatch (1954)  state that
Epstein's work shows this plot is a straight line
for operations such as crushing and grinding. An
investigation of test results on samples from crys-
tallization, spray drying,  calcining, and other
physical and chemical processes indicates that  the
particle size distribution of these processes usu-
ally follows the laws  of probability, and plots as
a straight line on logarithmic-probability paper.
The actual distribution used in the calculations
should be taken from the straight-line "smoothed
data."  Methods of  determining particle sizes have
an effect in determining the straight-line plot.
Most data from screen analyses plot as a curve
on logarithmic-probability paper if the values for
screens smaller  than 150-mesh Tyler or  140-
mesh U. S. Screen Scale are used.  Specifically,
minus 200 mesh and minus 325 mesh (both some-
times reported in screen analyses) give points
that are usually not in agreement with data ob-
tained when the minus~100-mesh material is sub-
jected to micromeragraph analysis.
                                        A fractional-efficiency curve for a geometrically
                                        similar cyclone may be constructed from a given
                                        fractional-efficiency curve by the following pro-
                                        cedure:

                                        1. Determine D^., from the fractional-efficiency
                                                        P^
                                           curve for a known cyclone.


                                        2. Replot the fractional-efficiency curve  as effi-
                                           ciency versus the ratio Dp/Dpc-

                                        3. Calculate DpC for the unknown cyclone from
                                           equation 44 or Figures  49 and 50.


                                        4. Assume efficiency versus Dp/DpC curve ap-
                                           plies to the unknown cyclone.

                                           Using the value of Dpc for the unknown cyclone,
                                           and the efficiency versus Dp/Dpc curve, cal-
                                           culate new values of D  versus efficiency and
                                           plot as  the fractional-efficiency curve of the
                                           unknown cyclone.

-------
                                          Inertial Separators
                                              97
  2 5
  2,0
C 1 5
                VISCOSITY (|l) . centijoises

                0 02     0 03   0.04     0 06  0 08 010
                02.     03   0405
                INLET AIDTH-'DIANETER (b D )
An alternative method of obtaining total weight
of the fraction charged to the cyclone consists of
dividing each weight fraction by the fractional ef-
ficiency.  The -weight loss is then the difference
bet-ween the amount collected and the feed calcu-
lated from the efficiency.

The  previously discussed method of predicting cy-
clone collection efficiencies is, of course, only
approximate.  It can be useful if applied correctly.
Its utility -will be increased once additional test in-
formation is obtained on various cyclones.  As
more information is obtained,  a family of curves
can be developed for various types  of cyclones. The
resulting data should be  similar to  the data herein,
and the use of the illustrated curves could be ex-
tended to many different cyclone designs without
appreciable error.
                  INLET VELOCITY (vc),  fps
                 20       30    40
    Figure  50.  Correction factors for Figure 49
    (Lapple,  1951).
 5.  In most cases, a range of Dpc for the unknown
    cyclone should be selected instead of a  single
    value.  Then,  using the maximum and mini-
    mum values for  D c,plot  two size efficiency
    curves.  The overall efficiencies obtainedfrom
    these curves serve as an engineering estimate
    of the expected cyclone performance.


 In  some cases, size data are available  only on the
 materials already collected  in a cyclone separator,
 •with no data on the  cyclone loss rate and size dis-
 tribution.   The calculation procedure is identical
 to the normal method except for the final loss  rate
 step.  Here a loss factor must  be determined from
 the size range efficiency.  If the efficiency is 50
 percent, the loss factor is 1, and the cyclone loses
 1 pound  of material for every pound collected in
 this size range.  If the efficiency is 75  percent, the
 loss rate is 1/3,  and similarly, if the efficiency is
 25  percent,  the loss rate is  3.  The loss rate for
 each particle size range is the  quantity collected
 multiplied by the loss factor.
Method  of  Solving  a  Problem
                                                       Knowing the cyclone dimensions, the inlet gas ve-
                                                       locity, the viscosity,  and the particle size distri-
                                                       bution of the dust,  predict cyclone  efficiencies  as
                                                       shown in example 18.
                                                       Example 18

                                                       Given:
                                                                           c
                                                                          be
Cyclone diameter, D
Inlet width,

Inlet velocity,     V
Specific gravity

Gas viscosity
=  72 in.

=  17 in. = 0. 235 D
                   c
=  2, 400 fpm = 40 fps

=  1.5
=  0.0185 centipoise
Particle size distribution of dust entering the cy-
clone (See curve in Figure 51).

Problem:

Determine the particle  cut size DpC and use these
data to determine expected  cyclone performance.

Solution:

1. Determine the particle cut size:
   From Figure 49,  the uncorrected D_c = 10. 5
   microns.

   The following correction factors are shown by
   calculation and can also  be  obtained from Fig-
   ure  50:
   Inlet -width factor =
  / 0.235
 / 0.250
                                    =   0. 97

-------
                   AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
        CUMULATIVE PERCENT \\EIGriT LARGER THAN

99.99   99.9  99.8 99.5 99   98   95    90    80  70  60  50








o 20
E
CC
-J
y
< 10
Q 9


Q_
















/
/
f














/















J
f















/

















/
























PA
OF







/












,
/











J
/
/










^
f
r


























RTICLE SIZE DISTRIBUTION
THE Ml \LS-2CO-MESH FRACTIO
















OF THE SAMPLE EIGHTY- FIVE
PERCENT OF THE MATERIAL AAS
GREATER THA\ 200 MESH







      l.01   0.05 O.I 0.2  0.5  I   2     5    10    20   30   40  50
                "I I A I I \ E  I'Fff C ,T  ,'.! . '",  ,M.'Ll '   I •'

         Figure 51.  Particle size distribution
         of dust in example problem.
   Velocity factor
   Viscosity factor   =
                  /0.0185
                I  0. 020
                                   =   1. 12
                                   =  0. 96
   Number of turns factor = 1.0 (Number of turns
                                  assumed to be 5)
   Corrected cut size =  (D  )(correction factors)

                      =  (10. 5)(0. 97)(1. 12)(0.96)(1.0)
                      =  11.0 microns.
2.  Calculate collection efficiencies by size incre-
   ments:

   Select size increments to obtain several values
   of Dp less than DpC, and five  or more values
   between Dp/Dpc  ratios of 1  to 10.  Calculate the
   average size of each increment and tabulate as
   Dp.  Calculate the ratio Dp/DpC and tabulate for
                                                            the range at D    Particles of such size that the
                                                            ratio Dp/DpC is greater than 10 are considered
                                                            to be collected at 100 percent efficiency.  From
                                                            Figure 48 obtain the collection efficiencies for
                                                            the size increments represented by the Dp/DpC
                                                            ratios and tabulate (Table 29).

                                                              Table 29.  COLLECTION EFFICIENCIES
                                                                      FOR SIZE INCREMENTS
Particle size, microns
Range
0 to 2
2 to 4
4 to 6
6 to 8
8 to 10
10 to 12
12 to 15
15 to 20
20 to 30
30 to 40
40 to 50
50 to 60
60 to 70
70 to 80
80 to 90
90 to 100
100+
Avg D
P
1
3
5
7
9
11
13. 5
17. 5
25
35
45
55
65
75
85
95
100+
Ratio
D /D
P PC
0.09
0.27
0. 45
0.64
0.82
1. 00
1.23
1.59
2.28
3. 18
4. 1
5. 0
5.9
6.8
7. 7
8.6
10+
Efficiency
% by wt
1
7
17
29
40
50
60
72
84
91
95
96
97
98
98. 5
99
100
3.  Plot the  given particle size data of the inlet
   dust to the cyclone:

   Plot the  particle size data on logarithmic -
   probability paper and draw the best straight
   line,  giving maximum consideration to the
   data that lie between 20 to 80 percent of the
   extreme upper and lower values of the parti-
   cle size  range (Drinker and Hatch,  1954).

4.  Tabulate the weight percentage  of the dust cor-
   responding to the micron size increments:

   Using the smoothed data, as shown  above, tab-
   ulate the weight percentages corresponding to
   the size  increments in microns (Table 30).

5.  Determine the overall efficiency:

   When the particle size distribution is for  the
   cyclone feed,  as given in this example, multi-
   ply the percentage for each size increment by
   its collection  efficiency.  The sum of these
   products is the overall efficiency.   This  cal-
   culation  is presented  in Table 31.

6.  hi some  existing installations, it may be dif-
   ficult or impossible to determine the particle
   size analysis  of the dust to the cyclone.  In

-------
                                     Wei Collection Devices
Table 30. WEIGHT PERCENTAGES the quotients gives the cyclone feed expressed
PER SIZE INCREMENTS as Perccnt of the cyclone catch. Divide 100 by


the cyclone catch to obtain the overall efficien-
Particle size, microns Wt % for CY-- These calculations are presented in Table
Range Avc

0 to 2
2 to 4
4 to 6
6 to 8
8 to 10
10 to 12
12 to 15
15 to 20
20 to 30
30 to 40






1
•s D 1 size 32, with the particle size distribution curve for
P
1
3


0
5 ; o
7
0
9 0
1 0
14 ; 0
1 0
I5
3

40 to 50
50 to 60

60 to 70
70 to 80
80 to 90
90 to 100
100+
5

45
55


65
75
8
5
95
100+


2
3

4
4

5
4
4
5
65


Table 31. CALCULATION
this problem, but it is assumed that these data
are the particle size distribution curve for the
.01 cyclone catch.
. 02
' °6 Table 32. CALCULATION OF OVERALL
• H EFFICIENCY FOR SPECIAL CASES
. 15
35 " I
Particle size, microns] % by wt
' 9° Range
.80 b
.60 „ , 7
0 to 2
•50 2 to 4
•50 ,
4 to 6
-°° 6 to 8
•°° 8 to 10
Avg D J efficiency
P i

1

< 1
3 7

5 17
7 29
9 40
' °° 10 to 12 11 50
' °° 12 to 15 14 60
.00 ™
15 to 20
20 to 30
30 to 40
QF 40 to 50
OVERALL EFFICIENCY 50 to 60

Particle size, microns
Range Avg D
p
0 to 2 1
2 to 4 3
4 to 6 5
6 to 8 7
8 to 10 9
10 to 12 11
12 to 15 14
15 to 20 18
?n fr, ?n PR

Efficiency,
To by wt

< i
7
17
29
40
50
60
72
Q/l
60 to 70
" 01 u 70 to 80
% by wt x
,,. . 80 to 90
efficiency
90 to 100
100+
0.001 Total
0.003 LOSS
0. 017
0. 044 Overall
0-075 efficiency
0. 210 Loss, % of
0.648 feed
-> ir.
18
72
25 84
35
45
55
65
75
85
91
95
96
97
98
98. 5
95 1 99
100+







100







% by wt x
efficiency


0. 14

0.11
0. 20
0. 27
0. 30
0. 58
1. 25
3. 33
3. 96
4. 74
4. 69
5. 15
4. 08
4. 06
5. 05
65. 00
102. 91
2. 91


97. 16

2. 84
12 to 15
15 to 20
20 to 30
30 to 40
40 to 50
50 to 60
60 to 70
70 to 80
80 to 90
90 to 100
100+
Total
Loss
Overall
efficiency
Loss, % of
feed
14 60
18
25
35
45
55
65
75
85
95
100+






72
84
91
95
96
97
98
98. 5
99
100






0. 210
0. 648
2. 35
3. 28
4. 28
4. 32
4. 85
3.92
3. 94
4. 95
65. 00
97.89
2. 11

97.89

2. 11
these cases, a particle size analysis of the per-
centage for each size increment should be di-
vided by its collection efficiency.  The sum of
From the preceding problem, the cyclone loss ex-
pressed as percent of feed is obviously 100 minus
the overall efficiency as calculated.  If the loss of
any incremental size fraction is desired,  this may
be calculated as follows:

1. Calculate the weight of each  incremental frac-
   tion of feed  by using particle size distribution
   data and total feed weight.

2. Multiply this weight by the percentage loss (100
   minus the efficiency) for each increment to de-
   termine the  weight loss.


         WET  COLLECTION  DEVICES

Wet collection  devices use a variety of methods to
wet the contaminant particles in order to remove
them from the  gas stream.   There is also a wide
234-767 O - 77 - 9

-------
100
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
range in their cost, their collection efficiency, and
the amount of power they expend.

Wet collectors have the following advantages:
They have a  constant pressure drop (at constant
volume),  they present no secondary dust prob-
lem in disposing of the collected dust, and they
can handle high-temperature or moisture-laden
gases.  They can also handle corrosive gases or
aerosols, but corrosion-resistant construction
may add materially to their cost.  Space require-
ments  are reasonably small.  Disposal of the waste
water or its  clarification for reuse may, however,
be difficult or expensive.

Their collection efficiency  varies widely with dif-
ferent  designs.   Most collectors decline rapidly
in efficiency for particles between 1 and 10 mi-
crons.  Many investigators believe that collection
efficiency is  directly related to the total power ex-
pended in forcing the gases through the collector
and in  generating the water spray.

The process  of  contacting an air-contaminated gas
with a  scrubbing liquid results in dissipation of me-
chanical energy in  fluid turbulence  and, ultimately,
in heat.  The power dissipated is termed the con-
tacting power.   Semrau (1960) made an exhaustive
literature survey to correlate scrubber efficiency
with contacting  power.   He  states that contacting
power  can be derived from   (1) the kinetic  energy
or pressure  head of the gas stream,  (Z) the kinet-
ic energy or  pressure head of the liquid, or (3) en-
ergy supplied mechanically by a rotor. He con-
cludes:  "Efficiency is  found to have little relation
to scrubber design and geometry,  but to be depen-
dent on the properties of the aerosol and on the
contacting power."


THEORY OF COLLECTION

The principal mechanisms  by which liquids may
be used to remove  aerosols from gas streams
are as follows:

1. Wetting of the particles  by contact with a liq-
   uid  droplet,

2. impingement of wetted or unwetted particles
   on collecting surfaces followed by their re-
   moval from the surfaces by a flush with a
   liquid.
MECHANISMS  FOR WETTING  THE PARTICLE

The particles can be wetted by the following
mechanisms:

1. Impingement by spray  droplets.  A spray di-
   rected across the path of the dust particles
   impinges upon them -with an efficiency propor-
                                         tional to the number of droplets and to the
                                         force imparted to them.  Johnstone and
                                         Roberts  (1949) states that the optimum drop-
                                         let particle si^e is about 100 microns. Above
                                         100 microns there are too few droplets,  and
                                         below 100 microns, the  droplets do not have
                                         sufficient force.   Fine spray is effective by
                                         another mechanism, diffusion.

                                      2.  Diffusion.  When liquid droplets are dis-
                                         persed among dust particles, the dust
                                         particles are deposited on the droplets by
                                         Brownian movement or diffusion.  This is
                                         the principal mechanism in the  collection
                                         of submicron particles.   Diffusion as the
                                         result of fluid turbulence may also be an
                                         appreciable mechanism  in the deposition
                                         of dust particles  on spray droplets.

                                      3.  Condensation (Lapple, 1963).  If a gas is
                                         cooled below the  dewpoint in passing through
                                         a wet collector, then condensation of mois-
                                         ture  occurs, the  dust particles  acting as
                                         condensation nuclei.  This effective increase
                                         in the particle size makes subsequent collec-
                                         tion easier.  Condensation is an important
                                         mechanism only for gases that  are initially
                                         hot.  Condensation alone can remove only
                                         relatively small amounts of dust, since the
                                         amount of condensation required to remove
                                         large concentrations is greater than can be
                                         achieved.

                                      4.  Humidification and electrostatic precipita-
                                         tion have been suggested as mechanisms
                                         that facilitate collection of particles by caus-
                                         ing them to agglomerate.  These effects are
                                         not, however, well understood  and cannot be
                                         relied upon to play any significant  role in the
                                         collection mechanisms.

                                      Several investigators have used wetting agents
                                      for scrubbing water in an effort to improve col-
                                      lection efficiency.  In most cases, little or no
                                      improvement has been found (Friedlander et al.,
                                      1952).   In order to be -wetted, a particle must
                                      either make contact with a  spray droplet or im-
                                      pinge upon a wetted  surface.  When either  of
                                      these occurs, the particle is apparently wetted
                                      as  adequately without the use of wetting agents
                                      as  it is with their use.

                                      Particles that have been wetted must  reach a
                                      collection surface if the collecting process is
                                      to  be completed.   They may be  impinged against
                                      surfaces placed in the path of the  gas  flow; or
                                      centrifugal action may be used to throw them to
                                      the outer walls of the collector; or simple  grav-
                                      ity settling may be employed.

                                      In  some devices impingement is the principal
                                      collection mechanism, the water sprays being

-------
                                        Wet Collection Devices
                                                                                                  101
used merely to remove the dust from the col-
lection surfaces.

Centrifugal action may be provided by a vessel
that is essentially the same as a dry cyclone
separator.  Helical vanes in a cylindrical ves-
sel are extensively used to supply centrifugal
action.  In some devices,  baffles are shaped
and placed so that they act both as impingement
and collection  surfaces, and as imparters of
cyclonic motion to the gas  stream.
 TYPES OF WET  COLLECTION DEVICES
 Spray  Chambers
 The simplest type of scrubber is a chamber in
•which  spray nozzles are placed.  The gas stream
velocity decreases as it enters the chamber,  and
the \vetted particles settle and are collected at the
bottom of the chamber.  The outlet of the chamber
 is sometimes equipped -with eliminator plates to
help prevent the liquid from being discharged -with
the clean air stream.  The spray chamber is  ex-
tensively used as a gas cooler.  Its efficiency as
a dust collector is low except for coarse dust.
 Efficiency can be improved by baffle plates upon
•which  particles can be impinged.  Water rates
 range  from 3 to 8 gallons per minute (gpm) per
 1, 000  cfm.  Installed  costs range  from $0. 25 to
$0. 50  per  cfm.
Cyclone-Type Scrubbers

Cyclone-type scrubbers range from simple dry
cyclones -with spray nozzles to specially con-
structed multistage devices.   All feature a tan-
gential inlet to a cylindrical body, and many fea-
ture additional vanes that accentuate the cyclonic
action and also act as impingement and collection
surfaces.

Figure 52  shows how a dry cyclone can be  con-
verted to a scrubber.   Some investigators  dis-
agree on the most effective placement of spray
nozzles; however,  the principal benefit is  de-
rived from the wetted walls in preventing reen-
trainment  of separated material.   Figure 53
shows a standard type of cyclone  scrubber.  The
gas enters tangentially at the bottom of the scrub-
ber and pursues  a spiral path upwards.  Liquid
spray is introduced into the rotating gas from an
axially located manifold in the lower part of the
unit.  The atomized fine-spray droplets are
caught in the rotating gas stream, and are, by
centrifugal force, swept across to the walls of
the cylinder,  colliding with, absorbing, and col-
lecting the dust or  fume particles en route.  The
scrubbing liquid  and particles  run down the walls
and out of the bottom of the unit; the clean  gas
         Figure 52.  Conventional  cyclone
         converted to a scrubber.
leaves through the top.  The scrubber in Figure
54 uses helical baffles to provide prolonged cen-
trifugal action, and  multiple spray nozzles to in-
crease spray contact time.

Since centrifugal force is the principal collecting
mechanism,  efficiency is promoted by compara-
tively high gas velocities.  Pressure  drop varies
from 2 to 8 inches water gage,  and water rates
vary from 4 to 10 gpm per  1, 000 cfm gas handled.
The purchase cost for completed units varies
from $0. 50 to $1. 50 per cfm gas handled for stan-
dard construction.  If corrosion-resistant materi-
als arc required,  costs may be much higher.

    I
Orifice-Type Scrubbers

Orifice-type scrubbers are devices in which the
velocity  of the air is used to provide liquid contact.
The flow of air through a restricted passage (usually
curved) partially filled with water causes the disper-
sion of the -water.  In turn, centrifugal forces, im-
pingement,  and turbulence  cause wetting of the parti-
cles and their collection.  Water quantities  in motion
are relatively large, but most of the water can be
recirculated -without pumps or spray nozzles.  Recir-
culation  rates are as high as 20  gpm per 1, 000 cfm
gas.  The degree  of dispersion of the water is, how-
ever, not as great as is attained with spray nozzles.
Pressure drop and purchase costs are comparable

-------
102
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
                             CLEANED CIS
       CORE BUSTER DISC
TANGENTIAL GAS INLET
                                                     to those for cyclone-type scrubbers.  Figure 55 il-
                                                     lustrates the action in an orifice-type scrubber.
                                                     Zig-zag plates  remove spray droplets at the gas ex
                                                     Figure 56 illustrates a type in which the orifice is
                                                     formed by a cone inside the entrance  ducts.  Baffle
                                                     plates remove spray droplets at the gas exit.
CONTAMINATED
GAS INLET
       Figure  53.  Cyclone scrubber (Chemical
       Construction Co., New York,  N.  Y.).
                                                             Figure 55.  Orifice scrubber (American
                                                             Air Filter Co., Inc.,  Louisville,  Ky.).
     Figure 54.  Double-chamber cyclone  scrubber
     with hel ical baffIes.
                                                      Mechanical Scrubbers

                                                      Mechanical scrubbers include those devices in whicl
                                                      the water spray is generated by a rotating element
                                                      such as a drum or disk.  As  with the orifice types,
                                                      the water is usually recirculated.  In the scrubber
                                                      in Figure 57,  the spray,  because it is generated in
                                                      a restricted passage,  promotes extreme turbulence
                                                      and increases chances for collision between dust
                                                      particles and  spray droplets.  Elecirculation rates
                                                      and degree of dispersion vary widely -with the  dif-
                                                      ferent types of rotating elements.  Installed costs
                                                      are around $1. 00 per  cfni gas for standard con-
                                                      struction.
                                      Mechanical,  Centrifugal  Collector With Water  Sprays

                                      A spray of water added to the inlet of a mechanical,
                                      centrifugal collector increases its  collection efficiei

-------
                                      Wet Collection Devices
                                                                                                 103
Figure 56.   Orifice  scrubber (Western Precipi-
tation,  Division  of  Joy Manufacturing Company,
Los AngeIes,  California).
                                                    cy.  The mechanism is mainly one of impingement
                                                    of dust particles on the rotating blades.  The spray
                                                    formed merely keeps the blades wet and flushes away
                                                    the collected dust  (Figure 58).  By the same mechan-
                                                    ism, good collection efficiencies can be  achieved by
                                                    injecting a spray of water into the inlet of an ordi-
                                                    nary paddle-type centrifugal fan.  This can substan-
                                                    tially increase the collection  efficiency of a scrub-
                                                    bing installation.  It also increases, however,  the
                                                    wear and corrosion rate of the fan.   Installed costs
                                                    for mechanical, centrifugal types arc  approximately
                                                    $1.00 per cfm gas.
Figure  57.   Mechanical scrubber (Schmieg Indus-
tries,  Division of Aero-Flow Dynamics,  Inc.,
Detroit,  Michigan).
                                                            Figure 58.  Mechanical,  centrifugal
                                                            scrubber  (American Air Filter  Co.,
                                                            Inc., Louisvi I le,  Ky.).
High-Pressure Sprays

Most scrubbers operate -with water pressure of
from 100 to 150 psi.  Increasing the pressure at
the spray nozzles has been found to increase col-
lection efficiency by creating more droplets and
giving them more force.   A number of scrubbers
are now  designed, therefore, to operate with water
pressures  at the spray nozzles of from 300 to 600
psi.   Very small nozzle orifices are used, and in
most cases this precludes recirculation of -water.
Nozzles  must be located so that collision between
water droplets is minimized, and the design must
ensure maximum collision between water droplets
and the dust particles. Very high collection ef-
ficiencies have been reported.  Water consumption
ranges from 5 to  10 gallons  per 1, 000 cfm.  In-
stalled costs are  about the same as those for cy-
clone scrubbers.  For a given •water rate, oper-
ating costs are greater, but collection efficien-
cies are  higher.

-------
104
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
Venturi Scrubbers

In the venturi scrubber, the gases are passed
through a venturi tube to which low-pressure
water is  added at the throat.  Gas velocities at
the throat are from 15, 000 to 20, 000 fpm,  and
pressure drops are from 10 to  30 inches water
gage.  Recirculation of water is feasible.  The
predominating mechanism is believed to be im-
paction.  In spite of the  relatively short contact
time, the extreme  turbulence in the venturi pro-
motes very intimate contact.  The wetted parti-
cles and  droplets are collected in a cyclone spray
separator, as shown in Figure  59.  Water  rates
are about 3 gpm per 1, 000 cfm gas.  Very high
collection efficiencies have been reported for
very fine dusts.  Costs are from $0. 50 to $2. 00
per cfm  for mild steel construction and $1. 00 to
$3.00 per cfm for stainless  steel.


Packed Towers

In packed towers the contaminant-laden stream
is passed through a bed  of a granular  or fibrous
collection material, and a liquid is passed over
the collecting surface to keep it clean and pre-
vent reentrainment of deposited particles.  Col-
lection of the  contaminant  depends upon the length
of contact time of the gas stream on the collecting
                                        surfaces.  This collecting surface material should
                                        have a relatively large surface area,  low weight
                                        pej: unit volume, and large free cross-section. Ir-
                                        regularly shaped ceramic saddles are commonly
                                        used as packing.  Coke, broken rock,  stoneware
                                        shapes, Raschig rings, and spiral-shaped rings
                                        are other materials and shapes often  used.  Bed
                                        depths may vary from a fraction of an inch to
                                        several feet depending upon the type of packing
                                        and the application.  Coarsely packed beds are
                                        used for removing coarse dusts and mists that
                                        are 10 microns or larger; velocities through the
                                        bed should be about 400 fpm.  Finely  packed beds
                                        may be used for removing contaminants  in the 1-
                                        to 5-micron range,  but the velocity through the bed
                                        must be kept very low, preferably below 50 fpm.
                                        Finely packed beds tend to clog; their applications
                                        are generally limited to dust-laden gases -with rel-
                                        atively low grain loadings or to liquid entrainment
                                        collection.

                                        Both costs and collection efficiency vary -widely
                                        with bed depths, design velocities, and types  of
                                        packing.  For comparatively shallow beds, high
                                        velocity,  and  coarse packing, the costs  and col-
                                        lection efficiency are comparable to those for a
                                        simple spray chamber.   For deep beds, fine  pack-
                                        ing,  and low velocities,  both the  costs and collec-
                                        tion  efficiencies are about the same as those for
                                        an electrical precipitator.   Figure 60 illustrates
                Figure 59.  Venturi  scrubber (Chemical Construction  Co., New York,  N.  Y.).

-------
                                         Wet Collection Devices
                                                                                                    105
one type of thin-bed tower.  The packing in this de-
vice consists of lightweight glass spheres kept in
motion by the air velocity.
                                           TR1NS i TI ON PIECE
   GAS
   INLET
         Figure 60.  Thin-bed packed tower
         (National Dust Collector Corpora-
         tion, Chicago, 111.).
 Wet Filters

 A wet filter consists of a spray chamber with filter
 pads composed of glass fibers, knitted wire mesh,
 or other fibrous materials.  The dust is collected
 on the filter pads.  The sprays are directed against
 the pads to keep the dust washed off,  as shown in
 Figure 61.  The pads are about 20 inches square
 and 3 to 8 inches thick.  The pads commonly used
 contain coarse fibers and are not very efficient
 for collecting fine dust.  Fine  glass wool fibers
 are efficient,  but their usefulness is limited be-
 cause the  pads mat and sag from their supports
 when wetted.

 Many wet collectors are a combination of the pre-
 ceding types.  One design consists of a spray cham-
 3er followed by impingement screens,  which are fol-
 lowed by a centrifugal section,  as in Figure 62. Sev-
 3ral other combinations are used.   The device  shown
 Ln Figure 63 combines centrifugal and impingement
 actions.  In many devices,  the  wetting action and  col-
 lecting action take place in the  same zone.   Perfor-
 mance data on a number of different kinds of wet col-
 Lectors are shown in Table 33.


 THE ROLE  OF WET COLLECTION DEVICES

 The collection efficiency of wet collection devices
is proportional to the energy input to the device.
Since high-energy devices are  expensive to install
    inches
                                         inches
                                                                           6 feet  8 inches
   1

              4 feet 2 inches OMITTING ACCESS DOOR
                                                     AIR FLOW
                    Figure 61.   Wet filter  (Buffalo  Forge Company, Buffalo,  N.  Y.).

-------
106
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
     Figure 62.  Multiple-action  scrubber  (Joy
     Manufacturing Company,  Pittsburgh,  Pa.).
      Figure  63.  Centrifugal  and impingement
      scrubber  (Claude B.  Schneible  Company,
      Detroi t, Michigan).
                                       and operate, there is a natural tendency to install
                                       wet collectors of limited efficiency.  In Los Angel
                                       County, in the early days  of the Air Pollution Con
                                       trol District,  many wet collectors were found to b
                                       inadequate for meeting the emission standards. F<
                                       instance,  many low-energy scrubbers were install
                                       to collect the  dust from asphsiltic concrete-batch-
                                       ing plants, but they were not efficient enough to lo
                                       er the emissions to the required level. A modera
                                       ly high-energy scrubber was required to meet the
                                       emission  limits, but even these were inadequate tc
                                       reduce the emissions of grey iron cupolas to the r
                                       quired level.  The  high operating cost of high-enei
                                       gy scrubbers  usually makes the total cost  at least
                                       as much as that of  a high-temperature baghouse 01
                                       an electrical precipitator.

                                       For collection of dusts and furncs,  the baghouse is
                                       to be  preferred over a scrubber.  The positive  col
                                       lection mechanism of the baghouse  ensures virtual
                                       complete  collection of almost any dust or fume,
                                       whereas only  the best scrubbers ensure good colle
                                       tion of very fine dusts and fumes.   If, however,
                                       mists or hygroscopic particles are present in the
                                       effluent, a baghouse cannot be used.  In many case
                                       a scrubber is  the only choice.  Mists that  form fre
                                       running liquids when collected can be successfully
                                       collected  in an electrical precipitator.  If,  howeve
                                       sticky or  gummy materials are  formed, removing
                                       the collected material is very difficult, and an  elec
                                       frical precipitator  is then impractical.


                                                        BAGHOUSES
                                       Suspended dust and  fumes  may be removed from
                                       an air stream  by a number of different devices.
                                       When high collection efficiency on small particle
                                       size  is required, however, the most "widely used
                                       method consists of separating the dust from the
                                       air by means  of a fabric filter.  The fabric is usu-
                                       ally made into bags of tubular or envelope shape.
                                       The entire structure housing the bags is called  a
                                       baghouse.  Typical  baghouses are illustrated in
                                       Figures 64, 65, 66, and 67.
                                       FILTRATION PROCESS


                                       Mechanisms

                                       Filter fabrics normallyused to remove dust and
                                       fumes from airstreams are usually woven with
                                       relatively large open spaces, sometimes 100 mi-
                                       crons or larger in size (Environmental Sciences
                                       and Engineering 1961 ; Drinker and Hatch, 1954;
                                       Spaite et al. , 1 961; and Stairmarid,  1956).  Since
                                       collection efficiencies for dust particles of 1 mi-
                                       cron or less may exceed 90 percent (Environmental
                                       Sciences and Engineering  1961), the filtering pro-
                                       cess obviously cannot be simple sieving.   Small
                                       particles are initially captured and retained on
                                       the fibers of the cloth by  means of interception,

-------
                                                     Baghouses
107
                         Table 33.   SCRUBBERS AND  OTHER WET COLLECTORS
                                             (Friedlander ctal., .1952)

Device
Wet cell washer
(a 9-element washer
consisting of 3 units
in series, each made
wet filter cells fol-
lowed by a dry elim-
inator pad)















(11)






Wet cell washer
(an 8-elernent washer.
Stage 1 has one coun-
ter-current13 followed
by one concurrent wet
cell. Stages 2 and 3
each have one roun-

r ur n an one
followed by a dry
eliminator pad)

(31)
Due on \o. S






(60)







(63)
Cyclone scrubber




(62)

Centri-merge
(62)
Multi-wash
(62)

Manufacturer
Buffalo I orge Co




























Buffalo Forge Co











Due on Co







ment Co.







Pease Anthony Lquip-
ment Co





SchmiejJ Industries,
Inc.
Claude B Schneible

I ebt aerosol
\'ormal air












Dust ( ompos. d
of sph, r.s 01
cr,ppi r sultatc













Dust '. ompofat d
o' UO, spheres










Dust from stone
and sand-drying
kiln





su"lfuri( acid
plant

SiCv from silicon
or< furnaie
Iron oxide fume
from open hearth
furnace (oxygen
lanced)
Lime dust from
lime kiln

Iron ore and coke
dust from blast
furnace

Na^CO} fume

Foundry dust
Inlet
concentration
0 2 to 0. 5
grain /1,000ft3











1 to 2
;r (mass
i-mdian)














0.8 (mass
mi dun)










1 ^









0. 01 to 0 3=i

0. 02 to 0. S



2. 0 to 40. 0


0. 5 to 20. 0





< IS
Efficiency,

= 7



t,s



( 7




ffO


r>2
<4





C umula'i,e
I 111! 11 -1 V
s'.lu, s
1 2


20 7" -,()




13 74 SU






74
(weight)








46. 7

92 to 9(i
(weight)


99


99
(weight)


96. 2
(rount)
sa. (*
(< uunt)
Ri sistance
H2°
0 1 "' to 0 2H
(pt r* p-.ris wert 2 in
^uk and , om-
nn-, d ol 10-M.
ib. rs packed
'i i lb/tt^
'• t 1 t , Us v., reB in
1 uk ,!•,
-------
108
AIR  POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
SHAKER
MECHANISM
OUTLET
PIPE
INLET
PIPE
DUSTY AIR
SIDE
                                            HOPPER
     Figure 64.  Typical  simple baghouse with
     mechanical shaking (Wheelabrator Corpora-
     tion, Mishawaka,  Indiana).
                                        impingement,  diffusion, gravitational settling,
                                        and electrostatic attraction.  Once a mat or cake
                                        of dust is accumulated,  further  collection is ac-
                                        complished by sieving as -well as by the previous-
                                        ly mentioned mechanisms.  The cloth then serves
                                        mainly as a supporting structure for the dust mat
                                        responsible for the high collection efficiency.  Per-
                                        iodically the accumulated  dust is removed for dis-
                                        posal.  Some residual dust remains and serves  as
                                        an aid to further  filtering.


                                        Direct interception

                                        Under conditions normally existing in air filtra-
                                        tion the flow is almost always laminar (Drinker
                                        and Hatch,  1954;Hemeon,  1955; Rodebush,  1950;
                                        and Underwood,  1962).  For conditions  of laminar
                                        flow, a small  inertialess particle will remain on
                                        a single streamline.   If the streamline passes
                                        close to an obstruction,  such as a fiber of the fil-
                                        ter fabric,  and within a distance equal to the radi-
                                        us of the particle, the particle will contact the ob-
                                        struction and will adhere because of the van der
                                        Waals forces.  While  no real particle is complete-
                                        ly inertialess,  small particles of 1 micron or less
                                        maybe considered,  without serious error, inertia-
                                        less (Rodebush,  1950).

                                        The shape of the  streamlines is not affected by the
                                        air stream velocity in  laminar flow, so that collec-
                                        tion by direct  interception is independent of veloc-
   SHAKER
 WALKWAY
              AIR REVERSAL
              VALVE
                                    INSPECTION
                                    DOOR
   SCREW
   CONVEYOR
                                                 T~t
                                                               _£•
                                                                   CLEAN AIR MANIFOLD
                                                                                  CLEAN AIR
                                                                                  TO FAN
                                        n
                                               '   i
                                               i   i
                                               i—i
r'l
!   I
i—i
                                                                          J.J.L-J.
i  i
i  i
L.J

                                                                             rr
                                                   T
                                                      DISCHARGE
                                                                  INSPECTION
                                                                  DOOR
                                                                                 SCRE» CONVEYOR
                                                                          n
    Figure 65.  Fully automatic,  compartmented baghouse with hopper  discharge  screw conveyor  (Northern
    Blower division,  Buell Engineering Company,  Inc.,  Cleveland,  Ohio).

-------
                                         Baghouses
                                                                                                   109

                                      CLEAN
                                     _ AIR
                                      TO FAN
                   CIEANI Nli" ' ' Ai R
                   FROM ATMOSPHERE
Figure 66.   Envelope-type baghouse with
automatic reverse-air  cleaning  ( W. W.
Sly Manufacturing Company, Cleveland,
Ohio).
ity.  The size of the obstruction is important since
streamlines pass closer to small  obstructions than
they do to larger  ones  (Rodebush,  1950).   Large
particles are also collected more  easily since the
streamline  need not pass as close, in the case of
a larger particle,  for the particle to contact the
collecting surface.  As the particle size increases,
however, inertial forces rapidly increase and pre-
dominate (Ranz, 1951).

Impingement

When a particle has an appreciable inertia,  it will
not follow a. streamline when the streamline is de-
flected from a  straight path as it approaches an
obstruction. Whether  or not the particle contacts
the surface of the obstruction depends upon the
size of the  obstruction and the size and  inertia of
the particle.  As  in the case of direct interception,
smaller obstructions are more effective collectors
for the mechanism of impingement or impaction
and for the  same  reason.  Other factors being equal,
a particle with greater inertia is more likely to
strike a collecting surface.

The inertia of a particle may be measured by its
so-called stopping distance.   This is the distance
that the particle would travel before  coming to
rest if the streamline were to turn abruptly at
90 degrees.
                                                                 Impaction is not a significant factor in
                                                                 collecting particles  of 1 micron di-
                                                                 ameter or less.  It is generally con-
                                                                 sidered significant for collecting parti-
                                                                 cles  of 2-microns diameter or larger
                                                                 (Rose et al. , 1958) and becomes  the
                                                                 predominant factor as particle  size
                                                                 increases (Rodebush,  1950).

                                                                 For  effective collection of particles
                                                                 by inertial forces, the direction  of
                                                                 the aerosol stream must change
                                                                 abruptly within a distance from the
                                                                 collector or obstacle approximate-
                                                                 ly equal to or less than the stopping
                                                                 distance (Ranz, 1951).  Effectively,
                                                                 this  requires a collector with a di-
                                                                 mension perpendicular to the aero-
                                                                 sol stream  of the same magnitude
                                                                 as the stopping distance (Ranz,  1951).
                                                                 Theoretical considerations indicate
                                                                 that  the collection efficiency  for a
                                                                 given size particle decreases as  the
                                                                 collector size increases.  Observa-
                                                                 tions have shown that large fibers
                                                                 do not collect small particles 'well.
                                                                 In fact,  for  a given size fiber and
                                                   Figure  67.   Reverse-jet baghouse (Western Pre-
                                                   cipitation  Corporation, Los Angelas,  Calif.).

-------
110
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
airstream velocity, there is a minimum, par-
ticle size below which virtually no collection
by inertial forces occurs (Ranz,  1951).  On
the other hand,  as fibers are made smaller,
collection continues to improve down to the
practical limits of fiber size (Rodebush,  1950).
The velocity of the airstream is important in im-
paction.   Collection efficiency increases with in-
creasing velocity since the stopping distance also
increases with velocity.  The underlying assump-
tion is that the particle velocity is the same  as
that of the airstream, which is approximately true.
If the velocity becomes excessive, however, the
drag forces increase rapidly and may exceed the
adhesive forces so that collected particles are
blown off and collection efficiency decreases.

The fibers of filter fabrics are in general rela-
tively large compared with the size of the parti-
cles to be  collected.  Fibers of cotton and wool,
for example, are about 10 to 20 microns in di-
ameter (Rodebush, 1950).  Fibers such as these
are too large to be effective collectors for parti-
cles a few microns or less in diameter.  Collec-
tion efficiency for fine  dusts and fumes can,  there-
fore,  be expected to be poor until a dust mat is
built up on the filter fabric.  This has been veri-
fied by many field observations.  For a short
time after new bags are installed or immediately
after the bags have been thoroughly cleaned,
visible emissions bleed through the fabric.   In
most cases,  bleeding ceases in a few seconds or
several minutes  at the  most (Rose et al. , 1958).
In some  cases where bleeding has been a problem
after each cleaning cycle, reducing the cleaning
effectiveness has been  found helpful.

Filter fabrics are sometimes woven from a  mix-
ture of asbestos  and wool fibers to take advantage
of the smaller diameter of the asbestos fibers and
to improve collection efficiency on fine dusts and
metallurgical fumes  (Rodebush, 1950).  Another
method reported successful is the use of a rela-
tively coarse dust as a precoat on the filter, which
then becomes highly  efficient on very fine dusts
and fumes (Drinker and Hatch, 1954).

Diffusion

When particles are very small,  of a dimension
about equal to the intermolecular distance,  or
less than about 0.1 to 0.2 micron in diameter,
diffusion becomes the predominant mechanism of
deposition.  Particles as  small as these no longer
follow the streamlines because collisions with gas
molecules occur, resulting in a random Brownian
motion that increases the chance of contact be-
tween the particles and the collecting surfaces.
Once a few particles are collected,  a concentra-
tion gradient is established that acts as a driving
force to increase the rate of deposition (Drinker
and Hatch,  1954).  Lower air velocity increases
                                       efficiency by increasing the time available and
                                       hence the chance of contacting a collecting sur-
                                       face.  Smaller collectors or obstructions also
                                       increase collection efficiency (Ranz,  1951).

                                       Electrostatics

                                       While electrostatics undoubtedly plays a role in
                                       the capture and retention of dust particles by a
                                       fabric filter, the evidence is inadequate to eval-
                                       uate this mechanism quantitatively.  Accord-
                                       ing to Frederick (1961), electrostatics not only
                                       may assist filtration by providing an attractive
                                       force between the dust and  fabric, but also may
                                       affect particle  agglomeration,  fabric  cleanability,
                                       and collection efficiency.  He attributes the  gen-
                                       eration  of charge to frictional effects, stating
                                       that the polarity, charge intensity,  and charge
                                       dissipation rate of both the dust and filter media,
                                       and their relation to  each other can enhance  or
                                       hinder the filtering process.  He cites qualita-
                                       tive differences only.  For example,  fabric  A
                                       may be  better than fabric B on dust X,  while
                                       fabric B is better than A on dust Y.  He gives
                                       a "triboelectric" series for a number  of filter
                                       fabrics  that may be useful as a guide  to selecting
                                       fabrics  -with desirable electrostatic properties.
                                       This  is  a fertile field for further investigations.

                                       Until  more information is  available, the relative
                                       importance of electrostatics in determining  the
                                       best filter fabric for a particular installation
                                       cannot be evaluated.   Certainly, however, if one
                                       fabric does not work effectively,  other fabrics
                                       should be tried regardless  of whether  the dif-
                                       ficulty is caused by the electrostatic properties
                                       or the physical characteristics.
                                       B ag house  Resistance

                                       Clean cloth resistance

                                       The resistance to airflow offered by clean filter
                                       cloth is determined by the fibers of the cloth and
                                       the manner in which they are woven together.  Ob-
                                       viously a tight weave offers more resistance than
                                       a loose weave at the same airflow rate.  Since the
                                       airflow is laminar, resistance will vary directly
                                       with airflow.  One of the characteristics of filter
                                       fabrics frequently specified is the Frazier or
                                       ASTM  permeability, which is  defined as the air
                                       volume, in cfm,  that will pass through a square
                                       foot of clean new cloth with a pressure differen-
                                       tial of  0. 50 inch WC.   The usual range of values
                                       varies from about 1 0 to  110 cfm per square  foot.
                                       The average airflow rate in use  for industrial
                                       filtration is about 3 cfm per  square foot, and the
                                       resistance of the clean cloth does not usually ex-
                                       ceed about 0. 10 inch WC; often it is much less.

-------
                                               Baghous cs
                                                                                                    111
 Resistance of dust mat

 Drinker and Hatch (1954), Hemeon (1955),  Mum-
 ford etal. (1940), Silverman (1950),  Williams et
 al.(1940), and others attempt to correlate the in-
 crease in resistance of the dust mat or the  com-
 bination of dust mat and filter fabric with the
 filtration velocity or filter ratio, gas viscosity
 and density,  dust concentration or absolute dust
 load,  elapsed time,  and dust characteristics such
 as particle size,  true specific gravity, a particle
 shape or specific surface factor, and a factor  for
 the percent of voids or the degree of packing.
 The equations may approach the problem from the
 theoretical point  of view,  building up relations
 from basic considerations, or they may be  com-
 pletely practical, ignoring entirely the mechan-
 isms involved and relating only the variables that
 may be measured most easily.   Regardless of
 the approach, in the final analysis a measurement
 must be made experimentally to determine  a pro-
 portionality constant or a "resistance  factor" for
 the particular dust  under consideration. One meth-
 od (Environmental Sciences and Engineering, 	)
 of  relating the variables follows:
            Up)
                rnat
k|J.d (1 - g)  V

      / V   *
   .3/
                                     (45)
 where

(Ap)
    mat
   k

   H-

   d

   £
=  pressure drop through 1  square foot of
   filtering area (force per  unit area),
   lb/ft2

=  a constant,  dimensionless

=  gas viscosity, Ib sec/ft

=  thickness  of the mat of dust particles, ft

=  fraction of voids in the mat of particles,
   dimensionless
   v     =  face velocity of the gas through the fab-
            ric,  ft/sec
   V
     "
         =  ratio of particle volume to particle sur-
            face, ft3/ft2.


                       K p  pg  6
 By substituting  k  =
 where
                            \ i  -  c
                                     (46)
    p     =  mass density of the particles, slugs

    p     =  mass density of the gas, slugs
                                                 g     =  acceleration of gravity, ft/sec

                                                 C    =  dimensional constant.
                                               and
                                                                d =
                                                                       G v t
                                                                     P  g (1 -£)
                                                                      P
                                                                                            (47)
                                               where
                                                  G    =  concentration of dust in the gas streams,
                                                          lb/ft3

                                                  t     =  elapsed time,  sec,

                                               it is possible to solve for (Apj.)mat, the pressure
                                               loss through the mat  of dust at the end of time
                                               period t.
                                                         Up )   ^   =  K
                                                            t mat
                                                                                 2
                                                                            P g v  t
                                             (48)
Values of K, the resistance coefficient, must be
determined experimentally.  In practice it is com-
mon to express the pressure drop in inches of water,
the dust  concentration in grains per cubic foot, the
face velocity in feet per minute, and the time in
minutes.   The dimensional constant C is  adjusted as
required for the actual units  used.

The.K values are usually determined by using a
scale model unit either in a laboratory or in the
field, though care must be exercised in applying
these results to a full-scale unit (Stephan  and
Walsh,  I960).   If a vertical bag is used,  elutria-
tion of particles may  occur,  and the  true value of
K may vary with time and position on the bag (En-
vironmental Sciences  and Engineering       ).  The
measured  value of K is an average value that may
not be the  same when the  scale  or configuration is
changed.   This is borne out by failure of some full-
scale units to function as anticipated from pilot
studies.

Williams et al. (1940) determined K values for a.
number of  dusts,  as shown in Table 34.  These
data were  obtained by laboratory experiments by
using an airflow of 2 cubic feet per minute through
0. 2 square foot of cloth area or a filtering velocity
of  10 feet per minute.  The tests were terminated
at  8 inches of water column,  maximum pressure
differential.  Resistance coefficients were calcu-
lated from the relationship
                                                                  7, 000 (h  - h )
                                                                  	f    i
                                                                     G t v
                                                                                                      (49)

-------
112
        AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
where

   Kl
=  resistance coefficient,  in. WC; per Ib
   of dust; per cloth area, ft^; per filter-
   ing velocity, fpm

=  final pressure drop across collected
   dust and filter cloth,  in.  WC
   h.     =  initial pressure drop across clean
    1        cloth, in.  WC

   G     =  dust loading, grains/ft

   t      =  elapsed time,  min

   v     =  filtering velocity,  fpm.

The pressure loss  through the collected dust mat
was found to increase uniformly with time,  indi-
cating a linear relationship between resistance
and the thickness of the accumulated dust mat.  The
data clearly show a trend  of increasing resistance
•with decreasing particle size.  The test dust for
the data on  particles 90 microns  or less in diame-
ter -was obtained by elutriation.   In a full-scale bag-
house,  particularly if relatively long vertical bags
are used, a substantial amount of elutriation can
be expected (Stephan etal., I960).  The dust-laden
gas usually enters  the filter bag at the bottom and
travels upward.  As the gas filters through the cloth,
the upward  velocity decreases so that only very
fine dust remains airborne to be  deposited on the
upper portion of the bag.  Since the actual pres-
sure  loss through the bag  must be the same through
all areas, the volume and filtering velocity through
some portions of the bag increase to excessively
high values.   Stephan and Walsh (I960) found that
local filtering velocities  vary by a factor of 4 or
more over a single filter bag.  This, in turn, may
lead to collapse or puncture of the filter cake
(Stephan  et al. , I960).  Punctures are small holes
in the dust mat.  They  are usually self-repairing
because  the increased  airflow through the small
area of low resistance  brings more  dust with it.
Collapse of the filter cake,  on  the other hand,
is a shift in cake structure to a more compacted
condition with a greater  resistance.  The collaps,e
may progress in several steps.

Both collapse and puncture of the filter cake are
phenomena  caused by excessive filtering veloci-
ties. Some dust may be surmised to be embed-
ded  in the interstices of the cloth when puncture
or collapse occur, so that normal cleaning will
not completely remove it.  This may lead to
"blinding, " which is  a  plugging of the fabric
pores to such an extent that the resistance be-
comes excessively high permanently.   Once it
starts, blinding tends to become worse rapid-
ly.  For  example,  Stephan (I960) found tran-
sient local filtering velocities of about  100 fpm
through areas of puncture -when the average
filtering  velocity was only 0. 75 fpm.  Further
evidence is cited by  Lemke et al. (I960) who
note that, for fumes  from galvanizing opera-
tions, filtering velocities must be kept below
approximately 2 feet per minute to avoid blind-
ing and cleaning difficulties.   When higher fil-
tering velocities  were employed, the residual
pressure loss aftjr cleaning  increased con-
tinuously from one cleaning cycle to the next
                  Table 34.  FILTER RESISTANCE COEFFICIENTS, Kj,  FOR CERTAIN
               INDUSTRIAL DUSTS ON CLOTH-TYPE AIR FILTERS (Williams et al. ,1940)
Dust
Granite
Foundry
Gypsum
Feldspar
Stone
Lampblack
Zinc oxide
Wood
Resin (cold)
Oats
Corn
KI, in. WC per Ib of dust per ft2 per minute of filtering velocity- -
for particle size less than
20 mesha
1. 58
0.62


0. 96




1. 58
0. 62
140 mesha
2.20
1.58






0.62


375 mesha

3.78
6. 30
6. 30






1.58
90 jib




6. 30


6. 30

9. 60
3.78
45 H>









11
8.80
20 \J.b
19.80

18. 90
27. 30




25.20


2^





47. 20
15.70C




             aCoarse.
             ^Less than 90 fj. or 45 fj., medium; less than 20 (i or 2 (j., fine; theoretical size of
              silica, no correction made for materials having other densities.
             cFlocculated material,  not dispersed; size actually larger.

-------
                                              Baghouses
                                                                                           113
until the volume was adversely affected.  The
fume in this case was largely ammonium
chloride.  With lower filtering velocities the
equipment functioned well.

Hemeon (1955) takes a more practical approach
to the evaluation of pressure loss in cloth fil-
tration.  He notes that the resistance of clean
new cloth can never again be attained once the
cloth has been used.  He takes, therefore, the
resistance  of the cloth-residual cake combina-
tion as the  basic cloth resistance.
                 R
                     =  K  V
                         o  f
                                  (50)
•where
   R    =  the basic cloth resistance,  in. WC
     o

   K    =  resistance factor, in.  WC/fpm

   V    =  the filtering velocity, fpm.
The magnitude of the factor Ko depends upon
the nature and quantity of dust that remains
lodged in the interstices of the cloth.  Thus,
it depends upon the effectiveness of the clean-
ing action as well as upon the dust and cloth
characteristics.  Values of Ko are listed in
Table 35.  The  removable dust mat contrib-
utes a varying resistance according to the
relationship
             Hemeon assumes that the basic dust resistance
             depends only upon the physical properties  of the
             dust.   Lunde and Lapple  (1957) claim, however,
             that the resistance coefficient of the dust cake
             also depends upon the fabric.  Too literal  an  ap-
             plication of these data and equations should not be
             attempted; rather they should  be used as a guide
             to be modified according to experience and the
             particular situation.

             Pring (1952) uses equation 49  to determine a
             number of resistance factors, Kg  as  shown in
             Table 37, which also lists typical  filtering veloc-
             ities for several dusts.

             Mumford  etal. (1940) investigated  the resistance
             of cotton filter cloth for coal dust.  They per-
             formed a  series of bench-scale, laboratory-
             type experiments using a minus-200-mesh coal
             dust.   The results confirmed a linear relation-
             ship between the resistance  and airflow rate
             when the dust loading was held constant.  As
             shown  in Figure 68, however, they report that
             the resistance varies with the 1. 5 power of the
             dust loading when the airflow rate is held con-
             stant.   Williams et al. (1940) and some other
             investigators  report that the resistance varies
             linearly "with dust loading.

             Campbell and Fullerton (1962) also report a non-
             linear  relationship bet-ween resistance and filter-
             ing velocity, as shown in Figures  69 and 70. These
        R   =  K  V  W  =
         a      a  i
                           Kn Q W
                             d
                                  (51)
where


   Rd

   Kd


   Vf

   W

   Q

   A
=  the basic  dust resistance, in.  WC

=  the resistance coefficient, in. WC/fpm/
   oz of dust/ft2

=  the filtering velocity,  fpm

=  dust loading, oz/ft

=  the air flow rate,  cfm
                         2
=  the total cloth area, ft .
Values  of the coefficient K^ are given in Table  36
for several different dusts and dust loadings. The
total pressure drop through the filter cloth may
then be calculated as the sum of the basic  cloth
resistance and the basic dust resistance.























•



>



'
0 02







y
/
/
^ /
/


/
/






/
/
/
/
/
/




0 04





/
/
/
f
/










/
f
/
/



/

/
/


f
'


/

'

t
*

/

/


' )
/ /
/ /
/
/



f







Fabric Cotton sateen 96 x 64 thread
with mixture of ammonium phos-
phate a nd bon c acid solution
tor flame proofing clean
cl oth permeabi 1 i ty 11 5 elm @
0 50 inch water
Dust Mi nus -200-mesh coal dust trom
ball mill
0 06 0 08 0 10 0 20
       R  =
      K  V   +  K  V  W
        of      d  f
(52)
              COAL DUST LOADING  Ib/ft2 FABRIC

Figure  68.   Pressure drop through cotton  sateen
cloth versus  coal dust  loading for different
filtering  velocities in a test unit (Mumford  et
al.,  1940).

-------
114
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
                      Table 35.   VALUES OF THE BASIC CLOTH RESISTANCE
                     FACTOR,  K0, OBSERVED IN SPECIFIED APPLICATIONS
                                           (Hemeon,  1955)
Type
of
dust
Cloth area,
ft2
K
o
                                         Flat, bag collectors
Stone-crushing operations
Stone-crushing operations
Stone-crushing operations



Stone-crushing operations
Stone-crushing operations
Svithetic abrasive crushing operations
Clay crushing in dry pan
250
250
500



2,250
9,000

500
0. 83
0. 49a
0. 83
0. 78
0. 75
0. 74
0. 79
1. 01
0. 80
1. 60
                                         Clean tube collectoL-s
Si one-crushing operations

Si one-crushing operations
Stone-crushing operations
Si one chiseling
Electric welding /ume
Iron cupola fumes
Foundry dust core knockout

Shot bla^t room ventilation


2, 150

4,300
1,500
400 to 1, 000
10
5,200

2, 350


Same- -pneumatic lift 950
Clay crushing in dry pan 500
0. 47
0.45
0. 60
3. 45
0. 37
0. 40
0. 17 to 0.27
0. 70
2, 50
0. 28
0. 25
0. 58
0. 63
0. 39
0. 39
0. 34,0. 36,0. 59
0. 60
                         as first operation but after installation of pneumatic vibrator.
data were obtained by venting a portion of the ef-
fluent from a direct-arc steel-melting furnace to
a pilot model baghouse  with glass fabric filtering
elements.  No effort was made to control or cor-
relate the dust loading with the pressure loss.

Caplan (1954) states that pressure loss is linear-
ly related to gas flow if, and only if, the absolute
amount of dust remains  constant when  the gas
flow rate is varied.  In practice this does some-
times happen.  The amount of  dust generated in
these  cases is independent of the ventilation rate.
Increasing the volume vented above that required
to ensure 100 percent capture  of emissions  does
not, therefore, increase the total amount of dust
carried to the baghouse.  In many cases,  how-
ever,  increasing the ventilation rate increases
the absolute amount of particulates,  though  the
increase  in emissions may be  less proportionate-
ly than the increase in gas rate.  Thus, the effect
                                      on the resistance of varying the filtering veloc-
                                      ity depends upon factors that may easily be over-
                                      looked or may be difficult to ascertain.
                                      If the grain loading (dust concentration in the gas
                                      stream in grains/ft^ as  distingxiished from abso-
                                      lute dust loading in Ib/min  ) remains constant,
                                      resistance is generally considered to vary as the
                                      filtering velocity squared (Environmental Sciences
                                      and Engineering      ).  The derivation of this
                                      relationship is from the  linear variation of resis-
                                      tance with changes  in volume when the absolute
                                      dust load remains constant combined with the
                                      linear variation of  resistance with changes in
                                      absolute dust loading when the volume remains
                                      constant.  The latter condition may be restated
                                      as a linear variation of resistance with changes
                                      in grain loading when the volume  remains con-
                                      stant.   If, however, the  grain loading remains

-------
                                               Baghouscs
                                                                                                   115
      Table 36.  VALUES OF BASIC DUST
    RESISTANCE FACTOR  (Kd)  OBSERVED
    ON SOME INDUSTRIAL INSTALLATIONS
                 (Hemeon,  1955)
Type of dust
Stone crushing (plant A)






Stone crushing (plant B)


Stone crushing (plant C)
Foundry, castings clean
Shot blasting


Pneumatic shot lift

Core knockout

Sandblasting (scale)
Cloth dust loading
(W),02/ft2
5
12
14
U
22
25
23
7
8
8
1

0. 2
0. 3
1. 3
0. 2
2. 4
0. 2
0. 1
7
Kd
0. 18
0. 12
0. 08
0. 12
0. 11
0. 02
0. 07
0. 16
0. 10
0. 08
0. 82

0. 82
0. 25
0. 25
0.66
0. 40
0. 55
0.68
0. 20
Table 37.  TYPICAL RESISTANCE FACTORS (K2)
   AND  COMMON FILTERING VELOCITIES (V)
 FOR SELECTED UNSIZED DUSTS (Pring,  1952)
Dust
Nut shell dust
Asbestos
Titanium dioxide

White lead
Copper powder
Tobacco
Carbon black
Bismuth and cadmium
Insulating brick
Calcimine
Cement
Clay
Flour
Glass sand
Milk powder
Mixed pigments
Soap
Wood flour
Cloth
Cotton sateen
Napped orlon
Cotton sateen
E-Z1 wool
C- 1 1 .lylon
E-21 wool
Napped vinyon
Cotton sateen
Napped orlon
Cotton sateen






Resistance,
factor (K)
0.2
2. 13
94 to 206
34. 6 to 70
47 to 104
32. 2
5. 1 to 10. 6
36
22. 4 to 28. 2
2. 7






Velocity
(V),fpm





1. 5
6 to 8
4
2.6
1. 5 to 2. 7
2.9
2. 7 to 3. 0
1. 2
4. 5
2. 3 to 2.9
1.6 to 3. 1
2. 8 to 4. 8
constant and the volume is increased, then
the absolute dust load must increase.  The
result is that, for a constant grain loading,  re-
sistance varies as the square of the volume or
filtering velocity (Brief et al.,  1956).

Silverman (1950) states that, not-withstanding
the theoretical equations, an exponential re-
lationship  exists in practice and that this has
been verified by Bloomfield and DallaValle.
   1234
           FILTER  RATIO, cfm gas/ft2 fabric

   Figure  69.  Pressure drop versus filter ratio
   for fabrics on 60-mmute  cleaning cycle (Camp-
   bell  and Fullerton, 1962).  A and C are sili-
   conized glass fabrics,  B  is a siliconized
   Dacron  fabric.

 The observation by Stephanet al., (I960) that
 filter resistance  coefficients  actually vary
 with time also supports an exponential rela-
 tionship since the coefficients are based up-
 on an assumed linearity.


 Effect of resistance on design

 In an actual installation the resistance of the
 cloth filter and dust cake  cannot be divorced
 from the  total exhaust system.   The operating
 characteristics of the exhaust blower  and the
 duct resistance will determine the -way in-
 creases in baghouse resistance affect the gas
 rate.  If the blower characteristic curve is
 steep, the gas flow  rate may be reduced  only
 slightly when the  resistance of the filter  bags
 changes markedly.   This  occurs because, as
 the volume decreases slightly, the pressure
 delivered by the blower increases proportion-
 ately more, while the duct resistance de-
 creases,  partially offsetting the  increase in
 resistance of the  filter cloth.  Some varia-
tion in resistance and air  volume must normal-
ly occur,  however,  in all  baghouse  installa-
tions,  even in the Hersey  type to be discussed
later.   Proper design requires the volume to
 234-767 O - 77 - 10

-------
116
               AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER

                                        90  m i n
                                        30  mi n
     I          2          3          4          E
         FILTER RATIO,  cfm gas/ft2  fabric
   Figure 70.   Pressure drop versus  filter  ratio
   for  glass  fabric at various cleaning cycles
   (Campbell  and Fullerton, 1962).
be adequate to capture the emissions at the
source when the system resistance is a max-
imum and the gas volume a minimum.   At
the same time, the filter  ratio must not be
excessive immediately after cleaning -when
the system resistance is a minimum and the
gas volume a maximum.
Selecting or designing a baghouse requires
the following initial steps:
1. The minimum volume to be vented from
   the basic equipment must be determined
   according to the principles set forth else-
   where in this manual.

2. A maximum desirable baghouse  resistance
   must be estimated.

3. The blower  operating point is  selected to
   provide the  minimum required volume at
   the maximum baghouse  resistance.

4. A minimum baghouse resistance is esti-
   mated for the condition immediately after
   the filter bags are  thoroughly  cleaned.

5. A second operating point on the blower charac-
   teristic curve is  determined for the  clean bag
   condition.
6. The minimum filtering area required is de-
   termined by the maximum filtering velocity
   permissible for the particular dust or fume
   being collected.

7. The calculations are re checked, with  the fil-
   tering area thus determined to ensure com-
   patibility.

The most common deficiency in selecting and
designing baghouses  and exhaust systems is
failure to take into consideration the normal
variation in  air volume.  The proper design
approach requires that the two extreme con-
ditions be considered separately rather than
on the basis of the average,  because on the
average,  conditions  are not average.
 Filtering  Velocity

Filtering velocity or filter ratio is defined as
the ratio  of gas.filtered in cubic feet per min-
ute to the area of the filtering media in square
feet.  The units  of filter ratio are, therefore,
cfm/ft  .  By cancelling, the units of filter
ratio are reduced to feet per minute,  and in
this form it  is often referred to as filtering
velocity.  Physically, filter ratio,  or filter-
ing velocity, represents the average velocity
with which the gas passes through the cloth
•without regard to the fact that much of the
area  is occupied by the  fibers from which the
cloth is -woven.   For this  reason, the term
"superficial  face velocity" is often used.  Fil-
tering velocity is an important factor in fil-
tration.   Too high a filter ratio results in
excessive pressure loss,  reduced collection
efficiency, blinding, and rapid wear.  Silver-
man (1950) recommends values of filtering
velocity from 0. 5 to 5. 0 fpm with an average
of 3. 0 for common dusts.  He states, how-
ever, that the velocity should be maintained
below 0. 5 fpm for fumes that tend to plug
fabrics.  Watts and Higgins (1962) report that,
for control of emissions from brass  smelter
operations, their experience indicates that
the filter  ratio must be  1. 0 to 1.5 fpm or
even less when  spun Orion filter bags are used.
Adams  (1964) recommends a maximum filter
ratio of 2. 0 for fumes from direct-arc steel-
melting furnaces with glass bags,  or 3. 0 if
Orion bags are used.  He estimates that  aver-
age bag life under these conditions  is 18 months
for the glass and 5 years for the Orion.  These
life figures generally appear to be too optimis-
tic in the  case of the Orion and slightly pessi-
mistic in  the case of the glass fiber bag.
Spaiteetal. (1961) recommend filter  ratios of
1. 5 to 2. 0 fpm when glass  cloth is used at high
temperature  compared to 3. 0 fpm average
practice for  low temperature filters.  Drinker

-------
                                             Baghouses
                                                    117
and Hatch (1954) also cite 3.0 as a design fil-
ter ratio for typical dust and average concen-
trations.  Stairmand (1956) gives a range of
1 to 6 feet per minute for normal fabric fil-
ters in actual practice but emphasizes the need
to operate with low filtering velocities since
higher velocities lead to compaction  resulting
in excessive pressure drop or to breakdown of
the dust cake,  which in turn results in reduced
collection efficiency.  Roseetal. (1958) observe
that filter ratios range from  1 to 6 cubic feet per
minute per  square  foot of cloth area in practice
with 3. 0 as  a common standard for normal dusts.
For metallurgical  fumes, however, he recom-
mends that  the filter ratio not exceed 1/2 to n
        cubic foot per minute per square foot of cloth
        area.  Brief et  al.  (1956) describe  successful
        baghouse installations serving direct-arc elec-
        tric steel-melting furnaces using Orion bags at
        filter ratios  of  1.91 and  1.79.
        Clement (1961) emphasizes that the filter ratio can-
          it be too low from an operational viewpoint.
        This is in conflict, however, 'with economic con-
        siderations,  which tend to prevent overdesign.
        His recommended maximum filter ratios for
        various dusts are shown in Table 38.  These
        values represent a compromise that experience
        has shown optimum for minimizing total cost
  Table 38.  RECOMMENDED MAXIMUM FILTERING VELOCITIES AND MINIMUM DUST-CONVEYING
                   VELOCITIES FOR VARIOUS DUSTS A.ND FUMES  (Clement, 1961)


Dust or fume


Alumina
Aluminum oxide
Abrasives
Asbestos
Buffing wheels
Bauxite
Baking powder
Bronze powder
Brunswick clay
Carbon
Coke
Charcoal
Cocoa
Chocolate
Cork
Ceramics
Clay
Chrome ore
Cotton
Cosmetics
Cleanser
Feeds and grain
Feldspar
Fertilizer
(bagging)
Fertilizer
(cooler, dryer)
Flour
Flint
Glass
Granite
Gyp sum
Graphite
-- 	 	 	 _,
Maximum
filtering
velocity,
cfm/ft2
cloth area
2. 25
2
3
2.75
3to3.25
2. 50
2.25to2.50
2
2. 25
2
2. 25
2. 25
2. 25
2. 25
3
2.50
2. 25
2. 50
3. 50
2
2. 25
3. 25
2. 50

2.40

2
2. 50
2. 50
2. 50
2. 50
2.50
2


Branch pipe
velocity,
fpm

4, 500c'f
4, 500
4, 500
3, 500 to 4, 000
3, 500 to 4, 000°'or d'b
4, 500
4, 000 to 4, 500
5, 000
4, 000 to 4, 500
4, 000 to 4, 500
4,000 to 4,500a'8'h
4, 500a« g»h
4, 000a> e, g,h
4, 000a'e'g'h
3,000 to 3,500a'b'f
4, 000 to 4, 500
4,000 to 4, 500
5, 000
3, 500a> b> c-f
4, 000
4, 000a-b> 8
3, 500a>h
4, 000 to 4, 500

4, 000

4, 500
3, 500a.h
4, 500
4,000 to 4,500
4, 500
4, 000
4, 500



Dust or fume


Iron ore
Iron oxide
Lampblack
Leather
Cement
crushing
Grinding (sep-
arators, cool-
ing, eic)
Conveying
Packers
Batch spouts
Limestone
Lead o>:ide
Lime
Manganese
Marble
Mica
Oyster shell
Paint pigments
Paper
Plastics
Quartz
Rock
Sanders
Silica
Soap
Starch
Sagar
Soapstone
Talc
Tobacco
Wood
Maximum
filtering
velocity,
cfm/ft2
cloth area
2
2
2
3. 50

1. 50


2. 25
2. 50
2. 75
3
2.75
2. 25
1
L-,
2. 25
3
2. 25
3
2
3. 50
2, 50
2,75
3.25
3. 25
2. 75
2.25
2. 25
2.25
2.25
2. 25
3. 50
3. 50


Branch pipe
velocity,
fpm

4, 500 to 5, 000
4, 500
4, 500
3, 500c»f

4, 500°' i


4, 000
4, 000
4, 000
4,000
4, 500
4, 500
4, 000
5, 000
4, 500
4, 000
4, 500
4, 000.
3, 5001"
4, 500a
4, 500
4, 500
4, 500b'd
4, 500
3, 500a. b
3, 500a> b
4, 000a
4, 000
4, 000
3,500a.-b>1-'
3, SOQa.f

   aPressure relief.  bFlame-retardant cloth
   eSprinklers.  fSpecial hoppers,  gates,  and
   1Insulate  casing.
  cCyclone-type precleaner.  "Spark arrester.
valves.  ^Grounded bags.  ^Special electricals.

-------
118
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
when both maintenance and capital outlay are
considered.

Maximum recommended filter ratios should be
used as a guide only.  Actual design values may
need to be reduced if grain loading is high or
particle size  small, especially if the range of
particle sizes is also narrow as  in a metallur-
gical fume.  When compartmented baghouses
are  used, the design filter ratio  must  be based
upon the available filter  area remaining with one
or two compartments  offstream for cleaning or
servicing.  Conventional baghouses for metallur-
gical fumes should in general be operated with
filtering velocities in the range of 1. 5 to 2. 0.  In
some cases,  however, such  as lead fumes, the
experience  of the Los Angeles County Air Pol-
lution Control District indicates  that filter ratios
must not exceed 1. 0 and even less is recom-
mended.  The values listed in Table 38 may be
used as  a guide for other dusts.


Filtering  Media

The filtering  media selected for  use in a baghouse
must be compatible with the  temperature and pH
of the effluent. Maximum permissible tempera-
tures and chemical resistance are listed in Table
39 for the various fibers normally used for fil-
ter media in dust collectors.  Each type of fiber
is also available in a wide range of cloth specifi-
cations, as illustrated by the data in Table 40,
which lists  specifications for only a few glass
fabrics.
 Fibers

 Cotton
 Cotton  has been for  many  years the standard
 fiber for filter fabrics for common dusts.  It
 is inexpensive, readily available, an effective
 filter media,  and durable as long as the tempera-
 ture is not excessive  and no acid  or strong alkali
      Table 39.  SUMMARY OF DATA ON
     THE COMMON FILTER MEDIA USED IN
           INDUSTRIAL BAGHOUSES


Maximum temperatiire
at baghouse inlet
Chemical
resistance
T^ ,_ . j for continuous duty



Cotton
Dynel
Wool
Nylon
Orion
Dacron
Glass
Summary of
published data.
"F
160 to 190
150 to 180
180 to 235
Recommended
maximum,
°F

Acid

180 Poor
175 , Good
220 , Good
200 to 290 J 220
200 to 350
250 to 350
500 to 700
275
275
550
Good
Good
Excellent
Excellent

Alkali

Fair
Good
Poor
Poor
Fair
Good
Excellent
                                       is present.   For applications such as abrasive
                                       blasting,  rock crushing,  and conveying, cotton
                                       will probably continue to be the favored choice
                                       for many years.

                                       Wool

                                       Before the development of the variety of synthetics
                                       now available, wool was the only choice when the
                                       temperature was around 200°F or an acid condition
                                       was present.  Wool or a wool asbestos mixture is
                                       still used in many metallurgical operations such as
                                       secondary lead smelters though it has been sup-
                                       planted to a great extent by Dacr on.  In felted form,
                                       wool has been the standard fabric for use inHersey-
                                       type reverse-jet baghouses.

                                       Nylon

                                       Nylon is a synthetic, organic fiber  originally
                                       developed by E.I. du Pont  de Nemours and Com-
                                       pany and now produced by du Pont and other
                                       manufacturers.  It is available in both  staple and
                                       filament form.  Nylon is  relatively high in initial
                                       cost,  but it has many desirable physical proper-
                                       ties.  It has  excellent resistance to  abrasion
                                       and flexing,  toughness  and elasticity,  and  resis-
                                       tance  to many chemicals  (Filter Fabric Facts,
                                       1954).  Its heat resistance is not,  however,  as
                                       good as that  of Orion and Dacron.   Because  of
                                       the slick surface, the filter cake may be removed
                                       with a minimum of cleaning action.  Nylon,  how-
                                       ever,  is  rarely used in baghouses,  because  other
                                       synthetic fiber fabrics have higher heat resis-
                                       tances and, in general, are equivalent  in regard
                                       to other properties.

                                       Dynel

                                       Acrylic fibers  generally have low  moisture
                                       absorption,  good strength, resilience, and
                                       resistance to many chemicals and destructive
                                       organisms such as mildew and bacteria.  An
                                       early acrylic-type fiber used for filter cloth •was
                                       Union Carbide and Carbon  Corporation's Vinyon N,
                                       a filament yarn.  Vinyon N, a copolymer of an
                                       acrylonitrile and vinyl chloride, was a modifica-
                                       tion of the original Vinyon  CF, which was  a  copoly-
                                       mer of vinyl chloride and vinyl acetate. A modi-
                                       fied version  of this fiber  in staple form is now
                                       marketed under the name Dynel.  Dynel has high
                                       chemical resistance, particularly to strong  alka-
                                       lies and acids,  and will not support  combustion
                                       (Filter Fabric Facts,  1954).

                                       Orion and Dacron

                                       Du Font's Orion,  the  first of the  100 percent
                                       acrylics,  is  produced only in the  staple form
                                       at  the present  time.   Originally  both filament
                                       and staple  forms  were available,   but du Pont
                                       discontinued  manufacture  of  filament  Orion
                                       about 1957.  Orion is light, strong, and resilient;
                                       it has good heat resistance and excellent chemical
                                       resistance,  especially to acids (Filter  Fabric Facts

-------
                                               Baghouses
                                             119
                 Table 40.  TYPICAL SPECIFICATIONS FOR GLASS FILTER FABRICS
Fabric number
Average permeability
Mullen burst strength
(Avg PSI)
Weight, oz per yd
Thread count
Weave
Warp yarn
Fill yarn
501
17
588
9.36
54 x 52
Crowfoot
150's 1/2
ISO's 1/2
502
12
593
9. 50
54 x 54
Crowfoot
150's 1/2
150's 1/2
600
81
485
8.27
64 x 34
3 x J Twill
150's 1/0
Bulked 1/4
601
75
595
10. 00
54 x 30
3 x 1 Twill
150's 1/2
Bulked 1/4
604
60
555
12. 50
42 x 30
3 x 1 Twill
150's 2/2
Bulked 1/4
300
45 to 60
400
16. 30
48 x 22
2x2
Reverse
twill
150's 2/2
31/2 Staple
300A
30 to 40
450
17. 67
48 x 24
2x2
Reverse
twill
150's 2/2
31/2 Staple
313A
33
540
13. 50
34 x 42
Crowfoot
150's 2/2
Bulked 1/4
  From: Menardi and Co. Bulletin
1954).  At the time du Pont discontinued manufac-
turing filament  Orion, Dacron was readily avail-
able.  Since Dacron could be obtained in filament-
type yarn, felt by many to be superior to staple
yarn in cleanability,  many users  switched to Da-
cron at that time.  Dacron, with similar physical
and  chemical resistance properties,  was also less
expensive  than Orion.

Teflon

An experimental tetrafluoroethylene  fiber, Teflon,
has  been produced by du Pont but has received
only limited use in air filtration.  It  has exception-
al heat and chemical resistance but is also expen-
sive (Filter  Fabric Facts,  1954). A  Teflon-Orion
mixture called HT1 is used when fluorides are
present in the effluent in significant quantity.

Glass

Of all  materials available for filtration, glass
fabrics have the highest resistance to high tem-
peratures  and all chemicals (except fluorine).
Its physical weakness, however, particularly its
low  abrasion and crushing resistance, requires
special precautions and design features.   Care
must be taken to avoid damage by crushing in
packing, shipping, and storing (Underwood,  1962).
Vigorous shaking must be avoided, though gentle
shaking with a period of about 50 cycles per min-
ute and amplitude about 5 percent of the bag length
is effective. The filtering  velocity recommended,
to avoid blinding, is usually less than for  other
fabrics on the same dust,  since a more gentle
cleaning action  is required.

Yarn

The characteristics of the filter cloth depend not
only on the material  of -which the yarn is  con-
structed, but also upon the construction of the
yarn,  that is, v/eave, count,  finish,  and so forth.
Filament yarns

Filament yarns, available only in synthetic fibers,
are manufactured by extruding the material through
a perforated nozzle or spinneret.  Individual  fila-
ments may be twisted together to  form a multi-
filament yarn.   Filament yarns have a greater  ten-
sile  strength in relation to bulk and  weight than
staple fiber yarns do.  In addition, they have a
slicker surface (Filter Fabric Facts, 1954).

Staple yarns

Staple yarns of  synthetic fibers are  produced in
a similar manner, except that the filaments are
finer and shorter.  One method of producing
staple fibers is to strike the filaments with a
blast of compressed air as they emerge from the
spinneret.  The staple fibers are then caught on a
revolving drum from which they are gathered and
spun into a staple yarn.  A variation of this pro-
cess is the production of a bulked filament.   The
bulked or textured filament is produced by using
compressed air to rough up the surface of the
filament as it is extruded from the spinneret
(Marzocchi et al. , 1962).

Cotton staple fibers are cleaned and drawn into
parallel order by carding and other  operations
and are  eventually twisted into yarns by a spin-
ning process.   Synthetic staple yarns are spun
in much the same manner.  The properties of
spun yarn depend upon the amount of twist in spin-
ning.  A highly twisted yarn tends to resist pene-
tration of particles into the interstices of the yarn
(Filter Fabric Facts. 1954).

Classification of yarns is different between cottons
and synthetics.  In the cotton system, which  is
used for spun yarns, yarns are measured in  hanks
of 840 yards,  and the yarn classification is the
number of hanks to the pound.  Cotton yarns  clas-
sified  as  20's are, therefore, only half the  weight

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 120
AIR POLLUTION CONTROL EQUIPMENT FOR  PARTICULATE MATTER
of 10's.  Filament yarns,  on the other hand, are
classified in the European denier system.   This
system,  which originated with the old 450-meter
silk skein in 5/100 gram units, has a higher denier
to denote a heavier yarn.  To convert, divide 5, 315
by the cotton yarn number to determine the filament
yarn denier (Filter Fabric Facts,  1954).

Weave

While the yarn and count are important,  the weave
Is also an important basic element in the construc-
tion and  should not be neglected.   There are three
basic variances of weave:  Plain, twill,  and satin.
The differences are the result of different  systems
used in interlacing the lengthwise warp yarns -with
the crosswise filling yarns.

Plain weave
The plain weave has a simple one up and one down
construction.  It permits maximum yarn interlacing
per square inch and,  in a tight weave,  affords high
impermeability.  If the count is lowered, this weave
may be made as open and porous as desired.  The
plain weave is common in certain cotton ducks and
many synthetic constructions (Filter Fabric Facts,
1954).

Twill weave
The twill weave may be recognized by the sharp
diagonal  twill line formed by the passage of a -warp
yarn over two or more filling yarns, the interlacing
moving one pick forward with each warp.  In equiva-
lent constructions, twills have fewer interlacings
than the  plain weave and, hence, greater porosity,
though this naturally depends on the count.  Cotton
and synthetic filter twills are widely used (Filter
Fabric Facts,  1954).

Satin weave
The satin weave, with even fewer interlacings
spaced widely but regularly,  provides  smooth
surface and increased porosity.   These qualities
make them particularly valuable in gaseous filtra-
tion such as dust collection.  Cotton fabrics in
this weave are commonly known as sateens. Cotton
sateen is probably more widely used than any other
fabric in baghouses for use at ambient temperature
(Filter Fabric Facts,  1954).

 Finish

Dimensional stability is an important factor in fil-
ter fabrics.  Cotton and wool fabrics must be pre-
 shrunk.  Synthetics are generally given  a corre-
 sponding treatment called heat-setting.  This pro-
 cess  contributes to a more even balance of warp
and filling yarn tension, provides better surface
 smoothness, reduces yarn slippage, controls poros-
ity, and  virtually eliminates shrinkage,  provided
the fabric is not subsequently exposed to exces-
 sive temperature.  The dimensional stability may
                                       be lost if the fabric is subjected to temperatures
                                       approaching that used in the original heat-setting
                                       process.  It is not unusual to observe bags that
                                       have been subjected to excessive temperature wit)
                                       shrinkage of 3 or 4 percent.  This amounts to ap<
                                       proximately 3 to 5 inches for a  6-inch-diameter
                                       bag  of average length.  As a result of the shrinka
                                       the bag may pull loose from its  connection to the
                                       floor plate or the upper support structure.  In
                                       some cases extensive damage to the baghouse str
                                       ture  has occurred as  a  result of shrinkage.

                                       Glass fabric bags are also given a treatment -with
                                       silicones derived from  phenylmethyl silanes or
                                       dimethyl silanes (Marzocchi et al. ,  1962). Glass
                                       ter fabrics may be constructed  of filament, sta-
                                       ple or bulked (texturized) yarns, or a combina-
                                       tion of these.  An organic size or binder is ap-
                                       plied to  the glass fiber  as it is extruded.  This
                                       later protects the fibers during  the manufactur-
                                       ing processes necessary to produce a fabric. Afte
                                       weaving, the fabric is given a heat treatment.  Du:
                                       ing this  treatment the organic size or binder is
                                       burned off, and subsequently the silicone is applie
                                       which serves as a lubricant to protect the individ-
                                       ual fibers from abrasion on each other.
                                       Glass fabric is woven from multifilament yarns.
                                       In one case investigated in Los  Angeles County,
                                       fumes from a  gray iron cupola were found de-
                                       posited among the fibers of the  yarn.  This  ef-
                                       fectively prevented relative motion of the individ-
                                       ual fibers when the cloth -was flexed.  The result
                                       was an apparent weakening of the cloth and a
                                       greatly reduced bag life.  This  is thought to be a
                                       result of the increased  stress in the outer fibers
                                       of each multifilament element because the yarn
                                       was forced to  bend as though it  •were a single sol-
                                       id fiber  instead of a bundle of individual fibers.
                                       Other factors  being equal, the maximum, stress
                                       introduced by  flexure is proportional to the  radi-
                                       us  of the fiber.   Washing the fabric -with -water
                                       and detergent  removed  the fume and restored
                                       the cloth to its original strength.  This illustrates
                                       the importance of using the silicone coating as a
                                       lubricant to permit the  individual fibers to slide
                                       upon one another as the cloth is flexed. Failure
                                       of the silicone coating to function as intended re-
                                       sults in  rapid  deterioration of the fabric.  Laun-
                                       dering glass filter bags periodically has become
                                       routine in a number of plants in  Los Angeles
                                       County.   A common practice is  to maintain  two
                                       complete sets of  bags.  One  set is laundered
                                       •while the second  is in use.   The bags usually last
                                       through  several launderings.

                                       Heat treatment relieves the stresses introduced
                                       into the  fibers because  of the processes to -which
                                       they  are  subjected during fabrication of the  yarn
                                       and cloth.  A  permanent set  is also put into the
                                       glass fibers as a result of the heat treatment

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                                              Baghouses
                                            121
(Marzocchi et al. ,  1962).  During the heat treating
process, glass fabrics may be subjected to tem-
peratures of from 700 to 1, 200°F.  It is not, however,
recommended that these fabrics be exposed to
such high temperatures  during use.  The most im-
portant reason for this is that the silicone coating
undergoes a gradual deterioration at temperatures
approximately greater than 500° F (Spaite et al. ,
1961).  The rate of deterioration of the silicones
increases with increasing temperatures.  Thus,
short periods of operation at temperatures of
600 to 700°F are permissible, but continuous oper-
ation at these temperatures  will materially short-
en the life of the fabric.  Tests  have shown that
increased life can be attained by an additional
treatment with graphite  (Spaite  et al., 1963).   At
present, the additional cost  of the graphite treat-
ment does not appear to be warranted for most
high-temperature operations, but additional de-
velopments in this  area  may produce a  superior
filter fabric for high-temperature operation.
Size and Shape  of  Filters

Diameters of tubular filtering elements

The most common shape of filter elements used
is a simple,  circular  cross-section tube.  Most
standard commercial  units employ tube diameters
of 5 or 6 inches.  Filter cloth is provided in sev-
eral standard -widths.   One common size is approx-
imately 38 or 39 inches wide.  Two 5- or 6-inch-
diameter bags  can be  obtained from a single
•width of cloth,  the necessary seam being allowed.
For high-temperature applications, an  11-1/2- or
12-inch-diameter glass fiber bag is most com-
monly  employed.  Again,  this is the most eco-
nomical size for the 38-inch-wide glass cloth that
is readily available.  A few baghouses are de-
signed for use  with 7- or 8-inch-diameter bags.
This size is probably  based upon a 54-inch-wide
cloth from which two  bags can be obtained from
a single width.   Wool  felts, which are used in
the Hersey reverse-air jet baghouses,  are gen-
erally either 9 or 10 or 20 inches in diameter.
In general,  bag diameters are determined main-
ly by the available widths  of yard goods.

The diameter of the filter bags used also influ-
ences  the size of the baghouse.  For example,
about  1, 750 square feet of filtering area can be
provided in about 80 square feet of floor area by
using 6-inch-diameter by 10-foot-long bags.  If
12-inch-diameter bags were  used instead, they
•would  need to be about 14 feet long to provide the
same filtering  area in the same floor space, though
12-inch-diameter bags can easily be made 20feet
long if there is  adequate head room.  This results
in a baghouse having about 2, 500 square feet of
filtering area in the same floor space.
Length of tubular bags

The length of cloth filter elements varies from
about 5 feet to approximately 30 feet. Most standard
baghouses employing 5- or 6-inch-diameter bags
use bag lengths from 5-1/2 feet to 10-1/2 feet.
The lengths for 11-1/2- or 12-inch-diameter bags
are generally about 15 to 25 feet.


Length-to-diameter ratio

Manufacturers have apparently not attempted to
establish a standard length-to-diameter  ratio.
Indeed, from a theoretical point of view, the
length-to-diameter ratio should have no  effect on
the collection efficiency of a bag except for the
influence of elutriation as previously discussed.
This ratio is, however,  important from  another
aspect.  Assume an extreme case of a 30-foot -
long and 5-inch-diameter bag.   When shaken,
such a bag will sway excessively.  This  could
easily result in one bag's rubbing upon the adja-
cent bag, which would be detrimental to  good bag
life.  Another  aspect of  the problem concerns the
cleaning of the bag by means of  shaking.   In order
to clean  the bags adequately, sufficient force must
be applied to break up the dust cake  and  dislodge
some of  the embedded dust from the fabric. Studies
have shown that, as the  force applied is  increased
(as measured by the acceleration given the bag by
the shaking mechanism), there is an increase in
the effectiveness of the cleaning up to a limiting
value (Walsh and Spaite,  1962).  The studies
have also shown that the  residual dust profile
varies along the length of the filter tube.  This
is a result both of the manner in which the shaking
force is  transmitted to the tube, and of the varia-
tion in dust cake properties.  The efficiency of
cleaning  by means  of mechanical shaking varies
depending upon the length-to-diameter ratio,
though the manner  of variation is not known.  Ob-
viously,  there is an optimum length-to-diameter
ratio that may differ  for different cloths, dusts,
shaking intensities,and shaking  frequencies
(Stephan  et al., I960).  Another  factor that effec-
tively limits  the length-to-diameter  ratio is the
difficulty of fabrication.   Sewing the longitudinal
seam becomes increasingly difficult as the length
of the bag increases.  Continuous tube weaving
could,  however,  be employed, if increased
lengths were advantageous.

Substantially more investigation is needed in this
field.  At present,  additional filtering area is
apparently frequently incorporated by increasing
the length of the filter tubes. When  the length
appears  to be unreasonably long or  if there is a
limitation on head room, then the number of
filter tubes is increased.

An absolute limiting length of 30 times the di-
ameter has been suggested by Silverman (1950),

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122
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
based upon some unspecified experiments in
metallurgical baghouses.  Some installations
using 11-1/2- or 12-inch-diameter bags operate
successfully with bag lengths up to about 30 feet.
These  are, however, exceptional instances,  and
a more practical limit appears to be about a 20-
to-1 length-to-diameter ratio.  Most 11-1/2-inch-
diameter bags in Los Angeles County are made of
glass cloth and are 15 to 20  feet long (Crabaugh
et al-,  1954).   Greater length increases the stress
because of the greater weight that must be sup-
ported by the fabric.  If mechanical shaking is
used,  cleaning maybe less  effective unless more
energy is applied to each bag.  This also in-
creases the stress.  In high-temperature instal-
lations,  dimensional instability may be increased.
Problems of stretching and  shrinking may occur
at times, which could be mitigated by using
shorter bags so that the same percent change in
length  would not be excessive in absolute amount.
Capital outlay and floor  space are both reduced
with an increase in bag length while maintenance
is increased. Many 5- or 6-inch-diameter bags
are 8 to 10 feet long.  Although no data establish
an optimum length-to-diameter ratio,  a 20-to-l
ratio appears to be an approximate practical
limit.   This  is one of many  areas  in baghouse de-
sign that could benefit from  further study.
                                       maintenance are, however, not as easily accom-
                                       plished as for the simple tube-type bag.  Wear
                                       is increased because of the friction between
                                       the filter cloth and the -wire frame support struc-
                                       ture.  It would not be advisable,  therefore,  to
                                       use this type of bag for application where  rapid
                                       wear of the filter media is anticipated.  Applica-
                                       tions for  temperatures in excess of 300°F are,
                                       therefore, ruled out completely because glass
                                       cloth is not able to withstand the abrasion. Only
                                       a relatively few baghouses of this type are used
                                       with  synthetic filter fabrics  such as  Orion or
                                       Dacron for intermediate temperatures.  Dust
                                       is collected on the outside of envelope bags as
                                       opposed to the inside of tubular-type bags.


                                       INSTALLATION  OF  FILTERS


                                       Arrangement

                                       The arrangement of tubular bags shown in Figure
                                       71  can materially affect the number of bags that
                                       can be installed in a given area.   The staggered
                                       arrangement  is not as desirable  as the straight,
                                       even though it uses the area more efficiently, be-
                                       cause access for maintenance, inspection, and
                                       bag replacement is more difficult.
Multiple-tube bags

A variation of the tube-type bag is  oval in cross-
section with vertical stitching that divides the
bag into several compartments.  When inflated,
each compartment assumes a nearly circular
cross-section.

When the blower is turned off and the pressure
relieved, the  bag returns to an oval shape,
which helps to break up the filter cake.  A bag
such as this requires a special mounting and is
somewhat more expensive for the same filtering
area than a standard round tubular  bag.  It has
an advantage in that a greater filtering area can
be accommodated in the same size  housing.
There is, however, a disadvantage in  that a hole
in one of the bags effectively destroys a greater
filtering area, and maintenance cost could thus
be substantially higher than for a conventional
baghouse in some cases.

Envelope type

Baghouses with envelope-shaped bags are second
only to the tubular-type bag in a number of units in
use.  The filtering elements must be mounted on a
supporting structure usually made of wire.  In
comparison to other designs,  the envelope-type
baghouse permits a greater filtering area  to be
installed in a  given size volume.  Inspection and
                                          j  . M.   M  - »   iS   i'-r    •=               I,-,

                                                                                   .

                                       Figure 71. Arrangements of  filter  bags:  78 bags
                                       arranged  in line (good);  108  bags  in staggered
                                       arrangement in same size  housing  (poor) (Northern
                                       Blower Division,  Buell  Engineering Co., Inc.,
                                       Cleveland, Ohio).

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                                              Baghouses
                                                                                                  123
 Bag Spacing

 The clearance between bags  is important for at
 least two reasons.  First, sufficient clearance
 must be provided so that one bag does not rub
 upon its neighbor.  This is particularly impor-
 tant for baghouses employing mechanical shaking
 where the vibration may cause the bags to oscil-
 late.  A minimum clearance of 2 inches is  sug-
 gested between bags of average length.  Larger
 clearances should be provided  if the bags are
 unusually long, for example, greater than 10 or
 12 feet.  Second,  access for examination and
 maintenance must be provided.
 Walkways between banks of bags must also be
 provided.  The depth of banks  should not be so
 great that it is  difficult or impossible to reach
 tu the farthest bag for maintenance and  replace-
 ment.  This means that if a walkway is  provided
 on one side only,  each bank  should be no more
 than three or four bags deep if 6-inch-diameter
 bags are used.  Twelve -inch-diameter bags
 should not be more than two  bags  deep if access
 is provided on one side only.  If access is pro-
 vided on both sides,  6-inch-diameter bags must
 not be more than  eight bags deep,  and 12-inch-
 diameter bags must not be more than four bags
 deep.   The total number of bags in s. bank de-
 pends upon the  shaking mechanism employed.
 A single bank,  in general,  is operated by a
 single shaking mechanism.   A  single compart-
 ment may contain  several banks of bags.

 Walkways must be provided  so that all portions
 of the mechanism  are easily accessible. Walk-
 ways should be at least 18 inches \\ide:  a 24-
 inch width is recommended.  When the bags are
 longer than about 10 or 12 feet, a. walkway should
 be provided at two levels, one  at the floor plate
 and a second for access to the  upper support
 structure.

 Bag Attachment

 Bottom attachments

 Tubular bags are  most frequently attached to a
 thimble on the tube sheet or  floor  plate, as il-
 lustrated in Figure 72.  A steel band is  instal-
 led around the bag bottom to  effect a tight seal
 between the cloth  and the thimble.  A cuff may
 be sewn into the bottom of the bag, or the bot-
 tom may be folded up once or twice to form a
 self-cuff.  This is the simplest, most trouble-
 free arrangement and probably the most widely
 used means of attaching tubular bags at the
bottom.   The steel bands should be made of
 stainless steel to  avoid rust  and corrosion prob-
 lems.   A simple screw-type  closure mechanism
 is usually employed,  but quick-closing clamps,
 as shown in Figure 72, are also available.
 In a second method of attachment,  a steel spring
 band is  sewed into the bottom cuff  of the bag.  To
 install a bag,  the steel  band is collapsed, insert-
 ed into the hole in the tube sheet, and allowed to
 expand. The tube-sheet hole is formed \vith an
 extension  and  grooved to accept the snap ring.  A
 tight seal  is required between the snap ring and
 groove to  prevent leakage.  A strip of compres-
 sible padding or gasketing is provided on the out-
 side of the snap ring  to ensure a seal.

 Close manufacturing  tolerances are required on
 both the tube sheet and  the bag cuff construction
 to achieve sufficient uniformity of  the bag and
 hole to insure a leakproof fit. This type  of con-
 struction has been tested by the Los Angeles
 County Air Pollution  Control District on bag-
 houses that serve direct-air steel-melting fur-
 naces. When improperly manufactured bags are
 used,  dust and fume losses from the tube-sheet
 "junction were  found to be 5  to 10  percent of the
 total in the effluent stream  entering the baghouse.
 The snap ring design permits rapid installation
 of bags, but each bag must  be checked thoroughly
 to determine whether the ring is seated in the
 tube sheet and not installed too deep or  too shal-
 low.  Additional care must be taken when collap-
 sing the steel  ring so that the ring is not bent
 beyond its elastic limit and a permanent crease
 formed. Such  creased rings leak because of a
 poor seal  between the bag and tube sheet, and are
 difficult to locate when  replacement is needed.
Top support

The top of the  bag may also be installed over a
thimble by using a steel band in a manner similar
to that used with a thimble at the bottom.  When
a thimble is used,  the bag may have a cuff sewed
into it,  or the  end of the bag may be folded to
form a self-cuff.  In most cases when mechani-
cal shaking is  employed, this type of attachment
offers an advantage,  since wear is usually most
severe near the bottom of the bag.  The life  of
the bag  can usually be extended  substantially by
making the bags extra long, folding the extra ma-
terial under the clamp at the top,  and then lower-
ing the bag periodically about 3 to 4 inches at a
time.  Bag life may be further extended by re-
versing the bags,  top to bottom,  provided this
is done before  wear proceeds too far.

Another method consists of attaching  the bag on-
to a steel disc  or  cap, which is  supported at the
center,  as illustrated in Figure 73.   A  common
method  of attaching 5- or  6-inch-diameter bags
consists  of sewing  a loop at  the end of the
bag; the loop  is  then, placed over a  hook as
shown in Figure 73.  Another method involves
sewing the end of the bag into a flat strap, which

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124
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
            Figure  72. Connection of filter bags to thimbles:  Men attaching filter bags and two examples
            of quick closing clamps (left and lower right, Northern Blower Division,  Buell  Engineering Co.,
            Inc., Cleveland,  Ohio; upper right, Fuller Company, Dracco Division, Cleveland, Ohio).
is looped back and forth over a special hanger as
illustrated in Figure 74.   This method is simple
and permits rapid installation.  The length of the
bag is not critical,  since  adjustments are easily
made during installation or at any time there-
after.

Some bags of this type, which have  a strap at the
upper end,  -were found to be developing small
holes near the top of the bag.  The same situation
was found to be developing in several baghouses
using bags of the  same design and manufacture.
Investigation revealed that the construction used
resulted in a stress concentration in a small area
of the bag.   This  problem was eliminated by using
a different sewing technique.


CLEANING OF FILTERS

Methods

As dust accumulates on the filtering elements,
the pressure loss increases until some maxi-
mum desirable value  is reached.  The filter
                                       must then be cleaned to reduce the pressure
                                       loss.  Cleaning cycles may be manual,  semi-
                                       automatic,  or fully automatic.  Fully automatic
                                       cycles may be initiated on a time cycle  or when
                                       the pressure reaches a preset amount.  Figure
                                       75 shows a pressure switch with this function.
                                       Some reverse-jet baghouses operate with con-
                                       tinuous cleaning.   Once a cleaning cycle is ini-
                                       tiated, it should be carried through to comple-
                                       tion with sufficient cleaning intensity and  time
                                       duration to ensure thorough cleaning. Thorough
                                       cleaning is  also recommended each and every
                                       time the blower is turned off  (Stephan et al. ,
                                       I960).
                                       Manual cleaning

                                       Small baghouses with up to about 500 or 600
                                       square feet of filtering area are frequently
                                       cleaned by hand levers. A manually operated
                                       handle transmits  a rap to the framework from
                                       which the  filtering elements are suspended.
                                       This shakes the dust loose.  Thorough clean-
                                       ing is rarely achieved since a great amount of

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                                              Baghouses
                                            125
                                                      b

        Figure 73.  Connection  of  filter bags to top support:   (a)  bag  loop and hook (Wheelabrator
        Corporation,  Mishawaka,  Indiana), (b) caps for use with  clamps  (Northern Blower  Division,
        Buell Engineering Company,  Inc., Cleveland,  Ohio).
vigor must be applied continuously for several
minutes.  Many workmen are not aware  of the
amount of cleaning required or are not con-
scientious enough to clean the baghouse thor-
oughly each time.  Since these  small baghouses
rarely have manometers to indicate  the pres-
sure, the operator cannot readily determine
when the baghouse has been adequately cleaned.
The use of a manometer appears to be almost
essential.  One must, of course, shut the fan
off or otherwise deflate  the bags before start-
ing to clean them.
Mechanical shakers

Most baghouses employ some type of mechan-
ical shaking.  The electric motor shaker is
most common.  A cam or eccentric translates
the rotary motion of the motor into an oscil-
lation.  Bags may be shaken horizontally or
vertically.

It is essential that there be no pressure inside
a tubular  filter bag during the shaking cycle.
A pressure too small to be measured with a
manometer may still be sufficient to interfere
•with adequate cleaning (Herrick,  1963).  In
one investigation a pressure as small as 0. 02
inch of water column prevented effective clean-
ing (Mumford et al., 1940).  Butterfly-type
dampers, unless they are positive seating,  can-
not be used to close off a section for  shaking
•while the blower is operating.  For this reason,
a small amount of reverse  airflow is  commonly
used to ensure complete bag collapse during shak-
ing unless  the blower  is off during the cleaning
cycle.-  When the baghouse  serves a hot source
such as a furnace,  the thermal drive  may be suf-
ficient to interfere with cleaning even after the
blower is off.
Pneumatic shakers

Two types of pneumatic cleaning mechanisms
are used.  In one type the air is used to operate
an air motor that imparts a high-frequency vi-
bration to the bag suspension framework.  Al-
though the frequency is high, the amplitude is
low.  This method is not effective for materials
difficult to shake loose from the bags,  since the
total amount of energy imparted to the bag is low.
For dust from sandblasting operations, themeth-

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  126
                  AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
Figure 74.  Method of hanging filter bags with strap top:   (1) The end of the strap on the tube is brought
up between  the two horizontal  bars of the tube hook.   (2) The strap end is folded over the bar, directly
under the vertical threaded spindle.   (3) The remainder of the strap and the tube proper are brought up
and over to the left,  with the strap  wrapping around  the  offset horizontal  bar of the tube hook,  and lying
on, or over,  the other end of  the strap,  originally threaded through the hook. The bag,  as shown,  can be
raised,  if  necessary,  by pulling with the right  hand  on the other end of the strap.   (4) The correctly in-
stalled  tube.   Note that the tube proper hangs directly under the vertical  threaded  spindle of the tube
hook (Wheelabrator Corporation,  Mishawaka,  Ind.).

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                                             Baghouses
                                                                                                 127
Figure 75.   Differential-pressure switch used  to
control  cleaning  of bags (F. W. Dwyer Manufact-
uring Company,  Michigan  City,  Indiana).
                                                     od has been found adequate for small baghouses.
                                                     For larger units, two or more air motor shakers
                                                     must be used.   This cleaning method is  econom-
                                                     ically feasible only when compressed air is al-
                                                     ready available close to the baghouse.

                                                     Pneumatic cylinders are often used  for cleaning
                                                     glass fiber filter bags.  This method is  used
                                                     on many of the baghouses serving gray iron
                                                     cupolas.  The pneumatic cylinder gently oscil-
                                                     lates the framework from which the bags are
                                                     suspended.  It is frequently used in  conjunction
                                                     with reverse-air collapse of the bags.  The am-
                                                     plitude  is relatively large and the frequency low.
                                                     Bag collapse

                                                     Efficiency of cleaning can frequently be improved
                                                     by permitting a small volume of air to flow in
                                                     the reverse direction through the bags, causing
                                                     them to collapse completely.  This method is
                                                     frequently used with glass fiber bags.   The bags
                                                     may be collapsed and reinflated several times
                                                     for each cleaning.  Usually a gentle action is ob-
                                                     tained by slowly opening and  closing the control
                                                     valves.  Sometimes, however, a stronger clean-
                                                     ing action is required, and the valves are opened
                                                     and closed quickly so that the bags "snap. "  Bag
                                                     collapse may also be used with mechanical shak-
                                                     ing, sonic cleaning,  or  air pulses.
                                                     In one variation of this method,  several rings
                                                     are installed on the inside  of glass fiber bags.
                                                     When the air is reversed,  the bags collapse in-
                                                     ward but the rings prevent the cloth from touch-
                                                     ing at the center.   The flexing of the fabric breaks
                                                     the filter cake loose.  This assertedly permits
                                                     the cake to fall free without interference.  Air
                                                     pulses are sometimes used for the same reason.
                                                     During the gentle  air reversal, before applica-
                                                     tion  of the air  pulse, the bags relax and have a
                                                     tendency towards  collapsing.  As the short air
                                                     pulses (generally  three pulses of 1 second each)
                                                     sweep down the filter tube, they create a gentle
                                                     waving or shaking action, as shown in Figure 76.
Sonic cleaning

Sonic cleaning is relatively new and has not been
fully evaluated in the field.  It is usually used
•with bag collapse.  The sonic horns employed
are relatively expensive, and it is doubtful that
the cleaning action is  superior to that provided
by simple mechanical shaking.   In addition, the
sound can be extremely annoying unless the bag-
house housing is insulated with sound-absorbing
materials.

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1Z8
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
     TUBE
     COLLECTING
     DUST
REVERSE
AIR  ON
ONLY
                    PRESSURE  JET
                    AND  REVERSE
                    AIR  ON

       \/
       yl,
    /\
 WALLS COLLAPSE  TOGETHER
 PREVENT OUST FROM  FALLING
                    SLUG OF AIR OPENS TUBE,-
                    ALLOWS DUST TO FALL  FREELY

  Figure 76.   Illustration of  method  of cleaning
  bags by collapse and air pulses  (Pangborn Cor-
  poration,  Hagerstown, Indiana).
Reverse airflow

Some envelope-type baghouses use reverse air
for cleaning.  The dust is collected on the out-
side of the filtering  elements.  A moving car-
riage seals off the outlet of one or several bags
at a time.  Valves permit outside air to be
drawn through the bags in the reverse direction,
as shown in Figure 66.  This permits continuous
cleaning, -with only a few bags,  at the most, out
of service  at any time.  Sometimes a separate
air blower is used to provide the  reverse  air for
cleaning.


Reverse-air jets

Another  reverse-air cleaning method is the re-
verse-jet mechanism developed by Hersey,  about
1950.  The Hersey-type baghouse, as shown in
Figure 67,uses  a blow ring that travels up and
down the tubular bag. Air for cleaning is blown
through  a narrow  slot on the traveling ring through
the filter media in the reverse direction.  The
filter fabric is also  indented or flexed at the
point of  contact with the ring.  The combination
of flexing and reverse airflow thoroughly cleans
the accumulated dust from the bag.  Filter bags
are usually made of felted wool cloth.  Felted
Orion or Dacron are used for higher tempera-
tures or for better resistance  to chemical at-
tack. Woven fabrics are sometimes used,but
they usually suffer from reduced collection ef-
ficiency because this cleaning  method is too
thorough.  A residual dust cake is essential to
the filtering process with woven fabrics. Felted
cloths,  however, do not require a residual dust
mat to filter effectively.  The  reverse-air jet
cleaning method sometimes results  in a high
rate of wear.  Even though reports have been
published indicating bag life of several years,
experience in  Los Angeles County has varied
depending upon the application. When this
method  has been applied to the collection of
metallurgical  fumes, extremely high rates of
bag wear have been experienced.  Mechanical
breakdowns of the reverse-air mechanisms
have also been encountered.   All the units in-
stalled in Los Angeles County to serve metal-
lurgical operations have been  abandoned after
a few months  of operation or modified to me-
chanical shaker cleaning.  A number of them
have, however,  been operated successfully
for controlling dust from grain transfer and
other common dust operations.

There is a tendency to believe that the  re-
verse-jet baghouse may be operated -with fil-
tering velocities of about 20 to 30 fpm or even
more.  This is not generally true, however,
as is shown by the Hersey data reproduced in
Figure 77. High filter  ratios are permissible
in special cases only.  For example, from
curve 9 in Figure  77, a filter  ratio of 30 would
be permissible for leather-buffing dust (a very
coarse material with 30-mesh  average  size)
only if the grain loading were low, not  over 3
or 4 grains per  cubic foot.  For higher grain
loadings the filter ratio should be reduced to
about 20 cfm per square foot.  For metallur-
gical fumes a  maximum filter  ratio of about
6 is often recommended,  as shown in Table
41.  If the grain loading is greater than aver-
age or the particle size is small,  the filter-
ing velocity should be reduced to 5 fpm or
less. These recommendations are confirmed
by Hersey's curves, which show that, for
very fine  dusts and fumes, the limiting filter
ratio should be approximately 6 as the  grain
loading  approaches zero.  For normal  condi-
tions,  the filter ratio  should be 3 to  5 for met-
allurgical fumes.   Caplan (I960) states that the
nature of the dust is the most  important variable.

Hersey-type baghouses should logically be  oper-
ated -with filter ratios that bear a fixed relation-
ship to those used with standard shaker-type bag-
houses.  From experience with a variety of medi-
um  and coarse  dusts, one •would expect that

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                                             Baghouses
                                                                                                  129
   20
                                      25
              FILTERING VELOCITY  elm It' FABRIC

 Figure 77.   Typical  performance  of  reverse-jet
 baghouses  on  a  variety of dusts--dust  load  ver-
 sus filtering velocity at 3^ inches  water col-
 umn pressure  drop  (Hersey, 1955).   The  key  to
 the numbers  is  as  follows:  (1)  magnesium tri-
 silicate,  (2) carbon black,  (3)  starch  dust, (4)
 resinox,  (5)  diatomaceous earth,  (6) kaolin, (7)
 cement or  limestone  dust, (8) coal  dust, and (9)
 leather-buffing dust.  For numbers  1 through 6,
 99.94 to  99.99% pass 325 mesh;  for  numbers  7 and
 8,  95% pass  200 mesh; number 9  is  the  60-mesh
 average.
reverse-air jet baghouses could be operated with
filtering velocities 5 or 6 times as great as those
for conventional baghouses.  It has been -well es-
tablished that, for most metallurgical dust and
fumes,  filtration should be 1 to 2 fpm in conven-
tional compartmented baghouses cleaned by shak-
ing, collapse,  air pulses, or combinations of
these.   When metallurgical or  other problem
dusts and fumes are involved, the design of Hersey
baghouses should be more conservative than-would
be indicated by strictly folio-wing any arbitrary
rule.

In order to avoid operating difficulties, the pres-
sure drop for a Hersey-type baghouse should usu-
ally be in the range of  3 to  5 inches water  column
(Caplan,  I960).  Too low a resistance is undesirable,
since it prevents proper inflation of the bag.  This
results  in improper cleaning action.  Too  high
resistance is also undesirable, since it increases
the friction between the blow ring and the bag,
which increases -wear excessively.  Hersey-type
baghouses should not be operated -with pressure
drops in excess of 8 inches -water column under
any circumstances (Caplan,  I960).  When  the
cleaning cycle is pressure controlled, these  lim-
its may be used as a  guide.  If, however,  the fil-
tering velocity is excessive,  some materials,
for example, metallurgical fumes,  have a tenden-
cy to blind the  bags so  that even continuous clean-
ing fails to reduce the pressure as required. When
materials such as these are handled, filtering
velocities must be reduced.  Using the values
recommended in Table 41 should provide trouble-
free operation in almost all cases.   Pilot model
studies are useful -when previous experience is
not available as a basis for determining  filter
ratio.  Sufficient time must be  allowed for the
pilot unit to reach equilibrium before tests are
started.  This may require several hundred
hours of continuous  operation.  Failure to allow
equilibrium to be attained can result in errone-
ous data and improper functioning of the full-
scale unit designed upon these data.

The speed  or rate of travel of the blow ring up
and down the bag may be  varied according to
the nature  of the dust being filtered.  In  general,
speeds of from 20 to 50 fpm are employed.   The
optimum rate of blow ring travel depends upon
the nature  of the dust.  As  the blow  ring travels,
the dust is blown off the inside  surface of the
bag.  This dust will tend  to  settle at a rate that
depends  upon the particle size and the specific
gravity of the individual particles.   It is prob-
ably desirable to adjust the blo\  ring rate of
travel so that it does not  exceed the  settling rate
of the dust.  A ring speed of approximately 20
fpm has  been found optimum for light materials
such as grain and flour dust.  Speeds of  40 or
50 fpm can be tolerated by high-density dust
such as uranium.  The volume  of air blown
through the slot of the blow ring is usually 1. 0
to 1. 5 cubic  feet per linear inch of slot.   Slot
widths are generally 0. 03 to 0. 25 inch (Caplan,
I960).  Newer designs employ-wider slots and
centrifugal blowers to provide the reverse air.
The original design used a positive-displace-
ment blower.  The reverse air must be  pro-
vided at a pressure greater than the pressure
drop through the filter cloth.  Furthermore,
since higher pressure drops generally indicate
finer dusts and fumes, -which tend to penetrate
the fabric to a greater extent,  the differential
between the reverse air pressure and the pres-
sure inside the bag probably should  be increased
somewhat as the pressure drop across the bags
increases.

When hot effluents -with a high moisture  content
are handled,  it may be necessary to preheat
the air used for  reverse-jet cleaning.  For ex-
ample, in  one case  encountered in Los Angeles
County,  the  effluent  from a direct-fired dryer
•was vented to a reverse-jet baghouse.  When
ambient air -was  used for cleaning, condensa-
tion occurred when the unit -was started  up early
in the morning.  After a  heat exchanger -was in-
stalled to preheat the reverse air, the bags re-
mained dry.   In  some cases  a portion of the hot,
clean exhaust may be used for  reverse-jet clean-
ing.  Care must be taken to remain  at least 50°F

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130
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
              Table 41.  RECOMMENDED FABRIC AND MAXIMUM FILTERING VELOCITY
                 FOR  DUST AND FUME COLLECTION IN REVERSE-J2T BAGHOUSES
                  (American Air Filter Co. , Inc., Bulletin  No. 279C,  Louisville, Ky. )
                           Material
                                               Fabric
  Filtering
velocity,  fpm
              Aluminum oxide
              Bauxite
              Carbon, calcined
              Carbon, green
              Carbon, banbury mixer
              Cement,  raw
              Cement,  finished
              Cement,  milling
              Chrome,  (ferro) crushing'
              Clay,  green
              Clay,  vitrified silicious
              Enamel,  (porcelain)
              Flour
              Grain
              Graphite
              Gypsum
              Lead oxide fume
              Lime
              Limestone  (crushing)
              Metallurgical  fumes
              Mica
              Paint pigments
              Phenolic  molding powdgrs
              Polyvinyl chloride (PVC)
              Refractory brick sizing  (after firing)
              Sand scrubber
              Silicon carbide
              Soap and  detergent powder
              Sov bean
              Starch
              Sugar
              Talc
              Tantalum fluoride
              Tobacco
              Wood flour
              Wood  sawing
              Zinc,  metallic
              Zinc,  oxide
              Zirconium  oxide
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen, -wool felt
                                      Orion felt
                                      Wool felt
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Wool felt, cotton sateen
                                      Wool felt
                                      Cotton sateen, Orion felt
                                      Orion felt,  wool felt
                                      Cotton sateen
                                      Cotton sateen
                                      Orion felt,  wool felt
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Wool felt
                                      Cotton sateen
                                      Cotton sateen, wool felt
                                      Cotton sateen
                                      Dacron felt, Orion  felt
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen, wool felt
                                      Cotton sateen
                                      Orion felt
                                      Cotton sateen
                                      Cotton sateen
                                      Cotton sateen
                                      Orion felt,  Dacron  felt
                                      Orion felt
                                      Orion felt
       9
       8
       7a
       5
       7a
       7
       9
       7
       9
       8
     10
     10
     10a
     12
       5a
       8
       6a
       8
       9
       6 a
       9
       8
       3
       7a
     10
       7a
     10
       ga
     10
       8
       8a
       9
       6a
       9
      6a
      7
              aDscrease 1 fpm if concentration is  great or particle size  small.
 above the dew point at all times to avoid trouble
 (Caplan,  I960).

 Metallurgical fumes may bleed through the filter
 bags.  In one case where a synthetic felted bag
 was used, a hard crust formed on the edges  of
 the blow ring slot.  This  crust rapidly wore  out
 the bags.  Substitution of wool felted bags cured
 the problem.  Particle size is not, however,  the
 sole determining factor in leakage.  Disturbance
 of the dust deposit causes some particles to  sift
 through even dense -wool felt.  Hence,  the less
 reverse-jet  activity,  the higher the average  col-
                                          lection efficiency (Hersey,  1955).   Collection
                                          efficiency of fly ash (mass median  size 16 pi) was
                                          found to be less than for either talc (mass medi-
                                          an size 2. 5  (j.) or vaporized silica (mass median
                                          size  0.6  |JL) (Hersey,  1955), but the reason for
                                          this was  not determined.

                                          Cleaning  Cycles

                                          Manually initiated  cycles

                                          Cleaning is  most commonly initiated  by manually
                                          operating the required controls.  Electrically or

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                                              Baghouses
                                                                                                  131
pneumatically operated shakers are activated by
pressing a control button or operating a. valve.
Interlocks  are frequently provided so that the fan
or blower must be shut off before the shaking
mechanism can be activated.  This arrangement
is most suitable for operations that may be shut
down whenever required for cleaning.   It is also
suitable when cleaning once  or twice a shift is
adequate.  In such cases, the  baghouse is cleaned
when the equipment  is shut down for  lunch  or at
the end of the shift.

Semiautomatic cycles

Some installations use a semiautomatic clean-
ing cycle whereby, as the blower is turned off,
a timer is  activated. After  a  delay to permit the
blower to come to rest,  the  shaking cycle is
initiated.   An interlock prevents turning the  blow-
er on again before the shaking cycle  is  completed.
This method has  been used with success on melt-
ing furnaces where a heat does not last more than
about 2 hours and the baghouse is adequately sized,
so that shaking is not required more than once per
heat.  At the end  of  the heat, when there are no
emissions  from the  furnace, the operator presses
the button  that initiates the cycle.  In about 5 or
6 minutes  the baghouse has  been cleaned and is
ready to control  emissions from the next heat.
While the baghouse  is being cleaned,  the fur-
nace is empty and no air contaminants are re-
leased.

Fully automatic cycles

The most desirable method  consists of cleaning
a fully automatic, compartmented baghouse  on
a programmed cycle.  The cycle may be initiated
at regular intervals or when the pressure  reaches
a predetermined value.   When the cleaning cycle
is initiated,  one  compartment of the baghouse is
isolated by means of appropriate dampers.  A
small volume of  reverse air is usually used to
ensure collapse of the filter bags.  The isolated
section is  then cleaned by one of the methods
previously discussed.  After the cleaning cycle
is completed, the compartment is again re-
turned to service. Each compartment, in  turn,
is cleaned  in the same manner.  The advantage
of fully automatic cleaning is that it  eliminates
the possibility of  the operator's forgetting  or
neglecting  to clean the baghouse.   Since, how-
ever, a greater amount of mechanism is re-
quired, the maintenance  and the possibility of a
breakdown are increased slightly. In many
cases, fully automatic cleaning is essential
since the basic equipment served cannot be shut
down -while the baghouse  is cleaned.   Equipment
that operates continuously or  requires cleaning
during the  cycle of operation requires the use
of a fully automatic,  compartmented baghouse.
Compartmented baghouses must be designed to
provide adequate filtering area during all phases
of the operation.  This means that, when one
section of the baghouse is out of service for
cleaning,  the remaining sections must provide
sufficient filtering area..  Frequently the design
permits two sections to be out of service at
one time and still provides sufficient filtering
area.  This allows one section to be serviced
when bags need replacement while the remain-
ing sections continue to operate -without exceed-
ing the maximum permissible filtering velocity.
Compartmented baghouses are not, however,
suitable for very small units.  A minimum  of
five or six compartments is required for effi-
cient operation.


Continuous  cleaning

Continuous  cleaning is  often used in Hersey-
type reverse-jet baghouses and in some  envelope
types.   It is suitable for installations that oper-
ate with a steady high dust load.  If the dust load
is variable  or light, continuous cleaning -will
result  in unnecessary operation of the carriage
and in  excessive wear.  Pressure control clean-
ing cycles allow an increase in the  resistance of
the filter above what the same unit would have
for continuous cleaning, as illustrated in Figure
78.  The curves show that, for a typical dust con-
centration of 0. 5 grain per cubic foot, operating
the cleaning mechanism 30 percent of the time
instead of 100 percent results in only a. 10 per-
cent increase in filter resistance.  If the filter-
ing area of  the unit were  increased 10 percent,
the pressure drop  could be expected to be about
the same, but the filtering media would last
about 3 times as long.  While the benefits are
not as  great for heavier dust,loading or fine
metallurgical fumes, pressure control cleaning
may still be advantageous since the cleaning
mechanism need not be operated  as much during
periods of very light loading.
DISPOSAL OF  COLLECTED  DUST

Once the dust is collected in a baghouse, it must
be disposed of without creating a new dust  prob-
lem.  Occasionally one  sees dust dropped on the
ground from the collecting hopper of a baghouse.
The  wind then picks it up and blows it around the
neighborhood.  The  result is substantially  the
same as if the dust had not been collected in the
first place.

The  most common means  of disposing  of the col-
lected dust is to transfer it from the hopper of
the baghouse into  a truck and then to a dump.  In
order to minimize dust emissions during trans-
fer from the hopper to the truck, a sleeve  or
  234-767 O - 77 - 11

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132
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
 sock of canvas is frequently installed on the out-
 let of the hopper.  The sleeve should be suffi-
 ciently long to reach to the floor of the truck
 body.  The dust must then be thoroughly wetted
 •with -water before it is transported to the dump.
 This method is suitable for  installations where-
 in the quantity of dust collected is such that
 emptying the hopper once a  day is sufficient.
    70
    60
    50
    40
    30
    20
     10
                          DUST AT  5  TO  10
                          gr/ft3 OR
                          METALLURGICAL  FUME
                          AT 1 gr/ft3
        TYPICAL  DUST AT
        0  5  gr/ft3
        	|	i
              20      40      60      BO
              REVERSE-JET OPERATION, %
                               100
  Figure 78.   Effect of pressure control on filter
  resistance  in a  reverse-jet baghouse  (Caplan,
  1960).
 When the quantity of dust collected is greater,
 the hoppers must be emptied more frequently.
 Some type of automatic or semiautomatic meth-
 od is then advisable.   One method consists of
 using a trickle valve as illustrated in Figure 79.
 The discharge may be to  a completely enclosed
 tote box.  Another method consists of using a
 rotary valve (Figure 79) that may be operated
 continuously or intermittently.  Both the trickle
 and the rotary valve may be connected to dis-
 charge to a screw conveyor  that collects the
 dust from several hoppers,  sometimes even
 from more than one baghouse, and discharges
 into a covered tote box or other common col-
 lection point.
                                       BAGHOUSE CONSTRUCTION

                                       Pushthrough versus Pullthrough


                                       The blower may be located on either side  of the
                                       baghouse.  If it is on the clean-air side,  it is
                                       referred to as a pullthrough baghouse.  This
                                       is desirable since it protects the blower from
                                       the dust or fume being handled.  On the other
                                       hand, it does require a relatively airtight hous-
                                       ing for the baghouse.  The pushthrough type can
                                       be operated with open sides as long as protection
                                       from the weather is provided.   This  is advantagec
                                       when handling hot gases,  since  it permits a great
                                       degree of cooling.  Thus,  a higher inlet gas tem-
                                       perature may be tolerated for the same tempera-
                                       ture  of the filtering media. For a pushthrough ba
                                       house, however,  the blower must handle the entir
                                       dust  load.  This frequently amounts to several
                                       hundred pounds of dust per hour,  which may causi
                                       substantial wear to the blower.   These blowers
                                       also  require frequent dynamic balancing.
Structural Design

The  gage  of metal used to construct the bag-
house walls, hoppers, and so forth must be
adequate, and sufficient bracing must be pro-
vided to  withstand the loads exerted.  A pres-
sure differential of 8 inches water column
represents approximately 42 pounds per  square
foot.  The total air pressure exerted on a side
panel of  a pullthrough baghouse may be in ex-
cess of 2. tons.  Baghouses have been known to
collapse  as a result of this air pressure  when
inadequate bracing was provided.  Pullthrough bag
houses are more of a problem in this  regard than
the pushthrough type for two reasons.  First, iden
tical baghouse  structures  can withstand more in-
ternal pressure than external pressure without
damage.   Second, the pressure differential betwee
the inside and outside of the baghouse housing is
usually greater for a pullthrough installation than
for an other-wise identical pushthrough type.

Hoppers

Size

The size of the hoppers provided must be suffi-
cient to hold the collected dust until it  is re-
moved for disposal.  If the hopper is emptied
once per day, it must be  large enough  to hold the
total amount of dust collected in a full  day's oper-
ation.  Some reserve capacity should also be pro-
vided since the quantity of dust may vary from day
to day depending upon variations  in the basic pro-
cess.  If the hopper does not have adequate capac-
ity, dust already collected becomes reentrained

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                                              Baghouses
                                                                                                   133
                                     10 INCHES
  EXPLODED VI Eld
           CROSS-SECTIONAL VIEH
           SHOWING ROTOR AND BODY
                                                    CUTAWAY VIEW SHOWING DOUBLE-
                                                    FLAP INTERNAL CONSTRUCTION
                                                    TYPICAL OF BOTH THE GRAVITY-
                                                    OPERATED AND MOTORIZED TIP-
                                                    PING VALVES
            Figure  79.  Hopper discharge valves (Western Precipitation Corporation,  Division  of
            Joy  Manufacturing Co.. Los Angeles, California).
increasing the total dust load on the filter cloth
and thereby the filter resistance.  This is detri-
mental to the performance of the baghouse.   De-
flectors are often installed to minimize or pre-
vent this reentrainment to some extent.

Slope of hopper sides

The  slope of the sides of the hopper must be suf-
ficient to permit the dust to slide or flow freely.
The  design must also consider the possibility of
bridging.  Continuous  emptying  of hoppers will
help to prevent bridging of material that has a
strong tendency to do so.  It -will also prevent
operating difficulties •with materials that tend to
become less fluid -with time.  For  example, some
materials have a tendency to cake  if permitted
to stand for a few hours or overnight.  This is
especially true of hygroscopic materials that
absorb moisture from the air.
Gage of metal

The gage  of metal required for constructing hop-
pers depends upon the size of the hopper and the
service.  For small hoppers and light duty,  16-
gage metal may be used.   The gage should be
increased as warranted by the size  of the hopper
and the total weight of the dust to be held at any
one time.  In addition, however, consideration
should be given to the fact that workers frequent-
ly hammer  on the  sides of hoppers to assist the
collected dust to flow freely from the  discharge
gate.   If materials tend to stick or cake  or are
not freely flowing, some hammering on the sides
of the hoppers will certainly result.  Many hop-
pers have been badly dented as a result of rough
treatment.
Use of vibrators and rappers

A much better solution than hammering on the
sides of the hoppers is to provide mechanical
rappers or vibrators.  The most frequently
used device is the electrically operated Syntron
vibrator.   Air-operated vibrators are also used
extensively.   A rapping device is highly desir-
able •when a rotary discharge valve  or screw con-
veyor is used.  The rapper may be  operated from
a cam attached to the shaft of the rotary valve. In
some cases the valve,  rapper,  and  screw are all
operated  from a single electric motor.

-------
134
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER,
Discharge

Many baghouses, especially small,  simple ones,
use a slide gate at the bottom of the hopper to
control the discharge of the collected dust from
the hopper.   Other valves commonly used are
shown in Figure 79.   The rotary valve is usually
used on fully automatic units.  The operation of
the gravity trickle valve may be affected by the
pressure in the baghouse.
MAINTENANCE

Service

Every mechanical device, no matter how well de-
signed and constructed,  must be serviced peri-
odically if it is to continue to operate properly.
A baghouse,  even the simplest, is no exception
to this rule.  Maintenance is usually adequate
when the collected dust has sufficient economic
value.  The self-interest of the operator then
requires that the equipment be kept in optimum
operating condition.  In  many cases, however,
baghouses are installed  because local air pollu-
tion regulations require it.  When the baghouse
is nonproductive,  the operator has little motiva-
tion to maintain it in optimum condition; however,
this is a foolish and shortsighted  attitude.  Unless
the baghouse is properly maintained,  the invest-
ment, large  or small, is wasted.   In many cases
the additional expense required to recondition
equipment, -which has long been neglected, is as
much or more than the  expense of continually
maintaining the equipment in optimum condition
would have been.
A proper maintenance program, requires estab-
lishing a schedule for the various operations
that must be performed periodically.   The hop-
pers should be emptied and the collected dust
disposed of at least once a day.  Depending upon
the nature of the dust, the quantity collected,
and the general severity of the service, the equip-
ment should be thoroughly inspected at intervals
of a week, a month,  or quarterly.  Moving parts
such as  the shaking mechanisms must be greased
and oiled at intervals specified by the manufac-
turer.  For baghouses in daily use, all bags
should be examined at least  once a week to de-
termine "whether any are showing wear.  Bags
having holes or rips should be replaced immedi-
ately.  Frequently,  trouble can be detected be-
fore it becomes fullblown.  Large baghouses
benefit by the maintenance of a chart on which
the history of each bag is recorded.   If bags  in
one area show a history of more frequent re-
placement than those in other  areas,  this should
be investigated.
                                       Bag  Replacement

                                       Some operators find it more economical to re-
                                       place all the bags periodically before serious
                                       trouble begins to develop.  For example,  one
                                       operator in the Los Angeles area replaces all
                                       the bags in a quarter of the baghouse every 3
                                       months.  Thus,  every bag is replaced once a
                                       year.  A thorough inspection is, moreover,
                                       made monthly.  If an individual bag develops a
                                       hole or a rip or shows any sign of wear, it is
                                       replaced -when detected.   The advantage of this
                                       maintenance schedule is that the overall cost
                                       may be lower compared with replacing bags
                                       only when they fail.   In this particular case,
                                       experience  with other, similar equipment in-
                                       dicates that bag failures generally occur be-
                                       tween  1 and 2 years  after installation, -with
                                       an average  life of 18  months.  Thus, after a
                                       year, frequent replacements -would  be required.
                                       The  labor required to replace  a bag -when one
                                       bag is  replaced at a time can be estimated to
                                       be approximately 1/2 to  1 man-hour.  If an
                                       entire  section (375 bags)  is replaced at  one
                                       time, the greater efficiency reduces the labor
                                       required to about 0. 086 man-hour per bag.  In
                                       either  case, the  cost of the bag itself is about
                                       $10.   While the labor and material  cost of
                                       group replacement is not necessarily less,
                                       there are many other advantages.   The bag-
                                       house in this illustration  serves a furnace
                                       operated 24 hours per day, 7 days per week.
                                       When a bag failure occurs, the baghouse must
                                       be shut down while the bag is replaced.   This
                                       means that the furnace must shut down or a
                                       citation -will be received for excessive emis-
                                       sions.   Obviously, lost production time is  ex-
                                       pensive.  When group replacement  is  used, ser-
                                       vice  is  scheduled to coincide -with furnace shut-
                                       down for relining without loss  of production.

                                       Each operator must decide which method is best
                                       in respect to his  own operating experience, the
                                       anticipated bag life,  and the material and labor
                                       cost.  Also to be considered is -whether or not
                                       the equipment can easily be shut down when trou-
                                       ble develops.

                                       Replacement of one or several bags in a large bag-
                                       house is not usually desirable though it is some-
                                       times unavoidable if an individual bag becomes de-
                                       fective.  In this case, the resistance of  the new
                                       bags during the initial startup will be very low
                                       compared -with that of the older bags.  As a result,
                                       the filtering velocity through the new bags -will be
                                       many times in excess of the normal rate.   This
                                       could result in blinding of a new bag during the
                                       first few minutes of operation.  It would be de-
                                       sirable to take the precaution of returning the
                                       equipment to service  gradually in such cases, but
                                       baghouses are not normally designed and con-
                                       structed in a manner  that permits this to be done.

-------
                                 Single-Stage Electrical Precipitators
                                                                                                  135
Precoating

One solution to the problem of high filtering ve-
locities for new bags would be to precoat the bags
-with dust to establish a cake immediately after
installation. Precoating is a very desirable pro-
cedure,  and some authorities have  recommended
that all bags should be precoated immediately
after each cleaning  cycle.  It has also been recom-
mended that compartmented baghouses have auto-
matic programming equipment so that each section,
after cleaning, is precoated before it is  returned
to service.   This was done in  one case by instal-
ling a cyclone precleaner.  The coarse  dust col-
lected by the cyclone was then automatically intro-
duced into the air stream immediately after each
cleaning cycle.
 Precoating with a relatively coarse dust is espe-
 cially beneficial -when a fine fume is being filtered
 (Drinker and Hatch, 1954).   The precoat ensures
 a high efficiency immediately after  the bags are
 cleaned, increases the capacity of the unit,  and
 decreases the pressure loss.  In many cases the
 additional expense of equipment for automatically
 precoating the bags would be repaid in additional
 usable life of the filter media,  improved collec-
 tion efficiency, and reduced draft loss.
 The design of some simple baghouses may un-
 intentionally result in automatically precoating
 the bags each time the unit is started.  The in-
 let duct usually enters the baghouse through the
 dust-collecting hopper.  At startup, some of the
 previously collected dust in the hopper is dis-
 turbed and serves as a precoat on the filter bags.
 Since the collected dust is usually agglomerated
 into relatively coarse particles, it is an effective
 precoat material.  If, however, an excessive
 quantity of dust is deposited upon the filter media,
 the capacity of the unit is reduced and the  resis-
 tance is increased unnecessarily.


         SINGLE-STAGE  ELECTRICAL

              PRECIPITATORS

 Electrical precipitation is frequently called the
 Cottrell process for Frederick Gardner Cottrell
 (1877 to 1948), who designed and built the  first
 successful commercial precipitator.  It is de-
 fined as the use of an electrostatic field for pre-
 cipitating  or removing solid or liquid particles
 from a gas in which the particles are carried
 in suspension.  The equipment used for this pro-
 cess is called a. precipitator or treater in  the
 United States.  In Europe it is  called an electro-
 filter.  A precipitator installation is shown in
 Figure 80.
HISTORY OF ELECTROSTATIC PRECIPITATION


Origins of  Electrostatic  Principles

The first recorded reference to the phenomenon
of electrostatic attraction,  which forms the basis
for the precipitating action in an electrical pre-
cipitator, is attributed (Priestley, 1958) to Thales
of Miletus  about 600 B. C.  He noted that a piece
of amber that has been rubbed attracts small, light
fibers.  The word electricity came from elektron,
the Greek word for amber.  Pliny wrote of the
attraction of chaff and other light objects to the
amber spindles of wheels in Syria.

It was not until William. Gilbert published his his-
torical De  Magnete in the year  1600 that serious
progress toward understanding electrical and
electrostatic phenomena commenced.  Gilbert
compiled a list of "electrics, " materials posses-
sing the property of attraction when rubbed,  and
"nonelectrics, " materials not having this proper-
ty.  In  1732 Stephen Gray succeeded in demon-
strating that the so-called nonelectrics  could be
given an electrical charge if they "were properly
insulated.  Since some materials could  be charged
positively and  others negatively, two different
types of electricity were postulated.  In 1754
John Canton demonstrated that  materials could
be charged either positively or negatively,  lead-
ing to  the development of the single-fluid theory
of electricity proposed by Benjamin Franklin.


In 1832 Faraday proposed an atomic theory of
electricity.  Faraday's theory resembled both
the one-fluid and two-fluid  theories.  He as-
sumed two kinds of charged particles,  which
we now call protons and electrons. He  as-
sumed that only the negative particles (elec-
trons) could be transferred from one body to
another.

Although the fact that  charged particles at-
tract or repel  each other, depending upon
•whether the charges are unlike  or  like, had
been known for some time,  it was  not until
Coulomb devised a torsion balance of suffi-
cient sensitivity that the relationship between
the charge, separation,  and force  was deter-
mined.   Coulomb demonstrated that the force
of attraction  or repulsion between  two static
charges is  proportional to the product of the
charges and inversely proportional to the
square of the distance between them, as ex-
pressed in equation 53:
                F  =
                       DS
(53)

-------
136
       AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
 Figure 80.  An electrical  precipitator controlling the  emissions from a 75-ton and  a  50-ton  electric-arc
 steel-melting furnace  (left)  precipitator off, (right) precipitator on (Bethlehem Steel  Co.,  Los Angeles,
 Calif.).
 where

     F
=  force of attraction or repulsion be-
   tween two particles, dynes

=  charge on particles, statcoulombs
     D  =  dielectric constant of medium be-
           tween the particles, dimensionless

     S  =  distance between the particles,  cm.
 In a vacuum, for which the dielectric  constant
 D = 1, if the force is  1 dyne and the distance
 between the (equal) charges is 1 centimeter,
 the fundamental electrostatic  unit of charge is
 defined.  Called a statcoulomb, it is the charge
 associated  with approximately 2.08 x 10' elec-
 trons .

 The forces exerted by electrical charges are
 dependent upon the medium through which they
 are exerted. Thus, the force as defined by
 Coulomb's  law depends upon D, the dielectric
constant of the medium.  Values of the dielec-
tric constant for a number of common materials
are given in  Table 42.   The dielectric constant
may be taken,  with negligible error, as unity
for air at normal temperature and pressure.

In order to explain the phenomenon of attrac-
tion and repulsion bet-ween charges, a hypo-
thetical electric  field is postulated.   The
strength of an electric field at any point may
be expressed as  the quotient of the force
exerted on a test charge placed  at that point
divided by the magnitude of the charge.  It
must be assumed, of course, that introducing
a charge into an  electric field does not alter
the field,  -which is a reasonable assumption
only if the charge is very small compared with
the strength of the field.  Field  strength may
also be expressed as the potential difference
divided by the distance.  Equation 54, defines
the strength of a uniform electric field:
                                                                                       (54)

-------
                                   Single-Stage Electrical Precipitators
                                            137
where
    E =  field strength or electrostatic potential
          gradient, statvolt/cm

    V =  electrostatic potential difference, statvolt.
      o
 Table 42.  DIELECTRIC CONSTANTS FOR SOME
              COMMON MATERIALS
Material
Air
Alumina
Ammonium chloride
Calcium carbonate
Dolomite
Ferrous oxide
Glass (pyrex)
Quartz (fused)
Sodium chloride
Steam
Sulfur
Titanium dioxide
Water
Dielectric constant3-
1.
4.
7
6.
6.
14.
3.
3.
6.
1.
4
14
80
0006
50 to

14
80 to
20
80 to
75 to
12
01

to


8.


8

6
4.



110


40




10





   aThese valued vary with the temperature,
    humidity, pressure,  and electrical fre-
    quency at •which measured.
 Early Experiments With Electrostatics on Air Contaminants

 In 1824, Hohlfeld performed an experiment in which
 he succeeded in clearing the air in a jar of fog by
 means  of an electrified point.  Guitard performed
 a similar experiment in 1850 in which tobacco
 smoke  was cleared from the air in a glass cylinder
 9 inches in diameter by 18 inches long.   These ex-
 periments •were forgotten until Sir Oliver Lodge
 uncovered them in  1905, more than 20 years after
 he had  independently demonstrated the same  phe-
 nomenon.   Information in this field -was also  pub-
 lished by Gaugain in 1862 on the disruptive dis-
 charge bet-ween  concentric cylindrical electrodes,
 and  by  Nahrwold, who, in  1878, found that the
 electric discharge from a  sharp point in a tin
 cylinder greatly increased the rate of settling or
 collection of atmospheric dust.   To make the col-
 lected particles adhere,  he coated the walls  of
 the  cylinder with glycerin  (White,  1957).

 The first attempt to use the principles of elec-
 trical precipitation commercially was made  by
 Walker and Hutchings  at a lead smelter works
 at Baggilt,  North Wales,  in  1885.  They were
 inspired by the early work of Sir Oliver Lodge
 in this  field.   This  first attempt was not success-
 ful,  partly because lead fume is one of  the most
 difficult materials to collect by electrical pre-
cipitation and partly because they were unable
to provide an adequate power supply with their
crude equipment (White,  1957).


Development  of  the  First  Successful Precipitator

The first successful commercial use of electri-
cal precipitation -was developed by Cottrell in
1907 (Cameron,  1952).  Cottrell, while an in-
structor at the University of California at
Berkeley, -was approached by the management of
the recently  constructed Du Pont Explosives and
Acids Manufacturing Plant near  Pinole, California,
about 12 miles north of Berkeley on San Pablo Bay.
This plant was using the then new Mannheim pro-
cess or "contact" method in place of the chamber
process to manufacture  sulfuric acid.  In the
contact process, sulfur  dioxide and oxygen are
passed through  an iron oxide catalyst to form
sulfur trioxide from which the sulfuric acid is
made. Difficulty was experienced owing to ar-
senic, which was poisoning the catalyst. Cottrell
first attempted  a solution to the  problem by
means of collecting the acid mist with a labora-
tory model centrifuge.  Although the centrifuge
principle was moderately successful in the lab-
oratory, the first pilot plant model tried at
Pinole was a failure.  Before Cottrell was able
to proceed further with this work, all his notes
and models -were destroyed in the fire that ac-
companied the San Francisco earthquake of 1906.
Discouraged but undaunted,  Cottrell  rejected an
appointment  to head the  Chemistry Department
at the Texas Agricultural and Mechanical Col-
lege in order to follow up an idea of collecting
the acid mist by electrical precipitation.

After demonstrating that electrical precipitation
would collect smoke,  Cottrell made a small con-
tact  acid plant and passed the sulfuric acid mist
into  a round  glass jar.  Inside the jar was a cyl-
inder of  wire screening  around which was wrapped
several turns of asbestos-wrapped sewing twine.
The  walls of the jar became the collecting elec-
trode.  Three factors contributed to  the ultimate
success  of  his  first  electrostatic  precipitator.
The  first was the use of a  pubescent electrode.
He also  discovered that the use of  negative
polarity  resulted in a more stable  and  effi-
cient operation.  The third  factor was his use
of rectified alternating current.  For this pur-
pose, he developed a  mechanical rectifier. With
financial backing from friends,  Cottrell organ-
ized two corporations and constructed a pilot
collector that handled 100 to 200 cubic feet of
gas per minute. This pilot unit -was  installed
at Pinole where it operated  satisfactorily, han-
dling a gas current representing about 3 tons of
sulfuric  acid per day  and  consuming  less than
1/3 kilowatt.  The apparatus is  shown in Figure
81, taken from Cottrell's 1908 patent.

-------
138
AIR  POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
  Figure 81.   Illustration from Cottrell's  first
  (1908) electrostatic precipitation patent,  No.
  895,729 (Research  Cottrell, Bound Book, N.  J.).
                                                      1.   High efficiency can be attained.  Efficiency
                                                          may exceed 99 percent in some cases.

                                                      2.   Very small particles can be collected.  Ther?
                                                          is no theoretical lower limit to the size of a
                                                          particle that can be  collected.

                                                      3.   Dusts may be collected dry for recovery of
                                                          valuable material.
                                        4.   Pressure and temperature drops are small.
                                             The pressure drop through an electrical
                                             precipitator seldom exceeds 0. 5 inch verti-
                                             cal water column.


                                        5.   Precipitators are normally designed to oper-
                                             ate continuously with little maintenance over
                                             long periods  of time.


                                        6.   There are very few,  if any,  moving parts,
                                             which tends to reduce the maintenance
                                             required.


                                        7.   Precipitators can be used at high tempera-
                                             tures.  Temperatures up to about 700 °F are
                                             normal.  Special designs have been used for
                                             temperatures as  high as 1,300°F,  but ordi-
                                             narily the temperature does  not exceed
                                             1, 000°F  (Sproull, 1951).
Improvements  in Design, and Acceptance by
Industry

After Cottrell proved that electrical precipita-
tion could be  applied successfully to the collec-
tion of industrial air contaminants, the use of
electrical precipitation expanded into many di-
verse fields.  Table 43 lists  some of the pioneej
installations.

Table 44  summarizes the extent of the use of
electrical precipitation in the United States only
50 years  after Cottrell first succeeded in demon-
strating the practicality of this principle for the
control of industrial air contaminants.   Table 45
lists data that typify installations  of modern elec-
trical precipitators.  Obviously,  precipitators
serve for a variety of industrial applications,
r.izes,  dust concentrations, particle sizes, and
efficiencies.

ADVANTAGES AND DISADVANTAGES  OF ELECTRICAL
PRECIPITATION
The use of  electrical precipitators for the collec-
tion of  air contaminants  has  grown because of
many inherent advantages, some  of which are
now listed.
                                        8.   Precipitators  can be used to collect acid and
                                             tar mists,  which are difficult, if not impos-
                                             sible, to collect by other methods.


                                        9.   Extremely corrosive materials can be collec-
                                             ted -with special construction.


                                        10.  Collection  efficiency may be adjusted to suit
                                             the application by increasing the unit  size.


                                        11.  Very large gas flow rates can  be handled.


                                        12.  The power requirements for flow handled are
                                             low.  For example,  the actual power  required
                                             to clean 500, 000 cubic  feet of gas per minute
                                             at 95 percent efficiency,  including the draft
                                             loss, is only about 65 kilowatts (White, 1953).
                                        Electrical precipitators are by no means a pan-
                                        acea for air pollution problems.  In many cases,
                                        disadvantages far outweigh the advantages. Some
                                        of the  drawbacks are now listed.

                                        1.   Initial cost is high.  In most cases the invest-
                                             ment  is greater than  that required for any
                                             other  form of air pollution control.

-------
                                Single-Stage Electrical Precipitators
                                            139
2.  Precipitators are not easily adaptable to vari-
    able conditions.  Automatic voltage control
    helps to a great extent, but precipitators are
    most efficient when operating conditions  re-
    main constant.

3.  Some materials are extremely difficult to col-
    lect in an electrical precipitator because of
    extremely high or low resistivity or other
    causes.  In some cases, this factor alone
    makes the use of electrical precipitation un-
    economical, if not physically impossible.


4.  Space requirements may sometimes be great-
    er than those for a baghouse.  In general, this
    is true  only when high collection efficiency is
    required for materials difficult to collect by
    precipitation.
5.   Electrical precipitation is not applicable to
     the removal of materials  in the gaseous phase.
6.   The use of a precleaner,  generally of the cy-
     clonic type,  may be required to reduce the
     dust load on a precipitator.
 7.   Special precautions are required to safeguard
     personnel from the high voltage.
        Table 43.  PIONEER PRECIPITATOR
           INSTALLATIONS,  1907 to 1920
                    (White, 1957)
Application
Sulfunc acid mist from contact acid
plant, 200 cfm
Date
1907
Location
Pinole, Calif.
Smelter, zinc and lead fumes,
300, 000 cfm
Cement kiln d ist, 1 million cfm
Copper converter (lead fume).
200,'OOD cfm

Gold and silver recovery from
furnace treatment of electrolytic
copper slimes
Absorption of chlorine gas by
powdered lime followed by precipi-
tator collection
Dwight-Lloyd sintering machine
lead fume, 20, 000 cfm

Tar removal from illuminating gas,
25,000 cfm
Cleaning ventilating air in factory;
air not recirculated, 55, 000 cfm
Paper pulp recovery of alkali salts
from waste liquor evaporated gases,
90,000 cfm
Central gas cleaning plant,
2 million cfm

1910

1912
1912


1913


1913


1914


1915

1915

1916


1919


Shasta Co. , Calif. ,
Balaklala
Riverside, Calif.
Garfield, Utah,
American Smelting and
Refining Co.
Perth Amboy, N. J, ,
Raritan Copper Works

Niagara Falls, N. Y. ,
Hooker Electro-
Chemical
Tooele, Utah, Inter-
national Smelting and
Refining Co,
Portland, Oregon

New Haven, Conn. ,
Winchester Arms
Canada


Anaconda, Mont. ,
Anaconda Copper
Smelting Co.
   Table 44.  SUMMARY OF UNITED STATES
   PRECIPITATOR INSTALLATIONS IN MAJOR
           FIELDS OF APPLICATION,
            1907 to 1957 (White,  1957)

Application
Electrical power industry:
(fly ash)
Metallurgical:
Copper, lead, and zinc
Steel industry
Aluminum smelters
Cement industry:
Paper mills:
Chemical industry:
D eta r ring of fuel gases:
Carbon black:
Total
First
installation
1923


1910
1919
1949
1911
1916
1907
1915
1926

Number of
precipitators
730


200
312
88
215
160
500
600'
50
2,855
Gas flow.
million cfm



15
22. 5
5.9






157

43.4



29
18
9
4. 5
3. 3
264.2
The decision 'whether to use an electrical precipi-
tator,  a baghouse, or some other type of collector
must be made after considering all the following
factors:
1.  Initial investment;
                                                       2.
    maintenance, including the cost of power to
    operate the device;
3.   space requirements;

4.   collection efficiency,  -which must be evalu-
     ated in terms of the value of the  collected
     material or restrictions placed on  the dis-
     charge of air contaminants by local regula-
     tions, or both (sometimes good public rela-
     tions require an even higher collection
     efficiency than can be justified solely on
     the basis of economics).

The cost of providing high efficiency  is illus-
trated by the fact  that the cost nearly doubles
when electrical precipitator collection  efficiency
is increased from 80 to 96 percent and  almost
triples from 80 to 99 percent.

MECHANISMS  INVOLVED IN ELECTRICAL  PRECIPITATION

The process of electrostatic precipitation con-
sists of a number of  elements or mechanisms,
•which are now listed.

1.   Gas ions are  formed by means of high-volt-
     age corona discharge.

2.   The solid or liquid particles are charged by
     bombardment by the gaseous ions or electrons.

3.   The electrostatic field causes the charged
     particles to migrate to a collecting electrode
     of opposite polarity.

4.   The charge on a particle must be neutralized
     by the collecting electrode.

-------
140
             AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
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-------
                                Single-Stage Electrical Precipitators
                                         141
5.  Reentrainment of the collected particles must
    be prevented.

6.  The collected particles must be transferred
    from the collecting electrode to storage for
    subsequent disposal.

                                              *s*
The accomplishment of these functions by an elec-
trical precipitator has required the development of
many specialized techniques for specific materials,
though the broad principles remain as enumerated.

 DIVERSE  APPLICATIONS OF ELECTRICAL PRECIPITATION

Table 46 illustrates the broad spectrum of ma-
terials that are collected by electrical precipita-
tion and the range of dust concentrations that may
be encountered in practice.

Dispersoids in gases may be a one-component
system, but two or more components are usual in
industrial air pollution control.  The dispersed
phase maybe a liquid, as in clouds, mists, or in
sprays, or may be a solid,  as in a dust cloud or
metallurgical fume.  Dispersed systems include
dusts,  fogs, clouds,  mists,  hazes,  fumes, or
smokes.

In general,  the  size of dust particles varies from
5 to 100 microns and fumes vary from 0. 1 to 5
microns.  Table 47 lists typical particle sizes
encountered in industrial dusts and fumes.
Construction Details of Electrical Precipitators

Essential features  of precipitator design, exem-
plified in Figure 82,  include the following ele-
ments:  Rappers,  shell, cable from rectifier,
support frame,  corona "wires, collecting plates,
gas inlet, hoppers,  wire-tensioning weights, and
hopper baffles.
Discharge electrodes

The discharge electrodes provide the corona,
without which the precipitator cannot function.
These may be round wire, square twisted rods,
ribbons, barbed wire, and so forth.  Steel al-
loys are commonly used, but other materials
that have been used include stainless steel,
fine silver, nichrome,  aluminum,  copper,
hastelloy, lead-covered steel wire,  and titani-
um alloy.  While the  choice of material is  usu-
ally dictated by the requirements of  corrosion
resistance, the physical configuration must be
determined to meet the  electrical characteris-
tics requirements.  When round wires are
used,  the diameter is usually about  3/32 inch,
though it may vary from about 1/16 to 1/8  inch.
Conventionally,  3/ 16-inch-square twisted wire
has been used for precipitators serving catalytic
cracking units.   The use of barbs and various
special shapes is strongly advocated by some
authorities, but others equally competent dispute
these claims, pointing out that no decided ad-
vantage has ever been established for the use of
special discharge electrodes.

Collecting  electrodes

The variety of collecting electrodes available
is even more diverse.  Materials of construc-
tion and special  shapes appear to be limited
only by the imagination of the  designer.  While
many of these special shapes have important
advantages, the use of smooth plates,  -with
fins to strengthen them and produce quiescent
zones, has become most common in recent
years.  The preference between one special
shape and  another frequently becomes one of
conjecture.  Figure 83 illustrates  some of the
special collecting electrode configurations
marketed.   These include perforated or ex-
panded plates,  rod curtains, and various hol-
low electrodes -with pocket arrangements on
the outside surfaces for conducting the pre-
cipitated dust to  the hopper in quiescent gas
zones.  Concrete plates were  used at one time
but were abandoned about 1930 because of
excessive  cost and weight.  Smooth transite
plates are  used occasionally because of their
excellent corrosion resistance.  These are,
however, for unusual cases, because of the
severe  reentrainment problem.  For fly ash,
perforated or expanded metal  plates provide
a multiplicity of  closely spaced holes that
hold the ash while end baffles  on the plates
shield the  perforated surfaces from the di-
rect scouring action of the gas.  Several vari-
ations of the V electrode have also been used
and have similar characteristics.  The hollow
or pocket-type electrodes are attractive in
principle,  but in practice,  a large proportion
of the dust actually falls  on the outside of the
plates.  Furthermore, much of the dust col-
lected in the upper openings actually escapes
to the outside through the lower  openings be-
cause of the piston action of the  falling dust
(White, 1953).

Tubular collecting electrodes

Plate-type precipitators  are usually preferred
because they can handle a larger volume of gas
in a smaller space for less investment than the
tube type.  The tube type, often  called "pipe
type," lends itself more  readily, however,  to
wet collection and is,  therefore, preferred for
acid mists and tars.  In the case of detarring
precipitators, the tar collects on the inside
walls of the tubes and runs by gravity to col-

-------
142
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
                     Table 46.  CONCENTRATIONS OF SUSPENDED MATTER
                       IN COMMERCIAL GASES IN TYPICAL ELECTRICAL
                    PRECIPITATOR INSTALLATIONS (Kirk and Othmer, 1947)



Acid mist--sulfuric acid (contact plant)
After roaster
Multiple-hearth roaster--zinc and pyrites
Flash roaster--zinc blend
After absorbers--tail gases
Acid mist- -phosphoric acid--from burning
phosphorus (basis 100% H3PO4>
Assay offices and mines — ventilating gases
from furnaces and assay operations
Carbon black
From cracking natural gas
From oil cracking
Carbureted water gas
Dry-tar basis
Wet-tar basis
Catalytic cracking units --oil
Atmospheric-pressure units --after me-
chanical collector
Natural catalyst
Synthetic catalyst
High-pressure units --after mechanical
collector
Natural catalyst
Synthetic catalyst
Cement-kiln gases (wet process)--dust con-
centrate entering stack
Wet-gas basis
Dry-gas basis
Coke-fired producer gas
Coke-oven gas
Ahead of exhausters, dry-tar basis
After positive -displacement exhausters,
wet-tar basis
After centrifugal exhauster, wet-tar basis
Fly ash from boilers burning pulverized
soft coal
Gypsum-plant gas
From rotary calciners, wet-gas basis
From dryers, wet-gas basis
From gypsum kettles, dry-gas basis
Incinerators burning dry sewage sludge
Silica-rock treatment
Oil-fired rotary dryer
Preheater gases
Ventilating system
Tin smelting
Reverberatory furnaces
Calcining tin ores--rotary kilns
Zinc sintering ma chine --straight and
chloridized roast
Zinc-ore roasting
Flash roaster
Multiple-hearth roaster
Zinc oxide- -Waelz plant
Concentrations,
grains /ft-1
of gas, STP


1.08 to 5.80
0. 00475 to 0. 05550
0.722 to 2.310
48. 3 to 66. 2

0.0028 to 0.0515


5. 1 to 17
19 to 40

0.765 to 1.590
1.08 to 2.26



19.45 to 85.60
16. 5 to 52. 9


7. 19 to 22. 75
4. 69 to 94. 60


2.62 to 3.80
3. 34 to 4. 68
0.03 to 0.06

4.51 to 4.88
3.14 to 4.58

1.66 to 3.74
1 to 5


32. 82 to 48. 07
64.52
6.72 to 26. 98
3.17 to 4.35

6.42 to 23. 50
6. 65 to 15.80
9.37 to 26.20

2,20 to 3.12
1.44 to 4.59
0.311 to 1.908


3. 92 to 45. 05
3.82 to 7.07
12.65 to 28. 62

-------
                                Single-Stage Electrical Precipitators
                                            143
        Table 47.  AVERAGE DIAMETER
   OF PARTICLES  IN VARIOUS INDUSTRIAL
   OPERATIONS  TYPICAL OF ELECTRICAL
       PRECIPITATOR INSTALLATIONS
            (Kirk and Othmer,  1947)
Particle
Coal dust
Powdered-coal ash
Tobacco smoke (tar mist)
Cement dust
Talc dust
Silica dust
Sprayed-zinc dust
Flour -mill dust
Alkali fume
Ammonium chloride fume
Zinc oxide fume
Condensed-zinc dust
Pigments
Sprayed dried milk
Average
diameter, |ji

1

5




1
0


0
0
10
to 150
0. 25
to 100
10
5
15
15
to 5
. 1 to 1
0. 05
2
.2 to 5
. 1 to 3
 lecting troughs below.  In the case of acid mist
 collectors, a continuous film of -water is main-
 tained on the tube wall by means of weirs.  The
 tube-type precipitator is also commonly used
 in the steel industry to clean combustible gas
 from blast furnaces to prevent fouling of the gas
 burners.
Removal of dust from collecting electrodes

Once the dust or fume has been precipitated
on the collecting electrode or plate, it must be
removed to a hopper or storage depository.  In
order to do this, rappers are commonly em-
ployed.  The plates are struck sharp,  hammer-
like blows to dislodge the collected dust,  which
then falls by gravity into the collecting hopper.
Reentrainment of a portion of the dust at this
point must be held to a minimum.   Frequently,
satisfactory collection efficiency is completely
negated by improperly operated or adjusted
rappers.

For fly ash precipitation, the dust buildup on
the collecting plates should be allowed to reach
about 1/4 to 1/2 inch before it is rapped off.
Discharge electrode rappers are necessary
•when treating "ashes predominantly composed
of fine particles less than 10 microns in di-
ameter (White,  1953).

A satisfactory rapping  system is characterized
by a high degree of reliability,  by ability to
maintain uniform and closely controlled raps
over long periods of time without attention, and
by flexible and easily controlled rapping inten-
sity.  The usual practice is  to rap sufficiently
to dislodge all the dust layer at one time. Stack
puffs are prevented by rapping only a small
fraction of the electrodes at a time and using
proper sequence.

Rapping mechanisms include mechanical (elec-
tric motor operated) and pneumatic or air oper-
ated.  Most new installations, however, now use
magnetic solenoid-operated rappers,  which can
be adjusted more accurately to control  both fre-
quency and intensity of the  raps.

Rapping is usually done in zones, the number
and location  of rappers being dictated by the
size and configuration of the precipitator.  Rap-
pers are always adjusted in the field under oper-
ating conditions.  Factors that influence the
intensity, frequency, and number of blows re-
quired per cycle include:

1.   Agglomerating characteristics of the dust,

2.   the rate  at which the dust is accumulated on
     the collecting electrode,

3.   the tendency of the dust to become  reen-
     trained,

4.   the effect of the accumulated dust on the
     electrical operation of the precipitator,  and

5.   the cycle of operation of the equipment being
     served.

In some cases where reentrainment is a severe
problem, precipitators may be designed so that
a number of  sections may be closed in turn dur-
ing rapping by means of dampers.  While this
may reduce the reentrainment loss during  rap-
ping, the usual practice is to rap during normal
operation. When the equipment being served
operates in cycles,  it may be possible to bypass
the precipitator for rapping during periods when
little or no air contaminants are being vented.
In some unusual cases it may be necessary to
deenergize the precipitator in order to  obtain
effective removal of the collected dust during
rapping.  In  other cases deenergizing may suf-
fice to permit the collected dust to fall to the
hopper by its own weight without the need to rap.
With tube-type precipitator s, when operated wet,
it is not necessary to use rapping.  Some plate-
type precipitators are also operated without
rappers for various reasons.  For example,
when transite plates are used, rapping  is unde-
sirable because these plates do not have ade-
quate mechanical strength to -withstand  repeated
blows.  Hence,  periodic -water sprays are  usu-
ally used in this case to -wash the collected dust
off the plates.   Cycling the -water sprays prop-
erly makes possible keeping the plates -wet be-
t-ween flushings, which is a great aid in improv-

-------
144
               AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
                                                 HT  CABLE FROM
                                                 RECTIFIER
                                                                                       GAS
                                                                                        NLET
                                                                                  HOPPERS
                                                                     WIRE-TENSIONING
                                                                     WEIGHTS
                                                                HOPPER BAFFLES
                Figure  82.  Basic structure  of a typical  precipitator (Western  Precipi-
                tation,  Division of  Joy  Manufacturing Co.,  Los Angeles,  Calif.).
ing collection efficiency by minimizing reen-
trainment.  The water sprays, •when used,  tem-
porarily disrupt the electrical operation, so
that this method is employed only in unusual cases.
ment, poured concrete,  carbon, tile, aluminum,
wood, •wrought iron, alloys of steel, rubber-
coated steel, and vinyl,  or other plastic coat-
ings on  steel or other  supporting structures.
Precipitator shells and hoppers

Precipitator shells may be made of a variety of
materials.  These include ordinary mild steel,
lead-coated steel, acid-resisting brick and ce-
The collected dust is ordinarily stored in hop-
pers below the collecting electrodes for peri-
odic or continuous disposal.  Adequate storage
must be provided to accommodate the collected
dust between hopper cleanouts. If the dust

-------
                              Single-Stage Electrical Precipitators
                                                                 145
  GAS  FLOW
       ROD CURTAIN
                             GAS  FLOW
                                 ZIG-ZAG PLATE
                     The values of the potential difference used in single-
                     stage electrical precipitation are usually from
                     20, 000 to  100, 000 volts.  Since unidirectional cur-
                     rent is required for electrical  precipitation,  it  is
                     necessary to transform the available power to a
                     high voltage and then  rectify the high voltage.
                     Early precipitators used mechanical rectification
                     exclusively, and many of them are still in use.
    [[33   [
    GAS  FLOW
    [  [  ]  3   [
      COMMON PLATE
                             GAS FLOW
DUAL  PLATES
Tube-type rectifiers

Electronic tube rectifiers were first used in elec-
trical precipitation around 1920.  The early tubes
•were unsatisfactory because of their short,  un-
certain life.  These tubes have now been devel-
oped to the point where the average life in elec-
trical precipitation service is  in excess of
20, 000 hours.  In some cases  over 30, 000 hours
of service have been obtained.
                    VERTICAL  GAS
                     FLOW PLATES

  Figure  83.  Some special  collecting  electrodes
  used  in  electrical  precipitators  (Western Pre-
  cipitation, Division of Joy  Manufacturing Co.,
  Los  Angeles, Cal i f.).
                     Filament voltage adjustment on tube rectifiers
                     is a critical factor in tube life.  As a rough
                     guide,  increasing filament voltage by 5 percent
                     reduces filament life by a factor of 2 while re-
                     ducing voltage by 5 percent increases filament
                     life by a factor of 2.   Thus, it is general prac-
                     tice to operate tube filaments in precipitator
                     service at 5 to  10 percent below rated values,
                     that is, at 18 to 19 volts rather than 20 volts,
                     •which is the rated value for most  precipitation
                     rectifier  tubes  (White,  1953).

                     Solid-state rectifiers
builds up to too high a level in the hopper, there
is danger of reentrainment or shorting the dis-
charge electrodes,  or both.  The sides of the
hoppers must have adequate slope to prevent
bridging and hangup.  Vibrators may be re-
quired if the dust or fume does not move free-
ly.  Discharge from the hoppers may be by
means of slide gates, motor-operated rotary
valves, or screw conveyors.  The latter two
are  suitable for continuous operation.

High Voltage for  Successful  Operation

In order to achieve maximum collection effi-
ciency, electrical precipitators are operated as
close to the sparking voltage as practicable with-
out excessive sparking.   The following gives the
order of magnitude of current and field strength
usually encountered in practice (Perry,  1950).

            3           4
i  =3x10   to  3 x  10  statampere/cm (0. 03
     to 0. 3 milliampere/ft)

E  = 5 to 20 statvolt/cm (3.8 to 15.3  kilovolts/in.
                     The development of solid-state rectifiers has
                     made mechanical rectification obsolete.  Se-
                     lenium rectifiers provide reliable service with
                     long  life; however, they are subject to damage
                     from excessively high temperatures.  Silicon
                     rectifiers, which are even newer in precipita-
                     tion  service, do not have the shortcoming of
                     being subject to temperature damage.  Al-
                     though  the solid-state  rectifiers  are somewhat
                     more expensive than the electronic-tube type,
                     their use is justified on the basis of a long,
                     useful life and troublefree  operation.  Life
                     expectancy of selenium rectifiers is estimated
                     to be about 100, 000 hours.  Silicon rectifiers,
                     which are hermetically sealed,  appear to have.
                     unlimited life (Peach,  1959).
                     Effects of Wave  Form

                     Rectifier connections are either half wave or
                     full wave.  The half wave connection is pre-
                     ferred in some  cases, since it permits a
                     greater degree  of precipitator sectionaliza-
                     tion with a given number of electrical  sets. In

-------
146
AIR POLLUTION CONTROL EQUIPMENT FOR P ARTICULATE MATTER
large precipitators,  the corona electrodes are
always  subdivided into several groups or sec-
tions,  and the individual sections separately
energized by individual rectifier  sets.  This
arrangement permits each section to be operated
under optimum  conditions and is  necessary for
optimum performance.  Although half wave con-
nection is  sometimes preferred,  full wave is
usually used on the outlet sections, to  supply the
greater corona  current demand required for these
sections.

Typical operating voltages for fly ash precipitators
of 8- or 9-inch  plate-to-plate spacing range between
40 and 55 kilovolts.   Corona currents usually lie
between 10 and  30 milliamperes per 1, 000 feet of
discharge wire.  The average electric power
supplied to the corona commonly ranges between
40 and 120 watts per 1, 000 cubic  feet per minute of
gas treated.  In general,  higher voltage and power
provides higher precipitator efficiency  and perfor-
mance (White,  1953).


Controlled  Sparking  Rate

Recent research has shown that,  contrary to
earlier ideas,  optimum collection efficiency is
usually obtained with precipitator voltages set
high enough  to produce a substantial amount of
sparking  (White, 1963).  Some precipitators,
however,  operate with practically no sparking.
The optimum degree of sparking  depends upon
many factors,  such as precipitator size,  fume
characteristics, fume concentration, and so forth.
Maximum efficiency usually occurs from 50 to 100
sparks  per minute.   Figure 84 illustrates the vari-
ation of precipitator efficiency with sparking  rate
for a particular combination of precipitator de-
sign and operating conditions, such as tempera-
ture, moisture  content, and so forth.
                50           100
                     SPARKS PER MINUTE
 Figure  84.   Variation of precipitator  efficiency
 with sparking  rate for a representative  fly-ash
 precipitator (White,  1953).
                                       Operating  Voltage

                                       The operating voltage of a precipitator cannot be
                                       predicted  precisely.  Dust conditions have an
                                       important bearing on the operating voltage.  For
                                       practical purposes,  each manufacturer standard-
                                       izes on a limited number of basic transformer
                                       voltages.  For example, one manufacturer (Cottre
                                       Electrical Precipitators, 1952) designs all equip-
                                       ment around transformer ratings of 30, 000; 60, 00
                                       75, 000; and 90, 000 volts secondary.

                                       The use of automatic voltage control results in
                                       increased  collection efficiency from the same
                                       size precipitator or  permits the use of a  smaller
                                       precipitator for  the same collection efficiency.
                                       The precipitator voltage is maintained at the  op-
                                       timum value by a spark counter or current-sensing
                                       feedback circuit.  Once the control has been set
                                       for the desired spark rate, the precipitator is
                                       held constantly at maximum efficiency regardless
                                       of fluctuating  conditions and without attention from
                                       an operator.

                                       Uniform Gas Distribution

                                       The average velocity of the gas in the duct up-
                                       stream from a precipitator is  usually 40 to 70
                                      feet per second.   In the treater, however, the
                                      gas velocity is 2 to 8 feet per  second. Because
                                      maintaining uniform  gas velocity and dust distri-
                                      bution in the treater  is  important, much atten-
                                      tion has been paid to the transition from a high
                                      velocity in the duct to a low velocity in the pre-
                                      cipitator.   Splitters are almost universally used
                                      in all bends or elbows in the approach to the pre-
                                      cipitator.   This also helps  reduce the draft loss.
                                      Distribution grids of many types have been devel-
                                      oped, some of -which are shown in Figure 85.
                                      The choice of type to use in a  particular instal-
                                      lation can usually be made reliably only by means
                                      of scale-model studies.  Much of the work in this
                                      field is trial and error  until a  reasonably uni-
                                      form gas velocity distribution  is obtained in the
                                      model.  The percentage of open area has  an im-
                                      portant bearing on the performance of distribu-
                                      tion grids.  Experience may reduce the problem
                                      to one of degree rather than of kind so that  all
                                      that need be determined is the optimum position
                                      of the grid. In some  cases, installing  a perfor-
                                      ated plate at the outlet of the precipitator has
                                      been found  as  important as  installing  one  at the
                                      inlet. A very common  type of design consists
                                      of one or two flat perforated plates at  the inlet
                                      of the treater.


                                      Cost of Electrical  Precipitator Installations

                                      Table 45 shows the variation of costs for  elec-
                                      trical precipitators depending  upon the size,
                                      type of dust or fume, and efficiency required.
                                      Preliminary engineering  studies and model
                                      studies for gas distribution may add substan-

-------
                                  Single-Stage Electrical Precipitators
                                             147
                 PROTRUDING FACE
                 OF BASKET TOHARD
                 COLLECTOR INLET
                                 POINT OF CONE TOWARD
                                 COLLECTOR INLET
 Figure 85.   Examples of  special  perforated plate
 gas distribution  grids  (Western  Precipitation
 Corporation,  Division of  Joy Manufacturing Co.,
 Los Angeles,  Cal if.).
tially to costs shown.  The costs  of ductwork
to and from the precipitator,  of foundations,
and of extending utility services to the area of
the precipitator  are in addition to the installed
cost of the precipitator itself.  Factors affect-
ing the cost of the precipitator include the pow-
er supply (rectifier, automatic voltage control,
number of sections individually energized, and
so forth), special plate design, electrical charac-
teristics of the dust or fume,  collection efficien-
cy required,  and special materials  or type of
construction needed to resist  corrosion or wear.

Theoretical  Analysis  of Precipitator Performance


A theoretical analysis of precipitator mechanisms
and performance involves two fundamental pro-
cesses, particle charging and particle migration.
Many factors affect both these mechanisms.
Particle charging

In order to derive  an expression for the rate of
particle charging (White, 1951) and the maximum
charge  attained by a particle, the following as-
sumptions are made:

1.   The particles  are spherical.
2.  Particle spacing is much larger than particle
    -dameter.

3.  The ion concentration and electric field in
    the region of a particle are uniform.

These assumptions are reasonable approxima-
tions  except for a few cases •where the shape of
the particle may depart radically from the spheri-
cal.

A particle entering the  charging field of an elec-
trical precipitator is bombarded by ions.  Some
strike the particle and impart their charge to it.
As  soon as  a charge has been acquired by the
particle,  an electric field is created that repels
similarly charged ions.  Some ions continue to
strike the particle, but the rate at which they do
so continually diminishes until the charge ac-
quired by the particle is sufficient to prevent
further ions' striking it.  This, then,is the lim-
iting  charge that can be acquired by the particle.

The motion of gas ions  in the electrostatic field
of an  electrical precipitator constitutes an elec-
tric current

             i  =  j A                       (55)
where
     i  =   electrical current, statampere

    j  =   current density,  statampere/cm
    A  =   area, cm .

The ion current density in the undistorted field
region outside the immediate influence of the
particle is
            j  =  N  £ M E
                                 (56)
where
     N  =  number of ions per cm"
     £  =  elementary electrical charge = 4. 80
                         ilomb
                          cm/sec
x 10"   statcoulomb
     M  =  ion mobility,
                        statvolt/cm
The area of the ion stream  that  enters the
particle is  determined by the total electric  flux
as follows
                A  =
                                                                             k E
                                                                                                   (57)
where
        =  total electric flue,  statcoulombs
     k  =  permittivity of free space, numerical-
           ly equal to 1 in the cgs electrostatic
           system of units.
234-767 O -77 - 12

-------
148
       AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
From electrostatic principles the electric flux
is found to be
  -e
1   (
                „     _
              p E cos 0-
                         n £
     = p TT  a  E
a  sin 6 d9

         (58)
where


    p =  a factor defined in equation 61


    n =  number of elementary electrical charges
          acquired by a particle


    a =  radius of a particle,  cm.


Substituting and noting that the  ion current is  de-
termined by the number of  elementary electronic
charges in a given time
                                             (59)
Upon integration,  the number of elementary elec-
tronic charges acquired by a particle of radius a
in time t is found  to be
                                                   n  =  the limiting number of elementary elec-
                                                        trical charges acquired by a particle
                                                        at saturation
                                                   E  =   strength of charging field at the point
                                                         where the particle acquired its charge,
                                                         statvolt/cm.

                                              For conditions normally existing in average pre-
                                              cipitators,  charging can be considered reason-
                                              ably complete in about 0. 1 second.  Since the
                                              gas velocities are usually 2 to 8 fps, a particle
                                              may travel only a few inches, or a foot at most,
                                              before it has for all practical purposes attained
                                              its  limiting or saturation charge.   Some charg-
                                              ing also occurs by means of ion diffusion but
                                              this can usually be neglected for particles larger
                                              than about 0, 5 micron in diameter and does  not
                                              become a significant factor unless the particles
                                              are smaller than about 0. 2 micron in diameter.
                                              The usual  practice is to  assume that only ion
                                              bombardment charging occurs.  Any error in-
                                              troduced by this simplification is  usually of  less
                                              magnitude than the effects  of nonuniform gas
                                              distribution, reentrainment, high dust resis-
                                              tivity, rapping losses, and other practical prob-
                                              lems that usually increase the actual losses by
                                              a factor 2  or 3 times  (White,  1953) the theoret-
                                              ical value.  The particle-charging time  con-
                                                      stant to is defined as
                                                                        1
                                                                     TT N £  M
                                                                                         (63)
                           t +
                                   1
                                             (60)
                                TT N £ M
where
    P  =
  a factor  that  depends upon the die-
  electric constant D of the particle.  The
  numerical value of p ranges from a
  value of 1 for materials 'with a dielectric
  constant of 1 to 3 for some dielectric
  materials,  and is defined by
                  =   1  +
                  2 (D - 1)
                    (D + 2)
                                    (61)
 As the time t becomes large the value of the lim-
 iting or saturation charge is
           =  n  £   =  p E a
              s
                                           (62)
 where
=  the limiting charge acquired by a par-
   ticle, statcoulomb
                                               and is the time required for 50 percent of the
                                               limiting charge to be attained.

                                               Particle migration

                                               The force Fj (in dynes) exerted on a charged
                                               particle in an electric field is proportional to
                                               the charge q (in statcoulombs) on the particle
                                               and the strength E  of the electric field.
                                                                       1
                                                                          =   qE
                                                                                        (64)
                                                      where
                                                           E =  strength of precipitating field, stat-
                                                                volt/cm.
                                              This force accelerates the particle until the
                                              viscous drag,  or resistance of the gas  in -which
                                              the particle is suspended,  exactly equals the
                                              force exerted by the electric field.  Under con-
                                              ditions normally existing in an electrical pre-
                                              cipitator, the viscous drag FZ (in dynes) is
                                              defined by Stokes law
                                                                         =   6
                                                                        a u w
                                                                                                (65)

-------
                                Single-Stage Electrical Precipitators
                                                                  149
where

     a  =   radius of particle,  cm

     u  =   viscosity of gas stream, poise

     w  =   velocity of a particle relative to the
           gas in -which it is suspended, cm/sec.

Substituting the charge q acquired by the particle

                                2
                F    =  p E E  a"
                 1           P
         (66)
Since F\ must be equal to F£ under equilibrium
conditions, the equations may be equated.  Solv-
ing for the particle velocity
                       p E E  a
                       	P
                 w  —     ,
                          6 TT U


For most common materials the dielectric con-
stant D is 2 to 8.  Thus, the value of p varies
from. 1. 50 to  2. 40,  or the average is very near-
ly 2.  The charging field E and the precipitating
field Ep are created by the same mechanism.
Tests have  shown that the field strength is not
uniform, being highest in the vicinity of the dis-
charge electrode (White and  Penney, 1961).  It is
a common practice, however, in calculating the
drift velocity, to assume  that these are approxi-
mately equal.  Making  this assumption, and  con-
verting the  cgs units to those more convenient for
practical application,  we  obtain for a particle in
air at 60° F
            =  8.42
dp
(68)
•where
     w  =  the particle drift velocity, ft/sec

     E  =  the potential applied to the discharge
          electrodes,  KV/in.

     d  =  the diameter of the particle, microns

     p  =  a factor as before.

If the medium is a gas other than air  or if the
air temperature departs from standard by more
than about 50°F, a multiplying factor of 0.  0178/u
must be used to  correct for the effect of viscosity,
with u in centipoises.

In tests performed by White  (1953) on an electri-
cal precipitator  collecting fly ash from an  elec-
tric steam power plant, the drift velocity was
calculated on the basis of actual measured  effi-
                     ciency.  The drift velocity was found to be con-
                     sistently about one-half that calculated from the
                     theoretical equations.  The theoretical equations,
                     however,  neglect such effects as nonuniform gas
                     velocity,  erosion of dust, rapping losses,  co-
                     rona quenching,  high resistivity, half-wave rec-
                     tification,  and so on.
            Theoretical Efficiency

            The trajectory of a particle in an electrical pre-
            cipitator can be determined if the folio-wing as-
            sumptions are made:

            1.   The strength of the precipitating field is
                uniform.  This  is nearly true except in the
                vicinity of the discharge electrode.

            2.   The migration or drift velocity w of the
                particle is constant.  This is true for a
                particle with a constant charge in a uni-
                form field.   Since the limiting  charge is
                closely approached within the first foot or
                less of travel, this is a valid approxima-
                tion for the conditions  actually encountered
                in precipitators.

            3.   The average forward velocity v of the par-
                ticles suspended in the gas stream is  uni-
                form.  Since precipitators almost always
                operate with Reynolds numbers in the tur-
                bulent range, the statistical mean velocity
                of the particles may be considered uniform
                in the direction of flow through the pre-
                cipitator.

            From the assumptions equation 69  is derived:
                                                                 dv
                                                                 dt
                                   =  C
                                           dw
                                                      (69)
                     -where

                         v =  mean velocity of a particle in the gas
                               stream in the direction of gas flow,
                               ft/sec

                         w =  mean velocity of a particle perpendic-
                               ular to the gas stream or in the direc-
                               tion of collecting electrodes, ft/sec.

                     By integration
                                        =  C  w +
                                           C.
(70)
                     The constants Cj and C^ depend upon dimensions
                     of the precipitator,  the field strength, the point
                     at which the particle enters the electrical field.

-------
150
     AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
the mean velocity of the particle through the pre-
cipitator, and the electrical properties of the
particle  and the particle diameter.  Thus, the
trajectory is different for each particle, but it
is approximately a straight line.   If all the par-
ticles have  the same electrical characteristics,
and the worst case of a particle's  entering mid-
way between the collecting electrodes is consid-
ered, the only variable is the particle diameter.
For each particle diameter there  is some finite
length of collecting  electrode  required in order
to achieve theoretical 100 percent collection
efficiency.  This length is defined by
                     L  =
                sv
                w
                                            (71)
where

     L
length of collecting electrode in di-
rection of gas flow, ft

separation of discharge and collec
ting electrodes, ft.
The calculation of the theoretical length required
for 100 percent collection efficiency is illustrated
by the folio-wing example:
Example  19

Given:

A plate-type precipitator -with 8-in.  plate-to-
plate spacing and an applied voltage of 40, 000
volts.   Mean gas velocity through the  precipita-
tor is 5 fps and the minimum particle diameter
is 0. 5 (j..

Problem:

Find the minimum length of collecting electrode
in the direction of gas flow required for 100%
collection efficiency.


Solution:

1.  Migration velocity from equation  68 using
    P = 1
                         -3  40
        w  =  (8.42 x 10   ) —   (0.5)  =  0.421 fps
 2.   Length of collecting electrode from equa-
     tion 71
                                     "  «•«*
     If charging is  considered practically com-
     plete in 0. 2 sec,  an additional 1 ft must be
     added to allow for the distance traveled by
     the particle -while being charged.  The length
     of collecting electrode in the direction of gas
     flow required  for 100% collection efficiency
     is therefore 5 ft theoretically.


Deficiencies in  Theoretical  Approach to Precipitator
Efficiency

Example 19 illustrates that 100 percent collec-
tion efficiency should result theoretically from
a precipitator 5 feet long  in the direction of gas
flow when the particles  suspended in the gas are
0. 5 micron or  larger.  This particle size  is
fairly typical of that encountered in practice.
The length of a precipitator is,  however, gen-
erally bet-ween 8 and 24 feet in the direction of
gas flow.   Yet no precipitator operates  -with
100 percent collection efficiency and, in fact,_
very few operate -with collection efficiencies
much greater than 98 percent.   The precipitator
in Example 19,  if only 5 feet long, might pos-
sibly fail to exceed 50 percent  collection effi-
ciency in an actual case,  depending upon the
electrical properties of the particles, opera-
tion of the  rappers, and other factors not con-
sidered in  the theoretical approach.


Effects of Resistivity

A dust such as  carbon with very low  electrical
resistivity (Schmidt et al. ,1950) readily re-
linquishes  its negative charge to the  collecting
electrode and assumes a positive charge.  Since
positive charges repel each other, the carbon
particle is repelled from  the collecting  elec-
trode into the gas stream -where it is bombarded
by negative ions  and becomes negatively charged
again.  The particles  are thus alternately  at-
tracted and repelled and so skip through the pre-
cipitator, knocking other  particles,  -which have
already been collected,  off the collecting elec-
trode.

If the dust,  for example   powdered sulfur,  has
a high electrical resistivity, it is unable to
give up its negative charge to the collecting
electrode.   As the layer of dust builds up on
the  electrode,  it acts  as an insulator.  The po-
tential drop across this dust layer may  build
up to high values,  -which may have an adverse
effect on the corona discharge  and may  set up
a secondary brush discharge at and within the
dust layer.   This condition is  called  "back dis-
charge" or  "back corona, " and may seriously
impair the performance of the precipitator.

When the dust, for example  cement dust, has
medium resistivity, it can relinquish part of

-------
                                   Single-Stage Electrical Precipitators
                                             151
its  charge to the collecting electrode.  The
rate at which the charge leaks off increases as
the dust layer builds up and the potential drop
across the dust layer increases  until a condi-
tion of equilibrium is achieved.  Sufficient neg-
ative charge is  retained by the particles to
maintain a force of attraction between the par-
ticles  and the collecting electrode.  When the
•weight of the collected dust becomes sufficient-
ly great, particles fall off, of their own weight,
or are jarred loose when the electrodes are
rapped.
The electrical resistivity varies with tempera-
ture and moisture,  as illustrated in Figure 86
for some representative dusts.   Collection ef-
ficiency is adversely affected •when the electrical
resistivity is as low as  10* ohm-centimeter or
as high as 10   ohm-centimeter.  Apparently
then, for many materials, collection efficiency
is adversely affected when the temperature is
250 to 400 °F, the range in which it is normal-
ly desired to operate the precipitator.  The ad-
verse effects of high resistivity may be avoided
by operating at a higher temperature, but this
is usually not desirable because  of the  addition-
al heat losses.  Operation at lower temperatures
to the  left of the peak of the resistivity curve is
frequently objectionable because of excessive
corrosion.  An alternative is to increase the
moisture content or add other conditioning agents.

The addition of water vapor, acid, or other con-
ducting material increases the surface conductiv-
ity of high-resistivity dusts by adsorption on the
particle surfaces,  which reduces the apparent
electrical resistivity.  Some materials used as
conditioning agents include water vapor,  am-
monia, salt, acid, oil, sulfur dioxide, and tri-
ethylamine  (Schmidt and  Flodin,  1952).

In addition to the beneficial effects on the  elec-
trical  resistivity of the dust by the addition of
moisture, water vapor has a pronounced effect
on the  sparking voltage in an electrical precipi-
tator.  This effect is shown graphically in Figure
87, plotted  from experimental data.  In most
cases  the effect of the moisture on the electri-
cal resistivity of the dust predominates when the
temperature is  below 500°F, and the effect of
the moisture in increasing the sparking potential
predominates at temperatures above  500°F
(Sproull  and Nakada, 1951).
                                                                             300
                                                                             TE«PEB1!UBES 'I
  Figure 86.  Variation of  apparent  resistivity with temperature  and  moisture  for some typical  dusts and
  fumes:  (left) apparent  resistivity  of powdered lime rock used  in  making Portland cement;  (right) ap-
  parent resistivity of fume  from  open-hearth furnace (Sproull  and  Nakada,  1951).

-------
152
               AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
  25
                                         I 2.in  G«P
                  10       15
              AIR MOISTURE. voI
                                  a tm
 Figure 87. Sparking potential  for  negative point-
 to-plane 0.5-inch gap as  a  function of the mois-
 ture content of air at 1  atmosphere pressure for
 various temperatures (Sproull  and  Nakada, 1951).
Although there is no doubt that the electrical prop-
erties of dusts and fumes may drastically affect
the operation of a precipitator, knowledge of
quantitative relationships in this  respect is lim-
ited.  It is known that perforrnance is reduced as
the electrical resistivity becomes exceptionally
large or small.  Some data have  been published
on the variation of electrical resistivity with
temperature and humidity for a few dusts and
fumes.  Sproull and Nakada (1951) analyze the
potential drop across a layer  of collected dust.
Precipitation theory has  not yet been developed
to the point -where collection  efficiency can be
accurately predicted without  reliance on empir-
ical data.
Methods of Reducing Reentroinment

Unless the dust collected by the precipitator can
be retained,  the entire effort is wasted.  Once
it is collected by the collecting electrode,  the
dust may be  reentrained into the gas stream owing
to (1) low resistivity, which permits the negative
charge to leak off too rapidly and a positive
charge to be acquired; (2)  rapping; and  (3) ero-
  sion of the collected dust from the collecting
  electrode.  This may be because of nonuniform
  gas velocity,  which results in excessively high
  velocity through some sections of the precipita-
  tor or excessive turbulence.

 The effects of low resistivity are not amenable to
 correction.  Fortunately, this problem does not
 frequently arise.  In the  case of carbon black,
 which has too  low a resistivity to permit pre-
 cipitation, a practical solution has  been found.
 The electrical precipitator agglomerates the
 particles  of carbon that cannot be retained on the
 collecting electrodes because of their low  resis-
 tivity.   The agglomerated particles are collected
 by a centrifugal collector that follows the pre-
 cipitator.

 To reduce erosion of dust from the collecting
 electrodes, various special designs of elec-
 trodes  are used.   The objective in all these de-
 signs is to provide quiescent zones to prevent or
 reduce erosion.  The difficulty is reduced  ma-
 terially by good gas distribution in the precipita-
 tor.  The  original design must take into considera-
 tion the nature  of the dust so that the maximum
 velocity through the treater will be less than the
 critical value at which erosion begins to increase
 sharply.   The  critical velocity for any particular
 dust can be determined only by actual test. Some
 typical values  for the gas velocity at which ero-
 sion becomes significant  are 2 fps for carbon
 black,  8 fps for fly ash and 10 to 12 fps for ce-
 ment kiln dust (Schmidt,  1949).

 Dust reentrainment during rapping is controlled
 by adjusting the rapping cycle and intensity to
 minimize the degree of reentrainment.  Rap-
 ping cycles are determined experimentally after
 the precipitator is placed in normal operation.

 Rose and Wood (1956) analyze the theoretical col-
 lection  efficiency when reentrainment is con-
 sidered to show that the equation for the loss takes
the form
             Loss  =  C
                          kt
                                           (72)
 where

C and k

constants that depend upon the con-
figuration of the precipitator, prop-
erties of the dust,  and many other
variables

the base for Naperian logarithms =
2.71828

the time a dust particle remains in
the precipitating field of the precipi-
tator,  sec.

-------
                                  Single-Stage Electrical Precipitators
                                                        153
Present knowledge of precipitation theory does
not permit an accurate evaluation of the con-
stants C and k.   Their values must be deter-
mined empirically.
 Practical Equations for Precipitator Design and
 Efficiency
Empirical equations have been developed by
Anderson (1924), Walker and Coolidge (1953),
Schmidt (1928),  Deutsch (1922),  and others.

Deutsch published a proposed equation with a
form similar to
                      -wf
                                           (73)
where
     r~i  =  weight fraction of dust collected

     w  =  velocity of drift or migration of a
          dust particle toward the collecting
          electrode,  fps

     f   =  ratio of area of collecting electrodes
          to the volume of gas passing through
          the treater, (ft2/ft3/sec).

Anderson proposed an equation of the form
                   =  I  -  K
(74)
            Frequently the following modified forms are
            used:

            Plate-type precipitators
                                                                          n  =  i  - K
                                                                                      Ct
                                                       (76)
                                                       tube-type precipitators
                                       - K
                                           2Ct
                        (77).
            K is a measure of the ease with which the dust or
            fume can be precipitated, and C depends upon the
            physical dimensions  of the precipitator and the
            voltage  applied.  For any particular installation
            both K and C must be considered constants since
            otherwise the equations are not useful.  It is  easy
            to show that the last  three equations are equivalent.

            For plate-type precipitator s
                         n  =  i - K
                         t  =
                                     ct
                         c  =  -
L
V
                                                                    T]  =  1 - K
                                                                                cL
                                                                                sv
where

     K  =  an empirical constant

     t   =  the time a dust particle remains in the
          electrical field of the treater, sec.

Schmidt modified the Anderson equation to
                                                                            Q
                       cA
                                           (75)
where

Kandc =  empirical constants

    A =  the area of the collecting electrodes
          or plates, ft2

    Q =  the gas volume,  cfs.
                                                      where
                               W 2s
                         A  =  2 L W
                                   cAr
                                                                       =  1 - K'
                                                                                Q
                c  =  a constant

                s  =  separation or distance between dis-
                      charge electrode and collecting  elec-
                      trode, ft

                L  =  length of collecting  electrode in the
                      direction  of gas flow,  ft

                v  =  mean velocity of gas in the direction
                      of flow through the treater,  fps

-------
154
               AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
     W  =   width of collecting electrode or dimen
           sion perpendicular to direction of gas
           flow, ft
                  2
     A  =   area, ft

     A  =   area of collecting electrode or plate,
-For tube-type precipitators
                        2cL
              =   1  - K
                   Q
                 ir s
           A =   2 TT s L
           rj  =   1  - K
 Figure 88 graphically illustrates the  relationship
 among several common forms of these efficiency
 equations.  Note that in each equation there is at
 least one  arbitrary constant whose value deter-
 mines the efficiency.  This is referred to as the
 precipitation constant in the Anderson and Schmidt
      Prlcipititor tllicicnc) iqultion!
         P =
          = Drift velocity U see
          = VolUH o( (is throutfi preeip
            itator rt> sec
          = IIM of Nipitriin logtrithii
            = i ntn
     0     01    02     03     04    05     OG     0
                DRIFT  VELOCITY  (w),  ft/sec

    Figure  88.   Relationship  among  various  precini
    tation  constants and  drift  velocity.
equations and the drift velocity in the Deutsch
equation.  In reality,  this is neither a constant
nor a true representation of the drift velocity.
Some typical values of the so-called drift or mi-
gration velocity are listed in Table 48.
    Table 48.  TYPICAL VALUES OF DRIFT
VELOCITY ENCOUNTERED IN PRACTICE FOR
      USE WITH EFFICIENCY EQUATION
                                                                          r) -  1 - e
                                                                                     A
                                                                                     -P
                                                                                     Q
                                                                       Application
  Pulverized coal (fly ash)
  Paper mills
  Open-hearth furnace
  Secondary blast furnace (80% ioundry iron)
  Gypsum
  Hot phosphorous
  Acid mist (H^SO.))
  Acid nisi (TiOz)
  Flash roaster
  Multiple-hearth roaster
  Portland cement manufacturing (wet process)
  Portlant cement manufacturing (dry process)
  Catalyst dust
  Grav iron cupola (iron-coke ratio ~  10)




•on)






}cess)
}cess)


\
0



0

0
0


0
0

0
elocity (\v),
ft/sec
33 to 0.
0. 25
0. 19
0. 41
. 52 to 0.
0. 09
. 19 to 0.
. 19 to 0.
0. 25
0. 26
33 to 0.
. 19 to 0.
0. 25
. 10 to 0.
44



64

25
25


37
23

12
 The drift velocity w and precipitation constant K
 are usually variables that are affected by the
 electrical properties of the particles, which in
 turn,  vary with temperature and humidity, and
 by the applied voltage and the  ionic current,
 which depend upon the temperature,  humidity,
 and dust load.  They must also reflect the ef-
 fects  of reentrainment  and rapping losses, as
 well as nonuniform gas velocity distribution.  In
 general,  the effects of  none of these  factors  can
 be predicted analytically with  any degree  of
 accuracy.

 The design of electrical precipitators is today
 almost entirely empirical.  Designs  are based
 either upon previous experience with similar
 processes or upon the results  of pilot model
 precipitator studies.  Table 49 shows average
 values for the major variables in precipitator
 design.  Precipitator manufacturers  have ac-
 cumulated considerable data through the years
 upon which they can base the design of new
 installations.


 Effects of  Nonuniform Gas Velocity

 The importance of uniform gas velocity through
 the treater cannot be overemphasized.  In all
 precipitator efficiency  equations  an increase in
 the gas velocity or  flow rate reduces the ef-
 ficiency exponentially.   Conversely,  a decrease

-------
                                 Single-Stage Electrical Precipitators
                                                                         155
     Table 49.   TYPICAL VALUES OF SOME
  DESIGN VARIABLES USED IN COMMERCIAL
   ELECTRICAL PRE'CIPITATOR PRACTICE
       Design variable
 Plate spacing
 Velocity through precipitator
 Vertical height of plates
 Horizontal length of plates
 Applied voltage
 Drift velocity w
 Gas temperature
  Treatment time
  Draft loss
  Efficiency

  Corona current
  Field strength
Normal range of values
 8    to 11 in.
 2    to  8 ft/sec
12    to 24 ft
 0. 5  to  1. 0 x height
30    to 75 kv
 0. 1  to  0. 7 ft/sec
 up to 700°F standard
 1, 000°F high tempera-
 ture 1,300°F special
 2    to 10 sec
 0. 1  to  0. 5 in. WC
 up to 99. 9+% usually
     90% to 98%
 0. 01 to  1.0 ma/ft wire
 7    to 15 kv/in.
in gas velocity or flow rate increases the effi-
ciency exponentially.  For a constant volume
of gas through the precipitator,  maximum ef-
ficiency is attained when the velocity is uni-
form. As the velocity increases through one
section of the precipitator, collection efficien-
cy decreases.  At the same time the  velocity
must decrease  through other parts of the pre-
cipitator since  the total  flow rate remains the
same.  The  efficiency for the sections having
the lower velocity will increase.   The increase
in efficiency through the low-velocity sections
of the precipitator can never compensate for
the loss  in efficiency through the high-velocity
portions of the  precipitator.   This is  illus-
trated by example 20:

Example 20

Given:

A horizontal-flow, single-stage  electrical pre-
cipitator consisting of two ducts formed by plates
8 ft -wide x  12 ft high on 10 in.  centers,  handling
3, 600 cfm with two grains of dust/ft-^.  The drift
velocity  is 0. 38 fps.

Problem:

Find  collection efficiency and dust loss in Ib/hr
for (1) Uniform gas velocity and (2) peak velocity
50% greater  than  average.


Solution:

For either case the loss is given by

               (1  - n)(60)(60)(Q)(G)
     L°SS  =              	
where G  =  dust concentration, grains/ft .
                            For uniform gas velocity, collection efficiency
                            is given by
                                                                    rj  =  1 -  e
The plate area of each duct is

       A  =  (2) (8)  (12)  =

The flow rate per duct is
                            192 ft
       Q  =
(3600)
(2)(60)
30 ft  /sec
                                                       For uniform gas velocity

                                                                               192
                                                                        -0. 38
                                                    30
Loss
                                                         =  0.912 or 91.2%
                                                                5.421b/hr
                            For simplicity, assume that the velocity through
                            one of the ducts is  50% greater than average or
                            the volume is 2, 700 cfm and the volume through
                            the other duct is 50% less than average or 900
                            cfm.  In an actual case where the velocity var-
                            ies continuously, it would be necessary to di-
                            vide the precipitator  into a great number of zones,
                            each having  approximately constant velocity. The
                            procedure is illustrated by this simplified approach.
                           For the high-velocity duct

                                            -0.38192
                               n  =  i  -  e
                       45
                           =  0.8025 or 80.25%
                                  =  (1-0.8025)(2.700)(60)(2)  =  9. 15 Ib/hr
                            For the low-velocity duct
                                                    192
                                             -0. 38
                                      1
                                                    15
                             =  0. 9922 or 99.22%
T
Loss   =
                                      (1  - 0. 9922)(900)(60)(2)
                                      -       -
                                                                    17iv,/v
                                                                =  0.12 Ib/hr
                            The total loss for the two ducts with nonuniform
                            velocity is 9.15 +  0. 12 =  9. 27 Ib/hr.   This is
                            71% greater than the 5. 42 Ib/hr loss with uni-
                            form gas velocity.

                            Figure 89 gives multiplying factors to correct
                            the loss for the effects of nonuniform gas ve-
                            locity.   This graph was  prepared by means  of

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156
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
calculations similar to those in example 20.
In an actual case, since less than 50 percent
of the precipitator would be subjected to peak
gas velocities, the adverse effects of nonuni-
form gas distribution would be less severe.
On the other hand, in an  actual precipitator,
reentrainment would be aggravated in the higher
velocity sections so that  the actual losses in  an
extreme case could be  several times that pre-
dicted solely on the basis of velocity distribu-
tion.
  3 5
                              7
            12       14      16      18
           PEAK VELOCITY 'AVERAGE  VELOCITY
                                             2 0
  Figure  89.  Multiplying factors  for  loss from
  electrical precipitator with  nonuniform gas
  distribution.  Loss equals FvLo.where L0 equals
  loss  with uniform gas distribution.
 Important Factors in the  Design of a Precipitator

 The following design factors are critical ele-
 ments in an electrical precipitator (Schmidt
 and Flodin, 1952):  (1) Proportion,  (2) capacity,
 (3) cleaning of electrodes,   (4) reliability of
 components,  (5) stability of electrical system,
 (6) accessibility for maintenance,  (7) control
 of gas flow,  (8) control of erosion of dust from
 electrodes, and (9) power supply.   This list is
 not intended to be exhaustive or in  order of im-
 portance.  All these items are interrelated,
 and optimum performance  cannot be achieved
 if there  are shortcomings in any of them.  The
 designer of an electrical precipitator is faced
 •with many decisions for •which there is no clear-
 cut solution.

 Oftentimes, the most  important factor in deter-
 mining the length  and  width of a precipitator is
                                       the available space.  This factor also intro-
                                       duces problems in the design of the ductwork
                                       leading to and from the precipitator.  Thus, it
                                       may be necessary to  increase the height of a
                                       horizontal -flow precipitator because of a space
                                       limitation on the length.  Since the time in the
                                       treater is reduced by restricting the length, an
                                       additional increment  of height is  required to
                                       compensate.  Because this increases the dif-
                                       ficulty of providing uniform gas distribution,
                                       an additional increment  of height is required
                                       to compensate for nonuniform gas velocity dis-
                                       tribution.  The increased plate height intro-
                                       duces additional problems in maintaining uni-
                                       form plate-to-plate distance and  in the  discharge
                                       electrode's  suspension system.   Optimum per-
                                       formance requires uniform field  strength
                                       through all sections of the precipitator,  which
                                       in turn, depends upon near perfect alignment
                                       of the electrode system.  Even a small varia-
                                       tion in spacing of discharge electrode to col-
                                       lecting electrode can seriously reduce the
                                       performance.  Greater plate height may also
                                       increase the dynamic instability of the discharge
                                       electrode system, that is, it may increase the
                                       tendency of  the discharge electrodes to swing
                                       or vibrate.

                                       The tendency of the discharge electrodes to swing
                                       or vibrate is overcome to  some extent by guides
                                       and heavy weights attached to the lower end of the
                                       •wires.  Some sparking  is desirable in a precipita-
                                       tor, but with less than perfect alignment, the spark-
                                       ing will occur most frequently only at points where
                                       the wire-to-plate spacing is the least,  usually at
                                       the lower edge of the  plate.  The difficulty is fre-
                                       quently reduced or overcome by using shrouds on
                                       the lower edge of the  plate or on this section of
                                       the discharge electrode.

                                       SUMMARY AND  CONCLUSIONS

                                       Electrical precipitation is suitable for the col-
                                       lection of a  wide range of dusts and fumes.  In
                                       some cases, for example  detarring, it is the
                                       only feasible method; in other cases, it may be
                                       the most economical  choice.  The design of an
                                       electrical precipitator requires considerable
                                       experience for successful application.  The
                                       fundamental theory of the mechanisms  involved
                                       in electrical precipitation is only partially under-
                                       stood at present.  Further research will tend to
                                       make the design of electrical precipitators more
                                       of a science and less of an art.
                                        TWO-STAGE  ELECTRICAL PRECIPITATORS
                                       The Cottrell-type precipitator is usually de-
                                       signed and custom built specifically for  instal-
                                       lations required to process large volumes of

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                                  Two-Stage Electrical Precipitators
                                            157
contaminated air.  Since 1937 a somewhat dif-
ferent type has been marketed.  This unit, de-
veloped by Penney (1937),  is now  called the low-
voltage, Penney,  or more  commonly, the two-
stage precipitator.   It is also occasionally re-
ferred to as the air-conditioning precipitator or
"electronic air filter" (White,  1957).

The two-stage unit differs  from the Cottrell
type in that the contaminated air is first passed
through a variable-strength ionizing field  be-
fore being subjected to a separate uniform
field where the charged particles  are  collected.
Figure 90  shows the fundamental arrangement
of the active electrical components.  Basic
operating principles  are the same as those dis-
cussed for the Cottrell precipitator.   A high-
voltage corona discharge ionizes gas molecules
that cause charging of particles passing through
the field.   The charged particles then tend to
migrate toward electrically grounded or op-
positely charged surfaces where they are re-
moved from the airstream.

Most of the early applications of the two-stage
precipitators were for removal of tobacco
smoke, pollen,  and similar air  contaminants in
commercial air-conditioning installations.  As
a result of mass production techniques,  pre-
cipitators for air-conditioning installations are
now available in "building block" cells provid-
ing capacities up to a million cubic feet per
minute.  Although these precipitators were de-
veloped principally for air-conditioning instal-
lations, their usefulness in  the control of air
pollution soon became known.   One of the first
units reported for the cleaning of process air
was for removal of ceramic overspray in pot-
tery glazing operations  (Penney, 1937).   Two-
stage precipitators are  widely used for re-
                                                                                   COLLECTOR CELL
                                                                                   (TO COLLECT PARTICLES)
 BAFFLE          ^
 (TO DISTRIBUTE £
 AIR UNIFORMLY) f^
          \
                            >/                 '
                            *'   IONIZER
                            .    (TO CHARGE  PARTICLES)
               Figure 90.   Components  of  standard two-stage precipitator  (Westinghouse Electric
               Corporation,  Hyde  Park,  Boston, Mass.).

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158
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
moving oil mist created during operation of
high-speed cutting or grinding tools.  Preci-
sion manufacturing and electronic assembly
areas are frequently equipped with precipita-
tors to  remove small quantities of dust and
impurities from their environmental air.
Hotels,  restaurants,  food-processing compan-
ies,  and pharmaceutical manufacturers often
use this method for cleaning circulating air.
Another installation,  shown in Figure 91, is
designed to remove contaminants from  the ex-
haust air of a meat-smoking operation.
                                         a short circuit,  and the precipitator1 s  efficiency
                                         drops correspondingly.

                                         Below the corona's starting voltage or  critical
                                         corona gradient, no ionization occurs and conse-
                                         quently no charging of particles takes place.  The
                                         critical corona gradient, for round wires,  is
                                         basically a function of wire size and condition.
                                         It may be determined by the equation
E   =  30 M
 s
                                                            1 +
                                                                0.
(78)
 THEORETICAL ASPECTS

 Theory of  Dust  Separation

 The physics of dust separation in a two-stage pre-
 cipitator may best be understood by examining the
 stages separately.  The function of the ionizing
 stage is to induce an electrical charge upon the
 particles in the airstream.  When an electrical
 potential is applied between a -wire and a grounded
 strut,  as shown in Figure 92, an electric field
 is created that varies from a high strength near
 the wire to a low at the strut.  When the potential
 is increased to the "critical corona voltage, "
 local ionization of the airstream near  the wire
 occurs and a blue corona is formed.  Arcing or
 "sparkover" results  if the voltage is further in-
 creased to a point where total ionization of the
 air between the electrodes  occurs.  This effects
                                        where

                                             E  =   critical corona gradient,  kv/cm
                                              S

                                             M  =   roughness factor,  usually between 0. 6
                                                   and 0. 9

                                             r  =   -wire radius,  cm.


                                        The required potential may then be  determined by
                                                      V   =  E  r In    -
                                                       s      s       3  r
(79)
                                        where
                                             V  =   corona starting voltage, kv
                                              S

                                             s  =   wire-to-strut spacing,  cm.
  Figure 91.  Two-Stage precipitator controlling smokehouse  emissions:  (left) precipitator  on,  (right)
  precipitator off (Luer Packing  Co., Vernon, Calif.).

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                                  Two-Stage Electrical Precipitators
                                                                      159
 ELECTROSTATIC FIELD


   DUST PiRTICLES

     — - »

   DISCHARGE ELECTRODES
                     GROUND RECEIVING
                     ELECTRODES
            	-(g ™°!
 Figure 92.   Schematic  representation of two-stage
 precipitator  principle  (Perry, 1950).
 Particle Charging

 The degree of electrical saturation of the dis-
 persed particles may be given, for a spherical
 conducting particle, by
                 3E a
                                           (80)
                          t+
                            TT N  k £
                               o
 vhere
     n  =  number of elementary  electric  charges
           acquired by a particle

     E  =  electric field strength, stat volts/cm.

     a  =  particle radius, cm

     t   =  time interval that particle is exposed to
           charging field, sec

   N   =  ion density in charging zone, ions /cm
     o
     £   =  charge on electron,  4.8 x  10    stat-
           coulomb

     k  =  ion mobility, cm  /sec-stat volt.


All units of this equation are expressed in  the elec-
trostatic centimeter-gram-second system. White
has given the term

                    TT N
the notation of t  ,
the particle-charging time constant, and states
that it ranges from 10-1 to  10~4 seconds with
charging normally effectively complete in about

  -2                      3E a2
10   seconds.   The term 	  is the limiting
                             c                  &
                          or saturation charge, ns,  for large values of
                          time (White,  1951).

                          Equation 80 applies to particles greater than 0. 5
                          micron in diameter, where charging is due pri-
                          marily to ion bombardment.  Charging by ion
                          diffusion predominates  for particles of about 0. 1
                          micron and smaller in diameter and requires a
                          somewhat different evaluation.   Normally, neg-
                          lect of the ultrafine particles in determining
                          charging time introduces no significant errors
                          because these particles represent a small weight
                          fraction of the material being treated.


                          Drift Velocity

                          The charged particle reaching the collector sec-
                          tion is acted upon by two vector forces--its mo-
                          mentum and the electrical attraction for the
                          grounded or oppositely charged electrode. Ad-
                          ditionally, the motion of the particle toward the
                          electrode is retarded by viscous drag according
                          to Stokes' law.  The net velocity component to-
                          ward the collecting electrode is termed the drift
                          velocity,  and  is described by the equation
                                                                           p E  E a
                                                                              c p
                                               6 7T |J.
                                                        where
     w  =  drift velocity,  cm/sec

     E  =  electric field strength, stat volts/cm

     H.  =  gas viscosity,  poises

     p  =  a constant.

The subscripts p and c represent precipitating
and charging zones, respectively.  Units are in
the electrostatic cgs  system.  The equation may
be modified by the Stokes-Cunningham correc-
tion factor for particles appreciably less than 1
micron in diameter, that  is, approaching the
mean free path between molecular collisions in
air.  For conducting particles, the  constant  p
equals 3, and for nonconductors, p  is a function
of the dielectric constant  and is  usually between
1.5 and  Z (Rose and Wood,  1956).

Equation 81  illustrates the significance  of the
electrical field's  strength in collection effi-
ciency.  The drift velocity varies with the
product of the charging field and collecting
field strengths.  For  this  reason it is always
advantageous to operate a precipitator at the
maximum possible voltages without incur-
ring excessive sparkover.  Field strength is
determined not only by impressed voltage

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160
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
 but by electrode configuration, dust loading,
 and  other variables, so that a considerable
 degree of experience is needed to evaluate
 the drift velocity properly.


 Efficiency

 Determining the effectiveness of a device
 for control of atmospheric pollution is fre-
 quently difficult.  When the airstream con-
 tains ultrafine particles, the increase in
 light transmittance may be  important.  In
 some cases the reduction in number of par-
 ticles or the reduction in darkness of filter
 papers through •which the air is  passed may
 be significant.  The normal method of deter-
 mining efficiency of precipitators is by
 •weight of material collected.  The exponen-
 tial  Deutsch equation (Perry,  1950),
              F  =  1 - e
             -wA
              Q
(82)
 where
     F  =  efficiency, decimal equivalent

     A  =  collecting area, ft

     Q  =  volumetric flow rate,  cfs,

 •with appropriate units for drift velocity,  has
 been developed primarily for application to
 single-stage precipitators.  Penney (1937)
 presents the relationship for two-stage pre-
 cipitators
              F  =
       wL
       "vcf
(83)
* where

     L  =  collector length,  fps

     d  =  distance between collector plates,
           ft

 for units with close plate spacing.   The ex-
 ponential-type equation is frequently found
 applicable in practice.   Walker and Coolidge
 (1953) have found the expression
 F  =  1 -  exp (-Kha)  (V-V ) —
                         (84)
 where

     h  =  relative humidity,  decimal equivalent

     a  =  particle radius,  p.
     V =  applied voltage,  kv

     K =  a constant

to apply to both single- and two-stage>precipita-
tors collecting gypsum dust under laboratory
conditions.   The efficiency varies with the avail-
able voltage  above the corona's  starting voltage.


DESIGN FACTORS


Electrical  Requirements

Normally, positive polarity in the ionizing sec-
tion is used in two-stage precipitators  since it
is thought that less ozone and oxides of nitrogen
are thus produced.  With positive polarity,  spark-
over voltage is much closer to the critical co-
rona voltage than is found with negative polarity.
The practical operating voltage limit for stan-
dard units is about 18 kilovolts, with most oper-
ating at 10 to 13  kilovolts.  Current flow under
these conditions  is small,  4 to 10 milliamperes.
The collecting plates are usually activated at
5. 5 to 6. 5 kilovolts with precipitation's occur-
ring on the grounded spacing plates.  The actual
current flow is very small since no  corona  ex-
ists bet-ween the  plates.

In single-stage units recent developments have
made available rather elaborate automatic con-
trol devices  to maintain the maximum practical
corona current.   This type of control is not
feasible for two-stage units.   For some applica-
tions,  however,  manually adjusted rheostats
have been used,  and •when a high degree of ef-
ficiency is required, the voltage can occasional-
ly be adjusted to compensate for buildup of col-
lected material.

Power consumption is a function chiefly of par-
ticle size, dust loading,  voltage,  and wire size.
The actual power required for removal of a
dust particle by precipitation is small com-
pared with that for mechanical collectors be-
cause the energy is applied primarily to the par-
ticle only and not to the total gas stream. In
practice,  power  requirements for standard two-
stage precipitators are  15 to 40 •watts per thou-
sand cfm. The operating cost is, therefore,
low.

High voltage is obtained  byvacuum tube recti-
fying power packs that operate from a  110- to
120-volt  a-c primary circuit.  On small units
one power pack may supply both ionizing and
collecting sections.  For larger volumes two
or more power packs  may be used in parallel
for various groupings of ionizing cells  with
separate  power packs for the collecting sections.

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                                   Two-Stage Electrical Precipitators
                                             161
Air Capacity

Manufacturers normally rate these unitg at 85 to
90 percent efficiency by tests based on discolora-
tion comparisons and  at velocities between 300
to 600 fpm.  For air-conditioning purposes these
values are usually adequate, but  for cleaning
process air, a more thorough evaluation is neces-
sary.  Efficiency of cleaning for  this latter pur-
pose is usually based  upon weight recovery and
will likely be lower than by discoloration com-
parison.

Equation 83 determines efficiency to be direct-
ly related to air velocity.  Equation 82, for
units  with constant collector area,  relates ve-
locity to efficiency by an exponential function.
If dust particles move smoothly between the
plates, collection efficiency is  a  function only
of drift velocity and residence time.  Penney
assumes streamline flow through the precipita-
tor, -while recognizing that some turbulence
occurs, in arriving at the required collector
plate area for  air-cleaning precipitators.  Al-
though 600 fpm is the  limiting velocity  for
streamline flow in most two-stage units now
being manufactured, mechanical  irregulari-
ties reduce the permissible velocity.  Figure
93 includes a graphical  representation  of
equations 82 and 83 for  data obtained on smoke-
houses .

It has been found that  collection area is not
always controlling.  At  a velocity of 300 fpm
a dust particle is in the ionizing field only
about 0. 05 second,  a  very brief time when
compared -with 1, 0 to  10 seconds for single-
stage units.  For some  contaminants the in-
creased efficiency at  low velocity is the ef-
fect of increased ionization time  rather than
of streamline flow through the collector
plates.

The degree of  ionization may be increased by
increasing the number of ionizing electrodes,
either by decreasing spacing or by installing
a second set of ionizing -wires in  series. Since
decreased spacing reduces the allowable volt-
age -without sparkover,  use of the series ar-
rangement appears  advantageous.  Decreased
spacing has the advantage of lower first cost
and lower  space  requirements.
Air  Distribution

The distribution of the airstream entering the
precipitator is as critical for high-efficiency
two-stage operation as many other factors
normally receiving more attention.  A super-
ficial velocity, the ratio of total airflow to
precipitator cross-sectional area,  is useful
for equipment selection but may be misleading
for close design.  For conditions of low overall
velocity of approximately 100 fpm,  pressure
drop through a precipitator is insignificant,
and redistribution of high- or low-velocity
areas of the airstream will not occur.  Var-
iations  in airflow from 3 times average ve-
locity to actual reverse flow have been ob-
served  in the vertical-velocity profile of these
units for hot gas streams.  Figure  93 shows
that high velocity produces low efficiency
while extremely low velocity does not result
in compensating improvement.   Overall ef-
ficiency is thus  lowered.  Two-stage precipi-
tators are normally installed -with horizontal
airflow and frequently in positions requiring
abrupt changes in direction of duct-work pre-
ceding the unit.   Design such as this results
in turbulent, uneven airflow.  If air enters the
precipitator plenum from an elbow or unsym-
metrical duct, the air tends to "pile up" on
the side of the precipitator opposite the  entry.

Numerous methods are available for balancing
the flow.   A straight section of duct upstream
eight duct diameters from the entry prevents
transverse unevenness if a gradually diverging
section precedes the precipitator.  If this is
not possible, mechanical means must be used.
Turning vanes installed in an elbow or curve
maintain a uniform distribution and also re-
duce pressure drop.across the elbow, but
do not balance flow satisfactorily.  Baffles of
various types or egg crate straightening vanes
may be used in the transition duct.   The most
effective air-balancing device found consists
of one or more perforated sheet metal plates
that fully cover  the cross-section of the ple-
num preceding the ionizers.

The sheet metal plates introduce an additional
pressure drop that must be considered in the
initial exhaust system design.  A study of
distribution in single-stage precipitators
found that  each subsequent plate installed in
series added materially to flow uniformity
(Randolph,  1956).  It has also been indicated
that, at low velocity,  a perforated sheet im-
mediately folio-wing the collector plates may
in some cases be more effective than one
preceding  the ionizers.  A sheet in this loca-
tion also has the advantage of acting as an
additional  collecting  surface for charged par-
ticles,  though this effect is usually minor.

An open area of 40 percent for  the perforated
sheet has been found optimal,  a range of 35
to 60 percent being generally adequate.  In-
stallations handling heated airstreams, above
100°F  , at low velocities, require  baffling to
prevent high velocities at the top of the cham-
ber due to thermal effects.  In these cases a

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162
       AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
  100

   90


 » 80

 I 70
 C_3
 t 60
 z
 I 50
 LU

 S 40

   30

   20
                   E,
A.   Smokehouses, extrapolated  with  Penney  equation
B.   Smokehouses, extrapolated  with  Deutsch  equation
C.   Asphalt  saturator, operating test  data
D.   Galvanizing kettle, operating test  data
F.   Air  conditioning, manufacturer's  recommendation
                        1.5
                               2
                                              GAS VELOCITY,  tps
       Figure  93.  Efficiency of two-stage  precipitator as function  of  velocity for several  industrial
       nnerat i nns.
operations.
perforated sheet covering only the upper half
of the plenum preceding the ionizers may
suitably equalize the flow.   Vertical-flow pre-
cipitators are not affected by thermal condi-
tions in this  manner.

Auxiliary Controls

Two-stage precipitators  have thus  far not
been extended to process exhaust  gases  -with
characteristics requiring unusual condition-
ing agents.   Humidity adjustments,  by water
sprays or heating coils,  are frequently used
to modify electrical properties of the con-
taminants to a suitably conductive condition.
For many materials,  maintenance of greater
than 50 percent relative humidity  is advanta-
geous. Under no condition, however, should
the gas stream to the ionizer be saturated;
reheating the airstream may be required to
avoid  saturation.   Water droplets should be
removed  by mist eliminators preceding  the
ionizer to prevent  excessive sparkover.

The collector plates  and  housing must be cleaned
periodically.  To keep this labor and downtime
to a minimum,  the use of precleaners is fre-
quently recommended for the more  easily re-
moved contaminants.  For dry materials a cy-
clone  is usually adequate, though  a  simple scrub-
ber is more  commonly used, and  the gas stream
                                               is thereby humidified.   If fibrous materials such
                                               as cotton lint or synthetic fibres are entrained
                                               in the exhaust air, they must be prevented from
                                               reaching the precipitator •where they may ac-
                                               cumulate and bridge the plates, resulting in
                                               arcing and possible duct fires.  Scrubbers and
                                               glass fiber filters have been successfully used
                                               to prevent problems such as this.
                                               Particles charged in the ionizing section may
                                               sometimes have a drift velocity too low to be
                                               completely removed in the collector section.
                                               Operating the precipitator without oil on the
                                               collector plates and periodically blowing off
                                               the flocculated material may also be desirable.
                                               In either case the contaminants may precipitate
                                               in the exhaust system or be collected by an af-
                                               tercleaner following the precipitator.   Inten-
                                               tional use of this procedure is usually restric-
                                               ted to dry dusts such as carbon black or normal
                                               atmospheric dust.   The aftercleaner may be a
                                               filter,  cyclone, or scrubber as required by the
                                               specific process.
                                               Air-conditioning installations are frequently
                                               equipped with automatic washing and reoiling
                                               devices.  The aftercleaner then removes en-
                                               trained •water from the airstream and permits
                                               uninterrupted air circulation through the system.

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                                 Two-Stage Electrical Precipitators
                                            163
CONSTRUCTION AND OPERATION
Assembly

Two-stage precipitators for capacities up to
20, 000 cfm may be supplied by the manufacturer
in completely preassembled package units re-
quiring only external wiring and duct connections.
For larger  capacities or for heavy contaminant
loading,  a field-assembled model is supplied.
This requires local fabrication of the precipita-
tor housing with necessary drains, doors, baf-
fles, and ductwork.  Usually the  ionizing and
collection sections are assembled on one frame
but they may be installed separately if desired.
The installed weight of the  precipitator is ap-
proximately 80 pounds per  square foot for units
with over 5 square feet of cross-sectional area.
Usually, no additional foundation support is re-
quired for floor installations.

Smaller  units may occasionally be adapted to fit
into existing ducts or  transition chambers of an
exhaust  system.  If the precipitator vents to the
outside atmosphere,  a shield must be provided
at the  discharge side to protect it from weather
elements.
Maintenance

Process air may contain approximately 2 grains
of air contaminants per cubic foot in contrast to
air-conditioning loads  of 2 grains  per  1, 000
cubic feet.  Because dusts and  tars may not drain
or fall off,  they may impose  a limitation of hold-
ing capacity on the collector.  Since no rapping
cycle is  used  on two-stage precipitators, the
collected materials are held  to the plates for
relatively long periods of time  and then washed
down.  The frequency of cleaning depends upon
the quantity of contaminant collected, though
cleaning cycles  of  1 to 6 weeks are typical. Some
installations are adaptable to automatic cleaning,
but in most, the collector plates must be washed
down manually or removed and washed in a tank.
If a dry dust is being collected, the plates  are
usually recoated with oil by either dipping  or
spraying.  When oils of low viscosity are col-
lected,  the  oil drips or runs  off and hence  only
occasional cleaning is needed to remove tars
or gummy deposits.

Ionizer wires do not require  frequent cleaning.
These  wires will, however, corrode slowly and
must occasionally be replaced.  Stainless steel
•wires rather than tungsten may be used if un-
usually corrosive conditions  exist.  The pre-
cipitator housing should be periodically washed
to remove deposited contaminants.  Since most
standard precipitators are partially constructed
of aluminum, uninhibited caustic cleaning  solu-
tion must not be used.  Cleaning time varies
•with the nature  of the collected contaminant.
Six to  12 man-hours  per month may be  consid-
ered average for a unit of 120 square feet
cross-sectional area.


Safety

Standard units are carefully constructed to
provide maximum electrical safety.  At the low
current used, accidents are not common,  but
normal high-voltage  precautions must be ob-
served.  Interlocks between access doors  and
electrical elements should be used,  and provi-
sions for delayed opening  after deenergizing
are desirable to allow drainage  of static charge.

The standard electrical systems are  constructed
to shut off automatically if a direct arc occurs.
The inherent delay may, however,  be sufficient
to ignite an excessive accumulation of combusti-
ble oils or tars. It is advisable, therefore,  to
include automatic -water sprinklers above the
collection unit.  The fire hazard is minimized
by frequent cleaning  if combustible contaminants
are being collected.  A precipitator is obviously
not adaptable for use in exhaust systems hand-
ling vapors  in explosive concentration.


APPLICATION

Among the types of operations that have been
successfully controlled by standard two-stage
precipitators are:  (1) High-speed grinding
machines,   (2) meat  product smokehouses,
(3)  continuous deep fat  cookers,  (4) asphalt
saturators,   (5) galvanizing kettles,  (6) rub-
ber-curing ovens,  (7)  carpeting dryers, and
(8)  vacuum pumps.


The emissions from  all these operations include
at least some oil mist.  Oils,  either mineral or
vegetable,  have a relatively high drift velocity
and probably act as a conditioning medium for
less conductive  emissions. In addition, the
oils deposited on the  collector plates  prevent
reentrainment of collected dust  or fumes.  Or-
ganic substances between  Cg and C£3 have been
collected and, though showing  some variation in
resistivity,  are usually precipitated in the first
3 to 6 inches of  a collector plate.  Velocity and
ionization conditions  that have been found ade-
quate for air pollution control purposes are
shown  in Table 50.

Reentrainment of fumes from nonoiled plates
does not always  occur.   On a  galvanizing in-
stallation, ammonium chloride  used in the  flux
is the largest constituent of the  emissions.
 234-767 O - 77 - 13

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164
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
               Table 50.  INDUSTRIAL OPERATION OF TWO-STAGE PRECIPITATORS
C ontaminant
source
Tool grinding
Meat smokehouse

Meat smokehouse


Galvanizing
Deep fat cooking
Asphalt saturator
(roofing paper)
Muller-type
mixer
Contaminant
type
Oil aerosol
Wood smoke
Vaporized fats
Wood smoke
Vaporized fats

Oil aerosol
NH4C1 fume
Bacon fat
Aerosol
Oil aerosol
Phenol -formal-
dehyde resin
Ionizing
voltage
13, 000
13, 000

10, 000


14,200
13, 000
12, 000
13, 000
No. ol
ionizer
banks
1
2

1


2
2
1
1
Collector
voltage
6, 500
6,500

5, 000


7,000
6, 500
6, 000
6, 500
Efficiency,
wt %
90
(discoloration)
90

50


91
75
(light trans -
mittance)
85
87
Velocity,
fpm
333
60

50


60
68
145
75
Inlet
concentration,
grains/scf
--
0. 103

0. 181


0. 154
--
0. 384
0.049
Remarks
Manufacturer ' s
recommendation
Humidified and
precleaned,
1 0-mil wire
Ionizer wires at
1-1/2-in. spacing,
poor air distribu-
tion
Second ionizer,
1-1/2-in. spacing,
15-mil wire
Humidified and
precleaned
Humidified and
precleaned
Odor not suitably
reduced
 During a test wherein fresh flux was added to
 the galvanizing kettle though no galvanizing was
 being done,  ammonium chloride was found to
 be flocculated in the precipitator and then re-
 entrained in the exhaust air.  During normal
 galvanizing operations this did not occur. An
 analysis  of the materials collected in the pre-
 cipitator showed that, during galvanizing, oil
 from the metal being galvanized is vaporized.
 Most of this is precipitated on the first few
 inches  of the collecting plates,  but a small
 quantity of the oil also precipitates with the
 ammonium chloride over the balance of the
 collecting area.  The oil provides a medium
 for holding the dry  fume to the plates.  This
 effect is, of course,  the reason for precoat-
 ing the plates with oil in air-conditioning in-
 stallations.  The difference in precipitation
 rate of oil mist and ammonium chloride fume
 in the above example is  illustrated in Figure 94.


 Odors are frequently difficult control problems.
 When the odor is due to  particulate matter,
 such as free fatty acids, the precipitator may
 be entirely adequate.  This is  frequently found
 to be the case with  deep fat fryers.   More com-
 monly the odor source is both liquid aerosol
 and vapor,  and the  degree of control by a pre-
 cipitator depends upon the relative odor strength
 of the two phases.  For  example, a precipita-
 tor intended to eliminate both odors and visible
 emissions from equipment blending hot phenolic
 resins with other material is not suitable with-
                                       Figure 94.   Precipitator collector plates showing
                                       rapid deposition  of  oil mist (dark area) compared
                                       with (light  area)  ammonium chloride fume (Advance
                                       Galvanizmg  Company,  Los Angeles, Calif.).

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                                    Two-Stage Electrical Precipitators
                                            165
out additional control  equipment.  Phenolic
resin dust is almost entirely removed from the
exhaust stream by the precipitator.  Since free
phenol is  present in both liquid and vapor form,
however,  the odors are not eliminated unless
the temperature of the gas stream is low enough
to condense most of the phenol.   The vapor pres-
sure of phenol at 220°F is about 5 times as great
as it is at 160°F.
Two-Stage  Precipitators of Special Design

The foregoing discussion has been primarily
concerned with precipitators available from
manufacturers as standard units. The theory
is applicable, however, to less common units.
Under some conditions, dust of high resistivity,
above lO^1 ohm-centimeters, causes ioniza-
tion at the collecting surface of single-stage pre-
cipitators.  A decrease in the sparkover voltage
results, and the impressed high voltage may
have to be decreased to prevent excessive spark-
ing.  The reduction may have to approach the
critical corona voltage, and if so, the corona
discharge and its resultant  ionization diminish
with a corresponding drop in collection  efficiency.

Sproull (1955) describes a two-stage unit designed
to circumvent this and other effects.  For avoid-
ing back ionization at the  grounded electrodes in
the ionization section,  wider spacing between
ionizing electrodes was used.  Here negative
ionization was  used and at a correspondingly high-
er voltage owing to the wide spacing.  For pre-
venting reentrainment at the collector plates and
minimizing ionization and sparkover,  electrodes
such as parallel sheets  of expanded metal -were
found to perform more efficiently than the usual
flat plate electrodes.  Optimum results  with this
unit -were obtained by using a 33-kilovolt reversing
polarity potential on the collector section.
For standard units the limiting air velocity is less
than 600 fpm.  White and Cole (I960) described a
two-stage precipitator designed for high-efficiency
collection of oil aerosols at velocities between
2, 000 and 6, 000 fpm.  The reentrainment of pre-
cipitated  oil is prevented by use of a  slotted tube
drain fitted over the trailing edge of the collecting
surface.  Units such as these are designed and
manufactured to very close tolerances to permit
maximum electric field strength and  the least
airflow disturbance.  In the unit described, col-
lection voltage is  held at 20 kilovolts while ioniz-
ing voltage  is about 35 kilovolts.   Negative ioniz-
ing polarity is used to provide a higher sparkover
level.  Collection efficiencies as high as  99. 8 per-
cent by light diffusion standards are reported on
oil mists.
For  continuous removal of collected contaminants,
wetted film plates have been used in the collector
section.   Installations have been  made in which
the collection section has been replaced by a
water scrubber,  which presumably acts as a more
efficient grounded electrode for some types of
contaminants.  Located after the collecting plates,
a perforated plate on which a. flowing film of -water
is maintained has been found to improve efficiency
slightly.  The wetted baffle plate alone  is not equiv-
alent to the effect of the normal collecting electrodes.

Sulfuric  acid mist is efficiently collected by two-
stage precipitators constructed of corrosion-re-
sistant alloys.  The Atomic Energy Commission
(1952)  reports 94 percent efficiency, by radio-
activity-testing techniques,  on acidic-cell ven-
tilation gases but adds  a qualifying statement that
two-stage units are not  recommended as the final
cleaner on exhaust gases containing radioactive
agents -without thorough trial in a pilot  stage.

Self-cleaning precipitators are available in which
the collector plates are mounted on a chain belt,
as shown in Figure 95.  The  plates are slowly
passed through an oil bath that removes collected
solids  and reapplies  an  oil coating to prevent re-
entrainment.  Another  somewhat similar unit
uses an automatically winding dry-filter medium
to trap the collected materials.  Cleaning re-
quires only the occasional replacement of the
filter medium roll,


Equipment Selection

The validity of the theoretical expressions has
been well established for closely controlled
small precipitators.  The design of industrial
units,  however,  invariably requires the use of
empirical correction factors and approxima-
tions.  An analysis of equations 78 through 82
shows  several physical  properties  on which in-
formation is not readily available to Industrial
users.  Particle size,  for example, affects di-
rectly the limiting charge on the particle and
affects,  therefore, the calculated drift velocity
and  efficiency of separation.   The actual size and
distribution of oil droplets in an industrial ex-
haust stream is rarely determined.  Similarly,
the ionic  current, which affects the field strength,
cannot be accurately measured by ammeters be-
cause the observed values also reflect current
leakage.  For a small two-stage  unit,  ionic-cur-
rent flow is small, and  any leakage affects the
total current very greatly.

Although operating costs of a precipitator are
low, the units are considered as  high-efficiency,
high-cost control devices.  A rule of thumb for
industrial installations  is about $1. 00 per cfm
for the installed  equipment.  When no preclean-
er is required and a package precipitator is ade-

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166
AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER
                           _,Biiiir
                    ' t-xMsssnii&si^m^S^
       Figure  95.  Automatic,  self-cleaning,
       two-stage precipitator.   Dust  parti-
       cles  charged in the ionizing section
       are  collected on aluminum plates.
       These are mounted on a  motor-driven
       chain that automatically  rinses  and
       reoils  the plates every 24 hours
       (American Air Filter Company,  Louis-
       vil le,  Ky.).
quate,  the cost may be as low as $0. 25 per cfm
excluding installation and duct-work.  A difficult
material to  collect might require a precleaner,
two ionizer  banks,  steam coil reheater and
perforated baffle plates -with an installed cost
of about $2.  00 per  cfm.

Since many  factors must be considered in de-
signing or selecting a two-stage unit for a given
process,  some field experience with the charac-
teristics of  the  air contaminant is necessary.
In addition,  a broad experience in precipitation
•work is essential.  If data on the specific pro-
cess to be controlled are lacking, then pilot or
laboratory-scale information must often be ob-
tained  before a full-size unit is installed.  Once
the pertinent data have been collected, the gen-
eral physical dimensions and electrical require-
ments  of the precipitator can be determined by
the equations previously discussed.
                                      OTHER  PARTICULATE-COLLECTING  DEVICES

                                       In addition to the devices already mentioned for
                                       the collection of particul'ate matter,  there  are
                                       other devices of more simple designs that  have
                                       very limited application in the control of air
                                       pollution.  These include settling chambers,
                                       impingement separators, and panel filters. Most
                                       are used principally as precleaners, but some
                                       are used as final collectors -where the air  con-
                                       taminant is of large size or where the grain
                                       loading is very  small, for example,  paper fil-
                                       ters for paint spray booths.


                                       SETTLING CHAMBERS

                                       Settling chambers are one of the simplest  and
                                       earliest types of collection devices.   The most
                                       common form consists of a long,  boxlike struc-
                                       ture in the exhaust system.  The velocity of the
                                       dirty gas stream is reduced by the enlargement
                                       in cross-sectional  area,  and particles with a
                                       sufficiently high settling velocity are collected
                                       by the  action of  gravity forces. A very long
                                       chamber is required to collect  small particles.
                                       Structural  limitations  usually restrict the usage
                                       of simple settling  chambers to  the collection of
                                       particles 40 microns or greater.   Their greatest
                                       use is  as a precleaner to remove coarse and
                                       abrasive particles  for the protection of the more
                                       efficient collection equipment that follows  the
                                       chamber.

                                       If horizontal shelves are closely spaced within a
                                       settling chamber,  the efficiency is greatly in-
                                       creased because particle-settling distances are
                                       reduced.   A device such as this,  known as a
                                       Howard dust chamber, was patented in 1908.  It
                                       has a serious disadvantage in that the  collected
                                       material is very difficult to remove  from the
                                       shelves.
                                        IMPINGEMENT SEPARATORS

                                        When a gas stream carrying particulate matter
                                        impinges on a body, the gas is deflected around
                                        the body, -while the particles,  because of their
                                        greater inertia, tend to strike the body and be
                                        collected on its surface.  A number of devices
                                        use this  principle.  The bodies may be  in the
                                        form of plates,  cylinders,  ribbons,  or  spheres.
                                        An impingement separator  element -with stag-
                                        gered channels  is shown in Figure 96.

                                        Impingement separators are best used in the
                                        collection of mists.  The collected droplets form.
                                        a film on the surface and then gradually drip off
                                        into  a collection pan or tank.  Conversely, col-
                                        lected dry dust  tends to become reentrained when

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                                 Other Particulate-Collecting Devices
                                            167
                 -STAGGERED CHANNELS
    Figure 96.   Impingement  separator elements.
it falls off the collecting surface.  For this rea-
son, -water sprays are sometimes used to wash
off  the collected dust.
PANEL  FILTERS

Panel filters are most commonly used in air con-
ditioning installations, though they do have several
important industrial applications.  Filters are
supplied in units of convenient  size, usually about
20 by 20 inches, to facilitate installation and clean-
ing.  Each unit consists of a frame and a pad of
filter material, as  shown in Figure 97. The frames
of similar units may be joined  together to form a
panel.   These  filters are  classified into two types,
viscous and dry.

Filters are called viscous because the filter medi-
um is coated -with a viscous material to help catch
the dust and prevent reentrainment.  The  coating
material is  usually an oil with  a high flash point
                                                         Figure 97.
                                                         LOUISVI I  le,
             Panel
             Ky.).
f11ter  (Amer ican  Air  FiIter,
and low volatility.   The filter pad consists  of ma-
terials  such as  glass  fibers,  hemp fibers,  ani-
mal hair, corrugated fiberboard,  split wire, or
metal screening.   When the maximum allowable
dust load has accumulated,  the metal trays are re-
moved, washed or steamed,  reoiled, and put back
into  service.   Other pads are thrown away when they
become loaded with dust as shown by their increased
resistance to airflow.   A common industrial applica-
tion  of the wire screen-type  filter is found in collec-
tion  of mist generated from cutting  oils used by
metal-cutting machines.
Dry filters are supplied in units similar to viscous
filters, except that the depth is usually greater.
The filter materials  usually have  smaller air
passages than the viscous filters do, and hence,
lower air velocities must be used to prevent ex-
cessive pressure drop.   Dry filters are usually
operated at 30 to 60 fpm,  as contrasted -with 300
to 500  fpm for viscous filters.  In order to in-
crease the filtering area per unit  of frontal  area,
the filter pads are often arranged in an accordian
form with pleats and pockets.   When the pressure
drop becomes excessive because of accumulated
dust,  the dry-type pads  are discarded.  Dry fil-
ters are frequently used to collect the overspray
from paint-spraying  operation.

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168	AIR POLLUTION CONTROL EQUIPMENT FOR PARTICULATE MATTER	


 PRECLEANERS                                         on the more efficient (and more expensive) final
                                                     collector.  If the collected material has value, a
 Devices of limited efficiency are often used           precleaner, for example, one ahead of a scrubber,
 ahead of the final cleaner.  If the gases contain       can sometimes collect the bulk of it in a more
 an appreciable amount of hard, coarse particles,      usable form.  Devices usually used as precleaners
 a precleaner can materially reduce erosive wear      are settling chambers and centrifugal separators.

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                                           CHAPTER 5
                     CONTROL EQUIPMENT FOR  GASES AND  VAPORS
                                          AFTERBURNERS

                       SANFORD M.  WEISS, Principal Air Pollution Engineer


                                   BOILERS USED AS AFTERBURNERS

                        WILLIAM L. POLGLASE, Air Pollution Engineer*


                                      ADSORPTION EQUIPMENT

                       MARC F. LeDUC,  Intermediate Air Pollution Engineert


                                        VAPOR CONDENSERS

                        ROBERT T.  WALSH,  Senior Air Pollution Engineer*

                       ROBERT C. MURRAY, Senior Air Pollution Engineer


                                    GAS ABSORPTION EQUIPMENT

                   HARRY E.  CHATFIELD, Intermediate Air Pollution Engineer

                            RAY M. INGELS, Air Pollution Engineerf
*Now with the Environmental Protection Agency,  Research Triangle Park, North Carolina.
TNow retired.
TNow with State of California Air Resources Board, Vehicle Emissions Control, Los Angeles, California.

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                                               CHAPTER  5
                        CONTROL  EQUIPMENT  FOR GASES  AND  VAPORS
                AFTERBURNERS

Afterburners,  also called vapor incinerators, are
air pollution control devices in which combustion
converts the combustible materials  in gaseous
effluents to carbon dioxide and water.  The com-
bustible materials maybe gases, vapors, or en-
trained particulate matter and may contribute
opacity, odor,  irritants, "fallout" materials,
photochemical  reactivity, and toxicity to the efflu-
ents.  In many cases, an afterburner can be de-
signed and operated at an efficiency high enough
to eliminate or reduce the opacity,  odor, irri-
tants,  and fallout and also the photochemically
reactive and toxic qualities  of the effluent to
levels  required for compliance with air  pollution
standards.

The two types of afterburners in use are (1)
direct  flame and (2) catalytic.  Direct -flame
afterburners, sometimes  called direct-fired
afterburners, depend upon flame  contact and
relatively high temperatures to burn the com-
bustible materials. Catalytic afterburners oper-
ate by  preheating the contaminated  effluent to a.
predetermined temperature  (usually lower than
the operating temperature of the direct-flame
afterburner) and then promoting further  oxidation
of the combustibles by bringing them into contact
with a  catalyst. In Los Angeles County,  which
has standards for emissions of organic materials
(Rule 66),  afterburners  are  essentially all of the
direct-flame type.
DIRECT-FLAME  AFTERBURNERS

Direct-flame  afterburners consist of a refractory-
lined chamber (which may vary in cross-sectional
size along its length), one or more burners, tem-
perature indicator-controllers,  safety equipment,
and sometimes heat-recovery equipment  such  as
heat exchangers.  Figures 98 through 106 show
external views of direct-flame afterburners and
illustrate the  diversity of shapes and processes
that can be vented.

DESIGN  PRINCIPLES

An efficient direct-flame afterburner designmust
provide for (1) contact between the air contami-
nants and the  burner flame, (2)  adequate time for
the combustion process,  (3) sufficiently high tem-
perature in the afterburner for the complete oxi-
dation of the combustibles, and  (4) adequate ve-
locities to insure that mixing take place without
quenching  combustion.

The operation of direct-flame afterburners is
relatively  simple.   The contaminated gases are
delivered to the afterburner by an exhaust sys-
tem.  The gases are mixed thoroughly with the
burner  flames in the upstream part  of the unit
and then pass through the remaining  part of the
chamber where the  combustion process is com-
pleted,  prior  to being discharged to the atmos-
phere.  Figure 107  shows a sectional view of a
typical  afterburner.
            Figure 98.   External  view of direct-flame afterburner (Gas  Processors, Inc.,  Brea, Calif.).
                                                 171

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172
                          CONTROL EQUIPMENT FOR GASES AND VAPORS
Figure  99   Direct-flame  afterburner venting automotive
assembly plant oven CGM  Assembly  Division,  General
Motors  Corporation, Van Nuys, Calif  ^

AFTERBURNER CHAMBER

The afterburner  chamber may be cylindrical or
rectangular in cross section and is  constructed
of refractory materials inside of a mild-steel
shell.  The refractory  may be fire brick or cast-
able refractory material.  The chamber consists
of a mixing section and a combustion section.
The mixing section must provide for intimate con-
tact between the  contaminated gases and the burn-
er flame.  This area, therefore, is designed to
provide high-velocity flow to insure turbulence
and hence good mixing. Usual velocities for this
zone vary bet-ween 25 and  50 feet per second (fps).

The portion of the chamber downstream of the
mixing section is called the  combustion chamber,
and the velocity in this  section is usually 20 to 40
fps.  The overall retention time of the gases
flowing through the unit should be 0. 3 to 0. 5
second.  Afterburner discharge  temperatures
range from 1000° to 1500° F,  depending upon the
particular  air  pollution problem.  Table 51 indi-
cates recommended temperature ranges for var-
ious types of equipment.  Higher  afterburner dis-
charge temperatures than those shown in this
table -will result in higher afterburner efficiencies.

GAS BURNERS FOR  AFTERBURNERS

Among the  several types of gas burners used suc-
cessfully are nozzle-mixing premixing, multi-
port, and mixing-plate burners. Nozzle-mixing,
premixing,  and multi-port burners are  described
in the burner section of this manual. Mixing-plate
burners have been specifically developed for
afterburner applications.   Figures 108, 109, and
110 show burners  of this type. These burners
consist of a pipe with orifices for natural gas and
vanes or plates, which are  perforated or shaped
in a variety of ways to give good mixing between
a contaminated air stream and the natural gas
fuel.  Most  of the contaminated gases go through
the burner.

The choice  of burner type and the arrangement of
the burners in the  afterburner vary widely.   The
exact method of burner placement depends  not
only on the  burner type,  but also on the design
consideration that  the contaminated gases be in
intimate contact with the burner flame.  Maximum
afterburner efficiency occurs when all of the con-
taminated material passes through the burner.  In
contrast, efficiencies are much  lower when the
contaminated air and burner flame mix far out-
side the burner.  Very low efficiency is associ-
ated with minimum flame contact.

Gas burner arrangements,  sources  of combustion
air, and methods for securing flame contact with
the contaminated air are discussed  below.

Mixing-Plate Burner (Figures 108, 109, and  110)

Mixing-plate burners  usually  are placed across
the inlet section of the afterburner body. All air
for combustion of  the natural  gas originates from
the contaminated air stream.

Intimate flame contact is  secured by positioning
the burners and "profile plates" to force the maxi-
mum amount of contaminated  air through the
burner  and  burner flames.  Profile plates,  usually
made of stainless  steel,  are installed around the
burner  bet-ween the afterburner walls and the
burners. A space of 1 to 2 inches remains
between the plate and the burner. The extremely
high velocity (200  fpm) ensures that the con-
taminated air not flowing through the burner will
mix -with the burner flames.

Multi-Port Burners

Multi-port  burners usually  are installed across a
section of the afterburner separate from the main
afterburner chamber. All air for combustion is
taken from  the contaminated air stream. However,
most multi-port burners are not capable of hand-
ling all of the contaminated stream through the

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                                             Afterburners
                                                                                                  173
Figure  100   Two direct-flame afterburners controlling venting of organic  emissions  (American  Cyanamid  Co., Azusa.
Calif.).
burner.  Therefore, some of the air must be by-
passed around the burner and then thoroughly
mixed downstream with burner flames in a re-
stricted  and baffled area. For this reason, after-
burners  with multi-port burners may not be as
efficient as units with mixing-plate burners. Effi-
ciency of afterburners with  multi-port burners
will be influenced by the amount of contaminants
that by-pass the burner.

Nozzle Mixing  and  Premixing  Burners

The operation of these two types of burners is
somewhat similar. They are arranged to fire
tangentially into a cylindrical afterburner.  Sev-
eral burners or nozzles are required to ensure
complete flame coverage. In addition, multiple
nozzles may be arranged to fire along the length
of the afterburner. Air for combustion of the fuel
can be taken from outside air or from the con-
taminated air stream.

Mixing between the contaminated gases and the
burner flame is achieved in a smaller cross-
sectional area  of the afterburner (called  the mix-
ing section). Tangentially fired afterburners may
have the contaminated gases introduced tangen-
tially or along  the major axis of the cylinder.

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174
CONTROL EQUIPMENT FOR GASES AND VAPORS
Figure 101.  Direct-flame afterburner venting metal sheet lithographing line (American  Can Co.,Los Angeles,  Calif.)-
Refractory baffles and orifices also may be re-
quired to give the best possible mixing between
flame and contaminated gases.

SOURCES OF COMBUSTION AIR FOR  GAS
BURNERS

As mentioned above, combustion air may be
taken from the contaminated air stream or from
ambient air. If the contaminated stream contains
sufficient oxygen for combustion of the fuel and
combustible contaminants,  then additional oxygen
is not required. Mixing-plate  and  multi-port
burners supply the correct volume of air auto-
matically.   Premix and nozzle-mix burners
require a blower and air-gas ratio controls to
meter the proper  mixture and combustion air.
The  combustion air for these burners comes
from the contaminated air stream by branch
                            ducting from the main exhaust duct.  Using this
                            contaminated air for combustion results in higher
                            afterburner efficiency and fuel savings  of 20 to
                            30 percent.

                            OIL FIRING  OF AFTERBURNERS

                            Oil firing of afterburners is feasible provided
                            that proper design practice is followed  and good
                            flame contact is assured.  Although  oil firing is
                            possible, it may be  undesirable from the stand-
                            point of overall air pollution emissions. The
                            combustion of oil produces oxides  of sulfur  from
                            the sulfur-containing oil and may produce oxides
                            of nitrogen greater than those from gas-fired
                            units. For these reasons, oil firing may not be
                            desirable for many locales or should be restrict-
                            ed, i.e. , used only  for periods when fuel gas is
                            not available.

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                                             Afterburners
                                                                                                   175
Figure 102. Direct-flame afterburner venting resin impregnating line (Synthane-Taylor  Corporation, LaVerne, Calif.)-
AFTERBURNER  CONTROLS
Afterburner operating  controls usually consist of
a shielded thermocouple located in the discharge
of the afterburner and  an indicating-controlling
pyrometer, which is coupled to the thermocouple.
The pyrometer electrically or pneumatically
controls gas and combustion air valves to modu-
late the amount of fuel fed  to the afterburner.  The
mode of operation is fully modulating or high-low.
The on-off control mode is undesirable since
there are substantial periods -when no burner
flame is present with accompanying very low
afterburner efficiency.

Safety controls consists of (1) flame safety de-
vices to prove the presence of pilot burner flame,
(2)  timing devices to ensure that the afterburner
is purged of combustibles before burner ignition,
(3)  high-temperature-limit controls to limit the
afterburner temperature to a safe limit,  and (4)
pressure switches to detect low gas and air pres-
sures and shut down the unit if pressures become
too low.

DIRECT-FLAME AFTERBURNER  EFFICIENCY

Afterburner efficiency is defined as:

              (Ib contam/hr in)-(lb contam/hr out)
Efficiency (%)=•
                      Ib contaminant/hr in
               x 100
As mentioned earlier,  the efficiency of an after-
burner is a function of retention time, operating
temperature, flame contact,  and velocity. There
is no quantitative mathematical relationship that
relates  efficiency to these variables because the
kinetics  of the combustion process are complex
and the  flow in afterburners is not easily defined.
Assuming good design, the following generaliza-
tions may be made with respect to afterburner
efficiency:

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176
CONTROL EQUIPMENT FOR  GASES AND VAPORS
Figure  103.  Direct-flame afterburner venting printing
system  (Avery Label Company,  Div.of Avery Products Cor-
poration, Monrovia, Cal if.).
     1.  Overall efficiency increases with increas-
        ing afterburner operating temperature.
        Figure 111 illustrates this point.

     2.  Overall efficiency decreases if excessive
        preheat is given to the contaminated  gases
        entering the afterburner.

     3.  Overall efficiency increases with increas-
        ed flame contact between the contaminated
        gases and the burner flame.

     4.  Efficiency increases with retention time
        for retention times of less than 1 second.

     5.  Efficiency is a function of the afterburner
        design,  and  the inlet concentration of
        organic materials. No direct comparison
        can be  made from one design to another.

     6.  An afterburner rarely attains 90 percent
        efficiency below 1300° F if the generation
        of carbon monoxide in the afterburner is
        included.

Tables  52 and  53  show typical data from tests on
a large and a small afterburner.
                            In moderately efficient afterburners organic
                            materials frequently decrease across the after-
                            burner,  but carbon monoxide  levels increase.
                            While this  indicates some oxidation of organic
                            materials, the materials discharged from the
                            afterburner may be considerably more photo-
                            chemically reactive, odorous, or irritating than
                            the organic materials entering the afterburner.
                            Thus, there may not be an overall improvement
                            in the environment. In addition, the venting of
                            carbon monoxide to the atmosphere is undesiralle.

                            DIRECT-FLAME AFTERBURNER  DESIGN PROBLEM

                                Given:

                                Source of air contaminants - paint bake oven
                                Oven effluent air volume - 4000 scfm

                                Contaminated air temperature at afterburner
                                 inlet - 300° F
                                Concentration of solvent - 300 ppm

                                Required  afterburner efficiency - 90%


                                Problem:
                                Determine dimensions of afterburner, burner
                                 type,  operating  temperature,  and  required
                                 natural  gas input.
                                1.  Burner selection:

                                   The afterburner inlet gases will be rela-
                                   tively low in concentration (300 ppm).  In
                                   addition, 90 percent  efficiency based on
                                   carbon is required by Rule 66,  which
                                   demands the best flame contact possible.
                                   On these bases, select a mixing plate
                                   burner.
                                2.  Temperature selection:
                                   The 90 percent efficiency requirement
                                   dictates the choice of 1400° F as the min-
                                   imum required operating temperature.
                                3.  Burner capacity:
                                   a. Net heat required  to raise contaminate
                                     air  stream to 1400° F from 300° F

                                      Assumed properties of air:
                                        Enthalpy at 1400° F = 26.13 Btu/scf
                                          (see  Table D4 in Appendix D)
                                        Enthalpy  at 300 °F =. 4. 42  Btu/scf
                                         (See Table D-4 in Appendix D)

                                        Net enthalpy =  21.71  Btu/scf

                                      Qnet = (4000)(60)(21. 71) =5.2xl06Btu/hr

                                   b, Natural gas input required:
                                      The hypothetical  available heat for
                                      natural gas with 0% outside primary

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                                             Afterburners
                                   177
Figure 104.   Direct-flame afterburner venting paint baking oven (Weber  Show Case and Fixture, Div. of Walter  Kidde
and  Company,  Inc., Los Angeles,  Calif.).
          air = 939Btu/ft3 (see Table Cl in
          Appendix C)


          Natural gas input =

           	Qnet	 =
           Hypothetical available heat
           5.2 x 10C
                     = 5,550 ft3/hr
              939
    4.  Combustion chamber diameter:
       Chamber is assumed to be cylindrical

       a.  Volume of gases  in afterburner:

          Vol = Oven effluent air - effluent used
           for combustion  products from com-
           bustion of natural gas.
(1) Air for combustion of natural gas in
   (3b) above:

   Air required =  10.36 ft3/ft3 natural
    gas  (see  Table D7 in Appendix D)

   (5, 550) (10. 36)
          60
                   = 959 scfm
(2) Products from combustion of
   natural gas:

   Combustion products = 11.45 scfm/ft3
    natural gas (see Table D7 in
    Appendix D)
    (5,550) (11.45)
           60
= 1060 scfm
(3) Volume of gases in afterburner:
   4000 - 959 + 1060 = 4100  scfm

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173
CONTROL EQUIPMENT FOR GASES AND VAPORS
Figure  105. Direct-flame afterburner  venting three var-
nish cooking kettles and a thinning station (National
Paint and Varnish Co.,  Los Angeles,  Calif.).
                                                                   (4)  Volume of gases at 1400° F (I860" R) :



                                                                                           C±S
                                                                         (60) (520)

                                                                b. Diameter of afterburner:

                                                                   Velocities of 20 to 40 fps are satisfac-
                                                                     tory.

                                                                   Assume 30 fps.

                                                                   Afterburner cross section= (244) (1/30) =
                                                                     8. 1  ft2

                                                                   Diameter corresponding to 8. 1 ft  =


                                                                       TT" =3.2 ft
                                  5.  Combustion chamber length:

                                      Retention times of 0. 3 to 0. 5 second are
                                       adequate.

                                      Assume 0.5  second.
 Figure  106.  Direct-flame afterburner with  induced-draft  fan, all mounted  on an  integral  frame and ready for  ship-
 ment (Hirt Combustion Engineers,  Montebello, Calif.).

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                                             Afterburners
                                                                 179
                                                                      FLAME SENSOR-

                                                                   BURNER.
                                                                                         STRAIGHTENING
                                                                                         VANKS
                              COOLING AIR
                             INDUCTION SYSTEM—,
                              <«dju>tabl»
                                                               UNITIZED MOUNTING
                                                          ^-SAMPLE PORT

                                                      TEMPERATURE ShNSOR
                                           BLOWER
                                         -INSULATION
          Figure 107.  Sectional  view of direct-flame  afterburner (Gas Processors,  Inc., Brea, Calif.).
  Table 51.  RECOMMENDED AFTERBURNER
         OPERATING TEMPERATURES
        Operation
Carpet laminating
Core oven
Cloth carbonization
Deep fat fryers
General  opacity problems
Odor control
Oil and grease smoke
Paint bake ovens
Pipe wrapping
Rendering operations
Smokehouse
Solvent control
Varnish  cookers
Vinyl plastisol curing	
Recommended
temperature,
      ° F
 1200 - 1400
     1400
     1800
     1200
 1200 - 1400
 1300 - 1500
 1200 - 1400
 1200 - 1500
     1400
     1200
     1200
 1300 - 1500
     1200
 1200 - 1400
         Length = (retention time) (velocity)

                 = (0.5)(30) = 15 ft
    Summary of design:
      Burner type--Mixing plate

      Afterburner temperature =  1400" F

      Burner input = 5,550 cfh
      Afterburner diameter =  3. 2 ft

      Afterburner chamber length =  15 ft

CATALYTIC  AFTERIURNERS

A  catalytic afterburner  consists of  a preheat
burner  section,  a chamber containing  catalyst,
temperature indicator-controllers, safety equip-
ment,  and heat recovery equipment.   Figures 112
through 115 show various  arrangements of cata-
lytic afterburners.
 234-767 0-77-14

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180
CONTROL EQUIPMENT FOR GASES AND VAPORS
    HIM!
      Illlllll
    IHmHHMfl
    iimiiiiirw  •
     iiuiiiiiM  i
              'fti
                                         to
Figure 108.  Mixing plate burner (J.T. Thorpe,  Inc.,
Los Angeles, Cal if.).
                          OPERATION

                          A catalyst is a substance that changes the rate of
                          a chemical reaction and does not appear to change
                          chemically in doing  so. In the case of afterburners,
                          the catalyst functions to promote the oxidation
                          reactions at a somewhat lower temperature than
                          occurs in a direct-flame afterburner. The catalyst
                          usually is platinum combined with other  metals
                          and deposited in porous form on an inert  substrate.
                          The substrate may be in the form of rods,  honey-
                          comb, or ribbons.  In any case,  the objective is to
                          present the maximum catalyst surface area to the
                          contaminated gases.
                                      o

                          In operation, the contaminated gases delivered to
                          the afterburner first enter the preheat zone,
                          where they are heated to the  temperature required
                          to sustain the catalytic combustion. The preheat
                          zone  temperature varies with the composition and
                          type of contaminants to be oxidized,  but is gener-
                          ally in the range  of 650° to 1100° F.  A substantial
                          portion of the overall efficiency  of the afterburner
                          can be attributed to  the burner in the preheated
                          zone.  The preheated gases then  flow through  the
                          catalytic  elements,  where the remaining  contami-
                          nants  are burned. The combustion reaction is
                          exothermic,  resulting in an  increase of  catalyst
                          temperature--the greater  the concentration   of
              Figure 109.  Mixing  plate  burner (Maxon Premix Burner Co.,  Inc., Muncie,  Ind.).

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                                          Afterburners
                                                                                                   181
                                                          100
Figure 110.  Schematic drawing of mixing plate  burner
(Maxon Primix Burner Co.,  Inc., Muncie, Inc.).
                                                           90
                                                       LU
                                                       O
                                                           70
                                                           60
     50
     1000
                                                                       1200         1400
                                                                      AFTERBURNER TEMPERATURE, °F
1600
combustible material,  the higher the catalyst
temperature.  Under some conditions it is possible
to reduce the preheat temperature of the  entering
gases after the reaction has been initiated.
 Figure 111.  Direct-flame afterburner efficiency  as a
 function of temperature.
EFFICIENCY

The efficiency of catalytic afterburners  is a func-
tion of many variables.  These include surface
area of the catalyst,  catalyst type, uniformity of
flow of the gases through the catalyst bed, nature
of the material being burned, oxygen concentra-
tion, volume of gases per unit of catalyst, and
temperature of the unit.

The efficiency of a catalytic afterburner deterio-
rates as the unit is used, and periodic replace-
ment of the elements is required. This replace-
ment time varies widely, depending upon the
service of the unit,  from a few months to 2 years.
In addition, the performance of the catalyst  is
seriously affected by materials that "poison" the
catalyst.  Some of these are mercury,  arsenic,
zinc, and lead.  Substances that coat the  catalytic
elements such as resin  solids and solid  oxides
must be  avoided since these materials will seal
off the catalyst from the gases to be treated.

Catalytic afterburners may not be capable of
meeting  local efficiency requirements,  such as
90 percent conversion of the carbon in the organic
materials to carbon dioxide. New catalysts
recently made available may increase the after-
burner efficiency at relatively high inlet concen-
trations (greater than 5000 ppm as carbon).  At
lower  concentrations, the catalytic afterburner
efficiency decreases markedly even at discharge
temperatures as high as  1100° F. Catalytic  after-
burners operating at less than 900° to 1000° F
may exhaust gases that are  odorous and eye irri-
tating.  This problem appears to be due to the in-
complete oxidation of the organic material,  re-
sulting in aldehydes, ketones, and organic acids.


RECOVERY OF HEAT FROM  AFTERBURNER EXHAUST
GASES

The heat discharge  in the afterburner exhaust
gases  frequently can be recovered, and thus the
overall cost of afterburner operation may be
reduced. Some of the heat recovery  schemes that
have been used successfully include:

    1. Heat  exchangers to heat the contaminated
      gases before  entry into the afterburner.

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132
CONTROL EQUIPMENT FOR GASES AND VAPORS
             Table 52.  TYPICAL ANALYSIS OF EMISSIONS ENTERING AND LEAVING

                               LARGE DIRECT-FIRED AFTERBURNER



CO2, ppm
C O , ppm
Organics as CO2, ppm
Volume (dry basis), scfm
Organics (as carbon), Ib/hr
Afterburner efficiency, %
Temperature
1400° F
In
6, 300
59
1,568
11, 950
35.6
Out
22, 000
230
235a
11, 800
5.26
85
1500° F
In
6, 600
65
1, 591
12, 000
36.2
Out
27,000
21
70
11, 800
1. 6
96
             Includes increase  of CO across afterburner.



             Table 53.  TYPICAL ANALYSIS OF EMISSIONS ENTERING AND LEAVING

                               SMALL DIRECT-FIRED AFTERBURNER



CO2, ppm
CO, ppm
Organics as CO2, ppm
Volume (dry basis), scfm
Organics (as carbon), Ib/hr
Afterburner efficiency, %
Temperature
1300° F
In
1, 950
8
521
2,240
2. 21
Out
19,000
110
122a
2,200
0. 50
77
1400° F
In
2, 000
9
408
2, 240
1. 74
Out
23, 500
24
33a
2, 200
0. 14
92
            Includes increase of CO across afterburner.
                                •DISCHARGE TO ATMOSPHERE
    Figure 112.  Typical  catalytic afterburner
    utilizing  indirect  heat recovery.
                              2. Heat exchangers to heat air as a source of
                                 heat for the equipment generating the con-
                                 taminated gases.

                              3. Venting of the afterburner gases to other
                                 process equipment such as waste heat boil-
                                 ers, water dry-off ovens, and vaporizers.


                           PREHEATING OF AFTERBURNER INLET GASES

                           Use  of a heat exchanger for preheating the con-
                           taminated gases entering the afterburner is one of
                           the most commonly used methods of recovery of
                           heat from afterburner exhaust gases. The usual
                           method is to use a  shell-and-tube heat exchanger
                           with the gases to be heated on the tube side and
                           the afterburner  discharge gases on  the shell side.
                           There may be one or two passes on the tube side
                           and one pass on the shell side.  In heat exchange

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                                     Boilers Used As Afterburners
                                             183
        Figure 113.   A catalytic  afterburner used to control
        Combustion Corporation, Detroit, Michigan).
      a foundry core  baking oven (Catalytic
terminology,  a pass is the number of times an
individual stream exchanges heat with another
stream. The temperature of the heated, contami-
nated gas leaving the exchanger usually is about
midway between  the cool gases entering the ex-
changer and the temperature  of the gases vented
to the exchanger  from the afterburner.

The  stream entering the afterburner should not
be preheated to too high a temperature. Excessive
preheat will substantially  reduce the amount of
burner flame present and  thus lower the efficiency.
      BOILERS  USED  AS AFTERBURNERS

Fireboxes of boilers and fired heaters can be
used, under proper conditions, as afterburners
to incinerate combustible air contaminants.
This use is unique in that a basic source of
air contaminants, a boiler,  is used to control
pollutants from another source.   Boiler fire-
box conditions  approximate those of a well-
designed afterburner, provided there are ade-
quate temperature,  retention time, turbulence,
and flame.  Oxidizable contaminants, including
smoke and organic vapors and gases, can be
converted essentially to carbon dioxide and
water in boiler fireboxes.
 The discussion of this  section is limited to the
 control of low-calorific-value gases and vapors
 with common types  of steam and hot water
 boilers and heaters.  When appreciable heat
 is contained in the contaminated gases, the
 firebox is usually of special design to take
 advantage of the heat potential.  These latter
 units,  commonly known as \vaste heat boilers,
 are discussed in Chapter 9.

 Completely satisfactory adaptations of boilers
for use as afterburners are not  common.  All
 aspects of operation should be thoroughly eval-
uated before this method of air pollution con-
trol is used.  The primary function of a boiler
 is to supply steam or hot water,  and whenever
 its use as a control device conflicts with this
function,  one or both of its purposes will
 suffer. Some advantages  and disadvantages of
boilers used as afterburners are shown in
 Table  54.

CONDITIONS FOR USE

 The determination to use a boiler as an after-
burner demands that the following conditions
exist:

 1.  The air contaminants  to be  controlled must
    be almost wholly combustible since a boiler

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184
CONTROL EQUIPMENT FOR GASES AND VAPORS
                                                                       ^DISCHARGE TO ATMOSPHERE
          CLEAN  HOI EXHAUST
                   TWO PASS OVERHEAD MONORAIL CORE BAKING OVEN
  Figure  114,  A catalytic afterburner  venting  a
  foundry  core baking oven (Catalytic Combustion
  Corporation, Detroit,  Michigan).

     firebox  cannot be expected to control non-
     combustible pollutants.  Inorganic dusts
     and fumes deposit on heat transfer surfaces
    • and foul them with resulting losses in boiler
     efficiency and steam-generating capacity.

2.   The volumes of contaminated gases must
     not be excessive or they will reduce thermal
     efficiencies in much the same way as  ex-
     cess combustion air does.  The additional
     volume  of products of combustion will also
     cause higher pressure drops  through the
     system, in some  cases exceeding the  draft
     provided by existing boiler  auxiliaries.

3.  The oxygen content of the contaminated gases
    when used as combustion air must be similar
                                                          Figure  115.   Typical catalytic afterburner
                                                          uti Iizing direct  heat  recovery.
                                 to that of air to ensure adequate combustion.
                                 Incomplete combustion can form tars or resins
                                 that will deposit on heat transfer  surfaces and
                                 result in reduction of boiler efficiency.  When
                                 these  contaminants exceed air pollution con-
                                 trol standards  for gas- or oil-fired boilers,
                                 tube fouling will already have become a
                                 major maintenance problem.
                                 An adequate flame must be maintained con-
                                 tinuously in the boiler firebox.   High-low
                                 or modulating burner controls are satis-
                                 factory provided  that the minimum firing
                                 rate is sufficient to incinerate the maximum
                                 volume of effluent that can be expected in
                                 the boiler firebox.  Obviously a burner equip-
                                 ped with on-off controls would not be feasible.
                                 Where steam demands are large and vary
                                 greatly,  a separate small boiler  should be
                                 installed in addition to the  regular boilers in
                                 the plant. This smaller  boiler is used as an
                                 afterburner and should have a capacity just
                                 sufficient to consume the emissions to be
                                 incinerated. Even with a low steam  demand,
                                 the afterburner boiler can be maintained on
                                 ample fire to incinerate the contaminants
                                 admitted to it.
                            Boilers used as afterburners have successfully
                            controlled visible emissions from meat smoke-
                            houses and also obnoxious  odors from rendering
                            cookers  and from oil refinery processes involv-
                            ing cresylic and naphthenic acids, hydrogen sul-
                            fide,  mercaptans,  sour water strippers, ammonia
                            compounds, regeneration air from doctor treat-
                            ing plants, oil mists and vapors from process
                            columns, and so forth.

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                                     Boilers Used As Afterburners
                                              185
         Table 54.  ADVANTAGES AND DISADVANTAGES OF USING A BOILER AS AN AFTER-
             BURNER RATHER THAN A CONVENTIONAL DIRECT-FIRED AFTERBURNER
                       Advantages
                Disadvantages
      1.  Large capital expenditure not required.


      2.  Boiler serves dual purpose as source of
         process steam and as an air pollution
         control device.
      3.  Auxiliary fuel not  required for operation
         of air pollution control device.


      4.  Operating and maintenance cost limited to
         one  piece of equipment.

      5.  Fuel saving, if effluent has some  calorific
         value (rare instances).
1.  If air contaminant volumes  are  relatively
   large,  boiler fuel cost may be excessive.

2.  High maintenance cost may be required
   because of burner and boiler tube fouling.


3.  Boiler must be fired at an adequate rate  at
   all times when effluent is vented to the fire-
   box,  regardless of steam requirements.

4.  Normally,  two or more boilers must be
   used, one as standby during shutdowns.
5.  Pressure drop through boiler may be  ex-
   cessive if large volume of effluent intro-
   duced into boiler causes back pressure on
   exhaust system.
 MANNER OF VENTING CONTAMINATED GASES

 Like other types of controls,  these units re-
 quire a properly designed exhaust  system to
 convey air pollutants effectively from the point
 of origin to the boiler firebox.

 Contaminated gases  may be introduced into the
 boiler firebox in two ways:  (1)  Through the
 burner,  serving as combustion  air, or  (2)
 downstream of the burner, serving as secon-
 dary air.

 Figures  116 and 117 show poor and good installa-
 tions wherein the contaminated gases are intro-
 duced through the burner.  The  oxygen content of
 these gases must be nearly equivalent to that of
 air to ensure good combustion.  Excessive vol-
 umes of  nonoxidizing gases such as CO2, t^O,
 and N£ can cause  undesirable  results ranging
 from flame popping to complete outage of the burn-
 er.  Introducing contaminated gases through
 the burner should promote  good flame contact,
 turburlence,  temperature, and retention time.

 Since the polluted gas stream furnishes a part
 of the  combustion air for the burner,  less ad-
 ditional air is required from the combustion air
 system.   Burner maintenance  costs, however,
 are higher.  Contaminated gases should not
be introduced through the burner if a high
moisture content or corrosive gases and vapors
are present.  In these cases,  the gases should
be introduced into the boiler downstream of
the burner.
   Figure  116.   Poor method of introducing  contam-
   inated  air  from  diffuser to boiler  firebox
   through the  burner air register.   Diffuser  re-
   stricts combustion air to burner.   Moreover,
   louver  may partially close restricting flow of
   contaminated  air  into boiler firebox.
  Figures 118,  119, and 120 show both desirable
  and undesirable methods of introducing con-
  taminated gases downstream of the burner.
  Gases must be carefully directed into the boil-
  er  firebox to  ensure adequate flame contact.
  An exhaust fan or a steam ejector is used to
  convey the effluent through an exhaust system

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 186
CONTROL EQUIPMENT FOR GASES AND  VAPORS
Figure 117.  Good method of introducing  contam-
inated air to boiler firebox  through  a custom-
made air register.   There is  good  flame  contact.
Contaminated air enters firebox  through  burner.
Note:  type of  burner  is critical;  contaminated
air  is portion  of combustion  air;  not applicable
where contaminated  gases are  corrosive.
                              Figure 119.  Boiler firebox showing entry of
                              contaminated air through a diffuser in the
                              floor near the burner.   The possibility for
                              flame contact is good.   Note:   Type of burner
                              is not critical; contaminated  air is secondary
                              air for boiler;  applicable where contaminated
                              gases are corrosive.
                                            CONTAMINATED-AIR
                                            DUCT ENTRANCE
     Figure  118.   Poor method showing entry of
     contaminated  air near  boiler  firebox rear
     firewall.   Flame contact is poor.
from the source into the boiler firebox. Some-

times, a flame arrestor is installed to prevent

flashback.   When gases of high moisture con-

tent must be incinerated, condensers are in-

stalled upstream of the boiler.


A reduction in boiler efficiency should be ex-

pected when gases are introduced directly in-

to the boiler firebox.   In addition,  incinera-

tion may not be complete, and partially oxi-

dized organics may be present in the products
                               Figure 120.  Boi ler  fi rebox
                               contaminated ai r  through  a
                               boi ler.   Flame  contact  and
showing entry of
duct at front of
mixing are poor.
                             of combustion.  As a result,  these particulates

                             deposit on boiler tubes and reduce heat trans-

                             fer.  Because of these disadvantages, this

                             latter method should be used only when the

                             contaminated gases  cannot be introduced di-

                             rectly through the burner.

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                                    Boilers Used As Afterburners
                                             187
 ADAPTABLE TYPES OF EQUIPMENT
 Boilers and Fired Heaters

 Water-tube, locomotive,  or HRT boilers and fired
 heaters are the units most frequently used as after-
 burners.  Burners used -with these units are usually
 adaptable to incineration, and the fireboxes
 are usually accessible.   Thus, the  contamina-
 ted gases may be properly introduced either
 through the burner or through the floor or
 sides of the fireboxes.
Some types of boilers do not provide these fea-
tures.  For example, polluted gases usually
cannot be introduced into the firing tube of a
Scotch marine boiler unless they are introduced
with the combustion air.  Admitting contamina-
ted gases through the integral blower of a forced-
draft burner is normally not feasible.
 Burners

 Burner selection is greatly influenced by boiler or
 heater firebox design,  the method of introducing
 polluted gases, and the characteristics of the pol-
 lutants  themselves.
boiler-afterburner is recommended.   Flaring
or intermediate gas storage for use as fuel
might well be a more practical approach than
on-line incineration.
 Contaminants in most exhaust gas streams  are
 normally well below explosive concentrations.
 In a few processes, however,  combustible gas
 concentrations can accumulate during shutdowns
 with resultant explosion hazards  on lightoff of
 the boiler.  For instance, a batch of  raw or
 partially cooked animal matter might be left
 overnight in a rendering cooker ducted to a
 boiler-incinerator.   This could generate enough
 methane, hydrogen  sulfide,  and other organics
 to produce an explosive mixture in the ductwork
 leading to the boiler.  If,  subsequently, the
 burner were ignited -without first purging the
 line,  an explosion could occur.  To avoid a
 rare possibility  such as this, both the boiler
 firebox and the  ductwork should be purged be-
 fore igniting the burner.
Some fire hazard is created by the accumulation
of organic material in ductwork.   Lines such as
these must usually be washed periodically.   The
degree of organic accumulation can sometimes
be reduced by frequent steam purging or by
heating the ductwork to prevent condensation.
Where gases are introduced as excess air through
the sides  or floor of the firebox,  any standard gas
or oil burner may be used.  The gases must,  how-
ever, be introduced near the burner end of the fire-
box  to ensure adequate incineration.
Where contaminated gases are used as combus-
tion air, natural or induced  draft is essential.
Multijet natural-gas burners and steam, pres-
sure, or air-atomizing oil burners are most
adaptable.   The burner must be  thoroughly main-
tained according to the character of contaminants
to be incinerated.  Forced draft burners are not
recommended because of the probability of cor-
roding and fouling burner controls and blowers.
SAFETY
As with any afterburner or flare used to incin-
erate combustible gases, care must be  taken to
prevent flashbacks and firebox explosions. This
problem is most acute when the contaminated
gas stream contains explosive hydrocarbon con-
centrations,  for example, a refinery flare. In
these instances,  suitable flame arrestors are re-
quired.  Where continuing explosive concentra-
tions are likely,  a control device other  than a
DESIGN PROCEDURE

When evaluating a control system -wherein a
boiler is to be used as an afterburner,  one
should:
1.  Determine the maximum volume, tempera-
    ture, and characteristics of the polluted
    gases to be vented to the boiler firebox;


2.  ascertain that the exhaust system from the
    source  of the pollutant to the boiler firebox
    is properly designed;


3.  determine the manner in which the pollutants
    are to be introduced into the boiler firebox;
4.   calculate whether the boiler and burners
    are of sufficient  size and design to handle
    the contaminated gases;


5.   calculate the minimum firing rate at which
    the boiler must be operated to ensure ade-
    quate incineration; if the existing boilers
    are too large,  then plan to install a smaller
    boiler to be used as the afterburner;

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188
CONTROL EQUIPMENT FOR GASES AND VAPORS
6.   provide that the firing rate does not fall
    below the minimum rate determined in item 5.

The following example shows some of the factors
that must be considered in determining the feasi-
bility of using a boiler to incinerate exhaust gas-
es from four meat processing  smokehouses.


Example 23 (Figure 121)

Given: Boiler data

Boiler, 150 hp, HRT type, multijet burner, gas
fired  only—minimum instantaneous firing rate,
38.2 cfm.

Automatic modulating controls, stack size,  30-
in. diameter x 40 ft high.

Assumptions:

Boiler operates at 80% efficiency, stack tem-
perature = 500 °F, 20% excess air to burner.

Effluent data:
Maximum volume of effluent = 1, 000 scfm,
(76. 4 Ib/min) -with smokehouse stacks  damp-
ered.  Minimum temperature  of effluent =
100°F.

Assumptions:

Effluent gases have  the same properties as
air.   Exhaust system has been designed to con-
vey effluent gases properly from smokehouses
to boiler firebox.  Effluent to  enter boiler fire-
box as secondary air through diffuser in floor,
near burner end.  Minimum incineration temper-
ature to be  1,200°F.
                          Solution:

                          1.   Btu input required to fire the 150-hp boiler
                               at rating:

                               1 boiler hp = 33,475 Btu/hr

                               (150hp)(33.475 Btu/hr)
                                       0  g eff          =  6, 277,000 Btu/hi

                          2.   Natural gas flow required to fire boiler at
                               rating:

                               Gross heat standard of natural gas taken at
                               1, 100 Btu/ft3 at 60°F.
                               6,277,000 Btu/hr
                                                 =  5, 707 cfh or 95. 1 cfm
                                 1, 100 Btu/ft"

                          3.  Determine minimum firing rate for boiler:

                              Instantaneous minimum firing rate for boiler
                              determined by actual measurement =  38.2 cfm

                              Therefore, minimum firing rate for boiler
                                  38.2
                                  95. 1
                                       (100) =  40.2% of rating
                          4.   Heat required from burner of boiler to raise
                               temperature of smokehouse effluent from
                               100°  to 1,200°F:

                               Enthalpy of gas (1,200°F)  = 287.2 Btu/lb
                               (See Table D3 in Appendix D. )

                               Enthalpy of gas (100°F)  =  9. 6 Btu/lb
                               (See Table D3 in Appendix D. )

                              (76.4 lb/min)(277.6 Btu/lb) = 21,209 Btu/min
/—BOILER
/ HRT TYPE
-i / ""'
jj;


6\1
/— EFFLUENT GAS
/ MAK VOL 1 COD scfm
/ HIN TEMP 100 °F
u /^
^- BURNER
^SMOKEHOUSE (TYP

\.
^
x'
\
	
^
       Figure 121. Sketch of proposed system.
 Problem:

 Determine whether use of a 150-hp HRT-type boiler
 as an afterburner is feasible.
                                                      5.   Natural gas flow required to supply 21,209
                                                           Btu/min:

                                                           Heat available at 1, 200°F from the burning
                                                           of 1 ft   of natural gas with 20% excess air
                                                           =  676.5 Btu/ft3 (see Table D7 in Appendix
                                                           D).
                                                                  21, 209 Btu/min

                                                                  676. 5 Btu/ft
                                                       =  31.4 cfm
                               Since only 31.4 cfm is required to raise
                               temperature of smokehouse effluent from
                               100°  to 1,200"F,  minimum firing rate for
                               boiler is adequate.

                          6.   Volume of products of combustion from boiler
                               firing at 150% rating with 20% excess  air:
                               One ft3  of natural gas yields 13. 473 ft3 of
                               products of combustion (see Table D7 in
                               Appendix D).

-------
                                         Adsorption Equipment
                                                                   189
    Vol =  (142.7 scfm)(13.473)  = 1,922.7 scfm
7.   Total volume vented from boiler:

     Volume of effluent (secondary air) = 1,000 scfm
     Volume of products of combustion = 1, 922. 7

     Total volume vented = 1,000  +  1,922.7
     =  2,922.7

8.   Volume of gases vented at stack tempera-
     ture of 500 °F:
    (2,922.7)  (500° + 460°)
                (60° + 460°)

9.   Stack velocity:

                 5, 396 cfm
=  5, 396 cfm
    Vel  =
           (60 sec/min)(4. 91 ft )
    = 18.32 ft/sec
    Note:  Stack velocities not exceeding 30 ft/sec
           are satisfactory for natural-draft units.

10. Heat required to raise temperature of ef-
    fluent from 100°  to 500°F (stack tem-
    perature):

    Enthalpy of gas (500°F) = 106.7 Btu/lb
    (See Table D3 in Appendix D. )

    Enthalpy of gas (100°F) = 9. 6 Btu/lb
    (See Table D3 in Appendix D. )

                           Ah =  97. 1 Btu/lb

    (76.4 lb/min)(97. 1 Btu/lb)  =  7,418 Btu/min
11. Natural gas flow required to supply 7, 418
    Btu/min:

    The net thermal energy per ft  natural gas
    above that required to bring the effluent to
    the stack temperature of 500°F  =  878 Btu/ft3
    (see Table D7 in Appendix D).
        -ir i       7, 418 Btu/min
        Vol gas = —'	—
                  878. 0 Btu/ft
    =  8. 45 cfm
12.  Incremental cost of natural gas (assume
    rate of $0. 50 per  1, 000 ftj):

    „  .   ft     60 min    24 hr
    8.45——  x —	  x —	
         mm      hr       day


                  =  $6.08/day
        $0. 50

      1,000 ft"
                        13.  Cost of operating a direct gas-fired after-
                            burner operating at same temperature
                            (neglecting initial capital expenditure):
                                    3
                             31.4
                                  ft"
                  60
24
                                            hr
                             day
  $0.50

1,000 ft"
                                           = $22.61/day
Problem note:  Calculations indicate that use of
this boiler as an afterburner is feasible.  The
boiler is fired at an adequate rate at all times,
and excessive volumes of effluent are not vented
to this boiler firebox.  Costs, including initial
capital expenditures,  are nominal.  Some ad-
ditional cost might be necessary to provide
more draft  to offset increased pressure drops
through the boiler.


TEST DATA

Tests have been conducted on  several boilers
used as afterburners.  The majority of tests
have been on boilers  used to incinerate the ef-
fluent from meat smokehouses.  One test, how-
ever, includes a boiler used to incinerate partial-
ly condensed vapors from rendering cookers.

Table 55 summarizes these test results and  shows
the apparent efficiencies  of boilers in control-
ling combustion contaminants, organic acids, and
aldehydes.  Installations  were such that tests
could not be conducted with the boilers operating
under identical conditions unless  the contamina-
ted gases were vented to  the boiler fireboxes.
          ADSORPTION EQUIPMENT

 Adsorption is the name for the phenomenon in
 which molecules of a fluid contact and adhere
 to the surface of a solid.  By this process,
 gases,  liquids,  or solids, even at very small
 concentrations, can be selectively captured
 or removed from airstreams with specific
 materials known as adsorbents.  The material
 adsorbed is called the adsorbate.

 A change in the composition of the fluid con-
 tacting the adsorbent results when one or
 more of the components are adsorbed by the
 adsorbent. The mechanism of this process
 is complex, and while adsorption can occur at
 all solid interfaces, it is usually small unless
 the solid is highly porous  and possesses fine
 capillaries. The most important character-
 istics of solid adsorbents  are their large sur-
 face-to-volume ratios and  preferential affinity
 for individual components.

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190
CONTROL EQUIPMENT FOR GASES AND VAPORS
                  Table 55.  TEST DATA ON BOILERS USED AS AFTERBURNERS
Equipment
tested
Volume of gases, sctm
Stack
Boiler inlet
Combustion contami-
nants, Ib/hr
Inlet
Outlet
Efficiency, %d
Organic acids, Ib/hr
Inlet
Outlet
Efficiency, %d
Aldehydes, Ib/hr
Inlet
Outlet
Efficiency, %d
426 -hp boile r ,
water -tube type,
gas fired3

8, 700
1,600


2.4
0. 45
84

1. 5
0. 56
60

0.22
0. 09
59
Two 268-hp boilers,
common stack
water-tube type,
gas fireda

10, 300
i, 930


4.6
0. 53
89

2. 7
0.64
78

0. 39
0. 40
0
200-hp boilers,
water-tube type,
gas fired°

4, 700
2, 400


2. 7
1. 6
41

2. 2
1. 4
36

0. 39
0. 30
23
	 _
Two 113-hp boilers,
common stack
locomotive type,
gas fireda

3, 800
320


0. 19
0. 16
16

0. 12
0
100

0. 03
0
100
150-hp boiler,
HRT type,
gas firedc

3, 400
470


0. 74
0.52
30

0. 35
0. 14
60

0. 012
0. 09
0

3,600
750


0.73
0.71
3

0.44
0. 38
14

0.03
0. 18
0
 aMeat smokehouse effluent was admitted into boiler firebox through the multijet burner.
 Meat smokehouse effluent was admitted into boiler firebox through diffuser located at front of firebox floor.
 cRendering cooker effluent was admitted into boiler firebox through diffuser located at rear of firebox floor.  Two tests were
 run. The use of this boiler as an afterburner has been discontinued, primarily because the minimum firing  rate of the boiler
 was insufficient to incinerate air contaminants.
 Efficiency shown is Apparent Efficiency. Boilers could not be tested unless air contaminant were vented to it.
Many theories have been advanced to explain
the selective adsorption of certain vapors or
gases,  the exact mechanism being still dis-
puted.  In some cases, certainly,  adsorption
is due to chemical combination of the gas with
the free valences of atoms on the surface of the
solid in the monomolecular layer,  as was pro-
posed by Langmuir in 1916  (Glasstone,  1946).
Other investigators hold that the adsorbents
exert strong attractive forces,  so  that many
adsorbed layers form.   These layers are under
pressure, partly because of layers on top and
because of the attractive force  of the surface
of the adsorbent.  In other cases,  the evidence
indicates that adsorption is due to  liquefaction
of the gas and its retention by capillary action
in the exceedingly fine pores of the adsorbing
solid.  In many cases,  the phenomena are
probably superimposed.  The adsorptive power
of activated  charcoal is  due mainly to molecu-
lar capillary condensations while the adsorp-
tive power of silica gel is due  mainly to cap-
illary condensation.  Note,  however, that the
adsorptive power of any solid adsorbent may
vary appreciably •with the method of prepara-
tion as  well  as  with the nature of the gas or
vapor adsorbed (Walker et al. , 1937).

In most processes involving adsorption, the
operation involves three steps.  First,  the
adsorbent is contacted with the fluid, and a
separation by adsorption results.  Second,
the unadsorbed portion of the fluid is sepa-
rated from the  adsorbent.   In the case of gas-
                               es,  this operation is  completed on their pas-
                               sage through the adsorbent bed.   Third, the
                               adsorbate is  removed from the adsorbent,
                               which thereby regenerates the adsorbent.  In
                               some cases the  adsorbent is regenerated with-
                               out  recovery of  the adsorbate, as in the de-
                               colorizing of sugar solutions -with bone char
                               and the treatment of lubricating  oils with
                               Fuller's earth.  In the treatment of domestic
                               water with finely divided activated carbon,
                               both the adsorbent and the adsorbate  are sep-
                               arated from the fluid and discarded.

                               Regeneration, which  involves raising the temper-
                               ature of the adsorbent, may be performed by
                               several methods,  depending upon the adsorbate.
                               In the examples cited previously, where the ad-
                               sorbate has no economic value,  the Fuller's
                               earth and  bone char are heated directly with hot
                               gases. In the recovery of chlorine and sulfur
                               dioxide from silica gel,  the adsorbent is heated
                               indirectly with a hot brine.  In the recovery of
                               solvents,  low-pressure steam is used and the
                               condensed vapors are separated from the -water
                               by decantation or distillation,  or both.

                               Adsorption can be specific and can, therefore,
                               be used to separate gases from gases,  as in
                               the  elimination of toxic materials such as sul-
                               fur  dioxide or chlorine;  the removal of vapor-
                               ized liquids from air, as in the capture of sol-
                               vents in surface coating operations; the re-
                               moval of colloids  or  suspended solids from
                               solutions, as in the decolorizing, clarification,
                               and purification of solutions; the removal of

-------
                                        Adsorption Equipment
                                                                                                  191
 ions from solutions, as in -water softening; and
 the removal of dissolved gases in solution to
 control odors or tastes,as in water treatment.
                               ly mixed.  The amount added is  sufficient only
                               to effect the purification; the separation is
                               made by settling or filtration.
 TYPES OF ADSORBENTS

 Solids possessing adsorptive properties exist
 in great variety.  Some of these solids and
 their industrial uses are as follows:
Activated carbon
Alumina
 Bauxite
 Bone char
Decolorizing carbons
Fuller's earth
Magnesia
Silica gel
Strontium sulfate
Solvent recovery, elim-
ination of odors, purifica-
tion of gases

Drying of gases, air,
and liquids

Treatment of petrole-
um fractions; drying
of gases and liquids

Decolorizing of sugar
solutions

Decolorizing of oils, fats,
and waxes; deodorizing of
domestic water

Refining of lube oils and
vegetable and animal oils,
fats,  and waxes

Treatment of gasoline and
solvents; removal of me-
tallic impurities from
caustic solutions

Drying and purification
of gases

Removal of iron from
caustic solutions
Activated carbon, silica gel, alumina, and
bauxite are used for selectively adsorbing
certain gaseous constituents from gas streams.
Activated carbon adsorbs organic gases and
vapors,  even when water is  present in the gas
stream.  Silica gel, in the absence of water
vapor,  adsorbs organic and  inorganic gases;
however, in the presence of water vapor, it
adsorbs -water  vapor almost exclusively.  Alu-
mina and bauxite are used chiefly in dehydra-
tion.  Bone char,  decolorizing  carbon, Fuller's
earth, magnesia,  and strontium sulfate are
used mainly in removing impurities from solu-
tions.   Bone char and  Fuller's  earth are normal-
ly used as beds through which the solutions  are
allowed to percolate.  Decolorizing  carbon,
magnesia, and strontium sulfate are added to
the  solution in  finely divided form, and intimate-
USE OF ACTIVATED CARBON IN AIR POLLUTION CONTROL
Generally, the concentrations of the organic ma-
terials discharged to the atmosphere are relative-
ly small and are usually governed by fire preven-
tion regulations and the  health hazard standards
(Barry,  I960).  The latter is usually smaller
and in many  cases is the governing concentration.
Concentrations may vary from 50 to 3, 000 ppm.

Activated carbon is the adsorbent most suitable
for removing organic vapors.   Carbon adsorbs
substantially all the organic vapor from the air
at ambient temperature  regardless of variation
in concentration and humidity  conditions.  Be-
cause the adsorbed compounds have practically
no vapor pressure at ambient  temperatures,
the carbon system is particularly adapted to
the efficient  recovery of solvents present in
air in small  concentrations.  This means the
system can always be designed for operation
without hazard because the vapor concentration
is always below the flammable range.

Since activated carbon adsorbs all the  usual low-
boiling solvent vapors, it can  be used to recover
practically any single solvent  or any combina-
tion of low-boiling solvents.  Turk and  Bownes
(1951) state that the limitation for molecules
capable of removal by physical adsorption is
that they must be higher in molecular weight
than the normal components of air.  In  general,
removal of gaseous vapors by physical  adsorp-
tion is practical for gases with molecular weight
over 45.  Probably the only solvent used with a.
molecular weight below 45 is methanol.


Saturation
Adsorption of a vapor by activated .carbon ap-
parently occurs in two stages.  Initially, ad-
sorption is rapid and complete, but  a stage is
reached in which the  carbon continues  to re-
move the material but at a decreasing  rate.
Eventually, the vapor concentration leaving
the carbon equals that of the inlet.   At this
point the carbon is saturated,  that is,  it has
adsorbed the maximum amount of vapor that
it can adsorb at the specific temperature and
pressure.  This saturation value  is  different
for each vapor and carbon.  It is  determined
experimentally by passing dry air saturated
with the gas  or vapor, with temperature and
pressure maintained  constant,  through  a
known amount of carbon until the  carbon
ceases to increase in weight.  Under these
conditions, the carbon is saturated with the
adsorbate.

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192
CONTROL EQUIPMENT FOR GASES AND VAPORS
Retentivity

The  retentive capacity of an activated carbon is
a. more useful figure.  It represents the amount
of adsorbate that a carbon, initially saturated,
can retain •when pure air is passed through the
carbon with the temperature and pressure main-
tained constant.  This indicates the weight of the
particular gas  or vapor  that the carbon can com-
pletely retain.   This is called the retentivity of
the carbon and is expressed as the ratio of the
weight of the adsorbate retained to the weight of
the carbon.
Breakpoint

When an air vapor mixture is passed over carbon,
adsorption is  100  percent at the beginning, but as
the retentive capacity of the carbon is  reached,
traces of vapor appear in the exit air.   This stage
of adsorption  is called the breakpoint of the carbon,
beyond which  the efficiency of removal decreases
rapidly.  As the flow of air is continued,  addition-
al amounts of solvent  are adsorbed,  but the con-
centration  of vapor in the exit air (Figure  122)
increases and eventually equals that in the inlet,
at which time the  carbon is saturated at the
particular  operating conditions.

Adsorption  of Mixed Vapors
The adsorption phenomenon becomes somewhat
more complex if the gas or vapors to be adsorbed
consist of not one but several compounds.  The
   50
                         TIME hours
   Figure 122.  Adsorption  efficiency, single sol-
   vent (Report No.  8,  Experimental Program for
   the Control  of Organic  Emissions from Protec-
   tive Coating Operations,  Los Angeles County
   Air Pollution Control District, Los Angeles,
   Calif., 1961).'
                            adsorption of the various components in a mix-
                            ture such as this is not uniform,  and generally.
                            these components are adsorbed in an approxi-
                            mately inverse relationship to their relative
                            volatilities.  Hence,  when air containing a mix-
                            ture of organic vapors is passed through an
                            activated-carbon bed, the vapors are equally
                            adsorbed at the  start; but as the amount of the
                            higher boiling constituent retained in the bed
                            increases, the more  volatile vapor revaporizes.
                            After the breakpoint is reached, the exit vapor
                            consists  largely of the more volatile material.
                            At this stage, the higher boiling component has
                            displaced the lower boiling component,  and this
                            is repeated for each additional component, as
                            shown in Figure 123.  This property of activated
                            carbon is the basis for hypers or ption, a process
                            used for  the  separation of low-boiling hydro-
                            carbons.  In the control of the discharge of or-
                            ganic vapors to the atmosphere, the adsorption
                            cycle should be  stopped  at the first breakpoint
                            as determined by the detection of vapors in
                            the discharge.
                             40
                                                         Figure 123.  Adsorption efficiency,  three-com-
                                                         ponent lacquer  solvent (Report No.  8,  Experi-
                                                         mental Program  for  the Control of Organic
                                                         Emissions  from  Protective Coating Operations,
                                                         Los Angeles  County  Air Pollution Control  Dis-
                                                         trict, Los  Angeles, Calif.,  1961).
                             Heat of Adsorption

                             The amount of organic vapors adsorbed by
                             activated carbon is a function of the boiling point,
                             molecular weight, concentration, pressure,  and
                             temperature.  Since adsorption is an  exothermic
                             process, heat is liberated, •which increases the
                             temperature of the carbon bed, and adsorption

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                                        Adsorption Equipment
                                           193
may be necessary to provide cooling.  The
same result can be obtained by diluting the gas
as it enters the adsorber.  The vapor concentra-
tions encountered in paint spraying or coating
operations result in a temperature rise of about
15°F (Elliott et al. ,  1961) and do not seriously
affect the capacity of the adsorbent.  On the
other hand, the use of activated carbon to cap-
ture vaporized organic compounds at relative-
ly large concentrations,  such as the discharge
from the filling of gasoline tanks,  can  result
in a temperature rise that can reach dangerous
levels.
sorbent.  The steam consumption per pound of
solvent varies with'time and the solvent adsorbed.
This is shown in Figure 124.   The ratio of the
pounds  of steam used per pound of perchloroethylene
recovered is plotted for 15-minute intervals.   This
reaches a minimum, of  about 4. 7 pounds after an
elapsed time of 90 minutes and then rises sharply.
The pounds of solvent recovered reaches a maxi-
mum at this time  and then decreases.  In Figure
124, the desorbing of toluene follows the same
pattern except that the  steam consumption is high-
er.  This is to be expected since its latent heat is
greater.
Carbon Regeneration

A desirable feature of using activated carbon
in the  control of solvent emissions is its ability
to recover the adsorbed solvents on  regenera-
tion.   To remove the adsorbate from the car-
bon, the carbon must be heated to a  tempera-
ture above that at which the solvents were ad-
sorbed.  Also essential to the process is  a
carrier to remove the vapors  released.

Regeneration is accomplished by passing  a hot
gas through the carbon bed.  Saturated  steam
at low pressure, up to  5 psig, is the usual
source of heat and is sufficient to remove most
solvents.  Steam superheated  to as high as
650 °F may,  however, be necessary  to reactiv-
ate the carbon to its  original condition (Barry,
I960).  This is necessary 'when the solvent
adsorbed contains high-boiling constituents
such as are found in mineral spirits. Normal-
ly the  flow of steam passes in a direction op-
posite to the flow of gases during adsorption.

With this arrangement, the steam, passes up-
ward through the carbon.  The steam through
the bed is only 1/5 to 1/10  of the air velocity
and is too low to initiate any boiling  or  crater-
ing of  the bed.  This countercurrent flow  is an
advantage in regeneration because a solvent
gradient exists across  the adsorbent bed and,
depending on the concentration of adsorbate
and bed depth, the inlet side of the bed may
be saturated before the outlet  reaches the
breakpoint.  Thus, with countercurrent re-
generation, the solvent, driven out of the ad-
sorbent from the outlet side by the incoming
steam, -will in turn start  to remove vapor at
the inlet before it becomes heated, since  it
is already saturated.  This results in lower
steam consumption.

Steam requirements depend on external heat
losses as well as the nature of the solvent.  The
heat liberated during adsorption is greater
(Mantell, 1961) than the heat of liquefaction, and
this difference may be  large -with an active ad-
                                              160
                 ELAPSED TIME, minutes
 Figure 124.  Steam consumption per pound of sol-
 vent  recovered (Report  No.  8, Experimental Pro-
 gram  for the Control  of Organic Emissions from
 Protective Coating Operations, Los Angeles
 County Air Pollution  Control District,  Los
 Angeles,  Calif.,  1961).
After the solvent is stripped,  the carbon is not
only hot but is saturated with water.  Cooling
and drying are usually done by blowing solvent-
free air through the carbon.  The ensuing  evap-
oration of the moisture is helpful in removing
the heat in the carbon.  In surface-coating
operations, where the solvent vapors may con-
tain some relatively high-boiling constituents,
high-temperature stripping  of the carbon is
periodically necessary to  remove these com-
pounds.   Superheated steam of about 650°F is
required (Elliott et al. , 1961), or the  capacity
of the carbon is eventually reduced. Air must
not be used in cooling the  carbon under these
conditions because of danger of a fire  or an
explosion.

EQUIPMENT DESIGN
Barry (I960),  reviewing the latest  developments
on evaluating adsorption as a  unit operation,

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194
CONTROL EQUIPMENT FOR GASES AND VAPORS
concludes that adequate design and scaleup proce-
dures are not available in the  chemical literature.
Manufacturers of adsorbents have, however,  ac-
cumulated much information on a confidential
basis -with their clients.  For  the larger per-
centage of processes discharging organic vapors
to the atmosphere, such as dry cleaning, de-
greasing, paint spraying,  tank dipping, and sol-
vent extracting, packaged equipment is available
that is suitable if certain precautions are taken.
These factors  are discussed in the following
paragraphs.

A research program also  was undertaken by
the Los Angeles  County Air Pollution Control
District in conjunction with the United States
Public Health Service (Elliott  et al. ,  1961)
to develop some much-needed design data
and evaluate methods for the removal  of
organic air contaminants.

In the capture  and removal of  organic  com-
pounds,  the vapor-laden air is passed through
a layer  of activated carbon.  The layer can be
either fixed or movable.   The enclosure for a
simple fixed bed may be a vertical or  a hori-
zontal cylindrical vessel.   If more than one
carbon bed in a single vessel is used,  the  beds
are usually arranged as shown in Figure 125.
Multiple beds such as these are best suited to
a vertical vessel.  Another type of fixed bed
is arranged in the shape of a cone, as shown
in Figures 126 and 127.  It can be used in  either
a vertical or horizontal enclosure and has  cer-
tain advantages over the flat bed,  as enumerated
later in this  section.
A movable bed is shown in Figures 128 and 129.
In this design, the carbon bed is  contained in a
drum, which rotates within an enclosure.
Fixed-Bed Adsorber

The type of enclosure used to house an activated-
carbon adsorber with a fixed bed depends primarily
upon the volume of gas to be handled and the allow-
able pressure drop.   The simplest equipment for
a fixed-bed adsorber  is a vertical, cylindrical
vessel fitted with a perforated  supporting screen
for the carbon.   The gas stream,  containing the
vapor, enters the vessel at  the top and flows
down through the carbon bed,  Downflow allows
the use of higher gas  velocities.  In upflow,  the
velocity must be maintained below a value that
prevents the boiling of the carbon,  since this
results in cratering and attrition of the adsorbent.
A  single fixed bed unit is  satisfactory if process
downtime is available for regeneration of the
carbon.  The horizontal,  cylindrical vessel with
a bed parallel to the axis  is normally used -when
large volumes of gas  must be handled.
                                                                                VAPOR TO CONDENSER
                                 CARBON
                         Figure 125.  Cross-section of adsorber with four
                         fixed beds of  activated carbon (Report No. 8,
                         Experimental  Program  for the Control of Organic
                         Emissions from Protective Coating Operations,
                         Los Angeles  County  Air Pollution Control  Dis-
                         trict,  Los Angeles, Cal if.,  1961).
                        Figure 126.   Top:   Horizontal  adsorber on the de-
                        sorbing cycle with the  superheated  steam entering
                        at the apex (1).   Condenser  is located at the va-
                        por outlet (2).   Bottom:   Horizontal carbon ad-
                        sorber.  On the  adsorption cycle  the vapor-laden
                        air enters at the  apex  of  the  cone.  The steam
                        enters either at  the  apex  or at the bottom of the
                        cone for desorption  (Report No. 3,  Experimental
                        Program for  the Control of Organic  Emissions from
                        Protective Coatings,  Los Angeles  County Air Pol-
                        lution Control  District, Los Angeles, Cal if., 1959;.

-------
                                         Adsorption Equipment
                                            195
, / 7 1 1
< 3S
•/•' \^-
1 ^ ^
I '> 1
/ / ' 1 -
n\ ^
: ! 1 ^-CARBON 5.
.' ) ^

\

                                    CYLINDRICAL
                                    SHELL HOUSING
                                          VAPOR FREE
                                          AIR OUT
 Figure 127.   Top:   Diagrammatic sketch of  verti-
 cal adsorber  with  two  cones, permitting studies
 on different  depths of carbon beds.   Bottom:
 Vertical  cone adsorber in operation.
For the capture of vapors in a continuous oper-
ation,  a minimum of two of  these units is desir-
able.   With this arrangement, one unit is ad-
sorbing while the  other is being stripped of sol-
vent and regenerated.  Sufficient time or means
must be available to cool this unit to nearly
ambient temperature before it is returned to
service.  A schematic diagram of this unit is
presented in Figure 130.  The vapor-laden air
enters the first adsorber and passes down-
ward through the carbon bed, •where it is di-
vested of its vapor, and then passes out to the
atmosphere.  During this period,  the second
adsorber is stripped of its  adsorbate
Regeneration and cooling of the adsorbent usu-
ally determines the cycle time that may be
used.  The stripping cycle  must thus allow
sufficient time for the  adsorbent to cool before
it is returned to the adsorption system.   Re-
generation releases the bulk of the adsorbed
vapor rapidly, the rate reaching a maximum
early, then slowly trailing  off as regeneration
is continued.  No attempt is made to remove
all  the adsorbate.
In Figure 131, a curve is shown in which the
pounds  of toluene and perchloroethylene re-
covered are  plotted against elapsed time, and
Figure  132 shows the pounds of steam, per
pound of solvent for each 15-minute period
during stripping.   The steam consumption is
approximately constant (Elliott et  al. , 1961),
and to continue  heating of the carbon bed until
all  the solvent is removed  would not be eco-
nomical in terms  either of  steam  or time.  It
is usually discontinued far  short of this  point.
This does, however, reduce the capacity of the
unit in the adsorption cycle.

Normally two adsorbing units are  sufficient
if the regeneration and cooling  of  the second
bed can be completed before the first unit has
reached the breakpoint in the adsorbing  cycle.

With three units it is possible to have one bed
adsorbing, one  cooling, and one regenerating.
Vapor-free air from the adsorbing unit is used
to cool the unit just regenerated.  An installa-
tion such as this is shown in Figure 133. By
operating two of the units in series, greater
adsorbing capacity can be realized with the
same size bed.  The air from the  first bed,
after being stripped of vapor,  is passed  through
the  second bed,  which has been regenerated
but  is still hot and wet. By using  the vapor-
free air from the first unit to remove this
moisture,  the ensuing  evaporation of the water
effectively cools the  carbon. After it cools,
it can more effectively adsorb and the first
bed can then be  operated beyond its break-
point, which increases its  capacity.  In the
meantime the third bed is regenerated.   This
should be completed before the breakpoint
is reached in the second bed.  A fourth bed
may also be used.  One arrangement would
be to have two units in parallel adsorbing and
both discharging to a third  unit, -which is on
the  cooling cycle while the  fourth unit is be-
ing  regenerated.  This arrangement is com-
plex, and the  increase  in efficiency and capac-
ity  may not justify the added cost.
  234-767 O - 77 - 15

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196
CONTROL EQUIPMENT FOR GASES AND VAPORS
        ROTATING ADSORBER
         MOTOR
                 FILTER

                COOLER
                                                           AIR AND SOLVENT
                                                           VAPOR IN
                                                          ACTIVE CARBON

                                                          STRIPPED AIR OUT
                                                              STEAM IN
                                                            ACTIVE CARBON
                                                                               •STEAM AND SOLVENT
                                                                                VAPOR OUT
      Figure  128.   Left:   Diagrammatic sketch of a  rotating fixed-bed continuous adsorber  showing the
      path  of  the  vapor-laden air to the carbon bed.   Right:   Cut of continuous adsorber showing path
      of steam  during  regeneration (Sutcliffe, Speakman  Canada,  Ltd.,  Hamilton, Ontario).
                                                           Figure 130.   Diagrammatic  sketch  of  a  two-unit,
                                                           fixed-bed adsorber.
                                                          Conical fixed-bed adsorber
Figure 129.  A continuous  carbon  adsorber serv-
ing a lithograph press.  (Continental  Can Co.,  Inc.,
Robert Gair Div., Los  Angeles,  Calif.).
                             A cone-shaped bed is one bed configuration

                             that can be used where a relatively low pres-

                             sure drop is desired  (Elliott et al. ,  1961).

-------
                                        Adsorption Equipment
                                             197
                   ELAPSED TIME
 Figure 131.  Pounds  of  solvent  recovered versus
 time (Report No.  8,  Experimental Program for
 the Control  of  Organic Emissions from Protec-
 tive Coating Operations,  Los Angeles County
 Air Pollution Control  District, Los  Angeles,
 Calif.,  1961).

A comparison of this type of bed -with a flat
bed is shown in Table 56.  Both beds are
the same diameter and contain about the
same 'weight of  carbon, yet the pressure
drop through the cone-shaped bed is  less
than half that through the flat bed,  even
when the volume of  air passing through the
cone-shaped bed is  more than twice that
through  the flat bed.  This cone carbon con-
tainer can be modified to a  cylinder config-
uration with similar properties.

Continuous Adsorber

A continuous, activated-carbon, solvent recov-
ery unit is available.   This  unit consists  of a
totally enclosed, rotating drum carrying the
bed.  Figure  128 shows the  cutaway view of the
unit.  The filtered air  containing the solvent
vapor is delivered by the fan into the enclosure
and in turn enters ports  to the  carbon section.
These ports  allow the solvent-laden air to  enter
                    ELAPSED TIME  minutes
   Figure  132.  Pounds of solvent recovered in 15-
   minute  intervals  (Report No. 8,  Experimental
   Program for  the Control of Organic Emissions
   from Protective Coating Operations,  Los Angeles
   County  Air  Pollution Control District,  Los
   Angeles,  Calif.,  1961).
the area above the carbon bed.  From here it
passes through the bed and enters a similar
space on the inside of the cylindrical bed.  It
then leaves this enclosure through ports located
at the end of the drum opposite the entrance.
The vapor-free air travels axially to the drum
and is discharged to the atmosphere.  The
steam,  in the regeneration of the  carbon,  enters
through a row of ports by means of a slide valve
as the cylinder rotates.   The  solvent and steam
leave through a second row of ports,  which is
served by a similar slide valve, and  are sepa-
rated continuously by decantation.


Pressure Drop

The pressure drop through the carbon bed is
a function  of the gas  velocity, bed depth, and
the carbon particle size.  Mantell (1961) pre-
          Table  56.  EXPERIMENTAL RESULTS OF FLAT- AND CONE-BED ADSORBERS

            (Report No.  8,  Experimental Program for the  Control of Organic Emissions
            from Protective Coating Operations, Los Angeles County Air  Pollution Con-
            trol District, Los Angeles, Calif.,  1961).
Adsorber type
Commercial flat bed
Vertical cone
Enclosure
diameter,
in.
36
36
Air volume,
cfm
530
1, 350
Air velocity
through bed,
fpm
75
71
Pressure drop
across adsorber,
in. H2O
4.25
1. 81
Weight of
carbon,
Ib
400
352
Carbon
beJ depth,
in.
18
6

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198
CONTROL EQUIPMENT FOR GASES AND VAPORS
                      VAPOR-LADEN AIR
                                                                        CONDENSER
                                                                               DECANTER
               CARBON-y
                                      VAPOR-FREE AIR
                                                    LOU-PRESSURE STEAM
                   Figure 133.  Diagrammatic  sketch of a three-unit operation  of a  fixed-
                   bed  adsorber showing No.  1  and  No. 2 adsorbing in series  and No.  3 re-
                   generating.  Second cycle,  No.  2 and No. 3 will  be adsorbing with No.
                   1  regenerating.   Final  cycle, No. 3 and No.  1  will  be  adsorbing  with
                   No.  2 regenerating.
sents three graphs in which pressure drop in
inches of water for different velocities  is plot-
ted against bed densities in  pounds per  square
foot of bed area for several activated carbons
of different meshes.   Carbon Products  Division,
Union Carbide Corporation (1955), presents an
empirical correlation representing the  pres-
sure drop through a carbon  bed at air veloci-
ties from 60 to 100 fpm against bed depth in
inches for two carbon mesh sizes.  With this
empirical formula,  Figure 134 was prepared
covering velocities from 60 to 140  fpm  and for
bed depths of 10 to 50 inches.  In the Report
No.  8 of the  Experimental Program for the
Control of Organic Emissions  (1961) pres-
sure drops for multiple-tray cone carbon
adsorbers are presented based on Union Car-
bide Corporation's empirical correlation, as
shown in Table 56.  Note that, except for the
horizontal-cone and four-tray adsorber, the
pressure drop also includes that resulting
from the abrupt directional  change of the  air-
stream at both inlet and outlet.

OPERATIONAL PROBLEMS

Participate Matter

An activated-carbon  adsorption bed should be
protected from particulate matter that  can
coat the surface of the carbon.  Without this
protection, the effective area  and the ability
to adsorb will be impaired,  and the life of
the carbon -will be reduced if the material is
not removed by regeneration.  In paint-spray-
                             ing operations (Elliott et al. ,  1961) it was
                             found that the carbon adsorbers could be
                             adequately protected from particulate
                             matter -with efficient filters without exces-
                             sive increase in the total pressure drop.
                             Corrosion

                             Corrosion of adsorbers occurs when steam
                             is used in  stripping solvents from activated
                             carbon.  The amount of this corrosion is in-
                             tensified with increased steam temperature.
                             Corrosion can be controlled or reduced by
                             the use of  stainless steel or by application of
                             a protective coating of a baked phenolic resin.


                             Polar  and Nonpolar Compounds

                             Polar and nonpolar solvents are equally ad-
                             sorbed by activated carbon, but the  recovery
                             of polar compounds on stripping -with steam
                             requires an additional step of  fractionation
                             by distillation to effect a separation from
                             the aqueous solution.
                                       VAPOR CONDENSERS
                             Air contaminants can be discharged into the
                             atmosphere in the form of gases or vapors.
                             These gases or  vapors can be controlled by
                             several different methods,  for example, ab-
                             sorption,  adsorption,  condensation, or incin-

-------
                                           Vapor Condensers
                                                                             199
    30
  "20
CARBON SIZE'  4-6 MESH (TYLER)
AP = 0 370 (TJJrj)1 5B
A? = PRESSURE DROP,  inches of water
D = BED DEPTH,  inches
V = VELOCITY,  fpra
    10
                        10
                                           2D
                                              BED DEPTH, inches
                                         30
                                                                                40
50
         Figure 134.  Pressure drop  versus carbon bed depth at  various air velocities (Bulletin:
         Solvent Recovery,  1955,  Union  Carbide Corporation,  New York, N.Y.).
eration.  In specific instances, control of
vapor-type discharges can best be accom-
plished by condensation.   Other applications
require a condenser to be an integral part
of other air pollution control equipment. In
these cases, a condenser reduces the load
on a more expensive control device or re-
moves vapor components that may affect the
operation or cause corrosion of the main con-
trol element.

TYPES  OF  CONDENSERS

 Surface and Contact Condensers

Vapors can be condensed either by increas-
ing pressure or extracting heat.  In practice,
air pollution control condensers operate
through removal of heat from the vapor. Con-
densers differ principally in the means  of
cooling.   In surface condensers,  the coolant
does not contact the vapors or condensate.
In contact condensers,  coolant, vapors,  and
condensate are intimately mixed.
                                 Most surface condensers are of the tube and shell
                                 type shown in Figure  135a.  Water flows inside
                                 the tubes,  and vapors condense on the shell side.
                                 Cooling water is normally chilled, as in a cooling
                                 tower, and reused. Air-cooled surface conden-
                                 sers, as shown in Figure  135b, and some water-
                                 cooled units  condense inside the  tubes.  Air-
                                 cooled condensers are usually  constructed with
                                 extended surface  fins.  Typical fin designs  are
                                 shown in Figures  135c and d,   A section of  an
                                 atmospheric condenser is shown in Figure 135e.
                                 Here vapors condense inside tubes cooled by
                                 a falling curtain of -water.  The water is cooled
                                 by air circulated  through the tube  bundle.  The
                                 bundles can be mounted directly in a  cooling
                                 tower or submerged in water.   Contact con-
                                 densers employ liquid coolants, usually -water,
                                 •which come in direct contact with  condensing
                                 vapors.  These  devices are  relatively uncom-
                                 plicated, as  shown by the typical designs of
                                 Figure 135f, g,  and h. Some contact con-
                                 densers are  simple spray chambers,  usually
                                 with baffles to ensure  adequate contact. Others
                                 are high-velocity  jets  designed to  produce a
                                 vacuum.

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200
CONTROL EQUIPMENT  FOR GASES AND VAPORS
     INLET    OUTLET
                                         INLET
   OUTLET
       VAPOR
                                                  PRESSURE
                                                   WATER
                                     ENTRAINED
                                       VAPORS
                                 WATER
                                                  DISCHARGE   8
                      SPRAY
   Figure  135.   Types of condensers.  Surface condensers:   (a)  Shell  and tube,  Schutte and Koerting  Co.
   Cornwell  Heights,  Penn. ,(b) fin  fan,  Hudson Engineering  Corp.,  Houston,  Texas,  (c) finned hairpin
   section,  Brown Fmtube Co., Elyria, Ohio, (d)  integral  finned  section,  Calumet & Hecla
   Park,  Mich., and (e) tubular,  Hudson Engineering  Corp., Houston,  Texas.  Contact
   (g) jet,  Schutte and Koerting Co., Cornwell Heights,  Penn.,  and (h) barometric
   Co.,  Cornwell  Heights,  Penn.
                                                       & Hecla Inc.,  Allen
                                                       condensers:  (f) Spray,
                                                        Schutte and Koerting

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                                          Vapor Condensers
                                            201
In comparison •with surface condensers,  con-
tact condensers are more flexible,  are simpler,
and considerably less expensive to  install.
On the other hand, surface condensers re-
quire far less water  and produce 10 to 20tim.es
less condensate.  Condensate from contact
units cannot be reused and may constitute a
waste disposal problem.   Surface condensers
can be used to recover salable  condensate,
if any.  Surface condensers must be equipped
with more auxiliary equipment and  generally
require a greater degree of maintenance.

Contact condensers normally afford a greater
degree of air pollution control than surface
condensers do because of  condensate dilution.
With direct-contact units, about 15 pounds of
60°F water is required to condense 1 pound
of steam at 212 °F and cool the conden-
sate to  140°F.  The resultant 15:1 dilution
greatly reduces the concentration and vapor
pressure of volatile materials that  are misci-
ble or soluble in water.


TYPICAL INSTALLATIONS


Condensers in Control Systems

Condensers collect condensable air contami-
nants and materially  reduce the  volume of
contaminated gas  streams containing conden-
sable vapors.  To a degree condensers are
also scrubbers, contact units being generally
more effective as scrubbers than surface con-
densers are.  Probably their most  common
application is as an auxiliary to  afterburners,
adsorbers, baghouses, and other control
devices.  A number of possible combinations
are shown in Figures 136, 137,  and 138. De-
signs depend on the particular air contami-
nants and condensable vapors and on their
concentrations in  the contaminated  stream.

The  system shown in Figure  136 is designed
to control odorous gases contained  in a high-
moisture  gas stream, as from a rendering
cooker or blood cooker.  The stream might
contain from 60 to 99 percent steam at tem-
peratures near 212°F. At the condenser,
vapors are liquefied  at the boiling point.  If
a strong vacuum is maintained,  condensing
temperatures may be well below 212 °F.  Sub-
cooling may also occur.  Uncondensed gases
are separated at the  condenser  and directed
to an afterburner  through a vacuum pump.
A volume reduction of 95 percent and great-
er can be effected through use of either a
contact or surface condenser.   Some air
contaminants may condense and  others may
be dissolved in the condensate.   A contact
condenser,  because of greater condensate
                                  TO ftTMOSHIERE
                                        AFTERBURNER
                       CDNOENSATE
                       TO SE»ER
     Figure 136.   A condenser-afterburner air
     pollution control  system  in which a vacu-
     um pump  is used to remove uncondensed
     gases from condensate.
                                  TO ATMOSPHERE
   Figure  137.  A contact condenser-afterburner
   air  pollution control  system  in  which mal-
   odorous,  uncondensed gases  are separated
   from condensate in a closed hot  well.
dilution, generally removes more air contami-
nants than a surface condenser does.

The  system,  shown in Figure 136 can be  used
with a contact or surface  condenser.  In
either case a  32-foot barometric leg is  re-
quired to pull  a strong vacuum.  Other vac-
uum devices,  such as steam or water ejec-

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202
CONTROL EQUIPMENT FOR GASES AND VAPORS
             HATER OUT
      KftRM ORGANIC
      LIQUID STREAM
                                 CONOENSATE
                                 RETURN
     Figure  138.  A surface condenser used to
     prevent surge  losses from an  accumulator
     tank  handling warm,  volatile,  organic
     I iquid.
tors, might be used in lieu of a vacuum pump.
With steam ejectors,  intercondensers and
aftercondensers are often required.  The lat-
ter auxiliary condensers  might require  closed
hot wells to separate uncondensed gases from
condensate.
A variation is shown in Figure 137.  Here a
contact condenser is used to control high-
moisture,  odorous gases.  Both condensate
and entrained gases drain to a closed hot well
where malodorous  gases separate by gravity.
Liquids are removed through a trap while
gases are vented to an afterburner or other
suitable control device.   The system, of
Figure 137 can be used with surface conden-
sers  but is more adaptable to  contact units
where adequate subcooling can be readily
achieved.
The surface  condenser arrangement shown
in Figure 138 is used to prevent the emis-
sion of condensable organics from blending
tanks, accumulator tanks, drying cleaning
equipment, and so forth.  This arrangement
is adaptable  to streams rich in condensable
vapors.  The condenser is mounted in the
tank vent.  Condensate is allowed to drain
to storage or to the original source.  No
secondary controls are shown;  however,
if further control  is required, the saturated
gas stream from the condenser can be vented
to a carbon adsorber, afterburner, or flare
for final cleaning.   The product recovered
often offsets  the cost of the  condenser.
                            Subcooling Condensate

                            When condensers are used as air pollution con-
                            trol devices, care should be taken to ensure
                            that there is no major evolution of volatiles
                            from the discharged condensate.  Uncondensable
                            air contaminants should be  either safely dissolved
                            in condensate or vented to further control equip-
                            ment.  In most instances the condensate is merely
                            cooled to a temperature at which  the vapor pres-
                            sure of contained air contaminants is  satisfactoril
                            low.   The required temperature varies  with the
                            condensate.  Most condensed aqueous solutions
                            should be cooled to 140°F or less before they
                            come into contact with the atmosphere.   For vola-
                            tile organics, lower temperatures are required.
                            In general, subcooling requirements are more
                            stringent for surface units than for  contact con-
                            densers where dilution is much greater.  Never-
                            theless, many surface condenser designs do not
                            permit adequate condensate cooling. In the
                            typical water-cooled, horizontal, tube-and-shell
                            condenser of Figure 135a, the shell side tem-
                            perature is the same throughout the vessel.
                            Vapors condense,  and condensate is removed
                            at the condensation temperature, which is gov-
                            erned by pressure.  In a horizontal-tube unit
                            of this type,  condensate temperature can be
                            lowered by:   (1) Reducing the  pressure on the
                            shell side,   (2) adding a separate subcooler,
                            or  (3) using  the lower tubes for subcooling as
                            shown in Figure 139. Reducing the  pressure
                            alters operating variables in the basic  equip-
                            ment and is not feasible in many instances.
                            The arrangement of Figure 139 is adaptable to
                            most processes though it  reduces the heat
                                                                COOLANT
                                                                OUT
                                                        VENT
                                                               COOLANT
                                                               IN
                               Figure  139.  Maintaining a  condensate level
                               above the  lower tubes to provide subcooling
                               in  a horizontal tube-and-shell  condenser.

-------
                                          Vapor Condensers
                                                                                                 203
transfer area available for condensation.  Here
a level of condensate is maintained in the con-
denser shell.  Condensate is chilled before
being discharged through the trap.

The latter arrangement can be used with
vertical-tube units,  though it may not be nec-
essary.  Vertical-tube condensers provide
some degree of  subcooling even with conden-
sation on the shell side.

With condensation inside  the tubes, subcooling
occurs in much  the same manner -whether tubes
are arranged vertically or horizontally.   With
inside-the-tube  condensation, both condensate
and uncondensed vapors pass through the  full
tube length.  A separate hot well  is usually
provided to separate gases before condensate
is discharged.

CONTACT CONDENSERS


Sizing Contact Condensers

Water requirements for  contact condensers
can be calculated  directly from the conden-
sation rate, by  assuming  equilibrium con-
ditions.  The cooling -water (or other medium)
must absorb enough heat  to balance the heat
of vaporization and condensate subcooling.  Pip-
ing and hot wells must be  sized on the maximum
condenser requirement.   The following example
illustrates the method of  calculating the quantity
of cooling water for a specific  service.


Example 24

Given:

Malodorous exhaust vapors from  a dry render-
ing cooker contain 95 percent steam at 200 °F
at 11. 5 psia.  The maximum evaporation  rate
in the cooker is  2, 000 Ib per hour.  Steam is
to be  condensed at 200°F and cooled to 140°F
in a contact condenser.  A vacuum pump re-
moves uncondensable vapors at the condenser
and maintains a  slight vacuum  on the cooker.

Problem:

Calculate the volume of 60 °F fresh water re-
quired and the resultant  condensate volume.


Solution:

Condensation:  2,000  x 977.9  Btu/hr =  1,960,000
Btu/hr

Subcooling: 2,000 (200-140) Btu/hr = 120,000
Btu/hr
Cooling load
2, 080,000 Btu/hr
                     2, 080,000 Btu/hr
Water requirement =   (14Q_60) Btu/lb

                   = 26,000 Ib/hr

                   = 51.4 gpm

                              2, OOP Ib/hr
 Total condensate  =  51.4 +
                           60 x 8.33 Ib/gal

                  =  55.4 gpm

 SURFACE CONDENSERS

 Characteristics of Condensation
 Condensation occurs through two distinct physical
 mechanisms, dropwise and filmwise condensation.
 When a saturated pure vapor comes in contact -with
 a sufficiently cold horizontal surface,  the vapor
 condenses and forms liquid droplets on the surface.
 These droplets fall from the surface, leaving bare
 metal exposed on which  successive condensate
 drops may form.  This is dropwise condensation.

 Normally, a. film occurs and coats the conden-
 sing surface.  Additional vapors must then con-
 dense on this film rather than  on the bare metal
 surface.  This is  called filmwise condensation
 and occurs in most condensation processes.
 Heat transfer coefficients are  one-fourth to one-
 eighth the transfer units associated with dropwise
 condensation (Kern, 1950).

 Steam is the only  pure vapor known to condense
 in a dropwise manner.  Dropwise condensation
has been found to  take place at various times
•when a mixture of vapors and gases is present.
 Some degree of drop-wise condensation may pos-
 sibly be attained by using certain promoters.
Promoters such as oleic acid on nickel or
 chrome plate, and benzyl mercaptan on copper
 or brass become absorbed on the surface as a
very thin layer to prevent the metal surface
from being wetted by any condensate.   Steel and
aluminum surfaces are difficult to treat to ac-
quire dropwise condensation.  Use of these pro-
moters increases  the heat transfer coefficient to
6 to 10 times the amount of filmwise coefficients
 (Perry, 1950).
Design of Surface Condensers
Nearly all condenser design calculations are
based on heat transfer that is affected by an
overall transfer coefficient, temperatures,
and surface area.  A mathematical solution to
the problem, is usually achieved by the expres-
sion
                Q =  UAT
                       (85)

-------
204
                CONTROL EQUIPMENT FOR GASES AND VAPORS
•where

     Q =

     U =


     A =
heat transferred,  Btu/hr

overall coefficient,  Btu/hr per ft
per °F

heat transfer,  ft

mean temperature difference, °F.
                           Mean heat transfer
                             coefficient, h
 Condenser design is often more difficult than in-
 dicated by the foregoing expression,  and a sim-
 plified or general overall heat transfer  coeffi-
 cient is not used.  This  is especially true when
 a vapor is condensed in presence  of a noncon-
 densable gas (Donahue,  1956). Nusselt  relations
 were developed for streamlined flow of  all vapor
 entering vertical- or horizontal-tube exchangers.
 These equations* account for the variation of the
 film thickness (thinnest at top of the tube and tube
 bundle of vertical and horizontal exchangers) by
 expressing the vapor side mean heat-transfer
 coefficient in terms of condensate loading.  The
 equations are based only upon vapor  entering the
 condenser and are as follows:
 *Symbol notations for these equations are defined at the end of
  this chapter on page 232.
                                                Kind of surface
Vertical-tube bundle
                                                      Horizontal-tube bundle
                                            In instances  of streamlined flow of condensate,
                                            the heat-transfer coefficient has been established
                                            as inversely proportional to film thickness.   Ob-
                                            servations have, however,  shown a decrease to
                                            a certain point, and then a reverse effect when
                                            the coefficient increased. This reversal oc-
                                            curred at a Reynolds number of approximately
                                            1,600, indicating that turbulence in liquid film
                                            increases the heat transfer coefficient.  Figure
                                            140 shows  the relationship between the coeffi-
                                            cient and Reynolds number.

                                            A temperature profile of vapor condensing in
                                            the presence of a noncondensable  gas on a tube
                                            wall, as shown in Figure 141, indicates the
                                            resistance to heat flow.  Heat is transferred
                                            in two ways from the vapor to the  interface.
                                            The sensible heat is removed  in cooling the
                                            vapor from t  to t at the convection  gas cool-
                                            ing rate.  The latent heat is removed only
       1.0
       0.1
       0.05
          100
                            1,000                        10,000
                                  REYNOLDS NUMBER = 4w/7rMfD
                                         100,000
                 Figure 140.   Heat-transfer coefficient  of  condensation (Donahue,  1956).

-------
                                          Vapor Condensers
                                                                                                  205
                                                       For mass transfer:
        Figure 141.  Temperature profile showing
        effect of vapor condensation on a tube
        wall in presence of a noncondensable gas.
 aftei the condensable vapor has been able to dif-
 fuse through the noncondensable part to reach
 the  tube wall.   This means the latent heat trans-
 fer  is governed by mass transfer laws.

 By using a heat balance around the interface,
 the  following equation is obtained:
 h(t  - t ) + KM  \(p  -p) = U(t  -t)
    v   c       v    v    c      c c    w
 (86)
When condensation of a pure vapor occurs, tc =
tv.   When a condensable  gas is present, however,
tc is lower than tv.   In solving this equation,  a.
value of tc is  selected by trial and error to satis-
fy the equilibrium condition.  The calculation is
repeated for different points in the condenser.
The surface area necessary is found by using
Uc  and  a mean temperature based on tc and tw
over the entire condensing range.

Simultaneous  heat and mass transfer must be
used to evaluate the equilibrium equation.  The
following  basic relations state the analogy
between friction,  heat transfer, and mass transfer:
                                                                          BM
                                                                                     12/3
                                                                               pD_
                                                                                          M
                                                       (89)
                                                       Flow inside tubes:
                                                                     = Jh = JD
                                                       Flow across tube banks:
                                                               J =  Jf = Jh = JD
                                                                                    0.027
                                              0.2
                                                                                                  (90)
                                                                                     0.33
                                                                                   DC
                                              0.4
                                                                                                  (91)
For solving equation 86,  the following procedure
is recommended:

1.  Using Raoult's law of partial pressures,  cal-
    culate the amount  of vapor condensing at in-
    let and outlet temperatures,  and at least
    three intermediate temperatures

2.  Obtain the following  physical properties at
    the average of inlet and outlet temperatures
    and pressures: p.,  p,  Dv,  Mm, Mv, X, c, k,
    (C(J./k)2/3,  and  (n/pD )2/3
             3.  Choose trial unit

             4.  Calculate GC,  G]-,, and Ge

             5.  Calculate A pc  +  Ap^ = Apg

             6.  Calculate h from equation:

                            DG  I0'6 F  V/3 P  -|0- 14
                               ^      cjJ     U
                              ^  J    LkJ     LH
For friction:
                jf = l/2f
(87)
                                                       7.   Calculate U
8.  Calculate j,  (for segmentally baffled shell),
For heat transfer:
              h   cG   k
                          )2/3
                                           (88)
                                                                             J =
                                                                                    0. 22
                                                                                        0.4

-------
206
               CONTROL EQUIPMENT FOR GASES AND VAPORS
9.  Calculate K from equation:
             K  =
                         JG
                           pD
(P -
                   - (P -
                                2/3
(Py  -
    BM
               In
         - Pc)
  (P - pc)
                 (P - P
                                 In
                         (P -
10. Corresponding to the inlet tv,  select by T
    and E, t  to balance equation (87)

11. Find tc in same manner for other points

12. Calculate the heat removed between each
    two successive temperature points, in-
    cluding condensate cooling

13. Between each two successive temperature
    points,  calculate At based on the tempera-
    ture difference between tc and tw

14. Using Uc> find the heat transfer surface re-
    quired between two successive temperature
    points,  using At from step 13.

The preceding discussion pertains to the design
of a condenser for condensation of vapor in
presence of a noncondensable gas. ' The design
of the many types of condensers is a vast field
and much too lengthy to cover in this text.
Many technical reference books and articles
have been published containing condenser de-
sign and cost data (Chilton,  1949; Diehl,  1957;
How,  1956; Friedman,  1959; Kern,  1950; Nelson,
1953;  Perry, 1950; Smith, 1958; and Thomas,
1959).

Some pertinent facts  compiled from these and
other references that will assist in handling
condenser problems include (Kern,  1950):

1.  Any saturated vapor can be condensed by
    a direct  spray of cold water under correct
    temperature and pressure.  If sufficient
    contact is provided, coolant and vapor will
    reach an equilibrium temperature.  The
    condensate created by the -water should
    not be  objectionable in its liquid form.

2.  Pure vapor  or substantially pure-vapor
    can be considered condensed isothermally,
    and during the condensate range the latent
    heat of condensation is uniform.

3.  If the temperature range of a mixture does
    not exceed 10°  to 20°F,  condensation  of
    this mixture may be treated as  a pure com-
    ponent.
4.   In condensation of streams consisting
     primarily of steam,  the condenser size
     ranges from 10, 000 to 60, 000 square feet
     per  shell (bundle), the tubes  averaging 26
     feet long.

5.   In water-cooled tube-and-shell condensers
     with shell side condensation, overall heat
     transfer coefficients for  essentially pure
     steam range from 200 to 800 Btu per hour
     per  square foot per °F.

6.   With tube side condensation,  coefficients
     are generally lower than for  comparable
     shell side condensers.  This phenomenon
     is attributed to:   (1) Lower coolant ve-
     locities outside the tubes than are possible
   ,  with tube side cooling, and  (2) increased
     film thicknesses,  namely,  film resistances
     inside the tubes.

7.   Noncondensable gases at condenser tem-
     perature blanket the condenser surface
     and reduce the condenser capacity.

8.   Condensation reduces the volume of the
     vapor present and can be assumed to occur
     at a  constant pressure drop.

9.   A balanced pressure  drop may be assumed
     in the horizontal condenser where partial
     condensation is  occurring.

10.  Within low-pressure  operating ranges, the
     slight pressure  loss due to friction in
     vapor pipes may mean an appreciable loss
     of total available temperature difference
     (Perry,  1950).

11.  Low-density steam under vacuum condi-
     tions can cause  a  linear velocity to be
    higher than is allowable \vith  steam, lines
     (Perry,  1950).

12.  Vapors should travel across the bundle
     as fast as possible (Kern, 1950).

13. Air or inerts can  cause up to 50 percent
    reduction in condensation coefficients
     (Kern, 1950; Perry,  1950).


14.  Sources of air or  inerts include:  Dissolved
    gas in  the cooling water in cases  of jet con-
     densers,  entrainrrient with steam,  entrain-
    ment with vapor,  leaks, and noncondensable
     gases (Perry, 1950).
                                            15. In vertical-tube condensers,  60 percent
                                                of the condensation occurs in the upper
                                                half (Kern,  1950).

-------
                                      Gas Absorption Equipment
                                            207
16. Horizontal position of a condenser dis-
    tributes the vapor better and permits
    easier removal of the condensate (Kern,
    1950).

17. In the horizontal condenser,  it is neces-
    sary to prevent cooled condensate from
    forming liquid pools and impeding the
    flow of  vapors (Kern, 1950).

18. Selection of which material should pass
    through tubes cannot be decided by
    fixed rules, because of factors at a vari-
    ance  with one another.  When corrosive
    condensate is encountered, condensation
    within the tubes rather than the  shell is
    usually desirable (Nelson,  1958).


APPLICATIONS

Condensers  have been used successfully
(either separately or with additional control
equipment) on the  following processes or
equipment:

REFINERY  AND PETROCHEMICAL

Alkylation unit accumulator vents

Amine stripper units

Butadiene accumulator vents

Coker blowdown

Ketone accumulator vents

Lube  oil rerefining
Polyethylene gas preparation accumulator vents
Residium stripper unit accumulator  vents

Storage equipment
Styrene-processing units
Toluene  recovery accumulator vents
Udex  extraction unit

CHEMICAL
Manufacture and storage of  ammonia

Manufacture of Cooper naphthenates

Chlorine  solution  preparation

Manufacture of ethylene dibromide

Manufacture of detergent

Manufacture of insecticide
Manufacture of latex
Manufacture of nitric acid
Manufacture of phthalic anhydride

Resin reactors
 Soil conditioner formulators

 Solvent recovery
 Thinning tanks

 MISCELLANEOUS

 Aluminum fluxing

 Asphalt  manufacturing

 Blood meal driers

 Coal tar-dipping operations

 Degreasers

 Dry cleaning units

 Esterfication processes

 Pectin preparation

 Rendering cookers (animal waste)

 Vitamin formulation



       GAS ABSORPTION EQUIPMENT

 Gas absorption  is the mechanism whereby one
 or more constituents  are removed from a gas
 stream by dissolving  them in a selective liquid
 solvent.   This is one  of the  major chemical
 engineering  unit operations  and is treated ex-
 tensively in  all  basic  chemical engineering text-
 books.  These texts deal with gas absorption as
 a method of  recovering valuable products from
 gas  streams, for example,  in petroleum produc-
 tion, natural gasoline is  removed from wellhead
 gas  steams by absorption in a special hydro-
 carbon oil.   Absorption is also practiced in  in-
 dustrial  chemical manufacturing as an important
 operation in  the production of a chemical com-
 pound.  For  example,  in the manufacture of
 hydrochloric acid, one step in the process in-
 volves the absorption of hydrogen chloride gas
 in water.

 From an air pollution standpoint, absorption is
 useful as a method of reducing or eliminating
 the discharge of air contaminants to the  atmo-
 sphere.  Even in this  application,  absorption
 can yield profits to the user.  For example,
 it can be employed to remove hydrogen sulfide
 from process gas streams in a petroleum re-
 finery to meet air pollution regulations.   With
 further processing,  this hydrogen sulfide can
 be converted to elemental sulfur, a valuable
 product.

 The  gaseous  air contaminants most commonly
 controlled by absorption include sulfur dioxide,
hydrogen sulfide,  hydrogen chloride,  chlorine,
 ammonia, oxides of nitrogen,  and light hydro-
 carbons.

-------
208
CONTROL EQUIPMENT FOR GASES AND VAPORS
In other examples, such as solvent recovery,
desorption or stripping may be practiced after
absorption not only to recover a valuable ab-
sorbed  constituent but also to recover valuable
solvent for reuse.  Sometimes,  after absorp-
tion,  solute and solvent are not separated but
are used as a product or intermediate com-
pound in chemical manufacture.
Treybal (1955) lists some important aspects
that should be considered in selecting absorp-
tion solvents.
1.   The gas solubility should be relatively high
     so as to enhance the rate of absorption and
     decrease the quantity of solvent required.
     Solvents similar chemically to the solute
     generally provide good  solubility.

2.   The solvents should have relatively low
     volatilities so as to reduce solvent losses.

3.   If possible,  the solvents should be non-
     corrosive so as to reduce construction
     costs of the  equipment.

4.   The solvents should be  inexpensive and
     readily available.

5.   The solvents should have relatively low
     viscosities so as to increase absorption
     and reduce flooding.

6.   If possible,  the solvents should be nontoxic,
     nonflammable, chemically stable,  and have
     low freezing points.
GENERAL TYPES Of ABSORBERS
                            PACKED TOWER DESIGN

                            A packed tower is a  tower that is filled with
                            one of the many available packing materials,
                            as shown in Figure 142.   The packing is de-
                            signed  so  as to expose a large surface area.
                            When this packing surface is wetted by the
                            solvent, it presents  a large area of liquid
                            film for contacting the solute gas.
                                                i GAS OUT
                                   LIQUID-
                                   IS
                                                       LIQUID DISTRIBUTOR
                                                       PACKING
                                                       RESTRAINER
                                                       SHELL
                                                       RANDOM
                                                       PACKING
                                                      .LIQUID
                                                      RE-DISTRIBUTOR
                                                     --PACKING SUPPORT
                                                       — GAS IN
                                                          LIQUID OUT
                                                               Figure  142.  Schematic diagram
                                                               of  a  packed tower (Treybal,  1955
                                                               p.  134).
Gas absorption equipment is designed to provide
thorough contact between the gas and liquid sol-
vent in order to permit interphase diffusion of
the materials.  The rate of mass transfer be-
tween the two phases is largely dependent upon
the surface exposed.  Other factors governing
the absorption rate, such as solubility of the
gas in the particular solvent  and degree of
chemical reaction, are characteristic of the
constituents involved and are more or less in-
dependent of the equipment used.  This contact
bet-ween gas and liquid can be  accomplished by
dispersing gas in liquid or vice versa.

Absorbers that disperse liquid include packed
towers, spray towers or spray chambers, and
venturi absorbers.  Equipment that uses gas
dispersion includes tray towers and vessels
with sparging equipment.
                            Usually the flow through a packed column is
                            counter cur rent, with the liquid introduced at
                            the top to trickle down through the packing
                            while gas is introduced at the bottom to pass
                            upward through the packing.  This results
                            in highest possible efficiency,  since, as the
                            solute concentration in the gas stream de-
                            creases as it rises through the tower,  there
                            is constantly fresher solvent available for con-
                            tact.   This gives maximum average  driving
                            force for the diffusion process throughout the
                            entire column.

                            In concurrent flow, where the gas stream and
                            solvent enter at the top  of the column,  there
                            is initially a very high rate of absorption that
                            constantly decreases until,  with an infinitely
                            tall tower,  the gas  and liquid -would leave in

-------
                                      Gas Absorption Equipment
                                          209
 equilibrium.  Concurrent flow is not often
 used except in the case of a very tall column
 built in two sections,  both located on the
 ground,  the second section using concurrent
 flow merely as  an economy measure to ob-
 viate the need for constructing the large gas
 pipe from the top of the first section to the
 bottom of the second.  Moreover, for an
 operation requiring an exceptionally high
 solvent flow rate,  concurrent flow might be
 used to prevent flooding that could occur in
 countercurrent  flow.


 Packing Materials

 The packing should provide a large surface
 area and, for good fluid flow characteristics,
 should be shaped to give large void space
 •when packed. It should likewise be  strong
 enough to handle and install without  exces-
 sive breakage,  be chemically inert,  and be
 inexpensive.

 Rock and gravel have been used but  have
 disadvantages of being too heavy, having
 small surface areas,  giving poor fluid flow
 and,  at times, not being chemically  inert.
 Coke lumps are also used sometimes and
 here  the weight disadvantage is not present.
 Owing to its porosity,  coke has a large
 surface area per unit volume.  The  exposed
 surface is not,  however, as large as might
 be expected since the pores  are  so small
 that they become filled or filmed over by
 the solvent, which considerably  reduces
 the effective surface.

 Generally,  packing in practice consists  of
 various  manufactured shapes.  Raschig
 rings are the most  common type,  consisting
 of hollow cylinders having an external di-
 ameter equal to the length.  Other shapes
 include Berl saddles, Intalox saddles,
 Lessing rings,  cross-partition rings,
 spiral-type rings, and drip-point grid
 tiles.  Figure 143 shows several common
 shapes.  Physical characteristics of these
 various types of packings have been  de-
 termined experimentally and compiled in
 tables by Leva (1953).

 Packing  may be dumped into the column  ran-
 domly,  or regularly shaped packing  may be
manually stacked  in an orderly fashion.  Ran-
domly dumped packing has a higher specific
 surface contact  area and a higher gas pressure
drop across the bed.  The stacked packings have
an advantage of  lower pressure drop and higher
possible liquid throughout, but the installation
cost is obviously higher.  Table  57 and Figure
 144 list typical packing costs and packed-tower
installed prices for 1959.
                                BERL SADDLE
 RASCHIG RING
                                 INTALOX SADDLE
    PALL RING
                                  TELLERETTE
  Figure  143.   Common tower packing materials
  (Teller,  1960, p. 122).
  Table 57.  COSTS OF REPRESENTATIVE
      TOWER PACKINGS (Teller, I960)
Packing
Raschig rings, ceramic
Raschig rings, carbon
Berl saddles, ceramic
Intalox saddles, ceramic
Intalox saddles, carbon
Tellerettes, polyethylene
Low density
High density
Pall rings, crramu (BASF)
Pall rings, polypropylene
Pall rings, stainless steel
Cost of packing, $/ft3 (1959basis)
1/2-in.
11. 70
16. 90
24. 80
23. 55
-

-
-
-
41. 00
186. 50
1-in.
6. 50
9. 60
9.90
9. 40
18.60

16. 00
23. 00
5. 00
26. 00
96. 00
1-1/2-m.
5. 05
8. 00
7.50
7. 15
18. 40

-
-
-
20.75
83. 00
2 -in.
4.85
6.60
7. 70
7. 30
-

-
-
-
18. 50
69. 00
Liquid Distribution

Since the effectiveness of a packed tower de-
pends on the availability of a large,  exposed,
liquid film, then obviously,  if poor liquid dis-
tribution prevents a portion of the packing from
being irrigated, that portion of the tower is
ineffective.  Poor distribution can be due to
improper introduction of the liquid at the top of
the tower and to channeling within the tower.

-------
210
CONTROL EQUIPMENT FOR GASES AND VAPORS
10 000

°l 000




u


D
->
" 100

^
z
50

30
20
1 0



















































































































































^

^























/'
X







2 345



































rV"l
&l
rS
^7
^
s\
X U
X]








/








/


^
r

















y
f




4
r


















/

























/



J




















(
j



J














10 20 30 40 50
DIAMETER inches






f

/
'












































































































































































100
                        Figure 144.  Packed-tower costs,
                        packing (Tel ler,  1960,  p. 123).
                             1959,  with Raschig  rings as
At least five points of introduction of liquid per
square foot of tower cross-section must general-
ly be provided to ensure complete wetting.  The
liquid rate must be sufficient to wet  the packing
but not to flood the tower.  Treybal  (1955)  states
that a superficial liquid velocity of at least 800
pounds of liquid per hour per square foot of
tower cross-section is desirable.

Solid-cone spray nozzles make excellent dis-
tributors  but may plug if solid particles  are
present in the solvent.  In randomly packed
towers, the liquid tends to channel toward the
walls, because  of the  usually lower  packing
density near the walls.  In tall towers this
channeling is controlled by liquid redistribu-
tors at intervals of 10 to 15  feet.  Moreover,
this effect is minimized if the packing pieces
are less than one-eighth the diameter  of the
tower.
Tower Capacity

The terms used to indicate capacity of a
packed column or tower are load point and
flood point.  For a given packing and liquid
                            rate, if gas pressure drop is plotted against
                            gas velocity on a logarithmic scale, there
                            are two distinct breakpoints where the  slope
                            of the curve increases.  At low gas veloci-
                            ties  the curve  is almost parallel  to that ob-
                            tained with dry packing, but above the break-
                            points,  the pressure drop increases more
                            rapidly with increased gas velocity.  The low-
                            er of these two breaks is the load point and the
                            higher one the flood point.


                            As gas velocity increases above the load
                            point,  the liquid holdup in the bed increases
                            until, at the second breakpoint, the flood
                            point,  most of the void space in the tower
                            is filled with liquid and there is liquid
                            entrainment in the gas stream.  Of course,
                            at this point there is an  excessive pressure
                            drop.  Columns should seldom be operated
                            above the load point, but since the load point
                            is sometimes more  difficult to establish than
                            the flood point, it is  common practice to  de-
                            sign for 40 to 70 percent of the flood point.
                            In general,  flooding velocities  are considerably
                            higher for stacked packing than for dumped
                            packing.  The plot of Lobo (Figure  145) can

-------
                                         Gas Absorption Equipment
                                            211
                      1 0
                      0 1
                     0 01
                                                                              N
                    0 001
                       0 01
                                            01                   10
                                                 (I'  V)(PG PL)° 5
                              10 0
                         Figure 145.   Correlation  for  flooding rate in randomly  packed
                         towers (Lobo,  1945,  p.  693).
be used to determine flow rates that will cause
flooding.   This curve is based on measurements
•with several liquids and gases on a  variety of
packings.

For many years packed towers were designed
on the same basis  as plate or tray towers.
The number of theoretical plates or trays re-
quired for a given  degree of  separation -was
calculated and this quantity multiplied by a
figure called height equivalent to a theoretical
plate (HETP).   This HETP was an experi-
mentally determined figure varying  widely •with
packing, flow rates of each fluid  used,  and
concentration of solute for any specific system.
Experimental evaluation  of these variables
made use of this system  too  cumbersome  and
it is now rarely used.  Design procedures now
employ the concept of the transfer unit.   The
major design items to be calculated are the
column diameter, number of transfer units,
the height  of a transfer unit,  and the system
pressure drop.  These will be discussed in-
dividually.
Tower Diameter

As mentioned previously, gas velocity is limited
by flooding conditions in the tower.  By  use of
the design gas volume,  design solvent flow rate,
and type of packing, the tower diameter can be
computed by using Lobe's correlation in Figure
145.  Packing factors are obtained from Figure
146,  The procedure is  as follows:
1.   Calculate the factor ~r~,
    •where

    L'  =  liquid flow rate, Ib/hr

    V  =  gas flow rate, Ib/hr


   p    =  gas density, lb/ft3


   PT    =  liquid density, lb/ft .
                                  0.5
  234-767 O - 77 - 16

-------
212
CONTROL EQUIPMENT FOR  GASES AND VAPORS
                    10 000
                    1,000
                      100
                              PACKING FACTOR FOR 1-in  INTALOX
                              SADDLES  a <3 - 90
                                0 5
                                                 15      20       25
                                             NOMINAL PACKING SIZE  inches
                                                                          3 0
                                                                                  3 5
                         Figure 146.   Packing factors for Raschig rings and saddles
                         (Lobo,  1945,  p.  693).
 2.   Using the calculated value in (1),  obtain
     from Figure 145 the value of
                            where
          gcPG
     G'  = gas flow rate,  Ib/sec-ft   of tower
     cross -section
     —r  = packing factor from Figure 146.
     p  =  gas density, Ib/ft
      G
                                 p  =  liquid density, Ib/ft

                                 fj.L =  liquid viscosity,  centipoises

                                 g  =  gravitational constant, 32. 2 ft/sec .


                             3.   Solve for G', the superficial mass gas ve-
                                 locity at flood point from the factor deter-
                                 mined in (2).

                             4.   Calculate S,  the tower cross-section area
                                 in ft^ for fraction of flooding velocity selec-
                                 ted, f,  by the equation
                                                                       S   =
                                                                                  V
                                                                             (G')(f)(3,600)
                                                                           (92)

-------
                                        Gas Absorption Equipment
                                                                                                  213
5.
    Calculate the tower's inside diameter,  DC,
    by the equation
             DC  =
                            0. 5
                                            (93)
    Tower diameter should be calculated for
    conditions at both top and bottom of the
    tower.  The tower is designed to the  larger
    diameter.


Number of Transfer Units (NTU)

A transfer unit is a measure of the difficulty of
the mass transfer operation and is a function of
the solubility and concentrations  of the solute
gas in the gas and liquid streams.  It is ex-
pressed as NQQ or  NQL,  depending upon whether
the gas film  or liquid film resistance controls
the absorption rate.  The gas film resistance
usually controls when solubility of solute in sol-
vent is high and conversely,  the liquid  film con-
trols when the solubility is low.

In air pollution control work where, in general,
a relatively small concentration of solute is to
be removed from an airstream, a solvent in
which the solute gas is highly soluble is usually
selected in order to obtain the highest possible
economic separation.  Thus, for the majority
of cases encountered, the gas film resistance
will be controlling.


One of the most widely used methods of determin-
ing the number of transfer units is that proposed
by Baker (1935), which  is based upon an operating
diagram consisting  of an equilibrium curve and
an operating line.  For  a given gas-liquid system,
if the temperature is constant and the gas partial
pressure is varied,  the gas concentration in the
liquid  changes to an equilibrium concentration
at each partial pressure.  If the system consists
of a soluble gas to be removed,  an insoluble
carrier gas,   and a solvent, then,  as the amount
of soluble gas in the system increases, the
equilibrium concentration of the soluble gas in
the liquid .increases but not proportionally.

These equilibrium conditions can exist for an
infinite number of concentration  states and, when
plotted on X-Y coordinates, become the equilib-
rium curve.   The operating line  represents the
concentrations of solute in the gas stream and
in the  liquid  phase at various points in the tower.
When plotted as moles solute per mole solvent
versus moles solute per mole gas on X-Y co-
ordinates, the result is a straight line.  Thus,
when the composition of the inlet gas and the
desired or required degree of absorption are
known,  the points on the operating line for each
end of the column can be calculated.  The oper-
ating  line is the straight line connecting the
two points.  For absorption to occur,  the oper-
ating  line must lie above the equilibrium curve
on the diagram.  The relative position  of the
operating line  and  equilibrium curve indicates
how far the tower conditions are from equilib-
rium.   The more widely separated the  lines,
the further the tower conditions  are from equi-
librium and the greater is the driving  force
for the  absorption  operation.

Figure  147 illustrates the graphical method
of determining the number of transfer units
for a  countercurrent packed tower with the
gas film controlling the absorption rate.  The
equilibrium curve  (line  AB) for  the particular
gas-liquid system  is plotted from experimental
data,  which,  for most common systems, has
been determined.  Much of these data  can be
located in the International Critical Tables
and in Perry (1950).   The operating line is
a straight line drawn between points D  and C.
D is the point representing the concentra-
tions  of solute in the gas stream and in the
liquid stream at the gas inlet and liquid out-
let  (bottom of the tower).  Point C corresponds
to these concentrations  at the top of the column.
Line EF is drawn so that all points on the line
are located midway on a vertical line between
the operating line and equilibrium curve.
Starting at point C on the operating line (con-
ditions  at the top of the  column), draw  a hori-
zontal line CH so that CG =  GH.   Then  draw a
vertical line  HJ back to the  operating line.
                                                                   X = SOLUTE  moles/SOLVENT  mole
                                                            Figure 147.  Graphical  determination of
                                                            the number of transfer  units.

-------
214
CONTROL EQUIPMENT FOR GASES AND VAPORS
The step CHJ represents one gas transfer unit.
This stepwise procedure is continued to the
end of the operating line (conditions at the
bottom of the column).  Two gas transfer units
(NOG) are shown in Figure 147.

If the liquid film resistance is the controlling
factor in the transfer  of solute  to solvent,  draw
the line EF  so that all points  on the line are
located midway on the horizontal  axis between
the operating line and equilibrium curve.  Then,
starting at point D on  the operating line, draw
a vertical line DK so that DL = LK.  The  step
is  completed by drawing a line  KJ back to  the
operating line.  This procedure is then con-
tinued to point C on the operating line.  Figure
147 does not accurately indicate the number  of
liquid transfer units since the line EF was
drawn for the case where the gas film resis-
tance controls.


Height  of a Transfer Unit
Generalized correlations are available for
computing the height of a transfer unit and
are expressed as HQ and HL for heights of gas
and liquid transfer units respectively.  These
use experimentally derived factors based on the
type of packing and the gas and liquid flow rates
as shown  in equations 94 and 95.
                           where

                              H
                               G
                              G

                              L

                              o
                              D
                                G
                                     HG =
                                                            0. 5
       =  height of a gas transfer unit,  ft

       =  superficial gas rate,  Ib/hr-ft

       =  superficial liquid rate, Ib/hr-ft

       =  a packing constant from Table 58

       =  a packing constant from Table 58

       =  a packing constant from Table 58

       =  gas viscosity,  Ib/hr-ft

       =  gas density,  Ib/ft

       =  gas diffusivity, ft /hr.
                                             (94)
The group
                                       PG  G
                                                 is known as the Schmidt
                           number as shown in Table 59.
                  Table 58.   CONSTANTS FOR USE IN DETERMINING GAS FILM'S
                       HEIGHT OF TRANSFER UNITS (Treybal,  1955, p. 239)
Packing
Raschig rings
3/8 in.
1 in.

1-1/2 in.

2 in.
Berl saddles
1/2 in.

1 in.
1-1/2 in.
3 -in. partition rings
Spiral rings (stacked
staggered)
3 -in. single spiral
3-in. triple spiral
Drip-point grids
No. 6146
No. 6295
a

2. 32
7. 00
6. 41
17. 30
2. 58
3. 82

32. 40
0. 81
1.97
5. 05
650


2.38
15.60

3.91
4.56
P

0. 45
0. 39
0. 32
0. 38
0. 38
0. 41

0. 30
0. 30
0. 36
0. 32
0. 58


0.35
0. 38

0. 37
0. 17
7

0. 47
0. 58
0. 51
0. 66
0. 40
0. 45

0. 74
0.24
0.40
0.45
1. 06


0. 29
0. 60

0.39
0. 27
Range of
G'

200 to 500
200 to 800
200 to 600
200 to 700
200 to 700
200 to 800

200 to 700
200 to 700
200 to 800
200 to 1, 000
150 to 900


130 to 700
200 to 1, 000

130 to 1, 000
100 to 1, 000
L

500 to 1,500
400 to 500
500 to 4, 500
500 to 1, 500
1, 500 to 4, 500
500 to 4, 500

500 to 1, 500
1, 500 to 4, 500
400 to 4, 500
400 to 4, 500
3,000 to 10, 000


3,000 to 10, 000
500 to 3, 000

3,000 to 6, 500
2, 000 to 11, 500

-------
                                      Gas Absorption Equipment
                                             215
   Table  59  DIFFUSION COEFFICIENTS OF
   GASES AND VAPORS IN AIR AT 25 °C AND
              1 ATM (Perry, 1950)
Substance
Ammonia
Carbon dioxide
Hydrogen
Oxygen
Water
Carbon disulfide
Ethyl ether
Methanol
Ethyl alcohol
Propyl alcohol
Butyl alcohol
Amyl alcohol
Hexyl alcohol
2 ,
D, cm /sec
0.236
0. 164
0. 410
0. 206
0. 256
0. 107
0. 093
0. 159
0. 119
0. 100
0. 090
0. 070
0. 059
Formic acid , 0. 159
Acetic acid
Propionic acid
i-Butyric acid
Valeric acid
i-Caproic acid
Diethyl amine
Butyl amine
Aniline
Chloro benzene
Chloro toluene
Propyl bromide
Propyl iodide
Benzene
Toluene
Xylene
Ethyl benzene
Propyl benzene
Diphenyl
n-Octane
Mesitylene
0. 133
0. 099
0. 081
0. 067
0. 060
0. 105
0. 101
0. 072
0. 073
0. 065
0. 105
0.096
0. 088
0. 084
0.071
0. 077
0. 059
0. 068
0. 060
0. 067
pD
0.66
0.94
0. 22
0.75
0. 60
1.45
1.66
0. 97
1. 30
1. 55
1. 72
2.21
2. 60
0. 97
1. 16
1.56
1.91
2.31
2. 58
1.47
1. 53
2. 14
2. 12
2. 38
1.47
1.61
1.76
1.84
2. 18
2.01
2.62
2.28
2.58
2.31
                                  0. 5
                                          (95)
'where
   H   =  height of a liquid transfer unit,  ft
    L

   L   =  superficial liquid  rate, Ib/hr-ft

   H   =  liquid viscosity,  Ib/hr-ft
    L

   0   =  a packing constant,  Table 60

   H   =  a packing constant,  Table 60

   p   =  liquid density, Ib/ft

   D   =  liquid diffusivity,  ft /hr.
      Table 60.  CONSTANTS FOR USE IN
   DETERMINING LIQUID FILM'S HEIGHT OF
   TRANSFER UNITS (Treybal, 1955, p. 237)
                                                      The group
Packing
Raschig rings
3/8 in.
1/2 in.
1 in.
1-1/2 in.
2 in.
Berl saddles
1/2 in.
1 in.
1-1/2 in.
3-in. partition rings
Spiral rings (stacked
staggered)
3-in. single spiral
3-in. triple spiral
Drip-point grids
No. 6146
No. 6295
*

0. 00182
0. 00357
0. 0100
0.0111
0. 0125

0. 00666
0. 00588
0. 00625
0. 0625


0. 00909
0. 01 16

0. 0154
0. 00725
r;

0. 46
0. 35
0. 22
0. 22
0. 22

0. 28
0. 28
0. 28
0. 09


0. 28
0. 28

0. 23
Range of L.

400 to 15, 000
400 to 15, 000
400 to 15, 000
400 to 15, 000
400 to 15, 000

400 to 15, 000
400 to 15, 000
400 to 15, 000
3, 000 to 14, 000


400 to 15, 000
3, 000 to 14, 000

3, 500 to 30, 000
0. 31 I 2, 500 to 22, 000
                                                                     L
                                                                       L,
                                                                            is the Schmidt number
                                                      as shown in Table 61.  Each of these empirical
                                                      equations neglects the effect of the other film's
                                                      resistance.   Actually, however, even in the
                                                      case of absorbing highly soluble ammonia in
                                                      water,  experimental results have  shown that
                                                      the liquid film resistance  is significant.  The
                                                      height of an overall gas transfer unit, H-^p,
                                                      is determined by the following equation, which
                                                      takes into account the liquid film resistance.
                                                           H
                                                             OG
                                                                  =  H
                                                                      G
                               (HL>
                                                                                                  (96)
where.

   m   =   slope of the equilibrium curve

   G   =   gas rate, Ib-moles/hr
     m
   L   =   liquid rate,  Ib-moles/hr.
     m

These equations are widely accepted for design
purposes.  Another group of equations listed
by Leva (1953) include overall gas and liquid
transfer coefficients,  Kga and K-^a.  Still more
recently,  Cornell et al. ,  (1960)  published corre-
lations based on a mass of experimental data re-
ported up to  1957.

-------
216
                         CONTROL EQUIPMENT FOR GASES AND VAPORS
    Table 61.  DIFFUSION COEFFICIENTS IN
        LIQUIDS AT 20°C (Perry, 1950)
                                                   mass flow rates, high-viscosity liquids cause
                                                   greater gas  pressure drop than those of low vis-
                                                   cosity do.
!
_ a
Solute

°2
C02
N2O
NH3
CI2
Br2
TJ
W2
N2
HC1
H2S
H2SO4
HNO3
Acetylene
Acetic acid
M ethanol
Ethanol
Propanol
Butanol
Allyl alcohol
Phenol
Glycerol
Pyrogallol
Hydroquinone
Urea
Resorcinol
Ur ethane
Lactose
Maltose
Glucose
Mannitol
Raffinose
Sue r os e
Sodium chloride
Sodium hydroxide
D x 105
(cm2/sec) x 105

1. 80
1.77
1.51
1.76
1.22
1.20
C I Q
_> . 1 J
1. 64
2.64
1. 41
1. 73
2. 60
1. 56
0.88
1.28
1. 00
0. 87
0. 77
0. 93
0. 84
0. 72
0. 70
0. 77
1. 06
0. 80
0. 92
0. 43
0. 43
0. 60
0. 58
0. 37
0. 45
1. 35
1. 51
3. 40
Phenolb 0. 80
Chloroform
Phenol0
Chloroform0
Acetic acidc
Ethylene dichloridec
1. 23
1. 54
2. 11
1. 92
2. 45

n
pD

558
559
665
570
824
840


613
381
712
580
390
645
1, 140
785
1, 005
1, 150
1, 310
1, 080
1,200
1,400
1, 440
1, 300
946
1, 260
1, 090
2, 340
2, 340
--
1,730
2, 720
2, 230
745
665
445
1, 900
1,230
479
350
384
301


Leva's empirical relation applies below the load
point. This is as follows :

2
AP ™ MrT8uinnL'/'3T \ G' ia-7\
- m (10 )(10 L) (97)
z i PG



where

P = pressure drop, Ib/ft
Z = packed height of tower, ft
m = pressure drop constant from Table 62
n = pressure drop constant from Table 62
L' = superficial mass liquid velocity, lb/
hr-ft2

G' = superficial mass gas velocity, Ib/hr-
ft2

p = liquid density, Ib/ft
L
p,, = gas density, Ib/ft .
Vj



Illustrative Problem

The following example illustrates the preceding
principles of packed tower design. Knowing the
amount of solute in the gas stream, the total flow
rate of the gas stream, the most suitable solvent,
an acceptable packing, and the desired degree of
absorption, calculate the tower dimensions.

Given:

Design a packed tower to remove 95% of the am-
aSolvent is water except
^Solvent is ethanol.
cSolvent is benzene.
                          where indicated.
Pressure Drop Through  Packing

Treybal (1955) states that pressure drop data of
various investigators varies •widely even for the
same packing and flow rates.  These discrep-
ancies were probably due to differences in pack-
ing density.  Moreover,  not enough work has
been done on liquids of high viscosity for proper
evaluation, though it is recognized that, at equal
monia from a gaseous mixture of 10% by volume
of ammonia and 90% by volume of air.   The gas
mixture consists of 80 Ib-moles/hr at 68°F and
1 atm.  Water containing no ammonia is to be
used as solvent and the packing will be  1-inch
Raschig rings.  The tower -will be designed to
operate at 60% of the flood point,  and isothermal
conditions at 68 °F  will be assumed.  The water
will not be recirculated.


Problem:

Determine -water flow rate, tower diameter,
packed height, and tower pressure drop.

-------
                                       Gas Absorption Equipment
                                            217
                        Table 62.   PRESSURE DROP CONSTANTS FOR TOWER
                                      PACKING (Treybal, 1955)
Packing
Raschig rings




Berl saddles



Intalox saddles

Drip-point grid
tiles






Nominal
size,
in.
1/2
3/4
1
1-1/2
2
1/2
3/4
1
1-1/2
1
1-1/2
No. 6146
Continuous
flue
Cross flue
No. 6295
Continuous
flue
Cross flue
m
139
32. 90
32. 10
12. 08
11. 13
60. 40
24. 10
16. 01
8. 01
12.44
5.66
1. 045


1. 218
1. 088


1. 435
n
0. 00720
0. 00450
0. 00434
0. 00398
0. 00295
0. 00340
0. 00295
0. 00295
0. 00225
0. 00277
0. 00225
0. 00214


0. 00227
0. 00224


0. 00167
Range of L/',
lb/hr-ft2
300 to 8, 600
1, 800 to 10, 800
360 to 27, 000
720 to 18, 000
720 to 21, 000
300 to 14, 100
360 to 14, 400
720 to 78, 800
720 to 21, 600
2, 520 to 14, 400
2, 520 to 14,400
3, 000 to 17, 000


300 to 17, 500
850 to 12, 500


900 to 12, 500
Range
of P/Z,
Ib/ft2-ft
0 to 2. 6
0 to 2.6
0 to 2.6
0 to 2.6
0 to 2.6
0 to 2. 6
0 to 2. 6
0 to 2.6
0 to 2. 6
0 to 2. 6
0 to 2.6
0 to 0. 5


0 to 0. 5
0 to 0. 5


0 to 0. 5
 Solution:

 1. Calculate the water rate:  :

 a. Equilibrium data for the system ammonia -
   water are as follows:
 X  0.0206  0.0310  0.0407  0.0502  0.0735 0.0962
 Y  0.0158  0.0240  0.0329  0.0418  0.0660 0.0920
   G
   Plot the equilibrium curve as  shown in Fig-
   ure 148:

   The curve is straight approximately to the
   point P, with a. slope of about  0. 75.  Above
   point P, the  slope is variable  and higher
   than 0. 75.  Use 0. 75 as the slope, m, of
   the equilibrium curve.


b. When the  temperature rise of  the solvent
   is negligible, apply the  relation
               G   (m)
                m
                        =  0. 70
gas rate = 80 Ib-moles/hr

liquid rate, Ib-moles/hr
          (80)(0.75)
             0. 70
                                                                            =  85. 8 Ib-moles/hr.
2. From the given gas flow rate, the calculated
   liquid rate, and the degree of absorption de-
   sired (95% of ammonia), tabulate gas and
   liquid flow rates at both ends of the tower:
                                        Density,
                   Ib-moles/hr  Ib/hr   lb/ft3
Inlet gas  (bottom)     80
Outlet gas (top)       72.4
Inlet water (top)      85.8
Outlet liquor (bottom) 93.4
                       2,221   0.0720
                       2,092   0.0750
                       1,542  62.4
                       1,671  62.4
3.  Calculate the tower diameter:

a. Use conditions  at top of tower:
   •where

      m =  slope of equilibrium curve = 0. 75
            1.542   O.
                                     \°-5
                                          = 0.0256

-------
 213
                           CONTROL EQUIPMENT FOR GASES AND  VAPORS

0 11


CO
cc
§
z
=- 0 03
0 02
0 01
0









A
/r.
Y











/
/
/








j
A
/
—

/










^y
•$/
&/
s

A
/


s
/
/^







/

y
>
^






/
r
/
j

c&







/
J
/







/
/




/
/
f
'








/
/
/








(2) From Figure 145, the relationship
,2 /_a_\ 0.2
(gc)(pG)(pL) ~ •
(3) From Figure 146, the packing factor/— J = 160
\e /
... ,,. (0. 19)(32.2)(0.0720)(62.4) „,,,,,,,
(4) G - Q 2 - 0.415 lb/scc
(160)(1)
(5) G' - 0 415 (0 60) - 0 249 Ib/sec-ft2
.„ „ 2,221 Ib/hr , An
      0   0 01  0 02  0 03  0 04  0 05 0 06 0 07 0 08  0 09  0 10
                 X - moles NH3 mole H20 - 68 °F
    Figure  148.  Equilibrium  curve for ammonia-
    water  system.


(2)  From Figure 145, the relationship
                         =  0. 19
                                                       (6)  S  =
                                                                  (0. 249 Ib/sec-ft  ) (3 , 600 sec/hr)
                                                       c.  Select tower with uniform cross-section of
                                                           2.48 ft2
                                                        1.   Tower diameter:
                                                           DC  =
                                                                     (2.43)(4)V
                                                                       3.14
                                                                               0. 5
                                                                                   =   1. 78 ft or 21. 4 in.
(3)  From Figure 146, the packing factor!—r-)=  160
(4)  From the  relationship in (2), calculate the
    superficial mass gas velocity (G ) at flooding:
                                                       4.   Determine the number of transfer units:

                                                       a.   Calculate mole fractions  of solute in gas
                                                            liquid streams at both ends of the tower.

                                                       (1)  Bottom of tower:
       ). 19)(32.2)(0.0750)(62.
                     ,0.2
                                           Ib/sec-ft2
                                                            y
                                                                    — —  =  0. Ill mole NH  /mole air
(5)  At 60% of flooding:
G   =   (G)(0.60) =  (0. 424)(0.60)  =  0. 254 Ib/sec-ft
(6)   To-wer cross section:
                                                            X  =  -—  =   0.088 mole NH  /mole  water
                                                              185.8                   3
                                                        (2)   Top of tower:
 S  =
                 2, 092 Ib/hr
                                         =  2.29 ft
      (0.254 Ib'/sec-ft )(3, 600 sec/hr)


b. Use conditions at bottom of tower:
                                                            y    =   ——  -  0. 0056 mole NH  /mole air
                                                            X   =   0    (entering water is NH  free)
                                               , 0256
                                                        b.  Plot the operating line from the data in (a)
                                                            on the same graph used for the equilibrium

-------
Gas Absorption Equipment
219
c. By the method of Baker (described previously)
graphically determine the number of transfer
units :
NTU - 6
5. Calculate the height of a transfer unit:
a. Gas transfer unit:
0. 5
a G1 / ^G \
Hg 7 (p D J
where
2, 221 Ib/hr .j ft2
2.48 ft2
L = LJii = 6221b/hr.ft2
2.48
Q- = 7. 00 from Table 58
/3 = 0. 39 from Table 58
7 = 0. 58 from Table 58
/ V \
(7.00)(896)°-39(0.66)°-5
(622)0'58
b. Liquid transfer unit:
•where
 = 0. 01 from Table 60
n = 0.22 from Table 60
L = 622 lb/hr-ft2
H = 1 centipoise = 2.42 lb/hr-ft
L
Ap -
•" I nn -fi-n,-,-, T-iV.ln Al
/622 \°'22 0 5
L ~ \2 42 j (5<0) - 0. /9IL
c. Overall gas transfer unit
/Gm\
HOG = HG + m VL J (HL}
\ m/
where
m = slope of equilibrium curve = 0. 75
G = gas rate = 80 Ib-moles/hr
m
L = liquid rate = 85. 8 Ib-moles/hr
m
, „-, (0.75)(80)(0.79) -, _ ,
OG (85.8)
6. Calculate the packed to-wer height (Z):
Z = NTU x H
ULr
Z = 6 x 2. 47 = 14. 8 ft
7. Calculate the tower pressure drop
z - mi(1° T0 )(PG)
where
Ap = pressure drop, Ib/ft
Z = packed height = 14.8ft
m - 32. 10 from Table 62
n = 0. 00434 from Table 62
L = 622 lb/hr-ft2
p = 62.4 Ib/ft3
G = 896 lb/hr-ft2
PG= Avg gas density = 0. 0736 Ib/ft 3.
(32. ix 10-8)(10)(0-°0434)(622)/62-4(896)2(14.8)
0. 0736
                   Ap  =  57.2 Ib/ft

-------
 220
                          CONTROL EQUIPMENT FOR GASES AND VAPORS
        57. 2 Ib/ft   (1 in.  WC)
             5. 197  Ib/ft2
    =  11. 0 in. WC
liquid.  The liquid enters at the top of the
tower, flows across  each plate and down-
ward from plate to plate through downspouts.
 PLATE  OR TRAY  TOWERS
In contrast to packed towers,  where gas and
solvent are in continuous contact throughout the
packed bed,  plate towers employ stepwise con-
tact by means of a number of  trays or plates
that are arranged so that the gas is dispersed
through a layer of liquid on each plate.  Each
plate is more or less  a separate stage, and
the number of plates required is dependent
upon the difficulty of the mass transfer oper-
ation and the degree of separation desired.

 Types  of  Plates

The bubble cap  plate or tray is most  common,
and most general references deal primarily
with it when discussing plate towers.  Other
types of plates include perforated trays,
Turbogrid trays,  and  Flexitrays.

A schematic section of a bubble cap tray tower
is  shown in Figure 149. Each plate is equipped
•with openings (vapor risers) surmounted with
bubble caps.  Typical bubble caps are illus-
trated  in Figure 150.   The gas rises through
the tower and passes through  the openings in
the plate and through slots in  the periphery
of the bubble caps, which  are  submerged in
                         3 CAP SUPPORTS
                         AT 12Q°F
                               VAPOR RISER
                            HOLD-DOWN BAR
                                                           SLOTS
                                CAST TRAY

                                 CAST CAP
                                                      SHEET METAL CAP
                                                       SHEET METAL TRAY
                                     Figure  150.   II lustration of
                                     some  typical  bubble caps.
         SHELL

         TRAY
        DOWNSPOUT-
      TRAY
      SUPPORT RING
       TRAY
       STIFFENED-
        VAPOR
        RISER
         FROTH—
~- LI QUID IN
                             — BUBBLE CAP
                              SIDESTREAM
                              'WITHDRAWAL
i_ INTERMEDIATE
  FEED
                             - GAS IN
                             4- LIO.UID OUT
The depth of liquid on the plate, and liquid
flow patterns across the plate are controlled
by various -weir arrangements,  which will be
discussed in greater detail.

In perforated plates or sieve trays, the gas
passes upward through a pattern of  holes
drilled or punched in the trays.  Three-
sixteenth-inch-diameter holes  spaced on a
3/4-inch triangular pitch are commonly used.
A disadvantage of this type is the tendency of
liquid to "weep" or leak  down through the
holes instead of through  the downspouts at
low gas velocities.  Moreover,  the  trays
must be  installed perfectly level,  or chan-
neling, with resultant loss of efficiency,
will occur.   On the other hand,  a perforated
tray costs only 60 to 70 percent as much as
a bubble cap plate designed for the  same
throughput.  With  towers of the same di-
ameter,  perforated trays supposedly have
a capacity 1 0 to 40 percent greater than
that of bubble cap plate  towers.
        Figure  149.   Schematic diagram
        of  a  bubble-cap  tray tower
        (Treybal,  1955,  p.  111).
                          With Turbogrid trays,  licensed by Shell Develop-
                          ment Company, the vapor passes up through the
                          spaces between parallel rods or bars, and the

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                                       Gas Absorption Equipment
                                                                                                  221
liquid level on the tray is maintained by the gas
pressure beneath the tray.   There are no down-
spouts, and the liquid flows downward through
the same openings used by  the upward flowing
gases.  A Turbogrid tray is shown in Figure  151.
These are reputed to have high absorption effi-
ciencies even at high capacities with liquids  con-
taining a  small amount of suspended solids.   For
example, a 50 percent increase in capacity has
been reported where bubble cap plates have been
replaced by Turbogrid trays in an existing tower.

Flexitrays,  licensed by the  Koch Engineering
Company, have floating caps that allow varia-
tions in the vapor openings  with varying gas flow.
Different weights can be put on the caps so that
the slots will  be only partially open at low gas
flow rates.  This tray also  has relatively low
resistance to  liquid  crossflow and supposedly
has advantages  over bubble  cap trays in large
                      TOP VIE*
                                           COLUMN
                                           SHELL
  COLUMN
  SHELL
SIDE VIEW
     \
             icaoooooocDoooooooooaociciooocioQaaci^.
              TRAY SUPPORT RING
         Figure  151.   Illustration of a  typical
         Turbogrid  tray (Shell Development  Co.,
         Emeryville, Calif.).
columns or operations that require high liquid
rates.  Flexitrays are claimed to have a capac-
ity 12 to 50 percent higher than that of bubble
cap plates and cost only 60 to 80  percent as
much.

Although the proponents of the various trays
make each sound attractive,  it should be re-
membered that the bubble cap plate is still
the standard of the industry and presently
outnumbers all the other types.   Thus further
discussion of plate towers will be devoted  ex-
clusively to the design of bubble cap plates.


BUBBLE CAP PLATE TOWER DESIGN


Liquid Flow

Common variations in liquid flow across a
bubble cap plate include:  (1) Crossflow  in
opposite directions on alternate plates,  (2)
crossflow in the same direction on all plates,
and (3) split-flow arrangements.  There are
also variations in weir and downspout design.
Several liquid flow patterns are diagrammed
in Figure 152, and typical bubble cap tray
arrangements for different liquid flow paths
are shown in  Figure 153.

The single-pass plate with a rectangular weir
shown in Figure 153a is the most common.
Much of its cross-sectional area  is devoted
to vapor flow, whereas, a split crossflow
plate, shown  in Figure 153b, has more of  its
cross-sectional area devoted to liquid flow.
The split-flow tray also has greater down-
spout area, and the liquid flows a shorter
distance from the tray inlet to the overflow
weir.  Thus split-flow trays handle higher
liquid flow rates and are suitable for large-
diameter towers.

Cascade tray arrangements,  shown in Fig-
ures  152d and 153c,  are used to keep the
liquid level at a more constant depth over  the
entire tray area despite considerable liquid
head differential across the tray.  These
are used for exceptionally large-diameter
towers.  Radial flow, Figure  153f, is also
a common arrangement in large-diameter
towers.  The  liquid flow may be to and from
the center on  alternate trays, or  it maybe in
the same direction on all the trays.


Plate  Design and Efficiency

For the most  efficient operation,  bubble cap
tray towers must be designed to compromise
opposing tendencies.  High liquid levels  on
the trays tend to give comparatively high
tray efficiency through long contact time but

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 222
CONTROL EQUIPMENT FOR GASES AND VAPORS
  LIQUID
  DOWN
     LIQUID
     DOWN
       VAPOR UP
         a.
         LIQUID
         DOWN

t

t










VAPC





f

1

1
c.









UP


J



t

t

INLET
WEIR
OVERFLOW
WEIR
 Figure 152.  Vapor and liquid  flow  patterns  for
 bubble cap tray towers:   (a) One-pass  tray bub-
 ble plate column,  liquid crossflow,  opposite  di-
 rection on alternate plates;  (b) one-pass tray
 bubble plate column, liquid crossflow,  same  di-
 rection all plates;  (c) two-pass tray  bubble
 plate column,  split liquid crossflow,  opposite
 directions on alternate plates;  (rJ)  one-pass
 cascade tray bubble plate column,  liquid cross-
 flow, opposite direction on alternate  plates
 (Edmister, 1948).
also give high pressure drop per tray.  High
gas velocity,  "within limits, gives efficient
vapor-liquid contact by creating turbulent
conditions but also leads to high pressure
drop as •well as high liquid entrainment.
Treybal (1955) lists recommended condi-
tions and dimensions for bubble cap trays
that have been found to be a useful com-
promise; these  are  listed in Table 63.  In
this table, the liquid seal (h ) is  the depth
of clear liquid over the top of the  bubble
cap slots.


As  stated before, each tray or plate is a sep-
arate stage and, for ultimate  efficiency, the gas
and liquid would leave  each tray in equilibrium
with each other at tray conditions.  This would
be a theoretical plate.   This theoretical condi-
tion does not normally exist in practice and
thus the actual number of trays required to
accomplish a specified degree of absorption
usually exceeds the number of theoretical
units required.   The overall plate efficiency
of a tower is defined as the number of theoret-
ical equilibrium stages required for a given
                                     Figure 153.   Typical  bubble  cap
                                     tray arrangements:   (a)  Single
                                     crossflow,  rectangular wei rs;
                                     (b) split  crossflow,  rectangular
                                     weirs;  (c) cascade  crossflow ,
                                     rectangular  weirs;  (d) reverse
                                     flow,  rectangular weir and di-
                                     viding dam;  (e)  crossflow, cir-
                                     CLflar  wei rs;  (f) radial  flow,
                                     circular  weirs  (Edmister,  1948).
                             degree of removal of solute from the gas
                             stream, or concentration of solute in solvent,
                             divided by the actual number  of trays required
                             for this same  operation.  According to  Clarke
                             (1947) an overall plate efficiency of 25 per-
                             cent is a conservative estimate for hydro-
                             carbon absorbers.  O'Connell (1946) corre-
                             lates plate efficiency with gas solubility and
                             liquid viscosity.  This correlation is shown
                             in Figure 154.  All such correlations are
                             empirically derived,  and attempted theoret-
                             ical methods based on mass-transfer prin-
                             ciples do not successfully predict overall
                             plate efficiency.


                             Flooding

                             When the liquid capacity of a  plate absorber
                             is exceeded, the downspouts become filled.
                             Then,  any slight increase in liquid or gas
                             flow increases the liquid level on the trays.
                             A further increase in pressure across the
                             trays causes more liquid to back up  through
                             the downspouts,  resulting in still higher
                             liquid levels on the trays until, eventually,
                             the tower fills with liquid.   This is known
                             as flooding, and at this point,  the tray ef-
                             ficiency falls  to a very low value, the gas

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                                        Gas Absorption Equipment
                                                           223
                   Table  63.  RECOMMENDED CONDITIONS AND DIMENSIONS FOR
                                 BUBBLE CAP TRAYS (Treybal,  1955)
              Tray spacing
              Liquid seal
              Liquid flow
              Superficial slot velocity


              Skirt clearance


              Cap spacing



              Downspout holdup

              Downspout seal


              Weir length



              Liquid gradient

              Pressure drop per tray
     Tower diameter,  ft
           4 or less
           4 or less
           4 to 10
          10 to 12
          12 to 24

          Pressure

          Vacuum
          Atm
          500 lb/in2
a. Not over 0. 22 ft3/sec-ft
   diameter for  single-pass
   crossflow trays
b. Not over 0.'35 ft3/sec-ft
   •weir length for others
3. 4/p  0.5 ft/sec minimum
12/Op 0.5 ft/sec maximum
     s

0. 5  in.  minimum; 1. 5  in. for
dirty liquids

1 in. minimum (low slot ve-
locities);  3  in. maximum
(high slot velocities)

Minimum of 0.5  sec

0.5  in. minimum at no liquid
flow

Straight rectangular weirs for
crossflow trays,   0. 6 to 0. 8 of
tower diameter

0.5 in. (1 in. maximum)

        Pressure
          Atm
          300 lb/in2
  Tray spacing, in.
     6 minimum
     18 to 20
        24
        30
        36
    Liquid seal,
       hs, in.
         0. 5
         1
         3
   Pressure drop
0. 07 to 0. 12 lb/in2
0. 15 lb/in2
flow is erratic, and liquid may be forced
out the gas exit pipe at the top of the tower.
Flooding occurs more rapidly -with liquids
that tend to froth.
Tower design should allow sufficient down-
spout area and tray spacing to prevent flood-
ing under anticipated operation variations in
both gas and liquid flow.  If there is  any
question, it is better to over-design  down-
spouts since they represent a relatively
small-cost item but are important from the
standpoint of potential flooding.
                 Liquid Gradient  on Plate

                 The liquid gradient on a plate is the de-
                 creasing liquid depth from the liquid inlet
                 to outlet of the plate due to resistance to
                 fluid flow by the bubble caps  and risers.
                 If this gradient is appreciable, more vapor
                 flows through the bubble caps where the
                 liquid depth is  least.   In extreme condi-
                 tions the caps near the liquid inlet may
                 become completely inoperative and liquid
                 may flow down through the risers.   This
                 is  called an unstable  plate.  Liquid gra-

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224
                           CONTROL EQUIPMENT FOR GASES AND VAPORS
                   100
                     0 i
                                              FACTOR, UML
                                         1 0                   10
                                                                                  100
                   I 0
                     100
                                          000
                                                            10 000
                                                                               100 000
                                              FACTOR
                      Figure 154.  Correlation of  plate  efficiencies of gas absorbers
                      with gas solubility and liquid  viscosity according to method of
                      O'Connell (Sherwood and Pigford,  1952,  p. 301).
dient problems •would naturally be more
likely in large towers, and in these cases,
the vapor distribution is  controlled by two-
pass, split-flow,  cascade- or radial-type
trays.
nance and are not placed close together un-
less headroom limits the overall tower height.
Six inches  is usually a minimum,  even for
very small-diameter towers,  and 18 to 24
inches is normally used for towers up to 4
feet in diameter.
Plate Spacing

Operationally, the main consideration re-
garding tray spacing is to allow sufficient
space for the desired liquid level plus
space above the liquid for disengagement
of the gas and liquid phases without en-
trainment.   Thus,  in this  respect,  tray
spacing is closely related to gas velocity
through the tower.  Spacing should also be
sufficient to provide insurance against
flooding.  If flooding conditions exist even
for a short time,  a tower  with closely
spaced trays could become flooded.  In
actual practice, however, trays are normal-
ly spaced for ease in cleaning and mainte-
Tower Diameter

The  superficial linear gas velocity that -will usu-
ally  ensure against excessive entrainment is chosen
by the equation
•where

   PL  =

   PG  =

     K  =
V  =  K
                                           (98)
liquid density, Ib/ft

gas density, Ib/ft

an empirical constant.

-------
                                        Gas Absorption Equipment
                                                       225
 The constant K can be determined by Figure 155,
 •which is based on results of experimental study
 and good commercial practice.  The velocity cal-
 culated in equation 98  is valid except for hydro-
 carbon absorbers,  which,  according to Perry
 (1950),  should be designed for vapor velocities
 65 to 80 percent that of the calculated values.
 From this calculated velocity, if the volumetric
 gas flow rate is known, the diameter can easily
 be determined.  In most cases the diameter
 chosen in this manner is also adequate to han-
 dle the normally expected liquid flow rate.
 Treybal (1955) states that a well-designed single-
 pass crossflow tray usually handles up to 100 gpm
 per foot of diameter without excessive liquid
 gradient.
               X   =  mole fraction of solute in liquid stream
                      at dilute end of countercurrent tower.
            Illustrative Problem

            The following example illustrates a method of
            determining the number of plates or trays  re-
            quired and estimated diameter for a tray tower.
            No attempt is made to design- the bubble  cap
            plate itself for characteristics such as number
            of caps,  cap  spacing, slot dimensions, and so
            forth.
                                                       Problem:
 Number of Theoretical Plates

 The number of theoretical plates or trays is
 usually determined graphically from an oper-
 ating diagram composed of an operating line
 and equilibrium curve constructed as previ-
 ously described in the discussion of packed
 towers.  The actual procedure will be de-
 scribed in the example problem that  follows.


 If the solute concentrations in the gas and
 liquid phases are low, as is frequently the
 case in air pollution control, both the equi-
 librium and operating curves can be  con-
 sidered as straight lines,  and an analytical
 solution may be used.  The relationship  as
 taken from Sherwood and Pigford (1952) is:

N   =  log
 P        e
 where
(99)
            Determine the number of actual plates and the
            diameter of a bubble cap plate tower for re-
            moving 90% of the ammonia from a gas stream
            containing 600 Ib-moles/hr of gas at 68 °F and
            1 atm composed of 10% by volume of ammonia
            and 90% by volume of air.
            Solvent rate expressed as moles solute/mole
            solvent is obtained from an operating line dis-
            placed substantially from the equilibrium curve
            (Treybal,  1955) as shown in the illustration that
            follows.
            Solvent rate selected is 900 Ib-moles/hr of water
            at 68°F.  The tower contains 24-inch tray spac-
            ing and 1-inch liquid seal and operates at iso-
            thermal conditions.
                                                     546 Ib-moles/hr
                                                        residue gas  1
                                             900 Ib-moles/hr
                                              fresh solvent
    N   =  number of theoretical plates
     P
    m  =  slope of equilibrium curve

   G    =  superficial molar mass flow of gas,
           lb-moles/hr-ft<" column cross-sec-
           tion

   L    =  liquor rate,  Ib-moles/hr-ft2 column
           cross-section
   Y   =  mole fraction of solute in gas stream
          at concentrated end of countercurrent
          tower
       =  mole fraction of solute in gas stream
          at dilute end of countercurrent tower
                              Bubble cap

                              Tray

                              Tower
          600 Ib-moles/hr,
              feed gas
          Feed gas
          Residue gas
          Absorbent liquid
          Rich liquid
   Flow,
Ib-moles/hr

     600
     546
     900
     954
                .954 Ib-moles/hr
                   rich liquid
                                            Flow,
                                            Ib/hr
         Density,
           lb/ft3
16,680    0.0722
15,762    0.0750
16,200   62.3
17, 118   62.3

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226
                          CONTROL EQUIPMENT FOR GASES AND VAPORS
  0 20
                10    12  14  16  18 20    24
                    TRAY SPACING (t) inches
                                          30   36 40
 Figure 155.   Tray-spacing constants to estimate
 bubble cap tray tower's superficial vapor  veloc-
 ity (adapted from Perry,  1950).
Solution:

1.   Calculate the mole ratios of solute in gas
     and liquid streams at both ends of the tower:

     (a) Mole ratios at bottom of tower:

              60
        Y
= 0. Ill mole NH /mole air
       X,  =
              54
= 0. 06 mole NH /mole HO
     (b)Mole ratios at top of tower:

       Y  = 	 = 0. 0111 mole NH0/mole air
         2   540                   3

       X, = 0. 0
2.   The operating line is plotted as shown in Fig-
     ure 156  from the conditions at top and bottom
     of the column  as  determined in step 1.   A
     straight line is drawn between points Xj, Yj
     and X2,  Y2.

3.   The curve of ammonia-water equilibrium is
     plotted on the  same graph from data taken
     from Leva (1953) in terms  of mole ratios.


4.   Number of theoretical plates  or trays:

     A horizontal line AB  is drawn from the oper-
     ating line  at the conditions  at the  top  of the
     column to the  equilibrium curve.   Line BC
     is then drawn  vertically from the equilibrium
     line back to the operating line.  The step ABC
     is a theoretical plate.  The step-wise  proce-
                                                       0 12
                                                       0 10
                                                       0 08
                                                      • 0 06
                                     0 04
                                                       0 02
                                                0  02
                                                         0 04
                                                                  0.06
                                                                           0 06     0.10
Figure 156.   Plot of  operating line  from the
conditions at top and bottom of  bubble  cap
plate tower.
                                     dure is repeated to the end of the operating
                                     line.  The solution shows 2. 45 theoretical
                                     plates.

                                     5.   Number of actual plates or trays:

                                         With a viscosity, J^LL, of 1 centipoise for
                                         water and a slope of the equilibrium curve,
                                         m, of 0. 83, (this assumes the equilibrium
                                         curve to be straight over the area covered
                                         by the operating line), the value m(j.L is
                                         (1)(0.83)  = 0.83.  From Figure 155, the
                                         overall plate efficiency is  72%.

                                         Actual plates required:
                                         2. 45
                                         0.72
        =  3.4  -  use 4 bubble cap trays.
                                     6.   Tower diameter:

                                         From Figure 157, -with a 24-inch tray spac-
                                         ing and 1-inch liquid seal, K = 0. 17

                                         (a) Superficial linear gas velocity at bottom
                                            of tower:

-------
                                      Gas Absorption Equipment
                                                                                                227
  Figure  157.  Venturi  scrubber or absorber  with
  cyclone-type liquid separator (Chemical  Con-
  struction  Corp., New  York,  N.Y.).
     (b) Volumetric flow rate at bottom of tower:
                                                     tion.  Design procedures for multicomponent
                                                     absorption are more complicated than those
                                                     described previously and will not be attempted
                                                     here.  Sherwood and Pigford (1952) devote an
                                                     entire chapter  to these procedures.
                                   COMPARISON OF PACKED AND PLATE TOWERS

                                   While devices such as agitated vessels, spray
                                   chambers, and  venturi absorbers have lim-
                                   ited application for gas absorption, the choice
                                   of equipment is  usually between a packed tower
                                   and  a plate tower.  Both devices have advantages
                                   and  disadvantages  for a given operation, de-
                                   pending upon many factors,  such as flow rates
                                   for both gas  and liquid, and degree of corrosive-
                                   ness of the streams.  Final selection should be
                                   based upon the following comparative informa-
                                   tion:

                                   1.   Packed  towers are less expensive than
                                        plate towers where materials  of con-
                                        struction must be corrosion resistant.
                                        This is  generally true for towers less
                                        than 2 feet  in diameter.

                                   2.   Packed  towers have smaller pressure
                                        drops than  plate towers designed for the
                                        same throughput and, thus, are more
                                        suitable for vacuum operation.

                                   3.   Packed  towers are preferred for foamy
                                        liquids.

                                   4.   The liquid holdup is usually less in a
                                        packed tower.
     (c) Tower cross-sectional area:
          64.00
           5.00
=  12.80 ft
    (d) Tower diameter:

       D  .  (mii^mf5=  «.„„.
The principles just discussed are for absorp-
tion of a single component.  Multicomponent
absorption is of great industrial importance in
the natural gasoline,  petroleum,  and petro-
chemical industries.  Absorption  of single
components such as H^S from multicomponent
gases -will be discussed in Chapter 11.  When
emissions consist of mixed-solvent vapors,
control by adsorption or incineration would
probably be more economical than by absorp-
5.  Plate towers are preferable where the
    liquid contains suspended solids since
    they can be more easily cleaned.  Packed
    towers tend to plug more readily.

6.  Plate towers are selected in larger sizes,
    to minimize channeling and reduce weight.
    Channeling is corrected in the larger di-
    ameter and tall  packed towers by instal-
    lation of redistributor trays at given in-
    tervals.

7.  Plate towers are more suitable where the
    operation involves appreciable tempera-
    ture variation since expansion and con-
    traction  due to temperature change may
    crush the packing in the tower.

8.  In operations where there is heat of solu-
    tion that must be removed,  plate towers
    are superior in  performance since cool-
    ing coils can be easily installed on the
    plates.
  234-767 O - 77 - 17

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228
CONTROL EQUIPMENT FOR GASES AND VAPORS
9.  Most conditions being equal,  economic con-
    siderations favor packed towers for sizes
    up to 2 feet in diameter.
VESSELS FOR  DISPERSION OF GAS  IN  LIQUID

Probably the simplest method of dispersing a
gas in a liquid for absorption is by injecting
the gas through a perforated pipe or sparger
of some type into a vessel filled  with the liq-
uid.  Unless  the sparger has minute perfora-
tions,  the gas bubbles formed tend to be too
large and thus present a relatively small
interfacial surface for the absorption oper-
ation.  If the sparger is designed to create the
necessary small bubbles,  power requirements
to force the gas through the small openings
are high.

Increased dispersion may also be achieved
by injecting the gas just below a  rotating
propeller,  where the shearing action of the
blade breaks up the large bubbles.  With a
single vessel, the advantage of true counter-
current flow cannot be fully realized since, if
there is good agitation, the concentration of
absorbed gas in the liquid is uniform through-
out the vessel.  Thus, absorption equivalent to
only one theoretical plate can be achieved per
vessel. Although absorption with this equip-
ment is usually batchwise, continuous oper-
ation can be  obtained with a series of vessels
wherein the gas and liquid pass from vessel
to vessel in opposite directions.

Vessels such as these have been used to  re-
move highly  odorous gaseous products  from the
reaction of sulfur and sperm oil  in the  manu-
facture of specialty lubricants.  Here the ef-
fluent gases, containing a considerable per-
centage of hydrogen sulfide,  are forced by their
own pressure from the closed  reactor, through
a vent pipe fitted with a sparger, into a tank
filled with caustic  soda.  This arrangement,
without auxiliary mechanical agitation  of the
liquid, reduces the odor  of the effluent gas to
an innocuous level.  Control, however, is ef-
fected primarily by chemical reaction  rather
than by true absorption.

Small tanks  containing water or  caustic soda are
used to eliminate visible emissions from vents
of hydrochloric acid storage tanks during tank
loading.  Without any control device,  these emis-
sions of hydrogen  chloride vapor are dense enough
to violate most air pollution ordinances regard-
ing opacity.  The opacity can be reduced to a
negligible amount by bubbling  the displaced tank
vapors through a  simple  perforated pipe into the
•water or  caustic soda.
                           SPRAY TOWERS AND SPRAY CHAMBERS

                           Interphase contact in spray-type absoroex.-  s
                           achieved by dispensing the liquid in the form
                           of a spray and passing the gas through this
                           spray.  In order to present a large liquid sur-
                           face available for  contact, sprays  of droplets
                           ranging in size from 500 to 1, 000 microns are
                           necessary.  Fine droplets require, however,
                           high pressure drop across the spray nozzles,
                           and there is danger of liquid entrainment at all
                           except very low gas velocities.

                           In a simple  countercurrent spray tower "where
                           the liquid is sprayed down from the top and the
                           gas passes upward through the spray, absorp-
                           tion equivalent to one transfer unit is  about
                           all that can  be expected.  Unless the diameter-
                           to-length ratio is very small, the gas will be
                           •well mixed with the spray, and true counter-
                           current flow will not be realized.   Higher gas
                           velocities without  excessive  entrainment  can
                           be obtained  -with a centrifugal-type spray cham-
                           ber, whereby the spray droplets are forced to
                           the chamber walls by the centrifugal action
                           of tangentially entering gas before  they can
                           be carried out the top of the  chamber.  With
                           this arrangement, there is a  crossflow type
                           of contact, and the degree  of  contact is lim-
                           ited to about one theoretical plate or transfer
                           unit.

                           Spray chambers or towers have been used
                           extensively for control of particulate matter
                           but, according to Sherwood and Pigford (1952),
                           their use for pure  gas absorption seems to be
                           limited to air conditioning  or deaeration of
                           water  where very few transfer units are re-
                           quired. These chambers may also be used
                           for  some highly soluble gases -when the de-
                           gree of required removal is small, but,  in
                           air  pollution control work, this type of oper-
                           ation is not common. They have been used
                           as precleaners for  particulate removal from
                           gas streams where other devices are used
                           for  ultimate control of air pollution.
                           VENTURI ABSORBERS

                           Like spray towers and spray chambers, equip-
                           ment using the venturi principle is primarily
                           used for removing particulates from gas streams,
                           though it has some application to gas absorption.
                           In gas absorbers, the necessary interphase con-
                           tact is obtained by differences between the ve-
                           locity of gas and liquid particles,  and by turbu-
                           lence created in the venturi throat.  Dispersion
                           in venturi devices is achieved in two ways:  By
                           injecting the liquid into the gas stream as it
                           passes through the venturi,  as shown in Figure
                           157,  or by admitting the  gas to the liquid stream

-------
                                      Gas Absorption Equipment
                                                                                                  229
as it passes  through the venturi,  as shown in
Figure  158.  In the  latter case,  the venturi is
also a vacuum-producing device and inspirates
the gas  into the venturi throat.  With both types,
a gas-liquid  separation chamber is necessary
to prevent entrainment.  This can be a simple
tank,  the stream from the venturi tube im-
pinging  on the liquid surface,  or,  more effi-
ciently,  a cyclone-type separator.

For the unit  shown in  Figure 157,  the gas ve-
locities in the venturi throat range from 200 to
300 feet per  second, and the liquid is injected
into the stream at a rate of  about  3 gpm per
1, 000 cfm of gas handled.  These  units are
designed  specifically for collection of submi-
cron particulate matter,  and utilize high horse-
power.   For the liquid-jet eductor types,  the
liquid consumption is  50 to 100 gpm per 1, 000
cfm of gas handled at  a draft of 1  inch  of  water.
The liquid-jet eductor types are capable of de-
veloping drafts  up to 8 inches  of water at high-
er liquid flow rates.  They find application
principally for the absorption  of soluble gases,
but are  also used for collection of particulate
matter larger than 1 or 2 microns in  diameter.
Venturi units obtain a  high degree of liquid-gas
mixing but have a disadvantage of  a relatively
short contact time.  Various literature sources
                             ft2/hr
                        DISCHARGE
           Figure 158.   Venturi  Iiquid-jet
           eductor-type  absorber  (Schutte
           and Koerting  Company,  Cornwells
           Heights,  Penna.).
have indicated a high efficiency of absorption
for very soluble gases  such as sulfur dioxide
and ammonia; however, for oxides of nitrogen
where contact time is of utmost importance,
Peters  (1955) reports efficiencies of absorp-
tion of from 1 to 3 percent.   Because of the
high degree of efficiency of venturi scrubbers
for particulate removal, they seem desirable
for use with a dirty gas stream that also con-
tains  a highly soluble gas that must be removed.
A major disadvantage of venturi units is the
high pressure drop (often as  high as 30 inches
of water) -with attendant high power require-
ments for operation.
NOTATIONS

A    -  surface separating hot and cold media,
       ft2
C    =  specific heat,  Btu/lb-°F
D    =  outside diameter tube, ft
D^   =  inside diameter tube, ft
D    =  diffusion  coefficient,
f    =  friction factor
g    =  acceleration of gravity, 64. 4 ft/sec-sec
G    =  mass velocity of flow, Ib/hr-ft
G-,   =  mass velocity through baffle opening,
       Ib/hr-ft2
GC   =  maximum cross flow velocity,  Ib/hr-ft
Ge   =  weighted  mass velocity, GC x  G^,  Ib/hr-
       ft2
Gj   =  mass velocity inside the tube,  Ib/hr-ft
h    =  coefficient of heat transfer, Btu/hr-ft2- °F
k    =  thermal conductivity, Btu/hr-ft2- ° F
K    =  coefficient of mass transfer, Ib moles/
       hr-ft  atmospheres
L    =  tube length,  ft
Mm =  molecular weight of mixture (vapor plus
       inert gas)
MV  =  molecular weight of vapor
PC   =  partial pressure of vapors at tc, atm
PV   =  partial pressure of vapors at tv, atm.
       logarithmic mean of  the vapor pressures
       at the interface and at the vapor stream,
       atm
P    =  total pressure on system, atm
q    =  quantity of heat,  Btu/hr
tc   =  condensate temperature,  °F
t    =  vapor temperature,  °F
tw   =  water temperature,  °F
UG   =  condensing coefficient for pure vapor be-
       tween tc and tw,  Btu/hr-ft2-°F
w    =  rate of flow, Ib/hr
X    =  latent heat, Btu/lb
|j.    =  viscosity at average  temperature,  Ib/hr-ft
(J.,   =  viscosity at average  film temperature,
       Ib/hr-ft
fj-w   =  viscosity  at tube wall temperature,  Ib/hr-ft
p    -  density at average fluid temperature,  Ib/ft

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                                              CHAPTER 6
                                   METALLURGICAL  EQUIPMENT
                                            FURNACE TYPES
                       JOHN A.  DANIELSON, Senior Air Pollution Engineer
                                    STEEL-MANUFACTURING PROCESSES
                      WILLIAM F.  HAMMOND,  Senior Air Pollution Engineer
                         JAMES T. NANCE,  Senior Air Pollution Engineer
                        KARL D. LUEDTKE,  Senior Air Pollution Engineer
                        JOEL F.  NENZELL,  Senior Air Pollution Engineer
                                            IRON CASTING
                      WILLIAM F.  HAMMOND,  Senior Air Pollution Engineer
                         JAMES T. NANCE,  Senior Air Pollution Engineer
                            SECONDARY BRASS- AND BRONZE-MELTING PROCESSES
                      WILLIAM F.  HAMMOND,  Senior Air Pollution Engineer
                         JAMES T. NANCE,  Senior Air Pollution Engineer
                    EMMET F. SPENCER,  Intermediate Air Pollution Engineer*
                                SECONDARY ALUMINUM-MELTING PROCESSES
                      WILLIAM F.  HAMMOND,  Senior Air Pollution Engineer
                         HERBERT SIMON, Senior Air Pollution Engineer
                     JOHN E.  WILLIAMSON,  Principal Air Pollution Engineer
                        JOEL F.  NENZELL,  Senior Air Pollution Engineer
                                    SECONDARY  ZINC-MELTING PROCESSES
                         GEORGE  THOMAS,  Senior Air Pollution Engineer
                                            LEAD REFINING
                        JAMES T.  NANCE, Senior Air Pollution Engineer
                        KARL D. LUEDTKE,  Senior Air Pollution Engineer
                                     METAL SEPARATION PROCESSES
                         JAMES T.  NANCE,-Senior Air Pollution Engineer
                    EMMET F. SPENCER,  Intermediate Air Pollution Engineer*
                                             CORE OVENS
                         GEORGE THOMAS, Senior Air Pollution Engineer
                                  FOUNDRY SAND-HANDLING EQUIPMENT
                     EDWIN J.  VINCENT, Intermediate Air Pollution Engineer!
                                         HEAT TREATING SYSTEMS
                     JULIEN A. VERSSEN,  Intermediate Air Pollution Analyst

i-Now with FMC Corporation, 633  Third Avenue, New York, N. Y.
 Now with the  Environmental Protection Agency, Research Triangle Park,  N.  C.

-------
                                              CHAPTER 6
                                  METALLURGICAL  EQUIPMENT
Efficient control of air contaminants from metal-
lurgical furnaces has been achieved only in re-
cent years.  Since most of these furnaces discharge
high-temperature effluents  containing submicron-
size dusts and fumes, these effluents must some-
times  be  cooled and often further conditioned be-
fore ducting to a control device.  The control device
must be one capable of high-efficiency collection
of submicron particles.

 This chapter discusses these control devices and
the  air pollution problems encountered in steel,
iron,  brass,  aluminum, zinc,  lead,  and metal
 separationproces ses. Processes related to met-
allurgical operations such  as manufacture of sand
 cores, foundry sand-handling equipment, and heat
treating systems-will be  discussed near the  end of
this chapter.


For those not acquainted -with the  many types of
melting furnaces,  the  first part of this chapter
describes briefly the more  common furnaces and
their  principles  of operation.   The air pollution
aspects  of  these furnaces  are not discussed im-
mediately since these problems are usually a func-
tion of the specific melting process and not of the
type of furnace used.
            FURNACE  TYPES

REVERBERATORY FURNACE
A reverberatory furnace operates by radiating heat
from its burner flame, roof,  and  walls onto the
material heated.  This type of furnace was  devel-
oped particularly for melting solids  and for refin-
ing and heating the resulting liquids.  It is gen-
erally one of the least expensive methods for melt-
ing since the flame and products of combustion
come in direct contact  -with the solid and molten
metal.   The  reverberatory furnace usually con-
sists of a shallow, generally rectangular, refrac-
tory hearth for holding the metal  charge.  The fur-
nace is enclosedby vertical side  walls and covered
with a low, arched,  refractory-lined roof.  Com-
bustion of fuel  occurs  directly above  the molten
bath; the walls  and  roof receive radiant heat from
the hot combustion products and, in turn, reradiate
this  heat to  the surface of the bath. Transfer of
heat is accomplished almost entirely by radiation.

Reverberatory furnaces are available in many types
and designs,  depending  upon specific job require-
ments.  Probablythe largest of the reverberatory
furnaces is the open-hearth furnace,  widely used
in the manufacture of  steel.  This furnace oper-
ates in conjunction with two heat regenerators con-
sisting  of brick checkerwork; these  remove  the
heat from the effluent and transfer it to the incom-
ing air (Figure 159).  The transfer is accomplished
by a system of butterfly valves,  which allows the
furnace gases to pass through one set of checker-
work, giving up  heat, -while  the incoming combus-
tion air  passes  through the second set of checker-
work, taking up  heat.  Periodically the valves  are
reversed,  which  allows incoming combustion air
to preheat in the first set  of checker-work -while
the  furnace  gases are heating the second regen-
erator.   The charge  is introduced through refrac-
tory-lined doors  in the front -wall; finished steel
and slag are removed through a taphole in the rear
wall. Heat is provided by passing a luminous flame
with excess air over the charged mate rial.  Details
of operation in the production of steel -with the open-
hearth furnace  are described later in  this chapter.
 AIR PORT
 GAS PORT

 REGENERATIVE
 CHAMBERS
                                         AIR PORT
   GAS PORT
REGENERATIVE
CHAMBERS
 Figure 159.  An  open-hearth furnace (Beaeman, 1947).
Another  type  of reverberatory furnace is the cy-
lindrical furnace, commonly used in the nonferrous
industries  for melting and holding small heats of
aluminum, brass, and various alloys.  Cylindrical
reverberatoryfurnaces are relatively small, usu-
ally rated at 500 pounds of aluminum.  These fur-
naces (Figure 160) are fired through two tangential
nozzles that promote excellent combustion charac-
teristics and provide very rapid melting.  The fur-
nace may be charged through a top opening or through
the end door.   The end door also serves as an ac-
cess to the metal bath for adding alloying materials
or dressing.


Reverberatory furnace designs often use rotary
tilting mechanisms.   A tilting furnace promotes
ease  of metal distribution for  all types of casting
                                                 233

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234
                                 METALLURGICAL EQUIPMENT
         Figure 160.   Gas-fired, cylindrical  reverberatory  furnace (Bulletin No.  6011,  Hevi-Duty
         Heating Equipment  Co.,  Watertown,  Wise.).
operations--permanent mold, die casting, and sand
operations.   Charging is accomplished by means
of a hopper  that acts as  a stack for the exhaust
gases; the metal charge lodges in the lower part of
the hopper where the melting  takes place.  The
furnace is end fired,  and tilting of the furnace is
accomplished by means of an air or hydraulic ram.

Another type  of tilting reverberatory furnace (Fig-
ure  161) normally finds application in nonferrous
metallurgical operations where large heats are re-
quired.  In this  installation, the  furnace is gas
fired tangentially with three burners.

Many other variations and combinations of furnaces
using the reverberatory principle are manufactured
by many firms throughout the United States and are
available  commercially as  prefabricated units.

CUPOLA FURNACE
For  many years the  cupola has been a standard
melting furnace for producing gray iron.  It is also
used to melt or  reduce copper,  brasses,  bronzes.
and lead.  In addition to  its high efficiency, the
cupola is simple in its construction and operation.
Unless  carefully considered, however, its oper-
ation may lead to difficulties because of variations
in quantity and quality of raw metal, fuel,  and air.

The basic equipment for a gray iron-melting oper-
ation consists of the cupola (Figure  162), which is
essentiallya refractory-lined cylinder open at the
top and equipped with  air ports (known  as tuyeres)
at the bottom. Air is  supplied from  a forced-draft
blower.  Alternate charges of metal,  coke, and
limestone are placed on top of the burning coke bed
to fill the  cupola.   The heat generated melts the
metal, which is drawn off through a  tap hole.  The
two principal dimensions of the cupola are its di-
ameter and operating height (charging door to tu-
yeres). The diameter determines the melting ca-
pacity,  and the height affects the thermal efficiency.

Combustion  Air
The control of air at the tuyeres influences  produc-
tion rates,  costs, metal losses, coke ratios, stack

-------
                                           Furnace Types
                                             235
         Figure 161.  Tangentially  fired  tilting reverberatory furnace  (Bulletin No. 6011,  Hevi-
         Duty Heating Equipment Co.,  Watertown,  Wise.).
temperature, physical properties of the metal, and
volume of stack emissions.  Air is required, not
only to furnish oxygen for the combustion of coke,
which supplies  the  heat required for melting the
iron, but also to aid in the potential combustion  of
the carbon, silicon, and manganese in the metal.
The latter function greatly influences the resultant
chemical and physical properties of the metal when
it is poured into the mold (Molcohy, 1950).


Combustion air maybe provided by a positive-dis -
placement-type  blower  or a centrifugal  blower.
The quantity of air theoretically required is deter-
mined primarily by the size of the  cupola, the
melting rate,  the metal-coke ratio, and the metal
temperature.  The actual  air supplied may be in-
creased as much as 15 percent to compensate for
leakage.  Air pressure varies from  8 to 40 ounces
per  square inch,  depending  upon design factors
such as duct-work layout, tuyere geometry, and the
height of the  bed through which the air must be
forced.  Automatic  controls  are frequently  in-
stalled to maintain a constant-weight flow of air.

Methods of Charging
Various  methods  of charging materials  into the
cupola are used.   The  smaller cupolas are  fre-
quently charged by hand while larger units may be
charged  with skip hoists with the various types  of
cars, buckets, cranes,  or trolleys.   Charging and
melting is a continuous operation.

Preheating Combustion Air

In order to increase the efficiency of a cupola, three
methods  are  available for preheating combustion

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236
METALLURGICAL EQUIPMENT
 SPARK
 ARRESTER
 LINING
  SHELL
                      TAPPING SPOUT
                    BOTTOM PLATE
                      BOTTOM
 Figure 162.  A cupola  furnace (American Foundrymen 's
 Association,  1949).
air.   In  the  Moore  system,  a heat exchanger is
used to transfer some of the waste heat of the stack
gases to the incoming combustion air.  The Whiting
system uses a  separate external heater for the
combustion air.   The Griffin system passes the
stackgases through a chamber where air  is intro-
duced  and the  CO is  burned to CO2.  The gases
then pass through a heat exchanger to preheat the
combustion air.
ELECTRIC FURNACE

Major advantages of the electric furnace over fuel-
fired furnaces are furnace atmosphere control and
high-temperature  operation.   Temperatures as
high as 6, 000°Fare possible for special processes.

The electric furnace has three functions (Porter
1959):

1.   Synthesis of compounds not available  in the
     natural state by fusing selected raw materials,

2.   purification of ores,

3.   alteration of crystalline structure of ores hav-
     ing a satisfactory chemical purity but  an un-
     desirable crystal structure.

There  are four types of  electric furnace:  Direct-
arc, indirect-arc,  resistance, and induction. Each
of these types will be discussed briefly.
                     Direct-Arc Furnace

                     In the direct-arc  furnace,  many and  varied ar-
                     rangements are used to heat the metal charge, but
                     radiation between arc and  the metal bath is the
                     principal method.  Here, the heat is  generated by
                     radiation from the arc as well as from the resis-
                     tance heat effect -within the bath, as shown in  Fig-
                     ure 163.  Graphite and carbon electrodes are  usu-
                     allyused and are  spaced just below the surface of
                     the slag cover.  The current passes from one elec-
                     trode through the slag, the metal charge, the slag,
                     and back to the other electrode. In some arrange-
                     ments, the  current is  carried  from the  metal
                     charge to the hearth. The slag serves a protective
                     function by shielding the metal charge from vapor-
                     ized carbon and the extremely high temperatures
                     at the arc.


                     Indirect-Arc Furnace

                     In the indirect-arc furnace,  the metal charge is
                     placed below the electrodes,  and the arc is formed
                     betv/een the electrodes  and above  the  charge (Fig-
                     ure  163).  Indirect-arc furnaces are used mainly
                     in the steel industry.  One of the common  smaller
                     furnaces  is  the  indirect-arc rocking furnace, in
                     which an automatic ' rocking action of  the furnace is
                     employed to  ensure a homogeneous melt.  This is
                     done by mounting the refractory-lined, steel shell
                     on cog bearings so that the furnace may be rocked
                     through a 200" range.  Radiated heat from the in-
                     direct arc, and conduction from the preheated re-
                     fractory  lining initially melt small scrap, form-
                     ing a pool of molten metal at  the bottom of the  fur-
                     nace.  Then the rocking action is initiated,  and the
                     molten metal washes against the refractory, pick-
                     ing up additional heat, -which is transferred  by  con-
                     vection and radiation to the  larger pieces of metal.
                     During the heat,  the rocking action is advanced
                     gradually to avoid a sudden tumbling of cold metal,
                     which could  fracture the graphite electrodes.
                                           ELECTRODES.
                       DIRECT
                                        ^CHARGE
INDIRECT
                           Figure  163.  Principles of operation
                           of  two  types of arc furnaces (Porter,
                           1959).

-------
                                           Furnace Types
                                            237
Induction Furnace
Resistance Furnace
The induction furnace consists of a crucible with-
in a water-cooled copper coil (Figure 164).  An
alternating current in the coil around the crucible
induces eddy currents in the metal charge and thus
develops heat'within the mass of the charge.  The
furnace is used for the production of both ferrous
andnonferrous metals and alloys, generally from
scrapmetal. It provides good furnace atmosphere
control and can be used for large-volume produc-
tion of high-purity materials.
Three varieties of resistance furnaces are illus-
trated in Figure  165.  The resistance furnace is
essentially a refractory-lined chamber •with elec-
trodes,  movable  or fixed,  buried in the charge.
It is characterized by its  simplicity of design and
operation.  The charge itself acts as an electrical
resistance that generates heat.

The resistance furnace is used in the production
of ferroalloys (ferrochrome,  ferrosilicon,  and
others),  cyanamide, silicon carbide,  and graphite,
and in hardening and tempering tools and machine
parts.
           CHARGE
                               CHARGE-
         Figure  164.   Principles of oper-
         ation of  an  induction furnace
         (Porter,  1959).
CRUCIBLE  FURNACE

Crucible  furnaces,  used to melt  metals having
melting points below 2,500°F are usually con-
structed with a shell of welded steel lined •with re-
fractory materials.  Their covers are constructed
of materials similar to the inner shell lining and
have  a  small hole  over the crucible for  charging
metal and exhausting the products  of combustion.
The  crucible  rests on a pedestal in  the center of
the furnace and js commonly constructed of a re-
fractory material such as clay-graphite mixtures
or silicon carbide.  Crucibles are made in several
shapes  and sizes for melting from  20 to 2, 000
pounds, rated in red  brass.

Crucible furnaces are classified as  tilting, pit,  or
stationary furnaces.   All types are provided with
one or more gas or oil burners mounted near the
                     •ELECTRODE
                                                                ELECTRODE'
                    Figure 165.  Principles  of operation of three types  of  resistance
                    furnace (Porter,  1959).

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238
                                  METALLURGICAL EQUIPMENT
bottom  of the unit.  Flames are directed tangen-
tially around the inside of the furnace.   The cruci-
ble is heated both by radiation and by contact with
the hot gases.
Tilting Furnace

The tilting  crucible furnace  (Figure  166) is pro-
vided with devices for affixing the crucible to the
furnace so that the furnace may be tilted with the
crucible when the metal  is  poured.   The entire
furnace is mounted on trunnions,  around which the
furnace may be tilted.  The tilting mechanism can
be operated manually, hydraulically, or electrically.
    Figure 166.  Tilting crucible  furnace (Lind-
    berg Engineer ing Co.,  Downey,  Calif.).
 Pit Crucible

 The pit crucible furnace derives its name from
 its location. The top of the furnace is near floor
 level,  which facilitates charging of the metal to
 the furnace and removing of the crucible for pour-
 ing.  Pouring  is usually accomplished by using
 the same crucible as  a  ladle.   The furnace cover
 is provided with rollers or swinging mechanisms
 for easy removal.

 Stationary Crucible

 The stationary crucible furnace is almost identical
 to a pit furnace  except that it is not sunk in a pit.
 These fur ,iaces are commonly used as holding fur-
naces, and the metal is poured by dipping with hand
ladles.  Pouring may also be accomplished by re-
moving the crucible and using it as a ladle.
POT FURNACE

Pot furnaces are used to melt metals with melting
temperatures below 1, 400 °F.  These furnaces may
be  cylindrical or rectangular  and consist of an
outer shell lined with refractory material, a com-
bustion chamber, and a pot.  The pots are made
of pressed steel, cast steel,  or cast iron -with
flanged tops.  The  flange  rests on the furnace
wall,  holds  the pot  above the furnace  floor,  and
seals  the  contents  of  the pot from the products
of combustion of the fuel  used.  The shape  of
the pot depends  upon  the  operation to be  con-
ducted.  Large rectangular  furnaces, general-
ly called kettles, are used to  melt large amounts
of metal for dipping operations, such as galvaniz-
ing.  For melting large castings,  shallow, large-
diameter pots are  used.  When ingots or other
small pieces of metal are to be melted, deep pots
are used to promote better heat transfer.  Pot
furnaces are usually emptied by tilting, dipping,
or pumping.   A small pot furnace is shown in
Figure 167.  Combustion equipment ranges from
    Figure 167.  A gas-fired  small  pot  furnace
    (Lindberg Engineer ing Co.,  Downey,  Calif.).

-------
                                 Steel Manufacturing Processes
                                                                                                239
simple atmospheric-type burners located directly
below the pot to premix-type burners tangential-
ly fired as in crucible furnaces.  The larger ket-
tles  are generally provided with many small
burners along both sides of the pot.
  STEEL-MANUFACTURING PROCESSES

Steel is  a crystalline alloy,  mainly  of iron and
carbon,  which attains greater hardness  when
quenched from above its critical temperature than
when cooled slowly.  Carbon is the  most important
constituent because of its effect on the strength of
the steel and its ability to harden.  Other constitu-
ents  that   may  be  present as impurities or as
added alloying elements  include manganese,  sili-
con, phosphorus, sulfur, aluminum, nickel, chro-
mium, cobalt, molybdenum, vanadium, and copper
(Begeman,  1947).

Steel is  made from  pig iron  and scrap steel by
oxidizing the impurities,  reducing the  iron oxides
to iron,  and adding the desired alloying constitu-
ents.  The two common steel-refining processes
are:  (1)  The basic process,  wherein oxidation
takes place in combination with  a strong base such
as lime; and (2) the acid  process,  wherein oxida-
tion takes place without the base addition.  The
two processes have the common pur pose of remov-
ing the undesirable elements  in the metal by the
chemical reaction of oxidation reduction. Depend-
ing upon the alloy being produced, the elements
removed from a melt maybe silicon, sulfur, man-
ganese, phosphorus,  or carbon.   These elements
are  not  removed by direct chemical reaction but
by indirect reaction.  Forabasic refining process,
limestone is added as a flux,  and iron  ore  or mill
scale  as an oxidizing agent.  The reactions may
be shown as follows (Clapp and Clark, 1944):
            CaCO,
                        -*- CaO   +  CO?
 CO2     +  Fe
 C
 Fe3C
            2FeO
         +  FeO
         +  FeO
                        -*• FeO   +  CO

                                  +  2Fe
                           CO    +  Fe
                           CO
                                  +  4Fe
 3SiO2   +  2FeO

 Mn      +  FeO

 MnO    +  SiO
2Fe3P
               2

            8FeO
                        — (FeO)2 •   (Si02)3 (Slag)

                        -» MnO   +  Fe
MnO   '   SiO2 (Slag)

(FeO)  •   P2O5 +
                                                    Sulfur is partially removed in the folio-wing man-
                                                    ner, CaO + FeS-^CaS + FeO.   The resulting CaS
                                                    is taken up by the slag.

                                                    For an acid refining process the sequence of reac-
                                                    tions can be shown in a similar manner as  follows
                                                    (Clapp and Clark, 1944):
                                     20,
                                                                                2FeO
                                                     2Fe

                                                     3Fe

                                                     Si

                                                     Si

                                                     Mn

                                                     Mn

                                                     4C

                                                     C
                                                     The metallic oxides and  silicon then form slags
                                                     according to the equations:


Fe3°4


" Oi^T

* MnO


T O.F e^J
+ ZFe
+ 3FeO
+ Fe
+ 3Fe
                                                     FeO

                                                     2FeO

                                                     MnO

                                                     2MnO
                                     SiO2

                                     3SiO
                            FeO

                            (FeO)2 •

                            MnO

                            (MnO)., '
                                                                                          SiO-,
Steel-refining processes are usually accomplished
in the open hearth furnace, the electric furnace,
or the Bessemer converter.

Open-hearthfurnaces have an approximate range
of 40  to 550 tons'  capacity  per heat with most
falling in the 100- to 200-ton range.  Because of
the large capacities of these furnaces,  they lend
themselves to large-volume steel production.

The three types of electric furnaces used are the
direct-arc,  the indirect-arc,  and the induction.
Electric furnaces are most often used where only
small quantities of pig iron are readily available
and where remelting of steel scrap, or small heats
of special alloys are  required.  Sometimes these
furnaces are used with open-hearth furnaces. In
such cases, the steel is first processed in an open-
hearth furnace  and is then further refined or al-
loyed in an electric furnace.

Still in limited use today is the Bessemer  con-
verter.  It consists  of a  pear-shaped  vessel or
converter, mounted on trunnions and easily tilted
for charging and pouring.   Oxidation  of manga-
nese,  silicon, and carbon is accomplished by blow-
ing air through the molten metal.  Converters have
been largely replaced owing to the increased pro-
duction rates achieved by the open-hearth and elec-
tric furnaces.

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240
                                  METALLURGICAL EQUIPMENT
In I960  over 4 million tons of steel (2. 7 percent
of the total production) was produced by a recent-
ly developed process called the oxygen process.
This  is  similar to the Bessemer process  in that
an oxidizing gas, oxygen instead of air in this case,
is blown  through the molten metal.  This oxygen-
blowing process can be used as a rapid source of
heat control to increase the temperature of the
furnace  bath or may be  used to refine the metal
by oxidizing  the undesirable elements in the bath.
The  principal advantage of this process is that it
shortens  the refining time and thus reduces pro-
duction costs.

In the oxygen process, pure oxygen is immediate-
ly available to promote  oxidation of the impurities
in the bath.  If oxygen is used to reduce the  carbon
content,  then carbon monoxide and iron oxide  are
formed,  some oxygen remaining in the bath. Fig-
ure  168  shows  this relationship for various bath
carbon percentages.   In  the  oxygen process,  the
oxygen also reacts at a slower rate with other ele-
ments such as silicon, manganese,  and chromium
to reduce the content of these elements in the mol-
ten bath.

Steel-making capacity in the United States by type
of furnace is depicted in Table 64.   In  I960 over
85 percent of the steel-making operating capacity
100
80
60
40
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OXYGEN
TO CO
OXYGEN TO
SLAG, Fed
OXYGEN TO
STEEL, 0
   '0 02    0 04 0.06   01     0.2     0406
                BATH CARBON, percent

 Figure  168.  The oxygen reaction  in molten steel
 (Obrzut, 1958).
was represented by 906 open-hearth furnaces,  10
percent, by 301 electric furnaces,  and 5 percent,
by 31 Bessemer converters and 12 oxygen process
furnaces. Total operating capacity was 148, 57 1, 000
tons.
   Table 64.  NUMBER AND CAPACITIES OF
      STEEL FURNACES OPERATED IN
UNITED STATES,  I960 (Steel Facts, American
 Iron and Steel Institutes, New York, New York)
Furnace type
Open hearth
Electric
Bessemer
Oxygen process
Number
906
301
31
12
Capacity, tons
126,621, 630
14, 395, 940
3, 396, 000
4, 157, 400
The  air  contaminants vented from steel-melting
furnaces include gases, smoke, fumes, and dusts.
The  quantities of these contaminants in the efflu-
ent gas stream depend upon the types of material
charged  to  the furnace.  The gaseous emissions
result from the combustion of fuels and other com-
bustible  contaminants in the furnace charge and
from the  refining process.  Smoke emissions re-
sult from incomplete combustion of the combusti-
bles  in the furnace charge or  of furnace fuels.
Particulate emissions  originate partially from dirt
and impurities in the charge, but the major quantity
results from the  refining process.

A  study  of the chemical reactions of the refining
processes reveals that a large portion of the par-
ticulate  matter is emitted from steel furnaces in
the form  of metallic oxides. These characteris-
tics are illustrated in Table 65,  where the results
of a spectrographic analysis of the particulate dis-
charge from an open-hearth furnace are given, and
in Table  66,  which gives  a  typical analysis of the
particulate  discharge  from an  electric-arc fur-
nace.  These fume emissions or metallic oxides
are very small,  65 to 70 percent falling  into the
0- to 5-micron range.   Table  67 shows a size
analysis  of the particulate emissions from  an open-
hearth furnace and  two electric-arc furnaces
along with other  data.  For  a  visual concept of
particle  size and shapes,  electron  photomicro-
graphs of fumes from an electric-arc furnace and
an open-hearth furnace are shown in Figures 169
and 170.


OPEN-HEARTH  FURNACES

The open-hearth  furnace, which features the re-
generative principle,  •was  invented  by William
Siemers  in 1858.  Although many improvements

-------
                                  Steel Manufacturing Processes
                                                                                                241
 Table 65.   SPECTROGRAPHIC ANALYSIS OF
PARTICULATE DISCHARGE FROM AN OPEN
            HEARTH FURNACEa
Element
Fe
Zn
Na
K
Al
Ca
Cr
Ni
Pb
Si
Sn
Cu
Mn
Mg
Li
Ba
Sr
Ag
Mo
Ti
V
Approximate amount, %
Remaining amount
10 to 15
1 to 2
1 to 2
5
5
2
2
5
5
1
0. 5
0. 5
0. 1
Trace
Trace
Trace
0. 05
Trace
Trace
0. 05
 aThese data are qualitative only and require
  supplementary quantitative analysis for actual
  amounts .
    Table 66.  TYPICAL EMISSIONS FROM
        AN ELECTRIC-ARC FURNACE
                (Coulter,  1954)
Component
Zinc oxide (ZnO)
Iron oxides
Lime (CaO)
Manganese oxide (MnO)
Alumina (Al^Oj)
Sulfur trioxide (SO-})
Silica (SiO2)
Magnesium oxide (MgO)
Copper oxide (CuO)
Phosphorus pentoxide (PzOc)
Weight %
37
25
6
4
3
3
2
2
0.2
0.2
and refinements have been made since then,  the
process remains essentially the same.  There  are
roughly four methods of making basic open-hearth
steel in the United States.  These are classed  ac-
cording to the iron-bearing materials in the charge
as follows  (Kirk and Othmer,  1947):

1.  Hot metal (pig iron) and molten  steel.  By this
    method, iron from the blast furnace, and steel
    from the  Bessemer converter are refined in
    the open-hearth furnace.
2.   Cold steel scrap and cold pig iron.  This com-
    bination is  used by plants that have access to
    supplies of inexpensive scrap and do not have
    a blast furnace.

3.   All steel  scrap,  This process is uncommon
    in the American steel industry.

4.   Steel scrap and molten pig iron.  Most of the
    integrated steel plants use this method, which
    is the predominant process in the United States
    and Canada.

In the last method, a typical initial charge consists
of 55  percent  cold pig iron and 45 percent steel
scrap.  Limestone and iron ore, equal in quanti-
ty to approximately 7 and 4 percent, respectively,
of the total weight of the  cold metal charged,  are
also added. If molten pig iron cannot be obtained
in sufficient quantity to complete the initial charge,
more  cold pig is  charged with the scrap, and the
entire mass is heated in the furnace.   The process
continues for approximately 2 hours until the scrap
has reached a temperature of about 2, 500 °F and
has slightly fused.  Molten pig  is then added and
a lively action occurs in which almost all the  sili-
con, manganese,  and phosphorus, and part of the
carbon are oxidized.  The  first three elements
form compounds that slag with iron oxide and join
the iron and lime silicates that are already melted.
The ore acts on the carbon for 3  or 4 hours long-
er while  the limestone forms carbon dioxide and
completes the purification.  The lime boil lasts  for
another 2 or 3 hours and  the heat, is then ready to
be adjusted for final carbon content by adding pig
iron,  ore, or oxygen gas.  The described operation
is commonly divided into three phases consisting
of the  ore boil,  the  lime  boil,  and the working
period.

The heat for the process  is provided by passing a
luminous flame with excess air over the charged
materials. The combustion air is alternately pre-
heated by two regenerating units, which, in turn,
are heatedby the products of combustion discharg-
ing from the furnace.
 The Air Pollution Problem

 Air contaminants are emitted from an open-hearth
 furnace throughout the process,  or heat, -which
 lasts from 8 to 10 hours.  These contaminants can
 be categorized as  combustion  contaminants and
 refining contaminants.  Combustion contaminants
 result  from  steel  scrap, which contains grease,
 oil, or other combustible material, and from the
 furnace fuel.

 The particulate emissions that occur in greatest
 quantities are the fumes, or oxides, of the vari-
 ous metal constituents in the steel alloy being made.
 These  fumes  are  formed  in accordance with the

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242
METALLURGICAL EQUIPMENT
                 Table  67.  DUST AND FUME DISCHARGE FROM STEEL FURNACES
Test number
Furnace data
Type of furnace
Size of furnace
Process wt, Ib/hr
Stack gas data
Volume, scfm
Temperature, °F
Dust and fume data
Type of control equipment
Concentration, gr/scf
Dust emissions, Ib/hr
Particle size, wt %
0 to 5 p.
5 to 10 (Ji
10 to 20 (j.
20 to 44 M.
> 44 |J.
Specific gravity
1

Electric arc
2 ton and 5 tona
3,755

7,541
125

None
0. 1245
8. 05

67.9
6.8
9. 8
9. 0
6. 5
--
2

Electric arc
50 ton
28, 823

23, 920
209

None
0.5373
110. 16

71.9
8. 3
6.0
7.5
6.3
3.93
3

Open hearth
50 ton
13, 300

14, 150
1, 270

None
1. 13
137

64.7
6.79
11.9
8.96
7.65
5
                 aBoth furnaces are vented by a common exhaust system and were tested
                  simultaneously.
 refining chemistry previously discussed.  The
 concentration of the particulates in the gas stream
 varies  over a wide  range during the heat, from
 0. 10 to a maximum  of 2. 0 grains per  cubic foot
 (Allen et al., 1952).  An average is 0.7 grain per
 cubic foot, or 16 pounds per ton of material charged.
 The  test results  in Table 67 for the open-hearth
 furnace show that 64.7  percent of the  emissions
 are below 5 microns in size.  The control device
 selected must, therefore, be capable of high col-
 lection efficiencies on small particles.
                    volume of gases to be vented from the furnace, the
                    maximum fuel input must be known:


                    Example 25

                    Given:
                     60-ton  open-hearth furnace.   Fuel input
                     of U. S.  Grade No. 6 fuel oil per min.
= 35 Ib
 Another serious  air,pollution problem occiirring
 with open-hearth furnace operation is that of fluo-
 ride emissions.   These emissions  have affected
 plants, which in turn, have caused chronic poison-
 ing of animals.  Surveys have shown that fluorides
 are contained in some iron ores such as those
 mined in southern Utah. Control of fluoride emis-
 sions presents a problem because these emissions
 are in both the gaseous and particulate state.
 Hooding and Ventilation Requirements
 The design parameters for an open-hearth furnace
 control system for duct sizes, gas velocities,  and
 so forth are the same as those to be outlined  for
 the electric-arc furnace. In order to establish the
                    Problem:

                    Determine the volume of gases to be vented from
                    the furnace stack to the air pollution control sys-
                    tem,
                     Solution:

                     1.   Volume  of products  of  combustion  from oil
                         burners:

                         One pound of U. S. Grade No. 6 fuel oil -with
                         theoretical  air  produces  186. 1 scf gas (see
                         Table D6 in Appendix D).
                         V     =  35  x  186.1   =  6, 510 scfm
                           -T \^i

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                                  Steel Manufacturing Processes
                                                                                               243
                                                     f
                                                                                   *».
        Figure  169.  Electron  photomicrographs of fumes from an  electric furnace producing steel
        for  castings (Allen  et al., 1952).
2.
    Volume of air infiltrated through leaks owing
     to reversing valves,  stack dampers, cracks
     in bricks, and so forth:

     Assume the average  150 percent excess air
     (combustion and infiltration) usually found in
     the  stacks  of regenerative furnaces. Theo-
     retical air for 1 pound of U. S. Grade No.  6
     fuel oil is 177.2 scf (see Table D6 in Appen-
     dix D).
V
           =  35 x  177.2 x 1.5 =  9,320 scfm
                                                3.   Total volume at 60 °F to air pollution control
                                                    equipment:
                                                       V     =  V     +  V
                                                        T60      PC      EA

                                                             =  6,510  +  9,320  =  15, 830 scfm
The temperature of the furnace gases leaving
the regenerator will be approximately 1, 300°F.
In some installations,  this heat source is used
to generate steam by delivering the gases to
a waste heat boiler in which the temperature
would be reduced to about 500°F.
 234-767 O - 77 - 18

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244
                               METALLURGICAL EQUIPMENT
      *^
    k*,Ak   _
               • t
          Figure  170.   Electron photomicrographs of  fumes from a cold-metal open-hearth steel
          furnace (Allen et al.,  1952).
4.   Total volume of the air pollution control equip-
    ment at 500°F operating temperature:
VT500=15'83°
460 + 500
460 + 60
=  29,200 cfm
Since  the efficient operation of the open-hearth
furnace requires that all the products of combus-
tion, along with the air contaminants created in the
furnace, aretobe conducted through the regener-
ator and  then to a stack,  it is necessary only to
direct the flow from the stack through suitable
ductwork to the control system.  The size of the
blower must, of course, be increased to overcome
the additional resistance introduced by the control
system.
Air Pollution Control Equipment

Open-hearth furnaces have been successfully con-
trolled by electrical precipitators.  On some in-
stallations,  the  control system has been refined
by installing a waste heat boiler bet-ween furnace
and control device.  In this manner,  heat is re-
claimed from the furnace exhaust gases,  and at
the same time, the gases are reduced in. tempera-
ture to within the design limits of the  control de-
vice.  In Table 68 are shown test results of  a con-
trol system  -wherein the -waste heat  boiler and
electrical precipitator vent an  open-hearth fur-
nace.   This test was made on one of four control
systems installed to serve open-hearth furnaces.
These control systems are shown in Figure 171.

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                                  Steel Manufacturing Processes
                                               245
                           Table 68.  DUST AND FUME EMISSIONS FROM
                           AN OPEN-HEARTH FURNACE SERVED BY AN
                                   ELECTRICAL PRECIPITATOR
                Furnace data:

                 Type of furnace  (constructed
                 1916)

                  Size of furnace, tons

                  Test interval

                  Fuel input
                 Waste heat boiler data:

                  Gas volume, inlet, scfm

                  Gas temperature, inlet,  °F

                  Gas temperature, outlet,  °F

                  Water in waste gas, %

                  Steam production  (average),
                  Ib/hr
Open hearth


63

1 hr during heat working period

Natural gas,  21,000cfh

Fuel oil,  1. 4 gpm
         14,900

          1, 330

            460

             12. 4

          8,400
                 Precipitation data:
                  Gas volume, scfm

                  Dust and fume concentration
                  (dry volume)
                   Inlet, gr/scf
                   Outlet,  gr/scf
                   Inlet, Ib/hr
                   Outlet,  Ib/hr

                  Collection efficiency, %
         14,900
              0. 355
              0. 004
             39.6
              0. 406

             98. 98
 The factors tobe considered in designing an elec-
 trical precipitator to control the emissions from
 an open-hearth furnace are the same as those that
 will be described next.

 Electric-Arc Furnaces

 The electric-arc  furnace  lends  itself  to accurate
 control of temperature and time  of reaction for
 producing desired alloy composition. These advan-
 tages  are achieved because no harmful gases are
 emitted from an electric arc that would otherwise
produce an adverse  effect upon the metal being
 refined. Steel may be produced in an arc furnace
 by either the basic or the acid process.  The fur-
nace  may  be  charged with molten metal from an
 open-hearth furnace (an operation known as duplex-
 ing),  or it may be charged with cold steel scrap.
Owing to  the  close  control that can be achieved,
low-grade scrap can be refined tomeetclose spec-
ifications of the various steel alloys.

 After  the furnace has  been charged -with metal,
 fluxes and other additions required to accomplish
 the refining chemistry  are charged according to
    schedule.  The additions vary depending upon the
    composition of steel desired and the metal charged.
    Lime is usually a basic addition along with others,
    such  as  sand, fluorspar, iron  ore, carbon, pig
    iron,  and other alloying elements.  The operation
    then continues in three phases: (1) The oxidizing
    period, in -which the undesirable elements are oxi-
    dized from the metal and removed as slag,  (2) the
    reducing period, in which oxygen is removed from
    the metal mostly through the reaction with carbon,
    and (3) the finishing period, in which  additions are
    made to bring the alloy within the desired specifi-
    cations.  The make-up of a  typical charge to an
    electric-arc furnace is shown in Table 69.


        Table 69.  TYPICAL CHARGE FOR AN
      ELECTRIC-ARC FURNACE (Coulter, 1954)
Material
Fluxes, carbon, and ore
Turnings and borings
Home scrap
No. 2 baled scrap
Miscellaneous scrap (auto, etc)
Weight %
5
7
20
25
43

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246
                                  METALLURGICAL EQUIPMENT
                  Figure  171.   Electrical precipitators  serving open-hearth  furnaces.
The Air Pollution Problem
Hooding and Ventilation Requirements
The  quantity and  type  of  fumes emitted from an
electric-arc furnace depend upon several factors:
Furnace size, type of scrap, composition of scrap,
cleanliness of scrap,  type of  furnace process,
order of charging materials, melting rate, refin-
ing procedure,  and tapping temperature.   A large
portion of the fumes  generated  in a furnace is re-
tained in the slag; however, sizable quantities  of
fumes escape and are discharged from the  furnace
vent.  Table 70 shows  emission data, which vary
from 4.5 to 29.4 pounds of fumes per ton of metal
melted.  Most  of  the  emissions originate during
the first half of the heat. Figure 172 shows  a curve
of emission rates  during a single heat.
Before the  emissions can be collected they must
first be  captured through some suitable hooding
arrangement at the furnace and must then be con-
veyed to a collection device that has a high collec-
tion efficiency on small particles.

Four  types  of hooding arrangements can be  in-
stalled.  The first is a canopy-type hood, which
is suspended directly over the furnace (Figure 1 73).
A hood such as this has serious deficiencies  in that
it must be mounted high enough above the furnace
to clear  the electrodes and not interfere with the
crane when overhead charging is employed.  As
the distance between  the furnace and hood is in-
creased, the  volume  of air to be inspirated into

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                                   Steel Manufacturing Processes
                                                                 247
                            Table 70.  ELECTRIC-ARC STEEL FURNACE
                                 EMISSION DATA (Brief et al.,  1956)
Case
A


B








C




D
E
F
Rated
furnace
size,
tons
50
75
75
50a
50a
75a
3
3
6
10
10
2^
3
3
3
6
6
18
6
3
Average
melting
rate,
tons/hr
18. 3
23. 5
23. 5
14. 4
13.6
21. 9
1. 5
1. 1
3. 1
6. 6
5. 4
1.5b
1.9
1.6
1.9
2. 6
3. 0
5. 4
4. 1
1. 8
Cycle
time,
hr
4
4
4
4
4
4
2
2

2
2

2
2
2
2.33
2
3
1. 2
1.75
Fume
emission /ton
melted,
Ib/ton
9.3C
18. 6d
--
7.6
6.9
12. 3
12. 6
7.6
10. 4
5. 5
5. 2
13.4
4. 5
5. 8
5. 7
15. 3
12. 8
6. 1
29. 4
12. 7
Furnace process

Basic, single slag


Basic, single slag

Acid, oxygen blow
Acid, oxygen blow

Basic, oxygen blow
Basic, oxygen blow

Acid
Acid
Acid



Acid, single slag
Acid, single slag
                     aRefer to same furnace as case A.
                      Two 2-ton furnaces operating in parallel.
                     GAverage for one 50-ton and two 75-ton furnaces processing
                      normal scrap.
                      Average for one 50-ton and two 75-ton furnaces processing
                      dirty,  sub-quality scrap.
  100
  80
° 60
  40
  20

        10   20   30   40   50   60
                  HEAT TIME, percent
70
    80   90
             100
Figure  172.   Curve showing rate of  fume  emission
during  a  heat  of an electric-arc furnace  (Coulter
1954).
                     the hood also must be increased to achieve satis-
                     factory capture of the furnace emissions.
                     The second hood type (Figure 174) is called a ple-
                     num roof.  Here a flat hood is attached to the fur-
                     nace roof ring and has pickup openings  over the
                     charging  door, the pouring  spout,  and the elec-
                     trode openings. Holes in the top of the hood admit
                     the  electrodes.   This type of hood must have a
                     telescoping or swivel connection,  or both,  to the
                     exhaust system to permit tilting and pouring oper-
                     ations  of the furnace.  For top-charge furnaces,
                     the  hood  must be sectioned and installed with an
                     exhaust system disconnect joint to permit  roof re-
                     moval.  Because of this feature,  these furnaces
                     are  neces sarily uncontrolled during the charging
                     operation.  This  type of hood is shown in Figure
                     175.  The 25-ton furnace with plenum hood is one
                     of three furnaces venting to the baghouse.
                    In the third type of hood, the furnace roof is tapped
                    and vented directly to the exhaust  system, which
                    permits the furnace to serve as its own hood.  With

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 248
METALLURGICAL EQUIPMENT
  Figure 173.  Electric-arc  furnace venting to  a
  canopy-type hood.
this arrangement, air is inspirated through all fur-
nace  openings and vented  directly to the exhaust
system. Here again, the furnace becomes uncon-
trolled when the  roof is removed during  charging.
It is also uncontrolled when tilted during the  pour-
ing operation unless  a telescoping and swivel duct
connection is installed.  Since this type of hooding
results in high effluent gas temperatures  from the
furnace, flame and cinder traps shouldbe installed
on  the  larger  furnaces,  and some provision for
cooling the gas stream may have to be made.   This
is particularly true if the charged scrap  contains
combustible  contaminants.  Depending upon the
materials and type of construction, the duct con-
nections to the furnace may have to be water  jack-
eted for cooling.  Figure  176  illustrates  a roof
tap with a stainless steel duct connection.

A fourth general  type of hood is  known as a side-
draft hood. This hood consists of a large  duct that
extends  from the side of  the furnace to  the area
where the electrodes enter the furnace through the
roof.   Here,  the  duct divides into three  sections
with each section flaring  to wrap approximately
180 degrees  around  each  electrode.  The flared
ends are positioned as closely as possible  to the
electrodes yet sufficient room is  retained to per-
                                                      mit movement  of  the electrode holder.   Smaller
                                                      ducts  extend from the  main duct to the slagging
                                                      door and tapping  spout.  The main duct joint  is
                                                      provided with a swivel and/or telescoping section
                                                      to permit some control during tapping.  No provi-
                                                      sion is made for collection of emissions that may
                                                      leak between the roof and the furnace,  except for
                                                      the use of a  soft sand seal.
                                                     This  system  provides high-velocity  indraft  air
                                                     around the electrodes (1,000 to 2,000 fpm) to cap-
                                                     ture the emissions released around the electrodes.
                                                     The hood over the slagging door captures emissions
                                                     generated from this  point, and the hood over the
                                                     tapping spout provides partial capture.
                                                     A hood should be designed  so that a positive in-
                                                     draft of air through all hood openings will prevent
                                                     escape of fumes.  The design air volume to venti-
                                                     late an electric-arc furnace with an integral hood
                                                     is approximately 2, 500 cfm per ton of charge.  If
                                                     a canopy-type hood is used,  a velocity of 200 fpm
                                                     should be maintained between the  furnace and the
                                                     hood (Committee on Industrial Ventilation,  I960).
                                                     Design figures  such as these must,  however, be
                                                     used with discretion, depending upon the individual
                                                     furnace to be controlled.  Table 71 contains design
                                                     data for  several actual installations.
                   The  duct  system  must be designed to maintain a
                   satisfactory  conveying velocity  for  the  furnace
                   emissions.  These fine metallic fumes can be sat-
                   isfactorily conveyed at a velocity of  3, 500 fpm.
                   Another design feature that must be considered is
                   that  of cooling the  effluent  gas stream to within
                   operating temperature limits for cloth filters. With
                   a canopy-type hood, large quantities of dilution air
                   are taken in through the hood, which effectively
                   reduce the effluent  gas  temperature.   With  the
                   plenum  roof,  direct furnace tap,  and side-draft
                   hoods, however,  there  are  intervals  when the
                   effluent gas  stream temperatures are excessive,
                   and some type of cooling  is required.
                   Cooling may be accomplished by radiation-convec -
                   tion cooling columns, by water-spray nozzles,  or
                   by  dilution air.  In installations where cooling is
                   required only during a short portion of the oper-
                   ating cycle, a dilution air damper can be installed
                   in the exhaust system that automatically opens to
                   prevent the gas  stream's temperature from ex-
                   ceeding the limits of the filter cloth.  The effects
                   of these cooling methods upon duct, fan, and motor
                   selection must be considered in designing the ex-
                   haust system. The introduction  of water into an
                   exhaust system invites  accelerated corrosion.

-------
                      Steel Manufacturing  Processes
249
(left) f74'   ClfSe"fitt!ng P|enum-type hood serving an electric-arc  furnace:

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250
                                  METALLURGICAL EQUIPMENT
             Figure  175.   (Left) electric-arc furnace  with  plenum hood,
             baghouse  (National Supply,  Torrance,  Calif.).
               (right)  venting  to  a
  Figure 176.  Direct roof  tap  on  an  electric-arc
  furnace (Alloy Steel  and  Metals  Company, Los
  Angeles,  Calif.).
 Sometimes,  local opacity regulations cannot  be
 met through the  use of only a close-fitting hood.
 This type of control leaves the furnace uncontrol-
 led during charging and  only partially controlled
 during  tapping.  While  the initial charge may not
 produce large quantities  of emissions, any later
 backcharge usually produces objectionable smoke
 and  fumes.  The  tapping  of  the furnace also pro-
 duces fumes that  escape collection.

 When additional equipment  is needed to control
 emissions created during charging and tapping, it
is  advantageous to select a  design adaptable to
existing plant facilities and compatible with furnace
operations.  A high  canopy hood can meet these
needs if itis located directly over the furnace be-
tween the roof and the crane line.  All roof moni-
tors or exhaust fans nearby  must be  closed and
sealed. The building  must be enclosed to prevent
free movement of wind through the plant.  Cross-
drafts must be kept to  a minimum near the furnace
to prevent  the emissions from being blown away
from the hood.  Free-standing side panels, adja-
cent to  the furnace and extending from near floor
level to crane height, may be required.  The size
of the hood and air volume required  to be exhausted
are determined by using  the  formulas developed
in Chapter  3.  During charging or tapping opera-
tions, the close-fitting-hood control system is not
used and is dampered, and the canopy hood captures
the emissions.  This procedure eliminates the need
for  exhausting  air  from  both hoods at the same
time, and thereby reduces the size of the control
system.  The  canopy hood  should have sufficient
internal volume to prevent spillage of fumes during
the violent bur st of emis sions  created bythe back-
charges.
When more than one  furnace is to be controlled,
the size of the control system can be minimized
by arranging the  furnace melting cycles to allow
only one furnace tapping and charging cycle  or  one
fxirnace melting  cycle to occur  at  any one time.
The control  system  also can be used to vent the
station  where  the  "skulls," or unpoured metal,
are burned out of the ladle.

-------
                                  Steel Manufacturing Processes
                                                                                                   251
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-------
252
                                   METALLURGICAL EQUIPMENT
Air Pollution Control Equipment

Baghouse dust collectors

The baghouse control device must be designed with
features that make its operation compatible with
the operation of the furnace and exhaust system.
The baghouse must have a filter area that efficient-
ly  removes  the  particulate matter from the gas
stream.  The filtering velocity should not exceed
2. 5 fpm.  Since high temperatures are reached
periodically,  Dacron  or glass  fiber are used for
this service.  Dacron can withstand temperatures
up to 275 °F, and glass fiber can withstand tem-
peratures  up to 500°F.  Electric furnace fumes
tend to agglomerate, and the bags must be shaken
sufficiently to remove  the collected fumes from
the cloth surface.  The  temperature of the efflu-
ent gas  stream entering the baghouse must not be
allowed to fall below  the dewpoint,  or blinding  of
the bags results.  This, in turn, reduces the ex-
haust air volume, causing poor pickup of fumes  at
the source.  Blinding  of the bags also makes bag
cleaning more difficult. The baghouse should be
compartmented so that one section at a timecanbe
isolated and bags shaken to allow continuous  sys-
tem operation. It should be equipped with hoppers
that facilitate  the  removal  of  the  collected ma-
terial.  Screw conveyors are frequently installed
on the hoppers as an aid for removing the materi-
al collected.

Control unit assembly must be constructed of ma-
terials that can withstand the temperatures of the
furnace and  the  effluent gas stream.  Provision
should  also be made to  prevent  sparks and burn-
ing material from entering the  collector.

An outline, of some of the design features of bag-
houses that serve electric steel -melting furnaces
is included in Table 71.  Only one of these instal-
lations  was  equipped  for  reverse  air cleaning.
This particular  baghouse has been replaced with
a  conventional shake cleaning unit because of the
high maintenance costs associated with the  re-
verse air cleaning mechanism and because of the
excessive bag -wear.
In Table 72 are shown test results of air pollution
control systems with baghouses serving  electric-
arc  steel-melting furnaces.  The collection effi-
ciencies of the baghouses in tests 1, 2,  and 3 are
within the range of  expected efficiencies for in-
stallations of this type.  In tests 4  and  5 the col-
lection efficiencies are  subnormal, indicating mal-
function of the systems.   This -was  evident  at the
time  of the tests from the visible discharge of
dust and fumes from the baghouse outlets. An in-
vestigation disclosed that those two baghouses had
many defective bags.   The results,  however, are
reported to emphasize the necessity of checking
the validity of tests  such as these.

Electrical precipitators

An electrical precipitator may be used to control
the emissions from an electric-arc  furnace.   The
fundamental design considerations for hooding, air
volume cooling, duct sizing, and fan  selection are
the same as those outlined for baghouse control.
The one major difference pertains to the condition-
ing of the effluent gas  stream.  A baghouse sys-
tem should be designed so that the gas tempera-
ture remains below the maximum operating tem-
perature of the cloth bags  and  above  the  dewpoint.
For an  electrical precipitator, control must be
much more accurate. The apparent resistivity
of the material to be collected must first be de-
termined.   After this is  known, the condition of
the gas stream, and  the temperature and humid-
ity that  will result  in the most efficient collec-
tion canbe determined. Efficient collection usu-
allyfalls within a narrow temperature range, in
which  case the conditioning system must be de-
signed to maintain the effluent gas  stream with-
in that range.   Figure  177 shows the relationship
between temperature, humidity, and collection
efficiency for  an electrical precipitator serving
an electric-arc furnace in a specific installation.
For this particular installation an acceptable ef-
ficiency was not  realized until the gas tempera-
ture was maintained  below 127 °F and the humid-
ity above 49 percent.  Table  73 shows operating
data for two installations of electrical precip-
itators  serving electric-arc furnaces.
One general equation (Brief et al. ,  1956) for ex-
pressing precipitator efficiency is
                E  =   1  -  K
                              L_
                              V
(100)
where
     E  =  collection efficiency

     K  =  precipitation constant (always less than
          unity and dependent upon the resistivity
          of the fume for a specific degree of gas
          conditioning)

     L  =  electrode  length, ft

     V  =  volumetric flow rate, cfm.

This equation shows some of the factors that must
be consideredbefore the control system can be de-
signed. Factors such as efficiency required,  re-
sistivity of fume,  gas conditioning, geometry of

-------
                                    Steel Manufacturing Processes
                                            253
                   Table 72.  DUST AND FUME EMISSIONS FROM ELECTRIC-ARC
                          STEEL FURNACES WITH BAGHOUSE CONTROLS
Test number
Furnace data
Type of furnace

Size of furnace,
tons
Process wt, Ib/hr
Baghouse data
Type of
baghouse
Filter material
Filter area, ft2
Filtering velocity,
fpm
Dust and fume data
Gas flow rate,scfm
Inlet
Outlet
Gas temperature, °F
Inlet average
Outlet average
Concentration,
gr/scf
Inlet
Outlet
Dust and fume
emission, Ib/hr
Inlet
Outlet
Control efficiency,%
Particle size, wt %
Inlet, 0 to 5 n
5 to 10
10 to 20
20 to 40
> 40
Outlet
1

3 -electrode
Direct arc

17
13,700

Sectioned
tubular
Orion
20, 800

1.95


38, 400
40, 600

172
137


0.507
0. 003


166.9
1. 04
99.4

72.0
10.5
2.7
4.7
10. 1
100% < 2 ^
2

3 -electrode
Direct arc

3-1/2
4, 250

Compartmented
tubular
Orion
5, 540

1.78


10, 300
9, 900

135
106


0.346
0.0067


30.5
0. 57
98. 1

57.2
37.8
3.4
1.6
0
100% < 1 p.
3

Two, 3-electrode
Direct arc

4/4
3, 380/5, 131

Sectioned
tubular
Orion
11, 760

1.20


12, 960
14, 110

129
121


0. 398
0. 0065


44. 2
0. 79
98. 2

63. 3
17. 7
8. 0
8. 1
2.9
100% < 2 |j.
4

3-electrode
Direct arc

14
17,650

Compartmented
tubular
Orion
25,760

1. 23


18, 700
31,700

186
139


0. 370
0. 0158


59.3
4.3
92. 7a

59.0
33. 1
4.9
3.0
0.0
72% < 5 HL
5

3-electrode
Direct arc

19
22, 300

Sectioned
tubular
Orion
26, 304

1. 75


42, 300
46, 100

167
153


0. 462
0. 047


167. 5
18.5
88. 9a

43.3
17.7
6.4
14. 60
18. 0
75% < 5 [i
 aAn investigation disclosed that poor efficiencies •were due to defective bags in the baghouse.
precipitator,  and others  should all be discussed
•with a manufacturer of electrical precipitators be-
fore  the design  of the control system is formu-
lated.  General  design information on electrical
precipitators has been discussed in Chapter 4.
Water scrubbers

Water scrubbers have been used in many process-
es in which  some  contaminant must be removed
from a gas stream.   These same  scrubbing meth-
ods have been used to control the emissions from
electric-arc  steel  furnaces with varied results.
Table  74 shows  the results of six tests on water
scrubbers serving electric-arc steel-melting fur-
naces.   Wet collectors  collect only the larger
particles and allow the submicron particles to pass
through  and be discharged to the atmosphere.
These submicron particles cause the greatest dif-
fusion of light and thus produce the greatest  visual
opacity.   A venturi scrubber can be operated at
greater  efficiencies than  those  achieved by the
scrubbers depicted in  Table 74.  A basic disad-
vantage  of many scrubbers is that their efficien-
cy of collection is proportional to their power in-
put; thus, if a scrubber has the feature of high col-
lection efficiency,  the  power input required to

-------
254
                                   METALLURGICAL EQUIPMENT

61


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a 49
i—
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31 41
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0 85 90 95 1
PRECIPITATOR EFFICIENCY, percent
145 realize this high efficiency is also large. In any
event, the decision to install a scrubber over some
143 other type of control device depends principally
upon the collection efficiency required and the
141 comparative costs of installation and operation.
u-
139 °
ELECTRIC-INDUCTION FURNACE
LU
137 "£
" The electric-induction furnace uses the material
U-
135 a to be heated as a secondary of a transformer.
g When a high-frequency current is applied to the
g furnace coils, an electromagnetic field is set up
£! in the core or space occupied by the metal to be
131 Z r r i
£ melted. This high-density electromagnetic field
,2g induces currents in the metal, caiising it to heat
and melt. These furnaces range in size from 30
127 pounds' to 8 tons' capacity. They are not well
adapted to a refining process and, for the most
125 part, are used for preparation of special alloys,
or for certified true heats, or for investment cast-
ings.
  Figure 177.   Curves showing  effects of variation
  of  the gas stream's temperature and humidity
  upon efficiency o\ a specific  electrical-pre-
  cipitator installation  (Coulter,  1954).
The Air Pollution Problem

The  fume  emissions from an  electric-induction
furnace processing steel alloys  have the same
characteristics as those from electric-arc fur-
naces.  Since  a high degree of  control is exer-
cised in preparing alloys in this type of furnace,
                    Table 73.  OPERATING DATA OF ELECTRICAL-PRECIPITATOR
                      CONTROL SYSTEMS SERVING ELECTRIC-ARC FURNACES
                                          (Brief et al. , 1956)
Case
Operational data
Inlet gas volume, cfm
Inlet gas temperature, °F
Absolute humidity, Ib/lb dry gas
Inlet fume concentration, gr/ft'
Electrical-precipitator data
Type
Rectification
Size

Gas velocity, fps
Gas retention time, sec
Electrode length
electrode length ?
L/VraUo, , bec/lL
volumetric rate
Gas conditioner data

Type
Collection efficiency
A
105, 000
127
0. 045
0. 68a to 1. 35b
High-eff plate
Mech, full wave
30 ducts, 10 in. n
18 ft x 18 ft
3. 9
4. 6
11, 880
6. 8:1

2-stage
evaporative
cooler
97 + %
B
33, 500
80
Ambient
0. 115
Exp rnetal plate
Mech, full wave
19 ducts, 8-3/4 in. x
17 ft 6 in. x 18 ft
2. 3
7. 8
7, 550
13. 6:1

Radiation and
tempering air
cooler
92%
             aAverage for one 50-ton and two 75-ton furnaces processing normal scrap.
             "Average for one 50-ton and two 75-ton furnaces processing dirty,  subquality
              scrap.

-------
                                    Steel Manufacturing Processes
                                            255
                            Table 74.  HYDROSTATIC SCRUBBER DATA
Test
Total number of furnaces
Furnace size, tons
Process wt, Ib/hr
Volume of gases inlet, scfm
Volume of gases outlet, scfm
Gas temperature inlet, °F
Gas temperature outlet, "F
Fume concentration inlet, gr/scf
Fume concentration outlet, gr/scf
Fume emission inlet, Ib/hr
Fume emission outlet, Ib/hr
Collection efficiency, %
A
2
6 and 20
12, 444
17, 500
20, 600
132
89
0. 158
0.055
23. 7
9.71
59. 1
B
1
20
4,720
22, 700
24,600
123
76
0. 0657
0. 0441
12.8
9. 3
27. 3
C
1
6
6,240
20, 700
20,700
110
92
0. 167
0. 102
29.6
13. 2
55. 4
D
2
3 and 3
5, 020
10, 140
10, 860
145
92.5
0. 329
0. 108
28.7
10. 1
65
E
1
50
27, 200
25, 900
29,800
297
99
0. 423
0. 109
94
27. 8
70. 4
F
1
75
43, 900
32, 400
35, 600
281
105
0.966
0. 551
268
168
37. 3
metals  contaminated with  combustible elements
such  as  rubber, grease,  and so  forth are  not
charged to the furnace.  This practice eliminates
the need for control of combustible contaminants.
The quantity of contaminants emitted from induc-
tion furnaces processing steel alloys varies.  The
factors affecting the fume generation include com-
position  of alloy,  method of making the alloy ad-
dition, temperature  of the melt,  and size of the
furnace.  When these factors are controlled, some
steel  alloys can be made without the need of air
pollution control equipment.


Hooding and Ventilation Requirements

Since induction furnaces are relatively small, the
canopy-type hood is readily  adaptable to capturing
the fumes. Recommended hood indraft velocities
vary  from 200  to  500 fpm, depending upon the
hood, furnace geometry, cross-drafts, and tem-
peratures involved.  The following example prob-
lem shows a method of calculating ventilation re-
quirements  for  a canopy-type hood serving an
induction furnace:
Solution:

q = 5.4  A  (m)1/3  (At)5/12  (from Chapter 3)
^         s
where
    q  =  rate of thermal air motion at top of heat
          source, cfm
   A   =  surface area of hot body and face area
    S     of hood, ft2
    m =  diameter  of  crucible,  ft.  For lack of
          proved  experimental values for m, the
          diameter of the moltenmetal (heat source)
          will be used in the operation

   At  =  temperature  differential between hot body
          and room air,  °F.
    q  =  (5.4)(3.14)(2)1/3(2,900)5/12

    q  =  590 cfm
Example 26

Given:

1, 000-Ib capacity electric-induction steel melt-
ing furnace

Pouring temperature =  3,000°F

Diameter of crucible =  2 ft

Surface area of molten metal =  3. 14 ft

Hood height above furnace  =  3 ft

Room air temperature  = 100°F.

Problem:

Determine the minimum ventilation requirements
for the furnace.
The formula used in calculating the ventilation re-
quirements is accurate only for low-canopy hoods
having an area equal to that of the heat source and
having a maximum height of approximately 3 feet
above  the  furnace.   For  high-canopy hoods, the
hood area and ventilation volume must be increased.
Air Pollution Control Equipment

The design considerations for the remainder of the
control system,  including duct-work,  type of col-
lector, and fan and motor selection, are the same
as outlined for electric-arc furnaces.  Figure 178
is a photograph of two induction furnaces served
by a canopy-type hood that vents to a baghouse.

-------
256
METALLURGICAL EQUIPMENT
      Figure 178.  Canopy-type hood serving two  electric-induction  furnaces (Centrifugal  Casting,
      Long Beach, Cal if.).
               IRON  CASTING

Control of the air pollution that results from the
melting and  casting of iron may be conveniently
considered according  to the type of furnace em-
ployed. The  cupola, electric,  and  reverberatory
furnaces are the types most widely encountered.
The air pollutants are similar, regardless of the
furnace used; the primary differences among the
air pollution  control systems  of the various fur-
nace types are to be found in the variations in hood-
ing, and the necessary preparation and treatment
of the contaminated gases from  the furnaces. Es-
sentially, the air pollution problem, becomes one
of entraining the smoke,  dust,  and fumes at the
furnace and  transporting these  contaminants  to
suitable collectors.
                  CUPOLA FURNACES

                  The most widely encountered piece of equipment in
                  the gray iron industry is the cupola furnace.  High
                  production rates are possible and production costs
                  per ton of metal are relatively low.  Despite this,
                  where the product permits, some gray iron found-
                  ries  have substituted reverberatory furnaces for
                  their cupolas rather than install  the air pollution
                  control equipment that cupolas require.   Table 75
                  shows one  manufacturer's  recommendations for
                  operating cupolas.


                  The Air Pollution Problem

                  Air contaminants emitted from  cupola furnaces
                  are (l)gases,   (2) dust and fumes, and  (3) smoke

-------
                   Iron Casting
                                                               257
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-------
258
METALLURGICAL EQUIPMENT
and oil vapor.  The following is a typical cupola
combustion gas analysis:   Carbon dioxide,  12.2
percent; carbon monoxide,  11.2 percent; oxygen,
0. 4 percent; nitrogen, 76. 2 percent.  Twenty to
thirty per cent by weight of the fumes are less than
5 microns in size.  A particle  size analysis of the
dust and fumes collected from gray iron cupolas
is shown in Table 76, as are  some emission rates.
Tables 77 and 78 show micromerograph and spec-
trographic particle  size analysis of two samples
taken from the hoppers of a bag filter serving a
gray iron cupola furnace.   Dust in the discharge
gases  arises from dirt on the metal  charge  and
from fines in the coke and limestone charge.  Smoke
and oil vapor arise primarily from the partial com-
bustion and distillation of oil from greasy scrap
charged to the furnace.

 Hooding and Ventilation Requirements

 One way to capture the contaminants discharged
 from a cupola furnace is to seal the  cupola top
 and vent all the gases to a control system.  A
 second method is to provide a vent in the side of
 the cupola a few feet below the top of the burden
 and vent the gases to a control system.  The con-
 trol system  consists of an  afterburner, a gas-
                  cooling device, and a dust collector, -which is
                  either a baghouse or an electrical precipitator.
                  The system, must be designed to exhaust enough
                  gas volume to remove all the products of combus-
                  tion from the cupola and to inspirate sufficient air
                  at the charge opening to prevent cupola gas  dis-
                  charge at that point.  In addition, the exhaust gas
                  volume must be sufficient to remove the products
                  of combustion from the  afterburner section. In
                  cupolas of large diameter (over 36 in. ),  enclosure
                  of the charge opening -with refractory-lined or
                  water-cooled doors is usually necessary.  These
                  doors  are pneumatically operated  to  open only
                  during the actual  dumping of a  charge into the cu-
                  pola.

                  Even  though a closed top cupola is equipped with a
                  door  to cover the charge opening, it is common
                  practice to design the ventilation unit to provide
                  at least 250 fpm  average indraft velocity across
                  the full open area of the charge  opening.
                  Air Pollution Control Equipment
                  Collection efficiencies of several small-scale con-
                  trol devices on gray iron cupolas are  shown in
                 Table 76.  DUST AND FUME EMISSIONS FROM GRAY IRON CUPOLAS
Test No.
Cupola data
Inside diameter, in.
Tuyere air, scfm
Iron - coke ratio
Process(wt, Ib/hr
Stack gas data
Volume, scfm
Temperature, °F
co2, %
02, %
CO. %
N2, %
Dust and fume data
Type of control
equipment
Concentration, gr/scf
Inlet
Outlet
Dust emission, Ib/hr
Inlet
Outlet
Control efficiency, %
Particle size, wt %
0 to 5 (a.
5 to 10 pi
10 to 20 \i
10 to 44 (j.
> 44 |i
Specific gravity
1

60
-
7/1
8, 200

8, 300
1, 085
-
-
-
-

None


-
0. 913

-
65
-

18. 1
6. 8
12. 8
32. 9
29. 3
3. 34
2

37
1, 950
6.66/1
8, 380

5, 520
1, 400
12. 3
-
-
-

None


-
1. 32

-
62.4
-

17. 2
8. 5
10. 1
17. 3
46. 9
2.78
3

63
7, 500
10. 1/1
39, 100

30, 500
213
2. 8
-
-
-

None


-
0. 413

-
108
-

23. 6
4. 5
4.8
9. 5
57.9

4

56
-
6. 5/1
24, 650

17, 700
210
4. 7
12. 7
0
67. 5

Baghouse


1. 33
0. 051

197
7. 7
96

25. 8
6. 3
2. 2
10. Oa
55. 7b

5

42
-
9.2/1
14, 000

20, 300
430
5.2
11.8
0. 1
67. 3

Elec precip
afterburner

2. 973
0. 0359

184. 7
6.24
96.6

-
-
-
_
-

6

60
-
9.6/1
36, 900

21, 000
222
-
-
-
-

Baghouse


0. 392
0. 0456

70. 6
8. 2
88. 4

-
-
-
_
-

7

48
-
7. 4/1
16, 800

8, 430
482
-
-
-
-

Elec Precip


1. 522
0. 186

110
13. 2
87.7

-
-
-
_
-

  aFrom 20 to 50 |J..
  bGreater than  50 |i

-------
                                            Iron Casting
                                             259
 Table 77.  MICROMEROGRAPH PARTICLE SIZE
 ANALYSIS OF TWO SAMPLES TAKEN FROM A
         BAGHOUSE SERVING A GRAY
           IRON CUPOLA FURNACE
Sample A
Equivalent
particle diameter,
M-
0. 9
1. 1
1.4
1.8
2. 3
2. 8
3. 7
4. 6
5. 5
6.4
6.9
7. 3
7.8
8.2
8. 7
9. 3
10. 1
11.0
12. 4
13. 7
16. 5
19.3
22. 0
24. 7
27. 5
30. 2
34. 4
41. 3
55. 0
68. 7
82.6
123
Cumulative
wt %
0. 0
1. 3
3. 4
7. 4
11.6
15.0
20. 4
24.6
27. 3
29. 0
29. 8
30. 3
30. 7
31. 2
31. 3
31.9
32. 1
33. 1
33. 5
33. 6
33. 9
34. 2
34. 4
34. 7
35 1
36. 0
37. 5
40. 6
46. 4
51. 1
55. 9
61. 4
Sample B
Equivalent
particle diameter
hi
1. 0
1. 3
1. 6
2. 1
2. 6
3. 0
4. 2
5. 2
6. 3
7. 3
7. 8
8. 4
8. 9
9. 4
10. 1
10. 4
10. 9
12. 5
14. 1
15. 6
18. 8
21 9
25
28. 1
31.3
34. 4
39. 1
46. 9
62. 5
78. 1
93. 8
148
Cumulative
wt %
0.0
1.7
3.6
7.0
10. 5
13. 3
19. 9
24.8
29. 0
32. 5
34. 9
36. 3
38.6
39. 8
41. 1
42. 0
43. 2
45. 4
46.7
47. 0
47. 4
47.6
47. 7
48. 0
48. 4
48. 8
49. 8
52. 3
56.7
63.4
69. 3
80. 5
  Table 78.  QUALITATIVE SPECTROGRAPHIC
  ANALYSIS OF TWO SAMPLES TAKEN FROM
            A BAGHOUSE SERVING A
        GRAY IRON CUPOLA FURNACEa
Element
Aluminum
Antimony
Boron
Cadmium
Calcium
Chromium
Copper
Gallium
Germanium
Iron
Lead
Magnesium
Manganese
Molybdenum
Nickel
Potassium
Silicon
Silver
Tin
Titanium
Zinc
Approx amount,
%
Sample A
0. 81
0. 24
0. 050
0. 13
0. 16
0.022
0. 42
0. 017
0. 018
6. 0
17.0
0. 29
1. 0
0. 0068
0. 023
1. 5
8.6
0. 0093
0. 41
0. 019
7. 1
Approx amount,
%
Sample B
1. 1
0. 24
0. 054
0. 064
0.25
0. 019
0. 32
0. 019
0. 015
7. 5
17. 0
0. 30
0. 81
0. 0075
0. 022
1. 2
15. 0
0. 0089
0. 38
0. 034
5.9
                                                        1 These data are qualitative only and require
                                                         supplementary quantitative analysis for actual
                                                         amounts of the elements found to be present.
                                                         These are the same samples as given in
                                                         Table 77.
Table  79.   These tests indicate the superior ef-
ficiencies  of baghouses and electrical precipita-
tors and, in practice, only these devices have been
found to operate satisfactorily in Los Angeles
County. As mentioned, these systems also include
auxiliary items such as afterburners, gas-cooling
devices, and settling chambers.

Afterburners
An afterburner is generally installed in a cupola
furnace control system for two reasons.  The
high carbon monoxide content of the  cupola ef-
fluent presents a definite explosion hazard; this
hazard can be avoided by burning the carbon
monoxide  to carbon dioxide.  Secondly, the after-
burner burns combustion particulates , such as
coke breeze and any smoke and oil vapors that
may be distilled from the furnace  charge.  This
combustion of oil vapors prevents  later condensa-
tion on the surface of the filter bags and their re-
sultant blinding.  While afterburners may be in-
stalled as  separate units,  the common practice is
to use  the  upper portion of the cupola between the
charging door and the cupola top as the afterburn-
er.  When this is done, the height of the standard
cupola must usually be increased to give a vol-
ume sufficient  to provide adequate residence time
to complete the combustion in the afterburner.
As described earlier, the pollution problem from
the various iron processes originates from emis-
sion of gases,  dust,  fumes, and smoke.  The
ratios of the quantities of the contaminants  emit-
ted from this equipment vary appreciably and
influence the selection of the control device or
devices to be employed.

An afterburner should be designed with heat ca-
pacity to  raise the temperature of the combusti-
bles,  inspirated air,  and cupola gases to at least
1,200°F.   The  geometry  of the secondary com-
bustion zone  should  be such that the products to
be  incinerated  have  a retention  time of at least
1/4 second.   A luminous flame burner is desir-
able,  since it presents more flame  exposure.
Enough turbulence must be created in  the gas
stream for thorough  mixing of combustibles and
air.  In large-diameter cupola furnaces, strati-
fication of the gas stream may make this a major
problem.   One device, proved successful in pro-
moting  mixing  in large-diameter cupolas,  is  the
inverted cone shown in Figure  179.  The combus-
tion air is  inspirated through the charging door
and, if necessary, may also be inspirated through
openings strategically located in the cupola cir-
cumference,  above the charging opening.  The
 234-767 O - 77 - 19

-------
260
                                  METALLURGICAL EQUIPMENT
            Table 79.  SOME  COLLECTION EFFICIENCIES OF EXPERIMENTAL SMALL-
                    SCALE CONTROL DEVICES TESTED ON GRAY IRON CUPOLASa
Equipment tested
Controls for cupolas"
High-efficiency cyclone
Dynamic water scrubber

Venturi-type scrubber


Dynamic --impingement
wet scrubber
Baghouse- -one sihcone-
treated glass wool bag,
10 in. dia x 10 ft length
Evaporative cooler and
redwood pipe electrical
precipitator
Other basic equipment
Natural gas-fired
reverberatory furnace

Inlet
gas
volume,
scfm

330
1, 410

375


605

52. 7


1, 160



--


Outlet
gas
volume,
scfm

384
1, 760

432


995

52. 7


1, 330



5, 160


Inlet
dust
load,
gr/scf

1.225
1. 06

1. 17


0. Q5

1. 32


1. 263



--


Outlet
dust
load,
gr/sci

0.826
0. 522

0. 291


0. 141

0. 046


0. 0289



0.00288


Collection
efficiency,

22. 5
38.2

71. 3


75. 6

96. 5


97.7



96. 2C


Remarks


Water added before control unit for
cooling totalled 6 gpm
Two gpm-water introduced for cooling
gas stream; 3. 5 gpm added at ventun
throat; cyclonic scrubber operated dry
Water rate in excess of 10 gpm

Average temp, 372°F, average filter-
ing velocity, 3. 22 gpm

Water rate to cooler, Z2. gpm; to
precipitator, 2 gpm


Melting rate, 546 Ib/hr; gas consump-
tion rate, 4,200 cfh; melting clean
scrap and pig iron
         aln all cases, equipment was installed and operated according to the manufacturer's recommendations.
          The six control devices were tested on the same cupola.
         cThis is not an actual collection efficiency, but a percent reduction when compared with average cup61a emissions.
rapid ignition  of the  combustible effluent by the
afterburner frequently results in a pulsating or
puffing emission discharge from the charging door.
This  can be eliminated by  the  installation  of an
ignition  burner below the level of the charging
door, which ignites and partially burns the com-
bustible  effluent.

A cupola afterburner need not be operated through
the entire furnace cycle.  Even without an after-
burner,  an active flame can be maintained in the
upper portion  of the cupola.   This requires con-
trol of the materials charged,  and likewise,  con-
trol of combustion air and mixing.  The afterburn-
er must, however,  be in operation during the fur-
nace light-off procedure.  It is desirable  to ignite
the coke bed with gas torches,  because consider-
able smoke may result if the light-off is done with
kindling  wood.

Baghouse dust  collectors

The temperature of the  gas stream discharged
from the top of a cupola may be as high as 2, 200°F.
If a baghouse  is used as  a control device, these
gases mustbe cooled to prevent burning or  scorch-
ing of the cloth bags.  Maximum temperatures
allowed vary from 180°F for cotton bags to 500°F
for glass fabric bags.

Cooling can be effected by radiant cooling  columns,
evaporative water coolers, or by dilution with am-
bient air.  Figure  180  shows  an installation in
which the gas stream is cooled by dilution and ra-
                                                      diation-convection cooling columns.  Of the three
                                                      types of coolers,  spraying is the most common.
                                                      All types have been discussed in Chapter 3.

                                                      For satisfactory baghouse operation, whenmetal-
                                                      lurgical fumes are to be collected, filtering ve-
                                                      locity should not exceed 2-1/2 fpm.  Provisions
                                                      for cleaning collected mate rial from the bags usu-
                                                      ally require compartmentation of the baghouse so
                                                      that one section of the baghouse may be isolated
                                                      and the bags  shaken  while  the  remainder of the
                                                      system is  in  operation.  The gas temperature
                                                      through the baghouse should not  be  allowed to fall
                                                      below the dew point, because condensation within
                                                      the baghouse  may cause the particles on the bag
                                                      surfaces to agglomerate,  deteriorate the cloth,
                                                      and  corrode the baghouse  enclosure.   A bypass
                                                      controlmust alsobe installed.  If the cooling sys-
                                                      tem fails, the bypass is opened,  which discharges
                                                      the effluent gas stream to the atmosphere and thus
                                                      prevents damage to the bags from excessive tem-
                                                      peratures.  Properly designed and maintained bag-
                                                      houses cannormally be expected to have efficien-
                                                      cies ranging upwards from 95 percent.
                                                      Electrical precipitators

                                                      Electrical precipitators  are an  efficient control
                                                      device for collecting most metallurgical fumes
                                                      •where steady-state conditions of temperature and
                                                      humidity can be maintained in the gases to be cleaned.
                                                      The procedures used in determining the effluent
                                                      gas  volume and temperatures for a precipitator

-------
                                             Iron Casting
                                                                                                  261
                              Figure 179.  Integral  afterburner wi
                              verted cone installed  in  top  part of
                              to create  turbulence  to  ensure compl
                              combust!on.
                                                                       GAS  BURNERS
           h  in-
           cupola
           te
control system are the same as those for a bag-
house  control  system.  The collection efficiency
of an electrical precipitator depends in part upon
the apparent resistivity of the material to be col-
lected. This,  in turn,  depends upon the charac-
teristics  of the  material,  and the moisture con-
tent and temperature of the effluent gas  stream.
After the  condition of the gas stream under which
precipitation is to take place has been determined,
the system's conditioning units for controlling the
temperature and humidity of the effluent gas stream
can be designed.  The large temperature fluctua-
tions of the effluent gas stream from a cupola re-
quire that the control system be designed to main-
tain proper levels of temperature  and humidity.
Installation and  operation  of equipment to main-
tain these levels maybe bulky and expensive,  and
should be  reviewed  with the manufacturer.  In
order  to avoid corrosion in the precipitator unit,
the control system must be designed to prevent
water  carryover or  condensation.   Figure  181
shows a cylindrical water spray conditioning cham-
ber,  upper left; electrical  precipitator, center;
fan and discharge duct,  upper right.  These con-
trol units vent a cupola with a separate afterburner,
not shown in the photograph.  The  precipitator
rectifier  is housed in the concrete block building
in the foreground.


Additional design information on electrical pre-
cipitators has been presented in Chapter 4.

-------
262
METALLURGICAL EQUIPMENT
      Figure  180.   Cupola  controlled  by  radiation convection coolers and baghouse (Alhambra Foundry
      Company,  Alhambra,  Cal i f. )•
                                              Cupola data
                Size ,  45-in.  ID
                Flue gas  vol,  7,980  scfm
                Tuyere air,  3,450  scfm
                     Iron  - coke  ratio, 8:1
                     Flue  gas temp,  1,875° to
                     Charging rate,  20,200 Ib,
 2,150°F
/hr
                                         Gas conditioner data
                Radiation  and convection type
                Cool ing area, 10,980  ft2
                Log  mean  temp diff, 670°F
                Heat  trans  coef,  1.59 Btu/hr-ft2 per°F
                     Gas vol  (mcl  reci rculation),  16,100 scfm
                     Size,  16 col  42-in.  dia  x  42-ft. H
                     Inlet  gas  temp,  1,030°F
                     Outlet gas temp,  404°F
                                             Baghouse data
                Tubular  and  compartmented type
                Inlet  gas  volume,  13,100 cfm
                Fi Iter area, 4,835  ft2
                Fi Iter media,  si Iicone  glass
                Shaking  cycle,  90  mm  (manual by
                   compartment)
                     Col lection  eff i ciency,  99+%
                     Tube  size,  11 - in. dia x 180-m. L
                     Inlet gas  temp,  4Q4°F
                     Fi Itering  velocity,  2.7 fpm
                     Pressure  drop,  3  to 4 in. WC
Illustrative Problem


The following  example shows  some of the factors
that must be consider ed in designing a control sys-
tem for a gray iron cupola furnace (Figure 182).
                    Example 27

                    Given:

                    A 32-in.-ID cupola

                    Charging door area, 4. 5 ft

-------
                                              Iron Casting
                                                               263
       Figure  181.  Photograph of an  electrical  precipitator  preceded by  a water spray  conditioning chamber;
       vented  cupola and afterburner  not shown (Alabama Pipe  Company, South Gate,  Calif.).
                                           Cupola data
             Size,  42-in.  ID                        Flue  gas  temp, 400°  to 1,400°F
             Flue gas vol,  8,700 scfm               Iron  -  coke  ratio,  9.2:1
             Tuyere air,  3,000 cfm                   Charging  rate, 14,000  Ib/hr
                                         Afterburner data
             Type of structure--an  unused cupola furnace  converted by  the  installation
             of four premix gas burners  with  full modulatirig  temperature controls to
             maintain 1,100°F minimum outlet  temperature.   Fuel  input,  10  million Btu/hr
             maximum
             Evaporator cooler type
             Water rate,  75 gpm (max)
Gas condi tioner data
             Gas temp inlet,  1,100°F  mm.
             Size,  10-ft 6-in.  dia  x  23-ft  6-in.  length
             Type,  expanded metal
             Col lectmg electrode,  size,  17 ft
               6  in.  x 4 ft 6 in.
             Discharge electrode,  0.109-in.  dia
             Gas  volume,  20,300 scfm
             Outlet dust loss,  0.0359 gr/scf
                                   Electrical  precipitator  data
             No.  of  sections,  2 in  series
             Size,  23 ducts 8-3/4 in.  x 17 ft 6 in.
               x  9 ft
             Average gas temp,  430°F
             % Moisture in  flue gas,  15%
             OveralI efficiency,  96,6
Tuyere air,  1,810 scfm

Maximum gas temperature at cupola outlet,
2,000°F

Minimum incineration temperature to be main-

tained at cupola  outlet, 1, 200 °F.
                 Assume a closely coupled unit from the cupola to
                 the evaporative cooling  chamber and an insulated
                 duct between the evaporative cooling chamber and
                 the baghouse.

                Assume the effluent gases have the same proper-
                ties  as air.   (Consideration of the enthalpies and

-------
264
   METALLURGICAL EQUIPMENT
EFFLUENT  GAS  TEMP
MAX :  2,000°F
MIN :  1.2000F    WATER SPRAY
               CONDITIONING EVAPORAT|VE
               PHIMRFU        nrUKfl II Vt
               LHAMBLH      COOLING WATER
^AFTERBURNER
  MAX  INPUT : ?
  MAX  INPUT z 500 cfh

-CHARGING DOOR
  AREA -  4.5 ft2
  INDRAFT VEL - 200  fpm
NUYERE  AIR : 1,810 scfm
V
/


FILTER
AREA- i

 CUPOLA
FURNACE
                                             FAN
                               BAGHOUSE  INPUT
                               TEMP z 225°F
                      3.  Heat re quired from afterburner to raise charg-
                          ing door indraft air from 60° to 1,2QO°F:
                          Assume a charging door indraft velocity of
                          200 fpm,  which will be adequate  to ensure an
                          indraft of air at all times.
                                                          Charge door indraft volume =  (4. 5)(200)  =
                                                          900 scfm or  69. 3 Ib/min
                                                          Enthalpy of gas (1,200 °F)  =  287.2Btu/lb
                                                          Enthalpy of gas (60 °F)
                                                                                Ah   =   287.2
   Figure 182.   Control  system  for a gray iron
   cupola furnace.
                                     (69. 3)(287.2)
                                                                                    19, 900 Btu/min
                                                      4.   Total heat to be supplied by afterburner:
specific  heats  of the  gaseous constituents in the
effluent gas  stream -will show that this is an ac-
curate assumption. Any corrections would intro-
duce an insignificant refinement to the calculations
when considered with respect to  the accuracy of
other design factors. )
Problem:
Determine the design features of an evaporative
cooling system and a baghouse to serve the cupola.
                           Heat to tuyere air
                           Heat to charge door
                           indraft volume

                                       Total
                                                                                - 25, 150 Btu/min

                                                                                = 19, 900 Btu/min
                                                                                  45, 050 Btu/min
                      5.   Required natural gas volume capacity of after-
                           burner to supply 45, 050 Btu/min:


                           Heating value of gas =  1, 100 Btu/ft
Solution:
1.  Volume  of gases  from tuyeres  = 1,810 scfm
    or 139. 3 Ib/min
                           Heat available at 1, 200°F, from the burning
                           of  1  ft  of gas  with theoretical air  =  721. 3
                           Btu/ft3 (see Table D7 in Appendix D)
                                                                 45,050
                                                                  721.3
                                           =  62. 4 cfm
2.   Heat required from afterburner to raise tem-
     perature of tuyere air products of combustion
     from an assumed low of 500°F to a minimum
     incineration temperature  of 1,200°F:
     Enthalpy of gas (1,200°F)
     (see Table D3 in Appen-
     dix D)
     Enthalpy of gas (500°F)
                        Ah
             (139. 3)(180. 5)
=  287.2 Btu/lb
=  106.7 Btu/lb
=  180.5
    25. 150 Btu/min
                                                  6.   Volume of products of combustion from after-
                                                       burner:

                                                       With theoretical air, 1 ft3 of gas yields 11.45
                                                       ft3 of products  of combustion (see Table D7
                                                       in Appendix D)
                                                                 (62.4)(11.45)  =  715 cfm
                                                  7.   Total volume of products ' to be vented from
                                                       cupola,  scfm:
                                                       Volume from tuyere air   =   1,810

-------
                                             Iron Casting
                                                                                          265
      Volume for charge door
      indraft                   =
      Volume from afterburner  =
                            900

                            715
                                  3, 425 scfm
                              or    264 Ib/min
      Volume of vented gases at 1, 200°F:
Volume of products from
cupola                   =  3, 425 scfm

Volume of evaporated
cooling water            =  1, 586 cfm (225 °F)
                                                          (3,425)
                                                                   60 4-  460
                                                                       +  1, 586  =  6, 106 cfm
(3,
 9.  Duct diameter from cupola exit to evapora-
     tive chamber:

     Use design velocity of 3, 500 fpm
     Duct cross-sectional area = — '  -—  =  3. 12 ft
                                  3, 500
                 •  •  Use 24-in.-dia.  duct
 10.  Cooling required  to  reduce temperature of
     vented products from cupola from 1,200°
     to 225°F:

     Baghouse inlet design temperature taken as
     225°F

     Enthalpyofgas at  1,200°F  =  287.2 Btu/lb
     Enthalpy of gas at 225 °F   =   39. 6 Btu/lb
                            Ah  =  247. 6 Btu/lb

            (264)(247.6)  =  65, 300 Btu/min
 11. Water to be evaporated to cool vented gas
     products from 1, 200°  to225°F:

     Heat absorbed per Ib of •water:
     Q = h  (225°F, 14. 7 psia) - h  (60°F)
                                                      14.  Duct diameter between spray chamber and
                                                          baghouse:

                                                          Use design velocity of 3, 500 fpm
                                                          6, 106              2
                                                                  =  1-745ft
                                                            .  • Use an 18-in.-dia. duct

                                              15.  Required filter  area of baghouse:

                                                  Design for a filtering velocity of 2 fpm
                                                           6, 106      „       2
                                                           -—   =  3, 053 ft
                                                  During burndown, the cupola discharge gases
                                                  will increase  in temperature to 2, 000°F and
                                                  the  afterburner input  will be  reduced to the
                                                  low fire  settling  at an input of 500 ft^ of gas
                                                  per hr (8. 33 cfm).   Calculations will be made
                                                  under this new operating condition to deter-
                                                  mine whether the previously calculated values
                                                  for duct sizes,  evaporative water quantity, and
                                                  filter area are compatible.

                                             16.  Volume of products of combustion from af-
                                                  terburner:

                                                      (8.  33)(11. 45)  =  95. 5 cfm

                                             17.  Total volume of products to be vented from
                                                  cupola:
        =  1, 156. 8 - 28. 06  = 1, 128. 74 Btu/lb
 12.  Volume of evaporated cooling water at 225 "F:
      v = 27. 36 ft/lb HO (14. 7 psia, 225°F)

             (58.0)(27. 36)  =  1,586 cfm
                                                  Volume from tuyere air           - 1,810

                                                  Volume from charge door indraft  =   900

                                                  Volume from afterburner         =     95. 5
                                                                                             2,805.5 scfm

                                                                                         or   2161b/min
                                                      18.  Volume of vented gases at 2, 000°F:
13.  Total volume of products vented from spray
    chamber:

-------
 266
                               METALLURGICAL EQUIPMENT
 19.  Gas velocity between cupola and spray cham-
     ber when using 24-in. duct from calculation 9:
                                                  25,  Filtering velocity using filter area from cal-
                                                      culation 15:
                13,280
                 3. 142
                    =  4, 230 fpm
     Velocity  is greater  than necessary but not
     excessive.

20.  Cooling  required to  reduce temperature  of
     vented prodxicts from cupola from 2, 000°
     to 225°F:

     Enthalpy of gas at 2,  000°F = 509. 5  Btu/lb
     Enthalpy of gas at    225° F =  39. 6  Btu/lb
                           Ah = 469. 9 Btu/lb

          (216)(469.9)  =  101, 300 Btu/min

21.  Water to be evaporated to cool vented gas
     products from 2,000°  to  225°F:

     Heat absorbed per Ib  of water =  1,128.74
     Btu/lb  (see calculation 11)


                   rT  =  90 lb H20/min
    This is greater than that determined in cal-
    culation  11 and must therefore be taken as
    the design value.

22. Volume of evaporated cooling water at 225 °F:

    v = 27. 36 ft3/lb H2O (14. 7 psia,  225"F)

                (90)(27. 36)  =   2,460 cfm

23. Total volume of products vented from spray
    chamber:

    Volume of products from
    cupola                    = 2, 805. 5 scfm
Volume of evaporated
cooling water
   (2,
                             =  2, 460 cfm (225 °F)
                                      = 6, 160 cfm
                                                                 6, 160
                                                                 3,053
                                                                             =  2. 02 fpm
                                                      This ratio is  in  agreement -with a filtering
                                                      velocity of 2 fpm


                                                  26.  The exhaust system and fan calculations are
                                                      made as outlined in Chapter 3.  After a sys-
                                                      tem resistance curve has been calculated and
                                                      plotted, a fan is selected whose characteris-
                                                      tic curve will  intersect the system curve at
                                                      the required air volume, which for this ex-
                                                      ample would be 6, 160 cfm.

                                                  Problem note:  This example problem illustrates
                                                  typical calculations that can be followed in de-
                                                  signing a  cupola control system.  Each installa-
                                                  tion must be evaluated separately,  considering
                                                  expected  maximum and minimum temperatures,
                                                  gas  volumes,  duct lengths,  and so forth.  For
                                                  example, this pr obi em was patterned after a small
                                                  cupola where the  charging  door remains open.
                                                  For large cupolas,  opening and closing the charg-
                                                  ing doors must be evaluated relative to its  effect
                                                  upon gas volumes and temperatures.  If duct runs
                                                  are long,  the radiation-convection losses maybe
                                                  worth considering. The sizing of the fan motor
                                                  depends  upon the  -weight of gas moved per unit
                                                  time.  This in turn depends upon the density (con-
                                                  sidering  air, water vapor,  and  temperature) of
                                                  the gas stream.  These items are taken into con-
                                                  sideration in making  the exhaust system resis-
                                                  tance  calculations.  It may be necessary to re-
                                                  duce the system's airflow by dampering in order
                                                  to prevent overloading of the fan motor -when mak-
                                                  ing a cold startup under ambient conditions.  See
                                                  Chapter   3 for design parameters for cooling of
                                                  effluent  gas stream  -with radiation-convection
                                                  cooling columns.  Since the temperature of the
                                                  effluent  gas stream  from the cupola will fall in
                                                  the range of 1, 200° to  2, 000°F,the duct connect-
                                                  ing the cupola and water spray conditioning cham-
                                                  ber should be made  of stainless steel or be re-
                                                  fractory  lined.
                                                      ELECTRIC-ARC FURNACES
24.  Gas velocity between spray chamber and bag-
    house using 18-in. duct from calculation 14:
               Hi?
    Velocity is comparable with design value of
    3,500 fpm
                                                  Electric-arc furnaces are commonly used in the
                                                  secondary melting  of iron -where special alloys
                                                  are to be made.  These furnaces may be either
                                                  ihe  direct-  or  indirect-arc  type.  Pig iron and
                                                  scrap iron are charged to the furnace and melted,
                                                  and alloying elements and fluxes  are added at
                                                  specified intervals.  These furnaces have the ad-
                                                  vantage of rapid and accurate heat control.

-------
                                             Iron Casting
                                                                                                 267
The Air Pollution Problem

Since no gases are used in the heating process,
some undesirable effects on the metal are elim-
inated.   Since  arc furnaces in the iron industry
are virtually always used to prepare special al-
loy irons, the quality of the material charged is
closely controlled.  The charging of greasy scrap,
which -would emit combustible air contaminants,
•would  only needlessly  complicate the alloying
procedure.  Afterburners are, therefore, rarely
required in conjunction with arc furnace opera-
tions.   The  emissions consist, primarily,  of
metallurgical fumes  and can  be controlled  by
either  a baghouse or an electrical precipitator.
The emission rates from electric-arc furnaces
vary according to the process from 5 to 10 pounds
per ton of metal processed.

Hooding and Ventilation Requirements

Direct-arc furnaces for melting gray iron pre-
sent a unique and difficult problem of hooding.
The hood1 s geometry and the indraft velocity must
be designed to ensure virtually complete  collec-
tion of the emissions from the furnace.  Hood  de-
sign varies  considerably for different furnaces.
Furnaces are most successfully hooded by build-
ing the hood  into the cover or  top of the furnace.
This,  of course,, means designing an air cham-
ber  or compartment above the furnace roof and
providing a  duct  connection  to  the chamber so
that the collected contaminants may be vented to
the control  device.   Since direct-arc furnaces
receive only a limited use for melting cast iron,
generalizing about the ventilation requriements
is difficult; however,  5, 000 to 7, 500 cfm per ton
of production apparently yields a reasonable  de-
gree  of dust and fume capture.  To be most ef-
fective,  the  ventilation air exhausted from the
furnace  should  also  be available  to the  furnace
hood  during  periods of tapping and charging the
furnace. This means that some type of telescop-
ing ductwork or slip-connection ductwork must
form the connection between the control device
and the hood.  Figure 183 illustrates an  adjust-
able-type hood used with a baghouse venting rock-
ing-arc furnaces.   The hood is positioned  by
means  of a  telescoping connection that is me-
chanically controlled.  In the right foreground of
the photograph, the  hood is shown lowered into
position with the  furnace in operation, while in
the left background, the hood is shown raised from
the furnace to facilitate charging  and furnace  ac-
cess.

Air  Pollution  Control Equipment

Baghouse dust collectors

Elaborate facilities  for cooling the effluent gas
stream from an electric furnace  may not  be nec-
essary for two reasons:  (1) No prod-acts of com-
bustion result from the  burning of fuel, and  (2)
canopy-type  or  roof-type hoods are  generally
used.  Thus,  the volume of the effluent gas stream
as low, and the ventilation air drawn in at the hood
provides  cooling.  As with cupola baghouses,  a
filtering velocity of 2-1/2 fpm should not be ex-
ceeded and a shaking mechanism and  compart-
mentation must be  provided.


Electrical precipitators

As in the case of baghouse dust collectors serv-
ing electric-arc  furnaces, no  elaborate  facili-
ties  are necessary for  cooling the effluent gas
stream from an electric  furnace  vented to an
electrical precipitator, though the design humid-
ity  and temperature of gases entering the elec-
trical  precipitator must be met.   This may re-
quire water spray sections or afterburner devices
to heat and humidify the gases vented to the pre-
cipitator.

INDUCTION FURNACES

Core-type electric-induction furnaces are also
used for melting cast iron.  In this type  of fur-
nace, alternating c\irrent is passedthrougha pri-
mary  coil with a  solid iron core.  The  molten
iron contained within a loop that  surrounds the
primary coil acts as the secondary.   The alter-
nating current that flows through the  primary
induces a current in the loop, and the electrical
resistance of the molten metal creates the heat
for melting.   The heated metal circulates to the
main furnace chamber and is replaced by cooler
metal.  This circulation results in uniform metal
temperature and alloy composition.
The electric-induction  furnace generates con-
siderably smaller amounts of air contaminants
than the cupola or electric-arc furnace does; the
amount is mainly dependent upon the condition of
the metal charged.  When pig iron and clean cast-
ing returns are charged, no air pollution control
equipment is necessary for  ordinary melting.
Contaminated scrap or the addition  of magnesium
for manufacturing ductile  iron would,  however,
necessitate  air pollution control equipment.  In
cases  such as these,  design  requirements for a
baghouse control system with canopy-type hood-
ing are the same as later described in this chap-
ter for coreless induction furnaces for  steel melt-
ing.

REVERBERATORY FURNACES

Small  reverberatory furnaces are also used in
preparing gray and  white  cast iron  alloys.   If
cleanmetalis charged to these furnaces,  no ex-
cessive air pollution results from their use. Fig-
ure 134 shows a small, gas-fired,  reverberatory

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268
                                    METALLURGICAL EQUIPMENT
Figure 183.   Rocking-arc furnaces venting through adjustable hoods to a baghouse
(Centrifugal Casting Company, Long Beach, Calif.).
                          Figure 184.
                          Rated capacity, 1,000 Ib
                          Fuel, natural gas
                          Furnace flue gases,  calculated
                             6,100 cfm at 2,850°F
                          Pouring temp, 2,700°F
Gray iron reverberatory furnace (Pomona Foundry,  Pomona,  Calif.).

             Reverberatory furnace data
                           Typical  charge,  300 Ib pig iron,  500 Ib
                              scrap iron,  200 Ib  foundry  returns,
                  at          2 Ib soda ash
                           Melting rate, 750  Ib/hr
                           Fuel rate,  4,200 ft3/hr
                          Gas volume at hood, 5,160 scfm
                          Dust loss in gr/scf, 0.00278
                   Test data
                           Average gas temp,  775°F
                           Loss in Ib/hr, 0.13

-------
                                 Brass- and Bronze-Melting Processes
                                           269
furnace used in a gray iron foundry.  Test results
made upon a furnace of this type,  rated at 1, 000-
pounds capacity,  while it was melting clean  scrap
iron and pig iron,  showed a particulate loss to
the atmosphere of 0. 0027S  grain per standard
cubic fool, or 0. 14 pound per hour.  Because of
this low rate of particulate discharge,  no air pol-
lution control devices have been found necessary
for the operations conducted in this type of fur-
nace melting iron.
to make commercial castings are usually melted
in low-frequency induction furnaces in the larger
foundries and in crucible-type,  fuel-fired fur-
naces in the smaller job foundries.  Electric fur-
naces, both arc and induction, are also used for
castings.  Generalizing in  regard to the uses of
various furaaces is difficult, since foundry prac-
tices are variable.  A comparison of emissions
from various  types of  furnaces is given in Table
SO.
    SECONDARY  BRASS- AND  BRONZE-

           MELTING  PROCESSES

Copper when alloyed with zinc is usually termed
brass, and when alloyed with tin is termed bronze.
Other copper alloys are  identified by the alloying
metals  such  as  aluminum bronze and silicon
bronze.   The true bronzes  should  not be con-
fused with some other common classifications of
bronzes,  which are actually misnomers.   For
example,  "commercial bronze" is a wrought red
brass,  and  "manganese bronze"  is a  high-zinc
brass.  Because of high strength,  workability,
corrosion resistance, color, and other  desirable
physical characteristics, the copper-base  alloys
have found wide use for hardware, radiator  cores,
condensers , jewelry, musical instruments , plumb-
ing fittings,  electrical equipment, ship propel-
lers, and many other devices.

The remelting of nearly pure copper and bronze
does not have great interest from the  standpoint
of air pollution since only small amounts of metal
are  volatilized.  This  is due to the high boiling
points of copper and tin (above 4, 000 °F) and their
lownormal pouring temperatures of about 2, 000°
to 2,200°F.   With good melting practice, total
emissions to the air should not exceed 0. 5 per-
cent of the process weight.  The brasses contain-
ing 15 to 40 percent zinc, however,  are poured
at temperatures near their boiling points  (about
2, 200°F), and some vaporization or combustion
of desirable elements,  particularly zinc,  is in-
evitable.  Emissions into the air may  vary from
less than 0. 5 percent to  6 percent or more of the
total metal  charge  (St.  John, 1955) and 2 to 15
percent of the zinc content through fuming  (Allen
et al. , 1952),  depending upon the composition of
the alloy,  the type of furnace used, and  the melt-
ing practice.

FURNACE TYPES

Brass  and bronze  shapes for working, such as
slabs and billets,  are usually produced in large
gas-and oil-fired furnaces  of the reverberatory
type. Most operators of secondary smelters also
use this type of furnace for reclaiming and re-
fining  scrap metal,  ordinarily casting the puri-
fied metal into pigs.  Brasses  and bronzes used
The Air Pollution Problem
Air  contaminants emitted from brass furnaces
consist of products of combustion from the fuel,
and  particulate matter  in the form of dusts and
metallic  fumes.  The particulate  matter com-
prising the dust and fume load varies according
to the fuel, alloy composition,  melting tempera-
ture, type of furnace,  and many operating  factors.
In addition to the ordinary solid particulate mat-
ter,   such as fly ash, carbon,  and mechanically
produced dust,  the fur/iace emissions generally
contain fumes resulting from condensation and
oxidation of the more volatile  elements,  includ-
ing zinc,  lead,  and others.

As was previously mentioned, air pollution re-
sulting  from  the volatilization of metals during
the  melting of nearly pure copper and bronze is
not too serious  because  of the high boiling-point
temperatures of copper, tin,  nickel,  aluminum,
and  even lead commonly used in  these  alloys.
Alloys containing zinc ranging up to 7 percent can
be successfully processed with a minimum of
fume emission when a cohesive, inert  slag cover
is used.   This nominal figure is subject to sortie
variation depending upon composition of alloy,
temperatures,  operation procedures, and other
factors.   Research  is  still necessary to deter-
mine the full range of  effects these variables
have upon the emission  rate.

Copper-base  alloys  containing 20 to  40 percent
zinc have low boiling points of approximately
2,100°F  and melting temperatures of approxi-
mately 1, 700° to 1, 900°F. These zinc-rich alloys
are  poured at approximately 1, 900°  to 2, 000°F,
•which is only  slightly below their boiling  points.
Pure zinc melts at 787°F and boils at 1,663°F.
Even within the pouring range,  therefore,  frac-
tions of high-zinc alloys  usually boil and flash to
zinc oxide (Allen et al.  , 1952).  The  zinc oxide
formed  is submicron  in size, and its escape to
the atmosphere can be prevented only by collect-
ing the fumes and using  highly efficient air pol-
lution control  equipment.

Characteristics of emissions

Perhaps the best way to understand the difficulty
of controlling metallic fumes from brass fur-

-------
270
METALLURGICAL EQUIPMENT
                 Table 80.  DUST AND FUME DISCHARGE FROM BRASS FURNACES
I ypr ol
Iiirn.it c
R otary
R otary
Rotary
Elec ind
Elec ind
Elec ind
Cyl reverb
Cyl reverb
Cyl reverb
Cyl reverb
Crueible
Crucible
Crueible
Composition of a
Cu
S^
76
85
60
71
71
87
77
80
80
65
60
77
Zn
5
14. 7
5
38
28
28
4
-
-
^
35
37
12
Pb
5
4. 7
5
2
-
-
0
18
13
10
-
1. 5
6
Sn
5
3. 4
5
-
1
1
8. 4
5
7
8
-
0. 5
3
loy, %
Other
-
0. 67 Fe
-
-
-
-
0.6
-
-
-
-
1
2
Type of
control
None
None
Slag cover
None
None
None
None
None
Slag cover
None
None
None
Slag eover
Fuel
Oil
Oil
Oil
Elect
Elect
Elect
Oil
Oil
Oil
Oil
Gas
Gas
Gas
Pouring
temp, "F
No data
No data
No data
No data
No data
No data
No data
2, 100
2, 100
1, 900 to 2, 100
2, 100
1, 800
No data
Process wt ,
Ib/hr
1, 104
3, 607
1, 165
1, 530
1, 600
1, 500
273
1, 267
1, 500
1, 250
470
108
500
Fume emission
Ib/hr
22.5
25
2.73
3. 47
0. 77
0. 54
2.42
26. 1
22. 2
10. 9
8. 67
0. 05
0.822
nacesisto consider the physical characteristics
of these fumes.  The particle sizes of zinc oxide
fumes vary from 0. 03 to 0. 3 micron.  Electron
photomicrographs of these fumes are shown in
Figures 185 and 186.  Lead oxide fumes, emitted
from many brass alloys, are  within this same
range of particle sizes.   The collection of these
very  small particles requires  high-efficiency
control devices. These metallic fumes also pro-
duce  very opaque effluents, since particles of
0. 2- to 0. 6-microii diameter produce a maximum
scattering of light.

In copper-base alloy foundries,  as much as 98
percent of the particulate matter contained in fur-
nace stack gases maybe zinc oxide and lead oxide,
depending upon the composition of the alloy.  A
series of tests  (Allenetal. , 1952) in Los Angeles
County indicated the zinc oxide content of fume
from representative red and yellow brass fur-
naces averaged 59 percent, while the lead oxide con-
tent averaged 15 percent.  Other tests by  the
same investigators showedthatthe dust and fume
loading from red and yellow brass furnaces varied
fromO. 022 to  0. 771 grain per cubic foot with an
average  of 0.212 grain  per cubic foot at stack
conditions.

Inhigh-lead alloys, these tests showed that lead
oxide constituted 56 percent of the particulate
matter  in the exit gas.  Lesser constituents of
fumes,  such as tin, copper, cadmium,  silicon,
and carbon,  may also be present in varying
amounts,  depending upon the composition  of the
alloy and upon foundry practice.

Investigations prove conclusively that the most
troublesome fumes  consist of particles of zinc
 and lead compounds  submicron in size, and that
                  air pollution control equipment capable of collect-
                  ing particulate matter from  1. 0  down to about
                  0. 03  micron is required.  Photomicrographs of
                  samples taken when furnace emissions were heavy
                  with smoke resulting from improper combustion
                  or melting of oily scrap indicated that the smoke
                  particles accompanying the fumes may be about
                  0.01  micron and smaller (Allen et al. , 1952).

                  Factors causing large concentrations of zinc
                  fumes

                  Four principal factors (Allen et al. , 1952) causing
                  relatively large concentrations of zinc fumes in
                  brass furnace gases are:

                  1.  Alloy composition.  The rate  of loss of zinc
                      is approximately proportional to the zinc per-
                       centage in the alloy.

                  2.  Pouring temperature.   For a given percen-
                      tage of zinc, an  increase of 100°F  increases
                      the rate of loss  of zinc  about  3 times.

                  3.   Type of furnace. Direct-fired furnaces pro-
                      duce larger fume concentrations than the cru-
                       cible type  does,  other conditions  being con-
                       stant.  The Los  Angeles Nonferrous Found-
                       rymen's Committee, 1948 stated, "It is im-
                      probable that any open-flame furnace melting
                       alloys containing zinc and lead can  be  oper-
                      ated without creating excessive emissions.
                      It is conceded that anyone choosing to operate
                      that type  of furnace •will be  required to in-
                       stall control equipment. "

                  4.   Poor foundrypractice.  Excessive emissions
                       result from improper combustion, overheat-
                       ing of the charge,  addition of zinc  at maxi-

-------
                           Brass- and Bronze-Melting Processes
                                            271
mum furnace temperature, flame impinge-
ment upon the metal  charged, heating the
metal  charged, heating the metal too fast,
and insufficient flux cover. Excessive super-
heating of the molten metal is to be avoided
for metallurgical and economic  as  well as
pollution control reasons.  From an air pol-
lution viewpoint, the early addition of zinc is
preferable to gross additions at maximum
furnace temperatures.
In any fuel-fired furnace, the internal atmosphere
is of prime importance since there exists a con-
stantflowof combustion gases  through the melt-
ing chamber, more  or less  in contact •with the
metal.  A reducing atmosphere  is undesirable
from, both the metallurgical and air pollution view-
points.  With too little  oxygen, the metal is  ex-
posed to a reducing atmosphere of utiburned fuel
and water vapor, which usually results  in gassy
metal,  Incomplete combustion, especially with
                      , M   **
                          ^
                        .<
///
   Figure 185.   Electron photomicrographs of  fume from zinc smelter  (Allen  et al., 1952).

-------
212
                                   METALLURGICAL EQUIPMENT
AB- 4
Figure  186.  Electron photomicrographs of fume
from a  yellow brass furnace  (Allen et al.,  1952).
oil firing, produces smoke and carbon.  In one
case,  a furnace was  operated with a fuel mix-
ture so  rich that incandescent carbon  from the
fuel ignited the cloth filter bags in the baghouse
serving the furnace.  To prevent these difficul-
ties, the atmosphere should be slightly  oxidiz-
ing.  Excess  oxygen content should be greater
than 0. 1 percent; otherwise,  castings will be af-
fected  by gas porosity.  Conversely, the excess
oxygen content must be less than 0. 5 percent to
prevent excessive metal oxidation (St. John, 1955).
The  need for such close control of the internal
furnace atmosphere requires careful regulation
ofthe fuel and air input and freqttent checking of
the combustion gases.


Crucible furnace--pit and tilt type

The indirect-fired, crucible-type furnace is used
extensively in  foundries requiring small- and
medium-sized melts.  The lift-out-type crucible
is frequently employed in small furnaces.  Tests
have  demonstrated that,  -with careful practice
and use  of  slag covers, the crucible furnace is
capable of low-fume operation  within the legal
limits for  red brasses containing as much as  7
percent zinc.  A slag cover does not sufficient-
ly suppress the emissions from alloys with a zinc
content in  excess of 7 percent  unless very low
pouring temperatures are used.

The slag cover, consisting mainly of crushed glass,
is not used as a true refining flux but as an inert,
cohesive slag of sufficient thickness to keep  the
molten metal covered.  If the quantity of slag is
carefully controlled, a  minimum of emissions
results from either melting or  pouring.  A slag
thickness of 1/4 to 3/8 inch is recommended.
Before  any metal is added  to the crucible,  the
flux  should be added so that,  as melting takes
place, a cover is formed of sufficient thickness
to keep the molten metal divorced from the  at-
mosphere.

When the crucible of molten metal has reached
the pouring floor,  two holes are punched in  the
slag cover on top of the metal, one through which
the metal is poured,  the other to permit the en-
trance of air (Haley, 1949).  Holding escaping
oxides to a minimum is possible either by using
patented attachments  to hold back the slag at  the
pouring sprue or using a hand-operated skimmer.

Electric furnace--low-frequency induction type

The  low-frequency, induction-type furnace has a
number of desirable characteristics for melting
brasses.  The heating is rapid and uniform, and
the metal temperature  can be accurately con-
trolled.  Contamination from combustion gases
is completely eliminated. High-frequency induc-
tion  furnaces are well  adapted to copper- and
nickel-rich alloys but  are not widely used  for
zinc-rich alloys.  Low-frequency induction fur-
naces are more suitable for melting zinc-rich
alloys. During melting  of clean metal, use of a
suitable flux cover over the metal prevents ex-
cessive fuming except during the back charging
and  pouring phases of the heat.  The usual flux
covers--borax,  soda ash,  and  others--are de-
structive to furnace walls, but charcoal is used

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                                Brass- and Bronze-Melting Processes
                                                                                                 273
with satisfactory  results.  During the test out-
lined in Table 81,  case C, two-thirds of the total
fumes were released during the pouring and charg-
ing periods.   A furnace, similar to that tested,
is shown in Figure 187.


Cupola furnace

The cupola furnace is used for reduction  of cop-
per-base alloy slag and residues.  The residues
charged have a recoverable metallic content of
25 to 30 percent.   The balance of the unrecover-
able material consists  of nonvolatile gangue,
mainly,  silicates.  In addition to the residues,
coke and flux are charged to the furnace.  Period-
ically the recovered metal is tapped from  the fur-
nace.  The slag produced in the cupola is elim-
inated through a  slag tap located slightly above
the metal tap.

In addition to the usual metallic fumes, the cupo-
la also discharges  smoke and fly ash.  Collec-
tion of these emissions is required at the cupola
stack, the charge door,  and the metal tap spout.
With no  control  equipment, emissions  of 60 to
100 percent  opacity  can be expected from the
charge door and stack.  The opacity of the fumes
emitted from the metal tap varies from  60 to 80
percent.
The  slag  discharged from the cupola is rich in
zinc oxide. Although the slag leaves the furnace
at a temperature of  approximately 1, 900 °F, the
zinc oxide is in solution and, at this tempera-
ture, does not volatilize to any extent.  The dis-
charge slag is immediately cooled by water.   The
emissions from the slag-tapping operation rarely
exceed 5 percent opacity.

Hooding and Ventilation Requirements

Regardless of the efficiency of the control device,
air pollution  control is not complete unless all
the fumes generated by the furnace are captured.
Since different problems are encountered with the
various types of furnace,  each will be discussed
separately.

Reverberatory furnace--open-hearth type

In a reverber atory open-hearth furnace, the prod-
ucts of combustion  and metallic fumes are nor-
mally  vented directly from the furnace through
a cooling device to a baghouse.  Auxiliary hoods
are  required over  the charge  door,  rabble (or
slag) door, and tap hole.  These may vent to the
baghouse serving the furnace and hence cool the
hot combustion gases by  dilution or may vent to
a smaller  auxiliary baghouse.
              Table 81.  BRASS-MELTING FURNACE AND BAGHOUSE COLLECTOR DATA
Case
Furnace data
Type of furnace
Fuel used
Metal melted
Composition of metal melted, %
Copper
Zinc
Tin
Lead
Other
Melting rate, Ib/hr
Pouring temperature, °F
Slag cover thickness, in.
Slag cover material
Baghouse collector data
Volume of gases, cfm
Type of baghouse

Filter material
Filter area, ftz
Filter velocity, fpm
Inlet fume emission rate, Ib/hr
Outlet fume emission rate, Ib/hr
Collection efficiency, %
A

Crucible
Gas
Yellow brass

70. 6
24.8
0.5
3.3
0.8
388
2, 160
1/2
Glass

9,500
Sectional
tubular
Orion
3, 836
2.47
2.55
0. 16
93.7
B

Crucible
Gas
Red brass

85. 9
3.8
4. 6
4. 4
1. 3
343
2, 350
1/2
Glass

9,700
Sectional
tubular
Orion
3,836
2. 53
1. 08
0. 04
96.2
C

Low-frequency induction
Electric
Red brass

82. 9
3. 5
4. 6
8.4
0.6
1, 600
2, 300
3/4
Charcoal

1, 140
Sectional
tubular
Orion
400
2.85
2.2a
0. 086
96. 0
         alncludes pouring and charging operations.

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274
METALLURGICAL EQUIPMENT

                      Figure 187.  Low-frequency  induction furnace with  fixed  hood.
Whether the auxiliary hoods vent to the furnace
baghouse or to a separate filter, the furnace burn-
ers  should be turned down or off during periods
when the furnace is opened for  charging,  rab-
bling,  air  lancing, removing slag,  adding metal,
or pouring metal.  Otherwise,  the exhaust fan
may not have  sufficient  capacity to  handle the
products of combustion and the additional air re-
quired to  capture the  fumes.  Since no two of
these operations  occur simultaneously, the re-
quired air  volume for  collection may be  reduced
by the use of properly  placed dampers within the
exhaust system.

If the entire furnace charge is made at the begin-
ning of the heat,  the  metal should be loaded in
such a  way that  the flame does not impinge di-
rectly upon the  charge. If periodic charges are
made throughout the heat,  the burners should be
turned off during charging operations .  The opac-
ity of escaping  fumes may vary from none to 15
percent with the burners off and may be  60 to 70
percent with the burners ignited.
                    Well-designed hoods,  properly located, with an
                    indraft velocity of 1 00 to 200 fpm, adequately cap-
                    ture the furnace emissions. If the hood is placed
                    too high for complete capture  or is improperly
                    shaped and poorly fitted,  higher indraft velocities
                    are required.

                    The rabble or slag door permits (1) mixing the
                    charge,  (2) removing slag from the metal sur-
                    face,  and (3) lancing the metal  with  compressed
                    air to eliminate iron from the metal when re-
                    quired by alloy specifications.  Emissions from
                    the furnace  may be  of  50 to 90 percent opacity
                    during these  operations,  even with the burners
                    partially throttled.   Again,  100 to  200 fpm in-
                    draft velocity is recommended for properly de-
                    signed hoods.

                    Generally, after the slag has been removed, metal,
                    usually  zinc,  must be  added to bring the brass
                    within specifications.  The furnace metal is at a
                    temperature well above the boiling point of zinc
                    and is no  longer covered by the tenacious slag

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                                 Brass- and Bronze-Melting Processes
                                            275
cover.  Hence, voluminous emissions of zinc
oxide result. The addition of slab zinc produces
1 00 percent opaque fumes in great quantity,  while
a brass addition may generate fumes of 50 per-
cent opacity.   A •well-designed hood is required
over  the  charge door  or  rabble  door, through
which the metal is charged.

Perhaps the most critical operation  from the
standpoint of  air pollution occurs when the fur-
nace is tapped.  Nearly continuous  emissions of
90 to 100 percent opacity may be expected.   Much
planning is required to design a hood  that com-
pletely captures the emissions and yet permits
sufficient working room and visibility of the mol-
ten metal.  Again, the  burners should be  turned
off or throttled as much  as  possible to reduce the
quantity of fume s emitted.

The fluxes used in reverberatory furnaces nor-
mally present no air pollution problems.  Gen-
erally, only nonvolatile fluxes such as borax,
soda ash, and iron oxide mill scale are used.
Reverberatory furnaces-cylindrical type

Cylindrical-type reverberatory furnaces present
all  the  collection problems of the open-hearth
type with the additional complication of furnace
rotation.   The cylindrical  furnace may be ro-
tatedupto 90° for charging, slag removing, and
metal tapping.  Withhoods installed in fixed posi-
tion, the source of emissions may be several feet
from the hood,  and thus no fumes would be col-
lected.  Either a hood attached to the furnace and
venting to the control device through flexible duct-
work, or an oversized close-fitting hood  covering
all  possible  locations of the emission source is
required.  A close-fitting hood and high indraft
velocities  are often necessary.  For example,
an auxiliary hood  over the combination charge
and slag  door of a cylindrical brass furnace was
incapable of collecting all emissions,  despite  an
indraft velocity of  1,370 fpm.  A similar hood
over the pouring spout  was  also inadequate, de-
spite an indraft velocity of 1, 540 fpm. Both hoods
v/ere improperly shaped and -were located too high
above the source for adequate capture.

A cylindrical furnace rotates on its longitudinal
axis, and  a  tight breeching is  mandatory at the
gas discharge end of the furnace.   Adequate in-
draft velocity must be maintained through the
breeching  connection to  prevent the  escape  of
fumes.

The exhaust system for the cylindrical furnace, as
well as  for all types of reverberatory furnaces,
must be designed to handle the products of com-
bustion  at  the maximum fuel rate.  Any lesser
capacity results in a positive pressure within the
furnace during  periods of maximum firing with
resultant  emissions from  all furnace openings.


Reverberatory furnace--tilting type

The tilting-type furnace differs from the rever-
beratory  furnaces  previously discussed in that
the exhaust stack is an integral part of the fur-
nace and  rotates with the furnace during charg-
ing, skimming,  and pouring.  One type of tilting
furnace is charged  through the stack, and skim-
ming  and pouring  are accomplished through a
small tap hole in the side of  the furnace.  Another
type has  a  closeable  charge door,  and a small
port through which the furnace gases  escape.
These  two furnace openings  may describe  a full
180° of arc during  the various phases of a heat.


The wide range  of position of the sources makes
complete capture of the fumes difficult. One  suc-
cessful system utilizes a canopy hood, •with side
panels that completely enclose the furnace. Clear-
ance for working around the furnace is provided
and a minimum indraft velocity of 125 fpm is re-
quired for this  opening.  This velocity provides
complete capture of the emissions unless a cross -
draft of 50 to 200 fpm prevails within the furnace
room, in  which case an estimated 10 percent  of
the fumes "within  the  furnace hood escape from
beneath the hood. This condition is corrected  by
suspending  an asbestos curtain from the wind-
ward  side of the hood  to the  floor.
Reverberatory furnace--rotary tilting type

The rotary-tilting-type of furnace not only tilts
for charging  and pouring but rotates durmg the
melting  period  to  improve heat transfe".  Two
types  are  common.  One is charged through the
burner end and is poured from the exhaust port
of the furnace,   opposite the burner.  The other
has a side charge door at  the center of the fur-
nace through which charging, slagging, and pour-
ing operations are conducted.

Because of the various movements  of this  type of
furnace, direct connection to the control device
is not feasible.   The furnace is under positive
pressure throughout the heat, and fumes are emit-
ted through all furnace openings.

Hooding a rotary-tilting-type reverberatory fur-
nace  for complete capture of fumes is difficult,
and complete collection is seldom achieved.
These furnaces  are undoubtedly the most diffi-
cult type of brass furnace to control.  To hood
them effectively requires  a comprehensive de-
sign.   The major source of emissions occurs at
the furnace discharge.  Capture of fumes is ac-
complished by a hood or stack placed approxi-
 234-767 O - 77 - 20

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276
                                   METALLURGICAL EQUIPMENT
matelylS inches from the furnace.   This  clear-
ance  is necessary to allow sufficient room for
tilting the furnace for pouring.  A minimum in-
draft velocity  of 1, 750 fpm is usually required.
Although this method controls the emissions dur-
ing the melting phase, capturing the  dense fumes
generated during the  pour is difficult.


Hooding is sometimes installed at the burner end
of a furnace to capture emissions that may escape
from  openings  during melting,  or  particularly
during the time the furnace is tilted to pour.  Be-
cause both ends of the furnace are open,  a venting
action is created during the pour,  causing fume
emissions to be discharged from the  elevated end
ofthe furnace.   Close hooding  is not practicable
becaase the operator must observe the conditions
within the  furnace through the  open ends.  An
overhead canopy hood is usually installed.  Fig-
ure 188 illustrates an installation in which a can-
opy hood is used to capture emissions from  one
end of the furnace  while,  at  the opposite end,
baffles have been extended from around the  stack
opening to  minimize crossdrafts and aid in cap-
turing emissions from the ladle being filled from
the furnace.

Additional heavy emissions maybe expected dur-
ing charging, alloying, and slagging.  High-over-
head  canopy hoods  are generally used.   These
overhead hoods are, however,  unsatisfactory un-
less they cover a  large area,  and a high indraft
velocity is provided.
    Figure 188.   Rotary-ti Itmg-type reverperatory furnace venting  to  canopy hood and stack vent:
    (top) Furnace during meltdown,  (bottom)  furnace during pour (Valley  Brass,   Inc.  El Monte,  Calif.).

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                                 Brass- and Bronze-Melting Processes
                                                                                                  277
The need for numerous hoods and large air vol-
umes,  with the resultant larger control device,
makes the  tilting-type open-flame furnace expen-
sive to control.  This type of furnace is  being
gradually replaced by more  easily controllable
equipment.
The following example illustrates the fundamental
design considerations of a side-draft hood for a
rotary-tilting-type furnace.


Example 28

Given:

Rotary-tilting-type brass -melting furnace. Fuel
input,  17gal/hrU.S.  Grade No.  5 fuel oil.  Max-
imum temperature of products of combustion dis-
charged from furnace,  2,600°F.
       Vol  =
       Wt  =
                     60
(17)(8)(15.96)
- '. -
      60
                              =  468scfm
                                  ,      .  .
                              =  36. 2 Ib/min
2.   Volume  of  ambient air required  to reduce
     temperature of products of combustion from
     2,600°  to 250°F:

     Baghouse inlet design temperature selected,
     250 °F. Ambient air temperature assumed to
     be  100°F.

     Heat gained by)  _  iHeat lost by products
     ambient air   j     (of combustion
       MC   At   =MC   At
         a p     a       pc p      pc
                                                          (M  )(0. 25)(250-100) = (36. 2)(0. 27)(2, 600-250)
                                                            3.
                                   TO  BAGHOUSE
                         HOOD
                FURNACE
BURNER
                                         REFRACTORY
  Figure 189.   Rotary-tilting-type brass-melting
  furnace.
 Problem:

 Determine the design features of a side-draft hood
 to vent the furnace.

 Solution:

 1.   Volume  and weight of products to be vented
     from furnace:
     With 10%>excess air, 1 Ib of  U.S.  Grade No.
     5 fuel  oil yields 206.6 ft3  or 15.96 ID  of
     products of combustion.   One gallon of fuel
     oil weighs 8 lt>.
          37.5 M   =  23,000
                 3,
               M   =  613 Ib/min
                 a
            613
           0. 071
                                                                          =   8, 640 cfm at 100°F
3.   Total volume of products to be vented through
    hood:


    Volume from furnace  =  (468)[—rr	777:1
                                  \  60 +  4607

                           =  639 cfm


 Volume from ambient air  =  (8, 640)1 ——	-7— I
                                     V100  + 460 /

                           =  10,950 cfm

          Total  =  11, 589 cfm  at 250°F
4.  Open area of hood: Design for a velocity of
    2, 000 ft/min.  This is adequate  to  ensure
    good pickup if the hood geometry is designed
    properly.


          n-589  =  5. 78 ft2
           2, 000

Problem  note:  Furnace gases should  discharge
directly into center  of hood  opening.  Position-
ing of the hood should be such that it  picks  up
emissions from the  ladle during the furnace tilt
and pour.   Sides  extending to ground level may
be  necessary  to  nullify  crossdrafts.  When the

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278
                                   METALLURGICAL EQUIPMENT
furnace is tilted, emissions will escape from the
high side or the firing end opening.  These may-
be stopped by blowing a portion of the burner com-
bustion air through the furnace,  which forces
emissions through the furnace discharge opening.
If  this is not possible, an auxiliary hood should
be installed over the firing end of the furnace.

Crucible-type furnaces

One large-volume foundry, using tilting-type
crucible furnaces,  installed an exhaust system
to control emissions  during pouring.  The ex-
haust system vents 14 furnaces to a baghouse.
The hooding collects all the fumes during pour-
ing without interfering with the furnace operation
in any way.  The hood  is equipped with a damper
that is closed when the furnace is in the normal
firing position. A linkage system opens the dam-
per  when pouring  begins.   After the furnace is
tilted 40°, the damper is  fully opened,  remain-
ing there for the rest of the pour.  It swings shut
automatically when the furnace is returned to the
firing  position.  The  ductwork leading from the
hood pivots when  the furnace is tilted.  The en-
tire hood is fixed to the  furnace with two bolts,
•which permit its  rapid removal for periodic re-
pairs to the furnace lining and crucible.  Since
only one furnace is poured at a time and the  sys-
tem operates only  during  the pour, only 1,500
cfmisrequiredtocollectthefum.es.  Tests show
that the amount of particulate matter emitted to
the  atmosphere with this system is 0. 125 pound
per  hour per furnace  (Anonymous,  1950).   This
contrasts with a loss of  over  2 pounds per  hour
uncontrolled.

Figure 190 shows an installation of a tilting-type
brass  crucible furnace with a plenum roof-type
hood,  which captures furnace emissions during
the meltdown and  ladle emissions during the pour.

Emissions resulting from the pouring of molten
metal from a ladle  into molds can be controlled
by three  devices.   The first  is  a fixed  pouring
station  that is  hooded so  that the emissions from
the ladle and molds  are captured during the pour-
ing (Figure 191).  A second solution,  for smaller
foundries, is a hood attached to the pouring ladle
and  vented to the  control system through flexible
ductwork.  One variation places a small baghouse
on the crane holding the ladle so that the ladle is
vented  over  the   whole pouring floor.  Another
variation is  a  stationary baghouse and sufficient
flexible ductwork to allow the hood to travel from
mold to mold.  A third  solution employs a hood
attached to the bale,  a  short section of flexible
ductwor k, and two ducts— one mounted on the bridge
crane  and one attached  to  the  stationary  crane
rails.  The ducts  are interconnected with a trans-
fer box, which is  sealed by a continuous loop of
rubberized belt.   This allows  complete freedom
Figure 190.   Tilt-type  crucible  brass  furnace witti
a  plenum roof-type hood.
    Figure 191. Fixed-mold pouring  station with
    fume mold.
of movement for the ladle •within the area served
by the overhead crane  (Figure  192).
Low-frequency induction furnace

The  control  of the emissions from an induction
furnace is much more expensive and difficult if
oilyturnings  are  charged to the furnace.  In ad-
dition to the fumes common to brass melting,

-------
                                Brass- and Bronze-Melting Processes
                                            279
Figure 192.   Exhaust system with moving  duct and  trans-
fer  connection venting brass-pouring ladle (''A'' Brass
Foundry,  Vernon, Calif.).
great  clouds  of  No. 5 Ringelmann black smoke
are generated when the oily shavings contact the
molten heel within the furnace. Adequate hooding
enclosing the furnace  is,  therefore,  required,
and a large volume of air is necessary to capture
thesmokeandfum.es.  Where  900 cfm was suffi-
cient to collect the pouring emissions from an in-
duction furnace using oil-free metal,  10, 000 cfm
was  required throughout  the heat for  a  similarly
sized  furnace melting turnings  with a  3 percent
oil content.   Figure 193  shows an induction fur-
nace with  an adjustable low-canopy hood that can
be positioned to cover  both  meltdown and pour-
ing operations.   A baghouse collects the fume.

Another,  smaller  induction furnace  is  shown in
Figure 194. In addition to capturing furnace emis-
sions  during  meltdown,  the hood  captures emis-
sions  during  the pour into the ladle.  Figure 194
also shows  the extent of emissions after the ladle
is removed from the hood area.
Cupola furnace

An exhaust system to control a cupola must have
sufficient capacity to remove the products of com-
bustion, collect the emissions from the metal tap
spout,  and  provide a minimum indraft velocity
of 250  fpm through the charge door.  In  addition,
side curtains may be required around the charge
door to shield adverse crosscurrents.  A canopy
hood  is recommended for  the  metal tap spout.
The air  requirement  for this hood is a function
of its size and proximity to the source of emis-
sions.

Air Pollution Control  Equipment

Baghouses

Baghouses -with tubular filters are used to con-
trol the emissions from brass furnaces.  This
type of collector is available in many useful and
effective forms.  Wool, cotton, and synthetic fil-
ter media effectively  separate submicron-sized
particulate matter from gases because of the
filtering action of the  "mat" of  particles previous-
ly collected.

The gases leaving a reverberatoryfurnace maybe
100°  to 200°F hotter than  the molten metal and
must be cooled  before reaching the filter  cloth.
Direct cooling, by spraying water into the hot com-
bustion gases, is not generally practiced because
(1)  there is increased corrosion of the ductwork
and collection equipment,  (2) the vaporized water
increases the exhaust  gas volume,  necessitating
a correspondingly larger baghouse, and (3) the
temperature of the gases in the baghouse must be
kept above the dewpoint to  prevent condensation
of water on the bags.   The exhaust gases may be
cooled by dilution -with cold air, but this increases
the size of the control equipment and the operating
costs of the exhaust system.
One cooling system employed consists of a'water-
jacketed cooler followed by air-cooled radiation-
convection columns, as shown in Figure  195.   The
water-jacketed section reduces the temperature
from  approximately 2, 000°  to 900°F.  The ra-
diation-convection coolers  then reduce the tem-
perature to the degree required to protect  the
fabric of the filter medium. Figure 196 depicts
an actual installation showing the  cooling columns
and baghouse.
Treated orlon is gradually  replacing glass  cloth
as  the most favored high-temperature fabric.
Although glass  bags  withstand higher tempera-
tures, the periodic shaking  of the bags gradually
breaks the glass  fibers and  causes  higher main-
tenance costs.
Probably the most critical design factor for a tu-
bular baghouse is the filtering velocity.  A filter-
ing velocity of 2. 5 fpm is recommended for col-
lecting the fumes from brass furnaces with  rela-
tively small concentrations  of fume.  Larger con-
centration!?  of  fume require a lower filtering
velocity.  A higher filtering velocity requires
more frequent shaking to  maintain a pressure
drop through the baghouse within reasonable lim-
its.   Excessive  bag wear results from frequent

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280
                                  METALLURGICAL EQUIPMENT
                                                   Figure  193.  Electric induction tilting-type brass
                                                   furnace  with adjustable canopy hood  and  baghouse
                                                   control  device  (American Brass Company,  Paramount,
                                                   Calif.).
                                                                     Furnace data
                                                   Type,  electric  induction
                                                   Capacity,  3,000  Ib/hr
                         Electrical rating,  450 kw
                         Metal processed,  brass
                                                                 Control  system data
                                                   Fan  motor  rating, 30 hp
                                                   Gas  volume, 12,700 cfm
                                                   Baghouse type, compart-
                                                     mented,  tubular
                                                   Filter area, 7,896 ft2
                                                   FiIter medium, orlon
                                                   Shaking, automatic by
                                                     compartment
                         Fi Itering velocity,  1
                         Pressure drop,  1.8  to
                           4 in.  WC
                         Gas stream cool ing,  tem-
                           perature-control led
                           water  sprays  in duct
                         Hood indraft velocity,
                           560 ft/min
6 fp
shaking and higher filtering velocities.  A pres-
sure  drop of 2 to 5 inches of -water column is
normal, and high pressure differentials  across
the bags are to be avoided.

The baghouse  should  be completely enclosed to
protect the bags  from inclement  weather and
•water  condensation during the night when  the
equipment is usually idle.  The exhaust fan should
be placed downstream from the baghouse to pre-
vent blade abrasion.  Moreover,  problems  with
fan balance  due  to  material's  adhering to the
blades will not occur. Furthermore, brokenbags
are more easily detected-when the exhaust system
discharges to the atmosphere through one opening.
In Table  81,  the  results  of tests performed on
baghouses venting brass furnaces are shown. Note
that the  melting rate  of the induction furnace is
over  4 times that of the crucible gas-fired fur-
naces, yet the baghouse is only one-tenth as large.
Larger baghouses are necessaryfor crucible gas-
fired furnaces because of the heat and volume of
the products of combustion from the gas  burners.

Electrical precipitators

Generally, electrical precipitators are extreme-
ly effective collectors for many substances in any
size range from 200 mesh (74 JJL) to perhaps  0.001
micron,  wet or dry,  ambient or up to  1, 200°F.

-------
                                Brass- and Bronze-Melting Processes
                                                                                                   281
Figure 194.   Electric  induction  furnace  with  an extended hood'over the pouring area:  (left) Hood in place
during pouring operations,  (right)  ladle  removed  from  the hood area (Western Brass Works,  Los Angeles,
Calif.).
                                           GLASS  BAGS
                                                                          2,000 °F
                                           WATER JACKET FLUE

                                           140 °F
                                                     110 °F

 SUCTION/FAN
 AND  STACK
HIGH-TEMPERATURE
FUME COLLECTOR
                                         RADIATION  COOLERS  WATER COOLING TOWER
       AUTOMATIC DRAFT CONTROL
                                                                                       MAIN BRICK STACK
REVERBERATORY
FURNACE
              Figure 195. Sketch of small  baghouse for zinc  fume  (Allen  et  al.,  1952).

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282
METALLURGICAL EQUIPMENT
 Figure 196.  Reverberatory  open-hearth furnace whose slagging  door and tap hole hoods vent to  radiation-
 convection cooling columns  and baghouse (H. Kramer and  Company, El Segundo, Calif.).
                                              Furnace  data
      Type,  reverberatory
      Capaci ty,  50 ton
                       Fuel  input,  7,260,000 Btu/hr
                       Temperature  of  gas discharge, 2,300°F
                                          Control  system data
      Three baghouses in  parallel serve three reverberatory  furnaces and other smaller furnaces.
      Fan motor rating,  three  50 hp                         Filter area (3 houses),  27,216 ft2
      Maximum gas volume,  54,400 cfm                        Maximum fi
      Baghouse inlet temperature, 220°to 250°F
      FiIter medium,  or Ion
      Baghouse type,  compartmented, tubular
                                 Iter  ratio, 2:1
                       Shaking,  automatic by compartment
 This equipment has not, however, proved entire-
 ly satisfactory on lead and zinc fumes.   Lead ox-
 ide in particular  is difficult to collect because  of
 its relatively high resistivity,  which can cause a
 high potential to develop across the dust layer on the
 collecting surface. This not only reduces the poten-
 tial across the gas stream but  may result in spark
 discharge -with resultant back ionization and re-
 entrainment of dust.  In addition, high-voltage
 precipitators have not  been available in  small
 units suitable for small nonferrous foundry use,
 and the first cost may, moreover, be prohibitive.

 Scrubbers
Dynamic scrubbers or mechanical washers have
proved in some applications to be effective from
                  10 to 1 micron, but in addition to being ineffec-
                  tive  in the submicron range, they  have the dis-
                  advantage of high power consumption and mechan-
                  ical  wear and usually require  separation of the
                  metallic fumes and other particulate matter from
                  the circulating water.
                  A number of dynamic and static  scrubbers have
                  been  tested on brass furnaces and all have been
                  found unsatisfactory.  The  scrubbers not only
                  failed to reduce the particulate matter sufficient-
                  ly, but the opacity of the fumes escaping collec-
                  tion-was excessive.  The results of several scrub-
                  ber tests  are  summarized  in Table 82.   These
                  scrubbers have been replaced by baghouses.

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                                    Aluminum-Melting Processes
                                            283
                 Table 82.  EFFICIENCIES OF WET SCRUBBER CONTROL DEVICES
                              SERVING BRASS-MELTING FURNACES
Type
of
scrubber
Venturi •with
•wet cyclone
Dynamic wet
Dynamic wet
Water
rate,
gpm
7.6
20. 0
50. 0
Flue gas
volume,
scfm
860
770
1, 870
Particulate
matter,
gr/scf
In
2. 71
0. 905
1.76
Out
0.704
0.367
0.598
Total dust,
Ib/hr
In
19.95
5.97
28.2
Out
7.04
3.00
13.2
Efficiency,
%
65
50
53
 Collectors depending upon centrifugal principles
 alone are not adapted to brass furnace dust col-
 lection because of the low efficiency of these de-
 vices on submicron-sized particulate matter. One
 Los Angeles foundry operated a wet cyclone gas
 conditioner venting to a wet entrainment separator
 for recovering partially agglomerated zinc  oxide
 fume.   The  concentration of particulate matter
 was relatively small, since tilting crucible fur-
 naces-with slag covers were used,  and the device
 •was able to reduce the weight of the dust and fume s
 emitted below the legal limits,  but the number  of
 unagglomerated  submicron-sized particles es-
 caping collection was sufficient to cause period-
 ic opacity violations.  Consequently, this unit has
 been replaced by a baghouse.
    SECONDARY  ALUMINUM-MELTING
                 PROCESSES


TYPES OF PROCESS

Secondary aluminum melting is essentially the
process of rerneIting aluminum, but the term en-
compasses the following additional practices:

1.  Fluxing.   This  term is applied to any pro-
    cess in which materials are addedto the melt
    to aid in removal of gases, oxides, or other
    impurities, but  do not remain in the final
    product.

2.  Alloying.   This term is applied to any pro-
    cess in -which materials are addedto give de-
    sired properties to the product and become
    part of the final product.

3.  Degassing. This includes any process used
    to reduce or eliminate  dissolved gases.

4.  "Demagging. "   This  includes  any process
    used to reduce the magnesium content of the
    alloy.
 These terms are often used vaguely and overlap
 to a great extent.  For  example, degassing and
 demagging are  usually  accomplished by means
 of fluxes. The use of zinc chloride and zinc flu-
 oride fluxes increases the zinc content of alumi-
 num  alloys.


 Aluminum for secondary melting comes  from
 three main sources:

 1.  Aluminum pigs.  These maybe primary met-
    al butmayalso be secondary aluminum pro-
    ducedby a large secondary smelter to meet
    standard  alloy specifications.

 2.  Foundry returns.  These include gates, ris-
    ers, runners, sprues, and rejected castings.
    In foundries producing  sand mold castings,
    foundry returns may amount to 40 to 60 per-
    cent of the metal poured.

 3.  Scrap.  This category includes aluminum
    contaminated with oil, grease, paint, rubber,
    plastics,and other metals such as iron, mag-
    nesium,  zinc,  and brass.

 The melting of clean aluminum pigs and foundry
 returns without the use of fluxes does not  result
 in the discharge of significant quantities of air
 contaminants.  The melting of aluminum scrap,
however,  frequently requires  air pollution con-
trol equipment to  prevent the discharge  of ex-
 cessive air contaminants.

 Crucible Furnaces
For melting small quantities of aluminum, up to
l.OOOpounds, crucible or pot-type furnaces are
used extensively.  Almost all crucibles are made
of silicon carbide or similar refractory material.
Small crucibles are  lifted out of the furnace and
used as ladles to pour into molds.  The larger
crucibles  are usually used with tilting-type fur-
naces.  For die casting, molten metal is ladled
out-with a  small hand ladle  or it can be fed auto-
matically to the die-casting machine.

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284
                                  METALLURGICAL EQUIPMENT
Reverberatory Furnaces

The reverberatoryfurnace is commonly used for
medium-and large-capacity heats.  Small re-
verberatory furnaces up to approximately 3, 000
pounds' capacitymay be of the tilting type.  Some-
times  a double-hearth construction is  employed
in furnaces of  1,000 to  3,000 pounds' holding
capacity.  This permits melting to take place in
one hearth,  the second hearth  serving only to
hold the molten metal at the appropriate temper-
ature.  Advocates of this design stress that it re-
duces or eliminates the tendency of the metal to
absorb gas.  The contention is that porosity re-
sults fromhydrogen gas, \vhich is liberated from
moisture trapped below the surface of molten
aluminum.  The use of a double hearth permits
moisture to be  driven off before  the metal melts
and runs to the holding hearth.  Sometimes the
melting hearth is also used as a sweat furnace to
separate the aluminum from contaminants such
as brass and steel.  The use  of double-hearth
furnaces for the larger capacity heats is  not com-
mon.

A charging well is frequently used on aluminum
reverberatoryfurnaces. Figure 197 shows a 20-
ton reverberatory furnace -with a charging well.
The well permits chips and other small aluminum
scrap to be introduced and immersed below the
liquid level.  Chips and small scrap have an un-
usually high surface area-to-volume  relation-
ship,  and  oxidation must be minimized.  Large
quantities of fluxare also added and stirred in to
dissolve the oxide coating and aid in the removal
of dirt  and other impurities.   The flux causes
the oxides and other impurities to rise to the sur-
face in the form of a dross that can be  skimmed
off easily.

Reverberatory furnaces of 20- to 50-ton holding
capacity are common.  Usually one heat is pro-
duced  in a 24-hour period; however,  the  time
per heat in different shops varies from 4 hours
to as much as 72 hours.   This type of furnace is
commonly used to melt a variety of scrap.   The
materials charged, method of charging, size and
design of the furn'ace,  heat input, and fluxing,
refining, and alloying procedures all have some
influence on the time required to complete a heat.
After the charge is completely melted, alloying
ingredients are  added to adjust the composition
to required specifications.  Large quantities of
fluxes are added when scrap of small size and low
grade  is melted.  The flux in some cases  may
amount to as much as 30 percent of the -weight of
scrap charged.


Fuel-Fired Furnaces

Both gas-  and  oil-fired furnaces  are common,
though gas-fired furnaces are usually preferred.
Frequently, combination burners are used so that
gas may be burned when available, with oil sub-
stituted during periods of gas curtailment.

Fuel-fired furnaces used for aluminum melting
are extremely inefficient. Approximately 50 per-
cent of the gross heating value in the fuel is un-
available in the products of combustion.  Radia-
tion and convection losses are high since little or
no insulation  is used.  Many small crucible fur-
naces probably do not achieve more than 5 per-
cent overall efficiency and some may not exceed
2 to 3 percent (Anderson,  1925).  At the other
extreme a properly designed and operated fur-
nace may be able to use as much as 20 percent
of the gross heat  in the fuel. Most furnaces can
be  assumed to operate -with efficiencies of  5 to
15 percent.  This may become an important fac-
tor when air pollution control equipment must be
provided to handle the products of combustion.
Fortunately,  this is seldomnecessary.  Controls,
if provided, are usually required only during the
degassing or demagging operations when the burn-
ers are  off.  Another possibility is to add fluxes
and  scrap  only to a charging -well that is vented
to control equipment.


Electrically Heated  Furnaces

Electric induction furnaces are becoming increas -
ingly common for both melting and holding alumi-
num in spite of higher installation and operating
costs.  Some of the advantages they offer over
other furnaces are higher efficiency, closer tem-
perature control, no contaminants from products
of combustion, less oxidation, and improved ho-
mogeneity of metal.  Electric resistance heating
is sometimes used for holding but rarely for melt-
ing furnaces.  Most electric furnaces for alumi-
num melting  are relatively small  though some
holding furnaces  have capacities up to about 15
tons.
 Charging  Practices

 Small crucible furnaces are usually charged by
 hand with pigs and foundry returns.  Many rever-
 beratoryfurnaces are also charged with the same
 type of materials, but mechanical means are used
 because of the larger quantity of materials in-
 volved.
 When chips  and light  scrap are melted, it is a
 common practice to melt some heavier scrap or
 pigs  first to form  a molten  "heel. "   The light
 scrap is  then added and immediately immersed
 below the surface of the molten  metal so that
 further oxidation is prevented.   The  heel may
 consist of 5, 000 to 20,000 pounds,  depending up-
 on the size of the furnace.

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                                      Aluminum-Melting Processes
                                             285
Figure 197.  A 20-ton aluminum-melting reverberatory furnace with charging well hood  (Aaron.Ferrer & Sons, Inc.,Los
Angeles, Cal if.).
 Pouring Practices

 Tilting-type crucible furnaces are used when the
 crucible is too large to be handled easily.  These
 furnaces are poured into smaller capacity ladles
 for transfer to the molds.  Larger reverberatory
 furnaces are either tapped from a tap hole or si-
 phoned into a ladle.  Ladles vary up to 3  or 4 tons
 capacity  in some cases.  Sometimes the ladles
 are equipped with covers with electric resistance
 heaters to prevent  loss of temperature when the
 ladle is not to be poured immediately or when the
 pouring requires too long a time.  Pouring mol-
 ten aluminum  does  not usually result in the dis-
 charge of air contaminants in significant quanti-
 ties.
Fluxing

The objectives of fluxing generally fall into four
main categories:


1.   Cover fluxes. These fluxes are used to cov-
     er the surface of the metal to prevent further
     oxidation and are usually liquid at the melting
     point of aluminum.  Some of these are also
     effective in preventing gas absorption.


2.   Solvent fluxes.  These fluxes generally cause
     the impurities  and oxides to float on  top of
     the melt in  the form of a dross that can be
     skimmed off easily.

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286
METALLURGICAL EQUIPMENT
3.  Degassing fluxes.   These  fluxes are used to
    purge the melt of dissolved gases.   The dis-
    solved  gas  is  assumed to be hydrogen,  but
    other gases are also highly soluble in alumi-
    num.   The  solubility of gases in molten alu-
    minum increases with temperature.  The gas-
    es  most  soluble in molten aluminum, in de-
    creasing  order of solubility, are  hydrogen,
    methane, carbon dioxide, sulfur dioxide, oxy-
    gen,  air,  and carbon monoxide.   The solu-
    bility of hydrogen is 6 or 7 times as great as
    that of methane and over 10 times that of car-
    bon dioxide.   Elimination  of hydrogen gas in
    aluminum is a major problem.

4.  Magnesium-reducing fluxes.  These fluxes
    are used to reduce  the magnesium content
    of  the  alloy (known as demagging).  During
    World War II it became necessary to recov-
    er large quantities of aluminum scrap, much
    of  which had a magnesium content too high
    for the intended use.  It was found that the
    magnesium could be  selectively  removed  by
    the use of appropriate fluxes.

The quantity and type of fluxing depend upon the
the type of furnace, the materials being melted,
and the  specifications of the final product.  A few
operators melting only pigs and returns find flux-
ing unnecessary. At the other extreme are large
secondary smelters that process very low-grade
scrap and sometimes use fluxes amounting to  as
much as one-third  of the  -weight of the aluminum
scrap charged.  About 10 percent by weight is  an
average figure  for the  amount of flux used  for
medium- to low-grade scrap.


Fluxes  for degassing or demagging may be either
solids or gases.   The gaseous types are usually
preferredbecause they are easier to use, and the
rate of application is simpler to control.   Some of
these,  for  example  chlorine,  may  be  used  for
either degassing or demagging, depending upon the
metal temperature.  In  general,  any flux that is
effective in removing magnesium also  removes
gas inclusions.
Cover fluxes

Cover fluxes are used to protect the metal from
contact with air and thereby prevent  oxidation.
Most of these fluxes use sodium chloride as one
of the ingredients  (Anderson,  1931).  Various
proportions  of sodium chloride are frequently
used with calcium chloride and  calcium fluoride.
Sometimes  cryolite or  cryolite with aluminum
fluoride is added to dissolve oxides.  Borax has
alsobeenused alone and in combination with so-
dium chloride.
                   Solvent fluxes

                   Solvent fluxes usually form a gas or vapor at the
                   temperature of the melt.  Their action is largely
                   physical.  The resulting agitation causes the ox-
                   ides and dirt to rise to the top of the molten metal
                   where they can be skimmed  off. Included in this
                   group  are aluminum chloride, ammonium chlo-
                   ride, and zinc chloride. Zinc chloride increases
                   the zinc  content of the alloy probably according
                   to the equation
                       3 Z  Cl,   +
                          n  2
2 Al —- 3 Z
2 A1C1   (100)
                   Aluminum chloride, which is formed in this re-
                   action, is a vapor at temperatures above 352 °F.
                   It bubbles out of the melt, forming a dense -white
                   fume as it condenses in the atmosphere.

                   So-called chemical fluxes are solvents for  alu-
                   minum oxide.  Cryolite, other fluorides, or borax
                   is  used for this purpose.   Part of the action of
                   the fluorides  is thought to be due to the libera-
                   tion of fluorine, which attacks silicates and dirt.
                   Some chlorides are also used extensively, but their
                   action is not understood.

                   Degassing fluxes

                   There  are many methods of removing dissolved
                   gas from molten aluminum, some of -which do not
                   require the addition  of a flux.  Among  the non-
                   flux methods are the use of vibration, high vac-
                   uum, and solidification -with remelting.  None is
                   as  effective as the  use of an active agent such as
                   chlorine gas.  Helium, argon, and nitrogen gases
                   have alsobeenused successfully.   Solid mate rials
                   that have been used include many metallic chlo-
                   rides. Some think  that  their  action is  physical
                   rather than chemical and that one gas is as good
                   as  another.  For this reason, nitrogen has been
                   used extensively.  Nitrogen is not toxic,  and  vir-
                   tually no visible air contaminants are released
                   when it is used.  In addition, it does not coarsen
                   the grain or remove sodium or magnesium from
                   the melt. The main objection to the use of nitro-
                   gen is that commercial nitrogen is usually con-
                   taminated with oxygen and -water vapor (East-wood,
                   1946).


                   Magnesium-reducing fluxes

                   The use of fluxes to reduce the magnesium con-
                   tent of aluminum alloys is a relatively new pro-
                   cedure.  Certain fluxes have  long been known to
                   tend to reduce the percent of magnesium in the
                   alloy, but this process did not become common-
                   place until the advent of World War II.  Several
                   fluxes may be used for this purpose.  Aluminum

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                                      Aluminum -Melting Processes
                                             287
fluoride  and chlorine gas are perhaps the most
commonly used.  The temperature of the melt
must be significantly greater in demagging than
in degassing, usually between 1, 400° and 1,500°F.
As  much as 1 ton of aluminum fluoride is com-
monly used in reverberatory furnaces of 40- to
50-ton capacity.  The aluminum fluoride is  usu-
ally added to the molten metal with smaller quan-
tities of other fluxes such as  sodium chloride,
potassium chloride, and cryolite, and the entire
melt is stirred vigorously.  Magnesium fluoride
is formed, which can then be skimmed off.  Large
quantities of  air contaminants  are  discharged
from this process.


Magnesium reduction -with chlorine

Chlorine  gas  used  for  demagging  is easier  to
regulate than fluxes used for that purpose.  Extra
precautions  must  be  taken because of the high
toxicity  of  this material.   The chlorine is sent
under pressure through carbon tubes or lances  to
the bottom  of the melt and permitted to bubble up
through  the molten aluminum.  Figure 198 (left)
shows a ladle of aluminum before  the lances are
lowered  into  the metal; Figure  198  (right)  shows
the hood in position.
Recently, aluminum reverberatory furnaces have
beenprovided -with chlorination chambers. A typ-
ical chamber is approximately 4 feet •wide  and 10
feet long,  and  is located alongside the furnace.
An archway beneath the molten metal level in the
common wall between the furnace and  the cham-
ber permits the flow of metal between the furnace
and the chamber. Chlorine under pressure is fed
through carbon lances to the bottom of the melt in
the chlorination chamber.  Use  of this chamber
permits  chlorination  during the latter part of the
melting cycle and has the  added advantage of iso-
lating  the contaminant gases and entrained emis-
sions, formed by the demagging process, from the
combustion products of the furnace.

THE AIR POLLUTION PROBLEM

Frequently, a large part of the material charged
to a reverberatory furnace is low-grade scrap and
chips.  Paint, dirt, oil, grease,  and other  con-
taminants from this scrap  cause large quantities
of  smoke and fumes  to be discharged.  Even if
the scrap is clean, large surface-to-volume ratios
require the use  of more fluxes, which can cause
serious air pollution problems.

In a study of the extent of  visible emissions dis-
charged from degassing aluminum -with chlorine
       Figure 198.  Ladle of molten aluminum with (left) lances  in the raised position, and (right) hood in place and
       lances lowered into aluminum.

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 288
                                   METALLURGICAL EQUIPMENT
gas, the major parameters were found to be metal
temperature, chlorine flow rate, and magnesium
content of the alloy.  Other factors affecting the
emissions to a lesser degree are the depth at
which the chlorine is released and the thickness
and composition of the dross on the metal  surface.
Other factors remaining constant,  the  opacity of
the emissions at any time is an inverse function
of the percent magnesium in the metal at that
time.

When the magnesium content is reduced, either
by combining -with chlorine to form magnesium
chloride (MgCl2)  or by using an alloy containing
less magnesium,  a greater fraction of the  chlo-
rine  combines -with  the aluminum to form, alu-
minum  chloride  (AlClj).  The magnesium  chlo-
ride melts at about 1, 312°F,  so that it is  a liquid
or solid at normal temperatures for this opera-
tion (about 1, 300° to 1, 350°F) and thus does not
contribute significantly to the emissions.  A very
small amount may sometimes be released into
the atmosphere as a result of mechanical entrain-
ment.  The aluminum chloride, on the other hand,
sublimes at about 352°F, so that it is a vapor at
the  temperature  of molten  aluminum.  As  the
vapors  cool in the  atmosphere, submicron fumes
are formed, -which have very great opacity in pro-
portion to the weight of material involved.

Chlorine has a much  greater affinity for magne-
sium than it has for aluminum.   This is shown by
the fact that alloys  containing more than  about
0. 5 percent magnesium (and 90 to 97 percent alu-
minum) usually produce only a moderate  quantity
of fume in degassing with chlorine, while alloys
with more than about 0. 75 percent magnesium do
not usually produce a significant quantity of  fume.


In alloys with greater magnesium content,  not
onlyis less aluminum chloride formed, but also
a thick  layer of dross (largely magnesium  chlo-
ride) is built up  on  the  surface,  -which further
suppresses the emission of  fumes.  Aluminum
chloride also reacts with magnesium to form mag-
nesium chloride  and aluminum.   The dross in-
creases the opportunities for this latter reaction.
When chlorine is used for demagging, it is added
so rapidly that large quantities of both aluminum
chloride and magnesium chloride are formed, the
molten bath is vigorously agitated,  and not all of
the chlorine reacts with the metals.  As a result,
a large quantity of aluminum  chloride is dis-
charged along with chlorine gas and  some en-
trained magnesium chloride.  The aluminum chlo-
ride is extremely hygroscopic and absorbs mois-
ture from the air,  with which  it reacts to form
hydrogen chloride.  These air contaminants are
toxic,  corrosive,  and irritating.
 Particle Size of Fumes From Fluxing

One study (McCabe,  1952) found that the major
constituent in  the fume from salt-cryolite flux-
ing in a furnace -was sodium chloride with con-
siderable smaller quantities of compounds of alu-
minum and magnesium.  Electron photomicro-
graphs of thermal precipitator samples indicated
that the particles of fume were all under 2 mi-
crons, most of them being 0. 1 micron. The fumes
were somewhat  corrosive when dry and, -when
collected wet,  formed a highly  corrosive sludge
that tended to setup and harden if allowed to stand
for any  appreciable time.  Another study made
of the fume from chlorinating aluminum to degas
revealed that 100 percent of the fume was smaller
than 2 microns and 90 to 95 percent smaller than
1 micron.  Mean particle  size appeared under a
microscope to  be about  0. 7 micron.

HOODING AND VENTILATION REQUIREMENTS

When no charging-well is  provided,  or when flux-
ing is done inside the furnace, or when dirty scrap
is charged directly into the furnace, then venting
the furnace may be necessary.  In some cases,
the products of  combustion must be vented to the
air pollution control equipment.  The volume to
be vented to the collector,  and the  determination
of temperature may be found similarly to metal-
lurgical furnace calculation procedures described
elsewhere in this manual.

A canopy hood (as previously shown in Figure 197)
is usually used  for capturing the emissions from
the charging well of an aluminum reverberatory
furnace.  Calculation of the quantity of air re-
quired can be accomplished as  shown in the fol-
lowing example.

Example 29

Given:
Metal surface, 2 ft 3 in.  x 11 ft 3 in.
Temperature of molten metal,  1, 350°F.
Hood opening dimensions, 3 ft 9 in.  x 13 ft 9 in.
Height of hood  face above metal surface, 2 ft 6 in.
Ambient air temperature, 80°F.

Problem:
Determine the  volume of air that must be vented
from a low-canopy hood over  the charging well
of  an aluminum-melting  reverberatory furnace
to  ensure complete  capture of the air contami-
nants.
 Solution:

 As discussed in Chapter 3, the folio-wing equation
 gives the  total ventilation rate for low-canopy
 hoods:

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                                    Aluminum-Melting Processes
                                                                             289
       =  5.4(A)(m/
/3
    (At)
5/12
•where
     q  =  total ventilation rate required, cfm

     A =  area of the hood face, ft

     m =  the width of the hot metal surface at
          the charging well, ft

   At  =  the difference in temperature  between
          the hot  surface and the ambient air,  °F.


q  =  (5.4)(3.75)(13.75)(2.25)1/3  (1, 350-80)5/12

   =  7, 170 cfm

Problemnote: The volume calculated here  is the
minimum ventilation required just to accommo-
date the rising column of air due to the  thermal
drive. An additional allowance must be  made to
take care of drafts.  If volatile fluxes are  used,
the volume of fumes generated must also be ac-
commodated. Inmost cases an allowance of about
25  percent additional volume is adequate to en-
sure complete pickup.   The exhaust system  should
therefore be designed to vent about  9, 000  cfm.

Although the gases vented from the charging well
are  hot,  sufficient air is drawn into the hood to
preclude any danger that the hot gas  -will damage
the  exhaust  system.  The temperature of the
mixed gas stream is calculated in example 30.
Example 30

Given:

The furnace with charging •well and canopy hood
venting 9, 000 cfm as shown in Example  29.

Problem:

Determine the temperature of the  air entering
the hood.

Solution:

1.   Determine the heat transferred from the hot
     metal surface to the air  by natural  convec-
     tion:

                             h  A  At
     From Chapter 3,   H1  =   C   S
                                60
•where
     H =  heat transferred from hot metal sur-
          face to the air by natural convection,
          Btu/min

    h  =  coefficient of heat transfer from hori-
          zontal plates  by natural convection,
          Btu/hr/ft2/°F
   A   =  area of hot metal surface, ft
    s

   At  =  temperature difference bet-ween hot
          metal surface and ambient air, °F.

Byusinghc  =  0.38 (At)0'25 and substituting this
quantity into the equation,

                          ,1.25
                                        H'
                                        0.38 (A )(At)
                                        	s
                                               60
                                 H
                                        (0. 38)(2. 25)(11. 25)(1,350-80)
                                                                     1.25
                                                       60
                                     =  1,210 Btu/min
                                 2.  Solve for temperature of the air entering the
                                     hood (assume specific volume of air  =  13.8
                                     ft3/lb):
                                                 q  =  We  At
                                                           P

                                     •where c  = specific heat of air at constant
                                     pressure.

                                            _  (1.210H13.8)   _
                                               (9, 000)(0.24)

                                     Temperature of air entering the hood = 80
                                     +  7.7  =  87.7°F.


                                 The actual  temperature  of  the  air entering the
                                 hood will be  slightly  higher than the value  cal-
                                 culated here, owing to radiation from the molten
                                 metal surface, and radiation and convection from
                                 the hood and the furnace.  In some cases, when
                                 the burners are operated at maximum capacity,
                                 there may be a positive pressure in the furnace.
                                 If  the design of the furnace permits  some of the
                                 products of combustion to be vented into the hood,
                                 the actual temperature maybe substantially high-
                                 er than shown here.  This  situation would  also
                                 require venting a greater volume to ensure cap-
                                 turing the emissions.


                                 AIR POLLUTION  CONTROL EQUIPMENT

                                 The emissions from aluminum fluxing may con-
                                 sist of hydrogen fluoride, hydrogen  chloride,  and
                                 chlorine  in a gaseous  state,  and  aluminum chlo-
                                 ride,  magnesium chloride,  aluminum fluoride,
                                 magnesium fluoride,  aluminum oxide,  magne-
                                 sium  oxide,  zinc chloride,  zinc oxide,  calcium
                                 fluoride, calcium chloride,  and sodium  chloride
                                 in the  solid state.  Not all will be present at one
                                 time,  and many other, minor contaminants may
                                 be emitted  in  a specific case.  Because of the
                                 widely divergent properties  of these various  air
                                 contaminants, the problem of control is compli-
                                 cated.

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 290
                                     METALLURGICAL EQUIPMENT
Some type of scrubber is required to remove the
soluble gaseous fraction of the effluent,  and either
abaghouse or an electricalprecipitator is needed
to control the solids.  In order to obtain adequate
collection efficiency,  the use of high-efficiency
scrubbers,  with a caustic solution as the scrub-
bing medium, has been found necessary.  This
is illustrated in  Table 83, which shows typical
test data on  collection efficiency for both ordi-
nary and high-efficiency scrubbers.
      Table 83.  SCRUBBER COLLECTION
      EFFICIENCY FOR EMISSIONS FROM
          CHLORINATING ALUMINUM

           Scrubber collection efficiencies, %a

Contaminants
HCL
CL2
Particulates
Slot scrubber
Water
90 to 95
30 to 50
30 to 50
10% caustic
solution
95 to 99
50 to 60
50 to 60
Packed-column scrubber
Water
95 to 98
75 to 85
70 to 80
10% caustic
solution
99 to 100
90 to 95
80 to 90
   Collection efficiency depends mainly upon scrubbing ratio
   (gal per 1,000 ft-'), velocity of gas in scrubber, and con-
   tact time and to a lesser extent on other aspects of the
   design.  These values are typical efficiencies obtained by
   actual tests  but do not reflect the entire range of results.
Table  84 summarizes the results of a series of
200 tests made of control efficiencies of nine de-
vices by  a major producer of aluminum (Jenny,
1951).   These results represent the average range
of efficiencies for a number of tests but are not
necessarily the maximum or minimum values ob-
tained. In spite of the high efficiencies obtained
with some of these devices, reducing the emis-
sions  sufficiently  to eliminate a visible plume
was very difficult.  For the dry ultrasonic unit,
the opacity of the emissions exceeded 40 percent
when the outlet  grain loading was greater than
0.25 grain per cubic foot.  The efficiency of this
unit varied widely with the inlet grain loading and
      Table 84.  AVERAGE COLLECTION
     EFFICIENCY OBTAINED BY VARIOUS
         DEVICES ON EMISSIONS FROM
    CHLORINATING ALUMINUM  (Jenny,  1951)
           Type of device
 Horizontal multipass wet cyclone
 Single-pass wet dynamic collector
 Packed-column water scrubber with
 limestone packing
 Ultrasonic agglomerator followed by
 a multitube dry cyclone
 Electrical precipitator
Efficiency,
   65 to 75
   70 to 80

   75 to 85

   85 to 98
   90 to 99
                    retention time, the efficiency increasing with in-
                    creasing values of either or both of these varia-
                    bles.  Other tests by the same company on  col-
                    lectors of a wet type revealed that the opacity
                    exceeded 40 percent periodically,  even when the
                    average  grain loading at the vent  was as low as
                    0. 002 grain per  cubic foot.

                    Figures 198, 199, and 200 show parts of a single
                    installation of air pollution  control equipment
                    for  the control  of emissions  from chlorinating
                    aluminum.  One of the three stations where chlo-
                    rinating  is  performed is  shown in  Figure  198.
                    Note that the hooding  closely encloses the source
                    so that a minimum volume of  air is required to
                    attain 100 percent pickup of air contaminants.  The
                    fumes are scrubbed in the packed-column scrubbers
                    shown in Figure  199.   Tnis  system was designed
                    touse two of the three scrubbers in parallel,  with
                    the  third as a standby.  The scrubbing medium
                    is a 10 percent caustic solution.   After the scrub-
                    bing, the effluent is vented to a five-compartment
                    baghouse with a fully automatic shaking mechan-
                    ism to remove residual particulate matter.   The
                    baghouse  contains a total of 300 orlon bags with
                    a net filtering area of 12,000 square feet.  In ad-
                    dition to  the fumes from  chlorine fluxing, which
                    are vented through the scrubbers,  two aluminum
                    dross-processingbarrels (Figure 200) are vented
                    directly to the baghouse.   The total volume han-
                    dled by the baghouse is about 30, 000 cfm,  of which
Figure 199.  High-efficiency packed-column water scrubbers
used with a baghouse for control  of emissions from chlorine
fluxing and dross processing.

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                                    Aluminum -Melting Processes
                                             291
approximately 6, 000 cfm is from the three chlo-
rine fluxing stations and the balance from the two
dross barrel hoods.  The beneficial effect of the
bag precoating  provided by the aluminum oxide
dust vented  from the dross-processing barrels
permits  a much higher  filtering  velocity than
•would  be advisable if  only the fluxing  stations
•were being served by the baghouse.

Tests  of the scrubber performance have shown
that virtually all the hydrogen chloride and more
than 90  percent of the chlorine are removed by
the caustic scrubbing solution.   Since the efficien-
cy of aluminum chloride removal averages in ex-
cess  of  80 percent, the loading of hygroscopic
and corrosive materials to the baghouse  is rela-
tively  light.   The aluminum oxide dust from the
dross  barrels acts as  a filter cake, -which im-
proves the collection efficiency of the aluminum
chloride fume -while simultaneously reducing or
eliminating the difficulties  usually associated
with collecting hygroscopic materials.  All ex-
posed metal parts are coated -with polyvinyl chlo-
ride or  other  appropriate protective coatings.
The first year of operation indicates that no seri-
ous operational or maintenance problems -will de-
velop.   This  installation  replaced an electrical
precipitator that -was found  extremely difficult
and expensive  to maintain because of corrosion.
An electrical precipitator thathas been used suc-
cessfully to control the emissions from fluxing
aluminum is illustrated in Figure 201. At present
the trend in control equipment for aluminum-flux-
ing emissions appears to be away from electrical
precipitators and toward the scrubber-baghouse
combination.
                 Figure 200.   Two aluminum dross-processing stations, one  shown with hood door raised.
 234-767 O - 77 - 21

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292
METALLURGICAL EQUIPMENT
     Figure 201.  Concrete shell-type electrical  precipitator used  for controlling emissions from fluoride fluxing
     aluminum metal.  The reverberatory furnace is shown in the left portion of the photograph (Apex Smelting Co.,
     Long Beach, Calif.).
As mentioned earlier in this section, the demagging
operation can be done  in a separate chlorination
chamber.  Exhaust volumes  required  to  control
the emissions are much lower when a chlorination
chamber is used than when demagging is done in
the main chamber of the furnace.  The chlorina-
tion  chamber is virtually sealed from  the atmos-
phere,  the  only exception being the cracks in the
refractory. An exhaust system  capable of provid-
ing 300  to  500 cfm  is sufficient to remove all of
the HC1  and chlorine gas from the chamber and,
additionally, to provide a slight  negative pressure
within it.


The control systemconsists of (1) a  settling cham-
ber, where some agglomeration and settling takes
place; (2) a packed-tray-type scrubber  utilizing
10 percent caustic solution, where  virtually all of
the chlorine and nearly all of the HC1 is removed,
together with the major portion of the remaining
particulate matter; and (3) a baghouse, where the
                   remaining particulate is separated from the efflu-
                   ent.  Since the particulates are hygroscopic and
                   the gas  stream from the scrubber to the baghouse
                   is nearly saturated with water,  the effluent must
                   be heated to about 175° F to prevent combustion
                   in the baghouse.
                   This combination control system has proved suc-
                   cessful in controlling demagging emissions; how-
                   ever,  maintenance  costs are high.   All duct-work
                   from the  chlorination chamber  to  the  scrubber
                   must be cleaned of settled particulates soon after
                   each chlorination; otherwise,  they harden and are
                   very difficult to remove.   The packed-tray-type
                   scrubber  also should be  washed free of all col-
                   lected  particulate after  each chlorination.  If this
                   is not  done,  stratification of  the  effluent  and
                   caustic  hampers  removal  of  the  chlorine  and
                   HC1.   Then corrosion occurs in the baghouse and
                   on structures near the baghouse.

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                                        Zinc-Melting Processes
                                             293
 SECONDARY  ZINC-MELTING  PROCESSES

 Zinc is  melted in crucible,  pot, kettle,  rever-
 beratory,  or electric-induction furnaces for use
 in alloying,  casting,  and galvanizing and is re-
 claimed from higher melting point metals in sweat
 furnaces.  Secondary refining of zinc is conduc-
 ted in retort furnaces, •which can also be used to
 manufacture zinc oxide by vaporizing and burn-
 ing zinc in air.   All these operations will be dis-
 cussed in this  section  except the reclaiming of
 zinc from other metals by use of  a sweat furnace.
 Information on this subject can be found in a fol-
 io-wing section entitled,  "Metal Separation Pro-
 cesses. "
 ZINC MELTING

 The melting operation is essentially the same in
 all the different types of furnaces.  In all but the
 low-frequency induction furnace, solid metal can
 be melted without the use of a molten heel.  Once
 a furnace is started, however, a molten heel is
 generally  retained  after each tap for the begin-
 ning of the next heat.

 Zinc  to be melted may be in the  form of ingots,
 reject castings, flashing,  or scrap.  Ingots,  re-
 jects,  and heavy scrap are generally melted first
 to provide a molten bath to which  light scrap and
 flashing are added.  After sufficient metal has
 been  melted, it is heated to the desired pouring
 temperature,  which may vary from 800°   to
 1, 100°F.  Before the pouring, aflux is added and
 the batch agitated to separate the  dross  accumu-
 lated during the melting  operation.  Dross is
 formed by the impurities charged with the  metal
 and from oxidation during the melting and heating
 cycles.  The flux tends to float any partially sub-
 merged dross and conditions it so that it can be
 skimmed from the surface.  When only clean in-
 got is melted, very little,  if any,  fluxing is nec-
 essary.  On the other  hand,  if  dirty scrap is
 melted, large amounts of fluxes are  needed.  Af-
 ter the skimming,  the melt is ready for pouring
 into molds or ladles. No fluxing or special pro-
 cedures are employed  while  the zinc  is  being
 poured.

 The Air Pollution Problem

The discharge  of air contaminants from melting
furnaces is generally caused by excessive tem-
peratures  and  by the melting of metal contami-
nated with organic  material.   Fluxing  can also
create excessive emissions, butfluxesare  avail-
able that clean the metal -without fuming.

Probably the first visible discharge noted from
a furnace is from organic material.  Before the
melt is hot enough to vaporize any zinc, accom-
panying organic material is either partially ox-
idized or vaporized, causing smoke or oily mists
tobe discharged.  This portion of the emissions
can be controlled either by removing the organic
material before the charging to the furnace  or by
completely burning the effluent in a  suitable in-
cinerator or afterburner.
Normally, zinc is  sufficiently fluid for pouring
attemperatures below 1, 100 °F. At that temper-
ature, its vapor pressure is 15.2 millimeters  of
mercury, low enough that the amount of fumes
formed cannot be  seen.   If the metal is heated
above 1, 100°F, excessive vaporization can occur
and the resulting fumes need to be controlled with
an air pollution control device.  Zinc can vapor-
ize and condense as metallic zinc if existing tem-
peratures and atmospheric conditions do not pro-
mote oxidation.  Finely  divided zinc so formed
is a definite fire hazard,  and fires have occurred
in baghouses collecting this material.

Many flux u° now in use do not fume,  and air con-
taminants are not  discharged.  In  some cases,
however, a specific fuming flux may be needed,
in which  case a baghouse  is required (,o collect
the  emissions.  An example of a fuming flux is
ammonium  chloride, -which, -when heated to the
temperature  of molten zinc,  decomposes  into
ammonia and  hydrogen chloride gases.  As the
gases rise into the atmosphere above the molten
metal, they recombine, forming a fume consisting
of very small particles  of ammonium  chloride.

Provided the temperature of the  melt does not
exceed 1, 100°F, there should be no appreciable
amounts of air contaminants discharged when the
zinc  is poured into molds.  Some molds, how-
ever,  especially in die casting, are coated with
mold release compounds containing  oils or other
volatile material.   The heat from the metal va-
porizes the oils, creating air contaminants.  Re-
cently mold release compounds have been de-
veloped that do not  contain oils, and this source
of air pollution is thereby eliminated.

ZINC VAPORIZATION
Retort furnaces are used for operations involving
the vaporization of zinc including  (1) reclaiming
zinc from alloys,   (2) refining by  distillation,
(3) recovering zinc from its oxide,  (4) manufac-
turing zinc oxide,  and   (5) manufacturing pow-
dered zinc.

Three basic types of retort furnaces are used in
Los Angeles County:  (1) Belgian retorts,  (2) dis-
tillation retorts (sometimes called bottle retorts),
and  (3) muffle furnaces.  Belgian  retorts; are
used to reduce zinc uxide to metallic zinc.  Dis-
tillation retorts, used for batch distillations, re-
claim zinc from alloys,  refine  zinc, make pow-
dered zinc,  and make zinc oxide.   Muffle fur-
naces, used for continuous distillation, reclaim

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 294
METALLURGICAL EQUIPMENT
zinc from alloys,  refine zinc,  and make zinc ox-
ide.

Although zinc boils at 1,665°F, most retort fur-
naces are operated at temperatures ranging from
1,800°  to2,280°F.  Zinc vapor burns spontane-
ously in air; therefore, air must be excluded from
the retort  and condenser  when metallic  zinc is
the desired product.  Condensers are designed,
either  for  rapid  cooling  of the zinc vapors to a
temperature  below  the melting point to produce
powdered zinc,  or for slower cooling to  a tem-
perature above the melting point to produce liq-
uid zinc.   When the desired, product is zinc ox-
ide,  the condenser is bypassed and the vapor is
discharged into a stream of air where spontane-
ous combustion converts the  zinc to zinc oxide.
Excess air is used,  not only to ensure sufficient
oxygen  for the combustion,  but also to cool the
products of combustion and convey the oxide to a
suitable collector.

REDUCTION RETORT FURNACES


Reduction in Belgian Retorts

The Belgian retort furnace is one of several hori-
zontal  retort furnaces that have been for many
years the most common device for the reduction
of zinc.  Although the horizontal retort process
is now being replaced by other methods capable
of handling larger volumes  of metal per retort
and by the electrolytic process for the reduction
of zinc ore, only Belgian retorts  are used in the
Los Angeles area.   In this area, zinc ores are
not reduced; the reduction process is used  to re-
claim zinc from the dross formed in zinc-melt-
ing operations,  the zinc oxide collected by air
pollution control systems serving zinc alloy-melt-
ing operations,  and the contaminated zinc oxide
from zinc oxide plants.

A typical Belgian retort (Figure 202) is about 8
inches in internal diameter and from 48 to 60 in-
ches long.  One end is closed and a conical  shaped
clay condenser  from 18 to 24 inches long is at-
tached to the open end. The retorts are arranged
in banks with rows four to seven high and as many
retorts in a row as  are needed to obtain the de-
sired production.  The retorts are generally gas
fired.

The retorts  are  charged with a mixture  of zinc
oxide and powdered coke.  Since these materials
are powdered, water is added to facilitate  charg-
ing and allow the mixture to be packed tightly into
the retort.  From three to four times more carbon
is used than is needed for the  reduction reaction.

After the charging, the condensers are replaced
and their mouths stuffed -with a porous material.
A small hole is left through the stuffing to allow
moisture and unwanted volatile materials to es-
                   cape.  About 3 hours are needed to expel all the
                   undesirable  volatile materials  from the  retort.
                   About 6 hours after charging is  completed,  zinc
                   vapors appear.  The charge in the retort is brought
                   up to 1, 832 °  to 2, 012 °F for about 8 hours, af-
                   ter  which it  may  rise  slowly to a maximum of
                   2,280°F.  The temperature on  the outside of
                   the  retorts  ranges from  2,375°   to 2, 550"F.
                   The condensers are operated at from  780'  to
                   1,020°F, atemperature range above the melting
                   point of zinc but where the vapor pressure is so
                   low that a minimum of zinc vapor is lost.


                   The reduction reaction of zinc oxide  can  be sum-
                   marized by the reaction:
                          ZnO  +  C  =  Zn +  CO
(101)
                   Very little,  if any, zinc oxide is,  however,  ac-
                   tually reduced by the solid carbon in the retort.
                   A series of reactions results in an atmosphere
                   rich  in  carbon monoxide, -which does the actual
                   reducing.  The reactions are reversible,  but by
                   the use of an excess of carbon,  they are forced
                   toward the  right.   The reactions probably  get
                   started by the oxidation of a small portion of the
                   coke by the oxygen in the residual air in the  re-
                   tort. The oxygen is quickly used, but the carbon
                   dioxide  formed  reacts  with the carbon to form
                   carbon monoxide according to the  equation:
                            CO   +  C  =  2CO
(102)
                   The carbon monoxide in turn reacts -with zinc ox-
                   ide to produce zinc and carbon dioxide:
                         CO
                                 ZnO  =  Zn +   CO,
(103)
                   Carbon monoxide is regenerated by use of equa-
                   tion 102,  and the reduction o± the zinc oxide pro-
                   ceeds.
                  About 8 hours after the first zinc begins to be
                  discharged, the heat needed to maintain produc-
                  tion begins to increase and the  amount of zinc
                  produced begins to decrease.   Although zinc can
                  still be produced, the amount of heat absorbed by
                  the reduction reaction decreases and the tempera-
                  ture of the retort and its contents increases. Care
                  must be taken not to damage the retort or fuse
                  its charge.  As a result, a 24-hour cycle has been
                  found to be an economical operation.  The zinc
                  values still in the spent charge are recovered by
                  recycling-withthe  fresh charges.  A single-pass
                  recovery yields  65 to 70 percent  of the zinc
                  charged, but, by recycling, an overall recovery
                  of 95 percent may be obtained.

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                                           Zinc-Melting Processes
                                            295
                                                         FRONT *ALL
                                                         OF FURNACE
            GROUT JOINT

            CONDENSED METAL
            VAPORS
            FLAME FROM
            COMBUSTIBLE GASES
    METALLIC OXIDE CHARGE
    WITH REDUCING MATERIALS
            BURNER PORT
                         Figure 202.   Diagram showing one bank of  a Belgian  retort furnace.
The Air Pollution Problem

The air  contaminants emitted vary in composi-
tion and concentration during the operating cycle
of Belgian retorts.  During  charging operation
very  low concentrations are emitted.   The feed
is moist  and,  therefore, not dusty.   As the re-
torts  are heated, steam is emitted.  After zinc
begins to form,  both carbon monoxide and zinc
vapors  are discharged.  These emissions burn
to form  gaseous  carbon dioxide and  solid zinc
oxide. During the heating cycle, zinc is poured
from  the condensers about three times at 6- to
7-hour intervals.  The amount of zinc vapors dis-
charged  increases during the tapping operation.
Before the spent charge is removed from the re-
torts, the temperature of the retorts  is lowered,
but zinc fumes and  dust from the spent charge
are discharged to the atmosphere.
Hooding and Ventilation Requirements

Air  contaminants are discharged from each re-
tort.  In one installation, a furnace has 240 re-
torts arranged in five horizontal rows -with 48 re-
torts per row.  The face of the furnace measures
70 feet long by 8 feet high; therefore, the air con-
taminants are discharged from 240 separate open-
ings and over an area of 560 square feet.   A hood
2 feet wide by 70 feet long positioned immediate-
ly above the front of the furnace is used to collect
the air contaminants.
fpm.
The hood indraft is 175
DISTILLATION RETORT FURNACES

The distillation retort furnace (Figure 203) con-
sists  of a pear-shaped,  graphite retort,  which
may be  5  feet long by 2 feet in diameter  at the
closed end by 1-1/2 feet in diameter at the open
end and 3 feet  in diameter at its widest cross-
section.  Normally,  the  retort is  encased in a
brick furnace with only the open end protruding
and it is heated externally with  gas- or oil-fired
burners. « The retorts are charged with molten,
impure zirrc through the open end, and a condens-
er is attached to the opening to  receive and con-
dense  the  zinc vapors. After the distillation is
completed,  the  condenser is moved away, the
residue  is removed  from the retort,  and  a new
batch is started.
The vaporized zinc is conducted either to a con-
denser or discharged through an orifice into a
stream  of  air.   Two types  of condensers are
used — a brick-lined steel condenser operated at
from 780° to 1,012° F to  condense the vapor to
liquid  zinc,  or a larger, unlined steel condenser
that cools the vapor to solid zinc. The latter con-
denser is used to  manufacture powered  zinc.
The condensers mustbe operated at a slight pos-
itive pressure to keep air from entering them and

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296
METALLURGICAL EQUIPMENT
                                                                          SPEISS HOLE
                          Figure 203.   Diagram of a distillation-type retort furnace.
oxidizing the zinc.  To ensure that there is a pos-
itive pressure, a  small hole, called a "speiss" '
hole, is provided through -which a small amount
of zinc vapor is allowed to escape continuously
into  the atmosphere.   The  vapor burns -with a
brightflame, indicating that there is a pressure
in the condenser.  Iftheflame gets too large,  the
pressure is toohigh.  Ifitgoes out,  the pressure
is too low.  In either  case, the proper adjust-
ments are made to obtain the desired condenser
pressure.

When it is  desired to make zinc oxide, the vapor
from a retort  is  discharged through an orifice
into  a stream of air where zinc oxide is formed
inside a refractory-lined chamber.  The com-
bustion gases and air, which bear the oxide par-
ticles,  are then carried to a baghouse collector
where the powdered oxide is collected.

The Air Pollution Problem

During the 24-hour  cycle of the distillation  re-
torts,  zinc vapors escape from the retort (l)when
the residue from the preceding batch is  removed
from the retort and a new batch is charged,  and
(2) when the second charge is added to the retort.
As the zinc vapors mix with air,  they oxidize  and
                   form a dense cloud of zinc oxide fumes.  Air con-
                   taminants  are discharged for about 1 hour each
                   time the charging hole is open.  When the zinc is
                   actually being distilled,  no fumes escape from
                   the retort; however, a small amount of zinc oxide
                   escapes from the  speiss hole in the condenser.
                   Although the emission rate is low,  air contami-
                   nants are discharged for about 20 hours per day.


                   Hooding and Ventilation Requirements

                   To capture the emissions from a distillation re-
                   tort  furnace,  simple canopy hoods placed close
                   to and directly over the sources  of emissions are
                   sufficient.   In the only installation in Los Angeles
                   County, the charging end of the retort protrudes
                   a  few  inches through a 4-foot-wide, flat wall of
                   the furnace.  The hood is 1 foot above the retort,
                   extends 1 - 1/4feet out from the furnace wall,  and
                   is4feetwide.  The ventilation provided is  2, 000
                   cfm,  giving a hood indraft of 400 fpm.   Fume
                   pickup  is  excellent.   The speiss  hole  is  small
                   and  all the fumes discharged are captured by a
                   1-foot-diameter hood provided with 200 cfm ven-
                   tilation. The hood indraft is 250 fpm.

                   The  retorts are gas fired and the  products of
                   combustion do not mix with the emissions from

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                                       Zinc-Melting Processes
                                             297
the retort or the condenser.  The exhausted gases
are heated slightly by the combustion of zinc and
from radiation and convection losses from the re-
tort,  but the amount of heating is so low that no
cooling is necessary.

MUFFLE  FURNACES

Muffle furnaces (Figure 204) are continuously fed
retort furnaces.   They generally have a much
greater vaporizing  capacity than either Belgian
retorts  or bottle retorts do,and they are  operated
continuously for several days at a time.   Heat for
vaporization is supplied by gas- or oil-fired burn-
ers by conduction and radiation through  a silicon
carbide arch that separates the  zinc vapors and
the products of combustion.   Molten zinc from
either a melting pot or  sweat  furnace is charged
through a feed well that also acts as an air lock.
The  zinc vapors are conducted to a condenser
where purified liquid zinc  is collected,  or the
condenser  is  bypassed and the  vapors are dis-
charged through an orifice into a stream of air
where zinc oxide is formed.

A muffle furnace installation in Los  Angeles
County consists of three identical furnaces, each
capable  of vaporizing  several tons  of  zinc per
day.  These furnaces can produce zinc of 99. 99
percent purity and  zinc  oxide of 99. 95 percent
purity from zinc alloys.  Each furnace has  three
sections: (1) A vaporizing chamber,  (2) a con-
denser,  and  (3). a  sweating  chamber.  Figure
205 shows the feed ends of the furnaces, includ-
ing the sweating chambers, and some of the  duct-
work and hoods  serving the furnaces.

Eachfurnace,  including the feed  well and sweat-
ing chamber, is heated indirectly-with a  combina-
tion  gas- or oil-fired burner.  The combustion
 chamber,  located directly  over the vaporizing
 chamber,  is heated to about 2, 500 °F.  On leav-
 ing the combustion chamber, the products of com-
 bustion are conducted over the zinc feed well and
 through the sweating chamber to supply the heat
 needed for melting the zinc alloys from the scrap
 charged and for heating the  zinc in the feed well
 to about 900°F.

 Zinc  vapors are  conducted  from the vaporizing
 section into a multiple-chamber condenser.  When
 zinc oxide is the desired  product,  the vapors  are
 allowed to escape through an orifice at the top of
 the first chamber of the condenser.   Even when
 maximum zinc oxide production is desired,  some
 molten zinc is nevertheless  formed and collects
 in the condenser.
When metallic zinc is the desired product,  the
size of the orifice  is greatly reduced,  but not
entirely closed, so that most of the vapors  enter
the second section  of the condenser where they
condense  to molten zinc.   The molten zinc col-
lected in the condenser is held at about 900°F in
a well, from which it is periodically tapped.  The
well and the tap hole are so arranged that  suffi-
cient molten zinc always remains in the well to
maintain an air lock.
The zinc that escapes from the orifice while mol-
ten zinc is being made burns to zinc oxide, which
is conducted to the product baghouse.
The Air Pollution Problem

Dust and fumes are created by the sweating oper-
tion.  Scrap is charged into the sweating chamber
through the door shown in Figure 205.  After the
                 •STACK
                                                                                  DUCT FOR OXIDE
                                                                                  COLLECTION
                                                                                 RISER CONDENSER
                                                                                 UNIT
                             Figure 204.  Diagram of a muffle furnace and condenser.

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298
METALLURGICAL EQUIPMENT
     Figure 205.  (Left) Zinc-vaporizing muffle furnaces,  (right) baghouse for collecting the zinc oxide manufactured
     (Pacific Smelting Co.,  Torrance,  Calif.).
zinc alloys have been  melted, the residue  is
pushed out of the chamber through a second door
and onto a shaker  screen where dross is sepa-
rated from solid metal.  Excessive dust and fumes
are thereby created.

The zinc alloys charged into the vaporizing sec-
tion  contain copper,  aluminum,  iron,  lead, and
other impurities.  As  zinc is distilled from the
metals,  the  concentration  of the impurities in-
creases until continued distillation becomes im-
practical.  After 10 to  14 days of operation,  the
residue,  containing  10 to  50 percent  zinc must
be removed.   When  tapped/ the temperature of
the residue is  about  1,900°F, hot  enough to re-
lease zinc oxide fumes.   The molds  collecting
the residue metal are so arranged that the metal
overflows  from one  mold  to another; however,
the metal cools so rapidly that fumes are released
only from the pouring  spout and the first two or
three molds.  The  fumes, almost entirely zinc
oxide,  are 100 percent opaque from the  pouring
spout and the first mold.  At the third  mold,  the
opacity decreases to 10 percent.

Any discharge  of zinc vapor from the condenser
forms zinc oxide of product purity; therefore,  the
condenser vents into the intake hood of a product-
collecting exhaust system.  Sinc'e some zinc oxide
is always produced,  even when the condenser is
set to  produce a maximum  of liquid  zinc,  the
product-collecting  exhaust system is always in
operation  to prevent air contaminants from es-
caping from the condenser to the atmosphere.
                  Hooding and Ventilation Requirements

                  The dust and fumes created  by the charging of
                  scrap and the sweating  of zinc alloys from the
                  scrap originate inside the sweat chamber.  The
                  thermal drafts  cause the emissions to escape
                  from the upper portion  of the  sweat chamber
                  doors.  Hoods are placed over the doors to col-
                  lect the emissions.   The  charging door hood ex-
                  tends 10 inches from the furnace -wall and covers
                  a little more than the width of the door (see Fig-
                  ure Z05).  With two furnaces in operation  at the
                  same time,  each  of the charging door hoods is
                  supplied -with 3, 200  cfm  ventilation,  -which pro-
                  vides an indraft velocity of 700 fpm.  All fumes
                  escaping from the charging doors are collected
                  by these hoods.

                  The unmelted scrap and dross  are raked from a
                  sweating chamber onto a shaker screen. A hood
                  enclosing the discharge lip and the screen is pro-
                  vided with 5, 500 cfm ventilation.  The inlet ve-
                  locity is 250 fpm,  sufficient to capture all  of the
                  emissions escaping from both the furnace and the
                  screen.

                  A hood 3 feet square positioned over the residue
                  metal-tapping spout and the first  mold is pro-
                  vided with 8, 700 cfm ventilation. During the tap-
                  ping, no metal is charged to either sweating
                  chamber,  and the exhaust system dampers are
                  arranged so that approximately one-half of the
                  available volume is used at the tapping spout.  The
                  indraft velocity is in excess of 900 fpm, and all

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                                            Lead Refining
                                                                                                 299
fumes released from the metal are collected, even
from the second and thirdmolds up to 6 feet away
from the hood.

The ductwork joining the hoods to the control de-
vices is manifolded and dampered so that  any or
all hoods  can be opened or closed.  The exhaust
system provides sufficient ventilation to control
the fumes created by two furnaces in operation at
the same time.  When residue  metal is  being
tapped from a furnace, no metal is being charged
to the other furnaces;  therefore,  all the ventila-
tion, or as much as is needed, can be used at the
tapping hood.
 AIR POLLUTION CONTROL EQUIPMENT

 For all the  furnaces  mentioned in this section,
 that is   reduction retort furnaces, distillation
 retort furnaces, and muffle furnaces, air pollu-
 tion control is achieved with a baghouse.  In the
 above-mentioned installation for a. muffle furnace,
 a low-efficiency cyclone and a baghouse are used
 to control the emissions from the sweating cham-
 bers and residue pouring operations of the three
 muffle furnaces.  Although the cyclone has a low
 collection efficiency,  it does collect from 5 to 10
 percent of the dust load and it is still used.  The
 cyclone was in existence before the  baghouse  was
 installed.

 The baghouse is a six-section, pull-through type
 using 5,616 square feet of glass  cloth filtering
 area.  The filtering velocity is 3 fpm and the bags
 are cleaned automatically at regular intervals by
 shutting off one section, which allows the  bags to
 collapse.   No shaking is required, and the col-
 lected material merely drops into the hopper be-
 low the bags.

 Another exhaust system -with a cyclone and bag-
 house is used to collect the zinc oxide manufac-
 tured by  the  muffle  furnaces.  The system has
 three inlet hoods, one for each furnace, and each
 is arranged to collect  the zinc vapors discharged
 from the orifice in the  condenser.   The ductwork
 is manifolded into a single duct entering  the cy-
 clone, and dampers are provided so that any one
 or any  combination of the hoods can be  used at
 onetime.  Since the exhausted gases and zinc ox-
 ide are heated by the combustion  of zinc  and by
 the sensible heat in  the zinc,  about 350  feet of
 additional ductwork is provided to allow  the ex-
 hausted material  to  cool  down to 180°F before
 entering the baghouse.

 The cyclone collects about 20 percent of the solid
 materials in the exhaust gases,  including  all the
 heavier particles such as vitrified zinc oxide and
 solid zinc. The baghouse collects essentially all
 the remaining 80 percent of the solids.
The  baghouse collector is actually two standard
nine-section baghouses  operating in parallel. In
this unit, orlonbags with a total of 16, 848 square
feet of filtering area are used to filter the solids
from the  gases.  A 50-hp fan provides 30, 500
cfm  ventilation--15, 250 cfm for each furnace.
The filtering velocity is 1. 8 fpm.  The bags are
cleaned at regular  intervals by shutting off one
section and shaking the bags for  a few seconds.
A screw  conveyor in the bottom  of each hopper
conveys the zinc oxide collected to a bagging ma-
chine.

This system provides excellent ventilation for the
installation.  None of the zinc oxide discharging
from the  condensers escapes collection by the
hoods, and no visible emissions can be seen es-
caping from the baghouse.

Dust collectors for other zinc-melting and zinc-
vaporizing furnaces are very similar to the ones
already described.  Glass bags have been found
adequate when gas temperatures exceed the limits
of cotton or orlon.  Filtering velocities of 3  fpm
are generally employed and have been found ade-
quate.
              LEAD REFINING

Control of the air pollution resulting from the
secondary smelting and reclaiming of lead scrap
maybe conveniently considered according to the
type of furnace employed.   The reverberatory,
blast, and pot furnaces are the three types most
commonly used.  In addition to refining lead,
most of the  secondary refineries also produce
lead oxide by the Barton process.

Various grades of lead metal along with the  oxides
are producedby the lead industry.  The grade  of
product desired determines the type of equipment
selected for its manufacture.  The most common
grades of lead produced are  soft, semisoft,  and
hard.  By starting with one  of these grades and
using accepted  refining and  alloying techniques,
any  special  grade of lead or  lead alloy  can be
made.

Soft lead  may be designated  as corroding, chem-
ical,  acid copper,  or  common desilverized lead.
These four types are high-purity leads.  Their
chemical requirements are presented in Table 85.
These leads are the products of the pot furnace after
a  considerable  amount of refining has been done.

Semisoft lead is the product of the  reverberatory-
type furnace and usually contains from 0. 3  to 0. 4
percent antimony and up to 0. 05  percent copper.

Hard lead is made in the blast furnace.  A typ-
ical composition for hard lead is 5 to 12 percent

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300
                                  METALLURGICAL EQUIPMENT
                       Table 85.  CHEMICAL REQUIREMENTS FOR LEADa
                                 (ASTM Standards,  Part 2 1958)

Silver, max %
Silver, min. %
Copper, max %
Copper, rnin. %
Silver and copper together,
max %
Arsenic, antimony, and
tin together, max %
Zinc, max %
Iron, max %
Bismuth, max %
Lead (by difference),
min. %
Corroding
lead
0. 0015

0. 0015

0. 0025
0. 002
0. 001
0. 002
0. 050
99. 94
Chemical
lead
0. 020
0. 002
0. 080
0. 040

0. 002
0. 001
0. 002
0.005
99. 90
Acid-
copper
lead
0. 002

0. 080
0. 040
0. 040
0. 002
0. 001
0. 002
0. 025
99. 90
Common
desilverized
lead
0. 002

0. 0025


0. 005
0. 002
0. 002
0. 150
99. 85
               aCorroding lead is a designation used in the trade for many years to
                describe lead refined to a high degree of purity.

                Chemical lead is a term used in the trade  to describe the undesilverized
                lead produced from Southeastern Missouri ores.

                Acid-copper lead is made by adding copper to fully refined lead.

                Common desilverized lead is  a designation used to describe fully
                refined desilverized lead.
antimony,  0. 2 to 0. 6 percent arsenic, 0. 5 to  1.2
percent  tin, 0.05 to  0. 15 percent copper,  and
0. 001 to 0. 01 percent nickel.


REVERBERATORY  FURNACES
Sweating operations are usually conducted in a
reverberatory-type  furnace or tube.   This type
of operation is discussed later in this chapter
in a  section on "Metal Separation Processes. "
The reverberatory furnace  is  also  used to re-
claim lead from oxides  and drosses.   Very often
material for both  sweating and  reducing such as
lead scrap, batteryplates, oxides, drosses, and
lead  residues  are charged  to  a  reverberatory
furnace. The charges are made up of a mixture
of these materials and put  into  the  furnace in
such a manner as to keep  a very small  mound
of unmelted material on top of  the bath.   As  the
mound becomes molten, more material is  charged.
This type of furnace may be  gas fired or oil fired,
or a combination of both. The temperature is main-
tained at approximately 2, 300°F.  Only sufficient
draft is pulled to remove the  smoke and fumes and
still allow the retention of as much heat as possible
over the hearth.  The molten metal is tapped off
at intervals as a semisoft lead as the level of the
metal  rises.  This  operation is  continuous,  and
recovery is generally about 10 to 12 pounds of met-
al per  hour per  square foot of hearth area.


The Air Pollution Problem

Afairly high percentage of sulfur is usually pres-
ent in  various forms in the charge to the rever-
beratory furnace.  The temperature maintained
is sufficiently high to  "kill" the sulfides and re-
sults in the formation of sulfur dioxide and sulfur
trioxide in  the  exit gases.   Also present in the
smoke and fumes produced are oxides,  sulfides,
and  sulfates of lead,  tin, arsenic, copper, and
antimony.  An overall material balance  shows  on
the product side approximately 47 percent recov-
ery of metal, 46 percent recovery of slag some-
times  called "litharge, "  and 7 percent of smoke
and fumes.

The unagglomerated particulate matter emitted
from secondary lead-smelting operations has been
found to have a particle size range from  0.07 to 0.4

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                                           Lead Refining
                                           301
micron with  a.  mean of  about  0. 3  micron (Allen
et al. ,  1952).  Figure Z06 shows electron photo-
micrographs  of lead fumes.  The particles are
nearly spherical and have a distinct tendency to
agglomerate.   The concentration  of particulate
matter in stack gases ranges  from  1.4 to 4. 5
grains per cubic foot.
Hooding and Ventilation Requirements
All the smoke and fumes produced by the rever-
beratory furnace must be collected  and,  since
they are combined -with the products of combus-
tion, the entire  volume emitted from the furnace
must pass through the collector.  It is not desir-
able to draw cool air into these furnaces through
the charge doors, inspection ports, or other open-
ings to keep air contaminants from escaping from
them; therefore, externalhoods are used to cap-
ture these  emissions.  The ventilating  air  for
thesehoods as well as for the hoods venting slag
stations must also pass through the collector.   In
large furnaces,  this  represents a considerable
volume  of gases at fairly high temperatures.

Air Pollution Control Equipment

The only control systems found to operate satis-
factorily in^Los Angeles County  have been those
                             • •
    IVT-7-3.
                Figure 206.  Electron photomicrographs of lead  fumes (Allen et  al., 1952).

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302
METALLURGICAL EQUIPMENT
employing a baghouse as a final collector.   These
systems also include auxiliary items such as gas -
cooling devices and settling chambers.
A  pull-through type  of baghouse with compart-
ments that can be shut off one at a time is very
satisfactory.   This allows  atmospheric  air  to
enter one compartment and relieve any flow.  The
bags may then be cleaned by a standard mechan-
ical shaking mechanism.
Provision should be made to prevent sparks and
burning mate rials from contacting the filtercloth,
and temperature must be controlled by preced-
ing the baghouse with radiant cooling ducts,  water-
jacketed cooling ducts, or other suitable devices
in  order that the type of cloth used will have a
reasonable life.   The type of cloth selected de-
pends upon parameters such as the temperature
and  corrosivity of the entering gases, and the
permeability and abrasion-  or stress-resisting
characteristics of the cloth.  Dacron bags are
being successfully used in this service. The fil-
tering velocity should not exceed 2 fpm.  Test
results of secondary lead-smelting furnaces vent-
ing to a baghouse control device  are shown in
Table 86.

The factors  to be considered in designing these
control systems are similar to those discussed
previously in the sections  on iron casting and
steel manufacturing.
LEAD BLAST FURNACES

The lead blast furnace or cupola is constructed
similarly to those used in the ferrous industry.
The materials forming the usual charge for the
blastfurnace, and a typical percentage composi-
tion are 4. 5 percent rerun slag, 4. 5 percent scrap
castiron, 3 percent limestone, 5.5 percent coke,
and 82. 5 percent drosses, oxides,  and reverbera-
tory slags.  The rerun slag is the highly silicated
slag from previous blast furnace runs.  The
drosses are miscellaneous  drosses  consisting
of  copper  drosses, caustic drosses,  and dry
drosses obtained from refining processes in the
pot furnaces.   The processes will be  described
in more detail in the following paragraphs.  The
coke is used as a source  of heat,  and combustion
air is introduced near the bottom of the furnace
through tuyeres at a gage pressure of about 8  to
12 ounces per square inch. Hard lead  is charged
into the cupola at the start  of the operation  to
provide molten metal to fill the crucible. Normal
charges,  as  outlined previously,  are  then added
as the material melts  down.  The limestone and
iron form the flux that  floats on top of  the molten
lead and retards its oxidation.

As  the level  of molten material rises, the  slag
is tapped at intervals while the molten lead flows
                  from the furnace at a more or less continuous
                  rate.  The lead product is "hard" or "antimonial. "
                  Approximately 70 percent of the molten material
                  is tapped off as hard lead,  and the remaining 30
                  percent, as slag.  About 5 percent of the slag is
                  retained for rerun later.


                  The Air Pollution Problem

                  Combustion air from the tuyeres passing verti-
                  cally upward through the charge in  a blast fur-
                  nace  conveys oxides, smoke, bits of coke fuel,
                  and other particulates present in the  charge.  A
                  typical material balance based upon the charge to
                  a  blast furnace in which battery groups are being
                  processed is 70 percent recovery of  lead,  8 per-
                  cent  slag,  10 percent matte (sulfur compounds
                  formed with slag), 5 percent water (moisture con-
                  tained in charge), and 7 percent dust (lead oxide
                  and  other particulates discharged from stack of
                  furnace with gaseous products of combustion).
                  Particulate matter loading in blast furnace gases
                  is exceedingly heavy, up to 4 grains  per cubic
                  foot.  The particle size distribution is very simi-
                  lar to that from gray iron cupolas, as described
                  previously  in the  section on "Iron Casting. "
                   Blast furnace stack gas temperatures range from
                   1, 200°  to 1, 350°F.  In addition to the particu-
                   late matter,  which consists  of smoke,  oil vapor,
                   fume,   and dust,  the  blast  furnace stack gases
                   contain carbon monoxide.  An afterburner is nec-
                   essary to control the gaseous, liquid, and solid
                   combustible material in the effluent.


                   Hooding and Ventilation Requirements

                   The only  practical way to capture the contami-
                   nants  discharged from a lead blast furnace is to
                   seal the furnace and vent all the gases to a con-
                   trol system.  The hooding and ventilation require-
                   ments  are very similar  to those  for the gray
                   iron cupola,  which are discussed in the section
                   on "Iron Casting. "
                   Air Pollution Control Equipment

                   The control system for  a lead blast furnace is
                   similar to that employed for gray iron cupola fur-
                   naces except that electrical precipitators are not
                   usedfor economic reasons. Moreover,  difficul-
                   ties are encountered in conditioning the particles
                   to give them resistivity characteristics in the
                   range that will allow efficient collection.

                   The factors to be considered  in designing a con-
                   trol system for a blast furnace,  including an af-
                   terburner and a baghouse, have been discussed
                   in the section on  "Iron Casting. "

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                                            Lead Refining
                                                                                                 303
     Table 86.  DUST AND FUME EMISSIONS FROM A SECONDARY LEAD-SMELTING FURNACE
Test No.
Furnace data
Type of furnace
Fuel used
Material charged
Process weight, Ib/hr
Control equipment data
Type of control equipment
Filter material
Filter area, ft
Filter velocity, fpm at 327 °F
Dust and fume data
Gas flow rate, scfm
Furnace outlet
Baghouse outlet
Gas temperature, °F
Furnace outlet
Baghouse outlet
Concentration, gr/scf
Furnace outlet
Baghouse outlet
Dust and fume emission, Ib/hr
Furnace outlet
Baghouse outlet
Baghouse efficiency, %
Baghouse catch, wt %
Particle size 0 to 1 (i
1 to 2
2 to 3
3 to 4
4 to 16
Sulfur compounds as SO2> vol %
Baghouse outlet
1

Reverberatory
Natural gas
Battery groups
2,500

Sectioned tubular baghousea
Dacron
16,000
0.98


3,060
10,400b

951
327

4.98
0.013

130.5
1.2
99. 1

13. 3
45.2
19. 1
14.0
8.4

0. 104
2

Blast
Coke
Battery groups, dross, slag
2,670

Sectioned tubular baghousea
Dacron
16,000
0.98


2, 170
13,000b

500
175

12. 3
0.035

229
3.9
98. 3

13.3
45.2
19. 1
14.0
8.4

0.03
      f^The same baghouse alternately serves the reverberatory furnace and the blast furnace.
      DT
       Dilution air admitted to- cool gas stream.

 POT-TYPE FURNACES

 Pot-type furnaces are used for remelting,  alloy-
 ing, and refining processes.  Remelting is usually
 done in small pot furnaces,  and  the materials
 charged are usually alloys in  the ingot form,
 which do not require any further processing ex-
 cept to be melted for casting  operations.
The pots  used in the secondary smelters range
from the smallest practical size of 1-ton capac-
ity up to 50 tons.  Figure 207 is a photograph of
two  pot furnaces utilizing a common ventilation
hood.  These furnaces are  usually gas  fired.
Various refining and alloying operations are car-
ried on in these pots.   Alloying usually begins
with a metal lower in  the  percentage of alloy-
ing materials than desired.  The percent desired
is calculated and the amount is then added.  An-
timony, tin, arsenic,  copper, and nickel are the
most common alloying elements used.

The refining processes most commonly employed
are those for the removal of copper and antimony
to produce soft lead, and those for the removal of
arsenic, copper, and nickel to produce hard lead.
For copper removal, the temperature of the mol-
tenleadis allowed to drop to 620°F and sulfur is
added.  The mixture is agitated and copper sulfide
is skimmed off as dross.  This is known as "cop-
per dross" and is charged into the blast furnace.

When aluminum is added to molten lead,  it reacts
preferentially with copper, antimony, and nickel
to form complex compounds that can be skimmed
from the surface of the metal.  The antimony con-
tent can also be reduced to about 0. 02 percent by
bubbling air through the molten lead.  It can be

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 304
METALLURGICAL EQUIPMENT
Figure 207.  An installation used to capture emissions from
two lead pot furnaces.  Hood serves either furnace alternately
(Morris P. Kirk & Son,  Inc., Los Angeles, Calif.).
 further  reduced by adding  a mixture of sodium
 nitrate and  sodium hydroxide and skimming the
 resulting dross from the surface of the metal.

 Another common refining procedure, "drydross-
 ing, " consists  of  introducing  sawdust into  the
 agitated mass of molten metal.  This forms car-
 bon, which aids in separating the globules of lead
 suspended in the dross,  and reduces some  of the
 lead oxide to elemental lead.

 In areas where there is no great concern about
 air pollution, a mixture of sal ammoniac and rosin
 may be used to clean the metal of  impurities.
 This method, however, produces  copious quanti-
 ties of dense, white fumes,  and obnoxious  odors.
 In areas having air pollution laws, this method
 is generally no longer used.


 The Air Pollution Problem

 Although the quantity of  air  contaminants dis-
 charged from pot furnaces as a result of remelt-
 ing,  alloying, and refining is much less than  that
 from reverberatory or blast furnaces, the cap-
 ture and control of these contaminants is equally
 important in order to prevent periodic violations
 of air pollution regulations and protect the  health
 of the employees.

 Problems of industrial hygiene  are inherent in
 this  industry.  People working with this equip-
 ment frequently inhale and ingest lead oxide fumes,
                   •which are cumulative,  systemic poisons.   Fre-
                   quent medical examinations are necessary for all
                   employees,  and a mandatory dosage of calcium
                   dis odium ver senate maybe required daily in order
                   to keep the harmful effects to a minimum.

                   Hooding and Ventilation Requirements

                   Hood design procedures for pot furnaces are the
                   same as those outlined for electric-induction fur-
                   naces mentioned earlier in this chapter.


                   Air  Pollution  Control Equipment

                   The control systems for pot furnaces,  as with the
                   other lead furnaces, require the use of a baghouse
                   for  the final collector.  The temperature of the
                   gases is,  however,   generally  much lower than
                   that from the other furnaces; therefore,  the gas-
                   cooling devices, if needed, will be much smaller.
                   Afterburners are generally not required.


                   BARTON PROCESS

                   A rather specialized phase of the industry is the
                   production  of lead  oxide.   Battery lead oxide,
                   containing about  20  percent finely divided free
                   lead, is usually produced by the Barton process.
                   Molten lead is run by gravity from a melting pot
                   into a kettle equipped  with paddles. The paddles
                   are rotated at about 150 rpm,  rapidly agitating
                   the molten lead, •which is at a temperature  of 700°
                   to  900°F.  Air is drawn through the kettles by
                   fans located on the air outlet side of a baghouse.
                   The -lead oxide thus  formed is conveyed pneu-
                   matically to  the baghouse where it is  collected
                   and delivered by screw conveyor to storage.

                   Other lead oxides requiring additional  processing
                   but  commonly made are red lead oxide (minium,
                   PbjC^), used in  the  paint industry,  and yellow
                   lead oxide (litharage or massicot,  PbO), used in
                   the  paint and ink industries.

                   Since the process requires the use of  a baghouse
                   to collect the product, and no  other contaminants
                   are  discharged, no air pollution control system
                   as such is needed.
                       METAL  SEPARATION  PROCESSES

                  Inadditionto the metallurgical processes previ-
                  ouslymentioned in this chapter,  there are  other
                  processes classified as metal separation that can
                  be troublesome from an air pollution standpoint.
                  In these, the metal  desired is  recovered from
                  scrap,  usually a  mixture  of several metals.
                  Probably the most  common of  these processes,
                  aluminum sweating, is the recovery of aluminum
                  fromaluminum drosses and other scrap.   Other

-------
                                     Metal Separation Processes
                                                                                                 305
 examples of metal separation processes include
 the recovery processes  for  zinc, lead, solder,
 tin, and low-melting alloys from a host of scrap
 materials.

 ALUMINUM SWEATING

 Open-flame,  reverberatory-type furnaces are
 used  by secondary smelters to produce alumi-
 num pigs for remelting. These furnaces are con-
 structed with the hearths sloping downward toward
 the rear of  the furnace.  All types of scrap alu-
 minum are charged into one of these  furnaces,
 which operates at temperatures  of  1,250°    to
 1,400°F.  In this temperature range, the alumi-
 num melts,  trickles down the hearth,  and flows
 from the furnace into a mold.  The higher melt-
 ing materials  such as iron,  brass,  and dross
 oxidation products formed during melting remain
 within the furnace.  This  residual material  is
 periodically raked from the furnace hearth.
 Some large secondary aluminum smelters sepa-
 rate the aluminum suspended in the dross by pro-
 cessing  the  hot dross immediately after its re-
 moval from the metal in the refining furnace.  The
 hot dross is raked into a refractory-lined barrel
 to which a  salt-cryolite flux is added.  The bar-
 rel is placed on a cradle and mechanically rotated
 for several minutes.  Periodically, the barrel is
 stopped  and the metal is tapped by removing a
 clay plug in the base of the barrel.  This process
 continues until essentially all the free aluminum
 has  been drained and only dry dross remains.
 The dross  is then dumped and removed from the
 premises.    A hot dross-processing station has
 been illustrated previously in Figure 200.
The aluminum globules suspended in the dross as
obtained from the hot dross process  can also be
separated and reclaimed by a. cold, dry, milling
process.  In this process the  large  chunks of
dross  are  reduced  in size by crushing  and then
fed continuously to a ball mill -where the oxides
and other nonmetallics are ground to  a fine pow-
der, which allows  separation from  the larger
solid particles  of aluminum.   At the mill dis-
charge, the fine  oxides are removed pneumatical-
ly and conveyed to  a baghouse for ultimate dis-
posal.   The  remaining material passes over a
magnetic roll to remove tramp iron and is then
discharged into storage  bins to await  melting.
This process is used primarily to process dross-
es having a low aluminum content.


ZINC, LEAD, TIN, SOLDER, AND LOW-MELTING
ALLOY SWEATING

Although recovery of aluminum is the  most com-
mon of the metal separation  processes, others
that contribute to air pollution deserve mention.
These include zinc, lead, tin, solder, and low-
melting alloy sweating. Separation of these metals
by  sweating is made possible by the differences
in their melting point temperatures.   Some  of
these melting temperatures  are:
        Tin
        Lead
        Zinc
        Aluminum
        Copper
        Iron
  450°F
  621 °F
  787°F
1,220°F
1,981°F
2,795°F
When the material charged to a sweating furnace
contains a combination of two of these metals,  it
can be separated by carefully controlling the fur-
nace temperature so that the metal with the lower
melting point is sweated when the furnace tem-
perature is maintained slightly above its melting
point.  After this metal has been melted and re-
moved, the furnace burners are extinguished and
the metal -with the higher melting point is raked
from the hearth.
Zinc  can  be recovered by sweating in a rotary,
reverberatory,  or muffle furnace.   Zinc-bear-
ing materials fed to a sweating furnace usually
consist of scrap die-cast products such as auto-
mobile  grilles,  license  plate  frames, and zinc
skims and drosses.
 The sweating of lead from scrap and  dross is
 widely practiced.   Junk automobile storage bat-
 teries supply most of the lead.  In addition, lead-
 sheathed  cable  and wire,  aircraft tooling dies,
 type metal drosses,  and lead dross and skims
 are also sweated.  The rotary furnace, or sweat-
 ing tube, is usually used when the material pro-
 cessed has alowpercent of metal to be recovered.
 The reverberatory box-type furnace is usually
 used-when the percent of metal recovered is high.
Rotary and reverberatory furnaces  are also used
to sweat solder and other low-melting alloys from
scrap metal.  Automobile  radiators and other
soldered articles such as gas meter boxes, radio
chassis,  and so forth,  make up the bulk of the
process metal.  For this recovery, the furnace
is usually maintained between 650 °F and 700°F.
Higher temperatures should be avoided in order
to prevent the possible loss of other recoverable
metals.   For example, sweating automobile ra-
diators at 900°F causes excessive oxidation of
the copper.

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306
                                   METALLURGICAL EQUIPMENT
The Air Pollution Problem

Contaminants from aluminum-separating
processes

In theory, an aluminum-sweating furnace can be
operated with  minor emissions of air contami-
nants if clean, carefully hand-picked metal free
of organic material  is processed.  In practice,
this selective  operation  does not  occur and ex-
cessive emissions periodically result from un-
controlled furnaces.   Stray magnesium pieces
scattered throughout the aluminum scrap are not
readily identified, and charging a small amount
of magnesium into a sweating furnace causes
large quantities of fumes to be  emitted.  Emis-
sions also result from the other materials charged,
such as skims,  drosses,  scrap aluminum sheet,
pots and pans, aircraft engines,  and wrecked air-
planes containing oil, insulated -wire, seats, in-
struments,  plastic assemblies, magnesium and
zinc components,  and so  forth.

Smoke is caused by the incomplete  combustion of
the organic constituents of rubber, oil and grease,
plastics,  paint,  cardboard, and paper.  Fumes
result from the oxidation  of stray magnesium or
zinc assemblies and from the volatilization  of
fluxes in the dross.  The sweating of dross and
skims is responsible  for the high rates of emis-
sion of dust and fumes.  Residual aluminum chlo-
ride flux in the dross is especially troublesome
because it sublimes at 352 °F and is  very hygro-
scopic. Inaddition, it hydrolyzes and forms  very
corrosive hydrogen chloride.  In Table 87, test  1
shows results from  an aluminum-sweating fur-
nace.

In the dry milling process, dust is generated at
the crusher, in the mill,  at the shaker screens,
and at points of transfer.   These locations must
be  hooded to prevent the  escape  of fine dust to
the atmosphere.

When aluminum is  reclaimed  by the  hot dross
process,  some fumes are  emitted from the flux
action;  however, the main  air pollution problem
is the collection  of  the mechanically generated
dust created by the rotation of  the dross barrel.

Contaminants from low-temperature sweating

Air contaminants released from a  zinc-sweating
furnace consist mainly of smoke and fumes.  The
smoke is generated by the  incomplete combustion
of the grease,  rubber, plastics,  and so forth
contained in the material.  Zinc fumes are  neg-
ligible at low furnace temperatures, for they have
a low vapor pressure even at 900 °F.  With ele-
vated furnace temperatures, however, heavyfum-
ing can result.  InTable 87, test 2  shows results
from a  zinc die-cast-sweating operation.
The discharge from a lead-sweating furnace may
be heavy with dust,  fumes, smoke, sulfur com-
pounds,  and fly ash.  This is particularly true
•when junk batteries are sweated.   The battery
groups  and plates removed from the cases  con-
tain bits of asphaltic case, oil and grease ar-ound
the terminals,  sulfuric acid, lead sulfate,  lead
oxide, and wooden or glass fiber plate separators.
The organic contaminants burn  poorly and the
sulfur compounds release SO2 and 803.   The sul-
fur trioxide is  particularly troublesome; -when
hydrolizedto sulfuric acid, the acid mist is dif-
ficult to collect and is extremely corrosive.  The
lead oxide  tumbles  within the  rotating furnace
and the finer material is entrained in the vented
combustion gases.

Unaggldmerated lead oxide fume particles  vary
in diameter from about 0. 07 to 0. 4 micron,  -with
a mean of  about 0.3 micron (Allen et al. , 1952).
Uncontrolled rotary lead sweat furnaces emit ex-
cessively high quantities of air contaminants. Al-
though the other types of scrap lead and drosses
sweated in a reverberatory furnace are normally
much less contaminated with organic matter and
acid, high emission rates occur periodically.

The contaminants generated during the sweating
of solder, tin, and other low-melting alloys  con-
sist almost entirely of smoke and  partially oxi-
dized organic material.  The scrap metal charged
is usually contaminated with paint, oil, grease,
rust, and scale.  Automobile radiators frequent-
ly contain residual  antifreeze and sealing com-
pounds.
Hooding and Ventilation Requirements

The ventilation and hooding of .reverberatory fur-
naces and rotary furnaces used for the reclama-
tion processes just mentioned are similar to those
of furnaces  of this type previously discussed in
this chapter.  The exhaust system must have suf-
ficient  capacity to remove  the products  of com-
bustion at the maximum firing rate and provide
adequate  collection of the  emissions  from  any
furnace opening.

In aluminum separation operations,  raking the
residual metal  and dross from the furnace is a
critical operation from an air pollution  standpoint,
and hoods should be installed to capture emis-
sions at these locations.  The required exhaust
volume may be effectively  reduced by providing
a guillotine-type furnace door and opening it only
as needed to accomplish charging and raking.  If
the burners  are turned off during these opera-
tions,  the indraft velocity  through the charging
and raking  opening is effectively increased and
the emissions from this location are reduced.

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                                     Metal Separation Processes
                                            307
                    Table 87.  DUST AND FUME EMISSIONS FROM ALUMINUM -
                  AND ZINC-SWEATING FURNACE CONTROLLED BY BAGHOUSE
Test No.
Furnace data
Type of furnace
Size of furnace
Width
Length
Height
Process weight, Ib/hr
Material sweated
Baghouse data
Type of baghouse
Filter material
Filter area, ft2
Filter velocity, fprn
Precleaner
Dust and fume data
Gas flow rate, scfm
Baghouse inlet
Baghouse outlet
Average gas temperature, °F
Baghouse inlet
Baghouse outlet
Concentration, gr/scf
Baghouse inlet
Baghouse outlet
Dust and fume emission, Ib/hr
Baghouse inlet
Baghouse outlet
Control efficiency, %
Test No.
Particle size data
Aluminum sweating
furnace












1

R everberatory

5 ft 9 in.
6 ft 4 in.
4 ft
760
Aluminum skims

Sectioned tubular
Orion
5, 184
1.9
None


8,620
9,580

137
104

0. 124
0.0138

9.16
a
1. 13
87. 7a
3
2


R everberatory

5 ft 9 in
6 ft 4 in
4 ft
2, 080





Zinc castings


Sectioned tubular
Orion
5, 184
1.
None


7,680
7,420

190
173

0.
0.

13.
0.
96.


85









205
0078

5
5
3

Particle Cumulative
diameter, |JL weight, %

1.79 4.8
2.38 10.8
3.57 24.3
4.76 37.3
7.10 55.6
8.90 65.8
10. 10 70.2
11.90 76.4
14. 30 82. 9
21.40 88.9
39.30 95.5
71.40 99.0















             Visible emissions released from the baghouse indicated that a bag had broken
            during the latter part of the test.
In low-temperature sweating operations, auxil-
iary hooding is usuallynecessary and varies with
the type of sweating furnace.  For the convention-
al reverberatory-type furnace, a hood should be
installed above the furnace door so that escaping
fumes  can be captured.   The  emissions occur
both during the normal melting process and dur-
ing the raking of the residual material from the
hearth. A rotary sweating furnace usually needs
only a hood over the high end of the tube.  In  cases
where the drosses are fine and  dusty, however,
a hood  is necessary at  the discharge end, too.
  234-767 O - 77 - 22

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 308
                                   METALLURGICAL EQUIPMENT
If  the hoods  are well designed  and no  unusual
crossdrafts are present,  an indraft velocity of
100 to 200 fpm is adequate to prevent the escape
of the air contaminants.

Air Pollution Control Equipment

Aluminum-separating processes

Although air pollution control equipment is nec-
essary in aluminum reclamation processes,  some
operating procedures reduce the quantity of emis -
sions.  Whenever  possible the  stray magnesium
pieces and combustible  material should be re-
moved from  the aluminum scrap to be sweated.
The furnace  burners should be operated  so that
the flame does not impinge on the scrap metal,
particularly if the burners are oil fired.

An afterburner followed by  a baghouse is recom-
mended as control equipment for an aluminum-
sweating furnace.   Baghouse filtering velocities
should not exceed  3 fpm.   The  afterburner  must
be  so designed that the carbonaceous  material
is  intimately mixed with the exhaust air and held
at a suitable temperature  for a sufficient length
of time to ensure complete incineration.  For
this service,  an  afterburner temperature of
1,  200°   to 1, 400°F is recommended with a re-
tention time of the  gases  in this hot zone of  about
0.3 second.  A luminous-flame  afterburner is
generally the most desirable because of the great-
erflamearea. Secondary air may have  to be ad-
mitted to the afterburner to  ensure complete com-
bustion.  The afterburner may be constructed as
a separate unit from the  furnace  or may be con-
structed as an integral part of the furnace some-
what similar to a multiple-chamber incinerator.
General design features of afterburners have been
discussed in Chapter 5.

The hot  gases must be cooled before entering a
baghouse,  and  radiant cooling or dilution with
cold air is recommended in preference to evapo-
rative cooling with water.   The sweating  of alu-
minum drosses  may result in severe  corrosion
problems owing to the aluminum  chloride flux
contained in the dross.   If the hot furnace gases
are cooled with water before entering the bag-
house, the aluminum chloride hydrolyzes,. pro-
ducing hydrochloric acid.   The ductwork and bags
are attacked, rapidly impairing the collection ef-
ficiency of the filter. Even the condensation from
night  air during  shutdowns provides  sufficient
moisture to  corrode the equipment in the pres-
ence of these chemicals.

Figure 208 shows  an aluminum sweating furnace
with integral afterburner  venting through hori-
zontally  positioned radiation-convection cooling
columns to a settling chamber andbaghouse.   The
furnace charging door hood is vented directly to
the baghouse. Table 88 shows test data acquired
while aluminum scrap heavily contaminated with
combustible material was  being sweated in the
furnace.  Combustible carbon was present in the
particulate discharge and was coexistent in the
vent stream -with excess oxygen as shown by the
Orsat analysis.   This  indicates that the rate of
combustible discharge from the scrap aluminum
was in excess of the  incinerating capacity of the
afterburner.

In thehot-dross process, the rotating barrel need
only be properly hooded and ducted to a baghouse.
No afterburning is required,  and because of the
relatively large indraft air volume, no gas-cool-
ing facilities are required in the exhaust system.

In the dry milling process, the ball mill, crusher,
and all transfer points must be hooded and vented
to a baghouse in order to prevent the escape of
the dust created.  The required hood indraft ve-
locities vary from 150 to 500 fpm, depending up-
on crossdrafts and the  force with •which the dust
is generated.  A baghouse filter  velocity of 3 fpm
or less is recommended. No afterburning or gas-
cooling facilities are required in a dry-dross con-
trol system.

Low-temperature  sweating

An  afterburner  should be provided to incinerate
the  combustible matter discharged from a low-
temperature sweating furnace.

Since an afterburner cannot remove the noncom-
bustible portion of the effluent, a baghouse should
be used with the afterburner to capture the dust
and fumes.  The maximum recommended bag-
house filter velocity is 3 fpm.  In certain special
applications  -where the only emissions are oils
or other combustible material, an afterburner
can be used to incinerate the contaminant, and a
baghouse may not be required.  Conversely, only
a baghouse is  required •when the process scrap
is always free of oils or  other combustible -waste.
Water scrubbers have not proved satisfactory in
the collection of metallic fumes of this type,

              CORE OVENS

In foundries, core ovens  are used  to bake the
cores used in sand molds.  Most cores contain
binders that require baking to develop the strength
needed to resist erosion and deformation by metal
during the filling of the mold.  Core ovens supply
the heat and, where necessary, the oxygen nec-
essary for the baking. Cores are made in a large
variety of sizes and_shapes and with a variety of
binders; therefore,  a  variety  of types of core
ovens  are needed  to provide the space and heat
requirements for baking the cores.

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                                            Core Ovens
                                            309
              Figure 208.  Aluminum-sweating  furnace vented  to  an afterburner  and  baghouse
              (Du-Pol  Enterprises,  Los Angeles, Calif.).
Generally, emissions from core ovens are a mi-
nor  source of air pollution -when compared with
other metallurgical processes.  If the ovens are
operated below 400°F and are fired -with natural
gas, emissions are usually tolerable.  Neverthe-
less, there are instances, for example, when
special core formulations are used, -when emis-
sions can have  opacities exceeding legal limits
permitted in Los Angeles County, and when emis-
sions can be extremely irritating to the eye be-
cause of aldehydes and other oxidation products.
In these cases, a control device is necessary,
normally an afterburner.

TYPES OF OVENS
The various types  of core ovens fall into the fol-
lowing five classes:   Shelf ovens,  drawer ovens,
portable-rack ovens, car ovens, conveyor ovens.

Shelf ovens are probably the  simplest form of
core ovens.   They  are  merely insulated steel
boxes,  divided into sections  by shelves.  Core
plates  carrying cores are placed directly on the
shelves.  When a  door is opened,  all or at least
several shelves are exposed and a large  amount
of heat escapes from the oven chamber.  Figure
209 shows a gas-fired shelf oven.  The hot gas-
es  escaping  during  loading and unloading of the
shelve snot only waste heat but also create unde-
sirable •working conditions.  Because of these un-
desirable characteristics, these ovens are gen-
erally limited to baking small cores, particular-
ly in a  small-core department where the  invest-
ment in oven equipment must be kept at a mini-
mum.
Shelf ovens have  been replaced largely by the
more efficient drawer oven.  One type of drawer
oven is shown in Figure 210.  With these ovens,
one or more drawers can be withdrawn for load-
ing or unloading  and,  since  the drawers are
equipped with rear-closing plates, hot gases do
not escape.  Within the oven,  the drawers are
supported  on  rollers  and, •when -withdrawn, the
front end is supported by an overhead drawer-
selector with an operating arrangement to per-
mit engagement of  any  one or any combination of
drawers.

These ovens are  suitable for baking small- and
medium-sized cores,  but they are limited in the
volume of cores that canbebakedbecause of labor
involved in transporting the cores from the core
maker to the oven, placing them in the drawers,
removing them from the drawers, and taking
them to storage.

To overcome some of the handling of  cores,  por-
table rack ovens were developed.  The core maker
places his cores  directly onto a rack, which,
when filled, is put into the oven. After the bak-
ing,  the rack is  removed and taken to storage.
A different, loaded rack can then be placed in the
oven.  Figure  211 shows  an empty  rack oven.
Racks are designed not only to fit the oven but
also to accommodate large or small cores.  They
can be transported by an overhead monorail or
lift trucks, either manually or power operated.


For large cores,  car ovens are generally used.
These ovens are similar to rack ovens but larger

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310
METALLURGICAL EQUIPMENT
                             Table 88.  DUST AND FUME EMISSIONS FROM
                        AN ALUMINUM-SWEATING FURNACE CONTROLLED BY
                                  AN AFTERBURNER AND BAGHOUSE
                Furnace data
                  Type of furnace
                  Furnace hearth area
                  Process weight, Ib/hr
                  Material sweated
               ^everberatory -with integral afterburner
                      4 ft 7 in. W.x 8 ft 10 in. L
                               2,870
               Scrap aluminum
Baghouse data
Type of bags
Filter material
Filter area, ft2
Filter velocity, fpm
Precleaner
Tubular
Dacron
4,800
2.
Settling chamber
16
Dust and fume data
Gas flow rate, scfm
Average gas temperature, °F
Concentration, gr/scf
Dust and fume emission, Ib/hr
Particulate control efficiency, %
Settling
chamber inlet
1, 360
350
0.505
5.89

Furnace charge
door hood
5, 580
204
0.081
3.88

Baghouse
outlet
8,850a
150
0. 0077
0. 58
94. 1
                  Orsat analysis at settling
                  chamber inlet, volume %
                       C02

                       CO

                       H2O
      6.8
      8.6
      0. 02
     77. 33
      7.25
                  Particle size analysis at bag
                  house outlet, wt %
                       +60 mesh       85. 9
                       -60 mesh       14. 1
                  Particle size analysis of -60
                  mesh portion, wt %
                       0 to  2 |JL
                       2 to  5 IJL
                       5 to 10 n
                       10 to 20 |JL
                       20 to 40 |j.
                       < 40 n
      6.9
     32. 4
     30. 9
     17. 7
      7. 7
      4.4
                  Combustible carbon in particu-
                  late discharge, dry wt %
                  Settling chamber
                  inlet                 83. 7
                  Furnace chamber
                  door hood exit        67. 3
                aVolume is greater at the baghouse exit than at the inlet because of leakage.
and, instead of portable racKs, cars riding on
rails are used.  The cores, being large and heavy,
are generally loaded on the cars by crane. Tiered
pallets are frequently used to facilitate car load-
ing. Because of the size of the cores, most of a
day is usually needed  to load  a car; therefore,
baking is usually done overnight.

Conveyor ovens are used in foundries where a
large volume of cores of approximately the  same
                   size arebaked.  Of course, larger cores can also
                   be baked by allowing them to make two or more
                   passes through the oven.
                   Conveyor ovens have loading and unloading sta-
                   tions,  a heated section, and  a cooling section.
                   A horizontal-conveyor oven is shown in Figure
                   212.  These ovens  are generally located above

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                                           Core  Ovens
                                                                                                311
Figure 209.  Shelf oven (The  Foundry Equipment Co.,
Cleveland, Ohio).
the floor level,  in roof trusses, or above area-
ways between buildings.   They have inclined en-
trances and exits to allow loading at the floor level
and, probably more important, to provide natural-
draft heat seals.   The vertical-conveyor oven
shown in Figure 213  requires little floor space
for a large volume of baking.   It is heated on the
side where the cores enter the  oven and through-
out the top of the oven.  With the use of baffles
and a blower, the lower portion of the unloading
side of the oven cools the baked cores.  Core
makers  can  be grouped  around the loading side
of the  oven to minimize the handling of  cores.


HEATING CORE OVENS

Probably the simplest and crudestmethod of heat-
ing  core ovens is to use burners along the floor
extending  the  entire  length of the oven.  These
burners cannot be  regulated automatically and
they do not  provide uniform heat throughout the
 oven.  They canbe dangerous,  because of damping
 out of the flame at the  back of  an oven, which al-
 lows  raw gas  to accumulate  resulting in explo-
 sions.  Although a few ovens are still heated  in
 this manner, most ovens use recirculating heater
 units.

 With recirculating heaters,  a portion of the oven
 gases is  returned to the heater, and the rest is
 vented through a  dampered  stack to the atmo-
  sphere.   Fresh air is mixed with the recirculated
    Figure 210.   Drawer oven (Despatch  Oven  Co.,
    Minneapolis,  Minn.).
       Figure  211.  Rack oven (Despatch  Oven Co.
       Minneapolis, Minn.).

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312
                                  METALLURGICAL EQUIPMENT
         Figure 212.   Horizontal,  continuous oven (The Foundry  Equipment Co.,  Cleveland,  Ohio).
gases, and the mixture is heated.  The hot gases
and the products of combustion are blown into the
oven.  The amount of fresh air  admitted is con-
trolled by the  amount  of gases vented from the
oven  and  only  enough is admitted to supply the
oxygen needed for the baking process.


CORE BINDERS

The primary reason for baking cores is to make
them strong enough so that they can be handled
while the mold is being made and so that they re-
sist  erosion and deformation by metal when the
mold is being filled.  The baking process drives
off water  and other volatiles,  which reduces the
total gas-forming material in the mold.  Most  of
the "volatiles" discharged can be considered air
contaminants.   Their  composition depends upon
the type of binder used in the core.

Numerous binders require baking, but they do
not all harden by the same chemical and physical
processes.   Based on their method of hardening,
the binders  can be subdivided  into three types:
(1) Those that harden upon heating,  (2) those that
harden upon cooling after  being heated,  and (3)
those  that adhere upon heating.  The binders of
the first  type  develop their strength by chemical
reaction,  while those of the  second and third types
function through physical phenomena.

Pitch, rosin,  and similar materials of type 2 are
solids at  room temperature,  but upon  heating,
they melt and flow around the sand grains.  When
the mixture of sand and binder cools, the binder
solidifies  and holds the  grains  together.  Those
binders are  frequently dissolved or dispersed in
solvent and,  when  baked,  the  solvent is  driven
off, becoming an air contaminant.

The binders  of type 3 are mixed with sand in the
dry state. Water is  then added and the  binder
becomes gelatinous, which imparts green strength
to the mixture.  Upon baking, these  binders dehy-
drate, harden, and adhere to the sand grains hold-
ing them together.  Since baking only drives water
from  the mixture,  no air contaminants are created.
Type-1 binders harden by chemical action, par-
tial oxidation, and polymerization.  Drying oils,

-------
                                            Core Ovens
                                                                                                 313
Figure  213.  Vertical,  continuous oven (The  Foundry
Equipment Co.,  Cleveland,  Ohio).
 of which linseed oil is typical, are made up of
 unsaturated hydrocarbons that are liquid at room
 temperature.  Because they are unsaturated,  the
 molecules can react with other molecules or ele-
 ments •without producing  side products.  These
 oils react -with oxygen very slowly at room tem-
 perature and faster at elevated temperatures, to
 the extent that their unsaturation is partially sat-
 isfied,  and then  they polymerize to form a solid
 film thatholds the sand grains together.  If, how-
 ever, toomuchheat is applied, the  oxidation pro-
 cess goes  too far and some molecules break up
 into lower molecular weight products instead of
 polymerizing. The result is a weaker film,  and
 smoke,  vapors,  and  gases are discharged.

 The resin-type binders, such as phenol-formalde-
 hyde, are intermediate, easily polymerized prod-
 ucts of  a phenol and formaldehyde condensation
 reaction.   When heated, these compounds poly-
 merize  rapidly into a hard film.   No side reac-
 tions should, however,  occur; these substances,
 too, are organic and  subject to burning if heated
 excessively.
In actual practice,  cores seldom contain only one
type of binder.  A typical core mixture contains
930 pounds of sand, 7-1/2 pounds of core oil, 9
pounds  of cereal  binder, 3 pounds of kerosene,
and 38  pounds of  water.   The core oil contains
45 percent linseed oil,  28 percent gum rosin,
and 27  percent  kerosene.  All three types  of
binder are present.  The linseed  oil in the core
oil  is a type-1 binder and hardens by an oxida*
tion-polymerization process.   The gum rosin of
the core oilis a type-2 binder  and,  after its sol-
vents are driven  off,  it melts and then hardens
when the cores are cooled.  The cereal binder is
cornflour, a type-3 binder, which  is used to im-
part green strength to the core by its  gelatinous
reaction with water before the core is baked.

During  the baking of these cores,  a series of
physical and chemical reactions occurs.  First,
the moisture and light fractions of the oil are dis-
tilled off. As the temperature  rises, the heavier
fractions of the kerosene are vaporized and  the
linseed oil begins to react with  oxygen and to poly-
merize. At about  300°F,  the  rosin melts, coat-
ing  the grains "with a thin film of rosin.

The  polymerization of the  linseed oil requires
more time than the physical  changes that take
place do, and so  the core is held at a tempera-
ture of375°F for 1-1/2 to 3-1/2 hours to develop
maximum strength. Ahigher temperature accel-
erates the polymerization, but the danger of over-
baking is also much greater. For instance, when
linseed oil is baked  at 375 °F,  its maximum
strength is  achieved in 1-1/2 hours,  and its
strength does not deteriorate if it is baked for 3-
l/2hours.  At400°F,  a maximum  strength, less
than that achieved at 375 °F,  is reached in 3/4
hour, but the strength begins to deteriorate if  the
core  is baked longer than 1-1/4 hours.  And at
450 °F,  the  maximum strength is reached  in a
little  less than 3/4 hour and immediately begins
to deteriorate if overbaked.  Of course, since  the
entire body of the core cannot reach the oven tem-
perature at the same time, if  high temperatures
are used the surface of the core is  overbaked be-
fore the inner portions are  completely baked.
Moreover, the high temperatures tend to create
smoke and objectionable gases that are discharged
from  the oven as air contaminants.

The  resinous-type binders also have kerosene
and cornflour added.  Baking time and tempera-
ture requirements are,  however, much less.  In
fact, high-frequency dielectric ovens can be used
with the fast-setting  synthetic resins.   In these
ovens, the electrical field created causes noncon-
ductors within the field to become hot.   The ovens
generally have a relatively small  heating space,
through which a conveyor carries the cores.   The
conveyor is one of the electrodes; therefore, only
the cores become heated.  There are no hot gases

-------
314
METALLURGICAL EQUIPMENT
to contend with, and  only  the  small amount of
volatile materials  in  the cores are discharged.
Baking time generally runs 2-1/2 minutes.
The Air Pollution Problem

The air contaminants discharged from core ovens
consist of organic acids, aldehydes, hydrocarbon
vapors,  and smoke.  The vapors are the result
of the evaporation of hydrocarbon solvents,  usu-
ally kerosene, and the light ends usually present
in core oils.  The organic acids,  aldehydes, and
smoke are  the  result of partial oxidation of the
various  organic materials in the  cores.  These
substances  have obnoxious odors  and are very
irritating to the eyes.  The quantity and irritating
quality of the  oxidation products generally in-
crease -with an increase in baking temperature.


Emission rates, in general, are low,  especially
from small- and medium-sized ovens operating
at 400 °F or less.  With some core  binders,  how-
ever, the emissions from small ovens operating
at low temperatures can be of sufficient quantity
to create a public nuisance.  The emissions  from
larger ovens are generally greater and are more
apt to create nuisances or be in excess of opacity
regulations. Table 89 shows the amounts of var-
ious contaminants  discharged from three  core
                   ovens.  Test 1  shows the emissions from an un-
                   controlled oven, and tests 2 and 3 show the emis-
                   sions from two ovens as well as the afterburners
                   that control the emissions from them.

                   Excessive amounts  of  emissions can generally
                   be expected  from ovens operated at 500°F  or
                   higher, and from ovens  in which the cores baked
                   contain larger than normal  amounts of kerosene,
                   fuel  oil,  or  core oils.  Visible emissions are
                   usually discharged fromlarge conveyorized ovens.
                   In many cases  the opacity of these plumes has
                   been  in excess  of Los Angeles County's opacity
                   regulations.
                   Hooding and Ventilation Requirements

                   Most core ovens are vented directly to the atmo-
                   sphere through a  stack.  The ovens require suf-
                   ficient fresh air to be mixed with recirculated
                   gases  and with the products of combustion from
                   the heater to keep the moisture  content low and
                   to supply the oxygen necessary for proper bak-
                   ing of the drying  oil-type core binders.

                   Generally, the excess gases and any contaminants
                   created are discharged from the oven through one
                   vent stack.  Occasionally more than one vent is
                   used, but if the emissions are  such that air pol-
                   lution controls are needed, then ducting the vents
                   to a control device is  all that is necessary.  The
                    Table 89. AIR CONTAMINANT EMISSIONS FROM CORE OVENS
Test No.
Oven data
Size

Type
Operating temp, °F
Core binders
Weight of cores baked, Ib
Baking time, hr
Afterburner data
Size

Type
Burner capacity, Btu/hr
Air contaminants from:
Effluent gas volume, scfm
Effluent gas temperature, °F
Particulate matter, Ib/hr
Organic acids, Ib/hr
Aldehydes, ppm
Hydrocarbons, ppm
Opacity, %
Odor
1

6 ft 2 in. W x 7 ft 11 in.
H x 1 9 f t L
Direct gas -fired
380
1 to 1/2% phenolic resin
700
11



None

Oven
100
380
0. 13
0.068
52
124
0
Slight
2

3 ft 10 in. W x 5 ft 3
in H x 18 ft L
Direct gas-fired
400
3% linseed oil
1,600
2-1/2 to 3

10 in. dia x 7 ft 6
in. H
Direct flame
200, 000
Oven
140
400
0.2
0. 008
10
-
-
-
Afterburner
260
1,400
0.013
0.000
10
< 10
0
Slight
3

4 ft 2 in. W x 6 ft 8
in. H x 5 ft 9 in. L
Indirect electric
400
1% linseed oil
600
6

3 ft dia x 4 ft H

Direct flame
600,000
Oven
250
400
0.27
0.44
377
158
-
-
Afterburner
440
1,780
0.02
0.087
4
< 19
0
None

-------
                                 Foundry Sand-Handling Equipment
                                                                                                315
use  of hoods  or  of  excess air is not necessary
to capture the emissions.
Air Pollution Control Equipment

As emphasized previously, when operated below
400 °F and when fired with natural gas, most core
ovens do not require air pollution control equip-
ment.  There have been, however,  several cases
where excessive emissions have been discharged
and control equipment has been necessary.

Excessive emissions from core ovens  have been
reduced to tolerable amounts by modifying the
composition of the core binders and lowering the
baking temperatures.   For instance,  smoke of
excessive opacity -was discharging from an oven
baking cores containing 3 percent fuel oil and  1. 5
percent core oil at 500°F. The core binder was
modified so that the cores contained 1. 5 percent
kerosene  and  1. 5 percent core oil, and the bak-
ing temperature was reduced to 400°F.  After
these modifications,  no visible emissions •were
discharged from the oven.
When it is not feasible or possible to reduce ex-
cessive emissions from an oven by modifying the
core mix or the baking temperature, afterburners
are the only control devices that have proved ef-
fective.  Since the quantity and concentration of
the contaminants  in the oven effluent are small,
no precleaners or flashback devices are needed!
Afterburners that have been used for controlling
the emissions from core ovens are predominantly
of the direct-flame type.  The burners are nor-
mally designed to be capable of reaching a tem-
perature of atleast 1, 200°F under maximum load
conditions.  For most operations, 1,200°F com-
pletely  controls all visible emissions  and prac-
tically all odors.

The afterburner shouldbe designed to have amax-
imum possible flame contact with the gases to be
controlled  and it  should be of sufficient size to
have a gas retention time of at least 0. 3 second.
Most authorities agree thatthe length-to-diameter
ratio should be in the range of  1-1/2 to 4

In some instances,  particularly on larger core
ovens,  catalytic afterburners have been used to
control the emissions.  With inlet temperatures
of from 600°to650°F all visible emissions and
most of the odors were controlled.  Wlien cata-
lytic afterburners are used,  however,  care must
be taken to keep the catalyst  in good condition;
otherwise, partial oxidation can result in the dis-
charge  of combustion contaminants more objec-
tionable than the oven effluent.
FOUNDRY  SAND-HANDLING EQUIPMENT

Afoundry sand-handling system consists of a de-
vice for separating the  casting from the mold,
and equipment for reconditioning the sand.  The
separating device is usually a mechanically vi-
brated grate called a shakeout.  For small cast-
ings a manual shakeout may be used.
TYPES OF EQUIPMENT

The  minimum  equipment required for recondi-
tioning  the sand is  a screen for removing over-
size particles,  and a mixer-muller where clay
and  •water are combined with the sand to render
it  ready for remolding.  In addition, equipment
may be used to perform the following functions:
Sand cooling, oversize crushing, fines removal,
adherent  coating removal, and conveying.  A
typical  sand-handling  system is shown in Figure
214.
Bothflat-deck screens  and revolving, cylindrical
screens  are used for  coarse-particle removal.
Revolving screens  can be ventilated  at  such  a
rate as  to remove excess fines.

Sand cooling can be  accomplished in  a number of
ways, depending upon  the cooling requirements.
The  amount of cooling  required depends mainly
upon the ratio of metal to sand in the molds and
on the rate of re-use of the sand.  With low metal-
to-sand and re-use ratios, no specific sand-cool-
ing equipment  is required.  When considerable
cooling  is required, a rotary drum-type cooler
is  usually used.  A  stream of air drawn through
the cascading sand both cools and removes fines.

Oversize  particles  are hard agglomerates  not
broken  up by the handling  operations  from the
shakeout grate to the screen.  Most  of these are
portions of baked cores. Many foundries discard
the oversize particles,  while  others  crush the
agglomerates to recover the sand.  A hammer-
or screen-type mill is  usually used for  crushing.

Since molding  sand is continuously reused, the
grains become coated with a hard,  adherent layer
of clay and carbonaceous matter from the bonding
materials used.  Intimethesandbecom.es unus-
able unless the  coating is removed or a certain
percentage  of new  sand is  continuously added.
Pneumatic reclamation is the method  most -widely
used for coating  removal.  The  sand  is  conveyed
in a high-velocity air stream from a turbine-type
blower  and  impinged  on the inner  surface of a
conical  target.   Abrasion removes  a  portion of
the coating material in each pass.  The fines thus
created are  carried away in the airstream while
the sand grains settle  in an expansion chamber,
as shown  in Figure  215.

-------
316
                                   METALLURGICAL EQUIPMENT
       TO  BAGHOUSE
                              Figure 214.   Typical  foundry sand-handling system.
Foundry sand is usually conveyed by belt convey-
ors and bucket  elevators, though pneumatic con-
veyors are used to some extent.   Pneumatic con-
veying aids in  cooling and fines removal.
The Air Pollution Problem

The air  contaminants that may be emitted are
dust from sandbreakdown, and smoke and organ-
ic vapors from the decomposition of the  core
binders by the hot metal.
Among the factors that influence emission rates
are size of casting, ratio of metal to sand, met-
al-pouring temperature, temperature  of  cast-
ing and sand at the shakeout, and handling meth-
ods.  These factors have a great influence on the
magnitude of the air pollution problem.   For in-
stance, a  steel foundry  making large castings,
with a high metal-to-sand ratio requires a very
efficient control system to prevent excessive
emissions.  A nonferrous foundry making small
castings with a low metal-to-sand ratio, on the
other hand,  may not require any controls, since
the bulk of the sand remains damp and emissions
are negligible.
Hooding ond Ventilation Requirements

The need for ventilation is determined by  the
same factors that influence emission rates.  Min-
imum volumes of ventilation air required to  en-
sure  the adequate collection of the air contami-
nants are indicated in the discussion that follows
on the various emission sources.

-------
                                Foundry Sand-Handling Equipment
                                                                                                317
            FINES TO
            OUST COLLECTOR
                  AIR FROM
                  TURBO-BLOWER
             Figure  215. Pneumatic sand  scrubber (National Engineering Co.,  Chicago,  III.).
Shakeout grates

The  amount of ventilation air required for a
shakeout grate is determined largely by the type
of hood or enclosure.  The more nearly complete
the enclosure,  the less the required  volume.
When large flasks are handled by  an overhead
crane,  an  enclosing hood cannot be used,  and a
side or lateral hood is used instead. Recom-
mended types of hood  are  shown in Figure 216
and Figure 217 (upper).  Downdraft hoods are not
recommended except for floor-dump type of oper-
ations where sand and castings are dropped from
a roller conveyor to a gathering conveyor  below
the floor level (Manual  of Exhaust Hood Designs,
1950).  An excessive exhaust volume is required
to achieve adequate control in a downdraft hood
because the indraft velocity is working against
the thermal bouyancy caused by the  hot sand and
casting.  The indraft velocity is lowest where it
is needed most--at the  center of the grate.  The
exhaust volume  requirements for the different
types  of hood  are shown in Table  90.  Shakeout
hoppers should be exhausted  with  quantities  of
about 10 percent of the total exhaust volume listed
in this  table.

Other sand-handling equipment

Recommended ventilation volumes  and hooding
procedure for bucket elevators and belt convey-
ors are given in Figure 218; for sand screens, in
Figure  219;  and for  mixer-mullers,  in Figure
220.  The ventilation requirement  for  rotary
coolers is 400 cfm per square foot of open area.
For crushers the requirement varies from 500 to
1,000 cfm per square foot of enclosure opening.
 Air Pollution Control  Equipment

 The most important  contaminant to be collected
 is dust, though smoke is sometimes intense enough
 to constitute a problem.  Organic vapors and gas-
 es are usually not emitted in sufficient quantities
 to be  bothersome.  The collectors  usually used
 are baghouses and scrubbers.

-------
318
                                               METALLURGICAL EQUIPMENT
  VELOCITY THROUGH OPENINGS
  700-1 000 fpm	1
         	3 2 L
      -MOVABLE PANELS  TO SECURE
       DESIRED DISTRIBUTION
                                -CHANNEL IRON GUARD

./\f 1
/ ' A/
—

--
-
/
^

•*--,
/
/





s

/

HAKE
- L

. L
/
y:

—




OUT




H
j_
                           OPTIONAL TOP
                           TAKE-OFF
                           .    ARRANGE  LENGTH
                            >  OF SLING CHAIN
                               TO CLEAR HOOD
                                                       45° OR
                                                    V  BORE
                                                    YV-RIGICLY
                                                     N\ BRACED
                        III MINIM PRACTICAL CLEARANCE

                           SIDE-DRAFT HOOD

                  OUCT VELOCITY = 3,500 fpm MINIMUM
                  ENTRY LOSS = 1  7B SLOT vp»0 25 DUCT v
 MOLDS IN
MOLD    l
CONVEYOR1
                      IORKING OPENINGS
                      KEEP AS SKAU  AS
                      POSSIBLE^
SHAKEOUT

                                                                                                                               RIGIDLY BRACED
                                                                              DOUBLE SIDE DRAFT
                                                            PROPORTIONS SAME AS SINGLE SIDE-DRAFT HOOD EXCEPT  FOR OVERHANG
                                                       CASTINGS
                                                       OUT HERE
                                                      PLENUM CHAMBER AND SLOTS FULL
                                                      LENGTH OF SHAKEOUT  IN TUNNEL
PROVIDE PLENUM-
CLEANOUTS
                                                                                                                                        SLOT
                                                                                                          HOPPER
                             ENCLOSING HOOD

                  PROVIDES BEST CONTROL HITH LEAST VOLUME
                  DUCT VELOCITY = 3 500 fpm MINIMUM
                  ENTRY LOSS =  0 25 vp
   Figure  216.   Foundry  shakeout  (Committee  on  In-
   dustrial  Venti  lation,   1960).
                                                                               DOINDRAFT HOOD

                                                                       SLATS SIZED FOR 1.000 TO 2 000 fpm
                                                                       DUCT VELOCITY - 4,000 fpm MINIMUM
                                                                       SIZE 0 FOR 1.000 fpm OR LESS
                                                                       ENTRY LOSS = 1 18 SLOT vp PLUS FITTINGS
                                                                       FOR COOL CASTINGS ONLY
                                                                       DIFFICULT TO PREVENT PLUGGING OR EXCESS
                                                                          FINES REMOVAL
                                                     Figure  217.   Foundry shakeout  (Committee  on
                                                     dustrial   Ventilation,  1960).
                                                                                                                                       In-
                                 Table 90.   EXHAUST VOLUME  REQUIREMENTS FOR
                                                DIFFERENT  TYPES OF HOOD
                                            VENTILATING SHAKEOUT  GRATES
Type of hood
Enclosing


Enclosed two sides and
1/3 of top area
Side hood (as shown or
equivalent)
Double side hood

Downdraft


Exhaust requirement
Hot castings
200 cfm/ft2 of open-
ing. At least 200
cfm/ft of grate area
300 cfm/ft2 of grate
area
400 to 500 cfm/ft2 of
grate area
400 cfm/ft2 of grate
area
600 cfm/ft2 of grate
area
Not recommended
Cool castings
200 cfm/ft2 of open-
ing. At least 150
cfm/ft2 of grate area
275 cfm/ft2 of grate
area
350 to 400 cfm/ft2 of
grate area
300 cfm/ft2 of grate
area
200 to 250 cfm/ft2 of
grate area

                       aChoose  higher values  when (1)  castings  are very hot,  (2) sand-to-
                        metal  ratio is  low,  (3) crossdrafts  are high.

-------
                                          Foundry Sand-Handling Equipment
                                                                                                  319
 TO HOPPER. BIN. OR SCREEN
ADDITIONAL VENTILATION HERE
TO SUIT OPERATION
     FDR CASING ONLY
 0 = 100 cfm/ftZ CASING CROSS
    SECTION
 DUCT VELOCITY = 3 500 fpro MINIMUM
 INTRY LOSS = I 0 »p OR CALCULATE
    FROM INDIVIDUAL LOSSES
    TAKE-OFF AT TOP FOR HOT BATE
    RIALS AT TOP AND BOTTOM IF
    ELEVATOR IS OVER 30 ft HIGH
    OTHERIISE OPTIONAL
                                           ALTERNATE EXHAUST POINT
                                           FOR ELEVATOR HEAD
                                           ADDITIONAL VENTILATION
                                            ADDITIONAL VENTILATION HERE
                                            AS PER BELT  TRANSFER
                  BELT SPEED          VOLUME
                LESS THAN 200 fpm  350 cfm/ft OF BELT WIDTH
                             NOT LESS THAN 150 elm/ft
                             OF OPENING
                OVER 200 fpm
          500 cfm/lt OF BELT IIDTH
          NOT LESS THAN 200 cfm/ft
          OF OPENING
                                                                        FEED
                                                                    -45° MIN  SLOPE


                                                                           -CANVAS CONNECTION IF DESIRED

                                                                            COMPLETE ENCLOSURE

                                                                               SCREEN

                                                                                     OVERSIZE
                                                                     FLAT DECK SCREEN

                                                   0 = 200 cfm/ft2 THROUGH HOOD OPENINGS  BUT NOT LESS THAN 50 cfm'ft2
                                                      SCREEN AREA   NO INCREASE FOR MULTIPLE DECKS
                                                   DUCT VELOCITY = 3,500 fpm MINIMUM
                                                   ENTRY LOSS = 0 5 vp
COMPLET
ENCLOSU
SCREEN
IE 	 j f~J r~ 45°
y
* /
| '/
MIN SLOPE
//LFEED
                                                                      ^—— rw
                                                                              HOPPER
                                                                         OVERSIZE
                       CYLINDRICAL SCREEN

                0 = 100 cfm/ft2 CIRCULAR CROSS SECTION OF
                   SCREEN. AT LEAST 400 cfm/ft2 OF EN-
                   CLOSURE OPENING
                OUCT VELOCITY = 3,500 fpm MINIMUM
                ENTRY LOSS = SEE "FLAT DECK SCREEN"
    Figure  218.  Bucket  elevator  ventilation  (Com-
    mittee  on  Industrial  Ventilation,  1960).
                                                 Figure 219.  Screens (Committee  on Industrial
                                                 Ventilation,  1960).
        INSULATION OR STRIP HEATERS
        MAY BE REQUIRED TO PREVENT
        CONDENSATION IN DUCT IF STEAM
        IS GIVEN OFF
  LOADING HOPPER
                                                    BAFFLE
   0 = 150 cfm/ft2 THROUGH ALL OPENINGS
      BUT NOT LESS THAN
   MIXER DIAMETER.
       ft
        4
EXHAUST.
 cfm
 650
 900
1.200
1,500
            NOTE.  OTHER TYPES OF MIXERS. ENCLOSE
                 AS MUCH AS POSSIBLE AND PRO-
                 VIDE 150 cfm/ft? OF REMAINING
                 OPENINGS
   DUCT VELOCITY =  3,500 fpm MINIMUM
   ENTRY LOSS = 0.25 vp
    Figure  220. Mixer and  muller hood  (Committee on
    Industrial Ventilation.  1960)
                                              Abaghouse in good condition collects all the dust
                                              and most of the smoke.  A scrubber of moderate-
                                              ly good efficiency collects the bulk of the dust, but
                                              the very fine dust and the  smoke  are not collected
                                              and in many cases leave a distinctly visible plume,
                                              sufficient to violate some  control regulations.  A
                                              baghouse,  therefore, is  the preferred collector
                                              •when the  maximum  control measures  are desired.
When only the shakeout is vented to a  separate
collector, there maybe sufficient moisture in the
gases  in some cases to cause condensation and
consequent  blinding of  the bags  in  a baghouse.
When,   however,   all  the  equipment in  a  sand-
handling  system  is served by a single exhaust
system, ample ambient air is drawn into the sys-
tem to preclude any moisture problem in the bag-
house.   The filtering velocity for this  type  of
service should not exceed 3 fpm.  Cotton sateen
cloth is adequate for this service.   Anoncompart-
mented-type baghouse is  adequate for  most job
shop foundries. For continuous-production found-
ries, a compartmented baghouse -with automatic
bag-shaking mechanisms gives the most trouble-
free performance.

-------
320
                                  METALLURGICAL EQUIPMENT
       HEAT  TREATING SYSTEMS
Heat  treating involves the carefully controlled
heating and cooling of solid metals and alloys for
effectin-g certain desired changes in their physical
properties.   At elevated  temperatures, various
phase changes such as grain growth,  recrystal-
lization, and diffusion or migration of atoms  take
place  in solid metals and alloys.  If sufficient
time is allowed at the elevated temperature, the
process goes on until equilibrium  is reached and
some stable form of the metal or alloy is obtained.
If, however, because of sudden and abrupt cooling,
time is not sufficient to achieve equilibrium  at the
elevated temperature, then some intermediate or
metastable form of the metal  or alloys is obtained.
The  tendency to  assume a stable form is always
present and  metals and alloys in a metastable form
can be made  to approach their stable form as close-
ly as  desired simply by reheating.   The widely
differing properties that  can be imparted to solid
metals and  alloys  in their stable and metastable
forms give  purpose to the whole process of heat
treating.

In general, the methods used to heat treat both fer-
rous and nonferrous metals are fundamentally sim-
ilar.  These methods include hardening, quenching,
annealing, tempering, normalizing ferrous metals ,
and refining grain of nonferrous metals. Also in-
cluded in the category of heat  treating are the var-
ious methods of case hardening steels  by carburiz-
ing, cyaniding, nitriding,  flame hardening, induc-
tion  hardening,   carbonitriding,  siliconizing,  and
so forth.
HEAT TREATING EQUIPMENT

Furnaces or ovens, atmosphere generators, and
quench  tanks  or spray tanks are representative
of the equipment used for heat treating.

Furnaces for  heat treating are of all sizes and
shapes  depending upon the temperature needed
and upon the dimensions and the number  of pieces
tobe treated.  A furnace maybe designed to oper-
ate continuously or batchwise.   The controls may
be either automatic or manual. These furnaces
are known by descriptive names  such as box,
oven, pit, pot, rotary, tunnel,  muffle, and others.
Regardless of the name, they all have the follow-
ing features  in  common:  A steel outer shell, a
refractory lining, a combustion or heating sys-
tem,  and a heavy door (either cast iron or re-
inforced steel with refractory lining) that may be
opened from the top,  the front,  or  from, both the
front and the back.

Atmosphere generators are used to supply a con-
trolled environment inside the heat treating cham-
ber of the furnace.  The atmosphere needed may
be either oxidizing, reducing, or neutral depend-
ing upon the particular metal or alloy undergoing
heat treatment and upon the final physical proper-
ties desired in the metal or alloy after treatment.
An atmosphere can be provided that will protect
the surface of the metal during heat  treatment so
that subsequent cleaning and buffing  of the part is
minimized, or one can be provided that-will cause
the surface of the metal to be alloyed by diffusion
•with certain  selected elements in order  to alter
the physical properties of the metal.


Quench tanks may  be  as simple as a tub of water
or as  elaborate as a well-engineered  vessel
equipped with properly designed means to circu-
late the quenching fluid and maintain the fluid at
the correct temperature.  The part to be quenched
is either immersed into the fluid or is subjected
to a spray that is dashed against the part so that
no air or steam bubbles  can remain attached to
the hot metal and  thereby  cause soft spots.   The
fluidused for quenching may be water,  oil,  mol-
ten salt,  liquid air, brine  solution,  and so forth.
The purpose of quenching is to retain some meta-
stable  form  of an alloy (pure metals are not af-
fected  by quenching) by rapidly cooling the alloy
to some temperature below the transformation
temperature.
 The Air Pollution Problem

 The heat treating process is currently regarded
 as only a minor source of air pollution.  Nonethe-
 less,   air pollutants  that may be  emitted from
 heat treating operations,  and their origin,  are
 as follows:
1.
2.
3.
     Smoke and products of incomplete combus-
     tion arising from the improper operation of
     a gas- or  oil-fired combustion system;
    vapors and fumes emanating from the
    tilization of organic material on the metal
    parts being heat treated;

    oil mists and fumes issuing from oil quench-
    ing baths (if water-soluble oils are used,  the
    fumeswillbea combination of steam and oil
    mist);
4.   saltfumes emittedfrom molten salt pot fur-
     naces;

5.   gases,  produced by atmosphere generators,
     used in the heat treating chamber of muffle
     furnaces.  (Insignificant amounts occasional-
     ly leak  out from some furnace openings that
     cannot be sealed, but somewhat larger amounts
     get  into the surrounding air during  purging
     and  also during loading and unloading oper-
     ations. )

-------
                                       Heat Treating Systems
                                                                                                  321
Hooding and Ventilation Requirements

Hooding and ventilation systems designed for heat
treating processes  should  be based on the rate
at which the hot, contaminated air is  delivered
to the receiving face of the exhaust hood.  To
prevent the hot, contaminated air from spilling
out around the edges of the exhaust hood, the rate
at which the exhaust system draws in air must in
all  cases exceed the rate at which the  hot, con-
taminated air is delivered to the exhaust system.

In the general case, a. canopy hood mounted about
3 or  4 feet above a hot body has  an  excellent
chance of capturing all the hot, contaminated air
rising by convection from the hot body.  The face
area  of a canopy hood  such as this  should be
slightly larger than the maximum cross-sectional
area of the hot body.  In order to avoid the need
for excessive  exhaust capacity,  it is  advisable
not to oversize the'canopy hood face area.

If a canopy hood is  mounted too high  above the
hot body, the column of hot, contaminated air is
influencedby turbulence, and the column becomes
more and more dilute by mixing with the  surround-
ing air. Consequently the exhaust capacity must
be sufficient to handle this entire volume of diluted,
contaminated  air.   This is an inefficient way to
collect hot,  contaminated air.

Many variations of canopy hoods are used because
of the many types of heat treating furnaces em-
ployed. Lateral-type hoods are also used.  Gen-
eral features of design of hoods for these hot pro-
cesses are discussed in Chapter 3.
1.  Proper selection of furnace burners and fuels
    along with  observance of correct operating
    procedures will eliminate smoke and prod-
    ucts of incomplete combustion as a source of
    air pollution. (See Chapter 9.)

2.  Removal of organic material adhering to metal
    parts to be heat treated by either steam clean-
    ing or solvent degreasing before heat treat-
    ing will eliminate this source of air pollu-
    tion.
3.  Mists and fumes issuing from oil quenching
    baths can be greatly reduced by selecting ap-
    propriate oils and by adequate cooling of the
    oil.

4.  Baghouses are a satisfactory method of con-
    trolling  salt fumes from molten salt pots.
    Particle sizes of fumes are usually between
    0.2  and 2 microns but may  vary from this
    range  depending upon local factors such as
    temperature, humidity, turbulence, and ag-
    glomeration tendencies of the effluent.  The
    fumes are  slightly hygroscopic and corro-
    sive; therefore,  operation of the baghouse
    must be continuous to prevent blinding and
    deterioration of the bag  cloth and corrosion
    of the metal structure.  Acrylic-treated or-
    lonisa satisfactory bag  cloth because of its
    chemical and thermal resistance and its gen-
    eral physical stability.   Filtering velocities
    should not be greater than 3 fpm.  With these
    design features, collection efficiencies ex-
    ceeding 95 percent are normally achieved.
Air Pollution Control Equipment

The following methods  effectively  prevent and
control emissions resulting from heat treating
operations.
5.  Flame  curtains placed  at the  open ends of
    continuous heat treating furnaces are effec-
    tive in the control  of any escaping, combus-
    tible  gases used  for  controlling the atmo-
    sphere  inside the  furnace.

-------
                                             CHAPTER 7

                                    MECHANICAL  EQUIPMENT
       HOT-MIX ASPHALT PAVING BATCH PLANTS
             JOHN A. DANIELSON
          Senior Air Pollution Engineer

             ROY S.  BROWN, JR.
            Air Pollution Engineer*

            CONCRETE-BATCHING PLANTS
              EDWIN J.  VINCENT
      Intermediate Air Pollution Engineert

             JOHN L. McGINNITY
      Intermediate Air Pollution Engineers

           CEMENT-HANDLING EQUIPMENT
              EDWIN J.  VINCENT
      Intermediate Air Pollution Engineer!

        ROCK AND GRAVEL AGGREGATE  PLANTS
              EDWIN J.  VINCENT
      Intermediate Air Pollution Engineer!

             MINERAL WOOL FURNACES
                JOHN L.  SPINKS
          Senior Air Pollution Engineer

           PERLITE-EXPANDING FURNACES
              EDWIN J.  VINCENT
      Intermediate Air Pollution Engineer!

               FEED AND GRAIN MILLS
           WILLIAM H.  DONNELLY
             Air Pollution Engineer

          PNEUMATIC CONVEYING EQUIPMENT
              EDWIN J.  VINCENT
       Intermediate Air Pollution Engineer!

                     DRIER
              EDWIN J.  VINCENT
      Intermediate Air Pollution Engineer!

              JOHN L. McGINNITY
      Intermediate Air Pollution Engineert

             WOODWORKING EQUIPMENT
              ROBERT GOLDBERG
             Air Pollution EngineerT
   RUBBER-COMPOUNDING EQUIPMENT
        JOSEPH D'IMPERIO
       Air Pollution Engineer**

   ASPHALT ROOFING FELT-SATURATORS
        SANE OR D M. WEISS
  Principal Air Pollution Engineer

      ARTHUR B. NETZLEY
   Senioi Air  Pollution Engineer

       PIPE-COATING EQUIPMENT
      HARRY  E.  CHATFIELD
Intermediate Air Pollution Engineer

       WILLIAM F. GANTHER
       Air Pollution Engineer

       AUTHUR B.  NETZLEY
    Senior Air Pollution Engineer

       ABRASIVE BLAST CLEANING
        EDWIN J. VINCENT
Intermediate Air Pollution Engineer!

     ZINC-GALVANIZING EQUIPMENT
         GEORGE THOMAS
    Senior Air  Pollution Engineer

      TIRE BUFFING EQUIPMENT
        C. RUSS ANDERSON
       Air Pollution Engineer

         HERBERT  SIMON
    Senior Air  Pollution Engineer

     WOOD TREATING EQUIPMENT

      WILLARD F.  GANTHER
       Air Pollution Engineer

      ARTHUR B. NETZLEY
   Senior Air  Pollution Engineer
         CERAMIC  SPRAYING
 AND METAL DEPOSITION  EQUIPMENT
         HERBERT SIMON
   Senior Air  Pollution Engineer

        C. RUSS ANDERSON
       Air Pollution Engineer

       ANDREW J. WILSON
   Senior Air Pollution Engineer
               EDWARD HIGGINS
             Air Pollution Engineer
 *Now in private business.
 TNow with Environmental Protection Agency,  Research Triangle Park,  North Carolina.
 TNow with U.S.  Public Health Service, Department of Health,  Education,  and Welfare,
  St.  Glenville, Illinois.
**Deceased.
 234-767 O - 77 - 23

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                                               CHAPTER 7
                                     MECHANICAL  EQUIPMENT
         HOT-MIX ASPHALT  PAVING
               BATCH  PLANTS

 INTRODUCTION
 Hot-mix asphalt paving consists of a combina-
 tion of aggregates* uniformly  mixed and  coated
 with asphalt cement.   An asphalt batch plant is
 used to heat, mix, and  combine the aggregate and
 asphalt in the  proper proportions to give the de-
 sired paving mix.  After the material is mixed, it
 is transported to the paving  site and spread as a
 loosely compacted layer •with a uniformly smooth
 surface.  While stillhot, the material is compacted
 and densified by heavy motor -driven rollers to pro-
 duce a smooth, -well-compacted course.

 Asphalt paving mixes maybe produced from a wide
 range of aggregate combinations, each having par-
 ticular characteristics  and suited to specific de-
 sign and construction uses. Aside from the amount
 and grade of asphalt cement used, the principal
 characteristics of the  mix are  determined by the
 relative amounts of:

 Coarse aggregate (retained on No. 8-mesh sieve),

 fine aggregate  (passing No. 8-mesh sieve),  and
 mineral dust (passing No.  ZOO-mesh sieve).

 The aggregate composition may vary from a coarse-
 textured mix having a predominance of coarse ag-
 gregate to a fine-textured mix having a predomi-
 nance  of  fine aggregate.  The  Asphalt Institute
 (1957)classifies'hot-mix asphalt paving  according
 to the  relative amounts of coarse aggregate, fine
 aggregate,  and mineral dust.  The general limits
 for each mix type are shown in Table 91.   The com-
 positions  used within each mix type are shown in
 Tables 92 and 93.


 Raw Materials Used

 Aggregates of all sizes up to 2-1/2 inches are used
 inhot-mix asphalt paving.  The  coarse aggregates
 usually consist of crushed stone,  crushed  slag,
 crushed gravel,  or combinations  thereof,  or of
 material  such  as decomposed  granite  naturally
 occurring  in a fractured condition, or of a highly
''Aggregate is a term used to describe the solid mineral load-bearing
 constituents of asphalt paving such as sand particles and fragments
 of stone, gravel, and so forth.
angular natural aggregate with a pitted or rough
surface texture. The fine aggregates usually con-
sist of natural sand and maty contain added materi-
als such as  crushed stone,  slag, or gravel.   All
aggregates mustbe free from coatings of clay,  silt,
or other  objectionable matter and should not con-
tain  clay particles or other fine materials.  The
aggregate must also meet tests for soundness
(ASTM designation C88) and wearability  (ASTM
designation C131).

Mineral filler is used in some types of  paving.  It
usually consists of finely ground particles of crushed
rock, limestone, hydrated lime, Portland  cement,
or other nonplastic mineral matter. A minimum
of 65 percent of this material must pass a 200-mesh
sieve. Another name for mineral filler  is mineral
dust.
Asphalt cement is used in amounts of 3 to 12 per-
centby weight and is made from refined petroleum.
It is  a  solid at ambient temperature but is usually
used as a liquid at 275°  to 325 °F.  One  property
measurement used in  selecting an asphalt cement
is the "penetration" as  determinedby ASTM Method
D5.  The most common penetration grades used in
asphalt paving are 60  to 70,  85 to 100, and 120 to
150. The grade used depends upon the type of  ag-
gregate, the paving use,  and the climatic condi-
tions.
Basic Equipment

A typical hot-mix asphalt paving batch plant usu-
ally consists of an oil- or gas-fired rotary drier,
a screening  and classifying system, weigh boxes
for asphalt cement  and aggregate, a mixer, and
the necessary conveying equipment consisting of
bucket elevators and belt conveyors.   Equipment
for the storage of sand, gravel,  asphalt cement,
and fuel oil  is provided in  most plants.  Heaters
for the asphalt cement and  fuel oil tanks are  also
used.
Plant Operation

Plants vary in size.  The majority in Los Angeles
Countyproduce 4, 000-poundbatches and have pro-
duction  rates of 100 to 150 tons of asphalt paving
mixperhour.  Some of the newer plants are 6, 000-
pound batch size and are capable  of producing 150
to 250 tons per hour.
                                                    325

-------
 326
                                      MECHANICAL EQUIPMENT
                    Table 91.  CLASSIFICATION OF HOT-MIX ASPHALT PAVING
                                     (The Asphalt Institute, 1957)
Pa\ mi; mix
ilc ML; nation
Fype
1
II
III
IV
V
VI
VII
VIII
l)e si r i|>l inn
Mai atl.ini
Open grade;!
Coarse graded
Dense graded
Fine graded
Stone sheet
Sand sheet
Fine sheet
Ma x imum s i,
U ,„
'(f, -°
i/4tol-l/2in. Q. U)
y.
o
1 to 1-1 //in. £ 40
(/)
W
<
3/4 - " 60
<,
'1
U
*/, • K 70
3/4 in. Q
O
<
qn
U u
g
3/8 in. U 90
B?
No. 4 lf)n
Aggregate i ombinal ions
"„ MIXKRAI. HI'S 1 (PASSINCi NO. 200 SI K VI-
0 *> 10 S i
, ; .




K",
** V* 	 •
\%
*vV'*
AGC'.UKC',
. *
	 \
r'"-\ i IN
\
•»i 	 i. 	 ,t NO
"4"
»,> V.
"* -^uRF>^csr;o'
^ % 'V1
, OAl AND ^
' |^\ LEVEL*'-
DASE, 4.^;Vi ING
~s
BINDER,
AND
LEVELING


?/\ MIXE;
\tlf


A 1 K PROP
THIS ARE
1' NORMA1
ECOMMF.N
— FOR PA1
0\
yt\ CONS
^IA**^*
' ''
'.,
''
'*
DK ITONS

A

i/ F M F N T

•RUC riON


\
— N, ^J 4- rj> c~- -O &- -Z O !
OOOOOCOOOOO II
% COARSE AGGREGATE (RETAINED XO. 8 SIEVE) ||
    aCritical 7,one - Dust contents in this region should
     not be used without a substantial background of ex-
     perience with  such mixes and/or suitable justifica-
     tion by laboratory design tests.
    ^Intermediate zone - Dust contents in this  region
     sometimes used in surface and leveling mixes as
     well as in base and binder mixes.
  0         5        10
  % MINERAL DUST  (PASSING NO. 200 SIEVE)
Figure  221 is  a. flow diagram of a typical plant.
Aggregate is usually conveyed from the storage
bins to the rotary drier by means of a belt con-
veyor  and bucket elevator.  The drier is usually
either oil-or gas-fired and heats  the aggregate to
temperatures ranging from 250°   to 35~0°F.  The
dried aggregate is conveyed by a bucket elevator
to the  screening equipment where it is classified
and dumped  into elevated storage bins.  Selected
amounts of the  proper size  aggregate  are dropped
from  the storage bins to the weigh hopper.  The
weighed aggregate is then  dropped into the mixer
along with hot asphalt cement.  The batch is mixed
and then dumped into waiting trucks for transporta-
tion to the paving site.  Mineral filler can be added
directly to the weigh hopper by means of an auxil-
iary bucket elevator and  screw conveyor.
Fine dust in the combustion gases from the rotary
drier is partially  recovered in a precleaner and
discharged  continuously into the hot dried aggre-
gate leaving the drier.

THE AIR  POLLUTION PROBLEM
The largest source of dust emissions is the rotary
drier.  Other sources are the hot aggregate bucket
elevator, the vibrating screens, the hot aggregate
bins, the aggregate weigh hopper, and the mixer.
Rotary  drier  emissions up to 6, 700  pounds per
hour  have  been measured,  as  shown  in Table 94.
In one  plant,  2, 000 pounds  of dust per hour was
collected from the discharge of the secondary dust
sources, that is, the vibrating screens, hot aggre-
gate bins,   the aggregate  weigh hopper, and the

-------
                                Hot-Mix Asphalt Paving  Batch  Plants
                                                                                                         327
Table 92.   COMPILATION OF SUGGESTED MIX COMPOSITIONS (The Asphalt Institute,  1957)
1 VII ,f>
VIII ,1



Table 93.  COMPILATION OF SUGGESTED MIX COMPOSITIONS (The Asphalt Institute,  1957)
Mix
type
i-\li in.
\-\li in.
1 in.
3/4 in
1/Z in.
3/S in.
No. 4
No. S
No 16
No. 30
No. SO
No. 100
No. ZOO
%
TTr
11 d
III b
III c
III d
IV i













100


100
100
100
70 lo 100
100
100
7S to 100
SO to 100
70 to 100

7S to 100
7S to 100


IS o 7S
is „ 60
60 o BS
60 o 8S
4S o 70
60 o SO
ZO to 40
IS to 3 S
3S to SS
iO to SO
iO to SO
IS lo 6S
S to ZO
S to ZO
ZO to iS
zo to ;s
ZO to iS
is to SO














10 to iL
S to ZO
S to ZO
19 to !0


6 to 16
3 lo 1Z
i to 1Z
1 3 to Zi


4 10 \i
i to S
i to S
7 to IS
0 to 4
0 to 4
Z to S
0 to 4
0 to 4
0 lo S
3 0 to 6. 0
i. 0 to 6 0
3 0 to 6. 0
i. 0 to 6. 0
i. 0 to 6. 0
i S to 7. 0
                                                  Le\ cling
III b
V ba
VI ba









100
100
100
7S to 100 1 60 to SS
8S to 100
SS to 100
iS to SS
6S to 80

ZO to 3S
SO to 6S
6S 10 SO

37 to SZ
17 to 68
10 to ZZ
ZS to 40
30 to SS
6 to 16
18 to iO
ZO to 40
4 to 1Z
10 to ZO
10 to ZS
Z to S I i. 0 to 6. 0
3 to 10 4.0 to 7. S
i to HI 1 S to 8.5
1 	
I a
II d
II e
III d
III c
IV d
aMay
100





be used to
3S to 70

100

100
100
r base \\ h e
	
100
70 to 100
100
7S to 100
SO to 100
re c oa r si' a
0 o IS
70 o 100
SO o 80
7S o 100
60 o SS
70 o '10
HBr'-K'itc i






s not e( ono

3S o 60
ZS o SO
4S o 70
10 o 6S
SS o 7S
iiu .illy a\

IS to iS
10 to iO
iO to SO
10 lo SO
4S to 6Z
nl.ible.
0 to s
S lo ZO
S to ZO
ZO to is
ZO lo iS
iS to SO











S to ZO
S to ZO
I'l to iO




3 to 1Z
i to 1Z
1 i to Zi




Z to
Z to
7 to

                                                                                                II 1C

                                                                                                0 K

                                                                                                0 tc

                                                                                                0 t<

                                                                                                0 tc
                                          CYCLONE
                        COLD AGGREGATE
                        BUCKET ELEVATOR
                                                                                                   STACK
                                                      HOT AGGREGATE-
                                                      BUCKET ELEVATOR
SCRUBBER
t

7
                   Figure 221. Flow diagram of a typical hot-mix  asphalt paving batch plant.

-------
328
MECHANICAL EQUIPMENT
             Table 94.  DUST AND FUME DISCHARGE FROM ASPHALT BATCH PLANTS
Test No.
Batch plant data
Mixer capacity, Ib
Process weight, Ib/hr
Drier fuel
Type of mix
Aggregate feed to drier, wt %
+ 10 mesh
-10 to +100 mesh
-100 to +200 mesh
-200 mesh
Dust and fume data
Gas volume, scfm
Gas temperature, °F
Dust loading, Ib/hr
Dust loading, grains/scf
Sieve analysis of dust, wt %
+ 100 mesh
-100 to +200 mesh
-200 mesh
Particle size of -200 mesh
0 to 5 (JL, wt %
5 to 10 n, wt %
10 to 20 jx, wt %
20 to 50 p., wt %
> 50 [i, wt %
C-426

6, 000
364, 000
Oil, PS300
City street, surface

70. 8
24.7
1. 7
2.8
Vent linea
2,800
215
2, 000
81.8

4. 3
6.5
89.2

19.3
20.4
21.0
25. 1
14.2
Drier
21,000
180
6,700
37.2

17.0
25.2
57.8

10. 1
11.0
11.0
21.4
46. 5
C-537

6, 000
346,000
Oil, PS300




Highway, surface

68.
28.
1.
1.
Vent line
3,715
200
740
23.29

0.5
4.6
94.9

18.8
27.6
40.4
12. 1
1.1

1
9
4
6
Drier
22,

4,











050
430
720
24. 98

18.9
32.2
48. 9

9.2
12. 3
22. 7
49. 3
6.5
              aVent line serves hot elevator,  screens,  bin, weigh hopper,  and mixer.
Drier  dust emissions increase with air mass ve-
locity,  increasing  rate  of rotation,and feed rate,
but are independent of drier slope (Friedman and
Marshall, 1949). Particle size distribution of the
drier feed has  an  appreciable effect  on the dis-
charge of dust.  Tests show that about 55 percent
of the  minus  200-mesh fraction in the drier feed
can be  lost in processing.  The dust emissions
from the secondary sources vary -with  the amount
of fine material in the feed and the mechanical con-
dition of the equipment.  Table 94 and  Figure 222
give results  of source tests of two typical plants.
Particle size of the dust emissions and of the ag-
gregate feed to the drier are also shown.


HOODING AND VENTILATION REQUIREMENTS

Dust pickup must be provided at all the sources of
dust discharge.  Total ventilation requirements
vary according to  the size of the plant.   For  a
6, 000-pound-per-batch plant,  22, 000 scfm is typ-
ical,  of which  18,000 to  19,000 scfm is  allotted
for use  in controlling the drier emissions.  The
top end of the drier must be closely hooded to pro-
vide for exhaust of the products of combustion and
entrained dust.  A ring-type hood located between
the stationary portion of the  burner housing and
the drier provides satisfactory  pickup at the lower
                end of the drier.   An indraft velocity  of 200 fpm
                should be provided at the annular opening between
                the circumference of  the drier and the ring-type
                hood.

                The secondary dust sources, that is, the elevator,
                vibrating screens, hot aggregate bins, weigh hop-
                per, and mixer, are all totally enclosed, and hence,
                no separate hooding is required.  Dust collection
                is provided by connecting this equipment through
                branch ducting to  the main exhaust system.  Ap-
                proximately  3,000 to 3,500 scfm will adequately
                ventilate these secondary sources.


                AIR POLLUTION CONTROL EQUIPMENT

                Primary dust collection equipment usually consists
                of a cyclone.  Twin or multiple cyclones are also
                used.  The catch of the primary dust collector
                is returned to the hot bucket elevator where it con-
                tinues on with the main bulk of the drier aggregate.
                The air discharge from the primary dust collector
                is ducted to the final dust collection system.

                Two principal types of final Control equipment have
                evolved from the many types  employed over the
                years: The multiple centrifugal-type spray cham-
                ber  (Figure 223) and the baffled-type spray tower

-------
                                  Hot-Mix Asphalt Paving Batch Plants
             VENT LINE
                                                 TEST C-426
                                           2,620 Ib/hr
                                                 TO ATMOSPHERE
              '6,080 Ib/hr
                                                            MULTIPLE
                                                            CENTRIFUGAL
                                                            SCRUBBER
                                                            EFFICIENCY
                                                            = 99 H
                                                 2 595 Ib/hr
                                                 DRY DUST
                                                  TEST C-537
             VENT LINE
             742 Ib/hr

             FROM DRYER
1 ,525 Ib/hr
             4,720 Ib/hr
               RETURN TO HOT ELEVATOR
                                     CYCLONE
                                     EFFICIENCY
   1,407 Ib/hr
                     MULTIPLE
                     CYCLONE
                     EFFICIENCY
                     = 92
                                                 TO ATMOSPHERE
                                                I  33 5 Ib/hr*
                                                            MULTIPLE
                                                            CENTRIFUGAL
                                                            SCRUBBER
                                                            EFFICIENCY
                                                            = 71 3«
                                                                                      WATER AND MUD
                5.344 Ib/hr
                                                 84 5  Ib/hr
                                                 DRY DUST
                 Figure 222. Test data on air pollution control equipment serving two hot-mix asphalt
                 paving plants (vent  line serves screens,  hot  bins, weigh hopper, and mixer).
Figure 223.  Typical multiple centrifugal-type scrubber
serving a 4,000-pound-batch-capacity hot-mix asphalt
paving plant.
                    (Figure 224).  The multiple centrifugal-type spray
                    chamber has proved the more efficient.  It consists
                    of two or more internally fluted, cylindrical spray
                    chambers in which  the dust-laden gases are ad-
                    mitted tangentially at high velocities.  These cham-
                    bers are each about the same size, that  is, 6 feet
                    in diameter by  15 feet in length, if two chambers
                    are used, and 6  feet in diameter by 9 or  12 feet in
                    length  if three  chambers  are used.  Usually 7 to
                    12 spraynozzles are evenly spaced within each
                    chamber.   The total water rate to the nozzles is
                    usually about 70  to  250 gpm at 50 to 100 psi.  In
                    the baffled-type spray tower, there have been many
                    variations  and  designs, but fundamentally, each
                    consists  of  a chamber that is baffled to  force the
                    gases to travel in a sinuous  path,  which encoura"ges
                    impingement of the dust particles against  the sides
                    of the chamber  and the baffles.   Water  spraynoz-
                    zles are located among the baffles,  and  the -water
                    rate through the spray nozzles  is usually between
                    100 to 300 gpm  at 50 to 100 psi.

                    In both types of scrubber the water may be either
                    fresh or recirculated.  Settling pits or concrete
                    tanks of sufficient capacity to allow most of the
                    collected  dust to  settle out of the water  are re-

-------
330
MECHANICAL EQUIPMENT
  Figure 224.  Typical baffled-type spray tower serving
  a 4,000-pound-batch-capacity hot-mix asphalt paving
  plant (Griffith Company, Wilmington, Calif.).
                                                        The effect of aggregate fines feed rate on stack
                                                        emissions at constant water-gas ratio (an average
                                                        value  for test considered) is shown in Figure 225
                                                        for multiple centrifugal-type scrubbers and  baffled
                                                        tower scrubbers.  Stack emissions increase lin-
                                                        early with an increase in the amount of minus 200-
                                                        mesh  material  processed.   These losses can be
                                                        greatly  reduced by using a clean or washed sand.
                                                        The required fines content of the hot-mix  asphalt
                                                        paving is then  obtained by  adding  mineral filler
                                                        directly  to the plant weigh hopper by means of an
                                                        auxiliary bucket elevator and screw conveyor.

                                                        Most asphalt paving batch plants burn natural gas.
                                                        When gas is  not  available, and if permitted by lav/,
                                                        a  heavy fuel oil (U. S. Grade No.  6 or heavier)  is
                                                        usually substituted.  Dust emissions to the atmo-
                                                        sphere from plants with air  pollution control de-
                                                        vices  were  found to be about 5. ] pounds per hour
                                                        greater when the drier was fired -with oil than they
                                                        were  when  the  drier  •was  fired -with natural gas.
                                                        The difference is believed to represent particulate
                                                        matter residing in,  or formed  by, the fuel oil,
                                                        rather than additional  dust from the drier.   Simi-
                                                        larly, the burning of heavy fuel oils in other kinds
                                                        of combustion equipment results in greater emis-
                                                        sions  of particulate matter.

                                                        The amount of water fed to the scrubber is a very
                                                        important consideration. The spray nozzles should
 quired with a  system  using recirculated water.
 The scrubber  catch is usually hauled away and
 discarded. It is usually unsuitable for use as min-
 eral filler in the paving  mix because it contains
 organic matter and clay particles.  The recircu-
 lated water may become acidic and corrosive,  de-
 pending upon the amount of sulfur in the drier fuel,
 and must then be treated with chemicals to protect
 the  scrubber  and stack from corrosion.   Caustic
 soda and lime have been used successfully for this
 purpose.


 Variables Affecting Scrubber  Emissions

 In a recent study (Ingels et  al. , I960), many source
 tests (see  Table 95) on asphalt paving plants in Los
 Angeles County were used to correlate the major
 variables  affecting stack losses.  Significant var-
 iables  include the aggregate fines  feed rate (the
 minus  200-mesh  fraction),  the type of fuel fired
 inthedrier, the scrubber's water-gas ratio,* and
 the type of scrubber used.  Other,  less important
 variables  were also revealed in the study.
-The water-gas ratio is defined as the total  quantity of water
 sprayed in gallons per 1,000 scf of effluent gas.
                      0       2,000     4,000     6,000      8,000     10,000
                        OUANTITY Of FINES (MINUS 200 MESH) IN DRYER FEED,  Ib/hr
                     Figure 225.  Effect of aggregate fines feed rate on
                     stack emissions at average water-gas ratio (Ingels.
                     et al.,  1960).

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                                  Hot-Mix Asphalt Paving Batch Plants
                                                                                                  331
 Table 95.  TEST DATA FROM HOT-MIX ASPHALT PAVING PLANTS CONTROLLED BY SCRUBBERS
Test No.
C-357
C-82
C-379
C-355
C-372B
C-372A
C-369
C-393
C-354
C-185
C-173
1
C-379
C-337
2
C-234
C-4Z6
C-417
C-425
3
C-385
C-433
C-422(l)
C-422(2)
C-418
Averages
Scrubber
inlet dust
loading,
Ib/hr
940
427
4, 110
2, 170
121
76
352
4, 260
__
1, 640
	
	
3, 850
305
	
372
2, 620
560
485
212
266
--
--
3, 400

Stack
emission,
Ib/hr
20. 7
35.6
37. 1
47. 0
19.2
10. 0
24. 4
26. 9
27.8
21.3
31.0
33. 5
30. 3
13.6
21. 1
21.2
25. 5
39. 9
32. 9
25. 5
17. 5
11.0
26. 6
37. 0
30. 8
26.7
Aggregate
fines rate, a
Ib/hr
9, 550
4, 460
8, 350
14, 000
2, 290
2, 840
4, 750
4, 050
6, 370
5, 220
8, 850
7, 520
6, 500
2, 510
3, 730
2, 530
10, 200
3, 050
2, 890
6, 590
4, 890
5, 960
7, 140
3, 340
9, 350
5, 900
Water-gas
ratio,
gal/ 1, 000 scf
6. 62
3. 94
6. 38
6. 81
10. 99
11.11
5. 41
12. 01
6. 10
19. 40
20. 40
11.01
5. 92
11.11
7.28
5. 70
7. 75
2. 94
4. 26
6. 60
4. 56
8. 12
4. 90
3. 02
8. 90

Overall
s c rubber
efficiency,
wt %
97. 8
91.6
99. 1
97. 8
84. 2
86. 8
93. 0
99. 3
--
98. 7
--
--
99.2
95.5
--
94. 3
99. 0
92. 8
93.2
91.7
95. 8
--
--
99. 1
94. 9
'I ypo
of
scrubber
C
C
C
C
C
C
C
T
T
T
T
T
C
C
T
T
C
C
C
c
c
c
c
c
T

Type
of
drier
fuel
Oil
Oil
Oil
Oil
Oil
Gas
Oil
Oil
Oil
Oil
Oil
Oil
Gas
Oil
Gas
Gas
Oil
Oil
Oil
Gas
Oil
Gas
Oil
Oil
Oil

	 1
Production
rate,
tons /hr
183. 9
96. 9
174. 0
209. 1
142. 9
158. 0
113.0
92. 3
118. 4
137. 8
184. 2
144. 6
191. 3
1 14. 6
124. 4
42. 0
182. 0
138. 9
131.4
131.7
174. 3
114. 5
198. 0
152. 0
116. 5

	
Gas
effluent
volume,
scfrri
23, 100
19,800
26, 200
25, 700
18, 200
18, 000
16, 100
19, 500
7, 720
18, 700
17, 000
23, 700
28, 300
24, 300
15, 900
17, 200
22, 000
24, 600
18, 000
18, 200
20, 000
19, 600
21, 000
22, 200
17, 100

 aQuantity of fines (minus 200 mesh) in dryer feed.
  C  -  Multiple centrifxigal-type spray chamber.
  T  -  Baffled tower scrubber.
be  located  so  as to cover the moving gas  stream
adequately with fine spray.  Sufficient water should
be used to cool the gases below the dew point.   One
typical scrubber  tested had an inlet gas at 200 °F
with 16. 8 percent water vapor content by volume,
and an outlet gas at 131°F with 16. 3 percent water
vapor  and saturated.  The temperature at the gas
outlet of efficient scrubbers rarely exceeds 140°F,
and the gas is usually saturated with \vater vapor.

Figure 226 shows the effect of the scrubber' s water-
gas ratio on dust emissions with the aggregate fines
feed rate held constant (an average value  for the
test considered).   Efficient scrubbers use water
at rates of 6 to 10 gallons per 1,000 standard cubic
feet of gas.  The efficiency falls off rapidly at water
rates less than  6 gallons per 1,000 scf of gas.  At
rates of more than  10 gallons  per 1,000 scf of gas,
the efficiency still increases,  but at a  lesser rate.

Curves are presented in Figures 227 and 228 from
which  probable stack emissions can be predicted
for oil-  and gas-fired plants with either multiple
centrifugal  or  baffled tower  scrubbers.   These
curves present emissions for various scrubbers'
water-gas ratios and aggregate fines rates.  Emis-
sion predictions from these curves are accurate
only for plants of the type and design already dis-
cussed.
The operation of  the rotary drier  is also an im-
portant variable. Dust emissions increase with an
increase  of air mass velocity through the drier.
Obviously then, car e should be taken to operate the
drier without  a great amount of excess  air.  This
care effects fuel economy and reduces  dust emis-
sions from the drier.

The firing rate of the drier  is determined by the
amount of moisture in the aggregate  and  by the re-
quired hot aggregate temperature.  The greater
the aggregate moisture content, the greater the
firing rate and the resulting  dust emissions to the
atmosphere.  In some plants,  the increase in mois-
ture content of the flue gases  may increase the ef-
ficiency  of  the  scrubber sufficiently to offset the
increase in  dust emissions from the drier.

Scrubber efficiencies also vary according to the
degree of precleaning done   by the primary dust
collector.  Tests (suchas those presented in Table
95) have shown that overall  efficiency  of the pre-

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332
                                         MECHANICAL EQUIPMENT
  10
    0    2    4    6    8   10   12    14   16    18   20
            SCRUBBER HATER-GAS RATIO, gal/1,000 scf
   Figure 226. Effect of scrubber's water-gas ratio on
   stack emissions at average aggregate fines feed rate
   in the drier feed (Ingels et al., 1960).
cleaner and final collector varies only slightly -with
large variations in precleaner efficiency.  Plants
with less effective cyclone precleaning had,  on the
average, larger particles entering the scrubber,
and consequently,  show greater scrubber collec-
tion efficiencies.   The principal advantage of an
efficient precleaner is  that the valuable fines col-
lected can be discharged directly to the hot  elevator
for use in the paving mix.  Furthermore, less dust
is discharged to the scrubber, where more trouble-
some dust disposal problems  are encountered.


Collection Efficiencies Attained

Collection efficiencies of cyclonic-type precleaners
vary  from approximately  70  to 90 percent on an
overall weight basis.   Scrubber efficiencies vary-
ing from 85 to nearly 100 percent have been found.
Overall collection efficiencies usually vary between
95 and 100 percent.
               4,000       8,000       12,000       16,000
      QUANTITY OF FINES (MINUS 200 MESH)  IN DRYER FEED, Ib/hr
Figure 227. Emission prediction  curves  for multiple centrifugal
scrubbers serving asphaltic concrete plants (Ingels et  al.,  1960

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                                   Hot-Mix Asphalt Paving Batch Plants
                                                                            333
  60
                                                     -  40
  20
   10
              4,000
                                                        20
',000 " "     12,000      16,000        0          4,
QUANTITY OF FINES (MINUS 200 MESH)  IN DRYER FEED, Ih/hr
                                                                                         12,000
16,000
                 Figure  228.  Emission prediction curves for baffled tower scrubbers serving asphaltic
                 concrete plants (Ingels et al., 1960).
Collection efficiencies of a simple cyclone and a
multiple  cyclone for various  particle  sizes are
shown in Table 96.  Multiple cyclones achieve high
efficiencies for particle sizes  down to 5 microns,
whereas  single  cyclones are  very inefficient for
particle sizes below 20 microns.  The particle size
data from this table are plotted on log-probability
paper  in  Figure 229.  This figure also shows the
particle size distribution of  the scrubber  outlet.
Other  data on this installation have already been
presented in Figure  222,  test  C-537.
                               Future Trends  in Air Pollution Control  Equipment

                              The air pollution control equipment discussed in
                              this  section has  been  adequate in the  past for
                              controlling dust emissions  from hot-mix asphalt-
                              paving batch plants in Los Angeles  County.  How-
                              ever, new  regulations on dust emissions, adopted
                              in January 1972, now require that more efficient
                              devices than wet collectors be used as final col-
                              lectors.    The batch plants are  now  converting
                              from scrubbers to baghouses.
                 Table 96.  COLLECTION EFFICIENCY DATA FOR A CYCLONE AND
                    A MULTIPLE CYCLONE SERVING A HOT-MIX PAVING PLANT
Dust
particle
size, |j.
0 to 5
5 to 10
10 to 20
20 to 50
50+
Dust loading
Ib/hr
Test C-537
cyclone
Inlet,
6.2
9.4
13.8
22.9
47. 7
5, 463
Outlet,
19.3
31. 9
31.6
15. 1
2. 1
1,525
Efficiency,
13. 3
5.4
36. 1
81.6
98. 8
72. 1%
Test C-537a
multiple cyclone
Inlet,
19.3
31. 9
31.6
15. 1
2. 1
1,525
Outlet,
57. 0
34. 0
8. 8
9.2
--
118. 3
Efficiency,
77. 1
91. 7
97.8
99.9
100. 0
92. 2%
                See Table 94,  test C-537 for plant operating data.

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334
                                  MECHANICAL EQUIPMENT
                                                             O  CYCLONE  INLET
                                                                 CYCLONE  OUTLET-MULTIPLE CYCLONE  INLET
                                                             *  MULTIPLE CYCLONE OUTLET--SCRUBBER  INLET
                                                             T  SCRUBBER OUTLET
                                                                                99 99.599.8 99.9
10    20   30  40  50  60  70
PERCENT LESS THAN GIVEN PARTICLE SIZE,
 90   95
microns
                  Figure 229. Plot of particle size of dust at the inlet and outlet of a cyclone  and
                  multiple cyclone from test C-537.
      CONCRETE-BATCHING  PLANTS

Concrete-batching plants  store, convey,  measure,
and discharge the ingredients for making concrete
to mixing or transportation equipment.  One type
is used to charge  sand,  aggregate, cement,  and
water to transit-mix trucks,  which mix the batch
en  route to the site where the  concrete is to be
poured; this operation is known as "wet batching. "
Another type  is used to  charge the  sand,  aggre-
gate,  and cement to flat bed trucks,  which trans-
port the batch to paving machines where water is
added and mixing takes  place; this operation is
known as "dry  batching. "  A third  type employs
the use  of a central mix plant, from which wet con-
crete is delivered to the pouring site in open dump
trucks.

WET-CONCRETE-BATCHING PLANTS

In a typical wet-concrete-batching plant,  sand  and
aggregates are elevated by belt conveyor or clam
                   shell crane, or bucket elevator to overhead storage
                   bins.  Cement from bottom-discharge hopper trucks
                   is conveyed to an elevated storage silo.   Sand and
                   aggregates for a batch are weighed by successive
                   additions from the overhead bins to a •weigh hopper.
                   Cement is deliveredby a screw conveyor from the
                   silotoa separate weigh hopper.  The weighed ag-
                   gregates and cement are  dropped into a gathering
                   hopper and flow into  the receiving hopper to the
                   transit-mix truck.  At the same time, the required
                   amount of water is injected into the flowing stream
                   of  solids.  Details and variations  of this general
                   procedure will be discussed later.
                   The Air Pollution Problem
                   Dust, the air contaminant from wet-concrete-batch-
                   ing, results from the material used.  Sand and ag-
                   gregates for concrete  production come directly
                   f rom a rock and gravel plant where they are washed
                   to remove silt and clay-like minerals.   They thus

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                                         Concrete -Batching Plants
                                             335
 arrive ai the batch plant in a moist condition and
 hence donot usually present adust problem.  When,
 however, lightweight aggregates are used, they do
 pose a problem.  These materials  are formed by
 thermal expansion of certain minerals .  They leave
 the aggregate plant very dry and create consider-
 able dust when handled.  The simplest way to deal
 with this problem is to wet each load of aggregate
 thoroughly before  it is dumped from the delivery
 truck.   Attempts to spray the aggregate as it is
 being dumped have had very limited effectiveness.


 If, therefore,  wet or damp aggregate is  used,
 practically  all the  dust generated from concrete-
 batching operations originates from the cement.
 Particle size distribution and other characteristics
 of the dust vary according to the grade of cement.
 A range of 10 to  20 percent by weight of particles
 of 5-micron size  or less is typical for the various
 grades of cement.  Bulk  density ranges from 50
 to 65 pounds per cubic foot of  cement.  Table 97
 shows additional  characteristics of three common
 grades of cement.
  Air Pollution Control Equipment
  Cement-receiving and storage system

  Atypical cement-receiving and storage system is
  shown in Figure 230.  The receiving hopper is at
  or  below ground level.  If it is designed to fit the
  canvas discharge  tube  of the hopper truck, little
  or  no dust is emitted at this point.  After a brief
  initial puff of dust,  the hopper fills completely  and
  the cement flows from the truck without any free
  fall.   Cement elevators are  either the vertical-
  screw type or the enclosed-bucket type.  Neither
  emits any dust if in good condition.  The  cement
  silo must be vented to allow the air displaced by
  the cementto escape.  Unless this vent is filtered,
  a significant amount of dust escapes.
 Figure  230 shows  one type of filter.  It consists
 of a cloth tube with a stack and weathercap for pro-
 tection.   The pulley arrangement  allows it to be
 shaken  from the ground so that the accumulated
 layer of dust on the inside of the cloth tube can be
 periodically removed.  The cloth's area should be
 sufficient to provide a filtering velocity of 3 fpm,
 based upon the displaced air rate.
   Table 97.  CHARACTERISTICS OF THREE
             GRADES OF CEMENT
Distribution, |_L
0 to 5
5 to 10
10 to 20
20 to 40
40 to 50
50 to 66
66 to 99
99 to 250
250 (60 mesh)
Bulk density,
lb/ft3
Specific gravity,
g/cm3 at 82°F
Cement, wt %
Grade I
13.2
15. 1
25.7
29.0
7.0
5. 0
4. 0
1. 0
0
54. 0
3.3
Grade II
9.6
16. 6
18. 8
36. 6
10. 4
6. 0
2. 0
0
0
51. 5
3. 3
Grade III
21. 8
22. 5
26.7
23.6
5. 4
0
0
0
0
62. 0
3. 3
                                                      Many  concrete batch plants now receive cement
                                                      pneumatically from trucks equippedwith compres-
                                                      sors and pneumatic delivery tubes.  In these plants,
                                                      a single filtered vent used for the gravity filling of
                                                      cement has proved inadequate,  and other  methods
                                                      of control are required.  In this pneumatic  delivery,
                                                      the  volume of conveying air is approximately 350
                                                      cfm during most of the loading cycle and increases
                                                      to 700 cfm at the  end  of the cycle.
                                                      To control this volume of air,  it is best to install
                                                      a small conventional cotton sateen baghouse with
                                                      a filtering area of 3 fpm (approximately 200 square
                                                      feet of cloth area) to vent the cement silo.  The
                                                      baghouse should be equipped with a blower to re-
                                                      lieve the pressure built up -within the silo.  A
                                                      mechanical shaking mechanism also should  be
                                                      provided to prevent cement from blinding the fil-
                                                      ter cloth  of the 'baghouse.
Cement dust can be emitted from several points.
The  receiving  hopper, the elevator, and the silo-
are the" points of possible emission from the ce-
ment-receiving station.  Other points of possible
dust emission are the cement weigh hopper, the
gathering hopper, and the mixer.
Another less expensive type of control device is
to mount a bank of approximately four simple fil-
tered vents atop the  cilo.  The filtering  area
should not exceed  7 fpm,  giving an area  of ap-
proximately 100 square feet for the 700 cfm  of air
encountered  at the  end  of the cycle.  The filter
design must include a shaking mechanism to pre-
vent blinding  of the filter cloth.  The major dis-

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336
MECHANICAL, EQUIPMENT
                                      /-CLOTH TUBE
                                       FILTER
      Figure 230. Cement-receiving and storage system.
advantage of using a bank of several simple filter
vents as just described is the possibility of pres-
sure build-up-within the silo. If, for some reason,
the filter should become blinded, there is  danger
of rupturing the silo.  Therefore, proper mainte-
nance and  regular inspection of the filter are
necessary.
                weigh hopper is  filled at a fairly rapid rate,  and
                the displaced air entrains a significant amount of
                dust.   This dust may be controlled by venting the
                displaced air back to the cement silo or by install-
                ing a filtered vent on the weigh hopper as described
                for cement silos.
                                                      The  vent should be of adequate size to provide a
                                                      filtering velocity of about 3 fpm, based upon the
                                                      cement's volumetric filling  rate.  For example,
                                                      if a weighhopper is filled at the rate of 1, 500 pounds
                                                      in 1 /Z minute, and the density of cement is 94 pounds
                                                      per cubic foot, the displaced air rate equals 1-, 500/
                                                      (94)(0.5), or 32 cfm. The required cloth area would
                                                      then be 32/3 or  10. 7 square feet.
                Gathering hoppers

                The dropping of a batch from the weigh hopper to
                the mixer can cause cement dust emissions from
                several points.  Intheloading of transit-mix trucks,
                a gathering hopper is usually used to control the
                flow of the materials.  Dust can be  emitted from
                the gathering hopper, the truck's  receiving hopper,
                andthemixer.  The design and location of the  gath-
                ering hopper can do much to minimize dust emis-
                sions.   The hopper should make a good fit with the
                truck  receiving  hopper, and its  vertical position
                should be adjustable. Figure 23]  illustrates  a de-
                sign that has been used  successfully in minimizing
                dust emissions.  Compressed-air cylinders  raise
                and lower the gathering hopper  to accommodate
                trucks  of varying heights.   A steel  plate  with a
                foam rubber  backing is attached to the bottom of
                the gathering hopper and is lowered until it rests
                on the  top of the truck's receiving hopper.  Water
                for the mix is introduced through a jacket around
                the discharge  spout of the gathering hopper and
                forms  a dust-reducing curtain.
Where baghouses are used to control other larger
cement dust sources such as those existing in a
dry-concrete-batching  plant or in a central mix
plant,  then the  cement silo can easily be vented
to the  same baghouse.
                Discharge of the cement hopper into the center of
                the aggregate stream, and choke feed between the
                weigh hopper and  the  gathering hopper suppress
                dust emissions from the top of the gathering hopper.
Cement weigh hopper

The  cement  weigh hopper may be a compartment
in the aggregate weigh hopper or it may be a sep-
arate weigh hopper.  Cement is usually delivered
from, the  silo to the v^eigh hopper by an enclosed
screw conveyor.  To permit accurate weighing,  a
flexible connection between the screw conveyor and
•weigh hopper is  necessary.  A canvas shroud is
usually used, and if properly installed and main-
tained, prevents dust emissions at this point.   The
                 DRY-CONCRETE-BATCHING PLANTS

                 Dry-concrete-batching plants are used in road con-
                 struction work.   Because of advances  in freeway
                 construction in recent years, plants such as these
                 are located in metropolitan areas,  often in resi-
                 dential zones.   The plants  are portable,  that is,
                 they mustbe designed to be moved easily from one
                 location to another.  This is, of course, a factor
                 in the design of the air pollution control equipment.

-------
                                        Concrete-Batching Plants
                                                                                                   337
              •WEIGH HOPPERS-
                   X
                                  GATHERING
                                  HOPPER
                                  COMPRESSED-AIR
                                  CYLINDERS
    HATER
                                      TRANSIT-MIX
                                      TRUCK
        Figure.231. An adjustable gathering hopper.
The Air Pollution Problem

Drybatching poses a muchmore difficult dust con-
trol problem than wet batching does.  Since most
plants that  do  dry batching also do wet batching,
the gathering hopper  must be set high enough to
accommodate transit-mix  trucks.   Since the re-
ceiving hopper  of most transit-mix trucks is sev-
eral feet higher than the top of the flat-bed trucks
used  in  dry batching, there is a long free fall of
material when  a dry batch  is dropped.  This pro-
duces a considerable amount of dust,  sufficient to
violate most codes that have an opacity limitation
applicable to this  type of operation.

From an air  pollution standpoint, the dust to be
collected has characteristics similar to those of
the cement dust  already discussed for  wet-con-
crete-batching plants. In dry batching,  however,
volumes of  dust created are considerably greater
because: (1)  The amount  of concrete batched is
large,   (2)  no  -water is used,  and (3) the batches
are dropped rapidly into the waiting trucks to con-
serve time.


Hooding and  Ventilation Requirements

A  local exhaust system -with an efficient dust col-
lector is required to control a dry batching plant
adequately.   This is  a difficult operation to hood
•without interfering with the truck's movement or
the batch operator's view.  The truckbed is usually
divided into several compartments,  a batch being
dropped into each compartment.  This necessitates
repeated spotting of each truck under the direction
of the batch operator; hence he must be able to see
the truck at the drop point. A canopy-type hood
just large enough to cover one compartment at a
time provides effective dust pickup and  affords
adequate  visibility.  Figure Z32 shows a closeup
view of a hood of this type.  The sides are made
of sheets of heavy  rubber to permit contact with
the truckbed without damage. This hood is mounted
on  rails to permit it to be -withdrawn to allow wet
batching into transit-mix  trucks.

The exhaust volume required  to collect the dust
varies  with the  shape  and position  of the hoods.
With reasonably good hooding, the required volume
is approximately 6, 000 to 7, 000 cfm.


Air Pollution Control Equipment

Abaghouse is the most suitable type of dust collec-
tor for this service.  Scrubbers have been used,but
they have been plagued with difficulties such as low
collection efficiency, plugged spray nozzles, cor-
rosion, and  waste-water disposal problems.    A
baghouse for  this  service should have a filtering
velocity of  3  fpm.  It may be of the intermittent
shaking type,  since sufficient  opportunities for
stopping the exhauster for bag shaking are usually
available. Figure 233 is  an overall view of a typ-
ically  controlled dry batching  plant with the bag-
house  shown  on the left.   The drop area tunnel is
enclosed  on the sides and partially on the ends.

Dust created  by truck movement

Inmany instances the greatest source of dust from
the operation of a concrete batch plant is that cre-
ated by the trucks  entering and leaving the plant
area.  If possible, the yard and access roads should
be  paved or oiled,  or if this is not feasible, they
should be watered  frequently  enough to suppress
the dust.
 CENTRAL MIX PLANTS

 The central mix plant, as shown in Figure 234,  is
 being used more and more extensively by the con-
 crete industry in the Los Angeles area.  In a cen-
 tral batch operation,  concrete is  mixed in a sta-
 tionary mixer, discharged into a dump truck, and
 transported in a wet mixed condition to the pour-
 ing  site.
 The handling of aggregate and cement atthese plants
 is similar to that at the other concrete batch plants.

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 338
MECHANICAL EQUIPMENT
               Figure 232. Closeup of hood for controlling dry batching:  (left) Hood in place, (right) hood
               in  retracted position (Graham Bros., El Monte, Calif.).
                                                              Figure 234. Overall view of a central mix concrete-
                                                              batching plant controlled by a baghouse (Griffith
                                                              Co., Los Angeles,  Calif.).
    Figure 233. Overall view of wet-  and dry-concrete-
    batching plant and baghouse located at a California
    Freeway project (Guy F.  Atkinson  Co.,  Long Beach
    Calif.).
Sand, aggregate, cement, and water are all weighed
ormeteredas in a wet-concrete-batching plant and
discharged through  an enclosed system  into  the
mixe r.
                The Air Pollution Problem

                From an air pollution control standpoint,  this type
                of .operation  is  preferable  to dry batching.   The
                dust is more easily captured at the batch plant, and
                further,  there is no generation of dust at the pour-
                ing  site.   The operation is  also preferable to wet
                batching because designing control equipment for
                a stationary mixer is easier than it is for  a transit-
                mix truck-loading area.

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                                       Cement-Handling Equipment
                                            339
Hooding and Ventilation Requirements

Effective control at the discharge end of the mixer
is a function of good hood design and adequate ven-
tilation air.  Ahydraulically operated,  swing-away,
cone-shapcdhood, as shown in Figure 235,  is nor-
mally  used  with a 2-inch clearance  between the
hood and  the mixer.  This installation  employs a
mixer  with a capacity of 8 cubic yards.  The  dis-
charge opening of the mixer is  40 inches in di-
ameter.  Ventilation air was found to be  2,500 cfm.
For a  hood  of this type,  indraft  face  velocities
should be between 1, 000 and 1, 500 fpm.   Velocities
 such as these are required for handling the air dis -
 charged from the mixer, which is displaced air and
 inspirated air from the aggregate and cement fall-
 ing into the mixer.
 Air Pollution Control Equipment

 A baghouse,  such as  is  shown in Figure 235, is
 required to collect the dust emissions.  A filter-
 ing velocity of 3 fpm is adequate.  Other baghouse
 features are similar to those previously discussed
 for dry-concrete-batching plants.
  Figure 235. Hood for central mix plant: (top) In re-
  tracted position, (bottom) in closed position (Griffith
  Co.,  Los Angeles, Calif.).
                                                           CEMENT-HANDLING  EQUIPMENT

                                                       Equipment used in handling cement includes hop-
                                                       pers, bins, screw conveyors, elevators, and pneu-
                                                       matic conveying equipment.  The equipment to be
                                                       discussed in this section is that  involved in the
                                                       operation of a bulk cement plant, which receives,
                                                       stores,  transships,  or bags  cement.  Its main
                                                       purpose  is usually to  transfer  cement fro?n one
                                                       type of  carrier to another,  such as from railway
                                                       cars to trucks or  ships.


                                                       THE AIR POLLUTION PROBLEM

                                                       In the handling of cement, a dust problem can occur
                                                       if the proper equipment or hooding  is not used.  A
                                                       well-designed system should create little  air pol-
                                                       lution.  Sources  of emissions include the storage
                                                       and receiving bins,  elevators, screw conveyors,
                                                       and the mobile conveyances.

                                                       Characteristics of cement dust have be en dis cussed
                                                       in the section on wet-concrete-batching plants.
HOODING AND VENTILATION REQUIREMENTS

Receiving Hoppers

Railway cars are usually unloaded into an under-
ground hopper  similar to  the  one described for
trucks in the preceding section.  The canvas tube
is usually, however,  permanently attached to the.
receiving hopper and is attached by a flange to the
discharge  spout of the hopper car.  When flanges
fit properly,  emissions  from  equipment such as
this are usually negligible.

Storage and Receiving Bins

Bins filled by bucket elevators  must be ventilated
at a rate equal to the maximum volumetric filling
rate plus 200 fpm indraft at all openings.   The area
of openings is usually very small.  Since most bulk
   234-767 O - 77 - 24

-------
340
MECHANICAL EQUIPMENT
plants  have a number of bins,  a regular exhaust
system with a dust collector provides a more prac-
tical solution than the silo filter vents do that were
described for concrete batch plants. Bins filled by
pneumatic conveyors  must, of course,  use a dust
collector to filter the conveying air.  Gravity-fed
bins and bins filled by bucket  elevators can use
individual filter vents if desired.


Elevators and Screw Conveyors

Bucket elevators used for cement service  are al-
ways  totally  enclosed.   Ventilation must be pro-
vided for  the bin into which it discharges.  Since
elevators  are nearly always  fed by a screw con-
veyor that makes a dust-tight fit at the feed end, no
additional ventilation is usually required.  Another
type of conveyor used for cement service is a ver-
tical screw conveyor.  These,  of course, cause no
dust emissions as long as they have no leaks.  Hori-
zontal screw  conveyors are frequently fed  or dis-
charged through canvas tubes or shrouds.   These
must be checked regularly for tears or leaks.

Hopper Truck and  Car Loading

Hopper trucks and railroad cars are usually filled
from overhead bins and silos.  The amount of dust
emitted is sufficient to cause a nuisance in almost
anylocation.  Figure 236 shows  a type of hood and
loading spout that permits these  emissions to be
collected with a minimum amount of air.  The ven-
tilation rate is the same as for bins, the displaced
air rate plus  200 fpm through  all openings.  If the
hood is designed to make a close fit -with the hatch
  AIR CONVEYOR
  FROM CEMENT BIN
                opening,  the  open spaces are very small and the
                required exhaust volume is  small.   The hood is
                attached to the telescoping cement discharge spout
                in  such a way that it  can be raised and lowered
                when hopper trucks are changed.
                AIR  POLLUTION CONTROL EQUIPMENT

                Abaghouse has been found to be the most satisfac-
                tory dust  collector for handling the ventilation
                points described.  All sources are normally ducted
                to a single baghouse.  Cotton sateen cloth with a
                filtering velocity of  3  fpm is adequate.  Dacron
                cloth, which provides longer wearing qualities but
                is more expensive, can also be used.

                ROCK AND GRAVEL  AGGREGATE PLANTS

                Rock  and gravel plants supply sand and variously
                sized aggregates for the construction and paving
                industries. The sources of most aggregates used
                in Los Angeles County are the gravel beds in the
                San  Fernando and San Gabriel valleys.  The pro-
                cessing of the gravel  consists of screening out the
                usable sizes and crushing the oversize into various
                size ranges.  A simplified flow diagram for  a typ-
                ical plant is shown in Figure 237.  Incoming  mate-
                rial is routed through a jaw crusher,  -which is set
                to act upon rocks larger than about 6  inches and
                to pass smaller  sizes.   The product  from this
                crusher is screened into sizes smaller  and larger
                than 1-1/2 to 2  inches,   the undersize going to a
                screening plant,  and the oversize to the crushing
                plant.  These next crushers  are of the cone or gy-
                ratory type,  as  shown in Figure 238.  In a large
                plant, two or three primary crushers are used in
                parallel followed by two to five  secondary crush-
                ers  in parallel.
T
*-

Ml
CRUSHED


3 4-in
GRAVEL
STOBAGE



-H



1 1 2- in
GRAVEL
STORAGE
^-



SCREEN


PR
CR

«lHf
HE
USHER

—

LINOERS 2C
SCREEN
I
	 1

SCREEN
L
L
PEA
GRAVEL
STORAGE



~~l
SCR£»
SAND
HASHER
1
SAND
STOBAGE






	 1
ROCK
DUST
STORAGE
SCREEN

I
SCREEN
L 	


-

SECONDARV
CONE
CRUSHER


*-!



SCREEN.
L
INE
CRUSHED
10CK
TORAGE




XEOIIIM
CRUSHED
ROCK
STORAGE

LARGE
CRUSHED
ROCK
STORAGE
       Figure 236.  Hood for truck-loading station.
                     Figure 237. Simplified flow diagram of a typical
                     rock gravel plant.

-------
                                   Rock and Gravel Aggregate Plants
                                                                                                   341
                               'SPIDER CUP
                                      SPIDER *R»
                                      SHIELD
                                           RUGGED
                                           TIO-MW
                                           SPIDER
      Figure 238. Gyratory crusher (Allis-Chalmers
      Manufacturing Company, Milwaukee, His.).
THE AIR POLLUTION PROBLEM

The sand  and rock,  as it comes from the pit, is
usually moist enough to remain nondusting through-
out the sand- and uncrushed-rock-screening stages.
When the pit material is not sufficiently moist, it
must be wetted before it  leaves the pit.   As the
larger rocks are  crushed,  dry surfaces  are ex-
posed and airborne dust can be  created.

Aninventory of sources of dust  emissions usually
begins with  the first crusher and continues with
the conveyor transfer points to and  including the
succeeding crushers.  Here the rock is more fine-
ly ground,  and dust emissions become greater.  As
the process  continues, dust emissions are again
prevalent from sources at conveyor transfer points
and at the  final screens.
 guide to  the  amount of ventilation air required
 (Committee on Industrial Ventilation,  I960):
 1.   Conveyor transfer points--350 cfm per foot of
     belt width for speeds of less than 200 fpm; 500
     cfm per foot of belt width for belt speeds over
     200 fpm;

 2.   bucket  elevators--tight  casing required •with
     a ventilation rate  of 100 cfm per square foot
     of casing cross section;

 3.   vibrating screens--50 cfm per square foot of
     screen area, no increase for multiple decks.


 AIR POLLUTION CONTROL EQUIPMENT

 One method of suppressing the dust emissions con-
 sists  of using water to keep the materials moist
 at  all  stages  of processing;  the other,  of using a
 local exhaust system and a dust collector to collect
 the dust from all sources.

 If  the  use of  water can be  tolerated, then -water
 can be  added with  spray nozzles, usually at the
 crusher locations  and the shaker screens.  Fig-
 ure 239 shows nozzle arrangements for control of
 emissions from the outlet of  the crushers, Figure
 240, nozzle arrangements at the inlet to the shak-
 er screens.   The amount of water to be used can
 best be determined by trial under normal operat-
 ing conditions. Water quantities vary -with crush-
 er size,  crusher setting, feed rate,  type of feed,
 and initial moisture content of the feed.
TIO FLAT ATOMIZING T
SPRAT NOZZLES ONE EACH
f.NO OF RUBBER SHIELD
                                       'HARD RUBBER SHIELD
T*0 FLAT ATOMIZING TYPE
SPRAT NOZZLES ONE EACH
END OF RUBBER SHIELD
       Figure 239. Nozzle arrangement for control of
       dust emissions upon discharge of crusher.
HOODING AND VENTILATION REQUIREMENTS

The points that require hooding and ventilation are
the crusher discharge points, all elevator and belt
conveyor transfer points, and all  screens.

All these dust sources should be enclosed as near-
ly completely  as possible and a minimum indraft
velocity  of  200 fpm  should be maintained  through
all open areas.   The following rules  are also a
 Adding  water in the described manner tends  to
 cause blinding of the finest size screens used in
 the screening plants, which thereby reduces their
 capacity.   It also  greatly  reduces  the amount of
 rock dust that can be recovered, since most of the
 finest particles adhere to larger particles. Since
 rock dust is in considerable demand,  some oper-
 ators prefer to keep the crushed material  dry and
 collect the airborne dust -with a local exhaust  sys-
 tem.

-------
342
                                      MECHANICAL EQUIPMENT
    Figure 240.  Nozzle arrangement for control of dust
    emissions from the inlet to the shaker  screens.
The preferred dust collector device is a baghouse.
Standard cotton sateen bags can be used at a filter-
ing velocity of 3 fpm.  For large plants that main-
tain continuous operation, compartmented collec-
tors  are required to allow for bag  shaking.  Most
plants,  however,  have shutdown periods of suffi-
cient frequency to allow the use of a noncompart-
mented collector.  Virtually 100 percent collection
canbe achieved, and as mentioned previously, the
dust is a salable  product.

A combination of a dry centrifugal  collector and a
wet  scrubber is  sometimes  used.   In this case,
only the centrifugal device collects  material in a
salable form. A centrifugal collector alone would
allow a considerable amount of very fine dust to be
emitted  to the atmosphere.  A  scrubber of good
design is  required,  therefore,  to  prevent such
emissions.

        MINERAL WOOL FURNACES

INTRODUCTION

The  general product  classification known as min-
eral wool  •was formerly divided into three cate-
gories:  Slag wool, rock wool, and glass wool.

Slag wool,  which was  made from  iron slag or cop-
per  slag,  was first successfully manufactured in
England in 1885, after earlier attempts had failed
in the United States (Kirk and Othmer, 1947).  The
first manufacture of rock wool (which was made
from natural rock) took place at Alexandria,  In-
diana, in 1897. Glass wool (made from glass cul-
let or high  silica sand, or  both) was  later pio-
neered in Newark, Ohio, in 1931.
Today, however, straight slag -wool and rock wool
as such are no longer manufactured.  A combina-
tion of slag and rock constitutes the cupola charge
materials in more recent times, yielding a product
generally classified as mineral wool, as contrasted
with glass wool.

Mineral wool is made today in Los Angeles County
with a cupola  by using blast furnace slag,  silica
rock, and coke (to serve as fuel). It has been pro-
duced here in the past by using a  reverberatory
furnace charged with  Borax ore tailings,  dolomite,
and lime rock heated with natural gas.


Types and Uses of Mineral Wool Products

Mineral wool consists of silicate fibers 5 to 7 mi-
crons in  diameter (Allen et al. , 1952) and about
1/2-inchlong, and is  used mainly for thermal and
acoustical insulation.  It has a density of about 6
pounds  per cubic foot and is collected initially as
a continuous loose blanket of fibers on a convey-
ingbelt.  Itissold, however, as quilt,  loose rolls,
industrial felt, batts, or in a granulated form.

Batts are rectangular sections of mineral wool ap-
proximately 4 by 15 by  48 to 60  inches in size.
These  sections are  covered on top and two sides
with paper,  and  the bottom is covered "with  either
an asphalt-coated paper or aluminum foil.  Batts
are used for thermal insulation in residential homes
and for  many other insulation needs.

Granulated  mineral wool, -which is handled pneu-
matically, isalsoused for home insulation.   Quilt
is normally 60 inches wide and 2 inches thick and
contains the binder  agent and paper  cover.  It is
used primarily for industrial insulation.  Loose
rolls, which contain no binder agent and are some-
times enclosed in a fine mesh cover,  are used for
applications such as water heaters and house trail-
ers.  Industrial felt  consists of wool blanket with
binder agent but without a paper covering and has
a slightly greater density than that  of batts.  It is
used for items such  as walk-in refrigerators and
industrial ovens.
Mineral Wool Production

The cupola or furnace charge is heated to the mol-
ten state at about 3,000°F, after which it is  fed by
gravity into a device at the receiving end of a large
blowchamber.  This device may be a trough-like
arrangement with  several drains,   or  a  cup-like
receiver on the end  of a revolving arm.  The mol-
ten material is atomized by steam,  and blasted hor-
izontally towards the other end of the blowchamber.
When the cup or spinner device is used,  the  action
of the steam is assisted by centrifugal force.  The
steam atomizes the molten rock into small  globules
that  develop and trail  long, fibrous tails as they

-------
                                        Mineral Wool Furnaces
                                             343
travel towards  the other end of the blowchamber.
These fibers reportedly can be drawn mechanically
or spun without steam, but this  process is foreign
to Los Angeles  County.

Phenolic resin or a mixture  of linseed oil and as-
phalt are examples of binding agents that can be
atomized at the center of the steam ring by a sep-
arate steam jet to act as a binder for the fibers.
Annealing oil can also be steam atomized near the
steam ring to incorporate a. quality of resilience
to the fibers that prevents breakage.

Atemperature between 150°  and  250DF is main-
tained in the blowchamber.  Blowers, which take
suction beneath the wire mesh conveyor belt in the
blowchamber, aid the fibers in  settling on the belt.
The mineral wool blanket of fibers is conveyed to
an  oven  for  curing the  binding agent.  Normally
gas fired, the oven has a temperature of 300°  to
500°F.

The mineral  wool  is next programmed through a
cooler,  as  shown  in the flow  diagram in Figure
241.  Usually consisting of an enclosure housing
a blower,  the cooler reduces the temperature of
the blanket to prevent the asphalt, which is applied
later to the paper cover, from  melting.

To make batts,  the blanket leaving the cooler is
processed through a multibladed, longitudinal cutter
to separate it into sections of desired widths.  Brown
paper  and either  asphalt-coated paper or alumi-
num foil are then applied to the sections of blanket.
The asphalt-coated paper is passed through a bath
of hot asphalt j\ist before its application to the un-
derside of each section.  This asphalt film serves
as  a moisture barrier as well as  a bonding agent
against walls.  The  paper-covered sections  are
cut to  desired lengths by a transverse saw, after
which  the finished product is packed for storage
and shipment.  The two cutters, paper and asphalt
applicators, and conveyor systems are sometimes
referred to collectively as a batt machine.

A granulated-wool production line differs from that
just described in that the mineral  wool blanket,
after leaving the blowchamber, is fed to a shredder
for granulation, then to a pelletizer. The pelletizer
serves two functions,  namely,  to form small 1-
inch-diameter wool  pellets and to drop out small
blackparticles called shot,  which form as the mol-
ten slag cools in the blowchamber.  A bagging oper-
ation completes the process. Since no binding agent
is required, the curing oven is eliminated.


THE AIR POLLUTION PROBLEM

The major  source of emissions  is  the cupola or
furnace stack.  Its  discharge consists primarily
of condensed fumes that have volatilized from the
                                                                                        PACKING
                                                                                      *- AND
                                                                                        STORAGE
                                                        T0_
                                                        ATMOSPHERE
                               Figure 241. Flow diagram of mineral  wool  process.

-------
 344
MECHANICAL EQUIPMENT
molten  charge,  and gases  such as sulfur oxides
andfluorides. Amounting to as much as 100 pounds
per hour and submicron in size, condensed fumes
create a considerable amount of visible emissions
andean  be a public nuisance.  Table 98 shows the
weights of emissions discharged from uncontrolled
cupolas and furnaces. A particle size distribution
of the emissions is shown in Table 99.

Another source of air pollution is the blowchamber.
Its emissions (see  Table 100)  consist of fumes,
oil vapors, binding agent aerosols, and wool fibers.
In terms of -weight, a blowchamber may also emit
as much as  100 pounds of particulate matter per
hour at  a production rate  of 2 tons per hour if the
blowchamber vent is  uncontrolled.   Approximately
90 percent of these emissions consists of mineral
wool fibers.

Types  of air  contaminants from  the curing oven
are identical  to those from the blowchamber ex-
cept that no metallurgical  fumes  are  involved.
These emissions amount to approximately 8 pounds
per hour at a production rate of  2 tons per hour,
as seen in  Table  101,  since the amount of wool
fibers discharged is muchless than that for a blow-
chamber.  From  a  visible standpoint, however,
these pollutants may create  opacities  as high as
70 percent.    Emissions from the cooler  are  only
4  or 5  pounds per hour  at a  production rate of 2
tons per hour (see  Table 102).  The asphalt appli-
cator can also  be a source of air pollution if the
temperature of the melting or holding pot exceeds
400°F.


HOODING AND VENTILATION REQUIREMENTS

No special hooding arrangements  as such are re-
quired  in any of the  exhaust systems employed in
               the control of pollution from mineral -wool process-
               es.  The one possible exception is that canopy hoods
               may oe used over the asphalt tanks if the emissions
               from these tanks are excessive  and are vented to
               an air pollution control device.

               The ventilation requirements for the various indi-
               vidual processes  in a  mineral  wool  system  are
               categorized as follows:

               1.   Cupolas.  Based on test data, exhaust require-
                    ments can  be  estimated to be 5, 000 to 7, 000
                    scfm for a cupola with a process -weight of
                    from 4,000 to 4,500 pounds per hour, on the
                    assumption that no outside  cooling air is in-
                    troduced.  The charge door should be kept in
                    the closed position to obtain maximum benefit
                    from the capacity of the  exhaust fan. A ba-
                    rometric damper in the line between the cu-
                    pola and the blower can be used to control the
                    amount of gases pulled from the cupola.   The
                    objective is to remove all tuyere air plus an
                    additional amount  of air  to maintain a slight
                    negative pressure above the burden.

               2.   Reverberatory furnaces. Ventilation require-
                    ments are  about 15,000  to 20,000  cfm  (at
                    600°F) for a furnace sized to produce 1,500
                    to 3, 000 pounds of mineral wool per hour.   The
                    heat in these  furnace gases  can  be used in
                    making steam before filtration.

               3.   Blowchambers.  For a blowchamber -with a
                    size of about 4, 500  cubic feet and -with a ca-
                    pacity for processing 4, 000 pounds of -wool an
                    hour,  the minimum  ventilation requirements
                    are 20, 000 to 25, 000 scfm.  All duct takeoffs
                    must be located at the bottom of the blowcham-
                    ber beneath the conveyor  to create downdraft,
                  Table 98.  DUST AND FUME  DISCHARGES FROM MINERAL WOOL
                                     CUPOLAS AND FURNACES
                                                          Test No.
Test data
Process wt, Ib/hr
Stack volume, scfm
Stack gas temp, °Fb
Stack emissions, Ib/hr
gr/scf
SO2, mg/scf
Total SO2, %
SO , mg/scf
CO, %
Cupola
1
3, 525
4, 550
309
49. 7
1.28
32.6
0. 04
18.5
0.9
3
4,429
4,545
295
45. 6
0.21
-
-
-
-
6A
-
4, 510
314
51. 1
1.33
-
-
-
-
13
3, 625
4, 760
338
29. 0
0.71
-
-
-
-
Reverberatory
furnace
19a
3, 050
2, 740
625
7. 3
0. 31
-
-
-
-
          aAn estimated 75 percent of the furnace gases was used for waste heat purposes
           and was not, therefore, included in the test.
          "As measured after cooling, just upstream from control device.

-------
                                       Mineral Wool Furnaces
                                                                                                 345
  which packs the newly formed wool fibers onto
  the conveyor.   From this viewpoint,  35, 000
  scfm •would  be more desirable.  In addition,
  this increased ventilation holds the blowcham-
  ber temperature down to tolerable limits, which
  determine the type  of air pollution control
  equipmentto be selected.  If the plant is pro-
  cessing granulated wool instead of batts, down-
  draft is less important and satisfactory oper-


  Table 99.  PARTICLE SIZE ANALYSIS
  BY MICROSCOPE OF TWO SAMPLES
   TAKEN FROM THE DISCHARGE OF
 A MINERAL WOOL CUPOLA FURNACE

                 Test No. 9A
Size
45
15
7.
1
1
range, ji
to 75
to 45
5 to 15
to 7. 5

Total
count
10
10
40
100
3,000
Percent
by number
0. 5
0. 5
2. 0
5. 0
92. 0
Percent
by wt
75.0
10.0
14.5
0. 5
Nil
Tyler screen analysis: Retained on 200 mesh (74 ^i):
                                       33.8%
                    Retained on 325 mesh (44 ji):
                                       20. 3%
                    Retained on pan (44 n): 49. 9%
Ignition loss:  10%
                 Test No. 9B
Average particle size, p.
200
60
40
10
5
1
Total
count
2
8
10
20
100
930
Percent
by number
0. 1
0. 4
0. 5
1. 0
5. 0
93. 0
Percent
by wt
85.0
9.5
3.5
1. 08
0.07
Nil
 ation can be achieved with a 25, 000-scfm ex-
 haust  system.   If a lint cage is used to trap
 •wool fibers in the discharge gases,  frequent
 cleaning  (four times an hour) of the cage is
 imperative for proper ventilation.

 Curing ovens.  Exhaust requirements for a
 2, 500-cubic-foot oven operating at 300°   to
 500 °F and capable of processing 4, 000 to 6, 000
 pounds of mineral wool an hour are about 5, 000
 scfm.  Sufficient oven gases must be removed
 to prevent a pressure buildup so that leakage
 does not occur.  In sizing the fan,  considera-
 tion must be given to temperature rises and
 possibly also  to the introduction of outside
 cooling air for proper fan operation, particu-
 larlyif the oven discharge gases are inciner-
 ated.

 Coolers.  Coolers normally do not require air
pollution control devices.   If outside ambient
air is used as the cooling medium, the ventila-
tion  requirements  are  10,000 to 20,000 cfm
for a cooler whose  area  is about 70 square
feet.
Asphalt tanks.  If temperature regulators are
successfully used  to  control emissions, the
ventilation requirements for melting, holding,
and  dip tanks  will be about 75 cfm for each
square foot of surface area.  This value is for
open tanks and  for hoods having one open side.
If the melting and holding tanks  are closed,
natural-draft stacks may be used.
                Table 100.  EMISSIONS FROM MINERAL WOOL BLOWCHAMBERS
                                                      Test No.

Process wt, Ib/hr
Stack volume, scfm
Stack gas temp, °F
Blowchamber emissions, Ib/hr
Type of control equipment


Dust concentration, gr/scf
Inlet
Outlet
Dust emissions, Ib/hr
Inlet
Outlet
Control efficiency, %
SO2, mg/scf
Total 303, %
Aldehydes, mg/scf
Total aldehydes, %
Combustibles, %
1
3,525
11, 100
196
9. 20
None



0. 097
0. 097

9. 20
9. 20
-
1. 04
0.0013
1.03
0. 0036
-
6C
-
17, 200
196
5. 02
a



0.034
0.011

5.02
1.62
67.90
-
-
-
-
-
13
3,625
15, 760
160
7. 11
None



0. 0526
0. 0526

7. 11
7. 11
-
-
-
-
-
-
17
3, 700
19,750
167
-
Lint cage



-
0. 012

-
2. 03
-
-
-
-
-
-
25
4, 120
15, 400
200
8.3
Two wet centrifugal
water scrubbers in
parallel

0.063
0. 028

8. 30
3.60
57
_
_
.
_
-
    aThis control equipment consisted of a water scrubber followed in series by an electrical precipitator.

-------
346
MECHANICAL EQUIPMENT
                      Table 101.  EMISSIONS FROM MINERAL WOOL  CURING OVENS
                                                            Test No.

Process wt, Ib/hr
Stack volume, scfm
Stack gas temp,°F
Oven emissions, Ib/hr
Type of control equipment

Dust concentration, gr/scf
Inlet
Outlet
Dust emissions, Ib/hr
Inlet
Outlet
Control efficiency, %
SO2> mg/scf
Total SO2, %
Aldehydes, mg/scf
Total aldehydes, Ib/hr
Inlet
Outlet
NO2, Ib/hr
Inlet
Outlet
Afterburner temp, °F
1
3,525
4,740
326
8. 95
None


0. 22
0. 22

8. 95
8. 95
-
3.23
0. 0053
1. 24

-
-

-
-
-
6E
-
6, 130
314
22. 30
b


0. 42
13
3, 625
4, 862
353
5. 20
None


0. 125
0.-083 0. 125

22. 30
4. 36
81
-
-
-

-
-

-
-
-

5.20
5.20
-
-
-
-

-
-

-
-
-
18a
3, 050
1,642
310
2. 27
22
5, 180
8, 000
200
15. 20
None Catalytic


afterburner

0. 161 0. 221
0. 161 0. 071

2. 27
2.27
-
-
-
-

-
-

-
-
-

15. 20
4.90
68


-

1.90
0. 90

0. 60
0. 70
840
24
3,500
4, 870
270
5
Direct- flame
afterburner

0. 119
0. 032

5
2. 50
50
-
-
-

2. 20
0. 94

0. 15
0. 45
1, 230
aDuring this test the oven was heated with waste heat from a reverberatory furnace.  The quantity of
  dust emissions'appears low as a result of considerable leakage at the oven.  Of the particulates col-
  lected, 95.4% were volatile or combustibles.
       control equipment consisted of a water scrubber followed in series by an electrical precipitator.
                     Table  102.  EMISSIONS FROM MINERAL WOOL COOLERS
                                                            Test No.

Process wt, Ib/hr
Stack volume, scfm
Stack gas temp, °F
Cooler emissions, Ib/hr
gr/scf
SO2, mg/scf
Total SO2, %
Aldehydes, mg/scf
Total aldehydes, %
1
3, 525
1, 850
128
0. 75
0. 047
0. 49
0. 0006
0. 304
0. 0009
17
3, 700
8, 500
273
2.55
0. 035
-
-
-
-
18
3, 050
16,696
170
3. 58
0. 025
-
-
-
-
19
3,050
8, 980
288
8. 39
0. 109
-
-
-
-

-------
                                          Mineral Wool Furnaces
                                                                                                    347
AIR POLLUTION CONTROL EQUIPMENT

Baghouse Collection and Cupola Air Contaminants

Baghouses  have proved to bf*  ... Affective and re-
liable means of controlling the discharge from
mineral wool cupolas.  An installation of this type
is shown in Figure  242.   Dacron or Orion bags,
which can withstand temperatures  up to 275°F,
should  be used.  Of these two synthetic fabrics,
Dacron is now the more common,  and features
several advantages over Orion, as  discussed in
Chapter 4.  Glass fabric bags cannot be used, owing
to the fluorides in the cupola effluent.   (Results of
a baghouse catch analysis disclose fluorides  in a
concentration of 9.85 percent by weightin the par-
ticulate matter discharged from a cupola.  The  life
of glass  bags  under these conditions  is  about 1
week. )

Provisions for automatic bag shaking should be in-
cluded  in the baghouse design.   Sufficient cloth
area should be provided so that the filtering veloc-
ity does not exceed 2. 5 fpm.

Since the discharge temperature of the gas is about
1, 000°F,  heat-removing equipment must be used
to prevent damage to the cloth  bags.   This can be
accomplished with heat  exchangers,  evaporative
coolers,  radiant cooling  columns,  or by dilution
with  ambient air.   The cooling device should not
permit the temperature in the baghouse to fall be-
low the dewpoint.  Safety devices should be included
to divert the gas stream and thus protect the  bag-
house from serious damage in the event of failure
of the cooling system.  In some instances it may
alsobe  desirable to include a cyclone or  knockout
trap  someplace  upstream of the baghouse to re-
move large chunks of hot metal that can burn holes
in the bags even after passing through the cooling
system.

The solution to a, typical design problem involving
a baghouse and an evaporative cooling system serv-
ing a  cupola is described in Chapter 6.

Baghouses should be equally effective in controlling
emissions from reverberatory furnaces. The com-
ments made about cupolas are generally applicable
to these furnaces. Excelsior-packed water scrub-
bers have been tried in Los Angeles County but did
not comply -with air pollution statutes  relating to
opacity limitations.


Afterburner Control of Curing Oven Air Contaminants

The effluent from the curing  oven is  composed
chiefly  of oil and binder particles.  These emis-
sions, while not a great contributor to air pollu-
tion in  terms  of weight,  are  severe in terms of
opacity.  Since they are combustible,  a possible
method of control is incineration.   This method,
in fact, has proved practical for the mineral wool
plant.

Generally, afterburners are divided into two cate-
gories,  depending upon  the  method of oxidation.
These are direct-flame and catalytic.  Important
considerations for the direct-flame type (see  Table
103) are flame contact, residence times, and tem-
perature.  The afterburner should be designed so
that a maximum of mixing is obtained with the flame.
The design should also provide sufficiently low gas
stream velocities to  achieve  a minimum retention
time  of 0. 3  second.  An  operating temperature of
1, 200 °F is the minimum  requirement for efficient
incineration.   Figure 243 shows the effectiveness
of the direct-flame type on curing oven emissions
at different operating temperatures.
      Table 103.  DATA FOR A MINERAL
    WOOL CURING OVEN CONTROLLED BY
      A DIRECT-FLAME AFTERBURNER
                    Oven data
 Type, gas fired, conveyorized
 Operating temp,  350°   to450°F
 Heat input, 4 million Btu/hr
                 Afterburner data
 Type, direct flame,  gas  fired, two-pass
 Flame contact device,  deflector plate
 Heat input,  5 million Btu/hr
 Size, 4 ft dia x 9 ft length with 3  ft dia x 10 ft length
    Insulated retention tube
 Gas temp inlet,  270°F
 Operating temp,  1,
-------
348
                                              MECHANICAL EQUIPMENT
                                      Figure 242. Baghouse controlling a mineral wool cupola.
                          No.  1
Heat exchanger data:

                No.  2
                          Tube side, gas
                            No. passes, 1
                          She 11 side,  cool mg air
                            No. passes, 4
                            Air vol, 2,840 scfm
                          Tube surface, 895 ft?
                          Inlet temp (gas), 650°F
                          Outlet temp  (gas),  440°F
                          Type,pulI through, tubular
                          Filter medium, or I on
                          Filter area, 5,232 ft2
                          Shaking cycle, 30 minutes
                          (Automatic, staggered by
                            compartment)
                Tube side,  gas
                  No.  passes,  1
                Shell  side,  cooling air
                  No.  passes,  3
                  Air  vol,  10,500 cfm
                Tube surface,  1,740 ft2
                Inlet  temp  (gas),  400°F
                Outlet temp (gas),  275°F
                                                    Baghouse data:
                Tube size,  }V/2 in.  dia
                Gas temp inlet,  250°F
x 15^ ft length
                Col lection  efficiency,  97%

-------
                                         Mineral Wool Furnaces
                                            349
   1 ODD
                                              1  300
                 I 100            I 200
                  AFTERBURNER TEMPERATURE °F
     Figure 243.  Effectiveness of direct-flame afterburner
     on curing oven emissions as a function of afterburner
     temperature.
Reducing Blowchomber Emissions

If  the  blowchamber's temperature  is maintained
below  175°F to preclude the formation of oil mist,
then the major air pollution problem is posed by
wool fibers.  The most practical means of collect-
ing these fibers is an efficient water scrubber,  as
shown in Figure 244.  If,  however, the blowcham-
ber's temperature  rises above 250°F, the feasi-
bility of using a water scrubber is diminished.  Test
25 shown in Table 100 gives the results of a stack
analysis of two  wet centrifugal 'water scrubbers
placed in parallel and venting a blowchamber.   A
deflector plate at the blowchamber's entrance can
be used to deflect a large portion  of the molten shot
and thereby reduce the blowchamber's temperature
as -well  as  reduce the chance for contact with oil
mists.  Water injection at the  receiving end  of the
blowchamber combined  with  adequate ventilation
air can further reduce this temperature to 150°F
or less.

A simple wire-mesh lint cage  collects as much as
90 pounds  of  large pieces of fibrous material per
hour.  Constant cleaning of the  lint  cage is, how-
ever, required; otherwise lack of ventilation results
in a temperature rise in the blowchamber.

Large water  content in the blowchamber effluent
precludes  classifying the baghouse  as  a practical
control device for the blowchamber.   In addition,
the resin binder  -would plug the  pores of the bags,
resulting in a severe maintenance problem.
Controlling  Asphalt Fumes

Asphalt  vapors emitted by the asphalt applicator
canbecome a serious source of air pollution if the
  Figure 244. Mineral  wool blowchamber controlled by an
  inertial-type water  scrubber.
asphalt's temperature is permitted to exceed 400 °F.
The simplest and most economical  method of re-
ducing  these  emissions  to  the  atmosphere is to
control the temperature.   The temperature  can
sometimes be held to a maximum of 325°F by
proper asphalt- selection,  thermostatic  control,
and use of a holding pot separate from the melt-
ing pot.  (Asphalts made from different crude  oils
have different vaporizing points. )

If  temperature  control is  used, best results can
be obtained by using three separate tanks: Melt-
ing tank,  holding tank,  and dip tank.  All three
should  be  provided with individual heating facili-
ties, whichtherebypermits minimum temperature
differentials between tanks.  In this manner, the
holding tank's temperature  can be held to a mini-
mum (about 400 °F) without regard to heat loss at
the dip tank.  Automatic temperature controls are
necessary for the holding  tank.  An asphalt feed
control bar  installed on the asphalt roller in the
dip tank permits the temperature  to be  reduced
even further.  This feed control bar, which is ad-
justable against the  roller,  controls the thickness
of the asphalt film applied to the  paper; other-wise
this thickness would have to be controlled by con-
trolling temperature and asphalt viscosity.

If  control  of asphalt temperature proves imprac-
tical,  then a collection  device should be used to
preventthe fumes from escaping to the atmosphere.
This can be done effectively with a two-stage, low-
voltage electrical precipitator, and sometimes -with
a high-efficiency "water  scrubber.  If a scrubber

-------
350
MECHANICAL EQUIPMENT
is used, recirculation  of the water is not advised,
since plugging of the water nozzles may occur un-
less the asphalt particles are somehow removed,
say by flotation.

    PERLITE-EXPANDING FURNACES

INTRODUCTION

Perlite is a glassy, volcanic rock of the composi-
tion of obsidian but divided into small, spherical
bodies by the tension  developed during its  con-
traction on cooling.  It is grayish with a soft, pearly
luster. Chemically, perlite consists chiefly of the
oxides of silicon and aluminum combined as a nat-
ural glass "with water  of hydration.   Upon rapid
heating, the escaping water of hydration causes the
spherules to expand and form white,  cellular,  low-
density particles .  This process is termed  exfolia-
tion.


Uses

About  90 percent of expanded perlite is used  as  an
aggregate in plaster and concrete. When mixed
with gypsum and \vater, perlite creates a plaster
that can'be  troweled or sprayed on lath to form a
lightweight, resilient \vall or ceiling.   Perlite in-
sulating  concrete  can be  used in the form of  pre-
cast slabs or poured on lath,  formboard,  or  steel
decking.  Loose  perlite  is  also used extensively
as  an  insulating  fill for  concrete block walls, as
a cavity wall insulation,  and as an insulating fill
in attic floors.  Other uses for perlite include: Oil
well cement; mineral filter aid; pipe, furnace, and
boiler insulation; foundry  sand additive; packaging
medium;  soil conditioner; and  ceramic and  paint
additive.
Mining Sites

Several perlite ore deposits are in California,  and
other deposits are  in  six  of the Rocky Mountain
States.  Perlite ore is  surface  mined or quarried
and  is normally dried,  crushed, and screened at
the mine.   The normal size of crude perlite for
plaster aggregate ranges fromminus 1Z or 14 mesh
to plus 40  or  60  mesh.   Some plants  use a size
range with no limitations on the fines.  Crude perlite
for concrete aggregate ranges from 1/8  inch, plus
16 mesh,  to 1/2 inch, plus 100 mesh.


Perlite Expansion Plants

A plant for the expansion of perlite consists of ore-
unloading and storage facilities, a furnace-feeding
device, expanding furnace,  provisions for gas and
product cooling, product-classifying and product-
collecting equipment, and  dust collection equip-
ment.  A schematic diagram of a typical plant is
                shown in Figure 245.  A plant producing a number
                of products has several bins for the storage  of dif-
                ferent grades of crude perlite.  If the minus 100-
                mesh material is not removed from the perlite  ore
                at the mines, filtered  vents are required on the
                storage bins to prevent dust emissions during ore-
                uiiloading  operations.


                Expansion  Furnaces

                Vertical furnaces,  horizontal stationary furnaces,
                and horizontal rotary furnaces  are used for the
                exfoliation of perlite, the vertical types being the
                most numerous.   Only a few of the furnaces  are
                refractory lined.

                Essentially all perlite furnaces are fired with nat-
                ural gas.   The natural gas rate,  amount of excess
                air,  and  ore feed rate are adjusted to give a fur-
                nace temperature, an  effluent gas flow rate, and
                a material residence time that will yield a prod-
                uct of the desired  density.  Product densities vary
                from  2 to 15 pounds per cubic foot, and furnace
                temperatures vary from 1, 450 °  to 1,800°F.   The
                relationships of temperature and residence time to
                product density are, for the  most part,  trade  se-
                crets.  The expanded product is  carried out the
                top of the  furnace by the combustion gases.

                Gas and Product Cooling

                Cooling by heat exchangers or by dilution with am-
                bient  air  are the two common methods that have
                been used. Combinations of the two are also used.
                The final  temperature to  which the gases must be
                cooled depends upon the type of dust collector used,
                as will be discussed later.

                Heat exchangers generally employed are of the
                tubular type with forced-air convection.  Large U-
                tubes  with natural convection would probably be
                practical  but have not  been used extensively be-
                cause of the space requirements.   Cooling by dilu-
                tion greatly increases,  of course, the volume of
                gases to  be handled by the dust collector.  Some
                of the smaller plants,  however, have  used  this
                method satisfactorily.


                Product Collectors and Classifiers

                Cyclone separators are used to collect the product.
                If only one product is made, a single cyclone sep-
                arator is  used.   To make more than one product,
                two cyclones in series are usually used, in which
                case some means is often provided for regulating
                the collection efficiency of the first cyclone so as
                to allow a controlled amount of fines to pass through
                to the second cyclone.   The product collected in
                the first   cyclone is used as  a plaster and cement
                aggregate, and  the fine  product collected in the
                second cyclone  has uses such as filter  aid, paint

-------
                                      Perlite-Expanding Furnaces
                                                                                                  351
                                            COOLING MR
            HOPPER

CE
;»•
LLJ
LLJ

\


CD
LLJ U-I
cc cu
ft *—
ac co
                                  \
                                   FEEDER



MAIN
PRODUCT
CYCLONE
— »•


FINE
PRODUCT
CYCLONE
\

                                                                        BAG PACKERS
                                              GAS
                           Figure 245. Flow diagram of a typical perl ite-expandmg plant.
additive,  insecticide  carrier,  and  others.   The
products  are packaged in 3-  or 4-cubic-foot bags
by packing  machines  with little  or no dust loss.
If  a  baghouse dust collector  is used, an ultrafine
product is collected in the baghouse hopper.


THE AIR POLLUTION  PROBLEM

A  fine dust  is emitted from the  outlet of the last
product collector.  The fineness of the dust varies
from one plant to another, depending upon the prod-
ucts desired. In any event, a baghouse is needed
to achieve complete control.  For example, one
plant that was tested produced perlite for use in
manufacturing insulated wallboard.  Only one prod-
uct cyclone was used.   A particle size analysis of
the baghouse catch revealed that 64. 3 percent by
weight of the sample was minus 200 mesh;  approx-
imately  20 percent by weight was less than 5 mi-
crons.  Specific gravity-was 2.69 at 69°F.  Table
104 shows a  complete particle size  analysis of the
cyclone and baghouse  catches.

HOODING AND VENTILATION  REQUIREMENTS

No hooding  is required  unless ventilation of the
sacking machines  receiving product from the cy-
clones is necessary.  For most plants,  this is not
required, and only the air outlet of the last product
cyclone needs to be ducted to a dust collector.  The
volume of ventilation air required depends upon the
quantity of  air needed to convey the product, the
amount of fuel burned, and the volume of dilution
air required to cool the effluent sufficiently for
admission to a dust collector.  The first two factors
are fundamental to the basic design of the plant.
 Once these are known, one can calculate the quan-
 tity of dilution air required as a function of the tem-
 perature limitation of the dust collector.


 AIR POLLUTION CONTROL EQUIPMENT

 Simple cyclones have  been found  inadequate for
 collecting fine  dust from perlite furnaces.  Even
 the relatively high-efficiency devices,  such  as
 multiple small cyclones, have been deficient in com-
 plying with air  pollution  prohibitions.  Several
 firms have attempted to use water scrubbers,  but
 most of these installations were unsuccessful.
 Virtually all the perlite-expanding plants in the Los
 Angeles area  are  now  equipped with baghouses.
 These efficient  collectors,  costing only  slightly
 more than  a well-designed  scrubber, are able to
 collect a salable product.

 Since the gases from  the  expanding furnace  are
 at a  relatively high temperature,  considerable
 cooling is necessary in order to  meet the temper-
 ature limitations of any fabric used in a cloth filter
 dust  collector.  When Dacron cloth is used,  the
 usual practice is to cool the  gases to400°to 500°F
 in a tubular heat exchanger.  Further cooling takes
 place in the cyclones,  and sufficient dilution air
 is admitted to cool the  gases  to200°to 250°F be-
 fore they enter  the baghouse.  Siliconized glass
 fabric has been used,  the  cooling accomplished
 entirely by dilution.  Other combinations are of
 course  possible, but these two are most popular.


In order to secure a uniform product from  the ex-
pansion  furnace and classifying system, mainte-
nance of a constant flow rate through the baghouse

-------
352
MECHANICAL EQUIPMENT
    Table 104.  PARTICLE SIZE ANALYSES
     FROM THE PRIMARY CYCLONE AND
          THE BAGHOUSE CATCH OF
      A PER LITE-EXPANDING FURNACE

Screen mesh size
+ 10
-10+30
-30+60
-60+100
-100+200
-200
Particle size analysis.
wt %
Primary cyclone
catch
0. 4
26. 0
30. 0
22. 2
14. 0
7. 4
Baghouse catch
0. 0
0. 4
2. 7
9.5
23. 1
64. 3
             Particle size analyses of
           -200-mesh portion of samples
Diameter (D), n
45. 7
40. 2
36. 6
32. 9
29. 3
25.6
22. 0
18. 3
16.5
14.6
12. 8
12. 2
11.6
11. 0
10. 4
9.8
9.2
8. 5
7. 3
6. 1
4.9
3. 7
3. 0
2. 4
1. 8
1. 5
1. 2
Sample with diameter < D,
wt %
Primary cyclone
catch
100. 0
99. 3
99. 0
96.3
93.7
90. 2
85. 4
80. 5
77. 1
71.2
63.2
60. 5
57.5
55.6
52. 0
48.8
46. 6
42. 0
35. 1
27. 3
19. 0
11. 7
7. 6
6. 1
3.9
3. 7
3. 2
Baghouse catch
__
--
--
--
100. 0
99. 4
97.6
96. 4
94. 5
93.6
91. 5
88.5
86. 1
82. 1
81.2
74. 2
70.6
66. 4
55. 2
43. 0
29. 4
16. 7
11. 5
7. 0
2. 4
1. 5
1. 2
is highly desirable.  In general, the resistance of
a baghouse  increases as the dust layer builds up.
This gives anonuniform flow rate unless measures
are taken to counteract this tendency.  Three gen-
eral methods have been used to maintain relative-
ly uniform flow rates:

1.  Use of  a  single-compartment baghouse with
    an adjustable restriction in the inlet duct.  The
    restriction is  set at a maximum value when
    the bags  are clean  and is decreased as the
    baghouse's resistance  increases,  and this
    maintains a relatively constant total resistance.
                    This  method requires frequent adjustment of
                    the restriction and reserve fan capacity.  When
                    the restriction  reaches its minimum value,
                    the process must be shut down.

               2.   Use of compartmented baghouses, which per-
                    mits one compartment at a time to be shut off
                    for bag shaking. This produces a resistance
                    that varies cyclicly,  but flow variations can
                    be  kept within tolerable limits.  The greater
                    the number of compartments, the smaller the
                    variations in flow.

               3.   Use of continuous-cleaning-type baghouses.
                    Included in this category are types using high-
                    pressure blow  rings  (Hersey types),  those
                    using  traveling  blow  chambers  on envelope-
                    type bags, and those using pulses  of  high-
                    pressure air. These types are capable of main-
                    taining almost completely uniform flow rates,
                    but their  costs  are somewhat greater than
                    those  of the other types.

               Filtering velocities should be 3 fpm or less for the
               standard types using woven fabrics and about 10
               fpm or less for the Hersey types.
                                                              FEED  AND GRAIN  MILLS

                                                     INTRODUCTION

                                                     Commercial development of feed mills, based up-
                                                     on scientific animal nutrition, has advanced rapid-
                                                     ly since 1930.  Enriching feed with vitamins and
                                                     minerals has accelerated the growth rates of poul-
                                                     try and livestock to  nearly double  the  average
                                                     growth rates of  1930.
               With changes in feeding,  the animals are increas-
               ingly being moved from cattle range  and rural
               farm forage areas to confined pens and feed lots
               near urban areas.  This transition tends to locate
               the feed and grain plants  in congested areas •where
               many conflicts  about air  pollution arise.   The
               handling and manufacture of feed and grain prod-
               ucts generates many varieties and concentrations
               of dust.  These dusts are the sole air contaminants
               from these plants.
               To pinpoint the  sources of dust, a simplified di-
               agram of feed mill flow is presented in Figure 246.
               The drawing delineates basic equipment in  solid
               lines and dust control equipment in dotted  lines.
               Solid-line arrows indicate the flow of basic mate-
               rial from process to process.  Dotted-line arrows
               indicate the forced discharge of dusty air to  col-
               lectors.

-------
                                         Feed and Grain Mills
                                            353
                      • BUGHOUSES•
                        -CYCLONES
                                                         I   I
                                                                    SHIPPING
             Figure 246.  Flow diagram  of a simplified feed mill.  Basic  equipment shown in solid
             lines, dust control equipment, in dotted lines.
 Receiving, Handling, and Storing Operations

 Feed materials are shipped to feed and grain plants
 in railroad cars and trucks.  These carriers may
 be  classified according to the type  of unloading
 operation used.

 One class includes hopper bottom railroad cars,
 trucks  and  trailers, trucks with self-contained
 conveyors,  and hoist dump vehicles.   The flow of
 materials from these self-unloading shipping con-
 tainers may be regulated so as to fill an inclined
 chute or shallow hopper as rapidly as the material
 is removed.  This is the choked-feed method of un-
 loading, in which a solid stream, of material moves
 slowly  into the receiving  system •with little or no
 dust emissions.   Figure  247  illustrates choked-
 feed receiving from a hopper bottom  railroad car.
 Canvas boots or socks maybe fastened to the spouts
 and extend down -within inches  of the hopper grat-
 ings,  though they are not very frequently used.

 Another class includes flat bed trucks and box cars
 capable  of being emptied into receiving hoppers
 only by mechanical plows or shovels.   The carrier
beds are about 3 feet above the hopper  gratings,
which  are located  at track or ground level.  The
flat bed carriers are usually unloaded into deep,
large-capacity receiving hoppers.   The  excess
surge-holding capacity allows enough time  between
car unloading s for an empty car to be replaced by
a full car, while the handling system continues to
convey material out of the hopper.   This method
provides  for receiving the  maximum number of
cars  or trucks  per day and may also effect some
savings in labor costs. Figure 248 shows the un-
loading of a boxcar into a deep hopper.

Feed materials are less commonly unloaded from
carriers  by pneumatic conveyors.   The material
may be fed manually to  a flexible  suction tube,
connectedto a pullthrough cyclone, which separates
the feed materials from the air conveying system
and drops them into a storage bin.  Another pneu-
matic  unloading  system type uses specially con-
structed hopper  bottom cars  or  trucks equipped
with air or mechanical agitation devices. These
devices feed the material through a rotary valve
to a pressure-type pneumatic conveyor.  The air-
borne material from this type of conveyor is also
separated by a cyclone and dropped into storage.

Grain and feed storage bins maybe single or multi-
ple compartmented.  They are usually constructed
of steel or concrete.  Each bin or  compartment is
enclosed by a dust-tight cover incorporating anade-

-------
354
                                       MECHANICAL EQUIPMENT
             HOPPER
                   Figure 247.  Hopper bottom railroad car unloading gram into a shallow hopper by the
                   choked-feed  method (Koppel Bulk Terminal, Long Beach,  Calif.).
  Figure 248. Boxcar unloading grain into deep receiving
  hopper.
quately sized vent.  This vent provides an escape
for displaced air during filling and prevents the bin
from buckling under external atmospheric pressure
during the discharge operation.
Feed-Manufacturing Processes

From the storage bins, -whole grains are conveyed
to cleaning, rolling, grinding, and other plant pro-
cesses.  The processed grains may be shipped to
consumers or held for feed formulation.  Finished
feed formulas are compounded from vitamins, anti-
biotics, minerals, and all the processed materials.
These compounds may be prepared in the form of
finely ground mash,  pellets, or mixed mash and
pellets.   The feeds may be  shipped from the mill
in plant-owned  delivery trucks,  common carrier
trucks, or by rail.

A certain amount of dockage  is acceptable,  by gov-
ernment grading standards, in all grains. Dockage
is made up of dust,  sticks,  stones, stalks,  stems,
weed seeds,  and other grains.   A portion,  if not
the majority of this  undesirable material,  must
be  removed if the grain is to go into  certain pro-
cesses.  The degree of separation required depends
upon  the  actual process, for example, barley to
be ground in a hammer mill needs minimum clean-
ing-whereas barley to be rolled requires a high de-
gree of cleaning. In some circumstances, received
grains may have be en cleaned before elevator  stor-
age or as preparation for export shipment, in  order
to  eliminate hazards of spontaneous heating,  in-
sect infestation, and so forth.

Cleaning includes the several mechanical process-
es  by which dockage is removed from grain.  By
the nature  of its purposes,  cleaning produces a
large  amount of dust.  The  amount of dust varies
widely with the different field sources of grain and
its  subsequent handling. A preliminary step  in the
cleaning process is termed scalping.  In this pro-
cess, the grain is run through a coarse mesh screen
in shaker or reel form, to remove sticks, stones,
stalk0- strings, and similar offal.   The grain is

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                                        Feed and Grain Mills
                                                                                                  355
usually poured through the screen at low velocity
with little or no aeration; very little dust is gen-
erated.  The shaker type of scalper maybe of dust-
tight design withnoventto the atmosphere. Another
step is called aspiration.  Crosscurrents or coun-
tercurrents of air are directed through dispersed
falling grain.  The process is designed to separate
field dust, fibers,  chaff, and light trash from the
grain.  The third step employs a stack of several
grading shaker screens to classify the grain.  Mixed
grains are separated at this point.   Noxious weed
seeds are also removed,  to prevent them from be-
ing disseminated.

The three steps of cleaning may be  accomplished
in separate  devices  or all in one piece of equip-
ment.   A traditional type of cleaner, as shown in
Figure 249 combines all three of these steps  in one
machine.  This type commonly employs three inte-
gral blowers and has two exhaust airstreams that
carry away different  types of separated materials.
      Figure 249. Grain cleaner (Koppel Bulk Terminal
      Long Beach, Calif.).

 Barley rolling is accomplished in equipment com-
 monly called barley steamers and barley rollers.
 Oats and milo may be processed in the same equip-
 ment.  Cleaned grain is conveyed and elevated from
 storage to an open-coil-type steamer, which heats
 and moistens  the grain.   It is then run  through
 steel rollers and dropped into a cooler  through
 which room air  is  pulled to cool the hot, moist
 grain.

 Many feed grains and some feeds such as copra or
 cotton  seed are  ground in hammer  mills.   This
type of mill is so constructed  that it is also in-
herently a centrifugal blower.  Granular materi-
al is fed into the center of a high-speed rotor, which
has pivoted or articulated hammers on the periph-
ery.  The material is thrown centrifugally against
and through a perforated, peripheral plate or screen.
The proper flow of material through the mill re-
quires a strong stream of air.  Supplemental air
capacity is generally supplied by a pullthrough
blower driven integrally from the mill shaft. The
ground product is then conveyed pneumatically to
a cyclone  separator,  which delivers the ground
meal to storage bins.   Size reduction  of feed is
sometimes  accomplished in a burr mill or other
type of equipment that requires no airstream for
operation.

Pelleted dairy feed consists  of several different
types  of finely ground feed materials,   combined
with molasses and a binder material,  steam condi-
tioned, and compressed into  pellets by a pellet
mill.  From  the mill, pellets are dropped into a
cooler where a blower pulls room air through them.
After their cooling, dairy pellets  are usually run
across a shaker screen for removal of any small
particles  that occurred during the breaking of ex-
truded pellets away from the mill die.  The parti-
cles are usually conveyed pneumatically from the
shaker back to the pellet mill  feed.

Feed formulations are  devised  to suit all varia-
tions of creature appetites  and conditions of live-
stock production, on a nation-wide basis,  or for in-
dividual flocks and herds.  Component grains may
be steamrolled, or dusty feed material fines may
be pelleted to improve the texture and flavor.


A formulating  equipment system, consists of from
one to three  scale hoppers,  sized according to the
bulk class of  products  each -weighs.  Materials
maybe measured intothe  scales by simple  manual
operations or by elaborate pushbutton consoles that
operate remote conveyors from multiple storage
bins. After the scales there may be a single mixer
or a  cascade of surge bins and parallel or  tandem
mixers with oil and molasses sprayers.  The batch-
es of finished feed may be conveyed to holding bins,
for later transfer to truck or railroad car,  or they
may be loaded directly to a carrier -without holding.
THE AIR POLLUTION PROBLEM

Many feed and grain plants,  originally located at
crossroads in sparsely settled farm  areas,  are
now surrounded by urban stores,  offices,  schools,
andmodern residential developments. As  a result
of frequent public complaints after community en-
circlement, the plants must either be relocated in
less sensitive industrial  areas,  or comprehensive
dust control programs must be initiated.
  234-767 O - 77 - 25

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 356
MECHANICAL EQUIPMENT
There is  now active medical research (McLouth
andPaulus, 1 961) showing the deleterious  or toxic
effects of feed grain dusts.  Many individuals ex-
perience  bronchial  or allergic disturbances after
exposure to feed and grain process effluents.  Per-
sons  affected may  be inside  a  grain-processing
plant or even some miles downwind (Cowan et al. ,
1963).

Pertinent to the control of dust inside plants is the
ever-present  spectre of fire,  sometimes sponta-
neous.  Fire  can run along dust deposits on mill
beams faster than a man can  run to cut it off and
can thus envelop an entire building before fire equip-
ment can  be used.

The destructive  force of cereal dust explosions is
well known,  especially the secondary type of  ex-
plosion that occurs after a primary shock wave has
lifted and mixed heavy dust  deposits  with air,  cre-
ating a massive, explosive mixture.

The vacuum cleaning of mill interiors is, there-
fore, a constant, expensive chore.  A likely answer
to the hazards of dust accumulation may be the con-
struction  of unhoused feed process systems as is
nowfrequent practice in the power-generating, oil
refinery,  and chemical process industries.

In undeveloped or farm areas, nopractical  purpose
maybe served by preventing feed mill dust emis-
sions, but in urban areas, dust losses from feed
materials  are likely to cause a nuisance.  Basic
process equipment for either open or housed plants
will be increasingly required to effect dust-tight
enclosure  by  the  use of  sealants,  gasketing, or
welded joints.   Air vented  from equipment will
need  to be controlled either by filters attached to
basic equipment or by duct systems connected to
air pollution control equipment.

Feed materials and field run  grains, received at
the mill,  commonly contain much fine dust in ad-
dition to long, fiber-shaped dust particles.  Fine
dust found in grain may include the actual soil in
which the grain  was grown,  owing to wind or rain
action in the field.   Other fine particles may orig-
inate from weeds  or insects or be produced from
the grain itself,  by abrasion in handling and stor-
ing. For  these reasons, no reliable prediction of
the kind and amount of dust in a shipment of field
run  grain may  be expected.  The amount of dust
found in the many  other miscellaneous feed mate-
rials varies far more widely than in grains.

The long-fibered  dust particles,  such as barley
beards  and even  weed seeds  and other particles,
are much more an expected,  characteristic  part
of any particular grain shipment.  These,  however,
seldom present an air pollution problem.

Table 105 presents the particle size distribution
of dusts from a boxcar of barley received in a deep
               hopper at a feed mill.  Dust picked up by a control
               hood was carried by a blower to a cyclone where
               the larger particles dropped out and were collected
               in a sack (sample No.  1).  The cyclone then vented
               to a baghouse, which  collected the finer material
               in a hopper  (sample No. 2).
                  Table 105.  PARTICLE SIZE ANALYSES OF
                  THE PRIMARY CYCLONE CATCH AND THE
                   SECONDARY BAGHOUSE CATCH OF DUST
                   FROM A RAILROAD RECEIVING HOPPER
                    HOOD CONTROLLING THE UNLOADING
                   OF A BOXCAR  OF FEED-TYPE BARLEYa
                            Particle size distribution by wt
Parlu
0
5
10
iO
44
74
1 1')
Ov c r i '-
1 C S 1 / C , |_L
o 5
o 10
o 10
o 44
o 74
0 1 19
o ^SO
0 (60 mesh)
Sample No. 1
Lytlone bottoms, °'i>
0.9
0. 9
?. 9
9. 5
1^.9
\(>.i
5. 4
SO. S
Sample No.
baghouse hoppc
4
zs
66
S
0
0
0
0
i
r , u,i>








                 ^Specific yra\:ty of both samples was 1.8.
               Receiving, Handling, and Storing Operations

               The dusts that cause air pollution problems in re-
               ceiving, handling, and storing ope.rations are gen-
               erally the  fine dusts found in field run grains, or
               in those feed materials from which much dust is
               generated.  When one of these materials is unload-
               ed from flat bed trucks or boxcars to deep hoppers,
               it is dropped from a height of 3 to 15 feet in sudden
               surges.  The particles in the stream of  free-falling
               material disperse as they accelerate, and inspirate
               a downward-moving column of air.  When the mass
               hits a hopper bottom,  the energy expended causes
               extreme air turbulence, abrasion, and deagglom-
               eration of the particles.  A violent generation of
               dust occurs.   It forms an ascending  column that
               boils out of the opposite end of the hopper.   A dust
               plume of 100 percent opacity and of sufficient vol-
               ume to envelop a boxcar completely may be formed
               from the unloading of grain.  Figure 250 shows how
               dust is generated during the dumping of grain from
               a boxcar into a deep hopper.

               Conveying equipment does not usually  present dif-
               ficult  dust problems;  however, the rubbing fric-
               tion of screw conveyors, drag conveyors, and buck-
               et elevators on feed and grain abrades  these mate-
               rials,  creating fine dust particles.  Dust is gen-
               erated at  the transfer points of enclosed convey-
               ing equipment, carried through bucket elevators,
               and emitted at the discharge of the conveyed mate-
               rials.
               Belt conveyors are the most efficient type of han-
               dling equipment,  especially for large volumes of

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                                        Feed and Grain Mills
                                                                                                  357
                                       DUST
                                       PLUME
          Figure 250.  Unloading a boxcar into
          a deep receiving hopper.
material  and for long conveyances.  They cause
less mechanical abrasion of the material and sep-
arate much less of the dusty fines from the grain
than screw conveyors do.  Dusty air,  however, is
usually generated at belt transfer points,  result-
ing from aeration of material as it  falls  onto or
away from a  belt. A secondary problem with belt
conveyors results from materials' adhering to the
belt as it turns around the head pulley.  These par-
ticles,  usually  coarse, drop from the returning
belt along its entire length.

Storage bins vent dust-laden air originating from
two sources-.  One  is  air displaced  by incoming
material  that falls  freely from a spout at the top
of the bin, mixing dust with the air in the bin.  The
other is air inspiratedby the  flow of incoming ma-
terial.  This air may contain  large  quantities of
dust.

Shipping feed out of the plant, by spout loading in-
to car s or trucks, is similar to  the storing opera-
tion.   Most  finished feeds are, however, some-
what agglomeratedby molasses  or oil  additives so
that a  minimum of dust is generated in the ship-
ping process.   Dusty feeds, of course,  require
special handling when they are bulk loaded  into
carriers.
When a large grain shipment is received, most car-
loads may contain a uniformly low content of fine
dust.  The  last several carloads, representing a
cleanup of fines that became segregated in handling
and storage, may be  excessively dusty.

Grain rolling and pelleting produce moist, agglom-
erated particles with no dust  emissions from the
coolers.

In size reduction of whole grains or other feed ma-
terials,  the amount  of  dust discharged from the
pneumatic conveyor  cyclone may increase as the
materials are more finely ground. The character
of the material, however, is the chief determinant
of the dust generated.

During the formulating and mixing, some open-top
dump or  cut-in hoppers,  used  to combine dust-
generating  ingredients for mixing,  require con-
trol.   The  methods of material handling  such as
free  fall,  choke feed, and so  forth determine the
character  of the  emissions in these .open systems.
Mixing  systems now tend to be designed for dust-
tight  enclosures of all conveying equipment, with
filter vents on surge bins and mixers.  This plan
of dust control requires no other control equipment.

Poultry  pellets are usually compounded with fish
oil  or animal  fats instead of molasses. If no fat
or pellet binder material  is used, poultry pellets
that have been run through a  shaker for removal
of fines may be moderately dusty.  A totally dust-
enclosed type  of  shaker is recommended to pre-
vent dust loss to the air.

Care must be taken in returning collected dust to
a basic  equipment system, or a heavy, recircu-
lating dust load may be  created.


HOODING AND VENTILATION REQUIREMENTS

Hooding requirements in  a feed mill are limited
to those for deep receiving hoppers,  open convey-
ing equipment,  and formulating hoppers in which
the material free falls  without being enclosed.  No
hooding  is  required  for choke-feed hoppers, en-
closed  conveying  equipment,  bins,  or for any of
the manufacturing  processes.
Feed-Manufacturing Processes

When grain is unloaded from carriers and conveyed
to storage, the granules flow in the form of a thick,
bulky stream that encloses and retains most of the
dust content.  Thus  the major proportion of dust
contained in the original grain shipment  remains
to be removed by cleaning equipment that  employs
large quantities of air.  The dustmustbe separated
before this air is discharged to the atmosphere.
Receiving, Handling, and Storing Operations

A preferred method of hooding a deep receiving
hopper,  to  control  dust emissions, is to exhaust
air from below the grating.   As shown in Figure
251, a hopper with V-shapedbaffles belowthe grat-
ing is vented to control equipment.   The baffles
reduce  the  area open to the  atmosphere and also
reduce the air capacity required to vent the hopper
face.  If the hopper is in a building, or complete-
ly sheltered from winds, an indraft velocity of 100

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 358
MECHANICAL EQUIPMENT
fpm through the open area of the hopper, between
baffles, may be effective.  If moderate winds of 3
or 4 mph are to be encountered,  an indraft veloc-
ity of 300 fpm may be required.  For higher winds,
fence-like baffles around the top of the hopper may
be  required,  to prevent the winnowing  action of
strong -wind currents across the hopper grating.
                             EXHAUST DUCT TO
                             DUST COLLECTOR
V BAFFLES — 7 P^—^ >-GRATES
i 	 1 	 f- 	 1 	 	 * 	 1 	 1
t
/\ /X/\^:A,/\/\/\/\/\/\
( ^} ' " " ' . f \
^—PICK-UP SLOTS
\ 	 	 /__

                   ELEVATION VIE*
    Figure 251.  Oust control hooding of deep receiving
    hopper.
Belt conveyors are almost never fully enclosed.
They must,  therefore, be hooded at both the point
where material is loaded onto the belt and the point
where it is discharged from the belt.  The loading
and  transfer  chutes must be cleverly designed to
reduce  dust generation at these locations.   The
first objective is to design chutes so as to  direct
the flowing material in the direction of belt  travel.
The  second objective is reduction of the open area
exposed to the atmosphere.  The enclosing of the
transfer point may be sealed right down  to the belt,
with flexible  rubber flaps.  Moderate volumes of
                pick-up air then suffice to control the dust.  Indraft
                velocities into the open-face areas of hoods, which
                control belt transfer, should follow the same cri-
                terion of 100 to 300 fpm recommended for receiv-
                ing hoppers.

                The secondary problem posed by material that does
                not fall cleanly away from the belt into the discharge
                chute maybe remedied by the use of a rotary brush.
                The brush is  installed inside the  combined dis-
                charge chute and control hood, with a flexible rub-
                ber wiper  to  close the hood up to the return belt.
                The brush is usually driven by chain or V-belt from
                the head pulley shaft at a speed 2 or 3 times that
                of the pulley.  This brush should be made of long-
                fibered nylonbristles since it is subject to damage
                by any sharpmetal fasteners in the conveyor belt
                splice.

                In a fully enclosed materials-handling system with
                one or  more  conveyors and elevators  in series,
                dust-laden air maybe conducted through the entire
                system and emitted at the location of the final ma-
                terial discharge.  Connecting a duct to the last piece
                of equipment in order to vent the entire  system to
                control equipment is, therefore,  desirable.

                Inventing storage bins and containers,  no hooding
                is required; the filter vent or control system duct
                attaches or connects directly to the bin vent.  The
                volume of air exhausted is simply the volume rate
                of the bulk material stream flowing  into the bin and
                displacing air.

                Feed-Manufacturing Processes

                The feed-processing machines do  not commonly
                require accessory hoods for picking up their ef-
                fluents.  The  hooding is an integral part of most
                basic machines. Cleaners and hammer mills, ad-
                ditionally, have integral blowers that may be vented
                to the control  equipment.

                Pellet and rolled-grain coolers are designed -with
                integral hooding.   The air capacity is based upon
                the  requirements  for  cooling  and drying  of the
                heated feed material only.

                Floor level cut-in hoppers  or  scale hoppers may
                be hooded and vented to control equipment.  On the
                assumption they are inside a building, 100-fpm face
                velocity into the hood should be adequate.

                AIR POLLUTION CONTROL EQUIPMENT

                Air pollution  from feed and grain mills consists
                entirely of dusts.  These dusts,  though varied,  may
                be collected by inertial devices and fabric filters.
                In practice,  all the collected material may be re-
                turned to the process.  Cyclones may be adequate
                as dust control equipment for feed plants in farm
                or nonsensitive areas.  Elsewhere, in  urban or

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                                         Feed and Grain Mills
                                           359
sensitive communities where nuisance complaints
and air pollution regulations take effect, baghouses
are needed for final dust control of feed plants.

Table 106 shows the results of three tests for de-
termining the loss of grain dusts from cyclone out-
lets to the atmosphere.


Receiving, Handling,  and Storing  Operations

The deep free-fall type of receiving hopper is not
normally controlled in farm or nonsensitive areas.
In urban areas it maybe adequately controlled only
by a baghouse or cyclone-baghouse combination.

Dust emanating from pneumatic unloaders,  pneu-
matic  conveyors, belt conveyors,  and elevators
need not be collected in nonsensitive areas.  Other-
wise, baghouse control is needed in urban areas.

Storage bins and shipping containers need no con-
trol in nonsensitive areas.  Elsewhere the two ap-
plicable control methods are  (1) to  exhaust the
bins and containers by duct connection to baghouse
control systems, or  (2) to employ some form of
a filter vent attached directly to each bin or ship-
ping container.


Feed-Manufacturing Processes

In urban  or  sensitive areas,  grain cleaner and
hammer mill cyclones and cut-in hopper hoods need
to be controlled by baghouses.   In undeveloped
areas, cleaner and hammer mill cyclones may be
vented to the atmosphere. If, however, much grain
is to be ground in a hammer mill, the use of a bag-
house to prevent economic loss may be feasible.

The hot, moist,  agglomerated particles in rolled-
grain cooler exhausts or  in pellet cooler  exhausts
are adequately controlled by a  cyclone in any type
of area, though condensed water vapor plumes
from  the  cyclone are very noticeable under high-
moisture  and  cold-weather conditions.
Filler Vents

A filter vent consists of a filter cloth bag or sock,
usually made of cotton sateen, tightly fastened over
a vent.  A  sheet  metal enclosure is added if the
vent is exposed to weather. The same control prin-
ciple can also be  used in loading feed into trucks
or railroad cars, through downspouts inserted into
the hatches.  A filter vent skirt is  sealed around
both the spout pipe  and the hatch opening, as  shown
in Figure 252.

The pneumatic loading of boxcar s maybe controlled
by a flat filter  cloth screen of cotton duck or cot-
ton drill across the door.  In loading a ship's hold,
at a high-volume rate  -with dusty material,  effec-
tive control may  be obtained with  similar filter
cloth screens.  A hatch opening, up to 25 by 30 feet
in size, can be enclosed by two 25- by 40-foot screens,
-with a wide center overlap around  the downspout,
as shown in Figure 253.

Filter vents vary in size, from about 1 foot in di-
ameter by 2 feet in height,  to perhaps  3 feet in di-
ameter by  5 feet in height.  They may,  however,
be of any size or shape.  Filtering velocities should
not exceed 4 to  6 fpm for control of miscellaneous
feed material dusts. Higher velocities maybe used
in filtering coarse dust or when a filter is used for
short or intermittent periods of operation.  Some
provision for shaking the bags shouldbe made when
necessary.  Insect infestation  should also be con-
sidered when filter bags are not cleaned or  changed
from one bin filling to the next.
Cyclones

Cyclones are used  with  great versatility in feed
mills.  They are an integral part of almost every
equipment system that handles air.  In practice,
nearly all cyclones found in feed plants  are of the
simple,  low- or medium-efficiency types.  High-
efficiency, multiple cyclones are subject to exces-
sive operational costs and maintenance  problems.
                             Table 106.  DUST LOSSES FROM CYCLONES
Grain
Basic equipment
Process wt, Ib/hr
Exhaust air volume, scfm
Dust concentration, gr/scf
Dust loss, Ib/hr
Malted barley
Grain cleaner
Test No. 1
53,000
2,970
0. 194
4.95
Test No. 2
50, 000
2,970
0.160
4.07
Feed barley
Hammer mill
10,350
3, 790
0.488
15.8
Milo
Grain cleaner
11,250
First cyclone
3,680
0.058
1.83
Second cyclone
2, 610
0. 006
0. 13

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360
MECHANICAL, EQUIPMENT
   Figure 252. Counterweighted,  telescoping downspouts
   used to fill a hopper car.  Loading is controlled
   by filter  vent skirts (Ralston Purina Company, Los
   Angeles, Calif.).
                Cyclones collect almost all grain dusts larger than
                10  to  20 microns in diameter.  They collect only
                a very small proportion of the particles smaller
                than  10 microns,  as shown in Table 105.  Thus,
                their percentage  efficiency, that is, the propor-
                tion of the total material  weight caught to the total
                material-weight in the exhaust air stream, is very
                high.   Nevertheless, the proportion of fine dust
                particles  caught by a cyclone  to the total number
                of  fine dust particles in an exhaust stream is in-
                variably  very low.   These fines are the particles
                that become  airborne and constitute an air pollu-
                tion problem.  Special design information for cy-
                clones is given in Chapter 4.


                Baghouses

                Baghouses for most mill operations tend to be of
                the simplest and least  expensive types, and use
                cotton  sateen in most cases.  Hand shaking of the
                filter  bags is preferred, to avoid any risk of fire
                from automatic shaking equipment,   Filtering ve-
                locities  are  from 2 to 3  fpm for continuous oper-
                ation,  and up to 6 fpm for intermittent use.   Cost
                of the baghouse maybe as low as $1. 00 per square
                foot of filter  cloth.
          Figure 253.  Loading alfalfa pellets into a ship's hold, controlled by two 25-  by 40-ft filter cloth
          screens (Pacific Vegetable Oil  Corporation,  Long Beach, Calif.).

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                                          Feed and Grain Mills
                                             361
The static pressure drop through the baghouse is,
in most cases directly proportional to the filter-
ing velocity. Where a dust cake is allowed to build
up for several hours before the shaking  or a per-
manent low-porosity cake has developed, the pres-
sure drop in inches of  water column may be esti-
mated as equal to the filtering velocity in fpm. Air-
streams with heavy dust or material loadings  are
usually exhausted to a  primary separator cyclone
and then to a baghouse.  This  method relieves the
baghouse  of handling an excessive volume of bulk
material.

Larger feed mills and those operated in conjunc-
tion with flour and cereal plants are usually equipped
•with the more  sophisticated  and expensive types
of baghouses.  These use elaborate, mechanically
programmed bag shaking with filtering velocities
as high as 10 fpm.  Reverse-jet and reverse-air-
blowing types are alsoused.  One modern feed and
grain terminal, shown in Figure 254,  makes very
extensive use of rever se-jet baghouses . It is prob-
ably the world's most completely controlled feed
and grain terminal facility.  Baghouses, as  shown
in Figures  255 and  256,  control dust  from truck-
and  railroad-receiving hoppers.   Several  other
baghouses,  which may be seen  in Figure 254, con-
trol all the material-handling conveyors and ele-
vators, storage and v/eighing facilities, and grain-
cleaning equipment.  Another baghouse  provides
ventilation  to  the hold of the ship,  which is cov-
ered by filter cloth screens during the loading oper-
ation. The  control equipment  incorporated in this
facility prevents  any visible  emissions and is an
outstanding example of the control of air  pollution
by this industry.
    Figure 254.  Modern bulk feed and grain terminal with
    reverse-jet  baghouses controlling all operations
    (Koppel Bulk Terminal, Long Beach, Calif.).
 Figure 255. Truck-receiving station with baghouse  control
 of the receiving hopper (Koppel  Bulk Terminal, Long Beach,
 Calif.;  and Wunsch Harvesters,  Phoenix, Ariz.).

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362
                                      MECHANICAL EQUIPMENT
    Figure 256. Automatic boxcar-unloading system with baghouse control of the receiving hopper (Koppel Bulk Terminal,
    Long Beach, Calif.).
  PNEUMATIC  CONVEYING  EQUIPMENT

INTRODUCTION
Pneumatic conveying involves the movement of
powdered,  granular,  or other free-flowing mate-
rial  in a stream  of air.  The bulk of the material
is separated from the  conveying air in a product
collector, usually a cyclone separator.  If the air
discharge contains an appreciable amount of dust,
it must be passed through a  dust collector before
being discharged to the atmosphere.  A cloth filter
dust collector  is almost invariably used for this
purpose.  The weight of dust passing the product
collector  is normally very small in puoportion to
the weight of material conveyed,  but it is usually
of veryfine particle size, a relatively small amount
of which may result in excessive  opacity.

Types of Pneumatic Conveying Systems

In general, there are two types of pneumatic con-
veying  systems:  Negative-pressure systems,
characterized  by low capacity and low pressure

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                                    Pneumatic Conveying Equipment
                                            363
losses; and positive-pressure systems,  charac-
terized by high capacity and high pressure losses
(Fischer,  1958).   To convey from several points
to one point,  a negative-pressure system is usu-
ally used.  To convey from, one point to several
points,  a positive-pressure system is usually used.

In a negative system, the material is drawn into
the conveying line by suction created at the far end
of the system by a centrifugal fan or a rotary posi-
tive-displacement blower.  The product is collected
in a cyclone separator, which has a rotary airlock
at its base enabling it to discharge material con-
tinuously while maintaining the vacuum.  The fan
or  blower is  located on the air discharge side  of
the cyclone to prevent excessive wear from product
abrasion.  Narrow-blade  centrifugal fans and cy-
clones are often made as integral units, as shown
in Figure 257.  The filter is on the discharge  side
of the fan.  A rotary positive-displacement blower
can also be used in a negative  system.  The much
higher vacuum producedby this unit gives it a much
greater  conveying capacity, but requires that the
cyclone collector be of heavier construction.  The
close clearances within these machines usually re-
quire that a filter be placed on  the "inlet  side of the
pump to prevent dust from being drawn through the
pump.
                                    NARHOl-BUDE-
                                    CENTRIFUGAL FAlT*
In positive-pressure systems, the air-moving unit
is at the head of the line instead of the end.  Mate-
rial is  fed into the airstream by a rotary airlock
or  feeder and is blown to its destination.  Rotary
positive-displacement blowers or sliding-vane ro-
tary compressors are used in positive-pressure
systems.  High pressures  obtainable with  these
units permit relatively large quantities of materi-
als to be conveyed with  smaller volumes  of air
than can be handled  in a negative system.   This
permits the use  of smaller diameter  conveying
lines and smaller dust filters  since the filter unit
is generally rated on the amount of air it can han-
dle.  The filter is placed  at the end of the  system
to filter  the air discharging from the product col-
lector,  as shown in Figure  258.

Types of Air-Moving Used in Conveying
The different  devices  used for moving air in con-
veying  systems  are  characterized principally by
the pressure that can be developed.   The following
four groups  (see Figure 259) include most of the
devices used:

1.  Industrial exhausters.  These centrifugal fans
    have a pressure limit of about 16 inches water
    column.  The weight  of material conveyed is
    only a fraction'of the weight of air moved.  Their
    use  for conveying is usually limited to bulky,
          Figure 257.  Negative-pressure conveying system
                                    ROTMIV POSITIVE
                                    DISPLACEMENT
                                    BLOHR
                                                   Figure 258. Positive-pressure conveying system.

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 364
MECHANICAL EQUIPMENT
Figure 259.  Types of air-moving devices  used  in  pneumatic  conveying  systems:   (top  left)  Industrial  exhauster
(Chicago  Blower  Corp.,  Franklin Park,  III.);  (top  right) narrow-blade  centrifugal  fan  (Chicago  Blower  Corp.);
(bottom left)  rotary positive-displacement blower   (Sutorbilt  Corp., Los  Angeles,  Calif.);  (bottom right)  slid-
ing-vane  rotary  compressor  (Fuller Company,  Catasauqua, Pa.).

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                                     Pneumatic Conveying Equipment
                                           365
     low-density materials such as sawdust,  wood
     shavings,  cotton,  and other fibrous materi-
     als.  They are used extensively to  convey
     materials from cutting, shredding,  and grind-
     ing machines to storage or further processing.
 2.   Narrow-blade centrifugal  fans.  These fans
     can developpressures of up to 50 or  60 inches
     •water column.  Weights of material conveyed
     are of  the same  magnitude  as the weight of
     conveying air.  These fans  are frequently
     mounted as an integral part of a cyclone col-
     lector.   They are extensively used to unload
     grains and other free-flowing materials.  Their
     use is confined almost exclusively to  negative-
     pressure systems. Conveying distance is lim-
     ited to about  150 or 200 feet at any practical
     conveying rate. Two of these fans are some-
     times placed  in serie.s to  give additional ca-
     pacity or extend the conveying distance.

 3.   Rotary positive-displacement blowers.  These
     units can produce pressures up to 15  psi.  The
     weight of material conveyed is several times
     the weight of the conveying air.  They can con-
     vey for distances of several hundred feet. They
     are used in both positive- and negative-pres-
     sure systems.

 4.   Sliding-vane rotary compressors.  These ma-
     chines  operate in the pressure  range of 15 to
     50 psi for single  stages and up to 100 psi for
     double  stages.  They  are water jacketed  to
     dissipate the heat of compression and can con-
     vey for  distances of several thousand feet  at
     very high ratios of solids to air.


 Preliminary Design Calculations

The  basic problem in  design is to determine the
energy requirements.   These can be expressed in
pressure  and volume  units, and from these  units,
the size of the blower and the required horsepower
can  be estimated.   These  procedures are useful,
for preliminary estimating purposes, to those con-
templating the installation of a pneumatic convey-
ing system, and would also be useful to an air pol-
lution control official in evaluating a proposed con-
veying system for permit requirements.

The  first step in designing a  conveying system is
to determine the required conveying velocity.  Many
theoretical methods of making  this determination
have been proposed.   These methods,   however,
give only the balancing or floating velocity,  such
as the terminal  velocity given by Stokes law.  In
order  to  ensure sustained movement of  solids,  a
velocity considerably in excess of the floating ve-
locity  must be  used.   Hence,  reliance upon em-
pirically  determined velocities is usually neces-
sary.  Table 1 07 gives velocity ranges found satis-
factory for a number of materials.
Fischer  (1957)  divides the energy requirements
into two  categories, one for overcoming material
losses and  the  other  for  overcoming air losses.
Air losses are those caused only by flow of the air.
Material losses are the  additional losses due to
conveying the material.  He subdivides the mate-
rial losses into four groups and estimates them by
the following empirical relationships:

1.  Acceleration.   Energy required  to bring the
    material from rest up to conveying velocity is
    given by the formula
                E  =  MV
                                        (104)
where
      energy, ft-lb/min
      solids moved, Ib/min
      velocity, ft/sec
    E =
    M =
    V =
    g =  acceleration due to gravity, ft/ sec
2.
Lifting energy. Energy required to lift a given
amount of material a given distance can be ex-
pressed as
                E  =  M (d
                                        (105)
3.
    where d  = vertical distance, ft.
            v
Horizontal requirements. The energy required
to move a material in a horizontal duct can be
estimated by the empirical formula
                    =  M(dh)(f)
                                        (106)
where

     f
      coefficient of friction (calculated as the
      tangent of the angle of slide) between the
      material being conveyed and the material
      from which the duct is  made
    d    =  horizontal distance,  ft.

4.   Bends and elbows.  The 'weight of solids mov-
     ing around the bend is multiplied by the cen-
     trifugal force imparted to it according to the
     formula
                  MV
                                             (107)
where

     R  ~   radius of bend, ft

     d  =   distance around bend,  ft.

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366
MECHANICAL EQUIPMENT
Table 107. VELOCITIES FOR LOW-PRESSURE
PNEUMATIC CONVEYING SYSTEMS
(Alden, 1948)
Material
Ashes, clinkers, ground
Barley
Cement, Portland
Coal, powdered
Coffee beans, stoned
Coffee beans, unstoned
Cork, ground
Corn
Cotton
Cotton seed
Flour
Hemp
Hog waste
Jute
Lime
Metal turnings
Oats
Pulp chips
Rags
Rye
Salt
Sand
Sawdust
Sugar
Tanbark, dry
Tanbark, leached, damp
Wheat
Wood flour
Wool
Velocity
6,
5,
6,
4,
3,
3,
3,
5,
4,
4,
3,
4,
4,
4,
5,
5,
4,
4,
4,
5,
5,
6,
4,
5,
4,
5,
5,
4,
4,
000
000
000
500
000
500
500
000
000
000
500
500
500
500
000
000
500
500
500
000
500
000
000
000
500
500
000
000
500
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
fpm
8,
6,
9,
6,
3,
4,
5,
7,
6,
6,
6,
6,
6,
6,
7,
7,
6,
7,
6,
7,
7,
9,
6,
6,
7,
7,
7,
6,
6,
500
500
000
000
500
000
500
000
000
000
000
000
500
000
000
000
000
000
500
000
500
000
000
000
000
500
000
000
000
Solution:
1. Mass rate:

With reference to Table 107, a conveying ve-
locity of 6, 500 fpm is selected (108. 3 ft/sec)
Mass rate = 15
2. Material losses

, 000/60 = 250 Ib/min


Acceleration loss = MV 1 is. =

250(108. 3)2
2(32. 1)

Lifting energy



Horizontal loss

250(300)(0.7)

Elb 1

3(250)(108.3)'
32.1(4)


54, 500 ft-lb/min

= M(d ) = 250 x 70
V
= 17,500 ft-lb/min

= M(d. )(f)
n
= 52,500 ft-lb/min
2
, MV (d)(f)
gR
1 2(3. 14)(4)(0. 7)
4

= 301, 000 ft-lb/min


Total material loss = 54,500 + 17,500

+ 52,500 + 301


, 000 = 425, 500 ft-lb/min

Air losses are calculated by the methods given in
Chapter 3.   Cyclone collector losses range from
2 to 4  inches  of water column,  and cloth  filter
resistances range from 3 to 5 inches of •water col-
umn.

To  illustrate the calculation methods,  a sample
problem will be  worked.
Example 31

Given:

Material, salt
Conveying rate,  15, 000 Ib/hr
Horizontal distance, 300 ft
Vertical distance,  70 ft
Three 90° elbows of 4-ft radius
Angle of slide,  35°  (tangent of 35° = 0. 7).


Problem:

Calculate the required power input.
                    Assume a 5-inch line:

                    Volume = —'—	 x (—} x  6, 500  =  885 cfm


                    Convert material loss to pressure drop:

                       425, OOP ft-lb/min
                          885 ft /min
                                                          Convert pressure drop to inches of water
                                                          column:
                                                               (48 lib/ft )(12in.)   =
                                                                   62.4 lb/ft2
                                                     3.   Air losses:

                                                          Total equivalent length of duct
                                                                         3(2)(3.14)(4)
                                                          =  300 + 70 +
                                                = 389 ft
                                                          The friction loss cannot be  read directly from
                                                          the Air Friction Chart (p. 46) because it is off the

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                                                Driers
                                                                                         367
     chart.  Read the loss at 5, OOOfpmand multiply
     by (6,500/5, OOO)2.

     Friction loss =  8. 9 (6, 500/5, OOO)2

                  =  15  in. WC per 100 ft of duct


     Total duct loss = (15) —  =   58 in.  WC


     Assume a cyclone loss of 3 in. and a filter loss
     of 4 in.  Total air loss = 58+ 3+4 = 65 in.  WC


4.   Total pressure loss:

     Loss = 92  + 65 =  157 in. WC, or
-
in
            i   (6Z.41b/£tZ)    (1 ft2)
           . )   - -— -    -
                  12 in.        , . .  .
                               144  in.
            =  5.7 Ib/in .

5.   Required power input:

     A rotary positive-displacement blower -will be
     used in a positive-pressure system such as
     shown in  Figure 259.

     Assume a blower efficiency of 60%.  The re-
     quired power input is:
                (5.7)(144)(885)
                 33,000(0.6)
                       =  37 hp
THE AIR POLLUTION PROBLEM
The tendency of dust to be emitted from the product
collector is  determined  largely by the amount of
fine material in the product. For finely pulverized
materials  such as cement and flour, a dust filter
is absolutelynecessarybothfrom the point of view
of loss of product and creation  of a dust nuisance.
For some materials, the  amount of foreign mate-
rial determines  the  need for a dust filter.  For
instance, whole  grains  do not require a filter if
they are completely  clean; however, they usually
contain enough dirt to require a filter.


AIR  POLLUTION CONTROL EQUIPMENT

A conventional  baghouse is the usual dust filter
used, though reverse-air cleaning types are also
used.  The dust filter for high  solids-to-air sys-
tems may consist of  cloth filter tubes mounted on
top  of a storage bin, which is the product collector.
Cloth tubular filters are sometimes mounted in-
tegrally with cyclone  product collectors.   The fil-
ter  tubes are mounted in a cylindrical housing whose
lower part is a cyclone separator.  The filter  hous-
                                             ing is divided into four compartments with auto-
                                             matic shaking devices to allow continuous opera-
                                             tion.

                                             Filtering velocities commonly used range  between
                                             2 and 4 fpm.  The optimum velocity varies -with
                                             particle size and the tendency of the dust  to pack.
                                             In general, the lower velocities tend to give more
                                             trouble-free operation and it is seldom profitable
                                             to economize  by increasing the filtering  velocity.
                                                                DRIERS
                                             INTRODUCTION
A drier  may be defined as a device for removing
•water or other volatile material from  a solid sub-
stance.  Air contaminants emitted are dusts,  va-
pors, and odors.  Several driers for specific prod-
ucts and processes have been discussed in other
sections. In this section, some general character-
istics of  driers and some details of a  few specific
types will be considered.
Rotary Driers

A rotary drier consists of a rotating cylinder in-
clined to the horizontal with  material fed to one
end and discharged atthe opposite end. In the most
common type, heated air or combustion gases flow-
through the cylinder in direct contact with the ma-
terial.   Flow may be either parallel or counter-
current. This type is  called a direct rotary drier.
In another type,  called an indirect rotary drier,
heat is applied by combustion gases on  the outside
of the cylinder or through steam tubes inside the
cylinder. In this type, a flow of air is  maintained
through the drier to assist  in the removal of water
or other  vapors.   In some  cases,  for example, in
heating of organic compounds for thermal decom-
position  only, the process may be accomplished
without air movement through the drier.

The direct rotary drier has flights,  •which lift the
material and shower it down through the gas stream.
as shown in Figure 260.  Thus, it has a very high
potentialfor dust emissions.  It cannot be used for
drying fine materials because loss of product would
be excessive. Indirect rotary driers have a much
lesser tendency to emit dust.  They are the usual
choice when a continuous drier for  powdery mate-
rial is required.

In I960, the Barber-Greene Company completed a
comprehensive testing program on full-scale rotary
driers to evaluate the effects  of the various de-
sign parameters.  Over  600 individual test runs
were  completed,  and the  company  spent over
$175, 000 of research  funds for the project.

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368
MECHANICAL EQUIPMENT
    Figure  260.  Typical flights used in rotary driers.
The most important of the factors  influencing drier
selection and performance that were varied or held
constant included:  Tonnage rate,  moisture content,
air flow rate through the drier, fuel oil rate to the
burner,  air flow rate to the burner, drum slope,
drum diameter, drumlength, and lifting flight de-
sign and arrangement.  Some of the important re-
sults of this investigation are shown graphically in
Figures 261 through 264.  While these results were
intended primarily for use in-the asphaltic concrete
industry, they may also be applied to similar rotary
driers for  other materials  in other industries.
Some of the conclusions drawn from this investiga-
tion are summarized and listed as follows.

1.   Dust carryout increased proportionally to the
     square of the gas exhaust volume as the vol-
     ume was increased in the same drum.

2.   On  driers  of the same length with the same
     drum gas velocity and with other factors held
     constant, the maximum production  capacity
     varied in direct ratio to drum cross-sectional
     area.

3.   An  increase in drum gas velocity permitted
     an increase in maximum production capacity,
     but on a  less than direct ratio,

4.   Thermal efficiency was a constant if the drier
     •was properly balanced and operated, regard-
     less of drier size, diameter, length,  or drum
     gas velocity.
                                                       5.   In a conventionally designed drum, a particle
                                                            spent only a fraction of its time in the veil
                                                            suspension while in the drum--usually not over
                                                            3 to 5 percent.  For the remaining time,  the
                                                            particle cascaded at the bottom of the drum or
                                                            rode up in the flight pocket.

                                                       6.   Flights in a drum usually retarded rather than
                                                            increased the flow of materials  through the
                                                            drums.
                                                          300
                                                          250
                                                          200
                                                          150
                                                          100
                   50
                     0        20       40       60
                               INCREASE IN DRUM GftS VELOCITY
                    600     700     800     900    1,000
                                   mm  GAS VELOCITY fpn
1 100
                                                              100
       1 200
                   Figure 261. Dust carryout versus drum gas velocity.
                   Example:  An increase of 50% in gas velocity  from
                   600 to 900 fpm  increases dust carryout by 125%
                   (Barber-Greene Company,  1960).
                Flash  Driers

                In a  flash drier,  or pneumatic conveying drier,
                moisture is removed by dispersing the material
                to be dried in a hot gas zone followed by convey-
                ing at high velocities.  The drier consists  of  a
                furnace or other source of hot gases,  a device for
                dispersing  the  wet material in the gases,  a duct
                through which the gases convey the material, and
                a  collection system for removing the dry product
                from the gas stream.  In the  simplest type of  sys-
                tem,  a screw conveyor drops  the material directly
                into a duct,  as shown in Figure 265.  Only free-
                flowing materials can be handled this way.   Some
                recycled dry product often must be mixed with the
                wet material in order to achieve good dispersion.

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                                                   Driers
                                             369
 100
  80
£ 60
- 40
  20
    0         20        40        60        80        100
           INCREASE IN  DRUM CROSS-SECTIONAL AREA, '/•

  Figure 262. Drier production capacity versus drum cross-
  sectional area.  Example:  A 50% increase  in cross-
  sectional area  increases drying capacity  by 50% (Barber-
  Greene Company, 1960).
150
i—
DUCTION CAPAC
o=
o_
ac
LU
— 50
C3
z
uj 9R
NCREAS













...........
20. 5%
r




-;;;.-•

^
-»50«l!





CREASE*-

,-— ~










0 5 10 15 20 25 30 35 40
DRUM LENGTH, f t
 Figure  263.  Drier production capacity versus drum length.
 Example: A 50% increase in drier  length, from 20 to  30 feet,
 increases drying capacity by 20.5% (Barber-Greene Company
 1960).
A cage mill is often used as the dispersing device
Flash drying is often combined with fine grinding
as  shown by the system in Figure Z66.

Spray Driers

A spray drier is a device in -which atomized par-
ticles of a solution,  slurry,  or gel  are dispersed
in a hot gas zone (Marshall and Friedman, 1950).
The drier consists of a drying chamber, a source
of hot gases,  a device for atomizing the feed,  and
a means of separating the dry product from the ex-
haust gases.   The last item is the  one of  concern
here.

Atomizationis achieved by three devices:  Centrif-
ugal discs,  high-pressure nozzles,  or two-fluid
nozzles.  Centrifugal discs rotate at high speed in
a horizontal plane.  The liquid is fed to the center
and discharged  at the periphery as a fine spray.
High-pressure nozzles contain a very small orifice
through  which the liquid is forced at a very high
pressure.  Particle  size is controlled by amount
of pressure and size of orifice.  Two-fluid  nozzles
use air or steam under moderate pressure to atom-
ize the liquid.  The fluids are fed by separate lines
to  the nozzle -where they impinge in  a variety of
different ways to produce a spray.

The hot gases for spray driers are usually obtained
from a direct-fired air heater using natural gas or
fuel oil.  In some cases-waste flue gas from  a boiler
is used.   When  carbon dioxide must  be excluded
from the drying atmosphere,  steam coils are used
to heat the air.

The drying chamber in some spray driers is shaped
like a cyclone separator and  serves as a primary
product collector. In other types the drying cham-
ber acts as a settling chamber to collect  the bulk
of the product. Sometimes, all the product is car-
ried out  in the  exhaust gases and  collected in an
external product collector.  The product collector
is nearly always a cyclone separator followed by a
secondary collector where needed.
J
f.
:
j
; 40
j
3
3
3
C
; 20
e
3
1
1 o
\

29 1

^


/
/



^


^


20 40 60 80 10
INCREASE IN DRUM GAS VELOCITY, ',,
600 700 800 900 1 000
100 1 2
DRUM GAS VELOCITY, fpm
Figure 264. Drier production capacity versus drum gas
velocity.   Example: An increase of 50% in gas velocity,
from 600 to 900 fpm, increases drying capacity by 29.1%
(Barber-Greene Company,  1960).

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 370
MECHANICAL EQUIPMENT
AIR FILTER
                                               VENT FAN
   EXPANSION JOINT
                               »ET FEEDER
                     XCLEANOUT DOOR
   Figure 265. Simplest type of flash drying system (Com-
   bustion Engineering,  Inc.,  Windsor, Conn.).
 Other Types of Driers

 The following types of driers usually emit negligible
 amounts  of dust.  In some  operations, however,
 organic vapors and mists may constitute  a problem.

 Tray and compartment driers consist of a chamber
 in which  heated air circulates over the  wet mate-
 rial until the material reaches the desired mois-
 ture content.  Granular material,  filter  cakes,
 pastes, and slurries are placed in trays,  which are
 put  on stationary  or  movable racks,  as shown in
 Figure 267.  Other materials are stacked or hung
 on racks.  The vertical turbodrier can  be  classi-
 fied as a continuous  tray drier.  It consists of a
 vertical,  cylindrical  housing with circular trays
 mounted on a frameworkthat slowly revolves. Ma-
 terial  fed  to the top tray is leveled by  stationary
 knives and, after about seven-eighths  of a revolu-
 tion,  is  pushed  through a  slot  to the tray below,
 where the procedure is  repeated.  Airflow across
 the trays is produced by fans mounted  on a  central
 shaft.  Heating coils at the periphery of the housing
 heats  the air as  it is  recirculated.
                                          \
                                       «ET FEED  \
                                              FINISHED
                                              PRODUCT
                   Figure  266.  Flash drying combined with size reduction
                   (Combustion Engineering, Inc., Windsor,  Conn.).
                    Figure 267. Tray drier (J.P.  Devme Mfg. Company
                    Pittsburgh, Pa.).
                Agitated pan driers consist of a bowl-shaped vessel,
                steam-jacketed on the bottom and part way up the
                sides, with stirrer or  scraper blades to keep the
                material agitated. The top may be open for atmo-
                spheric drying or provided with a cover for  vacuum
                drying.

-------
                                                Driers
                                                                                                 371
Rotaryvacuum driers are of two types.  One type
consists of a stationary, jacketed cylinder mounted
horizontally with agitator blades mounted on a cen-
tral revolving shaft.  Material is  charged through
a manhole at the top and discharged through a man-
hole at the bottom.  Another type of vacuum rotary
drier consists of a rotating, jacketed cylinder with
vacuum applied through hollow trunnions.

THE AIR POLLUTION PROBLEM

Air contaminants that may be emitted from driers
are dusts, vapors, smoke, and odors.  The nature
of the emissions is  determined  by the material
being dried and by the operating conditions.

Dust  can be a problem in any drier in 'which the
material is agitated or stirred during the drying
process.  Drier types that can be prolific dust pro-
ducers are direct-fired rotary driers, flash driers,
and  spray driers.  Types that produce less dust
are indirect-heated rotary driers, pan driers, and
cylinder driers.  Other types that may emit no dust
include tray driers,  sheeting driers, and driers
for products  such as lumber,  bricks, ceramic
ware,  and so  forth.

When an organic liquid is to be  removed from a
material, the emissions may include vapors,  mists,
odors,  and smoke.

HOODING AND VENTILATION REQUIREMENTS
Direct-fired rotary driers  are usually equipped
with an induced-draft fan or with  a  stack of suffi-
cient height to provide draft for the  combustion
process.  The ventilation  requirement is equal to
the volume of  the products of combustion, plus va-
pors  driven off from the  product, plus sufficient
excess to ensure an adequate indraft velocity through
all openings.

Flash driers and spray driers have no ventilation
requirement as such.  The exhaust fan is usually
placed at the product discharge end of the system,
and the entire  system is under negative pressure,
which precludes  emissions,  except for the final
collector.

AIR POLLUTION CONTROL EQUIPMENT
In general, three types of controls are used on
driers:   Dust  collectors,  condensers,  and after-
burners.  The type of material being dried deter-
mines the kind of control device needed.  Dust col-
lectors are the most frequentlyused type since dust
is usually the problem. All types of dust collec-
tors are used,  depending upon the amount and par-
ticle size  of the  dust emitted.   Condensers  are
used when a material'wet with an organic solvent
is dried. Afterburners are used to control smoke,
combustible particulate matter, vapors, and odors.
Dust Control

The types of dust collectors most commonly used
on driers are cyclones,  scrubbers, and baghouses.
If  there is only a negligible amount of dust in the
effluent finer than 20 microns, a cyclone is an ade-
quate collector; otherwise, it is not.  Cyclones  are
extensively used ahead of  scrubbers in order to
collect product materials in the dry form.   A bag-
house is the best collector if the exit gases can be
maintained above the dewpoint and the dust is not
sticky.  In some cases a scrubber is the only fea-
sible  control device.

The primary product collector for a flash drier is
nearly always a cyclone separator.  When fine ma-
terials are dried or -when grinding is incorporated
in the circuit, a baghouse following the cyclone is
normally required, both to prevent excessive loss
of product and to  ensure control of air pollution.
The size of the baghouse is determined by the vol-
ume of the drying  and conveying  gases.  The bag
material that can be used should be determined by
the temperature at the baghouse.  In some cases
the temperature may be low enough to permit use
of cotton or wool, but in most cases Dacron or Or-
ion is better.

Baghouses and  scrubbers  are used as secondary
collectors for spray driers.  A very efficient sec-
ondary collector is usually best in areas having a
strict limitation on particulate  emissions.   The
closeness of approach to the dewpoint determines
the suitability of a baghouse.  When the feed liquid
is dilute and requires concentration, it can be used
as the scrubbing liquid in a wet collector and there-
by increase the concentration and recover the dust
in the exhaust gases at the  same time.

Drying With Solvent Recovery

When a liquid  other than -water is to be removed
from a material,  recovery of the solvent is fre-
quently desirable in order to lower costs,  prevent
a safety hazard, and eliminate air pollution (Mar-
shall and Friedman, 1950).  The value of the sol-
vent may require its recovery for economic oper-
tion.  If the solvent is a toxic or flammable ma-
terial, health and safety considerations may dictate
its recovery.

Vacuum driers are  well suited to recovery of sol-
ventvapors.  The vapors are removed  under slight
or high vacuum  -with  only  a small quantity of air,
•whichis originally present  or  leaks into the sys-
tem during operation.  If dust is carried over, the
vapors are drawn through a  dust collector to pre-
vent losses  of product and fouling of condenser
surfaces.  The collector is usually a scrubber in
order to  preclude  difficulties with condensed va-
por.  In some cases,  -where  condensation at the
collector  can be prevented,  bag filters are used.
 234-767 O - 77 - 26

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 372
                                      MECHANICAL EQUIPMENT
From  the dust  collector the vapors usually pass
through a surface condenser where the solvent is
collected  in  a barometric leg or a tank kept at a
low pressure.  The gases  leaving the condenser
consist of the inert gases that have leaked in plus
enough solvent vapor to form a saturated mixture
at the  condenser's temperature and pressure.

Vacuum pumps,  both rotary and reciprocating, and
steam jets are used as vacuum sources.  The vac-
uum at the condenser must be adjusted so that the
boiling point of the solvent is -well above the tem-
perature attainable  in the condenser.  Otherwise,
solvent recovery will be poor  or 'will be reduced to
zero if the boiling point is brought down to the con-
denser temperature. Sometimes, recovery can be
improved by placing an additional  small condenser
on the  outlet of the vacuum pump.

Drying with solvent recovery can  be accomplished
with direct  drying under certain  circumstances.
Heated air or inert gases are used  and the vapor-
ized solvent is recovered in a condenser.  The non-
condensable gases are usually recirculated through
a heater.  If air is used,  the solvent concentration
must be kept -well below the lower  explosive limit.
Since the amount of inflammable solvents that could
be condensed at these concentrations and at fea-
sible  condenser temperatures is negligible,  this
method is  restricted to noninflammable solvents
such as  perchlorethylene,  carbon tetrachloride,
and so forth. An inert gas  atmosphere is needed
for recovering  inflammable solvents from direct
driers. Since the cost of maintaining an inert at-
mosphere is considerable, this method is not wide-
ly used.


Smoke  and Odor Emissions

Direct-fired rotary driers,  when drying certain
organic materials,  sometimes  emit smoke  and
odors.  Cannery or brewery -wastes used to pro-
duce fertilizer or animal food are  examples.  Most
of these driers  can be operated without excessive
air-contaminating emissions under the proper con-
ditions.  If feed rate  and temperature are properly
adjusted, a dry  product results -without any local-
ized overheating. If, however,the feed rate is  ex-
cessive,  the required higher temperature causes
localized overheating and partial  decomposition of
the product,  resulting in the emission of smoke and
odors. Scrubbers are usually used to control dust
emissions from these driers, but are not adequate
for controlling  smoke and odors.

Another drying operation that emits smoke is the
removal of  cutting  oils from metal turnings and
chips. This operation  nearly always produces
enough smoke  to violate smoke  prohibitions.   An
afterburner  is  the  only feasible control.  A tem-
perature of at least  1,200°F is required in the af-
terburner for complete smoke control.  Tempera-
ture control in the drier is rather critical.  The
temperature must be high enough to vaporize the
oil but not high enough to cause it to burn in the
drier  since  this would cause the chips to melt or
oxidize. A mechanical feeder is almost a neces-
sity to secure good control of the operation. Hand
feeding nearly always results  in poor temperature
regulation and  in undried and burned chips.


       WOODWORKING  EQUIPMENT
Wood-working machines  produce  large quantities
of waste sawdust,  chips,  and shavings that must
be  removed  from the equipment site.   For this
purpose, exhaust systems are constructed that also
alleviate conditions tending to impair health of
operating personnel, collect -wastes that may have
a resale value,  and reduce fire hazards.   The use
of an  exhaust  system,  however, requires a dust
collector  of  some type  to prevent an air pollution
problem.


EXHAUST SYSTEMS

Exhaust systems are used with many types of wood-
working machines capable of producing appreciable
sawdust,  chips, or shavings by drilling, carving,
cutting, routing, turning, sawing, grinding, shred-
ding, planing, or sanding wood.   Machines include
ripsaws,  bandsaws,  resaws,  trim saws, mitre
saws,  panel saws, out-off saws,  matchers, stick-
ers, grinders,  moulders, planers, jointers, spin-
dle sanders, edge  Sanders, tenoners, mortisers,
wood  hogs  (hammer  mills),  groovers, borers,
dovetailers,  and others.  Exhaust systems serv-
ing wood hogs might more properly be termed pneu-
matic conveyors.  In practice, however, wood hogs
are most often found connected to exhaust systems
that also serve  other wood-working machines.

Exhaust systems serving various -woodworking ma-
chinery are most frequently used at lumber mills,
furniture manufacturers, planing mills , furniture-
refinishing shops, model shops, maintenance shops,
cabinet shops,  sash and door  manufacturers, and
carpenter shops. Many of the larger systems han-
dle several tons of -waste products per day.  One
of the largest in the Los Angeles area burns 15 to
ZOtonsper day  in a multiple-chamber incinerator.
One ton of-waste  sawdust, chips,  and shavings oc-
cupies  approximately 150 to 200 cubic feet of space.


Construction of Exhaust Systems

Atypical woodworking exhaust system consists of
hoods for the pickup of -wood dust and  chips at the
machines,  ductwork, a collection device (usually
a cyclone), a storage bin, and a fan blower to supply
air for conveying purposes.   Almost all exhaust
systems are constructed of galvanized  sheet metal.

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                                        Woodworking Equipment
                                                                                                  373
THE AIR POLLUTION PROBLEM

Woodworking exhaust systems are some what unique
in that  they are almost always equipped with air
pollution  control devices.   If they •were  not so
equipped,  the  entrained  sawdust -would result in
excessive opacities and dust loadings in  exit gases
and could easily cause a local nuisance.   Air con-
taminant  emissions from systems such as these
are  functions of the particular  dust encountered
and  the particular control device employed.   The
dust particles  are not excessively small in most
systems,  and  elaborate  devices  are not usually
required.

Particles emitted by woodworking  machines vary
in size from less than 1 micron to chips and curls
several  inches  long.   Hammer  mill-type wood
hogs emit particles  running the  complete  size
range,  while sanders  generate only very small
dust particles.  Wood waste particles from most
other machines  are of larger  size and greater
uniformity, seldom less than 10 microns.  Other
factors  determining  particle size  are the type of
•wood processed and the sharpness of the cutting
tool. Hardwoods tend to splinter and break, yield-
ing  smaller particles than soft -woods do, which
tend to tear and shred.   A dull  cutting tool in-
creases tearing and shredding and  produces larger
particle sizes.

Generally, the configuration of -waste particles is
of little importance.   There are,  however,  in-
stances -where  toothpick-like splinters and curls
have presented difficulties' in collection and stor-
age  and in the emptying of storage bins.
HOODING AND VENTILATION REQUIREMENTS

Sawdust-weighs from 7 to 15 pounds per cubic foot.
The minimum recommended air volume for each
pound  of -wood waste to be conveyed is 45 cubic
feet  or, expressed differently, is  1, 500 cfm per
ton-hour of waste.  In actual practice the  air vol-
ume is usually much higher because of exhaust
velocity requirements.

Velocities recommended for conveying this mate-
rial  range from 3, 500  to 4, 500 fpm,   with most
ducts sized to give a velocity of 4, 000 fpm.  In
practice, velocities  of from 2, 000 to 6, 000 fpm
are encountered.

Table 108 lists recommended exhaust volumes for
average-sized  woodworking  machines.  In each
case the duct is  sized  to give a conveying velocity
of 4, 000 fpm.   Some modern high-speed or extra
large machines produce  such  large volumes of
wastes that greater exhaust volumes must be used.
Similarly,  some small machines of the home wood-
shop or bench type may not require  as  large a
volume as  that recommended.
Hooding  devices vary somewhat,  depending upon
the type of woodworking machine, and are of stan-
dard design throughout the industry.  Inmost cases
the hoods are merely scooped openings that catch
the wood waste as it is thrown from the saws or
blades of the machine.   In design practice,  no
problems should be  encountered if air volumes
are  chosen from those shown in Table 108,and if
hoods  are shaped  to  cover the area assumed by
the thrown particles.  Locating the hood as close
to the  saw or blade as possible is advisable.

AIR POLLUTION CONTROL EQUIPMENT

The simple cyclone separator is the most common
device used  for collecting wood  dust and chips
from -wood-working exhaust  systems.  For these
exhaust  systems,   cyclones outnumber all other
devices  by a large margin.  Properly designed
cyclones have been found satisfactory for  use with
exhaust  systems at cabinet shops, lumber yards,
planing mills, model shops, andmost other wood-
processing plants.

Higher efficiency centrifugal collectors separate
smaller particles, but these devices  are not com-
mon to woodworking systems.  The main advan-
tage of simple  cyclones over most other collec-
tion devices is simplicity of construction and ease
of operation. They are relatively inexpensive, re-
quire little maintenance, and have only moderate
power requirements.

The size and design of woodworking exhaust sys-
tem cyclones varies with air volume and the type
of wood waste being handled.  Where fine sander
dust predominates, cyclones  should  be of high-
efficiency design -with diameters not greater than
3 feet.  Coarse sawdust,  curls, and chips, such
as are produced with ripsaws, moulders, and drills,
can be effectively collected with low-efficiency
cyclones up  to  8  feet in diameter.  Most wood-
working exhaust systems are employed to collect
a mixture of wood waste  including both fine and
coarse particles.   The exhaust system designer
must,  therefore, carefully consider the quantities
of each type wood-waste that will be handled.  The
presence of  appreciable  percentages  of coarse
particles in most systems allows the use of low-
and medium-efficiency cyclones , in which the pres -
sure  drop does not normally  exceed 2 inches of
water  column.

Baghouses are sometimes  used -with woodworking
exhaust systems .  Their use is relegated to those
systems handling fine dusts such as wood flour or
where small amounts of dust losses cannot be tol-
erated in the surrounding area.  The efficiency of
baghouses on woodworking  exhaust systems is very
high--99 percent or more.  They can be used to
filter particles  as low as 1/10 micron in size.  In
some installations lower efficiency collectors such

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374
                                      MECHANICAL EQUIPMENT
                        Table 108.   EXHAUST VOLUMES AND DUCT SIZES FOR
                                       WOODWORKING EQUIPMENT
                              (Committee on Industrial Ventilation, I960)


Self-lord table ripsaw
Saw diameter, in.
Up to 16
Over 16
Seli-tt'od, not on table
Gang ripsaw, s
Sau diameter, in.
Up to 14
Over 24 up to 36
Over 36 up to 48
Over 48
ALL OTHER SAWS, includ-
ing table saws, mitre saws,
\ariety saws, and s^ing saws.
Saw diameter, in.
Up t o 16
Over 1 6 up to L-\
Over Z4
Variety saw \\ith Dado
head

belt and both pulleys one losed)
ami top run horizontal belt
sanders
Belt width, in.
Up to 6
Over 6 up to 9
Over 9 up to 14
Over 14
Swing arm Sander
Disc Sanders diameter, in.
Up to \i
Over \i up to IS
Over 18 up to 25
Over 26 up to 32, 2 pipes
Over 32 up to 38, 2 pipes
Over 38 up to 48, 3 pipes
Triple-drum Sanders
Length, in.
Less than 30
Over 30 up to 36
Over 36 up to 42
Over 42 up to 43
Over 48
Hon/ontal belt Sanders
Belt width, in.
Where bottom run of belt is
used
Up to 6
Over 6 up to 9
Over 9 up to 14
Over 14
Exhaust volume, elm
Bottom Top
hood hood
440 350
550 350
800 550
550 350
800 440
1, 100 550
1,400 550
350
440
550
550
440
550
800
1, 100
440
350
440
550
350 eaeh
350 and 550
550
350
1, 100
1, 400
1,800
2, 200
3, 100
440 350
550 350
800 440
1, 100 550
Duct di.inu-U'r , in.
liottom Top
hood hood
4-1/2 !
5 4
6 5
5 4
6 4-1/2
7 5
8 5
4
4-1/2
5
5
4-1/2
5
6
7
4-1/2
4
4-1/2
5
4 each
4 and 5
5
4
7
3
9
10
12
4-1/2 4
5 4
6 4-1/2
7 5


Band saws and band
resaws •
Blade width, in.
Up to 2
Over 2 up to 3
Over 3 up to 4
Over 4 up to 6
Over 6 up to 8
Jointers
Knife length, in.
Up to 6
Over 6 up to 1 2
Over 12 up to 20
Over 20
Single planers-
Knife length, in.
Up to 20
Over 20 up to 26
Over 26 up to 36
Over 36
Double planers-
Knife length, in.
Up to 20
Over 20 up to 26
Over 26 up to 36
Over 36
Molders, matchers,
and si/ers-
Si^es, in.
Up to 7
Over 7 up to 12
Over 12 up to 18
Over 18 up to 24
Over 24
Sash stickers
Woodshapers
Tenoner
Automatic lathe
Forming lathe
Chain mortise
Dowel machine
Panel raiser
Dovetail and lock
corner
Pulley pockets
Pulley stile
Glue jointer
Gainer
Router
Hogs
Up to 12 in. wide
Over 12 in. wide
Floorsweep
(6 to 8 in. dia)
Exhaust volume, cfm
Down run Up run
350 350
550 350
800 550
1,100 550
1,400 550
350
440
550
600
500
800
1, 100
1, 400
Bottom Top
hood hood
550 550
550 800
800 1, 100
1, 100 1, 100
Bottom Top Right Left
hood hood hood hood
440 550 350 350
550 800 440 440
800 1, 100 550 550
1, 100 1, 400 300 800
1, 400 1, 770 1,100 1, 100
550
440 to 1, 400
See moulder
800 to 5, 000
350 to 1,400
350
350 to 800
550
550 to 800
550
550
800
350 to 1, 400
350 to 800
1, 400
3, 100
800 to 1,400
Duct diameter, in.
Down run Up ran
4 4
5 4
6 5
7 5
8 5
4
4-1/2
5
6
5
6
7
8
Bottom Top
hood hood
5 5
5 6
6 7
7 7
Bottom Top Right Left
hood hood hood hood
4-1/2 54 4
5 6 4-12 4-1/2
6 755
7 866
8 977
5
4-1/2 to 8
6 to 15
4 to 8
4
4 to 6
4-1/2
4-1/2 to 6
4-1/2
4-1/2
6
4 to 8
4 to 6
8
12
6 to 8
as cyclones and impingement traps are installed
upstream to remove the bulk of entrained partic-
ulates before final filtering inabaghouse.   Filter-
ing velocities of 3 fpm are satisfactory.


Disposal of  Collected Wastes

Wood dust and  chips collected with exhaust sys-
tems must be disposed  of  since  they present a
storage problem and a fire hazard.  Very often
a profit can be  realized from this waste materi-
al.   Wood wastes  can be used  productively for
things such as:
1.  Plastics bulking  agent  for products such as
    plastic wood, masonite, and so forth;
Z.   pressed woods  such as fire-wood,  fiberboard,
     Firtex,  and others;

3.   soil additives;

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                                    Rubber-Compounding Equipment
                                                                                                  375
4.   smokehouse fuel--hard-wood sawdust is burned
     to produce  smoke in the processing of bacon,
     ham, pastrami,  and so forth;

5.   floor sweep — sawdust with and without oil is
     spread on floors before they are swept to help
     hold dust particles;

6.   woodfiller — sawdust can be mixed with •water
     resins  and other liquids  and used as wood
     filler;

7.   floor cover in butcher shops, restaurants,
     and so forth;

8.   -waste heat boilers—heat can be  recovered
     from incinerator flue gases to generate steam,
     hot water,  and so forth.

When no productive disposal method can be used,
•wood waste is  destroyed or removed in the most
convenient manner. Wood dust and chips  collec-
ted by the woodworking  exhaust systems can be
destroyed  smokelessly by  burning in a multiple-
chamber  incinerator.  Single-chamber incinera-
tors, for example,  silo-type or teepee-type incin-
erators, cannot be controlled adequately for satis-
factory air pollution abatement.  Generally, wood
waste is conveyed from the collection device to the
incinerator by  a pneumatic or a mechanical con-
veying system. In areas where the services of a
cut-and-cover dump are available,  disposal by in-
cineration is usually not economical.
   RUBBER-COMPOUNDING EQUIPMENT

INTRODUCTION

Rubber in its  raw state is too plastic for most
commercial applications, and its use is,  there-
fore, limited to a few items such as crepe rub-
ber shoe soles, rubber cements,  adhesives,  and
so forth (Shreve, 1945).   Through a curing pro-
cess termed vulcanizing, raw rubber can be made
to lose plasticity and gain elasticity.  By com-
pounding the raw rubber  with various types and
amounts of additives before the vulcanizing, ten-
sile strength,  abrasion resistance, resiliency,
and other desirable properties can be impartecj to
the rubber.  The proportions and types  of addi-
tives (including vulcanizing agents)  compounded
into the raw rubber, and the vulcanizing temper-
ature, pressure,  and time are varied in accor-
dance with the properties desired in the final prod-
uct.  After the rubber is compounded, it is formed
into  the desired shape and then cured at the re-
quired temperature.  In the forming steps,  large
amounts of organic  solvents are often used in the
form of rubber adhesives.  Since the solvent emis-
sions are not  controlled,  they will  not  be dis-
cussed further in this  section.
Additives Employed in Rubber Compounding

Types of additives  that are compounded into the
rubber  may be classified as  vulcanizing agents,
vulcanizing accelerators,  accelerator activators,
retarders,  antioxidants, pigments,  plasticizers
and  softeners,  and fillers.   Examples of addi-
tives that maybe encountered in rubber compound-
ing are tabulated by type  (Kirk  and Othmer, 1947).

1.   Vulcanizing agents.   Sulfur •was originally
     considered essential to vulcanizing and, though
     vulcanizing is now possible without it, sulfur
     or  sulfur  compounds  such as  sulfur mono-
     chloride are widely  used.  Selenium and tel-
     lurium can also be used for this purpose.
2.   Vulcanizing accelerators.  Aldehyde-amines,
     guanidines,  and thiuram  sulfides are used to
     decrease the time and temperature  required
     for vulcanization.

3.   Accelerator activators.   Zinc oxide, stearic
     acid, litharge, magnesium oxiHe, and amines
     supplement the accelerators  and,  in addition,
     modify finished product characteristics,  for
     example,  they increase the modules of elas-
     ticity.

4.   Retarders. Salicylic acid, benzoic acid,  and
     phthalic anhydride retard the rate of vulcaniz-
     ing.

5.   Antioxidants.  Several organic  compounds,
     mostly alkylated amines, are used to retard
     deterioration of the rubber caused by oxida-
     tion and improve aging and flexing ability.

6.   Pigments.  Carbon black, zinc oxide,  mag-
     nesium carbonate, and certain clays  are used
     to increase tensile strength,  abrasion resis-
     tance, and tear resistance.  Iron oxide, tita-
     nium oxide, and organic dyestuffs are used to
     color the rubber.

7.   Plasticizers and softeners. Resins, vegetable
     and mineral oils, and waxes  are used to im-
     prove resiliency, flexibility, and mixing  and
     processing characteristics.

8.   Fillers.  Whiting,   slate flour,  barytes,  and
     some of the pigments previously mentioned are
     used to improve processing  properties and
     lower the cost of the finished product.

In the compounding of blends,  the accelerators  are
added first to the mass of raw rubber being milled
or mixed.  Then  a portion of the plasticizers (if
present in the blend recipe) are  added,  followed
bythe reinforcing pigments,  the remainder of the
plasticizers, the antioxidants, and any inert fillers
or coloring agents.  The vulcanizing agent is  al-
ways introduced as the last ingredient.

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376
MECHANICAL EQUIPMENT
In order to be effective in imparting various chosen
characteristics, all additives employed in a blend
must be homogeneously dispersed throughout the
blend.  The two most commonly employed pieces
of equipment for blending rubber and  additives are
rubber  mills and Banbury mixers.

A typical rubber mill is shown in Figure 268.   The
two  rolls rotate  toward each other at different
speeds, creating a shearing and mixing action. Raw
rubber is placed in  the mill,  and the  additives are
introduced, generally one or two components at a
time.   Additives may  be  finely divided solids or
liquids.

Another device commonly used for compounding
rubber  stock  is the Banbury mixer.  Figure 269
shows cross-sections of two  typical Banbury  mix-
ers.  Each consists of a completely enclosed  mix-
ing chamber in -which two spiral-shaped  rotors, re-
volving in opposite directions and at different speeds,
operate to keep the stock in constant  circulation.
A ridge between the two cylindrical chamber sec-
tions forces intermixing, and the close tolerances
of the rotors with  the chamber walls results in a
shearing action. Afloating weight in the feed neck
confines the batch within the sphere of mixing.  This
combination  of forces  produces an ideally homo-
geneous batch.
                THE AIR POLLUTION PROBLEM

                Sources of air pollution from the mills are (1) fine-
                ly ground dusts introduced as additives,  (2) fumes
                generated by mechanical  working of the batch by
                the mill rollers,  (3) oil mists from liquid additives,
                and (4) odors.   A  major  source of air pollution
                from  rubber mills  occurs when the finely divided
                dusts are introduced into the batch. Opacity of the
                resultant  dust  cloud  depends  upon the character,
                density, and particle size of the additive.   Opacity
                generally ranges  from 5 to 50 percent, persisting
                from a few seconds to several minutes.

                Uncontrolled emissions vary  from a  negligible
                amount to about 1 pound per hour, depending upon
                the size of the mill, the size of the batch,  and the
                composition of the mix.   Emissions  average ap-
                proximately 0. 5  pound per hour.  Solvent vapors
                emanating from the mix are ordinarily uncontrolled
                and enter the atmosphere.

                Introduction of ingredients into  a Banbury mixer
                is effected through the feed hopper.  It is at this
                point,  during charging, that air contaminants may
                enter  the atmosphere.  Emissions are similar to
                those from the mills.  In general, most of the dry
                ingredients are  added at the Banbury mixer,  car-
                bon black being the most troublesome.
                            Figure 268.  Rubber mi 11 (Parrel Corporation, Ansonia,  Conn.).

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                                     Rubber-Compounding Equipment
                                                                                                         377
              CONNECTION FOR
              EXHAUST FAN
              TO REMOVE DUST
           BIN-TYPE HOPPER
  SPRAY SIDE
      FEED HOPPER DOOR
      AIR-OPERATED
     SINGLE-SLOPE FLOATING
     (EIGHT IN DO»N POSITION
     SLIDING DISCHARGE DOOR
     AIR-OPERATED
      FEED HOPPER DOOR
      AIR-OPERATED
                                   PLEXIGLASS COVER
                                   CONNECTION FOR
                                   POIOER FEED DUCT
ROTORS CORED FOR
CIRCULATION OF
COOLING WATER
OR STEAM
       EXTENDED NECK
     SIDES  AND ROTORS
     CORED  FOR
     CIRCULATION OF
     COOLING WATER
     OR STEAM
SLIDING DISCHARGE DOOR
AIR  OPERATED
                                     SINGLE-SLOPE
                                     FLOATING WEIGHT
HOODING AND VENTILATION REQUIREMENTS


Generally,  rubber mills are provided with hoods,
as shown in Figure 270.  The primary purpose of
ahood is to carry away heat generated by the mechan-
ical mixing action.  As a secondary consideration,
the exhaust hood removes dust, fumes, and mists
emitted from the rolls.   Sufficient volume should
be exhausted to give an indraft velocity of 100 fpm
through the open face of the enclosure.  Figure 269
shows the exhaust provisions  supplied with a stan-
dard  Banbury mixer.  If an unusual dust problem
is encountered,  supplementary hooding canbe added.
The minimum required exhaust volume is equal to
200 cfmper square foot of mixer charging opening.
                                                           Figure 270. Rubber mill with exhaust hood (National  Seal
                                                           Division,  Federal-Mogul-Bower Bearings, Inc., Downey,
                                                           Calif.).
                                                         AIR POLLUTION CONTROL EQUIPMENT
    Figure 269.  Two models of Banbury mixers  (Farrel
    Corporation, Ansonia, Conn.).
                       In  general,  emissions  from Banbury mixers and
                       rubber mills are in a finely divided form and small-
                       er than  15 microns.  Inertial  separators are not,
                       therefore,  effective  control devices for this  ser-
                       vice.  The most common  control device  employed

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378
                                      MECHANICAL EQUIPMENT
is the baghouse; a well-designed baghouse can be
operated with 98 to 99. 5 percent efficiency.

Standard cotton sateen bags are adequate at a  fil-
tering velocity of 3 fpm.  In some cases scrubbers
have also proved satisfactory and advantageous in
scrubbing out  some oil vapors and oil mists that
may be  present in some blends.
 ASPHALT  ROOFING FELT SATURATORS
Asphalt saturators are machines used to impreg-
nate a moving web of  paper felt with hot asphalt
by spraying and by dipping. The felted paper satu-
rated with asphalt is converted  by further process-
ing into shingles,  rolls with mineral granules  on
the  surface,  asphalt-saturated felt rolls,   and
built-up roofing (smooth) rolls, whichmay contain
small amount of mineral dust or mica on the  sur-
face.  While most of these products are used in
the construction of roofs, a relatively small quan-
tity is  used in walls and in other building applica -
tions.

The felt is made from waste paper with either
wood fiber or rags added to strengthen  it against
tearing.  Asbestos and other  inorganic  materials
maybe usedinfelt to produce  fire-resistant roof-
ing materials.  The  manufacture of the felt will
not be  discussed in this section.

Saturant asphalts or coating  asphalts for roofing
are manufactured from the bottom products of the
distillation of crude petroleum.  To meet roofing
material  specifications,  the  "bottoms"  may be
air-blown  or blended with lube oil  stocks.  They
are delivered to the roof ing plant in heated railroad
cars or tank trucks.  The asphalts are semisolids
having a softening point varyingfrom 100° to 240° F
and a minimum flash point of 437°  F by the Cleve-
land open cup method to meet Underwriters Lab-
oratories (UL) requirements.  Although coal tar
is  used in place of  asphalt in some parts of the
country, only equipment  used for manufacturing
asphalt roofing  material is   discussed  in  this
section.
DESCRIPTION AND OPERATION
Asphalt  Coating of Felt

Various  roofing  materials are manufactured by
continuously passing a web of paper felt through a
"line,"  or series of machines.  The line of ma-
chines is designed to manufacture either asphalt-
saturated felt rolls  or most of the other products
— shingles, mineral-surfaced rolls,  and built-up
(smooth) rolls.

Most products are manufactured  to  UL  require-
ments for Built-up label, ClassC label, and Class
A label.   Built-up label materials include smooth
rolls  and asphalt felt  that is laid down prior to
capping the roof with mineral-surfaced rolls or
crushed  rock.  Class A  and Class C labelmate-
rials  are mineral-surfaced rolls or asphalt shin-
gles.  Class A materials  provide the advantage of
having fire-re sistent properties because they con-
tain asbestos,  vermiculite,  or  other  inorganic
materials.

As  shown in  Figure 271, a  typical line  for  the
manufacture of  asphalt felt includes the following
sequence of machines for processing the felt roll:
unwind stand, dry floating looper, saturator  spray
section,  saturator  dip section, drying-in drums,
wet looper, cooling rolls,  finish floating looper,
and roll winder.  Auxiliary  equipment  includes
a heater  and  storage tank for the asphalt and hot
asphalt pumps.  Saturators are designed to satu-
rate felt by spraying or by dipping or a combina-
tion of spraying followed  by dipping.

Asphalt-saturated felt is manufactured from paper
felt indifferent widths and thicknesses.  A typical
line  in the  industry processes  paper  36  inches
wide; it  weighs from 16 to 75  pounds per  480
square feet of material  (a  common unit in  the
paper industry).

The felt is unrolled  from the unwind stand into the
dry looper, where  it passes  over rollers in a
series of vertical loops.   The top rollers can. be
raised so that the dry looper can be used as a live
storage or surge device to feed the saturator at a
uniform rate during feed  roll changes.

From the  dry looper the felt web passes into the
spray section of the saturator,  where the web is
again drawn into vertical loops.  Asphalt at 400°
to 450 ° F is sprayed onto one side of the felt through
several nozzles mounted  on  a. series of from 5 to
16 spray headers. The hot asphalt is sprayed only
on one side of the felt to  drive moisture from the
unsprayed side  of the  web and prevent moisture
trapped within the felt web from forming blisters.
The sprays also reduce the tendency of the  asphalt
to foam  in  the  presence of moisture eliminated
from the web. Paper felt normally contains from
5 to 10 percent by weight of moisture.

In the saturator  dip section, the felt web is also
drawn over a series of rollers, -with the  bottom
rollers  completely  submerged in hot  asphalt at
400°  to  450°  F.  The  bottom rollers are  called
"gates"  since they  are adjustable in a  vertical
position for threading the web.   Saturators may
have up to 16 gates in series.

The steam-heated drying-in  drums and the  wet
looper provide heat and  time  respectively,  for
the asphalt to penetrate the felt web.

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                                    Asphalt Roofing Felt Saturators
                                             379
                                                  VENT TO CONTROL
                                                    EQUIPMENT
         BURNER
                            PUMP
                 Figure 271.  Schematic drawing of line  for manufacturing asphalt-saturated  felt.
 The web then passes through water-cooled rolls
 and onto the  finish floating looper,  which serves
 as live storage or surge for the continuous opera-
 tion of the saturator while coupled to the intermit-
 tent operation of the roll winder. The finish float-
 ing looper  functions similarly to a dry floating
 looper and stores the product web  in a series of
 vertical  loops.   The web is rolled and cut on the
 roll winder to product  size.

 Asphalt-saturated felt usually is manufactured to
 the Built-up-label requirements of  Underwriters
 Laboratories. Two  common weights of asphalt
 felt are  15 and  30 pounds; these are the weights
 of 108 square feet of the  finished material. When
 these weights of material are  applied to a  roof,
 they cover exactly 100  square feet (a roofer's
 square) with 8 square feet of material used for lap
joints.

During operation the temperatures of the asphalt
 sprays and the asphalt in the dip tank are main-
tained by circulating the  asphalt through a heater
and an insulated, heated  storage tank.
Roof  Capping Materials

Equipment lines for manufacturing shingles, min-
eral-surfaced roll roofing,  and built-up smooth
rolls  employ in  sequence:  an  unwind stand,  dry
looper, asphalt saturator,  drying-in drums,  and
wet looper, as described for the manufacture of
asphalt-saturated felt, plus  additional machines
for applying filled asphalt  coating, sand, mica,
and rock  granules.  A typical line,  illustrated in
Figure 272, includes after the wet looper: a coat-
er, granule applicator, backing applicator, press
section, water-cooled rolls, finishfloating looper,
and either a roll winder or a shingle cutter and
stacker, depending upon  the product being made.

In addition to the  heaters  and storage tanks for
asphalt coating and  asphalt saturant, auxiliary
equipment includes conveying and storage equip-
ment  for mineral dust, sand, mica, and granules;
a mineral  dust dryer; and  a mixer for producing
filled asphalt coating.

In the  production  of  shingles,  mineral-surfaced
rolls,  and built-up smooth  rolls,  36-inch-wide

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380
                                       MECHANICAL EQUIPMENT
          TANK
          TRUCK
          TANK
          TRUCK
       SCREW	
CONTROL  CONVEYOR
EQUIPMENT
                                                         SHINGLE STACKER
           Figure 272.  Schematic drawing of  line for manufacturing asphalt shingles, mineral-surfaced
           rol Is, and  smooth rol Is.
paper felt weighing 27 to 72 pounds (per 480 square
feet) depending upon the  product being manufac-
tured   is unwound  from  the feed  roll and is fed
through the initial  asphalt saturation  process.
After  leaving  the  wet looper, the saturated  felt
web passes to the coater.  Filled asphalt coating
at 350° to 400° F is released through a valve onto
the web just as it passes  into the coater.  Heated
squeeze rolls  in the coater distribute the coating
evenly upon the web surface to form a thick base
coating to which rock granules, sand,  or mica
can adhere.
                Filled asphalt coating is prepared by heating min-
                eral dust to over 250° F  in  a rotary kiln or in
                heated flight screw conveyors to remove moisture.
                Hot  dry mineral dust and coating asphalt heated
                to about 400° F are mixed, usually in  about equal
                parts by weight, to form the filled asphalt coating
                that is piped to the coater. Asbestos andvermic-
                ulite are added to the filled coating inmaking roof-
                ing materials  with a Class A label.

                After leaving  the  coater,  a -web  to be made into
                shingles or mineral-surfaced rolls passes through

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                                     Asphalt Roofing Felt Saturators
                                                                                                   381
the granules applicator, where colored rock gran-
ules  are  fed volumetrically from multicompart-
mented bins onto the hot, coated  surface.  Various
colored patterns  are created by  controlling the
point of application, colors, and flow rates of the
granules.  The granules are pressed into the coat-
ing by passing  the coated web  through  squeeze
rolls.  Sand  or mica is applied to the back  or
opposite side of the web and is  also pressed into
the web surface.  In making built-up smooth rolls,
granules are eliminated, and fine sand or mica is
applied to  both sides of  the web.

Sand, mica, and granules are unloaded from trucks
or railroad cars into storage silos by combinations
of belt  conveyors, screw conveyors,  and bucket
elevators  or by pneumatic conveyors.  Sand and
granules  are  conveyed to multicompartmented
surge bins and then released through gravity drop
tubes into the applicators on the line.
      Table  109.  TYPICAL COMPOSITION
         OF CLASS C  LABEL SHINGLES
        AND MINERAL-COATED ROLLS
                 (weight percent)

Saturant asphalt
Coating asphalt
Mineral dust stabilizer
Felt paper
Sand
Granules
Total
235-lb
shingles
21
17
17
12
3
30_
100
95 -Ib
roll
17
15.2
18. 8
10
3
36.
100
 Following the application of sand, mica, and rock
 granules,  the web is cooled rapidly by passing it
 through a  series of water-cooled rolls to cool the
 finished roofing material for handling.  The finish
 floating looper, which follows  the  water-cooled
 rolls, provides  additional cooling for the web and
 live storage to match the continuous operation of
 the  line to the  intermittent operation of the roll
 winder. The finish looper also provides downtime
 for  quick  repairs  or adjustments to the shingle
 cutter and stacker during continuous line operation.


 As previously  stated, most shingles,   mineral-
 surfaced rolls,  and built-up  smooth rolls must
 meet UL  requirements for Built-up label,  Class
 C label, or Class A  label.
A common Class C label  shingle carries a 235-
pound designation.  This is the weight of the laid
shingles (including lap joints) to cover 100 square
feet of roof.  A common Class  C label mineral
roll carries a 90-pound designation.  This is the
weight  of  108  square feet of the web, which will
cover 100 square feet and provide 8 square feet of
material for lap joints. The composition of typical
Class C label 235-pound  shingles  and  90-pound
mineral-surfaced roll is shown on Table 109.
  Figure 273.  Emissions from asphalt saturator  tank
  (Lloyd A.  Fry Roof ing Company, Los Angeles, Calif.).
THE AIR POLLUTION PROBLEM

Heating asphalt saturant to 400° or 450° F under
agitation results in the vaporization of low-boiling-
point hydrocarbon oils  in the form of dense white
emissions  varying in opacity from 50 to 100 per-
cent.  Sources  of these emissions are  asphalt-
saturant  storage  tanks,   saturator,   drying-in
drums, and wet looper. Emissions from a satu-
rator are shown in Figure 273. Emissions of  ex-
cessive opacity also may occur from the cooling
drums used  in the  manufacture of asphalt-satu-
rated felt.   The heated asphalt used  in  coating
produces  dense white emissions emanating from
the storage tanks, filled-coating mixer, and coat-
er.  Although the opacities of the emissions from
this  equipment are  less  than those of emissions
from equipment containing saturant,  they  may
exceed 40 percent opacity.

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382
                                      MECHANICAL EQUIPMENT
In the saturator,  removal  of  moisture from the
paper felt  as water vapor or steam in effect dis-
tills the lower boiling hydrocarbons and produces
a great number  of small particles.  Many of these
particles  have diameters that match  the  wave-
lengths of visible  light (0. 4 to 0. 77 micron)  and
are, therefore, most effective  in blocking light to
produce a high percentage of opacity.

As  shown on Tables 110,  111,  and 112, the con-
centration of oil particulates  exhausted from three
different saturator  machines varied from 0.416 to
0. 768  grain per  standard  cubic  foot  (gr/scf).
Emission rates  as  well as opacities from satura-
tors and coaters are affected by: line speed, pro-
duct manufactured,  felt moisture  content,  air
temperature and humidity,  asphalt  composition
and  temperature,  number  of  sprays and gates,
and gas exhaust rate.  Generally, emissions in-
crease directly with increasing  line speed,  felt
moisture  content,  air temperature and humidity,
number of spray headers and gates in operation,
and  the asphalt  temperature.  Line speeds  for
some  installations  exceed  500 feet  per minute
(fpm). As expected, emission  rates and opacities
are  highest during  the  manufacture of  roofing
materials requiring the highest asphalt saturating
rates.

Emission rates  and opacities are also character-
istic of the particular  crude used for making as-
phalt saturant or asphalt coating.  Generally,  as-
phalts with the  highest content of volatile  oils
produce maximum  emissions.  A number of obser-
vations of the  effluent from an electrical precipi-
tator venting  a  saturator revealed a reduction of
opacities  by about  15  percentage points when an
asphalt containing lesser amounts of volatile com-
ponents was used.  While these observations were
being made, process variables  such as roofing
product,   saturant  temperature,  line speed,  and
air temperature and humidity were held as con-
stant as possible. In addition,  source test results
showed thatparticulate concentration in the exhaust
gas from the precipitator also were reduced from
0.07 to 0.03 gr/scf. Reductions in particulate emis-
sions are not always accompanied by correspond-
ing reductions in opacity. Conditions exist where-
in the number of submicron-size particles - -which
cause  dense opacities,  but which constitute only
a small fraction of the total weight of all the  par-
ticles emitted - are not reduced in proportion to
the larger,  heavier particles.

Typical specifications for roofing asphalts include:
gravity, API; flash point, Cleveland Open Cup; vis-
cosity,  210 ° F Saybolt Furol Seconds;  solubility in
CC14; amount of sediment; and water content.  Un-
fortunately,  these  specifications do not measure
the gaseous emission potential of  an asphalt.
Weight loss on heating  by the ASTM D-6-67 cup
method and the ASTM 1754-67T plate  method also
should be used with caution in determining volatile
potential since some  asphalt samples can air-po-
lymerize  and gain weight  at the same time they
lose weight by volatilization.

Sometimes  saturators are operated  at such high
speeds as to cause hot asphalt tobe flung from  the
top rollers of an asphalt dip section  and thereby
atomize oil particles. This condition  can be  cor-
rected  by  installing curved  adjustable   shields
about  1 inch from the  rollers to quickly capture
the hot asphalt spray and reduce the volatilization
of oil particles.  Shields  installed on a five-gate
saturator are shown  in Figure 274.

Dust is generated along with oilmists and aerosols
in the manufacture of shingles, mineral-surfaced
rolls,  and built-up (smooth) rolls.   The  sources
for these dust emissions,  which result in exces-
sive opacities  and particulate weight losses, are
conveying and storage equipment for mineral  dust,
sand, mica, talc, asbestos,  and other materials.
Excessive dust is  emitted from the mineral dust
         Table 110.  EMISSIONS FROM TWO SCRUBBER-PRECIPITATOR INSTALLATIONS
                                VENTING ASPHALT SATURATORS

Volume, scfm
Tempe rature ,
Emission rate,
gr/scf
Ib/hr
Water vapor, %
Collection
efficiency, %
Scrubber inlet
Unit 1
20,000
140

0.416
71.4
3. 7
Unit 2
12,500
130

0.59
63.2
-
Scrubber: 71, 28
Precipitator inlet
Unit 1
20,200
85

0. 115
20. 0
4.9
Unit 2
13,000
120

0.41
45.7
-
Precipitator: 30, 92
Precipitator outlet
Unit 1
20, 100
92

0. 058
10.8
4.8
Unit 2
12, 700
130

0.032
3.5
-
Overall: 36, 94

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                                    Asphalt Roofing Felt Saturators
                                            383
    Table 111.   EMISSIONS FROM SCRUBBER
           AND BAGHOUSE VENTING
            ASPHALT SATURATOR

Volume, scfm
Temperature ,
Emission rate,
gr/scf
Ib/hr
Water vapor, %
Collection
efficiency, %
Scrubber
inlet
10, 100
260
0. 789
68
4
Scrubber:
12
Baghouse
inlet
10, 100
150
0. 693
60
6
Baghouse:
88
Baghouse
outlet
10, 100
150
0. 085
74
6.2
Overall:
89
 Table  112. EMISSIONS FROM WATER SCRUBBER
       VENTING ASPHALT SATURATOR

Volume, scfm
Temperature,
0 F
Emission rate,
gr/scf
Ib/hr
Water, %
Collection
efficiency, %
Scrubber
inlet
12,000
138
0. 535
55. 0
2.7

Scrubber
discharge
12, 196
82
0.0737
7. 7
4. 2a
86
 At 3. 7 volume % of water,  vapor is  saturated
 air.   Other qualitative tests run simultaneously
 showed no particulate water.
dryer, the mixer for hot mineral dust and coating
asphalt,  and the applicators for sand and mica.

Generally, only slight quantities of dust are emit-
ted from the  conveying  and storage equipment and
applicators for granules.  This is  because typical
granules are  of relatively large size;  less than 2
percent, by •weight,  pass  a Number 35  U.S.  mesh
screen.  The granules also are treated with oil to
prevent dusting and promote bonding of the  gran-
ules to the filled asphalt coating.  On the  other
hand, sand, mica,  and mineral dust have signifi-
cant amounts of particles less than 10 microns,
which create dust problems during handling.  For
example, large quantities of dust are emitted when
storage bins  or  surge bins  are being filled with
these materials by pneumatic conveyor.
                                                      Figure 274.  Shields  installed over top  rollers of dip
                                                      saturator to reduce emissions of oil  particlesfCeletex
                                                      Corporation, Los Angeles, Calif.).
Perhaps the largest single source of dust is from
the direct-fired rotary kiln for  drying  mineral
dust.  A typical mineral dust may contain about 4
percent  by weight of particles under 10 microns.
Considerably less dust is generated if a heated
flight screw conveyor  is used instead of  the rotary
kiln.

Oilmists and aerosols as wellas  dust are emitted
in excess of those quantities allowed by Los Angeles
County air pollution regulations from  the  mixer
for producing filled asphalt coating.


HOODING  AND VENTILATION  REQUIREMENTS

Nearly all  asphalt saturators, drying-in drums,
and wet loopers in Los Angeles County have been
equipped  with canopy-type hoods.  An example of
such a hood is  shown in Figure 275.  With canopy
hoods, the  volume of air  to be exhausted through
the hood is in the  range of 10, 000 to 20, 000 cfm.

By designing a relatively large  room  enclosure
around an asphalt felt saturator, drying-in drums,
wet looper, and cooling drums, the volume of con-
taminated air to  be controlled can be drastically
reduced.  Such  a  room enclosure  should include
enough space for  the operators to remove broken
felt from the equipment.   The only openings into
this  enclosure would be 2-inch-high slots for the
inlet and outlet of the felt web and automatic  doors
for access to the machinery by operating person-
nel.  These  slot openings  should be as close to
the floor as possible.   Indraft  velocities  through

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384
MECHANICAL EQUIPMENT
Figure 275.   Asphalt saturator  hood at saturator dis-
charge (Lloyd A. Fry Roofing Company,  Los Angeles,
Calif.).

the slots for the  web and one open door should be
designed for  at least 20 ppm  so  that only about
3000 to 5000  cfm  of contaminated air ventilates
the saturator  and its associated equipment. A typ-
ical room enclosure  around a saturator  is shown
in Figure 276.

A  separate small enclosure  venting  to control
equipment should be built tight to the coater to
allow the line operator to control the product by
hand adjustments to the coater.  The operator  can
stand outside  of this enclosure, where he does not
have to breathe  contaminated  air.  All  openings
into this enclosure should be kept to a minimum
size. Design ventilation rates for the  coater should
not exceed 300 cfm, with indraft velocities rang-
ing from 150 to 200 fpm.

Oil mists and  aerosols emitted from the storage
tanks for  saturant and  coating asphalt are usually
vented to the same air pollution control equipment
that vents  the saturator drying-in drums and  wet
looper.  Design ventilation rates for each storage
tank and from each mixer average about 100 cfm.
AIR POLLUTION CONTROL EQUIPMENT

Baghouses, low-pressure  scrubbers,  and two-
stage electrical  precipitators have  been used to
control emissions from saturators,  coaters,  and
asphalt storage tanks. Most of the earlier control
                 devices vented  relatively large volumes (10,000
                 to 20, 000 cfm) of air contaminated with oil mists
                 and aerosols. Although these devices have proved
                 capable of controlling  the  particulate emissions
                 measured on the basis  of weight per effluent vol-
                 ume,  scrubbers  as  singular control devices have
                 in most instances failed to  collect the large num-
                 ber of  submicron-size  particles  that create the
                 opacity problem.  Even baghouses  and  electrical
                 precipitator s employing scrubbers as precleaners
                 have had difficulties in controlling opacities. Ex-
                 tensive modifications  of the earlier devices have
                 been necessary to keep these air pollution control
                 systems in  compliance.  Opacities of  emissions
                 from baghouses  and electrical precipitators fol-
                 lowing modifications have usually ranged from 15
                 to 35 percent white.

                 A new  approach  to this control problem involves
                 building a tight  enclosure  around  the  saturator
                 drying-in drums and -wet looper,  and a separate
                 enclosure around the  coater to reduce the total
                 volume of contaminated air to less  than 5000 cfm.
                 At this flow rate,  afterburners of the  size that
                 normally  operates without visible emissions and
                 with control efficiencies over  95 percent  based
                 uponmeasurement of total carbon  can be installed.
                 Afterburners  also are superior  to other control
                 devices in abating odors, which in some instances
                 are strong enough to create a nuisance.

                 Baghouses have been used almost exclusively to
                 control the  dust  emissions.   Line blenders  or
                 mixers for  filled asphalt coating  omit dust with
                 only trace amounts  of oil participates and essen-
                 tially no moisture.  These  emissions  have been
                 successfully controlled by baghouses. Large batch
                 blenders, however,  emit moisture from undried
                 mineral dust  along  with dust pa.rticles and rela-
                 tively large quantities of oil particulate s .   These
                 emissions  should be controlled by venturi scrub-
                 bers.  Afterburners, scrubbers,  electrical  pre-
                 cipitators, and baghouses are discussed  separately
                 below.
                 Afterburners

                 Direct-fired afterburners should be designed -with
                 natural-gas-fired burners capable of reaching ex-
                 haust  temperatures  of 1500°  F.  Two  different
                 afterburner installations venting  saturators  are
                 shown in Figures  277 and 278.   Figure 277  shows
                 a direct-fired afterburner venting aline for  manu-
                 facturing asphalt-saturated felt.  The afterburner
                 contains a preheat  section for  the contaminated
                 airstream;  this section consists  of a spiral flow
                 path along the outside surface of a stainless-steel-
                 tube combustion chamber.  Figure 278 shows a
                 direct-fired afterburner venting a line for manu-
                 facturing  asphalt  shingles  and  mineral-surfaced
                 rolls.  Results  of a  source test conducted on an

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                          Asphalt Roofing Felt Saturators
                                                                                                  385

Figure 276.   Total enclosure for  asphalt saturator  (The Flmtkote Co.,  Los Angeles, Calif.).

                                            no visible emissions  even with  afterburner ex-
            _„	                            haust temperatures as low as 1200°F.
                                            Design  parameters for direct-fired afterburners
                                            should  include an exit temperature of 1500° F, a
                                            residence  time between 0. 3 to 0. 5 second, and a
                                            gas velocity of 25 to 45 fps.   Flame contact with
                                            the contaminated air stream must be provided.

                                            Afterburners  should be protected against flash-
                                            back by installing a short section of  high-velocity
                                            ductwork.  This duct section increases gas veloc-
                                            ities well  above flame  propagation velocities in
                                            the reverse direction.

                                            Whenever possible,  the heat in the gases exhausted
                                            from  the  afterburner  should  be utilized.   The
                                            waste heat can be used to preheat incoming con-
                                            taminated  air, heat asphalt, dry mineral dust, or
                                            produce steam for plant use. Such a heat-recovery
                                            system may consist of a heat  exchanger mounted
                                            on the exhaust from the afterburner. A low-vapor-
                                            pressure,  heat-transfer liquid is heated to about
                                            500° F,  then circulated (1) through coils or jack-
                                            ets of the asphalt storage tanks  or (2) through the
                                            hollow  flights  and jacketed exterior •walls of the
                                            heated  screw  conveyor for drying mineral dust.
                                            Another alternative •would be  to install a  •waste
                                            heat boiler.  Steam produced  in this boiler could
Figure 277. Direct-fired  afterburner containing preheat
section, installed on roof of bui ldmg(Fortif iber Cor-
poration, Los Angeles, Calif.).
afterburner operating at an outlet temperature of
1400 °F and controlling oil particulates showed an
efficiency of over 99 percent, based upon the total
combustion of gaseous  and particulate   organic
compounds measured as total carbon.  There were

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386
                                      MECHANICAL EQUIPMENT
Figure278. Direct-fired afterburner venting large line
for  manufacturing asphalt shingles and mineral-surfaced
rolls (Lundy-Thagard  Oil Co.,  South Gate, Calif.).

be used in other parts of the plant.  A waste heat
boiler installed on an afterburner venting a chem-
ical manufacturing  plant has  been estimated  to
have a projected payout time of less than 4 years.

Scrubbers
Low-pressure scrubbers have not beenvery suc-
cessful in controlling emissions from saturators,
coaters,  and asphalt storage  tanks.   They are
used today primarily as a precleaner in line be-
fore electrical precipitators or baghouses.  Low-
pressure scrubbers  may consist  of  a  series  of
3/8 - inch wide - angle solid - cone  spray nozzles,
six or  more in a  series  about 1 foot apart mounted
along a  duct.  Other scrubbers  may consist  of
baffled chambers containing sprays or restricted
shower passages, metal mesh sections,  and pas-
sages,  all  of which  create impaction or inertial
forces for  collection of contaminant particles. Oil
mists and  aerosols collect as  oil in these scrub-
bers, and the oil  is removed by skimming to pre-
vent reintrainment before the water is recirculat-
ed to the sprays.
Table  112  shows results of a test  conducted on a
scrubber venting a saturator having a  collection
efficiency of  86  percent. Scrubbers used as pre-
cleaners should be installed as  near the saturator
as  possible to provide maximum residence  time
                                                     for agglomeration of particles from initial -water
                                                     contact in the scrubber to final collection in the
                                                     precipitator or baghouse.   Agglomeration of oil
                                                     mists  and aerosols is  believed  to proceed pro-
                                                     gressively  to larger  size  particles, upon -which
                                                     the final collector device operates more efficiently.

                                                     In contrast,  high-pressure  scrubbers  such as
                                                     venturi scrubbers  are capable of collecting sub-
                                                     micron-size particles.  Venturi scrubbers, how-
                                                     ever,  have not been  installed on saturators be-
                                                     cause  of  high  first cost and high  operating  ex-
                                                     penses.   Power  requirements  are high because
                                                     the venturi scrubber  operates  at 40 to  50 inches
                                                     of water across the throat of the venturi. Venturi
                                                     scrubbers can be  used, however, to control  the
                                                     emissions from the mixer for filled-asphalt coat-
                                                     ing where emissions  of low volume contain min-
                                                     eral dust,  oil particulates,  and moisture.  Bag-
                                                     houses  are not satisfactory  for this use because
                                                     bag fabric will blind in the  presence of  moisture.
Electrical  Precipitators
Low-voltage,  two-stage electrical precipitators,
preceded  by low-pressure scrubbers, have been
used to control a major emission source at the
saturator and minor sources at the  coater  and
asphalt storage tanks.  Water scrubbers and 4-
inch metal-mesh  filters should be used with the
precipitator  to assure compliance with opacity
regulations.   Tests conducted on a precipitator
operating 'without a scrubber and without 4-inch-
thick metal-mesh filters revealed an increase in
opacities  of 15 to 20 percent. With scrubbers  and
metal-mesh filters, precipitators should operate
at the  30 to 35 percent opacity  range.   Without
these precleaning devices, they -will violate opac-
ity regulations. The precleaners. also are needed
to prevent dropout  of  oil particles on equipment
near the stack.  Microphotographs in Figure  279
show a clean ionizer wire and wires after 8 and 30
days of operation with and after 4 days of operation
•without the scrubber.  These photographs demon-
strate the  desired effect since scrubbers  -with
metal-mesh filters should keep 80 percent or more
of the  oil  particulates from  reaching the precipi-
tator.
Figure 280 shows  a  schematic diagram of a satu-
rator venting to a  scrubber and electrical precip-
itator.  An  actual installation of  a scrubber and
precipitator is shown in Figure 281. The scrubber
not only removes  oil particles larger than 10 mi-
crons  in  diameter, but promotes agglomeration
of the  oilmist and aerosol, and thereby improves
the collection efficiency of the precipitator. With-
in the scrubber,  hot contaminated air is cooled
by contact with the sprays.

Metal-mesh eliminator s are installed between the
scrubber  and the  precipitator to avoid carryover

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                                    Asphalt Roofing Felt Saturators
                                              387
                  a.   Clean wire.
       b.   Four  days operation without  scrubber.
       c.   Eight days operation with  scrubber.
        d.  One month operation with scrubber.
   Figure 279.   Microphotographs showing precipitator  ionizer wire deposits with and without use of prescrubber
   (Celetex Corporation, Los  Angeles,  Calif.).
of water droplets into the precipitator, where they
cancause arcing. These metal-meshfilters should
not be more than 2 inches thick for easy cleaning
although banks of two  or three may be arranged
in series.

Table 110 shows emissions from two water scrub-
bers and a low-voltage, two-stage electrical pre-
cipitator venting an asphalt saturator. The design
parameters  of electrical precipitators are  par-
ticularly  critical  since many particles to be re-
moved are less than 1  micron in diameter.  Par-
ticular attention must be  directed to air distribu-
tion within the precipitator and  to  temperature
drop across the unit.
Examination of the theoretical considerations used
in designing electrical precipitator s indicates that
the time  a contaminant particle remains with the
ionizer and collector fields has a significant bear-
ing upon  the efficiency of the precipitators.  Be-
cause  the actual time in the electrical  field  is
difficult to calculate,  efficiency can be related  in
terms of superficial  velocity.   This  velocity  is
based upon the  velocity through the overall cross-
sectional area of  the precipitator  perpendicular
to the direction of airflow. A typical low-voltage,
two-stage precipitator has plate lengths of  12-1/2
inches  in the  direction  of airflow and spacing  of
3/8 inch between plates.  The ionizing wire spac-
ing to each door strut is 1-1/2 inches.  Electrical
   234-767 O - 77 - 27

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388
MECHANICAL EQUIPMENT
                                        ASPHALT
                                        SATURATOR
                                                       75-hp EXHAUSTER
                                                       27,000 cfm   v
                                                       AT 8  in.  SP
                                           INERTIAL SCRUBBER-
                                                                                     VISCOUS FILTER
                                          ELECTROSTATIC PRECIPITATOR
                                           13,000-volt IONIZING SECTION
                                           6,900-volt COLLECTION SECTION
 Figure 280.   Schematic drawing  of  electrical precipitator,  precleaner,  and exhaust system for asphalt  saturator.
  Figure 281.  Low-voltage, two-stage  electrical precipitator venting asphalt saturator  (Johns-ManviIle  Products
  Corp.,  Los Angeles,  Calif.).

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                                    Asphalt Roofing Felt Saturators
                                             389
precipitators are  usually  designed for 12 to 14
kilovolts on the ionizer  section and 6 to 7 kilovolts
on the collector plates.  With these parameters,
superficial velocities of less than 100 fpm provide
adequate control of emissions.

Electrical precipitators with double ionizer sec-
tions spaced  3  to  4  inches apart in the direction
of airflow show the highest  collection efficiencies.
Good air distribution across  the  precipitator is
essential for highest efficiency. Uneven distribu-
tion leads to high velocities in some sections and
yields low overall collector efficiency.   Uneven
air distribution can be caused by short duct bends,
abrupt transitions  from inlet duct to precipitator
housing, and bouyancy effects of warm air.  Per-
forated plates can be installed at the inlet and out-
let  of the precipitator to compensate for bouyancy
effects and uneven distribution.  Transition duct-
work from round ducting to the precipitator housing
should be carefully designed to provide for  smooth
and gradual  changes in the direction of airflow.
Turbulence  and poor velocity distribution due to
short radius duct bends  in the  exhaust system can
be  compensated  for,  in part, by the installing of
straightening vanes or adjustable or sectioned per-
forated plates.

The temperature  drop  across the precipitator is
another  important design  factor.   Water  evapo-
rated from the felt in the spray section of the sat-
urator as well  as  water evaporated in the  pre-
cleaner  scrubber increases the water content of
the contaminated  air entering  the  precipitator.
Because of conditions prevailing  at the scrubber
exit,  the  contaminated  air  may be near the  dew-
point temperature  and  an  additional temperature
drop  of  a few degrees in the precipitator  may be
sufficient to produce some condensation.   The
presence of -water droplets causes arcing between
the electrodes in the precipitator and thus results
in a decrease in collection  efficiency.   Water con-
densation may be minimized by  insulating  the ex -
haust system upstream  of the  precipitator and the
precipitator  housing or by  heating the  airstream
before it enters the precipitator.  The heat added
should be just sufficient to stop the arcing because
excessive heat prevents  the collection  of oil par-
ticles in the precipitator.

Electric insulators exposed to  the  contaminated
airstream accumulate oil,  dirt,  and water. These
deposits cause electrical leakage accompanied by
a voltage drop and a decrease in precipitator ef-
ficiency.  Insulators should, therefore, be enclos-
ed within channels  to isolate them from the  con-
taminated  airstream.   The channels  should be
pressurized  slightly by small blowers to prevent
infiltration of air contaminants.

Oil collection in a precipitator forms tarry mate-
rials  on precipitator components.  These deposits
decrease the  efficiency  of  the  precipitator  by
causing  breakdowns  of  insulators and arcing ef-
fects.  Proper maintenance  is vital,  therefore,
to efficient  collection.  The following minimum
maintenance procedures are  recommended:

      1.  The interior of the  precipitator  should
         be  cleaned in place at least once a month
         by  steam cleaning -with detergent.

      2.  Regular checks should be made of the
         condition  of  all  wires  and  insulators.
         Cracked or broken components should be
         replaced.

      3.  Components of the precipitator shouldbe
         completely removed and thoroughly clean-
         ed  at least once a year.

Doghouses

Baghousespreceded by low-pressure-drop scrub-
bers have been used  to control emissions from
saturators.   Figure  282 shows a baghouse  pre-
ceded by a scrubber and a  low-efficiency cyclone
installed downstream from the baghouse to elimi-
nate water mist. Table  111 gives the results of a
  Figure 282.  Baghouse venting saturator and  coater
  asphalt storage  tanks.   Baghouse  is enclosure above
  and slightly to  left of  truck.(The Flmtkote Co.,
  Los Angeles, Calif.).

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390
MECHANICAL EQUIPMENT
source test conducted on this equipment.  Further
modification to this  air  pollution control equip-
ment, following this test, resulted in a substantial
reduction in opacity of the emissions.  The modi-
fication consisted  of  installing  a scrubber in the
ductwork  near the gaseous  discharge  from  the
saturator.
The  scrubber  shown  in  Figure 283 consists of a
bank of high-velocity metal-mesh filters.  A bat-
tery of wide-angle  solid-cone  nozzles mounted a
few inches upstream spray 'water across the face
of the filter pads.  This scrubber supplements an
existing shower-type  scrubber located  near the
baghouse.  The new scrubber  provides  a longer
residence time for  agglomeration of oil  particles
following initial contact  by sprays until the par-
ticles finally are collected in the baghouse. In the
baghouse, both water and  oil  (equivalent to SAE
30 motor oil)  collect on  the surface of  16-ounce
heavy  •wool-felt bags, each 1.  5  feet in  diameter
and 12 feet long. Cleaning devices such as shakers
or air  jets  are not required since the oil drains
off of the fabric by gravity and is collected along
with water in the skimming tank.
Figure  283. Interior of scrubber  installed upstream of
baghouse shown in Figure  282. Note metal-mesh filters.
(The Fhntkote Co.,  Los Angeles,  Calif.).
                Maintenance of the bags  presents several prob-
                lems.  Some oil attaches itself permanently to the
                fabric; it oxidizes and polymerizes and eventually
                causes  plugging and failure  of  the fabric.  This
                problem is avoided by  systematically removing
                and washing the bags after  300 to 350 hours of
                operation.  The bags can be cleaned about   six
                times  before  they are discarded.   Since new  or
                clean bags  do not filter efficiently, bags must be
                preconditioned by hanging in the baghouse for sev-
                eral days so that oil particles can coat the fabric.
                This "preconditioning" step results in  good filtra-
                tion when the bags are attached  to the  tubesheet.

                Power requirements for  baghouses  exceed   the
                requirement for low-pressure  scrubbers  since
                the baghouse normally operates at pressure drops
                of 10  to  14 inches  of water  column,  and a filter
                ratio  of about 12. 5 cfm per square foot.

                With small sources of emissions from  the asphalt
                storage tanks  and coating mixer, along with emis-
                sions from the saturator and coater, opacities of
                20 to  35  percent white  can be expected from  the
                discharge  of the baghouse.

                Dry-type baghouses are used  to control dust emis-
                sions from the rock dust dryer  and the conveying
                and storage of sand, rock dust, mica, and other
                fine materials.   Figure  284 shows a baghouse
                venting a  sand applicator and  a belt conveyor.
                Baghouses alsomaybe used to control dust emis-
                sions from  small mixers used for preparing filled
                asphalt coating.

                Glass Fiber Mats

                A recent development in the control of effluent
                from roofing plant saturators consists of passing
                contaminated effluent through a  slowly  moving
                unrolled mat of glass fiber as  shown in Figure
                285.

                At velocities of 500 to 700 fpm through the  mat,
                over  90 percent  of the liquid particulates is  re-
                moved,  and there is  a  correspondingly high  re-
                duction in odor level. Pressure drop  through the
                mat can be increased from 16 to 25 inches  of water
                column for efficient collection of submicron-size
                particulates.  At higher pressure drops, the  stack
                discharge is reported tobe virtually free of visible
                pollutants.  The spent mat is  reroiled and dis-
                carded.  Operating costs are comparable or lower
                than those of other  methods of filtration.
                          PIPE-COATING  EQUIPMENT

                INTRODUCTION
                Iron  and steel pipes are subject to corrosion and
                oxidation, particularly in underground service .  In

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                                        Pipe-Coating Equipment
                                                                                                    391
Figure 284.
Calif.).
Baghouse venting sand applicator and  belt conveyor for mineral dust (The Flmtkote Co., Los  Angeles,
order to exclude the corrosive elements from con-
tact with  the  metal,  many surface coatings have
been used.  These include paints ,  lacquers, metal-
lic coatings, vitreous  enamels, greases, cements,
and bituminous materials, both asphalt and coal
tar based.  Only the bituminous materials \vill be
discussed in this section.

Asphalt, a residue  derived from the distillation  of
crude  petroleum,  becomes a dark brown  to black
rubbery solid when air blown at elevated tempera-
tures and allowed to cool.  Coal tar is a dark brown
toblack, amorphous,  solid residue resulting from.
the destructive distillation of coal.  Both materials
arc compounded with mineral fillers and other in-
gredients to form the  so-called enamel that is ap-
plied to the  pipe.  Both materials perform essen-
tially the same duty with some qualifications. With-
out the addition of plasticizers ,  the  coal tar enam-
els tend to have a fairly narrow satisfactorily oper -
ating temperature range. Above or below this range,
they are  too  soft to  stay in place or too brittle  to
                                           resist impact.   The asphalts have a wider  oper-
                                           ating  temperature range  but have a disadvantage
                                           of being slightly more permeable to moisture and
                                           are affected more by soil minerals.   Some com-
                                           mon qualities that make these materials excellent
                                           for  pipe coatings are as follows:

                                           1.  They resist moisture, and chemical and elec-
                                               trolytic action.

                                           2 .  Long-lasting adhesion can be expected between
                                               the coating and pipe.

                                           3.  They are stable over a wide temperature  range
                                               if properly compounded.

                                           4.  They are tough and resist mechanical abrasion.

                                           5.  They possess good ductility and can resist soil
                                               contraction  and  expansion  and  underground
                                               pipe movement.

                                           6.  They resist aging over  long periods of time.

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392
MECHANICAL EQUIPMENT
    Figure 285.  Glass fiber mat used to filter ef-
    fluent from asphalt saturator (Johns-ManviIle
    Corp., Manvilie,  N.J.).
METHODS OF APPLICATION

The three usual methods of applying asphalt or coal
tar coatings to pipe are  dipping,  \vrapping,  and
spinning (The  Asphalt Institute,  1954; American
Water Works  Association,  1951).  These will be
discussed individually.  With all application tech-
niques the pipe must be dry and rust free.  Most
often a primer is applied before the final coating
is added.
Pipe Dipping

Pipe  dipping involves applying the coating to both
the internal  and external  surfaces of the pipe by
completely immersing  it in a large vat of molten
asphalt. Coal tar enamel cannot be applied by dip-
ping  since it cannot be held in an open container
for long periods of time  without excessive changes
in its physical properties.   The tank used is usu-
ally rectangular with dimensions to accommodate
the largest size pipe to  be dipped.  The  asphalt is
kept  at a  specified temperature by heat-transfer
tubes submerged in the  enamel.  The pipe is low-
ered into the enamel until completely covered and
allowed to remain until the metal reaches the tem-
perature of the liquid.  This is necessary for good
adhesion.  It is then raised,  tilted off horizontal
in order to drain off excess enamel, and  allowed
to cool. Additional thickness may be obtained by
redipping.   For the second  and succeeding dips,
                 however, the pipe must not remain in the tank long
                 enough to remelt the material already deposited.


                 Pipe Spinning

                 Pipe  spinning is the name given to the procedure
                 wherein molten asphalt or coal tar enamel is ap-
                 plied to the interior surface of a rotating pipe.  The
                 spinning motion  is given  to the pipe by conveyor
                 wheels or er.dless chain slings.  The enamel is ap-
                 plied by spray heads on a lance attached to a travel-
                 ing, heated, enamel kettle.  The lance is inserted
                 the full length of the pipe and  then the hot enamel
                 is  sprayed  as the lance is withdrawn.  The spin-
                 ning of  the  pipe deposits the enamel in a uniform
                 layer  and holds  it in place until it hardens.  The
                 spinning is continued with usually a  cooling water
                 spray on the  outside  of the pipe until the enamel
                 temperature has cooled to about 100°F.


                 Pipe Wrapping

                 Pipe wrapping is the most  complex of the common
                 pipe protection  techniques involving asphalt and
                 coal tar because, in addition to the enamel, wrap-
                 pings  of rag or asbestos felt,  plastic film, fiber -
                 glas,  metallic foil, kraft  paper,  or a combina-
                 tion of these are used.  Two types of equipment are
                 used.  One type c onsists of apparatus both to rotate
                 the pipe and move it longitudinally past a station-
                 ary enamel dispensing and wrapping station,  as
                 shown in Figure  236.  In the other method, only
                 the pipe rotates,  and the coal tar or  asphalt kettle
                 and wrapping equipment travel on a track along the
                 length of the pipe (Figure 237).

                 The purpose  of  tlie wrapping is to  make the pipe
                 covering more durable during handling and install-
                 ing as well as  increase its aging and moisture ex-
                 clusion properties.  The  enamel  has a dual pur-
                 pose--in addition to its corrosion-resisting func-
                 tion,   it serves as an adhesive for  the wrapping.

                 Preparation  of Enamel

                 Both  coal tar and asphalt are shipped to the con-
                 sumer in solid,  100-pound,  cylindrical or octa-
                 gonal  castings or in 55-gallon fiber  drums weigh-
                  ing about 650 pounds.   Before being charged to the
                 melting equipment the material is manually chopped
                 into chunks weighing 20 pounds or less.  The ma-
                 terial  is melted and kept at application tempera-
                 ture in natural gas-, oil-,  or LPG-fired kettles.
                  THE AIR POLLUTION PROBLEM

                  By far the largest source  of air pollution from as-
                  phalt or coaltar operations is the dense white emis-
                  sions  caused by vaporization and subsequant con-
                  densation of volatile  components in the enamel.

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                                         Pipe-Coating Equipment
                                                                                                     393
                           Figure  286.  Stationary kettle type of pipe-wrapping equipment and scrubber:
                           (top) Closeup,  (bottom) overall  view (Pacific Pipeline Construction Co.
                           Montebello,  Calif.).
Figure 287.  Traveling kettle-type pipe-wrapping equipment  (Southern  Pipe  and  Casing  Co.,
Azusa,  Calif.).

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394
                                      MECHANICAL EQUIPMENT
This cloud is composed of minute oil droplets and is
especially dense whenever the surface of the molten
enamel is agitated.  These emissions are objection-
able on three counts  that  include opacity, odor,  and
toxicity--those from coal tar being the more  objec-
tionable.  The visible emissions are intense enough
to violate most opacity regulations .  The odor of the
emission is pungent and  irritating with consider-
able nuisance-creating potential, and there maybe
the added nuisance caused by  settling oil droplets.
Lastly, the  condensed vapors  and gases are toxic.
Prolonged breathing or  skin  exposure can cause
itching,  acne,  eczema,  psoriasis,  loss  of appe-
tite,  nausea,  diarrhea,  headache,  and other ail-
ments.   Some  medical researchers  have  stated
that the  fumes may also have some  cancer-pro-
ducing potential, but this has not been completely
substantiated.

Although  the fumes are  dense, the actual  weight
oi material emitted is relatively small.  Tests con-
ducted on pipe-wrapping operations using both as-
phalt and coal  tar enamels have shown emissions
ranging  from  a low of  1.8 pounds  per hour to a
maximum of 17.5 pounds per hour.

HOODING AND VENTILATION REQUIREMENTS

Because of  the nature of all three oi the  methods
used to apply asphalt and  coal tar enamels to pipe,
collection of the contaminants is difficult.  Large
quantities of air are  entrained because hoods usu-
ally cannot be placed  close to the  point of  emis-
sion.  In the pipe-dipping operation, after being
immersed,  the pipe must be raised vertically above
the tank and allowed to drain.   Although lip-type
hoods around the tank periphery may collect most
of the tank emissions, those from the pipe itself
cannot be collected by these hoods.  In wrapping,
especially for  the traveling  application  type of
equipment,  a hood as long as the pipe itself would
be  necessary.   A relatively  small hood over the
wrapping and tar-dispensing equipment can be used
in the stationary kettle  type  of  wrapper.  In the
spinning operation, emissions come from both ends
of the pipe.   Because of the need for  working with
various pipe lengths, hoods at both pipe ends arenot
practical.   One solution  is to install a  stationary
hood at  the end of the pipe where the lance is in-
serted.   A  portable fan  or blower  is used at the
other end to blow air through the pipe, conveying
the emissions  to the hood at the other end.

Another solution of the fume collection problem  is
to house  all the equipment and vent  the building  to
the air pollution  control  system selected.   The
building  itself  then  becomes  the collection hood.
This, of course, dictates a large exhaust air vol-
ume to provide enough draft to prevent  iume ac-
cumulation  and maintain  adequate  room ventila-
tion for  the workers'  comfort  and  safety.  This
method may not be necessary for an isolated spin-
ner or wrapper, but for a dipping process or a pro-
cess using several coating operations, it is more
satisfactory than using ] ocal exhaust systems.  As
adjuncts to the  overall building exhaust  system,
some local hoods at points  of heavy  emissions may
be desirable, especially if these points are in  areas
frequented by operating personnel.
The total volume of contaminated air from a pipe
dipping process can be reduced greatly by totally
enclosing the dip tank within a building.  One end
of the building contains movable panels for access
by cranes,  cables,  and bundles  of pipe.  Such an
arrangement is illustrated by Figures 288 and 239.
The structure above the tank serves as a plenum
chamber  for the collection of contaminant emis-
sions. These  emissions are vented through a duct
opening located at the top of the building at the op-
posite  end  from the end  containing movable panel
openings through which pipes are conveyed.
 The design of the tank and hood requires  installa-
 tion of adequate temperature limit safeguards  and
 sufficient  protection for the  tempe rature-sensing
 elements.  The  lowering of pipes into the dip tank
 can cause damage to unprotected sensing elements,
 and the  lack of adequate safeguards can  result in
 excessive  temperatures within the tank,  A fire
 hazard then exists because of the accumulation of
 vaporized  combustibles above the tank surface.
With  a  properly designed  dip  tank hood, an ex-
haust gas flow rate  of  about 4000  cfm  can ade-
quately control contaminant emissions from a dip
tank measuring  10 feet wide, 55 feet long, and 7
feet  deep.  With the movable panels fully open,
the indraft through the  open areas should be a
minimum  of  150 fpm during the loading and un-
loading of pipe.
The total volume  of  contaminated exhaust gases
from a pipe wrapper also canbe reduced consider-
ably by the proper design of an enclosure as shown
in Figure 290.  The openings  for pipe to enter and
leave the pipe wrapper enclosure  are designed for
less than 1 inch of clearance  with the largest size
of pipe processed.   Profile  templates are  in-
stalled over the  openings to maintain clearances
of less than 1 inch for each size of pipe processed.
Except for the pipe  clearances, the  only  other
access openings  needed during wrapping are for
insertion of the various  wrapping materials and
an  observation port.  These open areas should not
exceed 1 square foot. Other openings,  needed for
maintenance purposes, normally will be closed

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                                         Pipe-Coating Equipment
                                                                                                       3Q5
 Figure 288.   Bundle of pipe  being charged  to dip tank
 enclosed within a building,  which is vented to after-
 burner (Kelly Pipe Company,  Santa Fe Springs,  Calif.).
   Figure 290.  Pipe wrapper vented to afterburner
   (Kelly Pipe  Company,  Santa Fe Springs,  Calif.).
 Figure 289.   Dip tank building with movable panels
 closed after  charging pipe  (Kelly  Pipe Company, Santa
 Fe Spr ings, Ca 11f.).
•while  pipe  is being wrapped,  as shown in Figure
291. With this type of enclosure,  an exhaust rate
of about 1000 cfm is adequate for the collection of
all contaminants  from a pipe wrapper processing
pipe up to  16 inches  in  diameter.   Larger  pipe
requires a higher exhaust rate.  For proper venti-
lation, the minimum indraft at the enclosure open-
ing during  pipe  wrapping  should be at least 200
fpm; this includes allowance for pipe clearance,
insertion of •wrapping materials, and an observa-
tion port and  for air leakage around the various
movable panels.  The enclosure  should  be located
within a building  to avoid wind draft.
Figure 291.   Pipe wrapper  vented to afterburner with
panel removed to show wrapping mechanism  (Kelly Pipe
Company,  Santa Fe Springs, Calif.).
 AIR POLLUTION CONTROL EQUIPMENT

Three basic types of devices can be  considered for
control of the emissions from asphalt and coal tar
application.   These are (1) scrubbers,  (2) incin-
erators (afterburners), and  (3) electrical precip-
itator s.

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396
MECHANICAL EQUIPMENT
Until recently, water scrubbers were used most
frequently for controlling  opacity,  particulates,
and odors from pipe-coating equipment. The baf-
fled,  water spray type  of scrubber has been em-
ployed almost exclusively.  These scrubbers have
been operating satisfactorily by employing 30 gpm
water per l.OOOcfm air  to be scrubbed, at a water
pressure of 50 psig.  A typical scrubber  system
of this type is shown in  Figure 292.
 Figure 292.  Scrubber system to control  emissions
 from  a pipe-wrapping and pipe-spinning  operation
 (Southern Pipe and Casing Co., Azusa,  Calif.).
The  efficiency of scrubbers can be affected  not
only by their basic design, but by operational vari-
ables.  Of  most importance, the  scrubber water
must be kept clean.  If scum and oil are allowed
to collect for any extended period, and the dirty
water  is recirculated, the  spray heads  begin to
plug,   and this lowers the water rate and reduces
the efficiency.  An automatic skimming device is
helpful, but, even so, frequent water changes are
needed.  In some instances, daily water changes
and thorough weekly cleaning, including spray heads,
have been necessary.

Properly designed and operated water  scrubbers
venting pipe-dipping,  pipe-wrapping,  and  pipe-
spinning operations  have  been shown by tests  to
have collection efficiencies of up to 80 percent on
a weight basis and to reduce  visible white  emis-
sions from  over 70 percent to less than 40 percent
opacity.  Emissions  from some scrubbers, how-
ever,  are as high as 35 percent.

In the  largest installation of its type, two identi-
cal water scrubbers, each rated  at 40, 000 cfrn,
are used as  a single  air pollution control system,
as shown in Figure  293.  This equipment vents a
pipe wrapping system that handles pipe sizes from
3. 5 to 9 feet in diameter.
                                                       Figure 293.  Dual  scrubber  venting large-size pipe
                                                       wrapper (American  Bridge Division, U.S. Steel Cor-
                                                       poration, Los Angeles, Calif.).
                 Incineration is the most positive method of com-
                 plete control,  but until recently the cost of oper-
                 ating an afterburner  heating a large quantity of
                 air,  with a relatively small  amount  of contami-
                 nants, was considered to be prohibitive.  Properly
                 designed  enclosures  can reduce the quantity of
                 contaminated air to be handled so that it is  eco-
                 nomically  feasible to  consider the direct-fired
                 afterburner  as a control device.  A direct-fired
                 afterburner venting a pipe-dipping and pipe-wrap-
                 ping system is shown in Figure 294.
                    Figure 294.  Afterburner venting dip tank,  pipe
                    wrapper,  and two asphalt or coal-tar heaters
                    (Kelly Pipe Company,  Santa Fe Springs,  Calif.).

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                                       Abrasive Blast Cleaning
                                             397
The  efficiency  of an  afterburner  serving  pipe
coating operations is affected by both its  basic
design and operational variables.  In general, the
design features must provide for  (1) minimum
exit  combustion chamber temperature of 1500° F,
(2)  a retention time  in the afterburner (exclusive
of the stack)  of 0. 3 second or greater, and (3)  a
gas  velocity through the  combustion  chamber of
15 to 30  feet  per  second.   Refer to  Chapter  5 for
design details on afterburners.

Properlydesigned afterburners venting pipe-coat-
ing  equipment and operating at exit temperatures
of 1400°  F have  efficiencies  of  90 percent  or
greater, based upon the total combustion of hydro-
carbon contaminants. Such efficiencies will reduce
the   dense white  emissions to  zero opacity  and
eliminate odors.

Plant studies show that the heat in the afterburner
exhaust gases can be recovered in a waste heat
boiler. The steam produced can be used to steam-
clean equipment or if the plant manufactures con-
crete-lined pipe, the steam can be used in curing
the  concrete.  Exhaust  gases  also can be used to
heat the   steel pipe  directly prior to wrapping in
order  to  rid  the pipe of  excess moisture  for  a
better bond with materials.

Waste heat cannot be used economically to heat
asphalt or coal tar.   Large amounts  of heat are
required tobring asphalt and coal tar up to coating
temperature, but relatively little heat is  required
to maintain the coal tar or asphalt at coating tem-
peratures.

Electrical precipitator s canbe  used for controlling
emissions from pipe -coating operations , but, again,
their high initial  cost,  as compared with that of
scrubber  systems,  has made them unattractive.
When, however, some of the maintenance and clean-
ing problems connected -with scrubber s , as -well as
the higher basic scrubber-operating costs are con-
sidered, the higher installation cost for precipita-
tors  may be counterbalanced.   Precipitator s  have
been used successfully for controlling the emis-
sions from roofing and  building paper saturators.
In this operation  the emissions are of the same
type  as those from pipe coating, but are generally
much greater in concentration  and  quantity.  In
practically all cases a precleaner, such as a wet
dynamic precipitator,is used to remove large par-
ticles and prevent excessive tar buildup on the  pre-
cipitator parts .  For  pipe-coating operations, the
lower overall emissions may obviate the need for
the precleaner.

Although  scrubbers have been used in the past for
pipe-coating equipment, they are  not as efficient
as afterburners.   Opacities  of emissions from
the   scrubber  reach 35 percent in  some cases.
By having a minimum of access  openings, the en-
 closure  serving a pipe-coating operation can re-
 duce the total volume of gas handled to levels eco-
 nomically feasible  for utilizing an afterburner.
 Net operating cost for the afterburner can be re-
 duced further by utilizing the heat of the  after-
 burner exhaust gases to produce steam in a -waste
 heat boiler, or to preheat pipe prior to wrapping.
         ABRASIVE BLAST CLEANING
INTRODUCTION

Abrasive blast cleaning is the operation of clean-
ing or preparing  a  surface by forcibly propelling
a stream of abrasive material against the surface.
Blast cleaning operations may  be classified ac-
cording to: (1) The abrasive material used, (2) the
method of propelling the abrasive,  and (3) the
equipment used to control the abrasive stream or
move the articles being cleaned into the abrasive
stream.

Abrasive  Materials

Silica sand has been used longer than any other
material,  principally because of its ready avail-
ability and low cost.  It has a rather high breakdown
rate, but is still widely used where reclaiming the
abrasive is not feasible.  Synthetic abrasives,  such
as silicon carbide and aluminum oxide, are some-
times used as a substitute for sand in special appli-
cations.  Extremely fine sand and talc are used in a
water suspensionfor fine finishing. Soft abrasives
such as  ground corn cobs,  cereal  grains,  and
cracked  nut  shells  are  used to  clean without re-
moving  any metal.  Metallic abrasives are made
from cast iron and steel (Stine,   1955).

Cast iron shot is made  by  spraying molten cast
iron into a water bath.  The shot is hard and brittle,
but its breakdown rate is only 2. 5 percent that of
sand.  Cast iron grit is made by crushing the over-
size and irregular particles formed when cast iron
shot is  being made.  The sharp edges  of the grit
give it a very rapid cutting action.  The breakdown
of the  hard,  brittle particles continually exposes
new cutting edges.   Annealed shot is made from
special-alloy  cast iron  and is heat treated to re-
duce its  brittleness.  Its breakdown rate is only
one-third to one-half that of cast iron shot or grit.
Steel shot is produced by blowing molten steel.  It
is not as hard as cast iron shot but is much tougher.
Its  breakdown rate  is only about one-fifth that of
cast iron shot.

Method of Propelling  the Abrasive

Three means  of propelling the abrasive are com-
pressed air, high-pressure water,  and centrifugal
force.

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 398
    MECHANICAL EQUIPMENT
Two types  of  compressed-air blasting machines
used are suction blast and direct-pressure blast.
The suction method uses two rubber hoses connect-
ed to a blasting gun.  One of the hoses is connected
to the  compressed-air supply,  and the other is
connected to the bottom of the abrasive supply tank,
\vhose  top is open.  The gun,  as shown in Figure
295 (topleft), consists of a casting with an air noz-
zle that discharges into a larger nozzle.   The abra-
sive hose  is attached to the  chamber between the
nozzles.  The high-velocity air jet,  expanding into
the larger nozzle, creates  a partial vacuum (12 to
1 7 inches mercury) in the chamber, and the abra-
sive is drawn in and expelled through the discharge
nozzle.  In the  direct-pressure  types,  as shown
in Figure  295 (bottom left),  the abrasive supply
tank is  a pressure vessel with the compressed-
air line connected to both  the top and bottom dis-
charge  line.   This permits  abrasive  to  flow  by
gravity into the discharge hose without loss of pres-
sure.  Direct-pressure machines propel from 2 to
4times as much abrasive per cubic foot of air (at
equal pressures) as suction-type machines  do, but
the cost of the  suction machines is less.  Com-
pressed air is also used in wet sandblasting.  In
a specially designed direct-pressure machine, as
shown  in Figure 295  (bottom right), the abrasive
supply  tank is flooded with water,  and a mixture
                      of sand and water is propelled by the compressed
                      air.   Wet  sandblasting can also be accomplished
                      by attaching a special nozzle head v/ith a water hose
                      to the nozzle of a direct-pressure machine as shown
                      in Figure  296.

                      In hydraulic blasting, the propulsive force  is high-
                      pressure  water.  A mixture of water and sand is
                      propelled through  a nozzle with great force by a
                      pump that develops  a  pressure of 1, 000 to 2, 000
                      psi.  Sand reclamation is usually practiced in these
                      systems.   Figure 297  is a diagram of a complete
                      hydraulic blasting system.  Equipment such as this
                      is used for  core knockout and for cleaning very
                      large castings,  heat exchanger tube bundles, and
                      other large pieces of equipment.
                      Centrifugal force is the third method of propelling
                      abrasive .  Abrasive is  fed to the center of a rotating
                      impeller,  slides along spoke-like vanes,  and is
                      discharged with great force in a controlled pattern.
                      Figure 298  shows  one type of abrasive impeller.
                      Metallic abrasives are  used with this type of  equip-
                      ment.

                      Equipment  Used  to  Confine  the  Blast

                      The oldest and most widely used device to confine
                      and  control  the blast is the blasting room, which
                 RUBBER TIP
     NOZZLE
          ABRASIVE HOSE-
          CONNECT ION
         No. 6 HOSE CLAMP •
-NO  2', HOSE CLAMP
^ s-in  AIR HOSE
                                                              AIR -J
                             1 ABRASIVE  HOSE
                                                                                      ABRASIVE DRAWN INTO
                                                                                      GUN BY SUCTION
                                                             <*$
                              AIR SUPPLY VALVE
                                AIR
                               CHOKE
                               RELIEF
                               VALVE
                               EQUAL AIR PRESSURE
                               ABOVE AND BELOW
                               ABRASIVE
                                                                        ::S::f:ABRATrvTwSlti
                                                                        EUs ABRASIVE •;«•;>
                                                                                      AIR SUPPLY VALVE

                                                                                            AIR
                                                                                       fi-
                                                          CHOKE
                                                          RELIEF
                                                          VALVE
                                                         EQUAL AIR PRESSURE
                                                         ABOVE AND BELOW
                                                         ABRASIVE
    Figure 295.  Types of compressed-air blasting machines:  (top left) Suction  gun,
    type blasting machine,  (bottom left) direct-pressure blasting machine,  (bottom
    machine (Bulletin No. 100B,  Pangborn Corporation,  Hagerstown,  Md.).
                                                 (top  right) suction-
                                                 right) wet blasting

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                                        Abrasive Blast  Cleaning
                                                 399
                                      WATER
Figure 296.   Adapter  nozzle that  converts dry
sandblasting to  wet  sandblasting (Sanstorm
Manufacturing Co.,  Fresno, Calif.).
 consists  of  an enclosure with the operator inside
 manipulating the blast from a hose.  Blasting rooms
 vary widely in their  construction.  One popular
 design  is  the  all-steel,  prefabricated  room -with
 floor grating and a completely automatic abrasive
 recovery system.  These rooms usually use metal
 grit or shot and  often  have  monorail  conveyors,
 rail cars, or rotating tables  to aid the operator in
 handling the objects, which  are usually large and
 heavy.   Less  desirable designs,  but  sometimes
 adequate,  are  makeshift rooms  of wooden con-
 struction used for infrequent sandblasting opera-
 tions.
 For cleaning  small parts, the  blasting cabinet is
 frequently used.   A blasting cabinet consists of a
 relatively small enclosure with openings to which
 are attached long-sleeved rubber or  canvas  gloves
 by which the  operator,  from outside  the  cabinet,
 manipulates the blasting gun and objects to be abra-
 siveblasted, as depicted in Figure 299.  All types
 of  abrasives are  used  in cabinets --sand,  metal-
 lies, soft abrasives, and slurries.
 Centrifugal impellers are usually incorporated in-
 to  a machine that  handles the objects so as to ex-
 pose all surfaces to the blast.  The  two most com-
 mon types are those using tumbling action and those
 containing rotating tables, as shown in Figures 300
 and 301.  Special  machines are made for  specific
 jobs,  such as  cleaning  sheet metal strip.   The
 housing  of  these  machines confines the blast and
 its effects.   Automatic  abrasive recovery and re-
 cycle  equipment are used.

 Another machine consists of  a perforated drum  or
 barrel  rotating  inside   a  cabinet.    A blast gun is
               CITY H.O SUPPLY
                                HEW SAND ADDED THROUGH FLOOR OF ROOM
             NOTE'  SLOTS FOR GUN
             IN DOORS ALONG ENDS
             OF ROOM AND ACROSS
             FRONT OF mm.
             OPERATOR IS IN NORMAL
             POSITION
SLUDGE
PUMP
                                                                                              i 10 SEWER
FLO* HIGH-PRESSURE HATER FROM PUMP TO GUN
SLURRY OF SAND AND WATER FROM BLAST SAND TANK TO GUN
SAND, HATER  FLOWING THROUGH FLOOR ACROSS SCREEN
S»ND, WATER, FOULING  IN SLUDGE TANK PUMPED
TO CLASSIFIER SECTION
ACCEPTED SAND DROPS INTO BLAST SAND TANK FOR REUSE
FINES AND FOULING REJECTED BY CLASSIFIER
FLUMED TO SLUDGE COLLECTOR
SLUDGE COLLECTOR THICKENS AND REMOVES REJECTED
FINES AND FOULING AND THUS PROTECTS SEWERS
USED H,0 FLUMED TO SEWER
            Figure  297.  Hydraulic blasting system (Pangborn  Corporation, Hagerstown,

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400
                                      MECHANICAL EQUIPMENT
  Figure 298.   Centrifugal  impeller  for  metal I i c
  abrasives  (Wheelabrator  Corporation,  Mishawaka,
  Ind.).
                                                           Figure 300.  Blast cleaning machine that uses
                                                           tumbling action (Wheelabrator Corporation,
                                                           Mishawaka,  Ind.).
      Figure 299.  Blasting cabinet  (Pangborn
      Corporation, Hagerstown,  Md.).
Figure  301.  Blast cleaning machine containing
multiple rotary tables (Pangborn Corporation,
Hagerstown,  Md.).

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                                        Abrasive Blast Cleaning
                                                                                                   401
mounted  so  as  to project through one end of the
drum.  Tumbling  action  exposes all parts of the
objects to the blast.  Both sand and metallic abra-
sives are used.   Abrasive-recycling  equipment is
usually provided.
THE AIR POLLUTION PROBLEM

The amount of dust created by abrasive blast clean-
ing varies  widely with the abrasive used,  parts
being cleaned, and propelling medium.  Dry  sand-
blasting produces large dust concentrations as a re-
sult of breakdown of the sand.  Metallic abrasives,
of course, produce less dust but can produce  heavy
concentrations in cleaning such things as castings
with  considerable amounts of adhering  sand.  A
typical particle  size analysis of emissions when
using steel shot  or  when using  sand is shown in
Table 113. The dust  concentration is small during
wet blasting or when metallic abrasives are used
for tasks such as removing 'welding and  for heat
treating scale.
 Blast cleaning rooms  are ventilated by baffled in-
 let openings,  usually in the  roof,  and exhausted
 from near  the floor.  Recommended  ventilation
 rates vary from 60 to  100 fpm across the floor
 area with 80 fpm the usual choice (Industrial Ven-
 tilation, I960).  These rates  are based mainly on
 the  maintenance  of visibility in the room.  The
 usual requirement for dust control is an  indraft ve-
 locity of at least 500 fpm through  all openings (ibid).
 By making the openings small, a  small exhaust
 volume suffices to meet the requirement, but visi-
 bility is so poor during  sandblasting as to impair
 the  operator's  effectiveness seriously.   Health
 codes require that the operator wear an air-sup-
 plied,  Bureau of Mines  approved abrasive blast-
 ing helmet.


 The  ventilation requirement for blast  cabinets is
 similar  to  that for blasting rooms.   Twenty air
 changes per  minute are  usually recommended,
 based  primarily  on the  maintenance of visibility.
 Even during wet sandblasting,  this exhaust rate is
 usually required for maintenance of visibility.
   Table 113. MICROMEROGRAPH PARTICLE
  SIZE ANALYSIS FROM BAGHOUSE SERVING
    JOB-SHOP ZINC-GALVANIZING KETTLE
Steel shot
Particle
diameter,
M-
1. 7
2. 8
4. 5
6.7
8. 4
9.5
10. 6
11. 7
15. 1
20. 1
26.8
33. 5
41. 9
50. 3
67. 0
100. 6
150.3
Cumulative
weight,
%
1. 4
4.7
7. 8
10. 3
12. 2
13.4
14. 8
16. 0
19.3
23. 0
28. 6
35.7
44. 3
52. 1
62.7
73. 1
80. 5
Sand
Particle
diameter,
M-
1.6
2.7
4.4
6.6
8. 3
9.3
10.4
11.5
14.8
19. 8
26. 4
33. 0
41.2
49. 5
65. 9
98. 9
147. 8
Cumulative
weight,
%
0.4
1.8
5.3
11. 1
15. 6
18.2
21.6
24.6
33.2
41. 3
50. 1
58.7
65. 6
72. 1
82. 0
96.5
100. 0
For blasting barrels, rotary tables ,  and tumbling-
type machines, the general rule of 500 fpm indraft
velocity at all  openings is applicable.  The total
area  of openings of some machines is difficult to
measure; however,  the manufacturer usually speci-
fies the required ventilation rate.  This rate in-
cludes sufficient airflow to remove excess fines so
as  to maintain the abrasive in an optimum condi-
tion.
                                                      AIR POLLUTION CONTROL EQUIPMENT

                                                      For dust of such widely varying concentration and
                                                      particle size as is produced in the various blast-
                                                      ing operations,  the baghouse  is the most widely
                                                      used  type  of  collector.  The positive  collection
                                                      mechanism of the baghouse ensures virtually 100
                                                      percent collection efficiency for an adequately sized
                                                      unit in good condition.  The filtering velocity should
                                                      not exceed 3 fpm.  Standard cotton sateen cloth
                                                      bags are adequate for this service.  Since virtual-
                                                      ly all blast cleaning operations are intermittent,  a
                                                      noncomp.artmented baghouse can be  considered.

                                                      A scrubber of good design  collects the bulk of the
                                                      dust, and -wet collectors are used to some extent.
                                                      A scrubber  of high power  input is,  however,  re-
                                                      quired for collecting the very fine dust.
HOODING AND VENTILATION REQUIREMENTS

The structures previously described to control the
blast act as hoods,  and exhaust ducts  are attached
to them for ventilation.
Wet sandblasting does not require collection equip-
ment and provides a means of blast cleaning build-
ings, bridges,  and other structures without cre-
ating a dustnuisance.  Collecting the dust from dry
sandblasting of  structures such  as these would be
very difficult or impossible.

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 402
                                     MECHANICAL EQUIPMENT
     ZINC-GALVANIZING EQUIPMENT

INTRODUCTION

Zinc galvanizing may be defined as the art of coat-
ing clean, oxide-free iron or steel •with a thin layer
of zinc by immersion in molten zinc held at tem-
peratures  of  840° to 860°F (Elliott et al. ,  1961).
In order to achieve optimum results,  the  funda-
mental processing steps to be followed are:

1.  Degreasing in a hot, alkaline solution;

2.  rinsing thoroughly in  a water rinse;

3.  pickling in an acid bath;

4.  rinsing thoroughly in  a water rinse;

5.  prefluxing  in zinc ammonium chloride  solu-
    tion;

6.  immersing the article in the molten zinc
    through a molten flux cover;

7.  finishing  (dusting with sal  ammoniac to pro-
    duce smooth  finishes).
When considering  the air pollution aspects of the
galvanizing operation, one  might be  inclined to
omit the first five steps because they do not normal-
ly produce excessive air contaminants.  Improper
degreasing  does,  however,  increase the genera-
tion  of  air  contaminants when the article is im-
mersed in the hot zinc.  Moreover,  stripping pre-
vious zinc  coatings in the pickling tanks causes
excessive acid mists to be generated.
 Cleaning

 If an article  is  not thoroughly degreased, an oil
 mist is discharged  when the article is dipped into
 the  molten zinc. If the  articles are not properly
 pickled and  rinsed, more flux must be used to
 achieve the desired  coating, which in turn  creates
 more fumes.  It is important, therefore, to de-
 grease,  pickle,  and rinse thoroughly the articles
 being galvanized,  not only to obtain a good zinc
 coating, but also to reduce the  generation of fumes
 and  facilitate the collection of unavoidable fxim.es.
 it enters the zinc.  Figure 302 shows the flux cover
 on one end of a galvanizing kettle.
The flux is thought to create most of the air con-
taminants from a galvanizing operation; therefore,
a description of fluxes , their composition and action
is of value.  The  theory is that,  regardless  of
whether ammonium chloride  or zinc ammonium
chloride is used, the composition of the usable flux
cover is molten zinc chloride in which ammonium
chloride  is  absorbed and ammonia and hydrogen
chloride  gases are trapped.  The  active cleaning
agent is  the hydrogen chloride gas formed by the
dissociation of ammonium  chloride  due to  heat.
Zinc chloride  is present either because it was
placed  there with  the ammonium chloride  or be-
cause of the reaction of hydrogen chloride with the
molten  zinc.  The zinc  chloride  is necessary to
maintain the active ingredient on the zinc surface.
To  form a flux cover,  either ammonium chloride
or,  preferably, zinc ammonium chloride is placed
on  the molten zinc surface.   Usually a foaming
agent such as glycerine is added to the flux before
it is applied to the kettle.  If ammonium chloride
is  used, the heat from the zinc causes the salt to
decompose  and form hydrogen chloride and am-
monia gases.  Both gases tend to  rise and  escape
from the  kettle where they cool and recombine to
forma fume of ammonium chloride.  Because the
hydrogen chloride and zinc are very reactive,  they
form zinc chloride, which remains on the zinc as
a liquid at the temperature of the zinc bath.   Since
only part of the hydrogen chloride is used up in
this reaction, the fumes escaping contain an  excess
of ammonia. As more ammonium chloride is  add-
ed  to the zinc surface,  the zinc  chloride  that is
formed begins to absorb it.  At the  same  time  a
foam filled with hydrogen chloride and ammonia
gases is formed.  The foaming agent increases the
depth and fluidity of the foam.  If foaming-type zinc
ammonium chloride is used as a starting material,
the  zinc chloride merely melts, trapping the bulk
of  the gases  formed,  and retards the deposition
of the ammonium chloride.  The flux cover is made
much more  easily and with less fuming -when the
foaming-type zinc ammonium  chloride is used in
place of ammonium chloride.
Cover Fluxes

On the  assumption that  the  article was properly
prepared for dipping in  the  molten  zinc,  a flux
must still be used to remove the  oxide film that
forms as the  article is being transported from the
last rinse tank to the galvanizing kettle.  To exclude
air from the part after fluxing, the flux is floated
on the zinc surface  so that the article is fluxed as
The flux cover has a number of important functions
in addition to the cleaning action already mentioned.
It serves as a preheating and drying medium to re-
duce  spattering  or explosions in the molten zinc,
and distortion of thin metal sections.   It keeps the
zinc surface free of  oxides, which, if occluded in
the coating, tend to  dull it and retard drainage of
zinc from the work.  Heat losses  from the kettle
are also reduced.

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                                      Zinc-Galvanizing Equipment
                                                                                                   403
                            Figure 302.  Removing work through a cl
                            Flux cover in foreground (Los Angeles
                            Huntington Park,  Cal i f.).
           ean zinc surface.
           GaI vanizing Co.,
Foaming Agents

If  galvanizing  is  done with a thin layer of molten
flux,  a higher temperature is reached throughout
the flux layer that induces  fuming and loss of flux
ingredients.  The flux becomes  viscous and inac-
tive in a short period  of time,  requiring frequent
additions of fresh flux to keep it in prime condition.
The thin molten  flux  cover can be  fluffed  up by
additions of foaming agents  such as glycerine,  wheat
bran,  wood flour, sawdust,  and others.   The re-
sulting deep-foaming type of flux cover has the ad-
vantage of  reducing the quantity of objectionable
fumes. Some other advantages are longer  flux life,
greater ease of control in maintaining fluidity and
fluxing activity,  reduction of zinc spattering, and
saving of flux, zinc, and heat.
Dusting  Fluxes

After an article  to be galvanized has been charged
into the kettle through the flux cover,  and while it
is still completely immersed in the zinc bath, it is
moved to a portion of the kettle where it can be re-
moved through a clean zinc surface (see Figure 302).
If the articles are small, such as  bolts, nuts, nails,
and so forth,  they are usually dusted with powdered
ammonium  chloride  immediately upon  removal
from the molten zinc.  The dusting flux causes the
zinc to flow and results in a smooth, bright finish.
The dusting must be done before the work has time
to cool off,  since the zinc coating must still be
molten  in order to flow and drain properly from
the work.  At the  temperature of the molten zinc,
the flux decomposes  generating  fumes.
To  achieve the required foaming action,  a small
but definite amount of foaming agent is added to the
flux.   Too little or too much accelerates the rate
atwhichthe flux becomes too viscous.  To  reduce
the amount of fuming,  the foaming agent should be
mixed with the flux before the flux is placed on the
surface  of  the  zinc bath.   Of the foaming agents
mentioned, glycerine seems to be the most efficient.
Observations  of the fuming tendencies of various
proprietary foaming-type  fluxes  have shown that
some fume more than others.  The compositions
of the proprietary foaming agents have not been re-
vealed by vhe manufacturers.
THE AIR POLLUTION PROBLEM

Observations of many galvanizing kettles have re-
vealed that air contaminants  are discharged when-
ever the flux cover is disturbed,  fresh flux is add-
ed, or galvanized objects are dusted with ammoni-
um chloride.
Flux agitation occurs to some extent each time an
object is immersed in the zinc through  the flux
cover.  If  the objects are smooth and dry and the
agitation is  not  great,  the amount of fuming  is
 234-767 O - 77 - 28

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404
MECHANICAL EQUIPMENT
small.  When the agitation is severe a correspond-
ingly larger amount of fumes  is discharged.  Me-
chanical actions that break some of the bubbles
making up the flux cover release  fume-forming
gases.

When fresh  flux is placed on the molten metal in
a kettle,  some time is required for it to form a
foaming cover and,  during this interval, dense
fumes  escape.  Moreover, •when fresh  flux is
stirred into the existing flux cover, fumes are dis-
charged as a result of the agitation and the time
necessary for the fresh flux to be absorbed by and
become part of the foam.  If the air contaminants
were due only to the volatile constituent in the flux,
the fumes would consist only of ammonium chlo-
ride.  Zinc, zinc chloride,  and oil, among other
materials,  have,  however,  been identified in the
particulate matter  discharged  from  galvanizing
kettles.

Zinc and zinc chloride have very low vapor pres-
sures  at  normal galvanizing temperatures, and
one would expect neither of them to vaporize to any
great extent. The emissions from these materials
are believed to be the result of mechanical entrain-
ment,  -which occurs when  wet articles  are gal-
vanized.  Frequently an object is  immersed too
rapidly, which permits  some of the steam to vent
into the molten zinc belowthe flux cover,  the rapid-
ly escaping  steam  atomizing some zinc and flux
into the air.

Cases  have been observed where the articles to be
galvanized are not cleaned thoroughly  of materials
that volatilize at the temperature of the molten ^inc.
In one case, the cleaning and pickling solutions  did
not remove all the  lubricant from chain link fence
material.   The oil was vaporized and discharged
as  an  oil rnist with the fumes from the flux cover.
The oil,  in fact,   formed about half of the fumes
discharged.  In another case,  sulfur was not re-
moved from an object before it  was  charged to the
kettle.  The resulting fumes were yellow and much
more opaque than would normally be  expected.

To obtain brighter,  smoother finishes,  especially
on  small items, the items are dusted with finely
ground sal ammoniac immediately after being re-
moved from the molten zinc.  The items dusted are
still at a temperature well above the  decomposition
temperature of sal ammoniac.   Nearly all the flux
is, therefore, converted to fumes by the  operation.
Although only small amounts of dusting fluxes are
used,  dense fumes  are  always  created.
Physical  and Chemical  Composition
of the Contaminants

The appearance and, composition of the fumes dis-
charged from galvanizing operations vary accord-
                 ing to the ope ration being conducted.  For example,
                 the galvanizing of nuts, bolts,  and other small ar-
                 ticles  does not  create much agitation of the flux
                 cover, and emissions are slight.  Some fumes are,
                 however, generated when the articles are  dusted
                 •with ammonium chloride upon  removal  from the
                 zinc bath.  An analysis  of these fumes  revealed
                 that essentially only ammonium chloride was pres-
                 ent.

                 When many different articles are galvanized,  some
                 disturb the flux and produce more fumes than others.
                 The fumes also contain substantial amounts of com-
                 pounds other than ammonium chloride.   The gal-
                 vanizing of chain link fence material continuously
                 agitates  the flux  cover and results in a continuous
                 discharge of fumes from the kettle.  The visual ap-
                 pearance of the fumes as they are discharged into
                 the air from the  various operations is the same--
                 that of light gray smoke.  Even under a microscope
                 the fumes from the various sources have the same
                 appearance.  Figure  303  is a photomicrograph of
                 a sample of the fumes, indicating that  the average
                 particle  size  is approximately 2 microns.

                 Under some  circumstances  the fumes  may have
                 different characteristics, but these are attributed
                 to the influence of additional contaminants.  For
                 example, Table  114 shows  the  comparison of the
                 catch from an electric precipitator serving a chain
                 linkfencing process kettle •with the catch  of a bag-
                 house  serving a  job shop kettle.

                 The material collected by  the  baghouse was dry
                 and powdery,  but it did agglomerate and was diffi-
                 cult to shake from the bags with ordinary bag-
                 shaking procedures. The  material taken  from the
                 precipitator was  sticky and had the general appear-
                 ance  of  thick grease.  Table 114 shows that the
                 fumes are  different chemically,  which  explains
                 their different appearance  after  being  collected.
                 The oil  in the fumes collected by the precipitator
                 undoubtedly came from  a film  of oil on the chain
                 link fence material that was vaporized as the fence
                 material -was charged into the hot zinc.
                  HOODING AND VENTILATION REQUIREMENTS

                  In order to control the emissions from a galvaniz-
                  ing kettle, the fumes generated must be  conducted
                  to  an efficient  control device.   In job shops, the
                  headroom needed makes necessary the use of either
                  high-canopy or  room-type hoods as shown in Fig-
                  ures 304 and 305.  The amount  of ventilation vol-
                  ume required with high-canopy  hoods increases
                  considerably with the height of the hood; therefore,
                  the  size of the  collector must be large enough to
                  accommodate the large volumes required.

                  Slot hoods are used only when the area of fume gen-
                  eration is  small,  such  as  the flux box of a chain
                  link fence-galvanizing kettle shown in Figure 306.

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                                     Zinc-Galvanizing Equipment
                                             405
                          Figure 303. Photomicrograph of  fumes  discharged from a
                          galvanizing kettle.
      Table 114.  CHEMICAL ANALYSES OF
          THE FUMES COLLECTED BY
      A BAGHOUSE AND BY AN ELECTRIC
         PRECIPITATOR FROM ZINC-
            GALVANIZING KETTLES

Component
NH4C1
ZnO
ZnCl2
Zn
NH3
Oil
H2°
C
Not identified
Fumes collected
in a baghouse
(job shop kettle),
wt %
68.0
15. 8
3.6
4.9
1,0
1.4
2. 5
2.8
-
Fumes collected
in a precipitator
(chain link galvanizing)
wt,%
23. 5
6. 5
15. 2
-
3. 0
41. 4
1. 2
-
9. 2
The slot velocities needed to overcome the thermal
draft for the entire  surface of a large kettle are
high, and large air volumes  cool the surface of a
zinc bath.  This cooling effect creates problems in
applying a good zinc coating and increases fuel con-
sumption.  When a slot hood can be used, the amount
of ventilation required is smaller than that required
with high-canopy hoods,  and control devices are
correspondingly smaller.

Low-canopy hoods can be used  on a kettle when
headroom  is  not  required.   These hoods permit
Figure 304.   High-canopy hood over a galvanizing
kettle  (Superior  Pacific Galvanizing Company,  Inc.
Los Angeles,  Calif.).

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406
                                    MECHANICAL EQUIPMENT
 Figure 305.   Opening  to  a  room-type hood over a
 galvanizing kettle  (Los Angeles  Galvanizing Co.
 Huntington  Park,  Cali f.).
lower ventilation rates for adequate fume capture,
and smaller  control devices can be used.


AIR POLLUTION  CONTROL EQUIPMENT

To collect fumes having particle sizes of 2 microns
or less  requires  a high-efficiency collector such
as a baghouse or  an electrical  precipitator.   A
baghouse can be used for any galvanizing operation
where the air contaminants do not contain oil mists.
When an oil  mist  is present a precipitator should
be used.

Several  scrubbers,  similar to the one  shown  in
Figure 307, have been installed in attempts to con-
trol the  emissions from  galvanizing  kettles, but
all have been unsatisfactory.  Stack analyses dis-
closed that the amount of fumes collected by these
scrubbers was negligible.  In each of the scrubbers
the contaminated gases were conducted around baf-
fles,  through water  sprays,  and finally,  through
mist eliminators.   Water was recirculated through
the scrubbers with only  sufficient makeup to re-
place the amount lost due to evaporation and mist
discharge.  The water pressure at the spray heads
was approximately 25 psig in  each scrubber.


Baghouses

Cotton cloth bags have been found to be  an effective
filtering medium for  baghouse s serving the fumes
 Figure 306.  Slot-type hood  serving  a  chain  link fence-
 galvanizing flux box (Anchor  Post Products,  Inc.,  of
 California,  Hhittier,  Calif.).
             Figure 307.  Water-wash scrubber serving
            a continuous chain link galvanizing
             kettle.

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                                      Zinc-Galvanizing Equipment
                                                                         407
discharged from most galvanizing operations. Nei-
ther  the fumes nor the gases discharged are del-
eterious to  cotton,  nor are they corrosive to the
baghouse shell. Because of the large volume of air
needed to  capture the air contaminants,  the tem-
perature of the gases is well below the 180°F limit
of cotton bags.

The tendency  of  fumes  to agglomerate enhances
filtration;  however, the fumes also  cling  to the
bags,  and  cleaning of the bags becomes difficult.
Ammonium chloride, being hydroscopic, picks up
moisture from the air and  becomes a salt that
encrusts on  the bag surface.  If the  air stream is
heated  to  150° F, which is  above the dew point,
the fumes  are  a light,  fluffy powder and are easy
to remove from the bag  surface. When the filter-
ing velocity is below 2 fpm, mechanical shaking
is sufficient to remove the fume.   Between 2 and
3 fpm, more frequent  mechanical  shaking  is re-
quired,  with  additional vigorous  hand  shaking
every 2 weeks.  If filtering velocities  exceed  3
fpm,  the bags become blinded and the fumes can-
not be removed.

A typical particle-size analysis of emissions from
a baghouse  serving a job-shop zinc-galvanizing
kettle is given below:
       Particle
     diameter,  (j.

          1.7

          2. 1

          2.8

          3. 5

          5.6
          8.3
         10. 4
         11.8
         13. 9
         25. 0
         41.7
         83.4
        104. 0
Cumulative
 weight,  %

     0.0

     2.6

    11.5
    21.0

    41.5

    62.5
    70. 0
    74. 0
    80.5
    88.5
    92.0
    99.0
   100.0
Because low  filtering velocities are required for
effective filtration, andlargeexhaustvolum.es, for
adequate fume capture, the baghouse will be large.
Figure  308 shows a baghouse -with 13, 200  square
feet of filter area being used to control the fumes
discharged from the kettle shown in Figure 304.

The following example shows some of the factors
that mustbe considered in designing a control sys-
tem for a galvanizing kettle.
 Figure 308.  Baghouse serving a galvanizing kettle
 (Superior Pacific Galvanizing Co.,  Inc.,  Los
 Angeles,  Calif.).
Example 32 (Figure 309)

Given:

A galvanizing kettle, 4 feet wide by 25 feet long by
3 feet high contains molten zinc at a maximum tem-
perature of 860 °F.  The products of combustion
do not mix with the air contaminants from the ket-
tle.  The oil and moisture content of the contami-
nants are as sumed to be negligible.  The hood con-
figuration is such that one side will be  a part  of the
building \vall extending to the floor, and  the  oppo-
site side will be constructed of sheet metal,  extend-
ing to within 8 feet from the floor.  The ends  of the
hood must be provided with crane-way access open-
ings 16 feet above the floor.
        HOOD
                                                                       HOOD
                                                                      KETTLE
                                Figure  309.  Design  of  problem  presented  in
                                example 32.

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408
                                     MECHANICAL EQUIPMENT
Problem:

Determine the design features of an air pollution
control system using a baghouse.

Solution:

By using the methods described in Chapter 3, the
required exhaust rate (Q) can be determined.

The method involves calculating: (1)  The heat loss
(H) from the process,  (2) the hot air induction rate
(Qz)>  (3) the dimensions of the column of hot air
at the base  of the hood, (4) the hood dimensions,
(5) the required exhaust rate  (Q), and  (6) the tem-
perature  of  the  exhaust gases.  The  sizes of the
ductwork, baghouse, and fan can then be calculated.

1.  Heat loss from kettle:

    For horizontal hot surfaces
                                                      the hot surface.   The hot surface in this case
                                                      is  rectangular,  4 ft wide by 25 ft long.  The
                                                      expansion of the column of hot gases is due to
                                                      mixing with  cooler  air.   The cool air mixes
                                                      from  all sides and  is motivated by the tem-
                                                      perature differential.  When the cool air  pene-
                                                      trates  halfway through the  column it meets
                                                      cool air entering from the opposite side,  and
                                                      thus cancels the  driving force.  From this  it
                                                      is apparent that the short dimension of the ho.t-
                                                      air  column must control the  expansion  of the
                                                      column.  Therefore, B =  4 feet.

                                                      Z  =  13  + (2)(4) = 21 ft
                                                    Q   =  7.4 (21)    (2.660)1'3 =  9,800 cfm.
                                                      ^!_i
                                                  3.  Dimensions of hot gas column at base of hood:

                                                               V0. 88
                                                          D   =
                                                                 (Z)
                                                                         (from Chapter  3)
     H
     A
                         5/4
         --  A   (At)      (from Chapter 3)
        60     s
     =  Hot surface area =  (4)(25) = 100 ft
                                               2
                                                    D  =   B  (See explanation in Item 2 above.)

                                                              ,0. 88
                                                          D  =
                                                                 (21)
                                                                          14.6
                                                                                     =  7. 3 f t
 At
At
            Temperature difference between the hot
            surface and the atmosphere

            Assume air temperature to be 70 °F

            Maximum zinc temperature = 860°F

            860 - 70  =  790°F
H  =
            6 0
             (1QO)(790)
                          C / A
                               =  2,660 Btu/min.
2.   Hot air induction rate:

     Qz  =  7.4(Z)3/2 (H')1/3  (from Chapter  3)

     Z = effective height from the hypothetical point
     source to the base of the hood = Y + 2B

     Because  of the configuration  of the hood,  the
     value  of Y is not clear.  Although  one  side of
     the hood extends to the floor and the other side
     is 5 feet above the kettle, there will be open-
     ings in each end extending to 1 3 feet above the
     kettle. To ensure capturing the air contami-
     nants,  design for a hood height of  Y =  13 feet
     above the kettle.

     The value for B  also is not clear.   In the der-
     ivation of the equation, B is the  diameter of
     the hot surface and is used to calculate the  ex-
     pansion of the column of hot gases arising from
    Assume  that the length -will expand the same
    amount as the width.

       Width expansion  =   7.3   -   4   =   3. 3 ft

          Length  =  25  +  3.3  =  28.3ft

    Dimensions of hot gas  column = 7. 3-ft -width
    by 28. 3-ft length.

4.   Hood dimensions:

    Crossdrafts across  each hood  will be mini-
    mized because  the  sides of the hood  are low,
    extending to the floor  on one side and 5 feet
    above the  kettle on the other side.  The high
    openings on each end of the hood could,  how-
    ever,  cause crossdrafts,  blowing the fumes
    away from  the  hood.   The hood  dimensions
    should be  larger than  the dimensions of the
    rising hot  gas  stream,  the  length being ex-
    tended more than the -width.   A hood with di-
    mensions of 1 0 feet-wide by 40 feet long should,
    therefore,  be provided.


5.   Required exhaust rate:

    Q  =  Q    +  VA   (from Chapter 3)


    V  =  velocity of indraft required to keep air
           moving into all areas of hood.

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                                      Zinc-Galvanizing Equipment
                                                                     409
    A   =  hood area not occupied by the entering
          hot gas current.

    Design for V  =  100 fpm

A  = (10 x 40) - (7. 3 x 28. 3) = 400 - 206 = 194 ft2


 Q=  9,800  +  (100)(194) =  29, 200 cfm

      Design for 30, 000  cfm.

6.  Exhaust gas temperature:

    The temperature  rise of the air is:

                H        „   L
     Exhaust gas temperature = 75 °F.

     The temperature rise is not sufficient to affect
     any of the following calculations , and is, there-
     fore, neglected.


7.   Duct diameter between hood and baghouse:

     Use recommended velocity of 2, 000 ft/min
                                 30,OOP        2
     Duct cross-section area  =  ———•—  = Ib it
                         4
                         d
=  15 ft

=  4. 37 ft
    Use a duct diameter of 52-1/2 inches

    Note:  By using a velocity greater than the min-
    imum, the duct diameter can be decreased to
    reduce construction costs.  Horsepower re-
    quirements will,  however, be  increased.

    Required filter area of baghouse:

    Provide a filtering velocity of  2 fpm
    Filterarea =
9.   The exhaust  system and fan calculations are
     made  as  outlined in Chapter 3.   After a sys-
     tem resistance curve is plotted and calculated,
     a  fan  is selected whose characteristic curve
     will intersect the system curve at the required
     air volume of 30, 000 cfm.


Electrical  Preci pitators

The  use of a two-stage, low-voltage-type precip-
itator,  as shown in Figure  310,  has been investi-
  Figure 310.  Experimental  electric precipitator
  used in  a galvanizing  control study (Advance
  Galvanizing Co.,  Los Angeles, Calif.).
gated  for  the  control of galvanizing fumes in the
Los Angeles area.  The investigation led to the use
of the precipitator to control fumes containing oil
from the flux box of a. chain link fence-galvanizing
operation.  The investigation also revealed that the
precipitator could not compete economically "with
a baghouse  to control the  dry and much more di-
lute fumes capturedby a high-canopy hood serving
the entire  galvanizing kettle.

When  only the  flux box of a chain link fence-gal-
vanizing operation was vented,  the air contami-
nants  consisted of 41  percent by 'weight oil mist
and 59 percent fumes.   The  concentration of the
air contaminants in the exhaust stream was 0. 154
grain per  scf.  With an  exhaust gas velocity of 58
fpm through the precipitator, the collection effi-
ciency was  91  percent.   With an air contaminant
concentration  of 0. 072  grain  per cubic foot and a
velocity of  330 fpm through the  precipitator, the
collection efficiency was 79 percent.

When the entire  kettle was vented with the aid of a
room-type hood,  the air  contaminants consisted
of 5 percent by weight oil and 95 percent fumes.
With  an  air contaminant concentration in the ex-
haust gases  of 0. 0072 grain per scf and a gas ve-
locity of 340 fpm through the precipitator, the col-
lection efficiency was zero.  Further tests  of the

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410
                                    MECHANICAL EQUIPMENT
precipitalor at lower velocities were not warranted,
because  at this plant a full-scale precipitator to
serve  the  entire kettle would have to be operated
at a velocity of at least  340  fpm to compete eco-
nomically with a baghouse.

The  following example shows some of the factors
that  must be  considered in  designing an exhaust
system with an electrical precipitator to control
the air contaminants discharged from a chain link
fence-galvanizing operation.
Example 33 (Figure 311)

Given:

A  chain  link fence-galvanizing kettle is provided
with a flux box,  10 inches wide by 10 feel long by
1 foot high.  Zinc  ammonium chloride is used as
a cover  flux in the flux box.  A slot hood is to be
used  along  one side of the flux box to capture the
fumes created.
     Slot area =  "" = °- 85 it;  = i^. 4 in.
     Length = 10 ft  = 120 in.
     Width  =  ~~   =  1.02 in.
3.   Diameter of duct from hood to precipitator:

     Design for  2, 000 fpm
     Use 12- 1 /2-in. -diameter duct.


4.   Cross -sectional area of precipitator:

     Design for 100 fpm

               1, 700
     Area  =
                                                                     100
                         17 ft .
                                        SLOT HOOD
                        CH
                /     FE
                '        MA
        PRECIPITATOR
CHAIN LINK
FENCE
MATERIAL
      Figure 311. Design of problem presented  in
      example 33.
Problem:

Determine the design features of an air pollution
control system using an electrical precipitator.


Solution:

1.   Exhaust volume:

     Design for 200 cfm per ft  of flux box area


     Area  =  —  (10)   =   8. 33 ft


              (8. 33)(200)   =   1, 666 cfm

     Design for 1, 700 cfm.

2.   Slot width:

     Design for a slot velocity of 2, 000 fpm
 5.   The exhaust  system and i'an calculations are
     made  as outlined in Chapter 3.  After a sys-
     tem resistance curve is plotted and calculated,
     a fan  is  selected whose characteristic curve
     intersects  the system curve at the required
     volume, which in this  example, will be 1, 700
     cfm.

        TIRE  BUFFING   EQUIPMENT

 INTRODUCTION
 In recent years tire retreading  - the addition  of
 new rubber  to  the tread area of the  casing - has
 become an increasingly important business. Prior
 to 1950 the reliability of retreaded  tires was very
 low; but with the advent  of better manufacturing
 methods and the  introduction  of new  materials,
 the  basic tire  casing has become more durable
 and better adapted to subsequent retreading.  Bet-
 ter  materials and improved methods of applying
 tread  rubber have also increased the reliability
 of retreaded tires, and the volume  of the  industry
 has increased correspondingly.

The large demand and the  economic push  of com-
petition have brought about labor- and time-saving
 changes  that have modernized the retreading in-
dustry.  Particularly notable improvements have
been made in the equipment that removes material
from the tire and reshapes the carcass prepara-
tory to the addition of new tread rubber and mold-
ing. Early buffing machines consisted simply of a
 pedestal with a pivot  to hold the tire on a mandrel
 and a motor-driven  buffing or rasp head.   The
 operator rotated the tire manually against  the rasp

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                                        lire Buffing Equipment
                                                                                                   411
hear]  and  shaped it. by eye "with the help ot a tem-
plate that he placed against  the tire  occasionally
Present-day equipment has  been sophisticated to
the extent that an operator need only place the tire
on a mandrel shaft and then push a button.  The
tire is inflated, the buffing machine  proceeds
through its  cycle  of operation,  and then the ma-
chine stops   An automated  buffing machine is
shown in  T'igure 31Z
   Figure  312.  Tire buffing machine  which auto-
   matically buffs  a carcass to shape and stops,
   sidewall trimming is done manually (Rawls Divi-
   sion, National-Standard  Company, Lima, Ohio).
THE  AIR  POLLUTION PROBLEM
As high-powered, efficient rasp heads were
developed and the mandrels became power-driven,
temperatures at the rasp head increased with
the rate of removing old rubber.   Often  the
temperature of  vaporization for the plasticizers
used in the manufacture of tread rubber is
exceeded.  The  high-temperature  operation re-
sults  in the release of submicron-size fume and
smoke particles,  which are generated at various
rates depending upon the amount of plasticizer
present, the rate at which energy is being
converted into heat at the  rasp head,  and the
type and sharpness of the  rasp.  Although buffing
equipment can be operated at a sufficiently  slow
speed  not to cause smoking,  such slow-speed
operation is considered uneconomical by most
firms.
The two most commonly used types of rasps are
shown in Figure  313.  The rocket rasp consists
of a stack of circular  sectors on  metal saw blades
with teeth similar in appearance  to those of a
wood  ripsaw.  When assembled on a mandrel,
the rasp assembly forms a jagged-looking cylinder
about 8 inches in diameter with a cutting surface
of up  to 5 inches.  The tack rasp consists of a
series of tacks protruding through a cylindrical
piece of sheet metal.  Another cylinder  of sheet
metal riveted inside the outer cylinder holds the
tacks in place.

Quality control methods followed in the  retreading
of aircraft tires  prohibit operations at high
buffing  rates; therefore, the smoke problem is
usually minor and the particulate matter can be
collected by a cyclone alone or by a baghouse.
Figure  314  shows a cyclone and baghouse con-
trolling the emissions from an aircraft tire
buffing  operation.

Removal of old tread rubber from out-of-round
casings poses a problem for most of the re-
treading industry.   Although testing for  this  con-
dition before the tires are reworked is possible,
most  passenger car and truck tire recappers
delay discarding carcasses  until  the out-of-round
condition appears during buffing.  Performing
the out-of-round testing at the buffing  stage  is
considered  to be more economical than inspecting
all of the incoming tires because only  about  3
percent of the tires are  discarded as the result
of all inspections.   The concentricity  problem
can be avoided by employing a buffing  machine
such as that shown  in Figure  315 which  employs
a  contoured roller inside  the tire carcass in-
stead of a mandrel.

HOODING AND VENTILATION  REQUIREMENTS

A  small hood,  mounted  so that it surrounds all
but a  small sector of the rasp head, is used  al-
most  universally to gather the particulate rubber
and smoke  from the buffing operation.   The  hood
is  equipped with fiber or rubber  brushes to  re-
strict the size of the hood opening and thus
increase the velocity of  the  indraft.

Airflow rates as low as  1000 cfm have been used,
but 2000 cfm is a more  acceptable rate, espe-
cially if the hood has relatively large  clearances
around the rasp head.  The  indraft velocity should
be  at least  Z500  fpm,  and the duct conveying
velocity from the hood to the cyclone should  be
at least 6000 fpm.

Rubber particles that escape into the room are
usually larger than  50 microns in diameter and
are easily swept up from the floor.  Although
the fine particles and smoke that escape into the
room in small quantities are not  toxic, these con-

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412
                                       MECHANICAL EQUIPMENT
         a.  Nonspiral  rocket rasp.
                         c.   Tack  rasp.
     Figure 313.   Tire buffing rasps  (a and b,  B  and J Manufacturing Co.,  Gfenwood,  III.  c,  Tobey's Rasp Ser-
     vice, Inc.,  Sant-a Cruz,  Calif.).
                                                                                                        J
 Figure 314.  Air pollution control system venting ;n
 aircraft  tire buffing operation; skimmer  is at rigtit
 baghouse  is  at  left,  and  blower with stack  is in
 center of  picture (B.F. Goodrich Aerospace  and
 Defense Products, a Division of the B.F.  Goodrich
 Company,  City of Industry,  Calif.).
taminants could pose a health problem to a worker
who enhales them constantly.

AIR  POLLUTION  CONTROL EQUIPMENT

Cyclones

A cyclone,  or set of cyclones, is used almost
universally  as  the first stage in an air pollution
control system; often it is the only  piece of
equipment used to collect buffing emissions.
Even a relatively inefficient cyclone will  remove
99 percent by weight of the buffed-off material.
The 1 percent uncollected emissions consist of
Figure 315.  Tire buffing machine with contoured  rol-
ler  inside  tire (Rawls Division, National-Standard
Company,  Lima, Ohio).
particles that are smaller than 10 microns,  and
most of these are submicron in size.  As noted
previously,  this smoke is probably vaporized
oil used as the plasticizer in the original tread
rubber.  This" smoke is characterized by an
acrid odor,  and  even in small quantities, will
exceed opacity limits.

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                                        Tire Buffing Equipment
                                                                                                   413
Cyclones with  Afterburners

The most reliable type of equipment for elimina-
ting the smoke appears to be an afterburner.
However, afterburners are much, more expensive
than cyclones in first cost,  and operating costs
also are higher.  This is especially true for the
low •weight concentrations  of smoke in the
effluent from tire buffing.

Cyclones with  Dry Filters

Another equipment arrangement consists of the
cyclone, an added series of relatively inexpen-
sive prefilter panels, and a final stage of
"absolute filters. "  Absolute filters are of a fine
fibrous type,  are very expensive,  and are not de-
signed to intercept any particles larger than sub-
micron size.  If such filters are used, the
manufacturer's recommended number of filter
panels should be increased by a factor of about
two.  The big disadvantage of this system is  that
these filters plug almost immediately if some
malfunction causes  an appreciable carryover  of
large particles from the cyclone stage.

Cyclones with Baghouses and Dry Filters

To circumvent  this  problem,  some operators
use a baghouse in series with the cyclone and
follow the baghouse with the dry panel prefilters
and absolute filters  (Figure 316).  The system
is relatively  expensive but -works well in most
cases.
OTHER TREAD REMOVAL METHODS

Recently,  two devices have been introduced which
reduce or eliminate smoke and dust generation
at the source.  One of these substitutes cutting
for the primary buffing operation.  The other
utilizes a water spray to cool and lubricate the
buffing rasp.

Cutting Type Detreader

The cutting  type detreader  (Figure 317) eliminates
the primary buffing operation and  instead cuts
or saws the  rubber from the carcass  This
operation is followed by a light burr or grind cut
(0. 015 to 0. 030 inch)  for surface preparation to
ensure good bonding with the new tread rubber.
The amount  of dust generated by the burr cut is
very small,  about 1/8 pound for a  passenger tire
or 1/5 pound for a truck tire.  The dust generated
is collected  by a pickup hood mounted around the
burring wheel and employing  500 to 700 cfm  air-
flow.  The output of the blower can be  fed into any
suitable cyclone or baghouse.   The baghouse
should preferably have 175 to 250  square feet of
cloth and be equipped with a bag shaker.  A water
 Figure 316. Air pollution control system venting a
 truck and  passenger  tire buffing operation, cyclone
 is at left, baghouse at right,  and dry smoke filter
 box  at center  of picture, blower  is on top of
 cyclone (B.F.  Goodrich Retread Plant, Los Angeles,
 Calif.).
 Figure 317.  Detreader which uses a bandsaw to cut
 into slowly  rotating tire to pare off old tread rub-
 ber, burring wheel dresses surface to ensure uniform
 strong bond  with new tread rubber (American Machine
 and Foundry  Company,  Tire Equipment Division, Santa
 Ana, Calif.).
spray is recommended at the  cyclone  inlet to
eliminate the fire hazard.

Experience  indicates that one saw blade will trim
130 passenger tires or 60 average truck tires be-

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414
                                     MECHANICAL EQUIPMENT
fore needing replacement.  One tungsten carbide
burring wheel will dress more than 2000 tires and
can be reconditioned several times,  giving a total
life of over 8000 tires per wheel.  In contrast,
for a conventional buffing machine, one rasp will
buff about 250 passenger  tires or  50 truck tires
before needing to be replaced.  About 1 to 3
pounds of rubber per passenger tire or 5 to 10
pounds per truck tire are removed in the process.

Water Spray  at  Rasp

A fine mist of -water sprayed on the rasp has also
been employed to eliminate smoke generation at
the source by cooling and lubricating the rasp
(Figure 318).  The quantity of -water sprayed is
determined by an electronic controller which
operates in conjunction with a current sensor in
the rasp-head motor circuit. An airflow of about
2000 cfm is required to capture  the emissions
from this device.
Table 115. COST OF AIR POLLUTION CONTROL
     EQUIPMENT FOR NEW  TIRE BUFFING
                INSTALLATIONS a
 Figure 318.  Water injection unit, spray  heads
 (lower right) mounted in the rasp exhaust hood apply
 water to the rasp (B  and J Manufacturing  Company,
 Glenwood, III.).
Maintenance and operating costs for the  system
are very low, and experience indicates that rasp
life is almost doubled.  Also, because the rubber
compounds are not oxidized by too much heat,
the bonding strength is higher and more  uniform.

COST  OF POLLUTION  CONTROL

Table 115  shows  the comparative capital costs of
the various components of air pollution control
equipment required for tire buffing equipment.
These costs are  only part of the total picture and
are chosen to compare the influence of the type of
air pollution control equipment on the unit tire
cost.   No buffing machinery capital costs, in-
stallation costs,  or tire handling costs are in-
cluded.
Air
pollution
control
component
Blower, duct,
cyclone
With baghouse
after cyclone
Add dry filters
after baghouse
Water cooling,
cyclone
Number of
buffing machines
1
$1200
3400
4200
2700
2
$2000
6000
7400
5000
3
$2500
7700
9500
700C

For each
machine above
three add
$ 500
1500
1800
2000
aCosts are based on year 1969.  These costs are
   valid within t 25%.

       WOOD  TREATING  EQUIPMENT

INTRODUCTION

Wooden utility poles,  pilings, posts, and lumber
are subject to destruction from decay,  insects,
marine borers, fire,  -weathering, absorption of
water, and chemical action.  In order to prevent
this  destruction,  surface coatings are applied,
or preservatives and fire retardants are impreg-
nated into wood by application of pressure.   The
air pollution aspects of applying preservatives
and fire  retardants will be discussed in this  sec-
tion on-wood treating.  Surface coating is d iscus sed
in Chapter 12.

There are two general kinds of preservatives--
insoluble oils and -water solutions.  Insoluble
oils include  creosote, solutions of creosote-coal
tar,  creosote-petroleum oils, pentachlorophenol,
and other oil-borne preservatives.  In recent
years, treatment with insoluble oils has shifted
away from creosote to pentachlorophenol and
other oil-borne preservative solutions.  Insoluble
oil treatment results in darkened wood surfaces
and rather strong odors.  Applications of insoluble
oil treatment include utility poles, pilings,  and
railroad ties where painting is not required.  Dur-
ing the past years, there has also been a shift in
treatment away from insoluble oils to water-borne
(water soluble) preservatives because they leave
wood  surfaces clean and  free of odors; the sur-
faces also  can be painted.  Fire-r etardant formu-
lations are solutions of water-soluble compounds.

The composition standards for preservatives are
described in the American Wood Preservers'
Association Standards (AWPA P Standards).  Coal
tar creosote is  a dark oily liquid derived directly
from coal  tar or from distillation fractions  of

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                                      Wood Treating Equipment
                                                                                                 415
coal tar.  It is either used directly or compound-
ed with other preservatives  such as petroleum
oils  and pentachlorophenol.  Water-borne preser-
vatives include "Wolman Salts, " a tradename for
a preservative consisting chiefly of sodium
fluoride along -with small amounts of arsenates,
phenolic salts, or metal  dichromates.   Another
water-soluble preservative with the tradename
"Chemonite, " ammoniacal copper arsenite (ACA),
is made by dissolving cupric hydroxide, arsenic
trioxide, and acetic acid in aqua  ammonia.
METHODS OF TREATING WOOD

Coal tar creosote solutions and petroleum oils
are shipped to the treating plant in tank cars or
trucks.  While the heating of these oils  in the tank
cars and trucks is not required for pumping to
storage, heating is customary to reduce the heat-
ing requirements at the  retorts during wood
treating.  Oil-borne preservatives, aromatic
oils, and creosote usually are blended at the
treating plant.   In treating with water-borne
preservatives and fire-retardant formulations,
various chemicals are blended into water
solutions at the treating plant.

Regardless of-whether preservatives  are solu-
tions of creosote, oil-borne or water-borne
preservatives,  or flame retardants,  the same
type of process equipment is employed  as shown
in Figure 319.   Air-seasoned -wood in the form
of poles, timbers,  pilings, and lumber is trans-
ported on railroad trams pulled  by gasoline- or
diesel-powered locomotives.   The wood-laden
trams  are rolled into long,  horizontal,  heavy-
walled vessels called retorts.   Retorts usually
have inside diameters of 6 to 8 feet and lengths
up to 150 feet to accommodate  long poles.  A
typical wood treating plant consists of one to six
of these retorts.  Each  retort  contains  steam coils
for indirect heating  of the preservatives and
internal steam jets  for heat conditioning or for
direct cleaning  of the surface of the -wood.
Auxiliary equipment includes a vacuum system
capable of producing a vacuum of over 22 inches
of mercury absolute on the retort and a pressure
system capable of hydraulic pressures up to  250
psig -within the retort.  The vacuum system con-
sists of a condenser and receiver followed by a
reciprocating  vacuum pump or a two-stage steam
ejector system with barometric  condensers.
Hydraulic pressure usually is  produced by steam-
driven reciprocating pumps.

Pressure processes for injection of preservative
are described in the AWPA Treating Standards
or Commodities  Standards (C  Standards).
Process conditions are specified for different
kinds of wood,  the service for the treated wood,
and the particular preservative used.
A processing cycle can be classified into two
steps,  the  conditioning step and the treating step.
Wood is conditioned in the retort by immersing
it in hot preservative  at atmospheric pressure
or under vacuum to expand the cells  of the wood
and remove moisture; the cells of the -wood also
may be expanded by blowing superheated steam
into the wood.  In the  treating step following the
conditioning step, hydraulic pressure is employed
to  force the preservative into the cells of the
wood.

Cleanup follows hydraulic injection.  The wood is
subjected to heat and vacuum to remove excess
preservative, and live steam may be used to
clean the surface of the wood when insoluble  oils
are used.  Vacuum is applied after the  steam
cleaning  period  to remove excess moisture and
retard subsequent bleeding of the preservative.

The processing  time varies even for the same
kind of -wood since differences in cell structure
affect  preservative penetration.   Cell differences
are the result of variations in growing conditions
for each tree, such as weather, water,  soil, and
nutrients.  Moisture content of the wood also
affects processing  time.

C Standards  set limits on process variables for
conditioning  such as maximum steaming temper-
atures and duration, minimum vacuum, maximum
temperature of preservative, and duration.
Process variable limits for the treating step in-
clude:  minimum and maximum pressure,  max-
imum  expansion bath temperature,  and maximum
temperature and duration for final steaming -when
steaming is permitted.

Results of the treatment  include the pounds of
preservative injected  per cubic foot of wood on a
"gauge basis" or an "assay basis. "  Gauge basis
is  a measurement immediately after treating
based  on the ratio of the  total weight of liquid or
solid preservative  impregnated to the total volume
of wood  charged.  The volume of liquid preser-
vative  used is determined by measuring the dif-
ference in the liquid level in the preservative tank
before and after  treating.  The weight of preser-
vative  is then determined from the specific gravity
and composition  of the treating solution.  Inert
carriers such as water or petroleum oils are not
included in determining preservative weight.
The quantity of preservative  used also may be
determined by weighing wood before and after
treating.  For example,  on a gauge basis, Douglas
fir  crossarms for utility poles require only 4
pounds of creosote per cubic foot of wood, while
Douglas fir pilings for ocean service require 20
pounds of creosote per cubic  foot of -wood.

A more precise measurement is the assay basis,
•which  specifies the weight of dry preservative

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416
MECHANICAL EQUIPMENT
                                                                     OPTIONAL VACUUM SYSTEM
                                                                  STEAM
 NATURAL
  GAS
                     REUPING TANK
            SEMICIRCULAR
           SPRAY HEADER
            WITH NOZZLES-
               -TRAW-
                                                              HIGH-PRESSURE
                                                  TO WASTE       STEAM puMp
                                               PRESERVATIVE
                                                  WORKING
                                                   TANK
                                   L--~J.  RETORT
                       JUMP
                                                           •STEAM JETS
                                                           -STEAM COILS
                                                                'PUMP
                                                   'SCAVENGER PUMP
                         PUMP
                                                                                              SKIMMER
                                                                                 PUMP
 Figure 319.  Diagram of  a wood-treating plant using creosote solutions,  aromatic oils,  and oil-borne preservatives.
 (liquid or solid) per cubic foot of wood for a
 given zone of penetration into the wood.  Bored
 cores are taken from a specified number of wood
 pieces in each treated charge.  The  cores are
 analyzed by  AWPA A Standards  for  penetration.
 Preservative concentration and penetration depth
 vary, and C  Standards are written for the kind of
 wood and service for this wood.  Typical exam-
 ples are: crossarms must contain at least 0. 2
 pound  pentachlorophenol (solids) per cubic  foot
 at 100 percent penetration of sapwood (wood zone
 nearest  the bark); pilings must contain 20 pounds
 of creosote (liquid) per cubic foot at a minimum
                 depth of 1 inch  and at 85 percent of sapwood depth
                 if sapwood  depth is 2 inches or less or at 1. 75
                 inches maximum if sapwood depth is more than 2
                 inches.

                 There are two basic variations of pressure pro-
                 cesses for impregnating preservatives:  empty
                 cell and full cell.  The difference  between the
                 empty-cell process and the full-cell process in-
                 volves  only the pressure injection step.   Condi-
                 tioning steps which precede pressure injection
                 and cleanup steps which follow can be identical
                 for  either process.

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                                      Wood Treating Equipment
                                                                                                  417
In the empty-cell process,  the retort is either
filled with air at atmospheric pressure (Lowry
Process)  or pressurized with compressed air
up to some specified level (Rueping Process).
The retort is then filled completely -with pre-
servative liquid and hydraulically pressurized
to the C Standard selected for the kind of -wood
and service.   In each of the two  empty-cell
processes described above, air  imprisoned in
the cells of the •wood opposes the hydraulic
pressure  and restricts penetration by forcing
out part of the preservative.

In the full-cell process,  the retort is completely
filled with preservative while under vacuum and
then hydraulically pressurized as specified in
the C Standard.  There is negligible air in the
cells of the wood to oppose hydraulic pressure,
and thus penetration is greater for the full-cell
than for the empty-cell process.

Empty-cell processes result in stratified bands
of preservative located at the interface between
layers of wood at lower levels in a specified
penetration zone.   The full-cell  process results
in a continuous fill for  the entire depth of the
penetration zone without  stratified bands.  Thus,
the empty-cell process is used for light treat-
ment,  and the full-cell process for heavy treat-
ment.  For example, the empty-cell process is
used to inject 4 to about 12  pounds  creosote per
cubic foot (assay basis), and the full-cell process
to inject over 12 pounds creosote per cubit foot.
"Water-borne preservatives are injected only by
the full-cell process.   Creosote solutions and
oil-borne preservative solutions may be injected
by either  process.

Only the Rueping empty-cell process requires
the use of a special vessel  (the Reuping tank).
Following the conditioning step,  the  retort is
emptied of preservative except for a quantity
located in the bottom, which does not contact the
charge of wood.  The retort is pressurized -with
compressed air to  the C  Standard selected.  The
elevated Reuping tank is  filled with hot preserva-
tive,  and  the hot preservative in this tank is
allowed to slowly displace the compressed air in
the retort.  When the retort is completely filled
•with preservative,  it is  sealed and hydraulically
pressurized to the  C Standard selected.

A typical  processing cycle  for creosote treatment
using the  full-cell  process is as follows:  Wood
is charged to the retort and subjected to a vacuum
of 22 inches of mercury absolute within the re-
tort.  During the conditioning step, the wood
under vacuum in the retort is immersed in cre-
osote solution at 170° to 210° F.   During this
period, the vacuum is pulled from a small vapor
space at the top of  the retort.  The hot creosote
under vacuum causes moisture to vaporize and to
be expelled from the cells of the wood -which ex-
pand under heat.  The vacuum period continues
until the collection rate of condensate in a re-
ceiver below the -water-cooled shell-and-tube
condenser slows to a predetermined level, which
indicates that the wood is dry and ready  for
pressure injection.  This vacuum period  can vary
from one to several hours, or it may extend for
several days.

While the vacuum is maintained,  the retort is
filled completely -with creosote at 170° to 210° F.
The  retort is subjected to hydraulic pressure of
about 100 psig for periods up to several hours to
force the creosote into the cells of the wood.
Following pressure injection,  -with the -wood still
submerged in creosote, the retort is subjected to
an expansion bath to remove excess creosote.
The expansion bath  consists of a vacuum period,
during which the creosote may be reheated  to
220° F. Then  the vacuum is broken and the  cre-
osote is pumped out.  A vacuum period may
follow pump out to further remove excess pre-
servative.  Superheated steam at 8 to 12 psig may
be injected to clean the surface of the wood.
Then the wood is subjected to  a final vacuum
period to remove moisture, cool the surface of
the wood, and  retard subsequent bleeding of the
creosote.  Following the final vacuum period,
the wood is removed from the retort.  Depending
upon the C Standard selected,  one  complete
processing cycle may vary from 6 to over 60
hours.
A typical processing cycle for  ammoniacal
copper arsenite  (ACA) treatment using the full-
cell process is as follows (see  Figure 320):  The
conditioning step consists of sealing the wood in
the retort and subjecting it to a vacuum of about
25 inches of mercury for a period of 30 to 60
minutes.  Saturated steam at 5 to 10 psig is in-
jected directly into the retort until retort pressure
reaches  5 psig.   Steam injection is continued for
1 to 6 hours at 5 psig to expand the cells of the
wood.  The steam is shut off,  and the wood is
again subjected to a vacuum of  about 25 inches of
mercury  for up to 2 hours to remove moisture
from  the cells of the wood.  During the treating
step,  the retort is completely filled with ACA
solution  at  ambient  temperature.  Hydraulic
pressures of 75 to 150 psig are  applied to the re-
tort from 1 to 30 hours to inject the ACA into the
cells  of the wood. Hydraulic pressure is re-
leased, and the solution is pumped from the retort.
A final vacuum period of at least 20 inches of
mercury is  maintained for an hour or more in
order to remove  residual solution and reduce the
concentration of ammonia vapors before the
treated wood is removed from the retort.

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418
                                    MECHANICAL EQUIPMENT
                                        VENT TO ATMOSPHERE
                                               *
                      STACK
                      VENT
                                                                          I
                                                                  PRESERVATIVE
                                                                  CONCENTRATE
                                                                   STORAGE
                                          WATER
                                                                                    PRESERVATIVE
                                                                                      WORKING
                                                                                       TANK
                                                        SCAVENGER PUMP
        Figure 320.  Diagram of a  wood-treating plant using ammoniacal  copper arsenite (ACA) preservative.
THE  AIR POLLUTION  PROBLEM

The operation of equipment used for treating
wood -with creosote  solutions and oil-borne pre-
servatives results in the emission of air contam-
inants in  excess of air pollution regulations
governing opacity and concentration.

When these materials are heated, some of the
lower boiling organic compounds volatilize as.
aerosols  to form dense white emissions.  The
emission from treated wood on the tram cars
immediately  after removal from the  retort
usually exceeds  60 percent opacity beyond the
opaque  water vapor breakoff point and continues
to exceed 40 percent opacity up to 20 minutes.
Emissions of 60 percent opacity  or more beyond
the opaque steam plume from  the open end of the
retort continue only during  the few minutes it
takes to remove the treated wood and recharge
the retort.

Source tests revealed excessive particulate con-
centrations in the vacuum exhaust and in the
exhaust during the steam cleaning period.  Par-
ticulates averaged 0. 95 grain  per scf or 3. 6
pounds per hour in 440 scfm of gas from a
vacuum pump venting one retort during the initial
vacuum period.  Particulate concentration
averaged 19 grains per scf or  75  pounds per hour

-------
                                      Wood Treating Equipment
                                            419
in 460 scfm of gas from steam cleaning wood in
one retort.  Control of these emission sources
requires the installation of an air pollution con-
trol device.  Where vacuum is produced by a two-
stage steam ejector system with barometric con-
densers,  the vent from the vacuum system does
not exceed opacity regulations or regulations
governing the concentration and quantity of air
contaminants.   The vacuum steam ejector system
has barometric condensers which, in effect, act
as scrubbers  in controlling the emissions.  Two
source tests indicated particulate concentrations
of 0. 125 and 0. 260 grain per scf.

Preserving wood with ACA results in the emission
of ammonia vapors during vacuum and gas purg-
ing of the retort,  from mixing and storage tanks
for the preservatives,  and from the  treated wood
immediately following removal from the retort.
Although ammonia vapors do not cause opacity
problems, the vapor can cause a nuisance .

Ammonia vapors  entering the two-stage vacuum
system are scrubbed by barometric  condensers
so that the vacuum exhaust to the atmosphere
contains negligible ammonia odors.  The baro-
metric hot well, barometric  condenser recircu-
lation tank, and preservative mixing and  storage
tanks emit ammonia vapors and should be sealed
and vented to a control device as shown in Figure
320-

A steam plume may be present along with invisi-
ble ammonia vapors when the end cover  of the
retort is removed and the treated -wood is pulled
from  it. A final vacuum of at least  20 inches of
mercury absolute should be maintained for a
minimum of 1 hour prior to removal of the wood
in order to reduce the quantity of residual
ammonia in the treated wood to a level which
can safely be emitted to the atmosphere.  With
this vacuum period, the ammonia emitted is not
detectable at a distance of 75 feet from this
source; consequently, air pollution control equip-
ment  is not required.

Treating wood -with other water-soluble preserva-
tives  and fire retardant formulations generally
does not result in the emission of air contami-
nants.

HOODING AND  VENTILATION REQUIREMENTS

An enclosure or building to collect all the air
contaminants  emitted upon opening a retort would
have to cover the  entire end of the retort  and ex-
tend over 200  feet to accommodate railroad track
and switching  gear, retort appurtenances such as
movable track,  swing cover and piping, and
tram  cars loaded with wood up to 150 feet in
length.  Exhaust rates would have to be extremely
large to provide adequate ventilation within this
enclosure for the safety and comfort of the •work-
ers.  Any device to control emissions from such
a structure •would of necessity be very large and
costly.   As an alternative, some method is needed
to eliminate or reduce the emissions  as the •wood
is removed from the retort.

AIR POLLUTION CONTROL EQUIPMENT

A practical solution to the air pollution problem
occurring when wood treated •with solutions of
creosote and oil-borne preservatives is removed
from the retort is to spray the surface of the wood
with large quantities of water (Figure  321) to
cool the surface  of the wood from about 180° F to
below 115° F. At this lower surface temperature,
the volatilization of organic particulates is
greatly reduced,  and opacities which  exceed 60
percent white opacity beyond the  end of the  steam
plume before spraying are reduced to  10 percent
•white opacity or less.  Figure 322 shows emis-
sions from  treated wood on tram cars following
removal from the  retort with and without water
sprays.
 Figure 321. Treated  lumber on  railroad cars being pulled
 from retort through  a permanently installed spray header
 (J.H. Baxter and Company, Long Beach, Calif.).

A header containing spray nozzles is mounted
within a few inches of the  open end of the retort
to- blanket the entire open  end -with sprays.  If
space is available between the hinged retort
cover in an open position and the retort itself,
a permanently mounted semicircular header
can be installed as shown  in Figure 321.  With-
out the necessary space,  a portable header with
spray nozzles  (Figure 323) can be moved into
position after the  hinged cover is placed in  a
fully  open position.  About a dozen or more
flat spray nozzles are arranged in a semicircle
on each header.  A railroad switch engine moves
the treated wood on tram cars from the retort
slowly through the water sprays at a uniform
speed of not more than 17  fpm.  A minimum of
300 gallons of water per minute is sprayed on
the batch of treated wood for a total of at least
2500  gallons.
 234-767 O - 77 - i

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420
MECHANICAL EQUIPMENT
                  a. With sprays.
                                               "m
                                               „•*=
                 b. Without sprays.
 Figure 322.  Emissions from treated  lumber after removal
 from retort with and without water sprays (J.H. Baxter
 and Company,  Long Beach, Calif.).
 Figure 323.  Treated lumber being pulled through a porta-
 ble spray header (Forest Products Division, Koppers Com-
 pany, Inc., Wi Immgton, Cal if.).
Emissions which would normally escape from the
retort when the hinged cover is  open are control-
led by continued operation of the vacuum system
venting to the control equipment.  Emissions are
greatly reduced by installing a scavenger  pump
to remove most of the source of emissions,  i.e. ,
the hot residual preservative lying at the bottom
of the  retort. Spray  water is collected in  tanks
equipped with a skimmer to remove insoluble
preservatives prior  to respraying. Following
skimming operations,  the concentration of creo-
sote remaining  in the recirculating water  is about
                 0. 0002 percent by weight. Since the spray water
                 is heated up several degrees each time it is
                 sprayed,  the spray  system should be designed
                 with a large enough capacity to keep the spray
                 water near ambient air temperatures or  a spray
                 tower or  spray pond should be installed.  The
                 cooling load on the spray system can be reduced
                 by extending the  final vacuum period to a mini -
                 mum of 1 hour.  The longer the final vacuum
                 period, the lower the surface temperatures  of
                 the treated wood when removed from the retort.

                 During the steam cleaning of wood near the  end
                 of the treating process,  emissions to the atmos-
                 phere are at a maximum and may exceed 19
                 grains per scf. To comply with regulations  gov-
                 erning particulate losses, the control device
                 must have an efficiency over 96 percent. In  one
                 instance, a venturi  scrubber capable of this high
                 collection efficiency was rejected because of
                 high initial costs and high operating costs.  High
                 operating costs were based  upon the  calculated
                 pressure drop of at least 35 inches of water
                 column required across the venturi throat to col-
                 lect micron  size  particulates.

                 Incineration of air contaminants in an afterburner
                 is a proven method  for controlling emissions
                 during the steam cleaning period and during
                 operation of the vacuum pump. Figure  324 shows
                 an afterburner venting wood treating equipment.
                 The volume  of contaminated gaseous effluent
                 varies from about 300 to 1200 scfm.  A surface
                 condenser and knockout tank must be installed
                 ahead of the afterburner to condense live steam
                 during steam cleaning of the wood and to reduce
                 the load of the afterburner.  Provisions should be
                 made  for frequent internal cleaning of this sur-
                 face condenser since naphthalene crystals from
                 steam distillation of creosote -will cause fouling.
                 A special duct is installed at the inlet to the
                 afterburner to keep gas velocities •well above
                 flame propagation velocities in the reverse  direc-
                 tion and thus prevent flashback.

                 The afterburner should be designed for an exit
                 temperature of 1500° F and a retention time of
                 0. 3 second or more in the combustion  zone.
                 Source tests show efficiencies of 99 percent
                 based upon the complete combustion of gaseous
                 and particulate organic contaminants when oper-
                 ting at 1400° F exit temperature.  The afterburner
                 exhaust contains particulate concentrations  of
                 0. 04 grain per scf,  and at this concentration
                 there are no visible emissions.

                 Studies show that afterburner operating  costs can
                 be reduced by recovering the heat from the  after-
                 burner exhaust gases.  A shell-and-tube  exchanger
                 can be installed  at the outlet from the afterburner
                 to heat boiler  feed water or to supplement the
                 steam producing facilities of the wood-treating

-------
                          Ceramic Spraying and Metal Deposition Equipment
                                            421
 Figure 324. Afterburner mounted above knockout tank vent-
 ing wood-treating equipment ("Forest Products Division,
 Koppers Company, inc.,  Wilmington, Calif.).
plant.  A recent installation of a -waste heat boiler
venting an afterburner showed a payout time for
the boiler of less than 4 years.

The contaminant load on the afterburner can also
be reduced to a great extent by reducing the
steam consumption rate used for  cleaning to a
minimum.
When wood is treated with ACA, the emission of
ammonia vapors can cause nuisance violations;
however, the emissions do not violate any of the
other air pollution regulations. Ammonia vapors
released when treated wood is removed from the
retort can be substantially  reduced by employing
a 1 -hour vacuum period prior to removal.

Ammonia vapors emitted from the retort,  the
barometric  condenser hot wall, the barometric
condenser recirculation tank,  and the preserva-
tive mixing  and storage tanks  are vented to a
packed scrubber by displacement only.  A dia-
gram of  this system is shown  in Figure 320. An
exhaust fan  is not required since  gas flow rates
should remain as  slow as possible for efficient
operation of the scrubber.  The packed scrubber
shown in Figure 325 is 18 inches  in diameter and
is filled  with 4 feet of 1-inch Raschig rings. For
 Figure 325. Packed column venting wood-treating equipment
 (J.H. Baxter and Company, Long Beach, Calif.).

efficient absorption of ammonia vapors, recircu-
lating water to the contact barometric condenser
and the circulating water to the packed scrubber
should be cooled and kept below 1^ percent am-
monia by weight.

            CERAMIC  SPRAYING

  AND  METAL  DEPOSITION  EQUIPMENT


INTRODUCTION

Aqueous slurries  of porcelain or vitreous enam-
els and ceramic glaze often are sprayed onto
ceramic or metallic articles  in spray booths
using conventional spray equipment.  Metals,
metal alloys,  and metal oxides are deposited on
articles  of metal and other materials, also in
spray booths, usually by spraying in a molten,
atomized state using a gas  as  a carrier and spe-
cial spray  equipment.

In ceramic spraying operations, a spray gun,
operated by compressed air,  is used  to apply the
coating on  the object to be covered.  Sometimes,
in the process called airless  spraying,  the coat-
ing material itself is pressurized.

In metal deposition, three basic methods of ap-
plying the coating are in use.   These  are metal-
lizing, thermal spraying,  and plasma arc or
flame spraying.  These are discussed later in
this section.

-------
422
MECHANICAL EQUIPMENT
A booth or enclosure vented by a fan provides a
means of ventilating the spray area and protecting
the health of the spray gun operator.  The booth
also may be  equipped  to filter the incoming air as
well as to remove particulate matter from the
exhaust air.   Two typical spray booths are shown
in Figures 326 and 327.
CERAMIC SPRAYING

Air spray pressures may vary from nearly zero
for splatter coating to 125 psig for high production
spraying, and the simultaneous slurry delivery
pressure may vary from 5 to 40 psig.  Airless
spraying has  not proved to be very practical  for
ceramic spraying, primarily because of  the
abrasiveness of the particles.

Ceramic slurries for coatings are usually water
based,  with a weight fraction of water varying
from 25 to 55 percent depending on the particular
application.   The solids are usually mixtures of
quartz,  feldspars,  clays, finely ground glass frit,
pigments,  and small amounts of other additives
classed as fluxes, floating agents, opacifiers,
and electrolytes used for  special properties. See
the section "Frit Smelters"  in Chapter 11 for a
more detailed discussion  of  these materials  and
the terms used.

There are essentially  two classes  of ceramic
coatings, depending on whether they are  applied
to metals or  pottery.  When applied to metal, the
coating is generally referred to as porcelain
enamel in this country or vitreous enamel in
                 Europe, although sometimes known as glass
                 enamel in both places.  When applied to pottery,
                 the coating  is known as ceramic glaze.  After
                 application  to metal,  the enamel is  fired at high
                 temperature in  a furnace.  After application to
                 glass or pottery,  it is usually fired in a kiln. The
                 firing temperatures vary from 1300° to  2300°F
                 depending upon  the particular composition.

                 Some additives,  such as borax, soda ash,  oxides
                 of lead,  and cobalt, can be injurious if inhaled or
                 injested, but the final glaze coating, after  proper
                 firing,  is highly inert to all but a few chemicals
                 and thus is  safe for use on dishes,   cookware, etc.

                 As prepared for application, slurries usually
                 weigh from 11 to 18 pounds per  gallon, and  the
                 size distribution of the  solids may typically be
                 75 percent finer than  25 microns and  25 percent
                 finer than 5  microns, ranging down to possibly
                 0. I micron,  although  wide variations  are en-
                 countered from user to user.

                 The  Air Pollution Problem

                 The  particulate matter  in the unfiltered exhaust
                 from water-based  ceramic glaze or porcelain
                 enamel spraying can approach a concentration of
                 5 grains per scf for medium heavy  (25 gallons per
                 hour) spraying operations in open-face booths.
                 As much as  10 grains per scf has been observed
                 from closed or  semiclosed booths where the
                 slurry volume sprayed  may be as high as 160 gal-
                 lons per hour.  The particulate matter consists
                 primarily of particles of clay,  glass frit, and
                 pigment.
                                                              Hih
                                                     WORKING -LCOLLECTIOM
                                                      DEPTHPAN
                                                    	DEPTH OVERALL	
                                                     TOP EXHAUST
                                                                                     BACK EXHAUST
     Figure  326.  Binks Dynaprecipitator spray booth  featuring continuous  full-width spray bar and circulating
     water pump with induced-draft blower (Binks Manufacturing Company,  Los Angeles, Calif.).

-------
                           Ceramic Spraying  and Metal Deposition Equipment
                                              423
 Figure 327.  DeVilbiss pumpless water-wash spray booth
 featuring adjustable-orifice bar for pressure drop selec-
 tion to obtain desired scrubbing efficiency (The DeVilbiss
 Company, Chicago,  III.).
Overspray in porcelain enamel and ceramic glaze
spraying has been observed to be as low as 20
percent and as high as 60 percent of the total
sprayed during production runs.  It can be mini-
mized by proper spray trim pressure, electro-
static potential,  adjustments,  and by design,  such
as downward spraying into a sump,  etc. ; but there
will always be some airborne particulates  present.

Air  Pollution Control Equipment

Because of their affinity for water,  strong ag-
glomerating  tendencies when wet, and  relatively
high unit weight,  airborne particles from spraying
operations can be captured  relatively easily by
water-wash control sections.   Also, baffles placed
ahead of a water-wash section can be effective,  as
shown later.

Ceramic spraying on a very small work scale is
usually carried on in conventional single-stage
dry baffle booths,  sometimes with conventional
dry paint  filter panels in series.  However, where
average spraying rates are much over 1 gallon
                                                       per hour, deposits build rapidly in the exhaust
                                                       system and outside near the  stack outlet,  indica-
                                                       ting  that appreciable dusty material is entering
                                                       the atmosphere and probably being deposited over
                                                       the landscape by winds.  For this reason,  it is
                                                       considered  good practice for the higher spray
                                                       rates to use two or three staggered stages of dry
                                                       baffles  in series with a water-wash type booth
                                                       such as shown in Figures 326 and 327, or any of
                                                       a number of wet collection devices described in
                                                       Chapter 4.   Satisfactory operation requires fre-
                                                       quent cleaning of the baffles; otherwise the col-
                                                       lected material will sluff off in chunks and baffle
                                                       effectiveness will be lost.  If the baffles are made
                                                       easily removable,  then from 40 to 90 percent of
                                                       the oversprayed solids may be recovered  for re-
                                                       use or disposal.  Since some of these materials
                                                       are expensive,  recovery may be very desirable.

                                                       Spray pressure is  an important variable.  Higher
                                                       spray pressure results in smaller droplet size,
                                                       and small droplets are more difficult to collect.
                                                       The  relationship between spray pressure  and
                                                       droplet size produced by gas atomization  nozzles
                                                       has been investigated by Nukiyama and Tanasawa
                                                       (Perry,  1963).  Their equation, which follows,  is
                                                       applicable to conditions which are approximated
                                                       by most ceramic spraying operations,
                                                          Do =
where
                                                                 1920
         597
                                                                          0. 5
                                            (108)
      DQ = mean drop diameter,  microns

      V  = relative velocity of the gas with res-
           pect to  the liquid,  ft/sec

      
-------
424
                                     MECHANICAL EQUIPMENT
           face as  the total  sum of all drops
           formed), microns

      K.  = a constant,  empirically determined

      Pg = atomization air pressure, psig

with sufficient accuracy for our purpose.

The constant K was evaluated for this case by
correlating some observations of actual ceramic
spraying operations.  The resulting values for
K are  1200 for  single-stage baffles,  800 for  the
second stage of a dual- or triple-stage  set, and
500 for the third stage of  a  triple-stage set.
Physically,  this implies that the mean droplet
size reaching the second  stage is only two-thirds
that approaching the first stage, and the mean
droplet size reaching the  third stage is  approxi-
mately 60  percent of that  approaching the second
stage.  This phenomenon  occurs because of the
high percentage of the larger droplets removed
by each succeeding stage, leaving the small  ones
which cannot be intercepted by baffles.  Although
these are approximations, the loss ratios  chosen
give reasonable values  supported by experience.

Langmuir  and Blodgett and  others (Perry, 1963)
have shown that the target efficiency of an im-
pingement separator  such as  a  set of baffles
should be  a function of the dimensionless group
where

      Ui = terminal settling velocity for a given
          particle in air, ft/sec

      ~V  = relative velocity between  the fluid (air)
           and the baffle plates,  ft/sec

      g = acceleration of gravity (32. 3 ft/sec  )

     D, = width of an individual baffle  plate,  ft.


Figures  328 and 329 graphically represent the
overall collection efficiencies  for single-, dual-,
and triple-stage baffles when several simplifying
assumptions are made.  These assumptions  are
(1) the particles are spherical and have a specific
gravity of 1. 0 and (2) the individual baffle plates
are each 9 inches wide.   These assumptions
result in conservative results  in most cases.

The  effect of spray  pressure on the efficiency of
the baffles is clearly shown in Figures 328 and
329.  Also shown are the effects of the ratio of
open area to baffle area (d/w)  and the  indraft
velocity (V0).  Open area ratios greater than 20
percent are not recommended,  nor are indraft
velocities less than 120 fpm.
                                                           10   20   30   40   50   60   70   30   90   100   110  120
                                                                          ATOMIZATION AIR PRESSURE 
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                                                                   20    30   40 SO 60
                                                              ATOMIZATION AIR PRESSURE IP&I psig
                                                                                     90  120
                                                        Figure  329. Ceramic  dust-removal  efficiency versus
                                                        air-spray pressure for dual- and  triple-stage baf-
                                                        fles.
                                                       Electrostatic spraying also is very effective in
                                                       reducing emissions by causing more particles to
                                                       adhere to the work piece as •well as to the baffles.
                                                       The magnitude of the improvement is difficult to

-------
                            Ceramic Spraying  and Metal Deposition Equipment
                                                                                                      425
predict, but in one test the use of electrostatic
spraying on ceramic wash basins  increased the
expected efficiency of a  single-stage baffle from
20 percent to 50 percent.  When electrostatic
spraying is used,  it is primarily for the purpose
of obtaining a more  even coat on  an irregularly
shaped work piece,  and  not specifically for the
control of air pollution.

The effect of overspray  on required efficiency can
be seen in Figure  330.  These curves are plotted
based on an allowable loss of 0. 24 pound per hour
for spraying rates under 50 pounds per hour,
gradually increasing to 2.8 pounds per hour at
1000 pounds per hour spray rate.   For these
curves, it is assumed that the slurry is 70 per-
cent by weight solids.

                EQUIVALENT QUANTITY. jal/hr@15 Ib/fal
                                                                      EQUIVALENT QUANTITY.pl/hi® 15 Ib/pl

                                                                      0.5          10          15
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234 ; 10 20 40 7
AVERAGE TRIPLE STAGE BAFFLE
PLUS ORIFICE TYPE WET SECTION :
AVERAGE T
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CAL SEPARl
AVERAGE D
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CURVE A = 75* OVERSPRAY CONDITIONS
CURVE B = 50% OVERSPRAY CONDITIONS
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WED STACK LOSS, L :
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                 10  15    30  45 60   100 150
                 WET MIXED SLURRY SPRAYED (P,),*/1"
                                        300
Figure 330. Ceramic dust-removal efficiency versus spray
rate.
Baffle systems alone generally are not recom-
mended for use in production operations.  How-
ever, for the reader interested in the performance
to be expected from baffles for low spray rates
up to 25 pounds per hour (2 gallons per hour),
Figure  331 has been included.  The ability of noz-
zles to  deliver the higher volumes allowable at
the lower pressures probably limits the effective
use of baffles alone.  Also,  single-stage baffles
are not recommended for use at all except for
"art work"  or experimental type manual opera-
tions where  spraying  rates are less  than 2 pounds
per hour or  1 gallon per day.

Open-face booths such as shown in Figures  326
and 327 usually require  125 to 175 cubic feet of
air per square foot of opening in order to  trap
most of the airborne particles within the spray
booth exhaust system away from the breathing
                                                                         CURVE A- SINGLE STAGE BAFFLES
                                                                         CURVE B= DUAL STAGE BAFFLES (STAGGERED)
                                                                         CURVE C = TRIPLE STAGE BAFFLES (STAGGERED)
                                                                             CURVES BASED ON THE FOLLOWING
                                                                               STACK LOSS (L)=0.24 Ib/hi
                                                                               OVERSPRAY (0,1 : SOS
                                                                               SOLIDS IN SLURRY (SL)=70? BY WEIGHT
                                                                           10       15      20       25      30

                                                                           WET MIXED SLURRY SPRAYED (P,l,lb/ht
                                                         Figure 331. Maximum ceramic spraying rates for dry baf-
                                                         fle systems.
                                                        zone of the operator.  Obviously, a booth should
                                                        be  closed-in with a minimum of open inlet area.
                                                        Such a booth will require correspondingly less
                                                        airflow, thus reducing power requirements of
                                                        blowers and pumps.  Automated  systems usually
                                                        are able to take advantage of this savings,  since
                                                        the operator is not close enough  to be adversely
                                                        affected.   Figure 332  gives  the pressure drop in
                                                        inches of water  column  (we)  and  required horse-
                                                        power per 1000  cfm for  baffle systems.

                                                        Scrubber performance has been investigated by
                                                        Semrau (I960) and others who indicate that the
                                                        effectiveness of a scrubber  is dependent upon the
                                                        energy actually  utilized  in bringing the dust and
                                                        water together.   These  investigators have used
                                                        the concept  of "contacting power, " which is the
                                                        rate at which this energy is  expended  per unit
                                                        volume of gas flow.  Semrau (I960) gives the fol-
                                                        lowing equation  relating dust removal efficiency
                                                        of a scrubber to contacting power:
                                                                                                  (110)
                                                       where
                                                             L  = natural log

                                                             E  = fractional efficiency

                                                             PT = contacting power, hp/1000 cfm

-------
426
                                    MECHANICAL EQUIPMENT
REQUIRED UNIT HORSEPOWER . hp/1000 dm
n OSC3 £^ S f 00 S Cj! § Se
CURVE NO %
- NO STAGES OPE
1A 1 I
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'VALUES ARE FOR BAFFLE SYSTEMS
ONLY
ON COMPLETE DRY BAFFLE BOOTHS
A
0
0
DO 025
30 hp an
FHERP
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d or 10
DWERO
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1 PRESS
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URE LOSSES
1
                                           060
                                           006
                                           00?
            1?0      HO      160
                 INDRAFT VELOCITY |V0I Ipm
                                         ?00
Figure 332. Baffle system power and pressure loss charac-
teristics.
      a  = 3. 3

      r  = 1/3
empirical constants evaluated
from tests on ceramic spray
booths.
The equation plots as  a straight line on full-log
paper, and the constants  a and  ^ correspond very
closely to those found for talc dust removal by
either a venturi or an orifice type scrubber as
given by Semrau (1960) and others.

Semrau (1960) indicates that contacting powers
derived from gas pressure drop, hydraulic spray
nozzles, or mechanically driven inertial separa-
tors are equivalent; and if so, then evaluation of
the total contacting horsepower  of a multiple sys-
tem such as  a blower-pump combination booth
may be obtained  by direct addition of all or any
combination  of the three  types of power sources
as follows:
For air blowers,
         PG =  (0. 157) (AP)

For liquid pumps,
         PL =  (0.583) (P
                                           (111)
                                           (112)
                                          For mechanical or inertial separators,

                                                   PM = HPg - HPf - AHPa     (113)


                                     Since HPr and HP  are difficult to determine, a
                                             -1-        a
                                     good approximation is obtained by assuming
                                                                   PM=0.40HPs
                                                                                (114)
                                                     The minimum connected total horsepower,  as
                                                     shown graphically in Figure 333, may then be
                                                     expressed as follows:
                                                   PT =
                                                           and
                                                                               PL + PM
                                                                                L
                                                                                           (115)

                                                                                           (116)
                                                     where
                                                      PQ = blower contacting horsepower per
                                                           1000 cfm

                                                      PL = pump contacting horsepower per
                                                           1000 cfm

                                                      P^, = mechanical or inertial separator
                                                           contacting horsepower per 1000 cfm

                                                      Pj- = total system contacting horsepower
                                                           per 1000 cfm

                                                    HP   = minimum connected total horsepower
                                                           per 1000 cfm

                                                      AP = air pressure drop across water-wash
                                                           section, inches we

                                                      Pf = liquid  feed pressure,  psig

                                                      Q,  = liquid  feed rate, gallons per minute

                                                      Qp = air (gas) flow rate,  cfm
                                         HP  = actual shaft horsepower used by the
                                                mechanical separator
                                             r = bearing friction shaft horsepower  of
                                                the mechanical separator
                                        AHP  = shaft horsepower used in accelerating
                                            a
                                                the air through the mechanical sepa-
                                                rator.
                                     Figure 333 was  plotted assuming 60 percent
                                     pump or blower efficiency and reasonable match-
                                     ing of blower-motor and pump-motor character-
                                     istics.  For the pump plus blower booths,  the
                                     pump is usually sized to give from 35 to 50 gal-
                                     lons per minute per 1000 cfm airflow (Qj_,/QG
                                     per 1000 cfm) at a water pressure of approxi-

-------
                           Ceramic Spraying and Metal Deposition Equipment
                                                                                                       427
FRACTIONAL EFFICIENCY OF DUST REMOVAL BY WEIGHT (f.1
=S S S S SS S3 £ SS !K ss S3 8 S S
CURVE
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BASED ON W% MECHANICAL DRIVE EFF
RIFICE TYPE OR BLOWER PUMP
iECIRCULATION TYPE WET SECTIONS
BASED ON 60S BLOWER AND PUMP
:FFICIENCY AND WATER PRESSURE IPI
= X psij AND WATER/AIR RATIO |QL/Q(
= 35 8>m/1000 dm)
LOWER PUMP RECIRCULATION TYPE
ET SECTIONS WITH QL/QG 50|pm/100C
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4 0.6 0.8 1 0 15 2 3 456
            CONNECTED TOTAL HORSEPOWER IHPT>. hp/1000 elm
 Figure 333.  Efficiency versus power characteristics for
 three types  of wet collection systems (recommended only
 for ceramic  spraying applications).
mately 20 to 30 psig.  Water flow rates less than
35 gallons per minute per 1000 cfm are not
recommended.

Figures 332 and 333  are  sufficiently accurate for
quick evaluations and selection of type of equip-
ment,  but final equipment sizing must be made
using calculations based  on manufacturers' speci-
fications.   To determine horsepower, one must
consider the operating characteristics of the
particular blower  or  pump under actual operating
conditions and the power required by a drive.
Obviously, the values given in the figures  cannot
anticipate all situations.   Except for Figure 332,
applying these curves to  materials other than
water-based ceramic slurries is not recommend-
ed.  Semrau (1960) gives parameters of  equation
110 for various other materials which vary great-
ly from those shown  in these figures.

Figure 326 shows  a spray-bar water-curtain type
booth which has  a  maximum potential efficiency
of 97. 5 percent without precleaning baffles (Fig-
ure 334,  Curve C).   Figure  327 shows an orifice-
type spray booth,  also known  as a "pumpless
water-wash" type.  This type  has the advantage
that it has no water pump, which can be  a very
important item since ceramic particles are very
abrasive  and destructive to impellers, seals,
and bearings.  It has the disadvantage of being
slightly less efficient at equal differential  air
                                                                OUTLET STACK *ILL IMPOSE ADDITIONAL 1 0
                                                                incti*cAP ON SYSTEM
                                                                WHEN USING PRE
                                                              " BAFFLES SEE FIGURE
                                                                332 AND EQUATION
                                                              " 118
                                                                                   CURVE A = KIOTOR-DRIVEN »ET
                                                                                    MECHANICAL SEPARATORS
                                                                                   CURVE B = ORIFICE TYPE WET SECTIONS
                                                                                   CURVE C = BLOWER PUMP RECIRCULATION
                                                                                    TYPE WET SECTIONS
                                                                      WET SECTION PRESSURE DIFFERENTIAL (API inches we
                                                         Figure 334. Efficiency versus pressure drop characteris-
                                                         tics for three types of wet collection systems (recom-
                                                         mended only for ceramic spraying applications).
pressures, the maximum potential efficiency
without precleaning baffles being  96  percent (Fig-
ure 334,  Curve B).

Stack outlet opacities are not indicative of par-
ticulate emission rates  in ceramic spraying since
relatively high emissions can occur  with only
barely perceptible opacities.  However,  one can
evaluate equipment required to conform to a
desirable  or  acceptable particulate control  level,
or  conversely determine what type of equipment
may be necessary, by using the figures and the
following equations.   Numerical values for  emis-
sions  to the atmosphere through a spray booth
exhaust system can be approximated as follows:
              L = (Oy)(SL)(l-E)(PR)
(117)
where
       L =  emission to atmosphere,  Ib/hr

      Oy =  overspray,  estimated weight fraction
            of total  spray being drawn into the
            exhaust

      S,   =  solids in slurry, weight fraction of
            total

       E =  fractional efficiency from Figures
            328,  329, or 334 or from equation
            118

      Pj^ =  weight of wet mixed slurry sprayed,
            Ib/hr.
The unit weight fraction of solids in the slurry,
S^,  and the weight of slurry sprayed in a given
time,  PR,  are obtainable  by direct measurement
or by job requirements.   The overspray,  Oy,
must be visually  or otherwise estimated for any

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428
              MECHANICAL EQUIPMENT
given situation.  When no information is available
to make an estimate of overspray, 50 percent
may be used since it represents a value typical
of normal ceramic spraying operations.

The fractional efficiency, E,  is given for  the
various configurations of baffles already dis-
cussed in Figures 328 and 329 when the applicable
spray pressure is known or assumed.  For water-
wash sections, Figure 334 gives efficiency E
when the applicable differential pressure is
known.  If this pressure is not known,  it can be
easily measured with a manometer or draft  guage.
For equipment in the design stage, the manufac-
turer can usually supply the differential pressure.

When baffles are combined with a water-wash
section,  the following equation gives the resulting
efficiency of the combination, i. e. ,  E^ should be
used as E in equation  117.
Et =
+ E2
                                           (iis)
where
      Et = total system fractional efficiency

      EI = baffle stage fractional efficiency from
           Figures  328  and 329

      E2 = water-wash stage fractional efficiency
           from Figure 334.

 Baffles following a water-wash are primarily for
 removal of entrained dirty water and do not con-
 tribute significantly to dust removal.  They are
 neglected for efficiency calculations, although
 they are necessary  for proper -wet section opera-
 tion.

 The following examples illustrate the use of the
 previously discussed equations and figures.

 Example 34

 Given:

 A blower-pump, water-wash  type booth, 8 feet
 wide by 7-1/2 feet high, with a triple-stage baffle
 set with 20 percent  openings  is used with an air-
 atomized spray of 55 psig. Differential pressure
 across the water-wash section is 2. 5 inches of
 water  column.

      QG = 7200 cfm (V0 = 120 fpm indraft
           velocity)

      QL = 350 gallons per minute at 20 psig

    pump = 5 hp,  blower =10 hp

      SL = 70 percent
                                     Oy = 40 to 45 percent (average)

                                     P£ =105 pounds per hour (7 gallons per
                                          hour).
                               Problem:

                               Determine particulate emissions to the atmos-
                               phere (L) and verify horsepower adequacy.

                               Solution:
                               1.
                                           Obtain value of Ej from Figure 329,  Curve B,
                                           for the triple-stage baffles:  Ej = 0.76.
2.  Obtain value for E2 from Figure 334,  Curve C,
    for the water section:  E2 = 0. 958.

3.  Et = 0. 76 + (0. 958) (1-0. 76) = 0. 990 (from
    equation 118). (Note that baffles increased the
    efficiency from 0. 958 to 0. 990, an important
    increase.)

4.  L = (0. 43) (0. 70) (1-0. 990) (105) = 0. 314 pound
    per hour  (from equation 117).

5.  Blower requirements:

    a.  Total pressure drop = 2.5 inches of water
       column  across the water-wash section
       (from given data) 4- 0. 08 inch across the
       baffles  (from Figure  332) +1.0 inch
       across  the stack (from Figure 334) =  3.58
       inches of water column.

    b.  For the indicated blower operating point
       (7200 cfm at 3. 58 inches of water  column),
       catalog  data on a typical blower gives  5. 5
       to 6. 5 net brake horsepower, while from
       equation 111:

       PG =  (0. 157)(3. 58)  = 0. 562 hp/1000 cfm

    c.  Assuming 60 percent blower  efficiency
       •will give 6. 76 horsepower for 7200 cfm.
       Thus, a 7-1/2 horsepower motor might
       be sufficient, but this would depend upon
       the particular blower  power characteris-
       tics and power losses in the belt drive.
       The given 10-horsepower motor is suffi-
       cient.

6.  Pump requirements:

    a.  Equation 112 gives:

             (0.583)(20)(350)
                                      PT. =
                                                 (7200)
                                                                   =  0.58 hp/1000 cfm
                                   b.  Total horsepower required =
                                            (0.58)(7. 2)/(0.60) = 7. 0.

-------
                          Ceramic Spraying and Metal Deposition Equipment
                                                                                                 429
        Thus, the 5. 0-horsepower pump motor is
        insufficient.  For a conservative rating,
        the pump motor should be at least 7-1/2
        horsepower.

Example 35

Given:

A pumpless, orifice-type water-wash section, 8
feet wide by 7-1/2 feet high,  with a dual-stage
baffle set with 20 percent openings  is used with
an air-atomized spray of 50 psig.

        QG = 9000 cfm (V0 = 150 fpm
             indraft velocity)

        SL = 70 percent

        Oy = 40 percent

        PR = 100 Ib/hr

        L  =0.46 Ib/hr (allowable loss)

Problem:

Determine required fractional efficiency, E, to
meet L, probable suitability of equipment, and
required blower horsepower.

Solution:

1. Obtain required E  from equation 117:

    0.46 = (0.40)  (0.70) (1-E) (100)
               £* O
                   = 0.933
2.
3.
4.
    This value can be used for the total system
    fractional efficiency,  Et in equation 118.

    Figure 330  indicates that this level of efficien-
    cy is within the range of the equipment con-
    sidered; thus it should be suitable.

    Equation 118  is used to obtain the required
    water-wash efficiency,  E£.   Figure 329,
    Curve D, indicates 76 percent efficiency for
    the baffle (Ej) when spray pressure is  50 psig.
    Thus,

    0. 983 = 0.76  + E2 (1-0. 76)

            0.983 - 0. 76   n,
        2 = - 6724 -  = 9  Percent'

    Figure 334,  Curve  B,  indicates a minimum
    AP of 3. 3 inches of water column is required
    for 93 percent efficiency.  Design for a nomi-
    nal 3-1/2 inches of water column.
                                                      5.  From Figures 332 and 333, the required
                                                         horsepower is 0. 022 hp/1000 cfm for baffles,
                                                         0. 25 hp/1000 cfm for stack, and 0. 85 hp/1000
                                                         cfm for water wash.

                                                      6.  For 9000 cfm,  the total connected horsepower
                                                         required is
                                                                           ,9000
                                                         (0. 022+ 0. 25+ 0. 85)
                                                                            1000
                            = (1.122)(9) = 10. 1
                                                         Thus the blower will probably require a 15-
                                                         horsepower motor,  especially if an indirect
                                                         drive,  such as V-belts,  which requires appre-
                                                         ciable power is used.

                                                     7.  Cross-check on blower horsepower:

                                                         a.   Total pressure drop =3.5 inches of water
                                                             column across the water-wash section
                                                             (from step 4)  + 0. 09 inch  across the baffles
                                                             (from Figure  332) +1.0 inch across the
                                                             stack (from Figure  334) = 4. 59 inches of
                                                             water column.

                                                         b.   For the  indicated blower operating point
                                                             (9000 cfm at 4. 59 inches of water column),
                                                             catalog data on typical blowers indicate
                                                             a range  of 9 to 10.5 net brake horsepower,
                                                             thus justifying the choice  in step 6 of the
                                                             next larger size motor, i. e. ,  15 horse-
                                                             power.
METAL DEPOSITION

Metal deposition is accomplished by spraying
molten metal onto a surface to form a coating.
Pure or alloyed metal is melted in a flame or
arc and atomized by a blast of compressed gas
into  a fine  spray.  This  spray deposits on a pre-
viously prepared surface to form a solid metal
coating.  Because the molten metal is conveyed
by a relatively large  amount of  gas,  the object
being sprayed does not experience any apprecia-
ble temperature rise. Actually metallizing is
considered a "cold" process of  building up metal
on a part.

The  sprayed metal is  a new metallurgical materi-
al with entirely different physical properties  from
the original.  Sprayed metal is  generally harder,
more brittle, and more  porous  than  the original
metal and has excellent  bearing characteristics
owing to its ability to  retain lubricant in the pores
of the metal.

Sprayed metal  is most commonly used for machine
element work,  building up worn parts, or salvag-
ing mismachined parts.   It is particularly useful
for this class of work because the process does
not heat the parts and cause warpage.  Sprayed
metal also is used very  extensively for  a corro-

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 430
                                      MECHANICAL EQUIPMENT
 sion- and wear-resistant metal coating to iron or
 steel.  Aluminum and zinc are used as spraying
 metals for this purpose on structural  steel ele-
 ments .

 Sprayed metal also has many miscellaneous uses,
 such as for electrical shielding,  electrical con-
 ductive elements for radiant heaters,  rectifier
 plates, decorative uses (metallic spray has been
 applied on wood, paper, glass,  plastic, etc.),
 electrolytic capacitor plates,  and others.

 Metallizing was first used in 1910 by Schoop in
 Switzerland (Metco,  1964).  Schoop's  first work
 was done  by spraying heated metal powder.  A
 few years later,  the wire pistol, the prototype of
 present day metallizing guns,  was developed.   The
 metallizing process was introduced  into the United
 States when the  original Schoop wire gun was first
 imported  about  1920.  Since that time, fully auto-
 matic metallic production units have been put  into
 operation.

 In recent  years,  the  process has been extended
 for spraying high-melting-point metals and ce-
 ramics.   Thus the processes to be  considered
 will include those operations where  a  molten
 spray is  applied  and  the coating fuses  in place.
 Three  types of processes  are  in common use:
 metallizing,  thermal spraying,  and  plasma arc
 or flame spraying.  The metallizing process in-
 volves the use of metal in wire form.   The wire
 is drawn through a gun and nozzle by a pair of
 powered feed  rolls.   As illustrated  in Figure 335,
 the wire is continuously melted in an oxygen-fuel
 gas flame and atomized by a compressed gas
 blast (usually air) which carries the metal parti-
 cles to the previously prepared surface.   The
 individual particles  mesh  to produce a coating of
 the desired metal.  This meshing action still is
 not understood completely,  but the  effect appar-
 ently is due to a  combination of mechanical inter-
                             	4 in. MINIMUM	
                                 10 in. MAXIMUM
                             PREPARED BASE MATERIAL
                               (PART BEING SPRAYED)
 COMPRESSED AIR
WIRE SUPPLIED BY
AIR-DRIVEN MOTOR
BURNING GASES AND
  MELTING WIRE
OXYGEN AND ACETYLENE GAS
OR OXYGEN AND PROPANE GAS
  Figure 335. Metallizing gun showing nozzle portion and
  spray pattern (Metco, Inc., Westburg, N.Y.).
                                         locking and cementation of the oxides'formed
                                         during the passage of the particles from the  gun
                                         nozzle to the  sprayed surface.

                                         Almost any metal that can be drawn into wire
                                         form can be sprayed by metallizing gun deposi-
                                         tion.  The material can be sprayed by thermal or
                                         plasma arc deposition.   However,  there is a vari-
                                         ation in the efficiency with which the different
                                         materials can be applied. The causes for the vari-
                                         ations are not apparent,  but one factor may be the
                                         melting point of the material.  High-melting-point
                                         materials deposit more efficiently (Table 116).

                                         Table 116. AVERAGE DEPOSITION EFFICIENCIES
                                             OF VARIOUS METALLIZING MATERIALS
                                                   (Various Instruction Manuals,
                                                   Metco, Inc., Westbury,  N.  Y. )
Metal
Aluminum
Babbitt metal
Bronze
Copper
Lead
Monel
Nickel
Tin
Zinc
Ceramic
Cermet
Average
deposition
efficiency, a
%
89
69
77 to 82
79
55
80
80
65
66
80 to 90
60 to 70
Over spray, b
%
11
31
18 to 23
21
45
20
20
35
34
10 to 20
-
                                          Typical values only.  Spray head 4 to 10 inches
                                          from part being  sprayed.
                                          Over spray = 100 - deposit efficiency.
Theoretically there is no limit to the thickness of
the deposited coating which may be applied.  In
practical applications, however, internal stresses
can be set up in deposited coatings of unusual
thickness.

Thermal  spraying involves the application of
metals and other materials in powder form.
These include, but are not limited to, alloys of
nickel-chromium with boron-silicon  as fluxing
agents, tungsten carbide mixtures, ceramics
such as alumina and zirconis,  and certain
cermets.

As shown in  Figure 336, the powdered materials
are held in a hopper atop the gun and gravity fed

-------
                           Ceramic Spraying and Metal Deposition Equipment
                                                                      431
      POWDER TO BE SPRAYED
ASPIRATING GAS
 FUEL GASES:
 EITHER OXYGEN AND
ACETYLENE OR OXYGEN
   AND HYDROGEN
SPRAY
STREAM
                                 PART BEING SPRAYED
  Figure 336. Thermal spray powder gun showing nozzle por-
  tion and spray pattern (Metco,  Inc.,  Hestburg,  N.Y.).


into the gun where they are picked up by the  oxy-
acetylene (or hydrogen) gas mixture and carried
to the gun  nozzle.  They are melted almost
instantly owing  to the extremely high thermal
efficiency  of the gun.  The materials then are
carried to the surface being sprayed by means of
a siphon-jet arrangement at the gun nozzle.

In plasma  arc or flame spraying (Figure 337) the
spray gun  utilizes an electric arc contained within
a water-cooled  jacket.  An  inert gas, passed
through the arc, is excited  to temperatures up to
30,000°F.  The  plasma of ionized gas issuing
from the torch resembles an open oxy-acetylene
flame in shape and appearance.

The guns usually operate  on inexpensive  polyato-
mic gases for high electrical power conversion
efficiency  and long component life.  In some  ap-
plications  closed-circuit systems can be arranged
to permit recovery and  reuse of high percentages
of the gases sprayed.
    SPRAY POWDER SUSPENDED IN CARRIER GAS
CIRCULATING
 COOLANT
 PLASMA FLAME
                 ELECTRODE
                            'ARC
                           SPRAYED MATERIAL
  D.C. POWER TO ARC
                                 PART BEING SPRAYED
 Figure 337. Plasma arc or flame spraying device showing
 nozzle portion and spray pattern (Metco, Inc., dfestburg,
 N.Y.).
                         Table 117 is a list of materials that have been
                         sprayed in plasma arcs and their melting points.
                         Plasma arc deposition tends to be less efficient
                         than metallizing from an overspray standpoint
                         (Table 118),  probably due to the  highly excited
                         state of the ionized gas carrier;  but physical and
                         metallurgical properties of the coatings are gen-
                         erally superior to conventional flame-sprayed
                         coatings.   These include reduced porosity, im-
                         proved bond and tensile strengths,  less oxide
                         content when using metal,  and high density.
Table  117.  MELTING POINTS FOR MATERIALS
          SPRAYED BY PLASMA ARC
         (Various Technical Bulletins,
        Metco, Inc., Westbury, N.  Y. )
                                  Material
                         Aluminum oxide

                         Calcium zirconate

                         Chromium

                         Chromium carbide
                         Cobalt alloy

                         Cobalt-zirconia blend

                         Magnesium zirconate


                         Molybdenum

                         Nickel

                         Nickel-alumina blend
                         Titanium oxide
                         Tungsten

                         Tungsten carbide/cobalt
                         Zirconium oxide  (stabilized)
                         Zirconium silicate
                                   Melting point,
                                         °F
                                        3625

                                        4253

                                        3430
                                        3434

                                        2300
                                    2723 to 4892

                                        3848
                                     (approx.)

                                        4748
                                        2650

                                    2650 to 3772
                                        3490
                                        6170

                                        2300
                                    4650 to 4700

                                        4399
                                     (approx.)
The  Air  Pollution Problem

The  discharge from metal  deposition is composed
of clouds of molten metal fumes and/or finely
divided oxide particles interspersed with showers
of hot, relatively heavy agglomerations of the
finer particles.

The  deposition efficiencies of materials being
sprayed  by metallizing are quite high (see Table
116); however,  oversprays (material not depos-
ited  on the work piece) as high as 35 percent have
been reported in manufacturers' literature.  The
hot,  coarse particles and agglomerations are
easily and efficiently trapped by water-wash type
booths such as those described  in the  previous

-------
432
MECHANICAL EQUIPMENT
   Table 118.  DEPOSIT EFFICIENCIES FOR
      POWDERED MATERIALS SPRAYED
               BY PLASMA ARC
   (Various Technical Bulletins,  Metco, Inc. ,
               Westbury,  N.  Y. )
Material
Aluminum/ bronze
Copper
Nickel
Tungsten
Molybdenum
Tungsten carbide/
cobalt
Chromium carbide/
nickel chromium
Alumina
Alumina -titania
Nickel /aluminum
Cobalt alloy powder
Nickel -chromium
alloy
Deposition
efficiency,
%
55 to 80
65 to 75
65 to 75
60 to 70
60 to 80
60 to 65
30 to 65
55 to 60
90
60 to 90
65 to 70
60 to 80
Over spray,
%
20 to 45
25 to 35
25 to 35
30 to 40
20 to 40
30 to 35
35 to 70
40 to 45
10
10 to 40
30 to 35
20 to 40
section on ceramic spraying.  Even when applying
such materials as aluminum, magnesium, lead,
tin, zinc, and Babbitt metal, the resulting clouds
of whitish smoke can be reduced significantly if a
properly maintained wet collector is used.  The
metallic (or metallic oxide) dust and smoke over-
spray cannot be handled by ordinary dry baffle,
paint arrester,  or filter type paint spray booths.

Air Pollution Control  Equipment

The part to be  sprayed usually is mounted on a
lathe or a pedestal for ease of rotation.   Spraying
is accomplished within the confines of a hood to
protect the operator from dust and fumes.  Indraft
velocities of 120 to 200 fpm are acceptable.   The
higher value is recommended for toxic materials
in conjunction with the use of a good respirator.

The following air  pollution control  equipment has
been used to collect the metallic (or oxide)
particle emission:

1.  Absolute filters.  These are fine fibrous
    paper type  dry filters  which have the ability
    to trap submicron size particles with 99 per-
    cent efficiency.  They usually are used in
    series with one or more prefilters to remove
    the  larger size dust particles and reduce  the
    particle load on the more expensive  absolute
                     filters.  Collection efficiencies of 85 percent
                     by weight and better have been attained by
                     prefilters;  collection efficiencies of 99 percent
                     by weight and better have been attained by
                     absolute filters.  These filters will remove
                     the smoke, but only when used in a well de-
                     signed and  maintained air  pollution control
                     system.  A fire hazard may exist,  so  care
                     must be used.

                 2.  Baghouses.  Due to possible fire and explo-
                     sion hazards, baghouses are  not  recommended
                     for metallic dust collection from metallizing
                     operations  unless extreme precautions are
                     taken  to minimize the risk.  For metallic
                     oxide  dust  collection,  efficiencies over 99
                     percent by weight have been attained by pro-
                     perly  designed baghouses; however, smoke
                     removal is poor.

                 3.  Water-wash  scrubbers (Figure 338).   Two
                     types  have  been employed, pumpless and
                     water recirculation.   The  pumpless water-
                     wash  scrubber has  been used extensively. The
                     pumpless scrubbers have  the advantage of low
                     maintenance  and dependable performance  over
                     a wide range of operating  conditions.  They
                     have the disadvantage of somewhat lower col-
                     lection efficiencies for the same  differential
                     pressure when compared with the water re-
                     circulation type.
                                     EXHAUST TO OUTSIDE
                  VARIABLE SPEED
                  PULLEK
                                                 OVERFLO»CAP
                                                 TO ADJUST
                                                 •ATER LEVEL
                   Figure 338. Typical metal-deposition booth  (Metco, Inc.,
                   Westburg,  N.Y.).

-------
                       Ceramic Spraying and Metal Deposition Equipment
                                            433
Several manufacturers of metallizing equip-
ment also sell water-wash scrubbers as part
of a package design.  Smaller manufacturers
of metallizing equipment recommend standard
water-wash scrubbers by brand name and
model numbers  for use with their equipment.
When used to control emissions from metal
deposition, wet collectors usually are used
without baffles  preceding the water-wash
section.  Without baffles and with a pressure
drop of 4-1/2 inches  of water column across
the water-wash section, collection efficiencies
    of 96 percent by weight have been measured
    in source tests.

4.   Mechanical scrubbers.  When used intermit-
    tently,  metallizing processes can be controlled
    with mechanical scrubbers such as illustrated
    in Figures 57 and 58 of Chapter 4.  The initial
    capital  investment is less than for pumpless
    water scrubbers, they require less floor
    space,  and they are less expensive to operate.
    Their life expectancy is lower, however,  due
    to abrasion caused by high rotational speeds
    of moving parts.  Collection  efficiencies of
    95 percent and over have been attained.

-------
                                          CHAPTER 8

                                      INCINERATION

                     DESIGN PRINCIPLES FOR MULTIPLE-CHAMBER INCINERATORS
                  JOHN E.  WILLIAMSON, Principal Air Pollution Engineer

                                 GENERAL-REFUSE INCINERATORS
                 ROBERT  J. MAC  KNIGHT, Assistant Director of Engineering
                   JOHN E. WILLIAMSON, Principal Air Pollution Engineer

                            MOBILE MULTIPLE-CHAMBER INCINERATORS
                     ARTHUR B. NETZLEY, Senior Air Pollution Engineer
                   JOHN E. WILLIAMSON, Principal Air Pollution Engineer

                    MULTIPLE-CHAMBER INCINERATORS FOR BURNING WOOD WASTE
                     ARTHUR B. NETZLEY,  Senior Air Pollution Engineer
                   JOHN E. WILLIAMSON, Principal Air Pollution Engineer

                                  FLUE-FED APARTMENT INCINERATORS
                        JOSEPH J. SABLESKI, Air Pollution Engineer*
                   JOHNE. WILLIAMSON, Principal Air Pollution Engineer

                               PATHOLOGICAL-WASTE  INCINERATORS
                     WILLIAM F. HAMMOND,  Senior Air Pollution Engineer
                  JOSEPH M. TRAMMA, Intermediate Air  Pollution Engineer
                     PAUL G.  TALENS,  Intermediate Air Pollution Engineer

           DEBONDING OF BRAKESHOES AND RECLAMATION OF ELECTRICAL EQUIPMENT WINDINGS
                   ARTHUR B. NETZLEY,  Senior Air Pollution Engineer
                " DONALD F. WALTERS,  Intermediate Air Pollution Engineer*
                  JOHNE.  WILLIAMSON, Principal Air Pollution Engineer

                                 DRUM RECLAMATION  FURNACES
                          ROY S.  BROWN, Air Pollution Engineer*
                   ARTHUR B. NETZLEY,  Senior Air Pollution Engineer

                                      WIRE RECLAMATION
                     ARTHUR B. NETZLEY,  Senior  Air Pollution Engineer
                  JOSEPH M. TRAMMA, Intermediate Air  Pollution Engineer
 *Now with National Environmental Research Center,  U. S. Environmental Protection Agency,
  Research Triangle Park, North Carolina.
 tNow in private business.
234-767 O - 77 - :

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                                             CHAPTER 8
                                          INCINERATION
         DESIGN  PRINCIPLES FOR
   MULTIPLE-CHAMBER INCINERATORS
Disposal of combustible refuse and garbage is one
of the most perplexing problems facing urban so-
ciety today. The greater the population density the
more disturbing the problem.  This refuse is cre-
ated by all elements of a  community —industry,
commerce, and the public.

In the  past,  disposal of  combustible wastes was
looked upon as a necessary evil to be accomplished
as cheaply as possible.  Industrial and commercial
installations used a box-like,  single-chamber in-
cinerator to burn up to several tons  a day.  Refuse
from apartment houses was generally burned in a
chute-fed,  single-chamber incinerator.  In some
areas, especially southern California, each home-
owner disposed of his combustible refuse in a back-
yard incinerator.

During the past 15 years almost  every large urban
area in  the world has experienced a drastic in-
crease in the pollution of its atmosphere. As the
discomforts  of air pollution became more notice-
able, public clamor  for  rigid  regulation of air-
contaminating processes  increased steadily.  In
Los Angeles County this led to the banning of open
fires and single-chamber  incinerators in Septem-
ber  1957.   Since that date all  incinerators con-
structed and put  into operation  in the county have
had  to meet stringent criteria of performance as
well as definite minimum design requirements.
The standards presented  in this chapter are tools
for creating designs  for multiple-chamber incin-
erators that may be expected to burn rubbish with
a minimum discharge of  air contaminants.  Tab-
ular presentations alone are not sufficient for the
best application  and  understanding of the princi-
ples of design involved.  Also essential is an un-
derstanding  of the many factors that created the
need for a new  approach to  incineration and the
development of the multiple-chamber incinerator.
The design recommendations  and supplementary
discussions provide answers to  many of the  ques-
tions that confront designers and operators of multi-
ple-chamber equipment.  Caution is needed, howev-
er, in that only those qualified in combustion equip-
ment design and refractory  construction should
try  to apply the standards presented.  Adequacy
of design,  proper  methods of  construction, and
quality of materials  are important to  the satis-
factory completion of an incinerator that •will meet
air pollution control requirements and have an av-
erage  service life expectancy.
In this part of the chapter,  the two basic types  of
multiple-chamber incinerators  are compared.
Moreover, the principles of combustion, the funda-
mental  relationships for incinerator design, and
general design factors are discussed.  These data
are, for the most part, applicable to other  parts
of this chapter that discuss incinerators for spe-
cific uses.

In addition to discussing incinerators for burning
of combustible wood, paper refuse, and garbage,
this chapter includes the design of incinerators for
the reclamation  of  steel drums and wire and for
debonding of brakeshoes.

The configuration of modern multiple-chamber in-
cinerators falls into two general types as shown in
Figures 339 and 340.    These are the retort type,
named for the return flow of gases through the "U"
arrangement of  component chambers, and the in-
line type, so-called because the component cham-
bers  follow one after the other in a line.
RETORT TYPE

Essential features that distinguish the retort type
of design are as follows.

1.  The arrangement  of the chambers causes the
    combustion gases to flow through 90-degree
    turns in both lateral and vertical directions.

2.  The return flow of the gases  permits the use
    of a common wall between the  primary and
    secondary combustion stages.

3.  Mixing  chambers, flame ports, and curtain
    wall ports have length-to-width ratios in the
    range of 1:1 to 2.4:1.

4.  Bridge wall thickness under the flame port is
    a function of dimensional requirements in the
    mixing  and combustion chambers.  This re-
    sults in construction that is somewhat.unwieldy
    in the size range above 500 pounds per hour.

IN-LINE TYPE

Distinguishing  features of the in-line-type design
are as follows.

1.  Flow of the combustion gases is straight through
    the  incinerator with 90-degree  turns only in
    the vertical direction.
                                                 437

-------
438
                                                         INCINERATION
      SECONDARY
      COMBUSTION
      CHAMBER
CURTAIN
HALL PORT
                CLEANOUT
                DOOR
y I v | tip

CHAMBER
                                                                                       PORT
                                           CLEANOUT DOOR
                                           KITH UNDERGRATE
                                           AIR PORT
                                                                                                     — IGNITION
                                                                                                         CHAMBER
                                                                                                       CHARGING DOOR
                                                                                                       KITH OVERFIRE
                                                                                                       AIR PORT
                                                                                             GRATES
                                IGNITION  CHAMBER
                                      GRATES
                                                  ASH PIT
                                                                                                           STACK
                                                                                                                        SECONDARY
                                                                                                                        AIR PORT
                                                                                                                        MIXING  CHAMBER
                                                                                                                        BURNER  PORT
                                                                                                                   MIXING CHAMBER
                                                                                                           CURTAIN HALL  PORT
                                    Figure 339. Cutaway of a retort multiple-chamber  incinerator.

-------
                         Design Principles for Multiple-Chamber Incinerators
                                                                                                   439
                     CHARGING DOOR
                     KITH OVERFIRE
                     MR PORT
        GRATE!!
                 •CUANOUT DOORS WITH
                  UNDERGRATE AIR PORTS
                                       MIXING CHAMBER
                                                                        CURTAIN
                                                                        WALL PORT
                            Figure 340. Cutaway of an in-line multiple-chamber incinerator.
2.   The in-line arrangement is readily adaptable
     to installations that require separated spacing
     of the chambers  for operating, maintenance,
     or other reasons.

3.   All ports and chambers extend across the full
     width of the incinerator and are as  wide  as  the
     ignition  chamber.  Length-to-width ratios of
     the flame port,  mixing chamber,  and curtain
     wall port flow cross sections range from  2:1
     to 5:1.
DESCRIPTION OF THE PROCESS

The combustion process in a multiple-chamber in-
cinerator proceeds in two stages--primary or solid
fuel combustion in the ignition chamber,  followed
by secondary or gaseous-phase combustion.  The
secondary combustion zone  is composed of two
parts, a downdraft or mixing chamber and an up-
pass expansion or combustion chamber.

The two-stage multiple-chamber incineration  pro-
cess  begins  in  the ignition chamber and includes
the drying,  ignition,  and combustion of the solid
refuse.  As  the  burning proceeds, the moisture
and volatile components of the fuel are vaporized
and partially oxidized in passing from the ignition
chamber through the flame port connecting the ig-
nition chamber with the mixing chamber.   From the
flame  port,  the volatile components of the refuse
and the products of combustion flow down through
the mixing  chamber into which  secondary air is
introduced.  The combination of adequate temper-
ature and  additional air, augmented  by mixing
chamber or secondary burners as necessary,  as-
sists in initiating the second stage of the  combus-
tion process.  Turbulent mixing, resulting from
the restricted flow areas and abrupt changes in
flow direction, .furthers the gaseous-phase reac-
tion.   In passing  through the  curtain wall port
from the mixing chamber to the final combustion
chamber, the gases undergo additional changes in
direction accompanied by expansion and final ox-
idation of  combustible  components.  Fly ash and
other solid particulate matter are collected in the
combustion chamber by wall impingement and sim-
ple settling. The  gases finally discharge through
a stack or  a combination of a gas cooler (for ex-
ample, a water spray chamber) and  induced-draft
system.  Either draft system must limit combus-
tion air  to  the quantity  required at the nominal
capacity rating of the incinerator.

-------
 440
INCINERATION
DESIGN TYPES AND LIMITATIONS

During  the  evaluation  and development phases of
the multiple-chamber incinerator, different incin-
erator configurations -with variations in the sizes
and shapes of the several chambers and ports were
tested.  The results of these  tests defined the op-
timum operating limits for the two basic styles of
multiple-chamber  incinerators.  Each style  has
certain characteristics with regard to performance
and construction that limit its application.


Comparison of Types

The  basic  factors  that tend to cause  a difference
in performance in the two incinerators are  (1)
proportioning of the flame port and mixing cham-
ber to maintain adequate gas  velocities within di-
mensional  limitations  imposed by  the particular
type involved,   (2) maintenance  of proper flame
distribution over the flame port and across the mix-
ing chamber, and (3) flame travel through the mix-
ing chamber into the  combustion chamber.

A retort incinerator in its optimum  size range of-
fers the advantages of compactness  and structural
economy because of  its  cubic shape  and reduced
exterior wall length.  It performs more efficiently
than its  in-line counterpart in the capacity range
from 50 to 750 pounds per hour.  In these small
siz.es, the nearly square cross sections of the ports
and chambers  function well because of the abrupt
turns in this design.  In retort incinerators with a
capacity of 1, 000 pounds  per hour or greater,  the
increased size of the flow cross section reduces
the effective turbulence in the  mixing chamber  and
results in inadequate  flame distribution and pene-
tration and in poor secondary air mixing.

No outstanding factors favor either the retort or
the in-line configurations in the capacity range of
750 to 1, 000 pounds per  hour.  The choice of re-
tort or in-line configuration in this range is influ-
enced by personal preference, space limitations,
the nature  of the refuse, and charging conditions.

The  in-line incinerator is  well suited to high-ca-
pacity operation but is not very satisfactory for
service in  small sizes.   The smaller in-line in-
cinerators are  somewhatless efficient with regard
to secondary stage combustion than the retort type
is. In in-line incinerators with a capacity of less
than 750 pounds per hour,  the shortness of the grate
length tends to inhibit flame propagation across the
width of the ignition chamber.  This,  coupled with
thin  flame distribution over the bridge wall,  may
result in the  passage  of smoke from smoldering
grate sections straight through the incinerator and
out of the stack without adequate mixing and secon-
dary  combustion.  In-line models in sizes of 750
pounds per hour or larger have grates long  enough
           to maintain burning across their -width,  resulting
           in satisfactory flame distribution in the flame port
           and mixing chamber.  The shorter  grates  on the
           smaller in-line incinerators also create a mainte-
           nance  problem.  The bridge wall is  very suscep-
           tible to mechanical  abuse  since it is usually not
           provided with a structural support or backing and
           is thin where  the secondary airlanes  are located.
           Careless  stoking and grate cleaning in the short-
           grate in-line incinerators can break down the bridge
           wall in a short time.

           The upper limit for the use of the in-line  inciner-
           ator has not been established.  Incinerators -with
           a capacity of less than 2, 000 pounds per hour may
           be standardized for  construction purposes to  a
           great  degree.   Incinerators  of  larger capacity,
           however, are not readily standardized since  prob-
           lems of construction,  material usage, mechanized
           operation with  stoking grate, induced-draft sys-
           tems,  and  other factors make  each installation
           essentially  one of custom  design.  Even so, the
           design factors advocated herein are  as applicable
           to the design of large  incinerators as to the design
           of smaller units.

           PRINCIPLES OF COMBUSTION

           Theoretical treatment  of the  complex reactions
           taking place in combustion processes is as yet in-
           complete, but the empirical art of combustion en-
           gineering has developed to an advanced  state. The
           principles of solid-fuel combustion generally apply
           to incineration processes and include the  following.

           1.  Air and fuel must be in proper proportion.

           2.  Air  and fuel,  especially combustible  gases,
               must be mixed adequately.

           3.  Temperatures must be sufficient  for ignition
               of both the solid  fuel and the gaseous compo-
               nents.

           4.  Furnace volumes must be large enough to pro-
               vide the  retention time  needed for complete
               combustion.

           5.   Furnace  proportions must be such  that igni-
                tion temperatures are maintained and fly ash
                entrainment is minimized.

           Fluctuation in fuel quality  makes satisfactory in-
           cinerator design difficult. In addition to -wide ranges
           in composition, -wetness, and volatility of fuel, there
           is diversity in ash content,  bulk density, heat of
           combustion, burning  rate, and component particle
           size.  All these affect,  to some extent,  the oper-
           ating  variables  of flame propagation  rate, flame
           length, combustion air  requirement, and the need
           for auxiliary heat.

-------
                         Design Principles for Multiple-Chamber Incinerators
                                                                                                  441
Fundamental relationships for incinerator design
were investigated by Rose and Crabaugh (1955)
and  by the  ASME Subcommittee on Incineration
Design Standards.  The following were studied:

1.   The relationship of combustion air  distribu-
     tion to the degree and rate of combustion at-
     tained and to the  discharge  of  air  contami-
     nants;

2.   the  relationship of furnace proportions, that
     is, chambers and ports, to the degree and rate
     of combustion;

3.   the effects of temperature and furnace design
     on the  percentage of acid, volatile  organic,
     and solid contaminants discharged and the per-
     centage of combustibles in the solid  contami-
     nants discharged;

4.   the  relationship of combustion gas velocities
     to the effects on turbulence and flame travel
     and to the degree of combustion attained;

5.   the relationship  of the material burned to the
     formation of acid  and volatile organic com-
     pounds.


DESIGN FACTORS

Control of the combustion reaction, and reduction
in the amount of mechanically entrained fly ash are
most important in the efficient design of a multiple-
chamber incinerator.  Ignition chamber  parame-
ters are regarded as  fundamental  since solid con-
taminant discharges can be functions only of the
mechanical and  chemical processes taking place
in the primary stage.  Other important factors in-
clude the ratios of combustion air distribution, sup-
plementary draft and temperature criteria,  and
the secondary-combustion-stage velocity  and pro-
portion factors.  Some of these factors are func-
tions of the  desired hourly combustion  rate and
are expressed in empirical formulas, while others
are assigned values that are independent  of incin-
erator size.

Table  119  lists the basic parameters, evaluation
factors , and equations for designing multiple -cham-
ber  incinerators and gives  the minimum values
established for each.  The  allowable  deviations
should be interpreted with discretion to avoid con-
sistently high  or low deviation from the  optimum
values. Application of these factors to design eval-
uation must be tempered by judgment and by an ap-
preciation of the practical limitations of construc-
tion  and economy.

The values determined for the several parameters
are mean empirical values,  accurate in  the same
degree as  the experimental accuracy of  the eval-
uation tests.  The significance of exact figures is
 reduced further by the fluctuation of fuel composi-
 tion and conditions.  For purposes of  design, per-
 missible variations from the  optimum mean  are
 plus  or minus 10 percent, and velocities may  de-
 viate as much as 20 percent without  serious con-
 sequence.

 The  formulas governing ignition chamber design
 were tentatively postulated  from data  available
 through tests of units of varying proportions burn-
 ing at maximum combustion rates. Optimum values
 of the arch height and grate area maybe determined
 by using the gross heating value of  the refuse to
 be burned and interpolating between the  upper  and
 lower  curves in Figures 341 and 342.   An allow-
 able  deviation of these values of  plus or minus 10
 percent is  considered  reasonable.   Rather than
 establish formulas for both the upper  and lower
 curves of these figures, which represent 9,000
 Btu  per pound or more and 7, 500 Btu per pound
 or less, respectively, a formula  for the average
 values of  the two curves has  been given.  This
 curve  corresponds to a  gross heating  value  of
 8, 250 Btu per pound.

 Design Precepts

 The  ignition  mechanism should be one of fuel bed
 surface combustion.  This is attained by the pre-
 dominant use of overfire  combustion air  and by
 charging in such a manner as to attain concurrent
 travel of both air and refuse with minimum admis-
 sion  of underfire combustion  air.  Limiting  the
 admission of underfire air and thereby maintaining
 relatively low fuel bed temperatures  is important.
 With  a relatively high air rate through the fuel bed,
 the stack effluent contains appreciable quantities of
 metallic salts and oxides in microcrystalline form.
 A probable explanation is that vapor phase reac-
 tions and vaporization of metals take place in high
 fuel bed temperatures with resultant condensation
 of particles in the effluent gases as they  cool upon
 leaving the  stack.

 To accomplish fuel bed surface combustion through
 use of  overfire air, the charging door should be
 located at the end of the ignition chamber farthest
 from  the flame port, and the fuel moved through
 the ignition chamber from front to  rear.  This -way,
 the volatiles  from the fresh charge pass through
 the flames  of the stabilized and heated portion of
 the burning fuel bed.  Also, the rate of ignition of
 unburned refuse is controlled, •which prevents flash
 volatilization with its resultant flame quenching and
 smoke creation.  Top or side charging is consid-
 ered disadvantageous because of the suspension of
 dust,  disturbance of the  stabilized fuel bed, and
 the additional stoking required.

With  good regulation of  the burning rate through
 proper charging, air port adjustment,  and the use
 of an  ignition  or "primary" burner, the  need for

-------
442
                                                       INCINERATION
                     Table  119.   MULTIPLE-CHAMBER  INCINERATOR DESIGN FACTORS
                             Item and symbol
                                                                      Recommended value
                                            Allowable
                                            deviation
                Primary combustion zone:
                 Grate loading. L/-
                             6-   Q



                 Grate area,  AQ

                 Average arch height,  HA

                 Length-to-width ratio (approx):

                   Retort

                   In-line
10 Log Rc; Ib/hr-ft2 where Rc equals the
refuse combustion rate in Ib/hr  (refer to
Figure 341)
Rc  -  LG, ft2

4/3 (AG)4/'n; ft (refer to Figure 342)


Up to 500 Ib/hr,3:1; over 500 Ib/hr,  1. 75:1

Diminishing from about 1.7:1 for 750 Ib/hr
to about  1:2 for 2,000  Ib/hr capacity. Over-
square acceptable in units of more than 11 ft
ignition chamber length.
                                                10%
                                                10%
                Secondary combustion zone

                 Gas velocities:
                   Flame port at 1,000°F,  V^p

                   Mixing chamber at 1, 000°F, VMC
                   Curtain wall port at 950°F, VCWP

                   Combustion chamber at  900°F,  VQQ
                 Mixing chamber downpass length, Lj^^,
                 from top of ignition chamber arch to top
                 of curtain wall port.
                 Length-to-width ratios of flow cross
                 sections:

                   Retort, mixing chamber, and combus-
                   tion chamber
                   In-line
55 ft/sec

25 ft/sec

About 0. 7 of mixing chamber velocity

5 to 6 ft/sec; always  less than 10 ft/sec

Average arch height, ft
Range  - 1. 3 1 to 1.5  1


Fixed by gas velocities due to constant
incinerator width
                                                20%
                                                20%
                                              + 20%
                Combustion air:

                 Air requirement batch-charging opera-
                 tion
                  Combustion air distribution

                   Overfire air ports

                   Underfire air ports

                   Mixing chamber air ports

                  Port sizing,  nominal inlet velocity
                  pres sure

                  Air  inlet ports oversize factors

                   Primary air inlet

                   Underfire air  inlet

                   Secondary air inlet
Basis.  300% excess air.   50% air require-
ment  admitted through adjustable ports;
50% air requirement met by open charge
door and leakage
70% of total air  required

10% of total air  required

20% of total air  required

0. 1 inch water gage
1.2

1. 5 for over 500 Ib/hr to 2. 5 for 50 Ib/hr

2.0 for over 500 Ib/hr to 5. 0 for 50 Ib/hr
                Furnace temperature:
                 Average temperature,  combustion
                 products
1,000 °F
                                                20°F
                Auxiliary burners:
                 Normal duty requirements:

                   Primary burner

                   Secondary burner
3, 000 to 10, 000 \Btu per It
4, 000 to 12, 000/the refuse
3, 000 to 10, 000 ^Btu per Ib of moisture in
4,
                Draft requirements:
                  Theoretical stack draft,  DT
                  Available primary air induction draft,
                  DA-  (Assume equivalent to inlet ve-
                  locity pressure.)
                  Natural draft stack velocity, V^
0. 15 to 0. 35 inch water gage

0. 1 inch water gage



Less than 30 ft/sec at 900°F

-------
                                     General-Refuse Incinerators
                                                                                                 443
10,000
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i nnn
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* M
/ /
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/ / /
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•*' / •**
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VALUES,

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i /
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LG = 10 LOG Rc





REFUSE AND HIGH HE
USE +10% CURVE.
T REFUSE AND LOW H
USE -10% CURVE.




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EATING' - -

                           10
20
30
40
                                       GRATE LOADING (LG),  lb/Tt2-hr

              Figure 341. Relationship of grate loading to combustion rate  for multiple-chamber  incinerators.
50
stoking can be reduced to that necessary for fuel
bed movement before the charging.

Application of the fundamental evaluation precepts
combined with admission of secondary air and with
trials of various proportions in both chamber and
port dimensions established  parameters for the
mixing  and combustion  chamber portions  of the
multiple-chamber incinerator.   The primary ef-
fect of proper design has been attainment of a high-
er degree  of completion of combustion of volatile
arid solid combustible effluent  components.  De-
signing the combustion chamber as a settling cham-
ber has made possible a reduction in fly ash emis-
sions as well.
             GENERAL-REFUSE  INCINERATORS

         The general refuse incinerators discussed  here
         are  used for refuse originating from residences
         and commercial and industrial establishments. Ex-
         cluded,  however, are the flue-fed, -wood-burning,
         and mobile incinerators, which are discussed in-
         dividually in other parts of this chapter. General
         refuse may be defined as combustible refuse  such
         as dry paper or  a variable mixture of dry paper
         and other combustible materials -within the follow-
         ing approximate maximum limits (percent of weight):
         Drypaper (100); wood,  scrap (50); shrubbery (30);
         garbage (30); and  sawdust,  shavings (10).

-------
444
INCINERATION
            CD
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VALUES

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                          2     345
    ID       20   30  40 50
  GRATE AREA  (AG),  ft2
100
500 1,000
                 Figure 342. Relationship of arch height to grate area for multiple-chamber incinerators.
Basically,  disposal of general refuse may be ac-
complished by incineration or disposal in a dump.
The burning dump that has been used for centuries
is  rapidly  becoming outdated as more and more
communities become conscious of air pollution.
Other  types of incineration range from the use of
perforated 55-gallon  drums,  single-chamber  in-
cinerators, and multiple-chamber incinerators to
large municipal incinerators.  Where land is avail-
able, the cut and cover dump represents a more
desirable method of waste disposal than municipal
incineration from the standpoint both of economics
and air pollution control.


THE AIR POLLUTION PROBLEM

The  incineration process in general refuse incin-
erators produces emissions of fly  ash,  smoke,
gases, and odors. Fly ash and odors are undesir-
able primarily because of their nuisance potential
to the occupants of neighboring dwellings and busi-
nesses.  Smoke and gases,  which also have a nui-
sance potential, contribute to overall air pollution
through reduction  in visibility and  through their
ability to enter into  smog-forming photochemical
reactions in the air.
            Since single-chamber incinerators offer the advan-
            tage of positive control of combustion air distribu-
            tion and that of concentration of heat by virtue of
            enclosing the fire within refractory walls,  they are
            believed to be considerably more effective than an
            open fire.  Even  so,  single-chamber incinerators
            have  been  found to have particulate emissions of
            from 14 to 35 pounds per ton of material burned.
            By contrast,  the particulate discharges from well-
            designed multiple-chamber incinerators average
            4. 5 pounds per ton of refuse burned, which is one-
            tenth to one-fourth the  amount of solid and  liquid
            combustion contaminants emitted from single-
            chamber units.  Average amounts of particulate
            emissions, as well as of the major gaseous con-
            taminants, from single-  and multiple-chamber in-
            cinerators are given in  Table 120.


            AIR POLLUTION CONTROL EQUIPMENT

            As  always, the best methods of  air pollution con-
            trol are prevention of the creation of air pollutants
            by disposal of the  refuse in landfill projects.   The
            next best  means of controlling air pollution from
            the incineration of general refuse is complete com-
            bustion in  a multiple-chamber  incinerator.   The

-------
                                     General-Refuse Incinerators
                                            445
remainder of this part of the chapter is limited to
the design of multiple-chamber  incinerators for
effective disposal of general refuse with a minimum
creation of air pollution.


      Table 120.  COMPARISON BETWEEN
 AMOUNTS OF EMISSIONS FROM SINGLE- AND
    MULTIPLE-CHAMBER INCINERATORS
Item
Pa ticulate matter, gr/scfat 1 2% CO2
Vo atlle matter, gr/scf at 12% CO2
To al, gr/sc/ at U% CO2
To al, Ib/ton refuse burned
Ca bon monoxide, Ib/ton of refuse burned
Ammonia, Ib/ton of refuse burned
Organic acid (acetic), Ib/ton of refuse burned
Aldehydes (formaldehyde), Ib/ton of refuse burned
Nitrogen oxides, Ib/ton of refuse burned
Hydrocarbons (hexane), Ib/ton of refuse burned
Multiple
chamber
0. 11
0. 07
0. 19
3. SO
2.90
0
0.22
0. 22
2 50
< 1
Single
chamber
0.9
0. 5
1,4
23. 8
197 to 991
0. 9 to 4
< 3
5 to 64
< 0. 1

DESIGN PROCEDURE

The design factors itemized in Table 119 are the
basis for the design of a multiple-chamber incin-
erator.  These factors are used to determine the
area  of  the grate, the average height of the arch,
the proportioning of the ignition chamber, the siz-
ing of the gas ports, the cross section of the mix-
ing chamber,  the  sizes of the inlet air  ports, and
the other necessary dimensions  and proportions.
Application of these factors,  however, requires
that calculations be made to convert the data into
usable form.   These  calculations are illustrated
in the problem given at the end of this part of the
chapter.

These calculations fall into  three general cate-
gories:  (1) Combustion  calculations based  upon
the refuse composition, assumedair requirements,
and estimated heat loss; (2) flow calculations based
upon the properties of the products of combustion
and assumed gas temperatures; and (3) dimension-
al calculations based upon simple mensuration and
empirical sizing equations.  The calculations need-
ed  to determine weights, velocities, and average
temperatures of the products of combustion are de-
rived from standard  calculation  procedures  for
combustion.   Average gross heating values and
theoretical air quantities are used.  Chemical prop-
erties and combustion data for the major compo-
nents of general refuse are given in Table 121.  The
only omission  is  shrubbery, 'which may be safely
assumedtohave the same composition as average
wood.

The average temperature of the combustion prod-
ucts is determined through normal calculations of
heatloss.  The burning rate and average composi-
tion of the refuse are assumed to be constant.  When
extremes in quality and  composition of material
are encountered, the most difficult burning condi-
tion is assumed.  Heat losses due to radiation,  re-
fractory heat storage, and residue heat content are
assumed to average 20 to 30 percent of the gross
heating value of the refuse during the first hour of
operation.  Readily available furnace data indicate
thatthe losses fall to approximately 10 to 15 per-
cent of the gross heat after  4 to 5  hours of continu-
ous operation.

The  calculated overall average gas temperature
should be  about  1,000°F  when  calculations are
based  on  300 percent excess combustion air and
the assumption of 20 to 30 percent heat loss given
previously.  This calculated temperature  is not
flame temperature and does not indicate the prob-
able maximum temperatures attained in the flame
port or mixing  chamber.  If the calculated tem-
perature is lower than  1,000°F,  installation of
burners is indicated.

Only volume and temperature  data for the prod-
ucts of combustion  are required for determining
the cross-sectional flow  areas  of the respective
ports and chambers.  The temperatures used are
approximations of the actual  temperature gradient
in the incinerator as the products of combustion
cool while passing  through  the various ports and
chambers to the  stack outlet.

Air ports are sized for admission of theoretical air
plus  100  percent excess  air.  The remaining air
enters the  incinerator through the open charging
door during batch operation and through expansion
joints, cracks around doors,  and so forth.  Indraft
velocities  in the combustion  air  ports  (overfire,
underfire, and secondary) are assumed to be equal,
with a velocity pressure of 0. 1 inch water  column
(equivalent to 1, 265 fpm).  Designing the draft sys-
tem so that available firebox draft is about 0. 1 inch
water column, and  oversizing the adjustable air-
ports  ensure maintenance of proper air  induction.

Calculations of draft characteristics follow stan-
dard stack design procedures common to all com-
bustion engineering.  The stack velocity given for
natural draft systems accords with good practice
and  minimizes flow losses in the stack.

The remainder of the essential calculations needed
for designing an incinerator are based upon  substi-
tution in the parametric  equations and measure-
ment of the incinerator.  Recommended grate load-
ing, grate  area., and average arch height  may be
calculated by equation or  estimated from Figures
341  and 342.   Proper length-to-width ratios may
be determined and compared with proposed values.

Supplementary computations are usually required
in determining necessary auxiliary gas burner sizes
and  auxiliary fuel supply line piping.   Where the
moisture content of the refuse is less than  10 per-
cent by weight,  burners are usually not required.
Moisture contents of from 10  to 20 percent normal-

-------
446
                                          INCINERATION
                Table  121.  CHEMICAL PROPERTIES AND COMBUSTION DATA FOR
                                  PAPER, WOOD, AND GARBAGE
A
n
a
1
y
s
s


Material

Carbon (C)
Hydrogen (H)
Nitrogen (N)
Oxygen (O)
Ash
Gross Btu/lb
Dry basis
Constituent
(Based on 1 Ib)
Theoretical air
(40% sat at 60°F)
Flue gas with
theoretical air
CO,
N2
H^Oformed
H2O (air)
Total
Flue gas with
% excess air
as indicated
0%
50. 0
100. 0
150. 0
200. 0
300. 0
Sulfite paper, a

44. 34
6.27
48.39
1.00

7, 590
scf6
67.58
68.05
13.99
53.40
11.78
0. 47
79.65
79.65
113.44
147.23
181. 26
215.28
283. 33
Ib
5. 16
5. 18
1.62
3. 94
0. 56
0. 02
6. 15
6. 16
8. 74
11. 32
13. 91
16. 51
21. 70
Average wood,"

49. 56
6. 11
0. 07
43. 83
0. 42

8, 517
scf
77.30
77. 84
15.64
61. 10
11.48
0. 53
88. 77
88. 77
127.42
166.07
204. 99
243. 91
321. 75
Ib
5.90
5. 93
1. 81
4. 51
0. 54
0. 02
6. 90
6.91
9. 86
12. 81
15. 78
18. 75
24. 68
Douglas fir, c

52. 30
6. 30
0. 10
40. 50
0. 80

9,050
scf
84. 16
84. 75
16.61
66.53
11. 84
0. 58
95. 46
95. 47
137. 55
179. 63
222. 01
264. 38
349. 13
Ib
6.43
6.46
1.91
4.91
0. 56
0. 02
7.42
7.43
10.64
13.86
17.09
20. 12
26.58
Garbage, d

52. 78
6.27
39. 95
1. 00

8, 820
scf
85. 12
85. 72
16.66
67.23
11. 88
0. 59
96. 37
96.38
139. 24
182. 00
224. 86
267.72
353. 44
Ib
6. 50
6.53
1. 93
4. 97
0.56
0. 02
7.49
7.50
10. 77
14. 04
17.21
20. 58
27. 12
        aConstituents of sulfite paper,
C6H10°5
C5H10°5
         Cellulose
         Hemicellulose
         Lignin
         Resin
         Ash
        bKent, 1936.
        cKent, 1961.
        dEstimated.
        eMeasured at 60°F and 14. 7 psia.
C6H1005
C20H30°2
84
 8
 6
 2
 1
lynecessitate installation of mixing chamber burn-
ers, and moisture contents of over 20 percent usu-
ally necessitate inclusion of ignition chamber burn-
ers.

General Construction

The design and construction of multiple-chamber
incinerators are regulated in several ways.  Ordi-
nances and statutes that set forth basic building re-
quirements have been established by most, if not
all, municipalities.  Air pollution control authori-
ties have also set some limitations in material and
construction that must be met, and manufacturers'
                       associations have established recommended mini-
                       mum standards to be followed.
                       The building codes governing incinerator construc-
                       tion adopted in the past have been based primarily
                       upon concepts of structural safety and fire preven-
                       tion  by restriction  of the  rate  of heat transfer
                       through the walls.  Little or no attention was given
                       to the  abrasion,  erosion,  spalling, and slagging
                       that are encountered in a high-temperature incin-
                       erator, and yet these conditions lead to equipment
                       failures  that are  comparable to structural or in-
                       sulation failures.

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                                      General-Refuse Incinerators
                                                                                                  447
The structural features and materials used in the
construction of multiple-chamber incinerators  can
be  discussed only in general terms.  There  are
as many methods of erecting the walls of a multiple -
chamber incinerator as there are materials from
which  to build them.   Designs of multiple-cham-
ber  incinerators  are presented  schematically in
Figures 343 and 344.    The types of construction
and fabrication shown are typical of those in cur-
rent usage.  The  designs are shown with prefired
refractory  brick  linings and common brick ex-
terior walls.  Structural details  are not indicated
since the reinforcing and support of walls, arches,
and stack depend largely upon the size and type of
construction of the unit  under construction.  While
conventional "60° sprung  arches" are shown for
the main arches  and curtain wall port  openings,
flat suspended arches and other standard types of
sprung arches  may be substituted  satisfactorily.
Air inlets have been shown both as circular and as
rectangular ports. Either may be used to provide
adequate inlet areas.   The exterior of the incin-
erator  may be of either brick or steel plate con-
struction, and the refractory lining may be of fire-
brick,  castable  refractory,  or  plastic firebrick,
or combinations thereof.

In accordance with standard practices, the exteri-
or walls are protected further from extreme tem-
perature conditions by providing a suitable periph-
eral airspace in brick construction,  by providing
air-cooling lanes,  or  by using insulation in units
fabricated from steel.

Changes in the methods  of construction of multiple -
chamber incinerators  are  typified in the  portable
prefabricated units available today.  Installation
of incinerators such as  these  is reduced simply to
placement of the unit on its foundation and attach-
ment of an auxiliary fuel  supply 'where  needed,
though transportation considerations of weight  and
size limit their capacity to  500 pounds or  less  per
hour.   Plastic  and castable  refractory linings in
steel exteriors are used •widely for this type of
fabrication.  All  larger incinerators, regardless
of the type of construction,  and those incinerators
for which brick is  desired for an exterior   are
erected on the  site.

Refractories

The most important element in construction of
multiple-chamber incinerators, other than the  de-
sign, is the proper installation and use of refrac-
tories.  High-quality materials are absolutelynec-
essary if a reasonable and satisfactory  service  life
is to be expected. Manufacturers must use suit-
able materials  of  construction and be experienced
in high-temperature furnace fabrication and refrac-
tory installation, since  faulty construction may
well offset the benefits of good design.  In the choice
of one of the many available materials, maximum
service conditions should dictate the type of lining
for any furnace.  Minimum specifications  of mate-
rials in normal refuse service should include high-
heat-duty firebrick or  120 pounds per cubic foot
castable refractory.  These materials , when prop-
erly installed, have proved capable of resisting the
abrasion, spalling,  slagging,  and erosion result-
ing from high-temperature incineration.

As the incinerator's  capacity and severity of duty
increase,  superior refractory materials such as
super  duty  firebrick  and plastic firebrick should
be  employed.  A recent improvement in  standard
construction has been the lining of all stacks  with
2, 000°F refractory of 2-inch minimum thickness.


Grates and Hearths

The grates  commonly used in multiple-chamber
incinerators are made  of cast  iron  in  "Tee" or
channel  cross  section.   As the size of the incin-
erator increases, the length of the ignition cham-
ber  also increases.   In the larger hand-charged
incinerators, keeping the rear section of the grates
completely covered is difficult because of the great-
er length of the ignition chamber.  The substitution
of a hearth at the rear  of the ignition  chamber in
these units  has  been  accepted as good practice,
since a hearth in this region prevents open areas
from being formed in the normally thin refuse pile.
This prevents excessive  underfire air from enter-
ing in front of the bridge wall, which would increase
fly ash carryover and reduce combustion efficiency.
Since surface combustion is the primary combus-
tion principle, the use of a hearth has  little effect
upon combustion rate.

Installation  of a  sloping grate,  which slants down
from the front to the  rear of the ignition chamber,
facilitates charging.  A grate such as this also in-
creases  the  distance  from the arch to the grates
atthe rear of the chamber and reduces the possi-
bility of fly ash entrainment, which frequently oc-
curs when the fuel bed surface approaches the level
of the flame port.


Air  Inlets

Positive  control for all combustion air inlets should
be provided by means of fully adjustable dampers.
The retort incinerator designs shown in Figure 312
incorporate round, spinner-type controls  with ro-
tating shutters for both underfire and overfire air
openings, and  rectangular ports with sliding or
hinged dampers  for  the secondary air  openings.
The in-line incinerator designs  shown in Figure
313 have rectangular ports for both overfire and
secondary air  openings,  and spinner-style ports
for the underfire air openings.  Air ports may be
of any convenient shape, though the port arrange-
ment indicated in the in-line designs with rectan-

-------
448
                                                    INCINERATION
                                                                              1.  STACK
                                                                              2.  SECONDARY AIR PORT
                                                                              3.  GAS BURNERS
                                                                              4.  ASH PIT CLEANOUT DOOR
                                                                              5.  GRATES
                                                                              6.  CHARGING DOOR
                                                                              7.  FLAME PORT
                                                                              8.  UNDERFIRE AIR PORT
                                                                              9.  IGNITION CHAMBER
                                                                             10.  OVERFIRE AIR PORT
                                                                             11.  MIXING CHAMBER
                                                                             12.  COMBUSTION CHAMBER
                                                                             13.  CLEANOUT DOOR
                                                                             14.  CURTAIN WALL PORT
                              PLAN  VIEW

                          SIDE ELEVATION
SIZE OF INCINERATOR, Ib/hr
LENGTH, inches
ABCDEFGH*! JKLMNOPQRSTUVWXYZ
50
100
150
250
500
750
1000
314
404
45
54
764
854
944
134
18
224
27
36
494
54
224
284
334
374
474
54
594
9
134
154
18
27
36
36
63
9
114
134
18
224
27
20*
27
29
36
494
54
584
134
18
224
27
36
45
45
18
19
20
22
28
32
35
8
12
14
18
24
30
34
184
23
27
30
364
40
45
20
28
354
40
484
514
544
3S
5
5
74
124
15
174
10
15
164
18
23
28
30
44
24
44
44
9
9
9
24
24
24
44
44
44
44
24
4
44
44
4i
44
44
9
144
18
20
26
25
274
24
5
5
5
5
5
74
24
0
24
24
5
10
124
24
24
24
24
24
24
24
44
44
44
44
9
9
9
24
24
24
2i
4t
44
4i
44
44
44
tt
9
9
9
44
44
44
44
9
9
9
6
8
9
12
16
18
22
4
5
6
6
8
6
10
*Dimension "H" given in feet.
                           Figure 343. Design standards for multiple-chamber, retort  incinerators.

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                                     General-Refuse Incinerators
                                                                                                   449
                                                PLAN VIEW
                                              SIDE ELEVATION
1 .
2.
3.
4.
5.
STACK
SECONDARY AIR PORTS
ASH PIT CLEANOUT DOORS
GRATES
CHARGING DOOR
6.
7.
8.
9.
10.
FLAME PORT
IGNITION CHAMBER
OVERFIRE AIR PORTS
MIXING CHAMBER
COMBUSTION CHAMBER
1 I.
12.
13.
14.
15.
CLEANOUT DOORS
UNDERFIRE AIR PORTS
CURTAIN WALL PORT
DAMPER
GAS BURNERS
oc
c=»
1—
cc
LU
3E \
— _a
LJ_
a
UJ
r-j
CO
LENGTH, inches
ABCDEFGHIJK|_*MNOPQRSTUVWXY
750
1000
1500
2000
854
944
99
108
494
54
764
90
514
54
65
69i
45
474
55
574
15i
18
18
224
54
63
72
79i
27
31*
36
40i
27
31*
36
40i
*D'
94
11
124
15
me n s
24
29
32
36
18
224
27
31i
32
35
38
40
44
44
44
44
5
5
5
5
74
10
74
10
9
9
9
9
24
24
44
44
24
24
44
44
30
30
30
30
9
9
9
9
44
44
44
44
5
7
B
9
11
12
14
15
51
5?
61*
63i
7
R
9
10
on "L" given ir feet.
                      Figure 344.  Design standards for multiple-chamber,  in-line  incinerators.
gular overfire ports is preferred since the com-
bustion air is distributed more evenly across the
fuel bed.
Stack

Stacks for incinerators with a capacity of 500 pounds
or less per hour are usually constructed of a steel
shell lined with refractory and mounted over the
combustion chamber.  A refractory-lined rein-
forced,  red brick stack is an  alternative meth-
od  of  construction  -when  appearance  is  deemed
important.  Stacks for incinerators with a capacity
of more than 500 pounds  per hour are normally
constructed  in  the   same  manner  as  those for
smaller units but are often free standing for struc-
tural stability, as indicated in Figure 344.  Stack
linings should be increased in thickness  as the in-
cinerator becomes larger in size.

-------
450
INCINERATION
Induced-Draft System

The replacement of a stack by an induced-draft
system introduces  additional problems.  Cooling
the effluent gases becomes  necessary to reduce
their temperature to that  for which the draft fan
is rated.  Evaporative cooling with water is a stan-
dard  practice.   The contact of the flue gas  with
water forms  a  weak acid solution that eventually
corrodes  the  evaporative  cooler and  accessory
equipment,  making replacement necessary.   To
overcome these problems, stainless steel or acid-
resistant  brick may be installed.  The excess spray
water also creates a problem,  requiring a  sewer
outlet for its disposal or  a  recirculation system
for its reuse.  Recirculation of acidic water not
only results in more rapid corrosion of the spray
chamber and fan, but also subjects the  pump,  pip-
ing,  and  spray nozzles to  corrosion.  The  use  of
an induced-draft system with  a spray chamber ac-
complishes additional removal of large  particulate
matter and water-soluble gases.


Operation

The most  important single aspect of operation of a
multiple-chamber incinerator  is the  method of
charging  the  refuse into the  ignition chamber.  A
multiple-chamber incinerator  must be  charged
properly at all times in order  to  reduce the forma-
tion of fly  ash  and maintain adequate flame cover-
age of the burning rubbish  pile  and the flame  port.
A recommended  charging  cycle  starts  with  the
placing of the  initial charge of refuse in the  incin-
erator. The ignition chamber should be filled to a
depth approximately two-thirds to three-fourths  of
the distance between the grates and the  arch before
lightoff.  After  approximately half of the refuse
has been  burned,  the remaining refuse should be
carefully  stoked  and pushed  as far as possible  to
the rear of the ignition chamber. New refuse should
be  charged  over  the front section of the grates,
which have been emptied by the moving of the burn-
ing refuse.    To prevent smothering  the fire, no
material  should be charged  on top of  the burning
refuse at the rear of the chamber.  With this charg-
ing method,  live flames cover the rear half of the
chamber,  fill the flame port, and provide nearly
complete  flame coverage  in the mixing chamber.
The fire propagates over the surface of the newly
chargedmaterial,  spreading  evenly and minimiz-
ing the possibility of smoke emissions. Since the
refuse pile need not be disturbed unduly, little or
no fly ash is emitted.

Characteristic of the multiple-chamber incinerator
is that control  of air-polluting emissions is built
in, if the  incinerator is operated with reasonable
care.  The discharge of combustion contaminants
is almost entirely  a function of ignition chamber
design and the  actions of the operator.  Control  of
           smoke is attained by proper admission of combus-
           tion air and by use of secondary burners in cases
           of incineration  of refuse with a low heating value
           or high moisture content.  The use of secondary
           burners  is  required at times  since the efficiency
           of the mixing chamber depends upon both luminous
           flame and adequate temperatures for vapor phase
           combustion.  The need for supplementary burners
           maybe determined readily by observing the nature
           of the flame travel and coverage at both the flame
           port and the curtain wall port.
           The  overfire  and underfire air ports are usually
           half-open at lightoff and are opened gradually to a
           full  open position  as  the incinerator reaches its
           rated burning capacity.  If black smoke  is emitted,
           the admission of more secondary air and reduction
           of the capacity of other air ports are advisible.  On
           the other hand, white smoke is usually the result
           of a too cold furnace and may be eliminated by re-
           ducing or closing  all air  ports.  After the final
           charge or refuse, the air ports are closed gradually
           so that during the burndown period the only air  in-
           troduced into the furnace is  provided through leaks
           around door and port openings.


           When ignition and mixing chamber burners are nec-
           essary, the mixing chamber or secondary burner
           is lighted before the incinerator is placed into oper-
           tion.  The burner  should remain in  operation  for
           the first  15 to ZO minutes of operation and should
           be used thereafter as needed.  Under normal con-
           ditions,  the  ignition chamber  or primary burner
           is used only when wet refuse is  charged.  At other
           times, its use, too, maybe required when refuse
           tobe burned contains high percentages of inorganic
           compounds such as clay fillers used in quality paper.
            Illustrative  Problem

            Problem:

            Design a multiple-chamber  incinerator  to  burn
            paper with 1 5 percent moisture at a rate of 100 Ib/hr.

            Solution:

            1.   Composition of refuse:

                Dry combustibles (100 lb/hr)(0. 85)  = 85 Ib/hr
                Moisture          (100 lb/hr)(0. 15)  = 15 Ib/hr

            2.   Gross heat of combustion:

                From  Table 121, the gross  heating value of
                dry paper is 7, 590 Btu/lb.

                (85 lb/hr)(7,590  Btu/lb)  =  645,200 Btu/hr

-------
                                     General-Refuse Incinerators
                                                                                                  451
3.  Heat losses:

    From  Table  121,  0.56 Ib of water is formed
    from the combustion of 1 pound of dry paper.
     Radiation, etc =  (0. 20)
     (645, 200 Btu/hr)
=  129, 040 Btu/hr
    Evaporation of contained
    moisture (15 Ib/hr)
    (1, 060 Btu/lb)            =   15, 900 Btu/hr
    Evaporation of water
    from combustion
    (0.56 lb/lb)(85 Ib/hr)
    (1, 060 Btu/lb)
       Total

4.  Net heat:
=   50,400 Btu/hr

=  195, 340 Btu/hr
    645, 200 Btu/hr -  195, 340 Btu/hr = 449,860
    Btu/hr

5.  Weight of products of combustion with 300 per-
    cent excess air:

    From Table 121,   21.7 pounds of products of
    combustion result from the combustion  of 1
    pound of paper with 300 percent excess air.

    Paper  (85 lb/hr)(2 1. 7 Ib/lb)  = 1,844 Ib/hr
    Water  15 Ib/hr               =    15 Ib/hr

        Total                        1,859 Ib/hr

6.  Average gas temperature:

    The specific heat of the products of combus-
    tion is 0. 26 Btu/lb- °F.
    At =
                449.860 Btu/hr
                                       = 930°F
        (0. 26 Btu/lb-°F)(l, 859 Ib/hr)

     T= 930°F   +  60°F               = 990°F


7.   Combustion air requirements:

     Basis:

     Use 300 percent excess air; 200 percent ex-
     cess  air  is admitted through  open charging
     door and leakage around doors, ports, expansion
     joints,  etc.

     From Table 121, 68. 05 cf of air is theoretically
     necessary to burn  1 pound of dry paper.

     (85 lb/hr)(68.05 cf/lb)(2)   =   ll,580cfh
                               or     192.8 cfm
                               or        3.2 cfs
8.   Air port opening requirements at 0. 1 in.  WC:

    From Table D8 in Appendix D, 1, 255 fpm is
    equivalent to a velocity pressure of 0. 1 inch.


              (192.8 cfm)(144 in2/ft2)     „  ,  .  2
    Total =  —-—     " —:	 =  22.2  in.
                   1, 255 ft/mm

    Overfire  airport  (0. 7) (22 . 2  in?)  =  15. 6  in?
    Underfire airport (0. 1)(22. 2  in?)  =   2.2  in?
    Secondary airport (0. 2)(22. 2  in?)  =   4. 4  in?

9.   Volume of products of combustion:

    From Table 121, 283.33 cf of products of com-
 ,   bustion are formed from the combustion  of 1
    pound of paper with 300 percent excess air.

    Basis:

    60°F and 300 percent excess air

    Paper  (85  Ib/hr )(283. 33 cf/Ib)   =  24, 080 cfh
                             Water  (15 Ib/hr)
                                Total
                       379 ft /lb-mol
                         18 Ib/mol
                                                                    316 cfh
                                                                 24,396 cfh
                                                            or      6. 8 cfs
                        10.  Volume of products of combustion through flame
                             port:

                             Total volume minus  secondary air
                             6. 8 cfs  -  (3. 2  cfs){0. 20)         =  6. 16 cfs

                        11.  Flame  port area:

                             From Table 119, velocity is 55 fps.
                                                           (6. 16 cfs)(l, 560°R)
                                                             (55 fps)(520°R)
                                                         =  0. 34 ft
                        12. Mixing chamber area:

                            From Table 119, velocity is 25 fps.
                             (6. 8 cfs)(l, 460°R)
                              (25 fps)(520°R)
                                 =  0.76 ft
                        13. Curtain wall port area:

                            From Table 119,  velocity is 20 fps.
                             (6.8 cfs)(l, 410°R)
                              (20 fps)(520°R)
                                 =  0. 92 ft
                        14. Combustion chamber area:

                            From Table  119,  velocity is 6 to 10 fps.
  234-767 O - 77 - 31

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452
                                          INCINERATION
    (6.8 cfs)(l. 360°R)
        (6 fps)(520°R)
                                 =  2. 96 ft
15.  Stack area:
    From Table  119, velocity is < 30 fps.
                                 =  0. 71 ft
    (6. 8 cfs)(l, 360"R)
       (25 fps)(520°R)

16.  Grate area:
    From Figure 341, the grate loading for aver-
    age refuse is  18  Ib/ft^-hr.
     (100 Ib/hr)
           2
                                 =  5. 56 ft
    18 Ib/ft -hr

17.  Arch height:

    From Figure 342, the arch height = 27 in.


18.  Stack height:
    From Table  119, D  =  0. 17 in. WC.
        =  0. 52 PH (   - ~ )*
    where:
    D
    P
    H
    T
    T,
    H
    H
        =  draft, in. WC
        =  barometric pressure, psi
        =  height of stack above grates,  ft
        =  ambient temperature, "Rankine
        =  average stack temperature,  "Rankine.
                  D
                      0. 17
           (0.52)(14.
                        1
                                 1
                                         = 18.75 ft
                       V520    1,360'
        MOBILE MULTIPLE-CHAMBER
                INCINERATORS
 Mobile multiple-chamber incinerators provide a
 unique  method  for  on-the-site  disposal  of com-
 bustible refuse.  Limited numbers  of these units
 were constructed in Los Angeles  County in the  late
 1950's  and used successfully for land clearance,
 housing tract  construction,  and other industrial
 *Kent, 1938.
activities "where the permanent installation of an
incinerator or the hauling of refuse to another loca-
tion for disposal would have been less economical.
Although their technical efficiency was adequate,
mobile  multiple-chamber incinerators never
achieved a popularity of any consequence because
of availability of more economical disposal meth-
ods.

At first glance, one may presume that a standard
multiple-chamber incinerator mounted on a trail-
er can  serve as a mobile incinerator.  This pre-
sumption is quickly dispelled when weight and size
limitations,  draft, vibration, and  other problems
inherent in mobile construction are more closely
examined.   The discussion that follows provides
a designer  'with practical and economical answers
that  facilitate  the design and construction of suc-
cessful mobile multiple-chamber incinerators.


DESIGN  PROCEDURE

Although mobile incinerators are  designed -with
parameters identical to those of multiple-chamber
incinerators,  already described in this chapter,
they must be  constructed of lightweight materials
and limited in size to comply -with the State Vehicle
Code.   Design configurations generally  restrict
the maximum capacity of the retort style,  as  shown
in Figure 345,  to 500 pounds per hour, and that of
the in-line  style, as shown in Figure 346,  to 1,000
pounds per hour.

Draft for mobile incinerators may be produced in
two ways.  The first  and most conventional way is
the use of a stack, while the other incorporates  an
induced-draft system that  uses air to cool the ef-
fluent.

Stack Requirements

If a stack  is used, it must be retractable to meet
the height  requirements of the State Vehicle Code.
To accomplish this,  it is usually hinged at the base
and, if necessary, folds in the middle,  permitting
it to lie horizontally on the top of the incinerator.
The stack is unlined to reduce not only its  weight
but the size  and weight of the elevating equipment,
which consists of a  frame, steel cables, and pul-
leys, operatedby a hand crank or geared to a  small
gasoline engine.

 Induced-Draft  Fan System

A typical induced-draft system  consists of an un-
 insulated  breeching of 10-gage steel plate where
products of combustion from the incinerator are
 cooled by mixing with air to a temperature that can
be safely handled by an induced-draft fan.  Cooling
air is introduced through manually adjustable and
barometric  dampers located in the breeching.

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                                Mobile Multiple-Chamber Incinerators
                                                                                                  453
    Figure 345. A 500-pound-per-hour mobile  incinerator
    with retractable stack.
   Figure 346.  A  1,000-pound-per-hour mobile  incinerator
   with retractable stack.
Heat and material balances, necessary for design-
ing the breeching,  are computed by the methods
shown in the illustrative problem on page 456.  The
breeching  should be sized to give an average ve-
locity  through its  cross-sectional area of about
40fps.  At this velocity, adequate mixing of cool-
ing air with the products of combustion occurs with-
in 0. 4 second, producing a relatively uniform tem-
perature without excessive frictional losses.  De-
signing the breeching for low frictional losses per-
mits use of inexpensive axial -flow or propeller-type
fans .

Manually adjustable dampers allow for introduction
of dilution air into the breeching to cool the prod-
ucts of combustion.  These dampers must be sized
to provide  sufficient air at the maximum burning
rate of the incinerator to cool the gases  to  the de-
sign temperature of the fan.  Barometric dampers
balance the induced-draft system by sustaining an
adequate and uniform draft in the incinerator. Their
use comes into play primarily at  lightoff  and burn-
down when the charging door is closed and the  air-
ports are partially opened, restricting the gas  flow
through the incinerator.  Under these conditions,
the barometric dampers open more widely,  allow-
ing additional air to be induced into the breeching.
This prevents an increased draft from developing
in the ignition  chamber.  During capacity opera-
tion,  when the gas flow through the incinerator is
maximum, the balancing effect of barometric damp-
ers is not required.
A major problem in the design of the induced-draft
fan system is the proper selection of the fan.  Fans
capable  of  operating from ambient temperatures
to temperatures in excess of 1,200°F are avail-
able. Fans designed to operate in excess of 800°F
must be constructed of stainless steel and should
be equipped with water-cooled  bearings.  These
fans  are costly; their bearing-cooling requirements
virtually eliminate them from use on portable equip-
ment.

Low-temperature fans -with mild steel blades are
capable  of operating up to 300 °F.   The maximum
operating temperature of these fans  can be in-
creased to 800 °F by the addition of simple and in-
expensive  bearing coolers commonly called heat
slingers.  As the  temperature  increases  above
300 °F, the maximum permissible  rpm is reduced
for any class or duty of a specific fan.  This capac-
ity reduction ranges from about 1 0 percent at 600 °F
to 30 percent at 800 °F.  Therefore, it is necessary
to install a larger fan  of  the  same class or the
same size fan of higher  class when operating tem-
peratures exceed 600°F.

If dilution air is introduced in excess  of that neces-
saryto  cool the effluent to a temperature that  can
be handled by an inexpensive fan,  this excess  air
will  require an increase,  not only  in fan size, but
also in horsepower and operating cost.  All factors
considered, the apparently optimum operating tem-
perature of the fan is 600 °F.  At this temperature

-------
 454
                                           INCINERATION
an inexpensive and minimum sized fan constructed
of mild steel can be used.  Since  propeller-type
fans have the advantages  of compactness, low cost,
and light  weight,  they are  usually selected over
centrifugal  types.   Bronze  blades available at a
nominal increase in cost over  steel blades and
capable of  operation up to 800 °F are usually in-
stalled to provide a safety factor.

The induced-draft fan is powered by a small gaso-
line engine through a chain or belt drive.  The en-
gine is sized for maximum power requirements,
which occur at lightoff when the air handled by the
fan is  at ambient temperature.  As the tempera-
ture of the exhaust gases rises,  the fan horsepower
at a constant rpm decreases in proportion to the
change in density  of the gases.  The draft of the
incinerator  can also be  regulated by changing the
speed  of the gasoline engine driving the fan.
STANDARDS OF CONSTRUCTION

The mechanical design and construction of a mobile
incinerator mustnot only meet the dimensional and
weight requirements of the Vehicle Code but also
provide a rigid frame and refractories  of sufficient
quality to provide a satisfactory service life.


Refractories

Since refractories constitute  60 to 75 percent of
the total weight of a mobile incinerator,  low-den-
sity refractory materials must be selected.  These
materials should have a minimum pyrometric cone
equivalent (PCE) of 15 and be relatively  resistant
toabrasion, spalling, and physical shock. Thermal
conductivity  should be about 5.4  at  2,000°F by
ASTM C-201  so  that  backing with insulation will
not be necessary.

Because shaped firebricks are not suitable for mo-
bile installations because of excessive weight and
problems  in anchoring firmly to walls, other re-
fractories must  be investigated.  A  number of
standard castable refractories manufactured today
meetthese specifications.  They are composed of
approximately equal portions of alumina and silica,
are easy  to  cast,  and have a density of about 80
pounds per cubic foot.

Exterior walls and arches are secured against thin
corrugated steel sheets •with stainless steel anchors
arranged on 12-to  15-inch centers, while  interior
walls are self-supporting.   Walls and arches are
usually 4-1/2 inches  thick  for  incinerators with
capacities of less than 600 pounds per hour and 6
inches thick for  units of larger capacity. It is of
the utmost importance that castable  refractories
be installed strictly in accord with the information
and directions provided by the manufacturer.
The bridge-wall is susceptible to damage by care-
less operation, and the curtain wall is subjected to
high-temperature flame impingement accompanied
by high velocities, which tend to erode its surface.
At these locations, the use of heavier castable re-
fractories, which are more resistant to abrasion
and erosion, is advantageous.   A number of mate-
rials with  densities of about 120 pounds per cubic
foot have the special qualities  to fill this need.


Grates

Cast iron  grates,  available today in many sizes,
shapes,  and patterns,  are satisfactory for burn-
ing general refuse,  as described previously in this
chapter.   Castable refractory grates,  described
later in this chapter, should be installed in incin-
erators designed to burn large quantities of wood.

Air Inlets

Combustion air may be controlled by providing ad-
justable dampers  in the throats  of  all air ports.
Dampers used for controlling overfire and under-
fire air are  subject to warpage  from high tem-
peratures  and should  be constructed of stainless
steel or cast iron.   The secondary air port damp-
er is not subjected to much heat and may be con-
structed of 10-gage mild steel plate.


Structure

The trailer  and frame for supporting the incin-
erator  should be designed by qualified structural
engineers. A trailer of •welded steel construction
must be rigid enough to prevent the transmission
of stresses and strains to the refractory walls dur-
ing travel over rough terrain.   The external frame
should  also  be  engineered to  cope not only with
mechanical stresses imposed during transporta-
tion but also with thermal stresses produced dur-
ing the operation of the incinerator.
 Auxiliary Burners

 Mobile incinerators usually burn  refuse varying
 widely in  composition, requiring auxiliary burn-
 ers sized in accordance with the information pre-
 sented in Table 119.  These burners are fired with
 LPG supplied  from tanks  mounted  upon the incin-
 erator trailer.
 STACK EMISSIONS

 The quality and composition of emissions  from
 mobile multiple-chamber incinerators are similar
 to those from stationary multiple-chamber incin-
 erator s in burning general  refuse.  The air pollu-
 tants in pounds per  ton of refuse burned are given
 in Table  120.

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                                Mobile Multiple-Chamber Incinerators
                                                                                                 455
Illustrative Problem

Problem:

Design an induced-draft fan system for a mobile
multiple-chamber incinerator.
                                               3.   Flow of dilution air at 60°F:
                                                   (11, 100 lb/hr)l
                                                                 '379 ft /lb mole

                                                                   29 Ib/lb mole /\60 min/
                                                   =  2, 420 cfm or 40. 3 cfs
Given:

Refuse  to  be  burned is 1, 000 pounds of wood per
hour with 20 percent by weight moisture.

Solution:

1.  Weight of products of combustion with 300 per-
    cent excess air:

    From Table  121, there are 24.68 lb of com-
    bustion products from the combustion of 1 lb
    of  average dry wood with 300 percent excess
    air, 40 percent saturated.

    Wood  (800 lb/hr)(24.68 Ib/lb) =  19,7501b/hr
    Moisture                           200  Ib/hr
       Total                         19, 950  Ib/hr
2.   Weight of dilution air required to reduce prod-
    ucts of combustion from 900°   to 600°F:

    Assume  combustion products are equivalent
    to air  in composition.  Average specific heat
    of air  is 0. 26 Btu/lb-°F.
   (w )(c  )(t -t )  =   (w  )(c  )(t  -t  )
     a   p2  2  a        pc  pi   1  2
•where:
  pc
"Pi
 "P2
                                               4.   Gas flow through breeching:

                                                   From Table  121, there are 321.7 ft3  of com-
                                                   bustion products  at 60°F from combustion of
                                                   1 lb of average dry wood with 300 percent ex-
                                                   cess air.

                                                   Wood   (800 lb/hr)(321.7  ft3/lb)  =   257, 000 cfh

                                                Moisture (200 lb/hr)fc ^ ^ m°^}     4, 200 cfh
                                                                     \ 18 Ib/lb rnole /
        Total


    Dilution air at 60 °F (2, 420 cfm)


        Total



    Total gas flow at 600 °F

              (1,060°R)
                                                                                        261, 200 cfh
                                                                                   (&0 min\
                                                                                   -ThT-j
                                                                                     =   145, OOP cfh
                                                                                        406, 200 cfh
                                                                                    or     6, 770 cfm
                                                                                    or       113 cfs
                                                              (520°R)
                         (6, 770 cfm) = 13, 000 cfm
                                     or    230 cfs
                                               5.   Cross section of breeching:

                                                   Design breeching for an average gas flow rate
                                                   of 40 fps at 600°F:
                                                               Area   =
w  -
  a
=  weight of dilution air, Ib/hr

=  -weight of combustion products; Ib/hr

=  average specific heat of products of
   combustion,  Btu/lb-°F

=  average specific heat of air,  Btu/lb-°F

=  final temperature,  °F

=  initial temperature of combustion prod-
   ucts,  °F

=  air temperature, °F


 (19, 950  lb/hr)(0. 26 Btu/lb- °F)(900 °F - 600°F)
      (0.26 Btu/lb-°F)(600°F -  60°F)
                                                                   (230 cfs)
                                                                    (40 fps)
                                 5. 75 ft
    =  11,100 Ib/hr
                                                         Dimensions: 18 in.  high x 46 in.  wide.
6.   Length of breeching:

    Design breeching for a residence time of 0.45
    sec at 40 fps

    Length = (0.45 sec)(40fps) =  18ft

    Use a double-pass breeching 9 ft long to fit on
    top of the incinerator.
7.   Static pressure behind adjustable dampers and
    barometric dampers at capacity operation:

    Assume static pressure behind the adjustable
    dampers  and barometric dampers is essen-
    tially the  same.

-------
 456
                                           INCINERATION
 (a) Assume static pressure in combustion cham-
    ber, SP = 0. 30 in. WC

 (b) Contraction loss from combustion chamber
    into duct leading to breeching:
    Ratio r =
       cross-sectional area of duct
      horizontal cross-sectional area
            combustion chamber
          r =  JLZilL  =  o.33
               17. 5 ft
     Contract! on loss is 0. 38 VP* (velocity pres-
     sure head)  at the velocity through the duct.
     Velocity through 5. 75 ft2  port at 900 °F
 (261,200 Cfh)   (1.360'R)      (1)
(3,600 scfs/hr)    (520°R    (5. 75 ft2     ^-^
    Assume composition  of combustion prod-
    ucts is  equivalent to air.
    Velocity head of 32. 9  fps at 900°F
            v  =   2. 9Vth '

     where:

     v  =  gas velocity, fps

     t  =  absolute gas temperature, °R

     h  =  velocity pressure  (head), in.  WC
     h  =
/_2_\2iii
\2.<)J (t)

/32. 9fps\2 /
\  2.9   )  \l
     h

     h  =  0.090 in.  WC

     Contraction loss
     (0.38 VP)
       (0. 090 in. WC)
            1 VP
=  0. 04 in. WC
                        (c)  Right-angle bend into breeching.

                            Assume 1 VP loss for right-angle bend.
                            1 VP at 32. 9 fps and 900°F  =  0. 09 in.  WC

                        (d)  Total static pressure

                            a  +  b  +  c  = total  static pressure

                            (0. 30 in. WC)  +  (0. 04 in.  WC)  +
                                                   (0
                              . 09 in. WC)  =  0. 43 in.  WC
                                            8.   Indraft velocity through dampers:
                                                Design breeching for a gas velocity of 40 fps
                                                at 600°F.  At a velocity pressure of 40 fps
                                                and 600°F,
                                                                         ill
                                                                          (t)
                        Total pressure = velocity pressure + static
                        pressure.
                        Total pressure = 0. 18 in. WC + 0.43 in. WC
                        = 0. 61 in.  WC.
                        Assume static friction loss through dampers
                        is 0. 65 VP.
                        Total pressure = velocity pressure + static
                        pressure.
                        0.61 in. WC =  1  VP  +  0.65 VP
                                          VP  =  0. 37 in. WC

                        From Table D8, Appendix D, the velocity
                        at 60°F and  0. 37  in. WC is  2, 410 fpm.
9.   Size of adjustable dampers (assume barometric
    dampers closed):

    Design dampers  100% oversize  to  allow for
    operation  of the incinerator in excess of de-
    sign capacity.
    Dilution air  =  2, 420 cfm

    'Z'420cfm!  (2) =  2.03ft2
    (2, 410 fpm)
 •Badger and McCase, 1936.
                                           10.  Static-pressure drop through  induced-draft
                                                system at capacity operation with a 600 °F out-
                                                let temperature:
 *f"Research-Cottrell, Inc.
                                                        (a)  Static pressure at dampers, SP  = 0.43 in.  WC

-------
                                Mobile Multiple-Chamber Incinerators
                                                                                            457
(b)  Double pass breeching 18 feet long:

                       2*
          f  =

    where:
          0.002 hv
             mt
    f  =  friction, in.  WC

    h  =  duct length, ft

    v  =  gas velocity,  fps

    t  =  absolute gas temperature,  °R

    m =  hydraulic radius
                                                11.  Calculate points on system static-pressure
                                                    curve based upon capacity operation at 600 °F:
                                                                              2
                                                              SP2   =   (spj
                                                    where:
                                                       cfm   =
                                                       cfm   =
                                                                    unknown static pressure

                                                                    proposed cfm

                                                                    known cfm

                                                                    known static pressure
          cross-sectional area of breeching, ft
                 perimeter of breeching, ft

          (.002)(18)  (V  =        n_
        =
            (0.54)(1, 060)

 (c)  180°  bend at one end of breeching.

     Assume 2-VP loss at 40 fps and 600°F
          -  =
(2 vp)
                           =  0.36in.  wc
 (d)  90° bend at fan discharge.

     Use 9 ft   opening to reduce pressure drop.
     Assume 1-VP loss for 90° bend at 600°F.

     Velocity = (40 fps)7     }  = 25. 6 fps
          h  =
     h  =
           2.97 \1,060/
                         =  0. 07 in.  WC
         (0.07 in.  WC)   _
    1    '     (1 VP)     ~    'U' ln

(e)  Total static pressure for  system:

    (a) + (b) + (c) + (d)  =  total static pressure

    (0. 43) + (0. 10)  + (0. 36)  +  (0. 07) = 0. 96 in. WC
*Gnswold, 1946..
                                                    Assume cfm   =  10,000
                                                           sp2   =  (0.
                                                    Assume cfm   =  20, 000
                                                                                =  0.57in.  WC
                                                    12.  Fan specifications:

                                                        Select fan that will deliver,  as near as possi-
                                                        ble,  13, 000 cfm at 0. 96 in. WC and 600°F.
                                                        Fan performance given for 60 °F operation:
                                                                  1, 160 rpm 60°F
1.4 in.  WC
21, 000 cfm
10 bhp
                                                                      2.0 in. WC
                                                                      13, 800 cfm
                                                                      7. 5 bhp
                                                                                2. 2 in. WC
                                                                                10, 000 cfm
                                                                                6.7 bhp
                                                    Calculate  points for 600 °F fan performance
                                                    curve:  With rpm and cfm held constant, static
                                                    pressure and bhp vary directly with gas density
                                                    or inversely with absolute temperature.
                                                                  Ratio  =
                                                                        520 °F
                                                                       1,060°F
                                                                                     =  0. 49
                                                                   1, 160 rpm 600°F

                                                     0.7  in. WC    1.0 in. WC     1.1 in.  WC
                                                     21, 000 cfm    13, 800 cfm     10, 000  cfm
                                                     4.9  bhp       3.7 bhp        3. 3 bhp

-------
458
                                           INCINERATION
13.  Operating point at 600 °F:

    Intersection of 600 °F system curve with 600 °F
    fan curve is shown in Figure 347.

                13, 400 cfm
                1. 02 in.  WC at 600°F
                1, 160 rpm
                3. 7 bhp
14.  Static-pressure drop.for induced-draft system
    at 60°F:

    This  condition occurs at lightoff before igni-
    tion.   Assume negligible airflow through in-
    cinerator and  static pressure 0. 3  in. WC in
    combustion chamber and behind barometric
    and adjustable  dampers.

    Assume total airflow through fan is 13, 000 cfm.
                                                       (a) Behind dampers static pressure = 0. 30 in. WC.

                                                       (b) Friction through 18-foot-long breeching:

                                                           Cross-sectional area  =   5. 75 ft

                                                                           2
                                                              f  	
                                                                   0. 002
                                                                      mt
                                                                (0.002)t18)(40)
                                                                   (0. 54)(520)
                                                                                         ln' WC
                                                       (c)  180° bend at end of breeching:

                                                           Assume 2-VP loss  at 40 fps and 60°F

                                                           From Table D8, Appendix D, VP =
                                                           0.36 in. WC

                                                           (2 VP) ^
                                                                                             Q_
                                                                                             LU
                                                                                             V)
                                                                                             OC
                            5,000
                                          10,000        15,000
                                              VOLUME,  cfm
                            Figure 347.  Fan  and system curves at 60°F and  600°F.

-------
                                  Mobile Multiple-Chamber Incinerators
                                             459
    (d) 90° bend fan discharge through 9 ft  outlet:

       Assume 1 VP at 26.5 fps at 60°F

       From Table D8, Appendix D,  1  VP  =
       0. 16 in. WC

                              =   0. 16  in. WC
    (e) Total static pressure:

       a  +  b  +  c  +  d  =   1. 39 in. WC
15. System static-pressure curve development at
    60°F:
                            cfm2 \ 2
    Assume cfm   =  10,000
                                    ). 82 in. WC
    Assume cfm   =  16, 000
sp2   =   (1.
                       16,000\Z
                                 -
                                 =  2. 10 in.  WC
16.  Operating point at lightoff where the 60°F sys-
    tem curve intersects the 60°F fan curve (see
    Figure 347):

                15, 200 cfm
                1. 90 in. WC at 60°F
                1, 160 rpm
                8. 0 bhp

    Selecta 10-hp gasoline engine to drive the fan.

17.  Total system pressure behind dampers:

    Assume negligible airflow through incinerator
    at lightoff.
    Static pressure behind adjustable and baromet-
    ric dampers at 60 °F:
    Total air velocity at 60°F in breeching:


       15, 200 cfm     , ,  .„ ,.
       	'-	—  =  2, 640 fpm
         5. 75 ft

    From Table D8, Appendix D,  VP = 0.41
    in. WC

    Total pressure = velocity pressure + static
    pressure
    Total pressure = 0. 44  in. WC + 0.41 in.  WC

    Total pressure = 0. 85  in. WC


18. Air velocity through adjustable and baromet-
    ric dampers:

    Assume friction loss through dampers at 0.65
    VP inlet.

    Total pressure = velocity pressure + static
    pressure

    0. 85  in. WC =  1 VP + 0. 65 VP

                     VP = 0. 52 in. WC

    From Table D8, Appendix D,  inlet velocity
    is 2, 860 fpm.
19. Airflow through adjustable dampers:

          (2.03ft  )(2,860fpm)  =  5, 800 cfm


20. Airflow through barometric dampers:

    Assume negligible airflow through incinerator

    Total airflow through fan  15, 200  cfm

    Adjustable dampers       5, 800  cfm
    Barometric dampers      9, 400  cfm

21. Selection  of barometric dampers:

    Minimum damper area.
    Area  =
                                                             (9,400  cfm)
                                                             (2, 860  fpm)
=  3.28ft
                                     2
    Select four 15-in. -diameter barometric damp-
    ers with total area about 40% in excess of min-
    imum area to allow for operating flexibility.
                                                          Total open area of 4 dampers:

                                                                          (1. 23 ft )            2
                                                                4 dampers-;	;*-  =  4.9ft
                                                                          (damper)

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460
                                          INCINERATION
MULTIPLE-CHAMBER INCINERATORS FOR
          BURNING WOOD WASTE

INTRODUCTION

Although a small part of the wood waste produced
from lumber  mills  and wood-working industries
can be processed into useful products such as  chip
board, fireplace logs,  and paper, the bulk of this
waste is disposed of  by incineration, open burning,
or hauling to  a  dump.   The most satisfactory air
pollution  solution is, of course, landfill disposal.
The  final choice of the  method of disposal is  pri-
marily  determined  by  economics  and by the air
pollution regulations existing  in the locale.


There are, in general, three methods of burning
wood waste.  These are  (1) open burning, that is,
burning in a pile without any surrounding structure;
(2) burning in single-chamber incinerators, includ-
ing the tepee and silo structures; and  (3) burning
in multiple-chamber incinerators.  Of these, the
latter is the most satisfactory from an air pollu-
tion standpoint.

Open burning  with no control  over combustion air
produces more air contaminants than single-cham-
ber incinerators do with regulated air supply.  The
tepee and silo  single-chamber incinerators  also
differ in combustion efficiency and emission of air
contaminants.
 Tepee incinerators are simple structures consist-
 ing usually of nothing more than a sheet metal shell
 supportedby structural steel members in a shape
 similar to that of an Indian tepee.  They are usu-
 ally located at lumber  mills and have limited con-
 trol of primary combustion air.  Many units em-
 ploy blowers to supply air to the base of the burn-
 ing pile  to increase the burning rate.  The metal
 shell is cooled by peripheral air,  which flows  up-
 ward and  over the inside  surfaces.   Excessive
 combustion air admitted in this manner prevents
 good control of the combustion process and results
 in excessive smoke and other air contaminants.
 A silo  incinerator consists of a steel cylindrical
 chamber lined with high-duty refractory materials.
 The top of the cylindrical chamber usually tapers
 to a smaller diameter and extends upward, form-
 ing  a stack to promote  draft.  Air is admitted
 through louvers located near the base of the struc-
 ture. High temperatures can be maintained in the
 refractory-lined chamber, resulting in higher com-
 bustion efficiencies than in the tepee units.  Single-
 chamber silo incinerators are not, however, satis-
 factory  where air pollution is a serious problem,
 and have been found to emit particulate matter in
 excess  of 12 pounds per ton of wood waste burned.
Description  of the  Refuse

Wood waste is produced by industry in a great many
sizes and shapes  ranging from fine sander dust to
large pieces of lumber.  Physical properties and
combustion data  for  several common woods are
given in Table 121.  Green lumber at the mill varies
widely in moisture content.  For example, green
redwood may contain  over  50 percent moisture by
weight,  while construction-grade lumber such as
Douglas fir contains from 1 0 to 25 percent moisture
depending upon its age.  Kiln-dried wood may con-
tain as little as 5 or 6 percent moisture.


THE AIR  POLLUTION PROBLEM

Burning  of wood  •waste in open areas and at dump
sites or in single-chamber  incinerators is accom-
panied by dense clouds of smoke,  fly ash,  and dis-
agreeable odors.  Basically, these air contaminants
arecausedby incomplete combustion and are dis-
charged  in  the form of particulate matter,  alde-
hydes, hydrocarbons  and organic acids,as well as
smoke and  fly ash.  They are usually present in
the greatest concentrations after the lightoff peri-
od or during times  of heavy charging.

While single-chamber silo incinerators have been
found to have particulate  emissions in excess of
12 pounds  per ton of wood waste,  the particulate
discharge from multiple-chamber incinerators de-
signed to burn small wood particles ranges from
l-l/2to6-l/2 pounds per ton of wood -waste burned,
as shown in Table 122.  Smoke is visible from a
well-designed multiple-chamber incinerator only
for a few minutes  after lightoff and  is occasionally
accompanied by minute amounts of fly ash.

AIR POLLUTION CONTROL EQUIPMENT

Air pollution from the burning of wood waste can
be reduced to a minimum through the use of multi-
ple-chamber incinerators.  By promoting  com-
plete  combustion, multiple-chamber incinerators
produce considerably less air pollution than is
emitted from single-chamber  incinerators or  by
open burning. Multiple-chamber incinerators dis-
cussed in the remainder of this part of the chapter
are designed to  burn all  forms of wood waste--
from large pieces  of lumber  to sawdust particles
that  may comprise from  10 to 100 percent of the
total weight of the charge.   The  designs  of me-
chanical feed systems are also included since the
feed system must be properly integrated with the
design of the incinerator to promote maximum com-
bustion.

DESIGN PROCEDURE

The fundamental principles of combustion discussed
in the first  part of this chapter are applicable to
designing these  incinerators.  Where 10 percent

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                        Multiple - Chamber Incinerators for Burning Wood Waste
                                           461
                    Table 122.   SOURCE TEST DATA FOR MULTIPLE-CHAMBER
                                  INCINERATORS BURNING WOOD
Item
Incinerator capacity
Normal burning rate
Moisture content of refuse
Stack volume
Secondary chamber temperature
Particulate matter


Particulate matter
Sulfur dioxide
Carbon monoxide
Organic acid--as acetic
Aldehydes --as formaldehyde
Hydrocarbons--as hexane
Units
Ib/hr
lb/hra
wt %
scfm
OF
gr/scf
at 12%
CO2
lb/tonb
lb/tonb
lb/tonb
lb/tonb
lb/tonb
ppm
Test No.
1
150
170
10
420
1, 600
0.058


2.0
0
0
0.8
2.0
9
2
350
300
5
557
1,400
0. 038


1. 4
0
0
1. 2
1.9
9
3
750
740
10
3,260
1, 500
0. 095


3. 2
0
0
0. 54
0.8
9
4
1, 000
1,055
25
3, 300
1, 850
0.23


6.6
0
0
0.85
3.0
9
5
3,000
2, 910
10
15, 300
1,600
0. 11


3.6
0
0
1. 2
6.0
9
     Burning rate based on stack analysis.
    -"Pounds of contaminants per ton of wood burned.
or more of the -wood waste is in the form of saw-
dust and shavings,  it must be fed at a continuous
rate by a mechanical feed system.  Differences in
some design factors from those given at the  be-
ginning  of this chapter for hand-charged general-
refuse incinerators generally reflect  the  higher
temperatures developed from the exclusive and
continuous  mechanical charging of -wood, and dif-
ferences in the distribution of combustion air.

The gross heating value of kiln-dried wood is 9^000
Btu per  pound and  is represented by the upper
curves of Figures  341 and  342.  These  curves  can
be used  to  determine grate  loading and average
arch  height, respectively.  Other design factors
differing from those for general-refuse incinera-
tors are given in Table 123.  These design factors
include secondary chamber cross-sectional areas,
inlet air port sizes, and other values and propor-
tions .

An illustrative problem at the  end of this  part of
the chapter  shows how  these factors are used to
design a multiple-chamber incinerator  with a me-
chanical feed system.   The  calculations in this
problem fall into three general categories: (1) Com-
bustion calculations based upon refuse composi-
tion, projected air requirements,  and heat trans-
fer;   (2) gaseous flow calculations based upon the
products of  combustion at elevated temperatures;
and (3) dimensional calculations based  upon equa-
tions  determined empirically from source  testing.

Chemical properties and combustion data for  av-
erage -wood and Douglas fir,  given  in Table  121,
and similar values for other kinds of wood can be
 used to determine the weights,  velocities, and av-
 erage temperatures of the products of combustion.


 For calculation purposes, the burning rate and wood
 waste composition are assumed constant, and the
 incinerator is considered  to be under relatively
 steady-state conditions.  Calculations are always
 based upon refuse that is the most difficult to burn.
 Heat losses by radiation, heat stored in refractory,
 and heat content of the residue are assumed to av-
 erage 20 to 30 percent of the gross heating value
 of the refuse  during  the first  hour of  operation.
 These heat losses drop  to 10 to 15 percent after
 4 or 5 hours  of operation.
To determine the cross -sectional flow areas of the
secondary ports and chambers,  only volumes and
temperature levels of the products of combustion
are required.  The temperature gradient in which
the products of combustion cool as they pass from
the flame port to the stack are averages based upon
source tests of similar incinerators.

The  calculated overall  average gas temperature
shouldbe about 1, 300°F based on 200 percent ex-
cess combustion air and the 20 to 30 percent heat
losses.   The calculated temperatures are not flame
temperatures and do not indicate temperatures at-
tained in the flame port  or mixing chamber.

Indraft velocities through the ignition chamber air
ports are assumed to average 900 fpm, equivalent
to a velocity pressure of 0. 05 inch WC,  while in-
draft velocities through the secondary air ports av-

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462
                                                         INCINERATION
                            Table  123.  DESIGN  FACTORS  FOR MULTIPLE-CHAMBER
                                     INCINERATORS FOR  BURNING WOOD  WASTE
                                    Item and symbol
                                                                   Recommended value and units
                                     Allowable
                                      deviation
                           Primary combustion _zone
                            Grate loading,  LQ
                            Grate area,  AQ

                            Average arch height, H^

                            Length-to-width ratio (approx):
                              Retort
10 Log Rc, lb/hr-ft^ where RC equals
the reluse combustion rate in Ib/hr
(refer to Figure 341)


4/3 (AG)4//11; ft (refer to Figure  342
and + 10% curve)

Up to 500 Ib/hr, 2 1;  over 500 Ib/hr,

Diminishing  from about 1.7:1 for
750-lb/hr to  about 1:2 for 2, 000-
Ib/hr capacity.  Ovcrsqaure  ac-
ceptable in units of more than 11-ft
ignition chamber length
                                      + 10%
                                                                                                      + 10%
                           Secondary combustion zone
                            Gas velocities
                             Flame port at 1,900°F, Vpp

                             Mixing  chamber at 1, 550°F,

                             Curtain wall port at  1,  500°F,
                             VCWP
                             Combustion chamber at 1,200°F,
                              V
                               cc
                            Mixing chamber downpass length,
                            L,./-, from top of ignition chamber
                              MC          r    to
                            arch to top of curtain wall port

                            Length-to-width ratios of flow
                            cros s sections

                              Retort, mixing  chamber,  and
                              combustion chamber
50 ft/sec

25 ft/sec

20 ft/sec
5 to 10 ft/sec, always less than
10 ft/sec

Average arch height, ft
Range 1.  3 1 to 1. 5  1

Fixed by gas velocities due to
constant incinerator width
                                       1 20%
                                       + 20%

                                       + 20%
                                                                                                         20%
                           Combustion air
                            Air requirement, batch,  or con-
                            tinuous charging
                            Combustion air distribution,  % of
                            total air required
                              Overfire air ports
                              Underfire air ports
                              Mixing chamber air ports
                              Curtain wall port or side ports
                            Port sizing, nominal inlet,
                            velocity pressure, and velocity
                            (without oversize factors), in. WC
                            or fpm
                              Overfire port
                              Underfire port
                              Mixing chamber port
                              Curtain wall poi-t or side port
Basis   200% excess air.  100%
excess  air admitted into ignition
chamber, 50% theoretical air
through tniving chamber air ports
and 50°o theoretical air through
curtain wall air port  or side
air ports.
60%
6%
17%
17%
 0.051 or 900
 0. 051 or 900
 0. 062 or 1, 000
 0. 062 or 1, 000
                           Furnace temperature.
                             Average temperature, combus-
                             tion products at 200% excess air
 1,300"F
                                       + 20°F
                           Auxiliary burners
                             Secondary burner (if required)
 2, 500 to 5, 000 Btu per Ib of
 moisture in the refuse
                           Draft requirements:
                             Theoretical stack draft, DT

                             Available primary air induction
                             draft, D. (assume equivalent to
                             inlet velocity pressure)

                             Natural draft stack velocity, Vg
 0. 15 to 0. 35 in. WC

 0. 05 to 0. 10 m.WC


 Less than 25 ft/sec at 1, 100T

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                        Multiple-Chamber Incinerators for Burning  Wood Waste
                                            463
erage  1,000 fpm (0.06 in. WC).  The incinerator
draft system should be designed to produce a nega-
tive static pressure of at least 0. 05 inch WC in the
ignition chamber.

Primary air ports for continuously fed incinerators
are sized for induction of theoretical plus 100 per-
cent excess air.  Ten percent of this air is admitted
through ports located below the grates, and 90 per-
cent, above  the grates.  Additional primary air
canbe admittedby opening the charging door "when
necessary.  Air is induced into the mixing cham-
ber not only to support combustion but also to cool
the combustion gases and prolong the service life
of the refractories.  Mixing chamber air ports lo-
cated in  the bridge  wall  are sized to admit 50 to
100 percent of theoretical air.  Air is  sometimes
admitted  to  the combustion  chamber through air
ports located  in the curtain  wall and sized to ad-
mit an additional 50 percent  of theoretical air.

Although  some combustion air enters the ignition
chamber along with the sawdust from the pneumatic
conveying system, this air usually amounts to less
than 7 percent of the total combustion air and can
be neglected in determining the size  of the primary
airports.  Airports are designed with the factors
given in Table  123.

Unless the wood refuse is extremely wet, auxiliary
gas burners are not required  in the  ignition cham-
ber to initiate and sustain combustion.  If products
such as rubber, oily rags, and plastics are present
inappreciable  quantities in the wood wastes, they
produce partially oxidized compounds that require
high temperatures  for  complete secondary com-
bustion.  Thus,  secondary burners should be in-
stalled in the mixing chamber with  automatic con-
trols to maintain the required high temperatures
under  all phases of operation.
Incinerator Arrangements

Incinerators for burning wood use both in-line and
retort styles as shown in Figures 348 and 349.  In-
cinerators with capacities  of less than 500 pounds
per hour are usually constructed as retorts.  Units
ranging  from  500 to 1,000  pounds per hour may,
however,  follow either the in-line or retort style
for the arrangement of chambers.  In-line styles
are recommended for incinerators with capacities
in excess of 1,000 pounds per hour because of not
only the inherent higher costs of the retort but also
the difficulties in cooling the internal walls.  A
retort-type incinerator with a prefabricated steel
shell is  shown in Figure 349.  A single-chamber,
silo-type incinerator can be converted to multiple
chamber by attaching a dutch oven consisting of an
ignition chamber and a mixing chamber  as depicted
in Figures 350 and 351.
 Figure  348.  A 2,000-lb-per-hour, in-line multiple-chamber
 incinerator  (Metro Goldwyn Mayer,  Inc.,  Culver City,  Calif.).
     Figure 349.  A 150-lb-per-hour,  retort multiple-chamber
     incinerator  (Acme Woodcraft,  Los Angeles,  Calif.).

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464
INCINERATION
                                                                   Figure 350.  A 1, 000-1 b-per-hour,  in-line
                                                                   multiple-chamber  incinerator  (silo con-
                                                                   version)    (Orban Lumber Co.,  Pasadena
                                                                   Calif.).
          CHARGING
          DOOR WITH
          OVERFIRE
          AIR PORT
                                                                                                      SILO
                                 •ASH PIT-
                                  CLEANOUT
                                  DOORS
            CLEANOUT DOORS-
                               Figure 351.  Schematic diagram of an in-line multiple-chamber
                               incinerator  (silo conversion).

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                        Multiple-Chamber Incinerators for Burning Wood Waste
                                             465
In the design of the silo conversion, the size of the
ignition  chamber and mixing chamber attached to
an existing silo is limited by a maximum allowable
gas velocity of 10 fps through the horizontal cross-
sectionalbase of the silo, or by the effective draft
developed by the stack.  Effective draft, in turn,
is limited by the height of the silo and its internal
dimensions.

If the attachment of an ignition and mixing cham-
ber  to a silo  results in a gas velocity through the
base of  the silo of less than 5 fps,  a refractory
tunnel with a cross-sectional area equal to the cur-
tain wall port  area should extend from the curtain
wall halfway across the base of the silo.  The  tunnel
acts as  an  extension  of the mixing chamber and
provides additional flame residence time and turbu-
lence necessary to complete the  combustion pro-
cess.
DESIGN PROCEDURE FOR MECHANICAL FEED  SYSTEMS

During  the  development  of the multiple-chamber
incinerator, hand charging of sawdust  and inter-
mittent delivery of sawdust from local exhaust sys -
terns  serving woodworking equipment were found
to smother the flames periodically in the ignition
chamber and  thus cause  excessive smoke.  To
overcome this problem, a feed system was  devel-
oped for delivering small  wood particles to the ig-
nition chamber at a constant rate and thus  sustain
continuous  burning  over  the entire surface of the
pile.  This system, illustrated in Figure 352, con-
sists  basically of a surge bin for holding sawdust
and wood chips from local exhaust systems serv-
ing woodworking  equipment.  Screw or drag con-
veyor s in the bottom of the surge bin move the wood
waste  at a  uniform  rate  to the pickup point of a
pneumatic conveying system.  The pneumatic con-
veyor  transfers  the •waste to a cyclone •where the
waste drops into the  ignition chamber.


Surge Bin

Bins usually fabricated of  sheet metal are designed
in such  a •way as to augment gravity  flow of saw-
dust and wood chips to the conveyor at the bottom
of the bin.  Waste is produced in a -wide variety of
sizes and  shapes, ranging from fine sander dust
to large chips from hoggers.  Gravity flow of mate-
rial is a complex function  of the composition, size,
shape, density, packing pressure, adhesive quali-
ties,  and moisture content.   For  example, pine
wood shavings do not flow as  easily  as hardwood
shavings of identical size and shape do because the
resin content of the pine wood imparts an adhesive-
ness hindering the flow.  The flow characteristics
of a particular wood waste are,  therefore,  of pri-
mary importance in the final selection of the shape
of the bin.
                               WOODWORKING
                               EXHAUST SYSTEM
                               CYCLONE
                                      EXHAUST
                                      FAN
     Figure 352.  Diagram of a mechanical feed system.
Wood wastes that exhibit poor flow characteristics
should be handled in bins constructed with vertical
sides and  screw or  drag conveyors  covering the
entire flat  bottom of the bin, as shown in Figure
353.  If the-wood waste has fairly free flow charac-
teristics, a bin with four vertical sides and a  slop-
ing bottom may be used,  as shown in Figure 354.
The  included angle between the vertical  side and
sloping bottom should not exceed 45 degrees.  Wood
waste that exhibits ideal flow characteristics may
use  a  vee-bottom bin,  as depicted in Figure 355.
The included angle between sloping sections should
not exceed 60 degrees  for most efficient operation.

Although good bin design assists the  flow of saw-
dust to the  conveyors,  bins with sloping bottoms
require mechanical agitators or vibrators to pre-
vent bridging.  Vibrators are generally superior
for this  purpose  since reciprocating and rotating
bar  agitators tend to  shear and bend out of shape
under heavy loads. Tobe most effective, vibrators
are usually mounted about one -fourth of the distance
from the  base of the sloping bottom of the bin,  -which
is usually constructed of a large,  unsupported sec-
tion  of sheet metal.  This method of  construction
permits transmission of vibration more easily than

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466
INCINERATION
transmission from sloping sections  rigidly sup-
ported 'with  stiffened angles or  steel structural
members. If the bottom is so large as to require
some type of external cross-sectional support,  the
support members should  be attached only at the
edges of the  section.
  Figure 353. Vertical-sided  feed bin with four parallel
  screw conveyors (Brown Saltman Furniture Co., Los
  Angeles,  Calif.).
 Vibrators operating continuously may  cause the
 wood waste to pack and bridge in the bottom of the
 bin.  To remedy this  condition, the frequency of
 vibration or the amplitude of the vibratory stroke
 may be changed, or a mechanical timer maybe in-
 stalled to actuate the vibrator s at desired intervals.
 Screw  or Drag Conveying

 Screw or drag conveyors are placed in the bottom
 of a feed bin to remove sawdust and shavings from
 the bin at a regulated rate.  Screw conveyors are
 preferred, except where long,  tough, fibrous shav-
 ings are to be conveyed.  Since material such as
 this would bind in conveyor flights, the more ex-
 pensive  drag  conveyor must be  used.

 Screw conveyors with variable pitch are recom-
 mended  over  screws with uniform pitch because
 they permit more even loading of the  screw along
 the entire length and thus minimize the compress-
 ing of sawdust and shavings causing bridging above
 the discharge  end of the screw.  Because rela-
 tively large pieces of wood may enter the convey-
 ing system,  screw conveyors should be at  least  6
 inches in diameter to ensure their passage.
           Regulation of the flow of wood waste is dependent
           upon the bulk density of the waste to  be handled as
           well as upon the number, diameter,  and speed of
           the screw conveyors.   The bulk  density of most
           wood wastes varies from 4 to 12 pounds  per  cubic
           foot,  depending  upon  the kind of wood processed
           and the shape of the particles.  Determination of
           the density must be based upon sawdust in its  com-
           pressed form at the bottom of the bin,  rather than
           in a loose form.   Once  the density has been estab-
           lished,  the  type of bin selected,  and number of
           screws determined, the diameter and speed of the
           screws can be calculated.  Provisions should also
           be  made for a gear head or varidrive to regulate
           the speed of the conveyors so that they supply wood
           waste over a range of 33 to 100 percent of the burn-
           ing capacity of the  incinerator.

           To  prevent sawdust from being aspirated into the
           pneumatic conveying system faster than the normal
           delivery rate  of  the screw,  conveyors should ex-
           tend at least three screw diameter s beyond the  end
            '/'
            Ai *
                   Figure 354. Feed bin with sloping bottom
                   (California Moulding and Trim Mfg. Co.,
                   Los Angeles  Calif.).

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                        Multiple-Chamber Incinerators for Burning Wood Waste
                                             467
        Figure 355  Feed bin with vee bottom (Orban
        Lumber Co.,  Pasadena, Calif.).
of the bin, and the shrouds should be installed over
the extended  section,  as shown in Figure  356.
Shrouds are usually adjusted  after the unit is in
operation, to provide optimum  clearance over the
flights and prevent binding.

Pneumatic Conveying

While general design features for pneumatic con-
veying  systems are discussed in the preceding
chapter,  a  number of  specific features  should be
considered in  designing pneumatic conveying sys-
tems  for wood waste incineration.

Pneumatic  conveying  systems  are generally  de-
signed for a ratio of 2/3  cfm of conveying air  per
hour per pound of sawdust to be burned.  About 10
percent of this conveying air should be  admitted to
the incinerator along with the •wood waste to assist
in spreading the particles evenly over the entire
grate area  and to maintain active flame over the
surface of the burning pile. The amount of convey-
ing air entering the ignition chamber may be regu-
lated by installing either a butterfly damper in the
top outlet duct of the cyclone separator,  or spiral
vanes within the cone of the cyclone separator.

Sawdust pickup and conveying velocities  should be
at least 3, 000 fpm to prevent sawdust  blockage in
the duct-work.  Blower motors should be oversized
to accommodate occasional surges of sawdust
through the pneumatic  conveying  system.
                                                        Figure 356  Screw conveyor with shroud (Acme Woodcraft,
                                                        Los Angeles,  Cal if.).
Cyclone separators  used in conjunction with the
blower are of the small-diameter, high-efficien-
cy type with separation factor s that exceed  100,  as
described in Chapter 4.
A flap-type damper equipped with a counterbalance
weight  should be installed at the bottom outlet of
the cyclone  separator.   This damper is adjusted
to close automatically when the blower is not in
operation, which prevents the hot gases  of the ig-
nition  chamber from damaging the sheet metal of
the cyclone separator and also prevents smoke from
being emitted to the atmosphere  from  the top of
the cyclone.  This damper should be constructed of
1/4-inch stainless steel plate since it  is subject to
intense radiation from the burning pile.  By con-
struction of a square-shaped damper with a square
duct extending below, the damper is able to swing
out of the -way  of  the falling wood waste.  The
damper  should  be  large enough to form  a tight,
overlapping  seal with a  smooth,  stainless steel
flange located below the round duct at the bottom
of the cyclone separator.

To ensure proper operation,  the equipment should
be electrically interlocked to start simultaneously
or in the following order:  (1)  blower,   (2) convey-
ors,  (3) vibrators or agitators.


STANDARDS FOR  CONSTRUCTION

While  structural features  of wood-burning incin-
erators are similar to those of general-refuse in-
cinerators, •wood-burning incinerators mustbe de-
signedfor greater  stresses and strains caused by
increased thermal expansion resulting from higher
temperature operation.  Refractories, therefore,
are  selected to resist not  only normal abrasion
 234-767 O - 77 - 32

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468
      INCINERATION
from charging but also erosion, spalling, and slag-
ging resulting from high-temperature, high-veloc-
ity flame impingement.


Refractories

Super-duty plastic refractory or super-duty fire
clay firebrick are recommended for the interior
walls and arches that come into direct contact with
flames and hot gases,  since temperatures usually
exceed  2,000°F.  Expansion joints with 1/2-inch
minimum width should be installed for every 6-foot
section of refractory.  These joints must be sealed
completely with  high-duty ceramic  packing with
minimum service temperatures of 2, 500 °F. Pack-
ing of this type is  necessary to prevent ashes from
collecting in the open joints and fusing in such a
way  as to render the  joint useless.

Thefirst 10 feet  of stack must be lined with high-
duty firebrick or an equivalent castable refractory.
The  remainder of the  stack may be lined with a
lower duty material  since flame impingement in
this  area does not normally occur.   The charging
door and  other access doors, 'with  the exception
of the ash pit cleanout doors, should be lined with
120-pound-per-cubic-foot, ASTM Class 24,  cast-
able refractory.

 The minimum heights for free-standing firebrick
walls of given thickness are as follows.

 Thickness of -walls, in.     Unsupported height,  ft
          4-1/2
          9
         13-1/2
 4
10
14
 Firebrick walls extending above these heights should
 be  held to  exterior  supports -with stainless steel
 anchors that permit a differential rate of expan-
 sion.  Walls constructed of plastic refractory should
 be anchored to exterior structural steel members
 on  18-inch  centers.

 Arches may be  constructed of firebrick or plastic
 refractory.  Firebrick arranged to form 60-degree
 arches should be limited  to a maximum span of 5
 feet 10 inches for 4-1/2-inch thickness  and 8 feet
 for  9-inch  thickness.  Arches -with  spans greater
 than 8 feet  should be  constructed  of suspended,
 super-duty, fire clay shapes  or  super-duty,  plas-
 tic  refractory.   Plastic  refractory used for this
 purpose must be suspended from refractory cones
 or  stainless  steel anchors  spaced not more than
 15  inches apart.

 Grates

 Two materials   satisfactory  for construction of
 grates are cast iron and castable refractory.   Cast
iron grates are available in a. wide variety of sizes
and shapes.  They are of much heavier construc-
tion than those used in comparable general-refuse
incinerators, to minimize deformation at high tem-
peratures.  Where blocks or scraps of -wood are to
be burned,  bar- or channel-shaped grates should
be employed,  but when •wood waste accumulated
from woodworking equipment is to be burned, pin-
hole grates should be installed.   Typical pinhole
grates consist of 6-inch-wide by 24-inch-long by
3/4-inch-thick slab sections of cast iron  with 1/2-
inch holes on 2-inch centers.  Grates of this type
are capable of retaining small wood particles  that
might otherwise fall unburned into the ashpit.

Refractory  grates are nearly always constructed
in the form of 60-degree sprung arches.  On incin-
erators of  250-pound-per-hour  capacity or less,
grates are constructed of ASTM Class 24 refrac-
tory 5 to 6 inches thick,  with 1-inch holes on 5- to
6-inch centers.  ASTM Class  27 castable refrac-
tory 6 to 8 inches thick, with 1-inch holes on 6- to
9-inch centers is  used in larger incinerators.

Caution is required in operating incinerators with
cast irongrates.  Underfire air must not be unduly
restricted nor should the ash pit be allowed to fill
within 1 foot of the  grates.  Heat buildup in the ash
pit  from  either condition can cause the grates  to
warp and  sag.  Misoperation of this type  does not
deform grates  constructed of castable refractory.
These grates are,  however, susceptible to damage
from careless  stoking and cleaning.

When most of the charge  consists of sawdust or
similar small  wood particles  delivered by a uni-
form feed system, a solid hearth should be installed
at the  rear of the ignition chamber to prevent the
introduction of excessive underfire air at this lo-
cation.  As the size of the incinerator increases,
hearths are sometimes installed along the side-walls
also to prevent excessive underfire  air. In any
event,  the  hearth area should not exceed 30 per-
cent of the total  horizontal area  of  the  primary
ignition chamber.

Exterior Walls

Incinerators can be constructed with exterior walls
of red brick  or steel plate.  Red brick exteriors
are usually constructed of two layers  of red brick
bondedbya  reinforced concrete center.  Exterior
steel plate maybe of the thin, corrugated type used
toback plastic refractory,  or as heavy as  10 gauge
to support interior brick construction.

 Air Ports

 Combustion air port controls should be constructed
 of  cast iron  not  less than 1/2 inch thick.  These
 ports  should fit tightly to reduce air leakage to a
 minimum.

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                        Multiple-Chamber Incinerators for Burning Wood Waste
                                                                                                  469
OPERATION OF INCINERATORS

Certain differences exist between the operation of
wood-burning incinerators and general-refuse in-
cinerators.  The operator of a general-refuse in-
cinerator generally relies on auxiliary burners to
maintain temperatures  for maximum combustion
in the secondary chamber. The operator of a •wood-
burning incinerator, without provisions for auxil-
iary burners,  is able to maintain adequate  secon-
dary  chamber  temperatures by proper charging
and control  of combustion air.

Generous amounts of clean dry paper  are mixed
with the wood for the initial charge.  After the igni-
tion chamber is one-half to two-thirds full, addi-
tional paper is placed on top of the pile to ensure
quick flame  coverage  at the surface.  It is  impor-
tant,  in keeping smoke  to a minimum, that only
clean dry paper and dry scrap wood comprise the
initial charge.  After charging is completed, the
paper is ignited near  the front of the chamber and
the charge door is closed.  All combustion air ports
are almost completely closed to restrict combus-
tion air.
As burning proceeds,  the incinerator passes through
the most critical period of its operation.   By ob-
serving the  emissions from the stack, the  neces-
sary adjustments can be made promptly to reduce
or  eliminate smoke.   Gray or white smoke emit-
ted after lightoff indicates that the incinerator is
cold.   This smoke can be minimized or eliminated
by closing all air ports.   Smoke  of this color usu-
ally ceases within a fewminutes  after lightoff  when
flames completely cover the  refuse pile  and fill
the flame port.  A fewminutes later,  black smoke
may appear,  resulting  from a  lack  of adequate
combustion  air.  These emissions can usually be
eliminated  by opening primary air ports and then
the secondary air ports.  If additional combustion
air is required, it may be supplied by opening the
charge door.

Although each incinerator has  its own operating
characteristics, the  overfire and underfire air
ports  can usually be  opened 5 to 10 minutes  after
lightoff, and the secondary port,  20 to 30 minutes
later. If opening of the secondary ports results in
gray  or white  smoke emissions, the  ports should
be  closed immediately since the incinerator has
not yet reached its normal operating  temperature.

After  attaining normal 'operating temperatures,
maximum combustion is maintained by placing the
mechanical feed system in operation  or by hand
charging at regular intervals.

Illustrative Problem
Problem:
Design a multiple-chamber incinerator  to  burn
 1, 000 pounds of Douglas fir •waste per hour "with a
maximum moisture content of  10 percent.
Solution:

1.   Composition of the refuse:

     Dry combus-
     tibles         (1, 000 lb/hr)(0. 90) =   900 Ib/hr

     Moisture      (1, 000 lb/hr)(0. 10) =   100 Ib/hr
      Total                             1.000
2.   Gross heat input:

     From Table 121, the gross heat of combustion
     of  1 pound of dry Douglas fir is 9, 050 Btu/lb
     (900 lb/hr)(9,050 Btu/lb)  =  8, 140, 000 Btu/hr


3.   Heat losses:

    (a)  Assume radiation, convection, and storage
        heat  losses are 20 percent  of gross heat
        input:

        (0.20)(8, 140,000 Btu/hr)  =  1, 625,000 Btu/hr


    (b)  Evaporation of contained moisture:

        The gross heat of vaporization of water at
        60°F is 1, 060 Btu/lb
        (100  lb/hr)(l, 060 Btu/lb)  =  106, 000 Btu/hr


    (c)  Evaporation of water formed by  combus-
        tion:

        From Table 121, there is 0. 563 Ib of water
        formed from the combustion  of 1 pound of
        dry Douglas fir.
                  /O. 563 Ib H O\
                 4     ib      ) (i'
(900 Ib/h
        =  537,000 Btu/hr
060 Btu/lb)
    (d) Total heat losses:

        a  +  b  +  c  =  total losses

        1, 625,000 Btu/hr + 106, 000 Btu/hr +

        537, 000  Btu/hr   =   2, 268,000 Btu/hr


 4.   Net heat available:

     8,140,000 Btu/hr - 2, 268,000 Btu/hr  =

     5, 872,000 Btu/hr

 5.   Weight of products of  combustion:

     From Table 121, there  is  13.86 Ib of com-
     bustion products from  1 pound dry Douglas fir

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470
                                          INCINERATION
    with  100  percent excess air, and 20.301b of
    combustion products from 1 pound dry Doug-
    las fir with 200 percent excess air.  Weight
    of products of combustion at 100 percent ex-
    cess  air:

Wood     (900 lb/hr)(13. 86 Ib/lb) = 12,4501b/hr
Moisture  (100 Ib/hr)                  100 Ib/hr
                                   12,550 Ib/hr

    Weight of products of combustion at 200 per-
    cent excess air:

Wood     (900 lb/hr)(20. 30 Ib/lb) = 18, 200 Ib/hr
Moisture  (100 Ib/hr)                  100 Ib/hr
                                   18,300 Ib/hr

6.  Average gas  temperature at 200 percent ex-
    cess  air:
          Q  =  w  c  (T  - T  '
                 p  p   2     1
    •where :

       Q  =  net heat available,  Btu/hr

      w  =  weight of products of combustion,
        P    Ib/hr

      c   =  specific heat of products  of combus-
       P     tion, Btu/lb-°F

      T   =  average gas temperature, °F

      T   =  initial temperature, °F
        .
        Area  =
             T   =  T
              2  "    !
    =  60°F
     =  1,300°F
                       5, 872,OOP Btu/hr
                 (18, 300 lb/hr)(0. 26 Btu/lb-°F)
 7.  Combustion air port areas:

    (a) Primary air port sizes:

       Assume primary air at 100 percent excess.

       From Table 121, (84. 75)(2) scf of air
       is required per pound of dry Douglas fir.
       (900 Ib/hr) (169. 5 scf/lb) = 152, 000 scfh
                               or   2,540 scfm

       Assume the average air velocity through
       the primary air ports is 900 fpm or 0.052
       in. WC velocity pressure.
                 2, 540 scfm            2
                   '    -  =  2.83 ft
                   900 fpm
                              or  407 in.
        Overfire air port area:

        Assume overfire air port area is 90 per-
        cent of total.

        (0.90)(407 in.2)  =  366 in.2

        Underfire air port area:

        Assume underfire air port area  is 10 I er-
        cent of total.
        (0. 10)(407 in.
                     2
    (b) Secondary air ports  located in the bridge
       wall and curtain wall:

       Assume 50 percent theoretical air through
       each port.

       From  Table  121,  42.37 scf  of air is re-
       quired per pound of dry Douglas fir.

       (900 lb/hr)(42. 37 scf/lb) = 38, 100 scfh

                                or     634 scfm

       Average air velocity through secondary
       ports is assumed to be 1, 000 fpm or 0. 063
       in.  WC velocity pressure.
       Area  =
                 634 scfm
                 1, 000 fpm
                                0.63 ft
                                      2
                                       2
                             or  91 in.

8.   Volume of products of combustion:

   (a) Volume through flame port:

       Assume 100 percent excess  air  through
       flame port.
       From Table 121, there is 179. 6 scf of prod-
       ucts of combustion from 1 pound dry Doug-
       las fir.
                                                      Wood
Moisture
    (100
    (900 lb/hr)(179. 6 scf/lb)   =  161, 000 scfh


               379  scf/lb mole
                 01/1
                18 Ib/lb mole
                                    2-100 scfh
                                  163, 100 scfh
                              or    2, 720 scfm
                              or    45. 4 scfs
   (b)  Volume through mixing chamber:

       Assume 50 percent theoretical air is add-
       ed through  secondary port to combustion
       products from primary chamber.

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                                  Flue-Fed Apartment Incinerators
                                                                                                 471
       (900 lb/hr)(42. 37 scf/lb)  = 38, 100 scfh

                               or     10.6 scfs
                                                     10.  Grate area:
       Total volume = 45. 4 scfs
       + 10.6 scfs
                               56.0 scfs
    [ c)  Volume through combustion chamber:

       Assume 50 percent theoretical air is added
       through cooling air ports in curtain wall.

       Total volume = 56. 0 scfs + 10. 6 = 66. 6 scfs
9.   Incinerator cross-sectional areas:

   (a). Flame port area:

       From Table 123, designfor an average ve-
       locity of 50 fps and 1, 900°F  gas tempera-
       ture:
    From Figure  341, the grate loading is 33 lb/
    hr-ft  for the upper +10 percent curve  used
    for 9, 000 Btu/lb refuse.
                                                                   (1,000 Ib/hr)
                                                  Total grate area 33 Ib/hr.ft2
                                                                                          =  30. 3 ft
                                              11.  Horizontal dimensions of ignition chamber:

                                                  From Table  123, length-to-width ratio =1.5

                                                  Let  W =  width and L =  1. 5W
                                                  Then (W)(l. 5W) =  30. 3  ft2

                                                            1. 5W2 =  30. 3

                                                               W =  20. 1
                                                  Width                                 =  4. 5 ft

                                                  Length  =  (1.5)(4. 5)                   =  6.75ft
                (45.4 scfs)(2,360°R)          2
                   (50 fps)(520°R)

    (b) Mixing chamber cross-sectional area:

       From Table 123, designfor an average ve-
       locity of 25 fps and 1, 550°F  gas tempera-
       ture:
       Area  -   (56. 0 scf s)(2. 010 °R)  _         2
       Area  ""      (25 fps)(520°R)        b>
    (c) Curtain -wall port area:

       From Table 123, designfor an average ve-
       locity of 20. 0  fps and 1, 500°F gas tempera-
       ture:
                (56. 0 scfs)(l, 960°R)
                   (20. 0 fps)(520°R)
   (d) Combustion chamber cross-sectional area:

       From Table 123, designfor an average ve-
       locity of 7. 5 fps and 1, 200 °F  gas tempera-
       ture:
       Area  =
        (66.6 scfs)(l, 660°R)
            (7. 5 fps)(520°R)
                                     = 28.4 ft
   (e) Stack area:

       From Table 123, designfor a velocity of 20
       fps  and 1, 100°F gas temperature:
Area  =
                (66.6 scfs)(l,560°R)
                   (20fps)(520°R)
12. Arch height:

    From Figure 342, the arch height for the up-
    per + 10 percent curve is 5 ft.

13. Stack height:

    From Figure 344, stack height above grade is
    35 ft.


 FLUE-FED APARTMENT  INCINERATORS

INTRODUCTION

An incinerator  in which the chimney also serves
as a  chute for refuse charging,  as  shown in Fig-
ure 357,  is known as  a flue-fed incinerator (Mac-
Knight et al. ,  1960).  For some 40 years the sin-
gle-chamber,  flue-fed  incinerator  has  been built
as an integral part of apartment buildings.  The
incinerator is usually located centrally in the build-
ing to minimize the distance from the apartments
to the charging chutes located on each floor.  Oc-
casionally the  incinerator may  be  located  on an
outside wall with charging chutes outside the build-
ing and adjacent to a balcony or fire escape plat-
form.  The flue-fed  incinerator is  also used to
some extent in schools, hospitals, and office build-
ings.

The  single-chamber, flue-fed  incinerator has  a
box-like  combustion  chamber separated by dump
grates from  an ashpit  below.  Atmospheric gas
burners located below the grates are used primari-
ly for dehydration of garbage and other wet mate-
rial.   A  cleanout door is provided for removal of
ashes from the ash pit. A charging door above the
grates is used for igniting the refuse and for stok-

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472
                                          INCINERATION
 COMBUSTION CHAMBER

         GRATES
                                      BASEMENT
                                      FLOOR

                                   CLEANOUT DOOR
                              UNOERFIRE AIR PORT
   Figure  357. Unmodified flue-fed  incinerator
   (MacKnight et al., 1960).
ing the burning pile near  the  end of the burning
period. Inmost instances both doors are provided
with spinners to allow admission of underfire (under-
grate) and overfire  (overgrate) air.   The walls of
the incinerator are customarily constructed of two
layers of brick. The inner layer consists  of 4-1/2
inches  of firebrick separated  by a  1/2-inch air-
space from a 9-inch common brick exterior.  The
flue is normally constructed of 9 inches of common
brick with a 1-inch flue tile lining.  The inside  di-
mensions  of the  flue are usually 16 by 16 inches
for apartment  buildings 3 to 4 stories in height.


Description of Refuse

The  composition (% by wt,  minimum to maximum)
of apartment house  refuse  usually falls within the
following limits:  Dry paper,  50 to 100; garbage,
0 to 30; plastics,  0 to 3; noncombustibles, 2 to 10;
and other (including  rags,  waxed cartons, green-
ery, and so forth), 0 to  10.  If food is prepared in
the  apartments the  percent  of  garbage, plastics,
waxed cartons, and noncombustibles in refuse ap-
proaches the upper limits.  If food is  not prepared
on  the premises then the refuse is more likely to
have ahigher percentage of drypaper.   An average
value taken by incinerator designers for the produc-
tion of refuse by apartment dwellers is 1 pound per
person per day.


THE AIR POLLUTION PROBLEM

When first ignited,  refuse in a flue-fed inciner-
ator burns  very rapidly.  Air  inspiration during
this initial flash burning period  is usually insuffi-
cient to  meet the combustion requirements of the
rapidly burning dry refuse,  re suiting in incomplete
combustion and black smoke emissions.  The  con-
current extreme gas  turbulence  results in the en-
trainment  of large  quantities of fly  ash (ash and
charred  paper).

Once the initial flash burning  period has passed,
an excessive draft develops as a result of the  high
flue gas temperature and the long flue.  The amount
of air admitted through the air ports becomes great-
er  than  the  demand  for combustion  air, and the
temperature in the combustion chamber gradually
diminishes  as the excess air increases.  As this
process  continues,  the  combustible  gases,  oils,
tars, and fats, produced by low-temperature com-
bustion at the surface of  the refuse pile and by de-
structive distillation within the  pile,  pass out the
stack incompletely burned in the form of white or
light gray  smoke.

The use of undergrate burners tends to entrain fly
ash in the hot gases passing through and around the
fuel bed.  This problem is further aggravated by
stoking of the burning refuse pile under excessive
draft conditions,  resulting in the  discharge of large
quantities of fly ash from the  stack.   The  problem
is compounded by the charging of refuse down the
flue during the burning period, which smothers and
scatters  the burning pile and results in severe fly
ash emissions and smoke production.

Stack Emissions
The range  of particulate emissions  found by a
series of tests, in pounds per ton of refuse burned,
is  shown in Table 124.   Associated data are in-
cluded in the table as a matter of general interest.
Other,  less plentiful data indicate that emissions
(in  pounds per ton) are  as follows: organic acids,
9.5; aldehydes,  1. 5; hydrocarbons,  2; and nitro-
gen oxides,  6.

AIR POLLUTION CONTROL EQUIPMENT

There are three basic methods  of altering a  flue-
fed incinerator to prevent the discharge of air  con-

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                                    Flue-Fed Apartment Incinerators
                                             473
  Table 124.  PARTICULATE EMISSIONS FROM
     TYPICAL FLUE-FED INCINERATORS
Test
designation
C-95
652
881
C-116
D-3
D-2
C-499-1
650
D-l
C-43
C-50
C-44
Particulate matter,
Ib/ton
76
52
48
37
37
34
25
23
23
19
17
7
gr/scf
at 12% C02
2.27
1.40
1.60
1. 40
1. 18
1.06
0.94
0.99
0. 75
0.75
0.60
0.27


0. 61
0. 13
0.21
	
0. 20
0. 21
0. 18
0. 10
0. 2
0. ib
0. 09
0. 08
Average
stack
scfm
458
1, 190
326
213
820
930
500
1, 120
860
530
441
817
Grate
area,
ft2
1.5
16
9
3
12
12
6
12
12
4
20
8
Stack
height,
ft
25
35
68
32
80
80
54
56
80
25
56
46
taminants.  Two of these methods  involve the ad-
dition of an afterburner to the existing incinerator.
The third method involves the installation of a well-
designed  multiple-chamber  incinerator'. . Appur-
tenances  for  regulating  stack draft and effective-
ly controlling the charging during the burning peri-
od are essential to these methods.
INSTALLATION OF AFTERBURNER ON A ROOF
A  typical installation  of an afterburner  on a roof
includes the use of a damper located at the base  of
the stack to control the excessive draft and burn-
ing rate, and an afterburner mounted on top of the
existing stack to control the smoke and combustible
gases.   Chute door locks are installed to prevent
damage to the draft control damper from the charg -
ing of refuse during the burning period.
Design Procedure

Draft control
The excessive draft conditions prevailing in flue-fed
incinerator s must be reduced before an afterburn-
er will function successfully.  As-winging,  counter-
weighted damper can be used for draft control by
pivoting it on a rod along one edge so that it can be
swung flush with one  wall of the flue to permit
charging of refuse.  Swung back into  a horizontal
position, the damper can maintain the draft in the
basement combustion chamber within suitable lim-
its.  This damper is equipped with adjustable open-
ings in its surface since the exact restriction re-
quired  for a specific  unit  cannot be  determined.
By changing the  location  of the adjustable plates
fastened to the surface of the damper, the size  of
the openings  can be decreased until  the desired
draft,  usually from 0. 10 to 0.20 inch WC,  is at-
tained.  These dampers are located in the flue be-
neath the first-floor chute door to ensure a nega-
tive pressure at each door and thus prevent smoke
and sparks from blowing by the doors into the
building.
The effect  of a damper  on combustion chamber
draft, burning rate, and flue gas  velocity is shown
in Figures  358, 359,  and 360.  These graphs were
obtained by testing a 6-story,  flue-fed incinerator
equipped with a draft control damper having a 6-
1/2-inch-diameter orifice  and afterburner.  The
curves in the graphs designated "uncontrolled flue-
fed incinerator"  were  obtained  by operating the
incinerator with  the  damper open and the after-
burner  off.

Figure 358 shows the draft in the combustion cham-
ber of the incinerator to be lower and more stable
when the damper is in use.   Figure 359 shows that
the initial peak burning is considerably reduced
when the damper is used.   Figure 360 shows that
the flue gas  velocities are lower when the draft
control damper is used.

The lower draft condition in the combustion cham-
ber, attained from the use of a draft control damp-
er, minimizes the entrainment of fly ash in the flue
                                                          0 35
  0 30
  0 25
_ 0 20
- 0 15
  0 10
  0 05
                          UNMODIFIED FLUE-FED INCINERATOR
                                    V
                   FLUE-FED INCINERATOR WITH AFTERBURNER
                   AND DRAFT CONTROL DAMPER
                      I         I        I
                          LEGEND
                          B  OVERGRATE BURNERS IGNITED
                          S  REFUSE STOKED
                      20       30
                    TIME OF OPERATION  nm
                                      40
    Figure 358.  Draft in combustion  chamber  of
    modified and unmodified flue-fed incinera-
    tors (MacKnight et al., 1960).

-------
474
                                           INCINERATION
       =  500 -
                                                                      UNMODIFIED FLUE-FED INCINERATOR
                                                                      FLUE-FED  INCINERATOR MODIFIED
                                                                      WITH DRAFT CONTROL DAMPER
                                                                      UNDERGRATE BURNERS IGNITED
                                                                      REFUSE STOKED
                                          15          20         25
                                             TIME FROM LIGHTOFF  vir
                 Figure 359  Burning rate versus time for modified and unmodified flue-fed incinerators.
gases.   This condition also reduces the burning
rate,  permitting the use of a smaller afterburner
than otherwise would be required.  Installation and
operating costs of the afterburner are according-
ly reduced.

Chute door locks

The charging of refuse during the burning period
can be  prevented  easily  and economically by in-
stalling solenoid locks on each of the chute-charg-
ing doors.   The  use of this type of lock permits
their  actuation from a single  switch in the base-
ment before the damper is  closed and the burning
cycle begins.

If refuse is charged down the flue  during the burn-
ing period when  the draft-controlling  damper is
closed,  several undesirable events  may  occur.
The damper  may be bent,  or even detached from
its supports,  or  the refuse may pile  up on the
damper and block the flue,  'causing the gases from
the refuse burning  in the combustion chamber to
vent into the basement.  Chute door locks prevent
these problems in addition to preventing smother-
ing of the refuse  pile and the subsequent  creation
of smoke and fly ash.
Design parameters

Parameters for  roof afterburners are essentially
the same as the parameters  employed in design-
ing afterburners for smokehouses, ovens, and so
forth.  For a discussion of appropriate parameters
relating  to  retention time,  mixing of gases,  gas
velocities,  temperature levels,  flame character-
istics,  and  burner types  and arrangements,  see
the first part of  Chapter 5.

Limitations

Most flues  are  not  airtight since cracks develop
with age and use.  In particular,  relatively large
openings occur around  the chute doors.

Air  inspirated in this manner mixes  with the  flue
gases  and passes through the afterburner.   Addi-
tional air entering  the afterburner lowers exit gas
temperatures,  increases  gas velocities, and re-
duces  residence times.  Thus, this overall  effect
reduces the efficiency of the  afterburner.

As the height of the building increases,  the air in-
duced  into  the flue  also increases.   No definite
building height  limitation can be given since air

-------
                                     Flue-Fed Apartment Incinerators
                                           475
      r     T         i
      -FLUE-FED INCINERATOR KITH AFTERBURNER
       AND DRAFT CONTROL DAMPER
                                 LEGEND
                                 6  OVERGRATE BURNERS IGNITED
                                 S - REFUSE STOKED
                                 	I	
                      20         3D
                     TIKE OF OPERATION mm
Figure 360   Flue gas  velocity  at  inlet of afterburner
of modified and unmodified  flue-fed  incinerators (Mac-
Knight et al., 1960).
 leakage  increases  in  importance with increasing
 height.   As  of 1963, however, a 9-story building
 is  the tallest building in Los Angeles County on
 which a  roof  afterburner has been  successfully
 employed.

 Typical installations

 Figures  361 and 362 are  cutaway drawings  of two
 typical afterburners mounted  on flue-fed inciner-
 ators.  The inner  passage  of the  afterburner in
 Figure  361 is built in the  shape of a lazy L.  A
 premix gas burner fires horizontally into the pass-
 age just below the L.   The inclined section above
 the burner  provides an impingement surface for
 the burner  flames  and also deflects the effluent
 from  its  vertical path.  Mixing of the flames and
 flue gases beneath the  inclined section has proved
 adequate  to burn the contaminants in the inciner-
 ator gases.

 The afterburner shown in Figure 362 consists basic-
 ally of a ring  burner followed by a venturi throat,
 a  baffle  to ensure contact between burner flames
 and flue  gases,  and a combustion chamber.   The
 flue gases enter the afterburner through  the  ring
 burner.    The  cross section of the  burner ring is
                                   CHARGING
                                   DOOR
                                   OVERFIRE
                                   AIR PORT
                              CLEANOUT DOOR
                      UNDERFIRE
                      AIR PORT
 Figure 361. Flue-fed incinerator modified by a roof
 afterburner and a draft control damper.
         BLOWER
Figure 362. Flue-fed incinerator modified by a  roof
afterburner, and a draft control damper (Sargent
Afterburner, Kearney, N.J.).

-------
 476
INCINERATION
that of an isosceles  right triangle, the hypotenuse
connecting the two legs of the triangle forming the
inside surface  of the burner.  Equally spaced ori-
fices  are located in this surface of the burner  to
create a conical flame pattern and yet prevent the
flames from being extinguished by the rush of flue
gases  over its inner face.

The premix burner,  venturi throat,  and baffle are
empirically sized to cause maximum mixing between
the flue gases and  burner flames consistent with
minimum pressure loss through the afterburner.
All smoke and unburned volatiles passing through
the ring burner are brought into intimate contact
with the flames.  Additional combustion air may
be  supplied through openings below the burner  in
the wall of the afterburner. Because of the remote
location of the afterburner,  automatic spark igni-
tion and complete flame failure controls are usu-
ally installed.

Standards for Construction

There are several reasons why the maintenance  of
a roof afterburner is likely to be inadequate.  First,
it operates in an unfrequented  location. Second,
responsibility for its operation and service is usu-
ally assigned to unskilled  janitorial personnel.
Third,  its installation and use stem strictly from
legal compulsion, and little attention is given over
andabovethe minimum necessary to meet the re-
quirements of the law.  Consequently,  an  after-
burner should be constructed of durable materials
that require as little maintenance as possible.

Mounting and supports

The flue is dismantled to a height of 2 feet above
thereof, and the afterburner is constructed  on the
flue above  this point.   Shortening the flue facili-
tates  work on the unit,  reduces windloading and
earthquake stresses, andmakes the completed unit
less prominent.

One method successfully used to fasten the  after-
burner on the  flue consists of bolting a 1/4-inch -
thick steel plate to  the flue and welding the  after-
burner shell to the plate.  A central hole the  size
of  the  flue opening is,  of course, first cut in the
plate.
Additional support is usually provided by three  1/4-
inch guy cables evenly spaced  around the  after-
burner. The guys can be welded to the afterburner
shell near  its top  and attached to the building  by
bolts  going through the roof.   In buildings  con-
structed  of wood,  the bolts should enter the  roof
joists.

Metals

The following metals are recommended for use. in
afterburners  because  experience has  shown that
           they resist deterioration under the conditions of
           their  use.  Sheet steel with a minimum thickness
           of 12-gage is  recommended for use in fabricating
           afterburner shells.  Stainless steel, type 321, 1/8-
           inch thick,  is recommended for use in all after-
           burner baffles receiving direct flame impingement.
           Support  rods  for baffles  should have a minimum
           diameter of 1 /2 inch and should be made of type  321
           stainless steel.

           Castable refractories

           Castable  refractories  used near  the  burner  are
           invariably subjected to direct flame impingement.
           These linings should be  at least ASTM Class 27  re-
           fractories with a minimum thickness of 4 inches.
           (Class 27 refractories  are those castable refrac-
           tories capable of withstanding temperatures  of
           2,700°F.)  In addition, a 1-inch-thick backing of
           1,000°F castable insulation or equivalent should
           be placed between the refractory and the metal
           shell.   (The castable venturi throat in the after-
           burner of Figure  362 is so constructed. )

           Castable  refractory used to line  the afterburner
           shell  above the actual  burning zone should have a
           minimum thickness of 2  inches.  Class 24 cast-
           ables, that is,  those castable refractories capable
           of withstanding temperatures of 2,400°F, can be
           used in this area.  A popular method of installing
           these linings  consists  of casting  them in  a ring
           shape and slipping them into the shell.   Support  for
           each castable  section is derived from metal clips
           welded  to the inner wall just below the first sec-
           tion of the shell.  These clips fit into recesses pro-
           vided in this castable section so that they are pro-
           tected from the flames of the afterburner.

           Firebrick
           Of the four types of firebrick, only high-duty brick
           is normally used in afterburners.  When used, it
           is generally limited to areas receiving direct flame
           impingement or high-temperature  flame radiation.
           Lower duty castable refractories or insulating fire-
           brick are normally used instead  of  firebrick in
           places of less severe duty.

           Insulating firebrick
           In areas  of the  afterburner -without direct flame
           impingement, 2,  000 °F insulating firebrick may be
           successfully used. This type of brick is frequent-
           lyusedin 2-1/2-inch-thick rings to line the upper
           section of afterburners.  (The stack above  the ven-
           turi throat in the afterburner of Figure 362 is lined
           with this type of brick. ) When cut into wedge shapes
           and arranged around the inner shell, the individual
           bricks lock into place and mortar need not be used.

           Burners

           A forced-draft gas burner such as that described
           in the second part of  Chapter 9  should be used.

-------
                                   Flue-Fed Apartment Incinerators
                                                                                                   477
 This type of burner supplies much of its own air
 needed for combustion.  Since the amount of oxy-
 gen in the flue  gas is less than that in a normal
 atmosphere, the ability to supply a significant por-
 tion of its own oxygen requirements is an impor-
 tant factor in burner selection.

 Draft  control damper

 The draft control damper  receives direct  flame
 impingement from the refuse burning in the com-
 bustion  chamber.   For  this  reason,  the damper
 must be constructed of stainless steel.  Dampers
 of  20-gage  type 302 stainless steel with 3/4 inch
 of  each edge bent down to increase  stiffness have
 proved satisfactory.


 Chute  door locks

 Figure 363 shows a  typical chute door lock instal-
 lation.  The lock shown is  of the type that allows
 the door to be closed at all times without breaking
 the latch.  This  type of latch is recommended for
 use because  it permits the door to be closed dur-
 ing the incinerator's operation.


 Stack  Emissions

 Data obtained from stack tests on a typical flue-fed
 incinerator modified  •with a draft control damper
 and roof afterburner are given in Table 125.   Data
 obtained from the test designated in the table as
 C-546 also give emissions of aldehydes as formal-
 dehyde as 2 pounds  per ton,  emissions of organic
 acids  as acetic  acid  as 2. 1  pounds per  ton, and
 emissions of nitrogen  oxides as 7 pounds per ton.

 Operation

 The sequence  of operations performed in using a
flue-fed incinerator, modified as discussed here-
in,  starts with the locking of the chute doors  from
the main switch  in the  basement.  The draft con-
trol damper  is closed  and the afterburner ignited
by  remote control from another switch  also lo-
cated in the basement.
    Figure 363  Typical chute door lock  installation.
The  refuse is then ignited  and,  if  the  refuse is
moist,  the  grate burners are also lighted.  The
refuse may be stoked frequently to uncover fresh
material without fear of creating excessive fly ash
emissions because  of the draft-limiting action of
the damper.

When the refuse  has  been  destroyed,  the grate
burners are turned  off and the grates are cleaned
by dumping the ashes into the  ash pit.  After a brief
period of time is allowed, to permit smoke from
the smoldering ashes to clear, the afterburner is
turned off and the draft control damper opened.

The  final step,  that of unlocking the chute doors,
should not be performed until about 10 minutes after
the grates have  been  cleaned.  This delay  allows
         Table  125.  PARTICULATE EMISSIONS FROM A TYPICAL FLUE-FED INCINERATOR
             MODIFIED WITH A DRAFT CONTROL DAMPER AND A ROOF AFTERBURNER
Test
designa-
tion

C-586-A1
C-586-A2
C-586-A3
C-546
Burning
rate,
Ib/hr

100
80
68
49
Particulate matter
Ib/ton

5.9
5.2
5.6
1. 2
gr/scf
at 12% CO.,
2
0.20
0. 18
0. 20
0. 15
gr/scf

0.004
0.035
0. 034
0.027
Afterburner
efficiency,
%

80
82
80
85
Average
oxygen
content,
%
12. 1
11.6
12.7
9.5
Average
stack
volume,
scfm
760
690
710
590
Average
outlet
temperature,
°F
1, 130
1, 240
1, 130
1, 560

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478
                                           INCINERATION
the incinerator to cool so that newly charged refuse
is not ignited by the residual heat in the incinerator.


BASEMENT AFTERBURNER

A typical basement  afterburner installation uses
a damper located at the base of the stack to control
excessive draft and burning rate, and an afterburn-
er located directly above the damper to consume
smoke and combustible gases. Cooling air is ducted
from the basement and admitted into the flue just
below the first-floor charging chute to lower the
temperature of the flue gas, thereby protecting the
low-duty refractory lining of the flue and preventing
the chute doors  from becoming  excessively hot.
Chute door  locks are also used on  this unit to pre-
vent damage to the  damper from the charging of
refuse during the burning period.


Design  Procedure

The solenoid chute door locks and the draft control
damper described in the discussion of roof after-
burners are equally applicable to a basement after-
burner installation.   When used in a basement af-
terburner, the draft  control damper is positioned
in the flue as closely as possible to the combustion
chamber. If the damper in this location is allowed
to swing down-ward  into  the combustion chamber
to permit charging,  its upward swing may be ob-
structed by the accumulated refuse.  To  overcome
this  problem,  the damper must be hinged to per-
mit it to swing upward and lie against the flue wall.


Design parameters

The parameters,  such as  retention time, temper-
ature level, and so forth,  employed in designing a
basement afterburner are the same as those em-
ployed in designing afterburners for smokehouses,
ovens,  and  so forth as given in the first part of
Chapter  5.  The following specific  features not
encountered in the design of industrial afterburn-
ers must be considered  in designing a basement
afterburner.

1.   The burners  themselves must be located so
    that they do not obstruct the fall  of refuse
    through the  flue.  Relatively inexpensive at-
    mospheric or venturi burners are used in this
    installation since they can be  arranged to fire
    across  the flue.  While forced-draft burners
    may be used, their higher  cost usually makes
    them impractical.


2.   The shape of the flue cannot be modified to
    produce a desired gas velocity, induce turbu-
    lence, or promote flame coverage, as the com-
    bustion chamber of an industrial afterburner
    can.  The desired flame  contact and mixing
    are promoted in basement afterburners by the
    proper location of the orifices in the damper.
    This damper is designed with an orifice located
    directlybelow the mouth of each burner.  This
    arrangement provides the necessary contact
    between the afterburner flames and the prod-
    ucts of combustion.

It  it also necessary to provide for the admission
of outside air into the flue to lower the temperature
of the gases leaving the afterburner.  Cooling the
flue gas to 500 °F protects  the low-duty refractory
inner lining of the flue from deterioration and pre-
vents the outer walls of the flue, including  the chute
doors, from becoming excessively hot.

This air is supplied from the basement through a
duct installed through the  first floor and is intro-
duced into the flue just below the first-floor charg-
ing door.   This  arrangement is used to prevent
flue gases from venting directly into the living area
of the  building  if the flue becomes accidentally
blocked.   A uniform draft  on the downstream side
of the  afterburner is  maintained by a barometric
damper placed in the duct's entrance.  It  also pro-
vides the advantage  of closing  if any unexpected
back pressure occurs in the flue.
 Typical installation

 In the basement afterburner, as shown in Figure
 364,  the  burners are  mounted in  a rectangular
 hole located in the flue a short distance above the
 basement combustion chamber.  A steel frame in-
 serted in the hole supports the flue and the compo-
 nents of the afterburner. The afterburner unit con-
 sists of four venturi burners equally spaced across
 the opening.  The area  of the opening not occupied
 by the burners is covered by a steel plate to pre-
 vent  the entrance  of dilution air.   An adequate
 amount of secondary air is admitted through this
 plate by holes equally spaced around each burner.
 The burners are provided with a continuously oper-
 ating pilot.

 The draft control damper is  located just below the
 burners.  Four  slots in the surface of the damper
 are located directly under each burner and as near
 as practicable to the wall  in which the burners  are
 mounted.

 Because temperatures in the flue in the  afterburn-
 er  zone  may be approximately 1,200°F  or more,
 the flue tile lining has been replaced -with firebrick.
 The firebrick  extends  from the damper,  past the
 burners, and ends just below the first-floor chute
 door.

 Cooling air is admitted  to the flue above the after-
 burner zone through a duct fitted with a barometric
 damper.

-------
                                   Flue-Fed Apartment Incinerators
                                             479
                             ELECTRIC LOCK IN OPEN
                             POSITION FOR CHARGING
                             CHUTE DOOR

                             COOLING AIR DUCT

                             FIRST-FLOOR LEVEL
                             BAROMETRIC DAMPER
                             STEEL FRAME
                             AIR HOLES

                             PORTS FOR VENTURI
                             GAS BURNERS
                             DAMPER WITH ORIFICES
                             (SHOWN IN POSITION FOR
                             CHARGING OF REFUSE i
                                 NOTE  DURING THE BURNING
                                 CYCLE  THE CHUTE DOORS ARE
                                 LOCKED AND THE DAMPER WITH
                                 ORIFICES  IS PLACED IN A
                                 HORIZONTAL POSITION
      Figure 364. Flue-fed incinerator modified by an
      afterburner at the base of the flue.
 duty firebrick in the area between the hinged damp-
 er and the first-floor chute door.  High-duty fire-
 brick is recommended instead of lower duty firebrick
 or insulating firebrick because the refractory in
 this  area  must withstand both heat and compres-
 sive  load.

 Draft control damper

 Since the orifices of the draft control damper are
 used to direct  the combustion products from the
 refuse  into  the afterburner flames,  the  damper
 should be installed so as to minimize leakage around
 its edges.  A small ledge approximately 1/2  inch
 •wide  is built into the refractory lining of  the flue
 when the refractory is  installed.  The damper,
 •when in place,  rests against this ledge, prevent-
 ing excessive leakage.


 Stack Emissions

 Emission  data, in pounds per ton of refuse burned,
 obtained from tests on two typical flue-fed incin-
 erators modified with basement afterburners and
 draft control dampers are presented in Table 126.
 Organic acids  are reported  as  acetic acid,  and
 aldehydes  as formaldehyde.


 Operation

 The sequence of operation in using a flue-fed in-
 cinerator modified with a  basement afterburner is
 the same as that described in the corresponding
 section under roof afterburners.
     Advantages

     Comparedwith the roof afterburner, the base-
     ment afterburner has the advantages of shorter
     gas lines,  a less expensive ignition system,
     and greater accessibility.

     Disadvantages

     The basement unit has the disadvantage of cre-
     ating a hotter than normal flue,  and may re-
     quire  expensive rebricking  in the  area near
     the afterburner.

Standards for Construction

The construction standards applicable to the draft
control  damper and chute door  locks  have been
covered in the  discussion of roof afterburners.
Other standards are given in -what follows.

Hot-zone refractory

The flue tile lining, which is usually a low-refrac-
tory-duty terra  cotta, shouldbe replaced with high -
MULTIPLE-CHAMBER INCINERATOR, BASEMENT INSTALLATION

A flue-fed incineratoi modified by the installation
of amultiple-chamber incinerator in the basement
includes the conversion of the combustion chamber
of the flue-fed incinerator into a storage chamber
for refuse.   The refuse is manually transferred
from storage to the multiple-chamber incinerator
where it is  burned.  The products of combustion
are ducted back into the flue above a sliding damper
that seals off the refuse  chamber, preventing un-
controlled dilution air leakage.  As with other modi-
fications, chute door locks are  used to prevent the
charging of refuse during the burning period.

Design Procedure

The second part of this chapter may be consulted
for design procedures used for the multiple-cham-
ber incinerator.   Other design features embodied
in the completed assembly follow.

1.    The  distance between the  multiple-chamber
     incinerator and the storage bin should facilitate
    the transfer of rubbish.

-------
480
                                            INCINERATION
      Table  126.  EMISSIONS FROM FLUE-FED INCINERATORS MODIFIED WITH A BASEMENT
                           AFTERBURNER AND DRAFT CONTROL DAMPER
Test
designa-
tion
C-619
C-822
Number
of
stories
4
6
Burning
rate,
Ib/hr
32
104
Particulate matter
Ib/ton
6. 1
6.5
gr/scf
at 12% C02
0. 22
0. 23
gr/scf
0. Oil
0. 028
Organic
acids ,
Ib/ton
5. 2
5.9
Nitrogen
oxides,
Ib/ton
16. 0
4. 2
Alde-
hydes,
Ib/ton
3. 1
1. 8
Average
stack
volume,
scfm
970
1, 400
Average
temperature
at stack
outlet, °F
640
450
2.  As a further convenience in transferring the
    rubbish,  the multiple-chamber incinerator
    should be constructed with the ignition cham-
    ber side close to the storage bin.

3.  The multiple-chamber incinerator  installed
    shouldbe large enough  to allow all the refuse
    normally  collected  per day to be  consumed
    within 1 hour.

4.  The draft provided for the multiple-chamber
    incinerator shouldbe limited to its design value.
Draft control

The draft furnished for incinerators  of the size
commonly used in apartment houses, that is,  in-
cinerator s burning between 50 and 250 pounds per
hour,  should not exceed approximately 0. 20 inch
of water column.   Since the  existing  flue of the
former single chamber is usually excessively high
for the new installation, some provision for draft
control must be furnished.  A barometric damper,
as  shown in Figure 365, is installed at the end of
the breeching betweea the multiple-chamber incin-
erator and the flue to maintain the correct draft.

Typical installation

The multiple-chamber installation is  depicted in
Figure 365. Conversion of the combustion chamber
has been accomplished by removing the  grates and
smoothing the interior walls with plaster.   To fa-
cilitate the removal of refuse  for charging  into the
multiple-chamber  incinerator,  a large section of
the front wall has been removed  and replaced by a
steeldoor.  A breeching with a barometric  damper
has been installed from the top of the secondary
combustion  chamber of the multiple-chamber in-
cinerator to the existing flue.   A steel damper has
been installed  in  the  flue  below the breeching to
prevent dilution air from entering the flue  through
the refuse storage  chamber.
     Advantages

     The multiple-chamber incinerator installation
     has two advantages relative to roof afterburn-
     ers.
 SLIDING DAMPER -
DEFUSE COLLECTION h"
CHAMBER       •
     BASEMENT FLOOR
                       MULTIPLE CHAMBER INCINERATOR'
 Figure 365. Flue-fed  incinerator modified by the installa-
 tion of a multiple-chamber  incinerator (MacKnight  et  al.
 1960).
      1. The cost of installation is lower as com-
         pared with that of a roof  afterburner on
         buildings over  2 stories high.  The first
         cost  of  a  roof  afterburner increases with
         building height because of the additional size,
         and length of gas line required.
      2. It has no height limit.  As explained in the
         section on draft control for roof afterburn-
         ers,  the  height of a  building on which an
         afterburner can be installed is limited by
         the amount of air leaking into the flue above
         the draft  control damper.

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                                   Flue-Fed Apartment Incinerators
                                             481
     The only advantage a multiple-chamber base-
     ment  installation has relative to a basement
     afterburner is that  the  flue gases from the
     multiple-chamber installation are about ZOO°F
     cooler,  than those from a basement afterburn-
     er.   Because  the  flue linings and 'walls are
     correspondingly cooler,  they are subjected to
     less thermal stress,  and also  are less likely
     to cause painful burns to apartment tenants.
the refuse is of low heating value or high moisture
content.  The charging and operation of the incin-
erator are as described in the second part of this
chapter.  Burning is usually  carried  out once a
day, since the bin does not normally provide stor-
age for much more than that length  of time.  When
burning is completed, the incinerator burners are
turned off, the door s to the bin are closed,  the flue
damper is opened, and the chute doors unlocked.
     Disadvantages

     The multiple-chamber installation has the dis-
     advantage of requiring hand transfer of all ref-
     use from the  storage bin into the multiple -
     chamber incinerator--a distasteful and time-
     consuming task. A second disadvantage is the
     amount  of valuable basement space occupied
     by the multiple-chamber incinerator, which
     otherwise would be available for tenants' use.

Standards for  Construction

Standards  for constructing a multiple-chamber
incinerator may be found in the second part of this
chapter.


Stack Emissions

Emissions from typical flue-fed multiple-chamber
installations  are given in Table  127.  Associated
data have been included as a matter of interest.
Illustrative Problem

Problem:

Calculate the size  of a barometric damper to be
installed in the breeching between a basement  100-
pound-per-hour multiple-chamber incinerator and
the flue to limit the draft for the multiple—chamber
incinerator to 0.2 in. WC.


Given:

The flue is 18 inches square and has a cross-sec-
tional  area of 2.25 ft  .   The flue extends 92 feet
above the breeching. The breeching itself is a 12-
inch-diameter,  insulated, straight duct 10  feet
long.


Solution:

1.   Compute the theoretical draft in the breeching
     at various average gas temperatures:
Operation

Before burning is begun, the solenoid locks on the
charging chute doors are actuated and the damper
below the breeching is closed.   The mixing  cham-
ber burners of the incinerator are  then  ignited.
The  ignition chamber  burners are also ignited if
           =  0.52 PH  (-  -
"Kent,  la 36.

  Table 127.  EMISSIONS FROM MULTIPLE-CHAMBER INCINERATOR, BASEMENT INSTALLATION
Test
No.

C-511

C-514
C-515
C-513

C-512

Number
of
stories

4

4
5
11

11

Size of
incin-
erator,
Ib/hr

100

50
100
250

150

Burning
rate
during
test,
Ib/hr

65

38
77
217

140

Particulate matter
gr/scf
at 12% CO2

0. 2

0.2
0. 3
0. 5

0. 3

gr/scf

0 016

0. 035
0.023
0.020

0.016

Emissions, Ib per ton of refuse burned
Partic-
ulate

1. 7

8 4
5.2
4. 3

4. 5

Organic
acids as
acetic

1.2

10. 5
1. 0
2.6

4. 3

Nitrogen
oxides

0. 8

2. 3
3. 1
1. 7

2. 8

Alde-
hydes
as
formal-
dehyde
0. 14

0. 47
0. 52
0. 37

0.85

Hydro-
carbons
as

0. 14

3. 16
3. 10


4. 20

Avg
stack
vol.
scfm

860

510
1,000
2,700

2, 300

Temp at
top floor
chute
door,
•F

310

310
310
230

190

Draft at
ignition
chamber,
in. WC

Maximum
0. 04
M
0.06a
Maximum
0. 03b
Not
recorded
Maximum
0. 09
Dia of
baro-
metric
damper,

12

10
12
14C

14C

Airflow
through
baro-
metric
damper,
scfm
262

None
Not
recorded
Not
recorded
Estimate
850
  aA 1/2-m. x 20-in. air leak around sliding damper
   Air leaks around sliding damper.
  cTwo barometric dampers installed.

-------
 482
                                           INCINERATION
where:
    D =  theoretical draft,  in. WC

    P =  barometric pressure, psi

    H =  height of flue above breeching,  ft

    T =  ambient temperature, degrees  Rankine
      o
    T =  average stack temperature,  degrees
          Rankine.

    For an average flue gas temperature of 100°F:
   =  (0.52)(14. 7)(92)(
                       1
                        )  =  0. 092 in.  WC
                     520    560
     Theoretical draft (calculated by the same for-
     mula) versus temperature is  given in the fol-
     lowing tabulation:

Temp,  °F  Dt, in. WC  Temp,  °F  Dt, in.  WC
    100         0.09         400          0.53
    200         0.29         500          0.62
    300         0.43         600          0.69

2.   Compute the  weight of air  that must enter
     through the barometric damper  to  cool  the
     products of combustion from  the multiple-
     chamber incinerator to 300 °F, heat losses being
     neglected:

     Although neglecting losses causes the damper
     to be somewhat oversized, the draft can still
     be  regulated  with the weights on the damper.
     With the damper undersized,  however,  the
     draft cannot always be controlled.

     
-------
                                   Flue-Fed Apartment Incinerators
                                                                                                     483
 where:
    F   =  friction loss, in. WC
     B

    H   =  length of breeching, ft

    V   =  velocity,  fps

    D   =  duct diameter,  ft

    T   =  temperature, degrees Rankine.

                             ,2
       B
             (0. 008)(10)(51.9)
                  (1)(760)
                                 =  0.283 in.  WC
 8.   Velocity through the flue:

     Area of flue  =  2. 25 ft


     Velocity (300°F)  =  4°' 73 C^  =  18. 3 fps
                           2.25 ft

 9.   Friction loss in the flue:


                   0. 002(H)(V)2
where:

   F   =  friction loss,  in. WC

   H   =  height of flue above breeching, ft

   V   =  velocity, fps

   m   =  hydraulic radius, ft

   T   =  temperature,  degrees Rankine.

    For rectangular cross section, the hydraulic
    radius is:

                    area
              •wetted perimeter
     For the given flue, the hydraulic radius is:
           (2.25 ft )(12 in./ft)
           	
           (0.002)(92)(18.
                                 =  0.216 in.  WC.
                                                       11.  Frictional losses (calculatedby the same meth-
                                                            od) for assumed flue gas temperatures of 400 °
                                                            and 500 °F are given in the following tabulation:
                                                            Temp, °F
                                                               400
                                                               500
                                                                                    Friction loss, in.  WC
                                                                                             0.28
                                                                                             0. 18
                                                         12.  Determine the flue gas  temperature:

                                                             A flue gas temperature of 380 °F,  representing
                                                             a difference  of  0.2  in.  WC between the the-
                                                             oretical draft and the frictional losses, is ob-
                                                             tained from a plot of the data derived herein,
                                                             as shown in  Figure 366.
                                                                              300     400
                                                                             TEMPERATURE  °F
       F        (0.375)(760)

10.  Total friction losses in breeching and flue:

    Total friction losses = 0. 283 in. WC + 0.216 in. WC

                         = 0. 499 in.  WC
 •Gnswold, 1946.
                                                           Figure 366.  Draft at breeching of a multiple-chamber
                                                           basement installation versus average flue gas tem-
                                                           perature.
                                                        13.  Weight of air entering through the barometric
                                                            damper at 375 °F:
                                                                           - V  =
                                                        •where:

                                                          W.
                                                         W
                                                           pc
                                                               =   weight of air entering through baromet-
                                                                  ric damper,  Ib/sec

                                                               =   weight of flue gases, Ib/sec
234-767 O - 77 - 33

-------
484
                                          INCINERATION
  C    =  average specific heat of products of com-
          bustion from multiple-chamber incinera-
          tor over temperature range  of Tj to T£,
          Btu/lb-°F

  C    =  average specific heat of air  over tem-
          perature range T2 to T^,  Btu/lb-°F

   T   =  final temperature of flue gases,  °F

   T   =  average temperature of gases from mul-
          tiple-chamber incinerator,  °F
   T   =  temperature of air,  °F.
(W   lb/sec)(0. 24 Btu/lb-°F)(380 °F  -  60°F)  =
  A.
(0.517 lb/sec)(0. 26 Btu/lb-°F)(990°F  -  380°F)

          WA  =   1. 07 Ib/sec
                                                       PATHOLOGICAL-WASTE INCINERATORS
                                                      Pathological waste is defined to include all, or parts
                                                      of, organs, bones, muscles, other tissues,and or-
                                                      ganic wastes of human or animal origin.  This sec-
                                                      tion  is limited to those incinerators  used for the
                                                      burning of pathological "wastes and to crematory
                                                      furnaces that have design standards similar to those
                                                      of pathological waste incinerators.

                                                      Chemically, pathological waste is composed prin-
                                                      cipally of carbon,  hydrogen, and oxygen.   Slight
                                                      amounts  of many minerals, along with a trace of
                                                      nitrogen, are also present.  Physically, this  waste
                                                      consists of cellular structured materials and  fluids.
                                                      Each cell contains water,  along with the  elements
                                                      and compounds forming the cell.  The cells com-
                                                      prise thehair, fatty tissue, proteinaceous tissue,
                                                      and bone in proportions varying with different ani-
                                                      mals.  Blood and various other fluids in the organs
                                                      are almost completely water.
14.  Volume of air entering through the barometric
    damper:


    Volume (60 °F)  =
    (1.07 lb/sec)(60 sec/min)(379 ft /mol)
                 29 Ib/mol
                                          = 840 cfm
15. Area of barometric damper:

    The effective open area of a barometric damp-
    er  is about 70 percent of its cross-sectional
    area.  The area based on the calculated amount
    of air to be inspirated must,  therefore,  be
    increased accordingly.
    From Table D8, Appendix D,  one velocity
    head  at 0. 2 in.  WC and 60°F is  1,780 fpm.
             (840 cfm)(144 in. 2/ft2)
               (1, 780 fpm)(0. 70)


16.  Diameter of barometric damper:

                               ,2
          Area  =
      Diameter  =
                    (7r)(Diameter)
                   f(4)(97)-|
                   LnrJ
                            1/2
= 12 in.  (sized
  to the nearest
  inch)
                      The average  chemical composition of whole ani-
                      mals,  except for the proportion of water present,
                      is very similar in all animals.   The proportion of
                      •water  present,  compared with the total weight of
                      the animals , varies widely among different animals ,
                      and among various conditions of freshness or de-
                      composition of the animal material.  Average chem-
                      ical properties of pathological waste and combus-
                      tion data are given in Table 128.  These combus-
                      tion data have been found to provide good results
                      when used in design calculations for pathological-
                      waste  incinerators.  The cremation of human re-
                      mains differs from other pathological incineration
                      only in that the body is usually contained in a wood-
                                                        Table  128.  CHEMICAL COMPOSITION OF
                                                               PATHOLOGICAL WASTE AND
                                                                   COMBUSTION DATA

                                                                       Ultimate analysis
                                                                       (whole dead animal)
Constituent
Carbon
Hydrogen
Oxygen
Water
Nitrogen
Mineral (ash)
As charged
% by weight
14. 7
2. 7
11. 5
62. 1
Trace
9
Ash-free combustible
% by weight
50. 80
9. 35
39.85
-
                                                       Dry combustible empirical formula -
                                                                         Combustion data
                                                              (based on 1 Ib of dry ash-free combustible)
Constituent-
Theoretical air
40% sat at 60"F
Flue gas with
theoretical
air 40%
saturated
C02
N2
H^O formed
H2O air
Products of combustion total
Gross heat of combustion
Quantity
Ib
7. 028
7. 059
1. 858
5. 402
0. 763
0. 031
8. 054
Volume
scl
92. 40
93
16.06
73. 24
15. 99
0. 63
105. 92
8, 820 Btu per Ib

-------
                                   Pathological-Waste Incinerators
                                                                                                 485
en casket.  The casket must be considered when
designing these units and is usually assumed, for
design calculations, to-weigh 75 pounds and to have
the chemical analyses and combustion properties
of average •wood given in Table 121.
THE AIR POLLUTION PROBLEM

Pathological-waste incinerators can produce emis -
sions of fly ash,  smoke, gases,  and  odors that
would be highly objectionable.  Fly ash emission
is usually inconsequential in  this type of incinera-
tor, but odor emissions may be very great.  Vis-
ible smoke from this type of incinerator is highly
repugnant on esthetic grounds to most people and
is especially undesirable from crematory furnaces .

Poorly designed incinerators -with  inadequate
mixing, temperatures, and residence times  emit
highly objectional contaminants. Table  129 pre-
sents emission values measured for eight sepa-
rate multiple-chamber pathological-waste incin-
erators.

AIR POLLUTION CONTROL EQUIPMENT

The  prevention  of air contaminant emissions by
good equipment design is the best air pollution con-
     Table 129.   EMISSIONS FROM PATHOLOGICAL INCINERATORS WITHOUT GAS WASHERS
                     (U.S. Department of Health, Education, and Welfare,  1968)
                                                          Test number
Type of waste
Batch destruction rate to dry
bone and ash, Ib/hr
Participates,
gr/scf
gr/scf at 12% CO2
(CO2 from refuse only)
Organic acids.
gr/scf
Ib/hr
"Ib/ton
Aldehydes,
gr/scf
Ib/hr
Ib/ton
Nitrogen oxides.
ppm
Ib/hr
Ib/ton
Stack emissions:
Opacity, %
Time, min
Auxiliary fuel:
Primary, scfh
Mixing, scfh
Gas flow, scfm
Gas temperature, °F
Stack gases, %
CO2
02
CO
NZ
H20
Cost of incinerator, $
1
Human
tissue
19.2


0. 014
0. 240


0. 006
0.010
1. 04

N. A.
N. A.
N. A.

42. 7
0.085
8. 86

0


190
185
260
410

3. 4
12. 5
0. 0009
74.0
10. 1
2400
2
Human
tissue
64


0. 017
0.400


0.0003
0. 003
0. 093

0. 008
0. 076
2. 37

35
0.29
9. 05

0


700
230
1150
307

2. 1
16. 5
0.0
74. 8
6.6
2500
3
Animals
62


0. 032
0. 183


0. 010
0. 034
1. 10

0. 013
0. 041
1. 32

134
0. 37
12. 0

0


530
170
380
590

5.6
9. 8
0. 004
71. 5
13. 1
4250
4
Animals
35


0. 015
0. 106


N. A.
N. A.
N. A.

0. 004
0. 014
0. 80

111
0. 29
16. 6

0


600
300
370
950

6.3
7.7
0.0
71.9
14. 1
1300
5
Animals
99


0. 0936
0. 295


0. 013
0. 050
1. 01

0. 006
0. 020
0. 40

131
0. 099
2. 00

0


640
260
450
800

7. 6
4. 8
0. 02
67. 2
20. 4
2700
6
Animals
137


0. 013
0. 260


0.0033
0.075
1. 10

0. 0032
0. 072
1. 05

60
1. 2
17. 5

0


800
600
2640
346

1.6
17.7
0.0
75. 5
5.2
3200
7
Animals
149


0. 024
0.240


0. 0018
0. 012
0. 161

0.012
0.082
1. 10

165
0. 94
12.6

0


1020
480
780
1020

4.9
10. 8
0.0
71. 2
13. 1
3000
8
Animals
160


0. 0202
0. 135


0.0002
0.002
0.025

0. 010
0. 12
1. 50

102
1. 1
13.7

0


1800
500
1400
910

5.0
10. 8
0.0
73. 1
11. 1
6000

-------
486
INCINERATION
trol proc cdure  to  follow.  Inadequate; equipment
may be compensated for by use of an afterburner
designed according to precepts set forth in the first
part of this chapter.  New equipment employing
good design concepts can produce maximum com-
bustion of pathological-waste material with a min-
imum  of air contaminant emissions.

Design  Procedure

A principal  consideration  in the design of patho-
logical-waste incinerators is provision for the re-
lease of fluids as the material is destroyed.  These
fluids  are  frequently released in such quantities
that-theydo not immediately evaporate and,  hence,
require the use of a solid hearth rather  than grates
in the  ignition chamber.  Pathological waste can-
not be considered as forming a fuel bed when being
incinerated,  and the passage  of air through the
burning material is  not a requirement  in  these
units.

The presence of  a relatively  high percentage  of
moisture throughout each individual cell comprising
the pathological waste presents a difficult evapora-
tion problem. Evaporation of the moisture is nec-
essary before the combustible animal tissue can be
ignited.  Moisture, however,  evaporates only from
those cells upon and near the  surface of the mate-
rial exposed to heat.   Deeper lying tissue is al-
most completely  insulated from the heat in the
chamber and is heated only slowly.  Evaporation
of moisture from  deeper  cells cannot take place
until the destruction of the cellular material above
them causes them to be near the surface receiv-
ing heat.   While the heat of combustion of the dry
cellular  material  is considerable, the relatively
small proportion of this material to the large amount
of moisture present makes it ineffectual in initiating
the evaporation processes.  Auxiliary fuel must be
burned to accomplish the necessary dehydration.

As with other incinerator design calculations, those
for pathological-waste  incinerators also fall into
three general categories:  (1) Combustion calcula-
tions,  based upon the heat input of auxiliary fuel,
the composition of waste, the assumed require-
ments for air,  and heat losses;  (2) flow calcula-
tions based upon the products of combustion and
the expected gas temperatures; and  (3) dimen-
sional calculations based  upon simple mensura-
tion and empirical sizing equations.   The factors
to be  used in these calculations for pathological
incinerator design are given in Tables  130 and 131.

Simplifying assumptions may be made as follows:

1.   The evaporation and burning rates, auxiliary-
     fuel burning rate, and average waste composi-
     tion are taken as constant.  Design parameters
     should be based upon that -waste containing the
                 Table 130.   DESIGN FACTORS FOR
               PATHOLOGICAL IGNITION CHAMBER
                (Incinerator  capacity 25 to 200 Ib/hr)
               (U. S.  Department  of Health, Education,
                          and Welfare, 1968)
                 Item
          Hearth loading

          Hearth length-to-
            width ratio

          Primary fuel
          Arch height

          Gross heat release
            ignition chamber

          Specific heat of
            products of com-
            bustion including
            combustion of
            waste and natural
            gas
                Recommended
                    value
                See Figure 367
                        2

                See Figure 369
                See Figure 368
                See Figure 370

                0. 29 Btu/lb-°F
                                                Allowable
                                                deviation,
± 10
i 20

+ 10
± 20
+ 20
           4.
           5.
highest percentage  of moisture that may be
expected to be destroyed in the unit.

The  average  temperature of the combustion
products is determined through calculation of
heat loss by using radiation and storage loss-
es as determined in Table 132.

The  overall average gas temperature should
be about 1, 500°F when calculations are based
upon air for the combustible waste at 100 per-
cent in excess of theoretical, and upon air for
the primary burner at 20 percent in excess of
theoretical.  The minimum temperature of the
gases  leaving the ignition chamber should be
1, 600°F.

Indraft velocity in the air ports  is assumed to
beatO. 1 inch water column velocity pressure
(1,255 fpm).

The secondary air port is sized to provide  100
percent of the theoretical air for the combus-
tible material in the waste charged.
           A primary air port is not essential in these units.
           Adequate excess air  in the primary chamber
           normally will be provided for both the fuel and
           waste material by  leakage or by adjustment of
           the guillotine charging door.  When a  primary air
           port is desired,  5  square inches per  100 pounds
           of combustible waste is recommended.

           The combustion calculations needed to determine
           weights  and velocities  of the  products of combus-

-------
                                    Pathological-Waste Incinerators
                                                                                                    487
   Table 131.  GAS VELOCITIES AND DRAFT
FOR PATHOLOGICAL INCINERATORS WITH HOT
    GAS PASSAGE BELOW A SOLID HEARTH

    (U. S.  Department of Health,  Education,
           and Welfare,  1968)
Item
Gas velocities
Flame port at 1600 °F
Mixing chamber at
1600 °F
Port at bottom of
mixing chamber at
1550 °F
Chamber below hearth
at 1400 °F
Port at bottom of com-
bustion chamber at
1400 °F
Combustion chamber
at 1200 °F
Stack at 1000 °F
Draft
Combustion chamber

Ignition chamber

Recommended
values

15 fps
15 fps
15 fps
8 fps
10 fps

5 fps
15 fps

0.20 to 0. 25a
in. WC
0.05 to 0. 10
in. WC
Allowable
deviation,
%

+ 20
+ 20
i 20
± 50
± 20

+_ 50
± 25

± 10

± °

 Ignition chamber

 Ignition chamber dimensions are determined by
 deriving hearth loading, hearth area,  average
 arch height,  and chamber volume from Figures
 367 and 368 and from the factors given in Table
 131.  The ignition chamber burner capacity can
 be determined from Figure 369.  The maximum
 heat release rate, at gross fuel heating value,  in
 the whole  incinerator will range from 20, 000 to
 15, 000 Btu/hr-ft3 for sizes from  30 to 200 pounds
 per hour,  as  shown in Figure 370.
                                                          200
                                                       ,_  150
                                                       .c
                                                       \
                                                       &
                                                       UJ
                                                          100
                                                           50
                                                                              I
                                 BURNER FLAMES NOT
                              A  DIRECTLY IMPINGING
                                 ON ANIMAL
                              _J	I	
 Draft can be 0. 20 in.  WC for incinerators with
 cold hearth.
      0       5        10       15       20       25

                  HEARTH AREA, square feet

  Figure 367.  Pathological incinerator cremation rate (U.S.
  Department of Health, Education, and Welfare, 1968).
   Table 132.  HEAT LOSSES FROM IGNITION
   CHAMBER (STORAGE,  CONVECTION,  AND
     RADIATION LOSSES DURING INITIAL
       90 MINUTES OF PATHOLOGICAL
          INCINERATION OPERATION)
Incinerator capacity,
Ib/hr
25
50
100
200
250
Loss expressed as
% of gross heat input
36. 3,
32. 8
29.75
25. 3
23.6
 2   50

 ±   40
    30
                                                           20
                                                                              I
                                                                                       I
                                                                             10       15

                                                                         HEARTH AREA, square feet
                                                                                              20
                                                          Figure 368. Pathological incinerator arch height (U.S.
                                                          Department of Health, Education, and Welfare, 1968).
                                                                                                       25
tion along -with average temperatures may be de-
rived from standard calculation procedures  when
the preceding assumptions are followed.  The siz-
ing requirements for inlet air areas are minimum;
these areas should be oversized in practice to pro-
vide for operational latitude.
Length-to-width ratios for the hearth are not
critical. To provide for  single layer deposition
of the material upon the  hearth,  however, with
the resultant maximum exposure of the material
to the burner flames, a length-to-width ratio of
2:1 is the most practical.

-------
488
                      INCINERATION
    25
    20
    15
    10
               I         I
         BURNER FLAMES NOT
       A DIRECTLY IMPINGING
         ON ANIMAL
              _L
 _L
               5       10        15

                  HEARTH AREA, square feet
                                        20
                           25
   Figure 369.  Pathological incinerator fuel usage (U.S.
   Department of Health, Education, and Welfare, 1968).
 C/}
 <
 2i
                      I    I  I   I   T
                  I
I   I   I   I   I
      30     40    50  60     80    100

                 BATCH CREMATION RATE,  Ib/hr
                                                200
 Figure 370. Heat release rates for pathological incinerators
 (U.S. Department of Health, Education, and Welfare, 1968).
The location of the gas burner in the ignition
chamber is the most critical aspect of the design
of a pathological incinerator.  The flames from
the burner must impinge directly on the material
being incinerated or excessive fuel consumption
will result. Figures 367,  369,  and 371 graphically
illustrate this point.  Further  substantiation has
been obtained from operating data on an incinera-
tor with high fuel consumption.  It was found that
the cremation rate could be increased 100 percent
by merely allowing a 4-inch-thick layer of ash
and  bone residue to remain on  the hearth.  The
net effect was to raise the  material being cre-
mated into the direct path of the burner flames.

To provide maximum penetration of heat into  the
animal matter being cremated,  a flame retention
pressure burner equipped with a blower and full
IS

0 .fe
LU '
i-^L
< ^
LU •& ~
tr - 10
LU ^f
1- <

-------
                                   Pathological-Waste Incinerators
                                             489
Design of the secondary combustion zone for low-
velocity gas movement at average volumes will
provide for complete combustion, even during
the periods of abnormally high combustion rates.

An additional auxiliary burner  located in the
secondary combustion zone is necessary for these
incinerators. The type and location of the burner
is not nearly as critical as for the  one in the
ignition chamber. Atmospheric mixers equipped
•with full safety controls are adequate for incinera-
tors rated at 100 pounds  per hour or less, but in
the larger units, the nozzel mix  type is required
to obtain optimum incineration.

The burner capacity need only be sufficient to
maintain a 1600 °F temperature in  the gases. To
do this, the  burner  should be so  located that the
gas flowing from the ignition chamber can first
mix with introduced secondary air  before  flowing
through the flame of the burner.  Downstream of
the burner,  the mixing chamber must be designed
to provide adequate space for  secondary combus-
tion to occur.

Stack design

Calculations for stack design should be based on
a  gas temperature  of 1000 °F.  Because design
calculations are based on average rate  of  opera-
tion and there will  be periods when this  rate will
be exceeded, stack design velocity should be at
or below 15  fps.  Stack height should be determin-
ed so as to provide a minimum available draft of
0. 20  inch water column.   This is the minimum
draft  provision for pathological incinerators.
When a hot gas passage beneath the hearth is to
be provided,  the minimum available stack draft
at the breeching should be increased by  10 per-
cent.  This additional draft will compensate for
the additional gas flow resistance in the incinera-
tor caused by such a design.  The underhearth
chamber is not an essential  requirement and can
be eliminated, especially in units of less than  100
pounds per hour capacity.

Piping  requirements

Piping  requirements for  the gas fuel supply should
be determined.  The piping should be sized to
supply  the total maximum capacity of the burners
used in both the ignition and secondary  combus-
tion chambers.

Crematory design

The shape and size of the ignition chamber  in cre-
matory units is dictated  by the  dimensions of a
casket.  The same  factors influencing the design
of other pathological-waste units should, however,
be used for all other parameters of  the crematory
ignition chamber.  In calculating the volume and
weight  of products  of  combustion, consideration
mustbe given to the admission of somewhat larg-
er amounts of excess air when the design includes
a charge door at one  end and a  cleanout door at the
other end of the ignition chamber.   Increasing the
burner capacity in these installations  may be nec-
essary.   Parameters for  the  secondary combus-
tion zone of crematory furnaces will be based upon
the same factors as  those given for  normal patho-
logical-waste incinerators .  The volume and weight
of products of combustion will include those  from
the burning of the casket.  These units  cannot,  how-
ever, be designed on the basis of assuming that the
burning rate is constant. There will be some period
of time during the total operation in which a higher
rate of  production of combustion products  occurs.
Table 133 sets  forth two  possible  operating pro-
cedures with arbitrary but representative grouping
of  periods  of  operation that -will produce varying
combustion rates .  The factor s for the parameters
of  the secondary combustion  zone  should be used
for the period of operation that  produces the great-
est flow of combustion products.

Incinerator design configuration

There arc  several  possible configurations  that
might be used in the construction  of pathological-
waste incinerators.  Several are illustrated in Fig-
ures  372, 373,  and  374.

Figure  372  shows an adaptation of the design for
the retort-type multiple-chamber incinerator  for
destruction of pathological waste.  In  this adapta-
tion,  three  configuration differences  from the
comparable unit illustrated in Figure 339 are
immediately visible:

     1.  The  use of a solid hearth instead of  grates.

     2.  The provision for  heating the hearth  by
        passing the  products of combustion from
        the mixing chamber through a chamber
        beneath the  hearth before they exit to the
        combustion  chamber.  (Unless the inciner-
        ator operates continuously for several
        hours, little if any advantage is  gained by
        an underhearth chamber. )

     3.  The side charging door, which is neces-
        sary for frequent charging of large indi-
        vidual components of pathological waste.

Dimensions for multiple chamber pathological
incinerators are given  in Figure 375.  Individual
components in pathological waste are frequently
large in size.  In addition, the charge must be
disposed over the hearth in a single layer of com-
ponents to provide for maximum exposure  of sur-
face area to the burner flame.  These two  factors
make necessary the designing  of the charge open-
ing with width and height dimensions  close to the

-------
490
                                           INCINERATION
                     Table 133.  OPERATING PROCEDURES FOR CREMATORY


Phase

Charginga
Ignition
Full combustion
Final combustion
Calcining

Duration,
1-1/2 hr
operation,
mm
-
15
30
45
1 to 12 hr



Burner settings

Secondary zone on
All on
All on
All on
All off (or small
primary on)


Casket


20% burns
80% burns
-
-




Moisture


-
20% evap
80% evap
-

Body


Tissue


-
10% burns
90% burns
-




Bone
Calcined

-
-
50%
50%

                                                 OR




Ignition
Full combustion
Final combustion

Calcining

Duration,
2-1/2 hr
operation,
min
15
30
15
90
1 to 12 hr





All on
Primary off
All on
All on
All off (small primary
may be on)




20% burns
60% burns
20% burns
-






-
20% evap
20% evap
60% evap






-
-
20% burns
80% burns






_
-
50%
-


aCharge: Casket 75 Ib wood
Body 180 Ib
                    Moisture -  108 Ib
                    Tissue   -   50 Ib
                    Bone     -   22 Ib
                           Figure 372 Multiple-chamber pathological-waste incinerator.
maximum dimensions of the ignition chamber.
The side  charging door will not,  as with the in-
cineration of general refuse,  cause the  emission
of excessive particulate matter from these incin-
erators.
Figure 373  illustrates a retort for the burning of
pathological waste added to a standard multiple-
chamber incinerator.  When these retorts are used,
the gases from the retort should pass across the
rear  of the  ignition chamber  of the standard in-

-------
                                     Pathological-Waste Incinerators
                                                                                                         491
                                   MIXING
                                   CHAMBER
         SECONDARY
         COMBUSTION
         CHAMBER
    CLEANOUT
    DOOR
                                                                         IGNITION
                                                                         CHAMBER
              PATHOLOGICAL REFUSE-1
              CHARGING DOOR
                                  CLEANOUT DOOR KITH
                                  UNDERGRATE AIR PORT
-GENERAL REFUSE CHARGING DOOR
 WITH  OVERFIRE AIR PORT
                                     PATHOLOGICAL-
                                     PRIMARY
                                     BURNER PORT
                   Figure 373  Multiple-chamber incinerator with a pathological-waste retort.
         IGNITION
         CHAMBER
                                                    CLEANOUT
                                                    DOORS
CLEANOUT
DOOR
                          -SECONDARY
                           BURNER
                           PORT'
               Figure 374.  Crematory retort.
    cinerator.   The design of the retort incorpo-
    rates the factors given for the design of the
    ignition chamber of a pathological-waste incin-
    erator.  The design of  the remainder of the
    combination incinerator is only  slightly influ-
    enced by the addition of this retort under most
    circumstances. In order to prevent restriction
    to the flow of the products of combustion from
    the pathological chamber,  the gas passage from
    the chamber should be designed for about 10 fps.

    Figure 374 illustrates  a human crematory
    retort.   This illustration is but one design,  and
    many variations are found. Characteristically,
    these retorts  provide for a flame along the
    length of a shallow,  narrow,  long charging
    chamber. The design illustrated employs a
    "hot hearth. " Other  designs provide for flame
    passage  on all sides of the charge including
    the underside. The hot hearth principle is not
    always  employed in crematory retorts. The
    unit illustrated was not originally designed
    with secondary burners; these burners were

-------
492
INCINERATION
                       SECTION A-A.

                       SECTION B-B
                                                                 1. STACK
                                                                 2. SECONDARY AIR PORT
                                                                 3. GAS BURNERS
                                                                 4 UNDER HEARTH CHAMBER
                                                                 5 REFRACTORY HEARTH
                                                                 6. CHARGING DOOR
                                                                 7 FLAME PORT
                                                                 8 UNDER HEARTH PORT
                                                                 9 IGNITION CHAMBER
                                                                10 OVERFIRE AIR PORT
                                                                11 MIXING CHAMBER
                                                                12. COMBUSTION CHAMBER
                                                                13 CLEANOUT DOOR
                                                                14 CURTAIN WALL PORT
                                                                            SECTION C-C
LENGTH, INCHES
ABCDEFGH'IJK LMNOPO.RSTUVWXYZ
50
-C
^ 100
LU"
Ci! 150
V)
200
381/2
54
63
72
20'/2
27
36
42'/2
25
25
231/2
33
13V2
18
22'/2
24
111/2
131/2
18
22'/2
22'/2
26
36
45
18
221/z
27
36
20
22
25
31
14
16
20
24
25
26
28'/2
36
34
38
44
48
8
12
13
14
1T/2
0
0
0
4/2
4'/2
4'/2
7
2>2
21/2
4'/2
4
2'.i
2V2
41/2
7
20'/2
25
33'/2
35
41/2
4'/2
4
-------
                                  Pathological-Waste Incinerators
                                            493
Stack Emissions

Visual emissions  of fly ash are not evident from
pathological-waste incinerators.  Air  contaminants,
as solid,  liquid,  and gaseous emissions, which
have been determined are given in Table 129. The
stack effluent from a well-designed incinerator
will not be highly  objectionable from the stand-
point of odors when freshly killed or  frozen ani-
mals are  being cremated. However, cremation
of decayed animal matter will produce objection-
able odors which will not be entirely eliminated
by the  incinerator.

Operation

Operation of pathological-waste incinerators is, in
general, more simple than that for other types of
refuse incinerators.  Preheating the  secondary
combustion zone  before  charging and operating
these units is good practice.   The primary burner
or burners should  not be ignited until charging has
been completed and the charge door closed.  The
material to be destroyed should be disposed on the
hearth in a manner that provides for maximum ex-
posure to the flame of the primary burner.  Fur-
ther overcharging the unit by placing one compo-
nent of the charge  on top of another is not good
practice.  Care should be exercised to ensure that
the primary burner port is not blocked by any ele-
ment of the charge.

When the amount of material to be destroyed ex-
ceeds  what can be normally charged,  stoking and
additional charging  should be practiced only after
considerable reduction of the initial charge has oc-
curred.   The primary burner should be shut off
before the  charge door  is opened and stoking or
additional charging takes place.  Before an addi-
tional  charge is made, the material remaining on
the hearth should be  gently pushed towards the end
of the  hearth nearest the flame port.  The fresh
charge should then be disposed  on the  exposed
hearth toward the primary burner.  When recharg-
ing is  complete,  the charge door should first be
closed before the primary burner is  once again ig-
nited.

Air port adjustment normally has only a minor role
in the regulation of the operation of these incinera-
tors.  Making further adjustments to the secondary
air port after it has been adjusted to provide proper
operation under normal burning conditions is usu-
ally  not necessary.  The only operating difficulty
to be encountered occurs when large deposits of
fatty tissue or hair are exposed to the burner  flame.
As previously stated, the sudden volatilization of
this material occasions a sudden rush of gases and
vapors into the secondary chamber. On these oc-
casions some black smoke may issue from the stack.
This surge of gas volume,  if very large,  could even
result in pressurizing the  ignition  chamber,  caus-
ing smoke to be forced out around the  charge door.
Operational control, when this occurs,  is obtained
by reducing the burner rate in the ignition chamber.
Under exceptional conditions,  shutting this burner
off for a few minutes may even be necessary.  White
smoke issuing from the stack usually indicates that
air is entering the unit in an amount exceeding the
ability of the burners  to heat sufficiently.  This is
best overcome by increasing secondary or primary
burner fuel rates.  Very  rarely is it necessary to
adjust the secondary air  port to lower the admis-
sion of air when white smoke  persists.

Automatic temperature control may  be used to
operate these units.  Temperature control should
be achieved by using the primary burner only. The
secondary burner should not be  shut off or modu-
lated to a lower operating rate by these controls.
The  temperature-sensing element may be placed
in the combustion chamber,  breeching, or stack.
Precise temperature control at any of  these  points
is then achieved by modulating or shutting off the
primary burner.   This operation to control tem-
peratures does not affect the emission of air con-
taminants. When temperature control is attempted
by control of the secondary burner,  provision of
the response  desired will  be found difficult, and
the emissions of air contaminants will be increased
when the burner's rate of fire is reduced or shut
off by control action.

There is  no  burndown period in the  operation of
pathological-waste incinerators.  The degree  of
destruction desired for the waste  material dictates
the length of time the primary  burner is left in
operation. Some operations are normally ceased
when the material has been reduced to  clean, white
bone.  When reduction of the  bone to powdery ash
is desired,  the  primary burners are  continued in
operation until this is achieved.  After the shutoff
of the primary burner, the secondary burner should
not be shut off until smoldering from  the residual
material on the hearth in the primary chamber has
ceased.

The  hearth should be  frequently  cleaned to pre-
vent buildup of ash residue  and slag-like deposits.
Frequency of cleanout of the combustion or settling
chamber depends upon incinerator use.  Deposits
in this chamber should be  removed to avoid re-en-
trainment in the exhaust gases.

Illustrative Problem
Problem:

Design  an incinerator to dispose of 100 pounds of
dog bodies per hour.
Design:

Select a multiple-chamber, retort-type incinera-
tor with a hot gas passage below a solid hearth.

-------
494
          INCINERATION
Solution:

1.  Design features of ignition chamber:
   From Figure 367, at 100 Ib/hr

   Hearth area =  10 ft2

   From Table 130, hearth dimensions:

   Length- to -width ratio  =  2
   Let w = width of hearth in feet

      (w)(2w)  = hearth area

      2w2   =  10 ft2

      w                             =  2. 24 ft
      Length  =  2w                  =4. 48 ft

      From Figure 368,  arch height  = 26 in.

      Total ignition chamber volume  = 21. 6 ft

2.  Capacity of primary burner:

   From Figure 369, primary burner consump-
   tion  is 7000 Btu/lb

   (7000Btu/lbxl001b/hr -4-1100 Btu/ scf = 635 cfh)

3.  Composition by weight of pathological waste:

   From Table 128, carbon,  hydrogen, and
   oxygen constitute 29%,  water 62%, and  ash
   9%

   Dry  combustibles (1 00  Ib/hr)(0. 29)  =291b/hr
   Contained moisture  (100 lb/hr)(0. 62)= 62 Ib/hr
   Ash  (100 lb/hr)(0. 09)                =   91b/hr
   Total

4. Gross heat input:
       100 Ib/hr
   From Table 128, the gross heating value  of
   waste is 8820 Btu/lb,  and from Table D-7 in
   Appendix D, the gross heating value of natural
   gas is 1100 Btu/scf

   Waste
   (29 lb/hr)(8820 Btu/lb)    =  256, 000 Btu/hr

   Natural gas
   (635 cfh)(1100 Btu/scf)    =  700, 000 Btu/hr
   Total

5. Heat losses:
956,000 Btu/hr
   (a) From Table 132,  gross heat losses by
       storage,  conduction and radiation are
       29. 75% of gross heat input.
       (0. 2975)(956, 000  Btu/hr) = 285, 000 Btu/hr

   (b) Evaporation of contained moisture at 60 °F
                            The heat of vaporization of -water at 60 °F
                            is 1060 Btu/lb

                            (62 lb/hr)(1060 Btu/lb) = 65,700 Btu/hr

                        (c) Evaporation of water formed from the
                            combustion of waste at 60 °F
                            From Table 128,  combustion of 1 Ib of
                            waste yields 0. 763 Ib  of water.

                            (0.763 lb/lbX291b/hrX1060 Btu/lb)  =
                            23, 450 Btu/hr

                        (d) Evaporation of water formed from the
                            combustion of natural gas at 60 °F
                            From Table D-7 in Appendix D, 0. 099 Ib
                            of water is formed from combustion of
                            1 scf of  natural gas.
                            (0. 099 Ib water)
                                  1  scf
                            66,000 Btu/hr
                      (635 scfh)(1060 Btu/lb) =
   (e) Sensible heat in ash:

      Assume ash is equivalent in composition
      to calcium carbonate. Average specific
      heat is 0. 217 Btu/lb-°F

             H = WA (Cp)(T2 -  TI)

      where

           H = sensible heat, Btu/hr
         W^ = weight of ash, Ib/hr

          C  = average specific heat of ash,
               Btu/lb-°F

          T2 = final temperature, °F
          Tj = initial temperature,  °F
           H = (9 lb/hrX0.217 Btu/lb-°FX1600 °F-
               60 °F)' = 3000 Btu/hr

   (f) Total heat losses:

      (a) + (b) + (c) + (d) + (e) = total heat losses
      285,000 Btu/hr + 65,700 Btu/hr + 23,450
      Btu/hr + 66,600  Btu/hr + 3000 Btu/hr =
      443,750 Btu/hr

6.  Net heat available to raise  products of com-
   bustion (gross heat input - heat losses):

   956,000 Btu/hr - 443,750 Btu/hr =
   512,  250 Btu/hr

7.  Weight of products of combustion:

   From Table 128,  combustion of 1  Ib -waste
   with 100% excess air will yield 15. 113 Ib of

-------
                                    Pathological-Waste Incinerators
                                            495
    combustion products.

    From Table D-7 in Appendix D, combustion
    of 1 scf natural gas with 20% excess air will
    yield 0. 999 lb of combustion products.

    Waste (29 lb/hr)(15. 113 Ib/lb)       = 4381b/hr

    Contained moisture                  =  621b/hr

    Natural gas (635 cfh)(0. 999 Ib/scf)   = 6321b/hr

    Total weight of  combustion products = 11 32 Ib/hr

 8. Average gas temperature:

    From Table 130,  the average specific heat of
    combustion products  is 0. 29 Btu/lb-°F

                Q = (wc)(cp)(T2 - T!)


    where

         Q = net heat available, Btu/hr

        Wc = weight of combustion products, Ib/hr

        Cp = average specific heat of combustion
             products, Btu/lb-°F

        T2 = average gas temperature,  °F

        Tj = initial temperature,  °F

                            Q
                 = T
                     l   (Wc)(Cp)

                     512, 250
                           . 29)
     This average temperature exceeds the mini-
     mum design temperature of 1600 °F.  There-
     fore, the primary burner has  adequate capac-
     ity.

 9.  Secondary air port size:

     Design secondary air port 100% oversize
     with an indraft velocity of 1255 fpm at 0. 1 in.
     WC velocity pressure.

     From  Table 128,  1 lb waste requires 93 scf
     of air.

     (29 lb/hr)(93.0  scf/lb) = 2697  cfh

                          or   44. 93 cfm

                          or    0. 749 cfs

     (44. 93 cfm) (144 in. 2/ft2)(2)
             1255 fpm
                                = 10. 3 in. 2
10.  Weight of maximum air through secondary
    port:

    From  Table D-l in Appendix D, the density of
    air is 0. 0763 Ib/scf

    (2)(2697 cfh)(0.0763 Ib/scf) = 411. 5 Ib/hr

11. Heat required to raise maximum secondary
    air from 60 °F to 1600 °F:

    From Table  D-4 in Appendix D, 396. 8 Btu is
    required to raise 1 lb air from 60 °F to 1600
    °F

    (411.5 lb/hr)(396.8 Btu/lb) = 164,400 Btu/hr

12. Natural gas required by secondary burner:

    Design  for combustion of natural gas with 20%
    excess  air. From  Table D-7 in Appendix D,
    the calorific value of natural gas is 552. 9
    Btu/scf at 1600 °F

    (164,400 Btu/hr)(552 Btu/scf) = 300  cfh

13. Volume  of products of combustion:

    (a)  Through flame port

        From Table 128,  combustion of 1 lb waste
        with 100% excess air will yield 198. 92
        scf of combustion products.

        From Table D-7 in Appendix D, combus-
        tion of  1 scf natural gas with 20% excess
        air will yield 13. 53 scf of combustion
        products.

        Waste
        (29 lb/hr)(198. 92 scf/lb)   = 5769 scfh
        Water
        (63 lb/hr)(379 scf/lb mole) = 1305 scfh

        Natural gas

        (635  scfh)(13'53 Scf)       = 8550 scfh
                     scf             	

        Total volume of gases      -15, 624 scfh

                           or         260 scfrn

                           or           4.33 scfs

    (b)  Through exit from mixing chamber

        Design  secondary burner for combustion
        of 20% excess air.

        Products  of combustion
        through flame port      =15, 624 scfh

        Products  of combustion
       from secondary burner
       (300 cfh)(13. 53 scf/scf)  =  4, 060 scfh
       Maximum air through
        secondary air port
        (2)(2697)                =  5, 394 scfh

-------
496
   INCINERATION
        Total volume of gases     25, 078 scfh
                            or       418 scfm

                            or         6. 97 scfs

14. Incinerator cross -sectional areas:

    (a) Flame port area
        From Table 131, design flame port for
        15 fps velocity  at 1600 °F

               (4.33 8Cf8).(2060'R) _           2
                 (15 fps)(520 °R)   "    l-lSft

    (b) Mixing chamber area

        From Table 131, design mixing chamber
        for 15 fps velocity at 1600 °F
             _
               (6.97 scfs)(2060
                 (15 fps)(520 °R)    ~

    (c)  Port area at bottom of mixing chamber

        From Table 131,  design port for 15 fps
        velocity at 1550 °F
• 8° ft
               (6.97  scfs)(2010 °R)
                 (15 fps)(520 °R) -

    (d)  Chamber area beneath hearth
        From Table 131,  design chamber for 8
        fps velocity at 1400 °F
               (6-97  scfs)(1860 °R)   _
                 (8fps)(520 °R)      "   '

     (e) Port at bottom of combustion chamber

        From Table 131, design port for 10 fps
        velocity at 1400 °F

        Area - (6.97 scf s)(l 860 °R)  _         2
          rea ~  (10 fPs)(520°R)     -   2.50ft

     (f) Combustion chamber

        From Table 131, design combustion
        chamber for 5  fps velocity at 1200 °F

                                    =   4.45ft'
                  (5 fps)(520 °R)
     (g) Stack
        From Table 131, design stack for 15 fps
        velocity at 1000 °F
               (6.97 scfs)(1460
                                     =  1'3ft
                 (15fps)(520°R)

 15.  Stack height:

     From Table 131,  design stack for a draft of
                 0. 20 in.  WC in the combustion chamber.
                 Stack height
                           Dt = 0.52 PH (-

                 where
                     Dt = draft,  in. WC
                      T = ambient air temperature,  °R
                     Tj = average stack gas temperature, °R
                      P = atmospheric pressure,  Ib/in.
                      H = stack  height,  ft
                   H =
                           (0.20)
                       (0. 5Z)(14. 7)    1
                                    \520
                                   \= 21  ft
                               146(
DEBONDING OF BRAKE  SHOES AND RECLAMA-
TION OF ELECTRICAL EQUIPMENT WINDINGS
Brake shoe debonding and reclamation of electrical
equipment windings are similar combustion pro-
cesses,  both  using equipment nearly identical in
design.   These processes  differ from incineration
and other combustion reclamation processes in that
the combustible contents of the charge are usually
less than 10  percent by weight, and high tempera-
tures must be avoided to prevent damaging the sal-
vageable parts.
             DEBONDING OF BRAKE SHOES

             Bonded brake linings contain asbestos  mixed with
             binders consisting of phenolic resins, synthetic
             rubber, or bodied oils such as dehydrated linseed
             oil.   Carbon black, graphite,  metallic lead, thin
             brass  strips, and cashew  nut  shell oil  added in
             small  amounts  act as  friction-modifying agents
             (Kirk and  Othmer,  1947).   These materials are
             blended and  extruded into curved lining to fit the
             brake  shoe.  The lining is then heated to produce
             a hard surface.
             Adhesives  for  bonding the lining are  composed
             mostly of rubber or phenolic resins.  Small amounts
             of vinyl  are sometimes combined  with  phenolic
             resins.   The linings are originally bonded to steel
             shoes with adhesive, of a thickness of 0. 008 to 0.01
             inch, by subjecting them to pressure and a temper-
             ature of 400 °F for  a specific time  to develop max-
             imum bond strength.


             In the brake-debonding process,  brake shoes  are
             charged  to  an oven,   called a debonder,  to "which
             external  heat is applied carefully to minimize warp-
             age of the shoes.  Adhesive portions of the  lining
             start to  melt,  and destructive distillation  begins

-------
             Debonding of Brake Shoes and Reclamation of Electrical Equipment Windings
                                             497
at about 600°F (Kirk and Othmer, 1947).  In the
absence of flame, the melting of the adhesive pro-
ceeds until enough organic material is volatilized
to initiate burning.  At 800°F, thermal debonding
results in the adhesive's being burned or charred.
Burning continues at temperatures less than 1,000°F
until all combustibles have been consumed.   Once
combustion has been initiated, the heating value  of
the adhesive is usually sufficient to maintain burn-
ing without external heat.

After the brake  shoes are removed from the de-
bonder, the brittle linings either fall from the shoes
or are knocked loose by light tapping.  Carbonized
material adhering to the shoes is removed by abra-
sive blasting,  and the clean shoes are ready for
bonding with new linings.

RECLAMATION OF ELECTRICAL EQUIPMENT WINDING

Amajor  portion of the reclamation of direct-cur-
rent electrical equipment involves automotive start-
ers and  generators.  An average-size  starter or
generator •weighs 20 pounds and contains approxi-
mately 2 or 3 pounds of salvageable  copper wire.
Reclamation of alternating-current electrical equip-
ment usually involves squirrel cage motors.  Rotors
removed from squirrel cage motors  contain no or-
ganic material and, therefore,  require no process-
ing.  The starters of these motors contain 5 to 10
percent combustible organic materials.

Table 134 gives the average composition and the
amount of combustibles  in major components of
electrical equipment.  While these data still hold
true today, trends in new construction point to the
use of greater quantities of noncombustible  glass
cloth  in place of cambric.  Acrylic resin,  epoxy
resin, silicone elastomers, and polyvinyl chloride
are replacing  cambric  installation  and varnish
coatings.


In rebuilding electrical equipment and reclaiming
copper windings, the insulation is burned from the
windings of motors,  generators,  and transformers.
After combustion is completed,  the copper wire
windings  are  separated  and sold for scrap.  Pole
pieces, shafts, frames, and other parts are cleaned
of char  and  rewound with new wire.  During the
reclamation  process, combustible organic  com-
pounds used to insulate copper wire begin to  vola-
tilize upon application of heat.   Ignition occurs
above 600°F, and combustion is virtually completed
at 900°F. Since the combustible contents of the
charge are usually insufficient to sustain burning,
                 Table 134.   COMBUSTIBLE CONTENT OF ELECTRICAL EQUIPMENT
Components
A-C industrial
Motor and generators
Casing
Stator
Squirrel cage rotor
Wound rotor
D-C industrial
Motors and generators
Casing
Armature
Field rings


Automotive
Starters and generators
Casing
Armatures with shaft

Generator field coils
Starter field coils

Transformers
Casing
Windings

Average wt %
combustible


Nil
5 to 10
Nil
5 to 10


Nil
5 to 10
5 to 7




Nil
1 to 2

5 to 10
5 to 10


Nil
7 to 10

Combustible description



Cambric and varnish

Cambric and varnish



Cambric and varnish
Cambric and varnish, or
acrylic resin, epoxy resin,
silicones, PVC



Wood strips
Fish paper
Cambric and varnish
Varnish
Fish paper


Cambric and varnish
Oila
                 lOil-filled transformers only.

-------
498
INCINERATION
auxiliary heat is usually supplied by primary burn-
er s during the complete operation.  By restricting
the combustion air, the burning insulation may pro-
vide over 50 percent of the total process heat  re-
quirements.

The  temperature  in  the furnace is kept  below
1, 000°F to minimize warpage of metal parts  and
oxidation of  the copper wire.  The larger the in-
dividual item, the longer the preheat time, to pre-
vent warping of the steel components.  For example,
a 100-hp motor requires  a preheat time of over
1-1/2 hours.

THE  AIR POLLUTION PROBLEM
The practice  of reclaiming  electrical windings  and
debonding  brakeshoes by open burning or burning
in a single-chamber device results in the emission
of large quantities of smoke,  odors, and other
combustion contaminants.   Emissions of air con-
taminants  from these processes are summarized
in Tables 135 and  136.

AIR POLLUTION CONTROL  EQUIPMENT

Debonding of brake shoes and reclamation of elec-
trical windings conducted in a single-chamber unit
can  be  easily  controlled by using an  afterburner
as described in the first part of  Chapter 5.

Two basic configurations of equipment  using after-
burners effectively accomplish  these  reclamation
                Table 135.  STACK EMISSIONS FROM
                BRAKESHOE DEBONDING IN SINGLE
                 CHAMBERS WITHOUT CONTROLS


Co
Ch
Ou
CD
Sta

Pa
Sul
Ca
Or
Ah
Nil
Hy
Sm
R


1P0,1
rgi »
aticm
ibu^t
k Sa
K
In ill
ur .li
bon r
am,
hyd<
ogi n
rut a
k( I
nBi'li
Itom

ion of lharg.
right, 11)
of irst. -Tim
lie ontent of charge, wt To
flov ratr, s< fm

r n at IT, Ib/hr
\]d< , b/hr
moxid-, Ib/hr
dels a atcti, and, Ib/hr
as 10 maldi-hydi, Ib/hr
ixidi's as \O_, , Ib/hr
xins as hexane, Ib/hr
issions , opa< ity range
inn t harl
Test N
C-606
17S shoes
26S
58
5
180

0. 70
0. 21
0. S4
o. a
0 10
0. 02
0 05

0 to 80% broun-white

C-651
60 shoes

8.75
5
ISO

0.75
a
0
a
a
a
a

0 to 10% brown
           processes  with a minimum discharge of air con-
           taminants.  One is a single structure housing the
           primary and secondary combustion chambers, -while
           the other consists of two separate pieces of equip-
           ment,  a primary chamber and an afterburner or
           secondary  chamber.   Variations  in the design of
           these two  configurations  are many, and the final
           selection of a particular design is based upon con-
           siderations such as space limitation, process con-
           ditions,  maintenance, capital investment,  and
           operating expenses.   In designing an effective af-
           terburner, the size and appurtenances  of the pri-
           mary ignition chamber must be known or be  initial-
           ly designed.
          Table 136.  STACK EMISSIONS FROM RECLAIMING ELECTRICAL WINDINGS IN
                           SINGLE CHAMBERS WITHOUT CONTROLS
Item
Composition of charge


Charge weight, Ib
Duration of test, min
Combustible content of charge, wt %
Stack gas flow rate, scfm
Average gas temperature, °F
Particulate matter, gr/scf at 12% CO2
Particulate matter, Ib/hr
Sulfur dioxide, Ib/hr
Carbon monoxide, Ib/hr
Organic acids as acetic acid, Ib/hr
Aldehydes as formaldehyde, Ib/hr
Nitrogen oxides as NO2, Ib/hr
Hydrocarbons as hexane, Ib/hr
Smoke emissions, opacity range
Ringelmann chart

Odors
Test No.
C-342
100-hp
generator
stator
--
22. 5a
5
320
680
1.9
2.43
0. 13
1.90
0.35
0. 08
3.07
Nil

15 to 30%


C-497
14 pole
pieces

3,825
60
5
400
350
1. 1
0. 65
--
0. 35
0. 33
0.079
--
--

--


C-542
200 auto
armatures

161
55
1.7
210
360
3.3
1.64
0
0.50
0.62
0.29
0. 03
0. 16

0 to 100%


C-541-1
Auto
armatures

1,034
45. 4
1.2
790
470
0.54
1.04
0. 02
1.39
0. 42
0. 13
0. 12
0. 09

0 to 30%
white

C-541-3
Auto field
coils

356
16
5.9
950
290
1.33
2.51
0. 13
4.72
1.01
0.49
0.08
0. 11

0 to 80%
gray

   aTest duration does not include preheat period.

-------
              Debonding of Brake Shoes and Reclamation of Electrical Equipment Windings
                                            499
 Primary Ignition  Chamber

 The size of the  primary chamber is determined
 from the production rate or volume of the batch
 charge desired.   On the average,  1 cubic foot of
 space holds in random arrangement 27 brake shoes,
 or 34 automotive  field coils,  or 10 automotive ar-
 matures.  In sizing the primary chamber, addi-
 tional  space is provided over that space occupied
 by  the  charge,  to make it easier to load and un-
 load.  For example, in a batch process,  350 auto-
 motive generator field  coils or 200 average-size
 brake shoes canbe randomly placed in a  55-gallon
 drum.

 Primary burner capacity is computed by conven-
 tionalheat and material  balances to determine the
 amount  of heat necessary to  raise the  tempera-
 ture of the mate rial being processed to 850 °F. This
 temperature ensures ignition of combustibles, and
 maintenance of the temperature necessary for com-
 plete combustion.   Gas burners must supply suf-
 ficient heat not only for ignition, but also  to sus-
 tain burning.  The  lower the combustible  content
 of the charge, the more heat that must be supplied
 by  the primary burners.  Consequently, primary
 burners are sized for minimum combustible con-
 tent of the charge.

 Adjustable air ports near the bottom of the primary
 chamber should be large enough to provide theoret-
 ical air plus 100 percent excess air. These ports
 should be sized to provide this quantity  of air for
 the maximum combustible content of the charge.

 Secondary Combustion Chamber

 The mixing chamber or afterburner is designed for
 maximum effluent from the primary chamber using
 conventional heat and material balances.   For a
 given charge, maximum effluent occurs when the
 combustible content of the charge is at a maximum.
 The mixing chamber burner or afterburner must
 be capable of raising the temperature of the max-
 imum quantity of effluent expected from a tempera-
 ture of 850°   tol,400°F.  These burners are posi-
 tioned to blanket the cross-sectional area of the
 afterburner completely with flame.

 The cross-sectional area of the mixing chamber is
 based  upon an average gas velocity ranging from
 20 to 30 fps for the total effluent.   Gas velocities
 in this range promote turbulent mixing of the gas-
 eous effluent  from  the  ignition chamber with the
 flames from the mixing chamber burner.  Baffles
 and abrupt  changes in  direction of gas  flow also
 promote turbulent  mixing, -which is essential for
 complete combustion.  The mixing chamber or af-
terburner should be of sufficient length to allow a
 residence time of at least 0. 15  to 0. 2 second.

 Secondary air ports  should provide theoretical air
 for  maximum combustible content  of the charge.
Stack

In designing a stack for minimum height, stack
gas velocities should not exceed 20 fps at maximum
temperatures to minimize the effects of friction.
Effective draft  is  computed  as  theoretical stack
draft minus  friction losses at design flow condi-
tions.  An effective draft or negative static pres-
sure of from 0. 05 to 0. 10 inch WC should be avail-
able in the ignition chamber when the unit is oper-
ating at rated capacity.

Emissions

Stack emissions from brake-debonding and recla-
mation equipment using secondary combustion are
listed  in  Table 137.   Note that, in all cases, the
carbon monoxide has been eliminated, and the par-
ticulate matter reduced by approximately 90 per-
cent when compared with emissions from  uncon-
trolled units cited in Table 136.


Typical Reclamation Equipment

The multiple-chamber incinerator previously dis-
cussed in the first two parts of this  chapter  can be
adapted for these  processes.  Figure 376 shows
an incinerator of this kind that differs from a stan-
dard multiple-chamber incinerator by its oversize
ignition chamber and the absence of the grates and
ash pits.   The third chamber (the combustion cham-
ber) is less useful because there is little or no fly
ash tobe removed from the gas  stream.   The com-
bustion chamber does,  however, complete the sec-
ondary combustion process and protect the stack
lining from direct flame impingements.

Primary burners are of the atmospheric type and
canbe mounted through the sides  and at the bottom
of the primary chamber.  An alternative arrange-
ment consists of dual-pipe burners placed  across
the base of the primary  chamber, which results in
more even distribution of heat over  the  cross sec-
tion  of this chamber.  These burners must,  of
course, be positioned so thatthere will be no inter-
ference when the racks  containing the charge of
material are inserted or removed.  Mixing cham-
ber burners are located in the same  position as
shown for a standard multiple-chamber incinerator.
Air ports are also similar in construction and loca-
tionto those mounted on a standard multiple-cham-
ber incinerator.

Another satisfactory single-structure design con-
sists  of  only two refractory-lined chambers, as
illustrated in Figure 377.  It differs from the con-
ventional three-chamber unit already described
only in that the third chamber has been eliminated.

A relatively simple design using a separate primary
chamber  and afterburner is  shown in  Figure 378.
 234-767 O - 77 - 34

-------
500
INCINERATION
        Table 137.  STACK EMISSIONS FROM DEBONDERS AND RECLAMATION EQUIPMENT
                                  USING SECONDARY COMBUSTION
Item
Equipment description

Composition of charge

Charge weight, Ib
Combustible content, wt %
Duration of test, min
Stack gas flow rate, scfm
Stack gas temperature, °F
Secondary afterburner temperature, °F
Particulate matter, gr/scf at 12% CO2
Particulate matter, Ib/hr
Sulfur dioxide, Ib/hr
Carbon monoxide, Ib/hr
Organic acids as acetic acid, Ib/hr
Aldehydes as formaldehyde, Ib/hr
Nitrogen oxides as NO2, Ib/hr
Hydrocarbons as hexane, Ib/hr
Smoke emissions, opacity range
Ringelmann chart
Test No.
C-286
Dual -chamber
brake debonder
480 brake shoes

--
--
30
181
999

0.24
0. 12
0. 12
0
0.08
--
--
--

0
C-541-4
M-C incinerator

Auto field coils

386
6. 7
8
990
1, 340

0. 04
0. 37
0
0
0. 90
0. 08
0. 30
0.23

0
C-497
Oven with afterburner

(14 generator pole
pieces)
3,825

60
950
1, 250
2, 000
0. 016
0. 059
-_
0
__
0. 079



0
                                                                                  •HIKING CHAMBER
                                                       SECONDARY
                                                       COHBUStlON
                                                       CHAMBER
                                                     CIEANOUT OOOR

                                                         CURTAIN HALL PORT
           Figure 376. Multiple-chamber  incinerator adapted for use in reclamation processes (see Figure  339).
The primary chamber  consists of a tubular frame
with sheet metal siding.  Drilled-pipe gas burners
are  installed in the bottom of the chamber.  The
material to be  reclaimed is placed in a  55-gallon
drum with a  perforated bottom, and the drum is
placed  in the primary chamber.   The contents of
the drum are heated and ignited  by the pipe burn-
ers, and the hot gases and smoke flow to an after-
burner  mounted on  top  of  the  primary chamber.
Heat is supplied to the afterburner by a fan-air
burner  firing tangentially into the refractory-lined
           chamber.  This equipment is usually equipped with
           a  stack that is  16 to 20  feet above ground level.
           Since good heat control is difficult to maintain, this
           equipment is more suitable for brakeshoe debond-
           ing than for  electrical-winding and armature core
           reclamation.
           In  some  cases,  an oven vented to an afterburner
           is  used.   This  oven differs from the refractory-
           lined primary chamber  in that there is no direct

-------
             Debonding of Brake Shoes and Reclamation of Electrical Equipment Windings
                                                                                                  501
                                                      Standards  (or Construction

                                                      Materials and methods of construction are similar
                                                      to those used for multiple-chamber incinerators,
                                                      as  described in the second  part  of this chapter.
                                                      Exterior  shells  are constructed of 12-gage-min-
                                                      imum-thickness steel  plates properly placed and
                                                      supportedby external structure members.  Block
                                                      insulation with a minimum thickness of 2 inches
                                                      anda service temperature of 1,000°F is normally
                                                      used between the steel shell and  the refractory lin-
                                                      ing to conserve heat and protect the operator. High-
                                                      heat-duty firebrick \vith adequate expansion joints
                                                      is used for lining the primary chamber as well as
                                                      the  secondary chamber  or  afterburner.  Stacks
                                                      are constructed of 10-gage  steel plates and are
                                                      lined with 2 inches of insulating firebrick or cast-
                                                      able  refractory  having a minimum service tem-
                                                      perature of 2, 000°F.
    Figure 377.  Dual-chamber reclamation furnace (Auto
    Parts Exchange, City of Industry, Calif.).
 flame contact with the charge, and the hot combus-
 tion gases are recirculated within the chambers for
 more precise heat conservation and control.  The
 installation  of a  cam-operated temperature con-
 troller makes possible a  gradual eleVation  of
 primary-chamber temperature and an exact con-
 trol of temperature over extended periods of time.
 This type of  control is widely used for processing
 electrical windings  from motors and generators
 where warpage of the laminations is to be avoided.
 This  type of  reclamation equipment lends itself to
 either the batch or continuous  process.
A continuous-process  device is  shown in Figure
379; it consists of an endless-chain conveyor that
transports  material into  a tunnel-like chamber.
The products of combustion, smoke, and volatile
components  are collected near the center of the
tunnel and vented to an afterburner.  Asbestos cur-
tains are installed where the parts enter and leave
the  chamber; they  conserve heat by reducing the
induction of air.  Continuous-process equipment  of
this type usually has a higher heat requirement  than
corresponding batch equipment does because of the
induction of excessive air at the openings to the
primary chamber.
Another unique design, which canbe used for semi-
continuous operation,  consists of two refractory-
lined compartments connected back to back.  While
material is being processed in one of the compart-
ments,  the other compartment  is being unloaded
and  reloaded.  Again, the smoke and gaseous ef-
fluents are vented to a vertical afterburner and
stack.
Illustrative Problem

Problem:

Design batch equipment to debond 200 aver age-size
brake shoes or 175 average-size automobile gener-
ator field coils --eachbatch will require a 30-minute
period.


Solution:

1.  Ignition chamber dimensions:

    200  average-size brake shoes "weigh 350 Ib

    175  average-size field coils weigh 350 Ib

    Average  bulk density of brake  shoes is 27
    units/ft3

    Average  bulk density of field coils is 34
    units/ft3
    Brake shoes with 25% free  volume
                   ,   3
     (200
                             = 10 ft"
     Field coils with 50% free volume
(175 coils)
                        \~]
J  =  10 ft"
                  ~^-— I-1—
               ,34 coils/\0. 5,

    Primary-chamber dimensions

    2 ft wide  x 3 ft high x 1 ft  8 in.  deep


2.   Design capacity of primary gas burner:

    Design for minimum combustibles  content of
    3% by weight.

-------
502
                                            INCINERATION
    Figure  378.  Brake  debonding in a 55-gallon drum venting to an afterburner:  (1) drum holding brakeshoes
    (2) secondary combustion chamber,  (3) secondary burner (afterburner),  (4)  primary burner-pipe type
    (5) stack (Griggs Specialty  Products,  Huntmgton Park, Calif.).
   (a) Heat required to raise temperature of
      charge from 60 °  to 900  °F.  Neglect
      moisture in charge:

      Average specific heat of brakeshoes or
      automobile generators is 0. 21  Btu/lb-°F
         Q  =   (W)(Cp)(T2 -
   where

      Q  =  heat required, Btu/hr
 W =  weight of charge, Ib/hr

Cp  =  average specific heat of charge,  Btu/lb-
       °F

T   =  final temperature,  °F

       initial temperature, °F

                        •\ I 350 lb\
                        / \charge /
(0_97)/2charges\/  350 Ib
      \
           hr    / \ charge
(0.21 Btu/lb-°F)(900°F - 60°F)

-------
          Debonding of Brake Shoes and Reclamation of Electrical Equipment Windings
                                                                                               503
      Figure 379.   Continuous brakeshoe debonder  (Wagner Electric Corp.,  El  Segundo, Calif.).
    Q =   119, 800 Btu/hr

(b)  Heat required to raise products of combus-
    tion from 60°  to 900°F:

    Assume combustibles  have a composition
    equivalent to PS-400 fuel oil.  Design for
    200%  excess  air,  40%  saturated.   From
    Table  D6, Appendix; D, products of com-
    bustion weigh 41. 47 Ib from combustion of
    1  Ib combustible (PS-400 fuel).  Average
    specific heat of products of combustion is
    O.Z6 Btu/lb-°F.
   Weight of products of combustion, W:



   W = (0. 03) /j50jb\/2 charged/41. 47 Ib'
              \charge/\    hr   /\    Ib
      =  870 Ib/hr
Heat required
      Q  =  (W)(Cp)(T2 -
where

   Q  =  heat required,  Btu/hr

   W =  -weight of products of combustion,
         Ib/hr

  Cp  =  average specific heat of products of
         combustion, Btu/lb-°F


  T   =  final temperature,  °F

  T   =  initial temperature, °F

Q  =  (870 lb/hr)(0.26 Btu/lb-°F)(900°F -60°F)

   =  190,000 Btu/hr

-------
504
                INCINERATION
    (c) Net heat required for process:

       (a) +   (b)  =  Total net heat

119,800 Btu/hr + 190, 000 Btu/hr = 309,800 Btu/hr

    (d) Gross heat required for process:

       Assume radiation, convection, and storage
       heat losses are 30% of gross heat input. Net
       heat available for process is 70% of gross
       heat input.
          309,800 Btu/hr
               0.70
=  442,000 Btu/hr
(e) Heat supplied by combustibles in charge:

   From  Table D5,  Appendix D, the gross
   heat of combustion from 1 Ib combustible
   (PS-400 fuel oil) is  18, 000 Btu/lb

                   2c^rrSeS)(18,OOOBtu/lb)

   =  378, 000 Btu/hr
    (f)  Net heat required in primary chamber:

442, 000  Btu/hr -  378, 000 Btu/hr = 64, 000 Btu/hr


    (g) Primary burner capacity:

       From Table D7, Appendix D, the calorific
       value of natural gas is 765. 3 Btu/scf at
       900°F.
             64.000 Btu/hr  _
             765.3 Btu/ft3  -
 3.   Size of combustion air ports:

     Design all port areas 100% oversize.

     Assume 100% excess air through the primary
     air port and theoretical air through the secon-
     dary port.

     Designfora maximum combustible content of
     the charge of 5% by weight.  Assume the draft
     at all ports  is 0. 10 in. WC.  From Table  D8,
     Appendix  D,  0.10 in. WC is 1,255 fpm
                            (a) Primary air port:

                               Maximum  airflow.
 .05/f^
     Vcnarge
                           (0.05
                                                                   21Z cfm
                                        / 212 cfm  \
                                       ~\1,255 fpm )
 Port size =L2!LCfm \(2)  =  0.338ft2
                                                        or 48.6 in.
(b)  Secondary air port:

    Maximum airflow.
                                                                          hr
                                                               = 6, 200 cfh
                                                              or   103 cfm
                                                       Port size
                                        /  103 cfm \
                                        \1,255 fpm)
                        (2) =  0. 1640 ft
                                                                                    23. 5 in.
                        4.   Design  capacity  of  secondary burner (after-
                            burner):

                            Design for a maximum combustible content of
                            charge  of 5% by weight.

                           (a) Maximum products  of combustion with no
                               secondary air:

                               Weight of products of combustion of natural
                               gas with 20% excess air is 0. 999 Ib/scf.
                                                                      hr
                                                    (84 cfh natural gas)(0. 999 Ib/scf)
                                                              =  1, 460 Ib/hr

                                                              _   84 Ib/hr
                                                                1, 544 Ib/hr
                            (b) Heat required to raise products of combus-
                               tion from 900°  to 1,400°F:

                                  Q  =  WC  (T  - T) see item 2(b).
                                            p   2    1

                         Q =  (1,544 lb/hr)(0.26  Btu/lb- °F)(1, 400 °F - 900°F)

                         Q =  201,000 Btu/hr
     From Table D6, Appendix D,  363 scf of com-
     bustion air is required for combustion of 1 Ib
     (PS-400 fuel oil) at 100% excess air, and 177
     scf of combustion air is required for combustion
     of 1 Ib (PS-400 fuel oil) at theoretical air.
                            (c) Burner capacity:
                               From Table D7,  Appendix D, the calorific
                               value of natural gas at  1,400 °F is 616 Btu/scf.

-------
              Debonding of Brake Shoes  and Reclamation of Electrical Equipment Windings
                                                                                                  505
           201, OOP Btu/hr     ,,,   _
          	—*-	;	  =  326 cfh
             616  Btu/scf
5.   Size of mixing chamber (afterburner):

    From  Tables D6 and D7, Appendix D, there
    are 540 scf of products from combustion of
    1 Ib combustible (PS-400 fuel oil) at Z00% ex-
    cess air,  and 13. 53 scf of products  of com-
    bustion from 1 scf natural gas at 20% excess
    air.

    (a) Cross-sectional area of inlet duct:

       Design for gas flow of 20 fps at  900°F

       Gas flow at 60 °F

       Combustibles at 200% excess air
(0.05)
   /350 Ib
   ycharge
                                              cfh
       Natural gas at 20% excess air

       (84 cfh)(13.53 ft3/ft3)   =   1,133 cfh
                                20,023 cfh
                             or    333 cfm
                             or      5.55 cfs
       Cross-sectional area
(b)  Cross-sectional area of mixing chamber
    (afterburner):

    Design for gas flow of 25 fps at 1, 400°F
    Gas flow at 60 °F

    Combustibles from primary
      chamber

      Secondary gas burner

      (326 cfh)(13.53 ft3/ft3)
                               or
                               or
                                 20,055 cfh


                                 4,410 cfh
                                24,465 cfh
                                   408 cfm
                                     6.8 cfs
      Cross-sectional area
   (6. 8 cfs)
           '
                          fps
                                                      (c)  Length of mixing chamber (afterburner):

                                                          Design for  residence time of 0. 15 second
                                                          Length = (25 fps x  0. 15 second) = 3. 75 ft

                                                   6.   Stack diameter:

                                                       Design for a gas velocity of 20 fps at 1, 200CF
                                                       Cross-sectional area
                                                       Area  =  (6.8cfs)
                                                                         1,660°R
                                         = 1. 08 ft
                                                                          520°R

                                                       Stack diameter 13.9 in.

                                                       Select 14-inch diameter.

                                                   7.   Stack height:
                                                         (a)  Theoretical draft for a 10-ft section at
                                                             1,200°F:
                                                                 =  0.52 PH
                                                   where

                                                     D
                                                       t

                                                       P

                                                       H

                                                       T
        =  theoretical draft, in.  WC

        =  atmospheric pressure,  Ib/in.  absolute

        =  stack height,  ft

        =  temperature of stack gases,  °R

    T   =  temperature of air, °R


    D   =  (0.52)(14.


    D^   =  (76.5)
                                                                                        i,66oy

                                                                                (0. 00192 - 0. 00060)
                                                         D   =   0. 101 in. WC
    (b) Stack friction for a 10-ft section at 1,200°F:

             F  =  (0.008)(H)(V)2


where

    F =  friction, in.  WC

    H =  stack height,  ft
                            =  0. 975 ft
                                                      tGnswold, 1946.

-------
506
                                          INCINERATION
   V  =  velocity, fps

   D  =  stack diameter,  ft


   T  =  absolute stack temperature,  °R


                       2
        (0.008)(10)(20)
          (1.25)(1,660)
                                   .
                          =  °'015ln- WC
  (c) Net effective draft for a  10-ft section:

            (a)  -  (b)           = Net draft

   0. 101 in.  WC - 0.015 in. WC = 0. 086 in. WC


  (d) Ignition chamber:

      Assume static pressure  of 0. 05 in. WC


  (e) Friction loss in secondary-combustion
      zone:

      (1) Contraction loss into  secondary zone:

         Assume 0. 5  VP loss at 20 fps and 900°F

         Gas velocity 20 fps at 900 °F

                             "'
where

    V

    T

    h
           gas velocity,  fps

           absolute temperature ,°R

           static pressure, in.  WC
     T,
     h  =
     h  =  0. 035 in. WC
     Contraction loss (°" °3\f  WCj (0. 5 VP)
        =  0. 017 in. WC

        (2) Design for two 90-degree bends in sec-
           ondary zone:

           Assume 1-VP loss for each 90-degree
           bend and that the products of combus-.-
                                                              tion have a composition equivalent to
                                                              that of air.

                                                              Gas velocity 25 fps and 1,400°F
           (2^9) (T)
                                                              h  =
                                                               h  =
                                                              h  =  0. 04 in.  WC
                                                              Loss
                                                            (3) Friction loss through secondary zone:


                                                                  0.008 (H)(V)2
                                                            F  =   	—	   see item 7(b)
                                                            F  =
          (0. 008)(3. 75)(25)
            (1.25)(1,860)
 *Research-Cottrel \f Inc.
   F  =   0. 008 in. WC


(f) Total effective draft  required from stack:

   (d) + (e)(l) + (e)(2) +  (e)(3) = total

   0. 050  in. WC + 0. 017 in.  WC +

   0.080  in. WC + 0.008 in.  WC

   =   0. 155 in. WC


   (g) Stack height:

       Let H =  stack height,  ft

      /O. 086 in.  WC\ ,  v
      ( 10-ft stack j(H)  =  0-155 in. WC

       H  =  18.0 ft
                                                          DRUM RECLAMATION  FURNACES
                                                     INTRODUCTION

                                                     Drum  reclamation constitutes  an important seg-
                                                     ment of the  salvage industry.   In this operation,
                                                     steel drums used in transporting and storing chem-
                                                     icals and other industrial  materials are cleaned,
                                                     repaired, and repainted for  reuse.   Although steel
                                                     drums are made in many sizes, 30-gallon and 55-
                                                     gallon sizes are the two most common.

-------
                                     Drum Reclamation Furnaces
                                                                                                  507
Drum construction,  closed-top or open-top,  de-
termines the process  selected for  the  cleaning
phase of reclamation.  Closed-top drums are cleaned
with solvents, hot caustic, or other chemical solu-
tions; open-top drums can be cleaned not only with
chemicals but by burning the combustible materials
adhering to  the  drum  surfaces.  Since cleaning
open-top drums by incineration can usually be done
at a  cost lower than that of chemical cleaning,  it
has been widely adopted by industry. This incin-
eration process and its related equipment are dis-
cussed here.

 Description  of the Furnace Charge

Typical materials to be burned from open-top steel
drums include asphalt compounds, sealants, paints,
lacquers, resins, plastics, lard, foodstuffs, grease,
solvents, and numerous other industrial liquid and
solid materials.  Of course,  the variable amount
of residue remaining in the drums results not only
from the nature of the contained material but also
from the unpredictable degree of thoroughness with
which the drum is  emptied.   Although a few 55-
gallondrums received for processing may contain
as much as  20 pounds  of combustible material,
over  90 percent normally contain less than 3 or 4
pounds; most of the 30-gallon drums contain corre-
spondingly less.  In current plant operations in Los
Angeles County,  55-gallon drums constitute 75 to
80 percent  of  total open-top drums reclaimed by
incineration, with 30-gallon drums making up the
balance.

Description of the Process

Open-top steel drums  may be cleaned by burning
out the residual materials in the  open or in refrac-
tory-lined chambers.  The drums are generally
in an inverted position,  with the open top down so
that residual materials have a chance to melt and
flow free of the drum as well as burn.  In the fur-
nace, flame applied to the exterior  surface to burn
off grease, paint, and other coatings is also carried
into the interior  of the  drum by ignition of molten
material dripping from the interior surfaces.

After the combustibles are consumed, the drums
are allowed  to  cool.   They are then shot peened
to remove all ash and char.  Dents or surface ir-
regularities  are removed by special rolling ma-
chines; finally, the drums are tested hydraulically
and protective  coatings applied.

As -expected, burning residue  from drums in re-
fractory-lined furnaces is more efficient than burn-
ing in the open since heat is conserved within the
furnace, and combustion air can be controlled.

Refractory-lined furnaces can be classified as to
type  of process--batch or continuous.   A batch-
type single-chamber furnace, as shown in Figure
 380,  is  designed to  accommodate  one drum at a
 time; its capacity is usually limited to less than
 30  drums  per hour.   Continuous-type  furnaces,
 depicted in Figure 381, are constructed in the form
 of a tunnel and are usually designed to burn about
 150 drums per hour.

 Drums are supported  upside down upon a drag con-
 veyor, the drum covers sometimes resting across
 adjacent drum bottoms.   They move through the
 tunnel where burner flames impinge on the exterior
 surfaces.  Exterior coatings burn and peel off-while
 residual materials inside catch fire,  melt, and drip
 onto a flat surface atthe base of the conveyor.   Al-
 though melted materials  may burn upon the flat
 surface, they are scraped along and carried from
 the furnace by the returning flights of the conveyor.
 Water sprays are used to quench any burning mate-
 rials before they leave the furnace.

 Drums  are spaced at least 3 or 4 inches apart on
 the drag conveyor to allow flames from the primary
 burners  to cover the  drum surface  completely.


 THE AIR POLLUTION PROBLEM

 The practice of burning off  organic residues, paint,
 and other materials from drums  either in the open
 or in a single refractory-lined chamber  results
 in the emission of large quantities of smoke, odor,
 and combustion  contaminants.   These emissions
 can occur not only from the fan discharge or stack
 but also from the furnace ports and other openings.
AIR POLLUTION CONTROL EQUIPMENT

There is no feasible way of controlling emissions
from open burning.  However, emissions can be
controlled from properly designed single-chamber
furnaces by venting to an afterburner or a secon-
dary combustion chamber similar in arrangement
to the mixing chamber of a multiple-chamber in-
cinerator as described in the first two parts of this
chapter.  Information on the design of afterburners
is given in the first part of Chapter  5.  In design-
ing an effective afterburner or an equally  effective
secondary combustion chamber, however, the size
and appurtenances of the primary chamber must
be selected first.
Primary Ignition Chamber, Batch Type

A  batch-type  chamber,  shown in Figure 380,  is
designed to hold one 55-gallon drum with a  space
of 6 inches  or more between the drum and refrac-
tory walls.  Obviously, this  same chamber can
also be used to process the smaller 30-gallon  drum.
Since the drum is burned upside down to allow re-

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508
INCINERATION
Figure 380   Batch-type drum reclamation  furnace with
an afterburner  (Apex  Drum Co.,  Los Angeles,  Calif.).
sidual materials to melt and flow from the drum,
removing the products of combustion from the bot-
tom, of the chamber  rather than the top is  advan-
tageous in order to promote the carryover of flames
into the drum interior.

Several gas  burners are strategically  arranged
around the  chamber  so  as  to  cover the exterior
drum  surface completely with flame.  These gas
burners usually operate at 20 percent excess com-
bustion air.  Air is supplied for combustion of drum
residue through air ports in the  sides of the cham-
ber.

For design purposes, air ports should permit the
induction of 200 percent excess  air for combustion
of 4pounds of combustible materials within  a nom-
inal 4-minutc period.  The composition of the com-
bustible  is  considered  equivalent to US Grade 6
fuel oil.  The primary burners should be capable
of  raising the temperature of the induced air to
1, 000°F  and of the  steel drum to at least 900°F,
based upon the most severe operating condition--
that of maximum air induction and negligible com-
bustible  materials   on the drum.  Yet,  excessive
drum  temperatures  must be  avoided to prevent
drum warpage and scale formation.
           Primary Ignition Chamber, Continuous Type

           Although the design of a continuous-type ignition
           chamber for reclaiming 55- and 30-gallon drums
           involves  the same basic factors  of combustion as
           those for the batch-type chamber, certain factors
           such as combustion volume,  burner capacity,  and
           combustion  air  differ markedly  for this  dynamic
           process.

           The process requires  sustained temperatures for
           removal by  melting, and virtually complete com-
           bustion  of all residue  and surface coatings on the
           drum during its period of conveyance through the
           furnace.   As shown in Figure  331,  the furnace is
           constructed  in the form of a tunnel that can be con-
           veniently divided into three zones.  After entering
           the tunnel, the drums pass through the preheat zone
           where they are heated by radiation from  the igni-
           tion zone; they then pass through the ignition zone
           where  combustibles in direct contact  with burner
           flames ignite and burn; lastly, they pass through
           the cooling zone where a small amount of burning
           continues  until  combustion is complete  and the
           drums  are cooled by induced air.

           Of necessity, various dimensions  of the tunnel are
           established by the size of a standard 55-gallon drum,
           which averages 24 inches in diameter and 35 inches
           inheight.  With only minor adjustments,  this tun-
           nel  can also serve in  processing the  smaller 30-
           gallon drum, which averages 19 inches  in diameter
           and 29 inches in height.

           Although combustible  content  of the  combustible
           materials on each drum can vary drastically,  over
           90 percent of all drums as  received for processing
           contain from nearly zero to about 4 pounds  of com-
           bustible materials.   Fortunately,  it is possible to
           design a continuous furnace that will process drums
           containing this  range  of  combustible without re-
           quiring extensive and continual adjustments.

           Combustion  dynamics do, however, require a fur-
           nace of an optimum size to accommodate the vari-
           ations  in burning rates among the drums as they
           move along the tunnel so that all products  of com-
           bustion are retained for admission to the afterburn-
           er or secondary combustion chamber.  To process
           an average drum containing anywhere from zero to
           4 pounds of combustibles requires an average of 4
           minutes. The 55-gallon drums must be spaced on
           the  conveyor not less than 3 or  4 inches  apart to
           allow complete flame coverage oi the exterior sur-
           face  by flame passage among the drums.  In pro-
           cessing 150 drums  per hour  or 2. 5  drums per
           minute,  \vith a design space  of 5 inches between
           drums, the conveyor must move at the rate of 6 fpm;
           therefore, the combined length of  the ignition zone
           and the cooling zone in which all burning takes place
           is 24 feet. Most drums are allowed  to reach about
           900°Fin the furnace whereupon they begin to glow

-------
                             Drum Reclamation Furnaces
509
a.   Photograph  of  furnace with  afterburner (D and M  Drum Company, South ElMonte,  Calif.)
                     -STACK
                                                            SECONDARY
                                                            AIR PORT
                                                                 •SECONDARY
                                                                 BURNER
                                                                    PRIMARY
                                                                    BURNER
                 -BAFFLE
                        b.   Diagram of  furnace with afterburner.
        Figure 381.   Continuous-type  drum reclamation furnace  with afterburner.

-------
510
INCINERATION
a dull red,  but the temperature of the drum must
not exceed a bright orange color of 1,000°F;  other-
wise  excessive drum warpage and scaling occurs
with a subsequent loss in the  strength of the steel.
Of course,  drum temperatures  do not  represent
the temperature  of the exhaust gases leaving the
ignition zone.
Optimum, furnace performance requires that the
furnace be adjustable in conveyor speed and burn-
er setting. If drums containing negligible combus-
tibles are processed exclusively, the speed of the
conveyor and  production rate can be increased.
Conversely,  if  so-called difficult  drums, drums
containing more than 4 pounds of highly combus-
tible asphaltic and adhesive compounds, are burned
exclusively,  they must  be  spaced  6 feet or more
apart on the conveyor moving at a normal speed of
6 fpm in order to retain the same residence time
but prevent overloading the afterburner.
           US Grade 6 fuel oil.  Nevertheless,  in addition to
           combustion air through the tunnel openings, up to
           100 percent of theoretical air should be supplied
           through a secondary air port for operating flexi-
           bility.
           As shown in Figure 381. the ignition zone is located
           at the central part of the tunnel.  Primary burners
           are designed to attain drum temperatures of 900 °F
           and average effluent temperatures of about 1, 000 °F,
           based upon  the  drums' containing no appreciable
           combustible residue.  The volume of the ignition
           zone may be determined from a heat release factor
           of about 22, 000 Btu  per hour per cubic foot with
           primary burners at maximum design capacity and
           drums containing negligible combustible materials.
           This factor is in line with the heat release factors
           for oil-fired furnace fireboxes operating at tem-
           peratures of less than 1, 800°F.
Air for combustion of combustible materials on the
drums is supplied through minimum size drum in-
let  and  outlet openings  on  the  ends  of the tunnel,
in order to maximize indraft velocities.
A practical clearance of about 1 to 2 inches is pro-
vided between the 55-gallon drum and the walls and
arch of the refractory-lined opening.   The area
required for the protruding conveyor through which
air canbe  induced should also be kept as  small as
possible.  The internal dimensions of the opening
are 26 inches wide by 36-1/2 inches high.   A space
for the conveyor of about 14 square inches is pro-
vided at each end.  The openings should extend at
least 30 inches, which exceeds the minimum 27-
or 29-inch space allowance for 55-gallon drums
upon the conveyor.  At least one drum should al-
ways be inposition to blank off most of the area of
the opening and thereby create high indraft veloc-
ities.
Air curtains may also be installed at the ends of
the tunnel to help prevent the escape of smoke caused
by air currents or wind across the face of the tun-
nel.   They consist of drilled pipe located around
the inside edge of the tunnel opening through which
air is  injected across  the face of the opening to
flow inward to the center of the tunnel.
An average indraft velocity of 200 fpm through the
tunnel openings without drums on the conveyor sup-
plies  approximately 50 percent in excess of theo-
retical  air for burning a maximum of 4 pounds of
combustible per drum.  In this case,  the combus-
tibles are considered equivalent in composition to
           Since flames must effectively cover the exterior
           surface of the drum, the burners are mounted in
           refractory walls 6 inches from the sides of the 55-
           gallon  drum.  Thus, internal width of the zone is
           36 inches.  The arch rises about 78  inches, an ar-
           bitrary design  figure, above the base of the con-
           veyor to provide volume for collecting the products
           of combustion.
           As shown inFigure 381, onlythe ignition zone con-
           tains primary burners.   These  burners are ar-
           ranged in eight vertical rows of two or three burn-
           ers with four rows  on  each  side  of the chamber
           spaced about 2 to 2-1/2 feet apart.
           The rows are offset 1 to 1-1/4 feet from opposite
           sides  of the chamber to prevent the flames from
           the burner on one side of the chamber from direct-
           ly  opposing  flames from burners on the opposite
           side.
           Burners are mounted on at least two levels to cover
           the surface of the drum completely with flame.  If
           each row contains three burners, the burners are
           mounted 12 inches apart vertically, and the bottom
           burner is mounted 6 inches above the top of the con-
           veyor.   The first  row of burners on each side  is
           usually set for operation at maximum capacity, its
           flame  travel  extending about three-fourths of the
           width  of the zone.   The burners in the rows that
           follow are adjusted manually, usually at reduced
           capacity,  or  controlled automatically by a signal
           from a thermocouple at the inlet to the afterburner.

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                                     Drum Reclamation Furnaces
                                                                                                  511
 The cooling zone provides  for  completion of the
 combustion process within  the nominal 4-minute
 design residence time.  Usually only a small per-
 centage  of  the total combustion occurs within the
 zone.

 After the length of the ignition zone is computed,
 the length of the cooling zone is determined in feet
 by subtracting from the combined length of the igni-
 tion zone and cooling zone as described.  Internal
 cross section dimensions for the cooling zone match
 those of the ignition zone.

 The refractory-lined preheat zone  of 10 feet has
 been found  to conserve heat adequately within the
 tunnel and  protect  the operator  from excessive
 heat if he  is stationed at the inlet  opening.  In-
 ternal cross-section dimensions of the cooling zone
 also match  those of the ignition zone.
 Afterburner (Secondary Combustion Chamber)

 To meet air pollution regulations, afterburners or
 secondary combustion chambers should be designed
 to raise  the maximum volume of effluent from the
 ignition zone to at least 1, 400 °F for a minimum  of
 0.5  second.  These  conditions ensure essentially
 complete combustion of elemental carbon and most
 organic  combustion  contaminants in the  primary
 effluent.
For turbulent  mixing of the gaseous effluent with
flames  from natural gas-  or oil-fired secondary
burners, the cross section  of the secondary com-
bustion zone should  be designed for average gas
velocities  of 20  to  30  fps  and contain baffles or
abrupt changes in gas  flow.  Secondary air ports
shouldprovide  100 percent theoretical combustion
air for the combustible materials based upon a total
processing time of 4 minutes per drum containing
a maximum of  4 pounds of combustible materials.
Draft

Although  draft is usually produced by a natural-
draft stack or an induced-draft fan, the fan is pre-
ferred since it provides more nearly uniform draft
under all  phases  of operation.   Studies of various
induced-draft fan systems show lowest costs for a
system designed around a steel fan with heat  sling -
ers •where combustion gases to the fan are cooled
to 800 °F or less by either air dilution  or evapora-
tive  cooling.  Cooling by air dilution is, however,
preferred over  evaporative cooling for  several
reasons.  There is less corrosion of fan and duct-
work with air dilution and there is very little de-
posit of fly ash and other combustion particles up-
on the blades of the induced-draft fan as commonly
occurs when this fan follows a -water spray cham-
ber.  In fact,  with spray chambers, scraping de-
posits from the fanblades maybe necessary every
few days to keep the fan from becoming unbalanced.
A satisfactory air dilution system should consist
of a chamber with a cross section such that a mix-
ture of dilution air and combustion gases has an
average velocity  of 20  to  30 fps  for a residence
time of about 0. 2  or 0. 3 second.   Turbulent mix-
ing is further enhanced by adding baffles  or  right-
angle bends.   The induced-draft  fan can be pro-
tected from excessively high temperatures by
motor-driven dilution air dampers set to respond
to a signal from a thermocouple located at the fan
inlet.


 Standards for Construction

Mechanical design and structural features of drum
 reclamation furnaces are  discussed in general
terms  since most municipalities  have their own
 specific building requirements. While these codes
are  written primarily to provide  safe structures
and prevent fires,  designers should not hesitate to
go beyond the codes in specifying refractories that
will give a reasonably long service life and resist
abrasion,  erosion, spalling, and slagging.
 The exterior walls of the furnaces are usually con-
 structed of bonded brick or steel plate.   These ex-
 terior walls are separated from the inner refrac-
 tory lining by an airspace for cooling or by 2-1/2
 inches or more of insulating materials -with a ser-
 vice temperature of at least 2, 000 °F.


 Furnace parts encountering the most severe heat,
 such as the single-batch chamber, the ignition zone
 of the  continuous furnace, and the afterburner or
 secondary combustion chamber.shouldbe lined with
 at least 9 inches of superduty firebrick or plastic
 refractory.  Other parts of the continuous furnace
 under  less  severe heat conditions,  preheat zone,
 cooling zone,  and  tunnel  openings may be  lined
 with 9 inches of high-heat-duty firebrick or ASTM
 Class 27 castable refractory.

 Natural-draft stacks are usually constructed of 10-
 gage steel plate and lined with at least 2-1/2 inches
 of insulating castable with a minimum service  tem-
 perature of 2, 000°F.

 Induced-draft fans maybe constructed of low-carbon
 steel if gases are cooled by dilution air, but if water
 sprays are used to cool exhaust gases, then the fan
blades and the casing shouldbe constructed of stain-
 less steel or other corrosion- and heat-resistant
metals.

-------
 512
INCINERATION
Drag conveyors in continuous furnaces are driven
by gearhead motors •with bearings constructed of
heat-resistant alloy or with bearings cooled by
water.
Primary and secondary burners are usually nozzle
mix type to provide luminous flame. Combustion
air to the burners maybe supplied by a single blow-
er, but burner controls should allow for high turn-
down ratios.
Operation
              conveyor =  36- 1/2 in. ;  length  =  30 in.  Total
              opening area (2)(6. 8 ft2) =  13.6ft2.  Induced
              air 13. 6 ft2  x  200 fpm = 2, 720 scfm.

           b.  Size of ignition burners to raise effluent to
              1, 000°F.

              Design ignition burners for most  severe oper-
              ation, that of negligible  combustible per drum.
              Burners must raise temperature of drums to
              900°F.   From Table Dl, Appendix D, density
              of air at 60°F and 14. 7 psia is 0. 076 lb/ft3.
              Average specific heat of products of combus-
              tion is 0. 26  Btu/lb-°F.
Control of emissions from reclamation furnaces
with afterburners or secondary combustion cham-
bers  still depends to a great extent upon the skill
and vigilance of the operator.  If visible emissions
occur  as  a result  of overloading the afterburner,
the primary ignition burners should be cut back to
reduce the burning  rate.
              (1) Heat  required to raise induced air from
                 60° to 1, 000°F:
                 Q   = W   C   (T  - T  )
                   1     a   pa   2    a
              where
While black exhaust smoke may indicate a lack of
combustion air as well as an overloading of the after-
burner, white smoke usually indicates insufficient
temperature in the afterburner.  White smoke can
usually be reduced or eliminated by reducing the
combustion air or by increasing the fuel consump-
tion of the secondary burners.


Drum temperatures should be kept below 1, 000 °F
to minimize drum warpage and scaling.
                Q   =  heat required,  Btu/hr

                W   =  weight of air, Ib/hr
                 a
               C    =  average  specific heat over tern-
                pa
                       perature range
                T   =  final temperature,  °F

                T   =  ambient air temperature,  °F
                 a
Illustrative Problem

Problem:
                                            Q,  =
              720
                                   f t
                                                Btu/lb.
Design  a continuous-tunnel-type furnace for pro-
cessing  150  standard 55-gallon,  steel, open-top
drums per hour.
               (1, 000°F - 60°F)  =  3,030,000 Btu/hr

                (2) Heat required to raise temperature of
                   drums from  60° to 900°F:
Given:

Combustible material attached to each drum varies
from nearzeroto 4 pounds (typical of range of com-
bustibles on most drums as received for process-
ing)-

All combustible  material on the drums is con-
sidered to have a  composition equivalent to that of
US Grade 6 fuel oil.


Solution:

1.  Primary ignition chamber:
        air through openings at 200 fpm and
60°F.  Opening width  =  26 in., height above
a.  Induced
                   The  specific heat of steel for this tem-
                   perature range is 0. 12 Btu/lb-°F.
                      Q   =  W  C    (T  - T )
                       2       d  pd   2    1
                where
                  Q   =  heat required,  Btu/hr

                  W   =  weight of drums, Ib/hr
                   d
                 C    =  specific heat of steel, Btu/lb-°F
                  pd
                  T   =  final temperature

                  T   ="  initial temperature

-------
                                       Drum Reclamation Furnaces
                                                                                                   513
     /150 drums\/_55Jb
°Z=(   hr
                                     (900°F-60°F)
          =  833,000 Btu/hr

    (3) Total heat required in ignition zone:

       Assume heat losses through radiation,
       storage,  and so on are 10 percent of
       total gross heat input.
3, 030, OOP Btu/hr + 833, OOP Btu/hr
               0.90
                               = 4,300,000 Btu/hr
    (4) Natural-gas capacity of primary burners:

       From Table D7, Appendix D, the calorific
       value of 1 scf natural gas with 20 percent
       excess air is  736. 2 Btu at 1, 000°F.
Total capacity =
                                  '  '
                                   f
                      736. 2 Btu/scf

   (5) Individual burner capacity:
                                      = 5> 83°
       Install eight rows of three burners each
       (four rows  on each side of the zone)

       _           ..    5,830 scfh    ,„,
       Burner capacity = - - - = 243 scfh

   c.   Excess primary combustion air:

       Assume all air for burning materials on drums
       is  induced  through tunnel openings (including
       air supplied by air curtains).

      (1)  Maximum design  burning rate:
              drums\/4Jb_\ =
             hr    /ydrum/
                                 10 Ib/min
      (2)  Total combustion air available through tun-
          nel openings:
        Air  =
                    10
                                 =  272scf/lb
          From Table D6, Appendix D,  1 Ib US
          Grade 6 fuel oil requires 177 scf air
          40 percent  saturated at 60°F.
          % excess air available =
                                  272 scf - 177 scf
                                      177 scf
                                =  54%
                                                       Assume first ro\vs of burners on opposite sides
                                                       of zone are operating at 1 million Btu/hr
                                                       (910  scfh) to ignite  combustibles on drums.
                                                       Design gas burners to operate "with 20 percent
                                                       excess air.  Assume radiation,  storage,  and
                                                       other heat losses are 35 percent of gross heat
                                                       input at furnace temperatures near 2,000°F.
                                                       From Table D5, Appendix D, the gross heat
                                                       of combustion of 1  pound US Grade 6 fuel oil
                                                       is 18, 000 Btu.
   d.   Average gas temperature in ignition zone when
       burning a maximum of 4 pounds combustibles
       per drum:
                                                       (1) Gross heat:

                                                          Primary burner

                                                          Combustibles

                                                         /600 Ib


                                                          Total
                                                                        ], 000
 = 1 million Btu/hr




] = 10, 800,000 Btu/hr

 = 11, 800,000 Btu/hr
                                                       (2) Heat losses, radiation, storage, and
                                                          so on:

                                                          (0. 35)(11, 800, 000 Btu/hr) = 4, 130, 000 Btu/hr


                                                       (3) Evaporation of moisture contained in
                                                          drums :

                                                          Assume an average of 0. 5 Ib water per drum.
                                                          The heat of vaporization of 1 pound of water
                                                          at 60°F and 14. 7 psia is 1, 060 Btu.
                                                                   Ib
                                                                      ISO drums\/l, 060 Btu
                                                                 79,500 Btu/hr

                                                           (4) Evaporation of water formed by combus-
                                                              tion:

                                                              From Tables D7 and D6, Appendix D,
                                                              0. 099 Ib water is formed by burning 1 scf
                                                              natural gas with 20 percent excess air while
                                                              0. 91 Ib -water is  formed from burning 1 Ib
                                                              US Grade 6  fuel oil with 54 percent excess
                                                              air.
                                                          Natural gas:
                                                       (910 scfh)1
                                                                   . 099 Ib HO
                                                                  scf


                                                          Combustibles:
                                                                              •)('•
                                                                              «*»
              3, 500 Btu/hr
                                                      (coo^'^0)/^)
                                                      \ hr  /\     Ib     / \      Ib  /
                                                          Total
                                                                                           = 578,000 Btu/hr


                                                                                           = 673,500 Btu/hr

-------
514
                                    INCINERATION
    (5)  Total heat losses:

        (2)  +  (3)  +  (4)  =  4,883, 000 Btu/hr

    (6)  Net heat available to raise temperature of
        products of combustion:

        11, 800,000 Btu/hr  -  4, 883,000 Btu/hr
          =  6,917,000 Btu/hr

    (7)  Weight of products of combustion:
        From Tables D7 and D6,  Appendix D,
        there is  0. 999 lb products of com-
        bustion from 1  scf natural gas with 20
        percent excess air  and there is 21. 71
        lb products  of combustion from 1 pound
        US Grade  6  fuel oil with 54 percent ex-
        cess air.
(910 scfh)(0. 999 Ib/scf)
                                       909 Ib/hr
                                =  13, 000 Ib/hr
        Total
                                   13,909 Ib/hr
    (8) Average gas temperature:
       Average specific heat of products of com-
       bustion (equivalent  to  air) is taken to be
       0.26  Btu/lb-°F for  the given temperature
       range.
                     Q,
             AT =
                   W C
                     t pc
where

  AT  =  temperature rise, °F above 60°F

  Q   =  heat available,  Btu/hr

  W   =  weight of products of combustion,
   t     Ib/hr

C    =  average specific heat,  Btu/lb-°F
  pc
         6, 917,OOP Btu/hr
     (13, 909 lb/hr)(0.26
                       /0.
                                     = 1,910°F
       Final Temp =  60 + 1,910  =  1,970°F

e.  Volume of products of combustion at bO°F

    (1) With negligible  combustibles  on drums:

       Induced air:
       (2,720 scfm)(60 min/hr)    =  163,000 scfh
                                                   Primary burners:
                                                   (5,830 scfh)(13.53 scf/scf) =   79,000 scfh

                                                   Total                      =  242, 000 scfh

                                                                                  4, 040 scfrn

                                                                                   67.3 scfs


                                                 (2) With 4 pounds combustibles  per drum

                                                    Assume primary burners are operating at
                                                    910 scfh.  From Table D6,  Appendix D,
                                                    there is 281.9  ft^ products of combustion
                                                    from 1  pound US Grade  6 fuel oil with 54
                                                    percent excess  air.
                                                        Combustibles:

                                                        (600 lb/hr)(281. 9 ft3/lb)

                                                        Primary burners:

                                                        (910 scfh)(13.53 scf/scf)
                                                        Total
= 169,000 scfh


=   12,300 scfh
= 181,300 scfh
=    3,020 scfm
     50. 4 scfs
                                                    The most severe operating conditions exist,
                                                    therefore,  in the ignition  chamber when
                                                    drums with negligible combustible material
                                                    are processed.


                                             f.  Volume of ignition zone:

                                                 Assume aheat release factor of 22, 000 Btu/hr-
                                                 ft  ,  which  is similar to heat release factors
                                                 for oil-fired furnace fireboxes operating at
                                                 less than  1,800°F.  Assume  drums contain
                                                 negligible  combustible  materials.
                                                         Volume =
                                                            (5, 830 scfh)(l, 100 Btu/scf)
                                                                 Z2.000 Btu/hr-ft
                                                          =  292 ft


                                             g.  Length of ignition zone:

                                                 Assume  width = 36 in. ; height =  84 in. , in-
                                                 cluding the conveyor
                                             Length  =
                                                          volume
                                                          	   =   292 ft
                                                          (height)(width)   ~  (3 ft)(7 ft)
       = 14 ft
                                             h.  Cooling zone length:

                                                 Assume width  =  36 in. , height =  84 in. , in-
                                                 cluding the conveyor. Design ignition zone and
                                                 cooling zone for  a total residence time  of 4

-------
                                     Drum Reclamation Furnaces
                                                                                                  515
    min.  Assume a drum spacing of 29 in.  (5 in.
    between drums). Internal cross-sectional di-
    mensions match those of ignition zone.
Conveyor speed
   (150 drums
      hr

=  6 fpm
 :V   1 hr \(z. 41 ft\
 /\60 mln/\ drum /
     Length of ignition and cooling zones

     Total length =  (6 ft/min)(4 min)   = 2.4 ft

     Cooling zone length, 24 ft - 14 ft = 10 ft



i    Preheat zone length:

     Design this zone to minimize radiation losses
     and to protect operator.  Internal cross-sec-
     tional dimensions match those  of ignition zone.

     Design preheat zone length  =  10 ft

     Evaluation of existing design shows that a pre-
     heat zone length  of  1 0 ft will be adequate.


2.   Secondary-combustion chamber (afterburner):

a.   Design gas burners for  most severe operation
     (drums contain negligible combustibles).  Af-
     terburner will raise temperature of products
     of  combustion from ignition zone from 1, 000°
     to 1,400°F.

    (1)  Weight of products of combustion:

        From ignition zone:

        Induced air:
                                       where
                                         T   -  initial temperature,  °F
                                                         T   =   final temperature,  °F
                                                    Q3 =
                                       =  1, 900, 000 Btu/hr

                                       (3)  Total heat required in afterburner:

                                           Assume heat losses by radiation,  convec-
                                           tion, and so on are 10 percent of gross heat
                                           supply at 1, 400 °F
                                   Totalheat  =
                                                  1.900, 000 Btu/hr
       (2, 720 scfm)[0. 076 ^M ° """) =  12, 400 Ib/hr
                    \      ft:
3A
       Natural gas:
       (5, 830 scfh)
       Total
   (0.999 lb)
     scf
          =  5,870 Ib/hr

          = 18,270 Ib/hr
    (2) Heat required to raise temperature of prod-
       ucts of combustion to  1, 400°F:

       Average specific heat of products of com-
       bustion is 0.26  Btu/lb-°F over the given
       temperature range.
          Q
                                       (4)  Total capacity of secondary burners:

                                           From Table D7, Appendix D,  the calorific
                                           value of 1  scf natural gas is 615. 4 Btu at
                                           1, 400 °F  with 20 percent excess air.
                                                        2, 110, OOP Btu/hr
                                       (5) Individual secondary burner capacity:

                                          Install  four  burners—two  on each side of
                                          the horizontal section.
                                                             3,430 scfh    oc.    _
                                        Capacity of burner  = —:	  = 856 scfh
                                                             4 burners
                                     b.   Cross-sectional area:

                                          Design afterburner for  a cross-section veloc-
                                          ity of 30 fps maximum at  1,400°F.  From
                                          Table in Appendix, there are 13. 53 scf prod-
                                          ucts of combustion from 1 scf natural gas with
                                          20 percent excess air.
(1) Volume of  products of combustion when
   drums are burned with negligible combus-
   tibles:
                                  Induced air:

                                  (2, 720 scfm)(
                                                               in\
                                                            hr  /
                                                                    =  163, 000 scfh
                                             Primary burners:

                                                            , 53 scf
                                                             (5,830 scfh)
                                                                         /13.
                                                                        79,000 scfh
  234-767 0-77-35

-------
516
                                    INCINERATION
      Secondary burners:

                     . 53 scf'
       (3,430 scfh)>'
       Total
           /13.53 scf\
           \   scf   /
                                 46,500 scfh
                       =  288, 500 scfh
                       =    4, 810 scfm
                       =   80. 2 scfs
   (2)  Volume of products of combustion through
       afterburner  when  drums  are burned with
       4 Ib combustibles:

       Assume primary burners  are operating at
       910 scfh and that secondary burners operate
       at 20 per cent full capacity.  Assume after-
       burner outlet temperature is 2, 100°F.

       Products of  combustion:
Combustibles :

(600 lb/hr)(281. 9 cf/lb)
       Primary burners:

       (910 scfh)
         ( 13-53 Scf
                      r
                \   scf

       Secondary burners:
                                    169, 000 scfh
                                     12, 300 scfh
(0. 20)(3, 430 scfh) —-
                               Scf
                           scf
Total
                                   =  9, 300 scfh
                                 =   190, 600 scfh
                                      3, 180 scfm
                                     53. 0 scfs
   (3) Internal  cross -sectional  area and dimen-
       sions :
    Area
   _ /80. 2 scfs\/1,860°R\
     \ 30 fps  /\  520°R  /
                                   =  9. 6 ft


       Dimensions = 3 ft   2 in. wide x  3 ft high


c.  Length of afterburner:

    Design for a minimum residence time of 0. 5
    second.

    Length =  (30 fps)(0. 5  second)  = 15 ft


d.  Afterburner arrangement:

    Design for 2 right-angle bends and add dilution
    air at third right-angle bend.
e.   Secondary air port

    Design a secondary air port to supply up to 100
    percent theoretical air for drums containing
    4 Ib combustibles.  From Table D6, Appen-
    dix D,  177 scf air is  required to burn 1 pound
    of US Grade 6 fuel oil.
                                                       (1) Volume of combustion air at 60°F:

                                                                           scf
                                                    (600 lb/hr)
                                                                                =   106,000 scfh

                                                                                     1, 770 scfm
                                                 (2) Pressure drop  through opening at end of
                                                    tunnel:
                                                    Drum cross-sectional area:
                                               24 in. in diameter x  34 in. high = 5. 7 ft
                                                                                      2
                                                     Inlet velocity =
                                                     Inlet velocity =
                                                                              2, 720 scfm
                                                                     (2)(opening  area - drum area)
                                                                   2,720 scfm
                                                              	— = 1, 190 fpm
                                                              (2)(6. 8 ft  - 5. 7 ft )
       Total pressure behind opening:

       TP  = VP  +  SP

    where

      TP  =   total pressure, in.  WC

      SP  =   static pressure, in. WC

      VP  =   velocity pressure,  in. WC

      From Table D8, Appendix D, velocity
      pressure is 0. 090 in. WC  for a velocity
      of 1, 190 fpm at 60 °F.  Assume static
      pressure drop through sharp-edge orifice
      opening is 0. 5 VP and negligible friction
      loss in a 30-in. length of opening.


      TP  =   0. 090 in.  WC  +  0.5 (0. 090 in.  WC)
          =   0. 135 in.  WC



  (3)  Pressure drop through preheat zone:

     Cross-sectional area for  air flow with drums
      upon conveyor.  Assume half  of total com-
     bustion air  through preheat zone.
                                                         Area = 21 ft   - 5. 7 ft2  =  15. 3 ft2

-------
                                    Drum Reclamation Furnaces
                                                                                                 517
Velocity =
               (0. 5)(Z,720 scfm)
               - 2 -
                   15.3 ft
                                 !. 5 f prn
   Because of low velocity,  the pressure drop
   is negligible.

(4) Pressure drop through ignition zone:

   Assume friction is  negligible and pressure
   drop is 1  VP for 90-degree  bend (into af-
   terburner).

   Assume flow conditions for negligible com-
   bustibles on drums.   Cross  section inlet
   duct of afterburner 9. 6 ft .
 Induced air:
 Primary burners:
         -
         60 mm
                         scf
 Total
                              =  2,720 scfm



                              =  1, 320 scfm


                              =  4, 040 scfm
                                   67. 4 scfs
   Average velocity into afterburner at 1, 000 °F
VP  =   0.032 in. WCatl,000°F.

Pressure drop through one half ignition
zone =  0. 032 in. WC
(5)  Total  pressure at inlet to afterburner (be
    hind secondary air port):
    Tunnel opening
    Preheat zone
    Ignition zone
                          0. 045 in.  WC
                          0
                          0. 032 in.  WC
   Total static pressure  =  0. 077 in. WC

   TP  =  VP  +  SP

   TP  =  0.032  +  0.077  =  0. 109 in WC
             1. 5 VP  =  0. 109 in.  WC
                 VP  =  0. 073 in.  WC

       From Table D8 in Appendix D:

       Velocity  =  1, 070 fpm at 60 °F

    (7) Secondary air port area:

       ™-  •               1, 770 scfm     .  ,c   2
       Minimum area  =  —:	:	  =   1. ob it
                          1, 070 fpm

       Install oversize  secondary port with area
       =  2 ft2

3.   Dimensions of dilution air chamber:

    Design dilution air portto  reduce temperature
    of products  of combustion from afterburner
    to 700 °F for safe  fan operation.

a.   Dilution air required to lower products of com-
    bustion from  1, 400° to 700°F:

    Density of products of combustion 0. 076 Ib/scf
    at 14. 7 psia and 60°F

    W   C   (T   - T  )  =  W  C   (T  -  T )
      pc  pc    2    1        a   pa   1    a
                                                (4,810
                                                                                              . 700.F)
                                                    W   =  400 Ib/min
                                                      a

                                                    rvi <-•     •      400 Ib/min
                                                    Dilution air  =                 =   5, 260 scfm
                                                b.  Dilution air requiredto lower products of com-
                                                    bustion from  2,100° to  700°F;
                                                                                  I, 100°F  - 700°F)
(6) Velocity through secondary air port:

   Assume 0.5 VP static pressure drop through
   sharp-edge opening of secondary port.

   TP  =  VP  +  SP

   0. 109 in. WC   =  VP  +  0. 5 VP
                                                                       COO-F-60T,
                                                    W   =   529 Ib/hr
                                                      a
                                                    Dilution air  =           f     =   6, 950 scfm
                                                                    0. 076 Ib/scf

-------
 518
                                            INCINERATION
 c.  Cross section of dilution air chamber:

    Design for a velocity of 30 fps at 700 °F to en-
    sure turbulent flow for good mixing.

    Total flow to fan at 700 °F:

    Condition  1: (no combustibles on drums, max-
    imum primary burner capacity)
(4, 810 scfm + 5, 260 scfm)
                                      = 26, 400 cfm
     Condition 2:  (41b combustibles per drum,  pri-
     mary burners  910 scfrn)


(6, 950 scfm + 3, 180  scfm) (1',3,6°  R)  = 26, 500 cfm
                             bZ U K
Maximum cross-sectional area =
                                   26,500 cfm
                                 (30 fps)
                                        f
                                         '60 sec>
                                          min
                               =  14. 7 ft

    Cross -sectional dimensions  4 ft  8 in. wide
    x  3 ft   2 in. high


d.  Length  of dilution air chamber:

    Design  for a residence time of 0. 3 sec
    Length  = (30 fps)(0. 3  sec) =  9 ft


4.   Static pressure drop through system:

    Design  system with induced-draft fan mounted
    at ground level and a vertical stack on the fan
    outlet 50 in. in diameter x 20 ft high.   The 50-
    in. diameter will keep stack velocity near 30
    fps through afterburner.

a.  Static pressure  at afterburner inlet  = 0. 077
    in. WC, see item (5), page 517.

b.  Static pressure drop through afterburner:

    (1) Velocity pressure  at 30 fps and 1, 000°F:

       Assume  combustion products are equiva-
       lent  in composition to air.
       v  =  2.
                                                         •where

                                                            V =  gas velocity,  fps

                                                            t  =  absolute temperature,  °R

                                                            h  =  velocity pressure (head),  in. WC

                                                                      ,2
                                                            h  =
                             =  0. 073 in.  WC


(2)  Pressure drop from contraction at inlet to
    afterburner:

    Assume 0. 5 VP drop for abrupt contraction

        /      •      \
    (0. 5H0.07 ~777—)  =  0.035 in. WC
                                                        (3) Pressure drop for three right-angle bends:

                                                            Assume  1 VP for each right-angle bend.

                                                                      07 in. WC'
                                                            (3  VP)
          /O. 07 in. WC\ _
          \     VP     /     '
21 in.  WC
                                                        (4) Friction loss through 15 ft of ductwork hav-
                                                            ing dimensions     3  ft   2 in.  wide x 3 ft
                                                            high.
                                                            f  =
         0.002 h v
             mt
                                                                           2t
                                                         where

                                                            f  =  friction, in.  WC

                                                            h  -  duct length, ft

                                                            v  =  gas velocity, fps

                                                            t  =  absolute temperature,  °R

                                                            m =  hydraulic radius


                                                                  cross-sectional area of duct, ft
                                                                       perimeter of duct, ft

                                                                             2
                                                         (0. 002)(15 ft)(30 fps)
                                                                                 =  0. 024 in. WC
                                                           (0.778 ft)(l,460°R)

                                                         (5) Total drop through afterburner:

                                                            (2)  +  (3)  +  (4)  =  0.269 in. WC
 *Research-Cottrell, Inc.
                                                       tGnswold, 1946.

-------
                                      Drum Reclamation Furnaces
                                                                                         519
 c.  Static pressure drop through dilution air cham-
     ber having dimensions      4 ft 8 in.  wide x
     3 ft 2 in,  high.

    (1) Friction loss through ductwork at  700 "F:
                       2
        f  =
  0.002 h v"
     rnt
              (0.002)(9)(30r   =
              (0. 945)(1, 160)
 d.  Static pressure drop through 50-in. -diameter
     x 20-ft-high stack on discharge side  of fan:
     Stack velocity at 700 °F  =
                     26, 500  cfm
                      13. 64  ft2
                             =  1, 940 fpm
                             =  32.4fps
where
           f  =
D
-
4
     0.002 h v
         mt
                 4. 16
                   —
                           n  nA ,
                        =   1. 04 ft
           0.002  (20 ft)(32.4 fps)
        =
                                             .
                                    = 0.035ln.WC
             <1.04ft)(l,l60°F)

e.   Total static pressure drop through system:

     Tunnel                 =  0. 077 in.  WC
     Afterburner            =  0. 269 in.  WC
     Dilution air chamber   =  0.015 in.  WC
     Fan outlet duct         =  0. 035 in.  WC
     Total static pressure   =  0. 396 in.  WC

5.   Dilution air port size:

a.   Total pressure behind dilution air port:

     Velocity pressure 30 fps at 700°F,  VP = 0. 10
     in. WC

TP  =   VP +  SP

TP  =   0.10 +   (0.077  +   0. 269)  = 0.446 in. WC


b.   Inlet velocity through dilution air  port:

     Assume 0. 5 VP static pressure drop for sharp-
     edge orifice air port.

     TP  =  VP   +  SP

     0. 446 in.  WC = VP +  0. 5 VP; VP =  0. 298 in.
     WC at 60 °F
                                                Inlet velocity  =  2, 165 fpm
                                            c.   Size  of dilution air port:
                                                           Minimum size   =
                        6, 950 scfm
                        — , ,   .
                        2, 165 fpm
                                                                                                   ,
                                                                                                   it
                                                Select a port with area.  =   4 ft


                                           6.   System static pressure curve development at
                                                700°F:
                                                                  /cfm. - 2
where
  SP   =  static pressure, final conditions,  in. WC

  SP   =  static pressure, initial conditions, in. WC

 cfm   =  gas flow, final conditions,  cfm

 cfm   =  gas flow, initial conditions, cfm
                                                          Assume cfm   =  30, 000
                                                                                   =  °-507in- wc
                                               Assume cfm   =  20,000
                                                                 500 /
                                                                        =  0.226 in.  WC
                                           7.  Fan specifications:

                                               Select a fan that will deliver about 26, 500 cfm
                                               at 700°F and 0. 4 in. WC static pressure.

                                           a.  Fan performance at 60°F operation:
329 rpm
                                               0.75 in. WC
                                               26, 775 cfm
                                               14. 9 bhp
                      60°F
                                                                             1.0 in. WC
                                                                            .25, 245 cfm
                                                                             12.66 bhp
                                  1. 25 in.  WC
                                  22, 185 cfm
                                  10.79 bhp
                                           b.  Calculate points for 700°F fan performance
                                               curve:

                                               With rpm and cfm held constant,  static pres-
                                               sure and bhp vary directly with gas density or
                                               inversely with absolute temperature.

-------
 520
                                            INCINERATION
    Correction ratio  =
    329 rpm 700°F
    0. 336 in.  WC
    26,  775 cfm
    6.7 bhp
    520
   1, 160
                                =   0.448
           0. 448 in.  WC
           25, 245 cfm
           5.7 bhp
           0. 57 in.  WC
           22, 185 cfm
           4.9 bhp
c.  Operating point at 700°F:

    The intersection of the 700°F system curve
    with the 700°F fan curve, as shown in Figure
    347,  yields data indicating that  this system
    will handle a volume of 26, 000 cfm at 0. 38 in.
    WCat700°F.  The fan will operate at 329 rpm
    with 6. 3 bhp.
d.  Fan Selection:

    Select a 20-hp motor to drive fan since about
    14  bhp will be required when starting from a
    cold lightoff.
                  Select a fan with a capacity and static pressure
                  10 to 20 percent in excess of the operating
                  point shown in Figure  382 as  a safety factor
                  for overload capability.
                        WIRE  RECLAMATION

              Scrap insulated electrical -wire from construction
              sites and factories and worn-out insulated wire
              from utility companies and  other industrial opera-
              tions constitute the bulk  of the insulated wire
              processed for the  recovery of copper scrap.  The
              methods employed in removing insulation from the
              the copper core include combustion, mechanical,
              and manual.  The method selected depends not
              only upon  the size of the wire, but also upon the
              composition of the insulation.  When the combus-
              tion method is chosen, one  should consider that
              the combustible  content of the insulation is at
              least 10 percent by weight and usually exceeds
              20 percent.  This one distinguishing feature is
              reflected in the specialized designs of combustion
              equipment used exclusively for reclaiming insula-
              ted electrical wire.

              DESCRIPTION OF THE PROCESS

              Inorganic insulating materials such as fiber glass
              and  ceramics cannot be burned  and must be  re-
   0 6
     10,000
15,000
20,000               25,000
        VOLUME,  cfm
30,000
35,000
                                  Figure 382. Performance curve of 700°F fan.

-------
                                          Wire Reclamation
                                                                                                521
moved mechanically. Much insulation is composed
of organic compounds that will burn; however, not
all combustible insulation is removed by this meth-
od.  Because of excessive oxidation of copper,  wire
smaller  than  14 gage is not burned; it is actually
thrown away because of the lack of a satisfactory
economical method of removing insulation.  On the
other hand,  communication cable, 1 inch  in di-
ameter or greater,  is usually cut into pieces about
1 foot long and the insulation is hand stripped.   This
method has proved more satisfactory than burning
since the copper scrap is clean and free of the sur-
face oxides and foreign  matter associated with the
burning process.

Wire  of the intermediate sizes was formerly burned
in the open or  in single-chamber furnaces in Los
Angeles County.  When burned in the open, the wire
was spread in thin piles less than 1 foot high and
sprinkled with some type of petroleum distillate to
initiate combustion.   The  combustible content of
the wire was usually sufficient to maintain active
burning until the insulation was consumed.

In a single-chamber furnace, the wire was ignited
with a hand torch or a gas burner mounted through
the side of the chamber. After ignition,  the  burn-
ing process was also self-sustaining in this equip-
ment. After burning was complete,  the wire was
allowed to cool and the char adhering to the bare
copper wire was removed by rapping or by high ve-
locity jets  of water.


DESCRIPTION OF  THE CHARGE

The combustible portion of wire insulation com-
prises a great  variety  of materials,  including
rubber, paper,  cotton, asphalt-impregnated
fabrics,  silk, and  plastics  such as polyethylene,
polypropylene,  and polyvinyl chloride (PVC).
Additionally, the -wire  itself may have a baked-on
coating of  plastics, paint,  or varnish.

As  received for burning, the total combustible
content of the insulated wire may vary -widely
from  several percent to over 50 percent by weight.
Most  commercial wire contains from 20 to 35
percent insulation.


THE AIR POLLUTION  PROBLEM

Burning in the  open is  accompanied by copious
quantities of dense smoke,  disagreeable odors,
inorganic materials, and oxygenated hydrocar-
bons.  Burning  in single-chamber furnaces pro-
duces somewhat less air contaminants than open
burning does, since the combustion air  can be
regulated.  Furnaces employing secondary com-
bustion chambers or afterburners  significantly
reduce the amount  of particulates, aldehydes,
hydrocarbons,  and smoke discharged to the
atmosphere during their operation. The effective-
ness of secondary combustion was determined by
testing two multiple-chamber, retort-type wire
reclamation furnaces with their  secondary burn-
ers in operation and then with the secondary
burners shut off. Results of these source tests
are presented in Table 138.  In these two tests,
particulate matter  concentrations in the stack
effluent averaged 356 and 190  pounds per  ton of
insulation burned,  respectively,  with the  second-
ary burners shut off. With the burners operating,
the emissions measured -were 35 and 21 pounds
per ton  of insulation burned,  respectively. Opa-
cities of emissions varied as indicated in Table
138.

During recent years, reclamation of wire coated
with PVC or other  plastics  containing inorganic
fillers such as clay have been on the increase.
During combustion of this newer insulation, the
inorganic materials are volatilized in the form  of
fine particles,  -which are entrained by the combus-
tion products leaving the primary chamber  and
pass  through the secondary  combustion zone
without burning.  Addition of these inorganic
particles to the stack effluent  increases the
probability of having emissions of excessive
opacity and concentration discharged from the
furnace.

AIR POLLUTION CONTROL EQUIPMENT

Secondary combustion chambers or afterburners
by themselves  are  not adequate for controlling
combustion contaminants emitted from wire in-
sulation burn-off furnaces.   Results of source
tests  conducted on  a number of units are given in
Table 139.

One attempt has been  made  to control emissions
by venting  the  gases from a secondary combus-
tion chamber to a high-energy, venturi-type
scrubber, but the results were not always success-
ful.  Table 140 shows  the results of three tests
performed on the high-energy, venturi-type
scrubber.  Corrosion  was a major problem in the
operation of the carbon steel unit, but the problem
-was solved by constructing the internal elements
of the scrubber with stainless steel and by adding
ammonia  to the scrubber -water  to neutralize its
acidity.

Thus  far, the only  control system found to
operate satisfactorily  in  Los Angeles County
employs a baghouse as a final collection  device
following the secondary combustion chamber.
Results of a test performed  on this equipment
are also given  in Table 140.

Since the gases leaving the  secondary combus-
tion zone are at a relatively high temperature,
the gases must be  cooled before entering the

-------
5Z2
INCINERATION
         Table 138.  EFFECTIVENESS OF SECONDARY BURNERS FOR WIRE RECLAMATION
                            MULTIPLE-CHAMBER RETORT FURNACES
Test No.
Operation of secondary burners
Incinerator number
Charge composition


Test duration, mm
Charge weight, Ib
Combustibles in charge, wt %
Ash in charge, % by wt
Combustion rate, Ib/hr
Smoke opacities, %
Particulates, gr/scf at 12% CO2
Ib pa rticulates /ton combustible
Mixing chamber, °F
Mixing chamber velocity, fpm
Aldehydes, ppm
Hydrocarbons, ppm
Nitrogen oxides, ppm
Sulfur compounds as SO2, % by vol
C-624-1
Burners off
1
5/8 in. OD typical
rubber-covered wire


24
220
35
6
195
Constant 100% black
29.0
356
780
11
105
640
11
0.012
C-624-2
Burners on
1
5/8 in. OD typical
rubber -cove red
wire

40
233
16
6
56
0 to 25% white
"0. 26
35
l,880a
45. 0
5
8
25
0. 0039
C-543-1
Burners off
2
3/8 to 5/8 in. OD
cotton-rubber
plastic -cove reel
wire
20
100
19
4
57
20 to 90% gray
3. 5
190
300 est
9. 1
9 to 36
9 to 31
2. 9 to 8. 5
0. 0014
C-543-3
Burners on
2
3/8 to 5/8 in. OD
cot ton -rubber
plastic-covered
wire
17
147
34. 7
4
180
0 to 10% white
0. 32
21
1, 880a
31. 2
4
8
10. 4
0. 0027
         aTemperature measured by chromel alumel thermocouple in flame contact.
baghouse so as not to damage the filter fabric.
Gas cooling can be effected by radiant cooling
columns, by evaporative water coolers, or by
dilution with ambient air.  These types of cooling
were discussed in Chapter 3.  Filter  fabrics for
this service should be manufactured from Dacron
or glass fibers because they can withstand tem-
peratures up to Z75" and 500°F, respectively.
Also, the temperature within the  baghouse should
not be  allowed to fall below the dew point,  since
this will cause condensation,  which can cause
agglomeration of particles and blinding of filter
surfaces, deterioration of the fabric, and cor-
rosion of steel baghouse enclosures.

Final selection of equipment to  burn insulation
and control emissions is  based upon consider-
ations  such as space limitations, charge composi-
tion,  process conditions, maintenance, capital
investment, and operating expense.  Design  of an
effective afterburner or secondary combustion
chamber to be used in series with a final col-
lector  must be based upon the initial design for
the primary ignition chamber.  Recommended
values for  designing a wire burning furnace,
including primary and secondary chambers, are
presented in Table 141.  Design criteria for  the
baghouse or venturi scrubber final collector are
discussed in Chapter 4.

Primary Ignition Chamber

The size of the primary chamber is based upon the
density,  volume,  and burning  rate  of  a typical
           charge.  There is nothing critical about the  shape
           of  this chamber.  Any reasonable box shape will-
           suffice for a given batch charge provided addition-
           al  space is provided to facilitate loading and un-
           loading.

           Control of primary combustion air is critical since
           not only musthigh temperatures be prevented from
           excessively oxidizing copper,  but also the burning
           rate  must be restricted to prevent overloading of
           the secondary-combustion chamber.  Precise con-
           trol of combustion air is importantbecause itmakes
           possible  the  use of an  afterburner  or secondary
           combustion chamber of reasonable size.

           To minimize the size of the  afterburner or secon-
           dary combustion chamber,  the primary chamber
           should be equipped with a tightly fitting air  port
           and a side  swing charge door.  Although the pri-
           mary air ports are  designed  to supply 100 per-
           cent excess air for operating flexibility,  air
           leakage  around the edges of the charge door and
           air ports in most cases supplies the required
           combustion air so that  primary  air  ports are
           usually kept in a closed position.  For design pur-
           poses, indraft  velocities through the primary
           air ports should average 900  fpm,  equivalent to
           a velocity pressure  of 0. 05 inch of water column.

           Because the combustion process is self-sustaining,
           only a small-capacity  primary-chamber burner,
           that is, one capable of 50,000 Btu per hour,  is re-
           quired for igniting the refuse.  After ignition,  emis-
           sions from the primary chamber usually consist

-------
                                      Wire Reclamation
523
Table 139.  EMISSION DATA FROM WIRE RECLAMATION MULTIPLE-CHAMBER FURNACES
                       BURNING VARIOUS  TYPES OF INSULATION
Tent
number
C-543




C-624
C-655
C-696


C-953

C-1004



C-10Z3

C-1024


C-1025


C-1040


C-1042






C-1043

C-1055


C-1056



C-1058



C-10f>7


C-1069*



C-1069b



C-1075.


C-IOTSb



Number
of
batches
1




1
J
2


2

2



1

2


2


2


2






3

6


2



3



2


2



2



2


3



Batch
composition
10% plastic, 10%
rubber, and 80%
asphalt- impregna-
ted fabric insula-
tion
Rubber and plastic
insulation
50% oiled paper
and 50% cotton
insulation
,

35% plastic and 65
% rubber and
asphalt- impregnat-
ed fabric insulation
75% plastic insula-
tion
15% plastic and 85
% asphalt-impreg-
nated fabric and
100% rubber and
asphalt -impregnat-
ed fabric insulation
Asphalt-impreg-
nated fabric insula-
tion
Batch No. l--oil-
soaked paper insu-
lation. Batch No.
2- -80% asphalt-im
pregnated fabric
and 20% rubber
insulation
Plastic - insulated
telephone wire
20% plastic and
80% a«phalt-im-
inculation
Asphalt -impr eg -
nated fiber, cot-
ton, and cclluose
insulation
45% plaatic and 55
fc asphalt-impreg-
lated fabric and
rubber insulation
Asphalt -impreg-
nated fabric insu-
lation
40% plastic. 40%
asphalt- impregnat-
ed fabric, and 20%
rubber insulation
55% plastic, 30%
ftsphalt - impregnat -
ed fabric, and 15%
rubber insulation
20% plastic and HO
f* cloth and rubber
nsulation
20*". plastic and NO
'• rubber and
Isphalt-irnpn-Knnt -
rti fabru insulation
Initial
charge
Ib
147




233
750
960


554

1504



300

1230


979


3020


1385






249

421


1420



1160



1429


830



790



170


280



Charge
weight after
Ib
96




177

703


409

1178



221

1000


810


2280


1205






165

362


1160



HBO



1169


6)0



520



150


245



Weight
7.
34.7




24. 0

26. 8


26.2

21.6



26. 3

18.7


17. 3


24.5


13.0






33.8

14.0


18. 3



24. 1



18.2


24. 1



21.5



11.8


12. S



Test
mm
17




40
20
82


46

60



45

62


54


67


57






59

71


77



58



5)


40



45



32


32



Stack
opacities
0 to 1R
black



0
0 to 40%
brown
0 to 40%
gray

0 to 60%
brown
0 to 70%
blue-white
and brown

0 to 55%
brown
0


0


0 to 40%
white

0 to 15%
white





0

0 to 35%
gray

0 to 100%
gray


0 to 25%
brown


0


0 to 1R
black


0 lo 2R
black


0


0 lo 15'X,
Kf»y


Stack
gas
flow
scfm
1880




990
3940
1990


3300

3620



780

3060


2080


4500


3160






2670

810


7500



4300



2800


3900



3500



1020


860



Stack gas
•F
1100




1390
1 174
1560


1210

1360



1720

1180


930


1330


1300






1340

2150


1110



920



1510


890



960



1200


1520



Combustion
contaminants ,
gr/acf
at 12% CO2
0. 32




0.26
3 19
0. 16


1.4

1.01



0.62

0.24


0.21


0. 50


0. 12






0.81

0.21


0.48



0. 30



0. 31


0.65



0. b4



0.13


0.27



NOX,
ppm
10.4


1

28






_



33

21


29


32


35






24

76


41



29



-


17



23



9


42



Chlorides
-




0. 30
gr/scf
0. 023
gr/scf



_



3600 ppm




310 ppm


318 ppm


208 ppm






J230 ppm

.


470 ppm



780 ppm



.


_







,






Organic
acids,
ppm
121




53


-



_











_


9






_

-






.



.


_







_






Aldehydes,
ppm
4




5


-



_



.

,





.


_






.

.


_



.



-


_



_






.




-------
524
                                                        INCINERATION
        Table 140.   SOURCE  TEST DATA FOR WIRE RECLAMATION FURNACES CONTROLLED
   	BY  (1) A VENTURI SCRUBBER AND (2) A BAGHOUSE
   Water scrubber
     Furnace data
        Type of furnace
        Auxiliary heating
        Material processed
     Scrubber data
        Type of scrubber
        Water separator
        Pressure drop
     Test data
Multiple-chamber retort
1.820.000 Btu/hr
Scrap electrical wire

High-energy, venturi
Rotoclone
44 in. WC
Test number
Charge composition

•Initial charge weight, Ib
Charge weight after processing, Ib
Weight loss, %
Test duration, min
Stack opacity2
Gas flow rate, scfm
Gas temperature, °F
Combustion contaminants, gr/scf at 12% CO2
Combustion contaminants, gr/scf at 12% CO2 (less NH3)D
Material flow rate, Ib/hr
Baghouse
Furnace data
Type of furnace
Auxiliary heating
Material processed
C-120U
60% plastic, 35% rub-
ber and fabric and
5% paper insulation
640
500
21.9
38
15% avg. gray
Inlet
2370
1700
0.60
8.2
Outlet
6540
176
0. 30
0.26
0. 18
4. 7
C-1201b
45% plastic, 50% rub-
ber and fabric and
5% paper insulation
530
425
25.0
30
20% avg. gray
Inlet
2400
1700
0.74
8.8
Outlet
6540
176
0. 33
0.28
0.17
4. 3
C-1201c
80% plastic and
20% rubber and
fabric insulation
730
S80
20.6
23
25% avg, blue
Inlet
2290
1910
0.88
10.9
Outlet
6580
172
0.69
0.61
0.45
8.9


Multiple -chamber retort
1,980,000 Btu/hr


      Baghouse data
        Type of bags
        Filter material
        Filter area, ft2
        Cleaning method
        Gas cooling method
      Test data
        Test number
        Number of charges
        Charge composition
        Initial charge weight, Ib
        Charge weight after processing, Ib
        Weight lost, %
Tubular
Dacron
4080
Mechanical shaker
Radiation-convection cooling columns

C-1093
3
100% plastic-insulated wire
278
207
 25.5
Test duration, min
Stack opacity, %

Gas flow rate, scfm
Gas temperature, "F
Combustion contaminants, gr/scf at 12% CO2
Material flow rate, Ib/hr
Efficiency, %
54
0
Furnace outlet
925
1130
3.29
12.6



Baghouse
8600
165
0.18
0.67
95
     Readings made at point where steam plume dissipates.
    b
     Ammonia  added to system to neutralize the acidity of the water.

-------
                                          Wire Reclamation
                                              525
                              Table 141.  EQUIPMENT DESIGN FACTORS
                               Item
                Gas velocities
                 Primary-chamber outlet duct or
                 port at 1, 300°F

                 Afterburner or secondary mixing
                 chamber at 1, 600 °F

                 Extended secondary mixing
                 chamber curtain  wall port tunnel
                 at 1,600°F

                 Stack

                 Residence time

                 Maximum flow at 1, 600 °F
                Combustion air
                 Air requirements

                 Primary air
                 Secondary air

                 Combustion air distribution
                 Primary ports

                 Secondary ports

                 Airport inlet velocity
                 Primary airport

                 Secondary airport
                Auxiliary burners

                 Primary burner or torch capacity

                 Secondary burner capacity
                Draft requirements

                 Ignition chamber
                 Outlet from secondary chamber
                 (afterburner)
      Recommended
     value and units
         30 fps

         30 fps


         30 fps
         30 fps


         0.50 sec
        100% excess
      100% theoretical


           66%
           35%


 900 fpm or 0. 051 in.  WC

 900 fpm or 0. 051 in.  WC


          50 cfh
15,600 Btu/lb combustible


     0. 05 to 0. 10 in. WC

       0. 20 in. WC
Allowable
deviation
  +  20%

  +  20%


  +  20%
  +_  20%


  +  20%
of smoke and gases without flame and vary in tem-
perature from 900° to 1, 300°F upon entering the
secondary combustion chamber.

Ducts or ports connecting the secondary chamber
or afterburner -with the primary chamber are de-
signed for a  velocity of 30 fps or less,  at maxi-
mum combustion rates, to prevent excessive re-
striction  to the flow of gases.  Undue restriction
may result in  emission of smoke and flames from
the primary air ports  or  around the charging door.

Secondary  Combustion

As the gaseous emissions enter the secondary
combustion chamber  or afterburner, combustion
air  (up to 100  percent of theoretical based on
  initial combustion air requirements) is induced
  through the secondary air ports.  Inlet velocities
  for these air ports are designed for about 900
  fpm.  The  effluent then passes through the
  luminous flames of the secondary burner, which
  is  designed to attain an average exit gas temper-
  ature of 1600°F.  This temperature  is maintained
  for a minimum of  0. 5 second -with average gas
  velocities of 25 to 40 fps.  Baffles and abrupt
  changes in direction provide addition turbulence
  for mixing burner flames with the air and com-
  bustion gases.

  Emissions

  Table 138  shows significant reductions of
  particulate matter, aldehydes, hydrocarbons,

-------
526
INCINERATION
and smoke through secondary combustion.
Utilization of a properly designed final collector
to follow the secondary  combustion chamber re-
moves the noncombustible micron and submicron
inorganic particles of clay and metallic oxides
that are vaporized as the insulation burns (Table
140).
           multiple-chamber retort incinerator in that the
           primary chamber has  no grates  and the charge
           rests upon the floor  of the chamber.   To increase
           the  residence time  in  the  secondary combustion
           zone, the curtain wall port is extended across the
           bottom of the combustion chamber, forming a tun-
           nel.
Draft

Draft for a furnace that is vented to a final con-
trol device is usually produced by a fan.  Design
information for fans and ducts -was given in Chap-
ter 3.  At least 0. 05 inch water column negative
static pressure should be available  in the ignition
chamber,  and at least 0. 20  inch water column at
the outlet of the secondary combustion chamber.

Equipment Arrangement
Batch  equipment is  usually constructed  in one of
two configurations--a dual structure consisting of
a primary chamber venting through an afterburner
or a single structure containing a primary  chamber
and one or two  secondary  combustion chambers
arranged similarly to a multiple-chamber incin-
erator.
           Secondary  combustion can actually be initiated in
           the  primary chamber by installing an auxiliary
           burner with a  capacity  of about 300, 000 r3tu per
           hour through the outside wall of the primary cham-
           ber directly opposite the flame port.   Flames from
           this burner start secondary  combustion of the ef-
           fluent from the burning pile before this effluent
           enters the  flame  port.  Thus, residence time in
           the secondary combustion zone is increased.

           Since  fly ash is not a problem •when a high-
           efficiency final collector is utilized, the third
           chamber can be either eliminated or designed to
           maintain gas velocities equal to  or  less than
           those  in the mixing chamber.  Figure  384 shows
           a three-chamber  retort furnace  designed to burn
           1000 pounds of insulation-covered wire per hour.

           General Construction
A typical multiple-chamber retort wire reclama-
tion furnace, shown in Figure 333, differs from a
          Construction,  in general, follows many practices
          given for multiple-chamber incinerators described
                                                                        FLAME PORT
                     SECONDARY
                     COMBUSTION
                     CHAMBER
                CLEANOUT DOOR
                           TUNNEL
                                                                            CHARGING DOOR
                                                                            KITH AIR PORT
                                  Figure 383. Multiple-chamber retort furnace.

-------
                                          Wire Reclamation
                                                                                                  5Z7
   Figure 384. A 1,000-pound-per-hour, multiple-chamber
   retort furnace (Amana Scrap Metals, Compton,  Calif.).

in the first part of this chapter.  Only those skilled
in installing high-temperature refractories should
be employed in constructing this specialized equip-
ment.

Refractories

Although primary ignition chambers can be  lined
with high-duty fire clay firebrick, secondary  mix-
ing chambers,  curtain wall port tunnels, and af-
terburners should be lined with super duty firebrick
or superduty plastic refractory.

Since flames may extend into them, breechings
connecting the furnace and final collector equip-
ment must be fully lined -with insulating brick
or castable refactory with a service temperature
of at least 2500°F.  Expansion joints must be
provided as specified by  the refractory manufac-
turer.

Charge Door

A side swing charge door is installed in contrast to
the guillotine-type door found on multiple-chamber
                                                      incinerators. Mating surfaces of the door and door
                                                      jambs are grooved or recessed.  The door is pro-
                                                      vided with a positive locking device, such as a cam
                                                      or wedge lock, to hold the mating surfaces in close
                                                      contact.  High-heat-duty ASTM Class 24 castable
                                                      refractory is used to line the charge door.

                                                      Combustion  Air Ports

                                                      Air ports in  the primary chamber should be con-
                                                      structed of cast iron at least ^ inch thick to min-
                                                      imize warpage. Swing-type ports should be used
                                                      with positive locking devices.   Since the exterior
                                                      surface around the secondary air port is relative-
                                                      ly cool,  materials of construction used for secon-
                                                      dary  air ports  are not critical.   Ten-gage steel
                                                      plate can be  used  and snug fits are easily attained.
Gas Burners

To ignite the charge, hand-held natural gas torches
or low-capacity, permanently mounted, atmospheric
gas burners with flame  safety controls  maybe in-
stalled in the primary chamber.

Secondary burners  can be of several types—at-
mospheric, premix, or nozzle mix.  They should
have flame safety controls and be adjusted to give
along, luminous flame for maximum effectiveness
in promoting secondary combustion.   Secondary
burners should be mounted through the side of the
mixing chamber opposite the flame port, and flames
from these burners should completely blanket the
cross section of the mixing chamber.


Operation

One of the most important factors concerning  oper-
ation is to restrict the combustion rate in the ig-
nition chamber by tightly closing all primary air
ports and sealing the charge door to prevent gas-
eous  overloading  of  the  secondary combustion
chamber.  If overloading does occur with all open-
ings  closed in the ignition chamber, the combus-
tion rate canbe further reduced by spraying water
onto  the burning charge, being extremely careful
not to spray  directly  against the  hot refractory
walls.

Although  primary burners are used simply to ig-
nite the  charge,  secondary burners are operated
throughout the burning period.  In fact, the secon-
dary  chamber or afterburner should be preheated
10 minutes before a cold lightoff to minimize smoke.
Materials must not be removed from the primary
chamber  before the reclamation process is com-
plete since excessive smoke will be emitted  to the
atmosphere.   Wire is removed  from the chamber
•while hot •with only traces of smoke present,  and
it must be immediately quenched with -water to stop

-------
 528
                        INCINERATION
the smoke as well  as  to clean char and residual
materials from the reclaimed copper metal.

Secondary air ports should be adjusted to maintain
high temperatures in the  secondary combustion
zone without emissions of black or white smoke
from the  furnace.  Black smoke may indicate a
lack of combustion air and may be eliminated by
opening the secondary air ports.

Since the inorganic materials in vinyl-coated wire
are emitted to the atmosphere as submicron-size
particles even after passing through the secondary
combustion zone, the percentage of vinyl-coated
wire in a given charge may need to be restricted
in order to prevent excessive emissions.

Illustrative Problem

Problem:
Design  a wire insulation burn-off furnace, having
a secondary  combustion chamber,  to process
250-pound batches  of commercial insulated
electrical wire containing 25 percent combusti-
bles. Radiation-convection cooling columns will
be designed to cool the furnace exhaust gases to
225°F, and a baghouse -will be utilized for a final
collector.

Given:

Design calculations apply equally to a single cham-
ber venting to an afterburner or to a multiple-
chamber retort-type furnace.

Solution:

1.  Primary ignition chamber:

    Assume bulk density of randomly packed wire
    charge at 4 lb/ft .  Design ignition chamber
    50 percent oversize.
             (1.50)
/250 Ib \
\4 lb/ft3/
94. 0 ft"
                        3. 25
     Use dimensions of 2. 75 ft x 5. 25 ft
     ft high

2.   Ignition chamber gas burners:
    Install minimum size gas burners for lightoff.

    Burner capacity    =     50 cfh

3.  Primary air ports:

    Assume inlet velocity through port is 900 fpm
    at 0.052 in. WC.  Assume  100 percent excess
    air in ignition  chamber and composition  of
    combustibles equivalent to U.S.  Grade 6 (P.S.
                                        400) fuel oil.  From Table D6, Appendix D,
                                        354. 4 scf of air is required for  1 pound  of
                                        combustibles.
                   /250 lb wire\/0.
                   \ 30 min   A
                                                  25 lb combustibles
                                                      Ib wire
     A/354. 4 scf\
                        737 scfm


                        Port area:

                          ^737 cfm
                                                  \ A44 in. 2 \
                                                    V  ft2    /
                                                     118  in.
                                   4.
                       Port or duct connecting single chamber to an
                       afterburner  (equivalent to  a flame port in  a
                       multiple-chamber incinerator):

                       Design  for  30  fps  at  1,300°F.  Assume  100
                       percent excess  air in ignition chamber.  From
                       Table D6, Appendix D, there are 363. 3 scf
                       of products from combustion of 1 pound of
                       combustibles.
                                  (250 Ib wire\/0.
                                   30 min   }\
                                 25 Ib combustibles
                                    Ib wire
ibles\/60 min\/363. 3 scf 1
    A hr   A   lb    J
                                          =  45,300 scfh

                                         >r     755 scfm

                                         >r      12.6 scfs
                               /12. 6 scfs\/ 1, 76
                       Area  = I —rr—:	II —ipr;
                               \  30 fr>s  /\  520
                                \      ^  / \
                                                               760°R\144 in.
                                                                 =  204 in.
                   5.   Secondary air port size:

                       Design for 100 percent theoretical air through
                       secondary air ports.  Inlet velocity is 900 fpm
                       or 0.051 in.  WC.  From  Table D6,  Appendix
                       D, 177.2  scf of air is required per  pound of
                       combustibles.
                                  /250 lb wire\ /O.
                                  y  30 min   ) \
                                  25 lb combustibles
                                       lb wire
     A/177. 2 scf \ _
     "A    ib    /=
                                          368 scfm
                                       Port area
                                    /368 scfm\/144 in. 2 \ _
                                  = \900fpm )\  ft2    / =
              59 in. '

-------
                                           Wire Reclamation
                                                                                               529
 6.   Equilibrium temperature between products of
     combustion from ignition chamber at 1,300°F
     and secondary dilution air at 60 °F:

     Weight of secondary dilution air:


[250 Ib wire\/u. 251b combustibles^/13. 51 lb\ _
\  30 min   )\      Ib wire       )l   Ib     j~
30 min   M      Ib wire

     28. 1 Ib/min
                                ignition chamber and dilution air,
                                Ib/min

                                specific heat of products of combustion
                                from ignition chamber and dilution air,
                                Btu/lb-°F

                                final temperature

                                initial temperature
     Weight  of products of combustion from igni-
     tion chamber:
 (250 Ib wire\/0.
   30 min   JI
             25 Ib combustibles
30 min   /I      Ib wire

     58. 2 Ib/min
s\/27. 96 Ib \ =
71   ib   /
     (W )(C   )[T   - T  ]  =  W (C  )[T  - T ]
        a  pa   2    a       c  pc   1    2J

 •where

   W   =  •weight of secondary dilution air, Ib/min
     a
   C    =  specific heat of air, Btu/lb-°F
    pa
    T   =  final gas temperature, °F

    T   =  initial gas temperature,  °F

    T   =  inlet air temperature, °F

   W   =  weight of products of combustion, Ib/min

   C    =  specific heat of products of combustion,
    PC     Btu/lb-°F
 (28.1 lb/min)(0.26 Btu/lb-
                                      - 60°F)   =
     (58.2 lb/min)(0.26 Btu/lb- °F)(1, 300 °F -
                T   =  870°F
 7.   Secondary burner (afterburner) capacity:

     Design secondary burner to raise temperature of
     products of combustion from ignition chamber
     and secondary air from 870°   to  1,600°F.
     Assumed specific heat of products of combus-
     tion is 0.26 Btu/lb-°F.
           Q  =  W  C
                  c   p
where
Q  =  (28. 1 Ib/min +  58. 2 lb/min)(0. 26 Btu/lb-°F)

      (1,600°F - 870°F)

Q  =  16, 400 Btu/min   or  985, 000 Btu/hr

    Design secondary burners for 20 percent ex-
    cess air.  From Table D7, Appendix D, the
    calorific value of 1 scf of natural gas at
    1,600°F is 552.9 Btu.
                                                   „            .^      985, OOP Btu/hr     ,  „„,_
                                                   Burner capacity  =   ,„„„.,,,   =   1'175
                                                                    cfh
                                                   Gross secondary heat
                                                       Ib combustibles

                                                       =  15,600 Btu/lb
                                                (1,775 scfh)(l, 100 Btu/scf)
                                                        125 Ib/hr
                                                       Mixing chamber (afterburner) cross-section-
                                                       al area:

                                                       This area is also equivalent to the cross sec-
                                                       tion of the curtain -wall port tunnel of a multi-
                                                       ple-chamber unit. Designfor 30 fps at 1, 600°F
                                                       and secondary burners for 20 percent excess
                                                       air.  Total volume through mixing chamber:
                                                       Products  of combustion
                                                       from ignition chamber

                                                       Secondary gas burners
                                                       (1, 775 cfh)(13. 53 cf/cf)
                                                          Secondary air
                                                       10 LO   c  t
                                                       (368 scfm)(
                                                                    min\
                                                                   - — —
                                                                   hr
                                                                               or

                                                                               or
                                                          45,300 scfh


                                                          24,000 scfh



                                                          22,100 scfh

                                                          91, 400 scfh

                                                           1, 520 scfm

                                                              25.4 scfs
                                                          Cross-section area  =
     Q  =  heat required, Btu/min
                                                                          _ /25. 4 scfs\/2, 060°R\/144 in.   \
                                                                            I  30 fps  )1 520°R |\  ft2    j
   W   =  weight of products of combustion from
                                                                          =  483 in. '

-------
530
INCINERATION
 9.   Total length of secondary combustion chamber
     (afterburner):

     Assume cross -sect ion area of curtain wall port
     or tunnel is equal to cross  section of mixing
     chamber. Design for a residence time of 0.50
     second.

     Length of secondary zone  = (30 fps)(0. 50 sec)

                               = 15 ft

10.   Weight of gases  from secondary combustion
     chamber:

     From Table D-7,  Appendix D,  there are
     0. 999 lb of products of combustion from 1
     scf natural gas with 20 percent excess air.
                 At   - (1600 - 100) - (225 - 100)  _
                   m
    Products of combustion
    from ignition chamber

     Secondary air through
     port

     Secondary burner

     (1775 scfh)(0.999 Ib/scf) x
     /   hr  \
     \60  min/

     Total gases
                                    58. 2  Ib/min
                                    21. 8 Ib/min
                                    29. 6 Ib/min


                                   115. 9 Ib/min
                         or   6950 Ib/hr

11.   Heat  (Q)  to be  transferred:

     (From  Table  D-3,  Appendix D)
     Enthapy of gas (1600 °F)  =   396.8 Btu/lb

     Enthapy of gas (225 °F)  =    39.6 Btu/lb

       AH = 357. 2  Btu/lb

         Q = (357. 2)(6950) =  2,480,000 Btu/hr

12.   Determine  logarithmic  mean temperature
     difference ( A tm):
           13.   Determine inside  film coefficient (h-):

                                  k /c \/3
                          hi  =  JH D (if)

                (a)  Obtain j^j from Figure 40,  Chapter 3:
                                 D G^
                           R  =
                             e
               (Duct design for the cooling column requires
               the consideration of system resistance,  sys-
               tem balance,  pressure drop,  construction
               requirements,  and economy.  Many calcula-
               tions of the trial-and-error type would be
               required to determine the most desirable
               cooling column duct size when the  above
               mentioned parameters are considered. No
               air pollution control purpose would be  served
               by the presentation of these calculations.
               Therefore,  the cooling column duct size will
               be chosen to correspond with  similar instal-
               lations that are presently operational in  Los
               Angeles County. A duct diameter of 24
               inches is chosen for  this system. )

               Diameter (D) =  2. 0 ft

                                °2
                        Area = "•——-
                             = *-= 3. 14 f

                               6950 Ib/hr
                             =   3. 14 ft2

                             = 0. 086 Ib/hr-ft

                               (2. 0)(Z210)
                                                                                                    .,
                                                                                     = 2210 Ib/hr-ft2
                                                                              0. 086
                                                                                       = 51,450
                          jH = 130 (see Figure 40, Chapter 3)

                           k,  C,
                    Appendix D:
                                                            (b) Obtain k,  C, and ——from Table D-l,
        At,.
      where
        tj   = gas  temperature  of  inlet,  °F

        t^   = gas  temperature  of  outlet,  °F

        ta   = air temperature,  °F
                                                                k  =  0. 0272
                                                                   =  0. 77
                     C  = 0.245

                 (c) Substitute above data in formula and
                    solve for h^:

                        /0.0272\      ,/,                _
                 hi = 130(       1(0.77)1' * = 1.62 Btu/hr-ft2-°F

-------
                                          Wire Reclamation
                                                                                                   531
14.   Convert h^ to inside film coefficient (h^o)
     based on outside  surface area:

     Use a 10-gage duct wall, thickness = 0.141 in.

                      (2)(0. 141)
          D0 = 2.0+     12
                                = 2. 024 ft
      hio = 1.62
                  2. 0
                 2. 024
= 1. 60 Btu/hr-ft2-°F
15.   Determine the outside film coefficient (hQ):

                            + h_
                   ho = hc  ^
                    At \0. 25
     (a)hc  =  0.
        Assume a duct wall temperature (tw) of
        400 °F:
                    400  \
        h_  =  0.271	
         c        \2.024/
                          0. 25
                                =  0. 94
     (b) Obtain hr from Figure 41,  Chapter 3:

        hr =  2.45 (emissivity  = 1.0)

     (c) Use an emissivity of 0. 736 for rusted
        black iron duct

        hr =  (2.45)(0.736) = 1.81 Btu/hr-ft2-°F

        h0 =  hc  + hr

           =  0. 94 +  1. 81  = 2. 75 Btu/hr-ft2-°F
     (d) Since tw was assumed it must be checked:
                              (tm  -  t;
        •where t   = the average gas temp-
                    erature, °F
              1600 + 225       O
                                                                    100 + 100
                                                                    	 = 100 °F
                                                                          2. 75 + 1. 60,
                                                                                      (913 - 100) = 399°F
                                                               The assumed t,., was 400 °F, which
                                                                             w
                                                               checks closely with 399 °F.
                                                      16.  Determine the  overall heat transfer coeffi-
                                                           cient (U  ) based on the outside surface area:
                                                      17.  Determine heat transfer area (A):
                                                          A =
                                                                 Q
                                               2'480'000  = 4430 ft2
                                      U0Atm   (1.01)(555)

                              18.  Determine length of duct (L) required:

                                        4430
                                                           L =
                                                               (2. 0)U)
                                                                        = 704 ft
                                                      19.  Volume of gases vented from cooling ducts
                                                           at 225 °F:
                                                           1520
                                                               /225 +
                                                   = 2000  cfm
                                                               V 60 + 460'

                                                      20.  Required filter area of baghouse:

                                                           Design for a filtering velocity of 2 fpm.


                                                                = 1000 ft2
                                                      21.  Exhaust system and fan calculations are
                                                           made as outlined in Chapter  3.  After a sys-
                                                           tem resistance curve has been calculated
                                                           and plotted,  a fan-is selected whose charac-
                                                           teristic curve will intersect  the system
                                                           curve at the required air volume, which for
                                                           this example would be 2000 cfm.
 234-767 O - 77 - 36

-------
                                            CHAPTER 9

                                  COMBUSTION EQUIPMENT
                                    GASEOUS AND LIQUID FUELS
                      ROBERT T. WALSH,  Senior Air Pollution Engineer*
                     NORMAN R.  SHAFFER,  Senior Air Pollution Engineer
                                      GAS AND OIL  BURNERS

                      ROBERT T. WALSH, Senior  Air Pollution Engineer*
                      JOHN A. DANIELSON, Senior Air Pollution Engineer
                             BOILERS, HEATERS, AND STEAM GENERATORS

                       ROBERT T.  WALSH, Senior Air Pollution Engineer*
                       JOHN A. DANIELSON,  Senior Air Pollution Engineer
*Now with U. S.  Environmental Protection Agency,  Research Triangle Park, North Carolina.

-------
                                               CHAPTER 9
                                     COMBUSTION EQUIPMENT
       GASEOUS AND LIQUID FUELS

INTRODUCTION

For  centuries,  combustible materials  containing
carbon and hydrogen have furnished man with his
most versatile source  of heat and convertible-
energy.  Recent years have seen him,  to a large
degree,  weaned from the  conventional  solid iucls--
coal, wood, peat, and  lignite--in  favor of more
convenient gaseous  and liquid hydrocarbons.   Al-
though nuclear power and sunlight will probably
become  me reasmgly prominent,  hydrocarbons will
surely continue to provide a significant portion ol
our domestic  heat and  power supply and our  vehi-
cle fuels.

Ihc  burning of gaseous and liquid fuels is so com-
monplace that it enters directly into a  vast num-
ber of air-polluting processes.  Most boilers,
heaters, ovens,  and driers are heated by the com-
bustion of hydroc arbon fuels.   Many other process-
es use steam, hot water,  or  electrical  enei gy gen-
erated from the burning of hydrocarbons.

Whenever hydrocarbon fuels  are burned, gaseous
oxidation products are formed and,  in  almost ev-
ery case, vented to the atmosphere.  Optimum
combustion of "clean1'  fuels,  lor example,  natural
gas and  lightweight  oils, results in  gases contain-
ing essentially water vapor,  carbon dioxide,  nitro-
gen,  and oxygen — all normal constituents oj  the
atmosphere --as well as some oxides of nitrogen,
\\hich are air coiitamin ant s .   The- burning ol  any
luel  under  less  than optimum  conditions produces
some quantities  of carbon, ash, and unburned
and partially  burned hydrocarbons.   In addition,
many fuels contain  sulfur and metallic compounds
that  are, even in the oxidised state,  air pollutants.

The  fuel picture is changing.  Coal,  a  principal
solid fuel in some areas,  but not in Los Angeles,
has less acceptance than it once enjoyed, because
of inherent drawbacks  in material handling and
combustion,  as well as to its tendency to create
greater  quantities of air pollution.  In  many  in-
stances  where coal  is  employed on a large scale,
it is pulverized to lacilitate handling and burning.
Moreo\cr, treating coal to lower  its ash and
sulfur contents  has  become commonplace.  The
trend is  away from  high-sulfur, high-ash eoals
and fuel  oils and toward "cleaner'' gaseous and
liquid fuels.   In all  fairness it must be reported
that  coal producers are working vigorously to
regain their markets' by new techniques, such as
pipelining coal slurry, to eliminate certain pres-
ent disadvantages.


Gaseous Fuels

Most of the fuel gas consumed in the United States
is a naturally occurring mixture of low-molecular-
weight hydrocarbons, of which methane and ethane
predominate.  Some natural  gases  from the well
contain hydrogen  sulfide and other  gaseous  sulfur
compounds.  Natural gas  as  marketed is,  however,
extremely pure,  so much so that sulfur compounds
are usually added to distribution lines (about 0.  15
grain, calculated as sulfur,  per 100 scf) to impart
a detectable odor to the fuel.  Because available-
natural gas supplies often contain small quantities
of carbon dioxide and nitrogen and  a varying ratio
of methane  to ethane and higher hydrocarbons,
gross heating values range from 900 to  1,200 Btu
per scf in different localities.   Analyses of some
natural gases are presented  in Tables 142  and 143.
Table 142.  COMBUSTION DATA SUMMARY FOR
             A TEXAS NATURAL GAS
                              10. 36
                              \i. 43
                              20. li
          Products ot  combustion,  per 1 set

                                At 2 ()' , excess air
                                 0 . 4 3 S scf
                                          0.
                                                   535

-------
536
COMBUSTION EQUIPMENT
                  Table 143.  COMBUSTION CHARACTERISTICS OF GASEOUS FUELS
Material
Pure hydrocarbons*
Hydrogen
Methane
Ethane
Ethylene
Propane
Propylene
Butane
Natural gases
Los Angeles, Calif.
Birmingham, Ala.
Kansas City, Mo. b
Pittsburgh, Pa.b
Refinery process gasesa
Cracked, dry
Coking, dry
Reforming, dry
Cracked, dry
Fluid cat. , dry
Thermafor cat. , dry
Refinery, dry
Avg cat. reformer



Coke oven
Blast furnace
Water
Carbureted water
Density,
lb/ft3
at 60°F

0.0053
0.0422
0.0792
0.0746
0. 1162
0. 1110
0. 1530

0.0460
0.0460
0.0483
0.0467

0.0572
0.0628
0.0795
0.0755
0.0776
0. 0663
0.0740
0.0210



0.0306
0.0782
0 0536
0.0414

H2

100













9.5
4.9
3.8
5. 5
1 9. 5
3. 3
13 3
80. 8



51.9
1
32 5
49.6
CH4


100






81. 1
90
84. 1
83.4

64.5
44.6
27.5
40.2
31. 7
36
16 1
5



32, 3
4 6
10.9
Analysis, %
C2H4




100









	
3.6
7. 4
3.3
7
8 2
5. 4
7. 9






	
- —
C2H6



100





9.7
5
6.7
15.8

16
24.3
27.6
21.2
8.7
9 6
18.2
7. 1
4 9





	
2.5
C3H6






100







1.9
1.5
3
1. 1
15. 1
1 0
7.5
36. 4


C H „
4 10

3.2
0. 7
6 1
by volume
C3H8





100



3.5




6.7
14
22.4
23.8
24. 7
20. 6
19.7
19. 2
9 3

CO


5.5
27.5
28. 2
21.9
C4H8














1.3
	
	
	
	
----


CO,
2

2
11.5
5 5
3.6
C4H10







100

0.4




2.9
2.5
7.2
6.6
0.4
1. 9


O
2

0. 03
0 9
0.4
C5H12+









0. 1




0.6
	
	
	
	
---

N
2

4. 8
60
27. 6
5
Inert









5.2
5
9.2
0.8





6. 5
•J c
8







Heating value,
Btu/ft3
at 60'F
Gross

325
1,010
1,770
1,614
2, 520
2, 336
3,265

1, 100
1,002
974
1, 129

, 316
,463
,745
,617
,609
384
, 540
1 804
641



569
92
260
536
Net

275
910
1,619
1, 513
2, 319
I, 186
3,014

990
904
879
1, 021

200
340
592
475
470
264
407
621
569



509
92
239
461
Theoretical
ment, ft3
dry air/ft3
fuel

2.38
9. 57
16.75
14.29
23. 90
21.44
31. 10

10. 36
9. 44
9. 17
10. 62

12. 34
14
16.90
15.20
15.90
13 70
15.70
5.47



5. 45
0. 68
2. 07
5.05
CO2 in dry products
theoretical air,
% by volume

0
11.6
13. 1
15
13.7
15
14

11.9
11.8
11.8
12

11.5
--
--
--
--
-
7.02



10.8
25.5
14. 9
14
  aNel»on, 1958.
  **The North American Manufacturing Co. , 1952.
In addition to natural gas, several other gases,
some mixtures,  some pure compounds,  are used
as combustion fuels.  These  range from by-prod-
uct and manufactured gases to liquefied petrole-
um gas (LPG).  Typical analyses of available gas-
eous fuels are listed in Table 143.  Some by-prod-
uct gases such as refinery "make gas" contain ap-
preciable percentages of higher molecular weight
hydrocarbons so that their heating values are
somewhat greater than those  of natural gases.
Most by-product and manufactured gases contain
significant quantities of carbon monoxide and
inerts  such as nitrogen and carbon dioxide,  re-
sulting in heating values  ranging from 100 to 600
Btu per scf.

Bottled liquefied petroleum gas consists of one or
a mixture of the  following: Propane, propylene,
butane, and butylene.  Because of its ease of
liquefaction and relatively high gross heating val-
ue--2, 520 to  3, 265 Btu per scf--the use of LPG
has been  steadily increasing  over the past few
decades.  It finds its greatest application as nat-
ural gas standby fuel, as vehicular fuel, in porta-
ble equipment, and for general use in remote areas
to which piping less expensive fuels,  such as nat-
ural gas,  is not practical.


Oil Fuels

The term fuel oil applies to a -wide range of liq-
uid petroleum products including crude oil,  distil-
lates,  and residuals.  Most products marketed as
                 fuel oils have been refined to some degree to re-
                 move impurities and to fix upper and lower limits
                 of gravity,  flash point,  viscosity, and heating val-
                 ue.  The  sulfur and ash contents and the viscosity
                 are the major characteristics that affect air con-
                 taminant  emissions.

                 Table  144 provides United States Bureau of Stan-
                 dards  specifications for fuel oils.  These  stan-
                 dards  often serve  as guides in fuel selection rather
                 than as rigid limitations.   Suppliers are likely to
                 market fuels that meet  the needs of their locali-
                 ties and that are normal products of their partic-
                 ular crude  oil stocks and  refining processes.
                 These fuels frequently do not fit into any one of
                 the classifications listed in Table 144.  Products
                 such as these are  commonly sold under a  com-
                 pany name  such as Diesel  Furnace Oil,  Low-Sulfur
                 Stove Oil, or Light Crack  Residual Oil.

                 In Table 144, Numbers  1 and 2 are distillate oils,
                 •while Numbers 5 and 6  are residuals or "bottoms"
                 from refinery processes.  Number 4 oils  are like-
                 ly to be distillates or blends containing  appreciable
                 distillate stock.  The Bureau of Standards  does
                 not list a Number  3 oil.

                 In general,  the distillate oils contain appreciably
                 lesser concentrations of the  potential air con-
                 taminants--sulfur  and ash--than the more  viscous
                 residuals do.  This can be seen from the recom-
                 mended specifications in Table 144.  It  is  a result
                 of the fact that most of the sulfur and ash  in crude

-------
                                         Gaseous and Liquid Fuels
                                                537
     Table 144.  COMMERCIAL STANDARDS FOR FUEL OILSa  (Commercial Standard CS 12-48)
Grade of fuel oilb
Numb e r

1


^


4

5


6


Description


pot-type burners and other burners
requiring this grade^
Distillate oil for general purpose do-
mestic heating for use in burners not
requiring No. 1

ped with preheating facilities

tions equipped with preheating facili-
ties
Oil for use in b ners e d w th
preheaters permitting a high-viscosity
fuel

Flash
point,
°F
mm
100
or legal

100
or legal

1 30
or legal

or legal


or legal


Pour
point,
°F
max
0


2oe










Water
sedi-
ment,
%
max



0. 10










Carbon
residue
on 10%
residuum,
%
max
0 15


0.35











Ash,
%
max



-__











Gravity,
-API
mm



26










Distillation
temperatures, °F
10%
point
max



t










90%
point
max



675










End
point
max














Kinematic viscosity
Saybolt Seconds Centistokes at
Universal
at 100°F
max



40










mm














Furol
at 122°F
max














mm














100°F
max

'

(4 3)










mm














122°F
max














mm














  Recognizing the necessity for low-sulfur fuel oils used in connection with heat treatment, nonferrous metal, glass, and ceramic furnaces, and other special uses,
  a sulfur requirement may be specified in accordance with the following table-
                                    Grade of fuel oil
                                                         Sulfur max,
                               No. 1	  0. 5
                               No. Z	  1.0
                               Nos.4, 5, and 6	 No limit
  Other sulfur limits may be specified only by mutual agreement between the buyer and seller.

  It is the intent of these classifications that failure to meet any reqmremen: of a given grade does not automatically place an oil in the next lower grade unless in
  fact it meets all requirements of the lower grade.

 cGrade No. 3 became obsolete with the issuance of the 1948 commercial standard for fuel oils.

 dNo. 1 oil shall be tested for corrosion in accordance with ASTM Designation D130-30 for 3 hours at 122T. The exposed copper strip shall show no gray or

 eLower or higher pour points may be specified whenever required by conditions of storage or use  These specifications shall not however reouire a nour
  point lower than 0°F under any conditions.                                                         '      '   4     p

 £The 10% point may be specified at 440'F maximum for use in other than atomizing burners.

 SThe amount of water by distillation plus the sediment by extraction shall not exceed 2. 00%.  The amount of sediment by extraction shall not exceed 0. 50. A
  deduction in quantity shall be made for all water and sediment in excess of 1. 0%.
oil is tied up in long-chain, high-boiling-point or-
ganic compounds,  which tend to  concentrate in
residuals from refinery processes.   Table 145
provides data on straight-run low-sulfur residual
fuels (containing less than  0. 5 percent  sulfur by
weight) burned in Los Angeles County.   The
Sumatra-Minas crude oils  are paraffin base,
while the Alaskan  crude oils are asphaltic base.
Fuel oils produced from these crudes contain,  in
general,  less sulfur and ash than do the com-
mercial fuel oils listed  in Table  144.
Table  146 provides combustion data for a U. S.
Grade 6 residual fuel oil.  Residual fuel oils are
markedly less  expensive than distillate  oils but
require  more elaborate burner equipment for
proper combustion.  "Heavy-crack" residual fuels
are normally burned, therefore, only in large
combustion sources.  Most small operators, par-
ticularly those who burn natural  gas on  a curtail-
able basis,  prefer to use cleaner,  more trouble-
free distillate  oils as stand-by.

THE AIR  POLLUTION  PROBLEM

Air contaminants generated from fuel burning fall
into three categories:  (1) Carbon and the unburned
and partially oxidized organic materials that re-
sult from incomplete combustion,   (2) sulfur ox-
ides and ash directly attributable to fuel composi-
tion, and (3) oxides of nitrogen  formed at firebox
temperatures from oxygen and nitrogen of the air.
Incomplete combustion products can usually be
held to tolerable minimums "with proper operation
of modern burner  equipment.  Sulfur and ash emis-
sions  are governed by the fuel makeup.  Nitrogen
oxide  concentrations are primarily functions  of
firebox design and temperature.
Black Smoke
When hydrocarbon fuels are burned in a deficien-
cy of oxygen, some  carbon particles  can be found
in the  products  of  combustion.  With  poor  fuel
atomization, inadequate mixing, or marked oxy-
gen shortage, the  concentration of carbon in-
creases to the point where a visible blackness is
imparted to exit gases.  Black  smoke,  when  it
occurs, is usually connected -with the burning of
viscous, heavy-crack residual  oils and of solid
fuels.   Creating black smoke by burning gaseous
fuels is difficult,  though not  impossible.  Other
products of incomplete combustion,  such as
carbon monoxide,  usually accompany black smoke
emissions.   The degree of blackness  is historic-
ally significant,  since the Ringelmann Chart  was
developed for this  type of  smoke.  Heavy,  carbo-
naceous accumulations in  exhaust stacks,  com-
monly termed soot,  are attributable to  the  same
cause  as black smoke,  namely, poor combustion.

White Smoke
Visible  emissions  ranging from grey through
brown to -white can also be created  in the com-

-------
538
COMBUSTION EQUIPMENT
             Table 145.  ANALYSES OF STRAIGHT-RUN LOW-SULFUR RESIDUAL FUELS
                                   USED IN LOS ANGELES COUNTY


Source
and supplier
Alaskan (typical)
MacMillan Ring
Free Oil Co.
Golden Eagle Oil
Co.
Shell Oil Co.
Atlantic Richfield
Oil Co. (a)
(b)
Sumatra-Minas
(Range)
Standard Oil Co.
of California



Sulfur,
%

0. 27

0. 25

0. 36

0. 27
0. 35


0. 15
to
0. 30

Flash
point,
F

365

320

250

290
370


195
to
350

Pour
point,
F

70

75

55

75
85


105
to
115
Water
and
sedi-
ment,
0

0. 017

0. 050

0. Oil

0. 010
Trace


0. 05
to
0. 3

Rams -
bottom
carbon ,
wt %

_

-

-

-
-


3. 0
to
6. 0


Ash,
%

0. 020

0. 003

0. 010

0. 010
0. 007


0. 001
to
0. 013


Gravity ,
API

17. 8

17. 8

15. 1

15. 0
13. 2


22
to
31
Kinematic viscosity,
Saybolt seconds

Umve rsal
at 210 F

112

100. 3

178. 5

207. 6
587. 2


50
to
250

Furol
at 122 F

94

79. 5

207. 4

273
1148. 6


_

-

Firing
temp for
180 SSU, a
F

185

180

209

213
260


_

-

Fllfil
Uci
lb/gal

7. 893

7. 893

8. 038

8. 044
8. 144


7. 3
to
7. 7
Btu/lb

18, 962

18, 940

18, 735

18, 763
18, 720


19, 200
to
19, 700
 SSU - Saybolt Seconds Universal.

Table 146.  COMBUSTION DATA SUMMARY FOR
          A NUMBER SIX FUEL OIL

                    Analysis
Component
Carbon
Hydrogen
Sulfur
Water
Ash
% by weight
88. 3
9. 5
1. 6
0. 05
0. 10
Gross heating value
152, 000 Btu/gal
18, 000 Btu/lb
Combustion air requirement (dry)
Theoretical
10% excess
20% excess
100% excess
scf/lb Ib/lb
176. 3 13.4
193.9 14.8
211.6 16. 1
352. 6 26. 9
      Products ol combustion, per Ib ol tue 1 oil
           Assume air at 40% RH, 60°F
Component
C°2
Hz°
S°2
N
i
0,
2
Total
At theoretical air
27. 9 set'
19. 3
0. 2
139. 3

	

186. 7
3. 24 Ib
0. 92
0. 03
10. 30

	

14. 49
At 20% excess air
27. 9 scf
19. 5
0. 2
167. 5

7. 4

222. 5
3. 24 Ib
0. 93
0. 03
12. 38

0. 64

17. 22
 bustion of hydrocarbon fuels, particularly liq-
 uid fuels.  White or opaque smoke, that is, non-
 black smoke,  is the result of finely divided par-
 ticulates--usually liquid particulates --in the gas
                 stream.  These visible pollutants are most often
                 caused by vaporization of hydrocarbons in the
                 firebox,  sometimes accompanied by  cracking,  and
                 subsequent condensation  of droplets at 300°   to
                 500°F stack temperatures.  White  smoke is fre-
                 quently attributed to excessive combustion air
                 (cold fire) or loss of flame (gassing).  Visible
                 contaminants can also exist where  combustion is
                 optimum and the concentration of oxidizable ma-
                 terials is at a minimum.   This situation is  ap-
                 parently  limited  to large  power plant boilers where
                 there is measurable sulfur trioxide in exhaust
                 gases.

                 Participate Emissions

                 Combustion gases can contain particulate matter
                 in the form of unburned carbon and hydrocarbon as
                 well as  inorganic ash.  With the  proper use of ade-
                 quate burner equipment,  oxidizable particulates,
                 both solids and liquids,  can usually be kept  -well
                 below typical emission standards,  for example,
                 Rule 53b of the Los Angeles County Air Pollution
                 Control District  allows 0. 3 grain of particulate
                 matter per scf of exhaust gases calculated  on a
                 12 percent carbon dioxide basis.   Where unburned
                 particulate concentrations approach allowed limits,
                 the Ringelmann number or opacity  of the exhaust
                 gases is  usually  high and may exceed legal stan-
                 dards for visible contaminants.  The operator of
                 combustion equipment malfunctioning in this way
                 can almost always correct the combustion condi-
                 tions to control these emissions unless the  grade
                 of fuel is improper  for the combustion equipment
                 or vice versa.  Ash collected at large,  efficient
                 power plant boilers  during oil burning normally
                 contains  less than 10 percent  carbon and other
                 combustibles.

-------
                                       Gaseous and Liquid Fuels
                                             539
The quantity of inorganic solid particulates in ex-
haust gases is entirely dependent upon the charac-
teristics of the fuel.  There is no measurable in-
organic ash in exhaust gases from the combustion
of natural gas  or other clean gaseous hydrocarbons,
except for that small quantity attributable to the
dust usually present to some degree in all air used
for combustion. Low-sulfur fuel oils are known
to contain very small  amounts  of ash.   Table 145,
which gives typical  analyses  of straight-run low-
sulfur  residual fuel oils, indicates variations
from 0. 007  to  0. 020 percent by weight.  In resi-
dual oils, however, inorganic ash-forming
materials are  found in quantities up  to 0.1 per-
cent by weight. Most of this material is held in
long-chain organo-metallic compounds.   The
strong oxidation conditions present in most fire-
boxes convert  these materials  to metallic oxides,
sulfates, and  chlorides.  As would be expected,
the compounds show up as finely divided particu-
lates in exhaust gases.  Table  147 provides a
spectrographic analysis of the  inorganic fuel oil
ash collected  at a large power  plant  boiler.
The combined ash and unburned particulates in
exhaust gases from gaseous or liquid fuel com-
bustion are not likely to exceed local air pollution
control statutes.  For instance, the efficient burn-
ing of a common heavy residual oil of 0. 1 percent
ash results in a stack gas concentration of only
0. 030 grain per scf at 12 percent carbon dioxide.
Sulfur in Fuels

In liquid hydrocarbon fuels, sulfur occurs in con-
centrations ranging from a trace to more than 5
percent by weight.  Much of this  sulfur is present
as malodorous sulfides and mercaptans.  Natural
gas fuels contain very little sulfur as marketed,
usually only enough to impart a detectable odor to
the gas.   Some by-product gases, however,  contain
appreciable sulfides and mercaptans.  Distillate
oils may contain as much as  1 percent sulfur,
though most distillates have less than 0. 3 percent.
There is normally much more sulfur in heavy resid-
ual oils than in gaseous fuels and distillate oils.
Most of these oils  contain more than 1 percent
sulfur by weight.  In the Los Angeles area,  cracked
residual oils were commonly burned in power
plant boilers prior to 1968 when natural gas was
not available. These oils contained about 1. 6  per-
cent sulfur. In November 1968, Rule 62. 2,  limiting
sulfur content of fuels  to less  than 0. 5 percent by
weight, was enacted.  In essentially  all cases,
previous users of residual fuels are now burning
straight-run low-sulfur residual fuel oils when
natural gas is not available.
Table  147.  TYPICAL FUEL OIL ASH ANALYSIS
Constituent
Iron
Aluminum
Vanadium
Silicon
Nickel
Magnesium
Chromium
Calcium
Sodium
Cobalt
Titanium
Molybdenum
Lead
Copper
Silver
Total
Weight %
22.99
21. 90
19. 60
16. 42
11. 86
1. 78
1.37
1. 14
1
0. 91
0. 55
0. 23
0. 17
0. 05
0. 03
100
 Sulfur Oxides

 Most of the sulfur present in fuels is converted to
 sulfur dioxide on combustion.  A typical residual
 fuel oil  of 1. 6 percent sulfur yields a concentra-
 tion of 1, 000 ppm sulfur dioxide when burned with
 the theoretical amount of combustion air.  As
 shown in the  sample calculations, this is equiva-
 lent to 832 ppm at 20 percent excess combustion
 air, a point at which many industrial boilers are
 operated.  By comparison,  fuels containing 0. 5
 percent sulfur will yield a concentration of 310 ppm
 of sulfur dioxide when burned with a theoretical
 amount of combustion air or 260 ppm with 20 per-
 cent excess combustion air.

In some combustion processes,  a small portion
 of the  sulfur--usually no more than  5 percent of
the total — is converted to sulfur trioxide, the
 anhydride of sulfuric acid.  Sulfur trioxide  is
highly reactive and extremely hygroscopic as
 compared with sulfur dioxide.  It is considered
 a chief cause  of the visible plume created by
burning high-sulfur fuel oils in large power  plant
boilers.  Besides obscuj-ing visibility,  these con-
taminants can result in acid damage to vegetation
and property in downwind areas.  The factors
governing firebox formation of sulfur trioxide are
not fully understood, but it is  recognized to  occur
principally in large combustion  installations oper-
ated at high firebox temperatures.

Oxides of Nitrogen
In every combustion process the high temperatures
at the burner  result in the fixation of some  oxides
of nitrogen.  These compounds are found in  stack
gases mainly as nitric oxide (NO) with lesser
amounts of nitrogen dioxide (NO2> and only  traces
of other oxides.  Since NO continues to oxidize  to

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 540
                                      COMBUSTION EQUIPMENT
NO-, in the air at ordinary temperatures, there is
no way to predict with accuracy the amounts of
each separately in vented gases at a given time.
The total amount of NO + NO-, in a  sample is de-
termined and referred to as "oxides of nitrogen"
or NO  (Los Angeles  County Air Pollution Control
District,  1960a).
 AIR POLLUTION  CONTROL METHODS

 An operator can take only two options to reduce
 air contaminant emissions from a combustion
 source,  namely,  remove the sulfur  compounds
 and. ash  from his combustion gases or switch to a
 cleaner  and usually more expensive fuel.  Only
 limited progress has been made in removing air
 pollutants from combustion products. These meth-
 ods are  discussed later in this chapter in the sec-
 tion,  "Boilers, Heaters, and Steam Generators,"
 inasmuch as they are employed only at large com-
 bustion sources.
 Prohibitions Against  Sulfur Emissions

 Two types of regulations have been used to limit
 the concentration of sulfur contaminants at com-
 bustion sources and thus outlaw the burning of
 certain fuels.  One  sets a ceiling on the fuel's sul-
 fur content while the other fixes a maximum allow-
 able flue gas concentration.  Both types of pro-
 hibitions have been  enacted in Los Angeles County.
 Rule 53a limits the  concentration of sulfur com-
 pounds in exhaust gases from any combustion pro-
 cess to 0. 2 percent by volume calculated as sul-
 fur dioxide. Rules 62,  62.1,  and 62.2  prohibit the
burning of gaseous fuels  containing more than  50
 grains of sulfur compounds  per 100 cubic feet, cal-
 culated as hydrogen sulfide  at standard conditions,
 or any liquid or solid fuel having a sulfur  content
 in excess of 0. 5 percent by weight. These rules
are considerably more stringent than Rule 53a,
limiting sulfur concentration to roughly one-eighth
that allowed by Rule 53a.

 Supplementary provisions are sometimes used
 wherein allowable stack sulfur emissions are
 based upon ground level concentrations, usually
 measured as sulfur  dioxide.  The  regulations of
 the San Francisco Bay Area Air Pollution Control
 District,  for instance,  set an effluent limit of 0. 2
percent as sulfur dioxide but allow heavier dis-
charges of sulfur compounds, provided ground level
concentrations do not exceed specified limits.  The
allowed concentrations are on a sliding time basis
ranging from 3 minutes at 1. 5 ppm to  8 hours  at
0. 3 ppm,  sulfur compounds being measured as sul-
fur dioxide.  Obviously, statutes  such as these allow
heavier emissions where dispersion conditions are
favorable and -where the source is isolated from
 similar sulfur-emitting plants.
Removal of Sulfur and Ash From Fuels

To whatever degree is economically feasible,
hydrocarbon fuels are treated to remove sulfur
compounds  as well as inorganic ash.   The prac-
tical sulfur removal methods are essentially
restricted to scrubbing or liquid-liquid extrac-
tion,  sometimes accompanied by catalytic de-
composition.  Natural gas is commonly scrubbed
at the natural gas plant before its introduction
into transmission pipe lines.  Higher molecular
weight hydrocarbon gases and distillate oils are
treated at the refinery before they are marketed.

There is at present no economical method of re-
moving sulfur from heavy residual  oils.  As was
previously mentioned,  most of the sulfur in these
viscous oils is tied up in large molecules.  To
remove the undesirable sulfur,  one must remove
it  from the  molecule,  as with hydrocracking or
thermal cracking processes, and thereby cre-
ate hydrocarbons of considerably lower molecular
weights.  Both these processes  add appreciably
to fuel costs and are now used to yield products
such as gasoline and distillate oils,  which com-
mand markedly higher prices than residuals.
The ash tends to concentrate in  the residuals.

Apparently, on the basis of present technological
trends, yields  of residual oils from refineries
will be  steadily reduced in coming years.   New
processes  being  developed and perfected are
aimed primarily at greater yields of gasoline and
diesel and  aircraft fuels.  Much more work is
being done on the development of these processes
than on methods  of removing sulfur from highly
cracked residual oils.

Figure  385  shows production trends for  residual
and distillate oils over the period 1950 to 1969.
During  this period,  residual yields dropped off
sharply; distillate yields increased slightly from
1950  to  1956, then leveled  off. The yield curve
for residual oil is expected to remain at a low
level,  as indicated in  Figure 385,  unless new
processes  or methods are introduced into the re-
fineries.  Much of the distillate  oil is used  as motor
fuel or  premium standby fuel, while almost all
the residual oil is burned  in boilers  and heaters.
Over the 20-year period from 1950 to 1969, re-
finery crude oil  input increased approximately
two-fold.  Residual production decreased, there-
fore, in terms of both volume and yield in that
interval.  This situation has  been offset somewhat
by the increased importation of crudes yielding
straight-run low-sulfur residual fuel oils.

In Los Angeles during this period, the  decrease
in residual fuel demand was accompanied by
changes in the local refineries'  product composi-
tion.  Gasoline,  jet fuels,  and other lighter pro-
ducts increased  percentage--wise as fuel oil pro-

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                                        Gaseous and Liquid Fuels
                                               541
    25
    20
     15
 xT 10
 >-

 LU
        I  I  I   I  II  I!   I  I  ||  II

         f-~.~~"'          DISTILLATE OILS
                    RESIDUAL OILS
     0
     1950  1952 1954  1956  1958 1960  1962  1964 1966 1968 1970
                         YEAR

   Figure 385.  Production trends, U. S. refineries,
   1950 to 1969.
    Carbon  C   +   O   	*

    (0. 883 lb)f— J  =   2. 35 Ib O  = 132.5 scf of air
                                                            Hydrogen  H   +   1/2  O
    (0.0951b){ —)  =  0. 76 Ib O  = 42. 9 scf of air
              \2 /              2

    Sulfur  S  +  O   	-*•  SO

    (0.016)(~) =  0. 016 Ib O
                                                                                         -  0. 9 scf of air
    Total

    176. 3  scf of dry air/lb oil

    177. 6  scf air at 40% RH, 60°F per Ib oil

2.   Air requirement at 20% excess air:

    (176. 3)(1. 20)  =  212 scf dry air/lb oil

    (177. 6)(1. 20)  =  213 scf moist air/lb oil
 duction declined.  Heavy oil processing schemes,
 hydrocracking,  and coking have been adopted to
 achieve this  result.

 Illustrative Problem

 The following example illustrates calculations
 used in determining sulfur oxides and ash con-
 tent in flue gases  formed by burning a heavy
 residual fuel.

 Given:

 A heavy residual fuel is to be burned in a com-
 bustion process "with 20 percent excess air.  The
 oil analyses  (percent  by -weight), is as follows:
Carbon
Hydrogen
Sulfur
Water
Ash
88. 3
9.5
1.6
0. 05
0. 10
 Problem:

 Determine the combustion air requirement and
 the concentration of sulfur  oxides in flue gases
 while assurning  3 percent of the sulfur is con-
 verted  to sulfur trioxide.  Determine  the ash con-
 centration in flue gases at 12 percent  carbon di-
 oxide while assuming  complete combustion.  Use
 as a basis 1 pound  of fuel oil.

Solution:

1.    Theoretical combustion air requirement:
3.   Products of combustion (assume complete
    combustion and neglect SOj):

    Carbon dioxide


    (0.8831b)(W-f^-) =  27. 9 scf
              \12/ \44 lb/mol/

    Water from combustion


    (0. 095 lb)f~

    Water in fuel:

              '379
                    18
                                =   18.0 scf
                                                            0. 0005 Ib

                                                            Nitrogen
                                    0.Oil scf
                                                                                          =  167.5 scf
    (212 scf)(0.79)

    Water in air,  40% RH, 60 °F

    (0.0072 scf/scf air)(213  scf)  =     1.5 scf

    Sulfur  oxides as sulfur dioxide
          '64\/379\
          ~A~647
                                        0.2 scf
    Oxygen
    (176.3 scf)(1.20 -  1.00)(0.21)  =   7. 4 scf
    Total
                                     222.5 scf/
                                           Ib oil

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542
     COMBUSTION EQUIPMENT
4.   Sulfur dioxide concentration:
        -—  (10)(0. 97)  =  827 ppm
 5.   Sulfur trioxide concentration:
                     (10)(0.03)  =  26 ppm
 6.   Inorganic ash concentration:
 (0.001 lb)(7,000 gr/lb)
                        222.5
=  0.0314 gr/scf
           GAS AND  OIL BURNERS
 INTRODUCTION

 A burner is  essentially a triggering mechanism
 used to ignite and oxidize hydrocarbon fuels.  In
 general, burners are designed and operated to
 push the oxidation reactions as close as possible
 to completion with the maximum production of
 carbon dioxide and water, leaving a minimum of
 unburned and partially oxidized compounds in ex-
 haust gases.  Burner efficiency can be measured
 by the water and carbon dioxide contents of com-
 bustion gases or, conversely, by the concentrations
 of carbon monoxide, carbon, aldehydes, and other
 oxidizable compounds.  Insofar as hydrocarbon-
 derived pollutants are concerned, optimum burn-
 er operation goes hand in hand with minimum air
 pollution.

 The purpose of this part of the chapter is to pre-
 sent  general burner principles with emphasis on
 major design and operation variables  that affect
 air pollution.  There  are so many variations in
 burner design that discussing each separately
 would not be practical.  Specific operating instruc-
 tions for any given burner should be obtained from
 the manufacturer or agent.

 Burners and the combustion equipment in which
 they  are located are commonly thought of as
 sources of air pollution.  Burners,  however, are
 also  used frequently as air pollution control  equip-
 ment.  Their most common control application is
 in vapor incineration,  but many are used for pur-
 poses such as  refuse  incinerator auxiliaries  and
 as tempering heaters with baghouses, precipita-
 tors, and centrifugal  collectors.  Almost all
 burners used in air polhition control devices are
 designed to handle gaseous fuels exclusively.

 A burner consists primarily of a means  of meter-
 ing the two reactants,  oxygen and fuel,  and a
means of mixing the reactants before and con-
currently with ignition.  Many burners  also in-
clude flame safety devices  and  auxiliaries to  condi-
tion the temperature and viscosity of the fuel,
as well as  fans and pumps to move  or pressurize
air or fuel.  The simplest burners  are  employed
with gaseous combustion fuels while the most
complex units are used -with heavy oils  and •with
solid fuels.


Draft Requirements

In all combustion equipment, some energy is re-
quired to push or pull the combustion air,  fuel,
or products of combustion through the burner and
also through the heat exchange  portion  of the  com-
bustion equipment.  With small gas-fired appliances
the line gas pressure together with the  bouyancy of
warm  oxidation products are sufficient  to provide
the necessary draft.  With  larger equipment, either
extended natural-draft stacks or  blowers must be
used.  Blowers may be positioned ahead of or be-
hind the firebox.  When located ahead of the fire-
box, a blower is sometimes constructed as an in-
tegral part of the burner and is driven  by a motor
common to a fuel pump or atomizing device.  Forced
draft burners provide greater flexibility and  can
be used in situations where the firebox  itself  is
under  pressure.


Gas Burners

Owing principally to the low viscosity of gaseous
fuels,  gas  burners are considerably simpler  than
those used with liquid and solid fuels.  Gases can
be transmitted and mixed with combustion air much
more easily than other fuels  can. This is not to
say that all gas burners are necessarily uncompli-
cated mechanisms. Many are equipped with  elabor-
ate combustion air auxiliaries and flame control
features.  For a specific installation, however, a
gas burner is almost always  less complicated than
its liquid or solid fuel-burning  counterpart de-
signed for  the  same application.

In most gas burners, only a portion of  the air re-
quirement--termed primary combustion air — is
mixed with fuel before  ignition.   These burners
constitute  the large majority of equipment in  use
today, ranging from small  appliances to large
power plant gas burners.  Two other types in rea-
sonably wide use do not fall into  this category —
totally aerated burners and nonprimary aerated
burners.

With totally aerated burners, all combustion  air
is mixed \vith fuel before ignition.  These units
are employed at installations such as metallurgi-
cal furnaces,  where operation within narrow  oxy-
gen concentration limits  or  even  in reducing  at-
mospheres is desirable.

-------
                                         Gas and Oil Burners
                                                                                                   543
In nonprimary aerated burners, no combustion air
is mixed with fuel ahead of the burner port.  The
gaseous fuel is merely allowed to jet through an
orifice in such a pattern or manner as to provide
adequate mixing  -with oxygen.  Most of these units
employ narrow slotted ports,  giving the flame a
thin fan shape.  In other nonprimary aerated burn-
ers, a circular orifice is employed,  and the jet-
ted fuel is allowed to impinge on a target surface
in such a  manner as to provide turbulence and mix-
ing. Many nonprimary aerated burners are of
multiport design, employing  a number of slots or
orifices in order to provide maximum interface
surface between  fuel and combustion air.


Partially Aerated Burners

The venturi-shaped burner in Figure 386 can be
used to illustrate the basic operation of partially
aerated atmospheric gas burners.  Gaseous fuel
is introduced through the control valve into the
burner head and allowed to flow through the fixed
orifice into the throat.  The jetted gas  stream in-
duces  combustion air to flow through the primary
airport and creates enough turbulence to mix fuel
and air between  the orifice and the burner tip.
The quantity of primary air induced is  governed
by the airport setting,  the specific gravity of the
gas, and  the gas  pressure.  Ignition starts at the
burner tip where additional air--termed secondary
combustion air--contacts the  mixture.   Combus-
tion is  completed off the burner tip as additional
secondary air reacts with the burning mixture.
yellow tip curve results in a smoky flame with
possible flashback.   Natural gases are relative-
ly slow burning and are not likely to flash back
unless conditions are severe.
                          NATURAL GAS ANALYSIS
                                 50'i
                          C2H6 =  U 50
                          C02 -  0 20
                           02 -  0 20
                           N2   0 60
    Figure 386.  Typical  atmospheric gas burner.
                                                              INPUT RATE, 1 OOO's of Btu/tr per in   of port area
                                                         Figure 387.  Flame  stability  limits burning
                                                         a natural  gas in an  atmospheric burner
                                                         (American  Gas Association  Laboratories, 1940).
For a given fuel,  the combustion efficiency and
the stability,  shape, and luminosity of the  flame
are dependent upon the primary and secondary air
rates and the degree of turbulence.  A high pri-
mary air rate produces a short,  blue  flame, while
a low primary air rate results in a long, luminous
flame.  If primary air is  reduced too  greatly,  the
flame becomes smoky with yellow tips, and flash-
back may occur out the primary combustion air-
port.  If the primary air rate is increased too
much, the flame becomes unstable and lifts from
the burner port.  These limits are plotted  in Fig-
ure 387 for a 1, 100-Btu-per-cubic-foot natural
gas.  The cross-hatched area between the  two
curves represents the stable range of burner oper-
ation for a typical partially aerated burner. Oper-
ation above the lift curve  results in the flame's
lifting from the burner, while operation below  the
The effect of primary air at the same gas input
is illustrated in Figure  388 for the  same natural
gas  described in Figure 387.  At the maximum
primary air rate  shown, 66. 8 percent of the the-
oretical combustion requirement, the inner blue
cone of the flame is sharply defined while the out-
er luminous cone is almost indistinguishable at
the tip.  At the lowest primary air rate, 49. 1 per-
cent, the flame becomes extremely luminous, the
inner blue cone blending into the luminous outer
cone.

The burner characteristics  of different fuel  gases
are dependent  to a large degree upon speeds of
flame propagation.   Gases such as hydrogen, car-
bon monoxide, ethylene, benzene,  and propylene,
with high ignition velocities, are prone  to flash-
back through the burner at low primary air  rates.

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 544
        COMBUSTION EQUIPMENT
              66.8
63.4
60.4         57.1
  °* PRIMARY AIR
53.3
49.1
             Figure 388.  Natural gas flames  with varying primary air  (American Gas Association
             Laboratories,  1940).
Nevertheless,  the latter fast-burning gases do not
tend to blow off or lift from the burner tip as  read-
ily as the slower burning fuels, methane, ethane,
and butane.  Gases with high ignition velocities are,
therefore, normally operated at somewhat higher
primary air rates than natural gas and liquefied
petroleum gas  are.  This can be seen by compar-
ing the stability range of the  fast-burning manu-
factured gas of Figure  389 with that  of the natural
gas of Figure 387.  The lift curve for the manufac-
tured gas is considerably higher than for natural
gas.  For example,  at  70 percent primary air and
30, 000 Btu  per hour per square inch of port area,
the manufactured gas flame is stable, while that
of natural gas  is unstable.  The yellow tip curve
for this gas is  also higher.   Its marked propensity
to burn back out the airport is shown by the flash-
back limit curve.
Other factors,  such as port size and shape, also
influence burner operation.  The reader should con-
sult a burner handbook and publications of the Amer-
ican Gas Association for detailed discuss-ions of the
subject.
                         Multiple-Port Gas Burners

                         Burners with multiple orifices are widely used
                         in boilers, heaters, and vapor incinerators.  The
                         individual ports are usually of partial-aeration or
                         nonprimary-aeration design. Over a given cross -
                         section, a multiple-port burner provides better
                         distribution of flame and heat than a single-port
                         unit does.  For this reason, multiple-port burners
                         have an inherent  advantage in vapor incineration.
                         Forced-Draft Gas Burners

                         The availability of a combustion air blower pro-
                         vides  greater flexibility and often better combus-
                         tion than an atmospheric gas burner affords.  The
                         simplest forced-draft units consist merely of low-
                         pressure fans with gaseous fuel  orifices located
                         in the discharges.  In some cases, the fuel is in-
                         troduced ahead of the blower and allowed to mix
                         in the fan housing.  One of the more complex de-
                         signs  is the low-pressure premix unit,  shown in
                         Figure 390.  Here, a blower is used to force
                         combustion air through a venturi at pressures up

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                                          Gas and Oil Burners
                                                                                                    545
                                                                     DAMPER
                20     30     40      50
              INPUT RATE  MBTU hr-in2 of port area
   Figure 389.  Flame stability limits  burning  a
   manufactured gas in an atmospheric  burner
   (American Gas Association Laboratories,  1940).
to 3 psig.  Gaseous fuel is drawn into the system
at the throat of the venturi and mixes in fixed
proportion with combustion air ahead of the burn-
er nozzle.  With an arrangement such as this,  the
shape, makeup,  and luminosity of the flame can
be precisely controlled.  Moreover, the  flame
has appreciable velocity.  These burners are em-
ployed in metallurgical processes where precise
atmospheric control is  desired,  in  some vapor
incinerators, and in crematories and pathologi-
cal-waste incinerators,  where a strong flame
must be  directed on animal tissue.

Gas Flow  Rates

Gaseous fuel is commonly introduced through one
or more fixed orifices at the burner.  These ori-
fices constitute the principal pressure drop in the
gas-piping system and govern the flow of fuel to
the burner.  Flow through an orifice is propor-
tional to the  square root of gas pressure so that
minor upstream pressure fluctuations do not have
                                                           BtO»ER
                                                         GAS IN
                                                                                                   FIREBOX
                                                                      ZERO PRESSURE
                                                                      REGULATOR
                                                         Figure 390.  A multiple-port burner  (nonprimary
                                                         aerated)  installed in a vapor incinerator.
                                                       a great effect on flow rate.  The nomographs of
                                                       Figures 391 and  392  provide flow rates for 0.65
                                                       specific gravity  (referred to air) natural gas
                                                       through standard orifices at various gas pressures.
Oil Burners

Inasmuch as liquid fuels must be vaporized be-
fore combustion can take place, an oil burner
must accomplish an  additional  function not re-
quired of a gas burner.  Light  oils can be vapor-
ized from a static vessel or wick.  This princi-
ple is used with items  such as  kerosene lamps
and blow torches but is not practical for most
burners.  In almost  all industrial applications,
the fuel  is first atomized then allowed to vapor-
ize on absorbing heat from the flame.  The effi-
ciency of an oil burner depends largely upon
atomization and fuel-air mixing.
There are four basic types of oil burners,  differ-
ing principally in the methods of atomization: Low-
pressure air-atomizing; high-pressure steam- or
air-atomizing; high-pressure oil-atomizing;  and
centrifugal or  rotary cup burners.   A fifth type,
the mechanical atomizing burner, employs both
high-pressure oil and centrifugal action.
With low-pressure air-atomizing burners, such
as that shown in Figure 393, a major portion of
the combustion air requirement is supplied near
the oil orifice  at 1/2 to 5 psig.  This air abrades
and atomizes the jetted oil stream in an area of
high turbulence.  Secondary combustion air is
admitted around the periphery of the mixture. In
comparison -with other types of oil burners, these
units provide a greater volume of air  in close
proximity to the atomized oil — from 10 to 60 per-
cent of the theoretical combustion  requirement.
For  this reason, the flame is reasonably short.

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546
COMBUSTION EQUIPMENT



SAMPLE SOLUTION.
PRESSURE =5 in. we
REQUIRED INPUT =
30,000 Btu/hr
USE NO. 41 DS
ORIFICE






pr-15
— —
—
—10
, \ n
s _ 9 ^
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BASED ON EQUATION _/T~
(FROM ACTUAL FLOW Q=1326 A 1 G
TESTS)

WHERE:
Q DISCHARGE, scf/hr
A = AREA OF ORIFICE, in.2

H ^PRESSURE, in. we
G=SPECIFIC GRAVITY
OF GAS (G = 0.65)





300 -g
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           Figure  391.   Natural  gas  flow through standard orifices for  pressure  in  inches water column.
           (Southern California  Gas  Co.).

-------
                                        Gaseous and Liquid Fuels
547
SAMPLE SOLUTION:
GAGE PRESSURE
= 3'2psi
0.50 -g — 1/2"
__:
REQUIRED DISCHARGE = ±
400 ft3/hr :|
USE NO. 17 OS ORIFICE













(/)
Q.
LlJ
cr
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CO
CO
1 1 1
CC
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—
—1000
^800

rnn
— 600
—500 ___ _
==400 ~~

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~ ortn
r~200
n
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—


=-100
ir-80
— 60
^50
|-40
—
i-30

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— B
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	 7
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— 6
— 5




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-E
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On M ~~
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— 7/16"
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= 	 3/16"
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o
















  Figure 392.  Natural  gas flow through  standard orifices for pressure in pounds  per  square  inch. (Southern
  California Gas Co.).
234-767 O - 77 - 37

-------
548
        COMBUSTION EQUIPMENT
OIL
Figure 393.  Low-pressure,  air-atomizing  oil burner
(Hauck Manufacturing Co.,  1953).
With the high-pressure, steam- or air-atomiz-
ing burners  of Figure  394,  an auxiliary fluid--
steam or air--is used to break up the fuel oil
stream at the burner tip.   The auxiliary fluid,
moving at high velocity, atomizes the slower
moving oil stream as the mixture passes into
the burner tile.   The atomizing fluid is  provided
at pressures'ranging from 30 to 150 psig.  The
volume of atomizing air, when used, is normally
much smaller than that encountered with low-
pressure, air-atomizing burners.  Compressed-
air consumption ranges from 30 to 200 cubic
feet of free air  per gallon of oil,  that is,  from
2 to 14 percent  of the theoretical combustion
requirement.  These burners are reasonably in-
expensive and are likely to  be employed where oil
is burned only  infrequently,  as  on a  standby
basis.  Steam-atomizing burners perform satis-
factorily at viscosities of 150 to 200 Sabolt Sec-
onds Universal  (hereafter referred to as SSU).
Air-atomizing burners require lower viscosi-
ties, usually 80  to 100 SSU.

High-pressure oil-atomizing burners depend upon
high fuel pressure (75tol50 psig) to cause the oil to
break up into small droplets upon passing through
an orifice.  The fixed  orifices of these units  are
considerably smaller than those used with other
                     HOLE FOR PILOT TIP
                                        TILE
        CLEAN-OUT PLUG
  OIL VALVE   /   PACKING
   OIL  INLET
             STEAM OR COMPRESSED
             AIR INLET
AIR
REGISTER
-MOUNTING
 PLATE
    Figure  394.  High-pressure,  steam- or air-
    atomizing oil  burner  (North  American Manu-
    facturing Co.,  1952).
                         types of oil burners. An inherent disadvantage is
                         that the burner atomizes properly only over a fair-
                         ly narrow pressure range.

                         Mechanical atomizing  burners are the most com-
                         mon oil burners found at large power plant steara
                         generators.   In the wide-range mechanical atom-
                         izing assembly shown  in Figure 395, the fuel oil
                         is given a strong whirling  action before it is re-
                         leased through the orifice.   Proper  atomization
                         is dependent  upon centrifugal velocities,  which in
                         turn require  high pressures, that is, 100 to 200
                         psig.  The wide-range unit of Figure 396 over-
                         comes a principal disadvantage  of this  type burn-
                         er, namely a narrow turndown ratio.  In the burn-
                         er,  some  of the whirling oil flows through the ori-
                         fice while excess oil is  drawn off through the cen-
                         tral oil return line.
                           Figure  395. Wide-range mechanical  atomizing
                           burner(de  Lorenzi,  1947).
                                         TIP
                                         PLUG  BARREL
                                                                                            COUPLING
FERRULE VGASKET
                           Figure 396.  A wide-range mechanical-atomizing
                           assembly with central  oil  return line(de Lorenzi
                           1947).

-------
                                          Gas and Oil Burners
                                             549
 Rotary cup burners,  such as  that shown in Figure
 397,  provide atomlzation by centrifugally throw-
 ing the fuel from a rotating cup or plate. Oil is
 distributed on the cup in a thin film.  As with oil
 pressure atomizing burners,  no air is mixed with
 the oil before atomization.  Combustion air is ad-
 mitted through an annular port around the rotary
 cup.   These burners  are  usually constructed with
 integral forced-draft blowers.  A common motor
 often drives the oil pump, rotating  cup,  and blower.
 Rotary cup burners can be used to burn  oils of
 widely varying viscosity, ranging from distillates
 to residuals of greater than 300 SSU.
            MOUNTING
            HINGE
      MOTOR
OIL-
     Figure  397. Rotary cup oil burner (Hauck
     Manufacturing Co.,  1953).
 Viscosity and Oil Preheaters
 The key to optimum oil burner operation is care-
 ful control of fuel viscosity.  A given burner func-
 tions properly only if the  viscosity at the burner
 orifice is held between fairly narrow limits.  If
 the viscosity is too high,  effective atomization
 does  not take place.  If the  viscosity is too low,
 oil flow through the orifice  is too great, upsetting
 the balance between combustion air and fuel.
 There are several viscosity measurement  scales.

 At viscosities  of less than 100 SSU, fuel oils can
 be burned efficiently in almost any burner.  Most
 burners are designed for  optimum performance
 at 150 SSU or lower.  All distillate  oils and some
 blends  are of less than  100  SSU at 60°F,  as shown
 in Figure  398.  Where fuel  oil viscosity at am-
 bient temperature is not compatible with the burn-
 er, preheaters are  used.   With the  chart provided
 in Figure  398, fuel  oil viscosities can be estimated
 at different temperatures.  The sloped lines rep-
 resent  fuels with  average viscosity-temperature
 relationships.   When the viscosity at a given tem-
perature is known,  viscosities at other tempera-
tures can be predicted by extending lines of paral-
 lel slope.   The chart also allows  conversion from
 different viscosity scales.
 Oil preheaters may be mounted directly on the
 burner, at the supply tank, or just about any
 place in between.   Preheater selection is depen-
 dent  to a large degree upon the fuel itself.  Most
 heavy residual oil must be warm to allow pump-
 ing.  A preheater for such oil is likely,  therefore,
 to be located at or near the supply tank.  With
 lower viscosity oils,  preheaters are  often located
 at the burner,  preheat temperatures  are lower,
 and the heaters are normally smaller and less
 complicated.

 Oil preheaters are operated with either electricity
 or steam.  Electrical heaters  allow a greater de-
 gree  of flexibility.  They can be used at times -when
 the combustion equipment is cold and no steam is
 available.  Where only steam preheat is used,  an
 auxiliary source of steam independent of the com-
 bustion equipment on which the burner is located
 should be available. If an oil burner  is ignited
 from a cold start,  and the oil is not preheated to
 its normal  temperature,  igniting the burner is
 often difficult  or impossible.   Excessive air con-
 taminants can be expected from this practice.
 THE AIR POLLUTION PROBLEM

 The burning of combustion fuels can produce sul-
 fur oxides, inorganic ash, oxides of nitrogen,
 carbon,  and unburned and partially oxidized hy-
 drocarbons.  Most of these contaminants,  notably
 sulfur oxides and inorganic ash, are attributable
 directly to the fuel and  are independent of equip-
 ment design or operation. The principal air con-
 taminants affected by burner design and operation
 are oxidizable materials--carbon,  carbon  monox-
 ide, aldehydes,  organic acids,  and unburned hy-
 drocarbons.  To a lesser degree, burner design
 can also  affect oxides of nitrogen, particularly in
 large steam power plant boiler s .   Burner firing
 changes,  for example,  firing through use of off-
 stoichiometric combustion techniques,  can reduce
 oxides of nitrogen.  This technique is discussed
 later in this chapter under air pollution control
 methods for oxides of nitrogen.
Smoke and Unburned Contaminants

Modern burner equipment has been perfected to
the point where all common fuels can be burned
without causing excessive discharges of oxidiz-
able materials in exhaust gases. If the proper
combination of burner and fuel has  been selected,
and if the burner is operated properly, no visible
emissions should be caused by oxidizable air con-
taminants,  and the concentrations of items such
as aldehydes and carbon monoxide  should be neg-
ligible.  Nevertheless,  smoke and  oxidizable mate-
rials are often found in  burner exhaust products.

-------
550
COMBUSTION EQUIPMENT

-------
                                                   Gas and Oil Burners
                                                                                                                        551
                                VISCOSITY  TEMPERATURE  RELATION FOR  FUELS
Description of the  Chart

  The horizontal scales at  the top and bottom of the chart
are identical  and represent  temperature,  both in  degrees
Fahrenheit and  Centigrade.
  The vertical scales  represent viscosity in  terms  of  the
several methods of measurement now in common use. These
scales appear opposite  the  temperatures at which each cus-
tomarily is standardized for measuring liquid fuels; namely—
         Vi\ity Measurement
           Saybolt Universal

           Saybolt Furol

           Engler Degrees


           Redwood No. 1
            Redwood No. 2
              (Admiralty)
            Kinematic
  Temperature

   at IOO°F.
      210°F.
   at  77°F.
      122°F.
   at  20°C.
       50°C.
      IOO°C.
   at  70°F.
      IOO°F.
      140°F.
      200°F.
   at  77°F.

at both edges
  Conversion of viscosity from one unit to another by means
of the chart is reasonably accurate for all practical purposes.
Caution should be used, however, when using  the chart to
convert a  given viscosity unit to kinematic viscosity at vari-
ous temperatures. The reason for  this lies in the  fact that
the conversion  factors to  kinematic vary  slightly with tem-
perature and therefore, a single kinematic scale cannot  be
precise  at  all  temperatures. The  approximate  values  ob-
tained  from the chart, however,  should  be sufficiently accu-
rate for  practical  purposes,  such  as  finding  the  proper
atomizing  temperature or  limits  of  pumpability  in  this
viscosity unit. For a more precise conversion from Redwood,
Saybolt or  Engler  units  to  kinematic  viscosity, reference
should be  made  to  the specific conversion factors usually
found  in technical handbooks covering  flow of fluids.
  Viscosity, of course, decreases with  increase in  tempera-
ture. The  diagonal lines, accordingly, represent the average
slopes  in viscosity encountered with bunker and diesel fuels,
respectively.  As the chart is prepared  logarithmically, the
slopes  appear as two groups of straight  parallel lines.  While
these  particular  slopes will  not  hold  with all oils,  they  do
serve  as a  good index in the majority  of cases, and should
therefore  prove  sufficiently  accurate  for  most  practical
purposes.
  The dotted  horizontal  lines  in  the  right section  of the
chart  indicate the ranges of viscosity recommended  for best
atomizing  fluidity  by  American burner manufacturers.  In
Saybolt Universal measurement, the top  line represents  200
seconds; the center line  150 seconds;  the bottom  line  100
seconds. To obtain proper atomization with most  installa-
tions,  viscosity  at the burners should fall within the  upper
range  for  forced  draft, and  within  the lower range  for
natural  draft. This  rule, however,  has  certain important
exceptions  in the case of European  burner practice as ex-
plained on the chart.
  The dotted horizontal lines in the upper left  section indi-
cate the maximum range of viscosity which will assure free
and efficient pumping.  These lines represent,  respectively,
400 seconds and 500 seconds Saybolt Furol. When equipped
for heavy-duty transfer, in which suction head is not a prob-
lem, it is  possible to pump without  difficulty at the  upper
limit,  or even  above in some instances. However, it is pre-
ferable not to allow  viscosity to exceed the lower  limit.
To Find Viscosity at
Different Temperatures

  Knowing the viscosity  of an prl in one  scale at one tem-
perature, to determine its viscosity in the same or a different
scale at a different temperature  the procedure  given  in the
following example is used.
  Let us assume a diesel  fuel having a known viscosity Red-
wood No.  I  (at  I(M)°F ) of 44.7 seconds. This viscosity is
indicated by  point "O".
  Through "O" we draw  the line  E-E parallel to the nearest
diagonal. The line E-E intercepts Redwood No. 1 again at
"Q" (7()°F.) showing 64 seconds,  and at "S" (140°F.)  show-
ing 35.2 seconds  It also intercepts  Engler at "P" (20°C.)
showing  2 26 degrees, and  at  "R" (50°C.) showing  1.382
degrees.  In  this  particular  case, the only  interception  of
Saybolt  Universal which would fall  within  the  chart is
likewise at "O" ( 1()()°F ) showing 50 seconds.
  In a like manner,  viscosity conversions  between different
scales and  standardized temperatures can  quickly be  found
from any other known viscosity.
To Find the Proper
Atomizing Temperature

  Let us assume  that you have  a  bunker fuel oil  having a
viscosity  of  150 seconds Saybolt  Furol (at 122°F.). Through
this point draw the parallel "A-A".  The same line, of course,
would apply if we  assumed the same  oil,  knowing its  vis-
cosity only in terms of one of the other scales, such as 3500
seconds  Saybolt Universal (at 100°F.).
                                   The line  "A-A"  intercepts  the  upper and  lower ranges
                                 of atomizing viscosity between  "Y-X"  and "X-Z",  respec-
                                 tively. Temperature ranges corresponding to these viscosity
                                 ranges are then  readily found  by laying a straight-edge ver-
                                 tically on  the chart  and noting the points  "C",  "B" and
                                 "D"  on the top and bottom temperature scales. In  this case,
                                 the temperature  for 200  seconds Saybolt Universal viscosity
                                 is I93°F; for 150 seconds it is 207.5°F. and  for 100 seconds
                                 232.8°F. The atomizing  range would be 193-207.5°F. for
                                 forced draft  or  207.5-232.8°F. for  natural  draft.
                                    As a general  rule,  the lower the viscosity, the better the
                                  atomization: hence, where  difficulty  is experienced in ob-
                                  taining complete  combustion, as  evidenced  by  excessive
                                  smoke, or by dry soot  which sometimes is noticeable even
                                  with a clear stack,  it  may prove advisable  to operate in the
                                  higher temperature (lower  viscosity)  range with forced as
                                  well as natural  draft. Severe cases may  require raising the
                                  oil temperature  to  correspond to  the point of  lowest  prac-
                                  ticable  atomizing viscosity  (the interception of the lowest
                                  dotted line). However,  engineers  must be guided  by pre-
                                  vailing conditions. No fixed rule will  apply in all instances.
                                  To Find the Limit
                                  of Pumping Temperature

                                    Let us assume a Grade "C"  bunker  fuel oil  having a
                                  known viscosity Saybolt Furol (at I22°F.)  of  150 seconds.
                                  Through this point we draw  the parallel "A-A".  The tem-
                                  peratures "F" and "G" corresponding to the points of inter-
                                  ception  "T"  and  "U" are  found in the same manner as
                                  described above.
         Figure 398  (continued).   Viscosity-temperature  relation  for fuel oils.
         the  copyright  owner, Esso Research  and Engineering Co.,  Linden, N.J.).
                                                       (Reprinted by permission of

-------
552
COMBUSTION EQUIPMENT
The problem is almost always traceable to the
same origins,  that is,  the burner and fuel are
not compatible, or the  burner is not properly ad-
justed or operated.

Oxidizable emissions depend upon the degree to
which performance falls below the optimum capa-
bilities of combustion equipment.  Actual per-
formance is, however, a difficult thing to predict.
A  survey (Chass and George,  I960) of gas- or oil-
fired equipment in the  Los Angeles area was made
on this subject.  The fuel  oil was produced from
California crude stock  and ranged from 8. 0 to
45. 1  API gravity with sulfur contents  varying
between  0. 10 and 1. 6 percent by weight.  Some 27
representative equipment  items,  ranging from a
small water heater to an 370-horsepower boiler,
were tested for combustion  characteristics as
well  as air pollutants.  No attempts were made
to adjust the equipment before the tests; the data
reflected,  therefore, what can be considered
normal operation.

Thirteen of the equipment items tested were fired
alternately with both gas and oil, oil  being the
standby fuel.   Four items were fired only with
fuel  oil and 10 only with natural gas.   Natural gas
is the predominant fuel in the test area.  Curtail-
able gas users do not normally burn  standby fuel
more than 20 days in a given calendar year.  Dur-
ing some winter seasons, small users have not
been curtailed at all.  Thus, oil burning was not
an everyday occurrence in most  of the gas- or
oil-fired equipment tested.

The  survey disclosed some  points that would have
been anticipated and others  that would not.  Table
148  summarizes emission factors developed from
the data.

 The most surprising indication was that the fine-
 ness of combustion control  was much less when
 natural gas rather than fuel oil was used for fir-
 ing.  This "was shown  by the prevalence of car-
 bon  monoxide  and the  wide  variation  in fuel-air
 ratios during gas firing.  In contrast, only negli-
 gible carbon monoxide was  measured during fuel
 oil burning,  and fuel-air  ratios were held to much
more constant figures.  The same equipment found
                 to emit appreciable carbon monoxide on gas  firing
                 discharged essentially no carbon monoxide (0. 003%)
                 when burning heavy fuel oil.  In addition, combus-
                 tion efficiencies were better -when high-viscosity
                 fuels (less than 17° API) rather than low-viscosity
                 fuels (greater than 28°  API) were burned. Appar-
                 ently then, surveillance by the operator is a func-
                 tion of the complexity of burning the particular
                 fuel.  With a relatively easy-to-burn fuel such as
                 natural gas,  attentiveness can be expected to be
                 minimal;  while with high-viscosity oils, burner
                 control will be most  favorable.   This phenomenon
                 is probably peculiar  to areas  where natural  gas  is
                 the predominant fuel and would be difficult to pre-
                 dict for other areas.

                 This situation may be due in part to the fact that
                 smoke serves as a better alarm on oil  firing.
                 Smoke is  likely to be emitted  on oil firing when
                 combustion is only moderately inefficient.  An
                 operator would be expected to notice visible emis-
                 sions from the stack and make corrections  at the
                 burner.  During gas  firing, smoke does not  occur
                 unless combustion is markedly  incomplete.   A
                 gas-fired burner can emit appreciable  carbon
                 monoxide without imparting perceptible opacity
                 to products of combustion.  Thus, a gas burner
                 operator  can well be ignorant of the fact that his
                 equipment is not functioning efficiently.

                 As would be expected,  the survey showed that
                 emissions of particulate matter were appreciably
                 higher during oil burning.  Oil burning produced
                 almost 10 times more particulates than natural
                 gas burning did.  There was little measured dif-
                 ference in particulate emissions between distillate
                 and residual oil burning,  even though the residual
                 oils  contained  appreciably more inorganic ash.

                 In addition, the data showed,  surprisingly,  that
                 distillate oils produced slightly greater quantities
                 of aldehydes than residua] oils  did, probably be-
                 cause of the poorer  combustion efficiencies en-
                 countered with  light oils.  Natural gas produced
                 appreciably lesser aldehydes, even though com-
                 bustion efficiencies  in general were lower,  as
                 measured by the presence of  carbon monoxide.
                 During gas firing, high carbon  monoxide values
                 were generally accompanied by greater aldehyde
  Table 148.  EMISSIONS FROM GAS-FIRED AND OIL-FIRED EQUIPMENT (Chass and George,  I960)
Furl
burned
Natural gas
Light oilb
I leavy oil1
Hemb
tested
23
10
7
Carbon monoxide
Maximum, %
6. 400
0 020
0. 001
No. -> 0. 9%
3
0
0
No. > 0. 09%
5
0
0
Ib/equivalent barrel of fuel oila
Particulate matter
Range
0. 013 to 0.353
0. 126 to 1. 720
0. 420 to 1. 220
Average
0. 077
0. 735
0. 750
Aldehydes as formaldehydes
Range
0. 017 to 0. 191
0. 042 to 1. 008
0. 042 to 0. 462
Average
0. 068
0. 185
0. 160
Light oils ranged from 28. 7 to 45. 1 API gravity.
' 1 leavy oils ranged from 8. 0 to 16. 5 API gravity.

-------
                              Boilers,  Heaters^ and Steam Generators
                                                                                                  553
concentrations.  In no case, however, did alde-
hyde concentrations exceed 25 ppm (as formal-
dehyde) •when natural gas was burned.
Ash and Sulfur Oxides

Stack discharges of sulfur oxides and ash are
functions of fuel composition.  During gas firing,
both contaminants are well below nominal air
pollution control standards.  During firing of oils
produced from California crude stock,  the inor-
ganic ash content  of combustion gases is  normally
less than 0.1 grain per scf,  but sulfur oxide con-
centrations can be appreciable. Regulations
limiting stack emissions  of sulfur  and the sulfur
content of fuels have been enacted  in several
areas of the United States, as noted in the pre-
ceding part of this chapter.  Regulations on par-
ticulate matter are aimed collectively at both in-
organic ash and combustible solids.   When exces-
sive emissions are encountered during oil firing,
carbon and other oxidizable  particulates usually
predominate.
Oxides of Nitrogen

Combustion processes as a group represent the
major stationary source of oxides of nitrogen in
most communities,   Concentrations in products
of combustion range from less than 10 to over
1, 000 ppm by volume,  measured as nitrogen di-
oxide.  Concentrations appear to be a function of
temperature and firebox design.  The smallest
concentrations are found at small appliances in
•which there is appreciable excess air at the burn-
er.  The largest concentrations are found in gas-
es from the largest combustion  sources --steam
power plants, which are operated at high
temperatures.  Combustion equipment of less
than 20 million  Btu  per hour gross input does not
normally emit NOX  in concentrations greater than
100 ppm.   This subject is covered  more complete-
ly in the next part of this chapter.
 AIR POLLUTION CONTROL EQUIPMENT

 Wherever control equipment is considered for
 combustion processes, it is  almost always  for
 controlling nonoxidizable materials,  notably ash
 and sulfur oxides.   If unburned and partially burned
 hydrocarbons or carbon particulates are the prin-
 cipal contaminants, the normal procedure is to in-
 crease combustion  efficiency rather than collect
 these materials at the stack.  An efficient burner
 is, therefore, the best and most inexpensive means
 of controlling combustible air contaminants.
 BOILERS, HEATERS, AND STEAM GENERATORS

 INTRODUCTION

 Boilers, heaters,  steam generators, and similar
 combustion equipment fired with fossil fuels are
 used in commerce and industry to transfer heat
 from combustion gases to -water or other fluids.
 The only significant emissions to the atmosphere
 from this equipment in normal operation, regard-
 less of the fluid being heated or vaporized,  are
 those resulting from the burning of fossil fuels.
 Differences in design and  operation  of this equip-
 ment can,  however, affect production of air  con-
 taminants.

 A boiler or heater consists essentially of a burn-
 er,  firebox, heat exchanger, and a means of cre-
 ating and directing a flow  of gases through the unit.
 All combustion equipment--from the smallest
 domestic water heater to the largest power plant
 steam generator—includes these essentials.  Most
 also include some  auxiliaries.   The number  and
 complexity of axixiliaries tend to increase with
 size.  Larger  combustion equipment often includes
 flame  safety devices,  soot blowers, air preheaters,
 economizers,  superheaters, fuel heaters, and
 automatic flue  gas  analyzers.

 Inasmuch as coal is not used as boiler fuel in Los
Angeles  County,  this discussion is limited to boil-
 ers, heaters,  and power plant steam generators
fired with gas  or fuel oil.

 Industrial Boilers and Water Heaters

 The vast majority  of combustion equipment is used
 to heat or vaporize water,  or both.  For conve-
 nience, industrial water heaters are considered
 together with boilers inasmuch as identical equip-
 ment is frequently used for both purposes.  These
 boilers and heaters fall into three general classi-
 fications:  Fire tube, water tube, and  sectional.

 Fire tube boilers constitute the largest share of
 small  and medium-size industrial units, includ-
ing the Scotch marine and firebox types, as shown
 in Figures 399 and 400.  In fire tube boilers, the
products of combustion pass through the heat ex-
 changer  tubes, while water, steam,  or other fluid
is contained outside the tubes.  Many boilers such
as these are sold as packaged units, with burners,
blowers, pumps, and other auxiliaries  all mounted
 on the same framework.

Water tube boilers are constructed in a wide range
 of sizes.  Both the smallest and largest industrial
units are likely to be of water tube design and,
in fact, all large boilers (steam generators) are
of this type.  The smallest units are of simple
box construction,  commonly using tubing to cir-
 culate  water and  steam.  In the -water tube design

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 554
                                      COMBUSTION EQUIPMENT
 Figure 399.  A three-pass, Scotch-marine boiler.  (Ray
 Burner Co., Boiler Division, San Francisco, Calif.).
boilers have.  In all water tube boilers, the water,
steam, or heat transfer medium is circulated
through the tubes while hot products of combus-
tion pass outside the tubes.

Sectional boilers employ irregxilarly shaped heat
exchangers and cannot be classed as either -water
tube or fire tube.  Hot combustion gases are di-
rected through some of these passages, transfer-
ring heat through metal walls to water or  steam
in the other passages.  These units  are manu-
factured in identical sections,  such  as those  shown
in Figure 403, which can be  joined together accord-
ing to the needs  of the  operator. A  sectional boil-
er consists of one or more sections and can be en-
larged or reduced by adding  or  removing sections.
The heat exchanger assemblies are  usually fabri-
cated  of cast  iron.  For this  reason these boilers
are not suitable  for pressures  greatly exceeding
15 psig.  Cast iron sectional boilers find frequent
use as water  heaters and steam generators used
in conjunction with space heating and laundries.
                                    u
Figure 400.  A fire-tube boiler  with a refractory-lined
firebox.  (Erie, City Iron Works, Erie,  Pa).
shown in Figure 401, fluid is heated under pres-
sure in  a coil heat exchanger and flashed into
steam in an external chamber.  These relatively
small, controlled-circulation boilers are  capable
of producing steam within minutes after a cold
start.  Industrial water tube boilers, such as that
shown in Figure 402, are usually constructed -with
comparatively larger fireboxes than fire tube
 Power Plant Steam Generators

 The largest boilers are located at steam power
 plants where  high-pressure, superheated steam
 is used to drive turbo-electric generators.  These
 water tube  units are commonly termed steam
 generators.  Nevertheless, there is no definite
 size limitation for equipment such as this, and
 steam generator designs do not differ markedly
 from those of many smaller  industrial boilers.
 Power plant steam generators  produce from
 50, 000 to 5 million pounds of steam per hour at
 up to 2, 500 psig and 1, 000°F.  A typical medium-
 sized power plant steam generator consumes
 2, 500, 000 cubic feet of natural gas per hour or
 450 barrels of fuel oil per hour,  exhausts some
 700, 000 scfm combustion products and furnishes
 all the steam required to drive a 310, 000-kilowatt
 electric generator.

 A conventional front-fired power plant steam gen-
 erator is shown in Figure  404.  It is equipped with
 the full line of boiler auxiliaries:  Air preheater,
 oil heater,  economizer,  superheaters, and other
 equipment.  As much heat  as is practical  is ex-
 tracted from  combustion products.  Stack tempera
 tures as low as 225°F  are  normally maintained.
 Condensation  and resultant corrosion are  the
 principal deterrents  to lower power plant  tempera-
 tures.   When  exhaust gas temperatures approach
 the dew point, condensation and visible stack
 plumes are encountered.

Steam generators operate with  thermal efficiencies
of about 90 percent, and operating variables are
more carefully controlled than in any other type  of
combustion  equipment.  Of prime concern is the
excess air rate. Any air above the theoretical re-

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                       Boilers, Heaters, and Steam Generators
555
                       ELECTRIC CONTROL LINE

                       J CIRCULATING LIQUID LINE
Figure 401.  A  forced-circulation boiler with a coil water  tube  heat exchanger and an
external flash chamber-accumulator (The Clayton Manufacturing Co.,  El  Monte,  Calif.).
   Figure  402.  An industrial water  tube  boiler  (The Babcock and Wilcox Co., New  York).

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 556
COMBUSTION EQUIPMENT
    Figure 403.  A  cast  iron sectional  boiler
    (Crane Co.,  Johnstown, Pa.).
quirement represents a thermal loss,  but the fire-
box oxygen concentration must nevertheless be
sufficiently high to provide near perfect combus-
tion.  Power plant operators hold excess air rates
during fuel oil firing as low as feasible by provid-
ing strong mixing conditions and optimum fuel oil
atomization at the burner.   During gas firing,  ex-
cess air rates are about 10 percent above the the-
oretical requirement.  When fuel oil is burned,
excess  air is  usually held below  15 percent.  At-
tempts  have been made to operate with excess air
rates as low as 1  percent (about  0. 2 percent oxy-
gen) on oil firing (Glaubitz, 1963). The benefits
from this practice are reduced corrosion,  less
air contaminants, and  increased thermal efficien-
cies .


Refinery Heaters

Refinery oil heaters are noteworthy inasmuch as
they usually comprise  large combustion units and
are likely to be fired with a -wide variety of, re-
finery by-product fuels,  both gaseous  and liquid.
These fuels can be the least saleable refinery
products,  notably heavy residual oils and high-
sulfur-bearing gas streams.  The gaseous  fuels
are usually mixtures that for one reason or another,
are not marketed or further processed.   Typical
analyses of refinery make  gases are included in
Table  143.   Note  that  they can contain
appreciable amounts of sulfur, hydrogen, carbon
monoxide, and higher  molecular "weight hydrocar-
bons.   The latter are responsible for the.relative-
ly high heating values  of refinery make  gases.
                Petroleum process heaters are apt to be fired with
                the highest viscosity oil fuels produced at a re-
                finery.  Residual fuel oils have traditionally been
                difficult to market; consequently, operators pre-
                fer to burn as much of these as possible in their
                own equipment.

                In most refinery heaters,  such as those shown in
                Figures 405 and 406,  an oil or  other petroleum
                product flows  inside the heat exchange tubes.  Fire
                tube oil heaters find only occasional use.  These
                heaters,  like all other refinery equipment,  are
                normally operated 24 hours a day,  7 days a week.
                They are not likely to be shut down, except  dur-
                ing periods of inspection and repair.  Hot fuel
                oils are almost  always available, and there is
                little likelihood  of having to start a  cold heater
                with unheated, high-viscosity fuel oil.

                Hot Oil Heaters and Boilers

                In a number of industrial combustion equipment
                units, a stable heat transfer oil is heated or
                vaporized. Some of these  units are simple water
                tube boilers in which the heat transfer oil mere-
                ly replaces water.  Others are custom  designed
                for the particular oil and application.  These
                boilers, most often found in the chemical pro-
                cess industries, are used  to transfer heat to
                another fluid in  a heat exchanger device.  Their
                principal advantage is the  lower vapor pressures
                (higher boiling points) of the stable  organic  oils
                as compared with that of water.  Most have boil-
                ing points between 300°  and 800°F.  In this
                range,  the compounds, whether gases  or liquids,
                exhibit markedly less vapor pressure than steam
                does  at the same temperature.

                The most common heat transfer medium is  Dow-
                therm A, * a mixture of diphenyl  and diphenyl ox-
                ide, with a boiling point of 495°F at 14.7 psia
                (Dow Chemical  Co. ,  1963).  A number  of other
                oils are also marketed. Almost any liquid  that
                is stable at the  required elevated temperatures
                and has a suitable vapor pressure curve would be
                satisfactory for this use.  Most of  these materials
                are not highly toxic.   Moreover,  they  are not
                emitted to the atmosphere in quantities sufficient
                to cause an odor nuisance  or health hazard  ex-
                cept for in«tances of equipment failure or gross
                disrepair. Some oils have sharp,  penetrating
                odors that can be detected in the boiler room.
                These  odors  can be an annoyance to plant person-
                nel.


                Fireboxes

                Stack emissions from heaters and boilers are in-
                herently tied to the fuels and burners,  as noted in
                Registered Trademark of the Dow Chemical  Company.

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                               Boilers, Heaters,  and Steam Generators
                                              557
                                                                                    INDUCED DRAFT
                                                                                    UN
                  Figure 404.  A  front-fired power plant steam generator  (The Babcock and
                  Wilcox Co.,  New  York).
the preceding parts of this chapter.  Of prime air
pollution concern in the combustion equipment is
the firebox in which the burners are located. Most
fireboxes are constructed of such a shape and size
that the  burner flames are contained within the
firebox and do not impinge upon the firebox walls
or the heat exchange equipment.  Flame impinge-
ment on either heat transfer surfaces or firebox
walls usually results  in incomplete  combustion
and a marked increase in air contaminant emis-
s i on s.

The volume of the firebox is governed by the type
of flame and the heat  release rate.  Where flames
are luminous and relatively long,  allowable heat
release  rates are low as compared with those of
short, non-luminous flames.  Clean, gaseous fuels
can be burned at rates ranging up to 1 million Btu
per hour per cubic foot of firebox volume.  The
latter rate is possible only with strong mixing con-
ditions and necessarily high pressure drops across
the burner.  In practice, natural gas heat release
rates of 100, 000 Btu per hour per cubic foot and
lower  are more common.  When oil is burned,
even on a stand-by basis, heat release rates are
always below the latter figure.  The upper limit
for burning low-viscosity fuel oils is about
100, 000 Btu per hour per cubic foot of firebox
volume.  Heavy residual oils require greater
combustion space.  Design rates for residual-oil-
fired combustion fireboxes range from. 20, 000 to
40, 000 Btu per hour per  cubic  foot (The North
American Manufacturing Company,  1952).  Oil-
burning heat release rates often govern  firebox
design, even though gaseous fuels may be burned
in the  equipment most of the time.

Most fireboxes  of small and intermediate-size
boilers and heaters  are constructed  of firebrick
or refractory cement.  Some are of  metal con-

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558
COMBUSTION EQUIPMENT
                                                        Figure 405.  A large box-type  refinery  heater.
struction,  usually where firebox temperatures
are relatively low.  In large  installations, the
firebox,  which is often termed here a furnace,
is lined with water tubes or water walls through
which cooling water is circulated.  In these  de-
signs,  water must be circulated at a sufficient
rate to prevent heat damage to the metal walls
or tubes.  Much  of the heat transfer in the fur-
nace is  by radiation rather than convection.   Al-
most all large boilers, for example, steam  gen-
erators at power plants,  are constructed with
water-tube-lined fireboxes.

Soot Blowing

Whenever fuels  of measurable  ash content are
burned,  some solids, including both carbon  and
inorganic ash,  adhere to heat transfer surfaces in
the combustion equipment.  These deposits must
be periodically removed  to maintain adequate heat
transfer rates.   It is  common practice to remove
these deposits with jets of air or steam while the
combustion equipment is in operation.   The  re-
moved soot particulates are entrained in combus-
tion gases.  During periods of soot blowing,  par-
ticulate concentrations are, as would be expected,
considerably greater  than during normal opera-
tion.  Instantaneous particulate concentrations
vary greatly during soot blowing because of the
inherent operating characteristics  of the lances.
                 A typical long retractable  soot blower is shown
                 in Figure 407.  During operation the lance con-
                 taining the  air or steam jets rotates and moves
                 horizontally across the tube surface.   On the in-
                 stroke,  most of the particulates are removed.
                 Consequently, stack emissions  are heavier on the
                 instroke than on the outstroke lor a given lance.
                 Normally,  there are from 8 to  15 of these blow-
                 ers  on a large power plant's water tube boiler.
                 The blowers are usually operated in sequence, by
                 starting at  the front or upstream tube  surfaces and
                 "working downstream,  finally cleaning  the air pre-
                 heater.

                 Whenever residual fuel oils  or  solid fuels  are
                 burned in large steam generators, tube clean-
                 ing is usually conducted at least once during
                 every 24 hours of  operation.  When clean nat-
                 ural  gas fuels are burned, the same boiler or
                 heater can  be operated indefinitely without soot
                 blowing, except possibly for the air preheater.
                 In fact,  the burning of natural gas  gradually re-
                 moves materials deposited during  oil firing.  At
                 many highly integrated power plant boilers,  soot
                 blowers are operated  automatically, at 2- to 4-
                 hour intervals.  At many  older installations,
                 soot-blowing equipment is likely to be manual,
                 the  operation is time-consuming,  and intervals
                 between blowings  comparatively longer.  In the
                 latter cases, particulates are somewhat larger

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               Boilers, Heaters,  and Steam Generators
       559
                                                                         TO STUCK
                                                     OUT
                                                                     0000
                                                                  o o o o o o
                                                                   o o o o o
                                                                  o o o o o o
                                                                   O O O O '
                                                                                AIR PREHEAT
^1
    Figure  406. A vertical, cylindrical refinery heater (Union Oil  Co
    Los Angeles, Cal if.).
Figure 407.  A long-travel  retracting  soot  blower with  an air motor drive
(Diamond Power  Specialty  Corp.,  Lancaster,  Ohio).

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 560
                                       COMBUSTION EQUIPMENT
 and emissions during any one blowing are like-
 ly to be heavier in comparison with automated
 lancing operations.  Where soot blowers are
 manually operated, the tubes are not usually
 cleaned more than once per 24 hours of oil fir-
 THE AIR POLLUTION  PROBLEM

 Air contaminants emitted from combustion equip-
 ment  are described in the preceding parts of this
 chapter, covering fuels and burners.  Nevertheless,
 the size and design of combustion equipment greatly
 affect the quality and quantity of stack emissions.
 Most  air contaminants  in combustion equipment
 are formed in the firebox and are definitely influ-
 enced by firebox and burner design.  Tube sur-
 faces, without question, affect pollutants in that
 they collect enough particulates  to require lancing
 during periods of oil firing.

 Combustion equipment emits both visible and non-
 visible air contaminants.  Visible contaminants are
 principally liquid and solid particulates.  Nonvisible
 contaminants include nitrogen,oxides,  carbon mon-
 oxide,  and sulfur dioxide.   A material that strad-
 dles both categories is  sulfur trioxide,  the extreme-
 ly hygroscopic anhydride of sulfuric acid.
 Figure 408. Photomicrograph of  particulates
 collected during gas burning, IB.OQOX.
 Solid Parficulote Emission During Normal Oil Firing

 Where  combustion is most nearly complete,  in-
 organic ash constitutes the principal particulate
 emission.  The inorganic ash contents of most
 fuel oils and all gaseous fuels are normally well
 below the concentrations that would cause exces-
 sive particulate emissions.   As noted in the first
 part of  this chapter, an inorganic ash content of
 0. 1 percent in typical residual fuel oil results in a
 stack concentration of only 0. 03 grain per scf at
 12 percent  carbon dioxide.  Particulates  from re-
 sidual-oil firing are considerably larger  than those
 emitted during gas firing, as can be seen in Fig-
 ures 408 and 409.  Nevertheless,  particulates
 from oil burning are still principally in the sub-
 micron range and are in sufficiently large con-
 centration to cause  perceptible light scattering.
 Finely divided ash is considered a contributor to
 visible  stack plumes at a large power plant's
 steam generators.  Most of this material is in
the form of metal oxides, sulfates, and chlorides.
A spectrographic  analysis of a typical residual
 oil ash  is presented in Table 147.

 As  shown in Table 149,  over 85 percent of
 the particulates are less than 1 micron.  More
 than 98 percent are smaller than 5 microns. These
 data pertain only to equipment  in which combus-
 tion is most nearly  complete and where little car-
 bon or hydrocarbon is  present  in the ash.  If ap-
Figure 409.  Photomicrograph of particulates
collected  during  oil  burning, IB.OOOX.

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                                Boilers, Heaters, and Steam Generators
                                              561
 Table 149.  PARTICLE SIZE DISTRIBUTION OF
   TYPICAL MATERIAL COLLECTED FROM
     A STEAM GENERATOR STACK DURING
     THE BURNING OF  RESIDUAL FUEL OIL


Absolute filter
Millipore tiltcT
% in each micron range
0 to 1
86.6
88. 5
1 to 2
7. 3
7. 3
2 to 5
4. 2.
i. 3
> 5
1. 9
1. 9
Largest
particle size, [i
50
50
preciable amounts of carbon were present,  par-
ticles would be larger and possibly of different
shapes.

From this particle size distribution, two conclu-
sions  can be drawn:   (1) Visible opacities are high-
er than would be the case if particles "were noticeably
larger than 1 micron since maximum light scatter-
ing occurs at about 0. 7 micron;  (2) centrifugal dust
collectors are not effective in removing  particu-
lates from the gas stream. High-efficiency cen-
trifugal  collectors are not efficient in removing
particulates of less than 5 microns and are only
moderately so  in the 5- to 10-micron range.

Typical  regulations limiting airborne particulates
from combustion equipment allow a maximum of
0. 3 grain per  scf at  12 percent  carbon dioxide
(Rule  53b of the Los Angeles  County Air  Pollution
Control  District Rules and Regulations).   This in-
cludes combustible particulates as well as inorgan-
ic ash.  This limit may be exceeded when common
hydrocarbon gases or fuel oils are burned if ap-
preciable amounts of carbon or  carbonized high
molecular weight hydrocarbon materials,or both
are present.  The latter situation results from
either poor operation or incorrect selection of
burner and fuels.  In these instances, the result-
ing visible contaminants at the stack are black,
and are  apt to  exceed allowable  limits, most of
which are based on the  Ringelmann  Chart.

The shapes  of  carbon or combustible particulates
vary somewhat with fuels  and operating conditions.
If a light fuel oil or gaseous fuel is burned in a de-
ficiency  of oxygen, the  resulting carbon particles
are likely to be exceedingly fine.  If,  on  the other
hand,  these contaminants are the result of burning
heavy fuel oil with improper atomization, the car-
bon particles emitted are likely to be in the form
of cenospheres, as depicted in Figure 410.  Ceno-
spheres  are spherical,  hollow particles, essen-
tially the same as those produced during spray
drying.  Cenospheres have appreciably smaller
bulk densities  than solid particulates do  (MacPhee
et al. , 1957).

An operator  is  not likely to want to  discharge
carbon in either form,  or to have to control these
particulates  at  the stack.   When there is  evidence
of appreciably unburned particulates in combus-
tion gases,  steps should be taken to improve com-
    Figure 410.  Photograph with light  microscope
    of  cenospheres found in breeching  of  large
    oil-fired steam generator (Macphee,  1957).
bustion at the burner.   With high-viscosity oils,
these  steps can consist of using lower viscosi-
ties or increasing pressure drops across the burn-
er to provide proper atomization.

Soot-Blowing Particulates
At times when soot blowers are in operation, par -
ticulate matter concentrations in exit gases  in-
crease markedly.  Instantaneous concentrations
depend upon the dirtiness of tube surface and up-
on the rate at which the lance moves  across the
tubes.  Soot-blown air contaminants  can impart
excessive  opacities to  stack gases and cause
damage by acidified particulate deposition in im-
mediately  adjoining areas.  The air pollution po-
tential, in terms both of opacity and  nuisance,
increases  with the time interval between soot-
blowing operations.  Where tubes are blown at
2- to 4-hour intervals,  as is done on many mod-
ern combustion devices, there is little increase
in the  opacity of stack  emissions, and the small
sizes of particulates as well as the relatively
small  concentration reduce  the possibility of fall-
out damage.  Intervals  of 8  hours and longer be-
tween  tube lancings can result in excessive visi-
ble opacities as well as fallout damage.

Soot-blowing air contaminants are not considered
to be highly significant in the  overall air pollution
of a given  area,  inasmuch as  they are emitted only
for relatively short intervals  and tend to settle
close to the source.  They represent less than  10
percent of the total particulates emitted from an
oil-fired boiler.  Many operators avoid  technical
opacity violations by special scheduling  of soot-
blowing operations.  This involves  either more
frequent lancing  or the lengthening  of the total

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 562
            COMBUSTION EQUIPMENT
operation.  Neither course reduces overall air
pollution, but both can allow technical compliance
with air pollution control regulations involving
permitted opacities.


Sulfur Dioxide

As pointed out in the first part of this chapter,
practically all fuel-contained sulfur--upwards of
95 percent--shows up in exhaust gases as sulfur
dioxide, a colorless gas.  There is no •way of pre-
venting the formation of sulfur dioxide,  and con-
centrations  are functions of the fuel's sulfur con-
tent.  As undesirable as sulfur dioxide is,  it is,
nevertheless,  generally considered less obnoxious
than sulfur trioxide and the  odorous sulfides  and
mercaptans contained in the  fuel.

Sulfur Trioxide

Up to 5 percent of the total fuel's sulfur is con-
Verted to the higher oxide, sulfur trioxide, in
large combustion equipment.   The  volume of sul-
fur trioxide found in gases from power plant steam
generators  (5 to 50 ppm) is  considered to be a
principal cause of the visible plume often present
    3,500
    3,000
                             when high-sulfur fuel oils are used. Sulfur trioxide
                             readily combines with water to form sulfuric acid and,
                             as such, can cause acid damage in downwind areas .

                             The oxidation of sulfur is considered to proceed
                             in two  steps as follows:
                                                                SO.,
                             As shown in  Figure 411, equilibrium at ambient
                             temperatures strongly favors sulfur trioxide
                             rather than the dioxide.  At elevated tempera-
                             tures, the dioxide predominates.  The reaction
                             rate falls off rapidly, however,  below 700 °F; as
                             a result, the major portion of the fuel's  sulfur is
                             still in the dioxide form when discharged from
                             combustion equipment.

                             As might be expected, the degree of sulfur  tri-
                             oxide formation in combustion equipment varies
                             widely.  Concentrations are negligible in small
                             equipment,  even when fired with high-sulfur fuel
                             oils.  As equipment sizes  and firebox tempera-
                             tures increase,  sulfur trioxide  concentrations in-
                0.10
0 20
                                   0.30
0.40      0 50       0 60
VOLUME RATIO, S03/S03  + S02
                                                                         0 70
                                                         0.80
                                               0 90
1  00
             Figure 411.  Equilibrium concentrations of $03-802 at various oxygen concentrations
             as per the reaction  S02(i)  +  1/2 02(E)  - SOaCg). (Adapted from Hougen and Watson,
             1945).

-------
                                Boilers,  Heaters, and Steam Generators
                                             563
 crease appreciably though seldom exceeding 35
 ppm.  Heaviest emissions are found at the larg-
 est combustion sources--power plant steam
 generators.

 Formation of sulfur trioxide appears to depend
 upon several factors.  Concentrations tend to
 increase with increases in firebox temperatures
 and oxygen concentrations.  In addition,  oxida-
 tion catalysts such  as vanadium, iron,  and nickel
 oxides tend to increase SOj production.   Par-
 ticulates that adhere to tube surfaces usually
 contain appreciable quantities of all three of these
 catalytic materials.

 Crumley and Fletcher  (1956) ran a series of experi-
 ments on a small kerosene fuel furnace  from which
 they concluded that, for a given total sulfur oxide
 (SO2  + SO3) concentration:

 1.   SO^ formation  increases as flame tempera-
     tures are increased up to about 3, 150°F;

 2.   above 3, 150°F, SOj formation does not in-
     crease, that is, the SOj/SO^ rate   remains
     constant;
 3.  when flame temperatures are held constant,
     SOj formation  decreases  as the excess  air
     rate is reduced;

 4.   SOg formation  decreases  with coarser atom-
     ization.  This phenomenon may be a result of
     lower flame temperature.

 The work of Glaubitz (1963) generally agrees with
 these conclusions regarding small oxygen concen-
 trations  at the burner.   It is discussed later in this
 chapter.

 Sulfur trioxide is considered the principal cause
 of the visible plumes emitted from large power
 plant steam plant generators burning high-sulfur
 fuel oils.  It apparently unites with moisture in
 the air and with flue gases to form a finely divided
 sulfuric  acid aerosol.  Droplet condensation may
be enhanced by the presence of particulate mat-
 ter,  which provides condensation nuclei.

 These visible emissions are interrelated with so-
 called dew point  raising.  The presence  of sulfur
 trioxide  and sulfuric acid effectively results in a
 gaseous  mixture that appears to have a dew point
higher than would be predicted solely on the basis
 of the moisture content.  These dew point eleva-
tions  can exceed 200°F.  Figure 412 shows typi-
 cal dew points and sulfur trioxide concentrations
measured at an experimental oil-fired furnace
 (Rendle and Wilsdon, 1956).  Note that sulfur tri-
 oxide, in concentrations ranging from 5  to 25 ppm
by volume, increases the dew point  (about 115°F
based upon H2O alone)  by increments of  20°F and
 170°F respectively.  There are noticeable dif-
ferences  in published values of dew point eleva-
                100
                      ISO     200
                      ELEVATED DEI POINT,
   Figure 412. Dew point elevation  as  a  function
   of  sulfur  trioxide concentration  (Adapted
   from  Rendle and Wilsdon,  1956).
tion.  These are attributable in part at least to
the difficulties encountered in SOj  analysis.

Sulfur trioxide has a further disadvantage in that
it tends to acidify particulate matter discharged
from combustion equipment.  This is commonly
evidenced by acid spotting of painted and metallic
surfaces, as -well as of vegetation in the  down-
wind area.  Acid damage  is usually the result of
discharge of particulates  during soot blowing.

Excessive Visible Emissions

Combustion equipment has traditionally been  as-
sociated with visible smoke plumes caused by un-
burned carbon and organics.  With modern steam
generators, markedly incomplete  combustion is
a relative rarity.  Combustible air contaminants
are  seldom present in sufficient concentrations to
obscure visibility.   Nevertheless, visible plumes
of greater than 40 percent opacity are common at
large steam generators burning high-sulfur fuel
oils where there are only minimal quantities  of
unburned materials in exhaust  gases.  These
opaque emissions are commonly attributed to
finely divided inorganic materials, notably sul-
fur trioxide and inorganic particulates.

The  formation of visible plumes in  stack  gaset.
that  are practically devoid of unburned carbo-
naceous materials is not fully understood.  The
phenomenon is known  to occur only when  there
is appreciable sulfur in the fuel and when the
steam generator  is of relatively large capacity
  234-767 O - 77 - 38

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564
COMBUSTION EQUIPMENT
greater than about 60, 000 pounds of steam per
hour.  The plumes do not occur  during the burn-
ing of natural gas or low-sulfur,  low-ash fuel
oils.  At smaller power plants,  that is, those
with a  capacity of 50, 000 to 500, 000 pounds of
steam  per hour,  the opacity of exhaust gases does
not normally exceed 30 percent when the plant is
fired with residual oil of average sulfur content,
namely 1. 4 to 2. 0 percent. Steam generators  of
750, 000 pounds per hour and greater ratings can
be expected to emit gases of heavier than 40 per-
cent opacity when fired with oil of more than about
1. 0 percent sulfur.
Figure 413 illustrates the difference in visible
emissions from two identical side-by-side steam
generators on oil and gas  firing.  Both are rated
at 1, 200, 000 pounds  of steam per hour and are
of conventional front-fired design.  Stack tem-
peratures were  approximately 300 °F.  The unit
on the left was being fired with natural gas, and
there was no detectable opacity in the  exhaust
gases.  The identical unit on the right was being
fired •with fuel oil of  approximately 1. 6 percent
sulfur and was discharging gases of approximate-
ly 80 percent  opacity.  The visible  plume from an
oil-fired unit  such  as this normally varies from
white to brown,  depending upon weather  conditions
and the makeup of particulate matter.  In some
cases,  the visible plume appears to be detached
from the stack.   The gas stream immediately
above the stack outlet is clear or at least of low
opacity but becomes  opaque further downstream.
Apparently, cooling in the immediate stack dis-
charge area lowers temperatures below the dew
point, causing formation of extremely fine sulfur
trioxide and acid droplets.
  Figure 413. Exhaust gases from identical steam
  generators showing visible  plume  from oil-fired
  unit  (right) as compared with  clear stack of
  gas-fired  unit (left).
                 There is some difference of opinion as to the cause
                 of this  plume, but all evidence points to sulfur tri-
                 oxide as the principal determinant, with partic-
                 ulate matter as a possible contributor.  Observa-
                 tions have been made with residual fuel oils of
                 varying sulfur content.   In general, the fuels con-
                 taining greater percentages  of sulfur  were found
                 to produce heavier opacities.  Since low-sulfur
                 oils  also have lower ash contents,  there is less
                 particulate matter in stack gases during the burn-
                 ing of low-sulfur fuels as evidenced when opaci-
                 ties  are lowest or nonexistant.

                 Some trials  have been made  by injecting sulfur
                 trioxide into the relatively clean stack gases
                 from natural gas firing.   These experiments in-
                 dicate that definite visible opacity  can be imparted
                 at concentrations of 5 ppm SO^ by  volume and
                 greater.  Stack gases with 5 ppm SOj had an opac-
                 ity of approximately 20 percent.  An opacity of ap-
                 proximately 50 percent resulted  when the  803  con-
                 centration was increased to  15 ppm.   The test unit
                 was a 1, 200,000-pound-per-hour steam generator
                 from which there was no visible  plume during nor-
                 mal gas firing.  The stack gases during SOj addi-
                 tion appeared  •white when viewed with the sun at the
                 rear  of the observer and were not  unlike plumes
                 discharged from the same unit during oil firing.

                 There is evidence that "dirtiness, " that is,  ac-
                 cumulation of  deposits on tube surfaces,  also con-
                 tributes to opacity.  Identical side-by-side steam
                 generators have been observed to emit gases of
                 markedly different opacity when fired at the same
                 rate with the same fuel oil.  Invariably, the unit
                 with the thicker tube deposits is found to emit
                 heavier  visible emissions and to contain consider-
                 ably  larger 303 concentrations.  This phenomenon
                 indicates that  tube deposits are  effective in catalyt-
                 ically oxidizing SO^ to 803.   The deposits that
                 contribute to the "dirtiness" apparently are not
                 sufficiently removed by normal  soot-blowing proce-
                 dures.   To lower opacities and SO^ emissions ef-
                 fectively,  one should wash the tube surfaces with
                 an aqueous solution.  The cleaning of heat exchang-
                 er surfaces  in this manner requires that the unit
                 be shut down and allowed to cool beforehand.  At
                 most electric  power stations, steam generators
                 cannot be taken out of service often.   Consequent-
                 ly, tube washing is a relatively infrequent occur-
                 rence.
                 Oxides of  Nitrogen

                 Combustion equipment collectively represents the
                 largest nonvehicular source of oxides of nitrogen
                 air contaminants in most industrial areas.  In
                 Los Angeles County, where there is a high motor
                 vehicle density, boilers and heaters are still res-
                 ponsible for about 25 percent of  the total NOX
                 discharged to the atmosphere  and for about 80

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                               Boilers, Heaters, and Steam Generators
                                                                                                 565
percent of the total from all stationary sources
(Los Angeles County Air Pollution Control Dis-
trict, 1969).

Exhaust gas concentrations of oxides of nitrogen
range from  less than 10 ppm by volume for  small
gas-fired heaters to over 1000 ppm for large un-
controlled power plant steam generators.  Since
both concentrations and gas volumes increase
with size, power plant steam generators are
always large sources  of NOX.  These generators
are much more significant  in the overall air pol-
lution picture than the markedly large number of
domestic  and industrial heaters  and boilers.  As
shown in Table 150,  there is a wide variation in
NOX emissions, even from equipment of the same
general type and size.   The table does not include
power plant generators  over 250 megawatts.
Recent uncontrolled power  plant generators hav-
ing heat inputs up to 9 billion Btu/hr have NOx
concentrations as high as 1000 ppm during gas
firing.

Emissions of NOX from combustion equipment
result from fixation of atmospheric nitrogen in
the burner primary flame zone.   The principal
high-temperature reaction is the formation of
nitric oxide as follows:
                  +
                               2 NO
The reaction depends upon high temperatures
and occurs at an appreciable extent in power
plant furnaces only at temperatures above 3,200
Much of the nitric oxide is eventually further
oxidized to nitrogen  dioxide:

                               -NO2
The latter reaction reaches a maximum at about
600°F and is extremely slow at ambient tempera-
ture.  Nitrogen dioxide is considerably more
reactive than nitric  oxide,  and is a more obnox-
ious air contaminant.

A number of other oxides of nitrogen also are
formed to lesser degrees.  These include N2O,
N2O4, N2C>5, and NO3, but these are not con-
sidered to be emitted  in significant amounts.   For
purposes  of this discussion, all oxides  of nitrogen
are considered collectively under the term NOX.
In the quantitative analysis of oxides of nitrogen,
all  oxides are commonly oxidized to the dioxide.
Results are reported in concentrations  of NOX  as
NO2.

Recently,  an extensive test program was started
on Southern California Edison Company (SCE)
major boilers.  Their test program was aimed
at accomplishing reductions in nitric oxide pro-
duction.  As part of the program,  various means
for controlling NO formation have been studied
using digital computer techniques  (ICRPG Per-
formance Standardization Working Gruop, 1968,
and Frey et al. , 1968) and the most  recent kin-
etic rate  data (Bortner, 1968, and Caretto et al. ,
1968).  These studies  have provided an under —
standing of the factors influencing the formation
of NO and in correlation  of field test results with
theory.

The kinetic analysis results of this study (reported
in Bagwell et al. , 1970),  along with photographic
studies of residence times and temperatures,
permitted development of a physical description
of the NO formation in power plant furnaces.  The
report states, "Mixing of the fuel and air begins
  Table 150.  EMISSIONS OF OXIDES OF NITROGEN FROM INDUSTRIAL BOILERS AND HEATERS
                                         (Mills et al. , 1961)
Source
Small oil heaters
Natural gas
Fuel oil
Large refinery heaters
Natural gas
Fuel oil
Small boilers (less than "300 hp)
Natural gas
Fuel oil
Large boilers (500 hp and larger)
Natural gas
Fuel oil
Power plant steam generators
Natural gas
Fuel oil
Heat input range,
millions of Btu/hr
Less than 60


90 to ZOO


Less than 2.0


20 to 90


200 to 2, 000


Range of NOX cone
in flue gases,
ppm by vol
10 to 100


25 to 137



5 to 92
15 to 387

45 to 149
214 to 282

75 to 320
275 to 600
Avg NOX cone,
ppm by vol
47


59



33
122

91
258

205
4ZO
NOX emission factors,
avg Ib per
million Btu

0. 06
0. 33

0.25
0.52

0. 14
0. 49

0. 28
0. 62

0. 36
0. 78

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 566
COMBUSTION EQUIPMENT
in turbulent zones close to the burner,  and com-
bustion occurs  only when the  turbulent eddy mix-
ture ratio is close to stoichiometric.  Because the
combustion is extremely rapid,  the temperature
increases to adiabatic flame temperature (no
heat loss).  The NO formation begins with  the on-
set of combustion as the gas products expand into
the furnace. The amount of NO formed  depends
upon the subsequent temperature and concentra-
tion history of the combustion products with time.
Temperature decay of the combustion products
results from mixing with the  colder bulk gas  re-
circulating in the flame  zone.  As the temperature
decreases,  the  NO formation  rate falls  off and
almost ceases when the temperature drops  below
3200°F.

"The calculated NO formation is extremely tem-
perature dependent.  At a given temperature the
NO also increases with time as shown in Figure
2[Figure 414]. For example,  the peak adiabatic
temperature for an air preheat of 650°F is ap-
proximately 3SOO°F and it was determined  photo-
graphically that the characteristic lifetime of this
peak temperature zone was between 0. 01 and  0. 1
seconds.  Figure 3 [Figure 415] shows that at 0. 05
second   1500 ppm of NO will form.  Since turbu-
lent mixing is a statistical phenomenon, the range
of temperature and eddy  lifetime in the primary
zone is shown as a shaded range of NO formation
in Figure 3 [Figure 415].  The combustion gases
flow through the radiant section of the boiler  in
less than 2 seconds and  the NO formation in this
bulk gas  zone is less than 50  ppm NO as shown
by the second shaded zone of  Figure 3 [Figure 415]."
                                                         6000
                       0.90    1.0     1.1
                      EQUIVALENCE RATIO(<|>)
 Figure 414.   Effect of equivalence  ratio on kinetic
 nitric oxide  (NO) concentration for  various characteris-
 tic  residence times (A/F stoichiometric = 16.3; air
 preheat= 650 °F) ^Bagwell  et  al.,  1970).
                      — PRIMARY ZONE - ADIABATIC NO FORMATION
                      _ 3800°F FOR 0.05 sec—1500 ppm
                   1000
                 o
                 oc
                   100
— RECIRCULATION ZONE
  NO FORMATION
  3000 °F FOR 2.0 sec -50 ppm
                    10
                    2800
                                                          PEAK Zd
                                                          ADIABATIC
                                                          TEMPERATURE
     3000     3200    3400     3600
                TEMPERATURE, °F
3800
4000
                  Figure 415.   Kinetic nitric oxide (NO)  formation for
                  combustion of natural  gas  at stiochiometric mixture
                  ratio--atmosphenc pressure (Bagwell  et al.,  1970).
                 Table 151 illustrates that the rate of formation of
                 NO increases markedly above  3,200°F,  Times of
                 formation of 500 ppm nitric acid were calculated
                 at 3 percent oxygen and 75 percent  nitrogen. These
                 calculated values may be  somewhat low in that
                 all  the nitrogen fixation is assumed to occur at the
                 exit oxygen concentration.  Some fixation would
                 probably take place at larger oxygen concentra-
                 tions before combustion is completed.  The times
                 of formation illustrate the rapid change in rate
                 between 2, 800°  and 3,600°F.  At2,300°F, the time
                 for formation of 500 ppm  NO is 16.2 seconds;  at
                 3,200°F, the time is 1. 10 seconds; and at3,600°F,
                 the time is  0. 117 second.
                                                         Table 151.  EQUILIBRIUM CONCENTRATIONS
                                                           AND TIMES OF FORMATION OF NITRIC
                                                         OXIDE AT ELEVATED TEMPERATURES AT
                                                                 75  PERCENT NITROGEN AND
                                                                     3 PERCENT OXYGEN
Temperature,
°F
2,000
2, 400
2, 800
3, 200
3, 600
Equilibrium
c one ent rat ion
of nitric oxide,
ppma
180
550
1, 380
2, 600
4, 150
Time of formation
of 500 ppm NO,
seconds"

1, 370
16.200
1. 100
0. 1 17
                 aHougen and Watson, 1945.
                 bDaniels and Gilbert, 1948.

-------
                                Boilers, Heaters, and Steam Generators
                                               567
At any given temperature,  the decomposition
(2NO ^..    * INU +  O^) rate  constant is much
greater  than the formation  rate constant.  This
fact may lend  hope that NO could be decomposed
back to the elements  before other more stable
oxides are formed.   This latter possibility appears
blocked  by the marked slowness,  if not  stagnation,
of the decomposition  rate in the necessary tem-
perature range-- 2, 000 °F and lower.  Decomposition
becomes negligible below about 3,200°F,  according
to Ermenc (1956),  and no known data indicate that
measurable decomposition  occurs below 2,800°F.
For the  residence times possible  in boiler fur-
naces, any decomposition taking  place below
3, 000 °F would appear to be insignificant.  In any
case,  measured NOX emissions are well below
the 2, 800 °F equilibrium concentration of 1, 380
ppm.  Decomposition cannot occur when NO con-
centrations are less  than equilibrium concentra-
tions.

Since  NO formation rate constants are extremely
high in the range of 3,500° to3,800°F, a  fraction
ot a second's residence time more or less can
make  a significant difference in NO  concentrations.
Measurements of  NOX at large  steam generators,
in fact,  bear  this  out. NOX concentrations at these
sources are extremely variable,  indicating that
there  are small,  almost  imperceptible, changes
in operating conditions that greatly  increase or
decrease NOx emissions.   In studying effects of
any  specific operating condition on NOx, great
care must be taken to see that other variables are
not inadvertently changed in the process.
Estimating NOX  Emissions
Mills et al.  (1961) measured NOX emissions from
a wide variety of combustion equipment varying
from small kilns to large steam generators.
From these  data, they were able to establish a
general  relationship between gross heat input
and NOX which is shown in  Figure 416.  Data
cover both gas and oil firing; gross heat inputs
range from less than 10, 000 Btu per hour (9 scfh
natural gas) to 2 million Btu per hour  (a 220-
megawatt power plant steam generator)   The
data for both fuels plotted to straight lines on
log-log coordinates,  even though there are
decided  differences in firebox design,  excess
air,  and tlame temperature over the range  of
equipment tested.  NOX values are  lower for gas
firing than for oil firing.  Generally, this would
be expected,  although it is  not always  true.  For
large-sized  power plant boilers  where multiple
banks of burners are used and where adiabatic
flame temperatures  are often  reached on gas
firing,  one  may  find that oil firing gives lower
NOX emissions  than  gas firing.

NOX emissions from  almost any combustion
device,  within the limits of the curves,  can be
   10,000
   1,000
 i   100
 cc
 LU
 0-
  x
 o
     10
     1.0
     0.1
    0.01
LEGEND:
NOX = NO+N02 (CALCULATED AS NCM
BTU INPUT INCLUDES GROSS HEAT IN
THE FUEL4-HEAT CONTAINED IN THE
PREHEATED COMBUSTION AIR.
           THIS GRAPH APPLIES ONLY TO COM-
           BUSTION PROCESSES TAKING PLACE AT
           OR NEAR ONE ATMOSPHERE OF ABSOLUTE
           PRESSURE.
      105
     105
10?
108
109
         AVERAGE RATE OF HEAT INPUT TO A UNIT IN A
         GIVEN CLASS OF COMBUSTION EQUIPMENT, Btu/hr
 Figure 416.  Estimation of average unit NOX  emissions
 from similar pieces  of combustion equipment  (Mills
 et al.,  196U

 estimated from Figure 416.  For instance, a 200-
 horsepower oil-fired boiler operating at 80 per-
 cent overall efficiency would have a gross heat
 input of 3, 360, 000 Btu per hour.  From  Figure
 416,  emissions are 1.1 pounds of NOX per hour.

 When combustion air is preheated, preheat must
 be added to the gross input.  For  example,  a
 1, 100 , 000-pound-per-hour  steam generator has
 a  rated fuel input of 1 6 x 10" Btu  per hour.  In
 addition, combustion air is preheated from 60°
 to 600°F   The difference  in combustion air
 temperatures represents a 14 percent increase
 in gross heat  input.  The adjusted gross input is,
 therefore,  1. 82 x 10 Btu per hour, which, the
 curve shows,  is  equivalent to a discharge of
 1, 030 pounds of NOX per hour.

 AIR POLLUTION CONTROL METHODS

 Air pollution control of emissions from  large gas-
or oil-fired boilers and heaters is  a new field and
 one in which much  of the work done applies only
 to pilot plants or  experimental plants.

 Air pollution control equipment  is limited to
 power plant steam generators or other fired com-

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568
COMBUSTION EQUIPMENT
bustion equipment of comparable size.  Small- and
intermediate-sized  boilers and heaters are not
likely to need any control devices unless  the fuels
are highly contaminated.  Normally no attempt is
made to control even those relatively heavy par-
ticulate concentrations emitted from intermediate -
sized boilers during soot blowing. Where optimum
air pollution control is desired in smaller equip-
ment,  it is normal  practice to burn only  clean
fuels such as natural gas  and  low-sulfur  distil-
late oils and to employ high-efficiency burners.


The control of air contaminants from power plant
steam generators must be considered  from a
number of aspects.  Some contaminants are amen-
able to partial control through furnace  and burner
modifications or operational changes,  namely,
sulfur trioxide, oxides of nitrogen,  and combust-
ible particulates.  Others, such  as sulfur dioxide
and inorganic particulates,  can be removed only
by treatment of effluent gas. No  one control meth-
od now  under study  is capable of removing all
types of contaminants emitted to the atmosphere
from large combustion sources.

Combustible Particulates

As  explained in the  second section of this chapter,
combustible particulates are not common in exit
gases from small-  and medium-size combustion
equipment except during startup  periods.  Com-
bustibles almost always result from poor main-
tenance or  operation or from  improper selection
of burner or fuel.   In large  boilers, fuel usage
and combustion air  are  carefully monitored to
provide nearly perfect combustion.  Combustible
contaminants are seldom  emitted in concentra-
tions sufficient to impart  perceptible opacity or
blackness  to stack gases.  Conceivably,  com-
bustibles could be incinerated in an afterburner
in cases, for instance,  such as  that where  the
fuel burned is  essentially a  waste product.  Exam-
ples might be wood  pulp or petroleum  products
contaminated with inorganic sludge.

Soot Collectors

Air pollution control devices have been installed
on oil-fired power plant boilers to control par-
ticulates during soot blowing.   This equipment
serves  principally to collect large particulate
matter — greater than 10 microns --that would
otherwise  settle in  the  immediate area.  Soot
collectors are used only during periods of soot
blowing.   They are  not designed  to control  the
extremely fine particulates  emitted during  nor-
mal oil firing, particularly the submicron ash
particulates responsible for opaque plumes.

Small-diameter dry multiple cyclones are the
most common  soot  control devices installed. This
                 equipment is reasonably inexpensive,  and power
                 requirements are low.  Pressure drops usually
                 do not exceed 4 inches of water  column.  More
                 efficient controls,  such as  cloth filters, may
                 need to be installed to collect soot-blown air con-
                 taminants where fallout is causing a public nui-
                 sance .

                 No good data are available  regarding the soot col-
                 lection afforded by centrifugal collectors on large
                 steam generators.   This is due  principally to the
                 previously mentioned  difficulty of obtaining repre-
                 sentative  test samples during soot blowing.   Since
                 efficiency of particulate collection cannot be meas-
                 ured accurately, the common yardstick for accept-
                 ability of a soot collector is its  observed ability
                 to prevent fallout of large partLculates  in down-
                 wind areas.

                 As mentioned,  soot collectors are not designed to
                 collect  the submicron particles  emitted during
                 normal firing.   It is doubtful that  operators  of
                 large oil-fired boilers would install more efficient
                 particulate collection  devices unless they also
                 served  to remove sulfur or nitrogen oxides. Most
                 devices that  show promise  of  SO2 removal would
                 also collect solid particulate matter.

                 Collection of Sulfur  Oxides

                 It was estimated that about 50 billion pounds  of
                 SO2 would be emitted  into the atmosphere in  the
                 United States during 1970 from the combustion of
                 fossil fuels containing sulfur. In  Los  Angeles
                 County, the control of sulfur oxides has been
                 achieved by enactment of a rule  limiting the sul-
                 fur  content of fuels to 0. 5 percent by weight.
                 Already, however, the shortage of these low-
                 sulfur fuel oils  is complicating the problem.
                 Switching from  high- to low-sulfur fuel or to sul-
                 fur-free natural gas may be a stop-gap.  The
                 demand for these fossil fuels  far outstrips avail-
                 able sources.

                 Other means of removing sulfur products before
                 they reach the  atmosphere  are under study and
                 research.  Before the methods  can be used,  they
                 must be commercially practical and economical.
                 Removing  sulfur from the fuel is one possibility.
                 At present, there is no economical way to remove
                 sulfur from coal.  Removing sulfur from fuel oil
                 is possible but the cost is high--ranging from
                 $0. 50 to $1. 00  per barrel depending on initial and
                 final sulfur contents desired.  Costs  of removing
                 sulfur from fuel oil are shown in Figure 417.

                 There are a  number of processes for  removing
                 SOz from stack gases (Maurin and Jonakin,  1970).
                 Many of these processes are in  pilot plant or pro-
                 totype stages.   Many  others have  only been bench
                 scale tested.  The principal methods are (1) dry
                 and wet absorption and adsorption and  (2) catalyti

-------
                               Boilers, Heaters, and Steam Generators
                                                                   569
    1.10
 1  1.00
 Is  0.90
 .2
 1  0.80
 f  0.70
 >»
 §  0.60

 I  °-5°
 8  0.40
 _l
 £  0.30 —
 UJ
 g  0.20 —
 I  o.ioh-
                    f DISTILLATION     |
                    iSOLVENT DEASPHALTING
                    o RESIDUAL DESULFURIZATION
                    ^DELAYED COKING
                    A SOLVENT DEASPHALTING AND COKING
                    •SOLVENT DEASPHALTING AND RESIDUAL
                     DESULFURIZATION
                                           2.5
       0       0.5      1.0      1.5      2.0
                PERCENT SULFUR IN FINAL PRODUCT

  Figure 417.   Cost of removing  sulfur from fuel oil
  CMeredity,  1967s!.

 oxidation.  A complete rundown of all of these
 processes is  not justified  in this  manual,  and only
 those processes •which appear to  be most advanced
 in development will be discussed.

 Wet absorption

 The wet absorption process is the most popular
 system. For  this combustion engineering process,
 shown in Figure 413,  limestone is injected into
 the  combustion zone of a boiler where  it is cal-
 cined to reactive lime. The lime is collected  by
 a scrubber and forms  a  slurry of reactive milk-
 of-lime, which reacts with the SO2 in the flue gas
 to form sulfite and  sulfate salts.  The spent liquor
 COAL
,-SUPPLY
V...r ADDITIVE
              FURNACE
                                     TO STACK
        STACK GAS
        REHEATER
                              STACK GAS
                              REHEAT
                              SYSTEMS^
          ^-SETTING TANK

                  TO DISPOSAL
RECYCLE
AND
MAKEUP
WATER
Figure  418.  Combustion  engineering wet  absorption
process (Maurm and Jonakin, 1970).
                    and reaction products are settled; the ash and re-
                    acted limestone are removed for disposal.  Scrub-
                    ber liquid is reused. Operations on actual instal-
                    lations when firing 3.4 percent sulfur coal show
                    an SC>2 removal efficiency of about 85 percent.
                    Other benefits of this control system include a
                    particulate matter  collection efficiency of greater
                    than 99 percent and NOX collection efficiency of
                    30 percent.

                    Dry absorption

                    A dry absorption system developed by Japan's
                    Mitsubishi Heavy Industries employs sorbent
                    regeneration and recirculation. A flow  diagram of
                    the system is shown in Figure  419. Flue gas emit-
                    ted from the air preheater is led to  an absorption
                    tower. Activated manganese oxide in powdered
                    form is dispersed  uniformly from the inlet into
                    the flue gas. The  resulting manganese  dioxide
                    reacts with the SO2 and SOj to form manganese
                    sulfate. The absorbent,  consisting of this man-
                    ganese sulfate and unreacted activated  manganese
                    oxide,  is collected by a multiple cyclone, and the
                    largest portion is returned to the absorption tower
                    for recycling.  About 10 percent is fed into a water
                    slurry of ammonia and air,  yielding ammonium
                    sulfate and manganese dioxide. The  manganese
                    dioxide is separated by filtration and is returned
                    to the absorption tower.  The ammonium sulfate
                    solution is sent to  a crystallizer to recover good
                    quality ammonium sulfate crystals.  However,
                    the grade of ammonium sulfate formed  does not
                                                           FLUE GAS
                                                           0.1-0.13% S9o
                                                           TEMP 135-145 °C.
                                                         TREATED GAS
                                                         0.01% SO?
                                                         TEMP 100-110°C.
                                                                                             STACK
                                                                                           .AMMONIA
                                                                                           • OXYGEN OR AIR
                                                                                        	/AMMONWlA	
                                                                                        """^SULFATE J
                                                                                AMMONIA
                                                                                             MILK OF LIME
                                                   (GYPSUM)
                      Figure 419.  Dry  absorption process employing
                      manganese oxide and yielding ammonium sulfate on
                      gypsum as a by-product (Maurm  and Jonakin,  1970).

-------
 570
COMBUSTION EQUIPMENT
 have as ready a market in the U. S. as it does  in
 Japan. Another possibility,  as shown in Figure
 419, is treatment of ammonium sulfate with lime,
 and recovering ammonia for recycling and gyp-
 sum as a product.

 Pilot  plants tests have shown efficiencies of 90
 percent on SO^ removal.  A plant treating 25 per-
 cent of the effluent from a 220-megawatt oil-fired
 power plant is now operating at the Yokkachi Sta-
 tion of Chubu Electric Power Company.

 Wet adsorption

 The Lurgi process  is a wet adsorption process.
 Chemical absorption processes,  as discussed
 above,  have a  capacity for heavy loading,  but re-
 quire complex regeneration. Conversely,  adsor-
bents afford less loading capability but are sim-
pler to regenerate.  The Lurgi process uses wet
adsorption and yields a low-concentration sulfuric
acid as a by-product. As shown in Figure 420,  flue
gas from a dust collector passes through a cooler
to a carbon adsorption tower. Here,  intermittent
water  spraying removes the acid formed in the
pores  of the carbon adsorber.  The dilute acid re-
cycles and cools the flue gas from the dust collec-
tor. Presently,  the  system is in use  for treating
emissions  from  a sulfuric  acid plant (100, 000 cfm)
and from the equivalent of  a 2 , 000-kilowatt coal-
fired power plant.
                 GAS FROM BOILER

                      [850°F.

GAS FROM
DUST
COLLECTOR



1


GAS
COOLER

i
I

—




1 	 _
\ \


ABSORPTION
TOWER

1
	 j
TO
STAC






          SULFURIC ACID
  Figure 420.  Wet adsorption process employing a car
  carbon adsorber and yielding sulfuric acid  as a
  by-product  (Maunn and  Jonakin,  1970).
 Catalytic oxidation

 Monsanto's  Cat-ox process converts  sulfur oxides
 to  sulfuric acid by passing flue gases over a vana-
 dium pentoxide  catalyst which oxidizes  SO^ to SOj.
 The SO3 then combines with water vapor in the
 flue gas to form sulfuric acid.  Subsequent cooling
 condenses the acid. A flow diagram of  the system
 is  shown in  Figure 42 1. Flue gas from  the boiler
 must be tapped  upstream from the economizer so
ELECTROSTATIC
PRECIPITATOR
                                                           GAS TO
                                                           STACK
                                                       SULFURIC ACID
                 Figure 421.  Catalytic oxidation process  employing an
                 electrostatic precipitator and  yielding sulfuric acid
                 as a by-product (Maunn and Jonakin,  1970).

                 that hot gases (about 950°F) exist  in the converter.
                 The gases are first passed through an electrostatic
                 precipitator to remove the  particulate matter.  The
                 dust-free  gas  then passes through the  catalyst
                 bed.   The SOj formed combines with water upon
                 cooling in the  economizer and air  heater and is
                 maintained just above the dew point.  The gas
                 then enters a packed tower and shell-and-tube
                 heat exchanger, and condensation  of the acid fol-
                 lows as the stream of cool  acid contacts the gas,
                 Lowering the temperature to 225 °F. A Brinks mist
                 eliminator removes remaining entrained sulfuric
                 acid mist. A  90  percent removal  of SO2 is
                 achieved,  while recovering an acid with a con-
                 centration up to 30 percent   Trie  largest instal-
                 lation in present  operation is at Metropolitan
                 Edison Company's Portland,  Pennsylvania,  plant
                 where a prototype plant treats 6 percent of the
                 flue gas froiri  a 250-megawatt unit.

                 Other processes for removing SO  from stack
                 gases

                 There are many  other processes for removing
                 SO2 from stack gases, all  of which are  in develop-
                 ment  or prototype stages.  Maurin and Jonakin
                 (1970) mention a  total of 19 processes.  In addi-
                 tion to those mentioned  above,  they include  the
                 alkalized  aluminum process, the still process
                 using lignite ash  as the  sorberit, the Wellman-Lord
                 process,  the molten carbonate process,  the Showa
                 Denka process, the Grillo  process, the Wade pro-
                 cess,  the Chemico-Basic Corporation process,
                 the  Bischoff process , the Hitachi  process, the
                 Reinluft process, the Kiyoura process,  and others

                 Controlling Oxides of Nitrogen

                 Most  of the progress made in controlling oxides
                 of nitrogen has been accomplished in steam-

-------
                                Boilers, Heaters, and Steam Generators
                                                                                                     571
electric power plant boilers.   While the  total NOX
emissions from smaller industrial and commer-
cial boilers are substantial for a given area,  the
emissions from a few power plants  can easily
equal or exceed the total of other stationary com-
bustion sources.  Consequently, efforts  have been
concentrated towards reducing the emissions from
the larger sources.  Also,  the emissions from
power plants are concentrated in small geographi-
cal areas, and cause high ground concentrations
in those areas.  As a result of the Federal Clean
Air Act,  State ambient  air standards have been
established,  and it is necessary that high concen-
trations of NOX in  small geographical areas be
reduced to comply with these standards.

Electrical power output doubles about every 10
years.  Because of this growth,  power companies
have built more and  larger  generating stations.
Figure 422 shows how unit size has increased with
time.  As boiler furnaces were enlarged,  certain
other parameters were held constant.  James
(1970) states that three parameters held constant
were  (1) the velocity of the  combustion gases in
the furnace,  (2) the temperature of  the flue gas
entering the convection surface, and (3)  the time
required  to burn the fuel completely   Since these
parameters remained constant for larger boilers,
the ratio  of furnace cooling surface to furnace
volume in the active combustion zone of  the fur-
nace decreased.   This change  is shown in Figure
423   As  the surface-to-volume ratio in  the active
combustion zone decreases, the peak and average
flame  temperatures  increase.   Since this is the
                                                           0.24
   1200
   1000
    800
    600
    400
    200
     1920
1930
1940
1950
YEAR
1960
1970
1980
 Figure 422.  Trend in  size of utility steam  boilers
 with time  (James,  1970).
                                                0.22 —
                                                0.20 —
                                           as
                                           =3UJ
                                                0.18 —
                                                0.16 —
                                                0.14
                                                0.12 —
                                                0.10
                                                         OBLONG FURNACE
                                                         WIDTH = 2x DEPTH
                                                         WITH ONE DIVISION WALL
                                                    OBLONG FURNACE
                                                    WIDTH = 2 x DEPTH
                                                      SQUARE FURNACE
                                                        200    400     600    800    1000

                                                           STEAM GENERATOR SIZE, megawatts
                                                                                 1200
                                             Figure 423.  Change of surface-to-volume ratio with
                                             steam generator  size (James, 1970).
                                           hottest zone in the boiler, it has  the greatest ef-
                                           fect on NO formation.  As a result,  the larger
                                           boilers with their decreased cooling surface-to-
                                           volume ratios, have higher NO formation rates.
                                           In addition,  burners have been designed for high
                                           turbulence and rapid  burning rates to assure com-
                                           plete burning of the fuel over wide load ranges.
                                                        Reduction of NO by modification of boiler
                                                                        x
                                                        operation
Since the control  of NOX emissions is largely a
function of the control of temperature and resi-
dence time  in the primary flame zone, it is im-
portant to understand the  design and operating
characteristics of burner designs used in front-
fired and corner-fired gas-fired boilers.  The
discussion here will pertain to gas-fired boilers
only.  Only limited  work has been  done in reduc-
tion of NOX from  oil- and coal-fired boilers.

The two common  types of burner designs are
shown in Figure  424  (Bell et al. ,  1970).   In both
types of burners, the gas and air are introduced
separately.  The  type a_ burner  is used in a front-
fired boiler, illustrated previously in Figure  404.
The burner consists of a circular opening in the
furnace wall through  which air flows into the fur-
nace from the windbox.  The windbox is  part of
the air  duct which supplies forced  air, usually
preheated to 650°F, to the burners. The gas fuel
is injected into the  furnace through several noz-

-------
572
COMBUSTION EQUIPMENT
     FUEL NOZZLES
                                       FUEL
      AIR SWIRL
      REGISTER
                                          FURNACE
                                         -WALL
               a, Front-Fired Burner
                                          -FUEL
              b, Corner-Fired Burner

Figure 424.  Typical natural gas burner configurations
tions utilized in power plants (Bell et al.,  1970).
zles located  concentrically within the burner
throat.  Registers are provided which swirl the
air as it flows into the burner throat.  The com-
bustion  produces a blue donut-shaped zone just
off the burner face which is usually followed by a
bushy yellow flame where adjacent burners im-
pinge upon  one another.   A  number  of  these
burners are  arranged in rows and columns along
the bottom half of one wall of the boiler  furnace.
Sometimes the burners may be located on op-
posing walls  on a unit called an opposed-fired
boiler.

The type b burner  shown in Figure 424 is used in
corner-fired (sometimes called tangentially fired)
boilers.  The burners  are  aligned to produce a
tangential swirl in the  center of the furnace.   Blue
jets  extend out several feet from each gas slot,
and a large yellow flame ball fills the  center of
the furnace.   Mixing occurs less rapidly and
occurs  in the center  ball with this type of burner.
A  corner-fired boiler is shown in Figures 425
and 426.  In  the corner-fired unit, the number of
                 burner assemblies is considerably less than for
                 conventional front-fired units,  in which multiple
                 burner assemblies are used. Single-burner assem-
                 blies are mounted in the four corners  of the fur-
                 nace,  and there are usually three  to five burner
                 cells in a vertical line  in each assembly.  Because
                 of the long luminous flames produced, the fire from
                 each burner  can "see"  a larger area of wall heat
                 transfer surfaces  than  can those from burners in
                 front-fired units.   As  a result, maximum flame
                 temperatures are  apparently lowered.  Corner-
                 fired boilers also employ somewhat higher water
                 circulation rates through the furnace tubes.  This
                 probably provides faster cooling of gases in the
                 furnace.

                 The NOX formed in power plant boilers is essen-
                 tially a burner phenomenon,  since the tempera-
                 ture of  the bulk gas is too low to support  NO for-
                 mation  (Bell et al. , 1970).   In a large measure,
                 the amount of NO  formed is dependent upon the
                 type of burner utilized.  The front-fired burner
                 yields  complete mixing and combustion just off
                 the face of the burner.   Adiabatic  and stoichio-
                 metric  combustions occur,  and the combustion
                 products experience a subsequent  high tempera-
                 ture-time history, with a resultant high NO for-
                 mation (500 to 1,  500 ppm).  Conversely,  the
                 corner-fired burner mixes the fuel and air slowly,
                 and much of the fuel burns in the middle of the
                 furnace in a yellow fireball.  The combustion oc-
                 curs at lower than peak temperatures due to the
                 presence of mixed-in-bulk gas, and the rate of
                 NO formation is lower (typically 350 ppm).

                 Bell et  al. (1970)  also emphasize that  while NO
                 formation is a burner phenomenon, the furnace
                 design can have a substantial influence on the
                 amount of NO produced.  They state that  "this
                 influence is manifested in the temperature of the
                 bulk gas which controls the rate of temperature
                 decay of the combustion products  and  thus  the rate
                 of decrease in NO formation.  The bulk gas tern -
                 perature is fixed  by the heat release rate  per unit
                 volume and is  affected locally by circulation pat-
                 terns  and the proximity of cold surfaces.   The
                 tendency with new and larger furnace  designs
                 has been to increase heat release rates with a
                 resulting increase in bulk gas temperature and
                 NO formation.  An example of  NO reduction with
                 decreased bulk gas temperature is that a reduc-
                 tion in boiler load (lower fuel flow and hence a
                 lower heat release rate) always results in  a sig-
                 nificant decrease  in NO concentration. "

                 Reduction of NOX  both in existing  boilers and in
                 new installations  can be achieved  by modification
                 of operating conditions and by modification of
                 design features.   According  to Bartok et  al.
                 (1969) the following modifications  of operating
                 conditions have proved to be significant:

-------
                             Boilers, Heaters, and Steam Generators
                                          573
           Figure 425.  A corner-fired  steam  generator with tilting burners positioned  for
           varying load and superheat  (Combustion Engineering,  Inc.,  New York,  N.Y.).
Figure 426.  Cross-section of a corner-fired
boiler firebox  (Combustion Engineering, Inc.
New York,  N.Y.).
Low excess air firing.  The effectiveness of
low excess air firing is well documented for
gas and oil combustion, but  no test data are
available for  coal-firing equipment.  In coal-
firing equipment, the problems of unburned
fuel and carbon monoxide may occur because
of imbalances in fuel/air  distribution.   Barr
(1970) emphasizes that operating changes
available for  NO control often produce op-
posing and limiting effects.  For example,
reducing  the  excess air tends to lower NO by
eliminating the QI available  for reaction, but
the resulting  higher flame temperature tends
to produce more NO.  In  practice, however,
one cannot significantly reduce NO by increas-
ing the excess air to lower the flame tempera-
ture.  To do  so would require such large
amounts  of air that the boiler would  have to
be  derated.   Figure 427 illustrates  this con-
cept by showing that NO formation rates in-
crease with increasing excess air quantities,
even above 20 percent. Pacific Gas and Elec-
tric Company found that their two 750-mega-
watt units at  Moss Landing near Monterey,
California, could be fired safely at 5 percent
excess air.   Reducing their excess  air  quanti-
ties from 10 percent to 5  percent reduced NO
formation by about 30 percent. A further
reduction in excess air was considered to be
too dangerous. Minor drifts in control  equip-
ment calibration can result in a deficiency of
air during periods of changing loads.  Opera-
ting with deficient air is dangerous because
potentially explosive  mixtures of partially
burned gases are formed.

-------
 574
COMBUSTION EQUIPMENT
      REDUCING CONDITIONS
                                  OXIDIZING CONDITIONS
  10,000
o
Cd
             80      90     100     110     120

             PERCENT OF THEORETICAL COMBUSTION AIR

    Figure 427.   Thermodynamic equilibrium  data  for
    natural gas  (James,  1970).
  2.  Two-stage combustion.  By supplying sub-
     stoichiometric quantities of primary air to
     the burners in oil- or gas-fired combustion,
     substantial reduction in NOX emissions can
     be achieved.   Complete burn-out of the fuel
     is accomplished by injecting secondary air at
     lower temperatures,  where NO formation is
     limited by kinetics.

  3.  Flue gas recirculation.  This technique
     lowers the peak flame temperature by diluting
     the primary flame zone •with recirculated
     combustion flue gases.  The oxygen concen-
     tration also is lowered, which  favors reduc-
     tion in NOX emissions.

  4.  Steam or water injection.   Steam or water
     injection has the same effect as flue gas
     recirculation,  i. e. , a thermal dilution of  the
     flame.  This method,  however, lowers ther-
     mal efficiencies and has limited utility.

 Bartok et al.  (1969) report reductions in NOX by
 the  following modification of design features:

  1.  Burner configuration,  location, and  spacing.
     Levels of NOX formation differ with different
     burner designs.  Cyclone burners,  for exam-
     ple,  in coal-fired plants promote highly tur-
                    bulent combustion and yield high formation of
                    NOX.  One design feature to reduce NO forma-
                    tion is to space the burners so that radiant
                    heat transfer is increased.   Thus, flame
                    temperatures can be reduced by rapid heat
                    transfer from flame to water tube surfaces.
                 2. Tangential firing.  In tangential firing,  the
                    furnace itself is used as the burner, resulting
                    in lower peak flame temperatures.

                 3. Fluid bed combustion.  This technique, al-
                    though still under development, promotes
                    high heat transfer rates,  and hence low aver-
                    age combustion bed temperatures.  It also
                    offers the potential advantage of controlling
                    both SO2  and NOX by the addition  of limestone
                    or similar material directly into  the combus-
                    tion zone.  While these processes show prom-
                    ise, they are  still in the pilot plant stages.
                 Reductions in  NO formation by modification of
                 operating conditions and by modification of de-
                 sign features also are reported by Bell et al.
                 (1970), and they closely  agree with those  reported
                 by Bartok et al.  (1969).  Bell et al.  list the ways
                 to control combustion and minimize nitric oxide
                 as delayed mixing, premixed off- stoichiometric
                 flames, off-stoichiometric diffusion flames
                 (secondary combustion),  and direct  temperature
                 control.

                 1.  Delayed  mixing.   Burners can be designed to
                     delay mixing between the fuel and the  air  and
                     to  promote entrainment of bulk gas before
                     complete combustion occurs.   For example,
                     the design  of the burner used in  corner-fired
                     boilers  (Figure 424 ID) incorporates some of
                     these concepts, although the design was not
                     based on NO  considerations.  Combustion
                     occurs over a longer period and  in the center
                     of  the furnace.   Bulk gas is entrained,  and
                     adiabatic flame temperatures are prevented
                     by better radiant heat transfer from flame to
                     •water tube surfaces.

                 2.  Premixed off-stoichiometric flames.  Fuel
                     and air within the burner are premixed at
                     off-stoichiometric mixture ratios.  The over-
                     all furnace stoichiometry is preserved by
                     operating half of the  burners fuel-rich and the
                     remaining  half correspondingly air-rich.   Pri
                     mary zone combustion occurs at off - stoichio-
                     metric flame conditions \vith lower flame
                     temperatures.   Unburned hydrocarbons from
                     fuel-rich burners mix with the oxygen from
                     air-rich burners in the bulk gas.  This sec-
                     ondary combustion occurs at the lower bulk
                     gas temperatures and does not form additional
                     NO.  A limitation of  this technique is  that it IE
                     difficult  to design burners that can operate
                     fuel-rich and air-rich as desired over a wide
                     load range.

-------
                                Boilers, Heaters, and Steam Generators
                                                                                                 575
4.
 Off-stoichiometric diffusion flames.  In this
 type operation,  the burners are operated at
 off-stoichiometric mixture ratios without
 premixing the fuel and the air.  The overall
 furnace stoichiometry, however, is maintained
 to ensure complete combustion within the fur-
 nace.  This technique can be accomplished in
 various ways.  Some or all of the top burners
 can be taken out of service with the associated
 air  registers open to simulate two-stage com-
 bustion or  different numbers of burners can
 be  taken out of service within the matrix of
 the  burner  system.   In this manner,  some of
 the  burners will operate fuel-rich, -with the
 remaining burners operated either air-rich or
 on  air  alone to maintain the desired overall
 furnace stoichiometry with secondary combus-
 tion.  Combustion occurs in diffusion flame
 zones at near stoichiometric fuel-to-air ratios,
 and the product  gases initially experience
 peak temperatures.   However,  total formation
 of NO depends upon the burner mixture  ratio as
 shown in Figure 414.  For  fuel-rich  mixture
 ratios, the  rate of NO formation is reduced due
 to the increase in oxygen concentration; for air-
 rich mixtures,  the temperature decrease re-
 duces the NO formation rate.

 For a number of years, Southern California
 Edison Company has  used a variation of this
 technique called two-stage combustion.   About
 90 to 95 percent of stoichiometric air require-
 ment is admitted at the burners,  and the
 remaining air required is admitted a few feet
 downstream of the burners.   This modification
 is,  in itself,  effective in reducing NO forma-
 tion.

 Direct temperature control.  This technique
 involves  reducing  the temperature in the pri-
 mary combustion zone.  One way in which
 this can be  accomplished is by reducing the
 combustion air preheat.  Bell et al.  (1970)
 performed kinetic analyses to predict the ef-
 fect of combustion air preheat on NO forma-
 tion, and the results  at an equivalence ratio
 of 0. 95 are shown in  Figure 428.   A reduction
 in NO formation of 25 to 30 percent per 100°F
 decrease in  air preheat is apparent from this
 study.  This reduction in NO will be accom-
 panied by a decrease in thermal efficiency if
 the  heat leaving the air preheater is not uti-
 lized.

 A more practical way of reducing combustion
 temperatures is to recirculate the flue gas.
 This is done by taking a portion of the flue
 gas just upstream from the air preheater and
 recirculating it through the burners.  The flue
 gas  acts as  an inert and reduces the adiabatic
 combustion temperature.   Bell et al.  (1970)
made kinetic analysis predictions, substan-
                                                          2000

                                                          1000
                                                           100
                                                        o
                                                        cc
                                                           10
                                                                  0.01
               0.02
                                                                              0.03
0.04    0.05
                                       0.06
                                                                           TIME, seconds
                                                         Figure 428.   Effect of  combustion  air preheat on
                                                         nitric oxide  (NO) formation, * = 0.95 (Bell  et al.
                                                         1970).

                                                       tiated by full-scale power plant tests,  of the
                                                       reduction in NO formation for various  flue
                                                       gas recirculation rates.  As shown in Figure
                                                       429,  there is a very substantial  reduction in
                                                       NO concentration when recirculating moderate
                                                       rates of flue gas.  Moreover,  the recircula-
                                                       tion does not significantly reduce plant ther-
                                                         2000
                                                         1000
                                                            0
        0.01    0.02
     0.05   0.06
                    0.03    0.04
                    TIME, seconds
Figure 429.   Effect of product gas  recirculation
on nitric oxide  (NO) formation,  0 = 0.95,  recir-
0.07
culated gas =
(Bell et al,,
                                                                      1970).
                                                                                         = 700 °F

-------
576
COMBUSTION EQUIPMENT
   mal efficiency.   It can,  however, influence
   boiler operation,  inasmuch as radiant heat
   transfer is  reduced in the water tube sections
   of the furnace and convective heat transfer is
   increased in the convective  sections.  Final
   superheat temperature,  therefore,  may need
   to be controlled by 'water attemperation.

A summary of  NOX concentrations for gas firing
in Southern California Edison boiler units is given
in Table 152.  The results show large reductions
in NOX with two-stage or off-stoichiometric
operation.  On the 480-megawatt units,  overall
reduction resulting from use  of two-stage and off-
stoichiometric combustion  is about 75 percent.
Overall reduction from all  units tested was  over
50 percent.
                 Removal of NOX by Treatment of Flue Gas

                 To date,  the reduction of NOX from power plant
                 boilers has been accomplished by operation
                 changes or combustion modifications.  No flue
                 gas treatment process has been directly applied
                 to NOX control.  Power plants emit large volumes
                 of flue  gas which present engineering problems in
                 gas contacting, equipment size, temperature con-
                 trol, pressure drop,  and other difficulties.  Also,
                 the moisture,  COg, SO2, and Q£ in the  flue gas
                 often interfere with removal processes  using
                 sorption, scrubbing,  and catalytic conversion
                 techniques.

                 Some pilot plant work has been done and some
                 theories advanced  regarding methods of control-
                Table 152.  SUMMARY OF TEST RESULTS ON SOUTHERN CALIFORNIA
                          EDISON COMPANY UTILITY BOILERS - GAS FUEL
                                          (Bell et al. ,  1970)
Plant
Huntington
1
2
3
4
Alamitos
1 and 2
3 and 4
5 and 6
Etiwanda
3 and 4
El Segundo
1 and 2
3 and 4
Redondo
5 and 6
7 and 8
Mandalay
1 and 2
Unit
mfgra
B&W
B&W
B&W
B&W

B&W
CE
B&W

CE
B&W
CE

B&W
B&W
B&W
Size,
MW
215
215
225
225

175
320
480

320
175
330

175
480
215
NOX, ppm,
for normal
operation^3
Single-
stage
500
520
555
335

450
330
700

330
450
330

450
750
520
Two-
stage
—
—
500
285

330
—
390

—
330
—

330
400
—
Modified operation
Methodc
osb
OS
Two-stage + OS
Two-stage + OS

Two-stage + OS
Recirculation
Two-stage + OS

Recirculation
Two -stage + OS
Recirculation

Two- stage + OS
Two -stage + OS
OS
Excess
©2, %
3. 1
1. 8
3. 1
2. 2

2. 1
2. 0
2. 5

—
—
	

2. 3
3. 1
2.4
N0x,b
ppm
200
200
230
210

245
110
150

—
d
150

300
220
210
          B&W - The Babcock and Wilcox Co, New York; CE -  Combustion Engineering,
          New York.
          Based on ASTM D1608-60, reported dry at 3 percent  excess oxygen.
         "OS - off-stoichiometric.
                                                  Inc. ,
          Not yet tested; expected to give results comparable to Redondo 5 and 6.

-------
                               Boilers, Heaters, and Steam Generators
                                                                                                   577
ling NOx from stack gases.  Bartok et al  (1970)
list the potential processes as follows:
 1.  Aqueous scrubbing systems using aqueous
    alkaline  solutions on concentrated sulfuric
    acid appear to  offer the best potential for the
    control of both sulfur and nitrogen oxide
    emissions.  Equimolar concentrations of NO
    and NO2 (equivalent to ^03) are needed.
    Since homogeneous or catalytic oxidation tech-
    niques are too  slow or costly, the recycle of
    NO2 appears to offer the best possibility.
    Recycling of NO£  is done by oxidizing the
    concentrated NO stream produced by thermal,
    catalytic, or chemical regeneration of the
    spent absorbent.
2.  Selective reduction of NOX with ammonia,
   hydrogen sulfide,  or  hydrogen is  a less likely
   possibility.   Using ammonia or hydrogen
   sulfide would also control SO2 emissions.
   Such approaches have been  demonstrated
   only in laboratory-scale operations.

3.  Common adsorbents  such as silica gel, alu-
   mina, molecular sieves,  charcoal,  and ion
   exchange resins show some capacity for
   oxidizing NO to NO£  and adsorbing the resul-
   tant NO£.  However,  the  capacity of these
   adsorbents is quite low at typical NO flue
   gas concentrations.   Manganese and alkalized
   ferric oxides show some  potential,  but sor-
   bent attrition is a  problem in developing such
   processes.

-------
                                              CHAPTER 10
                                      PETROLEUM EQUIPMENT
               GENERAL INTRODUCTION
              ROBERT C.  MURRAY
          Senior Air Pollution Engineer
   OIL-WATER EFFLUENT SYSTEMS

    ROBERT H. KINSEY t
    Air Pollution Engineer
             WASTE-GAS DISPOSAL SYSTEMS

             DONALD F. WALTERS*
        Intermediate Air Pollution Engineer
            PUMPS


   ROBERT H. KINSEY +
   Air Pollution Engineer
             HAROLD B. COUGHLIN*
              Air Pollution Engineer
                                                                       A1RBLOWN ASPHALT

                                                                   ROBERT H.  KINSEY t
                                                                   Air Pollution Engineer
                  STORAGE VESSELS

              ROBERT C.  MURRAY
          Senior Air Pollution Engineer
            VALVES

    ROBERT H. KINSEY f
    Air Pollution Engineer
                 LOADING FACILITIES

              ROBERT H.  KINSEY t
              Air Pollution Engineer
        COOLING TOWERS

    ROBERT C. MURRAY
Senior Air Pollution Engineer
               CATALYST REGENERATION

              STANLEY  T.  CUFFE*
              Air Pollution Engineer
     MISCELLANEOUS SOURCES

   ROBERT H. KINSEY t
   Air Pollution Engineer
 *Now with U. S. Environmental Protection Agency, Research Triangle Park,  North Carolina.
 iNow with Lockheed Missiles Systems Company,  1111 Lockheed Way, Sunnyvale, California.
234-761 O - 77 - 39

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                                              CHAPTER 10
                                      PETROLEUM EQUIPMENT
          GENERAL INTRODUCTION

 Operations of the petroleum industry can logically
 be divided into production, refining, and market-
 ing.  Production includes  locating and drilling oil
 wells, pumping and pretreating the crude oil, re-
 covering gas condensate,  and shipping these raw
 products to the  refinery or, in the case of gas,  to
 commercial sales outlets.  Refining, -which ex-
 tends to the conversion of crude to a finished sal-
 able product,  includes oil refining and the manu-
 facture of various chemicals derived from petro-
 leum.  This chemical manufacture is often re-
 ferred to as the petrochemical industry.  Market-
 ing involves the distribution and the  actual sale
 of the finished products.   These activities and
 their sources of air pollution are briefly discussed
 in this introduction.  In the remainder of the chap-
 ter, they are  discussed much more thoroughly,
 and adequate air pollution controls are recom-
 mended.
CRUDE OIL PRODUCTION

The air contaminants emitted from crude oil pro-
duction consist chiefly  of the lighter saturated
hydrocarbons.  The main sources  are process
equipment and storage  vessels.  Hydrogen sul-
fide gas may be an additional contaminant in
some production areas. Internal combustion
equipment, mostly natural gas-fired compres-
sors, contributes relatively negligible quantities
of sulfur dioxide, nitrogen oxides, and particulate
matter.  Potential individual sources of air con-
taminants  are shown in Table 153.
Contribution of air contaminants from crude-oil
production varies widely with location and con-
centration of producing facilities.  In isolated or
scattered locations, many of the sources cannot
be controlled feasibly.   Control and pretreat-
ment facilities such as  natural gasoline plants
are more likely to be located in more developed
or highly productive areas.  These factors are
significant in determining where air  contami-
nant emissions from production equipment must
be minimized by proper use of air pollution con-
trol  equipment.   Control equipment for the vari-
ous air pollution sources associated  with crude-
oil production are listed in  Table 153.  Their ap-
plication can usually result in economic savings.
REFINING

Oil companies have installed or modified equip-
ment not only to prevent economic losses but
also to try to improve community relations, pre-
vent fire hazards,  and comply with air pollution
laws.  The air contaminants emitted from equip-
ment associated with oil refining include hydro-
carbons, carbon monoxide,  sulfur and nitrogen
compounds,  malodorous materials, particulate
matter, aldehydes,  organic  acids, and ammonia.
The potential sources of these pollutants are
shown in Table 154.
Flares and Slowdown Systems

To prevent unsafe operating pressures in process
units during  shutdowns and startups and to handle
miscellaneous hydrocarbon leaks, the refinery
must provide a means of venting hydrocarbon vapors
safely.   Either a properly sized elevated flare
using steam  injection or a series of venturi burn-
ers actuated by pressure increases is satisfactory.
Good instrumentation and properly balanced steam-
to-hydrocarbon ratios are prime factors in the de-
sign of a safe, smokeless flare.


Pressure Relief Valves

In refinery operations, process vessels are pro-
tected from overpressure by relief valves. These
pressure-relieving devices are normally spring-
loaded valves. Corrosion or improper reseat-
ing of the valve seat  results in leakage.  Prop-
er maintenance through routine inspections, or
use of rupture discs, or manifolding the discharge
side to vapor recovery or to a flare minimizes
air contamination from this  source.
Storage Vessels

Tanks used to store crude oil and volatile petro-
leum distillates are a large potential source of
hydrocarbon emissions.  Hydrocarbons can be
discharged to the atmosphere from a storage tank
as a result of diurnal temperature changes, fill-
ing operations,  and volatilization.  Control effi-
ciencies of 85 to 100  percent can be realized by
using properly designed vapor recovery or dis-r
posal systems,  floating-roof tanks, or pressure
tanks.
                                                 581

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582
             PETROLEUM EQUIPMENT
                 Table  153.   SOURCES AND  CONTROL OF AIR CONTAMINANTS FROM
                                 CRUDE-OIL PRODUCTION FACILITIES
       Phase of operation
                                    Source
                                Contaminant
                                                       Acceptable control
 Well drilling,  pumping
Gas venting for production
rate test
Oil well pumping
Effluent  sumps
Methane

Light hydrocarbon vapors
Hydrocarbon vapors, H^S
                        Smokeless flares, wet-gas-
                        gathering system
                        Proper maintenance
                        Replacement with closed vessels
                        connected to vapor recovery
 Storage, shipment
Gas-oil separators


Storage tanks


Dehydrating tanks


Tank truck loading


Effluent sumps


Heaters,  boilers
Light hydrocarbon vapors


Light hydrocarbon vapors,


Hydrocarbon vapors, H,S


Hydrocarbon vapors


Hydrocarbon vapors
                                                     H2S,  HC, SO2,  NOX,
                                                     particulate matter
                        Relief to wet-gas-gathering
                        system

                        Vapor recovery, floating roofs,
                        pressure tanks, white paint

                        Closed vessels, connected to
                        vapor recovery
                        Vapor return,  vapor recovery,
                        vapor incineration, bottom loading

                        Replacement with closed vessels
                        connected to vapor recovery

                        Proper operation,  use of gas fuel
 Compression, absorption,
 dehydrating,  water treating
Compressors, pumps


Scrubbers, KO pots

Absorbers,  fractionators,
strippers

Tank truck loading


Gas odorizing

Waste-effluent treating

Storage vessels


Heaters, boilers
Hydrocarbon vapors,


Hydrocarbon vapors,

Hydrocarbon vapors


Hydrocarbon vapors,


H^S mercaptans

Hydrocarbon vapors

Hydrocarbon vapors, H2S
                                                     Hydrocarbon, SO2, NOX,
                                                     particulate matter
                       Mechanical seals, packing glands
                       vented to vapor recovery

                       Relief to flare or vapor recovery

                       Relief to flare or vapor recovery


                       Vapor return,  vapor recovery,
                       vapor incineration, bottom loading

                       Positive pumping, adsorption

                       Enclosed separators, vapor  re-
                       covery or incineration
                       Vapor recovery, vapor balance,
                       floating roofs

                       Proper operation, substitute gas
                       as fuel
 Bulk-Loading Facilities
 The filling of vessels used for transport of petro-
 leum products  is potentially a large source of hy-
 drocarbon emissions.  As the product is loaded,
 it displaces gases  containing hydrocarbons to the
 atmosphere.  An adequate method of preventing
 these  emissions consists of  collecting the vapors
 by enclosing the filling hatch and piping the cap-
 tured  vapors to recovery or disposal equipment.
 Submerged filling and bottom loading also reduce
 the amount of displaced hydrocarbon vapors.

 Catalyst Regenerators

 Modern refining processes include many opera-
 tions using solid-type catalysts.  These catalysts
 become contaminated with coke buildup during
 operation and must be regenerated or' discarded.
 For certain processes to be economically feasible,
 for example,  catalytic cracking,  regeneration of
                               the catalyst is a necessity and is achieved by bur
                               ing off the coke under controlled combustion con-
                               ditions.  The  resulting flue gases may contain
                               catalyst dust, hydrocarbons,  and other impuritie
                               originating in the  charging stock,  as well as the
                               products of combustion.

                               The dust problem encountered in regeneration  of
                               moving-bed-type catalysts requires control by
                               water scrubbers and cyclones,  cyclones  and pre-
                               cipitators, or high-efficiency cyclones, depend-
                               ing upon the type of catalyst,  the process, and th
                               regenerator conditions.  Hydrocarbons,  carbon
                               monoxide, ammonia,  and organic acids can be
                               controlled effectively by incineration in carbon
                               monoxide waste-heat boilers.  The waste-heat
                               boiler offers a secondary control feature for
                               plumes emitted from fluid catalytic cracking
                               units.  This type of visible plume,  shown in Fig-
                               ure 430, whose degree of opacity is dependent
                               upon atmospheric humidity,  can be eliminated by
                               using the carbon monoxide waste-heat boiler.

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                                         General Introduction
                                                                               583
                Table 154.   POTENTIAL SOURCES OF EMISSIONS FROM OIL REFINING
 Type of emission
                               Potential source
Hydrocarbons
Sulfur oxides


Carbon monoxide

Nitrogen oxides

Particulate matter

Odors


Aldehydes

Ammonia
Air bio-wing, barometric condensers,  blind changing,  blowdown systems, boilers,
catalyst regenerators, compressors,  cooling towers,  decoking operations, flares,
heaters, incinerators, loading facilities, processing vessels, pumps, sampling
operations, tanks, turnaround operations, vacuum jets, waste-effluent-handling
equipment

Boilers, catalyst regenerators, decoking operations,  flares, heaters, incinerators,
treaters, acid sludge disposal

Catalyst regenerators, compressor engines,  coking operations, incinerators

Boilers, catalyst regenerators, compressor  engines,  flares

Boilers, catalyst regenerators, coking operations, heaters,  incinerators

Air blowing, barometric condensers,  drains,  process vessels,  steam blowing,
tanks, treaters,  waste-effluent-handling equipment

Catalyst regenerators, compressor engines

Catalyst regenerators
          Figure 430. A fluid catalytic cracking unit as a source of a visible plume.  Use of a carbon monoxide
          waste-heat boiler eliminates this plume formation.

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 584
                                      PETROLEUM EQUIPMENT
 Other processes in refining operations employ
 liquid or solid catalysts.  Regenerating some of
 these catalysts at the unit is feasible.  Other
 catalysts are consumed or require special treat-
 ment by their manufacturer.  Where regenera-
 tion  is possible, a closed system can be effected
 to minimize the release of any air contaminants
 by venting the regenerator effluent to the firebox
 of a  heater.
 Effluent-Waste Disposal

 Waste water, spent acids,  spent caustic and
 other waste liquid materials are generated by
 refining operations and present disposal prob-
 lems.  The waste water is processed through
 clarification units or gravity separators.  Un-
 less  adequate control measures are taken, hy~
• drocarbons contained in the waste 'water are
 emitted to the atmosphere.  Acceptable control
 is achieved by venting the clarifier to vapor re-
 covery and enclosing the separator with a float-
 ing roof or a vapor-tight cover.  In the latter
 case, the vapor section should be gas blanketed
 to prevent explosive mixtures and fires.  Spent
 •waste materials can be recovered as acids or
 phenolic compounds,  or hauled to an acceptable
 disposal site (ocean or desert).
Pipeline Valves and Flanges, Blind Changing,
Process Drains

Liquid and vapor leaks can develop at valve stems
as a result of heat,  pressure, friction, corro-
sion, and vibration.  Regular equipment inspec-
tions, followed by adequate maintenance can keep
losses at a minimum.  Leaks at flange  connec-
tions are negligible if the connections are proper-
ly installed and maintained.  Installation or re-
moval of pipeline blinds can result in spillage  of
some product.  A certain amount of this spilled
product evaporates regardless of drainage and
flushing facilities.   Special pipeline blinds have,
however, been developed to reduce the  amount of
spillage.
In refinery operation, condensate water and
flushing water must be drained from process
equipment.   These drains also remove  liquid
leakage or spills and water used to cool pump
glands.  Modern refining designs provide waste-
water-effluent systems with running-liquid-sealed
traps and liquid-sealed and covered junction
boxes.  These seals keep the amount of liquid
hydrocarbons exposed to the air at a minimum
and thereby reduce hydrocarbon losses.
 Pumps and Compressors

 Pumps and compressors required to move liq-
 uids and gases in the refinery can leak product
 at the point of contact between the moving shaft
 and stationary casing.  Properly maintained pack-
 ing  glands  or mechanical seals minimize the emis-
 sions from pumps.  Compressor glands can be
 vented to a vapor recovery system or smokeless
 flare.

 The internal combustion engines normally used to
 drive the compressors  are fueled by natural or
 refinery process gas.  Even with relatively high
 combustion efficiency and  steady load conditions,
 some fuel can pass through the engine unburned.
 Nitrogen oxides, aldehydes, and sulfur oxides
 can also be found in the exhaust gases.  Control
 methods for reducing these contaminants are
 being studied.

 Air-Blowing  Operations

 Venting the air used  for "brightening" and agita-
 tion of petroleum products or oxidation of asphalt
 results in  a discharge  of entrained hydrocarbon
 vapors  and mists,  and  malodorous compounds.
 Mechanical agitators that  replace air agitation
 can reduce the volumes of these emissions. For
 the effluent fumes from asphalt oxidation, incin-
 eration gives  effective  control of the hydrocar-
 bons and malodors.
Cooling Towers

The large amounts of -water used for cooling are
conserved by recooling the water in wooden tower
Cooling is accomplished by evaporating part of
this water.  Any hydrocarbons that might be en-
trained or dissolved in the "water as a  result of
leaking heat exchange equipment are readily dis-
charged to the atmosphere.  Proper design and
maintenance of heat exchange equipment mini-
mizes this loss.   Advancement of the fin-fan cool
ing equipment has also replaced the need of the
conventional cooling tower in many instances.
Process water that has come into contact -with a
hydrocarbon stream or has otherwise  been con-
taminated with odorous material should not be
piped to a cooling tower.
Vacuum Jets and Barometric Condensers

Some process equipment is  operated at less than
atmospheric pressure.  Steam-driven vacuum
jets and barometric condensers are used to ob-
tain the  desired vacuum.  The lighter hydrocar-
bons that are not condensed are discharged to
the atmosphere unless controlled.  These hydro-
carbons can be completely controlled by incin-
erating the discharge.  The barometric hot -well
can also b'e enclosed and vented to a vapor dis-
posal system.  The water of the hot -well  should
not be turned to a cooling tower.

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                                      Waste-Gas Disposal Systems
                                                                        585
 EFFECTIVE AIR POLLUTION CONTROL MEASURES

 Control of air contaminants can be accomplished
 by process change, installation of control equip-
 ment, improved housekeeping, and better equip-
 ment maintenance.  Some combination of these
 often proves the most effective solution.  Table
 155 indicates various methods of controlling
 most air pollution sources encountered in the
 oil refinery.   These techniques are also applicable
 to petrochemical operations.  Most of these con-
 trols result in some form of economic saving.


 MARKETING

 An extensive  network of pipelines,  terminals,
 truck fleets,  marine tankers, and storage and
 loading equipment must be used to deliver the
                              finished petroleum product to the user.  Hydro-
                              carbon emissions  from the distribution of prod-
                              ucts derive principally from storage vessels and
                              filling operations.  Additional hydrocarbon emis-
                              sions may occur from pump  seals, spillage,  and
                              effluent-water separators.  Table 156 lists prac-
                              tical methods of minimizing  these emissions
                              from this section of the industry.


                                   WASTE-GAS DISPOSAL SYSTEMS

                              INTRODUCTION
                              Large volumes of hydrocarbon gases are pro-
                              duced in modern refinery and petrochemical
                              plants.  Generally, these gases are used as fuel
                              or as raw material for further processing.  In
                              the past,  however, large  quantities of these gases
                Table 155.  SUGGESTED CONTROL MEASURES FOR REDUCTION OF
                       AIR CONTAMINANTS FROM PETROLEUM REFINING
        Source
                               Control method
Storage vessels


Catalyst regenerators

Accumulator vents
Slowdown systems

Pumps and compressors
Vacuum jets
Equipment valves

Pressure relief valves
Effluent-waste disposal

Bulk-loading facilities
Acid treating


Acid sludge storage and
shipping
Spent-caustic handling

Doctor treating


Sour-water treating


Mercaptan disposal


Asphalt blowing

Shutdowns, turnarounds
Vapor recovery systems; floating-roof tanks; pressure tanks; vapor balance;
painting tanks white

Cyclones - precipitator - CO boiler; cyclones - water scrubber; multiple cyclones

Vapor recovery; vapor incineration
Smokeless flares - gas recovery

Mechanical seals; vapor recovery; sealing glands by oil pressure; maintenance
Vapor incineration

Inspection and maintenance
Vapor recovery; vapor incineration; rupture discs; inspection and maintenance
Enclosing separators; covering sewer boxes and  using liquid seal; liquid seals
on drains

Vapor collection with recovery or incineration; submerged or bottom  loading
Continuous-type agitators with mechanical mixing; replace with catalytic
hydrogenation units; incinerate all vented cases;  stop sludge burning
Caustic scrubbing; incineration; vapor return system; disposal at sea


Incineration; scrubbing

Steam strip spent doctor solution to hydrocarbon recovery before air  regen-
eration;  replace treating unit with other, less objectionable units  (Merox)
Use sour-water oxidizers and gas incineration; conversion to ammonium
sulfate

Conversion to disulfides;  adding to catalytic cracking charge stock; incin-
eration; using material in organic synthesis

Incineration; water scrubbing (nonrecirculating type)

Depressure and purge to vapor recovery

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586
        PETROLEUM EQUIPMENT
                      Table 156.  SOURCES AND CONTROL OF HYDROCARBON
                             LOSSES FROM  PETROLEUM MARKETING
             Source
                          Control method-
      Storage vessels


      Bulk-loading facilities


      Service station delivery

      Automotive fueling

      Pumps

      Separators

      Spills, leaks
Floating-roof tanks; vapor recovery; vapor disposal; vapor balance;
pressure tanks; painting tanks white

Vapor collection with recovery or incineration; submerged loading,
bottom loading

Vapor return; vapor incineration

Vapor return

Mechanical seals; maintenance

Covers; use of  fixed-roof tanks

Maintenance; proper housekeeping
were considered waste gases,  and along with waste
liquids, were dumped to open pits and burned,
producing large volumes of black smoke.  With
modernization of processing units,  this method of
waste-gas disposal, even for emergency gas re-
leases, has become less acceptable to the indus-
try.  Moreover, many local governments have
adopted or are contemplating ordinances limit-
ing the opacity of smoke from, combustion  process-
es.

Nevertheless, petroleum refineries are still faced
with the problem of safe disposal of volatile liq-
uids and gases resulting from scheduled shut-
downs  and sudden or unexpected upsets in  process
units.  Emergencies that can cause  the sudden
venting of excessive amounts of gases and vapors
include fires, compressor failures, overpres-
sures in process vessels,  line breaks, leaks,  and
power  failures.  Uncontrolled releases of large
volumes of gases also constitute a serious safety
hazard to personnel and equipment.

A  system for disposal of emergency and waste
refinery gases consists of a manifolded pres-
sure-relieving or blowdown system, and a blow-
down recovery system or a system  of flares for
the combustion of the excess gases, or both. Many
refineries, however, do not operate blowdown
recovery systems.   In addition to disposing of
emergency and excess gas flows, these  systems
are used in the evacuation of units during  shut-
downs  and turnarounds.  Normally a unit is shut
down by depressuring into a fuel gas or vapor
recovery system with further depressuring to
essentially atmospheric pressure by venting to
a low-pressure flare system.  Thus, overall
emissions  of refinery hydrocarbons are sub-
stantially reduced.
                         Refinery pressure-relieving systems,  common-
                         ly called blowdown systems, are used primarily
                         to ensure the safety of personnel and protect
                         equipment in the event of emergencies  such as
                         process upset, equipment failure,  and  fire.  In
                         addition,  a properly designed pressure relief
                         system permits substantial reduction of hydro-
                         carbon emissions to the atmosphere.

                         The  equipment in a refinery can operate  at pres
                         sures  ranging from less than atmospheric to
                         1, 000  psig and higher.   This equipment must be
                         designed to permit safe  disposal of excess  gase
                         and liquids in case operational difficulties or
                         fires occur.  These materials  are  usually re-
                         moved from the process area by automatic safe
                         and relief valves, as well as by manually con-
                         trolled valves, manifolded to a header  that con-
                         ducts the  material away from the unit involved.
                         The preferred method of disposing of the waste
                         gases that cannot be recovered in a blowdowri
                         recovery  system is by burning in a smokeless
                         flare.  Liquid blowdowns are usually conducted
                         to appropriately designed holding vessels and
                         reclaimed.

                         A blowdown or pressure-relieving system  con-
                         sists  of relief valves, safety valves, manual
                         bypass valves, blowdown headers, knockout ves
                         sels,  and holding tanks.  A blowdown recovery
                         system also includes compressors and vapor si
                         vessels such as gas holders or vapor spheres.
                         Flares are usually considered as  part  of the bl<
                         down system in a modern refinery.
                         The pressure-relieving system can be used for
                         liquids or vapors or both.  For reasons of
                         economy and safety, vessels and equipment dis

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                                      Waste-Gas Disposal Systems
                                          587
charging to blowdown systems are usually segre-
gated according to their operating pressure.  In
other words,  there is a high-pressure blowdown
system for equipment working, for example,
above  100  psig, and low-pressure systems for
those vessels with working pressures below 100
psig.  Butane and propane are usually discharged
to a separate blowdown drum, which is operated
above  atmospheric pressure to increase recov-
ery of liquids.  Usually a direct-contact type of
condenser is used to permit recovery of as much
hydrocarbon liquid as possible from the blow-
down vapors.  The noncondensables are burned
in a flare.

A pressure-relieving  system used in one modern
petroleum, refinery is shown in Figure 431.  This
system is  used not only as  a safety measure but
also as a means  of reducing the emission of hy-
drocarbons to the atmosphere.  This  installation
actually includes four separate collecting systems
as  follows:  (1) The low-pressure blowdown  sys-
tem for vapors from equipment with working
pressure below 100 psig,  (2) the high-pressure
blowdown  system for  vapors from equipment
with working pressures above 100 psig,   (3) the
liquid blowdown system for liquids at all pres-
sures, and  (4) the light-ends blowdown for butanes
and lighter hydrocarbon blowdown products.
The liquid portion of light hydrocarbon products
released through the light-ends blowdown sys-
tem is recovered in a drum near the flare.  A
backpressure of 50 psig is maintained  on the
drum, which minimizes the amount of vapor that
vents through a backpressure regulator to the
high-pressure blowdown line.  The high-pres-
sure, low-pressure, and liquid-blowdown sys-
tems  all discharge into the main blowdovn ves-
sel.   Any entrained liquid is dropped  out and
pumped to a storage tank for  recovery.   Offgas
from this blowdown drum flows to  a vertical
vessel with baffle trays in which the  gases are
contacted directly with water, which condenses
some of the hydrocarbons and permits their re-
covery.  The  overhead vapors from this so-
called sump tank flow to the flare  system mani-
fold for disposal by burning in a smokeless  flare
system.

The unique blowdown system  shown in Figure 432
•was  installed primarily as an air pollution con-
trol measure.   The system serves a delayed cok-
                                                                                 TO FLARE STACK
                                                                                          *-
                                                                  LIGHT-ENDS CONDENSATE RECOVERY
                              Figure 431.  Typical modern refinery blowdown system.

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588
PETROLEUM EQUIPMENT
          GAS OIL
      STEAM, HATER,
      AND HYDROCARBONS
          GAS OIL
                        SCRUBBER
                                             AIR
                                             CONDENSERS
                                                         AIR
                                                         SUB-COOLER
                                                             7           \
                                                             I  ACCUMULATOR  f}-.
                                                           OIL
                                                           SEPARATION
                                                           TANK
                                                                                          FLARE
                                                                                HATER SEAL
                                                                                DRUM
                                                                           SKIMMED OIL TO STORAGE
                                                                            WATER TO TREATING UNIT
                                     Figure 432. Coke drum blowdown system.
ing unit.  In this process, each drum is taken off
the line as it is filled with coke.  The  drum is
then purged  with steam and  cooled with water.
The steam-water-hydrocarbon mixture flows to
a gas oil  scrubber whose  primary purpose  is to
remove entrained coke fines.   At the same time
some heavier hydrocarbons are condensed, and
the mixture  is pumped to  a  settling tank.  The
scrubbed gases flow to an air-cooled condenser
and then through an air-cooled subcooler to an
accumulator drum.


The air condenser sections  are controlled by
temperature and used as needed.  The design
outlet temperature range  of the condensers is
212°  to 270°F, and about 200°F for the sub-
cooler.
 The oil layer in the accumulator is skimmed
 off and pressured to the oil-settling tank while
 the water phase is sewered.  Offgas flows through
 a. water seal to a smokeless elevated flare.  The
 oil-settling tank is a 3, 000-barrel fixed-roof tank
 equipped -with an oil  skimmer.   The oil phase  is
 pumped to storage,  and the water is sewered
 for further treatment at a central waste-water
 facility.
                This installation has eliminated a previous nui-
                sance from heavy oil mist and the daily emission
                of approximately 5-1/2 tons of hydrocarbons.
                Design of Pressure Relief System

                The design of a pressure relief system is one of
                the most important problems in the planning of a
                refinery or petrochemical plant.  The safety of
                personnel  and  equipment depends upon the prop-
                er design and functioning of this type of  system.
                The consequences  of poor design can be disastrou

                A pressure relief system can consist of one re-
                lief valve,  safety valve,  or  rupture disc,  or of
                several relief  devices manifolded to a common
                header.  Usually the systems are segregated
                according  to the type of material handled, that
                is,  liquid or vapor, as well as to the operating
                pressures involved.

                The several factors that must be considered in
                designing  a pressure relief system are   (1) the
                governing code, such as that of ASME (American
                Society of Mechanical Engineers,  1962);  (2) chai
                acteristics of  the pressure  relief devices; (3) th'
                design pressure of the equipment protected by

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Waste-Gas Disposal Systems
                                                                                                 589
 the pressure relief devices,  (4) line sizes and
 lengths; and  (5) physical properties of the mate-
 rial to be relieved to the system.

 In discussing pressure relief systems, the
 terms commonly used  should be defined.  The
 following definitions are taken from the API
 Manual (I960).

 1.   A relief valve is an automatic pressure-
     relieving device actuated by the static pres-
     su^e upstream of the valve.  It opens further
     with increase  of pressure over the set pres-
     sure.   It is  used primarily for liquid service.

 2.   A safety valve is an automatic relieving de-
     vice actuated by the static pressure upstream
     of the valve and characterized by full opening
     or pop action upon opening.  It is used for
     gas or vapor service.

 3.   A rupture disc consists of a thin metal di-
     aphragm held between  flanges.

 4.   The maximum allowable working pressure
     (that is, design pressure),  as defined in the
     construction codes for  unfired pressure  ves-
     sels, depends  upon the type  of material, its
     thickness, and the  service condition set  as
     the basis for design.  The vessel may not be
     operated above this pressure or its equivalent
     at any metal temperature higher than that
     used in its design;  consequently,  for that
     metal temperature, it is the highest pressure
     at -which the primary safety  or relief valve
     may be set to open.

 5.   The operating pressure of a vessel is the
     pressure, in psig,  to which the vessel is
     usually subjected in service.  A processing
     vessel is usually designed to a maximum
     allowable working pressure, in psig,  that
     will provide  a suitable  margin above the
     operating pressure in order to prevent any
     undesirable  operation of the relief valves.
     (It is suggested that this margin be approxi-
     mately 10 percent higher, or 25 psi, which-
     ever is greater. )

6.   The set pressure, in psig, is the  inlet pres-
     sure at which the safety or relief valve is
     adjusted to open.

7.  Accumulation is the pressure increase over
    the maximum allowable working pressure of
    the vessel during discharge to the safety or
    relief valve expressed as a percent of that
    pressure  or  pounds per square inch.

8.  Over pressure is the pressure increase over
    the set pressure of the  primary relieving de-
    vice.  It is the same as accumulation when
                     the relieving device is set at the maximum
                     allowable working pressure of the vessel.
                     (From this definition note that  when the set
                     pressure of the first safety  or relief valve
                     to open is  less than the maximum  allowable
                     working pressure of the vessel  the over-
                     pressure may be  greater than 10 percent of
                     the set pressure of the first safety or relief
                     valve. )

                9.   Slowdown is the difference between the set
                     pressure and the  reseating pressure of a
                     safety or relief valve,  expressed as a per-
                     cent of a set pressure or pounds per square
                     inch.

                10.  Lift is the rise  of the disc in a safety or re-
                     lief valve.

                11.  Backpressure is the pressure developed on
                     the discharge side of the safety valves.

                12.  Superimposed backpressure is the pressure
                     in the  discharge header before the safety valve
                     opens  (discharged from other valves).

                13.  Built-up backpressure  is the pressure in the
                     discharge header  after the safety valve  opens.

                Safety Valves

                Nozzle-type  safety valves are available in the con-
                ventional or balanced-bellows configurations.
                These two  types of valves are shown schematic-
                ally in Figures 433 and 434.  Backpressure  in the
                piping downstream of the standard-type valve
                affects its  set pressure, but theoretically,  this
                backpressure does not affect the set pressure of
                the balanced-type valve.  Owing, however, to
                imperfections in manufacture and limitations of
                practical design, the balanced valves available
                vary in relieving pressure when  the backpres-
                sure reaches approximately 40 percent of the set
                pressure.  The actual accumulation depends up-
                on the manufacturer.

                Until the advent of balanced valves,  the general
                practice in the industry was to select safety valves
                that start relieving at the design pressure of the
                vessel and  reach full capacity at 3 to 10 percent
                above the design pressure.  This overpressure
                was  defined as  accumulation.   With the balanced
                safety valves, the allowable accumulation can be
                retained with smaller pipe size.

                Each safety valve installation is an individual
                problem.  The  required capacity of the valve
                depends upon the condition producing the over-
                pressure.  Some of the conditions that can cause
                overpressure in refinery process vessels, and
                the  required relief capacity for each condition
                are given in Table 157.

-------
590
                                          PETROLEUM EQUIPMENT
                             SPRING
                                                  TO VENT
                                                  LINE
                                             TO VENT
                                             LINE
      FROM PRESSURE VESSEL
      (BACK PRESSURE DECREASES SET PRESSURE)
FROM PRESSURE VESSEL
(BACK PRESSURE INCREASES SET  PRESSURE)
                         Figure 433. Schematic diagram of standard safety valves (Samans, 1955).
                             SPRING
                                          D
                                                                              BONNET VENT
                                                TO VENT
                                                LINE
                                           TO  VENT
                                           LINE
                                                                                              U
           FROM  PRESSURE VESSEL                                   FROM PRESSURE  VESSEL

                      (BACK PRESSURE HAS VERY LITTLE EFFECT ON SET PRESSURE)


                         Figure 434. Schematic diagram of balanced safety valves (Samans,  1955).
Rupture Discs

A  rupture disc is an emergency relief device
consisting of a thin metal diaphragm carefully
designed to rupture ?*• a predetermined pressure.
   The obvious difference between a relief or safety
   valve and a rupture disc is that the valve reseats
   and the  disc does not.  Rupture discs may be in-
   stalled in parallel or series with a relief valve.
   To prevent an incorrect  pressure  differential

-------
                                     Waste-Gas Disposal Systems
                                                                 591
from existing, the space between the disc and
the valve must be maintained at atmospheric
pressure.  The arrangement of a rupture disc
to supplement a  relief or safety valve is  shown
in Figure 435.  In an installation such as this,
                   the relief or safety valve is sized by convention-
                   al methods, presented later,  and the  rupture
                   disc is usually designed to relieve at  1. 5 times
                   the maximum allowable working pressure of the
                   vessel (Bingham, 1958).
 Table 157.   OPERATIONAL DIFFICULTIES OF A REFINERY AND REQUIRED RELIEF CAPACITIES
                                  (American Petroleum Institute,  I960)
              Condition
                                                             Required relief capacity
                                       Relief valve
                                     for liquid relief
                          Safety relief valve for vapor relief
 Closed outlets on vessels
 Cooling-water failure to condenser
                                     Maximum liquid
                                     pump-in rate
 Top-tower reflux failure

 Sidestrea'm reflux failure

 Lean-oil failure to absorber

 Accumulation of noncondensables


 Entrance of "highly volatile
 material:
  Water into hot oil
  Light hydrocarbons into hot oil
 Overfilling storage or surge vessel


 Failure of automatic controls:
  Tower pressure  controller,
  to closed position

  All valves,  to closed position,
  except water and reflux valves

 Abnormal heat or  vapor  input:
  Fired heaters or steam reboilers
  Split  reboiler tube


 Internal explosions


 Chemical reaction
 Hydraulic expansion:
  Cold fluid shut in

  Lines outside process area
  shut in
 Exterior  fire
Maximum liquid
pump-in rate
No operational
requirement
Nominal size

Nominal size
                 Total incoming steam and vapor, plus that generated
                 therein under normal operation
                 Total incoming steam and vapor, plus that generated
                 therein under normal operation,  less vapor  condensed
                 by sidestream reflux.  Consideration may be given to
                 the suppression of vapor  production as the result of the
                 valve's relieving pressure being above operating pres-
                 sure, with the assumption of constant heat input

                 Total vapor to condenser
                 Difference between vapor entering  and leaving section

                 None
                 Same effect in towers as  for cooling-water failure or
                 overfilling in other vessels
                 For towers--usually not predictable
                 For heat exchangers--assume an area twice the
                 internal cross-sectional area of one tube so as  to
                 provide for the vapor generated by the entrance of
                 the volatile fluid
Total normally uncondensed vapor


No operational requirement


Estimated maximum vapor generation including non-
condensable from overheating

Steam entering from twice the cross-sectional area
of one tube

Not controlled by conventional relief devices, but by
avoidance of circumstances

Estimated vapor generation from both normal and un-
controlled conditions
                                                     Estimate by the method given in Sect 6 of API Manual,
                                                     RP 520

-------
592
  PETROLEUM EQUIPMENT
                         TO VENT   RELIEF VALVE
                                  ATTACHES HERE
     RUPTURE DISC
   CONNECTION FOR
   PRESSURE GAGE
                                *•  TO VESSEL
                 In determining the size  of a disc, three important
                 effects that must be evaluated are low rupture
                 pressure,  elevated temperatures,  and corrosion.
                 Minimum rupture  pressures -with maximum
                 recommended temperatures  are given in  Table
                 158.  Manufacturers can supply discs that are
                 guaranteed to burst at plus or minus 5 percent
                 of their rated pressures.

                 The corrosive effects of a system determine
                 the type of material used in a disc.   Even a
                 slight amount of corrosion can drastically short-
                 en disc life.  Discs are available with plastic
                 linings, or they can be made from pure carbon
                 materials.
                                 RELIEF VALVE
                   PROCESS GAS LINE  ATTACHES HERE
                 Sizing rupture discs

                 The causes of overpressure,  and the required
                 capacity for a disc can be determined by meth-
                 ods  previously discussed.

                 The first estimate of the required rupture disc
                 area can be made by using the formula  (Bingham,
                 1958):
                                                                              Q
                                                                      A  =
                                                                             11.4 P
                                                               (119)
  Figure 435. Rupture disc and relief valve installation:
  (top) How rupture disc gives secondary protection,
  (bottom) assembly protects relief valve from disc
  fragments (Bingham, 1958).
                                                        where
                      A  =  area, of disc,  in.
                  Table 158.  MINIMUM RUPTURE PRESSURES,  psig (Puleo,  I960;
                        Copyrighted by Gulf Publishing  Co. ,  Houston, Texas)
Disc size,
in.
1/4
1/2
1
1-1/2
2
3
4
6
8
10
12
16
20
24
Aluminum
310
100
55
40
33
23
15
12
9
7
6
5
3
3
Aluminum
lead lined
405
160
84
60
44
31
21
17
19
16
10
8
8
8
Copper
500
250
120
85
50
35
28
25
35
42
55
55
70
60
Copper
lead lined
650
330
175
120
65
50
40
25
35
42
55
55
70
60
Silver
485
250
125
85
50
35
28
24
27
--
--
--

--
Platinum
500
250
140
120
65
45
35
26
--
--
--
--
--
--
Nickel
950
450
230
150
95
63
51
37
30
47
--
--
--
--
Monel
1, 085
530
265
180
105
74
58
43
34
28
360
270
215
178
In con el
1, 550
775
410
260
150
105
82
61
48
--
--
--
--
--
321 or 347
stainless
1, 600
820
435
280
160
115
90
70
55
45
45
33
27
65
    Maximum      250 °F     250 °F
   recommended    120°F     120°C
   temperature

  (base temperature, 72 °F [20°C])
250°F
120°C
250°F
120°C
250°F
120°C
600°F
320°C
750°F
400°C
800'
430'
900°F
480°C
600°F
320"C

-------
                                   Waste-Gas Disposal Systems
                                           593
   Q   =  required capacity,  cfm air
    3.

    P =  relieving pressure, psia.

When the  overpressure is caused by an explosion,
a method  of sizing discs has been presented by
Lowenstein (1958).  In an explosion, a relief or
safety valve does not respond fast enough and a
rupture disc is  required.

The maximum allowable backpressure in an in-
dividual discharge line from a disc  is 10 per-
cent of the disc's bursting pressure.  The max-
imum  allowable backpressure for a. manifolded
blowdown header  serving rupture discs and re-
lief or safety valves should  not exceed the in-
dividual allowable backpressure  for the  lowest
rupture pressure, or  25 percent of  the lowest
set pressure  of the included valves,  -whichever
is less.
Sizing liquid safety valves

To calculate the required area for a relief
valve handling liquid and with constant back-
pressure,  the following formula may be used:
                           .0.5
A  =
                                            (120)
    C  =  constant for relief valve and percent
          accumulation
    Q  =  required liquid flow at flowing tem-
          perature,  gpm
   P  =  relieving pressure at inlet, psia

   P  =;  discharge pressure at outlet, psia

     S  =  specific gravity of fluid at flowing
          conditions.
For one manufacturer, the valve constant is
27. 2.  The overpressure factor for 10 percent
accumulation,  or overpressure,  is determined
from Figure 436 to be 0. 6.  Equation 120 be-
comes, therefore, for this particular type of
valve with a  10 percent  accumulation:
      A  =
                                                                      Ql
             16
                                                               M-2—1
                                                               •"  Lpi-p/J
                                                                                      0.5
                                          (121)
The use of a balanced relief valve such as the
bellows type permits a variable percent back-
pressure but introduces another variable into
the valve-sizing equation.  Equation 121 now
becomes:
where
    A =  effective opening of valve, in.
                                                                        Q
                                                               A  =
                                                                         1
                                                                     16.32 L_
                         P  - P
                          1    2
                                                                                          0.5
                                           (122)
                                                                       EX»»PLE
                                                                      "FIHD cmcin OF 1-1 i
                                                                       IT 10 OVERPRESSURE

                                                                      "»«TERIH - »*TER
                                                                       SET PRESSURE - 100 gsi£
                                                                       «»TEO CUPACITY »T 25 OP = «3 5 |
                                                                        FACTOR = 0 6 (FROM CURVF'
                                                                       CAPACITY AT 10 OP = 0 6 (S3 5) = 50 I gp«
                                              HLOIIBU OVERPRESSURE. *
              Figure 436. Overpressure sizing factor for liquid relief valves  (Consolidated Safety Relief
              Valves, Manning,  Maxwell, and Moore,  Inc., Catalog 1900, Tulsa, Ok I a.).

-------
594
                                        PETROLEUM EQUIPMENT
where nomenclature is as before and L, is the
variable backpressure flow factor.  This factor
is supplied by the particular manufacturer, typ-
ified by Figure 437.

Sizing vapor and gas relief
and safety valves

The theoretical area required to vent a given
amount of gas or vapor can be calculated by
assuming adiabatic reversible flow of an ideal
gas  through a nozzle.  Based upon these as-
sumptions,  the following equation can be de-
rived:
        A  =
                  W
where

     A

     W

     C



   CD
                 CDP1
             rz
             LM
                            ,0. 5
(123)
area, in.

flow capacity, Ib/hr

nozzle gas constant, which varies as
the ratio of specific heats, as shown
in Figure 438

coefficient of discharge for nozzle  or
orifice
                                                   P   =  inlet pressure, psia

                                                    T  =  inlet temperature,  °R

                                                    M  =  average molecular -weight of gas.
                 =   c  /c
                    P  T.
                                                                   specific heat at
                                                                  constant pressure
                                                                   specific heat at
                                                                   constant volume
For hydrocarbon vapors where the actual value
of k is not known, the conservative value of
k = 1. 001 has been commonly used (C = 315).
The nozzle discharge  coefficient for a well-
designed  relief valve is about 0. 97. Hydro-
carbon gases can be corrected  for nonideality
by use of a compressibility factor.  With these
assumptions, equation 123 reduces to:

where
    A =

    Z =
                        area,  in.

                        compressibility factor.  For hydro-
                        carbons, Z may be determined from
                        Figure 439 or is usually taken as  1.0
                        if unknown.




0.6
0.5
0.3
0.2
0.1


















^





















CAP







ACITY C







EXAMPLE
~SET PRESSURE - 100 psig
FLOWING PRESSURE AT IDS OVERPRESSURE - 100 + 10
COHSTAHT BACK PRESSURE - 75 psig OR 69.7 psia
URVE















= 110 psig OR











^






124 7 psia
BACK PRESSURE PERCEHTAGE - 89.7/124.7 = 71.9*
FOLLOW DOTTED LIKE FROM BACK PRESSURE PERCEHTAGE
~ SCALE TO FLOW CORRECTIOH FACTOR SCALE AND FIND
THAT FACTOR EQUALS 0.93















	 .











»^T^










^
i


LlJ
0.
X
UJ

t


USE ONLY F(
WITH tSMSI

X










\







R STANDARD VALVES
IMI BACKPRESSURE


\
s









\
\
>









y
\
\
\
I)
               20        30        40
          BACK PRESSURE PERCENTAGE (ABSOLUTE) =
                                                     50        60        70
                                                       BACK PRESSURE - (ABSOLUTE)
                                                                      60
                                                                                         90
                                                                                       100
                                             FLOWING PRESSURE (SET PRESSURE + OVERPRESSURE)-(ABSOLUTE)
                                                                                    100
              Figure 437. Overpressure sizing factor  for standard  vapor  safety valves (Consolidated Safety
              Relief Valves,  Manning, Maxwell, and Moore, Inc., Tulsa, Okla.).

-------
                                    Waste-Gas Disposal Systems
                                                                                   595








330
3?0
310



















/
'








/
S








/
'








/
\/




0 12 14





/





1
K =




/






6
Vcv



x



FLOW
C ^ 5

1


x






/




ORMULI CIICUL
HI)

g

2

^





1IOKS

0











2
Figure 438.  Nozzle gas constant  (American  Society of
Mechanical Engineers,  1962).
Where the critical pressure ratio is  such that
subsonic fluid velocities are obtained,  a correc-
tion factor K-jjp  as  shown in Figure 440  may be
applied.   For more precise calculations,  the
following  formula may be used:
A =
        W
    2, 370 P
[(P2/P1!
           ZT/M
                                                0.5
                                                         An approximation of the absolute temperature at
                                                         the valve outlet can be calculated under critical
                                                         flow conditions from the following equation:
                                                   T   =  T
                                                                                                     (126)
                                                         where
                                             (125)
   T   =  temperature at valve outlet, °R

    T =  temperature at valve inlet, °R

    k =  ratio of specific heats,  c /c .
                                   p  v
Before 1957,  capacity conversion formulas for
valve sizing in petroleum service were given in
the API-ASME Code (1951).  Since 1957,  these
formulas have been incorporated in Section
VIII of the ASME  Unfired  Pressure Vessel Code
(1962).

The catalogs of relief valve manufacturers are
also sources of valve-sizing methods and  spe-
cific details about various types of valves.

Installing relief and safety valves
and rupture discs

The same general rules for discharge piping
apply equally  to relief and safety valves and
rupture discs.  Inlet piping should be such that
           1.0
           0.1
                         0.5
                                       1.0           1.5
                                            REDUCED PRESSURE PR=-jT
                                                                 2.0
                                                              2.5
                                                                           3.0
                   Figure  439.  Compressibility constants for hydrocarbons (American
                   Petroleum Institute,  1960).
 234-767 O - 77 - 40

-------
596
                                       PETROLEUM EQUIPMENT
  0.02

  0.66


  0.70

  0.74
2 0.82
£
  0.86

  0.90
   0.94
     0.5
             0 0
                      0.7
                              0 8
                                      0.9
                                              I 0
                    CORRECTION FACTOR. «bp
   Figure 440. Correction factor (KhD) for subsonic flow
   (Conison, 1960).
there is direct and unobstructed flow between the
vessel and the relief device.  A conservative
limit for the total pressure drop between the
vessel and the safety valve is 2 percent of the
absolute relieving pressure.

The discharge piping for relief and safety valves
and rupture discs should have  a minimum of
fittings and bends.  There should be minimum
loading on the valve, and  piping should be used
•with adequate supports and expansion joints.
Suitable drains  should be  used to prevent liq-
uid accumulation in the piping  and valves.

Figures 441  to 444 illustrate  good design of
relief device piping (for  further details on
Figures 442 and 444,  see Tables 159 and 160,
respectively).

Knockout vessels

In a vapor blowdown system,  a knockout drum
is used to remove entrained liquids from the
gas stream.  This is  particularly important if
the gas is to be burned in a smokeless flare. A
knockout drum  can be quickly sized or checked
by the use of a  graphical  calculation (see Fig-
ure 445; Kerns, I960).  The diameter of the
drum is based on the  allowable vapor velocity,
which can be determined  by the •well-known
equation:
                           0.5
                                           (127)
where
 u      =  maximum allowable vapor velocity,
  max       .
           ft/sec
                                                          p   -  liquid density, Ib/ft"
                                                                                     q
                                                          p   =  vapor density, Ib/ft"
                                                                 a constant.  Use   =  0. 2 to 0. 3.
                                                                   = 0.227 is often used for light liq-
                                                                 uid loading.
                                                       DESIGN (END TO
                                                       THE ORE OF
                                                       VESSEL EXPANSION
                                                         Figure 441.  Inlet  piping  for  safety valves:
                                                         (left) Horizontal  vessel  nozzles, when used
                                                         for safety valve mounting can  be  connected
                                                         in manner illustrated;  (right) valve can be
                                                         isolated from process  fluid  in manner  illus-
                                                         trated (Driskell,  1960; copyrighted by Gulf
                                                         Publishing Co.,  Houston,  Texas).
                                                       The maximum design velocity should be 0.5umax
                                                       to allow for gas surges.

                                                       Light liquid loads indicate the use of a vertical
                                                       vessel, and heavy liquid loads, a horizontal
                                                       vessel.  The optimum dimensions of the vessel
                                                       •will have a length-to-diameter ratio (L/D)  of 3
                                                       for larger drums and 4 for smaller drums,  and
                                                       never less than 4 feet bet-ween tangents (Kerns,
                                                       1960).

                                                       When wire mesh is used in the drum as an added
                                                       precaution against mist entrainment, the selected
                                                       diameter should be multiplied by 0. 65 for con-
                                                       ventional mesh  and 0. 62 for high-capacity mesh
                                                       (Neimeyer,  1961).

                                                       Surge time for most  designs is 5 to 10 minutes.
                                                       The graphical sizing method of Figure 445 is
                                                       based on a surge time of 7-1/2 minutes.

                                                       The preliminary sizing of a knockout drum is
                                                       illustrated by the following example.
                                                       Given:

                                                       Gas flow 100 ft  /sec (under flow conditions)
                                                       Vapor density,  pv, 0. 1 Ib/ft3
                                                       Liquid density,  p,,  50 Ib/ft3.

-------
                    Waste-Gas Disposal Systems
597
                      DRAIN
                                  B.
                                                    LONG-RADIUS ELBOW
                                                            PROVIDE HORIZONTAL RUN HERE IF
                                                            NECESSARY BECAUSE OF EXPANSION
               PURGE GAS INERT
               TO  PROCESS FLUID
                                                         ENTRANCE ANGLED TO
                                                         REDUCE FRICTION
                                                G.
Figure 442.  Discharge piping for  relief and safety valves:   (A)  For
air or gas  service,  (B) for air,  gas,  or steam service,  (C)  for
liquid service,  (D) for steam or  vapor service,  (E) for  steam  or
vapor service  to 3-inch pipe, (F)  closed system for hazardous
service,  (G) open system for pyrophoric gases (Oriskell,  1960;
copyrighted  by  Gulf Publishing Co.,  Houston,  Texas; for  further
detaiIs,  see Table 159).

-------
598
PETROLEUM EQUIPMENT
                                                         3.  Diameter of vessel:
                               'TOP OF VESSEL
        Figure 443. Discharge piping for relief and
        safety valves:  (top) A cap like one  illus-
        trated protects discharge pipe from being
        plugged with snow,  (bottom) piping must be
        adequately anchored to prevent sway or vi-
        bration while the valve is discharging
        (Driskell, I960; copyrighted by Gulf  Publish-
        ing Co.,  Houston,  Texas).
Problem:

Determine dimensions of knockout drum.

Solution:

1.   Maximum allowable vapor velocity, u
                               0.5
           max
                             0.1
                                   ,0.5
          u      = 5. 06 ft/sec.
           max
2.  Design vapor velocity, u  :
    u    =  u      x  0. 50
     D      max
    u    =  5.06  x  0.50   =   2. 5 ft/sec.
                                                                          f(4)(100) I
                                                                          Ll»(2.5) J
                                                                                     0. 5
                           D  =

                           D  =  7. 12 ft.

                           Use 7 -ft diameter.

                 4.   Height of vessel:

                     Assume  low liquid loading.
                     Use  vertical drum, L/D  =  3.

                     Height = 3  x 7 ft = 21 ft.

                 Alternative solution:

                 The same problem can be solved graphically as
                 follows:
                 1.
                                                                              =  500
                 2.   Enter Figure 445 at 100 cfs and proceed
                     vertically to
                     pjp    =  500.
                      1  v
                     Proceed horizontally and read drum di-
                     ameter as 7 feet.


                 3.   Again assume L/D  ratio  =  3.

                 4.   Therefore, drum dimensions are 7 ft in di-
                     ameter x  2 1 ft high.

                 Sizing a blowdown line

                 As previously stated,  the selection of a par-
                 ticular line  capacity depends upon the following
                 considerations:  (1) Maximum expected vapor
                 flow,  (2) maximum allowable backpressure in
                 the system,  (3)  type of relief device to be used,
                 and (4) governing code.

                 The maximum design capacity of a blowdown line
                 is generally based upon the operation of a group
                 of relief and safety valves.  Selection of a. de-
                 sign capacity is based upon upsets  in the process-
                 or by exterior  fire.  Table 157 indicates the re-
                 lief requirements for various conditions.

                 The maximum  allowable backpressure in the re-
                 lieving system depends  upon the vessel with the
                 lowest  operating or working pressure, the type
                 of valve used,  and the code used.  In the past,
                 the pressure drop in the relief manifold was
                 customarily limited to 10 percent of the set

-------
                                   Waste-Gas Disposal Systems
                                            599
                    Table 159.  SUPPLEMENTARY INFORMATION TO FIGURE 442
                 (Driskell,  I960;  copyrighted by Gulf Publishing Co. ,  Houston, Texas)
Service
Nonhazardous servicea
Air or gas
Liquid
Steam or vapor
Discharge pipe size to 1 in.
Discharge pipe size to 1-1/2 to 2-l/2in.
Discharge pipe size to 3 in. and over
Hazardous service3-
Closed system (to vent stack, burning
stack, or scrubber)
Open system (to atmosphere)
Gasc
Liquidd
Vapor0' d
Pyrophoric gases or vaporc
Letters keyed to
caption for Figure 403
Valve indoors

A,15 B,b E
C

D
B
E


F

A, B
C
A, B, D
G
Valve outdoors

A,bBb
C

D
B
B


F

A, B
C
A, B, D
G
              Low-temperature service

                At or below ambient — design discharge pipe so that snow or ice accumulate
                at any point in the line where the temperature  may be at or below freezing.
                Use A, if possible.   Where necessary, B may be used with a cover.

                Below 32°F--locate  safety valve to avoid need for discharge piping, if
                possible.  Discharge opening and exposed spring must be protected from
                the weather.  A housing or local heating may be  required.  The discharge,
                if properly designed, may be sealed with a  low-viscosity oil and covered
                with plastic to prevent the entrance of moisture.

              aFlammable or toxic fluids are considered hazardous.
              °Discharge pipe not  required if outlet over 7 feet above walkway, or directed
               away from personnel,  or both.
              cCarry discharge outdoors to a safe elevation.
              "Carry to an appropriate drain.
pressure.  As previously stated, however,  the
development of balanced  relief and safety valves
has removed this  restriction.  In the usual re-
finery application, there  can be  considerable
savings in piping and valves with balanced valves
and about a 40 percent backpressure.

Where several valves discharge to a common
header, the use of two separate  relieving sys-
tems--high- and low-pressure—may be econom-
ically advantageous.   Otherwise, a single mani-
fold design will be limited by the lowest pres-
sured vessel.

A reduction in the size of the manifold line may
be achieved if the  operating pressure of a vessel
is  less than the maximum working, or design,
pressure.  The set pressure of the relief or safety
valve can be made less than the  design pressure,
permitting a greater backpressure in the relief
line.
Another method that can be used with standard
safety valves  is to plug the guide and vent the
bonnet, as shown in Figure 433.  An increase in
backpressure lowers the  relieving pressure and
yet does not overpressure the vessel.  The ar-
rangement can, however,  upset the process if
the valve setting is too close  to the operating
pressure.  Thus,  in a manifold system,  an up-
set in one section of a process could cause ad-
ditional relief or safety valves to vent.

In determining the size of a vapor  relief line,
the pressure drop is usually large, and this pre-
cludes the direct use of a Fanning  equation.  In
calculations of compressible  fluid  flow, the follow-
ing criteria are used (Crane Company,  1957):

1.  If the pressure drop is less than 10 percent
    of the inlet pressure,  reasonable accuracy
    is  obtained if the density  of the gas is based
    upon either inlet or outlet conditions.

-------
600
                     PETROLEUM EQUIPMENT
          SAFE
          CLEARANCE
          7 ft
16-gage SHEET STACK
(MAX. WEIGHT 100  Ib
INCLUDING  FLANGE)
STACK WEIGHT OVER
100  Ib INCLUDING
FLANGE

3 JACK SCREWS
SPACED FOR
REMOVAL OF
DISC ASSEMBLY
 /
                                                              INSERTION TYPE
                                                              ASSEMBLY
                                                                                                 STACK
                                                                                                 INDEPENDENTLY
                                                                                                 SUPPORTED
   100-Ib  MAX. WEIGHT
   INCLUDING FLANGE
  lUO-lb MAX.-
                                                   1
                              VENT PIPE
                  \      7
                            v
                                                                STACK
                                                               -INDEPENDENTLY
                                                                SUPPORTED
                                                                -DRAKI BOLTS
                                                            K
                                                                              SUPPORT
                                                                              INDEPENDENT OF
                                                                              DISC ASSEMBLY
                                                                          ALLOW CLEARANCE
                                                                          FOR EASY REMOVAL
                                                                          --CONSIDER CROWN
                                                                          OF DISH
                                                                E.
            Figure 444. Discharge piping for  rupture discs: (A) For lightweight assembly, (B) for heavy assembly
            with short stacK, (C) for heavy assembly with  long stack,  (D) double disc with lightweight assembly,
            (E) double disc with heavy assembly, (F) closed system (Driskell, 1960;  copyrighted  by Gulf Publish-
            ing Co., Houston  Texas; for further details, see Table 162).
 Table 160.   SUPPLEMENTARY INFORMATION
         TO FIGURE 444 (Driskell,  I960;
       copyrighted by Gulf Publishing Co. ,
                 Houston,  Texas)

Service
Discharge to atmosphere
Outdoors, lightweight assembly3
Outdoors, heavy assembly
Indoors0
Closed system
Letters keyed to
caption for Figure 405
Single disc
A
B, C
C
F
Double disc
D
E
E
F
 aParts of assembly 100 Ib or less for ease of handling.
 "Parts of assembly exceed 100 Ib and require mechanical
  lifting.
 cVent stack through roof.
                                      2.   If the pressure drop is  greater than 10 per-
                                           cent but less than about 40 percent of inlet
                                           pressure, the Fanning  equation maybe used
                                           with  reasonable accuracy if an average den-
                                           sity is used.  Otherwise a. method -with a
                                           kinetic  energy correction can be used.


                                      3.   For greater pressure drops,  empirical equa-
                                           tions can  be used.


                                           API Manual RP520 presents kinetic-energy cor-
                                           rection factors, as  shown in Figure 446,  that
                                           may  be applied to the Fanning equation.


                                           Another method generally used involves dividin
                                           the line into increments having pressure drops

-------
                                    Waste-Gas Disposal Systems
                                            601
               100
               10
                                            00^
                                          n"*
                                          .
              1.0
              0.1
                                       10                     100
                             DRUM VAPOR CAPACITY (AT FLOWING TEMPERATURE AND PRESSURE), cfs
                               1,000
                    Figure  445. Knockout drum-sizing chart (Kerns,  1960; copyrighted
                    bv Gulf Publishing Co.,  Houston, Texas).
 10 percent or less and working from the line
 terminus back to the relief device.

With the greater availability of computers more
exact methods of calculation can be used. Machine
computers can handle the tedious equations for
calculating pressure drop  of compressible fluids
where the velocity is subsonic and the density of
the vapor or gas is constantly changing.

For hand calculations, a simplified method has
been proposed (Conison, I960) that gives con-
servative results.  The maximum carrying capac-
ity  of any line is limited by the acoustic velocity
at the outlet of the pipe and in turn sets the out-
let pressure. The equation developed by Crocker
for solving the maximum pipe capacity for flow-
ing gas  and vapors is as follows:
P~  =  -T-
    l/
W_ Vk
d2
                         RT
                       11,400
                                           (128)
 where
    P-,  -  outlet pressure, psia

     d  =  ID of pipe line,  in.
     R  =
              1,544
          mol wt of gas
     k  =  ratio of specific heats,c  /c
                                 p  v
     W  =  vapor or gas, Ib/hr
     T =
          outlet temperature, °R.
Equation 128 is used to determine the pressure
at the pipe line outlet with W pounds  of gas or
vapor flowing per hour.  If the vapors are dis-
charged to the atmosphere, the outlet pressure
must be equal to or greater than atmospheric
pressure.  If P2 calculated is less than 1 atmo-
sphere, then W can be increased before any ef-

-------
 602
                                           PETROLEUM EQUIPMENT
                                                              = KINETIC-ENERGY CORRECTION FACTOR
                                                              = INTERNAL DIAMETER OF PIPE,  in
                                                              = INLET PRESSURE  PSia
                                                              = PRESSURE DROP IN LINE BASED ON
                                                                INLET CONDITIONS (P, AND P, I
                                                              = CORRECTED PRESSURE DROP psi
                                                              = Ib tir GAS
                                                              = INLET DENSITY pel
                                          016    0.20    0.24   028   032
                                            PRESSURE DROP (BASED ON P,  AND P,_>
                                                INLET PRESSURE  psia
                         Figure 446.  Kinetic energy  correction for pressure  drop  for
                         isothermal  flow (American  Petroleum Institute,  1960).
feet is made on backpressure in the line.  If T?2
calculated is equal to atmospheric pressure,
then any increase in W increases  the  discharge
pressure at the pipe outlet.   If P2  calculated is
greater  than atmosphere,  then it must be added
to the line friction loss calculated  from the re-
lief device to the pipe  outlet in order  to determine
the total backpressure at the relief device.

To simplify the calculation of the line pres-
sure  drop,  the following equation can be used
when the line lengths are approximately 100 feet
or more  or velocity change is small:
                                         1/2
•where
   P   =  inlet pressure,  psig

-------
                                   Waste-Gas Disposal Systems
                                                                                                  603
      vt
      f   =

      1   =
outlet pressure,  psig  (equal to values
in equation 128 when ?2 = atmospheric
pressure  or greater)

vapor density, Ib/ft ,  at line terminus

a friction factor

line length,  ft
      g  =   32.2 ft/sec^

      D  =   line ID,  ft
         =  velocity at line outlet,  fps.

Inspection of equation 1 29 reveals that the quantity
'        2^
        j.
            is the Fanning equation for determin-

ing pressure drop in a line in pounds per square
foot.  This quantity is readily determined with the
aid of conventional charts in handbooks and other
publications.

All gas  or  vapor terms in the final or line outlet
conditions  are based on the inlet temperature T,
calculated  from equation  126  and P2 from equa-
tion 129.  Where the line lengths are less than
100 feet, equation 129 is  modified  as follows:
                                           (130)
where:  [i.  =   inlet velocity, fps.
Equation 130 can be rearranged to facilitate trial
and error solutions:
                                          1/2
                                           (131)

The constant-temperature approach provides  a
safety factor because the line temperature is  less
than the relief valve outlet temperature.  The de-
gree of cooling depends upon atmospheric condi-
tions.
                                                     The use of this method of sizing a vapor relief
                                                     line is illustrated by the following example:
                                                      Given:

                                                      Expected gas flow, 25, 000 Ib/hr

                                                      Outlet temperature at valve,  790°R

                                                      Atmospheric pressure,  14.5  psia
                                                      Specific  volume (v) at 14. 5 psia and 790°R,
                                                      13 ft3/lb

                                                      Length of line, 600 equivalent ft

                                                      Maximum allowable pressure drop,  psia
                                                      k of vapor,  1. 3

                                                      Molecular weight of vapor, 44
                                                      Friction factor of gas,  0. 017.
                                                      Problem:

                                                      Select diameter of blowdown line for given condi-
                                                      tions.

                                                      Solution:

                                                      1.  Assume a  6-inch ID pipe and calculate ter-
                                                          minal pressure P->:

                                                                    Vt
                                                                        RT
                                                                 W Vk (k+ 1)
                                                                   2   11,400
                                                                 25,000
                                                                   36
                                                              A| 1.544V     790     \
                                                               V\  44  /\1. 3  (1.3 + I)/
                                                                                   11,400
                                                          P    =  5. 86 psia.
                                                      Since P^ *s less than atmospheric pressure, the
                                                      outlet pressure P2 equals  14. 5 psia.
                                                      2.   Determine pressure drop in line using equa
                                                          tion 131:
                                                                    D
                                                                       + 2 lot
                                                                                460 \ (460)
                                                                                        0)Z(14. 5(.0771J1/2
                                                                                        (32.2)(144)   j
                                           P, =  210 + (20.4 +  2 log  —)  50.8
                                             1   L      v            e ^ /       J

-------
604
                                  PETROLEUM EQUIPMENT
                                          460
     As a first approximation,  ignore loge  	
     Then:
     P   =  [210 + (20. 4)(50. 8)]


         =  [1,249]1/2

         =  35.3 psia.
                               1/2
3.
          Correct P  for change in velocity:

                 W v.
     Velocity =
                      (25,000)(5.35)
                     (3,600)(0. Z006)
              =  185 fps
     50.8 x  2 log        =  101.6 log        =
                 e  (i.              e 185
     101. 6 log  2.49  =  (101. 6)(. 912)  =  92.6
Smoke From Flares

Smoke is the result of incomplete combustion.
Smokeless combustion can be achieved by:
(1) Adequate heat values to obtain the minimum
theoretical combustion temperatures,  (2) ade-
quate combustion air, and  (3) adequate mixing
of the air and fuel.

An insufficient supply of air results in a smoky
flame.  Combustion begins around the periphery
of the gas stream where the air and fuel mix,
and within this flame envelope the  supply of air
is limited.  Hydrocarbon side  reactions  occur
with the production of smoke.  In this reducing
atmosphere, hydrocarbons crack to elemental
hydrogen and carbon,  or polymerize to form
hydrocarbons.  Since the carbon particles are
difficult to burn, large volumes of carbon parti-
cles appear as smoke upon cooling.  Side reac-
tions become more pronounced as  molecular
weight and unsaturation of the  fuel gas increase.
Olefins,  diolefins,  and aromatics characteristic-
ally burn with smoky, sooty flames as compared
•with paraffins and naphthenes (Rupp,  1956).

A smokeless flame can be obtained when an ade-
quate amount of combustion  air is  mixed with the
fuel  so that it burns  completely and rapidly be-
fore any side  reactions can take place.
     And applying the correction for the log term:

     P1  =  [1,249 + 92.6]1/2  =  [1,342]1/2
     P   =  36. 7 psia.
 THE AIR POLLUTION PROBLEM

 The air pollution problem associated with the un-
 controlled disposal of waste gases is the  venting
 of large volumes of hydrocarbons and other odor-
 ous gases and aerosols. The preferred control
 method for excess gases and vapors is to re-
 cover them in a blowdown recovery system and,
 failing that,  to incinerate them in an elevated-
 type flare.  Such flares introduce the possibility
 of smoke and other objectionable gases such as
 carbon monoxide, sulfur dioxide, and nitrogen
 oxides.  Flares have been further developed to
 ensure that this combustion is smokeless and
 in some cases nonluminous.   Luminosity, -while
 not an air pollution problem,  does attract atten-
 tion to the refinery operation and in certain cases
 can cause bad public relations.   Noise also can
 result in a nuisance problem if the refinery is
 located in an area zoned for residential expansion
 into the property surrounding the plant or if a
 new facility  is built in  close  proximity to a resi-
 dential area.
                                                Noise From Flares

                                                The  noise produced by flares results from three
                                                distinct noise producing mechanisms.  The first
                                                of these occurs in elevated flares where steam
                                                is injected into the combustion zone and noise is
                                                produced by the release of the steam from jets
                                                and injector tubes at  sonic velocity.  The second
                                                noise producing mechanism is present in all
                                                flares but is  most noticeable  in the elevated type.
                                                In this case,  the noise is caused by the release
                                                of the vent gas stream itself into the atmosphere
                                                at the flare tip.  The third noise source, the
                                                combustion process itself, is present in all
                                                flares.

                                                The  noise produced by release of steam from in-
                                                jector tubes is generally more significant than
                                                that  caused by steam released through the  jets
                                                and can be reduced by the  use of a continuous
                                                muffler as shown in Figure 447.  The noise pro-
                                                duced by the  discharge  of  the vent gas  to the at-
                                                mosphere can be reduced  by ensuring that the
                                                flow is made as continuous as possible without
                                                incremental pressure increases -which result in
                                                an exploding  noise as the mass of gas is released
                                                and ignited.  If additional  noise control is requir-
                                                ed,  silencers are  commercially available.
                                                "Combustion" noise is not readily controlled but
                                                is not as significant as  that produced by the sud-
                                                den  expansion of steam and gas.

-------
                                     Waste-Gas Disposal Systems
                                                                    605
    PILOT
    ASSEMBLY
 STEAM
 HEADER
                                    PILOT AND
                                    MIXER
                      INTERNAL
                      STEANI
                      INJECTOR
                      TUBES
 STEAM
 DISTRIBUTION
 RING
      TIP SHELL
                    CONTINUOUS
                    MUFFLER
                                      CENTER STEAM
                                      JET
                        Other air contaminants that can be emitted from
                        flares depend upon the composition of the gases
                        burned.  The most commonly detected emission
                        is sulfur dioxide,  resulting from the combustion
                        of various sulfur compounds (usually hydrogen
                        sulfide) in the flared gas.  Toxicity, combined
                        with low odor threshold, make venting of hydro-
                        gen sulfide to a flare an unsuitable and some-
                        times dangerous method of disposal.  In addition,
                        burning relatively small amounts of hydrogen sul-
                        fide can create enough sulfur dioxide to cause
                        crop damage or local nuisance.

                        Materials that tend to cause health hazards or
                        nuisances should not be disposed of in flares.
                        Compounds such as mercaptans  or chlorinated
                        hydrocarbons require special combustion devices
                        with ch,emical treatment of the gas or its prod-
                        ucts of combustion.
         PLAN
     ELEVATION
 Figure 447.  Detail of John Zmk flare tip showing
 internal steam injection  system (Model  STF-SA; patent
 pending, John link Company, Tulsa, Okla.).
Other Air Contaminants From Flares
Combustion of hydrocarbons in the steam-in-
spirated-type elevated flare appears to be com-
plete.  The  results of a field test (Sussman  et al. ,
 1958) on a flare unit such as this were reported
in the form  of ratios as f ollows:
     CO :  hydrocarbons    2,100:1
     CO,:  CO
243:1
These results indicate that the hydrocarbon and
carbon monoxide emissions from a flare  can be
much greater than those from a properly oper-
ated refinery boiler or furnace.  Calculations
based  on these data,  with  the assumption of a
gas -with two carbon atoms and a molecular weight
of 30,  indicate that the flares in Los Angeles  County
cause an average daily emission of approximately
100 pounds of hydrocarbons per day and 840 pounds
of carbon monoxide per day.

Other  combustion contaminants  from a flare in-
clude nitrogen oxides.   The importance of these
compounds to the total air pollution problem de-
pends upon the particular  conditions in a  partic-
ular locality.  The total emission of nitrogen oxides
from the approximately 40 flares in Los Angeles
County has  been estimated (Chass and George,
I960) at 110 pounds per day.
 AIR POLLUTION CONTROL EQUIPMENT
 The ideal refinery flare, according to the Amer-
 ican Petroleum Institute,  is a simple device for
 safe and inconspicuous disposal of waste gases by
 combustion.  From an air pollution viewpoint, the
 ideal flare is a combustion device that burns waste
 gases  completely and smokelessly.

 Types  of Flares

 There are,  in general, three types of flares for
 the disposal of waste gases:  Elevated flares,
 ground-level flares, and burning pits.

 The burning pits are reserved for extremely
 large  gas flows caused by catastrophic  emergen-
 cies in which the  capacity of the primary smoke-
 less flares  is exceeded.  Ordinarily, the main
 gas header  to the flare system has a water seal
 bypass to a burning pit.  Excessive pressure in
 the header blows  the water seal and permits the
 vapors and  gases to vent a burning pit where
 combustion occurs.

 The  essential parts of a flare are  the burner,
 stack,  seal, liquid trap,  controls,  pilot burner,
and ignition system. In some cases, vented gas-
 es flow through chemical solutions to receive
treatment before combustion.  As an example,
gases vented from an isomerization unit that may
contain small amounts of hydrochloric acid are
scrubbed with caustic before being vented to the
flare.
                       Elevated flares

                       Smokeless combustion can be obtained in an ele-
                       vated flare by the injection of an inert gas to the
                       combustion zone to provide turbulence and inspi-
                       rateair. A mechanical air-mixing system would

-------
606
PETROLEUM EQUIPMENT
be ideal but is not economical in view of the large
volume of gases handled.  The most.commonly
encountered air-inspirating material for an ele-
vated flare is steam.  Three main types of steam-
injected elevated flares  are in use.  These types
vary in the manner in which the  steam is injected
into the combustion zone.

In the first type, there is a commercially  avail-
able multiple  nozzle, as shown in Figure 448,
which consists of an alloy steel tip mounted on
the top  of an elevated stack (Brumbaugh, 1947:
Hannaman and Etingen,  1956).  Steam injection
is accomplished by several small jets placed
concentrically around the flare tip.   These jets
are installed at an  angle, causing the steam, to
discharge in a converging pattern immediately
above the flare tip.
    Figure 448.  View of John Zink smokeless
    flare burner (John Zink Co.,  Tulsa, rjkla.)
Figure 447 shows a recent modification of the
multiple-nozzle type tip.  Modern refining pro-
cess units with large capacities and greater use
of high operating pressures have increased the
                mass folw rates to flares, thus requiring larger
                diameter tips.  To ensure satisfactory operation
                under varied flow conditions, internal injector
                tubes along with a center tube have been added.
                The injector tubes provide additional turbulence
                and combustion air,  while the central steam jet
                and attached diffuser plate provide additional
                steam to eliminate smoke at low flow conditions.
                The flare continues to employ steam jets placed
                concentrically around the tip as shown in Figure
                448, but in a modified form.  As discussed
                earlier,  noise problems may result at the  injec-
                tor tubes if muffling devices are not used.

                A second type of  elevated flare  has a  flare tip
                with no  obstruction to flow, that is, the flare tip
                is the same diameter as the stack.  The steam
                is injected by a single nozzle located  concen-
                trically within the burner tip.  In this type of
                flare, the steam  is premixed with the gas before
                ignition and discharge.

                A third  type of elevated flare has been used by
                the  Sinclair Oil Company (Decker, 1950).  It
                is equipped with a flare tip constructed  to cause
                the  gases to flow through several tangential open-
                ings to promote turbulence.  A  steam ring at the
                top  of the stack has numerous equally spaced
                holes about 1/8 inch in diameter for discharging
                steam into the gas stream.

                The injection of steam in this latter flare may  be
                automatically or manually controlled.  All the
                flares of this type located in Los Angeles County
                are instrumented to  the extent that steam is auto-
                matically supplied when  there is a measurable
                gas  flow.  In most cases, the steam is propor-
                tioned automatically to the rate of gas flow; how-
                ever, in some installations, the steam is auto-
                matically supplied at maximum rates, and manual
                throttling of a steam valve is required for  adjust-
                ing  the steam flow to the  particular gas flow rate.
                There are many variations  of instrumentation
                among various flares, some designs being more
                desirable than others.  For economic reasons,
                all designs attempt to proportion  steam flow to
                the  gas  flow rate.

                Steam injection is generally believed  to result
                in the following benefits:  (1) Energy available
                at relatively low  cost can be used to inspirate
                air  and  provide turbulence within the  flame,
                 (2) steam reacts  with the fuel to form oxygen-
                ated compounds that burn readily at relatively
                low temperatures,   (3) water-gas reactions
                also occur  with this  same end result, and  (4)
                steam reduces the partial pressure of the fuel
                and retards polymerization.  (Inert gases  such
                as  nitrogen have  also been found effective for
                this purpose; however, the expense of providing
                a diluent such as this is  prohibitive.)

-------
                                     Waste-Gas Disposal Systems
                                                                                                 607
The effectiveness of steam injection in an ele-
vated flare is graphically illustrated by compar-
ing Figures 449 and 450.
Mu I 11 steam-j et-type elevated flare

A multisteam-jet-type elevated flare  (Cleveland,
1952) is shown in Figure 451.  All relief headers
from process units combine into a common head-
er that  conducts the hydrocarbon gases and
vapors to a large knockout drum.  Any entrained
liquid is dropped out and pumped to storage.  The
gases then flow in one of two ways. For emer-
gency gas releases that  are  smaller than or  equal
to the design rate,  the flow  is directed to the main
flare stack. Hydrocarbons are ignited by continu-
ous pilot burners,  and  steam is injected by means
of small jet fingers placed concentrically about
the  stack tip.  The steam is injected in proportion
to the gas flow. The steam control system con-
sists of a. pressure controller, having a  range of
0 to 20 inches water column, that senses the pres-
sure in the vent line and sends an air signal to a
valve operator mounted  on a 2-inch V-Port control
valve in the steam line.  If the emergency gas flow
exceeds the designed capacity of the main flare,
backpressure in the vent line increases, displacing
the  water seal and permitting gas flow to the  auxi-
liary flare. Steam consumption of the burner  at a
peak flow is about 0. 2 to 0. 5 pound of steam per
pound of gas,  depending upon the amount and com-
position  of hydrocarbon gases being vented.  In
general,  the amount of steam required increases
with increases in molecular weight and the degree
of unsaturation of the gas.

A small  amount of steam (300 to 400 pounds per
hour) is  allowed to flow through the jet fingers at
all times.  This steam not only permits  smoke-
less combustion of gas flows too small to actuate
the steam control valves but also keeps  the jet
fingers cooled and open.
 Esso-type elevated flare

A second type of elevated, smokeless, steam-
injected flare is  the Esso type.  The design is
based  upon the original installation in the Bayway
Refinery of the Standard Oil Company of New
Jersey (Smolen,  1951  and 1952). A typical flare
system serving a petrochemical plant using this
type burner is shown in Figure 452. The type of
hydrocarbon gases vented can range from a sat-
urated to a completely unsaturated material.  The
injection of steam is not only proportioned by the
pressure in the blowdown lines but is  also regu-
lated according to the type of material being
flared.  This is accomplished by the use  of  a
ratio relay that is manually controlled.  The
relay is located in a central control room where
      Figure 449.  Refinery flare with steam
      injection  in  operation.
     Figure 450.  Refinery flare with steam
     injection  not  in operation.

-------
608
PETROLEUM EQUIPMENT
                                                              STtAM
                                                                                          3-in  STEAM RING
   CATALYTIC CRACKING COMPRESSORS
                                                                                              DRAIN
               Figure 451.  Waste-gas  flare system using multistream-jet burner (Cleveland, 1952).
the operator has  an unobstructed view of the
flare tip.  In normal operation the relay is set to
handle feed gas, which is most common  to this
installation.

In this installation, a blowdown header con-
ducts the gases to a water seal drum as
shown in Figure 453. The end of the blow-
down line is equipped with two slotted ori-
fices.  The flow transmitter senses the
pressure differential across the  seal drum
and transmits  an air  signal to  the ratio re-
lay.   The signal to this  relay is either ampli-
fied  or attenuated,  depending upon its setting.
An air signal is then transmitted to a flow
controller that operates two parallel steam
valves.  The 1-inch steam valve begins to
open  at an air  pressure of 3 psig and is fully
open  at 5 psig. The 3-inch valve starts to
open  at 5 psig  and is fully open at 15 psig
air pressure.  As the gas flow increases,
                 the water level in the pipe becomes lower
                 than the -water level in the drum, and more
                 of the slot is uncovered.  Thus, the difference
                 in pressure between the line and the seal drum
                 increases.  This information is transmitted
                 as an air  signal to actuate the steam valves.
                 The slotted  orifice senses flows that are too
                 small to be  indicated by a Pitot-tube-type
                 flow meter.  The  water level is maintained
                 1-1/2 inches above the top  of the  orifice to
                 take care of sudden surges of gas  to the system.

                 A 3-inch steam nozzle is so positioned with-
                 in the stack that the expansion of the steam
                 just fills the stack and mixes with the  gas to
                 provide smokeless combustion.  This  type of
                 flare is probably less efficient in the use of
                 steam than  some of the commercially avail-
                 able flares but is  desirable from the stand-
                 points of simpler  construction and lower
                 maintenance costs.

-------
                               Waste-Gas  Disposal Systems
                                                                            609
                     *"'" NLOT BURNERS
                    20° APART)

STEAM


(
C
INSTRUMENT AIR f^\
	 u
RATIO
RELAV
IASIE GAS
• ATER


1 LARGE FLOW
S~^

"UJ
SMALL FLOI
m, PURGE GAS
ONTROLLER
PRESSURE SENSOR
u rn -, , -, •
u [I
PRESSURE TAPS
< HIGH L01 >


t
0







Dh
FLAME ARRESTOR
SEAL
DRUM

r""-* "^ n
III LOOP
LOTTED 1 1 1 SEAL
RIFICE IJI
r
\









-*^
                 Figure 452. Baste-gas  flare system using Esso-type burner.
VENTED GASES
            FLOW
            CON
            TROLLER
        -*-r
                         PURGE GAS
                          JJ
                                                                                \
                                                          GAS TO
                                     MAKE-UP (ATER
                       It
                      -*=
i
jxt
                               3-in MOTOR
                               VALVE
                        -«*^-
                                  \
                                                                  SLOTTED
                                                                  ORIFICE
                               l-m. MOTOR VALVE
                                                      ^.
                                                           KNOCK OUT VESSEL
q
                                                                                          SEPARATOR
  Figure 453.  Water seal  drum with  slotted  orifice  for measuring  gas flow  to flare.

-------
610
PETROLEUM EQUIPMENT
Sinclair-type elevated flare

A diagram. (Decker, 1950) of an installation
using a Sinclair-type elevated flare is  shown
in Figure 454.  A detail of the  burner used
for this flare is  shown in Figure 455.
    Figure 454.  Diagram  of  waste-gas  flare system
    using a Sinclai r  burner.
 The flow of steam from the ring inspirates air
 into the combustion area,  and the shroud pro-
 tects the burner from -wind currents and pro-
 vides a partial mixing chamber for the air and
 gas.  Steam is automatically supplied when
 there is gas flow. A pressure-sensing ele-
 ment actuates a control valve in the steam
 supply  line.  A small bypass valve permits a
 small,  continuous flow of steam to  the ring,
 keeping the steam ring holes open and per-
 mitting smokeless burning of small gas flows.
 Ground level flares

 There are four principal types of ground level
 flare: Horizontal venturi, water injection,  multi-
 jet, and vertical venturi.
 Horizontal, venturi-type ground flare

 A typical horizontal, venturi-type ground
 flare  system is shown in Figure 456.  In this
 system, the refinery flare header discharges
                                                           SECTION
                                                                                       PROTECTING SHROUD
                                                                                 \\r	STEAK SUPPLY PIPES
                                                                                       FLAME ARRESTER
                                                          ELEVATION
                  Figure 455.  Detail of Sinclair flare burner,  plan
                  and elevation (Decker,  1950).
                 to a knockout drum where any entrained liq-
                 uid is separated and pumped to storage.  The
                 gas flows to the burner header, which is con-
                 nected to three separate banks of standard
                 gas burners through automatic valves  of the
                 snap-action type that open at predetermined
                 pressures.  If any or all  of the pressure
                 valves fail,  a bypass line with a liquid seal
                 is provided  (with no valves in the circuit),
                 which discharges to the largest bank of burn-
                  The automatic-valve  operation schedule is
                  determined by the quantity of gas most likely
                  to be relieved to the system.  The allowable
                  back-pressure  in the refinery flare header
                  determines the minimum pressure for the con-
                  trol valve on the No.  1 burner bank.  On the
                  assumption that the first valve was set at 3
                  psig, then the second valve for the No. 2 burner

-------
                                      Waste-Gas Disposal Systems
                                             611
                                                                 BURNER BUNKS
    G»S TO PILOT BURNERS
                   Figure 456.  Typical  yenturi ground flare.  The igniters  for pilot
                   burners  and  the  warning element for pilot  operation  are not shown
                   (American Petroleum  Institute, 1957).
bank would  be set for some higher pres-
sure,  say 5  psig.  The quantity of gas most
likely to be  released then determines the size
and the number of burners for this section.
Again, the third most  likely quantity of  gas
determines the pressure setting and the size
of the third  control valve.   Together, the burn-
er  capacity  should equal the maximum expected
flow rate.

The valve-operating schedule for the system
pictured in Figure 456 is set up  as follows:

1.  When the  relief header pressure reaches
    3 psig, the first control valve opens  and
    the four small venturi burners go into
    operation.  The controller setting keeps
   the valve  open until the pressure decreases
   to about 1-1/Z psig.

2. When the  header pressure reaches 5  psig,
   the second valve opens and remains open
   until the pressure drops  to about 3 psig.

3. When the  pressure reaches 6 psig, the
   third valve  opens and remains open until
   the pressure decreases to 4 psig.

4. At about 7 psig, the gas blows the liquid
   seal.

A small flare unit of this design, with a  capac-
ity  of 2 million scf per day,   reportedly cost
less than  $5, 000.  00 in 1953   (Beychok,  1953).
Another large, horizontal,  venturi-type  flare
that has a capacity of 14 million scfh and re-
quires  specially constructed venturi burners
(throat diameter ranges  from 5 to 18 inches)
cost $63,000.
Water-injection-type ground flare

Another type of ground flare used in petroleum
refineries has  a water spray to inspirate air
and provide water vapor for the smokeless
combustion of gases  (Figure 457).  This flare
requires an adequate supply of -water and a
reasonable amount of open space.

The  structure of the  flare consists of three
concentric stacks.   The combustion chamber
contains the burner,  the pilot  burner,  the end
of the ignitor tube, and  the water spray dis-
tributor ring.   The primary purpose of the
intermediate stack is to confine the water spray
so that it  will be mixed intimately with burn-
ing gases.  The outer stack confines the flame
and directs it upward.

Water sprays in elevated flares are not too
practical  for several reasons. Difficulty is
experienced in  keeping the water spray in the
flame  zone, and scale formed in the waterline
tends to plug the nozzles.   In  one case it  was
necessary to install a return system that per-
mitted continuous waterflow to bypass the
spray nozzle.   Water main pressure dictates
the height to which water can be injected with-
out the use of a booster pump.  For a  100- to
  234-767 O - 77 - 41

-------
612
PETROLEUM EQUIPMENT
                                                      BOTTLED GAS
                                                VENTURI BURNER
                                                 GAS TO PILOT
                                                 IGNITOR TUBE\^
                                                  TO PILOT \ \\0-~H-
                                                        *  \  ~ \   i. ^.
                                            SECTION A-A
                                            FLARE HEADER
v <> >Q , 1

RK IGNITOR-7 \
FLAME ARRESTER
1



? J I6PI WATER SUPPLY
??r^
_, L_I j WATER STRAINERS

                            Figure 457.  Typical water-spray-type sround flare.
                            Six watbr sprays are shown.  Two pilots and two
                            ignitors are  recommended (American Petroleum
                            Institute,  1957).
 250-foot stack, a booster pump would undoubted-
 ly be required.  Rain created by the  spray from
 the flare stack is objectionable  from the stand-
 point of corrosion of nearby structures  and
 other equipment.
 Water is not as effective as steam for control-
 ling smoke with high gas flow rates, unsatu-
 rated materials,  or wet gases.   The water
 spray flare is  economical when venting rates
 are not too high and slight smoking can be
 tolerated.   In Los Angeles County,  where re-
 strictions  on the emission of smoke from
 flares are very strict,  a water  spray smoke-
 less flare  is not acceptable.

 Mu/tijef-type  grand flare

 A recent type of flare developed by the refin-
 ing industry is known as a multijet  (Miller et
 al. ,  1956). This  type  of flare was designed
 to burn excess hydrocarbons without smoke,
 noise, or  visible  flame.   It is claimed to
 be less expensive than the steam-injected
 type,  on the assumption  that new  steam
 facilities  must be installed to  serve a
 steam-injected flare unit.  Where the steam
 can be diverted from noncritical operations
 such as tank heating,  the cost of the multijet
 flare  and the steam-inspirating  elevated flare
 may be similar.

 A sketch of an  installation of a multijet flare
 is shown in Figure 458.  The flare uses two
 sets of burners; the smaller group handles
 normal gas leakage and small gas releases,
                 while both burner groups are used at higher
                 flaring rates.  This sequential operation is
                 controlled by two water-sealed drums set to
                 release at different pressures.  In extreme
                 emergencies, the multijet burners are by-
                 passed by means of a water seal that directs
                 the gases to the center of the stack.  This
                 seal blows at flaring rates  higher  than the
                 design  capacity of the  flare.  At such an ex-
                 cessive rate, the combustion is both luminous
                 and smoky,  but the unit is usually sized so
                 that an overcapacity flow would be a rare
                 occurrence.  The overcapacity line may also
                 be designed  to  discharge through a water seal
                 to a nearby  elevated flare rather than  to the
                 center  of a multijet stack.  Similar staging
                 could be accomplished with automatic  valves
                 or backpressure regulators; however, in this
                 case,  the water seal drums are used because
                 of reliability and ease of maintenance.   The
                 staging system is balanced by adjusting the
                 hand control butterfly valve leading to the
                 first-stage drum.  After its initial setting,
                 this valve is locked into position.

                 Design details  of this  installation are given
                 in the literature  reference  (Miller et al. ,
                 1956).


                 Vertical,  ventun-fype ground flare

                 Another type of flare based upon the use of
                 commercial-type venturi burners  is shown
                 in Figure 459.   This type of flare  has  been
                 used to handle  vapors  from gas-blanketed
                 tanks,  and vapors displaced from  the depres-

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                                      Waste-Gas Disposal Systems
                                            613
        FLARED GASES
                                                                                        STACK SHELL
                 Figure 458. Flow diagram of  multijet-flare system (Miller  et  al., 1956).
 suring of butane and propane tank trucks.
 Since the commercial venturi burner requires
 a certain minimum pressure to operate  effi-
 ciently,  a gas blower must be provided.  In
 the installation  shown in Figure 460, two
 burners  operate at a pressure of 1/2 to  Spsig.
 A compressor takes vapors from tankage and
 discharges them at a rate of 6, 000 cfh and 7
 psig through a water seal tank and a flame
 arrester to the  flare.  This type of arrange-
 ment can readily be modified to handle dif-
 ferent volumes  of vapors by the installation
 of the necessary number of burners.

 This type of flare is suitable for relatively
 small flows of gas of a constant rate.  Its
 main application is in situations -where other
 means of disposing of gases and vapors  are
 not available.
Effect of steam injection

A flare installation that does not inspirate an ade-
quate amount of air or does not mix the air and
hydrocarbons properly emits dense, black clouds
of smoke that obscure the flame.   The injection
of steam into the zone of combustion causes  a
gradual decrease in the amount of smoke,  and the
flame becomes more visible.  When trailing smoke
has been eliminated, the flame is very luminous
and orange with a few wisps of black smoke around
the periphery.  The minimum amount of steam, re-
quired produces a yellowish-orange, luminous
flame with no smoke.  Increasing the amount of
steam injection further decreases the luminosity
of the flame.  As the steam rate increases, the
flame becomes colorless and finally invisible
during the day.  At night this flame  appears blue.

An injection of an excessive amount of steam
causes the flame to disappear completely and be
replaced  with a  steam plume.   An excessive
amount of steam may extinguish the burning gases
and permit unburned hydrocarbons to discharge to
the atmosphere.  When the flame is  out, there  is
a change in the sound of the flare because a steam
hiss replaces the roar  of combustion.  The com-
mercially available pilot burners are usually not
extinguished by excessive amounts of steam,  and
the flame reappears as the steam injection rate is
reduced.  As the use of automatic instrumentation
becomes more prevalent in flare installations,  the
use of excessive amounts of steam and the emis-
sion of unburned hydrocarbons decrease and great-
er steam  economies can be achieved.  In evaluat-
ing flare installations from an air pollution stand-
point,  controlling the volume of steam is important.
Too little  steam results in  black smoke, which,
obviously, is  objectionable.  Conversely, ex-
cessive use of steam produces a white steam
plume and an invisible  emission of unburned

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614
                          PETROLEUM EQUIPMENT
                                 STEEL SHfLL
                                 REFRACTORY
                               3 ft DIAMETER X 10 ft HIGH
                                        PILOT GAS
                                        1ASTE GAS
      Figure 459.  Vertical, venturi-type  flare.

hydrocarbons.  A condition such as this can also
be a serious air pollution problem-

Design of a smokeless flare

The choice  of a flare is dictated by the particular
requirements of the installation.  A flare may be
located either at ground level or on an elevated
structure.  Ground flares are less expensive,
but locations must be based upon considerations
such as proximity of combustible materials,
tanks, and refinery processing  equipment.  In a
congested refinery area,  there  may be no choice
but to use an elevated flare.

A method of determining the  distance  a  stack
should be from surrounding equipment and per-
sonnel has been developed (Hajek and Ludwig,
I960).  The recommended equation is
where

     D
                                           (132)
minimum distance, ft from the flame
to the object
                                               F  =  a dimensionless constant equal to 0. 20
                                                     for methane,  which has a hydrogen-to-
                                                     carbon weight ratio of 0. 333,  and equal
                                                     to 0. 33 for propane, which has a hydro-
                                                     gen-to-carbon weight ratio of 0. 222 .
                                                     (Use 0. 40  -when in doubt. )

                                               H  =  heat release,  Btu/hr

                                               K  =  a constant, Btu/hr-ft :

                                                     K   =   1, 000 for objects exposed 20
                                                     minutes or more

                                                     K   =   1, 500 for objects exposed less
                                                     than 20 minutes.
The usual flare system includes gas collection
equipment,  the liquid knockout tank preceding the
flare  stack.  A water seal tank is usually located
between the knockout pot and the flare stack to
prevent flashbacks into the system.  Flame ar-
restors are sometimes used in place of or in con-
junction with a water seal pot.  Pressure-tem-
perature-actuated check valves have been used
in small ground flares to prevent flash-back.  The
flare  stack  should be continuously purged with
steam,  refinery gas, or inert gas to prevent the
formation of a combustible mixture that could
cause an explosion in the stack (Hajek and
Ludwig,  I960).  The purge gas should not fall
below its dew point under any condition of flare
operation.

To prevent air from entering a flare stack which
is used to dispose of gases that are lighter than
air, a device known as a molecular seal (John
Zink Company) is  sometimes used in conjunction
with purge  gas. It is installed within the flare
stack immediately below the flare tip and acts
as a gas trap by preventing the lighter-than-air
gas from bleeding out of the system and being
displaced with air.  A cross-section of a flare
stack and seal is so shown in Figure 461.

The preferred method of inspirating air is inject-
ing steam either into the stack or into the combus-
tion zone.  Water  has sometimes been used in
ground flares where there is an abundant supply.
There is, however, less assurance of complete
combustion when water is used,  because the flare
is limited in its operation by the type and composi-
tion of gases it  can handle efficiently.


The diameter of the flare stack depends upon the
expected emergency gas flow rate and the per-
missible backpressure  in the vapor relief mani-
fold system.  The stack diameter is usually the
same or greater than that of the vapor header
discharging to the stack and should be the same
diameter as or  greater than that of the burner

-------
                                     Waste-Gas Disposal Systems
                                                                                                 615
                                                                                   STACK
                                                                                   BURNERS
                          Figure 460.  Flow diagram of  tank-gas-blanketing system
                          venting to a vertical,  venturi  flare.
section.   The velocity of the gas in the stack
should be as high as possible to permit use of
lower stack heights, promote turbulent flow with
resultant improved combustion, and prevent
flashback.  Stack gas velocity is limited to about
500 fps in order  to prevent extinction of  the
flame by blowout.  A discharge velocity  of 300
to 400 fps based  upon pressure drop considera-
tions is the optimum design figure of a patented
flare tip  manufactured by the John Zink Company.
The nature of the gas determines optimum dis-
charge velocity (John Zink  Company).
Adequate stack heights must be provided to per-
mit safe dispersion of toxic or combustible mate-
rial in the event of pilot burner failure.   Tech-
niques are available for calculating adequate  stack
heights to obtain certain ground concentrations at
various  distances from the stack, depending upon
atmospheric conditions  (Bodurtha, 1958; Gosline
et al. ,  1956).   These methods of calculation
should not be generally applied to any one loca-
tion, and meteorological data should be  obtained
for the particular location involved.
The structural support of an elevated-flare stack
over 40 to 50 feet high requires the use of guy
wires.  A self-supporting stack over 50 feet high
requires a large and expensive foundation. Stacks
over 100 feet high are usually supported by a
steel structure  such as is shown in Figure 462.

Three burner designs for elevated flares have
been discussed--the multisteam-jet, or Zink,
and the  Esso and Sinclair types.  The choice of
burner is a matter of personal preference.   The
Zink burner provides more efficient use of steam,
which is important in a flare that is  in constant
use. On the other hand,  the simplicity,  ease of
maintenance,  and large capacity of the Esso burn-
er might be important considerations in another
installation.

As previously mentioned, the  amount of steam
required for smokeless combustion varies accord-
ing to the maximum expected gas flow, the molec-
ular -weight, and the percent of unsaturated hydro-
carbons in the gas.   Data for steam  requirements
for elevated flares are shown  in Figure 463. Actu-
al tests should be run on the various materials to

-------
616
PETROLEUM EQUIPMENT
                               SEALING CAP
                              FLARE TIP MOUNT FLANGE
           LIQUID
           DRAIN
  Figure 461.   John Zink molecular  seal (U.S. patent
  3,055,417,  John Zink Company,  Tulsa, Okla.).

be flared in order to determine a suitable steam-
to-hydrocarbon ratio.  In the typical refinery,
the ratio of steam to hydrocarbon varies from
0. 2 to 0. 5 pound of steam per pound of hydrocar-
bon.  The John Zink Company's recommendation
for their burner is 5 to 6 pounds per 1, 000 cubic
feet of a 30-molecular-weight gas  at a pressure
drop of 0. 65 psig.

Pilot ignition system

The ignition of flare gases is normally accom-
plished with one of three pilot burne- s.   A sepa-
rate system must be provided for the ignition of
the pilot burner to safeguard  against flame fail-
ure.  In this system, an easily  ignited flame with
stable combustion and low fuel usage must be pro-
vided.  In addition, the  system  must be protected
from the weather.

One good arrangement for a pilot ignitor is shown
in Figure 464.  To obtain the  proper fuel-air  ratio
for ignition in this system, the  two plug valves
are opened  and adjustments are made with the
globe valves, or pressure regulator valves. After
the mixing, the fuel-air  mixture is lit in an igni-
                      Figure 462.  A 200-ft flare stack supported
                      by a steel tower (Atlantic-Richfield Co.,
                      Wilmington,  Calif.).

                 tion chamber by an automotive spark plug con-
                 trolled by  a momentary-contact switch.  The  igni-
                 tion chamber is  equipped -with a heavy Pyrex glass
                 window through which both the spark and ignition
                 flame can  be observed.   The flame  front travels
                 through the ignitor pipe to the top of the pilot
                 burner.  The mixing of  fuel gas and air in the
                 supply lines  is prevented by the use of double
                 check valves in both the fuel and air line.  The
                 collection  of water in the ignitor tube  can be pre-
                 vented by the installation of an automatic drain
                 in the lower  end of the tube  at the base of the
                 flare.  After the pilot burner  has been lit,  the
                 flame front generator is turned off by closing
                 the plug cocks in the fuel and  air lines.  This
                 prevents the collection  of condeiisate and the
                 overheating of the ignitor tube.
                 On elevated flares,  the pilot flame is usually
                 not visible, and an alarm system to indicate
                 flame failure is desirable.  This is usually ac-
                 complished by installing thermocouples in the
                 pilot burner flame.   In the event of flame fail-
                 ure, the temperature drops to a preset level,
                 and an alarm sounds.

-------
                                      Waste-Gas Disposal Systems
                                             617
                                                  &\
                                             40      50     60
                                             UNSATURATES,  '. tiy weight
                                                                  70
                                                                                90
                                 100
                          Figure 463.   Steam  requirements for smokeless burning  of
                          unsaturated  hydrocarbon vapor (American Petroleum Insti-
                          tnto   1 am \
                          tute,  1957).
 Instrumentation and control of steam and gas

 For adequate prevention of smoke emission
 and possible violations  of air pollution regula-
 tions, an elevated, smokeless flare  should be
 equipped to provide steam automatically and in
 proportion to the emergency gas flow.

 Basically, the instrumentation required for a
 flare is  a flow-sensing  element,  such as a Pitot
 tube, and a flow transmitter that  sends a  signal
 (usually pneumatic) to a control valve in  the
 steam line.  Although the Pitot tube has been
used extensively in flare systems, it is  limited
by the minimum linear  velocity required to pro-
duce a measurable velocity head.   Thus,  small
gas  flows will not  actuate the  steam control
valves.  This problem is usually overcome by
installing a small bypass valve to permit a
constant flow of steam to the flame burner.

A more  sensitive type of flow-measuring device
is the inverted weir.  A typical installation is
shown in Figure 465.  A variation of the inverted
weir  is the slotted orifice previously shown in
Figure 453.  The operation of this  installation
has already been described.

The hot-wire flow meter has also been used in
flare  systems (Huebner, 1959).  The sensing
element is basically a heat loss anemometer
consisting of  an electrically heated wire ex-
posed to the gas stream to measure the velocity.
The gas flow  is perpendicular to the axis of the
hot wire.  A conventional recorder is used with
this probe, modified for the resistance bridge
circuit  of the  gas flow meter.  As the flow of
gas past the probe varies,  the heat loss from
the hot  wire varies  and causes an imbalance of
the bridge circuit.  The recorder then adjusts
for the  imbalance in the bridge and indicates the
gas flow.  This type of installation provides sen-
sitivity at low velocities,  and the gas flow mea-
surement can be made without causing  an appre-
ciable pressure  drop.   This is an important ad-
vantage in a system using constant backpressure-

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618
                                       PETROLEUM EQUIPMENT
  Figure 464,   Remote-control  system for  igniting
  flare  pilot  burners  (American  Petroleum  Insti-
  tute,  1957).
             V»POR INLET
                      DRUM
                                    HATER LEVEL
               SEALING WATER INLET
                                                        type relief valves.  One flow meter of this type
                                                        in use has a velocity range of 0 to 6, 000 fpm.
                                                        The hot-wire flow meter can be used as a primary
                                                        flow-sensing element or as  a leak detector in
                                                        laterals connected to the main flare header.

                                                        Another system using a venturi tube as the
                                                        primary element for measuring the rate  of gas
                                                        flow to  a flare is shown in Figure 466.

                                                        Supply and control of steam

                                                        After the amount of steam required for maxi-
                                                        mum design gas flow rates is determined,  the
                                                        size of the steam supply line can  be  estimated
                                                        by conventional methods of calculation, such
                                                        as shown in  Figure 467.  The following example
                                                        illustrates the calculations for siting the steam
                                                        supply line.


                                                        Given:

                                                        200 psig (215 psia) saturated steam
                                                        9,000 Ib/hr propane

                                                        1, 000 Ib/hr propylene

                                                        10% (by weight) unsaturated  material.

^





^
FLO*
RECORDER
\ t T0
V W FLURE
                                                                     r
                                                                                    TO SEWER
                      Figure 465.   Inverted  weir  for  measuring  gas  flow  to  a  flare.
                      The  end of  the  low-pressure  line  to  the  flow  recorder  should
                      be at  the same  level  as  the  tops  of  the  slots  in  the  inverted
                      weir.  The  end  of  the high-pressure  line  to  the  recorder  should
                      be at  the same  level  as  the  bottoms  of the weir  slots  (American
                      Petroleum Institute,  1957).

-------
                                       Waste-Gas Disposal Systems
                                                                          619
                         FLOW RECORDER
                         IN BYPASS LINE
 Figure  466.  System  for measuring flare gas.  Small  flows of gas are measured by the  flow recorder  in the bypass
 line.   When a blow occurs that  is large enough to overcome the  static head  of the sealing liquid  in the seal pot,
 the liquid  is blown  to the slop and blowdown drum.   The gas flow  is measured by the venturi  in the mam line to
 the flare  (American  Petroleum Institute,  1957).
Problem:

Determine the size of the steam supply line re-
quired.

Solution:

From Figure 463, the steam-to-hydrocarbon
ratio should be 0. 55.

Steam required = (10, 000 lb/hr)(0. 55) = 5, 500
Ib/hr

With allowance for a future increase in steam re-
quirements, the steam line should be designed
to provide 7, 000 Ib/hr at a velocity of 6, 000 fpm.
From Figure 467, the pipe diameter is found
to be 3  inches.

The number and size of steam jets can be esti-
mated by the following empirical equation (Marks,
1951) for steam flow through a small nozzle:
         W  =   0. 0165 AP
0.97
1
(133)
where
     W  =   steam flow, Ib/sec
                                  A  =  nozzle area,  in.
                                 P   =  upstream pressure, psia.

                             Commercial burners use 1/8- to 1/2-inch-di-
                             ameter stainless steel pipe for the  steam jets
                             with orifices  of  1/8 to 7/16 inch in  diameter.
                             The number of jets depends upon the gas flow
                             rates and the steam to be delivered into the com-
                             bustion zone.
Figure 468 is a plot of steam flow versus up-
stream pressure for various  sizes of jet orifices.
This chart may be used for preliminary design
or for checking an existing installation as shown
in the following example.

Given:

Steam flow,  5, 500 Ib/hr
Available pressure upstream of jets,  80 psia

Assume jet orifice  diameter, 3/8 in.

Problem:

Determine minimum number  of steam jets re-
quired.

-------
 620
                                       PETROLEUM EQUIPMENT
                                900  1000  1100 1200'
              I - Temperature in Degrees Fahrenheit
                                                         Index
                                                                         1000
                                                                       1—800

                                                                         600
                                                                       |—500
                                                                         400
                 — 200
                 jj-150

                 — 100
                                                                       b-*>
                                                                          15
                                                                                    2.5
                                                                                       Schedule Number
                                                                                       Schedule Nui
             Figure 467,  Steam pipe sizing chart.   Establish  the  steam  pressure and  temperature
             intersection.   Draw a horizontal  line  to  specific  volume scale V.  Draw a  line
             from V to the  expected rate  of  flow, W.   Mark  the  intersect with the  index line.
             Using either known quantity,  pipe  size, d; or  velocity, V;  find the unknown by
             drawing a line from the  index  to  the known quantity  (Crane Company, 1957).
Solution:

From Figure 468, the steam flow per jet =
460 Ib/hr

                    .    ,    5, 500 Ib/hr    ,,  „
Number of jets required =  — .     .	  =  11. 97
                            460 Ib/hr

Use  12  steam jets -with 3/8-inch orifices.

As shown in Figure 469, a  jet located at an acute
angle to the  direction of a gas flow improves the
mixing  of the gas with air or steam.  Commer-
cial  flare burners usually have  steam jets  placed
at angles  of  15 to 60 degrees -with the gas flow.

A  steam control system is provided to ensure
correct proportions of gas and steam flow. A
control valve with equal percentage characteris-
tics is often  used in this application.  A  diagram
 of this type of valve is shown in Figure 470.  Flow
 curves  for valves  with various  characteristics
 are  shown in Figure 471.  The  manufacturer's
 literature should be consulted for specific valves.

 Accurate selection of the size of steam control
 valve requires a full knowledge of the actual
 flowing conditions.  In most cases, the pressure
 across  the valve must be estimated.  A con-
 servative "working rule is that one-third of the
 total system pressure drop, including all fittings
 and  equipment,  should be absorbed by the con-
 trol  valve.  The pressure drop across valves in
 long lines  or high-pressure drop lines may be
 somewhat  lower.  In these cases the pressure
 drop should be at least 15 to 25 percent of the
total system drop, provided the variations in
flow rates are small.  A control valve can reg-
ulate flow  only by absorbing energy and giving
a pressure drop to the system.

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                                      Waste-Gas Disposal Systems
                                               621
            1,400
            1,200
            1,000
          "-  600
             200
                                                        100      120

                                               IET UPSTREAM PRESSURE  psia
               Figure  468.   Jet  upstream pressure versus  jet  capacity  (based on equation
               W  --  0.0165 AP where P < 0.575  Patm).
                 30      45       60
                   JET ANGLE,  degrees
                                                                  ACTUATOR
                                                                  INLET
                                                                  LOWER GUIDED
                                                                  BRUSHING
                                   BLIND HEAD
Figure 469.  Relationship  between  flame  length
and jet  angle (Gumz,  1950).
Figure 470.   Diagram of  double-seated,  V-port
control  valve and valve power unit  (Holzbock,
1959).

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622
PETROLEUM EQUIPMENT
                   100
                                       4  5  6  7 8 9 10        20
                                           FLO* THRU VALVE.  * of maximum
                            30   40  50  60  60  100
                      Figure 471.   Flow curves for control  valves with characterized
                      plugs  (Lieblich, 1953).
The most convenient method of sizing control
valves involves the use of the flow coefficient,
Cv.  This flow coefficient is essentially a capac-
ity index of the valve and can be obtained from
the manufacturer's literature.
By using the basic conversion formulas shown
in Table 161, the  flow coefficient for any re-
striction can be determined.  Under special
conditions,  such as a high pressure drop or use
of special designs, deviation from the simple
fundamental law can be substantial.  For most
practical valve-sizing problems, the use of the
simplified formulas is adequate.

A brief method of selection of a control valve
is explained in the following example.

Given:
Gas flow, 10,000  Ib/hr
Steam-to-hydrocarbon ratio, 0. 55 (by wt)
Maximum steam flow, 5, 500 Ib/hr

Pj, upstream pressure,  160 psig
P2> downstream pressure, 100 psig
Steam density, downstream,  0. 226 Ib/ft  .

Problem:

Select a control valve for this system.
                Solution:

                Determine GV from the formula as shown in
                Table 161:

                C   =  	
                                                                         W
                                                             2.
                                                                                    J/2
                                                                                                (134)
                                        5, 500
                       2.1 [(174.7 -  114.7)(174.7 + 114.7)]

                    =  19. 8
                                                            1/2
                A valve with a Cv of 19. 8 is indicated.  Since
                an equal percentage characteristic is desired
                in this application, a correction factor should
                be applied.   This adjustment is necessary be-
                cause of the flow characteristics of this type of
                valve.   It is suggested by the manufacturer that
                a 20 percent increase in the GV be  taken to com-
                pensate for this adjustment.  Thus  the  GV for
                the equal percentage valve -would be 23. 8.

                Other items to consider in the  selection of con-
                trol valves  are the valve actuator,  valve posi-
                tioners, and future steam requirements.  The
                control valve actuator  supplies the  power for
                operating the valve.  In flare applications the
                power  unit is usually a pneumatic-spring-dia-
                phragm-type actuator  of the type shown in Fig-
                ure 464, operated by 3 to 15 psig air pressure.
                These  units are designed to open the valve if

-------
                                      Waste-Gas Disposal Systems
                                               623
                          Table  161.  EQUATIONS FOR CONTROL VALVE SIZING
                                      (Mason-Neilan Division, 1963)

                                          NOMINCUMURE FOR Cv FORMULAS
                    V  = flow in U.S. gpm
                    Q  = cfh @ 14.7 psia and 80° F
                    W = Ib/hr
                    Pi  = inlet pressure — psia (14.7 -f- psi guage)
                    PS  = outlet pressure — psia (14.7 + psi gauge)
G = gas sp. gr. (air = 1.0)
G, = sp. gr. 
-------
624
                    PETROLEUM EQUIPMENT
     W =  rate of flow, Ib/hr

     C  =  orifice discharge coefficient, dimen-
           sionless

     Y  =  expansion factor,  dimensionless

    h   =  differential pressure across orifice,
           in.  of water at 60°F

    p   =  density of air at upstream tap condi-
     a     tions, lb/ft3.

In this case pa is the  density of air at 60°F, Y
is assumed to be 1. 0,  and C is assigned the value
of 0. 6.  Equation 136 can now be reduced to
             A  =
                       W
                    20. 9 h
                                           (13?)
Test data indicate that water pressure is more
important in achieving smokeless burning than
the amount  of water delivered to the flare.  In
general,  a high water pressure results in better
mixing of gas.  Higher water pressure is  re-
quired as the molecular weight and unsaturated
content of the gas increase.  Table 162 lists
water  spray pressures required for smokeless
burning.

    Table 162.  WATER SPRAY PRESSURES
    REQUIRED FOR SMOKELESS BURNING21
      (American Petroleum Institute,  1957)
Gas rate,
scfh
200, 000
150, 000
125, 000
Unsaturatcs ,
% by vol
0 to 20
30
40
Molecular
weight
28
33
37
Water pressure,
psig
30 to 40
80
120
Water rate,
gpm
31 to 35
15
51
  aThe data in this table were obtained with a 1 - 1 / 2 -inch-diameter
  spray noz?le m a ground flare with the following dimensions
   Outer stack
   Intermediate stack
   Inner stack
Height, It   Diameter,

   30         14
   12         6
    4         2.5
 Satisfactory proportioning of the flow of water
 to the flow of gas is difficult to achieve because
 the pressure drop required for proper spray
 nozzle operation is high.  Where the opacity of
 smoke emission is  limited, some type of re-
 mote manual or automatic control is necessary.
                                    the particular blowdown system.  In general,
                                    the allowable pressure drop through the relief
                                    valve headers, liquid traps, burners,  and so
                                    forth,  must not exceed one-half the internal
                                    unit's  relieving pressure.  The burner cut-in
                                    schedule is based upon a knowledge of the  source,
                                    frequency, and quantity of the release gases.
                                    Pressure  downstream of the control valves must
                                    be adequate to provide  stable burner operation.

                                    Flare  installations  designed for relatively_small
                                    gas flows  can use clusters  of commercially avail-
                                    able venturi burners.   For large  gas  releases,
                                    special venturi burners must be constructed. The
                                    venturi (air-inspirating) burners  are  installed
                                    in clusters with a small venturi-type  pilot burn-
                                    er in the center.  This burner should be connected
                                    to an independent gas source.   The burners may
                                    be mounted vertically or horizontally.  The burn-
                                    ers should fire through a refractory wall to pro-
                                    vide protection for  personnel and equipment.  Con-
                                    trols can be installed to give remote indication of
                                    the pilot burner's operation.

                                    For large-capacity venturi burners, field  tests
                                    are necessary to obtain the proper throat-to-
                                    orifice ratio and  the minimum pressure for stable
                                    burner operation.  The design of  one  flare  sys-
                                    tem using special venturi burners has been re-
                                    ported  (Brumbaugh, 1947).  An analysis of the
                                    burner limitations and  the pressure relief sys-
                                    tem in this installation yielded the design data
                                    set forth in  Table 163.
                                                      Table 163.  DESIGN DATA FOR A FLARE SYSTEM
                                                             USING SPECIAL VENTURI BURNERS
                                                                      (Brumbaugh,  1947)

No.

1
I
3
4
Cut-in
pressure.
psi
2-1/4
2-3/4
3-1/4
3-3/4
Cut-out
pressure,
psi
1/4
1/2
3/4
1
Gas orifice
diameter,
in.
1.61
2. 90
4.03
7
Venturi
throat dia.
in.
5
8
11. 5
18
Rates of throat-
to-onfice
area
9.6
7. 8
B. 1
6. 6
                                    After 5 years,  this flare was reported to be
                                    satisfactory and had required relatively few
                                    changes (Green,- 1952).

                                    The selection of the control valves and burners
                                    for a small-capacity ground flare is indicated
                                    by the following example:
 Design of venturi-type ground flares

 The venturi-type ground flare,  as previously
 discussed,  consists of burners, pilots, ignitors,
 and control valves.

 The total pressure drop permitted in a given in-
 stallation depends upon the characteristics of
                                    Given:

                                    Range of gas flow,  2, 000 to 30, 000 cfh
                                    Most frequently expected gas flow, 12, 000 cfh

                                    Blowdown line size, 4-in.  dia

                                    Specific gravity of gas,  1. 2

-------
                                     Waste-Gas Disposal Systems
                                             625
Calorific value  of gas, 1,300 Btu/ft3

Flowing temperature  of gas, 100°F.

Problem:

Select control valves  and determine the number
and size of standard air-inspirating burners to
permit smokeless burning of all expected gas
flows.


Solution:

On the basis of  the range of expected gas flow,
try three banks  of burners with a -water seal
bypass  to the largest bank to handle gas  flows
in excess of flare capacity.  The maximum
allowable pressure at the burners has been set
at 5 psig.  Various intermediate pressures for
the control valves will be arbitrarily selected.
The intermediate pressures, which indicate
stable operations of the  different burner banks
relative to the gas flows, will be used as the
operating points for the  valves.

1.  Valve selection and capacity data:

    Try tv/o 1-inch and  one  2-inch single-seated,
    quick-opening valves.

     Valve  Capacity
size, index,
in. C,,
1 14



2 46

Pressure ,
psi
0. 5
1. 0
3. 0
5. 0
3. 0
5. 0
Capacity,
cfh
2, 070
2, 940
5, 080
6, 580
15, 000
20, 000
2.   Burner selection — No.  1 bank:

     No.  1 bank of burners  to handle a minimum
     flow of 2, 000 cfh at 0. 5 psig.

     Try a No.  16X NGE burner with a 1/2-in.
     orifice.

     From Table 164, capacity of a No. 16X burn-
     er at 0. 5 psig (1, 000 Btu/ft3 gas) is  1, 360  cfh.

Capacity of 1, 300 Btu/ft  gas:

   1,000
   1, 300
            x  1,360 cfh  =  1, 047 cfh/burner
Number of burners required:
       2,000 cfh
 Table  164.  VENTURI BURNER CAPACITIES,
   ft3/hr (Natural Gas Equipment, Inc.,  1955)a
Gas pressure,
in. H2O
i
4
6
8
10
III psig
1 psig
i psig
3 psig
4 psig
5 psig
6 psig
7 psig
8 psig
Type 14
3/1 6-111. orilic e
70
100
123
142
160
210
273
385






Type 16
7/16-in. onfitc





1, 042
1,488
2, 157
2,654
3, 065
3, 407
3, 742
4, 040
4, 320
Type 16X
1/2-in. unfit i-





1, 360
1, 900
2, 640
3, 200
3, 680
4, 080
4, 480
4,800
5, 160
 aBasis  1,000 Btu/ft3 natural gas

     Use two burners.

     No. 1 bank capacity at other operating pres-
     sures:
                         Capacity,  cfh
     No.  of	~	
     burners  0. 5 psig   1. 0 psig  3. 0 psig  5 psig

        2       2,094     2,930     4,920    6,270

     Range of No. 1 bank burners is 2, 000 to
     6, 000 cfh, with valve capacity  range from
     2, 000 to 7, 000 cfh.

3.    Burner selection — No. 2 bank:

     No. 2 bank of burners  to be sized such that
     capacity of the 1 and 2 banks -will equal the
     most frequently expected flow of 12, 000  cfh.
     Use 6,000 cfh  as approximate capacity of
     No. 1 bank.

        12, 000 cfh  -  6, 000 cfh  =   6, 000 cfh

     Size and capacity of No. 2 bank burners  and
     valves will be  the same as  those of No.  1
     bank.

4.    Burner selection--No. 3 bank:

    'No. 3 bank capacity must equal the difference
     between 30, 000 cfh and 12, 000  cfh.

        30,000 cfh - 12,000 cfh   =  18,000 cfh

     From Table 166, capacity of No. 16X burn-
     er  at 5 psig is  4, 080 cfh (1, 000 Btu/ft3 gas).

     Capacity for 1, 300 Btu/ft  gas:

        1, 000
                                                             1, 300
                                                                    x  4,080  =  3, 140 cfh/burner
   1, 047 cfh/burner
                       =   1.91 burners
    Number of burners  required:

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626
                PETROLEUM EQUIPMENT
        18,000/cfh
     3, 140 cfh/burner
      5. 7 burners
     Use six No.  16X NGE burners.
     No. 3 bank capacity at other pressures:
      No.  of
     burners
  Capacity, cfh
3. 0 psig    5.0 psig
14,760     18,830
     Range of No.  3 bank burners,  14, 760 to
     18,300 cfh, with 2-inch valve range of
     15,500 to 20,000 cfh.

5.  Safety seal:

    Basis:  Seal pressure    6 psig
            Sealing liquid
            Temperature
       Water
       70°F
    ft of water  =
    (6 + 14.7) Ib/in.  (144) in.  /ft
               62. 3 Ib/ft
6.   Summary of flare operation:

        Valve action
                = 47. 8 ft
Valve
No.
1
2
3

Open,
psig
1.0
3. 0
5.0

Closed,
psig
0.5
1.0
3. 0

Range,
psi
0.5-5
1-5
5-6

r>urner
capacity
at 5 psig
6, 270
6, 270
18, 830
31, 370
capacity
at 5 psig
6,580
6,580
20, 000
33, 160
The bypass seal is set to open to No. 3 burner
bank at 6 psig.
7.  Sketch of flare:
              Dank \,i. 1 Bank No. i    Bank No. 3
Gas flow
                                  nun
Maintenance of flares

Most refineries and petrochemical plants have
a fixed schedule for inspection and maintenance
of processing units and their auxiliaries.  The
flare system should not be exempted from this
practice.  Removal of a flare from service for
maintenance requires some type of standby equip-
ment to disperse emergency gas vents during the
shutdown.   A simple stack with pilot burner should
suffice for a standby.  Coordinating this inspec-
tion to take place at time when the major process-
ing units are also shut down is good practice.

Flare instrumentation requires scheduled main-
tenance to ensure proper operation.  Most of the
costs and problems  of flare maintenance arise
from the instrumentation.

Maintenance expenses for flare burners can be
reduced by constructing them of chrome-nickel
alloy. Because of the inaccessibility of elevated
flares, the use of alloy construction is recom-
mended.
           STORAGE VESSELS

TYPES OF STORAGE VESSELS

Even in the most modern petroleum refineries and
petrochemical plants,  storage facilities must be
provided for large volumes of liquids and gases.
These facilities can be classified as closed-stor-
age or open-storage vessels.  Closed-storage
vessels include fixed-roof  tanks, pressure tanks,
floating-roof tanks  and conservation tanks. Open-
storage vessels include open tanks,  reservoirs,
pits, and ponds.

Closed-storage vessels are constructed in a vari-
ety of shapes, but most commonly as cylinders,
spheres, or spheroids.  Steel plate is the  usual
material of construction though  concrete,  -wood,
and other materials are  sometimes used.  Before
modern welding methods, the sections  of the tank
shell were joined by rivets or bolts. Welded joints
are now used almost universally except for the
small bolted tank found in production fields.   The
definition of a welded shell tank is given by API
Standard 12  C entitled "Welded Oil Storage Tanks."
Capacities of storage vessels range from a few
gallons up to 500, 000 barrels,  but tanks with
capacities in excess of 150, 000  barrels are rel-
atively rare.

Open-storage vessels  are also found in a variety
of shapes and materials  of construction. Open
tanks generally have cylindrical or rectangular
shells of steel, wood,  or concrete.  Reservoirs,
pits, ponds, and sumps are usually oval,  circu-
lar, or rectangular depressions in the  ground.  The
sides and bottom may be the earth itself or may
be covered with an  asphalt-like material or con-
crete.  Any roofs or covers are usually of wood
with asphalt or tar  protection.   Capacities of the
larger reservoirs may be  as much as 3 million
barrels.

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                                           Storage Vessels
                                             627
 Vapors, gases, aerosols, and odors  are  exam-
 ples of air contaminants emitted from storage
 facilities.  In most cases, practical and feasible
 air pollution control measures are available to
 reduce the emissions.


 Pressure Tanks and Fixed-Roof  Tanks

 Pressure tanks and fixed-roof tanks are grouped
 together because,  in a sense, pressure tanks
 are special examples of fixed-roof tanks  de-
 signed to operate at greater than atmospheric
 pressure.  A horizontal, cylindrical  (bullet)
 pressure tank is shown in Figure 472.  Other
   Figure 472.  Horizontal,  cylindrical pressure
   tank  (Graver Tank and Manufacturing Company,
   Division Union Tank Car  Co.,  East  Chicago,
   Indiana).

 types of pressure tanks--spheres ,  plain and
 noded spheroids,  and noded hemispheroids—are
 illustrated in Figure 473.   Maximum capacities
 of these pressure tanks are as much as 30,000
 barrels for spheres and hemispheroids,  and
 120,000 barrels for noded spheroids.  Spheres
 can be  operated at pressures up to 217 psi;
 spheroids, up to 50 psi; noded spheroids,  up
to 20  psi; and plain or noded hemispheroids,  up
to 15  and 2-1/2  psi respectively.   Horizontal,
cylindrical pressure tanks are constructed with
various capacities and pressures.

The ordinary vertical, cylindrical, fixed-roof
tank is  shown in Figure 474.'  This type of storage
facility operates at or within a few ounces of pres-
sure and may have a flat,  recessed flat,  conical,
or domed roof.  The term gastight,  often applied
to welded tanks, is misleading.  Many of  the roofs
of the welded tanks have free vents open to the
atmosphere.   Others are equipped with conserva-
tion vents that open at very slight positive pres-
sures.  A tank also has many standard appurte-
nances  including gaging hatches,  sample hatches,
relief vents,  and foam mixers. Any of these acces-
sories may fail  in service and result in vapor leaks.
 The operating pressure of a tank is limited by the
 thicknes's (weight) of the roof, as noted in Table  165.
 A cone roof tank may be operated at higher pres-
 sures,  if necessary, by structural  reinforcement
 or weighting of the roof. Safe operating pressures
 up to 4 ounces can be realized by this added ex-
 pense.  Use  of unsupported dome-shaped roofs is
 another method of increasing the allowable  operat-
 ing pressure of the fixed-roof tank.

 Floating-Roof Tanks

 Floating-roof storage tanks  are used for  storing
 volatile material with vapor pressures  in the low-

 Table 165. ROOF PROPERTIES OF STEEL TANKS
                 (Bussard,  1956)
Thickness, in.
(gage)
1/16 (16)
5/64 (14)
7/64 (12)
1/8 (11)
9/64 (10)
5/32 (9)
11/64 (8)
3/16 (7)a
1/4 (3)
Wt, lb/ft2
2.553
3. 187
4.473
5. 107
5. 740
6.374
7.000
7.650
10. 200
Operating pressure,
oz/in.
0.284
0. 354
0.497
0.568
0.638
0.708
0. 778
0.850
1.333
aMinimum thickness specified by API Std 12C.

er explosive range, to minimize potential fire or
explosion hazards.  These vessels also economic-
ally store volatile products that do not boil at at-
mospheric pressures  or less and at storage tem-
peratures or below.  These tanks are subclassi-
fied by the type of floating-roof section as pan,
pontoon, or double-deck floating-roof tanks (Fig-
ure 475).

Pan-type floating-roof tanks were placed in ser-
vice more than 40 years ago.  These roofs re-
quire considerable support or trussing to prevent
the flat metal plate used as the roof  from buck-
ling (Figure 475, lower right).  These roofs  are
seldom used on new tanks because extreme tilting
and holes in the roof have caused more than one-
fifth of installed pan roofs to  sink, and because
their use results in high vaporization losses.
Solar heat falling on the metal roof in contact
with the  liquid surface results in higher than
normal liquid surface  temperatures.  Hydrocar-
bons boil away more rapidly at the higher tem-
peratures and escape  from the opening around
the periphery of the roof.

To  overcome these disadvantages, pontoon sec-
tions were added to the top of the exposed deck.
Better stability of the  roof was obtained, and a
center drain with hinged or flexible connections
solved the drainage problem.   Center-weighted
  234-767 O - 77 - 42

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628
                                       PETROLEUM EQUIPMENT
 Figure 473.   Types of pressure vessels:  (upper left) 51-foot-diameter spheres (Butane  is stored in  these spheres
 at a petroleum  refinery in California.  Capacity  of each is 15,000 barrels, diameter is 54 feet 9 inches and
 design working  pressure is 35 pounds  per square inch.),  (upper  right) two  5,000-barrel spheroids designed for 20-
 psi pressure; (lower left) large noded  spheroids,  each designed  for 100,000-barrel  capacity and 15-psi pressure;
 (lower right) a 20,000-barrel noded hemispheroid  designed for 2-1/2-psi  pressure (Chicago Bridge and  Iron Company
 (1959).
pontoons,  double pontoons, and high- and low-
deck-pontoon floating-roof tanks are available
today.  Current practice is to use the  pontoon
roof on tanks with very large diameters.  In-
cluded with some pontoon  roof designs is a vapor
trap or dam installed on the underside of the roof.
This trap helps  retain any vapors  formed as a
result of localized boiling and converts the dead
vapor space into an insulation medium.  This dead
vapor space tends to retard additional boiling.

The more  expensive double-deck floating roof was
eventually introduced to reduce the effect of solar
boiling and to gain roof rigidity.  The  final design
generally incorporates  compartmented dead-air
spaces more than 12 inches  deep over the  entire
liquid surface.   The top deck is  generally sloped
toward the center or to a drainage area.  Any
liquid fdrming or falling on the roof top  is drained
away through a flexible roof drain to prevent the
roof from sinking.  The bottom deck is normally
coned upwards.  This  traps under the roof any
vapors  entrained with  incoming liquid or any va-
pors  that might form in storage.   A vertical dam
similar to those used  on pan or pontoon floating
roofs can also be added to retain these vapors.

Conservation Tanks

Storage  vessels classified  as conservation
tanks include  lifter-roof tanks  and tanks
with  internal, flexible diaphragms  or in-
ternal,  plastic,  floating blankets.  The
lifter roof  or,  as more commonly known,
gas holder,  is used for low-pressure  gas-
eous  products or  for  low-volatility  liquids.
This  type of vessel can be employed as a
vapor surge tank  when manifolded  to vapor
spaces of fixed-roof tanks.

-------
                                         Storage Vessels
                                            629
                                              "~
Figure 474.  Vertical,  cylindrical,  fixed-roof
storage  tank.
Two types of lifter-roof tanks are available, as
shown in  Figure 476.  One type has a dry seal
consisting of a gastight, flexible fabric; the other
type employs  a liquid seal.   The sealing liquid
can be fuel oil, kerosene,  or water.  Water should
not be employed as a sealing liquid where there
is danger of freezing.

The physical weight of the roof itself floating  on
vapor  maintains a slight positive pressure in  the
lifter-roof tank.  When the  roof has reached its
maximum height, the vapor is vented to prevent
overpressure and damage to tank.

The conservation tank classification also includes
fixed-roof tanks with an internal coated-fabric
diaphragm, as  shown in Figure 477.  The dia-
phragm is flexible and  rises and falls to balance
changes  in vapor volume.   Normal  operating
                                                                       ?       s «!?. s*|

         Figure 475.  Types of floating-roof tanks:  (upper  left)  Sectional  view of  single-deck,
         center-weighted (pan-type) floating roof;  (upper  right)  sectional  view of pontoon
         deck floating roof;  (lower left) cutaway  view of  double-deck  floating roof;  (lower
         right) cutaway view of  trussed-pan floating roof  (Graver  Tank  and  Manufacturing
         Company,  East Chicago,  Ind.),

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630
                                         PETROLEUM EQUIPMENT
                     Figure 476.   Types  of  lifter-roof  tanks:   (left)  Sectional  view of
                     expansion roof  tank with a  liquid  seal,  (right)  closeup  view  of
                     liquid seal  and vapor piping  (Graver  TanK  and  Manufacturing  Co.,
                     Division of  Union  Tank Car  Co., East  Chicago,  Indiana).
                                                                                         J
                    Figure 477.  Conservation tanks; (left) Sectional view of  inte-
                    grated conservation tank with  internal, flexible diaphragm;
                    (right) cutaway view of a vapor conservation tank showing
                    flexible membrane (Chicago Bridge and  Iron Co., Chicago,  III.)-

-------
                                           Storage Vessels
                                                                                                 631
pressure is 1/2 ounce per square inch, which is
approximately one-eighth the operating pressure
possible -with most gas holders.  Two basic types
of diaphragm tanks are the integrated tank, which
stores both liquid and vapor, and the separate
tank, which stores only vapor.   Common trade
names for  integrated tanks are "diaflote, " "dia-
lift, " and "vapor-mizer" tanks (Bussard,  1956),
or they may be referred to as vapor spheres or
vapor tanks.  The separate type of tank offers
more flexibility and does not require extensive
alteration of existing tanks.

Open-Top Tanks, Reservoirs, Pits, and Ponds

The  open-top tank is not used as extensively as
in the past. Safety,  conservation, and house-
keeping are factors effecting the elimination of
open vessels.   Even tanks that require full access
can and should be equipped with  removable covers.
The  open vessels generally have a cylindrical
shell,  but some have a rectangular shell.

Reservoirs were devised to store the large quanti-
ties  of residual oils, fuel  oils, and,  sometimes,
crude oils  resulting from petroleum production
and refining.   Safety considerations, larger fixed-
roof tanks,  and controlled crude oil production
have reduced the number of reservoirs in  use to-
day.  Even when covered,  reservoirs have open
vents, which maintain atmospheric pressures in
the reservoir.  Windbreaks divert the windflow
pattern over a large roof area and prevent the
roof from raising and buckling.

Open ponds or earthen pits were created by diking
low areas or by excavation.  These storage facili-
ties  served for holding waste products, refinery
effluent water, or inexpensive oil products for
considerable periods of time. In these,  oils
"weathered" extensively, leaving viscous,  tar-
like materials, and water  seeped into the lower
ground levels.  As the pond filled with solids and
semisolids, the contents were removed by me-
chanical means,  covered in place, or the pond
•was  simply abandoned.  The  use of these ponds
has diminished, and the remaining ponds are usu-
ally  reserved  for emergency service.

Smaller ponds or sumps were once used extensive-
ly in the crude oil production fields.  This use was
primarily for  drilling muds though oil-water emul-
sions and crude oil were also stored by this method.
Their use is gradually disappearing because unat-
tended or abandoned sumps cause nuisance problems
to a  community.

THE AIR POLLUTION PROBLEM

Different types and quantities of air pollution can be
associated with the storage vessel.   The types  of
pollution can be separated into three categories--
vapors, aerosols  or mists,  and  odors.   Of these
pollutants, the largest in quantity and concentra-
tion are hydrocarbon vapors.
Factors Affecting Hydrocarbon Vapor Emissions


Emissions of hydrocarbon vapors result from the
volatility of the materials being stored.  They are
effected by physical actions  on the material stored
or on the storage itself.  Changes in heat or pres-
sure change  the rate of evaporation.  Heat is a
prime factor and can cause unlimited vaporization
of a volatile  liquid.  Heat is received from direct
solar radiation or contact with the warm ambient
air, or is introduced during processing.  The rate
of evaporation is correlated •with atmospheric tem-
perature, weather conditions, tank shell tempera-
ture,  vapor  space temperature, and liquid body
and surface temperatures.

The vapor space  of a tank can contain any degree
of saturation of air -with vapor of the liquid up to
the degree corresponding to the total vapor pres-
sure exerted by the  liquid at storage temperatures.
Since the pressure in this vapor space increases
with temperature increase,  some of the air-vapor
mixture may have to be discharged  or  "breathed
out" to prevent the safe operating pressure of the
tank from being exceeded.  These emissions are
continually promoted by the  diurnal change in at-
mospheric temperatures, referred  to as the tank's
breathing cycle.

When the air temperature cools, as at night, the
vapor  space  within the tank cools and the vapors
contract.  Fresh air is drawn in through tank vac-
uum vents to compensate for the decrease in vapor
volume.  As this fresh air upsets any existing
equilibrium  of saturation by diluting the vapor con-
centration, more volatile hydrocarbons evaporate
from the liquid to restore the equilibrium.  When
the atmospheric temperature increases, as occurs
with daylight, the vapor space warms, and the
volume of rich vapors and the pressure in the tank
increase.  In freely vented tanks, or when the
pressure settings of the relief vents have been ex-
ceeded, the vapors are forced out of the tank. This
cycle is repeated each day and night.  Variation
in vapor space temperature  also results from
cloudiness, wind, or rain.

Filling operations also result in expulsion of part
or all  of the  vapors from the tank.  The rate and
quantity of vapor emissions from filling are di-
rectly proportional to the amount and the rate at
which  liquid  is charged to the vessel.  Moreover,
as the liquid contents are withdrawn from the
tank,  air replaces the empty space.  This fresh
air allows more evaporation to take place.

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632
PETROLEUM EQUIPMENT
Another emission of vapors caused by atmospheric
conditions is termed a windage emission.  This
emission results from wind's blowing through a
free-vented  tank and entraining or educting some of
the saturated vapors.  The windage emission is
not as large as that occurring during breathing
or filling cycles.  Other variables affecting emis-
sions include:  Volume of vapor space, frequency
of filling,  and  vapor tightness of the vessel. Tanks
that can be kept completely full of liquid  limit the
volume of the vapor  space into which volatile hy-
drocarbons can vaporize and eventually be emitted
to the atmosphere.   The frequency of filling and
emptying a tank influences the overall vapor emis-
sions.  When extensive periods of time elapse
between pumping operations, the vapor space  of a
tank becomes more nearly fully saturated with
vapor from the liquid.   Then, during filling of the
tank or during breathing cycles,  a larger concen-
tration  of vapors exists in the air-vapor  mixture
vented to the atmosphere.  Vapor tightness of the
tank can influence the evaporation rate.   The mov-
ing molecule in the vapor state tends to keep going
if there is no restraining  force such as a tight shell
or roof.

Different causes of emissions are associated with
a floating-roof tank.   These causes are known as
wicking and  •wetting.   Wicking emissions  are caused
by the capillary flow of the liquid between the  outer
side of  the sealing ring and  the inner side of the
tank wall.   The "wetting emission results  when the
floating roof moves towards the bottom of the tank
during emptying and leaves  the inner tank shell
covered with a film of liquid,  which evaporates
•when exposed to the  atmosphere.
 Hydrocarbon Emissions From Floating-Roof Tanks

 The American Petroleum Institute  (1962b) has
 published a method of determining  the standing
 (wicking) and withdrawal (wetting) evaporation
 emissions associated with floating  roof-tanks.
 The method is applicable  to tanks in crude  oil as
 well as gasoline service.  It is based upon  field
 test data for the standing  emission, and labora-
 tory data for the withdrawal emission.   The corre-
 lation presents factors under many  combinations
 of tank construction, type and condition of roof
 seal, and color of tank paint.   Parameters in-
 clude range of vapor pressure  from 2 to 11 psia
 true vapor pressure,  4 to 16 mph average wind
 velocity, and 20- to 200-foot-diameter tanks.

 The standing storage emission is determined
 from Table 166 and Figure 478.  It  is the product
 of emission factor L/f obtained  from the graph and
 corresponding factors  obtained from the table.
 One must know the following factors to find the
 value of the standing storage emissions: (1) Type
               of product stored, (2) Reid vapor pressure,  (3)
               average storage temperature, (4) type of shell
               construction,  (5) tank diameter, (6) color of
               tank paint,  (7) type of floating roof,  (8) type  and
               condition of seal, and (9) average -wind velocity
               in area.

               The standing storage emission formula is given as
                                                           P
                                                          (138)
               where Ly = standing storage evaporation emis-
               sion, bbl/yr

                k   =  tank factor with values as follows:
                     0. 045 for welded tank with pan or pontoon roc
                     single or double seal;

                     0. 11 for riveted tank with pontoon roof,  doub'
                     seal;

                     0. 13 for riveted tank with pontoon roof,  singl
                     seal;

                     0. 13 for riveted tank with pan roof,  double se
                     0. 14 for riveted tank with pan roof,  single se
                     (double  deck  roof is similar to a pontoon roof
                D  = tank diameter, ft [for tanks larger than  150ft
                in  diameter use 1 50 l • 5  (D/ ] 50)]
                P  = true vapor pressure of stock at its average
                storage temperature,  psia

                Vw -  average wind velocity, mph
                k   = seal factor:

                    1. 00 for tight-fitting seals (typical of modern
                    metallic or tube seals)
                    1.33 for loose-fitting seals
                    k  =  stock factor:
                     c
                    1. 00 for gasoline stocks
                    0. 75 for crude oils

                k   = paint factor  for color of shell and roof:

                    1. 00 for aluminum or light grey

                    0. 90 for white.

               Actual standing storage emissions of petroleum
               hydrocarbons  from tanks  equipped with seals in
               good operation should not deviate from the esti-
               mated emissions determined by this equation by
               more than -f 25 percent.  The  actual  emissions,
               however,  can  exceed the calculated amount by
               two  or three times  for a seal in poor condition.

               The seal length can be expressed in terms of tank
               diameter because the two are directly proportion-
               al to each other.  The actual emission is not di-

-------
                                               Storage  Vessels
                                                                                       633
    Table 166.   STANDING STORAGE EVAPORATION EMISSIONS FROM FLOATING-ROOF TANKS:
     L   (LOSS IN bbl/yr)  = Lf (LOSS  FACTOR FROM FIGURE 478) TIMES MULTIPLYING FACTOR
                        (FROM THIS TABLE;  American Petroleum Institute,  1962b)
Multiplying
factors
apply to
Lt
Gasoline
Crude oil
Welded tanks
Pan or pontoon roof
Single or double seal
Modern
Tank
paintb
Lt
grey
1.0
0.75
White
0.90
0.68
Olda
Tank
paint
Lt
grey
1. 33
1.0
White
1.20
0.90
Riveted tanks
Pan roof
Single seal
Modern
Tank
paint
Lt
grey
3. 2
2.4
White
2.9
2.2
Old*
Tank
paint
Lt
grey
4.2
3. 1
Wrute
3.8
2.8
Double seal
Modern
Tank
paint
Lt
grey
2. 8
2. 1
White
2. 5
1. 9
Olda
Tank
paint
Lt
grey
3.8
2.8
White
3. 4
2. 5
Pontoon roof
Single seal
Modern
Tank
paint
Lt
grey
2.8
2. 1
White
2.5
1.9
Olda
Tank
paint
Lt
grey
3.8
2.8
White
3.4
2. 5
Double seal
Modern
Tank
paint
Lt
grey
2. 5
1. 9
White
2. 2
1.7
Olda
Tank
paint
Lt
grey
3. 3
2. 5
White
3.0
2. 2
  Seals installed before 1942 are classed as old seals.
  Aluminum paint is considered light grey in loss estimation.
      \
         \
 FOR AVERAGE HIND VELOCITY
• REFER TO API BULLETIN
 2513, EVAPORATION LOSS IN
 THE PETROLEUM INDUSTRY-
 CAUSES AND CONTROL,  OR
 LOCAL WEATHER BUREAU DATA
             /i  i   I   i\   r\ /    /\/   x
30 4050 60  70 SO  90  100 110 120  130  140  ISO
                                                                             FOR TANKS LARGER THAN 150 ft
                                                                             DIAMETER, MULTIPLY LOSS FOR
                                                                             150-U-DIAMETER TANK BY RATIO
                   8    7654
                  TRUE VAPOR PRESSURE,PSia
                                                              200
                                                                                    600
                                                                                          700
                                                                                                800
                                                                                                     900   1000
                                                                           LOSS FACTOR,  L,
                                                            (MULTIPLY BY VALUE FROM TABLE TO OBTAIN ADJUSTED LOSS)
              Figure 478.  Calculation of emission  factor, Lf,  for  standing storage  evaporation
              emissions from  floating-roof tanks  (see Table  166).
rectly proportional to the diameter because sev-
eral other variables are involved.  Items such as
wind velocity and the decreased shading effect
of the shell on the roof of large-diameter tanks
are  examples.
                                       Emissions  increase,  but not directly, as the vapor
                                       pressure increases.  The relationship P/(14. 7 - P)
                                       correctly identifies this phenomenon,  and no sub-
                                       stantial error exists within the  valid range of
                                       this correlation.

-------
634
PETROLEUM EQUIPMENT
Standing storage emissions increase but do not
double when the average wind velocity doubles.
The 0. 7 exponent applied to the wind factor fits
data for average wind velocities exceeding 4  mph.
No  localities were  recorded as having less than
this 4 mph average wind velocity.

Withdrawal emissions

As  product is withdrawn from a floating-roof tank,
the wetted inner shell is exposed to the  atmosphere.
Part of the stock clinging to the inner surface drains
down the shell.   The remainder evaporates to the
atmosphere.   Tests made  determined the amount
of gasoline clinging to a rusty steel surface as
ranging from  0. 02 to 0. 10 barrel of gasoline per
1,000 square  feet of surface.

The withdrawal emissions  are represented by the
equation
           W  =  22,400
    (139)
where
This chart is intended for stabilized crudes that
have not been subjected to extreme weathering
or mixed with light oils.

The average stock temperatures should be used
in these  vapor pressure determinations.

Withdrawal emissions should be added to the stand-
ing storage emissions when gunited tanks are en-
countered.

Hydrocarbon Emissions From  Low-Pressure Tanks

Low-pressure tanks are used to store petroleum
stocks of up to 30 pounds RVP* •with relief valve
settings  of 15 psig.  The  American Petroleum In-
stitute's Evaporation Loss  Committee (1962c)
recommends a theoretical approach to emission
calculations from tanks such as  these.  Insufficient
data are available to establish any accurate corre-
lation with actual field  conditions.

Application of the following  equation indicates the
theoretical pressure (P£) required to prevent
breathing losses:
     W  =  withdrawal emissions, bbl per million
           bbl throughout

     C  =  0. 02 (based on barrels of clingage per
           1,000 ft2 of shell surface)

     D  =  tank diameter, ft

 Withdrawal emissions for gunited tanks can be
 significant.  Laboratory data indicated a  factor
 of C  =  2. 0.  Since withdrawal emissions counter
 standing storage emissions, a factor C  = 1. 0 is
 recommended  for gunite-lined tanks storing gaso-
 line.

 Application of results

 The emissions from floating-roof tanks can be
 estimated from  Table 166.  Necessary data in-
 clude:  Tank diameter; color of tank paint; type
 of tank shell, roof, and seal; Reid vapor  pres-
 sure and average temperature of stored product;
 and the average wind velocity at tank site.

 The true vapor pressure, P, can be obtained
 from vapor pressure charts by  the use of data
 in Figures 479 and 480.  To use these charts,
 one must know the Reid vapor pressure  of the
 stock.  Figure 479 is used for gasoline or other
 finished stocks.  The value of S (slope of the
 ASTM distillation curve at 10 percent evaporated)
 can be  estimated by  using suggested values given
 in a note of the chart.  The value of S is  zero for
 a single component stock.  The vapor pressure
 chart,  Figure 480, should be used for crude oils.
                    =   1.1  (P_  + P,
-PI) -
\ - P2>
                                            (140)
               where
                   P   =  gage pressure at which pressure vent
                         opens,  psig

                   P   =  atmospheric pressure

                   P   =  gage pressure at which vacuum vent
                         opens,  psig

                   p   =  true vapor pressure at  90°F minimum
                         liquid surface temperature, psia

                   p   =  true vapor pressure at  100"F maximum
                         liquid surface temperature, psia.

               This equation is applicable only when the vapor
               pressure  at minimum surface temperature (Pj)
               is less  than the absolute pressure (Pj +  P ) at
               which the vacuum vent opens.  Air always exists
               in the vapor space under a condition such as this.
               Figure  481 is .a plot of equation 140.  The pres-
               sure required to eliminate breathing emissions
               from products ranging up to 17. 5 psia TVPt at
               100°F  storage temperature and 14. 7 atmospheric
               pressure  can  be determined from this curve. The
               gage pressure at which the vacuum vent opens
              *i7vPrefers to Reid vapor pressure as measured by ASTM D
               323-5b Standard Method of Test  for Vapor Pressure of
               Petroleum Products (Reid Method).
               tTVP refers  to true vapor pressure.

-------
                                             Storage Vessels
                                                                                                      635
                    —  0.20


                    —  0.30

                        0.40

                        0.50
                        0.60
                        0.70
                        0.80
                        0.90
                        1.00
                        I.SO


                        2.00

                        2.50

                        3.00

                        3.50

                        4.00


                        5.00

                        6.00

                        7.00

                        e.oo

                        9.00
                       10.0
                       I I .0
                       12.0
                       13.0
                       14.0
                       15.0
                       16.0
                       I 7.0
                       18.0
                       I 9.O
                       20.0
                       21.0
                       22.0
                       23.0
                       24.0
                                      120—,
    ,1 0
S = SLOPE OF THE astm DISTILLATION
CURVE AT 10« EVAPORATED=
   °F AT 15% MINUS °F AT 5%
            10
IN THE ABSENCE OF DISTILLATION
DATA THE FOLLOWING AVERAGE VALUE
OF S MAY BE USED:
                                      IOO-E
                                                                               90 —
                                       80 —
                                       70 —
                                       60 —
                                       50 —
                                       40 —
                                       30 —
                                       ZO-
                   IC—
                                        O-3
MOTOR GASOLINE
AVIATION GASOLINE
LIGHT NAPHTHA (9 TO  14 Ib
NAPHTHA (2 TO 8 Ib rvp)
rvp)
3
2
3.5
2.5
                     Figure 479.  Vapor pressures of gasolines and finished petroleum
                     products,  1  Ib to 20 Ib RVP.   Nomograph drawn from data of the
                     National  Bureau of Standards (American Petroleum Institute, 1962b).
(Pi) is zero for this curve.  The values of pj and
P2 were obtained from Figure 479.  Since higher
vapor pressure stocks have a smaller distillation
slope  (s),  a range of distillation slopes was used.

The altitude of the storage vessel's  location af-
fects the required storage pressure. Proper ad-
justments  for  various altitudes can be made by
substituting the proper atmospheric pressure
(Pa) in equation 140. Table  167 lists atmospher-
ic pressures at various  altitudes.
                Some pressure tanks must be operated at relative-
                ly low pressures — some by design, others  because
                of corroded tank conditions. Pressure  settings
                from zero to 2. 5 psig are believed to  decrease the
                breathing emissions from 100 percent to zero per-
                cent, depending upon the  vapor  pressure of the
                material stored.   This  is shown in Figure 482.
                Each additional increment of pressure  reduces
                the  breathing emissions by a progressively smaller
                amount.   Boiling emissions occur when the true
                vapor  pressure of the liquid exceeds the pressure

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636
PETROLEUM EQUIPMENT
                                               ,— 2


                                                  3

                                                  4

                                                  5
                    9
                    10
                    I I
                    12
                    13
                    14
                    15
                   20
                                               — 10
       •— 15
                                                                                 140
                                                                                 130 —E
                                                                                120
                                                                                 I 10  —E
                                         I 00 —E
                                          90 —E
                                                                                 80  —=
                                                                                 70
                                                                                 60
                                                                                 50  -E
                                          30 -E
                                         20
                                                                                 10 —E
                   25
                     Figure 480.  Vapor  pressures of crude oil  (American  Petroleum
                     Institute,  1962b).
   Table  167.  ATMOSPHERIC PRESSURE AT
       ALTITUDES ABOVE SEA LEVEL
     (American Petroleum Institute, 1962c)
Altitude, ft
1, 000
2, 000
3, 000
4, 000
5, 000
Pressure, psia
14. 17
13.66
13. 17
12.69
12.23
              vent setting.  If this vapor pressure equals or
              exceeds the absolute pressure (Pj  +  P ) at 'which
              the tank vent opens, air is kept out of the tank.
              The absolute tank pressure then equals the vapor
              pressure of the liquid at the liquid surface  tem-
              perature.   The storage pressure required to pre-
              vent boiling is
                                                                P
                                                                 2
                                                                           -  P
                                                         (141)
                                                      This equation is also indicated in Figure 481.
                                                      These minimum pressure requirements have

-------
                                                Storage Vessels
                                                                                  637
                                                                                                            7
                                                                                                  z
                                                                                                  f
                                                                                                I
                                                                                              7
                                                                                       CURVE /
                                                                                 BOILING
                                                                                   t
                                                                                L
                   NOTE   FOR VALUES OF P2 BETWEEN 20 AND 30 psia,
                        MULTIPLY  THE REID VAPOR PRESSURE AT
                        IOO°F BY  1 07
                                                 7
                                                                         7
                                              BREATHI G CURVE-
       ^••^^^•••••••••••••••••••••••••••••••••••••••••(•••••••••••••l*••••••••ill*
       • •••••••••••••••••••••••••••••••••••••.••••••••••••••••••••••••••.••••••••••I*
      ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••fl
I       ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
       •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••*••••••••••••
       •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••^•••••••••••M
       •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••^••••••••••••l
                                               • ^•••••••••••••••••••••••||M
                                               • ^•••••••••••••••••••••••l|a
                                               :|i::::i::::!:::::::::::i:i|:
                                               •••••••••••••••••••••••••••••
                                               ••••••••••••!••••••••••••••••
                                               •II•••••••••!•••••••••*••••••
                Figure  481.
                For values
                100°F by  1
                                        10                 15
                                      TRUE  VAPOR  PRESSURE AT  100°F
                                                                     (P,) .
                                                20
                                                p s i i
                                                                                             25
 Storage  pressure  required to eliminate breathing and boiling  losses.
of p? between 20 and  30 psia, multiply the Reid  vapor pressure  at
07 (American Petroleum  Institute,  1962c).
proved adequate to prevent boiling emissions
under usual storage  conditions.  The true vapor
pressure at 100°F can be  obtained from Figure
479 up to 20 pounds RVP.   In the range of 20 to
30  RVP,  P-, is approximately 7 percent higher
than the  RVP at 100°F.

A filling or working  emission occurs if the tank
pressure exceeds the Vent setting.  During the
initial stage of filling, compression of the air-
hydrocarbon mixture with some condensation of
                                vapor takes  place if the tank pressure is less
                                than the pressure vent setting.   This condensa-
                                tion maintains a fairly constant hydrocarbon
                                partial  pressure.   Thus,  a certain fraction of
                                the vapor space can be filled with  a liquid be-
                                fore  the tank pressure increases above the vent
                                setting.  As filling  continues, the  total pressure
                                increases to the pressure at which the  relief
                                valve opens.  Venting to the atmosphere  occurs
                                beyond  this point.   If there is no change in tem-
                                perature of the liquid or vapor during the filling

-------
638
                           PETROLEUM EQUIPMENT
       100
        80
       60
    5- 20
                  10
           OPERATING
              20
         PRESSURE
     30
RANGE,  o z/i n.
                                           40
    Figure 482.  Relationship for estimating motor
    gasoline breathing  emissions from tanks oper-
    ating at jess  than  the recommended 2.5-psig
    vent setting (American Petroleum Institute,
    1962c).
period, the liquid entering the tank displaces
to the atmosphere an equal volume  of vapors.

The total emissions depend upon the capacity of
the vapor space of the tank.   Since  the tempera-
ture changes as condensation occurs, the rates
of filling and emptying can also affect the vapor
emissions.  These variables  increase the diffi-
culty of determining the actual emissions. In
order that theoretical emissions can be calcu-
lated, two assumptions are made:

1.  Equilibrium exists between the hydrocarbon
    content in the vapor and liquid  phases under
    given temperature  and pressure conditions.

2.  Filling begins at slightly below atmospheric
    pressure.
The following equation can then be derived:
            3 pv (P  - PI - p )
100 (P  +
                         - p )
                                           (142)
where

   F   =  •working emissions,  % of volume pump

   p   =  true vapor pressure at liquid tempera-
          ture, psia
   P  =  gage pressure at which vacuum vent
          opens, psig

   P, =  gage pressure at which pressure vent
          opens, psig.

This calculated emission is correct on the assump
tion  that the vapor pressure of the liquid at its sur
face temperature and the vapor space temperature
are the same at the start and end of filling.  The
emissions, expressed as a percentage,  are re-
duced to the extent that the tank is not completely
filled.

Obtaining the true liquid-surface  temperature is
difficult.  Thus, the value of pv is based upon the
average main body temperature of the liquid.  As
a result of possible variables, the required pres-
sure to prevent breathing emissions from  low-
pressure tanks, as found by Figure 481, should
be considered to have no pressure rise available
to decrease the •working emissions.   The working
emissions can be found in the same  manner as
for an atmospheric tank.

Figure 483 is based upon equation 142,  except
that the emission values  are plotted for various
vapor pressures and pressure vent settings
greater than atmospheric pressure.  The straight
line gives theoretical filling emissions from tanks
with vents set at only slightly greater than  at-
mospheric pressure.  The values are representa-
tive for 12 turnovers per year normally experi-
enced with this type of low-pressure storage.

Hydrocarbon Emissions From Fixed-Roof Tanks

A revised method of determining  hydrocarbon
emissions from fixed-roof tanks has been pub-
lished by the American Petroleum Institute
(1962a).   Various  test data were evaluated and
correlated to obtain methods  of estimating breath-
ing emissions and filling and  emptying (working)
emissions from fixed-roof storage tanks.  The
method is applicable to the full range of petroleum
products, from crude oil to finished gasoline.
Data -were considered only for tanks with tight
bottoms,  shells, and roofs.   All tank connections
were assumed to be vapor tight and liquid tight.
Of 256 separate tests recorded and screened, 178
were found acceptable for correlation.  A limited
number of factors were definitely found to  estab-
lish  a  correlation.  The following factors were
applied in the  correlation:

1.    True vapor pressure, P,  at storage condi-
    tions, in pounds per  square inch absolute
     (if temperature of the liquid -was not available,
    a temperature 5°F above average atmospheric
    temperature was selected);
   P  =  atmospheric pressure, psia
                                         2.  tank diameter, D,  in feet;

-------
                                            Storage Vessels
                                                                                         639
             O 5
                                                                                           0 5
                                                                                           04
                                                                                           0 2
                            TRUE VAPOR PRESSURE AT LIQUID  TEMPERATURE (pv), psia
            Figure  483.  Emissions, % volume pumped into tank  for  various vent settings.  AP is
            the difference  between the pressure vent  setting  and  the pressure required to  pre-
            vent breathing  loss (American Petroleum Institute,  1962c).
3.  average tank outage, H,  in feet (outage in-
    volves height of the vapor space and includes
    an allowance for the roof);

4.  average daily ambient temperature change,  T,
    in degrees Fahrenheit, as reported by the U. S.
    Weather Bureau for area where tank is located;

5.  paint factor  Fp (vessels  with white paint in
    good condition have a factor of unity).

A correlation applicable to tanks with  diameters of
20 feet or larger was developed:
I       24
  y    1,000
where
        (\0. 68
14. 7 - P )    °
                                            (143)
   L  =  breathing emissions,  bbl/yr
     y
     P
true vapor pressure at bulk liquid tem-
perature, psia, from  Figure 479.  If the
average liquid body temperature  is not
available,  it may be estimated at 5 ° F
above average ambient temperature
     D  =  tank diameter,  ft
                                                 H  =  average outage,  ft.  This value includes
                                                      correction for roof volume.  A  cone  roof
                                                      is equal in volume to a cylinder with the
                                                      same base diameter of the cone and one-
                                                      third the height of the  cone

                                                 T  =  average daily ambient temperature change,
                                                      °F

                                                F   =  paint factor  (see  Table 168).

                                            Smaller diameter tanks require a modification  of
                                            equation 143.  Observed emissions were less than
                                            calculated emissions for tanks of less than 30 feet
                                            diameter.  If an adjustment factor,  as indicated in
                                            Figure  484,  is applied to the calculated  emissions
                                            from equation 143, the correlation between ob-
                                            served  and calculated data becomes more exact.
                                            By combining the adjustment factor with the tank
                                            diameter factor, a final equation is
L  =
 y
                                                             24
                                                  1,000
                                                   / _P_\°-
                                                   I 14. 7 - P)
                                                       •where

                                                           C
                                                                                                  (144)
                                                       an adjustment factor for small-diameter
                                                       tanks,  determined from Figure 484. For

-------
640
PETROLEUM EQUIPMENT
               l.O
               0.8
               0 G
               0.4
               0.2
                          Table 168.  PAINT FACTORS FOR DETERMINING
                       EVAPORATION EMISSION FROM FIXED-ROOF TANKS
                                 (American Petroleum Institute, 1962a)
Tank color
Roof
White
Aluminum3-
White
Aluminum3-
White
Aluminum
White
Light gray
Medium gray
Shell
White
White
Aluminum3-
Aluminum3-
Aluminum^
Aluminum
Gray
Light gray
Medium gray
Paint factor
Paint in
good condition
1. 00
1.04
1. 16
1.20
1.30
1.39
1.30
1.33
1.46
Paint in
poor condition
1. 15
1. 18
1.24
1.29
1. 38
1.46
1.38
1.38
1.38
                     aSpecular.
                     bD if fuse.
                                                                20
                                               TANK DIMETER, ft
                         Figure  484.  Adjustment  factor for smalI-diameter tanks
                         (American Petroleum  Institute, 1962a).
           tanks 30 feet or more in diameter, use
           a factor = 1.   The breathing emissions
           from fixed-roof tanks can also be esti-
           mated from Figure 485, as well as from
           equation 144.

 The working emissions include two phases of stor-
 age:  (1) The filling emissions under which vapors
 are displaced by incoming liquid,  and  (2) the
 emptying emissions, which draw in fresh air and
 thus allow additional vaporization to take place.
               Variables considered in determining this loss are
               true vapor pressure, throughput,  and  tank turn-
               overs, which yield the  equation:
                                 /3 PV  \
                                 110,oooy  t
(145)
               where

                    F  -  working loss,  bbl

-------
                                   Storage  Vessels
641



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-------
642
                    PETROLEUM EQUIPMENT
   P =  true vapor pressure at storage temper-
         atures, psia (if these temperature data
         are not available, estimation of 5 °F
         above average  ambient temperature is
         satisfactory)

   V =  volume of liquid pumped into tank, bbl

  K  =  turnover factor determined from Figure
         486.
      1.0
      0.8
    S0.6
      0.4
      0.2
                     NOTE: FOR 36 TURNOVERS PER TEAR
                         OR LESS. K, = 1.0
        0  36
               106
  200     30D
TURNOVERS PER YEAR
                                   400
                                           500
      Figure 486.  Effect of turnover  on working
      emissions. For 36 or  less  turnovers per
      year, K+ = 1.0 (American  Petroleum Insti-
      tute, 1962a).
By using equation 145, a nomograph has been de-
veloped in Figure 487 showing the working emis-
sions of gasoline and crude oil from fixed-roof
tanks. Limited data resulted in the committee's
using the  same formula for crude  oil breathing
emissions as for gasoline  breathing emissions
with an applied adjustment factor Kc.  This ap-
proach is based upon an assumption that the emis-
sions from crude  oil storage vary in the same
manner as the emissions from gasoline storage,
calculated from variables  in equation 143.  The
adjustment factor, KC, represents the ratio be-
tween the respective emissions.  The true vapor
pressure  of crude oil must be determined from
Figure 480.  This figure applies to stabilized
crude oil  only.  The breathing emission factor of
0. 58 results in part from  slower convective move-
ment.  This is true in the  case  of  a liquid surface
less volatile than  the body of the liquid.  In con-
sidering  the working emissions from crude oil
storage,  however, filling  cycles are normally
less frequent than daily breathing  cycles are. Thus
more crude oil evaporates between cycles,  creat-
ing a more saturated vapor space.   The action of
                                  filling causes fresh liquid to move to the surface.
                                  A factor somewhere between 0. 58 and unity ap-
                                  pears feasible.  A review of the scattered data
                                  available supports a factor of 0. 75.   Equation 145
                                  then becomes
                                                   /2.Z5 PV\
                                                   I 10,000  I  t
                                           (146)
                                  •where
                                                        F    =  working emissions for crude oil,  bbl
                                                         CO

                                                          P
                                            true vapor pressure,  psia, determined
                                            from Figure 439 (again this may be
                                            estimated at 5°F higher than average
                                            ambient temperature in lieu of better
                                            data)
                                      V =  volume pumped into tank, bbl

                                      K  =  turnover factor, determined from
                                            Figure 486.
Aerosol  Emissions

Storage equipment can also cause air pollution in
the form of aerosols or mists.  An aerosol-type
discharge is associated -with  storage of heated
asphalt.  This  discharge is more predominant
during filling operations.  The reasons for this
emission,  other than basic displacement,  are not
thoroughly understood.  Continued oxidation of
the asphalt followed by condensation, or conden-
sation of any moisture in the  hot gases upon their
entering the  cooler atmosphere, are believed to
be the primary causes of the mists.  An analysis
conducted during the filling operation found essen-
tially air and water as the main components of the
displaced vapor.  Table 169 shows the results of
this analysis.  These vapors  are frequently highly
odoriferous.

Whenever live  steam or air is added to a vessel
for mixing, heating,  oxidizing,  or brightening,
droplets or aerosols can be entrained with the
discharge gases.  Visible discharges, product
loss, and odors can result.
                                   Odors

                                   The release of odors is closely related to evapo-
                                   ration and filling operations associated with the
                                   storage vessel.   The concentration of odors is
                                   not, however, directly proportional to the amount
                                   of material released.  Some relatively heavy
                                   compounds are very noticeable at dilutions of 1
                                   to 5 ppm.  These compounds are often toxic or
                                   highly malodorous and generally contain sulfur or
                                   nitrogen compounds.

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                                              Storage Vessels
                                                                               643
Agitation, especially by means of air or live
steam, will increase the release of odors to
the atmosphere.
AIR POLLUTION CONTROL EQUIPMENT
Control of air pollution originating from storage
vessels serves a three-fold purpose: (1) Elimina-
                                tion  or reduction of air contaminants,  (2) elimina-
                                tion  or reduction of fire hazards,  and  (3) economic
                                savings through recovery of valuable products.
                                Methods of control include use  of floating roofs,
                                plastic blankets, spheres, variable vapor space
                                systems, various recovery systems,  and altered
                                pumping and storage operations.
                                                                                            20
              EXAMPLE:
                 56000 Barrel Tank
                 Througnput=:560000 Barrels per Year
                 Turnovers^ 10
                 True Vapor Pressures 5.8 psia
                 Working loss    =   975 Barrels per year
                         10.0-
                          90'-
                          8.0-
                                                                . - 15
              1500 -
              2000 -
              3000-
              4000 -
              6000
              7000
              8000
              9000
              10000
7.0-

60-

5.0-
                          3.0-
                          2.0 -
1.5 -
1.0 -J
                                                     Pivot
                                = Z
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90-
80-
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40-
-
30-
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- 60 15-
-70 "
-80
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-100 i.o-
-125
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-200 07-
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-300 0.6-
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- 70
-60

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-4.0
- 3.0


- 20


- 1.5




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- 0.9
- 0.8
- 0.7
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                  Figure 487.  Working emissions of gasoline  and  crude oil from  fixed-roof
                  tanks.  The throughput is divided by  a  number  (1,10,100,1,000)  to  bring
                  it into the range  of  the  scale.   The  working  emission,  read from the
                  scale, must then  be multiplied by the same  number (American Petroleum
                  Institute, 1962a).
 234-767 O - 77 - 43

-------
644
PETROLEUM EQUIPMENT
 Table 169.  ANALYSIS OF  VAPORS DISPLACED
    DURING FILLING 85/100 PAVING-GRADE
     ASPHALT INTO A FIXED-ROOF TANKa
              Component
Methane
Ethane
Heavy hydrocarbons (28° API gravity)
Nitrogen
Oxygen
Carbon dioxide
Water
Argon
Volume %
  Trace
  Trace
    0. 1
  67. 3
  13. 0
    1. 4
  18. Z
  Trace
aSample was collected over 3-1/2-hour filling
  period, the noncondensables were analyzed by
  mass  spectrometer.  Condensable hydrocarbons
  were separated from the  steam, and gravity and
  distillation curves were determined.
Seals  for Floating-Roof Tanks

The principle by which a floating roof controls
emissions from a volatile liquid is that of elim-
inating the vapor  space so that the liquid cannot
evaporate and later be vented.  To be successful
the floating roof must  completely seal  off the liq-
uid surface from the atmosphere (Chicago Bridge
and Iron Company,  1959).   The seal for the float-
ing roof is therefore very important.  A sectional
view of the sealing  mechanism is  shown in Figure
488.  The floating  section is customarily construc-
ted about 8 inches less in diameter than the tank
shell.  A sealing mechanism must be provided for
the remaining open annular gap.   The seal  also
helps keep the roof centered.

Conventional  seals  generally consist of vertical
metal plates or shoes  connected by braces  or
pantograph devices to  the floating roof.  The shoes
are suspended in  such a way that they are forced
outward against the inner tank wall.  An impervi-
ous fabric bridges the annular area between the
tops of the shoes  contacting the tank wall and the
circumference  of the floating  roof.  To reduce
emissions, a secondary seal or wiper  blade has
been added to the floating-roof design by extend-
ing the fabric seal or by adding a  second section
of fabric as shown in Figure 489.  This seal re-
mains in contact "with the tank wall.  Its flexibility
allows  it to make contact even in rivet head areas
of the inner shell or in places where the shell
might be slightly  out of round.  This improvement
lowers hydrocarbon emissions further by reducing
the effect of wetting and wicking associated with
floating-roof tanks.

Recently,  other types  of sealing devices to close
the annular gap have been marketed, as shown in
Figure 490.   These  devices consist of  a fabric
tube that rests  on the surface of liquid exposed
FIEXURE CLOSURE
FtEXUSE

UPPER INSULATOR
               LOWES INSULATOR
                                                      PANTAGRAPH HANGER
               SEALING SING
               Figure 488.   Sectional view of double-deck floating-
               roof's  sealing mechanism (Chicago Bridge and Iron
               Co.,  Chicago,  III.).
               in the annular space.  The fabric tube is filled
               with air, liquid or plastic material.  The pneu-
               matic, inflated seal is provided with uniform air
               pressure by means of a small expansion chamber
               and control valves.  The sides of the tube remain
               in contact with the roof and inner shell.   The liq-
               uid-filled tube holds a ribbed scuff band against
               the tank wall.  The ribbed band acts as a series
               of wiper blades  as well as a closure.  All tubes
               are protected by some type of weather covering.

               A weather  covering can also be added to protect
               the  sealing fabric of the conventional seals.  The
               covering includes flat metal sections held in place
               by a metal band.  The metal protects the fabric
               seal from the elements.  When floating-roof sec-
               tions are added to older tanks  constructed  of
               riveted sections,  better contact of the shoes with
               the  shell can be ensured by guniting or plastic
               coating the inner  shell.   The wetting condition  of
               gunited walls may, however, olfset the  gain of
               better contact.

               Floating Plastic Blankets

               A floating  plastic blanket,  operates on the  same
               principle of control as a floating roof.   It is also

-------
                                           Storage Vessels
                                            645
                                 EXPANSION JOINT FABRIC
 SECONDARY SEAL
     FABRIC
 STANDARD HORTON
 SEALING RING
    WITH
 PANTAGRAPH
      HANGERS
Figure 489.   Secondary seals  stop  vapor  loss  from
high winds on riveted tanks  by  sealing off  the
space between the tank shell  and the  sealing  ring
sole plate (Chicago Bridge  and  Iron Co.,   Chicago,
 III.).
available as a surface cover, as depicted in Fig-
ure 491.  It was developed in France and has been
tried principally in foreign markets (Laroche
Bouvier and Company).  Recent applications have
been made in the United States. The blanket is
usually made of polyvinyl chloride but can be
made of other plastics such as polyvinyl alcohol,
superpolyamides,  polyesters,  fluoride hydrocar-
bons, and so forth.  The blanket's underside is
constructed of a large number  of floats  of the
same plastic material.  The blanket  is custom
manufactured so that only a 1-inch gap remains
around the periphery.  A vertical  raised skirt
is provided at the edge of the blanket to serve as
a vapor seal over the annular area.  Once this
area is saturated,  further evaporation diminish-
es.  The  only remaining loss is gaseous diffusion.
The  seal  is made as effective as possible by  using
an elastic,  Z-shaped skirt.

Provisions  are  made in the blanket for openings
fitted with vertical sleeves for measuring and
sampling operations.  These openings have a
crosscut, flexible  inner diaphragm to minimize
exposure of the  liquid surface.  Small holes
with downspouts to effect a liquid  seal are  used
to provide drainage of any condensate from the
top of the blanket.  Another feature includes a
stainless steel cable grid to prevent a buildup
of static charges.   The grid is closely attached
just under the blanket in parallel lines and con-
nected to the  tank shell by a flexible conductor
cable.  Installation of a plastic blanket is con-
venient for both new and existing tanks.  The
blanket is  made in sections and can be introduced
into a tank through  a manhole.

A rigid foam-plastic cover constructed of poly-
is ocyanate foam is  also available to equip small
fixed-roof tanks  with a floating cover.   The cov-
er is manufactured in radial  sections,  each
equipped with a flexible neoprene seal attached
on the outer edge.  The sections are easily in-
stalled through roof manholes and assembled
•with slip-fit joints.
 Plastic Microsph eres

An outgrowth of application of plastic material
provides another type of control mechanism.
This type of control is also similar to the float-
ing roof.  A phenolic or urea resin in the shape
of tiny, hollow, spherical particles has been de-
veloped by Standard Oil Company of Ohio (Ameri-
can Petroleum Institute, 1962d).  This material
has the physical properties necessary to form a
foam covering over the denser petroleum prod-
ucts.  The fluidity of the layer enables it to flow
around any  internal tank parts while keeping the
liquid  surface sealed throughout any level changes.
These plastic spheres  are  known under  their trade-
mark names of microballoons or Microspheres.
These coverings have proved to be effective con-
trols for fixed-roof crude oil tanks.  Excessive
amounts of  condensation or high turbulence  should
be avoided.  The plastic foam has not proved as
satisfactory for one-component liquid or gasoline
products.

A  1/2-inch  layer of foam has been found sufficient
for crude oil where pumping rates do not exceed
4, 000 barrels per hour.  A layer 1  inch thick is
recommended for pumping rates up to 10, 000
barrels per hour.  In order to overcome wall
holdup in smaller tanks, it is suggested that a
1-inch layer be used regardless of pumping rates.
For tanks storing gasoline, the  recommended
foam thickness  is 2 inches  for tanks up to 40 feet
in diameter, and 1 inch for all larger diameter
vessels.

Various methods can be used to put the foam cov-
ering on the crude oil.   One method is to inject
the plastic spheres with the crude oil as  it is
charged to the tank.  Spheres are added by means
of an aspirator  and hopper  similar to equipment
used in fire-fighting foam systems.  The spheres
can also be added by placing the ctesired quantity

-------
646
PETROLEUM EQUIPMENT
WEATHER SHIELD
SEAUNG BAND
SEALING LIQUID
NORMAL
PRODUCT LEVEL
TANK SHEU
ADAPTABLE
SEAl SUPPORT
V/EATHER SHIELD
HANGER BAR


CURTAIN SEAl


SEAL ENVELOPE
SEAL SUPPORT
   RING
   RESILIENT
URETHANE FOAM
                   Figure 490.  Sealing devices  for  float!ng-roof
                   tanks:   (upper  left) Liquid-filled tube  seal,
                   (upper  right)  inflated  tube  seal,  (lower left)
                   foam-filled tube  seal  (Chicago  Bridge  and  Iron
                   Co.,   Chicago,   III.)

-------
                                           Storage Vessels
                                             647
    DETAIL OF PANELS ASSEHBLY                  DEGASSING IRAP
                 ^f ALUmNlM AUO< PANEL
  BUTT STRAP
             PERIPHERAL ANGLE

    DETAIL OF PERIPHERAL SEAL

Figure 491.  Fixed-roof  tank with  internal plastic
floating blanket  (Laroche Bouvier and Company,
5.  Boulevard  Edgar-Qumet, Colombes (Seine), France).
 in the water or sediment.  At high temperatures,
 the thermo-setting resins  soften, liquefy, and
 mix with the fuel oil, asphalt,  or coke.


 Vapor  Balance Systems

 Variable vapor space or vapor balance systems
 are  designed to contain the vapors produced in
 storage.   They  do not  achieve  as  great a re-
 duction  in  emissions as an appropriately  de-
 signed vapor recovery  system  does.   A well-
 planned unit includes storage of similar or
 related  products,  and  uses the advantage  of
 in-balance  pumping situations.   Only the  vapor
 space of the tanks is  manifolded together in
 these  systems.  Other  systems include a vapor
 reservoir tank that is either a lifter-roof type
 or a vessel with an internal diaphragm.   The
 latter vessel can be an integrated vapor-liquid
 tank or a separate vaporsphere.  The  manifold
 system includes various sizes of lightweight
 lines installed to effect a balanced pressure
 drop in all the branches while  not exceeding
 allowable pressure drops.  Providing  isolating
 valves for  each tank so that each tank  can be
 removed from the vapor balance system dur-
 ing gaging  or sampling  operations  is also good
 practice.   Excessive vapors that exceed the
 capacity of the balance  system should  be  incin-
 erated in a smokeless flare or used as fuel.
on the clean,  dry floor of the tank just before the
crude oil is charged.  A wetting agent must be
used  when the foam covering is to be  used on gas-
oline  products.  This is  accomplished by  slurry-
ing the plastic spheres,  wetting agent, and gaso-
line in a separate container.  The slurry  is then
injected into the tank.  Changes in tank operation
are not necessary except for gaging or sampling.
A floating-type well attached to a  common-type
gaging tape allows accurate measurement of the
tank's contents.  A sample thief with  a piercing-
type bottom is needed for sampling.
Protection against excessive loss of the plastic
spheres is necessary because of the relative
value of the foam covering.  Precaution must be
taken against overfilling and pumping the tank too
low.  Standard precautions against air entrainment
in pipelines normally safeguard against the latter.
Overfilling can be prevented by automatic shutoff
valves or preset shutoff operations.   Low-level
shutoff should prevent vortices  created during
tank emptying.  Other than loss of the foam, no
trouble should be encountered if the  spheres
escape into process lines.  The plastic material
is not as abrasive as  the  sand particles normally
found entrained in crude oil.  Excessive  pres-
sures crush  the spheres and the plastic settles
 Vapor Recovery Systems

 The vapor recovery system is in many ways
 similar to and yet superior to a  vapor balance
 system in terms of emissions prevented.  The
 service of this type of vapor recovery system
 is more flexible as to the number of tanks and
 products being stored.  The  recovery unit is
 designed to handle vapors  originating from fill-
 ing operations as well as  from breathing.  The
 recovered vapors are compressed and charged
 to an absorption unit  for recovery of  condensable
 hydrocarbons.  Noncondensable vapors are piped
 to the fuel gas system or  to a  smokeless flare.
 When absorption of the condensable  vapors is
 not practical from an economic standpoint, these
 vapors,  too, are sent directly to the  fuel system
 or incinerated in a smokeless  flare.

 The recovery system, like the vapor  balance
 system, includes vapor lines  interconnecting
 the vapor space of the tanks  that the  system
 serves.  Each tank should be  capable  of being
 isolated from the system.  This  enables  the
tanks to be sampled or gaged without  a result-
ing loss of vapors from the entire system.  The
branches are usually  isolated by providing a
butterfly-type valve,  a regulator, or  a check
valve.   Since the valves offer more  line resis-
tance,  their use is sometimes  restricted.  Small

-------
648
                                        PETROLEUM EQUIPMENT
vessels or knockout pots should be installed at
low points on the vapor manifold lines to remove
any condensate.

In some vapor recovery systems, certain tanks
must be blanketed with an inert atmosphere in
order to prevent explosive mixtures and product
contamination.  In other,  larger systems, the
entire  manifolded section is maintained under a
vacuum.  Each tank is isolated by a regulator-
control valve. The valves operate from pressure
changes occurring in the tank vapor space.
Because the vapor-gathering system is based
upon positive  net vapor flow to the terminus
(suction of compressors), the proper size of
the vapor lines is important.  Sizing of the line,
as "well as that of the compressors,  absorption
unit,  or flare, is based upon the anticipated
amount of vapors.   These vapors are the result
of filling operations and breathing.   The distance
through which the vapors must be moved is also
important.
                                 I NTERMEOI ATE
                                 LOCATING FLANGE
                                 x
                                 POSITIONING ROD
                                   \
   BAFFLE  PLATE
Miscellaneous Control Measures
Recent tests have shown that breathing emissions
from fixed-roof tanks can be reduced by increas-
ing the storage pressure.   An increase of 1 ounce
per square inch was found to result in an 8 per-
cent decrease in emissions  due to breathing.
Tanks operated at 2-1/2 psig or higher were found
to have little or no breathing emissions.  The
pressure setting, however,  should not exceed  the
weight of the roof.

A major  supplier (Shand and Jurs  Co. ) of tank
accessories  offers another method of reducing
breathing losses.  The method is based upon the
degree of saturation in the vapor space.  A baffle
located in a horizontal position immediately below
the vent,  as  shown in Figure 492,  directs  enter-
ing atmospheric  air into a stratified layer next to
the top of the tank.  Since this air is lighter,  it
tends to  remain in the top area;  thus,  there is
less mixing of the free air and any of the rich
vapor immediately above the liquid surface.  The
top stratified layer is first expelled during the
outbreathing cycle.  Test  data indicate a reduced
surface evaporation of 25  to 50 percent.

Hydrocarbon emissions can be minimized further
by the proper selection of paint for the tank shell
and roof.  The protective  coating applied to the
outside of shell and roof influences the vapor
space and liquid  temperatures.  Reflectivity and
glossiness of a paint determine the quantity of
heat a vessel can receive  via radiation.  A cooler
roof and  shell also allows any heat retained in the
stored material to dissipate.  Weathering  of the
paint also influences  its effectiveness.  The  rela-
Figure 492.    Air baffle (Shand and Jurs Co.,  Berkeley,
Cal if.).
 tionship of paints in keeping tanks from warming
 in the sun is indicated in Table 170.  Vapor  space
 temperature reductions  of 60°F have been reported.
 Similarly,  liquid-surface temperature  reductions
 of 3 to 11  degrees have been achieved.  Data
 gathered by the American Petroleum Institute on
 hydrocarbon emissions indicate breathing emis-
 sion  reductions of 25 percent for aluminum  over
 black paint and 25 percent for white over aluminum
 paint.  All paints revert  to "black body" heat ab-
 sorption media in a  corrosive or dirt-laden  atmo-
 sphere.

-------
                                             Loading Facilities
                                            649
   Table 170,  RELATIVE EFFECTIVENESS OF
PAINTS IN KEEPING TANKS FROM WARMING IN
             THE SUN (Nelson,  1953)
Color
Black
No paint
Red (bright)
Red (dark)
Green (dark)
Red"
Aluminum (weathered)
Green (dark chrome)
Green
Blue
Gray
Blue (dark Prussian)
Yellow
Gray (light)
Aluminum
Tan
Aluminum (new)
Red iron oxide
Cream or pale blue
Green (light)
Gray (glossy)
Blue (light)
Pink (light)
Cream (light)
White
Tin plate
Mirror or sun shaded
Relative effectiveness
as reflector or
rejector of heat, %
0
10.0
17.2
21. 3
21.3
27.6
35.5
40. 4
40.8
45.5
47. 0
49.5
56.5
57.0
59.2
64.5
67. 0
69.5
72.8
78.5
81.0
85.0
86.5
88.5
90.0
97.5
100, 0
 Insulation applied to the outside of the tank is one
 method of reducing the heat energy normally con-
 ducted through the wall and roof of the vessel.
 Another method of controlling tank temperatures
 is the use of water.   The water can be sprayed
 or retained on the roof surface.  The evaporation
 of the water  results in cooling of the tank vapors.
 Increased maintenance and corrosion problems
 may, however, be encountered.

 Storage temperatures  may be reduced by external
 refrigeration or autorefrigeration.  External re-
 frigeration units  require the circulation  of the re-
 frigerant or  of the tank contents. Autorefrigera-
 tion is  practical in one-component liquid hydro-
 carbon storage where  high vapor  pressure mate-
 rial is  involved.   The  pressure in the tank is re-
 duced by removing a portion of the vapor.  Addi-
 tional vapor is immediately formed.   This flash
 vaporization results in lowering the temperature
 of the main liquid body.

 Routine operations can be  conducted in such a
 manner as to minimize other emissions associ-
 ated \vith storage tanks.  Use of remote-level
 reading gages and sampling devices  reduces
 emissions by eliminating the need to open tank
 gage hatches.  Emissions can be further re-
 duced by proper production scheduling to  (1)
 maintain a minimum of vapor space,  (2) pump
 liquid to the  storage tank during cool hours  and
 withdraw during hotter periods, and (3) main-
 tain short periods between pumping operations.

 Using wet scrubbers  as control equipment for
 certain stored materials  that are sufficiently
 soluble in the scrubbing media employed is  both
 possible and practical.  The  scrubbers  can  be
 located over  the vent when the scrubbing medi-
 um, for example,  a water scrubber for aqua
 ammonia storage, can be tolerated in the product.
 In other cases, the vent of one or more tanks
 can be manifolded so that any displaced gas  is
 passed through a scrubbing unit before being
 discharged to the atmosphere.  A typical ex-
 ample is a scrubber packed with plastic spirals
 that serves ketone storage vessels.  The scrub-
 bing liquid is water, which is  drained to a
 closed waste effluent disposal system.

 Properly designed condensers can be used to
 reduce the vapor load from tank vents in order
 that smaller  control devices can be employed.


 Masking Agents

 Masking agents do not afford  any degree of con-
 trol of the emissions  from storage equipment.
 The agent is  employed to make the vapor or gas
 less objectionable.  On the basis of local experi-
 ence,  the use of these agents is impractical, and
 in the long run, proper control equipment is nec-
 essary.

 Costs of Storage Vessels

 The installed costs  of various  storage vessels
 are indicated in Figures 493 through 500.  In-
 cluded are standard tank accessories such as
 manholes, vents, ladders, stairways, drains,
 gage hatches, and flanged connections.
          LOADING FACILITIES

INTRODUCTION

Gasoline and other petroleum products  are
distributed  from the manufacturing facility to
the consumer by a network of pipelines, tank
vehicle routes,  railroad tank cars, and ocean-
going tankers,  as shown in Figure 501.

As integral  parts of the network, intermediate
storage and loading stations receive products
from refineries by either pipelines or tank ve-

-------
650
                                       PETROLEUM EQUIPMENT
10U
80
60
40
20
0

















/
X







/
r







/
r *







/
'







.
'

















^








/


















                                                                       1,000
                                                                        100
                    20       40       60       80

                    CAPACITY, thousands of barrels
                                           100
                                                                 10
                                                                           20       40       60       80

                                                                            CAPACITY, thousands of barrels
100
       Figure  493.   Installed  costs  of cone roof
       tanks.*
                                                              Figure  494.   Installed  costs of  double-deck
                                                              floating-roof tanks.*
1UU
80
60
40
20
0








/







/
/







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^







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) 20 40 60 80 1
                                                                       1,000
                                                                         100
                                                                          10
                                                                                 ~7
                                                                                              50psi
            CAPACITY, thousands of barrels


Figure  495.  Installed  costs  of pontoon
floating-roof  tanks,*
                                                                                    10       20       30       40

                                                                                     CAPACITY, thousands of barrels
                                                                                                              5C
                                                                        Figure 496.   Installed  costs  of spherical
                                                                        pressure storage  tanks.*
'Including accessories, delivered and erected (Prater and Mylo
1961; copyrighted by Gulf Publishing Co., Houston, Texas).

-------
                                                   Loading  Facilities
                                                                                                                       651
       1,000
        100
         10
                        5psi

                      15psi
                   10       20      30       40

                   CAPACITY, thousands of barrels
50
COST, thousands of dollars
ro -Ck  S S <=> •=> <=

















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/







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«•••"








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                                   10       20       30       40

                                   CAPACITY, thousands of barrels
                                                                 50
      Figure 497.   Installed  costs  of spheroids.*
                         Figure 498.   Installed  costs  of basic
                         hemispheroids.*
     1,000
       100
        10
























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                  1,000
                                                                   -g
                                                                       100
«l
D_
•I
O

cc
o
0.
                                                                   o
                                                                   o
                                                                        10
                                                                                                                   1,0001
                                                                                                                   100
                                                                     o
                                                                     
-------
652
PETROLEUM EQUIPMENT
Figure  501.  Representation of gasoline distribution
system  in  Los  Angeles County, showing flow of gaso-
line  from  refinery  to consumer.
hides.  If the intermediate station is supplied
by pipeline,  it is called a bulk terminal, to
distinguish it from the station supplied by tank
vehicle, which is called  a bulk plant. Retail
service stations fueling motor vehicles  for the
public are, as a general rule, supplied  by tank
vehicle from bulk terminals or bulk  plants.
Consumer accounts, which are privately owned
facilities operated, for example,  to  fuel vehicles
of a company fleet, are supplied by tank vehicles
from intermediate bulk installations  or  directly
from refineries.

Gasoline and other petroleum products are
loaded into tank trucks,  trailers, or tank cars
at bulk installations and  refineries by means of
loading racks.  Bulk products are also delivered
into tankers at bulk marine terminals.


Loading Racks

Loading racks are facilities containing equip-
ment to meter and deliver the various products
into tank vehicles from storage.  Sizes  of
loading  racks vary in accordance  with the
number of products to be loaded and the num-
ber of trucks or  railroad  tank  cars to be
accommodated.   The loading platform may
be  an  elevated structure for overhead filling
of vehicles, that is,  through the top  hatches in
the tank vehicle,  or a ground-level facility for
                 bottom filling.  The elevated-platform structure
                 employed for overhead filling, shown in Figures
                 502 and 503, is generally constructed with hinged
                 side platforms attached to the sides of a central
                 walkway in such a way that they can be raised
                 when not in  use.   Thus,  when a vehicle  is
                 positioned adjacent to the central walkway  for
                 loading,  the  hinged side platforms can be  low-
                 ered to  rest  upon the top of the vehicle to  pro-
                 vide an  access to the compartment hatches.  The
                 meters,  valves, loading tubes or  spouts, motor
                 switches, and  similar necessary loading equip-
                 ment are located on the central walkway.  Bottom-
                 loading  installations are less  elaborate, since
                 the tank vehicle is filled through easily accessi-
                 ble fittings on  the  underside of the vehicles.


                 Marine Terminals

                 Marine  terminals  have storage facilities for
                 crude oil, gasoline, and other petroleum prod-
                 ucts, and facilities for loading and unloading
                 these products to and from oceangoing tankers
                 or barges.  The loading equipment is  on the  dock
                 and, in  modern terminals, is  similar to elevated-
                 tank vehicle-loading facilities except for size
                 (see Figure 504).  A pipeline  manifold with
                 flexible  hoses  is used for  loading  at older
                 terminals.  Marine installations  are consider-
                 ably larger and operate at much greater loading
                 rates than inland loading installations.

                 Loading Arm Assemblies

                 The term loading arm assembly refers to the
                 equipment and appurtenances  at the discharge
                 end of a product pipeline that  are  necessary  to
                 the filling of an individual tank vehicle or  tanker
                 compartment.   Component parts  may include
                 piping,  valves, meters, swivel joints, fill spouts,
                 and vapor collection adapters.  These  installa-
                 tions are commonly called loading arms.   A
                 loading  arm  without provisions to control  vapors
                 displaced from the compartment during filling is
                 shown in Figure 505.

                 Overhead loading arms  employed  for filling of
                 tank trucks or railroad tank cars  may be classi-
                 fied in accordance with the manner in which  ver-
                 tical movement of the arm  is achieved,  such as
                 pneumatic, counterweighted,  or torsion spring.
                 The pneumatically operated arm is a successor
                 to the common spring-loaded,  automatic-locking
                 arm in which the spring-loaded cylinder has  been
                 replaced by an air cylinder (see  Figure 506).
                 Bottom  loading employs a flexible hose or  a  non-
                 flexible, swing-type arm  connected to the vehicle
                 from ground-level pipeline termini.

                 Loading arms  at modern marine terminals are
                 similar in design to those used for overhead
                 loading  of tank vehicles.  The tanker loading

-------
                                        Loading Facilities
                                                                                                653
                        Figure 502.   An overhead-controlled  loading rack (Phillips
                        Petroleum, Los Angeles,  Calif.).
arms are too large for manual operation,  re-
quiring a hydraulic system to effect arm motion.
Older installations use reinforced, flexible hoses
to convey products from pipeline discharge mani-
folds to the tanker.  The hoses are positioned by
means of a winch or crane.
THE AIR POLLUTION PROBLEM

When a compartment of a tank vehicle or tanker
is filled through an open overhead hatch or bot-
tom connection, the incoming liquid displaces
the vapors in the compartment  to the atmosphere.
Except in rare instances, where a tank vehicle
or tanker is  free of hydrocarbon vapor,  as when
being used for the first time, the  displaced  va-
pors  consist of a  mixture of air and  hydro-
carbon concentration,  depending  upon the  prod-
uct being loaded,  the  temperature  of  the prod-
uct and of the  tank compartment,  and the  type
of loading.   Ordinarily, but not always,  when
gasoline is loaded, the  hydrocarbon  concen-
tration of the vapors is from 30 to 50 percent
by volume and consists  of gasoline fractions
ranging from methane through hexane (Deckert
et al. ,  1958).  Table 171 shows a typical analy-
sis of the vapors emitted during the loading of
motor gasoline into tank vehicles.

The volume of vapors produced during the load-
ing operation, as well as their composition,  is
greatly influenced by the type of loading or fill-
ing employed. The types in use throughout the
industry may be classified  under two general
headings, overhead loading and bottom loading.

Overhead loading, presently the most widely
used method,  may be further divided into
splash and submerged filling.  In splash fill-
ing, the outlet of the delivery tube is above the
liquid surface  during all or most of the loading.
In submerged filling the outlet of the delivery
tube is  extended to within 6 inches of the bottom
and is submerged beneath the liquid during most of
the loading.  Splash filling  generates more turbu-
lence and therefore more hydrocarbon vapors

-------
   654
PETROLEUM EQUIPMENT
                                                           than submerged filling does, other conditions
                                                           being  equal.  On the basis  of a typical 50 percent
                                                           splash filling operation,  vapor losses from the
                                                           overhead filling of tank vehicles with gasoline
                                                           have been determined empirically to amount to
                                                           0. 1 to 0. 3 percent of the volume loaded (Deckert
                                                           et al. , 1958).  Figure 507  presents a correlation
                                                           of loading losses with gasoline vapor pressures.
Figure 503.   A closeup  view  of  a  controlled  loading
arm with the access  platform in a  lowered  position
(Phillips  Petroleum,  Los Angeles,  Calif.).
                 Figure 505.  View of uncontrolled loading arm.
                                                                                                        M
       Figure 504.   Marine  terminal  loading  station
       (Chiksan  Company,  Brea,  Calif.).
               Figure 506.  View of a pneumatically operated loading
              arm (Union Oil Company of California,  Los Angeles,
              Cal if.).

-------
                                         Loading Facilities
                                            655
     Table 171.   TYPICAL ANALYSIS OF
  VAPORS FROM THE BULK LOADING OF
       GASOLINE INTO TANK TRUCKS
            (Deckert et al. ,  1958)
Fraction
Air
Hydrocarbon
Propane
Iso-Butane
Butene
N-Butane
Iso-Pentane
Pentene
N-Pentane
Hexane

Vol %
58. 1

0.6 ]
2.9
3.2
17.4 > 41.9
7.7
5. 1
z.ol
3.0J
1 •..'•:. 0
Wt %
37.6




22. 5 > 62. 4
12.4
8.0
3. 1
8.oJ
100. 0
             GASOLINE LIQUID TEMPERATURE °F
Figure  507.  Correlation of tank vehicle-loading
losses  (50% submerged  filling) with Reid  vapor
pressure  and liquid  temperatures of the motor
gasol me.
Bottom loading has been introduced by a few oil
companies and found practical for loading trucks
(Hunter, 1959).  The  equipment  required is
simpler than that  used for overhead loading.
Loading by this method is accomplished by connect-
ing a swing-type loading arm or hose at ground level,
as shown in Figure 508, to a matching fitting on
the underside of  the tank vehicles.  Aircraft-
type,  quick-coupling valves arc used to ensure
a fast,  positive shutoff and prevent liquid  spills.
Several companies experienced in aircraft-fuel-
i:ig operations have developed fully automatic
bottom-loading systems.  All the loading is sub-
merged and under a slight pressure;  thus, turbu-
lence and resultant production of vapors are
minimised.

The method employed for loading marine tankers
is essentially a bottom-loading operation.   Liquid
is delivered to the  various  compartments  through
lines that discharge at the bottom of each  com-
partment.  The vapors displaced during loading
are vented through a manifold line to the top of
the ship's mast for discharge  to the atmosphere.

In addition to  the emissions resulting from the
displacement  of hydrocarbon vapors from the
tank vehicles, additional emissions during load-
ing result from evaporation of spillage,  drain-
age, and leakage of product.
                                                      AIR POLLUTION CONTROL EQUIPMENT

                                                      An effective system for control of vapor emis-
                                                      sions from loading  must include a device to col-
                                                      lect the vapors at the tank vehicle hatch  and a
                                                      means for disposal of these vapors.
Types of Vapor Collection Devices for Overhead Loading

Four types of vapor  collectors or closures, fitting
the loading tube,  have been developed for use dur-
ing overhead-loading operations of trucks: The
General Petroleum Corporation unit, the Vernon
Tool Company or Greenwood unit,  the  SOCO unit,
and the Chiksan unit. All are essentially plug-
shaped devices that fit into the hatch openings
and have a central channel through which gasoline
can flow into the tank vehicle compartment.  This
central channel,  actually a section of the loading
tube, is surrounded  by an annular vapor  space.
Entry into this vapor space is achieved through
openings on  the bottom of the closure that are
below the point of contact of the external closure
surface with the  sides of the hatch  opening. Thus,
vapors are prevented from passing around the
closure and  out of the hatch, and must  flow in-

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656
PETROLEUM EQUIPMENT
                                             CHEVRON
            Figure 508.  View of a bottom-Ioading station (Standard  Oil  Company of California,
            Western Operations Inc.,  Los  Angeles, Calif.).
 stead into the annular space,  which in turn, is
 connected to a hose or pipe leading to a vapor
 disposal  system.
 The vapor closure device developed by the  Gen-
 eral  Petroleum Corporation (now Mobil Oil Corp. )
 has the annular vapor  space connected  to an
 auxiliary, transparent,  plexiglas  vapor chamber
 section above the closure to allow the  operator
 to  observe the calibrated capacity markers.5'"  A
 typical Mobil Oil Corporation vapor closure is
 shown in  Figure 509. A neoprene  rubber bellows
 above the plexiglas chamber compensates for ver-
 tical misalignment of the closure in the hatch open-
 ing.  The closure  is aluminum and is cast  in the
 shape of  a truncated cone.  The lateral surface of
 the closure is faced with a neoprene rubber gasket
 in the shape of a spherical section  so as  to give a
 vaportight seal between the closure and the hatch
 when the  closure is positioned in the hatch  for
 loading.  The top of the closure has openings for
 the loading tube and the vapor takeoff line.  An
 adjustable slipring serves as a positioner enabling
 the loading operators to slide the closure to the
 proper height on the loading tube for various
 depths  of tank vehicle compartments.   This
 closure requires  a constant downward force to
 keep it in contact with the hatch opening's sides
 at all times during filling and is built to fit only
 hatches 8 to 10 inches in diameter.
 "These markers are gages located within the tank compartment
  and positioned at a calibrated volume to indicate visually
  the amount of liquid loaded.
               The second type of closure, the Greenwood Unit,
               (Figures 510 and 511), which also requires a
               downward force  during the filling operation, was
               developed by the Vernon Tool Company.  This
               closure is also cast aluminum  in the  shape  of
               a plug similar to the Mobil Oil Corporation closure
               and with a neoprene rubber gasket.  This closure
               has no auxiliary, transparent,  vapor chamber
               section,  though some  versions  of this  closure do
               have  auxiliary, metal vapor chambers or a trans-
               parent, light well.   The  closure fits tank truck
               compartments  with hatches from 8 to  10 inches
               in diameter.  Since compartments with hatches
               of larger diameters are  sometimes encountered,
               an adapter has been provided.  The adapter con-
               sists of a flat,  gasketed plate with an  8-inch-di-
               ameter hole in the  center through which the
               closure can be inserted.

               The third type  of vapor closure,  referred to as
               SOCO, was developed by Standard Oil  Company
               of California (Figures 512,  513,  and 514).  It
               consists of  an  aluminum  cast plug of more com-
               plicated design.  This closure  is locked into the
               hatch opening by a  cam lever that forces a float-
               ing, internal,  cylindrical section to move upward
               and squeeze a  neoprene  rubber collar  out against
               the sides of the hatch  opening,  which effects a
               vaportight  seal during all phases of loading.   As
               the floating, internal, cylindrical section is
               rolied upward  by the action of the cam lever de-
               vice, it exposes  the vapor entry opening. A pis-
               ton-type,  internal filling valve, similar to an
               aircraft-fueling valve, was  developed  for this
               closure.   A safety  shut off float operates a needle

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                                          Lioadiiig Facilities
                                                                                                   657

Figure 509.   View of  General  Petroleum Corporation
Vapor  closure (Mobil  Oil  Corporation, Los Angeles,
Calif.).
pilot valve that controls the internal valve to pre-
vent overfilling.  The cam lever must be released
to remove the vapor closure.  The floating cyl-
inder is returned to the closed position at the
same time.   Thus,  the vapor side is sealed off
to prevent any leakage from the vapor-gathering
lines.  At the same time the internal valve is
locked  in the closed position.  SOCO closures
fit only hatches  8 inches  in diameter,  though
adapters have been developed  for hatches  of
greater diameter.  This  adapter is a circular
casting with an 8-inch opening and is placed over
the hatch opening.  When the SOCO unit is insert-
ed,  spring-loaded arms act to clamp and seal the
adapter against  the top of the hatch.
                                                       Figure  510.   View of  the  Greenwood  vapor  closure
                                                       (Atlantic-Richfield Oil  Corporation,  Los  Angeles,
                                                       Calif.).
Figure 511.   Closeup  view  of Greenwood vapor closure
(Atlantic-Richield  Oil  Corporation, Los Angeles, Calif.).
  The Chiksan Company has recently offered a
  fourth system,  a modern loading arm that in-
  corporates the hatch closure,  the vapor return
  line, and the fill line as an as sembled unit (Fig-
  ure 515).  This unit incorporates features to
  prevent overfills,  topping off, or filling unless

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  658
                                         PETROLEUM EQUIPMENT
Figure 512.    Closeup view of SOCO vapor  closure,
withdrawn position (American Airlines,  Los  Angeles,
Cal if.).
 Figure 513.   Closeup view of  SOCO  vapor  closure,
 filling position (American Airlines,  Los Angeles
 Calif.).
 the assembly is properly seated in the truck
 hatch.  A pneumatic system ensures  contact with
 the tank truck as the gasoline  is added and pro-
 vides a delay at the end of the loading cycle to
 achieve adequate drainage of the arm before it is
 withdrawn from the truck hatch.

 The slide positioner of the Mobil Oil Corporation
 vapor closure, though permitting adjustments
 for submerged  loading,  can be a  source of
 vapor leaks and requires proper attention by the
 operator.  SOCO closures with inner valves  are
 considerably heavier than other types,  and the
 inner valve involves added pressure drops, which
 slow the loading rates.  Both the Greenwood and
 the Mobil Oil Corporation closures require vapor
 check valves in the vapor-gathering lines to  pre-
 vent the vapor from discharging back to the at-
 mosphere when the loading assembly is with-
 drawn.   In addition, inspections have shown  that
 the Mobil Oil Corporation and Greenwood closures
 require nearly vertical entry of the loading tube
 into the compartment hatch opening in order to
 provide a tight seal against vapor  leaks.  A
 connecting rod between the riser and filling stem
 has been added to some assemblies,  as shown
in Figure 516, to form a pantograph arrange-
ment to maintain the filling  stem of the loading
arm in the vertical position at all times.   The
loading operator is thus able to obtain good seal-
ing contact more quickly between the vapor col-
lector and the hatch opening.

Collection of Vapors From Bottom Loading

Vapors displaced from tank vehicles  during the
bottom-loading  operation are more easily col-
lected than those are that result from overhead
loading.   The filling line and the  vapor collection
line are  independent of each other with resultant
simplification of the design  (see  Figure 517).
The vapor collection line is usually similar to
the loading line, consisting  of a flexible hose or
swing-type arm connected to a quick-acting
valve fitting  on  the dome of  the vehicle.  This
fitting could  be  placed at ground level to simplify
the operation further.

A check  valve must be installed on the vapor  col-
lection line to prevent backflow of vapors to the
atmosphere when the connection to the tank ve-
hicle is broken.

-------
                                             Loading Facilities
                                                                                      659
         LOADINS-ARM
         CONNECTION
       SCHULZ AUTOMATIC
          VAUE
  VAPOB-RETURN
   CONNECTION
                        OEAD-MAN CONTROL
                           VALVE
                         3   r*    ' '*" * *
                       =5-3   \,'.'.f.'-jK
                        -^5,—y-  r-/ •<
TANK HATCH
       rrij;
     VAPOR IHLET
   EMERGENCY OVEBFILl
    SHUT-OFF FLOAT
'"<^>r^
     first'/  /k <
     fMrf .-;-'•.('
     Ll4tl|,aJ,'/' ,*  ,'       FOOT-OPERATED
       !, jj ,'/ /  '•• 'j      CAM LEVER
       ,\''/'/    ^ '
     fVi' ••-     : (
     s  fH"- -;     ,   •
      ' H4-W-"    ! ' I .
                                         SEALING RING
                                         VAPOR-SEALING
                                            RIN6
    Figure 514.  Schematic  drawing  of  SOCO vapor
    closure used to collect  displaced vapors
    during loading (Standard  Oil  Company of
    California, Western  Operations,  Inc.,  Los
    Angeles,  Calif.).
Factors Affecting  Design of Vapor Collection Apparatus
In designing for complete vapor pickup at the
tank vehicle hatch, several factors, including
tank settling,  liquid drainage,  and topping off
must be considered.

The settling of a tank vehicle due to the weight
of product being added requires that provision
be made for vertical travel of  the loading arm
to follow the motion of the vehicle so that the
vapor collector remains sealed in the tank hatch
during the entire loading cycle.  Two  solutions
to the problem of settling have been used.   The
first,  applicable to pneumatically operated arms,
includes the continuous application  of  air pres-
sure  to the piston in the air cylinder acting on
the arm.  The arm is thus forced to follow the
motion of the  vehicle without need for clamping
or fastening the vapor collector to the tank ve-
hicle.  The second solution, employed on  coun-
terweighted and torsion spring loading arms,
provides for  locking  the vapor collector to the
tank vehicle hatch.  The arm then necessarily
follows the motion of the vehicle.  The second
solution is  also applicable to vapor collection
arms or hoses that are connected to the top of a
tank vehicle during bottom loading.

The second problem,  that of preventing  consid-
erable liquid drainage  from a loading arm as it
is withdrawn after completion of  filling opera-
tions, has been adequately  solved.  The air valve
that operates the air cylinder of pneumatically
operated loading arms may be modified by addi-
tion of an orifice on the discharge side of  the
valve.  The orifice allows 30 to 45 seconds to
elapse before the loading  assembly clears  the
hatch compartment.  This time interval is suffi-
                                          Figure 515.   View  of  a  pneumatically operated
                                          loading  assembly  with  an integrated vapor
                                          closure  and  return  line  (Chiksan Co.,  Brea,
                                          Calif.).
  234-767 O - 77 - 44

-------
660
PETROLEUM EQUIPMENT
  Figure 516.   View of a pneumatically  operated
  loading arm showing pantograph  linkage  (Atlan-
  tic-Richfleld Oil Corporation,  Los  Angeles,
  Calif.).
  Figure 517.  Bottom loading of tank trucks  pro-
  vides  one way to collect vapor during loading
  in  conjunction with the use of return line to
  storage  tanks (Standard Oil Company of Cali-
  fornia,  Western Operations, Inc.,  Los Angeles,
  Pa I i f  ^
cient to permit  complete draining of liquid into
tank compartments from arms fitted with loading
valves located in an outboard position.  Loading
arms with inboard valves require additional drain-
age time and present the problem of gasoline re-
tention in the horizontal section of the arm.  To
prevent drainage the SOCO vapor collection clo-
sure is  fitted with an internal shutoff valve that
                is closed before the loading arm is withdrawn
                from the tank hatch.   Providing for thermal ex-
                pansion has been found necessary when an in-
                board valve and a SOCO vapor closure are used.
                This has been accomplished by installing a small
                expansion chamber at the normal position of the
                loading  arm's vacuum breaker.  In bottom load-
                ing,  the valve coupling at the  end of the loading
                arm or  hose, as well as  the mating portion of the
                valve on the  trucks,  is self-sealing to prevent
                drainage of product when the  connection is made
                or broken.

                The  third factor to be considered in the design
                of an effective vapor collection system is  top-
                ping off.  Topping off is the term applied to the
                loading  operation during  which the liquid level
                is adjusted to the  capacity marker inside the
                tank vehicle  compartment.  Since the loading
                arm is  out of the compartment hatch during the
                topping  operation,  vapor pickup by the collector
                is nil.   Metering the desired  volumes  during
                loading  is one solution to the  problem.  Metered
                loading  must, however, be restricted  to empty
                trucks or to  trucks prechecked for loading
                volume  available.  Accuracy  of certain totaliz-
                ing meters or preset stop meters is  satisfactory
                for loading without the need for subsequent open
                topping. An interlock device  for the pneumatic-
                type loading  arms, consisting of pneumatic con-
                trol  or  mechanical linkage, prevents  opening of
                the loading valve unless the air cylinder valve
                is in the down position.   Thus, open topping is
                theoretically impossible.

                Topping off is not a problem •when bottom load-
                ing is employed.  Metered loading,  or installa-
                tion  of a sensing device in the vehicle  compart-
                ments that actuates a shutoff  valve located either
                on the truck or the loading island, eliminates the
                need for topping off.
                 Methods of Vapor Disposal

                 I he methods of disposing of vapors collected
                 during loading operations may be considered
                 under three headings:  Using the vapors as fuel,
                 processing the vapors for  recovery of hydro-
                 carbons,  or effecting a vapor balance system in
                 conjunction with submerged loading.

                 Tha first method of disposal, using the vapors
                 directly as fuel, may be employed when the load-
                 ing iacilitics are located in or near a facility
                 that includes fired heaters  or boilers.  In a typ-
                 ical disposal system,  the displaced vapors flow
                 through a  drip pot to a small vapor holder that
                 is gas blanketed to prevent forming of explosive
                 mixtures.  The vapors are drawn from the holder
                 by a  compressor and are discharged  to the fuel
                 gas system.

-------
                                          Loading Facilities
                                           661
The  second method of disposal uses equipment
designed to recover the hydrocarbon vapors.
Vapors have been successfully absorbed in a
liquid  such as gasoline or kerosine.  If the loading
facility is located near a refinery or gas absorp-
tion  plant,  the vapor line can be connected from
the loading facility to an existing vapor recovery
system through a regulator valve.

Vapors are recovered from loading  installations
distant from existing processing  facilities by
use of package units.  One such unit (Figures 518
and  519) that absorbs hydrocarbon vapors  in gaso-
line  has been developed by the Superior Tank and
Construction Company.  This unit includes a va-
porsphere  or  tank equipped with flexible mem-
brane  diaphragm, saturator,  absorber,  compres-
sor,  pumps, and instrumentation.  Units are
available to fit any size operation at any desired
loading location since they use the gasoline prod-
uct as  the absorbent.

Explosive mixtures  must be prevented from ex-
isting  in this unit.  This is accomplished by pass-
ing the vapors displaced at the loading rack through
a saturator countercurrently to gasoline pumped
from storage.  The saturated vapors then flow to
the vaporsphere.  Position of the diaphragm in
the vaporsphere automatically actuates a com-
pressor that draws the vapors from the sphere
and injects them at about 200 psig into the ab-
sorber.  Countercurrent flow of stripped gasoline
from the saturator or of fresh gasoline from stor-
age is used to absorb the hydrocarbon vapors.
Gasoline from the absorber bottoms is  returned
to storage while the tail gases, essentially air,
are released to the atmosphere through a back-
pressure regulator.  Some difficulty has been
experienced with air entrained or dissolved in
the sponge gasoline returning to storage. Any
air released in the storage tank is discharged to
the atmosphere saturated with hydrocarbon vapors.
A considerable portion of the air  can be removed
by flashing the liquid gasoline from the absorber
in one or more additional vessels operating at
successively lower pressures.

Another type of package unit  adsorbs the hydro-
carbon vapors on activated carbon, but no in-
stallation of this kind has been observed in Los
Angeles County.   The application of this type of
unit is presently restricted to loading installations

               Figure 518.  View of smalI-capacity vaporsaver gasoline absorption  unit
               (American  Airlines, Los Angeles,  Calif.).

-------
662
                                        PETROLEUM EQUIPMENT
 SATURATION POT-

FLASH 	7
ARRESTOR f
 -^	L
 •VAPOR HOOD   L

PUMP
TO ATMOSPHERE
ABSORBER,, -k
l*f
GASOLINE 	 7
K> |
	 j
•^


i- COMPRESSOR
,| 2-STAGE
/ r
                                                                                  TANK GAGE
                                                                                  AND SWITCH
                                                                                     TO COMPRESSOR
                                                                                     STARTER
       TANK
       TRUCK
                                                                     INTERCOOLER
                 PUMP GASOLINE  FEED
                 TO SATURATION  POT
                                              GASOLINE TO LOADING RACK
                                                                  Q—'
                                                                       LOADING RACK FEED PUMP
                Figure 519.   Schematic  flow diagram of a vaporsaver unit used for recovery
                of  loading  rack  vapors  at a bulk terminal.
that have low throughputs of gasoline, since the
adsorbing capacity and the life of the carbon are
limited.   Units  of this type  find application in con-
trol of vapors resulting from  fueling of  jet aircraft.

The vapors displaced during bottom filling are
minimal.  Data indicate  a volume displacement
ratio  of vapor to liquid of nearly 1:1.  A closed
system can then be employed  by returning all the
displaced vapors to a storage tank.   The storage
tank should be connected to a  vapor recovery
system.


         CATALYST REGENERATION

Modern petroleum processes  of cracking,  re-
forming,  hydrotreating,  alkylation, polymeriza-
tion,  isomerization, and hydrocracking are com-
mercially feasible because of materials called
catalysts.  Catalysts have the ability, when in
contact with a reactant or  mixture of reactants,
to accelerate preferentially or retard the rate
of specific reactions and to do this, with few
exceptions,  without being chemically altered
themselves.  Different catalysts vary in their
effects.   One might, for example, increase  oxi-
dation rates while another might change the  rate
of dehydrogenation or alkylation.

Contact  between the catalyst  and reactants is
achieved in some processes bypassing the reac-
tants through fixed beds  or layers of catalysts
contained in a reactor vessel.  Contact in other
processes involves  simultaneous charging of
                                             catalyst and reactants  to a reactor vessel and
                                             withdrawal of used catalyst in one stream,  and
                                             products and unreacted materials in another
                                             stream.  The first process may be  termed  a
                                             fixed-bed system and the latter a moving-bed
                                             system.  Moving-bed systems may be further
                                             subclassified by the type of catalyst and meth-
                                             od of transporting it through the process.  Ex-
                                             amples are the use  of vaporized charge material
                                             to fluidize powdered catalyst,  as in fluid catalyt-
                                             ic cracking units (FCC), and  the use  of bucket
                                             elevators,  screws,  airlifts, and so forth,  to
                                             move the catalyst pellets or beads,  as in Thermo-
                                             for catalytic cracking units (TCC)  (see Figures
                                             520,  521,  and 522).
                                             TYPES OF CATALYSTS

                                             Generally,  the catalysts are used in the form of
                                             solids at process temperatures,  though some
                                             liquid catalysts are used alone or impregnated
                                             into inert solid carriers.  Pellets, beads,  and
                                             powders  are the common physical shapes.  Crack-
                                             ing catalysts are usually beads or powders of
                                             synthetic silica-alumina compositions, includ-
                                             ing acid-treated bentonite clay, Fuller's earth,
                                             aluminum hydrosilicates,  and bauxite.  Little-
                                             used synthetic catalysts include silica-magnesia,
                                             alumina-boria, and  silica-zirconia (Nelson,  1958).
                                             Bead or pelleted  catalyst, noted  for ease of han-
                                             dling and freedom from plugging, is used in  TCC
                                             units while powdered catalyst is  used  in FCC
                                             units.  Natural catalysts are sotter and fail more
                                             rapidly at high temperatures than most synthetic

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                                          Catalyst Regeneration
                                             663
Figure 520.  Simplified  flow diagram of a Model IV
fluid  catalytic  cracking unit (Oil and Gas
Journal,  1957).
catalysts  do.  The cost of natural catalysts, how-
ever, is under $100 per ton while synthetic types
cost $300 or more per ton.

Catalysts employed in catalytic reforming include
the platinum-containing catalysts used in modern
fixed-bed reformers, except for the  bauxite pellet
catalyst for Cycloversion used at 950° to 1,000°F
and 50 to 57 psig,  and the molybdena-alumina
catalysts  used for fluid hydroiorming.  Fixed-bed
reactors  operate  at 825°  to 1,000°F and 200 to
1,000 psig with catalyst pellets about 1/8 inch in
diameter.  These catalysts  contain less than 1
percent platinum  and  are supported on a base of
either  alumina or silica-alumina.  Acid-type
catalyst required for  reforming processes may
be provided by one of the oxides  as the catalyst
base.  The  acid may be a halogen compound add-
                                         \
  Figure 521.  Thermofor catalytic  cracking  unit
  (Union Oil Company of California,  Los  Angeles
  Calif.).
                                                       Figure 522.  Simplified flow diagram of Thermofor
                                                       catalytic cracking unit with modern catalyst air-
                                                       lift  (Oil and Gas Journal,  1957).
ed to the catalyst,  or may be directly added to
the reformer charge.  The flow diagram of a
platforming process is shown in Figure 523.

The major desulfurization proces ses-Autofining,
Dieselforming, HDS, Hydrofining,  Ultrafining,
Unifining,  and so forth--employ a cobalt-molyb-
denum catalyst supported on bauxite  and operate
within a range of 450°   to 850°F and 50 to 1, 500
psig.

Commercial alkylation processes employ  as
catalysts either  sulfuric acid, hydrogen fluoride,
or aluminum chloride -with a hydrogen chloride
promoter.

Commercial polymerization  catalysts consist
of a thin film of  phosphoric acid on fine-mesh
quartz, copper pyrophosphate, or a calcined
mixture  of phosphoric  acid.

-------
664
PETROLEUM EQUIPMENT
                          STABILIZE* GAS I
 A
    REACTOR   REACTOR
           HO 2
Figure  523.  Simplified  flow  diagram of platformmg
process (Oil  and Gas  Journal,  1957).
Isomerization processes such as Butamer, Iso-
kel,  Isomeratc,  Penex, and PentaJining employ
a noble metal,  usually platinum, as the catalyst
in a hydrogen atmosphere.  Liquid-phase iso-
merization is accomplished with aluminum chlo-
ride in molten  antimony chloride \\ith a hydrogen
chloride activator.

Loss  of Catalyst Activity

The activity  of a catalyst,  or its effectiveness
in changing rates of specific reactions decreases
with on-stream time.   The rate of decrease is
related to  composition of  reactants contacted,
throughput rate, and operating conditions.  Loss
of activity results from metal contamination  and
poisoning or deposits  that coat the catalyst sur-
faces and thus  reduce the catalytic area available
for contact with the reactants.   Frequently car-
bon from the coking of organic materials is the
main deposit.  To continue in  successful opera-
tion,  catalyst activity must be  restored. One
procedure  consists of replacing the spent cata-
lyst with fresh catalyst.  A second procedure
consists of treating the spent catalyst for remov-
al of contaminants.  This latter procedure, called
catalyst regeneration,  is the more significant
from the standpoint of air pollution,  since com-
bustion is  frequently the method of regeneration.

In fixed-bed  systems,  catalysts are regenerated
periodically  in the reactor or  removed and re-
turned to the manufacturer for regeneration.   In
moving-bed systems,  catalysts are continuously
removed from  the reactor,  regenerated in a  spe-
cial  regenerator vessel, and returned to the  re-
actor.

REGENERATION PROCESSES

Catalysts for the catalytic cracking and reform-
ing processes are regenerated to restore activity
                 by burning off the carbon (coke) and other deposits
                 from the catalyst surface at controlled tempera-
                 ture and regeneration air rates.  Actually, the
                 so-called "carbon" on the catalyst is not all pure
                 carbon but contains  other compounds.  Moreover,
                 the catalyst is not entirely  freed of the carbon
                 deposits during  regeneration,  though an effort is
                 made to keep the residual carbon below 0. 9 per-
                 cent by weight on the regenerated catalyst.  FCC
                 units, all of which have  continuous  catalyst regen-
                 eration,  have a  coke burnoff rate 5 to 10 times
                 higher  than TCC unit regenerators  have.  Since
                 fixed-bed reformer  units, which incorporate cata-
                 lyst regeneration, have  a very small coke laydown
                 011 the catalyst surface,  they require regeneration
                 only once or twice a year,  as  the desulfurizer
                 reactors do,  which have both a coke and sulfur
                 laydown.
                 FCC Catalyst Regenerators

                 Catalyst regenerators for FCC units may be
                 located alongside, above,  or below the reactor.
                 Regenerators normally have a vertical,  cylin-
                 drical shape with a domed top.   The inside shell
                 of the regenerator is insulated with 4 to 6  inches
                 of refractory lining.  This lining may  also be ex-
                 tended into the  regenerator's discharge line and
                 the regenerator's catalyst charge line.

                 The upper section of the regenerator is equipped
                 with internal cyclone separators  to separate the
                 catalyst dust from the regeneration "combustion
                 gases.  The number of cyclone separators varies
                 from a single-stage  or two-stage separator to
                 as many as 12 sets of three-stage cyclone  sepa-
                 rators.  External size of the regenerator varies
                 from 
-------
                                         Catalyst Regeneration
                                                                        665
15 feet to prevent the load on the cyclones from
being excessive.  Regenerated catalyst flows
down through the overflow well to the reactor
as a result of a slight pressure differential.
The flue gases pass  through the regenerator's
cyclone separators,  for removal of most of the
catalyst more than 10 microns in size; through
a steam generator,  where process steam is
made; through a pressure-reducing chamber to
air pollution control units; and then to the atmo-
sphere.   The pressure-reducing chamber serves
as a noise suppressor.  Final dust cleanup is
accomplished by passing the effluent gases from
the cyclone separators through an electric  pre-
cipitator.   The  gases from the precipitator are
introduced  into  a carbon monoxide boiler where
the sensible heat and the heat content of the CO
is used to produce steam in some flow schemes.
Other operations place the waste-heat boiler be-
fore the precipitator.

According to  Brown  and Wainwright (1952), the
\veight of dust per cubic foot of exit gas remains
constant at about 0. 002 pound at bed velocities
up to a critical  velocity of 1. 5  fps, \vhereupon
it rises rapidly with  higher velocities,  for  exam-
ple, to 0. 01 pound at 1. 8 fps.  The pressures in
FCC unit  regenerators are always  low,  between
1 and 10 psig.  Regeneration temperatures are
usually between  1,050°   and 1,150°F.   Other
general operating data for large and small  FCC
unit regenerators are as follows:
Catalyst circulation
rate, tons/min

Coke burnoff rate,
Ib/hr
                        Small unit  Large unit
   10
                60
5,000       34,000
Regeneration air rate,
scfm                    13,000      102,000

TCC Catalyst Regenerators

TCC (and Houdry unit) catalyst regenerators,
referred to as kilns, are usually vertical struc-
tures with horizontal, rectangular, or square
cross sections. A regenerator that has a cata-
lyst  circulation rate of 150 tons per hour would
have an outside dimension of about 1 1 feet square
by 43 feet high.  This size  regenerator, or kiln,
has approximately 10 regeneration zones and a
topside kiln hopper.  Each  zone is equipped with
a flue gas duct, air distributors,  and steam- or
water-cooling coils.  The carbon steel  shell of
the regenerator is  lined with about 4 inches of
firebrick,  which is,  in turn,  covered with alloy
steel.  The discharge flue gases  from the regen-
eration kilns are usually vented through dry-type,
centrifugal dust collectors.

In a  TCC unit, Figure 521, spent catalyst (beads)
from the base  of the reactor  is steam purged for
removal of hydrocarbons and lifted by a bucket
elevator to a hopper above the  regeneration kiln.
Catalyst fines  at this point in the process  are
separated from catalyst beads  in an elutriator
vessel using up-flowing gases and are collected
from these gases in a cyclone separator dis-
charging  to a fines bin.   Spent  catalyst beads
drop through a series of combustion zones,  each
of which contains flue gas collectors,  combustion
air distributors,  and cooling coils.  The cata-
lyst is regenerated as it flows  downward through
the kiln zones  countercurrent to preheated air
(400°  to  900°F).   The  pressure is  essentially
atmospheric in the kiln. Water is circulated
through cooling coils in each kiln zone to control
the rate  of coke combustion.  The regeneration
temperatures  at the top of the kiln are between
800°  and 900°F, while the bottom section of the
kiln operates between 1, 000°   and 1, 100°F. A
minimum temperature of 900°F is required for
catalyst  regeneration.   An average-size TCC unit
regenerator with  a catalyst  circulation of  2. 5 tons
per  minute has a  coke burnoff rate of 3, 500 pounds
per  hour  and a regeneration air rate of 24, 000
s cfm.

Regenerated catalyst from the bottom of the kiln
is then transferred  by bucket elevator to the cata-
lyst bin for reuse in the reactor.  The more
modern TCC units use a catalyst airlift  (Figure
522) rather than bucket  elevators for returning
regenerated catalyst to  the reactor,  and gravity
flow for moving spent catalyst to the regenerator.
The  elevators  of those units must be vented
through wet  centrifugal  collectors or scrubbers
to the atmosphere.

Catalyst Regeneration  in Catalytic  Reformer
Units

Some types  of catalytic reformer  units  are
shut  down once or  twice  each  year  for  re-
generation of the catalyst in the desulfurizer re-
actor. Reforming units using Sinclair-Baker
catalyst are in this  category.  Before the regen-
erating,  the reformer system is depressured,
first to the fuel gas system  and  then to vapor re-
covery.  A steam, jet discharging to  vapor recov-
ery is then used to evacuate the reformer  further
to 100 millimeters of mercury absolute pressure.
An inert gas such as nitrogen is introduced to
purge and then repressure the system to 50 psig.
The  nitrogen is circulated by the recycle gas
compressor through the heaters, reactors,  heat
exchangers,  flash drum, and regeneration gas
drier. Inert gas circulation is continued while
combustion air for burning off the coke is  intro-
duced into the  top of the first reactor by the re-
generation air  compressor.   The rate of air is
controlled to maintain catalyst bed temperatures
below 850°F.  Pressure is controlled to 150 psig
by releasing products of combustion to the fire-

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666
PETROLEUM EQUIPMENT
box of the reformer heater. After burning is
completed dn the first reactor,  as indicated by
the rise in oxygen content in the effluent,  the air
supply is then switched to the second reactor.
The same procedure is repeated for the other
reactors.

In the regeneration cycle, circulation of approx-
imately 15, 000 scfm flue gas is maintained by
using the  reformer recycle gas compressor, and
approximately 500 scfm regeneration air  is added
for burning  off the coke.  About 24 to 30 hours
is required  for regeneration, based  upon a coke
content of 5 percent by weight in the catalyst. The
coke may run about  90 percent  carbon and 10 per-
cent hydrogen.

Desulfurization  reactors  are depressured in the
same manner as the  catalytic reformer described.
During catalyst  regeneration, however, super-
heated steam is added along with  inert air con-
taining about 1. 4 mol percent oxygen to effect
temperature control.  In  addition to  coke, there
are also sulfur deposits that are burned to sulfur
dioxide.  In some installations  the regeneration
gases are passed through packed  scrubbers that
use water or caustic for  partial absorption of
sulfur dioxide.  These reactors are  also  regen-
erated for a period of approximately 24 hours
about once or twice  a year.

Regeneration of fluid hydroforming catalyst, a
white powder consisting of molybdena-coated
alumina,  is accomplished by continuously with-
drawing a portion of the catalyst  recirculating
in the reactor and burning the carbon off  in  a
separate regenerator using fresh air with no pre-
heat.   The regeneration temperature is 1, 100°
to 1, 150°F at 200 to 250  psig with 100 percent
carbon  removal.  Molybdenum  sulfide,  formed by
the reaction of catalyst molybdenum oxide and
feed stock sulfur, is reoxidized to molybdenum
oxide with the release of  sulfur dioxide  during
regeneration.

In alkylation units using hydrogen fluoride as
catalyst,  the acid strength is restored by remov-
ing the water of dilution by distillation.   The ef-
fectiveness  of alkylation  units using  sulfuric acid
as the catalyst is maintained by adding fresh acid
as spent acid is withdrawn.  The  spent acid may
be reconcentrated or used as is for  other purposes.

Phosphoric  acid  catalyst  used in  polymerization
units  is regenerated by \vater washing,  steaming,
and drying the fine-mesh quartz carrier,  and
adding fresh phosphoric acid.   After the excess acid
is drained,  the reactor is ready to go back on
stream.

Many of the remaining catalytic processes re-
quire only infrequent catalyst replacement or
                 regeneration (Unicracking and Isomax).  In the
                 H-Oil process, however, catalyst is continuously
                 replaced.


                 THE AIR POLLUTION  PROBLEM


                 Air contaminants are invariably released to the
                 atmosphere from regeneration  operations,
                 especially from operations  involving combus-
                 tion.  The variety of air contaminants  released
                 is broad  and may include catalyst dust and other
                 particulate matter,  oil mists,  hydrocarbons,
                 ammonia, sulfur  oxides,  chlorides,  cyanides,
                 nitrogen  oxides,  carbon monoxide, and aerosols.
                 The contaminants evolved by any one type of re-
                 generator are a function of  the compositions of
                 the catalyst and reactant, and  operating conditions.

                 Tables 172 through  177 show stack emissions
                 for  regeneration  of both FCC and TCC units.
                 The data in these tables are the results of a
                 testing program  (Sussman,   1957) to  establish
                 the magnitude of  the listed  components in the
                 catalyst  regeneration gases.

                 The largest quantities  of air pollution from cat-
                 alyst-regenerating operations are experienced in
                 FCC units.  The  pollutants include carbon  mon-
                 oxide, hydrocarbons,  catalyst fines  dust,  oxides
                 of nitrogen and sulfur, ammonia,  aldehydes, and
                 cyanide.  Typical losses from fluid  catalytic crack-
                 ing regenerators, based upon  Tables 173 through
                 176, include:
                                                     Loss to
                            Pollutant          atmosphere, Ib/hr

                 Carbon monoxide                   24, 300
                 Sulfur  dioxide                           545
                 Hydrocarbons                           231
                 NO as nitrogen  dioxide                  80. 2
                 Particulate matter                       65. 5
                 Ammonia                                57. 4
                 Sulfur  trioxide                           32. 7
                 Aldehydes  as formaldehyde              21.6
                 Cyanides as hydrogen cyanide              0. 27
                 TCC catalyst regeneration produces air contami-
                 nants similar to those from  FCC catalyst regen-
                 eration.  Quantities produced, however, are con-
                 siderably less, as  can be  seen from Tables 173
                 through 176. The bead-type catalyst used in TCC
                 units does not result in the large amount of cata-
                 lyst fines that are encountered in FCC units.

                 Air pollution problems are not as severe from
                 catalyst regeneration of reforming  and  desulfuriza-
                 tion reactors as those from  FCC and TCC  units.
                 These  reactors are regenerated only once  or
                 twice a year for a period of  about 24 hours.  The
                 burning-off  of the coke and sulfur deposits on the

-------
                                         Catalyst Regeneration
                                                      667
              Table 172.  OPERATING CHARACTERISTICS OF FLUID AND THERMOFOR
                            CATALYTIC CRACKING UNITS (Sussman, 1957)
„ a
Type
FCC
FCC
FCC
FCC
TCC
TCC
FCC
TCC
TCC
TCC
TCC
TCC
TCC
FCC
TCC
Date
tested,
1956
10/4
12/4
8/30
11/27
11/1
11/1
10/9
10/18
10/18
9/19
9/19
9/12
9/12
11/8
12/19
Feed rate
Fresh,
bpd
40, 000
29, 500
24, 000
32, 610
9, 525
8, 525
25, 000
10, 000
8, 000
7, 071
6, 506
7,099
6, 053
6,462
8, 000
Recycle,
bpd
10, 000
2,045
0
13, 680
1, 500
7,400
9, 000
0
3, 000
5, 538
5, 602
6, 004
6, 013
606
3, 000
Catalyst
circulation
rate,tons/hr
4, 500
1,560
1, 380
2, 532
180
150
3,240
165
150
150
150
150
120
390
200
Regenerator
air rate,
scfm
112, 000
28, 000
22,200
97,500
27,000
27, 000
64, 000
22, 000
27, 600
24, 000
25, 000
27,000
23, 000
13, 300
16,800
Coke burn-
off rate,
Ib/hr
38,000
23, 000
21, 300
36,416
4,715
2, 610
21, 600
5, 655
4, 620
4,410
5,020
3, 420
3, 000
5,400
3, 760
Avg gas
temp,
°F
820
510
520
485
840
700
530
660
610
850
740
810
710
610
680
           aAll fluid catalytic cracking units
            all Thermofor catalytic cracking
are equipped -with electrical precipitators;
units are equipped with cyclone collectors.
    Table 173.  PARTICULATE LOSS FROM
     FLUID AND THERMOFOR CATALYTIC
           CRACKING UNIT STACKS
                (Sussman,  1957)
Type
FCC
FCC
FCC
FCC
TCC
TCC
FCC
TCC
TCC
TCC
TCC
TCC
TCC
FCC
TCC
Total particulate, a
Ib/hr
57. 50
61. 00
181. 00
58.70
1.36
1.64
28. 30
13.80
8. 06
3. 44
2.22
9.53
10. 01
6.42
4.30
   aThe total particulate loss includes
    weight of insoluble solids in the water,
    and HCL impinger solution added to the
    alundum thimble catch.
          AIR POLLUTION CONTROL EQUIPMENT

          Dust from FCC catalyst regenerators is collected
          by centrifugal  collectors or centrifugal collectors
          and  electrical  precipitators.  General design fea-
          tures of these  collectors are discussed in Chapter
          4.   Carbon monoxide waste-heat boilers eliminate
          carbon monoxide and hydrocarbon emissions in
          FCC regeneration  gases.  Dry-type, centrifugal
          dust collectors are used to collect the catalyst
          fines from TCC regeneration gas.  Dust emis-
          sions from TCC unit reactors and regenerator
          catalyst elevators  can be adequately  controlled
          by wet- or dry-type, centrifugal collectors.
          Presently,  no  TCC units are equipped with car-
          bon monoxide waste-heat boilers.  Manifolding
          several TCC units  could possibly result in a
          quantity of flue gas large enough to improve
          economic justification for a CO boiler.

          The carbon monoxide and hydrocarbons in re-
          forming and desulfurization catalyst  regeneration
          gases  can be efficiently incinerated by passing
          the regeneration gases through a heater firebox.
          In some installations the sulfur dioxide is  scrubbed
          by passing the regeneration gases through a packed
          water  or  caustic tower.
catalyst surface produces hydrocarbons,  sulfur
dioxide,  and carbon monoxide, in addition to
carbon dioxide and water.
          Wet- and Dry-Type, Centrifugal  Dust Collectors

          Cyclone separators are widely used for catalyst
          dust collection systems in refineries.  They are
          located in the upper sections of both FCC unit

-------
 668
PETROLEUM EQUIPMENT
   Table  174.  TOTAL HYDROCARBON EMISSIONS FROM FLUID AND THERMOFOR CATALYTIC
                              CRACKING UNIT STACKS3- (Sussman, 1957)

Type


FCC
FCC
FCC
FCCC
TCCe
TCCe
FCCd'e
TCCd
TCCd

TCCb, c

TCCb> c
TCC
TCC
FCC
TCC
Mass spectrometer

Hydrocarbons

7. 4
3. 1
2. 1
1
_
_
_
0. 4
0. 5


0. 1

0. 5

0.3
1. 4

Hydrocarbons

1, 213
1, 150
760
98
_
_
_
308
4, 484


87

121

328
1, 655

Wt % C and C

67.7
84. 1
68.3
42. 3
_
_
_
40. 9
55. 1


79. 5

67. 4

51. 2
61. 9

Vol % C and C

87.4
94. 6
85. 5
54. 1
_
_
_
70.8
81. 4


77

67. 8

75. 3
18. 8
Infrared spectrophotometer
Hydrocarbons
(as hexane),
tons /day
2. 80
0.89
0. 60
0. 30
0. 02
0. 02h
1. 20
0. 04
0. 15
g


0. 02
f
0. 02
_
0. 30
Hydrocarbons
(as hexane),
ppm
142
78
65
12
8

116
13
43
_


14
-
9
Trace
108
aAll concentrations are reported on a dry basis.
 Only the mass spectrometer results for Units F-2T and F-4T were reliable.  Since Units  F-1T and F-2T
 and Units F-3T and F-4T are twin units, the data shown result from combining the twin units.
cNo methane present as determined by mass spectrometer.
 Mass spectrometer determinations include oxygenated C^ and Cj hydrocarbons.
eThe mass spectrometer results were not reliable.
 The infrared spectrophotometer results  were  not reliable.
^Concentrations  of hydrocarbons are below limit  of accuracy of the  infrared spectrophotometer.
 Infrared spectrophotometric determinations were made on Unit D-1T only.  The results shown -were
 obtained by assuming that twin Unit D-1T and D-2T emit the  same  quantity of hydrocarbons.
reactors and regenerators for collecting en-
trained catalyst.  Some TCC units also use cy-
clones for catalyst fines collection from kiln  re-
generation gases.  The cyclones  are employed
as a single unit or in multiple two-stage or three-
stage series systems.   Large FCC unit  regen-
erators may have as many as 12  three-stage  cy-
clones, while smaller  units may  have only 1 two-
stage cyclone.  In general,  high-efficiency cy-
clones have dust collection  efficiencies of over
90 percent for particle sizes of more than 15
microns.  The efficiency drops off rapidly for
particles of less than 10 microns.

Multiple cyclones are used  in some cases for
catalyst fines collection catalyst  regeneration
gases in TCC units.  Dust collection efficiencies
are in the same range  as those for high-efficien-
cy cyclones.  Wet-type, centrifugal collectors or
scrubbers adequately clean the gas  streams from
the catalyst elevators,  and  part of the regenera-
tion gases from the kilns.  Untreated water in the
                wet collector, however,  can cause a carbonate
                deposit on the impeller,  -which is responsible
                for excessive wear on the collector bearings.
                This can and has resulted in excessive shutdown
                time for  repairs.  Table 178 shows particulate
                emissions from two wet-type,  centrifugal cata-
                lyst dust collectors.

                 Electrical Precipitators

                Many FCC units incorporate electrical precipita-
                tors for final collection of catalyst dust from
                 catalyst regeneration gases.  Electrical precipi-
                tators  (see  Figure 524) are normally installed in
                parallel systems because of the  large volume of
                 regeneration gases involved in FCC  unit regen-
                 erators.  Power requirements for these precip-
                 itators may range from 35 kva for small FCC
                units to 140 kva for the larger installations.  The
                hot gases from the regenerator must be cooled
                from approximately 1, 100"  to below 500°F be-
                fore entering the precipitator.  This  is accom-

-------
                                         Catalyst Regeneration
                                            669
     Table 175.  EMISSIONS OF SULFUR OXIDES, AMMONIA, AND CYANIDES FROM STACKS OF
            FLUID AND THERMOFOR CATALYTIC CRACKING UNITSa (Sussman,  1957)
Type
FCC
FCC
FCC
FCC
TCC
TCC
FCC
TCC
TCC
TCC
TCC
TCC
TCC
FCC
TCC
so3
Ib/hr
164
12. 0
1. 20
8. 90
1. 25
-
6. 90
5. 10
2. 0
1. 60
2. 70
5. 74
7. 77
3. 07
0.62
S02,
Chemical anal.
Ib/hr
535
362
1,260
453
17.5
-
648
15. 1
14. 0
18.7
13.2
13. 0
11. 1
205
24. 4
ppm
438
512
2, 190
308
114
-
984
86
65
151
136
105
97
1, 310
141
MS,b
ppm
47
220
1,850
20
-
-
-
15
10
-
91
-
60
360
15
Totals
as SO2,
vol %
0. 055
0. 540
0.220
0. 031
0. Oil
-
0. 098
0. Oil
0. 008
0.016
0. 016
0. 015
0. 015
0. 130
0. 014
Wt % S03
in total
oxides
of sulfur
23.5
3.2
0. 1
1.8
6.7
-
1. 1
25. 0
13. 0
7.9
17.0
30.6
41.2
1.4
2.5
NH3,
Ib/hr
130
27. 0
20. 5
26. 0
1. 20
-
118
4. 60
3.40
2. 20
1. 90
1.56
3. 12
23. 0
2. 80
ppm
401
140
134
67
29
_
675
99
60
67
74
47
103
550
61
Cyanides as HCN,
Chemical anal.
Ib/hr
0.250
0.280
Trace
0.291
0. 010
_
0.054
0.005
0.060
Trace
Trace
Trace
Trace
0.018
0. 039
ppm
0.48
0. 94
Trace
0. 47
0. 15
_
0. 19
0. 07
0. 70
Trace
Trace
Trace
Trace
0. 27
0.54
MS,b
ppm
430
360
240
170
-
_
_
370
230
-
90
-
180
190
220
     All concentrations are reported on a dry basis.
     MS =  mass  spectrophotometer.
    Table 176.   EMISSIONS OF ALDEHYDES, OXIDES OF NITROGEN, CO2,  O2, CO, AND N2 FROM
        STACKS OF FLUID AND THERMOFOR CATALYTIC CRACKING UNITSa (Sussman,  1957)
Type
FCC
FCC
FCC
FCC
TCC
TCC
FCC
TCC
TCC
TCC
TCC
TCC
TCC
FCC
TCC
Aldehydes as HCHO,
Ib/hr
77. 0
18. 0
25.9
4.0
3. 5
-
0. 9
2. 2
1.2
0.6
0. 4
2.6
3. 4
1. 5
14. 3
ppm
130
53
96
5
49
-
3
26
12
12
9
44
63
20
177
NOX as NO2,
Ib/hr
26. 0
4. 2
163
202
5. 7
-
5. 9
0
0
3. 1
2. 2
2. 7
0.6
-
7. 7
ppm
29
8
394
191
51
_
12
0
0
34
32
30
7
-
62
NO by
MS,
ppm
250
-
160
11
-
_
-
200
170
-
190
-
130
310
230
CO2, vol %,
ORSAT
8. 7
8.5
10. 0
13.4
8.2
_
9.5
9.2
4. 7
9.6
12.8
8.4
8.8
7.8
9. 0
MS
11. 1
8.8
11.8
13. 4
-
_
-
12. 1
9. 0
-
13. 3
-
9.2
7. 8
9.0
O2, vol %,
ORSAT
5. 1
3. 5
2. 3
2.0
7.9
_
2. 7
6.6
13. 5
8. 3
2. 5
9.8
7.8
5. 1
6.9
MS
2.2
4. 1
2. 3
2.3
-
_
_
-
_
-
2. 5
_
11. 1
5. 5
7.3
CO, vol %,
ORSAT
4.9
7.8
6. 1
0
1.4
_
6.8
3.2
0.7
1.5
3.6
0
2.6
6. 1
4. 1
N2, vol %
by diff,
ORSAT
81. 0
80.2
81.6
84.6
82.5
_
81. 0
81. 0
81. 1
80. 6
81. 1
81.6
80.8
81.0
80. 0
  All concentrations are reported on a dry basis.
plished by a waste-heat boiler.  The electrical
conductivity of the gas stream may be increased
by injecting ammonia upstream of the  precipitator.

The inlet ducting is designed to effect  a uniform
gas distribution through the precipitator cross
section.  A perforated-plate inlet or  vane sec-
tion assists in accomplishing the desired dis-
tribution.
The precipitators usually employ either a con-
tinuous-type electrode-rapping and plate-vibrating
sequence  or an intermittent hourly rapping cycle.
A dust plume up to 90 percent opacity arises for
a period  of 1 to  2  minutes from the precipita-
tor's  discharge  stack during the intermittent hour-
ly rapping cycle.  This high-opacity, short-in-
terval plume is  not normally encountered with
the  continuous rapping sequence.

-------
670
PETROLEUM EQUIPMENT
                  Table 177.  MOISTURE AND FLUE GAS VOLUMES, %, FROM
                STACKS OF FLUID AND THERMOFOR CATALYTIC CRACKING UNITS
                                          (Sussman, 1957)
Type
FCC
FCC
FCC
FCC
TCC
TCC
FCC
TCC
TCC
TCC
TCC
TCC
TCC
FCC
TCC
Vol % H2O
as determined
from sampling
trains
19. 7
19.2
26.3
18. 7
12. 1
-
18
16. 5
11. 1
12. 2
19
11
11
25. 3
7. 5
Vol % H2O
in
MSa sample
0.480
0.470
0. 186
0.229
-
-
-
0.626
2.448
-
0.885
-
0.600
0. 458
1.762
Rate of flow of
flue gases (wet
basis), scfm
151, 000
86, 300
77, 200
178, 800
17, 300
20,800
80, 900
20, 700
23, 600
13, 970
11,660
13, 800
12, 700
20, 800
18, 400
Rate of flow of
flue gases (dry
basis), scfm
121,300
69, 700
56, 900
145,400
15,200
-
65, 000
17,280
20, 980
12,270
9,600
12, 300
11, 300
15,540
17, 000
                 MS  -  mass spectrophotometer.
   Figure 524.  Top of fluid  catalytic  cracking
   unit's Cottrell precipitator.   Electrode
   terminals and 3R-inch-diameter  flue gashne
   between precipitator  and  silencer are shown
   (Union Oil Company of California, Los Angeles,
   Calif.).
                Carbon Monoxide Waste-Heat Boilers

                Large amounts of carbon monoxide gases are
                discharged to the atmosphere with the regenera-
                tion flue gases of an FCC unit.  The carbon mon-
                oxide waste-heat boiler is a means of using the
                heat of combustion of carbon monoxide and other
                combustible,  and the sensible heat of the regen-
                eration gases.  From the air pollution viewpoint,
                the CO boiler oxidizes the carbon monoxide and
                other combustibles,  mainly hydrocarbons, to
                carbon dioxide and water.


                In most cases,  auxiliary  fuel is required in addi-
                tion to  the carbon monoxide and may be either
                fuel oil, refinery process gas, or  natural gas.
                The CO boiler may be a vertical structure with
                either a rectangular or  circular  cross  section
                with water-cooled walls,  as shown in Figure 525.
                The outer dimensions of a typical  rectangular
                boiler arc 32 feet wide by 44 feet deep by 64 feet
                high, with a ZOO-foot-high stack.   The boiler is
                equipped  with a forced-draft fan and four sets of
                fixed,  tangential-type burners  (one set for each
                corner).  A typical set of burners  includes two
                carbon monoxide gas compartments, four fuel
                gas nozzles, and two steam-atomized oil burners,
                as  shown in Figure 526.   The burners are approxi-
                mately 1-1/2 feet \vide by 6 feet high.  A tangen-
                tial-type  mixing of the gases for more nearly
                complete combustion is achieved by arranging
                the burners slightly  off center.

-------
                                          Catalyst Regeneration
                                             671
                Table 178.  EMISSIONS FROM WET-TYPE,  CENTRIFUGAL CATALYST
                  DUST COLLECTORS (THERMOFOR CATALYTIC CRACKING UNIT)a
Inlet gas volume, scfm
Inlet gas temperature, °F
Inlet gas F^O content, vol%
Particulate matter, Ib/hr
Outlet gas volume, scfm
Outlet gas temperature, °F
Outlet gas H2O content, vol%
Particulate loss, Ib/hr
Collection efficiency, %
Collector No. 1
with two inlet streams
TCC No. 1
1, 780
720
38.8
31.7
TCC No. 2
2, 090
690
39. 3
40. 1
Collector No. 1 discharge
4,230
210
41.2
10.2
85.8
Collector No. 2
with two inlet streams
TCC No. 3
2, 350
740
27.6
23.2
TCC No. 4
1, 680
650
22. 1
52.0
Collector No. 2 discharge
5,090
210
30. 4
8.6
88.6
               The inlet of each collector is connected by ductwork to the reactor elevator and
               the Thermofor kiln of two Thermofor catalytic cracking units.
   Figure 525.   Cylindrical, water-cooled,  carbon
   monoxide waste-heat boiler (Combustion  En-
   gineering,  Inc., Windsor, Conn.).
                                                       elude oxidation of the  sulfur compounds in the fuel
                                                       oil or refinery gas to  sulfur dioxide.   The small
                                                       amount of ammonia in the regeneration flue gas
                                                       is primarily converted to oxides of nitrogen at
                                                       the firebox temperature of between 1, 800°   and
                                                       2,000°F.  Table  179 shows the emissions from
                                                       an FCC unit's CO boiler.
 Economic Considerations

 The economics of a CO boiler  installation can
 be generalized sufficiently to determine a range
 of catalytic cracking unit sizes that can pay out
 a boiler (Alexander and Bradley,  1958).  The
 main variable vised in determining the size of the
 catalytic cracking unit is coke-burning rate.
 Other variables that affect payout include the
 following in the  order of decreasing importance:
 (1) Fuel value,  (2) CO2/CO  ratio,  (3) flue gas
 temperatures,   (4) excess oxygen in  CO gas,
 (5) hydrogen content of regenerator coke.
Regeneration gases from the FCC unit are nor-
mally delivered to the inlet of the CO boiler
ductwork at about  1, 100°F and 2 psig.  When-
ever  the overhead regenerator gases  first pass
through an electrical precipitator,  the inlet gas
to the precipitator must be  cooled below 500°F.
The CO boiler would then receive regeneration
flue gas between 450°   and 500°F,

The main reactions of the CO boiler's firebox in-
clude burning the refinery gas or fuel oil to car-
bon dioxide and water and completing  the oxida-
tion of the carbon monoxide.  Other reactions in-
On the assumption that additional steam is re-
quired in the refinery, a coke burnoff rate of
10, 000 pounds per hour or more can be econom-
ically attractive for installation of a  CO boiler
when the fuel has a value of 20 cents  per million
Btu.  If, however, additional steam is  not re-
quired,  the minimum coke-burning rate to pro-
vide a reasonable payout for a CO boiler is
about 18,000 pounds per hour.  A payout of 6
years after taxes is assumed to be an attractive
investment.  In some  areas, the  reduction in
the air contaminants is sufficiently important to
justify a payout longer than  6 years.

-------
672
PETROLEUM EQUIPMENT
                      Figure  526.   Corner-fired burners  of  a  carbon monoxide waste-heat
                      boiler:  (left) Elevation view showing  a  typical  set of burners
                      for one corner;  (right)  plan  view of firebox showing  location of
                      the four sets of burners  (Combustion  Engineering,  Inc., Windsor,
                      Sonn.).
   Table 179.  EMISSIONS FROM THE STACKS
    OF FLUID CATALYTIC CRACKING UNITS'
           CARBON MONOXIDE  WASTE-
                 HEAT BOILERSa

Gas volume, scfm
Gas temperature, °F
Dust loss, Ib/hr
NOX as NO2, ppm
Aldehydes as HCHO, ppm
NH3, Ib/hr
SO2, Ib/hr
SO3, Ib/hr
Organic acids as acetic, ppm
Hydrocarbons as C^, ppm
CO2, vol % dry basis
CO, vol % dry basis
O, vol % dry basis
H2O, vol %
Unit I
East
stack
96,800
470
44
173
15
19.8
269
0. 16
-
None
14
0
3
22.4
West
stack
97, 200
450
33
190
11
22.5
282
0.4
-
None
14.4
0
2.6
22.7
Unit II
60, 700
570
34. 9
67
5
Noneb
265
1.61
11. 7
< 8
8.8
0
3. 5
23.9
  Both FCC Units I and II are equipped with electrostatic
  precipitators.
 bFCC Unit II does not use NH3 injection for precipitator
  conditioning.
                      OIL-WATER EFFLUENT SYSTEMS
                 FUNCTIONS OF SYSTEMS

                 Oil-water effluent systems are found in the three
                 phases of the petroleum industry—production,
                 refining,  and marketing.  The systems  vary in
                 size and complexity though their basic function
                 remains the same,  that is, to collect and sep-
                 arate wastes, to recover valuable oils,  and to
                 remove undesirable contaminants before dis-
                 charge of the water to ocean,  rivers, or channels.


                 Handling of  Crude-Oil Production Effluents

                 In the production of crude oil, wastes such as
                 oily brine,  drilling  muds, tank bottoms, and
                 free oil are generated.  Of these, the oilfield
                 brines present the most difficult disposal prob-
                 lem because of the  large volume encountered

-------
                                     Oil-Water Effluent Systems
                                            673
(Rudolfs, 1953).  Community disposal facilities
capable of processing the brines to meet local
•water pollution standards are often set up to
handle the treatment of brines.   The most effec-
tive method of disposal of brines has been in-
jection into underground formations.

A typical collection system associated with  the
crude-oil production phase  of the industry usu-
ally includes a number  of small gathering lines
or channels transmitting waste water from wash
tanks, leaky equipment, and treaters to an earthen
pit,  a concrete-lined  sump,  or a steel waste-water
tank.  A pump decants waste water from these
containers to water-treating facilities before in-
jection into underground formations  or disposal
to sewer  systems.  Any oil accumulating on the
surface of the water is  skimmed off  to storage
tanks.

Handling of Refinery Effluents

The effluent disposal  systems found  in refineries
are larger and more elaborate than those in the
production phase.  A  typical modern refinery
gathering system usually includes  gathering
lines,  drain seals,  junction boxes, and channels
of vitrified clay or concrete for transmitting
waste water from processing units to large
basins or ponds used  as oil-water  separators.
These basins are sized to receive  all effluent
water,  sometimes even including rain runoff,
and may be earthen pits,  concrete-lined basins,
or steel tanks.

Liquid wastes  discharging to these systems
originate at a wide variety of sources such as
pump glands, accumulators, spills,  cleanouts,
sampling lines, relief valves, and  many  others.
The types of liquid wastes may be  classified as
waste water with:

1.   Oil present as free oil,  emulsified oil,  or
     as  oil coating  on  suspended matter;

2.   chemicals present  as suspensoids,  emulsoids,
     or  solutes.  These chemicals  include acids,
     alkalies, phenols,  sulfur compounds, clay,
     and others.

Emissions from these varied liquid wastes can
best be controlled by  properly maintaining,  iso-
lating, and treating the wastes at  their source; by
using efficient oil-water separators; and by
minimizing the formation of emulsions.  Recov-
ery of some  of the wastes as valuable byproducts
is growing in importance.


Treatment  of Effluents by Oil-Water Separators

The waste water from the process  facilities  and
treating units just discussed flows  to the oil-
water separator for recovery of free oil and
settleable solids.

The American Petroleum Institute is recognized
as an authoritative source of information on the
design of oil-water separators,  and its recom-
mended methods are used generally by refineries
in Los Angeles County.  The basis  for design
of a. separator is the difference in gravity of oil
and  water. A drawing of a  typical separator is
shown in  Figure 527.

Factors affecting the efficiency of separation
include temperature of water,  particle size,
density, and amounts and characteristics of sus-
pended matter.  Stable emulsions are not affected
by gravity-type separators  and must be treated
separately.

The oil-water separator design must provide for
efficient inlet and  outlet  construction, sediment
collection mechanisms,  and oil skimmers.   Re-
inforced concrete  construction has  been found
most desirable for reasons of  economy, mainte-
nance,  and efficiency.
 Clarification of Final-Effluent Water Streams

 The effluent water from the oil-water separator
 may require further treatment before final dis-
 charge to municipal sewer systems,  channels,
 rivers,  or streams.  The type and extent of
 treatment depend upon the nature of the contami-
 nants present,  and on the local water pollution
 ordinances governing the concentration and
 amounts of contaminants to be discharged  in re-
 finery effluent waters.   The methods  of final-ef-
 fluent  clarification to be briefly discussed here
 include  (1) filtration,   (2) chemical flocculation,
 and  (3) biological treatment.


 Several different types  of filters may be used to
 clarify the separator effluent. Hay-type filters,
 sand filters, and vacuum precoat filters are  the
 most common.   The selection of any  one type de-
 pends  upon the  properties of the  effluent stream
 and upon economic considerations.

 The application of chemical flocculation to the
treatment of separator effluent water is a rela-
tively  recent development (Reno et al. ,  1958;
 Castler et al. ,  1956).  Methods of treatment are
 either by sedimentation  or flotation.  In sedimen-
 tation  processes,  chemicals such as copper  sul-
 fate, activated  silica, alum,  and lime are  added
to the  waste-water stream before it is fed  to the
 clarifiers.  The chemicals cause  the  suspended
particles to agglomerate and  settle out.  Sedi-
ment is removed from the bottom of the clarifiers
by mechanical scrapers.

-------
674
PETROLEUM EQUIPMENT
                                                                                          REFINERY
                                                                                          «ASU 1AUR
                                                                              FLOATING DECKS     i
                   TO «ATER DISPOSAL
                                                           TRANSVERSE OPENINGS
                                                              ELEVATION
                                                                                  LEGS
                                Figure 527.  A modern  oil-water  separator.
Effectiveness of the sedimentation techniques in
the treatment of separator effluents is limited by
the small oil particles contained in the waste
water.  These particles, being lighter than water,
do not settle out easily.  They may also become
attached to particles of suspended solids and
thereby increase in buoyancy.
In the flotation process a colloidal floe  and air
under pressure are injected into the waste water.
The  stream is then fed to a clarifier through a
backpressure valve that reduces the pressure to
atmospheric.  The dissolved air is suddenly re-
leased in the form of tiny bubbles that carry the
particles of oil and coalesced solids to the surface
where they are skimmed off by mechanical flight
scrapers. Of the two,  the flotation process has
the potential to become the more  efficient  and
economical.
Biological treating units such as trickling filters,
activated-sludge basins, and stabilization basins
have been incorporated into  modern refinery
waste  disposal  systems.  By combining adsorp-
tion and oxidation, these units are capable of re-
ducing oil, biological oxygen demand,  and pheno-
lic content from effluent water streams.  To pre-
vent the release of air pollutants  to the atmosphere,
certain pieces of equipment, such as clarifiers, di-
gesters,  and filters,  used in biological treatment
should be covered  and vented to recovery facili-
ties or incinerated.
                 Effluent Wastes From Marketing Operations

                 In the marketing and transportation phase of the
                 industry, waste water containing oil may be dis-
                 charged during the cleaning of ballast tanks or
                 ships, tank trucks,  and tank cars.  Leaky valves
                 and connections  and flushing of pipelines are
                 other sources of effluents.  The methods used
                 for treatment and disposal of these waters  are
                 similar  to  those used in the other phases of the
                 industry.

                 THE AIR POLLUTION PROBLEM

                 From an air  pollution standpoint the most objec-
                 tionable contaminants emitted from liquid -waste
                 streams are  hydrocarbons, sulfur  compounds,
                 and other malodorous materials.
                  The effect of hydrocarbons in smog-producing
                  reactions is well known,  and sulfur compounds
                  such as mercaptans and sulfidcs  produce very
                  objectionable odors,  even in high dilution.   These
                  contaminants can escape to  the atmosphere  from
                  openings in the sewer system,  open channels,
                  open vessels, and open oil-water separators.
                  The large exposed  surface area of  these sep-
                  arators requires that effective means of control
                  be instituted  to minimize hydrocarbon losses to
                  the atmosphere from this source.  A method
                  (Jones  and Viles,  1952)  developed by personnel
                  of Humble Oil and Refining Company  may be
                  used to estimate the  hydrocarbon losses from

-------
                                     Oil-Water Effluent Systems
                                           675
 open oil-water separators.  In the development
 of this method the principal variables that in-
 fluence evaporation rates were assumed to be
 vapor pressure of the oil,  and wind velocity.
 Experimental work was done to observe and
 correlate the effects of these  factors on evapo-
 ration rates.  From the data compiled, a proce-
 dure for calculation of losses was  devised.  Es-
 sentially,  this procedure is as follows:

 1.   Obtain a. representative sample of oil at the
     surface of the separator.

 2.   Obtain the vapor pressure of the samp.le and
     the average wind velocity at the surface of
     the separator.

 3.   Using Figure 528,  find the loss in bbl/day
     per ft2.

 4.   Since the  data compiled were collected
     under ideal conditions, a correlation
     factor is needed to correct the value ob
     tained from Figure 487 to actual separator
     conditions.   This correlation factor may
     be found by measuring the evaporation rate
     of a weighted sample of a constantly boiling
     hydrocarbon from a shallow vessel placed
     on the surface of the separator.  The cor-
     relation factor is then calculated as the
     ratio  of the measured rate of evaporation
     to the theoretical evaporation rate from
     Figure  487.

 5.   The product of the theoretical separator loss,
     the correlation factor, and the separator area
     represents  the total evaporation loss.

 AIR POLLUTION CONTROL EQUIPMENT
 Hydrocarbons From Oil-Water Separators

 The most effective means  of control of hydrocar-
 bon emissions from oil-water  separators has been
 the covering  of forebays or primary separator
 sections.  Either fixed roofs or floating roofs
 (Brown and Sublett, 1957)  are  acceptable  covers.
 Separation and skimming of over 80 percent  of
 the flotable oil layer is effected in the covered
 sections.  Thus,  only  a minimum of oil is con-
 tained in the  effluent water, which flows under
 concrete curtains  to the open afterbays  or secon-
 dary separator sections.

 Satisfactory fixed  roofs have been constructed
 by using wooden beams for structural support,
 and asbestos paper as a cover. Ajnastic-type
 sealing  compound  is then used to seal all joints
 and- cracks.  Although this  form of roof is ac-
 ceptable for the control of pollutants, in practice,
 making the roof completely vapour tight is difficult.
 The resultant leakage  of air into the vapor space,
                     7
                         7
                              7
 0      02     04     06    08     1C     12     14
                   VAPOR PRESSURE psia
Figure 528.  Relationship of laboratory  evapora-
tion rates for  various wind velocities  to  vapor
pressure  of  oil  (Jones and Viles,  1952).
 and vapor leakage into the atmosphere are not
 desirable from standpoints of air pollution or
 safety.  For example, an explosive mixture re-
 sulting from leakage  of air from gaging opera-
 tions into the vapor space  of a fixed-roof sep-
 arator  at a Los Angeles  refinery was ignited by
 a  static electric spark.  The destruction of the
 \vooden roof has emphasized the  need for elim-
 ination of the vapor space.  Another type of en-
 closed  separator with a concrete cover and gas
 blanketing of the vapor space has proved satis-
 factory.  The effluent vapors from this system
 are vented to vapor recovery.

 The explosion hazard associated  -with fixed roofs
 is  not present in a floating-roof installation.  These
 roofs are similar to those  developed for storage
 tanks.   The floating covers are built to fit into
 bays with about 1 inch of clearance around the
 perimeter. Fabric or rubber may be used to seal
 the gap between the roof  edge and the container
 wall.  The roofs are  fitted with access manholes,
 skimmers, gage hatches, and supporting legs.
 Floating roofs  on refinery  separators are  shown
 in Figures 529 and 530.  In operation,  skimmed
 oil flows through lines from the skimmers  to
 a  covered tank  (floating roof  or connected to
 vapor recovery) or sump and then is pumped to de-
234-767 O - 77 - 45

-------
 676
                                      PETROLEUM EQUIPMENT
                  Figure 529.  Floating-roof  cover  on  refinery oil-water  separator
                  (Union Oil Company of California, Los Angeles,  Calif.).
emulsifying processing facilities.  Effluent water
from the oil-water separator is handled in the
manner described previously.

In addition to covering the separator, open sewer
lines that may  carry volatile products are  con-
verted to closed, underground lines with water-
seal-type vents.  Junction boxes are vented to
vapor recovery facilities, and steam is used to
blanket the sewer lines to inhibit formation of ex-
plosive mixtures.

Accurate calculation of the hydrocarbon losses
from separators  fitted with fixed roofs is  difficult
because of the  many variables of weather  and re-
finery operations involved.  One empirical equa-
tion that has been used with reasonable  success
to calculate losses from separators is
                       AdHm
                      (12)(379)
                               (147)
•where

    w

    A

    d
weight of hydrocarbon loss,  Ib/hr

area of covered separator, ft

depth of vapor space,  in.
    H ~  vol % of hydrocarbons as hexane in
          the vapor space

    m -  molecular weight of hexane.

In using this equation, assume that the density of
condensed vapors (C^Hj^) equals 5.5 pounds per
gallon and that the vapor in the separator is dis-
placed once per hour.  The vapor concentration is
determined  by using the average of readings from
a calibrated explosion meter over the entire cov-
ered area.  The assumption that the vapors are
displaced once every hour was determined by us-
ing data from work done by the Pacific Coast Gas
Association (Powell, 1950).

The previously discussed methods of obtaining
emissions from uncovered  separators may also
be applied to sections covered with fixed roofs.
Use of more than one method and a number of
tests  of one source over a considerable period
of time are  necessary to ensure an acceptable
estimate of  emissions.

Emissions from separators fitted with floating-
roof covers  may be  assumed to be almost negli-
gible.  A  rough approximation of the magnitude of
the emission can be made by assuming the emis-
sion to be from a  floating-roof storage tank of

-------
                                    Oil-Water Effluent Systems
                                            677
 Figure 530.   Floating  roof on refinery oil-water
 separator  (Atlantic-Richfield Oil Company,  Los
 Angeles,  Calif.).
particles  in water that cannot be divided effec-
tively by means of gravity alone.  Gravity-type
oil-water separators are, in most cases,  inef-
fective in breaking the emulsions, and means
are provided for separate treatment where the
problem is serious.

Oil-in-water emulsions are objectionable  in the
drainage system since the separation  of other-
wise recoverable oil may be impaired by their
presence.  Moreover,  when emulsions of  this
type are discharged into large bodies  of -water,
the oil is  released by the effect of dilution, and
serious pollution of the water may result.

Formation of emulsions  may be minimized by
proper design of process equipment and piping.
Several methods, both physical and  chemical,
are available for use in breaking emulsions.
Physical methods of separation include direct
application of heat, distillation,  centrifuging,
filtration, and use of an electric field.  The ef-
fectiveness  of any  one  method depends upon the
type of emulsion to be  treated.  Chemical meth-
ods of separation are many and varied.  During
recent years the treatment  of waste water con-
taining emulsions with coagulating chemicals has
become increasingly popular.

Variations of this form of treatment include air
flotation systems,  and biological treatment of the
•waste water,  as discussed previously in this sec-
tion.
equivalent perimeter.  The API method of calcu-
lating losses from storage tanks can then be ap-
plied.
Treatment of Refinery Liquid Wastes at Their Source

Isolation of certain odor- and chemical-bearing
liquid wastes at their source for treatment be-
fore discharge of the water to the  refinery waste-
water-gathering  system has been found to be the
most effective and economical means of minimiz-
ing odor and chemicals problems.  The unit that
is the source of wastes must be studied for possi-
ble changes in the operating process to reduce
wastes.  In some cases the wastes from one pro-
cess may be used to  treat the wastes from anoth-
er.  Among the principal streams that  are treat-
ed separately are oil-in-water emulsions,  sulfur-
bearing waters,  acid sludge, and spent caustic
wastes.

Oil-in-water emulsions

Oil-in-water emulsions are types  of wastes that
can be treated at their source.  An oil-in-water
emulsion may be defined as a suspension of oil
Sulfur-bear ing waters

Sulfides and  mercaptans are removed from waste-
water streams by various methods.  Some refin-
eries strip the waste water in a column with live
steam.   The overhead vapors from the column
are condensed and collected in an accumulator
from which the noncondensables flow to sulfur-
recovery facilities or are incinerated.  One Los
Angeles refinery removes  all the  hydrogen sul-
fide  and about 90 percent of the ammonia from a
waste stream by this method.  Flue gas has also
been  used successfully as the stripping medium
in pilot-plant studies.  Bottoms water from steam-
stripping towers, being essentially sulfide free,
can then be drained to the refinery's sewer sys-
tem.
Oxidation of sulfides in waste water is also an
effective means of treatment  (Smith,  1956a).  Air
and heat are used to convert sulfides and mer-
captans to thiosulfates, which are water soluble
and not objectionable.  Figure 531 depicts the
flow through an air oxidation unit.  Experience
has shown that, under  certain conditions,  the
thiosulfates may be reduced by the action  of
Vibrio desulfuricans bacteria, which results  in

-------
 678
                                       PETROLEUM EQUIPMENT
       STEAM
       AIR
       SULFIOE HATER
                                                                                     TO FURNACE FIREBOX
                                                                                     OR INCINERATOR
                                              COOLER
                          OXIDIZER COLUMN
                                                                               TO SE»ER
                     Figure 531. Flow diagram of  air  oxidation process (Smith, 1956b).
the release of hydrogen sulfide.   The reduction
takes place only in the absence of dissolved oxy-
gen.  Care must be used to keep this water from
entering retention sumps  or pits subject to this
bacterial attack.
 2.   processing to produce byproducts such as
     ammonium, sulfate, metallic sulfates, oils,
     tars, and other materials;

 3.   processing for recovery of acid.
Chlorine is also used as an oxidizing agent for
sulfides.   It is added in stoichiometric quanti-
ties proportional to the waste water.  This meth-
od is limited by  the high cost of chlorine.  Water
containing dissolved sulfur dioxide has been used
to reduce sulfide concentration in waste waters.
For removing  small amounts of hydrogen sulfide,
copper sulfate and zinc chloride have been used
to react and precipitate the sulfur as copper  and
zinc sulfides.  Hydrogen sulfide maybe released,
however,  if the water treated with these  com-
pounds contacts  an acid stream.
Acid sludge

The acid sludge produced from treating opera-
tions varies with the stock treated and the con-
ditions  of treatment.  The sludge  may vary from
a low-viscosity liquid to a solid.  Methods of dis-
posal of this sludge are many and varied. Basic-
ally, they may be considered under three general
headings:

1.  Disposal by burning as fuel,  or dumping in
    the ground  or at sea;
The burning of sludge results in discharge to the
atmosphere of excessive amounts of sulfur  dioxide
and sulfur trioxide from furnace stacks.  This
latter consideration has  caused the discontinuance
of this method of disposal in Los Angeles County.
If sludge is solid or semisolid it may be buried
in specially constructed  pits.  This method of
disposal, however, creates the problem of  acid
leaching out to adjacent waters.  Dumping in
designated  sea areas  eliminates pollution of the
potable waters and atmosphere of populated areas.
Recovery of sulfuric acid from sludge is accom-
plished essentially by either hydrolysis or thermal
decomposition processes.  Sulfuric acid sludge is
hydrolyzed by heating it with live steam in the
presence of water.  The  resulting product sepa-
rates into two distinct phases.  One phase con-
sists of diluted  sulfuric acid -with a small amount
of suspended carbonaceous material,  and the  sec-
ond phase,  of a viscous acid-oil  layer.  The dilute
sulfuric acid may be  (1) neutralized by alkaline
wastes,   (2) reacted chemically with ammonia-
water solution to produce ammonium sulfate for
fertilizer,  or (3) concentrated by heating.

-------
                                              Pumps
                                            679
Acid sludge may be decomposed by heating to
SOOT to form coke, sulfur dioxide, oil, water,
and  lighter boiling hydrocarbons  as a gas.  Sev-
eral commercial decomposition processes have
been developed to use the sulfur present in the
sludge.  In all these processes a kiln is used
wherein the sludge-is mixed with hot coke  or
some other carrying agent and heated to the re-
quired temperature.  Another process  allows
the acid sludge to be burned directly.   The sul-
fur dioxide gases from the reaction are purified
and  then either converted to sulfuric acid (con-
tact process)  or to free elemental sulfur.   The
tail  gases  emitted  from these  decomposition pro-
cesses  may create an odor nuisance as well as
cause damage to vegetation in the surrounding
area.  Because of this,  the tail gases may  re-
quire additional treatment to preclude the  possi-
bility of a  nuisance.

Of all the methods discussed,  hydrolysis and de-
composition are the most desirable from the
standpoint of  air pollution control,  though they
are  not the most economical when the volume of
acid is  small.
Spent caustic wastes

Caustic soda is widely used in the industry to
neutralize acidic materials found in crude oil
and its fractions.   It is also used to remove
mercaptans, naphthenates, or cresols from gas,
gasoline,  kerosene, and other product streams.
The resulting spent caustic is imbued with the
odors of the  compounds that have been extracted
in the various treating processes (American
Petroleum Institute,  I960).  This spent caustic
can be a source of intense objectionable odors
and can result  in nuisance complaints.
Spent caustic is treated by direct methods or
chemical processing,  or both. • Direct methods
of disposal include ponding, dilution, disposal
•wells, and sale.   Of these, ponding is not recom-
mended, since the pond could become a source
of air pollutants as well as a possible source of
contamination of underground water  through seep-
age.  Dilution of spent caustic in large bodies  of
•water is a commonly used method of disposal.
The ocean and brackish •waters are the only desir-
able areas for this disposal, to preclude  pollu-
tion of fresh-water streams.
Disposal wells afford another convenient means
of disposing of spent-caustic solutions,  provided
that local conditions are favorable.  The method
consists of pumping the liquid •wastes into  under-
ground formations that contain saline or nonpotable
water.  Spent caustics that contain phenolates,
cresolates, and sulfides may be sold outside the
industry for  recovery of these materials.

In addition to these direct methods of disposal,
chemical processing methods are  available.
These include neutralization, combination of
neutralization and oxidation,  and combination of
oxidation and chemical separation.

Neutralization  of high-alkaline caustic wastes may
be effected by means of spent acids from other  re-
finery operations.  After neutralization, the result-
ing salt solution may be suitable for discharge into
the refinery's drainage system.   In some cases
odorous  or oily materials may have  to be stripped
from the product before discharge.  In these in-
stances effluent gases should be incinerated.

Spent-caustic solutions can also be neutralized
with acid gases such as flue gases (Fisher and
Moriarty,  1953).  Oxygen contained  in the flue
gas tends to  oxidize sulfides and mercaptides as
a secondary  reaction.  Effluent gases from this
reaction must be properly incinerated to prevent
odor problems.  The resulting treated solution
contains carbonates, bicarbonates, thiosulfates,
sulfates, and sulfites and may be suitable for dis-
charge into the drainage system.

A recently developed method of treating  caustic
wastes involves the  addition of pickling acid.  The
acid is mixed with caustic and is airblown.  The
resulting solution is filtered and naphtha is added
to extract organic acids for recovery. Fumes
from the airblowing operation must be incinerated.
The treated salt solution is discharged to a drain-
age system.
                                                                        PUMPS
TYPES OF PUMPS
Pumps are used in every phase of the petroleum
industry.  Their applications range from the lift-
ing of crude  oil from the depths of a well to the
dispensing of fuel to automobile engines.  Leakage
from pumps  can cause air pollution wherever or-
ganic liquids are handled.

Pumps are available in a -wide variety of models
and sizes.  Their capacities may range from
several milliliters per hour, required for some
laboratory pumps, to  3/4 million gallons  per min-
ute,  required of each  of the new pumps at Grand
Coulee Dam  (Dolman,  1952).

Materials used  for construction of pumps are also
many and varied.  All the common machinable
metals and alloys, as well as plastics,  rubber,

-------
680
                          PETROLEUM EQUIPMENT
and ceramics, are used.  Pumps may be classi-
fied under two general headings, positive displace-
ment and centrifugal.
                                           pict some typical pumps of each type.  When a
                                           positive-displacement pump is  stopped, it serves
                                           as a check valve to prevent backflow.
Positive-Displacement Pumps

Positive-displacement pumps have as their prin-
ciple of operation the displacement of the liquid
from the pump case by reciprocating action of a
piston or  diaphragm,  or rotating action of a gear,
cam, vane, or screw.  The type of action may he
used to classify positive-displacement pumps as
reciprocating or rotary.  Figures 532  and 533 de-
                                           Centrifugal Pumps

                                           Centrifugal pumps operate by the principle of con-
                                           verting velocity pressure generated by centrifugal
                                           force to static pressure.  Velocity is imparted to
                                           the fluid by an impeller that is  rotated  at high
                                           speeds.   The fluid enters at the center of the im-
                                           peller and is discharged from its periphery.  Un-
                                           like positive-displacement pumps,  when the cen-
                                                                    FLUID
                                                                    PI STON--9=
                                                                 -PROCESS ,•
                                                                   LIQUID
                                                  SUCTION POSITION
                                    DISCHARGE   DISCHARGE  PIPE
                                     CHAMBERis«g™»*«^CDNNECT ION
                                  D I S C H A R G E-IT
                                 7\  VALVES '
                                  I S U C T I L
                                   ^VALVEi
                                                                       DISCHARGE POSITION
                                                                       b
                      CYLINDER   LI QUID CYLINDER
COUNTER-
 BORES =
           GEAR COVER
             3 EAR
                   SUCTION- PIPE CONNECTION'
                      C
                   DISCHARGE  VALVES
                                                                      i-PLUNGER
                                                                      ICROSSHEADS
                            .
                         -   CROSSHEAbSUCTION
                                                                                 CONNECTING
                                                                                  RODS
                                                                                 CONNECT ING
                                                                                  RODS
                 Figure 532.  Reciprocating pumps:   (a)  Principle of  reciprocating pump,
                 (b) principle of  fluid-operated  diaphragm pump, (c) direct-acting steam
                 pump,  (d) principle  of  mechanical  diaphragm pump, (e) piston-type power
                 pump,  (f) plunger-type  pov«er  pump  with  adjustable stroke, (g)  inverted,
                 vertical,  triplex power pump  (Dolman,  1952).

-------
                                              Pumps
                                                681
                        SUCTION  DISCHARGE
                                     GEAR
                                      INTERNAL
                                      GEAR
                                     CRESCENT
                                                                                    0 ISCHARGE
                                                         DISCHARGE
    THREE-  . .
    LOBE    '-'SUCTION
    .ROTOR
                                                            INLET  DISCHARGE

                 DISCHARGE  DRIV,NG  GEAR     R „ T 0 R   D, S C H A_R G c  SEAL
                                                            KEY
                               DISCHARGE
                                                                       SHAFT
                                                                            SUCTION
                                                                        ECCENTRIC
                         SUCTI ON
                                            DISCHARGE
                                       SHUTTLE!; M.ROTOR
      ROLLER-  ECCENTRIC
              h
      FLEXIBLE RUBBER
           T U B E,
           IDLER070RS
                                      PISTON
SUCTION

    ECCENTR ilT"
                                                               SQUEEZE RING
                                                                I
                 Figure 533.  Rotary  pumps:  (a) External-gear pump,  (b) internal-gear
                 pump,  (c) three-lobe  pump, (d) four-lobe pump,  (e) si iding-vane  pump,
                 (f) single-screw  pump,  (g) swinging-vane pump,  (h) cam or  roller  pump,
                 (i) cam-and-piston  pump,  (j) three-screw pump;(K) shuttle-block  pump,
                 (I) squeegee  pump,  (m)  neoprene vane pump (Dolman,  1952).
trifugal type of pump is stopped there is a tenden-
cy for the fluid to backflow.  Figures 534 and 535
depict some centrifugal pumps.


Other  specialized types of pumps  are available,
but,  generally, the pumps used by the petroleum
industry fall into the two categories discussed.

Power for driving  the various types of pumps is
usually derived from electric motors, internal
combustion engines, or steam drives.  Any one
of these sources may be adapted for use with
either reciprocating pumps or centrifugal pumps.
Most rotary pumps are driven by electric motor.
     The opening in the cylinder or fluid  end through
     which the connecting rod actuates the piston is
     the major potential source of contaminants from
     a reciprocating pump.  In centrifugal pumps,
     normally the only potential source of leakage
     occurs where the  drive shaft passes through the
     impeller casing.


     AIR POLLUTION CONTROL EQUIPMENT

     Several means have been devised  for sealing the
     annular clearance between pump shafts and fluid
     casings to retard  leakage.  For most refinery ap-
     plications, packed seals and mechanical seals are
     widely used.
THE AIR POLLUTION PROBLEM

Operation of various pumps in the handling of fluids
in petroleum process units can result in the re-
lease of air contaminants.  Volatile materials such
as hydrocarbons,  and odorous substances such as
hydrogen sulfide or mercaptans are of particular
concern because of the large volumes handled.  Both
reciprocating and centrifugal  pumps  can be sources
of emissions.
     Packed seals can be used on both positive dis-
     placement and  centrifugal type pumps (Elonka,
     1956).   Typical packed seals,  as shown in Fig-
     ure 536, generally consist of a stuffing box filled
     with sealing material that encases the moving
     shaft.  The stuffing box is fitted with a takeup
     ring that is made to compress the packing and
     cause it to tighten around the shaft.   Materials
     used for packing vary with the product temper-
     ature,  physical and chemical properties, pres-

-------
682
PETROLEUM EQUIPMENT
               DISCMAKGE
               ,' NOZZLE*
                                    IMPELLER
                                                   D I SCHARGE
                                                            D I FFUSER -
                                                            IMPELLER
                                                       VOLUTE
                                                  MPELLER VANES   VANES
                                                             SHROUDS
                                          'DISCHARGE
             VANES
                                                 VANES
                    d
                     f
                   Figure 534.  Centrifugal  pumps:   (a)  Principle of centrifugal-type
                   pump,  (b)  radial section through volute-type pump, (c) radial  sec-
                   tion  through diffuser-type pump,  (d) open  impeller, (e) semi-en-
                   closed  impeller, (f) closed impeller,  (g)  nonclog  impeller (Dolman,
                   1952).
 sure,  and pump type.  Some commonly used
 materials are metal, rubber, leather, wood, and
 plastics.

 Lubrication of the contact surfaces of the pack-
 ing and shaft is effected by a controlled amount
 of product leakage to the atmosphere.  This fea-
 ture makes packing seals undesirable in applica-
 tions where the product can cause a pollution prob-
 lem.   The packing itself may also be saturated with
 some material such as  graphite or oil that acts as
 a lubricant.  In some cases cooling or quench
 water is  used to cool the impeller shaft and the
 bearings.

 The second commonly used means of  sealing is
 the mechanical seal (Elonka,  1956), which was
 developed over a period of years as a means of
 reducing leakage from pump glands.   This type
 of seal can be used only in pumps that have a
 rotary shaft motion.  A simple mechanical seal
 consists  of two rings with wearing surfaces at
 right angles to the shaft (see  Figure 537).  One
 ring is stationary while the other is attached to
 the shaft and rotates with it.  A spring and the
 action of fluid pressure keep  the two faces in
 contact.  Lubrication of the wearing faces  is ef-
 fected by a thin film  of the material being pumped.
 The wearing faces are precisely finished to en-
 sure perfectly flat surfaces.  Materials used in
                   the manufacture of the sealing rings are many
                   and varied.  Choice of materials depends pri-
                   marily upon properties of fluid being pumped,
                   pressure, temperature,  and speed of rotation.
                   The vast majority of rotating faces in com-
                   mercial use are made of carbon (Woodhouse,
                   1957).

                   Emissions to the atmosphere from centrifugal
                   pumps may be  controlled in some cases by use
                   of the described mechanical-type seals instead
                   of packing glands.  For  cases not feasible to
                   control with mechanical seals, specialized types
                   of pumps, such as  canned, diaphragm,  or elec-
                   tromagnetic, are required.

                   The canned-type pump is totally enclosed, with
                   its motor built as  an integral part of the pump.
                   Seals  and attendant leakage are  eliminated.  The
                   diaphragm pump is another type devoid of seals.
                   A diaphragm is actuated hydraulically,  me-
                   chanically, or  pneumatically to effect a pump-
                   ing action.  The electromagnetic pumps use an
                   electric current passed  through the fluid,  which
                   is in the presence  of a strong magnetic field,
                   to cause motion.

                   A pressure-seal-type application can reduce
                   packing gland leakage.   A liquid,  less volatile
                   or dangerous than  the product being pumped, is

-------
                                             Pumps
                                                                                                   683
                                          '•BALL  BEARING
                                   Q/ISUCTION CHAMBER
                                                                                  FOR  WATER
                                                                                  COOLING
                                                                  -,,   -
                                                                    ""•'PIPING  AND
                                                                   VALVE FOR CONTROL
                                                                  STUFFING-BOX PRESSURE
                                                                          j
                                                                                 MOTOR CASE
                                                                                  /
                                                                                  'MOTOR ROTOR
                                                                                   » i N D LN_G s
                                                                                   iINTEGRAL
                                                                                     WITH
                                                                                    IMPELLER)
                                                                                   • MOTOR STAT-
                                                                                   OR WINDING
                                                                                   •DIAPHRAGM
                                                                                    PROTECTS
                                                                                     STATOR)
                                                                                    \BEARING
           STRAINER
                   Figure 535.  Centrifugal  pumps:   (h)  single-stage,  double-suction,
                   split-case,  centrifugal  pump;  (i)  close-coupled  water  pump;  (j)
                   four-stage pump with opposed  impellers;  (k)  turbine-type,  deep-well
                   pump;  (I) submersible-motor,  deep-well  pump;  (m)  close-coupled,
                   vertical,  turret-type  pump;  (n)  pump  with  integral motor  (Dolman,
                   1952).
                                           PRODUCT
                                          * PRODUCT
                                 u
Figure 536. Diagram of simple uncooled packed  seal.
introduced between two sets of packing.  This
sealing liquid must also be compatible with the
product.  Since this liquid is maintained at a
higher pressure than  the product,  some  of it
passes by the packing into the product.   The
pressure differential  prevents the product from.
leaking outward,  and  the sealing liquid pro-
vides the necessary lubricant for the packing
gland.  Some of the sealing liquid passes the
outer packing (hence  the necessity of low vola-
tility), and  a means should be provided for its
disposal.

This application is  also  adaptable to pumps
•with mechanical seals.   A dual  set of mechan-
ical seals similar to  the two sets of  packing is
used.

-------
684
PETROLEUM EQUIPMENT
           SPRING
   SET SCREHS
                               UP    ^SEAL FLANGE
                                         LOCK PIN
SPRING HOLDER
       U-CUP FOi.LOȣR
                        SHTIONAR1 FACE
                                         SEAT GASKET
                                     SEAL FLANGE GASKET
  Figure 537.   Diagram of simple mechanical  seal
  (Borg-Ylarner Mechanical Seals.   A  Division  of
  Borg-Warner Corporation,  Vernon,  Calif.).
                  Volatile vapors that leak past a main seal may-
                  be vented to vapor recovery by using dual seals
                  and a shaft housing.

                  Other than  the direct methods used to control
                  leakage, operational changes may  minimize re-
                  lease of contaminants to the atmosphere.   One
                  desirable change is  to bleed off pump casings
                  during shutdown to the fuel gas system, vapor
                  recovery facilities,  or a flare  instead of di-
                  rectly to the atmosphere.

                  Results of Study to Measure Losses From  Pumps

                  The  results of a testing program (Steigerwald,
                  1958) to establish the  magnitude of hydrocarbon
                  losses from pumps are  presented in Tables 180
                  through  183.   The data collected during the study
                  are presented in  Table 182 as a comparison of
                  the effectiveness of packing glands and mechani-
                  cal seals in preventing leakage.
      Table  180.  SCOPE AND RESULTS OF FIELD  TESTS ON PUMP SEALS (Steigerwald, 1958)

Group No. a


1
i
3
4
5
6
7
8
9
Subtotal
10
11
12
13
14
15
16
17
18
Subtotal
19
20
21
22
23
24
25
26
27
Subtotal
Totals
Total
number
of seals

76
82
66
127
266
56
163
191
150
1, 177
92
78
68
49
179
103
100
175
124
968
26
32
38
72
173
150
60
40
50
641
2, 786
Seals inspected

Number

14
13
12
21
59
16
34
35
19
223
15
9
9
0
21
18
15
26
25
138
6
5
8
13
29
17
7
7
20
112
473

% of total

18
16
18
17
22
28
21
18
13
19
16
12
13
0
12
18
15
15
20
14
23
16
21
18
17
11
12
18
40
17
17
Measured leaks

Number

2
0
0
6
3
0
13
2
2
28
5
1
0
0
12
0
6
6
2
32
1
0
0
6
1
0
4
3
0
15
75
Hydrocarbon
loss,
Ib/day
60
0
0
294
19
0
262
23
7
665
26
4
0
0
83
0
280
226
16
635
23
0
0
383
71
0
19
82
0
578
1,878
Small leaks

Number

2
2
2
7
1 3
5
6
4
2
43
2
2
3
0
5
3
4
11
0
30
3
0
3
3
7
0
2
3
1
22
95
I lydrocarbon
loss,
lb/dayb
2
I
2
7
13
5
6
4
£
43
2
2
3
0
5
3
4
1 1
0
30
3
0
3
3
7
0
2
3
1
22
95
Hydrocarbon loss
from inspected pumps,
Ib/day

62
2
2
301
32
5
268
27
9
708
28
6
3
0
88
3
284
237
16
665
26
0
3
386
78
0
21
85
1
600
1,973
  Group numbers represent a specific combination of pump type, seal type, pump operation,  and product.
  A value of 1 pound per day was assigned to a small leak on a pump seal.

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                                         Airblown Asphalt
                                            685
              Table 181.  EXTRAPOLATION OF FIELD DATA BY SAMPLING GROUPS TO
                         OBTAIN A TOTAL LOSS FIGURE (Steigerwald, 1958)
1

Group No. a


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Totals


2
Total
number
of seals

76
82
66
127
266
56
163
191
150
92
78
68
49
179
103
100
175
124
26
32
38
72
173
150
60
40
50
2,786


3
Number
of seals
inspected

14
13
12
21
59
16
34
35
19
15
9
9
0
21
18
15
26
25
6
5
8
13
29
17
7
7
20
473


4
Hydrocarbon
loss from
inspected seal,
IV, /day
62
2
2
301
32
5
268
27
9
28
6
3
--
88
3
284
237
16
26
0
3
386
78
0
21
85
1
1,973


5
Avg hydrocarbon
loss per inspected
seal, lb/dayb

4. 4
0.2
0.2
14. 4
0.6
0.3
7.9
0.8
0.5
1.8
0. 7
0.3
--
4.2
0.2
18. 8
9. 1
0.6
4.3
0
0.4
29.6
2.7
0
3.0
12. 1
0. 1
4.2


6
Total
hydrocarbon
loss, lb/dayc

335
16
13
1, 830
160
17
1,289
153
75
166
55
20
--
752
21
1,880
1, 592
74
112
0
15
2, 131
467
0
180
484
5
11,842 or
6 tons per
day
            aGroup numbers represent a specific combination of pump type, seal type, pump
             operation, and product.
             Divide hydrocarbon loss  from inspected seal, Ib/day, by number of seals inspected.
            cMultiply average hydrocarbon loss per  inspected seal,  Ib/day,  by total number of
             seals.
The slight difference between the  average losses
from mechanical seals and packed glands  during
handling of highly volatile hydrocarbons needs
further clarification.  Pumps in continuous ser-
vice show an average loss per seal of 18. 3 and
7. 9 pounds per day for packed and mechanical
seals,  respectively,  indicating that mechanical
seals are far more efficient when running con-
tinuously.  On spare or standby service the
packed seals are more effective,  losing 1. 8
pounds per day to an average  loss  of 4. 4 pounds
from mechanical seals.  Reciprocating pumps
handling light products are the worst offenders
both in incidence of  leak and magnitude of av-
erage emissions.  The largest leak encountered
in the study,  266 pounds per day,  was from a
reciprocating pump on intermittent service han-
dling liquefied petroleum gas.
            AIRBLOWN ASPHALT

Asphalt is a dark brown to black, solid or semi-
solid material found in naturally occurring de-
posits  or as a colloidal suspension in crude  oil.
Analytical methods have been used to separate
asphalt into three  component groups--asphaltenes,
resins, and oils.  A particular grade of asphalt
may be characterized  by the amounts of each
group it contains.   The asphaltene particle pro-
vides a nucleus about which the resin forms a
protective coating.  The particles are suspended

-------
686
PETROLEUM EQUIPMENT
              Table 182.  EFFECTIVENESS OF MECHANICAL AND PACKED SEALS ON
                      VARIOUS TYPES OF HYDROCARBONS (Steigerwald,  1958)
Seal type
Mechanical

Avg
Packed


Avg
Packed

Avg
Pump type
Centrifugal


Centrifugal



Reciprocating


Type
hydrocarbon
being pumped,
Ib Reid
> 26
5 to 26
0. 5 to 5
> 0. 5
> 26
5 to 26
0. 5 to 5
> 0. 5
26
5 to 26
0. 5 to 5
> 0.5
Avg hydrocarbon
loss per
inspected seal,
Ib/day
9.2
0.6
0.3
3.2
10.3
5.9
0.4
4.8
16.6
4.0
0. 1
5.4
Leak incidence
Small leaks, a
% of total
inspected
19
18
19
19
20
32
12
22
31
24
9
20
Large leaks,
% of total
inspected
21
5
4
13
37
34
4
23
42
10
0
13
      aSmall leaks lose less than 1 pound of hydrocarbon per day.
 Table 183. AVERAGE PUMP SEAL LOSSES BY
  VOLATILITY OF PRODUCT BEING PUMPED
               (Steigerwald, 1958)
Product,
Ib Reid
26
5 to 26
0. 5 to 5
Total number
of seals
reported
765
1,216
805
Number ot
seals
inspected
125
204
144
A\ ^ hyrl roc a rbon
loss per inspected
seal, Ib/day
11.1
2. 7
0. 3
in an oil that is usually paraffinic but can be
naphthenic or naptheno-aromatic.

RECOVERY OF ASPHALT FROM CRUDE OIL
Over 90 percent of all asphalt used in the United
States is recovered from crude oil (Kirk and Othmer,
1947). The method of recovery depends upon the
type of crude  oil being processed.  Practically
all types of crudes are first distilled at atmospher-
ic pressure to remove the lower  boiling materials
such as gasoline, kerosene, diesel oil, and others.
Recovery of nondistillable asphalt from selected
topped crudes may then be accomplished by vac-
uum distillation, solvent extraction, or a com-
bination  of both.

A typical vacuum distillation unit is depicted in
Figure 538.  A  unit such as this uses a heater,
preflash tower, vacuum vessel, and appurtenances
for processing topped crudes.  Distillation of topped
crude under a high vacuum removes oils and wax
as distillate products,  leaving the asphalt as a
residue.  The amount of oil distilled from the  resi-
due  asphalt controls its properties; the more oil
and  resin or oily constituents  removed by dis-
                  tillation, the harder the residual asphalt.  Resid-
                  ual asphalt can be used as paving material or it
                  can be further refined by airblowing.

                  Asphalt is also produced as  a secondary product
                  in solvent extraction processes.  As shown in
                  Figure 539, this  process-separates the asphalt
                  from  remaining constituents  of topped crudes by
                  differences in chemical types and molecular
                  weights rather than boiling points as in vacuum
                  distillation processes.   The solvent,  usually a
                  light hydrocarbon such as propane or butane, is
                  used to remove selectively a gas-oil fraction
                  from  the asphalt  residue.

                  AIRBLOWING OF ASPHALT

                  Economical removal of the gas-oil fraction from
                  topped crude, leaving an asphaltic product,  is
                  occasionally feasible only by airblowing the  crude
                  residue at elevated temperatures.  Excellent pav-
                  ing-grade asphalts are produced by this method.
                  Another important application of airblowing  is in
                  the production of high-quality specialty asphalts
                  for roofing, pipe coating, and similar uses.
                  These asphalts require  certain plastic proper-
                  ties imparted by reacting with air.

                  Airblowing is mainly a dehydrogenation process.
                  Oxygen in the air combines  with hydrogen in the
                  oil molecules to  form "water vapor.  The pro-
                  gressive loss of  hydrogen results in polymeriza-
                  tion or  condensation of the asphalt to the desired
                  consistency.  Blowing is usually carried out batch
                  wise  in horizontal  or vertical stills  equipped to
                  blanket the charge with steam, but it may also be

-------
                                            Airblown Asphalt
                                             687
                                                                         EJECTOR
     TOPPED
     CRUDE Oil
                                   PREFUSH
                                   TO»ER
                                                                                     1  VNONCONDENSABLE
                                                                                    >-f GAS TO TREATER UNIT
                                              ACCUMULATOR
                                                                VACUUM
                                                                TOWER
                                                                                          GAS OIL
                                                  GAS OIL
                                                                                          ASPHALT
                  HEATER
                             Figure 538.   Flow  diagram  of  vacuum distillation
                             unit.
done  continuously.  Vertical stills are more ef-
ficient because of longer air-asphalt contact time.
The asphalt is heated by an internal fire-tube
heater or by circulating the charge material
through a separate tubestill.  A temperature of
300°   to 400 °F is reached before the airblow-
ing cycle begins.   Air quantities used range from
5 to 20 cubic feet per minute per ton of charge
(Earth, 1958).  Little additional heat is' then
needed since the  reaction becomes  exothermic.
Figure 540 depicts the flow through a typical
batch-type unit.
THE AIR POLLUTION PROBLEM


Effluents from the asphalt airblowing stills in-
clude oxygen, nitrogen and its compounds, water
vapor,  sulfur compounds,  and hydrocarbons as
gases,  odors,  and aerosols.  Discharge of these
vapors directly to  the  atmosphere  is objectionable
from an air pollution control  standpoint.  The  dis-
agreeable odors and airborne oil particles en-
trained with the gases  result  in nuisance com-
plaints.   Disposal  methods are available that can
satisfactorily eliminate the pollution potential  of
the effluents.
 AIR POLLUTION CONTROL EQUIPMENT
Control of effluent vapors from asphalt airblow-
ing stills has been accomplished by scrubbing and
incineration, singly or in combination.   Most in-
stallations use the combination.   Potential air
pollutants can be removed from asphalt still gas-
es by scrubbing  alone.  One effective control in-
stallation in Los Angeles County uses sea water
for one-pass scrubbing of effluent gases from four
asphalt airblowing stills.  The fume scrubber is
a standard venturi-type unit.  The scrubber ef-
fluent is discharged into an enclosed oil-water
gravity-type separator for recovery of oil,  which
is reprocessed  or used as fuel.  Effluent gases
from the covered separator that  collects the
scrubber discharge are not incinerated but flow
through a steam-blanketed stack to the atmosphere.
The system, shown in Figure 541,  removes es-
sentially all potential air pollutants from the ef-
fluent stream.  A limiting factor  in the applica-
tion of this method of control is the water supply.
Since a high water -to -vapor scrubbing ratio
(100 gallons/1, 000 scf) is necessary, an econom-
ical source of water should be readily available
to supply the large volume required for one-pass
operation.

-------
                                         PETROLEUM EQUIPMENT
    PROPANE
REDUCED CRUDE
OIL
/
K10KJ
1
I-/S\_


                       DEASPHALTING
                       TOKER
OIL
STRIPPER
                                                                       HEATER
                               Figure  539.  Flow diagram of  propane  deasphaI ting
                               uni t.
                                                                                                          TO COVERED EFFLUENT
                                                                                                          HATER SEPARATOR
ASPHALT
STRIPPER
                                          STEAM
                                                                                                   OFF GAS  TO
                                                                                                   COVERED OIL-KATER
                                                                                                   SEPARATOR
                             HEATER
                                                 BLOWING STILL
                                                                          SCRUBBER        KNOCKOUT  DRUM
                   Figure 540.   Flow diagram  of  airblown asphalt manufacture  (batch process).

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                                                  Valves
                                             689
                                                              OCEAN HATER
                                                              (80 psi)
                                                              FUME
                                                              SCRUBBER
                         EXHAUST GASES
                         TO ATMOSPHERE
                                                                          STEAM
                                            KNOCKOUT
                                            DRUM
                  BLANKET

                   MIST ELIMINATOR
                                                                    COVERED SEPARATOR
                AIR BLOWN
                ASPHALT STILLS
                (BATCH OPERATION)
                                            CONOENSATE
                                            TO STORAGE
                                                                              SKIMMED OIL  EFFLUENT HATER TO
                                                                              TO STORAGE   COVERED SEPARATOR
                               Figure 541.   Flow diagram  of  scrubbing system.
Where  removal  of most of the potential air pollu-
tants is not feasible by scrubbing alone, the non-
condensables must be incinerated.   Essential to
effective  incineration is direct-flame contact
with the vapors,  a.  minimum retention time  of
0. 3 second in the combustion zone,  and mainte-
nance of a minimum  combustion chamber  tem-
perature  of 1,200°F.  Other desirable features
include turbulent mixing of vapors in the combus-
tion chamber, tangential flame entry, and ade-
quate instrumentation.  Primary condensation
of any steam or  water vapor allows  use of small-
er incinerators  and results  in fuel savings. Some
of the heat released by incineration  of the waste
gases may be recovered and used for generation
of steam.  General design features of waste
gas afterburners and boilers are discussed else-
where in  this manual.

Catalytic fume burners are not recommended
for the  disposal  of vapors from the airblowing
of asphalt because the matter entrained in the
vapors  would quickly clog the catalyst bed.
                 VALVES
TYPES OF VALVES
Valves  are employed in every phase of the  petro-
leum industry where petroleum or petroleum
product is transferred by piping from one point
to another.  There  is a great variety of valve
designs, but, generally, valves may be  classi-
fied by  their application as flow control or  pres-
sure relief.

Manual and Automatic Flow Control Valves

Manual and automatic flow control valves are
used to regulate the flow of fluids through a sys-
tem. Included under this classification are the
gate, globe, angle, plug, and other common
types of valves.  These valves are subject  to
product leakage from the valve stem as a result
of the action of vibration,  heat,  pressure,  cor-
rosion,or improper maintenance of valve stem
packing (see Figure 542).

-------
690
PETROLEUM EQUIPMENT
  GUIDE BUSHING
  SEAT RINGS
   GUIDE BUSHING
 PLUG

 BLINDHEAD
  Figure 542.  Typical valve showing various  parts
  and  potential source of hydrocarbon  emission
  from  the valve stem (Mason-NeiIan, Division of
  Worthington Corporation,  Norwood,  Mass.).
 Pressure Relief and Safety Valves

 Pressure relief and  safety valves arc used to
 prevent excessive  pressures from developing
 in process vessels and lines.   The relief valve
 designates liquid flow while the safety valve
 designates vapor or  gas  flow.  These valves
 may develop leaks because of the corrosive
 action of the product or because of failure  of the
 valve to reseat properly after blowoff.  Rup-
 ture discs arc sometimes used  in place of
 pressure relief valves.  Their use is restricted
 to equipment in batch-type processes.  The
 maintenance and operational difficulties caused
 by the inaccessibility of  many pressure relief
 valves may allow leakage to become  substantial.
THE AIR POLLUTION PROBLEM

Quantitative data as to actual extent of emissions
to the atmosphere from this  leakage are some-
what limited, but available data indicate that
emissions vary over a wide range.  Liquid leak-
age results in emissions from evaporation of liq-
uid while gas leakage results in immediate emis-
sions.   The results of a test program (Kanter et
al. , 1958) conducted to establish the magnitude
of hydrocarbon  emissions from valves are pre-
sented in Table 184.  In this program, valves in
a group of 1 1 Los Angeles County refineries
were surveyed.  Both liquid  and gaseous leaks
were measured or estimated in the survey. Leaks
were detected by visible means for liquid leaks,
and by spraying with soap solution followed by
inspection for bubble formation for gaseous leaks.
Liquid leakage rates were measured by collect-
ing liquid over a period of time.  Flow rates for
gaseous  leaks were determined by enclosing the
valve in  polyethylene bags and venting the vapor
through a wet test meter.

Apparent from Table 184 is that 70 percent of the
measurable leaks in gas service average less
than 9. 1  pounds of emissions per  day.   In liquid
service,  90 percent of the measurable leaks av-
erage less than 8. 8 pounds of emissions per day.
Consideration of remaining  data shows that the
frequency distribution  of leaks is  extremely
skewed.

An example of low leakage  rate was observed
in one  refinery where over 3, 500  valves han-
dling a wide variety of products under all con-
ditions of temperature and pressure were in-
spected.   The average leak  rate was 0. 038
pound per day per valve.

Examples of high leakage rates were found in
two refineries where all 440 valves  inspected in
gas service had an average  leak rate of 1. 6 pounds
per day per valve, and in one other  refinery "where
all 1, 335 valves inspected in liquid service had  an
average  leak  rate of 0. 32 pound per day per valve.

These  examples illustrate the wide divergence
from the average valve leak  rate that can exist
among refineries in a single area, all subject
to the same obligations to restrict their emis-
sions to  the greatest possible extent.  These re-
sults could  not be applied,  even approximately,
to refineries  in other areas where standards
may be different.

These  testing programs were also conducted on
pressure relief valves in the same oil refineries.
Trie results of this phase of the program are shown
in Table 185.  As can be seen from the  data, re-
lief valves on operational units  have a slightly
lower leak incidence but a much higher  average

-------
                                               Valves
                                            691
                    Table 184. LEAKAGE OF HYDROCARBONS FROM VALVES OF
                    REFINERIES IN LOS ANGELES COUNTY (Kanter et al. , 1958)


Total number of valves
Number of valves inspected
Small leaksa
Large leaks
Leaks measured
Total measured leakage, Ib /day
Average leak rate—large
leaks, Ib/day
Total from all large leaks,
Ib/day
Estimated total from small
leaks, lb/dayb
Total estimated leakage from
all inspected valves, Ib/day
Average leakage per inspected
valve, Ib/day
Valves in
gaseous service
31, 000
2, 258
256
118
24
218

9. 1

1, 072

26

1, 098

0.486
Valves in
liquid service
101, 000
7,263
768
79
76
670

8.8

708

77

785

0. 108
All valves

132, 000
9, 521
1, 024
197
100
888

8.9

1, 780

103

1,883

0. 198
             aSmall leaks are defined as leaks too small to be measured--those estimated to
              be less than 0. 2 pound per day.
             "Leaks  too small to be measured were estimated to have an average rate of 0. 1
              pound per day.  This is one-half the smallest measured rate.
leakage rate than valves on pressure storage ves-
sels do.  Moreover,  dual-type valves (two single
relief valves connected in parallel to ensure ef-
fective release of abnormal pressures) on pres-
sure storage vessels have a greater leak inci-
dence and a larger average leakage rate than
single-type valves  on similar service do.  For
valves on operational vessels, the average for
all  refineries was 2. 9 pounds of hydrocarbons
per day per valve.   Average losses from spe-
cific refineries, however, varied from 0 to 9. 1
pounds per day per valve.  Under diverse con-
ditions of operation and maintenance,  emissions
can vary greatly from one refinery to another.
Total Emissions From Valves

Since emissions to the  atmosphere from valves
are highly dependent upon maintenance, total
valve losses cannot be  estimated accurately.
From the testing program mentioned,  emis-
sions from valves averaged 12 percent of the
total emissions from all refineries  in  Los An-
geles County.  As of 1963,  hydrocarbon emis-
sions from valves in Los Angeles County refin-
eries are estimated at  about 11 tons per day. As
stated previously,  however, these emissions
varied greatly from one refinery to another, and
average percentage figures  should not  be  used in
predicting emissions from a given refinery.
  Table 185.  LEAKAGE OF HYDROCARBONS
    FROM PRESSURE RELIEF AND SAFETY
  VALVES OF REFINERIES IN LOS ANGELES
         COUNTY (Kanter et al. ,  1958)
Valve

group
Operational
units
Pressure
storage-
Single
Dual
Number
of valves
reported

1, 113


237
115
Number
of valves
tested

165


174
79
Hydrocarbon
emission,
Ib/day

480


56
98
aDivide hydrocarbon emissions, Ib/clay, by num
Emission per
tested valve,
lb/daya

2. 90


0. 32
1. 24
Total
emission ,
Ib/day

3,230


80
140
ber of valves tested.
Multiply number of valves reported by emission per tested valve, Ib/day.
 AIR POLLUTION CONTROL EQUIPMENT

Obviously, the controlling factor in preventing
leakage from valves  is maintenance.  An effec-
tive  schedule of inspection and preventive mainte-
nance can keep leakage at a minimum.  Minor
leaks that might not be detected by casual obser-
vation can be located and eliminated by thorough
periodic inspections.  New blind designs are
being incorporated in refinery pipeline  systems
in conjunction with flow valves  (see Figure 543).
This is done to ensure against normal leakage
that  can occur through a closed valve.
 234-767 0-77-46

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692
PETROLEUM EQUIPMENT
 Figure 543.  Bar-operated  line blind that is ideal
 for installation ahead  of  shutoff valve to ensure
 against valve leaks  and vapor emissions from valve
 stem (Hamer Oil  Tool  Co.   Catalog Sheet.,  Long
 Beach, Calif.).
 Emissions from pressure relief valves are
 sometimes controlled by manifolding to a
 vapor control device, such as described in
 Chapter 5.  Normally, these disposal systems
 are not designed exclusively to  collect vapors
 from relief valves.  The primary function of
 the system may be to collect off gases produced
 by a process unit,  or vapors released from
 storage facilities,  or those  released by depres-
 surizing equipment during shutdowns.

 Another method of control to prevent excessive
 emissions from relief valve leakage is the use  of
 a dual valve -with a shutoff interlock.  A means
 of removing and repairing a detected leaking
 valve without waiting until the equipment can be
 taken out of service  is thus  provided.  The prac-
 tice of allowing a valve with a minor leak to
 continue in service without correction until the
 operating unit is shut down for general inspection
 is common in many refineries.  This practice
 should be kept at a minimum.

 A rupture disc  is sometimes used to protect
 against relief valve leakage caused  by excessive
                 corrosion.  The disc is installed on the pressure
                 side of the relief valve.   The space between the
                 rupture disc and  relief valve seat should be pro-
                 tected from pinhole leaks that could occur in
                 the  rupture disc.  Otherwise,  an incorrect pres-
                 sure differential  could keep the rupture disc from
                 breaking at its specified pressure.  This,  in
                 turn, could keep  the relief  valve from opening,
                 and excessive pressures  could occur  in the oper-
                 ating equipment.

                 One method of ensuring against these  small leaks
                 in rupture discs is to install a pressure gage and
                 a small manually operated  purge valve in the
                 system.   The pressure gage would  easily detect
                 any pressure increases from even small leaks.
                 In the event of leaks, the vessel would be re-
                 moved  from service, and the faulty rupture  disc
                 \vould then be replaced.   A second,  but less
                 satisfactory method  from  an  air pollution con-
                 trol standpoint,  is to maintain the space at at-
                 mospheric pressure by installing a small vent
                 opening.  Any minute leaks  would then be vent-
                 ed directly to the atmosphere, a,nd  a  pressure
                 increase could not exist.

                              COOLING TOWERS

                 Cooling towers are major items  of heat-transfer
                 equipment in the petroleum and  petrochemical
                 industries.  They are designed to cool, by air,
                 the water used to cool industrial processes.
                 Cooling of the water by air  involves evapora-
                 tion of a portion  of the water into the air so that
                 the remaining water is cooled by furnishing heat
                 for this evaporation process.  This cooled water
                 is  used, in turn, in heat-exchange equipment to
                 cool other liquids and gases.

                 There  are two styles of cooling  towers—classified
                 by means of air movement. In one style,  the
                 earliest developed,  the prevailing wind is used
                 for the  required  ventilation.  It  has become  known
                 as the  natural draft or atmospheric type of  cool-
                 ing tower (see Figure 544).

                 The other type of cooling tower employs fans to
                 move the air  and is known as  a mechanical-draft
                 cooling tower (see Figure  545).  Fan location is
                 used in further classifying the tower as  a  forced-
                 or induced-draft cooling  tower.   The forced-draft
                 cooling tower has not proved very satisfactory,
                 since it has a tendency to recirculate its hot,
                 humid exhaust vapor in place  of fresh air,  and
                 its  air distribution is  poor because of the 90-degree
                 turn the air must make at high velocity (Kern,
                 1950).

                 Spray ponds,  once used extensively for cooling
                 of water, have been abandoned in favor of cool-
                 ing towers.  Spray ponds are  limited in their per-
                 formance and suffer from high water losses.

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                                             Cooling Towers
                                              693
                        Figure 544.  Natural-draft cooling tower  (Shell Oil Company,
                        Los  Angeles, Calif.).
CHARACTERISTICS OF COOLING TOWER OPERATION

Petroleum and petrochemical operations require
large quantities of water for temperature con-
trol purposes.  The water is normally circulated
by pump between the heat-exchange equipment and
the cooling tower.  The hydrocarbon stream to
be cooled can also be circulated directly through
the cooling tower.  Approximately 1,000 Btu is
required to evaporate 1 pound of water.   This
is equivalent to cooling 100  pounds of water 10°F.
Thus,  1 percent of water is lost through evapora-
tion for every 10 degrees of cooling accomplished.
Additionally,  a spray loss amounting to  no  more
than 0. 2 percent must be included for properly
designed atmospheric or mechanical-draft
towers.  Water cannot be cooled below the  wet
bulb temperature  of the air  entering the  cooling
tower.

The performance  of an individual cooling tower
is governed by the ratio of weights of air to water
and the time of contact between  the air and water.
Commercially,  the variation in  the ratio of air
to water is first obtained by maintaining the air
velocity constant at approximately 350 fpm per
square foot of active  tower area and by varying
the-water concentration (Perry, 1950).  A secon-
dary operation calls for varying the air velocity to
meet the cooling requirements .  The contact time
between water and air is a function of the time r e -
quired for the water to be discharged from distribu-
tion nozzles and fall through aseriesofgridded decks
to the tower basin.  Thus, the contact time is gov-
erned by the tower height.  If the contact time is in-
sufficient, the ratio of air to water cannot be increased
to obtain the required cooling.  A minimum cooling
tower height must be maintained . Where a wide ap-
proach (difference between the cold water tempera-
ture and the wet bulb temperature of the inlet air) of
15°   to 20 "F to the wetbulb temperature , and a
25°   to 35°F cooling range (difference between the
temperature of the hot and cold water) are required,
a relatively low cooling tower is adequate (15 to 20
feet).   Other ranges are shown in Table 186.
The  cooling performance of a tower with a set
depth of packing varies with water concentration.
Maximum contact and performance have been
found with a water concentration of 2 to 3 gallons
of water per minute per square  foot of ground
area.  The problem in designing a cooling tower
is one of determining  the proper concentration

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694
PETROLEUM EQUIPMENT
                                                         Table 186.  COOLING TOWER APPROACH
                                                                  VERSUS WATER TRAVEL
  Figure 545.  Cutaway view of a mechanical-draft
  cooling tower  (Fluor Products Company,  Inc.,
  Santa  Rosa,  Calif.).

 of water to obtain desired cooling.   A high cool-
 ing tower must be used if the  water concentration
 is less  than 1. 6 gallons per square foot.   Low
 towers  can be employed if the water concentration
 exceeds 3 gallons per square  foot.   If the  required
 water concentration is known,  the tower area can
 be found by dividing the water circulation  rate
 (gallons per minute) by the water concentration
 (gallons per minute per square foot).

 The  required tower size (Perry,  1950) is thereby
 dependent upon:  (1) cooling  range  (hot water
 minus cold water temperature); (2) approach
 (cold water minus wet bulb temperature);  (3)
 amount  of liquid to be cooled;  (4) wet bulb tem-
 perature;  (5) air velocity through cell; and  (6)
 tower height.

 Various technical articles are available by which
 a cooling tower may be  designed for a specific
 duty (Natural Gas Processors Suppliers Associa-
tion,  1957; Perry, 1950).

 THE AIR  POLLUTION PROBLEM

 Cooling towers  used in conjunction  with equip-
 ment processing hydrocarbons and  their deriva-
 tives are potential sources of air pollution be-
 cause of possible contamination of the water. The
 cooling  water may be contaminated by leaks from
 the process side of heat-exchange equipment, di-
Approach, °F
15 to 20
8 to 15
4 to 8
4a
Cooling range, °F
25 to 35
25 to 35
25 to 35
Water travel, ft
15 to 20
25 to 30
35 to 40
35 to 40
                                                       Designing cooling towers with an approach of less
                                                       than 4°F is not economical.
                rect and intentional contact -with process  streams,
                or improper process unit operation.  As  this
                water is passed over a cooling tower, volatile
                hydrocarbons and other materials accumulated
                in the water  readily evaporate into the atmosphere.
                When odorous materials  are contained in the water,
                a nuisance is easily created.

                Inhibitors or additives  used in the cooling tower
                to combat corrosion or algae growth should not
                cause any significant air pollution emissions, nor
                should the water-s oftening facilities common to
                many cooling towers be a problem.

                A survey (Bonamassa and Yee, 1957) of the oil
                refineries operating in Los Angeles County in-
                dicated hydrocarbon concentrations of approxi-
                mately  20 percent in the  cooling water of the
                c.ooling towers (see Table 187).  Cooling towers
                in which hydrocarbons  were detected were tested
                quantitatively.  Three tons of hydrocarbons per
                day were found being discharged  into the atmo-
                sphere  from these  sources.  Individually the emis-
                sions varied from 4 to 1,500 pounds per cooling
                 Table 187.  HYDROCARBON EMISSIONS FROM
                 COOLING TOWERS (Bonamassa and Yee,  1957)
Cooling
tower
1
i
3
4
5
6
7
S
9
10
1 1
12
13
14
15
16
17

Water circulation,
gpm
14, 000
3, 120
28, 000
3, 000
1, 000
14, 000
14, 000
\i, 000
IS, 000
1, 000
15, 000
10, 000
8, 000
1, SOO
700
1, 000
400

Hydrocarbon emissions,
Ib/tlay (as hexane)
1, 570
1, 400
700
616
-32
31S
2S"
23 >
10
10
S
4
Total 6, 2 3b

-------
                                        Miscellaneous Sources
                                                                                                  695
tower per day.  A  study of operating variables
failed to indicate any correlation among the emis-
sions, the size  of the tower, the water circulation
rate, or the particular duty of the tower.  Apparent-
ly the amount of hydrocarbon present in the water
depends upon the state  of maintenance of the pro-
cess equipment, particularly the heat-exchange
equipment,  condensers, and coolers through which
the water is circulated.  The quantity and type of
emissions should be determined by  observing and
testing  each tower individually.

One survey of the cooling towers in a designated
area is felt to be representative of the emissions
under existing operating conditions  and mainte-
nance practices.  The actual emission rate of any
specific tower  and the  degree of odor nuisance
vary as leaks develop,  are detected, and repaired.
Overall leakage probably remains constant in view
of the large number of potential sources that can
cause new leaks even as the  old ones are repaired.
  product.   The exhaust air is saturated with hydro-
  carbon vapors or aerosols, and,  if discharged
  directly to the atmosphere, is a source of air
  pollution.   The extent of airblowiiig operations
  and the magnitude of emissions from the equip-
  ment vary widely among refineries.  Results  of
  a survey (Kanter et  al. ,  1958) on the magnitude
  of hydrocarbon emissions  from airblowing of
 'petroleum fractions  in Los Angeles County re-
  fineries, presented  in Table 188, show emis-
  sions  of less than  1/2 ton per day.  These re-
  fineries operated a total of seven airblowing
  units with a combined capacity of 25, 000 barrels
  per day and a total airflow rate of 3, 300 cfm.
  The tabulated results do not include airblowing
  of asphalt, which has been dis cus sed-elsewhere
  in this chapter.  Emissions from airblowing for
  removal of moisture,  or for agitation of products
  may be minimized by replacing the airblowing
  equipment with mechanical agitators and incin-
  erating the exhaust vapors.
 AIR POLLUTION CONTROL EQUIPMENT

 The control of hydrocarbon discharges or of re-
 lease of odoriferous compounds at the cooling
 tower is not practical.  Instead, the  control must
 be at the point where the contaminant enters the
 cooling water.  Hence,  systems of detection of
 contamination in water, proper maintenance,
 speedy repair of leakage from process equipment
 and piping, and good housekeeping programs in.
 general are necessary to minimize the air pollu-
 tion occurring at the cooling tower.  Water that
 has been used in contact with process streams,
 as in direct-contact or barometric-type con-
 densers, should be eliminated  from the cooling
 tower if this air pollution  source is to be com-
 pletely controlled.   Greater use of fin-fan cool-
 ers can also control  the emissions indirectly by
 reducing or eliminating the volume of cooling
 water to be aerated in a cooling tower.
         MISCELLANEOUS SOURCES

A number of relatively minor sources of air pollu-
tion contribute approximately 10 percent of the
total hydrocarbon emissions to the atmosphere
from refineries (Kanter et al. ,  1958).  Six of
these sources, not discussed elsewhere in this
manual, include airblowing,  blind changing, equip-
ment turnaround,  tank cleaning,  use  of vacuum
jets,  and use of compressor engine exhausts.

AIRBLOWING

In certain refining operations, air  is  blown through
heavier petroleum fractions  (see Figure 546) for
the purpose of removing moisture or  agitating the
                 tlR SMURtTED IIIH
                 HYDROCARBONS AND HATER
             O  O   o
            ' o  o
                        o  o o 0  o
Figure 546.  Improvement of product color  by  means
of air  agitation, a source of air pollution.
 BLIND CHANGING

 Refinery operations frequently require that a
 pipeline be used for more than one product.  To
 prevent leakage and contamination of a particular
 product,  other product-connecting and product-
 feeding lines are customarily  "blinded off. "  "Blind-
 ing a line" is the term commonly used for the in-
 serting of a flat,  solid plate between two flanges

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696
PETROLEUM EQUIPMENT
of a pipe connection.  Blinds are normally used
instead of valves to isolate pipelines because a
more positive shutoff can be secured and because
of generally lower costs.  In opening,  or break-
ing,  the flanged connection to insert the blind,
spillage of product in that portion of the pipeline can
occur.  The magnitude of emissions to the atmosphere
from this spillage is a function of the vapor pressure
of the product, type of ground surface beneath the
blind,  distance to the nearest drain, and amount of
liquid  holdup in the pipeline.

    Table 188.  HYDROCARBON EMISSIONS
     FROM AIRBLOWING OPERATIONS OF
        REFINERIES IN LOS ANGELES
         COUNTY (Kanter et al. ,  1953)
Number of units
Refinery A (one unit)
Refinery B (five units)
Refinery C (one unit)
Total
Emissions ,
905
35
2
942
Ib/day


Results of a survey (Kanter et al. ,  1958) conducted
to evaluate the emissions from blind changing in
Los Angeles County refineries indicated that a
wide variation exists  in the number of pipeline
service and corresponding blind  changes and in
the amount of spillage for different refineries
of comparable size.   The average  emission from
blind changing in Los Angeles  County refineries
was calculated at 0. 1 ton per day.

Emissions  to the atmosphere from the changing
of blinds  can be  minimized by pumping out the
pipeline and then flushing the line with water be-
fore breaking the flange.  In the  case of highly
volatile hydrocarbons, a slight vacuum may be
maintained in the line.  Spillage  resulting from
blind changing can also be  minimized by use  of
"line" blinds in place of  the common "slip" blinds.
Line blinds, depicted in  Figure 547, do not re-
quire a complete break of the flange connection
during the changing operation.  These blinds use
a gear mechanism to  release the spectacle plate
without actually  breaking the line.   Combinations
of this device in conjunction with gate valves are
available to allow changing of the line blind while
the line is under pressure  from either direction.
The line blind is finding  many applications in
new process equipment where frequent changes
in services of pipelines occur.  Data compiled
during the survey (Kanter et al. ,  1958)  indicate
that slip blinds  spilled an average  of 5 gallons
per change compared with  line blind valves,
•which spilled an average of 2 gallons per change.

EQUIPMENT TURNAROUNDS

Periodic  maintenance and repair of process
equipment are essential  to refinery operations.
                    A major phase of the maintenance program is
                    the shutting down and starting up of the various
                    units,  usually called a turnaround.

                    The procedure for shutting down a unit varies
                    from refinery to refinery and between units in
                    a refinery.  In general,  shutdowns are effected
                    by first shutting off the heat  supply to the unit
                    and  circulating  the feed stock through the unit
                   Figure 547.  Typical  line blind  valve  (Hamer  Oil
                   Tool Company,  Long Beach,  Calif.).

-------
                                        Miscellaneous Sources
                                            697
as it cools.  Gas oil may be blended into the
feedstock to prevent its solidification as the
temperature  drops.  The cooled liquid is then
pumped out to storage facilities,  leaving hydro-
carbon vapors in the  unit.  The pressure of the
hydrocarbon  vapors in the unit is reduced by
evacuating the various items of equipment  to a
disposal facility such as a fuel gas system, a va-
por recovery system, aflare, orinsome cases,
to the atmosphere.  Discharging vapors to the
atmosphere is undesirable from the standpoint
of air pollution control since as much as sev-
eral thousand pounds of hydrocarbons or other
objectionable vapors  or odors can be released
during a shutdown.  The residual hydrocarbons
remaining in the unit after depressuring are
purged out with  steam,  nitrogen,  or water.  Any
purged gases should be  discharged to the afore-
mentioned disposal facilities.  Condensed  steam
and water  effluent that may be contaminated with
hydrocarbons or malodorous compounds during
purging should be handled by closed water-treat-
ing systems.

Results of a survey (Kanter  et al. , 1958) to de-
termine the magnitude of hydrocarbon emissions
from turnarounds in Los Angeles County refin-
eries showed emissions totaling a maximum of
254 tons per  year or  0. 7 ton per  day.  Sixty per-
cent of all shutdowns were found  to occur on
Sunday and Monday.  On this basis,  the 2-day
emissions totaled 3 tons or  152 tons per year.

TANK CLEANING

Storage tanks in a refinery require periodic clean-
ing and  repair.  For  this purpose, the contents of
a tank are removed and residual vapors are purged
until the tank is  considered safe for entry by main-
tenance crews.  Purging can result in  the release
of hydrocarbon or odorous material in the  form
of vapors to the  atmosphere.  These vapors should
be discharged to a  vapor recovery system  or flare.
Data obtained from the refinery survey (Kanter
et al. , 1958) were used to estimate the quantity
of hydrocarbon emis'sions to the atmosphere
from tank cleaning as follows:

1.   When the vapors in the tank were released
     to a recovery or disposal system before the
     tank was  opened for maintenance,  the emis-
     sions "were  considered negligible.

2.   When the stored liquid was transferred to
     another tank, and the emptied vessel was
     opened for maintenance without purging  to
     a recovery  or disposal system, the emis-
     sion to the atmosphere was considered to be
     equal to the weight of hydrocarbon  vapor
     occupying the total volume of the tank at the
     reported pressure.  (For floating-roof tanks,
     the minimum volume was used. )

3.   For vapor storage, when tanks were not purged
     to a recovery or disposal system,  estimates
     were made as described in item  2.

The calculated emissions, for an average of 174
tanks cleaned per year, were 1. 3 tons  of hydro-
carbons per day.

Steam cleaning of railroad tank cars  used for
transporting petroleum products can  similarly be
a source of emissions  if the injected  steam and
entrained hydrocarbons are vented directly to
the atmosphere.  Although no quantitative data
are available to determine the magnitude of these
emissions, the main objection to this type of
operation is its nuisance-causing potential. Some
measure of control of these emissions  may be
effected by condensing the effluent  steam and
vapors.  The condensate can then be  separated
into hydrocarbon  and water phases  for  recovery.
Noncondensable vapors should be incinerated.


 USE OF VACUUM JETS

 Certain relinery processes arc  conducted under
 vacuum conditions.  The most practical way to
 create  and maintain the necessary  vacuum is to
 use steam-actuated vacuum jets, singly or in
 series  (see Figure 548).  Barometric condensers
 are often used after each vacuum jet to remove
 steam and condensable hydrocarbons.

 The effluent stream from the last stage of the
 vacuum jet system should be  controlled by con-
 densing as much of the effluent as is  practical
 and incinerating the noncondensables in an after-
burner or  heater firebox.  Condensate  should be
handled by a closed treating  system for recovery
 of hydrocarbons.   The hot well that receives
water from the barometric condensers may also
 have to be enclosed and any off gases incinerated.


.USE OF  COMPRESSOR ENGINE  EXHAUSTS

 Refining operations' require the use of various
types of gas compressors.  These  machines are
 often driven by internal combustion engines that
 exhaust air contaminants  to the atmosphere.  Al-
though  these engines arc normally  fired with nat-
ural gas and operate at essentially constant loads,
 some unburned fuel passes through the engine.
Oxides of nitrogen arc also found in the exhaust
 gases as a result of nitrogen fixation in the com-
bustion cylinders.

Results  of a survey (Kanter ct al. ,  1958) con-
ducted to determine the contribution  made by
compressor engine exhausts  to overall cmis-

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698
PETROLEUM EQUIPMENT
sions from refineries are presented in  Table
189.  The composition of the hydrocarbons  shown
was generally over 90 percent methane.

In addition to the compounds listed in the table,
aldehydes and ammonia may also be present in
engine  exhausts.  Test data on these components
were, however, inconclusive.
                   Table  189.   EMISSIONS FROM COMPRESSOR
                      INTERNAL COMBUSTION ENGINES IN
                       LOS ANGELES COUNTY REFINERIES
                                (Kanter et al. ,  1958)
                   Number of compros sor engines
                   Fuel gas burnrd, mcfd
                   Exhaust gas,  scfm
                   Contaminants in exhaust gases,  ppm
                    Hyd roca rbons
                    Oxides  of nitrogen, as NO-,
    130
 10, 500
165,000

  1,240
    315
                                                                     STEAM
                                                            NONCQNOENSABLES TO
                                                            FUME INCINERATOR
                                                       WATER AND  CONDENSABLES
                               Figure 548.  Schematic drawing of a two-stage,
                               steam-actuated  vacuum jet.

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                                              CHAPTER 11

                               CHEMICAL  PROCESSING EQUIPMENT
                  RESIN KETTLES
             HARRY E. CHATFIELD
        Intermediate Air Pollution Engineer
                 VARNISH COOKERS
             HARRY E. CHATFIELD
        Intermediate Air Pollution Engineer
                 PAUL G. TALENS
        Intermediate Air Pollution Engineer
           SULFURIC ACID  MANUFACTURING
              ROBERT J. MacKNIGHT
         Assistant  Director of Engineering
   STANLEY T. CUFFE,  Air  Pollution Engineer'!
             SULFUR SCAVENGER PLANTS
      E.E.  LARSSON, Air Pollution Engineer
               GLASS  MANUFACTURE
ARTHURS. NETZLEY, Senior Air Pollution Engineer
               JOHN L.  McGINNITY
       Intermediate Air  Pollution Engineer*
                  FRIT SMELTERS
 JOHN L. SPINKS,  Senior Air Pollution Engineer
           FOOD-PROCESSING EQUIPMENT
    W. L.  POLGLASE, Air Pollution Engineer*
  H.  F. DEY,  Intermediate Air Pollution Engineer
 ROBERT T. WALSH, Senior Air Pollution Engineer*
    FISH CANNERIES AND  FISH REDUCTION PLANTS
 ROBERT T. WALSH, Senior Air Pollution Engineer •
 KARLD. LUEDTKE, Senior Air Pollution Engineer
     LEWIS K. SMITH, Air Pollution Engineer**
   WILLIAM C.  ROGERS, Air Pollution Engineer
          PHOSPHORIC ACID MANUFACTURING
            EMMET F.  SPENCER,  JR.
        Intermediate Air Pollution Engineer f
      RAY M. INGELS, Air Pollution Engineerf
        SOAPS, FATTY  ACIDS, AND GLYCERINE
            MANUFACTURING EQUIPMENT
                PAUL G.  TALENS
        Intermediate Air Pollution Engineer


         SYNTHETIC  DETERGENT SURFACTANT
            MANUFACTURING PROCESSES
                PAUL G.  TALENS
        Intermediate Air Pollution Engineer
ARTHUR B.  NETZLEY, Senior Air Pollution Engineer
      REDUCTION  OF INEDIBLE  ANIMAL MATTER
 ROBERT T. WALSH, Senior Air Pollution Engineer *
                PAUL G. TALENS
        Intermediate Air Pollution Engineer
   WILLIAM C. ROGERS, Air Pollution Engineer

                  ELECTROPLATING
            EMMET F.  SPENCER, JR.
        Intermediate Air Pollution Engineer f
  GEORGE THOMAS, Senior Air Pollution Engineer


             INSECTICIDE MANUFACTURE
   WILLIAM C.  BAILOR, Air Pollution Engineer
    JOSEPH D'IMPERIO,  Air Pollution Engineer **


         HAZARDOUS RADIOACTIVE MATERIAL
   WILLIAM C.  BAILOR, Air Pollution Engineer
           SYNTHETIC DETERGENT  PRODUCT
            MANUFACTURING EQUIPMENT
                PAUL G.  TALENS
        Intermediate Air Pollution Engineer
ARTHUR B. NETZLEY, Senior Air Pollution Engineer
           OIL AND SOLVENT RE-REFINING
    JOSEPH D'IMPERIO, Air Pollution Engineer **

                 CHEMICAL MILLING
  GEORGE THOMAS, Senior Air Pollution Engineer
  *Now with U.S. Environmental Protection Agency, Research Triangle Park,  N. C.
  fNow with FMC Corporation, 633 Third Ave. , New York, N. Y.
  ^Now with State of California Vehicle Laboratories, 434 S. San Pedro St. ,  Los Angeles,  Calif.
 **Now deceased.

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                                              CHAPTER 11

                             CHEMICAL  PROCESSING  EQUIPMENT
                RESIN  KETTLES

TYPES  OF RESINS

A resin is defined by the American Society for
Testing Materials (ASTM) as a solid or semi-
solid,  water-insoluble,  organic substance, with
little or no tendency to crystallize.  Resins are
the  basic components of plastics and are impor-
tant components of surface-coating formulations.
For both uses, growth in recent years has been
phenomenal; more than 5,  000  companies in the
United States now produce plastics.


There  are two types of resins --natural and syn-
thetic.  The  natural resins are obtained directly
from sources such as  fossil remains and tree sap.
These  include Congo,  Batu,  and East India resins
from fossils; lac from insects; and damar  and
rosin from tree sap.
 resisting qualities to cross-linked molecular
 structures.


 Phenolic Resins

 Phenolic  resins  can be made from almost any
 phenolic compound and an aldehyde.  Phenol and
 formaldehyde are  by far the most common in-
 gredients used,  but others include phenol-fur-
 fural, res or cinol-formaldehyde, and many simi-
 lar combinations.   Since a large proportion of
 phenolic-resin production goes  into the manu-
 facture of molding materials, the most desirable
 process for this manufacture will be described.
 Phenol and formaldehyde,  along with an acid
 catalyst (usually sulfuric,  hydrochloric,  or
 phosphoric acid),  are charged to a steam-
 jacketed or otherwise indirectly heated resin
 kettle that is provided with a reflux condenser
 and is capable of being operated under vacuum.
 The following formula shows the basic reaction:
Synthetic resins can be classified by physical
properties as thermoplastic or thermosetting.
Thermoplastic resins undergo no permanent
change upon heating.  They can be softened,
melted,  and molded without change in their physi-
cal properties.  Thermosetting resins, on the
other hand, can be softened,  melted, and molded,
but with  continued heating, they harden or set to
a permanent,  rigid  state and cannot be  remolded
In this section,  several synthetic resins are dis-
cussed briefly.  For each,  an example  of ingre-
dients is given and a typical manufacturing  opera-
tion is discussed.  Each basic resin type requires
many modifications both in ingredients  and  tech-
niques of synthesis  in order to satisfy proposed
uses and provide desired properties (Kirk and
Othmer, 1947; Plastics Catalog  Corporation,
1959; Shreve, 1956).  Not all of  these variations
will be discussed,  however, since not all present
individual air pollution problems.


Thermosetting resins are obtained from fusible
ingredients that  undergo condensation and poly-
merization reactions under the influence of heat,
pressure,  and a catalyst and form rigid shapes
that resist the actions  of heat and solvents.
These resins,  including phenolic,  amino, poly-
ester, and polyurethane resins,  owe their heat-
                           H2S04
       PHENOL
         OH   H
 H    H
FORMALDEHYDE
                                                              TYPICAL (INTERMEDIATE) CONDENSATION PRODUCT
Heat is applied to start the reaction,  and then
the exothermic reaction sustains itself for a
while without additional heat.  Water formed
during the reaction is totally refluxed to the
kettle.  After the reaction is complete, the upper
layer of water in the kettle is  removed by draw-
ing a vacuum on the kettle.  The warm,  dehy~
drated resin is poured onto a cooling floor or
into shallow trays and then ground to powder
after it hardens.   This powder is mixed  with
other ingredients to make the  final plastic mate-
rial.   Characteristics of the molding powder,
as well as the time and rate of reaction, depend
upon the concentration of catalyst used,  the
phenol-formaldehyde ratio used, and the reac-
tion temperature maintained.
                                                 701

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702
      CHEMICAL PROCESSING EQUIPMENT
 Amino Resins

The most important amino resins are the urea-
formaldehyde and melamine-formaldehyde resins.
The urea-formaldehyde reaction is simple:  1
mole of urea is mixed with  2 moles of formalde-
hyde as 38 percent  solution.  The mixture is
kept alkaline with ammonia pH 7.6 to 8.   The
reaction is carried out at 77°F for 2 days at
atmospheric pressure without  any reflux.

The melamine resins are made in much  the same
manner except that the reactants must be heated
to about 176 °F initially,  in  order to dissolve the
melamine.   The solution is then cooled to 77°F
for 2 days to complete the reaction.

The equipment needed for the synthesis of the
amino resins consists of kettles  for the conden-
sation reaction (usually nickel or nickel-clad
steel),  evaporators for concentrating the resin,
and some type of dryer.

The amino resins are used  as molding compounds,
adhesives,  and protective coatings, and  for treat-
ing textiles and paper.


Polyester and  Alkyd Resins

There is much confusion concerning the  mean-
ing of the two terms polyester and alkyd.  Ap-
parently, by chemical definition,  the product
obtained by the condensation reaction between
a polyhydric alcohol and a polybasic acid, whether
or not it is modified by other materials, is prop-
erly called a polyester.  All polyesters can then
be divided into three  basic classes:  Unsaturated
polyesters,  saturated polyesters,  andalkyds.

1.   Unsaturated  polyesters are formed when
     either of the reactants  (alcohol and acid)
     contains,  or both contain, a double-bonded
     pair of carbon  atoms.  The materials usu-
     ally used are glycols of ethylene, propylene,
     and butylene and Unsaturated dibasic acids
     such as maleic anhydride and fumaric acid.
     A typical reaction is  as follows:
               HC -
               HC -
                   0
 H
HC - OH
 i      	*•
HC - OH
 H
ETHYLENE GLYCOL
         MALEIC ANHYDRIDE

           8         B      H   H
        — C - C = C - C - 0 -  C - C  - 0 ---»•
              H   H          H   H
        REPRESENTATIVE SEGMENT  OF CHAIN-FORMED
                                 The resulting polyester is capable of cross-
                                 linking and is usually blended with a poly-
                                 merizable material such as styrene. Under
                                 heat or a peroxide catalyst, or both, this
                                 blend  copolymerizes into a thermosetting
                                 resin.  It has recently found extensive  use
                                 in the reinforced-plastics field where it is
                                 laminated with fibrous  glass.  It is  also
                                 molded into many forms for a variety of  uses.

                                 Saturated polyesters are made from saturated
                                 acids  and alcohols,  as  indicated by the follow-
                                 ing reaction:
     0        I  	n      H   H
                          H - 0 -  C - C - 0 -  H-
                                 H   H
TEREPHTHALIC ACID                ETHYLENE GLYCOL
                                   II   ,	v  II  	
                              - o - c  -(	)- c -IO_-_H_
                                        0
                                                        H  H
                                        II   /	y  II      "  "
                                 --- 0 - C  -{)- C -  0 - C - C ---i
                                                        H  H

                                        POLYESTER (REPEATING UNIT)
  The polyesters formed are long-chain, sat-
  urated materials not capable  of cross-linking.
  Several of these are used as plasticizers.  A
  special type made from ethylene glycol and
  terephthalic acid has  been made into fiber
  (Dacron)  and film (MylarCS}.  Still others of
  this type  with lower molecular weights are
  being used with di-isocyanates to form poly-
  urethane  resins.

  Alkyd resins differ from other polyesters
  as a result of modification by additions of
  fatty, monobasic acids. This is known as oil
  modification since the fatty acids are usu-
  ally in the form of naturally occurring oils
  such as linseed,  tung,  soya,  cottonseed, and,
  at times, fish oil.  The alkyds, thinned with
  organic solvents,  are  used predominantly in
  the protective coating  industry in varnishes,
  paints,  and  enamels.

  The most widely used  base ingredients are
  phthalic anhydride and glycerol.  Smaller
  quantities of other acids such as maleic,
  fumaric,  and others and alcohols such as
  pentaerythritol, sorbitol,  mannitol, ethylene
  glycol,  and  others are used.  These are re-
  acted with the oils already mentioned to
  form the  resin.

  The oils, as they exist naturally,  are  pre-
  dominantly in the form of triglycerides and
  do not react with the polybasic acid.   They
  are changed to the reactive monoglyceride
  by  reaction  with a portion of  the glycerol or
  other alcohol to be used.   Heat and a cata-
  lyst are needed to promote this reaction,

-------
                                                Resin Kettles
                                                                                 703
    which is known as alcoholysis.   The resin
    is then formed by reacting  this monoglyceride
    with the acid by agitation and sparging with
    inert gas until the condensation reaction prod-
    uct has reached the proper viscosity.  The
    reaction takes place in an enclosed resin ket-
    tle equipped with a condenser and usually a
    scrubber, at temperatures slightly below
    500°F.  The alcoholysis can be accomplished
    first  and  then the acid and more alcohol can
    be added  to the kettle, or all the ingredients
    can be added simultaneously.

    An example of an alcoholysis reaction followed
    by reaction of the monoglyceride formed with
    phthalic anhydride is shown in the following:
            C3 H5  (C17  H33 C00)3  +

     GLYCEROL TRIES1ER OF OLEIC ACID
        H
       HC -  OH  0
        i       n
       -HC -  0 - C  - C
       HC -  OH
        H
              C3 H5 (OH)3

               GLYCERIN
                  0
17 H33
a
0
     MONOGLYCERIDE OF OLEIC ACID   PH1HALIC ANHYDRIDE

             H   H   H      0       8
    •*	 0 - C - C - C - 0 -  C^   ^ C
             u   I   u
             H   0   H
        C,7 H33 - C = 0
       REPEATING UNIT FOR OIL-MODIFIED ALKYD
Polyurethane

The manufacture of the finished polyurethane
resin differs  from the others described in that
no heated reaction in a kettle is involved.  One
of the reactants,  however,  is a saturated poly-
ester resin, as already mentioned, or, more
recently, a polyether resin.  To form a flexible
foam product, the resin,  typically a polyether
such as polyoxypropylenetriol,  is reacted with
tolylene  diisocyanate and water in an approximate
100: 42:  3 ratio by weight, along with small quanti-
ties of an emulsifying agent, a polymerization
catalyst,  and a silicone lubricant.  The ingredi-
ents are metered to  a mixing head that deposits
the mixture onto a moving conveyor.   The resin
and tolylene diisocyanate (TDI)  polymerize and
cross-link to form the urethane resin.  The  TDI
also reacts with the water,  yielding urea and
carbon dioxide.  The evolved gas  forms a foam-
like structure.   The product forms as a contin-
uous loaf.  After room temperature curing for
about a day, the loaf can be cut into desired
sizes and shapes, depending upon required use.
                                     The flexible  foams have found wide use  in auto-
                                     mobile and furniture upholstery and in many
                                     other specialty items.

                                     By varying the ingredients and adding other blow-
                                     ing agents such as Freon  11, rigid foams with
                                     fine,  close-cell structure can be formed.  These
                                     can be formed in place by spraying techniques
                                     and are used extensively as insulating materials.

                                     Thermoplastic  Resins

                                     As already stated, thermoplastic  resins are
                                     capable of being reworked after they have been
                                     formed into  rigid  shapes.   The subdivisions in
                                     this group that are discussed here are the vinyls,
                                     styrencs, and the coal tar and petroleum base
Polyvinyl Resins

The polyvinyl resins are those having a vinyl
(CH = CH2) group.  The most important of these
are made from the polymerization of vinyl ace-
tate and vinyl chloride.  Other associated resins
arc also discussed briefly.

Vinyl acetate monomer is a clear liquid made
from  the reaction between acetylene and acetic
acid.   The monomer can be polymerized in bulk,
in solution,  or in beads or emulsion. In the bulk
reaction, only small batches can be safely han-
dled because of the almost explosive violence of
the reaction once it has been catalyzed by a small
amount of peroxide.  Probably the most common
method of preparation  is in solution.  In this
process, a  mixture of  60 volumes vinyl acetate
and 40 volumes benzene is fed to a  jacketed,
stirred resin kettle equipped "with a reflux con-
denser.  A  small amount of peroxide catalyst
is added and the mixture is heated until gentle
refluxing is  obtained.  After about 3 hours, ap-
proximately 70 percent is polymerized,  and the
run is transferred to another kettle where the
solvent and unreacted monomer are removed by
steam distillation.  The wet polymer is then
dried.  Polyvinyl acetate is used extensively in
•water-based paints,  and for adhesives,  textile
finishes, and production of polyvinyl butyral.

Vinyl chloride monomer under normal conditions
is a gas that boils  at -14°C. It is usually stored
and reacted as a liquid under pressure.   It is
made by the catalytic combination of acetylene
and hydrogen chloride  gas  or by the chlorination
of ethylene  followed by the catalytic removal of hy-
drogen chloride.  It is polymerized in a jacketed,
stirred autoclave.   Since the reaction is highly exo-
thermic and can result in local overheating and poor
quality,  it is usually carried out as a water emul-
sion to facilitate more precise control.   To ensure

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704
CHEMICAL PROCESSING EQUIPMENT
quality and a properly controlled reaction,  se\eral
additives are used.   These include an  emulsifying
agent such as soap,  a protective colloid such as glue,
a pH control such as acetic acid or other moderate-
ly weak acid (2.5 is common),  oxidation and re-
duction agents  such as ammonium persulfatc and
sodium bisulfite,  respectively,  to control the oxi-
dation-reduction atmosphere, a catalyst or initia-
tor like benzoyl peroxide, and a chain length-con-
trolling agent such as carbon tetrachloride.   The
reaction is carried  out in a completely enclosed
vessel with the pressure controlled to maintain
the unreacted vinyl  chloride in the liquid state.
As the reaction progresses,  a suspension of latex
or polymer is  formed.  This raw latex is removed
from the kettle, and the unreacted monomer is
removed by evaporation and recovered by com-
pression and condensation.

A modification of the emulsion reaction is known
as suspension  polymerization.   In this  process,
droplets of monomer are kept dispersed by rapid
agitation in a water solution of sodium sulfate or
in a  colloidal suspension such as gelatin in water.
During the reaction, the  droplets  of monomer are
converted to beads of polymer that are easily re-
covered and  cleaned.  This process is  more
troublesome and exacting than the emulsion reac-
tion  but eliminates the contaminating effects of
the emulsifying agent and other  additives.

Other vinyl-type resins are polyvinylidene chloride
(Saran®9,  polytetrafluoroethylene (fluoroethene),
polyvinyl  alcohol, polyvinyl butyral, and others.
The  first  two of these are made by controlled poly-
merization of the monomers  in a manner similar to
that  previously described for polyvinyl chloride.
Polyvinyl alcohol has no existing monomer and
is prepared from polyvinyl acetate by hydrolysis.
Polyvinyl alcohol is unique among resins in that
it is completely soluble in both hot and cold water.
Polyvinyl butyral is made by the condensation
reaction of butyraldehyde and polyvinyl alcohol.
All have specific properties that make them super-
ior for  certain applications.
 Polystyrene

Polystyrene,  discovered in 1831, is one of the
oldest resins  known.  Because of its transparent,
glasslike properties,  its practical application
was recognized even then.   Two  major obstacles
prevented its  commercial development--prepara-
tion of styrene monomer itself, and some means
of preventing  premature polymerization.  These
obstacles were  not overcome until nearly 100
years later.

Styrene is a colorless liquid that boils at 145°C.
It is prepared commercially from ethylbenzene,
which, .in turn,  is made by reaction of benzene
                      with ethylene in presence of a Kridel-Crafts cata-
                      lyst such as aluminum chloride.   During storage
                      or  shipment the styrene  must contain a polymeriza-
                      tion inhibitor such as hydroqumone and must be
                      kept under a protective atmosphere of nitrogen
                      or  natural gas.

                      Styrene  can be polymerized in bulk,  emulsion,
                      or  suspension by using techniques similar to
                      those previously described.  The reaction is
                      exothermic and has a runaway tendency unless
                      the temperature is carefully controlled.   Oxygen
                      must be excluded from the reaction since it causes
                      a yellowing of the product and affects the  rate of
                      polymerization.

                      Polystyrene is used in tremendous quantities for
                      many purposes.  Because of its ease  of handling,
                      dimensional stability,  and unlimited color possi-
                      bilities, it is used widely for toys,  novelties,
                      toilet articles, houseware parts,  radio and tele-
                      vision parts, wall tile, and other products.  Dis-
                      advantages  include limited heat resistance, brit-
                      tleness, and vulnerability to attack by organic
                      solvents such  as kerosine and carbon tetrachloride.


                      Petroleum and Coal Tar  Resins

                      Petroleum and coal tar resins  are the least ex-
                      pensive  of the synthetic resins.  They are made
                      from the polymerization of unsaturated hydrocarbons
                      found in crude distillate  from coal tar in coke ovens
                      or  from cracking of petroleum.  The  exact chemical
                      nature of these hydrocarbons has  not been deter-
                      mined,  but  the unsaturates  of coal tar origin are
                      known to be primarily cyclic while petroleum deriva-
                      tives are both straight- and close-chain types.

                      Most typical of the coal tar resins are those
                      called Coumarone -Indene resin because these
                      two compounds constitute a large  portion  of the
                      distillate used for the reaction.  The polymeriza-
                      tion is initiated by a  catalyst (usually sulfuric
                      acid).  After the reaction has proceeded as far as
                      is desired,  the unreacted monomer is  removed
                      by distillation.  By controlling time, temperature,
                      and proportions, many modifications of color and
                      physical characteristics  can be produced.  The
                      petroleum base distillate is polymerized in the
                      same manner, yielding resins  of  slightly lower
                      specific  gravity than that of the coal tar resins.
                      These resins are used in coating  adhesives,  in
                      oleoresinous varnishes,  and in floor coverings
                      (the so-called asphalt tile).


                      RESIN-MANUFACTURING EQUIPMENT

                      Most resins  are polymerized or otherwise reacted
                      in a stainless steel,  jacketed,  indirectly heated
                      vessel, which is completely enclosed,  equipped

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                                            Resin Kettles
                                            705
with a stirring mechanism,  and generally contains
an integral reflux condenser (Figure 549).  Since
most of the  reactions previously described are
exothermic,  cooling coils are usually required.
Some resins, such as the phenolics,  require
that the kettle be under vacuum during part of
the cycle.  This can be supplied either by a vac-
uum pump or by a steam or water jet ejector.
Moreover, for some  reactions,  that of polyvinyl
chloride for  example, the vessel must be capable
of being operated under pressure.  This is nec-
essary to keep the normally gaseous  monomer in
a liquid state.  The size  of resin-processing  ket-
tles varies from a few hundred to  several thou-
sand gallons' capacity.

Because of the many types of raw  materials,
ranging from gases to solids, storage facilities
vary accordingly--ethylene ,  a gas,  is handled
as  such; vinyl chloride, a gas at standard condi-
tions, is liquefied easily under pressure.  It  is
stored, therefore,  as a liquid in a pressurized
vessel.  Most of the  other liquid monomers do
   Figure  549.  Typical resin-manufacturing unit
   showing process kettle and liquid feed tanks
   (Silmar Chemical Company,  Hawthorne,  Calif.).
not present any particular storage problems.
Some, such as styrene, must be stored under an
inert atmosphere to prevent premature poly-
merization.  Some of the  more volatile mate-
rials are stored in cooled tanks to prevent ex-
cessive vapor loss.  Some of the materials have
strong odors, and care must be taken to prevent
emission of ociors to the atmosphere.   Solids,
such as phthalic anhydride, are usually packaged
and  stored in bags or fiber drums.

Treatment of the resin after polymerization varies
with the  proposed use.  Resins for  moldings are
dried and crushed or ground into molding  powder.
Resins,  such as the alkyd resins, to be used for
protective coatings are normally transferred to
an agitated thinning tank,  as shown in Figure 550,
where they arc  thinned with some type of solvent
and then stored in large steel  tanks  equipped
\vith water-cooled condensers to prevent loss  of
solvent to the atmosphere (Figure 551). Still
other resins are stored in latex form  as they
come from the kettle.

THE  AIR  POLLUTION PROBLEM

The  major sources of possible air contamination
in resin manufacturing are the emissions of raw
materials or monomer to  the atmosphere,  emis-
sions of  solvent or other volatile liquids during
the reaction, emissions of sublimed solids such
as phthalic anhydride in alkyd production,  emis-
sions of  solvents during thinning  of some resins,
and emissions of solvents  during storage and
handling  of thinned resins. Table 190  lists the
most probable types and sources of air contami-
nants from various resin-manufacturing opera-
tions.

In the formulation of polyurethane foam, a slight
excess of tolylene diisocyanate is usually added.
Some of this  is vaporized  and  emitted  along
with carbon dioxide during the reaction. The
TDI  fumes are extremely  irritating to the  eyes
and respiratory system and are a. source of local
air pollution.  Since the vapor pressure of TDI
is small,  the fumes are minute in quantity and,
if exhausted from the immediate  work area and
discharged to the outside atmosphere,  are soon
diluted to a nondetectible  concentration. No
specific controls have been needed to prevent
emission of TDI fumes to  the atmosphere.

The finished  solid resin represents a very small
problem--chiefly some dust from crushing and
grinding  operations for molding powders.  Gen-
erally the material is pneumatically conveyed
from the grinder or pulverizer through a cyclone
separator to  a storage  hopper.  The fines  escap-
ing the cyclone outlet are  collected  by a baghouse-
type dust collector.   The  collector should  be de-
signed for a filter velocity of about  4 fpm or less.

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706
CHEMICAL PROCESSING EQUIPMENT
    Figure 550. Resin-thinning  tanks with water-cooled  condensers (Allied Chemical  Corp.
    Lynnwood,  Calif.).
                                                       Plastics  Div.
 Figure 551.  Resin  storage tanks with condensers
 (Allied  Chemical Corp., Plastics Division,  Lynn-
 wood,  Calif.).
                      Most of the contaminants are readily condensable.
                      In addition to these, however, small quantities
                      of noncondensable, odorous  gases similar to those
                      from varnish cooking may be emitted.  These are
                      more prevalent in the manufacture of oil-modi-
                      fied alkyds where a drying oil such as tung, lin-
                      seed, or soya is reacted with glycerin and phtha-
                      lic anhydride.  When a  drying oil is  heated,
                      acrolein and other  odorous  materials are emitted
                      at temperatures exceeding about  350 °F (see
                      further  discussion  under Varnish Cookers).  The
                      intensity of these emissions is directly propor-
                      tional to maximum reaction  temperatures.  Thus,
                      the intensity of noncondensable gases from resin
                      formulation should be considerably less than
                      that of gases from  varnish cooking since the  re-
                      action temperature is approximately 100°F lower.

                      AIR POLLUTION CONTROL  EQUIPMENT

                      Control of monomer and volatile solvent emis-
                      sions  during storage before  the reaction  and of

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                                             Resin Kettles
                                                                                                   707
           Table 190.  PRINCIPAL AIR CONTAMINANTS AND SOURCES OF EMISSION FROM
                               RESIN-MANUFACTURING  OPERATIONS
                  Resin
     Air contaminant
       Possible  sources
          of emission
           Phenolic


           Amino

           Polyester and alkyds



           Polyvinyl acetate
           Polyvinyl chloride
           Polystyrene


           Petroleum and coal
           tar resins
           Polyurethane resins
Aldehyde odor
Aldehyde odor

Oil-cooking odors
Phthalic anhydride fumes
Solvent
Vinyl acetate  odor
Solvent
Vinyl chloride odor

Styrene odor

Monomer odors


Tolylene diisocyanate
Storage, leaks, condenser outlet,
vacuum pump discharge

Storage, leaks

Uncontrolled resin kettle discharge
Kettle or condenser discharge


Storage, condenser outlet during
reaction, condenser outlet during
steam distillation to recover sol-
vent and unreacted monomer

Leaks in pressurized  system

Leaks in storage and reaction
equipment
Leaks in storage and reaction
equipment

Emission from finished foam result-
ing from excess TDI in formulation
solvent emissions  during thinning and storage
after the polymerization of the resin is relatively
simple.  It involves care in maintaining gastight
containers for gases or liquefied gases stored
under pressure, and condensers or cooling coils
on other vessels handling liquids that might vapor-
ize.  Since most resins are thinned at elevated
temperatures near the boiling point of the thinner,
resin-thinning tanks,  especially,  require ade-
quate condensers.  Aside from the necessity  for
control of  air pollution, these steps are needed
to prevent the loss of valuable products.

Heated tanks used  for storage of liquid phthalic
and maleic anhydrides should be equipped with
condensation devices to prevent losses of sub-
limed material.  An excellent device is a water-
jacketed,  vertical  condenser with provisions  for
admitting steam to the jacket and provisions  for
a pressure relief valve at the condenser  outlet
set at perhaps 4 ounces' pressure.  During stor-
age the tank is kept under a slight pressure of
about 2 ounces, an inert gas  making the tank
completely closed.  During filling, the displaced
gas, with any sublimed phthalic anhydride, is forced
through the cooled  condenser where the phthalic is
deposited on the condenser walls.  After  filling is
completed, the  condensed phthalic is remelted by
passing steam through the condenser jacket.

Addition of solids such as phthalic anhydride  to
other ingredients that are above the sublimation
temperature of the phthalic anhydride  causes
                       temporary emissions that violate most air pollu-
                       tion standards regarding opacity of smoke  or
                       fumes.  These emissions subside somewhat as
                       soon as the solid is completely dissolved but re-
                       main in evidence at a reduced opacity until the
                       reaction has been completed.  The emissions
                       can be controlled fairly easily with simple scrub-
                       bing devices.  Various types of  scrubbers  can
                       be  used.  A  common system that has been  proved
                       effective  consists of a settling chamber,  com-
                       monly called a resin slop tank,  followed by an
                       exhaust stack equipped with -water sprays.  The
                       spray system should provide for at least 2 gallons
                       per 1, 000 scf at a velocity of  5 fps.   The settling
                       chamber  can consist of an enclosed vessel par-
                       tially filled with water capable of being circulated
                       with gas connections from the reaction vessel and
                       to the exhaust stack.  Some solids and water of
                       reaction are collected in the settling  tank,  the
                       remainder being knocked down by the water sprays
                       in the stack.  Another example is shown in Fig-
                       ure 552.  Here the vapors from a polyester resin
                       process kettle are first passed through a spray
                       chamber-type precleaner followed by a venturi
                       scrubber. This  system effectively reduces visi-
                       ble emissions.  Scrubber water  may  be recircu-
                       lated or used on a once-through basis, depend-
                       ing primarily upon the available waste-water dis-
                       posal system.  The scrubber water can be  odor-
                       ous and should be discharged to a sanitary sewer.

                       Many resin polymerization reactions, for example,
                       polyvinyl  acetate  by the  solution method,  require
 234-767 O - 77 - 47

-------
 708
CHEMICAL PROCESSING EQUIPMENT
 Figure  552.  Venturi scrubber venting resin-man-
 ufacturing  equipment (Silmar Chemical  Corporation,
 Hawthorne,  Calif.).

refluxing of ingredients during the reaction.  Thus,
all reactors  for this or other reactions involving
the vaporization of portions of the reactor con-
tents must be equipped with suitable reflux-  or
horizontal-type condensers or a combination of
both.  The only problems involved here are prop-
er sizing of the condensers and maintaining the
cooling  medium at the temperature necessary  to
effect complete condensation.

When noncondensable,  odor-bearing gases are
emitted during the reaction, especially with  alkyd
resin production as already mentioned, and these
gases are in sufficient  concentration to create
a public nuisance,  more extensive air pollution
control  equipment  is necessary.  Such equipment
is discussed thoroughly under other sections con-
cerning odors  (Varnish Cookers and Reduction of
Inedible Animal Matter) and includes equipment
for absorption and chemical oxidation,  adsorption,
and combustion, both catalytic and direct-flame
type.
                                 VARNISH  COOKERS

                      INTRODUCTION

                     Varnish cooking processes discussed in this sec-
                     tion include both the heated processes used to
                     modify  natural or synthetic oils or resins  which
                     will be  the film-forming vehicles in inks or
                     coatings (i.e., varnish, paint, enamel,  lacquer)
                     and those processes completely synthesizing
                     1 ilm-forming  vehicles.  The effect of the various
                     processes is to shorten the drying time and im-
                     prove the qualities of  chemicals which would,
                     without  modification,  dry  and  form a film.  Some
                     varnish cooking processes will involve  the manu-
                     lacture  of a resin simultaneously with the  modi-
                     fication oi the drying  oils  and  in the same  equip-
                     ment.

                     Varnish cooking,  until the 1930's, involved only
                     two basic processes:  heat processing of natural
                     oils to purify  them or improve their drying time
                     for use  in coatings and manufacture of oleoresin-
                     ous varnish by heat processing the natural oils
                     with natural resins.   Since that time  synthetic
                     resins and synthetic film-forming compounds
                     have greatly expanded the number of  heating
                     processes employed.  Many new coatings do not
                     use the  film-forming  products of varnish cooking.
                     As  a result, the products  of varnish cooking con-
                     stitute a much lower percentage of all coating
                     materials than they did a decade ago. Neverthe-
                     less, varnish cooking products still are exten-
                     sively produced for use in the manufacture of
                     surface coatings.

                     DEFINITIONS - PRODUCTS AND PROCESSES

                     Table 191 lists the various oils that are processed
                     in varnish cooking equipment and the resins,  both
                     natural  and synthetic, most  frequently used in the
                     manufacture of the film-forming materials.  Var-
                     nish cooking operations are  varied.   All opera-
                     tions of this type, however,  involve the applica-
                     tion of heat to these materials  and their resultant
                     polymerization, depolymerization, melting,
                     esterification, isomerization,  etc.  Some  of the
                     most common processes are defined  below.

                     Boiled Oil.  Linseed oil, soybean  oil or other
                     natural  oils heated with small percentages of
                     oxides,  acetates,  or other salts of lead, manga-
                     nese, or cobalt are known as boiled oils.   During
                     the process, the oil thickens,  its density in-
                     creases,  and  its color darkens, principally due
                     to polymerization but  also to some oxidation.
                     When catalysts, certain metal oxides, activated
                     nickel,  or sulfur dioxide are added, isomeriza-
                     tion,  or conjugation,  occurs.   This process is
                     performed to  accelerate the normal drying time
                     of the oil.  While  oil so treated is known as

-------
                                           Varnish Cookers
                                             709
 Table 191.  VARNISH COOKING INGREDIENTS
                 (Shreve,  1967)

"Oils
   Linseed oil
   Tung oil
   Dehydrated castor  oil
   Castor oil
   Fish oils
   Tall oils
   Soya oil
   Cottonseed oil
   Coconut oil

Natural resins
   Shellac, insect secretion
   Rosin
   East India
   Manila
   Kauri,  old fossil resin
   Copal,  fossil  resin
   Dammar,  recent fossil resin

Synthetic resins
   Phenol-aldehyde  (oil-soluble)
   Alkyd resins
   Mannitol esters
   Pentaerythritol esters and interesters
   Limed  rosin
   Ester gum
   Cumarone-indene
   Melamine and urea-formaldehyde
   Chlorinated  rubber and diphenyl
   Acrylates
   Vinyl resins
   Silicone s
   Depolymerized copals
   Epoxies
   Polyurethanes

boiled oil, the oil actually is heated only to tem-
peratures of 360° to 580°F, which are below the
boiling point.

Heat-Bodied Oil. Linseed and other natural oils,
including nut, vegetable, and marine  oils,  heated
to temperatures from 485° to 6ZO°F are known as
heat-bodied oils. The viscosity of the oil,  or its
"body,"  is increased; the amount  of increase de-
pends upon the kind of oil and the  time and tem-
perature  levels to which the oils are heated.
Bodying is done  principally for oils to be used in
enamels and printing  inks and results mainly from
polymerization,  although some oxidation also
takes place.

Blown Oil.  Linseed oil and other natural oils may
also be bodied by bubbling  air through them and,
in this case, are known as blown oils.  The reac-
tion is mainly oxidation; however,  some polymeri-
zation of  the oxidized molecules also  occurs.
During the blowing process,  the oil is heated to
temperatures of 212 ° to 390 °F.
Estenfication.   The reaction of an organic  acid
(or acid anhydride) with an alcohol is known as
esterification.  In varnish cooking,  copolymer
oils, such as soybean oil-maleic anhydride, are
esterified with  glycerol  or other polyhydric alco-
hols, or the vegetable oil may first be alcoholized
and  then treated with the anhydride.   These opera-
tions produce good drying  oils from  less desirable
ones by increasing the double bond structures of
the molecules.   Polymeric esters, good synthetic
film-forming materials, are prepared by esteri-
fication of glycerol, fatty acids, and phthalic
anhydride.   These processes are performed in
closed  vessels  at moderate temperatures.

Spirit Varnish.  Most spirit varnishes do not
involve varnish cooking, but are mostly solutions
of resins and volatile solvents mixed at room
temperature.  However, one spirit varnish, gloss
oil,  does involve varnish cooking. Resins are
cooked  at moderate to high temperatures with
slaked  lime, and the  hot calcium resinate product
is thinned with  petroleum spirits.

Oleoresinous Varnish.   These varnishes are manu-
factured by heating various combinations of natu-
ral oils with various  synthetic or natural resins
to high  temperatures, 520 ° to 650 °F.   The final
product is thinned with solvent,  and  drying  agents
are  added after thinning.

Oil Breaking.   Linseed oil, or other natural oils,
contain some unsapomfiable matter,  usually 1 to
2 percent.  Those oils to be used in  coatings
without any other treatment will be cleared  of
most of this unsaponifiable material  by the  "break-
ing" process.  If the  oils were allowed to age,
this  material would eventually separate and, along
with other foreign matter,  would settle as foots.
Heating the oil to about 450 °F accelerates this
separation and the oil is said to  "break. "

Gum Running.   Some  natural resins,   such as
kauri gum, are insoluble in oil.  In order to use
them, they first are heated to temperatures of
570  ° to 700 °F.  Then they are mixed with  heated
oils  to produce  the desired varnish product.  This
high temperature process, called gum running,
serves  to depolymerize the resin.

MAJOR  TYPES OF VARNISH COOKING EQUIPMENT
Varnish cooking processes are conducted in two
types of vessels--the open-topped portable kettle
and the newer,  totally enclosed,  stationary kettle.

The open kettles are cylindrical vessels  with
dished or flat bottoms.  They usually are trans-
ported on a three- or four-wheel truck, and are
heated over an open flame.  This type of kettle
usually varies in capacity from 185 to 375  gallons

-------
710
CHEMICAL PROCESSING EQUIPMENT
and is  made  of steel,  copper,  monel,  aluminum,
nickel,  or stainless steel.  Under most operating
conditions, the kettle  is charged  in a loading
room and then moved  to the fire pit.  It is heated
over the fire pit and then, when the  reaction is
complete,  transferred to another location for
cooling.  When the contents have cooled to the
proper temperature,  the kettle may be trans-
ferred to a third location for the  addition of  thin-
ners and dryers or for transfer of its contents to
a thinning tank.  In the past,  it was  common to
manually agitate the contents during cooking.
Materials in open kettles now are seldom agitated
manually.  Agitation is provided  by  air-driven or
electrically driven mixers and by sparging the
contents with an inert gas, such as  carbon dioxide
or nitrogen.   Figure 553 shows a kettle of this
type.  The open kettle still is  employed extensive-
ly in paint manufacturing establishments.

The  enclosed stationary kettles are  indirectly
heated or cooled by jacketing or by  coils.  The
kettles are vertical cylinders  with dished  tops
and dished bottoms.   They are constructed of an
appropriate grade  of stainless steel to resist cor-
rosion.  Some kettles are glass lined.  An electri-
cally driven  agitator is mounted on  the kettle.
Batch  weighing or  metering equipment, pumps,
and piping for the charging of liquid raw materi-
als are installed with the kettle.   The kettles are
equipped with scalable openings through which
solid or liquid materials can be charged manually.
Inert gas is  sparged into the bottom so as to per-
meate the entire contents of the kettle.  For some
types of production,  condensers for reflux or
vapor  recovery are installed on the  kettle.
Figure 553.  uncontrolled  open kettle for varnish
            cooking.
                      Thinning for viscosity adjustment, or the addi-
                      tion of dryers  or unreacted monomers,  usually
                      is not done in the reaction kettle.  Instead,  the
                      contents are pumped to other vessels designed
                      for these purposes.  These second vessels, or
                      thinning vessels,  also are closed and equipped
                      with agitators.  Jackets  or  coils for  indirect
                      heating or cooling,  and nozzles for sparging
                      with inert  gas  are  installed.  The thinning ves-
                      sels are equipped with water-cooled  vent con-
                      densers mounted so that condensed solvent -will
                      drain back into the  vessel.  The closed  station-
                      ary kettles are almost exclusively found at chemi-
                      cal companies engaged in manufacturing a wide
                      variety of  paint bases.
                       THE AIR POLLUTION  PROBLEM

                       Varnish cooking processes in  both open and closed
                       kettles are carried out at temperatures ranging
                       from 200  ° to 650 °F or higher.  At times, rapid
                       cooling of the cook is necessary to  control the
                       reaction or to control the composition of a parti-
                       cular product.  At approximately 350 °F,  almost
                       all of the  solid or liquid materials begin to voli-
                       tilize and  emit vapors or gases from the vessel.
                       As long as the ingredients are held at or above
                       this temperature, the emissions continue.  Some
                       varnish cooking operations require 3 to 10 hours
                       or longer. The quantity, composition,  and rate
                       of emissions depend upon ingredients in the cook,
                       maximum temperature levels, method of  intro-
                       ducing additives, degree of stirring, cooking time,
                       and extent of air or inert gas  blowing (Stenburg,
                       1953).  Total emissions for oleoresinous  varnish
                       cooking can be as high as  6 to 12 percent  by
                       weight of  the materials in the  kettle, and  those
                       from oil cooking and bio-wing,  4 to  6 percent by
                       weight.

                       Cooker emissions vary in composition, depending
                       upon the ingredients in the  cook.  Mattiello (1943)
                       states that compounds emitted from cooking of
                       oleoresinous varnish include -water vapor, fatty
                       acids, glycerine,  acrolein,  phenols, aldehydes,
                       ketones, terpene oils, terpenes,  and carbon diox-
                       ide.  Heat-bodying of oils causes the emission of
                       these same compounds less the phenols, terpene
                       oils, and  terpenes.  Gum running yields water
                       vapor,  fatty acids, terpenes,  terpene oils, and
                       tar.  Besides the air contaminants  listed  by Mat-
                       tiello,  some  highly offensive sulfur  compounds
                       such as hydrogen sulfide,  allylsulfide,  butyl mer-
                       captan, and thiophene are formed when tall oil is
                       esterified with glycerine and pentaerythritol.
                       These compounds are emitted as a  result of small
                       amounts of sulfur in the tall oil.  Attempts to
                       alleviate this problem involve further refining of
                       the tall oil to remove as much sulfur as possible.

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                                          Varnish Cookers
                                            711
Of all the compounds emitted, acrolein is the one
most generally associated with oil cooking because
of its pungent, disagreeable odor and irritating
characteristics.  Some of the more odorous com-
pounds have very low odor thresholds; acrolein,
for example,  has a threshold at 1. 8 ppm and some
of the sulfur compounds have a threshold at about
0. 001 ppm.

A good portion of the emissions from these opera-
tions are in the form of noncondensibles,  insoluble
gases or vapors, or condensible vapors which
tend to form submicron size droplets. Emissions
in the form of particulate  matter have been found,
upon examination under the microscope,  to be in
a size range between 2 and 20 microns in diame-
ter.  The median size of several samples varied
from 8 to 10 microns.

An important source of emissions is the thinning
of varnish with solvent.  In most of the newer
stationary enclosed kettle installations, the
cooked varnish is pumped from the reaction kettle
to a thinning tank that  is equipped with an  integral-
ly mounted condenser.   In the older portable open-
kettle operations,  however,  the thinning operation
is carried out near the boiling point of the  solvent,
and emissions of vapor can be considerable.   Con-
sequently, the thinning tank can be hooded  and the
vapors can be ducted to the same control system
that removes  the fumes  from the cooker.   While
emission of solvents from the thinning tanks con-
stitutes a greater potential for formation of photo-
chemical smog than emissions from the varnish
cooker,  emissions from varnish cookers cause
greater local  nuisance problems because of nox-
ious odors.  Both operations  result in the emis-
sion of visible dense white plumes.

HOODING AND  VENTILATION REQUIREMENTS

For air pollution control to succeed,  all fumes
emitted from  the kettles and thinning  vessels
must be  captured and conveyed to a control device
under all operating conditions without hindering
production.

Stationary closed kettle  emission volumes  are
entirely  dependent upon the type of operation per-
formed,  whether the kettle is sealed shut,  oper-
ated under partial vacuum, or merely vented with-
out sealing so that air may be drawn into it and
over its  contents.   Air volumes necessary to  ex-
haust open portable kettles are considerably
reduced with properly designed close-fitting hoods.
Sufficient air  must continuously be swept through
the open kettles so as  to prevent the build up of
explosive concentrations of the volatiles above
the surface of the liquids within the kettle and in
the exhaust ductwork.

Figure 554 shows two  open kettles in  place over
two open furnaces.  The kettles are equipped with
well designed removable hoods.   The hoods are
provided with openings for the manual addition of
materials, for thermometers, and for agitators.
The openings have hinged covers  so that they can
be kept closed  except when being  used.

Indraft velocities of at least 100 to 150 fpm should
be provided through the face of all the openings
when the largest covered area is  open to prevent
the escape of contaminants  from the kettle during
charging or observation.  Good hood design pro-
vides the necessary indraft velocities when gas
volumes of 100 to 300  cfm are exhausted from the
kettle.  Because the volatiles coming from a kettle
condense on the hood,  the hoods for open kettles
should be  provided with an outer trough to  collect
the condensed liquids which will appear on the
hood surfaces.  This trough should have provi-
sions for drainage, usually to a small container.
In the past, exhaust ductwork was  sized for velo-
cities of 1500 to 2000 fpm.  Currently, ductwork
frequently is designed for higher velocities, usual-
ly 3000 to  3500 fpm.  Higher velocities help reduce
the rate of deposition of condensed vapors  on the
duct walls. An exhaust gas blower in the exhaust
system is  necessary -when venting  open kettles.
A blower  also is  required for closed kettles oper-
ated at atmospheric conditions rather than under
pressure  or vacuum.  When the air pollution con-
trol system includes an afterburner, reliance upon
the natural draft  generated by its stack can be
hazardous. Positive ventilation should be  pro-
vided to keep the vapor composition above  the
kettle below explosive limits and to maintain suf-
ficient velocity in the exhaust system and at the
entrance to the afterburner to prevent flashback.

When the  exhaust system includes  an afterburner,
the best placement of the exhaust blower is down-
stream from the  afterburner.  If it is installed in
front of the afterburner, serious maintenance and
operating problems occur because deposits quickly
build on the fan blades,  resulting in unbalanced
operation. With  the blower on the discharge side
of the afterburner, blower blades remain clean
and in balance.  Exhaust gases  are cooled  by dilu-
tion with ambient air before entering the blower
to a temperature of about 500 °F.  Blowers of
standard construction are  available for operation
at this temperature.

The exhaust ductwork is subject to severe  corro-
sion and to heavy fouling.  Use  of appropriate
corrosion-resistant material  such as stainless
steel will overcome most corrosion problems.
Fouling problems require  that the  ductwork con-
tain a number of sealed clean-out openings for
access to the interior and  that a regular  cleaning
schedule be maintained.

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 712
                                 CHEMICAL PROCESSING EQUIPMENT
            Figure 554-  Open  varnish-cooking kettles  with  exhaust hoods (Standard  Brand Paints
            Company,  Torrance,  Calif.).
Fouling has been reduced greatly or completely
eliminated in  some recent installations where the
air pollution control device is  an afterburner.  In
these installations, concentric type ductwork,
with the outer duct insulated, has been used.  A
portion of the  hot exhaust gas from the afterburn-
er, after dilution to temperatures  in the  range of
500°  to 600 °F, is blown into  the annular space
between the inner  and outer duct.  The hot gas in
the annular space  heats the  internal duct carry-
ing the contaminated  effluent from the kettles.
The heated gases pass countercurrent to flow in
the interior duct.   The temperature of the wall of
the duct carrying the contaminated effluent is
raised, and condensation on the  ductwork is
limited.  Condensation usually is restricted to
low-viscosity  liquids which may be carried along
in the exhaust gas stream.   The concentric duct-
work is usually used  only for the main section.
Where dibasic acids, especially phthalic anhy-
dride,  are employed  in the cooking operation,
the concentric ductwork is extended to the ex-
haust port  on  each kettle.  Figure  555 illustrates
one such exhaust system.  Experience for 3 years
with this system has  demonstrated that cleaning
of the duct has not been necessary.  However,
some provision for draining fluids from the duct
should be included.  In the installation illustrated,
the downcomer duct to the afterburner is  equipped
with a well for fluid accumulation.   The well has
a removable cover, and it is cleaned after each
week of operation.
The  cost of installing the concentric ductwork and
its insulation adds approximately 150 percent to
the cost of single  ductwork.   However,  the reduc-
tion  of maintenance, the reduction of fire hazards,
and the elimination of deposits  inside the duct
make the additional capital expenditure worthwhile.

AIR  POLLUTION  CONTROL EQUIPMENT

All operations in -which varnish or paint base is
cooked or in which drying oils are bodied or other-
wise prepared by  the application of heat should be
vented to air pollution control devices.   From 1
to 5  percent or more of the total material charged
to a  kettle  for these processes  otherwise is emit-
ted to the atmosphere  during operation.   The
material emitted includes the odorous irritating
compounds previously mentioned.  In addition to
odors, the  emissions contain considerable parti -
culate matter and frequently form a  highly visible
plume.  The  control devices applicable to varnish
cooking are the  same as those used for controlling
other sources of organic vapors,  particulates,
odors, and visible emissions, with some modifi-
cations to meet  those situations unique to the var-
nish cooking  operations.

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                                                 Varnish Cookers
                                                                                                                  713
       STACK
EXHAUST
BLOWER
                                AFTERBURNER
                                                                                              STACK GAS
                                                                                              TO AT1YIOS
                                                                                              PHERE-
                                                                                  INSULATED
                                                                                  EXTERIOR DUCT -;
                                                                             EXHAUST DUCT
                                                                             INSIDE-
                                                                                HOOD
                                                                    CONTAMINATED
                                                                    EXHAUST DUCT
                                                                    TO AFTERBURNER
     GAS BURNER

CLEAN-OUT
WELL ON
EXHAUST DUCT
                                                                                     STACK GAS
                                                                                   ,' TO
                                                                                  '  ATWOSP.HE-RE-
                                                                                                   OPEN KETTLE
    Figure 555.  Varnish-cooking control system using heated concentric  ductwork and an afterburner  (Old  Quaker
    Paint Co., Torrance,  California).

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714
CHEMICAL PROCESSING EQUIPMENT
Scrubbers

Scrubbers,  in the past,  were the only devices
installed to control emissions from varnish cook-
ing.   The inherent hazard of fire or explosion pre-
vented serious consideration of afterburners. As
the control of air pollution became more critical,
direct-fired  afterburners were chosen to comply
with the more stringent regulations.   For some
processes, however,  scrubbers still are adequate
for controlling emissions of condensibles and are
less costly to install and operate than afterburners.
Sampling  results  (test 20,  Table 192) for a spray
scrubber  venting  a closed vessel producing alkyd
modified varnish, illustrated in Figure 556,  indi-
cated that emissions from certain processes can
                      be controlled sufficiently to meet stringent emis-
                      sion limitations.

                      Many existing scrubbers have been left in place
                      when afterburners were installed to serve as  con-
                      densers and to provide  flashback protection before
                      the contaminated  emissions enter the afterburner.
                      The various types of scrubbers which have been
                      used include simple spray towers,  sieve plate
                      towers, chambers or columns with  series of baf-
                      fles and water curtains, agitated tanks, and -water
                      venturi jets.   Scrubbers employing spray nozzles
                      have suffered  from a major disadvantage.  The
                      excessive maintenance  required to  keep the noz-
                      zles free from clogging or to replace the nozzles
                      because of erosion by recirculated  scrubbing
      Table 192.  SUMMARY OF RESULTS OF STACK DISCHARGE TESTS, VARNISH COOKING
                        CONTROLLED BY  AFTERBURNERS AND SCRUBBERS
Item
Process
Material processed
Kettle types
Total process time, hr
Process time of test,
hr
Temperature of
material. °F
Stage of process
Exhaust volume, scfm
Temperature of
exhaust. °F
Particulate loading ,a
gr/scf
Rate of participates, Ib/hr
Organic acids, gr/scf
Aldehyde s -ketonee, ppm
Hydrocarbon a, ppm
Air pollution control
equipment
Afterburner temperature,
°F
Particulate emissions,
gr/scf
Ib/hr
Organic acids, gr/scf
Efficiency1"
Particulates. %
Organic acids, %
Aldehydes -ketones, %
Hydrocarbons, %
Test No. 3

2. Oleoresin varnish

Two - closed
COg atmos.
6 to 8
5th
1. 460 to 520
2. 560 to 583
Heating to
maximum temperature
Total, 950
106
0.64
5.20
0. 174
67
103
3 spray towers
Vertical afterburner
1200 to 1240
0.028
0.31
0.066
94
48
73
99-f
Test No. 5
Alkyd resin varnish
Two kettles
Glycerine - fatty acids
Pentaerythritol
Phthalic anhydride
Closed, gas fired
N£ atmos .
8 to 9
8th 6th
450 to 415 480 to 245
End Phthahc
heating addition
380
98
4.7S
15.5
2.81
61
29
Heat body-
ing oil
Linseed
oil
Open
2
1st
480 to 570
Heating to
maximum
temperature
940
147
0.48
3.87
0. 181
36 j
11 \
Single spray in duct
Vertical afterburner
1240 to 1410
0. 028
0.53
None
97.3
99.9 +
99.9+ t
Test No. 16
Phenolic resin varnish
Linseed oil
Phenolic resin
Two, open
Final } cook, 7 cooling
410 to 500
Heating to maximum
temperature and
cooling
370d
118
0.093
0. 30
-
860e
370d
119
0.30
0.95
-
1709e
Horizontal afterburner
1 1 80 to
1210
0. 0045
0.089
73
85
1240 to
1310
0. 0039
0.074
93
94
Test No. 20
Alkyd resin varnish
Soy, chinawood oils
Glycerine
Phthalic anhydride
Closed
N£ atmos. ,
light vacuum
14
5th
425 to 325
Major
phthalic
add.
260f
90
-
-

1 spray
in stack
0.21
0.15
8th
430
Minor
phthalic
add.
170
-
-

2 sprays
in stack
0.75
0.082
  *See Rule Z, in appendix.
   Basis - reduction of total weight.
   Accuracy limited to 10 ppm.
   Dilution air included.
   Analytic of combustible gas«a by CCIR method. Total ppm.
   With one and two ate am jets in stack.

-------
                                          Varnish Cookers
                                            715
                   STEAM
STEAM
     KETTLE
                                          WATER

                                          WATER
(F
GAS BURNER
                                         SEWER
 Figure 556. Diagram of a spray scrubber venting oleoresin
 manufacturing equipment.
fluids has  resulted in every scrubber of this type
being taken out of service.  Packed scrubbers
have not been used in these operations because
the condensed fumes rapidly plug the packing.

The scrubbers employed in these systems usually
are  designed -with the flow of the contaminated gas
stream countercurrent to that  of the scrubbing
medium.   Generally,  water is the scrubbing
medium, and is not recirculated.  Attempts have
been made to use acids,  bases, various oils,  and
solvents as scrubbing materials,  but these scrub-
bing solutions have not resulted in an increase in
efficiency  that  would warrant their higher costs.
Wetting agents have been added to scrubbing water,
and  in some special circumstances have resulted
in increased collection efficiency.

Condensers

Condensers have been used both to conserve sol-
vent and to control visible emissions  during the
thinning operation.  Varnish is thinned by the  slow
addition of the hot varnish to cold solvent or vice
versa.  Maximum solvent vaporization occurs
during the  initial contact between the  solvent and
hot varnish.  Condensers must be designed to
control the higher rate of emissions  during the
initial contact.  When thinning vessels are vented
directly to the atmosphere, loss of solvent,  in the
form of a dense white plume, is considerable. A
condenser, usually a water-cooled shell-and-tube
type, is mounted on the top of  the thinning vessel
vertically or at an angle  so that the condensed sol-
vent can drain back into the vessel.

At one installation, a water-cooled shell-and-tube
condenser  having 52 square feet of transfer  area
and using copper tubes was mounted  on  a 350-gal-
lon batch thinning tank.   The condenser prevented
visible emissions when 125 gallons of solvent was
added to 195 gallons of varnish at  340 °F.   The
initial solvent flow rate was 7j gallons per minute
for 3^ minutes; and the final flow rate was 12 gal-
lons per minute over an additional 14-minute
period.

Gas flow velocity from the condenser should be
kept below 1000 fpm to minimize entrainment of
condensate droplets.   An entrainment separator
should be installed on the discharge  side of the
condenser.   The separator retains liquid particu-
lates released  during the initial high-volume surge
of solvent vapors,  which occurs when cold solvent
and hot varnish first  contact each  other.  Details
on designing vapor condensers  are given in Chap-
ter 5 of this  manual.
Afterburners

Incineration of the effluent from varnish cooking
processes has proved to be the most effective con-
trol method and one relatively free of major main-
tenance problems.  Incineration has been effective
for both open  portable kettles and closed station-
ary kettles.  A direct-fired afterburner designed
with appropriate parameters can reduce inlet odor
concentration  by 99 percent or more, and can
oxidize 90 percent or more of the carbon in con-
taminated effluent to carbon dioxide.  Figures 555
and 557 show  two types of afterburners used to
vent open kettle installations.  Table 192 summar-
izes results of stack tests conducted on direct-
fired afterburners.

In Los Angeles County, afterburners controlling
emissions from varnish cookers have been pre-
dominantly of the direct-fired type.  Catalytic
afterburners,  however,  are known to have been
installed to control emissions from varnish cook-
ers in  other areas  of the  United  States.   Although
a few catalytic units have been installed in the past
in Los Angeles County, they have since been re-
placed with direct-fired afterburners.

One of the two most important design requirements
for direct-fired afterburners is  the capacity to
operate at outlet temperatures of 1200° to 1400  °F
under all  conditions.  When afterburner tempera-
tures fall below 1200 °F, odor reduction is  inade-
quate and combustion efficiency  for particulate
matter and organic gases and vapors falls below
90 percent on a carbon basis.  The second impor-
tant design requirement is the provision for direct
flame contact -with all vapors  and gases emitted
from the varnish cookers.  Tests of afterburners,
where  direct flame contact of all the emissions
did not occur,  even with outlet temperatures of
1400 °F and retention times greater than 0. 3
second, have  revealed that combustion efficiencies
for carbon have fallen well below 90 percent.

-------
 716
CHEMICAL PROCESSING EQUIPMENT
 Figure 557.  Direct-fired vertical afterburner (Great
 Western Paint Co.,  a  division of Western Wood
 Preserving Co.,  Los Angeles, Calif.).

A serious concern in venting varnish cookers and
similar process equipment to an afterburner is
the danger of flashback and fire.  Where scrubbing
equipment is used in the exhaust system prior to
entry to the afterburner,  this danger is usually
overcome.  Newer installations of afterburners
on this type of  equipment have not used a scrubber
upstream from the afterburner.  A  short section
of ductwork just prior to the entrance of the after-
burner is designed so that the  gases and vapors
passing into this section are at a velocity consi-
derably greater than the flame propagation rate
of the effluent gases in the reverse  direction.
Generally, flame propagation rates are 1 8 to 20
fps, but the ductwork is designed for gas veloci-
ties of about 50 fps.

If there are considerable  deposits inside the duct
at the entrance to  the afterburner, these deposits
will start to burn after a lengthy afterburner oper-
ation.  Fire control  dampers,  when employed in
the exhaust  system ductwork,  require  constant
maintenance and inspection if they are  to be effec-
tive.  Several fires  and explosions have been
                                                     traced to failure of,  or  slow operation of,  these
                                                     devices.

                                                     Heat-recovery equipment should be seriously con-
                                                     sidered -when an afterburner is used to control
                                                     emissions.  Heat exchangers can be installed so
                                                     that the hot exhaust gases from  the afterburner
                                                     are  cooled to below 600 °F by transferring waste
                                                     heat to either Dowtherm,  water (steam), or  other
                                                     heat-transfer media. The recovered heat then
                                                     can be used in jacketed  or coil-equipped kettles
                                                     or in other plant process  equipment.  At a recent
                                                     installation,  a waste heat boiler utilizing the heat
                                                     of the afterburner exhaust reduced fuel costs by
                                                     supplying process steam in  the plant.  The payout
                                                     time for the  waste heat  boiler is expected to be
                                                     2 to 4 years.
                          SULFURIC  ACID  MANUFACTURING

                      Sulfuric acid is used as  a basic raw material
                      in an extremely wide range of industrial pro-
                      cesses  and manufacturing operations.  Because
                      of its widespread usage,  sulfuric acid plants are
                      scattered throughout the nation near every indus-
                      trial complex.

                      Basically, the production of sulfuric acid involves
                      the generation of sulfur dioxide (802),  its oxida-
                      tion to sulfur trioxide (SO,),  and the hydration of
                      the SO-j to form sulfuric acid.  The two main pro-
                      cesses  are the chamber process and the contact
                      process.   The chamber process uses the reduc-
                      tion of nitrogen dioxide to nitric oxide  as the oxi-
                      dizing mechanism to convert  the SO2 to SO^. The
                      contact process, using a catalyst to oxidize the
                      SO  to SO , is the  more modern and the more
                      commonly encountered.   For these reasons fur-
                      ther discussion will be restricted to the  contact
                      process of sulfuric acid manufacture.
                     CONTACT PROCESS

                     A flow diagram of a "Type S" (sulfur-burning,
                     hot-gas purification type) contact sulfuric acid
                     plant is shown in Figure 558.  Combustion air is
                     drawn through a silencer,  or a filter when the air
                     is  dust laden, by either a single-stage  centrif-
                     ugal blower or a positive-pressure-type blower.
                     Since the blower is located on the upstream side,
                     the entire plant is under a slight pressure, vary-
                     ing from 1.5 to 3.0 psig.  The combustion air
                     is  passed through a drying tower before it enters
                     the sulfur burner.  In the drying tower, moisture
                     is  removed from the  air by countercurrent scrub-
                     bing with 98 to 99 percent  sulfuric acid at tem-
                     peratures from 90°   to 120 °F.  The drying tower
                     has a topside  internal-spray eliminator located
                     just below the air outlet to minimize acid mist
                     carryover to the sulfur burner.

-------
                                     Sulfuric Acid Manufacturing
                                                                                         717
                              FILTERED MR
                                                                                                 STACK
         ACID ^
               DRYING
               TO«ER
              MOLTEN
              SULFUR
SULFUR
BURNER




BOILER
1

                                                                              ABSORBING
                                                                              TO»ER
                                                                                               H;SO,
                                                                                     «E»K IMPURE ACID
                             Figure 558.  Flow diagram  of  a  typical " Type S"
                             sulfur-burning contact  sulfunc acid plant.
Molten sulfur is pumped to the burner where it
is burned with the dried  combustion air to form
SO-).   Normally a gas containing approximately
9 percent SC>2  is produced in a Type S plant.  The
combustion gases together with excess air leave
the burner at about  1, 600°F and are cooled to
approximately 800°F in a water tube-type waste-
heat boiler.  The combustion gases then pass
through a hot-gas filter into the first stage  or
"pass" of the catalytic converter at between
750° and 800°F to begin the  oxidation of the  SO2
to SOi
If the molten sulfur feed has been fil-
tered at the start of the process, the hot-gas
filter may be omitted.   Because the conversion
reaction is exothermic, the gas mixture from-
the first stage of the converter is cooled in a
smaller -waste-heat boiler.  Gas  cooling after
the second and third converter stages is achieved
by steam superheaters.  Gas leaving the fourth
stage of the converter is partially cooled to ap-
proximately  450°F in an economizer.  Further
cooling takes place in the gas  duct before the
gas enters the absorber.  The extent of  cooling
required depends largely upon -whether or  not
oleum is to be produced.  The total  equivalent
conversion from SC>2 to SO^ in the four con-
version stages is about 98 percent.  Table 193
shows typical temperatures and conversions
at each stage of the four-stage converter.  These
figures vary somewhat with variations in gas
composition,  operating rate, and  catalyst  con-
dition.

The cooled 803 combustion gas mixture enters
the lower  section of the absorbing tower, -which
is similar to the drying tower.  The SOj is ab-
sorbed in a circulating stream of 99 percent
sulfuric acid.  The nonabsorbed tail gases pass
overhead through mist  removal equipment to
the exit gas stack (Duecker and West, 1959).

A contact process plant intended mainly for use
with various  concentrations of hydrogen sulfide
(H2S) as a feed material is known as a wet-gas
                                              Table 193.  TEMPERATURES AND CONVERSIONS
                                              IN EACH STAGE OF A FOUR-STAGE CONVERTER
                                              FOR A  "TYPE S" SULFUR-BURNING CONTACT
                                                          SULFURIC ACID PLANT
Location of gas
Entering 1st pass
Leaving 1st pass
Entering 2d pass
Leaving 2d pass
Entering 3d pass
Leaving 3d pass
Entering 4th pass
Leaving 4th pass
Total rise
Tempe
°C
410
601. 8
191.8
438
485. 3
47.3
412
443
11
427
430. 3
3.3
253. 4
ratures ,
°F
770
1, 115
345
820
906
86
810
830
20
800
806
6
457
Equivalent
conversion, %
74. 0
18. 4
4. 3
1. 3
98.0
                                             plant, as shown in  Figure 559.   The wet-gas
                                             plant's combustion furnace is also used for burn-
                                             ing sulfur or dissociating spent sulfuric acid.  A
                                             common procedure  for wet-gas plants located near
                                             petroleum refineries is to burn simultaneously
                                             H2S, molten sulfur, and spent sulfuric acid from
                                             the alkylation processes at the refineries.  In
                                             some instances  a plant of this type may produce
                                             sulfuric acid by using only  H->S or spent acid.

                                             In  a wet-gas plant,  the f^S gas, saturated with
                                             •water vapor, is  charged to the combustion fur-
                                             nace along with  atmospheric air.   The SO2
                                             formed, together with the other combustion
                                             products,  is then cooled and treated for mist
                                             removal.  Gas may be cooled by a waste-heat
                                             boiler or by a. quench tower followed by Karbate
                                             and updraft  coolers.  Mist  formed is  removed

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718
                               CHEMICAL PROCESSING EQUIPMENT
                                                                             ABSORBER
                                                                                         STACK
                                                                                    HCIO TO STORAGE
                  Figure 559.  Flow diagram of a contact-type  wet-gas sulfunc acid plant.
by an electrical precipitator.  Moisture is re-
moved from the SO2 and airstream with con-
centrated sulfuric acid in a drying tower.  A
centrifugal blower takes suction on the drying
tower and discharges the dried SO2 and air to
the converters.  The balance of the -wet-gas pro-
cess is essentially the  same as that of the pre-
viously discussed sulfur-burning  process.


THE AIR POLLUTION PROBLEM

The only significant source of air contaminant
discharge from a contact sulfuric acid plant
is the tail gas discharge from the SO3 absorber.
While these tail gases consist primarily of in-
nocuous nitrogen, oxygen, and some  carbon di-
oxide, they also contain small concentrations
of SOg and smaller amounts of 803 and sulfuric
acid mist.  Table 194 shows the SO2  and  SOj
discharged  from two wet-gas sulfuric plant ab-
sorbers.

A well-designed contact process  sulfuric acid
plant operates at 90 to 95 percent conversion of
the sulfur feed into product sulfuric acid.   Thus
a 250-ton-per-day plant can discharge 1. 25 to 2. 5
tons of SO2 and SOj per day.  When present in
sufficient concentration,  SO2 is irritating to
throat and nasal passages and injurious to vege-
  Table 194.  SULFUR TRIOXIDE AND SULFUR
DIOXIDE EMISSIONS FROM TWO ABSORBERS IN
        CONTACT SULFURIC ACID PLANTS

Gas flow rate,
scfm
Sulfur trioxide,
gr/scf
% by vol as SO2
Ib/hr
Sulfur dioxide,
gr/scf
% by vol
Ib/hr
Outlet of
absorber No. 1

9, 600

0. 033
0. 002
2. 73

2.63
0.22
216
Outlet of
absorber No. 2

7, 200

0. 39

2. 4

2. 45

151. 2
  tation.  SO2 concentrations greater than 0.25 ppm
  cause injury to plants on long exposure.  The
  permissible limit for humans for prolonged ex-
  posure is  10 ppm.

  Tail gases that contain  SOj, owing to incomplete
  absorption in the absorber stack, hydrate and
  form a finely divided mist upon contact with at-
  mospheric moisture. According to Fairlie
  (1936) the process temperature of gas  going to
  the absorber should be  on the lower side of a
  temperature range  between 150°  and  230 °C.

-------
                                      Sulfuric Acid Manufacturing
                                            719
 The optimum acid concentration in the absorb-
 ing tower is 98. 5 percent.  This concentration
 has the lowest SO-j vapor pressure.  The partial
 pressure of 803 increases if the absorbing acid
 is too strong,  and 803 passes out with the tail
 gases. If a concentration of absorbing acid
 less than 98. 5 percent is used,  the beta phase
 of SOj, which is less easily absorbed, is pro-
 duced. A mist may also form when the pro-
 cess  gases are cooled before  final absorption,
 as in the manufacture of oleum.

 Water-based mists can form  as a result of the
 presence of water vapor in  the process gases  fed
 to the converter.  This condition is often caused
 by poor performance of  the drying tower.   Effi-
 cient  performance should result in a moisture
 loading of 5 milligrams  or  less per cubic  foot.
 In sulfur-burning  plants, mists may be formed
 from  water resulting from  the combustion of
 hydrocarbon impurities  in the sulfur.  Mists
 formed in the -wet-purification systems of an
 acid  sludge regeneration plant are not complete-
 ly removed by electrostatic precipitation.  The
 mists pass through the drying tower and are
 volatilized in the converter.  The mist reforms,
 however,  when the gases are cooled in the ab-
 sorption tower.  Water-based mists can also  form
 from  any  steam or water leaks  into the system.

 The 803 mist presents the most difficult prob-
 lem of air pollution control  since it is generally
 of the  smallest particle size.  The particle size
 of these acid mists ranges from submicron to
 10 microns and larger.   Acid  mist composed of
 particles  of less than 10  microns in size is visible
 in the  absorber tail gases if present in amounts
 greater than 1 milligram of sulfuric acid per
 cubic foot of gas.  As the particle size decreases,
 the plume becomes more dense because of the
 greater light-scattering  effect of the  smaller
 particles.   Maximum light scattering occurs
 •when  the particle size approximates the wave
 length of light.  Thus,  the predominant factor
 in the  visibility of  an acid plant's plume is
 particle size of the acid mists rather than the
 weight of mist discharged.  Acid particles larg-
 er than 10 microns are probably present as a
 result of mechanical entrainment.  These larg-
 er particles deposit readily on duct and stack
 walls and contribute little to the opacity of the
 plume.

As stated  previously,  even with  a well designed
 conventional contact H2SC>4 unit,  the tail gas emit-
ted to the  atmosphere contains considerable SOo;
concentrations can be as  high  as 2000 ppm.  In
recent years, the intensified emphasis  on air
quality standards has dictated that emissions of
sulfur  compounds from t^SC^ plants  be greatly
reduced.  This  can be accomplished by two meth-
ods,  both utilizing  basic  technology that has been
known for some years.  One method involves
"double or total absorption. "  In this process SC>2
is reacted to SO?  in a three-pass catalytic con-
verter, and the SOo is absorbed in an interpass
H^SO^ absorption tower.  The gases  from this
tower, still containing unreacted SC^, are then
recycled to another single-pass catalytic conver-
ter, and then  to a final absorber.   This process
has been developed by Monsanto Enviro Chem in
this country and by Lurgi,  Chemiebau, and
others in Europe.

The other method consists  of a tail gas unit added
to the end of a conventional acid plant.  One  such
unit,  known as AMMSOX and developed by Mon-
santo Enviro Chem, absorbs the SO-, in the tail gas
in an  aqueous ammonium sulfite-bisulfite solution.
The absorbing liquid is then treated and the SO£
stripped and returned to the H->SO.| plant.  Other
similar processes exist.

By such  applications,  SO2 concentration in tail
gases vented to the atmosphere can be reduced to
less than 500  ppm, and total plant efficiency for
sulfur recovery can be increased to greater  than
99 percent.


AIR POLLUTION CONTROL  EQUIPMENT

Sulfur Dioxide Removal

Water scrubbing of the SOj absorber tail gases
can remove 50 to  75 percent of the  SO£ content.
Scrubbing towers  using 3-inch or larger stacked
rings  or red-wood  slats are often employed.  On
startups, when SO^ concentrations  are large,
soda ash solution  is usually used in place of
straight water. Water scrubbing is feasible where
disposal of the acidic  waste water does not present
a problem.

Tail gases may be scrubbed "with soda ash solution
to produce marketable sodium bisulfite.  A cyclic
process using  sodium sulfite-bisulfite has  also
been reported.  Steam regeneration costs in the
cyclic process are, however,  relatively high, and
the capacity of the scrubbing solution is limited
by the low solubility of sodium bisulfite.  The
dilute scrubber solution has, moreover, little
economic value.

The most -widely known process for removal of
SO2 from a  gas stream is scrubbing with am-
monia solution. It was developed by Consolidated
Mining and Smelting Company and installed at its
Trail, British Columbia, plant (Duecker and West,
1959).  Single- and two-stage absorber systems
reportedly reduce SO2 concentrations in tail gases
to 0. 08 and  0. 03 percent respectively.  Two-
stage  systems are designed to handle SO2 gas
concentrations as  great as  0. 9 percent.  Large

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 720
CHEMICAL PROCESSING EQUIPMENT
SO;? concentrations resulting from acid plant
startups and upsets could be handled adequate-
ly by a system such as this.

Acid Mist Removal

Electrical precipitators

Electrical precipitators are widely used for re-
moval of sulfuric acid mist from the cold  SCs
gas stream of wet-purification systems.   The
wet-lead-tube type  is used extensively in this
service.

Tube-type precipitators have also been used for
treating tail gases from 803 absorber towers.
More recently,  however,  two-stage, plate-type
precipitators have been used successfully.  One
such unit, lead lined throughout to prevent corro-
sion, is designed to handle approximately 20, 000
cfm tail gas from a 300-ton-per-day contact
sulfuric acid plant.  This wet-gas plant process-
es  H^S,  sulfur, and spent alkylation acid.  Dry
gas containing SO2, carbon dioxide,  oxygen,
nitrogen, and 5 to 10  milligrams of acid mist
per cubic foot enters  two inlet  ducts  to the pre-
cipitator.  The gas flows upward through dis-
tribution tiles to the humidifying section.   This
section contains  5 feet of 3-inch single-spiral
tile irrigated by 800 gpm weak sulfuric acid.
The conditioned gas then flows to the ionizing
section, which consists of about 75 grounded
curtain electrodes and 100 electrode wire ex-
tensions.

Ionized gas then flows to the precipitator section
where charged acid particles migrate to the col-
lector plate  electrodes.  There are twelve 14-
by  14-foot lead plates and 375 electrode wires.
The negative wire voltage is 75, 000.  Acid mi-
grating to the plates flows  down through the pre-
cipitator and is collected in the humidifying sec-
tion.  The gas from the precipitator section flows
to a 5-foot-diameter, lead-lined stack that dis-
charges to the atmosphere 150 feet above  grade.

The high-voltage electrode wires  are suspended
vertically by three sets of insulators.  Horizontal
motion is eliminated by four diagonally placed in-
sulators, which  are isolated from  the gas stream
by  oil seals.  All structural material in contact
with the acid mist is lead clad. Electrical wires
are stainless steel cores with lead cladding.  Volt-
age is supplied from a generator with a maximum
capacity of 30 kilovolt-amperes.  A battery of
silicon rectifiers supplies 75, 000 volts of direct
current to the electrode wires.

Table 195 shows the sulfur trioxide and sulfur
dioxide emissions from the previously described
two-stage electrical precipitator.  The acid mist
collection efficiency was only 93 percent.   A
                        Table  195.  SULFUR  TRIOXIDE AND SULFUR
                        DIOXIDE EMISSIONS FROM A TWO-STAGE
                          ELECTRICAL PRECIPITATOR SERVING
                            A CONTACT SULFURIC ACID PLANT

Gas flow rate, scfm
Gas temperature, °F
Average gas velocity, fps
Collection efficiency, a %
Moisture in gas, %
CO^, % (stack conditions)
O^, %(stack conditions)
CO, % (stack conditions)
N^, % (stack conditions)
Sulfur trioxide,
gr/scf
Ib/hr
% by volume
Sulfur dioxide,
gr/scf
Ib/hr
% by volume
Inlet of
precipitator
13, 400
160
36. 5

0.8
5. 9
9.6
0
83.4

0. 062
7. 1
0. 0042

4. 1
470
0. 345
Outlet of
precipitator
13,100
80
20. 6
93
4. 1
6
8.4
0
81.2

0. 0048
0. 54
0. 00032

4. 1
460
0. 345b
                       aA mechanical rectifier was supplying only 36, 000
                        volts to the precipitator.  During normal  operation,
                        silicon rectifiers supply 75, 000 volts to the  electrode
                        wires. This should increase the acid mist collection
                        efficiency appreciably.
                        Rule 53. 1 for "scavenger plants" is applicable to
                        this plant rather than Rule 53a, which limits emis-
                        sions  of SO;> to 0. 2 percent by volume.  This plant
                        recovers SO£ that would otherwise be emitted to the
                        atmosphere.

                       mechanical rectifier was, however, supplying
                       only 36, 000 volts  to the precipitator during this
                       test.  During normal operation,  silicon rectifiers
                       supply 75, 000 volts  to  the electrode wires.


                       Packed-bed separators

                       Packed-bed separators employ sand, coke, or
                       glass or metal fibers to intercept acid mist par-
                       ticles.   The packing also causes the particles to
                       coalesce by reason of high turbulence in the small
                       spaces between  packing.  Moderate-sized particles
                       of mist have been  effectively removed in  a 12-inch -
                       deep bed of 1-inch Berl saddles with gas  veloc-
                       ities of approximately 10 fps.

                       Glass fiber filters have not been  very effective
                       in mist removal because  of a tendency  on the
                       part of the fiber to sag and mat.  Nevertheless,
                       experimental reports by Fairs (1958) on acid
                       mist removal by silicone-treated glass wool are
                       encouraging.  A special fine-glass wool with a
                       fiber diameter bet-ween 5 and 30 microns  -was
                       used.   The coarser fibers allowed adequate pene-
                       tration of the bed  by the mist particles  to ensure
                       a reasonable long  life and provided sufficient
                       support for the finer fibers in their trapping of
                       the  small  acid mist particles.

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                                      Sulfuric Acid Manufacturing
                                                                     721
The glass wool 'was treated by compressing it
into a filter 2 inches thick to a density of 10
pounds per cubic foot.  It was then placed in
a sheet metal container and heated at 500 "C
for 1 hour.  By this treatment, the stresses
in the compressed fibers were relieved,  and
the fiber mass could be removed from the mold
without losing  shape or compression.  The
fibers were then treated with a solution of meth-
yl chlorosilane.

The threshold  concentration for mist visibility
after scrubbing has been found experimentally
by Fairs (1958) to be about 3. 6 x  10~4 gram
SOj per cubic  foot.   The discharge gases from
the silicone-treated filter had an SO, concen-
tration of 1.8 to 2.5 x 10"4 gram  per cubic
foot and no appreciable acid mist plume.   A
faint plume became perceptible at approximate-
ly weekly intervals but was eliminated by flush-
ing the filter bed with water.  The average tail
gas-filtering rate for the treated filter was
15. 6 cfm per square foot of filtering  area for
a pressure drop of 9-1/2 to 10 inches water
column.  According to Fairs, the  effective
life  of the silicone fiber should be at  least
5, 000 hours.   Garnetted terylene -was also
used but was not as efficient  as silicone-treated
glass wool.  It should,  however,  prove ade-
quate for less  stringent duties.  Its life should
be long  since it does not require silicone pre-
treatment.  The use of untreated glass wool
fiber proved unsatisfactory in reducing the
opacity of the acid mist plume.

Table 196 shows the SC>2  and acid mist emis-
sions from the outlet of a typical silicone-
treated, glass  fiber mist eliminator.   This
control unit processes  absorber discharge gas
from a contact sulfuric acid plant.  The acid
mist collection efficiency for the fiber glass
mist eliminator -was  98. 9 percent.  A success-
ful application  of a. mist eliminator using treat-
                        ed fiber (Figure 560) has been made by the
                        Monsanto Chemical Company (Brink,  1959).  The
                        exact treatment given to the  fiber is not available
                        since it is the property of the inventor, J. A.
                        Brink,  Jr.
                                            RETAINER PLATE
                       SUPPORT
                       PLATE
                                  SUPPORT PLATE
                                   WIRE  MESH —
                                  FIBER PACKING
     &
                                     -BRINK
                                      ELEMENT
                         Figure  560.  Brink  fiber mist eliminator (Brink,
                         1959).
                                                       Wire mesh mist eliminators
 Table 196.  EMISSIONS OF SULFUR DIOXIDE
   AND ACID MIST FROM THE OUTLET OF
 A SILICONE-TREATED,  GLASS FIBER MIST
     ELIMINATOR SERVING A CONTACT
           SULFURIC ACID PLANT





Concentration, gr/scf
Concentration, ppm
Weight, Ib/hr
Mist
eliminator
inlet
Acid
mist
0. 30
200
45

Mist eliminator outlet

Acid
mist
0. 035
25
0. 5
Sulfur
dioxide
1. 50
1, 300
160
 Collection efficiency,
 Gas flow rate, scfm
 Avg gas velocity, fps
 Gas temperature,  °F
   98.9
14,000
   19
   160
Wire mesh mist eliminators are usually con-
structed in two stages.  The lower stage of
•wire mesh may have a bulk density of about
14 pounds per  cubic foot,  while the upper stage
is less dense.   The two stages are separated
by several feet in a vertical duct.  The high-
density lower stage acts as a coalescer.  The
reentrained coalesced particles are removed
in the upper stage.  Typical gas velocities for
these units range from 11 to 18 fps.  The kinet-
ic energy of the mist particle is apparently too
low to promote coalescence at velocities less
than 11 fps, and reentrainment becomes a
problem at velocities  greater than 18 fps.  The
tail gas pressure drop through a wire mesh
mist installation is approximately 3 inches
water column.

-------
722
CHEMICAL PROCESSING EQUIPMENT
Exit sulfuric acid mist loadings of less than 5
milligrams per cubic foot of gas are normally
obtained from, wire mesh units  serving plants
making 98 percent acid. No type of mechan-
ical coalescer, however, has satisfactorily
controlled acid mists from oleum-producing
plants.   Corrosion possibilities from, concen-
trated sulfuric acid must be  considered in se-
lecting wire mesh material.   The initial cost of
wire mesh equipment is modest.  The value of
recovered sulfuric acid is usually sufficient to
pay the first investment in 1 or 2 years (Duecker
and West, 1959).
                      5 microns in size.  A considerable amount of
                      the larger size acid mist particles may be re-
                      moved; however, the visibility of the stack
                      plume is not greatly affected, since the smallest
                      particle size contributes most to visibility.  Vane-
                      type  separators operate  at relatively high gas
                      velocities and thus  make better  use of the parti-
                      cles' kinetic energy.  They have been found  to be
                      moderately  effective for contact plants having
                      wet-purification systems in reducing stack plume
                      opacities (Duecker  and West, 1959).
Ceramic filters

Porous ceramic filter tubes have proved success-
ful in removing acid mist.  The filter tubes are
usually several feet in length and several inches
in diameter with a wall thickness of about 3/8 inch.
The tubes are mounted in a horizontal tube sheet,
with the tops open and the bottoms closed.   The
tail gases flow downward into the tubes and  pass
out through porous walls.  Appreciably more fil-
tering area is required for  the ceramic  filter
than for the -wire mesh type.  The porous ceramic
filter is composed of small particles of alumina
or similar refractory material fused with a binder.

The maintenance costs for ceramic tubes is con-
siderably higher than those for wire mesh filters
because of tube breakage.   Initial installation
costs are also considerably higher than those for
wire mesh.  A pressure drop of 8 to 10  inches
water column is required to effect mist removal
equivalent to that of a wire  mesh filter.   Thus,
operating costs would also be appreciable (Duecker
and West,  1959).

Sonic agglomeration

The principle of sonic agglomeration is  also
used to remove acid particles from waste-gas
streams.   Sound -waves cause smaller particles
in an aerosol to vibrate and thereby coalesce
into larger particles. Conventional cyclone sep-
arators can then be used for removal of these
larger particles.  One installation treating exit
stack gases from a contact  acid plant has been
reported to remove 90 percent by •weight of  acid
in the gas stream.  The tail gases leaving the
sonic collector contained 2  to 3 milligrams  of
100 percent sulfuric acid mist per cubic foot. A
nuisance factor must be taken  into consideration,
however,  since some of the sound frequencies
are in the audible range (Duecker and West, 1959).


Miscellaneous devices

Simple  baffles and cyclone separators are not
effective in collecting particles smaller than
                            SULFUR  SCAVENGER PLANTS
                      INTRODUCTION

                      A sulfur scavenger plant scavenges elemental
                      sulfur from the waste gases and fuel gases pro-
                      duced in an oil refinery.  Elemental sulfur has a
                      •wide variety of industrial uses and the amount of
                      sulfur produced by scavenger plants is becoming
                      increasingly important.  As the demand for sul-
                      fur increases and as natural sulfur  deposits are
                      depleted or their recovery becomes uneconomical,
                      the price of sulfur will rise.  Accordingly, the
                      "recovery of sulfur from  refinery gases containing
                      high concentrations  of hydrogen  sulfide (H^S)
                      becomes increasingly economical.  From an air
                      pollution standpoint, the vital function of the  sul-
                      fur scavenger plant  is to prevent or reduce the
                      emission of sulfur compounds to the atmosphere.

                      SULFUR  IN  CRUDE  OIL

                      All crude oils contain sulfur and sulfur compounds
                      in widely varying  amounts.   Some crudes contain
                      as little as 0. 1 percent while others contain 5.0
                      percent or  more,  with most crudes having between
                      1 and 2 percent by weight of sulfur and sulfur com-
                      pounds.  It is beneficial  to refinery operations to
                      remove the sulfur compounds because of their
                      deleterious effects.   The major effects are illus-
                      trated in Table 197.

                      In a variety of crude oil  refining processes, most
                      of the sulfur and sulfur compounds in the original
                      crude oil are converted to H2S.  This t^S gas is
                      contained in the overhead off-gas streams from
                      these processes and, after  separation of product
                      gas fractions, remains in the final -waste gases
                      which usually are  used as fuel in refinery heaters.
                      The burning of these gases  results in large quanti-
                      ties of sulfur dioxide (802)  being formed and emit-
                      ted from the heater  stacks.  To reduce emissions
                      of SO2 from this source, it is necessary to re-
                      move as  much H2S as possible from these gases
                      before they are used as heater fuel.

-------
                                       Sulfur Scavenger Plants
                                                                          723
                 Table 197.  EFFECT OF SULFUR COMPOUNDS DURING REFINING
 Purpose
 Primary
 c ontamin ant s
Effect of contaminant
 Reduce
 odor

 Reduce
 corrosion
 Reduce oper-
 ational pro-
 blems
 Improve color,
 reduce gum
 Improve
 gasoline octane
 Avoid catalyst
 poisoning
 Extend lube
 oil life
Mercaptans


Elemental S

H2S

Mercaptans

Corrosion compounds


H2S
Iron sulfide

Sulfur compounds

Disulfides


Thiophenol
(mercaptan)

Disulfides
Sulfides
Thiophene

Elemental S
Sulfur compounds


Sulfur in gasoline
Offensive product odors 0. 002% max.  tolerable con-
centration

Attacks iron, copper, etc.,  forming sulfides
Attacks zinc, copper, iron

Mildly corrosive

Plug exchangers,  collect on fractionator trays;
spontaneous  combustion during cleanout

Highly toxic  (dangerous during cleanout)

Foaming in amine systems (reduced efficiency)
Foaming in caustic wash  systems

Oxidation (in sunlight) to  form acids and haze in gas-
olines

Catalyst in gum formation reactions
In the listed order of severity,  sulfur compounds
reduce the effectiveness of TEL in raising octane
ratings

In reforming operations,  sulfur compounds are con-
verted to HpS which may react with catalyst to form
sulfides

Sulfur compounds formed during combustion drastic-
ally reduce lube oil  life
 REMOVAL  OF H2S FROM REFINERY WASTE GASES
There are numerous methods by •which HoS can be
separated from hydrocarbon gas streams, and
other methods  are in the development stage.   The
three methods  which are in common use in the
petroleum industry are illustrated in Table 198.
As noted in the table, the iron-sponge process is
not practical for  large gas streams or  gas streams
with a high H2S content.  This process is used
most commonly in desulfurizing natural gas
streams,  and the carbonate or amine absorption
processes are  used most commonly in  petroleum
refinery operations.  Of the latter two  processes,
the amine is  the most popular since refinery waste
gases generally have H2S concentrations well
suited to this process, and a greater removal  effi-
ciency is  obtained than by the carbonate process.
Both DEA (diethanolomine) and  MEA (monoethano-
lamine) are used, with DEA being preferred since
chemical  degradation and make-up rates are lower.
Amine solutions will absorb both H2S and CO2
according to the folio-wing reactions:
                                          RNH2

                                     RNH2 + CO2 + H2O;
                                 rRNH^HS
                                                                                    :RNH3HCO3
                               Absorption of H2S occurs at 100  °F or below, and
                               rejection of sulfide is active at 240 °F.  The amine
                               desulfurization process, therefore, involves con-
                               tacting the sour (sulfur bearing) gas stream with
                               a cool amine solution to absorb the H2S and then
                               regenerating the amine and stripping  the H2S from
                               the amine solution by heating.  A typical amine
                               H2S removal system is shown in  Figure 561.

                               The treated gas leaving the amine de sulfur ization
                               process will be used as refinery  fuel  or be burned
                               in a flare.   It is necessary, therefore,  to ensure
                               proper capacity and functioning of the amine sys-
                               tem.  The efficiency of an operating amine system
                               can readily be determined by laboratory analysis
                               of the sour inlet gas,  treated outlet gas, and acid
                               outlet gas streams.  It may also  be necessary to
                               verify the adequacy of a proposed new amine sys-
                               tem, and the following parameters  may be used
                               for this purpose:
 234-767 O - 77 . 48

-------
724
CHEMICAL PROCESSING EQUIPMENT
                         Table 198.  REMOVAL OF H2S FROM REFINERY GAS
Progress
Iron sponge




Hot potassium
carbonate







Amine
(MEA or DEA)







Gas to be
treated
1. Low gas volume
2. Low H2S content



1. High volume
2. Very sour gas
(5 to 50% H2S)






1. High volume
2. Low or intermediate
H2S content






Process
stages
1. Reaction to
Fe2S3
2. Revivification
or
3. Repacking
1. Absorption
2. Regeneration
by decrease in
pressure





1. Absorption
2. Regeneration
by heat striping






Advantages
of method
1, Low initial cost
2. High efficiency
for gas streams
•with low H2S content

1. Will reduce H2S
to less than 0. 1% in
very sour gas streams
2. Extensive heat ex-
change equipment not
required
3. Absorbent (K2CO3)
does not degrade
readily.
1. Will reduce H2S
to less than 1 grain
/100 ft3 in sour gas
stream
2. DEA preferred over
MEA due to degradation
of MEA by carbonyl
sulfide and carbon
disulfide in gas stream
                                      COOL WATER
  TREATED
                              ACID GAS





SOUR
GAS


a:
0 =
OQO
•SO
V
1 COOL WATER
^X
V
[COOLER
^1
AMINE
PUMP


EXCHANGER
rC
i



>
»-





r

UJ Z
^ ID
us
V
RICH AMINE LEAN AMINE
UUULtK




m*m
JL^ STEAM
© .
t-JT'
REBOILER
      Figure 561.  Amine desulfurization process.
                      1.  Actual H2S/DEA ratio versus H2S/DEA
                          equilibrium ratio

                      2.  corrosion limitation

                      3.  absorber column sizing.

                      The following example illustrates the calculations
                      used in verifying the adequacy of a proposed
                      amine  (DEA) desulfurization system:

                      Given:

                      Total sour gas feed,  scf/day             = 20xl()6

                      Specific gravity of sour gas              =  0.8

                      H2S in sour gas feed, weight %          =2.5

                      DEA solution circulation  rate, gal. /min =160

                      DEA concentration,  %                   = 20

                      Absorber temperature, °F              =100

                      Absorber pressure, psig                =120

                      Absorber diameter, feet                 =  5.0

                      Absorber tray spacing, feet             =  2.0

                      Problem:

                      Verify performance of proposed system against
                      standard parameters.

-------
                                         Sulfur Scavenger Plants
                                                                               725
 Solution:

 1.  Actual H2S/DEA ratio:

                        2. 5%   20 x 106 scf/day
    Total H?S in feed =  ,-.-  x 	———r-	*-
            *•            100       24 hr/day
                                      H2S /DEA  (actual)  =
                    1
                            = 1870  Ib/hr
               11. 14 ft^/lb

    Total H2S in DEA (based on 98% regeneration)

       =  (1870)(0. 02) = .37 Ib/hr

    Total H2S to absorber  = 1907 Ib/hr

    Total DEA flow (20% solution) =  (160 gal/min)

    x  (60 min/hr) = 9600 gal/hr

         20% DEA = 1920 gal/hr

         80% H2O = 7680 gal/hr

    Total DEA flow = (1920 gal/hr)(9. 09 Ib/gal) +

                      (7680 gal/hr)(8. 34 Ib/gal)

                    = 17,500 + 64,000
                    = 81,500 Ib/hr
    H2S/DEA ratio =
 1907
81,500

weight)
                            x 100 = 2. 34%  (by
    Partial pressure H2S = (120 psi + 14. 7 psi*)

    x (760 mm Hg/14. 7 psi) x (2. 34%/100) =

      163 mm Hg
    H2S/DEA equilibrium = 0. 23
                                 Ib H2S
                                 Ib DEA
                         (from Figure 562)
     1.0
     0.8
     0.6
a   0.2
o>
=i   0.10
  ,  0.08
  :  0.06
  I ' 0.04
    0.02
    0.01
       10     20  30  40  60 80100     200    400 600   1000
                H2S PRESSURE, mm.Hg (GAS PHASE)
   Figure 562.  Equilibrium plots of fyS in  20% DEA
   aqueous solution.
* Atmospheric pressure.
                                              19071bH2S
                                             17, 500 Ib DEA
                                                                                                   (OK)
                                  2.  Corrosion limitation:
                                                           Total HS =
                                                                _„ .
                                                           Total DEA =
                 34 Ib/mol

                 17.500 Ib/hr
                 105. 1 Ib/mol
                                                           * = 56. 0 mol/hr
                                                                = 166. 5 mol/hr
                                      H2S/DEA ratio (maximum recommended) =

                                                 mol


                                      H2S DEA ratio (actual) = . , .    = 0. 336  (OK)
                                                               loo. b   	

                                  3.   Absorber column sizing:

                                      Experience has shown that a satisfactory
                                      absorber tower cross-sectional area may be
                                      derived from the following equation (Connors,
                                      1958):
                                                                        A =
                                                                            BQ /DT\2
                                                                            C \KP,
                                                                                                  (148)
where

    A = absorber cross-sectional area,  ft2

    B = Brown tray spacing factor
        (24 in. )                           0. 82

    C = Barton plate  correction
        factor (120 psig)              =   1. 56

    D = specific gravity of sour gas   =   0. 80

    K = specific gravity of liquid
        (DEA)                        =   1.09

    P = gas pressure, psia            = 134. 7

    Q = acid  gas volume,  10  scf/day =  20. 0

    T = temperature,  °R              = 560

                                                1.56
                                             0. 82(20. 0)  f 0.80(560)1
                                                                                       60)1^
                                                                                       . 7)J
                                                              A = 10. 52(3. 05)  = 10. 52(1. 746)

                                                              A = 18. 35 ft2
                                                             D2 = ~  (18. 35) = 23. 35
                                                                                _
                                     Required absorber diameter, Dr = (23. 35)2

                                                                      = 4. 83 ft

                                     Actual absorber diameter, Da   = 5. 0 ft (OK)

-------
726
    CHEMICAL PROCESSING EQUIPMENT
THE  AIR  POLLUTION PROBLEM

The  acid gas stream from typical refinery amine
(or potassium carbonate) units will contain well
over 95 percent acid gas (H2S and carbon dioxide).
If desired, there are processes for selective re-
moval of the CC>2 from the  acid gas, but this is
not essential for processing the gas.  The remain-
der of the stream will be largely hydrocarbons,
with small amounts of carried-over amine.  With-
out air pollution control equipment, this highly
toxic and undesirable gas stream would have to be
burned to convert the H2S to SOg,  which is less
toxic but also highly undesirable.  Air pollution
control equipment is required, therefore, for
reduction of H2S emission to the atmosphere with-
out a corresponding substitution of SC>2  emission.
This may be done  by conversion of HgS  to elemen-
tal sulfur.

AIR POLLUTION CONTROL  EQUIPMENT

There are numerous processes by which H2S
can be removed from hydrocarbon gas streams
by conversion to free sulfur, but these are pri-
marily natural gas purification processes.  The
sulfur scavenger plant,  however, serves  solely
to produce free  sulfur from H2S streams which
have been removed from hydrocarbon streams by
other (amine, etc.) methods.  The standard sulfur
scavenger plant is  based on the Glaus process
which  involves oxidation of one-third of the H2S
to SC>2 and then  catalytically reacting the  remain-
ing H2S with the SC>2 to form water and  free sul-
fur:
    and
           H2S + - 02-
          2 H2S + SO2-
                                 + HoO
-3  S + 2 HoO
The second (catalyzed) reaction usually is accom-
plished in two stages, but more recently, three
stages are being used for  more complete conver-
sion.  Final off-gas is incinerated to prevent un-
reacted H2S from being emitted into the  atmos-
phere.  This results in some SO2 emission,  al-
though only a fraction of that which would have
been emitted upon combustion of all the H2S.

A variation of the basic Claus (split-stream) pro-
cess is the  partial-combustion process wherein
the acid gas stream is partially oxidized by con-
trolling the supply of air.   The reaction  gas  is
cooled to condense sulfur  vapors and comingled
with air and a slip-stream of acid gas, which are
burned "in-line" so  as to reheat the mixture be-
fore it is passed to the first converter.  This
reaction gas is again cooled to condense  sulfur
vapors before being reheated by '"in-line" com-
bustion of additional slip-stream acid gas and
being passed to the second catalytic  converter.
Again, the reaction gas  is cooled for condensation
of sulfur and then passed to  a coalescer for
removal oi the remaining sulfur mist before being
incinerated.  All condensed  sulfur drains to mol-
ten sulfur storage, from which it may be  pumped
out and shipped in the molten state or may be
solidified,  by cooling in vats or blocks, for han-
dling in the solid  state.   The basic split-stream
process is illustrated in Figure 563, and the
more commonly used partial -oxidation process
is illustrated in Figure  564.

However  high the efficiency of a scavenger
plant,  the plant will  be a source of SO2 air pol-
lution  since  remaining sulfur  compounds in the
final vent gas will be incinerated to  SO2 and then
discharged through a stack  to  the atmosphere.
Operation  of the scavenger  plant, however, re-
duces  the amount of  SO2 emission  in proportion
to the  amount of sulfur which is recovered,  and
this reduces overall  emission of pollutants.  In
Los Angeles County, APCD Rule 53. 1 specifies
that the  scavenger plant must "substantially"
reduce the amount of pollutants which would
otherwise  be emitted.  In practice,  a well-
designed and properly operated scavenger plant
can be expected to recover  more than 90 percent
of the  sulfur  contained in the acid gas feed.  The
criterion for evaluating scavenger plants has,
therefore, been the achievement of a recovery
efficiency of 90 percent or  greater.   Even at
satisfactory plant efficiency,  however,  the SO2
concentration in incinerated flue gas may exceed
allowable limits and it may, therefore,  be neces-
sary to add dilution  air  to the incinerated gas
(see Figures 563 and 564) before discharge to the
atmosphere.

The efficiency of an  operating  scavenger plant
may be determined by methods similar to that
illustrated by  the following  example:
 Given:

 Test period,  hours

 Total feed gas volume, scf

 Feed gas composition:

    H,S,  mol %
                                                          =      24

                                                          = 600, 000
                                                                 65. 0
    CO2, mol %
                                                                 33.0

                              Hydrocarbons, mol %        =       2.0

                              Sulfur produced,  short tons  =      15. 0

                          Problem:

                          Calculate efficiency of sulfur recovery.

-------
                                        Sulfur Scavenger Plants
                                                             727
 ACID GAS
     2/3 STREAM
                                                        FLUE GAS
           OXIDATION UNIT AND
           WASTE-HEAT BOILER
  OXIDATION
  AIR BLOWER
                   Figure 563.  Sulfur scavenger plant  using the split-stream process  (Giusti,  1965).
Solution:
1.  Available sulfur in feed gas
    600, OOP ft3    „  ,r     32 Ib/mol
   	  x 0. 65 x  —
                                                       4.   reheater 2: in-line combustion (or other
                                                                      means) to reheat gases to 450
                                                       5.   converters 1 and 2:
    379 ftVmol  " "' ~" "  2000 Ib/ton

2.  Sulfur  recovery efficiency

            15.0 tons
= 1 6.45 tons
each to have sufficient
bauxite catalyst that the
ratio  of H->S flow  (cfs) to
                   o
catalyst volume (ft  ) does
not exceed 2:1.
            16. 45 tons
                        x 100 =  Ml.2"/0
In addition to supplying the correct amount of
oxygen  (air)  to permit comersion reactions to
take place,  optimum operating conditions also
must be maintained.  The waste  heat boiler,  cool-
ers, reheaters,  and converters must be sized and
operated to achie\e conditions approximating
those sho\\n  below:

1.  Waste heat boiler: boiler feed water to cool
                       reaction gases to 450  °F

2.  coolers 1,  2,  and 3: each  to have capacity to
                        cool gases  to 300 °F

3.  reheater 1: in-line combustion (or other
               means) to reheat gases to 475 °F
               The above conditions can be achieved by various
               combinations of vessel sizing  and/or flow rates
               and need not be further illustrated.

               Incineration Requirements

               Even in an efficient scavenger plant, a portion of
               the H^S in the acid gas is unreacted and passes
               through the  plant.  The final vent gas is composed
               of the products of reaction  (other than recovered
               sulfur) and the inert nitrogen  contained in the  air
               used for supply of reaction oxygen,  plus the com-
               ponents of the feed stream  which do not take part
               in the conversion reactions and the unreacteci  ^S.
               Because of the remaining HnS, this  vent gas must
               be incinerated  to convert the H^S to SO-, before
               the vent gas is discharged  to the atmosphere.
               Although the oxidation of H^S  is exothermic,  it
               may be necessary to supply additional heat at  the

-------
728
CHEMICAL PROCESSING EQUIPMENT
          SLIP STREA'"
                                                  AIR
                                                                         AIR
                                                 NO.l \7
                                                REHEATERY    NQ j
                                                       I  CONVERTER
                                         N0.2  \
                                       REHEATER
                                                   NO. 2
                                                 CONVERTER
                                                                               STEAM
                                                                         NO. 3
                                                                       CONDENSER

                                                                      SULFUR
                                                                                               VENT
                                                                                               GAS
                                                       SULFUR
                                  AIR FUEL GAS
VAPOR



AS
	 1



PU1VIP c|1LF
r-i SULF

i
MOLTEN !
SULFUR J.,



                                                                             STORAGE
                                                                               PIT
       k^
       BLOWER   I
                  DILUTION
                    AIR
                 Figure 564.  Sulfur scavenger  plant using  the partial  oxidation process (Giusti,  1965).
incinerator in order to maintain incineration tem-
perature for the total vent gas stream.  Determina-
tion of incineration requirements is illustrated by
the following  example  for a scavenger plant simi-
lar to that shown in Figure 563 and for the same
feed stream used in the preceding example.  All
data are for a 24-hour  period.

Given:

Feed composition:

    Total feed, scf                    =  600, 000

    H2S, mol %                        =       65

    CO2,  mol %                       =       33

    CH4,  mol %                       =1.5

         ,  mol %                              0. 5
    Sulfur recovery efficiency, %      =       91. 2

    Free  sulfur carry-over (0. 1%), Ib  =       30.0

    Final vent gas temperature, °F   =      320

Problem  A:

Determine quantities of unreacted products  pass-
ing through the unit to the incinerator.

Solution:

1.  Weight of unreacted H2S

    H2S = 100  -91.2  =  8. 8%

              , OOP f<-3
                           H2S = ,67°Q0''33°/° ft   x0.65x0.088x-^-
                            ^    379 ft-Vmol                    24 hr

                               = 3. 77 mol/hr

-------
                                        Sulfur Scavenger Plants
                                                                                                  729
2.  Weight of unreacted CO2

    „_    600,000 ft3    .
    C°2 = 379 ft^/mol  X °"
         = 21.7 mol/hr

Problem B:
Using basic reaction formulas, determine quanti-
ties  of reaction products from oxidation of both
H2S  and hydrocarbons.

Solution:

1.  Basic reaction formulas for conversion of H2S:

          H2S + - O2 	~SO2 + H2O

           2H2S + SO2	-3S + 2H2O

                        or

          3H2S + -| O2	-3S + 3H2O
2.   Weight of reacted H2S '•

    M <;   600,000 ft 3
    H?s = 3-70 ,..'•{ , - r- x °-
     ^    379 ft^/mol

        = 60. 1 mol/hr
                                   1
                                 24 hr
3.  Weight of H2S reaction products (other than
    sulfur):
   H0 =
           3  mol
                 x 60. 1 mol/hr  = 60. 1 mol/hr
     O2 =  (60.1 mol/hr)/2 = 30. 05 mol/hr

                          0.79 N2
     N2 =  30. 05 mol/hr x .         = 113. 0 mol/hr
       "-                   0. 21 O2

4.  Reaction formulas for oxidation of
    hydrocarbons:
                                     3H2O
             CH4 +  202—•—— CO2 + 2H2O

            C2H6 + -|°2-

5.   Weight of hydrocarbons in feed stream:

          600, 000 ft3             i
    CH4=379ft3/molX°-015x2TC
               =  0. 99 mol/hr


            600,  000 ft3
                                                      6.  Reaction quantities  for hydrocarbon oxidation :

                                                         02 = 2(0.99 mol/hr)+-^(0.33 mol/hr) =

                                                                 3.14 mol/hr

                                                                            0.79N2
                                                         N?= 3.14 mol/hr x-	—-=•= 11. 8 mol/hr
                                                           L                0. 21 O2   	

                                                        CO2 = 1(0. 99) + 2(0. 33) = 1.65 mol/hr

                                                        H20 = 2(0. 99) + 3(0. 33) = 2.97 mol/hr

                                                      7.  Total reaction products (other than sulfur):

                                                               from 3    from 6

                                                                                        63.07 mol/hr
                                                          H?O =60.1   +   2. 97
                                                           N7 =113. 0   +  11.
                                                          CO2 =
                                                                  0
                   +  1.65
                                                                                    =   124.8 mol/hr

                                                                                         1. 65 mol/hr
Problem C:

Determine quantity of free sulfur carry-over.

Solution:

1.  Weight of sulfur carry-over

   „    15.0 tons (0.001)x2000 Ib/ton
      --   -
                                                                      , - .     i - =
                                                                   24 hr x 64 Ib/mol
                                                                                          = 0.02 mol/hr
Oxidation of H2S to SO2 is  rapid and essentially
complete at temperatures over 1050 °F, provided
there is  adequate air supply and mixing.  For
given operating conditions, additional fuel gas and
air requirements may be determined and effective-
ness of incineration  may be verified.

Given:

Vent gas temperature,  °R = 320 + 460   = 780

Incineration pressure, psia            =  14. 7

Proposed incineration  temperature, °R = 1700

Excess air to  be supplied, %            =  25
                                                      Dimensions of incinerator chamber
                                                                                            = 4 ft diam
                                                                                              x 8 ft long
              = 0. 033 mol/hr
                                                     Heat value (refinery gas),  Btu/ft3      =  800

                                                     Temperature refinery gas and air,   °F  =  100

                                                     Problem D:

                                                     Determine air required  for  incineration of vent
                                                     gas  stream.

-------
730
CHEMICAL PROCESSING EQUIPMENT
Solution:
Composition,
mol/hr Oxidation reaction
S2 = 0. 02 S2 + 2 O2 	 -2 SO2
H2S = 3. 77 H2S + | O2 	 ~SO2 + H2O
p <~\ _ -> -3 T c p o .CO
HO f, ° f!7 TT O... -.- ^M O
124.80 ^r
2 215.01 2 "*
1. Theoretical O? required
O2 = 2(0. 02) + -|(3. 77) = 5. 70 mol/hr
2. Amount N-, for required O2
-, — X ( U x • m - £1, 4D mol/hr
<-• 21/0
3. Excess air for 25% excess
Air (5. 70 mol/hr) .,„ ,,,
Problem E:
Determine heat evolved from incineration of vent
gases.
Solution: Heat
value,
mol/hr x Ib/mol x Btu/lb = Btu/hr
S2 0.02 64 3,984 5,100
i' H2 3.77 2 51,593 389,000
' S 3. 77 32 3, 984 480, 500
Total evolved heat 874, 600
Problem F:
Calculate heat required to raise other (reacted)
vent gases from 320 °F to 1240 °F.
Solution:
1. Total vent gases, after oxidation of combusti-
bles (from quantities in Problems A, C, and
D, and reaction equations in Problem D)
CO2 = 21.70+ 1.65 = 23.35 mol/hr
N2 =113.0 (from reaction) = 11 3.00 mol/hr
N2 =21.45 (from
incineration) = 21.45mol/hr
Air = 6. 78 (excess, from
incineration) = 6.78 mol/hr
2. Total heat required
HI (at initial
H2(1700 °F) - temperature) = Btu/mol
SO2 25,350 16,200 (780 °R) 9,150
H20 34,450 21,650 (780 °R) 12,800
CO2 14,270 3, 510 (780 °R) 10,760
N2 9,600 2, 850 (780 °R) 6,750
N2 9,600 1,310(560 °R) 8,290
Air 9,680 1,310 (560 °R) 8,370
3. Total heat required for incineration
mol/hr x Btu/mol = Btu/hr
SO2 3.81 9,150 34,800
H2O 66.84 12,800 856,000
CO2 23.35 10,760 255,000
N2 113.00 6,750 763,000
N2 21.45 8,290 177,800
Air 6.78 8,370 56,700
Total = 2,143, 300
4. Additional heat required
H = Heat required to raise products to 1240
°F, minus incineration-evolved heat.
H = 2, 143, 300 - 874, 600 = 1, 268, 700 Btu/hr
5. Refinery gas required for additional heat
H = 800 Btu/ft3 x 379 ft3/mol = 313, 000
Btu/mol
,,,-,, • i 1,268, 700 Btu/hr
   SO2 = 2(0.02) +1('3.7




   H2O = (3.77) + 63.07
     3.81 mol/hr




 =  66.84 mol/hr
                                     mol/hr
Use 5. 0 mol/hr (for  safety factor)

-------
                                       Sulfur Scavenger Plants
                                                                                              731
When burning refinery gas to obtain the required
additional heat necessary to achieve the proposed
incineration temperature,  additional air for com-
bustion of this gas must be supplied.   The requir-
ed air can be determined by calculations similar
to those above.  A final incineration heat balance
can then be made, and the actual incineration
temperature  can be predicted.  It is also neces-
sary that the incinerator mixing velocity be such
that  the retention time exceeds 0. 3 second to
ensure  adequate time for  conversion of H2S to
so2.

Given:

Refinery gas essentially 75% CH4 and 25%  C2H^.

    Excess air for combustion = 25%

Problem G:

Determine air requirement for fuel gas combus-
tion  and make final heat balance of combined vent
gases,  fuel gas,  and air for fuel gas. Determine
predicted incineration temperature and check
against desired 1240 °F.  Verify incinerator
mixing  velocity and  retention time.

Solution:

1. Air  requirement for 5. 0 mol/hr fuel gas
                                                     Total
                                                                   = 2,390,600 Btu/hr
         CH4 + 202
            75
                           2H2O
     O2 = 2(r-—x 5. 0 mol/hr) =7.5 mol/hr
       C2H6 + 7 °2
 °2 =
                              2 + 3H2O


                              = 4- 375
    Required O2 = 7. 5 + 4. 375 = 11. 875 mol/hr
Required N2  =
Excess air =

                       - x 11. 875 = 44. 7 mol/hr

                          '

                               mol/hr = 14. 14
                                        mol/hr

    Additional CO2 and H2O from fuel gas

    H2O = 2(3. 75) + 3(1. 25) = 11. 25 mol/hr

    C02 = 1(3. 75) + 2(1.25) =  6. 25 mol/hr

2.   Total heat added

    Incineration heat (Problem E)  = 874, 600 Btu/hr
Fuel gas heat = 5. 0
                   hr
                       x 379
                                  — x 800
                                 mol        ft
                                                  3.  Anticipated incinerator temperature

                                                               T2 - Tl =   ^~             (149)
                                                     Where

                                                        T2 = final  temperature,  °F

                                                        T^ = initial temperature, °F

                                                        AQ = heat  added,  Btu/hr

                                                         W = weight of gas,  Ib

                                                        Cp = specific heat of gas .

                                                     Assumed:

                                                        Tj = 300 °F (vent gas at 320 °F; fuel and air
                                                              at  100 °F)

                                                        Cp - 0. 27 (based on weighted average of C
                                                              for major vent gas  components)

                                                        Incinerator heat loss = 15%

                                                     W, weight of gases (Problem F and 1 above)

                                                              mol/hr   x Ib/mol  = Ib/hr
so2
H2O
co2
N2
Air
3. 81
f 66. 84
\ 11.25
(23. 35
I 6.25
(113. 00
< 21.45
V. 44. 70
f 6.78
(14. 14
64
18
18
44
44
28
28
28
29
29
244
1232
203
1028
275
3164
600
1252
196
410
                                                         T2 - Tl =
                                                                311. 57     W, Ib/hr = 8604

                                                                   2, 327, 900 x 0. 85
                                                                     8604 x 0.27
                                                                                     = 853 °F
                 = 1, 516, 000 Btu/hr
        T2 = 853 +  300 = 1153 °F

   (checks with assumed temperature of 1240 °F,
   allowing for heat loss)

4.  Incinerator mixing velocity:

   Volume of gases
   to incinerator    = 311.57 mol/hr x 379 ft3/hr

                    = 119,700 ft3/hr

-------
732
                             CHEMICAL PROCESSING EQUIPMENT
   Area of
   incinerator
   Mixing velocity  =
5.  Retention time:
                  119, 700 ft3/hr
                    3600 sec/hr~
                 = 2.65 fps
                                       12. 56 ft
   Length of incinerator = 8. 0 ft

                         '
Retention time =
Stack Dilution Air
                     2. 65 ft/sec
                                 = 3 seconds  (OK)
As shown in the preceding problems,  unconverted
H2S and carried-over  sulfur are burned in the
incinerator to SO2.  However,  even when the
scavenger plant is operating efficiently, the vol-
ume concentration of SO£ in the flue gas from the
incinerator may be  high. To meet acceptable  con-
centration levels at  the stack,  dilution air may
be added  at the base of the stack. The required
amount of dilution air may be  determined as
illustrated in the  following problem.

Example

Problem:

Determine the SO2  concentration in the flue gas
and the amount of dilution air required to lower
the concentration to an acceptable level.

Given:

   Total  SO2  (from Problem G)=    3. 81 mol/hr

   Total  gas                   =  311. 57 mol/hr

   Maximum  allowable SO2    =    0. 2 vol %

Solution:

1.  Undiluted SO^ concentration

                 3. 81
    Volume % =
                   x 100 = 1.207%
                311.57

2.  Required dilution air

    Total volume required           .    -,-,^0.1   i
                           3. 81mol/hr x 379 ft/mol
    for 0. 2% SO?          = ——	:—j~	     	
               L             60 min/hr x 0. 002

                          = 12, 040 cfm

    Total incinerator gas  =

    311. 57  mol/hr x 379 ft3/mol
   Required air  =  total volume  - incinerated gas

                 =  12, 040 -  1970 =  10, 070 cfm

            Use  11, 000-cfm blower

In some localities,  there may be no established
criterion for maximum allowable SO2 concentra-
tion in the flue gas.  Nevertheless, SO;? is itself
toxic and it is  necessary to ensure that safe
ground level concentrations are not exceeded.
Additionally,  some  of the SO-> may be oxidized
to 30-5 which,  in turn, could combine with atmo-
spheric moisture to  form acid mist and lead to
extensive ground level damage.  The  addition of
dilution air, in addition to reducing SO2 concen-
tration,  has the  added advantage of "quenching"
the incinerated gases and greatly reducing SO?
formation.

Incinerator Stack  Height

Where there is no set limit for stack SO2 con-
centration, an attempt may  be made  to keep
ground level concentration to  an acceptable  level
by providing a high stack.   The  required stack
height may  be determined by methods illustrated
in the following  example:

Given:

   Total flue gas volume, cfm            = 2000

   SO2 concentration,  vol %              = 0. 5

   Allowable SO2 at 500 ft from base
     of stack, ppm                        = 3
                                                      Wind velocity,  mph

                                                   Solution:

                                                   The general concentration equation is
                                          =  10
                                                          C  = 9. 4 x 10  x
                                                                                 x K
                                            (150)
            60 min/hr
                                 = 1970 cfm
                       V x X2

where

   C = ground concentration,  ft-' SO2/10" ft  air

   M = SO2 emission rate, tons/day

   V = wind velocity, mph

   X = distance from stack base, ft

   K = e (-20 H/X)

   (Values of K are plotted in Figure 565. )

      _ 2000 cfm x 0. 005   1440 min/day
      ~     5. 93 ft3/lb    X  2000 Ib/ton

      = 121 tons/day

-------
                                        Sulfur Scavenger Plants
                                                                              733
   6,000
h-
^  4,000
~  3,000
S  2,000
   1,000
uj   800
|   600
I   400
    300
     0.002  0.004    0.01        0.04     0.1
                  VALUE OF COEFFICIENT K
                    0.4   0.7
Figure  565. Coefficient K for  use  in equation 150,
which gives ground  concentration at any distance from
stack for any stack height and wind velocity CStembock
   K =
        (C)(V)(X2)
3(10)(500)
                            i—i OJ
   JTT EFFECTIVE
      STACK HEIGHT
 0.0050.010.020.030.050.1 0.20.30.5   1.0  2  3  5  10  2030 50 100
          MAXIMUM S02 GROUND CONCENTRATION, ppm

  Figure 566.  Maximum ground  concentration of sulfur
  dioxide discharged from stacks of various heights
  (Stembock,  1952).
4.  The point of intersection is the required stack
    height.
    By interpolation of height curves, H = 230 ft.

Plant Operational Procedures

Even in properly designed plants,  operational
problems which result in decreased sulfur re-
covery efficiency and consequent increase in H£S
vented to the incinerator are often encountered.
Most of these problems  stem from either varia-
tion in  the feed gas stream or from  inadequate
reaction air and/or cooling water  controls.
Problems  in these areas,  in turn,  affect the cata-
lyst and  may drastically reduce conversion
efficiency.

Based upon a fixed feed stream composition,  the
correct  amount of oxidation air can readily be
controlled by flow controllers. However, feed
gas composition monitoring equipment is  expen-
sive and difficult to maintain and is therefore
not generally used. The  H^S content can be
readily checked,  and this is generally done on a
periodic basis, with air  supply adjustment as
necessary.

A more difficult problem  is an increase  in the
hydrocarbon content, •which may not be detected
until the imbalance in feed is reflected in abnor-
mal temperature differentials in the waste heat
boiler,  coolers, and/or  reactors.   It is necessary,
therefore, that operating temperatures be con-
stantly monitored  to detect hydrocarbon fluctua-
tions. If not, the excess hydrocarbons will dis-
rupt the  oxygen supply and not  permit full H^S
conversion to SC>2 in the first-stage reaction.
Secondly,  if not controlled,  temperatures may
rise to the point  of equipment damage and pos-
sible breakdown. Thirdly,  the  excess hydrocar-
bons may not be fully oxidized in the  controlled
air supply and, particularly when  the hydrocar-
bons are heavier than Cj fractions,  carbon may
be deposited on the catalyst and thus  reduce con-
version efficiency.

As  discussed earlier,  a two-stage conversion
plant should attain a sulfur recovery  efficiency of
at least 90 percent.  Many modern plants  will
yield 94  to 96 percent, and the  efficiencies may
be raised  to as high as  98 percent where a third
stage is  used.  Although the addition  of a  third
stage to  an existing two-stage  plant may not be
economical solely on a  sulfur  recovery basis,
the provision of a third stage in new plants is
relatively  inexpensive.   In either case, this third
stage is highly desirable from  an  air pollution
standpoint since large amounts of  pollutant are
represented by each percentage point of recovery
efficiency.  Also, the third stage can act as a
stand-by for the other  stages during upset con-

-------
 734
                                CHEMICAL PROCESSING EQUIPMENT
ditions. As activity of catalyst in the  first stage
is reduced (by surface deposits of sulfur or car-
bon), abnormal quantities of H2S will pass
through. However, this  can then be reacted in
the subsequent stages and high efficiencies can
still be maintained until  the first stage catalyst
is reactivated. With the additional flexibility of
three stages,  any one of the stages can be by-
passed for replacement of inactive catalyst.

Generally, however,  catalyst is reactivated rather
than replaced, and this  is done during periodic
plant maintenance shutdown. Sour  gas feed is
shut off and fuel gas is burned with theoretical
air in the combustion  chamber until all sour gas
is purged from the reaction system.  Thereafter,
air supply is raised to 25 percent excess for a
period and then to 50 percent excess.  In doing so,
the hot excess air burns  surface  carbon and
sulfur  from the reactor catalyst,  and this  is
reflected  by a temperature  rise across the re-
actor.  When the temperature becomes equal at
inlet and  outlet,  surface  material has  been fully
oxidized and the  catalyst is reactivated.

In all areas where  either oil refining or sour
natural gas processing operations take place,
the sulfur scavenger  plant may be  one of the most,
if not the most, important single  air pollution
control method. The  provision of such plants,
properly designed and efficiently  operated, will
prevent the emission to  the atmosphere of  intoler-
ably high  amounts of material 'which is toxic to
both man and his  environment.

Inasmuch as the  gas  treating plants,  as well  as
the sulfur recovery facilities, are processing a
highly  odorous and toxic  gas, it is of utmost
importance that the area  be designed for easy
cleaning of spills,  and that an efficient plant
housekeeping  program be followed.


Tail  Gas Treatment

As previously discussed, the main portion  of the
sulfur from the crude oil can be removed and  re-
covered.  Recent attention to further reduced
ambient air quality standards for  sulfur oxides
requires added treatment to the tail gases from
the scavenger plants.  Conversion efficiencies
must be raised from  the 90 to 95 percent range
to a  level greater than 99 percent.

Two approaches are available to achieve the addi-
tional clean-up.  One  requires the tail gas  efflu-
ent from the sulfur plant  to be totally  in an oxi-
dized state.  The gas  is then  conditioned and
treated by chemical scrubbing. The treated gas,
containing less than 100 ppm  sulfur compounds,
discharges to  the atmosphere, the chemical solu-
tion  is regenerated, and the resulting sulfur
oxides are recycled back to the sulfur recovery
units.  This process was developed by Wellman-
Power Gas, Inc., of Lakeland, Florida.

The other approach to this  problem is to provide
the tail gas in a reduced state of H£S before chemi-
cally  scrubbing.  It is necessary to minimize car-
bon disulfide and carbonyl sulfides to prevent high
degradation of the scrubbing solution.  Two pro-
cesses of this type are known as the Beavon Stret-
ford  (R.  M. Parsons Co. of Los Angeles,  Califor-
nia) and the Cleanair (The Pritchard Companies of
Kansas City,  Missouri).  Both processes are
capable of reducing the sulfur compounds to less
than  100  ppm.

Various other approaches to tail gas treatment
are in development stages.   Many involve chemi-
cal scrubbing of the gaseous streams although
adsorption and molecular separation processes
are being evaluated.

   PHOSPHORIC  ACID  MANUFACTURING

During the past 20  years, the use of phosphorus-
containing chemical fertilizers, phosphoric acid,
and phosphate salts and derivatives has increased
greatly.   In addition to their very large use in
fertilizers,  phosphorus derivatives are widely
used in food and medicine,  and for treating water,
plasticizing in the plastic and lacquer industries,
flameproofing cloth and paper, refining petroleum,
rustproofing  metal, and for a large number of
miscellaneous purposes.  Most of the phosphate
salts  are  produced for  detergents in washing
compounds.

With the  exception  of the fertilizer products,
most phosphorus compounds are derived from
orthophosphoric acid,  produced by the oxidation
of elemental  phosphorus. At present, elemental
phosphorus is manufactured on a large enough
scale to be classed as a heavy chemical and is
shipped in tank cars from the point  of initial
manufacture,  where the raw materials are inex-
pensive,  to distant plants for its conversion to
phosphoric acid,  phosphates, and other compounds.


PHOSPHORIC ACID PROCESS

Generally, phosphoric  acid is made by burning
phosphorus to form the pentoxide  and reacting
the pentoxide  with water to  form the acid.  Spe-
cifically,  liquid phosphorus (melting point 112°F)
is pumped into a refractory-lined tower where it
is burned to form phosphoric oxide,  P^OjQ,  -which
is equivalent algebraicly to two molecules of the
theoretical pentoxide,  p20r,  and is,  therefore,
commonly termed phosphorus pentoxide:
                  5O
P4°10

-------
                                    Phosphoric Acid Manufacturing
 An excess of air is provided to ensure complete
 oxidation so that no phosphorus trioxide (P2O3)
 or yellow phosphorus is coproduced.  The  reac-
 tion is exothermic, and considerable  heat must
 be removed to reduce corrosion.   Generally,
 •water is sprayed into the hot gases to reduce
 their temperature before they  enter the hydrating
 section.

 Additional water is sprayed countercurrently to
 the gas  stream, hydrating the  phosphorus pent-
 oxide to orthophosphoric acid and diluting the
 acid to about 75 to  85 percent:
        P4°10
6H2°
4H  PO
  3   4
 The hot phosphoric acid discharges  continuously
 into a tank, from which it is periodically re-
 moved for storage or purification.   The tail gas
 from the hydrator is discharged to a final col-
 lector where most of the residual acid misl  is
 removed before the tail gas is vented to the  air.
 A general  flow diagram for a phosphoric acid
 plant is shown in  Figure  567.
  Figure  567. General flow diagram  for  phosphoric
  acid  production.
The raw acid contains arsenic and other heavy
metals.  These impurities  are precipitated as
sulfides.  A slight excess of hydrogen sulfide,
sodium hydrosulfide, or  sodium sulfide is add-
ed and the treated acid is filtered.  The  excess
hydrogen sulfide is removed from the acid by
air blowing.

The entire process is very corrosive,  and
special materials of construction are required.
Stainless steel, carbon,  and graphite are com-
monly used for this severe service.

Special facilities are required for handling
elemental yellow phosphorus  since it ignites
spontaneously on contact with air at atmospher-
ic temperatures and is highly toxic.  Phosphorus
is always shipped and stored under water to pre-
vent combustion.  The tank car of phosphorus is
heated by steam coils to melt the water-covered
phosphorus.  Heated water at about 135°F is
then pumped into the lank car and displaces the
phosphorus,  which flows into a storage tank,
A similar system using hot displacement \vater
is frequently used to feed phosphorus to the
burning tower.

THE AIR POLLUTION  PROBLEM

A number ol air contaminants,  such as phosphine,
phosphorus pentoxidc, hydrogen sulfide,  and phos-
phoric aci 1 mist,  may be released by the phosphor-
ic acid process.

Phosphine  (PII->),  a very toxic gas, may be formed
by the hydrolysis of metallic phosphides that exist
as impurities in the phosphorus.  When the tank
car is opened,  the  phosphine usually ignites spon-
taneously but only momentarily.

Phosphorus pentoxide (P^OJQ), created when
phosphorus is burned  \vith excess air, forms
an extremely dense fume.  Our military forces
take advantage of this property by using this com-
pound to form smoke  screens.  The fumes are
submicron in size and arc 100 percent opaque.
Except lor this military use, phosphorus pent-
oxiclc is never  released to the atmosphere unless
phosphorus is accidentally spilled and exposed
to air.  Since handling elemental phosphorus is
extremely hazardous, stringent safety precau-
tions are mandatory,  and phosphorus spills are
very infrequent.

Hydrogen sulfide (H?S) is released from the acid
during treatment with NaHS to precipitate sulfides
of antimony and arsenic and other heavy metals.
Removal of these heavy metals is necessary for
manufacture of good grade acid.  H2S is highly
toxic and flammable.  Health authorities recom-
mend a maximum allowable  concentration of this
gas of 20 ppm for an 8-hour exposure.   The odor
threshold is  0. 19 ppm (Gillespie and Johnstone,
1955). In practice, however, H^S  is blown from
the treating tank and piped to the phosphorous-
burning tower where it is burned to SC^.  Source
test information indicates that the concentration
of SC>2 in the gaseous  effluent from the acid tower
scrubber will not exceed 0. 03 volume percent. Evo-
lution of HzS is also minimized by  restricting the
amount of NaHS in excess of that needed to precipitate
arsenic and antimony  and other heavy metals.

The manufacture of phosphoric acid cannot be
accomplished in a practical way by burning
phosphorus and bubbling the resultant products
through either  water or dilute phosphoric acid

-------
736
      CHEMICAL PROCESSING EQUIPMENT
(Slaik and Turk,  1953).  When water vapor comes
into contact with a gas stream that contains a
volatile anhydride,  such as phosphorus pentoxide,
an acid mist consisting of liquid particles of var-
ious  sizes is formed  almost instantly.  An investi-
gation  (Brink,  1959) indicates  that the particle
size  of the phosphoric acid aerosol is small,
about 2 microns or less,  and that it has a median
diameter of 1.6 microns,  with a range of 0. 4   to
2. 6 microns.
The tail gas discharged from the phosphoric acid
plant is saturated with water vapor and produces
a 100 percent opaque plume.   The  concentration
of phosphoric acid in this plume may be kept
small with a well-designed plant.  This loss
amounts to 0. 2 percent or less of the phosphorus
charged to the combustion chamber as phosphorus
pentoxide.

HOODING AND  VENTILATION REQUIREMENTS
All the  reactions involved take place in closed
vessels.  The phosphorus-burning chamber and
the hydrator vessel are kept under a slight neg-
ative pressure by the fan that  handles the effluent
gases,  as shown in Figure 520.  This is  neces-
sary to prevent loss  of product as  well as to pre-
vent air pollution.

The hydrogen sulfide generated during the acid
purification treatment must be captured and col-
lected,  and sufficient ventilation must be  pro-
vided to prevent an explosive concentration, for
hydrogen sulfide has  a lower explosive limit of
4. 3 percent.  The sulfiding agent must be care-
fully metered into the acid to prevent excessive-
ly rapid evolution of  hydrogen sulfide.

AIR POLLUTION CONTROL  EQUIPMENT

The  hydrogen sulfide can be removed by chem-
ical  absorption or by combustion.   Weak  solu-
tions of caustic soda or soda ash sprayed
countercurrently to the gas  stream react with
the hydrogen  sulfide  and neutralize it:
     Na2C°3
      2NaOH +
 NaHC03 + NaHS
                          Na S
 The hydrogen sulfide may also be oxidized in
 a suitable afterburner:
      2H S
           +  3CL
2H2°
+ 2SO,
 The phosphoric acid mist in the tail gas is
 commonly removed by an electrical precip-
 itator,  a venturi scrubber, or a Brink fiber
 mist eliminator (Brink,  1959).  All are very
 effective in this service.
                            The Tennessee Valley Authority has used elec-
                            trical precipitators for many years to reduce
                            the emission of phosphoric acid mist (Striplin,
                            1948).  Severe corrosion has always been a
                            problem  with these precipitators.  Published
                            data  (Slaik and Turk, 1953) indicate that the
                            problem  has been partially solved by reducing
                            the tail gas temperature to 135°   to 185°F.
                            The acid discharged amounts to about 0. 15 per-
                            cent  of the phosphorus pentoxide charged to the
                            combustion chamber as phosphorus.  The rela-
                            tively low gas temperatures and consequently
                            infrequent failure of the wires are given as the
                            reason for the high mist recovery from the gas
                            stream.

                            The TVA replaced one of the electrical  precip-
                            itators with a venturi scrubber in 1954.  The
                            venturi scrubber is constructed  of stainless
                            steel and is 14 feet 6 inches high, with  a 30-
                            inch-diameter inlet and  outlet and a 11-1/2-
                            inch-diameter throat (Barber,  1958).  The
                            scrubber is followed by a  centrifugal entrain-
                            rnent separator.   Stack analyses of emissions
                            from this production unit are summarized in
                            Table 199.


                              Table  199.  STACK ANALYSES OF EMISSIONS
                                  FROM A PHOSPHORIC ACID PLANT
                                      WITH A VENTURI SCRUBBER

                             Phosphorus burning rate, Ib/hr        2,650
                             Temperature,  °F
                              Vaporizer outlet                      1,650
                              Burner outlet                           880
                              Venturi scrubber  outlet                 195
                              Stack gas                              175
                             Pressure drop,  in. WC
                              Across venturi scrubber                 25.2
                              Across entrainment separator              1.9
                             Emissions as % of phosphorous burned      0. 2
In 1962,  the TVA constructed a stainless steel
phosphoric acid unit that has an adjustable ven-
turi scrubber,  followed by a packed scrubber,
and a wire mesh mist eliminator.  When the
venturi scrubber is adjusted to give a pressure
drop of 37 inches of water column or higher,
losses of PT^ from  the unit amount to only
about 5 pounds per hour at phosphorus-burn-
ing rates  up to 6, 000 pounds per hour.

Considerable research and development work
by the TVA demonstrated that  good recovery of
phosphoric acid mist could be  achieved by intro-
ducing-water vapor into the hot gases from the
combustion of phosphorus,  passing the  mixture
through a packed tower, and condensing it
(Slaik and Turk,  1953).

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                      Soap,  Fatty Acid, and Glycerine Manufacturing Equipment
                                                                                                  737
A large-scale plant using a Raschig  ring-packed
tower followed by three gas coolers  was built.
Overall phosphorus pentoxide recovery exceeded
99. 9 percent, but the process  was eventually
abandoned because of the excessive rate of corro-
sion of the gas coolers.
This same process, with a second packed scrubber
or glass  fiber-packed filter unit for acid mist re-
moval replacing the gas cooler,  is used by a number
of phosphoric acid  producers throughout the country.
These plants routinely operate with phosphorus
pentoxide recovery efficiencies in excess of 99. 8
percent.   A visible phosphoric acid plume still
remains, though the phosphorus content has been
reduced  to less  than 0. 1 grain per scf.  A plant
such as this  is in operation in  Los Angeles County
and is shown in  Figure 568.  The plume contains
a large percentage of water vapor and does not
violate local air  pollution prohibitions.  Stack
analyses of emissions from this plant are shown
in Table  200.

The packed scrubber must be thoroughly and uni-
formly wetted with either water or weak acid and
must have  uniform, gas distribution to achieve high
collection  efficiency.  Good gas distribution is also
mandatory for glass fiber filter units, and a  super-
ficial gas velocity  of less than 100 fpm is recom-
mended.
Figure 568.  Phosphoric acid plant with a  Raschig
ring-packed  scrubber.
The Brink (1959) fiber mist eliminator is a rela-
tively new type of collector that has been used
successfully on sulfuric acid mist,  oleum, phos-
phoric acid,  ammonium chloride  fume, and various
organics.  Collectors of this type have been dis-
cussed in the preceding section of this chapter.

At one plant  owned by Monsanto Chemical Company,
the stack plume was very persistent and visible.
Thirty milligrams  of fine sulfuric acid mists  per
standard cubic foot and 80 to 200  milligrams of
phosphoric acid particles per standard cubic foot
were emitted from the stack.  To correct the
situation,  a gas absorption apparatus followed
by a fiber  mist collector was installed.  Collec-
tion efficiencies of 99 percent on  particles less
than 3 microns in diameter and of 100 percent
on larger particles were achieved.  The stack
plume, which consists of 15 percent water vapor,
disappears within 40 to 50 feet  of the  stack on
dry days and within 150 feet on wet days. No
maintenance problems or changes in pressure drop
through the apparatus have been encountered.


  SOAP,   FATTY  ACID,  AND  GLYCERINE

     MANUFACTURING  EQUIPMENT

INTRODUCTION

Soap for  washing and emulsifying purposes has
been manufactured and used for over  two thou-
sand years.   Traditionally,  soap has been manu-
factured  in batches by  saponifying natural oils
and fats with a solution of  caustic soda,  salting
out the soluble soap formed,  and  drawing off the
dilute glycerol produced.   Shortly before World
War II,  major changes started  to occur in the
industry.   Pretreatment of the  fats  and oils was
introduced and changes were made in plant pro-
cedures and in finishing of the soap.  Since  Wrorld
Was II,  with the advent of  synthetic detergents,
soap use has declined precipitously until its pro-
duction today  constitutes less than 20 percent of
the combined  production of soaps  and detergents
(Silvas, 1969).  Figure 569 illustrates the vast
change in relative production of soap  and deter-
gent since 1944.  The manufacture of detergents
is discussed in another section  of this manual.

When the direct neutralization of fatty acids by
soda ash and/or caustic soda •was introduced as
a soap-making process, fat  splitting, or hydroly-
sis,  became   a basic operation  of the soap indus-
try.   Prior to 1955, the soap industry generated
its own supply of fatty acids for use in soap mak-
ing by splitting of natural fats and oils and pro-
vided fatty acids to other chemical process in-
dustries.   Since 1955,  however, fatty acids have
also been synthesized from petroleum products,
so that today fatty acids are produced synthetical-
ly in greater quantities than by  splitting natural

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738
CHEMICAL PROCESSING EQUIPMENT
              Table 200.  STACK ANALYSES OF EMISSIONS FROM A PHOSPHORIC ACID
                      PLANT WITH TWO RASCHIG RING-PACKED SCRUBBERS


Phosphorus burning rate, Ib/hr
Gas rate, stack outlet, scfm
Gas temperature, stack outlet, °F
Diameter of first packed scrubber, ft
Height of first scrubber's Raschig ring packing, ft
Diameter of final packed scrubber, ft
Height of final scrubber's Raschig ring packing, ft
Final scrubber's superficial velocity, fpm
^2^5 emitted, gr/scf
P2O5 emitted, Ib/hr
Emissions as % of phosphorus burned
Report series No.
C-167 A
1,875
12,200
175
8.5
12
20
3
47
0.095
9.9
0.23
C-167 B
895
3, 420
162
8.5
12
20
3
13
0. 108
3.2
0. 16
  1944
 Figure  569. Production of  soap and detergents  in the
 United  States,  1944 to 1968  (Chemical Week,  1969).

fats and oils.   The soap industry, however,  still
uses fatty acids produced almost exclusively by
splitting natural oils and fats, and still supplies
a significant amount  of fatty acids to  other chemi-
cal process industries.   The soap industry had
been the principal supplier of glycerine to chemi-
cal process industries.   However,  glycerine is
now produced synthetically, and presently the
soap industry supplies only about one-half of the
total glycerine consumed in this country.

Metallic soaps have uses entirely different from
those for ordinary soaps, so that theyare not in
direct competition.   These soaps are alkaline
earth, metal, or heavy-metal salts of fatty acids.
They  are made  either by heating fatty acids  with
metallic oxides, carbonates,  etc. , or by the re-
a.ction of soluble ordinary soap with solutions of
heavy-metal salts.   Their  manufacture will not
be discussed in this  section.
                      RAW MATERIALS

                      The soap industry applies the term "oil" to those
                      natural fats which are liquid at ambient conditions,
                      excluding hydrocarbon oils obtained from petro-
                      leum.   "Fats, " in the soap industry, refers to
                      all natural oils  and  fats, liquid or  solid.  Soap
                      is produced almost  exclusively from these natu-
                      ral fats and oils.

                      Ordinary soluble  soaps  are  classifiable in a num-
                      ber of -ways.  They may be  generally classed as
                      toilet soaps, household  soaps or industrial soaps.
                      Traditionally,  sodium soaps have been called hard
                      soaps,  and potassium soaps  called soft soaps.
                      Today such classification is  no longer meaningful,
                      as the hard or soft quality of soap  is much more
                      dependent on the type and quality of fats and oils
                      used to make the  soap.

                      The properties  of soaps are  directly related  to the
                      type of fatty acids used.  The most desirable  fatty
                      acids are lauric,  myristic,  paluitic, stearic, and
                      olsic,  which are acids having 1Z to 18 carbon
                      atoms.  These acids constitute the bulk of the
                      fatty acids found in  tallow and  coconut oil. As a
                      result, many soaps are combinations of these two
                      oils,  usually in ratios of 3 or 4 parts of tallow to
                      1 part coconut oil.  Because of its favorable  acid
                      content, availability,  and low price,  tallow is the
                      most predominant fat used for soap making.   It
                      constitutes 80 percent or more of the total fats
                      used by the soap industry.  Greases,  the  rendered
                      fats from hogs and  other small domestic animals,
                      are the next most often  consumed fatty material
                      (Shreve,  1967).  Other  natural oils,  including
                      marine oils, may also be used in the soap making
                      processes.  Many of the marine oils are used in
                      special applications.  They represent only an
                      insignificant  portion  of the total fats used.

                      Sodium hydroxide is the saponifying alkali used
                      for most soap manufacture.  Potassium hydroxide

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                      Soap, Fatty Acid, and Glycerine Manufacturing Equipment
                                                                         739
still is used to some degree, and because potas-
sium soaps are more soluble than the sodium
soaps, they are used, or blended with sodium
soaps, for making liquid soap solutions.  Miner-
als, including soda ash, caustic potash, sodium
silicate, sodium bicarbonate,  and trisodium
phosphate,  are used  extensively as builders or
fillers.  Used in smaller quantities, but of ex-
ceeding importance as synergetic  soap  builders,
are tetrasodium pyrophosphate and sodium tri-
polyphosphate.  Carboxylmethylcellulose (CMC)
also is an additive for most heavy-duty soaps.

Finished soaps also may contain small  quantities
of chemicals used as preservatives, pigments,
dyes, and perfumes, as -well as antioxidants  or
chelating compounds.  Bar toilet soaps and pow-
der or granular laundry soaps may be manufac-
tured as a  combination of synthetic detergents
and the neutralized fatty acid soluble  soaps.
Detergents  used are  either anionic or nonionic,
but not cationic.

FATTY ACID  PRODUCTION

Fatty acid  production from natural fats may be
performed by any one of several processes.  The
processes  all result  in "splitting" or hydrolysis
of the fat.   This may be represented as:
H
H

H
              H
              I
         H —C —OH
              I
3RCOO +  H —C —OH
              I
         H —C —OH
              I
              H
     FAT
FATTY
ACID
GLYCEROL
Three current processes for  splitting or hydro-
lyzing fats to produce fatty acids and glycerol
utilizing either batch or continuous processes
are detailed  and compared in Table 201.  Several
older process methods,  such as panning and
pressing procedures,  fractional distillation, and
solvent crystalization, no longer are used.  Of
the three current processes,  the continuous high-
pressure hydrolysis process  is the one  most often
used by the soap industry.  A flow diagram  of the
process is shown in Figure 570.

In the continuous high-pressure hydrolysis pro-
cess, fat and water, both in liquid phase, are
heated in contact with each other to temperatures
in excess of  about 400 °F, and  some of  the water
becomes dissolved in  the fatty matter.   The pro-
portion of water that becomes dissolved in the
fatty layer increases rapidly with rise in tempera-
ture,  causing a reduction in the aqueous layer.
At temperatures approaching 550 °F, depending
upon the type of oil used, the aqueous phase
merges into  the fatty phase, leaving but a single
liquid phase  (Ittner, 1942).  In practice, the
equipment is operated at temperatures  and pres-
sures -where the two components show consider-
able mutual solubility but below the temperatures
•where  only one phase exists.  The glycerine
formed is  continuously removed in the water
stream,  and at the same time  the product fatty
acids are removed as a separate stream.

The equipment used for this process is a vertical
column (Figure 570).  The  fats,  in liquid form,
are first vacuum deaerated, -which prevents dar-
kening, and then pumped into the bottom of the
column through a sparge ring.  Deaerated, de-
mineralized water is pumped at high temperature
and high pressure into  the top  of the tower.  High-
pressure steam, at pressures  of 700 to 750 psi,
is introduced into the tower either along with the
oil or directly into the  reaction zone at the center
of the tower,  or, in some  cases,  at both the top
and bottom of the tower.  Tower operating pres-
sures are usually 650 to 800 psi,  and temperature
of the fats is usually around 485 °  to 500  °F.   The
oil droplets travel up the column, while the water-
glycerine solution flows down the column.  The
fatty acids then pass  overhead to a flash tank for
the removal  of entrained -water,  or they may be
decanted from the water after  cooling and then
passed to a settling tank -where further  separation
occurs.

As  shown in Figure 570, the glycerine and water
solution,  called sweetwater, is drawn  from the
bottom of the hydrolyzer tower and is passed
through a series of evaporators, or to a flash
tank to remove some of the water, and then to
storage as crude glycerine.

The fatty acids produced are characteristic of
the particular type oils being processed.  Distil-
lation is employed frequently on-stream with con-
tinuous hydrolization to further refine  fatty acids.
When chemical and industrial products are manu-
factured from these fatty acids, fractional distil-
lation is used.  When soap  stock is produced,
simple distillation in a continuous vacuum-type
still is used as shown in Figure 570.

In the vacuum still,  the boiling fatty acids pass
overhead through a series  of condensers.   They
are then either drawn off and pumped to storage
as fatty acids or passed through a line mixer
•where caustic soda or soda ash is added to pro-
duce the salt of the fatty acids, which is a soluble
soap.  The soap stock thus produced is then held
in storage for use in the various soap manufac-
turing and finishing operations.
   234-767 O - 77 - 49

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740
             CHEMICAL PROCESSING EQUIPMENT
    Table 201.  COMPARISON OF THREE CURRENT FAT-SPLITTING PROCESSES (Shreve. 1967)
                   Twitchell
                              Batch autoclave
                                  Continuous
                                countercurrent
Temperature,  "F
Pressure, psig

 Catalyst
Time,  hr
Operation
 Equipment
 Hydrolyzed
 Advantages
Disadvantages
212 to220
0

Alkyl-aryl sulfonic acids
 or cycloaliphatic sulfonic
 acids, both used with sul-
 fur ic acid,  0. 75  to 1.25%
 of the charge
12 to 48
Batch
Lead-lined, copper-lined,
  monel-lined, or
  wooden tanks

85 to 98 % hydrolyzed;
5 to 15 % glycerol solution
 obtained, depending on
 number of stages and
 type of fat

Lo,v temperature and
  pressure; adaptable to
  small scales; low first
  cost because of relatively
  simple and inexpensive
  equipment
Catalyst handling; long
  reaction time; fat stocks
  of poor quality must
  often be acid-refined to
  avoid catalyst poison-
  ing; high steam consump-
  tion; tendency to form
  dark-colored acids;
  need for more than one
  stage for good yield and
  high glycerin concentra-
  tion; not adaptable to
  automatic control;
  high labor cost
300 to350 (450 without catalyst)
75 to  150 (425 to 450 without
  catalyst)
Zinc
  calcium,
  or magne-
  sium
  oxides .
  1 to 2%

5 to 10
Batch
Copper or  stainless-steel
  autoclave
85 to 98 % hydrolyzed;
10 to 15 % glycerol,
  depending  on
  number  of stages and
  type of fat

Adaptable to small
  scale; lower first cost
  for small  scale than
  continuous process;
  faster than Twitchell
High first cost; catalyst
  handling; longer
  reaction time than
  continuous process;
  not so adaptable to
  automatic control as
  continuous; high
  labor cost; need for
  more than one
  stage for good yield
  and high glycerin
  concentration
485 approx.
600 to700

Optional
2 to 3
Continuous
Type 316 stainless
  tower
97 to 99 %. hydolyzid;
10 to 25 % glycerol,
 depending on type
 of fat
Small floor space;
 uniform product
 quality; high
 glycerin concen-
 tration; low
 labor cost; more
 accurate and
 automatic control;
 constant utility
 load

High first cost;
  high temperature
  and pressure;
  greater operating
  skill
The fatty acids, -which may contain considerable
unsaturated organic acids,  can be  further pro-
cessed by hydrogenation.  Hydrogenation, with
the use of a catalyst, saturates the double bonds
of the unsaturated fatty acids.   The process helps
to eliminate objectionable odors and hardens the
                                   soap stock.   The hydrogenation operation is usu-
                                   ally on-stream with the hydrolysis operation.

                                   GLYCERINE PRODUCTION
                                   The saponification of natural oils can be repre-
                                   sented by the following reaction:

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                       Soap, Fatty Acid, and Glycerine Manufacturing Equipment
                                                                          741
                                                                         FATTY ACID
                                                                      TO HYDROGENATION
                                                                        OR STORAGE
                                                                   CRUDE
                                                                 GLYCERINE
                                                                  SETTLING
                                                                   TANK
                 Figure 570. Flow diagram of a continuous  process  for hydrolysis of natural  fats.
     H
     I
H — COOCR
     I
H — COOCR +  3NaOH
     I
H — COOCR
     I
     H
    FAT
                H
                I
            H —C —OH
                I
•SNaCOOR  + H —C — OH
                I
            H —C — OH
                I
                H
  SOAP
GLYCEROL
Whether soap is manufactured by the older method
of saponification of natural oils illustrated by the
preceding reaction or by the newer method of
direct saponification of fatty acids, glycerine is
always an accompanying product.

Figure 571 illustrates a typical soap plant  glyc-
erine purification operation.  The crude weak
glycerine solution derived from the hydrolysis
process  is refined  to produce both commercial
and pharmaceutical grades of glycerine.  The
processing of the glycerine obtained from the
continuous hydrolysis process is a much easier
operation than the processing of the  spent soap
lye glycerine from the kettle or batch processes
of soap making.  The  sweetwater drawn from
the bottom of the hydrolizer column  has a con-
centration of about 12  percent glycerol.  This
sweetwater usually is so hot that, upon passing
through three evaporators in sequence, the  glyc-
erol concentration  increases to about 75 to  80
percent by weight.   This crude  glycerine then is
held in a settling tank for at least 48 hours  at
elevated  temperatures to reduce whatever fatty
impurities are still present. It then is  distilled
under  vacuum (60 mm Hg absolute) at tempera-
tures of  approximately 400 °F.   Small  amounts
of caustic are added to the  still feed to saponify the

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742
                               CHEMICAL PROCESSING EQUIPMENT
                                                            HOT WATER
                                                                    BLEACH
                                                                  AND FILTER
                                                                  FEED TANKS
                                                                                    REFINED PRODUCT
                    STEAM
                                             FOOTS
                Figure 571. Flow diagram  for glycerine manufacture  from hydrolysis sweetwaters.
small amounts of fatty acid impurities which are
present so that they will not boil off.  The overhead
product glycerine from the vacuum still then is
condensed in a three-stage condensing system
with progressively lower temperatures at each
stage.   The staged condensation yields  different
grades of glycerine.   The highest temperature
first-stage condensate usually contains 99 percent
glycerol.   Lower quality grades are collected
from the lower temperature condensers. The
glycerine is purified by bleaching and filtration
or ion  exchange.

In the making of soap by alkaline saponification
of fats, glycerine always is formed and  common-
ly is recovered in solution in the soap lye. The
spent lye  removed from the saponification process
averages  around 4 to 5 percent glycerine when
removed directly, and may exceed  10 percent
when other washing  processes are used.  The
spent lye,  in addition to the glycerine,  contains
roughly 10 percent by weight of salt and  some
small amount of soaps that are still soluble in
the lye.

Figure 572 illustrates a typical spent soap lye
processing plant. The first step is the purifica-
tion of the lye solution removed from the saponifi-
cation operation.  The lye is neutralized by treat-
ing with mineral acids to form a salt.   The neu-
tralized solution is heated and agitated to precip-
itate any remaining soap.  After filtration, the
solution then is  evaporated.   Vacuum evaporation,
either in a series of batch vessels or continuously
in cone bottom vessels, causes  the salt crystal-
lization point to be reached.

As the salt concentration increases, salt crystal-
lizes  out and separates.  In the continuous vessel,
a portion  of the separated salt is intermittently
removed from the bottom.   In the batch separation,
the salt is removed from the slurry by pumping it
through filters or centrifuges.  Recovered salt is
reused in the  soap making process.  The concen-
trated glycerine is boiled down to remove even
more salt until  a concentrated crude soap lye
glycerine is obtained.  At this stage the crude
glycerine constitutes  80 to 82 percent by weight
of the solution with approximately 2 percent by
weight of  nonvolatile organic matter, the remain-
der being a mild salt  solution in water. Further
treatment of this crude glycerine follows the same
procedures used with the crude glycerine  obtained
from fat splitting operations.

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                       Soap, Fatty Acid, and Glycerine Manufacturing Equipment
                                                                                                   743
                                                                                        VACUUM PUMP
      FATTY ACID OR
      HIGH F.A. STOCK
                       SPENT SOAP LYE
                      FROM SOAP MAKING
                                                                            SALT -TO SOAP MAKING
                        Figure 572. Spent soap lye  plant for  recovery of crude glycerine.
SOAP MANUFACTURING

The soap-making processes, either those utiliz-
ing the alkaline saponification of fats and oils or
those employing the saponification of fatty acids,
are variously batch or continuous.   The kettle or
full-boiled process is a. batch process which fol-
lows the historical and traditional soap-making
methods since the beginning of the industry.  This
process  involves several steps or operations in a.
single kettle or, in large operations, a series of
kettles.  The kettles or pans used in these pro-
cesses vary considerably in size depending upon
production requirements.   Small operations or
producers  of specialty soaps may employ a kettle
which will  only produce a few hundred pounds of
soap.  Large commercial producers of soaps may
use kettles which will produce 150,000 pounds of
soap per batch.
The steps or operations performed include sapon-
ification of the fats and oils by boiling in a caustic
solution using live steam, followed by "graining"
or precipitating the soft curds of soap out of the
aqueous lye solution by adding sodium chloride
salt.  The soap solution then is washed to remove
glycerine and color body impurities to leave the
settled  or "neat" soap to form on standing.   Neat
soap is  the almost pure  soap produced in the full-
boiled process and remains as the upper layer of
soap from which "nigre" soap and lye solutions
have settled.  The steps described above in the
full-boiled process, including that of the final
settling, can require a period of several days.
The smaller kettles using this process may re-
quire up to 24 hours per batch, while the larger
kettles  may require up to a full week to complete
a batch.

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744
                              CHEMICAL PROCESSING EQUIPMENT
Other batch processes of saponification of fats
and oils, still used for  small production runs of
specialty soaps, include the  semiboiled process,
the cold process, the autoclave process,  the
methyl ester process and the jet saponification
process.

Two proprietary processes for continuous sapon-
ification of natural  oils are used by some soap
manufacturers.  These are the Sharpies  Process
and the Mon Savon Process.  Both processes,
while dissimilar, eliminate the large kettles and
lengthy process  time required  by the old tradi-
tional batch operations.  All processes,  however,
accomplish the same steps of soap manufacture.

The manufacture of soap by direct saponification
of fatty acids is  easily accomplished in continuous
processes.  However, many plants employ con-
ventional soap kettle processes.   Batch saponifi-
cation also is performed in mixing kettles, com-
monly called crutchers.  Fatty acids obtained by
continuous hydrolysis are usually neutralized with
50 percent caustic soda continuously in a  high-
speed mixer-neutralizer to form soap. The neat
soap produced is discharged at 200 T into an
agitated blending tank to even out any inequalities
of neutralization.   The  neat  soap contains approx-
imately 30 percent  water at this  stage. This soap
stock then is held at an elevated temperature for
use in the various soap finishing operations.
SOAP FINISHING

Soap is finished for consumer use in various
forms such as liquid, powder, granule, chip,
flake,  or bar. Part of the finishing operation
for soap is the addition of various ingredients to
accomplish the purposes  for which the final pro-
duct is designed.  Toilet  bars of the purest type
of soap will have the minimum of additional in-
gredients.   Heavy-duty laundry soaps will have a
maximum of other  ingredients added.   All soap,
after finishing,  contains  some water,  usually be-
tween  10 and 30 percent,  because anhydrous soap
would  be too insoluble to  use easily.   The finished
soap product contains perfume which, while fre-
quently not apparent, has been mixed  in with the
soap to disguise somewhat unappealing odors.

Bar soap is produced in three general processes.
The oldest process, the framing process, seldom
is used today except for some special types of
soap.  In this process, liquid soap, after mixing
or crutching -with other necessary ingredients, is
poured as a semiliquid paste into large vertical
molds.  The soap hardens upon cooling in these
molds.  The sides  of the  molds or  frames are
removed and the soap  is cut by mechanical saw-
ing processes into  rough  shapes  and sizes of the
bars.  They are then stamped into  the final  shape,
with whatever markings are desired, and wrapped
for shipment.

Most bar soap today is  manufactured by a second
process, the "milling"  process.  Milled  soaps,
as they are  called by the industry, usually are
manufactured in one of  two processes.  In the
older and still more commonly used process
shown in Figure 573, the soap stock is batched
in a mixer,  called a "crutcher", with other  in-
gredients.   The batch is then flowed onto chill
rolls,  and then flaked off and passed through a
steam-heated hot-air dryer.  The flakes  can be
packaged as flake soap  or  ground and packaged as
powder. When soap bars are made,  the  flakes
from the dryer are "plodded" (mixed in a screw
or sugar tubular mixer) or mixed with  final  in-
gredients such as perfume.  The plodded material
then is fed to a roll mill.  The flaky  soap produced
by the roll mill  then is  plodded again to throughly
mix ingredients and improve texture and is ex-
truded in a continuous bar shape for  cutting,
stamping, and-wrapping.
GRINDER


POWDER
PACKAGING
              STEAIY!
MIXER


PLODDER
CUTTER


STAMPER


BAR
PACKAGING
  Figure 573. Flow diagram of milling soap finishing
  process.

In the second and more recent milled soap pro-
cess, the basic blended soap  stock is pumped
through atomizing nozzles against the inside wall
of a vacuum chamber and dropped from the cham-
ber into a plodder.  Figure 574 is a diagram of
this process.   The plodded soap is immediately

-------
                       Soap,  Fatty Acid, and Glycerine Manufacturing Equipment
                                                           745
                 MINOR INGREDIENTS
TO VACUUM
    Figure 574. Flow diagram of vacuum  flash drying
    process for bar soap production.
mixed with the necessary additional ingredients
and then passed through a  series of roll mills
and plodders until it is extruded in a continuous
bar for cutting,  stamping, and •wrapping.

A third process, illustrated in Figure  575, pro-
duces aerated soap bars.  Neat soap is heated
under pressure  and then -water is flashed off.
Air is mixed with the  soap, perfume is added, and
the paste chilled and then extruded continuously.
After cutting to  rough  shape, the bars  are  "aged"
or cooled, and then stamped and -wrapped.

Soap also is finished for marketing in flake or
chip form.  In manufacturing this type of product,
the same procedures are folio-wed as were de-
scribed for the framing process.  The only ex-
ception is that after hot air-drying, the soap is
not milled or plodded.

Soap powder formerly was produced by grinding
the chips coming from the hot air-dryer discussed
above and shown in Figure 573.  This method of
soap powder manufacture has been highly unsat-
isfactory since it produced a product containing
excessive fines.  However, this process is still
used occasionaly in some soap plants.  Soap
powders now are manufactured almost exclusive-
ly by first crutching the soap stock with the fillers
and other additives to  produce the final composi-
tion and then spray drying the slurry mix.  The
spray drying of  soap and the spray drying of  syn-
CUTTER


CTAMPFR



BAR
PACKAGING
                    Figure 575. Flow diagram of  aerated  soap bar
                    production.
              thetic detergent compounds are very similar pro-
              cesses.  Spray drying is discussed in much great-
              er detail in the section of this manual dealing
              with detergents.

              Liquid soaps very rarely are manufactured today
              except for some very specialized products such
              as "pure soap hair shampoo. "  Top quality liquid
              soap is blended in tanks with the other ingredients
              desired and then packaged in standard bottle
              filling  equipment.

              THE AIR POLLUTION PROBLEM

              All chemical processes and  some of the other
              operations involved in the making of soap,  pro-
              duction of fatty acids,  and the purification of
              glycerine have odors as a common air pollution
              problem.  Blending, mixing, drying, packaging,
              and other physical operations are subject to the
              air pollution problems of dust emissions.

              Odors  may be emitted from  equipment used for
              the following operations:

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 746
CHEMICAL PROCESSING EQUIPMENT
   1.  Receiving and storage of animal and vege-
      table oils

   2.  saponification of fats and oils or  of fatty
      acids

   3.  hydrolization of natural fats  and oils to
      produce fatty acids

   4.  distillation of fatty acids

   5.  hydrogenation of fatty acids

   6.  concentration and  distillation of glycerine.

During their  receiving and storage, natural fats
and oils are heated to temperatures not over 150°F
to reduce viscosity for pumping.  The fats and oils
used by most soap manufacturers are of high qual-
ity, and odors usually do not cause a local nuisance
unless the equipment is located adjacent to homes
or businesses.

Fats and oils are heated during the direct saponi-
fication, resulting in the emission of odors.
These odors  may cause a local nuisance, depend-
ing upon the location of the  equipment in the  com-
munity, and may require control equipment.

Odors also are emitted during the  deaeration and
hydrolization of fats and oils to produce fatty acids.
Distillation and hydrogenation of the fatty acids
emit odors.  Fortunately, the flash deaeration of
fats and oils  is performed under a vacuum, pro-
duced usually by •water or steam jets.  Steam jets
are followed  by contact barometric condensers
•which in effect serve as  scrubbers.  This arrange-
ment  of equipment provides  satisfactory odor con-
trol so that the installation of additional control
equipment usually is not necessary.  All  stages of
these operations are vented similarly.  Figure 576
illustrates several vacuum ejector and condenser
systems.

The flash dehydration of glycerine has  been found
to emit only  mild odors. Equipment for glycerine
distillation under vacuum is vented through steam
jets and barometric condensers.  Emissions again
are very light and odors do not  cause any nuisance
problems.

In soap-finishing operations, dust can be emitted
from equipment performing the following opera-
tions: Addition of powdered and fine crystalline
materials to crutchers,  mechanical sawing and
cutting of cold frame soap, milling and plodding
soap, air drying of soap in steam-heated dryers,
milling, forming, and packaging.  Although dust
emissions from these equipment sources rarely
violate existing air pollution regulations, the dust
emissions cause an internal plant hygiene problem.
                      Various pieces of process equipment must there-
                      fore be vented to control equipment for worker
                      comfort and safety.

                      There are, however, other equipment sources of
                      dust emissions which usually exceed air pollution
                      regulations.  The sources are:  Grinding of  soap
                      chips, pneumatic conveying of powders, and spray
                      drying of soap.  Installation of control equipment
                      is necessary for compliance with air pollution
                      regulations as well as -worker comfort and safety.

                      The production of soap powder by spray drying
                      creates  the largest single  source of dust in the
                      manufacture  of soap.  Spray drying is designed to
                      produce relatively coarse  granules followed by
                      highly efficient separation of soap granules from
                      the  drying air before the air is vented to the at-
                      mosphere.  Most towers for the  spray drying of
                      soap are the  concurrent type where both the heat-
                      ed air and soap  slurry spray are introduced at
                      the  top of the tower.  Heated air and soap granu-
                      les  are  separated at the bottom of the tower in a
                      baffled area which causes  the granule-laden air  to
                      make sharp 180° turns.  Most of the soap is de-
                      posited  in the baffled section and drops into  the
                      cone bottom of the spray dryer.  However, a few
                      soap particles still remain in the heated air after
                      passage through the baffled area.  The particles
                      range in size from 2 to 200 microns, with a medi-
                      ian particle size of over 20 microns.  Air pollution
                      control  equipment is required before venting the
                      contaminated air to the atmosphere.

                      The hot soap granules removed from the bottom
                      of the spray dryer must be cooled to prevent cak-
                      ing and  then screened and stored or sent to pack-
                      aging equipment.  The most common way  to cool
                      soap granules is by pneumatic conveying of the
                      soap granules to elevated locations for gravity
                      flow through screens into  storage or packaging
                      equipment.  Cyclone separators or  gravity settling
                      chambers are used to remove the soap granules
                      from the conveying air. Soap particles venting
                      from the separator or settling chamber are finer
                      in size than the soap particles in the exhaust air
                      from the spray  drying tower  and are in  such con-
                      centrations that they must be collected by control
                      equipment in order to comply with air pollution
                      regulations.
                       AIR  POLLUTION CONTROL EQUIPMENT

                       The elimination of odors from the manufacture of
                       raw soap,  fatty acids,  and glycerine can be accom-
                       plished by scrubbers such as water ejectors or
                       barometric condensers.  Figure  576a  shows a
                       contact type scrubber which successfully vents
                       odorous emissions from a vessel used for  dehy-
                       drating blends of tallow and foots oils by heating
                       them above 200 °F.  This water jet contact scrubber

-------
                        Soap, Fatty Acid, and Glycerine Manufacturing Equipment
                                                747
                                                                                      INTERCONDENSER
                                                                     BAROMETRIC CONDENSER
                              iy2 - in. INLET
                                         BAROMETRIC
                                         CONDENSER
                                         75°F
                                         175 dm
                                         500 odor units
                                         PER ft3
                                      OUTLET
       TALLOW AND FOOTS>
      BLEND fANKS  T85°FJ

   50,000 to 100,000 odor units per ft3
    a.  Barometric condenser and fan venting odorous oil
    blending operations.
                                       TWO-STAGE
                                      s STEAM JET
                                       VACUUM PUMPS
     b. Vacuum still which also provides odor reduction.
                                                                   DRUNI DRIER
                                                                                        EJECTOR- VENTURI
                                                                                        SCRUBBER
                                                                                              GAS
                                                                                       SEPARATOR
                                 RECIRCULATINGPUMP
                                OVERFLOW
                                                                         MAKE UP WATER PUMP
      c. Flash tank which provides both jet exhaust
      and odor reduction.
   d. Drum dryer which provides both vapor removal
   and odor reduction.
     Figure 576. Steam and water ejector and  barometric condenser  combinations which also effect odor reduction.
(condenser) reduces odor levels by over 90 per-
cent.  The odor-containing gases vented front this
scrubber are in very low volumes.  The residual
odors are diluted in the atmosphere well below
their threshold levels in traveling through the
atmosphere for  only a short distance from the
scrubber exhaust.
Dust emissions from equipment used in the soap-
finishing operations  other than spray drying can
be controlled by dry filters and baghouses.   Mois-
ture content of the dust-laden air is well below
saturation and close to ambient so that condensa-
tion in the baghouse  is not a problem.  Dust col-
lected in filters or baghouses can be recycled

-------
748
                               CHEMICAL PROCESSING EQUIPMENT
to the process.  Methods for hooding and ventila-
tion of equipment emitting dust and the design of
baghouses or filters are discussed in Chapter 4
of this manual.
Air pollution control equipment for soap spray
drying towers is designed specifically for the op-
erating parameters of the particular tower.  These
parameters include:  Materials sprayed, tower
operating temperature, tower dimensions, gas
velocities, and others.  Because of the relatively
large size of the particulates in  soap drying, high-
efficiency cyclones installed in series may be sat-
isfactory in controlling emissions.  Cyclones per-
mit the recovery of materials for reuse in the
process.  However,  small particulates may escape
collection by the second cyclone and may be in
such concentrations and quantities as to cause
emissions which violate regulations.   Control
equipment of higher collection efficiency than the
cyclones must be used in place of the cyclones or
be installed in series  on the exhaust from the last
cyclone when  this occurs.  A baghouse presents
problems because the exhaust air is usually sat-
urated at temperatures of 100° to 150  °F and,  at
this  saturated condition,  caking and blinding of the
bag fabric can occur unless a  special heated bag-
house design is  employed.   Figure  577 is a flow-
diagram illustrating the control of a soap spray
drying operation.   Multistage  centrifugal scrubbers
or venturi scrubbers have proven to be satisfac-
tory when additional control is required.  Recir-
culation of scrubbing liquid has not been employed
because soap  slurry can cause severe foaming
problems.  Details  on the design of scrubbers are
given in Chapter 4 of this manual.  Further dis-
cussion-which is applicable  to spray drying towers
for soap also  can be found in the following section
on synthetic detergents.
                   WATER
  BUILDERS
                                   CONCURRENT
                                   SPRAY DRYING
                                     TOWER
                               PRODUCT TO
                               STORAGE AND
                               PACKAGING
                                                 BELT CONVEYOR - SOAP GRANULES
    STEAM-^^~\

       "* V^HEATER
                                                                                             AIR INTAKE
   Figure 577.  Flow diagram of soap spray drying process with cyclones and baghouse for  air pollution control.

-------
                       Synthetic Detergent Surfactant Manufacturing Equipment
                                            749
  SYNTHETIC  DETERGENT  SURFACTANT

     MANUFACTURING  EQUIPMENT

 INTRODUCTION

 Surfactants are organic compounds that encom-
 pass in the same molecule two dissimilar struc-
 tural groups, e.g., a water-soluble (hydrophilic)
 and a water-insoluble (hydrophobic) group.  The
 composition, solubility properties, location,  and
 relative sizes of these dissimilar  groups in rela-
 tion to the overall molecular configuration deter-
 mine the surface activity of the  compound (Kirk
 and Othmer,  1969).  Every surfactant possesses
 detergent, dispersing, emulsifying, foaming,
 solubilizing,  and •wetting properties in varying
 degrees.  The predominant property of any parti-
 cular surfactant dictates its use.  Those surfact-
 ants -with strong detergent properties when in
 aqueous solutions are used as  the  active  agents
 in formulating various synthetic detergent pro-
 ducts.  Detergent surfactant production for use
 in compounding of laundry and other cleaning  com-
 pounds  represents  over 80 percent of all synthetic
 surfactant production.  The remaining synthetic
 surfactants produced,  of all types, are used in
 various industrial and  chemical  processes.

 Soap, as  discussed earlier in this  chapter, is a
 detergent type surfactant derived from saponifi-
 cation of natural oils and fats.  It  is generally
 not included in the present meaning of the term
 "detergent. " Detergent is now almost exclusive-
 ly considered to apply to the synthetic organic
 surfactants.  Synthetic detergents  were first
 commercially employed in the textile industry
 during the 1930' s.  Just prior  to World War II,
 some commercial production of  laundry products
 containing detergents was started.   Since the
 close of World War II, products incorporating
 detergents greatly increased in use -with  a con-
 comitant  decline in the use of soap.  By 1968,
 synthetic detergent products accounted for 83
 percent of the total combined production  of soap
 and detergent cleaning compounds  in the  United
 States (Silvas, 1969).  Figure 569  graphically
 illustrates this  change in relationship.
Surfactants are classified into four categories
on the basis of their hydrophilic grouping: (1)
Anionic surfactants have hydrophilic groups that
are carboxylates, sulfonates,  sulfates,  or phos-
phates,  e.g., _OSO3" or-SOs"; (2) cationic sur-
factants have hydrophilic  groups that are primary,
secondary,  and tertiary amines and quaternary
ammonium groups, e.g., —.N(CH3)3+ or C5H5N+_;
(3) nonionic surfactants have hydrophilic groups
that are hydroxyl groups and polyoxyethylene
chains,  e.g., _(OCH2CH2)n OH; (4) amphoteric
or zwitterionic surfactants include more than
one solubilizing group of differing types.
 Table 202  shows the total 1966 U.S. production of
 surfactants divided among several major catego-
 ries.  All  soaps, both those for cleaning and
 •washing products and those for metallic soaps
 for industrial and chemical processes, are in-
 cluded under carboxylates in the table.  The  over-
 whelming bulk of surfactant is produced by the
 soap and detergent manufacturing companies, and
 consists almost exclusively of the anionic types.
 Limited amounts of anionic surfactants used in
 detergent cleaning and washing compounds are
 produced by petrochemical or chemical manufac-
 turing companies.  The  other two major catego-
 ries of synthetic surfactants, cationic and non-
 ionic, are  almost entirely produced by chemical
 manufacturing companies.  Their total produc-
 tion is relatively minor  compared to anionic pro-
 duction. Therefore,  cationic and nonionic sur-
 factants will not be discussed in this section.

Raw  Materials

 The hydrophobic portion of most anionic surfac-
 tants is a hydrocarbon containing 8 to 18 carbon
 atoms in a straight or slightly branched chain.
 In certain cases, a benzene ring may replace
 some of the carbon atoms in the chain, e.g.,
 ^12^25~'  '"'q^'lQ' ^""6^4"'  ^le bulk of anionic
 surfactants are made with dodecylbenzene, or
 commonly  termed "detergent alkylate, " as the
 hydrophobic group.  Prior to 1965, the alkylates
 were produced by reacting benzene or its homo-
 logs -with branched-chain olefins such as propy-
 lene trimer or tetramer.  Since 1965, the alky-
 lates used  for detergents are "soft", or biode-
 gradable, and are made  from long  straight-chain
 normal paraffins, which are combined -with ben-
 zene by the Friedel-Crafts  reaction.  Most deter-
 gent alkylates are produced at petroleum refiner-
 ies or petrochemical plants.  Their production
 •will not be discussed in  this section.  Some
 anionic detergents are made with normal fatty
 alcohols.  Most of these alcohols are produced
 by large soap  and detergent plants by hydro-
 genation of the fatty acids obtained by the hydro-
 lization of  natural oils and fats.  Synthetic alco-
 hols are also used.  The production of natural
 or synthetic alcohol will not be discussed in this
 section.

 The hydrophilic grouping in the anionic synthetic
 detergent surfactants is  either a sulfonate or a
 sulfate.  Sulfur trioxide  or  one of its hydrates,
 sulfuric acid or oleum,  is reacted with alkylate
 or fatty alcohols to organic acids which are later
 neutralized to form salts.   Neutralization is ac-
 complished by employing sodium hydroxide,  so-
 dium bicarbonate, or other sodium bases to form
 the sodium salts  of the sulfonate or sulfate.   Other
 neutralization procedures employ ammonia,  po-
 tassium, diethanolamine, or triethanolamine to
 form their respective salts.

-------
750
                               CHEMICAL PROCESSING EQUIPMENT
                Table 202.  TOTAL U. S. PRODUCTION OF SURFACTANTS, DIVIDED
                INTO MAJOR CATEGORIES.  ALL FIGURES ARE FOR 100  PERCENT
                               SURFACE-ACTIVE MATERIALS
                                         (Kirk-Othmer,  1969)
Type
Anionic synthetics
Sulfonic acids and salts
Sulfuric acids esters and salts (sulfates)
Others
Total anionic synthetic
Nonionic -total all types
Cationic- total all types
Amphoteric- total all types
Carboxylic acids and salts- soaps and others
Total-all surfactants
Production,
pounds
963,812,000
111,925,000
12,956,000
1088,693,000
685,693,000
161,843,000
5, 052, 000
962,222,000
2,903,503,000
Processes

There are  several separate and distinctive pro-
cesses for sulfonation or sulfation of various or-
ganic bases to produce the detergents most com-
monly manufactured.  These processes variously
employ oleum, sulfur trioxide in liquid or in va-
port phase, sulfuric acid in high concentration,
or chlorosulfuric acid.
 The attachment of the sulfonic acid group,
 OH, to a carbon atom of a hydrocarbon group
 (RH) is termed sulfonation.  As

   with sulfur  trioxide  RH + SO3—RSO2OH
   with sulfuric acid ]
   with oleum
                    RH + HSO^
                                   H2O
with chlorosulfuricl RH +
acid (sulfone)      [
                                      + HClf
Sulfation in detergent manufacturing denotes the
attachment of an SO2OH group to an oxygen atom
of an alcohol group.   As
with sulfur trioxide  ROH+ SO3—ROSO2OH

                  >  ROH + HSO^I
   with sulfuric acid
   with oleum
   with chlorosulfurici ROH+C1SO3H—ROSO2OH
   acid (sulfone)      /                + HClf
Oleum is the most frequently used reactant for
sulfonation.  Oleum of 20 or 25 percent strength
(20 or 25 parts by "weight of sulfur trioxide liquid
dissolved in 75 or 80 parts by -weight or concen-
trated sulfuric acid) is most frequently employed.
During the early period of commercial production
of synthetic detergents,  all sulfonation processes
employed 20 percent oleum in batch  operations.
Today almost all sulfonation of alkylate with oleum
is performed in continuous operations.  There are
two typical processes:  (1) Oleum sulfonation and
(2) oleum sulfonation and sulfation.

OLEUM SULFONATION

The most frequently encountered oleum sulfona-
tion is the patented packaged plant illustrated in
Figure 578.  Although the feed  equipment and dis-
charge equipment may differ, the essential sul-
fonation and neutralization processes are the same
for all of these plants.   Oleum  and alkylate are
precisely metered and introduced to a centrifugal
mixing pump.  The reacting mixture is then  cool-
ed in  heat exchangers.   Some reacting product
recirculates to the mixing pump.  The discharged
reacting product enters  a digester tube section to
allow the reaction to go  to completion.  The  pro-
duct is then diluted with water -which hydrolizes
sulfuric acid anhyrides and makes possible sub-
sequent layer separation of spent sulfuric acid
from  the  sulfonic acid.  The  layer separation
step,  which would normally require  several hours,
is effected in only a few minutes by  adding sul-
fonic  acid product to the large mass of recycling
spent acid.  A centrifugal mixing pump is used

-------
                      Synthetic Detergent Surfactant Manufacturing Equipment
                                             751
ALKYL BENEZENE
FROM
STORAGE f—!
ft
OLEUM ;S1
STORAGE PROPORT|ON|NG
PUMP


I
r~\
WH
MIXING
PUMP
i
m
REACl
COIL
?
SULFO
COOLE

'ION
NATION
R
1

t
I — ^
MIXING
PUMP

~vr '
S} SPENT
•DILUTION ACID
COOLER
Al KAI 1



i
€U
MIXING
PUMP
NEUTRALIZED
DETERGENT
SLURRY
y
NEUTRALIZATION
COOLER
                           SULFONATION
                                             DILUTION
         SULFONIC
         CONCENTRATION
NEUTRALIZATION
        Figure 578.  Sulfonation of detergent alkylate with oleum in package plant with vacuum deodorizing
        (Chemithon Corp.,  Seattle, Wash.).
to add dilution water, and the pump recirculates
part of the dilute sulfonic acid along with part of
the spent acid from the separation vessel.  The
spent acid is pumped from the bottom of the
separation vessel,  and sulfonic acid is pumped
from the top.   At this point in the process, differ-
ences from one installation to another are found.
Various  arrangements of equipment provide for:
Neutralization of the sulfonic acid followed by
storage;  deodorization by vacuum treating follow-
ed either by storage  or neutralization and  storage;
storage of the sulfonic acid without any further
treating.


The Air Pollution Problem

Emissions of highly visible -white opacity occur
•when oleum, formerly termed fuming sulfuric
acid, is  charged to a. vessel and the displaced
vapors are allowed to escape to the atmosphere.
The visible emissions result from the reaction  of
sulfur trioxide vapor with water vapor in the  air
to form sulfuric acid particles in mist form.  The
particle  size of this mist is directly comparable to
the sulfuric acid mist in  tail gases from sulfuric
acid manufacturing.  The particles of this mist
are all less than 2 microns and 10 percent by
weight are less than 1 micron.  The threshold of
visibility for this mist has been found experimen-
tally to be of the order of 3.6 x 10~4 grains/ft3
(0.0203 mg/ft  ), the precise value depending upon
the temperature and humidity of the atmosphere
(Fairs, 1958).   Dense white emissions up to 100
percent opacity occur from vents of storage tanks
and process vessels  during filling operations
with oleum.

Continuous sulfonation occurs in this  equipment
in a closed system without venting (except for
emergency relief).  The sulfonic acid separation
vessel is not vented, and the discharge of sul-
fonic acid product and the waste sulfuric  acid,
after separation, to storage tanks does not cause
emissions of more than trace opacities from vents
of these tanks.  When the sulfonic acid is neutra-
lized, no visible emissions occur from the pro-
cess  equipment or from the final storage vessel.

Depending upon the reagents used, the presence
of long alkyl chains in the alkylate can lead to
some dealkylation.  Dealkylation results  in the
formation of small amounts of long-chain olefins
which can cause product odor problems.  To over-
come odors, some plants deodorize the sulfonic
acid product in a vacuum tank.  The thresholds
of the odorous materials removed depend upon
the organic base feed stock.   The ejectors and
barometric condensers used for producing the
vacuum scrub out odorous compounds from the
gaseous stream.  The odorous materials are
skimmed from the water in the hot well.  After
skimming,  the water may safely be cooled with-
out creating odor emissions from the cooling
tower.

Air Pollution Control  Equipment

The transfer of liquid sulfur trioxide into vessels
creates the same dense  visible emissions as de-
scribed for the  transfer of oleum.  When oleum
and liquid SOg were first introduced in industrial
operations, control of emissions was attempted
with simple water or caustic  solution traps or
scrubbers,  but without success.  Scrubbers and
packed towers employing concentrated sulfuric
acid as the  scrubbing or  absorbing medium were
next employed.  Many of these control installa-
tions  succeeded in reducing the opacity of the
visible  mist emissions,  but did not reduce them

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752
CHEMICAL PROCESSING EQUIPMENT
to a point that their corrosive effects on adjoin-
ing equipment were eliminated.

Sulfur trioxide liquid is usually stored, shipped,
and handled at a temperature between  90° and
100 °F.  Commercial stabilized SO3 has a melt-
ing point of about 62.2 "F and a boiling point of
about 112 °F. It is best handled and stored at
92. 2 °F.  Pure SOj has a vapor pressure of 1 at-
mosphere at its boiling point,  but the pressure
will vary,  at some lower value, from  one suppli-
er to  another depending on the stabilizers em-
ployed.  The vapor pressure of 803 over 20 per-
cent oleum, however, is only  0.8 mm Hg at
35 °C  (0.24 ounces/in. 2 at 95 °F).  The vapor
readily reacts  either with water or water vapor
to form sulfuric acid.  Because it is a vapor
phase reaction, and the sulfuric acid formed
immediatley condenses to a  liquid,  the acid drop-
lets are very small. Effective collection of these
mists from tanks and vessels  receiving  SOj or
oleum will require exceedingly high-energy
scrubbers or very high-efficiency filters.   An
effective high-efficiency filter •was constructed
by Fairs (1958).  The filter was made  by com-
pressing silicone treated ultrafine glass fibers
to a bulk density of 10 pounds per cubic foot.  Pro-
vision was made to throughly humidify the acid
bearing exhaust gases before passing them to this
filter.

A high-efficiency filter installation is  illustrated
in Figure 579.  This oleum tank vent control con-
sists  of a Brink Mist Eliminator  filter, manufac-

                                  TO ATMOSPHERE
      FROM
      OLEUM TANK
                                  HIGH-EFFICIENCY
                                  MINERAL FIBER
                                  FILTER UNIT
 Figure 579.  High-efficiency mineral  fiber filter in-
 stalled to vent acid mists  from oleum storage  tank,
 back flow not shown (Brink  Filter,  Monsanto Co., St.
 Louis,  Mo.).
                      tured by Monsanto Company.  Efficient operation
                      of the filter is dependent upon adequately contact-
                      ing the  off-gases with water before entering the
                      filter to convert all sulfur trioxide vapor to sul-
                      furic acid mist for filtration.   This is accomplish-
                      ed by water sprayed concurrent with  the gas flow.
                      A 20 percent  oleum was charged to the vented
                      vessel at a rate of approximately 1000 pounds per
                      minute,  and the filter reduced  the dense white
                      emissions to  a barely visible plume.
                       OLEUM SULFONATION AND SULFATION

                       Another continuous sulfonation process employs
                       both sulfonation of an alkylate and sulfation of an
                       alcohol in a two-stage series reaction with oleum
                       in both stages.  Figure 580 is a schematic flow
                       diagram of this process.   This process is pro-
                       prietary and is  operated by The Procter and Gam-
                       ble Manufacturing Company.
                       Process

                       In this process,  20 percent oleum is continuously
                       introduced to a mixing pump along with alkylate.
                       The process proceeds according to what is termed
                       the "dominant bath" principle to control the heat
                       of sulfonation conversion and maintain the temp-
                       erature at a steady 130 CF.  A high recirculation
                       ratio (volume of recirculating material divided
                       by the volume of throughput) of  at least 20: 1 is
                       maintained to produce a favorable system.  The
                       discharged sulfonic mixture is passed through
                       coils to provide  sufficient time  for sulfonation to
                       reach the desired high conversion.  In the second
                       stage of the process, fatty tallow alcohol, more
                       oleum, and the first-stage sulfonic product  are
                       mixed in a  centrifugal pump. This  stage also
                       employs the dominant bath principle -with a high
                       recirculation ratio.   The discharged sulfonic-
                       sulphate product then passes to a continuous line
                       mixer where a sodium hydroxide solution is in-
                       troduced for  neutralization.  Again, the dominant
                       bath principle with a high recirculation ratio is
                       used in the neutralization step.   The surfactant
                       slurry then is pumped to  storage.  This process
                       makes no attempt  to separate and remove any
                       unreacted sulfuric acid as waste acid. All residual
                       sulfuric acid is neutralized to sodium sulfate.
                       The  Air Pollution Problem

                       The Procter and Gamble process requires an en-
                       tirely closed system.  Venting to the atmosphere
                       occurs only when the surfactant  slurry is dis-
                       charged into a storage vessel.  Gaseous emissions
                       from the storage vessel are minimal, and no air
                       pollution control equipment is required.

-------
                       Synthetic Detergent Surfactant Manufacturing Equipment
                                             753
                                                                 HEAT EXCHANGER!

                                                           MIXING PUMP

                                                                SULFATION

                                                               PROCESS WATER
                           COOL WATER	1

                             NEUTRALIZATION
                                    STORAGE^ \JjJUjy,
                                                                                        HEAT EXCHANGER
                                                                                AGITATOR TANK
                                           HEAT EXCHANGER*
 Figure 580. Continuous series  sulfonation-sulfation with oleum, ending with  neutralization,  employing circulating
 heat-exchanging dominant bath  to control heat (The Procter  and Gamble Manufacturing Co., Long Beach, Calif.).
SULFUR  TRIOXIDE  VAPOR SULFONATION

When liquid detergent compounds •were introduced
as household products, it became necessary to
reduce  the  sodium sulfate content of the surfac-
tant.  Sulfonation -with oleum resulted in excess-
ively high sodium sulfate content when the sur-
factant  was neutralized and used in liquid deter-
gent products.  The high sulfate content (11 to 12
percent) caused  cloudiness in the liquid deter-
gent products and the sulfate settled out in the
bottom  of the  containers.  Sulfonation with pure
sulfur trioxide vapor provided neutralized sur-
factants with much lower sodium sulfate content
(1 to 3 percent) and thus became an important
process.  The first major installations of 803
vapor sulfonation equipment included sulfur burn-
ers for production of SOg.  However,  with the
commercial development and  availability of
stabilized SO, at low costs, many installations
eliminated the SO, production equipment (SO,
production is  discussed earlier in this chapter).

Earliest processes for SO, vapor sulfonation were
batch operations.  Several proprietary continuous
operations are now used for this process.   The
continuous processes employ  several types of
reactors.  One reactor is a mechanically agitated
unit,  and two  others are film type reactors.  The
processes are similar and cause similar air
pollution problems.  SO, is vaporized and diluted
in a dry air stream (dew point 40 °F) to 2f to 8
percent by volume before entering the reactor.
Either alkylates or alcohols may be used in the
processes.   Figure 581 is a schematic flow dia-
gram of one  installation utilizing a film reactor.
In this process,  air is compressed, cooled, and
dehydrated,  then accurately metered to the reac-
tion column.  Simultaneously, stabilized  liquid
SO, is •weighed,  then metered to a  steam heat
exchanger to be vaporized.  Metered air  is mix-
ed -with the SO.j vapor just before entering the
reaction column.  Alkylate, alcohol, or other
organic materials  are  metered and pumped to the
reaction column.  The reactor is a vertical column
designed for concurrent flow from top to  bottom of
the dilute SOj vapor in air and the organic liquid.
Cooling water flows on the outside of the  reactor
from the bottom to top in an opposite direction to
the descending reactants.   The sulfonic acid dis-
charges from the bottom of the column to a cen-
trifugal separator  where liquid sulfonic acid is
drawn from the bottom, and gas is vented from
the top of the separator to the atmosphere (other
installations may recycle the discharged  gas  and
only vent some bleed-off).  The  liquid sulfonic
acid then passes through a. degassing column,
maintained under vacuum,  to remove unreacted
SO, vapors  in the liquid phase.  Depending  upon
the product  manufactured,  the product is  pumped
either to  storage or neutralization tanks or to an
"ageing tank" maintained under  slight vacuum
•where it is agitated and cooled by water coils to
ensure completion  of the sulfonation reaction.
It is then pumped either to storage or to neutra-
lization equipment. Trace amounts of sulfuric

-------
754
    CHEMICAL PROCESSING EQUIPMENT
        COMPRESSED AIR
                                COOL WATER
              LIQUID
              SULFUR TRIOXIDE

                       STEAM
 VAPORIZER
0-
                              ALKYLATE OR ALCOHOL
                                                    COOL WATER-
                                                    INTERNAL SEPARATOR
                                                                          AIR TO
                                                                          POLLUTION CONTROL
                                                                     FILM
                                                                     REACTOR
                             VACUUM LINE
                                                           SULFONICACID
                                                           PRODUCT
                 VACUUM
                 DEGASSER

COOL WATER ^
COOLING TANK
( AGING)
— •>.

*,
<=

*t»
0

"~


                                                                 TO STORAGE
                                                                 OR
                                                                 NEUTRALIZER
                                                              ^ TO STORAGE
                                                                  OR
                                                                 NEUTRALIZER
                                                         PROCESS
                                                         WATER
  Figure 581. Sulfonation with sulfur  trioxide  vapor using  a film reactor (Textilana Corp., Hawthorne, Calif.).
acid anhydrides may be present in the  sulfonic
product, and form sodium sulfate when neutra-
lized.  Fatty alcohols must be neutralized immed-
iately after the reaction with SO^ because sulfuric
acid esters hydrolize rapidly.  Some sulfonic
acid is  diluted with water to eliminate  anhydrides
before being stored.  Neutralization of the sulfonic
acid or sulfate is accomplished batchwise in an
agitated water-cooled tank or in  a dominant bath
continuous neutralizer.  The sulfonic acid or sul-
fate products may be neutralized by sodium or
potassium alkalies or by ammonia.

The  Air Pollution Problem

In the SOo vapor sulfonation process described,
there are three point sources from which air
contaminants can be emitted.  The principal
source  of emission is the venting of gas  separated
from the sulfonic product upon discharge from the
reactor.  When the film reactor  equipment was
first installed,  the emissions were believed to be
                           mostly air with a small amount of SOg vapor as
                           acid mist.  Control of this emission was attempt-
                           ed by employing a mist eliminator followed by a
                           packed scrubber using 99 percent  sulfuric acid
                           as the scrubbing medium.   This method of con-
                           trol did not eliminate the visible emission ranging
                           from 50 to 100 percent opacity.  Upon investiga-
                           tion, the emission was found to be almost com-
                           pletely water soluble and to cause suds in water.
                           The sulfuric  acid in the  scrubber did not in-
                           crease in strength as would be the case if SO-$
                           were absorbed in the scrubber.  Infrared spectro-
                           meter analysis of the gaseous  emissions indicated
                           the principle constituent of the visible  emission to
                           be sulfonic acid.  Fine mists are produced in the
                           reactor and may be formed in  several  ways.  Some
                           alkylate may vaporize in excess of normal equili-
                           brium conditions due to localized hot zones in the
                           reactor to later  condense in the gas  phase with
                           the SOg gas to produce sulfonic acid.  Since the
                           sulfonic acid is produced under conditions below
                           its dewpoint, it immediately condenses from the

-------
                      Synthetic Detergent ^Surfactant Manufacturing Equipment
                                            755
gas phase as a very fine mist.  Some water is
produced by side reactions.   The water vaporizes
and reacts with the SO^ gas in the vapor phase
to form sulfuric acid below its dewpoint result-
ing in a fine mist (Brink, et al. 1966).

The other two points of emissions have not been
found to cause  emissions of excessive  opacities.
One of these points is the exhaust from the single-
stage steam ejector employed to provide vacuum.
The ejector exhaust was found to contain little if
any air contaminants and is not controlled.  The
third point of emission is the  by-pass discharge
from the reactor.   The by-pass discharges liquids
from the reactor during start-up procedures to a
sump for disposal to the sewer system.  When
carefully operated to avoid wasting materials or
product, the start-up by-pass discharge is used
for only a very short period,  usually less than
1 minute.   Visible air contaminants from this
source have been observed only during these
short periods.

Air Pollution Control  Equipment

The visible mist emitted from the vent of the re-
actor is not readily  controlled by scrubbing.  In-
cineration  of the off-gasses eliminates visible
emissions  but results in emission of sulfur oxides.
The high-efficiency  filter discussed previously for
SOg acid mist control may be expected to control
emissions  from the  reactor.  The volume of ex-
haust gas is determined by the operating para-
meters of the  sulfonation equipment.  Pressure
drop through the high-efficiency filter arranged
for horizontal gas flow •with velocities of 15 to 30
fpm ranges between 5 and  8 inches of -water col-
umn.   Provisions  should be made for back-wash-
ing of the filter elements.
SULFUR TRIOXIDE LIQUID SULFONATION

Since liquid sulfur trioxide with even a trace of
moisture present forms solid polymers at room
temperatures,  it was not a commerically feasible
reactant until it was stabilized by addition of small
quantities of suitable compounds.  First processes
employing liquid SOj resulted in surfactants  of
poor color or with unpleasant odors.  Liquid SOj
added to undiluted alkylate causes heavy dealkyla-
tion with the formation of odorous long-chain ole-
fins.  Pilot Chemical Company developed a com-
mercial process employing the liquid,  shown
schematically in Figure 582.  The process is op-
erated in batches and employs liquid sulfur diox-
ide as a diluent and as a refrigerant to maintain
low batch temperatures  (30 °F) during the highly
exothermic sulfonation reaction.

Alkylate to be sulfonated is metered into the  re-
actor, and then the liquid SC>2 and 803  are meter-
ed to the reactor.   The heat generated by the sul-
fonation reaction causes evaporation of the SC>2,
•which holds the reaction mass at low temperature.
The  reactor is maintained under negative condition
by pumping the SC>2 vapor  from it.  The reaction
is completed after  several hours, and the sulfonic
product is  then heated to 85 "F to drive off remain-
ing SOo liquid as a vapor.   The SC>2 vapor removed
from the reactor is compressed,  scrubbed with
concentrated sulfuric acid to remove any SOj,
condensed, and returned to storage.  The sulfonic
product discharged from the reactor passes to  a
vacuum stripper to remove traces of SC>2 and then
to either storage or a neutralization tank.  The
vacuum pump for the vacuum stripper discharges
to the compressors and returns any removed SC>2
to storage.
The Air Pollution Problem

The Pilot Chemical process employs an entirely
closed system until the sulfonic product is dis-
charged to storage.  The product in storage does
not cause any air contaminant emissions other
than very dilute and mild odors.  The only air
pollution problem found from the operation is
from the necessary purge venting of the liquid
SCK storage tank.  The tank must be continuously
purged whenever the  compressor is discharging
SOT back to it from the sulfonation reaction.  This
prevents any build-up of air which enters the
system by leakage  into the compressor and other
equipment. SO2 vapors  are present in the gas
flow from  the purge vent line.
Air  Pollution Control Equipment

SO2 vapor emitted from the storage tank receiv-
ing recovered SO2 from this process is readily
controlled by absorption in a caustic solution.
Moderate energy scrubbers such as packed
columns and spargers using 10 percent sodium
hydroxide  solution as the scrubbing medium are
effective.  An air pollution control scrubber is
schematically shown in Figure 583.  At this
installation, gas flow rate from the tank is limi-
ted to approximately 1 to 2 cfrn by a needle valve
for the purge operation.  SO2 vapor is sparged
beneath the caustic solution contained in two
scrubber vessels connected in series.   The caus-
tic  solution is sampled regularly and maintained
above 5 percent concentration.  The same system
can serve to vent the storage tank when it is fill-
ed with liquid SO2 from a tank truck.  The SO2
vapor displaced during filling is returned to the
truck tank so that the purge line vents only a  low
gas flow to the scrubber.  The knock-out pot in
the purge line between the tank and the scrubber
principally serves to prevent back-flow of caustic
solution to the SO2  storage tank.
 234-767 O - 77 - 50

-------
756
CHEMICAL PROCESSING EQUIPMENT
                                                     »- BLEED VENT TO
                                                       AIR POLLUTION CONTROL
                                                              COOL'
                                                              WATER  CONDENSER
                                 VACUUM LINE
                          VACUUM
                         STRIPPER
                                                       COMPRESSOR
                                                 SULFUR DIOXIDE
                    VAPORS
                                                                               cc
                                                                               UJ
                                                                               ca
                                                                                   98SSULFURIC
                                                                                       4CID
                                                  CIRCULATING PUMP
                                         VACUUM PUMP
                             COMPRESSOR
                       SULFONIC ACID
                       TO
                       NEUTRALIZATION
                       OR
                       STORAGE

          Figure 582. Sulfonation with liquid sulfur trioxide diluted with liquid sulfur  dioxide (Pilot
          Chemical Co., Santa  Fe Springs, Calif.).
CHLOROSULFURIC ACID SULFATION

Chlorosulfuric acid as an acid reactant requires
considerably different process  equipment than
any of the other processes discussed previously.
The reaction is carried out with fatty alcohols.
It is employed to produce surfactants used in for-
mulating detergent products of high quality.   Fig-
ure 584 is a schematic flow diagram illustrating
this process.   Fatty alcohols are transferred
from storage by a vacuum applied to the reactor.
In the  reactor, the alcohols are first cooled to the
point of solidification by circulation of refrigera-
ted water in the reactor jacket.  The reactor is
purged with inert gas (nitrogen) and chlorosulfuric
acid is then slowly metered into the reactor.  This
reaction is  characterized by the highly unbalanced
pattern of heat and  gas evolution.  When the  acid
is first added to the alcohol, the exothermic  for-
mation of alkoxonium chloride  occurs,  and the
hydrogen chloride generated by the sulfonation re-
action is retained in the reactant mass. As acid
addition continues,  the HC1 is endothermically
evolved as a gas and released from the reacting
mass with considerable foaming.  The  heat  evo-
                      lution is highest at the start of the reaction, with
                      approximately 60 percent of the total heat
                      generated when only 20 percent of the total acid
                      reagent has been added.  Inert gas must be con-
                      tinuously bled from the reactor along with the
                      generated HC1.  Off-gases containing HC1 pass to
                      a falling film reactor for recovery of the HC1 by
                      absorption in water to form hydrochloric acid as
                      a valuable byproduct.  When the reaction has
                      reached completion, the sulfated alcohol is trans-
                      ferred to another vessel for neutralization.  So-
                      dium hydroxide, triethanolamine, or ammonia is
                      used for neutralization.   The sulfated alcohol must
                      be neutralized immediately after completion of
                      the reaction to avoid hydrolization.

                       The Air Pollution Problem

                       The receiving, storage, and handling of chloro-
                       sulfuric acid results in more severe air pollution
                      problems  than those encountered with liquid SOg
                      and oleum.  Chlorosulfuric acid is a fuming liquid
                      which is extremely corrosive and reacts violently
                      with water to produce  hydrochloric and sulfuric
                      acid.  It is not normally exposed to  air, and inert

-------
                       Synthetic Detergent Surfactant Manufacturing Equipment
                                                                               757
SULFUR DIOXIDE RETURN
FROM PROCESS ,

NEEDLE VALVE
? SULFUR
_^, DIOXIDE VAPOR
I ' 	 J
         LIQUID SULFUR DIOXIDE
              TANK
    TO ATMOSPHERE
                                     LIQUID
                                    (NOCKOUT
                                      TRAP
    CAUSTIC
    OVER
       pH GUAGE
 u
TO SEWER
                              CAUSTIC V	/
                              16% CONCENTRATION
                               -oo-
  Figure 583. Air pollution control  system venting
  liquid sulfur dioxide tank receiving recycled  sulfur
  dioxide from sulfonation process (Pilot Chemical Co.,
  Sante Fe Springs,  Calif.}.
gas under positive pressure is used in place of
atmosphere when charging or discharging any
containers or vessels.  Venting of the displaced
gas from vessels when filling with chlorosulfuric
acid produces visible emissions of the acid mist.
The chlorosulfation process evolves HC1 gas which
is vented along with inert gas to a falling film ab-
sorber.  Most of the HC1 is absorbed in water,
but a small amount of unabsorbed HC1 is carried
out with the inert gas to the atmosphere, causing
visible  emissions of acid mist.  Hydrochloric
acid produced by absorption of the HC1 in water
(usually 25 to 28 percent solution) is transferred
to storage.   Displaced vapors vented during fill-
ing of the storage tank also consist of visible
acid mist.  The balance between the reactor op-
eration and the absorber operation is critical if
absorption of the HC1 gas  is to be reasonably com-
plete.  If absorption is inefficient, larger quanti-
ties of acid mists are emitted from the storage
tank vent.  If inert gas flow volume to the reac-
tor is excessively high, the absorption efficiency
for HC1 decreases.  The flow of HC1 from the re-
actor is not constant.  Therefore the feed water
rate and other absorption  variables must be con-
trolled  to keep the  byproduct acid concentration
from the absorber  constant in spite of varying
HC1 gas loads.
Air Pollution Control Equipment

HC1 acid mist displaced during filling of the stor-
age tank is readily controlled with a caustic solu-
tion scrubber or packed column.  Two simple
submersion type scrubbers illustrated in Figure
585 serve  to control emissions -with high efficiency.
The volume of HC1 solution discharged from the
chlorosulfation unit absorber is quite  low,  and
this scrubber contains an excess of caustic for
neutralizing all the  HC1 vented during the batch
operation.  The caustic solution is tested after
each batch operation to maintain the pH of the
solution at 8 or greater.

SULFOALKYLATION

Sulfoalkylation is a  condensation-type reaction
producing  a more complex sulfonate from a sim-
ple one. One sulfoalkylation process,  the manu-
facture of  N-acyl-N-alkyltaurate, is performed
in the  same equipment schematically illustrated
in Figure 584 for a  chlorosulfation process.
Fatty acids are moved to the reactor, and phos-
phorous trichloride is  added as  a reactant to pro-
duce a fatty acyl chloride.   Inert gas sparging is
used, and  hydrogen chloride is released by the
reaction to be vented from the reactor with the
inert gas.   In this reaction, phosphoric acid is
also formed in the reactor and settles out at its
bottom.  When the reaction is complete, remain-
ing HC1 is  purged with the  inert gas, and the
phosphoric acid is drawn off.  The fatty acyl
chloride product of  the first reaction is then re-
acted with N-methyltaurine (taurine is 2-amino-
ethane sulfonic acid) to form the final detergent
surfactant (one of the  "Igepon T" series of Gen-
eral Aniline and Film Corporation).  The HC1 and
inert gas vented from the reactor during the first
reaction flows to the falling film absorber for
HC1 recovery.  The surfactant is pumped from
the reactor to a neutralization tank for final
treatment with a caustic solution.

Another  sulfoalkylation process  is a reaction be-
tween fatty acids and isethionate, the  sodium
salt of isethionic acid (2-hydroxyethane sulfonic
acid),  as the sulfating agent, and fatty acids in the
presence of a. catalyst to produce g -sulfoesters.
These detergents are sensitive to hydrolysis and
are used only in specialty products.   Hydrolysis
does not deter their use in  personal products.
The sodium salt of 2-sulfoethyl ester of lauric
acid or of coconut acid is used in manufacturing
synthetic detergent bars.

In this process, isethionic  acid and coconut fatty
acid are metered to a closed reactor,  and a cat-
alyst in powder form is added.   The mix is agita-
ted and circulated through a heat exchanger to
add heat to the  reactant mass.   Inert gas is sparg-
ed into the reactor to prevent discoloration of pro-

-------
758
          CHEMICAL PROCESSING EQUIPMENT
                                                          VENT LINE
     BRINE
     OR
     STEAM
         CAUSTIC OR
         AMMONIA OR
         TRIETHANOLAMINE
                                                                SALT
                                                                               TO STORAGE
         Figure 584. Chlorosulfonation of fatty alcohols and recovery of  hydrogen chloride (Textilana Corp.
         Hawthorne, Calif.).
 HYDROGEN CHLORIDE
 FROM PROCESS
 VESSEL	y
                                     EXHAUST
                                     TO ATMOSPHERE
                                     CHECK VALVE


                  HYDROGEN CHLORIDE LIQUID!
          VACUUM RELIEF VALVE

                           PRESSURE RELIEF VALVE



                                     2-m. PVC PIPE
                                      /

                                      CHECK VALVE
                                      S
                                       EXHAUST TO
                                       ATMOSPHERE
                                                            SUBMERGED FILL LINE	
FLANGED
COVER.
-y=K

— —
Kr_ HYDROGEN
- - CHLORIDE
STORAGE
! ~~ TANK '
-i — • 	 —
\
\P
*
1
	
	
—

	
	
            2-in. CLEARANCE
            ON BOTTOM
^""sS-GALLON SCRUBBER
       a.  Low-volume hydrogen chloride acid mist
          vented from Chlorosulfonation process.
         SPARGER CONSISTING OF   55-GALLON SCRUBBER
         AN "H"-SHAPED 2- in. PIPE CONTAINING 5% CAUSTIC
         ASSEMBLY CONTAINING    SOLUTION
          ABOUT 60 1/4 in. HOLES


b.  Low-volume hydrogen chloride acid mist vented
   from hydrogen chloride storage tank.
          Figure 585.  Submersion  type  scrubbers using caustic  solution (Textilana  Corp.,  Hawthorne,  Calif.).

-------
                        Synthetic Detergent Product Manufacturing Equipment
                                            759
duct.  Fatty acid vapor, water vapor, and inert
gas are vented from the reactor through a con-
denser to a separator tank.  Fatty acids separa-
ted are recycled to the  reactor, the water is sent
to the  sewer,  and the inert gas is returned to a
gas holder. The reaction is completed after sev-
eral hours, and the product is then pumped to a
jacketed vacuum stripper tank.  The temperature
is maintained, tallow fatty acid and more catalyst
are added, and inert gas is sparged into the tank.
The vessel is  held under slight vacuum for a short
period while the contents are agitated.  The vacu-
um is then increased to strip any  remaining unre-
acted fatty acid.  Water vapor, inert gas,  and
fatty acid vapors are vented through a condenser.
The condensate from the condenser  consists pri-
marily of coconut fatty  acid and is returned to
storage.  The fresh surfactant is  discharged
through a line mixer -where a small amount of wa-
ter is  added for cooling purposes.  It is then trans-
ferred to a holding vessel for use in formulation
of toilet bars.  The water content flashes off in
the holding vessel.

The Air Pollution  Problem

The first of the two reactions involved in the pro-
duction of alkyItaurate s, the fatty acyl chloride
reaction, also creates HC1 acid mist emissions
similar to those from the chlorosulfonation reac-
tion.   The second reaction, -with the N-methyl-
taurine, is accomplished in the vessel without
venting until the reaction is complete.

The vacuum system employed in the second pro-
cess to produce the sulfoester consists of  com-
pound  steam ejectors with barometric condensers.
The condensers discharge  to a hot •well.  Visible
and odiferous  emissions, principally fatty acid
vapors,  occur from the hot •well.  Uncondensable
gases  in the reactor recirculation system  also are
vented and cause odors and visible emissions.
The flashed off water vapor from  the product hold
tank can also  contain contaminants of an odorous
nature.  No other air pollutant emissions occur
from this process.

Air Pollution Control Equipment

The same control equipment shown in Figure 584
for HC1 acid mist serves to control  the emissions
from the first sulfoalkylation process producing
the alkyltaurate.

The hot well receiving condenser water and uncon-
densed gas and vapor from the vacuum  jet systems
in the  second process for sulfoesters must be
closed and vented to control equipment  to eliminate
odors and visible acid mist emissions.  Scrubbers
with gas pressure drops ranging from 7 to 12 in-
ches water column usually control these emissions.
    SYNTHETIC  DETERGENT  PRODUCT

      MANUFACTURING  EQUIPMENT

INTRODUCTION

"Synthetic detergent products" applies broadly to
cleaning and laundering compounds containing sur-
factants along -with other ingredients formulated
for use  in aqueous solutions.  These products are
marketed as heavy- or light-duty granules or liquids,
cleansers, and laundry or toilet bar s. Theheavy-
duty granules represent the major portion of all pro-
ducts manufactured,  with the light- andheavy-duty
liquid or light-duty granules in far lesser production.
The manufacture of all detergent products incorpo-
rates equipment and processes similar to those for
manufacturing soap products. The manufacture of
the granular products is of paramount interest, with
more severe air pollution problems than those en-
countered with soap granule production.  The manu-
facture of liquid detergent and bar products is of less -
er importance, with little or no difference from simi-
lar soap products in either process equipment or air
pollution potential, and will not be discussed.

Raw  Materials

The  surfactants used in formulating synthetic de-
tergent  products are either anionic or nonionic.
The products also contain other chemical com-
pounds which supplement the detergent of the sur-
factant.  Each particular formulation depends upon
the ultimate design for consumer  use.  Table 203
illustrates the formulations commonly used in
large-volume  granule and liquid detergent manu-
facture.

Sodium  tripolyphosphate (STP) or tetrasodium
pyrophosphate (TSPP) are incorporated in most
granular formulations as  "builders" or seques-
tering agents.  They serve to eliminate inter-
ference -with the detergent action by the calcium
and magnesium ions (hardness) in the water used
in the wash solution. STP and TSPP may be used
in powder, prill, or granule form, and are re-
ceived in carlots. These ingredients are most
often blended into the slurry before spray drying.

Nitrilotriacetic acid (NTA) and its sodium salts
have recently been incorporated in some heavy-
duty granule products to replace part of the STP.
It is more expensive than STP,  but is a better
sequestrant.   The growing public  concern with the
role phosphates in detergents may play in deteri-
oration  of water quality has generated manufac-
turers'  interest in this substitute. Indications
are that it -will be employed in the near future in
more formulations and in larger quantities.  The
acid is a crystalline powder and the salts (disodi-
um or trisodium) are powders.  They are receiv-
ed in carlots.   NTA  is added to the slurry mix be-
fore drying.

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760
CHEMICAL PROCESSING EQUIPMENT
        Table 203.  FORMULATIONS (IN PERCENT) FOR LARGE-VOLUME DETERGENT
                              MANUFACTURE IN THE UNITED STATES
Constituent
Surfactants
Alcohol sulfate
Alkyl sulfonate
Ethoxulated
fatty alcohol
Alkyl amine oxide
Soap
Builders
Fatty alcohol
or amines
STP/NTA
TSP
Additives
CMC
Sodium silicate
Sodium sulfate
Enzyme
Other
Heavy duty
High suds
granules
Brand A

8
8
-
-
-


1. 5-2
60
-

0. 5-0.9
5-7
10-20
0. 2-0. 73
0-5
Brand B

18
-
-
-


OrO. 5
50-60
-

0. 5-0. 9
5-7
10-20
0. 2-0. 75
0-5
Low suds
granules
Brand C

6
6
-
2


-
50-60
-

0. 5-0. 9
7-9
10-30
0. 2-0. 75
0-5
Brand D

17
-
-
-


-
50-60
-

0. 5-0. 9
7-9
10-30
0. 2-0.75
0-5
Liquid

0-35
0-35
0-35
0-15
-


0-12
-
0-20

0. 5-0. 9
5-7
-
0. 2-0. 75
0-5
Light duty
Granules

25-32
25-32
-
-
-


-
-
-

0-5
0-4
60-70
-
0-5
Liquid

20-25
or
20-25
-
10-12


5-12
2-15
0-20

-
0-4
-
-
0-5
Function

Cleaning
agent
for oily
and organic
soil


Foam booster
or stabilizer

Overcome
water hardness
and clean
inorganic stains

Antiredeposition
Corrosion
inhibitor
Filler
Clean protein
stain
Perfume, dye,
bleach, etc.
 Fillers, usually sodium sulfate or sodium car--
 bonate, are incorporated in granule products.
 They are either powders or crystalline powders
 and are added in bulk form to the slurry before
 drying.

 Amides of various types are used as supplemen-
 tary surfactants in many formulations.  They im-
 prove detergency  of the sulfonic and sulfate sur-
 factants  and act as foam boosters or stabilizers.
 Amides  used include the higher fatty amides
 (e.g. cocomonethanolamide), ethanolamides,
 dialkyl and alkylol (hydroxyalkyl) amides, mor-
 pholides, and nitriles,  as well as the lower acyl
 derivatives of higher fatty amines.   These ma-
 terials are handled as liquids and received in
 tank cars or barrels.  In granule manufacture,
 they are either incorporated in the slurry before
 drying or blended with  the detergent granules
 after drying.
                      Trisodium phosphate (TSP) is used in detergent
                      granule formulations such as dishwasher com-
                      pounds and wall cleaners which are designed to
                      clean hard surfaces.  TSP is considered func-
                      tionally as an alkali rather than a sequestering
                      agent.  It is usually handled as a crystalline
                      powder and is received in carlots, drums, or
                      bags.

                      Carboxy methylcellulose (CMC; sodium cellulose
                      glycolate) usually is added to heavy-duty granules
                      and serves to prevent redeposition onto the  fabric
                      of the dirt removed by the detergent.  This chemical
                      is received in bags or  drums as a powder  or
                      granule.  It is added to the  slurry  mixture before
                      drying.

                      Sodium silicate is added in most synthetic deter-
                      gent formulations to inhibit the  surfactant' s ten-
                      dency to corrode metal.  It also is used to over-

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                         Synthetic Detergent Product Manufacturing Equipment
                                                                                                 761
come production and packaging problems encoun-
tered with detergent granules.  It is functionally
used as a primary detergent alkali in compounds
designed for hard surface washing, e.g. ,  machine
dishwashing compounds.  It can serve to retain
uniform viscosity in the mixing and pumping of
the slurry before it is dried,  and it reduces the
"tackiness" of the dried granules, facilitating
their handling and reducing caking of the product
after packaging.  The  sodium silicates are re-
ceived in tank cars as water solutions.

Optical brightners are added to many formulations.
These are usually fluorescent dyes •which  absorb
ultraviolet rays and reflect them as visible light.
The dyes are received as powders in bags or as
liquids in drums, and they are usually blended in
the slurry before drying.

Perfumes are added to almost all detergent pro-
ducts to  overcome unpleasant odors and impart a
pleasing scent to laundered fabrics.  The  per-
fumes are added by  spraying onto the dried gran-
ules or mixing with the liquid detergents.   They
are handled as liquids in small-size containers
or drums.

Bleaches of various kinds are frequently incor-
porated in heavy-duty detergents.  Sodium per-
borate, along  with magnesium silicate as  a sta-
bilizer, is commonly employed.  They are re-
ceived as powders or crystals in boxes or bags
and are added to the granules after drying.

Enzymes have recently been introduced as part
of the formulation of heavy-duty detergent pro-
ducts to assist in the removal of protein-based
stains from fabrics.  The enzymes are received
as powders  in bags or drums.   The enzymes are
heat sensitive and are destroyed if heated to212°F.
Most manufacturers blend the enzymes into the
detergent granules  after drying.

Many other  compounds may be incorporated in
various products.   Preservatives, antioxidants,
foam-suppressors and other types of additives
are used.  The scouring cleansers are composed
principally of  finely pulverized  silica, active
detergent, small amounts of phosphates, and fre-
quently a bleach.

Detergent surfactants include alkyl sulfonic,
alkyl  sulfate,  and alcohol sulfates, discussed
above, and almost the entire range of anionic
and nonionic detergents, including soap.   Plants
manufacturing their own sulfonic and sulfate sur-
factants  also use other surfactants in some or all
of their products.   The detergents are received
and handled mostly as liquid solutions of varying
strength, but  some surfactants are received as
flake or powder. Surfactants are principally mix-
ed with the slurry before  drying.
Processes

The only manufacturing process to be discussed
here will be the production of detergent granule
formulations incorporating spray-drying pro-
cesses.  All other products are produced in pro-
cesses, such as drum drying,  similar to soap
production, discussed in the previous section.


Manufacture  of detergent granules incorporates
three separate steps:  Slurry preparation, spray
drying, and granule handling (including cooling,
additive blending,  and packaging). Figure 586
illustrates the various operations.

SLURRY PREPARATION

The formulation of slurry for detergent granules
requires the  intimate mixing of various liquid,
powdered,  and granulated materials.  The soap
crutcher is almost universally used for this mix-
ing operation.  Premixing  of various minor  ingre-
dients is performed in a variety of equipment prior
to charging to the crutcher  or final mixer.   The
slurry, mixed in batch operations, is then held
in surge vessels for continuous pumping to the
spray drier.

The Air Pollution Problem

The receiving, storage, and batching of the  vari-
ous dry ingredients creates dust emissions.
Pneumatic conveying  of fine materials causes
dust emissions when conveying air is separated
from the bulk solids.   Many detergent products re-
quire raw materials -with high percentages of
fines,  viz. , typical specifications for some  raw
materials include the following percentage of
fine materials passing a 200 mesh screen:  Sodium
sulfate - 12 percent; sodium tetrapyrophosphate -
74 percent; sodium tripolyphosphate  - 53 percent.

The storage and handling of the liquid ingredients,
including the sulfonic acids, sulfonic salts,  and
sulfates, do not cause emission problems other
than mild odors.

In the batching and mixing  of fine dry ingredients
to form, slurry,  dust emissions are  generated at
scale hoppers, mixers, and the crutcher.  Liquid
ingredient addition to the slurry creates no vis-
ible emissions but may cause odors.

Air Pollution  Control Equipment

Control of dusts generated from pneumatic or
mechanical conveying or from discharge of fine
materials into bins or vessels  is  described in
Chapters 3 and 4.   There are no unique problems
in hooding  or exhaust systems  for controlling dust
emissions  from conveying  and slurry preparation.

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762
CHEMICAL PROCESSING EQUIPMENT
Baghouses are employed not only to reduce and
eliminate the dust emissions but for salvage of
raw materials.  None of the dusts causes any
serious corrosion problems.  Filter fabrics should
be selected which have good resistance to alkalis.
Filter ratios for baghouses with intermittent
shaking cleaning mechanisms should be under  3
cfm per  square foot.

SPRAY DRYING

All spray drying equipment designed for detergent
granule production incorporates the following com-
ponents:  Spray-drying tower, air heating and
supply system, slurry atomizing equipment,
slurry pumping equipment, product cooling equip-
ment, and conveying equipment.  The  towers are
cylindrical with cone bottoms and range in size
from 12 to 24 feet in diameter and 40 to 125 feet
in height.  Single towers may be of varying dia-
meter,  being larger at the top and  smaller at the
bottom.  Air is supplied to the towers from di-
rect-heated furnaces fired with either natural  gas
or fuel oil. The products  of combustion are tem-
pered with outside air to lower temperatures and
then are blown to the dryer under forced draft.
The towers are usually maintained under slightly
negative pres sure, between 0. 05 and 1. 5 inches of
water column, with exhaust blowers adjusted to pro-
vide this balance. Most towers designed for de-
tergent production are of the counter cur rent type,
with the  slurry introduced at the top and the heat-
ed air introduced at  the bottom.  A few towers of
the concurrent type are used for detergent spray
drying, with both hot air and slurry introduced at
the top.  Some towers are equipped for either
mode of operation as illustrated in Figure 586.

In most towers today, the  slurry is atomized by
spraying through a number of nozzles, rather
than by centrifugal action.  The slurry is sprayed
at pressures of 600  to 1000 psi in single-fluid
nozzles, and at pressures of 50 to  100 psi in two-
fluid nozzles.  Steam or air is used as the atomiz-
ing fluid in the two-fluid nozzles.

Tower operations vary widely between manufac-
turers and between products.  Heated  air supplied
to the tower varies from 350° to 750 °F.  Temp-
eratures of air supplied to counter cur rent towers
are generally lower, and most often range from
500° to 650 °F.  Concurrent tower temperatures
are somewhat higher.   Solids content  of slurrys
for detergent  spray drying varies from 50 to 65
percent  by weight, with some operations to as
high as 70 percent.  Moisture content of the dried
product varies from 10  to 17 percent.  Towers are
designed for specific air-flow rates, and these
rates are maintained throughout all phases of  op-
eration.  Slurry temperatures may vary, but in
most formulations they do not exceed  160 °F.
Frequently, they are as low as  80°F.  Exit gas
                      temperatures range from 150° to 250°F with wet-
                      bulb temperatures of 120° to 150°F.  Air velocities
                      in concurrent towers are usually higher than ve-
                      locities in countercurrent towers.  The concurrent
                      towers produce granules which are mostly hollow
                      beads of light specific gravity (0.05 to  0.20).
                      Countercurrent towers produce granules which
                      are multicellular and irregularly shaped and which
                      have higher specific gravities ranging from  0.25
                      to 0.45.

                      In countercurrent towers, -with lower air velocities
                      and droplets descending  against a rising column
                      of air, most of the  dried granules fall into the
                      cone at the bottom of the tower.  They  are dis-
                      charged through a star valve, or regulated open-
                      ing,  while still hot.   Cooling of the granules is
                      discussed below with other granule processing
                      procedures.  Unlike other product spray drying
                      operations,  e.g. , powdered milk, the desired de-
                      tergent granule product is comparatively large in
                      size.  The specifications for some well known
                      granular products require 50 percent by weight
                      or more  to be retained on a 28-mesh screen.  A
                      certain amount of the product is  dried to compar-
                      atively small size.   This amount is dependent  on
                      tower feed rates, the liquid droplet size in slurry
                      atomization, the paste viscosity, the particular
                      product,  and other variables.  Usually the exhaust
                      air entrains  7 to 10 percent of that portion of the
                      granular product which is too fine to  settle out at
                      the base  of the tower.

                      Concurrent towers,  operate with higher air  veloci-
                      ties than countercurrent towers.   The air is vented
                      just above the bottom of  these towers through a
                      baffle •which  causes violent changes of direction to
                      the exhaust  air to dynamically separate the dried
                      granules, -which then fall to the cone bottom for
                      discharge.  Concurrent towers producing very
                      low-gravity granules vent air still  conveying the
                      product to auxiliary equipment for  separation.
                      The loss of detergent fines entrained in the ex-
                      haust air  stream will be somewhat higher from
                      concurrent towers than from countercurrent
                      towers.

                      The Air Pollution Problem

                      The exhaust air from detergent spray drying tow-
                      ers contains two types of air contaminants.  One
                      is the fine detergent particles entrained in the
                      exhaust air discussed above; the second consists
                      of organic materials vaporized in the higher temp-
                      erature zones of the tower.

                      The  detergent particles entrained in the exhaust
                      air are relatively large in size.  Over  50 percent
                      by weight of these particles are over 40 microns.
                      These particles constitute over 95 percent of the
                      total weight of air contaminants in the  exhaust air
                      (Phelps, 1967).  They consist principally of  deter-

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                         Synthetic Detergent Product Manufacturing Equipment
                                                                                                  763
                                                                          TO FAN AND
                                                                          AIR POLLUTION
                                                                          CONTROL,
                                                                                      CYCLONE OR
                                                                                      GRAVITY SEPARATOR
1
f 	
\
\
1 1 	
_________
/ \ li,
/ \ u .

1 1


    /
   /
  '    \    /     x
/"    \  '  "    \
•   i  o  \/   ^   N
"!  ^ll  T~
         I
                
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764
CHEMICAL PROCESSING EQUIPMENT
Slurry formulations containing ethoxylated alcohol
surfactants cause  similar aerosol emissions.
When this nonionic detergent is used in the  slurry,
source tests  of the aerosol leaving the scrubber
indicate a particle  size range of 0. 2 to 1 micron.
Plumes persist for long distances following the
disappearance of the water vapor plume.

Air Pollution  Control Equipment
The collection of air contaminants  not only pro-
vides for the economic return  of detergent fines
to the process, but also provides for control of
submicron particles to ensure compliance with
air pollution  prohibitory rules.
Manufacturers producing  detergent granules have
developed two separate approaches  for capturing
the detergent fines in the  spray drier effluent for
return to process.  One method utilizes centri-
fugal separators to capture most of the product
dust.  The exhaust gases  then  are vented from
the separators to scrubbers for removal of mi-
cron-size particles.  The cyclone separators re-
move approximately 90 percent by  weight of the
detergent product fines in the tower exhaust air.
The detergent dust remaining in the effluent
vented from the  cyclones  consists of particles
almost all of which are over  2 microns in size.
Size distribution of these particles by weight will
peak in the range of 7 to 10 microns.  Particulate
concentrations vary from 0.1 to 1.0 grain per scf.
The cyclones are designed for  relatively high
efficiencies and  operate at pressure drops from
8 to 10 inches of water  column (Phelps,  1967).
A venturi type scrubber is used downstream of the
cyclone,  using water at 8 to  10 psig distributed
through nozzles  in the  throat.  Throat velocities
of the exhaust gases average 8, 500  fpm.  With
•water supplied to the throat at a ratio of 4.5 to
5. 0 gallons per 1 , 000 cubic feet of effluent,  scrubber
exhaust gases have loadings  of about 0.085  grain
per  scf when slurries with amides  are spray dried.
A highly visible  plume persists after the condensed
water vapor plume has dissipated.
In the second method of recovery of detergent
fines,  the centrifugal collector is eliminated,  and
only a scrubber  is used.  However , the scrubber
uses detergent slurry as a scrubbing medium
rather than -water.   The scrubbing  slurry is main-
tained at a high enough concentration to prevent
foam,  but at  a low enough concentration to permit
pumping  and  spraying.  No further control device
is used to cleanse the exhaust gases from the
scrubber.  When slurries with volatile organic
materials are spray dried, highly visible plumes
persist after the condensed water vapor plume
has dissipated.  A plume  was even observed from
a pilot venturi scrubber operating at a high pres-
sure drop of  50 inches of water column.  A 40 per-
cent solids slurry was used as the  scrubbing fluid
delivered at gas scrubbing ratios of 60 to 100 gal-
lons per  1000 cubic feet of gas.
                      An alternative method for controlling emissions
                      from the drier  caused by volatile organics in the
                      slurry is to reformulate the  slurry to eliminate
                      these  offending organic compounds.   When amide
                      compounds were identified as causing the emission
                      problems,  some manufacturers developed other
                      formulations or methods for adding the amides
                      to the spray dried granules to achieve a compar-
                      able product.

                      When  reformulation is not possible, the tower
                      production rate may be reduced, permitting oper-
                      ation at lower air  inlet temperatures and lower
                      exhaust gas temperatures.  When tower tempera-
                      tures  are reduced, lesser amounts of organic
                      compounds are vaporized in  the spray drier, and
                      the  scrubber is able to collect these emissions.

                      GRANULE HANDLING

                      Many  manufacturers discharge hot granules from
                      the  spray tower into mixers  where dry or liquid
                      ingredients are added.  The  granules are usually
                      mechanically conveyed away from the tower or
                      mixer  discharge and then are air-conveyed to
                      storage and packaging. Air  conveying serves to
                      cool the granules and to elevate them for gravity
                      flow through further processing equipment to
                      storage and packaging. Air  conveying of low-
                      density granules usually is designed for 50 to 75
                      scfm air per pound of granules conveyed.  At the
                      end of the  conveyor, centrifugal separators  re-
                      move  granule product from the conveying air.
                      Some  manufacturers mechanically lift the granules
                      from the spray tower to aeration bins -where  the
                      granules are cooled or aged by injecting air at
                      the  bottom of the bin.   This air  percolates upward
                      through the scrubber.

                      The cooled granules are screened to deagglomerate
                      the  large granules and to remove undersize  or
                      oversize particles.  Further mixing or blending
                      may be performed to add heat-sensitive compounds
                      to the detergent products.  Many manufacturers
                      do not store the finished granules, but convey
                      them directly to packaging equipment.  Some de-
                      tergent products are held in storage,  either in
                      large  fixed bins or small-wheeled buggy bins, and
                      then are charged to packaging equipment.  Pack-
                      aging is done with either scale or volumetric fill-
                      ing  machines.

                      The Air Pollution  Problem

                      Conveying,  mixing,  packaging,  and other equip-
                      ment used for granules can cause dust emissions.
                      The granule particles, which are  hollow beads, are
                      crushed during mixing and conveying, and generate
                      fine dusts.  Dusts emitted from screens, mixers,
                      bins,  mechanical-conveying equipment, and air-
                      conveying equipment are quite irritating to eyes
                      and nostrils with continuous exposure.  Some of

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                                           Glass Manufacture
                                            765
the additive materials, such as enzymes also
cause serious health problems.  Equipment in-
volving enzymes requires very efficient ventila-
tion in addition to proper dust collection.  Dust
emissions in most cases represent a significant
product loss, and their collection and return to
process (usually as an ingredient of the slurry to
be spray  dried) is necessary for economic plant
operation as well as for air pollution control.


Air Pollution Control Equipment

Dust generated by granule processing, convey-
ing,  and  storage equipment  does not create unique
air pollution control problems.  Usually, bag-
houses provide the best control.  Collection effi-
ciencies  for baghouses are high; in many cases,
efficiencies exceed  99 percent.  No extreme con-
ditions of temperature or humidity have to be met,
but filter fabrics selected must show good resis-
tance to alkaline materials.  Baghouses utilizing
intermittent shaking mechanisms should not have
filtering  velocities exceeding 3 fpm.   Baghouses
with  continuous cleaning  mechanisms may have
filtering  velocities as high as 6 fpm.
          GLASS  MANUFACTURE

Glass has been made for over 3, 500 years, but
only in the last 75 years have engineering and
science been able to exploit its basic properties
of hardness, smoothness, and transparency so
that it can now be made into thousands of diverse
products.
The economics and techniques connected with
mass production of glass articles have led to
the construction  of glass-manufacturing plants
near or 'within highly populated areas. Un-
fortunately, airborne contaminants  generated
by these glass plants can contribute substantial-
ly to the air pollution problem of the surround-
ing community.   Control of dust and fumes has,
therefore, been, and must continue to be,  in-
herent to the progress of this expanding industry.
Air pollution control is necessary,  not only to
eliminate nuisances, but also to bring substan-
tial savings by extending the service life of
the equipment and by reducing operating ex-
penses and down time for repair.  Reduction
in plant source emissions can be accomplished
by several methods,  including control of raw
materials, batch formulation,  efficient  com-
bustion of fuel, proper design of glass-melt-
ing furnaces,  and the installation of control
equipment.
TYPES OF GLASS

Nearly all glass produced commercially is one
of five basic and broad types:  Soda-lime, lead,
fused silica, borosilicate, and 96 percent silica.
Of these, modern soda-lime glass is well suited
for melting and shaping into window glass, plate
glass, containers, inexpensive tableware,  elec-
tric light bulbs, and many other inexpensive,
mass-produced articles.  It presently consti-
tutes 90 percent of the total production of com-
mercial glass  (Kirk and Othmer, 1947).

Typical  compositions  of soda-lime  glass and
the four other  major types of commercial glass
are  shown on Table 204.  Major ingredients of
soda-lime glass are sand, limestone,  soda ash,
and  cullet.  Minor ingredients include  salt cake,
aluminum oxide, barium oxide,  and boron oxide.
Minor ingredients may be included  as  impuri-
ties in one or more of the major raw ingredients.
Soda-lime glasses are colored by adding a
small percentage of oxides of nickel, iron,
manganese,  copper,  and cobalt, and elemen-
tal carbon as solutions or colloidal particles
(Tooley,  1953).

Although glass production results in tens of
thousands of different articles,  it can  be divid-
ed into the following general types (Kirk and
Othmer,  1947):
Flat glass                                 25
Containers                                 50
Tableware                                   8
Miscellaneous instruments, scientific
  equipment, and others                    17


GLASS-MANUFACTURING PROCESS

Soda-lime glass is produced on a massive scale
in large,  direct-fired,  continuous melting fur-
naces.  Other types of glass are melted in small
batch furnaces having capacities ranging from
only a few pounds to several tons per day. Air
pollution from the batch furnaces is minor, but
the production of soda-lime glass creates major
problems of air pollution control.

A complete  process flow diagram for the  con-
tinuous production of soda-lime glass is  shown
in Figure 587.  Silica sand, dry powders,
granular oxides,  carbonates, cullet (broken
glass),  and  other raw materials  are transferred
from railroad hopper cars and trucks to  storage
bins.  These materials are withdrawn from the
storage bins,  batch weighed,  and blended in a
mixer.  The mixed batch is then conveyed to
the feeders  attached to the side of the furnace.
Although dust emissions are created during

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766
CHEMICAL PROCESSING EQUIPMENT
          Table 204.  COMPOSITIONS OF  COMMERCIAL GLASSES  (Kirk and Othmer,  1947)
Component
Si02
Na2O
K20
cao
PbO
B203
A1203
MO
Composition, %a
Soda-lime
70 to 75 (72)
12 to 18 (15)
0 to 1
5 to 14 (9)
-
-
0.5 to 2.5 (1)
0 to 4 (3)
Lead
53 to 68 (68)
5 to 10 (10)
1 to 10 (6)
0 to 6 (1)
15 to 40 (15)
-
0 to 2
—
Borosilicate
73 to 82 (80)
3 to 10 (4)
0.4 to 1
0 to 1
0 to 10
5 to 20 (14)
2 to 3 (2)
-
96% silica
96
-
-
-
-
3
-
-
Silica glass
99.8
-
-
-
-
-
-
-
            lThe figures in parentheses give the approximate composition of a typical member.
FELDSPAR
R20 A!?03,6Si02
to yield alumina.AlzOs
Also yields SiOr,
and NaaO or KZ0
Pulverized or granular










Borax or boric acid
to yield BjOj, and
other additions to
yield K20. MgO,
ZnO, 8aO, and PbO
Fining, oxidizing,
decolorizing, and
coloring agents
                              Materials dry, or nearly dry
                          Continuous tank furnace looking
                           down through top (crown)
                          Submerged throat in bridge wall -
                           At about 1,472- 2.012
                         depending on article and process
                            Hot zone about 930
                             60 90 minutes in
                           continuous bolt tunne' Ich1


1
Melting
about 2 . 700° F
_^sf
Refining
fining and
homogenizing
Crushed cullet
of same composition
as that to be melted


                                                                              Cullet crushing
                   Fabrication
               Hot, viscous liquid glass
               shaped by pressing,
               blowing, pressing and
               blowing, drawing, or rolling
                       Figure 587.  Flow  diagram for soda-lime  glass  manufacture (Kirk
                       and Othmer,  1947).
 these operations,  control can be accomplished
 by totally enclosing the equipment and install-
 ing filter vents, exhaust systems, and bag-
 houses.

 Screw- or reciprocating-type feeders contin-
 uously supply batch-blended materials to the
 direct-fired, regenerative furnace.   These dry
 materials float upon the molten glass  within
                        the furnace until they melt.  Carbonates  de-
                        compose releasing carbon dioxide in the  form
                        of bubbles.   Volatilized particulates,  com-
                        posed mostly of alkali oxides and sulfates,
                        are captured by the flame  and hot  gases pass-
                        ing across the molten surface.  The particu-
                        lates are  either deposited  in the checkers and
                        refractory-lined passages or expelled to the
                        atmosphere.

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                                          Glass Manufacture
                                                                                                 767
The mixture of materials is held around 2, 700°F
in a molten state until it acquires the homogeneous
character of glass.  Then it is gradually cooled
to about 2, 200°F to make it viscous enough to
form.  In a matter of seconds, while  at a yellow-
orange hot temperature, the glass is  drawn
from the furnace and worked on forming machines
by a variety of methods including pressing, blow-
ing in molds,  drawing,  rolling, and casting.

One source of air pollution is hydrocarbon greases
and oils used to lubricate the hot delivery systems
and molds of glass-forming machines.  The smoke
from these  greases and oils creates  a significant
amount of air pollution  separate from furnace
emissions.

Immediately after being shaped in the machines,
the glass  articles are conveyed to continuous
annealing ovens, where they are heat treated
to remove strains that have developed during
the molding or shaping operations and then
subjected to slow, controlled cooling. Gas-
fired  or electrically heated annealing ovens
are not emitters of air  contaminants in any
significant  quantity.  After leaving the anneal-
ing ovens, the glass articles are inspected and
packed or subjected to further finishing opera-
tions.

Glass-forming machines  for mass production
of other articles such as  rod,  tube, and sheet
usually do not emit contaminants in significant
amounts.
HANDLING,  MIXING, AND STORAGE SYSTEMS
FOR  RAW MATERIALS

Material-handling systems for batch mixing
and  conveying materials for making soda-
lime glass normally use commercial  equip-
ment of standard  design.  This equipment is
usually housed in a structure separate from
the glass-melting furnace and is commonly
referred to as a "batch plant. " A flow dia-
gram of a  typical batch plant is shown in Figure
588. In most batch plants, the storage bins  are
located on top,  and the weigh hoppers and mixers
are  below  them to make use of the gravity flow.

Major raw materials and cullet (broken scrap
glass) are  conveyed from  railroad hopper cars
or hopper trucks  by a combination of  screw
conveyors, belt conveyors,  and bucket eleva-
tors, or by pneumatic conveyors  (not shown  in
Figure 588) to the elevated storage bins.  Minor
ingredients are  usually delivered to the plant
in paper bags or cardboard drums and trans-
ferred by hand to  small bins.
Ingredients comprising a batch of glass are
dropped by gravity from the storage bins  into
weigh hoppers and then released to fall into
the mixer.  Cullet is ground and then mixed
with the dry ingredients in the mixer.  Ground
cullet may also bypass the mixer and be mixed
instead with the other blended materials in the
bottom  of a bucket elevator.  A typical batch
charge  for making soda-lime flint glass in a
mixer with a  capacity of 55 cubic feet  consists
of:
                              Ib
        Silica sand          2, 300
        Cullet                650
        Soda  ash              690
        Limestone            570
        Niter                    7
        Salt cake               12
        Arsenic                  2
        Decolorizer         	1
                            4,232

Raw materials are blended in the  mixer for peri-
ods of 3 to 5 minutes and then  conveyed to a
charge bin located alongside the melting furnace.
At the bottom of the  charge bin, rotary valves
feed the blended materials into reciprocating- or
screw-type furnace feeders.

In a slightly different arrangement of equipment
to permit closer control of batch  composition,
blended materials are discharged from the mixer
into batch cans that have a capacity of  one mixer
load each.   Loaded cans are then conveyed by
monorail to the furnace feeders.  Trends  in
batch plant design are toward  single reinforced-
concrete structures  in which outer walls and
partitions constitute the storage bins.  Complete
automation is provided so that the batch plant is
under direct and instant control of the  furnace
foreman.

The Air  Pollution  Problem
The major raw materials for making soda-lime
glass--sand, soda-ash, and lime stone--usually con-
tain particles averaging about  300 microns in size.
Particles less than 50 microns constitute  only a
small portion of the  materials, but are present in
sufficient quantities  to cause dust emissions during
conveying, mixing, and storage operations. More-
over, minor raw materials such as salt cake and
sulfur can create dust emissions during handling.
Dust is  the only air contaminant from batch plants,
and the  control of dust emissions  poses problems
similar  to those in industrial plants handling simi-
lar dusty powder or  granular materials.

Hooding  and Ventilation Requirements

Dust control equipment can be installed on con-
veying systems that use open conveyor belts.
A  considerable reduction in the size of the dust

-------
768
CHEMICAL PROCESSING EQUIPMENT
              GULLET
       RAW MATERIALS
       RECEIVING
       HOPPER
                SCREW
                CONVEYOR   '—'
                                                       FILTER
                                                       VENTS
 STORAGE BINS
 MAJOR  RAW MATERIALS
                                                    MINOR
                                                    INGREDIENT
                                                    STORAGE
                                                    BINS
                                                     BELT CONVEYOR
BATCH
STORAGE
BIN
                                                                            FURNACE
                                                                            FEEDER
                             Figure  588.  Process flow diagram of a batch  plant.
control equipment can be realized by totally en-
closing all conveying  equipment and sealing all
covers and access openings 'with gaskets of
polyurethane foam. In fact,  by totally enclos-
ing all conveying  equipment, exhaust systems
become unnecessary, and relatively small filter
vents or dust cabinets can be attached directly
to the  conveying equipment and storage bins.

On the other hand, exhaust systems are re-
quired for ventilating the weigh hoppers and
mixers.   For example,  a 60-cubic-foot-capacity
mixer and a 4, 500-pound-capacity mixer each
require about 600 cfm ventilation air.   Seals of
polyvinylchloride  should be  installed between
the rotating body  of the mixer and its frame to
reduce ventilation to a minimum.

Railroad hopper cars  and hopper bottom trucks
must be connected to  sealed receiving hoppers
by fabric  sleeves  so that dust generated in the
hoppers during the loading operation is either
filtered through the sleeves  or  exhausted through
a baghouse.

Local exhaust systems for dust pickup are de-
signed by using the recommended practice of the
Committee on Industrial Ventilation (I960).  For
example,  the ventilation rate at the transfer
point between two open belt  conveyors is  350
                      cfm per foot of belt width, with 200 fpm minimum
                      velocity through the hood openings.


                      Air Pollution Control Equipment

                      Because dust emissions  contain particles only
                      a few microns in diameter, cyclones, and  cen-
                      trifugal scrubbers are not as  effective as bag-
                      houses or filters are in collecting  these small
                      particles; consequently,  simple cloth filters and
                      baghouses are used almost exclusively in con-
                      trolling dust emissions from batch plants.

                      Filter socks or simple baghouses with inter-
                      mittent shaking mechanisms  are usually de-
                      signed for a filter velocity of  3 fpm, but bag-
                      houses with continuous cleaning devices such  as
                      pulse jets or reverse air systems  can be de-
                      signed for filter velocities as high as  10 fpm.
                      Filtration cloths are usually cotton, though ny-
                      lon, orlon, and dacron are sometimes used.
                      Dusts  collected are generally noncorrosive.
                      Filters or baghouses for storage bins are de-
                      signed to accommodate not only displaced air
                      from the filling operation but  also  air induced
                      by falling materials.  Filtration of air exhaust
                      from pneumatic conveyors used in filling the
                      bins must also be provided.  Filters with at least
                      a 1-square-foot area should be mounted on the
                      hand-filled minor-ingredient bins.

-------
                                          Glass Manufacture
                                            769
Transfer chutes of special design are used for
hand filling the minor ingredient bins.   They are
first attached securely with  gaskets to the top of
the bins.   The bags  are  dropped into  a chute
containing knives across  the bottom.  The knives
split the bag,  and as the materials fall into the
bin, the broken bag seals off the escape of dust
from the top of the chute.
CONTINUOUS SODA-LIME  GLASS-MELTING FURNACES

While limited quantities of special glasses such
as lead or borosilicate are melted in electrically
heated pots or in small-batch,  regenerative fur-
naces with capacities up to 10 tons per day, the
bulk of production,  soda-lime glass,  is melted
in direct-fired, continuous, regenerative furnaces.
Many of these furnaces have added electric induc-
tion systems called "boosters" to increase capac-
ity.   Continuous,  regenerative furnaces  usually
range in capacity from 50 to 300 tons of glass
per  day; 100 tons is the most common capac-
ity found in the United States.

Continuous, regenerative,  tank furnaces differ
in design according to the type  of glass products
manufactured.   All  have two compartments.  In
the first compartment,  called  the melter,  the dry
ingredients are mixed in correct proportions and
are continuously fed onto a molten mass  of glass
having a temperature near 2, 700° F.   The dry mate-
rials melt  after floating a third to one-half of the
way across the compartment and disappearing  into
the surface of a clear, viscous-liquid glass.  Glass
flows from the melter into the second compartment,
commonly  referred to as the refiner, where it is
mixed for homogeneity and heat conditioned to
eliminate bubbles and stones.   The temperature
is gradually lowered to about 2,200°F.   The
amount of glass circulating within the melter
and refiner is about 10 times the amount with-
drawn for production (Sharp,  1954).

Regenerative furnaces for container  and  tableware
manufacture have a submerged opening or  throat
separating the refiner from the melter.  The throat
prevents undissolved materials and scum on the
surface from, entering the refiner.  Glass flows
from the semicircular refining compartment into
long, refractory-lined chambers called forehearths.
Oil or gas burners and ventilating dampers ac-
curately control the temperature and viscosity  of
the glass that is fed from the end of the forehearth
to glass-forming machines.

Continuous furnaces for manufacturing rod, tube,
and sheet glass differ from furnaces for  container
and tableware manufacture in that they have no
throat between the melter and  refiner.  The com-
partments are separated from each other by float-
ing refractory beams riding in a drop arch across
the entire width of the furnace.  Glass flows from
the rectangular-shaped  refiner directly into the
forming machines.

Regenerative firing systems for continuous glass
furnaces  were first devised by Siemens in 1852,
and since then, nearly all continuous glass fur-
naces in the United States have used them.  In
Europe, continuous glass furnaces employ both
recuperative and  regenerative systems.

Regenerative firing systems consist of dual
chambers filled with brick checkerwork.   While
the products of combustion from the melter pass
through and heat one chamber,  combustion air
is preheated in the opposite chamber. The func-
tions of each chamber are interchanged during
the reverse flow of air and combustion products.
Reversals occur every 15 to 20 minutes as re-
quired for maximum conservation of heat.

Two basic configurations  are used in designing
continuous,  regenerative  furnaces - end port,
Figure 589, and side port, Figure 590.  In the
side port furnace, combustion products and
flames pass in one direction across  the melter
during one-half of the cycle.   The flow is re-
versed during the other  half cycle.  The side
port design is commonly used in large furnaces
with melter areas in excess of 300 square feet
(Tooley,  1953).

In the end port configuration, combustion products
and flames  travel in a horizontal U-shaped path
across the  surface of the glass within the melter.
Fuel  and  air mix  and ignite at one port and dis-
charge through a  second port adjacent to the first
on the same end wall of  the furnace.  While the
end port design has been used extensively  in small-
er furnaces with melter areas from 50 to 300
square feet, it has also  been used in furnaces with
melter areas up to 800 square feet.

Continuous  furnaces are usually operated slightly
above atmospheric pressure within the melter to
prevent air induction at  the feeders and an over-
all loss in combustion efficiency.  Furnace draft
can be produced by several methods:  Induced-
draft fans,  natural-draft stacks, and ejectors.


The Air Pollution Problem

Particulates expelled from the melter are  the re-
sult of complex physical and chemical reactions
that occur during  the melting process.

Glass  has properties akin to those of  crystalline
solids, including rigidity, cold flow,  and hard-
ness.  At the same time,  it behaves  like a super-

-------
 770
CHEMICAL PROCESSING EQUIPMENT
                                                                        REFINER SIDE WALL

                                                                                GLASS SURFACE IN REFINER
                                                                                            FOREHEARTH
 INDUCED DRAFT FAN
                                                                        FEEDER
     PARTING WALL

     SECONDARY CHECKERS'
                                                  'CURTAIN WALL
                                                RIDER ARCHES
                        Figure  589.  Regenerative end port glass-melting furnace.
cooled liquid.  It has nondirectional properties,
fracture characteristics of an amorphous solid,
and no freezing or melting point.  To account for
the wide range of properties,  glass  is considered
to be a configuration of atoms rather than an ag-
gregate of molecules.  Zachariasen (1932) pro-
posed the theory that glass consists of an extended,
continuous, three-dimensional network of ions with
a certain amount of short-distance-ordered ar-
rangement similar to that of a polyhedral crystal.


These dissimilar properties explain in part why
predictions of particulate  losses from the melter
based solely upon known temperatures and vapor
pressures of pure compounds have been inaccurate.
Other phenomena affect the  generation of par-
ticulates.  During the melting process,  carbon
dioxide bubbles and propels particulates from the
melting batch.  Particulates are entrained by the
fast-moving stream of flames and combustion
                       gases.  As consumption of fuel and refractory tem-
                       peratures of the furnace increase with glass ton-
                       nage,  particulates also increase in quantity.  Par-
                       ticulates, swept from the melter,  are either col-
                       lected in the checkerwork and gas  passages or
                       exhausted to the atmosphere.

                       Source test  data

                       In a recent study,  many source tests  of glass
                       furnaces in  Los Angeles County were used for
                       determining the major variables influencing stack
                       emissions.  As summarized in Table 205, data
                       include:  Particulate  emissions, opacities,  pro-
                       cess variables, and furnace design factors.
                       Particle size distributions of two typical stack
                       samples are shown in Table 206.   These particu-
                       late samples were obtained from the catch of a
                       pilot baghouse venting part  of the effluent from
                       a large  soda-lime container furnace.

-------
                                           Glass Manufacture
                                                                                                      771
                GLASS SURFACE IN MELTER

         NATURAL DRAFT STACK

              BACK WALL
                   REFINER SIDE WALLi

MELTER SIDE VIALL       THROATV
           MELTER BOTTOM
                                                                                        GLASS SURFACE IN REFINER
                                                            FOREHEARTH
                          COMBUSTION AIR BLOWER
                        MOVABLE  REFRACTORY BAFFLE
                                                                     RIDER ARCHES
                                                 BURNER
                         Figure 590.  Regenerative side port glass-melting furnace.
Chemical composition of the particulates "was
determined by microquantitative methods or by
spectrographic analysis.  Five separate samples,
four from a pilot baghouse, and one from the
stack of a soda-lime   regenerative furnace, are
given in Table 207.  They were found to be com-
posed mostly of alkali sulfates although alkalies
are reported as  oxides.   The chemical composi-
tion of sample 5 was also checked by X-ray
crystallography.  In this analysis,  the  only
crystalline material present in identifiable
amounts 'was two polymorphic forms of sodium
sulfate.
Opacity of stack emissions

From the source test data available,  particu-
late emissions did not correlate with the  opacity
*~r the stack emissions.  Some generalizations on
opacity can, however, be made.  Opacities usu-
                  ally increase  as  particulate emissions increase.
                  More often than not, furnaces burning U. S. Grade
                  5 fuel oil have plumes exceeding 40 percent white
                  opacity while  operating  at a maximum pull rate,
                  which is the glass industry's common term for
                  production rate.   Plumes from these  same  fur-
                  naces were  only  15  to 30 percent white opacity
                  while burning natural gas or U.  S. Grade 3
                  (P.S. 200) fuel oil.   Somewhat lower  opacities
                  may  be expected from furnaces  with ejector
                  draft systems  as compared with furnaces with
                  natural-draft  stacks or  induced-draft fans.


                  Hooding and Ventilation  Requirements

                  In order to determine the correct size of air
                  pollution control equipment,  the volume  of dirty
                  exhaust gas from, a  furnace must be known.  Some
                  of the more important factors affecting exhaust
                  volumes include:  Furnace size,  pull  rate,  com-
 234-767 O - 77 - 51

-------
772
CHEMICAL PROCESSING EQUIPMENT
               Table 205.  SOURCE TEST DATA FOR GLASS-MELTING FURNACES
Test No.
C-339b
C-339
C-382-1
C-382-2
C-536
C-383
Pri Lab
Pri Lab
Pri Lab
Pri Lab
Pri Lab
Pri Lab
Pri Lab
C-101
C-120
C-577
C-278-1
C-278-2
C-653
C-244-1
C-244-2
C-420-1
C-420-2
C-743
C-471
Type
of
furnacea
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
SP
SP
SP
SP
SP
SP
SP
SP
SP
SP
Type
Of u
fuelb
0-300
G
G
G
0-200
G
G
G
G
G
G
0-300
G
G
G
0-300
G
0-300
G
G
G
G
G
G
G
Xl
(particulate
emissions),
Ib/hr
7. 00
3.00
4.60
6. 40
4. 70
8.40
3. 86
4. 76
4.26
6. 84
4. 62
3.96
7. 16
9. 54
9.90
12. 70
3. 97
8. 44
8.90
6. 30
3. 00
6. 30
6.60
10. 20
6. 70
X2
process wt ratio),
lb/hr-ft2
of melter area
16.7
13.8
16.5
18.2
17.5
17.9
10.9
14.6
17. 1
17.4
18.5
14.6
20.2
15.2
14.2
24.2
18.3
18.5
22.0
7. 5
5.4
10. 7
13.2
26.2
11.6
X3,
wt fraction
of cullet in
charge0
0. 300
0. 300
0. 300
0. 300
0. 199
0. 300
0. 094
0. 094
0. 157
0.094
0. 365
0.269
0. 175
0. 300
0. 320
0. 134
0. 361
0. 360
0. 131
0. 182
0. 100
0. 100
0. 100
0.047
0.276
x4
(checker volum^,
ft3/ft2 of melter
5.40
5. 40
5. 40
5. 40
5. 40
6.50
8. 00
8.00
8.00
8.00
9.00
9.00
9. 00
5. 00
5.00
6. 90
6.93
6. 93
8.74
7. 60
7. 60
7. 60
7. 60
8.25
5. 60
Maximum
opacity
of stack
emissions, %
50
10
10
10
10
20
25
25
25
25
—
45
20
20
20
35
20
20
40
25
25
10
5
25
30
 aEP = end port,  regenerative furnace; SP  =  side port, regenerative furnace.
 bG  =  natural gas; 0-200 = U.S.  Grade 3 fuel oil; 0-300  =  U.S. Grade 5 fuel oil.
 cConstants: Sulfate content of charge 0. 18 to 0. 34 wt %.
             Fines (-325 mesh)  content of charge 0. 2 to  0. 3 wt %.
bustion efficiency,  checker volume, and furnace
condition.

Exhaust volumes can be determined from fuel
requirements for container furnaces given by
the formula of Cressey and Lyle (1956).
    F  =  [50 + 0.6A]  + 4.8T           (151)

where

    F  =  total heat,  106 Btu/day

    A  =  melter area, ft

    T  =  pull rate, tons/day.

This straight-line formula includes minimum
heat to sustain an idle condition plus additional
heat for a specified pull rate.  Fuel require-
ments for bridgewall-type,  regenerative fur-
naces are also given by Sharp (1955) and are
                      shown in Figure 591.  The melter rating para-
                      meter of 4 square feet of melter surface area
                      per daily ton of glass  should be used to estimate
                      the fuel requirements of container furnaces at
                      maximum pull rates,  but 8 square feet per ton
                      can be used for estimating fuel requirements
                      for non-bridgewall furnaces supplying glass
                      for tableware and for  sheet, rod, and tube
                      manufacture.   Fuel requirements given are
                      averages for furnaces constructed before 1955;
                      consequently, these furnaces generally require
                      more fuel per ton of glass than do furnaces con-
                      structed since 1955.  After the fuel require-
                      ments are determined, exhaust volumes are com-
                      puted on the basis of combustion with 40 percent
                      excess combustion air.  Forty percent excess
                      combustion air  is chosen as representing av-
                      erage combustion conditions near the end of the
                      campaign/ (a total period of operation without shut-
                      ting down for  repairs  to the furnace).

                      Exhaust volumes determined from fuel require-
                      ments are  for furnaces with induced-draft sys-

-------
                                        Glass Manufacture
                                            773
     Table 206.  SIZE DISTRIBUTION OF
         PARTICULATE EMISSIONS
      (MICROMEROGRAPH ANALYSES)
Furnace 1 Flint glass
Diameter (D),
H
36. 60
22.00
18. 30
16. 50
14. 60
12.80
12.20
11. 60
11.00
10. 40
9.80
9.20
8. 50
7. 30
6. 10
4.88
3.66
3. 05
2. 44
1.83
1. 52
1.22
% (by wt)
less than D
100
99. 5
98. 6
97. 7
94.0
84. 6
80. 7
76. 6
72. 7
67. 7
62.4
58. 3
51.8
43. 1
34. 4
28. 0
21. 3
18. 6
14. 9
11.0
8. 3
4. 1
Furnace 2 Amber glass
Diameter (D),
H
17. 40
15.70
14. 00
12.20
11.60
11. 00
10.50
9.90
9. 30
8. 80
8. 10
7. 00
5.80
4.65
3.49
2,91
2.33
1.74
1.45
1. 16

	 . 	 . 	
% (by wt)
less than D
100
99. 8
99.4
96. 8
92. 5
89. 5
87.2
83.4
78. 7
75.0
73. 4
60. 3
47.6
35.6
25. 4
20. 5
16. 4
10. 9
8.9
5. 3


terns or natural-draft stacks.  Exhaust volumes
for ejector systems can be estimated by increas-
ing the exhaust volume by 30 to 40 percent to
account for ejector air mixed with the furnace
effluent.

Exhaust gases from furnaces with natural-draft
stacks or induced-draft fan systems usually range
in temperature from 600°   to 850°F,  but exhaust
gas temperatures from furnaces containing ejec-
tors are lower and vary from 400°  to 600°F.
In Table 208 are found chemical analyses of gas-
eous components of exhaust gases from large,
regenerating, gas-fired furnaces melting three
kinds of soda-lime  glass.


Air Pollution Control Methods

As the furnace campaign progresses,  dust carry-
over speeds destruction of the checkers.  Upper
courses of the firebrick checker glaze when sub-
jected to high temperatures. Dust and condensate
collect  on the brick surface and form  slag that
drips downward into the lower courses where it
solidifies at the lower temperature and plugs the
checkers.  Slag may also act somewhat like fly-
paper,  tenaciously clinging to the upper courses
and eventually sealing off upper gas passages.

Hot spots develop around clogged checkers  and
intensify the destructive forces, which are  re-
flected  by a drop in regenerator efficiency and a
rise in  fuel consumption and horsepower required
to overcome additional gas flow resistance  through
the checkers.  Checker damage can finally  reach
a point  where operation  is no longer economical or
is physically impossible because of collapse. Thus,
successful operation of modern regenerative fur-
naces requires keeping dust carryover from the
melter  to an absolute minimum, which also coin-
cides with air pollution control  objectives by prevent-
ing air  contaminants from entering the atmosphere.
Aside from reducing air contaminants, benefits de-
                Table 207.  CHEMICAL COMPOSITION OF PARTICULATE EMISSIONS
               (QUANTITATIVE ANALYSES), METALLIC IONS REPORTED AS OXIDES
Sample source
Test
type of glass
components
Silica (SiO2)
Calcium oxide (C_O)
a
Sulfuric anhydride (SO,)
Boric anhydride (B2Oj)
Arsenic oxide (As-^Oj)
Chloride (Cl)
Lead oxide (PbO)
K2O + Na2O
AL2°3
Fluoride
Fe203
MgO
ZnO
Unknown metallic oxide (R2Oj)
Loss on ignition
Baghouse
catch
No. 1
amber,
wt %
0.03
1.70
46. 92
3.67
7. 71
0. 01
0. 39
29.47






10. 10
Baghouse
catch
No. 2
flint,
wt %
0. 3
2. 3
25. 1
1.3



28. 1
3. 5
8.6




30.8
Baghouse
catch
No. 3
amber,
wt %
0. 1
0. 8
46.7




26. 1


0. 1

0.5

25. 7
Baghouse
catch
No. 4
flint,
wt %
4. 1
19.2
30.5




36.5
0.2

0.6
1.4


7.5
Millipore
filter
No. 5
flint,
wt %
3. 3

39.4




39.2





6.5
11.6

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774
CHEMICAL PROCESSING EQUIPMENT
  12 000 |
                     MELTER AREA, ' l
       Figure  591. Natural  gas for  br idgevial I -type
       regenerative furnaces (Sharp,  1955).
 rived from reducing dust carryover are many and
 include longer furnace campaigns, lower mainte-
 nance costs,  and savings on fuel.

 In order to determine which design and operating
 variables have the greatest effect upon dust carry-
 over and particulate emissions,  statistical analysis
 was performed on the  source test data given in
 Table 205.

 By the method of Brandon (1959), particulate emis-
 sions, the dependent variable were found to corre-
 late with the  following  independent variables  and
 nonquantitative factors:
 1.   Process weight, Ib/hr-ft  ;

 2.   cullet, wt % of charge;
                        o  7
 3.   checker  volume, ft  /ft  melter;

 4.   type of furnace, side port or end port;
                       5.  type of fuel, U.S.  Grade 5 (PS300) oil or
                           natural gas;

                       6.  melter area,  ft .

                       Several simplifying assumptions are made so that
                       furnaces of different sizes can be  compared. Pro-
                       cess weight per square foot of melter  describes a
                       unit process occurring in each furnace regardless
                       of size.  Cubic feet of checkers per square foot
                       of melter not only defines the unit's dust-collect-
                       ing capability but is also a measure of fuel econorrr
                       Source tests C-382 and C-536 in Table 205  (and
                       other source tests) show no appreciable difference
                       in particulate emissions  from burning natural  gas
                       or U. S. Grade  3 fuel oil.

                       Correlation of particulate emissions with weight
                       percent sulfate (SOj) and minus 325-mesh fines
                       in the charge was  not possible because of insuffi-
                       cient test data.  Limited data available indicate
                       that particulate  emissions may double when  total
                       sulfate (SO,) content of the batch  charge is in-
                       creased from 0. 3  to 1. 0  weight percent.  Total
                       sulfates (303) include equivalent amounts of ele-
                       mental sulfur and  all compounds containing sulfur.
                       Sulfates usually comprise over 50 percent of the
                       particulate emissions.   They act  as fluxing agents
                       preventing the melting  dry-batch  charge from
                       forming a crust that interferes with heat trans-
                       fer and melting  (Tooley,  1953).  Compounds of
                       arsenic,  boron, fluorine, and metallic selenium
                       are also  expected  to be found along with sodium
                       sulfate in the particulate emissions because of
                       their high vapor pressures.

                       Data roughly indicate that particulate  emissions
                       increase severalfold when the quantity of minus
                       325-mesh fines  increases from 0. 3 weight per-
                       cent  to 1 or 2 weight percent.

                       Statistical analysis using the method of curvilinear
                       multiple  correlation by Ezekiel (1941) results  in the
                       following  equation, which describes particulate
                       emissions,  the dependent variable, as a function
                   Table 208.  CHEMICAL COMPOSITION OF GASEOUS EMISSIONS
                           FROM GAS-FIRED, REGENERATIVE FURNACES
Gaseous components
Nitrogen, vol %
Oxygen, vol %
Water vapor, vol %
Carbon dioxide, vol %
Carbon monoxide, vol %
Sulfur dioxide (SO,), ppm
Sulfur trioxide (SOj), ppm
Nitrogen oxides (NO,NO2), ppm
Organic acids, ppm
Aldehydes, ppm
Flint glass
71. 9
9. 3
12.4
6. 4
0
0
0
724
NAa
NA
Amber glass
81. S
10.2
7. 7
8. 0
0. 007
61
12
137
50
7
Georgia green
72.5
8. 0
12. 1
7.4
0
14
15
NA
NA
NA
               aNA  =  not available.

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                                         Glass Manufacture
                                                                                                   775
of four independent variables and two nonquanti-
tative independent factors.  This equation is
valid only when two other  independent variables--
sulfate content and content of minus 325-mesh fines
of the batch--lie between 0. 1 to 0. 3 weight percent
and, also,  when fluorine,  boron, and lead com-
pounds are either absent from the batch charge or
present only in trace amounts.

X  = a + 0.0226(X)  -0.329X-4. 412 X  -
      0. 9379 X  -0.635(XC)  + 6.170 Xc
               45             5
                                         (152)
 vhere
    X   =  particulate emissions,  Ib/hr

    X   =  process wt, Ib/hr-ft  melter
    X   =  wt fraction of cullet in charge
    X
                   3   2
checker volume, ft /ft  melter
    X   =  melter area, ft /100

     a  =  constant involving two nonquantitative
           independent factors  relating the type
           of furnace  (side port or end port) and
           the type of fuel (U. S. Grade 5 fuel or
           natural  gas).

           a =   -0. 493 end port - U. S. Grade 5
                 fuel oil
           a =   -0.623 side port  - U.S. Grade 5
                 fuel oil

           a =   -1. 286 end port - natural gas
           a =   -1.416 side port  - natural gas.

 Particulate emissions computed by this equation
 for 25 source tests show a standard deviation
 from measured particulate  emissions of +_ 1.4
 pounds per hour.  Further statistical  refine-  ^
 ment failed to yield a lower standard deviation.

 Emissions to the atmosphere can  be predicted
 by using equation 152  or Figures 592 to 595, which
 are based upon this equation.  The curves should
 be used only within the limits indicated for the
 variables.  The curves should  not be extrapolated
 in either direction -with the  expectation of any de-
 gree  of accuracy,  even though  they appear as
 straight lines.  Particulate emissions  are first
 determined from Figure 592, then positive or
 negative corrections obtained from Figures  593
 to 595 are added to the emissions obtained from
 Figure 592.

 Design and operation of soda-lime, continuous,
 regenerative furnaces  to alleviate dust carry-
over and minimize particulate emissions are
discussed in succeeding paragraphs.  Advantages
of all-electric,  continuous furnaces for melting
glass are also cited.

Control of raw materials

Although glassmakers have traditionally sought
fine-particle materials for easier melting, these
materials have  intensified dust carryover in re-
generative furnaces.  A compromise must be
reached.  Major raw materials  should be  in the
form of small particles,  many of them passing
U. S.  30-mesh screen, but not more than 0. 3
weight percent passing U, S.  325-mesh screen.
Because crystals of  soda  ash, limestone,  and
other materials may be friable and  crush  in the
mixer,  producing excessive amounts of fines,
screen analyses of individual raw materials
should not be combined for estimating the screen
analyses of the  batch charge.  Crystalline shape
and density of raw materials should be thoroughly
investigated before raw material suppliers are
selected.

Since particulate emissions from soda-lime re-
generative furnaces  increase with an increase in
equivalent sulfate (SO-j) present in the batch
charge,  sulfate content should be reduced to an
absolute minimum consistent with good glass-
making.  Preferably, it should be below 0. 3
weight percent.  Equivalent sulfate  (SCO content
of the batch includes all sulfur compounds and
elemental sulfur.  Compounds of fluorine, boron,
lead, and arsenic are also known to promote dust
carryover (Tooley,  1953), but the magnitude of
their effect upon emissions is still unknown.  In
soda-lime glass manufacture, these materials
should be eliminated or should be present in only
trace amounts.

From the standpoint of suppressing stack emis-
sions, cullet content of the batch charge  should
be  kept as high as possible.  Plant  economics may,
nevertheless,  dictate reduction in cullet where fuel
or  cullet is high in cost or •where cullet is in short
supply.  Some manufacturing plants are able to
supply all their cullet requirements from scrap and
reject glassware.

Batch preparation

There are a number  of ways to condition a batch
charge and reduce dust carryover.  Some  soda-
lime glass manufacturers add moisture to the
dry batch, but the relative merits of this process
are debatable.   Moisture is sprayed into the dry-
batch charge at the mixer as a solution containing
1  gallon of surface-active wetting agent to 750
gallons  of water.  Surface tension of the water is
reduced by the wetting agent so that the water
wets the finest particles and is evenly distributed

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776
CHEMICAL PROCESSING EQUIPMENT
               X4,  ft3 checkers-'! t2 me I ter
  Figure 592. Particulate emissions versus checker
  volume per  ft2 of melter.
                                                     6

                                                     5
                                                   x

                                                   CO
                                                   I  3

                                                   S 2
                                                   K
                                                   O=
                                                   2  i
                               X2 PROCESS HEIGHT. I b'h r per  ft' melter

                       Figure 593.  Correction  to  particulate  emissions
                       for process  weight  per  ft2  melter.
                      0 05
                                  0 10         0 15          0 20
                                        X,  KEIGHT FRACTION OF CUUET II
                                                                      0 25
                                                                                 0 30
                                                                                              0 35
                               CHARGE
                    Figure 594.  Correction  to  particulate emissions for cullet content
                    of the batch charge.
                             500
                        ft' meltir
  Figure 595. Correction to particulate  emissions
  for melter area.
                       throughout the batch (Wilson,  I960).  Fluxing
                       materials such as salt  cake appear more effec-
                       tive, since the unmelted batch does not usually
                       travel so far in the melter tank before it melts.
                       Moisture content of the batch is  normally in-
                       creased to about 2 percent by weight.  If the
                       moisture content exceeds  3 percent, batch in-
                       gredients  adhere to materials-handling equip-
                       ment and may cake in storage bins or  batch cans.

                       Other batch preparation methods have been em-
                       ployed on a limited-production or experimental
                       basis to reduce dust carryover from soda-ash
                       glass manufacture.  One method involves prer
                       sintering the batch to form cullet and then  charg-
                       ing  only this cullet to the furnace.  Advantages

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                                         Glass Manufacture
                                                                                                 777
claimed  are faster  melting,  better batch con-
trol, less seed formation, reduced clogging in
the checkers, and lower stack losses (Arrandale,
196Z).  A Dutch oven doghouse cover also reduces
dust carryover by sintering the top of the floating
dry batch before it enters the melter.  This meth-
od is probably not as efficient as  is complete pre-
sintering in reducing dust carryover.

Other methods include:  (1) Charging briquets,
•which are made from regular batch ingredients
by adding up to  10 percent by weight of water;
(2) charging wet batches containing 6 percent
moisture, which are made by first dissolving
soda-ash to form a saturated solution and mix-
ing this solution with sand and the other dry
materials;  (3) charging the dry batch (Submerged)
in the melter;  (4) enclosing batch feeders (Fabri-
anio,  1961); and (5) installing batch feeders  on
opposite  sides of end port,  regenerative furnaces
and charging alternately on the side under fire.


Checkers
The design  concept  of modern regenerative fur-
naces, with its  emphasis on maximum use of
fuel, is also indirectly committed to reducing
dust carryover.  All things being equal,  less
fuel burned per ton  of glass means  less dust
entrainment by  hot combustion gases and flames
flowing across the surface  of the melting glass.
Although container furnaces constructed over
15 years ago  required over 7,000 cubic feet of
natural gas per ton of glass at maximum pull
rates,  container furnaces built today can melt
a ton of glass with less than 5, 000 cubic feet
of natural gas.

While several design changes are responsible
for this improvement, one of the  most important
is the increase  in checker volume.   The ratio of
checker  volume (cubic feet) to meter area (square
feet) has been rising during the years from about
5 in earlier furnaces to  about 9 today.   Enlarged
checkers not only reduce fuel consumption and
particulate formation but also present a more
effective trap for dust particles that are expelled
from the melter.  Source tests conducted by  a
large glass-manufacturing company indicated
that over 50 percent of the dust carryover from
the melter is collected by the checkers and gas
passages instead of entering the  atmosphere.

Of course, the economics connected with regen-
erative furnace  operation dictates the checker
volume.   The law of diminishing returns oper-
ates where capital outlay for an added volume
of checkers will no longer be paid within a spe-
cified period by an incremental reduction in fuel
costs.  Checkers have been designed in double-
pass arrangements to recover as much as 55 per-
cent of the heat  from the waste gases (Sharp,  1954).
 Although dust collects within checkers by mechan-
 isms of impingement and settling, the relationship
 among  various factors influencing dust collection
 is unknown.  These factors include:  Gas velocity,
 brick size, flue  spacing, brick setting, and brick
 composition.   Checkers designed for maximum
 fuel economy may not necessarily have the high-
 est collection efficiency.  Further testing  will
 be necessary in  order to evaluate checker  de-
 signs.   Checkers designed for maximum heat
 exchange contain maximum heat transfer surface
 per unit volume,  a condition met only by smaller
 refractories with tighter spacing.   Heat transfer
 surfaces can be  computed by the method given in
 Trinks (1955).  Since gas  velocities are also
 highest for maximum heat transfer, less dust
 collects by simple settling than by impingement.
 Dust collection is further  complicated in that
 smaller brick increases the potential for clogging.

 To prevent clogging  in the checkers and ensure
 a reasonable level of heat transfer,  checkers
 should  be cleaned once per month or more often;
 an adequate number  of access doors should be
 provided for this purpose (Spain,  1956b). Com-
 pressed air, water,  or steam may be used to
 flush fine particles from the checkers.   Virtual-
 ly nothing can be done to remove  slag after it
 has formed.  Checkers can be arranged in a
 double  vertical pass  to reduce overall furnace
 height and make  cleaning easier.   Access  doors
 should  also be provided for removing dust de-
 posits from the flues.
 Preheaters

 Further reductions in fuel consumption to re-
 duce dust emissions may be realized by install-
 ing rotary, regenerative air preheaters in series
 with the checkers.  Additional benefits include
 less checker  plugging, reduced maintenance, and
 increased checker life. Rotating elements of
 the preheater are constructed of mild steel,  low-
 alloy steel, or ceramic materials.   Preheaters
 raise the temperature  of the air to  over 1, 000°F,
 and the increased velocity of this preheated air
 aids in purging dust deposits that block gas pas-
 sages of the checkers.  Exhaust gases passing
 through the opposite side of the preheater are
 cooled below  800°F before being exhausted to
 the atmosphere.  A heat balance study of a plate
 glass, regenerative furnace shows a 9 percent
 increase in heat use by the  installation of a
 rotary, regenerative air preheater  (Waitkus,
 1962).   To maintain heat transfer and prevent
re-entrainment, dust deposits on the preheater
elements must be removed by periodic cleaning.
Ductwork and valves should be installed for by-
passing rotary air preheaters during the cleaning
stage.

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                              CHEMICAL PROCESSING EQUIPMENT
Refractories and insulation

Slagging of the upper courses of checker-work
can be alleviated in most cases by installing
basic (high alumina content) brick in place of
superduty firebrick (Robertson et al. ,  1957).
Basic brick courses extend from the top down-
ward to positions where checker temperatures
are below 1, 500 °F.  At this temperature, fire-
brick no longer "wets" and forms slag with dust
particles.  Dust usually collects in the lower
courses  of firebrick in the form of fine particles
that are  easily removed by cleaning.  Although
basic brick costs 3  or 4 times as much as super-
duty firebrick, some glass manufacturers are
constructing entire  checkerworks of basic brick
where  slagging and  clogging are most  severe.
In some  instances,  basic refractories are re-
placing fireclay rider tiles and rider arches
in checker supports (Van Dreser,  1962).  A
word of caution, basic brick is no panacea for
all ills of checkers.  Chemical composition of
the dust  should be known,  to determine com-
patibility with the checkers (Fabrianio, 1961).

Regenerative furnaces can be designed to con-
sume less fuel and emit less dust by proper
selection and application of insulating refrac-
tories.   A heat balance study of a side port, re-
generative furnace shows that, in the melting
process,  glass receives 10 percent of heat
transfer from convection and 90 percent from
radiation.  Of the radiation portion of heat
transferred, the crown accounts for 33 percent
(Merritt, 1958).  Since heat losses  through  the un-
insulated crown can run as high as  10 percent of
the total heat input, there  is need for  insulation
at this spot.

Most crowns are constructed of silica brick
with a maximum furnace capacity restricted to an
operating temperature of 2,850°F (Sharp,  1955).
Insulation  usually consists of insulating silica
brick backed with high-duty plastic refractory.
Furnaces are first operated without insulation,
so that cracks can  be  observed.   Then the cracks
are sealed with silica cement, and the insulation
is applied.

Insulation is  needed on the melter sidewall and
at the port necks to prevent glassy buildup caused
by condensation of vapors.  Condensate buildup
flows across port sills into the melter  and can
become a major source of stones.

While insulation of sidewalls shows negligible
fuel reduction for flint glass manufacture, it
does show substantial fuel reduction for colored
glasses.   The problem in manufacturing colored
glass is to maintain a high enough temperature
below the surface to speed the solution of stones
and prevent stagnation.  Insulation on sidewalls
raises the mean temperature to a point where
stones dissolve and glass circulates freely.

Six inches or more of electrofusion cast  block
laid over  a clay bottom in a bed of mortar  (Baque,
1954) not  only saves fuel but is also less subject
to erosion than is fireclay block.

Insulation is seldom needed on the refining end
of the furnace since refiners have become  cool-
ing chambers  at today's high pull rates.  Nose
crowns, however,  are insulated to minimize con-
densation and  drip (Bailey,  1957).   Checkers  are
sometimes encased in steel to prevent air  infiltra-
tion through cracks and holes that develop  in the
refractory regenerator walls during the  campaign.


Combustion of fuel

Furnace size also has an effect upon use of fuel,
with a corresponding effect on the emissions of
dust.   Large furnaces are more economical than
are small furnaces because the radiating surface
or heat loss per unit  volume of glass is greater
for small furnaces.

Slightly greater fuel economy may be expected
from end  port furnaces as compared -with side
port furnaces  of equal capacity.  Here again,  the
end port furnace  has  a heat loss advantage over
the side port furnace because  it has less exposed
exterior surface  area for radiating heat.  Side
port furnaces  can, however, be operated at great-
er percentages in excess of capacity since mixing
of fuel with air is more  efficient through several
smaller inlet ports than it is through only one
large inlet port.  In fact, end port furnaces are
limited in design to the amount of fuel  that can
be efficiently mixed with air and burned through
this one inlet port (Spain,  1955).  As far as dust
losses are concerned, there are only negligible
differences between end port and side  port furnaces
of equal size.   Reduced fuel consumption to re-
duce dust carryover can also be realized by in-
creasing the depth of the melter to  the maximum
consistent with good-quality glass.  Maximum
depths for container furnaces  are 42 inches for
flint glass (Tooley,  1953) and  about 36 inches for
amber glass and  emerald green glass.

Dust emissions as well as fuel consumption can
also be reduced by firing practice.  Rapid changes
in pull rates are  wasteful of fuel and increase
stack emissions.  Hence,  charge rates and glass
pull rates for continuous furnaces  should remain
as constant as possible by balancing loads  be-
tween the glass-forming machines.  If possible,
furnaces  should be fired on natural gas or U. S.
Grade 3 or lighter fuel oil.  Particulate  emis-
sions increase an average of about 1 pound per
hour -when U. S. Grade 5 fuel oil is  used  instead

-------
                                         Glass Manufacture
                                             779
of natural gas or U. S. Grade 3 fuel oil, and
opacities may exceed 40 percent white.

Combustion air should be thoroughly mixed with
fuel with only enough excess air present to en-
sure complete combustion without smoke.  Ex-
cess air robs the furnace of process heat by
dilution, and this heat loss must be overcome
by burning additional fuel.  Volume of the melter
should be designed for a maximum fuel heat re-
lease of about 13, 000 Btu per  hour per cubic foot.


Furnace reversals should be performed by an
automatic  control system  to ensure optimum
combustion.  Only automatic systems  can pro-
vide the exact timing required for opening and
closing the dampers and valves and for co-
ordinating fuel and combustion airflow (Bulcraig
and Haigh,  1961).  For instance, fuel  flow and
ignition must be delayed until  combustion air
travels through the checkers after reversal to
mix with fuel at the inlet port  to the melter.  Fur-
nace reversals are usually performed in fixed
periods of 15 to 20 minutes, but an improvement
in regenerator efficiency can be realized by pro-
gramming reversal periods to checker tempera-
tures measured optically.   Reversals  can then
occur when checker temperatures reach preset
values consistent with maximum heat transfer
(Robertson et al. ,  1957).
An excellent system for controlling air-to-fuel
ratios incorporates continuous flue gas analyzers
for oxygen and combustible hydrocarbons.   With
this system, the most efficient combustion and
best flame shape and coverage occur  at optimum
oxygen with a trace of combustible hydrocarbons
present in the flue  gas.  Sample gas is cleaned
for the analyzers through water-cooled probes
containing sprays.  The system  automatically
adjusts to compensate for changes in  ambient
air density.  Fuel savings of 6 to 8 percent
can be accomplished  on furnaces with analyzers
over furnaces not so  equipped (Gunsaulus,  1958).

Combustion of natural gas in new furnaces  occurs
efficiently when the-oxygen content of the flue
gases in the exhaust ports is less than 2 percent
by volume.  As  the campaign progresses, air
infiltration through cracks and pores  in the
brickwork,  air leakage through valves and  damp-
ers, increased pressure drop through the regen-
erators,  and other effects combine to make
combustion less efficient.   To maintain maxi-
mum combustion throughout the  campaign,  pres-
sure checks with draft gages should be run peri-
odically at specified locations (Spain,  1956a).
Fuel savings can also be expedited by placing
furnace operators on an incentive plan to keep
combustion air to a minimum.
Electric melting
Although melting glass by electricity is a more
costly process than melting glass by natural
gas or fuel oil,  melting electrically is a more
thermally  efficient process  since heat can be
applied directly to the body  of the glass.

Electric induction systems installed on regen-
erative furnaces are designed to increase max-
imum pull rates by as much as 50 percent.  These
systems are called boosters and consist of sev-
eral water-cooled graphite or molybdenum elec-
trodes equally spaced along the sides of the melt-
er 18 to 32 inches below the surface of the glass.
Source test results indicate that pull rates can
be increased -without any appreciable  increase in
dust carryover or particulate  emissions.   Fur-
nace  temperatures may also be reduced by
boosters,  preventing refractory damage at peak
operations.

Furnace capacity increase is nearly proportional
to the amount of electrical energy expended.  A
56-ton-per-day regenerative furnace  requires
480 kilowatt-hours in the booster to melt an addi-
tional ton of glass, which  is close to the theoret-
ical amount of heat needed to melt a ton of glass
(Tooley, 1953).

Electric induction can also be used  exclusively
for melting glass on a large scale.  Design of
this type of furnace  is simplified since regen-
erative checkerworks and large ductwork are  no
longer required (Tooley, 1953).  One recently
constructed 10-ton-per-day, all-electric  furnace
consists of a simple tank with molybdenum elec-
trodes.   A small vent leads  directly to the at-
mosphere, and dust emissions through this vent
are very small.  The furnace operates with a
crown temperature below  600 °F and with a
thermal efficiency of over 60 percent.  Glass
quality is excellent, with homogeneity nearly
that of optical glass. After  the first 11 months
of operation, there was  no apparent wear  on the
refractories (Peckham,  1962).  First costs and
maintenance expenses are substantially lower
than for a  comparable-size regenerative furnace.
An electric furnace may prove competitive with
regenerative furnaces in areas with low-cost
electrical power.

Baghouses and centrifugal scrubbers
Air pollution control equipment can be installed
on regenerative furnaces where particulate
emissions  or  opacities cannot be reduced to
required amounts through changes in furnace de-
sign,  control  of raw materials, and operating
procedures.  Regenerative furnaces may be
vented by two  types  of common industrial  con-
trol devices--wet centrifugal scrubbers and
baghouses.

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780
                              CHEMICAL PROCESSING EQUIPMENT
Figure 596 shows a low-pressure, wet, cen-
trifugal scrubber containing two separate con-
tacting sections within a single  casing.  Sep-
arate 50-horsepower,  circulating fans force
dirty gas through each section containing two
to three impingement elements  similar to fixed
blades of a turbine.  Although the collection
efficiency of this device is considered about the
highest for its type,  source tests show an over-
all efficiency of only 52 percent.  This low ef-
ficiency demonstrates the inherent inability of
the  low-pressure, •wet, centrifugal scrubbers
to collect particulates of submicron size.
 Figure  596. Wet,  centrifugal-type scrubber  con-
 trolling emissions from a  glass-melting furnace
 (Thatcher  Glass Co.,  Saugus,  Calif.).

On the other hand,  baghouses show collection
efficiencies of over 99 percent.  Although
baghouses  have not as yet  been installed on
large continuous,  regenerative furnaces, they
have been installed on small regenerative fur-
naces.  One baghouse alternately vents a 1, 800-
pound- and a 5, 000-pound-batch regenerative
furnace used for melting optical and  special
glasses used in scientific instruments.  Bags
are made of silicone-treated glass fiber.  Off-
gases are tempered by ambient air to reduce the
temperature to 400°F,  a safe operating temper-
ature for this  fabric.

Another baghouse,  although no longer in operation,
venteda 10-ton-per-day regenerative furnace for
melting soda-lime  flint glass.  Stack gases were
cooled to 250°F by radiation and convection from
an uninsulated steel duct before entering the  bag-
house containing orlon bags.
To determine the feasibility of using a cloth fil-
tering device on large continuous,  regenerative
furnaces, a pilot baghouse was  used with bags
made of various commercial fabrics.  An air-
to-gas heat exchanger containing 38 tubes, each
1-1/2 inches in outer diameter  by  120 inches in
length,  cooled furnace exhaust gases  before the
gases entered the pilot baghouse.  The baghouse
contained 36 bags,  each 6 inches in diameter by
111 inches in length, with a  432-net-square-foot
filter area.  A 3-horsepower exhaust fan was
mounted on the discharge duct of the baghouse.


When subjected to exhaust gases from amber
glass manufacture,  bags made  of cotton,  orlon,
dynel, and dacron showed rapid deterioration
and stiffening. Only orlon and  dacron bags ap-
peared in satisfactory condition when controlling
dirty gas  from flint glass manufacture and when  the
dirty gas  was held well above its dew point.  This
difference in corrosion between amber and flint
glass was found to be caused by the difference in
concentrations of sulfur trioxide (803) present in
the flue gas.
To reduce the concentration of SO-j from amber
glass manufacture,  iron pyrites were substituted
for elemental sulfur in the batch, but this  change
met with no marked success.  Stoichiometric
amounts of ammonia gas were also injected to
remove SOj as ammonium sulfate.  Ammonia in-
jection not only failed to lessen bag deterioration
but also caused the heat exch-anger tubes to foul
more rapidly.

In all cases, the  baghouse temperature  had to be
kept above the dew point of the furnace effluent
to prevent condensation from blinding the bags
and promoting  rapid chemical attack. At times,
the baghouse had to be operated with an inlet
temperature as high as 280°F to stay above the
elevated dew point caused by the presence of SO^.

Additional pilot baghouse studies are needed to
evaluate orlon and dacron properly for flint glass
manufacture.  Experiments  are also required for
evaluating silicone-treated glass fiber bags in con-
trolling exhaust gases from  regenerative  furnaces
melting all types of glass.

Information r.ow available indicates that glass
fiber  bags can perform at temperatures as
high as  500 °F, well above the elevated dew-
points.  They are virtually unaffected by rela-
tively large concentrations of
                                  and SO, and
there is less danger from condensation.  One
advantage of glass fiber is that less precooling
of exhaust gases is required because of the high-
er allowable operating temperatures.  Reverse
air collapse is generally conceded to be the best
method of cleaning glass fiber bags, since this

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                                         Glass Manufacture
                                                                                                  781
material is fragile and easily breaks when regu-
lar shakers are installed.

Furnace effluent can be cooled by several meth-
ods: Air dilution, radiation cooling columns,
air-gas heat exchangers, and water spray
chambers.  Regardless of the cooling method se-
lected,  automatic controls should be installed to
ensure  proper temperatures during the complete
firing cycle.  Each cooling method has its  ad-
vantages and disadvantages.  Dilution of offgases
•with air is the simplest and most troublefree
way to reduce temperature but requires the larg-
est baghouse. Air-to-gas heat exchangers and
radiation and convection ductwork are  subject to
rapid fouling from dust in the effluent.  Automatic
surface-cleaning devices should be  provided, or
access  openings  installed for frequent  manual
cleaning to maintain clean surfaces for adequate
heat transfer.  If spray chambers are  used,  se-
vere problems in condensation and temperature
control are anticipated.
 GLASS-FORMING MACHINES

 From ancient times, bottles and tableware were
 made by handblowing until mechanical production
 began in .the decade preceding the  turn of the cen-
 tury with the discovery of the "press and blow"
 and the "blow and blow" processes.  At first,
 machines were semiautomatic in operation.
 Machine feeding was done by hand.  Fully auto-
 matic machines made their  appearance during
 World War I and completely replaced the semi-
 automatic machines by 1925.  Two types  of auto-
 matic feeders  were developed and are in  use today.
 The first type  consists of a  device for dipping and
 evacuating the blank mold in a revolving pot of
 glass.  The second type, called a  gob  feeder,
 consists of an  orifice in the forehearth combined
 with shears and gathering chutes (Tooley, 1953).
Glass container-forming machines are of two
general types.  The first type is a rotating ma-
chine in which glass is processed through a
sequence  of stations involving pressing,  blowing,
or both.  An example of this type of machine is
a Lynch machine.  A second type is used in con-
junction with a gob feeder  and consists of inde-
pendent sections  in which each section is a com-
plete manufacturing unit.  There is no rotation,
and the molds have only to open  and close.  An
example of this type is the Hartford-Empire
Individual Section (I. S. ) six-section machine
shown in  Figure 597.  Mechanical details and
operations of various glass-forming machines
for manufacturing containers, flat glass,  and
tableware are found in the Handbook of Glass
Manufacture (Tooley,  1953).
Figure  597. Hartford-Empire  I.S.  six-section glass-
forming machine. (Thatcher  Glass  Co., Sangus,  Calif.).
 The Air  Pollution  Problem

 Dense smoke is generated by flash vaporization
 of hydrocarbon greases and oils from contact
 lubrication of hot gob shears and gob delivery
 systems.  This smoke emission can exceed 40
 percent white opacity.

 Molds are lubricated with mixtures of greases
 and oils and graphite applied to the hot internal
 surfaces once during 10-  to 20-minute periods.
 This smoke is usually 100 percent -white in
 opacity  and exists for 1 or 2 seconds.  It rapid-
 ly loses its opacity and is completely dissipated
 •within several  seconds.
 Air  Pollution  Control Methods

 During the past decade,  grease and oil lubri-
 cants for gob shears and gob delivery systems
 have been replaced by silicone emulsions and
 water-soluble oils at ratios of 90 to 150 parts
 of water to 1 part oil or  silicone.  The effect
 has been the virtual elimination of smoke.  The
 emulsions and  solutions  are applied by intermittent
 sprays to the delivery system and shears only when
 the  shears are  in an opened position.

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782
                              CHEMICAL PROCESSING EQUIPMENT
Lubricating properties of silicone-based emul-
sions appear in some respects superior to those
of soluble oil solutions.  Gob drop speeds are
increased by 20 to 25 percent.  Apparently,  the
gob rides down the delivery chute on a cushion
of steam.  Heat from the gob breaks the silicone
emulsion, forming an extremely stable resin,  a
condensation product of siloxane, which acts as
a smooth base for the cushioning effect of steam.
This resin is  degraded in a matter of seconds
and must be reformed continuously by reapply-
ing the silicone  emulsion.

While graphite gives no apparent advantages to
emulsions, a  combination of water soluble oil  and
silicone  emulsion appears to be most effective
(Singer,  1956).  Oil aids the wetting of metal
surfaces with silicone and coats metal surfaces,
retarding rust formation.  Sodium nitrite is also
helpful in inhibiting rust when added to silicone
emulsion.  Water for mixtures must be pure,  and
in most cases, requires  treatment in ion ex-
changers or demineralizers.

Water treatment is most critical for soluble oil to
prevent growth of algae and bacteria.  Oil  solutions
form gelatinous, icicle-like deposits upon  drying
on the surfaces  of pipes and arms of the I. S. ma-
chine.  These particles should not be allowed to
fall into  the mold.  Optimum results are obtained
by flood  lubrication of the delivery system to the
maximum amount that can be handled by a  runoff
wire or blown off by air.  Dry lubrication of
delivery systems has  been tried on an experi-
mental basis by coating the metal contact sur-
faces with molybdenum disulfide or graphite.

Although future developments  in the application
of emulsions to molds look promising,  present
practice still relies upon mixtures of hydro-
carbon greases,  oils, and graphite.   Silicone
emulsions and soluble oils eliminate smoke,
but several  difficulties must be overcome be-
fore they can be widely used for mold  lubrica-
tion.  Water emulsions with their high specific
heat cause excessive  cooling if they are not ap-
plied evenly to the mold  surfaces by proper
atomization.  Fine sprays meet with wind re-
sistance, and these sprays cannot be effectively
directed to cover the  shoulder  sections of some
molds.   Because of the low viscosity of water
emulsions, the emulsions are very difficult to
meter through existing sight oil feeders.  One
company has equipped its machine with individual
positive-displacement pumps for each nozzle.
Invert-post cross-spraying is found to be most
effective in giving a uniform coating to the molds
of I. S. machines (Bailey, 1957).

Rotating machines are much easier to lubricate
than are individual section machines.  Emulsion
sprays are most effective on rotating machines
when mounted at the point of transfer  of gobs
from the blank mold to the blow mold.

              FRIT  SMELTERS

INTRODUCTION

Ceramic coatings are generally divided into two
classes, depending upon whether they are applied
to metal or to glass  and pottery.  In the case of
metal,  the coating is widely referred  to in this
country as porcelain enamel.   The use of the
term vitreous  enamel seems to be preferred in
Europe. Glass enamel is sometimes  used inter-
changeably with both terms.  On the other hand,
the coating applied to glass or  pottery is known
as ceramic glaze.

Ceramic coatings are essentially  water suspen-
sions of ground frit and clay.   Frit is prepared
by fusing various minerals in a smelter.  The
molten material is then quenched  -with air or
water.  This quenching operation  causes the
melt to solidify rapidly and shatter into numerous
small glass particles,  called frit.  After a drying
process, the frit is finely ground  in a ball mill,
where other materials are added.   When suspend-
ed in a solution of -water and  clay,  the resulting
mixture is known as a ceramic  slip.   Enamel
slip is applied to metals and  fired at high tem-
peratures  in a furnace.  Glaze slip is applied to
pottery or  glass and fired in  a  kiln.

Raw Materials

The raw materials that go into the manufacture
of various  frits are similar to  each other whether
the frit is  for enameling on steel or aluminum or
for glazing.   The basic difference  is in the chem-
ical composition.

The raw materials used in enamels and glazes
may be divided into the following six groups:
Refractories,  fluxes, opacifiers,  colors, float-
ing agents, and electrolytes (Andrews,  1961).
The refractories include materials such as
quartz, feldspar,  and clay,  -which contribute to
the acidic  part of the melt and  give body to the
glass.  The fluxes include minerals such as
borax,  soda ash, cryolite, fluorspar, and litharge,
which are basic in character and react with the
acidic refractories to form the glass and, more-
over, tend to  lower the fusion temperatures of
the glasses.   These  refractory and flux materials
chiefly comprise the ingredients that go into the
raw batch that is charged  to the smelter.

Materials falling into the  other four groups are-
introduced later as mill additions  and rarely ex-
ceed 15 percent of the total frit composition.

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                                           Frit Smelters
                                                                                                   783
They include opacifiers, which are compounds
added to the glass to give it an opaque appear-
ance  such as the characteristic white of porce-
lain enamels.  Examples are tin  oxide,  anti-
mony oxide, sodium antimonate,  and zirconium
oxide.  The color materials include compounds
such  as the oxides of cobalt, copper, iron, and
nickel.   The floating agents consist of clay and
gums and are used to suspend the enamel  or
glaze in water.   Electrolytes such as borax,
soda  ash,  magnesium sulfate, and magnesium
carbonate  are added to flocculate the clay and
further aid the clay in keeping the enamel or
glaze in suspension (Parmelee,  1951).

Types of Smelters

Smelters used in frit making,  whether for
enamel or glaze, may be grouped into three
classes:  Rotary, hearth, and crucible.   The
rotary smelter is cylindrical and can be rotated
in either direction to facilitate fusing, as shown
in Figure 598.  It can also be tilted vertically
for the pouring operation, as demonstrated in
Figure 599.  The smelter is open at one end for
the introduction  of fuel and combustion air.  It
is similarly open at the opposite end for the dis-
charge of flue gases  and for charging raw mate-
rials. Operated solely as a batch-type smelter,
it is normally charged by means  of a screw con-
veyor, which  is  inserted through the  opening.
Rotary smelters are normally sized to take
batches varying from approximately 100 to 3, 000
pounds.  Fired with either gas or oil,  the  smelter
is lined with high-alumina, refractory firebrick
with an average life  of from 400 to 600 melts.
Firing cycles  vary from 1 to 4 hours.

The hearth smelter  consists of a  brick floor, on
which the raw materials are melted,  surrounded
by a boxlike enclosure.   This type  of smelter
can be either  continuous, as illustrated  in Figure
600,  or batch type,  as  shown in Figure 601.  In
either case, the  hearth  (or bottom) is  sloped
from one side to a point on the opposite  side
where the molten material is tapped.  The  con-
tinuous  type is usually screw fed.  A flue  stack
is located  on the opposite end.  Oil or gas is
normally used as fuel for the one or more burn-
ers.  The walls and floor are lined with a  first-
quality,  refractory firebrick.  The batch type is
sized to take batches ranging from 100 to several
thousand pounds.  About 30 pounds of batch can
be smelted for each square foot of hearth area.
The typical continuous-hearth smelter can pro-
cess  1, 000 to 1, 500 pounds of raw materials
per hour.

The crucible smelter consists of  a high-refrac-
tory,  fireclay, removable crucible mounted
•within a circular, insulated,  steel shell  lined
•with high-grade firebrick, as shown in Figure
602.  Heating is usually accomplished with oil
or gas burners, though electricity can be used.
The combustion chamber surrounds  the crucible,
occupying the space between the crucible and the
shell lining.   Because the heat must be trans-
mitted through the crucible to the batch,  re-
fractory and fuel costs are high.  Crucibles can
be sized to smelt  a 5-pound batch for laboratory
purposes, but the commercial crucibles are
sized to take batches from 100 pounds to  3, 000
pounds.  Smelting  cycles vary from  2 to 3 hours
at temperatures around 2,200°F, depending
upon the size of the batch and its composition.
The steel shell is supported by trunnions so
that the crucible can be tilted for the pouring
operation.
 Frit Manufacturing

 Since the ivv materials that comprise the
 smelter batch consist of refractories and
 fluxes, thorough and uniform mixing of these
 ingredients before the  charging operation is
 essential for efficient smelting.  Smelting
 involves the heating of raw materials until  a
 fairly homogeneous glass is  formed.  The
 fundamental changes that occur are inter-
 action of acids and bases,  decomposition,
 fusion, and solution.  A considerable quanti-
 ty of steam is evolved as the borax begins to
 melt.  The order of melting for some of the
 materials  is: Sodium nitrate at 586°F, borax
 at 1, 366°F,  soda ash at 1, 564°F, litharge  at
 1, 630°F, feldspar at 2, 138°F, and quartz at
 3, 110°F.

 If white  or light-colored frits are being smelted,
 smelter  refractory linings must be high in  alumi-
 na and low in iron to prevent discoloration  and
 dark specks in the frit.   The batch is protected
 from contact with fuel gases  during the-early
 stages of smelting by the evolution of gases
 within the  smelter.  To illustrate,  a batch
 containing 35 percent borax and 10 percent
 soda ash loses about 165 pounds of water and
 42 pounds  of carbon dioxide for a  1,000-pound
 batch of  frit. This  is equivalent to 483 cfm
 water vapor and 60  cfm CO2  at a smelter tem-
 perature of 1, 700°F and for a smelting period
 of 30 minutes.

 The rate and period of heat application is criti-
 cal in  smelting  enamels and glazes.  A temper-
 ature too low may be sufficient only to vaporize
 the more fusible materials instead of volatilizing
 them,  and thereby result in a very slow reaction
 •with the  more refractory ingredients.  A higher
 operating temperature  eliminates this low pro-
 duction rate. If the batch is  heated too rapidly,
 however, the more  fusible elements  are melted

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784
                            CHEMICAL PROCESSING EQUIPMENT
                                    Figure 598.  Rotary-type frit smelter  (Ferro Corp.
                                    Los Angeles,  Calif.).
     Figure 599.  Rotary-type frit smelter  in  pouring position  (Ferro  Corp.,
     Los Angeles,  Cali f.).

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                                   Frit Smelters
785
                     Figure  600. Continuous-hearth-type  frit  smelter  (Ferro  Corporation,
                     Los Angeles, Cali f.).
Figure 601.  Batch-hearth-type frit smelter (Ferro Corporation,
Los Angeles,  Cal if.).

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786
                               CHEMICAL PROCESSING EQUIPMENT
Figure  602.  Crucible-type frit smelter  (California
Metal  Enameling  Company, Los Angeles,  Calif.).
 and volatilized before they have a chance to react
 with the more refractory materials.   Driving off
 the fluxes in this manner results in a harder (less
 fusible) final batch.  Excessive smelting,  after the
 melt is  ready to pour,  results in a similar condi-
 tion and, if permitted to continue,  necessitates a
 further  increase  in temperature to facilitate
 pouring.  Oversmelting also causes loss of opac-
 ity, poor gloss,  and discoloration in the frit.
 Insufficient smelting, on the other  hand, causes
 blistering, loss  of acid resistance, and poor
 texture  in the  finished  coating.  Batch composi-
 tion is  the determining factor in selecting op-
 timum  smelter temperatures and cycles.

 After the smelting operation, the molten material
 is quenched.   Rapid cooling can be accomplished
 with either air, water,  or a  combination of the
 two.  Air quenching produces a better product
 but is not normally practiced,  owing  to the quench-
 ing a'nd  storage space required.  Water quench-
 ing is commonly  practiced in the industry by
 pouring the molten material  from the tilted
 smelter into a large pan of water.  Water quench-
 ing is also frequently done by pouring molten mate-
 rial into a metal  trough in which a  continuous
 stream  of water is flowing.   The trough empties
 into a large wire basket  suspended in a well,
 which holds the shattered frit but permits the
 water to flow out through an  overflow.  Rapid
 cooling  is somewhat impeded by this  method
 owing to a layer of  steam that forms  over the
 glass.  Air-water quenching appears to be the
 most economical and effective method since a
more thorough shattering of the glass  results.
In this method the molten material is poured
from the smelter and passed through a blast of
air and water.  Quenching causes the molten ma-
terial to solidify and shatter  into numerous small
glass particles  (called frit) ranging from 1/4 inch
in diameter down to submicron sizes.   Its main
purpose is to facilitate grinding.

After draining,  the frit contains 5 to 15 percent
water and may be milled in this condition or
may first be dried.   Three types of dryers are
employed:   The drying table, the stationary
dryer,  and the rotary dryer.  The drying table
is a flat hearth on which  the frit is placed.  Heat
is applied beneath the hearth, arid the  frit is
raked manually. The stationary dryer consists
of a sheet iron chamber in which a basket of
frit is placed.   Heated air from an exchanger on
the smelter flue is passed through the basket of
frit.  The rotary dryer consists of a  porcelain-
lined rotating cylinder that is inclined slightly,
causing the frit to move through continuously.
The typical size is approximately 2 feet in di-
ameter and 20 feet long,  though larger cylinders
are used.  The  rotary dryer, which is  economical
and efficient, can be heated by waste  heat or by
oil or gas.  The frit  can  be further refined by
using magnetic separation to remove small iron
particles,  which would otherwise cause black
specks in the enamel.

The final step in frit making is size reduction,
which is normally done with  a ball mill.  Frits
used in porcelain enamel are required to pass
a No.  100  seive (150 microns),  though a certain
percent of fines must remain as  residue on a
finer sieve.  In  the case of ceramic glaze frits,  a
finer grind is necessary. About one-half  of a
batch must be less than 2. 5 microns with  the
remainder no greater than 10 microns. Effi-
cient milling is best obtained when the speed of
rotation is such that the  balls ride three-fourths
of the way up one side of the cylinder,  and the inner-
most balls slide back down over  the outermost
balls.  This is  achieved,  for example, at  a speed
of 25 rpm for a 4-foot-diameter  cylinder.  Porce-
lain balls or flint pebbles are used in  the mill. The
diameter of the balls ranges from. 1 to 3 inches,
and the charge  should be maintained at about 55
percent of the mill volume.   Ball wear amounts to
5 to 10 pounds in milling  1, 000 pounds of frit.

Colors, opacifiers,  floating  agents, and electro-
lytes are mixed with the frit before it is charged
to the ball mill. After the milling operation be-
gins, water  is added at a constant rate to  keep
the specific gravity of the slurry (referred to  as
slip) at the correct value at all times.  After the
milling operation,  the ceramic slip is  screened
to remove large particles.  A 1 - to 2-day aging
process then takes place at a temperature close

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                                              Frit Smelters
                                                                                                      787
 to that at which the enamel or glaze is to be ap-
 plied.  Aging is necessary to set up an equilibrium
 among the  clay, frit,  and solution.  The enamel
 or glaze slip is now ready for application.

 Application,  Firing, and Uses of Enamels

 Enamels and glazes may be applied to ware
 blanks by immersion  or spraying  (Hansen,
 1932).   The pouring and brushing methods  are
 seldom employed  today.  In the dipping opera-
 tion, the blank is  immersed  in the slip and then
 withdrawn  and  allowed to drain.  If the slip is
 thick,  the excess  enamel must be shaken from
 the ware, a process called slushing.  Spraying
 is the application  of enamel or glaze slip to
 •ware by atomizing it through an air gun.

 After the enamel  or glaze has been applied, it
 must then be burned or fired on the ware to
 fuse the coating to a smooth, continuous, glassy
 layer.   The firing temperatures and cycles for
 porcelain enamel  on steel and aluminum are
 approximately  1,500°F (Shreve,  1945) for  5
 minutes and  l.OOOT for 5 minutes, respective-
 ly.  Ceramic glaze, however,  is fired on pottery
 at about 2,  300 °F for several hours or even days.
 The firing  is accomplished in what is  called a
 furnace in  the porcelain enamel industry,  and a
 kiln in the  ceramic glaze  industry.

 Porcelain enamel  is used as  a protective coating
 for metals--primarily steel, cast iron, and
 aluminum.   Familiar  items are bathtubs,  water
 heater tanks, refrigerators,  washing machines,
 and cooking ranges.  Coated  aluminum is being
 used more  and  more in recent times for signs
 such as those installed on highways.   Ceramic
 glazes  are  used as a decorative or protective
 coating on a wide  variety of pottery and glass
 articles. Examples are lavatory basins, water
 closets, closet bowls,  chinaware,  and figurines.


THE AIR POLLUTION PROBLEM

 Significant  dust and fume emissions are created
 by the frit-smelting operation.   These emissions
 consist primarily  of condensed metallic oxide
 fumes that  have volatilized from the molten charge.
 They also contain  mineral dust carryover and
 sometimes  contain noxious gases such as hydro-
 gen fluoride. In addition, products of combus-
 tion  and glass  fibers  are released.  The quanti-
 ty of these  air contaminants can be reduced by
 following good smelter-operating procedures.
 This can be accomplished by not rotating the
 smelter too rapidly, to prevent excessive dust
 carryover,  and by not heating the batch too rapid-
 ly or too long, to prevent volatilizing the more
 fusible elements before they  react with the  more
 refractory  materials.   A typical rotary smelter,
for example, discharges 10 to 15 pounds  of dust
and fumes to the atmosphere  per hour per ton of
material charged.  In some cases, where ingredi-
ents require high melting temperatures (1,500°F
or higher),  emissions as great as 50 pounds per
hour per ton of material have been observed.
Depending upon the composition of the batch, a
significant visible plume may or may not be
present.  Tables 209 to 212 indicate the extent of
emissions from uncontrolled, rotary frit smelters
for various-sized batches and compositions.


Table  209.  DUST AND FUME DISCHARGE FROM
   A 1,000-POUND,  ROTARY FRIT SMELTER
                              Test No.
Test data
Process wt, Ib/hr
Stack vol. scfm
Stack gas temp, °F
Concentration, gr/scf
Stack emissions, Ib/hr
CO, vol % (stack condition)
N2, vol % (stack condition)

Process wt, Ib/hr
Stack vol, scfm
Stack gas temp, "F
Concentration, gr/scf
Stack emissions , Ib/hr
CO, vol % (stack condition)
N2, vol % (stack condition)
1
174a
1, 390
450
0. 118
1.41
0. 002
76.9
4
292b
1, 310
960
0. Ill
1.25
0
73
i 	 	
2
174a
1,540
750
0. 387
5. 11
0. 001
75. 10
*
5
292b
1, 400
950
0. 141
1. 79
0
72. 60
3
174a
1,630
900
0. 381
5. 32
0. 002
73. 50
6
292b
1, 480
930
0. 124
1.57
0
73. 30
  These three tests represent approximately the 1st, 2d, and 3d
  hours of a 248-minute smelting cycle. The total charge amounted
  to 717 pounds of material consisting of borax, feldspar, sodium
  fluoride, soda ash, and zmc oxide.
  These three tests represent approximately the 1st, 2d, and 3d
  hours of a 195-minute smelting cycle. The total charge amounted
  to 949 pounds of material consisting of litharge, silica, boric
  acid, feldspar, fluorspar, borax, and zircon.
Table 210.  DUST AND FUME DISCHARGE FROM
   A 3,000-POUND, ROTARY FRIT SMELTER


Process wt, Ib/hr
Stack vol, scfm
Stack gas temp, *F
Concentration, gr/scf
Stack emissions , Ib/hr
CO, vol % (stack condition)
N->, vol % (stack condition)
Test No.
7
472a
2,240
630
0. 143
2.70
0.02
75. 30
8
472a
2,270
800
0. 114
2.20
0.02
75.60
9
47 2a
2, 260
840
0. 172
3.30
0.02
76.30
  aThese three tests represent approximately the 1st,  2d, and 3d
   hours of a 248-minute smelting cycle. The total charge
   amounted to 1, 951 pounds of material consisting of litharge,
   silica, boric acid, feldspar, whiting, borax, and zircon.
HOODING AND VENTILATION REQUIREMENTS

Rotary smelters require a detached canopy-type
hood suspended from the lower end of a vertical
stack as shown in Figures  598 and 599.  It is
suspended far enough above the floor to trap the
discharge gases from the smelter •when in the
horizontal position.  Refractory-lined,  it is  of
sufficient size to prevent gases from escaping
   234-767 O - 77 - 52

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788
CHEMICAL PROCESSING EQUIPMENT
  Table 211.   FLUORIDE DISCHARGE FROM
         A ROTARY FRIT SMELTER
                              Test No.
Test data
Process wt, Ib/hr
Stack vol, scfm
Stack gas temp, °F
Concentration, gr/scf
Stack emissions, Ib/hr
10
174a
1, 400
530
0. 061
0.73
11
174a
1,600
840
0. 035
0. 48
12
162b
1, 000
4SO
0. 196
1. 68
13
162b
1,000
480
0.058
0.50
aThese two tests were of 90 minutes' duration each and represented
 approximately the first half and the second half of a 248-minute
 smelting cycle.  The total charge amounted to 717 pounds of material
 consisting of borax, feldspar, sodium fluoride, soda ash, and zinc
 oxide.
bThcs<:> two 60-rmnute tests represented approximately the 1st and the
 4th hours of a 450-mmute smelting cycle. The total charge amounted
 to 1, 213 pounds of material consisting of sodium  carbonate, calcium
 tarbonate, pyrobar, and silica. The test was specifically conducted
 for a batch containing maximum carbonates (19%) and no litharge.
Table 212.  DUST AND FUME DISCHARGE FROM
  A 2, 000-POUND  ROTARY FRIT SMELTER


Process v.t , Ib/hr
Stack \ ol, scfm
Stack gas temp, ° F
Concentration, gr/3cf
Stack emissions, Ib/hr
Test No.
14
857a
2,430
600
0. 1 30
2. 710
15
857a
L, 430
600
0. 1 12
2. 340
16
890b
4, 347
340
0. 1 11
4. 150
17
890b
4, 347
340
0. 103
i. 820
 aThese two 60-rmnute tests represent the 1st and 2d hours of a 140-
 minute smelting cycle.  The total charge amounted to 2,000 pounds
 of material containing silica, litharge, and \vhitmg.
 These two 60-minule tests represent the 1st hour and 37 minutes of
 a 135-nnnute smelting cycle. The total charge amounted to 2,000
 pounds of material containing silica, litharge, and v.hitmg.
into the room,  its size varying with the size of
the smelter.   The typical hood opening area
ranges from  3 to 5 square feet.   The stack should
be of sufficient height to obtain good draft--about
20 feet--if it is not vented to air pollution control
equipment.  If it  is vented to control equipment,
ventilation requirements are approximately 3, 000
scfm for a 2, 000-pound batch smelter as an ex-
ample.  Hood indraft velocity should be about 500
fpm.

Crucible and hearth smelters do not require hoods
but do require a. 20- or  25-foot stack to conform
•with good chimney design practice if not vented to
air pollution  control equipment.  Some crucible
smelters are vented directly into the room.  If
vented to air pollution control equipment, a canopy
hood must be used on the  crucible smelter.   Hood
indraft velocities should be approximately 200 fpm.
The requirement for a  hearth- (box-) type smelter
is approximately 4, 000  scfm for a 3, 000-pound
batch smelter. As a general rule, about 70 scfm
is required for each square foot  of hearth area.
 AIR  POLLUTION  CONTROL EQUIPMENT

 The two most feasible control devices for frit
 smelters are baghouses and venturi water scrub-
 bers.   Of these devices,  baghouses  are more ef-
 fective.  Glass bags cannot be used,  however,
                        owing to the occasional presence of fluorides in
                        the effluent.  The discharge gases  must be cooled
                        by heat exchangers, quench chambers, cooling
                        columns, or by some other device  to a tempera-
                        ture compatible with the fabric material  selected.
                        Filtering velocities  should not exceed 2. 5 fpm.

                        A venturi-type water scrubber is satisfactory if
                        at least 20  to 25 inches of pressure drop is main-
                        tained across  the venturi throat.  The throat veloc-
                        ity should be between 15, 000 and 20, 000  fpm.  The
                        water requirement at the throat is  about  6 gallons
                        per minute for each 1, 000 cubic feet of gas treated.
                        Power consumption is high owing to the high pres-
                        sure  drop.  The venturi scrubber shown in Figure
                        603 was installed to serve one rotary and two
                        hearth smelters simultaneously. Table 213 in-
                        cludes data indicating the collection efficiency of
                        this scrubber  when venting a frit smelter.

                        A baghouse installation venting four rotary, gas-
                        fired frit smelters is shown in Figure  604.  The
                        production  capacity of one of the smelters is
                        3, 000 pounds while that of the other three is  1, 000
                        pounds each.  Maximum  gas  temperatures encoun-
                        tered in the discharge stack at a point 20 feet down-
                        stream of the  smelters are approximately 950°F
                        while the average temperature is 780 °F.

                        The baghouse is a cloth-tubular, pullthrough
                        type,  containing 4, 400 square feet of  cloth area.
                        It is  equipped with an exhaust fan that  delivers
                        9, 300 cfm  at approximately 170°F.  The filtering
                        velocity is  2. 2 fpm.

                        Radiation cooling columns are used to reduce the
                        effluent gas temperature from 585 °F  at the inlet
                        to the cooling columns to 185°F at the baghouse
                        inlet.  Approximately 1, 300  lineal feet of 30-
                        inch-diameter, heavy-gage  steel duct  with a sur-
                        face  area of 10, 000 square feet is  used.   The av-
                        erage overall heat transfer  coefficient is 1.35 Btu
                        per hour per square foot per  °F,  as calculated
                        from actual test data.  The  cooling columns  are not
                         one continuous run, but consist of single, double,
                        and triple  runs.   Thus, the  gas mass velocity
                        varies considerably throughout the unit,  with
                        resulting changes in heat transfer  coefficients.
                        Additional  cooling is accomplished with dilution
                        air at the detached hoods, which are suspended
                        about 1 foot away from the discharge end of each
                        smelter.   The baghouse  inlet temperature of
                         185°F is satisfactory for the  dacron cloth mate-
                        rial used,  and excellent bag  life can be expected.
                               FOOD PROCESSING  EQUIPMENT

                         Most foods consumed in the United States today,
                         whether of animal or vegetable origin,  are pro-
                         cessed to  some degree before marketing.  His-
                         torically,  certain foods have been subjected to

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                                    Food Processing Equipment
789
                            Figure 603. Venturi  water  scrubber venting
                            three frit smelters  (Ferro  Corporation,  Los
                            Angeles,  Calif.).
         Table 213.  EFFICIENCY OF VENTURI WATER SCRUBBER ON PARTICULATE
             MATTER AND FLUORIDES WHEN VENTING THREE FRIT SMELTERS

Test data

Process wt, Ib/hr
Stack vol, scfm
Stack gas temp, °F
Dust concentration, gr/scf
Inlet
Outlet
Dust emissions, Ib/hr
Inlet
Outlet
Control efficiency, %
Test No. a
18
19
20
Dust and fumes
1,360
4,280
570

0.228
0. 074

8. 37
2. 72
67.50
1, 360
4,280
552

0.234
0. 077

8. 60
2.85
67.20
1, 360
4, 280
564

0. 127
0.088

1.78
1. 35
30.70
21
22
23
Fluorides
1, 360
4,280
570

0,092
0.006

3.38
0.22
93.20
1, 360
4, 280
552

0. 137
0.008

5.03
0.29
94
1, 360
4, 280
564

0.034
0.017

0.48
0.26
50
aTests No.  18 and 21 represent the first 54 minutes  of the 107-minute smelting cycle, tests No. 19
 and 22 represent the last 54 minutes, and tests No. 20 and 23 represent the 23-minute tapping
 period.  Total process weight was 3, 000  pounds of material consisting of borax, potassium car-
 bonate, potassium nitrate,  zinc oxide, titanium oxide, ammonium phosphate, lithium carbonate,
 sodium silico-fluoride,  fluorspar, silica, and talc.  Pressure drop across throat was 21 in. WC.
 Water  flow rate to throat -was  50 gpm.

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790
                              CHEMICAL PROCESSING EQUIPMENT
                                                                                        \
                               Figure 604. Baghouse with  radiant  cooling
                               columns venting four rotary frit  smelters
                               (Glostex  Chemicals,  Inc.,  Vernon,  Calif.).
various preserving processes.  More recently
we find food purveyors increasingly concerned
with processes that render foods more flavorful
and easier to prepare.  The trend toward great-
er presale food preparation has possibly caused
a shift of at least some air pollutants from many
domestic kitchens to a significantly smaller num-
ber of food-processing plants.

Food processing includes  operations such as
slaughtering,  smoking,  drying, cooking, bak-
ing,  frying, boiling,  dehydrating, hydrogenating,
fermenting, distilling, curing, ripening, roast-
ing,  broiling, barbecuing,  canning, freezing,
enriching, and packaging.  Some produce large
volumes of air contaminants;  others,  only in-
significant amounts.   Equipment used to process
food is legion.  Some of the unit operations in-
volved are the following (Kirk and Othmer,   1947):

Material handling. Conveying, elevating, pump-
ing,  packing, and shipping.

Separating.  Centrifuging,  draining, evacuating,
filtering, percolating, fitting,  pressing, skimming,
sorting, and trimming.  (Drying,  screening, sifting,
and washing fall into this  category. )

Heat  exchanging.  Chilling, freezing,  and refrig-
erating;  heating, cooking, broiling, roasting, bak-
ing,  and so forth.
                                                      Mixing.   Agitating, beating, blending, diffusing,
                                                      dispersing, emulsifying,  homogenizing,  kneading,
                                                      stirring,  whipping,  working, and so forth.

                                                      Disintegrating.  Breaking, chipping, chopping,
                                                      crushing,  cutting, grinding,  milling,  maturating,
                                                      pulverizing, refining  (as by punching,  rolling,
                                                      and so forth),  shredding,  slicing, and  spraying.

                                                      Forming.  Casting,  extruding, flaking, molding,
                                                      pelletizing, rolling,  shaping, stamping,  and die
                                                      casting.

                                                      Coating.   Dipping,  enrobing, glazing,  icing, pan-
                                                      ning,  and so forth.

                                                      Decorating.   Embossing, imprinting,  sugaring,
                                                      topping,  and so forth.

                                                      Controlling.  Controlling air humidity, temperature,
                                                      pressure,  and velocity; inspecting, measuring, tem-
                                                      pering, weighing, and so forth.

                                                      Packaging.  Capping,  closing, filling,  labeling,
                                                      packing, -wrapping,  and so forth.

                                                      Storing.   Piling,  stacking, warehousing,  and so
                                                      forth.

                                                      A description and discussion of each type of equip-
                                                      ment used for food processing is not within the

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                                       Food Processing Equipment
                                               791
 scope of this manual.   The following discussion
 will be limited to food processes in which air pollu-
 tion problems are inherent and in -which typical
 food-processing air contaminants are encountered.
 This section is not concerned with the production
 of pet foods or livestock feeds, though in some
 instances,  these materials are byproducts  of food
 processes.
 COFFEE PROCESSING

 Most coffee is grown in Central and South America.
 After harvesting and drying at or near the  coffee
 plantation, most "green"  coffee beans are  exported
 and further processed  before sale to the consumer.
 Coffee processing  in the United States consists  es-
 sentially of cleaning, roasting, grinding, and packag-
 ing.


 Roasting is the key operation and produces most
 of the air contaminants associated with the indus-
 try.  Roasting reduces the sugar and moisture
 contents  of green coffee and also renders the bulk
 density of the beans about 50 percent lighter.  An
 apparently desired result  is the production of
 water-soluble degradation products that impart
 most of the flavor  to the brewed  coffee.  Roasting
                                                 o
 also causes the beans to expand and split into
 halves, releasing small quantities of  chaff.
Botch Roasting

The oldest and simplest coffee roasters are direct-
fired (usually by natural gas),  rotary,  cylindrical
chambers.  These units are designed to handle
from 200 to 500 pounds of green beans  per 15- to
20-minute cycle and are normally operated at
about 400°F.  A calculated quantity of water is
added at the completion of the roast to  quench the
beans before discharge from the  roaster.   After
they are dumped, the beans are further cooled
with air and run through a "stoner" air classifier
to remove metal and other  heavy objects before
the grinding and packaging.   The roaster and
cooler and all air-cleaning devices are normally
equipped with cyclone  separators to remove dust
and chaff from exhaust gases.  Most present-day
coffee roasters are of batch design, though the
newer and larger installations tend to favor con-
tinuous roasters.

In the batch  roaster shown  in Figure 605,  some
of the gases are recirculated.  A portion of the
gases is bled off at a point between the  burner
and the roaster.  Thus, the burner incinerates
combustible contaminants and becomes both an
air pollution control device and a heat source for
the roaster.
                         •ERIOD I - BEFDUE SMOKE APPEARS Heating medium l
                        I circulated normally for about '4 of the roasting
                        (cycle  Damper c is open to vent excess gases pai
                         et B is closed. Cut-off Slide A is open for norm
                         i rculat ion
                        1 PERIOD II - MEN FIRST SMOKE APPEARS  Dampei C is
                        , ciosed- forcing excess gases if?rough tfie Maine < f.
                        ' num smoke)  Damper B is open to vent excess gase
                        I after smoke ts burned  Cut-off Stide A is open fo
                            circulation Roasting period completed ex-
                        ( cept for appi icaiion of *aiei
                        [PERIOD in  - WHEN WATER is APPLIED cut-off siide
                        I A is closed to prevent return of watsi to She cof
                        t Damper C remains closed to force ah smoKe and sts
                        ] th o gh thp flame Dampei B renains open to ven'
                           gi i*  a ter smke is tinned anil steam (s
                                VTpO!
                 THERMALO ROASTER
    Figure  605.  A  reel rculatirig-batch  coffee
    roaster  (Jabez  Burns  -  Gump Divisi on,Blaw-
    Knox  Company,  New  York,  N.Y.j.
 An Integrated Coffee Plant

 A process flow diagram of a typical large integra-
 ted coffee plant is shown in Figure 606.  Green
 beans are first run through mechanical cleaning
 equipment to remove any remaining hulls and
 foreign matter before the  roasting.  This system
 includes a dump tank, scalper, weigh hopper,
 mixer, and several bins,  elevators, and convey-
 ors.  Cleaning systems  such as this commonly
 include one or more centrifugal separators from
 which process air is  exhausted.

 The  direct, gas-fired roasters depicted in Fig-
 ures 606 and 607 are of  continuous rather than
 batch design.  Temperatures of 400°F to 500°F
 are maintained in the roaster,  and the residence
 time is adjusted by controlling the drum speed.
 Roaster exhaust products are  drawn off through
 a cyclone separator  and afterburner, with some
 recirculation from the cyclone to the roaster.
 Chaff and other particulates from the cyclone
 are fed to  a chaff collection system.  Hot beans
 are continuously conveyed through the air cooler
 and stoner sections.  Both the cooler and the
 stoner are equipped with cyclones  to collect par-
ticulates.

 The  equipment following the stoner is  used only
to blend, grind, and package roasted coffee.
Normally, there are no points in these systems
where process air is  emitted to the atmosphere.

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792
CHEMICAL PROCESSING EQUIPMENT
    GREEN
    COFFEE
    DUMP
                                  ii
                                                           TO
                                                           ATMOSPHERE
                                       TO             TO
                                       ATMOSPHERE       ATMOSPHERE
                                          1
                                                                                               TO GRINDING
                                                                                               BLENDING AND
                                                                                               AND PACKAGING
                        Figure  606.  Typical  flow  sheet for a coffee-roasting plant.
                   Figure  607.  A continuous coffee  roaster and cooler:(left)  continuous
                   roaster,  showing course of  the  heated gases as  they  are  drawn through
                   the  coffee beans in  the perforated,  he I ical-flanged  cylinder and then
                   into  the  reelrculation system;  (right) left-side elevation of contin-
                   uous  roaster, showing  relationship of recirculating  and  cooler fans
                   and  the respective collectors  on the roof  (Jabez Burns  - Gump Division,
                   Blaw-Knox Company,  New York,  N.Y.).

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                                      Food Processing Equipment
                                             793
 At the plant shown on the flow diagram, chaff is
 collected from several points and run to a hold-
 ing bin from which it is fed at a uniform rate to
 an incinerator.  Conveyors in the chaff system
 may be of almost any type,  though pneumatic con-
 veyors are most common.  The design of the in-
 cinerator  depicted is similar to that of the saw-
 dust burners described in Chapter 8 but the
 incinerator is  much  smaller.

 The Air Pollution Problem

 Dust,  chaff, coffee bean oils (as mists),  smoke,
 and odors are  the principal air contaminants
 emitted from coffee  processing.  In addition,
 combustion  contaminants are discharged if chaff
 is  incinerated. Dust is exhausted from several
 points in the process, while smoke and odors are
 confined to the roaster,  chaff incinerator, and, in
 some cases, to the cooler.

 Coffee chaff is the main  source of particulates,
 but green  beans, as  received, also contain ap-
 preciable  quantities  of sand and miscellaneous
 dirt.  The major portion of this dirt is removed
 by air washing in the green coffee-cleaning sys-
 tem.  Some  chaff (about  1 percent of the green
 weight) is released from the bean on roasting and
 is  removed with roaster  exhaust gases. A small
 amount of chaff carries through to the cooler and
 stoner.  After the roasting, coffee chaff is light
 and flaky, particle sizes usually exceeding 100
 microns.  As shown  in Table 214, particulate-
 matter emissions from coffee processing are well
 below the  limits permitted by typical dust and
 fume prohibitions.

      Table 214.  ANALYSIS OF COFFEE
          ROASTER EXHAUST GASES

                        Contaminant concentration

Particulate matter, gr/scf
Aldehydes
(as formaldehyde), ppm
Organic acids
(as acetic acid), ppm
Oxides of nitrogen
(as NO2), ppm
Continuous roaster
Roaster
0. 189

139

223

26.8
Cooler
0.006

--

--

--
Batch roaster
0. 160

42.

175

21. 4
Coffee roaster odors are attributed to alcohols,
aldehydes, organic acids, and nitrogen  and sulfur
compounds, which are all probably breakdown
products of sugars and oils.  Roasted coffee odors
are considered pleasant by many people, and in-
deed, they may often be pleasant under  certain
conditions.  Nevertheless,  continual exposure to
uncontrolled  roaster  exhaust gases usually elicits
widespread complaints  from adjacent residents.
The pleasant aroma of a short sniff apparently
develops into an annoyance upon long exposure.
 Visible bluish-white smoke emissions from coffee
 roasters are caused by distilled oils and organic
 breakdown products.  The moisture content of
 green coffee is only 6 to 14 percent,  and thus
 there is not  sufficient water vapor in the 400°
 to 500"F exhaust gases to form a  visible steam
 plume.  From uncontrolled, continuous  roasters,
 the opacity of exhaust gases exceeds 40  percent
 almost continuously.  From batch roasters, ex-
 haust opacities normally exceed 40 percent only
 during the last 10 to 15 minutes of a 20-rninute
 roast.  Smoke opacity appears to  be a function
 of the oil content, the more oily coffee producing
 the heavier smoke.   The water quenching of
 batch-roasted coffee causes visible  steam emis -
 sions that seldom persist longer than 30 seconds
 per batch.


 Hooding and Ventilation Requirements

 Exhaust volumes from coffee-processing sys-
 tems do not vary greatly from one plant  to
 another insofar as roasting, cooling, and stoning
 are concerned.  Roasters equipped with  gas re-
 circulation systems exhaust about 24 scf per
 pound of finished coffee.  Volumes from nonre-
 circulation roasters average about 40 scf per
 pound.  A 10,000-pound-per-hour, continuous
 roaster with a recirculation system exhausts
 about 4,000 scfm. A 500-pound-per-batch, non-
 recirculation roaster exhausts about 1, 000  scfm.
 Each batch cycle lasts about 20 minutes.

 Coolers  of the continuous  type exhaust about
 120 scf per pound of coffee.  Batch-type  cool-
 ers are operated at ratios of about 10 scfm per
 pound.  The time required for batch cooling
 varies somewhat with the  operator.  Batch-cool-
 ing requirements are inversely related to the
 degree of water quenching employed.

 Continuous-type stoners use about 40 scf air per
 pound of coffee.   Batch-stoning processes require
 from 4 to 10 scfm per pound,  depending upon duct-
 work size and batch time.
 Air Pollution Control Equipment

Air contaminants from coffee-processing plants
have been successfully controlled with afterburn-
ers and cyclone separators, and combinations
thereof.  Incineration is necessary only with roaster
exhaust gases.  There is little smoke in other coffee
plant exit gas streams where only dust collectors
are required to comply with air pollution control
regulations.

Separate afterburners are preferable to the com-
bination heater-incinerator of the batch roaster
shown in Figure 605.  When the afterburner serves
as the roaster's heat source, its maximum operat-

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794
CHEMICAL PROCESSING EQUIPMENT
ing temperature is limited to about 1,000°F.  A
temperature of 1,200°F or  greater is necessary
to provide good particulate  incineration and odor
removal.

A roaster afterburner should always be preceded
by an efficient cyclone separator in which most
of the particulates are removed.  A residence
time of 0. 3  second is sufficient to  incinerate
most vapors and small-diameter particles at
1,200°F.  Higher  temperatures and longer resi-
dences are, however, required to  burn large-
diameter, solid particles.  Afterburner design
is discussed in Chapter  5.

Properly designed centrifugal separators  are
required on essentially all process airstreams
up to and including the stoner and chaff collec-
tion system.  With the plant shown, cyclones
are required at the roaster, cooler, stoner,
chaff storage bin,  and chaff incinerator.   In
addition, the scalper is  a centrifugal classifier
venting process  air.  Some plants  also vent the
green coffee dump tank and several conveyors and
elevators to centrifugal  dust collectors.

For best results,  the chaff incinerator should be
of the design discussed in Chapter 8 in which
combustible material is fed at a uniform rate.
It is, however,  considerably smaller and has
burning rates usually below 100 pounds per hour.

The inorganic ash content of the chaff, at approxi-
mately 5 percent by weight, is considerably great-
er than that of most combustible refuse fed to
incinerators.  Provisions should be made in the
incinerator design so that this material does
not become entrained in the exhaust gases.  If
most of the noncombustible material is dis-
charged with products of combustion from the
incinerator, the combustion contaminants then
exceed 0. 3  grain per cubic  foot calculated to
12 percent carbon dioxide.
SMOKEHOUSES

Smoking has been used for centuries to preserve
meat and fish products.  Modern smoking opera-
tions do not differ greatly from those used by our
forefathers,  though the prime purposes of smoking
today appear to be the imparting of flavor, color,
and  "customer appeal" to the food product.  Cur-
ing and storage processes have been improved
to the point where 'preservation is no longer the
principal objective.

The vast majority of smoked products  are meats
of porcine and bovine origin.  Some fish and
poultry and,  in rare instances, vegetable prod-
ucts are also smoked as  gourmet items.
                       The Smoking Process

                       Smoking is a diffusion process in which food
                       products are exposed to an atmosphere of hard-
                       wood smoke.  Table 215 is an analysis of smoke
                       produced through the destructive distillation of
                       a hardwood.  As smoke is circulated over the
                       food, aldehydes, organic acids,  and other
                       organics are adsorbed  onto its outer surface.
                       Smoking usually darkens the food's natural color,
                       and in some cases, glazes the outer surface.
                          Table 215.  ANALYSIS OF WOOD SMOKE
                               USED IN MEAT SMOKEHOUSES
                                       (Jensen, 1945)
Contaminant Concentration, ppm
Formaldehyde
Higher aldehydes
Formic acid
Acetic and higher acids
Phenols
Ketones
Resins
20 to 40
140 to 180
90 to 125
460 to 500
20 to 30
190 to 200
1,000
                        Regardless of smokehouse design,  some spent
                        gases are always exhausted to the atmosphere.
                        These contain odorous,  eye-irritating gases and
                        finely divided, organic particulates, often in
                        sufficient concentration to exceed local opacity
                        restrictions.

                        Smokehouses  are also used to cook and dry food
                        products  either before or  after smoking.  Air
                        contaminants  emitted during cooking and drying
                        are normally well below allowable control limits.

                        Atmospheric Smokehouses

                        The oldest smokehouses are of atmospheric or
                        natural-draft design.  These boxlike structures
                        are usually heated directly with natural gas or
                        wood.  Smoke is often generated by heating
                        sawdust on a  steel plate.  These smoke gener-
                        ators are normally heated with natural gas  pipe
                        burners located in the bottom of the house.  Hot,
                        smoky gases  are  allowed to rise by natural con-
                        vection through racks of meat.   Large atmospheric
                        houses are often built with two  or three levels of
                        meat racks.   One or more stacks are provided
                        to exhaust spent gases at the top of the house. In
                        some instances the vents are equipped with ex-
                        haust fans. During the  smoking and drying cy-
                        cles, exhaust gas temperatures range from
                        120°   to 150°F.  Slightly  higher temperatures
                        are sometimes encountered during the cooking
                        cycle.

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                                        Food Processing Equipment
                                                     795
   Recirculoting Smokehouses

   Most large,  modern,  production meat smoke-
   houses are of the recirculating type (Figure 608)
   wherein smoke is circulated at reasonably high
   velocities  over the surface of the product.  The
   purpose is to provide faster and more nearly
   uniform diffusion of organics  onto the product,
   and more uniform temperatures throughout the
   house.   These units are usually of stainless
   steel construction and are heated by steam  or
   gas.  Smoke is piped  to the house from external
   smoke generators.  Each unit is  equipped with
   a large circulating fan and,  in some instances, a
   smaller exhaust fan.  During  smoking and cooking,
   exhaust  volumes of  1  to 4 cfm per square foot of
   floor area, are maintained.   The exhaust rate is
   increased to 5 to 10 cfm per  square foot during
   the drying cycle. Recirculating smokehouses
   are usually equipped with temperature and hu-
   midity controls, and the opacity and makeup of
   exhaust  gas are usually more constant than those
   from atmospheric units.
                                      AUTOMATIC
                                      ALTERNATING
                                      DAMPERS
•HOT
•AIR
 AND
 SMOKE
 SJPPLY
HOT
AIR
AND
SMOKE
SUPPLY
   Figure 608. A modern recirculating smokehouse
   (Atmos Corp.,  Chicago,  III.).
 Smoking  by Immersion

 Conventional smoking operations  can.be seen
 as an extremely devious method of coating food
 products with a myriad of hardwood distillation
 products.  One might wonder why this coating
 is not applied by  simple immersion.   Unfortu-
 nately, many of the compounds present in smoke
 are  highly toxic.  If these were deposited heavily
 on the food product, results could be fatal. Smok-
 ing,  therefore, provides a reasonably foolproof,
 if quaint, means of assuring that these toxic com-
 pounds do not accumulate in lethal concentrations.
 Many states have  laws prohibiting the smoking of
 meats by liquid immersion.


 Smoking  by  Electrical Precipitation

 Some attempts have been made to precipitate
 smoke particles electrically onto food products
 in the smokehouse, and a few smokehouses so
 designed are in operation today.   From the opera-
 tors' point of view, this  arrangement offers the
 advantages of faster smoking  and greater use
 of generated smoke.   From the standpoint of air
 pollution control, it is desirable  inasmuch as
 considerably lesser quantities of air  contami-
 nants  are vented to the atmosphere than are
 vented from a conventional, uncontrolled smoke-
 house.

 These units  normally consist  of a conveyorized
 enclosure equipped with an ionizer section simi-
 lar to those  used with two-stage precipitators.
 The foo'd  product is usually passed Z to 3 inches
 below the ionizing wires,  which are charged with
 about 15, 000 volts.  No electrical charge is  ap-
 plied to the food products or the conveyor.  These
 smokers  are operated at ambient temperatures
 and  do not lend themselves to  use for either cook-
 ing or drying food products.  As would be  expected,
 spacing is a critical factor.

 There are very few precipitation  smokehouses
 in the  Unites States today,  and for this reason,
 little reliable data about the operating charac-
 teristics  or the air pollutants  emitted are avail-
 able.  Smokehouses of this design have been
 reported  to operate with visible emissions of
 only 5 to  10 percent opacity.   Concentrations of
 air  contaminants in gases from precipitation-
 type smokehouses would, under optimum condi-
 tions,  be  expected to be approximately equiva-
 lent  to those from conventional smokehouses
 equipped with two-stage electrical precipitators.

 These units offer the potential of  markedly re-
 duced smoking times.   Indeed, the few operating
 units have residence times of  less than 5 minutes.
If equipment such  as this were perfected for  a
wider range  of operation,  residence times -would
not be  expected to exceed 10 minutes.

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796
CHEMICAL PROCESSING EQUIPMENT
The application of precipitation smokehouses
is today limited by a number of inherent problems,
the foremost of which is the irregular shape of
many smoked products,  that is,  hams,  ham hocks,
and salami.  The degree of smoke deposition in
a unit such as this  is governed by the distance
between the ionizer and  the food product.  Irregu-
lar spacing  results, therefore,  in irregular smok-
ing of round and odd-shaped products that cannot
be positioned  so that all surfaces are equidistant
from ionizer wires.  The few existing installa-
tions are used to impart a light smoke to regular-
shaped, flat items  such  as fish fillets and sliced
meat products.
The Air Pollution Problem

Smokehouse exhaust products include organic
gases, liquids,  and solids,  all of which must
be considered air contaminants.   Many of the
gaseous compounds are irritating to the eyes
and relatively odorous.  A large portion of the
particulates is in the submicron  size range where
light scattering is maximum.  These air con-
taminants are attributable to smoke, that  is, to
smoke generated from hardwood, rather than
from the cooked product itself.

Exhaust gases  from both atmospheric and re-
circulating smokehouses can be periodically
expected to exceed 40 percent opacity,  the
maximum allowable under many  local air  pollu-
tion control regulations.  With the possible ex-
ception of public nuisance,  smokehouse exhaust
gases are not likely to exceed other local  air
quality standards.  As shown in  Table  215, con-
centrations of particulate matter average  only
0, 14 grain per scf.
Hooding and Ventilation Requirements

Atmospheric smokehouses  are designed with ex-
haust volumes of about 3 cubic feet per square
foot of floor area.  Somewhat higher volumes are
used with atmospheric houses of two or more
stories.  Inasmuch as there are  no air recircula-
tion and normally little provision for forced draft,
the exhaust rate for an atmospheric house is es-
sentially constant over the drying, cooking,  and
smoking cycles.  Moreover, there is often some
smoke in the house even during the cooking and
drying cycles.   This  is particularly  true where
smoke is generated in the house  rather than in
an external smoke  generator.  If gases are to be
ducted to air pollution control equipment,  an ex-
haust fan should be employed to  offset the added
pressure drop.  When an afterburner is used,  it
can often be positioned to provide additional nat-
ural draft.
                       Recirculation smokehouses have a considerably
                       wider range of exhaust rates.  During smoking
                       and cooking cycles, volumes of 1 to 4 cubic
                       feet per square foot of floor area are exhausted.
                       The rate increases to 5 to 10 cubic feet per square
                       foot during the drying cycle.  Recirculation houses
                       are almost always equipped with external smoke
                       generators, and a control of smoke flow is much
                       more positive.   There is essentially no smoke in
                       the houses  during the cooking and drying cycles.
                       Most smokehouses do not require hooding.  Ex-
                       haust gases are normally ducted directly to the
                       atmosphere or  to control equipment.  Some at-
                       mospheric houses are,  however,  equipped  with
                       hoods over the  loading doors to gather smoke that
                       might escape during the shifting of meat racks.  The
                       latter situation is due to the inherently poor dis-
                       tribution of smoke and heat in an atmospheric house.
                       To maintain product uniformity, the meat racks
                       must often be shifted while there is smoke  in the
                       house.   Most atmospheric houses do not have ex-
                       haust systems adequate to prevent appreciable
                       smoke  emissions from  the door during these  in-
                       stances.  Hoods and exhaust systems  are some-
                       times installed principally for worker comfort.  The
                       hoods or fans,  or both, may be located in corridor
                       ceilings immediately above the  doors. These ven-
                       tilators are often operated automatically whenever
                       the  doors are opened.   Volumes can be appreciable,
                       in some instances exceeding the smokehouse's  ex-
                       haust rate.
                       There are normally no appreciable  smoke emis-
                       sions from doors of recirculation-type smoke-
                       houses.  Temperature and smoke distribution
                       are sufficient so that there is no need to shift
                       meat in the houses.  Moreover,  the doors are
                       designed to provide tighter closures.  Recircula-
                       tion houses are  operated under positive pressure,
                       and any small opening causes large emissions of
                       smoke.
                       Air Pollution Control  Equipment

                       Afterburners

                       Smoke,  odors, eye irritants, and organic partic-
                       ulate matter can be controlled with afterburners,
                       provided temperature and design are adequate.
                       Most of these  contaminants can be eliminated at
                       temperatures  of 1, 000°F to  1, 200 °F in well-de-
                       signed units.  Larger diameter particulate matter
                       is somewhat more difficult to burn at these tem-
                       peratures; however,  since concentrations of  par-
                       ticulate  matter from  smokehouses are  reasonably
                       small, this limitation is not critical.

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                                      Food Processing Equipment
                                                                                                   797
Electrical precipitators

Low-voltage,  two-stage electrical precipitators
were installed in the Los Angeles area as  early
as 1957 to control visible smokehouse air  con-
taminants.  They have since been used at many
other locations in the United States.  Before
1957, their use had been confined principally to
air-conditioning applications.

Electrical precipitators are, of course, effective
only in the collection of particulate matter.  They
cannot be used to control gases  or vapors.  At
smokehouse installations, their purpose is to
collect the submicron smoke particles  responsi-
ble for visible opacity.  Two-stage precipitators
have been shown capable of reducing smoke opaci-
ties to less than  10  percent under ideal conditions.

A typical two-stage precipitator control system
•with a wet, centrifugal collector is shown  in Fig-
ure 609.  The wet collector is used to control
temperature and humidity and also remove a
small amount of particulates.   This is  followed
by a heater in which gas temperatures  are  regu-
lated before the gases enter the ionizer.  Voltages
of 6, 000 to 15, 000 volts are applied to  the ionizer
and plate sections.   Particulate matter collects
on the plates and drains, as a gummy liquid,  to
the collection pan below.

For satisfactory control of visible emissions, it
has been found that  superficial gas  velocities
through the plate collector section should not ex-
ceed 100 fpm. Some difficulty has  been experienced
owing to channeling in the collector.  For best oper-
ation, vanes or other means of ensuring uniform
flow should be used ahead of the plate section.

Even under optimum conditions, a slight trace of
smoke can be expected from the precipitator's
outlet.  At the discharge of the unit,  eye irrita-
tion is usually severe,  and odors are strong
though not overpowering.   These odors and eye
irritants can constitute a public nuisance, de-
pending upon plant location.

Electrical precipitation versus incineration

Both electrical precipitation and incineration
offer the classical choice of high initial  cost
versus high operating cost, but in addition, they
differ markedly from the standpoint of air pollu-
tion control.

Electrical precipitators are capable of collect-
ing particulate matter and thereby reducing
visible emissions to tolerable amounts.   They
have no effect  on nitrogen oxides and little
effect, if any,  on gaseous eye irritants and
odors.  If arcing occurs, some small and prob-
ably insignificant quantity of ozone is also pro-
duced.  The initial cost of precipitators  is high,
and their operating  cost low in comparison with
that  of  afterburners.  Smokehouse precipita-
tors do,  however,  require  a relatively high
degree of maintenance.  If  they are not proper-
ly maintained, poor control efficiency and fire
damage are probable.  Fire damage can result
in extended outage periods  during which  uncon-
                   Figure  609. A two-stage precipitator  and wet  centrifugal
                   collector  venting smokehouses (The  Rath Packing Co., Vernon, Calif.).

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798
CHEMICAL PROCESSING EQUIPMENT
trolled exhaust gases may vent directly to the
atmosphere.

Incineration is much more effective than elec-
trical precipitation is  in controlling gaseous
organics and finely divided particulates. Large
particles are, however, relatively difficult to
burn at the normal operating temperatures and
residence times of smokehouse afterburners.
Under average conditions, collection efficiency
for particulate matter (about 65 percent) is
roughly the  same as that of a two-stage elec-
trical precipitator.  Fuel costs make the  oper-
ation of an incineration device more expensive
than that of a precipitator.   Nevertheless,
maintenance is much less a  problem.   There
is no buildup of tars and resins in the afterburner
or stack to impede its operation.  As with any
smokehouse control device,  tars  accumulate in
the ductwork between the house and afterburner,
necessitating periodic cleaning.  As shown in
Table 216,  incineration creates additional nitro-
gen oxides,  increasing concentrations from about
4 ppm to approximately 12 ppm on the average.
                       Comparative test data on smokehouse afterburners
                       and electrical precipitators,  as shown in Tables
                       216 and 217,  indicate that collection efficiencies
                       for particulate matter, aldehydes,  and  organic
                       acids are of the same magnitude for both types
                       of control dequipment.   These data fail to re-
                       flect larger concentrations of odors and eye
                       irritants from electrical precipitators that are
                       readily apparent upon personal inspection of the
                       devices.

                       Bypassing control devices during nonsmoking
                       periods

                       Many operators of recirculation smokehouses
                       find it desirable to bypass air pollution control
                       devices during nonsmoking periods.  From the
                       standpoint of air pollution control,  this practice
                       is not unreasonable.  The major smokehouse air
                       contaminant is smoke.   Concentrations of air con-
                       taminants during  cooking and drying are relative-
                       ly small,  comparable to those of ordinary meat-
                       cooking ovens.  Drying-cycle exhaust gases are
                       2 to 4 times more voluminous than  those vented
          Table 216.  ANALYSES OF MEAT SMOKEHOUSE EXHAUST GASES BEFORE AND
                AFTER INCINERATION IN NATURAL GAS-FIRED AFTERBURNERS
Particulate matter,
gr/scf
Aldehydes (as form-
aldehyde), ppm
Organic acids (as
acetic acid)
Oxides of nitrogen
(as NO2), ppm
Contaminant concentration
Smokehouse
Range
0. 016 to 0. 234
8 to 74
30 to 156
1. 2 to 7. 2
Average
0. 141
40
87
3.9
Afterburner
Range
0. Oil to 0. 070
5 to 61
0 to 76
3.7 to 33.8
Average
0. 048
25
33. 5
11. 7
Control
efficiency,
66
38
62
Negative
      Table 217.  ANALYSES OF MEAT SMOKEHOUSE EXHAUST GASES BEFORE AND AFTER
               CONTROL IN TWO-STAGE ELECTRICAL PRECIPITATION SYSTEMS
Particulate matter,
gr/scf
Aldehydes (as formalde-
hyde), ppm
Organic acids (as acetic
acid), ppm
Contaminant concentration
Smokehouse
Range

0.33 to 0. 181
	
	
Average

0.090
74
91
Control systema
Range

0. 016 to 0. 051
	
	
Average

0. 032
47
48
Control
efficiency, %

65
37
47
      aEach control system is equipped with a wet centrifugal collector upstream from the
       precipitator.

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                                      Food Processing Equipment
                                             799
during the smoking cycle.  The size of control
equipment is materially increased if drying
gases are ducted to it.  The initial cost and oper-
ating cost of a smokehouse's air pollution control
system can,  therefore,  be  considerably reduced
if exhaust gases are bypassed during drying and
cooking cycles when no smoke is  introduced into
the house.

If control devices are to be bypassed during nonsmok-
ing periods ,  the ductwork and valving should be de -
signed to provide automatic or nearly automatic
operation.  Water seal dampers (Figure 610) are
preferable.  Mechanical  dampers demand optimum
maintenance  for satisfactory closure.   They are
considerably more likely to malfunction owing to
corrosion and contamination with greases and tars.
Moreover, mechanical dampers are more  suscepti-
ble to physical damage than water dampers are.
Ideally,  damper operation should be keyed to other
smokehouse auxiliaries  such as fans and smoke
generators.  Where controls are  manually oper-
ated, there is a strong possibility that dampers
will not be opened or closed at proper  times,
causing either overloading  of the  control device
or the discharge of untreated air  contaminants
directly to the atmosphere.
                 GASES FROM
                 SMOKEHOUSE
  Figure  610. Diagram of a water-operated damper
  used  to bypass the air pollution  control device
  during  nonsmoking periods.

DEEP FAT FRYING

Deep fat or "French" frying involves the cooking
of foods  in hot  oils or greases.  Deep-fried prod-
ucts include doughnuts,  fritters, croquettes, vari-
ous potato shapes, and breaded and batter-dipped
fish and  meat.   Most of these foods contain some
moisture,  a large portion of which is volatilized
out as  steam during frying.  Some cooking oils,
as well as animal or vegetable oils from the prod-
uct, are usually steam distilled during the pro-
cess.
Deep fat frying is in common usage in homes,
restaurants, and frozen food plants.  In the home
and in smaller commercial establishments, batch-
type operation is more common.   The principal
equipment is an externally heated cooking oil vat.
Oil temperatures are usually controlled to be-
tween 3Z5°  and 400°F.  Almost any type.of
heating is  possible.  Where  combustion fuels
are used,  burner gases are  vented separately.
The product to be fried is either  manually or
mechanically inserted into the hot grease and
removed after a definite time interval.

In large commercial establishments, highly
mechanized, conveyorized fryers, such as that
shown in Figure 611,  are  used.   The raw food
product is loaded onto an endless conveyor belt
and passed through hot grease at a rate adjusted
to provide the proper cook time.  Almost all
fryers  are of one-pass design.   Frequently,  cook-
ing units are followed by product coolers and pack-
aging and  freezing  equipment.
The Air Pollution Problem

In a typical large industrial operation of this
type, the cooking vat constitutes the principal
source  of air contaminants.  Uncooked materials
are usually wet or pasty, and the feed system
produces little or no air pollution.  Most cooked-
product-handling  systems are also innocuous,
except in rare instances where fine, dusty mate-
rials are encountered.

Odors,  visible smoke,  and entrained fat particles
are emitted from the cooking vats.  Depending
upon  operating conditions and the surrounding
area, these contaminants may or may not be in
sufficient concentration to exceed  the limits of
local opacity or nuisance regulations.

From the standpoint of air  pollution  control,  the
most objectionable operations involve foods con-
taining  appreciable fats and oils.   Light  ends of
these oils are distilled during cooking.   In gen-
eral, the deep frying of vegetable  products is
less troublesome  than that  of fish  and meat prod-
ucts, which contain higher  percentages of fats
and oils.

Most food products cooked  in this  manner con-
tain bet-ween 30 and 75  percent moisture  before
the cooking.  Almost all moisture  is driven off
in the cooking vat and appears as  steam  in ex-
haust gases.  Moisture concentrations in stack
gases are usually bet-ween 5 and 20 percent, de-
pending upon the volume of air drawn into the
cooker hood and exhaust system.   In highly
mechanized installations, very little air  enters
under the cooker hood.  As a result, the warm
air-stream from a fryer such as this is  often

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800
CHEMICAL PROCESSING EQUIPMENT
                   Figure  611. A continuous deep  fat  fryer; (left) Interior  view,
                   (right) end view (J.C.  Pitman  &  Sons,  Inc., Concord,  N.H.).
saturated, and downstream cooling causes visi-
ble condensation at or near the stack exit.

Moisture has two effects:  (1) It causes fats and
oils to be steam distilled from the cooking vat,
and (2) it masks visible stack  emissions.  Smoke
observations of equipment such as this must be
made at the point in the stack plume -where water
vapor has disappeared.  This is best accomplished
when the  weather is warm and  dry.  On a cold,
moist day, the vapor plume may extend as far
as the  smoke.

Excessive smoking is most often due either to
overheating or to the characteristics of the
material  being cooked.  When, for instance,
potato chip or corn chip fryers are operated
in normal temperature ranges, there is usually
no more than a trace of smoke in exhaust gases.
On  the other hand, several meat product fryers
have been found to exhaust gases of high opacity,
and control equipment was needed to bring them
into compliance with local regulations. These
visible emissions appear to be  finely divided
fat  and oil particles distilled either from the
product or the  cooking oil.  Cooking oils are
usually compounded within reasonably narrow
boiling ranges,  and -when fresh, very little of
the oils is steam distilled.  Most objectionable
air contaminants probably originate,  therefore,
in the product or in spent cooking  oil.

The carryover of oil droplets can  also  cause a
nuisance  by spotting fabrics,  painted surfaces,
                        and other property in the surrounding area.
                        This problem is most likely to occur when the
                        raw food contains  relatively large concentrations
                        of moisture, a situation in -which steam distilla-
                        tion is proportionally higher.


                        Hooding and Ventilation Requirements

                        Deep fat fryers should always be hooded and
                        vented through a fan.  Axial -flow fans  are pre-
                        ferred.  Exhaust volumes are governed by the
                        open area under the hood.  Where there  is open
                        area around the full hood periphery, the indraft
                        velocity should be at least 100 fpm.  In many
                        modern units, the dryer sides are completely
                        enclosed, and the  only open areas are  at the con-
                        veyor's inlet and outlet.  At these installations,
                        exhaust volumes are considerably less,  even
                        though indraft velocities are well above 100 fpm.
                        If control equipment is to be employed, exhaust
                        volumes become an important factor.  In these
                        instances, redesigning the existing hoods to low-
                        er the  exhaust rates is often desirable.
                        Air Pollution Control Equipment

                        Incineration, low-voltage electrical precipita-
                        tion, and entrainment separation have been used
                        to control air contaminants from deep fat fryers.
                        Since practically all air contaminants from fry-
                        ers are combustible,  a well-designed afterburn-
                        er provides adequate control if the operating tem-
                        perature is  sufficiently high.  Temperatures from

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                                      Food Processing Equipment
                                                                                                  801
1,000"   to 1,200°F are often sufficient to eliminate
smoke-causing particulates and to incinerate odors
and eye irritants.  The combustion of larger par-
ticles usually requires higher temperatures, some-
times as high as 1,600°F.  The concentration of
particulates in fryer exit gases is,  however, nor-
mally less than 0. 1 grain per scf, which is well
below common limits for particulate emissions.

Two-stage,  low-voltage electrical precipitators
(6, 000 to 15, 000 volts) can be used to collect a
substantial portion of the particulates responsible
for visible air contamination.   These devices,
unfortunately,  do not remove the  gaseous con-
taminants that are usually responsible for odors
and eye irritation.  As would be expected, the
effectiveness  of a precipitator depends upon the
particular fryer it is serving.   If particulates
are the only significant contaminants in the ex-
haust gases,  a precipitator can provide an ade-
quate means  of control.  If,  on the  other hand, the
problem is due to odors of overheated  oil or prod-
uct,  a device  such as this is of little benefit. For
optimum performance, the temperature,  humidity,
and volume of gases vented to a two-stage pre-
cipitator must be controlled within reasonably
narrow limits.   The oils collected  are usually
free flowing and readily drain from collector
plates.  A collection trough  should be provided
to prevent plate fouling and damage to the roof
or other supporting structure on  -which the pre-
cipitator is located.

Entrainment separators have been  employed
with varying success to remove entrained oils
in fryer exhaust stacks.  These are most use-
ful where the concentration of oils  is relatively
large.  The material collected can represent  a
savings  in oil and can prevent damage  to  ad-
jacent roofing.   Because of the inherently low
collection efficiency of these  devices, their
use  is  not recommended -where  smoke or
odors  constitute the major air pollution prob-
lem.   Some cooking oils usually collect on the
inner surfaces of uninsulated exhaust stacks
and drain back towards the cooker.  Most com-
mercial fryers are .equipped -with pans to col-
lect this drainage at the bottom of the stack.


LIVESTOCK SLAUGHTERING

Slaughtering operations have traditionally
been associated with odorous air  contaminants,
though much of these odors is  due to byproduct
operations rather than to slaughtering  and meat
dressing itself.  Slaughtering is considered to
include only the killing of the animal and the
separation of  the carcass into humanly edible
meat and inedible byproducts.   The smoking
of edible meat products,  and reduction of edi-
ble materials are discussed in  this subsection,
while the reduction of inedible materials is
covered in another part of this chapter.

Cattle-, sheep-, and hog-killing operations are
necessarily more extensive than those concerned
with poultry, though poultry houses usually han-
dle appreciably larger  numbers of animals.

A flow diagram of a typical cattle-slaughtering
operation is shown in Figure  612.  The animal
is  stunned, bled, skinned, eviscerated, and
trimmed as shown.  Blood is drained and col-
lected in a holding  tank.  After removal,  en-
trails are sliced in a "gut hasher, " then washed
to  separate the partially digested food termed
"paunch manure. "  Many slaughterers have
heated reduction facilities in  which blood, in-
testines, bones,  and other inedible materials
are processed to recover  tallow,  fertilizer,
and animal feeds.  The firms that do not oper-
ate this equipment usually sell their offal to
scavenger  plants that deal exclusively in by-
products.   Hides are almost always  shipped to
leather-processing firms.  Dressed beef, nor-
mally about 56 percent of  the live weight, is
refrigerated before it is shipped.


The Air Pollution Problem

Odors represent the  only air  contaminants
emitted from  slaughtering operations.  The
odors could be differentiated as  (1)  those
released from the animal  upon the killing and
cutting, and upon the exposure of blood and
flesh to air; and (2) those resulting  from the
decay of animal matter spilled on exposed sur-
faces or otherwise exposed to the atmosphere.
Odors from the first source are not  appreciable
•when healthy livestock is used.  Where nuisance-
causing odors  are encountered from slaughter-
ing, they are  almost always attributable to  in-
adequate sanitary measures.   These odors  are
probably breakdown products of proteins. Amines
and sulfur  compounds are considered to be  the
most disagreeably odorous breakdown products.

In addition to  these sources,  there are odors
at slaughterhouse stockyards and from the stor-
age of blood,  intestines,  hides, and  paunch
manure before their  shipping or further process-
ing.
Air Pollution Control Equipment

As has been explained, odorous  air contami-
nants are emitted from several points in a
slaughtering operation.  Installing control equip-
ment at each source would be difficult if not im-
possible.  Methods of odor control available in-
clude: (1) Rigid sanitation measures  to prevent

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802
                              CHEMICAL PROCESSING EQUIPMENT
COOLING


CUTTING
                                                                          INEDIBLE  \ (  EDIBLE
                                                                          MATERIALS I V  FATS
                   Figure 612.  Typical  livestock-slaughtering and  processing area
                   (The Globe Company, Chicago,  III.).
the decomposition of animal matter, and (2) com-
plete enclosure of the operation to capture the
effluent and exhaust it through a control device.


Where slaughtering is government inspected,
the operators are required to -wash their kill
rooms constantly, clean manure from stock
pens, and dispose of all byproducts as rapidly
as possible.   These measures normally hold
plant odors to a tolerable minimum.


When a slaughterer is located in a residential
area, the odor reduction afforded by strict
sanitation may not be sufficient.  In these in-
stances, full-plant air conditioning might be
necessary.  Filtration with activated carbon
would appear  to be the only practical means
of controlling the  large volume of exhaust
gases from a  plant of this type.  The latter
method has not yet been employed at slaughter-
houses in the  United States.   Nevertheless,
activated-carbon filtration of the entire plant
has been employed to control similar odors
at animal matter byproduct plants.  With in-
creasing urbanization,  this method of control
may, conceivably, be used in the near future.
EDIBLE-LARD AND TALLOW RENDERING

Methods used to produce edible lard and tallow
are similar to those described later in this
chapter for rendering of  inedibles.  As -with
processes for inedibles,  feedstocks are heated
either directly or indirectly with steam, to ef-
fect a phase separation yielding  fats, "water,
and solids.  Moisture is  removed either by
vaporizzition or by mechanical means.  Tallow
and solids are mechanically separated from
one another in presses,  centrifuges,  and filters.
The only major process differences between
rendering edibles and rendering inedibles are
due to the composition and freshness of the
materials handled.  Edible feedstocks contain
80 to 90 percent lard or tallow, 10 to 20 per-
cent moisture,  and less than 5 percent muscle
tissue. Inedible feedstocks contain appreciably
higher precentages of both moisture and solids.
Edible feedstocks, in addition to being more
select portions  of the animal, are generally
much fresher than inedible cooker  materials
are.

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                                     Food Processing Equipment
                                                                                                 803
Whenever its products are intended for human
consumption,  the process is much more stringent-
ly supervised and regulated by Federal and local
agencies.  There are numerous government regu-
lations concerning  the freshness of edible-render-
ing feedstocks,  the cleanliness of processing
equipment,  and the handling of rendered fats.
For instance, paragraph 15. 1 of the United States
Department of Agriculture's Meat Inspection
Regulations specifies that inspected feed mate-
rial must be heated to a temperature  not lower
than 170°F for a period of not less  than 30
minutes when edible  lard or tallow  is being pro-
duced.

Dry Rendering

Batchwise rendering

Most of the high-quality edible  lard and tallow
are produced in indirectly steam-heated cookers.
These processes are frequently carried out at
temperatures of less than 212°F.  The lower
operating temperatures  are afforded either by
vacuum cooking or by finely grinding  the feed-
stocks.  The vacuum process is usually per-
formed batchwise in  a horizontal, steam-jac-
keted cooker very  similar to  those  used for
rendering of inedibles.   The vacuum is usually
created through the use  of steam- or  water-
operated ejectors.  Variations  in dry, edible-
rendering processes  are usually concerned
with temperatures  and the degree of comminu-
tion of fats.  Where raw materials  are ground
into fine particles, operation at lower tem-
peratures is usually  possible, even -without
a. vacuum-producing  device.

Continuous low-temperature rendering

Dry rendering processes have been developed
to produce edible lard and tallow on a continu-
ous basis from high-fat feedstocks.  A typical
process is shown in Figure 613.  Feedstocks
are first introduced to a grinder, where  they
are finely shredded at 120 °F,  and then heated
to approximately 185 °F  before  being passed
through a desludging  centrifuge in which solids
are removed from  the water and tallow.  Liq-
uids are then reheated to about 200°F in a
steam jet heater.  The  remaining moisture is
removed from the hot tallow in a second  cen-
trifuge from which edible lard or tallow is
run to storage.   The  separated water  is piped
to a  skimming pond where it is  cooled before
being sewered.  Vapors from the several
vessels are vented  to a fume  scrubber (con-
tact  condenser).

Wet Rendering

The  wet rendering  process involves rendering
of fats in a vertical,'closed tank with the feed
material in direct contact with live steam.


The principal advantage of this type of render-
ing is that large quantities of lard or tallow
can be produced without finely grinding the feed
material.  Low-cost equipment and labor can
be used.

Wet rendering,  however,  necessarily requires
higher temperatures (280°  to 300°F) and in-
ternal pressures of 38 to 40 psig.  The quality
of the lard or tallow produced is  relatively low,
owing to the high temperatures to which it is
subjected.


 The Air Pollution Problem

The only noteworthy air contaminants generated
from edible-rendering processes are odors.  In
comparison  with odors generated from inedible-
rendering processes, however,  those from
edible-rendering processes are relatively minor.

In Los Angeles  County, rendering of edibles ac-
counts for only  about 10 percent of the total ani-
mal matter rendered.  Rendering of inedibles
at packing houses constitutes approximately 32
percent and that at scavenger  plants accounts
for the remaining 58 percent of the tonnage.

In addition,  rates of odor emissions from ren-
dering of edibles are low compared with those
from inedible-rendering processes.   Inasmuch
as edible feedstocks contain relatively low per-
centages of water,  the resultant steam generated
from cookers, 6, 300 scf per ton, is not appre-
ciable. Feedstocks contain approximately 15 per-
cent moisture, as compared with 50 percent
from inedible cooker materials.  Odor concen-
trations in exhaust gases from the rendering
of edibles are significant at 3,  000 odor units
per scf but not excessive.   Equipment at plants
rendering edibles is kept scrupulously clean,
which substantially reduces odors from inplant
handling  operations.

Hooding and Ventilation Requirements

Almost always,   cooker gases  from rendering of
edibles can be piped directly to air pollution con-
trol devices. Where  condenser odor control de-
vices are used,  there is usually enough vacuum,
that is, pressure differential,  in the  duct-work
to cause vapors to flow from the  cooker  at a
sufficiently high rate.  Steam  or water ejectors
are sometimes  employed to lower operating
temperatures or to remove water vapor  more
rapidly.  Uncondensible gases do not exceed
5 percent of  cooker gases  unless  there is ap-
preciable leakage into the system,  as through
seals on shafts,  doors, and so forth.
   234-767 O - 77 - 53

-------
804
     CHEMICAL PROCESSING EQUIPMENT
                                      HEADER SLOPE TO SCRUBBER, NO POCKETS OR TRAPS
                                           	.	,_	i	< i	>.

                                                                            FUME
                                                                         i cr	
                                                 TEMP CONTROLLER

                                                  STEAM
                                                  hunt V
                                                ISCRUBBEFT
                                                     ^	DE LAVAL
                                                     n_n ANIMAL FAT
                                                     L-^  SEPARATOR
                                                     —i
                                                         \
                                                      CRACKLINGS •=	p,
                                                       EDIBLE  ~F|  "
                                                      DEFATTED  fJ-OAT
                                                       TISSUE   lANKp
                                                                                  COLD WATER
                                                                 TO SEWER
                                                                i	*.
                                                                               CATCH BASIN
                    (SSI TEMP CONTROLLER
                   ._^	J
         STEAM (-.-tin

         DIAPHRAGM
          VALVE
                                	VAPOR VENT LINES
TEMP AT
STRAIGHT FAT
RENDERING
A
120°F
B
180° TO 190°F
C
185° TO 215°F
                                                        EDIBLE FAT
          PURIFIER
           PUMP
DE LAVAL FAT
 PURIFIER
SLUDGE i      PUMP
 PUMP  T0 STICKWATER PLANT
       OR CATCH BASIN
              Figure  613. DeLaval continuous centriflow process for edible protein  recovery
              and  edible  fat rendering (The DeLaval  Separator Co.,  Hillbrae,  Calif.).
 Where cooking is performed at pressures
 greater than 1 atmosphere, piping must usually
 be arranged in a manner that prevents  surging
 •when high-pressure gases  are released.  If
 the main valve is released quickly, the high-
 pressure vapors usually cause slugs  of grease
 and  solids to be carried over into the control
 system.   Severe surging can cause siphoning
 of all the material from cooker  to the control
 system.   To prevent this,  the piping  is often
 arranged with a small pipe,  1 to 2 inches in
 diameter,  that bypasses the  main cooker's
 exhaust line.  High pressures are reduced by
 venting first through the small pipe to the con-
 trol device.   Once the high pressure  is relieved,
 the large valve  can be opened to provide great-
 er flow.


 Air Pollution Control Equipment

 Water spray contact condensers are  the simplest
 devices used for controlling  odorous  air con-
 taminants  from rendering  of edibles.  These con-
 dense a major portion of the steam-laden effluent
 vapors and dissolve much  of the odorous  materi-
 als.  Water requirements  of the contact condenser
 for edible-rendering operations are considerably
 lower than those for the contact condenser used
 to control cooker gases from rendering of in-
 edibles.  This is due primarily to the lower
 moisture content of feedstocks and the resultant
                             lower volume of steam exhausted from the cook-
                             er.   Exit water temperatures should be held
                             below 140°F to prevent the release of  volatile,
                             odorous materials from downstream piping
                             and sewers.

                             Surface condensers  are  also satisfactory con-
                             trol devices for edible-rendering processes.
                             At the  same condensate  volume and tempera-
                             ture, however, surface  condensers by them-
                             selves  are not as effective as contact con-
                             densers.  This is due to the inherently lower
                             condensate volume and larger concentration
                             of odorous materials in  the condensate of sur-
                             face condensers.

                             That an edible-rendering process would  require
                             more extensive odor control than would be af-
                             forded by an adequate condenser is unlikely.
                             Nevertheless,  uncondensed offgases from con-
                             densers could be further controlled by incin-
                             eration or carbon adsorption,  as outlined for
                             processing of inedibles  later in this chapter.

                                     FISH  CANNERIES AND  FISH

                                          REDUCTION  PLANTS

                              Canning is the principal method of preserving
                              highly perishable fish foodstuffs .  Canneries
                              for this purpose are usually located near har-
                              bors where fish  can be  unloaded directly from

-------
                          Fish Canneries and Fish Reduction Plants
                                                                                                805
boats.  Byproduct reduction plants are operated
at or near fish canneries to process  scrap ma-
terials, and much of the odorous air contami-
nants generally attributed to canneries emanate
from byproduct processes.  Only choice por-
tions of sound fish are canned for human con-
sumption.   The remainder is converted into by-
products, notably fish oil  and high-protein
animal feed supplements.

Basically there are  two types of fish-canning
operations in use today.   In the older,  so-called
"wet-fish" method,  trimmed fish are cooked
directly in the  can.   The more popular "pre-
cooked" process is used primarily to can  tuna.
The latter method is characterized by the cook-
ing of whole, eviscerated  fish,  and the hand
sorting of choice parts before canning.


WET-FISH CANNING

Wet-fish canning is  used to preserve salmon,
anchovies,  mackerel, sardines, and similar
species that can be  obtained locally and brought
to the cannery quickly.  The distinctive feature
of the wet-fish process is  the complete removal
of heads, tails, and entrails before the cooking.
Trimmed and eviscerated raw fish is packed
into open cans that are conveyed through a 100-
to 200-foot-long hot-exhaust box.  Here live
steam is employed to cook the fish.  Hot-ex-
haust boxes are vented through several stacks
located along their lengths (Figure 614).   At
the discharge end,  cans may be mechanically
upended so that "stick water" is decanted from
the cans -while the cooked fish remains.  Stick
water consists of condensed steam, juices,  and
oils that have cooked out of the fish.   This liq-
uid is collected and retained for byproduct
processing as described later  in this section.
The cans of drained fish are filled with tomato
sauce,  olive oil,  or other suitable liquid before
being sealed. Sealed cans are pressure  cooked
before their  labeling,  packing,  and shipping.


TUNA CANNING

The precooked canning method was developed
to improve the physical appearance of  canned
fish.  It is confined to the commercial canning
of larger fishes,  principally tuna.  Whole,
eviscerated fish are placed in wire baskets and
charged to live-steam-heated cookers  such as
those of Figure 615.  The cookers are  operated
                    Figure  614. Unsealed cans  of  cooked mackerel  being  conveyed from
                    the hot-exhaust box cooker of  a wet-fish process  (Star-Kist Foods,
                    Inc.,  Terminal Island,  Calif.).

-------
 806
CHEMICAL PROCESSING EQUIPMENT
 Figure 615. A bank of  live-steam-heated cookers
 used  to process raw,  whole  tuna (Star-Kist Foods,
 Inc., Terminal Island,   Calif.).
at about 5 psig pressure, condensate being dis-
charged through steam traps.  Air,  steam,  and
any uncondensed,  odorous gases are bled from
the cookers through one or more small vents in
the ceiling.

As the fish are  cooked,  juices, condensed steam,
and oils are  collected, centrifuged,  and pumped
to stick water and oil storage tanks.  Cooking
reduces the -weight of a fish by about one-third.
After the cooking, the flesh is cooled so that it
becomes firm before it is handled.   It is then
placed on a conveyorized picking line. Operators
stationed along  the conveyor select the portions
to be  canned  for human consumption. After being
packed  and sealed in cans,  the fish is pressure
cooked  for sterilization before its labeling,  pack-
ing,  and shipping.  Much of the dark meat is
canned  for pet food.  Only about one-third of the
raw tuna -weight is canned as food for humans and
pets.  The remaining  skin, bone, and other scrap,
roughly amounting to one-third of the raw weight,
is fed to the fish meal reduction system.


CANNERY BYPRODUCTS

A large fraction of the fish received in a cannery
is processed into byproducts.  In the precook
process,  about two-thirds of the raw fish weight
is directed to byproduct reduction systems as
stick  -water or solid scrap. The wet-fish  process
usually  produces somewhat less offal,  depending
principally upon the size of fish.  Typical head-
and-tail mackerel scrap is pictured in Figure 616.
In addition, whole fish may be rejected at the can-
ning line because of spoilage, freezer burns, bad
color, and so forth.  Any fish  or portions of fish
                       Figure 616. Typical  raw head-and-tai I mackerel
                       scrap awaiting processing in  a  fish  meal reduction
                       system (Star-Kist Foods,  Inc.,  Terminal  Island,
                       Calif.).
                       not suitable for human consumption or for pet
                       food are handled in the reduction plant.  In order
                       of volume and relative importance, the byproducts
                       are: Fish meal,  used almost exclusively as  an
                       animal feed supplement; fish oil,  used in the
                       paint industry and in vitamin manufacture;  and
                       "liquid fish" and "fish solubles, "  high-protein
                       concentrates.   The latter are manufactured
                       somewhat differently,  but both are used  as ani-
                       mal feed supplements and as fertilizers.


                       FISH MEAL PRODUCTION

                       Fish scrap from the canning lines,  including
                       any rejected whole fish,  is  charged to contin-
                       uous live-steam cookers  in the meal plant.
                       Flow through a typical fish  meal plant is dia-
                       grammed in Figure 617.   Cookers of  the type
                       shown in Figure 618 are operated at between 10
                       and 25 psig  steam pressure.  Material charged
                       to the cookers normally contains 20 to 30 percent
                       solids.  Cooked scrap has a slightly smaller
                       solids content owing to the condensed steam
                       picked up in cooking.  After the material
                       leaves the cooker, it is pressed to remove
                       oil and water, and this pressing lowers the
                       moisture content of the press cake to approxi-
                       mately 50 percent.  The press cake is broken up,
                       usually in a hammer mill, and dried in a direct-
                       fired rotary drier or in a steam-tube rotary
                       drier.  Typical fish meal driers yield 2  to 10
                       tons of meal per hour with a moisture content
                       of 4 to 10 percent.  Both  types of driers  em-

-------
                              Fish Canneries and Fish Reduction Plants
                                                                                                   807
      FISH SCRAP
                                                                 VAPORS TO CONDENSER
                   Figure  617.  Flow  diagram of a fish meal  reduction  system  including
                   oil-separating  and oiI-clarifying equipment.
Figure 618.  A live-steam  reduction cooker and a
continuous press  (Standard Steel Corp.,  Los Angeles,
Calif.).
ploy air as the drying medium.  Moisture is
removed -with exhaust gases, which are volu-
minous .

Direct-fired driers include stationary fireboxes
ahead of the rotating section,  as shown in Fig-
ure 619.  They are normally fired with natural
gas or fuel oil.   Combustion is completed in
the firebox.  Hot products of combustion are
mixed with air to provide a  temperature of 400°
to 1, 000°F at the point where wet meal is initial-
ly contacted.  Hot, moist exhaust gases from
the drier  contain appreciable fine meal, which
is commonly collected in a cyclone separator.

The essential feature of  steamtube driers is
a bank of  longitudinal,  rotating steamtubes
arranged  in a cylindrical pattern, as shown in
Figure 620.  Steam pressures range from 50
to 100 psig in the tubes.  Heat is transferred
both to the meal and air.  As with direct-fired
units,  gases pass parallel to meal along the
axis of the drier and are vented through a cy-
clone separator.  Meal produced in  steamtube
driers is  less likely to be over-heated and is
generally of higher quality than  that from direct-
fired units.

FISH SOLUBLES  AND FISH OIL PRODUCTION

Fish solubles is the  term used to designate the
molasses-like concentrate containing soluble
proteins and vitamins that have  been extracted
from fish flesh  by  cooking processes.  The
flow diagram of Figure 617  includes the sep-
aration of press •water and fish oil.   The sources
of solubles and  oils are the  juices and conden-
sate collected as press water and stick water.

-------
808
                                  CHEMICAL PROCESSING EQUIPMENT
AUTOMATIC OIL
OR GAS BURNER
         FEED
                                 FULL FLOATING TIRES
        FURNACE
                                                                                   VAPOR AND PRODUCT   EXHAUST
                                                                                       SEPARATOR
                                          VAPOR LADEN GASES -
                                                                   7*
TEMPERATURE LIMIT
 SAFETY CONTROL

    THERMOSTATIC
    TEMPERATURE
      CONTROL
  DRAFT FAILURE
 SAFETY CONTROL
                                                                                          SEAL
      CONTINUOUS BED FRAME
           OPTIONAL
ROLLER BEARING
  TRUNNIONS
                                                          MOTORIZED
                                                          REDUCER
        VAPOR AND
       PRODUCT FAN
 PRODUCT
DISCHARGE
                    Figure 619.  A parallei-flow,  direct-fired,  rotary,  fish meal drier
                    (Standard Steel  Corp.,  Los Angeles,  Calif.).
                  Figure  620.  A steamtube,
                  Los Angeles,  Cal if.).
                                           rotary, fish  meal  drier  (Standard Steel  Corp.,

-------
                                 Fish Canneries and Fish Reduction Plants
                                                                                                809
These two liquids may be processed separately
or blended before their processing.  The liq-
uids are first acidified to prevent bacterial de-
composition.  Some protein is flocculated up-
on the addition of acid.  The floe and other
suspended solids are removed in a centrifuge
and recycled to the fish meal reduction process.
Liquids pass through a second centrifuge, where
the fish oils are  removed.  The water layer is
pumped to multiple-effect evaporators where
the solids content is increased from approxi-
mately 6 to 50 percent by weight.   Uncondensed
gases are removed from the process at one  of
the evaporator effects, which is operated under
high vacuum.   The vacuum is held by a water
or steam ejector. Where steam ejectors are
used they are equipped with barometric-leg
aftercondensers.


DIGESTION PROCESSES

Fish viscera are usually digested by enzymatic
and bacterial  action rather than by thermal re-
duction.   The product is a liquid that is  concen-
trated by evaporation and marketed as a high-
protein livestock feed supplement very similar
to fish solubles.

Most cannery-operated digestion processes  are
of the enzymatic  type and are used only to pro-
cess viscera.  Stomach enzymes, under  con-
trolled pH and temperature,  reduce the  viscera
to a liquid.  The  process is u'sually carried  out
in a simple tank at atmospheric pressure, near-
ambient temperature,  and an acid pH.  Essen-
tially no moisture is evaporated during digestion.
Before concentration,  the digested liquid is  fil-
tered and centrifuged to remove small quantities
of scales, bones, and oil.  The evaporation  pro-
cess is identical  to that used for fish solubles,
yielding a liquid of 50 percent solids.

Bacterial digestion is used to reduce all types
of fish flesh.  It is carried out at an alkaline
pH in equipment similar to that used for en-
zymatic processes.  Again, there is no appre-
ciable moisture evaporation,  but odors evolved
are considerably stronger and more likely to
elicit nuisance complaints.
THE AIR POLLUTION PROBLEM

Air contaminants emanate from a number of
sources in fish canneries and fish reduction
plants,  including both edible-rendering and
byproduct processes.  Odors  are the most ob-
jectionable of these contaminants, though dust
and smoke can be a major problem.  In a fish
cannery, some odor is unavoidable owing to
the nature of the species.  Heavy odor emis-
sions that cause nuisance complaints can usu-
ally,  however, be traced to poor sanitation or
inadequate control of air contaminants.  Tri-
methyl amine,  (CH-^jN, is the principal com-
pound identified -with fish odors.

Reduction processes produce more odors than
cannery operations do.  Materials fed to re-
duction processes are generally in a greater
state  of decay than the fish are that are  pro-
cessed for human consumption.   Edible  por-
tions  of the fish are  always handled first,  and
great care is maintained to guarantee the qual-
ity of edible products.  The portions  that are
unsuitable  for human consumption have much
less value, and it is not uncommon for opera-
tors to allow reduction plant feedstocks  to
decompose markedly before the processing.

The largest sources of reduction plant odors
are fish meal driers.  Lesser quantities of
odors are emitted from  cookers preceding
meal  driers, from digestion processes, oil-
water separators, and evaporators.  Dust
emissions  are limited to driers and the  pneu-
matic conveyors  and grinders following  them.
Smoke can be created by overheating or burn-
ing meal in the drier.
Odors From Meal Driers

Fish meal driers  exhaust large volumes  of gases
at significantly large odor concentrations.  Dur-
ing the processing of fresh fish scrap, odor con-
centrations in exhaust gases range from 1, 000 to
5,000  odor units per scf (see Appendix B for defi-
nition  of odor units and method of measuring odor
concentrations).   If the feedstocks are highly de-
cayed, much greater odor concentrations can
be expected.  The result is an extremely heavy
rate of odor emission,  even when fresh fish
scrap  is processed.  For example, a direct-fired
drier operating under "low-temperature" condi-
tions and producing 4 or 5 tons of dried fish meal
per hour  exhausts about 30 to 40 million odor
units per minute if the concentration is about
2,000  odor units per scf and the exhaust rate is
15,000 to 20,000  scfm.  Drier  exit temperatures
average  about 200° F, and  the moisture  content
normally ranges between 15 and 25 percent by
volume.                                '

A more startling  example  is that of the direct-
fired rotary drier operating under "high^-tempera-
ture" conditions.   It produces  10 tons of dried
fish meal per hour and exhausts 600 to 800 million
odor units per minute.   The odor concentration is
about 40, 000  odor units  per scf with an exhaust
rate of 15,000 to  20,000 scfm.   Drier exit tem-
peratures average above 300°  F during high-
temperature operation.

-------
810
                               CHEMICAL PROCESSING EQUIPMENT
Emissions from steamtube driers are less
voluminous and can be less odorous than those
from direct-fired units.  With steamtube driers,
there is less likelihood of burning or overheat-
ing the meal and,  therefore, excessively heavy
odor concentrations are encountered less  often.
Moisture contents are comparatively greater
in gases from steamtube driers.  Typical gases
from emitted steamtube driers  during tuna scrap
processing contain about 25 percent moisture  as
compared with approximately 15 percent from
a direct-fired unit processing the same material.
As a result, volumes from steamtube driers are
30 to 45 percent lower than those from compar-
able direct-fired units.  Odor concentrations
from steamtube driers are generally in the  same
range as those from direct-fired units when
fresh fish  scrap is being processed under prop-
er operating conditions, that is, when meal is
not overheated.


Smoke From Driers

Excessive visible air contaminants  can be cre-
ated in fish meal driers by the  overheating of
meal and volatilization of low-boiling oils and
other organic compounds.  Smoke is more likely
to be emitted from direct-fired driers than  from
steam-tube units, particularly if the drier is
operated under high-temperature conditions.

All driers have limits for gas discharge tempera-
tures above which excessive visible contaminants
appear in the exit gas steam.   The smoking lim-
it is a function of drier design as well as  of feed-
stocks and varies somewhat from unit to unit.
For direct-fired units, this limit is about 300° F.
Direct-fired driers operated under  low-tempera-
ture conditions process fish meal at about one-
half the rate for high-temperature conditions,
and the limit for gas discharge temperature is
about 200° F.  Only low-temperature operation
is suitable for control by chlorinator-scrubbers.
Chlorination of a drier exit gas steam which is
in excess of 200°  F will predictably produce an
opacity coupled with a corresponding rise in odor
level.

The addition of certain low-boiling  materials to
drier feedstocks can also create visible emis-
sions when there is essentially no overheating
of meal in the drier.  One such material is  di-
gested fish concentrate.  Some operators add
this high-protein liquid to drier feedstocks to
upgrade the protein content of meal.  Digested
fish concentrate  can contain low-boiling com-
pounds that are vaporized into exhaust gases and
condense  upon discharge to the atmosphere.
These finely divided,  organic,  liquid particulates
can impart greater than 40 percent opacities to
drier gases.  Scrubbing the drier gases with
water aggravates the problem by lowering the
temperature, which increases condensation and,
thereby, the opacity.


Dust From Driers and Conveyors

The only major points of dust emission in can-
neries and reduction plants are the driers them-
selves and the  grinders  and conveyors used to
handle dried fish meal.  Driers and pneumatic
conveyors  are  equipped  with  cyclone separators,
and emissions  are functions of collection effi-
ciencies .

Fish rneal  does not usually contain a large frac-
tion of fines.  A particle size analysis of a typ-
ical meal is  provided in Table 218.  This meal
sample -was collected in a pneumatic conveyor
handling ground fish meal. It can be seen that
the sample contains only 0. 6 percent by -weight
less than 5 microns in diameter,  and 1.4 per-
cent less than 10 microns  in diameter.   Ninety-
six percent is larger than  20  microns.
  Table 218.  PARTICLE SIZE ANALYSIS OF
             A TYPICAL GROUND,
             DRIED FISH MEALa
Range of particle diameter,
0 to 5
5 to 10
10 to 20
20 to 44
44 to 74
74 to 149
149 to 246
246 to 590
590 to 1, 651
1, 651 to 2, 450
more than 2, 450
wt %
0.6
0.8
2.6
7.5
11.5
29.9
16.4
22.8
7.4
0.4
0. 1
   aSample drawn from a pneumatic conveyor
    following a direct-fired drier and hammer
    mill.
    Size determination by mlcromerograph.
Concentrations of fines in exit gases are usually
less than 0. 4 grain per scf.  The pneumatic con-
veyor cyclone handling the meal of Table 218 was
found to be better than 99. 9 percent efficient,
with an exit dust concentration of less than 0. 01
grain per scf. This  efficiency is much greater
than would be predicted on the basis of cyclone
design and particle size.  It indicates  that ap-
preciable agglomeration probably takes place
in the cyclone.

-------
                              Fish Canneries and Fish Reduction Plants
                                            811
Odors From Reduction Cookers

The cookers preceding fish meal driers exhaust
gases of heavy odor concentration.  Nevertheless,
the volumes  of these offgases are appreciably less
than those from driers.  Cooker gases are simi-
lar to those from indirectly heated rendering
cookers.   They consist almost entirely of water
vapor but contain significant quantities of ex-
tremely odorous organic gases and vapors.  Odor
concentrations from live-steam-heated cookers
range from 5, 000 to over 100, 000  odor units per
scf, depending to a large degree upon the state
of feedstocks.  Any malodorous gases  contained
in the cellular flesh structure are  usually liberated
when the material is  first heated in the cooker.

Essentially no solids are in the effluent from the
cookers,  though some entrained oil particulates
are usually present.  The volumes of exhaust
vapors  depend upon the degree of sealing provided
in the cooker.  All the  steam can be  contained in
the cooker with no leakage.  Most  cookers,  how-
ever, are designed to bleed off 100 to 1, 000 cfm
through one or more stacks.  The  latter  arrange-
ment is recommended, since it provides  a posi-
tive exhaust point at which air contaminants can
be controlled.  Otherwise the malodorous gases
would be liberated at the press and grinder where
they are difficult to contain.


Odors From Digesters

The digestion of fish scrap  produces only small
volumes of exhaust gases, though these gases
can have a large odor concentration.  The en-
zymatic,  acid-pH decomposition of viscera
does not normally produce odor concentrations
greater than 20, 000 odor units per scf, depend-
ing again upon the quality of feedstocks.  Alka-
line digestion of fish scrap,  on the other  hand,
is productive of strong odors that  are likely to
create a public nuisance.

Odors From Evaporators

The evaporation of the water-soluble extracts--
stick -water and press water—does not  generally
result in heavy odor emissions.  This is  pri-
marily due to the use of water ejector-condensers.
Odors could be considerably heavier if different
types of vacuum-producing  equipment were em-
ployed.   Most fish canneries are located  near
large bodies of water,and it is common to use
water jet ejectors to maintain a vacuum on the
evaporator system.  All uncondensed gases  and
vapors from the evaporators are vented to the
ejectors,  which act as contact condensers. Most
of the odorous compounds are condensed  or  dis-
solved in the effluent water. If steam ejectors
and surface condensers,  rather than contact
condensers,  are used to produce the vacuum,
odor emissions to the atmosphere are much
greater.  Contact  condensers (water ejectors)
provide a dilution  of condensate 10 to ZO times
greater than that produced by surface-type con-
densers used "with steam ejectors or vacuum
pumps.


Odors From Edibles Cookers

While most odorous air contaminants are con-
sidered to emanate from fish reduction processes,
the handling and cooking of edible fish  also pro-
duce measurable odors.  The largest single sources
are  the cookers described earlier in this  section.

The precooked process is  less productive of odors
than the wet-fish process is. When tuna is  cooked
in the live-steam  cookers  of Figure 615, much of
the odorous gases and vapors is condensed in  the
cooker and the steam trap.  Only the volatile,
albeit highly odorous, compounds are vented
through the steamtrap.

The hot-exhaust boxes  of wet-fish production
systems are commonly vented directly to the
atmosphere.  These  offgases consist mostly of
steam with some noncondensible air and  mal-
odorous gases  entrained.  Hot-exhaust boxes
are the points of initial cooking of wet  fish,  and
are,  therefore, origins of large quantities of
gases and vapors.

HOODING AND VENTILATION REQUIREMENTS

When air pollution control is employed, most
fish cannery and reduction processes are vented
directly to the  control device.   Cookers, presses,
grinders, and the hot press-water auxiliary
equipment require hooding.  Hot material from
the  cooker  evolves  appreciable steam and odors
•when the  oil and  water are pressed from it
and  when the resultant press cake is broken
up before the drying.  The vapors liberated at
these points  consist principally of steam. When
the gases  are vented to a condenser, hooding
should be as tight  as  possible to prevent  dilu-
tion with air. Indraft velocities of  100 fpm
across the open area under the hood are  nor-
mally satisfactory.  Where possible, the source
itself should be totally enclosed and ducted to
control equipment.  Unfortunately,  the designs
of many presses and grinders are not conducive
to complete enclosure,  and hoods must be em-
ployed.

The largest contaminated gas streams  are ex-
hausted from fish  meal driers.  As shown in
Table 219,  volume rates are lower  from steam-
tube driers  than from direct-fired units.  For
the hypothetical comparison made in this table,

-------
 812
                               CHEMICAL PROCESSING EQUIPMENT
Table 219.  CHARACTERISTICS OF EXHAUST
GASES FROM TYPICAL DIRECT-FIRED AND
     STEAMTUBE FISH MEAL DRIERSa


Moisture evaporated from meal, scfm
Natural gas fuel, scfmc
Moisture in products of combustion, scfm
Total moisture in exhaust gases, scfm
Dry exhaust gases, scfm
Total exhaust gases, scfm
Moisture content, % by volume
Temperature of exhaust gases, °F

drier
320
-
-
338
1, 012
1,350
24
180

drier
320
16
31
369
1,914
2,283
15
205
 aBasis:  1 ton of feed per hour to drier.  Moisture content of press
 cake to drier, 50% by weight.
 "Moisture content of dried meal,  8% by weight.
 GNatural gas of 1, 100 Btu per scf gross heating value.
the fired drier exhausts 70 percent more gases
than the steamtube drier does and the moisture
content is comparatively less,  15 percent com-
pared with 24 percent. A 10-ton-per-hour fired
drier would exhaust 22,830 scfm at about 200°F,
while a steamtube unit of the same  size would
exhaust only 13, 500 scfm at about 180°F.

Exhaust volumes from live-steam-heated cook-
ers range from 100 to 1, 000 cfm and depend
to a large degree upon cooker design.  Inlet
and exit seals should be tight to prevent leakage.
Most  cookers are vented through  a  single  stack.

Digestion tanks with a capacity of 2, 000 gallons
or less seldom exhaust more than 50 scfm. Ex-
haust volumes from digesters vary appreciably
during the processing of a batch,  exit rates being
negligible much of the time.

Where water ejector contact condensers are em-
ployed on evaporators, exhaust rates are well
below 50 scfm.  If surface condensers or vacuum
pumps are employed instead of contact condensers,
exhaust volumes  can exceed 100 cfm.

Fish meal pneumatic conveyors are designed to
provide from 45 to 70 cubic  feet of  air per pound
of meal conveyed.  A pneumatic conveyor handling
5 tons of dried meal per hour exhausts about
10,000  cfm.

Exhaust gases from cookers used in the precooked
tuna process are relatively small in volume and
include only those gases that are not condensed or
dissolved at the steamtrap or the  cooker itself.
Gases evolved from the hot-exhaust boxes  of the
wet-fish lines are considerably more voluminous.


AIR POLLUTION CONTROL EQUIPMENT

Fish  cannery and fish reduction equipment are
controlled principally with condensers, scrub-
bers, afterburners, and centrifugal dust col-
lectors. Where  odors are concerned, incinera-
 tion is preferable if it can be adapted to the pro-
 cess.  Incineration provides the most positive
 control of nuisance-causing odorous compounds.
 Condensers are effective  where exhaust gases
 contain appreciable moisture, while centrifugal
 collectors are usually satisfactory to prevent
 excessive dust emissions.  Scrubber-chlorina-
 tors find  particular use in the control of odors
 from fish meal driers.

 Controlling  Fish Meal Driers

Because of the exceedingly large volume of mal-
odorous exhaust products  from driers,  they
constitute the  most costly air pollution  control
problem in a reduction plant.  Drier gases nor-
mally contain  only  15 to 25 percent moisture.
Thus, even after condensation,  the volume is
great.  Moreover,  there are enough entrained
solids in drier exit gases  to  make  incineration
difficult.

 Incinerating Drier Gases

 Incineration of odorous air contaminants from
 fish meal driers is possible, though costly. It
 is, however,  the only feasible method presently
 available to control driers operated under high-
 temperature conditions.  This occurs when the
 operator  processes fish meal at such a rate that
 the drier gases emerge at a temperature above
 300° F, and the feed scrap is  subjected to hot
 gases between 1,200° and 1,700°  F.

 A properly designed afterburner control system
requires a dust collector ahead of  the afterburner
to remove solids that cannot readily be  burned.
The incineration of solid particulates at 1,200°F
or lower can result in partial oxidation  of partic-
ulates, -which tends to increase rather than de-
crease odor concentrations.  A contact  condenser-
scrubber  removes  much of the difficult-to-burn
particulates and materially reduces the volume
rate by condensing the  moisture.   If the partic-
ulate matter concentration in gases to the after-
burner is  sufficiently small, incineration at
 1,200°F reduces odor concentrations to about
 50 odor units per scf.   Owing to the high cost
of fuel in  such an arrangement, few large in-
 stallations of afterburners serve fish meal
driers.   To make incineration economically at-
tractive,  heat from the afterburner should be
 reclaimed in some manner.  The most  likely
arrangement is the preheating of air to the drier.
An afterburner operating at  1,200°F provides
all the heat necessary to operate the drier, which
thus eliminates the need for a firebox.

 Chlorinating and Scrubbing Drier  Gases

 A unique  scrubber-chlorinator design has been
 developed to control the odors from fish meal

-------
                              Fish Canneries and Fish Reduction Plants
                                            813
driers.  Units of this design have proved to be
satisfactory, provided the driers are operated
under low-temperature conditions.  During low-
temperature operation, the drier exit gas tem-
perature is not allowed to exceed 200°  F.  The
driving force for drying air and products of com-
bustion is maintained below 6 Btu per scf,  and
the temperature at the zone -where the fish scrap
enters is maintained below 600"  F. Such strin-
gent conditions placed upon the operation of the
drier cause the production rate to be reduced to
approximately one-half of design if the moisture
content of the dried meal is to be maintained at
an acceptable level.  This unit is demonstrated
in the flow diagram of Figure 621 and pictured in
Figure 622.

The process depends largely upon the reaction of
chlorine  gas with odorous compounds at drier exit
temperatures.  As shown in Figure 621, gases
from the drier  are first directed through a cyclone
separator to remove fine particulates. Chlorine is
then added at a rate calculated to provide a concen-
tration of 20 ppm by volume in the gas  stream.
The reaction is allowed to proceed at about 200° F--
the drier exit temperature--in the ductwork for
approximately 0.6  second before the stream is
chilled and  scrubbed with sea water in a packed
tower.  Gases pass up through the packing coun-
tercurrently to the sea water.

In Figure 623,  odor concentrations from the
scrubber exit are plotted against the chlorine
addition  rate at constant gas and sea water
throughput.  As can be seen from the curve,
odors  reach a minimum at about 20 ppm chlo-
rine.  When more than 20 ppm is added, chlo-
rine odors become readily detectable in treated
gases,  and odor concentrations tend to increase.
All the odor measurements used to draw this
curve  were made  on drier gas samples taken
between 170°   and 205°F, when there was es-
sentially no overheating of meal in the drier.
This method provides an overall odor reduction
of 95 to 99 percent when fresh fish scrap is being
processed in the drier.  Chlorination itself pro-
vides a 50 to 80 percent reduction  in odor con-
centration. Scrubbing reduces the remaining
odor concentration by another 50 to 80 percent.
Condensation provides a 12 to 22 percent re-
duction in  volume, depending upon the original
moisture content of the gases.

The exact  mechanism of the chlorination reac-
tion is uncertain,  but  it is assumed that chlorine
reacts with odorous compounds, probably amines,
to form additional products that are less odorous
than the original compounds.  Chlorine is not
considered to be a sufficiently strong oxidizing
agent to oxidize fully the odorous organic mate-
rials present in drier gases.

Controlling Reduction Cookers and Auxiliary
Equipment

There  is a tendency for the operator to use more
live steam to cook fish scrap before it is fed into
the rotary drier if low-temperature operation  of
the drier itself is  employed.  The  entire prepara-
tion of the  drier feed is carried out at tempera-
tures above 170°F, and large volumes of contam-
inated  steam are released to the atmosphere.
These  occur at the cooker, press,  grinder, and
press-water screen and  sump.  They can be con-
                                                CHLORINE GAS
                                                                          TO ATMOSPHERE.
                  Figure 621.  A chlorinator-scrubber odor  control system venting a fish
                  meal drier.

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814
CHEMICAL PROCESSING EQUIPMENT
  Figure 622. A chlorinator-scrubber odor  control
  system venting a fish meal drier (Star-Kist
  Foods, Inc., Terminal Island,  Calif.).

trolled by hooding the component parts and  ex-
hausting to  a condenser followed by an after-
burner.   The firebox of the rotary drier  may
provide a satisfactory substitute for the  after-
burner if adequate control is maintained on the
drier exit gases.

Controlling Digesters

Digester gases are  most easily controlled with
afterburners.  These gases are small in volume
and require only minimal fuel for incineration.
Digester offgases contain no appreciable moisture
or particulates.   Odor concentrations can normal-
ly be reduced by 99 percent or more at 1, 200°F
in a properly designed afterburner.

Controlling Evaporators

Evaporators for stick water,  press water,  and
digested liquor can be controlled with condensers
and afterburners  and combinations thereof.  Most
                                                                          NOTE  SAMPLES HEBE COLLECTED HHEM DRIER DISCHARGE
                                                                              TEKPERATDRES HERE BELO* 205°F  A! HIGHER
                                                                              TEMPERATURES ODOR LEVELS INCREASE MARKEDLY
                                                                              REGARDLESS OF CHLORIUE COHCENTBUT>0»
                                                         0        5       10       15       20       25       30
                                                                 CHLORINE GAS ADDITION RATE, ppm by volume
                                                       Figure  623.  Exit  odor concentrations from a chlo-
                                                       rinator-scrubber  as  a function of the chlorine gas
                                                       addition  rate.  Temperatures of gas discharged from
                                                       drier are  less  than  205°F.
                        evaporators are equipped with water ejector con-
                        tact condensers to provide the necessary vacuum
                        in the one effect of the multiple evaporator effects.
                        Condensate temperatures from these  ejectors  are
                        usually less than 80 °F.  As  a result,  they con-
                        dense and dissolve most of the  odorous compounds
                        that would otherwise be discharged to the atmo-
                        sphere.   Condensate cannot  be  circulated through
                        cooling towers  without causing  the emission of
                        strong odors.   Ideally,  sea  water or harbor
                        water is used for this purpose, with no recircu-
                        lation.  The entrained air contaminants do not
                        add enough material to tail waters to create a
                        water pollution problem.

                        If water ejectors are not used, odorous air con-
                        taminants are  emitted in much heavier concen-
                        tration.  The most likely alternative is a steam
                         ejector  and surface-type aftercondenser,  possi-
                        bly with multiple ejector stages.  Noxious  odors
                        from an  operation such as this are stronger and
                        more voluminous than those emitted from contact
                        condensers.  Hooding of the condenser hot-well
                        and exhausting to an afterburner operating at
                         1,200° F or greater is usually the most feasible
                        means of controlling these processes.   Activated
                         carbon can be  used in lieu of an afterburner.

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                                 Reduction of Inedible Animal Matter
                                             815
Collecting Dust

As previously noted, fish meal does not contain
a large amount of extremely fine particles,  that
is, those less than 10 microns.  For this  reason,
cyclone separators are normally sufficient to
prevent excessive emissions from the drier and
subsequent pneumatic conveyors.  If the meal
from a particular plant were to contain appre-
ciably more fine material than the sample shown
in Table 218,  more efficient dust collectors,
such as small-diameter, multiple  cyclones  or
baghouses, would have to be used.


Controlling Edible-Fish Cookers

Exhaust gases from both precooked and wet-fish
process  cookers consist essentially of water
vapor.  At tuna  cookers, most of this vapor is
condensed in the steamtraps on the cookers. If
further control is desired,  an  afterburner,
carbon adsorber, or low-temperature contact
condenser is recommended.

The hot-exhaust  boxes of wet-fish  processes
represent large odor sources that  can be  con-
trolled with contact condensers, often at little
expense  to the operator.  Most canneries  are
located near large bodies of water.  Sea water
or harbor water  can be directed to contact con-
densers  at little  cost in  these instances.   Since
exhaust box gases are principally -water,  there
is a marked reduction in volume across a con-
denser such as this,  in addition  to a decrease
in odor concentration.

         REDUCTION  OF INEDIBLE

             ANIMAL  MATTER
Animal matter not suitable as  food for humajis
or pets is converted into salable byproducts
through various reduction processes. Animal
matter reduction is the principal -waste disposal
outlet for slaughterhouses, butcher shops,
poultry dressers, and other processors of
flesh loods.  In addition, it is used to dispose
of whole animals such as cows, horses, sheep,
poultry,  dogs, and cats that have died through
natural or accidental causes.   If it were not
for reduction facilities,  these  remains would
have to be buried to prevent a  serious health
hazard.  The principal products  of reduction
processes are proteinaceous meals, which find
primary use as poultry and livestock feeds,  and
tallow.

Much reduction equipment is operated in meat-
packing plants to handle  only the "captive" blood,
meat,  and bone scrap offal produced on the
premises. Other reduction cookers and driers
are located in scavenger rendering plants,
 which are operated solely for the byproducts.
 In Figure 624,  "dead stock" is shown awaiting
 dismemberment at a scavenger plant.   Com-
 mon rendering  cooker feedstocks are pictured
 in Figure 625.  In general, the materials pro-
 cessed in captive packing house systems are
 fresher than those handled at  scavenger plants
 where feedstocks can be highly decayed.  Typ-
 ical slaughterhouse yields  of inedible offal,
 bone, and blood are listed in  Table 220.
 Figure 624.   Dead  stock  awaiting skinning and dis-
 memberment at a  scavenger rendering plant (Califor-
 nia Rendering Co..Ltd., Los Angeles,  Calif.).
Figure  625T  Inedible animal  matter  in the receiving
pit of  a  rendering system (California Rendering  Co.,
Ltd., Los Angeles, Cali f.).

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816
CHEMICAL PROCESSING EQUIPMENT
 Table 220.  INEDIBLE, REDUCTION PROCESS
        RAW MATERIALS ORIGINATING
           FROM SLAUGHTERHOUSES
         (The Globe Co.,  Chicago,  111.)
Source, Ib live wt
Steers, 1, 000
Cows
Calves, 200
Sheep, 80
Hogs, 200
Inedible offal and bone,
Ib/head
90 to 100
110 to 125
15 to 20
S to 10
10 to 15
Blood,
Vb/head
55
55
5
4
7
The animal  "Batter reduction industry has been
traditionally considered one of the "offensive
trades. "  The reputation is not undeserved.
Raw materials and process exhaust gases are
highly malodorous and capable of eliciting nui-
sance complaints in surrounding areas.  In
recognition  of these facts, specific air pollution
control regulations have been enacted requiring
the control of odorous process vapors.

Rendering is  a specific heated  reduction
process wherein fat-containing  materials are
reduced  to  tallow  and  proteinaceous meal.
Blood drying, feather cooking, and grease re-
claiming are other reduction operations usually
performed as companion processes in render-
ing plants.

Reduction processes are influenced largely by
the makeup of feedstocks.  As can be seen from
Table 221, some materials,  such as blood and
feathers,  are essentially grease  free, while
others contain more than 30 percent tallow.
Where no  tallow is present, the reduction pro-
cess becomes primarily evaporation -with, possi-
bly, some thermal digestion.
                       BATCHWISE  DRY RENDERING

                       The most wide.ly used reduction process is dry
                       rendering,  wherein materials containing tallow
                       are heated  indirectly, usually in a steam-jac-
                       keted vessel.  Heat breaks  down the flesh and
                       bone structure,  allowing tallow to separate
                       from  solids and water. In the process, most
                       of the moisture  is evaporated.   Emissions con-
                       sist essentially  of steam with small quantities
                       of entrained tallow, solids, and gases.

                       Dry rendering may be performed batchwise or
                       continuously and may be accomplished at pres-
                       sures greater or less than atmospheric.   A
                       typical batch-type, steam-jacketed, dry render-
                       ing cooker  is  shown in Figure 626.  These ves-
                       sels  are normally charged with 3, 000 to 10, 000
                       pounds of animal matter per batch. The cookers
                       are equipped with longitudinal agitators that are
                       driven at 25 to 65  rpm.  Each batch is cooked
                       for 3/4 to 4 hours.

                       Pressures  of  50 psig and greater are  used to
                       digest bones,  hooves, hides, and hair.  At the
                       resulting temperature (about 300°F),  these
                       materials are reduced to a  pulpy  mass.  In typ-
                       ical dry-pressure-rendering cycles, the cooker
                       vent  is initially  closed to cause pressure and
                       temperature to increase.  Some materials are
                       cooked as long as  2 hours at elevated  pressure
                       to obtain the necessary digestion.  After pres-
                       sures a.re reduced, the batch is cooked or dried
                       to remove additional  moisture and to complete
                       tallow-solids  separation.

                       Some dry rendering operations  are carried out
                       under vacuum to remove moisture rapidly at
                       temperatures  sufficiently low to inhibit degrada-
                       tion of products.  Vacuum rendering processes
                Table 221.  COMPOSITION OF TYPICAL INEDIBLE RAW MATERIALS
                              CHARGED TO REDUCTION PROCESSES
                                  (The  Globe Co.,  Chicago, 111.)
Source
Packing house offal and bone
Steers
Cows
Calves
Sheep
Hogs
Dead stock (whole animals)
Cattle
Cows
Sheep
Hogs
Blood
Feathers (from poultry houses)
Butcher shop scrap
Tallow or grease,
wt %
15 to 20
10 to 20
8 to 12
25 to 35
15 to 20
12
8 to 10
22
30
37
Solids,
wt %
30 to 35
20 to 30
20 to 25
20 to 25
18 to 25
25
23
25
25 to 30
12 to 13
20 to 30
25
Moisture ,
wt %
45 to 55
50 to 70
60 to 70
45 to 55
55 to 67
63
67 to 69
53
40 to 45
87 to 88
70 to 80
38

-------
                                Reduction of Inedible Animal Matter
                                            817
r

<^
D C

H C

6^
D L

n c

A>JJr %/*'*?« >
 are essentially all of the batch type.  The vacu-
 um is usually produced with a precondenser,
 steam ejector,  and aftercondenser.  Cooker
 pressures are close to atmospheric at the start,
 then diminish markedly as the moisture content
 of the charge decreases.  Vacuum rendering
 produces high-quality tallow but has a  disadvan-
 tage in that temperatures are low and incomplete
 cooking of bones, hair,  and so forth, may occur.
 CONTINUOUS DRY RENDERING

 Because of the increased demand for processing
 meat,  bone, and offal,  highly mechanized con-
 tinuous dry rendering processes are used today.
 The advantages readily become  apparent when it
is shown that one operator can process 1-1/4
million pounds of material in 16 hours.  It would
Figure 626.  A horizontal,  batch-type, dry-rendering
cooker equipped with a charging elevator (Standard
Steel Corp., Los Angeles,  Calif.).

otherwise take 40 batch cookers and an undeter-
mined crew of men to produce the same volume
of throughputo  Some processes consist essen-
tially of a series of grinders, steam-jacketed
conveyor-cookers,  and presses.   The  continuous
system of Figure 627 uses recycle tallow and a
vertical-tube vacuum cooker. Selected meat and
bone scrap is ground and  slurried with hot tallow
before being charged to the cooker. Slurry is
circulated through the tubes, and vapors are
vented to a contact  condenser.  Steam is con-
densed ahead of the ejector, and a barometric
leg is employed.  Tallow and solids are  continu-
ously withdrawn from the bottom of the cooker.

In another continuous system, material is con-
veyed to a hasher or hogger before it is fed to the
first cooker.  Here the temperature is brought
up to approximately 180° F.  Then the material is
fed to a high-speed hammer mill or blender be-
fore it is conveyed to the next cooker. The mate-
rial is brought up to a temperature of about 210°  F
in the second cooker  and then continuously con-
veyed to a stacked set of finishing cookers.  The
finishing cookers consist  of long jacketed continu-
ous-tube screw conveyors where the material is
brought up to 275° F  before it is discharged onto
a screen or into a prepresser.   The prepresser,
a press with extra spacing, gently  squeezes the
crax before it is fed to a press, or many presses
in parallel.  The press-cake is ground in a high-
speed hammer mill and emerges as a meat meal
product. Pressed and free-running tallow is
settled, centrifuged,  bleached, dried,  and fil-
tered to a premium grade tallow.

Another continuous  process consists of a hasher
and one large continuous-tube cooker without

-------
818
                              CHEMICAL PROCESSING EQUIPMENT
                               «ATER SUPPLY

                        BAROMETRIC CONDENSER x

                             DISINTEGRATOR
      RAW MATERIAL
  PREBREAKER
 STEAM SUPPLY


-AIR AND NON CONDENSIBLE EJECTOR
    TRAMP METAL DISCHARGE
                   HATER DISCHARGE
    Figure 62V.  A continuous,  vacuum  rendering system employing tallow recycling (Carver-Greenfield
    Process,  The V.D.  Anderson Co., Cleveland, Ohio).
finishing  cookers.  The material is brought to
250° to 300° F before being discharged to the
prepresser.  The feed rate to a unit without
finishing  cookers must necessarily be adjusted
to allow more residence time in the single cooker.

Another variation in the finishing cycle involves
the use of a multiple-effect evaporator.  The
feed rate  through the continuous-tube cooker may
be approximately doubled and the material
emerges  half-cooked at approximately 210° to
220° F.   The steam driven off from the half-
cooked material goes to an evaporator, where
the remainder of the moisture is cooked off at a
temperature of approximately 190° F and a
vacuum of approximately 27 inches of water
column.

WET RENDERING

One of the  oldest reduction methods is the wet
process,  wherein animal matter is cooked in a
closed vessel  with live steam.  There is little
evolution of steam.  Most of the contained mois-
ture is removed as a liquid.  Live steam is fed
to a charge in a closed, vertical kettle until the
  internal pressure reaches approximately 60 psig
  (about 307°F).   Heat causes a phase separation
  of water,  tallow,  and solids.  After initial cook-
  ing,  the pressure is  released,  and some steam
  is flashed from the system.  The charge is then
  cooked at atmospheric pressure until tallow
  separation is complete.  Water, tallow, and
  solids are  separated by settling,  pressing, and
  centrifuging.
  The water layer from a wet rendering process
  contains 6 to 7 percent solids.  Soluble  proteins
  can be recovered by evaporation, as in  the
  processing of stick water at fish reduction
  plants.
  Wet rendering finds some use today in the han-
  dling  of dead stock, namely whole animals that
  have died through accidents or natural causes.
  It has given way to dry rendering at most pack-
  ing houses and scavenger plants.  Wet rendering
  is  used to a limited degree in the production of
  edible fats and oils, as noted previously in this
  chapter.

-------
                                  Reduction of Inedible Animal Matter
                                              819
 REFINING RENDERED  PRODUCTS

At the completion of the cook cycle,  tallow and
 solids are run through a series of separation
 equipment as in the integrated plant  of Figure
 628.  Some systems are more complex than
 others, but the essential purpose is to produce
 dry, proteinaceous cracklings and  clear,  mois-
 ture-free tallow.   In almost  all cases, the cook-
 ers are discharged into perforated percolator
 pans that allow free-running tallow to drain from
hot solids.  The remaining solids are pressed to
 remove residual tallow.  Dry cracklings are usu-
 ally ground to a meal before being marketed. In
 Figure 629,  grease-laden cracklings are being
 dumped from a percolator pan after free tallow
 has been drained.

 Tallow from the percolators and presses is
 further treated to remove minor quantities of
 solids and water.   Solids may be removed in
 desludging centrifuges, filters, or settling tanks.
 Traces of moisture are often removed from it
by boiling or  blowing  air through heated tallow.
 Some operators remove moisture by settling in
 cone-bottom tanks, often with the aid of soda
 ash or sulfuric acid to provide better phase
 separation.
Belgian De Smet process,  in which hexane is
employed, has been adopted by some Tenderers
in the  United States and Canada.  The entire
process  is enclosed in a vaportight building to
minimize the explosion hazard.  After extrac-
tion, hexane is  stripped from tallow and solids.
The only measurable  air contaminants, solvent
vapors,  are vented at one  or more  condensers.


DRYING BLOOD

Animal blood is evaporated and thermally di-
gested to produce a dry meal used as  a fertiliz-
er, as a livestock feed  supplement, and, to a
limited degree, as a glue.   Blood contains only
10 to 15  percent solids and essentially no fat.
At most  packing houses, it is  dried in horizontal,
dry rendering cookers.   In typical slaughtering
operations, blood is continually drained from
the kill floor to one or more cookers, throughout
the day.   Initially, while there is  appreciable
moisture in the blood, heat transfer through the
jacket  is reasonably rapid. As the moisture
content decreases, however, heat transfer be-
comes slower.  During the final portion of the
cycle,  drying is extremely slow,  and dusty meal
can be entrained in exit gases.
In some instances,  solvents  are used to extract
tallow from rendered solids.  Solvent extraction
allows extremely fine control of products.   The
In some instances,  a tubular evaporator is used
to remove the initial portion of the water.  When
the moisture content decreases to about 65 per-
                                EXHAUST VAPORS TO CONTROL  EQUIPMENT
             DUMP
             PIT



HOGGER

i
COOKER
NO 1

t
PERCOLATOR
NO. 1


1
COOKER
NO 2

t
PERCOLATOR
NO 2



J
COOKER
NO 3

t
PERCOLATOR
NO 3
                                                                              FINISH
                                                                              TALLON
                                                                          SETTLING
                                                                          TANK
                                     MEAL
                                                                                        GRINDER
                                                                                        SURGE
                                                                                        BIN
                                                                              TALLO*
                              CRACKLINGS TROUGH KITH SCREK CONVEYOR
             DRAINED CRACKLINGS
                                                                                     EXPELLER
                                                                                     PRESS
                 Figure  628.  An. integrated dry rendering plant equipped with batch
                 cookers,  percolators,  a cracklings press,  and a tallow-settling tank.
   234-767 O - 77 - 54

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820
                              CHEMICAL PROCESSING EQUIPMENT
Figure  629. Tallow-laden cracklings being dumped
from a  percolator after  free  tallow has been  allowed
to drain (California  Rendering Co., Ltd.,  Los Angeles,
Cal i fornia).
cent, the material is transferred to a dry ren-
dering cooker for final evaporation.

Continuous dry rendering is also used to process
blood into blood meal.  The raw or green blood
is screened and air blown,  then fed to a continu-
ous coagulator where the blood is "set" with live
steam.   It then goes to a separator, where serum
is removed from the  coagulated blood.  The co-
agulated blood is then fed into  a recycling hot-air
drying system called a Ring drier.  The Ring
drier system consists of a feed port and hammer
mill where the coagulated blood is fed into the
system.   It is pulverized in an atmosphere of
180° to 200° F and blown to the manifold where
it meets  the air from the furnace.  The furnace
gases of 600°  to 800° F provide the make-up air
to the system and enter at the  control manifold.
Control dampers are located in the manifold and
regulate  the recirculation rate of the material as
well as the product take-off ratio.  A  cyclone col-
lecting system also is ducted to the control mani-
fold and  driven by an exhaust fan at the  outlet.
Product  is withdrawn through  star valves located
in the solids discharge leg of the cyclones.

Some animal blood is spray dried to produce
a plywood glue that commands  a price con-
siderably higher than that of fertilizer or live-
stock feed.  This is an air-drying process,  and
exhaust gases are markedly more voluminous
than those of rendering equipment.  Feedstocks
are usually concentrated in an evaporator be-
fore the  spray drying.
 PROCESSING FEATHERS

 Poultry feathers are  pressure cooked and sub-
 sequently dried to produce a high-protein meal
 used principally as a poultry feed supplement.
 Feathers, like blood, contain practically no fat,
 and meal is the only product of the system.
 Feathers are pressure cooked at about 50 psig
 to hydrolyze the protein keratin, their principal
 constittaent.  Initial cooking is usually carried
 out in a dry rendering cooker.  Final moisture
 removal may be accomplished in the cooker at
 ambient pressure or  in separate air-drying
 equipment.  Rotary steamtube air driers, such
 as that  shown in Figure 630, are frequently
 used for this purpose.  If separate driers are
 employed,  the  material is transferred from
 cooker to drier at a moisture content of about
 50 percent.

 The Ring drier described under  "Drying  Blood"
 can also be used to dry feather meal.  However,
 continuous dry rendering of poultry feathers still
 appears to be in the pilot stage.  The pressure
 required to break down the feathers requires
 choking in the continuous-tube cookers.  Another
problem is the lack of free-running tallow for
 heat transfer.  Economically,  although a large
 continuous supply of feed feathers is  available,
 continuous rendering  does not  show the tremen-
 dous advantage for feathers that it does for meat
 and bone for tallow and meat meal because of the
 relatively lower price for feather meal.

 ROTARY  AIR DRIERS

 Direct-fired rotary driers are seldom used in
 the reduction of inedible packing house waste
 or dead stock.   As noted previously in this
 chapter, they find wide use in the reduction of
 fish scrap.  Fired driers have been used to a
 limited degree to dry -wet rendering  tankage
 and some materials  of low tallow content.
 Where air driers are required,  steamtube
 units are generally more satisfactory from the
 standpoint of both product quality and odor emis-
 sion.
 THE AIR POLLUTION PROBLEM

 Malodors are the principal air contaminants
 emitted from inedible-rendering equipment and
 from other heated animal matter reduction pro-
 cesses. Reduction plant odors emanate from
 the handling and storage of raw materials  and
 products as well as from heated reduction pro-
 cesses.  Some feed materials are highly decayed,
 even before delivery to scavenger rendering
 plants, and the  grinding, conveying, and storage
 of these materials cannot help but generate some
 malodors.  Cooking and drying processes  are,

-------
                                     Reduction of Inedible Animal Matter
                                              821
   SIDE ELEVATION SHOWING
    ARRANGEMENT OF TUBES
           MATERIAL DISCHARGE
                     FRONT ELEVATION SHOWING STEAM FLOW
            VARIABLE FEEDER-OPTIONAL - USED
             r-WITH PARALLEL DRYER SYSTEMS
                                  MATERIAL INLET
                                                               AIR EXHAUST
                                                                                        CONDENSATE
                                                                                          OUTLET
                                                                                 — MATERIAL DISCHARGE

                                                                               OUTER PIPE
                                                           CUTAWAY OF PIPES
nevertheless,  considered the largest odor sources,
and most odor control programs have been di-
rected at them.  Handling and storage odors can
usually be kept to a tolerable minimum by fre-
quently washing working surfaces and by pro-
cessing uncooked feedstocks as  rapidly as possible.

McCord and Witheridge (1949),  who discuss
the "offensive  trades" at length, attribute
rendering plant malodors to a variety of  com-
pounds.   Ronald (1935) identifies rendering
odors as principally ammonia,  ethylamines,
and hydrogen sulfide,  all decomposition products
of proteins.  Skatole, other amines,  sulfides,
and mercaptans are  also usually present.  Tallow
and fats do not generate as great quantities of
odorous materials.  Aldehydes, organic acids,
and other partial oxidation products are the
principal odorous breakdown products  of fats.
Putrescine, NH2 (CH^^NH^, and cadaverine,
NH2(CH2)5NH2,  are two extremely malodorous
diamines associated with  decaying flesh and
rendering plants.  Several specific compounds
have extremely low odor thresholds and are de-
tectable in concentrations as small as  10 parts
per billion  (ppb).  Odor threshold concentra-
tions of compounds are listed in Table D2,
Appendix D.  Many suspected compounds have
not been positively identified nor have  their
odor thresholds been determined.

-------
822
CHEMICAL PROCESSING EQUIPMENT
Cookers As Prominent Odor Sources

When animal matter is subjected to heat, the
cell structure breaks down liberating volatile
gases and vapors.  Further heating causes some
chemical decomposition,  and the resultant prod-
ucts  are often highly odorous.  All these mal-
odorous  gases and vapors  are entrained in ex-
haust gases.

Exhaust  products from cooking processes  con-
sist essentially of steam.  Entrained gases and
vapors are, nevertheless, highly odorous  and
apt to elicit nuisance complaints in areas  sur-
rounding animal matter reduction plants.  Odor
concentrations measured in exhaust gases of
typical reduction processes are listed in Table
222.   Evidently there is a  wide variation in
odor concentrations  from similar equipment.
For instance, dry-batch rendering processes
range from 5, 000 to 500, 000 odor units  per  scf,
depending principally upon the type and "ripe-
ness" of feedstocks.  Blood drying can be  even
more odorous,  with concentrations  as great as
1 million odor units  per scf if the blood is allowed
to age for only 24 hours before processing.  High-
ly odorous steam emissions  also are generated
whenever fresh feed material is  dropped into a
hot cooker.  Approximately 4 hours rest time
would be required between loads to prevent fresh
material from being distilled during the loading
operation.
                       Odors From Air Driers

                       As can be  seen from Table 222, feather drier
                       odor concentrations, though generally smaller,
                       are more variable than those from rendering
                       cookers.  Their largest odor concentrations--
                       25,000 odor units per scf--are associated with
                       operations where feedstocks are putrefied or
                       not completely cooked beforehand or where  the
                       meal is overheated in the drier.  Under optimum
                       conditions,  odor concentrations from these  driers
                       should not  exceed 2, 000 odor units per scf.  With
                       blood spray driers, where extreme care is  main-
                       tained to ensure freshness of feedstocks,  con-
                       centrations can be  less than 1, 000 odor units per
                       scf.  In general, air drier odor concentrations
                       are less than those of cookers for the following
                       reasons:  (1) In most instances feedstocks are
                       cooked or partially evaporated before the air
                       drying;  (2) odorous gases are more dilute in
                       drier exit gases;  (3) feedstocks are often fresher.

                       Odors and Dust From Rendered-Product Systems

                       Some odors and dust are emitted from cooked
                       animal matter  as it is separated and refined.
                       The heaviest points of odor emission are the
                       percolators into which hot cooker  contents are
                       dumped.  Steam and odors evolve  from the  hot
                       material, particularly during times of cooker
                       unloading.   Cookers  are normally dumped at or
                       near 212°F.
                  Table 222.  ODOR CONCENTRATIONS AND EMISSION RATES FROM
                                 INEDIBLE REDUCTION PROCESSES
Source
Rendering cooker,
dry-batch type
Blood cooker,
dry-batch type
Feather drier,
steamtubec
Blood spray
drier0' d
Grease-drying tank,
air blowing
156°F
170°F
225°F
Odor concentration,
odor unit/scf
Range
5, 000 to
500, 000
10, 000 to
1 million
600 to
25,000
600 to
1, 000





Typical average
50, 000

100, 000

2, 000

800



4, 500
15, 000
60, 000
Typical moisture
content of
feeding stocks, %
50

90

50

60

< 5




Exhaust products,
scf/ton of feeda
20, 000

38, 000

77, 000

100, 000

100 scfm
per tank



Odor emission
rate, odor unit/
ton of feed
1, 000 x 106

3, 800 x 106

153 x 106'

80 x 106






 aAssuming 5 percent moisture in solid products of system.
 ^Noncondensable gases are neglected in determining emission rates.
 cExhaust gases are assumed to contain 25 percent moisture.
 ^Blood handled in spray drier before any appreciable decomposition occurs.

-------
                                Reduction of Inedible Animal Matter
                                                                                                 823
Table 223 shows odor threshold concentrations of
emissions from cookers during the dumping oper-
ation.  The type of material being rendered has a
great effect on the  odor concentration.  As indi-
cated,  meat and bone trimmings from restaurants,
•which contain large quantities of rancid grease,
produce high odor concentrations which would
require hooding and incineration in an afterburner.
Entrails from turkeys and chickens would be bor-
derline, as shown in the table.  The type of mate-
rial, quantity of tallow or grease in the batch,
freshness of  the material, and unloading tempera-
tures all are factors which influence the odor con-
centration.  Each rendering operation should be
sampled for odors before deciding whether or not
air pollution  control equipment is required for
the dump operation.

Odorous steam emissions and smoke generated
by the presses usually require control.  Centri-
fuges and settling tanks where meal and tallow
are heated to accomplish the desired separation
also emit odorous steam.

The grinding of pressed solids, and subsequent
meal conveying are the only points of  dust emis-
sion from rendering systems.   These particulates
are reasonably coarse, and dust is usually not
excessive.

Grease-Processing Odors

Some odors are generated at processing tanks
when moisture is removed from grease or tallow
by boiling or by air blowing  or both.   If air is
used for this purpose, exhaust volumes seldom
exceed 100 scfm, but odor concentrations are
measurable.  Odor concentration is a function
of operating temperature.  As shown in Table
222, measured concentrations have been found
to range  from 4,500 odor units per  scf at 150° F,
to 60,000 odor units per scf at 225° F.  Odor
concentrations vary greatly with the type of
grease processed and the air  rate,  as -well as
with temperature.

Row-Materials Odors

Some malodors emanate from the cutting and
handling  of raw materials.  In most instances
these emissions are not great.  Odors usually
originate at the point where raw material is
first sliced,  ground, or otherwise  broken into
smaller  parts.  Most feedstocks are ground in
a hammer mill before the cooking.  Large,
whole animals (dead stock) must be skinned,
eviscerated, and at least partially  dismembered
before being fed to rendering  equipment.  If the
animal is badly decomposed,  this skinning and
cutting operation can evolve strong odors.

HOODING  AND VENTILATION REQUIREMENTS

All heated animal matter reduction processes
should be vented directly to control equipment.
Hooding  is used in some instances  to  collect
malodors generated in  the processing of raw
materials and cooked products.

The loading of material into a hot  batch cooker
generates highly odorous steam emissions.  It is
impractical to require a cooker to  be  cooled be-
    Table 223.  ODOR CONCENTRATIONS OF EMISSIONS FROM INEDIBLE RENDERING COOKERS
                               DURING THE DUMPING OPERATION
Type of material cooked
Poultry feathers
Entrails from turkeys and chickens
Meat and bone trimmings with large quantities
of rancid restaurant grease
Fresh meat and bone trimmings from a beef
slaughterhouse
Mixture of dead cats and dogs, fish scrap,
poultry offal, etc.
Slaughterhouse viscera and bones
Emissions during
dump from cooker,
odor units/cf
200
2,000
25, 000
40, 000
100
1,000
150
200
Emissions 5
minutes after
dumping,
odor units/cf
20
500
3, 000
200
70
1,500
150
Emissions x
minutes after
dumping,
odor units/cf
-
-
-
-
800a
I50b
 x = 7 minutes.
 x = 18 minutes.

-------
824
CHEMICAL PROCESSING EQUIPMENT
fore receiving the next charge.  One method to
prevent escape of air contaminants during the
loading of a cooker is  to provide a choked feed
arrangement. A hopper maybe constructed above
the cooker that holds one full load.  The material
is dumped quickly and there is enough mass of
material to prevent  steaming.  Another method
is to blow the material into the cooker  through a
closed feed system.

The methods described above, unfortunately, are
not feasible for loading poultry feathers because
of their density and texture.  Grinding the feathers
beforehand has not proven to be satisfactory.  A
successful method to control the loading of feathers,
however, has been developed. The feather cooker
is provided with a separate dome  and vent at the
drive end. Both  exhaust systems may  be valved
at the dome.  An indraft of 100 fpm  through the
charge door is usually adequate.  The exhaust
system used for cooking must be closed during
the loading cycle and vice versa.

If highly decayed dead stock is being processed,
the entire dead stock room should be ventilated
at a rate of 40 or more air changes  per hour for
•worker comfort.   Areas should also be ventilated
where raw materials are stored unrefrigerated
for any appreciable time before processing.

Hooding may be employed on raw-material
grinders preceding cookers and percolator
pans and expeller presses used to handle
cooked products.   Although the volume  of
steam and odors evolved at any of these points
does not exceed  100  cfm, greater volumes are
normally required to offset crossdrafts.  In-
draft velocities of 100 fpm under hoods are usu-
ally satisfactory.


Emission Rates From Cookers

The ventilation rates of cookers can be esti-
mated directly from the quantity of moisture
removed and the time  of removal.  Maximum
emission rates from dry cookers are approxi-
mately twice the average moisture evaporation
rates.  In the determination of exhaust volumes,
noneondensable gases can normally be neglected.
Consider a batch cooker that removes 3, 000
pounds of moisture from. 6, 000 pounds  of animal
matter in 3 hours, a relatively long  cook cycle.
The average rate of emission is 16.7 pounds
per minute or 450 cfm steam at about 212°F.
The instantaneous evaporation rate and cumula-
tive moisture removal are plotted in Figure
631.  The maximum evolution rate apparently
occurs near the initial portion of the cook at
29 pounds per minute or 790 cfm at  212°F. As
moisture is removed from a batch cooker,  the
heat transfer rate decreases, the temperatures
                           Figure 631.  Steam emission pattern  from a
                           batch-type,  dry  rendering cooker  operated
                           at ambient  pressure.

                       rise,  and the evaporation rate falls off.  The
                       general shapes of the curves in Figure 631 are
                       typical of batch-cooking cycles.  Where cook
                       times are appreciably shorter,  evaporation
                       rates  are greater; nevertheless, the  ratio of
                       maximum to average evaporation rate is main-
                       tained at approximately 2 to 1.

                       The length of a cooking cycle,  and  the evapo-
                       ration rate are dependent upon the  temperature
                       in the steam jacket,  and the rotational  speed
                       of the agitator.  The highest permissible agita-
                       tor  speeds (about 65 rpm) can result  in cooking
                       times of 45  minutes  to  1 hour.  Many operators,
                       particularly at  packing  houses,  use slower
                       agitator speeds, and cycles are as  long as 4
                       hours.

                       If vacuum cooking is employed, volume rates
                       and temperatures decrease as the batch pro-
                       gresses.  With these systems,  the vacuum-
                       producing devices largely govern cooking times.
                       The evaporation rate in a vacuum system is lim-
                       ited by the rate at which steam can be  removed,
                       usually by condensation.  If vapor  cannot be
                       condensed as fast as it  is evaporated, the cycle
                       is merely lengthened.

                       Pressure cookers have a slightly different emis-
                       sion pattern, but maximum emission rates are
                       again twice  the average.  During the initial
                       portion of the cycle, there  are  no emissions
                       while pressures are increasing to  the desired
                       maximum.  The cooker is vented at  elevated

-------
                                Reduction of Inedible Animal Matter
                                            825
pressure, usually about 50 psig.  High-pres-
sure vapors are relieved through small bypass
lines  so that the surge of steam is not more than '
the control system can handle.  Most of the con-
tained moisture is evaporated after pressures
are reduced to ambient levels.

Vapor emission rates from wet rendering cook-
ers are considerably lower than those from dry
cookers, comparable to  initial volumes during
pressure cooking.  Only enough steam  is flash
evaporated to  reduce the pressure to 1  atmos-
phere.  The large percentage of moisture in
a •wet rendering process is removed as water
by physical separation rather than by evapora-
tion.

Emission rates from continuous,  dry rendering
processes are steady and can be calculated
directly from the moisture content of feedstocks
and products.   To lower the  moisture content
from 36 to 6 percent in typical meat, bone,  and
offal scrap, 2,750 scfm or 110 pounds  of steam
per minute would be evaporated if the charge
rate to the cooker were 20,000 pounds  per hour.
Since it is difficult to operate continuous  systems
gas-tight, it is necessary to produce an indraft
at the feed and outlet ends of the system in order
to ensure that cooker effluent does not  escape
into the atmosphere.  Thus,  another 490  scfm,
or 15 percent by volume, must be accounted for
in the emission rate from continuous tube systems.

Emission rates from blood cookers are general-
ly lower than those from dry rendering cookers
owing to the longer cook cycles employed.  Blood
is continually  added to an operating cooker during
a typical packinghouse workday.   The emission
rate fluctuates as a function  of the moisture con-
tent in the cooker.  A cook cycle may extend
over 8 or  10 hours,  and  charging  patterns can
vary tremendously.  Emission rates do not
normally exceed 500 cfm,  and at times, are con-
siderably lower.

Emission rates from feather cookers follow the
same pattern as those from other dry pressure
cookers though rates are lower and cooking
times usually  longer.  Inasmuch as feathers
contain no appreciable tallow, heat transfer is
relatively slow.  At some plants,  batches of
feathers are cooked as long as 8 hours.  Where
separate driers are used,  feathers are still
cooked 2 to 4 hours, which reduces the moisture
content to 50 percent before  the charging to a
drier.

Emission Rates From Driers

Most air-drying processes are operated on a
continuous basis with no measurable fluctua-
tions in exhaust rates.  Enough air and, in some
instances,  products  of combustion are added to
yield a moisture content of 10 to  30 percent by
volume  in the exit gas stream.  To dry 2, 000
pounds of cooked feathers per hour from 50 to
5 percent moisture requires  a drier (steamtube)
exhaust volume of 1, 660 scfm at  20 percent
moisture in the gases.  Volumes from air driers
are always much greater than those from  cook-
ing processes, and they contain far greater
quantities of noneondensable gases.

AIR POLLUTION CONTROL EQUIPMENT

The principal devices used to control reduction
plant odors are afterburners and condensers,
installed separately and in combination.  Ad-
sorbers and scrubbers also find use.  Dust is
not a major problem at animal matter reduction
plants,  and simple cyclones are usually suffi-
cient to prevent excessive emissions.

Selection  of odor control equipment is influenced
greatly by the moisture content of the malodorous
stream, or conversely,  by the percentage of non-
condensable gases.  It is usually more costly to
control none ondens able gases  than moisture.
Reduction plant exhaust streams  fall into two
general types:  (1) Those consisting almost en-
tirely (95 percent or greater) of water vapor,
as from rendering cookers and blood cookers,
and  (2) air drier exhaust gases,  -which seldom
contain more than 30 percent moisture by volume.


Controlling  High-Moisture Streams

Condensing moisture from wet cooker gases is
almost always economically attractive.  Some
malodors are usually condensed or dissolved in
the condensate. In any case the volume is re-
duced by a factor of 10 or more.   The remaining
noxious gases can be directed to a further control
device such as an afterburner or carbon adsorber
before being vented to the atmosphere.

Selection  of the condenser depends upon the par-
ticular facilities of the operator.  The principal
types  of condensers noted in Chapter 5 are adapt-
able to reduction cooker exhaust  streams.  Con-
tact condensers and air-cooled and water-cooled
surface condensers have been successfully used
for this purpose.

Contact condensers are more efficient control
devices than surface condensers  are, though
both types are highly effective when coupled with
an afterburner or carbon adsorber.  This  is
illustrated by data in Table 224.  Odor  concen-
trations are seen to be considerably greater in
gases from surface condensers than in  those
from contact condensers.  With condensate at

-------
826
CHEMICAL PROCESSING EQUIPMENT
        Table 224.  ODOR REMOVAL EFFICIENCIES OF  CONDENSERS OR AFTERBURNERS,
                   OR BOTH, VENTING A TYPICAL DRY RENDERING COOKERa
                                (Calculated from Mills et al. , 1963)
Odors from cookers
Concentration,
odor units /scf
50, 000











Emission rate,
odor units /mm
25, 000, 000












Condense r
type
None

Surface


Surface

Contact


Contact


Condensate
tcmpe rature ,
0 F
--

30


140

80


140


Afterburner
temperature ,
" F
1, 200

None


1, 200

None


1, 200

Odors from control system
Concentration,
odors
units/ scf
100 to 150
(Mode 120)
100, 000 to
1 0 million
(Mode 500, 000)
50 to 100
(Mode 75)
2, 000 to
20, 000
(Mode 10, 000)
20 to 50
(Mode 25)
Modal emission
rate, odor
units /mm
90, 000

12, 500, 000


6, 000

250, 000


2, 000


Odor removal
efficiency,
%
99 40

50


99. 93

99


99. 99

 Based on a hypothetical cooker that emits 500 scfm of vapor containing 5 percent none onden sable gases.
80°F,  a contact condenser reduces odor concen-
trations by about 80 percent and odor emission
rates by 99 percent.  At the same condensate
temperature, odor concentrations increase across
a surface condenser.  Either type of condenser,
however, reduces the volume  of cooker vapors
by 95 percent or more.  Thus, even a surface
condenser lowers the odor emission rate by about
50 percent.
Contact condensers are relatively inexpensive
to install but require large quantities of one -
pass cooling water.  From 15 to 20 pounds  of
cooling water is necessary to condense and sub-
cool adequately 1  pound of steam.  Since cooling
water and condensate are intimately mixed,  the
resultant liquid cannot  be cooled in an atmospheric
cooling tower without emission of  malodors to the
atmosphere.  The large condensate volume that
must be disposed of can overload  sewer facili-
ties in reduction plant  areas.
 Subcooling Condensate

 Surface condensers, whether air cooled or water
 cooled,  should be designed to provide subcooling
 of condensate  to 140 "F or lower.  This may be
 accomplished  in several ways, as noted in Chapter
 5.  The need for subcooling is negated when high
 vacuum is employed.  With vacuum operation,
 volatile,  malodorous gases  are drawn off  through
 the ejector or  vacuum pump,  and condensation
 temperatures  are often less  than 140°F.   At a
 vacuum of 24 inches of mercury (2. 9 psia), the
 condensation temperature of steam is 140°F.
                        Condenser Tube Materials

                        Reduction process  vapors can be highly corro-
                        sive to the metals commonly used in surface
                        condenser tubes.  Both acid and alkaline vapors
                        can be present, sometimes alternately in the
                        same equipment.  Vapors from relatively fresh
                        meat and bone  scrap reiiderir ; are mildly acidic,
                        and some brasses are satisfactory.  Brasses
                        fail rapidly, however, under alkaline conditions.
                        Mild steel tubes are adequate where the pH is
                        greater than 7. 0 but quickly corrode under  acid
                        conditions.

                        Some operations,  such as dead stock rendering,
                        can produce alkaline and acid gases alternately
                        during the cook cycle.  Here neither brass  nor
                        mild steel is satisfactory.  In these cases,  stain-
                        less steels have been successfully employed.
                        With a relatively constant pH condition, less ex-
                        pensive metals could be used.

                        Where acid-base conditions are uncertain, a
                        pH determination should be made.  The vapors
                        should be sampled over the complete process
                        cycle with all representative  feedstocks in the
                        cookers.
                        Interceptors in Cooker Vent Lines

                        Air pollution control systems venting cookers
                        should be equipped with interceptor traps to pre-
                        vent fouling of condensers and other control de-
                        vices.   So-called wild blows are relatively com-
                        mon in dry rendering operations.  They result
                        from momentary plugging of the cooker vent.
                        Steam pressures increase until they are suffi-

-------
                                 Reduction of Inedible Animal Matter
                                                                                                 827
cient to unblock the line.  In the unblocking,  a
measurable quantity of animal matter is forced
through the vent line at high velocity.  If there
is no interceptor, this material fouls condensers,
hot 'wells,  afterburners,  and other connected con-
trol devices.  Although a wild  blow is an opera-
tional problem,  it greatly affects the efficiency
of odor control equipment.

The systems shown in Figures 632 and 633 in-
clude interceptors  in the vent lines between the
cookers and condensers.  The installation de-
picted in Figure 633 uses an air-cooled con-
denser and afterburner.  Most tanks are of suffi-
cient size to hold approximately one-half of a full
cooker charge.  They are designed so that col-
lected materials can be drained while the cooker
and control system, are in operation.
  Figure 632.  A  condenser-afterburner  control
  system with  an  interceptor located  between
  the rendering  cooker and condenser.
 Vapor Incineration

 For animal matter reduction processes, as with
 most odor sources, flame incineration is the most
 positive control method. Afterburners have been
 used individually and in combination with other de-
 vices, principally condensers.  Rule  64 of the
 Los Angeles County Air Pollution  Control District
 (see Appendix A), which specifically governs heat-
 ed animal matter reduction processes, uses incin-
 eration at 1,200°F as an odor control  standard.
 Any control method or device as effective as
 flame incineration at 1,200°F is acceptable under
 the regulation.

 Total incineration is used to  control low-mois-
 ture reduction process streams, as from driers,
 and various other streams of small volume.   At
 reduction plants, steamtube driers are normal-
 ly the largest equipment controlled in  this manner.
Gases from the driers are vented directly to after-
burners, which are operated at temperatures of
1,200° For higher. Dust is usually not in sufficient
concentration to impede incineration.  If there is
appreciable particulate matter in the gas  stream,
auxiliary dust collectors must be installed or the
afterburner must be operated at 1,600° F or high-
er.  At 1,200°  F, solids are only partially incin-
erated.

Flame incineration at 1,200° F reduces odor con-
centrations from steamtube  driers to 100 to  150
odor units  per scf where dust loading is not ex-
cessive.  Some variation can be expected when
concentrations are greatly in excess of the nomi-
nal 2,000 odor units per scf usually  encountered
in drier  gases.

Because of the large  volumes exhausted from
driers, afterburner fuel requirements are a
major consideration.  A drier emitting 3,000
scfm requires about 4, 800 scfh natural gas for
1,200° F incineration.   Several means of recov-
ering waste heat from large afterburner  streams
have been used.  The most common  are the
generation of steam and preheating of drier
inlet gases.

In the control of spray driers, dust collectors
must often be employed  ahead of the  afterburner.
High-efficiency centrifugal collectors, baghouses,
or precipitators may be required as  precleaners,
depending upon  the size  and  concentration of par-
ticulate s.

Condensation-Incineration  Systems

As  noted earlier,  wet cooker vapors are  seldom
incinerated in toto.  While 100 percent incinera-
tion is feasible, operating costs are  much great-
er than for condenser-afterburner combinations.
Both types of control systems provide better than
99 percent odor removal, but the combination sys-
tem results in a much lower odor emission rate.

 The cooker control systems shown in Figures 632
and 633  and in Chapter 5, illustrate  typical com-
binations of condensers and afterburners. Un-
condensed gases are separated from condensate
at either the condenser  or hot well.  Gases enter
the afterburner near ambient temperature.   Ei-
ther contact or surface  condensers serve to  re-
move essentially all  particulates. The remaining
 "clean" uncondensed gases can be readily incin-
erated at 1,200° F.  In  some instances there are
minor concentrations of methane and other fuel
gases in the stream.  Uncondensed gases from
surface  condensers are richer in combustibles
than are those from contact condensers . As shown
in Table 224, odor removal efficiencies greater than
99.9 percent are possible with condenser-after-
burner systems serving dry rendering cookers.

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828
                              CHEMICAL PROCESSING EQUIPMENT
                   Figure 633.  A  cooker control  system  including an interceptor,
                   air-cooled  condenser, and afterburner  (California Protein  Products,
                   Los Angeles,  Cal i f.).
When the moisture content of the contaminated
stream is from 15 to 40 percent, the use of
condensers may or may not be advantageous.
In these cases, a number  of factors must be
weighed including volumes,  exit temperatures,
fuel costs,  water availability, and equipment
costs among others.

Carbon Adsorption of Odors

Most of the malodorous gases emitted from  re-
duction processes can  be adsorbed on activated
carbon to some degree.  The capacities  of
activated carbons for hydrogen sulfide, uric
acid, skatole,  putrescine,  and several other
specific compounds found  in reduction plant gas-
es are considered "satisfactory" to  "high. "  For
ammonia and low-molecular-weight amines,
they have somewhat lower capacities. The latter
compounds  tend to be desorbed as the carbon be-
comes saturated with high-molecular-weight
compounds  (Barnebey-Cheney Co. ,  Bulletin
T-642).  For the  mixture  of malodorous mate-
rials encountered at reduction plants, a  high-
quality carbon would be expected to  adsorb
from 10 to  25 percent of its weight before the
breakthrough point is  reached.
Carbon adsorbers are as efficient as afterburn-
ers but have limitations that often make them
unattractive for cooker control.  Their most
useful application is the control of large volumes
of relatively cool and dry gases.  Adsorbers
usually cannot be employed  in reduction process
streams 'without auxiliary dust collectors, con-
densers,  or coolers.

Carbon adsorbers cannot be  used to control
emissions from wet cookers unless the  adsorb-
ers are preceded by condensers.  Activated
carbon does not adsorb satisfactorily at tem-
peratures greater than 120°F.  To cool cooker
vapors, which are predominantly steam,  to
this temperature, most of the moisture must
be recovered.  At 120°F,  saturated air contains
only 11.5 percent water vapor by volume.  Con-
denser-adsorber systems  are reported to re-
move odors as efficiently as  condenser-after-
burner systems.  No comparative odor con-
centration data are available.

Drier  exhaust  streams can be controlled with
adsorbers if inlet temperatures and dust con-
centrations  can be held sufficiently low and
small, respectively.  Many  driers are  exhausted

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                                         ELECTROPLATING
                                           829
at temperatures higher than 200 °F and contain
enough fine particulates to foul adsorbers.  A
scrubber-contact condenser is often a satis-
factory means of removing  particulates and low-
ering temperatures before adsorption.   If, how-
ever, there are appreciable  particulates of less
than 10 microns  diameter, more efficient dust
control devices are necessary.

Regeneration of activated carbon is a major con-
sideration at animal matter reduction plants.
Carbon life between regenerations can be as
short as  24 hours, particularly where malodors
are in heavy concentration, and the carbon has
a low capacity for the compounds  being adsorbed.
Regeneration frequency is a function of many
factors,  including malodor  concentration, the
quality and quantity of carbon, and the  kind of
compounds that must be adsorbed.

Some means must be employed to contain or
destroy the desorbed gases; otherwise,  mal-
odors are vented to the atmosphere in essentially
the same  form that they 'were collected.  Incin-
eration at  1,200°F or higher is the  most common
method of  controlling these gases.  For streams
of low volume, afterburners used during regen-
eration can be as large and as costly as those
used to incinerate odors from  the basic reduc-
tion equipment.   The need for  incineration of
desorbed  gases usually offsets the advantages
of carbon adsorption for streams  of low volume.
If the exhaust rate is sufficiently  small,  incin-
erating vapors directly, as they are evolved
from  the reduction equipment or condenser, is
considerably simpler.
Odor Scrubbers

Conventional scrubbers are seldom used to
control reduction process odors.  Of course,
contact condensers provide some scrubbing
of cooker gases; nevertheless,  these devices
are principally  condensers, and tail -waters
cannot be recirculated.  It is conceivable that
alkaline or acid scrubbers would be  effective
for drier gases if all the odorous compounds
reacted in the same manner. Unfortunately,
the malodorous mixtures encountered in typical
reduction processes are not homogenous from
the acid-base standpoint.

Strong oxidizing solutions, such as chlorine
dioxide, are reported to destroy many of the
odorous organic materials (Woodward and
Fenrich,  1952).  With any type  of recirculating
chemical scrubber, the contaminated stream
would first have to be cooled to ambient tem-
perature, by condensation if necessary.
Odor Masking and Counteraction

Masking agents and odor counteractants have
been used with some success to offset in-plant
odors.  These materials are added to cooker
feedstocks and sprayed in processing and storage
areas.  They are reported to provide a degree
of nuisance elimination and worker comfort,
particularly in high-odor areas such as dead
stock skinning rooms.  Masking agents and
counteractants,  however,  are not recommended
for the control of odors  from heated animal
matter reduction equipment.


             ELECTROPLATING

Electroplating is a process used to deposit,
or plate, a  coating of metal  upon the surface
of another  metal by electrochemical reactions.
In variations of this process, nonmetallic sur-
faces have been plated with metals, and a non-
metal such  as rubber has been used as a plating
material.  Industrial and commercial applica-
tions  of electroplating are numerous, ranging
from manufactured parts for automobiles,  tools,
other hardware, and furniture to toys.  Brass,
bronze,  chromium (chrome), copper, cadmium,
iron,  lead,  nickel, tin,  zinc, and the precious
metals are  most commonly electroplated.

Platings are applied to decorate,  to reduce
corrosion,  to improve wearing  qualities  and
other mechanical properties, or to serve as
a base for  subsequent plating -with another  metal.
The purpose and type of plating determine  the de-
tails of the  process  employed and,  indirectly,
the air pollution potential, which is a function of
the type  and rate of "gassing, "  or  release  of gas
bubbles from plating solutions  with entrainment
of droplets  of solution as a mist.   The degree
of severity  of air pollution from these process-
es may vary from being an insignificant problem
to a nuisance.

An electroplating system consists  of two elec-
trodes--an  anode and a cathode--immersed in
an electrolyte and connected to  an  external
source of direct-current electricity.  The base
material upon which the plating is  to be deposited
makes up the cathode.  In most electroplating
systems, a bar of the metal  to be deposited is
used as the anode.   The electrolyte is a solution
containing:  (1) Ions of the metal to be deposited
and  (2) additional dissolved  materials to aid in
electrical conductivity and produce desirable
characteristics in the deposited plating.

When an electric current is  passed through the
electrolyte,  ions from the electrolyte are re-
duced, or deposited, at  the cathode, and an

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830
                              CHEMICAL PROCESSING EQUIPMENT
equivalent amount of either the same or a dif-
ferent element is oxidized or dissolved at the
anode.  In some systems, for example, chrome
plating, the deposited metal does not dissolve
at the anode,  and hence,  insoluble anodes are
used, the source of the deposited metal being
ions formed from salts of that metal previously
dissolved in the electrolyte.

The character of the deposited metal is affected
by many factors, including the pH of the  electro-
lyte, the metallic ion concentration, the  sim-
plicity or complexity of the metallic ion (includ-
ing its primary and secondary ionization prod-
ucts),  the anodic and cathodic current densities,
the temperature of the electrolyte,  and the
presence  of modifying or "addition agents.1'  By
varying these factors,  the deposit can be varied
from a rough,  granular,  loosely adherent plat-
ing to a strong, adherent, mirror-finish plating.
If the electromotive force used is greater than
that needed to deposit the metal,  hydrogen is
also formed at the  cathode,  and oxygen forms
at the anode.  When insoluble anodes are used,
oxygen or a halogen (if halide salts are used in
the electrolyte) is formed at the anode.  Both of
these situations produce  gassing.

A potential air pollution  problem can also occur
in the  preparation  of articles for plating.  These
procedures,  primarily cleaning processes, are
as  important as the plating operation itself for
the production of high-quality finishes of im-
pervious,  adherent metal coatings.  The clean-
ing of  metals  before electroplating generally
requires a multistage procedure  as follows:

1.   Precleaning by vapor degreasing or by soak-
     ing in a solvent, an  emulsifiable solvent, or
     an emulsion (used for heavily soiled items);

2.   intermediate cleaning with an alkaline bath
     soak treatment;

3.   electrocleaning with an alkaline anodic or
     cathodic bath treatment, or both (the chem-
     ical and mechanical  [gassing] action created
     by passing a current through the bath between
     the immersed article and an electrode pro-
     duces the  cleaning);

4.   pickling with an acid bath soak treatment,
     with or without electricity.

The selection of an appropriate cleaning method
in any  given case depends upon three important
factors:  The type and quantity of the soil,  com-
position and surface texture of the base metal,
and the degree of cleanliness required. In gen-
eral, oil, grease,  and loose dirt are removed
first; then scale is removed, and, just before
the plating, the pickling process is employed.
The articles to be plated are thoroughly rinsed
after  each treatment to keep them from contami-
nating succeeding baths.  A cold rinse is usually
used after the pickling to keep the articles from
drying before their immersion in the plating bath.
Electrocleaning and electropickling are generally
faster than similar soak procedures; however,
the electroprocesses always produce more gas-
sing (hydrogen at the cathode and oxygen  at the
anode) than the nonelectroprocesses.  The gas-
sing from cleaning solutions tends to create
mists that may,  but usually do not, cause signi-
ficant air pollution problems.


THE AIR POLLUTION PROBLEM

The electrolytic  processes do not  operate with
100 percent efficiency, and some of the current
decomposes water in the bath, evolving hydrogen
and oxygen gases.  In fact,  the chief advantage
of electrocleaning is the mechanical action pro-
duced by the vigorous evolution of hydrogen at
the cathode, which tends to lift off films of oil,
grease, paint, and dirt.  The rate of gassing
varies widely with the individual process. If
the gassing rate  is high,  entrained mists of
acids, alkaline materials,  or other bath con-
stituents are discharged to the atmosphere.

Most  of the electrolytic plating and cleaning  pro-
cesses are of little interest from a standpoint  of
air pollution because the emissions are inoffen-
sive and of negligible volume, owing  to low gas-
sing rates. Generally,  air pollution control
equipment is not required for any of these pro-
cesses except the chromium-plating process.
In this process,  large volumes of hydrogen and
oxygen gases  are evolved.   The bubbles rise
and break the surface with  considerable energy,
entraining chromic acid mist, 'which is dis-
charged to the atmosphere. Chromic acid mist
is very toxic and corrosive and its discharge
to the atmosphere should be prevented.

Chromic acid emissions have caused numerous
nuisance complaints  and frequently cause prop-
erty damage.   Particularly vulnerable are auto-
mobiles parked downwind of chrome-plating in-
stallations. The acid mist spots car finishes severe-
ly. The amounts of acid involved  are relatively
small but are sufficient to  cause damage.  In a
typical decorative chromium-plating installation
with an exhaust system but without mist control
equipment, a stack test disclosed that 0.45 pound
of chromic acid per hour was being discharged
from  a 1, 300-gallon tank.

Chromium-plating processes can be  divided into
two general classes,  one of -which offers  a con-

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                                          Electroplating
                                            831
siderably greater air pollution problem than the
other.  "Hard chrome" plating, which causes
the more  severe problem, produces a thick,
hard, smooth,  corrosion-resistant coating.
This plating process requires a current density
of about 250 amperes per square foot, which
results  in a high rate of gassing and a heavy
evolution  of acid mist.   The less severe problem
is presented by the process  called "decorative
chrome" plating, which requires a current
density of only about 100 amperes  per square
foot and results in a definitely lower gassing
rate.

HOODING AND VENTILATING REQUIREMENTS

Local exhaust systems are installed on many
electroplating tanks to reduce the  concentra-
tions  of steam,  gases, and mists to what are
commonly accepted as  safe  amounts for person-
nel in the plating room. In  the past,  these  ex-
haust systems were often omitted  altogether,
and the resulting working conditions were often
unhealthful.

In 1951, the American Standards Association
introduced Code Z9. 1 for Ventilation and Oper-
ation  of Open Surface  Tanks.  This code is  an
organized engineering approach designed to re-
place the  rule-of-thumb methods applied  in the
past.   The use of this code in designing plating
tank exhaust systems is recommended by public
health officials  and  industrial hygienists.

Most  exhaust systems use slot hoods to capture
the mists discharged from the plating solutions.
These hoods have been found satisfactory when
properly  designed.  To obtain adequate distribu-
tion of ventilation along the  entire  length  of the
slot hood, the slot velocity should be high, 2, 000
fpm or  more, and the plenum velocity should
be one-half of the slot velocity or  less.  With
hoods over 10 feet in length, either multiple
takeoffs or splitter  vanes are needed. Enough
takeoffs or splitter  vanes should be used to re-
duce the length  of the slot to sections not more
than 10 feet long.

Ventilation rates for tanks,  as previously dis-
cussed  in Chapter 3, are for tanks located  in
areas having no crossdrafts.  In drafty areas,
ventilation rates must be increased and baffles
should be used to shield the  tank.
AIR POLLUTION CONTROL EQUIPMENT

Scrubbers

The device most commonly used to control air
contaminants in hard-chrome-plating tank ex-
haust gases is a wet collector.  This type of
equipment is also suitable for controlling mists
from any other type of plating or cleaning tank
that may cause a problem.  Figure 634 shows
a ventilation system with a spray-type scrubber
used to control mists from two 18-foot  chrome-
plating tanks.  Many other types of commercial
wet collectors are available,  constructed of
various corrosion-resistant materials.   Water
circulation rates are usually  10 to 12 gpm per
1, 000 cfm.  If the water is recirculated, the
makeup rate is about 2.5 to 4 gph per 1, 000 cfm.

The  scrubber -water, of course, becomes con-
taminated with the acid discharged from the plat-
ing tank; therefore, efficient  mist eliminators
must be used in the scrubber to prevent a con-
taminated water mist from discharging  to the
atmosphere.

The  scrubber water is  commonly used for plat-
ing tank makeup.   This procedure not only re-
moves the acid from the  scrubber but also re-
duces the amount of makeup acid needed for the
plating solution.   In some scrubbers, a very
small quantity of fresh water is used to collect
the acid mist; the resulting solution is continu-
ously drained from the scrubber either into the
plating tank or into a holding  tank,  from which
it can be  taken for plating solution makeup.

The  mists collected by the air  pollution control
system are corrosive to  iron or steel; therefore,
hood, ducts, and  scrubbers of  these materials
must be  lined -with, or  replaced by,  corrosion-
resistant materials. Steel ducts and scrubbers
lined -with materials such as polyvinyl chloride
have been found to resist adequately the corro-
sive action of the  mists.  In recent years, hoods,
ducts,  and scrubbers made entirely of polyester
resins reinforced with  glass fibers have been
used in air pollution control systems handling
acid or alkaline solutions.  These systems have
been found to be very resistant to the corrosive
effects of plating solutions.

The  scrubber removes chromic acid mist with
high efficiency.  A commonly used field method
of determining chromic acid mist evolution
consists of holding a sheet of -white paper over
the surface of the tank  or scrubber discharge.
Any mist contacting the paper immediately
stains  it. A piece of paper held in the discharge
of a well-designed scrubber shows no signs of
staining.

Mist  Inhibitors

The mist emissions from a decorative-chrome-
plating tank and from other tanks with lesser
mist problems can be substantially eliminated
by adding a suitable surface-active agent to the
plating solutions.   The action of the surface-

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832
CHEMICAL PROCESSING EQUIPMENT
                Figure  634. Two control  systems with scrubbers  venting four chrome-
                plating  tanks. Each scrubber vents two tanks  (industrial  Systems,  Inc.,
                South  Gate, Calif.).
active agent reduces the surface tension, which,
in turn, reduces the size of the hydrogen bubbles.
Their rates of rise, and the energy of their evolu-
tion are greatly reduced, and the amount of mist
is also greatly reduced.  Several of these mist
inhibitors are commercially available.

If the proper concentration of mist inhibitor is
maintained, a sheet of paper placed 1 inch above
the bath surface shows  no spotting.
                        Table  225.  SOME COMMON INSECTICIDES
                              CLASSIFIED ACCORDING TO
                                  METHOD OF ACTION
Stomach poisons
Paris green
Lead arsenate
Calcium arsenate
Sodium fluoride
Cryolite
Rotenone
Contact poisons
DDT
Pyrethrum
Sulfur
Lame -sulfur
Nicotine sulfate
Methoxychlor
Furmgants
Sulfur dioxide
Nicotine
Hydrocyanic acid
Naphthalene
P-dichloro-benzene
Ethylene oxide
       INSECTICIDE  MANUFACTURE

The innumerable substances used commercially
as insecticides can be conveniently classified
according to method of action, namely:  (1) Stom-
ach poisons, -which act in the digestive system;
(2)  contact poisons,  which act by direct external
contact with the insect at some  stage of its life
cycle; and  (3) fumigants, which attack the
respiratory system.

A few of the commonly used insecticides,  clas-
sified according to method of action, are shown
in Table 225.  The classification is  somewhat
arbitrary in that many poisons, such as nicotine,
possess  the characteristics of two or three
classes.
                      Human threshold limit values of various insecti-
                      cides are shown in Table 226.  They represent
                      conditions under which it is believed that nearly
                      all workers may be repeatedly exposed day after
                      day, without adverse effect.  The amount by which
                      these figures may be exceeded for short periods
                      •without injury to health depends  upon factors such
                      as  (1) the nature of the  contaminant,   (2) whether
                      large concentrations over short  periods produce
                      acute poisoning, (3) -whether the effects are
                      cumulative,  (4) the frequency with which large
                      concentrations occur, and  (5) the  duration of
                      these periods.

                      METHODS OF PRODUCTION

                      Production of the toxic substances used in in-
                      secticides involves the same  operations employed
                      for general chemical processing.  Similarly,

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                                       Insecticide Manufacture
                                            833
                Table 226.  THRESHOLD LIMIT VALUES OF VARIOUS INSECTICIDES
                                  Substance
            Threshold limit value,
                 mg/meter
              Aldrin (1,2,3,4,10,10-hexachloro-
                1,4,4a,5, 8, 8a-hexahydro-l,4,5,8-
                dimethanonaphthalene)
              Arsenic
              Calcium ar senate
              Chlordane (1,2,4,5,6,7,8,8-octachloro-3a, 4,7,
                7a-tetrahydro-4, 7 -methanoindane)
              Chlorinated camphene,  60%
              2,4-D (2, 4-dichlorophenoxyacetic  acid)
              DDT (2, 2-bis(p-chlorophenyl)
                -1,1, 1-trichloroethane)
              Dieldrin (1,2,3,4,10, 10-hexachloro-6, 7,
                epoxy-1, 4,4a,5,6,7,8,8a-octahydro-
                1, 4, 5, 8-dimethano-naphthalene)
              Dinitro-o-cresol
              EPN (O-ethyl O-p-nitrophenyl thionobenzenephos-
                phonate)
              Ferbam (ferric dimethyl dithiocarbamate)
              Lead arsenate
              Lindane (hexachlorocyclohexane gamma isomer)
              Malathion (O, O-dimethyl dithiophosphate of
                diethyl mercaptosuccinate)
              Methoxychlor (2,  2 -di-p-methoxyphenyl-1, 1, 1 -
                trichloroethane)
              Nicotine
              Parathion (O, O-diethyl-O-p-nitrophenyl
                thiophosphate)
              Pentachlorophenol
              Phosphorus pentasulfide
              Picric acid
              Pyrethrum
              Rotenone
              TEDP (tetraethyl dithionopyrophosphate)
              TEPP (tetraethyl pyrophosphate)
              Thiram (tetramethyl thiuram disulfide)
              Warfarin (3-(a-acetonylbenzyl) 4-
                hydroxycoumarin)
                      0.25
                      0. 5
                      1

                      0.5
                      0. 5
                     10

                      1
                      0.25
                      0. 2
                      0.
                     15
                      0.
                      0.

                     15
15
5
                     15
                      0. 5
                      0. 1
                      0. 5
                      1
                      0. 1
                      5
                      5
                      0. 2
                      0. 05
                      0. 1
chemical-processing equipment,  that is,  reac-
tion kettles, filters, heat exchangers, and so
forth,  are the same as discussed in other sec-
tions of this chapter.  Emphasis is given, there-
fore, to the equipment and techniques encoun-
tered in the compounding and blending of com-
mercial insecticides to achieve specific chemi-
cal and physical properties.

Most commercial insecticides are used as either
dusts or  sprays.   Insecticides employed as dusts
are in the solid state in the 0. 5- to 10-micron
size range.  Insecticides employed as sprays
may be manufactured and  sold as either solids
or liquids.  The solids are designed to go into
solution in an appropriate solvent or to form a
colloidal suspension; liquids may be either solu-
tions or water base emulsions.   No matter "what
physical state or form is involved,  insecticides
are usually a blend of several ingredients in
order to achieve desirable characteristics.   A
convenient means of classifying equipment and
their related processing techniques is to differ-
entiate them by the state  of the end product.
Equipment used to process  insecticides where
the end product is a solid is designated solid-
insecticide-processing equipment.  Equipment
used to process insecticides -where the end
product is  a liquid is designated as liquid-in-
secticide-processing equipment.
Solid-Insecticide Production Methods

Solid mixtures of insecticides may be com-
pounded by either  (1) adding the toxicant in

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834
CHEMICAL, PROCESSING EQUIPMENT
liquid state to a dust mixture or  (2) adding a
solid toxicant to the dust mixture.

Figure  635 illustrates equipment used if the
toxicant in liquid state is sprayed into a dust
mixture during the blending process.  After
leaving the rotary sifter, the solid  raw mate-
rials are  carried  by elevator  to the  upper
mixer where the liquid toxicant is introduced
by means of spray nozzles.  This particular
unit has discharge  gates at each end of the up-
per mixer, which permit the wetted mixture
to be introduced either directly into the second
mixer or into the high-speed fine-grinding pul-
verizer and then into the second mixer.  From
the second mixer,  a discharge  gate with a built-
in feeder screw conveys the mixture to a second
elevator for transfer to the holding bin where the
finished batch is  available for packaging.  Al-
though as much as  50 percent by  weight of liq-
uid toxicant may be added to the blend, the di-
luent clays are porous and absorb the  liquid
to such a degree that the ingredients of the mix
are essentially solids and act as  such.  In in-
secticide processing, the type  of mixer general-
ly employed to blend liquids with dusts is the
ribbon blender.

Figure  636 is an illustration of a ribbon blender
screw.   This screw consists of two or more
                       ribbon flights of different diameters and opposite
                       hand,  mounted  one within the other on the same
                       shaft by rigid supporting lugs.  Ingredients of
                       the mix are moved forward by one flight and
                       backward by the other,  which thereby induces
                       positive and thorough mixing with a gradual
                       propulsion  of the mixed material to the  discharge.

                       An example of  an insecticide compound produced
                       by this method  is toxaphene dust.  A commonly
                       used formulation is:
                           Toxaphene (chlorinated
                           camphene)                      40

                           Kerosine                        4. 5

                           Finely divided porous clay      55. 5
                       The toxaphene is melted and mixed -with the
                       kerosine,  then sprayed into the clay and thor-
                       oughly blended.

                       When the toxicant is in the solid state, the in-
                       gredients of the blend are intimately ground,  usu-
                       ally in stages, and blended by mechanical mixing
                       operations.  The equipment employed consists of
                       standard grinding and size reduction machines
          Figure  635. Sol id-insecticide-processing unit (Poulsen  Company, Los Angeles,  Calif.)

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                                       Insecticide Manufacture
                                                                                                  835
               Figure  636. Ribbon blender screw (Link-Belt Company, Los Angeles,  Calif.).
such as ball mills,  hammer mills, air mills,
disc mills, roller mills, and others.  A spe-
cific example of a grinding and blending facility
for solid insecticide is shown in Figures 637 and
638.  This installation is used for compounding
DDT dust.  The grinding and blending operations
are  done in two stages. First, the material is
processed in the premix grinding unit and then
transferred to the final grinding and blending unit.
•y
DDT
CRUSHER

JHDPP

R




i-
SLENOER




B1RREL
f mtRS
        Figure 637.  premix  grinding unit.
Figure 637 illustrates the equipment comprising
the premix grinding unit.  This unit is used for
the initial grading and blending of DDT and silica
mixtures.  DDT flakes, 75 percent of which have a
particle  size of 1-centimeter diameter,  are emp-
tied from sacks into a hopper.   A conveyor takes
this DDT to a crusher from which it is conveyed
to a pulverizer.  Finely ground silica (0. 2- to
2-micron size) is introduced to the pulverizer.
Silica  is added because DDT becomes waxy at
temperatures approaching its melting point and
has a tendency to cake  and resist grinding.
Silica  acts as a stabilizing agent.  The coarsely
ground silica-DDT mixture is then discharged
into a  ribbon blender for thorough mixing be-
fore being conveyed to  a barrel-filling unit,
•which  packs the mixture for aging before its
further grinding.
 The final grinding unit shown in Figure 638 takes
 the coarsely ground DDT-silica mixture and  sub-
 jects it to fine grinding and blending.  The aged
 DDT-silica mixture is fed into a ribbon blender
 where additional silica and wetting agents are
 added to the mix.  The mix is then screw  con-
 veyed to a high-speed grinding mill that uses
 rotating blades to  shear the insecticidal mix-
 ture.  A pneumatic conveying system carries
 the material to a  cyclone  separator from which
 it drops into another blender.  After this mix-
 ing operation, the blend is finely ground by high-
 pressure air in an airmill.  The blend is air
 conveyed to a reverse-jet baghouse that dis-
 charges into another blender.  Additional  air
 grinding is then repeated  before the barrel
 filling and packing.
Liquid-Insecticide Production Methods

Liquid insecticides may be produced as either
solutions,  emulsions, or suspensions.  The
most common means of production consists of
introducing a solid toxicant into a liquid carrier,
which results in either a solution, emulsion,
or suspension.
Figure 639 shows equipment employed in a liq-
uid-emulsion insecticide plant that makes the
emulsion by  introducing a solid toxicant into a
liquid carrier in the presence of an emulsifying
agent.  A typical formulation is:
    DDT (technical)
    Emulsifying agent No. 1
    Emulsifying agent No. 2
    Organic solvent
 Ib

200
 12
 12
569 (79.5 gal)
   234-767 O - 77 - 55

-------
836
                              CHEMICAL PROCESSING EQUIPMENT
                                                                                  NI SHED PRODUCT
                               Figure 638.  Final  grinding and blending unit.
The operation consists of adding the DDT to the
mixing tank, the DDT being held on a horizontal
wire screen located at the vertical midpoint of
the tank.  Organic solvent and emulsifying agents
are  then pumped into the mixing tank at the ap-
proximate level of the dry DDT.  The mixture is
continually  agitated,  both during and after the
addition of  the liquids, until the desired emulsi-
fied state is achieved.  The finished product is
then pumped to the drum-filling station for pack-
aging.


THE AIR POLLUTION PROBLEM

As can be seen from the installations just de-
scribed,   air pollutants generated by the insecti-
cide industry are of two types--dusts and or-
ganic solvent vapors.

To collect insecticide dusts, high-efficiency
collectors are mandatory, since in many in-
stances,  the dust is extremely toxic and cannot
be allowed to escape into the atmosphere,  even
in small  amounts.  The moderate fineness, 0. 5
to 10 microns, of the dust necessitates using
collectors that are effective in these particle
size ranges.  For the most part, the dusts en-
countered are noncorrosive.

Organic solvent vapors emitted from liquid-in-
secticide production processes ordinarily orig-
inate from relatively nonvolatile solvents.  These
vapors  are of such concentration,  nature,  and
quantity as to be inoffensive from a viewpoint of
air pollution.


HOODING AND VENTILATION  REQUIREMENTS

Because of the toxicity of the dusts used in the
manufacture of insecticides,  it is important
that all sources of dust be enclosed or tightly
hooded  to prevent exposure of this dust to per-
sonnel in the working  area.  Wherever possible,
the sources should be completely enclosed and
ventilated to an air pollution control device.
Some of the sources emitting dust are bag pack-
ers, barrel fillers,  hoppers,  crushers,  con-
veyors,  blenders, mixing tanks, and grinding
mills.  Of these, the crushing and grinding
operations are the largest sources  of emission.
In most cases, these are not conducive to com-
plete enclosure,  and hoods must be employed.

-------
                                      Insecticide Manufacture
                                            837
                                    TO ATMOSPHERE
 Figure  639. Liquid-insecticide-formulating unit.
Indraft velocities through openings  in hoods
around crushers and mills should be 400 fpm
or higher.  Velocities through hood openings
for the other operations, where dust is re-
leased with low velocities, should be  200 to
300 fpm.

AIR POLLUTION  CONTROL EQUIPMENT

Baghouses employing cotton sateen bags are the
most common means of controlling emissions
from the insecticide-manufacturing industry.
In some applications, water scrubbers,  of both
the spray chamber and the packed-tower types,
are used to control dust emissions.  Inertial
separators  such as cyclones and mechanical
centrifugal  separators are not used because
collection efficiencies are not high  enough to
prevent the smaller size toxic particles from
being emitted into the atmosphere.

In the solid-insecticide-processing  unit previ-
ously discussed and illustrated  in Figure 635,
air pollution control is achieved by dust pickup
hoods located at the inlet rotary sifter and at
the automatic bag packer.  The dust picked up
at these points is filtered by the use of cloth
bags.  Most units of this type are entirely
enclosed, air contaminants being discharged
only at the inlet to the unit and  at the  outlet.
 The contaminants emitted are extremely
 fine dust and, since no elevated temperatures
 are  encountered and the materials handled are
not particularly corrosive to cloth, can be
easily collected by simple cloth bag filters.
If extremely large throughputs  are encountered,
a conventional baghouse may be required.  Since
no extreme conditions of operation are general-
ly involved, the most widely used filter material
is a  cotton sateen cloth.

In larger installations, such as those illustrated
in Figures 637 and 638 for compounding DDT
dust, several baghouses are usually used.  In
the premix grinding unit shown in Figure 637,
the air pollution  control equipment consists of
an exhaust system discharging  into a baghouse,
which  is equipped with a pullthrough exhaust
fan.  The exhaust ducting connects to both the
DDT and the silica hoppers, the DDT crusher,
the blender,  and the barrel-filling unit.  Dust
collected in the baghouse is  conveyed to the
barrel-filling unit for packaging.

The  final grinding unit, shown in Figure 638,
uses air pollution control equipment consisting
of a baghouse that serves the receiving hopper,
the blenders,  and the cyclone air discharge of
the high-speed grinding mill.  Dust collected
in this baghouse  is recycled to  the feed blender.
The  final blenders and the barrel filler and
packer are vented to one  of the reverse-jet
baghouses serving the fluid  energy mill.  As
in the  case of mixing liquid  toxicant with dust,
the material collected is  not corrosive to
cotton  cloth, and no elevated temperatures are
encountered.  In this installation,  cotton sateen
bags of 1. 12 to 1. 24 pounds  weight per yard
with an average pore size of 0. 004 inch are
employed as the  filtering medium.

In liquid-insecticide manufacturing,  air pollu-
tion control problems  usually entail collection
of dusts in a wet airstream.  Baghouses  can-
not,  therefore, be used,  and some type of
scrubber must be employed. For  the liquid-
emulsion insecticide plant shown in Figure 639,
the air pollution control equipment for the solid
 and liquid  aerosols consists of a packed tower
 that vents  the mixing tank.   The tower is packed
•with 1-inch Intalox saddles,  the packing being
 4-1/2  feet high,  which equals a volume of 14
 cubic feet.  The  water rate  through the tower
is approximately 20 gpm.  The tower is used
to control  dust emissions from the mixing tank,
which  occur when dry material is charged to the
tank, and also occur during  the first stages of
agitation.  Solvent vapors are not effectively
prevented by the tower from entering the atmo-
sphere since the solvent is insoluble in water.
Solvent emissions originate  from the  storage
tank and drum-filling unit.   In the  installation

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838
CHEMICAL PROCESSING EQUIPMENT
 described,  no provision is made to prevent the
 solvent from escaping to the atmosphere since
 total solvent emissions are calculated to be
 only 5. 4 pounds per day.
  HAZARDOUS RADIOACTIVE  MATERIAL

Although the responsibility for overseeing the
control of radioactive materials is predomi-
nantly that of the Federal government, more
and more responsibility is  expected to be placed
at state and local levels. For this reason,
those concerned with air pollution must become
acquainted -with the problems associated with
this new field, particularly those problems
arising as more and smaller industries make
use of radioactive materials.


HAZARDS IN  THE HANDLING  OF RADIOISOTOPES

The hazards encountered in handling of radio-
isotopes may be classified  in order of impor-
tance as follows:  (1) Deposition of radio-
isotope in the body,   (2) exposure of the whole
body to gamma  radiation,   (3) exposure of the
body to beta radiation, and  (4)  exposure of the
hands or other limited parts to beta or gamma
radiation.  Deposition of a  radioisotope in the
body occurs by ingestion,  inhalation,  or ab-
sorption through either the intact or injured
body surface.  Inhalation of a radioactive gas,
vapor,  spray, or dust may occur.   Spray or
dust is particularly hazardous because of the
large fraction of contamination retained by the
   o                                    J
lungs (National Bureau of Standards,  1949).

Types of radiation are listed in Table 227.   The
ranges  of activity may be defined as:   (1) Tracer
level,  less  than 1 x 10'6 curie; (2) low level,
1 x 10~° to  1 x 10~3  curie;  (3) medium level,
1 x 10-3 curie  to 1 curie; and  (4)  high level,
1 curie and over.  The handling  of tracer quan-
tities of radioisotopes usually presents no ex-
ternal hazard.  Ordinary laboratory manipula-
tions  are performed with special precautions
to prevent absorption  of radioactive material
by the body.


THE AIR POLLUTION PROBLEM

Radioactive materials used in industry are a
definite hazard today and will become an in-
creasing rather than a diminishing hazard in
the future.  In industry, the maximum per-
missible dose of direct, whole-body radiation
of persons from all radioactive materials,
airborne or nonairborne,  is 5,000 millirem
per year.   There is greater likelihood that this
limit will be reduced than that it will  be  in-
                       creased.  Airborne radiological hazards can
                       result from routine or accidental venting of
                       radioactive mists, dusts, metallurgical fumes,
                       and gases and from spillages of liquids or
                       solids.  Presently existing governmental regu-
                       lation of the rate of venting airborne,  radio-
                       active materials consists primarily of spe-
                       cific  limitations based upon individual chemi-
                       cal compounds or upon concentrations of ra-
                       dioactivity from single vents.   No concepts
                       have  been promulgated concerning methods
                       of controlling total radioactive air pollution
                       from all sources in an entire area.  Whether
                       it will be either desirable or necessary to
                       find a solution or  solutions to  these problems
                       is an unanswered  question.

                       The characteristics of radioactive, gaseous
                       or airborne, particulate  wastes vary -widely
                       depending upon the nature of the operation from
                       which they originate.  In gaseous form they may
                       range from rare gases, such as argon (A"*l)
                       from air-cooled reactors, to highly corrosive
                       gases, such as  hydrogen fluoride from chemi-
                       cal and metallurgical processes.  Particulate
                       matter or aerosols may be organic or inorganic
                       and range in size  from less than 0. 05 micron
                       to 20 microns.  The  smaller particles originate
                       from metallurgical fumes caused by oxidation
                       or vaporization.  The larger particles may be
                       acid mist droplets,  which are low in specific
                       gravity and remain suspended in air or gas
                       streams for longer periods  (Liberman,  1957).


                       Characteristics of Solid, Radioactive Waste

                       Solid, radioactive wastes are  of two general
                       classes--combustible and noncombustible.
                       Typical combustible  solid wastes are paper,
                       clothes, filters, and -wood.  Noncombustible,
                       solid wastes may include nonrecoverable scrap,
                       evaporator bottoms,  contaminated process equip-
                       ment, floor sweepings, and broken glassware.
                       If inadequate provisions are made for proper
                       handling and disposal of these -wastes, a distinct
                       nuisance, and,  under certain circumstances,
                       even  a hazard,  could result.

                       Characteristics of Liquid, Radioactive Waste

                       Liquid, radioactive wastes are evolved in  all
                       nuclear energy  operations—from laboratory
                       research to full-scale production.  Liquid
                       -wastes with relatively small concentrations
                       of radioactivity originate in laboratory oper-
                       ations where relatively small  quantities  of
                       radioactive materials are involved.  Other
                       sources are the processing of uranium ore and
                       feed material; the normal operation of essen-
                       tially all reactors, particularly -water-cooled
                       types; and the routine chemical processing of
                       reactor fuels.  High-activity liquid wastes

-------
                                    Hazardous Radioactive Material
                                             839
                                  Table 227.  TYPES OF RADIATION
Type of
radiation
Alpha (a)
Beta (/3)
Gamma (7)
Neutron (r\)
Physical nature
Heavy particle,
helium nucleus,
double positive
charge
Light -particle
electron, single
negative charge
Ray, similar to
X-ray
Moderately heavy
particle, neutral
charge
Distance of
travel in air
Few inches maximum
Few yards maximum
Very long
Very long
Effective shielding
Skin or thin layer
of any solid mate-
rial
One -half inch of
any solid material
Lead, other heavy
metals, concrete,
tightly packed soil
Water, paraffin
Usual means of
detection
Proportional counter,
ion chamber, scin-
tillation counter
Geiger counter, film
badge, dosimeter
Geiger counter, ion
chamber, film badge,
dosimeter
Proportional counter
containing boric com-
pound, ion chamber
with cadmium shield
 are produced by the chemical processing of
 reactor fuels.

 Problems in Control  of Airborne,  Radioactive Waste

Removal of radioactive suspended particles,
vapors, and gases from "hot" (radioactive)
exhaust systems before discharge to the at-
mosphere  is a serious problem confronting
all nuclear energy and radiochemistry instal-
lations. Removal is necessary in order to pre-
vent dangerous contamination of the immediate
and neighboring areas.  Air pollution brought
about through discharge of radioactive stack
gas wastes from ventilation systems is only
partially avoided by filter devices, no matter
how efficient they may be,  if the discharge
contains radioactive gases.  In  systems using
filter media such as paper, cloth, glass fiber,
and so  forth, activity eventually builds up in
the filter media through dust loading; the same
situation applies to electrical precipitators.

Another problem in the control  of airborne,
radioactive waste is the low dust loading  of
exhaust streams.  The dust concentration of
ambient air is usually about 1 grain per 1, 000
cubic feet.  At installations handling radio-
active material, owing to precleaning of the
entering air, aerosols may have concentra-
tions as small as 10"2 to 10~3 grain per 1, 000
cubic feet.  In contrast, loadings of some in-
dustrial gases may reach several hundred
grains per cubic foot, though values of 20
grains  or less per cubic foot are more com-
mon.

An outstanding feature to consider •with air-
cleaning requirements for many nuclear oper-
ations is the extremely small permissible con-
centrations of various  radioisotopes in the at-
mosphere (see Table 228).  Often, removal ef-
ficiencies of about 99. 9 percent or greater for
particles less  than 1 micron in diameter are
necessary.   This high  removal efficiency lim-
its the selection of control equipment for ra-
dioactive applications.

HOODING  AND VENTILATION REQUIREMENTS


Hooding

Hooding for radiochemical processes must pre-
vent radioactive contaminants, such as dust
and fumes,  from escaping into the work area
and must deliver them to  suitable control de-
vices.  Radioactive sources require proper
shielding to prevent the escape of radiation
and are not considered in this section.   The
materials used for construction for hoods depend
upon the type and quantities of radioactivity and
the nature  of the process.  Stainless steel,
masonite, transite, or sheet steel, surfaced
with a washable  or strippable paint,  can be
used (Ward,  1952).  Where it is necessary in
a process to handle material that may cause
dusts or fumes to form, a completely enclosed
hood should be used,  equipped with a glove box
or dry box.   Any tools  used for manipulation
should not be removed  from the hood.


Ventilation

The recommended airflow for toxic material
across the face of a hood is  150 fpm (Manufac-
turing Chemists' Association, 1954).  Turbu-
lence of air entering a hood can be reduced by

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840
CHEMICAL PROCESSING EQUIPMENT
             Table 228.  PROPERTIES OF RADIOISOTOPES (Benedict and Pigford, 1957)
Isotop
"n3
Be7
C14
F18
Na24
P32
S"
Cl3*
A41
K42
Ca45
Sc46
V48
Cr51
Fe55
Mn56
Fe59
Ni"
Co60
Ni"
Cu64
Zn«
Ge71
Ga72
As76
Br82
Kr85
Rb86
QO
Sr89
Sr90
y90
Y91
Nb95
Tc96
Mo^9
Pd103
Rh103
Rh^
1 AC
Ag105
Ru106
Cd1Q9
Agii6
Ag111
Sr?13
In114

Half-life
12.5 yr
52.9 days
5, 568 yr
112 min
15 hr
14.3 days
87. 1 days
4. 4 x IO5 y
109 min
12.4 hr
152 days
85 days
16 days
27.8 days
2.9 yr
2.6 hr
45. 1 days
8 x IO4 yr
5.3 yr
85 yr
12.8 hr
250 days
11.4 days
14.3 hr
26.8 hr
35.9 hr
9.4 yr
19.5 days
53 days
19.9 yr
61 hr
61 days
35 days
4. 2 days
67 hr
17 days
57 min
36.5 hr
40 days
1 yr
470 days
270 days
7.6 days
112 days
49 days

Type of
decay
Beta
ECO
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta, EC
EC, no beta
EC, no beta
Beta
Beta
EC
'Beta
Beta
EC, beta
EC, beta
EC, no beta
Beta
Beta
Beta, no EC
Beta
Beta, no EC
Beta
Beta
Beta
Beta
Beta
EC, no beta
Beta
EC
Tc
Beta
EC
Beta
EC, no beta
Beta.ITno EC
Beta
£C, no beta
IT, no EC

Maximum permissible
concentration in air,
microcuries /ml
Soluble
2 x IO-7
2 x IO-7
1 x IO-7
2 x 10-?
4 x 10-8
2 x ID'9
9 x 10-9
1 x 10-8
7 x 10-8
1 x ID"9
8 x 10-9
6x 10-9
4 x ID'7
3 x ID"8
3 x ID'8
5 x 10-9
2 x 10-8
1 x lO-8
2x 10-9
7 x ID"8
4 x ID'9
4 x 10'7
8 x ID'9
4x ID'9
4x 10-8
1 x 10-8
3 x ID'10
3x ID"11
4 x 10-9
1 x ID'9
2 x 10-8
2 x 10'8
3 x 10-8
5 x ID'8
3 x 10~6
3 x ID"8
2x IO-8
3x 10-9
2 x 10-9
7x 10-9
1 x ID'8
1 x ID"8
4x 10"9

Insoluble
4 x IO-5 Suba
4 x 10-8
9 x ID'8
5 x ID"9
3 x 10-9
9x 10-9
8 x 10-10
4 x 10-8 Sub
4 x ID'9
4 x ID'9
8 x IO-10
2 x JO'9
8 x ID"8
3 x IO-8
2 x lO"8
2 x 10-9
3 x ID"8
3 x ID'10
1 x ID'8
4 x IO-8
2 x 10-9
2 x IO-7
6 x 10-9
3x 10-9
6 x 10-9
3 x lO'7 Sub
2 x 10-9
1 x 10-9
2 x IO-10
3 x 10-9
1 x 10-9
3x10-9
8 x 10-9
7 x 10-9
3x IO-8
2 x 10"6
2x lO-8
3 x ID'9
2x lO-iO
3x10-9
3xlO-10
8x 10-9
2 x ID"9
7X10-1"

Isotop
Sb122
Sb124
Sb1"
Te127
Te129
X131
Xe133
Cs134
Xe135
Cs137
Ba140
La140
Ce141
Pr143
Ce144
Pm147
Sm151
Eu154
Ho1"
Tm170
Lu177
Re183
Ir190
Ir192
Au^8
Au^9
Hg203
Tj204
Po210
At211
Ac227
Th232
Pa.233
U233
Th234
U238
Pu239
Am241

Cm242

Half- life
i. 8 days
60 days
~2. 7 yr
115 days
33. 5 days
8. 1 days
5. 3 days
2. 3 yr
9. 1 hr
33 yr
12.8 days
40 hr
33. 1 days
13.7 days
282 days
2.6 yr
73 yr
16 yr
>30 yr
129 days
6.8 days
155 days
12.6 days
74. 4 days
2. 7 days
3. 1 days
47.9 days
3. 5 yr
138. 3 days
7.5 hr
22 yr
1.39 x IO10
y
27.4 days
1, 62 x IO5
y
24. 1 days
4. 49 x IO9
yr A
2. 44 x IO4
yr
470 yr

162.5 days

Type of
decay
Beta
Beta, no EC
Beta
IT
IT
Beta
Beta
Beta, no EC
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta
Beta, no EC
Beta
EC
EC
EC, beta
Beta, no EC
Beta
Beta
Beta, EC
Alpha, beta
stable
Alpha, EC
Alpha, beta
Alpha, beta
stable
Beta
Alpha, beta
stable
Beta
Alpha, beta
stable
Alpha, beta
stable
Alpha, beta
stable
Alpha, beta
stable
Maximum permissible
concentration in air,
microcuries /ml
Soluble
6 x ID'9
5 x 10"9
2 x ID"8
6 x ID'8
2 x ID'7
1 x 10"1
1 x 10"9
2 x 10-9
4 x ID'9
5 x ID"9
2 x 1C"8
1 x 10"8
3x ID'10
2 x 10"9
2 x ID'9
1 x 10'10
7 x ID"9
1 x ID"9
2 x IO-8
9 x ID"8
4 x ID"8
4x ID'9
1 x IO-8
4 x lO"8
2 x ID'9
2 x 10"8
2 x ID"11
2xlO-10
8 x ID"14
io-12
2 x 10-8
2xlO-U
2 x 10"9
3xlO-12
6 x 10'14
2 x IO-13

4 x IO-12

Insoluble
5 x ID"9
7x IO-10
9 x IO-10
3 x ID"8
1 x 10'7
1 x 10"8
3 x IO"7 Sub
4xlO-10
1 x 10'7 Sub
5x ID-1"
1 x ID"9
4 x ID'9
5 x ID"9
6x 10-9
2xlO-10
3x ID'9
5 x 10'9
2xlO-10
6 x ID"9
1 x ID"9
2 x ID'8
5 x ID'9
1 x lO-8
9x IO-10
8x 10-9
3 x IO-8
4 x ID"9
9x IO-10
7xlO-12
x 10-9
9xlO-13
io-12
6x ID'9
4xlO-12
10-9
5xlO-12
xlO-12
4xlO-12

6xlO-12

 aValues given are for submersion in an infinite cloud of
 gaseous material.
 bOrbital-electron capture.
 °Isomeric transition.
 the addition of picture frame airfoils to the edges.
 Hoods  should not be located -where drafts will
 affect their operation.  When more than one hood
 is  located in a room, fan motors should be oper-
 ated by a single switch.  The fan should freely
 discharge to the atmosphere and be connected
 to  the outlet side of any control device,  the
 motors being located outside the air ducts to
 prevent their contamination.  Hood and ducts
 should be equipped with manometers to indi-
 cate that they are operating under  a negative
 pressure.
                         AIR  POLLUTION CONTROL EQUIPMENT


                         Reduction of Radioactive, Particulate Matter at Source

                         Reduction at the source has been defined as the
                         design of processes so as to minimize the initial
                         release of particulate matter at its source.   The
                         principle is not new; it is  applied, for example,
                         in the ceramics industry •where dry powders
                         are  wetted and mixed as a slurry to minimize
                         the production of dust. But its application to

-------
                                   Hazardous Radioactive Material
                                                                                                  841
radioactive aerosols is particularly worthwhile
since it  (1) provides a cleaner effluent,  (2) re-
duces radiation hazards involved in the mainte-
nance of air-cleaning equipment or those re-
sulting from the buildup of dust activity,  (3) per-
mits the use of simpler and less expensive air-
cleaning equipment,  and (4) becomes a part of
the process once reduction has been established.
In general,  preventing  the formation of highly
toxic aerosols  is preferable to cleaning by
secondary equipment.


The design or  redesign of processes for reduc-
tion at the source should be based upon a study
of the quantity and physical characteristics of
the contaminant, and the manner in -which it is
released.  Examples of this concept are instal-
lation of glass fiber filters on the inlet of ven-
tilating or cooling air to minimize the irradia-
tion of ambient dust particles,  and treatment
of ducts to minimize corrosion and flaking
(Friedlander et al. , 1952).
Design of Suitable Air-Cleaning Equipment

The most satisfactory control of particulate
contamination  with air-cleaning equipment re-
sults from using combinations of the various
collectors.   These installations should be de-
signed to terminate with the most  efficient
separator possible, the nature of the gases
being considered.  To reduce maintenance,
less efficient cleaners  capable of holding or
disposing of most of the weight load should be
placed before the final  stage.  It is good prac-
tice to arrange the equipment  in order of in-
creasing  efficiency.  A typical example of such
an arrangement is a wet collector such as a
centrifugal  scrubber to cool the gases and re-
move most  of the larger particles, an efficient
dry filter such as a glass  fiber filter to remove
most of the remaining particulate  matter,  and
a highly efficient paper filter to perform the
final cleaning.  If the gases are moist,  as  in
this example, the paper filter  should be pre-
ceded by a preheater to dry the gases (Fried-
lander,  1952).


An  air-cleaning installation for highly toxic
aerosols should fulfill the following require-
ments (Friedlander et al.  , 1952):

1.   "It should  discharge innocuous air.

2.   "The equipment should require only occa-
     sional replacement and should be designed
     for easy maintenance. Frequent replace-
     ment or cleaning entails excessive exposure
     to radiation and the danger of redispersing
     the collected material.
3.   "The particulate matter should be separated
     in a form allowing easy disposal.  The use
     of wet collectors, for example,  poses the
     additional problem of disposing  of volumes
     of contaminated liquid.  Wet collection does,
     however, reduce considerably the danger of
     redispersion.
       f
4.   "Initial and maintenance costs,  as well as
     operating costs, should be as low as possi-
     ble while fulfilling the preceding three con-
     ditions.  In this respect, pressure drop is
     generally an important consideration. "


Reverse-jet baghouse

One  type of commercially available dust collector
that  meets the requirements of filtering  airborne,
radioactive particles from ventilation exhaust
streams is a bag filter employing what is called
reverse-jet cleaning.  This type of baghouse
(described in Chapter 4) has an efficiency as
high as the conventional cloth bag or cloth screen
collector and is particularly adapted to an in-
stallation where the grain loading of the  effluent
is low.   The bag material is a hard wool felt of
the pressed type,  about  1/16-inch thick, or a
cloth woven of glass fibers.   The gas flow is
likely to be around 10 to 40 cfm per  square foot
of bag  area when the pressure drop is maintained
at usual values such as 2 to  7 inches water col-
umn (Anderson, 1958).

The  conventional cloth bag or cloth screen col-
lectors, which are cleaned periodically by auto-
matic shaking devices, may allow a  puff of dust
to escape after the shaking operation.  The prob-
lem  of maintenance in this instance presents a
contamination and radiation hazard.  For this
reason,  the reverse-jet baghouse is generally
preferred.

Wet  collectors

Another method of treating contaminated ex-
haust air before discharge to the atmosphere
involves the use of wet collectors  of various
types.   These collectors are relatively effec-
tive  on gases.  Investigation covering changing
of water supply or recirculating has shown the
latter procedure useful for considerable periods
of time without apparent adverse effect.   Evapo-
ration  is compensated for by fresh supply.  In-
soluble radioactive salts,  soluble  salts,  and
other radioactive  particles that may form a
solution, suspension,  or sludge in the reser-
voir result in fairly high radioactivity of the
scrubbing media.   Precautions must be taken
during maintenance to avoid carryover of the
scrubbing media since the radioactive con-
tamination of entrained liquid -would  be trans-

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842
                               CHEMICAL PROCESSING EQUIPMENT
ferred to the preheater or filter, resulting in
high radiation levels at those points.


Some important disadvantages of wet collectors
make them less attractive than other types of
collectors. Wet collectors present the difficult
problem of separating the radioactive,  solid
material from the water in which it is suspended.
Maintenance and corrosion are serious problems.
Considerable quantities of water are  required,
and, if the radioactive  solids are not separated
from the •water, this in turn leads to  a final
storage and disposal problem.


Electrical precipitators

Radioactive,  airborne particles,  when given an
electrical charge, can be collected on grounded
surfaces.  The fact  that the particles are radio-
active has very little to do with their  behavior
in an electrical precipitator.   Experiments con-
ducted with precipitators using the alpha emitter
polonium  and the beta emitter sulfur  35 indicate
that neither material behaves in a way different
from nonradioactive material.

Water-flushed-type, single-stage, industrial
precipitators,  and air-conditioning-type, two-
stage precipitators  are used for separating ra-
dioactive  dusts and  fumes  from gases at atomic
energy plants and laboratories.  A small elec-
trical precipitator of the water-flushed type with
a design capacity  of 200 cfm was installed to
test efficiency  of collecting and removing par-
ticulate radioactivity from the offgas  system
of an isotope recovery operation.  This precip-
itator consists of  23 vertical  collecting pipes
with an ionizing wire centered in each pipe. The
inside  surfaces of the pipes serve as  collecting
walls.   For -wet operation,  the collecting walls
are -water flushed by means of spray  nozzles in-
stalled at the top of each pipe.   This  water is re-
cycled continuously at a rate  of 35 gpm over the
collecting walls while high voltage is applied to
the electrodes.  This unit reportedly collects
more than 99. 99 percent of the particulate radio-
activity in the offgas at 50 to 55 kilovolts when
the concentration of radioactivity as  solids is
greater than 5. 0 x  ID"'* microcuries per cubic
centimeter of offgas (Anderson, 1958).


Based upon tests made at the Oak Ridge Nation-
al Laboratory, Anderson (1958) makes  the follow-
ing evaluation of precipitators used in radio-
active  applications:

1.   "Electrical precipitators are not intended
     to collect the ultra fine particles which
     may be discharged from  radiochemistry
     installations.
2.   ''With uneven airflow,  the air velocity
     through some of the collector cells may
     be sufficiently above velocity limits to blow
     off collected wastes which would then be
     discharged to the atmosphere.


3.   "Efficient operation depends a great deal
     on the regularity -with  -which the unit is
     cleaned. At best the electrical precip-
     itator is only approximately 90 percent
     efficient.  This may be demonstrated by
     the fact that dense  clouds of tobacco smoke
     fed into the precipitator -will escape from
     it in  concentrations great enough  so that the
     escaping smoke can be seen.  The blue
     color of tobacco smoke is evidence that
     most of its particles have a  diameter less
     than  the wavelength of light, -which is
     roughly 0. 5 micron.

4.   "For absolute efficiency an after-filter of
     the Cainbridge  or MSA Ultra-Aire type is
     necessary to catch  the dirt  should the pre-
     cipitator short  circuit.

5.   "Difficulty may be  experienced if the  dust-
     load  builds up faster than it  can be removed,
     eventually becoming so heavy that arcing
     occurs between the dirt bridges resulting
     in  a fire hazard.

6.   "Devices such as the single-stage indus-
     trial  precipitator and the air-conditioning
     type two-stage precipitator  accomplish
     only one phase of the problem.  The final
     disposal of radioactive -wastes  collected
     and accumulated during operation and main-
     tenance  still remains."
Glass fiber filters

Glass fiber or glass fiber paper is often used
as a filter medium and is effective in the oper-
ation of radiochemistry hoods, canopies, and
gloved boxes.  One  of the most efficient light-
weight, inorganic filters developed to date is
made with a continuous,  pleated sheet of micro-
glass fiber paper.  The pleats of the glass paper
are separated by a corrugated material (paper,
glass paper,  aluminum foil,  plastic, or as-
bestos paper) for easy passage of air to the  deep
pleats of the filter paper.  The assembly of  the
filter paper and  corrugated separators is sealed
in a frame  of wood,  cadmium plated steel,  stain-
less steel,  or aluminum.  This construction per-
mits a large area of filter paper to be presented
to the  airstream of  a correspondingly low re-
sistance (Flanders Filters, Inc. ,  Riverhead,
N. Y. ).

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                                    Hazardous Radioactive Material
                                                                                                   843
Glass fiber, from which filters  are made, with-
stands temperatures up to 1, 000"F.  It is non-
combustible and has extremely low thermal
conductivity and low heat capacity.  The fibers
are noncellular, are like minute rods of glass,
and do not absorb moisture; however, •water
can enter the interstices.  The material is
relatively nonsettling,  noncorrosive, and durable.
It is resistant to acid fumes and vapors,  except
hydrogen fluoride.

The installation and replacement costs of glass
fiber filters are low.   Final disposal of used
filters may be accomplished by  incinerating at
over 1, 000°F with provisions for decontaminating
the stack gases.  This melts the glass fibers,
reducing the physical mass to the size of a glass
bead.  Thus,  glass  fiber filters  provide,  in part,
a very good answer to  the problem of control
and final disposal of radioactive contaminants.
Paper filters

A highly efficient paper filter medium can be
used with adequate effectiveness on incoming
ventilating air and as a final cleaner in many
instances.  This type filter is composed of as-
bestos cellulose paper. A more recently de-
veloped filter has a glass  fiber web.  It is de-
signed and manufactured in corrugated form
to increase the available filter area and load-
ing  capacity and to reduce initial resistance.
The filter units are tested at rated capacity
•with standard U. S. Army Chemical Corps test
equipment for  resistance  and initial penetra-
tion and are unconditionally guaranteed to be
at least 99. 95  percent effective against 0. 3-
micron-diameter dioctyl phthalate particles.
This filter performs as -well as,  or better
than, the earlier paper types and under tem-
peratures up to 1, 000°F.

Airborne,  radioactive wastes are only part of
the control and disposal problem of nuclear
energy and radiochemistry installations.   Solid
and liquid,  radioactive wastes  are subject to
the same limitations on disposal to the environ-
ment.

The methods of disposing  of the final waste from
the collection systems present additional prob-
lems,  as follows (Anderson, 1958):

1.   "Incineration results  in stack gas and par-
     ticle discharge which is a  cycle  of the en-
     tire problem repeated over again.

2.   "Direct burial results in redispersal and
     ground contamination with associated prob-
     lems related to the ground water table.
3.   "High dust or particle loading capacity re-
     sults in high radioactivity of the collecting
     media.

4.   "Vapors,  acid fumes and unfilterable gases
     may cause rapid deterioration and disinte-
     gration of filter media resulting in a main-
     tenance and health hazard problem.

5.   "Mechanical replacement costs are high
     because of the remote handling involved.

6.   "An auxiliary unit for emergency or main-
     tenance shutdown must be available to pre-
     vent the possibility of reverse flow of the
     air  stream out of "hot" equipment into
     controlled rooms and areas."
Disposal and Control of Solid,  Radioactive Waste

The most common method of disposal of solid,
radioactive wastes is land burial at isolated
and controlled areas.  The earth cover over
these burial pits is usually about 12 feet, and
the surface is monitored regularly. A method
used for disposal of low-level, radioactive,
solid wastes consists of putting the wastes in
concrete and dumping it at sea.  Incineration
of combustible, solid wastes is practiced, with
provisions for decontaminating the flue gases
(Shamos and Roth, 1950).
Disposal and Control of Liquid, Radioactive Waste

Low-level, radioactive, liquid wastes,  under
proper environmental conditions,  are suscepti-
ble to either direct disposal to nature or dis-
posal after minimum treatment.   Treatment
processes used include coprecipitation, ion ex-
change,  biological systems similar to sewage
treatment methods, and others.   Only to the
extent that it is absolutely safe,  maximum use
is made of the dilution factors that may be avail-
able in the environment and that can be assessed
quantitatively.

High-activity,  liquid wastes associated with the
chemical processing of reactor fuels constitute
the bulk of the engineering problem of disposal
of radioactive  wastes.  Highly radioactive,  liq-
uid wastes are currently stored in specially de-
signed tanks.   Since the effective  life of the fis-
sion products constituting the wastes may be
measured in terms of hundreds of years, tank
storage is not  a permanent solution to the dis-
posal problem.  Evaporation before storage is
generally practiced to  reduce storage volume
and cost. The degree  to which evaporation is
carried out  is  limited in  some instances by the

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844
CHEMICAL PROCESSING EQUIPMENT
percentage of solids present in the waste or by
considerations of corrosion.

There are several practical approaches to
ultimate,  safe disposal of high-activity, liquid
•wastes.  The  actual fission products in radio-
active waste material may be fixed in an inert,
solid carrier  so that the possibility of migra-
tion of the radioactivity into the environment
is eliminated  or reduced  to acceptable  and safe
limits.  The carrier containing the radioactive
material could then be permanently stored or
buried in  selected locations.  Fixation  on clay,
incorporation  in feldspars, conversion to oxide,
elutriation of  the oxide, and fixation of the
elutriant are examples of systems under devel-
opment.

Because of the particular radiotoxicity and long
half-life of strontium-90  and cesium-137, the
removal and separate fixation  and handling of
these two isotopes would  substantially reduce
the effective life  and activity of the waste and
facilitate  its final disposal.  With cesium and
strontium removed, the possibilities of safe
disposal into the  environment under controlled
conditions are greatly increased.

It may be practical to dispose  of the wastes
underground in some cases without any treat-
ment, into formations such as  (1) spaces pre-
pared by dissolution in salt beds or salt domes,
(2) deep basins containing connate brines and
with no hydraulic or hydrologic connection to
potable waters or other potentially valuable
natural resources, and  (3) special excavations
in selected shale formations (Liberman, 1957).
    OIL  AND  SOLVENT  RE-REFINING

Many millions  of gallons of oils  and solvents
are used annually for lubricating vehicle en-
gines and other machinery, transmitting pres-
sure hydraulically,  cleaning manufactured arti-
cles and textiles,  and dissolving or extracting
soluble materials.  In the course of their usage,
these oils and solvents accumulate  impurities,
decompose, and lose effectiveness.  The im-
purities include dirt, scale, water,  acids, de-
composition products,  and other foreign mate-
rials.   Reclaiming some of these oils and sol-
vents for reuse by removal of the impurities
can be effected in many instances by re-refining
processes.

Most re-refiners must practice  stringent econ-
omies  to survive,  and for this reason, second-
hand, cannibalized,  or makeshift equipment is
often employed.  Many re-refiners  also neglect
maintenance, repairs,  and general  housekeeping
in order to keep operating costs  low. As  a result,
                        air pollution control is minimal or lacking unless
                        made mandatory by legislation.


                        RE-REFINING PROCESS FOR OILS
                        Lubricating oils collected from service stations
                        are the main source of supply.  A typical  scheme
                        for re-refining lubricating oil is shown in Figure
                        640.  Re-refining is normally a batch process.
                        Treating clay, for example,  Fuller's  earth, is
                        added to the contaminated oil at ambient tem-
                        perature to aid in the removal  of carbon mate-
                        rials.  The mixture is next circulated through a
                        fired heater, usually a pipe or tube still, to a flast
                        tower for removal of diluent  hydrocarbons and
                        water.   The oil being reclaimed and the products
                        desired determine the final temperature (300°
                        to 600°F).  Live steam,  introduced at the base
                        of the flash tower, is used to assist in this phase
                        of the operation.  Besides  distilling off the light
                        fractions contained in the oil, the steam pre-
                        vents excessive cracking of the oil at  the higher
                        temperatures.

                        A barometric condenser maintains a vacuum on
                        the tower.  The overhead vapors containing
                        steam,  low-boiling organic materials, and en-
                        trained hydrocarbons are aspirated through the
                        condenser to a separator tank.  The condensate,
                        consisting of light gas,  oil, and water, is col-
                        lected and separated in the separator tank.  Non-
                        condensible gases  are usually incinerated in
                        fireboxes of adjacent combustion equipment. The
                        light  oil condensate is decanted from the water
                        and is suitable as liquid  fuel.  The contaminated
                        water is piped to a skimming pond where it is
                        cooled  and  either reused or disposed of by drain-
                        ing to a sewer.  The oil-clay mixture is with-
                        drawn from the tower and filtered.  The oil is
                        blended with additives and is canned or drummed.
                        The clay is usually hauled to a dump.

                        In some re-refineries,  the process is  preceded
                        by a dehydration operation.  Water is removed
                        from the oil by using sodium silicate,  sodium
                        hydroxide,  and heat.  Dehydrated oil is decanted
                        from the mixture and charged to the still.  Sul-
                        furic acid treatment is also  employed at some
                        re-refineries before the refining process.  The
                        acid-treated oil is settled, decanted from the
                        acid sludge, and neutralized with caustic.  Be-
                        fore the clay is added,  sulfuric acid treatment
                        or air blowing may also be used to improve
                        color of the re-refined  oil.
                        RE-REFINING PROCESS FOR ORGANIC SOLVENTS

                        The typical organic solvent re-refining process
                        is similar to that described for oil re-refining.
                        The prime difference between the processes is
                        that the volatilities of the organic solvents re-

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                                      Oil and Solvent Re-Refining
                                             845
                    HaOH

FLI
BOILER
SHB»rK
                       Figure 640.  Composite  flow sheet for re-refining  process.
refined are much greater than those of lubrica-
ting oils.  Mineral spirits, benzene,  toluene,
xylene, ketones, esters, alcohols, trichloro-
ethylene, and tetrachloroethylene from paint,
lacquer, degreasers, and dry cleaners are ex-
amples of  solvents reclaimed by re-refining.

Figure 641 illustrates a typical solvent recov-
ery system.  The mixture to be  processed is
introduced into a settling tank to  permit the
solids to settle out.  The supernatant liquid is
then preheated and charged to a  pot still topped
by a fractionating section, which may be under
                                           IATER OUT
                             CONOEMATE
                                       MTER    PRODUCT
                                       TO SEIER
Figure  641. Typical solvent  re-refining  installation.
vacuum.  Vapors from the still are condensed
in a water-cooled surface condenser.  Reflux-
ing may or may not be done, depending upon the
product, the degree of purity desired, and the
contaminants present.  The condensate is ac-
cumulated in a holding tank,  where a salt such
as sodium carbonate is  added to "break"  the
water from the solvent.  After the water  settles
out, it is removed, and the solvent is  drummed
off as product.
THE AIR POLLUTION PROBLEM


Air Pollution From Oil Re-refining

The  two  primary air pollution problems connected
with oil  re-refining are odors and hydrocarbon
vapors.

Chief odor sources are the contaminated water
and the noncondensible gases from the separator
tank and dehydration tank.  Obnoxious odors
emanate from the skimming pond.  Odors also
occur from the barometric condenser leg.  If
the process water  is aerated in a cooling tower
or spray pond, a serious odor problem occurs.
Other odors can originate from the dehydration
operation and from sulfuric acid  sludges and  '
clay filter cakes.

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846
CHEMICAL PROCESSING EQUIPMENT
In addition to air pollution from odors, oil re-
refining processes can emit some hydrocarbons
into the atmosphere.  These originate from the
noncondensible gases and the layers of light,
volatile hydrocarbons on the surface  of the sep-
arator tank and the  skimming pond.


Air Pollution  From Solvent Re-refining

As in oil re-refining, the chief air pollution
problems are odors but these are less severe
than those occurring from re-refining of lubri-
cating oil.  Sources of emissions are the  settling
tanks during filling  and sludge drawoff, the draw-
off of bottoms  from the still, the product  receiv-
ers, and the water jet reservoir  (if vacuum is
produced by a barometric water  jet).  By creating
a vacuum, the water jet entraps the solvent va-
pors from the  still.


AIR POLLUTION CONTROL EQUIPMENT


Oil Re-refining

The most acceptable method of controlling emis-
sions from re-refining is incineration.  Usually
the firebox of a boiler or heater provides  ade-
quate incineration.  The separator tank must be
covered and vented to a firebox.  The vent line
should be equipped -with a knockout drum and a
flashback arrester.   Additional safety protection
can be achieved by introducing live steam into
the vent line upstream from the firebox.  Other
vessels, for example,  dehydrating tanks and
mixing tanks, may be tied into this system.
Emissions from the barometric,  or contact,
condenser can be  controlled by maintaining a
closed recycle water system or by modifying
the operation by substituting a shell-and-tube-
type condenser.

Recycle  water, highly odorous from contact
with the  oil and heated by contact with the hot
vapors,  must be allowed to cool before reuse.
It  can be controlled by cooling in a covered
settling tank that is properly vented to an
operating boiler or heater firebox. Con-
taminated recycle water must not be  cooled
by aerating in  a spray pond or cooling tower.


Solvent Re-refining

Usually, in the solvent re-refining industry, air
pollution control is  lacking without enforcement,
and solvent vapors are allowed to escape  into
the atmosphere.   If, however, control is  re-
quired, it can  easily be accomplished by venting
the barometric •water jet vacuum system to a
boiler firebox, provided appropriate  flashback
prevention measures have been taken.  Emis-
                       sions from the bottom drawoff of the still are
                       slight since most of the volatiles have been
                       flashed off.  Emissions from the settling tank
                       and the product receivers are normally too
                       small to create any problems, but they can be
                       controlled by being vented also to a boiler fire-
                       box.
                                 CHEMICAL MILLING

                       The chemical milling process was developed
                       by the aircraft industry as a solution to the
                       problem of making light-weight parts of intri-
                       cate shapes for missiles.  These parts could
                       not be formed if mechanically milled first, and
                       no machines -were available that could mill them
                       after they were formed.  Chemical milling is
                       based upon the theory that an appropriate etch
                       solution dissolves equal quantities of metal per
                       given time from either flat or curved surfaces.
                       The process was quickly adopted by the aircraft
                       industry, and etchants were developed for
                       chemically milling many metals used in aircraft
                       and missiles, including aluminum, titanium,
                       stainless steel, and magnesium.


                       DESCRIPTION OF THE PROCESS

                       Before an article can be  chemically milled, the
                       surface of the metal must be clean.   The usual
                       metal surface preparation includes  (1) degreas-
                       ing,  (2) alkaline cleaning,  (3) pickling,  and
                       (4) surface passivation.  The cleaning is needed
                       to provide a clean surface  in order to ensure uni-
                       form dissolving of the metal when it is submerged
                       in the milling solution.   The passivation is needed
                       to protect the surface from oxidation in  air and
                       provide: a  surface that -will accept and hold a
                       masking agent or material.

                       Maskings  are either tapes  with pressure-sensi-
                       tive adhesives or paint-like substances that are
                       applied by brushing, dipping, spraying,  or flow-
                       coating.  Figure 642 shows a sheet of stainless
                       steel being flow-coated with a rubber base mask-
                       ing material.  These paint-like maskings must
                       be  cured,  usually in a bake oven. After curing,
                       the masking is  removed  or  stripped from those
                       areas to be milled.   Figure 643 shows one meth-
                       od  of scribing the masking by use of a template.

                       Milling is accomplished by  submerging the pre-
                       pared article in an appropriate etching solution.
                       The depth of the cut  is controlled by the length
                       of time the article is held in the  etching solu-
                       tion.  To stop the milling action, the article is
                       removed from the etchant and the adhering solu-
                       tion is  rinsed off with water.  During the milling
                       step, some metals are discolored by their etch-
                       ing solutions.   The  smutty discoloration is re-

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                                              Chemical Milling
                                                                                                          847
   Figure  642.  An 18- by 6-foot,  stainless steel
   sheet being  masked by flow-coating with a rub-
   ber-based masking (U.S. Chemical  Milling Corp.,
   Manhattan Beach,  Cal i f.).
                                                                  INCOMING PARTS
                 FINISHED PARTS
 1 SOLVENT DECREASED 180" F  6 PARTS REQUIRING NO
 2 HOT ALKALINE CLEANER 180 F  MASKING
             7 SA
 4 CHROMIC ACID
                                                                                        ETCHING AREA
                                                                                   MASKING FOR SPRAY COAT 13 ETCHING TANK
                                                                                   TEMPLATE MASKING
                                                                                             14 CONTROL PANEL
                                                                                  10 pfllNT BOOTH
                                                                                  H DRYING OVEN
                                                                                  u TAPER ETCHING TANK
                                   15 COLD WATER RINSE

                                   IE SMUT REMOVAL
17 MASKING REMOVAL

13 INSPECTION

19 CENTRIFUGE

20 BVPROOUCr
      This  process is patented and  licensed by
      Turco Products Co., Wilmington,  Calif.
  Figure 644.  A  flow diagram showing  the  typical
  steps necessary to the chem-mi11 ing process
  (Scheer,   1956).
Figure  643.  The  masking on a  titanium part is being
scribed  bv  use  of  a template. After  scribing,  the
masking  will  be  stripped from those  areas shown by
the holes  in  the templates.  The  stripped areas will
then be  milled.  The black part  in  the foreground and
those  in the  background have not yet  been scribed
(U.S.  Chemical Milling Corporation, Manhatten  Beach
Calif.).
 moved in a brightening solution such as cold,
 dilute nitric acid.  A flow diagram of the pro-
 cess is shown in  Figure 644.

 After the milling, the paint-like masking is
 softened in a solution consisting, for example,
 of 80 percent chlorinated hydrocarbons and 20
                                                           percent high-boiling alcohols,  and is then
                                                           stripped off by hand.  Figure 645 shows the in-
                                                           spection of a part.  The metal thickness is mea-
                                                           sured before the masking is  removed.  Figure
                                                           646 shows the masking being removed from a
                                                           section of a wing skin.   The  entire side shown
                                                           was masked,  and some areas of the  other  side
                                                           were etched.   In Figure 647, the masking  is
                                                           being stripped from a milled part.
Figure 645.  Inspection of milled parts.  The  in-
strument measures  the metal thickness  before the
masking  is  removed  (U.S.  Chemical Mi 11 ing  Corpora-
tion,  Manhatten  Beach,  Calif.).

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 848
                              CHEMICAL PROCESSING EQUIPMENT
             Figure  646. Stripping masking from a section of  a  wing skin  of  a
             B-58. The entire side shown was masked.  Some areas of  the  other
             side  were milled (U.S. Chemical Milling Corporation,  Manhatten  Beach
             Cal if.).
                           Figure  647.'Masking being stripped,  milled parts with masking still
                           in  place,  and milled parts with masking removed (U.S. Chemical  Mil-
                           ling Corporation,  Manhatten Beach, Calif.).
ETCHANT SOLUTIONS

Etchants range from sodium hydroxide solution
for aluminum to aqua regia for stainless steel.
For milling a specific metal, the concentration
of the chemical in the solution may vary widely
between different operators; however,  each
operator controls the concentration of his solu-
tion to -within very close limits.  The concen-
tration of the solution affects the milling rat.e;
therefore, it must be closely controlled to ob-
tain the desired rate.  For milling aluminum,
the solutions in use contain from 7 to 30  per-
cent sodium hydroxide.  For milling magnesi-
um, dilute sulfuric acid  solutions are adequate.
Stainless steels require  strong  solutions, usu-
ally aqua regia fortified  with sulfuric acid.  In
most of the milling solutions, surface-active

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                                          Chemical Milling
                                            849
agents are used to ensure smooth, even cuts.
The surface-active agents also reduce the ten-
dency toward mist formation by reducing  the
surface tension of the solution.  The solutions,
during milling  operations, are generally main-
tained at constant temperatures ranging from
105° to 190° F.

THE  AIR POLLUTION PROBLEM

The air contaminants emitted  in the prepara-
tion of metals  by chemical milling consist of
mists, vapors, gases, and organic solvents.

 Mists

A mist of the etching solution  used in a milling
process is discharged from the milling tank
owing to entrainrnent of droplets of the solution
by the gas bubbles formed by the chemical
action of the etchant  on the metal.  The amount
of mist generated depends upon factors such as
the nature of the chemical reaction,  the solu-
tion temperature, and the surface tension of the
solution.   Since the solutions from which the
mists are formed are very corrosive, the mists,
too,  are very  corrosive and are capable of caus-
ing annoyance, or a nuisance,  or a health hazard
to persons,  or damage to property.

 Vapors

Some of the  acid solutions used,  such as  hydro-
 chloric and  nitric, have high  vapor pressures
 at  the temperatures  used for  the milling  pro-
 cess; therefore,  appreciable  amounts of  acid
 vapors are discharged.  Unlike the discharge
 of  mists,  which occurs only during the milling,
 the vapors are discharged continuously from the
 hot solution.  Under certain atmospheric condi-
tions, the vapors condense, forming acid mists
 in the atmosphere.

Gases

Since hydrogen is formed in chemical  milling,
proper ventilation must be provided to prevent
the accumulation of dangerous concentrations of
this gas.

Solvents

Organic solvent vapors may be emitted from the
vapor degreaser, the maskant area,  and the
curing station  in the  cleaning and masking pro-
cesses.  This type of air contaminant, and the
method of controlling it  are  described elsewhere
in this manual.  Alkaline cleaning, pickling, and
passivating tanks from the other phases of the
cleaning processes have been found to be  minor
sources of air  pollution.
HOODING AND VENTILATION REQUIREMENTS

The air contaminants  released from chemical
milling tanks can be captured by local exhaust
systems.  Since  open  tanks are used to provide
unobstructed working  area, most exhaust sys-
tems employ slotted hoods to capture the mists
and vapors.  In designing slot hoods for chem-
ical milling equipment,  it is particularly im-
portant to provide for the elimination of exces-
sive cross-drafts as well as for adequate dis-
tribution of ventilation along the entire length
of the hoods.  The minimum ventilation rates
previously mentioned  in Chapter 3 are for tanks
located in an area having no cr oss-drafts.  If
the tank is to be  located outside or in a very
drafty building, either the ventilation rate will
have  to be  greatly increased or baffles must be
used  to shield the tank from -winds or drafts.
In some instances, both baffles and increased
ventilation are needed.

Adequate distribution  of ventilation along the
entire length of a slot can be attained by pro-
viding a high slot velocity and a relatively low
plenum velocity.   The slot velocity should be at
least 2, 000 fpm,  and the plenum velocity should
be not more than half  of the slot velocity.  With
hoods more than  10 feet in length,  either multi-
ple takeoffs or splitter vanes are needed. Enough
takeoffs or  splitters should be used to reduce
the length of the  slot to sections not more than
10 feet long.

Under excessively drafty conditions,  a hood en-
closing the  tank can be used to advantage.   The
hood  should cover the entire tank and have suf-
ficient height to accommodate  the largest metal
sections that can be handled in the tank. Vari-
ous methods have been used to get work into and
out of the tank.   In one installation, the hood has
doors on one end, and a monorail, suspended
below the hood roof, that runs out through the
doors.  The -work is carried on the monorail
into the hood and above the solution.  After the
•work is lowered  into the solution, the doors are
closed, -when necessary, to ensure  complete
capture of .the air contaminants created.  In
another installation, the hood is left open on one
end,  and a slot hood placed across the opening.
The top of  the hood is  slotted to provide for the
movement  of the  crane cable.  This slot is
nominally closed with rubber strips,  which are
pushed aside by the cable during movement of
the crane.
AIR POLLUTION CONTROL EQUIPMENT

Many types of wet collectors that can control
the emissions from, chemical milling tanks are
commercially available.  The one most common-

-------
850
                               CHEMICAL PROCESSING EQUIPMENT
 ly used is the spray and baffle type, owing prob-
 ably to its low cost and ease  of coating with cor-
 rosion-inhibiting materials.  Moreover, the oper-
 ation and maintenance  of this type are simple
 and inexpensive  compared with those of other
 types of scrubbers.

 Figure 648 shows an exhaust and mist control
 system employing  two  scrubbers, one for each
 side of a 24-foot-long by 6-foot-wide tank used
 for chemically milling stainless steel and ti-
 tanium.   The etching solution is a mixture of
 hydrochloric, nitric, and sulfuric acids and is
 heated to 150°F.  Acid vapors discharged from
 the solution are  captured by slot hoods, one on
 each side of the  tank.   The ducts from each
 hood exit downward from the center.   Each hood
 has four splitter vanes, which divide it into four
 sections.  The overall hood length is 24 feet,
 the end-sections and those adjacent being 4 feet
 long each, and the  center section being 8 feet
 long.   Distribution of ventilation is excellent.
 Each hood is supplied with 18, 000 cfm ventila-
 L
Figure  648.  A  tank used for the  chemical milling of
stainless  steel, and part of its air  pollution
control  system. The hoods,  ductwork,  and scrubbers
shown are  made  entirely of  polyester  resin rein-
forced  with  fiberglas. The  fans  and discharge ducts,
not shown, are  steel-coated with polyester resin.
(U.S.  Chemical  Mi 11 ing Corporation, Manhatten Beach,
Calif.).
 tion, and the slot is  sized to give an intake ve-
 locity of 2, 000 fpm.   The plenum velocity is
 less than 1, 000 fpm.  It is estimated that this
 system provides sufficient ventilation to  capture
 at least 95  percent of the vapors emerging from
 the process.

 The scrubbers are of the spray and baffle type,
 as shown in Figure 649.  They are cylindrical,
 two baffles forming three concentric chambers.
 Gases enter at the top and flow down through
 the center cylindrical section.   Water from a
 bank of sprays scrubs the gases as they enter
 this  section.  The bottom of the scrubber is
 filled with water to a depth of 1 foot.  The gases
 and scrubbing water  flow downward through the
 center section and impinge on the water.  The
 gases turn 180 degrees and flow upward through the
 second chamber.  Most of the scrubbing water
 remains in the sump.  The depth of water in the
 sump is maintained at a uniform level with a
 float valve  and an overflow line.  The  scrubber
 is equipped with a pump to circulate the sump
 water to the sprays.   In this  installation, how-
 ever, only fresh water is used, the  sump being
 kept full and overflowing all the time.

 The gases flowupward through the second section and
over the second baffle. They turn 180 degrees to enter
 the third section.  In the third  section,  the gas-
 es flow down and around to the  outlet port. Most
 of the entrained moisture entering the  second
 section is removed either by impingement on
 the walls of that section or by centrifugal im-
 pingement during the 180-degree change of direction
 into the third section.  The last of the  entrained
 water is  deposited on the walls of the third sec-
tion.  The  gases then flow from the  scrubber  to
the fan, from which they are discharged to the
 atmosphere through ducts.

 The hoods,  the scrubber,  and the duct-work con-
necting the  hoods to the scrubbers and the scrub-
bers to the  fans are made entirely of polyester
 resin reinforced with glass fibers.   The fans  and
 discharge ducts are made of  steel  coated with
 polyester resin.

 The existing system, provides satisfactory con-
trol  of the  vapors.  It captures an  estimated 95
percent of  the vapors at the tank, and the gases
 discharged  have only a slight acid  odor.


 Corrosion Problems

 Whenever moisture is present  in an exhaust
 system,  the iron or steel surfaces  should be
 coated to prevent corrosion.  However,  since
 zinc is soluble in both acid and alkaline solu-
 tions,  galvanized iron cannot be used when
 chemical milling tanks are vented.   A coating

-------
                                            Chemical Milling
                                                                                       851
                                             ACCESS'U,
                                              DOOR\
                                              INNER +
                                              SPRAYT
                                            NOZZLES
                         AUTOMATIC
                            FLOAT
                            VALVE
               WATER  OVERFLOW
              SUPPLYV
           MOTOR AND.
          PUMP ASS'

             DRAIN
?M
                                  I  PI  /STANDPIPE
                                       AND OVERFLOW
                                             DRAIN
                                                                      ACCESS
                                                                     TOOR
                                              *_*-;
                                        fl>^t-*4	,,
                                        I!  ACCESS   |+
                                       i{S__MR___!t
Model
24
30
42
60
72
Motor3
hp
1
1
1*
1*
2
Pump
gpm
14
14
18
20
22
Drain h
weight"
110
260
380
800
963
A
24
30
42
60
72
B
12
18
24
32
42
C
22
32*
43
51*
64*
D
12
IB
24
32
42
E
12S
12
12
12
12
F
69%
80
92
102
132
G
9
10*
12
14
24
H
9
9
8
12
18
J
22*
38
42
50
60
K
35*
40
46
55
76*
I
6
9
12
18
24
Spray
nozzl es
7
7
9
10
11
Drain
size, i n .
1
1
1
1
1
Min.- range-max.
fpm
1,000
1,000
1,000
1,000
1.000
cfm
800
1,700
3,000
5.200
9,500
fpm
3,000
3,000
3,000
3,000
3,000
cfm
2,300
5,200
9,000
16,000
28,000
           aMotor is 440/220 volts, 3 phase, 60 cycle  Exhaust fan and motor furnished upon request.
            Does not include reelrculat ing motor and pump.

                    Figure 649. A  scrubber used  to  control  the  acid  vapors  discharged
                    from a tank used to mill  stainless  steel  (Lin-0-Coat  scrubber,
                    manufactured by Diversified  Plastics,  Inc.,  Paramount,  Calif.).
such as polyvinylchloride  (PVC), which is not
attacked by either dilute acids or dilute alkalies,
should be used.  It has been found, however,
that the PVC linings in ducts and scrubbers can-
not withstand the strongly oxidizing acids used
for stainless steel and titanium milling.  These
highly corrosive acids have been successfully
handled in exhaust systems made of polyester
resins reinforced with fiberglas.  Hoods, ducts,
and scrubbers are available made entirely of
polyester-fiberglas material.  Figure  648 shows
                                        an air pollution control system venting a 24-foot -
                                        long tank for  stainless steel chemical milling.
                                        The hoods,  ductwork up to the blowers, and the
                                        scrubbers are made entirely of polyester-fiber-
                                        glas material.  The steel blowers and discharge
                                        ducts are coated with polyester resin.  Some
                                        blower manufacturers are now advertising blow-
                                        ers with scrolls made entirely of polyester-
                                        fiberglas and with steel -wheels coated with the
                                        same material.
  234-767 O - 77 - 56

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                     CHAPTER  12




   ORGANIC  SOLVENT EMITTING  EQUIPMENT
              SOLVENTS AND THEIR USES






      STANLEY CAVDEK, Air Pollution Engineer
             SURFACE COATING OPERATIONS






       MILTON COHEN,  Air Pollution Engineer
PAINT BAKING OVENS AND OTHER SOLVENT-EMITTING OVENS






 GEORGE RHETT, Intermediate Air Pollution Engineer




JULIEN A. VERSSEN,  Intermediate Air Pollution Analyst
                 SOLVENT  DEGREASERS





 SANFORD M. WEISS, Principal Air Pollution Engineer
              DRY CLEANING EQUIPMENT






     WILLIAM C. BAILOR, Air Pollution Engineer




 PAUL G.  TALENS,  Intermediate Air Pollution Engineer

-------
                                            CHAPTER 12

                          ORGANIC  SOLVENT EMITTING  EQUIPMENT
       SOLVENTS AND  THEIR  USES
INTRODUCTION
Organic solvents are some of the most common
and -widely used products of our society.  They
are involved deeply in our daily lives in such ac-
tivities as  making and cleaning the clothes we
•wear,  making and coating the vehicles we drive,
packaging the foods we eat,  printing the materi-
als we read, and finishing the furniture we use.
The utility and value of organic  solvents can be
recognized from the following listing of their uses,
classified by the functions and actions they per-
form (Scheflan and Jacobs,  1953):

    1.  Reducing viscosity of liquids as  in the
       thinning of paints, enamels, lacquers,
       and other coatings;

    2.  plasticizing of  resins as in lacquer manu-
       facture to impart toughness and flexibili-
       ty to the film;

    3.  forming azeotropic mixtures as a means
       of separating two or more  liquids;

    4.  extracting one  or more substances from
       a mixture by differences in solubility  as
       in the extracting  of fats and tallows from
       meat packing -wastes;

    5.  degreasing and removing oils and grease
       from equipment,  textiles,  and other ob-
       jects;

    6.  dissolving solids  as for purifying or re-
       fining pharmaceuticals by recrystalliza-
       tion or as in dissolving waxes;

    7.  producing solutions containing waterproof-
       ing or fire-retardant agents using the so-
       lution to impregnate a material with those
       agents;

    8.  serving as carriers for some chemicals
       for  facilitating chemical reactions.

In none of the preceding  listed uses do the organ-
ic solvents enter into reactions -whereby they are
chemically changed.  After an organic solvent
has served its purpose,  its continued presence in
the product is usually not desired and it must be
removed.  In so doing,  it may be recovered for
reuse and recycling.  Too often, however,  the
solvent is wasted to the atmosphere by  natural
or forced evaporation.  When architectural coat-
ings are  applied with solvents, the solvents must
evaporate into the atmosphere so that the coating
can form a film or barrier.  When industrial
coatings  are applied-with solvents, the  solvents
are discharged into the atmosphere by forced
evaporation in ovens. When clothes are cleaned-with
solvents, the solvents must be removed, usually
by heat,  before the clothes can be worn again.

Thus,  it  is found that solvent vapors are emitted
from paint bake ovens,  spray booths, dip tanks,
flow coaters,  roller coaters, degreasers, dry
cleaning  equipment, printing presses, architec-
tural coating operations,  and other equipment
wherein  solvents or materials containing solvents
are used.  These organic emissions may repre-
sent a  substantial portion of  all  organic vapors
present in a community' s atmosphere.   A rule
of thumb which has been reasonably close for Los
Angeles  County indicates that about 1/6 pound of
solvent is emitted each day for each person.

As  of 1969, control legislation had been  enacted
in a few  California areas for the purpose of re-
stricting these emissions. An example  of such
prohibitive requirements is Rule 66 of the Los
Angeles  County Air Pollution Control District.

RULE 66

Rule 66 limits organic solvent emissions by apply-
ing standards  to essentially two types of industrial
operations where organic solvents are present:
(1)  heat curing,  baking, heat polymerizing, or
operations -where solvents come into contact with
flame; (2) other operations using organic solvents
classified as "photochemically reactive. "

For the purposes of Rule 66, organic solvents
are defined as organic materials which are liquids
at standard conditions and which are used as
dissolvers, viscosity reducers, or cleaning
agents. Organic materials are defined by the  rule
as chemical compounds of carbon,  excluding car-
bon monoxide,  carbon dioxide, carbonic acid,
metallic  carbonates, and ammonium carbonate.
Not all solvents have the same photochemical
reactivity; hence,  all need not be controlled to the
                                                855

-------
856
ORGANIC SOLVENT EMITTING EQUIPMENT
same degree.  Olefins, generally the most photo -
chemically reactive,  require the most stringent
restrictions; xylene and other aromatics of equal
or higher molecular weight require slightly less
restrictive measures; compounds such as toluene,
branched chain ketones, and trichloroethylene re-
quire still less restriction.  Benzene,  saturated
halogenated hydrocarbons,  perchlorethylene,
trichloroethane,  saturated aliphatics, and naph-
thenes are relatively nonreactive.  The varying
photochemical reactivities of solvents are taken
into account by Rule 66k, which defines solvents
as photochemically reactive or nonphotochemically
reactive by the volume percentages of certain
components.  This classification is then used to
determine the degree of control required by other
sections of  Rule  66.  A photochemically reactive
solvent has been defined as any solvent with an
aggregate of more than 20 percent of its total
volume composed of the compounds classified be-
low or which  exceeds any of the following individ-
ual volume  limitations:

    1.  A combination of hydrocarbons,  alcohols,
       aldehydes, esters, ethers, or ketones
       having an olefinic or cyclo-olefinic  type of
       unsaturation.  Subclass limitation - 5 per-
       cent.

    2.  A combination of aromatic compounds
        with eight or more carbon atoms to the
        molecule, except ethylbenzene.   Subclass
        limitation - 8 percent.

    3.  A combination of ethylbenzene, ketones
        having branched hydrocarbon structures,
        trichloroethylene,  or toluene.  Subclass
        limitation - 20 percent.

The following examples illustrate the use of Rule
66 to determine  "photochemical  reactivity. "  In
addition, Table 229 lists examples  of photochemi-
cally reactive solvents and Table 230 lists non-
photochemically reactive solvents as defined by
Rule 66k.

Given:

The solvent system for  an industrial coating  has
the following  composition:
         Toluene
                             Table 229.  EXAMPLES OF SOLVENTS
                              IN PHOTOCHEMICALLY REACTIVE
                                       CATEGORIES21
         Xylene
         Isopropyl alcohol
         Saturated aliphatic
          solvents
         Total
   10. 0%

   10. 0%

   20. 0%
   60. 0%

  100. 0% by volume
k(l)
solvents
(limited
to 5% of
solvent
system)
Turpentine
Isophorone
Mesityl
oxide
Dipentene




k(2)
solvents
(limited
to 8% of
solvent
system)
Xylene
Tetralin
Cumene





k(3) solvents
(limited to 20%
of solvent system)
Toluene
Diacetone alcohol
Trichloroethylene
Methyl isobutyl ketone
Diisobutyl ketone
Methyl isoamyl ketone
Ethyl isoamyl ketone
Ethylbenzene
                          The total of the three categories cannot exceed
                          20 percent.

                         Solution:
                         Tabulate the materials in the solvent that may be
                         photochemically reactive as follows: [(1), (2),
                         (3) refer to photochemically reactive groupings
                         listed above].
                            Toluene

                            Xylene
                            Isopropyl alcohol
                            Saturated aliphatic
                             solvents

                            To*-al
(1)
0
0
0
0
(2)
0
10.0
0
0
(3)
10. 0
0
0
0
                           0
 10.0    10.0
The (2) group is limited to 8 percent by volume;
the (3) group is limited to 20 percent by volume.
Since the 8 percent limit of the (2) group has been
exceeded, the solvent system is photochemically
reactive.  This in spite  of the  fact that the sum of
(1), (2), and (3) does not exceed 20 percent.
Given:

A coating solvent system has the following com-
position:
       Toluene
 Problem:
 Determine if the solvent system is photochemically
 reactive as defined by Rule 66.
      Xylene

      Methyl isobutyl ketone

      Isophorone
      Saturated aliphatic
        solvents

      Total
 15. 0%

  2. 0%

  7. 0%
 10. 0%

 66. 0%

100. 0% by volume

-------
                                      Solvents and Their Uses
                                                                     857
          Table 230.   EXAMPLES OF SOLVENTS EXEMPT FROM RULE 66 REQUIREMENTS
         Alcohols
      Esters
    Ketones and
 chlorinated solvents
   Miscellaneous
   Tetrahydrofurfuryl
   Ethanol
   Propanol
   Isobutanol
   Butanol
   Isopropanol
   Methanol
   sec-butanol
   Methyl amyl alcohol
   Amyl alcohol
   Hexanol
   2 ethyl butanol
   2 ethylhexanol
   Isooctanol
   Isodecanol
   Isohexanol
 Ethyl acetate
 Isopropylacetate
 Isobutyl acetate
 n-butyl acetate
 Isobutyl isobutyrate
 2 ethylhexyl acetate
 Methyl amyl acetate
 n-propyl acetate
 sec-butyl acetate
 Amyl acetate
 Methyl acetate
Ketones
 Acetone
 Methyl ethyl ketone
 Cyclohexanone

Chlorinated solvents
 Perchlorethylene
 1,1, 1-trichlor ethane
 Carbon tetrachloride
Paraffins
Naphthenes
1 -nitr opropane
2-nitropropane
Tetrahydrofuran
Dimethyl formamide
Benzene
Nit rome thane
Nitroethane
Problem:

Determine if the solvent system is photochernically
reactive as defined by Rule 66.
Solution:

Tabulate the materials in the solvent that may be
photochernically reactive as follows: [(1), (2),
(3) refer to photochernically reactive groupings
listed above]:
    Toluene

    Xylene

    Methyl isobutyl ketone

    Isophorone

    Aliphatic solvents

    Total
(1)
0
0
0
10. 0
0
(2)
0
2. 0
0
0
0
(3)
15. 0
0
7. 0
0
0
10.0   2.0   22.0
This solvent system is photochernically reactive
for three reasons:

    1.  The group (1) total exceeds the allowable
       5 percent.

    2.   The  group (3) total exceeds the allowable
       20 percent.

    3.  The  total of all groups (34 percent) exceeds
       the allowable total of 20 percent.

Limitations  on  the Use of  Pbotochemically
Reactive Solvents

Rule 66 (b) limits the quantity of photochernically
reactive material which may be discharged.  A
limit of 40 pounds per day is placed on the quan-
tity of organic material which may be discharged
into the atmosphere in any one day from any one
article or machine which employs, applies,  evap-
orates, or dries such a solvent.  Rule 66(c) (effec-
tive September 1, 1974) limits the discharge of
nonphotochemically reactive organic solvents to
no more than 3, 000 pounds per  day.  It is impor-
tant to note that drying does not encompass such
operations as baking, heat polymerization, or
heat curing.  In addition,  no contact with flame
is permitted.  Operations involving such proc-
esses are covered below.
Baking  and Curing Operations

Emissions resulting from processes where sol-
vent-containing materials are heat-cured, baked,
or heat-polymerized, or where solvents  come in-
to contact with flame, are generally more photo -
chemically reactive than the raw  solvents alone.
For this reason, Rule 66a limits  the discharge
from the baking operations listed above to 15
pounds per day.  The limit applies regardless of
whether the solvents used in the original material
are defined as photochernically  reactive or non-
photochemically reactive.

AIR POLLUTION  CONTROL  MEASURES

If the 15-pound and 40-pound daily limits of Rules
66a and 66b are exceeded, the total emissions
must be reduced by at least 85 percent overall
or to not more than the stated limit.   Reduction
for compliance with Rule 66  can be achieved by
the use of afterburners or adsorption devices or
by any other method considered by the  Los Angeles
County Air Pollution Control District as being
equally effective.

-------
858
ORGANIC SOLVENT EMITTING EQUIPMENT
Incineration, if employed, must be capable of ox-
idizing at least 90 percent of the carbon in the or-
ganic material to carbon dioxide.  This require-
ment is not waived by the 85 percent reduction
above.  Since temperatures of 1400° to 1500 °F
are sometimes required,  heat recovery for use
elsewhere in the process  or for preheating the in-
coming gases will reduce the  costs of  the after-
burner operation. The determination  of •whether
90 percent of the carbon in the organic materials
has been oxidized to carbon dioxide is  made by
chromatographic separation of the components in
the incoming and exit streams to the afterburner
and combustion and measurement of the resulting
carbon dioxide in an infrared  spectrophotometer.

Activated carbon adsorbers that can be regenera-
ted by the use of steam,  with the  subsequent
condensation and separation of solvent and water,
are also possible alternatives.  They are especial-
ly suitable where solvent  recovery is desirable be-
cause of cost considerations or where  incineration
is impractical as with chlorinated solvents.

Generally, neither of these methods is feasible
where large air volumes are involved, as in
paint spraying operations. In such instances, it
has proven more economical to reformulate the
solvent systems to the extent  of making them non-
photochemically reactive  and  thereby removing
the limitation on the quantity of organic material
which may be emitted.

Various problems are encountered in this approach,
such as cost considerations,  relative  solvency,
evaporation rates, compatibilities, and partial
solvation  of undercoats to name a few. Never-
theless, since the inception of Rule 66, it has
been proven that reformulation can almost invari-
ably be accomplished.  In the rare instance where
a solution cannot be found, a change from one
basic coating system to another may be required.

Research is underway to develop solventless
coatings.   Some of these coatings already have
been developed, including powder coatings,
plastisols, and electrocoating and radiation
curing, which enable low viscosity monomers
to be used.


     SURFACE  COATING OPERATIONS
INTRODUCTION

Many manufactured articles receive coatings for
surface decoration and/or protection before being
marketed. A number of basic coating operations
are utilized for this purpose,  including spraying,
dipping,  flowcoating, roller coating and electro-
coating.   There are variations and combinations
                         of these operations, each designed for a special
                         task.  For example, articles may be coated by
                         spraying with either an air-atomized, airless,
                         electrostatic, airless-electrostatic,  or hot-spray
                         method.   The coatings applied in these operations
                         vary widely as to composition and physical pro-
                         perties.

                         TYPES  OF  EQUIPMENT

                         Spray  Booths

                         In spraying operations, a coating from a supply
                         tank is forced, usually by compressed air, through
                         a "gun'1 -which is used  to direct the coating as a
                         spray  upon the article to be coated.  Many spray-
                         ing operations are  conducted in a booth or enclo-
                         sure vented by a fan to protect the health and safety
                         of the  spray gun operator by ensuring that explo-
                         sive and toxic concentration levels of solvent va-
                         pors do not develop.  Table 231 shows threshold
                         limit values of typical coating solvents.  These
                         values are average concentrations  to which work-
                         ers may be safely exposed for an 8-hour day •with-
                         out adverse effect to their health.

                         Booths used in spraying operations, for conven-
                         ience, are referred to as paint spray booths, al-
                         though the actual coating sprayed may be other
                         than paint.  Such booths are discussed in relation
                         to particulate removal for ceramic and metal
                         deposition equipment in Chapter 7.

                         Paint spray booths may have an independent air
                         supply delivering heated, filtered,  and/or humid-
                         ified air.   Booths  not having a direct independent
                         air supply may or may not be equipped to filter
                         incoming  plant air  as well as to remove particu-
                         late matter from the exhausted air.  Typical
                         floor type paint spray booths are shown in Figures
                         650,651,  and 652.

                         Flowcoating Machines

                         In flowcoating  operations,  such as  shown in Fig-
                         ures 653  and 654, a coating is fed through over-
                         head nozzles so as to flow in a steady stream
                         over the article to be coated, which is  suspended
                         from a conveyor line.  Excess paint drains from
                         the article to a catch basin from which it is re-
                         circulated by a pump back to the flow nozzles.
                         Impinging heated air jets aid in the removal of
                         superfluous coating and solvent from the coated
                         article prior to its entering an oven for baking.

                         Flowcoating is used on articles which cannot be
                         dipped because of their buoyancy,  such as fuel-
                         oil tanks, gas  cylinders, pressure bottles, etc.

                         A new variation of the flowcoating  process, elec-
                         trophoretic flowcoating, has been developed and
                         already has reached production scale in Europe.

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                                    Surface Coating Operations
                                                                                                  859
           Table 231.   THRESHOLD LIMIT VALUES OF TYPICAL PAINT SOLVENTS

Acetone
Amyl acetate
Methyl ethyl ketone
Butyl acetate
Cellosolve
Ethyl acetate
Cellosolve acetate
Ethanal
Naphtha (petroleum)
Toluene
Xylene
Mineral spirits
Trichloroethylenec
Lower explosive
limit (LEL)a
%
2. 15
1. 1
1. 81
1.7
2.6
2. 18
1.71
3.28
0. 92 to 1. 1
1.27
1.0
0.77
ppm
22, 000
11, 100
18, 400
17, 300
26,700
22, 300
17,400
33, 900
9,290
12, 600
10, 100
7,760
25% of
LEL,
ppm
5, 500
2, 770
4, 600
4, 320
6,670
5, 570
4, 350
8,470
2, 320
3, 150
2, 520
1, 940
Maximum allowance
concentration, "
ppm
1, 000
200
250
200
200
400
100
1,000
500
200
200
500
100d
        Adapted from:  Factory Mutual Engineering Division,  1959.

        Adapted from:  American Medical Association, 1956,  except as noted.

        Nonexplosive at ordinary temperatures.

        Adapted from:  American Conference of Governmental Industrial Hygienists, I960.
Figure 650.  Water-wash spray  booth (The  Devilbiss
Co.,  Toledo,  Ohio).
Figure 651.  Paint arrester  spray booth  (The Devil-
biss  Co., Toledo, Ohio).

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860
ORGANIC SOLVENT EMITTING EQUIPMENT
  Figure 652.   Dry baffle spray booth (The Devilbiss
  Co., Toledo,  Ohio).
 Figure 653.   Side view of a flowcoating machine (In-
 dustrial Systems, Inc.,  South Gate, Calif.).

The item to be coated is made the anode and the
flow nozzle is made the cathode.  The same prin-
ciples are applied in electrocoating,  or electro-
phoretic deposition,  which is  described briefly
under "Dip Tanks. "
                                                       Figure 654.  View of  a flowcoating machine showing
                                                       dram decks and enclosures (Industrial  Systems,  Inc.,
                                                       South Gate, Cal if.1.
                         Dip Tanks

                         Dip tanks are simple vessels which contain a work-
                         ing supply of coating material.  They usually are
                         equipped with a close-off lid and a  drainage res-
                         ervoir, which are activated in case of fire.  The
                         object to be coated is immersed in the coating ma-
                         terial long enough to be coated completely and
                         then removed from the tank.  Provision is made
                         to drain the excess coating from the object back
                         to the tank, either by suspending the work over
                         the tank or by using drain boards that return  the
                         paint to the dip tank.  Some method usually is
                         provided for agitation of the coating material in
                         the tank, in order to keep it uniformly mixed.
                         The most frequently used  method consists of
                         withdrawing coating by a pump from the tank
                         bottom and returning it to a point near the tank
                         top but still under the liquid surface.

                         Electrocoating, a variation of the ordinary dip
                         tank process of coating, is the electrodeposition
                         of resinous materials on surfaces.  This opera-
                         tion is sustained from water solutions, suspen-
                         sions, or dispersions.  In the electrocoating  pro-
                         cess, the object being coated is the anode and
                         the tank containing the dilute solution, suspension
                         or dispersion of film-forming materials usually
                         is the cathode.  The dilute coating  system is  con-
                         verted from a water soluble or dispersible form
                         to a dense, -water insoluble film on the surface be-

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                                       Surface Coating Operations
                                            861
ing coated.  An advantage of electrocoating com-
pared with dipping,  flowcoating, or electrostatic
spraying is its built-in property of producing uni-
form thickness on all solution-wetted surfaces,
including sharp edges and remote  areas.

Roller Coating Machines

Roller coating machines are similar to printing
presses in principle.  The machines usually
have  three or more  power-driven  rollers.  One
roller runs partially immersed in the coating and
transfers the  coating to a  second,  parallel roller.
The strip or sheet to be coated is  run between the
second and third roller and is  coated by transfer
of coating from the  second roller.  The quantity of
coating applied to the  sheet or strip is established
by the distance between the rollers.


THE AIR  POLLUTION PROBLEM

Air Contaminants from Paint  Spray Booths

The discharge from a paint spray  booth consists
of particulate matter and organic solvent  vapors.
The particulate matter, representing solids in the
coating,  derives from that portion of the coating
which does not adhere to the target of the spray-
ing, the inside of the booth,  or its accessories.
The organic solvent vapors derive from the
organic solvent,  diluent,  or  thinner which is used
with the coating and evaporates from coating sus-
pended in the  air stream,  on the target of  the
spraying, or on the inside surfaces  of the booth and
its accessories.  The choice of the spraying method,
air atomization, electrostatic, or other,  is a fac-
tor in determining the amount  of overspray, that
is,  the amount of sprayed coating which misses
the article being coated.   The  configuration of the
surface to be  sprayed is another factor influencing
the amount of overspray.  Table 232 gives some
typical overspray percentages.

The particulate matter consists of fine coating
particles, whose concentration seldom exceeds
0.01 grain per scf of unfiltered exhaust.  Despite
this small concentration,  the location of the ex-
haust stack must be carefully  selected so as to
prevent the coating  from depositing or spotting on
neighboring or company property.

Solvent concentrations in spray booth effluents
vary from 100 to 200 ppm.  Solvent emissions
from  the spray booth stacks  vary widely with
extent of operation,  from  less  than 1 to over 3,000
pounds per day.  Organic  solvent vapors,  in
general,  take  part in atmospheric  photochemical
reactions leading to eye irritation and other photo-
chemical  smog effects.  A more detailed  discus-
sion and listing of the principal photochemically
reactive and nonphotochemically reactive  solvents
     Table 232.   PERCENT OF OVERSPRAY
    AS A FUNCTION OF SPRAYING METHOD
           AND SPRAYED SURFACE
Method of
spraying
Air atomization
Airless
Electrostatic
Disc
Airless
Air -atomized
Flat
surfaces
50
20 to 25

5
20
25
Table leg
surface
85
90

5 to 10
30
35
Bird cage
surface
90
90

5 to 10
30
35
are found in the section "Solvents and Their Uses. "
Solvent odors also may cause local public nuisances.
Essentially,  all the solvent in or added to the
coating mixture eventually is evaporated and
emitted to the atmosphere.   A notable  exception,
however, would be the styrene diluent  in a poly-
ester resin coating mixture.  The  styrene  diluent
is polymerized along with the polyester resin,
thus classifying it as a reactant.  Although organ-
ic solvents have different evaporation rates,  sol-
vent emissions by flash-off can be estimated at
various times following the coating operation from
the specific composite solvent formulation.  Fig-
ure 655 relates solvent flash-off time with percent
solvent emission for various  classifications of
coatings.  Flash-off can be defined as  that quantity
(in terms of percent or weight) of solvent evapo-
rated, under ambient or forced conditions, from
the surfaces  of coated parts during a specified
time period.

The following examples show some factors to be
considered in determining the solvent control
measures  required  to operate the surface  coating
equipment in compliance  with air pollution emis-
sion standards.  Note that the solvent emission
due to flash-off of solvent in the air space  sur-
rounding the coated article after it leaves  a spray
booth is  added to other emissions because  of the
provisions of Rule 66(b) and (c).

Problem:

1.  Calculate the weight of solvent emitted  from a
   spray booth and associated oven.

2.  Evaluate  spray booth emissions with  respect
   to Rule 66.

Given:

A conveyorized air-atomized electrostatic  spray
booth in which  15 gallons  per day of reduced alkyd
enamel (5 gallons of enamel plus 10 gallons of

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862
ORGANIC SOLVENT EMITTING EQUIPMENT
                                        1. LACQUER: CLEAR, SEMI-GLOSS. FLAT, PIGMENTED, PRIMERS, PUTTIES, SEALERS
                                          VINYL ORGANISOLS, STRIPPABLES, SOLVATED POLYESTERS
                                        2. SOLVATED VINYL PLASTISOLS
                                        3. STAINS: SPIRIT, OIL
                                        4. VARNISH: CLEAR AND PIGMENTED
                                        5. ALKYDS, ACRYLICS, POLYURETHANES
                                        6. EXPOXIES
                       3   4  5  6  7  8 9,10
                             minutes
                                                     TIME
                                                                             3hr 4hr   6 hr  Ibr   12k 1C kr
           Figure 655.   Evaporation curves relating percent  solvent losses to solvent  flash-off times.
toluene as thinner) are sprayed onto flat surfaces.
After spraying,  solvent is allowed to flash-off
from the  coated parts  for 2 minutes  before the
parts enter the bake oven.

Alkyd enamel:  Percent volatiles  53% by weight
(fictitious)                        50% by volume

                Weight 9. 7 Ib/gal

                Xylene 58% by volume of solvent
                in unthinned paint
                Saturated aliphatic hydrocarbons
                42% by volume of solvent in un-
                thinned paint
                Toluene thinner 7. 2  Ib/gal

Solution:

1. Solvent emissions from spray booth and oven:

   Total  solvent sprayed

               S = (G)(Pi)(V) + T (P2)

   •where
      S = solvent sprayed, Ib/day

                .,            % volatiles by weight
      V = volatile fraction =	r-pr~	

      G = unthinned paint sprayed, gal/day
      pi = density of unthinned paint,  Ib/gal
                                                              T =  thinner added,  gal/day

                                                             ?2 =  density of thinner, Ib/gal.

                                                          S = (5)(9.7)(0.53) + (10)(7.2) = 25.6 + 72
                                                            = 97.6 Ib/day

                                                          Solvent emissions from spray booth and flash-
                                                          off area

                                                                     E =
                                                          •where

                                                             S = solvent sprayed,  Ib/day
                                                             „ ,             -    ..     % over spray
                                                             M= overspray fraction = --   r - —
                                                                 (from Table 232)

                                                             F = flash-off fraction =

                                                                 (from Figure 655).
                                                      % flash-off
                                                         100
                                                           Table 232 indicates an overspray factor of
                                                           25 percent for flat-surface, air-atomized
                                                           electrostatic spraying.  Figure 655, Curve 5,
                                                           indicates a weight loss of 36 percent from the
                                                           coating during a 2-minute flash-off period.


                                                           E=(97.6)(0.25) + (97.6)(l-0.25)(0.36)

                                                            = 50.8 Ib/day

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                                     Surface Coating Operations
                                                                    863
   Solvent emissions from oven

      Oven emission = solvent sprayed - spray
      booth and flash-off area emissions
      = 97.6  -  50.8 = 46.8 Ib/day

2. Spray booth compliance with Rule 66:

   Rule 66b applies to the operation of coating
   equipment of this type and therefore solvent
   photochemical reactivity must be  evaluated.

   Solvent from unthinned paint

      = (gal/day unthinned paint ((volatile fraction,
        by volume) = (5)(0. 5)  =  2.5  gal/day

   Saturated  hydrocarbons = (2.5)(0.42)
                             =  1.05 gal/day

   Xylene =2.5 (0.58)        =  1.45 gal/day

   Toluene (added)           = 10.00 gal/day

             Total            = 12.50 gal/day

   Volume percent composition of composite
   solvent system
      Saturated hydrocarbons
      Xylene


      Toluene
12.50
 1.45
12.50
10.00
12.50
             Total
x 100 =  8.40%


x 100 = 11.60%

x 100 = 80.00%


       100.00%
The composite solvent system is classified
photochemically reactive for the following
reasons (see also "Solvents and Their Uses"):

   1.  Xylene exceeds the 8 percent by volume
      limitation of Rule 66k-2.

   2.  Toluene exceeds the 20 percent by volume
      limitation of Rule 66k-3.

   3.  The total of the volume percents of photo-
      chemically reactive solvents exceeds the
      20 percent allowed  by Rule 66k.


Since the  composite solvent system is photochemi-
cally  reactive, the solvent emissions from the
spray booth may not exceed 40 Ib/day under the
provisions of Rule 66b.   The  calculations  showed
that the booth emits 50. 8 Ib/day,  and therefore the
unit exceeds the limits of Rule 66.  Compliance
with Rule 66 can be achieved by reducing or con-
trolling the emissions to  40 Ib/day or less,  or by
                       reformulating the coating and solvent system to
                       make it a nonphotochemically reactive system.


                       An alkyd enamel having the composition listed in
                       Table 233 can be used to eliminate the photochemi-
                       cally reactive xylene nonconforming factor.  How-
                       ever, the added toluene thinner -would continue to
                       cause the composite solvent system to exceed the
                       limitation of 20 percent by volume total photo-
                       chemically reactive solvents.  A nonphotochemi-
                       cally reactive toluene replacement thinner, as
                       listed in Table 233, can be used which, in  con-
                       junction with the conforming alkyd enamel, will
                       result in a composite  solvent system meeting
                       regulatory requirements.


                       The emissions from the bake oven in the preceding
                       example also violate the provisions of Rule 66.
                       Such ovens and their relationship to  Rule 66 are
                       discussed in a later section.
Air Contaminants  from  Other  Devices

Air contaminants from dipping, flowcoating,  and
roller coating exist only in the form of organic
solvent vapors since no particulate matter is
formed.  Solvent emission rates from these opera-
tions  maybe estimated by the methods  given in the
spray booth example with the omission of the over-
spray factor.
HOODING AND  VENTILATION REQUIREMENTS

Requirements for  Point Spray Booths

The usual spray booth ventilation rate is 100 to
150 fpm per square foot of booth opening.   In-
surance standards  require that the enclosure for
spraying operations be designed and maintained
so that the average velocity over the face  of the
booth during spraying operations is not  less than
100 fpm. Flow into the booth must be adequate to
maintain capture velocity and overcome opposing
air currents.  Therefore, the booth should enclose
the operation,  and  extraneous  air motion  near
the booth should be eliminated or minimized.
                        Requirements for  Other  Devices

                        Dip tanks, flowcoaters, and roller coaters
                        frequently are operated without ventilation hoods.
                        When local ventilation at the unit is desirable,
                        total enclosure or partial enclosure by a canopy
                        hood may be installed.  Hoods  should encompass
                        and be located close to the source of emissions.
                        The  flow into the hood must be sufficient to
                        maintain capture  velocity and  overcome any
                        opposing air currents.

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864
ORGANIC SOLVENT EMITTING EQUIPMENT
         Table 233.  EXAMPLES OF SURFACE COATING AND ADDED THINNER FORMULAS
             ON AN AS-PURCHASED BASIS HAVING CONFORMING SOLVENT SYSTEMS
                             (See section on "Solvents and Their Uses")
Type of surface
coating
Enamel, air dry
Enamel, baking
Enamel, dipping
Acrylic enamel
Alkyd enamel
Primer sur facer
Primer, epoxy
Primer, zinc
chromate
Primer, vinyl zinc
chromate
Epoxy -polyamide
Varnish, baking
Lacquer, spraying
Lacquer, hot spray
Lacquer, acrylic
Vinyl, roller coat
Vinyl
Vinyl acrylic
Polyur ethane
Stain
Glaze
Wash coat
Sealer
Toluene replace-
ment thinner
Xylene replacement
thinner
Weight,
Ib/gal
7.6
9. 1
9.9
8.9
8.0
9.4
10.5
10. 3
8.4
10.5
6.6
7.9
8.4
8.4
7.7
8.9
7.5
9.2
7. 3
7. 8
7. 1
7.0
6.7
6.5
Composition of surface coatings, % vol
Nonvolatile
portion
39.6
42. 8
59. 0
30. 3
47. 2
49.0
57. 2
37. 8
34. 0
34.7
35. 3
26. 1
16.5
38. 2
12
22. 00
15. 2
31.7
21.6
40. 9
12.4
11.7


Hydrocarbon
Aliphatic
saturated
93. 5
82. 1
58. 2

92.5
18. 0
44. 8
80. 0
17. 5


7. 0
16.4
10.0




80.6
91.6
40. 6
41. 2
55. 5
56.5
Aromatic
6.5
11.7
7. 2
6.9
7.5
8.9
15.9
7. 2
7. 9
19.9

1.7
6. 8
18. 5

18. 9

19.7
14. 0
8.4
14. 7
7. 0
17. 5
(Toluene)
7. 5
Alcohols
saturated

6.2
30.9


21.8
3.0
12. 8

26.4

21. 3
24. 3
3.5






10. 8
14.7

24.0
Ketones



80. 6

16. 5


60.0
34. 5
97. 0
23. 2
17. 2
42.0
43. 5
81. 1
84. 9
13.9
0. 1

13. 7
19. 1


Esters
saturated


3. 7
12.5

16. 8
28. 8


19.2

45. 1
14. 8
26. 0


15. 1
66.4


15.7
18.0
9.0
12.0
Ethers
saturated





18. 0
7. 5

14. 6

3. 0
1.7
20.5

56.5



5. 3

4. 5

18.0

AIR POLLUTION  CONTROL EQUIPMENT
Control of Paint Spray  Booth  Participates
A considerable quantity of particulate matter
results from the use of the common air atomiza-
tion spray gun.  During coating of flat surfaces,
a minimum of 50 percent of the coating sprayed
is not deposited on the  surfaces and is called
over spray. During the  spraying of other articles,
the over spray may be as high as 90 percent,  as
shown in  Table 232.  Baffle plates, filters, or
                          water-spray curtains are used to reduce the
                          emissions of particulate matter from paint spray
                          booths.  Reduction is further enhanced with elec-
                          trostatic spraying, which decreases overspray.

                          Baffle plates control particulates from enamel
                          spraying by adhesion, with removal efficiencies
                          of 50 to 90 percent. Baffle plates have very low
                          efficiencies  in collecting lacquer spray particu-
                          lates because of the rapid drying (solvent flash-
                          off) of the lacquer and consequent slight adhesion

-------
                         Paint Baking Ovens and Other Solvent-Emitting Ovens
                                            865
to the baffles. Figure 655,  Curve 1, illustrates
the rapid drying of lacquer  coatings. Filter pads
satisfactorily remove paint particulates with
efficiencies as high as 98 percent. The filtering
velocity  should be less than 250 fpm.

Water curtains and sprays are satisfactory for
removing paint particulates, and  -well-designed
units have efficiencies up to 95 percent.  A water
circulation rate of 10 to 38  gallons per 1000 cubic
feet of exhaust air is recommended.  Surface
active agents are  added to the water to aid in the
removal of paint from the circulating tank.

Control of Organic Vapors from  Surface  Coating
Operations

Organic solvents used in coatings and thinners
are not controllable by filters,  baffles, or water
curtains. Solvent  vapors can be controlled or
recovered by the application of condensation,
compression, absorption, adsorption, or com-
bustion principles, when necessary for either
economic or regulatory requirements.

The composite solvent vapor emissions from
coating operations are classified  either as photo-
chemically reactive or nonphotochemically reac-
tive under Rule 66.  If the composite  emission is
classified nonphotochemically reactive, its emis-
sion into the atmosphere is limited by regulatory
requirements -where large quantities are used. If
the composite emission is classified as photochem-
ically reactive,  then its emission into the atmos-
phere is limited to small quantities.  If it is desir-
able to recover  the solvent for reuse, then,  in view
of the small  solvent vapor concentration in the air-
stream from the spray booth, applicator hood, or
enclosure, the o'nly economically feasible solvent
recovery method is adsorption.

Control  efficiencies of 90 percent or greater are
possible by adsorption using activated carbon,
provided particulates are removed from the con-
taminated air stream by filtration before the air-
stream enters the carbon bed.  An industrial
illustration of this method is in the application of
stain or soil repellent chemicals  (fluorocarbons)
to fabrics.   The fluorocarbon is dissolved in a
chlorinated solvent,  and the solution is sprayed
onto the surface of the fabric.  The solvent then
is evaporated from the cloth as it passes through
a dryer.  The effluent from the spray booth and
dryer is collected and ducted to the activated  car-
bon adsorbers for solvent recovery.

When the solvent emission  is not  to be recovered
and the emission is deemed photochemically reac-
tive, then incineration would be the practical
method of control, provided the solvent system
cannot be reformulated to a nonphotochemically
reactive system.  An industrial illustration of
 this is the roller coater application of a vinyl top-
 coat coating to can body tin plate sheets.  The
 roller coater and conveyor are tightly encased to
 capture the solvent emissions, -which are in turn
 ducted to an associated oven-afterburner  unit for
 incineration. Generally, the vinyl topcoat coat-
 ings contain isophorone,  -which is a highly photo-
 chemically reactive solvent.   General design fea-
 tures of adsorption-type devices  and afterburners
 are discussed in Chapter 5.


   PAINT BAKING  OVENS  AND  OTHER

       SOLVENT-EMITTING OVENS

 INTRODUCTION

The term "paint baking, " as used in this section,
refers to both the process of drying and the pro-
cess of baking, curing, or polymerizing coatings.
In both instances, heat is used to  remove  residual
solvents,  but in baking, curing, or polymerizing,
the heat also serves to produce desired chemical
changes in the coatings.   These changes result in
a hardened, toughened, less penetrable coating.

 A rough, not always conclusive, method to dis-
 tinguish a baking process from a drying process
 in the field is to wipe  the finished coating  with the
coating solvent or the liquid coating.   If the coating
on the product from the oven wipes off,  not abrades
off, the process was drying; if it does not  wipe off,
the process was baking.

In its simplest form, paint baking may result only
in speeding the evaporation of  solvents and thin-
ners which would normally air-dry.  In a  complex
system,  the following  factors may be  critical:

   1.  There must be sufficient time before heat-
      ing to permit the coated surface to "level"
      and allow highly  volatile  solvents to  evapo-
      rate  slowly to prevent the formation of
      bubbles in the coating.

   2.  The heated process must start with a low
      temperature to provide for continued slow
      evaporation of residual solvents without
      bubbling.

   3.  Sufficient time and temperature  must be
      provided for full curing of the coating.

   4.  The heated process must be ended before
      damage to the coating occurs.

   5.  Volatilized curing products must be  re-
     moved from the area of the coated surface
     to prevent interference with the  curing
     process.

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866
ORGANIC SOLVENT EMITTING EQUIPMENT
Additionally, the design of all systems involving
the heating of coatings must include, as primary
considerations, the  safety,  health, and comfort
requirements of operating personnel.  Concentra-
tions of organic materials in oven gases must be
kept well below explosive levels.  The exhausting
of toxic oven gases must be regulated to prevent
inhalation by operators.  Excessive heat,  in both
oven gases and the product,  may have to be con-
trolled to prevent operator discomfort or injury.
BAKE OVEN  EQUIPMENT

Bake ovens are designed for processing on either
an intermittent batch basis, or on a continuous
web- or conveyor-fed basis.
Botch Type Ovens

Processing on a batch basis is best suited to low
production rates or to prolonged, complex, or
critical heating  cycles.  A common batch type
oven (Figure 656)  consists of an insulated enclo-
sure with access doors on one end, equipped
with temperature-regulating, air-circulating,
and exhaust systems.  Coated parts are placed
on portable shelves or racks which can be easily
rolled in and out of the oven.  Both oven installa-
tion and heating costs  are usually minimal for a
particular process requirement.  Labor costs
will be high on a per-unit basis.
 Figure 656.  An indirectly heated gas-fired recircu-
 lating batch-type paint baking oven.
                         Continuous Ovens

                         A continuous conveyor-fed system becomes
                         essential to facilitate handling and to reduce
                         labor costs  where high production rates are in-
                         volved. Equipment requirements can range from
                         what is essentially a batch oven with a pass-through
                         conveyor installed to large structures  enclosing
                         tens of thousands of cubic feet with provisions for
                         maintaining several different temperature levels,
                         air circulation rates,  and exhaust rates,  with air
                         curtains at the access openings to control the
                         escape  of heated,  contaminated gases into work
                         areas, with equipment to filter and to precondi-
                         tion the make-up air supply, and with fire- and
                         explosion-prevention devices.  A typical continu-
                         ous oven is  shown in Figure  657.

                         Heating of Ovens

                         The heat input for an oven process must be
                         sufficient to:

                            1. Attain the desired temperature in the
                               coating material and the substrate,

                            2. heat the ventilation air,  and

                            3. compensate for heat losses from the oven
                               exterior.

                         Common methods of oven heating include gas,
                         electric,  steam, and waste  heat from other
                         processes.

                         Ovens heated by gaseous  fuels may be  either
                         direct- or indirect-fired.  In a direct gas-fired
                         oven, the  products of combustion combine with
                         the process air.  Oven burners may use only
                         fresh make-up air or recirculated oven gases
                         combined with make-up air.  In the latter pro-
                         cedure, organic materials in the recirculated
                         oven gases come into contact -with flame.   The
                         flame contact may cause  the oven emissions to
                         become more  photochemically reactive and may
                         make them subject to certain air pollution regula-
                         tions  such as Rule 66aof  the Los Angeles  County
                         Air Pollution  Control District.  In an indirect-
                         fired system,  the  circulated air is passed
                         through a heat exchanger.    Combustion pro-
                         ducts pass through the hot side of the exchanger
                         and discharge directly to the atmosphere.  The
                         indirect method of firing  is used either when the
                         explosion  hazard is considered high or when com-
                         bustion products in the  circulated oven gases might
                         interfere with the  chemistry of the baking process.

                         Electrically heated ovens are of two types:

                            1. Resistance - Fresh make-up air or  oven
                               gases are passed over electrical resist-
                               ance heaters.  The heating system is

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                          Paint Baking Ovens and Other Solvent-Emitting Ovens
                                                                   867
  WORK
 	+
  IN
                   CONTAMINATED
                   GAS EXHAUST
                 \  50 '/.CUT
                    DAMPER
                                                        AMBIENT AIR
                                                                                        CURIAIN
FAN FOR
RECIRCULATING
HOT AIR
             SOLVENT EVAPORATION
                  ZONE 1
                 -17 ft-
                                       -14 ft •
                                                                     -27  ft-
              Figure 657.  A  direct-heated gas-fired recirculating continuous paint baking oven.
      similar to a direct gas-fired type but elimi-
      nates combustion products.

   2.  Infrared - Either bulb,  tube,  or reflected
      resistance heating elements are used as
      heat sources. The system is practical
      where all coated surfaces  can be directly
      exposed to the heat sources.  The infrared
      method of heating can reduce  the energy
      input requirement because heat absorbed
      by the substrate may be minimal, the oven
      atmosphere  absorbs little heat,  and exte-
      rior oven surface temperatures  may be low.

Steam heating of ovens is an  indirect heating
method in which oven gases or make-up air is
heated by passing over steam coils. This method
normally is used where the fire or  explosion
hazard is high.

Heat discharged from other processes also may be
used to meet all or part of the heating  requirements of
a bake oven.  If the incoming hot gases contain no
components which could interfere with the baking
process,  direct heating is practical; otherwise,
indirect heating with heat exchangers can be used.

Oven  Circulating  and  Exhaust  Systems

An oven circulating system serves  two neces-
sary functions. It distributes heat  uniformly
throughout the enclosure,  and it facilitates heat
transfer to the coating material by  disrupting
laminar conditions next to the coated surfaces.

An oven exhaust system must be designed to re-
move the organic materials volatilizing from the
coating and organic solvent at a  rate which will
prevent their build-up to explosive  levels.  Nor-
                       mally the highest concentrations of  organics in
                       the oven gases will occur at the onset of the
                       heated process.   In batch ovens, the period
                       immediately following loading is critical.  In
                       continuous ovens,  the area near the conveyor
                       entrance will have the highest concentration of
                       organics.

                       Where a coating  material requires drying and
                       curing by stages, conveyorized  ovens can in-
                       clude  two or more zones.  Each zone is equipped
                       for independent control of temperature.  Adja-
                       cent zones are able to function separately through
                       careful regulation of exhaust rates and of velo-
                       city and direction of circulating  oven gases.

                       Air Seals

                       "Air seals" or "air curtains" are streams of gases
                       circulated at or near conveyor access openings in
                       ovens. The air flow is intended to prevent the
                       escape of oven gases into work areas.  Blowers,
                       circulating either oven gases or  ambient air, dis-
                       charge through slotted plenums or nozzles direct-
                       ed across the conveyor  openings or into the oven
                       chamber near such openings.  The moving gas
                       streams tend  to induce a flow of oven gases in
                       the same direction.
                       THE AIR POLLUTION PROBLEM

                       The air pollutants emitted from paint baking
                       ovens are:

                          1. Smoke and products of incomplete combus-
                            tion resulting from the improper operation
                            of a gas or  oil-fired combustion system
                            used for heating the oven.
 234-767 O - 77 - 57

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868
ORGANIC SOLVENT EMITTING EQUIPMENT
   2.  Organic solvent vapors evolved from the
      evaporation of the organic thinners and
      diluents used in the surface coatings.  The
      composition of the organic solvent vapors
      emitted from a paint baking oven will differ
      from the composition of the system used in
      the coating material.  The proportion of
      high-volatility components will decrease
      because of more rapid evaporation during
      spraying and because of air drying prior to
      the start of the oven process.

   3.  Aerosols arising from the partial oxidation
      of organic solvents which are exposed  to
      flame and high temperatures and from the
      chemical reactions which occur  in the
      resins.

The air pollutants from paint baking ovens are
odorous and can be extremely irritating to the
eyes. When irradiated by sunlight in the presence
of oxides of nitrogen, even more noxious pro-
ducts are formed. The  emissions from paint
baking ovens may exceed the limits of local air
pollution regulations such as solvent and opacity
limits.
 HOODING  AND VENTILATION REQUIREMENTS

 Fire underwriters' standards require that suffi-
 cient fresh air be adequately mixed with the
 organic-solvent vapors inside the oven  so that
 the  concentrations of flammable vapor in all parts
 of the oven are well under the lower explosive
 limit (LEL) at all times.  The LEL of a gas or
 vapor in air is the minimum concentration at
 which it will burn,  expressed in percent by volume.
 As an approximate  rule, the vapors produced by
 1 gallon of most organic solvents,  when diffused
 in 2,500 cubic feet  of air at 70 °F, form the lean-
 est  mixture that will explode or flash -when exposed
 to a flame or spark.  A factor of safety four
 times the LEL usually is provided.  For each
 gallon of  organic solvent evaporated in  a paint
 baking oven, therefore, at least 10,000 cubic
 feet of fresh air  (computed at 70 °F) must be sup-
 plied to the oven.

 Additional requirements which normally are
 imposed by insurance and governmental agencies
 include:

    1.  The exhaust  duct openings must be located
      in the area of the greatest concentration of
      vapors.

    2.  The oven must be mechanically ventilated
      with power-driven fans.

    3.  Each oven must have a separate exhaust
       system which is not connected to  any other
                              equipment (there are  some exceptions for
                              very small units).

                           4.  Fresh air supplied must be thoroughly
                              circulated to all parts of the  oven.

                           5.  Dampers must be so designed that, even
                              when fully closed,  they permit the entire
                              volume of fresh air needed for meeting the
                              requirements of safe  ventilation to pass
                              through the ovens.

                           6.  A volume of air equal to that of the fresh
                              air supplied must be exhausted from the
                              oven in order to keep the system in balance.

                           7.  If a shutdown occurs during which vapors
                              could accumulate,  the oven must be purged
                              for a length of time sufficient to permit at
                              least four complete oven volume  air
                              changes.

                           8.  Gas firing systems must be provided with
                              safety controls to minimize the possibility
                              of accidental fire or explosion.
                        Where pollution of the atmosphere is a problem,
                        the design of an oven is important in achieving
                        control of air contaminants.  An inadequate de-
                        sign may result in emissions from the  oven at
                        areas other than those vented to air pollution con-
                        trol equipment. If effective control of  oven emis-
                        sions is to be achieved, it is necessary that all
                        possible points of emissions be examined.   Ade-
                        quate regulation of construction, maintenance, and
                        repair  will minimize all  emissions except those
                        from conveyor access openings and from the ex-
                        haust system.  Large conveyor access openings
                        which are above the  horizontal plane of the oven
                        floor are a special problem.  Vertical draft effects,
                        resulting from differences in density between
                        atmospheric and oven gases, can cause the spil-
                        lage of uncontrolled contaminants.  It is impracti-
                        cal to  eliminate such emissions by increasing
                        the discharge through the exhaust system because
                        of increased operating costs.  Significant re-
                        ductions in emissions can be attained by the use
                        of carefully designed air  curtains.  However, the
                        control of contaminants may be impaired by the
                        passage of parts through  the curtains,  diverting
                        part of the circulated air to the atmosphere.
                        The greatest degree of control is possible  where
                        conveyor  access openings are below the plane of
                        the oven floor; parts enter  and leave the oven
                        either through floor openings or beneath cano-
                        pies which extend down-ward below the  floor.
                        With this arrangement, it is likely that an  exhaust
                        system designed to meet minimum ventilation
                        requirements will prevent emissions from the
                        door, provided there is a measurable indraft at
                        such openings.

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                          Paint Baking Ovens and Other Solvent-Emitting Ovens
                                            869
Estimating the emission rate of organic materials
from an oven involves consideration of: (1) the
quantity and composition of coating materials
used, (2) the method of application, (3) the fact-
ors affecting solvent evaporation prior to oven
treatment (ambient temperature, pressure and
humidity, air  movement, surface charateristics
of the coating, solvent volatility, time),  and (4)
reduction by combustion in the oven heating sys-
tem.

The following  example illustrates the method
which can be employed to estimate organic emis-
sions from paint baking ovens.

Given:

A continuous oven (similar to that shown in Figure
657) is  to be used to bake an alkyd enamel  coat-
ing on steel parts of various shapes for metal
furniture.  The parts are formed and placed on
a conveyor which carries them successively
through a washing-phosphatizing process,  a
water dry-off oven,  a spray-coating process, and
a bake oven.  The time interval between the water
dry-off oven and the spray-coating is sufficient to
allow the parts to cool to ambient temperature.
Spraying is  done using hand-held, air-atomized,
electrostatic equipment.  Paint is consumed at
the rate of 40  gallons per 8-hour day.  The paint,
thinned for spraying', contains 5.5 pounds per gal-
lon of organic solvents.  The solvent system is
nonphotochemically  reactive as defined by  Rule 66k
of the Los Angeles County Air Pollution Control
District.  The time  interval between the  spraying
and entrance into the bake oven is 15 minutes.

Problem:

Estimate the emission rate of organic  materials
into the atmosphere from the bake oven.

Solution:

1. Total solvent contained in the 40 gallons of
   coating materials used in 8 hours:
          (5.5)(40) = 220 Ib of solvent per day

2. Solvents emitted from spraying process:
   From Table  232, the over spray factor for an
   air-atomized, electrostatic spray application
   on table leg surfaces is  35 percent. The
   amount of  solvent loss in the  spraying opera-
   tion is (0.35)(220) = 77 Ib of solvent per day.

3. The solvent remaining on the  parts  is 220 -  77
   = 143 Ib  of solvent per day.

4. Solvents evaporated to the atmosphere be-
   tween the completion of spraying and  the oven
   entrance:
   From Figure 655, the solvent evaporation
   from an alkyd coating during the first 15-
   minute interval following coating is 48 percent.
   The solvent evaporated to the atmosphere
   between the spraying and the baking processes
   is
       (0.48)(143) = 68 Ib of solvent per day.

5. Total weight of solvent released in the oven
   per day is the total contained in the coatings
   consumed, less the quantity lost as overspray
   and the quantity evaporated between the  spray-
   ing and the baking operations,  220 -  (77 + 68)
   = 75 Ib per day.

Operation of the oven,  as given in the foregoing
problem,  would be in violation of Rule 66a  of the
Los Angeles County Air Pollution Control Dis-
trict. Compliance could be achieved by  modifying
the procedure such that either:

   1. Oven gases are vented to an air pollution
      control device as specified in Rules 66a
      and 66f,

   2. the  amount of solvent reaching the oven is
      reduced by extending the time interval
      between coating and baking operations or
      by introducing a low-temperature heat
      source to accelerate solvent flashing, or

   3. coating materials are converted to types
      which do not cure in the  oven heating
      process and circulation of solvent contami-
      nated oven gases through the oven gas-
      burning equipment is prevented.
AIR POLLUTION CONTROL EQUIPMENT

Effluent streams from paint baking ovens can
best be controlled by the use of afterburner
equipment.  Other possible methods of control
are usually  impractical for the following reasons:

   1. The concentration of organic materials is
      too low to permit extraction by condensa-
      tion and compression.

   2. Vaporized resins can rapidly blind activated
      carbon beds. Further, recoverable organic
      materials are likely to have little  or no
      value  to justify relatively high installation
      and maintenance costs of such equipment.

   3. Where visible oven  emissions occur,
      particle sizes are too small for efficient
      removal by filtration or by inertial separa-
      tion. Solvent vapors -would not be collected
      by either method nor by electrical precipi-
      tation.

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870
ORGANIC SOLVENT EMITTING EQUIPMENT
The choice between direct flame and catalytic
incineration methods must be based on economic
factors and on the requirements of local air pol-
lution control agencies.

OTHER OVENS  EMITTING AIR CONTAMINANTS

There are two common applications for ovens
that present special air pollution problems.
These processes include food container litho-
graphing and printing  systems.  Some of the
principles previously  mentioned for the control
of paint baking ovens can be applied, but there
are other parameters  which need to be discussed
separately.

Can Lithograph Oven

Preparation of the  sheet metal stock from, which
food containers are made involves the applica-
tion and baking of coating materials.  Following
coating on one side, the sheets are passed
through a conveyorized oven.  The conveyor is
                          made up of metal frames  (wickets) which are
                          inclined and closely spaced.  At a conveyor
                          speed of 10 fpm,  a feed rate of 80 sheets per
                          minute (approximately 36 by 36 inches) can be
                          maintained.

                          A typical oven, shown in Figure 658, is about 100
                          feet long,  -with a 30- to 40-square foot cross-
                          sectional area.  Multiple heating zones, as many
                          as four to six, are used, each with an indepen-
                          dently controlled gas-fired heating system.  The
                          oven chamber is vented by a single exhaust sys-
                          tem located near the conveyor entrance.  Heating
                          zones along the length of the oven vent by cascad-
                          ing toward the conveyor entrance end.  As the
                          conveyor leaves the  oven, a large volume of am-
                          bient air is passed through it to cool the sheets
                          prior to stacking.  The empty conveyor is pre-
                          heated to oven temperature as it  returns below
                          the oven chamber.

                          Air contaminants from a can lithograph oven are
                          primarily organic solvents and vaporized resins.
    Figure 658.  Can  lithograph oven (Wagner Litho Machinery Division,  National  Standard Co.,  Secaucus,  N.J.).

-------
                                        Solvent Degreasers
                                                                                                 871
Control of contaminants  is normally accomplished
by incineration in an afterburner.  The design of
the oven circulating and  exhaust  systems is criti-
cal.  In order to  assure  that control can be effec-
tive, it is necessary that:

    1. An air inflow be established at the convey-
      or entrance,

    2. there be no significant emission of oven
      gases to the cooling zone at the conveyor
      exit,  and

    3. the equipment be adequately maintained to
      prevent leakage from the oven housing or
      from the ducting,  fans, and other acces-
      sories.

 Printing System  Ovens

 High-volume web printing systems can emit  sig-
 nificant quantities of air contaminants from
 drying  ovens in the form of organic solvents and,
 in some processes, vaporized resins and smoke.
 Rotogravure and flexographic systems normally
 release only solvent vapors. Letterpress and
 lithographic systems, when heat setting inks are
 used,  emit both  organic solvents and vaporized
 resins.

A high-speed printing process which functions
without a heating system,  such as one used for
news print, uses inks which contain small
amounts of high-boiling-point solvents.  The
emission of air contaminants from such equip-
ment is small. Capture  of emissions from the
ovens in printing systems  can be readily attained
because exhaust volumes are relatively high,
providing good indraft velocities at web slots.
Cost for control of such  emissions, if required
by air pollution control regulations, will be high
because of high exhaust  rates.  Incineration
usually is used for controlling emissions from
printing ovens. Emissions from printing and
heating processes in these types of press  systems
can be in excess  of that  allowed  by Rule 66 of Los
Angeles County Air Pollution Control Regulations
depending on:


    1.  The status of the  solvents contained in the
       inks applied, under Rule  66k which defines
       certain types as being photochemically
       reactive,
    2.  whether or not the ink resins cure, bake,
       or heat-polymerize in the oven, or


    3.  whether or not solvent contaminated oven
       gases pass through flame in the oven heat-
       ing system.
           SOLVENT  DEGREASERS

INTRODUCTION

In many industries, articles fabricated from
metals must be washed or degreased before
being electroplated, painted,  or given another
surface finishing. Most degreasing operations
are carried out in packaged degreaser units in
which a chlorinated organic solvent,  either in the
gaseous or liquid state, is used to wash the parts
free of  grease and  oil.  Measurable solvent is
emitted as vapor from even the smallest de-
greaser, and the sheer number of these units in
large manufacturing areas makes their combined
solvent emissions significant to a community' s
air pollution.

Design  and  Operation

Solvent degreasers vary in size from simple un-
heated wash basins to large heated conveyorized
units in which articles are washed in hot solvent
vapors. The vapor spray unit depicted in Figure
659 is typical of the majority of industrial de-
greasers. Solvent is vaporized in the left portion
of the tank either by electric,  steam, or gas
heat.  The vapors diffuse and fill that portion of
the tank below the water-cooled condenser. At
the condenser level, a definite interface between
the vapor and air can be observed from the top
of the tank.  Solvent condensed at this level runs
into the collection trough and from there to the
clean-solvent receptacle at the right of the tank.
Articles to be degreased are lowered in baskets
into the vapor space of  the tank. Solvent vapors
condense on the cooler  metal parts, and the hot
condensate washes  oil and grease from the parts.
The contaminated condensate  drains back into the
heated tank from which it can be revaporized.
When necessary, dirty  parts are hand sprayed
with hot solvent by use  of a flexible hose and
spray pump to aid in cleaning. Many degreasers
are equipped with lip-mounted exhaust hoods
that draw off the vapors reaching the top of the
tank and vent them  outside the working  area.

Types of Solvent

Nonflammable chlorinated solvents are used almost
exclusively with degreasers.  Because  of Rule
66, an estimated 90 percent of the solvent used
in Los Angeles County is  divided equally between
perchloroethylene (C^C = CC12) and 1, 1, 1-tri-
chloroethane (CH3CC13); the  remaining 10 per-
cent is trichloroethylene  (ClHC=CCl2).  In
other localities that do  not have air pollution
control  laws  restricting organic solvent emissions,
an estimated 90 percent of the solvent used for
degreasing is trichloroethylene. Most of the
remaining 10 percent of the solvent is the higher
boiling perchloroethylene. Selection of  solvent

-------
 872
ORGANIC SOLVENT EMITTING EQUIPMENT
 WATER JACKET—«-(
   VAPOR AREA
    WORK REST-
BOILING LIQUIDI-
    IMMERSION,
    HEATER
      DRAIN-
          FINNED COIL
          CONDENSER
          CONDENSATE
          COLLECTOR
          WATER SEPARATOR
          DRAIN
          WATER SEPARATOR
          STORAGE TANK
          OVERFOL* LINE
          PUMP SUMP
          SPRAY PUMP
                   Figure 659.  Vapor-spray degreaser (Baron  Industries, Los Angeles,  Calif.).
  usually is dictated by the operator's temperature
  requirements.  Most greases and tars dissolve
  readily at the  189 °F boiling point of trichloro-
  ethylene.  Perchloroethylene,  which boils at
  249 °F,  consequently is  used only when higher
  temperatures  are required, or when compliance
  with air pollution control legislation is required.

  THE AIR  POLLUTION PROBLEM

  The only air pollutant emitted from solvent-
  degreasing operations is the vaporized organic
  solvent.  Trichloroethylene vapors are  classified
  as photochemically reactive under Rule 66  and
  are limited to 40 pounds per day from each de-
  greaser. Perchloroethylene and 1, 1, 1-trichloro-
  ethane are not considered photochemically  reac-
  tive under Rule 66 and their emissions are not
  limited by Rule 66 unless large quantities are
  used.  Because vapor control is expensive, all
  large  degreasers in Los Angeles County now use
  perchloroethylene or trichloroethane.

  Trichloroethylene, perchloroethylene, and 1, 1, 1-
  trichloroethene are  considered toxic. Acute ex-
  posure produces dizziness, severe headaches,
  irritation of the mucous membranes,  and intoxi-
  cation (Sax, 1963).

  Daily  emissions of solvents from individual
  degreasers vary from a few pounds to as high as
  1, 300 pounds  (two 55-gallon drums).  Total emis-
  sions  in large industrial areas are impressive
  (Lunche,  et al. , 1957).

  Solvent  escapes from degreaser tanks in essen-
  tially  two ways: vapor diffusion or "boil over"
                          from the tank,  and "carryout" or entrainment
                          with degreased articles. About 0. 05 pound of
                          solvent leaves the tank by  diffusion per hour per
                          square foot of open tank area where no appreci-
                          able drafts cross the top of the tank.  Obviously,
                          a much higher quantity of  solvent is carried
                          away when crossdrafts are strong.

                          The quantity  of solvent carried out  with the pro-
                          duct and later evaporated  into the atmosphere is
                          a function of  product shape and the  distribution
                          of the articles in the basket.  In many instances,
                          proper alignment in the degreaser's basket can
                          greatly reduce these losses.

                          The cost of chlorinated solvents often makes it
                          desirable to  install special equipment to minimize
                          diffusion and carryout losses.
                          HOODING AND VENTILATION REQUIREMENTS


                          When a control device is used to collect the
                          vapors  from the top of the tank, a lateral slot
                          hood may be used, as shown in Figure 660.  Slot
                          hoods also are used sometimes without vapor
                          recovery devices.  In both cases, a minimum
                          volume of air is used to prevent excessive  loss
                          of valuable  solvent or to preclude overloading
                          the air  pollution control device. Slot hood velo-
                          cities should not exceed 1, 000 fpm for this ser-
                          vice,  and in many cases,  these velocities may be
                          reduced by  experimentation. The size of the tank,
                          objects  degreased, and drafts within the building
                          all influence slot velocities.

-------
                                          Solvent Degreasers
                                            873
  Figure 660.  Vapor degreaser and hooding vented to
  activated carbon unit shown in  Figure 662 (General
  Controls Co.,  Burbank, Calif.).
 The slot hoods discussed above can be used where
 the only consideration is collection and recovery
 of a valuable solvent.  Where trichloroethylene
 is emitted in quantities of 200 pounds per day or
 greater,  and air pollution control equipment
 must be used to achieve compliance with Rule 66,
 the slot hoods are not effective enough to provide
 the overall 85 percent collection  efficiency re-
 quired by Rule 66b. In this case,  it is almost a
 necessity to enclose the entire degreaser plus
 the drying area for  the degreased articles  so
 that virtually all the vaporized trichloroethylene
 can be collected and vented to the control system.
         heaters, exhaust fans,  and so forth.  If
         possible,  a 12- to 18-inch-high shield
         should be placed  on the -windward side
         of the unit to eliminate drafts.

      2.  Work items should be  placed in the bas-
         ket in such a way as to allow efficient
         drainage and thus prevent  extensive
         solvent loss.

      3.  Metal construction should  be used for all
         baskets, hangers, separators,  and so
         forth. Use of rope and fabric that adsorbs
         solvent should be avoided.

      4.  The speed of work entering and leaving
         the vapor zone  should be held to 12 fpm
         or less.  The rapid movement of work in
         the vapor zone  causes  vapor to be lifted
         out of the machine.

      5.  Spraying above the vapor level should be
         avoided. The spray nozzle should be
         positioned in the vapor space where it
         will not create disturbances in the con-
         tents of the vapor space.

      6.  Work should be held in the vapor until it
         reaches the vapor temperature where all
         condensation ceases.  Removal before
         condensation has  ceased causes the work
         to come out wet with liquid solvent.

      7.  When the metal articles are of such con-
         struction that liquid collects in pockets,
         the -work should be suspended in the
         free-board area above the  tank to allow
         further liquid drainage.

      8.  The degreaser tank should be kept
         covered whenever possible. "
 AIR  POLLUTION  CONTROL  METHODS

 Emission of solvent from degreasers can be
 minimized by location, operational methods,  and
 tank covers. In a few cases,  surface condensers
 and activated-carbon adsorbers have been used to
 to collect solvent vapors.
Methods of Minimizing Solvent Emissions

In a discussion of degreaser operation,  The
Metal Finishing-Guidebook-Directory (1957)
recommends several techniques for reducing
losses of  solvent and, consequently,  air pollution:

    "1. A degreaser should always be located in
        a position where it will not be subject to
        drafts from open windows, doors, unit
Tank Covers

As operators have become more cognizant of the
costs of degreaser solvent and of the hazards to
worker health, the use of tank closures has be-
come universal.  Prior to 1950,  most degreasers
were equipped with relatively heavy one-piece
metal covers.  The weight and unwieldy shape of
these covers were  such that most operators would
not place them over the tanks at the end of a work-
ing day.  With modern tank closures operated hy-
draulically or electrically,  workers can easily
cover tanks,  even during short periods of work
stoppage.   There are several varieties of auto-
matically operated closures,  one of which is shown
in Figure  661.  Most are fabricated from plastic-
impregnated fabrics.  Closure is usually by roll

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874
                            ORGANIC SOLVENT EMITTING EQUIPMENT
   Figure 661.  A  hydraul ical ly operated screen-type closure
   dustnes, Los Angeles,  Cal if.).
   left—cover closed, nght--cover  open (Baron  In-
or guillotine action, which affords a minimum of
vapor disturbance.  Solid hinged lids should be a-
voided because air movement entrains the solvent
vapor.

The solvent savings and air pollution control that
can be accomplished with automatic closures is  a
function of prior operating technique.  Where de-
greaser operation has been relatively haphazard,
covers have been shown to reduce  emissions of
solvent well over 50 percent.  On the other hand,
when a degreaser has  been located and operated
properly, the savings  provided by these devices
has been small.  Because  of the high cost of  chlor-
inated  solvents, however,  automatic closures fre-
quently pay off in short periods even at moderate
usage of solvent.

Controlling Vaporized Solvent

Although most solvent conservation efforts have
been directed toward prevention of emission  at the
tank,  solvent  vapors can be removed from a  carry-
ing airstream that  otherwise would be exhausted to
the atmosphere.  Practical control methods are
extremely limited and industrial application of
chlorinated-solvent controls has been uncommon.
Adsorption with activated carbon is a currently
feasible means that can be adapted to most de-
greasers.  Activated carbon has a relatively high
capacity for trichloroethylene,  perchloroethylene,
and 1, 1, 1 -trichloroethane, and  adsorption units
can recover nearly 100 percent of the solvent va-
pors in exhaust gases from a degreaser.

An activated carbon adsorber used to recover
trichloroethylene is shown in Figure 662.  It con-
sists essentially of two parallel-flow activated car-
bon chambers that  can be operated either separate-
ly or simultaneously.  Solvent-laden air is collect-
ed at spray degreasing booths,  as depicted in Fig-
ure 663, and at the vapor degreaser, previously
shown  in Figure 660.  The solvent-laden airstream
is directed to both  activated carbon chambers ex-
cept when one chamber is being regenerated.   The
adsorber must be designed  to handle the required
exhaust volume through only one chamber.  The
operator of this particular adsorber reports a 90
percent reduction in usage of chlorinated solvent
(1, 100 gallons per month) since its installation
Carbon adsorption  is suitable especially for spray
degreasing operations where the spray chamber
must be exhausted  to protect the operator.

When solvent concentrations in exhaust gases are
relatively large,  surface condensers can be used

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                                       Dry Cleaning Equipment
                                             875
 Figure 662.   Two-chamber activated carbon adsorbtion
 unit  used to  recover trichloroethylene  from degreas-
 mg exhaust gases (General Controls Co., Burbank,
 Calif.).
Figure 663.   Spray degreasmg table and hooding vented
to activated carbon unit shown in Figure 662 (General
Controls Co.,  Burbank,  Cal if.).

to collect appreciable quantities of  solvent   The
principal deterrent to the use of this type of con-
trol is the  small concentration of chlorinated  sol-
vent usually  encountered in exhaust gases from de-
greasers.  At the 68 °F  operating temperature of
most atmospheric water-cooled condensers, the
trichloroethylene concentration in the escaping
vapors can be reduced  only to 7 . 4 percent,  and
the perchloroethylene concentration to 2. 4 percent
Chlorinated-solvent concentrations in exhaust
gases from degreasers are usually well below these
values.

Since degreaser solvents are essentially non-
combustible, incineration is not a feasible method
of control.  Moreover, the thermal decomposi-
tion of chlorinated  solvents can produce corrosive
and toxic compounds,  such as hydrochloric acid
and phosgene, which are  more objectionable air
contaminants than the solvents


         DRY  CLEANING EQUIPMENT

INTRODUCTION

Dry cleaning is the process of cleaning fabrics  by
•washing in a substantially nonaqueous  solvent.
Two classes of organic solvents are used most
frequently by the dry cleaning industry.  One class
includes petroleum solvents, mostly Stoddard
solvent or 140-F solvent. The other class in-
cludes chlorinated hydrocarbon solvents, called
"synthetic solvents" in the industry, consisting
almost exclusively of perchloroethylene,  also
known as tetrachloroethylene.

The process of dry cleaning fabrics is performed
in three steps.  The fabric first is cleaned by ag-
itation in a solvent bath and then rinsed -with clean
solvent.  This first step  is referred to as "wash-
ing. "  Next, excess solvent is removed by cen-
trifugal  force.  This second step is referred to
as  "extraction. "  The fabric then is tumbled
•while -warm air is  passed through it to  complete-
ly vaporize and remove the remaining solvent.
This third step  is referred to as "drying" when
petroleum solvent  is used or "reclaiming" when
synthetic solvent is used.

While older petroleum solvent equipment gener-
ally employs separate machines for each step,
commercial synthetic solvent equipment and
modern  petroleum solvent equipment usually em-
ploy a machine which combines the washing and
extracting stages •with a  separate machine for
drying or reclaiming.  Newer equipment employ-
ing synthetic solvent, which incidentally includes
most coin-operated machines, combines all
three steps in one  machine.


Wash  Machines

Dry cleaning washers that perform only the wash
step consist of a rotating perforated horizontal
cylinder inside a vapor-tight housing.  Housing
and drum are each equipped with a door for load-

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876
                             ORGANIC SOLVENT EMITTING EQUIPMENT
ing and unloading.  This type of -washer uses only
petroleum solvent and is shown in Figure 664.
                                                      Figure 666.   Petroleum  solvent combination wash-extract
                                                      unit (Washex  Machinery  Corp., Plainview, N.Y.).
 Figure 664.  Petroleum solvent dry cleaning installa-
 tion (Century Park Cleaners,  Inglewood, Calif.).

Combination  Machines

Machines which perform both washing and extrac-
tion employ a perforated horizontal rotating drum
enclosed in a vapor-tight housing.   This type of
machine usually has only one  door  in the housing
and is mounted on a flat base  solvent tank.   Fig-
ures 665 and 666 illustrate two-step machines.
This machine slowly agitates  the clothes during
the wash cycle  and then, after the washing  sol-
vent is drained, the drum rotates at high speed
to wring further solvent from the fabrics.  Ex-
tracted solvent drains to the base tank.  Fabrics
then are transferred by hand to a separate  tum-
bler.
 Figure 665.  Synthetic solvent dry cleaning plant
 with combination wash-extract unit, reclaim tumbler,
 filter, and still (Vic Mfg.  Co., Minneapolis,  Minn.).
A machine designed to perform all three dry
cleaning steps consists of a horizontal rotating
drum which is mounted with one door  in the va-
por-tight housing.  In this machine, the drum
rotates slowly during the wash cycle.   After
washing is completed, the solvent returns to the
tank, and the drum rotates at high  speed to  ex-
tract more solvent, which also  is returned to the
tank.  The drum again rotates slowly  -while  heat-
ed air is blown through the fabrics.  This air is
recycled to the tumbler through a condenser to
recover the evaporated solvent.  The  three-step
machine is used  only with synthetic solvent.
Figures 667  and  668  illustrate coin-operated and
commercial  machines of this  type.
Extractors

When a single machine performs the -wash step,
a separate centrifuge is  used for the extraction
step.  The plant shown in Figure 664 includes a
centrifuge commonly called an "extractor. "  The
extractor consists of a vertically mounted drum
with an open top, mounted inside a vapor-tight
enclosure.  A door in the enclosure is used to
charge the drum and to seal the operation.  The
drum is rotated at high speed to extract the sol-
vent which drains to a tank.
 Tumblers

 In installations where the machine does not per-
 form all three steps,  a separate tumbler is used
 to dry the fabrics after they leave the extractor.

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                                       Dry Cleaning Equipment
                                             877
Figure 667.  Synthetic solvent  coin-operated dry  clean-
ing unit (Norge Sales Corp.,  Los Angeles, Calif.).
The tumbler is a revolving perforated cylinder
through which air is passed after the air has been
heated by passage through steam-heated coils.
A few synthetic solvent tumblers use electrical
resistance heating coils instead of steam.

In drying tumblers used to dry fabrics cleaned
with petroleum solvent, the heated air makes a
single pass through the fabric.  The solvent-
vapor-laden air then is exhausted to the atmos-
phere.  Drying tumblers designed for use  in syn-
thetic solvent service are called "reclaimers" or
"reclaiming tumblers, " and the drying  air is  re-
ciculated in a closed system.

Heated air vaporizes the solvent in the fabric and
this vapor-laden mixture is carried through water
or through refrigerant-cooled coils.  Solvent va-
por is condensed and decanted from water, and is
returned to the wash machine tank.  The air then
is recirculated through the heater to the tumbling
fabric.  When the concentration of solvent vapor
in the air stream from the drum drops below its
dew point and the solvent no longer can be con-
densed, a small amount of solvent will  remain in
the fabric being dried. At this point, the air  is
no longer recirculated to the heater, but is ex-
hausted to the atmosphere after one  pass.   This
phase of the drying step both cools the fabric  and
deodorizes it by  serving to evaporate and remove
the final traces of solvent.  A synthetic solvent
reclaim tumbler is shown in Figure  669.
   Figure 668.  Three-function 'dry-to-dry' dry cleaning machine,  front and  rear views  (American Permac,  Inc.,
   Garden City, N.Y.).

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878
ORGANIC SOLVENT EMITTING EQUIPMENT
Figure  669.  Synthetic solvent dry cleaning  unit with
an activated carbon  adsorber (Joseph's Cleaners and
Dryers, Los Angeles, Cal if.).
                                                        Filters

                                                        Filters are  installed with all dry cleaning equip-
                                                        ment to remove suspended material from the
                                                        used solvent.   The filter medium consists  either
                                                        of tubular or flat plate elements of cloth, metal
                                                        woven fabrics, or metal screening.  Figure 670
                                                        illustrates one type of filter, mounted over a still,
                                                        used in a  synthetic solvent cleaning plant.   Filter
                                                        aids,  diatomaceous earth, are used to coat the
                                                        cloth or screens for efficient removal of insoluble
                                                        soils.
                           Stills

                           A still frequently is used in petroleum solvent
                           installations and usually is included with the syn-
                           thetic solvent installations.  It is used to distill
                           solvent from higher boiling soluble impurities,
                           such as fatty acids. Figure 671 illustrates a still
                           used in petroleum plants.   Petroleum solvent
                           stills are continuous vacuum types.   Synthetic
                           solvent stills are atmospheric batch-type stills.
     Figure 670.   Filter mounted  on combination still  and  cooker; right view  illustrates  woven flexible  stain-
     less steel tubes (Per  Corp., Orange,  N.J.).

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                                        Dry Cleaning Equipment
                                                    879
                                                       WATER OUT
                                              CONDENSATING TUBES
                                                 SOLVENT VAPOR
                                              EXPANDING BELLOW
                              MOISTURE SEPARATOR -
                              DISTILLED SOLVENT/*
                                     OUTLET
                                  COTTON RAGS-^"
                                     WATER OUT-
m
<-^w
& I->
                                                      DISTILLED
                                                      SOLVENT
                                     fREHEATER CHAMBER
                                         PREHEATER COIL
                                            STILL BODY
LEVEL CONTROL
VALVE
STEAM CHEST
                                                                                       DIRTY SOLVENT IN
                                                  PUMP  WATER IN  STEAM IN  STEAM         SUMP DRAIN
                                              •CONDENSER                CONDENSATE OUT  VALVE
                                             "SOLVENT AFTERCOOLER
        Figure 671.  Vacuum still  for petroleum solvent  plant (Washex Machinery Corp., Plamview, N.Y.).
Muck Reclaimers

"Muck, " which is filter aid containing the dirt
filtered from the  solvent, periodically is removed
from the filter  elements.   Muck from petroleum
solvent filters usually is discarded.  A few petro-
leum solvent plants still employ a press to squeeze
the muck for  recovery of some  of the solvent.  In
most synthetic solvent plants, the muck is "cooked"
to vaporize the solvent.  The  solvent vapor is re-
covered by condensation.   "Muck cooking" in most
modern synthetic plants is performed in the same
unit used for  distillation of the solvent for  its pur-
ification (Figure 670).  Very few plants have sep-
arate vessels for muck cooking.  Centrifuges or
presses for recovery of solvent from the muck
rarely are found today.  This also applies  to equip-
ment for air-bio-wing muck followed by condensa-
tion of solvent vapors in the solvent storage tank.
THE  AIR  POLLUTION  PROBLEM

The  operation of dry cleaning equipment causes
two types of air pollution problems.  A  local
nuisance may occur from solvent vapor  odors or
lint.  Secondly, the photochemically reactive
materials used are  detrimental to the overall
quality of the atmosphere.

Solvents

The  amount of solvent vapors emitted to the atmos-
phere from any one dry cleaning plant is depen-
dent upon the type of equipment used,  the amount
of cleaning performed,  and the precautions prac-
ticed by  the operating personnel.
       The petroleum solvents used in Los Angeles Coun-
       ty prior to enactment of Rule 66 contained a total
       of 11 to 13 percent by volume of highly reactive
       components.  Photochemical reactivity as defined
       in Rule 66 is the "reactivity" referred to here.
       Both the Stoddard solvent and 140-F solvent now
       used in Los Angeles County have been reformu-
       lated to contain no more than 7. 5 percent by
       volume of reactive components and therefore,
       are classed as nonreactive.  Table 234 lists the
       properties of dry cleaning solvents.

       Virtually all the synthetic solvents are classed
       as nonreactive. Perchloroethylene is used  in al-
       most all synthetic plants, but a few plants employ
       carbon tetrachloride, although its use is in dis-
       favor, or a proprietory brand  "Freon" (trichlo-
       rotrifluoroethane).   The preceding three solvents
       are nonreactive under Rule 66. Trichloroethylene,
       a reactive solvent, was a major synthetic dry
       cleaning solvent a few years ago but is no longer
       used since perchloroethylene is preferred.

       The average daily emission to  the atmosphere
       from synthetic dry cleaning, determined from a
       study of 1, 000 plants, is 2.2 gallons or 30 pounds
       of synthetic solvent vapors per plant.  Petroleum
       solvent average daily emissions, determined from
       200 plants, are 26.9 gallons or 175 pounds per
       plant.   Figure 672 illustrates the distribution  of
       solvent emissions by number of plants on a cum-
       ulative basis for the two types  of solvents.  The
       curve was drawn by plotting the percent of the
       number  of plants against the cumulative percent
       of total daily solvent emissions from the plants.
       Data were used representing 200 petroleum plants
       •with a total daily solvent emission of 35,000 pounds

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880
ORGANIC SOLVENT EMITTING EQUIPMENT
                      Table 234.  PROPERTIES OF DRY CLEANING SOLVENTS
Property
Flash point (TCC), °F
Initial boiling point, °F
Dry end point, °F
API gravity
Specific gravity at 60 °F
Weight, Ib/gal
Paraffins, volume %
Aromatics, volume %
Naphthenes, volume %
Olefins, volume %
Toluene /ethylbenzene,
volume %
Corrosiveness
Caution
Odor
Color
Cost (average size
plant), $/gal
140-F
138. 2
357. 8
396
47. 9
0.789
6.57
45.7
12. 1
42.2


None
Flammable
Mild
Water white
0. 29
Typical
140-F,
R 66
143
366
400
44.0
0. 8063
6.604
82.5
7.0

0.5

None
Flammable
Mild
Water white
0. 30
Stoddard
100
305
350
50. 1
0.779
6.49
46. 5
11.6
41. 9


None
Flammable
Sweet
Water -white
0. 28
Typical
Stoddard,
R 66
108
316
356
48. 1
0. 788
6. 56
88. 3
5.9

0. 8
5. 0
None
Flammable
Sweet
Water white
0. 29
Perchloro-
ethylene
Extinguishes
fire
250
254

1. 623
13. 55





Slight on metal
Toxic
Ether like
Colorless
2. 05
and 1, 000 synthetic plants with a total daily sol-
vent loss of 30,000 pounds.  The curves should
approximate roughly the distribution of total
solvent emissions  for any other large population
center. Validity of the distribution for petroleum
solvent plants can be affected by one large vol-
ume plant, particularly in lower population cen-
ters. Caution must be taken -when using the curve
in such cases.

The older type petroleum solvent dry cleaning in-
stallation is illustrated in Figure 664.   Here the
fabrics are first washed in solvent, removed,
then placed in a centrifuge for extraction and a-
gain transferred to a tumbler for drying.   This
results in a much higher  solvent vapor emission
than the newer type petroleum plant with a com-
bination washer-extractor illustrated in Figure
666.  In the newer  plant,  fabrics are washed and
then extracted in the same unit. The extracted
fabric then is transferred to a tumbler for final
drying.

The  synthetic solvent system illustrated in Figure
665 washes and extracts the fabrics in one machine.
After extraction, the fabrics are hand transferred
to the tumbler for drying.  Solvent vapors  are re-
claimed in the tumbler by condensation. The so-
                         called "hot" or "dry-to-dry" machine illustrated
                         in Figure 668 operates with the lowest emissions
                         of solvent vapors to the atmosphere.

                         In one coin-operated synthetic solvent dry cleaning
                         unit,  clothing is washed and extracted in one ma-
                         chine and then must be transferred to another ma-
                         chine for drying. The vapors driven from the
                         clothing during the drying operation are not re-
                         covered. Consequently,  solvent emissions to the
                         atmosphere are higher than from the coin-opera-
                         ted synthetic solvent unit illustrated in Figure  667.
                         This machine performs washing,  extraction, dry-
                         ing, and recovery of solvent vapors all in the same
                         machine.  Coin-operated units lose much more sol-
                         vent to the atmosphere than the larger commercial
                         units processing the  same amount of fabrics.  The
                         amount of solvent emitted is more nearly propor-
                         tional to the number  of -wash operations than to
                         the amount  of fabric per operation.  Five loads of
                         textiles  dry cleaned in 8-pound-capacity units will
                         result in much more of a solvent emission than 40
                         pounds of textiles cleaned in one similar 40-pound-
                         capacity unit.

                         The operators of plants using synthetic  solvents
                         have a strong incentive to follow good practices
                         to conserve solvent.   Because the solvent costs

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                                       Dry Cleaning Equipment
                                                                                   881
                INDIVIDUAL DAILY EMISSION, Ib
      UPTO-
 PETROLEUM SOLVENT PLANTS
- 135 (MAXIMUM 3000lli)|75
125175195225625
 1  1  I   Inil
      UP TO
 SYNTHETIC SOLVENT PLANTS
       110 MAXIMUM m Ih)   130
o
                      40        60
                    ALL PLANTS, percent
 Figure 672.   Emissions  from dry  cleaning: cumulative
 curves by number of plants, total  loss to atmosphere,
 and  amount of  individual plant  losses. (Basis  1000
 synthetic and  200 petroleum solvent plants.)
 over $2.00 per gallon, providing high "mileage, "
 or pounds of clothes cleaned per gallon of solvent
 consumed is always a goal in their operation.


 A typical small neighborhood synthetic  solvent
 plant, processing 1,500 pounds of textiles per 5-
 day week, using a separate combination washer-
 extractor and a separate tumbler reclaimer, will
 average between  5,000 and 7,500 pounds of clothes
 cleaned per 55-gallon drum of solvent (a consump-
 tion of 7. 3  to 11 gallons of  solvent for each 1, 000
 pounds of fabric).  This average includes reuse
 of solvent recovered from the filter  sludge or
 muck.   The small neighborhood cleaning plant
 using the "hot" type unit,  where all three functions
 are performed in the same machine, will produce
 a mileage figure  of from 10, 000 to 15, 000 pounds
 or higher of textiles cleaned per drum of solvent
 (a consumption of 3. 6 to 5. 5 gallons of solvent
 for each 1,000 pounds of fabric).  Coin-operated
 units, averaging  somewhat less than 8 pounds per
 load but performing all three functions in one unit,
 •will average as low as 1,500 pounds  of textiles per
 drum of solvent and very rarely achieve 5, 000
 pounds of textiles per drum of solvent (a consump-
 tion of 11 to 36 gallons of solvent for each 1,000
 t>ounds of fabric).
The low cost of the petroleum solvents provides
little  economic incentive to the operator to con-
serve solvent and to prevent or control its emis-
sion to  the atmosphere.  The solvents driven off
as they evaporate during the drying of the fabrics
in the tumbler are all emitted to the atmosphere.
Large amounts of solvent are emitted in trans-
ferring wet fabrics from one machine to another,
especially from a washer to an extractor.  Nor-
mally,  the fabrics are placed on a  drain board
within the washing machine and allowed to drain
for 3  to 5 minutes before being transferred.  Fre-
quently, fabrics are moved almost immediately,
without draining,  and  the solvent spilled on the
floor  later evaporates.  The muck  removed from
the filter is discarded, with a resultant loss of  all
solvent contained in the muck to the atmosphere.
Mileage is not too important to the petroleum plant
operator, and typical  mileage is about 24 pounds
of fabric per gallon of solvent consumed (a con-
sumption of 42 gallons of solvent for  each 1,000
pounds  of fabric).

Obviously,  in similar plants performing the same
amount of  cleaning, the use of petroleum solvents
can result in the emission to the  atmosphere of
4 to 7 times more solvent (by volume) than the
emission from operation with synthetic solvent.
The ratio on a weight basis is different since a
gallon of synthetic solvent is much heavier than
a gallon of petroleum solvent (13.6 pounds versus
6.5 pounds).  Thus, petroleum solvent use results
in two-fold greater emission by weight than if
synthetic solvent were used for the same level  of
operations in average plants.

In Los  Angeles County, 2.2 gallons of synthetic
solvents is emitted per day per average plant,
26.9 gallons of petroleum solvents is emitted
per day per average plant, and there is a ratio
of 5  synthetic  solvent plants to 1 petroleum sol-
vent  plant. The total solvent emissions by weight
to the atmosphere on this basis from dry cleaning
operations in Los Angeles County are almost
equally divided between chlorinated solvents and
petroleum solvents.
                                       Lint
                                       Whenever fabrics are tumbled to a dry state,
                                       abrasion and attrition of the fabric produce lint.
                                       Lint is carried in the air exhausted from the
                                       tumblers.  The tumblers used in petroleum plants
                                       of recent construction have self-contained  lint
                                       filters of either cloth or metal screening.  The
                                       older design tumblers vent directly to the atmos-
                                       phere.  Tumblers designed for use with  synthetic
                                       solvent are all provided with a built-in lint filter.
                                       Older tumblers were equipped with a cloth bag,
                                       and some newer units have -wire  screening.

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882
ORGANIC SOLVENT EMITTING EQUIPMENT
HOODING AND  VENTILATION REQUIREMENTS

Ventilation requirements for dry cleaning equip-
ment installations are established by fire and
health codes of the various state and city govern-
mental agencies.  Equipment using petroleum
solvents, whether of the Stoddard or 140-F type,
is considered hazardous or dangerous equipment.
Ventilation requirements generally are estab-
lished for the room or building housing this
equipment.  Most health and safety codes require
that the room air be changed once every 2 to 3
minutes.  No  standards are set for ventilation of
either the washer or extractor using petroleum
solvents. Washers and extractors generally are
not equipped for direct ventilation.  The drying
tumbler  is required to be vented so  that 50 times
its volume of  air is exhausted to the atmosphere
each minute of its operation.

Washing, extracting, and drying equipment using
synthetic solvents is designed •with self-contained
hooding and ventilation provisions.  Dry cleaning
machines which combine -washing and extraction
functions must be vented to the atmosphere
•whenever the  charge door is opened.  They are
not vented when the charge door is closed and
•washing  or extraction is taking place.  The tum-
bler used for  drying and reclaiming must be ven-
ted to the outside atmosphere •when it is in opera-
tion and  its  door is open.  When the charge door
is closed, the ventilation may be entirely closed-
circuit,  recirculating through the clothes,  the
heat exchanger, and the condenser.  The room or
building  housing the synthetic solvent equipment
must be  vented for at least one change of air every
2 minutes.  Such room ventilation must be from
pickup points  not more than 1 foot above the floor
since the vapors are heavier than air.

Minimum allowable concentrations (MAC) for
worker exposure in an 8-hour period for the chlor-
inated hydrocarbon solvents are much lower than
those for the petroleum solvents.  For petroleum
solvents, both Stoddard and the 140-F solvent,
the MAC is 500 ppm; for  perchloroethylene, it is
100 ppm. Carbon tetrachloride, which still is
used in some  establishments, has a MAC,  de-
pending upon  authority selected, of between 10
and 50 ppm.  Trichloroethylene, which no longer
is used,  also  has a MAC  of 100 ppm.

AIR  POLLUTION CONTROL METHODS

The major problem due to contaminant emissions
from dry cleaning  operations,  that of the effect on
overall atmospheric quality through the contribu-
tion of photochemically reactive materials, can
be minimized.  The two types  of petroleum sol-
vents can be formulated so that they are nonreac-
tive under Rule 66. The original solvents  of this
type used in Los Angeles County contributed 2.28
                         tons per day of highly reactive vapors to the at-
                         mosphere.  The presently used petroleum solvents
                         result in highly reactive emissions of only 1. 31
                         tons per day.  The synthetic solvents now used are
                         all of low reactivity.

                         The other problem caused by these emissions
                         is local nuisance complaints. Odor complaints
                         from operation of synthetic solvent plants very
                         rarely occur. Operators of such plants exert
                         every effort to prevent solvent emissions because
                         of the high cost of chlorinated solvents. Petroleum
                         solvent operations also rarely cause odor com-
                         plaints.  The dangerous or hazardous nature of
                         the solvent vapors requires high rates  of ventila-
                         tion, -which usually results in their dilution
                         below detection threshold levels.  Lint discharge
                         can cause some local nuisance problems if not
                         controlled but should rarely do  so since control
                         is relatively easy.

                         No attempts have been made at  petroleum solvent
                         dry cleaning installations to control the emissions
                         of solvent vapors.  With the fire and health  code
                         requirements of room ventilation at such high
                         levels, the  concentration of  solvent vapors in the
                         exhaust air is very low.  The cost of petroleum
                         solvent is so low that no economic pressure exists
                         to prevent its evaporation to the atmosphere.   The
                         principal control exercised in the  solvent emissions
                         is in the detail of the operations performed.
                         Where the fabrics are washed in a separate wash-
                         er and then removed for extraction, it is impera-
                         tive that a drain board be placed within the wash-
                         ing machine and the wet fabric be allowed to drain
                         for a period of not less than 4 minutes.  The pre-
                         vention of spillage of solvent on the floor and the
                         maintenance of liquid- and vapor-tight equipment
                         (required by most fire or health codes) also act
                         to prevent air contaminant emissions from these
                         operations.  Newer equipment installations  where
                         the washing and extraction is performed in the
                         same equipment serve to reduce  solvent vapor
                         emissions.
                         Equipment designed to operate with the synthetic
                         solvents lends itself to easy installation of air
                         pollution control equipment.  Equipment which
                         washes and extracts in one drum is provided with
                         an exhaust blower and vent.  This vent usually is
                         extended directly to the atmosphere  outside the
                         room.  The tumbler used for drying the fabric
                         and reclaiming some  of the solvent vapors driven
                         off in the drying operation also is equipped to vent
                         to the atmosphere during the final stage of opera-
                         tion,  at which time  the final traces of solvent es-
                         cape to the atmosphere during the cooling and de-
                         odorizing stage. These ducts may readily be
                         connected to a simple exhaust system to convey
                         the vapors to control  equipment.

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                                      Dry Cleaning Equipment
                                            883
Adsorbers

Adsorption is almost the only practical means
of controlling synthetic solvent vapors from dry
cleaning equipment.  Incineration is not a likely
means of control since (1) it results in destruction
of the vapors rather than recovery of the solvent
and (2) it will produce toxic gases by incineration
of the chlorinated hydrocarbon solvents.   Economic
incentive has dictated installation of adsorption
equipment by operators.  Synthetic  solvent cost
is approximately ten times that of petroleum sol-
vents,  and recovery of otherwise -wasted solvent
by adsorption represents a considerable cost re-
duction.

Packaged adsorption units employing activated
carbon,  similar to those shown in Figure 673,
are manufactured in standard sizes and are
readily available to the operators of synthetic sol-
vent dry cleaning plants. The package units are
designed with a separate exhaust fan to overcome
the additional resistance of the adsorption unit,
and are easily  connected without special system
balancing to the exhaust vents  of the dry cleaning
equipment.

Vapor-laden air collected from the washer-ex-
tractor,  tumbler, and floor vents passes through
a filter for removal of lint and then to a bed of
activated carbon.  The adsorption units are man-
ufactured with either  one or two activated carbon
containing vessels.  Solvent vapors passing through
the beds are adsorbed at efficiencies approaching
100 percent until the  "breakpoint" of the carbon at
the particular vapor concentration and tempera-
ture is reached (see "Adsorption Equipment, "
Chapter  5).  At that point, the solvent vapors be-
gin escaping to the atmosphere.   Thus, prior to
reaching the breakpoint,  the carbon bed must be
reactivated. Reactivation of the bed and recovery
of the solvent are effected by passing low pres-
sure steam (usually 5  to  15 psig) through the bed.
Figure 674  illustrates the cycles of operation.
The steam causes the  solvent to be stripped from
the bed and to exit from the vessel with the steam-
vapor mixture.   The mixture then is cooled and
condensed,  and the solvent is separated from the
•water by decantation.   The solvent either is re-
covered  in a separate  container,  flows by gravity,
or is pumped back to the tanks in the  dry cleaning
equipment.

The adsorption unit using two vessels is arranged
so that the exhaust vapors and air from the equip-
ment pass  either through both beds in parallel  or
only through one bed.   One or both vessels may be
in the stripping and reactivation cycle.  The  stan-
dard operating procedure for determining the
length of time between stripping operations is to
measure the amount of solvent reclaimed versus
the amount  of solvent  being used in the dry clean-
ing equipment.  Tabulation of solvent recovery
versus use  will determine the point at which  the
adsorption unit stops effecting recovery of sol-
vent.  The  stripping schedule then is  established
at some  point below this final ultimate point of
solvent recovery.  Some triple-function dry-to-
dry cleaning machines for commercial operation
are equipped with integral adsorption units.  All
                Figure 673.  Dual vessel carbon adsorber (Hoyt  Mfg. Corp., Westport,  Mass.).
  234-767 O - 77 - 58

-------
884
                            ORGANIC SOLVENT EMITTING EQUIPMENT
exhaust air from the machine passes through the
adsorber before being emitted to the atmosphere.
Stripping and other operation of the unit is simi-
lar to the package add-on units.

At those establishments using a separate tumbler
for drying  the fabric, installation of the adsorp-
tion unit generally represents a reduction in the
emission of solvents of about 50 percent. When
the adsorption unit is used to control the vapor
emissions  from a triple-function dry-to-dry
machine, savings in  solvent emissions  of between
50 and 70 percent are achieved.  Despite the high
efficiency of adsorption and  operating methods
used to prevent the emissions, a reduction of
more than  70 percent seldom is achieved, when
calculated  on the basis of total solvents purchased
and used -with or without  adsorption.  In the aver-
age dry cleaning establishment, the  amortization
of an adsorption unit, considering capital costs
and operating expenses,  occurs in from 1 to 3
years.

Lint  Traps

The control of lint requires very simple equip-
ment.   Tumblers used in the petroleum solvent
cleaning plants,  if they are not equipped with self-
contained filters, are vented over water tanks in-
side a fine screen enclosure.  The lint particles
impinge upon the  surface of the water in the tank
and gradually sink to the bottom.  Particles which
are reintrained in the air stream are  somewhat
wetted and cling to the screen enclosure.  Fre-
quent cleaning of the tank and the screen enclosure
is required.  Some newer designs of tumbling
equipment for petroleum solvent dry cleaning op-
erations incorporate dry lint traps in the tumbler
housing which are able to meet fire  safety require-
ments.
                             Vapor-laden air
                                      "in"
                                 Solvent vapors
                                 trapped in
                                 carbon
                                 bed
      Condenser
                                                  Waste water
                                          Solvent to "storage1^   r-^-=-^
                                Pneumatic dampers

            ADSORPTION  CYCLE
                DESORPTION CYCLE
       Figure 674. Adsorption and desorption cycles for carbon adsorbers (Hoyt Mfg. Corp., Westport,  Mass.).

-------
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  Gilbert, N. ,  and F. Daniels.   1948.
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  Gillespie,  G.R., andH.F.  Johnstone.   1955.
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Hauck Manufacturing Company.  1953.
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-------
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Leva,  M.  1953.
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896                                   References - Mantell
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                                         References - Mills                        	_897
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898                                     References - Peach
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-------
                                  References - Report                   	899
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 Schmidt, W. A. , W. T. Sproull, and Y. Nakada.  1950.
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 Semrau, K. T.  I960.
     Correlation of Dust Scrubber Efficiency.  JAPCA.  10:200-07 (June).

 Shamos, M. H. , and S. G. Roth.  1950.
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 Sharp, D.E.   1954.
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 Sharp, D.E.   1955.
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 Sherwood,  T.K.,  and R. L. Pigford.  1952.
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 Silverman,  L.  1950.
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 Singer, S.J.  1956.
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                                        References  - Smolen                          	901
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Spain,  R.W.  1956b.
    How to Control Poor Operating Conditions.  Ceram. Ind.  67:80-83 (Dec).


Spaite, P. W. , J.E. Hagan, and W. F. Todd.   1963.
    A Protective Finish for Glass  Fiber Fabrics.   Chem.  Eng. Progr.   59:54-57 (Apr).

Spaite, P. W. , D. G.  Stephan, and A. H. Rose,  Jr.  1961.
    High Temperature Fabric  Filtration of Industrial Gases.  JAPCA.  11:243-47  (May).

Spencer, E. F. ,  Jr.,  N. Kayne, M. F. Le Due, and J. H. Elliott.  1959.
    Experimental Program for the Control of  Organic Emissions From Protective Coating Opera-
    tions.  Report No.  3.  Los Angeles County Air Pollution Control District, Los Angeles, Calif.
     (July).

Sproull, W. T.  1951.
    Precipitators Stop Dust and Fumes.  Chem. Eng.  58:151-54 (May).

Sproull, W. T., and Y. Nakada.  1951.
    Operation of Cottrell Precipitators--Effects of Moisture and Temperature.  Ind.  Eng. Chem.
    43:1350-58 (June).

Sproull, W. T.  1955.
    Collecting High Resistivity Dusts and Fumes.  Ind.  Eng. Chem.  47:940-44 (Apr).

Stairmand, C. J.  1956.
    The Design and Performance of Modern Gas-Cleaning  Equipment.  J. Inst. Fuel.  29:58-76 (Feb).

Steigerwald, B. J.  1958.
    Emissions  of Hydrocarbons to the Atmosphere From Seals on Pumps and Compressors. Report
    No. 6.  Joint District, Federal,  and  State Project for  the Evaluation of Refinery  Emissions.
    Los Angeles County Air Pollution Control  District,  Los Angeles,  Calif. (Apr).

Steinbock, R. S.  1952.
    Stacks for Pollution Control.  Chemical Engineering.   Copyright 1952 by McGraw-Hill, Inc.  New
    York, N.Y.  (Feb).

Stenburg, R.L.   1958.
    Control of Atmospheric Emissions From Paint and Varnish Manufacturing Operations.  U.  S. Depart-
    ment of Health, Education, and Welfare, Robert A.  Taft  Sanitary Engineering Center,  Cincinnati,
    Ohio.  Technical Report  A58-4 (June).  Also in:  Paint and Varnish Production.  49:61-65,  111-14.
    (1959).

Stephan, D.G. ,  and G. W.  Walsh.   I960.
    Residual Dust Profiles in -- Air Filtration.  Ind. Eng. Chem.  52:999-1002 (Dec).

Stephan, D. G. ,  G. W.  Walsh,  and Rl A. Herrick.  I960.
    Concepts in Fabric Air Filtration.  Am. Ind.  Hyg. Assoc.  J.  21:1-14  (Feb).

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902	References - Stern	


 Stern, A. C, , K.J.  Caplan, andP.D.  Bush.  1956.
     Removal of Particulate Matter From Gaseous Wastes:  Cyclone Dust Collectors.  Division of
     Refining,  American Petroleum Institute, New York, N. Y.

 Stine, V. F.  1955.
     Blast Cleaning in Industry, Bulletin No.  1500.  Pangborn Corporation, Hagerstown, Md.
 Streeter, V. L.  1951.
     Fluid Mechanics.  McGraw-Hill Book Co. ,  Inc., New York, N. Y.

 Striplin,  M. M. , Jr.  1948.
     Development of Processes and Equipment for Production of Phosphoric Acid.  Chemical Engineer-
     ing Report No. 2.  Tennessee Valley Authority.

 Sussman,  V. H.  1957.
     Atmospheric Emissions From Catalytic Cracking Unit Regenerator Stacks.   Report No. 4.  Joint
     District, Federal,  and State Project for Evaluation of Refinery Emissions.   Los Angeles County
     Air Pollution Control District, Los Angeles, Calif. (June).

 Sussman, V.H. , R.K. Palmer, F. Bonamassa, B. J.  Steigerwald, and R. G. Lunche.  1958.
     Emissions to the Atmosphere From Eight Miscellaneous Sources  in Oil Refineries.  Report No. 8.
     Joint District,  Federal, and State Project for the Evaluation of Refinery Emissions.  Los Angeles
     County Air Pollution Control  District,  Los Angeles, Calif.  (June).

 Sutton, O.G.  1950.
     The Dispersion of Hot Gases  in the Atmosphere.   J. Meteorol. 7:307-12 (Oct).

 Teller, A. J.  I960.
     Absorption With Chemical Reaction.  Chem. Eng.  67:111-24 (July 11).

 Thomas,  J. W.   1959.
     Air vs. Water  Cooling, Cost  Comparison.   Chem.  Eng.  Progr.  55:38-41 (Apr).
 Tooley, F. V.   1953.
     Handbook of Glass Manufacture.   Volumes I and II.  Ogden Publishing Co. ,  New York, N. Y.

 Treybal,  R. E.   1955.
     Mass-Transfer Operations.   McGraw-Hill  Book Co.,  Inc.,  New  York, N. Y.

 Trinks, W.  1955.
     Industrial Furnaces. Volume  I.  3d ed.  John Wiley and Sons,  New York, N. Y.

 Turk, A.,  andK.A. Bownes.  1951.
     Adsorption Can Control Odors.  Chem. Eng.  58:156-58  (May).

 Underwood, G.  1962.
     Removal of Sub-Micron Particles From Industrial Gases, Particularly in the Steel and Electricity
     Industries.  Intern.  J. Air Water  Pollution.   6:229-63  (May-Aug).

 U.S.  Department of Health, Education, and Welfare.   1968.
     Interim Guide  to Good Practice for Selecting Incinerators for Federal Facilities.  Durham,  N. C.

 U. S. National Bureau of Standards.
     Fuel Oils.   Commercial Standard CS-48.  Clearinghouse for Federal Scientific  and Technical
     Information, Springfield, Va. 22151.

 U.S. National Bureau of Standards.  1949.
     Handbook No.   42.  Safe Handling  of Radioactive Isotopes.  Washington, D. C.

 Van Dreser,  M. L.   1962.
     Basic  Refractories for the Glass  Industry.  Glass Ind.  43:18-21  (Jan).

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                                       References - Waitkus                                       9°3
Waitkus, J.  1962.
    Recover Waste Heat to Reduce Glass Tank Operating Cost.   Ceram.  Ind.  79:38-42,  68-70 (Dec).

Walker,  E.A. ,  andJ.E. Coolidge.  1953.
    Semiempirical Equation of Electrostatic  Precipitation.  Ind. Eng. Chem.  45:2417-22 (Nov).

Walker,  W. H. ,  W.K. Lewis, W. H. McAdams, and E. R. Gilliland.  1937.
    Principles of Chemical Engineering.  3d ed.  McGraw-Hill Publishing Co., Inc., New York,  N. Y.

Walsh, G. W. ,  and P. W. Spaite.   1962.
    An Analysis of Mechanical Shaking in Air Filtration, JAPCA.  12:57-61 (Feb).

Ward, D.R.  1952.
    Design of Laboratories  for Safe Use  of Radioisotopes.  AECU-2226.   U.S. Atomic Energy Com-
    mission Advisory Field Service Branch,  Isotopes Division, Oak  Ridge,  Tenn. (Nov).

Watts, D.L. ,  and J.F.  Higgins.   1962.
    The  New Baghouse Installation for Cleaning Smelter Gases at Phelps Dodge Refining Corporation.
    JAPCA.  12:217-20 (May).

Weisburd.
    See, Griswold, 1962.

Western  Precipitation Corporation,  1952.
    Cottrell Electrical Precipitators.   3d ed. Los Angeles, Calif.

White, H. J.  1951.
    Particle Charging in Electrostatic Precipitation.  Trans. Am. Inst.  Elec. Engrs.  70(II):1186-91.


White, H.J.  1953.
    Electrostatic Precipitators for Electric  Generating Stations.  Trans. Am. Inst. Elec. Engrs.
    72(III):229-41.


White, H. J.  1957.
    Fifty Years of Electrostatic Precipitation.  JAPCA.  7:166-77 (Nov).

White, H.J.  1963.
    Industrial Electrostatic Precipitation. Addison-Wesley Publication  Co. , Reading,  Mass.

White, H.J., andW.H.  Cole.   I960.
    Design and Performance Characteristics of High-Velocity, High-Efficiency Air Cleaning Pre-
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White, H.J., and G. W.  Penney.  1961.
    Basic Concepts.  In: Electrical Precipitation Fundamentals.  Proceedings for  Engineering Seminar
    on Electrostatic  Precipitation,  June 17-21,  1957.  Pennsylvania State University, Department of
    Electrical Engineering and General Extension, University Park, Pa.

 Williams,  C.E.,  et al.  1940.
      Determination of Cloth Area for Industrial Air Filters.  Heating, Piping, Air Conditioning.
      12:259-63 (Apr).

 Williams Patent Crusher and Pulverizer Co. , Inc.
      Bulletin  696.   St. Louis 6, Mo.

 Willington  Sears  Co.   1954.
      Filter Fabric Facts.  New York, N. Y.

 Wilson, E.F.  I960.
      Dust Control  in Glass Manufacturing. Glass Ind.  41:202-03, 236, 237 (Apr).

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904                                   References - Woodhouse
 Woodhouse,  H.   1957.
     Centrifugal Pump Packings and Seals.  Pt. 3.  Mechanical Seals.  Petrol.  Refiner.  36:207-11
     (Apr).

 Woodward,  E. R. , andE.R. Fenrich.  1952.
     Odor Control With Chlorine Dioxide.  Chem. Eng.  59:174-75  (Apr).

 Zachariasen, W. H.   1932.
     The Atomic Arrangement of Glass.  J. Am. Chem. Soc.  54:3841-51.

 John Zink Company.
     Flare Bulletin.   Tulsa, Okla.

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                        APPENDICES
             APPENDIX  A:  RULES AND REGULATIONS
             APPENDIX B:  ODOR-TESTING TECHNIQUES

      KARL D. LUEDTKE,  Senior Air Pollution Engineer
  APPENDIX  C:  HYPOTHETICAL AVAILABLE HEATS FROM NATURAL GAS

     SANFORD M.  WEISS, Principal Air Pollution Engineer
                APPENDIX D:  MISCELLANEOUS DATA
       APPENDIX E:  EMISSION SURVEYS, INVENTORIES, AND FACTORS

ROBERT G. LUNCHE, Chief Deputy Air Pollution Control Officer
          ERIC E. LEMKE,  Director of Engineering
       GEORGE THOMAS, Senior Air Pollution Engineer

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                             APPENDIX A
The Rules and Regulations of the County of Los Angeles Air Pollution
Control District are reproduced in this appendix as published by the
District.  These rules were effective as of January 1,  1973.
                                 906

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                          APPENDIX  A:    RULES  AND  REGULATIONS  OF THE  AIR  POLLUTION
                                       CONTROL  DISTRICT,  COUNTY  OF  LOS  ANGELES
 REGULATION I.  GENERAL PROVISIONS

 Rule 1.  Title.
     These  rules and regulations shall be  known  as  the  rules of the Air
 Pollution Control  District

 Rule 2.  Definitions.
     a   Except as otherwise specifically provided in these rules and except
 where the  context otherwise indicates, words used in  these rules are used
 in exactly the same sense as the same words are used in Chapter 2, Division
 20 of the Health and Safety Code.
     b.  Parson   "Person" means  any person, firm, association, organiza-
 tion, partnership, business  trust,  corporation, company, contractor, sup-
 plier, installer, user   or  owner, or  any state or local  governmental  agency
 or public district or any  officer or employee thereof.  "Person" also means
 the  United  States or its  agencies, to the extent authorized by federal law.
     c    Bcieird   "Board" means the Air  Pollution Control  Board of the
Air Pollution Control District of Los Angeles County.
     e   Section   "Section" means  section of the Health and Safety  Code
of the State of California  unless some other statute  is specifically  men-
tioned
     f   Rule   "Rule" means a  rule of the Air Pollution  Control District
of Los Angeles County.
     g   Air  BJSIIIS and G^ogidphical Areas  Three major  "air basins" and
two  "geographical areas" within Los Angeles County  are  defined as being
within the following  described boundaries

         1     Los Angeles Basin Beginning at the intersection of the south
              erly boundary of the  Angeles National Forest with the easier
               ly boundary of the County of Los Angeles, thence along said
              easterly boundary in  a general southwesterly direction to the
              contiguous |unsdictional limit of Los Angeles County in the
              Pacific  Ocean, thence continuing along the boundary of the
              County  of Los Angeles (in  the Pacific  Ocean) in  a  general
              northwesterly and  westerly   direction to its most westerly
              intersection with  the westerly boundary of the County  of
              Los Angeles  (in the Pacific Ocean), thence in  a general nor-
              therly direction along the generally  westerly boundary  of
              the  County   of  Los  Angeles   to  the   most  norther-
              ly  intersection of said westerly County line with the south-
              ern boundary of Hydrographic Unit 2 of the South Coastal
              area as  defined by the  California Water Resources Board,
              thence easterly along said southern boundary to its intersec-
              tion with  the westerly boundary  of the Angeles National
              Forest; thence southerly  along the said boundary  of the
              Angeles  National  Forest to  its intersection with the Los
              Angeles  City  limits;  thence  in a general easterly  direction
              along the northerly boundary of said City of Los Angeles to
              the  southwesterly corner of Section  16,  Township 2 North,
              Range 13  West,  S.B.B. &  M , thence in a  general easterly
              direction along said southerly boundary  of  the Angeles Na-
              tional  Forest to said easterly  boundary of the County of Los
              Angeles
          2    Upper Santa Clara River Valley Basin  Beginning at the inter-
               section of the northern boundary of Los Angeles Basin, with
               the western boundary of Los Angeles County, thence gener-
               ally  northerly along the western  boundary of the County of
               Los  Angeles to  its  intersection  with the southern  bound-
               ary of the Angeles National  Forest, thence generally easter-
               ly along  the  southern boundary of the Angeles National
               Forest  to its  intersection with a line defining the drainage
               separation  between the Santa Clara  River Valley drainage
               area  and the Antelope Valley drainage area, thence gener-
               ally easterly along said drainage  separation line to its inter-
               section  with the northerly boundary of the Angeles Nation-
               al Forest, thence generally southwesterly along the northern
               boundary of the Angeles National Forest to its intersection
               with the northern boundary of the Los Angeles Basin, thence
               westward along  said  northern boundary of the Los Angeles
               Basin to the said westerly boundary of the County of Los
               Angeles

          3    Antelope Valley Basin. That  portion of Los Angeles County
               northerly  of the Angeles National  Forest and  the  Upper
               Santa  Clara River Valley Basin.

          4.    Mountain  Area of Los Angeles County.  This area is com-
               posed of the two segments of the Angeles National Forest
               and adjoining areas not included  in an air basin.

          5    Island Area  of  Los Angeles County. This area is composed
              of Santa Catalma Island and San  Clemente Island.

     h.    Rpyuldlion.   "Rixjuldticm"  means one  of the major subdivisions
of the Rules of the Air Pollution Control District  of Los Angeles County
     i.  Particular  Mdttpr    "Paniculate Matter"  is any  material, except
uncombmed  water,  which  exists in  a finely divided form as a liquid  or
solid  at standard conditions
     1   Process Weight Per Hour  "Process  Weight" is the total  weight of
all materials  introduced into any specific process which process may cause
any discharge into the atmosphere.   Solid fuels charged will be considered
as part  of the process weight, but liquid and gaseous fuels and combustion
air will  not.  "The  Process Weight Per Hour" will be derived by dividing
the total  process weight by the number of  hours in one complete opera-
tion  from  the  beginning of any given process  to  the completion thereof,
excluding any time during  which the equipment is idle
     k.   Dusts   "Dusts" are minute solid  particles  released into the air
by natural forces or  by mechanical processes  such as crushing, grinding
milling, drilling, demolishing, shoveling, conveying, covering, bagging, sweep-
ing, etc.
     I.  Condensed  Fumes   "Condensed Fumes" are minute solid particles
generated by the condensation of vapors from solid matter after volatiliza-
tion  from  the  molten  state, or  may  be  generated  by sublimation, distilla-
tion,  calcination, or  chemical  reaction,  when  these processes  create air-
borne particles.
     m.    Combustion  Contaminants   "Combustion  Contaminants"  are
                                                                       907

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908
                                                           RULES AND REGULATIONS
 participate  matter  discharged  into the atmosphere from  the  burning  of
 any kind of material containing carbon in a free or combined state.
     n   Atmosphere   "Atmosphere" means  the  air that envelops  or sur-
 rounds  the earth    Where air  pollutants are emitted into a building not
 designed specifically  as a piece of air pollution  control equipment,  such
 emission into the building shall be considered an emission into the atmos-
 phere
     o.   Combustible  Refuse   "Combustible  Refuse" is any solid or liquid
 combustible waste  material containing carbon in  a free  or combined state.
     p.   Multiple-Chamber Incinerator.   "Multiple-Chamber Incinerator"
 is any article, machine, equipment, contrivance, structure or part of a struc-
 ture, used  to dispose of combustible refuse by burning,  consisting of three
 or more refractory  lined combustion furnaces in series, physically  separated
 by refractory walls, interconnected by gas passage ports or ducts and em-
 ploying  adequate  design parameters  necessary  for  maximum combustion
 of the  material to be  burned.   The  refractories shall  have a Pyrometric
 Cone Equivalent of at  least 17, tested according  to  the method described
 in the American Society for Testing Materials, Method C-24.
     q.   Oil-Effluent Water Separator.  "Oil-Effluent Water Separator" is
 any tank,  box, sump or other  container in  which any  petroleum or  prod-
 uct thereof,   floating on or entrained or contained in water entering  such
 tank, box,  sump or  other container, is physically separated and removed
 from such  water prior to outfall, drainage, or  recovery of such water.
 Rule 3.  Standard Conditions.
     Standard  conditions are a gas temperature  of  60 degrees  Fahrenheit
 and a gas  pressure of  14.7  pounds  per square inch absolute.   Results of
 all analyses and tests shall be calculated or  reported at this gas tempera-
 ture and pressure.
 Rule 4. Authority to Arrest.
     The Air  Pollution Control Officer  and every  officer and  employee
 of the  Los  Angeles  County Air  Pollution Control  District designated  by
 him is  authorized, during reasonable hours,  to arrest a person without a
 warrant whenever  he has reasonable cause  to believe  that the person to
 be arrested has committed a  misdemeanor m his presence which is a vio-
 lation of  Chapter  2,  Division  20 of  the Health  and Safety Code,  or any
 provision of  the Vehicle Code relating to the emission  or control  of air
 contaminants, or any  order, regulation, or rule adopted  pursuant  thereto.
 Such authority to arrest is granted in accordance with  Penal Code  Section
 836.5.

 REGULATION  II.  PERMITS

  Rule 10. Permits Required.
      a.  Authority to  Construct.  Any person  building,  erecting, altering
 or replacing any  article, machine,  equipment or  other  contrivance,  the
 use of  which may  cause the issuance of air contaminants or the use of which
 may eliminate or reduce or control the  issuance of  air contaminants,
 shall first  obtain  authorization for such construction from  the Air Pol-
 lution  Control Officer.  An authority to  construct shall remain in  effect
 until the  permit to  operate the equipment for which  the application was
 filed is granted or denied or the  application is canceled.
      b.  Permit to Operate.   Before any article,  machine, equipment or
 other  contrivance described  in Rule  1.0  (a)  may  be operated or used,  a
 written permit shall  be obtained from  the  Air  Pollution Control Officer.
 No permit to operate or use shall be granted either by the Air Pollution
 Control Officer or  the Hearing  Board for  any article,  machine, equip-
 ment  or  contrivance  described  in  Rule 10 (a), constructed  or installed
without authorization as required  by Rule  10 (a),  until the information
required  is presented to the  Air Pollution  Control  Officer and such ar-
ticle,  machine,  equipment  or  contrivance  is  altered,  if  necessary, and
made to conform  to the standards  set forth  in Rule  20 and  elsewhere
in these  Rules and  Regulations.
     c.  Posting of  Permit  to Operate.   A  person who  has been granted
under  Rule  10 a  permit to operate any  article, machine, equipment,  or
other contrivance described m Rule 10 (b),  shall firmly  affix  such permit
to operate,  an approved facsimile, or other approved identification bear-
ing the permit  number upon the article, machine,  equipment,  or other
contrivance  in such a manner as to be clearly visible and accessible.   In
the event that the article, machine, equipment, or  other contrivance  is
so constructed or operated that the permit to operate cannot be  so  placed,
the permit to operate  shall be mounted so as to be clearly visible in  an
accessible place within  25 feet of  the  article,  machine, equipment,  or
other contrivance, or maintained readily available at all times on the operat-
ing premrses.
     d. A person shall not wilfully deface, alter, forge, counterfeit, or falsify
a  permit to operate any article, machine, equipment, or  other contrivance.
     f.  Permit to  Sell  or Rent. Any person who sells or rents to another
person an incinerator which may be used to dispose of combustible refuse
by burning within the  Los Angeles Basin and which incinerator is to  be
used  exclusively  in connection with any structure, which  structure is de-
signed for  and used exclusively as a dwelling for not  more than  four fami-
lies, shall first obtain a permit from the Air Pollution Control  Officer to
sell or rent such incinerator.
     g.   Permit  for Open  Burning.  A person shall  not set or permit any
open outdoor fire without first having applied  for and been issued a permit
for such fire by the Air Pollution Control Officer, except that an application
for burning permit shall  not  be required for recreational fires, ceremonial
fires, or cooking fires.
Rule 11.  Exemptions.
     An authority to construct or a permit to operate shall not be required
for:
     a.  Vehicles as defined  by the Vehicle Code of the State of California
but not including  any article,  machine,  equipment or other contrivance
mounted on such vehicle that would otherwise require a permit under the
provisions of these Rules and  Regulations.
     b.  Vehicles used  to transport passengers or freight.
     c.   Equipment utilized  exclusively  in  connection with any structure,
which structure is  designed for and used  exclusively  as  a dwelling for not
more than four families.
     d.   The following equipment:
          1. Comfort air conditioning or comfort ventilating systems which
            are not designed to remove air contaminants generated by or re-
            leased  from specific units or equipment.
          2. Refrigeration  units except  those  used  as, or in conjunction
            with, air pollution control  equipment.
          3. Piston type internal  combustion  engines.
          5. Water  cooling  towers and water cooling ponds not used ior
            evaporative cooling of process water or not used for evaporative
            cooling of  water  from barometric jets or  from  barometric con-
            densers.
          6. Equipment used exclusively for steam cleaning.
          7. Presses used exclusively for extruding metals, minerals, plastics
            or wood.
          8. Porcelain enameling furnaces, porcelain enameling drying ovens.

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                                Rules  and Regulations of the Air Pollution Control  District
                                                                                                                                          909
   vitreous enameling furnaces or vitreous enameling drying ovens.
 9. Presses used for the curing of rubber products and plastic prod-
   ucts.
10. Equipment used exclusively  for space heating, other than boil-
   ers.
13. Equipment used for hydraulic  or hydrostatic  testing.
14. All  sheet-fed printing presses; and  all  other printing presses
   without driers.
17. Tanks, vessels and pumping equipment used exclusively for the
   storage or dispensing  of fresh  commercial  or purer  grades of:
   a.   Sulfuric acid with an acid strength of 99 per cent or less
        by weight.
   b.   Phosphoric acid with an acid  strength of 99 per cent or
        less by weight.
   c.   Nitric acid  with an acid strength of 70 per cent or less by
        weight.
18. Ovens used  exclusively for  the curing of plastics  which are
   concurrently being vacuum held to a mold  or for the softening
   or annealing of plastics.
19. Equipment used exclusively for the dyeing or  stripping (bleach-
   ing) of textiles where no organic solvents,  diluents,  or thinners
   are used.
20. Equipment used exclusively to mill or grind coatings  and mold-
   ing compounds where all  materials  charged  are in a paste form.
21. Crucible type or pot  type furnaces with a  brimful capacity of
   less than 450 cubic inches of any molten metal.
22. Equipment used exclusively for the melting or applying of wax
   where no organic solvents, diluents, or thinners are used.
23. Equipment used exclusively  for bonding lining to brake shoes.
24. Lint traps used exclusively  in conjunction with dry cleaning
   tumblers.
25. Equipment used in eating  establishments  for the purpose of
   preparing food  for  human consumption.
26. Equipment used exclusively to compress or  hold dry  natural
   gas.
27. Tumblers used for the cleaning or debarring of metal products
   without abrasive blasting.
28. Shell core and shell-mold manufacturing machines.
29. Molds  used for the casting of metals.
30. Abrasive  blast cabinet-dust  filter  integral  combination  units
   where  the total internal volume of  the blast section is 50 cubic
   feet or less.
31. Batch  mixers of 5  cubic  feet rated working capacity or less.
32. Equipment used  exclusively for the packaging of  lubricants
   or greases.
33. Equipment used exclusively for the manufacture of water emul-
   sions of asphalt, greases, oils or waxes.
34. Ovens used exclusively for the curing of vinyl plastisols by the
   closed mold curing process.
35. Equipment used exclusively for conveying and  storing plastic
   pellets.
36. Equipment used  exclusively for  the mixing and  blending of
   materials at ambient  temperature  to make water based  adhe-
   sives.
37. Smokehouses in which  the  maximum horizontal inside  cross-
   sectional area does not exceed 20 square feet.
38. Platen presses used  for laminating.
  The following equipment or  any exhaust  system or  collector
  serving exclusively  such equipment:
  1. Blast cleaning equipment using  a  suspension of abrasive in
    water.
  2. Ovens,  mixers and blenders used in bakeries where the prod-
    ucts are  edible  and intended for  human consumption.
  3. Kilns  used  for  firing ceramic ware,  heated exclusively by
    natural gas, liquefied petroleum  gas, electricity  or  any com-
    bination thereof.
 4. Laboratory equipment used  exclusively  for chemical or physi-
    cal analyses and bench scale  laboratory equipment.
  5. Equipment used for inspection of metal  products.
 6. Confection cookers where the products are edible and intend-
    ed for human consumption.
  7. Equipment used  exclusively for forging,  pressing,  rolling or
    drawing of metals or for heating metals immediately prior to
    forging, pressing, rolling or drawing.
 8. Die  casting machines.
 9  Atmosphere generators used in connection  with metal heat
    treating processes.
10. Photographic  process equipment  by which an image is repro-
    duced upon material sensitized to radiant energy.
11. Brazing, soldering or welding equipment.
12. Equipment used exclusively for the sintering of glass or metals.
13. Equipment used for buffing (except automatic or semi-auto-
    matic tire  buffers) or polishing, carving, cutting,  drilling, ma-
    chining, routing, sanding, sawing, surface grinding or turning of
    ceramic artwork, ceramic precision parts, leather, metals, plas-
    tics, rubber, fiberboard, masonry, asbestos, carbon or graphite.
14. Equipment used for carving, cutting, drilling, surface grinding,
    planing, routing, sanding, sawing, shredding or turning of wood,
    or the  pressing or storing of sawdust,  wood chips  or wood
    shavings.
15. Equipment using   aqueous  solutions  for  surface  preparation,
    cleaning, stripping, etching (does not include chemical milling)
    or the electrolytic  plating with electrolytic polishing of, or  the
    electrolytic stripping of brass, bronze, cadmium, copper, iron,
    lead, nickel, tin, zinc, and precious metals.
16  Equipment used  for washing  or  drying products  fabricated
    from metal or glass, provided that no volatile  organic materials
    are used in the process and that no oil or solid fuel is burned.
17. Laundry dryers, extractors or tumblers used for fabrics cleaned
    only with water solutions of bleach or detergents.
19. Foundry  sand mold forming equipment to which no heat is
    applied.
20. Ovens used exclusively for curing potting materials or castings
    made with epoxy  resins.
21. Equipment used to liquefy or separate oxygen, nitrogen or the
    rare gases from the air.
22. Equipment used for  compression molding and injection mold-
    ing of plastics.
23. Mixers for rubber  or  plastics where no material in  powder form
    is added and no organic solvents, diluents or thinners are used.
24. Equipment used  exclusively  to package Pharmaceuticals and
    cosmetics  or to coat pharmaceutical  tablets.
25. Equipment used  exclusively  to grind,  blend  or  package  tea,
    cocoa, spices or roasted  coffee.

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910
                                                         RULES AND REGULATIONS
         26. Roll mills or calenders for rubber or plastics where no organic
             solvents, diluents or thinners are used.
         27. Vacuum producing devices used in laboratory operations or in
             connection with other equipment which is exempt by Rule 11.
      f.   Steam generators, steam superheaters, water boilers, water heaters,
 and closed  heat transfer  systems that have a maximum heat input rate of
 less than 250,000,000 British Thermal  Units (BTU) per hour (gross), and
 are fired exclusively with one of the following.
          1. Natural gas.
          2. Liquefied petroleum gas.
          3. A combination of natural gas and liquefied petroleum gas.
      g.   Natural draft hoods,  natural draft stacks qr natural draft ventila-
 tors.
      h.   Containers, reservoirs, or tanks used exclusively for:
          1. Dipping  operations for coating objects with oils, waxes or
             greases  where  no  organic  solvents,  diluents  or thinners  are
             used.
          2. Dipping operations for applying coatings of natural or synthe-
             tic resins which contain  no organic solvents.
          3. Storage of liquefied gases
          5. Unheated storage of organic  materials with  an initial boiling
             point of 300°F.  or greater.
          6. The storage of fuel oils with  a gravity of 25°A.P.I. or lower.
          7. The storage of lubricating oils.
          8. The storage of fuel oils with a gravity of 40°A.P.I, or lower and
             having a capacity of 10,000 gallons or less.
          9. The storage of  organic liquids, except gasoline, normally used as
             solvents, diluents or thinners,  inks, colorants,  paints, lacquers,
             enamels, varnishes, liquid resins or other surface coatings, and
             having a capacity of 6,000 gallons or less.
         10. The storage of liquid  soaps,  liquid detergents, vegetable oils,
            waxes or wax emulsions.
         11. The storage of asphalt.
         12. Unheated  solvent dispensing containers, unheated non-convey-
            onzed solvent rinsing containers or unheated non-conveyonzed
            coating dip tanks of 100 gallons capacity or less.
         14. The storage of gasoline  having a capacity of less than 250 gal-
            lons.
         15. Transporting  materials on streets or highways.
     i    Equipment  used exclusively for  heat treating glass or metals,  or
 used  exclusively for case hardening, carburizmg, cyaniding, nitriding, carbon-
 itriding, sihconizmg or diffusion treating of metal objects.
     j.    Crucible furnaces, pot furnaces or induction furnaces, with a capa-
 city of 1000 pounds or less each, in which  no sweating or distilling is con-
 ducted and from which only the following metals are poured or in which
 only  the following metals are held  in a molten state
          1. Aluminum or any alloy containing over 50 per cent aluminum.
          2. Magnesium or any alloy  containing over 50 per cent magnesium.
          3. Lead or any  alloy containing over 50 per cent lead.
          4. Tin or any alloy containing over 50 per cent tin.
          5. Zinc or any alloy containing over 50 per cent zinc.
          6. Copper.
          7. Precious metals.
     k.   Vacuum cleaning systems used exclusively for industrial, commer-
 cial or residential housekeeping purposes.
     I.    Structural changes  which  cannot change the  quality, nature or
 quantity of air contaminant  emissions.
     m.   Repairs  or  maintenance not  involving structural changes to any
equipment for which a permit  has been granted.
     n.    Identical replacements in whole or in part of any article, machine,
equipment or other  contrivance where a permit to operate had previously
been granted for such equipment under Rule 10.

Rule 12. Transfer.
  An authority to construct,  permit to operate or  permit to sell  or rent
shall not be  transferable,  whether by operation of law or otherwise, either
from one location to another, from one piece of equipment to another, or
from one person to another.

Rule 14.  Applications.
   Every application  for an authority  to construct, permit to operate or per-
mit to sell or rent required under Rule 10 shall be filed in the manner and
form  prescribed by the Air Pollution Control Officer, and shall give all the
information  necessary to  enable the Air Pollution  Control  Officer to  make
the determination required by  Rule 20 hereof.

Rule 17.  Cancellation of Applications.
     a.   An authority to construct shall expire and the application shall
be  canceled  two years from the date of issuance of the authority to con-
struct.
     b.   An application  for permit to operate existing equipment shall  be
canceled two years from the date of  filing of the application.

Rule 18.  Action On Applications.
  The Air Pollution  Control Officer  shall act, within a reasonable time, on
an  application for authority to construct, permit  to operate or permit to
sell or rent, and shall notify the applicant in writing  of his approval, condi-
tional approval or denial.

Rule 19.  Provision Of Sampling And Testing Facilities.
   A person operating or using any article, machine, equipment or other con-
trivance  for  which these rules require a  permit shall provide  and maintain
such sampling and testing facilities as specified in the authority to construct
or permit to  operate.

Rule 20.  Standards For Granting Applications.
     a    The Air Pollution Control Officer shall deny an authority to con-
struct, permit to operate or permit to sell or rent, except as provided in Rule
21, if  the applicant does not show that every article, machine, equipment
or  other contrivance,  the use of which  may cause the  issuance  of air
contaminants, or the use  of  which may  eliminate or  reduce or control
the issuance of  air contaminants, is so designed, controlled,  or equipped
with such air pollution control  equipment,  that it may be expected to oper-
ate without  emitting or without causing to be emitted air contaminants in
violation of  Sections 24242 or  24243,  Health and Safety Code, or of these
 Rules and Regulations.
     b.    Before  an authority to construct or permit to operate  is granted,
the Air  Pollution Control  Officer may require the applicant to provide
and maintain such facilities as  are necessary for sampling and testing pur-
poses  in ordei to secure  information that  will disclose  the nature, extent,
quantity  or  degree  of  air  contaminants  discharged  into the atmosphere
from the article,  machine, equipment or other contrivance described  in the
authority to construct or permit to operate.  In the  event of such a require-
ment, the Air Pollution Control Officer shall notify  the applicant in writing

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                                        Rules and Regulations  of the Air Pollution  Control District
                                                                   911
of the required size, number and location of sampling holes; the size and lo-
cation of the  sampling platform; the access to the sampling platform; and
the utilities for operating the sampling and testing equipment.  The platform
and  access shall  be constructed in accordance with the General Industry
Safety Orders of the State of California.
     c.    In acting upon a Permit to Operate, if the Air Pollution Control
Officer finds that the article,  machine, equipment or other contrivance has
been  constructed  not  in accordance with the Authority to Construct, he
shall deny the Permit  to Operate.   The Air Pollution Control Officer shall
not  accept any further application  for Permit to Operate  the article,  ma-
chine, equipment or other contrivance  so constructed until  he finds that
the article, machine, equipment or other contrivance has been reconstruct-
ed in accordance with  the Authority to Construct.

Rule 21.  Conditional Approval.
     a.    The Air Pollution Control Officer may issue an authority to con-
struct or a permit to  operate, subject to conditions which will bring the
operation of any  article, machine, equipment or  other contrivance within
the standards of Rule 20, in which case the conditions shall be specified in
writing.  Commencing  work under such an authority to construct or opera-
tion under such a permit to operate shall be deemed acceptance of all the
conditions so specified.  The Air Pollution  Control  Officer shall issue an
authority to construct or a permit to operate with revised conditions upon
receipt of a new application,  if the applicant  demonstrates that the article,
machine,  equipment or other contrivance can operate within the standards
of Rule 20 under the revised conditions.
     b.    The Air Pollution Control Officer may  issue a permit to sell or
rent,  subject to conditions which will bring the  operation of any article,
machine,  equipment or other contrivance within the  standards of Rule 20,
in which case the conditions shall be specified in writing. Selling or renting
under such a permit to sell or rent shall be  deemed acceptance of all the
conditions so specified.  The Air Pollution Control Officer shall issue a per-
mit to sell or rent with revised conditions upon receipt of a new application,
if the applicant demonstrates  that the article, machine,  equipment or other
contrivance can operate within the  standards of Rule 20 under the revised
conditions.

Rule 22.  Denial Of Applications.
   In  the event of denial of an authority to  construct, permit  to operate or
permit to sell or rent,  the Air Pollution  Control Officer shall  notify the ap-
plicant  in writing of the reasons therefor. Service of this notification  may
be made in person or  by mail, and such service may  be proved by the writ-
ten acknowledgment of the persons served or affidavit of the person making
the service. The Air Pollution Control Officer shall not accept a further ap-
plication  unless the applicant has complied  with the objections specified by
the  Air  Pollution Control Officer as his reasons for denial of the authority
to construct, the permit to operate  or the permit  to sell or rent.

Rule 23.  Further Information.
   Before acting on an application  for authority to construct, permit to
operate  or permit to sell or rent,  the Air Pollution Control Officer may re-
quire the applicant to furnish further information or further plans or speci-
fications.

Rule 24.  Applications Deemed Denied.
   The applicant may at his option deem the authority to construct, permit
to operate or permit to sell or rent denied if the Air  Pollution Control Offi-
cer fails to act on the application within 30 days after filing, or within 30
days after applicant furnishes the further information, plans and specifica-
tions  requested  by the  Air  Pollution Control  Officer,  whichever is later.

Rule 25.  Appeals.
   Within  10 days  after notice,  by the  Air  Pollution Control  Officer,  of
denial or conditional approval of an authority to construct, permit to oper-
ate or permit to sell or rent, the  applicant may  petition  the  Hearing Board,
in writing, for a public hearing.   The Hearing  Board, after notice and a pub-
lic  hearing held within 30 days after filing the  petition, may sustain or re-
verse  the  action of the  Air  Pollution Control Officer; such order may be
made subject to specified  conditions

REGULATION III.   FEES

Rule 40.   Permit Fees.
   Every applicant,  except  any state or local governmental agency or public
district, for an  authority to construct or a permit to operate any article, ma-
chine, equipment or other  contrivance, for which  an authority to construct
or  permit to operate is required  by the State law or the Rules and  Regula-
tions  of the Air Pollution  Control District, shall pay a filing fee of $40.00.
Where an application  is filed for a  permit to operate any article, machine,
equipment or other contrivance  by reason of transfer from one person  to
another, and where a permit to operate had previously been granted under
Rule  10 and no alteration, addition or transfer of location has been made,
the applicant shall pay only  a $10.00 filing fee.
   Every applicant, except any state or local governmental  agency or pub-
lic  district, for a permit to  operate, who files  an application with the Air
Pollution Control Officer,  shall,  in addition to the filing fee  prescribed  here-
in, pay the fee for the issuance  of a permit to operate in the amount  pre-
scribed in the following schedules, provided, however, that the filing fee shall
be  applied to the fee prescribed for the  issuance  of the permit to operate.
   If an application  for  an authority to construct  or a permit to operate is
canceled,  or  if an authority to  construct or  a  permit to operate is denied
and such denial becomes final, the filing fee required  herein  shall not be re-
funded  nor applied to any subsequent application.
   Where an application  is  filed for a permit to operate any article, machine,
equipment or other contrivance by reason of transfer of location or transfer
from one  person to another, or both, and where a permit to operate had pre-
viously  been  granted for such equipment under  Rule 10 and an alteration or
addition has been made, the applicant shall be assessed a fee  based upon the
increase in total  horsepower rating, the increase  in total fuel consumption
expressed in thousands  of British Thermal  Units (BTU) per  hour, the  in-
crease in  total  electrical energy  rating,  the increase in maximum horizontal
inside cross sectional area  or the  increase  in total stationary container capac-
ity resulting from such alterations  or additions,  as  described  m the fee
schedules contained herein.  Where the application is for transfer of  loca-
tion and no  alteration or  addition  has been  made, the applicant shall pay
only a filing  fee of $40
   Where an  application is filed  for an authority  to  construct  or a permit
to operate exclusively  involving  revisions to  the  conditions of an existing
permit to operate or involving alterations  or additions resulting m a change
to  any  existing article,  machine, equipment or  other  contrivance holding a
permit under the provisions  of Rule 10 of these Rules and Regulations, the
applicant shall  be assessed  a  fee based upon the  increase  in total horsepower
rating,  the  increase  in  total fuel  consumption expressed   m thousands of
British Thermal Units (BTU) per hour, the increase in  total electrical energy

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912
                                                         RULES AND REGULATIONS
 rating, the increase in maximum horizontal  inside cross sectional area or the
 increase in total  stationary  container capacity resulting from such altera-
 tions or additions, as described in the fee schedules contained herein. Where
 there  is no change or is a decrease in such ratings, the applicant shall pay
 only the amount of the filing fee required herein.
   After the provisions for granting permits as set forth in Chapter 2, Divi-
 sion 20, of the Health and Safety Code and the Rules and Regulations have
 been complied with,  the applicant shall be notified by the Air Pollution
 Control Officer, in writing, of the fee to be paid for issuance of the permit
 to operate.  Such notice may be given  by  personal service or by  deposit,
 postpaid, in  the United States mail and shall serve as a temporary permit to
 operate for 30 days from the date of personal service or mailing.  Nonpay-
 ment  of the fee within this period of time shall result in the automatic can-
 cellation of the application.
    In the event that more than one fee schedule is applicable to a permit to
 operate, the governing schedule shall be that which results in the higher
 fee.
   Where a single  permit to operate has been granted under Rule 10 prior to
 July 1,  1957,  and where the Air Pollution Control Officer would, since that
 date,  have issued separate or revised permits for each permit unit included
 in the original application, the Air Pollution Control Officer may issue such
 separate or revised permits without fees.
    In the event that a permit to operate is granted by the Hearing Board after
 denial by the Air Pollution Control Officer or after the applicant deems his
 application denied, the applicant shall pay the fee prescribed in the follow-
 ing schedules  within 30 days after the date of the  decision of the Hearing
 Board.  Nonpayment of the  fee within this  period of time shall result in
 automatic cancellation of the permit and the application.   Such a  fee shall
 not be charged for  a permit to operate granted by the Hearing Board for
 the duration of a variance.
   A request for a duplicate permit  to operate shall be made in writing to
 the Air Pollution Control Officer within 10 days after the destruction,  loss
 or defacement of a  permit to operate.  A fee of S2.00 shall be charged, ex-
 cept to any  state  or local governmental agency or public district, for issuing
 a duplicate permit to operate.
    It is hereby determined that the cost of issuing permits and of inspections
 pertaining to such issuance exceeds the fees prescribed.
                                                  Schedule 2
                                       Fuel  Burning Equipment Schedule

                      Any article,  machine,  equipment or other contrivance in which fuel is
                    burned, with the exception of  incinerators which  are covered in Schedule
                    4, shall be assessed a permit fee based upon the design fuel consumption
                    of the article, machine, equipment or other contrivance expressed in thou-
                    sands of British Thermal Units (BTU)  per hour, using gross heating values
                    of the fuel, in accordance with  the following schedule.

                          1000 BRITISH THERMAL UNITS PER HOUR         FEE
                         (a)   up to and including  150	$     40.00
                         Ib)  greater than 150 but less than 400	     700.00
                         (c)   400 or greater but less than 650	     200.00
                         id)  650 or greater but less than 1500	     300.00
                         (e)   1500 or greater  but  less  than 2500	     400.00
                         (ft   2500 or greater  but  less  than 5000	     500.00
                         tg)   5000 or greater  but  less  than 75000   	     600.00
                         (h)  15000 or greater  	     800.00

                                                   Schedule 3
                                          Electrical Energy Schedule

                      Any article,  machine, equipment or  other contrivance which uses electri
                    cal energy, with the exception of electric  motors covered  in Schedule 1; shall
                    be assessed a permit fee based  on the  total kilovolt ampere (KVA) ratings,
                    in accordance with the following schedule:

                                KILOVOLT AMPERE                           FEE
                         (at  up  to and including 20	$    40.00
                         Ib)  greater than 20 but less than 40	      700.00
                         (c)  40 or greater but less than  145  	     200.00
                         (dl   145 or greater but less than 450	     300.00
                         (e)  450 or greater but less than 4500	     400.00
                         (f)  4500 or greater but less than  14500	     500.00
                         (g)   14500 or greater but less  than 45000	     600.00
                         (hi  45000 or greater   	     800.00
                               Schedule 1
                    Electric Motor Horsepower  Schedule

   Any article, machine, equipment, or other contrivance where an electric
 motor is used as the power supply shall be assessed a permit fee based on the
 total rated motor horsepower of all electric motors included m any article,
 machine,  equipment or other contrivance, in accordance with the following
 schedule:
             HORSEPOWER
      (a)  up to and including 2Va  	
      (b)  greater than 2% but less than 5 .
      (c)  5 or greater but less than 15   ..
      Id)  15 or greater but less than 45 ..
      (e)  45 or greater but less than 65 ..
      If I  65 or greater but less than 125 .
      Ig)  125 or greater but less than 200
      fh)  200 or greater	
FEE
 40.00
100.00
200.00
300.00
400.00
500.00
600.00
800.00
                                                  Schedule 4
                                              Incinerator Schedule

                       Any article, machine, equipment or other contrivance designed and used
                     primarily to dispose of combustible refuse by wholly consuming the materi-
                     al charged leaving only the ashes or  residue shall be assessed a permit fee
                     based  on the following schedule of  the maximum  horizontal inside cross
                     sectional area, in square feet, of the  primary combustion chamber:
       AREA,  IN SQUARE  FEET
la)   up to and including 3  	
Ib)   greater than 3 but less than 4 .
(c)   4 or  greater but less than 7 . .
Id)   7 or  greater but less than 10. .
(el   10 or greater but less than 15.
ffl   15 or greater but less than 23.
Ig)   23 or greater but less than 40.
fh)   40 or greater	
FEE
 40.00
100.00
200.00
300.00
400.00
500.00
600.00
800.00

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                                       Rules  and Regulations  of the Air Pollution Control District
                                                                                                                                               913
                              Schedule 5
                    Stationary Container Schedule

  Any stationary tank, reservoir, or other container shall be assessed a per-
mit fee based on the following schedule  of capacities in gallons or cubic
equivalent

            GALLONS                                    FEE
     (al  up to and including 4000	$   40.00
     Ib)  greater than 4000 but less than 10000	     60 00
     id   WOOD or greater but less than 40000  	    700.00
     (dl  40000 or greater but less than 100000. .    .   .     20000
     (e)   100000 or greater but less than 400000   	    300 00
     If I  400000 or greater but less than  1000000.  .         400 00
     !g)   WOOOOO or greater but less than 4000000.  ..  .    500.00
     (hi  4000000 or greater	     600.00

                               Schedule  6   .
                         Miscellaneous Schedule

   Any article, machine,  equipment or other contrivance  which is not in-
cluded in the preceding schedules shall be assessed a permit fee  of S40 00

Rule 42.  Hearing Board Fees.
   a   Every  applicant or petitioner for variance, or for the extension,  revo-
cation or modification of a variance, or for an appeal from a denial or condi-
tional  approval of an authority to construct, permit to operate or permit to
sell or rent, except any state or local governmental agency or public district,
shall pay to the Clerk of  the Hearing Board, on filing, a fee in the sum of
$16 50.  It is hereby determined that the cost of  administration of Article
5,  Chapter  2,  Division 20, Health and Safety Code, or Rule 25 of  these
Rules  and Regulations, exceeds $1650 per petition.
   b   Any person requesting a transcript of the hearing shall pay the cost
of such transcript
   c    This rule shall  not apply to petitions filed  by the Air Pollution Con
 trol Officer.

 Rule 43. Analysis Fees
   Whenever the Air Pollution Control Officer finds that an analysis of the
 emission from any source is necessary to determine the extent and  amount
 of pollutants being discharged into the atmosphere which  cannot be deter
 mined by  visual  observations, he may order the collection of samples and
 the analysis made by  qualified  personnel of the Air Pollution Control Dis-
 trict.  The time required for collecting samples,  making  the analysis and
 preparing the necessary reports, but excluding time required in going to and
 from  such  premises, shall be charged against the owner or operator of said
 premises in a reasonable sum to be determined by the Air Pollution Control
 Officer,  which said sum  is  not to  exceed the actual  cost of such work

 Rule 44.  Technical Reports - Charges For
   Information,  circulars,  reports of technical work, and other reports pre-
 pared  by the Air Pollution Control District when supplied to other govern-
 mental agencies or individuals or groups requesting copies of the same may
be charged  for by the District in a sum not to exceed the cost of preparation
and distribution of such documents   All such monies collected shall be
turned into the general funds of the said  District
Rule 45.  Permit Fees • Open Burning.
     Every applicant  for a  permit  to conduct an open fire, who files an
application with the Air Pollution Control Officer, except any state or local
government agency or  public  district,  shall pay  a  filing  fee  of  $20 00
Where an application  is canceled  or denied, the filing  fee shall not  be re
funded nor applied to any subsequent application

REGULATION IV.  PROHIBITIONS

  Rule 50    Ringelmann Chart.
      (Effective until  January 1, 1973 for all sources completed and put into
 service  before January 6,  1972   See amended  Rule below)
      A  person  shall not  discharge  into  the  atmosphere  from  any single
 source  of emission  whatsoever  any  air  contaminants  for  a  period or
 periods  aggregating more  than three minutes in any  one hour which  is:
      a    As dark  or darker in shade as that designated as No. 2  on the
 Ringelmann Chart,  as  published by the United  States Bureau  of Mines,
 or
      b.   Of such  opacity  as  to obscure an observer's view  to  a  degree
 equal to or greater  than does smoke  described  in subsection (a)  of this
 Rule.

  Rule 50   Ringelmann Chart.
      (Effective January 6, 1972 for any source not completed and put into
 service  Effective for all sources on January 1, 1973 )
      A  person  shall  not  discharge into  the  atmosphere  from  any single
 source of emission whatsoever any air contaminant for a period or  periods
 aggregating more than three minutes in any one hour which is
      a    As dark or daiker in shade as that designated No  1 on the  Ringel
 mann Chart, as published by the United States Bureau of Mines, or
      b   Of such  opacity  as  to obscure an observer's view  to  a  degree
 equal to or greater  than does smoke  described  in subsection (a)  of this
 Rule
      This  amendment shall  be  effective on  the date  of its adoption  for any
 source of emission not  then completed and put into service As to ail other
 sources of emission  this amendment shall bt? effective  on January  1, 1973.
 Rule 51.  Nuisance.
      A person shall not discharge from any source whatsoever such  quanti-
 ties of air contaminants or other  material which cause injury, detriment,
 nuisance or annoyance to  any considerable number of persons  or  to the
 public or which endanger the comfort, repose, health or safety of  any such
 persons  or the public or which cause or have a natural tendency to cause
 injury or damage to business or property
 Rule 52.  Particulate Matter.
     (Effective until January 1, 1973 for all equipment completed and put
 into service before January 6, 1972. See amended Rule below)
      Except as otherwise provided in Rules 53 and 54, a person shall not
 discharge into the atmosphere  from any source paniculate matter in excess
 of 0.3 grain per cubic foot  of gas at standard conditions.

 Rule 52.  Particulate Matter -  Concentration.
     (Effective January 6, 1972 for any equipment not completed and put
 into service  Effective for all equipment on January 1, 1973,1
     A person shall not discharge into the atmosphere  from any source par
 ticulate matter in excess of  the concentration shown in the following table
 (See Rule 52 Table)

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914
                                                         RULES AND REGULATIONS
     Where the volume  discharged falls  between figures listed in the table,
the exact concentration permitted to be discharged shall be determined by
linear interpolation
     The provisions of this rule shall not apply to  emissions resulting from
the combustion of liquid or gaseous fuels in steam generators or gas turbines
     For the  purposes of this rule "paniculate matter" includes any material
which  would  become paniculate  matter if cooled to standard conditions
     This amendment shall be  effective on the date of its adoption for any
equipment  not then completed and put  into service.  As to all  other equip-
ment this amendment shall be effective on January 1, 1973.
                          Table  For Rule  52
Volume Discharged-
Catcuiated as Drv Gas
at Standard Conditions


1000 or less
1200
1400
1600
1800
2000
2500
3000
3500
4000
5000
6000
7000
8000
10000
15000
Maximum Concentra-
ter Allowed m Dis-
charged Gas-Grams Per
Cubic Foot of Dry Gas
at Standard Conditions
0200
.187
176
.167
160
.153
.141
.131
124
.118
108
101
.0949
0902
0828
.0709
Volume Discharqed-
Calculated ds Dry Ga
at Standard Conditio


20000
30000
40000
50000
60000
70000
80000
100000
200000
400000
600000
800000
1000000
1500000
2000000
2500000 or
Maximum Conceniia
s ter Allowed in Dis
ns chared Gas-Grams Per
Cubic Fool of Dry Gas
at Standard Conditions
00635
0544
.0487
0447
0417
.0393
0374
0343
0263
0202
0173
0155
0142
0122
0109
more 0100
Rule 53. Sulfur Compounds - Concentration.
     A  person  shall  not discharge into the atmosphere sulfur compounds,
which would exist as a liquid or gas at  standard conditions, exceeding in
concentration at the point of discharge,  0 2 per cent by volume calculated
as sulfur dioxide (S02)

Rule 53.1.  Scavenger Plants.
     Where  a separate source of air pollution is  a scavenger  or  recovery
 plant, recovering pollutants which would otherwise be emitted to the atmos
 phere,  the  Air Pollution Control Officer may grant a permit  to operate
 where the total emission of pollutants is substantially less  with  the plant in
 operation than when closed,  even  though the concentration exceeds that
 permitted  by Rule 53(a)   The Air Pollution Control Officer  shall report
 immediately in writing  to the Air  Pollution  Control Board the granting of
 any such permit, together with the  facts and  reasons theiefor
     Effective July 1,  1973, this Rule is repealed for sulfur recovery units
     Effective January 1, 1974,  this Rule is repealed for sulfunc acid units

 Rule 53.2.  Sulfur Recovery Units.
     A  person shall not, after  June  30, 1973, discharge into the atmosphere
 from any sulfur recovery unit producing elemental sulfur, effluent process
 gas containing more than
     1    500 parts per million  by volume of sulfur compounds calculated
         as sulfur dioxide
     2.    10 parts per million by volume of hydrogen sulfide.
     3    200  pounds per hour of sulfur compounds calculated as  sulfur
         dioxide.
     Any sulfur recovery unit  having an effluent process gas discharge con-
taining  less than 10 pounds per hour of sulfur compounds calculated as sul-
fur dioxide may dilute to meet the provision of number (1) above.

Rule 53.3 Sulfunc Acid Units.
     A person shall not, after December 31,  1973, discharge into the atmos-
phere from any sulfunc acid unit, effluent process gas containing more than
     1    500 parts  per million  by  volume of sulfur compounds calculated
          as SLIfur dioxide.
     2    200  pounds per  hour of sulfur compounds calculated  as sulfur
          dioxide

Rule 54.   Dust and Fumes.
     (Effective  until  January 1,  1973 for all equipment completed and put
into service before January 6, 1972. See amended Rule  below)
     A person shall not discharge in any  one hour from any source whatso-
ever dust or fumes in total quantities in excess of the amount shown in the
following table   (see next page)
     To use the following table,  take the process weight per hour as such is
defined in  Rule 2(j). Then find this figure on the table, opposite  which is
the maximum number of pounds of contaminants which  may be discharged
into the atmosphere in any one  hour.  As  an example,  if A has a process
which  emits contaminants  into the atmosphere and which process takes 3
hours to complete, he will divide the weight of all materials in the specific
process, in this example,  1,500 Ibs.  by  3  giving a process weight per hour of
500 Ibs.  The table shows that A may not discharge more than  1.77 ibs. in
any one hour during the  process. Where the process weight per  hour falls
between figures in the left hand  column,  the exact weight of permitted dis-
charge may be interpolated.

  *  (You will  find Table for Rule 54   with amended  Rule following)

Rule 54   Solid Particulate Matter - Weight.
     (Effective January 6,  1972 for any  equipment not completed and put
into service.  Effective for all equipment  on  January 1, 1973.)
     A person  shall  not  discharge  into  the  atmosphere  from  any source
solid  paniculate  matter,  including  lead and lead compounds, m excess of
the rate shown in the following table   (See  Rule  54 Table}
     Where the process weight per hour falls between figures listed in the
table,  the exact weight of permitted discharge shall  be determined  by linear
interpolation.
     For  the purposes of this rule "solid particulate matter" includes any
material which would become solid particulate matter if  cooled to standard
conditions.
     This amendment shall  be effective on the date of its adoption for any
equipment not then completed and put into service.  As to all other equip-
ment this amendment shall  be effective on January 1, 1973.

 Rule 55.   Exceptions
     The  provisions of Rule 50  do not  apply to:
          a.    Smoke from fires set by  or permitted by any public officer
     if such fire  is set  or permission given in the performance of the official
     duty of such officer, and such fire m the opinion  of such  officer is
     necessary
               1.    For  the purpose  of the prevention of  a fire hazard
                    which cannot  be  abated  by any other  means, or
               2.    The  instruction of public employees in the methods of
                    fighting fire.
          b.    Smoke from fires set pursuant to permit on  property used
     for industrial purposes for the purpose of instruction of employees in

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                                        Rules and Regulations of the Air Pollution Control District
                                                                  915
TABLE FOR RULE 54

Wt/hi(lbs)

50
KM)

150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1 000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
*See Defmiti
TABLE FOR RULE 54
Etech/hrClbs) Wt/lu(]bs)

24
46

66
.85
03
.20
35
.50
63
77
.89
01
12
24
34
2.43
253
262
2.72
2.80
2.97
3 12
3 26
340
354
366
379
3.91
4.03
4 14
424
4.34
4.44
4.55
4.64
4.74
4.84
4.92
5.02
5 10
5 18
5.27
5.36
3400
3500

3600
3700
3800
3900
4000
4100
4200
4300
4400
4500
4600
470(1
4800
4900
5000
5500
6000
6500
7000
7500
8000
8500
9000
9500
10000
1 1 000
1 2000
1 3000
14000
15000
1 6000
17000
1 8000
19000
20000
30000
40000
50000
60000
w
ninru
in m Rule 20).

Dlsch/hrdbs)

.44
52

61
69
77
85
5 93
601
6.08
6 15
622
6 30
6.37
645
652
660
667
703
7 37
7 71
805
839
871
903
936
967
100
1063
11 28
11 89
1250
13 13
1374
14 36
1497
1558
16 19
22 22
283
343
400




Per Hour-
Pounds Per Hour





250 or less
300
350
400

450
500
600
700

800
900
1000
1200
1400
1600
1800
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
9500
10000
(Amended
Rate Allowed (or Solid
Paniculate Matter
(Aggregate Discharged
From All Points of

Processl-Pounds
Per Hour
1.00
1 12
1 23
1 34

1.44
1 54
1.73
1 90

207
222
238
266
2.93
3 19
343
366
421
472
5 19
5.64
607
6.49
689
727
764
8 00
8.36
870
904
936
9.68
1000
January 6, 19721
Per Hour--
Pounds Per Hour





12000
14000
16000
18000

20000
25000
30000
35000

40000
45000
50000
60000
70000
80000
90000
100000
120000
140000
160000
180000
200000
250000
300000
350000
400000
450000
500000
600000
700000
800000
900000
1000000 or
Maximum Discharge
Rate Allowed tor Solid
Paniculate Matter
(Aggregate Discharged
From All Points of

Processl-Pounds
Per Hour
104
10.8
11 2
11 5

11 8
12 4
130
135

139
143
14.7
15 3
15.9
16.4
169
17.3
18 1
18.8
194
199
204
21 6
22.5
234
24 1
O/1 Q
Z4 O
254
266
27 6
28.4
29.3
more 30 0
     methods of fighting fire.
         c.   Agricultural operations in the growing of crops, or raising of
     fowls or animals
         d.   The use of an orchard or citrus grove heater which does not
     produce unconsumed solid carbonaceous matter at a rate in excess of
     one(1) gram per minute
         e.   The use of other equipment in agricultural operations in the
     growing of crops, or raising of fowls or animals.

Rule 56. Storage of Petroleum Products.
     A person shall not  place,  store or hold in any stationary tank,  reser
voir or other container of more  than 40,000 gallons capacity any gasoline
or any petroleum distillate having a vapor pressure of 1 5 pounds per square
inch absolute or greater under actual storage conditions, unless such tank,
reservoir or other container is a pressure tank maintaining working pressures
sufficient at all times to prevent hydrocarbon vapor or gas loss to the atmos-
phere, or is designed and equipped with one of the following vapor loss con-
trol devices, properly installed, in good working order and in operation.
         a.  A floating  roof, consisting of a pontoon type or double-deck
     type roof, resting on the  surface of the liquid contents and equipped
     with a closure seal, or seals, to close the space between the roof edge
     and tank wall. The control equipment provided for in this paragraph
     shall not be used if the gasoline or petroleum distillate has a vapor pres-
     sure of  11.0  pounds per square inch absolute or greater under actual
     storage conditions.  All tank gauging and sampling devices shall be gas-
     tight except when gauging or sampling is taking place.
         b.   A vapor recovery system, consisting of a vapor gathering sys-
     tem capable of collecting the hydrocarbon vapors and gases discharged
     and a vapor disposal system  capable of processing  such hydrocarbon
     vapors and  gases so as to prevent their emission to the atmosphere and
     with all tank gauging and sampling devices gas-tight  except when gaug-
     ing or sampling is taking place.
         c.   Other equipment of equal efficiency,  provided  such  equip
     ment  is submitted to and approved by the Air Pollution Control Offi-
     cer.

Rule 57.  Open  Fires.
     A person shall not  burn  any combustible refuse in  any open outdoor
fire within the Los Angeles Basin,  except
          a   When such fire is set or permission for such  fire is given in
     the performance of the official duty of any public officer, and such fire
     in the opinion of such officer  is necessary
              1.   For the purpose of the prevention of a fire hazard which
                   cannot be abated by any other means, or
              2    The instruction of public employees in  the  methods  of
                   fighting  fire
          b.   When such fire is  set pursuant to permit on property used for
     industrial  purposes for the  purpose of  instruction of employees  in
     methods  of fighting fire.
         c.   When such fire is set in the course of any agricultural opera-
     tion in the growing of crops, or raising of fowls or animals
     These exceptions shall  not  be effective on any calendar day on which
the Air  Pollution Control Officer determines that.
  234-767 O - 77 - 60

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916
                                                         RULES AND REGULATIONS
              1.   The inversion base at 4-00 A.M., Pacific Standard Time,
                   will be lower than one thousand five hundred feet above
                   mean sea level, and
              2    The maximum  mixing height will not be above three
                   thousand five hundred feet, and
              3.   The average surface wind speed between 6J00 A.M  and
                   12'00 Noon, Pacific Standard  Time, will  not  exceed
                   five miles per hour.

 Rule 57.1. Open Burning - Upper Santa Clara  River Valley Basin.
     A person shall  not burn any combustible refuse in any open outdoor
 fire  within the Upper Santa Clara River Valley  Basin as defined m Rule 2.g
 except that he may do so when a written permit for such fire is issued by
 both the Air Pollution Control Officer and a fire protection agency  official,
 for any of the following reasons'
      1.   Where  a fire hazard to life or property is declared by a fire protec-
          tion agency official and such fire hazard cannot be abated by any
          other means, or
     2.   For the  purpose  of  instructing  fire fighting personnel  of any
          state,  county, or city fire department, or
     3.   For the purpose of instructing personnel in private  industry  in
          fire fighting methods, or
     4.   In emergency situations where the  public health is endangered,  or
     5.   For the burning of agricultural wastes.
          These  exceptions   shall   not  apply   in   the  Upper  Santa
          Clara  River Valley Basin on any calendar day on which the Air
          Pollution Control Officer determines that
          a.   The inversion base at 6:00 A.M., Pacific Standard Time, will
              be lower than two thousand seven hundred  feet above mean
              sea level, and
          b.   The maximum  mixing height will be below four thousand
              seven  hundred feet above  mean sea level, and
          c.   The  average  surface wind  speed  between 6'00 A.M. and
               12:00 Noon, Pacific Standard  Time, will  not  exceed five
              miles  per hour.
 This Rule shall become effective on December 31,  1971

 Rule 57.2.   Open  Burning - Antelope Valley Basin.
     A person shall  not burn any combustible refuse in any open outdoor
 fire  within the Antelope Valley Basin as defined in  Rule 2.g. except that he
 may do so when  a written permit for such fire is issued by both the Air Pol-
 lution  Control Officer and a fire protection agency official, for  any of the
 following reasons
     1    Where  a fire hazard to life or property is declared by a fire  pro-
          tection agency official and such fire  hazard cannot be abated by
          any other means, or
     2.   For the purpose of instructing fire fighting personnel  of any state,
          county, or city fire department, or
     3.   For the purpose of instructing personnel in private industry in fire
          fighting methods, or
     4    In emergency situations where the public health is endangered, or
     5.   For the burning of agricultural wastes
          These   exceptions  shall   not  apply  in  the Antelope  Valley
          Basin  on  any calendar day on  which the Air Pollution Control
          Officer determines that
          a.   The inversion  base at 6  00  A M  , Pacific Standard Time, will
              be lower than four thousand feet above mean sea level, and
          b.   The maximum mixing height will be below six thousand feet
              above mean sea level, and
         c.    The  average  surface wind speed  between 6:00  A.M. and
              12:00  Noon,  Pacific Standard Time, will  not exceed five
              miles per  hour.
This Rule shall become effective on December 31, 1972.

Rule 57.3.  Open  Burning  - Mountain  Area.
     A person shall not burn any combustible refuse in any open outdoor
fire in  the Mountain Area of Los Angeles County as defined in Rule 2.g.
except that  he may do so when a written permit for such fire is issued  by
both the Air Pollution Control Officer and a fire protection agency official,
for any of the following reasons:
     1.  Where a fire hazard to life, property or watershed is declared by a
         fire protection agency official  and such fire hazard cannot  be
         abated by any other means, or
     2.  For  the  purpose  of  instructing  fire fighting  personnel  of any
         governmental fire protection agency, or
     3.  In emergency situations where  the public health is endangered, or
     4   For the burning of agricultural wastes.
         These exceptions  shall  not apply in the Mountain Area of Los
         Angeles County on any calendar day on which the Air Pollution
         Control Officer determines that:
         a.    The  inversion base at 6:00 A.M., Pacific Standard Time, will
              be between  2500 feet  and 5000 feet above mean sea  level,
              and
         b.    The  maximum mixing height will be between 2500 feet and
              6000 feet above mean sea level, and
         c    The  average  surface wind speed  between 6'00 A.M. and
              12 00  Noon,  Pacific Standard Time, will not exceed five
              miles per  hour.
This Rule shall  become  effective on  December  31, 1971.

Rule 57.4   Open Burning - Island Area.
     A person shall not burn any combustible refuse in any  open outdoor
fire in the  Island Area of  Los  Angeles County  as  defined in  Rule   2.g.
except that  he may do so when a written permit for such fire is issued by
both the Air Pollution Control Officer and a fire protection agency official,
for any of the following reasons:
     1.   Where a fire hazard to life, property or watershed is declared by a
         fire protection agency official and such fire hazard cannot be abat-
         ed by any other means, or
     2.   For  the purpose  of  instructing fire fighting personnel  of any
         governmental fire  protection agency, or
     3.   In  emergency situations where the public health is endangered, or
    4    For the burning of agricultural wastes.
         These exceptions  shall not apply in the Island Area of Los Angeles
         County on any calendar day on which the Air  Pollution  Control
         Officer determines that:
         a.    The  inversion base  at  6:00  A.M., Pacific Standard Time,
              will  be  lower than one thousand  five hundred feet above
              mean sea level, and
         b.    The  maximum mixing  height will be  below three thousand
              five hundred feet above mean sea level, and
         c    The  average  surface wind speed  between 6:00  A.M  and
              12 00  Noon,  Pacific Standard Time, will  not exceed five
              miles per  hour.
This Rule shall  become  effective  on  December 31, 1971.

-------
                                        Rules and Regulations  of the Air Pollution Control District
                                                                  917
Rule  58.   Disposal  of  Solid  and Liquid Wastes.
     a.    A person shall not burn any combustible refuse in any incinerator
except in a multiple-chamber  incinerator as  described in  Rule 2 (p), or in
equipment found  by the Air  Pollution  Control  Officer in  advance of such
use to be equally  effective  for the purpose  of air pollution control as an
approved  multiple-chamber incinerator.   Rule 58 (a) shall be effective in the
Los Angeles Basin  on the date of its adoption, and in the Upper Santa Clara
River Valley Basin on January 1, 1972  In  all other areas of  Los Angeles
County, this Rule  shall  be effective on January 1, 1973

     b.    A person shall not discharge into the atmosphere from any incin-
erator or  other  equipment used  to dispose of combustible refuse by burn-
ing,  having  design burning rates  greater than 100 pounds  per hour, except
as provided in subsection (d}  of this rule, particulate matter in excess of 0 1
grain per cubic foot of gas calculated to  1 2 per cent of carbon dioxide (C02)
at standard  conditions.  Any carbon dioxide (COj) produced by combustion
of any  liquid or gaseous fuels shall be excluded from the calculation to 12
per cent of carbon dioxide (
     c.    A person shall not discharge into the atmosphere from any equip
ment whatsoever, used to process combustible refuse, except as provided in
subsection (d)  of this  rule, particulate  matter in excess of 0 1 grain per
cubic foot of  gas calculated to 12  per cent of carbon dioxide (CC>2) at
standard conditions.  Any carbon dioxide (C02)  produced by combustion
of any  liquid or gaseous fuels shall be excluded from the calculation to 12
per cent of carbon dioxide  (CO2)

     d.    A person shall not discharge into the atmosphere  from any incin-
erator or other equipment  used to dispose of  combustible  refuse by burn-
ing,  having design  burning rates of  100 pounds per hour or less, or for
which an application for permit is filed before  Janaury 1, 1972, particulate
matter  in excess of 0 3 grain per cubic foot of  gas calculated to 12 per cent
of carbon dioxide (CC>2)  at standard conditions  and shall not discharge
particles which are individually large enough to be visible while suspended
in the atmosphere  Any carbon dioxide (C02) produced by combustion of
any  liquid or gaseous fuels shall be excluded from the calculation to 12 per
cent of  carbon dioxide (C02>

Rule 59.  Oil-Effluent Water Separator.
     (Effective until July 1, 1972 for  all equipment operating under permit
as of June 29, 1971.  See amended Rule on following page)
     A person shall not use any compartment of any single or multiple com-
partment oil-etfiuent water  separator  which compartment receives effluent
water containing  200 gallons a day or more of any petroleum product or
mixture of petroleum  products from any equipment processing,  refining,
treating, storing or handling kerosine or other petroleum product of equal
or greater volatility than kerosine, unless such compartment is equipped with
one of the following vapor  loss control devices, properly installed, in good
working order and in operation.
         a.   A  solid  cover with all  openings  sealed and totally enclosing
     the liquid contents. All gauging  and sampling devices shall be gas-tight
     except when gauging or sampling  is taking place.
         b,   A floating roof,  consisting of a pontoon type  or double-deck
     type roof, resting on the  surface of the liquid contents and equipped
     with a closure seal, or seals, to close the space between the roof edge
     and container wall.  All gauging and sampling devices shall be gas-tight
     except when gauging or sampling  is taking place.
         c.   A  vapor recovery system, consisting of a vapor  gathering
     system capable of collecting the hydrocarbon vapors and gases dis-
     charged and a vapor disposal system capable of processing such hydro-
     carbon vapors and  gases so as to prevent their emission to the atmos-
     phere and with all  tank gauging and sampling devices gas-tight except
     when gauging or sampling is taking place
          d.   Other equipment of  equal efficiency, provided such equip-
     ment is  submitted to  and approved  by  the Air Pollution  Control
     Officer
     This rule shall  not  apply to any oil-effluent water separator used ex-
clusively in conjunction  with the production of  crude oil.
     For  the purpose  of this rule,  "kerosine" is defined as any petroleum
product  which,  when distilled  by  ASTM  standard test Method D 86-56,
will give a temperature of 401°F. or less at  the 10 per cent point recovered.

Rule 59.  Effluent Oil Water Separators.
     (Effective June 29, 1971 for any equipment  not  completed and  put
into service  Effective for  all equipment after July 1, 1972)
     A person shall not use any compartment of any vessel or device operat-
ed for the recovery of oil from  effluent water which recovers  200 gallons a
day  or  more of any petroleum products from  any equipment which proc-
esses,  refines, stores or handles hydrocarbons  with  a  Reid vapor pressure
of 0.5 pound or  greater, unless such compartment is equipped with one  of
the following vapor Joss control devices,  except when  gauging or sampling
is taking place
          a   A solid cover with all openings sealed and totally enclosing
     the liquid contents  of that compartment
          b   A floating  pontoon  or double-deck  type cover, equipped
     with closure seals to  enclose any space  between the cover's edge and
     compartment wall
          c   A vapor recovery system, which reduces the emission of all
     hydrocarbon vapors and gases  into 'the atmosphere by at least 90 per
     cent by weight.
          d   Other equipment of  an efficiency equal to or greater than
     a, b, or c,  if approved  by the  Air Pollution Control Officer.
     This rule shall  not  apply to any oil-effluent water separator used ex-
clusively  in conjunction with the  production  of  crude  oil,  if the water
fraction of the oil-water effluent entering the separator contains less than
5 parts per million hydrogen sutfide, organic  sulfides, or  a  combination
thereof
     This amendment  shall  be effective at the date of its adoption  for any
equipment not then completed and put into service.  As to all other equip-
ment this amendment shall be effective on July 1, 1972

Rule 60  Circumvention
     A person  shall not build,  erect, install, or use any article, machine,
equipment or other contrivance, the use of which, without resulting in a
reduction in  the total release of air contaminants to the atmosphere,  re-
duces or conceals an emission which would otherwise constitute a violation
of Division 20, Chapter  2  of the Health and Safety Code of the State of
California or of these  Rules and Regulations  This Rule shall  not apply to
cases in which the only violation involved is of Section 24243 of the Health
and Safety Code of the State of California, or of  Rule 51 of these Rules and
Regulations

Rule 61.  Gasoline Loading into Tank Trucks and  Trailers.
     (Effective until July 1, 1972 for all equipment operating under permit
as of June 29, 1971.  See  amended Rule on following pagel
    A person shall not load gasoline into any tank truck or trailer from any
loading facility unless such loading facility is equipped with a vapor collec-

-------
918
                                                          RULES AND REGULATIONS
 tion and disposal system or its equivalent, properly  installed, in good work-
 ing order and in operation.
     When loading  is effected through the hatches of a tank truck or trailer
 with a  loading arm equipped with a vapor collecting adaptor, a pneumatic,
 hydraulic or other mechanical means shall be provided to force  a vapor-tight
 seal between the adaptor and  the hatch.  A means shall be provided to pre-
 vent liquid gasoline drainage  from the loading device  when it is removed
 from  the hatch  of  any tank truck  or trailer,  or to accomplish complete
 drainage before such removal.
     When loading  is effected  through means other than hatches, all loading
 and vapor lines shall be equipped with fittings which make vapor tight con-
 nections and which close automatically when disconnected.
     The vapor  disposal portion of  the system  shall consist of one of the
 following
         a    A vapor-liquid absorber system with a minimum recovery
     efficiency of 90 per cent by weight of all  the hydrocarbon vapors and
     gases entering such disposal system
         b.   A variable vapor space tank, compressoi, and fuel gas system
     of sufficient capacity to  receive all hydrocarbon i/apors and gases dis-
     placed from the tank  trucks and trailers being loaded.
         c.   Other  equipment of at  least 90 per cent efficiency, provided
     such equipment is submitted to and  approved by the Air Pollution
     Control Officer
     This rule shall  not apply to the loading of gasoline into tank trucks and
 trailers  from any loading facility from which not more than 20,000 gallons
 of gasoline are loaded m any one day
     For the purpose of  this rule, any petroleum  distillate having a Reid
 vapor pressure of four pounds or greater  shall be  included  by the term
 "gasoline"
     For the purpose of this rule,  "loading  facility" means any aggregation
 or combination of  gasoline loading  equipment  which is both  (1) possessed
 by one person,  and (2) located so that all the gasoline loading outlets for
 such aggregation or combination of loading equipment can be encompassed
 within any circle of 300 feet in diameter.

 Rule 61. Organic Liquid Loading.
     (Effective June  29, 1971 for any equipment  not completed and put
 into service.  Effective for all  equipment  after July 1, "972)
     A  person shall not load organic liquids having a vapor pressure of 1 5
 psia or greater under actual loading conditions  into any tank truck, trailer,
 or railroad  tank car from  any loading facility unless the loading facility is
 equipped with a vapor collection and disposal  system  or its equivalent ap-
 proved by the Air Pollution Control Officer
     Loading shall  be accomplished  in  such  a manner  that  all displaced
 vapor and  air will be vented only  to the vapor collection system  Measures
 shall be taken to prevent  liquid  drainage  from the loading  device when it is
 not  in  use  or to accomplish complete drainage  before 'he loading device is
 disconnected
     The vapor  disposal portion of the vapor collection and disposal system
 shall consist of one of the following
          a    An absorber system or condensation system which processes
     all vapors  and recovers at  least 90  per cent by weight of the organic
     vapors  and gases from the equipment being controlled
          b    A vapor handling system which directs all vapors to a fuel gas
     system
          c    Other equipment of an efficiency equal to  or greater  than a
     or b if  approved by the Air Pollution Control Officer
     This  rule shall apply only to the loading  of  organic  liquids having a
vapor pressure of 1.5  psia or greater under actual loading conditions at a
facility from which at  least 20,000 gallons of such organic liquids are loaded
in any one day
     "Loading facility",  for the purpose of this rule, shall mean any aggre-
gation or combination of organic liquid  loading equipment which  is both
(1) possessed  by one person, and (2)  located so that all  the organic liquid
loading outlets for such  aggregation or combination of loading equipment
can be encompassed within any circle of 300 feet in  diameter.
     This amendment  shall  be effective at the  date of its adoption for any
equipment not then completed and put into service.  As to all other equip-
ment this amendment shall be effective on July 1, 1972.

Rule 62. Sulfur Contents of Fuels.
     A person shall  not  burn within the Los Angeles Basin at any time be-
tween  May  1  and September 30, both dates inclusive, during the calendar
year 1959, and  each year thereafter between April  15 and November 15,
both inclusive, of the same calendar year, any gaseous fuel containing sulfur
compounds  in excess of  50 grains per 100 cubic feet of gaseous fuel, calcu-
lated as hydrogen sulfide at  standard conditions, or any liquid fuel or solid
fuel having a sulfur content m excess of 0.5 per cent by weight
     The provisions of this rule shall ncjt apply to
         a    The burning of sulfur,  hydrogen sulfide, acid sludge or other
     sulfur compounds in the manufacturing of sulfur or sulfur compounds
         b    The incinerating of waste gases provided that the gross heat-
     ing value of such gases  is less than 300 British Thermal Units per cubic
     foot at standard conditions and the fuel used to incinerate such waste
     gases does  not contain sulfur or sulfur compounds m excess of the a
     mount  specified in this rule
          c    The use of solid fuels in any metallurgical  process.
          d    The use of fuels where the gaseous products of combustion
     are  used  as raw materials for other processes
         e    The use of liquid  or solid fuel to propel or test any vehicle,
     aircraft, missile, locomotive, boat or ship.
          f    The use of liquid  fuel whenever the supply of gaseous fuel,
     the  burning of which is permitted by this rule, is not physically avail-
     able to  [he user due to accident,  act of God,  act of  war, act of the
     public enemy, or failure of the supplier

Rule 62.1   Sulfur Contents of Fuels
     a   A person  shall not  burn  within  the Los  Angeles  Basin  at any
time between the days of November 16 of any year and April 14 of the
next succeeding calendar year, both dates inclusive, any fuel described in the
first-paragraph of Rule 62 of these Rules and Regulations.
     b   The provisions  of this Rule do not apply to.
          1    Any use of fuel described in Subsections a,b,c,d,e, and f of
              said Rule  62  under the conditions and for the  uses set forth
              in said Subsections.
          2    The use of liquid fuel during a period  for which the supplier
              of gaseous fuel, the burning of  which is not prohibited by
              this Rule, interrupts the  delivery of gaseous fuel to the user
     c.   Every holder of, and every applicant for a  permit to operate fuel-
 burning  equipment  under these  Rules  and  Regulations shall notify  the Air
 Pollution Control Officer m the manner and form prescribed by him, of each
 interruption in and resumption of delivery of gaseous fuel to his equipment

 Rule 62.2   Sulfur Contents of Fuels.
      Notwithstanding  the provisions of Section  (f)  of Rule 62 or any pro-
 vision of said section as incorporated into  Rule 62 1 or any  provision of

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                                        Rules and Regulations  of the Air Pollution  Control District
                                                                   919
Subsection (2) of Section b of Rule 62.1, a person shall not burn within the
Los Angeles Basin any liquid fuel or solid fuel having a sulfur content in ex-
cess of 0.5 per cent by weight.
     It shall not be a violation of this rule to burn  such fuel for a period of
not to exceed three calendar days (and  in addition  for that period of time
necessary  for the Hearing Board to render a decision,  provided that an ap-
plication for a variance is promptly filed) when other fuel which complies with
this Rule is not used due to accident, strike, sabotage, or act of God.

Rule 63. Gasoline Specif ications.
     a.    A person shall  not,  after June 30, 1960, sell or supply for use
within the District as a fuel for motor vehicles  as defined by the Vehicle
Code of the State of California, gasoline  having a degree  of unsaturation
greater than that indicated by a Bromine Number of 30 as determined by
ASTM Method D1159-57T modified  by omission of the mercuric chloride
catalyst.
     b.    For the purpose of this  rule, the term "gasoline" means any pe-
troleum distillate having a Reid vapor  pressure of  more than four pounds

 Rule 64.  Reduction of  Animal Matter.
     A person shall  not operate or use any article, machine, equipment or
 other contrivance for the reduction of animal matter unless all gases, vapors
 and  gas-entrained effluents  from such an article, machine, equipment or
 other contrivance are*
          a.   Incinerated at temperatures of not less than  1200 degrees
     Fahrenheit for  a period of not  less than 0.3 second, or
          b.   Processed in such a manner determined by the Air Pollution
     Control Officer to be equally, or more, effective for the purpose of air
     pollution control than (a) above.
     A person incinerating or processing gases, vapors or gas-entrained efflu-
 ents pursuant to this rule shall provide, properly  install  and maintain in cali-
 bration, in good working order and in operation  devices, as specified in the
 Authority to Construct or Permit to  Operate or  as specified by the Air Pol-
 lution Control Officer,  for indicating temperature,  pressure or other operat-
 ing conditions.
      For  the purpose of this rule, "reduction" is defined as any heated proc-
 ess,   including rendering, cooking, drying, dehydrating, digesting, evaporat-
 ing and protein  concentrating.
     The  provisions of this  rule shall not apply  to any article,   machine,
 equipment or other contrivance used exclusively  for the processing of food
 for human consumption.

 Rule 65.  Gasoline Loading  Into Tanks.
      A person shall  not after January 1, 1965, load or permit the loading of
 gasoline into  any stationary tank  with a capacity of 250  gallons or more
 from any tank  truck or trailer, except through a permanent submerged fill
 pipe, unless such tank  is equipped with a vapor loss control device as  de-
 scribed in Rule 56, or is a pressure tank as described in Rule 56.
     The  provisions  of  the first paragraph of this rule shall  not apply to the
 loading of gasoline into any tank having a capacity of less than 2,000 gallons
 which was installed prior  to the  date of adoption of this rule nor to any
 underground tank installed prior to the date of adoption of this rule where
 the fill line between the fill connection and tank is offset.
      Any person operating  or using any gasoline  tank with  a capacity of
 250 gallons or more  installed prior to the date of adoption of this rule shall
 apply for a permit to operate such tank before January 1, 1965. The provi-
 sions of Rule 40 shall not apply during  the period between the date of adop-
 tion of this rule and January 1, 1965, to any gasoline tank  installed prior to
the date of adoption of this rule provided an application for permit to oper-
ate is filed before January 1,  1965.
     A person shall not install any gasoline tank with a capacity of 250 gal-
lons or more unless such tank is equipped as described in the first paragraph
of this rule.
     For the purpose of this rule, the term "gasoline" is defined as any pe-
troleum  distillate having  a  Reid vapor pressure of 4 pounds or  greater.
     For the purpose of this rule, the term "submerged fill pipe" is defined
as any fill pipe the discharge opening of which is entirely submerged when
the liquid  level is 6 inches above the bottom of the tank.  "Submerged fill
pipe" when applied to a tank which is loaded from the side is defined as any
fill pipe  the discharge opening of which is  entirely submerged when the liq-
uid  level  is 18 inches above the bottom of the tank.
     The provisions of this rule do not apply to any stationary tank which is
used primarily for the fueling of implements of husbandry, as such vehicles
are defined  in Division 16  (Section 36000,  et seq.) of the Vehicle Code.

Rule 66. Organic Solvents.
     a.    A person shall  not discharge  into the atmosphere more than  15
pounds of organic materials  in any one day, nor more than 3 pounds in any
one hour, from any article, machine,  equipment or other contrivance,  in
which any organic solvent or any material containing organic solvent comes
into contact with flame or  is baked, heat-cured or heat-polymerized, in the
presence of oxygen, unless said discharge has been reduced by at least 85 per
cent  Those portions of any series of articles, machines, equipment or other
contrivances designed for processing a continuous web, strip or wire which
emit organic materials and using  operations described in this section shall be
collectively subject to compliance with this section.
     b.   A  person shall  not discharge  into the atmosphere more than 40
pounds of organic materials  in any one day, nor more than 8 pounds in any
one hour,  from  any article,  machine, equipment or other contrivance used
under conditions other than described  in section (a), for employing or ap-
plying, any photochemically reactive solvent, as defined  in section (k), or
material  containing such  photochemically  reactive solvent, unless said dis-
charge has been reduced by  at least 85  per  cent.  Emissions of organic ma-
terials into the atmosphere  resulting from air or heated drying of products
for the first 12 hours after  their removal from any article, machine, equip-
ment, or other contrivance described in this section shall be included in de-
termining compliance  with this  section.  Emissions resulting from  baking,
heat-curing, or heat-polymerizing as described in section (a) shall be exclud-
ed from  determination of compliance with  this section.  Those  portions of
any  series  of articles,  machines,  equipment or other contrivances designed
for processing a continuous  web, strip or wire which emit organic materials
and using operations described in this section shall be collectively subject to
compliance with this section.
     c.   A person shall  not, after August 31, 1974, discharge into the at-
mosphere more than 3,000 pounds of organic materials in any one day, nor
more than 450 pounds in any one hour, from any article, machine, equip-
ment or other contrivance in which any  non-photochemically reactive organ-
ic solvent or any material containing such  solvent is employed  or applied,
unless said discharge has been reduced by at least 85 per cent.  Emissions of
organic materials into the  atmosphere resulting from air or heated drying of
products for the first 12 hours after their removal from any article, machine,
equipment,  or other contrivance described in this section shall be  included
in determining compliance with this section. Emissions resulting from bak-
ing, heat-curing, or heat-polymerizing as described in section (a)  shall be ex-
cluded from determination of compliance with this section. Those portions

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920
                                                          RULES AND  REGULATIONS
of any series of articles, machines, equipment or other contrivances designed
for processing a continuous web, strip or wire which emit organic materials
and using operations described in this section shall be collectively subject
to compliance with this section.
     d.    Emissions of organic  materials to the atmosphere from the clean-
up with photochemically reactive solvent, as defined in section  (k), of any
article, machine,  equipment or other contrivance described in sections (a),
(b) or (c), shall  be included with the other emissions of organic materials
from  that article, machine, equipment or other contrivance for determining
compliance with this rule.
     f.    Emissions of organic  materials into the atmosphere required to be
controlled by sections (a), (b) or (c), shall be reduced by:
          1.   Incineration, provided that 90 per cent  or more of the car-
              bon in the organic material being incinerated is oxidized to
              carbon dioxide,  or
          2.   Adsorption, or
          3.   Processing m a manner determined by the Air Pollution Con-
              trol Officer to  be not less  effective than  (1) or  (2)  above.
     g.    A person  incinerating, adsorbing, or otherwise processing organic
materials pursuant to this rule  shall provide, properly install and  maintain in
calibration,  in good working order and in operation, devices as  specified in
the authority to construct or the permit to operate, or as specified  by the
Air Pollution Control  Officer,  for  indicating temperatures, pressures, rates
of flow or other  operating conditions necessary to determine the degree and
effectiveness of air pollution control.
     h.    Any person using organic solvents or any materials containing or-
ganic solvents shall supply the Air Pollution Control Officer, upon request
and in  the  manner and  form  prescribed by  him, written evidence  of  the
chemical composition, physical properties  and amount consumed for each
organic solvent used.
     i.    The provisions  of this rule  shall not apply to.
          1.   The  manufacture of  organic solvents, or the transport  or
              storage of  organic solvents  or materials containing organic
              solvents.
          2.   The use  of equipment  for  which other requirements are
              specified by Rules  56, 59, 61 or 65 or which  are exempt
              from air  pollution control requirements by said rules.
          3.   The spraying or other employment of insecticides, pesticides
              or herbicides
          4,   The employment, application, evaporation or drying of satu-
              rated halogenated hydrocarbons or perchloroethylene.
          5    I he use of any  material, in any article, machine, equipment
              or other contrivance described in  sections (a), (b), (c) or (d),
              if
          (i)       the  volatile content of  such material consists only of
                   water and  organic solvents, and
          (n)       the  organic solvents comprise not more than  20  per
                    cent  by volume of said volatile content, and
          (in)      the volatile content is not photochemically reactive as
                   defined in  section (k),  and
          (iv)       the  organic solvent or any  material containing  organic
                    solvent does not come into contact with flame.
          6.  The use of any material, in any article,  machine, equipment
              or other contrivance described in sections  (a), (b), (c) or (d),
              if

              d)   the  organic solvent content  of such  material does not
                   exceed  20 per cent  by volume of said material, and
               (ii)  the volatile content is not photochemically reactive as
                   defined in  section (k), and
               (in)  more than  50 per cent  by  volume  of such volatile
                   material is evaporated before entering a chamber heated
                   above ambient application temperature, and
               (iv)  the organic solvent or any material containing organic
                   solvent  does not come into contact with flame.
          7    The use of any  material, in any article, machine, equipment
               or other contrivance described in sections (a), (b), (c) or (d),
               if
               d)   the organic solvent content of  such material does not
                   exceed  5  per cent  by  volume of  said  material, and
               (ii)  the volatile content is not photochemically reactive as
                   defined in  section (k), and
               (in)  the organic solvent or any material containing organic
                   solvent  does not come into contact with flame.
     I     For the purposes of this rule, organic solvents include diluents and
thinners and are defined as organic materials which are liquids at standard
conditions and  which are used as dissolvers, viscosity  reducers or cleaning
agents,  except  that such materials which  exhibit a boiling  point higher than
220°F  at 0 5 millimeter mercury  absolute pressure  or having an equivalent
vapor pressure  shall not be  considered to be solvents unless exposed to tem-
peratures exceeding 220°F
     k    For the purposes  of this rule, a photochemically reactive solvent is
any solvent with an aggregate of more than 20 per cent of its total volume
composed of the chemical compounds classified below or which exceeds any
of the following individual  percentage composition limitations, referred  to
the total volume of solvent
          1.    A combination  of hydrocarbons, alcohols, aldehydes, esters,
               ethers or ketones having an olefmic or cyclo-olefimc type of
               unsaturation  5 per cent,
          2.    A combination  of aromatic compounds with eight or  more
               carbon atoms to the  molecule except ethylbenzene.  8 per
               cent,
          3    A combination  of ethylbenzene,   ketones  having branched
               hydrocarbon structures, trichloroethylene or toluene 20 per
              cent
     Whenever  any organic solvent or any constituent of an organic solvent
may  be classified  from its chemical structure  into  more than  one of  the
above  groups  of organic compounds, it  shall be considered as a  member
of the  most reactive chemical group, that is, that  group  having the least
allowable per cent of the total volume of solvents
     I.     For the  purposes  of this rule, organic materials are defined  as
chemical compounds  of carbon excluding  carbon monoxide, carbon dioxide,
carbonic acid, metallic carbides, metallic carbonates and ammonium carbon-
ate

Rule 66.1  Architectural Coatings.
     a     A person shall not sell  or offer for sale  for use in  Los Angeles
County, in  containers  of one quart capacity or larger, any  architectural
coating  containing photochemically  reactive solvent,  as  defined in  Rule
66(k).
     b.    A person shall not employ, apply, evaporate or dry m Los Angeles
County any architectural  coating, purchased in  containers  of one quart
capacity or larger,  containing photochemically reactive solvent, as defined
in Rule 66 (k).

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                                        Rules  and Regulations  of the Air Pollution Control District
                                                                                                                                               921
      c.   A person shall not thin or dilute any architectural coating with a
 photochemically reactive solvent, as defined in Rule 66(k|.
      d   For the purposes of this rule, an architectural coating is defined as
 a coating used for  residential or commercial buildings  and  their appurte-
 nances; or  industrial  buildings.

 Rule 66.2 Disposal and Evaporation of Solvents.
     A person shall not during any one day dispose of a  total of more than
 1Vj gallons of any photochemically reactive solvent, as defined in Rule66(k),
 or of any material containing more than 1V4 gallons of any such photochemi-
 cally reactive solvent  by any means which will  permit the evaporation of
 such solvent mto the  atmosphere.

 Rule 67. Fuel Burning Equipment.
     A person shall not build, erect, install or expand any non-mobile  fuel
 burning equipment unit unless the discharge mto the  atmosphere of contam-
 inants   will not and does not exceed any  one or more of the  following
 rates:
      1.   200 pounds per  hour of sulfur compounds, calculated as  sulfur
          dioxide (S02>,
     2.   140 pounds per  hour of nitrogen oxides, calculated as nitrogen
          dioxide (NC>2).
     3.   10 pounds  per  hour of combustion contaminants as defined in
          Rule  2m and derived from the fuel
     For  the purpose of this rule, a fuel burning equipment unit shall be
 comprised of the minimum number of boilers, furnaces, |et engines or other
 fuel  burning equipment, the simultaneous operations of which are required
 for the production of useful heat or power.
     Fuel burning equipment serving primarily  as air  pollution control
 equipment  by  using  a combustion process  to destroy  air contaminants
 shall  be exempt  from  the provisions  of this rule.
     Nothing in this  rule shall be construed as preventing the  maintenance
 or preventing the alteration or modification of an existing  fuel   burning
 equipment unit which  will reduce  its mass rate of air contaminant emissions.

 Rule 68. Fuel Burning Equipment -* Oxides of Nitrogen.
     A  person  shall   not discharge into  the  atmosphere from any non-
mobile fuel burning article,  machine, equipment or other contrivance, having
a maximum heat input rate of  more  than  1775 million British Thermal
Units (BTU) per hour (gross), flue gas having a concentration of nitrogen
oxides,  calculated as nitrogen dioxide (N02)  at  3 per cent oxygen, in  ex-
cess  of that  shown in  the following table:
NITROGEN OXIDES - PARTS PER MILLION PARTS  OF FLUE GAS
FUEL
Gas
Liquid or Solid
EFFECTIVE DATE
DECEMBER 31. 1971
225
325
DECEMBER 31, 1974
125
225
Rule 68.1  Fuel Burning Equipment - Combustion Contaminants.
     A person  shall not discharge into the atmosphere combustion contami-
nants exceeding in concentration at the point of discharge, 0.3 grain per
cubic foot of gas calculated to 12  per cent  of carbon  dioxide (C02> at
standard conditions.

Rule 69.  Vacuum Producing Devices or Systems.
     A person shall not discharge into the atmosphere more than 3 pounds
of organic materials in any one hour from any vacuum producing devices or
systems including hot wells and accumulators, unless said discharge has been
  reduced by at least 90 per cent.
       This  rule shall  be effective at the date of  its adoption for any equip-
  ment not  then  completed and put into service.  As  to all other equipment
  this rule shall be effective on July 1,  1972.

  Rule 70. Asphalt Air Blowing,
      A person shall  not operate  or use any article, machine, equipment or
  other contrivance for the air blowing of asphalt unless all gases, vapors and
  gas-entrained effluents from  such an article, machine, equipment or other
  contrivance are
           a   Incinerated at temperatures  of not less than  1400 degrees
      Fahrenheit  for a period of  not less than 0.3 second, or
           b   Processed in such  a manner determined by the Air Pollution
      Control Officer to be equally, or more, effective for the purpose of air
      pollution control than (a) above
      This rule shall  be  effective  at  the date of its adoption for any equip-
  ment not then completed and put mto service   As to all other equipment
  this rule shall be effective on July 1, 1972

  Rule 71.  Carbon Monoxide.
      A person shall not, after December 31, 1971, discharge mto the atmos-
 phere carbon monoxide  (CO) in  concentrations  exceeding 0.2 per cent by
 volume measured on a dry basis.
      The provisions  of this rule  shall  not apply  to emissions from internal
 combustion engines

  Rule 72.  Pumps and Compressors.
      A  person shall  not, after July  1,  1973, use any pump or compressor
  handling organic materials having a Reid Vapor Pressure of 1 5 pounds or
 greater unless such pump or compressor is equipped with a  mechanical seal
 or other device of equal  or greater efficiency approved by the Air Pollution
 Control Officer
      The provisions  of this rule shall not apply to any pump or compressor
 which has a driver  of  less  than one (1) horsepower motor or equivalent
  rated energy or  to any pump or compressor operating  at temperatures in
 excess of 500° F

  Rule 73.  Safety Pressure Relief  Valves.
      A  person  shall not, after July  1,  1973,  use any  safety pressure
 relief valve on any equipment handling organic materials above 15 pounds
 per square inch  absolute pressure unless  the safety pressure relief valve is
 vented to a vapor recovery or disposal system, protected by a rupture disc,
 or  is maintained by an inspection  system approved by the Air Pollution
 Control  Officer
      The provisions  of this rule shall not apply to any safety pressure relief
 valve of one (1) inch pipe size or less.

 REGULATION V.  PROCEDURE BEFORE  THE  HEARING
 BOARD

 Rule 75.  General.
   This regulation shall apply to all hearings before the Hearing Board of the
 Air Pollution Control  District.

 Rule 76.  Filing Petitions.
   Requests  for hearing shall be initiated by the filing  of a petition in tripli-
cate with the  Clerk of the Hearing Board at  Room 433P, 313 N. Figueroa
St., Los Angeles,  California, 90012, and the payment  of the fee  of $16.50
 provided for in Rule 42 of these  Rules and  Regulations, after service of a

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922
                                                          RULES AND REGULATIONS
copy of the petition has been made on the Air Pollution Control Officer at
434 South San Pedro Street, Los Angeles, California, 90013, and one copy
on  the holder of the permit or variance, if any, involved.  Service may be
made in person or by mail,  and service may be proved by written  acknow-
ledgment of the person served or by the affidavit of the person making the
service.

Rule 77. Contents of Petitions.
   Every petition shall state'
     a.   The name,  address  and telephone number of the petitioner, or
other person authorized to  receive service of notices.
     b.   Whether the  petitioner is an individual, co-partnership, corpora-
tion or other entity, and names and address of the partners if a co-partner-
ship, names and address of the officers, if a corporation, and the names and
address of the persons in control, if other entity.
     c.   The type of business or activity involved in  the application and the
street address at which it is conducted.
     d.   A brief  description  of the article, machine, equipment or other
contrivance, if any, involved in  the  application.
     e.   The section or rule under  which  the petition  is filed; that is,
whether petitioner  desires  a hearing:
         1.   To determine whether a permit shall be revoked or suspend-
              ed permit reinstated  under Section 24274, Health and Safety
              Code of the State of California;
         2.   For a variance under Section 24292, Health and Safety Code;
         3.   To revoke or modify a variance under Section 24298, Health
              and Safety Code;
         4.   To review the denial or conditional granting of an authority
              to construct, permit to  operate or permit to  sell or rent un-
              der Rule 25 of  these Rules and Regulations.
     f.   Each petition shall be  signed by the petitioner, or by some person
on his behalf, and where the person signing is not  the petitioner it shall set
forth his authority to sign.
     g.   Petitions for revocation of permits shall allege in addition the rule
under which permit was granted, the rule or section which is alleged to have
been violated, together with a  brief statement of the facts constituting such
alleged violation.
     h.   Petitions for reinstatement of suspended  permits shall allege in ad-
dition the rule under which  the permit was granted,  the request and alleged
refusal which formed the basis for such suspension, together with a brief
statement as to why information requested,  if any, was  not furnished,
whether such information  is  believed by petitioner to be  pertinent, and,
if so, when it will be furnished.
     i.   All petitions shall be typewritten, double spaced,  on legal or let-
ter size paper, on one side of the paper only, leaving  a margin of at least one
inch at the top and left side  of each  sheet.

Rule 78. Petitions For Variances.
   In addition to the matters required by Rule 77, petitions for variances
shall state briefly:
     a.    The section, rule  or order complained of.
     b.    The facts showing why compliance with the section, rule, or order
is unreasonable.
     c.    For what period of time the variance is sought and why.
     d.    The damage or harm resulting or which would result to petitioner
from a compliance with such section, rule or order.
     e.    The requirements which  petitioner can meet and  the date when
petitioner can comply with  such requirements.
     f.    The advantages and disadvantages to the residents of the district
resulting from requiring compliance or resulting from granting a variance.
     g.    Whether or not operations under such variance, if  granted, would
constitute a nuisance.
     h.    Whether or not any case involving the same identical equipment
or process  is pending in any court,  civil or criminal.
     i.    Whether or not the subject equipment or process is covered by a
permit to operate  issued by the Air Pollution Control  Officer.

Rule 79. Appeal From Denial.
    A petition to review a denial or conditional approval of an authority to
construct, permit to operate or permit to sell or rent shall, in addition to the
matters required by Rule 77, set forth a summary of the application or a
copy thereof and the alleged reasons for the denial or conditional approval
and the reasons for appeal.

Rule 80.  Failure To Comply With  Rules.
     The Clerk of  the Hearing Board shall not accept for filing any petition
which does not comply with these  Rules relating to the form, filing and ser-
vice of  petitions unless the chairman or any two members  of the Hearing
Board direct otherwise and confirm such direction in writing. Such direc-
tion need not be made at a  meeting of the Hearing Board.  The chairman or
any two members, without a meeting,  may require the petitioner to state
further  facts or reframe  a  petition so as to  disclose  clearly the issues  in-
volved.

Rule 82.   Answers.
     Any person  may file an answer within 10 days  after service.  All an-
swers shall be served the same as petitions under Rule 76.

Rule 83.  Dismissal Of Petition.
     The petitioner  may dismiss his petition at any time before submission
of the case to the  Hearing Board, without a hearing or meeting of the Hear-
ing Board.  The Clerk of the Hearing Board shall notify all  interested per-
sons of  such  dismissal.

Rule 84.   Place Of  Hearing.
    All  hearings shall  be held  at  Room  903, 313  N. Figueroa St.,  Los
Angeles, California,  90012, unless  some  other place  is designated  by  the
Hearing Board.

Rule 85.   Notice  Of Hearing.
     The Clerk of  the Hearing Board shall mail or deliver a notice of hearing
to the petitioner, the Air Pollution  Control Officer, the holder of the permit
or variance involved, if any, and to any person entitled to notice under Sec-
tions 24275, 24295 or 24299, Health and Safety Code.

Rule 86. Evidence.
     a.    Oral evidence shall be taken only on oath or affirmation.
     b.    Each party shall have these rights1  to call and examine witnesses;
to introduce exhibits, to cross-examine opposing witnesses  on any matter
relevant to the issues even though that matter was not covered in the direct
examination; to impeach any witness  regardless of which  party first called

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                                        Rules  and Regulations of the  Air Pollution Control District
                                                                   923
him to testify; and to rebut the evidence against him.  If respondent does
not testify in his  own behalf he may be called  and examined as  if under
cross-examination.
     c.    The hearing need not be conducted according to technical rules
relating to evidence and witnesses.  Any relevant evidence shall be admitted
if it is the sort of  evidence on which  responsible persons are accustomed to
rely in the conduct of serious affairs,  regardless of the existence of any com-
mon law or statutory  rule which might make improper the admission of such
evidence over objection in civil actions.  Hearsay evidence may be  used for
the purpose of supplementing or explaining any direct evidence but shall not
be sufficient in itself  to support a finding unless it would be admissible over
objection in civil actions  The rules of privilege shall be effective to the same
extent that they are now  or hereafter may be recognized  in civil actions, and
irrelevant and unduly  repetitious evidence shall be excluded.

Rule 87. Preliminary Matters.
     Preliminary matters such as setting a date for hearing, granting contin-
uances,  approving petitions for filing, allowing amendments and other pre-
liminary rulings not determinative of the merits of the case may be made by
the chairman or any  two  members of the Hearing Board without a hearing
or meeting of the  Hearing Board and  without notice.

Rule 88.  Official  Notice.
     The Hearing  Board may take official notice of any  matter which may
be judicially noticed by the courts of this State.

Rule 89.  Continuances.
     The chairman or any two members of the  Hearing Board shall grant
any continuance of 15 days or  less, concurred in by petitioner, the  Air Pol-
lution  Control Officer and by every person who  has filed an answer in the
action  and may grant  any  reasonable continuance; in either case such action
may be ex parte, without  a meeting of the Hearing Board and without prior
notice.

Rule 90. Decision.
     The decision  shall be in writing, served and filed  within 15 days after
submission of the cause by the parties thereto and shall  contain a brief state-
ment of facts found to be true,  the  determination of the issues presented
and the order of the Hearing Board. A copy shall be mailed or delivered to
the Air Pollution Control Officer, the petitioner and to every person who
has filed an answer or who has  appeared as a party  in person or by  counsel
at the hearing.

Rule 91. Effective Date Of Decision.
     The decision  shall become effective 15 days after  delivering or mailing
a copy  of  the decision, as provided in Rule 90, or the Hearing Board may
order that the decision shall become effective sooner.

Rule 95.  Lack-Of Permit.
     The Hearing Board shall not receive or accept a petition for a variance
for the operation or use of any article, machine, equipment or other contriv
ance  until a permit to operate has been granted or denied by the Air Pollu-
tion Control  Officer; except that an appeal from  a denial of a permit to op-
erate and a petition for a  variance may be filed with the  Hearing Board in a
single petition  A  variance granted  by the Hearing Board after a denial of a
 permit to operate by the Air Pollution Control Officer may include a permit
 to operate for the duration of the variance.

REGULATION VI.   ORCHARD OR CITRUS GROVE HEATERS

 Rule 100.  Definition.
     "Orchard or citrus grove heater" means any article, machine, equip-
 ment or other contrivance, burning any type of  fuel, capable of emitting
 air  contaminants, used or capable of being used  for the purpose of giving
 protection from frost damage.

 Rule 101.  Exceptions.
     Rules 10, 14, 20, 21, 24,  40, 62, and 62.1 do not apply to orchard or
 citrus grove heaters.

 Rule 102.  Permits Required.
     Any person erecting, altering, replacing, operating or using any orchard
 or citrus grove heater shall first obtain a permit from the Air Pollution Con-
 trol Officer to do so.

 Rule 103.  Transfer.
     A permit to operate shall  not be transferable, whether by operation of
 law or otherwise, either from  one location to another,  from one piece of
 equipment to another, or from one person to another.

 Rule 105.  Application For Permits.
     Every application  for a permit  required under Rule 102 shall be filed
 in the  manner and form required by  the Air Pollution Control Officer. In-
 complete applications will not be accepted.

 Rule 106.  Action On Applications.
     The Air Pollution Control Officer shall act on all applications within a
 reasonable time and shall notify the  applicant in writing of the approval,
conditional approval or denial  of the application.

 Rule 107.  Standards  For Granting Permits.
     The Air Pollution Control Officer shall deny  a permit if the applicant
does not show that equipment described in Rules 100 and 102 is so designed
or controlled that it will not produce  unconsumed solid carbonaceous mat-
ter at the rate in excess of one  (1) gram per minute except as prescribed un-
der  Rule 108.

 Rule 108.  Conditional Approval.
     a    The Air Pollution  Control  Officer may  issue a permit subject to
conditions which  will  bring the orchard  or  citrus grove  heater within the
 standards of  Rule 107  in  which case the conditions shall be specified in writ-
 ing
     b.    Erecting, altering,  operating or using under conditional permit
shall be  deemed acceptance of all conditions so specified.

 Rule 109.   Denial Of  Applications.
     In the event  of denial of  a permit, the Air Pollution Control Officer
shall notify the applicant  in writing of the reasons therefor.   Service of this
notification may be  made in person  or by mail,  and such service may be
proved by the written acknowledgment of the person served  or affidavit of
the  person making the service.  The Air Pollution  Control Officer shall not
accept  a further application unless the applicant has complied with the ob-
denial.

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924
                                                          RULES AND REGULATIONS
 Rule 110.  Appeals.
     Within 10  days after notice of denial  or conditional approval of a
 permit  by the Air Pollution  Control  Officer, the applicant may petition
 the  Hearing Board,  in writing, for a public  hearing.  The Hearing Board,
 after notice and a public hearing held within 30 days after filing the peti-
 tion, may sustain or reverse the action of the Air Pollution Control Officer;
 such order may be made subject to specified conditions.
 Rule 120.  Fees.
     A  request for a duplicate  permit for orchard or citrus grove heaters
 shall be made in writing to the Air Pollution Control Officer within 10 days
 after the destruction, loss or defacement of a permit. The fee for issuing a
 duplicate permit shall be $1.00.
Rule 130. Prohibitions.
     a.   These  rules prohibit the erecting, altering, replacing, operating or
using any orchard or citrus grove heater which  produces unconsumed solid
carbonaceous matter at the rate of more than one (1) gram per minute, ex-
cept under the conditions as set forth in Rule 108.
     b.   Open  fires for  orchard or citrus grove heating are prohibited.
     c.   The use of rubber tires or any rubber products in any combus-
tion process in connection with any orchard or citrus grove heating is hereby
prohibited.
     d.   All types of orchard or  citrus grove heating equipment commonly
known or designated  as follows
                                                    mum area designated above.
                                                        f.    All types of orchard or citrus grove heating equipment commonly
                                                    known or designated as follows:
      1.  Garbage pail
      2.  Smith  Evans
      3.  Citrus  with Olsen Stack
      4.  Canco  5 gallon
      5.  Dunn
      6.  Hamilton  Bread Pan
      7.  Wheeling
      8.  Canco  3 gallon
      9.  Chinn
     10.  Baby Cone
              11.  Citrus  Regular
              12.  Stub Stack
              13.  Citrus  15-inch stack
              14.  Exchange Model 5%-inch
                  diameter stack
              15.  Exchange Model 6-inch
                  diameter stack
              16.  Hy-Lo  Drum
              17.  Hy-Lo  Hot  Blast
              18.  Pheysey Beacon
may not be used or operated for the purpose of giving protection from frost
damage.
     e.    All types of orchard or citrus grove heating equipment commonly
known or designated as follows.
     Name
   7. Hy-Lo 1929
   2. Hy-Lo 148
   3. Hy-Lo Double Stack
   4. Jumbo Cone
   5. Lemora
   6. National Double
     Stack
   7. Surplus Chemical
     Warfare Service
     Smoke Generator
Maximum Primary Air Orifice in Square Inches
0.606(equivalent to one hole of 7/8 in. diameter)
0.606(equivalent to one hole of 7/8 in. diameter)
0.606(equivalent to one hole of 7/8 in. diameter)
0.196lequivalent to one hole of 1/2 in. diameter)
0.606(equivalent to one hole of 7/8in. diameter)
0.802(equivalem to one hole of 7/8 in. diameter
              and one hole of 1/2 in. diameter}
0.802(equivalem to one hole of 7/8 in. diameter
              and one hole of 1/2 in. diameter)
                                                        Name
                                                      1. Exchange Model
                                                        7 in. dia. stack
                                                      2. Hy-Lo 148 Special
                                                      3. Hy-Lo 230
                                                      4. Lazy Flame 24 in.
                                                        stack
                                                      5. Lazy Flame 18 in.
                                                        stack
                                                      6. NationalJunior
                          Maximum Primary Air Orifice in Square Inches
                          0.606(equivalent to one hole of 7/8 in. diameter)

                          0.606(equivalent to one hole of 7/8 in. diameter)
                          0.606(equivalent to one hole of 7/8 in. diameter)
                          0.606(equivalent to one hole of 7/8 in. diameter)

                          1.212(equivalent to two holes of 7/8 in. diameter)
may not be used or operated for the purpose of giving protection from frost
damage unless the primary air onfice(s) contain(s) not more than the maxi-
                          1.212(equivalent to two holes of 7/8 in. diameter)
may not be used or operated for the purpose of giving protection from frost
damage unless the  primary air orifice(s) is (are) so adjusted or regulated to a
maximum opening of not greater than the area designated above.
     g.    Any new complete  orchard or citrus grove heating equipment of
the distilling type  not listed in subsection "e" and "f" of this rule must con-
tain a primary air  orifice of such design that not more than one (1) gram per
minute of unconsumed solid carbonaceous matter is emitted.
     h.    No heater may be placed, be permitted to be placed or be permit-
ted to remain in  any orchard or citrus grove or in  any other place where
heaters  may be fired to furnish protection from frost damage unless a per-
mit or conditional permit has  been issued.
     i.    The use  or operation of any partial assembly of any type heater
for the purpose of giving protection from frost damage is hereby prohibited.
A  permit  or conditional permit issued for  the use or operation of any type
orchard or citrus grove heater  is for the use or operation of a complete heat-
er assembly.

REGULATION  VII.  EMERGENCIES
    This  emergency regulation is designed to  prevent the excessive buildup
of air contaminants and to avoid any possibility of a catastrophe caused by
toxic  concentrations of air contaminants.   Past history indicates that  the
possibility of such a catastrophe  is extremely remote.
     The  Air Pollution Control Board  deems  it desirable to have ready an
adequate  plan to prevent such an occurrence, and  in case of the happening
of this  unforeseen event,  to  provide  for adequate actions to  protect  the
health of  the citizens in the Air  Pollution Control District.

Rule  150.  General.
     Notwithstanding any  other  provisions of these rules and regulations,
the provisions of this regulation shall apply to each air basin separately for
the control of emissions of air contaminants during any "alert" stage as pro-
vided herein.

Rule 151. Sampling Stations.
     The  Air Pollution Control Officer shall maintain at  least twelve (12)
permanently  located atmospheric  sampling stations adequately  equipped.
These sampling stations shall be continuously maintained at locations desig-
nated by  the Air Pollution Control Officer after consultation with the Scien-
tific Committee.   At least  ten (10)  of these stations shall be located in  the
Los Angeles Basin, at  least one (1) station shall  be  located in the Upper
Santa Clara River  Valley Basin and at  least one (1) station shall be located
in the Antelope Valley Basin.  The Air Pollution Control Officer may mam-

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                                        Rules  and  Regulations of the Air Pollution Control District
                                                                                                                                                  925
tain such additional sampling stations as may be necessary  These addition-
al stations may be permanent, temporary, fixed, or mobile, and may be ac-
tivated upon orders of the Air Pollution Control Officer.

Rule 152.  Air Sampling.
    The Air Pollution  Control  Officer shall establish procedures whereby
adequate samplings and analyses of air contaminants will be taken at each
of the stations established under Rule 151.

Rule 153.  Reports.
    The Air Pollution  Control  Officer shall make daily  summaries of the
readings required by Rule 152.  The summaries shall be in such form as to
be understandable by the public. These summaries shall  be public records
and immediately after preparation  shall  be filed at the main office of the
Air Pollution  Control District and  be. available to  the public,  press,  radio,
television, and other mass media of communication.

Rule 154.  Continuing Program  Of Voluntary Cooperation.
     Upon the adoption of this  regulation the Air Pollution Control Officer
shall inform the  public of ways in which air pollution can  be  reduced and
shall request voluntary  cooperation from all persons in all  activities which
contribute  to  air pollution. Civic groups shall  be encouraged  to undertake
campaigns  of  education and voluntary air pollution reduction in their re-
spective communities.  Public officials shall be  urged to take promptly such
steps as may be  helpful to reduce air contamination to a minimum  within
the areas of their authority.  Employers shall be requested to  establish car
pools.  Users of automotive vehicles shall be urged  to keep  motors in good
condition and  to plan routes and schedules which will contribute minimum
contamination to critical areas of pollution. All industrial, commercial and
business establishments which emit hydrocarbons or the air contaminants
named in  Rule 156 should critically study their operations from the stand-
point of air contamination and  should  take appropriate action voluntarily
to reduce air pollution.

Rule 154.1. Plans.
     a.   If the Air Pollution Control Officer finds  that any industrial, busi-
ness or commercial establishment or activity emits  hydrocarbons or  any of
the contaminants named  in  Rule 156,  he  may give written  notice to the
owner or operator of such industrial, business or commercial establishment
or activity to submit to the Air  Pollution Control Officer plans for immedi-
ate shutdown or curtailment, in  the event of an air pollution emergency, all
of the sources of hydrocarbons  or any of the contaminants named in Rule
156, including vehicles owned or operated by such person, his agents or em-
ployees in  the scope of the business or operation of such establishment or
activity.  Such plans shall  include, in addition to the other matters set forth
in this rule, a list of all such sources of hydrocarbons and any of the contam-
inants named  in  Rule 156, and  a statement of the minimum  time and the
recommended  time to  effect a  complete shutdown of each source in the
event of an air pollution emergency. Such notice may be served in the man-
ner prescribed by law for  the service of summons, or by registered or certi-
fied mail.   Each such person shall, within sixty (60) days after the  receipt
of such notice, or within  such additional time  as the Air  Pollution Control
Officer may specify in writing, submit to the Air Pollution  Control Officer
the plans and  information described in the notice.
    b.   The  Air Pollution Control Officer shall prepare appropriate plans
to be made effective and action  to be taken in respect to a First or Second
Alert as follows:
    In respect to a First Alert, the Air Pollution Control Officer shall de-
 velop  plans calling for the operation of all privately owned vehicles on a
 pool basis as may be arranged by persons and employers of persons operat-
 ing  vehicles  from home  to work and  in the business of such employer.
     In respect to a  Second Alert, the Control Officer shall prepare a pro-
 gram of action and  steps  to  be  taken  under the provisions of Rule  158,
 paragraph  c.  The general  nature of  the plans to be made effective upon a
 Second Alert shall be  reported to and  subject to review and approval by
 the  Air Pollution Control Board.
     It shall be the objective of such program to result in bringing about a
 diminution of air contaminants  which  occasioned the Second Alert and to
 prevent any increase thereof in  order to protect the health of all  persons
 within the air basin  affected by the alert.  It shall also be the objective of
 such plans that they  may be effective to curtail the operations of industrial,
 business, commercial and other activities within  the basin, but without un-
 due interference with the operations  of  public utilities or other productive,
 industrial,  business and other activities, which  are essential to the  health
 and welfare of the community. It is further intended that any said plan of
 action shall not jeopardize the welfare of the public or result in irreparable
 injury to any means of production or  distribution.
     The  Air Pollution Control Officer  shall  further, by  cooperative agree-
 ments or in addition  to cooperative agreements,  prepare plans for action in
 respect to industry,  business, transportation, hospitals, schools and other
 appropriate public and private institutions, and the public generally, to ac-
 complish the purposes of the Second Alert  action as set forth in Rule 158d.
 The general  nature of  the  plans to be made effective upon a Second Alert
 shall be reported to and subject to review and approval by the Air Pollution
 Control Board.
     All plans and programs  of  action to make  effective the procedures
 prescribed in Rule 158, paragraphs c., and d., shall be consistent with and
 designed to accomplish the purposes, and shall be subject to the conditions
 and limitations, set forth in  said paragraphs c., and d.
     The Air Pollution  Control Officer shall give, or cause to be given, wide
 publicity in regard to plans for action to be  applicable under Rule 158, para-
 graphs c., and d., in order that all persons within the district shall be able to
 understand and be prepared to render compliance therewith in the event of
 the sounding of a Second Alert.

 Rule 155.  Declaration Of Alerts.
     The Air Pollution  Control Officer shall declare the appropriate "alert"
 in an air basin whenever the concentration of any air contaminant in that
 air basin has been verified  to  have reached the  concentration set forth in
 Rule 156.  For the purposes of this regulation "verfied" means that the per-
 tinent measuring instrument has been checked over the ensuing five minute
 period and found to be operating correctly.

 Rule 155.1. Notification Of Alerts.
     Following the declaration of  the appropriate "alert,"the Air Pollution
 Control Officer shall communicate notification  of the declaration of the
 alert to:
     a.   The Los Angeles  County Sheriff  and  the Sheriff shall broadcast
the declaration of the "alert"  by  the  Sheriff's teletype and radio system to:
         1.   All Sheriff's substations.
         2.   All city police departments.
         3.   California Highway Patrol.
     b.   Local  public  safety  personnel, who have responsibilities or inter-
ests in air pollution alerts.
     c.   Air polluting industrial plants and processes which requ ire "alert"

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926
                                                         RULES AND REGULATIONS
data in order to effect pre-arranged plans designed to reduce the output of
air contaminants.
    d.   The general public.
    e.   Air Pollution Control District personnel.
Rule 155.2  Radio Communication System.
     The Air Pollution Control Officer shall install and maintain, in contin-
uous   operation, a radio transmitter with selective calling facilities for the
purpose of broadcasting the declaration of alerts and information and in-
structions which may  be appropriate to carry out the provisions of this rej
ulation.
     Radio receiving equipment with decoding device capable of receiving
broadcasts from the Air Pollution Control  Officer of the declaration of alerts
and information and  instructions thereto shall  be  installed  and properly
maintained and  operated during all hours of plant operation by any person
who operates or uses any:
     a.   Petroleum refinery.
     b.   Bulk gasoline  loading facility for tank vehicles, tank cars, or ma-
rine vessels, from which facility 20,000 gallons or more of gasoline are load-
ed  per day.  For purposes of this paragraph, "gasoline" means any petroleum
distillate having a Reid vapor pressure of four pounds or greater, and "facili-
ty" means all gasoline loading equipment  which is both:   (1)  possessed by
one person, and (2)  located so that all the gasoline loading outlets for such
aggregation or combination of  loading equipment can be encompassed with-
in any circle of 300 feet in diameter.
     c.   Asphalt saturator.
   j  d.   Asphalt paving manufacturing plant.
     e.   Asphalt manufacturing plant.
     f.   Chemical plant which:
          1.   Reacts or produces any organic liquids or gases.
          2.   Produces sulfunc acid, nitric acid, phosphoric acid, or sulfur.
     g.   Paint, enamel, lacquer,  or varnish  manufacturing plant in  which
10,000 gallons or more per month of organic solvents, diluents orthinners,
or  any combination  thereof are combined or manufactured into paint,  en-
amel, lacquer, or varnish.
     h.   Rubber tire manufacturing or rubber reclaiming plant.
     i.    Automobile assembly or automobile body plant.
     j.    Metal  melting plant requiring molten  metal temperatures in ex-
cess of 1000°F. or  metal refining plant or metal smelting plant.  This sub-
paragraph applies only to a plant in which a total of 2,500 pounds or more
of  metal are in a molten state at any one time or  are poured in any one
hour.
     k.   Rock  wool manufacturing plant.
     I.    Glass  or frit manufacturing plant in which a total of 4,000 pounds
or  more of glass or frit or both are in a molten state at any one time or are
poured in any one hour.
     m.  Fossil fuel fired steam electric generating plant having a total rated
capacity of 50 megawatts or more.
     n.   Container manufacturing or decorating plant in which  1,000 gal-
lons or more per month of organic solvents, diluents or thinners,  or any
combination thereof are consumed.
     o.   Fabric dry  cleaning plant  in  which  1,000 gallons or more per
month of organic solvents are consumed.
     p.   Printing plant with heated oven enclosure(s) and consuming more
than 1,000 pounds per day of ink containing organic solvents.
 Rule 156.  Alert Stages For  Toxic Air Pollutants*
           (In parts per million parts of air)

Carbon Monoxide
Nitrogen Oxides3
Sulfur Dioxide
Ozone
First Alert Second Alert
50 100
3 5
3 5
0.5 1.0
Third Alert
150
10
10
1.5
a. Sum of nitrogen dioxide and nitric oxide.
 First Alert:  Close approach to maximum  allowable concentration for the
     population at large, a point where preventive action is required.
 Second Alert:   Air contamination level at  which a serious health menace
     exists in a preliminary state.
 Third  Alert:   Air contamination level at which a dangerous health menace
     exists.
 *How measured   The concentrations of air contaminants shall be measured
 in accordance with the procedures and recommendations established by the
 Scientific Committee

 Rule 157.  First Alert  Action.
     This is a warning alert requiring preventive action and shall be declared
 in an air  basin whenever the concentration  of an air contaminant has been
verified to have reached the standards for the "first alert" set forth in Rule
 156.  The following actions shall be taken in the affected air basin upon the
calling of the  First Alert.
     a.    A person shall not burn  any combustible refuse at any location
within the affected air basin.
     b.    Any  person operating or maintaining any industrial, commercial
or business establishment,  which establishments emit hydrocarbons or any
of the contaminants named in Rule 156, and any person operating any pri-
 vate noncommercial vehicle, shall, during the First Alert period in the affect-
 ed air  basin, take the necessary  preliminary  steps to the  action required
 should a Second Alert be declared.
     c.   The  Air Pollution Control Officer shall, by  the use of all appro-
 priate mass media of communication,  request the public to stop all unessen-
 tial  use of vehicles  in the affected air basin,  and to operate all privately
 owned vehicles on a pool basis, and shall request all employers to activate
 employee car pools.
      d.   When, after the declaration of the First Alert it appears to the Air
 Pollution Control Officer that the concentration of any contaminants in all
 or any portion of the affected air basin is increasing in such a manner that
 a Second Alert is likely to be called, he shall take the  following actions:
           1.    Call into session the Emergency Action Committee and re-
               quest  advice on actions to be  taken.
           2.    Give all possible notice to the public by all mass media of
               communication that a Second Alert may be called.

 Rule 158. Second Alert  Action.
      This is  a serious health hazard alert and shall be declared in an air basin
 when the concentration  of an air contaminant has been  verified to have
 reached the  standards set forth for the "Second Alert"  in Rule 156.
      The  following action shall be taken  upon the calling of the Second
 Alert:
      a.    The action set forth  in  Rule 157.
      b.    The  Emergency Action  Committee, the Air Pollution  Control
 Board and the County Counsel, if not already activated, shall be called into
 session and shall remain in session or  reconvene from time to time as direct-
 ed by the Air  Pollution  Control  Officer to study all pertinent information
 relating to the emergency and to recommend  to the Air Pollution Control

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                                       Rules and Regulations  of the Air Pollution Control District
                                                                                                                                                 927
Officer actions to be taken from time to time as conditions change.
     c.   The Air Pollution Control Officer shall make effective, upon no-
tice  as provided in Rule 155.1, the program of action to be taken as pre-
viously developed  pursuant to  Rule 154.1, paragraph b., and to carry out
the policy stated therein.
     Pursuant to this alert, the Air Pollution Control Officer may impose
limitations as to the general operation of vehicles as provided in Rule 154.1,
permitting  limited  operation essential to accommodate industry, business,
public utility and  other services as may be necessary  in the public welfare.
     d.   In the event the control  measures made effective under paragraph
c. above prove to be inadequate to control the increase in the concentration
of air contaminants, the Air Pollution Control Officer, with the advice of the
Emergency Action Committee and  with the concurrence of the Air Pollution
Control Board shall take  such steps as he may deem necessary to assure ade-
quate control of existing air contaminants and to protect the  health and
safety  of the public, but, if possible, without employing such drastic reme-
dial  measures as to completely disrupt the economic life of the community
or to result in irreparable  injury to any form  of production,  manufacture
or business.
     The Air Pollution Control  Officer may, with the  concurrence of the
Air Pollution Control  Board, order the closing of any industrial, commercial
or business establishment and stop vehicular traffic where deemed necessary
by the Emergency Action Committee, except  authorized emergency vehicles
used in public  transportation and  vehicles the operation of which is neces-
sary  for the  protection of  the  health and welfare of the public, if, in the
opinion of the Air Pollution Control Officer,  the continued operation of
such establishment or vehicle contributes to the further concentration of
any  air contaminant,  the concentration of which caused the declaration of
the "alert".
     The Air Pollution Control  Officer,  during a Second Alert,  shall keep
the public suitably  informed of all significant changes in the concentrations
of toxic air contaminants.
     e.   In the event that the Air  Pollution Control Officer determines that
the public health and safety is in danger, the Emergency Action  Committee
and  the Air Pollution Control Board may take any action authorized by this
rule  with less than a quorum present.  A majority vote of the members pres-
ent  is required for any such action.

Rule 159. Third Alert.
     This  is a dangerous health hazard alert  and  shall be declared in an air
basin when the concentration  of  an air contaminant has been verified to
have reached in that air basin the  standards set forth  for the "Third Alert"
in Rule 156.
     The following action shall be  taken upon the calling of the Third Alert:
     a.   The actions set forth in Rules 157 and 158, and
     b.  If it appears that the steps taken  by the Air Pollution  Control
Officer will be inadequate to cope with  the emergency,  the Air Pollution
Control Board  shall request the Governor to declare that a state of emer-
gency  exists  and to take appropriate actions as set forth in the California
Emergency Services Act.

Rule 160. End Of Alert.
     The Air Pollution Control Officer shall declare the termination of the
appropriate alert whenever the concentration of an air contaminant which
caused the declaration of such alert has  been verified to have fallen below
the standards set forth in  Rule 156 for the calling of such alert and the
available scientific and meteorological data indicate that the concentration
of such air  contaminant will not immediately increase again so as to reach
the standards set forth for such alert in Rule 156.  The Air Pollution Con-
trol Officer shall immediately communicate the declaration  of the termina-
tion of the  alert in the manner provided  in Rule 155.1 for  the declaration
of alerts.  The Sheriff shall  broadcast the termination of the alert in  the
same  manner as provided  in  Rule  155.1  for  the declaration  of alerts.

Rule  161.  Enforcement.
     When an "alert"  has been declared  in an air basin,  the Air Pollution
Control Officer, the Sheriff, their deputies, and all other peace officers with-
in that air basin  shall  enforce  the appropriate provisions  of this regulation
and all orders of the Air Pollution Control Board or the Air Pollution Con-
trol Officer  made pursuant to this regulation against any person who, having
knowledge of the declaration of an alert, refuses to comply with the rules
set forth in  this regulation or any order of the Air Pollution Control Board
or the Air Pollution Control Officer made pursuant to this regulation.

Rule 163. Scientific Committee.
     A Scientific Committee shall be appointed by  the Air Pollution Con-
trol Board.  Members  shall be licensed physicians, medical scientists, biolo-
gists,  chemists, engineers, or meteorologists, each of whom has had experi-
ence in air pollution control work, or other experts with scientific training.
    The Air Pollution Control Officer and the County Counsel shall be ex-
officio members of the Scientific Committee.
    The term of appointment of all members except the ex-officio mem-
bers shall  be two (2) years.  The Scientific Committee shall act through a
majority.  There shall  be at least fifteen (15) members on the Committee.
    The Scientific Committee  shall have the following duties-
    a.   Study and recommend. The Scientific Committee shall study and
make  recommendations to the  Air Pollution Control Board of the most suit-
able methods  for measurement of air contaminants and on any changes rec-
ommended  for the concentrations set forth in Rule 156.  The Air Pollution
Control Board may adopt such recommended changes for the concentrations
of toxic air contaminants for each  alert stage by amendment to Rule 156.
    b.   Consult. The Scientific Committee shall serve in a consultant ad-
visory capacity to the  Air Pollution Control Officer concerning any air pol-
lution health problem which  may arise. The Scientific Committee shall also
advise the Air Pollution Control Board on any recommended changes in this
emergency regulation which will provide greater protection of the health and
welfare of all persons within the Air Pollution Control District.

Rule 164. Emergency Action Committee.
    An Emergency Action Committee shall be appointed by the Air Pollu-
tion Control Board.  The Committee shall be composed of ten (10) appoint-
ed members and of these members two shall be experts with scientific train-
ing or knowledge in air pollution matters, two shall be licensed physicians,
two shall be representatives of industry, two shall be representatives of  law
enforcement, and two  shall be  members of the public at large.
    The County Health Officer, the Sheriff, and the County Counsel shall
be ex-officio members of the Committee. In the absence of an ex-officio
member, his deputy may act for him.
    The term of appointment of appointed members shall  be two years.
    The duties of the Emergency Action  Committee shall be to meet with
the Air Pollution Control Officer when called into session, to evaluate data,
and to advise the Air Pollution Control Officer as to the appropriate action
to be taken when the concentration  of any of the contaminants set forth in
Rule  156  has  been verified to be approaching the standards set forth in Rule
156 for a Second Alert.

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928
RULES AND REGULATIONS
     The Committee shall meet when  called into session and not less than
every three months.

REGULATION  VIII.  ORDERS FOR ABATEMENT

Rule 180  General

     Notwithstanding Rule 75,  this regulation shall apply to all hearings on
orders for abatement before the Hearing Board  of the Air Pollution Control
District
Rule 181. Order for Abatement
     In  accordance with  Health  and  Safety Code  Section  242605, the
Hearing  Board,  when petitioned  as provided herein,  is  authorized  and
directed to notice and hold hearings for the purpose of issuing orders for
abatement   The Hearing Board in  holding hearings on the issuance of orders
for abatement shall have all powers and duties conferred upon it by Health
and Safety Code Division 20, Chapter 2
Rule 182. Filing Petitions.
     Requests by the Air Pollution Control  Officer for a hearing on an order
for abatement shall be initiated by the filing of the original and two copies
of the petition with the Clerk of the Hearing Board   One copy of the peti
tion will then be served upon the  person against whom the order for abate-
ment is  sought (the respondent) Service may be made in person or by  mail,
and service may be proved by written acknowledgment of the person served
or by the affadavit of the person making the service
Rule  183. Contents of Petition
     The  petition for  order  for  abatement shall  contain the  following
information
     a   The  name,  address  and telephone number of  the  respondent
     b   The type of business or activity invoiced  nnd  the  street address
at which  it  is conducted
     c   A brief  description of the article,  machine, equipment, or other
contrivance, if any, involved in the v/iolative emission
     d   The section  or rule  which is alleged to have been violated, to-
gether with a brief statement of the facts constituting such alleged violation
     The permit status  and history of the source sought to be abated  may
be included in the petition.  A proposed order for abatement may also be
included.
     All  petitions  shall  be typewritten, double-spaced, on  letter-size paper
(8Vj inches by  11  inches), on one  side of the paper, only,  leaving a margin
of at least one  inch at the top  and each side of the paper.
Rule  184.  Scope  of Order.
     An  order  for abatement issued by the Hearing Board shall include an
order to comply with the statute or rule being violated.   Such order may
provide for installation of control  equipment and for a schedule of comple-
tion and compliance.  As an alternative to an order to comply, the Hearing
Board may  order  the shutdown of  any source of emissions which violates
any statute or rule.  An  order for  abatement may also include a directive to
to  take other  action determined  appropriate to accomplish the  necessary
abatement.
Rule 185.   Findings.
     No order for abatement  shall  be granted unless the Hearing Board
makes all of the following findings
     a.    That the respondent is  in violation of Section  24242 or 24243,
Health and  Safety Code, or  of any rule or regulation of  the Air Pollution
Control Board
                         b    That the order of abatement will not constitute a taking of pro-
                     perty without due process of law
                         c    That if the order for abatement  results in the closing or elimi-
                     nation of an otherwise lawful business, such closing  would not be without
                     a corresponding bL'npfit in reducing air contaminants
                     Rule 186.   Pleadings
                         Any  person may file  a written answer, other responsive pleading,
                     memorandum,  or brief  not less than five  days before the hearing   Said
                     documents  shall  be served  the  same as petitions  under Rule 182
                     Rule 187.  Evidence.
                         a    Oral  evidence  shall  be  taken only on  oath  or  affirmation.
                         b    Each party shall have these rights   to call and examine witnesses;
                     to  introduce exhibits, to cross-examine opposing witnesses on any matter
                     relevant to  the issues even though that matter was not covered in the direct
                     examination, to  impeach any  witness  regardless of which party first called
                     him to testify, and to rebut the evidence against him  If respondent  does
                     not testify  ir his own behalf  he may be called and  examined as if under
                     cross-examination
                         c    The  hearing need not be conducted according  to technical  rules
                     relating to  evidence and witnesses   Any  relevant evidence shall be admitted
                     if it is the sort of evidence on which  responsible persons are accustomed to
                     rely  in the conduct of serious affairs,  regardless of the existence of any
                     common  law or statutory  rule which might make improper the admission of
                     such evidence over objection in civil actions. Hearsay evidence may be used
                     for the purpose of supplementing or explaining any direct evidence but shall
                     not be sufficient  in itself to support a finding unless it would be admissible
                     over objection in civil actions  The rules  of privilege shall be effective to the
                     same extent that  they  are now or hereafter  may  be  recognized in  civil
                     actions, and irrelevant and  unduly repetitious evidence  shall  be excluded.
                     Rule 188  Failure to Comply with  Rules
                          The Cler< of the Hearing Board  shall not  accept for filing any petition
                     which does not comply with these  Rules relating to the form, filing and ser
                     vice of petitions  unless the chairman  or any two members of the Hearing
                     Board direct otherwise and confirm such direction in writing  Such direc
                     tion need not be made dt d meeting of the Hearing Board  The chairman or
                     any two  members,  without a meeting, may require the petitioner to  state
                     further  facts or reframe a petition  so as to disclose clearly  the  issues
                     involved
                     Rule 189.  Dismissal of Petition.
                         The Air Pollution Control Officer may  dismiss his petition at any  time
                     before submission of the case to the Board without a hearing or meeting of
                     the Hearing  Board    The  Clerk  of  the  Hearing Board shall  notify  all
                     interested  persons  of  such dismissal
                     Rule 190.   Place  of  Hearing.
                         All hearings shall be  held at  Room  903, 313  N  Figueroa St., Los
                     Angeles,  California  90012,  unless  some  other place is  designated by the
                     Hearing Board
                     Rule 191.  Notice  of Hearing.
                          The  Clerk  of the Hearing Board  shall mail or deliver a  Notice  of
                     Hearing to the  respondent and to  any person entitled  to  notice under
                     applicable  provisions  of  Division  20  of  the Health  and  Safety Code
                     Rule 192   Preliminary  Matters.
                          Preliminary  matters  such  as setting  a  date  for   hearing, granting
                     continuances, approving petitions for filing, allowing amendments and other

-------
                                        Rules and Regulations of the Air Pollution  Control District
                                                                                                                                                929
preliminary rulings not determinative of the merits of the case may be made
by  the chairman  or  any two  members of the Hearing Board  without a
hearing or meeting of the Hearing Board and without  notice

Rule 193. Official  Notice.
     The Hearing Board may take  official  notice of any  matter which may
be judicially noticed by the courts  of this  State.
Rule 194.  Continuance.
     The chairman or any two members of  the Hearing Board shall grant any
continuance of 15 days  or  less, concurred in by the respondent, the Air
Pollution Control  Officer, and by  every person who has filed an  answer or
other pleading in the action and may grant any reasonable  continuance; in
either case such  action may be ex  parte, without a meeting of the Hearing
Board and without prior notice
Rule 195.  Order and Decision.
     The decision shall  be in writing, served and filed within  15 days after
submission of the cause by the parties thereto and shall contain a brief state-
ment of facts found to be true, the determination of the issues presented
and the order of the Hearing Board.  A copy  shall be mailed or delivered to
the Air Pollution Control Officer, the respondent, and to every person who
has filed an answer or other pleading or who has applied as a party in person
or by counsel at the hearing.
Rule 196.  Effective Date of Decision.
     The decision shall become effective 15 days after delivering or mailing a
copy of the  decision, as provided  in  Rule  194, or the Hearing  Board may
order that the decision shall become effective sooner.

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                         APPENDIX  B:   ODOR-TESTING TECHNIQUES
Modern technology has not yet produced a precise
method of analyzing odor concentration or odor
quality.  In some instances, it has been possible
to measure concentrations of specific odorous
compounds through chemical or spectroscopic
analyses.  The odors  of concern to air pollution
engineers, however, are usually mixtures of sev-
eral odorous compounds (McCord and Witheridge,
1949).  Identification and measurement of each
constituent is usually  a tedious, if not impossible,
task.  For this reason, it is more practical to
measure the aggregate odor concentration or
detectability of a gas stream in terms of odor
units.   An odor unit is defined as  the quantity of
any odor or mixture of odors that, when dispersed
in one cubic  foot  of odor-free air,  produces a
median threshold odor detection response.  The
overall odor measurement techniques to determine
odor units require that human olfactory organs
serve as analytical tools.  Inasmuch as olfactory
responses are somewhat transitory,  particular
care must be taken to eliminate extraneous odors
and false  olfactory responses.

A dilution method has been developed (Fox and
Gex,  1957) that uses the human nose to measure
odor concentration.  It generally follows  the
American Society for  Testing Materials Method
D1391-57 (Standard Method for Measurement of
Odor in Atmospheres  [Dilution Method]) and in-
corporates some refinements.  The method con-
sists,  in essence,  of successively diluting a gas
sample with odor-free air until a threshold dilu-
tion is reached, that is, at further dilution no
odor is detectable by the  human nose.  To mini-
mize the effect of variations in olfactory sys-
tems,  a panel of  several  persons  is used.  The
odor concentration is  determined by plotting di-
lution response data on log-probability coordi-
nates.

This dilution method serves, principally to mea-
sure odor concentration.  It is a valuable  tool
with which to evaluate the performance of odor
control equipment, and the  quantitative odor
nuisance potential of a source.  The quality or
objectionability of an odor cannot be evaluated
with the same assurance.  While the dilution
method can be used to measure objectionability
thresholds,  results are not as reproducible as
detectability measurements  are.  This is  due
principally to the subjective nature of human
olfactory responses.  The average' subject can
report the presence or absence of an odor with
more certainty than he can determine objection-
ability.
Odor testing is a comparatively recent develop-
ment.  Certain modifications (Mills et al. ,  1963)
of the American Society for  Testing Materials
static test procedure were developed to accom-
modate the method to field problems and to  ac-
celerate  the testing procedure,  at the same  time
maintaining or improving the reproducibility and
reliability of results.
For  employment  of this method for odor evalua-
tion,  a selected group of individuals must be used
as odor panel members, and an air-conditioned,
odor-free room must be used for the test.

 THE  ODOR PANEL
The  ASTM procedure describes a suitable meth-
od of screening and selecting members of the
odor panel.   The selectees  should be persons who
are neither  the most  sensitive to odors nor  the
most insensitive  of those screened.  The choice
of panel  members should be limited to those with
the most generally reliable olfactory perception.

Consistent and reproducible results have been
found to  be obtained with a panel consisting  of at
least eight persons.  Although a panel  of six per-
sons is adequate  at times, eight is preferred,
because  the probabilities of  inconclusive results
(with the resultant necessity of rerunning the test)
are thereby reduced.

If possible,  the panel members should be allowed
to relax  in the odor-free room for  10 to 15 min-
utes  before the test.  This ensures that their
olfactory senses  are not fatigued or dulled by ex-
traneous odors.  Test periods should be limited
to 30 minutes or  less.  If testing is  required over
a longer  period,  adequate rest periods should be
scheduled to preclude fatigue.

THE  ODOR EVALUATION ROOM

A typical plan for an  odor evaluation room is
shown in Figure  Bl.  Essential features are:
(1) Separation of the work area from the evalua-
tion  area,   (2) provision for relatively odor-free
air at room temperature with moderate humidity
by use of an air-conditioning unit,  and (3) an
activated-carbon adsorption unit to  provide  and
circulate odor-free air to the evaluation area.

An odor  evaluation room should be designed to
minimize the possibility of extraneous odors in
the vicinity of the panelists.  It should be devoid
of fabrics,  such  as carpeting, draperies,  or up-
holstery, that might hold odorous materials. The
room should be so located in the building that
                                                931
  234-767 O - 17 - 61

-------
932
                                    ODOR-TESTING TECHNIQUES
there is no introduction of odors into the air con-
ditioner inlet or through doors, cracks,  and so
forth.  Air circulation should be such that the
activated-carbon unit  discharges air near the
panelists.  All air from the •work area should be
filtered before it comes into contact with panelists.


SAMPLING  TECHNIQUES

Representative sampling points are chosen ac-
cording to standard air-sampling techniques.  In
most instances, 250-milliliter grab samples are
sufficient. These are collected in gas-sampling
tubes such as those shown in Figure B2.  Possible
sources of error are foreign odors from the sam-
pling train,  improperly cleaned glassware,  and
condensation in the sample tube.

The use of rubber or plastic tubing and other
heat-sensitive materials in the sample probe
should be avoided,  particularly if the  gas stream
is at an elevated temperature.  The apparatus of
Figure B2 is recommended wherein all tubing
and joints upstream of the sampling tube are con-
structed of glass.  The rubber bulb evacuator is
on the downstream side of the tube and does not
contaminate  the sample.

The problems of condensation and adsorption  of
odorous material on the inner walls of the sam-
pling apparatus are the most difficult  to over-
come or even to evaluate.   Odor adsorption can
be minimized by flushing the sampling equipment
with enough of the gas stream to allow tempera-
ture and humidity to reach equilibrium.  The area
of ground glass in contact with the sample  should be
held to a minimum.

Condensation in the tube  can introduce a large
error when the moisture content is much more
than 20 percent by volume.  When the gas  stream
bears a high moisture content, a second sampling
technique has been devised in •which the sample
is diluted in the sample tube with dry, odor-free
air. Dilution air is drawn through a cartridge
charged with activated carbon and a suitable des-
sicant.   This sampling technique provides  a di-
lution of 10:1 or greater  in the tube.  Equipment
used for dilution sampling is diagrammed  in Fig-
ure B3.  The 1-millimeter-outside-diameter
capillary tube used as a probe is inserted  through
a new,  size 000, cork stopper with the aid of an
18-gage hypodermic needle  as a sleeve.  The
sample is obtained by placing the free end  of the
capillary into the gas  stream and withdrawing
the required 5 to 10 milliliters of  air from the
sample tube with the 10-milliliter syringe.  The
volume withdrawn is replaced by an equal  volume,
which enters through the  capillary tube.  The
small diameter of the capillary minimizes diffu-
sion across the tube.

In both techniques, the stopcock nearest the
squeeze bulb is closed first.  When equilibrium
conditions are established,  the other stopcock
is closed and the probe removed from the  gas
stream.
                                                                    J-
                             EVALUATION  AREA


                                  ACTIVATED CARBON UNIT
                                   6OO  TO  12OO  CFM
                                                           -] j	 ENTRANCE
                                                                        (CLOSED)
                                                         AIR  FLOW
             WORK  AREA
                    QQQQQQQQQ
                                   CHAIRS
                              ODOR-FREE  AIR PLENUM
          AIR
        INTAKE
                                                                               BENCH
                                        Figure B1.  Odor-free room.

-------
                                     Evaluation of Odor Samples
                                      933
                                        SAMPLE  TUBE  (250ml.)
                            Figure B2.  Odor sampling equipment for dry gases.
      MEMCIl miNGf (II »H
      MINIMI
                                        GUSS MFILUIY IIIIC
                                          , 0 mm 00)
                          NtEDU (11 GMI6E)
                           SIMPLE TUK
                            (HI ml)
    Figure B3.  Odor sampling equipment for wet gases.
EVALUATION OF  ODOR  SAMPLES

In the work area  of the odor evaluation room,
mercury displacement is used to transfer the
odorous gases from the sample  tube to a 100-
milliliter glass syringe.   Figure B4 shows
schematically the equipment needed.  Ten milli-
liters is  drawn into a syringe, and then 90 milli-
liters of  odor-free air.  This  provides a 10:1
dilution.  Further dilutions  are  made  in other
syringes including the  panel member's syringe.

The last  dilution  (usually 10:1) is performed by
the panelist,  who is furnished with  10 milliliters
of sample injected into his 100-milliliter  syringe.
He dilutes the sample to 100 milliliters with am-
bient air before sniffing.  Most panelists  prefer
to eject the sample near their noses.  Each panel
member  should,  however, choose the method of
smelling the  sample  by which he feels his results
are most accurate and reproducible.  He  records
                                                                                               PANEL

                                                                                             MEMBER S

                                                                                             SYRINGE I
DILUTION

SYRINGE

;ro"
(100  ml )
                                       Ji
   STEP  1
                         STEP 2
                                      STEP 3
Figure B4.  Equipment used for transferring and
diluting odor samples.

-------
934
ODOR-TESTING TECHNIQUES
a positive or negative detection of odors on a
tally sheet together with the number of the sample.
Each panelist purges his  syringe  with air between
samples.

Some compounds such as aldehydes deaden the
sense of smell and cause erratic  results, that
is,  the dilution response  data do not plot to a
straight line on log-probability coordinates.
While there is no entirely satisfactory method
of overcoming this effect, it can be at least
partially offset by allowing more  time between
samples for panelists' olfactory systems to re-
cover.

DETERMINATION  OF ODOR CONCENTRATION

The odor  responses of the panel are quantified by
calculating the percent of the panel members  de-
tecting  odors at each dilution, as shown in Table
Bl.  The  ratio of the diluted volume to the orig-
inal sample is termed the dilution factor.  Odor
responses are plotted against dilution factors to
determine odor concentration.

Dilution response data follow a cumulative normal
distribution curve.  If plotted on  rectilinear co-
ordinates, these data produce an s-shaped curve.
The points at the extremes of the curve would
represent panelists who are the most and the
least sensitive to the particular odors.   The area
in the middle of the curve would represent average
olfactory responses.

When dilution response data are plotted on log-
arithmic-probability coordinates, they tend to
follow a straight line.  This phenomenon is shown
in Figure B5, -where the  test data of Table Bl are
plotted.   The subject gases evaluated were repli-
cate samples of discharge gases  from a fish meal
drier.  The data plot to a reasonably straight line.
Maximum deviation from a straight line is prin-
cipally  a function  of the number of panelists.
                              ODOR RESPONSE  CHART
^
3—
	
— —
^

-
-
	
-^

-- -

^_
-



^-s.


—
^

\--~-
t
1
3,
^"
000 o

OFF-GASES FROM FISH MEAL DRIER
EVALUATED IY THE STATIC METHOD
— - 1 	 I

-r -.-t^t__
2 5 10 20 30 40 5 60 70 8
-"
— —
^— —.




•»--.

—


— —
- - --


-*:



— »^,



S
; — i



-

1.400 0
J
r
OFF-OASES FROM FISH MEAL DRIER
EVALUATED *Y THE DYNAMIC METHOD
— -M — \ I

r —

----
5 10 20 30 40 50 60 70 8
MRCCNT OF PANIL BIPOHTING POSITI>

u/scl
"s^
UMfLE
SAMPL



•x^
W 1
Na ?
	



•"
0 90 95


u/sc.

SAMPl



-— — .
HI
SAMPLE No




i •
*
0 90 95 9
11 RESPONSES
                     Figure  B5.  Plot of dilution response  data.
                 The point at which the plotted line crosses the
                 50 percent panel response line is the threshold
                 concentration.  The dilution factor at the thres-
                 hold is the odor concentration, usually stated in
                 terms of odor units per scf.   The total rate of
                 odor emission in odor units per minute may
                 then be calculated by multiplying the concen-
                 tration by the total volume  of the effluent.
                        Table Bl.  DATA FROM A TYPICAL DILUTION TEST
Sample
No.
1



2

2
Dilution
designation
A
B
C
D
A
B
C
Dilution
factora
1, 000
2, 500
10, 000
5, 000
2, 500
5, 000
10, 000
No. of
panel
members
8
8
8
8
8
8
8
No. of
panel members
detecting odor
6
4
3
2
5
3
1
% of
panel members
detecting odor
75
50
38
25
63
38
13
                The dilution factor is the volume of the diluted sample evaluated by the
                panel members, divided by the volume of the original undiluted sample
                contained therein.
                Zero and 100 percent responses are considered indeterminate.

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          APPENDIX  C:   HYPOTHETICAL AVAILABLE HEATS  FROM NATURAL GAS
Burners lor combustion devices such as after-
burners frequently use the oxygen present in the
contaminated effluent stream.  An example would
be a natural gas-fired afterburner that takes in
60 percent of its combustion air from the atmo-
sphere,  and 40 percent from  an air containing
contaminated effluent stream.

One step in checking afterburner design is the cal-
culation of the natural gas flow rate required to
raise an effluent stream to a  given temperature.
A calculation such as this normally makes use  of
the available heat from natural gas.  Available
heat is  the amount of heat remaining after the
products of combustion from  a  cubic foot of natural
gas are  raised to the afterburner temperature.
Available heat from natural gas is shown in Table
D7.

If the afterburner gas burner  takes a portion of
the combustion air from the effluent stream,
then the calculation of the gas flow rate becomes
a trial-and-error procedure.   By the method of
hypothetical available heats given here, the  trial-
and-error solution is eliminated.

The natural gas used in illustrating this calcula-
tion procedure  requires 10. 36 cubic feet of air
for theoretical  combustion of  1  cubic foot of gas
(Los Angeles area natural gas).  Products of
complete combustion evolved  from this  process
are carbon dioxide, water, and nitrogen.  If
the combustion of 1 cubic foot of natural gas is
thought of as taking place at 60 °F, then a portion
of the heat released by combustion must be used
to raise  the products of combustion from 60 °F to
the  temperature of the device.  The remaining
heat is called available heat.  This quantity  repre-
sents the heat from natural gas  that can be used
to do useful work in the combustion device,  such
as heating an effluent stream  in an afterburner.
Consider a gas-fired afterburner adjusted to pro-
vide a fraction,  X, of theoretical air through the
burner.  If the contaminated effluent contains air,
then the remaining air for combustion, 1-X, is
taken from the effluent stream.  This means that
a smaller quantity of effluent has to be heated by
the natural gas,  since a  portion of  the effluent is
involved in the combustion reaction.   Thus,  a
burner taking combustion air from an effluent
stream can be fired to raise the  temperature of
the effluent at a  natural gas input lower than that
of a burner firing  with all combustion air taken
from the atmosphere.
Let the heat content of an effluent stream, at the
desired final temperature, be H Btu/lb.  Since
10.36 cubic feet of air is required for combus-
tion of 1 cubic foot of natural gas,  the weight of
air taken from the effluent would be
       W  =  (10.36)(l-X)(p)
                 (Cl)
The heat contents of this secondary combustion
air •would be
    Q  =  WH  =  (10.36)(l-X)(p)(H)

where
                 (C2)
    W =  weight of combustion air from the ef-
          fluent per cubic foot of natural gas,
          Ib/ft  natural gas

    H =  heat content of the effluent at the re-
          quired temperature,  Btu/lb

    X =  fraction of theoretical combustion air,
          furnished as primary air through burn-
    p  =  density of air at 60°F

       =  0.0764 Ib/ft3.

Since Q Btu per cubic foot of natural gas is not
required to heat the effluent,, it can be added to
the available heat,  A, at the afterburner tem-
perature, or
               A   =  A  +   Q
                 (C3)
where
    A =  hypothetical available heat, Btu/ft
          natural gas

    Q =  heat content of secondary combustion air
          from equation C2.

Equation C3 is given in terms of temperature in the
following equations:

               ,_   Hypothetical available heat,
Temperature,  °F    y*l  .3
    r                  Btu/ft0 natural gas
       600
       700
       800
       900
     1,000
     1, 100
871 +  104 (1-X)
846 +  124 (1-X)
821 +  144 (1-X)
798 +  167 (1-X)
773 +  185 (1-X)
747 +  206 (1-X)
                                                  935

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 936
HYPOTHETICAL AVAILABLE HEATS FROM NATURAL GAS
1,200
1,300
1,400
1,500
1,600
1,700
1,800
721 H
693 -:
669 H
643 -{
615 H
590 -\
562 H
h 227 (1-X)
h 249 (1-X)
h 270 (1-X)
h 292 (1-X)
,- 314 (1-X)
- 336 (1-X)
h 358 (1-X)
3. The gases in the afterburner will consist of:

a. Products of combustion from

1,230 cfh
natural gas with theoretical air - 1, 230
x 11. 45 scfh,
b. the portion of the effluent not
f* or"n Tin <3^1 on a n V z: offln*anf T7-r\1

used for
n-m^i T'a'f-^ _
     X =  fraction of theoretical air furnished
     as the burner's primary air.

Hypothetical available heats are given in Table
Cl for varying temperatures and percentages
of primary air.

The use of this concept is illustrated  in the follow-
ing examples.
Example C1:

An afterburner is used to heat an effluent stream
to 1,200°F by using 1 x 106 Btu/hr.  The burner
is installed and adjusted so that 60% of the theoret-
ical combustion air is furnished through the burner,
and the remainder is taken from the effluent.  De-
termine the required natural gas  rate.

1.  The percent  primary air is 60%,  the  required
    temperature is 1,200°F, the hypothetical
    available heat from Table Cl is 812 Btu/ft3
    of gas.

2.  Burner flow  rate  = 106/812  =  1,230 cfh gas.
                                        (1, 230)(10.36)(1-X).

                                 Example C2:

                                 An afterburner is used to heat an effluent stream
                                 to 1,200°F by using 1 x  106 Btu/hr.  The burner
                                 is installed and adjusted so that all the combustion
                                 air is taken from the effluent stream.  Determine
                                 the natural gas rate.

                                 This  is equivalent to the  burner's operating at 0%
                                 primary air.

                                 1.   At 1,200°F the hypothetical available heat is
                                     948 Btu/ft3 for 0% primary air.

                                 2.   Burner flow rate =  106/948  = 1,058 cfh.

                                 3.   Gases  in afterburner will consist of:

                                     a. Combustion  products from 1, 058 cfh nat-
                                        ural gas with theoretical air =  1, 058 x
                                        11. 45,

                                     b. the  portion of the effluent not used for
                                        secondary combustion air  =  effluent
                                        volume  -  (1,058)(10. 36)(1-X).
                          Table Cl.  HYPOTHETICAL AVAILABLE HEATS
                                  Hypothetical available heats, Btu/ft  gas
lemp,
°F
600
700
800
900
1, 000
1, 100
1, 200
1, 300
1, 400
1,500
1, 600
1, 700
1, 800
% primary air through the burner
0
975
970
965
965
958
953
948
942
939
935
929
926
920
10
965
958
950
948
939
933
926
917
912
906
897
892
885
20
954
945
936
931
921
912
903
892
885
976
866
859
949
30
944
933
922
915
902
891
880
867
858
847
834
825
813
40
933
921
907
898
884
871
858
842
831
818
803
791
777
50
923
908
893
881
865
850
835
818
804
789
772
758
741
60
913
896
878
865
847
830
812
793
777
760
740
724
706
70
902
883
864
848
828
809
789
768
750
730
709
691
670
80
892
971
850
831
810
788
767
743
723
701
677
657
634
90
881
859
835
814
791
768
744
718
696
672
646
623
598

-------
            APPENDIX D:   MISCELLANEOUS DATA
                 Table Dl.  PROPERTIES OF AIR
Temp,
°F
0
20
40
60
80
100
120
140
160
180
200
250
300
350
400
450
500
600
700
800
900
1, 000
1,200
1,400
1, 600
1,800
2, 000
Specific heat
at constant
pressure (C ),
Btu/lb-°F
0.240
0.240
0.240
0.240
0.240
0. 240
0.240
0.240
0. 240
0.240
0.240
0.241
0.241
0.241
0.241
0.242
0.242
0.242
0.243
0.244
0.245
0.246
0.248
0.251
0. 254
0.257
0.260
Absolute
viscosity (p.),
Ib/hr-ft
0. 040
0.041
0. 042
0.043
0.045
0.047
0. 047
0.048
0.050
0.051
0.052
0.055
0. 058
0.060
0.063
0. 065
0. 067
0.072
0.076
0.080
0.085
0.089
0.097
0. 105
0. 112
0. 120
0. 127
Thermal
conductivity
(k),
Btu/hr-ft-°F
0.0124
0. 0128
0.0132
0.0136
0. 0140
0.0145
0. 0149
0.0153
0. 0158
0.0162
0.0166
0.0174
0. 0182
0.0191
0. 0200
0.0207
0. 0214
0.0229
0.0243
0.0257
0. 0270
0.0283
0.0308
0. 0328
0. 0346
0.0360
0.0370
Prandtl No.
(CfX/k),
(dimensionless)
0. 77
0. 77
0. 77
0.76
0. 77
0.76
0. 76
0. 76
0.76
0.76
0.76
0. 76
0. 76
0. 76
0.76
0. 76
0. 76
0.76
0.76
0. 76
0. 77
0.77
0.78
0. 80
0. 82
0.85
0.83
Density
(P),
Ib/ft3 a
0. 0863
0. 0827
0. 0794
0. 0763
0.0734
0. 0708
0. 0684
0. 0662
0. 0639
0. 0619
0. 0601
0. 0558
0. 0521
0. 0489
0. 0460
0. 0435
0. 0412
0. 0373
0. 0341
0. 0314
0. 0295
0. 0275
0. 0238
0. 0212
0. 0192
0. 0175
0. 0161
p taken at pressure of 29.92 inches of mercury.
                              937

-------
938
                                      MISCELLANEOUS DATA
          Table D2.   THRESHOLD LIMIT VALUES (Copyright,  1966,  American Conference of
                                 Governmental Industrial Hygienists)*

                                       Recommended Values
a
Substance PPm
Acetaldehyde
Acetic acid
Acetic anhydride
Acetone 1
Acetonitrile
Acetylene dichloride, see 1,
2 Dichloroethylene
Acetylene tetrabromide
Acrolein
Acrylonitrile-skin
Aldrin-skin
Allyl alcohol -skin
Allyl chloride
cAllyl glycidyl ether (AGE)
Allyl propyl disulfide
2 Aminoethanol, see
Ethanolamine
Ammonia
Ammonium sulfamate (Am-
mate)
n-Amyl acetate
Aniline -skin
^Anisidine (o, p-isomers}-
skin
Antimony and compounds
(as Sb)
ANTU (alpha naphthyl thio-
urea)
Arsenic and compounds
(as As)
Arsine
Barium (soluble compounds)
cBenzene (benzol) -skin
fBenzidine-skin
p-Benzoquinone, see Quinone
^Benzoyl peroxide
Benzyl chloride
Beryllium
eBiphenyl, see Diphenyl
Boron oxide
cBoron trifluoride
Bromine
Butadiene (1, 3 -butadiene) 1
Butanethiol, see Butyl
mercaptan
2-Butanone
2-Butoxy ethanol (Butyl
Cellos olve)- skin
eButyl acetate (n-butyl acetate)
Butyl alcohol
tert. Butyl alcohol
cButylamine-skin
ctert. Butyl chr ornate (as
CrO3)-skin
n-Butyl glycidyl ether (BGE)
200
10
5
,000
40


1
0. 1
20
—
2
1
10
2


50

__
100
5

__

--

--

--
0.05
--
25
—

--
1
--

	
1
0. 1
, 000


200

50
--
100
100
5

__
50
mg/m3 b
360
25
20
2,400
70


14
0.25
45
0.25
5
3
45
12


35

15
525
19

0.5

0.5

0.3

0.5
0.2
0.5
80
A1

5
5
0.002

15
3
0.7
2,200


590

240
--
300
300
15

0. 1
270
a.
Substance PPm
Butyl mercaptan 10
p-tert. Butyltoluene 10
Cadmium oxide fume
Calcium arsenate
Calcium oxide
Camphor
dCarbaryl (Sevin) (R)
Carbon dioxide 5,000
Carbon disulfide -skin 20
e Carbon monoxide
Carbon tetrachloride-skin 10
Chlor dane - skin
Chlorinated camphene, -skin
Chlorinated diphenyl oxide
e Chlorine
Chlorine dioxide 0. 1
cChlorine trifluoride 0. 1
c Chlor oacetaldehyde 1
Chlorobenzene (mono-
chlorobenzene) 75
Chlorobromomethane 200
2-Chloro-l,3 butadiene,
see Chloroprene
Chlorodiphenyl (42% chlo-
rine)- skin
Chlorodiphenyl (54% chlo-
rine)-skin
1, Chlor o, 2, 3 epoxypropane,
see Epichlorhydrin
2, Chlor oethanol, see
Ethylene chlorohydrin
Chloroethylene, see Vinyl
chloride
cChloroform (trichloro-
me thane) 50
1 - Chlor o- 1 -nitropropane 20
Chloropicrin 0. 1
Chloroprene (2-chloro-l, 3-
butadiene)-skin 25
Chromic acid and chromates
(as CrO3)
e Cobalt
Copper fume
Dusts and mists
dCotton dust (raw)
Crag (R) herbicide
Cresol (all isomers)-skin 5
Cyanide (as CN)-skin
Cyclohexane —
Cyclohexanol 50
Cyclohexanone 50
eCyclohexene
^Cyclopentadiene 75
2, 4-D
DDT-skin
mg/m3 b
35
60
0. 1
1
5
2
5
9,000
60
--
65
0.5
0.5
0.5
--
0.3
0.4
3

350
1,050



1

0.5







240
100
0.7

90

0. 1
--
0. 1
1.0
1
15
22
5
--
200
200
—
200
10
1
*See Table D2 Footnotes, pages 942 and 944

-------
                                        Threshold Limit Values
                                                                  939
  Substance
ppm     mg/m^ b
Substance
                                                                                ppm
  DDVP-skin                     --           1
  Decaborane-skin                 0.05        0. 3
  Demeton (R)-skin               --           0.1
  Diacetone alcohol(4-hy-
   droxy~4-methyl-2-penta-
   none)                         50         240
  1,2 Diaminoethane, see
   Ethylenediamine Diborane
 el, 2-Dibromoethane (ethylene
   dibromide)-skin
 Co-Dichlorobenzene              50         300
  p-Dichlorobenzene              75         450
  Dichlorodifluoromethane     1,000      4,950
 dl, 3-Dichloro-5-dimethyl
   hydantoin                     --           0.2
  1, 1, -Dichloroethane           100         400
  1, 2-Dichloroethane             50         200
  1, 2-Dichloroethylene           200         790
 cDichloroethyl ether-skin        15         90
  Dichloromethane, see
   Me thylene chloride
  Dichloromonofluoromethane  1,000      4.200
 cl, 1-Dichloro-l-nitroethane     10         60
  1, 2-Dichloropropane,  see
   Propylenedichloride
  Dichlorotetrafluoroethane    1,000      7,000
  Dieldrin-skin                   --           0.25
  Diethylamlne                    25         75
  Diethylether,  see Ethyl ether
  Difluorodibromomethane        100        860
 cDiglycidyl ether  (DGE)           0.5         2.8
  Dihydroxybenzene,  see
   Hydroquinone
  Diisobutyl ketone               50        290
  Dimethoxymethane,  see
   Methylal
  Dimethyl acetamide-skin        10         35
dDimethylamine                  10         18
  Dimethylaminobenzene,  see
   Xylidene
  Dimethylaniline (N-di-
   methylaniline)-skin             5         25
  Dimethylbenzene, see  Xylene
dDimethyl 1,2-dibro-2, 2-
   dichloroethyl phosphate,
   (Dibrom) (R)                  --           3
dDimethylformanide-skin         10         30
  2, 6 Dimethylheptanone, see
   Diisobutyl ketone
  1, 1-Dimethylhydrazine-skin      0.5        1
 Dime thylsulf ate-skin             1          5
 Dinitrobenzene (all isomers)-
   s kin                          - -           1
 Dinitro-o-cresol-skin           --           0.2
 Dinitrotoluene-skin             --           1.5
 Dioxane (Diethylene  dioxide)-
   skin                          100        360
 Dipropylene glycol methyl
   ether-skin                    100        600
                    c, eT
  aDi-sec, octyl phthalate (Di-
     2-ethylhexylphthalate          --           5
   Endrin-skin                     --           0. 1
   Epichlorhydrin-skin              5          19
   EPN-skin                       --           0.5
   1, 2-Epoxypropane, see
     Propylene oxide
   2, 3-Epoxy-1-propanol see
     Glycidol
   Ethanethiol,  see Ethyl-
     mercaptan
   Ethanolamine                    3           6
   2 Ethoxyethanol-skin           200         740
   2 Ethoxyethylacetate (Cello-
     solve acetate)-skin            100         540
   Ethyl acetate                  400       1,400
   Ethyl acrylate-skin              25         100
   Ethyl alcohol (ethanol)        1,000       1,900
  eEthylamine
c> eEthylbenzene
   Ethyl bromide                  200         890
   Ethyl chloride                1,000       2,600
   Ethyl ether                    400       1, 200
   Ethyl formate                  100         300
   Ethyl mercaptan                —          —
   Ethyl silicate                  100         850
   Ethylene chlorohydrin-skin       5          16
   Ethylenediamine                10          25
   Ethylene dibromide, see
     1, 2-Dibromoethane
   Ethylene dichloride, see
     1, 2-Dichloroethane
  cEthylene glycol dinitrate-
     skin                            0.2         1.2
   Ethylene glycol monomethyl
     ether acetate,  see Methyl
     cellosolve acetate
  eEthylene imine-skin
   Ethylene oxide                   50          90
   Ethylidine chloride, see
     1, 1-Dichloroethane
   Ferbam                        --          15
   Ferrovanadium dust            --           1
   Fluoride (as  F)                 --           2.5
   Fluorine                         0.  1         0.2
   Fluorotrichloromethane      1,000      5,600
  cFormaldehyde                    5           6
   Freon 11, see Fluorotri-
    chloromethane
   Freon 12, see Dichlorodi-
    f luor ome thane
   Freon 13B1,  see Trifluoro-
    monobr ome thane
   Freon 21,  see Dichloromono-
    fluoromethane
   Freon 112,  see 1, 1, 2, 2-
    Tetrachloro-1, 2 difluoro-
    ethane

-------
940
MISCELLANEOUS DATA
Substance
Freon 113, see 1,1,2-Tri-
chloro, 1, 2, 2-trifluoro-
ethane
Freon 114, see Dichloro-
tetrafluoroethane
Fur f ural - s kin
Furfuryl alcohol
Gasoline
Glycidol (2, 3-Epoxy-l-pro-
panol)
Glycol monoethyl ether, see
2 -Ethoxyethanol
eGuthion, see Azinphosmethyl
Hafnium
Heptachlor-skin
Heptane (n-heptane)
Hexa chlor oethane - s kin
Hexane (n-hexane)
2-Hexanone
Hexone
sec-Hexyl acetate
Hydrazine-skin
Hydrogen bromide
cHydrogen chloride
Hydrogen cyanide-skin
Hydrogen fluoride
Hydrogen peroxide, 90%
Hydrogen selenide
j
Hydrogen sulfide
Hydr oquinone
clodine
elron oxide fume
Isoamyl alcohol
Isophorone
Isopropyl alcohol
Isopropylamine
Isopropylether
Isopropyl glycidyl ether (IGE)
Ketene
Lead
Lead arsenate
Lindane - s kin
Lithium hydride
dL. P. G. (Liquified petroleum
gas) 1
Magnesium oxide fume
Malathion-skin
cManganese
Mercury- skin
Mercury (organic compounds)-
skin
Mesityl oxide
Methanethiol, see Methyl
mercaptan
Methoxy chlor
2-Methoxyethanol, see
Methyl cellos olve
Methyl acetate
Methyl acetylene (prqpyne) 1
ppma





5
50
--

50



_-
--
500
1
500
100
100
50
1
3
5
10
3
1
0.05
10
__
0. 1
- _
100
25
400
5
500
50
0.5


_ _
— _

,000
--
_ _
- _

_ _
25


__


200
,000
mg/m3 b





20
200
A6

150



0.5
0.5
2,000
10
1,800
410
410
295
1.3
10
7
11
2
1. 4
0.2
15
2
1
	
360
140
980
12
2, 100
240
0.9
0. 2
0. 15
0. 5
0. 025

1,800
15
15
5
0. 1

0.01
100


15


610
1,650
a
Substance PPm
Methyl acetylene -propadiene
mixture (MAPP) 1,
Methyl acrylate-skin
Methylal (dimethoxymethane) 1,
Methyl alcohol (methanol)
Methyl amyl alcohol, see
Methyl isobutyl carbinol
cMethyl bromide-skin
Methyl butyl ketone, see
2-Hexanone
Methyl cellosolve-skin
Methyl cellosolve acetate-
skin
GMethyl chloride
Methyl chloroform
Methylcyclohexane
Methyl cyclohexanol
o-Methylcyclohexanone-skin
Methyl ethyl ketone (MEK),
see 2-Butanone
Methyl formate
Methyl isobutyl carbinol- skin
Methyl isobutyl ketone, see
Hexone
C) ^Methyl mercaptan
^Methyl methacrylate
Methyl propyl ketone, see
2-Pentanone
caMethyl styrene
cMethylene bisphenyl iso-
cyanate (MDI)
Methylene chloride (dichlo-
romethane)
Molybdenum (soluble com-
pounds)
(insoluble compounds)
Monomethyl aniline -skin
Morpholine-skin
Naphtha (coal tar)
Naphtha (petroleum)
dNaphthalene
jS-Naphthylamine
Nickel carbonyl
Nickel, metal and soluble
compounds
Nicotine -skin
dNitric acid
p-Nitroaniline-skin
Nitrobenzene -skin
dp -Nit rochloro -benzene -skin
Nitroethane
"-Nitrogen dioxide
^Nitrogen trifluoride
cNitroglycerin- + EGDN-skin
Nitrome thane
1 -Nitropropane
2 -Nitropropane
N-Nitrosodimethyl-amine
(Di-methyl-nitrosoamine)-
skin
mg/m3

000 1,
10
000 3,
200


20


25

25
100
350 1,
500 2,
100
100


100
25

10
100


100

0. 02

500 1,

--
--
2
20
200
500 2,
10
--
0.001

—
2
1
1
--
100
5
10
0.2
100
25
25

_• —
b

800
35
100
260


80


80

120
210
900
000
470
460


250
100

20
410


480

0.2

740

5
15
9
70
800
000
50
A2
0.007

1
0.5
5
6
5
1
310
9
29
2
250
90
90

A3

-------
                                      Threshold Limit Values
                                                                                                  941
 Substance
                               ppm
ig/m
                                              3 b
  Substance
                               ppma
          mg/m
                                                         3 b
 Nitrotoluene-skin                5         30
 Nitrotrichloromethane, see
   Chloropicrin
 Octane                         500      2, 350
 Oil mist (mineral)               --           5
 Osmium tetroxide               --           0. 002
dOxygen difluoride                0.05       0.1
 Ozone                           0.1        0.2
 Parathion-skin                  --           0.1
 Pentaborane                     0.005      0.01
 Pentachloronaphthalene-skin     --           0.5
 Pentachlorophenol-skin         --           0.5
 Pentane                     1,000      2,950
 2-Pentanone                   200        700
 Perchloroethylene              100        670
 Perchloromethyl mercaptan      0.1        0. 8
 Perchloryl fluoride               3         13.5
 Phenol-skin                     5         19
 p-Phenylene diamine-skin       --           0. 1
 Phenylethylene, see Styrene
 Phenyl  glycidyl ether (PGE)     50        310
 Phenylhydrazine-skin            5         22
 Phosdrin (Mevinphos) (R)-
   skin                          --           0.1
^Phosgene (carbonyl chloride)     0.1        0.4
 Phosphine                       0.3        0.4
 Phosphoric acid                 --           1
 Phosphorus (yellow)             --           0. 1
 Phosphorus pentachloride       --           1
 Phosphorus pentasulfide         --           1
 Phosphorus trichloride           0.5        3
dPhthalic anhydride               2         12
 Picric acid-skin                 --           0. 1
 Platinum (Soluble salts)         --           0.002
 Polytetrafluoroethylene de-
   composition products          --          A.
dPropane                     1,000      1,800
 Propyne, see Methyl -
   acetylene
 /3Propiolactone                  --          A->
 n-Propyl acetate               200        840
 n-Propyl nitrate                 25        110
 Propylene dichloride            75        350
ePropylene imine-skin
 Propylene oxide                100        240
 Pyrethrum                      --           5
 Pyridine                         5         15
 Quinone                         0.1        0. 4
 Rotenone (commercial)          --           5
"Selenium compounds (as Se)     --           0.2
 Silver,  metal and soluble
   compounds                    --           0.01
 Sodium fluoroacetate (1080) -
   skin                          --           0.05
 Sodium hydroxide               --           2
 Stibine                           0.1        0.5
 Stoddard solvent                500      2,900
 Strychnine                      --           0. 15
 cStyrene monomer (phenyl-
   ethylene)
  100
    5
1,000
  Sulfur dioxide
  Sulfur hexafluoride
  Sulfuric acid                   --
  Sulfur monochloride              1
  Sulfur pentafluoride               0.025
  Sulfuryl fluoride                  5
  Systox,  see Demeton
  2,4,5 T                        --
  Tantalum                       - -
  TEDP - skin                   --
  Teflon (R) decomposition
   products                      --
  Tellurium                      --
  TEPP - skin                   --
dl, 1, l,2-Tetrachloro-2,2-
   difluoroethane                500
  1,1, 2,2-Tetrachloro-l,2-
   difluoroethane                500
  1, 1, 2, 2-Tetrachloroethane-
   skin                           5
  Tetrachloroethylene, see
   Perchloroethylene
  Tetrachloromethane, see
   Carbon tetrachloride
 Tetraethyl lead (as Pb)-skin     --
 Tetrahydrofuran                200
 Tetranitromethane               1
 Tetryl (2, 4, 6-trinitrophenyl-
   methylnitramine)-skin         --
 Thallium (soluble compounds)-
   skin                          --
 Thiram                         --
 Tin (inorganic compounds,
   except  oxide)                  --
 Tin (organic  compounds)         --
 Titanium dioxide                --
 Toluene  (toluol)                200
cToluene-2, 4-diisocyanate         0.02
 o-Toluidine-skin                 5
 Toxaphene,  see Chlorinated
   camphene
 1, 1, 1-Trichloroethane, see
   Methyl chloroform
 Trichloroethylene              100
 Trichloromethane, see
   Chloroform
 Trichloronaphthalene-skin       --
 1, 2, 3-Trichloropropane         50
 1, 1, 2-Trichloro  1,2,2-tri-
   fluoroethane                1,000
 Triethylamine                  25
 Trifluoromonobromomethane  1,000
 2, 4, 6-Trinitrophenol see
   Picric  acid
 2, 4, 6-Trinitrophenylmethyl-
   nitramine,  see  Tetryl
                                                       420
                                                        13
                                                     6,000
                                                         1
                                                         6
                                                         0.25
                                                        20

                                                        10
                                                         5
                                                         0.2
                                                       A
                                                         0. 1
                                                         0. 05
                                                    4, 170

                                                    4, 170

                                                       35
                                                        0.075
                                                      590
                                                        8

                                                        1.5

                                                        0. 1
                                                        5

                                                        2
                                                        0. 1
                                                       15
                                                      750
                                                        0.14
                                                       22
                                                      535
                                                        5
                                                      300

                                                    7,600
                                                      100
                                                    6,100

-------
 942
                                   MISCELLANEOUS DATA
Substance
Trinitrotoluene -skin
Triorthocresyl phosphate
Triphenyl phosphate
Turpentine
Uranium (soluble compounds)
(insoluble compounds)
c Vanadium (V2O5 dust)
(V2O5 fume)
Vinyl benzene, see Styrene
°Vinyl chloride
ppma
--
--
--
100
--
--
--
--

500
mg/m3 b
1.5
0. 1
3
560
0.05
0.25
0.5
0. 1

1,300
Substance Ppma
Vinylcyanide, see Acrylo-
nitrile
Vinyl toluene 100
Warfarin
eXylene (xylol)
Xylidine-skin 5
d Yttrium
Zinc oxide fume
Zirconium compounds (as Zr)

mg/mj b


480
0. 1
-_
25
1
5
5

Radioactivity:  For permissible concentrations of radioisotopes in air,  see U. S. Department of Commerce,
National Bureau of Standards, Handbook 69,  "Maximum Permissible Body Burdens and Maximum Permis-
sible  Concentrations  of Radionuclides in Air  and in Water for Occupational Exposure, " June" 5,  1959.  Also,
see U.S. Department of Commerce National  Bureau of Standards, Handbook 59,  "Permissible Dose from
External Sources of Ionizing Radiation," September 24, 1954,  and addendum of April 15,  1958.

Note:  Footnotes to Recommended Values.
aParts of vapor or gas per million parts of air plus vapor by volume at 25 °C and 760 mm. Hg
 pressure.
"Approximate milligrams of particulate per  cubic meter of air.
clndicates a value that should not be exceeded.
d!966 addition.
eSee tentative limits.
 See A values on page 944.
 Substance
                               Respirable Dusts Evaluated by Count

                                        mp/ft3 a Substance
                                       mp/ft3 a
                                          250C
 Silica
  Crystalline
    Quartz, threshold limit calculated
     from the formula
  Cristobalite formula calculated           "
  Amorphous, including natural
   diatomaceous earth                     20
Silicates (less than 1% crystalline silica)
  Asbestos                                 5
  Mica                                    20
  Soapstone                               20
  Talc
  Portland Cement
Miscellaneous (less than 1% crystalline
  silica)d
Graphite (natural)
   "Inert" or Nuisance Par-
      ticulate s
   see Appendix D
20
50

50
                                                                                 50 (or 15 mg/m  which-
                                                                                 ever is the smaller)
                                                    Conversion factors
                                                       mppcf x  35. 3 = million particles per cubic meter
                                                                     = particles per c.c.
 Note: Footnotes  to Respirable Dusts Evaluated by Count.

 aMillions of particles per cubic foot of air,  based on impinger samples counted by light-field technics.
  The percentage  of crystalline silica in the  formula is the amount determined from air-borne  samples,
  except in those instances in which other methods have been shown to be applicable.

-------
                                       Threshold Limit Values
                                                                                                      943
                                           Tentative Values

These substances, -with their corresponding tentative limits, comprise those for which a limit has been
assigned for the first time or for which a. change in the  'Recommended' listing has been made.  In both
cases, the assigned limits should be considered trial values that will remain in the tentative listing for a
period of  at least  two years, during which time difinitive evidence and experience is sought.  If accept-
able at the end of  two years, these  substances and values will be moved to the RECOMMENDED list.
Documentation for tentative values  are available for each of these substances.
Substance
Acrylamide -skin
2 - Aminopyridine
sec-Amyl acetate
Azinphos -methyl-skin
Bromoform-skin
n-Butyl acetate
sec-Butyl acetate
tert- Butyl acetate
e sec -Butyl alcohol
Cadmium (metal dust and
soluble salts)
Carbon black
Carbon monoxide
ea-Chloroacetophenone
(phenacychloride)
o-Chlorobenzylidene malono-
nitrile (OCBM)
cChlorine
eChromium, sol. chromic,
chromous salts, as Cr
metallic and insoluble salts
Coal tar pitch volatiles (ben-
zene soluble fraction)
(anthracene, BaP, phenan-
threne, acridine, chrysene,
pyrene)
eCobalt, metal fume and dust
Crotonaldehyde
Cumene-skin
Cyclohexane
Cyclohexene
Diazomethane
cl, 2-Dibromo-ethane-skin
Dibutyl phosphate
dD ibutylphthalate
Diethylamino ethanol-skin
eDiis opr opylamine - s kin
Dimethylphthalate
eDiphenyl
E thy lam in e
Ethyl sec-amyl ketone (5-
methyl-3 -heptanone)
Ethyl benzene
Ethyl butyl ketone (3 -Heptan-
one)
Ethylene glycol dinitrate and/
or nitroglycerin-skin
Ethylene imine-skin

ppma
--
0.5
1Z5
--
0.5
150.
200
200.
150.

--
_-
50.

0.05

.05
1.

--
--




--
--
2.
50.
300.
300.
0. 2
25.
1.
--
10.
5.
	
0.2
10.

25.
100.

50.

0.02f
0.5

mg/m3 b
0.3
2
650
0.2
5
710.
950
950.
450.

0.2
3.5
55.

0.3

0.4
3.

0.5
1.




0.2
0. 1
6.
245.
1,050.
1,015.
0. 4
190.
5.
5.
50.
20.
5.
1.
18.

130.
435.

230.

O.lf
1.

Substance
cEthyl mercaptan
N-Ethylmorpholine-skin
Fibrous glass
Formic acid
eGasoline
sec-Hexyl acetate
eHexachloronaphthalene-skin
Iron oxide fume
Isoamyl acetate
Isobutyl acetate
elsobutyl alcohol
Isopropyl acetate
"Maleic anhydride
Methylamine
Methyl (n-amyl) ketone (2-
Heptanone)
Methyl iodide -skin
Methyl isocyanate-skin
Monomethyl hydrazine-skin
dNaphtha (coal tar)
eNitric oxide
eOctachloronaphthalene-skin
Oxalic acid
eParquat-skin
Phenyl ether (vapor)
Phenyl ether-Biphenyl mix-
ture (vapor)
dPhenyl glycidyl ether (PGE)
Pival (2-Pivalyl-l, 3-in-
dandione)
ePropyl alcohol
Propylene imine-skin
Rhodium, metal fume and
dusts
Soluble salts
eRonnel
Selenium hexafluoride
Tellurium hexafluoride
c> eTerphenyls
eTetrachloronaphthalene-skin
Tetramethyl lead (TML) (as
lead)-skin
Tetramethyl succinonitrile-
skin
Tremolite
eTributyl phosphate
1, 1, 2-Trichloroethane-skin
Xylene
eZinc chloride
ppma
10.
20.
--
5.
A6
50.
--
--
100.
150.
100.
250.
0.25
10.

100.
5.
0. 02
0. 2
100.
25.
—
—
--
1.

1.
10.

—
200.
2.

__
	
	
0.05
0.02
1.
--


0.5
mg/m3 b
25.
94.
5.
9.

300.
0.2
10.
525.
700.
300.
950.
1.
12.

465.
28.
0.05
0.35
400.
30.
0. 1
1.
0.5
7.

7.
62.

0. 1
450
5.

0. 1
0.001
15.
0.4
0.2
9.4
2.

0.075
3.
5 mppcf
--
10.
100.
—
5.
45.
435.
1.
   234-767 O - 77 - 62

-------
944                                   MISCELLANEOUS DATA
 Note: Footnotes to Tentative Values.
 aParts of vapor or gas per million parts of air plus vapor by volume at 25°C and 760 mm Hg pres-
  sure.
  Approximate milligrams  of particulate per cubic meter of air.
 ""Indicates a value that should not be exceeded.
  1966 revision.
 e!966 additions.
  For intermittent exposures  only.
                                            "A"  Values


 A   Benzidine.  Because of high incidence of bladder tumors  in man,  any exposure, including skin,  is
     extremely hazardous.

 A   j6-Naphthylamine.  Because of the extremely high incidence of bladder tumors in •workers handling
     this  compound and the inability to control exposures, /3-naphthylamine has been prohibited from
     manufacture,  use and other activities that involve human contact  by the State  of Pennsylvania.

 A   N-Nitrosodimethylamine.   Because of extremely high toxicity and presumed carcinogenic potential
     of this compound,  contact by any route should not be permitted.
  4
 A   Polytetrafluoroethylene* decomposition products.  Thermal decomposition of the fluorocarbon
     chain in air leads to the formation of oxidized products containing carbon, fluorine,and oxygen.
     Because these products  decompose by hydrolysis  in alkaline solution,  they can be quantitatively
     determined in air as fluoride to provide an index of exposure.  No TLV is recommended pending
     determination of the toxicity of the products, but air concentrations should be minimal.

 A   /3Propiolactone.  Because of high acute toxicity and demonstrated skin tumor production in animals,
     contact by any route should be avoided.

 A   Gasoline.  The composition of gasoline varies  greatly and thus a single TLV  for all types of gaso-
     line is no longer applicable.  In general,  the aromatic hydrocarbon content will determine what
     TLV applies.   Consequently the content of benzene, other aromatics and  additives should be de-
     termined to arrive at the appropriate TLV (Elkins, et al. , A. I. H.A. J. 24, 99, 1963).
 *Trade Names: Algoflon, Fluon, Halon,  Teflon,  Tetran

-------
       Enthalpies of Various Gases Expressed in Btu/lb of Gas
945
            Table D3.  ENTHALPIES OF VARIOUS GASES
                   EXPRESSED IN Btu/lb OF GAS
Temp,
°F
100
150
200
250
300
350
400
450
500
550
600
700
800
900
1,000
1, 100
1,200
1,300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
2, 100
2,200
2,300
2,400
2,500
3,000
3,500
C°2
5.8
17.6
29.3
40.3
51.3
63.1
74.9
87.0
99.1
111.8
124. 5
150.2
176.8
204. 1
231.9
260.2
289. 0
318.0
347.6
377.6
407.8
438.2
469. 1
500. 1
531.4
562.8
594.3
626.2
658.2
690.2
852.3
1,017.4
N2
6.4
20. 6
34.8
47.7
59.8
73.3
84.9
97.5
110. 1
122.9
135.6
161.4
187.4
213.8
240.5
267.5
294.9
326. 1
350.5
378.7
407.3
435.9
464.8
493.7
523.0
552.7
582.0
612.3
642.3
672.3
823.8
978.0
H20>
17.8
40.3
62.7
85.5
108.2
131.3
154.3
177.7
201. 0
224.8
248.7
297. 1
346.4
396.7
447.7
499.7
552.9
606.8
661.3
717.6
774.2
831.4
889.8
948.7
1,003. 1
1,069.2
1, 130.3
1, 192.6
1,256.8
1, 318. 1
1, 640.2
1,975.4
°2
8.8
19.8
30.9
42.1
53.4
64.8
76.2
87.8
99.5
111.3
123.2
147.2
171.7
196.5
221. 6
247.0
272.7
298.5
324.6
350.8
377.3
403.7
430.4
457.3
484. 5
511.4
538.6
566.1
593.5
621.0
760. 1
901.7
Air
9.6
21.6
33.6
45.7
57.8
70.0
82. 1
94.4
106.7
119.2
131.6
156.7
182.2
211.4
234. 1
260.5
287.2
314.2
341.5
369-0
396.8
424.6
452.9
481.2
509.5
538. 1
567. 1
596. 1
625.0
654.3
802.3
950.3
aThe enthalpies tabulated for H?O represent a gaseous system,  and
 the enthalpies do not include the latent heat of vaporization.  It is
 recommended that the latent heat of vaporization at 60°F (1, 059- 9
 Btu/lb) be used -where necessary.

-------
946
MISCELLANEOUS DATA
      Table D4.  ENTHALPIES OF GASES EXPRESSED IN Btu/scf OF GAS, REFERENCE 60°F
°F
60
77
100
200
300
400
500
600
700
800
900
1,000
1, 100
1,200
1,300
1, 400
1,500
1,600
1,700
1,800
1,900
2,000
2, 100
2,200
2,300
2,400
2,500
3,000
3,500
4, 000
4,500
5,000
5,500
6,000
6, 500
N2
-
0. 31
0.74
2.58
4.42
6.27
8. 14
10.02
11. 93
13.85
15.80
17.77
19.78
21.79
23.84
25. 90
27. 98
30. 10
32. 21
34. 34
36.48
38.65
40. 84
43. 00
45.24
47.46
49.67
60.91
72. 31
83.79
95.37
107. 04
118. 78
132.54
142.37
°2
-
0. 31
0. 74
2. 61
4. 50
6. 43
8. 40
10.40
12.43
14.49
16. 59
18. 71
20.85
23. 02
25.20
27. 40
29.62
31.85
34. 10
36.34
38. 61
40. 90
43. 17
45. 47
47. 79
50. 11
52. 43
64. 18
76. 13
88. 29
100. 64
113. 20
125.89
139. 74
151. 72
Air
-
0.32
0.74
2.58
4.42
6.29
8. 17
10.07
12.00
13.95
15.92
17. 92
19.94
21.98
24.05
26. 13
28.24
30.38
32.50
34.66
36.82
38.99
41. 18
43. 39
45. 61
47.83
50.07
61.39
72.87
84.42
96. 11
107. 91
119.78
131. 73
143. 76
H2
-
0. 31
0. 73
2. 55
4.40
6.24
8. 09
9.89
11.77
13.61
15. 47
17. 36
19.20
21. 08
22.95
24. 87
26.80
28. 70
30.62
32.52
34.45
36. 43
38.49
40. 57
42.66
44. 71
46.82
57.22
68. 14
79.38
90. 68
102.42
114. 21
126. 16
138.35
CO
_
0. 32
0.74
2. 58
4.43
6.29
8. 18
10. 08
12. 01
13.96
15. 94
17. 94
19.97
22. 02
24. 10
26. 19
28. 31
30. 44
32.58
34.74
36. 93
39. 12
41.31
43. 53
45. 74
47. 99
50.23
61.55
73.00
84.56
96.21
107. 93
119. 70
131. 52
143.37
CO2
-
0.39
0. 94
3.39
5.98
8. 69
11.52
14. 44
17.45
20.54
23. 70
26. 92
30. 21
33. 55
36. 93
40. 36
43. 85
47. 35
50.89
54. 48
58. 07
61. 71
65. 35
69. 02
72. 71
76. 43
80. 15
98. 96
118. 15
137. 62
157. 20
176. 93
196. 77
216. 77
236.88
H2Oa
_
0. 36
0.85
2.98
5. 14
7.33
9.52
11.81
14. 11
16.45
18.84
21.27
23. 74
26.26
28.82
31.42
34. 08
36.77
39.49
42.26
45. 06
47. 91
50. 78
53.68
56.64
59.59
62.60
77. 98
93.92
110.28
126. 96
143. 92
161. 07
178. 41
195.82
      Enthalpies are for a gaseous system, and do not include latent heat
      Lv =  1, 059. 9 Btu/lb or 50. 34 Btu/scf of H2O vapor at 60°F and 14.
                                 of vaporization.
                                 696 psia.

-------
                       Combustion Data Based on 1 Pound of Fuel Oil
                                                                                                  947
             Table D5.  TYPICAL PHYSICAL, PROPERTIES OF FUEL OILS
Pacific standard No.
Grade
Common name

T
y a
P n
i a
c 1
a y
1 s
i
s



S
P c
e a
c t
i i
f 0
i n
c s
Carbon '(C)
Hydrogen (H)
Sulfur (S)d
Water (H2O)
Other
(°Be')
Ib/gal
Sp gr 60°/60°
Approximate
Btu/gal
Appr oximate
Btu/lb

Max viscosity
Flash) Min
point) Max
Max water and
sediment
Max 10% point
Max 90% point
Max endpoint
PS No. 100
1
Kerosine
2
Distillate
84. 7%
15.3%
0. 02%
-
_
41.8°
6.83
0.82

136,000

19, 910
1
-
110°F
l65°Fa

0. 05%
420°F
-
600°F
2
-
125°F
190°Fa

0. 05%
440 °F
620°F
-
PS No. 200
3
Straight-run fuel oil
85. 8%
12. 1%
1.2%
-
0.9%
26.2°
7.50
0. 90

142,000

18, 950

45 sec (100°F)b
150°F
200°Fa

0. 1%
460 °F
675°F
-
PS No. 300
5
Low-crack fuel oil
87.5%
10.2%
1. 1%
0. 05%
1. 1%
16.5°
8
0.96

146,000

18,250

40 sec (122°F)C
150°F
-

1. 0%
-
-
-
PS No. 400
6
Heavy-crack fuel oil
88.3%
9.5%
1.2%
0. 05%
1.0%
8.9°
8.33
1

152,000

18,000

300 sec (122°F)C
150°F
-

2.0%
-
-
-
 Or legal maximum.
^Saybolt Universal.
cSaybolt Furol.
^Sulfur contents are only typical and will vary in different locales.
         Table D6.  COMBUSTION DATA BASED ON 1 POUND OF FUEL OILa> b- c
Constituent
Theoretical air
(40% sat'd at 60°F)
Flue gas
constitu-
ents with
theoret-
ical air
co2
SO2
N2
H,O formed
H2O (fuel)
H2O (air)
Total
Amount of
flue gas
with %
excess
air as
indicated:






0
7.5
10
12.5
15
17.5
20
30
40
50
75
100
SO2 % by vol and wt
with theoretical air
PS No. 100
ft3

197. 3
26.73
0.002
154.8
28.76
1. 367
211.659
211.7
226.5
231.4
236.4
241.3
246.2
251.2
270.9
290.6
310.4
359.7
409. 0
0.0011
Ib

15. 04
3. 104
0. 0004
11.44
1. 368
0. 0662
15.9786
15. 98
17. 11
17.48
17. 86
18.24
18.61
18.99
20.49
22. 00
23.50
27.26
31.02
0.0025
PS No. 200
ft3

185. 1
27.08
0. 142
145.2
22.75
1.283
196.455
196.5
210.4
215.0
219.6
224.3
228.9
233.5
252.0
270.5
289. 1
335.3
381.6
0.072
Ib

14. 11
3. 144
0.0240
10. 74
1.082
0.0621
15. 0521
15.05
16. 11
16.46
16.81
17. 17
17.52
17.87
19.28
20.69
22. 11
25.63
29. 16
0. 16
PS No. 300
ft3

179. 1
27.61
0. 130
140.5
19.18
0.011
1.242
188.673
188.7
202. 1
206.6
211. 1
215.6
220.0
224.5
242.4
260.3
278.3
323.0
367.8
0.069
Ib

13.66
3.207
0. 0220
10. 39
0. 9118
0.0005
0.0601
14. 5914
14.59
15.62
15.96
16.30
16.64
16.98
17. 32
18.69
20.05
21.42
24.84
28.25
0. 15
PS No. 400
ft3

177.2
27.86
0. 142
139.0
17.86
0.011
1.228
186. 101
186.0
199.4
203.8
208.3
212.7
217. 1
221.5
239.3
257.0
274.7
319.0
363.3
0.076
Ib

13.51
3.236
0.0240
10.28
0.8491
0.0005
0. 0595
14. 4491
14.45
15.46
15.80
16. 14
16.48
16.81
17. 15
18.50
19.85
21.21
24.58
27.96
0. 17
     aCombustion products calculated for combustion with air 40% saturated at 60°F. All volumes
      measured as gases at 60"F.  Moisture in fuel included where indicated.
     ^Maximum accuracy of calculations: 1:1,000.
     cBased on physical properties in Table D5.

-------
948
                                             MISCELLANEOUS DATA
                      Table D7.   COMBUSTION CHARACTERISTICS OF NATURAL  GAS
                                               Average analysis,  volume %a
                                                   C0
                             26
                            n-C4H10
                            V
                                                                   0
                                                                   5. 15
                                                                   0
                                                                  81. 11
                                                                   9.665
                                                                   3.505
                                                                   0. 19
                                                                   0.24
                                                                   0.09
                                                                   0.05
                                                                  100.00
                                               Average gross heat,  1, 1 00 Btu/ft

                                               Air required for combustion

                                               Theoretical - 10.360ft  /ft  gas
                                               20% excess air - 12. 432 £t3/ft3 gas

                                               Products of combustion/ft  of gas
                              Theoretical air
                                                                                20% excess air
                        Vol
                                                Wt
                                                                         Vol
                                                                                                 Wt
                 C02
                 H2°
               Total
 1. 134 ff3
 2.083
 8.236

11.453 ft3
0. 132 Ib
0. 099
0.609
                                            0.840 Ib
 1. 134 ftj
 2. 083
 9.873
 0.435
13. 525 ft3
0. 132 Ib
0. 099
0. 731
0. 037
0. 999 Ib
                Available heat,  Btu/ft  gas,a based on latent heat of vaporization of water at 60°F
                         Temp,  °F
                             Available heat, Btu,
                             with theoretical air
                                                                           Available heat, Btu, 20% excess air
100
150
200
250
300
350
400
450
500
550
600
700
800
900
1,000
1, 100
1,200
1,300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
2, 100
2,200
2,300
2,400
2,500
3,000
3,500
988.6
976. 1
963. 7
952. 1
941.0
928. 8
917.8
906.2
894.6
882.7
870.9
846.2
820.7
797. 7
772.6
747.2
721.3
693.0
668.6
642.7
614.6
589.8
562.3
534.8
507.5
478.7
450.7
421.9
393.0
364.6
219. 1
70.4
992.2
973. 0
958. 5
949.9
932.0
917. 8
905. 1
891.5
878.0
864. 1
850.4
821.8
792. 3
765.3
736.2
706.6
676.5
643.6
615.4
584.5
552.9
523.7
491.7
459.9
428.2
394.9
362.5
329. 1
295.6
262.6
94.2
--
                aAverage of two samples analyzed by Southern Calif.  Gas Co. ,  1956.

-------
           Conversion Table of Velocity (V) to Velocity Pressure (VP)
949
Table D8.  CONVERSION TABLE OF VELOCITY (V) TO VELOCITY PRESSURE (VP)
Velocity,
fpm
800
850
900
950
1,000
1,050
1, 100
1, 150
1,200
1,250
1, 300
1,350
1,400
1,450
1, 500
1,550
1,600
1, 650
1, 700
1,750
1,800
1,850
1,900
1, 950
2,000
2, 050
2, 100
2, 150
2,200
2,250
2,300
2, 350
2,400
2,450
2,500
VP at 70 °F
in. WC
0.040
0.045
0.051
0.056
0.062
' 0.069
0.075
0.082
0.090
0.097
0. 105
0. 114
0. 122
0. 131
0. 140
0. 150
0. 160
0. 170
0. 180
0. 191
0.202
0.213
0.225
0.237
0.249
0.262
0.275
0.288
0.301
0.316
0.329
0.344
0.359
0.375
0.389
VPat 60°F
in. WC
0.041
0.046
0.052
0.057
0.063
0.070
0.077
0.084
0.092
0.099
0. 107
0.116
0. 124
0. 134
0. 143
0. 153
0. 163
0. 173
0.184
0. 195
0.206
0.217
0.229
0.242
0.254
0.267
0.280
0.294
0.307
0.322
0.335
0.351
0.366
0.382
0.396
Velocity,
fpm
2,550
2,600
2,650
2,700
2,750
2,800
2,850
2,900
2,950
3,000
3,050
3, 100
3, 150
3,200
3,250
3, 300
3,350
3,400
3,450
3,500
3,550
3,600
3, 650
3,700
3,750
3,800
3,850
3,900
3,950
4,000
4,050
4, 100
4, 150
4,200
4, 250
VP at70°F
in. WC
0.406
0.421
0.438
0.454
0.472
0.489
0.507
0.524
0.543
0. 561
0. 581
0.599
0.618
0.638
0. 658
0.678
0.699
0. 720
0.742
0. 764
0.785
0.808
0.830
0.853
0.876
0.900
0. 924
0. 948
0. 973
0.998
1.022
1.049
1.073
1. 100
1. 126
VP at 60°F
in. WC
0.414
0.429
0.446
0.463
0.481
0.498
0.517
0.534
0.553
0.572
0.592
0.611
0.630
0.650
0.671
0.691
0.712
0.734
0.756
0.779
0.800
0.824
0.846
0.869
0.893
0.917
0.942
0.966
0.992
1.017
1.042
1.069
1.094
1. 122
1. 148
Velocity,
fpm
4,300
4,350
4,400
4,450
4,500
4,550
4,600
4,650
4,700
4,750
4,800
4,850
4,900
4,950
5,000
5,050
5, 100
5, 150
5,200
5,250
5,300
5,350
5,400
5,450
5,500
5,550
5,600
5,650
5,700
5,750
5,800
5,850
5,900
5,950
6,000
VPat 70°F
in. WC
1. 152
1.179
1.208
1.235
1.262
1.291
1.319
1. 348
1.377
1.407
1.435
1.466
1.496
1. 527
1.558
1.590
1.621
1.654
1.685
1.718
1.751
1. 784
1.817
1.851
1.886
1.919
1.955
1.991
2.026
2.061
2.098
2. 134
2. 170
2.207
2.244
VP at 60°F
in. WC
1. 174
1.202
1.231
1.259
1.286
1.316
1.344
1.374
1.403
1.434
1.463
1.494
1.525
1.556
1.588
1.621
1.652
1.686
1.717
1.751
1.785
1.818
1.852
1.887
1.922
1.956
1.993
2.029
2.065
2. 101
2. 138
2. 175
2.212
2.249
2.287

-------
950
                                      MISCELLANEOUS DATA
             Table D9.  DENSITIES OF  TYPICAL SOLID MATERIALS AS THEY OCCUR  IN
                      MATERIAL-HANDLING AND PROCESSING OPERATIONS
                                     Material
Densities,
  lb/ft3
Ashes, dry,  loose	 . . .  . „	        38
Ashes, wet,  loose	        47

Baking powder	        56
Bone,  ground, dry	,	        75
Borax		    105 to 110

Calcium carbide,  crushed
   3-1/2 in.  x 2 in. ,  loose	        77
   2 in. x 1/2 in. , loose	        75
   1/2  in.  x 1/8 in. ,  loose	        80
   1/8  in.  x 0 in. , loose	        82
Carbon, activated, very fine, dry	      8 to 20
Cement, Portland, loose	        94
Cement, Portland, clinker	        95
Charcoal,  broken, all sizes	     15 to 30
Charcoal,  broken, 1-1/2 in.  x  0 in	        14
Charcoal,  ground	        10
Chips,  -wood	        18
Cinders, blast furnace	        57
Cinders,  coal, ashes, and clinker	        40
Clay,  dry  in lumps, loose	        63
Coal,  anthracite,  broken, loose	„	     55 to 60
Coal,  bituminous, broken,  loose	     50 to 54
Coal,  bituminous, 5 in.  x 0 in. , dry	        54
Coal,  bituminous,  1/2 in. x  0 in. ,  dry	        45
Coal,  bituminous,  1/8 in. x  0 in. ,  dry	        43
Coke,  lump, average	     28 to 32
Coke,  breeze		     30 to 34
Coke,  petroleum, lump	     40 to 50
Cork,  solid	        15
Cork,  in bales .	      8 to 9
Cork,  ground, 10 in.  mesh x 0  in	      4 to 5
Gullet, glass,  average	     85 to 100
Gullet, glass,  3/4 in. x  0 in	     80 to 90

Dolemite,  crushed,  2 in. x 1/2 in	        94
Dolemite,  crushed,  1/2 in.  x 0 in	        98

Earth,  common loam, dry,  loose	        76
Earth,  common loam, moist, loose	        73

Feldspar,  broken, in loose piles	     90 to 100
Fluorspar, broken,  in loose piles	    110 to 125
Fluorspar, ground,  100 mesh x 0 in	     90 to 100
Flint,  pebbles	,	       105
Fullers Earth, dry	     30 to 35

Glass  batch	     90 to 110
Gniess, broken,  in loose piles	        96
Granite, broken,  in loose piles  	        96
Granite, crushed,  1-1/4 in.  x  10 mesh	        98
Gravel, mixed sizes,  loose	     96 to 100
Gravel, 2  in. x  1/4 in. , loose	    105 to 110
Gravel, 3/4 in. x  1/8 in. , loose	     98 to 100
Greenstone, broken, in loose piles	       107

-------
                                 Densities of Typical Solid Materials
       951
                                     Material
Densities,
   lb/ft3
Gypsum, broken,  in loose piles	     90 to 94
Gypsum, crushed, 1 in. x  0 in. ,  loose	        90
Gypsum, ground,  loose	     50 to 56

Iron (cast) borings, fine	    120 to 155
Iron ore,  loose	    125 to 150

Lime, hydrated, -200 mesh	     20 to 25
Lime, quick,  lump, 1-1/2 in,  x 0 in	     70 to 80
Lime, quick,  lump, 1/2 in.  x 0 in	        70
Lime, quick,  ground	     60 to 65
Lime, quick,  from oyster shells, loose	     45 to 50
Limestone, broken, in loose piles	        95
Limestone, sized 3 in. x 2 in. ,  loose   	        95
Limestone, sized, 2 in. x  1/2 in. ,  loose	        92
Limestone, sized, 1/2 in.  x  0 in. ,  loose	        96
Limestone, ground, -50 mesh,  loose	        84
Limestone, ground, -200 mesh,  loose	        65

Marble,  crushed	        95

Oyster shells, piled	        60
Phosphate  rock, broken,  in loose piles	     75 to 85
Phosphate  rock, pebble	     90 to 100

Quartz, broken, in loose piles	        94

Rubber,  shredded  scrap	        46

Salt,  coarse	     45 to 52
Salt,  fine	     42 to 50
Salt,  table	     42 to 45
Salt,  rock, broken, in loose piles	        50
Salt,  cake, coarse	     55 to 60
Salt, cake,  fine	     45 to 50
Sand, dry, loose	     90 to 95
Sand, wet, loose	    105 to 110
Sand and gravel, dry	     90 to 105
Sand and gravel, wet	    105 to 125
Sand, molding,  prepared and loose	     77 to 80
Sand, molding,  rammed	     90 to 100
Sand, molding,  shaken out or new  	       100
Sandstone,   broken, in loose piles  	     82 to 86
Sawdust, dry	      7 to 12
Scale, rolling mill	       105
Shale, crushed, in loose piles	        92
Slag,  bank, crushed	        80
Slag,  furnace, granulated	        60
Soda ash, dense	     60 to 62
Soda ash, light	     28 to 32
Soda, bicarbonate, loose	     50 to 58
Starch,  granular	     22 to 25
Stone, crushed, 1 in.  x 0 in	     85 to 105
Sugar, granulated, loose	     42 to 50
Sugar, brown	     45 to 55
Sulphur,  ground,  -100 mesh	     75 to 85
Sulphur,  ground,  -200 mesh	     50 to 55

Trap  rock, broken, in loose piles	       107
Trap  rock,  crushed	     95 to 105

-------
952
                                             MISCELLANEOUS DATA
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Concentrations  of Materials in the  Air
953
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-------
954
                                              MISCELLANEOUS DATA





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UltramicfOSC
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MICIOSCO
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6
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13, 19
Permeability
9 11 17
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2,5
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15.21
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                                                                                                	«• PARTICLE SIZE LIMITS
                                                                                                 UNDER AVERAGE CONDITIONS
                                                                                                 	». STATED METHOD IS OF
                                                                                                  DOUBTFUL UTILITY IN THESE
                                                                                                  SIZE RANGES
                                                                                               VARIATIONS IN THE LIMITS OF EACH
                                                                                               METHOD ARE POSSIBLE DEPENDING
                                                                                               ON THE QUALITY OF THE INSTRUMENT
                                                                                               SKILL Of THE OPERATOR ETC
                                                                                           Note:  The  numbers in Figures
                                                                                           D2 and  D3  represent bibllog-
      oooos oooi     0005001      005 oi      05  i        5  10       so  ioo       500 1,000     5,000 10,000 raphy  references that can  be
                                      PARTICLE SIZE (Microns)                 CONVENTIONS              furnished  upon request.

              Figure D2.  Limits of  particle size-measuring  equipment  (Issued  as a  public  service
              by  Mines  Safety Appliances  Co.,  201  N.  Braddock Ave.,  Pittsburgh, Pa.   Prepared  by
              Southwest Research  Institute.).
H,0-NH


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Tobacco
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CONVENTIONS
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Small Range-Average
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22,24

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lents 
-------
                          The Frank Chart
                                                                                    955
DIAM.
OF
PAR-
TICLES
IN
MIC80W
8000
6000
4000
2000
1000
800
600
400
200
100
&0
60
40
20
10
8
6
4
2
1
.8
.6
.4
.2
.1
.01
.001
US.
ST'D
MESH
10-
20-
60-
100-
isn-
200-
250-
325-
soo-
IOOIH
SCALE OF
ATMOSPHERIC IMPURITIES







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-------
956
MISCELLANEOUS DATA
                            Figure D5.  Range of particle  sizes,  concentrations, and
                            collector  performance (Compiled by S. Sylvan,  April 1952-
                            Copyright,  1952,  American  Air  Filter Co.,  Inc.,  Louisville,
                            Ky.).
                                                          P5YCHROMETRIC  CHART  FOR HUMID AIR
                                                                EASED ON ONE POUND DRY WEIGHT
                                                                  AMERICAN AIR FILTER CO INC
                                                                       LOUIS
                              IOO    200    3OO    40O   SOO   «OO   TOO   BOO   »OO   IOOO  MOO   L2OO  130O  MOO liOC
                                                DRY BULB TEMPERATURE-DEGREES F
                      Figure D6. Psychrometric chart  for  humid air based  on 1  Ib
                      dry  weight.  (Copyright,  1951,  American Air Filter  Co.,  Inc.,
                      Louisville, Ky.).

-------
        High-Temperature Psychrometric Chart
                                                  957
o
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                                                                      CO

-------
958
           MISCELLANEOUS DATA
                                                                              o
                                                                              >

                                                                              bJJ
                                                                              Q_




                                                                              00
awnioA   A9
                                             HO«IVA

-------
            APPENDIX E:  EMISSION  SURVEYS,  INVENTORIES,  AND FACTORS
INTRODUCTION

The compilation of air burden estimates is an
important tool in assessing an air pollution prob-
lem.  Used in conjunction -with air monitoring
data,  the emission inventory is instrumental
in suggesting direction for a remedial program.
In the event that a multiphase program is required,
the emission survey serves to bring the problem
into focus and thereby helps to set priorities for
planning for  clean air.  With the publication of
air quality criteria for specific  contaminants and
the subsequent promulgation of ambient air quality
standards, local or regional agencies must set
and enforce emission standards consistent with
the goals delineated by these air quality stand-
ards.  Emission data from surveys,  when com-
piled into emission inventories, provide some of
the information needed to develop plans for the
attainment of realistic emission  standards.

VALUES  OF SURVEYS

Primarily, emission surveys reveal the identity
of air contaminant emitters, the contaminants
emitted, the  quantity of contaminants emitted,
the periods of emissions,  and the location of
emitters.  In brief, surveys reveal the "who,"
"what, " "how much, " "when, " and the 'Where"
of emissions.

From these basic inputs, it is possible to estimate
contributions to local air pollution problems  by
activity, industry, operation, and  specific con-
taminant or species of contaminant.  Variations
in emissions with time of day, season, and geo-
graphic location also may be learned from the
data.  Emission survey data, when processed,
can serve to  evaluate the progress made by a
control program,  the areas requiring additional
control emphasis,  and the effort required for fur-
ther control  progress.  These evaluations, in
turn,  can guide in the adoption of new legislation
and revision  of existing legislation as more
effective control methods become available.

Information gathered by emission surveys pro-
vides the technical basis for drawing the line in
legislation between sources to be controlled and
sources for which control will not be significantly
productive or is not feasible. Emission surveys
can reveal the number of sources of  air pollution
to be affected by proposed legislation,  the emis-
sions from those sources, and the effect of the
legislation on those emissions.   Testifying as to
the extent of  current air pollution emissions,
nuisance potentials, relationships of emissions to
the overall air pollution problem, control methods
or control devices  currently in use,  controls
available to meet proposed emission standards,
and the feasibility of control also are facilitated
by emission survey data.

In combination with air monitoring data,  emission
estimates from emission surveys may give clues
to reactions occurring in the atmosphere involving
primary air contaminants.  These reactions
might explain the presence in the atmosphere of
certain substances or their presence in concen-
trations greater than expected on the basis of
their direct emissions into the atmosphere. Con-
trol action then can be directed towards the pri-
mary contaminant or contaminants responsible
for the  unexpected  presence of other substances.

A study of contaminants emitted at one geographi-
cal location, the prevailing wind flow patterns,
and air pollution effects detected at downwind
locations can contribute to an understanding of
the formation and transport of air pollution.  By
a study of emission data, atmospheric  concentra-
tions,  and influential meteorological factors,
proper  relationships may be established between
emission source areas  and air pollution effect
areas.   These relationships then may serve to
justify imposition,  by appropriate legislation,  of
controls on the emission sources.  An  understand-
ing of the relative importance of control measures
and weather conditions  to air  quality may be
helped by expanded studies of emissions originating
from specific areas and air pollution effects down-
wind of the sources.

Evidence provided  on hourly,  daily, monthly,  and
yearly emissions helps in the understanding of
diurnal, seasonal,  and  annual emission variations.
Knowledge of  seasonal changes in emissions may
help explain the variation of atmospheric contami-
nant concentrations and the occurrence of air
pollution effects during certain periods of the day
or year and not during other periods.  Conversely,
knowledge that emission rates have remained
essentially unchanged may point out the relative
importance of meteorological factors when air
pollution effects are inconsistent with the emis-
sion rates.


NEED FOR CONTINUING SURVEYS

Emission surveys must be a continuing activity
because the geographical areas affected by pollu-
tion expand and the pollution generated is changed
                                                959
  234-767 O - 77 - 63

-------
960
EMISSION SURVEYS, INVENTORIES, AND FACTORS
in quality and quantity with population growth,
industrial growth, commercial growth,  and
changes in technology.   This growth and changed
technology may offset gains made by control pro-
grams in reducing air pollution and, in  time,
pollution levels may increase to or beyond levels
existing before control measures -were adopted.
Continuing emission surveys are needed to give
advance warning of such trends so counteractions
may be planned.

Alterations in basic fuel mixtures  change  the
quality and quantity of emissions from fuel com-
bustion equipment.  Because of the ubiquity and
sheer number of fuel combustion equipment and
fuel quantities used, these changes are  reflected
in overall air pollution problems.  New refining
and chemical processes may create products with
higher volatilities or with other  properties •which
will increase emission rates. Fractional increases
in sulfur contents of gasoline and oil fuels in mass
use may result in sulfur dioxide problems and
visibility problems.  Other new  raw materials  or
new products may be more dusty,  more odorous,
more radioactive, or more photochemically re-
active and generate new or more air pollution.
The higher standard of living enjoyed and  sought
by  more  people increases the amount of waste per
person, the amount of fossil fuels  burned  per
person, and the amount of manufacturing  and other
pollution-producing activities associated with the
higher standard of living.  There also may be
changes in the other direction  from the  effect of
control measures which may be  preventing emis-
sions. All the above possibilities  for changes in
the overall air pollution picture  bring on obso-
lescence of emission data and  make updating of
emission surveys a necessary activity.

CONDUCTING  THE  SURVEY

Surveys may be made by mailing questionnaires,
personally interrogating emission  source  opera-
tors, or, in some cases,  by researching  litera-
ture and records.  Generally, surveys are
aimed at discovering fuels usage,  raw materials
usage, processes and equipment employed, pro-
duct quantities, operating schedules,  number and
identity of sources,  controls in use, control
efficiencies,  etc. Emission factors,  relating
emission rates to an easily measurable quantity,
can be used to convert the survey data into emis-
sion estimates.  If emission factors are not
available,  source tests  must be  made to identify
the contaminants and quantities emitted.  The
measurable quantities used with emission factors
may relate to type and quantity of fuel used,
materials charged, or product quantities
produced.

Values of emission factors for various  source
equipment,  processes,  or operations sometimes
                             can be found in the literature.  The circumstances
                             under which these factors were determined must
                             be examined to determine their suitability for the
                             specific equipment or processes being surveyed.
                             Application of these factors must be made cau-
                             tiously  because the local situation may not be
                             comparable to the situation for which the factors
                             •were determined.  For example,  the given emis-
                             sion factor may have been determined for equip-
                             ment equipped 'with a specific control device or
                             for a certain operating mode not consistent with
                             the equipment or process being surveyed. Simi-
                             larly, source testing data for other than the  spe-
                             cific  equipment or process being  surveyed must
                             be applied with caution.  If the source testing
                             data are furnished by the firm or organization
                             responsible for the emission,  the local agency
                             should evaluate the sampling and testing proce-
                             dures for validity and acceptability and,  if possi-
                             ble, have an observer present during the source
                             test.

                             SOURCES OF SURVEY INFORMATION

                             Literature research may show how, when, -where,
                             and by whom similar surveys have been  done.
                             Literature research also may provide valuable
                             assistance by reporting source testing results of
                             health departments, research organizations, com-
                             mercial laboratories, other agencies, and indus-
                             tries.  Valuable information also may be found in
                             publications of chambers of commerce,  govern-
                             mental  agencies, research organizations, and
                             scientific groups.  This information may include
                             new and existing industry listings, population
                             growth  statistics, area distribution of population
                             and industry, vehicle registration,  fuel usage, and
                             product quantities.  This can be supplemented -with
                             data from utilities, industrial associations,  and
                             individual  companies.
                             DETAILED VERSUS  "SHORTCUT" SURVEYS
                             Cost and time are important considerations in
                             making surveys,  and careful planning is a must
                             in order to get a maximum return from the sur-
                             vey dollar.  In most cases where many sources
                             are to be surveyed, time and cost considerations
                             rule out surveys made by personal interrogations.
                             Although detailed surveys provide extensive in-
                             formation, some  of the information falls in the
                             category of "nice to have for future possibilities. "
                             However,  the collection of data not necessary to
                             the  specific goals of the survey •will result in
                             higher expenditures of time and money.

                             It is not always necessary to survey every source
                             in the category of industry, operation, or  contami-
                             nant being  studied. Evidence is sometimes avail-
                             able to show that the emissions from  the larger

-------
                                        Elements of a Survey
                                            961
sources constitute essentially all the emissions
from the category under study.  In these cases,
a "short-cut" survey, consisting of a detailed
check of the large sources and approximations
for small sources, may achieve the  goals of the
survey.  Most emission surveys need not be all-
inclusive with respect to the very small sources
or to tabulating contaminant emissions  down to the
last pound.  Disproportionate  concern with a few
installations or even many installations emitting
minor quantities of contaminants and having an
insignificant effect on the  final results is not
justified.

Reasonably accurate emission estimates can be
made for multiple sources such  as transportation,
heat and power production, and waste incineration
by considering them  on a collective rather than an
individual basis.  Quantities of fuels burned and
waste incinerated can be combined with existing
data on products of combustion for aggregate
emission estimates of those multiple sources.
In an organic  solvent survey,  it  may be possible
to contact a relatively few suppliers of  solvents
for easier  and quicker results than to contact the
many users.  Many times  a "short-cut" survey
method can supplement or  spot check a more
thorough survey.

ELEMENTS OF  A  SURVEY

After the decision has been made to  conduct an
emission survey and the objectives have been
outlined, the  survey  process  can be divided into
the following elements:

  1.  Developing a list of surveyees,

  2.  developing a list of suitable emission factors
     including an evaluation of their applicability,
     or planning a source  testing program to
     obtain the emission factors,

  3.  determining  and phrasing appropriate ques-
     tions,

  4.  designing effective questionnaires,

  5.  developing explanatory transmittal letters,

  6.  transmitting the questionnaires to the
     surveyees,

  7.  treating  and  evaluating the  data, reporting
     results,  and recommending action.

Developing a  List  of  Surveyees

A list of potential surveyees may be developed
from several  sources by exercising ingenuity
and initiative.  In some cases, a list may have
to be used which is not too accurate or complete
but does cover most of the emission sources
involved, or the important ones.  Lists compiled
by chambers of commerce, industrial associa-
tions,  telephone companies, fire  departments,
business licensing agencies, building departments,
tax offices, planning  commissions, and industrial
waste  departments are useful starting points.

A general review  of contaminants usually emitted
from various activities also may  assist in develop-
ing a list of surveyees.  For example, smoke
particulates and fumes are among the contami-
nants produced by activities involving combustion,
metal melting, transportation,  and incineration.
Gaseous contaminants such as hydrocarbons are
produced by activities involving vaporization and
decomposition in chemical and  manufacturing pro-
cesses.  Gasolines, solvents,  and other materials
•with high vapor pressures will  evaporate into the
atmosphere at ambient atmospheric temperatures
and pressures.  Carbon monoxide and nitrogen
oxides are common to combustion processes, and
nitrogen oxides to high temperature processes in
general.  Sulfur dioxide is emitted from combus-
tion of high sulfur fuels and from sulfur  and sul-
furic acid plants.   Dust and mists are dispersed
into the atmosphere from mechanical attrition pro-
cesses such as crushing, grinding, drilling, de-
molishing, mixing, batching, blending, sweeping,
sanding, cutting,  pulverizing,  spraying, and atom-
izing.   Electrical power generation, municipal
incineration, and  sewage treatment and disposal
constitute large single point sources of air pol-
lution.  Salvage operations such as  removing in-
sulation from wire or combustibles from junked
cars by fire may involve smoke and local nuisance.
Odorous contaminants result from decomposition
processes  of organic materials or animal tissues
containing  nitrogen and sulfur compounds.  Sewage
and industrial waste treatment  plants, stockyards,
hog farms,  rendering plants,  fish canneries,  tan-
neries, refineries, and chemical plants  are among
the many activities which produce malodors.

Each industry or activity presents its own air pol-
lution problem in  terms of emissions of smoke,
fumes, dusts, mists,  vapors,  or gases.  This is
true not only for manufacturing industries indivi-
dually, but also for private households and  serv-
ice activities collectively.  Transportation, tele-
communications,  retail and -wholesale trade,
finance, insurance, real estate, hotels,  motels,
schools, governmental facilities, repair services,
laundries,  entertainment, salvaging,  and dumping
are examples of service activities.   The air pollu-
tion from these service activities derives mainly
from fuel combustion for space and water heating,
incineration of rubbish, and combustion  of gaso-
line for transportation of people and supplies.

The sources of emission in service activities  are
mostly small and usually are dispersed throughout

-------
962
EMISSION SURVEYS, INVENTORIES, AND FACTORS
the community. In some instances, these small
sources may constitute the majority of emissions
because of their preponderance in the population.
The extensive use of organic solvents in dry
cleaning,  printing, degreasing, and in the appli-
cation of protective  coatings from service type
activities results in widespread solvent vapor
emissions.

An essential survey for  any community  is that of
fuel usage.  Consumption rates of fuels may be
secured from individual users or from fuel sup-
pliers.  In some communities, fuel suppliers can
furnish information  on fuels used for commercial
and residential heating and for small industrial
plants.  For railroads,  fuel use in a given area
may be estimated  from mileage records and other
information on train movements and fuel consump-
tion per mile of travel.  In addition to securing
data on consumption of fuel,  fuel compositions
also should be  solicited, particularly with res-
pect to sulfur contents and ash contents.

A  complete emission inventory should consider
as many  of the preceding activities and  industries
as possible. The  compilation should include
surveys of industrial, public, commercial, and
private activities with assessment of both sta-
tionary and mobile sources.

Since the use of air  pollution controls alters the
emission quantities, data on control efficiencies
should be incorporated into the emission esti-
mating process.  Housekeeping and maintenance
practices should be  checked  so that emission
factors or estimates can be adjusted to  reflect
sloppy or exceptionally good practices.
Developing Emission  Factors

Emission factors can be found in the literature,
but care must be excercised in using them.  The
emission factors in  Table El were determined
by measuring the contaminants discharged from
processes and equipment operating in Los Angeles
County.   These  factors may not apply to similar
operations in other areas.  For example, the
combustion factors for fuels depend upon the type
of fuels burned and the type of boilers or heaters
in which they are burned.  The composition of
natural gases, manufactured gases, and fuel oils
varies from  one locality to another , and  emission
factors must be determined for the fuels being
used in the locality being surveyed.

To use the factors presented,  it is necessary  to
compare the  operations in Los Angeles  County to
those in the locality under study.   If the  operations
and raw materials are  not similar, a testing pro-
gram is needed  to obtain proper emission factors.
                            Determining and  Phrasing Appropriate Questions
                           The questions to solicit information from the
                           surveyee must be phrased in a vocabulary under-
                           standable to the surveyee.  To accomplish this,
                           the engineer  conducting the survey should be
                           familiar with the operations of the sources being
                           surveyed or become familiar by studying reports
                           and other literature on the subject.   Terms
                           should be used in the questions  that are commonly
                           understood by the surveyee. If special terms are
                           used, they  should be defined for the  surveyee.
                           Units or dimensions for expressing data must be
                           stated clearly and definitely for the surveyee.  A
                           sample questionnaire form which has been filled
                           out can be helpful to the surveyee in  completing
                           his questionnaire.

                           Without any question, the best assurance of  a
                           good response to a  survey is the legal authority
                           of the surveying agency to require the survey  in-
                           formation,  but other factors also are very impor-
                           tant.  These other factors include an appropriate
                           transmittal letter,  explicit instructions,  sample
                           questionnaire form, good form design, and follow-
                           up letters or  visits  -when response is lacking,

                           Designing  Effective  Questionnaires

                           A good questionnaire form design can reduce work
                           for the surveyee and for the surveying agency in
                           extracting data.  The mental attitude of the  sur-
                           veyee and his degree of response can be affected
                           by the appearance of the questionnaire form as
                           well  as the length.  Whenever possible, design
                           the questionnaire form to fit in  the average type-
                           writer and  -with proper line spacing for the average
                           type-writer.  This will make entry of data easier
                           for the surveyee.  The type face and style for the
                           form should be selected for easy reading but -with
                           the proper  weight and blackness so that the data
                           entered can be seen and extracted more easily.
                           The weight and blackness of lines used to separate
                           questions or groups of questions must also be
                           selected carefully to yield a good appearance and
                           facilitate use of the form by the  surveyee.

                           The questions on the drafted questionnaire form
                           should be checked carefully for clarity and lack
                           of ambiguity.   Consideration during the design
                           stages of the questionnaire form should be given
                           to the possibility of using automatic data process-
                           ing.   If this can be  done,  then the design of the
                           form should make abstraction of the data conven-
                           ient.  Questions  should be as  short as possible
                           but compatible with intelligibility.  The units or
                           dimensions to be used for numerical data should
                           be specified.  It is  important to  require that the
                           form be signed by a responsible company official
                           who  can be accountable for the data.  He must be

-------
       Emission Factors
963
Table El.  EMISSION FACTORS
Source
Combustion of fuels
Fuel oils
Power plants
California crude
Indonesia crude
Alaskan crude
Refineries
Other industries
Commercial and domestic
Natural gas
Power plants
Refineries
Other industries
Commercial and domestic
Petroleum refineries
Cooling towers
Compressor exhausts
Pressure relief valves
Catalytic cracking
Fluid
Controlled6
Thermofor
Valves and flanges
Pump seals*
ControlledS
Loading racks
Controlled"-
Slowdowns, turnaro\mds,
vessel and tank maintenance
Controlled11
Treating
Controlled11
Vacuum jets
Controlled1
Separators and sewers
Controlled^
Filling service station tanks
Controlled^
Filling automobile tanks
Incineration
Open burning!
Single chamber0-1
Multiple chamber11
Metallurgical
Aluminum furnaces
Crucible
Controlled0
Reverberatory
Controlled0
Sweating
Controlled0
Chlorination
Controlled?
Emission factor units



lb/103 equivalent bblb
lb/103 equivalent bbl
lb/103 equivalent bbl
lb/103 equivalent bbl
lb/103 equivalent bbl
lb/103 equivalent bbl

lb/103 equivalent bbl
lb/103 equivalent bbl
lb/103 equivalent bbl
lb/103 equivalent bbl

lb/10 gal. cooling water
lb/103 ft3 fuel burned
Ib/day/valve

lb/103 bbl of feed
lb/103 bbl of feed
lb/103 bbl of feed
lb/103 bbl crude capacity
lb/103 bbl crude capacity
lb/103 bbl crude capacity
lb/103 bbl loaded
lb/103 bbl loaded
lb/103 bbl crude capacity

lb/10 bbl crude capacity
lb/103 bbl crude capacity
lb/10 bbl crude capacity
lb/103 bbl crude capacity
lb/103 bbl crude capacity
lb/103 bbl crude capacity
lb/103 bbl crude capacity
lb/103 gal. delivered
lb/103 gal. delivered
lb/103 gal. delivered

Ib/ton refuse
Ib/ton refuse
Ib/ton refuse


Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton chlorine

Emission factors'1
HC



210
210
210
500
127
112

73
102
42
N

6
1. 2
3. 5

191
N
79
28
125
20
150
2
25

5
8
2
150
0
270
8
11.5
7. 2
15.6

45
22
4










NOX



5000
1500
1500
3200
3360
3060

2340
1009
1285
696


0.9


52
52
6


















3.9
3.9
3










Partic-
ulates



800
50
250
821
839
593

90
126
105
112





49
N
12


















16
22
4


1.9
0.2
4.3
1. 3
32. 3
3. 3
1000

SO2



11500
800
1800
7000Sd
7000S
7000S

N
2. 5
2. 5
2. 5





449
449
37


















2. 8
2. 8
2. 8










CO



Nc
N
N
N
6. 5
N

N
25
2. 4
2. 4


N


2
N
18


















85
30
3











-------
964
EMISSION SURVEYS, INVENTORIES,  AND FACTORS
                            Table El  (continued).  EMISSION FACTORS
Source
Metallurgical (continued)
Brass furnaces
Crucible
Controlled0
Electric induction
Controlled0
Reverberatory
Controlled0
Rotary
Controlled0
Iron furnaces
Cupola
Controlled^
Electric induction
Controlled0
Reverberatory
Controlled0
Lead furnaces
Cupola
Controlled0
Pot
Controlled0
Reverberatory
Controlled0
Magnesium furnaces
Pot
Steel furnaces
Electric arc
Controlled0
Electric induction
Open hearth
Controlledr
Zinc furnaces
Pot
Controlled0
Sweat
Controlled0
Calcine
Controlled0
Sand handling0
Core ovens
Core machines
Coffee processing8
Roasters
Indirect fired
Controlled
Direct fired
Controlled'-
Final cleaning system
Controlled
Mineral
Hot asphalt plants
Controlledu
Hot asphalt saturators
Controlledr
Emission factor units


Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged

Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged

Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged

Ib/ton metal charged

Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged

Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton metal charged
Ib/ton calcine charged
Ib/ton calcine charged
Ib/ton sand handled
Ib/ton cores
Ib/ton cores


Ib/ton green beans
Ib/ton green beans
Ib/ton green beans
Ib/ton green beans
Ib/ton green beans
Ib/ton green beans

Ib/ton product
Ib/ton product
Ib/ton product
Ib/ton product
Emission factorsa
HC





















































3.8
0.7
NOX























































Partic-
ulates


3.9
0.7
3.0
0.6
26. 3
1. 8
20. 9
1. 5

17.4
2.7
2
1.6
2
1.6

300
5. 1
0. 1
0. 01
154
1. 4

4.4

15
1.4
0. 1
10. 6
0. 5

0. 1
0. 01
10. 8
0.4
89
1
0. 3
1. 3
0.4


5
1.2
8
2. 2
1. 3
0.4

10.4
0. 2


SO2


















63. 8
57. 5


149
129































CO











247
7.7











































-------
              Treating and Evaluating the Data, Reporting Results, and Recommending Action
                                                                                                965
                               Table El (continued).   EMISSION FACTORS

Source
Mineral (continued)
Glass furnaces
Frit furnaces
Controlled

Emission factor units
Ib/ton product
Ib/ton product
Ib/ton product
Emission factorsa

HC


NOX

Partic-
ulates
3.4
9.4
0.2

S02


CO

 J
 1
 HC =  hydrocarbons and other organic gases.  NOX = oxides of nitrogen measured as nitrogen dioxide.
 SO2 = oxides of sulfur measured as sulfur dioxide. CO = carbon monoxide.

 An equivalent barrel is that amount of fuel equal in heating value to a fuel oil of 10 API gravity weigh-
 ing 350 pounds per barrel and having a heating value of 6, 300, 000 Btu.  Approximately 6, 000 standard
 cubic feet of natural gas is equal to an equivalent barrel.
Q
 N  = negligible.

 S = percent sulfur by weight.
^
 Catalyst dust was controlled -with a precipitator.  The HC and CO were controlled with a waste heat
 boiler.

 Pumps -were sealed with packed glands.
or
 Mechanical seals were used on pumps in light hydrocarbon service.

 Vapor recovery or disposal systems.

 Condensation and incineration of noncondensibles.

 Separators were either covered or had floating roofs.

 Submerged fill tubes.

 HC, particulate,  and CO based on burning of municipal refuse in Cincinnati, Ohio, prior to 1967
 (Gerstle  and  Kemnitz, 1967).

 Burning household refuse in Los Angeles, 1950.

 Burning commercial and industrial refuse in Los Angeles, 1964.

 Controlled with a baghouse.

 Particulates  controlled with baghouse, chlorine and hydrogen chloride controlled with packed scrubbers
 irrigated with caustic  solution.

 CO controlled with afterburner, particulates with baghouse.

 Controlled with electric precipitator.

 From Loquercio,  1967.

' Controlled with cyclone.

 Controlled with scrubbers.
informed as to where the completed questionnaire
should be sent and whom to contact in the surveying
agency if he has questions about the questionnaire.
Since it is  rare for all surveyees to respond to
questionnaires, the agency conducting the survey
must be prepared to follow up the original request
for data by additional contacts.   In some cases,
personal interrogation must be  used to supplement
the mail type of emission survey.
                                                     Treating and Evaluating  the  Data,  Reporting

                                                     Results,  and  Recommending  Action

                                                    Survey data must be evaluated and digested to
                                                    obtain its meaning and significance.  The infor-
                                                    mation must be translated into language useful
                                                    to those responsible for planning the control pro-
                                                    gram.  Treatment of the data includes  tabulating,

-------
966
           EMISSION SURVEYS, INVENTORIES, AND FACTORS
card punching, graphing, and calculating.  The
reduction of the data to a workable form is a
laborious task, especially where a large number
of sources are being surveyed.  Technical per-
sonnel assigned to this portion of the survey
should be thoroughly trained to under stand the
operating details of the sources  involved in the
survey.

After emission estimates have been  prepared,
they should be presented in a form that easily
answers questions of the control program planning
                                       group.   There are many such questions of concern,
                                       such as  geographical distribution of contaminants,
                                       seasonal distribution, daily distribution,  trends,
                                       etc. , which can be  shown on various charts,
                                       tables,  and graphs.   Examples of some of these
                                       data presentation methods are shown in Table
                                       E2 and  Figures El  and E2.  Table E2  shows  an
                                       air quality profile of air contaminant emissions
                                       in Los Angeles County.  Figures El and E2
                                       depict the trends  in the emissions of oxides of
                                       nitrogen and hydrocarbons  and other organic
                                       acids from 1940 to  1990.
   s
   I/)
   g
   LU
   CO
   a
   x
   o
      1200
      1000
       800
       600
       400
       200
              NATURAL GAS
            SUPPLY INCREASED
    DECREASED BY RULE 62       ^% —
         _OTHER_^	
        J	I	I	
                                                             3500
                                                             3000
                                          g 2500
                                          CO
                                          a:
                                          o
                                                          o
                                                          a
                                                             2000
                                   o  1500
                                   CO
                                   a:
                                   cj
                                   o
                                   ce
                                   |  1000
                                                             500
                                                          MOTOR VEHICLES
                                                    PETROLEUM
                                                     INDUSTRY
                                                                                       "*•••••• • "^ ••• »*•*••
        1940
1950
1960    1970
   YEAR
                                      1980
                              1990
1940
                                                                       1950
1960     1970
   YEAR
1980
1990
   Figure El.   Oxides of  nitrogen — emissions from all
   sources in  Los Angeles County.
                                          Figure E2.  Hydrocarbons and other organic gases--
                                          emissions from all  sources  in Los Angeles County.

-------
              Treating and Evaluating the  Data, Reporting Results, and Recommending Action
967
                Table E2.  AIR QUALITY PROFILE  OF AIR CONTAMINANT EMISSIONS
                                LOS ANGELES  COUNTY  -  JANUARY 1971a
Sources
Stationary
Industrial
Chemical
Metallurgical
Mineral
Petroleum
Other
Power plants
Commercial
Residential
Total stationary
Mobile
Motor vehicles
Gasoline powered
Diesel powered
Aircraft
Total transportation
Grand total
Emissions it tht-rt- virrr
program, tons/c
Hydrocarbons
Total


155
5
10
1495
325
15
110
220
2335


2620
10
85
2715
5050
Reac-
tive


80

-
170
195
-
55
110
610


1935
-
30
1965
2575
MO


25
25
15
1 30
5
305
K
50
590


565
15
15
595
1185
Par-
tlt U-
lau-b


50
125
140
15
25
45
40
1 10
550


60
10
15
85
635
no i out i ol
bO


17,5
45
15
1 (20
15
490
35
50
2145


35
-
5
40
2185
CO


10
180
-
16i5
30
-
55
190
2120


12175
15
135
12325
14445
1 mini iiini pri'M nli d JH I hi- result tit

TDI..I


50
5
10
1200
85
10
55
155
1570


1010

5
1015
2585
Ki-.u -
u\ i-


•t,=,
-

i in
140
-
45
'.5
455


765
-
-
765
1220
MO


15
10
5
J5
5
205
10
25
ilO


-175


-175
135
P.ir-
lll u-


40
115
1 i5
5
20
40
)0
105
490


15


15
505
^


60
40
15
1265
15
455
35
50
1935



-


1935
CO


to
175

1630
30
-
55
190
2110


3230
-

3230
5340
Current emissions,
tunb /flay
Hydrot-a rbonb
Total


105


295
240
5
55
65
765


1610
10
80
1700
2465
K.'.K -
ti\ t-


15


60
55
-
10
15
155


1170

30
1200
1355
\0V


10
15
10
95
-
100
25
25
280


740
15
15
770
1050
Par-
ticu-
lates


10
10
5
10
5
5
10
5
60


45
10
15
70
130
S02


115
5
-
55
-
35
-
-
210


35
-
5
40
250
CO


-
5
-
5



-
10


8945
15
135
9095
9105
Hydrocarbons = hydrocarbons and other organic gases. NOX - oxides of nitrogen.  SO^ = sulfur dioxide.  CO = carbon monoxide.
"Reactive" means those hydrocarbons which are photochermcally reactive.
All reported values above have been rounded to the nearest 5 tons/day.  A dash denotes 2,5 tons/day or less.
Under Rule 66 reactive hydrocarbons can be controlled by substitution with  low reactive hydrocarbons; therefore, when showing the prevention of
emissions, the reactive hydrocarbons controlled could be greater than the total hydrocarbons controlled.

-------
                                        SUBJECT  INDEX
Abrasive Blast Cleaning   397-401

   Abrasive Materials  397
   Equipment Used to Confine the Blast
    398-401

   Methods of Propelling the Abrasive
    397-398
Absorption, see Gas Absorption Equipment

Acrolein,  Odors from Varnish Cooking  711

Activated  Carbon in Air Pollution Control
  191-198
   Adsorption of Mixed Vapors  192

   Breakpoint  192
   Carbon Regeneration   193

   Dry Cleaning Equipment   883-884

   Heat of Adsorption  192-193

   Pressure Drop versus Carbon Bed Depth
    197-199
   Retentivity  192

   Saturation   191
Additives,  Rubber Compounding  375

Adsorbents, Types  of, also  see Activated
  Carbon  191
Adsorption Equipment, also see Gas Adsorption
  Equipment  189-198

   Continuous Adsorber   197
   Design  193-198
   Fixed-Bed Adsorber   194-197
   Operational Problems   198
Aerosols   16-18

Afterburners   171-183
   Boilers Used as  183-189

   Catalytic   179-184
   Chamber   172

   Controls for   175

   Direct  Flame   171-172

   Efficiencies of Catalytic   181

   Efficiencies of Direct Flame   175-176

   Emissions from  182

   Gas Burners for   172-174
   Mixing Plate Burners  172

   Multi-Port Burners   172-173
   Nozzle Mixing and Premixing Burners
     173-174

   Oil Firing of  174

   Operation  171, 180-181

   Preheating of Inlet Gases   182-183

   Recommended Operating Temperatures  179

   Recovery of Heat from Exhaust Gases
     181-182
   Sources of  Combustion Air for Gas Burners
     174
Aggregate

   Asphalt Batch Plants   325-333

   Rock and Gravel Plants  340-342
Airblowing, Petroleum Refining  584, 695

Airblown Asphalt  685-689

Air Flow into  a Duct   28
Air, Properties   941

Alloying, Aluminum Melting   283

Alloys,  Low Melting, Sweating  305-308

Aluminum Melting, see Secondary Aluminum
 Melting Processes

Amino Resins   702, 707
Apartment Incinerators,  see Flue-Fed
 Apartment Incinerators

Architectural  Coatings, Rule 66. 1  6

Asphalt,  Airblown  685-689
Asphalt Paving Batch Plants   325-333

   Dust and Fume Discharge from  328

   Raw Materials   325-327
Asphalt Roofing Felt Saturators  378-390

Atmospheric Pressure at Altitudes  above Sea
 Level   636

B
Baghouses   106-135

   Bag Attachment  123-124

   Bag Replacement  134

   Clean Cloth Resistance   110
   Cleaning Cycles  130-131
                                               969

-------
970
                                   SubjsctIndex - Baghouses
Baghouses (continued)
   Cleaning of Filters,  124-131
   Construction of  132-134
   Diameter of Tubular Elements   121
   Diffusion  110
   Direct Interception   108-109
   Disposal of Collected Dust  131
   Dust Mat Resistance  111-115
   Effect of Resistance on Design   115-116
   Electrostatics  110
   Envelope-Type  109, 122
   Fibers   118-120
   Filtering Media   118
   Filtering Velocity   116-118, 130
   Filtration Process   106-110
   Finish  120-121
   Hoppers  132-134
   Impingement  109-110
   Installation of Filters  122-124
   Length of Tubular Bags   121
   Length-to-Diameter Ratio  121-122
   Maintenance   134-135
   Multiple-Tube Bags   122
   Precoating the Bags  135
   Pushthrough versus  Pullthrough  132
   Recommended Fabric and Maximum
    Filtering Velocity  130
   Resistance  110-116
   Reverse-Jet  109,  128-130
   Service  134
   Size and Shape of Filters   121-122
   Structural Design   132
   Vibrators and Rappers   133
   Weave   120
Banbury Mixers  377
Barton Process,  Lead Refining  304
Belgian Retort Furnace, Zinc Melting  294-295
Berl Saddles  212, 217
Bernoulli's Equation   25, 26
Bessemer Converter  239
Black Smoke from Combustion of  Fuels   537
Blind Changing, Petroleum  Pipelines  695-696
Blowchamber, Mineral Wool Manufacture   342
Slowdown System   581,  586-588
Blown Oil  709
Boiled Oil   708
Boilers,  Heaters, and Steam Generators
 554-577
   Emissions of Oxides of Nitrogen from
    564-567
   Firebox  556-558
   Hot Oil Heaters   556
   Industrial Boilers and Water Heaters  553
   Power Plant Steam  Generators  554-555
   Refinery Heaters  556
   Soot Blowing   558-560
Boilers Used as Afterburners  183-189
   Adaptable Types of  Equipment   187
   Advantages and Disadvantages of  185
   Burners for  187
   Conditions for Use  183-184
   Design Procedure  190-192
   Manner  of Venting Contaminated Gas
    187-189
   Safety  187
   Test Data on Specific  Installations  189
Brake Shoe Debonding   496-506
Brass Melting, see Secondary Brass and
 Bronze Melting Processes
Bronze Melting, see Secondary  Brass and
 Bronze Melting Processes
Bubble Cap Plate Towers  221-227
Bulk-Loading Facilities,  Petroleum,
 see Loading Facilities,  Petroleum
Burners, Gas  and Oil  542-554
Carbon Adsorption,  see Activated Carbon
Catalyst Regeneration  582-584, 662-672
   Carbon Monoxide Waste-Heat Boilers
    670-671
   Catalytic Reformer  Units 665-666
   FCC Catalyst Regenerators 664-665
   Loss of Catalyst Activity   664
   TCC Catalyst Regenerators  665

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                                     Subject Index - Catalyst
                                           971
Catalyst Regeneration (continued)
    Types of Catalyst  662-664
Catalytic Afterburners   179-181
    Efficiencies of  181
Cement, also see Concrete
    Elevators and Screw Conveyors   340
    Grades  335
    Handling Equipment  339-340
    Hopper Truck and Car Loading   340
    Receiving   335-336, 339
    Storage and Receiving Bins  339-340
    Weigh Hopper   336
Centrifugal Pumps   680-683
Centrifugal Separators,  see Inertial Separators
Ceramic Spraying and Metal Deposition
  421-433
    Ceramic Glaze   421-429
    Deposit Efficiencies, Metalizing  430, 432
    Metalizing  429-433
    Plasma Arc Spraying  431
    Spray  Booth  422-429
    Thermal Spraying  430-431
Chemical Milling  846-851
    Etchant Solutions  848-849
    Hooding and Ventilation Requirements
      849-851
    Process  846-847
Chemical Processing Equipment   699-851
    Chemical Milling  846-851
    Coffee Processing   791-794
    Deep Fat Frying  799-801
    Edible-Lard and Tallow  Rendering
      802-804
    Electroplating   829-832
    Fish Canneries and Fish Reduction Plants
      804-815
    Food Processing Equipment   788-804
    Frit Smelters  782-788
    Glass Manufacture  765-782
    Hazardous Radioactive Materials  838-844
    Insecticide Manufacture   832-838
    Livestock Slaughtering   801-802
    Oil and Solvent Re-Refining  844-846
    Phosphoric Acid Manufacturing  734-737
    Reduction of Inedible Animal Matter
      815-829
    Resin Kettles  701-708
    Soap, Fatty Acid,  and Glycerine  737-749
    Smokehouses 794-799
    Sulfuric Acid Manufacturing 716-722
    Sulfur Scavenger Plants  722-734
    Synthetic Detergents  759-765
    Synthetic Detergent Surfactant  749-765
    Varnish Cookers  708-716
Chlorosulfuric  Acid Sulfation  756-757
Coffee Processing   791-794
Coke Drum Slowdown System  587-588
Combustion Equipment   533-577
    Boilers,  Heaters, and Steam Generators
      554-577
    Gas  and Oil Burners   542-554
    Gaseous  and Liquid Fuels   535-542
    Gaseous  Fuels  535-536
    Oil Fuels  536-537
Compressibility Constants for Hydrocarbons
 595
Concentrations of Suspended Matter in
 Commercial Gases   142
Concrete-Batching  Plants  334-339
    Central Mix Plants   337-339
    Dry-Concrete-Batching Plants   336-337
    Wet-Concrete-Batching Plants   334-336
Condensers,  see Vapor Condensers
Contact Condensers  199-201,  203
Contact Process, Sulfuric Acid Manufacturing
 716-718
Contaminants   9-21
    Specific, Rule  53  5
Continuity Equation, Fluid Flow  27
Control Equipment  for Gases and Vapors
 169-229
    Adsorption Equipment  189-198
    Afterburners   171-189
    Continuous Adsorbers  197
    Fixed-Bed Adsorbers  194-197
    Gas Absorption Equipment  207-229

-------
972
                                     Subject Index - Control
Control Equipment for Gases and Vapors
  (continued)

    Steam Consumption per Pound of Solvent
      Recovered   193

    Vapor Condensers   198-207

Control Equipment for Particulates   89-168
    Baghouses  106-135

    Electrical Precipitators  135-166

    Impingement Separators  166-167

    Inertial Separators  91-99
    Panel Filters   167

    Precleaners   168

    Settling Chambers   166

    Wet Collection Devices  99-106

Coolers, Mineral Wool Manufacture
  343, 345-346

Cooling of Gaseous Effluents,  see Gaseous
  Effluents, Cooling of

Cooling Towers, Petroleum Equipment
  584, 692-695

Core Ovens  308-315
    Core  Binders   312-315

    Emissions from   314

    Types of Ovens   309-311

Correction Factors

    Adjustment Factor for Small-Diameter
      Tanks   640
    Altitude,  Temperature, Density  58

    Cyclone Separators  97
    Elevation  57-59
    Hood  Volume  58
    Kinetic Energy for Pressure Drop,
      Isothermal Flow  602

    Pitot  Tube Calculations  27,  73

    Subsonic Flow   596

    Swinging Vane Velocity Meter  74

    Temperature  57-59

Cottrell-Type Electrical Precipitator,  see
  Electrical Precipitators,  Single-Stage

Crucible Furnace  237-238
    Aluminum Melting   283

    Brass and Bronze Melting  272
    Calculation for Cooling Effluent  76-79

    Pit  238
    Stationary  238
    Tilting   238

Crude Oil Production  581

    Breathing Emissions from Fixed-Roof Tanks
      641

    Working Emissions  from Fixed-Roof Tanks
     643

Cupola Furnace  234-236

    Brass and Bronze Melting  273

    Calculation for Cooling Effluent   79-86
    Iron Casting  256-266

    Mineral Wool Manufacture   342-348
Curing Ovens

    Afterburner Control  347

    Mineral Wool Manufacture   343-349

Cut Size, Cyclone Separators  95-99
Cyclones, also see Inertial  Separators

    Cyclone-Type Scrubbers   101
    Predicting Efficiencies of  95
Debonding of Brake Shoes and Reclamation of
 Electrical Equipment  496-506
Deep Fat Frying   799-801
Degassing, Aluminum Melting   283

    Degassing Fluxes  286
Demagging, Aluminum Melting   283
    Demagging Fluxes  286-287
Densities of Typical Materials  954
Detergent Surfactants   749-759
Detergents, see Synthetic Detergents
Dew Point as a Function of 803  Concentration
 563

Dielectric Constants   137

Diethanolomine (DEA), Removal of H2S from
 Refinery Waste Gas  723-725

Diffusion Coefficients  of Gases and Vapors
 215-216

Dip Tanks   860-861, 863

Direct Arc Furnace  236

Direct Flame Afterburners   171-172
    Design Problem  176-179
    Efficiencies   175-176

-------
                                      Subject Index - Direct
                                                                                               973
Direct Flame Afterburners  (continued)

   Efficiencies versus Temperatures   181

   Emissions from  182
   Mineral Wool Manufacture  347
Distillation Retort Furnace,  Zinc Melting
  295-297

Driers   367-372
   Emissions from  371-372

   Flash  368-369
   Rotary  367-368

   Smoke and Odor Emissions from  372

   Solvent Recovery from   371-372

   Spray  369
   Tray   370
Driers, Fish Meal   806-807, 809-810,  812-813
   Chlorinating and Scrubbing Drier Gases
    812-813

   Dust from   810
   Incinerating Drier Gases   812

   Odors from  809

   Smoke from  810

Driers, Rendering

   Blood Driers  819
   Emission Rates from  822, 825

   Feather Driers  820
   Odors from Air Driers   822

   Rotary Air Driers   820

Drum Reclamation Furnaces  506-520
Dry Cleaning Equipment  875-884

   Adsorbers   883-884
   Combination Machines  876

   Extractors  876
   Filters  878

   Lint  881

   Lint Traps  884

   Muck Reclaimers   879

   Solvents used in  879-881

   Stills   878

   Tumblers   876-877

   Wash Machines  875-876
Dust and Fumes

   Aluminum Melting   288
    Aluminum Sweating   310

    Brass and Bronze Melting  269-273

    Core Ovens  314

    Process Weight  5

    Rule 54   5, 917
    Zinc Sweating  307

Duct Design   44-60

    Balanced-Duct Method   49-52
    Blast Gate Method  49-52

    Density Corrections 58

    Design Procedures  47-52

    Duct Construction  59-60

    Elevation Corrections 57-59
    Exhaust Volumes and Duct Sizes for Wood-
      working Equipment   374

    Hood Volume Corrections  58

    Layout Considerations   44

    Losses,  Types of  44-47
    Sample Calculations  52-56

    Temperature Corrections  57-59
Edible-Lard and Tallow Rendering,  see
 Rendering

Efficiencies

    Boilers Used as Afterburners (Apparent)
      190

    Catalytic Afterburner   181
    Cyclone Separators  93, 95-99
    Direct Flame Afterburner   175-176

    Electrical  Precipitators   140, 149-150,
      153-154,  160,  162, 164

    Plate or Tray Towers   221-222
Effluent-Waste Disposal, Refining   564

Electrical Equipment,  Reclamation of  496-506

Electric  Furnace  236-237
    Aluminum  Melting  284

    Brass  and  Bronze Melting   272

    Direct Arc 236

    Glass Manufacture  779
    Indirect Arc   236-237
    Induction   237

    Iron Casting   266-267

-------
974
                                    Subject Index - Electric
Electric Furnace (continued)
    Resistance   237
    Steel Manufacturing  Z45-255
Electrical Precipitators  135-166
    Advantages  and Disadvantages of
      138-139, 163
    Average Diameter of Particles in Various
      Industrial Applications   143
    Concentrations of Suspended Matter
      in Commercial Gases   142
    Data  on Typical Applications   140
    Dielectric Constants for Some Common
      Materials  137
    Diverse Applications of  141
    History   135-138
    Mechanisms Involved in  139-141
    Pioneer Installations,  1907 to 1920  139
    Summary of U.S.  Installations,  1907 to 1957
      139
Electrical Precipitators, Single-Stage   135-156
    Construction, Details of   141-147
    Cost  of Installation  146-147
    Design, Practical Equations for  153-154
    Design Variables,  Values for   155
    Drift Velocity   154
    Efficiency,  Theoretical  149-150
    Nonuniform Gas Flow,  Effects of  154-156
    Operating Voltage   145-146
    Performance,  Theoretical Analysis of
      147-150
    Reentrainment,  Methods of Reducing
      152-153
    Resistivity, Effect of   150-152
    Sparking  Potential versus Air Moisture  152
    Sparking Rate   146
Electrical Precipitators, Two-Stage  156-166
    Air Capacity   161
    Air Distribution   161-162
    Applications  163-166
    Assembly  163
    Auxiliary Controls  162
    Construction and Operation   163
    Design Factors  160-162
    Drift Velocity   159-160
    Dust Separation, Theory of   158-159
    Efficiency  160
    Efficiency versus Gas Velocity  162
    Electrical Requirements  160
    Equipment Selection  165-166
    Maintenance   163
    Particle Charging   159
    Safety  163
    Special Design   165
    Theoretical Aspects  158-160
Electroplating   829-832
Emission Surveys, Inventories,  and Factors
 963-971
Engineer, Air Pollution, Role of  6-7
Enthalpies of Gases  945-946
Esterification  709
Exfoliation, Perlite-Expanding Furnace   350
Exhaust Systems   23-87
    Calculator  45
    Checking  of   72-75
    Cooling of Gaseous  Effluents in   76-87
    Duct Design   44-60
    Fan  Design  60-67
    Fluid Flow Fundamentals  25-27
    Hood Design   27-44
    Requirements  for Various Operations   31
    Vapor Compressors  67-72

Exhaust System for Woodworking Equipment
 372-374
Exhaust Volumes for Woodworking Equipment
 374
F
Fan Design  60-67
    Characteristic Curves   61
    Drives  67
    Fan Curve Calculator  57
    Laws   63-65
    Multirating Table  66
    Static  Pressure   50
Feather  Processing  820

-------
                                        Subject Index - Feed
                                                                                               975
Feed and Grain Mills  352-361

    Feed Manufacturing Processes  354-361
    Receiving, Handling and Storage 353-361

Filters, Wet,  also see Baghouse  105
Fireboxes, Boiler   556-558
Fish Canneries and Fish Reduction Plants
 804-815

    Cannery Byproducts  806
    Chlorinating and Scrubbing Drier Gases  812

    Collecting Dust   815

    Controlling  Digesters   814

    Controlling  Edible Fish Cookers  815

    Controlling  Evaporators  814
    Controlling  Fish Meal Driers  812

    Controlling  Reduction Cookers and
     Auxiliary Equipment  813-814
    Digester Process   809

    Dust from Driers and Conveyors  810
    Fish Meal Production   806-807

    Fish Solubles and Fish Oil Production
     807-809
    Incinerating Drier Gases  812

    Odors  from Digesters   811
    Odors  from Edibles Cookers   811

    Odors  from Evaporators   811
    Odors  from Fish Meal Driers   809
    Odors  from Reduction Cookers   811

    Smoke from Driers   810
    Tuna Canning  805-806
    Wet-Fish Canning   805
Fixed-Roof Tanks,  Petroleum Equipment   627
    Breathing Emissions of Gasoline and
     Crude Oil  from 641

    Floating Plastic Blankets  644-645
    Hydrocarbon Emissions from  638-642

    Plastic Microspheres   645-647

    Working Emissions  of Gasoline and
     Crude Oil  from  643

Flares and Slowdown Systems   581,  586-626

    Design of   623-626
    Measuring Gas Flow  617-618

    Smoke from  604

    Types  of Flares  605-613
Flexitrays,  Plate Towers   221

Floating-Roof Tanks, Petroleum Equipment
  627-628
    Hydrocarbon Emissions from  632-634

    Roof Properties of Steel Tanks   627

    Seals for  644
    Standard Storage Evaporation Emissions
      from   633

Fluoride Emissions from Frit Smelters
  787-788

Flowcoating   858-860,  863

Flue-Fed Apartment Incinerators  471-484

Fluid Flow   25-67
    Bernoulli's Equation   25
    Continuity Equation  27

    Correction Factors  27, 73

    Duct Design  44-60
    Fan Design  60-67

    Fundamentals  25-27

    Hood Design   27-44

    Pitot Tube for Flow Measurements   25-27
Fluxes,  Zinc Galvanizing   402

Fluxing

    Aluminum Melting  285-288
    Brass,  Hood Design Calculation   39-40

Foaming Agents,  Zinc Galvanizing Equipment
  402

Food  Processing  Equipment  788-804
    Coffee Processing  791-794
    Deep Fat Frying   799-801
    Edible-Lard  and  Tallow Rendering
      802-804
    Fish Canning, see  Fish Canneries and
      Fish Reduction  Plants
    Livestock Slaughtering  801-802

    Operations Involved  790

    Smokehouses   794-799
Foundry Sand-Handling Equipment 315-319

Friction Losses  45-47
    Contraction and Expansion   47

    Elbow and Branch Entry  45-47

    Straight Duct  45
   234-767 O - 77 - 64

-------
976
Subject Index - Frit
Frit Smelters  782-788
    Dust and Fume Discharge from   787-788
    Fluoride Emissions from  787-788
    Raw Materials  782-783
    Types of  783
Fuels, see Gaseous Fuels and Oil Fuels
Fuel-Fired Furnace,  Aluminum Melting   284
Fuel Gas,  Combustion Characteristics  536
Fuel Oils, see Oil Fuels
Furnaces
    Electric Melting, Glass Manufacture   779
    Frit Smelters  782-788
    Glass Melting  769-781
    Metallurgical, see process involved
    Mineral Wool  342-350
    Perlite-Expanding  350-352
    Regenerative, Glass Melting  769-781
    Wire Reclamation  520-531
Furnaces, Types  235-241
    Belgian Retort  294-295
    Crucible  237-238, 272, 283
    Cupola   234-236, 256-266, 273
    Distillation Retort  295-297
    Electric  236-237, 245-255,  266-267, 272,
      284
    Lead Blast   302
    Muffle   297-299
    Open Hearth  235, 240-245, 273-275
    Pit Crucible   238
    Pot Furnace   238-239, 303-304
    Reduction Retort  294-295
    Reverberators  233-234, 267-269, 273-278,
      284,  300-302
    Stationary Crucible   238
    Tilting Crucible   238
Gas Absorption Equipment,  also see Absorption
  Equipment  207-229
    Comparison of Packed and Plate  Towers
      227-228
    General  Types  208
    Packed Towers  209-220
                 Plate or Tray Towers   220-227
                 Spray Towers and Chambers  228
                 Venturi Absorbers  228-229
             Gas and Oil Burners  542-554
                 Emissions from Gas- and Oil-Fired
                  Equipment  553
             Gas Burners
                 For Afterburners  172-174
                 Mixing Plate  Burners for Afterburners   172
                 Multi-Port Burners for Afterburners
                  172-173
                 Nozzle Mixing and Premixing Burners for
                  Afterburners   173-174
             Gaseous Effluents, Cooling of   76-87
                 Dilution with Ambient Air   76-79
                 Factors in Selecting Devices for  86-87
                 Forced Draft Cooling   86
                 Methods  76-86
                 Natural Convection and Radiation  81-86
                 Quenching with Water  79-81
             Gaseous Fuels  535-536
                 Combustion Characteristics for   536
                 Combustion Data for  Texas Natural Gas
                  535
                 Removal of Sulfur and Ash from Fuels  539
             Gases and Vapors
                 Control of,  see Control Equipment for Gases
                  and Vapors
                 Diffusion  Coefficients   215-216
             Gasoline
                 Loading into Tanks,  Rule 65  6, 919
                 Loading Tank Trucks and Trailers,  Rule 61
                  5,  917-918
                 Specifications, Rule 63  6, 919
                 Storage, Rule 56  5,  915
             Glass Manufacture  765-782
                 Glass-Forming Machines   781-782
                 Glass-Melting Furnaces  769-781
                 Process  765-767
                 Raw Materials Handling for  767-769
                 Types  of Glass   765
             Glass Wool, see Mineral Wool
             Grate Loading, Multiple-Chamber Incinerators
             443

-------
                                        Subject Index - Gum
                                           977
Gum Running   709

Gyratory Crusher, Rock and Gravel Aggregate
  Plants   341
Hazardous Radioactive Material  838-844

    Hazards in the Handling of Radioisotopes
      838
    Properties of Radioisotopes   795

    Types of Radiation  839

    Waste Disposal  843-844

Heat-Bodied Oil  709

Heat Recovery from Exhaust Gases of
  Afterburner  181-182

Heat Transfer  76-86,  204-207

    Calculations   76-86, 204-207

    Coefficient of Heat Transfer by Radiation
      83

    Convection and Radiation  81

Heat Treating Systems, Metals   320-321

Heaters,  see Boilers, Heaters, and Steam
  Generators

High-Efficiency Cyclones  91-94

High-Pressure Water Spray Scrubber   103

Hood Construction  43

Hood Design  27-44

    Abrasive Blasting  32

    Air Flow into a. Duct   28

    Circular Low Canopy   39-41

    Cold  Processes  30

    Construction  43

    Exhaust Requirements for Various
      Operations   31

    Flow Contours into Circular Openings  29

    Hot Processes  34-43

    Leakage from  42-43

    Null Point  28-30

    Rectangular High Canopy  38-39

    Spray Booths   32

    Ventilation Rates for Low Canopy  40-41

    Ventilation Rates for Open Surface Tanks
      34

    Ventilation Rates Required for Tanks   33

    Ventilation Requirements for Blending Dry
      Powdered Materials   51
Hot Oil Heaters and Boilers   556

Hydrocarbons

    Compressibility Constants for  595

    Emissions, Percent Volume Pumped into
      Tank for Various Vent Settings  639

    Emissions from Airblowing   696

    Emissions from Cooling Towers  694

    Emissions from Fixed-Roof Tanks  638-642

    Emissions from Floating-Roof Tanks
      632-634

    Emissions from Low-Pressure Tanks
      634-638

    Leakage of Hydrocarbons from Valves   671

    Losses from Pump Seals  684-685

    Paint Factors for Determining Evaporation
      Emissions from Fixed-Roof Tanks  640

Hydrogen Sulfide Removal from Refinery Waste
  Gases  723-725


I

Impingement Separators  166-167

Incineration   435-531

    Debonding of Brake Shoes and Reclamation
      of Electrical Equipment Windings  496-506

    Drum Reclamation Furnaces   506-520

    Flue-Fed Apartment Incinerators   471-404

    General-Refuse Incinerators 443-452

    Mobile Multiple-Chamber  Incinerators
      452-459

    Multiple-Chamber Incinerators  437-443

    Multiple-Chamber Incinerators for Burning
      Wood Waste  460-471

    Pathological-Waste Incinerators  484-496

    Rules 57 and 58   5, 915-917

    Wire Reclamation  520-531

Indirect Arc Furnace  236-237

Induction Furnace  237

Inertial Separators  91-99

    Cyclone Diameter versus Cut Size  96

    Cyclone Efficiency versus  Particle Size
      Ratio   95

    Diameter Cut Size 95-99

    High-Efficiency Cyclones  91-94

    Mechanical, Centrifugal Separators  94

    Multiple-Cyclone Separators   94

-------
978
Subject Index - Inertial
Inertial Separators (continued)
    Pressure Drop   93-94
    Separation Efficiency   93, 95-99
    Single-Cyclone Separators   91-94
    Theory of Operation   92-94
Inorganic Gases   14-16
Insecticide Manufacture   832-838
    Liquid-Insecticide Production Methods
     835-836

    Production Methods  832-836
    Solid-Insecticide Production Methods
      833-835
    Threshold Limit Values  833

Intalox Saddle  209,  217
Iron Casting  256-269
    Cupola Furnace  256-266
    Electric-Arc  Furnace  266-267
    Electric-Induction Furnace  267

    Reverberatory Furnaces   267-269
Kinetic Energy Correction for Pressure Drop
  for Isothermal Flow   602

Knockout Drum Sizing  601

L

Lacquers,  Weights and Dilutions  956
Lead Melting, Hood Design Calculation  38-39
Lead Refining  299-304
     Barton Process   304
     Blast Furnace  302
     Lead Oxide Production  304
     Pot-Type Furnace  303-304

     Reverberatory Furnaces   300-302
     Sweating   305-308

Liquid Fuels,  see Oil  Fuels
Livestock Slaughtering  801-802
Loading Facilities, Petroleum  582, 649-666

     Analysis of Vapors from the Bulk Loading of
     Gasoline into Tank Trucks  655
     Factors Affecting Design  of Vapor  Collection
     Apparatus   659-660
     Loading Arm Assemblies   652-653

     Loading Racks  652
                  Marine Terminals  652

                  Vapor Collection for Overhead Loading
                    655-658
                  Vapor Collection for Bottom Loading
                    658-659
                  Vapor Disposal Methods  660-662
              Local Exhaust Systems,  see  Exhaust Systems
              Log-Mean Temperature Difference   81, 85
                  Calculation  85
              Los Angeles Basin   3
                  Permit System, Accomplishments  6-7
                  Rules and Regulations  for   3-6,  907-929
              M
              Marketing, Petroleum  585

                  Sources and Control of Hydrocarbon Losses
                    from  586

              Mechanical, Centrifugal Collector with Water
               Sprays   102-103

              Mechanical, Centrifugal Separators  94

              Mechanical Scrubber  102

              Melting Points of Materials Sprayed by Plasma
               Arc   431

              Metal Deposition,  Metalizing, see Ceramic
               Spraying and Metal Deposition

              Metal Separation Processes   304-308

                  Aluminum Sweating   305

                  Zinc, Lead, Tin, Solder and Low-Melting
                    Alloy Sweating  305-308

              Meters

                  Quantity Meters  72

                  Swinging Vane Meters  73-74

                  Velocity Meters  72

              Mineral Wool Furnaces   342-350

              Mobile Multiple-Chamber Incinerators   452-459

                  Design Procedure  452-454

                  Standards of Construction  454

              Monoethanolamine  (MEA),  Removal of H2S from
               Refinery Waste Gas  723-725

              Multiple-Chamber  Incinerators  437-443,  452-471

                  Arch Height to Grate Area  444

                  Comparison of Emissions with Single
                    Chamber Incinerators  445

                  Design Factors   441-443

                  Grate Loading   443

-------
                                     Subject Index - Multiple
                                           979
Multiple-Chamber Incinerators (continued)
     In-Line  437-438
     Mobile  452-459
     Principles of Combustion  440-441
     Retort  437
     Wood Waste  460-471
Multiple-Cyclone Separators   94
Multirating Tables, Fans   66
Muffle Furnace  297-299
     Zinc  Melting  294-297
Natural Gas
     Combustion Characteristics   948
     Flow through Orifices   546-547
     Heat from  935-936
     Texas   535
Nozzle Gas Constant  595
Nuisance,  Rule 51   4,  913
Null Point, Hood Design   28-30
Odor and Smoke Emissions from Driers   372
Odor Testing Techniques  931-934
Oil and Solvent Re-Refining   844-846
Oil Breaking  709
Oil-Effluent Water Separator  672-679
     Rule 59   5, 917
Oil Fuels  536-537
     Analysis of Low Sulfur Fuels Used in Los
      Angeles County   538
     Combustion Data for  538
     Commercial Standards for   537
     Production Trends, U.S. Refineries, 1950-
      1969  541
     Properties   947
     Removal of Sulfur and Ash from Fuels  539
     Typical Ash Analysis   539
     Viscosity-Temperature Relation  551
Oleoresinous Varnish   709
Oleum Sulfonation  750-752
Oleum Sulfonation and Sulfation   752
Opacity, Ringlemann Chart,  Rule 50  4, 913

Open Fires and Incinerators, Rules 57 and 58
  5,  915-916
Open-Hearth Furnace  235
     Brass and Bronze Melting  273-275
     Steel Manufacturing   240-245
Open-Top Tanks,  Reservoirs, Pits,  and Ponds
  631
Organic Gases  12-14
Organic Solvent Emitting Equipment   853-884
     Dry Cleaning Equipment  875-884
     Paint Baking Ovens and  Other Solvent
      Emitting Ovens   865-871
     SolventDegreasers  871-875
     Solvents and Their Uses   855-858
     Surface Coating Operations   858-865
Organic Solvents, also  see Solvents
     Disposal   6
     Evaporation   6
     Re-Refining   844-846
     Rule 66  6,  855-857,  919-921
Orifice-Type Scrubber   101-102
Overpressure Sizing Factor  for Standard Vapor
  Safety Valves   594
Oxides of Nitrogen  564-567
     Estimating Emissions   567
     Fuel-Burning Equipment,  Rule 68   6, 921
     Reduction  of in Combustion Equipment
      570-577
Packed Towers   208-220
    Ammonia-Water Equilibrium  217-218
    Capacity  210-211
    Comparison with Plate  Towers   227-228
    Cost of  210
    Design   208-220
    Diameter  211-213
    Height of Transfer Unit   214-215
    Liquid Distribution  209-210
    Number of Transfer Units  213-214
    Packing Materials   209

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980
Subject Index - Packed
Packed Towers (continued)

    Pressure Drop Through Packing   216

    Scrubbers   104-105

Paint Baking Ovens and Other Solvent-Emitting
 Ovens  865-871

    Air Seals  867
    Batch Type Ovens  866

    Can Lithograph Ovens  870-871

    Circulating and Exhaust Systems  867
    Continuous Ovens  866

    Equipment  866-867

    Heating of Ovens   866-877
    Printing System Ovens   871

Paint Dip Tanks  860-861, 863

Pall Rings   209
Panel Filters  167

Particulate Control Equipment, see Control
 Equipment for Particulates

Particulates

    Carrier  Gas Characteristics  91
    Characteristics of  91
    Mechanism for Wetting the Particle   100-101

    Operational Factors  91

    Process Factors   91

    Rule 52  5, 917

    Size Data  143,  954-956
Pathological-Waste Incinerators   484-496
    Design   486-492
    Emissions from  493
Per lite-Expanding Furnace   350-352
Permit System,  Los Angeles  4, 6-7

    Accomplishments  6-7

    Operation of  4

Petroleum and Coal Tar Resins   704-705
Petroleum Equipment  579-698

    Airblowing  584, 695

    Airblown Asphalt  685-689
    Blind Changing   695-696
    Bulk-Loading Facilities   582,  649-662

    Catalyst Regenerators  582-584,  662-672

    Compressor Engine Exhaust   697-698
    Compressibility Constants for Hydrocarbons
      595
                  Cooling Towers  584, 692-695

                  Crude Oil Production  581

                  Marketing   585

                  Oil-Water Effluent System  672-679

                  Operational Difficulties of a Refinery and
                   Required Relief Capacities  591

                  Overpressure Sizing Factor for Liquid
                   Relief Valves  593

                  Pumps and Compressors   584,  679-685

                  Refining  581-585

                  Storage Vessels  581, 626-649

                  Tank  Cleaning   697

                  Vacuum Jets  584, 697

                  Valves  689-692

                  Waste-Gas Disposal Systems   585-626

              Phenolic Resins  701

              Phosphoric Acid Manufacturing  734-737

                  Phosphorous Pentoxide Emissions   735

              Photochemically Reactive Solvents, see Solvents
               and Their Uses

              Pipe-Coating Equipment   390-397

                  Pipe Dipping  392

                  Pipe Spinning  392

                  Pipe Wrapping   392

                  Preparation of Enamel   392

              Pipeline Valves and Flanges, Blind Changing,
               Process  Drains  584

              Pit Crucible Furnace  238

              Pitot Tube  25-27,  72-76

                  Altitude and Temperature Corrections for
                   73

                  Correction Factors  27, 73

                  Standard  72

                  Static Pressure   26

                  Total  Pressure  26

                  Traversing for  Round and Rectangular Ducts
                   73

                  Velocity Pressure  26

              Plasma Arc Spraying  431

              Plate or Tray Towers  220-227

                  Comparison with Packed Towers   227-228

                  Efficiency   221-222

                  Flooding  222-223

-------
                                       Subject Index - Plate
                                           981
Plate or Tray Towers (continued)
     Liquid Flow  221
     Liquid Gradient   223-224
     Number of Theoretical Plates   225
     Plate Design and Efficiency  221-222
     Plate Spacing  224
     Tower Design   221-227
     Tower Diameter  224-225
     Types of Plates   220-221
Pneumatic Conveying Equipment   362-367
     Design Calculations  365-367
     Types of  362-365
     Velocities for Conveying  Various Materials
      366
Polyester and Alkyd Resins   702-703
Polystyrene   704
Polyvinyl Resins  703-704
Polyurethane   703
Positive-Displacement Pumps 680
Pot Furnace  238-239
     Lead Refining   303-304
Pouring Practices, Aluminum Melting   285
Power Plant Steam Generators   554-556
     Emissions and Control  560-577
Precleaners   168
Preheating of Afterburner Inlet Gases   182-183
Pressure Drop
     Carbon Bed Adsorber   197-198
     Through Tower Packing  216
Pressure Relief System, Petroleum Equipment
 588-604
    Discharge Piping for  597,  600
    Knockout Vessels   596-604
    Leakage of Hydrocarbons from Valves   692
    Minimum Rupture Pressures   592
    Overpressure Sizing Factor for  593
    Required Relief Capacities   591
    Rupture Discs   590-593,  595-596
    Safety Valves   589,  593-596
    Valves   581
Process Weight, Rule  54   5,  914
Prohibitions, also see Rules and  Regulations,
Los Angeles County
Regulation IV, 4
Pumps and Compressors, Petroleum Equipment
  584,  679-685
    Hydrocarbon Losses from Seals   684-685
    Seals  681-685
    Types of  679-681
Quantity Meters  72
Quench Tanks, Heat Treating  320-321
Radioactive Materials,  see Hazardous Radio-
  active Materials
Raschig Rings   209-210,  211,  214-215
Reclamation of Electrical Equipment Windings
  496-506
Rectangular High-Canopy Hoods   38-39
Reduction of Animal Matter, Rule 64 6,  919
Reduction of Inedible Animal Matter, also see
  Rendering  815-829
Reduction Retort Furnace, Zinc Melting
  294-295
Refinery Heaters  556
Refinery Production, Fuel Oils  541
Refining,  Petroleum, also see Petroleum
  Equipment  581-585
Refuse Incinerator   443-452
Regenerative Furnace,  Glass Manufacture
  769-781
Rendering   802-804, 815-829
    Carbon Adsorption  of Odors   828-829
    Condensation-Incineration  System  827-828
    Condenser Tube Materials  826
    Continuous Dry  Rendering   817-818
    Controlling High-Moisture Streams
      825-826
    Cookers as Prominent Odor Sources   822
    Dry   803,  816-818
    Drying Blood  819-820
    Edible-Lard and Tallow  802-804
    Emission Rates  from Cookers   824-825
    Emission Rates  from Driers  825
    Feather Processing  820

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982
Subject Index - Rendering
Rendering (continued)

    Interceptors in Cooker Vent Lines   826-827

    Odors and Dusts from Rendered-Product
      Systems   822-823

    Odors from Air Driers  822

    Odors from Grease Processing  823

    Odors from Raw Materials   823

    Odor Masking and Counteraction 829

    Odor Scrubbers  829

    Refined Products of  819

    Rotary Air Driers   820-821

    Subcooling Condensate   826

    Vapor Incineration  827

    Wet  803, 818

Resins   701-709

    Amino  702

    Kettles   701-708

    Manufacturing Equipment   704

    Natural   704

    Petroleum and Coal Tar  704-705

    Phenolic  701

    Polyester  and Alkyd   702-703

    Polystyrene   704

    Polyur ethane  703

    Polyvinyl  703-704

    Synthetic   709
    Thermoplastic  703

Resistance Furnace   237

Retreading Equipment,  see Tire Buffing

Reverberatory Furnace  233-234

    Aluminum Melting   284

    Brass and Bronze Melting  273-278

    Cylindrical  233

    Iron Casting  267-269

    Lead Refining  300-302

    Open-Hearth 233

    Tilting   233-234

Renolds Number   82

    Vapor Condenser Calculations  204

Ringelmann Chart,  Rule 50  4, 913

Rock  and Gravel Aggregate Plants  340-342

Rock  Wool,  see Mineral Wool
                 Roller Coaters   861,  863

                 Rubber-Compounding Equipment  375-378

                     Additives   375

                 Rueping Process, Wood Treating Equipment
                   417

                 Rules and Regulations, Los Angeles County
                   3-6,  907-929
                     Architectural Coatings,  Rule 66. 1  6,920-921

                     Disposal and Evaporation of Solvents,
                       Rule 66. 2  6, 921

                     Dust and Fumes,  Rule 54   5,  914

                     Fuel Burning Equipment, Rules 67 and 68
                       6,  921

                     Gasoline Loading,  Rule  61   5, 917-918

                     Gasoline Loading  into Tanks, Rule 65
                       6,  919
                     Gasoline Specification, Rule 63  6, 919

                     Nuisance,  Rule 51  4, 913

                     Oil-Effluent Water Separators, Rule 59
                       5,  917

                     Open Fires and Incinerators, Rules 57
                       and 58  5, 915-917

                     Organic Solvents, Rule 66   6, 855-857,
                       919-921

                     Particulate Matter, Rule 52  5,  913-914

                     Permits,  Regulation II  4, 908-911

                     Prohibition, Regulation  IV   4, 913-921

                     Reduction of Animal Matter,  Rule 64
                       6,  919

                     Ringelmann  Chart,  Rule 50   4, 913

                     Scavenger Plants,  Rule  53. 1  5,  914

                     Specific Contaminants, Rule 53  5, 914

                     Storage of Petroleum  Products, Rule 56
                       5,  915

                     Sulfur Content of Fuels, Rules 62 and 62.1
                       6,  918-919
                 Rupture Discs,  Petroleum Equipment  590-596

                     Minimum Rupture Pressures  592

                     Required  Relief Capacities  591

                     Sizing of   590-596
                 Safety Valves,  Petroleum Equipment   589

                      Overpressure Sizing Factor for  593

-------
                                       Subject Index - Safety
                                                                                               983
Safety Valves,  Petroleum Equipment (continued)
    Required Relief Capacities   591
    Schematic  Diagram of  590
Sand Handling Equipment for Foundries  315-319
Scavenger Plants, Rule 53. 1  5, 914
Schmidt Number   214-215
Scrubbers   101-105
    Cyclone-Type   101
    High-Pressure Water Sprays  103
    Mechanical  102
    Mechanical,  Centrifugal Collector with
      Water Sprays   102-103
    Orifice Type   101-102
    Packed Towers  104-105
    Spray Chamber  101
    Venturi  104
    Wet Filters   105
Secondary Aluminum-Melting Processes
  283-292
    Charging Practices   284
    Crucible Furnace  283
    Electrically Heated Furnaces  284
    Fluxing  285-288
    Fuel-Fired Furnaces  284
    Pouring Practices  285
    Reverberatory Furnace   284
    Sweating   305
    Types  of Processes  283-287
Secondary Brass- and Bronze-Melting
  Processes  269-283
    Calculations  for Cooling Effluent  76-79
    Crucible Furnace  272
    Cupola Furnace  273
    Dust and Fume Discharge   269-272
    Electric Furnace   272
    Furnace Types   269
    Open-Hearth Furnace   273-275
    Reverberatory Furnace   273-278
Secondary Zinc-Melting Processes  293-299
    Belgian Retort Furnace   294-295
    Distillation Retort Furnace   295-297
    Hood Design  Calculation  37-38
    Muffle Furnace   297-299
    Reduction Retort Furnaces   294-295
    Sweating   305-308
    Zinc Melting  293
    Z,inc Vaporization  293-294
Separators, Oil-Effluent Water, Rule 59   5, 917

Settling Chambers   166
Slag Wool,  see Mineral Wool
Smoke and Odor Emission From Driers   372
Smokehouses   794-799
Soap,  Fatty Acid,  and Glycerine Manufacturing
  Equipment  737-749
    Fatty Acid Production  739-740
    Glycerine Production  740-742
    Raw Materials  738-739
    Soap Finishing  744-745
    Soap Manufacturing   743-744
Soap and Detergent Production in U. S.   738
Solder, Sweating  305-308
Solvents,  see Organic Solvent Emitting Equipment
Solvent Degreasers   871-875
    Controlling Vaporized Solvent  874-875
    Design and Operation  871
    Emission  from   872
    Method of Minimizing Solvent Emissions  873
    Tank Covers  873-874
    Types  of Solvents  871-872
Solvents Emissions, Control of Polar and Non-
  polar Compounds,   also see Absorption Equip-
  ment  198
Solvents, Properties of Dry Cleaning  880
Solvents and Their Uses   855-858
    Baking and Curing Operations  857,  865-871
    Control Measures  857-858
    Dry Cleaning  Equipment  875-884
    Evaporation Curve,  Relating Percent Solvent
      Losses to Flashoff Time  862
    Limitations on the Use of Photochemically
      Reactive  Solvents   857
    Percent of Overspray as a Function of
      Spraying  Method  861
    Rule 66  6, 855-857, 919-921

-------
984
Subject Index - Solvents
Solvents and Their Uses (continued)

    Solvent Degreasers   871-875

    Surface Coating and Added Thinner Formulas
      858-865

    Threshold Limit Values   859

Solvent Recovery from Drier   879

Solvents,  Re-Refining   844-846
Sonic Agglomeration  722

Soot Blowing, Boilers   558-560

    Collectors  568
Sources of Combustion Air for Gas Burners for
 Afterburners  174

Speiss Hole  296

Spirit Varnish   709
Spray Booths   858,  861-865

    Air Contaminants from  861-863

    Control of Particulates from   864-865
    Design Calculation   32

Spray Chamber   101
    Gas Absorption   228

Standard Conditions, Rule 52   5

Stationary Crucible Furnace   238

Steam Generators, see  Boilers, Heaters, and
 Steam Generators

Steam Pipe Sizing Chart  620

Steel-Manufacturing Processes   239-255
    Bessemer Converter  239
    Electric-Arc  Furnaces  245-254
    Electric-Induction Furnace  254-255
    Open-Hearth Furnaces  240-245
    Oxygen Process  240
Storage of Petroleum Products, Rule 56  5, 915


Storage Vessels,  Petroleum Equipment  581,
 626-649
    Adjustment Factor  for Small-Diameter Tank
      640

    Aerosol Emissions from   642
     Conservation  Tanks   628-631

    Cost  of  649
    Factors  Affecting Hydrocarbon Vapor Emis-
      sions  631-632

    Fixed-Roof Tanks   627

    Floating Plastic Blankets  644-645
                  Floating-Roof Tanks   627-628

                  Hydrocarbon Vapor Emissions  631-642
                  Masking Agents  649

                  Miscellaneous Pollution Control Measures
                   648-649
                  Odors from  642-643

                  Open-Top Tanks, Reservoirs,  Pits and
                   Ponds  631

                  Plastic  Microspheres  645-647
                  Pressure  Tanks  627

                  Relative Effectiveness of Paints in Keeping
                   Tanks from Warming in the Sun   649

                  Seals for Floating-Roof Tanks   644
                  Storage Pressure Required to Eliminate
                   Breathing and Boiling Losses  637
                  Submerged Filling  633

                  Types of  626-631

                  Vapor Balance  Systems  647
                  Vapor Recovery Systems   647-648

              Submerged Filling,  Gasoline  Tanks  653-654

              Sulfoalkylation   757-759
              Sulfonation  743-744, 755-757

              Sulfur,

                  Contaminants,  Rule 53  5,  914

                  Contents of Fuels, Rules 62  and 62. 1
                   5, 918-919
                  Scavenger Plants, Rule 53. 1   5, 914
              Sulfur Dioxide-Sulfur Trioxide  Equilibrium at
               Various Oxygen Concentrations  562
              Sulfuric Acid Manufacture  716-722
                  Contact Process  716-718
              Sulfur in Fuels  539

                  Removal of  540-542

              Sulfur Oxides, Collection of from Burning  of
               Fuels   568-570

              Sulfur Scavenger Plants 722-734

                  Effect of Sulfur Compounds During Refining
                   723

                  Incineration Requirements   727-732

                  Incinerator Stack Height  732-733

                  Plant Operational Procedures  733-734
                  Removal of H2S from Refinery Waste Gas
                   723-725

                  Stack Dilution Air  732

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                                      Subject Index  - Sulfur
                                                                                               985
Sulfur Scavenger Plants  (continued)
     Sulfur in Crude Oil  722
     Tail Gas Treatment  732
Sulfur Trioxide Liquid Sulfonation  755
Sulfur Trioxide Vapor Sulfonation  743-744
Sulfur Trioxide from Sulfuric Acid Manufacturing
  716-722
Surface Coating Operations   858-865
     Control of Organic Vapors from   865
     Control of Paint Spray Booth Particulates
      864-865
     Dip Tanks  860-861, 863
     Evaporation  Curves  Relating Percent Solvent
      Losses to Flash-Off Times  862
     Flowcoating   858-860
     Overspray   861
     Roller Coating Machines   861, 863
     Spray Booths  858,  861-865
     Surface Coating and  Added Thinner Formulas
      864
     Types of Equipment   858-861
Surface Condensers  199-201,  203-207
Surfactant Processes  749-759
Sweating  305-308
     Aluminum  305
     Zinc, Lead,  Tin,  Solder, and Low Melting
      Alloy  305-308
Swinging Vane Velocity Meter  73-74
     Correction Factors  74
Synthetic Detergents   759-765
     Granule Handling  764-766
     Processes  761
     Raw Materials  759-761
     Slurry Preparation  761-762
     Spray Drying  762-764
Synthetic Detergent Surfactants   749-759
Tanks, Petroleum, see Storage Vessels
Tellerette   209
Thermal Spraying  430-431
    Powder Gun   431
Thermoplastic Resins   703
 Threshold Limit Values   938-944
     Paint Solvents  859
 Tin, Sweating   305-308
 Tilting Crucible Furnace  238
 Tire Buffing Equipment  410-414
     Cost of Control Equipment for  414
 Tolylene Diisocyanate, Resin Manufacture  703,
  705,  707
 Transfer Units, Packed  Towers   213-215
 Tray Towers,  see Plate or Tray Towers
 Tuna Canning  805-806
 Turbogrid,  Tray Towers  200-221
u
Use of this Manual  7
Valves, Petroleum Equipment   689-692
     Control   621-622
     Leakage of Hydrocarbons from   691
     Safety  589, 593-594
     Total Emissions from  691
Vapor Balance Systems, Petroleum Storage
  Vessels   647
Vapor Compressors  67-72
     Dynamic Compressors   69
     Positive-Displacement Compressors   68-69
     Reciprocating Compressors   69-72
     Types  67-72
     Use in Air Pollution Control  72
Vapor Condensers   198-207
     Applications   207
     Contact Condensers  199-201, 203
     Surface Condensers  199-201, 203-207
     Types of   199-201
Vapor Pressures
     Crude Oil  636
     Gasoline and Finished Petroleum Products
      635
Vapor Recovery Systems, Petroleum Storage
 647-648
Varnish Cooking  708-716
     Blown Oil  709

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986
                                      Subject Index - Varnish
Varnish Cooking (continued)
    Boiled Oil  708-709
    Equipment  709-710
    Esterification  709
    Gum running  709
    Heat-Bodied Oil  709
    Ingredients  709
    Oil Breaking  709
    Oleoresinous Varnish   709,  715
    Open Kettles  709-710
    Products and Processes, 708-709
    Spirit Varnish   709
    Stationary Kettles  710
    Stack Discharge Tests   714
    Thinning   710
Velocities for Pneumatic Conveying of Various
  Materials   366
Velocity Measurements
    Circular Stacks   74
    Meters  72-74
    Pitot Tube  25-27, 72-73
    Rectangular Ducts  74
    Swinging Vane Meter   73-74
Velocity Pressure  26
    Conversion Table,  VP to fpm  45
    Conversion Table, fpm to VP  949
    Corrections  27
    Friction Loss Chart  46
    Loss Calculation  52-56
    Loss,  Contraction  49
    Loss,  Hood Entry  45
    Pitot Tube  26
Ventilation Rates
    Minimum for Circular Low Canopy Hoods   40
    Minimum for Rectangular Low Canopy Hoods
      41
    Minimum for Tanks  33
    Open-Surface Tanks   34
Venturi Absorbers   228-229
Venturi Scrubbers  104
w
Waste-Gas Disposal Systems, Petroleum Equip-
  ment  585-626
    Control Valves   621-622
    Flares   581,  586-626
    Knockout Vessels  596-598
    Minimum Rupture Pressures  592
    Operational Difficulties of a  Refinery and
      Required Relief Capacities  591
    Overpressure Sizing  Factor  for Liquid
      Relief Valves   593
    Overpressure Sizing  Factor  for Vapor
      Safety Valves   594
    Pressure Relief System  588-604
    Removal of Hydrogen Sulfide from  723-725
    Rupture Disc   590-596
    Safety Valves  589, 593-594
    Sizing a Slowdown Line   598-604
Water Sprays
    High-Pressure Scrubber   103
    Mechanical,  Centrifugal Collector with Water
      Sprays   102-103
Water Vapor   957-958
Wet Collection Devices   99-106
    Cyclone-Type Scrubbers   101
    High-Pressure Water Sprays  103
    Mechanical,  Centrifugal Collector with Water
      Sprays   102-103
    Mechanical Scrubbers  102
    Mechanisms for Wetting the  Particle  100-10
    Orifice-Type Scrubbers   101-102
    Packed Towers   104-105
    Spray Chambers   101
    Theory of Collection   100
    Types of   101-105
    Venturi Scrubbers   104
    Wet Filters  105
White Smoke  from Combustion of Fuels  537-538
Wire  Reclamation  520-531
    Equipment Design Factors   525

Wood Treating  Equipment  414-421
    Ammoniacal Copper Arsenite Process   417
    Methods  of Treating Wood  415-417
    Rueping Process  417

Wood Waste Incinerators   460-471
    Design Factors for   462

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                                    Subject Index - Woodworking	987
Woodworking Equipment   372-375
    Disposal of Collected Wastes   374-375
    Exhaust System for   372-374

z
Zinc-Galvanizing Equipment   402-410
    Cleaning  402
    Control of Emissions from 405-410
    Cover Fluxes  402
    Dusting Fluxes  402
    Emissions from   403-406
    Foaming Agents   402
Zinc Melting,  see Secondary Zinc Melting Processes
Zinc Vaporization  293-294
                                     US GOVERNMENT PRINTING OFFICE 1977 O-234-767

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0S. Environmental Promotion Agenc,

Region 5, Library (PL-12J)
77 West Jackson Boulevard, I2ttl
Chicago, IL  60604-3590

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