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
activities and of cooperative studies conducted in conjunction -with state and local
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.
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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
-------
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
-------
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.
-------
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
-------
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.
-------
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
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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.
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X
X
x
X
x
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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.
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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).
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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.
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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
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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
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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_
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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
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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
YSTE
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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.
-------
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.
-------
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.
-------
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.
-------
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
-------
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.
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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.
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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.
-------
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)
-------
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.
-------
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
-------
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.
-------
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.
-------
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.
-------
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.
-------
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-
-------
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
-------
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
-------
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
-------
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-
-------
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.).
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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.
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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
-------
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
-------
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.).
-------
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.).
-------
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
-------
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.
-------
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
-------
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.
-------
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.).
-------
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-
-------
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
-------
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.
-------
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.
-------
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.
-------
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
-------
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.
-------
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
-------
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.).
-------
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
-------
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.
-------
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;
-------
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.
-------
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.
-------
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
-------
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,
-------
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
-------
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
-------
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.
-------
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
-------
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-
-------
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
-------
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
-------
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
-------
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-
-------
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
-------
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
-------
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
-------
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
-------
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).
-------
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.
-------
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
§20
OJ
z
LLJ
" in
^ 10
° 8
^ 6
t—
rs .
cc.
\ —
C3
i n
n a
S-^l
— -
A
/
/
SLAC
SLAG
^,
•—.
J
f
BA:
VOL
k.
A
1C
UME
v
/
•.
TH
•• fc
/
/
*• fc
- 3
170
*» S
x
/ \
' >^
1
x^
X,
\
\
"
0
Ib/ton
4*
r
\
\
L
\
N
^
L
\
\
\
\
^
\
L
\
\
^
t
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
-------
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
-------
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
-------
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.
-------
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
-------
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
-------
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
-------
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:
-------
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
s SJ
CD
a 49
i—
a 45
31 41
LU
>•
5 37
UJ
or
33
29
25
e
\
'•••.., Tfu,,
"•"t
__Ji^p^
*!U*f
i
«
I
^s\
x
X
/
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
-------
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
-------
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
-------
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.).
-------
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.
-------
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.
-------
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
-------
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.
-------
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:
-------
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.
-------
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.
-------
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
-------
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.
-------
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
-------
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
-------
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.
-------
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
-------
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
-------
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
-------
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.
-------
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.
-------
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
-------
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
-------
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.).
-------
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
-------
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).
-------
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-
-------
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
-------
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.
-------
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
-------
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-
-------
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.
-------
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.
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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.
-------
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.).
-------
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.
-------
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
-------
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.
-------
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.
-------
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).
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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.
-------
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.
-------
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.).
-------
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
-------
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.
-------
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.).
-------
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.
-------
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
-------
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,
-------
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.).
-------
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.
-------
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.
-------
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
-------
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.
-------
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.).
-------
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.
-------
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.
-------
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.
-------
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
-------
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
-------
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-
-------
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-
-------
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
-------
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
-------
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.
-------
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
-------
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
\
x\
^^^w
,\
\
™
1
—t
1L
\
\\
N\
\
\
•H
i r~
JL
t
\)
\
'
k
\
\
\
\
w
U
\
s
\
S
\
s
s.
^s\
o\[
h- — II— "T
L-IL-JJ
i M f:
TRIPLE -STAGE
BAFFLES
\
A
\
\
\
\
k V
S
^
\
\
>
\
\
—
\
\,
k.
V
V
\
^v_
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
I
>-
to
1
OC.
3
&
o
09%
0994
0992
0990
0988
0985
098
097
0%
093
090
085
080
O.?0
060
040
n
05 07
234 ; 10 20 40 7
AVERAGE TRIPLE STAGE BAFFLE
PLUS ORIFICE TYPE WET SECTION :
AVERAGE T
PLUS MOTO
CAL SEPARl
AVERAGE D
BAFFLE PL
TYPE WET S
A ,
/
/ /
'/
/ /
_*£.AVE
/ > STA
RIPLE ST
R DRIVEN
VTOR
UAL -STAG
JS ORIFICE
/
/ /
Xc,
/
/
RAGE SING
3E BAFFL
«GEE
IETK
e-^
/
r
/
/
IF
;s
IAFFLE
/
/
r
/
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(
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/
/
'J
_AVt
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V
-A
RAG
EN
WERAC
RECIRC
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EMOT
WET ME
EBL
JLAT
ORII
CHAI
CAL SEPARATORS
*GE DUAL STAGE BAF
1
---
**~~
DWER PUMP
ON TYPE WET SEC
ICE TYPE WET SEC
> I
TAVE
rf™
RAGE TRI
GE BAFFL
CURVE A = 75* OVERSPRAY CONDITIONS
CURVE B = 50% OVERSPRAY CONDITIONS
CUR\
FOR
50 <
SOLI
E C = 25* OVERSPRAY
WED STACK LOSS, L :
0LE
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
- 2A 2 U
3A 3 J
~ IB 1 ]
2B 2 >-20
.36 3 1
3A/
2*^
'V
V
2X
1Bx
/
X
.
X
.
x^
/
/
.
/
X"
s
s
s
S1
/
'
/
/
/
s
/
_/
r
J
^
/
/
/
/
^
/
S
'
/>
S>
.,
"^
/
^s
**
^
^
s*
^
s*
^
^
s
^
,
^
'VALUES ARE FOR BAFFLE SYSTEMS
ONLY
ON COMPLETE DRY BAFFLE BOOTHS
A
0
0
DO 025
30 hp an
FHERP
hp 1000
d or 10
DWERO
dm BU
inch we
1 PRESS
r AT LEAST
cf TO COVER
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
CURVE
CURVE
y
//
/
S
A 1
(
B (
— 1
C E
»
C
^
^
r
/
10TORORIVEN WET MECHANICAL SEPA
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
fm
A
/
' ^
r
A
/
/
/
/
/
/
^
A
*J
/
.
/.
s ^c
//
f J
f f
/w
/ I
u
]
//
S/
f y
/
.Ar
iLUES AR
UTLET ST
25 hp/lOOC
IF PRE
ED SEE
8
3TE THE
ONL
FIN
WTORS
ICIfNC
S
//
'
/
'
LFOR
HCKWI
cfmiu
CLEAN
"IGURE
SECUR
Y AND
«LhpD
«S5AN
Yl
//
/
»ETS
.LRE
SEND
NG B
332 A
VESA
SHOU
ETER
D6.E
'
/
.CTI
3UIR
r LE
*FFL
ND E
RE A
_DN
AINA
XAMF
^
/\
)NO
EAD
SST
ESA
QUA1
PPR
DTB
riON
LE
/
^
/
tLY
DIT
AN
LSO
riON
MM
EU
SIS
/
/
ON
03
AF
AT
ED
:E
7
/
/
AL
3
IONS-
FOR
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
-------
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-
-------
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 - :
-------
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
5nnn
, UUU
4nnn
, UUU
3 nnn
, UUU
t nnn
L , UUU
i nnn
i_
cnn
x— v OUU
5 400
LU
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0=
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^D on n
COMBUST 1
-^ r^
=> c
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Kn
40
30
on
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f /
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f / J
/ / /
/ / /
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r
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•*' / •**
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FOR DRY
VALUES,
FOR MO IS
VALUES,
•• f
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S f
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i /
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f *
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LG = 10 LOG Rc
REFUSE AND HIGH HE
USE +10% CURVE.
T REFUSE AND LOW H
USE -10% CURVE.
,*
#*
•'
4TINH
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
cr:
q
R
7
Cj
2
X/
/xXj
X*"
x
X".«|
.•*
X
#**
X
X
t*l
'
•'
^*
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c^:-
x^Xx
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l^x
FOR Dl
s
x1
x*;
x
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«*
^#*
#*
'*
..•
A
HA = 1 T
Y REF
USE
AN!
) H
IG
,
/
H
**
*
H
*
.•
•/
XX
XX
»*
JING
VALUES, USE +10% CURVE.
FOR HOIST REFUSE AND LOW HEATING
VALUES
, USE
-1C
% (
;UR
VE
X1
x'
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.
-------
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.
-------
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
-------
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.
-------
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.
-------
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)
-------
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
-------
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-
-------
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
-------
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.).
-------
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).
-------
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
-------
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.).
-------
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
-------
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.
-------
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
-------
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.
-------
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-
-------
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-
-------
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
-------
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.
-------
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-
-------
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.
-------
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
-------
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-
-------
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
-------
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.
-------
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
-------
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.
-------
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 ^
"" ^•" """"^
.5 ~ 8 .--
uJ — 7 ^ •*"" ^"
cc - --
oo — 6 »•» ""*"
00 .»"•
LU - ^ **
of •*- 5
—
— 4
— 3
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
™
200-^
~
—
100 _Z
—
80 -E
60 —
_
40^
—
^^
^^ •""^ i\r\ —
^-^ 20— =
-C _
f ~Z
^ Z
UJ —
g 10^
o ° -
00
Q c —
0 *••"
ll t
O
U- —
r^ ii ~~
o * -
24
-^
i—
_
0.5—
0.3 —
=-300,000
1-
E- 200, 000
-
E"
—
^ i nn nnn
E- 80,000
— KG nno
QU, UUU
~~ jin nnn ^^
r-
— CJ
_ ZUfUUU ^
r o:
— ID
~ h—
Z
r- 10,000 ~.
r- 8,000 S
_— CSJ
L.6,000 S
^-4,000 °°
r >-
~ a.
~ ^
E-2,000
_
1,000
-
-500
-400
0.23 -j—1
0.20—1
_:
•j
i
~
0.15-=
";
-;
~
•
~
o.io-i
^,-*=
- "0.09-1
~z
0.08-=
r n m —
o —
™- -^
Qi z
2 0.06-E
o -
a: -^
UJ ~
h-
"J 0.05 —
_ ~
a
0.04—
— '
0.03—
-
On1)
0.015-
=-5
i-10
f-15
i-20
=-25
— 30
=-35
^40
— */>
p
45 =
— ~sl
~ so -
•o
<~i
1
_ UJ"
M
LU
o
__ II
0
— 60
— 65
-
'"
-
— «n
0.013— » "
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
ZD
CO
CO
1 1 1
CC
O-
UJ
0
—
—1000
^800
rnn
— 600
—500 ___ _
==400 ~~
^300
E~
~ ortn
r~200
n
^
—
=-100
ir-80
— 60
^50
|-40
—
i-30
E-20
~~ in
ZT" 1U
— B
a
7
/
— 6
— 5
0.40^
-E
*~
-E
0.30-^
^
_z
—
-
0.20-^
=
^a
c/> -
^ 0.15-i
.E -
u r -
L±J
o _;
U- I
*^» ~
IX. —
o ;
______ ""
o -3
Q;
LU n m -
|- 0.10—=
LU _:
| 0.09-f
0.08^
0.07-1
_5
-
0.06-^
0.05-f
~
"_j
On M ~~
.04 -
Ono
.Uo —
007S —
— 7/16"
— Y
1 — W i /nit
=0-3/8"
._ 5
— Q
___^5/16"
— M
— K
ZI |
— G
=E-l/4"
z11
—
i-5
= 10
= 3/16"
— 1C
rr~lb
=-20
=-25
on
: fiii /„,.
1/8
^-35
*~
— «n
_ 40
=-45
z
—50
— 1/16"
— 55
-
/*n
2_ 60
rr
03
in
— - /u
!2
X
E
c
•5
'_»
^
to
•g
43
M
LU
M
CO
LU
O
LL.
o:
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
-------
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-
-------
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).
-------
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.
-------
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-
-------
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
-------
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).
-------
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.
-------
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
-------
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
-------
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
-------
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
-------
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-
-------
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
-------
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
-------
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.
-------
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.
-------
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.
-------
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
-------
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
-------
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.
-------
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
-------
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-
-------
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
-------
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-
-------
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.
-------
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).
-------
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:
-------
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.
-------
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
-------
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.),
-------
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.
-------
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
-------
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
a
!"
a.
c
o
c
2
c
g
c
^
c
c
4
•^
c
j
1
J
g ^ o
oa 4-*
bo E
-------
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.
-------
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
10 -
90-
80-
70«=
S^ 60 -
' 50-
40-
-
30-
— — M 0 to 36
-40 2.0-
-50 '
- 60 15-
-70 "
-80
-90
-100 i.o-
-125
09-
-150 08-
-175
-200 07-
-250
-300 0.6-
t400
0.5-
C -
o
0.4-
u_
•i 03-
t
o
09
C
° 0.2-
Ol
J
| 015
6
4)
1 010
O 009
008
007
006
- 9.0
80
- 70
-60
- 50
-4.0
- 3.0
- 20
- 1.5
— 1 0
- 0.9
- 0.8
- 0.7
- 06
-0.5
- OX
- 03
.
- 02
•
-0 15
•
- 0 10
- 009
- 008
- 007
-
J!
£
&
•a
2
I
o
0
C
~o
0
O
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
/
/
/
/
^
/
•
/
*
/
) 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 <=> •=> <=
/
/
/
/
x
^
r^
«•••"
^--
^•*"
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
y
/
^
X
^,x"
^X
"f
-r"
^*-
^i*0*
— *-
ir-j
—I. —•
10
I
) 20 40 60 80 100
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-
-------
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
-------
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
-------
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
-------
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-
-------
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.
-------
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).
-------
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
-------
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.
-------
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
-------
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
-------
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-
-------
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
-------
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
-------
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.
-------
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
-------
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.
-------
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.
-------
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
-------
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
-------
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.
-------
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).
-------
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
-------
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
-------
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
-------
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:
-------
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
-------
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.
-------
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.
-------
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:
-------
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
-------
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.
-------
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-
-------
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.
-------
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-
-------
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
-------
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
-------
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
-------
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.
-------
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
-------
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.
-------
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
-------
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
-------
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.
-------
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.
-------
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
-------
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.
-------
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.
-------
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
-------
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.).
-------
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.).
-------
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
-------
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
-------
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
-------
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.
-------
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
-------
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.
-------
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.).
-------
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-
-------
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.
-------
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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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.
-------
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
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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.
-------
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.
-------
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.).
-------
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
-------
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.
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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
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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
-------
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-
-------
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-
-------
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,
-------
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
-------
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.)
-------
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
-------
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
-------
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-
-------
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. ).
-------
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
-------
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-
-------
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.
-------
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-
-------
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.).
-------
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
-------
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
-------
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.
-------
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).
-------
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-
-------
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
-------
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
-------
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.
-------
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.
-------
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
-------
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
-------
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.
-------
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.
-------
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
-------
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
-------
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-
-------
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.
-------
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.).
-------
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.).
-------
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
-------
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
-------
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.
-------
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.
-------
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.).
-------
REFERENCES
Adams, R. L. 1964.
Application of Baghouses to Electric Furnace Fume Control. JAPCA, 14(8):299-302 (Aug).
Air Moving and Conditioning Assn. , Inc. 1963.
Bulletin 210. 205 W. Touhy Ave. , Park Ridge, 111.
Air Pollution Handbook.
See Magill et al.
Alden, J. L. 1948.
Design of Industrial Exhaust Systems. The Industrial Press, New York, N. Y.
Alexander, W. H. , and R. L. Bradley. 1958.
Can You Justify a CO Boiler? Petrol. Refiner. 37:107-12 (Aug).
Allen, G. L. , F.H. Viets, and L. C. McCabe. 1952.
Control of Metallurgical and Mineral Dusts and Fumes in Los Angeles County, California. Bureau
of Mines Information Circular 7627, U. S. Department of Interior, Washington, D. C. (Apr).
American Air Filter Company, Inc. 1958.
American Filter Handbook. Louisville, Ky. 40208.
American Air Filter Company, Inc. 1964.
Calendar-Memo-Handbook. Louisville, Ky. 40208.
American Conference of Governmental Industrial Hygienists. I960.
Threshold Limit Values for 1960. Arch. Environ. Health. 1:140-44 (Aug).
American Foundrymen's Association. 1949.
Handbook of Cupola Operation. American Foundrymen's Association, Chicago, 111. (Des Plaines,
111.)
American Gas Association Laboratories. 1940.
Research in Fundamentals of Atmospheric Gas Burner Design. Research Bulletin No. 10. Cleveland,
Ohio (Mar).
American Medical Association. 1956.
Arch. Environ. Health. 14:186-189.
American Petroleum Institute. I960.
Recommended Practice for the Design and Installation of Pressure-Relieving Systems in Refineries.
Part I. 2d ed. (Sept).
American Petroleum Institute. 1962a.
Evaporation Loss From Fixed-Roof Tanks. Bulletin 2518 (June).
American Petroleum Institute. 1962b.
Evaporation Loss From Floating-Roof Tanks. Bulletin 2517 (Feb).
American Petroleum Institute. 1962c.
Evaporation Loss From Low-Pressure Tanks. Bulletin 2516 (Mar).
American Petroleum Institute. 1962d.
Use of Plastic Foam to Reduce Evaporation Loss. Bulletin 2515 (Jan).
American Petroleum Institute - American Society of Mechanical Engineers. 1951.
Unfired Pressure Vessel Code. 5th ed.
-------
References - American
American Petroleum Institute. Division of Refining. 1951.
Manual on Disposal of Refinery Wastes. Vol III. Chemical Wastes. 2d ed. New York, N. Y.
American Petroleum Institute. Division of Refining. 1957.
Manual on Disposal of Refinery Wastes. Vol II. Waste Gases and Particulate Matter. 5th ed.
New York, N. Y.
American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. 1963.
ASHRAE Guide and Data Book. New York, N. Y.
American Society of Mechanical Engineers. 196Z.
ASME Unfired Pressure Vessel Code. Section VIII. New York, N. Y.
American Society for Testing Materials. 1958.
Specifications for Pig Lead, B29-55. In: 1958 Book of ASTM Standards, Part 2, Non-Ferrous
Metals. Philadelphia, Pa.
American Society for Testing Materials. 1959.
Standard Method for Measurement of Odor in Atmospheres (Dilution Method). Designation D1391-57.
In: ASTM Standards on Methods of Atmospheric Sampling and Analysis. Prepared by ASTM Com-
mittee D-22. Philadelphia, Pa.
American Water Works Association. 1951.
Standard Specifications for CoaL-Tar Enamel Protective Coatings for Steel Water Pipe. New York,
N. Y.
Anderson, E. 1924.
Some Factors and Principles Involved in the Separation and Collection of Dust, Mist and Fume From
Gases. Trans. Am. Inst. Chem. Engrs., Part 1. 16:69-86.
Anderson, H.E. 1958.
Filtering Radioactive Particles From Stack Gas. Air Conditioning, Heating, and Ventilating. 55:71-
77 (Feb).
Anderson, R. J. 1925.
The Metallurgy of Aluminium and Aluminium Alloys. Henry Gary Baird and Co. , Inc. , New York,
N. Y.
Anderson, R. J. 1931.
Secondary Aluminum. The Sherwood Press, Inc., Cleveland, Ohio.
Andrews, A.I. 1961.
Porcelain Enamels. Garrard Press, Champaign, 111.
Anonymous. 1950.
Repeal Brass Installs Unique Fume Control System. Western Metalworking. 8:32 (Mar).
Anonymous. 1957.
Metal Finishing-Guidebook-Directory. Metals and Plastics Publications, Inc. , Westwood, N. J.
Anonymous. 1961.
1961 Petrochemical Handbook Indexes. Alkyl Aryl Sulfonates. Hydrocarbon Processing and
Petroleum Refiner. 40:217 (Nov).
Arrandale, R. S. 1962.
Can Presintering Solve Glass Batch Problems? Ceram. Ind. 78:82. 83, 127, 138 (Apr).
ASHRAE Guide and Data Book.
See American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. 1963.
The Asphalt Institute. 1954.
Asphalt Protective Coatings for Pipelines. College Park, Md.
The Asphalt Institute. 1957.
Specifications and Construction Methods for Hot-Mix Asphalt Paving for Streets and Highways.
College Park, Md. (May).
-------
References - Atomic 887
Atomic Energy Commission.
See Ward, 1952.
Badger, W. L. , and W. L. McCase. 1936.
Elements of Chemical Engineering. 2d ed. McGraw-Hill Book Co. , Inc. , New York, N. Y.
Bagwell, F. A. , et al. 1970.
Oxides of Nitrogen Emission Reduction Program for Oil- and Gas-Fired Utility Boilers. F. A. Bag-
well and K. E. Rosenthal, Southern California Edison Company, Los Angeles, Calif. , and B. P.
Breen, N. Bayard de Volo, and A. W. Bell, Dynamic Science, a Division of Marshall Industries,
Irvine, Calif. Presented before the 32nd Annual Meeting of the American Power Conference,
Chicago, 111. (Apr).
Bailey, T. W. 1957.
A Report on the Use of Silicone Lubricants at the Wheaton Glass Company. Glass Ind. 38:433-40
(Aug).
Baker, T. C. 1935.
Distillation and Absorption in Packed Columns. Ind. Eng. Chem. 27:977 (Aug).
Baque, H.W. 1954.
Cut Heating Costs 10% With Proper Insulation. Ceram. Ind. 62:77, 111 (Mar).
Barber, J. C. 1958.
Corrosion Problems in the Manufacture of Phosphoric Acid From Elemental Phosphorus. Corro-
sion. 14:21-26 (Aug).
Barker-Greene Company. 1960.
Drier Principles. Aurora, 111.
Barnebey-Cheney Co.
Bulletin T-642. Columbus 19, Ohio.
Barr, W. H. 1970.
Control of NOX in Power Plant Operations. Pacific Gas and Electric Company, Monterrey, Calif.
Presented at the Fifth Technical Meeting of West Coast Section of Air Pollution Control Association,
San Francisco, Calif.
Barry, H.M. I960.
Fixed-Bed Adsorption. Chem. Eng. 67:105-07 (Feb 8).
Earth, E.J. 1958.
How to Make Roofing Asphalts. Petrol. Refiner. 37:172 (Mar).
Bartok, W. , A. R. Cunningham, H. J. Hall, E. H. Manny, and A. Skopp. 1969.
Systems Study of Nitrogen Oxide Control Methods for Stationary Sources. Prepared under Contract
No. PH-22-68-55 for Division of Process Control Engineering, National Air Pollution Control Ad-
ministration. Esso Research and Engineering Company, Government Research Laboratory New
York, N. Y. (Nov).
Begeman, M. L. 1947.
Manufacturing Processes. 2d ed. , John Wiley and Sons, Inc., New York, N. Y.
Bell, A. W. , et al. 1970.
Combustion Control for Elimination of Nitric Oxide Emissions from Fossil-Fuel Power Plants.
A. W. Bell, N. Bayard de Volo and B. P. Breen, Dynamic Science, Irvine, Calif. , and F. A. Bag-
well and K. Rosenthal, Southern California Edison Company, Los Angeles. Presented at the I3th
International Symposium on Combustion, University of Utah, Salt Lake City, Utah (Mar).
Benedict, M. , and T. H. Pigford. 1957.
Nuclear Chemical Engineering. McGraw-Hill Book Co. , Inc. , New York, N. Y.
-------
References - Beychok
Beychok, M. 1953.
Build a Flare for Under $5000. Petrol. Processing. 8:1162-63 (Aug).
Bingham, J. E. 1958.
Check Your Procedures on Rupture Disc Installation. Chem. Eng. 65:143-45 (Apr 17).
Bodurtha, F. T. , Jr. 1958.
Flare Stacks - How Tall? Chem. Eng. 65:177-80 (Dec 15).
Bonamassa, F. , and Y. S. Yee. 1957.
Emission of Hydrocarbons to the Atmosphere From Cooling Towers. Report No. 5. Joint District,
Federal, and State Project for the Evaluation of Refinery Elmissions. Los Angeles County Air
Pollution Control District, Los Angeles, Calif. (Aug).
Bortner, M. 1968.
A Review of Rate Constants of Reaction in Re-Entry Flow Fields. General Electric, TIS R68SD13
(June).
Brandon, D. B. 1959.
Developing Mathematical Models for Computer Control. ISA Journal 6:70-73.
Brandt, A.D. . 1947.
Industrial Health Engineering, John Wiley and Sons, Inc. , New York, N. Y.
Brief, R. S. , A. H. Rose, and D. G. Stephan. 1956.
Properties and Control of Electric-Arc Steel Furnace Fumes. JAPCA. 6:220-24 (Feb).
Brink, J. A. , Jr. 1959.
Monsanto Solves Air Pollution Problems With New Fiber Mist Eliminator. Chem. Eng. 66:183-86
(Nov 19).
Brink, J. A. , Jr., W. F. Burggrabe, and L. E. Green-well. 1966.
Mist Removal from Compressed Gases. Chem. Eng. Prog. 62:4-60 (Apr).
Brown, C. O. , and R. B. Wainright. 1952.
Synthetic Fluid Cracking Catalyst; Their Application and Utilization. Oil Gas J. 51(30): 133-37.
Brown, G. W. , andJ.E. Sublett. 1957.
Union Oil Company Builds New Waste-Water Facilities. Ind. Water and Wastes. 2:6-8 (Jan-Feb).
Bruce, W. L. , andW.A. Schubert. 1956.
Rotary Compressors and Vacuum Pumps. Chem. Eng. 63:224-26 (June).
Brumbaugh, A. K. , Jr. 1947.
Smokeless Burning of Refinery Vent Gases. Petrol. Processing. 2:181.
Bulcraig, W. R., and J. B. Haigh. 1961.
The Reduction of Air Pollution During the Reversal of a Producer Gas-Fired Regenerative Glass
Tank Furnace. J. Inst. Fuel. 34:73-78 (Feb).
Bussard, W. A. 1956.
Evaporation Losses and Their Control in Storage. Petrol. Processing. 11:104-26 (July).
Cameron, F. 1952.
Cottrell, Samaritan of Science. Doubleday and Co. , Inc. , Garden City, New York.
Campbell, W. W. , and R. W. Fullerton. 1962.
Development of an Electric-Furnace Dust-Control System. JAPCA. 12:574-77, 590 (Dec).
Caplan, K.J. 1954.
A Self-Cleaning Air Filter. Chem. Eng. Progr. 50:409-14 (Aug).
-------
References - Caplan 889
Caplan, K.J. I960.
Predicting the Performance of Reverse-Jet Filters. Air Conditioning, Heating, and Ventilating.
57:62-65 (Oct).
Carbon Products Division, Union Carbide Corporation. 1955.
Solvent Recovery by the "Columbia" Activated Carbon System. 270 Park Ave. , New York, N. Y.
Caretto, L. S. , R. F. Sawyer, and E. S. Starkman. 1968.
The Formation of Nitric Oxide in Combustion Processes. Report No. TS-68-1. Thermal Systems
Division, Department of Mechanical Engineering. University of California, Berkeley, Calif. (Mar).
Case, E.L. 1956.
Reciprocating Compressors. Chem. Eng. 63:216-23 (June).
Castler, L. A. , E.K. Daniels, andJ.R. Lutz. 1956.
Pollution Control at Ferndale, Washington. Presented at 21st American Petroleum Institute
Division of Refining Midyear Meeting, May 14-17, 1956.
Chass, R.L. 1959.
Engineering Control of Air Pollution in Los Angeles County. Presented at the Sanitary Engineer-
ing Division Program of the American Society of Civil Engineers, Los Angeles, Calif. , Feb. 1959.
Chass, R.L., and R. E. George. I960.
Contaminant Emissions From the Combustion of Fuels. JAPCA. 10:34-43 (Feb).
Chemical Week. 1969.
Chem. Week. 105(12):69 (Sept 20).
Chicago Bridge and Iron Company. 1959.
The Storage of Volatile Liquids. Technical Bulletin No. 20. Oakbrook, Hinsdale P. O. , 111.
Chilton, C. H. 1949.
Cost Data Correlated. Chem. Eng. 46:97-106 (June).
Clapp, W. H. , and S. Clark. 1944.
Engineering Materials and Processes. International Textbook Co. , Scranton, Pa.
Clarke, L. 1947.
Manual for Process Engineering Calculations. McGraw-Hill Book Co. , Inc. , New York, N. Y.
Claude, R.E. 1956.
Axial Compressors. Chem. Eng. 63:212-15 (June).
Clement, R. L. 1961.
Selection, Application and Maintenance of Cloth Dust Filters. Plant Eng. 15:92-97 (Aug).
Cleveland, D.L. 1952.
Design and Operation of a Steam Inspirating Flare. Presented at 17th American Petroleum Insti-
tute Division of Refining Midyear Meeting, May 13, 1952.
Committee on Industrial Ventilation. I960.
Industrial Ventilation. 6th ed. American Conference of Governmental Industrial Hygienists,
Lansing, Mich. (4th ed. , 1956; 7th ed., 1962)
Conison, J. I960.
How to Design a Pressure Relief System. Chem. Eng. 67:109-14 (July 25).
Connors, J. S. 1958.
Aqueous-Amine Acid-Removal Process Needn't Be Corrosive. Oil and Gas Journal. Tulsa, Okla.
(Mar 3).
-------
890 References - Cornell
Cornell, D. , W. G. Knapp, and J. R. Fair. I960.
Mass Transfer Efficiency - Packed Columns. Pts. 1 and 2. Chem. Eng. Progr. 56:68-74 (July);
48-53 (Aug).
Cottrell Electrical Precipitators.
See Western Precipitation Corporation, 1952.
Coulter, R.S. 1954.
Smoke, Dust, Fumes Closely Controlled in Electric Furnaces. Iron Age. 173:107-10 (Jan 14).
Cowan, D.W., H. J. Thompson, H.J. Paulus, and P. W. Mielke, Jr. 1963.
Bronchial Asthma Associated With Air Pollutants From the Grain Industry. JAPCA. 13:546-52 (Nov).
Crabaugh, H.R., A. H. Rose, Jr., and R. L. Chass. 1954.
Dust and Fumes From Gray Iron Cupolas--How They Are Controlled in Los Angeles County. Air Re-
pair. 4:125-30 (Nov).
Crane Company. 1957.
Flow of Fluids. Technical Paper No. 410. Chicago, 111.
Creesey, M.S., andA.K. Lyle. 1956.
What's New in Container Plant Design. Ceram. Ind. 67:98-101 (Sept).
Crumley, P. H. , and A. W. Fletcher. 1956.
The Formation of Sulphur Trioxide in Flue Gases. J. Inst. Fuel. 29:322-27 (Aug).
Cumiskey, J.E. 1956.
Reciprocating Compressor Special Report, Introduction to Principles. Petrol. Refiner. 35:120-23
(Nov).
Dalla Valle, J. M. 1952.
Exhaust Hoods. 2d ed. The Industrial Press, New York, N. Y.
Dalla Valle, J. M. , and H. C. Dudley. 1939.
Evaluation of Odor Nuisances in Manufacturing of Kraft Paper. Public Health Repts. 54:35-43
(Jan 13).
Decker, W. H. 1950.
Safe, Smokeless Combustion Features Waste Gas Burner at Sinclair Refinery. Petrol. Process-
ing. 5:965-66, 968 (Sept).
Deckert, I. S. , R. G. Lunche, and R. C. Murray. 1958.
Control of Vapors From Bulk Gasoline Loading. JAPCA. 8:223-33 (Nov).
de Lorenzi, O. 1947.
Combustion Engineering. Combustion Engineering--Superheater, Inc., New York, N. Y.
(de Lorenzi, O. , 1947. Courtesy Peabody Engineering Corp. ).
Des Jardins, P. R. 1956.
Handling Compressible Fluids in Chemical Processing. Chem. Eng. 63:178-87 (June).
Deutsch, W. 1922.
Movement and Charge of Electrical Carriers in a Cylindrical Condenser. Ann. Physik, 68,
4th Ser. (373, orig. ser.):335-44.
Diehl, J.E. 1957.
Calculate Condenser Pressure Drop. Petrol. Refiner. 36:147-53. (Oct).
Dolman, R.E. 1952.
Pumps. Chem. Eng. 59:155-69 (Mar).
-------
References - Donahue 891
Donahue, D.A. 1956.
Heat Exchangers. Petrol. Processing. 11:102-32 (Mar).
Dow Chemical Co. 1963.
Dowtherm Handbook. Midland, Mich.
Drinker, P., and T. Hatch. 1954.
Industrial Dust. 2d ed. McGraw-Hill Book Co. , Inc. , New York, N. Y.
Driskell, L. R. I960.
Design Tips for Piping of Pressure Relief Devices. Petrol. Refiner. 39:127-32 (July).
Duecker, W. W. , arid J. R. West. 1959.
Manufacture of Sulfuric Acid. 1st ed. . Reinhold Publishing Corp. , New York, N. Y.
Eastwood, L. W. 1946.
Gas in Light Alloys. John Wiley and Sons, New York, N. Y.
Edmister, W. C. 1948.
Hydrocarbon Absorption and Fractionation Process Design Methods. Petrol. Engr. 20(3): 193-98,
200 (Dec).
Elliott, J. , N. Kayne, and M. Le Due. 1961.
Experimental Program for the Control of Organic Emissions From Protective Coating Operations.
Report No. 8. Los Angeles County Air Pollution Control District, Los Angeles, Calif. (Jan).
Elonka, S. 1955.
Manual on Packing. Power. 99:107-30 (Mar).
Elonka, S. 1956.
Manual on Mechanical Seal. Power. 100:109-32 (Mar).
Environmental Sciences and Engineering, Division of Air Pollution.
Control of Particulate Emissions (Training Course Manual). Robert A. Taft Sanitary Engineer-
ing Center, Cincinnati, Ohio.
Ermenc, E. D. 1956.
Wisconsin Process Pebble Furnace Fixes Atmospheric Nitrogen. Chem. Eng. Progr. 52:149 (Apr).
Ezekiel, M. 1941.
Methods of Correlation Analysis. 2d ed. John Wiley and Sons, Inc. , New York, N. Y.
Fabrianio, W. L. 1961.
How to Combat Checker Clogging and Carry-Over. Ceram. Ind. 77:102, 103, 127 (Sept).
Factory Mutual Engineering Division. I960.
Handbook of Industrial Loss Prevention. McGraw-Hill Book Co., Inc., New York.
Fairlie, A.M. 1936.
Sulfuric Acid Manufacture. 5th ed. Reinhold Publishing Corp. , New York, N. Y.
Fairs, G. L. 1958.
High Efficiency Fibre Filters for the Treatment of Fine Mists. Trans. Inst. Chem. Engrs.
36:476-85.
Filter Fabric Facts.
See Willington Sears Co., 1954.
-------
892 References - Fischer
Fischer, J. 1957.
Air Conveying of Dry Materials. Northwest. Miller (Minneapolis, Minn.). Dec 31, 1957.
Fischer, J. 1958.
Practical Pneumatic Conveyor Design. Chem. Eng. 65:114-18 (June 2).
Fisher, M. M. , and F. C. Moriarty. 1953.
Waste Disposal in Urban Areas. Industry and Power (St. Joseph, Mich.). 64:83-85 (Apr).
Fox, E.A. , and V.E. Gex. 1957.
Procedure for Measuring Odor Concentration in Air and Gases. JAPCA. 7:60-61 (May).
Frederick, E. R. 1961.
How Dust Filter Selection Depends Upon Electrostatics. Chem. Eng. 68:107 (June 26).
Frey, H. M. , J. R. Kliegel, G. R. Nicherson, and T. J. Tyson. 1968.
One-Dimensional Kinetic Nozzle Analysis Computer Program (ODK). Prepared for the ICRPG Per-
formance Standardization Working Group (July).
Friedlander, S.K., L. Silverman, P. Drinker, and M. W. First. 1952.
Handbook on Air Cleaning. U.S. Atomic Energy Commission, Washington, D. C. (Sept). (AECD-
3361; NYO-1572).
Friedman, S. H. 1959.
Use These Computation Shortcuts. Chem. Eng. 66:149-50 (Sept 21).
Friedman, S.J., and W. R. Marshall, Jr. 1949.
Studies in Rotary Drying. Chem. Eng. Progr. 45:482 (Aug).
Gerstle and Kemnitz. 1967.
Atmospheric Emissions from Open Burning. JAPCA. (May).
Gilbert, N. , and F. Daniels. 1948.
Fixation of Atmospheric Nitrogen in a Gas Heated Furnace. Ind. Eng. Chem. 40:1719-23 (Sept).
Gillespie, G.R., andH.F. Johnstone. 1955.
Particle Size Distribution in Some Hygroscopic Aerosols. Chem. Eng. Prog. 51:78 (Feb).
Giusti, Gino P. 1965.
Sulfur Recovery by the Split-Stream Process and by the Partial Combustion Process. Oil and Gas
Journal. Tulsa, Okla. (Feb 22).
Glasstone, S. 1946.
Textbook of Physical Chemistry. D. Van Nostrand Co. , Inc., Princeton, N.J.
Glaubitz, F. 1963.
The Sconomic Combustion of Sulfur-Containing Heating Oil. Parts I and II. Combustion. 34(7):31-
35 (Jan); 34(9):25-32 (Mar).
Gosline, C. A. , L. L. Falk, andE.N. Helmers. 1956.
Evaluation of Weather Effects Section 5. In: Air Pollution Handbook. McGraw-Hill Book Co. , Inc. ,
New York, N. Y.
Green, W. G. 1952.
Smokeless Burning of Refinery Vent Gases. Presented at 17th American Petroleum Institute
Division of Refining Midyear Meeting, May 13, 1952.
Griswold, J. 1946.
Fuels, Combustion, and Furnaces. 1st ed. McGraw-Hill Book Co., Inc., New York, N. Y.
-------
References - Griswold
893
Griswold, S. S. , and I. Weisburd, eds. 1962.
Air Pollution Control Field Operations Manual Guide for Inspection and Enforcement. Public
Health Service Publication No. 937. Division of Air Pollution, Public Health Service, U.S.
Department of Health, Education, and Welfare, Washington, D. C.
Gumz, W. 1950.
Overfire Air Jets in European Practice. Combustion. 22:39-48 (Apr).
Gunsaulus, R.K. 1958.
How to Record and Control Furnace Flue Gas Automatically. Ceram. Ind. 70:70-73, 93, 95 (Mar).
Hajek, J.D. , and E. E. Ludwig. I960.
How to Design Safe Flare Stacks. Parts land II. Petrol. Engr. 32:C31-C38; C44-C51 (June,
July).
Haley, R. H. 1949.
How to Control Fumes in Non-Ferrous Melting. Foundry. 77:118, 121 (Sept).
Hannaman, J.R., andA.J. Etingen. 1956.
Here's a Workable Smokeless Flare System. Petrol. Processing. 11:66-69 (Mar).
Hauck Manufacturing Company. 1953.
Industrial Combustion Data. Brooklyn, N. Y.
Hemeon, W. C. L. 1955.
Plant and Process Ventilation. 1st ed. The Industrial Press, New York, N. Y. (2d ed, 1963).
Hansen, J.E. 1932.
The Advanced Technique of Porcelain Enameling. Enamelist Publishing Co. , Cleveland, Ohio.
Herrick, R. A. 1963.
A Baghouse Test Program for Oxygen Lanced Open Hearth Fume Control. JAPCA. 13:28-32
(Jan).
Hersey, H.J., Jr. 1955.
Reverse-Jet Filters. Ind. Chemist. 31:138 (Mar).
Hicks, T. 1951.
Power's Handbook on Fans. Power. 95:87-102 (Oct).
Holzbock, W. G. 1959.
Control Valve Construction. Chem. Eng. 66:135-38 (Apr 6).
Hougen, O.A., andK.M. Watson. 1945.
Industrial Chemical Calculations. 2d ed. John Wiley and Sons, Inc. , New York, N. Y.
How, H. 1956.
How to Design Barometric Condensers. Chem. Eng. 63:174-82 (Feb).
Huebner, W. O. 1959.
How Esso Cuts Flare Gas Losses. Air Eng. 1:38-39 (Apr).
Hunter, W. L. 1959.
Bottom-Loading Tank Trucks Successful. Petrol. Refiner. 38:171-72. (Oct).
ICRPG Performance Standardization Working Group. 1968.
ICRPG One-Dimensional Equilibrium Reference Program--Preliminary Description of ODE, a Com-
puter Program for the Calculation of Chemical Equilibrium Composition with Applications. ICRPG
Performance Standardization Working Group (July).
-------
894 References - Industrial
Industrial Hygiene Codes Committee. 1938.
Fundamentals of Design, Construction, Operation and Maintenance of Exhaust Systems. American
Foundrymen's Association, Chicago, 111. (Des Plaines, 111.)
Industrial Ventilation.
See Committee on Industrial Ventilation, I960.
Ingels, R.M., N. R. Shaffer, and J. A. Danielson. I960.
Control of Asphaltic Concrete Plants in Los Angeles County. JAPCA. 10:29-33 (Feb).
Ittner, M. H. 1940 and 1942.
U.S. Patent Nos. Re. 22,006 (Jan 1942) and 2, 221, 779 (Nov 1940).
James, D. E. 1970.
A Boiler Manufacturer's View of Nitric Oxide Formation. Babcock and Wilcox. Presented at the
Fifth Technical Meeting of the West Coast Section of the Air Pollution Control Association. San
Francisco, Calif.
Jenny, J. P. 1951.
Smelter Fume Control. Proceedings of Forty-Fourth Annual Convention, Air Pollution and Smoke
Prevention Association of America (Air Pollution Control Association), Roanoke, Va. , May 7-10,
1951.
Jensen, L. B. 1945.
Microbiology of Meats. 2d ed. Garrard Press, Champaign, 111.
Johnstone, H. F. , and M. H. Roberts. 1949.
Deposition of Aerosol Particles From Moving Gas Streams. Ind. Eng. Chem. 41:2417-23 (Nov).
Jones, C. T. , and P. S. Viles. 1952.
Estimating Oil Losses by Atmospheric Evaporation From Refinery Separator Surfaces. Petrol.
Refiner. 31:117-20 (Jan).
Kane, John M. .
Manual of Exhaust Hood Designs. Vol. 2. Bull. No. 270-E2B. American Air Filter Co. , Inc.,
Louisville, Ky. 40208.
Ranter, C. V. , R. G. Lunche, F. Bonamassa, B.J. Steigerwald, andR.K. Palmer. 1958.
Emissions to the Atmosphere From Petroleum Refineries in Los Angeles County. Report No. 9.
Joint District, Federal, and State Project for the Evaluation of Refinery Emissions. Los Angeles
County Air Pollution Control District, Los Angeles, Calif.
Kent, R. T. ed. 1938.
Mechanical Engineers Handbook, llth ed. John Wiley and Sons, Inc, New York, N. Y. (12th ed. ,
1950).
Kern, D. Q. 1950.
Process Heat Transfer. McGraw-Hill Book Co. , Inc. , New York, N. Y.
Kerns, G. D. I960.
New Charts Speed Drum Sizing. Petrol. Refiner. 39:168-70 (July).
Kirk, R.E., andD.F. Othmer. eds. 1947 and 1969.
Encyclopedia of Chemical Technology. 1st ed. Interscience Encyclopedia, Inc., New York, N. Y.
(Volumes 2, 5, 1, 8, 9, 10, 14 and 19).
Lapple, C.E. 1951.
Processes Use Many Collection Types. Chem. Eng. 58:145-51 (May).
-------
References - Lapple 895
Lapple, C.E. 1963.
Dust and Mist Collection. In: Chemical Engineers' Handbook. Perry, J. H. , ed. McGraw-Hill
Book Co. , Inc. See also, Air Pollution Abatement Manual. C. A. Gosline, ed. Manufacturing
Chemists' Association, Inc. , Washington, D. C. 1952.
Lemke, E.E., W. F. Hammond, and G. Thomas. I960.
Air Pollution Control Measures for Hot Dip Galvanizing Kettles. JAPCA. 10(l):70-76 (Feb).
Leonard, E. S. 1956.
Centrifugal Compressors. Chem. Eng. 63:206-11 (June).
Leva, M. 1953.
Tower Packings and Packed Tower Design. The United States Stoneware Co. Akron, Ohio.
Liberman, J.A. 1957.
Engineering Aspects of the Disposal of Radioactive Wastes From the Peace-Time Applications of
Nuclear Technology. Am. J. Public Health. 47:345-51 (Mar).
Lieblich, N. 1953.
Selection of Diaphragm Control Valv.es and Regulators. Proceedings of the Southwestern Gas
Measurement Short Course, University of Oklahoma.
Lobo, W.E. , L. Friend, F. Hashmall, and F. Zenz. 1945.
The Limiting Capacity of Dumped Tower Packings. Trans. Am. Inst. Chem. Engrs. 41:693-710.
Loquercio. 1967.
Air Pollution Potential for Coffee Roasting. Air Eng. (Nov).
Los Angeles County Air Pollution Control District. 1960a.
Organization and Program. Report No. 1. Emissions of Oxides of Nitrogen From Stationary
Sources in Los Angeles County. Los Angeles, Calif.
Los Angeles County Air Pollution Control District. 1960b.
Oxides of Nitrogen Emitted by Small Sources. Report No. 2. Emissions of Oxides of Nitrogen
From Stationary Sources in Los Angeles County. Los Angeles, Calif. (Sept).
Los Angeles County Air Pollution Control District. 1970.
Profile of Air Pollution Control in Los Angeles County. Los Angeles, Calif. (Jan).
Lowenstein, J. G. 1958.
Calculate Adequate Rupture Disc Size. Chem. Eng. 65:157-58 (Jan 13).
Lunche, R. G. , A. Stein, C.J. Seymour, and R. L. Weimer. 1957.
Distribution Survey of Products Emitting Organic Vapors in Los Angeles County. Chem. Eng. Prog.
53:371-76 (Aug).
Lunde, K.E., and C.E. Lapple. 1957.
Dust and Mist Collection—A Critique on the State of the Art. Chem. Eng. Prog. 53:385-91
(Aug).
MacKnight, R. J. , J. E. Williamson, J. J. Sableski, Jr., and J. O. Dealy. I960.
Controlling the Flue-Fed Incinerator. JAPCA. 10:103-09 (Apr).
MacPhee, R.D., J.R. Taylor, and A. L. Chaney. 1957.
Some Data on Particulates From Fuel Oil Burning. Proceedings of Semi-Annual Technical Con-
ference, Air Pollution Control Association, San Francisco, Calif., Nov. 18-19, 1957.
Magill, P.L., F.R. Holden, and C. Ackley, eds. 1956.
Air Pollution Handbook. McGraw-Hill Book Co. , Inc. , New York, N. Y.
-------
896 References - Mantell
Mantell, C. L. 1961.
Adsorption. 2d ed. McGraw-Hill Book Co., Inc., New York, N. Y.
Manual of Exhaust Hood Designs.
See Kane, J. M.
Manufacturing Chemists' Association, General Safety Committee. 1954.
Guide for Safety in the Chemical Laboratory. Van Nostrand, New York, N. Y.
Marks, L.S. , ed. 1951.
Mechanical Engineers' Handbook. 5th ed. McGraw-Hill Book Co. , Inc. , New York, N. Y.
Marshall, W. R. , Jr., and S. J. Friedman. 1950.
Drying. In: Chemical Engineers' Handbook, 3d ed. Perry, J. H. , ed. McGraw-Hill Book Co. ,
Inc. , New York, N. Y.
Marzocchi, A., F. Lachut, and W. H. Willis, Jr. 1962.
Glass Fibers and Their Use as Filter Media. JAPCA. 12:38-42 (Jan).
Mason-Neilan Division. 1963.
Valve Slide Rule Instructions. Worthington Corp. , Norwood, Mass.
Mattiello, J. J. 1943.
Protective and Decorative Coatings. Vol. III. John Wiley and Sons, New York, N. Y.
Maurin, P. G. and J. Jonakin. 1970.
Removing Sulfur Oxides from Stacks. Chemical Engineering. Copyright 1970 by McGraw-Hill, Inc.
New York, N. Y. (Apr 27).
McAdams, W. H. 1942.
Heat Transmission. 2d ed. McGraw-Hill Book Co. , Inc. , New York, N. Y.
McCabe, L. C. 1952.
Secondary Processing of Aluminum. Ind. Eng. Chem. 44:121A-122A (May).
McCord, C. P. , and W. N. Witheridge. 1949.
Odors, Physiology and Control. McGraw-Hill Book Co. , Inc., New York, N. Y.
McLouth, M.E., and H. J. Paulus. 1961.
Air Pollution From the Grain Industry. JAPCA. 11:313-17 (July).
Mellan, I. 1944.
Industrial Solvents. Reinhold Publishing Corp. , New York, N. Y.
Meredith, H. H. , Jr., 1967.
Desulfurization of Caribbean Fuel. Humble Oil and Refining Company. Presented before the 60th
Annual Meeting of the Air Pollution Control Association. Cleveland, Ohio (June).
Merritt, F. H. 1958.
Side Port Furnaces. Glass Ind. 39:375-96 (July).
Metal Finishing-Guidebook Directory. 1957.
Solvent Degreasers. Nulle, Howard, Finishing Publications, Inc. Westwood, N. J.
Metco, Inc. 1964.
Flame Spray Handbook, Vols. I, II, III. Westbury, N. Y.
Miller, P.D., Jr., E. J. Hibshman, and J. R. Connell. 1956.
The Design of Smokeless, Nonluminous Flares. Presented at 21st American Petroleum Institute
Division of Refining Midyear Meeting, May 14-17, 1956.
-------
References - Mills _897
Mills, J.L., K.D. Luedtke, P.F. Woolrich, and L. B. Perry. 1961.
A Summary of Data on Air Pollution by Oxides of Nitrogen Vented From Stationary Sources. Final
Report. Report No. 4. Emissions of Oxides of Nitrogen From Stationary Sources in Los Angeles
County. Los Angeles, Calif. (July).
Mills, J.L. , R.T. Walsh, K.D. Luedtke, andL.K. Smith. 1963.
Quantitative Odor Measurement. JAPCA. 13:467-75 (Oct).
Molcohy, B.D, 1950.
The Cupola--Its Raw Materials and Operation. Foundry. 78:75-76 (Mar).
Monstross, C.F. 1953.
Entrainment Separation. Chem. Eng. 60:213-36 (Oct).
Mumford, A. R. , et al. 1940.
Characteristics of Cloth Filters on Coal Dust-Air Mixtures. Trans. Am. Soc. Mech. Engrs.
62:271-81.
National Bureau of Standards. 1949.
Safe Handling of Radioactive Isotopes. Handbook No. 42.
Natural Gas Equipment, Inc. 1955.
Venturi-Type Burner Catalog. 1810 Fair Oaks Ave. , South Pasadena, Calif.
Natural Gas Processors Suppliers Association. 1957.
Engineering Data Book. 7th ed. Tulsa, Okla.
Neimeyer, E.R. 1961.
Check These Points When Designing Knockout Drums. Hydrocarbon Process. Petrol. Refiner.
40:155-56 (June).
Nelson, W. L. 1953.
How Painting Affects Storage Tank Losses. Oil Gas J. 52:130 (Nov 2).
Nelson, W. L. 1958.
Petroleum Refinery Engineering. 4th ed. McGraw-Hill Book Co. , Inc. , New York, N. Y.
New York Blower Company. 1948.
Bulletin 482, La Porte, Ind.
Nonferrous Foundrymen's Smog Committee. .
Furnace Practice Manual, Los Angeles, California.
Obrzut, J.J. 1958.
Will the Big Demand for Oxygen Come From Open Hearths? Iron Age. 182(Pt. 2): 172-74 (Sept 11).
O'Connell, H.E. 1946.
Plate Efficiency of Fractionating Columns and Absorbers. Trans. Am. Inst. Chem. Engrs.
42:741-55.
Oil and Gas Journal. 1957.
Special Processing Section: Processing in Today's Refineries. Oil Gas J. 55:121-68 (Mar 25).
Parmelee, C. W. 1951.
Ceramic Glazes. 2d ed. Industrial Publications, Inc. , Chicago 3, 111.
-------
898 References - Peach
Peach, N. 1959.
Electrical Conversion. Power. 103:67-90 (Dec).
Peckham, G. W. 1962.
New Electric Furnace Reduces Melting Costs. Glass Ind. 43:552, 568, 573 (Oct).
Penney, G.W. 1937.
A New Electrostatic Precipitator. Elec. Eng. 56:159-63 (Jan).
Perry, J. H. , ed. 1950andl963.
Chemical Engineers' Handbook. 3d. and 4th ed. McGraw-Hill Book Co. , Inc., New York, N. Y.
Peters, M.S. 1955a.
Principles and Processes for Removing Nitrogen Oxides From Gases. Engineering Experiment
Station, University of Illinois. Technical Report No. 14 (Aug).
Phelps, A. H. , Jr. 1967.
Air Pollution Aspects of Soap and Detergent Manufacture. Technical Information Report from the
Tl-2 Committee. JAPCA. 17:8-505 (Aug).
Plastics Catalog Corporation. 1959.
Modern Plastics Encyclopedia Issue for I960. 37(1 A):68- 180. Bristol, Conn.
Porter, E. D. 1959.
Electric Furnaces. Chem. Eng. 66:133-36 (Mar 9).
Powell, J.S. 1950.
Selection of an Odorant for Natural Gas Odorization. Proceedings of Pacific Coast Gas Associa-
tion. 41:134-38.
Prater, N. H. , and J. Mylo. 1961.
Equipment Cost Data File. Hydrocarbon Process. Petrol. Refiner. 40:209-10 (May); 173-74
(June); 163-64 (July); 131-32 (Aug).
Priestley, H. 1958.
Introductory Physics. Allyn and Bacon, Inc. , Boston, Mass.
Pring, R. T. 1952.
Bag-Type Cloth Dust and Fume Collectors. In: United States Technical Conference on Air Pollu-
tion, May 3-5, 1950, Washington, D. C. , L. C. McCabe, chairman. McGraw-Hill Book Co., Inc.,
New York, N. Y.
Puleo, P. A. 1960.
Which to Use — Relief Valve or Rupture Disc? Petrol. Refiner. 39:157-62 (Oct).
Randolph, W. W. 1956.
Gas Distribution in Electrostatic Precipitators. Proceedings for Engineering Seminar on Electro-
static Precipitation. Pennsylvania State University, University Park, Pa.
Ranz, W.E. 1951.
The Impaction of Aerosol Particles on Cylindrical and Spherical Collectors. Engineering Ex-
periment Station, University of Illinois, Technical Report No. 3. (March 31).
Rendle, L.K., andR.D. Wilsdon. 1956.
The Prevention of Acid Condensation in Oil-Fired Boilers. J. Inst. Fuel. 29:372-80 (Sept).
Reno, G. J. , E.D. Neumann, and L. C. Burroughs. 1958.
How Shell Treats Refinery Wastes. Petrol. Refiner. 37:153-60 (May).
Report No. 3, Experimental Program for the Control of Organic Emissions From Protective Coat-
inp Operations. See Snpnrpr pt al 1
-------
References - Report 899
Report No. 8, Experimental Program for the Control of Organic Emissions From Protective Coat-
ing Operations. See Elliott et al. , 1961.
Research-Cottrell, Inc.
Velocity Tables. Bound Brook, N. J. , (p. 1).
Robertson, L. F. , F. V. Halvonik, and J.J. McMackin. 1957.
Regenerator Efficiency and Basic Brick in a Glass Furnace. Am. Ceram. Soc. Bull. 36:381-84
(Nov).
Rodebush, W.H. 1950.
Filtration of Aerosols. Chapter 9. In: Handbook on Aerosols. U.S. Atomic Energy Commission,
Washington, D. C. , 1950. Reprinted 1963 (Available From U.S. Department of Commerce, Office
of Technical Services).
Ronald, D. 1935.
Handbook of Offensive Trades. William Hodge and Co. , Ltd. , London, Eng.
Rose, A.H. , and H. R. Crabaugh. 1955.
Incinerator Design Standards: Research Findings. Publication 60. Los Angeles County Air
Pollution Control District, Los Angeles, Calif.
Rose, A.H., Jr., D. G. Stephan, andR.L. Stenburg. 1958.
Prevention and Control of Air Pollution by Process Changes or Equipment. Tech. Rept. A58-11.
Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio; See also, Air Pollution World
Health Organization Monograph Series No. 46, Columbia University Press, New York, N. Y. , 1961.
Rose, H. E. , and A. J. Wood. 1956.
An Introduction to Electrostatic Precipitation in Theory and Practice. Essential Books, Fairlawn,
N. J.
Rudolfs, W. 1953.
Industrial Water and Wastes, Their Disposal and Treatment. Reinhold Publishing Corp. , New
York, N. Y.
Rupp, W.H. 1956.
Air Pollution Sources and Their Control. Section 1. In: Air Pollution Handbook. McGraw-Hill
Book Co. , Inc. , New York, N. Y.
St, John, H.M. 1955.
Melting Practice in the Brass Foundry. Foundry. 83:107-08 (Nov).
Samans, W. 1955.
Pressure Relief Devices. Petrol. Processing. 10:849-53 (June).
Sax, N.R. 1963.
Dangerous Properties of Industrial Materials. 2d ed. Reinhold Publishing Corp. New York, N. Y.
Scheer, J.F. 1956.
The Big Etch. Skyline (North American Aviation, Inc.). 14:23 (May).
Scheflan, L. , and M. B. Jacobs. 1953.
The Handbook of Solvents. Van Nostrand Reinhold Co. New York, N. Y.
Schmidt, A. 1928.
Progress in the Art of Electrical Precipitation. Trans. Am. Inst. Chem. Engrs. 21:11-33.
Schmidt, W. A. 1949.
Electrical Precipitation and Mechanical Dust Collection. Ind. Eng. Chem. 41:2428-32 (Nov).
234-767 O - 77 - 59
-------
900 References - Schmidt
Schmidt, W. A., andC.R. Flodin. 1952.
Fundamental Principles, Design, Application, Performance, and Limitations of Electrical Pre-
cipitation Equipment. In: United States Technical Conference on Air Pollution, May 3-5, 1950,
Washington, D. C. L. C. McCabe, chairman. McGraw-Hill Book Co. , New York, N. Y.
Schmidt, W. A. , W. T. Sproull, and Y. Nakada. 1950.
How the Operation of a Cottrell Precipitator is Affected by the Resistivity of the Collected Mate-
rial. Presented at 170th General Meeting, American Institute of Mining and Metallurgical En-
gineers, New York, N. Y. , Feb. 15, 1950.
Semrau, K. T. I960.
Correlation of Dust Scrubber Efficiency. JAPCA. 10:200-07 (June).
Shamos, M. H. , and S. G. Roth. 1950.
Industrial and Safety Problems of Nuclear Technology. Harper Bros. , New York, N. Y.
Shand and Jurs Co.
Bulletin 52-D. Berkeley, Calif.
Sharp, D.E. 1954.
Fuel Utilization in Glass Melting. Ceram. Ind. 63:45-51 (Dec).
Sharp, D.E. 1955.
Tank Design Aids in Melting and Fining. Ceram. Ind. 64:49-51, 88 (Feb).
Sherwood, T.K., and R. L. Pigford. 1952.
Absorption and Extraction. McGraw-Hill Book Co. , Inc. , New York, N. Y.
Shreve, R.N. 1945, 1956, and 1967.
The Chemical Process Industries. Copyright 1945, 1956, and 1967 by McGraw-Hill, Inc.
Used with permission of McGraw-Hill Book Co. , Inc., New York, N. Y.
Silvas, Sal J. 1969.
The World of Synthetic Detergents. Chem. Week. 105:12-67 (Sept 20); 16-79 (Oct 18).
Silverman, L. 1950.
Filtration Through Porous Materials. Am. Ind. Hyg. Assoc. Quart. 11:11-20.
Singer, S.J. 1956.
Silicones Open New Era in Glass Making. Ceram. Ind. 57:82, 83, 117 (Nov).
Slaik, H. , and A. Turk. 1953.
Air Conservation Engineering. 2d ed. Connor Engineering Corp. , Danbury, Conn.
Smith, A. G. 1956a.
Air Oxidation of Sulfides in Process Waters and Caustic Solutions. Presented at 21st American
Petroleum Institute Division of Refining Midyear Meeting, May 14-17, 1956.
Smith, A.G. 1956b.
Ridding Process Waters and Caustic Solutions of Sulfides. Oil Gas J. 54:95-96, 98-99 (July 9).
Smith, E. C. 1958.
Air-Cooled Heat Exchangers. Chem. Eng. 65:145-50 (Nov 17).
Smolen, W. H. 1951.
Smokeless Flare Stacks. Petrol. Processing. 6:978-82 (Sept).
-------
References - Smolen 901
Smolen, W. H. 1953.
Design of Smokeless Flares. Presented at 17th American Petroleum Institute Division of Re-
fining Midyear Meeting, May 13, 1952.
Spain, R. W. 1955.
Glass Furnaces and How They Operate. Ceram. Ind. 65:71-74 (Aug).
Spain, R. W. 1956a.
How to Get Better Results From Long Campaigns. Ceram. Ind. 67:84-85, 87 (Nov).
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).
-------
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).
-------
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-
cipitators. JAPCA. 10:239-45 (June).
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).
-------
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
-------
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
-------
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)
-------
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
-------
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
-------
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.
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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-
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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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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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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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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
-------
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.
-------
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.
-------
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
-------
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
O> CD
V) -!-•
CO -I-*
o> t/t
c c
•£.
J=
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ra
a> ra
3 a.
w ai
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-------
954
MISCELLANEOUS DATA
X R
y Dif
6 2
UltramicfOSC
10
E
Ult
UHiacenlnlu
raction
0
ope
ectro
Micioscope
— fH
afiltiation
8
e
Cent
Sei
Tu
Li
MICIOSCO
i
i uge
6
imentation &
13, 19
Permeability
9 11 17
rbidimetry
2,5
;ht Scattering
15.21
pe
Gas
iravi
21
ilutnalion
1 18
y Settling
^M!
-
hine
Visi
ools (Microrm
xevrn
3
bleto
12 24
ter V
Eye
ermer Cahper,
etc)
«• 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
Jianv
Tobacco
Mosaic
et of Gas Miy
CONVENTIONS
Range of Sizes
Small Range-Average
Doubtful Values
|
Nor
Toba
Necr
Virus
c.
ecule"
TiaJ Impuntie
Zinc Ox
s sr
•J*TT*
rbon Black
22,24
Magnesii
Silver Iodide
25
Combustion
. In
Aerosols
21
met Outdoor
Air
5, 10) 1
Metallurgical Dust and
deFi
16
co Sm
15, 16,
momum Chlo
* 16
Al
ike
5, 16 1
Oil Smoke
I 15. 16
i Oxide Smoke
16
Ro
luclei
' "1 "
SeaSa
n Smoke
12
(Enamels)
t Nudei
7
Fog
6,8, 1
Fumes |
20 | |
Smelter Dust & fan
deF
all Fu
15, 1
1
Pift
R
10, i:
es
Foundry Dust
Flour M II Dust
nes Sprayed Z nc Dust
s
ulfuric Acid
13, 15, 15
Condensed
Zinc Dust
{To7f3
tsecticide Dus
1,18
Bacteria
3,15
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
o
Jo
o
01
aina
o
o
1C
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CM
O3
cn
CNI
o
o.
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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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