&EFK
                United States
                Environmental Protection
                Agency
            Office of Air Quality
            Planning and Standards
            Research Triangle Park NC 27711
EPA-340/1-84-012
July 1984
               Air
Performance
Evaluation Guide
For Large  Flow
Ventilation Systems
                                  M>R
f EPA LIBRARY SERVICES RTP NC


Eft 340/1- £4--0

TECHNICAL DOCUMENT COLLECTION

-------
                                    EPA-340/1-84-012
    Performance Evaluation Guide
For  Large Flow Ventilation Systems
                        by
                    William Kemner
                    Richard Gerstle
                    Yatendra Shah
                  Contract No. 68-01 -6310
                  Work Assignment No 119
               EPA Project Officer: John Busik
              EPA Project Manager: Dwight Hlustick
            U.S. ENVIRONMENTAL PROTECTION AGENCY
            Office of Air Quality Planning and Standards       *«>»•'
              Stationary Source Compliance Division    {  Pt"r,-T-!?C» ?
                  Washington, DC 20460
                      May 1984

-------
                                 DISCLAIMER
     The Information in this document has  been funded wholly or in part by
the United States Environmental  Protection Agency under Contract No.  68-01-
6310 to PEDCo Environmental, Inc.   It has  been subject to the Agency's peer
and administrative review, but it  does not necessarily reflect the views of
the Agency and no official endorsement should be  inferred.

-------
                                  CONTENTS


                                                                        Page

Figures                                                                    v
Tables                                                                  viii
Acknowledgment                                                            ix

1.   Introduction                                                         1

2.   General Ventilation and Hooding Principles                           3

          Design basis                                                    5

3.   Hood Design Considerations                                          11

          Determining air flow requirements                              16

4.   Duct Design and Considerations                                      33

          Transport velocities                                           34
          Energy losses                                                  36
          Branched systems                                               43

5.   Fan Systems                                                         46

          Fan types and operating characteristics                        46
          Forced versus induced draft                                    55
          Fan requirements for emission control system applications      57
          Fan arrangements                                               60
          Fan drives                                                     60
          Fan controls                                                   61
          Fan sizing                                                     66

6.   Ventilation System Inspection                                       71

          Preparing for inspection                                       71
          Safety considerations                                          72
          Onsite company-inspector interaction                           73
          Inspection procedures                                          73
          Operation and maintenance (O&M) considerations                 79

-------
                            CONTENTS (continued)


                                                                        Page

7.   Total Furnace Enclosures                                            85

          Electric arc furnaces                                          85
          Basic oxygen furnaces                                          95

8.   Special Applications                                               103

          Coke oven sheds                                               103
          Electric arc furnace ventilation                              107
          Blast furnace casthouse control                                115
          Control systems on basic oxygen  furnaces (BOF's)              117
          Building evacuation                                           123
          Copper converters                                             124

References                                                              128

Appendix A - Bibliography                                               A-l

-------
                                   FIGURES


Number                                                                Page

 1        Matrix of Hooding Applications for Participate Control        4

 2        Example of Open and Closed Hooding on the Discharge End
            of a Sinter Strand                                          6

 3        Direct Shell Evacuation on an Electric Arc Furnace            8

 4        Variation in Gas Flow Rate From a BOF During the Course
            of a Heat                                                  10

 5        Conveyor Transfer Point Hooding Using Total Enclosure        12

 6        Exterior EAF Canopy Hood                                     14

 7        Effect of Excessive Plume Velocity                           17

 8        Velocity Contours (Expressed in Percentage of Opening
            Velocity) and Streamlines for Circular Openings            19

 9        Velocity Contours and Streamlines for Flanged Hood           19

10        Formulas for Estimating Hood Air Flows                       20

11        Dimensions Used to Design High-Canopy Hoods for Hot
            Sources                                                    21

12        Schematic Arrangement of Ladle Hood for Reladling
            Emission Control                                           25

13        Controlled Airflow From a Heated Source                      28

14        Uncontrolled Airflow From a Heated Source                    28

15        General Principle of the Push-Pull (Air-Curtain) Type
            System                                                     29

16        Comparison of Face Velocity Decay for Blowing Versus
            Exhausting                                                 31

-------
                             FIGURES (continued)


Number

 17       Air Curtain Control System on a Capped Converter               32

 18       Dew-Point of Air Containing Various S03 Concentrations         35

 19       Pressure Measurements in Ducts                                 38

 20       Simple Pressure Diagram                                        42

 21       Taper Duct System                                              44

 22       Centrifugal Fan Components and Layout of a Typical
            Industrial Fan System                                        47

 23       Centrifugal Fan Blade Configurations and Impeller
            Arrangements                                                 48

 24       Fan Testing Procedure and Typical Characteristic Curves        50

 25       Typical Characteristic Curves for a Backward-Curved-Blade
            Centrifugal Fan                                              51

 26       Typical Characteristic Curves for a Forward-Curved-Blade
            Fan                                                          53

 27       Typical Characteristic Curves for a Straight-Blade Fan         54

 28       Basic Principle of Induced Versus Forced Draft                 56

 29       Louvre Damper:  (a) Parallel Blade Multilouvre; (b) Opposed
            Blade Multilouvre; (c) View of Parallel Blade, Multi-
            louvre Damper View Showing Linkage                           63

 30       Guillotine Damper:  (a) Simplified Cross-Sectional View of
            a Guillotine Damper; (b) Guillotine Isolation Damper
            Using Seal Air;  (c) Top-Entry Type Guillotine Damper,
            Showing Operation                                            64

 31       Butterfly Damper:  (a) Simplified Cross-Sectional View of
            a Butterfly Damper; (b) Butterfly Damper Showing Hand
            Operator                                                     65

 32       Typical Furnace Enclosure                                      87

 33       Furnace Enclosure at North Star Steel Company                  91

 34       Furnace Enclosure at Birdsboro Corporation                     93


                                      vi

-------
                             FIGURES (continued)

Number                                                                  Page
 35       Typical BOF Furnace Enclosure                                  97
 36       Schematic of Basic Oxygen Secondary Emission Control
            System of Kaiser Steel-Fontana                               98
 37       Schematic of Q-BOP Secondary  (Charging) Emissions
            Control System of Republic  Steel, Chicago                   100
 38       Various Shed Configurations                                   104
 39       Thermal Expansion of Hot Gases  From a Push                    105
 40       Electric Arc Furnace Utilizing  Partial Enclosure              108
 41       Ventilation Systems for Electric Arc Furnaces                 110
 42       Combined Direct Shell  Evacuation With Canopy Hood             111
 43       Multiple Pickup Points Vented to Common Control Device        112
 44       Flow  Rate Required for Electric Arc Furnace Control           114
 45       BOF Hood Arrangements                                         119
 46       Canopy  Hood Concept for BOF  Charging Emissions                121
 47       Gaw Damper  (Closure Plate) Use  in  BOF Control                 122
 48       Pierce-Smith Converter                                        125
 49       Secondary Converter Hood Configuration                        126

-------
                                   TABLES
Number                                                                  Page

  1       Comparison of Principal  Data for 10, 30, and 100 Percent
            Combustion in BOF Hooding                                     9

  2       Range of Capture Velocities                                    15

  3       Range of Design Velocities                                     37

  4       Conversion Table for Duct Velocity to Velocity Pressure        39

  5       Relative Advantages of Using Duct Dampers                      45

  6       Basic Fan Laws                                                 58

  7       Basic Damper Types                                             62

  8       Air Density Correction Factor                                  68

  9       Density of Common Gases                                        69

 10       Data on EAF Plants Designed for Total Furnace Enclosure        94

 11       Flow Balancing of a Typical Furnace Enclosure With
            Additional Pickup Hoods, Connected to a Common Baghouse      95

 12       BOF/Q-BOP Shops Utilizing Furnace Enclosures                  101

 13       Example of Flow Balancing of Multiple Evacuation System
            on Electric Arc Furnace                                     113

 14       Blast Furnace Casthouse Typical Volume Requirements           116
                                     vm

-------
                               ACKNOWLEDGMENT


     This report was prepared for the U.S. Environmental Protection Agency by
PEDCo Environmental, Inc., Cincinnati, Ohio.  Mr. Dwight Hlustick was the EPA
Project Officer.  Mr. William Kemner served as the PEDCo Project Manager.
The principal authors were Mr. Kemner and Messrs. Richard Gerstle and Yatendra
Shah.  Messrs. Gopal Annamraju, Gary Saunders, and Lario Yerino prepared
specific sections of the report.  The authors wish to thank Mr. Hlustick for
his overall guidance and direction on this task.

-------
                                  SECTION 1
                                INTRODUCTION

     The purpose of this manual is to  familiarize  Agency  inspectors with  the
design  principles  and O&M  considerations  for  large-scale (i.e., generally
>50,000 cfm)  ventilation  systems  commonly found in the metallurgical  indus-
try.   The  emphasis  is  on  the steel  industry  because most  large,   complex
systems are  found in the  many individual  processes  used in this industry.
Applications  in copper  smelting  and  other industries are  also  discussed.
Inasmuch as  ventilation  systems  are  highly complex from  a design  standpoint
and  experience  plays a  major role  in  most designs,  this  manual  should  be
considered an introductory primer rather than a  detailed design  manual.
     Several  standard publications  discuss ventilation  principles  and  fan
             1-4
engineering.      In  general,  however,  these publications  emphasize  smaller,
more traditional applications.  Furthermore, their emphasis is on ventilation
in  the  general  sense, as  opposed  to  air pollution control.   The complicating
factors  found  in ventilation  of  large  metallurgical   systems  are  either
treated in  the  abstract  or not at all.   Literature on operation and  mainte-
nance practices and inspection procedures is very limited.
     Air pollution  control  systems in the  primary metals industry,  particu-
larly  the  steel and copper segments,  rely on  large  capture and ventilation
systems with  flow rates commonly in the range of 50,000 to 1,000,000  acfm and
greater.  These systems  are used  primarily to control process  fugitive emis-
sions from various furnaces and for building evacuation.
     Because  these systems are an integral feature of the  compliance  programs
of  the industries  involved,   this  manual  was  initiated  to accomplish  the
following:
     0    To  provide  inspection  and operation  and  maintenance  guidance to
          state and  local  agency personnel  who evaluate  the performance of
          these systems.

-------
     0    To provide  a comprehensive  treatment of  the existing  literature
          with  regard to technical  and  specific  aspects  of  typical  designs.
     0    To provide an easy-to-read  technical manual  on design and operation
          for the use of inspectors.
     Although not treated  in  detail  in this  manual,  other technologies  are
available for  control   of  process  fugitive  emissions  in  the  metallurgical
industries.   These technologies,  which  do  not  involve  hooding  and  ventilation
systems,  include  roof-mounted  electrostatic  precipitators  '   and fume  sup-
pression utilizing  inert  gases  to  suppress the  oxidation  of  molten  metal.
Both  of  these  technologies offer  promise of  lower  cost  than conventional
ventilation  approaches.  They have been applied for control of charging  and
tapping emissions in steel  making plants and control of  blast  furnace  casting
emissions.  The former  have not yet found  application  in the United States.
     Sections 2  through  5  present  technical  factors  of design for  hooding,
ducting,  and  fans.   Section  6  describes  inspection  procedures  for  use  in
assessing the effectiveness and maintenance of  ventilation  systems.   Section
7 deals with total furnace enclosures.   In Section 8, the  foregoing  informa-
tion  is  supplemented  in the context of  special problems  that are found  in
several  specific  applications.   The  appendix  contains a  bibliography  for
those interested  in  pursuing the  subject matter  further.

-------
                                  SECTION 2
                 GENERAL VENTILATION AND HOODING PRINCIPLES

     Process  hooding  and  ventilation  systems  are  required  to capture  and
transport emissions to some control device or vent.   These hooding  and venti-
lation systems sometimes also eliminate potential  industrial  hygiene problems
by reducing  employees'  exposure to an air contaminant  and by  removing  heat
from the process area.  Figure 1 summarizes the various  types  of hooding  used
in processes in the metallurgical industries.
     The three  basic  parts of a  ventilation  system are the hood or  air in-
take, for  initial  capture of the  emissions;  the  ductwork, for  transport  of
the  gas  stream to  the  vent or  control  device; and a  fan,  to move  the gas
stream.  Whereas the design of the  basic  hood  and ventilation  system  is  well
understood  for  small  and  medium-sized systems,  the application of the  same
principles  to  large processes often results  in marginal or  inadequate  sys-
tems, especially when high-temperature  processes are  involved.   This  inabil-
ity to apply the same principles results primarily  from the large size of the
equipment,  the  high heat  loads,  the variability of  conditions  in batch proc-
esses, the  need for access to the  process,  and  greater maintenance require-
ments.   For larger  systems,  much of the design is  left  to  the ingenuity and
experience  of the designer, who must fit  the  hood around the  process  and lay
out the ductwork with minimal interferences.
     Inadequate  design  of a ventilation  system can compromise  overall  per-
formance.   In all  cases,  the hood must be  sized and oriented  to capture the
maximum  quantity of  emissions  without  requiring   excessive  gas volumes  (a
trade-off between performance and energy consumption).    It makes little sense
to install  a  high-efficiency  control  device if a major  portion  of  the emis-
sions are not captured initially.  The hood should  be as close as possible to
the  point   of  generation  without  interfering  with equipment  movement and
process  operation.   It  should  be oriented  to  minimize cross-drafts  and to
take advantage of thermal drafts.

-------
Application







§
U-







errous
*-
i


L.
V
O
Coke oven pushing
Basic oxygen furnace blowing
Basic oxygen furnace fugitives
Electric arc furnace refining
Electric arc furnace fugitives
Open hearth taoptng
Blast furnace casting
Blast furnace slag granulation
Steel scarfing
Grinding and shotblastlng
Hot rolling operations
Sinter strand discharge
Hot metal transfer
Raw metal conveyors
Gray Iron cupola
Primary copper converters
Primary copper reverberatory
furnaces
Primary lead blast furnace
Primary aluminum electrolytic
furnace
Casting shakeout system
Minerals handling
Minerals crushing
Type of hooding used
Fixed
hoods
X
X
X



X
X
X
X
X
X
X
X

X


X
X
X
X
Movable
hoods
X




X
X





X

X
X

X
X



Air
curtain/
push-pull
systems



X
X

X








X






Enclosures

X
X
X
X






X

X




X
X
X
X
Curtain
walls



X
X

X
X














Runner
covers






X







X

X
X




Roof
canopies



X
X

















Ladle
hoods


X


X






X



X





Close-
fitting
hoods
X
X

X




X
X

X
X
X








S1de-
draft
hoods



X


















Telescoping
hoods
X





X













X

Sheds
X





















Figure  1.    Matrix of hooding applications  for participate  control.

-------
     The ductwork  leading from  the hood  (or pickup  point)  to the  control
device  must  be  sized to  provide  the  needed transport  velocity—generally
between  15  and  25  m/s  (2700 and  4500 ft/min)  --depending on  particulate
loading  and  size distribution.   Layout of  ductwork  should minimize  energy
losses caused by bends, transitions, branches, etc., and should also minimize
air inleakage.  If the source is hot, refractory lining or water-cooled hoods
and ducts may be required.
     The three basic  types of process  hooding and  venting systems  are close-
fitting  hoods, canopy  hoods,  and  so-called  building evacuation.   (The latter
term is  used loosely because  in very few cases is an entire building actually
evacuated.)  More than one of these three systems may  be utilized on a single
process.

2.1  DESIGN BASIS
     The most important of the three ventilation system components  (i.e., the
hood,  the  duct,  and the fan)  is  the hood.   The ventilation system  will  not
perform  well  unless the  hood effectively  captures the emissions.   The  hood
design and open  face  area  determine the  amount of  air  that is  drawn  into the
system to capture the  emissions.  The volume of air and the process emissions
then determine the  size  of the ductwork, and these factors  and  the  pressure
drop  required  by the  control  device  in turn determine the  size of  the  fan.
To  minimize  capital  cost and  fan  power requirements,  the  designer  tries  to
minimize the amount of outside air  drawn into the system.   A face velocity of
200 to 500 ft/min is usually  required through the hood's open area.  Thus, to
minimize total ventilation air requirements, the hood must fit closely to the
process  and have a  small  open area.  The inability to  achieve  these goals is
the  major  problem  in  the applications  discussed  in  this  manual.   Figure 2
illustrates the enclosure principle applied to a hood on the discharge end of
a sinter strand.  In this application, nearly total enclosure is possible.
     Under some  conditions,  the hood  may  be fitted directly  to  the process
[(e.g.,  direct  shell   evacuation  (DSE) on  an  electric arc  furnace  (EAF)  in
which the furnace roof serves as the hood)]; this arrangement allows only the
process  gases (and minimal air infiltration) to pass through the vent system.
Even in  these cases,  however, high temperatures and explosive  gases must be
considered.  The  qases must  be  transported at concentrations  that  are less

-------
INDRAFT AIR
               COOLER

                0	V*
                LOSED
                                ENCLOSING
                                  HOOD
                                                   SINTER  f ,~
                                                   STRAND  V v
NDRAFT AIR
                   Figure  2.     Example  of open  and closed hooding on the
                              discharge  end  of a sinter  strand.
         Courtesy:   Industrial  Ventilation.   16th Ed.   Published by American
                    Conference  of Governmental  Industrial  Hygienists.   1980.

-------
than the  lower  explosive limit (LEL).  In the  electric  arc  furnace arrange-
ment just mentioned,  for example,  a gap  is  provided  to allow  sufficient
infiltration  of air for  combustion  of carbon  monoxide  and dilution of  its
concentration (CO).  This gap also permits the furnace to be tilted as illus-
trated in Figure 3.
     In other arrangements, the hood is separated from the process for access
purposes or to allow outside air to mix with and cool, dilute,  or combust the
process exhaust.   The  much larger open  area of these arrangements requires
much greater  total  exhaust flow.   Two basic designs  are  used  in  the control
of emissions  from  basic  oxygen  furnaces  (BOF's),  the so-called open-hood and
the more-energy-efficient closed-hood approach.  Application of a ventilation
system to a BOF is more  complex  than most  applications  because  the exhaust
gas is primarily  carbon monoxide, which, in  open-hood systems,  is combusted
in  the  hood by the  indraft air.   This  combustion  leads to temperature  and
volume variations  that must  be accounted for  in  the design  of  the exhaust
system.   With closed-hood systems,  the  CO  is  not  burned in  the  hood.   The
CO-rich gas is  cleaned and then flared or used as  a fuel.  Thus,  for closed-
hood systems, air  infiltration  must  be minimized to  avoid explosions  in the
gas-cleaning  system; its major advantage is the greatly  reduced  size  of the
gas  cleaning  equipment.   Table 1  illustrates  the  difference in  flow  rate
associated with these  BOF  systems.  The difference in flow rate also dictates
the  type  of  control  device used.   A scrubber, for  example,  would  be  very
expensive to  operate on the high flows resulting from the open-hood approach.
     Another  common problem in many systems  is the variability of conditions.
Conditions  may  vary from one season  to  another (i.e.,  ambient  temperature
and/or ventilation requirements), from one heat to  another,  or even from one
moment  to the  next as  process  conditions  change.   For example,  Figure  4
illustrates the variation  in gas flow during a heat in the BOF process.  This
variation occurs over  a period of 15 to 20 minutes.

-------
            INFILTRATED
                AIR,
  EXHAUST POSITION
TILT POSITION
Figure 3.    Direct shell  evacuation on an electric arc furnace.

-------
   TABLE 1.   COMPARISON OF PRINCIPAL  DATA FOR  10.  30,  AND  100  PERCENT
                       COMBUSTION IN  BOF  HOODING3
Varying parameters
Total gas volume, scfm
Theoretical gas temperature
inlet hood, °F
Heat to be removed in hood,
106 Btu/h
Fan horsepower of high-energy
scrubber, kW
Type of hooding and combustion rate
Semi -open
100%
158,800
4352
889
4100
Semi -closed
30%
87,000
3992
325
2200
Closed
10%
66,700
3272
167
1640
Open
200%
318,600
b
b
8200
Reference 8.
NA = Not available.

-------
                              SHOP A
                            BLOWING TIME
         Figure  4.    Variation in gas flow rate from a BOF
                    during the course of a heat.

Courtesy:   JAPCA, 18(2):98-101,  February 1968.   Article by D.  H.  Wheeler
           entitled  "Fume Control  in  L-D Plants."
                                  10

-------
                                  SECTION 3
                         HOOD DESIGN CONSIDERATIONS

     The three principles of optimum hood design are:
     0    Enclosure of the process or source insofar as possible.
     0    Location of exterior hood in path of exhaust.
     0    When  exterior  hood  is  used,  minimization  of  interference  from
          cross-drafts.
     The goal  of good  hood  design is  high  capture efficiency.   Ideally,  a
process should  be entirely enclosed, which  would  permit almost  100  percent
capture efficiency.   Simple conveyor  transfer hoods  (Figure  5)   provide  an
example of total  enclosure.  Because  frequent  access to  a  process (to charge
materials, remove products, or perform maintenance) is  usually  required,  most
hoods  have  open  areas to  provide this  access.   These open  areas  must  be
maintained under  a  negative pressure by  drawing air  into the  system, which
prevents fumes from escaping.  Although  this  concept is  simple  in principle,
its application  is  complicated by  variations  in process emissions,  thermal
currents from hot processes, and  cross-drafts  that  interfere with the inflow
of air into the hood.
     Hoods can be classified  into three broad groups:   enclosures, receiving
hoods, and  exterior hoods.  Enclosures  usually  surround the point of emis-
sion, but sometimes one  face  is  partially or even  completely open.  Examples
of enclosures  are  paint  spray booths,  abrasive blasting cabinets,  totally
enclosed bucket elevators,  and enclosures for conveyor belt  transfer  points,
screens, crushers, etc.  The sides of the enclosure effectively reduce cross-
drafts and also direct the plume toward the capture hood.
     Receiving hoods  are those  in which  the  air  contaminants are  injected
into  the  hoods  and inertial  forces carry  these   emissions  into the  hood.
These hoods are generally applied to smaller processes  that impart a velocity
                                     11

-------
                                  ENCLOSE  TO PROVIDE  150-200 fpm
                                     INDRAFT AT ALL OPENINGS

                                  MIN.  Q = 350 efm/ft  BELT WIDTH  FOR BELT
                                           SPEEDS <200 fpm

                                         = 500 cfm/ft BELT WIDTH  FOR BELT
                                           SPEEDS >200 fpm
                                  FOR FALLS GREATER THAN 3 FT WITH DUSTY
                                  MATERIAL, PROVIDE ADDITIONAL EXHAUST QA

                                  BELT WIDTH 12 in. to 36 in. QA = 700 cfm
                                              ABOVE 36 in. QA = 1000 cfm
                                                             FLEX STRIPS
                                        RUBBER SKIRT
Figure  5.   Conveyor transfer point hooding using total  enclosure,
                                12

-------
to the emissions,  such  as  grinders and paint sprayers.  They  are  not  appli-
cable to the large systems discussed in this manual.
     Exterior hoods  must capture  air  contaminants  that are being  generated
from a  point outside the  hood itself.  These  hoods are generally  used  for
large systems that generate heat and require  frequent  access.   Figure  6  is  a
simplified diagram of an exterior  or canopy-type  hood.   In  this example,  the
hood design is augmented with baffles and dampers to direct suction to  one of
three  sections,  depending  on  the  source  of the  emissions.    This  enhances
capture efficiency by deer-easing the effective face area.
     The total air flow into the hood system is determined by  Equation  1:
                              Q = A V                     (Eq.  1)
where Q = Total air flow, cfm     ~
      A = Cross-sectional area, ft
      V = Air velocity perpendicular to open face area, ft/min
This simple  equation  is  the root of inadequate system  design.   Because  cost
is  directly proportional  to  flow,  Q, the  user is  continually tempted  to
decrease  either  hood area, A,  or  face velocity,  V.   As described  later,  a
decrease  in  either of these causes rapid  deterioration  in  hood capture  per-
formance.
     The  desired  air velocity, or capture velocity, designed  into  the  hood
must be  based  on  experience, but  the  guidelines  in Table 2 may  be  helpful.
In  many  larger industrial  processes,  the third  category—active  generation
into a zone  of  rapid air motion—is encountered, and  face  velocities  in  the
range of  200  to 500  ft/min are required.   Air motion or currents in the  room
may be caused by thermal drafts from hot processes, building drafts, movement
of  machinery or  material,  movement of  the  process,  or rapid  discharge  of
gaseous emissions.
     Because all of these factors  cannot be accurately evaluated, a high-effi-
                                       k>
ciency hood must have high  face  velocities in which a  large safety factor is
incorporated.  In addition, reducing cross drafts by using partial enclosures
(both fixed and movable) will greatly enhance capture efficiency.
     In the  design of a  hood system,  it is useful to consider the concept of
a null point.  This  point is defined as the  point  where the  inertia!  energy
(mass  times  velocity)  of  the emission  has  decreased  to zero  or  been  nul-
lified.   Because   the  mass  of most  emissions   (gases  and/or  particles)  is

                                     13

-------
  TAPPING
  DAMPER
                                                                  PERIMETER FLANGE
                          INTERNAL BAFFLES
FURNACE ROOF
IN OPEN POSITION
                                                        SIDE DRAFT HOOD
         TAPPING PIT
FURNACE
                        Figure 6.     Exterior  EAF canopy hood.
                                       14

-------
                                 TABLE 2,
   RANGE OF CAPTURE VELOCITIES
Condition of dispersion of contaminant
             Examples
Capture velocity, ft/min
Released with practically no initial
velocity into quiet air.

Released at low velocity into
moderately still air.
Active generation into zone of rapid
air motion.
Released at high initial velocity into
zone of very rapid air motion.
Evaporation from tanks; degreasing,
etc.

Spray booths; intermittent container
filling; low speed conveyor transfers;
welding; plating; pickling

Spray painting in shallow booths;
barrel filling; conveyor loading;
crushers; melting and refining

Grinding; abrasive blasting; tumbling
         50-100
        100-200
        200-500
        500-2000
NOTE:  In each category above, a range of capture velocity is shown.   The proper choice of values depends
       on several factors:

                    Lower end of range                                     Upper end of range

1. Room air currents minimal or favorable to capture.         1.  Disturbing room air and thermal  currents.

2. Contaminants of low toxicity or of nuisance value only.    2.  Contaminants of high toxicity.

3. Intermittent, low production.                              3.  High production,  heavy use.

4. Large hood, large air mass in motion.                       4.  Small  hood,  local  control  only.
Courtesy:  Brandt, A. D.  Industrial Health Engineering, John Wiley and Sons, New York.   1947.
           Kane, J. M.  Design of Exhaust Systems.  Heating and Ventilatino, 42, 68.   November  1945.

-------
small, their  momentum is  soon dissipated  by air  resistance.   Hot  process
exhausts  often  have  significant momentum  due to thermal  updraft.   Examples
are  electric  arc  furnace emissions  and  coke  pushing  emissions.   Thermal
momentum can  be  misinterpreted in the sense,  that  one might think  the gases
would be easily  captured  because  they are  headed  directly into the  capture
hood.  If the upward velocity is greater than  the hood face capture velocity,
however,  the  gas stream will be deflected  to  the side as  if it  had struck a
barrier.   This is illustrated in Figure 7.
     At the null point the emissions have no momentum of their  own, and if an
adequate draft or air velocity toward the hood is provided at  the null point,
the  contaminants  will be  captured.   What  constitutes  an  adequate velocity
toward the  hood  depends  on the drafts  in  the area, and  therefore  cannot be
determined precisely.
     Establishing the null  point  in advance for a new  process  is  not always
possible.   For  existing  equipment,  however, direct  observation  will  usually
establish a  locus  of null  points.  In the  absence  of  external  disturbances,
any  positive  velocity toward the  hood at  the null   point  will  give complete
capture.    In  practice,  however,  complete  capture   is  difficult to  achieve
because of drafts and thermal  currents that disturb  the  air flow and prevent
the  formation of the null point.   Sufficient velocity  must  be  induced to
overcome  the  disturbance  caused  by  drafts and  thermal   currents.   Because
these drafts  and thermal  currents  vary with the activity near  the process, an
exact entrainment velocity cannot be calculated; therefore, a  safety factor
must be incorporated to ensure good capture.

3.1  DETERMINING AIR FLOW  REQUIREMENTS
3.1.1  Cold Processes
     As  shown in Figure  8, air  moves from  all  directions toward openings
under suction.   By  definition, flow  contours  are  lines  of constant velocity
in front of a hood.   Similarly, streamlines are lines perpendicular to veloc-
ity contours.
     The equation for air  flow around free-hanging  round hoods  and rectangu-
lar hoods that are approximately square is  :
                                     16

-------
                        / £	
                                  \CAPTURE
                        AFACE VELOCITY!
                        1300 ^gn     J ^—
                    HOOD
          DEFLECTION
PLUME VELOCITY,  500 fpm
Figure 7.    Effect of excessive plume velocity.
                         17

-------
                    v -                                      .  2)
                    v   10X2  + A
where V = Center!ine velocity at X distance from hood, ft/min
      X = Distance  outward  along  axis,  ft  (Equation is  accurate only  for
          limited  distance of X, where X  is within 1.5D.)
      Q = Air flow, cfm
      A = Area of  hood opening, in ft2
      D = Diameter of round hoods or side of essentially square hoods

     As  shown  in  Equation 2  and Figure 8,  velocity decreases rapidly  with
increasing  distances from  the  hood  and  varies  almost  inversely with  the
square of  the  distance.   The velocity decreases  less rapidly  with a  flanged
hood, as shown in  Figure 9.
     Where  distances of  X  are  greater  than 1.5D  (as  is the case  in  most
applications), the  velocity  decreases less rapidly with distance  than  Equa-
tion 2  indicates.   Figure 10 illustrates other hood  types and gives  the air
volume formulae that apply.
     In addition to canopy-type hooding systems, many other configurations of
hood systems  are  applied  to  spray booths,  grinding, end open  tanks.   Few of
these systems have exhaust flows greater than 100,000 cfm.
3.1.2  Hot Processes—High Canopy Hoods
     In hot  processes,  significant  quantities of  heat are  transferred to the
surrounding air by  conduction  end  convection, and a  thermal  draft is created
that causes a rising air current.  The design of the hood and the  ventilation
rate provided must take this thermal draft into consideration.
     As the  heated  air  stream  that rises from a hot surface  moves upward, it
mixes turbulently with the surrounding air.  The higher the air column rises,
the larger it becomes and the more it is diluted with ambient air.  As illus-
trated in Figure 11, the rising air column expands approximately according to
the following empirical formula:

                         Dc - 0.5 xf°'88                  (Eq.  3)

where D  = The diameter of the hot column of air at the level of
           the hood face, ft
                                     18-

-------
vo
                                            -STREAMLINE


                                               FLOW
                                               CONTOURS
                                             AIR FLOW
                                             DIRECTION
                                            (TANGENT TO
                                            STREAMLINE)
                       0       50      100
                   X OF OPENING DIAMETER
                                - STREAMLINE

                                FLOW CONTOURS
                  50      100
             X OF DIAMETER
         Figure 8.    Velocity contours (expressed in
             percentage of opening velocity) and
              streamlines for circular openings.

         Courtesy:  Silverman, L.  Velocity Characteristics
                    of Narrow Exhaust Slots.  Journal of In-
                    dustrial Hygiene and Toxicology, 24,
                    267.  November 1942.
Figure 9.     Velocity contours  and stream-
         lines  for flanged  hood.
Courtesy:   Silverman, L.   Centerline Velocity
           Characteristics of Round Openings Under
           Suction.   Journal  of Industrial  Hygiene
           and Toxicology, 24,  259.   November 1942.

-------
ro
o
                    HOOD TYPE
                   w
                    A*WL(sq.ft)
DESGRPTION
                                          SLOT
                                      FLANGED SLOT
                                     PLAIN OPENING
                                    FLANGED OPENING
                                         CANOPY
ASPECT RATIO,"
                   0.2 or less
                   0.2 or less
                  0.2 or greater
                    and round
                  0.2 or greater
                    ond round
                   To suit work
AIR VOLUME
                    0-37LVX
                     Q*2.8LVX
                    0' VflOX +A)
                  Qs0.75V(K)X*+A)
                   Qst.4POV
                  P -perfneter of wont
                  Ds height above work
                              Figure  10.   Formulas for estimating  hood air flows.

                Courtesy:  DallaValle,  J. M.  Exhaust Hoods.   Industrial Press,  New York.  1946.
                          Silverman,  L.  Velocity Characteristics of Narrow Exhaust Slots.
                           Journal  of  Industrial Hygiene and  Toxicology,  24,  267.  November 1942.

-------
                               o
                                , HOT SOURCE
                  HYPOTHETICAL
                  POINT SOURCE     X
Figure  11.   Dimensions used to design high-canopy hoods for  hot sources.
                                                                              12
                                        21

-------
      xf = The distance from the  hypothetical  point source to the
           hood face,  ft (equal  to y + z)
                           1 3R
           where  z =  (2D )1'JO  and D  =  diameter of source,  ft
                  y =  Distance from top of source to hood, ft

     To allow  for  drift in the rising column  of emissions  caused  by  cross-
drafts  and  air disturbances,  the designer  must  increase  the  overall  hood
diameter by adding 80  percent of  the  distance  between  the hood and  the proc-
ess, as shown in Equation 4.

                          Dh = Dc + 0.8y                   (Eq.  4)

where D. = Overall hood diameter,  ft
     Where  cross  drafts  occur,   the  hood diameter  may  be  increased  still
farther and the distance between  the hood and  source may  be  decreased.  When
possible, side  shields  in  the form  of  steel  sheets (curtain  walls)  or  chains
suspended from  the hood should be utilized to  decrease  cross drafts.   Asbes-
tos and tarpaulin  curtains have  been  tried,  but they are  rarely  successful
because  their  light  weight makes  them  tear  easily and they  do  not  hang
straight.
     The  total  flow through the  hood system may  be  estimated by the  use of
Equation 5:

          Vf - "TO? <<£ As "I"'"                    
-------
     In addition to the volume of the hot gases  rising  through  the  hood  area
defined by  diameter D  (Figure  3-8),  room air  is  also drawn into the  hood
                      \f
through the balance of  the  hood  area.   Estimates of the desired  velocity  of
the  air through  this portion of the  hood depend  entirely on  engineering
judgment and  are  based on  expected  cross-drafts,  air  disturbances, and the
toxicity of the emissions.
     A  velocity between 100 and  200  ft/mi n is recommended,  and the velocity
should  increase  with  greater  air disturbances.   In  extreme cases in which
more violent  reactions occur with sudden heat  release (such  as  in the  charg-
ing  and tapping of steelmeking  furnaces), even  greater velocities are re-
quired:
                    Q = VfAc + Vr (Ah - Ac)               (Eq. 6)
where  Q = Total hood flow, cfm
                                               »
      V, = Velocity of hot air, ft/mir
      A  = Area of hood face through which hot gases enter
       C   (= *Dc2/4), ft2
      V  = Desired velocity of air entering balance of hood
           (100 to 200 ft/min)
      A.  = Area of total hood, ft2
       n         /
     The  control  of emissions from  sources  that are other than  circular  in
shape is best handled by hoods of the appropriate shape.  Thus, a rectangular
source would  require  a  rectangular  hood to minimize the ventilation require-
ments.  The equations used for circular hoods are appropriate for rectangular
hoods, but  increases  of 0.8 times  the  distance to the  source  (y)  should  be
made in both length and width.
     Total  hood volume determines  retention time  in  the hood.   For  inter-
mittent processes of  short  duration, such as charging,  a  large  hood  has the
advantage of  containing the exhaust gas  for several minutes  until  the ven-
tilation  system can  withdraw the fumes.   Partitions  can be added  that will
not only  minimize  cross-drafts,  but also  essentially  increase  hood size and
retention time.  In any  event,  it is difficult  to  predict performance based
solely on theoretical design.  Scale model studies  can be helpful during the
                                     23

-------
design stage, but final modifications in  the  field  may be necessary based on
observation of system performance.
3.1.3  Hot Processes--Low Canopy Hoods
     An exact distinction cannot be made  between a  low and high canopy hood,
but a  low  hood  is usually defined as one in which the  distance  between the
hood and the  source  does  not exceed the  diameter  of  the  source, or  3 feet,
whichever is  smaller.   The  primary difference in the  design of low hoods is
that  the  hood  diameter and  source  diameter  are  essentially  the  same.   A
safety  factor  is  usually included,  and  for practical  purposes,  the  hood
diameter should exceed the source diameter by  at least one foot.  The dimen-
sions of larger rectangular hoods should exceed the source's dimensions by at
least one foot in all directions.
     For circular hoods, the  total  exhaust  flow  may  be determined  by  the
                  12
following equation  :

                    Q = 4.7(Dh)2'33(At)°-417              (Eq.  7)

where D.  = Hood diameter in feet and is  equal  to the source
           diameter plus 1 or 2 feet

For rectangular hoods, the exhaust flow  may be determined by:

                    Q = (6.2JW1-33 (At)°'417L             (Eq.  8)

where VI = Hood width, which is 1 to 2 feet larger than the source
          width
      L = Length, which is 1 to 2 feet longer than  the source
          length

     Lowest  flow rates  are  achieved  with  close-fitting  hoods.   Figure 12
illustrates  the  latest design  for hooding a  hot  metal  transfer operation.
Note that the open area is essentially limited to the hood slot through which
the metal  is poured.
3.1.4  Building Evacuation
     A building  acts  as a large  process enclosure.   By  drawing  air through
the building  and out the roof,  the building  essentially serves as  a hood.

                                     24

-------
               TORPEDO CAR
LADLE MOOD
tn
           HOT METAL LADLE
               Figure  12.  Schematic arrangement of ladle hood for reladling emission control
          Courtesy:  Pennsylvania Engineering Corporation, Pittsburgh.

-------
The large  size  of a building  compared  with a more  closely fitted  hood  re-
quires utilization of a much larger exhaust  flow.  Many large  buildings,  and
especially those that contain processes that release  heat,  are ventilated by
natural draft.  Heat released by the processes  warms  the air, which rises  and
is pushed  out through openings  (roof  monitors) in the  roof.   Cooler ambient
air  is drawn into  the  building  through  openings near ground  level.   Wind
action at  the building  openings  may either increase or  decrease  the natural
ventilation rate, depending on the  location  and  size  of the openings end  the
wind speed and direction.
     A forced-ventilation system that is applied to a  building must be sized
to include the air flow resulting from natural  draft  and also maintain suffi-
cient  draft into the building to  prevent any emissions  from escaping through
building openings.
     For buildings containing hot processes, the  natural ventilation rate  can
be estimated by the ASHRAE equation  :

                    Q = 9.4(AL)°-5(Atavg)°-5              (Eq.  9)

where     Q = Air flow, cfm
          A = Total inlet or outlet air flow area,  whichever is
              smaller,  ft2
          L = Building  height from air inlet to outlet, ft
       At    = Difference between average temperature  in building
          y   and air entering building, °F

     When  the  heat released from  sources  within  the  building can  be  quan-
tified, Equation 10 can be utilized:

                Q = 20(0.67L)°-33(0.67H)0-33A0'67        (Eq. 10)

where Q = Air flow, cfm
      L = Building height from air inlet to outlet, ft
      H = Heat released within building, Btu/min
      A = Total  inlet or outlet area (whichever is  smaller), ft2
                                     26

-------
     Building ventilation  requirements  may also be  defined  in terms of  air
changes per  unit  of time.  Again, a  great deal of judgment enters  into  the
selection of the  number  of changes  required,  which depends on the  heat  gen-
erated  in  the  building  and  the industrial hygiene  considerations  regarding
fumes and gases within the building.   On the order of at least  20 air changes
per hour are required for metallurgical  processes.
     The distribution  of ventilation is  also very  important.   Uncontrolled
air flowing  into  a  building  as  a  result of negative  pressure in  the building
or  because  of  poorly  designed air-supply distributors not only may  cause
recirculation  of contaminants,  but  also may  upset  the  local   ventilation
systems.  Therefore,  the amount of air,  the  location  of its  entry  into  the
building, and its direction must be controlled.   Figure 13  shows  a controlled
air supply  that results  in a convective  flow from a  heat  source (such as  a
ladle  of molten  metal)  rising to  be exhausted through  a roof  ventilator.
Figure  14  shows  an uncontrolled  air  supply,  which results  in   a  disrupted
plume  and   recirculation  of the  contaminant  throughout the   building.   The
latter  could cause  a  buildup  of  contaminants  in  the  building and  possible
leakage to the outside air.
     Because of the huge air volumes  it would require (on the order  of  5 to
10  million  cfm), true building evacuation is  rare.   Care must   be  taken in
closing  the roof monitors  or  ventilators in a  building and  replacing  this
natural  ventilation with induced-draft  ventilation.  If  the  induced draft is
inadequate,  both ambient  dust and  heat  levels  in  the  building  can  rise
rapidly  and  create  health and  safety hazards.   This is  particularly true in
hot climates.
3.1.5   Push-Pull  Systems
     Hood capture efficiency can sometimes be improved  by  the  use of a  push-
pull or air  curtain approach.   This  approach  involves  a source of compressed
air  (push)   to  direct the  emission  plume toward the  exhaust  hood  (pull).
These  applications   are  used  to  control  blast  furnace  casthouses,  copper
converters,  and  electric arc furnace enclosures.  Figure  15  illustrates the
general  principle of  the push-pull  system. The effective  face velocity of a
                                     27

-------
  Figure  13.    Controlled airflow from a heated source.^
Figure 14.    Uncontrolled airflow from a heated source.
                                                        13
                           28

-------
          NO MAJOR OBSTRUCTIONS
            IN PATH OF JET
 PRESSURE  SLOT
                                                              EXHAUST HOOD
                                PUSH PULL HOODS
Figure  15.    General principle of the push-pull (air-curtain) type system.
                                     29

-------
blowing source is sustained  at  much  larger distances than that of  a  suction
source (as illustrated in  Figure 16).
     In one system used to control  tapping  emissions  from a  blast  furnace,  an
air curtain in front  of the taphole directs  the  emissions  into  the  capture
hood above the taphole  in  an arrangement very similar to that in Figure  15.
Figure  17  illustrates  the air  curtain  application  on  a  copper  converter
furnace.  The total enclosure uses an  air  curtain to prevent emissions from
escaping the  enclosure  when the doors ere opened for  access.   Each  appli-
cation is unique  in its design  and must  be evaluated by  actual observation.
It is difficult  to base suitability on  design  data  alone.
                                    30

-------
   FAN
                                        30 diameters
                    BLOWING
                                                                       400 f pm
r^
)
         4000 fpm Alfc
         VELOCITY AT
         FACE OF BOTH
                        I I
                             400 fpm
                          APPROXIMATELY 10% OF FACE VELOCITY
                          AT 30 DIA.  AWAY FROM PRESSURE JET
                          OPENING.
                          EXHAUSTING

                          APPROXIMATELY 10% OF FACE VELOCITY
                          AT ONE DIA.  AUAY FROM EXHAUST
                          OPENING.
Figure  16.    Comparison of face velocity decay for blowing versus exhausting.

Courtesy:   Industrial  Ventilation,  16th  Ed.
                                      31

-------
           JET  SIDE
                                                     EXHAUST SIDF
  AIR
CURTAIN
  JET
                                   CONVERTER
                               (FUME SOURCE)
                                   LADLE
                                                        BAFFLE
                                                         WALL
                                                                 TO SUCTION FAN AND
                                                                HOOD  SAMPLE LOCATION
      Figure  17.   Air curtain control  system  on a  copper  converter.
                                        32

-------
                                  SECTION 4
                       DUCT DESIGN AND CONSIDERATIONS

     The three design principles for ducting are:
     0    Minimization of changes in flow direction.
     0    Maintenance of smooth duct surfaces.
     0    Avoidance of abrupt expansions.
     Basically, a duct is  a  pipe  or channel  that  conveys  a  gas  and  contained
emissions from a collection  point to  a more  convenient  point  for  rehandling,
cleaning, or blending.  In some cases a duct also  acts  as  a  cooler.
     Duct configurations  range  from small-diameter  ducting  (6 to 12 in.)  to
ducting having  cross-sectional  areas of 600 square  feet  or more.   Ductwork
can be a combination  of circular, square,  or rectangular, based on  location,
space  limitations,  equipment or  building  design, and  length of  run to  the
control point.  Flows  should be continuous and smooth  in direction, with  no
abrupt expansions or  contractions.   Larger duct sizes  usually are fabricated
in the  field in square  or  rectangular  cross  sections.   Circular ducts  are
limited  in  size by  the  availability of  plate widths.  The cost  of  wider
plates must be balanced against  forming  and  welding  costs.  Theoretically,  a
circular cross section is preferable because it minimizes  friction losses  and
nonstreamline flow.   Duct configuration  is generally dictated  by economics,
however.  Duct  thickness  in large metallurgical  systems  usually varies from
1/4 to  3/8  in.  Strengthening  ribs and expansion  joints are generally  re-
quired for  larger  sections  (over about  6  feet in diameter or  square).   Ex-
pansion joints  are  required for ductwork carrying hot  gases  (above  about
300°F).   If temperature  fluctuations  occur regularly, cracking  of the  ex-
pansion joints and the resultant leakage can be a  major source of maintenance
problems.
                                      33

-------
     Ducting must  be designed  to deal  with  the  following gas  conditions:
temperature, abrasiveness,  acidity,  dust concentration,  and moisture.   For
temperature control, the ductwork may  be lined with refractory  materials  or
water-cooled in its entirety.  An example of this is the  BOF shop,  where the
hood and duct  above  the  furnace  are  cooled  by a variety  of designs that are
discussed later.
     Damage from abrasion,  acidity,  and moisture may be controlled by special
types of refractory  or,  depending on the temperature,  by the use  of various
coatings or special  alloyed  steels.  Carbon steel,  for example,  generally  is
considered  suitable  for  gas  temperatures up to 1000°F.   Above this tempera-
ture,  stainless  steel  or  refractory-lined  carbon  steel  is required.   Acid
condensation (primarily from sulfates)  is a problem  if gas  temperature  falls
below the acid dew point.   In copper converters,  sulfur trioxide (SOg)  typi-
cally  constitutes  about  1  percent of  the sulfur dioxide (SO^)   present,  or
about  0.02  to  0.1 percent  of  the total gas  stream.   This  can  condense and
form  sulfuric  acid.   Figure 18  indicates  the  dewpoint of  air  containing
various SO, concentrations.

4.1  TRANSPORT VELOCITIES
     The minimum design duct velocity  is that  required to prevent buildup  in
a duct.  At elbows  and  other sections  where the gas stream slows  down,  pro-
vision  should  be  made  for  inspection  for dust dropout  and  for cleaning.  If
the substances in  the gas  tend  to be  sticky,  or if  moisture condensation  is
possible,  cleanout  ports  or flanged  sections should be  provided to  gain
access.  Buildup  decreases the  effective duct  cross-sectional  area and in-
creases  transport  velocity;  the  latter  counterbalances the former  and  thus
prevents  further  buildup.    If  buildup  is  due  to  stickiness  or  moisture,
however, it can proceed to  the point of total  pluggage, especially in smaller
branch  ducts.   A further concern caused  by buildup  is  the possibility  of its
breaking loose during startups or vibration.   Serious buildup can also create
an excessive mechanical  load on  the duct structure and supports.
     Normally, the minimum transport  velocity required  is  greater than  that
required merely  to  prevent  settling   or buildup.    Buildup or  pluggage can
cause  system upset  in  the  main  duct or  in  any of the  branches,  and this  in
                                      34

-------
CO
en
                      Figure 18.   Dew-point of air containing various $03 concentrations.


               Courtesy:  "Combating Fuel Oil Heating Problems", Plant Engineering, January 7, 1974.

-------
turn affects the  remainder  of  the  system because of the  increase  in  resist-
ance and decrease  in  flow in the  blocked  section.   Anything that  decreases
the duct size (such as damage from  outside  forces)  affects overall  collection
performance.
     A change in the  temperature of the  gas at any  point  can  also  affect the
overall collection efficiency of the system.
     The transport velocity must account for the velocity needed for  gas and
particulate removal,  resistance  due  to  friction  along the duct surface, end
dynamic losses due to air turbulence.
     Table  3 gives  a  recommended range  of design velocities.   Metallurgical
process control  systems with heavy  dust loadings  operate in the  transport
velocity range  of 3500  to  4500 fpm.   When  the dust  consists  primarily  of
small  particles  at low  concentration,  lower transport  velocities ere  pos-
sible.  Higher  velocities are  still  preferable, however,  to decreese  duct
diameter.    Duct  cost  savings  normally   outweigh  the energy  penalty  of the
higher velocity.

4.2  ENERGY LOSSES
     Figure  19  summarizes the  three  pressure  measurements of  concern  in  a
duct.   The sum  of the  energy  losses that must be considered  in the  duct
system are:
     0     Inertia  - The  energy required to accelerate  the gas from  zero  to
           duct velocity  is equal to (V /4005)2, where V   is the  gas velocity
           in feet per minute.  This vafue is  referred to8 as velocity pressure
           or  as  the  velocity  head  (h  ).   Table 4  can  be  used  to  convert
           velocity  (V  or V)  in feet per minute to  velocity  pressure (h  or
           VP) in inches of water.2                                        v
     0     Straight duct friction  -  Friction   loss   (or  pressure   drop)  in
           streight duct  runs  is usuelly negligible  relative  to the pressure
           drop required  for  elbows,  branch entries, and  the  control  device.
           As shown  in  the following  equation,  the  total  loss in 500  feet  of
           10-foot diameter duct (essuming V =  4000 fpm)  is about 0.5 in.  H20.
           The equation used for clean round ducts is:
                    f - 2.74                            ,_   ...
                      -- TT2 —                  (Eq. 11
                              D
                                      36

-------
                    TABLE 3.    RANGE OF DESIGN VELOCITIES'
   Nature of
  contaminant
            Examples
  Design velocity
Vapors, gases,
 smoke
Fumes

Very fine light
 dust

Dry dusts and
 powders
Average indus-
 trial dust
Heavy dusts
Heavy or moist
All vapors, gases, and smokes
Zinc and aluminum oxide fumes

Cotton lint, wood flour, litho
powder

Fine rubber dust, Bakelite
molding powder dust, jute
lint, cotton dust, shavings
(light), soap dust, leather
shavings

Sawdust (heavy and wet),
grinding dust, buffing
lint (dry), wool jute dust
(shaker waste), coffee beans,
shoe dust, granite dust,
silica flour, general mate-
rial handling, brick cutting,
clay dust, foundry (general),
limestone dust, packaging and
weighing, asbestos dust in
textile industries

Metal turnings, foundry tumbling
barrels and shakeout, sand
blast dust, wood blocks, hog
waste, brass turnings, cast
iron boring dust, lead dust

Lead dust with small chips,
moist cement dust, asbestos
chunks from transit pipe
cutting machines, buffing
lint (sticky), quick-lime
dust
Any desired velocity
(economic optimum
velocity usually
1000-1200 fpm)

      1400-2000

      2000-2500


      2500-3500
      3500-4000
      4000-4500
     4500 and up
     A rule of thumb for items or contaminants not tested is to operate in the
3500-4500 fpm transport velocity range.

a From Reference  14.
                                       37

-------
                AIR FLOW
     TOTAL
   PRESSURE
 STATIC
PRESSURE
VELOCITY
PRESSURE
Figure  19.   Pressure measurements in ducts.
                                            14
                     38

-------
TABLE 4.    CONVERSION TABLE FOR DUCT VELOCITY TO VELOCITY  PRESSURE15
v , fpm
d
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.H20
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

hy, in.H20
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

                                39

-------
where

f = friction loss in inches of water per 100 feet

V = velocity in fpm in duct

D = inside diameter of duct in inches
Actual values can  be  twice as high because duct  internal  surfaces
are  not  ideally  clean  and  smooth.   Note  that  as  duct  diameter
decreases and  length  of  ductwork  increases (as  in  a  system  with
multiple miscellaneous  pickup  points),  pressure  drop  can  become
significant.  If  the  system  fan  is  not  designed to provide  this
pressure drop (for example, where miscellaneous  pickup  points  have
been  added  letter),  the  duct  pressure  drop  will  result in  less
suction at the hoods.

A  rectangular duct  can  be converted  to the circular  equivalent  in
the following manner:

1.   A = the duct cross-sectional  area  in square feet

2.   P = the perimeter in feet

         A
3.   R = -p the hydraulic radius in feet


4.   12R = Conversion of R to inches, r

5.   D = 4r = equivalent diameter in  inches

Elbows -  Losses  for 90-degree elbows are  determined  as equivalent
resistance in feet of straight duct.   For other elbow angles, use:

     60-degree elbow = 0.67 x loss for 90-degree elbow
     45-degree elbow = 0.5 x loss for 90-degree elbow
     30-degree elbow = 0.33 x loss for 90-degree elbow

     For radius of 1.5D:

                                 D  1.175
         Equivalent feet = 130 (^-)           (Eq. 12)


     For a radius of 2D:
                                D
         Equivalent feet = 89 (—-}           (Eq. 13)
                            40

-------
               For radius of 2.5D:
                                          D   <
                   Equivalent feet = 73 (--)           (Eq.  14)
          Branch Entry - Losses due to branch entry are best expressed as the
          equivalent feet of straight duct of the same diameter.   The equiva-
          lent length is added to the actual  length  of  straight  duct and the
          loss is computed from the earlier friction loss equation.

          For an entry angle of 30 degrees:
                             D  1>214
                    Z = 20 (£.)                        (Eq. 15)

          where

                Z = equivalent feet

                D = diameter in inches

          For an entry angle of 45 degrees:
                             D
                    Z = 32 (^g-)                        (Eq.  16)


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

     0    Contraction and Expansion - When the cross-sectional area  of  a duct
          contracts, a  pressure loss occurs.   This  loss  is  a  function  of the
          abruptness  of  the  contraction.   When  the  cross-sectional   area
          expands, a  portion  of  the decrease  in  velocity pressure becomes
          static  pressure.   The  increases and  decreases  in pressure  from
          expansion and contraction are calculated from equations  in  Refer-
          ence 15:

     The summation of  the transport velocity requirements from  all  of  these

losses plus  the hood  or entry losses plus the control device and stack dis-

charge loss determines  the size and power of the fan.   A pressure diagram can

be useful  in characterizing and  understanding  a  given  system.   Figure  20

presents a hypothetical pressure diagram for a simple system.
                                      41

-------
                        DUCT. ELBOW, DAMPER. AND BRANCH ENTRY LOSSES =1.1
>

N
CONT
LO
(FAB

v ,
\
ROL DEVICE
SS = 10
RIC FILTER)
                  CANOPY HOOD\


                      -0.2
                     /CANOPY  HOOD\
                         -0.2
                                                                                                            DISCHARGE

                                                                                                          PRESSURE = 1.5
ro
     2


     0

o

i~  -2



5  .4

 •

tt  -6
=>


2  -8
o:

°- -10



   -12
                                                  TOTAL PRESSURE REQUIRED TO SIZE  FAN
                                                                                                          A-12.8
                                                Figure 20.   Simple  pressure  diagram.

-------
4.3  BRANCHED SYSTEMS
     The addition  of new or additional  pickup  points that are  in  turn  tied
into a main  duct system has to be carefully  designed to  achieve the desired
flow balance  throughout the system.   If  duct sizes  are  not  compatible  with
the static pressure  throughout  the  system,  the  desired air flows will  not be
achieved.  Thus, it  is  necessary  to  provide  a means of distributing air  flow
between branches, either by balanced design or by the use of dampers.  Figure
21  illustrates  the  widely  used  approach of tapered  cross  section for  branch
entry  systems.   This  design  maintains  constant duct  velocity  in  the  main
duct.
     The  two approaches for  designing duct  systems  are  1) to  balance  duct
diameters  to match  desired flows  in each branch,  and  2) to use  dampers or
blast  gates  to  control flow.  Many  systems use a  combination  of  both  ap-
proaches.
     Balanced  design is theoretically preferable to minimize the tampering
with dampers  and the dependence on  operating personnel.  The design calcula-
tions  begin  at  the branch of  greatest  resistance  and proceed  as follows:
branch to main,  section of main to section of main, main to control equipment
on  to  the fan.   At  each  junction  point,  the  static  pressure  necessary to
achieve the  desired  flow in one stream must  match the static pressure  in the
other.
     Damper  adjustments permit  the  desired  flow to be  varied  through  each
portion  of the system  after initial  design.  This  permits adjustments to be
made by  trial  and error to accommodate  variation  in actual conditions.   The
design calculations  begin  at  the branch of greatest  resistance,  and pressure
drops  are  calculated through  the branches and duct  sections  to  the fan.  At
each point where two gas  streams  meet, the  combined flow is  then used, and
when it  reaches  the main duct,  this combined flow  is added to the main  duct
flow  with no attempt  to  balance  the  static  pressure  in the  joining gas
streams.  Branches  are  sized for  the desired  minimum  duct  or transport veloc-
ity at the desired  flow rate.
     Advantages  and  shortcomings  of  these two methods are  further  outlined in
Table 5.
                                      43

-------
                            SIZE FOR BALANCE
                            AND TRANSPORT
                            VELOCITY
TO FAN
                    BRANCH
                    DUCTS
                  Figure 21.   Taper duct system.

Courtesy:  Industrial Ventilation.

-------
        TABLE  5.    RELATIVE ADVANTAGES OF USING DUCT DAMPERS
                                                              14
     Balance without dampers
       Balance with dampers
Air volumes cannot be easily
changed by the operator.

Small degree of flexibility for
future equipment changes or addi-
tions; the ductwork is "tailor-
made" for the job.

Choice of exhaust volumes for a
new unknown operation may be in-
correct; in such cases some duct-
work revision is necessary.

No unusual erosion or accumulation
problems.
Ductwork will not plug if veloci-
ties are chosen wisely.
Total air volumes are slightly
greater than design air volumes
because of the additional air
handled to achieve balance.

Poor choice of "branch of greatest
resistance" will show up in design
calculations.
Layout of system must be in com-
plete detail, with all obstructions
cleared and length of runs accu-
rately determined.  Installations
must follow layout exactly.
Air volumes may be changed rela-
tively easily.

Greater degree of flexibility for
future changes or additions.
Correction of improperly esti-
mated exhaust volumes is easy
within certain ranges.
Partially closed dampers or blast
gates may cause erosion and
thereby change the degree of
restriction or cause accumula-
tions of material.

Ductwork may plug if persons have
tampered with the blast gate
adjustment.

Balance may be achieved with
design air volume.
Poor choice of "branch of
greatest resistance" may remain
undiscovered.  In such case the
branch or branches of greater
resistance will be "starved."

Leeway is allowed for moderate
variation in duct location to
miss obstructions or interfer-
ences not known at time of
layout.
                                  45

-------
                                   SECTION  5
                                  FAN  SYSTEMS

     Centrifugal  fans  are normally used  in conjunction  with large  emission
control  systems because  of the large  flow rates and  high  pressure  drops  in
these systems.  Although  some  axial fans  can  deliver large volumes of  air  at
high resistance, they  are best suited for clean-air applications.  The pres-
ence of dust causes rapid  erosion  of  axial fan  components because  of  the high
tip  speed  of  the  fan and the high  air  velocity  through  the  fan  housing.
Centrifugal fans can be designed for differing  gas  characteristics  encountered
in various  emission  control  applications.   This  section  discusses the major
aspects of centrifugal  fans  with  regard  to  their applicability for  large
ventilation systems.

5.1  FAN TYPES AND OPERATING CHARACTERISTICS
     A  centrifugal  fan is  used to transfer  energy to  gases by  centrifugal
action.   Figure 22 shows  the components of  the  centrifugal  fan and  layout of a
typical  industrial fan system.   It consists  of a wheel  or  rotor  that  is ro-
tated by an electric  motor in  a  scroll-shaped  housing.   The gases enter the
housing axielly, make a right-angle turn,  and  are forced  through  the blades  of
the  rotor  end  into the  housing  by centrifugal  force.   The  centrifugal force
imparts velocity  pressure to  the air, and  the  diverging shape of the  scroll
converts a  portion of the velocity head into static head.
     Centrifugal fans are classified according  to the following blade configu-
rations:
     0    Backward-curved blade
     0    Forward-curved  blade
          Straight blade
Figure 23 shows a  few  basic centrifugal  fan  blade  configurations and impeller
arrangements.
                                       46

-------
       COUPLING   INBOARD  END
       DRIVE UNIT\!EAVRING
                                     IMPELLER

                                         OUTBOARD END
                          E F*OUNDAffoN^5^2^S:
BEARING

  STEEL PEDESTAL

MAIN SHAFT


    GRADE LINE
   'CONCRETE  PEDESTAL
                              Figure 22a.
Courtesy:  Hydrocarbon Processing, June 1975.  Article by J. W. Martz
           and R. R. Pfahler entitled "How to Troubleshoot Large Indus-
           trial Fans."
                          SCROLL SIDE
                        BLACKPLATE

                    BLADES
                                                           'OUTLET
       OUTLET
        AREA
       \^
CUTOFF
        INLET
                                                         SCROLL
                                                        SUPPORTS
                  INLET  COLLAR
  BEARING SUPPORT
                              Figure 22b.
Courtesy:   "With  permission of  the  American  Society of  Heating,  Refrig-
            erating  & Air  Conditioning  Engineers,  Inc.,  Atlanta,  GA.
Figure 22.  Centrifugal  fan  components and layout of a typical industrial
                                fan  system.
                                   47

-------
   RADIAL BLADE FAN
                                     RADIAL TIP FAN
    SINGLE  INLET
     AIRFOIL  FAN
                                       DOUBLE  INLET
                                        AIRFOIL FAN
                             Figure 23a.
   Courtesy:   Hydrocarbon  Processing, June 1975.  Article by J. W.
              Martz  and  R.  R. Rfahler entitled  "How to Troubleshoot
              Large  Industrial  Fans,"
             BACKWARD-
             INCLINED
                  X
                  STRAIGHT
                    I
                  AIRFOIL
                          FORWARD-
                           CURVED
                              Figure  23b.
    Courtesy:
Excerpted by special  permission from CHEMICAL ENGINEER-
ING (date of issue)  Copyright (c) (year), by McGraw-
Hill,  Inc., New York, N.Y.   10020.
Figure 23.   Centrifugal  fan blade configurations and impeller arrangements.
                                  48

-------
     The size, shape,  and  number of blades affect  the  operating characteris-
tics of the fan.   Fan  performance  is  characterized  by the volume of gas flow,
pressure, fan  speed,  power requirement, and operating  efficiency.   The rela-
tionship of  these  parameters  is  measured  according to  the  testing  methods
sponsored by  the National  Association  of  Fan  Manufacturers or  the  American
Society of Mechanical Engineers.  The fan is tested from shutoff conditions to
free-delivery conditions.   At shutoff,  the  duct  is  completely  blanked  off; at
free delivery, the  outlet  resistance is zero.   Between these  two conditions,
various flow restrictions  are placed at the end  of  the  duct to simulate vari-
ous operating  conditions.   The  operating  parameters are measured at each test
point and plotted  against  volume on the abscissa.   Figure  24  illustrates  the
fan testing procedure and  shows the typical  fan characteristic curves.
     Each fan  type  has a  different performance  characteristic.   The  fan per-
formance  curves  are  used   in  the  selection  of  a  fan  type.   Generally,  the
characteristics  of  geometrically similar fens  are  identical.    The  fan manu-
facturers  can predict  the performance of  a   large fan from  the tests on  a
smaller but geometrically  similar fan.
5.1.1  Backward-Curved-Blade Fan
     The blades  in a backward-curved-blade centrifugal  fan  are  inclined in  a
direction opposite  to the  direction  of rotation.   The blades  (usually 14 to
24) are supported by a solid steel backplate and shroud ring.  The scroll-type
housing permits  efficient  conversion of velocity head into static head.
     The  characteristics of a  backward-curved-blade  fan  are  shown  in Figure
25.  The static  pressure of this fan rises sharply  from free delivery to about
50  percent  volume point.   Beyond  this  point  and up  to the no-delivery point
the  pressure  remains  approximately constant.   Maximum efficiency  occurs at
maximum  horsepower  input.   The horsepower  requirement is  self-limiting; it
rises  to  a maximum  as the capacity  increases and  then  decreases  with addi-
tional  capacity.  This  self-limiting  horsepower characteristic  of  the back-
ward-curved-blade  centrifugal  fan  prevents overloading of  the motor when the
fan load  exceeds its design capacity.  The operating efficiency of the back-
ward-curved-blade fan  is  high,  and this fan develops higher pressure than the
forward-curved-blade fan.
                                       49

-------
                             Ji—BLANKED OFF
                                          RESTRICTED
                                                  LESS RESTRICTED
                                                       FLOW STRAIGHTENERS
                                                             WIDE OPEN
               VOLUME  FLOW  RATE, Q      /

                                 FREE DELIVERY

                                Figure  24a.

        Courtesy:   ASHRAE Handbook.   Equipment Volume.
 SP   VP
MEASURING
 STATION
                      i      i     i      i     I      I     i      i
                      20    30   40    50    60    70    80    90   100
                       PERCENT OF WIDE  OPEN VOLUME

                                  Figure 24b.

 Source:   U.S.  Environmental  Protection  Agency.   Standards Support Documents:
          An Investigation of the  Best Systems  of Emission Reduction for Elec-
          tric  Arc Furnaces in the  Steel Industry.   (Draft) June 1974.

Figure 24.   Fan testing procedure  and typical characteristic curves.
                                    50

-------
                       VOLUME
Figure  25.   Typical characteristic curves  for  a
         backward-curved-blade centrifugal fan.
                         51

-------
     Because the backward-curved blades are conducive  to  buildup  of material,
they are not recommended for dirty streams.   These  fans  are generally used in
ventilating applications where  large  volumes of clean air are to be handled on
e continuous basis.   When  used for  emission  control  applications,  the  back-
ward-curved-blade fan must be  installed  on  the clean-air side  of the control
system.
5.1.2  Forward-Curved-Blade Fan
     The forward-curved-blade  fan generally  has  20  to 64 blades.   The blades
are  shallow, and both  the  heel  and tip  are curved  toward the  direction  of
rotation.  The rotor of the forward-curved-blade fan  is  known  as  a "squirrel-
cage" rotor.  A solid steel backplate holds  one end  of the blade,  and a shroud
ring  supports  the other end.   The   scroll  design  is  similar  to  that of the
backward-curved-blade fan.
     As  shown in  Figure 26, the static pressure  of  this  fan rises from a free
delivery to a point  at  approximate maximum  efficiency, drops to  about the  25
percent volume  point, and then  rises  back up to the  no-delivery point.  Horse-
power requirement increases with volume.   Because horsepower increases rapidly
with capacity,  there is a danger of  overloading the  motor if system resistance
is not accurately estimated.   Forward-curved-blade  fans are  designed to handle
large volumes of air at low pressures.   The  fan speeds ere relatively low, end
the  pressures  developed by forward-curved-blade fans are  generally insuffi-
cient  for  emission  control system applications.  These  fans are  used exten-
sively in heating, ventilating, and  air conditioning applications.
5.1.3  Straight-Blade Fan
     Straight-blade  fans are  the  simplest  of all  centrifugal   fans.   The fan
usually  has  5  to 12  blades, which  are generally attached  to  the  rotor by a
solid  steel  backplate  or  a  spider  built up  from  the hub.   The  rotors are
relatively large in diameter.
     Figure  27  shows  the  performance characteristics of  the  straight-blade
fan.   The  static pressure  of  this fan  rises  sharply  from  free delivery to a
maximum  point  near  no  delivery,  where it  falls off.   Mechanical  efficiency
rises  rapidly from  no delivery to a  maximum near maximum  pressure, and then
drops slowly as the fan capacity approaches  free delivery.
                                       52

-------
                                    VOLUME
Figure 26.   Typical characteristics  curves for a forward-curved-blade fan.
                                     53

-------
                              VOLUME
Figure 27.    Typical characteristics curves  for  a  straight-blade fan.
                                54

-------
     The  straight-blade fan  can  be used  in  exhaust  systems  handling  gas
streams that are contaminated with dusts and fumes.  Various blade designs and
scroll designs have been developed for specific dust-handling applications.
5.1.4  Backward-Inclined Blade Fan
     The two  types of  backward-inclined  blades  in the  centrifugal  fan  class
are air foil blades and flat blades.
5.1.5  Rim-Type Wheel Fans
     With abrasive material, or materiel that tends to stick, a rim-type  wheel
provides more  structural  integrity; some of  these have back  plates  on  them.
Literally dozens  of  rim-type fans are on the  market.   Each fan  typically has
at least six blades.  The  radial  tip tends  to develop more static pressure  so
it can develop  the same gas flow as the straight-blade radial  at higher  pres-
sure drop.

5.2   FORCED VERSUS INDUCED  DRAFT
     The terms  "forced  draft" and  "induced draft" come from boiler technology,
where  they  refer  to  either forcing  air through  the boiler (with  a  blower)  or
pulling air through  the boiler with  a fan located on the exhaust side.  Figure
28  illustrates the  meaning of  these  terms  in  the  context of  air pollution
control ventilation  systems.   Essentially,  the control  device  takes the  place
of  the boiler.  Two  considerations  are important in  the  use  of forced-draft
systems:
      1.   Whether  the fan  is exposed to cleaned  gas or dirty gas
      2.   Whether  the control device is under  pressure or  suction
      The  suitability of the centrifugal fan for  dirty applications has already
been  discussed.   The axial fan would clearly  only be suitable in an induced-
draft system.   The  forced-draft system  is  generally preferred  in  large ap-
plications, particularly  those  controlled by a fabric filter, because control
costs  are  lower,  even when the higher fan cost  and maintenance are taken into
account.  Many  large (i.e., 300,000 cfm and greater) systems  treat relatively
clean  gas  because the  process  gas has been  diluted  with  indraft air.  Thus,
                                        55

-------
        DUCT
      SOURCE
                                       C>
                                      TO
                                      STACK OR
                                      MONITOR
                           CONTROL
                          EQUIPMENT(UNDER PRESSURE)
                     FORCED-DRAFT
                        FAN  (Dirty)
DUCT





   YsOURCE /
                  u
     CONTROL
     EQUIPMENT(UNDER SUCTION)
INDUCED- DRAFT
Figure 28.  Basic principle of induced versus forced draft.
                       56

-------
even the  "dirty"  gas  inlet  to the fan  is  relatively low in  dust  concentra-
tions, i.e., 1.0  gr/scf  or less.   Also, this type of  system  does not  usually
require a  stack.   Systems that use scrubbers or  electrostatic precipitators,
on the other hand, usually have induced-draft fans.   In  scrubber systems  with
variable pressure drops, the induced-draft fan is  especially  needed  to  control
pressure drop.
     Forced-draft  fans that  are  used  on the  "dirty" gas  side are  usually
larger and rotate at a slower speed than fans on the clean side to cut  down on
the abrasion of the fan blades.

5.3  FAN REQUIREMENTS  FOR EMISSION CONTROL SYSTEM APPLICATIONS
     Basically, a  fan  can develop  static pressure without delivering much gas
volume,  or it can  deliver very  little static  pressure  at  high gas  volume.
Unfortunately,  it cannot  do both  at  the  same  time.  Any  given fan  cannot
perform beyond the limitation of its operating curve.
     Increasing  the  rotation  speed  and the gas volume  through the  system
doesn't shift the  system  resistance curve,  but  it permits the fan to  overcome
more  resistance  and  move more gas through  the  system  by  shifting  the  fan
operating  curve.   A fan is basically a  volumetric energy machine.  A  certain
gas volume is  carried between each blade.  Therefore, if the number  of times
the blades pass the  outlet is  increased, more ges is moved and at an  increase
in  pressure.   Any  increase  in fan rotation speed  increases  fan  horsepower
requirements.  Two ways  to control  capacity are 1)  to put in  dampers  to waste
static  pressure  across the  damper  to  reduce gas  flow,  and   2)  to  reduce fan
rotation  speed.   If dampers are  added, the fan  is  still  expending energy to
develop  pressure  drop; therefore,  reducing  fan rotation  speed  is  more effi-
cient  because  it  develops  a  lower horsepower and  uses  less energy  than  a
damper.  Table 6  summarizes  the basic fan laws.
     In  the design  of fans  for  emission  control   system applications,  con-
siderations must  be  given to the  nature of the gases being handled.  Emission
control system fans may be subjected to one or more  of the following operating
conditions:
                                       57

-------
                         TABLE  6.    BASIC FAN LAWS
Variable
                  When speed changes
                                                       When density changes
Volume
            Varies directly with speed ratio
                                               Does not change
Pressure
            Varies with square of speed ratio
                            RPM  2
Horsepower
                   P2 =
            Varies with cube of speed ratio
                                   3
                   HP2 = HP1
                                               Varies directly with density ratio
                                                       P2 =
                                               Varies directly with density ratio
                                                           = Hpi  (TT)
                                                               JL   U i
                                     58

-------
     0     High temperatures
     0     Corrosive gases
     0     Dust-laden gases
     0     Presence of abrasive particles
     0     Presence of explosive materials in the gases
     Special  construction  materials  can provide protection against high  tem-
peratures  end corrosive  properties.   Bronze  alloys  are used  for  handling
sulfuric acid fumes and other  sulfates,  halogen  acids, various organic  gases,
and mercury compounds.   Stainless  steel  is the most commonly used  corrosion-
resistant metal for  impellers  and  fan housings.  Protective coatings such as
bisonite,  cadmium  plating, hot galvanizing, and rubber  covering provide  re-
sistance to corrosive  gases.   Depending on the  particular application,  soft,
medium, or firm rubber can be  bonded to the metal.   A  good bond  will  yield an
adhesive  strength  of 700  pounds  per square inch.   Rubber-covered fans  have
proved exceptionally durable.
     When a fan must handle  explosive gases, the construction material  should
be  such that  it  does not produce  a  spark if  accidentally  struck by  other
metal—e.g., bronze and aluminum alloys.   In most applications,  it  is  prefer-
able to  combust explosive gases prior to entering the ductwork.   In  the  case
of  a BOF  controlled by the  closed-hood  system,  however,  the  gas is  not  com-
busted,  so  the inherent  heating value  rising  from  the contained  carbon  mon-
oxide can be retained.
     Fans  handling  dust-laden  gases  must be protected from wear due  to abra-
sion.   When wear  is expected,  some  manufacturers equip  their fans with  wear
strips  and weld beads.   The  strips consist of  a thick, cross-hatched  hardened
floor plate welded to the blade at the centerplate or backplate,  and the plate
is  built  up at the edges with weld  beads.  The  inertia of  the  dust particles
carries them  toward  the  backplate  or centerplate, where  the wear  plate with-
stands  most of the  abrasion.   The  weld  beads,  which  are  angled  along  the edge
of  the  wear  plate,  break up  the  particle flow  and prevent impingement  and
scouring.   For severe abrasion  conditions, fans can  be  equipped  with full-
blade liners  or heavy-duty rotors  with  thick wear plates bolted or welded to
the  full  face of  the  blades.  The  fan construction  is  such that worn  wear
plates can be replaced on  site.
                                       59

-------
5.4  FAN ARRANGEMENTS
     Whenever possible, the fan  should  be installed on the clean  side  of the
emission control system, where it  will  be subjected to less  severe  operating
conditions.   Plants  with  multiple emission  control  systems generally  have
separate fans for  each  control  system.   If a fen  is shared by more  than one
emission control system, fan  operation  can be difficult  to control.   At  such
installations, the fan may operate at less than  optimum conditions because it
may be subjected to fluctuating loads.
     For applications where fan  load  is  expected to vary widely and  the  peak
fan load  is  relatively large, multiple  fens  may provide better control  over
the system operation.   A  parallel  fan  system will  increase   reliability and
flexibility.   The  performance of  two  fans  in  parallel   can  be predicted  by
combining  the ordinates  and abscissas of  the pressure-volume curves  of  both
fans.   At  low loads, the parallel  system  can  also  be operated as a single fan
system.  Individual fan  loads  can  be  adjusted to optimize  the  performance of
the system at a  given load.

5.5  FAN DRIVES
     Large centrifugal  fans  are  generally driven  by three-phase,  alternat-
ing-current motors.  The two  principal  types  of  motors used  for driving  fans
are 1)  the squirrel-cage  induction  motor, and  2)  the wound-rotor  induction
motor.  Although both motor types are self-starting, special starting controls
are needed in many applications  to limit  starting  time to  acceptable values.
Both types operate at rated load with very little slip.
     The  squirrel-cage motor  takes  its   name  from  the  rotor  construction.
Among the  various  standard designs, the one designated as Design B is usually
used on fans.   This motor  is  suitable for continuous operation at  rated  load,
and its starting current is relatively low.
     Wound-rotor motors, also  known  as  slip-ring motors, can provide adjust-
able-speed drive if desired.  Speed reductions below 50 percent are not recom-
mended,  however.   Top  speed  and  efficiency  are  about  the  seme  as  for the
squirrel-cage motor.
                                       60

-------
5.6  FAN CONTROLS
     The throughput of fans may be changed by varying the speed or by changing
the  pressure condition  at  the  inlet  and/or outlet.   Variable inlet  vanes
provide  control  on the  inlet side  of the  fan,  and dampers  can be  used  on
either the  inlet  or outlet side.  Each of  the fan control methods  entails  a
loss in  efficiency  over most of the  operating  range.   Because most  large-ca-
pacity fans are ordinarily  driven  by  constant-speed  motors,  it is usually not
possible to  control  the fan  by  varying the speed.  Variable  inlet  vanes can
provide  gradual  load  adjustment;  however,  these  must  be purchased with the
fan.   Dampers  offer flexibility of  location  and control.  A  fan system with
dampers  can  be  designed to meet a wide range of  load  fluctuations.   Table  7
lists  the  basic  damper types,  and  the  following subsections  provide  brief
descriptions of the major types.
5.6.1  Louvre
     Louvre  or  multiblade dampers may  be  of  the  opposed-blade  or the paral-
lel-blade design  (Figures  29a and  29b).   An overall  view of a parallel-blade,
multilouvre  damper  is  shown in Figure 29c.   Parallel-blade louvre dampers can
be  closed  tight, but  they  offer little modulation  ability.   Conversely, op-
posed-blade  louvre dampers  offer excellent modulation ability, but they cannot
be  closed as tightly as  the  parallel-blade louvre  dampers can.  Louvre dampers
may be used  to  regulate  and isolate  gas flow.   For isolation, two dampers can
be  used  together and sealed  by pressurizing the chamber formed by the ductwork
between  the  dampers with a  seal-air  fan.   A single damper may be used for gas
flow regulation.
5.6.2  Guillotine Damper
     A guillotine  damper may be  a top-entry or  bottom-entry  design,  with or
without  seal air  (Figure 30).  Guillotine dampers for system isolation may be
equipped with  a seal-air blower,  single-  or  double-bladed,  to pressurize the
sealing  space and thus ensure against  gas leakage  past  the damper.
5.6.3  Butterfly Damper
     Butterfly  dampers  are  often  used for  secondary duct runs  (Figure 31).
They are mounted by a  center shaft that crosses the duct, and  the damper  plate
                                       61

-------
                        TABLE  7.    BASIC  DAMPER TYPES
   Generic
            Specific
    Common designs
Louvre
Guillotine
Parallel-blade multilouvre
                   Opposed-blade  multilouvre
Top-entry guillotine
Top-entry guillotine/seal-air
Bottom-entry guillotine
Bottom-entry guillotine/seal-air
Single louvre
Double louvre
Double louvre/seal-air

Single louvre
Double louvre
Double louvre/seal-air
Butterfly

Blanking plate
                                     62

-------


\
\
                (a)
(b)
                                    (c)


Courtesy:  Frisch Division, DAYCO Company.  Chicago,  Illinois.

   Figure 29.  Louvre damper:  (a) parallel-blade multilouvre;  (b)  opposed-
 blade multilouvre; (c) view of parallel-blade, multilouvre damper  showing
                                   linkage.
                                    63

-------
                                     11
                                      (a)
                   DAMPER BLADE
                         STAINLESS STEEL
                           SEALS
          COVER PLATE
  PRESSURIZED CHAMBER
          GAS FLOW
          0  0
      PRESSURIZED
       CHAMBER
              FAN INLET
                       COVER PLATE
                   (b)                                     (c)
     Courtesy:   Frisch Division, DAYCO Company,  Chicago,  Illinois.

Figure 30.   Guillotine damper:   (a)  simplified cross-sectional  view of a
  guillotine damper; (b) guillotine  isolation damper using  seal  air;
         (c)  top-entry type guillotine damper, showing operation.
                                     64

-------
                              BUTTERFLY
                                  (a)
                                  (b)

              Courtesy:  Frisch Division,  DAYCO Company,  Chicago,  Illinois.

Figure 31.  Butterfly damper:   (a)  simplified cross-sectional view of a
   butterfly damper; (b)  butterfly  damper  showing  hand  operator.
                                   65

-------
rotates about  the  shaft from  a  plane parallel  to the gas  flow (open)  to a
plane perpendicular to the  gas  flow (closed).   Butterfly dampers are used most
often to  regulate  gas flow, but they  have  been used for  opening  and closing
off ducts and fan systems.
5.6.4  Blanking-Plate Damper
     The most basic damper  is the simple  blank-off plate.   Blanking plates are
essential when  a  process must  be  isolated  for the protection  of  the mainte-
nance crew.   Should  it become  necessary for  persons  to enter  any  section of
the ductwork, the blanking  plate ensures  isolation of that section.   When used
in conjunction with positive-ventilation  air purge, the blanking plates ensure
the safety of personnel.
     Blanking plates are similar to guillotine dampers in  that they cut across
the duct  opening;  however,  the track design for a blanking  plate  is intended
only to guide the plate as  it is put in place and bolted down.

5.7  FAN SIZING
     The  air (base)  horsepower  requirement  of a  fan can  be  calculated by
Equation 17:

               Air hp = Qh/6356                          (Eq. 17)

where Q = inlet volume, ft3/min
      h = total static pressure rise, in. H20

     Fan  brake  horsepower  can  be  obtained  by dividing the  air horsepower by
the mechanical  efficiency of the fan.  Mechanical  efficiency for most centri-
fugal fan  operating  points will be  50 to  65  percent.   Fan  size can also be
determined  from  the  fan   manufacturer's   catalog.   Manufacturers'  catalogs
generally include multirating  tables  that give the operating parameter ranges
for  different  fan models.    Many  larger fans,  however, are  custom-built and
thus not found  in multirating tables.  If the inspector needs to do a detailed
analysis  on  a  custom-built fan, he/she  must  obtain the fan  ratings and  per-
formance curves from either the manufacturer or the plant.
                                       66

-------
     The multirating tables  are  generally  based  on  standard  conditions.   When
air is not  at  standard conditions, corrections must be made  to  volume,  pres-
sure, and horsepower corrections to select a fan at an "equivalent" volume and
pressure.  For a manufacturer's  rating  table  to  be  used,  the fan requirements
must be converted  to the  density used in the ratings.   The density correction
is generally made  by using the ratio  of air  density at standard  conditions to
the actual  density of  the air at the  fan inlet.   Table 8  provides air density
correction  factors at  various temperatures and altitudes.  Table  9  lists the
densities  of various  common gases.   It is  usually sufficient to assume the
density  of  air because it  is the predominant gas,  but in some  cases  (e.g.,
saturated  gas  from a  scrubber),  a density correction  for composition may be
necessary.   A further  density correction is theoretically required because the
air at the fan inlet is under suction, which lowers the density-   For example,
the correction factor  from -60  in. H?0 to sea level is about 1.18.   Before a
fan is chosen from the multirating tables, the following adjustments should be
made:
     1.   Determine  density  factor (d  = 0.075 for  air at 70°F  and  29.92 in.
          Hg)
     2.    If the  gas flow is indicated  at  standard conditions,  convert  it to
          actual fan conditions:
          where     Q  =  actual volume of air entering the fan
                    A  -  barometric pressure corresponding to fan
                          site altitude, psia
                    T  =  inlet temperature, °F
                 Vscfm  =  volume of air at standard conditions
                          (70°F and 14.7 psia)
     3.   Multiply  static pressure by the density factor, d
     4.   Using  corrected static pressure and actual gas  flow,  Q, select fan
          from multirating tables
     5.   Divide the fan bhp selected in Step 4 by the density factor.
                                        67

-------
                                     TABLE 8.    AIR DENSITY CORRECTION FACTOR,  d
Altitude, ft.
Barometer, in
Air temp. , °F



















Hg
Wg
-40
0
40
70
100
150
200
250
300
350
400
450
500
550
600
700
800
900
1000
-1000
31.02
422.2
1.31
1.19
1.10
1.04
.98
.90
.83
.77
.72
.68
.64
.60
.57
.54
.52
.47
.44
.40
.37
Sea
level
29.92
407.5
1.26
1.15
1.06
1.00
0.95
0.87
0.80
0.75
0.70
0.65
0.62
0.58
0.55
0.53
0.50
0.46
0.42
0.39
0.36
1000
28.86
392.8
1.22
1.11
1.02
0.96
0.92
0.84
0.77
0.72
0.67
0.62
0.60
0.56
0.53
0.51
0.48
0.44
0.40
0.37
0.35
2000
27.82
378.6
1.17
1.07
0.99
0.93
0.88
0.81
0.74
0.70
0.65
0.60
0.57
0.54
0.51
0.49
0.46
0.43
0.39
0.36
0.33
3000
26.82
365.0
1.13
1.03
0.95
0.89
0.85
0.78
0.71
0.67
0.62
0.58
0.55
0.52
0.49
0.47
0.45
0.41
0.37
0.35
0.32
4000
25.84
351.7
1.09
0.99
0.92
0.86
0.81
0.75
0.69
0.64
0.60
0.56
0.53
0.50
0.47
0.45
0.43
0.39
0.36
0.33
0.31
5000
24.90
338.9
1.05
0.95
0.88
0.83
0.78
0.72
0.66
0.62
0.58
0.54
0.51
0.48
0.45
0.44
0.41
0.38
0.35
0.32
0.30
6000
23.98
326.4
1.01
0.91
0.85
0.80
0.75
0.69
0.64
0.60
0.56
0.52
0.49
0.46
0.44
0.42
0.40
0.37
0.33
0.31
0.29
7000
23.09
314.3
0.97
0.89
0.82
0.77
0.73
0.67
0.62
0.58
0.54
0.51
0.48
0.45
0.43
0.41
0.39
0.35
0.32
0.30
0.28
8000
22.22
302.1
0.93
0.85
0.79
0.74
0.70
0.65
0.60
0.56
0.52
0.49
0.46
0.43
0.41
0.39
0.37
0.34
0.31
0.29
0.27
9000
21.39
291.1
0.90
0.82
0.76
0.71
0.68
0.62
0.57
0.58
0.50
0.57
0.44
0.42
0.39
0.38
0.35
0.33
0.30
0.28
0.26
10,000
20.58
280.1
0.87
0.79
0.73
0.69
0.65
0.60
0.55
0.51
0.48
0.45
0.42
0.40
0.38
0.36
0.34
0.32
0.29
0.27
0.25
en
co
     Standard  air  density,  sea  level,  70°F  = 0.075  lb/ft3.

-------
TABLE 9.    DENSITY OF COMMON GASES
Gas
Hydrogen
Oxygen
CO
co2
N2
Benzene
Ammonia
so2
Water vapor
Air
lb/ft3
0.0052
0.0828
0.072
0.1146
0.0728
0.2017-
0.0446
0.1697
0.0466
0.075
               69

-------
     The fan brake horespower obtained from the above  calculations  is  divided
by the  motor efficiency  to obtain  motor horsepower.   Motor efficiency  for
three-phase motors such as  those used  on  large systems is typically 85  to  90
percent.
     Usually, fan horsepower is designed for so-called  cold-start  conditions,
in which  case  the density  correction  factor  is not  used.   This enables  the
motor end fan to pull  the  full  quantity of "cold"  (i.e., ambient) dry air upon
startup  without overloed.   After  startup,  when  the   air  reaches operating
conditions of temperature  and  humidity,  it is  less  dense and the  horsepower
load is reduced.
                                       70

-------
                                  SECTION 6
                        VENTILATION SYSTEM INSPECTION

     Careful preparation  and  planning are  vital  to a  successful  inspection
and evaluation of ventilation systems.  An inspection will  be meaningful  only
if the inspector knows what information he/she wants to collect and is  famil-
iar with  the  equipment at  the site.  Time  invested  in a  file review  will
reduce the  inspector's field  time  and  that of  the  source  representative.
Also, if  the  inspector can obtain all  the required data during the  inspec-
tion, later  time-consuming efforts  to secure missing  data  can be  avoided.
Furthermore,  if the  inspector  has  performed  his/her  homework,  the  plant
personnel are  more likely  to  view  the  inspector as  a professional  and  to
provide  the information  and  cooperation  the  Agency  needs.   This  section
presents  guidelines to assist  the inspector  in conducting a  successful  in-
spection.

6.1  PREPARING FOR INSPECTION
     When inspecting a ventilation system, the inspector must record the data
on  site  for  later use in  evaluating compliance  practices.  The  following
items will help to ensure that the inspection is complete and that  the perti-
nent information is obtained while the inspector is on site:
     Plot Plan
     The  plot  plan should show  entrances,  major buildings,  and the  process
     area to scale and  include other appropriate  details that provide orien-
     tation.
     Equipment Drawings
     Photographs or  sketches  of  the equipment  configuration  are  useful  for
     reference or  comparison.   These  should  show major process and  control
     equipment for easy reference at a later date.
                                      71

-------
     Process Flowsheet and Equipment Checklist
     These should provide  the  inspector with a  clear  idea of  the  operating
     procedures, factors affecting emissions, a  listing  of necessary data to
     collect for determining compliance, and data collection methodology.
     Before beginning the  inspection,  the inspector should review  the work-
sheets and  process  flows  with  the  plant's  representative at  the  plant  to
assure that the  information  obtained during the file review  is  accurate  and
up to  date.   This also  informs  the plant  representative  of the  inspection
procedures so that he/she can assist the inspector in collecting information.

6.2  SAFETY CONSIDERATIONS
     To aovid  injury  while conducting  a  thorough inspection,  the  inspector
must:
     0    Wear the requisite safety equipment
     0    Be aware of the safety  hazards
     0    Respect the company's  safety procedures
     0    Never become overconfident
The  last  point  is  particularly   important.   A   relatively  new   inspector  or
engineer may begin to  feel  like  an  "oldtimer"  after the first  few  trips  to
the  plant,  and  this  can be  dangerous.   For safety reasons,  the  inspector
should make it a practice to stay with the plant escort.
6.2.1  Safety Equipment
     For proper  fit, the  inspector  should  have  his/her own safety equipment.
The following equipment is recommended:
          Hard hat
     0    Safety glasses with side shields or full-cover  goggles
     0    Steel-toed safety shoes
     0    Fire-resistant pants and jacket
     0    OSHA-approved respirator (fit-tested)
     0    Heavy-duty gloves
     Although  incidents may  seem ulikely, when   the  inspector's  attention is
often focused  on  observing  emissions  and/or operating  procedures, he/she can
easily become unmindful of potential hazards.  Part of the. preparation of the
observation procedures  should  be to  review the location  of  the observation
point,  any required  movements,   the expected  activities   in  the   immediate
                                      72

-------
vicinity, and the availability of an escape route.  It is generally advisable
to stay as far away from moving equipment as possible.
     Unfortunately, a thorough inspection entails some risk.   Respect for the
hazards,  familiarity  with operations,  and  constant concern for  safety  will
minimize the chance of an unpleasant or fatal accident.

6.3  ONSITE COMPANY-INSPECTOR INTERACTION
     The  success of an  inspection  depends  greatly on  the interaction between
the  inspector and  plant  representative.   Upon  arrival  at  the  plant,  the
inspector should be prepared to discuss the following:
     0    Authority for the  inspection
     0    Agency organization
     0    Scope,  timing,  and  organization  of the  inspection  (preferred  in-
          spection agenda)
     0    Treatment of confidential data
     It  is  also  important  to  inquire  about the  operational  status  of  the
equipment to  be  inspected and the kinds and frequencies of any malfunctions.
If  equipment  is not  operating at or  near normal  conditions,  the  inspector
should  note the reasons  and when the plant expects  it  to  be  operating nor-
mally  (for  followup inspection  scheduling).
     Before collecting  any data,  the inspector should observe  process opera-
tions  for a while  to  become familiar with process variations,  wind patterns,
plume  characteristics, etc.

6.4  INSPECTION  PROCEDURES
     The  inspection  and  testing  of  large ventilation  systems  present some
problems  not  normally associated with  smaller  ventilation  systems.   Most of
the  problems  are associated  with  access to  the  ductwork  and the physical size
of the  system.   In many instances, access  limits  the  measurements that can be
taken.
     The  first  criterion  in the  evaluation of  the performance of large sys-
tems is  to  determine  whether capture is proper at  the source.   Poor  lighting
sometimes  limits visual  observation  of  capture  capabilities and  makes  it
difficult to  evaluate the effectiveness of the system.  The second criterion
is  to   determine  the  integrity  of  the ductwork  to the  control  equipment.

                                       73

-------
Again, access  conditions may  limit  this  visual  inspection  to  what can  be

observed  from  the ground  or  from  a nearby  roof.   Nevertheless,  excessive

inleakage is occurring and the need for  maintenance  should be determinable.

6.4.1  Duct System Inspection

     The inspector should have the following before  he/she begins the inspec-

tion:

     0    Knowledge of the operations in the process.

     0    Knowledge  of  the  physical/chemical  nature  of  the process  charge
          materials.

     0    A layout of the  operations showing  the  controlled and  uncontrolled
          areas.

     0    A line  sketch  showing the  elevation(s)  and  layout of  the ductwork;
          the  locations  of  the  collector, fan,  control  equipment; and  the
          flow patterns.

     0    Layout(s)  and  sketch(es) of  the duct  size  (length and  diameter)
          showing the main duct,  branch or interconnecting  ducts,  and  their
          respective flow  (actual  cubic  feet per minute);  temperature (°F)  of
          actual  gas flow;  slope  ratio  for transition points of  branch  duct-
          ing  to the  main  or interconnecting  ducts  and   their  respective
          angles; type  and thickness  of duct lining;  and the location, type
          and size of blast gates and dampers and how  they are controlled.

     0    Copies  of plant tests for velocity, pressure  drop, and  temperature,
          and the production or process  rate during  the  test.

     0    The production or process rate during the  inspection.

     During the  inspection, the  inspector  should note  the  condition of  the

duct  (e.g., erosion,  corrosion,  rusted-through  openings), flanges, expansion

joints, fits of  swing-away  joints, etc., all  of which affect the workability
of a ducting system.

     He/she should check to see that any emergency air inlet dampers, such as

those located in  the duct on electric arc furnace systems, are closed.   These

are  designed to  open when  temperatures  are high,  and  they should close auto-

matically and stay closed during normal  operation.

     For  inspection  purposes,  the  ventilation  system  is  defined  as the duct-

work  leading from the emission points  to  the  control devices.   It is   recom-

mended  that static  pressure  taps  be  made  throughout  the  length of this
                                      74

-------
ductwork to provide  data  on air inleakage and ductwork  plugging,  two  of the
major problems  with  ventilation systems.  Both will change  the  static pres-
sure and temperature profiles of the  ductwork  system.   If a  problem is indi-
cated,  the inspector  should  carefully  examine  the  ventilation   system  to
pinpoint the problem.
     Duct  blockage,  which  is  characterized by  a  large increase  in  static
pressure between the blockage and fan, reduces hood face velocity and results
in failure of  the  hooding to capture fugitive  emissions.  Blockage typically
occurs in ductwork bends  and cooling  loops  and may  be  attributable to insuf-
ficient  duct   velocity  (improper duct  sizing),  sedimentation  of  dust  par-
ticles,  or  excessive cooling of  the gas stream  (which tends to  change the
particulate matter into sticky particles  that deposit in the duct).
     Air inleakage can be a  major contributor to excessive cooling of the gas
stream.  Although  air  inleakage  may not occur  at a  single point, it is char-
acterized by  lower static pressures and lower  temperatures downstream of the
inleakage  points.   Excessive inleakage may  result  in  fugitive  emissions due
to decreased collection efficiency  at the emission point and, as noted above,
increased potential  for duct blockage.
     The  inspector  should  check the  face   velocity and positioning  of all
fugitive hooding.  Improper positioning  of  hooding  or  hood damage can reduce
capture  efficiency.   Also,  a negative pressure of at  least  24  to  49 Pa (0.1
to 0.2  in.  HpO) should be maintained at fugitive and process emission points
to accommodate  any surges in gas volume and  emissions.
6.4.2  Fan Inspection
     Lower duct static pressures can  also indicate an undersized or underper-
forming  fan.    The  fan  system  components  should  be  inspected  for  wear  or
corrosion  and  excessive  dust  buildup  or grease accumulation  removed.   Fan
couplings  should be  inspected  for  loose bolts or  misalignments.  Bearings
should be clean and  lubricated.  Shaft  seals should be  inspected for  leakage.
Although  a certain  amount  of  leakage  is  tolerable,   excessive  leakage may
indicate a need for  seal  replacement.
     A  major   factor  to   be  checked during  an inspection is  fan  vibration.
Vibration  is  a  function  of fan speed.    Normal  vibration  amplitudes at dif-
ferent fan speeds are as  follows:
                                       75

-------
                                          Normal  vibration
               Speed,  rpm                  amplitude,  in.
                 400                         0.003
                 800                         0.002
                1200                         0.0013
                1800                         0.0008
                3600                         0.0005
Although vibration  amplitudes  up  to 2.5 times the  normal  value are  accept-
able, corrective measures are required  when this  limit is exceeded.
     Excessive vibration can  result  from several things,  including  material
buildup on a  blade  or bearing wear.  Excessive  vibration  requires  immediate
attention, as  it  may  quickly  lead  to  catastrophic  failure  of the fan.   An
out-of-balance fan  wheel  rotating  at 300 to  700 rpm  can fracture the  shaft
and break through the  housing.  This can damage  other equipment in  the  area
and endanger the welfare of  people  in  the  immediate vicinity.   The  inspector
should vacate  the area  immediately  and promptly  report any  severe  vibration
to the plant.
     Performance tests  may  be necessary to  ensure  the proper  fan  operation
after major maintenance,  including  rebalancing the  fan wheel  if any  repairs
were  made  to  rotating  components.   Using  a pitot  tube  and  manometer,  an
inspector can  measure velocity pressures at  various  points  in the  duct and
calculate the volume flow rate from  these  readings after correcting  them for
density at  the operating temperature  and pressure.   Fan  horsepower can  be
calculated from readings of voltage and current supplied to the motor, but it
also must be  corrected  for  actual  density.   The horsepower  and static  pres-
sure should be  plotted  on  the fan's original characteristic curves  for com-
parison.
     Each fan  has a set of  isolation  sleeves, the  size of  which  depends  on
the fan size.   Cracks  or tears in  the inlet sleeves  permit  in-draft air to be
pulled in by the fan, which  reduces  suction  from the  hood.   In high-tempera-
ture operations,  inlet  sleeves are  made of  an asbestos  compound.   In lower-
temperature  operations,  they are  made  of  neoprene type  rubber.   Rubber
sleeves should never be painted; any type of paint will attack rubber.
     Fans are designed to rotate in a given direction.  If electrical connec-
tions are reversed, the fan  will  still  move air, but  not  efficiently.  Fan
rotation direction  should be confirmed against design direction.

                                      76

-------
     Fan curves cannot be used directly  on  a  scrubber that has water droplet
carryover, as the water  droplets  represent  a  mass that the fan has to accel-
erate.  A wet  fan indicates that  a  mist eliminator  isn't working properly.
This will require  the fan to have higher horsepower,  and  the  fan  curve will
inaccurately project  that more gas  is  going  through the system  than  there
actually is.  Uncondensed moisture in the  gas  stream also must be corrected
because it  changes  the density.   At  some  sources,  a Fyrite test  kit  can  be
used  to  check the  change in oxygen  content  throughout the  system.   Severe
inleakage will cause  a  sudden jump in oxygen  content.  This technique cannot
be used for an ambient system.
6.4.3  Gas Flow Check
     Gas flow is  a  useful parameter in evaluating system performance because
it  provides  an  indication of the  capture  velocity at  the  hood(s).   In gen-
eral,  as  the quantity  of the gas moved through the  fan  increases,  the re-
quired horsepower  also  increases.   This  increase is reflected by an increase
in motor current,  which  is often  measured  in  a control room.  Although motor
current sometimes  can be measured by  a  portable clamp-on ammeter, inexperi-
enced  personnel  should  not attempt this  kind  of measurement, particularly at
high  operating  voltages.   The  current  flow  is  a  useful  indicator  for all
types  of systems, regardless of the flow control method (i.e., damper type or
speed  control).   Static  pressure  across  a  fan operating at a fixed speed and
without  inlet  spin-vane  dampers  also will indicate  gas  flow;  gas  flow de-
creases as static pressure or resistance increases.
     The  use of  fan curves  is  one  method  of  determining gas  flow.   This
requires  the measurement of  fan  rotation  speed, gas  temperature, and motor
horsepower or static  pressure  across  the fan.  This method cannot be used if
inlet  spin vane dampers  are used.
     The  use of  a  pitot traverse  is  a  more  traditional  approach to deter-
mining gas velocity.   In  this method  (outlined  in EPA Reference  Methods  1 and
2)  a  pitot  tube  is used  to measure velocity  profile across the duct and the
known  cross-sectional area of the  duct for  calculating  gas volume  through the
system.   Again,  the  limiting  factor  may  be  access  to  the ductwork.   Long,
difficult-to-handle pitot tubes may be required  to  obtain  the  measurements in
large  ducts.
                                       77

-------
     Once gas volume  is  estimated,  the average hood capture  velocity  may be
estimated by comparing the measured gas volume with  the  cross-sectional  area
of the hood.  This  indicates  whether  the  average hood face velocity  is  ade-
quate to  provide the  desired capture efficiency.   When multiple-hoods  are
interconnected,  the flow in each branch may  have  to  be  measured to establish
the proper flow  balance  from  each  hood.   The difficulty with  this  method is
that it  provides  only an average hood face  velocity,  which may  be substan-
tially different from localized velocities in large  ventilation hoods.
     Pitot tubes generally will not  accurately indicate  hood face velocity at
the relatively low velocity encountered at most ventilation  hoods (250 to 750
fpm).  Therefore,  other  types of instrumentation must  be used such as  hot-
wire and low-pressure gauges.   Hand-held  instruments  such as vane and  propel-
ler-type  anemometers  cannot  be used  to  measure localized  face  velocity.
Hot-wire anemometers may be attached  to  long probes  for measurement of  face
velocity at  various  points  across  the hood face, but the results  would  have
to  be  corrected  for  the additional  wire length  (resistance), which would
affect  the   readings.  Again, access   would  have to be  provided  for  these
tests, which could be impractical or unsafe  during source operation.   A  test
of this nature,  however,  would establish minimum and  maximum hood face veloc-
ities, flow  distribution, and average  hood face velocity, whereas measurement
of the gas volume/hood opening area  provides  only an  average velocity.
6.4.4  Visual Observations
     If no measurements are made, inspection  is limited  to visual observation
of the system performance, including hood  and  duct integrity,  the effects of
cross-drafts, and  operational procedures   that may  affect  the  capture  effi-
ciency of the ventilation system.  Hoods  should remain  intact and as close to
the source as possible, not only to capture emissions,  but also to reduce gas
volume  requirements.   Ducts   should be checked for  damage, which  can  cause
pressure  losses,  wear,  and inleakage.  Cross-drafts should be  minimal.   If
the system  is not  designed  to operate with cross-drafts, it  may not  perform
satisfactorily.   Wind direction and open doors and windows should be noted.
                                      78

-------
6.5  OPERATION AND MAINTENANCE (O&M) CONSIDERATIONS
     Because  the  fan  systems used  in  large  ventilation  systems  represent
substantial  capital  outlay  and  are  costly to  operate,  it  is  in  the  best
interest of  the  plants to maintain  this equipment in a  fashion  that lowers
the  incidence of failures  that  lead  to excessive downtime  and  extends  the
useful life of the equipment.  The fan system should be considered as includ-
ing the fan,  the  motor and  drive systems, the inlet and outlet duct systems,
and any flow-control dampers  used  to  control  the quantity of gas  being moved
through the ventilation system.
     The  successful  operation  and maintenance  of the  fan system  on  large
industrial ventilation systems does not depend  on any one  item,  but on  the
proper design and operation of  several  components.   Although  some items  are
more  critical than others,  all  must  operate  as a unit  for the  ventilation
system to  deliver the  desired  gas  volume most efficiently.
     For economic reasons,  most single  fan  installations  are limited to  gas
volumes of approximately  1.0 to 1.3 million acfm at  nominal static pressure
drops.  If greater  gas volumes are needed than can be economically delivered
by  a  single   fan, two  or  more fans  arranged  in  parallel may  be  used.   This
arrangement allows the use of  several  smaller "off-the-shelf" fans, which are
less  costly   than  custom engineered  fans; however,  when multiple  fans  are
used,  care must be taken to see  that the  ductwork and  fans match, particu-
larly  when fans  of different sizes are  used.  This approach permits the  use
of  smaller individual  fan drive  motors and  also  allows the ventilation system
to  remain  partly  operational in the event  of the  failure  of one  of the fans
or  fan drive  motor systems.
     Although many  components in  the  fan system may  be  subject  to  failure,
two areas  are of  the greatest  concern:   1)  improper balance  and the resulting
excessive  vibration  of the  fan, and  2)  failure of the  drive  motor system.
Either can result in  expensive repairs or replacements.  Proper design and a
preventive maintenance program can reduce the incidence of  such failure.
     Some  drive  systems are  quite large and require motor sizes in excess of
500  hp (up to as high as  8000).  The initial purchase  is  generally propor-
tional to  the motor size.   On the other hand, the larger systems tend to be
more efficient,  and  energy  savings over the  life of  the unit may offset the
                                       79

-------
initial  cost.   Proper matching  of  motor size  with horsepower  requirements
also will  usually increase motor efficiency.
     Most  drive  motors  are  at  their highest  efficiency  and  lowest  power
factor losses when operated at 80 to  90  percent  of  their  maximum  rated load.
If motors are always operated at 100 percent of  rated  load,  they  may require
more maintenance and  may not  have  sufficient reserve  for  occasional  periods
when more  horsepower  is  needed.   The "service  factor" rating of  the  motor,
which usually ranges between 1.0 and  1.15, is an indicator of the sturdiness
of the motor and its ability to run  at higher than rated load for  an extended
period of time without experiencing  damage.
     Because many  of  these fans are  used in systems  that  control  fugitive
emissions  varying  in  gas  temperature  (and  gas   volume to be captured),  the
maximum and  minimum gas  temperatures must  be considered  in sizing the  fan
motor.  If the fan  is  sized only for  gas conditions  at the maximum operating
temperatures, problems with motor overload may occur when  gas temperature de-
creases.   This results  in a  denser  gas,  and  more energy  is  required  to move
it.  Eventually, such continual overloading of the motor  may lead to burnout
of the motor windings  and motor  failure  if  efforts are not  made  to minimize
the problem.
     Motor startup  is  also related  to motor overload.  The  larger the motor
size is,  the  higher the  operating  voltage required to  keep  the  current flow
at a  reasonable  level.  Operating  voltage will  typically be 440  to  460 for
motors having  350  hp  or less  (but in some cases up to 500  hp).   For  larger
motors, operating  voltages generally increase to  2130 or 4260.   When  a fan
motor is  started "across the  line,"  however,  it can  draw 6 to  7  times its
normal operating current (regardless  of  voltage) during  acceleration  of the
fan wheel  to its normal  rotation speed.  Although  this current  surge  is of
short duration  and diminishes  as  the fan approaches  its running  speed, it
could damage  the motor on startup with  a cold  gas stream and  cause circuit
breakers  to  trip,  both  at the  fan and in other  areas of the plant that might
be  affected  if  the surge of  current into  the  fan circuit were  to  reduce
operating  voltages to unacceptably low voltages  and cause  undervoltage trips.
     Two  methods  that  can be used  to   reduce  the  possibility  of  circuit
breaker trips or damage  to the motor  upon startup are reduced-voltage starts
and  closed-damper   starts.   Reduced-voltage  starts  allow  the  fan  wheel to

                                      80

-------
accelerate  to  a  portion  of  its  rotation  speed,  and  then  full  voltage  is
applied!  to  accelerate  the  fan wheel  and gas  to  full  speed.   Although  the
current will  still  surge upon  startup,  the  levels  of  surge should  be  more
acceptable,  particularly  if  other  circuits  are  involved.   Closed-damper
starts  allow  the motor to  accelerate the  fan wheel without simultaneously
moving  the  gas;  much of the current  surge  results  from accelerated gas  flow
through the system.  Opening the dampers gradually to allow gas to flow after
the fan wheel is rotating permits the flow of current to be controlled.
     A  third method  is  to control the rotation  speed.  This method is similar
to  the  reduced-voltage start.   The primary  difference  is that  this method
uses a  variable-speed motor or a transmission coupling, which allows variable
fan  rotation speeds.   A gradual   increase  in rotation  speed  controls  the
current surge.
     Excessively  high  currents  in  the  motor  create heat in the windings,
which can  destroy the winding insulation and result  in the  loss of windings
because of  short-circuiting.  Heat  buildup in the motor can be a major reason
for  motor  failure.   Other   reasons for  heat buildup  in  the motor  include
improper or restricted  ventilation  due to the location of the motor or exces-
sive dust buildup.   Motors must be  kept clean to maintain the flow of cooling
air through them.  Additional cooling considerations may be necessary if fans
are  located  where  ambient  temperatures  are  high.    Normally,  solid-state
controls for  variable-speed  motors  also  must be protected from high tempera-
tures.
     Transmission  of the motor energy  to  the fan  shaft is  usually accom-
plished by  direct   drive,  by V-belts,  or  through  a  variable-speed trans-
mission.  The belts  must be  tensioned properly  and kept free of grease or oil
to  prevent  slippage  and belt damage.   The fluid levels  of fluid-drive trans-
missions  for  variable-speed  operation  must  be  maintained (and   possibly
cooled)  for reliable operation.
     Most  fan shafts are  supported  by bearings at the fan housing and at the
drive  connections.   Worn  bearings can  cause  excessive  fan vibration  and
increase  energy  costs.  Bearings  for  smaller fans can  be  installed  with
grease  seals and a  grease fitting  for  routine  lubrication.   The  bearing
lubrication should  be  checked at least  daily to  ensure that it  is adequate.
                                       81

-------
On  fans  operating  with  high-temperature  gas  streams,  it  is  particularly
important to  keep  the  bearings cool to  prevent  breakdown of  the  lubricant.
Heat can be transmitted through the shaft to  the  bearing assembly.
     Although most fans  are  designed with some  inleakage of air  around  the
shaft to the  fan  housing, this may  not  be enough for  adequate  cooling.   In
this case, heat fins may be  installed on  the  fan  shaft where it  exits  from
the fan.  These fins rotate with  the  shaft and provide  extra cooling surface
by conducting heat away from  the bearings.   In  situations where this approach
is inadequate, a continuous lubrication  system that  utilizes circulating  oil
can be applied.    This  system,  which consists of  a  pump, circulation lines, a
filter, and  a cooling  system (usually water), simultaneously  provides  bear-
ings  with  continuous  lubrication  and  cooling.    More   complex  than  simple
grease lubrication, this  system has  the  disadvantage of requiring  continuous
operation.
     On  large fan systems,  the  use  of vibration  monitoring equipment  can
prevent continued  operation of a fan that is  unbalanced  or has worn bearings.
If a  severely vibrating  fan  is allowed to continue  operating, a  "fan explo-
sion" could  occur  when the fan is  no  longer able  to withstand  the stresses
and simply comes apart during  operation.   This can  be extremely  dangerous to
personnel working  in the area and also costly to  repair.
     All fan  systems are equipped with inspection hatches and the fans should
be inspected  through these hatches at least annually to  evaluate  the severity
of  fan  wheel wear.   Generally, evidence  of fan blade  wear appears on  the
edges of the  fan  wheel,  on the side  opposite  the  inlet.  The chance of  fan
wear  and  blade buildup  is greater  on fans that  are  installed  in  the  gas
stream prior  to the air pollution control equipment than on fans  placed  down-
stream of  the control  equipment,  and they should  be checked more  frequently
for wear and vibration.   When blades  are  replaced,  the  fan  usually must be
rebalanced.
     Particulate  buildup on  fan  blades can lead to improper  fan balance.
Because the buildup on fan wheels tends to be relatively uniform, it does not
affect the fan wheel balanced  until it flakes  off,  at  which time  a substan-
tial change  in fan balance can  occur.   This, in  turn, leads  to fan vibration
and bearing wear,  and  can eventually cause  fan  wheel failure.   This buildup
problem can be severe when the dust is sticky or oily or  if the fan follows  a

                                      82

-------
wet scrubber,  in which  case  wet gas conditions enhance the buildup problems.
(Water can  be applied  to  a  fan that  is  used after the  scrubber  to prevent
particulate buildup.)   The higher the rotation  speed  of  fans,  the more sus-
ceptible they are to the severe  inbalance problems of particulate buildup.
     Fans with  linings  should  be inspected  as often or more often than other
fans to ascertain that  the lining  is  still  intact.   Care  should be taken not
to  damage  the  lining during inspection.   Because fans are  most often lined
for  corrosion resistance, these linings  must be  kept in good  condition to
prevent excessive fan wheel  or housing corrosion.   The key to the successful
application of  lining is  good  surface preparation,  which  seems  to be as much
an  art as a science.
     Another  area of concern is the  delivery  of proper gas  flow through the
ventilation  system.   This flow control  is  usually  accomplished through the
use  of  dampers or by controlling  the  rotation of  the  fan speed.  The latter
method  is  the most  energy-efficient.   The quantity of gas delivered by a fan
is  proportional  to  the  change  in rotation speed, but the horsepower required
changes by  a  cubic  relationship.  Thus, very  small changes in rotation speed
can  result in  significant changes in  horsepower.   The  initial cost  of the
speed control  equipment will offset the energy savings somewhat.
     The  next most  efficient  method  of controlling gas  flow is  the  use of
inlet spin  vane dampers.   As the vanes close,  gas is spun in the direction of
the fan wheel  rotation.  The quantity of  gas delivered by the fan is a func-
tion of the difference  in inlet and outlet  gas velocity.   Because the gas is
spinning  in the direction of rotation, the difference in velocity is smaller
and the quantity of gas  delivered  is smaller  with  no waste  in  the static
pressure  developed  by the fan.  These dampers should be checked periodically
to  guard against improper  functioning and excessive wear of  the  vanes.
     The  least  efficient  but simplest method of  controlling  gas  flow involves
the  use of  blade-type  dampers.   These dampers place additional resistance
(variable)  into the  system  to  control the  gas  flow.  Even  at reduced  flow
rates,  the  fan still delivers  a high static pressure and thus  requires  more
energy  to  move the  reduced  gas  volume.   This method  is  also the  simplest to
maintain unless excessive  wear occurs.
     Air  inleakage   is  one reason why  systems may not perform as  designed.
Air  can flow  into the system wherever a leak  occurs, e.g.,  through  a  hole in

                                       83

-------
the ductwork,  an  expansion joint,  or  open branches  that  should be  closed.
The fan will  pull  gas through  the  point of  least  resistance,  and this  can
leave the  ventilation system with  inadequate draft.  Any  damage should  be
repaired before it leads  to inadequate  control of emissions,  corrosion (lead-
ing to  increased  air  inleakage),  and  higher  energy  costs  for  transporting
unwanted dilution  air though the system.
     Ductwork design also affects how much gas the  system will  deliver.   The
shortest,  straightest  duct  is  the  most desirable for the design,  operation,
and maintainance  of  the  system.   On  large   systems,  rectangular ducts  are
often easier to install  than  round  ones because  it  is  easier to weld  large
flat sections of  steel;  however,  particulate  matter has a tendency to  build
up in the  corners of rectangular  ducts and close off usable area.  For  this
reason rectangular ducts may  require periodic cleanout.   On the  other  hand,
some fans  (e.g., double-inlet centrifugal  fans) are  more  adaptable to  rectan-
gular ducts.
     Improper design of the inlet design of the ductwork  can  cause a swirling
gas flow  to the fan, which creates an  effect similar to that obtained  from
inlet spin  vane dampers.   This can cause  reduced  gas  flow and  inadequate
capture by the ventilation system.   This is  particularly true  if  smooth
transitions are not  provided  to  the  fan, in which case flow-straightening
vanes or redesign  of the  ductwork may be required.
                                      84

-------
                                  SECTION 7
                          TOTAL FURNACE ENCLOSURES

     This section discusses total furnace enclosures in the metallurgical
industries.  It is assumed that the reader is generally familiar with the
metallurgical processes that use these enclosures.  The basic ventilation
principles outlined in previous sections are valid for these special  appli-
cations.

7.1  ELECTRIC ARC FURNACES
     The recent trend in electric arc furnace (EAF) emission control  is to
totally enclose the furnace operations.  This system allows the collection
of both primary and secondary emissions from EAF operations.  Several
smaller furnaces (<100 tons) have installed total furnace enclosures.  The
essential features of these enclosures are sliding doors that create access
for the crane and scrap charging bucket and an air curtain to block the
escape of fumes from the roof when the roof doors are parted for crane cable
access during charging.  The advantages of total furnace enclosure are:
                                                       s
     °    Effective fume capture.
     0    Low volumes of air handled as emissions collected at the source.
     0    Capture of both primary and secondary emissions.
     0    Access for furnace maintenance.
     0    Lower noise levels outside the enclosure
     0    Lower capital and operating costs.
     0    Better working environment and lower roof temperature in the EAF
          shop.
     0    Minimal effect of cross winds because the entire operation  is
          enclosed.
                                      85

-------
     0    Lower maintenance of cranes  and  other equipment because of reduced
          dust-fall  within the shop.
     Figure 32 illustrates a typical furnace  enclosure.
7.1.1  Description
     A typical enclosure should have adequate space around the furnace to
provide a suitable working area and reduce the effect of heat on the enclo-
sure structure and furnace components.   The enclosure structure is generally
lined with hi-rib aluminized sheeting  and  joints sealed  with  closure strips.
Bi-parting vertical  doors in front of  the  furnace are controlled by air
cylinders to allow the overhead crane  to enter the enclosure.   A rectangular
roof slot provides clearance for crane cables when the crane  is operated
within the enclosure.   This slot is closed by roof doors that are pneumati-
cally operated.  An air curtain under  the  roof slot area contains and guides
the emissions to the pickup hood located opposite the air curtain nozzles.
The air curtain fan is usually located on  the roof of the furnace transformer
room.  Removable roof panels above the roof doors allow  access for furnace
maintenance.  The furnace operations,  air  curtain, and pickup hood can be
observed safely from the control room.   The control room usually has a full
glass window that forms a part of the  enclosure wall. Doors  to the enclosure
allow access to the furnace for oxygen lancing and for taking metal and slag
samples.
     To charge the furnace, the crane  operator positions the  charging bucket
in front of the enclosure and aligns  the crane cable in  front of the roof
slot.  The furnace operator swings the furnace roof aside and opens the
front vertical bi-parting doors and the roof  doors of the enclosure.  The
crane operator then brings the charging bucket into the  enclosure.  At
ground level, a furnace operator guides the crane operator in positioning
the charge bucket directly over the furnace.   The crane  operator dumps the
scrap by opening the bottom of the bucket  and then reverses the crane out of
the enclosure.  The control room operator  closes the vertical and roof doors
and swings the furnace roof in position to seal the furnace.   The melting
operation commences after the furnace  roof is in position.  During the
entire period when the bi-parting doors and roof doors are open, the air
curtain is in operation along with the enclosure exhaust.  During melting,
                                      86

-------
00
            LOCAL TAP  HOOD
                                                           AIR CURTAIN

                                                           PICKUP HOOD
                                                                 BI-PARTING DOORS
                                                                                        TO  BAGHOUSE
                                                                                        CRANE RAIL LEVEL
                                                                                    FURNACE LEVEL
                                                                                    GROUND LEVEL
                                       Figure  32.  Typical  furnace enclosure.
                                                   (Not   to  scale)

-------
oxygen lancing, deslagging, and sampling, the doors are closed and the
enclosure is exhausted to a gas cleaning device, generally a baghouse.
     A stack in the fourth hole position of the furnace roof leads the
emissions generated during melting and refining closer to the exhaust hood.
Depending on the design of the enclosure, the furnace tapping occurs either
within or outside the enclosure.  In most cases a transfer car brings the
teeming ladle into the tapping position underneath the furnace.   If tapping
takes place outside the enclosure, a local hood is provided to capture
tapping emissions.  In the design where tapping takes place within the
enclosure, the enclosure exhaust evacuates the tapping emissions.
7.1.2  Design Considerations
     Charging, melting, refining, and tapping emissions occur during the
operation of the EAF.  The maximum emissions (85 - 90%) occur during melt-
                 i p
down or refining.    Direct shell evacuation or side draft hoods adequately
control these primary emissions.  Several techniques including canopy hoods
and building evacuation control secondary emissions.  Although canopy hoods
have few operating restrictions, they have the disadvantages of high volume
requirements, high capital, and high operating costs.  Crosswinds  within the
shop affect capture efficiency.  Local hoods have provided limited success
in collecting tapping fumes.  A compromise solution to the high volumes
required for canopy hood systems is a modified canopy approach where fixed
curtain walls form a partial enclosure around the furnace to act as a
chimney to direct charging emissions to the canopy hood, while local hoods
are utilized to control tapping emissions.
     The ultimate control of furnace emissions involves furnace enclosure
technology.  On small electric furnaces, complete emissions control can be
achieved by collecting emissions at the source by adopting furnace enclosure
technology.  Emissions generated during all phases of the EAF operations can
be withdrawn from the enclosure using relatively low flow volumes.  If
emission volumes are high as a result of the use of UHP furnaces, oxyfuel
burners, or larger furnaces, however, additional primary controls such as a
DSE (fourth hole) system may be required.  The approximate volume of air
required for a furnace enclosure in a small furnace will be equivalent to
the volume required by a side-draft hood system; a  larger furnace will
                                      88

-------
                                                                    IP
require an amount equivalent to the volume required by a DSE system.    The
actual air flow required will depend on many factors such as furnace size,
oxygen lancing rate, exhaust-duct position, scrap cleanliness, furnace
power, types of steel produced, operating practices, and enclosure volume.
7.1.3  Retrofit Installations
     Because each retrofit installation is unique, enclosures must be
tailored to meet individual  requirements, furnace practices, and shop
layout.  Examples of two retrofit EAF enclosures in the United States are
found at the North Star Steel Company and Birdsboro Corporation.
North Star Steel Company--
     This company has two 60-ton furnaces that are controlled by DSE and a
roof canopy system.  The capture efficiency of the canopy system was low
during charging and tapping  because of the flat design of the roof canopy
and insufficient extraction  volume.  Each furnace was retrofitted with an
enclosure.  The furnace enclosure is a steel structure c-lad with ribbed
aluminized sheets and sealed.  Mechanical bi-parting side doors and roof
doors allow entry of the crane for charging.  The bi-parting vertical doors
are closed during charging and an air curtain seals the roof.  The entire
available flow is used to extract the charging emissions through a high-
level evacuation duct.  Emissions from melting, oxygen lancing, and slagging
operations are controlled by a DSE system.  During tapping, mechanical
bi-parting doors on the tapside of the enclosure are opened to permit entry
of the tap ladle.  These doors have a top horizontal roof with a slot for
cables holding the tap ladle.  Once the  ladle is positioned, the bi-parting
doors close to contain the fumes.  During tapping, fume is evacuated by a
high-level duct.  On the charge side, the mechanical roof door, the roof
section complete with air curtain, and the charge section evacuation duct
can all be mechanically wheeled aside for maintenance operations such as
replacement of furnace parts and removal of the shell and roof.  Salient
                                  19
data  on this plant are as follows:
      Furnaces:                Two: 15-ft diameter; 60-ton capacity  each
      Transformer:             30,000 to  33,000  kVA
                                       89

-------
     Meltdown rate:            55  tons/hour
     02  consumption:           300 ft3/ton
     Approximate enclosure
       size:                   40  x 36  x  31 ft  high
     Extraction volume:        170,000  acfm per enclosure
     Air curtain volume:       6000 acfm
Figure 33 shows the  enclosure at  the North Star Steel  Company.
Birdsboro Corporation--
     This new facility initially  designed  with a side-draft  hood  for primary
emission control had to  be redesigned  to control  both  primary  and secondary
emissions.   The furnace  enclosure design allowed an  acceptable solution  with
an exhaust volume of 75,000 acfm  for a 40-ton  furnace.  Tapping and  charging
are carried out from the same side.  A mechanical hood  car moves  away from
the enclosure to provide an opening for  the scrap bucket  and tap  ladle.
Three cylinder-operated  movable roof doors seal  the  crane cable entry slot.
These doors are linked to dampers in the air-curtain duct system.  The air
curtains seal the opening when the doors are opened  for charging  or  tapping.
Overhead removable panels at the  enclosure roof level  aid maintenance
operations.  In the  initial startup, the enclosure was  not effective during
lancing.  Measures adopted to overcome this problem  were  better sealing  of
the furnsce enclosure, upgrading  the air curtain fan,  adjusting air  nozzles
to deflect the lancing emissions  into  the  extraction duct, and installing a
                                                          ] Q
deflector plate.  Salient data on this shop are as follows:
     Furnaces:                One: 13-ft,  6 in.  diameter; 40 tons capacity
     Transformer:             10,000  kVA
     Maximum meltdown rate:   18.6 tons/hour
     Oxygen lancing:          250 scfm (design)
     Enclosure size
      (approximate):          36  x 30  x  28 ft  high
     Extraction volume:        75,000  acfm  (design);  81,600 acfm
                               operating
                                      90

-------
Figure 33.  Furnace enclosure at North Star Steel Company.
                            91

-------
     Temperature:              Normal  150°F;  Maximum  275°F
     Air curtain volume:       9,900  acfm (design)  increased  to
                               11,700 acfm.
     Figure 34 shows the  furnace  enclosure  at  Birdsboro  Corporation.
7.1.4  New Installations
     Some of the new EAF  installations required  to meet  NSPS have  adopted
furnace enclosures for smaller furnaces (<100  tons).   Table  10  is  a  list of
the essential features of new EAF shops designed for furnace enclosures.
Plant 3 has additional pickup points including a local tapping  hood,  an
additional hood to evacuate tundish  lancing  emissions, and a scavenging  hood
located above the roof slot of the enclosure,  all  connected  to  a common
baghouse.  Balancing the  draft for such multiple pickup  points  is  difficult,
but adjustments are made  with operating experience.   A typical  flow  balance
during various phases of  the EAF  operations  is shown in  Table 11.  Dampers
on each hood control the  flow.
7.1.5  Inspection
     To achieve good evacuation,  the enclosure should be well sealed.   This
will depend on the integrity of the enclosure.  The  inspector should observe
and note the general condition of the enclosure  walls in regard to any loose
sealing strips, misalignment of the bi-parting doors (which  creates  large
gaps), holes in the panels, damaged or warped  panels, open access  doors, and
any other openings that reduce the capture  efficiency of the enclosure.
During scrap charging and at other periods  when  the  air  curtain is operated,
the inspector should observe the  air curtain as  it diverts the  thermally-
driven plume into the pickup hood.  Improperly placed air  nozzles  in the air
curtain may not completely seal the roof door area and thus  allow  emissions
to escape.  The air curtain operation can be safely  observed from  the
control room.  The performance of the enclosure  can  be assessed by simultane-
ous observations by two inspectors, one inside the control  room and  the
other outside the enclosure, during all phases of a  heat cycle.  The inspector
in the control room should observe and note the  fit and  closure of the roof
doors, ?nd the buildup of emissions within  the enclosure and how effectively
they are evacuated at various stages of the furnace operation.   The inspector
                                      92

-------
                 EXHAUST DUCT
                 	REMOVABLE PANELS
                                    OVERHEAD MAINTENANCE ACCESS
                                             ROOF DOORS
                                              NORTH
                                             CHARGING AND
                                             TAPPING HOOD CAR
                                             LADLE ADDITIVE CHUTE
                                             ROOF AND HOOD CAR
                                             CONTROL PANEL
                                      FURNACE CONTROL PANEL
                                 EAST ROLL-UP DOOR
                           SOUTH ROLL-UP DOOR
                     FURNACE  CONTROL  PANEL
Figure 34.   Furnace enclosure at Birdsboro Corporation.
                           93

-------
                    TABLE 10.  DATA ON EAF PLANTS DESIGNED FOR TOTAL FURNACE ENCLOSURE20'21
                                   Plant 1
                                       Plant 2
                                       Plant 3
Number of furnaces

Furnace size


Transformer

Type of steel made

Meltdown rate

Approximate enclosure
 size

Extraction volume
Air curtains at the
 roof slot

Other features
            1

  12-ft,-6 in diameter;
   28-32 tons/heat

  16,800 kVA

  Specialty

  s20 tons/hour

  42 x 51 x 35 ft


  150,000 acfm


        Yes
Vertical bi-parting
doors and roof slot with
doors for crane cable
access.
   16-ft diameter;
    60 tons/heat

   33,600 kVA

   Carbon steel

   =72 tons/hour

   34 x 53 x 44 ft (curved
   at the top, dome shaped)

   175 to 200,000 acfm at
   150°F

          Yes
Vertical bi-parting doors
and roof slot with doors
for crane cable access.
           1

  15-ft diameter;
   55 tons/heat

  17,000 kVA

  Medium-carbon steels

  =16 tons/hour

  Not available


  150,000 acfm at 130°F


         Yes
Vertical bi-parting doors
and roof slot with doors
for crane cable access.
A separate tapping hood
and a scavenging hood above
the crane slot, evacuated
to the same baghouse.
 Each  furnace has  a separate enclosure.

-------
         TABLE  11.   FLOW  BALANCING  OF  A  TYPICAL  FURNACE  ENCLOSURE WITH
             ADDITIONAL PICKUP HOODS,  CONNECTED  TO A  COMMON BAGHOUSE
                                 (150,000  acfm)

Operating Mode
Furnace charging
Melting and refining
Tapping
Lancing at Lancing
Station
Roof
scavenging
hood
73,000 acfm
73,000 acfm
73,000 acfm
43,000 acfm
Furnace
enclosure
pickup hood
77,000 acfm
77,000 acfm
22,000 acfm
77,000 acfm
Local
tapping
hood
Closed
Closed
55,000 acfm
Closed

Lancing
hood
Closed
Closed
Closed
30,000 acfm
NOTE:   Lancing hood cannot be operated during charging  or when  air  curtain  is
       operated, and during tapping.   Roof scavenging hood can  evacuate at  a
       higher rate than 73,000 acfm,  if needed.
outside the enclosure should observe  and note the shop  layout,  any  leakage
of emissions from the enclosure, crossdrafts inside the shop, emissions
fromancillary operations, additional  pickup points, and the overall  flow
balance under different operating modes.  Although crosswinds generally do
not affect the performance of an enclosure, emissions that build  up near  the
shop roof above the enclosure will escape the building.  If a separate
scavenger hood is provided above the  enclosure,  its capture efficiency
should be observed.

7.2  BASIC OXYGEN FURNACES
     Primary emissions from basic oxygen furnaces are captured  in specially
designed hoods.  The hood is erected  above the mouth of the vessel  to
control the primary emissions when the vessel is in the vertical  position.
The primary hood is not as effective, however, when the vessel  is tilted  for
various operations such as charging,  sampling, tapping, and deslagging.
Additional hoods or enclosures are required to control  these secondary
emissions.  The trend is toward total enclosures.
                                      95

-------
7.2.1  Description
     The vessel  is enclosed on all  sides, with a door or bi-parting doors in
the front to facilitate scrap and hot metal  charging.   Since these
operations occur at and above the vessel, natural  convection will  permit a
plume of hot dusty gases to escape during charging.   To reduce this
possibility, charging should occur as close  to the vessel  as possible and
under the hood.   A separate charging hood is provided within the enclosure
for capturing the charging emissions.  The enclosure can extend partially or
completely at the tap side.  Tapping is carried out  at and below the level
of the vessel, and the hot dusty gases have  a tendency to escape in the
natural draft induced by the process heat.  In the newer designs,  a permanent
tap hood is installed at the back of the enclosure.   Figure 35 shows a
typical arrangement of a BOF vessel  enclosure.  The  furnace enclosure
extends below the charging floor, and the only openings are for the ladle
car.  These openings can be effectively reduced by the addition of vertical
shields on the end of the ladle car.
     In the bottom blown BOF (Q-BOP), oxygen is blown through tuyeres.
During charging and turndown, gas (either oxygen or nitrogen) must be blown
through the tuyeres to prevent liquid metal, slag, or solids from entering
and clogging the tuyeres.  This generates heavy emissions and makes capture
of the secondary emissions more difficult; hence,  invariably all the Q-BOP
furnaces are completely enclosed.
7.2.2  Gas Cleaning Systems
     The gas cleaning system employed to control secondary emissions may be
an extension of the primary control  system.   One hood designed to collect
charging emissions and another for collecting tapping emissions could be
ducted to the same primary gas cleaning system.  The gas flow would be
adjusted for the different demands of the heat cycle.  Another alternative
is to duct the charging and tapping hoods in the furnace enclosure to a
secondary control unit, generally a bag filter.  Figure 36 indicates a
schematic of the secondary control system at Kaiser Steel in Fontana,
Cal i form' a.
                                      96

-------
        SECONDARY
HOT METAL CHARGMG
FURNACE CHARGMG
     (Rctractebto)

     SLAG POT
              HOOD
              LADLE
 WATER COOLED HOOD
 HOOD TRANSFER CAR
 ADJUSTABLE SKRT
 TAPPING EMISSIONS DUCT
 SEAL RING
 FURNACE ENCLOSURE
OPERATING FLOOR
        TEEMING LADLE
                                                                            SHOP AM
                                                                         INDRAFT DURMG
                                                                            SLAGGMGA
                                                                             TAPPING
Courtesy:
                                  Figure 35.   Typical  BOF  furnace enclosure.
                Pennsylvania Engineering Corporation.

-------
      HOT METAL
      TRANSFER
          1
SKIMMING
    1
HOT METAL
 TRANSFER
    2
                                            \   /
                         SLAG
                       SKIMMING
                          2
        FURNACE
     CHARGING HOOD
           1
               \
        FURNACE
     CHARGING  HOOD
           2
                                A
V
TAPPING HOOD
V
                 TAPPING HOOD
                BAGHOUSE

             1,020,000 m3/hr
        MAXIMUM TEMPERATURE 230°C
                                                         EXHAUST FANS
 Figure 36.  Schematic of basic oxygen secondary emission control system
                        of Kaiser Steel-Fontana.
                                  98

-------
     A common baghouse with a I,020,000-m3/h (600,000 acfm) design flow
serves not only the charging and tapping hoods within the furnace enclosure
but other areas such as the hot metal transfer and slag skimming stations.
     In the closed-hood system that intermittently handles a flammable gas
(CO), use of the primary system to control the secondary sources could
result in an explosion.
     At the Q-BOP plant of Republic Steel in Chicago, which has a suppressed
combustion or closed-hood system, charging emissions are safely collected by
diverting the emissions to the primary system of the nonoperating vessel.
The shop has two vessels, and one furnace is operated at a time.  Figure 37
shows the schematic arrangement of the gas cleaning operation.  When both
gas cleaning system fans are operated, a flow rate of 634,000 m3/h (373,000
                                                                  ??
acfm) is available at the charging hood during hot metal charging.    Fumes
captured in the charging hood bypass the quencher and pass directly to the
venturi scrubber.  The design pressure drop of the venturi during furnace
                                            22
charging is 218 cm (56 inches) water column.
     Table 12 lists the BOF/Q-BOP shops that utilize the furnace enclosure
for emission control.
7.2.3  Inspection
     The integrity of the furnace enclosure is important in obtaining good
evacuation within the enclosure.  The inspector should observe and note the
condition of the bi-parting doors to detect any misalignments or warpage
that leads to large gaps between the doors.  The inspector should also check
for gaps between the water-cooled sections of the duct work and inspect the
condition of the pickup hoods within the enclosure and all the associated
ductwork leading to the cleaning unit.
     During scrap charging, the vessel tilt angle should be estimated along
with the effective capture efficiency of charging emissions in the secondary
charging hood.  During hot metal charging the tilt angle and  the  pouring
rate of hot metal play an important part in the effective capture of the
secondary emissions.  The primary hood capture and enclosure  evacuation
should be observed during slopping.  In top-blown furnaces, lanse hole
emissions or fume rollout (puffing) from the primary hood indicate  in-
sufficient draft at the primary hood.  This will increase the load  on the
secondary controls within the enclosure.

                                      99

-------
o
o
                           NO. 1
                           Q-BOP
                      FURNACE CLOSURE
K
MBH







Ic
s 	
s->
1


L,

r«


-t
»-/
.^
)


fr>

*•


)
X
1

1





z
_1
SECONDARY
HOOD NO. 1
SHUTOFF NO. 1
OPEN j^BELL VALVE NO. 1
£4"
CLOSED" —^ 1 ^~
~^" '><' "^ W
QUENCHER wn , r^
90% OPEN N0- ] SCNR(
QUENCHER N0 2 SCR
20% OPEN^ NC
-* Q -*P
OPEN^. ~ If ^
V gj -I
SHUTOFF BELL VALVE NO. 2
CLOSED NO. 2
SECONDARY
HOOD NO. 2
                                                                       D
                                                                      FAN
                                                                     NO. 1
                                                                      FAN
                                                                     NO. 2
                                                                       D
                          NO. 2
                          Q-BOP
                     FURNACE CLOSURE
                                                                                   STACK NO. 1
STACK NO. 2
              Figure  37.   Schematic of Q-BOP  secondary  (charging) emissions control system of
                                         Republic  Steel,  Chicago.

-------
                  TABLE 12.  BOF/Q-BOP SHOPS UTILIZING FURNACE ENCLOSURES'
 Company and location
   Type of enclosure
     Type of gas cleaning
Startup date
Republic Steel Corp.
 Chicago, Illinois
Bethlehem Steel Corp.
 Burns Harbor, Ind.
CF&I Steel Corp.
 Pueblo, Colorado

Kaiser Steel Corp.
 Fontana, California
Granite City Steel Div.
 Granite City, Illinois
Rouge Steel Co.
 Dearborn, Michigan

Sharon Steel Corp.
 Farrell, Pennsylvania
4-sided enclosure with
 mechanized biparting
 charging doors

4-sided enclosure with
 mechanized biparting
 charging doors

3-sided enclosure with-
 out charging doors

4-sided enclosure with
 single mechanized
 charging door

4-sided enclosure with
 single mechanized
 charging door

3-sided enclosure with-
 out charging doors

4-sided enclosure with
 single mechanized
 charging door
High-energy scrubber (420,000
 acfm at 143°F)
High-energy scrubber (350,000
 acfm at 145°F)
Fabric filter (540,000 acfm at
 275°F)

Fabric filter (500,000 acfm at
 600°F)
Electrostatic precipitator
 (900,000 acfm at 550°F)
Electrostatic precipitator
 (1,050,000 acfm at 500°F)

High-energy scrubber (320,000
 acfm at 168°F)
  1976-77



    1977



    1978


    1978



    1980



    1981


    1982
   Source:   Pennsylvania  Engineering  Corporation.

-------
     The inspector should observe and note the  shop  layout,  gas  cleaning
equipment, and multiple-pickup points connected to the  same  gas  cleaning
source and become familiar with the flow-balancing scheme  under  different
operating modes.   This is very important  as each plant  is  unique and  equip-
ment operation varies from plant to plant.
                                      102

-------
                                  SECTION 8
                            SPECIAL APPLICATIONS

     The basic  principles  of ventilation  outlined  in previous sections  are
valid for  all  applications.   This  section  discusses  some  additional  con-
siderations of interest in common control systems in the metallurgical  indus-
tries.  It is assumed that the reader  is  already  generally familiar with  the
processes involved.
                                                           *
8.1  COKE OVEN SHEDS
8.1.1  Description
     The coke oven  shed  for control  of  coke  oven  pushing  emissions is  a
special   kind of  hooding.   Many  variations  in  configuration  are possible
(Figure 38) but all are designed to meet three basic objectives:
     0    To  contain excessive emissions  during the brief  (45-second)  period
          of  a  single  push; cooling and  exhausting of these emissions  take
          place over a longer period.
     0    To  arrest  the upward  travel  of the  plume and to  roll  the  plume
          within the shed; heavier particles fall out to the  ground.
     0    To  contain all of the  emissions  from  the  coke  side  of  the  battery,
          including  door  emissions,  coke  spillage emissions,  and  hot  car
          emissions.
     Shed control  systems  require ducting, fans, and a  control  device,  usu-
ally a fabric filter.  This discussion  is limited to the ventilation  princi-
ples and O&M  considerations associated with the shed itself.
     Figure  39  presents  a general  illustration of the  thermal  expansion of
hot gases from  a  push  that the  shed must  accommodate.   In the  original  shed
designs, a duct ran along the length of the shed, and the exhaust suction was
distributed  along  the  entire length.   These  sheds required  high  flow rates
(300,000 acfm or  more) to  achieve reasonable  face  velocity.   Newer  designs
                                      103

-------
Figure 38.   Various shed configurations.
                  104

-------
                                             1MIN
2MIN
3MIN
o
tn
                  BASE AMBIENT TEMP.
                                         THERMAL EXPANSION
                                            /v
4MIN
                                                         TIME
                             Figure 39.   Thermal  expansion of hot  gases  from  a  push.
                                                                                     23

-------
entail a  partition approach  in  which  dampers  are used  to concentrate  the
suction in  the  segment  of the shed  where  the push is occurring.   In  either
design, an  inherent  design  principle is the  holding  of  it within  the  large
confines of the  shed  until  it can be fully exhausted.  The design  relies on
the theory of fully exhausting a  given push before the next push occurs.
     Because containment  of  the  plume  is  an  important factor,  several  dif-
ferent  shed configurations  have  been  offered  to  maximize  containment.   A
common feature of all designs is  an enlarged upper portion of  the shed,  which
serves as a plenum (see Figure 38).   The containment  volume must be designed
to match the size of the push and pushing rate expected at the  battery.
     A potential  weak point  in  shed  control  is  the  influence of  wind  cur-
rents,  especially at the ends of  the  shed.   Even  in the  absence of  wind
disruption, emissions from  "dirty  pushes," i.e.,  heavy plumes,  have a  tend-
ency to "roll out" from under the shed near the ends.   The only two  solutions
to this problem are
1) to  close the  ends insofar as  possible  to  interrupt wind currents,  and 2)
to extend  the overall shed  structure beyond the ends of  the battery.   Sheds
can  be designed  to  extend  beyond  the battery  toward the  quench  tower  to
capture emissions during travel of the hot  car.
8.1.2  Inspection
      In the inspection of a coke-side shed, the inspector  should consider the
following:
      1.   The integrity of the shed  structure and  any  missing  roof  panels or
          holes in the roof.
     2.   Leakage between the battery top and the shed interface.
     3.   Integrity and cleanliness of the  baffle plates  and heat shields.
     4.   Effect  of cross-drafts  and heavy-particle fallout.
     5.   The time required for the plume to clear under  the shed.
     6.   Efficacy  of capture and  evacuation  of  emissions   resulting  from
          pushes  from the ovens near the ends of the shed.
     7.   The greenness  of the  push;  a shed that  can contain  clean  pushes
          will not necessarily be  able  to  contain the much larger gas volume
          generated during a  dirty push.
                                      106

-------
8.2  ELECTRIC ARC FURNACE VENTILATION
8.2.1  Description
     Canopy hoods  are  widely used to control  secondary  emissions  from elec-
tric arc furnace (EAF) refining.  The advantages of these hoods are that they
do not interface with  the  furnace;  they provide ventilation during charging,
tapping, and  slagging  off; they do not  affect furnace metallurgy;  and their
maintenance costs are  low.   The  disadvantages  are  that they require high air
volume; they  are subject  to cross-flow  air currents that interface with fume
control; and  the plume  can interfere with  crane  operator's line  of vision
during charging and tapping.
     The need for  high air  volumes  can be overcome by  combining  the canopy
with  a partial  enclosure,  as   illustrated  in Figure  40.   The  three-sided
enclosure reduces the  effect of  cross-flow interference and directs the plume
toward the  hood.   As  shown earlier in  Figure  6 and explained  in  the discus-
sion  regarding  coke oven  sheds, another approach  is  to use a baffled hood
that concentrates suction  towards the heaviest area of emissions.
     The ultimate expansion  of this approach is total furnace enclosure which
was previously discussed in  Section 7.
     A complicating factor in  EAF ventilation  is  the control system required
to  combine  fourth-hole evacuation and a  canopy hood on  the same  fan system.
A balanced draft is difficult to achieve, and  it must be established by trial
and  error.    For  example,  the  canopy  hood  is often  dampered  off  when the
furnace cover is in place  so that suction will be concentrated on the fourth-
hole takeoff.  In this configuration, the control system directs total  system
suction to  the  canopy hood  when the  cover is off  for  charging and when the
furnace is tilted for  tapping.   In some  cases, however,  the  charging emission
plume  is  still  rising toward the  hood  while the cover  is  being  quickly re-
placed.  Thus, when the  cover has been replaced and suction is taken off the
canopy  hood,  the rising plume  is not captured.   In such  an arrangement,  it
would  be  desirable either to replace  the  cover  more  slowly or  to build  an
electrical delay into  the  automatic damper  control  system.
                                       107

-------
                       SLAGGING HOOO-


                             5LAG POT"
Figure  40.   Electric arc furnace utilizing  partial  enclosure,

Source:  U.S.  Environmental  Protection Agency, Office of Air
         Quality  Planning  and Standards, Research Triangle
         Park,  North  Carolina  27711
                              108

-------
     Figure 41 shows the  basic  types  of ventilation systems  used on electric
arc furnaces.  Figure 42  illustrates  a  popular  approach  in which the fourth-
hole direct  evacuation is  combined with  a canopy hood.   In some  cases,  a
third stage  of  capture  is included by  closing  off the roof  monitors  in  the
area of the  furnace  and connecting a take-off  duct to the roof.   This third
stage captures smoke that has escaped the canopy.
     In the combined direct evacuation canopy system, baghouse temperature is
controlled by mixing the  cool  gas from the canopy with the  hot  gas from  the
furnace.  A  cool-air  emergency inlet damper is  usually  located  prior  to  the
baghouse.  If this damper remains open, it will  cause a  ventilation "short-
circuit" and rob the hood of suction.
     As shown in Figure 43, two or more furnaces are  typically combined on a
system,  which can  produce complex flow  balancing  requirements.   Table  13
presents  an  example  of  the  ideal  flow  balance on  a   two-furnace  system.
Actually, flows  through various  duct  sections  must be monitored  to confirm
their desirability.  All  elements of the system must be  kept in good  condi-
tion to maintain the  ideal  balance.  Misalignment of the gap in the DSE duct
(see Figure  43) will result  in the  indraft of more combustion  air at this
point  and lower  suction  elsewhere.   Figure  44  summarizes  total  flow rate
requirements  for  various EAF  control   approaches  and  indicates  the  rapid
increase  in  flow requirements  with the move from direct evacuation to build-
ing  evacuation.   These data  are  based on averages  of  various  systems  and
should be used only as a  general  indicator  of reasonable flow requirements.
     Compromises were made  in  most plants  where hoods had to be  retrofitted.
The furnace and bay configuration,  clearance for  canopy hoods above the crane
gantry level, and ductwork layout  became important factors because  they could
mitigate  the  efficiency of the  canopy  hood.   Failure to consider  activities
that increase  the  fume generation  rate, such  as  oxygen  blowing and oxyfuel
burners,  during  the  initial design of  the hoods can  cause  the system to be
overloaded and capture efficiency  to  be reduced.
8.2.2  Inspection
     The  inspector should consider  the  following when  inspecting  EAF's:
                                       109

-------
           FOURTH HOLE
  SIDE DRAFT
         COMBINATION HOOD
CANOPY HOOD
Figure  41.   Ventilation systems for electric arc furnaces.

-------
                                 CLEANED GAS LOUVERS
       t
   CANOPY HOOD
    DIRECT SHELL EVACUATION
    ROOF TAP (WATER COOLED)
                             FAN
             L
               COMBUSTION AIR GAP
            V
                                         BAGHOUSE
\7\7\7
            COLLECTED
              DUST
Figure  42.  Combined direct shell evacuation with canopy hood.
                            in

-------
       POLLUTION CONTROL SYSTEM
                                       CANOPY
                                       HOOD
                                     SLAG POT
                                     HOOD
Figure 43.  Multiple pickup points vented to common control device.
                       112

-------
TABLE 13.  EXAMPLE OF FLOW BALANCING OF MULTIPLE EVACUATION
                SYSTEM ON ELECTRIC ARC FURNACE
Item
Furnace 1 charging
Furnace 1 slagging hood leakage
Furnace 1 tapping hood leakage
Furnace 1 direct shell leakage
Furnace 2 oxygen lancing
Furance 2 slagging (simultaneous with
oxygen blowing)
Furnace 2 canopy leakage
Furnace 2 tapping hood leakage
Total system capacity
Air flow, cfm
800,000
12,000
18,000
25,000
265,000
118,000
44,000
18,000
1,000,000
                            113

-------
1200
            100      200      300       400       500      600
                 H = SUM OF HEAT SIZES  IN SHOP, tons
700
   Figure 44.  Flow rate required for electric arc  furnace  control.

-------
     1.    The integrity of the canopy hoods, the side-draft hood,  and  all  the
          duct work leading to the cleaning unit.   In the case of  an enclosed
          or sealed roof,  any large holes or missing panels  will  reduce  the
          capture efficiency.
     2.    Additional thermal  currents  produced  by ancillary  operations  such
          as overflow of slag and/or metal on dumping ladles should be noted.
          These operations increase the load on  the evacuation system.
     3.    Furnaces  and  bay layout have an  important bearing on  the  capture
          efficiency of the hoods.
     4.    Multiple-furnace  operations, additional   pickup  points, and  the
          overall flow  balance  under different  modes of operation should  be
          observed.
     5.    Crosswinds inside the  shop can severely disrupt  the  capture  effi-
          ciency of the hoods.

8.3  BLAST FURNACE CASTHOUSE CONTROL
8.3.1  Description
                                            24
     Although  recently  developed technology    does  not use  ventilation  for
control   of casting  emissions,  numerous  ventilation-based  systems  are  in-
stalled  or  planned on  blast  furnace casthouses.   Sources  of  fugitive  emis-
sions in the casthouse  are  the tap  hole,  trough,  skimmer,  runners, hot metal
spouts,  and  slag spouts.   These  various  sources  require  a  multiple  hooding
system or total  building  evacuation.   Local  control  is  favored because total
flow  requirements  are  less;  however,  the  design of  many  older casthouses
precludes their use.  Table 14 lists the typical flow volume requirements for
a large blast furnace casthouse system.
     These  systems require flow  balancing,  proper design,  and the  other
factors  discussed  earlier.   Also,  the frequent  removal  and  replacement  of
close-fitting  hoods or  runner  covers  invite  both  damage  and misplacement.
Because  of  the  proximity of the  hooding  to  the molten  metal, frequent main-
tenance of the refractory  linings and  runner covers  is required.  Large blast
furnaces with  multiple  tapholes  and casthouses require  a  carefully  designed
flow  balancing  and damper system  for switching   from  one casthouse  to the
other.  Such systems have been designed for full evacuation of one taphole at
a time.   If damper  settings are such that two tapholes are  evacuated simulta-
neously, capture efficiency will  be curtailed.
                                      115

-------
TABLE 14.   BLAST FURNACE CASTHOUSE TYPICAL VOLUME REQUIREMENTS
Location
Taphole
Skimmer
Iron runner
Hot metal spouts
Slag spouts
Total
Volume
requirements ,
cfm
70,000
35,000
70,000
75,000
50,000
300,000
Volume
requirements ,
m3/min
1978
989
1978
2119
1413
8477
                             116

-------
8.3.2  Inspection

     When  inspecting  blast furnace  casthouse systems, the  inspector should
consider the following:

     1.   The performance  of  the taphole  hood  during various stages  of the
          tap (i.e.,  immediately after  taphole  opening,  during  heavy metal
          flow, and during slag and metal flow).  The  capture  efficiency of
          the hoods  (covers)  at the  trough,  skimmer, runners, and  slag and
          metal spouts  also  should  be observed during  various stages  of the
          cast  and  under  different  conditions,  such as  high and  low metal
          temperature and  high and low slag basicity.

     2.   When  there  are multiple casthouses,  the flow balance  between the
          casthouses should be observed.  The flow is sometimes equally split
          between  the  casthouses,  which  significantly  reduces   the  capture
          efficiency.

     3.   The furnace  layout, casthouse  layout, and ductwork location have an
          important bearing on the efficiency of the evacuation system.

     4.   Cross-currents inside  the  casthouse mitigate  the  hood  capture.  It
          is  common  practice  to remove  and  replace  the siding in  the cast-
          house,  depending on  the  season.  A  system  designed for  a  closed
          structure is  not likely  to perform adequately if  the  structure is
          opened.


8.4  CONTROL SYSTEMS ON BASIC OXYGEN  FURNACES (BOF's)

8.4.1  Description

     Primary capture  systems  on BOF's use a  specially designed hood over the

mouth of the  furnace.   This usually  operates  effectively  when the furnace is

in  an  upright  position;  however,  when  the  furnace  is tilted  for charging,

tapping, or testing,  emissions  generally escape  the  hood  (for  the  reasons

discussed earlier).  Capture of  these secondary emissions requires additional

hooding or  enclosures.  The total  enclosure  of  BOF  was previously discussed

in Section  7.
     Water-cooled primary  hoods are  sometimes used to generate steam  because

the gas temperatures  in the hood are initially over 3000°F.  These  hoods are

exposed to  the  most  severe operating conditions  of  all the process  applica-

tions discussed—fluctuating  high  temperatures  and the possibility of physi-

cal damage  from cranes or ejections  of  material  from the furnace.  The  hood

may be elevated several  feet above the  furnace to  allow indraft of  combustion

air  (open), or they  may be closely  mated with the furnace  to  conserve the

                                      117

-------
carbon monoxide inherent in the exhaust gas  (closed).   Figure  45 illustrates
these BOF hood arrangements.
     Many  different  hood  constructions  have  been tried  to  cope  with  the
severe  operating  conditions.   The  membrane  or  "tube-bar"  type is  usually
favored today.  Table  15 presents the  performance  characteristics  of various
hood constructions.  Table 16 lists the various hood types  that  are used for
full combustion and  limited combustion systems in  the  United States, Canada,
           25
and Mexico.
     Control of secondary emissions  is achieved by local hoods  or enclosures.
Local  hoods  are  generally ineffective because  they  are  too  far  from  the
source, are too small  to encompass  the emissions,  and  because  the  evacuation
rate is usually insufficient.  Figure  46  illustrates a  simple  external  hood-
ing arrangement for charging emissions.
     Figure 47 illustrates the Gaw damper approach, which enables the primary
hood  to function   as  a secondary hood for  charging emissions.  The movable
damper  increases hood suction by restricting the  hood  face area.   Maintenance
of  the  damper is  high because of the  harsh environment.  As  in the case of
the local hood discussed previously, effective use of  the Gaw damper requires
a slow  pouring  rate  of charged metal  to  decrease  fume  generation and a mini-
mum tilt angle of the vessel to generally direct  the fumes toward the hood.
8.4.2   Inspection
     When  inspecting  BOF  ventilation systems, the  inspector should consider
the following:

     1.   Primary  hood capture efficiency during operations such as slopping.
     2.   The  tilt  angle  and  hot metal pour  rate  during hot metal  charging,
          which greatly affects the capture efficiency.
     3.   The performance  and capture of secondary controls.
     4.   Emissions  from  the  lance  hole  or fume  rollout  (puffing) from  the
          primary  hood, which indicate insufficient draft on the hood.
     5.    In  closed hood  systems,  the  snug fit  of  the  hood  skirt  at  the
          furnace.   (Indraft of  air above  the design  level will overload  the
          fan  and  cause  the variable-throat  scrubber  to open, which reduces
          pressure drop.)
                                      118

-------
              RELIEF OOOft
                                                                    RELIEF DOOM
                      — GAS COOLER
WATER-COOLED FLANGES

           SANO SEAL



      MOVEABLE SKIRT
                                     REMOVABLE HOOD
                                       FIXED HOOD
                                                                            — GAS COOLER
                                                                                   LANCE
                                                          WATER-COOLED FLANGES *

                                                                     SANO SEAL
                                                                                            REMOVABLE HOOD
                                                                                              FIXED HOOD


                                                                                             NO SKffTT HERE
                            VESSEL
                            CLOSED
                                                                                 VESSEL
                                                                                  OPEN
                         Figure  45.     BOF hood arrangements.

Courtesy:   BOF Steelmaking,  Volume III.  Published  by  American Institute of  Mining, Metallurgical
            and Petroleum Engineers.

-------
TABLE 15.    PERFORMANCE CHARACTERISTICS OF DIFFERENT BOF HOOD CONSTRUCTIONS
                                                                            25

Initial cost
Ability to take
high tempera-
ture
Ability to take
temperature
change
Resistance to
slag buildup
Resistance to
scaling
Maintenance Cost
Refractory-
lined
Lowest
Poor
Poor

Poor

--
Very high
Water-
cooled
plate
panels
Low
Fair
Fair

Good

Poor
High
Formed
panels
Moderate
Good
Good

Good

Fair
Fair
Double
pass
High
Very good
Very good

Very good

Good
Low
Water wall
boiler
High
Very good
Very good

Fai r

Good
Fair
Membrane
High
Very good
Very good

Good

Good
Fair
             TABLE 16.    BOF HOOD CONSTRUCTION  DESIGNS  IN  USE
                 IN THE UNITED STATES,  CANADA,  AND  MEXICO25

Construction
Tube
Panel/jacket
Membrane
Not known
Total
Full combustion
Number
10
41
30
4
85
Percent
12
48
35
5
100
Limited combustion
Number
3
4
13
0
20
Percent
15
20
65
0
100
Total
Number
13
45
43
4
105
Percent
12
43
41
4
100
                                     120

-------
                   FURNACE
 CHARGING AISLE


--CRANE GIRDER


  CANOPY  HOOD
                                        CHARGING
                                        LADLE
Figure  46.    Canopy hood concept for BOF charging emissions,
                          121

-------
          CLOSURE  PLATE CONCEPT
                 FURNACE
CHARGING AISLE
                                  CRANE
                                  GIRDER
                                   CHARGING
                                   LADLE
Figure 47.   Gaw damper (closure plate) use in BOF control.
                      122

-------
8.5  BUILDING EVACUATION

     The use of total building evacuation to control air pollution contamina-

tion or  to  improve  the work  area  environment is  normally  a difficult  and
costly approach.

     The problem areas are:

     1.   Achieving the necessary number of air changes per hour  (20 or more,
          depending on the contaminants).

     2.   The ability  to  reach the specific work  areas to supply  these  air
          changes.   (Some  areas have  dead  air  pockets,  and either ducting or
          forced ventilation has to be provided.)

     3.   The volume  of air required.  (A building 800 ft long,  80 ft wide,
          and 40 ft  high has a volume of  2,560,000  ft3.   With  20  air changes
          per hour,  :850,000 scfm of  air is  required.   If contaminants, open
          doorways,  heat emissions, and  air  currents caused by thermal  proc-
          esses  or vehicle movement  are  added,  the  actual  requirement  fog
          effective  ventilation  of such  a building would  be  3  to 4  x  10
          scfm.)

     4.   The existing  building  structure not  being  designed for  total  en-
          closure.   (The  weight  of siding,  ducting,  and  wind loads  may  re-
          quire  strengthening  of the  building  columns and roof  trusses  and
          the addition of more purlins, struts, and bracing.)

     5.   The location  of process equipment and  the  flow patterns  of mate-
          rials  not  being conducive  to  the proper collection of emissions.
          (Lighting may also be a problem.)

     6.   Need  for redundancy  of the  fans.  (Clean-out mechanisms should be
          built  into  the  ducting  that are readily accessible  and repairable.
          Ducting  is long  and huge.)

     A newly designed building in which process equipment  is located specifi-

cally for total building evacuation can greatly reduce  these problems.

     A variation  of  building evacuation that  does  not involve local hooding
                                                                             ?
and ventilation systems is the roof-mounted electrostatic  precipitator  (REP).

This system  has not  yet been  applied in the United States, but  it has  been
                            ?fi
successfully  used  in Japan.     The   technique  involves roof  modification  to

help channel  the natural  plume  rise  of BOF fugitive  emissions  into an  REP,

which  collects  the process fugitive  emissions.  The  system  has  no fan,  and
                                                          pc
the plates are  generally cleaned by use of a water  spray.    The  REP  specifi-

cation provided by Sumitomo Heavy Industries for controlling  two  BOF's,  each
                                                                   ?fi
with 300-ton capacity,  offers a design efficiency of 91.5  percent.


                                       123

-------
8.6  COPPER CONVERTERS
8.6.1  Description
     Capture of emissions  from Peirce-Smith type copper  converters  presents
some unique  problems.  The  converter  is  essentially  a  horizontal  cylinder
with a circular opening on  top.   This  cylinder is rotated around  its  longi-
tudinal axis so the  opening can face toward the  ladle.   This  rotation  makes
it  impossible  to  achieve  an absolutely tight  seal  between the hood and  the
converter.  Also,  when the converter is rotated for  charging  and tapping,  the
opening is no  longer  under  the hood, and fumes tend to escape  into  the con-
verter building.  The  heat  and collisions with the ladle  suspended  from  the
crane  tend to  cause  the  hood to warp, and  eventually  it  does  not fit  well.
Figure 48 shows a  converter and the primary hood.
     At copper  plants,  the emissions  from  all  converters (usually  three  to
five units)  are  ducted together to  a  common particulate  control  device  and
sometimes  to a sulfuric  acid  plant.   Dampers in  the individual  breeching
control the  draft on  any  single  converter.   These  dampers   require  routine
maintenance to ensure proper functioning.
     Primary converter hoods have sliding gates on the  front  side as  shown in
Figure 48.   These gates  are  really movable hood extensions  that  serve  to
cover  the converter opening and improve capture efficiency.
     Some smelters have installed  secondary  hoods (Figure 49)  or air curtain
systems to capture fumes when rotation causes the converter opening not to be
unde'~  the main hood.   By providing a strong blast of air to blow fumes  into a
suction hood, the air curtain provides an open area  for locating the charging
and tapping  ladle and the crane  hooks  and cables.   Secondary hoods suspended
above  the converter opening and ladle have the same  weaknesses found in other
processes.   For example,  because  of their  distance  above the  converter  and
ladle, they  are  affected  by  thermal  and cross-drafts  and are  not effective
unless face velocities of the hood are high.
                                      124

-------
             (END VIEW)
en
(SIDE VIEW)
                       (1) SHELL; (2) HOOD; (3) AIR BAFFLE; (4) CONVERTER MOUTH; (5) ROLLERS;
                       (6) TURNING RINGS; (7) AIR - SUPPLY DUCT;

                       Reprinted from the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd edition,
                       Fig. 9, Page 836.  Copyright©  John Wiley & Sons, Inc.  1979.
                                     Figure 48.   Peirce-Smith  converter.

-------
                                  TO SECONDARY
                                     HOODING
                                    MAIN  DUCT
Figure  49.    Secondary converter hood configuration.
                            126

-------
8.6.2  Inspection
     Converter  hoods  are  inspected  by making  a  visual  assessment  of  their
physical condition and the emissions that escape during the various converter
cycles.  The hood and  duct system should not contain any openings that allow
air to  be  drawn in and  reduce the  suction  at  the converter.  The  hood  lip
should come  within  about  6  inches of the converter  opening  during  blowing.
The hood gate  or slide should be  extended when the converter is  in  the  up-
right  position  to  ensure  that  the  converter  opening  is covered.   During
converter  rollout,  the draft  should be  reduced  so that a high-suction  air
flow   can    be   maintained   on    the   converters   in   the   blowing   mode.
                                       127

-------
                                 REFERENCES


 1.   American  Conference of Governmental  Industrial  Hygienists.   Industrial
     Ventilation.   16th  Ed.  1980.

 2.   Hemeon,  w.  C.  L.   Plant and Process Ventilation.  The  Industrial  Press,
     New  York.   1963.

 3.   Department  of  Health,  Education and Welfare.  Air Pollution  Engineering
     Manual.   J. A. Danielson  (Ed.) Public  Health  Service Publication  999-
     AP-40,  1967-

 4.   Buffalo  Forge  Company.   Fan Engineering.  8th  Ed.   Buffalo, New  York.
     1983.

 5.   Jablin,  R. , and D. W.  Coy.   Engineering Study of Roof-Mounted  Electro-
     static  Precipitator for  Fugitive  Emission Control  on  Two Basic  Oxygen
     Furnaces  of 300-ton capacity.   In:   Proceedings  of Symposium  on  Iron and
     Steel   Pollution   Abatement   Technology   for   1981.    EPA  600/9-82-021,
     December,  1982.   pp.  120-138.

 6.   Coy, D.  W.,  and  L.  E. Sparks.   Roof-Mounted  Electrostatic  Precipita-
     tors -  Visible Emissions  Evaluation and  Computer Modeling  Performance
     Predictions.   Presented at the 1983 Symposium on  Iron  &  Steel  Pollution
     Abatement Technology.

 7.   Vajda,  S.   Blast  Furnace Casthouse  Emission Control  Without  Evacuation.
     In:   Proceedings  of   Symposium on  Iron and Steel   Pollution  Abatement
     Technology.   EPA  600/9-83-016, November  1982.   pp. 232-240.

 3.   Dixon,  T. E., and  H.  Nomine.   Capital   and Operating  Costs of OBM/Q-BOP
     Gas  Cleaning Systems.   Iron  and Steel  Engineer,  March 1978.  p.  37.

 9.   U.S. Department  of Health  Education and  Welfare.   Air  Pollution Engi-
     neering Manual.   J. A. Danielson  (Ed.).   Public  Health Service  Publica-
     tion 999-AP-40,  1967.   Chapter 3.

lO.   Dalla Valle,  J.  M.   Exhaust  Hoods.   The  Industrial  Press, New York.
     1946.

11.   Kriechelt,  T.  E.  et  al.   Natural  Ventilation in  Hot Process Buildings.
     Iron and  Steel Engineer,  December  1976.

12.   Hemeon,  W.  C.  L.    Plant and Process Ventilation.  The Industrial Press,
     New  York.   1955.
                                     128

-------
13.  Davis, J. A.  Unidirectional  Flow  Ventilation  System.   Presented at the
     140th Annual AIME Meeting, New York, February 18, 1975.

14.  American Conference  of Governmental  Industrial  Hygienists.   Industrial
     Ventilation, A Manual of Recommended Practice.   17th Ed.  1982.

15.  U.S. Environmental Protection Agency.  Air Pollution Engineering Manual.
     2nd Ed.  AP40, May 1973.

16.  Pollak, R.   Selecting  Fans and Blowers.   Chemical  Engineering, January
     22, 1973.

17.  Fan Engineering.  8th Ed.  Published by Buffalo Forge Company, New York.
     1983.

18.  Nicola,  A.  G.   Best  Available Control  Technology (BACT)  for Electric
     Furnace  Shop   Emission   Control.    36th  Electric  Furnace  Conference
     Proceedings,  Vol.  36,  Toronto December  1978,  Sponsored by  The Electric
     Furnace  Division  of  I&S  Society  of   American   Institute  of  Mining,
     Metallurgical and Petroleum Engineers.

19.  Brand, P. G.  A.  Current  Trends  in Electric  Furnace  Emission Control.
     Iron and Steel Engineer, February  1981.  p. 59.

20.  Henninger, J. L. et. al.  Closing  In On Arc Furnace Emissions at Carpenter
     Technology.    Iron & Steel Engineer.  March 1984.

21.  Canefield,  G.  Jr. Pollution  Control Using  a  Furnace  Enclosure.   36th
     Electric Furnace Conference Proceedings, Vol. 36, Toronto December 1978,
     Sponsored by  The Electric  Furnace Division  of I&S Society  of American
     Institute of Mining, Metallurgical and Petroleum Engineers.

22.  U.S.  Environmental  Protection  Agency.    Revised  Standards  for  Basic
     Oxygen Process Furnaces - Background Information for Proposed Standards.
     Preliminary Draft.  1980.

23.  Roe, et al.   United States Patent  No. 3,844,901.  October 29, 1974.

24.  Vajda, S.   Blast Furnace  Casthouse Emission  Control  Without Evacuation.
     Iron and Steel Engineer, June  1983.  p.  29.

25.  American  Institute of  Mining, Metallurgical  and  Petroleum Engineers.
     BOF Steelmaking.  Vol. III.  345 E. 47th Street, New York.

26.  Jablin,  R.,  and D.  W. Coy.   Engineering Study of Roof-Mounted Electro-
     static  Precipitator  (REP)  for Fugitive  Emission  Control on  Two Basic
     Oxygen Furnaces  of 300-ton Capacity.  In:   Proceedings  of  Symposium on
     Iron and  Steel  Pollution Abatement  Technology  for 1981.  EPA 600/9-82-
     021, December 1982.  pp.  120-138.

27.  U.S. Environmental  Protection Agency.   Control of Copper Smelter Fugi-
     tive Emissions.  EPA-600/2-80-079, May 1980.


                                      129

-------
                                 APPENDIX A

                                BIBLIOGRAPHY

Adams, R.  W.   1976.   Waste Gas Handling.   In:   BOF Steelmaking,  Volume  3,
Design.  Iron and Steel Society of AIME.

American Iron and Steel Institute.  1965.  Steel Mill Ventilation.

Ban, E.  1980.  Innovations and Improvements in the Ore Sintering Process for
Air Pollution  Control.   In:  Proceedings of the  First  Symposium on Iron and
Steel  Pollution Abatement  Technology,  Chicago,  Illinois,  October 30-November
1, 1979.  EPA-600/9-80-012.

Baturin, V. V.  1972.   Fundamentals  of Industrial  Ventilation.   3rd Edition,
Pergamon Press.

Bender,  M.   1979.   Fume  Hoods,  Open  Canopy Type-Their  Ability  to  Capture
Pollutants in  Various  Environments.  American  Industrial  Hygiene Association
Journal,  pp 119-127.

Bender, M., and W.  D.  Baines.  1976.  Operation of  an  Open Canopy Fume Hood
in a Crossflow.  ASME Ser., 97(2):242-243.

Blast Furnace Cast House Emission Control Technology Development in the USSR.
Translated by SCITRAN for U.S. Environmental Protection Agency.

Blessing, K. E.   1963.  Electric  Furnace Fume  Control.   Chemical Engineering
Progress.  59:60-64.                 ^ .

Brand, P. G. A.   1981.  Current  Trends in Electric Furnace Emission Control.
Iron and Steel Engineer, 58:59.

Brough, J. R.  1964.   Air  Pollution  Control  of An Electric Furnace Steelmak-
ing Shop.  Journal of the Air Pollution Control Assn.   22:170.

Brown, C. M.   1980.  Control  of  Secondary Emissions from Basic  Oxygen  Steel-
making Furnaces.   Iron and  Steel Engineer.  57:39.

Buffalo Forge Co.   1970.  Fan Engineering.

Burroughs, J. D.  et al.  1976.  Application of Enclosed Coke  Pushing Emission
Controls at Granite  City  Steel.   In:   Proceedings  of 69th Annual Meeting  of
Air Pollution  Control  Association,  Portland,  Oregon,  June  27-July 1,  1976.
Calderon, A.   1977.   Controlling  Emissions from  Coke  Ovens.   Iron and  Steel
Engineer, 54(8):42.


                                     A-l

-------
Campbell,  W.  W.   1962.    Development  of  an  Electric  Furnace  Dust-Control
System.  Journal of the Air Pollution Control Assn.  12:576.

Canfield, G., Jr.   1978.   Pollution Control Using a  Furnace  Enclosure.   In:
Proceedings of  the  Electric  Arc Furnace Conference, Vol.  36.   Toronto Meet-
ing.  December 5-8, 1978.

Cheever, C. L., et al.  1972.  Proceedings (two volumes) of 12th Air Cleaning
Conference, Oak Ridge, Tennessee.

Cheremisinoff,  P. N.  and  N.  P.   1976,   Calculating Air  Flow Requirements for
Fume Exhaust Hoods.  Plant Engineering, 30(4):111-114.

Cheremisinoff,  P.  N.  and  N.  P.   1976.  Calculating Air  Volume Requirements
for  Fume  Exhaust Hoods--Nonenclosure  Types.   Plant Engineering,  30(6):143-
144.

Clarke,  J.  H.   Practical Industrial  Ventilation Design.   A  collection  of
article reprints, Heating, Piping, and Air Conditioning  Journal.

Coleman,  R.  T., Jr.,  and R. Vandervort.   1980.   Demonstration  of Fugitive
Emission  Controls  at  a  Secondary Lead Smelter.   In:   Proceedings  of World
Symposium of Metallurgy and Environmental  Control, Las Vegas, February 24-28,
1980.

Conners, A.  1980.  Developments in Coke-Oven Emission Control.  Iron & Steel
Engineer, 57(6):33.

Coy, D.  W.,  and R. Jablin.   1980.   Review of Foreign  Air Pollution Control
Technology for  BOF  Fugitive  Emissions.  In:   Proceedings  of the First Sympo-
sium on Iron and  Steel   Pollution  Abatement Technology,  Chicago,  Illinois,
October 30-November 1, 1979.  EPA-600/9-80-012.

Current,  P.   1980.   Sinter  Plant Windbox  Gas  Recirculation and  Gravel Bed
Filtration  Demonstration.   In:   Proceedings of  the First  Symposium on Iron
arid  Steel  Pollution  Abatement  Technology,  Chicago,  Illinois,  October 30-
November 1, 1979.  EPA-600/9-80-012.

Drivas,  P.  J.,  et  al.   1972.  Experimental Characterization  of Ventilation
Systems in Buildings.  Environmental Science Technology. 6(7):609-614.

Eisenbarth, M.  J.  1981.   Fume Extraction Hoods in the  Iron & Steel  Industry.
In:  A Specialty Conference on  Air  Pollution  Control   in  the  Iron  and  Steel
Industry, April 21-23, 1981.

Emswiler,  J.  E.  1926.   Neutral  Zone in  Ventilation.   ASHRAE Transactions,
Vol. 32.

Escudier,  and   J.  Maxworthy.   1973.   On  the  Motion of  Turbulent Thermals.
Fluid Mechanics, V. 61 -  Pt.  3.  pp 541-552.
                                     A-2

-------
Field, A.  A.   1977.  New  Concepts  in Industrial Air  Replacement.   Heating,
Piping, and Air Conditioning, 49(3):84, 86, 88, 90.

Fields,  S.  F.,  et  al.    1982.   Modeling  of  Hood Control  of Blast  Furnace
Casting  Emissions.    In:   Proceedings of  the  Symposium  on  Iron  and  Steel
Pollution  Abatement Technology  for  1981,  Chicago,  Illinois,  10/6-10/8/81.
EPA-600/9-82-021.

Flannigan, L.  J., et  al.   1974.   Development of  Design Criteria for  Exhaust
Systems  for  Open  Surface Tanks.   Prepared  for NIOSH,  Cincinnati,  Ohio.
NIOSH-75/108.

Flux,  J.  H.   1974.    Containment  of Melting Shop Roof  Emissions in  Electric
Arc  Furnace  Practice.   Ironmaking  and Steelmaking  (Quarterly).   No.  3,  pp
121-133.

Forestier,  G., and  X.  Tinchant.   1981.   Cooling of  Oxygen  Converter Gas,
Efficiency of  the Exhaust Hood,  and  the  Stack of the  Gas  collection Equip-
ment.  Tech. Rev. Metal!., 78(12):937-948.

Franza,  M.   E.   1982.   Controlling  Fugitive  VOC Emissions  From  the  Metal
Finishing Industry.  Met.  Finish, 80(12):39-45.

Fuller, H.   1981.   The Alliance/Mitsubishi Pushing Emission Control System at
Ironton Coke Corp.  Iron and Steel Engineer, 58(5):29.

Goldman,  J.   Technical  Support   Document  for Control   of  Coke Oven  Pushing
Emissions.  Research Triangle Institute.   EPA Contract 68-01-4141,  Task 33.

Goodfellow,  H. D.   1978.   Fume  System Design  for  Sidbec's  Pellet  Melting
Furnaces.  In:   Proceedings  of  the Electric Arc Furnace Conference,  Vol. 36.
Toronto Meeting, December  5-8, 1978.

Great  Lakes Carbon  Shuns Naysayers, Uses Hood to  Collect Smoke from St. Louis
Coke Battery.  33 Magazine.

Haddrill, D. M.  1979.  Control of Welding Fumes  in Fabrication Shops.  Metal
Construction and British Welding  J.,  ll(2):84-89.

Hanks,  D.  J.  1979.  M/E  Update:  Fans  and  Blowers.   Specif.  Eng.,  41(1):
129-134.

Hartung,  Kuhn and  Co.   Pushing  Emission Control  System;  Minister  Stein.
Dusseldorf, West Germany.

Hayashi, T., et  al.  1976.  Land Based, Mobile Haroley "Trar-L-Vent" Exhaust
System  for Coke-Side Pushing  Emission Control.  Hawley  Manufacturing  Corp.
Indianapolis,  Indiana.   On the  Elimination of Welding  Fumes by Richard  Hodd.
Trans. Japan Weld.  Soc., 7(1):18-26.
                                     A-3

-------
Helfritch, D.   1978.   Arc  Furnace  Fume Control  by an  Electrostatic Fabric
Filter.   In:   Proceedings  of the Electric  Arc Furnace  Conference,  Vol. 36.
Toronto Meeting.  December 5-8, 1978.

Hemeon, W. C. L.  1963.  Plant and Process Ventilation, The Industrial Press,
New York, New York, 2nd Edition.

Hoult, D.  P.   1972.   Turbulent Plume  in  a  Laminar  Cross  Flow.   Atmospheric
Environment, Vol. 6, pp 513-531.

Iron and Steel Engineer.  1978.  55(3):83.   Hooded Quench Car System Controls
Coke Pushing Emissions.

Iron and  Steel  Engineer.   1980.  American Air  Filter.   Local  Capture System
Controls.  Coke Pushing Emissions.  57:69.

Irvine, H. B.  1980.  Waste Heat Recovery From a Dust Collection System.  In:
Proceedings of 38th Electrical Furnace Conference, Pittsburgh, December  9-12,
1980.

Jacobs,  C.  0.   1979.    Exhaust  System for  Electric  Arc  Welding  Instruction.
Presented at the Winter Meeting of ASAE, New Orleans, December 11-14, 1979.

Kaercher,  L.  T.   1974.  Air  Pollution  Control  for  an  Electric  Furnace Melt
Shop.  Iron and Steel  Engineer Year Book,   pp 216.

Karnaukh, N. N., et al.  1973.  Trapping of Gases From Ingot Molds in Pouring
of Steel With Exothermic Mixtures.  Metallugist (USSR), 17(3-4):189-190.

Kosarev,  L.  V.,  et al.  1978.  Complex Systems  of Technological  Ventilation
Apparatus  for  Collecting  and  Purifying Gases  in Arc  Furnaces.   Metallurg.,
21(5-6):26-29.

Kreichelt,  T.  W.,  and  T.   G.  Keller.  1972.   Roof Monitor  Emissions;  Test
Methodology.  Journal  APCA, Vol. 22, No. 8.

Kreichelt, T. E., G. R. Kern, and F. G. Higgins, Jr.  1976.  Natural Ventila-
tion  in  Hot  Process Buildings  in the Steel  Industry.   Iron  and  Steel   Engi-
neer.

Krueger,  D.   1964.  Gas Cleaning  in Iron  and Steel Works.   Blast Furnace and
Steel  Plant.  52:503.

Lawrie,  W. G.   1970.   Dust  Collection in  Industry.  Filtr. Separ.,  7(6)'695-
699.

Lusty,  V.   1980.   Collecting  Emissions  From  Electric  Induction   Furnaces.
Foundry Trade Journal,  148(3185):550, 553, 558, 562.

Malchaire, J. B.  1981.  Design of  Industrial Exhaust Systems Using   Program-
mable  Calculator.  Annuals Occup. Hyg., 24(2):217-224.
                                     A-4

-------
Marchisio,  I.  C.   1981.   Fiat/Teksid  Goes  "Snuff Box."   Iron and Steelmaker.
8(6):36+.

Marchland,  D.   1976.  Possible  Improvements  to Dust Collection  in Electric
Steelplants, etc.   Ironmaking and Steelmaking.  No. 4, pp 221-229.

Marchland,  D.   1981.  Waste  Gas Collection  on Electric Arc  Furnaces:   BFI
Research  & Development  During  the Last  20  Years.   In:   A  Speciality  Con-
ference on Air Pollution Control in the Iron and Steel Industry, April 21-23,
1981.

Martin J.  R.,  A.  D. Robertson,  and A. T.  Sheridan.   1974.   Modeling Studies
of  Roof   Extraction Systems  for Arc  Furnace  Melting  Shops.   Presented  at
Conference:  Quality of  the  Environment  and the  Iron  and  Steel  Industry.
Luxembourg, September 24-26, 1974.

Masany, T. J.  1982.  Blast Furnace Casthouse Control  Technology - Fall  1982
Update.   In:   Proceedings  of  the Symposium  on  Iron  and   Steel  Pollution
Abatement Technology  for 1981,  Chicago, Illinois,  10/6-10/8/81.  EPA-600/9-
82-021.

McCluskey, E. J.   1976.  Design  Engineering of  the  OH Gas Cleaning System at
Inland's  No. 2 BOF Shop.   Iron and Steel Engineer, 53(12):53.

McCrillis,  R.  C.    1978.    Basic  Iron  Blast  Furnace Casthouse  Emissions and
Emission   control.   Paper  presented  at the  71st annual  meeting of  the Air
Pollution Control  Association at Houston, June 25-30, 1978.

McDermoth,  H.  J.    1976.   Handbook of  Ventilation for  Contaminant Control.
Ann Arbor Science Publishers, Ann Arbor, Michigan.

Mertz, J. W. and  R.  R. Pfahler.   1975.  How to Troubleshoot Large Industrial
Fans.  Hydrocarbon  Process, 54(6):57-62.

Molnar,  J.   1978.   Graphical  Method  for Determining  Air   Requirements  of
Exhaust Hoods.   Plant Engineering, 32(4):132-133.

Mortimer, V. D., Jr., et al.   1982.   In-Depth Survey Report  of Valley Chrome
Platers.   Bay  City, Michigan, April  27-May  1,  1981.  Prepared  for National
Institute for Occupational Safety and Health, Cincinnati, Ohio.

Muermann, H.   1978.  Ventilation and  Air  Conditioning of Modern Industrial
Buildings.  Wasser, Luft Und Betrieb, 22(4):126-128.

Natalizio, A., and  C. Twiffe-Molecey.   Ventilation of Mill   Buildings  - New
Directions.  Iron and Steel Engineer.   57(7):51-56.

Nelson, F. D., et  al.   1976.   Plant Layout and  Material  Handling.   In:   BOF
Steelmaking, Volume 3, Design.   Iron and Steel Society of AIME.
                                     A-5

-------
Nicola, A.  G.   1979.   Blast  Furnace  Cast House Emission  Control.   Iron and
Steel Engineer.  56:33.  1979.

Nijhawan,  P.    1981.   Ventilation:   Looking  at  Close  Capture  Ventilation
Control.  33 Metal Producing.  19.-FE54.

Ochs, J. T.  1975.  Venting and Extraction in Electroplating Plants.  Wasser,
Luft and Betr.  (Germany), 19(7):400-402.

Odasso,  A.    1980.   Air  Pollution  Abatement  at  the  Brackenridge  Works  of
Allegheny Ludlum Steel Corp.  Iron and Steel Engineer, 57(6):51.

Patton,  S.   1973.  Hooded  Coke  Quenching  System  for  Air  Quality Control.
Iron and Steel Engineer, 50(8):37.

Pfeiffer, W.  1982.  Exhaust Air Quantities of Open Type Exhaust Hoods, Staub
Reinhart Luft, 42(8):303-308.

Puri, R.  1974.  System Design for Particulate Control in Woodworking Plants.
Heating, Piping, and Air Conditioning, 46(9):54-58.

Randall,  W.  C., and  E.  W.  Conover.   1931.   Predetermining the  Aeration  of
Industrial  Buildings.   ASHVE Transactions  (American  Society of  Heating and
Ventilating Engineers), Vol. 37.

Richter, G.   1975.  Modern Ventilation Plant.  The Current Technical Position
in  the  Light  of New  Legislation  on Protection  of the  Environment  Ind.-Anz.
(Germany), 97(75):1644-1648.

Rounds   W.  P.  1977.   Energy Considerations  in  Paper  Machine Hood and Air
Systems   Design.    Presented  at  TAPPI   Engineering   Conference,  Atlanta,
September 19-22, 1977.  pp 149-153.

Rowe,  A.  D.   1970.    Waste  Gas  Cleaning  Systems  for  Large  Capacity Basic
Oxygen  Furnaces.   Iron and Steel Engineer, 47(1):74.

Rudolph,  H.   1977.   Engineering  Criteria  for a  Hooded Quench  Car System,
Iron and Steel Engineer, 54(3):27.

Rudolph,  H.,  and  S.  Sayer.   1977.  Engineering  Criteria  for a Hooded Quench
Car  System.   Iron  and  Steel Engineering, 54(3):27-32.

Sesistnbaugh,  J.  D. , and  G.  G.  Persons.   1978.    Electric  Furnace  Melt Shop
Fume Control  System at the  Timken Co.   Iron and Steel Engineering  55(10):53-
5ri.

Shaughnessy,  J.   1981.  A Review  of  Shed and Gas  Cleaning  Systems for Con-
trolling  Coke Pushing Emissions  from  Coke Plants.   In:   Proceedings  of the
Symposium on  Iron  and  Steel Pollution Abatement  Technology for  1981, Chicago,
Illinois, October  6-8, 1981.  EPA-600/9-82-021.
                                     A-6

-------
Shcherbakov,  K.  L.   1976.   Floor  Layouts and Air  Conditioning  in Foundries
for Mass and  Large-Batch  Production.  Liteinde Proizyod (USSR), No. 10:34-5.

Siegel, M.  E., and A.  Shacter.   1978.   Engineering Design  Handbook  for Air
Cleaning For  Chemical Demilitarization.  ARCSL-CR-78022; AD-E410 041.

Spawn,  D.   1981.   Blast Furnace  Cast  House  Control  Technology  and Recent
Emissions Test Data for  1980-81.  In:  A  Specialty Conference on Air Pollu-
tion Control  in the Iron  and Steel Industry, April  21-23, 1981.

Spawn, D.  1981.   Field Evaluation of Fugitive Emissions from  BOF Steelmaking
Shops.  In:   Proceedings  of the Symposium on  Iron  and  Steel Abatement Tech-
nology for 1980, Philadelphia, PA.  November 18-20, 1980.  EPA-600/9-81-017.

Spawn,  D.    1981.   Status  of  Casthouse   Control  Technology  in  the United
States, Canada, and West  Germany in  1980.   In:  Proceedings of the Symposium
on Iron and Steel  Abatement Technology  for 1980, Philadelphia, PA.   November
18-20, 1980.    EPA-600/9-81-017.

Squires, B. J.  1971.  Electric Arc  Furnace  Fume  Control  and Gas Cleaning.
Filter Separ., 7(4):447-450, 453-455.

Steiner,  J.,   and  L.  F.  Kertcher.    1980.    Fugitive  Particulate   Emission
Factors for BOP Operations.   In:   Proceedings  of the First Symposium on Iron
and  Steel  Pollution  Abatement  Technology,  Chicago,  Illinois,   October  30-
November 1, 1979.   EPA-600/9-80-012.

Thaxton, L. A.  1971.  Technology for  Pollution Control.   Exhaust  Systems.
Hood Close to  Source  Is Key Consideration.  Metal Progr., 100(7):56-58.

Tsuji, K., T.  Hayaski,  and M.  Shibatu.   1979.  Required  Exhaust Volume for
Local Lateral  Hoods.   Bulletin,  University of Osaka  Prefect Ser. A., 27(1):
109-124.

Turner, H.   1981.   Performance  of BOF  Emission Control  Systems.   In:   Pro-
ceedings of the  Symposium  on  Iron  and Steel  Pollution  Abatement Technology
for 1981, Chicago, Illinois.  October 6-8, 1981.

Under EPA Duress,  U.S. Steel  Finds New  Ways  to Operate  its Veteran Homestead
OH Shop.  1979.  33 Metal Producing,   pp 49-51.

U.S.  EPA.  1974.   Standards Support  Document:   An  Investigation  of the Best
Systems of Emission  Reduction for Electric Arc  Furnaces  in  the  Steel Indus-
try.   Draft.

U.S.  EPA  1977.  Blast  Furnace  Casthouse   Control Technology Assessment.   PB
276999.

U.S.   EPA.   1980.   Revised  Standards  for  Basic Oxygen  Process  Furnaces  -
Background Information for  Proposed Standards.   Preliminary Draft.
                                     A-7

-------
U.S. EPA.  Undated.  An Investigation of  the  Best  Systems  of Emission Reduc-
tion  for Pushing  Operation of  Byproduct  Coke  Ovens  Standard  Support  and
Environmental  Impact  Statement.   Office  of Air Quality  Planning  and Stan-
dards, Research Triangle Park,  North Carolina.

Vatavuk, W.  M.,  and  R.  B.  Neveril.   1980.   Estimating the Size  and  Cost of
Pollutant Capture Hoods--3.  Chemical Engineering,  87(24):111-112, 114-115.

Vaughan,  J.    1975.   A Residuals  Management  Model  of  the  Iron and  Steel
Industry:  Part I.  Ph.D.  Dissertation,  Georgetown  University.

Vinson,  R.  P., et al.  1980.  SF6  Tracer Gas TEsts of  Bagging-Machine Hood
Enclosures.  Bureau of Mines, Pittsburgh Research Center BUMINES-R1-8527.

Voldshina,  R.  K., and A.   I.  Sukhareva.  1972.  Means  of Reducing  the Dust
Concentration  of the Air  in Glass  Plant  Batching  Departments.    Glass  and
Coram.   (USA), 29(9-10):585-586.

Wheeler,  F.  M.,  and  A.  G.  W.  L.  Lament.    1979.   Current  Trends  in Electric
Meltshop Design.  Iron and Steelmaker,  pp 36-43.

Whike, A.  S.   1979.   Energy Conservation and  Pollution  Control—Two Advant-
ages of  Coil Coating.   In:   Proceedings of  the 14th  International Society of
Energy Conservation Engineers Conference,  Boston, August 5-10, 1979.

Williams, A.  E.   1982.  New Developments  in  Coke-Oven  Machinery  Technology.
Iron and Steel Engineer, 59(7):25+.

Zaryankin, A.  E., and V. P.  Zhilinskii.   1975.   Analysis  of  Design of Soviet
Exhaust  Hoods  of Steam Turbines  and the Possibility  of Lowering  Their  Re-
sistance.           Therm.          Eng.          (GB),          22(3):58-62.
                                     A-8

-------
                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing!
1. REPORT NO.
                              2.
                                                            3. RECIPIENT'S ACCESSIOI
4. TITLE AND SUBTITLE
     Performance Evaluation Guide  for  Large Flow
     Ventilation Systems
             5 REPORT DATE
                May 1984
             6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)

     W.  F.  Kemner, R. W. Gerstle,  and  Y.  M.  Shah
             B PERFORMING ORGANIZATION REPORT NO.


                  3760-1-119
9. PERFORMING ORGANIZATION NAME AND ADDRESS

     PEDCo Environmental,  Inc.
     11499 Chester Rd.
     Cincinnati, OH  45246
                                                            10. PROGRAM ELEMENT NO.
              11. CONTRACT/GRANT NO.

                  68-01-6310
                  Work Assignment  119
12. SPONSORING AGENCY NAME AND ADDRESS
     U.  S.  Environmental Protection  Agency
     Control  & Process Engineering
     Stationary Source Compliance Division
     Washington, D.C.	
              13. TYPE OF REPORT AND PERIOD COVERED

                  Final
              14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
     Project Officer for SSCD:   Dwight Hlustick
16. ABSTRACT
          Air pollution control systems  in the primary metals  industry,  particularly the
     steel  and copper segments, rely  on  large capture and ventilation systems with flow
     rates  commonly in the range  of 50,000 to  1,000,000 acfm  and  greater.  These systems
     are used primarily to control process fugitive emissions  from various furnaces and
     for building evacuation.
          Because these systems are in integral feature of the compliance programs of the
     industries involved, this manual  was initiated to accomplish  the following:

          *   To provide design and operation and maintenance  guidelines to state and
              local agency personnel  who evaluate the performance  of these systems.
          *   To provide a comprehensive treatment of the existing literature with
              regard to technical  and specific aspects of typical  designs.
          *   To provide an easy-to-read technical manual on design and  operation for the
              use of inspectors.

     Inasmuch as ventilation  systems  are highly complex from a design standpoint and
     experience plays a major role in most designs, this manual  should be considered an
     introductory primer rather than  a detailed design manual.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS  C. COSATI Field/Group
     Ventilation
     Industrial Engineering
    Fans, Ducts, Hoods

    Steel Industry
    Copper Smelting
13A

13H
18. DISTRIBUTION STATEMENT
                                               19 SECURITY CLASS (This Report)
                                                   Unclassified
                            21. NO. OF PAGES
                               146 p.
                                               20 SECURITY CLASS (This page)

                                                   Unclassified
                            22. PRICE

                               A07
   Form 2220-1 (R«v. 4-77)   PREVIOUS EDITION is OBSOLETE

-------