&EPA
United States Industrial Environmental Research
Environmental Protection Laboratory
Agency Research Triangle Park NC 27711
EPA-600/2-78-1185
June 1978
Research and Development
Pollution Effects of
Abnormal
Operations in Iron
and Steel Making -
Volume II.
Sintering, Manual
of Practice
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RESEARCH REPORTING SERIES
Research reports of the Off ice of Research and Development, U.S. Environmental Protec-
tion Agency, have been grouped into nine series. These nine broad categories were
established to facilitate further development and application of environmental tech-
nology. Elimination of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECHNOLOGY
series. This series describes research performed to develop and demonstrate instrumen-
tation, equipment, and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the new or improved tech-
nology required for the control and treatment of pollution sources to meet environmental
quality standards.
REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-118b
June 1978
Pollution Effects of Abnormal Operations
in Iron and Steel Making - Volume II.
Sintering, Manual of Practice
by
B.H. Carpenter, D.W. VanOsdell, D.W. Coy, and R. Jablin
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
Contract No. 68-02-2186
Program Element No. 1AB604
EPA Project Officer: Robert V. Hendriks
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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PREFACE
This study of the environmental effects of substandard, breakdown, or
abnormal operation of steelmaking processes and their controls has been made to
provide needed perspective concerning these factors and their relevance to
attainment of pollution control. The use of the term Abnormal Operating
Condition (AOC) herein, in characterizing any specific condition should not be
construed to mean that any operator is not responsible under the Clean Air Act
as amended for designing the systems to account for potential occurrence in
order to comply with applicable State Implementation Plans or New Source
Performance Standards.
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ACKNOWLEDGMENT
This report presents the results of a study conducted by the Research
Triangle Institute (RTI) for the Industrial Environmental Research Laboratory
of the Environmental Protection Agency (EPA) under Contract 68-02-2186. The
EPA Project Officer was Mr. Robert V. Hendriks.
The project was carried out in RTI's Energy and Environmental Research
Division under the general direction of Dr. J. J. Wortman. The work was
accomplished by members of the Process Engineering Department's Industrial
Process Studies Section, Dr. Forest 0. Mixon, Jr., Department Manager, Mr. Ben
H. Carpenter, Section Head.
The authors wish to thank the American Iron and Steel Institute for their
help in initiating contacts with the various steel companies and for their
review of this report. Members of the AISI study committee were: Mr. William
Benzer, American Iron and Steel Institute; Mr. Stephen Vajda, Jones and
Laughlin Steel Corporation; Dr. W. R. Samples, Wheeling-Pittsburgh Steel
Corporation; Mr. Tedford M. Hendrickson, Youngstown Steel; and Mr. John R.
Brough, Inland Steel Company. Acknowledgment is also given to the steel
companies who participated in this study.
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TABLE OF CONTENTS
Page
LIST OF FIGURES vi
LIST OF TABLES
INTERNATIONAL SYSTEM OF UNITS AND ALTERNATIVE (METRIC) UNITS
WITH CONVERSION FACTORS viii
1.0 INTRODUCTION 1
1 .1 Purpose and Scope 1
1.2 Definition of AOC 2
2.0 DISCUSSION OF THE SINTERING PROCESS, NORMAL OPERATION 3
2.1 Process Flow Sheet 3
2.2 Material Balance 3
2.3 Methods of Operation 5
Raw Materials Handling, Preliminary Mixing 5
Raw Materials Handling, Final Mixing 7
Emissions from Materials Handling 9
Sintering 9
Emissions from Sintering 12
Startup 15
Shutdown 19
3.0 CONTROL TECHNIQUES AND EQUIPMENT 21
3.1 Wastewater Pollutants 21
3.2 Emissions and Sources 23
3.3 Types of Controls Used 23
3.3.1 Windboxes 23
Electrostatic Precipitators (ESP's) 25
Fabric Filters 27
Scrubbers 31
Wet Electrostatic Precipitators (WESP'S) 36
Gravel Bed Filter 40
3.3.2 Product Handling 40
3.3.3 Materials Handling 42
3.3-4 Process Modification 42
4.0 ABNORMAL OPERATING CONDITIONS 44
4.1 Process Related AOC's 44
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TABLE OF CONTENTS (cont'd)
Page
4.1.1 Startup 44
4.1.2 Shutdown 45
4.1.3 Abnormal Operating Conditions 45
Product Handling 49
4.2 Control Equipment Related AOC's 50
4.2.1 Startup 50
Preci pita tors 50
Warmup 50
Stack Puff 52
Unbalanced Flow Among Manifolded Fans 52
Insufficient Draft, Fan Malfunctions 53
Fabric Filters 54
Scrubbers 55
4.2.2 Shutdown 55
Preci pita tors 55
Baghouses 55
Scrubbers 55
4.2.3 Abnormal Operation 55
Downtime of Control Systems 55
Preci pi tators 57
Downtime of Secondary Systems 57
Rapping 58
Rapper Failure 58
Wire Breakage 59
Dust Removal System Breakdown 62
Sprays Plugged or Corroded 63
Transformer-Rectifier Set Failure 63
Insulator Failures 64
ESP Maintenance 65
Fabric Filters 65
Baghouse Maintenance 66
Scrubbers 66
Sprays Corroded or Plugged 69
Plugged or Corroded Pipes 70
Corroded Pump Impellers, Pump Failure 71
Plugged or Failed Demister 71
Drum Filter Failure 72
Acid Cleaning Scrubber Components 73
Control Process Modifications 73
5.0 TABULATED SUMMARY OF AOC 74
6.0 REFERENCES 84
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LIST OF FIGURES
1. Typical sinter plant flow diagram for superfluxed sinter 4
2. Typical material balance for superfluxed sinter from a
modern sinter plant 6
3. Typical duct electrostatic precipitator 25
4. Schematic diagram showing flow and controls for a sinter
plant baghouse 29
5. Recycle plant, Middletown Works scrubber system flow diagram 32
6. Scrubber plant, Houston Works, scrubber system flow diagram 35
7. Mikropul pilot WESP test setup at a sinter plant 37
8. Full scale WESP demonstration at a sinter plant 38
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LIST OF TABLES
3-1. Uncontrolled Scrubber Water Pollutants From a Sinter Plant
and Estimated Control Required ,, 22
3-2. Uncontrolled Pollutant Emissions from Sinter Plants and
Estimated Control Required 24
5-1. Sinter Plant Abnormal Operating Conditions 75
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INTERNATIONAL SYSTEM OF UNITS AND ALTERNATIVE (METRIC) UNITS
WITH CONVERSION FACTORS
Quantity
mass
volume
concentration or
rate
energy
force
area
SI Unit/Modified SI Unit
kg
Mg (megagram =10 grams)
Mg
q
Gg (gigagram = 10 grams)
o
m (cubic meter)
dscm (dry standard cubic meter)
scm (standard cubic meter: 21°C, 1 atm)
a (liter = 0.001 m3)
3 3
g/m (grams/m )
3 O
mg/m (mi 111grams/m )
g/kg
J (joule)
kJ/m3 (kilojoules/m3)
MJ (megajoules = 10 joules)
MJ/Mg
kPa (kiloPascal)
1 Pascal = 1 N/m2 (Newton/m2)
p
m (square meter)
Equivalent To
2.205 Ib
2205 Ib
1.1025 ton
35.32 cf
0.437 gr/ff3
0.000437 gr/ft;
2 Ib/ton
0.000948 Btu
0.02684 Btu/fr
0.430 Btu/lb
859 Btu/ton
0.146 lb/in2
10.76 fr
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1.0 INTRODUCTION
1.1 PURPOSE AND SCOPE
Air and water pollution standards, generally based upon control of discharges
during normal (steady-state) operation of a control system, are frequently
exceeded during "upsets" in operation. When such upsets become repetitive
and frequent, the regional and local enforcement agencies undertake, through
consent agreements, to work with the plant toward resolution of the problem,
and plans are developed for such equipment and operating practice changes as
will eliminate or alleviate the frequent violations. Should the planning
process fail to resolve abnormally frequent occurrences of abnormal operating
conditions, the problem may lead to litigation. Thus, periods of abnormal
operation are becoming recognized as possibly contributing to the emission of
high concentration of pollutants. Similarly, upsets may contribute to spills
of increased amounts of effluent-borne pollutants into waterways.
There is a need for information concerning abnormal operating conditions
(AOC): their identity, cause, resulting discharges, prevention, and minimiza-
tion.
The purpose of the manual is to alert those who deal with environmental
problems on a day-to-day basis to the potential problem areas caused by
abnormal conditions, to assist in determining the extent of the problem created
by abnormal conditions in a specific plant, and to provide help in evaluating
any efforts to reduce or eliminate the problems. The processes considered are
those in the primary section of the integrated iron and steel plant. Included
are the sintering, blast furnace ironmaking, open hearth, electric furnace, and
basic oxygen steelmaking. This manual covers the sintering process.
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This manual is based on reviews of somewhat limited data, visits to a few
of the many steel plants, interviews with persons intimately involved in either
steel making or attendant environmental regulations, and the expertise of the
study team. It is, therefore, a preliminary assessment which concentrates on
enumerating as many of the conditions as possible, with emphasis on those which
have the most severe environmental impact.
Each process is described separately. Descriptions include flow diagrams
and material balances, operating procedures and conditions. The flow sheets
and material balances presented are representative of the most typical process
configurations.
Within each process are variations, both in the process itself and in the
equipment for control of pollution. Variations in equipment and process are
accompanied by variations in AOC. It is, therefore, of value to identify as
many of the variations as possible. At the same time, it is necessary to limit
consideration of the numerous alternatives to those which are currently in
greatest application and use.
1.2 DEFINITION OF AOC
In general, an abnormal operating condition (AOC) is considered to be that
which departs from normal, characteristic or steady-state operation, and results
in increased emissions or discharges. In addition to abnormal operations,
this study includes startup and shut down difficulties of processes and control
equipment. It also includes substantial variations in operating practice and
process variables, and outages for maintenance, either scheduled or unscheduled.
The use of the term Abnormal Operating Condition (AOC) in characterizing
any specific condition should not be construed to mean that any operator is
not responsible under the Clean Air Act as amended for designing the systems
to account for potential occurrence in order to comply with applicable State
Implementation Plans or New Source Performance Standards.
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2.0 DISCUSSION OF THE SINTERING PROCESS, NORMAL OPERATION
The primary function of sintering is to agglomerate dusts and sludges from
pollution control sources and fine ores into lumps suitable for charging into
the blast furnace. The secondary function of sintering is to provide part or
all of the flux material for the ironmaking process.
The primary function stems from the need to provide physical mass, size,
and strength to the material. Fine particles, if charged into the blast
furnace, will be blown out by the rapid countercurrent flow of the furnace
gases. Lumps, being physically larger, will not be so affected.
The secondary function stems from the economics of the ironmaking process.
A blast furnace operates more economically if the flux is pre-calcined, that is
if lime (CaO) is charged rather than limestone (CaCO,). It is, however, too
expensive to substitute purchased lime for limestone in the blast furnace. The
preferred course is to mix limestone in the sinter feed and use the heat of the
sintering process for calcining it.
2.1 PROCESS FLOW SHEET
The sintering process, as described herein, includes receiving, mixing,
feeding, and agglomerating the raw materials; the actual sintering operation;
and the crushing, screening, cooling, and transferring of the sinter product.
A flow sheet for the process is shown in Figure 1. The letters in brackets ( )
indicate the areas of greatest potential for AOC.
2.2 MATERIAL BALANCE
Feed material to the sintering process includes primarily ore fines, and
also reverts (blast furnace dust, mill scale, and other byproducts of steelmaking)
recycled hot and cold fines from the sintering process and trim materials
(calcite fines, and other supplemental materials needed to produce a sinter
product with prescribed chemistry and tonnage). Generally, some 2.5 tons of
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83.2
20.0 WATER
VAPOR AND GASEOUS
EMISSIONS
MECHANICAL
COLLECTOR
WATER
I
5.2
i
0.1
PARTICULATE
AIR POLLUTION
CONTROL SYSTEM
^WINDBOX
STACK
MIXING
DRUM
<
a
u
MAIN
WINDBOX
FAN
I I
AIR POLLUTION
CONTROL DEVICE
I I
DISCHARGE, B
BEAKER,
COOLER, AND SCREEN
EMISSIONS 0.5
B.4
HEARTH LAYER 11.6 * fc>
0.3 20.4
BURDEN »100.0
JU
IGNITION
23.8
VV FURNACE
v v i i.
Q SINTER MACHINE
FINES I SCALE \ FLUX COKE | ORE
23.8 AND jl 11.4 I 2.2
SLUDGE!!
83.2
:YYYYYYY
(*>
12.6
23.2
10.6
I
TO BLAST
FURNACE
"PROCESS THROUGHPUTS DO NOT INCLUDE AIR.
Figure 1. Typical sinter plant flow diagram for superfluxed sinter.
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strand burden, including water and fuel, are fed per ton of sinter produced,
and about 2832 standard cubic meters (son) of pollutant-containing air must be
cleaned.
Figure 2 shows a material balance for a typical sinter plant making
superfluxed sinter.
Variations in the material balance may result from the following factors:
1. The amount of return fines may increase (or decrease) if
the quality of sinter degrades (or improves), or if the
efficiency of screening improves (or reduces).
2. The use of a hearth layer is optional. Although it is a
preferred technique, some older plants do not have the
necessary equipment for creating the hearth layer.
3. The amount of flux material varies from plant to plant
depending on the percentage of sinter used in the blast
furnace burden, the flux requirements of the blast fur-
nace, and other production factors in the ironmaking
complex. In general, economics favor the high flux,
or superflux sinter.
2.3 METHODS OF OPERATION
Raw Materials Handling, Preliminary Mixing
Consistent and accurate proportioning of sinter strand feed materials
followed by thorough mixing is necessary if a uniform product of desired
quality is to be obtained. Preliminary blending of a portion of the feed may
be done either using a bedding system or a conveyor belt system.
A bedded pile constructed at the bedding plant may consist of some 45.4 Gg
(50,000 tons), in which revert materials may account for 40 percent of the
total quantity. The pile can be constructed over a period of about five opera-
ting days. It is constructed longitudinally with up to 500 layers stacked as
prescribed by the blending scheme. It is reclaimed cross-sectionally to provide
a raw-mix feed to the sinter plant.
The materials are proportioned and mixed in order to prepare a chemically
uniform feed to the sinter strand, with a composition prescribed so that the
sinter resulting will have qualities desired for satisfactory blast furnace
operation. The chemical quality of the sinter is often assessed in terms of
its basicity (B/A), the percent total basic oxides divided by the percent total
acid oxides:
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CTl
.2% COKE
1 gx
MOISTURE
11.4% FLUX^v
;..-; -v
' "" \^
RAW FEED
44.1% ORE,
SCALE, etc. DRY
BURDEN WET
i ' * BURDEN
^^
n.M RFTIJRN FTNFS .._.
^f / 1
<*>,H ADDED WATER ' ' /
^^ /
11.6% HEARTH LAYER . _^S
SS"**V^ BURDEN IN COMBUi
S^S >AND CALCINATION
kXHAUil BMtS _ ^4.8,pA^TICUUTEA11D
GASEOUS EMISSIONS1'
TOTAL
j««f*fk >«%
BURDEN X
^X "\\
^f ^
23.5% RETURN 11.6% HEARTH
FINES3 LAYER
JTION
GASES
N
V
44.0% PRODUCT
>TO BLAST
FURNACE
'includes fines from cooling, screening, and transfer points also.
'includes particulate emissions from cooling, screening, and transfer points also.
Figure 2. Typical material balance for superfluxed sinter from a modern sinter plant.
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B/A = (XCaO + %MgO)/(%Si02 + %A1203)
The basicity each material to be blended is often utilized, along with time and
quantity constraints, to obtain a preparation schedule for the bedded pile. A
more meaningful chemical quality criterion for blending calculations is the
stone equivalent (SE) defined as the pounds of stone available for fluxing per
100 kilograms (220 Ibs) of material:
SE . IOQ - B/S((%Si02)n1 - 2.14
((XCaO + %MgO)s - B/S((%Si02)$ - 2.14 («S1-)hm(%Fe)s/(%Fe)hm))
where m = material to be blended
s = the stone being charged to the blast furnace
hm = the blast furnace hot metal
2.14 converts Si to Si02, and
B/S = the base to silica ratio of the blast furnace slag: (%CaO + %MgO)/
(%Si02).
Using Direct Digital Computer control of the mixing process, to convert
the analyses of each material to stone equivalents, develop a schedule for the
bedded pile (required tonnages, feed rates, and time schedules for refilling
storage bins), one new bedding plant met its target stone equivalent value of
12.0 with a standard deviation of 0.7 over a one quarter year period. Most
current mixing operations would not be expected to attain such uniformity.
Raw Materials Handling, Final Mixing
Material from preliminary mixing goes to feed bins at the sinter plant.
Other feed bins there hold fluxing materials, coke breeze or coal fines and
sinter fines. These materials are proportioned onto a conveyor belt, pre-
ferably by separate variable feed rate weigh belt feeders. The relative
amounts of each material are determined by calculation, considering the desired
B/A or SE value, the rate of consumption of material, at the sinter strand, the
amount of sinter fines that must be recycled, and the total carbon content
needed for proper ignition and sintering.
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Water is added as the material conveyed from the feed bins reaches a pug
mill or balling drum where it is pelletized (rice-sized pellets) and fed to the
roll feeder surge hopper. The surge hopper can serve to uncouple, momentarily,
the rate of strand burden production from the sinter strand feed rate. The
surge hopper level is monitored and fed back manually or automatically to
control the feed bins discharge rates.
BOP dusts, if returned to the sinter plant, require special handling to
control fugitive emissions.
The successful transport of BOP flue dust to the sinter plant has been
reported using (1) center flow hopper cars to haul the dust to the plant, (2)
14" screw conveyors to unload the cars, (3) 18" belt conveyors to the feed
chute which discharged directly onto the sinter mix gathering conveyor.
Baffles were hung inside the gathering conveyor cover and steam was introduced
inside the last drop point. The steam cloud moved, back under the enclosed
cnveyors and effectively dedusted the system. This dust contained calcined
lime (CaO and Mg). Prior to adoption of this system, the dust cake after
treatment with water sprays and clogged a verticlone feeder. Mixing the dust
with blast furnace thickener sludge proved not to be satisfactory.
Rounds and Germinder report that mixing BOF dust with wet mill scale
o
mitigates the fugitive dust problem. Ostrowski and Hass report the successful
pilot testing of a vertical mixer to blend mill scale, BOP dust, blast furnace
o
flue dust, and blast furnace sludge. Sludge was fed from a ribbon feeder and
flue dust, BOP dust, and mill scale from bins onto a common collector belt
leading to the mixer. Water was added, using conventional spray nozzles, onto
the conveyed mix upstream and downstream of the BOP dust feed bin. The final
blend was fed onto the sinter mix conveyor belt from conventional storage bins
using the conventional table-type feeder. While no increase in dust loading of
the waste gas stack were observed while consuming the blended BOP dust, the
zinc content of the particulate matter increased. A zinc balance, made during
the tests, showed a 22-26 percent loss, potentially to the environment.
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Emissions From Materials Handling
Fugitive dusts are predominant emissions from raw material handling.
While such dusts are evident in nearly every plant, exhausts from building
ventilation are not usually visible unless fine dusts such as BOF flue dust are
handled with conventional miscellaneous material systems. Pugh and Fletcher
reported 60 percent loss of this dust in transfer and transport by uncovered
conveyors,
Sintering
The sintering machine accepts feed material from the roll feeder surge
hopper, and conveys it down the length of the moving strand. On the way, the
fuel in the mix is ignited, then burned using an induced draft. The heat (some
174 MO per Mg of product (150,000 BTU per ton) agglomerates the fine particles
forming a cake of porous clinker. The cake is discharged from the sinter
strand to a breaker which reduces it to pieces up to six inches in size. In
modern sinter plants, the crushed product is screened before and/or after
cooling; in older plants one or both steps of screening may be absent. Fines
and, usually, pieces suitable for use as a hearth layer are returned to the
feed system. The sinter product is transported to feed areas for the blast
furnace.
The sinter machine strand is composed of pallets (small cars) which ride
on rails over the windboxes. Each pallet has a grated bottom, open ends where
the cars come together and sideboards of maximum height for the sinter bed. The
active surfaces on sinter machines are up to 4 meters wide and 61 meters long.
2
Material is fed to a depth of up to 40 cm. Grate speed can range from 15 to
3 meters per minute. At the discharge end of the machine, the cars pass down
and return upside down as would a normal conveyor.
The windboxes (compartments under the bed) provide for a controlled distri-
bution of combustion air as it is drawn through the sinter bed. Air is drawn
down through the burden, into the windboxes and through an initial separator to
a large fan. Very coarse particulates (up to 1 cm diameter) are recovered in
the windboxes. Other somewhat less coarse particulates are removed by the
separator. Over 14,000 m/min (500,000 cfm) of air at about 190°C may be drawn
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through the burden at a static pressure of 120 cm (40 inches) of water gauge.
(Fans are typically designed to draw 935 to 1029 son (30,000 to 33,000 scfm)
per net Mg (ton) of raw material on the strand.) After the fan the gases are
subject to further cleaning and possibly recirculation before discharge to the
air.
The discharge end has a separate ventilation system for the crusher and
hot screens, with a gas volume of some 1.65 scm/min (50 scfm) per Mg per day of
sinter. These gases are subjected to cleaning before discharge to the air.
Sinter coolers are most commonly either quiescent, circular, or straight
line moving beds (with forced or induced draft). A portion of the cooling air
may be fed to the windbox system to utilize its heat content.
The sintering process operates normally under controls which maintain
conditions set to achieve the desired product, with further controls to sense
3 4
and adjust for irregularities in materials flow and system breakdown. "
Interlocking switches are used to insure that subsystems are started and
stopped in prescribed sequence. The subsystems themselves are interlocked so
that for example, if the product conveyors failed, the entire system (burden-
si nter-and-product groups) would shut down until the trouble is corrected.
Typically, six categories of control (control loops) are applied by the
operators or by computers under their direction.
1. Control loop 1 sets and maintains the material discharge
rates from the feed bins. The rates themselves are cal-
culated to meet four constraints. The stone equivalent of
the sinter after combustion, must be equal to a prescribed
value. The total amount of feed material discharged onto
the main conveyor must equal the amount being consumed
by the sinter machine, modulated upward or downward by
the current material level in the roll feed surge hopper.
The total amount of material being discharged from feed
bins must include a specified percentage of sinter fines.
The total carbon content in the feed material must meet a
specified setpoint percentage.
10
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2. Control loop 2 monitors the material level in the roll
feeder sunge hopper and reacts thereto. If the level
becomes extremely high, the entire feed line is stopped
until the conditions is corrected. Less extreme variations
. in the level will actuate proportionate adjustment of all bin
feed rates.
3. Control loop 3 controls water addition to the raw sinter
mix. Water is added just prior to the mixing (balling)
unit to promote balling of the fine material. While
water may be added directly proportioned to the mass flow
of material, further control is often applied based on measuring
the actual moisture in the raw mix at the discharge of the
balling unit and comparing with the moisture setpoint.
4. Control loop 4 regulates the speed of the roll feeder (or
alternate) which regulates the discharge of balled sinter
mix onto the loading station of the moving grate sinter
strand. Proper loading occurs when sufficient material
is maintained at the loading station to generate a wave of
material wiped from the top surface of the raw mix bed be-
hind the strike-off plate. Probes sense the existence and
extent of material at this point, and actuate adjustments
to match the discharge rate of the feeder to the volumetric
consumption rate of the strand. Several changes can be made
to achieve the match. The feeder may be slowed down relative
to the sinter strand feed, the strand may be speeded up
ten percent until the probes are cleared of excess material,
or the entire feed line may be stopped momentarily.*
5. Control loop 5 regulates the speed of the strand's traveling
grates based upon the rate of combustion of the fuel in the
feed mix. The combustion is supported by suction produced
below the strand by an induced draft fan system, so that
the heat and combustion products are drawn down through the
bed. Conventional practice aims to have the vertical com-
bustion burn through as the grate pallet has just traversed
the length of the strand. The burn-through point is detected
by monitoring the induced draft gas temperatures in the
windbox segments throughout the length of the strand. The
resulting temperature profile is evaluated yielding a cal-
culated burn-through point. This point is compared with the
prescribed location, and the strand speed is adjusted to
minimize the difference. The sinter draft fan is controlled
to maintain a preset suction (-AP) in the windboxes. A
pressure sensor signals changes in the fan damper subject to
limits on the fan motor load current.
*Speeding up the sinter strand may be the least desirable change from the
standpoint of emissions control.
11
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6. Control loop 6 matches the speed of the sinter cooler.
These rates are usually uncoupled by a small-capacity surge
chute at the cooler loading station. Using the level of
hot sinter in the chute for control, it maybe sensed by a
nuclear level detector, with attendant modulation of the
cooler speed to keep sufficient material available so that
bed voids will not occur on the cooler, and to prevent chute
overfill.
A breakdown in the product cooler system (which includes cooling, screening,
fines return, and product storage operations), will shut down the whole pro-
ducing plant pending corrective action.
Emissions from Sintering
Emissions from sintering occur in the windbox exhaust gases, in the
sinter product handling ventilation gases, and as fugitive emissions. Windbox
emissions consist of filterable and condensible particulates, hydrocarbons,
SO , CO, NO , and, possibly, fluorides. Uncontrolled filterable particulate
A A
concentrations in windbox exhausts before the mechanical collectors have been
shown by tests to be 4.6 - 9.2 g/scm. Genton gives the following typical
particle size analysis:
Size, microns Percent by weight
100 and over 7.6
100 - 80 1.3
80 - 60 0.9
60 - 40 4.0
40 - 20 17.5
20 - 10 41.3
10 - 1 27.4
Windbox particulate emissions are influenced by particle size distribution,
burden composition, bed air flow rate, sinter machine design, and operating
techniques.
12
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Some operating techniques which affect windbox participate emissions are:
1. Very fine materials in the burden, such as dust from the
BOF operation, may result in an increase in the amount of
particulate emitted as well as in its fineness.
2. Improper proportioning or mixing of the raw feed may result
in non-uniform sintering. Some of the feed may not become
sintered and may be drawn through the grate bars.
3. Improper maintenance of grate bars may allow a portion of
the raw feed to fall through the grates thereby increasing
the amount of transported particulates. The holes in the
bed of feed material which result also increase the volume
of gas to be handled by the pollution control device.
This will increase emissions to the atmosphere by virtue of
the increased mass of particulates carried out with the
increased flow of gas and compounded by the increased con-
centration of particulates in the gas. The increase in
concentration together with the increased flow intensifies
the adverse environmental effect of the leakage.
4. Improper maintenance of machine seals increases gas flow,
resulting in increased emissions.TFe same results from
unpatched holes in windboxes and ducts, improperly operating
dust valves, etc. Minimal emissions are directly related to
minimal air flow. To achieve minimal air flow when handling
highly abrasive sinter dust requires constant vigilence and
effort on the part of operating and maintenance personnel.
5. A hearth layer, if used, serves the dual function of protecting
the grate bars from heat, thereby prolonging their life, and
helping to keep feed material from passing into the windboxes,
thus decreasing the concentration of emissions carried into the
gas.
Visible plumes due to particulates are usually reddish while hydrocarbon
emissions are bluish. Sulfur oxides emissions depend on the sulfur content of
the iron-bearing material and the amounts of coke, ignition fuel, and limestone
used. Average emissions (12 U. S. plants) were found to be 112 ppmv, equi-
valent to about 0.9 g S02 per kg of sinter (1.8 Ib/ton).
About one fourth of the carbon fed is burnt to carbon monoxide (CO), and
the rest to COp.7 Emission rates will depend on the coke content of the sinter
burden and the completeness of combustion but run about 12 g/kg of feed, or 28
g/kg of sinter produced (24 Ib/ton of feed, or 56 Ib/ton of sinter produced).
13
-------
Source tests show about 70 ppmv NO (equivalent to 0.3 g NO/kg (0.6 lb/
f* X
ton) of strand feed or 0.7 g/kg (1.4 Ib/ton) of sinter).
In a sinter plant with a well-operating scrubber of medium differential
pressure (75 to 100 cm of water) or a well-operating dry precipitator of
adequate size, one of the chief causes of excess opacity is the presence of
these vaporized hydrocarbons. Neither of these control units are particularly
efficient in capturing these vapors. If the control device is a baghouse, the
presence of hydrocarbon vapors is particularly detrimental because the vapors
contribute to the blinding of the bags and add a considerable fire hazard.
Hydrocarbon vapors in a sinter plant generally originate from oil in the
feed material. Some sources of oil-bearing feed are:
1 Mill scale which absorbs oil that finds its way into mill
water from leaky bearings, hydraulic equipment, etc.
2. Blast furnace sludge which absorbs oil that finds its way
into blast furnace scrubber water from the blast furnace
process itself.
3. Coke breeze which may contain tarry material and which
absorbs oil from the water in the sump of the quench
tower.
If the oil-bearing feed material is not uniformly distributed through the
total feed burden, there may be occasions where the concentration of these
materials becomes much higher than normal. Under such conditions, the con-
centration of hydrocarbon vapors in the stack may be expected to increase and
give rise to increased opacity. The oil present in the feed material appears
o
to be vaporized on the strand ahead of the flame front and pyrolyzed. Mea-
sured emission rates have averaged 1.0 gm/kg of strand feed (2.3 gm/kg of
sinter product), expressed as methane (2 Ib/ton and 5.6 Ib/ton respectively).
Ore fines are the source of fluorides, reported to run as high as 150
2
ppmv. Source tests show a range of 2 - 15 ppmv following mechanical col-
lectors (0.004 to 0.025 g/kg of strand feed; 0.008 to 0.050 Ib/ton).
Odorous substances may be emitted if significant quantities of mill
scale, filter cake, or other oily scrap materials are used, but odor problems
were identified only once during plant visits conducted for this study.
14
-------
Particulate matter from the sinter breaker and product handling operations
will depend somewhat on the completeness of sintering. Uncontrolled parti -
culates have been estimated at 11 g/kg of sinter product.5 (The joint EPA-AISI
estimate is 14 g/kg or 28 Ib/ton.) Hernick has reported uncontrolled dust
concentrations of 7 - 18 g/scm (3-8 gr/scf).2 If screens and conveyor transfer
points are not hooded, dense visible emissions may occur. If water sprays are
used, steam and mist will be generated.
Startup
Startup procedures vary from plant to plant as to sequence, depending upon
the nature of the interlocking controls and the relative importance assigned to
the different systems. Best practice with respect to control of emissions
appears to be that which starts up the emissions controls the earliest. The
following startup sequence was selected from among those compared to represent
better current practice.
1. A roll of paper is used to cover the empty strand. The
paper is removed as it reaches the discharge end of the
machine.
2. Start sinter cooler fans.
3. Start hearth layer group (interlocked conveyors and
controls) if a hearth layer is used.
4. Start dust group, which conveys collected dust from the
windboxes and emissions controls and returns it to the
feed system.
5. Start windbox control unit.
a. Control by ESP If the control is an ESP, its power
unit will likely be permissive from its attendant dust
conveyors, that is, the conveyors must be running before
the power unit can be started. After startup, the
permissive interlock is bypassed and the ESP continues
to run until shut down by its own stopping devices.
After start of the dust conveyor system, determine
that air (414 kPa, 60 psig) is available for rapper
controls; provide power to the rapper control panel;
turn on suspension insulator electric heaters; determine
that all grounding switches are properly set and all
doors closed and locked; admit air to the precipitator;
allow 60 minutes warmup to drive off any condensed
15
-------
moisture from the insulators; put ESP power supply
into operation; after about one minute to warmup
tube filaments, apply plate voltage; review readings
of current and voltage to the primary of the high
voltage step-up transformer and the voltage drop
across the power saturable reactor; review power out-
put as shown by control potentiometer.
Note: Admitting air to the ESP involves startup of the
windbox fan. The load on this fan is regulated by a
hydraulic-electrical mechanism (e.g., an Askania regu-
lator) which adjusts the fan inlet damper between the
limits of fully closed and fully open. The regulator
will function to maintain a manually set inlet suction
pressure cotrol point (within the load limit of the fan
driving motor). When the main draft fan is stopped, the
regulator automatically closes the inlet damper. To
start the fan, the regulator hydraulic pumping unit must
be started first. If the regulator is shut off, it
should automatically drive the fan damper to the closed
portion before the hydraulic pump unit shuts itself down.
The pumping unit cannot be shut down while the fan is
running; if the unit shuts down on overload, it also
shuts down the fan.
After the regulator is started, the draft fan is started
using the following steps: turn on the excitation
power supply (normal or emergency) for the motor field;
actuate high voltage switch gear unit switches; start
the motor; (allow some 20 seconds to accelerate to
full speed, automatically apply the field at the proper
instant, and pull into synchronization). If starting
is unsuccessful, the high voltage circuit breaker will
trip out, and a waiting period is required before
attempting to restart.
Stopping Windbox Fan Normal stopping begins with
tripping the fan switch. Interlocks reset the Askania
regulator timer, closing its contacts and thus driving
the damper to its closed position. A.C. power for
field excitation is then turned off, and the regulator
pump unit is stopped.
b. Control by Baghouse -- If the control is a baghouse,
make sure all chamber doors are closed and latched,
and that no more than the prescribed number of chambers
are on maintenance settings, which isolate them. Close
the inlet damper. When the gas temperature in the by-
pass duct before the baghouse reaches the desired set
16
-------
point value (70°C or whatever is needed to exceed the
dew point) start the motor, turn on the fan load con-
trol, and close the bypass duct. Turn on the clean
cycles and the dust screw conveyors.
Baghouse Shutdown To shutdown the baghouse, open the
bypass duct, trip the motor switch, stop the reverse
air fan and the conveyors.
c. Control by Scrubber If the control is a Venturi scrub-
ber, and is to be started cold, all system equipment
should be inspected with particular attention to where
maintenance has taken place. Verify that no foreign
objects have been left in the equipment or ductwork,
and that all access hatches are closed and secured.
Thereupon, startup may precede generally in the following
sequence:
1) Start cooling water flow to the gas cooling tower and
periodically monitor gas cooling water level alarms.
2) Most scrubber units have a classifier of some type
to remove larger particles of the highly abrasive solid
material that may be carried in the exhaust gases. If
not removed, this material can be carried into pumps
where the resulting abrasion can reduce the impeller life
to a few weeks. The classifier (e.g., rake, screw con-
veyor, or hydroclone) should be started up at this time.
3) Start the water filter system. Generally the fol-
lowing sequence can apply: sludge hopper vibrator, drum
filter agitator, thickener drive motor, thickener rake
positioner, thickener underflow pump, drum filter drive,
vacuum pump motor, filter air blower motor, and filter
filtrate pump.
4) Start venturi pumps, and the attendant water flow
flow recorders. Pump discharge valves may require
manual adjustment to achieve the desired flow rate.
5) Start fan motor bearing lube pump (and fluid drive
oil pumping if the system uses fluid drive) and system
temperature recorders.
6) Start fan motor. Typically this is a constant speed
motor, with the load controlled by adjustment of the
venturi throat to allow for variations in gas flow while
maintaining the cleaning efficiency necessary. When
the sinter machine is started cold, the strand is covered
with paper to partially limit the flow of air until bur-
den is supplied. Scrubbers with a variable venturi
throat sometimes are set to close the throat before
17
-------
starting the fan. Others close a fan inlet damper to
protect the fan motor during startup. At this time,
such pre-start controls are set and the fan is started.
(Note: automatic fan shutdown may occur due to high
fan vibration, or motor overload). Adjust differential
pressure controller and the motor power controller.
Scrubber shutdown -- Shutdown is essentially the reverse
of the system startup procedure, depending somewhat on
the anticipated duration of the shutdown. Under a short
duration shutdown, the main fan is stopped, while lubri-
cant recirculation systems, etc. continue to function.
All water clarification equipment must continue to
operate. Under a long duration shutdown, all scrubber
equipment is stopped. Water clarification equipment
is operated, however, long enough to purge the system
of settled solids. In sub-freezing temperatures, water
collection areas are drained or run at minimum water
flow to prevent ice formation.
6. Start sinter machine.
a. Permissive interlocks of equipment activated in pre-
vious steps will be closed so that the sintering machine
may be started. Start the ignition furnace blower (the
burners should not be lighted until the burden line is
running).
b. Start the sinter cooler drive, which actuates the breaker,
vibrating conveyors and feeders to the sinter screens.
c. Start sinter machine drive. (All safety rails and entry
guides should be closed.) Set machine speed. When the
drive is started, interlocks permissive to the roll
feeder will close. If limits on the maximum torque
during start are exceeded, the machine and all equipment
permissive from it will stop.
7. Start the burden system. The roll feeder is permissive from
the sinter machine, and will be started at this point if all
emergency stop switches and the feed hopper overfill probe
relay are closed. Startup includes the interlocked units from
the roll feeder through the feed proportioning system.
8. Start vibrating feeder serving the dust collection system,
which returns fines to the feed lines.
9. Light and adjust ignition furnaces.
10. Turn on and adjust water supply to balling drum (or
alternative device).
18
-------
11. Startup of product handling emission control.
a. Control by Baghouse
The startup procedure is essentially the same as the
procedure for the windbox control, except that the
by-pass of raw exhaust gases may not always be required.
If required, it will generally be shorter of duration.
There are two situations in which the by-pass may have
to be opened:
1) there is a source of moisture within the emission
control system and the gases are being fed below
the dew point. Such a source may be the vapors'
which evolve when water is sprayed on hot return
fines.
2) There has been a substantial change in atmospheric
conditions in the time period immediately preceding
the startup. Such a condition would be the sharp
rise in atmospheric temperature and humidity which
can result in condensation unless the colder steel
of the baghouse is brought up to temperature by the
heated gases from the sintering process.
b. Control by Scrubber
The procedure is the same as the windbox control except that
the classifier will usually not be required or provided in
the water circuit.
Shutdown
Shutdown of part or all of the process can occur when ever probes sense an
abnormal condition, e.g., accumulation of material, parameter changes beyond
limits, or equipment failure. Interlocks tend to actuate shutdown of equipment
ahead of or directly related to the equipment the operation of which has
suffered an upset. Five systems can be thus interlocked. Each is discussed in
turn.
1. Materials receipt (recycled material, limestone, and fuel),
screening, grinding, and transport to feed bins. This system
shuts down independently if:
the rod mill (for fuel sizing) blower fails,
the rod mill lube pump fails,
the conveyors fail.
2. Hearth layer conveyors are shutdown when a high level of material
is sensed in the hearth layer bin.
19
-------
3. Raw ore processing, from receiving hoppers to feed bins shut-
down when a high level of material is sensed in the screen
feeder chutes. The feed circuit or parts thereof may be
stopped if:
someone opens any emergency switch,
a thermal overload is sensed,
the material level in the roll feeder bin gets too high,
a backup of material of the feeder is sensed,
the table feeder lube pumps fail,
the sinter machine stops, or
the conveyors fail.
4. The sinter machine may be stopped if:
a part of the product handling system breaks down,
a drive motor develops excessive full load torque,
there is a lack of burden or hearth layer material,
there is a jamb in the machine drive,
the ignition furnace shuts down, or
there is loss of suction in the windbox.
5. The windbox fan may be stopped if:
bearings become too hot, or
vibration becomes excessive.
20
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3.0 CONTROL TECHNIQUES AND EQUIPMENT
3.1 WASTEWATER POLLUTANTS
Sintering is essentially a dry process. Water added to the burden to
assist in its agglomeration is evaporated and passes out the stack as vapor.
Water is sometimes used to control fugitive dusts, to facilitate the conveying
of collected dusts, to cool the sinter product, or to minimize the possibility
of spontaneous combustion in the windbox dusts if collected by baghouses. This
water is unlikely to cause water pollution problems if it is returned to the
sintering plant along with the collected dust. When a scrubber or a wet ESP is
used as a control technique, the attendant wastewater must be treated and
controlled. The wet scrubber could be a major source of water pollution if the
effluent were not controlled. A venturi scrubber or a wet ESP will require a
liquid to gas ratio (L/6) of approximately 1240 £/scm. Typically, the recir-
culating effluent may contain up to 1600 ppm chloride, up to 520 ppm sulfur, a
high amount of suspended and dissolved solids, and have a pH of 2.1 to
3.1.2'7
Effluent New Source Performance Standards for the sintering industry have
been promulgated in 40 CFR 420.25 and are shown in Table 3-1 together with
characteristics of raw scrubber waters. The standards are based on the use of
a tight water recycled system with only 0.2 liters of discharge per kg of
sinter produced. The best available treatment methods for suspended solids are
reported to be chemical polymer flocculation and settling in a clarifier, the
overflow of which is recycled through the control device. The sludge drained
from the bottom of the clarifier (underflow) is dried with a vacuum filter and
the filter cake is landfilled. Oil and grease adhere to the suspended solids
and are settled out with them or are skimmed off at the clarifier overflow.
Aeration is required for sulfide treatment and lime is added for fluoride
treatment and pH adjustment.
21
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TABLE 3-1. UNCONTROLLED SCRUBBER WATER POLLUTANTS FROM A SINTER PLANT AND ESTIMATED CONTROL
REQUIRED3
Facility
Pollutant
Estimated Pollutant Loading, mg/£
Unless otherwise stated
Raw Federal Stds. mg/kg Sinter
waters max, 1 day 30 day avg.
Water
Discharge
Limits
L/teg Sinter
Control
Efficiency
Required
1 day
Scrubber
Total suspended solids
(a) Using Blast Furnace Scrubber 341
Water
(b) Using River Water 223
Oil and grease
Sulfide
Fluoride
(a) Using Blast Furnace Scrubber 24.3
Water
(b) Using river water 9.8
pH
(a) Using Blast Furnace Scrubber 3.07
Water
(b) Using river water 2.95
0.2
15.5
6.3
0.18
12.6
5.2
2.1
0.06
4.2
Allowable Range 6-9
99.9
99.9
99.9
Based on tests at one sinter plant. The scrubber pressure drop was 112 cm w.g. when using scrubber water and
130 cm when using river water. The increase was effected by adjustment of the scrubber throat.
3Based on L/G rate of 1240 liters/SCM of gas treated.
-------
3.2 EMISSIONS AND SOURCES
Emissions from ten sources, are shown in Table 3-2. Of these, the windbox
exhaust system is the most important because of the number of pollutants to be
controlled and the high volume flow rate of exhaust air to be handled. The
process equipment exhaust system is second in importance for the same reasons;
this system (estimated at about 2400 son per Mg of sinter poduct) may control
the discharge hood, sinter breaker, and hot screens. The sinter cooler usually
has no control of emissions except for those at the material tranfer points.
Cold screens, conveyor transfer points, and conveyors may or may not be (but
should be) controlled.
At this time, there are no National Performance Standards for Sinter
plants. Standards of Performance for New Stationary Sources (40 CFR, Part 60,
FR 38, 84, Wed. May 2, 1973) impose no standards for abnormal operating con-
ditions, but require reports from plants when controls exceed mass emissions
levels for compliance tests. State regulations do, however, impose limitations.
Some representative state regulations are shown in Table 3~2.
3.3 TYPES OF CONTROLS USED
3.3.1 Windboxes
Electrostatic precipitators (ESP's), scrubbers, and cyclones are the
principal current means for controlling emissions from the windboxes of sinter
machines, while fabric filters are the preferred method for control at other
points: sinter discharge, crushing, screening, material transfer. The distri-
bution of air pollution control equipment used on windboxes of 45 sinter plants
follows:11
Type of Control Number of Plants
ESP 22
Cyclones 11
Scrubbers 9
Baghouse 1
Steam ejector 1
Mechanical 1
TOTAL 45
23
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TABLE 3-2. UNCONTROLLED POLLUTANT EMISSIONS FROM SINTER PLANTS AND ESTIMATED
CONTROL REQUIRED.
Production
Rate
Facility, Pollutant rig/day
(1) Windbox Exhaust System
Participates, filterable 900
5400
13600
Participates, conden* All rates
slble
SO, All rates
(,
CO All rates
HC All rates
NO. All rates
^
Fluorides All rates
(2) Product Handling
bxnaust systein
Partlculates 900
6300
13600
(3) Process Equipment
(a) Raw Materials Handling
(b) Discharge Hood
(c) Sinter Breaker
(d) Sinter Cooler
(e) Hot Screens
(f ) Cold Screens
(q) Conveyor Transfer
Point
(h) Conveyors
Estimated Emissions, Kg/hr, Unless Otherwise Stated
Control
From Primary State Efficiencies Possible, Opacity Monitoring
Collectors Regs. Reg. Required Standard4 Standard Requirements
82
572
1224
0.2 gm/kg sinter
112 ppm7
0.9 gm/kg sinter
7000 ppm8
19 gm/kg sinter
2.4 gin/kg sin-
ter8
130 ppm9
0.7 gm/kg sinter
O.OS gm/kg sin-
ter
Uncontrolled
m11
918
1983
8-16-23 2,6-3-5,6 90-80-72 Participate: Operating
65 mg/kg strand Parameters'-
feed
33-37-38 5,6-2,fi-3 93-93-94
37-43-61 5,6-3-2,6 97-96-95
None Ap- - 120 rag/kg strand
pi 1 cable feed
500 ppm 1, 2. 3 None
None
Best Avail . 4
Mone 1 * Opac1tyb'c
None 1 * Opacity
None -
7-13-23 2,7-3,12-5,13 98-97-94
26-32-33 2,7-2-12,5-,13- 99-99-99- 25 mg/tstd.nr 1 % Opacity
36-37-56 3-5,12,13-2,14 99-99-99
1 %
1 %
1 %
1 %
1 1
1 *
1 1
1 2
al. Strand feed includes all materials fed to sinter machine except the hearth layer.
2. If wlndbox exhaust and process equipment exhaust emissions are combined prior to entering 3 common control device the combined discharge
standards for particulate matter are prorated on the ventilation rate of process exhaust system.
The opacity standard and opacity monitoring requirements do not apply if:
1. A scrubber or other control device 1s used which causes interference with opacity monitoring.
2. Windbox exhaust and process exhaust emissions are combined prior to entering a common control device.
clf one opacity standard does not apply, the operating parameters of the exhaust system control device are monitored (pressure drop and gas flow
rate through control device and liquid flow rate to control device as applicable).
Based on source test emissions after the mechanical collector, Windbox particulate emissions averaged 2,06 pounds per ton of strand burden. State
regulations define particulate matter as any material that exists as a solid or liquid at 7CTF and 14 Ib/1n2 absolute pressure.
Pennsylvania: Allowable - 0.76 (20 Ib/ton feed x W tons feed/hr)0'42 or 0.02 gr/dscf whichever ts greater (for exhaust rates over 150,000 scfm,
0.02 gr/dscf is greater).
Illinois Rule 203d (2): process weight for new sources x 1.2.
Maryland
^Indiana
Equivalent process weight regulation - based on total strand feed (excludes hearth layer), Test data, indicates that production is. approximately
43 percent of total strand feed.
Based on source test data in Table 3-4.
Based on source tests at Plants E and G.
a
Based on source tests at Plants E and 5.
10Based on source tests at Plants F and G.
Based on 22 Ib particulate per ton of product.
120hio
Process weight regulation - Based on total strand feed (excludes hearth layer). Based on test data, production Is judged to be 43 percent of
total strand feed.
Grain loading regulation - Based on test data; total air flow rate of processing operations is estimated to be 68,300 dscf/ton sinter
product.
15Values set by EPA-AISI analysis.
24
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The control of emissions from windboxes is made difficult by factors such
as the high volume rate of gas, the sometimes high resistivity of the dust and
the presence of hydrocarbon vapors and fluorides. Because of state opacity
regulations, and the need to recycle oil-bearing wastes (see discussion under
emissions from sintering), steel plants are being required to use high energy
scrubbers and wet ESP's. * * Generally, any final control unit will be
preceded by a mechanical collector to remove the large, heavy, abrasive
particles.
Electrostatic Precipitators (ESP's)
Sinter plant ESP's are typically single-stage, horizontal-flow units.
F-igure 3 shows the gas flow plan. The power supply generally consists of a
11
CLEAN GAS FLOW
COLLECTING PLATES ARE
TIED INTO THE TOP SHELL
OF THE PRECIPITATOR
SPACER PLATES AT THE
BOTTOM KEEP PLATES
PROPERLY ALIGNED.
PLATES CAN BE RAPPED
SEPARATELY OR IN
SECTIONS BY A BAR
CONNECTING THE ENDS
OR BOTTOMS.
THE MAIN DISCHARGE
ELECTRODE FRAME IS
SUSPENDED BY POST
INSULATORS FROM THE
PRECIPITATOR ROOF
THUS MAINTAINING
ELECTRICAL CLEARANCE
FROM GROUNDED
COLLECTING PLATES.
USUALLY STIFFENER
BAFFLES ARE PRESENT
ON ENDS TO HELP
MINIMIZE DUST /
EROSION. /
DIRTY GAS FLOW -* ^
Figure 3. Typical duct electrostatic precipitator.
single phase, high voltage transformer, appropriate control equipment, and a
bridge rectifier circuit, which may use a mechanical type of rectifier, or the
newer Kenotron vacuum tubes, selenium, or silicon rectifiers. Normal trans-
former ratings are between 25 and 50-kva, 440 volt primary and 50 to 75 kv
secondary. The collection area consists of duct collection electrodes with
high voltage discharge electrodes uniformly spaced and of uniform length.
25
-------
Collecting electrodes (metal surfaces that collect the particles) are at
ground potential and are connected directly to the frame of the precipitator.
Dust is removed by rapping or vibrating the plates. Material loosens and falls
into collection hoppers for subsequent removal. Chambers and hoppers are
usually fabricated of plain carbon steel, with or without thermal insulation.
Plain-carbon steels have suffered from the corrosive action of acids formed in
the gas by reaction of sulfur oxides with moisture. A high sulfur level in
feed raises the acid dewpoint of the gases, leading to possible condensation.
Air in-leakage will lower the temperature of the gases, thus favoring conden-
sation. This corrosion increases maintenance costs, e.g., for replacement of
electrodes, collector plates, and internal supporting members.
The collection process consists of charging dust particles with a corona
discharge and then passing them through an electric field where they are
attracted to the collecting surfaces. The collection efficiency of the ESP
depends upon the effective collecting electrode area of the ESP, the particle
migration velocity, and the gas flow rate through the ESP. The particle
migration velocity depends in turn upon its size, the strengths of the elec-
trical fields in which the particles are charged and collected, and the vis-
cosity of the gas. The resistivity of the dust is a factor of major importance
in the design and application of dry precipitators to sinter plants. Changes
in the composition of the sinter can cause changes in the resistivity of the
dust, the most significant sinter-relationship being that between the basicity
of the sinter and the resistivity of the dust. Burdens suitable for production
of low basicity sinter tend to yield a dust with proper resistivity for efficient
precipitator operation (resistivity less than 2 x 10 ohm-cm). In the steel
industry, there has been a trend toward increasing the basicity of the sinter,
often after installation of a precipitator. The reason for the trend is to
improve the economics of production. Limestone is needed in the blast furnace
to remove certain impurities such as sulfur from the iron. If this flux
material is charged into the furnace as limestone, the heat to calcine the
stone is supplied by lump coke, a high cost fuel. If the limestone is added,
either wholly or in part, to the sintering process, calcining takes place
there. Since the fuel for sintering is often relatively less expensive (e.g.,
Cuban coal, coke breeze), the cost of energy for calcining is lower in the
sintering process than in the blast furnace.
26
-------
High basicity sinter production yields a dust with a high resistivity
(above 2 x 10 ohm-cm). This is generally too high for good removal using a
dry ESP, and the trend from low to high basicity sinter has thus caused an
increase in emissions from the windbox stack. The high resistivity of the high
basicity sinter dust can cause severe sparking between electrodes. When this
occurs, the power input must be reduced to reach the desirable spark-over rate
of 50-100 sparks per minute. As a result, efficiency can drop 5 to 20 percent
below design values.
Oglesby et al. have reported that ESP's for sinter plants are generally
designed for a gas velocity of 1.3 m/sec; an inlet gas temperature of 118°C
(although 150°C would be better for high basicity sinter); an electric field of
3.2 kV/cm; an inlet dust loading of 2.3 gms/actual m (1 gr/ft ); a precipitator
3 -I r
power rating of 251 watts/100 m gas per minute (251 watts/3500 cfm).
Depending on the characteristics of the particular operation, these parameters
may be altered considerably. The resistivity of dust from a plant making
12 11
sinter at a basicity of 4 was 1 x 10 at 150°C. Using power requirements
for flyash of equivalent resistivity indicates that an ESP for this dust should
3
have a corona power rating of 450 watts/100 m gas per minute, instead of
generally used 251. To meet a state regulation of 33 kg/hr (73 Ib/hr) for a
5.400 Mg/day (6 tons/day) sinter plant (Table 3-2) with the design inlet gas
o
loading of 2.3 gms/actual m , a collection efficiency of 98.5 percent would be
required. (ESP efficiencies have been reported to exceed 99 percent .) The
? 2
ESP would require an estimated 49000 m (527000 ft ) collecting plate area, and
73000 watts of power. In this case, the generally designed ESP would be
considerably under designed.
If hydrocarbon vapors are present, opacity regulations are not usually
met. One plant using an ESP showed a condensable hydrocarbon concentration in
the outlet gas of 1.2 mg/scm (0.00051 g/dscf).
Fabric Filters
A fabric filter has been installed on the windbox discharge of two US
plants.16'17'18 One plant (Kaiser) has operated the baghouse fairly successfully
for several years. The plant is in a warm climate where the year-round high
27
-------
temperatures help to avoid plugging the bags with condensation of hydrocarbon
vapors. The plant has found it necessary to restrict oily feed materials to
avoid problems with condensed hydrocarbons. A second plant, operating in a
cold climate, has had difficulties with blinded bags, in consequence of which
there has been increased emissions. A program there is underway to overcome
this difficulty by changing to a slicker cloth bag material. At the same time,
the construction of the bag is being altered to minimize its susceptibility to
rupture. The value of these changes has not been yet determined.
Apparently collected dusts are pyrophoric. Heating takes place in the
collection hoppers due to hydration of the alkali oxides which are present.
Fire ensues when the temperature reaches the ignition point of the collected
hydrocarbons. To avoid this damage with a baghouse, it has been necessary to
rather severely restrict the use steel plant wastes such as mill scale, blast
furnace sludge, and coke fines. These wastes must then be disposed of in an
environmentally acceptable manner leading to increased costs and a loss of
useful material.
The baghouse at Kaiser's Fontana Mill is a bottom-entry, reverse-load-
clean filter. It consists of 14 compartments (7 per sinter machine), each
containing 184 bags, 30 feet in diameter by 9.6 meters long. The air-to-cloth
ratio is 74 cm/sec (1.47 cfm/sq. ft.) at 10195 cmm (360,000 cfm/min). Actual
inlet conditions were found to be very close to design conditions, and include:
gas temperature, 121°C-150°C; moisture, 6%-10% by volume; particulate, 686-1144
mg/scm; gaseous sulfur, under 500 ppm. The design provided for two baghouses
under a single roof (Figure 5). The gases from the two sinter machines have
been kept separated until discharged into the base of the stack. There were
three reasons for choosing the 2-baghouse design. If one sinter strand were
started cold while the other was running hot, a considerable amount of cold air
would be introduced into this system, producing a cooling effect that could
cause condensation and its attendant problems within the baghouse; since each
machine had an independent fan, and these fans were running at full load, it
was necessary to install those two fans in series with them to supply the added
energy requirements of the baghouse. By maintaining separate gas systems, all
air flow balancing problems between the machines were avoided. Third, the
28
-------
ATM03PHERI
BUSTION
SINTERED MAT'L.
10
TO STORAGE
* r*i
MOVING GRATES
r.o. e*a FIRED
IGNITIOH FURHACl
' .1 I ' '
WIND BOXES
S.P.-20ln WG
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nr
3
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i i
1 I
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S.P.-.5ln WG
MAIN FAN
1100HP 180,000 C.F.M.
DRY CHEH.
FEEDER
CATCH RETURN
TO RAW MATERIALS
S.P.-13'n WG
rVANE POSITION
INDICATOR t
r 1
I
I
COSTER FAH !
ITH VARIABLE j
t
REVERSE AIR PITOT TUBE
AUTOMATIC DAMPER
TO CONTROL
4- -<₯&&* CONSTANT P
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AP ACROSS BAGHOUSE
\
REVERSE AIR BLEEDER
-CLEAN GAS RUE-
HOU8E y '
"""""" "i_J ~"""""""
...J L-
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I. RECORD AP I. RECORD DAMPER
ACROSS BAGHOUSE. POSITION..
2. RECORD MAIN FAN
SUCTION PRESSURE
& CONTROL WITH
BOOSTER FAN DAMPER.
COMTROLS
I. RECORD REVERSE
AIRFLOW.
2. RECORD & CONTROL
A P ACROSS
SECTION BEING
CLEANED.
EACH SECTION
DURING REVERSAL
\xxxx\\
VG
SCREW CONVEYORS
CATCH RETURN TO
RAW MATERIAL FEED
Figure 4. Schematic diagram showing flow and controls for a sinter plant baghouse.
-------
baghouse is installed without a bypass. It was expected that most breakdowns
could be handled on an individual compartment basis. However, with this
separation a major bypassing could be avoided. The design features were
selected based on experience with pilot models and include the following:
1. Valves were stem vertical, flat plate type, and positioned
on the clean air side.
2. Air cylinder rods were kept out of the gas stream, thereby
keeping them cool and clean and extending rod seal life.
3. All mechanical equipment was protected from the heat
and located for easy servicing in relative comfort.
4. Clearance between bags was set at a minimum of 4 inches,
to reduce the probability of the jet from a blown bag
destroying an adjacent bag.
5. Elongated (45 to 61 cm) (18 to 24 inches) bag thimbles
were provided to streamline the gas flow and minimize
the possibility of wear at the bottom.
6. Trough-type hoppers were used for recycling the dust
continuously to the sinter machine feed.
7. Side entry hopper screws, discharging through double
flap tipping valves were installed to avoid maintenance
problems connected with rotary valves.
8. Five sewn-in stainless steel, He!iarc-welded anti-collapse
rings were used per bag. This controlled collapsing when
reverse air cleaning was used, and prevented the bag from
pinching off during reversal.
9. Provision was made to isolate a compartment for entry while
the rest of the baghouse was operating.
10. An independent vacuum cleaning system was provided for
cleaning the cell plates of dust that bleeds through the
bags or comes through broken bags.
11. Completely flexible, easily monitored cleaning system controls
were provided that could be readily varied to suit operating
needs.
The bags selected were made of a 3X112, 8.9 ounce, silicone, graphite,
o
teflon-coated, fiberglass fabric with a permeability of 17 cmm/m (55 cfm/sq
ft.). This material was selected for its superior temperature properties and
chemical resistance. Only 12 bags had been replaced within a years operation.
As aging continued, a bag-replacement rate of 12 per month has been experienced.
Isolated instances of visible plume from the plant stack have been observed
under normal operation. Particulate removal efficiency has been measured at
30
-------
better than 99 percent with a discharge dust load of the order of 4.6 to 9.2
mg/scm.
In operation, temperatures below 150°C are avoided if possible. The
particular gases showed an S03 dewpoint in the neighborhood of 93-121°C.
Condensation of S03 in the baghouse would be fatal to the bags in precipitation
of gypsum in the filter fabric.
The fabric filter achieves only about 40 percent efficiency in removing
oil charged to the strands. Because the light ends of the organic emissions
are thus inefficiently collected, a significant stack emission will result if
the oil to the sinter strand is excessive. A 40 percent opacity rating will be
obtained if one or more of the following five conditions are met:
1. if the feed is greater than .01 percent oil,
2. if the coke breeze feed is greater than .1 percent oil,
3. if the baghouse dust contains more than 1.0 to 1.5 percent oil,
4. if the stack condensibles at 0°C equal or exceed 4.6 mg/scm,
5. if water fed to the pug mill contains greater than 0.01 percent
oil (the feed is 10 percent water).
Scrubbers
High energy scrubbers offer better control of particulate condensible
hydrocarbons, and, in addition, offer control of the fluorides and sulfur
dioxide contained in sinter plant windbox gases. Both the venturi scrubber and
the stream hydro scrubber have been tested in actual operation.
Armco's Middletown, Ohio sinter (recycle) plant, rated at 2395 Mg/day
sinter product, uses a high energy, variable throat, orifice venturi scrubber
i ?
with an adjustable plug. The windbox gas cleaning system (Figure 5) consists
of, in sequence, dry primary and secondary cyclones, two induced draft fans in
series, the wet scrubber, and a cyclonic mist eliminator with a stub stack.
The system is designed for 8630 acmm (304,500 acfm) at 150°C with a venturi
pressure drop of 114 cm w.c. with an outlet loading of 46 mg/scm. Water is
supplied to the scrubber throat and inlet at 6813 ppm recirculated from the
mist eliminator tank. Makeup water to the mist eliminator is at 1514 ppm from
other sinter plant noncontact cooling water sources. A blowdown of 1230 ppm
from the bottom of the mist eliminator is pumped to the blast furnace sludge
settling pond and becomes part of the blast furnace system blowdown. The pH of
recirculated water is controlled using hydrated lime.
31
-------
oo
Primary
Cyclones
Recycle Plant
Wii.dbox Gases
30^,500 ACPM
@ 300°F
Figure 5. Recycle plant, Middletown Works scrubber system flow diagram.
-------
Armco's Houston Works 1430 Mg (1360 kkg/day) sinter plant installed a Lone
Star Steel Steam-Hydro scrubbing system in 1975, to control stack opacity.12'19
This system was considered the best, economically, due to the availability of
low cost steam generating capacity at the time of initial installation. This
may no longer be the case due to sharp increases in the cost of natural gas.
The system (Figure 6) consists of six parallel units, one serving as a spare.
Each unit consists of (1) a combination steam-water nozzle where the steam
atomizes the water droplets, (2) a mixing tube, where the particles and droplets
contact, and (3) twin cyclone separators where the particle-laden droplets are
removed and the clean gas is discharged through the stub stacks. An existing
induced draft fan supplies dirty gas to the units, and the motive force of the
steam forces the gas through the gas cleaning system. The system reduced an
inlet gas particulate load of 1146 mg/m to 68.9 mg/m . Actual emissions
translate to 17.5 kg/hr versus a regulation allowable 41 kg/hr. Some periodic
opacity problems exist.
Tests made on normally operating existing steam hydro units show an
38
opacity rating of 7.4 percent (6 min average, EPA Method 9). This opacity
value would exceed limits under consideration for proposed New Source Per-
formance Standards.
Data obtained using a pilot venturi scrubber (Kinpactor, adjustable throat)
indicate that hydrocarbons (oil) are collected in the demister that follows the
scrubber proper. The oil is collected either as droplets or adsorbed on solid
particles.
Control of hydrocarbon emissions by this venturi scrubber system was shown
to depend upon three factors listed in decreasing order of importance: the
concentration of hydrocarbons in the inlet gas; the particle size of the hydro-
carbon mist; the pressure drop across the venturi throat. The relative impor-
tance of inlet oil levels in emission control was shown by regression analysis
of the data: the correlation coefficient between the oil outlet concentration
and oil inlet concentration was 0.49; that between oil outlet concentration and
venturi pressure drop was 0.06. These data were taken over a pressure drop
range for the venturi of up to 115 cm w.c. It is apparent from these correla-
tions that the most critical factor in controlling oil emissions when using
33
-------
such a scrubber is the control of oily emission from the sinter strand itself.
To a lesser extent, the maintenance of adequate pressure differential is
needed.
As a result of this inherent behavior of the system, the efficiency of
oil removal seldom exceeded 80 percent. Hydrocarbon emissions limits set for
the scrubber were not greater than 69 mg/scm. To meet this level, it would be
necessary in this system to limit the hydrocarbons in the inlet gases to a
value not exceeding 230 mg/scm.
Several methods of control could be used in conjunction with the scrubber
to insure desired hydrocarbon emission abatement, when the quantities of
hydrocarbons released from the sinter bed exceeded the capability of the
venturi scrubber. These include: regulating the hydrocarbon content of the
burden feed material; adjusting the ratio of ore feed to other materials in
the sinter mix; recycling a portion of the oil laden windbox gases through the
burning bed; incineration of the stack gas after wet scrubbing. However,
incineration is not a viable approach from either an investment or fuel stand-
point.
Scrubber water discharges are either "once through" or recycled through a
thickener. The thickener underflow is decanted with centrifuges or vacuum
filters. The filtrate is returned to the thickeners. The filter cake is
returned to the sinter plant. When high energy scrubbers are used, magnetic or
chemical flocculation may also be required.
Where scrubbers are used, a range of net plant raw waste loads in the
untreated wastewaters are as follows:
Raw Wastewater Treated Effluent*
flow, £/Mg of sinter 434 - 1420
susp. solids, mg/& 4340 - 19500 25
oil and grease, mg/£ 457 - 504 10
fluoride, mg/a 0 - 0.644 20
sulfide, mg/i 64 - 188 0.3
pH 0-9
*These are estimated results of the best available technology economically
achievable for wastewater treatment: (1) classifier, (2) thickener with
chemical flocculation, (3) thickener overflow recycled to scrubber with
blowdown treated by settling, aeration, lime neutralization, and sedimen-
tation. An oil skimmer is added to the thickener.
34
-------
Sir.ter
Plant
Stauk
Gases
cn
Steam
B0,000#/Hr
t
Sta^k
3:
Mixing tut>e
Steam-Hydro
Units
xa
V
i
1
Cyclones
Lima
Bin
pH 5.6
TSS 1500 PPM
Mixer *
D I
^
Feeder
m
Meutralizatior.
Tank
1
I
To Blast Furnace
Thickener
PH 8.5
Plocoulators
Slurry Pumps
14J4 GPM
TSS 350 PPM
Recirc. Pumps
370 GPM
Lamella
Separators
Make-up
Wat-jr
1^6 GPM
pH 9.1
TSS 15 PPM
Figure 6. Scrubber plant, Houston Works, scrubber system flow diagram.
-------
Wet Electrostatic Precipitators (WESP'S)
Wet ESP's appear to be a potential feasible alternative to wet scrubbers.
The water wash provides a clean collecting surface, tends to prevent reentrain-
ment of the particulates, and cools the gas with attendent condensation and
collection of some of the hydrocarbons. Water may be injected ahead of the
WESP to saturate the exhaust gas.
Most of the experience with WESP'S has been acquired while testing pilot
plants. One full scale system is in operation and is not performing satis-
factorily. However, a full-sized WESP module at another plant has operated
since August 1976, together with associated liquor handling facilities for
control of a windbox gas slip stream (of about 2000 acm/min). '
Two types have been tested in pilot plants. One, supplied by the MikroPul
Division of the U. S. Filter Corp., was a horizontal flow precipitator con-
tinuously wetted by water sprays directed at the inlet baffles and internal
21
components. The equipment arrangement is shown in Figure 7. A slip stream
of windbox gas was fed to this system from a sampling location downstream
of large twin cyclones and upstream of a full-steel dry ESP. The pilot study
ESP liquor-handling system was operated in once-through and recirculation
modes, both with and without pH control for the recirculation mode.
The throughput rate was limited by the existing capabilities of the WESP
pilot unit. When operated up to maximum gas flow rates thus limited, the
outlet particulate loadings were consistently less than 69 mg/dscm, regardless
of the gas flow rate or strand mix tested.
The main difficulties with this system were those associated with opera-
tion in a recirculating mode using minimum blowdown. The recirculating liquor
tended to have a pH of 3 and to contain 500 ppm of fluoride ion. It was
excessively corrosive for the design of facilities utilizing available "cor-
rosion resistant" austenitic stainless steels, etc., Type 316L. When pH
control was tested, it became necessary to provide a pH of 10 liquor to the
sprays in order to control the WESP discharge water at a pH of 7. As a result,
calcium and magnesium carbonate deposition occurred in all parts of the system
including WESP spray nozzles. It was concluded that a satisfactory WESP system
36
-------
TO SPRAYS
rixw ..us
-J IX
*«2
1
c
PRESCRUBBER
TO SPRAYS
VSS?
MAKE-UP
WATER
CLEAN GAS
OUT
FAN
CAUSTIC
I
SLOWDOWN
nilnt WESP tftst SRtim at a sinter olant.
-------
DEMONSTRATION
FAN
HIGH VOLTAGE WATER
PRESCRUBBER WATER
DRAIN I/ATER
MAKE-UP
WATER
TO DRAIN < * V
4
Figure 8. Full scale WESP demonstration at a sinter plant.
-------
would have to be capable of being operated in the recirculating acidic liquor
regime. The second WESP tested was a Fluidlonic Systems Division of Dart
Industries, Inc. model. This design (Figure 8) utilized a cyclonic-entry
prescrubber spray system and straightening vanes, above which was located a
precipitation section. The high voltage section consisted of a concentric
array of a discharge electrode (an expanded metal cage) and fiberglass rein-
forced plastic collection cylinders. The cylinders were continuously flushed
with a water film provided by water distributors mounted on the top of the
cylinders. The system, including its water handling facilities, was modified
based on early pilot tests, in a full-size single WESP module was installed to
clean windbox gases. The unit was installed downstream from a full-scale dry
electrostatic precipitator.
Baseline tests were made with a sinter plant base-to-acid ratio equal to
0.85. The system was operated at a maximum gas flow rate, typically 1925 acm/m
at 120°C. This rate was slightly less than half the entire flow rate of
windbox exit gases from the sinter strand. Power consumption at the primary
side of WESP high voltage supply transformer was typically 20 amps and 210
volts, i.e., the WESP required about 1 percent of the power that would have
been consumed by a high-energy scrubber for an equivalent outlet gas clean-
liness. The tests conducted under baseline conditions showed outlet particu-
late loadings ranging from 7 to 50 mg/dscm. The average loading was 27 mg/dscm,
including all the dry particulate matter and the organic-solvent extractable
matter (hydrocarbons). The single test result which showed 50 mg/m outlet
3
loading corresponded to an abnormally high inlet loading of 1960 mg/m .
Outlets loadings were also affected by the basicity; when basicity was
changed from 0.85 to 1.5, the particulate plus hydrocarbon loading increased in
the outlet gas from 27 to 41 mg/dscm.
In assessing the performance of this WESP it is important to recognize
that the system operated on a gas stream that had previously been treated with
a dry electrostatic precipitator. With this precipitator turned off, dust
concentrations at the inlet to the WESP were increased to values in excess of
4500 mg/dscm, and the emissions from the WESP increased to as much 103 mg/dscm.
Despite the fact that the dry ESP was in operation, emissions through the WESP
39
-------
during a cold start of the sinter strand exceeded those associated with steady
state operations. (For an inlet loading of 2450 mg/dscm, the outlet loading
was 210 mg/dscm of which 13 mg/dscm was hydrocarbons and the balance inorganic
(nonextractable particulates). These abnormally high emissions were reported
to prevail for only up to about one hour.
For every operating condition the opacity of the fumes from the demonstra-
tion stack was less than the main stack. However, at times plume opacities in
excess of 20 percent can be expected from a full scale system, even at outlet
loadings of 23 mg/dscm or less. It was observed that when gas flow rate
through the WESP was reduced, the outlet particulate loadings were corres-
pondingly reduced. It is anticipated that greater outlet loadings would be
obtained at greater gas throughputs. Apparently the performance of this system
is affected by the gas throughput rate.
Gravel Bed Filter
A 24 module gravel bed filter system is under evaluation by the Wierton
Steel Division of the National Steel Corporation. The filter has been used in
connection with windbox gas recirculation and in that mode, the outlet gases
have been cleaned to 23-114 mg/dscm. At dust loadings below 46, the stack is
clear. The filter requires a gas pressure booster fan and reverse flow cleaning
fan. It is a totally dry system, however, with relatively low capital investment.
At this time, with gas recirculation to reduce the hydrocarbon loading, the
filter merits further study. It is of particular interest because the system
is dry and avoids the problems of handling scrubber water. Initially operating
problems occurred in the proper function of the gas valves which control
switching from normal flow to reverse flow for the purpose of cleaning the bed.
These problems have apparently been overcome.
3.3.2 Product Handling
Product handling control is primarily concerned with the sinter breaker,
screens, coolers, and the associated conveyors. These points of emission can
be hooded and the dust aspirated to one or more collectors. The sinter is
generally cooled by air, although water sprays are sometimes used.
40
-------
Mechanical collectors, followed by either fabric filters or low energy wet
scrubbers have been used for dust control. Another technique used in various
modifications is to direct the discharge exhaust to a hood located over the
sinter strand to serve as a (preheated) portion of the process air. Dust so
returned is filtered by the sinter or passed to the windbox waste gas system.
One plant using this approach was unable to sufficiently to move all the
processing exhausts through the strand.
The suppression of dusts by water sprayed onto the hot sinter is an
inadequate emissions control technique. Even the careful addition of water
treated with a surfactant will not eliminate emissions associated with mists or
steam and the spray nozzles require regular and careful maintenance. The
addition of water to the hot sinter causes fractures and spall ing of the sinter
and, in consequence, degrades the sinter product.
The fabric filter is the best demonstrated collecting device for product
handling emissions control. In designing a suitable baghouse, the high abrasion
characteristics and temperature of the dust require special consideration. A
primary mechanical collector could be used prior to the filter to remove large
particles and sparks. Bags made of silicon treated fiberglass, in use with -
reverse air cleaning, have lasted 18-24 months. Air to cloth ratios varied
from 0.74 to 3.7 cm/sec. Most units consist of several compartments, with one
serving as a spare.
The fabric filter can reduce inlet loadings to one hundredth their value
over a reasonable range of gas flow. Better performing units are characterized
by lower air to cloth ratios, wider bag spacing (e.g., 29 cm diameter bags on
35 cm centers), construction that facilitates inspection and maintenance, and
outlet dust loadings of 10-12 mg/scm dry basis. Outlet dust loadings up to 23
mg/scm are within the range of presently operating scm baghouses.
The minimum quantity of ventilation air handled by the product handling
exhaust equipment must be sufficient to assure that the fugitive emissions from
the process are drawn into the collection hoods and enclosures. This amount is
related to the process equipment configuration, hood and exhaust system design.
Thus the necessary exhaust air volume is only nominally related to the sinter
plant capacity.
41
-------
Based upon available test data, a baghouse that controls particulates to
less than 25 mg/scm should show an opacity (visible emission) level of less
than one percent (6 minute averages, EPA Reference Method 9).
3.3.3 Materials Handling
Fugitive emissions escaping the raw material handling equipment are
largely confined within the building in which they are usually carried out, and
primarily affect the worker environment. The normal practice of handling
materials that are moist alleviates the need for hoods and ventilation of
conveyor transfer points. Water sprays can often be used to wet the material
at transfer points.
Water sprays by themselves may be effective on such materials as dry ore.
They are not effective in control of hot fines. Sprays cause steam clouds
which entrain dust, also dust is hard to wet. If water sprays are used in
evaporation with hooding, the moisture is carried to the baghouse where it may
cause problems of bag plugging.
Where fine steelmaking dusts, dry ore fines, dry screened sinter fines,
and_ similar materials are handled, separate fabric filters are the most common
means of control.
There are numerous sinter cooler configurations, and many are forced-draft
rotary coolers discharging through a stack. Cooler exhausts can contain
entrained sinter dust. Most, however, show no visible emissions if the sinter
is properly screened ahead of the cooler. A cooler emission of 1.7 kg/Mg of
sinter has been measured, however, and at least one plant has installed a
23
fabric filter on a cooler discharge.
3.3.4 Process Modification
A recent variation in the design and operation of sinter plants is to
recycle about 40 percent of the gases from the windboxes at the entry of the
sinter machine to the top of the bed at the discharge end of the sinter machine.
This has two advantages. One is that it reduces the quantity of gas passing
through the final control device, thereby reducing the last emission rate at
any given concentration of particulates. The other is that it provides control
of emissions of hydrocarbons. That portion which is recycled is incinerated
partially when it is passed through the glowing bed of sinter.
42
-------
Wlndbox gas recirculation combined with a gravel bed filter may find a
place for controlling participates at future sinter plants. The energy require-
ments are estimated to be less than two percent of the amount required to
;s
25
24
produce sinter. Preliminary test data indicate filterable particulates may
be reduced to the same level achievable with a high energy wet scrubber.'
Typical inlet gas loadings reported for the tests were: particulate matter 497
mg/scm; condensible hydrocarbons 160 mg/scm. The filter outlet particulates
have ranged from 23 to 114 mg/scm; at loadings below 46, the stack shows no
opacity. The effects of inlet dust concentration, gas flux rate (cm/sec), and
particle size are under investigation.
One plant has gained better control of windbox emissions by adding the
collected product handling emissions to the windbox gases as they are conveyed
into the windbox baghouse. The addition of the hard abrasive particulate
material from the product handling baghouse has been demonstrated to condition
25
the windbox emissions for better collection at the windbox control baghouse.
43
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4.0 ABNORMAL OPERATING CONDITIONS
This section discusses abnormal operating conditions and techniques for
eliminating or minimizing discharges thereunder. Abnormal operating conditions
(AOC) can occur in the sintering process and in its control equipment. In
addition, startup and shutdown .difficulties are included. These are all addressed
relative to resulting increases in pollution. From this perspective, their
causes may be inherent difficiencies in the design of equipment relative to
standards set for pollutant control, changes in operating practices and feed
material, limitations in the applied technology, equipment or power failure.
In assessing AOC's, therefore, attention is given to the role of and need for
redesign of control equipment, preventive maintenance, redundant capacity,
sensing impending upsets, and alternative strategies for response to AOC's at
the plant. The application of various strategies in a given plant will depend
on the availability of space and the characteristics of the particular system,
and requires process engineering effort.
4.1 PROCESS RELATED AOC'S
4.1.1 Startup
When the sintering machine is started after a shutdown of one turn or
more, it requires about an hour for the process to achieve full operating
temperatures. During this period of time, condensation may take place in
ductwork and in dust collection equipment. If the latter is a baghouse, the
condensation may cause plugging of the bags and it may be necessary to bypass
this type of pollution control during startup to prevent plugging. Precipi-
tators are usually not powered fully until the gases have become warm enough to
evaporate condensed moisture (Section 4.2). In both cases, a cold startup
involves an hour or so of uncontrolled emissions, which can vary from 400 - 750
yc
mg/scm. Startups can occur once a week, due to normal downturns.
A cold startup can result in increased emissions (e.g., a cooler gas will
tend to have higher hydrocarbon loadings). No data are available to show the
44
-------
extent of additional emissions. Mazer, et. al. show an inlet loading increase
(to a Wet ESP) from a baseline value of 900 mg/dscm to a cold start value of
2450 mg/dscm. Outlet emissions (for the Wet ESP) increased from 23 to 210
mg/dscm, with a threefold increase in outlet hydrocarbon loadings from 4.6 to
13 mg/dscm. One advantage of a high energy scrubber on the windbox gases is
that this type of equipment shows substantially no decrease in performance
under startup conditions.
4.1.2 Shut down
Stopping the sinter strand without stopping the fan(s) can result in
burn through of the ignited burden while it remains stationary. This allows
the temperature of the windbox gases and the characteristics of its pollutant
load to change.
The frequency depends on how reliably the systems supporting the sinter
strand perform without upset. The duration would be expected to be about 25
minutes, or the time required for burn through at normal strand speed. No data
or estimates of the extent of additional emissions are available.
Normal shut down usually involves reversing the startup procedure, e.g.,
stopping the main fan and strand. No increase in emissions is anticipated from
such a shut down. Some increase in fugitive dusts would be expected as the
strand is cleared of burden, if this is done after the fan is stopped.
4.1.3 Abnormal Operating Conditions
The major AOC's of a sinter plant are mechanical and electrical. The
major problem in operating the sinter plant is maintenance. The raw materials,
and especially the sinter, are highly abrasive. Special materials of con-
struction and continual attention to points of wear are mandatory. Distortion
of the grate bars due to heat allows an excess of the sinter feed to pass into
the windboxes. Special alloys for the grate bars and the use of a hearth layer
can relieve this condition. Excessive leakage of air into the process overloads
the suction fans and the dust collecting equipment. This can be avoided by
maintaining machine seals, eliminating holes in the sinter bed, eliminating
holes in the ductwork, and persistently maintaining the flapper valves which
discharge dust from the windboxes and the suction mains.
Good maintenance, periodically scheduled during reasonably frequent
planned down times, is the best way to alleviate the effects of malfunctions.
45
-------
Plant shutdowns for one eight hour turn each week or two to do routine main-
?fi ?7
tenance are common practice. ' What is done will depend on the needs
identified by daily inspection of the operating system, and is best illustrated
by example. The following exerpt from one of the plants maintenance schedules
shows thorough attention to 16 mechanical items, 4 electrical items, and 12
28
labor items considered necessary at the time.
MECHANICAL
1. Changed 3 crusher teeth. Tightened loose bolts in teeth and
hard surface welded door.
2. Changed discharge deck plate; tightened bolts in leaf springs.
3. Changed 6 bags and stripped #4 cross conveyor for cleaning,
changed V-belts on same, Main Stack Baghouse. (4 men-32 hrs).
4. Changed both 24" x 38" bend pulleys for counterweight pulley.
5. Repaired and readjusted hearth layer gate - insulated new
swivel hangers.
6. Changed pallets and replaced 3 axles and wheels.
7. Repaired scrapper (will change 1/7/77 with new assembly).
8. Repaired and replaced scrapers and clamps on seven conveyors.
9. Changed lo-speed drive reduction coupling.
10. Pulled pallets for furnace drilling. Blew out impulse lines
for all furnaces.
11. Replaced 30' section of 4" diameter pipe for make-up strainer
water.
12. Blew out spray headers and repaired water leak for dust
suppression line.
13. Repaired doors on screening building.
14. Welded patches on windboxes as needed.
15. Welded fan blades and rebolted wear liners - rebalanced fan.
16. Checked and made repairs to drags.
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ELECTRICAL
1. Cleaned and tested tilt switches.
2. Installed safety disconnect switch at machine.
3. Cleared ground terminal block at sinter cooler feeder.
4. Furnished temporary lighting and welding equipment.
LABOR
1. Cleaned sinter feeder decking and inclines.
2. Cleaned standard feeder decking, head to tail.
3. Cleaned sinter breaker.
4. Cleaned return fines conveyor.
5. Cleaned hot fines floor.
6. Cleaned operating area floors.
7. Cleaned top of store room.
8. Cleaned burden mix conveyors.
9. Cleaned screen decking.
10. Cleaned burden materials system.
11. Cleaned and emptied roll feed hopper.
12. One laborer worked in Main Stack Baghouse.
In response to increasingly stringent environmental control regulations
which require reduction in the discharge of steel plant waste products to the
atmosphere, receiving streams, and solid waste disposal sites, sintering
plants have been and probably will continue to be recipients of increasing
1 q
quantities of materials previously disposed of to the environment. This
can result in alteration of the operation in terms of departure from conditions
for which the control system was designed. The base to acid ratio (B/A)
and the concentration and characteristics of reverts both have significant
effects on windbox aerosols. While the mechanics by which these factors
exert their effects are not completely established, the effects have been
repeatedly observed. An increase in the B/A ratio usually is accompanied by
13
an increase in the concentration of KC1 and NaCl fume generated upon sintering.
Blast furnace flue dust can contain K,,0 and Na^O distilled from the blast
furnace burden. Thus, flue dust contributes to the generation of hard to
47
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remove KC1 and NaCl fume in the sinter plant windbox aerosol. Mill scales
charged to the sinter mix may contain oils from the rolling operation. These
would enhance the hydrocarbon concentration of the sinter plant aerosol. Other
reverts that may contribute adversely to the sinter strand aerosol include,
e.g., filter cakes from water treatment facilities which provides increased
amounts of hydrocarbon and chloride, and coke breeze which also contains hydro-
carbons.
Transient departures of any of these factors from their design levels can
alter the pollutant load in the gases fed to control systems; if the departures
are sufficiently great, they can alter the emissions from the controls. Per-
sistent departures from normal operation (e.g., making a sinter of higher
basicity than that for which the system's controls were designed, Section
3.3.1) can result in continuous excess emissions.
The production of sinter of higher basicity can alter the resistivity of
particulate emissions and lead to lower ESP efficiency, with a corresponding
increase in emissions. The effect is intermittant if due to malfunction in
feed bins such that excessive fluxes are added to the strand feed mix. It is
persistent if increased basicity is maintained.
Increased strand loading with oil-bearing materials can raise the inlet HC
load to the ESP and lead to increased emissions. No data or estimate of the
extent of additional emissions are available.
Excessively oily or greasy mill scale in the burden mix can produce a blue
hydrocarbon plume, the intensity of which, in the case of control with scrubbers,
tends to be inversely proportional to the pressure drop.
Lack of control of burden moisture, or fuel, or ignition can lead to poor
quality sinter with increased dust loading to the gas cleaning device. Good
control of these factors will alleviate the problem. No data are available
concerning the increased emissions; loadings of 2.5 to 10 g/kg of product would
be expected.
Improper ignition yields either poor, spotty burning leaving unsintered
material over the sinter bed surface, or if too intense, produces slagging over
the bed surface leading to reduced sintering rates. Both are related to the
proper distribution of coke in the burden. Unsintered material can cause
increased emissions at the discharge end of the strand.
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During burden preparation whenever fuel is not properly mixed throughout
the bed some of the feed will not be properly sintered because there is no
fuel available in the immediate vicinity. Where fine BOP dust is added to the
burden, any lack of thorough mixing can lead to high dust concentration spots
on the strand, and this leads to higher emissions. Where excessive oil occurs
in spots resulting from lack of mixing, intermittant high stack opacities can
occur. This would lead to increased emissions into the windbox and at the
discharge and product handling stages of the process.
The key to minimizing abnormal emissions in the sinter plant is to take
advantage of the continuous nature of the process and to pay careful attention
to accurate proportioning of the feed material and adequate mixing to produce
a uniform feed.
Use of excessive oil-bearing materials. There is some evidence that a
given high energy venturi scrubber system may effectively reduce windbox gas
hydrocarbon loadings only if the inlet loading is kept below a level set by the
characteristics of the particular device. Coke, mill scale, and sludge all
contain hydrocarbons. The feed composition must, therefore, be regulated by
limiting the proportions of these (and any other) oily materials. These limits
will depend on the oil content of the materials. One plant recommended that
bedding be regulated so that mill scale and filter cake would not exceed 20
Q
percent and 5 percent respectively of the feed going to the sinter plant.
When an acceptable ratio of hydrocarbon containing feed material to ore is
exceeded, melt shop slag, pellet screening fines, and additional limestone
slag could be substituted to improve the ratio.
Steam failure to steam hydro-scrubbers in series with a fan can result in
increased emissions up to levels contained in gases fed to the steam hydro
unit.
Product Handling
Screening station failure can lead to accumulation of unscreened sinter.
If this is handled with front-end loaders and screened using unhooded screens,
substantial quantities of fugitive emissions result.
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When a baghouse is used, a bypass stack is usually installed upstream.
This is opened to deliver gas directly to the atmosphere when its temperature
is below a set value (about 65°C), to avoid condensation in the bags and
plugging.
4.2 CONTROL EQUIPMENT RELATED AOC'S
There are ususally several pollution control systems operating in a
sinter plant, as discussed in Section 3.0- Most of the systems have common
features, i.e., ducting, fans, monitoring devices, and one of the three generic
types of control devices. Therefore, many of the AOC's are common to more than
one of the systems. Where a listed AOC occurs in only one of the systems or is
more prevalent in one of the systems the narrative will provide this information.
4.2.1 Startup
Startup includes bringing the system on-line after a shut down for
maintenance, rebuild, or strike, and bringing a new system into service.
Precipitators
Warmup
Most precipitator manufacturers recommend not energizing the precipitator
until the gas temperature entering the precipitator has reached 66 to 93°C.
Some prefer to have the unenergized condition remain for some time after this
point to allow the collecting plates and wires to reach these temperatures. The
intent is to drive off moisture which tends to condense on the internal surfaces.
Condensed moisture is a problem for two reasons. On the collecting plates and
wires it may cause collected dust to cake, leaving a layer not removable by
normal rapping. Secondly, the frames that support the discharge electrodes
(wires) are stabilized by insulators that attach to the grounded walls of the
structure. Moisture on these insulators will cause dust to stick providing a
conductive path across the insulator. This "tracking" can burn out the insula-
tor, thus grounding a section of the precipitator until it can be replaced.
Startup of an entire precipitator installation occurs frequently (at least once
a week in a sinter plant).
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The warmup period is about an hour for the windbox gases. The impact of
the warmup period is varied depending on whether a full or partial precipitator
is involved. Obviously, if a whole installation is involved all the particul-
ate matter discharged from the process will be emitted during this period. If
only one chamber out of a n-chambered precipitator is involved, about one nth
of the total process particulate will be discharged in addition to the emissions
that normally escape the operating chambers. The uncontrolled windbox particulate
concentration is in the range of 450 - 700 mg/scm depending on the efficiency
?fi
of the multiclone or other primary cleaning device upstream.
If an unenergized warmup practice is followed, emissions may be reduced by
energizing immediately upon startup at a reduced secondary voltage level.
Operation at reduced voltage (change from automatic to manual operation, then
adjust voltage manually) means that collection efficiency will also be reduced;
however, reduced efficiency is better than no collection. Reduced voltage,
however, reduces the potential for burning out insulators. The operator might
find it necessary to increase plate and wire rapping (or vibrator) frequency
intensities during this warmup period to reduce plate and wire buildups.
One plant following this practice of reduced voltage energizing has found
that 60 percent of the normal operating voltage gives them good results, i.e.,
no insulator damage and partial collection. Certain types of electrical
control sets make operation at these reduced voltage levels on a temporary
basis more difficult. Most new sets are solid state static switch gear that
can accomodate reduced voltage operation. Older electrical sets, particularly
those with saturable reactors, do not work well under these temporary con-
ditions.
Some plants may find they can operate during startup (without warmup) with
no serious consequences. Experimenting on one chamber reduces the risk
involved.
Preheating the precipitator is another means of minimizing warmup emis-
sions. Use of natural gas just to preheat the precipitator is wasteful from a
fuel economy standpoint, however.
Design of precipitators with individually isolatable chambers permits on-
line maintenance of these chambers and would avoid the need to shut down the
whole precipitator for maintenance. As a result the need to put a whole pre-
cipitator through the warmup period would be reduced in frequency.
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Stack Puff
Stack puff refers to a momentary increase in particulate emissions,
visually recognizable, leaving the process stack. There are stack puffs
resulting from continuous operating problems, but stack puffs during startup
are caused by particulate lying on the dust floor or attached to flow control
louvers in the system reentraining into the gas stream. During a fan or
system shutdown dust being conveyed by the gas stream settles onto the duct
floors, and in the breeching between precipitator and fan. Also, where a
single fan in a multiple fan system is shutdown, dead or low flow areas may
develop in some duct runs leaving dust on the duct floors and flow control
surfaces. Upon startup and shutdown as the fan damper position is being
changed, the settled dust sometimes is picked up by the redirected air flow and
carried out the stack.
The effect of this action is the greatest when the deposits are downstream
of the collecting device where no chance to collect the dust exists. It also
occurs upstream of the collector in which case the net effect is minimized by
the collector.
The frequency in a multiple fan system can be as often as once per week,
to as little as once per year in a single fan system. The duration of the
puffs is widely variable. An estimate is one to five minutes, supported by
observation of these and many other sources. No data or estimates of the
extent of additional emissions are available.
No good corrective action for this AOC can be recommended. If dust
dropout in the flues is an extensive problem during normal operation, it is
periodically (perhaps once per year) necessary to remove the dust to prevent
overloading of the duct structures. Since the dust deposits under normal
operating circumstances, it is unlikely that dust puffs upon startup would be
any less had the flue not been cleaned.
Unbalanced Flow Among Manifolded Fans
This is a startup problem peculiar to systems with multiple fans in a
parallel flow arrangement inducing draft through a common precipitator. The
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startup referred to is that of a single fan when the other system fans have
been in operation. This would occur when one of the other fans is shutdown as
a result of a failure or for scheduled or unscheduled maintenance.
Maintaining an even flow distribution among chambers of a precipitator is
essential to maximizing particulate removal efficiency. In a manifolded fan
system fans tend to draw more gas from the chanbers closest to them (path of
least resistance) than those farther away (in a well designed flow system this
tendency can be minimized by proper plenum sizing and the use of gas distri-
bution devices). Flow control dampers may be located at the outlet of each
precipitator chamber and balance restored manually, but the process is time
consuming. After some experience it may be possible to reduce this time by
having set points marked for the various possible fan combinations.
The consequences of unbalanced flow is reduced total collection efficiency
for a number of reasons. Though a volume increase in one chamber is offset by
a volume decrease in another chamber, the efficiency changes do not average out
because gas flow rate is exponentially related to efficiency. The overall
effect is reduced efficiency. Higher gas flow in one chamber may induce reen-
trainment of dust from the collecting plates.
Insufficient Draft, Fan Malfunction
Fan malfunction, either overheated bearings or motor bearings, motor
overload, or vibration can be sensed by sensor controllers which feed back
to shut down the fan. If so, the altered power to the precipitator can lead to
lower particulate removal efficiency and increased emissions. Such fan
abnormal operation can activate process shutdown if necessary to protect the
motor. Most often, this is an upset that occurs in a control system with
common multiple (manifolded) fans. Insufficient draft results from one fan
being shutdown with a simultaneous failure of a spare fan to start. This upset
potential exists wherever below-freezing temperatures occur. The upset was
reported to have been due to ice in the fan housing. Condensed moisture
accumulated and froze in the housing to a point where movement of the fan wheel
was prevented.
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The fan design, its inlet dust loading, its age, and the frequency of its
regular maintenance all affect the frequency and duration of less efficient
precipitator operation. One plant showed five mechanical fan rapairs in a four
month period, during which nine regular shutdowns followed by maintenance were
scheduled. Presumably, precipitator power adjustment occurred prior to each of
these shutdowns. No data or estimates of the additional emissions are available.
Fabric Filters
Baghouses are generally protected from "cold" inlet gases during startup.
Gases at temperatures below their dewpoint carry condensed moisture that will
promote clogging of the bags when mixed with the solid particulate material.
Moisture can also inhibit bag cleaning by causing the collected material to
cling to the bags. Because of the total interaction between moisture and the
collected particulates, the clogging is not overcome by simply drying the
system with warm gases. The effect of condensed moisture is to increase
pressure drop across the bags beyond the normal 10 - 15 cm W.C. The increase
can lead to back pressure and eventual shutdown for maintenance.
To prevent this effect of moisture, the temperature of the inlet gases is
sensed and if below the setpoint, the controls open a bypass stack, so that the
gases are diverted to the atmosphere until the prescribed temperature is reached.
Emissions during this time (about an hour) are equal to the loadings of the
exhaust gases after only primary treatment in a cyclone or multiclone system,
estimated at 400 - 750 mg/scm.
While such bypassing is a part of normal baghouse operation, the quick and
accurate sensing of the condition of the inlet gases can minimize the attendant
emissions. One plant is testing a Dewcell as an alternative sensor to indicate
more precisely when the gases are above the dewpoint and may be sent into the
baghouse.
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Scrubbers
No data or estimates are available concerning increased emissions under
normal startup of scrubbers.
4.2.2 Shut down
Generally the shut down of pollution control devices, when done upon the
attendant shut down of the sintering operation itself, does not lead to in-
creased emissions. Of course, when failure of the equipment results in the
shutdown of the control device itself while the rest of the sintering operation
is kept going, then excessive emission always occur.
Precipitators
When a chamber of a precipitator is deactivated for maintenance or other
reasons, frequently rapping is continued after the tower is cut off or reduced.
This is done to more effectively clean the plates and thus prepare the system
for maintenance. Under such circumstances, increased emissions would be
expected from this particular chamber until such time as the air flow itself
would be turned off. No data or estimate of additional emissions are available,
nor is this particular operation considered of significance with respect to the
general control level obtainable by precipitators.
Baghouses
No special abnormal operating conditions leading to increased emissions
would be expected from normal shut down of the baghouse.
Scrubbers
No data or estimates are available concerning increased emissions due to
normal shut down of these types of control equipment.
4.2.3 Abnormal Operation ..
Downtime of Control Systems
Downtime of the control system refers to shutdown of the entire gas cleaning
facility. One source of total pollution control system failure is catastrophic
utility failure, i.e., power loss for a section of the entire plant. Several
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plants reported this to occur three times per year to once every five years.
A power failure that affects both process and control equipment causes both
to shut down and, therefore, the immediate environmental effect is small.
If the failure is selective and only the control equipment is affected,
then the sinter process will continue to operate subject to interlock protection
built into the system. It is conceivable to have a power failure that affects
only an ESP without stopping the fans. This kind of upset was not reported by
any plant. What plant practice under these conditions would be is not known.
Pump failure and fan failure due to mechanical or electrical problems
can likewise shut down the total control system. Most of the plants visited,
however, had installed fans and pumps to avoid shutdown due to a problem with
a single fan or pump. With installed spares it is likely that at worst the
capability to clean or provide draft will be reduced when a failure in one of
the control equipment components.
Clarifier rake failure can shut down a scrubber wastewater treatment
system. Such failures result from drive motor breakdowns and mechanical
failures in the rake drive system. Chunks of material or a buildup of coarse,
dense, skirty particulate on the thickener bottom were two things cited as a
cause of rake problems. One plant reported that near union labor contract
negotiation time there was increased frequency of rake failures due to rocks
in the thickener.
Shutdown of the air pollution control portion of the system (scrubbers)
may be avoided during a rake failure if the scrubber can be switched from three
cycle mode to a once through mode of operation. If no spare thickener capacity
exits or no terminal settling basins are in use downstream of the bypass
thickener, the increased solids content of the water will be about 6 - 20 g/Mg
of steel produced. Many of the plants visited did have terminal settling
basins of some sort that would reduce the amount of particulate reaching plant
outfall.
Reported frequency of rake failures in the plants visited were between
zero and two times per year. The length of time required to repair the equip-
ment and return it to service was reported at one to three days. Both increased
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solids and increased water waste blowdown result from this AOC unless pro-
duction operations are suspended during the repairs. The repair operations
require draining the thickener and removal of accumulated solids.
In the area of wastewater treatment backup capability, installed spare
pumps and thickeners are a powerful tool to overcome failures in single com-
ponents. With thickeners, however, an additional alternative may be available
through terminal lagoons or settling basins immediately upstream of the plant
outfall.
To prevent the failure of thickener rakes, several plants have installed
preclassifiers upstream of the thickeners. The commercial forms of preclassifier
are varied, but their common purpose is to remove grit and heavy solids from
the dirty scrubber water thus affording deposition of such materials in the
thickener. One plant covered their thickener with a wire screen to prevent
foreign matter (rocks, etc.) from falling into the thickener and fouling the
rake.
Precipitators
Downtime of Secondary Systems
Secondary control systems include such units as baghouses to control the
pug mill operation and materials handling or emissions from transfer and
conveying points as distinguished from the main controls applied to the windbox
gases and product handling system. The basic causes of total primary control
system failure enumerated in the preceding section are also responsible for
total failure of secondary control systems. As was pointed out previously,
power failures may be plant wide or local in nature. Where the failure affects
the process as well as control equipment the environmental impact is not
significant. The comments on duration and frequency in the primary section
apply to secondary systems as well.
Fan failures in secondary systems are expected to be more significant
environmentally than in a primary system because spare fan capacity does not
generally exist. A single fan failure is likely to mean an entire secondary
emission control system will shut down without corresponding shutdown of the
process system itself. Of course, emissions from secondary sources in sin-
tering are much lower in quantity than those from the main systems.
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No data were obtained concerning estimations of the frequency or duration
of these AOC's for secondary systems.
Rapping
The successful removal of collected dust by rapping depends on the forma-
tion of a coherent dust that will fall in sheets and agglomerate into the
hoppers. Within the collected layer, adsorbed gases on the particles provide
cohesive forces; interlocking of the particles provides mechanical forces;
particle proximity provides Van du Waal's forces; and the preciptator induces
electrical forces. The primary consideration in any rapping system is the
magnitude of the forces required to dislodge the dust without mechanical damage
to the electrodes or support structure, or excessive reentrainment. Because of
the height of the plates, it is apparent that some dust will be reentrained as
it falls toward the hoppers. This gives rise to a rapping puff, often visible
in the plume during the rap. While rapping is a normal part of ESP operation,
excessive emissions from rapping are not. To minimize this puff, rapping is
done in stages with only a portion of the plates rapped at one time. Various
collecting electrode shapes are also used to shield the falling dust from the
gas stream, thereby minimizing reentrainment.
The efficiency of rapping, measured in terms of residual dust, is usually
improved if the power is removed during the rap. Power-off rapping may be
resorted to if normal practice is inadequate. For example, dust would be
allowed to build up and then power-off rapped every fifteen minutes, or power-
off rapping would be done only once an hour with normal rapping applied during
the intervening periods. Of course, that portion of the precipitator that is
being rapped with power-off will not be collecting material and stack puffs may
result. If parallel units are used, the gas flow can be directed by dampers
during rapping so that there is no gas flow through the unit.
Rapper Failure
Collecting plate or wire cleaning mechanisms fail due to age or low relia-
bility. Fialure to remove dust from the electrode surfaces when the plate and
wire cleaning systems are in operation may also be due to design deficiencies.
Failures of adequately designed equipment can occur either in the control
system for the rappers (or vibrators) or in the individual rappers
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(or vibrators). The latter type of failure is more common. A control
system failure will cause a large group of rappers to fail as opposed to
individual rapper failure.
The increase in particulate emissions due to rapper failure may result
from grounding a precipitator electrical section (because of dust bridging
the wire to plate gap) or reduced collection efficiency in that section when
the buildup has not reached the point of bridging the gap. If the section
is grounded the additional particulate emissions can be estimated by the
methodology presented in the broken wire discussion.
The frequency and duration of rapper and vibrator failures is now known.
Frequent inspections will permit early detection of a failure. Inspection is
relatively easy for the external rapping and vibrating equipment common to
U. S. designed precipitators.
Wire Breakage
Wire breakage is a problem common to the precipitators using wire discharge
electrodes as opposed to rigid fixed charge discharge electrodes. Wire breakage
can result from fatigue, corrosion, and electrical stress due to sparking or
electrical arcing. When a wire breaks, the broken wire generally contacts
one of the adjacent colleciton plates causing the electrical section to short.
The transformer-rectifier sets supplying power to the section then trips. With
no power in that section of the precipitator, collection ceases. All the
sections of the precipitator connected to that transformer-rectifier would be
deenergized unless it is possible to disconnect the section with the broken
wire and reengerize the remaining sections.
Unless there is a problem with the original alignment of internal components,
substandard fabrication of materials, or an unusual event like an excursion
with corrosive gases, wire breakage tends to be a random event. With a common
random failure rate, larger precipitators will have proportionally more wires
failed than smaller precipitators. The data on wire failures do not indicate
the size of the precipitators involved, but some variation in failure rates can
be attributed to difference in precipitator size. Three plants have reported
annual wire .breakage of one or more per month, and in other steel plant uses,
wire breakage rates up to 200 per year have been reported.
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Duration of section outages, which is of course accompanied by increased
particulate emissions, is dictated by the plants need and desire to repair
broken wires. If there is spare collection capacity, there is not need to shut
down a precipitator or a precipitator chamber to repair it immediately.
Several breakages may accumulate before a shutdown is necessary. However, most
shops have a weekly turndown for maintenance and broken wires can be replaced
at this time.
Cutting out broken wires as opposed to replacement does not cause per-
formance to significantly deteriorate unless the wires are adjacent.
The increase in particulate emissions with a section out of service due to
wire breakage can be calculated given the operating efficiency of the preci-
pitator fully energized, total collection surface area, gas flow, and the area
of collection surface out of service. Following is an example of the cal-
culation.
Gas Flow
Chamber Chamber Chamber Chamber
1234
^\\\\\\
Given: Four chamber, four field precipitator
Operating efficiency, n, = 98%, fully energized
Gas flowrate, Q, = 8496 m3/min (300,000 acfm)
Total collection surface area, A, = 12,115 m2 (130,400 ft2)
Area not in service, 757 m2 (8150 ft2, 1/16)
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The efficiency of chamber 3 with one field out of service is 94.7 percent
obtained by:
1) Evaluate w = migration velocity using the given operating
efficiency of 98 percent:
w = -Q/A ln(l - fr eff) = ^00.000 1n (0>Q2) = g>Q
2) Using this value of w, evaluate efficiency of the chamber with
one field out of service:
(24450 ;( g)
Efficiency =100(1 - e 7500° ) = 94.7
The average efficiency, with the one field out of service is 97.2.
n, average = <3 x *\+ 94'7 = 97.2
Particulate emissions should increase by a factor of 1.4
100 - 97.2/100 - 98 = 1 .4 times the normal emissions.
This technique can be applied to precipitators with more than one field
out of service in several chambers equally well.
Where wire breakage rates are high the alignment of electrodes should be
checked to be sure erection tolerances are being met. Sometimes when mass
failure occurs the material of construction is found to be inferior.
If high spark rates in a particular section are observed with a high
incidence of breakage and yet the alignment is satisfactory, shrouded wires
should be installed in place of standard discharge wires. The shrouded wires
have protective sheathes at the top and/or bottom of the wire to decrease
electrical stresses caused by sparking or arcing. Use of shrouded electrodes
in some cases has decreased the frequency of wire failures by a factor of five.
Heavy sparking may also be caused by the inability of some older type
transformer-rectifiers to properly modulate current input. This problem may be
eased by use of solid state controls with better controlling characteristics.
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Dust Removal System Breakdown
This AOC is produced by a myriad of causes. Among them are broken
screw conveyor shafts, plugged dust valves, dust bridging or sticking in the
hoppers, hopper heater failures, and hopper vibrator failures. Problems with
dust removal are frequent and common to all plants using dry collection
systems.
Filaure of dust storage and removal equipment leads to full hoppers.
When the dust level in the hoppers reaches the bottom of the discharge wires
or the steadying frame that aligns them, two things can occur. The preferable
occurrence is to have the TR set trip due to undervoltage (caused by shorting
through the dust to ground). Collection will stop in the electrical section
above the effected hopper and in any other section energized by the same TR
set, thus preventing any damage to the internal components. If the under-
voltage trip protection does not work or does not exist, the dust level will
continue to rise and begin lifting discharge electrodes and their steadying
frame. Permanent damage to the electrode system may be done in this case.
Repairs to the steadying frame and wires require a precipitator shudown more
lengthy and costly than the usual repairs required by the dust removal sys-
tem. Therefore, it is a better choice to shutdown the affected collecting
area for repairs to the dust removal equipment.
Sometimes secondary problems develop from efforts to solve the primary
problems. One of the methods chosen to breakup dust plugs in the double
flapper type dust valves is to strike the valve casings with a hammer. While
the dust plug may be broken the valve casing is often bent thus preventing a
good seal between the flapper valve and the valve seat. On negative pressure
installations, this allows dust to be drawn back into the precipitator along
with cold air. The cold air may produce corrosion damage to the collecting
plates and some of the dust bypasses the precipitator going uncoilected.
Because dust valves produce many sticking or plugging problems, some operators
remove them. This solution is only satisfactory if the hoppers are always
left with enough dust at the bottom to act as a seal. If not, the same air
inleakage problem will occur.
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Sprays Plugged or Corroded
Moisture may be added to the exhaust gases as a conditioning agent,
or it may be present because of the collection of vapors from spraying hot
fines. Without moisture, the particulate resistivity remains high and the
collection efficiency is reduced. A lack of conditioning may be evident as
more opaque visible emissions from the stack.
Most spray systems are fed by recycled water, so that common cause of
spray plugging is solids buildup in the nozzle. The reduced flow area reduces
the amount of water atomized and consequently evaporated. Corrosion is also a
cause of problems. Atomization may be impaired by corrosion damage to the
nozzle, even though the quantity discharged is normal.
The frequency of this AOC is highly variable. In a plant with a regularly
scheduled downturn, say once per week, an inspection and/or change is possible
often enough to avoid the problem.
The duration of the problem is as long as it takes to repair or replace
the nozzles. With no maintenance, emissions will continue to increase. Some
of the plants visited indicated that repair is possible within an hour or two
after discovery of the problem.
The quantitative increase in particulate emissions during this AOC cannot
be readily calculated. The fact that the degree of induced conditioning
effects is so variable is the primary reason.
To reduce the frequency of this AOC regularly scheduled inspections of the
spray systems should be made. The schedule must be more frequent than plugging
or corroding frequency to be an effective preventative maintenance program.
Transformer-Rectifier Set Failure
Transformer-rectifier (TR) sets are the power supplies for the electrical
sections in the ESP. When a TR set fails, the section energized by that TR set
is out of service for as long as it takes to replace the faulty set or until a
temporary connection is made into an adjacent set. Set failures are typically
caused by age and/or overheating. The failure may occur in either of two
portions: the transformer or the rectifier and control portion. The control
portion of the unit is the more frequent scene of the failures. The newer
solid state controls are particularly vulnerable to damage or shorting from
overheating.
63
-------
The estimate frequency of TR set failures is from once to twice a year.
A failure that occurs in the printed circuit card is readily repaired. A
failure that occurs in the transformer may take a month to obtain a replacement
and install it. The range of duration of this type of failure is thus two
hours to one month. Increased particulate emissions can be calculated using
the same methodology presented in the wire breakage discussion secton.
If a severe period of overheating (e.g., in the summer) is anticipated,
the room housing the ESP controls can be air conditioned to reduce failures.
The effects of a failure may be minimized by temporarily connecting the failed
electrical section to a TR set feeding an adjacent collecting area. The
adjacent section may suffer some performance decrease, but the net effect will
improve overall ESP performance under the conditions. Because of the time
involved in making such a connection, it is probably only justified when
replacement is expected to take more than several days.
Insulator Failures
Insulators that support the discharge electrode system are subject to
failure from cracking or tracking. Failures are caused primarily by dust or
moisture on the insulator surface that allows current to track across the
insulator and short out a precipitator electrical section. Cracking may be
produced by either mechanical or electrical stress.
The failure of insulators produce the same effect as broken wires or
transformer failures. The increase in particulate emission can be calculated
by the same methodology presented in the broken wire discussion.
Insulator failures are not a frequent problem according to a survey done
in the electric utility industry. No data on frequency of occurrence or
duration were reported during the plant visits.
Insulator failures are best prevented by frequent inspections of the
insulator housing pressurizing fan and filter or inspection and cleaning of the
insulators themselves where the fan and filter system are not used. For a
typical steel plant environment, a pressurizing fan and filter system to supply
air to the insulator housing is good design practice. This type of inspection
is a maintenance item that can be done on the weekly downturn for repairs and
adjustment.
64
-------
ESP Maintenance
Most successfully controlled sinter plants shut down one shift (turn) per
week. In this 8-10 hour period, planned maintenance is performed. ESP's
should be checked daily: vibrators, transformers, and voltages. Insulators
need cleaning weekly, and at that time transformers can be inspected for oil
leaks.
Fabric Filters
Torn or punctured bags allow unfiltered gases to pass. Extreme conditions
can be detected at the control panel (pressure drop) and by visible emissions
from the baghouse, or under planned inspection.
The frequency depends upon how old the bags are relative to their service
life. Good bags have been lasting 18-24 months. Near the end of bag life
cycles, plants have counted up to 150 broken bags out of 7200 on each two-week
inspection. As bags near the end of their use cycle, failures persist for up
to four months unless a complete replacement of old bags is carried out at one
time. Best practice includes planned replacement before the critical failure
rate occurs.
Isolation of the bag compartment and replacement of the bags is the
proper corrective action. Replacement labor may run 1 to 3 hours per bag.
Sudden changes in baghouse operating pressure can usually be traced to a
malfunction.
1. If torn or punctured bags are the cause, there will be
dust in the clean air plenum where bags need replacement.
2. If there is loss of compressed air pressure required for
the cleaning cycle, the pilot valves should be removed
and cleaned.
3. If the air-to-cloth ratio is too high, it is necessary
to check the fan speed and air flow to correct (design)
values.
65
-------
Where a baghouse has been used on windbox gases, the amount of oil-bearing
feed has been limited to a low percent of the total to prevent either clogging
of the bags, or chemical reactivity in the collected particulate material.
Excessive hydrocarbon in the collected dust can contribute to ignition of the
collected dust, and its fusion and bridging in the collection hoppers.
Baghouse Maintenance
Exhibit 1 shows an example maintenance guide for a baghouse serving a
27
sinter plant. Most well-operating baghouses have a spare compartment so that
cleaning may be performed without losing gas handling capacity. If one com-
partment is tied up for repairs when the second is removed for cleaning, there
would be two out of service and a consequent loss in capacity.
Scrubbers
High velocity inertia! type scrubbers can show a sudden loss in efficiency,
which usually is apparent from the attendant change to a highly visible plume.
The first particles to penetrate the scrubbers if there is low pressure drop
for example due to reduced gas flow, will be the finest (smallest) ones. These
will usually form an opaque cloud.
Adjustment of the scrubber throat to restore the pressure drop is the
corrective action where van"able-throat scrubbers are used. Most sinter plant
scrubbers have variable-throats. If no such adjustment is possible, then
provision should be made for varying the liquid flow in order to maintain the
pressure drop.
To determine how much pressure drop might be controlled by changing water
flow, data for pilot scrubbers by Eberhardt and Graham were analyzed to obtain
the following relationship:
Ap, in. of water = -10 + 1.7 (1000 cfm gas/ft of throat area)
+ 0.96 (gal water/1000 cfm gas).
Thus, an increase of one gal water/1000 cfm gas should raise the AP 0.96
42
inch of water.
66
-------
EXHIBIT 1
SINTER PLANT FABRIC FILTER (BAGHOUSE) MAINTENANCE AND TROUBLESHOOTING GUIDE
REQUIRED MAINTENANCE - OPERATORS AND OTHER PERSONNEL
DAILY
1.
2.
WEEKLY
1.
2.
3.
4.
5.
6.
7.
8.
9.
MONTHLY
1.
2.
3.
4.
Inspect all screw conveyors and conveyor drive belts for seepage
and wear. Listen for unusual sounds. (Operators)
Make sure main control room, walkways, and conveyor housings
are clean of all dust and debris. Be sure pressurizing fan is
operating and keep doors closed.
Lubricate screw conveyors until slight lubricant seepage (Operators).
Lubricate shake shafts. (Operators)
Inspect fan motor bearings. (Electrical)
Inspect fan damper bearings. (Operators)
Inspect hoppers by removing some bags from tube-sheet and looking
down into hoppers, then reinserting bags. (Operators)
Inspect bags for proper seating, tension holes, or burns. (Operators)
Inspect compartments for excess dust, water, etc. (Operators)
Inspect control room pressurizing fan filter and housing. (Operators)
Inspect double-dump valve cams and cam followers. (Operators)
Lubricate fan bearings every 30 days with 2 1/4 to 2 1/2 oz. of
grease. (Mechanical)
Lubricate bullseye damper shafts. (See Figure 4 for location)
(Operators)
Inspect shaker assembly for V-belt tension, etc. (Mechanical)
Lubricate double-dump valve gear box. (Operators)
67
-------
EXHIBIT 1 (cont'd.)
5. Inspect ID fan, fan blades, internal housing, for wear or other
damage. (Mechanical)
EVERY 6 MONTHS
1. Check inlet damper lubrication level; lubricate when necessary.
(Operators)
2. Inspect inlet manifold and ductwork for dust build-up and leaks.
(Operators)
3. Inspect outlet manifold and ductwork for dust build-up and leaks.
(Operators)
4. Inspect screw conveyors internally for damage and proper operation.
(Mechanical)
AS NEEDED
1. Lubricate access door latch bearings. (Operators)
2. Clean hoppers in event of a blocked hopper of malfunctioning
screw conveyor. (Operators)
68
-------
Where scrubbers show incomplete throat coverage with liquid, there may be
insufficient liquid injection points, leaving spaces where unscrubbed gases
can pass. The use of liquid weirs within the venturi, with the gas atomizing
the liquid before the throat may help avoid liquid distribution problems. No
data or estimates of the increased emissions from these causes are available.
Where low pressure drop is caused from an eroded or poorly set orifice or
low water flow due to low pump delivery or plugged nozzles, preventive main-
tenance is required. These AOC's can yield increased emissions of 2.5 - 10
g/kg of product.
Excessive water emission from a scrubber may indicate an eroded or
damaged demister. The effect is an increase in corrosion of the system and
emissions of (usually) acidic dirty water. Repairs are the remedy. While no
data are available, estimates could be made of the increased emissions in
specific cases.
Sprays Corroded or Plugged
Sprays located in the venturi are the most frequent cause of performance
problems. Solids accumulation in particular is reported as a major cause.
After a year or two of operation, the best material of construction to avoid
corrosion damage will likely have been chosen and installed. However, excur-
sions in the system pH could occur in some plants causing some unexpected
corrosion problems. The most typical situation is perhaps an alkaline con-
dition resulting from carryover of the fluxing agents added to the sinter
burden. Because of alkaline conditions, scaling is an important factor in
this AOC.
The result of improper atomization and/or insufficient water flow to the
scrubber is reduced efficiency of particulate collection. In conventional
venturi scrubbers with high pressure drop, scrubber efficiency may not decrease
with decreasing liquid gas ratio (L/G) over a range of L/G values. Some work
done in West Germany has shown that scrubbing efficiency begins to decrease
when the L/G drops below 0.6 £/scm (approximately 5 g/1000 scf). The exact
quantity of relationship between decreasing water rate and scrubbing efficiency
may be available from the scrubber manufacturer.
69
-------
No direct data on frequency of plugging and/or corrosion of sprays were
obtained. Related to findings on sprays for precipitators, the highest would
be three times per week. A low estimate would be six times per year. Esti-
mated time to repair the venturi sprays would be up to 8 hours after identifying
the problem.
Where spray damage is identified as a corrosion problem, special alloys
must be considered for use. In a recycled water system care must be taken
with respect to chloride buildup. High chloride concentration will attack
Type 316 ELC stainless steel, so higher alloys such as Inconel 625 or Hastalloy
C may be necessary, even though much more expensive than stainless steel.
Since maintenance can be provided each week during the downturn, the optimum
choice may be partly material selection and partly chemical control of corrosion.
Since nozzle losses in sinter plants are caused mostly by abrasion rather than
corrosion, the higher alloys will not show much improvement in life over Type
316 ELC stainless steel.
Where plugging, not corrosion, is the problem, improvement of the water
supply is important or regular maintenance during the downturn period will be
required. Certain scrubber designs include automatic cleaning devices to
clean the nozzles. These devices may be effective, but apparently work well
only with some minimum water quality, say 100 ppm maximum suspended solids.
Solids in the recycled water may be reduced by the reduced by the use of
polyelectrolytes to improve settling characteristics. If the plugging is due
to scaling, the use of scale inhibitors and pH control canbe considered.
Plugged or Corroded Pipes
The cause of this AOC is scaling resulting from contaminants carried into
the recyle water. The discussion in the previous paragraphs on causes and
solutions to the problems generally apply. Piping is considered less expendable
than nozzles, however, and so more resistant materials of construction may be
chosen. Rubber lining is used to avoid corrosion losses as an alternative to
higher grade alloy steel. One plant reported plugged or unbalanced water sys-
tem problems five times over a 10 month period. No duration was reported.
70
-------
The consequences of plugged pipes include reduced scrubber efficiency due
to low water flow, and overflow of tanks or thickeners in the recycle water
system leading to spills to the sewer. Corroded pipes can lead to spills to
the sewer and inadequate scrubber water flow also.
Corroded Pump Impellers, Pump Failure
In addition to the problems and solutions presented in the previous two
topics, pum failure can be caused by abrasive wear to the impellers and motor
failures. The resulting low water flow may reduce the scrubber efficiency.
Most plants have installed spare pumps so that if one fails another can be
brought into service.
Without a spare available, low flow conditions could last two to eight
hours before repairs are completed. No data or estimates are available
concerning the frequency with which this problem has occurred in sinter
plants.
Sensors to detect low water flow and the pump operating status are keys
to early warning of an impending problem. Rubber lined pumps can be used to
provide corrosion and abrasion protection. Alternatively, pH control and
corrosion inhibitors can be used to avoid corrosion damage. If the water
system has not preclassifier such a device may be installed to reduce abrasive
wear. If a preclassifer does exist its adequacy and location relative to the
system should be investigated.
Plugged or Failed Demister
Scrubber systems have some sort of device to separate entrained water
from the gas stream. This prevents water droplets containing particulate
matter from being carried out the stack, adding materially to the emission
rate. It also prevents chemical damage due to the acidity or alkalinity of
the water.
The entrained separator or demister is usually some type of baffle device
that presents an impingement surface to the gas stream or a cyclonic type of
separator. Solids can build up in these devices. The result is reduced flow
area and consequently increased pressure drop. In a system with fixed fan
71
-------
capability, the static pressure developed must be used either upstream or
downstream of the fan. If a mist eliminator pressure drop increases at the
normal system flow rate, then the scrubber pressure drop must increase by a
corresponding amount. Alternatively a total gas flow rate may be decreased
and the scrubber pressure drop maintained. In the latter case, fugitive
emissions develop at the hood, in the former case the scrubber efficiency
decreases.
The frequency and duration of this AOC are unknown. The increase in
S
particulate emissions might be calculated if the scrubber pressure drop
decreases. The scrubber manufacturer usually has developed a curve of outlet
concentration versus pressure drop for this purpose.
Pressure drop across the demister can be monitored within an alarm to
warm of a developing problem. Periodic washing of the demister will prevent
this AOC, and this can be done at the regular sinter plant downturn each week
for maintenance.
Drum Filter Failure
Underflow from the thickener(s) in the recycle system is often dewatered
by vacuum filtration either by rotary drum or disc-type. The vacuum system
required in these installations are reported to be high maintenance items. A
number of plants have found it necessary to retrofit spare filters as a
result. One problem is apparently related to solids spillover into the
vacuum pump resulting in abrasive wear.
With no spare drum filter available if repairs can be made within an hour
or two the AOC will not necessarily produce increased solids in the effluent.
There is some solids surge capacity in a thickener. Longer repair means
either solids spillover or all the underflow must be transported to the
disposal site. The underflow gives a much larger volume to dispose of than
the dewatered sludge. Depending on the disposal site liquid runoff could be
a problem.
No data on frequency of occurrence were found, but the general impression
from the operators was frequently with onlg enough repair times to justify a
spare drum filter. Spare filter capacity then is a primary means of avoiding
the AOC.
72
-------
Acid Cleaning Scrubber Components
Acid washing of scrubber system components may be used periodically to
remove accumulated scale deposits. Particularly the quencher, the venturi,
the entrainment separator, the gas cooling tower, pumps, pipes, and nozzles
are susceptible to scale deposits that impair scrubber system operation. The
acid wash itself is not an AOC if precautions are taken to prevent spilling to
the sewer without neutralizing.
Review of NPDES data shows that spills do occur. Data from one plant
showed low pH discharges (< 6.0) for periods of 10 minutes to 3 hours due to
acid washing of various plant scrubbing systems, including BOP furnaces and
blast furnaces. Over a period of 18 months, this AOC occurred twice for the
BOP furnace system and four times for the blast furnace. Prevention of this
AOC is possible by proper planning. Piping, pumps, and tanks can be arranged
to capture the used acid, settle suspended solids, and neutralize the acid
before discharge.
Control Process Modifications
One plant, which used a baghouse on the windbox gases, found that by
recycling product handling dusts to the windboxes, the plugging of the windbox
fabric filters was alleviated. The hard particles seemed to condition the
33
windbox dusts for better collection by baghouse.
73
-------
5.0 TABULATED SUMMARY OF AOC
Table 5.1 summarizes the AOC's described herein. The identification of
an AOC carries no implication whatsoever concerning liability for resulting
air or water pollution. Liability for an AOC can only be determined by the
enforcement officer responsible for a given set of regulations (NSPS, SIP)
or permit requirements (NPDES, special conditions, etc.).
74
-------
TABLE 5.1. SINTER PLANT ABNORMAL OPERATING CONDITIONS
Abnormal
Operating
Condition
Condensation 1n
ductowork
Hearth layer not
formed properly
Burn through 1f
--J fan continues to
01 run
Cause
Cold duct
Improper startup
Strand stopped,
burden Ignited
Effect on
Process
Corrosion, changes In
dust character
Excessive dust load-
Ings, wlndbox gases
Exhuast gases cool
down
Corrective
Action
Frequency
PROCESS RELATED STARTUP
None practical
Proper startup, shut
down till hearth
layer problem Is
corrected
Potentially each
startup, > 1/2 wk
Varies
PROCESS RELATED SHUT DOWN
Stop fan
Varies
Duration
1 hour
5 mln
Varies
Environmental
Effects
In practice, ESP or
Baghouse bypassed
Increased emissions
450-700 rog/scm
Excessive emissions
> 50 kg/hr
Increased emissions
opacity
Reference
26
43
Est.
PROCESS RELATED ABNORMAL OPERATING CONDITIONS
Baghouse acci-
dentally shut
down
Excess air leak-
age
Grate bar dis-
tortion
Excess load-
ing or wlndbox
or discharge
exhaust
Error by service
personnel
Failure of seals,
holes In sinter
burden
Heat from process,
failure of hearth
Poor sinter quality
too much fine mater-
ial , poor moisture
control or feed con-
trol, or Ignition
None
Holes 1n ducts, over-
loads fans and dust
collectors
Excess dust into
wtndbox
Poor quality, lower
yield
Avoid error
Maintain seals.
adjust feed mix,
patch holes, mtn.
of flapper valves
Use sp. alloys,
hearth layer
Good practice and
control
Seldom
Varies > 3/yr
Varies
Varies
35 mln
Depends on mtn.
Depends on mtn.
Persistent until
corrected
Increased emissions
est. 400 kg/hr
Increased load on
emissions controls.
Increased emissions
Increased emissions
Increased emissions
43
35
26
26
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
Condition
Screening sta-
tion equipment
fails
Increased partl-
culate resis-
tivity
Inadequate mixing
of burden
Inaccurate burden
mix proportioning
Hood picks up
chunks of sinter
Use of petroleum
coke for fuel
Cause
Breakdown
Increase In MgO, CaO
In dust due to In-
creased target B/A
ratio
Failure of equip. ,
e.g., pug mill water
pump
Failure of feeder
controls
Hood too close to
process equipment
Shortage of coke
breeze
Effect on
Process
Stops production, or
product handled by
temporary procedure
w.o. controls
Lower temp, of sin-
tering, changes 1n
dust characteristics
Ion-uniform sinter-
Ing
Shut down, short
time
\bras1on In fan
housing, fan rotor
Smoke emissions
from ESP
Corrective
Action
Preventive mtn.;
shut down sinter
plant
Reduce 'basicity of
sinter; adopt alter-
native control
equl pment
Shut down, adjust,
repair
Adjust, repair
Reset hood
Use correct fuel ,
modify ESP, or con-
vert scrubber
Frequency
Varies
. i
Varies
Varies, 0-4 /yr
Varies to several
times per week
Persistent
Varies
Duration
Several days to hand
screen accumulated
product
Persistent
Until corrected, 10
hours
1-2 hours
Till corrected
> 1 hour
Environmental
Effects
Severe dust problems
and uncontrolled
emissions
Increased emissions
If ESP used
Increased emissions
None if fans, pumps
are stopped
None If process
shut down for mtn.
Increased hydro-
carbon emissions
Reference
40
26,11
26,40
26
34
35
CONTROL EQUIPMENT RELATED STARTUP
ESP
Low temp, gases
Settled dust re-
entralnment
Dust overload
on conveyor belt
Cold startup
Change In damper
Hoppers all dump
dust at once
Not powered till gas
Is hot
Higher Inlet loading
Fugitive emissions
Put heaters on In-
sulators, defog
before start
None practical
Sequence dumping
of hoppers
Entire unit 1/wk
Single chamber to
1/wk
1/yr - > 1/wk
Periodic,
repetitive
1 hour
5 rain
Cyclic
Increased emissions
450-700 mg/scm
Increased emissions
Persistent addi-
tional fugitive
emissions
26
35
40
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
Condition
Dust overload on
conveyor belt
Settled dust re-
entrainment
Low temp, gases
Low temp, inlet
gas
ESP shut down
ahead of process
Cause
Effect on
Process
Hoppers all dump
dust at once
Change In damper
setting
Cold startup
Cold start, loss of
ignition
Operating practice
avoid deposit of
condensate
Fugitive emissions
Higher Inlet loading
Not powered till gas
Is hot
Plugs, blinds bags
Control bypassed
Corrective
Action
ONTROL EQUIPMENT REL/
Sequence dumping of
hoppers
None practical
Put heaters on In-
sulators, defog
before start
Bypass baghouse
Al ternate control ,
revise shut down
Frequency
TED SHUT DOWN
Periodic,
>l/wk
Varies, 1/wk
Once-twice/wk
Each shut down
(iVwk)
CONTROL EQUIPMENT RELATED ABNORMAL OPERATING CONDI
ESP
Transformer or
rectifier abnor-
mal oper. cond.
Screw conveyor
breakdown
Dust bridging in
hoppers
Poor operating prac-
tice or Inadequate
design
Foreign material
Inadequate dust dis-
charge design, or
condensation or
cooling of dust
Reduced efficiency
Shut down (partial
shut down) of con-
trol equipment
Dust buildup to
lower high tension
stabilizing frame,
leading to shut down
Repair or replace
Repair, replace
Impact rapper, or
compressed air
rapper, heat
trace and Insulate
Varies
Varies to 7/yr
Varies
Duration
0 - >_ 1/wk
5 min
1 hour
1 hour
1 hour
Environmental
Effects
Additional fugitive
emissions
Increased emissions
Increased emissions
450-700 mg/scm
Increased emissions
400-700 mg/scm.
Raw emissions to air
450-700 mg/kg -
TIONS
Varies, till re-
paired
1-4 hours
Varies
Increased emissions
0.05-1 gm/kg product
Efficiency loss 30-
100% emissions In-
crease 450-700 mg/
scm
Increased emissions
450-700 mg/scm
Reference
26
40
26
26,40
34,26
26
26,35
26,40
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
Condition
Loss of chamber
High resistivity
part Icul ate
Broken or shorte<
electrodes (15
or 20 before
shut down)
Malfunction of
rappers & heater;
Reduced voltage
Fan failure
Power failure
Excessively open
hoods
' Eroded fan blade
-
in-
Cause
Failure of Insula-
tor wear, erosion
Change In process
feed composition
Fatigue failure
Poor maintenance
ID fan malfunctions
with ESP Interlock
Miscellaneous cause;
Miscellaneous cause;
Inadequate mtn. or
design
Infrequent mtn.
Effect on
Process
Loss of efficiency
Reduced efficiency
Reduced efficiency
Reduced efficiency
plates don't clean
Lower efficiency
Loss of control
Loss of control
Fugitive emissions
at hoods
Fugitive emissions
- 1 1 U 1 ILU
Corrective
Action
Repair, activate
spare chamber
Additional pre-
clpltators, change
of feed
Repair
Repair
Maintenance of fan
Adequate standby
and mtn. or shut
down sinter plant
Shut down source
Close hoods
Do not use
hollow plate, use
floor-plate tread
on blades. Repair
fan
Frequency
Varies, 2/yr
-.'
Frequent or persis-
tent
Variable
Varies, depends on
dust and ESP
Once or more/month
Infrequent, < 5/yr
Infrequent
Varies
Varies
Duration
Varies, 1-4 hours to
2 days
Continuous when
occur ing
Variable, 3 hrs -
2 days
Varies, gradual
decline In eff.
Varies, 1-2 days
Varies, fan repair
5-97 hours
Varies
Varies
Varies with mtn.
^^^^ . "
Environmental
Effects
Partial loss of eff.
emissions > 120
gm/kg
Substantially In-
creased emissions
1.5-7.5 gm/kg
Increased emissions
0.05-1 gm/kg
Increased emissions
0.05-1 gm/kg
Increased emission
est. to 450 mg/scm
None If strand
shuts down
Some Increased
emissions
Increased emissions
0.05-1 gm/kg
Increased emissions
depending on indivi-
dual situation
Reference
26,35,
40
Est.
Est.,
40
Est.
26
26,35
26
Est.
26
00
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
Condition
Cause
Effect on
Process
Corrective
Action
Frequency
Duration
Environmental
Effects
Reference
CONTROL EQUIPMENT RELATED STARTUP
Baghouse
Low temp, inlet
gas
Cold start, loss of
Ignition
Plugs, blinds bags
Bypass baghouse
1
Once-tw1ce/wk
1 hour
Increased emissions
150-700 mg/scm +
>pac1ty
26,40
CONTROL EQUIPMENT RELATED - SHUT DOWN
*
Baghouse shut
down (bypassed)
ahead of process
Desire to avoid
cooler gases plugging
bags
Control bypassed
Alternative control
Each shut down
(i 1/wk)
1 hour Raw emissions to air
1450-700 mg/kg
1
CONTROL EQUIPMENT RELATED - ABNORMAL OPERATING CONDITIONS
Baghouse
Excessive oil in
burden mix
Excessive visi-
ble emissions
Fire in baghouse
ducts (or wind-
box)
Excessively open
hoods
Eroded fan
blades
Poor balance of raw
materials
Torn bags
Ignition of HC 1n
dusts
Inadequate mtn. or
design
Infrequent mtn.
Blue hydrocarbon
plume
Change in compart-
ment &P
Damage to system
Fugitive emissions
at hoods
Fugitive emissions
at hoods
Planned raw material
consumption limit
on oil content of
feed
Preventive mtn.
Limit HC in feed,
dump hoppers con-
tinuously
Close hoods
Repair fan
Varies
Constant when occur-
ing f(bag age) at
near end of life, up
150 bags/two wk
inspection
Varies
Varies
Varies
Persistent
Till repaired, 1-7
days
Until brought under
control
Varies
Varies with mtn.
Increased emissions
0.1 to 0175 gm/kg
Increased emissions
300 mg/scm
Increased emissions
Increased emissions
0.05-1 gm/kg
Increased emissions
depending on indivi-
dual situation
34
Est,
40
40
Est.
26
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
Condition
Power failure
Fan failure
Duct abrasion
Shut down for
major repairs
Plugged bags
Failure of dust
removal system
SCRUBBER
Fan failure
Power failure
Eroded fan
blades
Excessively
open hoods
Excessive oil
In burden mix
Cause
Miscellaneous causes
Miscellaneous causes
Abrasive dust
Postponement of mtn.
due to need to mod-
ify system under
contract
Moisture and/or oil
vapors 1n gas
Poor mtn.
Miscellaneous cause;
Miscellaneous cause;
Wrong materials of
construction
Inadequate mtn. or
design
Poor balance of raw
materials
Effect on
Process
Loss of control
Loss of control
Infiltration of air
Baghouse out of ser-
vice
Fugitive emissions
discharge end of
process
Loss of control
Loss of control
Loss of control
Fugitive emissions
Fugitive emissions
at hoods
Blue hydrocarbon
plume
Corrective
Action
Shut down source
Adequate standby and
mtn.
Lime with high
alumina ceramic
None, but shut down
of sinter plant
during relnstalla-
tlon of control
Eliminate or reduce
moisture or oil
vapors In gas
Proper mtn.
Adequate standby &
mtn. or shut down
sinter plant
Shut down source
Repair fan
Close hoods
Planned raw material
consumption limit
on oil content of
feed
Frequency
Infrequent
Infrequent < 6/yr
Varies
No data. Should be
one time occurrence
Varies
1-3/yr
Infrequent <_ 5/yr
Infrequent
Varies
Varies
Varies
Duration
Variable
Variable; fan re-
pair 5-97 hours
Till repaired
5 wks
Varies up to time
better bags are
(7 mos) If this Is
the cause
Variable 3-10 hours
Variable fan repair
5-97 hours
Variable
Varies with mtn.
Varies
Persistent
Environmental
Effects
Some Increased
emissions
Increased emissions
150-700 gm/kg
'osslble Increased
"missions
Increased emissions
tSO-700 gm/kg
Increased emissions
severity depends on
situation
Fugitive emissions
Increased emissions
450-700 mg/kg
Some Increased
emissions
Increased emissions
depends on Individual
situation
Increased emission
0.1-1 gm/kg
Increased emissions
0.1 to 0.75 gm/kg
Reference
26
26,35
26
26,35
33
35
26,35
26
26
Est.
Est.
00
o
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
.Condition
Low water
flow
Demlster fail-
ure
.Plugged, eroded
sprays and/or
water supply
Erosion of rub-
ber lining of
scrubber
Excessive over-
flow, reclrcu-
latlon water
Low gas flow
Low pH
Water carry-
over from
demister
Cause
Poor mtn. pump
failure
Plugging, air flow
too high, corrosion
Solids buildup,
eroded or poorly set
orifice, corrosion
Abrasion
Poor control, line
blockage In settling
basin
Throttled fan to
avoid fan Imbalance
Control excursion,
faulty signal from
pH controls
Inadequate disengag-
ing height
Effect on
Process
Reduced efficiency
Mists escape collec-
tion
Reduced efficiency
Plugging, Interrup-
tion
None
Reduce &? on scrub-
ber
None
Demlster plugged w/
CaS04, shut down,
poor mtn. practice
Corrective
Action
Repair pump
Mtn. repair, adopt
better equipment
Preventive mtn.,
adjust, control
water chemistry,
clean scrubber
Rebuild scrubber,
use refractory lin-
ing, use plastic
pipes, cement grout
(S102, Al203 aggre-
gate w/epoxy resin)
behind refractory
lining
Better control ,
clear lines
Mtn. repair, clean
fan
Mtn. controls, bet-
ter, more durable
pH meter
Redesign; larger
disengage height.
Chevron demister of
304 stainless steel
Frequency
1-6/yr
Varies 1/yr
Varies 1-4/month
Varies 1-6/yr
once/month
Varies < 5/yr
Once/month
Varies, if mtn. re-
lated 1/yr
Duration
0.1-1 day
Unltl corrected
1-3 days
Until corrected
1-8 hours
Till repaired 3-30
days
1 day
Until repaired 5-
97 hours
Unknown
Until corrected
1-3 days if mtn.
related
Environmental
Effects
Increased emissions
0.1-1 gin/kg, 80*
loss efficiency
Increased emissions
0.5-1 gm/kg
Increased emissions
400-500 mg/scm
Increased emissions
SS exceeded daily
limit
Increased HC emis-
sions, some Increase
In participates
Eff. exceeded daily
limit
Increased emissions
Reference
35
Est.
35
40
4
5
5
0
CO
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
Condition
WESP1
Power failure
Fan failure
Breakdown
SS too high 1n
wastewater
WASTEWATER
TREATMENT
Clar1f1er fail-
ure
High level 1n
sump
Low sludge den-
sity
Poor performance
Change 1n com-
position of
wastewater
Cause
Miscellaneous causes
Miscellaneous causes
Corrosion
Drain water from ESP
cleaning entered
sewer directly due
to broken dam
Rake failure, sludge
pipe plugged, sludge
pump failed
Level control. of
pump failure
Broken dewaterlng
equipment
Corrosion of Inter-
nal elements
Change of gas com-
position
Effect on
Process
Loss of control
Loss of control
Shut down
No affect on control
process
Reclrculated water
1s turbid
Overflow of waste-
water
^circulated water
1s turbid
Increased mtn. &
Increased emissions
Possible corrosion
Corrective
Action
Shut down source
Adequate standby &
ntn. or shut down
sinter plant
Control of reclrcu-
latlng water, better
materials of con-
struction, pH contro
Drain water to treat-
ment plant
Repair, better mtn.
Repair, mtn.
iepair, mtn.
'reventlve mtn. ,
)H adjustment
todlfy process
operation or treat-
ment of water
Frequency
Infrequent
Infrequent < 5/yr
Varies
Up to twice/month
1/yr
1-6/yr
1/yr
Varies
Varies
Duration
Variable
Variable, fan repair
5-97 hours
Till repaired
One day
1-5 days
0.5-1 day
1-3 days
Persistent until
corrected
Varies
.
Environmental
Effects
Some Increased
emissions
Increased emissions
450-700 gm/kg
Increased emissions
SS exceeded dally
limit
Increased solids In
blowdown 0.222-660
gm/kg
Increased pollution
0.22-2.2 gm/kg
Increased solids in
blowdown, decreased
sludge density,
0.05-1.5 gm/kg
Increased emissions
Can cause Increased
discharge of dis-
solved solids (e.g.,
heavy metals)
Reference
?6
26,35
to
44
40
Est.
Est.
26
26
00
ro
-------
TABLE 5.1. (cont'd)
Abnormal
Operating
Condition
Inadequate floc-
culatloh
Feed mix change
GRAVEL BED
FILTER
Poor dust re-
moval from
gravel
Malfunction of
back wash valves
Cause
Chemical addition
failure
Adherence to garnet
media
Design deficiency
Effect on
Process
(eclrculated water
Is turbid
to effect on scrub-
jer
Clogging
Unit plugs
Corrective
Action
Repair, better mtn.
Modify feed mix
Use cracked steel
shot as gravel
Redesign valves
Frequency
Unknown
-: i
Varies
Till corrected
Persistent
Duration
Unknown
Varies
Persistent
Till corrected
Environmental
Effects
Increased solids In
>lowdown, decreased
sludge density
Increased discharge
dissolved solids
If bed bypassed,
Increased emissions
increased emissions
Reference
26
26
39
No full-scale WESP Is now In operation. Units are expected In two years. Limited experience means limited data on AOC's at this time.
-------
6.0 REFERENCES
1. Pugh, J. L. and L. N. Fletcher, Experience in Handling and Consuming
Basic Oxygen Flue Dust in a Sinter Plant, Armco Steel Corp., Ashland
Works, Proc. Waste Oxide Recycling, Steel Plants, 1974, 4, p. 1-9.
2. Herrick, R. A., Background Information for National Standards of Per-
formance. Iron and Steel Industry, Environmental Engineering, Inc.
for EPA Division of Abatement, Air Pollution Control Office, Durham,
N. C., Contract CPA 70-142, March, 1971.
3. Ostrowski, E. J. and K. P. Mass, Conditioning and Sinter Plant Con-
sumption of BOP Dust-Bearing Inplant Ferrous Fines, Res. and Dvmt.
Dept., National Steel Corp, Weirton, W. Va.
4. Hess, J. E. and 6. S. Black, Direct Digital Control at Burns Harbor
Plant Sinter Plant Complex Provides Product Uniformity, AISE Journal.
5. Genton, R. G., Steel Mill Sinter Plant, The Carborundum Co., 65th Annual
Meeting of the Air Pollution Control Assoc., Miami Beach, June 18-22,
1972, p. 8.
6. AISI Committee correspondence with Don R. Goodwin, USEPA, Res. Tri.
Park, N. C., September 28, 1976.
7. Ball, D. F., A. F. Bradley, and A. Grieve, Environmental Control in
Iron Sintering, Simon-Carves Ltd., Minerals and Environment Symposium,
London, June 1974, p. 23.
8. Rounds, G. R. and G. Geminder, Problems of Recycling Waste Oxides through
the Sinter Strand (Baghouse Experience), Kaiser Steel Corporation,
Fontana, California, A.I.M.E., 1974.
9. Bakke, E., Application of Wet Electrostatic Precipitators for Control
of Fine Particulate Matter (Presented at the Symposium on Control of
Fine Particulate Emissions from Industrial Sources, San Francisco,
Jan. 1974).
10. Egley, B. D., Selection of the Gas Cleaning Equipment for an Ore Pre-
paration Plant, Iron and Steel Engineer, Nov. 1970.
11. Varga, J. Jr., Control Reclamation (Sinter) Plant Emissions Using ESP's,
EPA-600/2-76-002, January 1976.
12. Steiner, B. A., and R. J. Thompson, Wet Scrubbing Experiences for Steel
Mill Applications, Armco Steel Corp., Middletown, Ohio, Second EPA
Symposium on Fine Particle Scrubbing, May 2-3, 1977, New Orleans, La.
84
-------
13. Mazer, M. R., S. T. Hernan, and S. A. Jaasund, Adaptation of Wet
Electrostatic Precipitators for Control of Sinter Plant Windbox
Emission, Bethlehem Steel Corp., Bethlehem, Pa., 1977.
14. Jaasund, S. A. and M. R. Mazer, Application of Wet Electrostatic
Precipitators for Control of Emissions from Three Metallurgical Pro-
cesses, EPA Sympsoium on Particulate Collection Problems Using
Electrostatic Precipitators in the Metallurgical Industry, June 1-3,
1977. EPA 600/2-77-208.
15. Oglesby, S. and 6. B. Nichols, A Manual of Electrostatic Precipitator
Technology, Part IIApplication Areas, EPA Contract No. CPA 22-69-
73, August 25, 1970.
16. T. T. Nowak, Sinter Plant Baghouse, Proc. 31st Ironmaking Conf.,
Chicago, April 10-12, 1972, The Metallurgical Society, A.I.M.E., pp.
75-86.
17. Op. Cit., Reference 8.
18. Inland Steel, Indiana Harbor Works, Main Stack Baghouse Dust Collection
System, Brock O'Kelley, Training Department, May 1977.
19. Evan, T. K. and J. S. Master, Fine Particle Scrubbing with LSS Hydronic
Cleaner, presented at the Second Symposium on Fine Particle Scrubbing,
New Orleans, La., May 2-3, 1977.
20. Op. Cit.. Reference 13.
21. Baake, E., "Wet Electrostatic Precipitators for Control of Submicron
Particles," JAPCA. Vol. 25, No. 2, pp. 163-167, 1975.
22. Ball, D. F. et al., Environmental Control in Iron Ore Sintering. Pre-
sented at the Minerals and the Environment Symposium, London, England,
June 1974.
23. ibid..
24. Pengidore, D. A., Sinter Plant Windbox Gas Recirculation System Demon-
stration, Phase 1, Engineering and Design, National Steel Corporation,
Wierton, W. Va., EPA Report No. EPA-600/2-75-014, August, 1975.
25. Jablin, R., Communication with Mr. H. R. Wood, Wierton Steel Company,
December 21, 1977.
26. Steiner, B. A., Air Pollution Control in the Iron and Steel Industry,
International Metals Review, Sept. 1970, pp. 171-192.
27. Communication with U.S. Steel Company, Gary, Indiana.
-------
28. Data provided by Inland Steel Company, So. Chicago, Indiana and con-
sidered typical of good maintenance practice.
29. Development Document for Effluent Guidelines and New Source Performance
Standards, Steelmaking, Iron and Steel Mfg. Category, EPA, Office of
Water and Hazardous Materials, June 1974.
30. Carpenter, B. H., communication with Inland Steel Company.
31. Sinter Plant Air Pollution Control Pilot Plant Study at Houston Works,
Armco Steel Co., 1972.
32. Armco Steel Company, Sinter Plant Pilot Scrubber Study at Ashland Works,
August 9, 1971.
33. Carpenter, B. H., communication with Republic Steel Co.
34. Air Pollution Control Division, Allegheny Co. Health Department,
Pittsburgh, Pa.
35. Erie County Air Pollution Control Division, Buffalo, N. Y.
36. Nicola, Arthur G., "Fugitive Emission Control in the Steel Industry,"
Iron and Steel Engineer. July 1976, pp. 25-30.
37. Bradley, J. G., "Operation and Maintenance of a Modified 0. G. Gas
Cleaning System," U. S. Steel Corporation, National Open Hearth and Basic
Oxygen Steel Conference, 55th Proceedings. 3Q> Personal communication,
Environmental Protection Agency.
39. Data provided by Weirton Steel Division, National Steel Corporation
at Eastern States Blast Furnace and Coke Oven Association Meeting,
February 4, 1977. 4Q> Trip Reportj Eastern states Blast Furnace and
Coke Oven Association
Meeting, February 4, 1977. 4]^ communication with Bethlehem Steel
Company. 42< Ebernardt> j. E< and H- s_ Qraham, "The Venturi Washer for Blast
Furnace
Gas," Iron and Steel Engineer. March 1955, pp. 66-72. 4, T . ReDort
EPA Region V, Chicago, Illinois, January 7, 1977.
44. Trip Report, EPA Region III, Philadelphia, Pennsylvania, February 2, 1977.
86
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-118b
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE Pollution Effects of Abnormal Oper-
ations in Iron and Steel Making - Volume n. Sintering,
Manual of Practice
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
B.H.Carpenter, D.W.VanOsdell, D.W.Coy, and
R. Jablin
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
1AB604
11. CONTRACT/GRANT NO.
68-02-2186
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
13. TYPE OF REPORT AND
Final; 10/76-1/78
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTESJERL-RTP project officer is Robert V. Hendriks, Mail Drop 62,
919/541-2733.
16. ABSTRACT
The report is one in a six-volume series considering abnormal operating
conditions (AOCs) in the primary section (sintering, blast furnace ironmaking, open
hearth, electric furnace, and basic oxygen steelmaking) of an integrated iron and
steel plant. Pollution standards, generally based on controlling discharges during
normal (steady-state) operation of a process and control system, are often exceeded
during upsets in operation. Such periods of abnormal operation are becoming recog-
nized as contributing to excess air emissions and water discharges. In general, an
AOC includes process and control equipment startup and shutdown, substantial var-
iations in operating practice and process variables, and outages for maintenance.
The purpose of this volume, which covers the sintering process, is to alert those
who deal with environmental problems on a day-to-day basis to the potential problems
caused by AOCs, to assist in determining the extent of the problems in a specific
plant, and to help evaluate efforts to reduce or eliminate the problems. The report
enumerates as many AOCs as possible, with emphasis on those which have the most
severe environmental impact. Descriptions include flow diagrams , material balan-
ces , operating procedures, and conditions representing typical process configura-
tions.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Shutdowns
Iron and Steel Industry
Sintering
Abnormalities
Failure
Staring
Pollution Control
Stationary Sources
Abnormal Operations
13B
11F
13H
1S. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
95
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
87
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