&EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/2-78-118f
June 1978
Research and Development
Pollution Effects
of Abnormal
Operations
in Iron and Steel
Making - Volume VI.
Basic Oxygen
Process, Manual
of
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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-pornt 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 re viewed 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-600/2-78-118f
June 1978
Pollution Effects of Abnormal Operations
in Iron and Steel Making - Volume VI.
Basic Oxygen Process,
Manual of Practice
by
D.W. Coy, D.W. VanOsdell, B.H. Carpenter, 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.
ii
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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.
m
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TABLE OF CONTENTS
LIST OF FIGURES vii
LIST OF TABLES viii
INTERNATIONAL SYSTEM OF UNITS AND ALTERNATIVE (METRIC) UNITS WITH
CONVERSION FACTORS ix
1.0 INTRODUCTION 1
1.1 Purpose and Scope 1
1.2 Definition of AOC 2
2.0 Steelmaking in the Basic Oxygen Process Furnace 3
2.1 Flow Sheet 5
2.2 Material Balance 10
2.3 Methods of Operation 12
Top Blown Furnace 12
Bottom Blown Furnace 14
2.4 Pollution Sources 14
Air Pollution 14
Water Pollution 18
3.0 CONTROL TECHNIQUES AND EQUIPMENT 19
3.1 Emission Standards 19
3.2 Primary Emissions Control 20
Equipment Configurations 21
Precipitator System Hardware 21
Precipitator Startup 26
Precipitator Maintenance 27
Scrubber System Hardware--Combustion Hood 28
Scrubber Startup 32
Scrubber Shut Down 33
Scrubber Maintenance 33
Scrubber System Hardware—Closed Hood 34
3.3 Secondary Emissions Control 38
Secondary System -- Maintenance 40
4.0 ABNORMAL OPERATING CONDITIONS 41
4.1 Process Related 41
iv
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TABLE OF CONTENTS (cont'd)
Page
4.1.1 Startup 41
Burn In 41
4.1.2 Shut Down 43
4.1.3 Abnormal Operating Conditions 43
Puffing at Hood 42
Improper Transfer of Hot Metal to Vessel 43
Improper Charge Material 44
Foaming and Slopping 45
Relief Damper Opening 47
Pit or Charging Explosions 50
Running Stopper 50
4.2 Control Equipment Related 51
4.2.1 Startup 52
Precipitator Warmup 52
Stack Puff 54
Unbalanced Flow Among Manifolded Fans 55
Insufficient Draft 56
4.2.2 Shut Down 57
Dampers Stuck or Jammed 57
4.2.3 Abnormal Operating Conditions 58
Downtime of Primary Collection Systems 58
Downtime of Secondary Systems 61
Precipitator Commong 63
1) Wire Breakage 63
2) Sprays Plugged or Corroded 66
3) Insufficient Conditioning of Gases 67
4) Corroded Pump Impeller, Pump Failure 67
5) Transformer-Rectifier Set Failure 68
6} Insulator Failures 68
7) Rapper Failure 69
8) Dust Removal System Breakdown 70
Scrubbers Common 71
1) Sprays Corroded or Plugged 71
2) Plugged or Corroded Pipes 73
3) Corroded Pump Impellers, Pump Failure 74
4) Plugged or Failed Demister 74
5) Drum Filter Failure 75
6) Acid Cleaning Scrubber Components 76
7) Unbalanced Water System 76
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TABLE OF CONTENTS (cont'd)
Baghouse Common 77
1) Bag Breakage or Plugging 77
2) Shaker or Reverse Air System Failure 78
3) Open Bypass Damper 79
4) Dust Removal System Breakdown 80
Fan Common 81
1) Draft Loss 81
2) Fan Failure 82
Other 83
1) Loss of Instrument Air 83
2) Failure to Flare Gas 83
5.0 TABULATED SUMMARY OF AOC 84
6.0 REFERENCES 92
vi
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LIST OF FIGURES
Figure Page
1 BOP -- schematic elevation of a two furnace facility 6
2 BOP -- schematic cross-section of operating units 7
3 BOP furnace flow sheet 8
4 Typical configuration for a precipitator installed on a
BOP furnace 22
5 Typical configuration for a scrubber installed on a BOP
furnace with an open or combustion hood 29
6 Typical configuration for a scrubber installed on a BOP
with a closed hood 35
vi i
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LIST OF TABLES
Table Page
1 Emissions and Effluent Limitations 19
2 Basic Oxygen Process Abnormal Operating Conditions 85
vm
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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
Gg (gigagram =10 grams)
m (cubic meter)
dsctn (dry standard cubic meter)
scm (standard cubic meter: 21°C, 1 atm)
i (liter = 0.001 m3)
g/m (grams/m)
mg/m (milligrams/m )
9/kg
J (joule)
kJ/m3 (kilojoules/m3)
MO (megajoules = 10 joules)
MJ/Mg
kPa (kiloPascal)
1 Pascal = 1 N/m2 (Newton/m2)
o
m (square meter)
Equivalent To
2.205 Ib
2205 Ib
1.1025 ton
35.32 cf
0.437 gr/fr
0.000437 gr/fr
2 Ib/ton
0.000948 Btu
0.02684 Btu/fr
0.430 Btu/lb
859 Btu/ton
0.146 lb/in2
10.76 ft'
IX
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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 agencits 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 contributing to the emission of
high concentrations of pollutants. Similarly, upsets contribute to spills of
excessive 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 this 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 basic oxygen 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
steelmaking 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 STEELMAKING IN THE BASIC OXYGEN PROCESS FURNACE
The basic oxygen process (BOP) furnace receives a charge composed of
molten iron and scrap and converts it to molten steel. A jet of high purity
oxygen oxidizes the carbon and the silicon in the molten iron in order to
remove these products and to provide heat for melting the scrap. After the
oxygen jet is started, lime, usually in the form of pebble lime, is added to
the top of the bath to provide a slag of the desired basicity. Fluorspar and
mill scale are also added in order to achieve the desired slag fluidity.
The basic oxygen steelmaking process is essentially a thermochemical
process which lends itself, more or less, to the application of computer
control. The process starts with the analysis of the composition of the molten
iron and its temperature. These data are applied to the desired chemistry of
the finished product and computations are made which determine the percentage
of molten iron, the percentage of scrap, the amount of flux materials and the
amount of alloy additions. If all goes exactly as planned, after the injection
of the precalculated amount of oxygen, the vessel is turned down, a steel
analysis is made, and the heat is tapped. If, on the other hand, the heat is
off analysis, it may be necessary to either blow with additional oxygen
to elevate temperature and/or cool the steel by coolant additions to the bath.
A basic oxygen furnace facility is generally arranged with three parallel
aisles. One aisle, called the charging aisle, has one or more cranes for
handling charge materials, that is, molten iron and scrap, to the furnace, as
well as handling ladles of molten slag away from the furnace. The second
aisle, called the furnace aisle, contains the furnaces, the collection hoods
for the fumes, the lances for injecting the oxygen into the bath, and also the
overhead bins for storing and metering out the various flux materials and alloy
additions. The third aisle, the pouring aisle, serves to handle the finished
heats of steel. It has one or more overhead cranes and facilities for receiving
the heat of steel either into ingot molds or into continuous casting machines.
-------
Adjacent to and generally parallel to the charging aisle, there is a scrap
yard with overhead cranes where scrap is transferred from railroad cars into
the charging boxes. The charging boxes are moved by special railed cars from
the scrap yard into the charging aisle. There are also railed cars which are
under the furnace. These cars hold the steel and slag ladles and serve to
transfer the ladles from under the furnace to the charging aisle in the case of
the slag or to the pouring aisle in the case of the steel.
During the oxygen blow, the oxygen lance is lowered through a special hole
in the top wall of the hood, is stopped a short distance above the bath of
steel and the oxygen flow is initiated. The vessel is upright during the blow
and the fumes have a direct access from the mouth of the furnace into the mouth
of the hood. At other times in the process, the vessel may be tilted so that
the mouth of the vessel does not align with the opening in the hood and capture
of the fumes becomes more difficult. The vessel is tilted toward the charging
aisle for at least four of the operations; namely, charging with scrap, charging
with molten iron, sampling the heat for analysis and dumping the slag. It is
tilted toward the pouring aisle usually only when pouring the finished heat of
steel from the furnace into the steel ladle. Alloy additions may be made to
the bath while it is upright under the hood. However, the normal case is to
make them to the ladle while it is being filled with steel from the furnace.
There are several ancillary operations associated with the basic oxygen
process for making steel. The first is the scrap handling operation which was
described above. The next is the transfer of molten iron from the railroad
ladle to the shop ladle and from the shop ladle to the furnace itself. The
handling of molten iron may include the operation of mechanically skimming slag
from the top of the bath of iron. A third operation is the teeming of the
finished steel into ingot molds or into continuous casting machines. Finally,
there is the handling and disposing of molten slag, generally accomplished by
carrying the ladle of slag to the end of the shop and pouring it on the ground
or into slag pots where it is allowed to cool. The solidified slag is then
loaded into trucks or railroad cars for transport to a disposal site. Alter-
nately, the molten slag may be carried by means of special trucks directly to
the disposal site.
4
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A BOP shop generally has either two or three steelmaking vessels. In
either case, one of the vessels is generally out of service for a reline, while
the other one or two are in operation. In the two-vessel shop, oxygen is blown
intermittently, generally for a period of about 20 minutes of the total heat
time. In a three-vessel shop, the operation of the two on-line vessels are
staggered so that blowing alternates from one vessel to the other and so that
two vessels are not blown at the same time.
Figure 1 shows a schematic elevation of a typical two furnace shop and
indicates all of the facilities which have been described above. Figure 2
shows a schematic cross-section which indicates the various operating units.
2.1 FLOW SHEET
The flow sheet for steelmaking in the BOP furnace is shown in Figure 3.
The principal components of the charge are molten iron and scrap. Scrap
is received in the shop by means of railroad gondola cars and is transferred to
the charging box by means of an overhead magnet and crane. Molten iron is
brought to the shop by means of railroad ladle cars and is transferred to the
shop ladle at the ladle transfer station. This station is often equipped with
a hood for capturing the kish (exuded carbon) which evolves during th£ transfer
operation. When the vessel is ready for charging, it is tilted toward the
charging aisle and the charging box lifted and dumped into the vessel. Next,
the ladle of molten iron is poured into the vessel over the scrap. The vessel
is turned upright, the oxygen lance lowered, and the blow commences. Immediately
after the start of the blow, lime and fluorspar in the desired quantities are
fed through the chute into the vessel from the weigh hopper.
The gases which evolve from the steelmaking operation are captured by the
hood, enter the hood cooling section, where some heat is extracted and pass
through the conditioning chamber where the gas is cooled to the required tempera-
ture for the precipitator and at the same time humidified for proper preci-
pitator operation. The gas cleaning system consists of precipitators, fans,
dust handling equipment, and a stack for carrying away the cleaned gases.
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•LANCE
HOIST
RIGS
STORAGE
FLOOR
WEIGHING
FLOOR
BATCHING
FLOOR
SERVICE
FLOOR
CONVEYOR
FROM
RAW-MATERIALS
STORAGE
BUILDING
OPERATING
FLOOR '
GROUND
LEVEL
uuuuw
COKEFl
STOVE'TT'
T- STOVE
CONVEYOR
BATCHING HOPPER
HOOD
FURNACE
TILTING
MECHANISM
LADLE
ADDITIVE
STORAGE
BINS
LADLE ADDITIVE
TRANSFER CAR
STEEL
LADLES
(Copyright 1971 by United States
Steel Corporation)
Figure 1. BOP -- schematic elevation of a two furnace facility.
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CONVEYOR FROM
-RAW-MATERIAL
STORAGE
STORAGE BINS
WEIGHING
BINS
CONVEYORS
OXYGEN
LANCE
CAR \ -
\TAPHOLEN
W I
CHUTE
DOTTED LINES SHOW POSITIONS
OF TILTED FURNACE AND SCRAP
BOX WHEN CHARGING SCRAP
SCRAP
CHARGING
CAR
SLAG POT ON
TRANSFER CAR
TEEMING
LADLE ON
TRANSFER
CAR
rx
(Copyright 1971 by United States Steel Corp.)
3
HOT-METAL
TRANSFER
LADLE ON
TRANSFER CAR
IN PIT
Fa
Figure 2. BOP -- schematic cross-section of operating units.
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00
SLAG LADLE
STEEL LADLE
INGOT MOLD
Figure 3. BOP flow sheet.
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Two other forms of gas cleaning equipment are in common use. One is the
open hood which is similar to that shown in Figure 3, but connected to a
scrubber system. The other is the closed hood in which the diameter of the
entry into the hood is roughly the same as the diameter of the mouth of the
vessel and in which the lower portion of the hood is equipped with a skirt that
can be dropped onto the mouth of the vessel, sealing off the space between the
hood and the vessel proper. In this manner, the gases are collected in an
uncombusted state; their volume is reduced as compared to those in the open
hood and the yield of the process is increased. Because the gases are combustible,
gas cleaning is performed by means of a scrubber, the precipitator being a
potential source of explosions. The gas from the closed system may be stored
in a holder and utilized as an energy source. If not, it must be flared at the
top of the stack.
Because there is no danger of explosion in the open hood system, all of
the vessels in the shop may be connected to a common gas cleaning system,
thereby effecting economies in installation and increasing reliability due to
standby units. The closed system, on the other hand, because of the danger of
explosion, must have a separate scrubber system for each vessel.
The flux,bins are generally filled by a belt conveyor system from a hopper
at ground level. This hopper is usually equipped to be loaded from a railroad
car, or a truck, or both. Transfer points of the conveyor system are generally
fitted with hooding and small individual baghouses.
When the heat is complete, the vessel is tilted and the steel is poured
into the steel ladle. The transfer car moves the steel ladle into the pouring
aisle, the crane picks up the ladle and carries it over to the train of ingot
molds. A stopper or slide gate in the bottom of the ladle is opened and each
ingot is filled in turn. Alternatively, the ladle may be carried to the top of
a continuous casting machine for the production of continuously cast product.
After the steel is out of the vessel, the slag is poured into a ladle or slag
pots. When the ladle is filled, it is run into the charging aisle by means of
a transfer car. The charging crane then picks up the ladle and carries it away
for disposal.
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Disposal of the slag may be accomplished by pouring it on the ground at
the end of the shop. Alternatively, the ladle of molten slag may be carried
away from the shop by a mobile vehicle and the slag processed in a remote site.
In either case, the metal lies are generally removed from the slag by magnetic
means and returned to the blast furnace or sinter plant and charged as a portion
of the burden. The remaining slag is generally disposed of in a dump area.
2.2 MATERIAL BALANCE
As indicated on the flow sheet, in order to produce a metric ton of steel
in the BOP, the following raw materials are required:
1. Ferrous charge materials consisting of molten iron, approxi-
mately 70 percent, and scrap, approximately 30 percent (higher
percentages of hot metal may be used if desired). The typical
yield in a BOP with an open hood is 85 percent. Therefore,
to produce 1000 kilograms (kg) (2205 pounds) of steel, 825 kg
(1819 pounds) of molten iron and 350 kg (772 pounds) of scrap
are required. In the closed hood, the yield increases to
approximately 87 percent and the usage of molten iron and
scrap drops correspondingly. Some of the shops practice scrap
pre-heating prior to the admission of molten iron. This prac-
tice generally adds about 15 minutes to the tap-to-tap time;
however, less molten iron and more scrap may be used. In
general, the hot metal drops from 70 percent to 60 percent
under scrap pre-heating.
2. Flux materials consisting of lime and fluorspar. Lime is
the principal ingredient. Its quantity is generally about
90 kg per metric ton (198 pounds) of steel and varies
corresponding to the sulfur content of the iron and
the specification of the finished steel in regard to freedom
from sulfur. The quantity of fluorspar is determined by the
need to maintain a fluid slag and is generally 3 percent by
weight of the amount of lime.
3. Oxygen in the amount of 3.1 standard cubic meters per minute
(110 standard cubic feet per minute (scfm))/per metric ton of
steel is injected into the bath. The amount of oxygen used depends
on two factors. One is the composition of the molten iron,
especially in respect to its content of such materials as
silicon and manganese. The other is the final carbon level
required in the finished steel.
10
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4- Ladle additions consist of alloying elements such as
manganese, nickel, chromium, etc., which are required in
varying amounts depending upon the final composition of
steel. In addition, aluminum may be added to cleanse the
steel of dissolved oxygen. The aluminum reacts with
oxygen forming aluminum oxide, most of which migrates to
and is included with the slag.
The basic oxygen process, in addition to producing steel, yields slag,
gases, and particulates in the gases. The amount of slag is essentially equal
to the amount of lime and spar that is added to the bath plus additions for
refining of the bath and less the emissions of slag to the hood along with the
furnace gases.
The amount of gases from the furnace varies according to the type of fume
collection system which is employed and is described below:
1. Open hood with ESP produces the greatest volume of gas,
approximately 62 scmm per metric ton (2,000 scfm/ton) of
steel. This high value results from two causes. One is
the absolute necessity to completely combust all of the
carbon monoxide which evolves from the furnace, thereby
avoiding any possiblity of explosion in the precipitator.
The other is that the precipitator in having a low
pressure drop, generally under 51 mm (2 inches) of water
gauge does not result in high consumption of energy at the fan,
even though the volumes may be high. A supplementary
benefit of the high volume is that it facilitates the
capture of emissions from the mouth of the vessel when it
is tilted partially out of the hood to receive scrap and molten
iron.
2. Open Hood--Wet Scrubber generally produces less flow of gases than
does the precipitator, the amount being approximately 28 scmm
per metric ton (900 scfm/ton) of steel. The reasons for the
reduced volume result from the need to conserve energy in a
scrubber system operating somewhere in the range of 127 to
178 centimeters (cm) (50 to 70 inches) of water. Also, the
presence of combustibles in the scrubber system would not
entail a significant risk of explosion.
3. Closed Hood—Wet Scrubber involves the least flow of any of
the three systems, approximately 16 scmm per metric ton (500
scfm/ton) of steel. This reduced value results because
secondary air to complete the combustion of carbon monoxide
is not permitted to enter the hood. Energy requirements for
cleaning the gases in the closed system, because of the
sharply reduced volumes, are lower than those for the open
system.
11
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The amount of participates carried out of the furnace into the gas cleaning
system amounts to about 6 to 20 kg per metric ton (12 to 40 pounds/ton) of
103
steel produced. ' ' Each of the gas cleaning systems described above are
capable of reducing the concentration of particulates in the clean gas to the
level of New Source Performance Standards, 50 milligrams (mg)/scm (0.022 grains
per standard cubic foot (gr/scf))dry or better. The mass rate of particulates
in the clean gas therefore depends essentially upon the volume of gas leaving
the stack and in turn is related to the type of cleaning system employed. The
environmental effectiveness of the three control systems ranked from lowest
emission rate to highest is, in terms of particulate control, the closed hood,
the open hood with a scrubber and the open hood with the precipitator.
\
2.3 METHODS OF OPERATION
Top Blown Furnace
In the basic oxygen steelmaking process, molten iron is converted to steel
using a jet of oxygen to remove most of the carbon and silicon. The heat that
is generated by oxidation is used to melt scrap. Refining of impurities is
accomplished by means of the slag, the chief goal being to remove as much of
the sulfur from the steel as is possible. The desired specifications of the
end product are usually accomplished by the additions of suitable alloying
materials to the ladle of finished steel as it is filled.
A typical BOP furnace produces a heat of steel in a very short time; tap-
to-tap times in a high performance shop may be as little as 30 minutes. To
accomplish this the process is fully mechanized and, in addition, is under some
form of computer control. Computer control may be applied directly from the
computer through electrical circuits to the furnace (DOC); however, the more
usual practice is for the computer to provide information for the operator who
then controls the process. High performance depends on equipment that is
sophisticated and reliable. Both of these factors tend not only to produce
steel at a rapid rate, but also to avoid abnormal operating conditions.
The lining of the BOP furnace is made of high quality basic refractory.
During a campaign which may last 1000 heats or more, the linings become worn
generally near the slag line. These points of wear are patched between heats
by various gunning techniques (spraying of patching materials onto the wear
12
-------
points). Eventually linings wear so much that the furnace must be taken out of
service, the refractory removed, and a new lining installed. About one week
is required to remove the old lining and replace it with a new one. During
this period, the vessel is out of service.
In a two-vessel shop, the vessels are alternated with each other in
respect to on-time. One vessel is either being relined or, having been relined,
is on standby and the other vessel is in operation. (Some two vessel shops
operate both vessels when the reline is complete.) In a three-vessel shop, the
relining schedule is arranged so that two vessels may be kept in operation. In
this case, the two operating vessels are alternated one with the other in
respect to the flow of oxygen. While one vessel is being blown, the other is
being tapped and being recharged.
The nature of the process is such that when an upset occurs of potential
damage to equipment, to the environment, or to the process itself, it is
possible to shut it down instantly. All that is required is to stop the flow
of oxygen and to raise the lance. The heat may remain in the vessel for a
relatively long period of time, possibly six or more hours, until necessary
repairs have been made. It is preferred, however, to dump the heat in the case
of a long delay.
The hood which conveys the gases away from the furnace is water cooled.
Water may be recirculated through a heat exchanger and returned again for use
in the hood. Alternatively, the water may be converted to steam and delivered
to other steelmaking operations. On some steam generating hoods, fuel is fired
into the hood between blow periods in order to maintain a constant rate of
steam output. Another way of maintaining the output at a constant rate is to
use a steam accumulator; however, in this case, the generation of steam per ton
of steel is less because there is no use of supplementary fuel.
As indicated above, it is possible to decrease the amount of molten iron
required by using a technique of scrap pre-heating. This is accomplished by
means of a second lance which is inserted in place of the oxygen lance. The
second lance injects oxygen and natural gas or oil and pre-heats the scrap to a
glowing red color. After pre-heating the scrap, the lance is withdrawn and the
oxygen lance lowered in its place. The vessel is tilted and molten iron
13
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is poured into it. Pouring of molten iron over the heated scrap results in a
violent reaction and the production of copious emissions. The pouring rate
must be carefully controlled in order to insure that the hood may capture
substantially all of the emissions.
Bottom Blown Furnace
An alternative to the use of an oxygen lance is found in the Q-BOP. This
is a recent development in which oxygen and natural gas are injected through
tuyeres in the bottom of the vessel. The metallurgy of the process, the
ancillary equipment employed with the process, and the details of the fume
collection system are generally the same as for the BOP.
The principal advantage claimed for the Q-BOP is that it requires less
headroom in the furnace aisle than does the BOP. This has allowed the Q-BOP to
be installed in an existing open hearth building, thereby saving cost in
construction of the facility. The Q-BOP is also capable of producing steel at
a somewhat faster rate than does the BOP.
When the Q-BOP vessel is tilted to receive scrap and molten iron, or to
sample for steel analysis, it is necessary to maintain a flow through the
tuyeres so that they may not become blocked. In normal practice, the oxygen
and natural gas are turned off when the vessel is tilted and these gases are
replaced by a flow of nitrogen. In any event, there is a copious flow of
emissions of fumes from the mouth of the vessel due to the gas flow from the
tuyeres. For this reason, the Q-BOP needs to be more fully enclosed at the
level of the charging floor than is the BOP. In order to direct the gases back
into the collection system and to protect the men who are on the charging
floor, a pair of large horizontally sliding doors are provided. These doors
are opened to permit the addition of scrap and molten iron; however, they are
closed at all other times.
2.4 POLLUTION SOURCES
Air Pollution
The operations in the BOP shop are directly responsible for two general
categories of pollution, namely, air pollution and solid waste. Water pollu-
tion, where it occurs, is invariably a byproduct of gas cleaning operations.
-------
There are two principal types of air pollution. The first is the direct
result of the steelmaking process itself and consists of dense emissions of
fumes from the mouth of the basic oxygen vessel. The fumes are mostly metallic
oxides which result from the reaction between the jet of oxygen and the molten
bath. Also included in these fumes are particles of slag. Carbon monoxide
produced by the reaction of both carbon and oxygen is also emitted. For some
plants, raw materials used in the process contain fluoride that is emitted
during the blow.
The gases which leave the mouth of the furnace, in addition to being
dusty, are extremely hot. In the closed hood system, temperatures are in the
neighborhood of 1650°C (3000°F). In the open system, CO combustion takes place
at the entrance to the hood, raising the temperature perhaps another 540°C
(1000°F). Before the gases may be cleaned of their particulate matter, it is
necessary that they be cooled. The methods of cooling and of cleaning the gas
are briefly described under Section 2.2. Control equipment is described in
detail in Section 3.0.
The second type of air pollution source comprises a variety of operations
from which the emissions are generally classed as fugitive emissions. Descrip-
tions of these follow:
1. Reladling of molten iron from the torpedo railroad car to '
the shop ladle is accompanied by the emissions of kish, a
mixture of fine iron oxide particulates together with
larger graphite particles. The usual method of control is
to provide a close fitting hood and a baghouse. A spark
box between the hood and the baghouse protects the bags
from destruction due to large hot particulates. Normally,
the spark box is built integrally with the baghouse.
2. Desulfurizing of molten iron may be accomplished by means
of various reagents such as soda ash, lime and magnesium,
etc. Injection of the reagents is accomplished pneumati-
cally, either with dry air or nitrogen. Desulfurizing
may take place at various locations within the iron and
steelmaking facility; however, if the location is the BOP
shop, then it is most often accomplished at the reladling
station to take advantage of the fume collection system
at that location.
3. Skimming of slag from the ladle of molten iron serves the
purpose of keeping this source of high sulfur out of the
steelmaking process. Skimming results in the emissions of
kish and for this reason is often done under a hood. The
hood may be connected to a baghouse, or to just a vent
stack.
15
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4. Charging of scrap and molten iron into the BOP vessel results
in a dense cloud of emissions. Emissions from the charging
of scrap are particularly severe if the scrap is dirty, oily,
otherwise contaminated, or contains such potential sources
of explosion as excess water or ice. Emissions from the
charging of molten iron are particularly severe if the scrap
over which it has been charged is dirty or contaminated, or
if the scrap has been preheated. In some facilities, if the
main hood is large enough and the volume of air flow is
also large enough, it is possible to capture most of the
fumes in the main collection system for the vessel. In
this case, as much of the vessel mouth as possible is kept
under the hood and, in the case of pouring the iron, it is
done at a slow, controlled rate. In other facilities, it
is necessary to provide auxiliary hoods in front of the main
collection hood. On occasion, a facility may also have a
hood at the building monitor to capture any fumes which by-
pass the hoods at the vessel.
5. Pouring of the molten steel from the BOP vessel into the
ladle results in iron oxide fumes. The quantity of fumes
are substantially increased by additions into the ladle
of such alloys as silicon, manganese, etc. Some BOP
facilities enclose the space at the rear of the furnace in
such a manner that the fumes are ducted into the main
collection system. In other facilities the fumes are
permitted to exit through the roof monitors.
6« Turning down the vessel for the purpose of taking samples
or for pouring out the slag results in emissions. These
emissions are particularly great in the case of the Q-BOP
The reason for this is that, when turned down, a flow of
nitrogen must be maintained in the tuyeres in the bottom
of the latter vessel in order to keep out the molten metal
and slag. Some facilities have a pair of sliding doors
on the charging floor in front of the vessel. These doors
are kept closed as much as possible in order to direct the
fumes into the main collection system.
7. Slag handling may consist of transporting the ladle of molten
slag from the shop to a remote dump area, or it may consist
of dumping the molten slag on the ground at the end of the
shop and cooling it there. In the latter case, the cooling
of the slag as well as its subsequent digging by bulldozer
is a very dusty operation that is generally uncontrolled.
8. Teeming of steel from the ladle to the ingot mold or con-
caster results in emissions which are normally uncontrolled.
In some shops, where leaded steels are poured, the resultant
fumes are extremely hazardous to the health of the workers.
In this case, local hooding is provided.
16
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9. Flux handling takes place in a sophisticated system
comprising receiving hoppers from truck or railroad car,
belt conveyors, large overhead storage bins, weigh
hoppers, feeders, controls, etc. Hooding is provided
at the various transfer points to capture the particu
lates which arise from the falling of the bulk material.
Exhaust ducts lead from the hoods to one or more bag
houses.
10. Skull burning and ladle dumping. Some molten metal remains
in the ladle after teeming. Between successive uses the
metal cools and solidifies. After accumulating for some
time, these skulls may interfere with proper ladle opera
tion, so they are burned out with oxygen lances. Iron oxide
fume is emitted. Ladles must also be relined at intervals
to protect the steel shell. The ladles are turned upside
down to dump loose material onto the shop floor. This
generates fugitive dust. These sources can be locally
hooded, but normally are not.
Other sources of pollution are those associated with the disposal of solid
waste from the process. The first results from the transportation and disposal
of the BOP dust. Unless closed containers or trucks are used, the act of
transporting the dust can cause some of it to be re-entrained into the air. If
the dust is recycled to the ironmaking process, its disposal does not cause
further environmental problems. However, in most BOP facilities, the con-
taminants in the dust, principally oxides of zinc and tin, may cause serious
problems in the blast furnace. Rather than recycle the dust, the operators
find it necessary to either "store" it on the ground in the open or dump it in
a landfill. In either case, special precautions must be taken to prevent the
winds from picking up the dust and re-entraining it into the air or the rains
from leaching out toxic compounds from the dust and delivering them to the
underground aquifer or the nearby water course.
The second source results when a portion of the slag which is removed from
the BOP vessel is utilized. In a separate facility, metal!ics are recovered by
magnets and returned to the steel making operations. Some of the slag, because
it is relatively low in sulfur and high in lime, may be charged into the blast
furnace. The remaining slag is disposed of in the landfill. As with the dust,
special care is required to avoid the adverse aspects of leaching.
17
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Water Pollution
There are no direct sources of water pollution within the process. Such
water pollution sources as may exist result from the particular type of fume
collection system employed. If a scrubber is used, there is discharge of
scrubber water. Normally, most of this is recycled through a clarifier;
however, facilities are required for dealing with the necessary blowdown
to the water system. Even the dry precipitator may result in a discharge of
contaminated water. This results from the final step in gas cooling, which is
the quenching and conditioning of the gases by means of water sprays. If the
quantity of water used in conditioning or its method of application is not
carefully controlled, there is an overflow of water from the conditioning
process which is contaminated with BOP dust and must be treated.
18
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3.0 CONTROL TECHNIQUES AND EQUIPMENT
The various sources of emissions from a BOP furnace shop were addressed in
Section 2.4 of this manual. In this section, the various techniques and
equipment used to control these emissions sources will be discussed.
3.1 EMISSION STANDARDS
Table 1 shows the current standards for air and water pollutant emissions
established by the Environmental Protection Agency. The standard for parti -
culate emissions applies only to new or modified units on which construction
was begun after June 11, 1973.
TABLE 1. EMISSIONS AND EFFLUENT LIMITATIONS
BOP
Dry
Semi-Wet
Wet
4
New Source Air Standard -
Particulates mg/scm dry
Effluent Guideline Existing5
Sources
Total Suspended Solids - kg/
metric ton of steel
PH
5
Effluent Guidelines New
Sources
Total Suspended Solids - kg/
metric ton of steel
pH
Fluoride - kg/metric ton
of steel
50
50
zero
dis-
charge
zero
dis-
charge
50
Max. 1 30 day
day average
0.0312 0.0101
6.0 <_ pH <_ 9.0
0.0156 0.0052
6.0 <_ pH £9.0
0.0126 0.0042
19
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Two sets of effluent limitations are applicable. One set applies to all
new sources on which construction was begun after February 19, 1974. The other
set applies to existing sources as of that date. More stringent limitations on
existing source effluents are scheduled to be implemented in 1983.
The individual states or municipalities may or may not have standards more
strict than those cited in Table 1 both for new and existing sources. Because
of the large number of jurisdictions involved and various bases for these
standards, no compilation has been attempted for this manual. The reader
should refer to the particular area of interest for this information.
3.2 PRIMARY EMISSIONS CONTROL
Primary emissions refers to those emissions leaving the mouth of the
furnace vessel. The generic types of control equipment used in the United
States to capture particulate emissions from the vessel mouth are scrubbers and
electrostatic precipitators. Selection of a control device for the vessel
waste gases is interrelated with the selection of hood design for capturing the
gases.
Carbon monoxide (CO) is emitted from the vessel mouth during the oxygen
blowing phase of the cycle. The gas temperature is sufficiently hot to promote
combustion of CO if air is permitted to mix with the waste gas. A design
decision must be made to determine how much air, if any, is allowed to mix with
the gas, so that hood cooling capacity can be matched to the system needs.
Obviously, some air admission is necessary to obtain the capture velocity
required to contain fume emissions within the hood.
Many of the early BOP furnace installations used precipitators for con-
trolling particulate emissions. Because of the potential for ignition of CO-
air mixtures by precipitator sparking, it was necessary to admit large quantities
of excess combustion air at the hood and facilitate complete combustion of CO.
This design decision led.to having to treat larger gas volumes for control of
particulate emissions than is necessary for scrubbers. The treated gas flow
rate is approximately 62 scrnm per metric ton (2,000 scfm per ton) of steel.
With scrubbers for primary control the risk of explosion is considerably
less, but choosing to burn the CO to carbon dioxide still requires the admission
20
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of air and consequent gas dilution. The combustion hood gas volumes for
scrubber systems are designed for approximately 28 scrnm per metric ton (900
scfm per ton) of steel.
More recent plant designs have incorporated limited or partial combustion
of CO, thereby reducing the heat generated in the hood and the gas volume to be
treated. Careful control of the amount of air admitted to the hood allows ten
to fifty percent combustion of CO according to the designer's preference. Gas
cleaning now is exclusively scrubbers. The design gas flow rates are approxi-
matley 16 scrnm per metric ton (500 scfm per ton) of steel. The advantages of
partial combustion are reduced energy consumption for gas cleaning as compared
to a scrubber on a full combustion hood, and the potential for recovering CO as
a low grade fuel source 7,500,000 joules/scm (200 BTU/scf). Though several
plants in the United States are now operating with partial combustion hoods,
none of the plants are recovering the CO and the gas must be flared before
discharging it to the atmosphere. Plant managers claim that the investment in
gas holding facilities is not yet economically attractive (approximate installed
cost for new plant with 227 metric ton [250 ton] vessels is $10 million).
Equipment Configurations
Precipitator System Hardware
Figure 4 shows a typical configuration for a precipitator installed on a
BOP furnace. Initial cooling of the waste gases is by means of a water cooled
hood or waste heat boiler. As mentioned in Section 2.3, some plants use
auxiliary fuel firing during the non-blowing part of the cycle to generate a
continuous flow of steam.
Cooling is continued by the use of water sprays located in the upper part
of the hood. These sprays are generally controlled by time and/or temperature
to turn on and off at various points in the operating cycle. The intent is to
limit the gas temperature reaching the precipitator and to moisture condition
the gases for better precipitation. The maximum temperature of gases entering
the precipitator is usually kept under 343°C (650°F).
Following the water sprays there is usually a spark box or chamber to
knock out chunks of refractory or other coarse material carried over from the
21
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ro
ro
GAS
COOLING SPRAY WATER
HOOD COOLING WATER
SPARK BOX SPRAY WATER
{ ALTERNATE IN PLACE OF
WET EVAPORATION CHAMBER)
TRUNNION RING-*
COOLING WATER
EFFLUENT
WATER TO
THICKENER
HEATED WATER
DRY
PRECIPITATORS
n
PRECIPITATED
DRY DUST
EXHAUST
STACK
INDUCED DRAFT FAN
W/GAS TURBINE OR
ELECTRIC DRIVE
Figure 4. Typical configuration for a precipitator installed on a BOP furnace.
-------
vessel. The spark box is also the point for dirty water separation, if any
results from excess water spraying. Some plants operate with essentially no
water discharge at this point.
Because the gas temperature is relatively low during hot metal charging
and the early minutes of a blow, some plants use steam injection either at the
hood sprays or spark box location to achieve the desired conditioning of gases.
Water sprays do not evaporate sufficiently under the low temperature conditions
and puffs of iron oxide fume are typically observed coming from the stack
during this period. Steam injection both at the beginning and end of the heat
can eliminate these puffing emissions.
Downstream of the sparkbox the gases are carried to an inlet plenum that
distributes the gases to multi-chambered precipitators. On the outlet side of
the precipitator there is usually a manifold arrangement that distributes the
gases among multiple fans. The preciptators may or may not have spare capacity
in terms of an extra chamber or extra collection field in the direction of gas
flow. It is common that at least one spare fan is available.
In a two vessel shop, somewhere just upstream of the precipitator inlet
plenum, ducts from each vessel join into a common flue. Isolation of each
vessel from the precipitator is usually managed by installing guillotine
dampers upstream of the junction point. When a vessel is being relined the
fans are then drafting only the operating vessel, otherwise much draft is
wasted on the non-operating vessel.
Draft and temperature monitoring is normally done at several locations in
the system. Sprays are used to control precipiptator temperatures; so the
sprays must, to a certain extent, be temperature controlled.
At several locations in the system, suction pressure is sensed and used to
control the opening and closing of flow control (louver) dampers. For certain
phases of the operating cycle there are specific draft set points that control
the evacuation rate of the system. Full system draft is used during hot metal
charging and the oxygen blow. Partial draft is used during scrap charge and
reblows. There may be little or no draft during the remainder of the operating
cycle. Draft is limited when hot gases are not available to prevent too much
precipitator cooling. The continual expansion and contraction of hood, ducting,
23
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and precipitator is structurally detrimental, resulting in leaks. Corrosion,
too, may be a problem for a precipitator if cold air is alternated with hot,
moist gas.
Dust removal from the precipitator hoppers is most often done by screw
conveyors to some common discharge point. Though there are many operating pro-
blems related to the use of screw conveyors, no clearly superior alternative
equipment has been found to eliminate their use. Dust removal from the pre-
cipitator site is usually by truck to a landfill site. t
Whether the landfill is storage or a permanent disposal site depends on
the economics of recovering metal values from the dust. At present most plant
operators have no plans for the dust because of the presence of zinc in it.
Zinc enters the process through scrap charged to the vessel. This metal causes
spelling (crumbling) of the refractory lining of blast furnaces, so reinjection
into the plant cycle at the sinter plant or blast furnace is not suitable.
Numerous schemes have been investigated to recover the zinc and make the iron
available for recycle, but to date no U.S. plants have attempted full scale
installations of the required process equipment.
Overflow water from the spray chamber or spark box flows or is pumped to a
settling tank of some sort and the settled solids dragged out by conveyor. If
not recycled, plants generally combine the overflow or the blowdown with process
water from other plant areas for clarification prior to discharge.
Some further insight into the pollution control system can be gained by
examining typical design data. For a two 227 metric ton (250 ton) vessel shop,
the typical gas flow rate would be about 519 actual cubic meters per second
(acms) (1,100,000 actual cubic feet per minute (acfm)) at 316°C (600°F) entering
the precipitator. The moisture content of the gas stream would be about 30 to
40 percent by volume at this temperature. Inlet dust concentration during the
blow would average about 16 grams (g)/scm (7 gr/scf) or about 24.8 g/scm (10.8
gr/scf) dry. To achieve compliance with the New Source Performance Standard
(NSPS), 50 mg/scm (0.022 gr/scf) dry, a collection efficiency of 99.8 percent
would be required.
On the basis of past practice the precipitator installation might consist
of four double-chambered precipitators. The total collection surface required
to achieve 99.8 percent would be approximately 91,974 square meters (990,000 ft )
24
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Many existing precipitators have much less collecting surface per unit gas
volume than this because they were designed for lower efficiencies prior to the
new emission standards.
Ideally each chamber would be individually isolatable to permit on-line
maintenance, especially for a shop that has no weekly downturn for maintenance.
Four fans would be available to serve this installation, three operating and
one spare.
For the system with excess water fed to the hood sprays and spark box, the
effluent rate would be about 1893 liters per minute (500 gallons per minute).
This effluent would be treated in a settling tank initially and then sent to a
thickener for solids settling with other process wastewater.
To monitor control equipment operations and furnace draft the following
systems' sensors and alarms are used:
Low Pressure Alarms: instrument air, oxygen supply, lance
cooling water, hood cooling water, service
water, waste gas duct, clean gas duct,
plant air
Low Level Alarm: hood water cooling tower
High Temperature:' cooling water, dirty gas at precipitator
inlet
Failure: precipitator transformer-rectifiers
Vibration: for all fans
High Bearing Tempera-
ture: for all fans
Many of the above items also have continuous strip charts to record data,
e.g., oxygen supply, water flow rates, system temperatures at various points,
system draft at various points. Combustible content of gas or CO concentration
is an additional important process variable that should be monitored and
alarmed with precipitator systems.
The type of staffing used to operate and maintain precipitator systems
varies from plant to plant. One plant producing 32 heats per day, seven days a
week has two operator/maintenance people assigned at all times to observe
precipitator conditions and inspect equipment for problems. The estimated
actual maintenance for the precipitator systems is 75 to 100 hours per week
including sprays, dust valves, hoppers, and all things related to the gas
cleaning system.
25
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Another plant operating on two shifts daily has no permanent maintenance
people assigned to the precipitator, but does required work during the two 4-
hour down periods each day. Daily work includes duties such as rodding out
differential pressure instrument lines to maintain accurate draft measurements.
Precipitator Startup
Following is an abridged version of startup instructions for an electro-
static precipitator system.
These procedures should be followed on initial startup and on startup
after a lengthy outage. For short outages, the precipitator would
normally be deenergized at the power distribution panel and the high
voltage disconnects switches, if. used would be grounded.
1. Observe all safety precautions.
2. Inspect all hoppers and conveyors to make sure they are clear
of accumulated dust and that conveyors operate smoothly.
3. On positive pressure precipitators, energize the insulator
compartment ventilating system, move the disconnect switch
handle to on position, turn the power switch on the ventilating
system control panel to on, and press the blower motor start
button.
4. If high voltage disconnect switches are used, make sure all are
at on position releasing power distribution panel interlock
keys. These switches are on the roof of the precipitator.
5. Check position of dampers in the inlet and outlet flues; make
sure the outlet damper is more open than the inlet.
6. Start the fan or fans to move flue gas through the precipitator.
If both a forced draft fan is used ahead of the precipitator
and an induced draft fan after the precipitator, start the
induced draft fan first.
7. Allow the flue gas to pass through the precipitator sufficiently
long to purge the system before energy is supplied to the high
voltage system. This lessens the danger of possible explosive
gas and air mixtures, eliminates free moisture, and establishes
minimum startup temperature of 82°C (180°F) at the precipitator
inlet before operation is started.
8. Energize the dust removal system.
9. Energize the rapper system by turning each chamber rapper control
switch on the rapper control or if present the single control switch
for all chambers to on position.
10. Energize the transformer-rectifier sets.
26
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Precipitator Maintenance
Following are maintenance recommendations for a precipitator system.
Precipitator maintenance procedures daily:
1. Take readings at all instruments, preferably hourly or at
least once per shift except on basic oxygen open hearth appli-
cations where closer monitoring during blowing cycles is advisable.
2. Make sure all insulator compartments are properly ventilated. Be
sure the vents are clear.
3. Make sure all rappers are functioning properly, replace faulty
units.
Weekly:
1. Remove dust and foreign matter from electrical equipment.
2. Thoroughly inspect the interior of the precipitator and make
necessary adjustment or repairs. Give particular attention
to the high voltage electrodes each of which should be cen
tered between the collecting surfaces. Misalignment of
even a single unit reduces the electrical clearance between
high voltage electrodes and collection surfaces resulting
in marked reduction of collection efficiency.
The next section is on maintenance records that are recommended. To
aid in maintaining and operating the precipitator, a precipitator
operating logbook should be used. The following data should be recorded
in it:
1. Air load readings taken by the manufacturer's startup engineer
when the precipitator was installed and air load readings taken
after maintenance, repair, or inspection.
2. Precipitator condition observed during each inspection such as
evidence of dust buildup, bent or burned discharge electrodes,
poor alignment, dirty or broken insulators, evidence of corrosion,
and all other unusual conditions.
3. All lubrication, maintenance, and repair work.
4. Automatic voltage control readings should be recorded at regular
intervals.
5. Describe unusual operating conditions as fully as possible,
include date and time at which these conditions occur so that this
data can be correlated with the plant operating data.
27
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Scrubber System Hardware—Combustion Hood
Figure 5 shows a typical configuration for a scrubber installed on a BOP
furnace with an open or combustion hood. As in the case of the preciptator
system initial cooling is via a water cooled hood or waste heat boiler. Also,
auxiliary fuel firing may be designed into the system to provide a continuous
steam source.
Cooling is continued by the use of a spark box or quencher where grit and
coarse particles resulting from refractory and chunks of slag or metal are
separated from the gas stream. Quenchers reduce the gas temperature to less
than 93°C (200°F) and saturate the gas with water vapor.
From the quencher the waste flows to a high energy scrubbing device where
removal of fine particles occurs. The most common scrubber type is a venturi
with an adjustable throat. The venturi is opened or closed to increase or
decrease gas velocity, i.e. pressure drop through the throat. The flooded disc
scrubber is another type wherein opening and closing of an annular space by
moving the disc achieves the velocity and pressure drop changes.
An integral part of the scrubbing unit is some type of moisture separating
device to knock out drops of water carried out of the throat. This may be a
series of baffles or a centrifugal chamber in which the gas is spun to cause
the drops to impinge on the chamber walls. Also sometimes used is an after-
cooling chamber where cooling water is sprayed to further reduce the gas
temperature. At cooler temperatures, moisture condenses from the gas thus
reducing the volume of gas to be handled by the fan.
The scrubber systems usually have multiple venturi throats. Two and three
vessel shops may have two to six separate scrubbing units in a parallel flow
arrangement. As in the case of precipitators, the scrubbers are typically
manifolded to a multiple fan installation. Spare fan capacity is available in
some installations.
One or two scrubber systems may be shared by a two or three vessel shop.
The flues come together into a common inlet downstream of the quenchers.
Isolation of non-operating units is important to prevent loss of draft capacity
at the operating units. This is accomplished by the use of guillotine dampers
upstream of the juncture point.
28
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WATER COOLED
OXYGEN LANCE
BY- PASS STACK
SLOWDOWN
SPRAY WATER
X
POR
«•
J
1
MBBi
-—
y
ia
i
>
HIGH ENERGY
VENTURI
SCRUBBER
STACK
SOLIDS
Figure 5. Typical configuration for a scrubber installed on a BOP furnace
with an open or combustion hood.
29
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Draft control for the scrubbing system is provided by the ability to vary
scrubber throat openings and fan dampers. As in the case of precipitators,
temperature and draft are monitored at several locations in the system. The
fan dampers are closed to minimize power consumption during certain portions of
the heat cycle.
During the hot metal charge the vessel is tilted away from the hood,
reducing the amount of fumes that can be captured. The draft or evacuation
rate can be maximized (improving the chance to capture some charging emissions)
by opening the scrubber throat as far as possible. When this is done, however,
it reduces gas cleaning efficiency for any particulates captured in the hood.
Practice with respect to these operations varies from shop to shop.
A recycle water system is the typical way in which scrubber wastewater is
handled. This system incorporates a preclassifier of some design, a thickener(s),
and some thickener underflow dewatering device. Schematically, the "clean"
water overflow from the thickener is pumped to the venturi throat. Use of high
pressure spray nozzles dictates the need for a relatively clean water supply at
this point. This water and solids are separated from the gas stream in the
moisture separator.
The water out of the separator flows to a recycle or surge tank. From the
tank, part of this water is pumped to the quencher and part to the thickener(s).
The used quench water, containing coarse particles, flows through the pre-
classifier before return to the thickener. There are variations on this flow
arrangement as to location of the preclassifier and the recycle tank, but the
water supply to the venturi must be the cleanest water available in the system.
Underflow from the thickener(s) is pumped to a rotary drum vacuum filter
or centrifuge for dewatering. The cake produced is usually trucked to landfill
in an open or tank truck. If the dewatering operation is not sufficiently
effective, the tank truck would be the preferred method of transport. The
comments made in the precipitator section on recovery of metal values in the
solid waste apply in this case as well.
Improved settling and sludge dewatering may be achieved by the addition of
polyelectrolytes. Blowdown from the recycle system may require pH adjustment
and further removal of suspended solids to meet effluent guideline limitatons.
30
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Recycle water systems typically have problems with corrosion and scaling.
Chemical additions are made to control the scaling problems. Corrosion condi-
tions can be improved by pH adjustment or careful material selection.
A further understanding of an open hood scrubbing system can be gained by
examining typical design conditions. Just upstream of the quencher the off-gas
rate is about 106 scms dry (225,000 scfm dry) for a 227 metric ton vessel (250
ton). Actual temperature conditions at this location would be about 1538°C
(2800°F). Through the quencher the gas is saturated and the temperature reduced
to about 82°C (180°F) at a volume of 310 acms (650,000 acfm) saturated (approxi-
mately 50 percent moisture by volume). On the above basis the inlet particulate
concentration would be 35.5 g/scm dry (15.6 gr/scf dry) at the quencher inlet.
To achieve compliance with the New Source Performance Standard of 50 mg/scm
(0.022 gr/scf) dry, an efficiency of 99.86 percent is required.
Scrubber pressure drops vary widely in practice, ranging from 100 to 180
centimeters (cm) H90 (39 inches to 71 inches). To reach compliance with NSPS
18
the range of 150 to 180 cm would probably be necessary. ' Water flow rates to
the quencher and venturi nozzles would be about 1 liter(L)/scm (7.5 gallon
(G)/1000 scf) each.
Monitors and alarms are provided for the following equipment:
Low Pressure Alarms: quencher water, scrubber water, after-
cooler
Level Alarms: surge or recycle tank
High Pressure Alarm: drop across aftercooler
High Temperature Alarm: downstream of quencher
Vibration: all fans
Bearing Temperature Alarm: all fans
Interlocks with the oxygen lance prevent oxygen from being turned on
without some minimum draft in the flues. Temperature sensors may be tied to
the opening of a relief damper in some systems. Water supply failure to the
scrubber can shut down the fan(s).
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Fan starts may be interlocked with the following system status:
1. quench water on,
2. at least one isolation damper open,
3. scrubber water on,
4. aftercooler water on,
5. manual fan dampers open,
6. flow control louver at fan must be closed (to prevent motor
overload during startup).
Staffing for BOP scrubber systems may require two full-time operators,
one to attend the gas portion of the system and one to attend the wastewater
treatment system. The location of the operators with respect to each other
depends on where the control boards for each part of the system are located.
Heavy maintenance work, both mechanical and electrical, is usually staffed from
the shop maintenance staffs.
Scrubber Startup
Following is a condensed version of startup instructions for a scrubber
g
system.
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 following
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 quencher and venturi pumps, and the attendant water
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 tempera-
ture recorders.
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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 the gas flow
while maintaining the cleaning efficiency necessary.
Scrubbers with a variable venturi throat sometimes
are set to close the throat before 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: auto-
matic fan shutdown may occur due to high fan vibration,
or motor overload). Adjust differential pressure con-
troller and the motor power controller.
Scrubber Shut Down
Shut down is essentially the reverse of the system startup procedure,
depending somewhat on the anticipated duration of the shut down. Under a short
duration shut down, the main fan is stopped, while lubricant recirculation
systems, etc. continue to function. All water clarification equipment must
continue to operate. Under a long duration shut down, 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.
Scrubber Mai ntenance
Following is a condensed version of recommended maintenance for a BOP
Q
scrubber system.
1. Inspection of the quencher area is recommended after each
furnace campaign. All water cooling connections to the
quencher should be inspected for possible leaks. Quencher
sprays should be spot checked for possible spray pipe
pluggage. Heavy accumulation of sludge in the quencher
elbow should be flushed.
2. The main gas duct between the quenchers and the venturi
scrubbers should be walked monthly for an inspection. Any
significant solids accumulation should be removed at the
time of inspection. Brick linings should be inspected for
wear as well and repaired if damage is detected.
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3. At convenient periods, and based on operating experience
with the equipment, the preclassifier should be drained
and cleaned. Daily inspection to observe the operating
conditions should be maintained.
4. Hose or pipe connections to individual venturi scrubber
nozzles should be checked frequently for leaks and
pluggage. Individual valves at each of the nozzles may
permit isolation of the nozzles for maintenance during
equipment operation. Drive components for the venturi
throat should be inspected weekly. The throat drive
gears should be lubricated at the time of inspection.
Scrubber water manifolds must be maintained free of
solids accumulation. Based on operating experience,
periodic purging of the manifold lines should be prac-
ticed.
5. The internal scrubber throat should be inspected about
every three months. Examine the brick lining for evidence
of wear. Repair cracked or eroded refractories as soon
as possible to prevent further damage and possible damage
to the metal shell.
6. Aftercooling towers should be inspected during system
shutdown periods. Accumulated solid material in the after-
cooling tower should be flushed. The cooling tower spray
nozzles should be operated to verify that all nozzles are
functioning properly and not worn or plugged.
7. General inspections of the induced draft fans and associated
equipment should be conducted daily. The induced draft
fans internal components should be inspected weekly. Heavy
accumulation of material on the fan wheels should be sand-
blasted until the fan wheel is clean. Fan wheel sprays
should be checked to determine that their operation is
satisfactory.
8. Rotary drum filters and their associated equipment should
be visually inspected daily. Piping to each drum filter
should be maintained free of pluggage. Cake chutes from
which the drum filter discharges the sludge must also
be maintained free of accumulation.
Scrubber System Hardware -- Closed Hood
Figure 6 shows a typical configuration for a scrubber installed on a BOP
furnace with a closed hood. The system closely resembles an open hood venturi
scrubber system. One of the principal differences between the two systems is
the position of the hood with respect to the vessel mouth. The hood must fit
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GAS STORAGE HOLDER
BY-PASS STACK
SPRAY QUENCH WATER
WATER COOLED
OXYGEN LANCE
SOLIDS
Figure 6. Typical configuration for a scrubber installed on a BOP with a
closed hood.
35
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closer to restrict the inflow of combustion air. Since a closed hood would
restrict vessel tilting, the hood skirt must be movable or the flow of combus-
tion air must be restricted by some other means than a close fitting hood.
Another important difference is the need to limit the amount of air
infiltration downstream of the hood. Normal points of leakage in an open hood
system such as the lance port and flux chutes must be sealed and are nitrogen
purged before use.
Gas flow sequence is the same as for open hood systems. The water-
cooled hood or waste heat boiler is followed by a quencher, venturi scrubber,
mist eliminator, fan, and flare stack. There may be multiple venturi throats,
but draft is provided by a single fan.
Wastewater treatment is also basically the same. Preclassifiers, thick-
eners, vacuum filtration, pH control, chemical addition for control of scaling
and corrosion are all part of some systems.
The gas cleaning facilities are not shared between adjacent vessels; each
vessel has an independent gas cleaning system. The wastewater treatment
facilities may be shared by adjacent vessels.
Draft control for the closed hood systems is critical to proper control of
the combustion reaction. The systems typically include hood pressure sensors
to alter draft via the adjustable venturi throat.
Because hood draft is so carefully limited to near atmospheric pressure,
there is a tendency for these primary systems to emit hood puffs. It is,
therefore, not unusual to have secondary emissions control systems that are
used to control puffs.
The off-gas rate entering the quencher from a 227 metric ton vessel (250
ton) is approximately 59 scms (125,000 scfm) dry. On this basis the inlet
particulate concentration would be 32 g/scm dry (14 gr/scf dry). To achieve
compliance with New Source Performance Standards requires a control device
efficiency of 99.84 percent.
To achieve 50 mg/scm (0.022 gr/scf) dry the total scrubber pressure drop
is about 165 to 170 cm H,,0 (65 to 67 inches). One system type with a quencher
pressure drop of 13 to 18 cm HO (5 to 7 inches) captures about 75 percent by
36
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weight of the particulate at the quencher. The remainder is captured at the
venturi with a pressure drop of about 152 cm H20 (60 inches).
Operated in the suppressed combustion manner, the waste gas system can
recover as much as 62 scm (2,200 scf) per metric ton of steel produced. The
heating value of the waste gas is over 7,500,000 joules/scm (200 BTU/scf).
An example of the alarms and interlocks in the closed hood system that are
not present in the open hood system is available from a technical paper by U.
S. Steel. The following alarms were identified as causing no process shut
downs:
1. Increasing negative pressure in the waste gas duct that might
pull in water seals and reduce hood draft.
2. High oxygen content in the flare stack. This indicates air-
leakage downstream of the quencher; 1 to 2 percent oxygen is
normal.
3. Ruptured disc at the relief door (for emergency pressure
relief) that might let air enter the system.
4. High waste gas temperature (> 1093°C, 2000°F) at the top of
the water cooled hood indicates a combustion rate greater
than 25 percent.
5. Hydraulic system for the hood skirt malfunctions.
Failures that will not allow a blow to begin, but will not interrupt a
blow in progress include:
1. Low water level in relief door seals.
2. Relief door at top of water cooled hood open,
3. Relief door before the venturi open,
4. Relief door before the fan open.
Major faults cause equipment shutdown in the following ways:
1. Local emergency stop, 4160 volt power failure, or fan starter
failure cause the venturi throat and fan inlet damper to open
to let the coasting fan evacuate the duct. The oxygen lance
is raised; the hood skirt is raised; nitrogen seals remain on
for two minutes; scrubbing water is stopped.
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2. High fan or motor bearing temperature, low fan lubricating
oil pressure, or pressing the fan stop button permits the fan
to continue for two minutes after the oxygen lance is re-
tracted. Other actions follow (1) above except scrubber
water is left running.
3. High waste gas temperature [sic., second stage of temperature
alarm], low hood cooling water flow, low waste gas flow,
nitrogen purge failure, high hood cooling water temperature,
low quencher water flow, or water in the fan inlet allows the
fan to continue to run; the oxygen flow is shutoff; nitrogen
is shutoff; the hood skirt is manually raised; the gas flow
is normally regulated by the venturi and fan damper until
the fault is corrected.
3.2 SECONDARY EMISSIONS CONTROL
Secondary emissions are the emissions that escape capture in the primary
control hoods and those emissions from ancillary operations in the BOP shop.
The typical ancillary operations are described in Section 2.4 of this manual.
The pollutants to be captured during charging, tapping, and puffing of the
vessel are those cited previously, mainly particulate, with some carbon monoxide,
and perhaps fluorides. Some primary emission control systems, especially those
built more recently, include design features to control the vessel secondary
emissions. Smaller hoods can be placed over the position of the vessel mouth
during charging and tapping. Gas trapped by these hoods is ducted to the main
duct leading to the primary system collector. Such an arrangement would be
found on combustion hood primary systems where some leakage through secondary
dampers is not of great concern.
Charging fume emissions have been reduced in some plants by the use of a
Gaw damper in conjunction with the primary collection system. The Gaw damper
is a plate that is fitted into the lower portion of a combustion hood. The
damper slides horizontally across the hood, limiting flow in some hood areas.
During charging the damper is positioned to close off the tapping aisle side of
the hood, thus concentrating the draft on the charging side of the furnace
capturing more charging emissions. This damper may be especially useful where
retrofitting a separate charging and tapping control system is difficult.
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Emissions of charging fumes may be substantially reduced by careful
attention to operating practice. Maximum reduction is accomplished by two
methods. One is to pour the metal into the vessel as slowly as possible. The
other is to tilt the vessel as little as practicable, thereby keeping its mouth
as far into the hood as possible.
Separate systems may be supplied to control charging, tapping, and puffing.
Such systems are more common in shops with a closed hood primary system. Some
systems presently in use have gas flow rates in the range of 71 to 94 scms
(150,000 to 200,000 scfm). There are no industry wide standards, however.
Although the usual control device is a baghouse, in two U. S. plants scrubbers
are being used to remove the captured particulate emissions. The configuration
of capture systems may be small local hoods or furnace enclosure plus local
hoods depending on the designer's preference.
Complete furnace enclosures were initially designed to service Q-BOP
installations that must continue nitrogen and/or oxygen blowing while tilting
or rotating the vessel. The concept is also applicable to top-blown vessels
for fugitive emission control.
Many of the secondary emissions sources are intermittent in nature.
Advantage can be taken of this characteristic by combining gas flow from a
number of sources and conveying the gas to common or shared collectors. With
common fans it is possible to concentrate draft on a single operation for a few
minutes and then switch to other sources by means of dampers.
The shared equipment approach has many advantages, but most of the existing
plants have added secondary emission equipment as required, resulting in con-
trol of one process at a time. Then too, some of the operations are not near
enough to one another to accommodate this approach.
Hot metal reladling is one operation often found individually controlled.
Early attempts at controlling these emissions were made with multicyclones.
The multicyclones could remove kish, but iron oxide penetrated the collector.
It is now recognized that fabric filters or scrubbers can be used to collect
these emissions at high efficiency. With fabric filters some kind of knockout
chamber or spark box is needed to prevent hot sparks from entering the baghouse
and burning holes in the bags. For a close fitting hood the gas evacuation
rate is about 50 acms (106,000 acfm) at 49°C (120°F). Canopy hoods in place of
39
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a tight fitting hood might require three times this volume for effective
capture.
One or more flux handling systems are found in BOP shops. Secondary
emissions are generated at the railroad car or truck unloading stations, at
all conveyor transfer points, and in the storage bins above the BOP furnace.
One recently built plant has a 25 acms (75,000 acfm) system with a baghouse for
flux truck unloading. In addition there are two flux handling and flux
storage bin control systems using baghouses with gas flow rates of 12 acms
(25,000 acfm).
Plants making alloy steels with toxic alloying elements have fume control
systems for these operations. Leaded steel, in particular, is an example of
this situation. The same plant cited in the above paragraph has a secondary
control system controlling fumes from the station where lead is added to the
ladle, at the teeming stand. The system gas flow rate is 28 acms (60,000 acfm)
and particulate is collected by a fabric filter.
Secondary System — Maintenance
Fabric filters are used frequently in the control of secondary emissions
as is suggested by the above discussion. The amount of maintenance required
depends to a great extent on how well the system is designed. Proper fabric
selection, air-to-cloth ratio, and bag spacing are important. If not properly
selected, they will cause frequent replacement or unacceptably high pressure
drop. Construction with a spare compartment in addition to the one down for
cleaning at any moment permits on-line maintenance. On some installations
where the use of the baghouse is intermittent, a spare compartment for on-line
cleaning is not required. An example of this situation is the baghouse which
serves the reladling station.
Data gathered through plant visits and discussions with control agencies
suggest that many secondary systems do not receive as much preventive main-
tenance and consequently suffer complete failure more often than primary
systems. The systems may also be underdesigned and/or equipment with poor
reliability may be purchased.
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4.0 ABNORMAL OPERATING CONDITIONS
In the following sections are discussions of the AOC's related to BOP
shops, broken into a group related to process problems and a group related to
pollution control equipment. The importance of each of these AOC's in terms of
environmental effects is not necessarily indicated by the length of discussion.
Simple descriptions of problems that produce serious effects are possible while
less severe problems may require more elaborate explanations.
4.1 PROCESS RELATED
4.1.1 Startup
For the purposes of this manual, startup will be defined to include
bringing a new vessel into service or restarting a cold vessel. It will not
include the cyclic nature of the basic oxygen process that could be interpreted
to produce a startup with each new heat. No special emissions problem has
been found to occur in the restart of a cold vessel.
Burn In
This is a situation related to bringing a new or newly relined vessel into
service. The vessel is lined with tar bonded refractory. Tar bonding after
heating, leaves a residue of tough coke around and between refractory grains to
bind and protect the grains. It makes reactions between slag and refractory
more difficult thus promoting longer vessel lining life.
To burn in a vessel, a load of coke is dumped onto the bottom of the
vessel. Another load of burning coke is added and the oxygen lance is actuated
to speed up the burning process. The fire ignites the surface tar near the
vessel bottom and gradually moves up the vessel walls as the oxygen lance is
raised.
41
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It is necessary to complete the burn in rapidly as opposed to gradual
heating to avoid slumping of the refractory lining. The process generally
occurs over a time period of 20 to 100 minutes. Vessel reline frequency is
related to whether the shop is at full production, the type of steel produced,
refractory maintenance practice (gunning), and refractory material. Lining
lives in excess of 1,200 heats are not unusual. Some new plants achieve up to
2,000 heats. As recently as five years ago, 500 to 600 heats was typical and
could now be found in some instances.
The problem resulting from burn in is the production of carbonaceous fumes
or incompletely burned organics. The emissions from this operation are, in
some cases, put through the primary fume collection system. Scrubbers can
treat the gases; how effectively is not known. Use of primary collectors is
the only method known for minimizing emissions.
4.1.2 Shut Down
When a BOP vessel is taken out of service, the lining is broken loose.
After completing the breaking operation, the lining is dumped on the ground
by rotating the vessel. This usually causes a cloud of dust. Its frequency is
the same as vessel burn ins.
4.1.3 Abnormal Operating Conditions
Puffing at Hood
Puffing at the hood refers to escape of fume from the area between the
mouth of the vessel and the hood face; although if the hood is not well main-
tained, fume loss can occur at cracks between the hood panels. Puffing is
produced by waste gas pressure surges that the hood draft cannot contain. An
inadequate gas removal rate from the hood is one potential cause. However,
where initial system design provides a removal rate sufficient to control fume
but subsequent deterioration occurs, the cause may be leaks in the hood.
42
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In an open hood system, these leaks may develop between adjacent hood panel
sections and are produced by the continual expansion and contraction of the
hoods during a campaign. Leaks at points in the gas cleaning system such as
expansion joints or duct walls would have the same effect, i.e., reduce draft
available at the hood face.
If maintenance practices include complete repair of leaks during vessel
relines, it follows that hood puffing from this cause will be of low frequency
after reline and get progressively worse as the vessel approaches the end of a
campaign. Puffing, however, can occur even on a well drafted furnace when
furnace reactions become more active than usual. Foaming and slopping of the
bath (discussed later), for instance, can produce puffs.
In a closed hood or suppressed combustion waste gas system, air intake
must be carefully limited to prevent more CO combustion than that for which the
system was designed. Therefore, the draft at the vessel mouth is controlled to
be slightly negative by a sensitive pressure control circuit. Sudden surges in
vessel reactions make these systems more prone to puffing. For this and other
reasons, suppressed combustion systems should be equipped with secondary fume
removal systems.
The frequency of puffing is highly variable from plant to plant depending
on the design of the gas cleaning system, its condition, and furnace practice.
Puffing can last from a few seconds to an entire oxygen blow (about 20 minutes).
No measurement of particulate loss from puffing has been reported in the
technical literature reviewed. The quantity per heat would be variable with
the severity of the problem.
-Recommendations for minimizing puffing due to foaming and slopping and
hood or duct leaks are discussed later in this manual under those specific
sections.
Improper Transfer of Hot Metal to Vessel
Charging is a routine part of BOP operations, therefore, charging emissions
cannot be viewed as an AOC. Charging emissions are fugitive emissions presently
regulated only by limitations on the opacity of visible emissions.
There is, however, good operating practice by which charging emissions
(hot metal addition to the vessel) can be minimized. Departure from this
43
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practice can be viewed as an AOC. To achieve the highest degree of control
possible, it is necessary to control the vessel tilt angle and the speed of
pouring hot metal.
Minimizing the tilt angle of the vessel keeps the mouth of the vessel
closer to the main fume hood (or secondary hood where a charging control
system is present). The closer to the hood the more effective is the hood
draft in capturing fumes. Since the capture velocity produced by the hood is
about inversely proportional to the square of the distance from the hood face,
small decreases in the distance between hood and vessel mouth can produce big
improvements in capture efficiency and vice versa.
Slow pouring apparently reduces the agitation of the bath and splashing.
The severity of charging emissions can also be related to other variables such
as charge material and scrap preheating. This will be addressed in a succeeding
item.
The frequency of excessive charging emissions can vary widely. The skill
of the charging crane operator for instance is important to this AOC. The
duration of the emissions can be anything from 1 to 3 minutes per heat. The
question of the excess quantity of emissions cannot be answered at this time
because the quantity of normal charging emissions is not well defined.
Slow pouring reduces the level of emissions. A hot metal pour of two
minutes or longer effectively reduces pouring emissions.
Improper Charge Material
Deviations of hot metal composition and extraneous matter in the scrap are
responsible for this AOC. In particular, oil, water, or cement in the scrap
are capable of producing increased emissions. The emissions occur where hot
metal comes into contact with the contaminated scrap. Hot metal having a high
silicon content (>2%) produces increased emissions during pouring.
A rough estimate of the frequency of occurrence is two per week. The
duration is that of typical pours or about 1 to 3 minutes per heat. No quanti-
tative data defining the level of increased emissions is available.
44
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Improved control of raw materials and quality of hot metal must be
achieved to reduce frequency of this AOC.
Foaming and Slopping
Foaming and slopping describe an AOC in which material from the bath
spills over the mouth of the vessel, down the sides, and/or onto the operating
floor. This AOC occurs during the oxygen blow while the bath is active due to
the various chemical reactions taking place. Spilled material releases iron
oxide fume that carries out through the roof monitor.
Often accompanying the spillover is an excursion in the waste gas tem-
perature that may cause a relief damper in the waste gas system to open. The
latter problem occurs primarily in systems using electrostatic precipitators
for particulate emission control. .Precipitator systems are vulnerable to
temperature damage because of limitations in the gas cooling and conditioning
equipment.
The occurrences of foaming and slopping or perhaps the severity of it
seems to have declined as compared to the earlier years of BOP furnace steel-
making. This may be partially related to improved process control which
developed as time has progressed.
Several things have been identified as contributing to foaming and slopping
problems. The presence of unusually high amounts of silicon and/or manganese
in the hot metal charged to the vessel is one factor. In this case, more iron
12
is oxidized and the slag becomes overly oxidized. Later in the heat, the
oxygen in the slag begins to react with carbon. Combustion of the additional
CO in addition to that produced by lance oxygen increases the waste gas tempera-
ture and carbon dioxide (C02) content. In a precipitator waste gas control
system the relief damper may open with the sudden temperature rise.
When too much oxygen reacts with the carbon too rapidly, the amount of
12
iron oxide formed is insufficient and the slag melting point increases.
Solidification of slag compounds stabilizes the foam. The stable and viscous
slag leads to spark emissions and vessel slopping.
45
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12 13
Slopping is reported to be more prevalent when vessel linings are new.
This is presumed to be related to the fact that the working volume of the
vessel is smaller when the lining is new and thus easier to overflow.
The estimated range of durations for vessel foaming and slopping is one to
five minutes. At best, it may occur twice per week. Some shops seem to be
prone to the problem. One plant reported two per day average and up to 25
14
percent of heats could be affected by foaming and slopping.
In response to frequent problems with this AOC, Ford Motor undertook a
study to define the problem and find a solution. They found that by adjusting
the operating practice they could reduce the frequency of foaming and slopping.
Their solution included continuous monitoring of the waste gas concentra-
tion of C02. During normal heats C02 evolution was found to increase steadily
as the blow proceeded, reaching a plateau about ten minutes into the blow.
With sloppy heats C02 evolution deviated from the gradual increase normally
found. Adjustment of lance height and blowing rate were used to maintain the
proper rise in CCL concentration.
The Ford study cited three variables that had a major effect on maintaining
the proper rise in CCL concentration. They are:
1. nozzle design,
2. nozzle wear or erosion, and
3. lance height and oxygen blowing rate.
During a heat they found slopping could be reduced by the following steps:
1. "To increase the decarburization rate (rate of'formation of C02),
lower the lance and/or increase the oxygen rate."
2. "If an early plateau in the curve [sic., blowing time versus
CCL curve] cannot be corrected within one or two minutes by
actions indicated above, decrease the oxygen rate to avoid
driving excessive amounts of oxygen into the slag and lower the
lance to maintain penetration."
3. "To decrease the decarburization rate, raise the lance and/or
decrease the oxygen rate."
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All of the above steps were used to control the rate of CCL evolution, and
thus cause the blowing time versus C02 curve to follow the path it follows in a
normal non-slopping heat. Accomplishment of these manipulations in an effective
manner depends on the skill of the operators. Ford reported a wide variation
in the ability of operators to reduce slopping. Overall, however, they reported
that with good training and supervision they felt they could reduce occurrence
of sloppy heats by 90 percent.
All of the above cited experience is for conventional, top blown BOP
furnaces. Q-BOP operations are reported to effectively prevent slopping by
injection of powdered lime with oxygen through the tuyeres.
Relief Damper Opening
Many BOP furnace systems have relief dampers in the gas system downstream
of the water cooled hoods. The purposes of these dampers include pressure
relief, temperature protection for the downstream gas cleaning system, and a
means of drafting the furnace hood in case of failure or shutdown of the gas
cleaning system fans that provide the induced hood draft. When open these
dampers release furnace emissions directly to the atmosphere.
The necessity of having such a damper to serve the latter two purposes,
i.e., temperature protection and emergency draft, is not certain. Temperature
protection of the gas cleaning systems can be accomplished by reducing blowing
rate or retracting the lance should a temperature excursion occur.
The need to complete an interrupted heat is certainly a necessity if the
metal may solidify before the malfunction can be corrected. In most cases the
delay is not long enough to have to finish the heat without control. It can be
vented, however, into the building roof and consequently emitted through the
roof monitor as is done in plants without the damper. The argument in favor of
this approach is that leaks commonly develop because of dirt on the damper
sealing surface. These leaks would be avoided where the damper is closed off
or excluded.
Emergency pressure relief is a necessity, but can be accomplished with a
relief port covered by a rupture disc. This is the kind of equipment used in a
suppressed combustion gas cleaning system to prevent leakage during normal
operations.
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Causes of relief damper opening are combustible gas (in a precipitator
system), pressure relief, temperature excursion, and failure of the draft
system. The draft system failures will be discussed later in the control
equipment section.
The situations in which pressure relief is necessary are not clear.
Explosions do occur during charging when the vessel is tipped, but presumably
this could also happen on a delayed basis while the vessel is upright owing to
water or other foreign material in the charge or a hood water leak. In a
partial or suppressed combustion system, carbon monoxide is a potential explo-
sion source if air becomes mixed with it, so great pains are taken to prevent
inleakage. In a full combustion hood all carbon monoxide should be burned; but
if it is not, it represents an explosion threat when coupled with an electrostatic
precipitator.
Temperature excursions can be produced by the vessel reactions that pro-
duce foaming and slopping as described previously. Failure of the cooling and
conditioning sprays for a precipitator installation would likewise produce an
excursion.
The frequency of relief damper openings has been estimated at one to ten
per month. Durations could be as little as 20 seconds to as long as the whole
blowing time (about 20 minutes). The short duration would probably relate to
temperature excursions while the longer duration would likely be related to
equipment failure.
123
Based on data cited in the literature ' ' the uncontrolled emission rate
of particulate is 6 to 20 kg per metric ton (12 to 40 pounds per ton) of steel
produced. If the relief damper is open for a complete blowing cycle, this
would be the emission rate. If only a portion of the blowing cycle is included,
the emissions are not directly proportional to the fraction of blowing time.
Emissions are higher early in the heat and taper off as the heat progresses. A
study performed in West Germany of one furnace showed the dust emissions two
minutes into the blow to be 125 g/scm. The dust concentration tapered off
nearly linearly until 16 minutes into the blow it was 40 g/scm. These con-
centrations are not necessarily representative of all types of BOP furnace
48
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operation, but demonstrate the decrease in dust emissions as the blow pro-
gresses and provide a means for roughly estimating uncontrolled emissions at a
given moment.
In the above discussion several means of reducing or minimizing the
occurrence of relief damper openings have been mentioned. Some plants with
relief dampers in their original gas cleaning system have permanently sealed
them. As pointed out, the function of pressure relief can be handled in other
ways, i.e., doors covered with rupture discs and doors which open only under
pressure surges.
Temperature excursions can be sensed and then alarmed and/or tied into
reduction of blowing rate or lance retraction to prevent damper opening. Lance
retraction would be reserved for the more serious problems and actuated as the
second stage of a two stage sensing system.
Another potential solution is to make the precipitator less sensitive to
short term excursions thus permitting continued operation without damper
opening except under extreme circumstances, e.g., 800°F for 15 minutes or more.
Performance of the collector may be poorer at higher temperatures, but some
collection is better than no collection. The primary considerations are
insulators and steel expansion.
Porcelain high tension insulators are not used in service over about
450°F. In precipitators designed for continuous service over 500°F and as high
as 850°F, alumina insulators are normally used.
If the precipitator has not been designed for continuous service over 500
to 600°F, there may not be sufficient provision for expansion during an excur-
sion to higher temperatures. This could result in permanent deformation of
supporting members. Obviously little can be done after the initial structural
design is completed, however, a short term excursion may be tolerable. Five or
ten minutes flow of hot gas is not long enough to heat the great mass of preci-
pitator steel to the same temperature as the gas stream. Heating occurs gradually,
therefore, expansion occurs gradually perhaps providing a short period during
which high temperatures can be accommodated without damage.
At the least a change to high temperature insulators will make the pre-
cipitator operable at higher temperatures. The equipment designer can be
contacted to determine how long an excursion can be tolerated from a structural
standpoint.
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The presence of a combustible gas mixture can be treated by stopping the
blow long enough to clear the system without opening a relief damper. As
previously mentioned, if it is necessary to complete a blow to get the metal
out of the vessel, it can be done without a relief damper by venting through
the building with proper precautions to protect people working the upper
building floors, or preferably the heat may be dumped.
Pit or Charging Explosions
These explosions occur in the slag pit or in the vessel. They are generally
caused by water getting into the pit or vessel and having molten metal dumped
on top of the puddle. The water flashes to steam causing an explosion which
throws molten metal or slag randomly around the shop.
The explosions usually shake the building sufficiently to stir up settled
dust resulting in some dust emissions from various building openings. Most of
the effect is internal and may include serious injury or fatality of workers in
the vicinity of the source.
If the vessel is tilted down to receive the charge, the metal is expelled
across the charging aisle. If it is tilted up and under the hood, the surge
could open pressure relief doors in the gas cleaning system as well.
Pit explosions are estimated to occur three times per year and charging
explosions once per year. The explosion is momentary, but may produce effects
lasting up to 20 seconds.
The only recommendation for reducing these occurrances is to avoid hood
water leaks and any other water spills. Unfortunately, water in the vessel may
enter with the scrap.
Running Stopper
Steel from the BOP furnace vessel is tapped into a steel ladle upon
completion of the heat. The ladle's function is to carry the steel from the
vessel to either ingot molds or, in the case of continuous casting, to tundishes.
Molten steel is transferred through a pouring nozzle in the bottom of the
ladle. Flow of the molten metal is regulated—on, off, and speed—by movement
50
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of a stopper rod whose tip is inserted into the base of the nozzle. The
stopper rod head is made of a hard clay-graphite mixture and mates with the
nozzle seat made of heavy-duty fireclay.16 The fireclay softens under molten
metal temperature conditions giving a good seal in combination with the hard
rod tip.
The causes of a running stopper include an improperly set nozzle, i.e., a
rod not mating well with the nozzle seat because of improper installation,
teeming a cold heat that leaves a skull at the nozzle seat, and high FeO slag.
The consequence of a running stopper is having steel spill onto the
ground in the teeming aisle, reducing product yield, evolving iron oxide parti-
culates, and stirring up pit dust, the latter two of which may escape through
the building doors or roof monitor.
Estimated frequency of occurrence is one to three per month lasting from
30 to 60 minutes. No emission measurements of this source alone have been
reported. Slide gates are known to have fewer leaks than stoppers, but poor
ingot surface conditions may result from using slide gates; so slide gates
cannot be used for casting all types of steel.
4.2 CONTROL EQUIPMENT RELATED
There are usually several pollution control systems operating in BOP shops
as discussed in Section 3.0 of this manual. 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, the
narrative will .provide this information. Where it is more prevalent in one of
the systems, it likewise will be stated in the narrative.
The bulk of data obtained was in reference to the primary particulate
control system for two reasons. One reason is that secondary emission control
is far from universal, and therefore, a lesser amount of data exist. The
second reason is that the visual and production impact of failures in the
secondary systems is less evident than primary system failures. For instance,
a flux handling dust control system is prone to maintenance problems due to
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duct buildups of lime dust. The dust control system is not essential to
continuing production and is usually located where there are few employees.
The result is it receives less attention and less maintenance (though it may
need more), and therefore, less data is available concerning its malfunctions.
Where the secondary systems are similar to the primary system one may extra-
polate that similar AOC's may occur in both systems.
4.2.1 Startup
Here again, as in the case of process startup, startup excludes the
normal cycling accompanying the production of each heat. Startup would include
bringing the system on-line after a shutdown for maintenance, rebuild, or
strike, and bringing a new system into service.
Precipitator Warmup ^
Most precipitator manufacturers recommend not energizing the precipitator
until the gas temperature entering the precipitator has reached 150 to 200°F.
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 dust collected on it 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 insulator, thus grounding a section of the precipitator until it is replaced.
Startup of an entire precipitator installation does not occur often,
perhaps once every year or two to as little as once in five or ten. More
frequently a single chamber of a multichamber precipitator will be taken down
for maintenance and restarted. This could occur as often as once per week to
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once per month. The warmup period Is relatively short for the BOP in that the
gas temperature reaching the'precipitator rises to 260 or 315°C (500 or 600°F)
by the middle of the blowing period. Including the charging period the duration
is estimated at 10 to 20 minutes.
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 particulate 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 process particulate discharge rate is in the range of 6 to 20 kg
1 p O
per metric ton (12 to 40 pounds per ton) of steel produced. ' '
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 means that collection efficiency will also be
reduced, but better than no collection. Reduced voltage, however, reduces the
potential for burning out insulators. One potential problem with this approach
is the buildup of dust (or mud because of moisture) on the plates and wires.
If the moisture condensation is severe, then this is not a satisfactory solu-
tion. In some cases increased rapper (or vibrator) intensities may be capable
of preventing 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.,
I Q
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 devices that can accomo-
date reduced voltage operation. Older electrical sets, particularly those with
saturable reactors, do not work well under these temporary conditions.
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, but some shops practice scrap preheating in the vessel
with natural gas. Scrap preheating in this manner increases the percentage
53
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of scrap that can be charged to the vessel. Precipitator preheating then is a
byproduct of the production operation.
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
precipitator through the warmup period would be reduced in frequency.
Stack Puff
Stack puff refers to a temporary 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 duct floor or attached to flow control
louvers in the system reentraining into the gas stream. During a fan or system
shut down dust being conveyed by the gas stream settles onto the duct floors.
Also, where a single fan in a multiple fan system is shut down, dead or low
flow areas may develop in some duct runs leaving dust on the duct floors and
flow control surfaces. Upon restarting the fan, the settled dust begins to
sluff into the gas stream.
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 sixty minutes. No data or
estimate of the extent of additional emissions is available.
No good corrective action for this AOC can be recommended. If dust
dropout in the flues is an extensive problem occurring 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 is deposited under
normal operating circumstances, it cannot be stated certainly that dust emis-
sions upon startup would be any less than had the flue not been cleaned.
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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
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 chambers 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, but the corresponding lower gas
flow in the other chamber(s) does not necessarily produce correspondingly less
reentrainment.
An additional consequence of unbalanced flow is preferential deposition of
dust in hoppers under the precipitator chamber with higher gas flow. This can
lead to upsetting the hopper dust removal cycle at the least, andi in some
cases, may shut down a portion of the precipitator above the problem hopper
because of collected dust contacting the discharge electrode frame.
Reestablishing balance in the system was estimated at 12 to 16 hours in
one plant affected by this problem.6 The frequency of occurrence could be as
often as once per week to as little as once per year. The practice of preventa-
tive maintenance on the fans, however, would typically require more frequent
shutdowns than once per year.
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The amount of additional emissions resulting can be estimated only if the
percentage of gas flow through each chamber is known and the efficiency of the
precipitator under normal even flow conditions is known. The emissions can be
highly variable from one startup to the next. For instance, in a four fan
system where only three operate at any given time, there are four combinations
of three fans possible. Each of these combinations can produce different
initial flow conditions.
Insufficient Draft
This is an upset that occurs in a control system with common multiple
(manifolded) fans. The control device(s) may be precipitators or wet scrubbers
in an open or combustion hood type system (manifolded fans in a closed hood
system are not typical of present design practice).
Insufficient draft results from one fan being shut down with a simul-
taneous failure of a spare fan to start. In particular, the upset was reported
to occur due to ice in the fan housing. Moisture from the process gas stream
condensed, accumulated and froze in the housing to a point where movement of
the fan wheel was prevented.
When such an upset occurs the reduced draft leaves emissions to spill over
into the shop creating building monitor emissions. The blow rate can be
reduced to attempt to match the process emission rate, but hood capture will
not be as good because the intake velocity at the hood periphery is reduced at
lower gas evacuation rates. The quantity of additional emissions can be
relatively low if the blowing rate is reduced and high if production is main-
tained at the normal blowing rate.
Obviously this upset is confined to the winter season. Its frequency of
occurrence was not obtained, but it could potentially occur two or three times
per winter season. Its duration would be the time required to melt enough ice
to get the fan wheel turning, perhaps two or three hours.
Method of minimizing its effect would include reducing the blow rate as
previously discussed. The-plant reporting this AOC does the necessary maintenance
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or fan repairs and restarts the fan when the work is completed.6 The fan is
then kept turning at low speed (idle) to avoid the icing problem and can easily
be brought up to speed when required to replace a fan in service. Of course,
this practice is only necessary in cold weather.
4.2.2 Shut Down
AOC's relating to shutdown refer to those things occurring when a vessel
is taken out of service for maintenance or reline, not to the period at the
completion of each heat.
Dampers Stuck or Jammed
This AOC can occur in a two or three vessel shop that shares a common gas
cleaning system. Each vessel has its own hood and spray chamber (in the case
of a precipitator control device) or quencher (in the scrubber case), but at
some point downstream of these the waste gas is combined in a single flue.
When one of the vessels is shut down for reline, the ducting to the off-line
vessel needs to be isolated from the gas cleaning equipment to prevent fan
draft capacity from being lost to the off-line hood. This is accomplished with
a butterfly or guillotine type damper.
Occasionally these dampers will not completely close or become jammed,
thus allowing leaks of ambient air into the gas cleaning system. These mal-
functions reduce the draft available to the operating vessel(s).
Failure to close or jamming is produced in several ways. One way is a
failure of the electrical actuating and sensing system. Perhaps limit switches
or some other component fails. The accumulation of dust on the sealing or
sliding surfaces of the damper may also prevent closing or at least reduce the
effectiveness of the seal. Butterfly type dampers are prone to the poor
sealing problem. This has led to retrofitting guillotine type dampers into
existing systems to provide a better seal. The guillotine type, of course, is
not completely trouble-free either. The effect of this damper AOC is reduced
draft for the operating vessel(s) with consequent spillover of fumes into the
building unless blow rate is reduced. The level of increased fugitive emissions
from the building monitor is not known and depends on whether the blowing rate
is adjusted.
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To determine how often this can occur, it is necessary to know the
frequency of vessel relines. The AOC, however, does not necessarily occur each
time a vessel is shut down for reline. An estimate of the range of frequencies
is once per month to twice per year. The increased emissions will continue
until blowing rate is reduced or the repairs have been completed. On this
basis the expected duration is one to twenty-four hours.
Duration of these AOC's may be shortened by installation of damper position
sensing devices to provide immediate recognition of the problem. The frequency
may be reduced by the practice of preventive maintenance, e.g., frequent cleaning
of sealing surfaces, cleaning and checking of electrical contacts. Instal-
lation of more reliable equipment should also be considered.
4.2.3 Abnormal Operating Conditions
Downtime of Primary Collection Systems
Downtime of primary collection systems refers to shutdown of the entire
gas cleaning facility for capturing BOP furnace hood emissions. Failure of
portions of the system that do not result in entire facility failure are
treated in subsequent sections of this manual. Total failure of secondary
systems (charging, tapping, reladling, etc.) are treated in the next section.
One source of total pollution control system failure is catastrophic
utility failure, i.e., power loss for a section of or the entire plant.
Several plants reported this to occur three times per year to once every five
years. A power failure that affects both the process and control equipment
causes both to shutdown and, therefore, the immediate environmental effect is
small. If the failure is selective and only the control equipment is affected,
then the vessel will continue to operate subject to interlock protection built
into the system. Some plants may finish a blow at reduced blowing rate to
prevent the risk of damaging the vessel if the outage will exceed several
hours. The emissions escape the building through the roof monitors or through
emergency relief dampers. Under these conditions, continued operation of the
vessel would be unlikely past the completion of the heat in the vessel at the
time the failure occurred. This was the consensus of plant operator's opinions.
The effects of the power failure would be limited to the total vessel emissions
from the time the failure occurred until the blow was completed, i.e., some
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fraction of 6 to 20 kg of parti oil ate per metric ton (12 to 40 pounds per
ton) of steel.1'2'3
It is conceivable to have a power failure that affects only a precipitator
without stopping the fans. This kind of upset was not reported by any plant.
Plant practice under these conditions would be is unknown.
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 spare fans and pumps to avoid a shutdown due to a pro-
blem with a single fan or pump. With installed spares it is likely that at
worst the system capacity to clean or provide draft will be reduced when a
failure in one of the operating components occurs. For instance in a system
with four fans (three operating, one spare) when one fan fails the spare is
started. In the less likely event that two fail, the vessel can still be
operated at a reduced blowing rate. For scrubber pumps the analogous problem
is reduced scrubbing efficiency instead of reduced draft.
Clarifier rake failure can shut down the scrubber wastewater treatment
system. Rake failures are produced by drive motor breakdowns and mechanical
failures in the rake drive system. Chunks of material and a buildup of coarse,
dense, gritty particulate on the thickener bottom were two things cited as a
cause of rake problems. One plant reported rake failures due to rocks in the
thickener, presumably thrown in by employees.
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 the
recycle mode, to a once through mode of operation. If no spare thickener
capacity exists or no terminal settling basins are in use downstream of the
bypassed thickener, the increased solids content of the water will be about the
6 to 20 kg per metric ton (12 to 40 pounds per ton) of steel cited previously
as particulate production rate. Many of the plants visited did have terminal
settling basins of some sort that would reduce the amount of particulate
reaching the 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 rates to blowdown result from this AOC unless pro-
duction operations are suspended during the repairs. The repair operations
often require draining the thickener to remove accumulated solids.
Increased emissions resulting from fan, pump, or power failures may be
reduced by interlocking the failure sensors with oxygen lance retraction. If
the failure is one that is expected to prevent normal operation for a period
long enough to damage production equipment, then the interlocks can be over-
ridden and the blow completed or the heat dumped from the vessel into a ladle
for handling much the same as slag.
Installed spare capacity is a powerful tool to overcome the failures in
single components. As was mentioned, installed spares are widely used and
especially evident in the more recently constructed systems. An exception to
this is the fan in a suppressed combustion or closed hood system. In accordance
with present design practice there is no installed spare fan in these systems.
The concern about air leakage into the system (with the accompanying risk of
explosion) is the overriding factor.
Though less effective, the concept of multiple units with no spare capacity
is useful. Two units sized for 50+ percent of total capacity leaves the capability
for control at reduced efficiency when one of the two fails as opposed to no
control when a single 100 percent unit fails. Obviously two units sized for 75
percent capacity would be even more desirable.
In the area of wastewater treatment backup capability, similar concepts
are applied to pumps and thickeners. With thickeners, however, an additional
alternative may be available through terminal lagoons or settling basins
immediately upstream of the plant outfall.
In the way of prevention of thickener rake failures, a number of plants
have chosen to install preclassifiers upstream of the thickeners. The com-
mercial forms of the preclassifiers are varied, but their common purpose is to
remove grit and heavy solids from the dirty scrubber water thus avoiding its
deposition in the thickener. One plant employed a wire screen cover over their
thickeners to prevent foreign matter (rocks, etc.) from being thrown into the
I Q
thickener and consequent fouling of the rake.
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Downtime of Secondary Systems
The basic causes of total primary control system failure enumerated in the
preceding section are also responsible for total failure of secondary control
systems. In addition to those causes, the use of baghouses in control of
secondary emissions brings other causes into the picture not present in the
primary system (baghouses for primary BOP furnace control are used in Europe,
but the first U. S. installation is only now being constructed).20 The
prevalent means for controlling secondary emissions from charging and tapping,
hot metal transfer, flux handling, slag raking and desulfurization have been
identified in Section 3.0 of this manual. Contrary to the situation with
primary emission control, many plants have no secondary emission control
systems. Of the listed secondary sources above, flux handling controls are the
most common.
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 the case of 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.
Pump failures will affect performance much the same as in primary systems.
Wastewater treatment (classifying and thickening) may be shared with the
primary control system.
Complete failure of a baghouse can be produced by high temperature or high
pressure drop causing a bypass damper to open. Bag blinding due to the pre-
sence of mositure or fine fume particle size are possible sources of high
pressure drop. Shaker or reverse air system failures may cause a complete
shutdown as well as screw conveyor failures depending on where in the system
they occur.
If a down turn for maintenance is not provided for the whole shop, main-
tenance on the secondary emission control systems will mean that the systems
must be shut down while the remainder of the shop is running. The environmental
effect is the same as though a system failure has occurred.
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The limited data obtained on frequency of AOC's on secondary systems
indicate relatively high frequencies when compared to primary system AOC's.
Data from one charging control system show 28 AOC's over a ten month period.
Data from two hot metal transfer stations showed 18 and 47 AOC's over a period
11 21
of roughly one year. * Data from two flux handling systems show 1 to 8
AOC's over about a one year period.
No data were obtained for slag raking and desulfurization AOC frequency.
One secondary system for teeming leaded steel experienced 17 AOC's over a ten
month period.
When an AOC occurs, the environmental effects are periodic. For charging
during an AOC, additional emissions occur for about two minutes per heat.
Additional tapping emissions are vented for about 4 to 8 minutes per heat. Hot
metal emissions occur for about 2 to 4 minutes per heat during a complete
control system failure. Slag raking and desulfurization emissions cover a 5 to
20 minute period per heat.
The above data provide estimates of the duration of periodic increased
emissions while an AOC is in progress, but say nothing about how long these
periodic emissions continue. The length is dictated by the amount of time
needed for repairs. Data provided by the Erie County, New York control agency
shows repair and maintenance durations for hot metal transfer control equipment
to cover the range of 1 to 96 hours.
Literature reference to uncontrolled charging emissions estimate 0.15 to
0.2 kg per metric ton (0.3 to 0.4 pounds per ton) of hot metal poured (approxi-
22
mately 0.13 kg per metric ton of steel assuming 70 percent hot metal charge).
Tapping emissions are estimated at 0.08 to 0.1 kg per metric ton (0.15 to 0.2
pounds per ton) of steel in the same source. A second source estimates combined
charging and tapping emissions at 0.3 to 0.45 kg per metric ton (0.6 to 0.9
23
pounds per ton) of steel. Hot metal transfer emissions are estimated to 0.25
to 0.35 kg per metric ton (0.5 to 0.7 pounds per ton) of steel. An estimate
of uncontrolled flux handling emissions is 0.75 kg per metric ton (1.5 pounds
per ton) of steel based on a material loss of about 0.8 percent during handling.
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Precipitator Common
1) Wire Breakage
This is a problem common to precipitators using wire discharge electrodes
as opposed to rigid discharge electrodes. The typical configuration of wire
electrode is a wire suspended from a frame at the top of a precipitator tensioned
with weights at the bottom of each wire. The tensioning weights are about 4.5
to 13.6 kg (10 to 30 pounds) and help maintain the wires in a fixed position
between collecting plates. Some additional type of steadying device is pro-
vided to keep the wires from swinging with the gas flow. Wire breakage can
result from fatigue, corrosion, and electrical stress due to sparking or
electrical arcing.
The environmental consequences of wire breakage is increased particulate
emissions due to partial failure of the precipitators. When a wire breaks the
broken wire generally contacts one of the collecting plates adjacent to it
causing the electrical section it is in to short. The transformer-rectifier
set supplying power to the section trips. With no power in that section of the
precipitator, collection ceases. All the section of the precipitator connected
to the transformer-rectifier will be deenergized unless it is possible to
disconnect the section with the broken wire and reenergize the remaining
sections.
Unless there is a problem with the original alignment of internal components,
substandard fabrication 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
fail than smaller precipitators. The data on wire failures obtained for this
study do not indicate the size of the precipitators involved, but some varia-
tion in failure rates can be attributed to difference in precipitator size.
Three plants with precipitators serving the BOP furnace reported annual
wire breakage of 2, 12, and 200, respectively.6'7'24 The 200 broken wires is
a very high breakage rate and the plant is replacing the transformer-rectifier
sets in an effort to achieve better electrical control and reduced wire loss
from sparking. Even 12 breaks may be higher than need be experienced.
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The duration of section outages caused by wire failures is dictated by the
plants' need and desire to repair them. If a shop has spare collection capacity,
there is no need to shut down a precipitator or precipitator chamber to repair
it immediately. Several may accumulate before a shutdown is necessary. With no
spare capacity and isolation capability for each chamber, one chamber may be
\
deactivated and cooled down enough to permit cutting out a broken wire within
two or three hours. If a chamber cannot be isolated, the repair must be made
when plant operations are curtailed for maintenance.
Cutting out broken wires as opposed to replacement does not cause per-
formance to significantly deteriorate unless they are adjacent wires. Replacement
of the cut wires can be made during an annual outage or scheduled maintenance
period when more time is available for repairs.
The increase in particulate emissions with a section out of service due to
wire breakage can be calculated given the operating efficiency of the precipita-
tor fully energized, total collection surface area, gas flow, and the area of
collection surface out of service. Following is an example of the calculation.
Gas Flow
4-
Given: Four chamber, four field precipitator
Operating efficiency - 98%
Gas flow rate - 8,500 acmm (300,000 acfm)
Total collection surface area - 12,114 m2 (130,400 ft2)
2 ?
Area not in service - 757 m (8150 ft ) or 1/16 of the total area
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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) = ^g§ In (0.02) = 9.0
2) Using this value of w, evaluate efficiency of the chamber with
one field out of service:
Efficiency = 100(1 - e 7500° X ) = 94.7
The average efficiency with the one field out of service is 97.2
n, average = <3 x 98j * 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 the alignment is satisfactory, installation of
shrouded wires in place of standard discharge wires should be made. 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.
65
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As was mentioned previously in the discussion, 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.
2) Sprays Plugged or Corroded
Successful collection of particulate from the BOP furnace by precipitator
is dependent on the addition of moisture to the gas stream as, a conditioning
agent. Without the moisture the particulate resistivity remains high and the
collection efficiency is reduced. Demonstration of the effects produced by a
lack of conditioning are often evident at the start of an oxygen blow when the
stack exhibits more opaque visible emissions than after two or three minutes
into the blowing period.
Many of the spray systems are fed by recycled water, so a 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. If atomization is impaired by corrosion damage to the
nozzle, the quantity of water going through the nozzle may be sufficient but
the amount evaporated will be too little.
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 may be
possible often enough to avoid the problem. One plant reported plugged sprays
14
occur three times per week.
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. Apparently nozzle manifolds may be inter-
changed between blowing periods.
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.
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The quality of water being fed to the sprays is of prime importance. One
plant reported that establishment of pH control and the use of scaling inhibitors
in the spray feed water significantly reduced the problems with the spray
conditioning system.
3) Insufficient Conditioning of Gases
This AOC is related to the previous one discussed in terms of its effects
on precipitator performance. In this case insufficient conditioning results
from process conditions (usually temperature too low to activate the spray
system).
Water sprays are usually activated on the basis of gas temperatures
entering the spray chambers. If for some reason the gas temperatures do not
reach the appropriate set points, the sprays will not operate, thus preventing
proper conditioning of the gas stream. One problem is a period at the beginning
of the oxygen blow when the gas temperature is too low to evaporate the sprayed
water, so even if the water is available, conditioning will not occur. Another
problem is that process conditions may keep the gas temperature low longer than
normal, again preventing proper conditioning.
The lag period, the period when the blow is proceeding but conditioning is
poor, may occur with every heat. The duration may be one to six minutes per
heat. The increased particulate emissions cannot be readily calculated, but
increased visible emissions are observable.
The increase in emissions produced by the lag in temperature after the
oxygen blow begins may be eliminated by the use of steam injection during the
lag period. Steam provides a source of already vaporized moisture to function
as a conditioning agent. Two plants practice steam injection also during hot
metal addition and reblows, when conditioning by water sprays is not adequate. '
4) Corroded Pump Impeller, Pump Failure
The problem with these malfunctions again is inadequate moisture condi-
tioning leading to increased particulate emissions. These malfunctions may
completely stop water flow to the conditioning chamber which also allows the
gas temperature entering the precipitator to rise. Improper or no pH control
or pump motor failures are possible causes.
-------
This AOC was not mentioned as a frequent problem at the plants visited.
No estimate of frequency has been made. The duration is until repaired which
is estimated at two to eight hours. The quantity of increased emissions
cannot be readily calculated.
Possible preventive actions include preventive maintenance and the use of
pH control for the spray water.
5) Transformer-Rectifier Set Failure
Transformer-rectifier (TR) sets are the power supplies for the electrical
sections in the precipitator. 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 to 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 failures. The newer
solid state controls are particularly vulnerable to damage or shortened life
from overheating.
The estimated frequency of TR set failures are once every year or every
two years. If the failure occurs in the printed circuit cards, it is readily
repaired. If the failure occurs in the transformer (rare), it may take a month
to obtain a replacement and install it. The range of durations is two hours to
one month. The increased particulate emissions can be calculated using the
same methodology presented in the wire breakage discussion section.
In a severe area of overheating (in the summer) the room housing the
precipitator 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 be improved
performance. 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.
6) Insulator Failures
Insulators that support the discharge electrode system are subject to
failure from cracking or tracking. Failures are caused primarily by dust
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or moisture deposition 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.
Failure of an insulator produces the same effect as broken wires or trans-
former failures. The increase in particulate emissions can be calculated by
the same methodology presented in the broken wire discussion.
Data available showed two to four insulator failures per year. Repairs
?1 9^
required from one to twelve hours. '
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.
7) Rapper Failure
Collecting plate or wire cleaning mechanisms fail due to age or low
reliability. Failure 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 (or vibra-
tors). 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 method-
ology presented in the broken wire discussion.
The frequency and duration of rapper and vibrator failures is not 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.
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8) 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.
Failure 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
affected hopper and in any other section energized by the same TR set, thus
preventing any damage to the internal components. If the undervoltage 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. Per-
manent damage to the electrode system may be done in this case. Repairs to the
steadying frame and wires require a precipitator shutdown more lengthy and
costly than the usual repairs required by the dust removal system. 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 break up 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 in-
leakage problem will occur.
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For the case where a section of the precipitator is deenergized, the
increased participate emissions can be calculated in the manner used for broken
wires. Additional emissions resulting from air inleakage cannot be estimated.
The frequency of dust removal equipment problems is highly variable. An
estimate of the range is one time per week to once per two months. Simple
problems typically require at least an hour to correct. A more complex repair
such as a conveyor shaft replacement might require eight hours to perform.
Impending problems with a dust removal system can be sensed with hopper
dust level indicators. Level indicators can be placed at two levels in each
hopper for a more complete picture of operations. Conveyor on/off indicators
should be included in a good monitoring system. Regularly scheduled or con-
tinuous dust removal operations are important to prevent damage from overfilled
hoppers.
Though operations may be attempted without them, hopper insulation, hopper
heaters, and hopper vibrators contribute to more trouble-free operations
according to plant operators. If nothing else, the insulation and heating
prevent moisture condensation in the hoppers. Some people believe that hot
dust is more fluid or less "sticky" than cold dust without considering the
effects of moisture. The dusty environment of the dust valves and conveyor
drives makes preventive maintenance and frequent inspections essential to
minimizing AOC's.
Because of problems with screw conveyors at least one operator has designed
18
a dust handling system to avoid the use of screw conveyors. An enclosure was
built under the precipitator hoppers. Dust falling from the hoppers passes
through "star" dust valves into the enclosure. Dust is removed from the
enclosure by a front end loader. Since the operation was not observed, it is
not known if there are significant fugitive emissions from the loading opera-
tion or not.
Scrubbers Common
1) Sprays Corroded or Plugged
Sprays are used in several locations in a scrubber system applied to a BOP
furnace. Sprays are used in the quencher or precooler upstream of the venturi
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There are sprays in gas cooling towers downstream of the venturi. The sprays
that most frequently cause performance problems are those in the venturi.
Solids accumulation in particular is reported as a major cause. After the
first year or two of use, presumably the best material of construction to avoid
corrosion damage will have been chosen. However, excursions in the system pH
occur in some plants causing unexpected corrosion problems. Acid scrubbing
water conditions can exist if resulfurizing of steel is practiced or if the
shop is equipped with auxiliary oil-fired waste heat boilers. The more typical
situation, however, is an alkaline condition resulting from carryover of the
lime used as a fluxing agent in the process. Because of the alkaline conditions,
scaling is a significant factor for this AOC.
The result of improper atomization and/or insufficient water flow to the
scrubber is reduced efficiency of particulate collection. In conventional
variable throat venturi scrubbers with high pressure drop, scrubber efficiency
may not decrease with decreasing liquid to 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 L/scm (~ 5 G/1000 scf). The
exact quantitative relationship between decreasing water rate and scrubbing
efficiency may be available from the scrubber manufacturer.
No direct data on frequency of plugging and/or corrosion of sprays were
obtained. Related to findings on sprays for precipitators, a high estimate
would be three times per week. A low estimate would be once per furnace
campaign (about two months). Estimated time to repair the venturi sprays would
be one to three hours after identifying the problem. The venturi sprays are
more accessible then quencher or gas cooler sprays. Repair of these latter
sprays may require more time.
Where spray damage is identified as a corrosion problem, special alloys
must be considered for use. At least, stainless steel (Type 316 ELC) can be
considered for resistance to sulfuric acid attack. In a recycle water system
care must be taken with respect to chloride buildup. High chloride concentra-
tions will attack Type 316 ELC stainless, so higher alloys such as Inconel 625
72
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or HasteaTloy C may be necessary for long life. The latter two are much more
expensive than stainless steel. Alternatively, corrosion control may be
attempted by pH control and corrosion inhibitors. If maintenance is provided
at the end of each furnace campaign, the optimum choice may be partly material
selection and partly chemical control. If the nozzle losses are caused by
abrasion rather than corrosion, the higher alloys will not show much improve-
ment in life over Type 316 ELC stainless.26
Where plugging is the problem, improvement of the water supply is important
or alternatively a regularly scheduled down turn for scrubber maintenance can
be used. Some scrubber designs have automatic reaming devices to clean the
nozzles. These devices are effective primarily with good quality recycle
water, 50-70 ppm suspended solids, but can be a maintenance problem with
?7
high solids content streams, e.g., 5 percent.
The use of a scheduled down turn for maintenance is a successful approach.
One plant utilizing this approach claims 90 percent of their total scrubber
maintenance can be performed during these scheduled maintenance periods.
Solids in the recycled water may be reduced by the use of polyelectrolytes
to improve settling characteristics. If the plugging is due to scaling, use of
scale inhibitors and pH control can be considered.
Maintenance of proper chemical balance in the recycled water system for a
BOP furnace can be quite complicated due to the cyclic nature of the process.
Wide variation in system pH from acidic to basic conditions and back can occur
during each heat. Corrosion potential and scaling potential must, therefore,
be examined together for the whole cycle and at numerous locations within the
recycle water system where conditions change. One literature reference cites
the experience of a British Steel Corporation plant that found their operation
so complex they finally chose a once through scrubber water system. Their
conclusion was that each system must be studied and treated on an individual
basis.
2) Plugged or Corroded Pipes
The cause of this AOC is scaling resulting from lime carryover from the
BOP furnace or low pH due to acid removal from the gas stream. The discussion
73
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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 (also more expensive) materials of construction may be chosen. In
addition to higher grade alloy steel, rubber lining is used to avoid corrosion
losses. One plant reported plugged or unbalanced water system problems
(possibly caused by plugging) five times over a ten month period. No '
duration was reported.
The consequences of plugged pipes may 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.
3) Corroded Pump Impellers, Pump Failure
Discussion on corrosion problems and solutions in the previous two topics
apply to corroded pump impellers. Pump failure can also be caused by abrasive
wear to the impellers and motor failures. As in the case of the previous two
AOC's low water flow may result in reduced scrubber efficiency. Most plants
have installed spare pumps so that if one fails another can be brought into
service.
In the event there is no spare available, the low flow condition could
last two to eight hours before repairs are completed. One plant reported five
pump failures over a ten month period in a BOP furnace scrubber system.
Sensors to detect low water flow and the pump operating status are keys to
early warning of an impending problem or a statement that a failure has occurred.
Rubber lined pumps can be used to provide corrosion and abrasion protection.
Alternatively, pH control and corrosion inhibitors can be used to avoid cor-
rosion damage. If the system has no preclassifier to allow coarse, gritty
material to settle before reaching the pumps, such a device may be installed to
reduce abrasive wear. If a preclassifier does exist, its adequacy and its
location in the system should be investigated.
4) Plugged or Failed Demister
All scrubbers have some sort of device to separate entrained water from
the gas stream. The purpose is to prevent water droplets containing particulate
matter from carrying out the stack and adding materially to the emission rate
74
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matter from carrying out the stack and adding materially to the emission rate
or to prevent chemical damage due to the acid or alkalinity of the water.
The entrapment separator or demister is usually some type of baffled
device that presents an impingement surface to the gas stream or a cyclonic
separator. There is a potential for solids buildup to occur in these devices.
The buildup results in reduced flow area and consequently increased pressure
drop. Given a scrubber system with fixed fan capability, the static pressure
developed must be used either upstream or downstream of the fan. If the mist
eliminator pressure drop increases at the normal system flow rate, then the
scrubber pressure drop must decrease by a corresponding amount. Alternatively
the total gas flow rate may be decreased and the scrubber pressure drop main-
tained. In the later 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
particulate emissions might be calculated if the scrubber pressure drop de-
creases. The scrubber manufacturer can supply a curve of outlet concentration
versus pressure drop.
Pressure drop across the demister can be monitored and alarmed to give
warning of a developing problem. Periodically the demister needs to be washed
to prevent this AOC. A regularly scheduled weekly or monthly outage would
allow an inspection to determine whether the washing is necessary. Plant
experience should dictate the length of time between inspections.
5) 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 and repairs that 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
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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 that it occurs frequently, with long enough repair times
to justify a spare drum filter. Spare filter capacity then is a primary means
of avoiding the AOC.
6) 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
29
blast furnaces. Over a period of 18 months, this AOC occurred twice for the
BOP furnace system and four times for the blast furnaces. 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.
7) Unbalanced Water System
In a recycle water system typical of BOP furnace scrubbing systems, surge
capacity exists at several locations. Thickeners, recycle tanks, and classifiers
have some capacity to store surges. With multiple pump groups in the system,
it is possible to have a water imbalance within the system. Too much water may
flow to the thickeners while a lower amount is pumped away. The net result is
an increasing water level in the thickener. Taken to the extreme, this situa-
tion leads to overflows or spills to the sewer. Depending on the spill source,
pH and/or suspended solids may exceed the effluent guideline limitations.
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A pump failure without a spare, or plugged pipes can also lead to this
AOC. Another cause is poor coordination of system operations. Successful
operation of a recycle system may require the attention of a full-time operator.
Proper monitoring of system status must include level sensors in the tanks or
other holding equipment, pumping rates, and on/off status of the pumps.
One plant reported unbalanced or plugged water systems to have occurred
five times in a ten month reporting period.11 No duration was reported for
these incidents nor was there any indication whether spills resulted.
Baghouse Common
1) Bag Breakage or Plugging
Baghouse applications in the BOP shops in the United States are all for
secondary particulate emissions control. The first baghouse application to
control of primary vessel emissions is at present in the design stage.20
Applications to hot metal transfer, charging and tapping, slag raking, and
desulfurization run the risk of having bag failures from spark carryover. In
some instances sparks are conveyed through the duct system into the bags,
burning holes in the bags. Usually there are some devices installed in the gas
flow stream to prevent this, but it still can happen.
The other failure, plugging or blinding of the bags, can result from
moisture condensation, oil vapor, or fine particulate in the gas stream. Fine
particulate can be collected readily by fabric filters given the proper choice
of fabrics and appropriate operating procedures. When using new bags on a fine
particulate, the manufacturer may recommend precoating the bags with a coarse
particulate to prevent blinding. Preconditioning of the fabric may even be
recommended periodically after cleaning cycles. The plugging AOC refers to
blinding caused by poor choice of fabric or operating practice not consistent
with achieving long bag life.
With spark damage, particulate will pass through the burned bag uncol-
lected. If bag plugging occurs, draft on the process hood(s) will be decreased,
increasing fugitive emissions from the hood periphery. The rate of increased
emissions when bag breakage occurs depends on the number of bags affected. The
increase in fugitive emissions from plugging depends on how much draft
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reduction occurs. In neither case is the increased emissions readily cal-
culable. While completely shut down, the emissions are as reported in the
Section on Downtime of Secondary System.
When spark carryover occurs it often only affects a few bags. If the
baghouse is well designed, one compartment at a time can be isolated and bag
replacement made while the rest of the unit is in operation. This procedure
minimizes increased emissions by avoiding a complete shutdown of the baghouse=
Bag blinding or plugging, on the other hand, tends to affect most of the bags
instead of a few. It is more likely to necessitate a complete shut down for
bag replacement. Obviously, in a shop that takes a weekly down turn for main-
tenance, the probability of long emission producing outages will be minimized.
Erie County, New York supplied data for one plant showing three outages in
a year for bag inspection and replacement on a hot metal transfer baghouse.
The duration of these was 13, 17, and 96 hours. Another plant reported
frequent bag replacements for a hot metal transfer baghouse without indicating
whether complete shutdowns were necessary. The latter plant does have a
weekly maintenance down turn; presumably some replacements were accommodated in
this way. A third plant reports this AOC frequency to be four to six times per
year.
Baghouse design with an extra compartment (above that required for normal
cycle with one down for cleaning) and compartment isolating capability is a
useful means of minimizing increased emissions during this AOC. A weekly shop-
wide maintenance turn is also an effective method.
2) Shaker or Reverse Air System Failure
Shakers or reverse air cleaning are common ways to perform bag cleaning.
Either of these systems may break down in such a way as to affect a single
compartment or the entire baghouse. When not operating, dust continues to
buildup on the bags in the affected compartment(s) thus increasing the pressure
drop and reducing gas flow.
If a single compartment is the scene of the problem, the other compart-
ments must gradually absorb the gas and dust load from that compartment as the
situation worsens. The ultimate effect is increased pressure drop through the
entire baghouse or reduced flow that leads to increased fugitive emissions.
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Data from a hot metal transfer baghouse reported by Erie County, New York
showed four failures in one year due to problems with shaker cleaning equipment.30
The duration for repairs varied between 2 and 17 hours. While shut down, the
increased particulate emissions for hot metal transfer are about 0.25 to 0.35
kg per metric ton (0.5 to 0.7 pounds per ton) of steel produced.23
Efforts to minimize emissions for this AOC should be directed toward
frequent inspection of the cleaning mechanism and preventive maintenance.
3)' Open Bypass Damper
The extent to which this is a problem for secondary emissions systems is
not known. It does occur in many fabric filter installations exhausting hot
process gases. The operations typically controlled by baghouses in the BOP
shops involve molten metal, but large quantities of ambient air are also aspi-
rated giving a mixture much lower in temperature than the process. It is
common for baghouses connected to hot processes to have bypasses or dilution
air dampers. Dilution air dampers admit more ambient air to the duct to cool
the gas, but consequently reduce the draft on the process hood(s). A bypass
damper would allow the emissions to escape directly to the atmosphere. Of the
two, the dilution air damper is a better choice from an emissions standpoint in
that there is a lower increase in emissions as compared to bypassing the
baghouse.
No data on frequency and duration of this AOC are reported. A complete
bypass of hot metal emissions, for instance, would produce the same level of
emissions cited for complete shut down of the system. Bypassing for charging
and tapping would similarly produce the emissions cited for complete shut down
of the system.
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4) 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 bypass,
hopper heater failures, and hopper vibrator failures. Problems with dust
removal are frequent and common to all plants using dry collection systems.
Failure of dust storage and removal equipment leads to full hoppers. When
the dust level reaches the bottom of the bags it begins to reduce the available
filter cloth area. Pressure drop has to increase if the same flow is main-
tained or pressure drop can remain the same if flow rate is reduced. The
former may produce a higher residual dust cake (after the bags are cleaned) and
the latter reduces draft at the process hood.
Sometimes secondary problems develop from efforts to solve the primary
problems. One of the methods chosen to break 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 instal-
lations this allows dust to be drawn back into the baghouse along with cold
air. The cold air may produce corrosion damage to the metal internals and some
of the dust will return to the bag surface. Because dust valves produce many
sticking and 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.
Deactivation of a compartment due to dust buildup will increase the burden
to the other compartments resulting in a higher pressure drop and reduced gas
flow. This leads to increased fugitive emissions. The increase cannot be
readily calculated.
The frequency of dust removal equipment problems is highly variable. An
estimate of the range is one time per week to once per two months. Simple
problems typically require at least an hour to correct. A more complex repair
such as a conveyor shaft replacement might require eight hours to perform.
80
-------
Impending problems with a dust removal system can be sensed with hopper
dust level indicators. Level indicators can be placed at two levels in each
hopper for a more complete picture of operations. Conveyor on/off indicators
should be included in a good monitoring system. Regularly scheduled or con-
tinuous dust removal operations are important to prevent damage from overfilled
hoppers.
Though operations can be maintained without them, hopper insulation,
hopper heaters, and hopper vibrators contribute to more trouble-free operations
according to plant operators. If nothing else, the insulation and heating
prevent moisture condensation in the hoppers. Some people believe that hot
dust is more fluid or less "sticky" than cold dust without considering the
effects of moisture. The dusty environment of the dust valves and conveyor
drives makes preventive maintenance and frequent inspections essential to
minimizing AOC's.
Because of problems with screw conveyors at least one operator has de-
18
signed a dust handling system to avoid the use of screw conveyors. An
enclosure was built under precipitator hoppers. Dust falling from the hoppers
passes through "star" dust valves into the enclosure. Dust is removed from the
enclosure by a front end loader. Since the operation was not observed, it is
not known if there are significant fugitive emissions from the loading opera-
tion or not.
Fan Common
1) Draft Loss
Draft losses in a system other than complete fan failures are produced by
corroded or eroded fan blades, leaks in the system ductwork, and leaks in the
process hoods. All of these problems develop over a period of time. Causes of
corrosion and erosion are those things cited in the discussion of spray nozzles,
pipes, etc. Leaks in ductwork and hoods develop from the continual expansion
and contraction of metal in the system, characteristic of BOP cyclic operations.
Draft losses reduce the gas flow withdrawal from the process hood. In-
creased fugitive particulate emissions result. These fugitive emissions would
be visible as increased roof monitor emissions. A conceivable means of estimating
81
-------
the quantity of increased emissions would be to observe and estimate the hood
capture efficiency as compared to normal operations. The percentage of un-
captured emissions can be multiplied by the uncontrolled emission rate to yield
an answer. Admittedly the estimate is partially subjective, but a rough
estimate may be obtained in this manner.
For primary BOP control systems it may be necessary to do some hood panel
closing or welding after each vessel campaign, perhaps once per month to two
months. One plant reported cleaning or replacing portions of a hot metal
transfer hood about once per year. A lead fume control hood was cleaned or
portions replaced five times in one year. Duration of poor draft conditions
in these cases was not supplied.
Since most of these problems develop gradually, preventive maintenance is
a good method to minimize emissions from this AOC. Reduction of corrosion and
erosion losses may be achieved through careful selection of construction
materials and the use of lined or protectively coated surfaces.
2) Fan Failure
Common causes of fan failures include high bearing temperature, vibration,
loss of bearing oil, and motor failures. Vibration can be produced when parti-
culate deposits on the fan blades in an uneven manner and when corrosion or
abrasion destroys metal on some blades leaving the fan wheel out of balance.
It is common practice to highly instrument fans, especially those of the
primary control systems. Bearing temperature, cooling water flow, and vibra-
tion monitors are used to sense impending problems with fans.
Fan failures in a single fan system shut down the entire control system
leaving all the process emissions uncontrolled. In multiple fan systems,
especially for primary control, a single fan failure probably will not have any
environmental effect other than that of starting a spare fan.
If two fail simultaneously, blowing rate may have to be reduced to have
sufficient drafting capacity. If the blowing rate is not reduced increased
particulate emissions will result.
Fan failures from the above causes were reported to occur four to ten
times per year. The durations were estimated to be in the range of 8 to 48
11 31
hours. » One plant indicated they matched their blowing rate to the available
82
-------
fan capacity. Another indicated they would complete the heat in progress,
then shut down until repairs are complete.31 Fan fialure in a suppressed
combustion system would mean no further operations until repaired or the heat
would have to be completed with an open hood at low enough blowing rates to
prevent damage to hood panels.
The increased particulate from a partially complete heat would be some
fraction of the 6 to 20 kg per metric ton (12 to 40 pounds per ton) of steel
reported earlier as uncontrolled emissions.1'2'3 Early sensing, preventive
maintenance, and spare fan capacity all are means of minimizing this AOC.
Other
1) Loss of Instrument Air
Control instrumentation in some plants is pneumatically operated. If the
air supply to the instruments fails, flow control devices and other equipment
(fans) go to the fail-safe mode to prevent damage, explosions, etc. One plant
with a suppressed combustion control system uses pneumatic instrumentation.
Fan losses were reported to have occurred six times over a ten month period for
two vessels due to instrument air loss. The duration of the AOC was not
reported. In this system, the oxygen lance retracts under this condition. The
sudden fan loss may cause no environmental effect other than a puff, if the
fans can be started quickly enough to complete the heat. Otherwise, it would
be necessary to complete the blow uncontrolled and dump the heat.
2) Failure to Flare Gas
This also is an AOC that affects suppressed combustion systems. All of
the systems must flare off unwanted carbon monoxide. Failure to flare results
from igniter failure. One plant reported this to occur three times over a ten
month period in a two vessel shop.17 Carbon monoxide will continue to be
vented during each blow until the igniter or pilot is restored to service. The
flare may be tied to oxygen lance retraction, in which case the blow will be
interrupted upon failure.
For a 227 metric ton vessel (250 tons) the approximate amount of CO re-
leased unflared is 25,000 son (900,000 scf) per heat assuming 10 percent
combustion of C0-
83
-------
5.0 TABULATED SUMMARY OF AOC
Table 2 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.).
84
-------
TABLE 2. BASIC OXYGEN PROCESS ABNORMAL OPERATING CONDITIONS
Abnormal
Operating
Condition
Burn In
Cause
Burning tar bonded
linings
Vessel lining
dump
Puffing at hood
CO
01 Improper ladle to
vessel hot metal
transfer
Relief damper
opening
Foaming and
slopping
•
Pit or charging
explosions
Improper charge
material
Dumping broken re-
fractory material
by rotating vessel
Poor hood draft.
rapid furnace
reactions
Pouring too fast,
Improper furnace
angle
High gas temp.,
or combustible con-
tent of gas
Excess oxidation of
slag, eroded lance
nozzle
Mater In pit or
scrap
High silicon, hot
metal, dirty scrap
Effect on
Process
None
None
Corrective
Action
PROCESS RELATED --
None available
Observed
Frequency
STARTUP
1/2 to 2/montb
Duration
Environmental
Effects
Reference
1
Up to 2 hours (Emissions of car-
bonaceous fumes
7,11
PROCESS RELATED — SHUT DOWN
None available
1/2 to 2/month
PROCESS RELATED — ABNORMAL OPERATING CONDITION
None
None
May cause lance to
retract
Decreased product
yield
Possible equipment
damage, metal loss
Excessive charging
reactions
Repair gas leaks,
Improve process
control :
Slow pouring, proper
furnace angle
Stop oxygen blow.
Improved process
control
Revised furnace
practice, lance mtn.
Initial design of
vessel
Avoid water leaks or
spills
Improved control of
scrap quality, qual-
ity control of hot
metal
Variable
Variable
1 to 10/month
2/week, could be
up to 25% of heats
3/yr - pit
1/yr - charge
2/week
1 min IPartlculate from
(dust cloud
1
S
1-20 mlns
1-3 mlns
20 sec to 20 min
1-5 mlns
20 sec
1-3 mins
taste gas emissions
iverflow hood to
•oof monitor
Excess charging
emissions
taste qas directly
o atmosphere, 6-20
;q/metric ton of
steel 1f total blow
'articulate emissions
from spilled material
tirs up settled
ust, may damage
quip, or injure
>ersonnel
ncreased fugitive
missions from
harglng operation
n
17, Est.
1,2,3,11,
12
H.lZvU
Est. ,17
Est.
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
tunning stopper
Cause
High FeO slag,
poorly set nozzle or
rod, cold heat with
a skull
Effect on
Process
Loss of yield
Corrective
Action
Improved practice of
setting rods and
nozzles. Consider
use of slide gates
Observed
Frequency
3/month
Duration
30-60 mlns
Environmental
Effects
Stirs up pit dust,
roof monitor Iron
oxide emissions
Reference
17,31
00
en
CONTROL EQUIPMENT RELATED — STARTUP
Stack puff
Insufficient
draft
Unbalanced flow
among manifolded
fans
Predpltator
warmup
Startup out of ser-
vice fan
Failure of spare fan
to start due to
ice In housing
Restarting a down
fan in a multiple
fan system
Manufacturer's re-
commendation
None
Reduced draft
None
None
None available
Run fan at Idle after
mtn., reduce blow
rate to match capa-
city
Attention to design
of system ductwork
and manifolds
Reduced voltage oper
tlon. Increased
rapping intensity
I/week - 1/yr
0-3/yr
I/week - 1/yr
I/week - 1/month for
chambers.
1/yr - 1/5 yrs for
whole precipitator
1-60 mins
Several hours unless
blowing rate 1s
reduced
12-16 hours
10-20 mlns
Particulate emis-
sions from dust on
duct floor or
louvers
Particulate emis-
sions spillover
hood
Increased particu-
late emissions due
to overload on some
collector chambers
Increased particu-
late emissions to
air, could be 6-20
kg/metric ton of
steel if not turned
on during blow. It
usually turned on
part way through the
blow.
6.11
6,Est.
IS.Est.
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
tempers stuck
>pen or jammed
ind leaking
Cause
D1rt on sealing sur-
faces or Inoperative
electrical controls
Effect on
Process
cor
Reduced draft on
operating vessel
hood
Corrective
Action
TROL EQUIPMENT RELATE
Repair controls,
clean surfaces.
preventive mtn.,
Improved damper
design
Observed
Frequency
D — SHUT DOWN
1 /month - 2/yr
Duration
1-24 hours
Environmental
Effects
Increased emissions
due to hood spill-
over caused by re-
reduced draft
Reference
11,19
CO
--J
CONTROL EQUIPMENT RELATED — ABNORMAL OPERATING CONDITIONS
Downtime of pri-
mary collection
systems
Downtime of
Secondary Systems
Charging and
tapping
Power failure
Jump failure
Fan failure
Clarlfler rake
failure
Same as primary
Hay or may not shut
down process
May or may not shut
down process
Reduced blowing rate
None
Preventive mtn.
Provide spare capa-
city
Provide spare capa-
city
3xygen lance retrac-
tion can be added to
all of the above
Provide spare capa-
city
Preventive mtn., In-
stalled spare capa-
city
3/yr - 1/5 yrs
0-2/74
30/yr
All emissions direct
to atmosphere unless
blow Is stopped (6-
20 kg/metric ton)
1-3 days
Charging - 2 mlns/
heat. l/2hr - 13
days
Tapping - 4 mlns/
heat
Increased solids In
blowdown, Increased
blowdown
partlculate - 0.13
kg/metric ton of
steel
Partlculate-O.J kg/
metric ton steel
1,2,3/5,7,17
1,22,23
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Hot metal trans-
fer
Flux handling
Slag raking and
desulfurization
Preclpitator -
Common
Wire breakage
Sprays plugged or
corroded
Insufficient
conditioning of
gases
Corroded pump
impel lar, pump
failure In spray
system
TR set failure
,
Cause
Fan failure, power
failure, open by-
pass damper due to
high temp, or pres-
sure drop, screw
conveyor failure,
cleaning
Power failure,
fan failure
Power failure, fan
failure, open bypass
damper
Corrosion, high
spark rate
Solids in water, pH
problems
Low temp, gas, lag
time
Improper pH control ,
motor failure
Age, overheating
Effect on
Process
None
None
None
None
None
None
None
None
Corrective
Action
Preventive mtn. ,
Installed spare
capacity •
Preventive mtn..
Installed spare
capacity
Preventive mtn.,
Installed spare
capacity
Replace with
shrouded wires or
higher strength
wires
pH control , Improved
materials, frequent
inspection and mtn.
Use steam injection
during charging and
start of blow
pH control , preven-
tive mtn.
Air condition con-
trol enclosure
Observed
Frequency
18-47/yr
1-8/yr
Not available
2-12/yr
3/week - 1 /month
I/heat
Variable
1/yr to 1/2 yrs
Duration
2-4 rains/pour or
1-96 hours overall
2-3 hrs/day
5-20 rains/heat
8 hrs-14 days
Continuous until
repaired, 1-3 days
1-6 mins
2-8 hours
2 hours - 1 month
Environmental
Effects
Particulate -0.25
0.35 kg/metric ton
of steel released to
air
Particulate - 0.75
kg/metric ton re-
leased to air
Particulate released
to air
Increased particu-
late emissions , can
be calculated, see
text
Increased parti -
culate emissions due
to high resistivity
Increased emis-
sions due to high
resistivity
Increased emissions
due to high resis-
tivity
Increased parti cu-
late emissions, can
be calculated, see
text
Reference
11,21.22,23
Est.
Est.
6,7,18,24,
Est.
14,18,24
24,32
Est.
Est.
00
oo
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Cracked Insula-
tor
Rapper or hopper
heater burned out
Dust removal
system breakdown
Scrubber-Common
Sprays corroded
or plugged
Plugged or
corroded pipes
Corroded pump
Impel) ars, pump
failure
Plugged or
failed demister
Drum filter
failure
Cause
Dust on Insulator
Age, low reliability
Screw shaft broken,
dust valve plugged,
dust bridge In hop-
per
Low pH, solids In
water
Low pH, scaling
Low pH, motor
failure
Scaling, solids
carryover
Vacuum pump failure
due to sol Ids spill
over
Effect on
Process
None
None
None
None
None
None
Increased pressure
drop, may shut down
process
May cause shut down
1f no alternate
sludge handling
available
Corrective
Action
Replace, clean and
Inspect frequently
Replace, Inspect
and maintain fre-
quently
Use of hopper heat-
ers, heat insulation
and hopper vibrators;
level Indicators
pH control , improved
settling by chemical
additions, control
of scaling condi-
tions
pH control , corro-
sion Inhibitors,
scale inhibitors
pH control , corro-
sion Inhibitors,
scale inhibitors,
Preventive mtn.
Wash demister
(may be acid wash)
Use centrifugal de-
mister
Spare capacity
Observed
frequency
2-4/yr
Not available
I/week - 1/2 months
3/week - 1/2 months
6/yr
6/yr
Not available
Not available
Duration
1-12 hours
Not available
1-8 hours
1-7 hours
3 hours
2-8 hours
Not available
Not available
Environmental
Effects
Increased particu-
late emissions, can
be calculated, see
text
Hay cause increased
emissions
Increased emissions
when section shut
down, can be calcu-
lated, see text
Reduced scrubber
efficiency
Reduced scrubber
efficiency
Reduced scrubber
efficiency
Increased hood
spillover as draft
decreases
Suspended solids In
blowdown may In-
crease, watery
sludge, may have to
be landfilled
Reference
21,25
11,21
Est.,9,11,14,
18,24
11
Est.,11
6,7,19
00
IO
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Acid cleaning
scrubbers over-
flow to sewer
Unbalanced water
flow
Baghouse -Common
Bag breakage or
plugging
Shaker or reversf
air system fail-
ure
Open bypass
damper
Oust removal
system breakdown
Fan-Common
Draft loss
Fan failure
Cause
Insufficient
planning for
handling wastes
Poorly coordinated
system operation
Spark carryover,
overloaded bags,
moisture or oil
carryover
Low reliability,
lack of mtn.
High temp, due to
cooling failure or
high pressure drop
Corroded or eroded
blades, leaks In
duct and hoods
High bearing temp..
vibration, loss of
bearing oil
Effect on
Process
None
None
May be reduced draft
None
None
-
(SEE
Hay need to reduce
blow rate
Reduced draft
Corrective
Action
Capture and neu-
tralize add
More surge capacity.
better operator
training, and
communication
Spare compartments
Preventive mtn. ,
frequent Inspection
Frequent inspection
Preventive mtn.
PRECIPITATOR-COMMON)
Preventive mtn.,
coat exposed sur-
faces, resistant
materials of con-
struction
Interrupt blow.
preventive rotn
during scheduled
downturn
Observed
frequency
1/yr
6/yr
3-6/yr
4-6/yr
Not available
1 /month - I/year
4-10/yr
Duration
10 mlns - 3 hours
Not available
13-96 hours
2-17 hours
(1 compartment-1 wk]
Not available
1-17 days
8-120 hours
Environmental
Effects
pH < 6.0 for dis-
charge
Spill of untreated
wastewater
Increased partlcu-
late for bag breaks,
reduced draft and
Increased hood
emissions for plug-
ging
Increased particu-
late emissions
All process parti -
culate to atmosphere
Increased hood
emissions
Total or partial
discharge of pol-
lutants to atmos-
phere
Reference
29
6,17,19
14,21
17,21
17,18
11,31
ID
o
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Other
Loss of Instru-
ment air
Failure to flare
gas
Cause
Various
Igniter failure
Effect on
Process
Mill shut down pro-
cess, but blow might
be completed 1f re-
pair requires
lengthy shut down
May cause oxygen
lance retraction
Corrective
Action
Repair Igniter
Observed
frequency
6/yr per 2 vessels
3/yr In 2 vessel
shop
Duration
1 hour
-
Length of blow
Environmental
Effects
Discharge blowing
emission to atmos-
phere If lance is
not retracted
CO emissions about
25,000 son per blow
for 227 metric ton
vessel at 10% com-
bustion
Reference
17,
17, Est.
<£>
-------
6.0 REFERENCES
1. Weber, E., "Treatment of Waste Gases from the Basic Oxygen Furnace
in West Germany," SteelIndustry and the Environment, Proceedings of the
Furnas Memorial Conference, 2nd, SUNY, Buffalo, New York, 1971. Published
by Marcel Dekker, Inc., pp. 225-247.
2. Williams, D. B., "Fume Cleaning at the BOS Plant, BSC, Port Talbot,"
Publication No. 128, Iron and Steel Institute, London, 1970, pp. 75-80.
3. Air Pollution Aspects of the Iron and Steel Industry, U.S. Department
of Health, Education, and Welfare, Cincinnati, Ohio, 1963.
4. Federal Register, Vol. 39, No. 47-Friday, March 8, 1974., p. 9318.
5. EPA Reg. 40CFR, Para. 420.62, 420.63, 420.72, 420.73.
6. Trip Report, Jones and Laugh!in Steel, Cleveland, Ohio, August 2-3, 1977.
7. Trip Report, Republic Steel, Gadsden, Alabama, July 5-7, 1977.
8. Culhane, F. R. and Conley, C. M., "Air Pollution Control Electric Arc
Melting Furnaces," Proceedings of 2nd Annual Industrial Air Pollution
Control Conference, 1972, pp. 90-112.
9. Based on data supplied by U.S. Steel, Gary Works.
10. Bradley, J. G., "Operation and Maintenance of a Modified O.G. Gas Cleaning
System," National Open Hearth and Basic Oxygen Steel Conference, 55th
Proceedings, Metallurgical Society. AIME, April 10-12, 1972, pp. 305-311.
11. Data supplied by Inland Steel Company.
12. O'Shaughnessy, E. J. and Bicknese, E. H., "Improved BOF Practice Through
Waste Gas Analysis," Open Hearth Proceedings, Metallurgical Society, AIME,
Volume 57, 1974, pp. 169-177.
13. Civallero, M. and Picarello, C., "Italsider's Taranto No. 1 BOF Shop-
Problems and Results," Iron and Steel Engineer, March 1974, pp. 57-61.
14. Data supplied by Jones and Laughlin Steel.
15. Pearce, J., "Q-BOP Steelmaking Developments," Iron and Steel Engineer,
February 1975, pp. 29-38.
16. The Making, Shaping, and Treating of Steel, edited by H. E. McGannon,
United States Steel Corporation, Ninth Edition, 1971, pp. 527-528.
17. Trip Report, Inland Steel Company, April 19-20, 1977.
18. Communication with Interlake Steel.
19. Trip Report, U.S. Steel, Gary Works, April 21-22, 1977.
92
-------
20. Trip Report, Crucible, Inc., August 4, 1977.
21. Trip Report, Erie County Department of Environmental Quality, Buffalo,
New York, June 30, 1977.
22. Nicola, A. G., "Fugitive Emission Control In the Steel Industry,"
Iron and Steel Engineer. July 1976, pp. 25-30.
23. Pilkington, S., "Collection of Secondary Fume in EOF Steelmaking,"
Engineering Aspects of Pollution Control in the Metal Industries Proceedings.
Activity Group Committee III of the Metals Society, The Metals Society,
London, November 27-29, 1974, pp. 25-31.
24. Trip Report, Youngstown Sheet & Tube, Indiana Harbor Plant, May 5, 1977.
25. Data supplied by CF&I Steel.
26. Gleason, T. G., "Halt Corrosion in Particulate Scrubbers," Chemical
Engineering, October 24, 1977, pp. 145-148.
27. Communication with Chemico Air Pollution Control Company.
28. Weeks, D. J., "Water Requirements for Fume Cleaning LD Furnaces," Publi-
cation No. 128, Iron and Steel Institute, London, 1970, pp. 72-74.
29. Data from Region III NPDES files for Bethlehem Steel Corporation,
Sparrow's Point Plant.
30. Data for Bethlehem Steel, Lackawanna Plant, supplied by Erie County
(see Ref. 21).
31. Data supplied by Wheeling-Pittsburgh Steel.
32. Discussion by J. Y. Scott, "Engineering Experience in Basic Oxygen Steel-
works," Proceedings of the Meeting on Engineering Experience in Basic
Oxygen Steelworks. Publication No. 98, Iron and Steel Institute, London,
1966, p. 56.
93
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-600/2-78-118f
4.TITLEANDSUBT.TLE Pollution Effects of Abnormal Oper-
ations in Iron and Steel Making - Volume VI. Basic
Oxygen Process , Manual of Practice
7. AUTHOR(S)
D.W.Coy, D.W.VanOsdell, B.H. Carpenter, and
R. Jablin
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1AB604
11. CONTRACT/GRANT NO.
68-02-2186
13. TYPE OF REPORT AND PERIOD COVERED
Final; 10/76-1/78
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES T£RL-RTP project of£iceT is Robert V. Hendriks, Mail Drop 62,
919/541-2733.
16. ABSTRACT
repOrt. jg one m 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 basic oxygen process , is to alert those
who deal with environmental problems on a day-to-day basis to the potential pro-
blems caused by AOCs , to assist in determining the extent of the problems is 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, mater-
ial balances , operating procedures , and conditions representing typical process
configurations .
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Pollution Starting
Iron and Steel Industry Shutdowns
Basic Converters
Oxygen Blown Converters
Abnormalities
Failure
13. DISTRIBUTION STATEMENT
Unlimited
b.lDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
Basic Oxygen Process
Abnormal Operations
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COSATI Field/Group
13B
11F
21. NO. OF PAGES
103
22. PRICE
EPA Form 2220-1 (9-73)
94
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