&EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/2-78-118d
June 1978
Research and Development
Pollution Effects of
Abnormal
Operations
in Iron and Steel
Making - Volume IV
Open Hearth
Furnace, Manual
of Practice
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental Protec-
tion Agency, have been grouped into nine series. These nine broad categories were
established to facilitate further development and application of environmental tech-
nology. Elimination of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECHNOLOGY
series. This series describes research performed to develop and demonstrate instrumen-
tation, equipment, and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the new or improved tech-
nology required for the control and treatment of pollution sources to meet environmental
quality standards.
REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-118d
June 1978
Pollution Effects of Abnormal Operations
in Iron and Steel Making - Volume IV.
Open Hearth Furnace,
Manual of Practice
by
D.W. VanOsdell, D.W. Coy, 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.
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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
Laugh!in 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 yi
LIST OF TABLES vli
INTERNATIONAL SYSTEM OF UNITS AND ALTERNATIVE (METRIC) UNITS WITH
CONVERSION FACTORS viii
1.0 INTRODUCTION 1
1.1 Purpose and Scope 1
1.2 Definition of Abnormal Operating Conditions (AOC) 2
2.0 STEELMAKIN6 IN THE OPEN HEARTH FURNACE 3
2.1 Description of Production Facilities 3
2.2 Flow Sheet and Material Balance 8
3.0 CONTROL TECHNIQUES AND EQUIPMENT 11
3.1 Performance Standards 11
3.2 Emissions Sources 12
3.3 Primary Emissions Control 14
Pred pita tor System Hardware 14
Precipitator Startup 17
Precipitator Maintenance 18
Scrubber System Hardware 19
Scrubber Startup 20
Scrubber Shut Down 21
Scrubber Maintenance 21
4.0 ABNORMAL OPERATING CONDITIONS 23
4.1 Process Related 23
4.1.1 Startup 23
4.1.2 Shut Down 23
4.1.3 Abnormal Operating Conditions 24
Poor Oil Atomization 24
Plugged Checkers 24
Poor Combustion, General 24
Furnace Puffing 25
Tap Hole Breakout 25
Cleaning Checkers and Waste Heat Boilers 25
Boil-out 26
IV
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TABLE OF CONTENTS (cont'd)
Page
Ladle Reactions 26
Improper Control of Oxygen Blowing 26
Breakouts 26
Pit or Charging Explosions 26
Running Stopper 27
Waste Heat Boiler Failure 27
4.2 Control Equipment Related 28
4.2.1 Startup 28
Precipitator Warmup 28
Stack Puff 30
Unbalanced Flow Among Manifolded Fans 31
4.2.2 Shut Down 32
4.2.3 Abnormal Operating Conditions 32
Downtime of Primary Collection Systems 32
AOC's Common to Precipitators 34
1) Wire Breakage 34
2) Transformer-Rectifier Set Failure 37
3) Insulator Failures 38
4) Rapper Failure 39
5) Broken Support Cable 40
6) Dust Removal System Breakdown 40
7) Inspection 42
Scrubber Common 42
1) Sprays Corroded or PIugged 42
2) Plugged or Corroded Pipes 44
3) Corroded Pump Impellers, Pump Failure 44
4) Plugged or Failed Demister 45
5) Vacuum Filter Failure 46
6) Acid Cleaning Scrubber Components 46
7) Unbalanced Water System 47
AOC's Common to Fans 47
1) Draft Loss 47
2) Fan Failure 47
5.0 TABULATED SUMMARY OF AOC 49
6.0 REFERENCES 55
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LIST OF FIGURES
Figure • Page
1 Open Hearth Furnace 5
2 Flow sheet and material balance for an open hearth furnace 9
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LIST OF TABLES
Table
1 Effluent Guideline Limitations 11
2 Open Hearth Furnace Abnormal Operating Conditions 50
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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
g
Gg (gigagram =10 grams)
o
m (cubic meter)
dscm (dry standard cubic meter)
scm (standard cubic meter: 21 °C, 1 atm)
a (liter = 0.001 m3)
3 3
g/m (grams/m )
3 3
mg/m (mi 11i grams/m )
9/kg
J (joule)
kJ/m3 (kilojoules/m3)
MJ (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/ft0
0.000437 gr/fr
2 1b/ton
0.000948 Btu
0.02684 Btu/fr
0.430 Btu/lb
859 Btu/ton
0.146 lb/in2
10.76 fr
vm
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1.0 INTRODUCTION
1.1 PURPOSE AND SCOPE
Air and water pollution standards, generally based upon control of dis-
charges during normal (steady-state) operation of a control system, are fre-
quently exceeded during "upsets" in operation. When such upsets become
repetitive and frequent, the regional and local enforcement agencies undertake,
through consent agreements, to work with the plant toward resolution of the
problem, and plans are developed for equipment and operating practice changes
that will eliminate or alleviate the frequent violations. Should the planning
process fail to resolve abnormally frequent occurrences of malfunctions, 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 abnor-
mal 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. Open hearth furnace steelmaking
is discussed in this manual. The other manuals developed as part of this
project deal with sintering, blast furnace ironmaking, electric arc steelmaking,
and basic oxygen process steelmaking.
This manual is based on review of somewhat limited data, including one
visit to an open hearth shop, interviews with persons immediately involved in
either steelmaking or attendant environmental regulations, and the expertise
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of the study team. It is, therefore, a preliminary assessment which concen-
trates on enumerating as many of the conditions as possible, with emphasis on
those which have the most severe environmental impact.
The open hearth furnace shop visited was only one of many. Other shops
differ in furnace design, shop design, fume collection equipment, emission
control equipment, and operating practice and philosophy. Variations in
equipment and process are reflected by variations in AOC's. The flow sheet
and material balance presented are examples and not average values, as the
available information is generally insufficient to justify averages.
1.2 DEFINITION OF ABNORMAL OPERATING CONDITION (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 opera-
tions, this study includes startup and shut down difficulties of processes and
control equipment. It also includes substantial variations in operation
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 OPEN HEARTH FURNACE
The open hearth furnace (OHF) is a long-established process of making
steel which originated in the 19th Century. Present day open hearth furnaces
are essentially the same in general form and concept to the original furnaces
except that they are larger in capacity and better instrumented and controlled.
The open hearth, in comparison to the Basic Oxygen Process (BOP) which is
replacing it, is less automated, requiring more skilled operating manpower.
Open hearth furnaces are being phased out of production. A previous EPA
study indicates that the OHF currently provides less than 20 percent of the
steel in the United States. The same report projects that this, tonnage will
drop to only a few percent in the 1980's. Unlike the BOP's, open hearth
furnace shops were built before the advent of today's environmental regulations.
The original designs did not provide for control of emissions from any of the
sources. Such controls as have been provided in later years are all retrofits.
As is usually the case with retrofitting a facility, its design and operation
are compromises, and performance is often less than optimal. There is also a
reluctance on the part of the steel companies to invest monies for environ-
mental control on facilities such as the open hearth which have a limited
life. In fact, in many shops the need to provide such control is the final
impetus driving the company to replace the open hearth with the BOP and in
some cases the electric furnace.
2.1 DESCRIPTION OF PRODUCTION FACILITIES
The production of steel in an OHF is in concept simple. The raw mater-
ials (scrap steel, molten iron, and fluxes) are placed in a large rectangular
refractory lined chamber, heated with burners and refined with blown oxygen
until the steel is of the desired composition, and the product steel is drawn
off into a ladle. Disposal of the slag follows, and a new cycle is begun.
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Ancillary facilities are provided to preheat combustion air, recover waste
heat, and to transport raw materials to the furnace and product away.
As shown in Figure 1, OHF is in appearance an elongated box-shaped
refractory structure. Facing the charging aisle (above the regenerative
chambers) are several openings in the front wall refractory which serve as
charging ports. All solid materials are placed in charging boxes which are
positioned within the OHF by the charging machine, a large vehicle which moves
on tracks in front of the furnace. When the box is inside the furnace, it is
rotated about its axis, dumping its contents into the furnace. There are
usually at least five doors in the front of the furnace through which the
charge is inserted, thereby providing distribution over the hearth.
The first component of the charge to be placed in the furnace is the
limestone, then light scrap and finally the heavier scrap. During the charging
operations, the burners are being fired and the scrap is being heated. After
the scrap has been charged and has begun to melt, the overhead crane pours
molten iron from the lip of a shop ladle into a trough which is inserted in a
door of the furnace.
Near the bottom center of the back wall is the tapping spout. The molten
steel is contained in a relatively shallow depression constructed in the
center half of the furnace. Flues which connect the furnace to the regenerative
chambers are built into both ends of the OHF, occupying roughly the outer
fourth of each end of the furnace. Below the furnace and extending out under
the charging floor are the regenerative chambers. The primary source of
energy in an OHF is fuel (often No. 6 fuel oil) which is injected into the
furnace by water-cooled artillery burners at each end of the hearth. The fuel
mixes with air and burns over the bath. Combustion air for the fuel is pre-
heated as it passes through the checkers.
With respect to furnace type, the OHF is both regenerative and rever-
beratory. The regenerative aspect is provided by the checkers. Hot combus-
tion gases are routed out through one end of the furnace, heating the mass of
brickwork (checkers) in the regenerative chamber. Once the checkers are hot,
the gas flow is reversed, and the incoming combustion air is preheated by the
checkers. The combustion gases pass through and heat the cool checkers. The
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STACI
TAPPING
SPOUT
FLUES TO
STACK AMD
WASTE HEAT
HOOF.
NUT VALL
REMOVED
BW VALL
REMOVED
CHECKER FLUE
K6ENERATIVE CHAMBER
WH ROOF AHD SIDE
HALL REMOVED
(Copyright 1971
United States Steel
Corporation)
Fi gure 1. Open Hearth Furnace
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OHF is reverberatory in that the bath (relatively shallow and elongated) is
heated both directly by the burner flame and by radiant heat from the furnace
roof.
t
A blower is required for the combustion air to an OHF, as the checkers
provide significant pressure drop. A set of dampers is provided in the duct-
work to allow for the reversal of gas flow. In operation, air enters through
a forced air inlet valve, passes through the checkers, rises through the
uptakes at the end of the furnace, and passes by the burner where it combines
with the injected fuel. The combustion products pass over the bath, go down
the uptakes on the other side of the furnace, pass through the checkers giving
up heat to the brick, and exit through the waste heat boiler to the stack (or
control device followed by the stack).
In recent years, the end burners of the open hearth furnace have been
supplemented by burners mounted in the furnace roof and firing downward onto
the bath. These supplementary burners are used in order to expedite melting
of the scrap. Also, oxygen lances, either through the charging doors or
through the roof have been added to assist in the refining operations. The
result of these measures has been to reduce the tap-to-tap time of the open
hearth furnace. Where previously tap-to-tap times of 8 to 10 hours were not
uncommon, present day speed of the open hearth furnace has increased and tap-
to-tap times of 4 to 5 hours are being achieved. The use of these techniques
for increasing productivity, especially the use of oxygen, has given rise to
increased emissions of particulates.
The more modern open hearths have been provided with means of improving
control of the process, especially in respect to the control of the combustion
process, including fuel rates, air flows, furnace pressures and temperatures.
Reversing of the furnace, as required by the needs of the regenerator equip-
ment, is also automated. The remainder of the process has little automation;
however, mechanization is provided where feasible.
Examples of mechanization are the charging of scrap and fluxes by charging
machine, the repair of refractories between heats by a dolomite-throwing
machine which directs a stream of dolomite against worn and eroded areas of
the refractory hearth and sidewalls, the mechanical feeding of alloys into the
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steel ladle, the power operation of doors and dampers, etc. Some operations
still are manual and it is not uncommon to observe a man carrying additions
for the bath across the floor of the shop in a wheelbarrow and then throwing
the material through the open door by means of a shovel.
There is still a great deal of art to properly finishing the heat of
steel in an open hearth furnace. At appropriate times, a sample of slag is
taken in a spoon and, by its appearance after cooling, the operator is able to
determine the progress of the heat. Samples of the metal are also taken for
the purpose of guiding the operator in finishing the heat.
The operations in the pit side of the open hearth, that is, the handling
of the molten steel and molten slag, are similar to those in the electric arc
furnace and the basic oxygen process. The finished steel is drained from the
OHF into a teeming ladle. Once the steel is out of the furnace and an insu-
lating layer of slag has been poured on top of the steel, the ladle is lifted
by crane and transported to the teeming aisle, where the ingot molds are
filled. Ladle additions of alloys are made prior to allowing the slag to
blanket the steel in the ladle. The ladles are generally of the stopper rod
variety.
An open hearth facility is generally arranged with two main parallel
aisles. One aisle contains the furnaces, together with the charging cranes
for the molten iron and the charging machines for the scrap. The other aisle
provides for teeming the heat. In addition, on the side of the charging aisle
opposite from the teeming aisle, there is usually a lean-to which contains
waste heat boilers, the combustion fans, the control panels, and storage for
various alloying materials. Furnace stacks are located outside of the lean-
to. In some shops, there is still another parallel building beyond the stacks
which is a stockyard for loading scrap from railroad cars. In other facilities,
the stockyard may be located remotely from the open hearth proper.
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2.2 FLOW SHEET AND MATERIAL BALANCE
The flow sheet for steelmaking in the open hearth furnace is given in
Figure 2. As shown, scrap, molten iron, fluxes, and certain alloys are charged
through the charging doors and placed on the hearth of the furnace. Combustion
air is delivered to the forced air inlet valve in the flue system by means of
combustion fans. Fuel in the form of heavy oil, tar, pitch, natural gas, or
coke oven gas is injected through the burner. If the coke oven gas is used,
it is normally desulfurized to avoid transferring sulfur from the flue gases
to the molten steel in the bath. Oxygen may be injected through lances either
through the charging doors or through the roof in order to speed up the re-
fining. After giving up heat to the checkers, the flue gases are ducted to
the waste heat boiler where they produce steam. Finally, the gases are tapped
off the old stack to the emissions control equipment. In the diagram, the
emission control equipment is a dry precipitator; scrubbers are also employed
for this service. Dust from the precipitator is hauled away for disposal.
The refining of steel within the furnace consists primarily of the oxida-
tion of various components and impurities. These are the carbon, silicon, and
manganese in the iron as well as phosphorus, etc. Oxidation takes place by
reaction of these products with oxygen from the ore, from the decomposition
products of the limestone and from the jet of pure oxygen which may be injected
into the bath. The result of this reaction is an "ore boil" which stirs the
furnace and promotes the reaction between the various components.
Steel and slag leave the furnace by means of the tapping spout and dis-
charge to one or two steel ladles, the number of ladles depending on the heat
size. The steel ladles are located in the pouring aisle directly in front of
the furnace as shown. Slag overflows from the steel ladles into the slag
thimbles (not shown). The slag thimbles are placed to the side of the ladle.
Alternatively, the slag may be allowed to overflow from the steel ladle onto
the ground where it solidifies and is later removed.
As indicated on the flow sheet, in order to produce steel in the open
hearth, the following raw materials are required and the indicated by-products
are generated:
8
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RELIEF DAMPER
STEEL
LADLE
FUEL:
No. 6 FIM! Oil
Coke Owen Ga*
Natural Gat
Tar. Pitch Blend
CHARGING
AISLE
HOT METAL
710 kg
FUEL HEAT
INPUT
ai-4.2 GJ
ORE,
SCRAP-
620 kg
FLUX -
80 ko
CHARGING MACHINE
ELECTRO-
STATIC
PRECIPITATOR
1000 kg
STEEL
1.BGJ
RECOVERED AS
STEAM
SCREW
CONVEYOR
16BO°C
FURNACE
2070 *cm
NEW
STACK
Figure 2. Flow sheet and material balance for an open hearth furnace. Basis: 1000 Kn steel produced,
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1. Ferrous charge consisting of cold scrap, molten iron and ore
or mill scale. The percentage of each component may vary
widely depending upon the production requirements of the furnace
in question and the available supply of molten iron. A preferred
ratio is about 45 percent molten iron to 55 percent scrap. If
more iron is available, the open hearth may use as much as 80 per-
cent hot metal in the charge. The open hearth may also operate on
all cold scrap. The amount of ore or mill scale that is added
varies from 0 to 25 percent depending upon the percentage of
molten iron in the bath. Since the purpose of the ore is to
react with the silicon and carbon in the iron, more iron requires
more ore. A typical yield for an OHF is about 89 percent of the
incoming iron in the product steel.
2. Flux materials (limestone) in the amount of 5 to 8 percent of
the metal lies in the furnace. Under the heat of the process,
the limestone breaks down into lime which, among other things,
serves to react with the sulfur and remove it from the finished
steel. The higher the content of sulfur in the charge, the
greater the amount of limestone needed. Since molten iron is one
of the chief contributors of sulfur to the process, an increase
in the ratio of molten iron to scrap usually is accompanied
by an increase in the usage of limestone. Silica is also needed
in an amount equal to 12 to 25 percent of the limestone.
3. Slag overflows from the steel ladle in an amount equal to
approximately 300 kg/Mg (600 pounds per ton) of steel produced.
4. Oxygen is often used to accelerate the refining period. The
quantity ranges from about 20 to 33 scm/Mg (600-1000 scf per
ton) of steel. The use of this amount of oxygen saves from 10
to 25 percent in heat time and 18 to 35 percent in fuel usage.
Oxygen used in this manner replaces part, or all, of the ore
charge to the furnace.
5. Dust from the flue gas, approximately 5-10 kg/Mg (10-20 pounds
per ton) steel.
6. Fuel in the form of heavy oil, tar, pitch, desufurized coke
oven gas, or natural gas is fired through the end burners. When
molten iron is used in the charge, the heat input from the fuel
is 3.1 to 4.2 GJ per Mg steel (3 to 4 million BTU per ton).
When the charge consists of all cold scrap, the fuel usage rises
to an amount equal to 4.3 to 5.2 GJ per Mg steel (4.2-5 million
BTU per ton).
7. Steam is produced in the waste heat boiler in an amount approxi-
mately equivalent to 1/3 of the heat supplied by the fuel burning
in the furnace.
10
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3.0 CONTROL TECHNIQUES AND EQUIPMENT
3.1 PERFORMANCE STANDARDS
Table 1 shows the current standards for water pollutant emissions as
established by the Environmental Protection Agency. No air emissions standards
for new sources applicable to open hearth furnaces have been promulgated.
TABLET. EFFLUENT GUIDELINE LIMITATIONS3
Effluent Guidelines - Existing Sources
Maximum
One Day
Thirty
Day Average
Total Suspended Solids - kg/Mg of
steel
PH
Effluent Guidelines - New Sources
Total Suspended Solids - kg/Mg of
steel
Fluoride - kg/Mg of steel
Zinc - kg/Mg of steel
PH
0.0312
0.0104
6.0 <_ pH <_9.0
0.0156
0.0052
0.0126 0.0042
0.0030 0.0010
6.0 <_ pH <_ 9.0
Two sets of effluent limitations apply to open hearths; one set to all new
sources on which construction was begun after February 19, 1974 and the other
to sources existing on that date. A further reduction of existing source
effluents is scheduled for 1983.
11
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The individual states or local control agencies may or may not have
standards more strict than those cited in Table 1 for either new or existing
sources. Because of the large number of agencies involved and various bases
for computation of emissions, the reader should refer to the particular area
of interest for this information.
3.2 EMISSIONS SOURCES
In most open hearth shops, the only pollution control device is that
which has been retrofitted to control the furnace outlet gases. Two types of
control equipment have been used for this service, the dry electrostatic
precipitator and the high energy scrubber.
In either case, a tap is taken into the duct work (Figure 2) or the stack
immediately after the waste heat boiler. Appropriate dampers are inserted in
the duct work so that the gases from the boiler may be directed either up the
dirty stack, or into the gas cleaning system and thence through a fan and on
to the clean stack. The fan may be located on either the entry or the delivery
end of the gas cleaning device. During the initial startup of the furnace,
when it is being brought up to temperature and there is no charge being melted
or refined, it is common practice to run the flue gases through the dirty
stack, thereby avoiding the entry of cold gases into the gas cleaning equip-
ment and consequent condensation. One plant reports shifting to the precipi-
tator where oil is fed, after an initial startup with natural gas. The
system has eight furnaces.
If a precipitator is used there is sometimes difficulty in obtaining the
required degree of gas cleaning because of the high resistivity of the dust.
This is partially overcome by the combustion products contained in the gas,
such as water vapor and sulfur dioxide. If a scrubber is used, the fine
particles in the gas require a pressure drop of 150 to 200 cm (60 to 80 inches)
of water for adequate cleaning. In addition, the use of a scrubber requires
facilities for cleaning and disposing of contaminated water from the process.
By and large, if there is adequate land area for the dry precipitator, the ESP
is usually selected over the scrubber for this service.
In order to supply preheated air to the burners, the OHF is "reversed"
about every 20 minutes; that is, the flow of gas is reversed. In a modern
12
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furnace, reversal takes place automatically and there are controls provided for
sequencing the operation of the various valves as well as adjusting the forced
and induced draft fans to maintain the desired level of pressure in the
furnace. As the furnace progresses along the length of a campaign (i.e., as
time passes since the last rebuild), the checkers begin to accumulate dust and
the flow of gases through them becomes impeded. In consequence of this
situation it is often difficult for the automatic controls to maintain the
desired level of pressure when reversal takes place and, until manual
corrections are made, there is an increase in fugitive emissions from the
furnace.
An OHF facility also has ancillary operations which normally cause emissions,
For the most part, because the facilities are not of modern vintage, control of
these emissions is not provided. The various sources of these emissions are
listed below with a description of the nature of the emissions.
1. Transfer of molten iron from one vessel to another is
accompanied by "kish" emissions, which consist of fine
iron oxide particulate together with larger graphite parti-
cles. Molten iron transfers occur between the torpedo car
and the hot metal mixer, between the mixer and the shop
ladle, and between the shop ladle and the OHF charging spout.
2. Tapping of the molten steel from the furnace 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 and manganese.
3. 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.
4. Teeming of steel from the ladle to the ingot mold 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.
13
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5. Disposal of the open hearth dust and slag may result In
fugitive dust emissions from storage areas or contaminated
water runoff.
6. Skull burning and ladle dumping generate fugitive emissions.
Some molten metal remains in the ladle after teeming. Between
successive uses the metal cools and solidifies. After accumu-
lating for some time, these skulls may interfer with proper
ladle operation, so they are burned out with oxygen lances.
Iron oxide fume is emitted. Ladles must also be relined at
intervals to protect the steel sheel. 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.
3.3 PRIMARY EMISSIONS CONTROL
Primary emissions refers to those emissions leaving the OHF through the
regenerative chambers. The generic types of control equipment used in the
United States to capture particulate emissions from the OHF are electrostatic
precipitators and scrubbers. The fact that fossil fuels are fired as an
energy source for the process means any of the other pollutants typically
associated with fossil fuel firing will be attendant with OHF operation. In
addition to particulate emissions, sulfur oxides and nitrogen oxides are
present. At this time control of the latter two pollutants has not been
addressed as a separate subject. Some removal of SO and NO may occur in the
A X
particulate control devices. No data are available.
Precipitator System Hardware
Figure 2 shows a typical configuration for a precipitator installed on an
open hearth furnace. Initial cooling of the waste gases leaving the furnace is
accomplished in the regenerative chambers used alternately to cool the waste
gas and preheat the combustion air. The gas leaving the furnace is at a
temperature of about 1650°C (3000°F) and is typically cooled to about 700°C
(1300°F) as it passes through the regenerative chambers. Cooling the waste gas
continues as it passes through the waste heat boiler.
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Downstream of the waste heat boiler there may be an induced draft fan or
the gases may pass directly to the inlet manifold of the electrostatic
precipitator installation. The inlet manifold for the precipitator distributes
the waste gases from the several OHF's evenly among the precipitator chambers
available. On the outlet side of the precipitator there is usually another
manifold arrangement that collects the gas and then distributes it among the
induced draft fan(s). The precipitators may or may not have spare capacity in
terms of an extra chamber or extra collection field in the direction of gas
flow. In a multiple furnace system, it is common to have spare fan capacity.
Some systems have a common header upstream from the waste heat boilers
to permit diversion of gases to a boiler at all times. Some have a common
heater after the waste heat boiler so no single precipitator is connected
to a single furnace.
Furnace draft is controlled by a pressure sensor upstream of the pre-
cipitator. To prevent draft reductions due to air flow through furnaces that
are shut down for maintenance, guillotine dampers may be closed at the indivi-
dual furnace offtakes. Isolation of a precipitator chamber for on-line
maintenance of that chamber would be accomplished through the use of guillotine
dampers located at the inlet and outlet of each chamber. Likewise fans can be
maintained while the rest of the system is operating by use of guillotine
dampers located at the inlet and outlet of each fan. Many, if not all, of the
open hearth systems are equipped with bypass dampers and the old stack to use
in case of failure of the control equipment fans.
Heat insulation for ducts, precipitator body, and hoppers is common. It
is important to keep the operating temperature of the precipitator above the
dew point of the waste gas. Because of the sulfur content of the gas (from
the fuel being fired and sulfur being removed from the metal), the minimum
operating temperature will be controlled by the sulfuric acid dew point. Use
of hopper heaters and hopper heat insulation is especially important because
of the potential for moisture condensation from the firing of fossil fuels.
Dust removal from the precipitator hoppers is most often done by screw
conveyors to some common discharge point. Though there are many operating
problems related to the use of screw conveyors, no clearly superior alternative
equipment has been found. Dust removal from the precipitator site is usually
by truck to a landfill site.
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Whether the landfill is storage or a permanent disposal site depends on
the economics of recovering metal values from the dust. At present, most
plants have no plans for the dust because of its zinc content. Zinc enters
the process through scrap charged to the furnace. It causes spall ing (crumbling)
of the refractory lining of blast furnaces so recycle into the plant materials
flow 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. plant has attempted full-scale installation of
the required process equipment.
To monitor control equipment operations and furnace draft the following
systems' sensors and alarms might be used:
Low Pressure Alarms: instrument air, oxygen supply, lance
cooling water, service water, waste
gas duct, clean gas duct, plant air
High Temperature: cooling water, dirty gas at precipitator
inlet
Failure: precipitator transformer-rectifiers
Vibration: for all fans
High Bearing Temperature: for all fans
Many of the above items might 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.
The type of staffing used to operate and maintain precipitator systems
varies from plant to plant. One open hearth shop with a five-ESP installation
has one operator assigned at all times to observe precipitator conditions and
inspect equipment for problems. The actual maintenance required for the
precipitator system is about 100 manhours per week for general maintenance and
60-80 manhours per week for electrical maintenance.
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Precipitator Startup
The following is an abridged version of startup instructions for an
electrostatic 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 disconnect 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 the opposition, 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 opposition, releasing power distribution panel interlock
keys.
5. Check position of dampers in the inlet and outlet flues; make
sure the outlet damper is open more than the inlet.
6. Start the fan or fans to move flue gas through the precipitator.
If both a forced draft fan (ahead of the precipitator) and an
induced draft fan (after the precipitator) are used, 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. Some manufacturers specify that the precipitator
be warmed to the inlet gas temperature. This lessens the danger
of possible explosive gas and air mixtures and eliminates free
moisture.
8. Energize the dust removal system.
9. Energize the rapper system.
10. Energize the transformer-rectifier sets.
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Freeipitator Maintenance
5
The following are maintenance recommendations for a precipitator system.
Daily precipitator maintenance procedures:
1. Take readings at all instruments, preferably hourly or at
least once per shift.
2. Make sure all insulator compartments are properly ventilated.
3. Make sure all rappers are functioning properly.
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:
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.
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Scrubber System Hardware
As is true of precipitator installations, scrubbers on OHF shops are
generally retrofits. They are very similar to the precipitator up through
tapping the dirty gas off an existing stack. The dirty gas is then cooled and
humidified in a quencher (optional) and cleaned in a high energy venturi
scrubber. Entrained water is removed in a demister prior to the fan. The
very high pressure drops required to remove fine particulate necessitate the
use of a large induced draft fan. The gas is discharged into a new stack.
The solids must be removed from the scrubber water; a typical system might
include a preseparator feeding into a recycle tank from which scrubber water
is recirculated. About half of the dirty scrubber water is treated in a
thickener, the solids removed, and the overflow fed back to the scrubber.
Another process scheme cleans all the dirty scrubber water before recirculating
to the scrubber.
Water rates to the scrubbers vary widely, but a high energy venturi
without a quencher would have a water consumption of around 1250 to 2500 liters
per Mg steel (300-600 gal/ton). Slowdown from the treatment plant is 8-17
percent of the scrubber flow rate.
Underflow from the thickener(s) is often pumped to a vacuum filter or
centrifuge for dewatering. The cake produced is usually trucked to a 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. Slowdown from the recycle system may require pH adjustment
and further removal of suspended solids to meet effluent guideline limitations.
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.
For a large open hearth shop, the scrubber system usually has multiple
venturi throats or multiple parallel scrubbers, depending on the design of the
system. As in the case of precipitators, the scrubbers are generally manifolded
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to a multiple fan installation. Isolation of idle scrubbers or open hearths
is vital to the maintenance of effective gas cleaning and adequate draft.
This is generally accomplished by the use of guillotine dampers at appropriate
locations. Draft control for the system is provided by the ability to adjust
the venturi throat openings and fan dampers.
Monitors and alarms are sometimes provided for the following equipment:
Low Pressure Alarms: quencher water, scrubber water,
Level Alarms: surge or recycle tank
High Pressure Alarm: drop across demister
High Temperature Alarm: downstream of quencher
Vibration: all fans
Bearing Temperature Alarm: all fans
Staffing for scrubber systems may require two full time operators, one to
attend the gas portion of the system and one to attend the wastewater treat-
ment 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
The following is a condensed version of startup instructions for a
scrubber system.
1. 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 conveyor, or hydroclone) should be started
up at this time.
2. 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.
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3. Start quencher and venturi pumps, and the attendant water flow
recorders. Pump discharge valves may require manual adjust
ment to achieve the desired flow rate.
4. Start fan motor bearing lube pump (and fluid drive oil pump
if the system uses fluid drive) and system temperature recorders.
5. 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: automatic fan shut down may
occur due to high fan vibration, or motor overload.) Adjust
differential pressure controller and the motor power controller.
Scrubber Shut Down
Shutdown is essentially the reverse of the system startup procedure,
depending somewhat on the anticipated duration of the shutdown. Under a short
duration shutdown, the main fan is stopped, while lubricant recirculation
systems, etc. continue to function. All water clarification equipment must
continue to operate. Under a long duration shutdown, all scrubber equipment
is stopped. Water clarification equipment is operated, however, long enough
to purge the system of settled solids. In sub-freezing temperatures, water
collection areas are drained or run at minimum water flow to prevent ice
formation.
Scrubber Maintenance
The following is a condensed version of recommended maintenance for a
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.
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2. The main gas duct between the quenchers and the venturi
scrubbers should be inspected monthly. 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.
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 iso-
lation 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
practiced.
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.
6. 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 accumu-
lation of material on the fan wheels should be removed.
Fan wheel sprays should be checked to determine that their
operation is satisfactory.
7. 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.
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4.0 ABNORMAL OPERATING CONDITIONS
4.1 PROCESS RELATED
4.1.1 Startup
Startup of an OHF requires a special heat-up procedure. Natural gas
burners are initially used to heat the furnace. For one shop, a preheat rate
of about 90 GJ/hr (90 mm BTU/hr) of natural gas was used, the furnace being
drafted through the waste heat boiler and out the furnace stack, bypassing the
control device. After 8-12 hours, No. 6 oil was fired to the furnace at about
155 GJ/hr (150 mm BTU/hr). Two to three hours of oil firing were needed
before the system was hot enough to provide hot gas (150°C in this case) to
the control device. About 24 hours of heating are required before iron and
scrap can be charged to the furnace to begin steelmaking.
Emissions during this furnace startup period have not been quantified.
If natural gas is used for the initial heating period as described above,
emissions should be minimal. The exhaust gas flow rate would be on the order
of 570 scnm. With light distillate firing, there would probably be some soot
emissions. The firing of No. 6 fuel oil is more likely to cause emissions,
particularly early in the startup cycle while the furnace is relatively cool.
Proper oil atomization is a must. Again, no data on emissions is available.
The environmental effect depends greatly on whether the control device can be
used on the relatively cool combustion gases.
4.1.2 Shut Down
Routine furnace shut downs are generally needed every month or two for
furnace checker cleaning and some furnace repair. No emissions are known to
be associated with the actual shut down of a furnace.
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4.1.3 Abnormal Operating Conditions
Poor Oil Atomization
Efficient combustion of No. 6 fuel oil requires efficient fuel atomiza-
tion. The atomization is provided by high pressure air or steam in special
fuel injection nozzles. Poor atomization results in incomplete combustion and
consequent excessive smoking, along with the possibility of checker plugging
and leading to improper heating of the bath.
A sudden loss of effective atomization is likely to be caused by a loss
of the air or steam to the nozzle. This AOC would be expected to cause the
largest emission, but is also likely to get immediate attention. More subtle
is a gradual deterioration due to plugging or nozzle wear, and gradually
increasing emissions. The extent of this AOC is directly dependent on the
level of maintenance the nozzles receive.
No data were available to document this AOC, although its occurrence was
recognized. The emissions would tend to be captured in the control device.
Plugged Checkers
Plugged checkers is a furnace condition which causes low intake air
temperature or volume and poor combustion. Potential causes are poor cleaning
practice and/or excessive dust, soot, and slag carryover. With respect to
AOC's, plugged checkers is a matter of degree. The checkers normally plug
eventually; to be considered an AOC, the checkers must plug and require
cleaning more often than normal for the shop.
The emissions caused by plugged checkers are essentially those of an
incomplete combustion. No data are available to quantify this AOC.
Poor Combustion, General
In addition to the two AOC's discussed above, poor combustion can be
caused by poor reversing practice, excessive fugitive air intake, or an
oxygen/fuel ratio problem. These problems are corrected by returning to
correct operating practice. Again, no data are available to quantify the
emissions. These AOC's cause low heating efficiency in the furnace, and will
be corrected when observed by operating personnel.
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Furnace Puffing
Fugitive emissions through the furnace doors are the result of a high
furnace pressure, which in turn may be caused by insufficient draft, plugged
checkers, or active furnace conditions such as hot metal addition, some alloy
additions, and the lime boil. The condition can be improved by either reducing
the rate of fuel input or oxygen blowing or by increasing the draft. Properly
anticipating the periods of high fume generation and reducing fuel input or
increasing draft can do much to control furnace puffing. The problem can range
from an occasional episode to essentially continual door leaks if the checkers
are seriously plugged. The emissions from furnace puffing have not been
quantified; escape to the atmosphere is usually through the building roof
monitor.
Tap Hole Breakout
Molten steel escaping the furnace through an improperly sealed tap hole
and spilling onto the shop floor causes a loss of steel, safety problems, and
emissions within the building. No data are available on this AOC. It is
thought to be rare, and of course is highly undesirable to the furnace operator.
If a tap hole breakout occurs, it is likely to be controlled within a half
hour.
Cleaning Checkers and Waste Heat Boilers
This equipment must be cleaned of soot and dust accumulations on a regular
basis, and the cleaning is generally accomplished by blowing with air or steam.
The dust is generally routed through the collection device, slightly increasing
emissions due to the high parti oil ate loadings. If the control device is not
operating for some reason (gas temperature below the dew point), blowing out
the checkers or waste heat boiler would cause significant emissions. An
alternative to using compressed gas for cleaning is to hand rod the equipment,
collecting the dust by hand from the bottom of the flue. Uncontrolled emissions
from blowing-out a boiler have been estimated at 180 kg/hr (400 Ibs/hr).
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Boil-out
Boil-out from an OHF is due to occasional violent furnace reactions
caused by hot metal additions, highly oxidized scrap, a violent lime boil, or
high silicon hot metal. The emissions occur when the furnace material splashes
out of the furnace and onto the shop floor. No data are available on boil-
outs. Frequency is highly variable both within a shop and between shops.
Duration is likely to be one to a few minutes.
Ladle Reactions
Ladle reactions occur due to excessive FeO in the bath, a rapid tap, or
a furnace overcharge. No data on occurrance are availble. The emissions have
not been quantified.,
Improper Control of Oxygen Blowing
Both blowing oxygen at too high a rate and blowing at high carbon contents
(> 0.3) can overwhelm the furnace control system. The result is loss of steel
yield due to excessive reaction products, high particulate loadings and gas
rates to the control device and furnace puffing. No documentation was avail-
able; estimated duration was 1-30 minutes.
Breakouts
Breakouts can occur with either the furnaces or the ladles. One seven
furnace shop estimated that it suffered either a ladle or furnace breakout
4
about once a month, the emissions lasting about 15 minutes. No emissions
rates were available. Corrective action is to contain the spill with dikes;
preventive action is close attention to the condition of the vessels and
prompt repair when necessary.
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 water. The water flashes to steam causing an
explosion which throws molten metal or slag randomly around the shop.
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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 the explosions are threats to worker safety.
Pit explosions are estimated to occur three times per year and charging
explosions once per year in EOF shops. The explosion is momentary, but may
produce effects lasting up to 20 seconds. No. data are available from OHF
shops.
The only recommendation for reducing these occurrences is to avoid water
leaks and spills. Unfortunately, water in the vessel may enter with the
scrap.
Running Stopper
Steel from the OHF is tapped into a brick-lined steel ladle upon comple-
tion of the heat. The ladle's function is to carry the steel from the vessel
to ingot molds. Molten steel is transferred through a pouring nozzle in the
bottom of the ladle. Flow of the molten metal is regulated—on, off, and
rate—by movement of a stopper rod whose tip is inserted into the base of the
nozzle.
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
particulates, and stirring up pit dust, the latter two of which may escape
through the building doors or roof monitor.
Estimated frequency of occurrence, by analogy with records for a BOP
shop, is one to three per month lasting from 30 to 60 minutes. No emission
measurements of this source alone have been reported.
Waste Heat Boiler Failure
Failure of the waste heat boiler in an OHF shop can cause increased
emissions if the waste heat boiler is an integral part of the gas conditioning
system for the control device. If the waste heat boiler is not cooling the
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process emissions, some shops must bypass the control device. Emissions would
be from the single furnace affected and would amount to uncontrolled emissions
for the duration of the AOC.
One shop reported nine waste heat boiler AOC's over eight months, for a
total of 135 hours of downtime. Causes included low water level, ruptured or
leaking tubes, and problems with instruments. The longer outages were those
due to tube repairs.
4.2 CONTROL EQUIPMENT RELATED
As discussed in Section 3.0 of this manual, OHF shops generally utilize
either electrostatic precipitators (ESP's) or venturi scrubbers. The two
techniques share common features, such as ducting, fans, and instrumentation.
Therefore, many of the AOC's are common to both systems. The data presented
in this section was obtained from a single visit to an OHF shop (ESP controlled),
from BOF control systems, and from data available from control agencies.
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 shut down for maintenance, re-
build, 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 65 to 150°C
(150 to 300°F). Some prefer to have the unenergized condition remain for some
time (an hour or so) after this point to allow the collecting plates and wires
to reach these temperatures. The intent is to drive off moisture which tends
to condense on the internal surfaces. Condensed moisture is a problem for two
reasons. On the collecting plates and wires it may cause collected dust to
cake leaving a layer not removable by normal rapping. Secondly, the frames
that support the discharge electrodes (wires) are stabilized by insulators
that attach to the grounded walls of the structure. Moisture on these insula-
tors will cause dust to stick, providing a conductive path across the
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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
once per month.
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 pre-
cipitator 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 5 to 10 kg/Mg (10 to 20 Ibs/ton) of steel produced.8
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 is better than no collection. Reduced voltage, however, reduces
the potential for burning out insulators. One potential problem with this
approach is buildup of dust (or mud because of moisture) on the plates and
wires. If the moisture condensation is severe, then this is not a satis-
factory solution. 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.,
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.
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Some plants may find they can operate during startup (without warmup)
with no serious consequences. Experimenting on one chamber reduces the risk
involved.
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 being reentrained 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
beings to sluff into the gas stream.
The effect of this action is the greatest when the deposits are down-
stream 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,
or 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 actions 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 the duct structures with the weight of the accumulated
dust.
Unbalanced Flow Among Manifolded Fans
This is a startup problem peculiar to systems with multiple fans in a
parallel flow arrangment 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 operating fans is shut
down as a result of a failure, or for scheduled or unscheduled maintenance.
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Maintaining an even flow distribution among chambers of a precipitator is
essential to maximizing participate 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 distribution
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 consequence 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
reentrainment 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, and, in some
cases, may shut down the portion of the precipitator above the overloaded
hopper because of collected dust contacting the discharge electrode frame.
Reestablishing balance in the system was estimated to require 12 to 16
hours in one plant affected by this problem. The frequency of occurrence
could be as often as once per week to as little as once per year. The practice
of preventive maintenance on the fans, however, would typically require shut
downs more frequently than once per year.
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, balanced 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
31
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combinations of three fans possible. Each of these combinations can produce
different initial flow conditions. If several individual stacks are used,
opacity monitors can assist in adjusting flow among the chambers.
4.2.2 Shut Down
AOC's relating to shut down refer to upsets occurring when a vessel is
taken out of service for maintenance, not to the period at the completion of
each heat. No AOC's related to shut down were identified during this study.
4.2.3 Abnormal Operating Conditions
M^^^^M^B«4^^^M^M^^M^^HWM^^MMa*^M^^^^^^^^M^^^^^^^^^^H^^^^^^^^^^^^^^^^^ ^
Downtime of Primary Collection Systems
Downtime of primary collection systems refers to shut down of the entire
gas cleaning facility for capturing OHF furnace emissions. Failure of por-
tions of the system that do not result in entire facility failure are treated
in subsequent sections of this manual.
One source of total pollution control system failure is catastrophic
utility failure, i.e., power loss for the entire plant or a section thereof.
Several plants reported this to occur, the frequency ranging from three times
in one year to once every five years. A power failure that affects both the
process and control equipment causes both to shut down and, therefore, the
immediate environmental effect is small. If the power failure leads to the
failure of only the control equipment, the OHF operator will have the option
of shutting down or continuing the heat. As the control devices are generally
retrofits, the OHF process can sometimes operate without controls, though at a
reduced rate. In addition, the plant's emergency power system may be available
for the process and not for the control device.
One plant reported shutting down an ESP in order to clean and inspect the
duct work. During this period (15 hours) the OHF's were operated at reduced
oxygen blow rates without a control device.
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
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problem with a single fan or pump. With installed spares it is likely at
worst that 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. 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 caused 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.
Shut down 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 5 to 10 kg per Mg (10-20 Ibs per ton) of steel cited previously as particu-
late 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
equipment and return it to service was reported at one to three days. Both
increased solids and increased water rates to blowdown result from this AOC
unless production operations are suspended during the repairs. The repair
operations often require draining the thickener to remove accumulated solids.
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. 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
33
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control when a single 100 percent unit fails. Obviously two units sized for
75 percent capacity would be preferable.
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 preclassifieres upstream of the thickeners. The com-
mercial forms of the preclassifiers are varied, but their common purpose is to
remove 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 thickener
and consequent fouling of the rake.
AOC's Common to Precipitators
1) Wire Breakage
This is a problem common to precipitators using wire discharge electrodes
as opposed to rigid discharge electrodes. The typical configuration of a wire
electrode is a wire suspended from a frame at the top of a precipitator and
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 provided 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 consequence 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. The section of the precipitator connected
to the transformer-rectifier must remain deenergized unless it is possible to
disconnect the section with the broken wire and reenergize the remaining
sections.
34
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Unless there is a problem with the original alignment of internal com-
ponents, 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 propor-
tionally more wires fail than smaller precipitators. The data on wire failures
do not indicate the size of the precipitators involved, but some variation in
failure rates can be attributed to difference in precipitator size. One plant
with precipitators serving seven OHF's reported annual wire breakage of 50 out
of 10,850 wires.
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 shut down 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 several adjacent wires are
involved. 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 caluclated given the operating efficiency of the fully
energized precipitator, total collection surface area, gas flow, and the area
of collection surface out of service. The following is an example of the
calculation.
From the given precipitator data, the migration velocity can be calculated
for the precipitator. It will remain constant whether or not the field is
energized. Rearranging the Deutsch equation to
w = _ In (1 - n) Q
60 A
35
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Gas Flow
4. 4. 4, 4, 4. 4,4.4.4,4,4,
Given: Four chambers, four fields/chamber; one field out of service
Operating efficiency of each chamber: 98%
Gas flow rate: 8500 acmm (300,000 acfm)
Total collection surface area:
12,114 m2 (130,400 ft2)
2 2
Area not in service: one sixteenth of total area, 757 m (8150 ft )
Each of the four chambers is assumed to achieve 98 percent efficiency when
fully energized. The Deutsch equation provides the basis for calculating
the reduction in efficiency due to the loss of one field:
n = 1 - e
(-60 AW/Q)
where: TI = collection efficiency in mass fraction
2 2
A = collection surface area, m (ft )
W = migration velocity, m/sec (ft/sec)
Q = volumetric flow rate, acmm (acfm)
e = Naperian base = 2.718
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and substituting, the migration velocity is found to be 0.046 m/sec (0.15 ft/
sec) in the precipitator. The efficiency of the chamber with one field out of
service can now be calculated. The chamber volumetric flow rate is one fourth
of the total, and the migration velocity is that calculated above. The col-
lection surface area has been reduced from one fourth of the precipitator
total to 3/16ths of the total because of the out-of-service field. The single
chamber efficiency is calculated to be 94.7 percent.
The efficiencies of the four chambers can now be averaged (3 chambers at
98 percent and one at 94.7) to arrive at an overall efficiency of 97.2 percent.
The increase in particulate emissions is 2.8 percent/2.0 percent, or a factor
of 1.4 times the normal emissions. This calculation can be applied equally
well to precipitators with more than one field out of service in several
chambers.
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.
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
devices with better controlling characteristics.
2) 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
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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 two in
a typical OHF precipitator installation. If the failure occurs in the printed
circuit cards, it is readily repaired. If the failure occurs in the trans-
former (rare), it may take a month to obtain a replacement and install it.
Duration ranges overall from two hours to one month. The increased particu-
late 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.
3) Insulator Failures
Insulators that support the discharge electrode system are subject to
failure from cracking or tracking. Failures are caused primarily by dust or
moisture 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
transformer failures. The increase in particulate emissions can be calculated
by the same methodology presented in the broken wire discussion.
At one OHF shop, shorted fields due to bushing shorts as well as other
4
causes amounted to more than 5 percent of the total compartment availability.
(This is probably somewhat high, as the shop was at low production rates and
38
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had excess control device capacity; hence control equipment was not repaired
as rapidly as it might have been.) Maintenance time to clean insulators
accounted for nearly 0.5 percent of precipitator availability. Insulators and
rapper repair together accounted for another 2.9 percent of ESP availability.
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.
4) Rapper Failure
Collecting plate and wire cleaning mechanisms (rappers) 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 vibrators). The latter type of failure is more common. A control system
failure will cause a large group of rappers to fail as opposed to individual
rapper failure.
The increase in particulate emissions due to rapper failure may result
from grounding a precipitator electrical section (because of dust bridging the
wire to plate gap) or reduced collection efficiency in that section when the
buildup has not reached the point of bridging the gap. If the section is
grounded the additional particulate emissions can be estimated by the method-
ology presented in the broken wire discussion.
As was mentioned above, one OHF shop reported that insulator and rapper
repair together accounted for 2.9 percent of compartment availability.
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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5) Broken Support Cable
The collection plates of an ESP are in one design hung by cables from the
support framework above the compartment. One OHF shop reported a 0.4 percent
A
loss of compartment availability due to repair of broken support cables.
Apparently inspection was adequate, as no plates had yet dropped due to
multiple cable failure.
6) 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 system.
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 under-
voltage trip protection does not work or does not exist, the dust level will
continue to rise and begin lifiting discharge electrodes and their steadying
frame. Permanent damage to the electrode system may occur in this case.
Repairs to the steadying frame and wires require a precipitator shut down more
lengthy and costly than the usual repairs required by the dust removal system.
Therefore, it is a better choice to shut down the affected collecting area for
repairs to the dust removal equipment.
Sometimes secondary problems develop from efforts to solve the primary
problems. One of the methods chosen to breakup dust plugs in the double
flapper type dust valves is to strike the valve casings with a hammer. While
the dust plug may be broken the valve casing is often bent thus preventing a
good seal between the flapper valve and the valve seat. On negative pressure
installations, this allows dust to be drawn back into the precipitator along
with cold air. The cold air may produce corrosion damage to the collecting
40
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plates and some of the dust bypasses the precipitator, going uncollected.
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
leakage problem will occur.
For the case where a section of the precipitator is deenergized the
increased particulate emissions can be calculated in the manner used for
broken wires. Additional emissions resulting from air leakage 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.
One OHF shop reported maintenance due to specific dust handling problems at
0.4 percent of availability due to a dust blockage in a hopper, 0.2 percent
A
for repair of a screw conveyor, and 0.3 percent to replace a hopper vibrator.
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 attempted without them, hopper insulation,
hopper heaters, and hopper vibrators contribute to more trouble-free opera-
tions, 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 con-
veyor drives makes preventive maintenance and frequent inspections essential
to minimizing AOC's.
Because of problems with screw conveyors at least one operator has designed
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
41
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enclosure by a front end loader. Since the operation was not observed, it is
not known if there are significant fugitive emissions from theloading operation
or not.
7) Inspection
Many of the failures that afflict ESP's are not amenable to preventative
maintenance (wire breakage, TR set failure, etc.), and frequent and complete
inspection is a must. The only shop reporting data utilized 3.7 percent of
the precipitator availability in routine inspections, requiring that the
compartment be shut down, allowed to cool, then opened for inspection. This
is a significant level of effort, and indicates the committment needed to keep
A
control equipment operating properly.
Scrubber Common
The information on scrubbers presented below is essentially all from BOP
furnace shops, as no OHF shop controlled by scrubbers was visited and there
was little data available. The systems should be similiar, however.
1) Sprays Corroded or Plugged
Sprays are used in the quencher (if present) upstream of the venturi as
well as in the venturi itself. The sprays that most frequently cause per-
formance 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.
The result of improper atomization and/or insufficient water flow to the
scrubber is reduced efficiency of particulate collection. In conventional
venturi scrubbers with high pressure drop, scrubber efficiency may not decrease
with decreasing liquid to gas ratio (L/6) 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 Ji/scm (~ 5 gal/1000 scf).10 The exact quanti-
tative relationship between decreasing water rate and scrubbing efficiency may
be available from the scrubber manufacturer.
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No direct data on frequency of plugging and/or corrosion of sprays were
obtained. Related to findings on sprays for conditioning gases 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, although
inaccessible designs could require more time.
Where spray damage is identified as a corrosion problem, special alloys
must be considered for use. In a recycle water system care must be taken with
respect to chloride buildup and potential stress-corrosion cracking. Alter-
natively, 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,
corrosion resistant alloys will not show much improvement.
Where plugging is the problem, improvement of the water supply is impor-
tant; alternatively a regularly scheduled period for scrubber maintenance can
be used. Some scrubber designs have automatic reaming devices to clean the
nozzles. These devices are effective, primarily with good recycle water, 50
to 70 ppm suspended solids, but can be a problem with high solids content
12
streams, e.g., 5 percent.
The use of a scheduled period for maintenance is a successful approach.
One plant utilzing 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 polyelectro-
lytes 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
steelmaking 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 re-
ference cites the experience of a British Steel Corporation plant that found
43
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their operation so complex they finally chose a once-through scrubber water
13
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
furnace or low pH due to acid removal from the gas stream. The discussion in
the previous paragraphs on causes and solutions to the problems generally
applies. 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/erosion losses. One plant reported plugged or unbalanced water
system problems (possibly caused by plugging) five times over a ten month
4
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 also lead to
spills to the sewer and inadequate scrubber water flow.
3) Corroded Pump Impellers, Pump Failure
The discussion of corrosion problems and solutions in the previous two
topics also applies to corroded pump impeller. 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
4
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 knowledge that a failure has
occurred. Rubber lined pumps can be used to provide corrosion and abrasion
protection.
44
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Alternatively, pH control and corrosion inhibitors can be used to reduce
corrosion 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 are important.
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
or to prevent chemical damage due to the acidity or alkalinity of the water.
The entrainment 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 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 a constant 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 increase; 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 is
reduced. 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 outage would allow an inspection to
determine whether the washing is necessary. Plant experience should dictate
the length of time between inspections.
45
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5) Vacuum Filter Failure
Underflow from the thickener(s) in the recycle system is often dewatered
by vacuum filtration (rotary drum or disc-type). The vacuum systems required
in these installations are reported to be high maintenance items. A number of
plants have found it necessary to retrofit spare filters. One problem is
apparently related to solids spillover into the vacuum pump resulting in
abrasive wear.
Failure of a filter will not immediately result in increased solids in
the effluent. There is some solids surge capacity in a thickener, and some
filtration operations are deliberately interim'ttant. Longer outages will lead
to increased suspended solids in the effluent. Alternatively, the underflow
may be manually removed and transported to the disposal site. The compara-
tively wet underflow is a much larger volume to dispose of than is dewatered
sludge. Depending on the disposal site, liquid runoff could be a problem.
No data on frequency of occurrence were found, but the general impression
from the operators was "frequently", with 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. The venturi, the entrainment separator,
pumps, pipes, and nozzles are particularly 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
14
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, and adequately treat the waste before discharge.
46
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7) Unbalanced Water System
In a recycle water system typical of furnace scrubbing systems, surge
capacity exists at several locations. Thickeners, recycle tanks, and classi-
fiers have some capacity to store water. 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 less is pumped away. The net result is
an increasing water level in the thickener. Taken to the extreme, this
situation leads to overflows or spills to the sewer. Depending on the spill
source, pH and/or suspended solids may exceed the effluent guideline limitations,
AOC's Common to Fans
1) Draft Loss
Draft losses in a system (other than complete failure of the fans) are
commonly caused by leaks in the system, the checkers, corroded or eroded fan
blades, and leaks into the furnace. Draft loss reduces the effective rate of
withdrawal from the furnace, increasing the potential for fugitive emissions
from furnace openings.
No quantitative estimates are available concerning the impact of gradual
loss of draft on emissions. 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. Checkers should be sprayed with refractory material to
keep brick work sealed.
2) Fan Failure
Common causes of fan failures include high bearing temperature, vibra-
tion, loss of bearing oil, and motor failures. Vibration can be produced when
particulate 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.
Bearing temperature, cooling water flow, and vibration are commonly monitored
in order to sense impending problems with fans.
47
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Failure of the fan in a single fan system shuts 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. If two fans fail simultaneously, the
firing or oxygen blowing rate may have to be reduced to have sufficient
drafting capacity to prevent particulate emissions.
Only one example of fan failure leading to increased emissions was re-
4
ported by an OHF shop, and frequency was estimated at once per year.
Estimates from BOF shops are generally higher. Duration of the outage would
be on the order of 4 to 24 hours in most cases. No emissions estimates are
available for this AOC. Preventative maintenance, good instrumentations, and
spare capacity all are means of minimizing this AOC.
48
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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.).
49
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TABLE 2. OPEN HEARTH FURNACE ABNORMAL OPERATING CONDITIONS
Abnormal
Operating
Condition
Cause
Effect on
Process
Corrective
Action
Frequency
Duration
Environmental
Effects
Reference
PROCESS RELATED — ABNORMAL OPERATING CONDITIONS
Poor oil atomlza-
tlon
Plugged checkers
Poor combustion,
en General
0
Furnace puffing
Tap hole break-
out
Cleaning checker;
and waste heat,
boilers - exces-
sive emissions
Boil -out
Loss of air or
steam, plugging,
worn nozzles, Im-
proper oil: air
ratio
Poor cleaning prac-
tice, excessive
dust, soot or slag
carryover
Poor reversing prac-
tice, excessive
fugitive air Intake,
fuel/oxygen ratio
problem
High furnace pres-
sure (Insufficient
draft, plugged
checkers, active
furnace condition)
Improperly sealed
taphole
Routine maintenance,
roddlng causes fewei
emissions than blow-
Ing
Violent furnace re-
action (hot metal
addition, highly
oxidized scrap,
violent lime boll ,
high slUcone hot
metal
Incomplete combus-
tion, Increased fuel
usage, Increased
checker plugging
Low Intake air tem-
perature or volume,
poor combustion
Low heating effi-
ciency In furnace
Requires careful
attention to furn-
ace conditions
Loss of steel safety
problems
Required periodi-
cally
Safety of personnel
Repair problem
Correct cause as
stated; reduce furn-
ace pressure If
puffing.
Return to proper
operating practice
Increase draft,
reduce fuel Input
or oxygen blowing
Contain steel; pre-
vent by good prac-
tice
If emissions notice-
able, clean equip-
ment by roddlng out
rather than blowing
Better operating
practice
Unknown
Unknown
Unknown
At least each month
or so as checkers
plug; more often
with other causes
Rare
One case reported;
frequency unknown
Unknown
Unknown
Unknown
Unknown
Estimated to occur
sporadically
throughout one or
two heats
0.5 hour estimated
0.5 hour estimated
1-5 minutes
Increased smoking,
not quantified
Increased smoking
and Increased fugi-
tive emissions If
furnace pressure
goes up
Increased smoking,
not quantified
Increased fugitive
emissions
Fugitive emissions,
not quantified
Excessive emissions,
5 kg/mg steel uncon-
trolled, less if
control device on
Increased fugitive
emissions, not
quantified
Study
team
experience
4
Study
team
experience
4
4
4,5
4
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Ladle reactions
Improper control
of oxygen blow-
Ing
Breakouts
Pit or charging
explosions
Running stopper
Waste heat boil-
er failure
Cause
Excessive FeO In
bath, rapid tap,
furnace overcharge
Too high an oxygen
rate; blowing at
high carbon contents
Ih1n spots 1n furn-
ace or ladle refrac-
tory
Mater In slag pit or
scrap
Improperly set noz-
zle
Low water level,
tube leaks, Instru-
mentation problems
Effect on
Process
None
Loss of yield due to
excessive reaction
products; furnace
puffing
Safety of personnel;
loss of steel
Dangerous to person-
nel
Dangerous, loss of
steel
May have to bypass
control equipment
Corrective
Action
Good operating prac-
tice
Reduce oxygen rate
Careful Inspection
of ladle and furnace
between heats; good
gunning practice
Control water, cover
scrap
Better Inspection,
repair of ladle
Repair problem
Frequency
Unknown
Unknown
1 to 2/year per
furnace
Unknown
Estimated at 1-2
percent some leaks
from nozzle
17 hours outage per
month
Duration
1-10 minutes
1-30 minutes
15 minutes
10 minutes
1-10 minutes
1-48 hours
Environmental
Effects
Increased fugitive
emissions, unquan-
tlfled
Increased emissions,
both fugitive and
through control
device
Increased fugitive
emissions
)ust stirred up,
fugitive emissions
:ugitive emissions
Emission train OHF
uncontrolled
Reference
Study team
experience
Study team
experience
4
Study team
experience
4
7
ioi
Preciplitator
Warm-up
Stack puff
Unbalanced flow
among manifolded
fans
CONTROL EQUIPMENT RELATED -- STARTUP
freclpltator must be
wanned up before
energizing
Dust settled In duct
and other surfaces
Flow distribution
problems leading to
overloading one chant
her while underload-
ing another
None
None
None
None
None
Use dampers to bal-
ance flow
Every startup of a
compartment
Each startup of a
duct section
One/week to one/year
Approximately 1 hr
1-60 minutes
12-16 hours
Emissions through
cold compartments
Depends on whether
dust is upstream or
downstream of col lee.
Not quantified
4,5
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Cause
Effect on
Process
Corrective
Action
Frequency
Duration
CONTROL EQUIPMENT RELATED — ABNORMAL OPERATING CONDITIONS
Downtime of pri-
mary collection
systems
Precl pita tor
Wire breakage
Transformer--
rectifier set
failure
Insulator fail-
ure
Rapper failure
Broken support
cable
Dust removal
system breakdown
Power failure;
Inspection, failure
of key mechanical
component(s)
Fatigue, corrosion,
electrical stress
Age, overheating
Cracking, shorting
due to tracking
Age, poor design
for conditions if
frequent
Corrosion
Screw conveyor
motor, shaft, of
plugged dust
valves, dust stick-
Ing In hoppers, hop*
per vibrator, heat-
er failures
Leads to shutdown
at some point
None
None
None
None
None
None
Repair problem; ade-
quate spares help
alleviate problem
Replace wire
Repair or replace
Repair; prevent by
stopping condensa-
tion
Repair
Repair
Repair
Highly variable
Annual loss 0.5%
One per year
Variable
Variable
Applicability de-
pends on ESP design
Variable
Highly variable
Variable
2 hours to one month
Approximately 2-5
percent of compart-
ment availability
Around 1-2 percent
of compartment
availability
Approximately 0.4%
of compartment
availability
0.2-0.4% of compart-
ment availability
Environmental
Effects
Uncontrolled emis-
sions for duration
Loss of efficiency-
Hay be serious or
not
Reduction in ESP
efficiency
Reduction in ESP
efficiency
Reduction in ESP
efficiency
Requires compartment
shutdown
Negligible to com-
plete shutdown of
control device
Reference
4
4,5
Study team
experience
4
4
4
4
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Scrubbers
Sprays corroded
or plugged
Plugged or cor-
roded pipes
Corroded pump
impellers, pump
failure
Plugged or
failed demlster
Vacuum filter
failure
Spills of clean-
Ing solutions
Unbalanced water
system
•
Cause
pH excursions, scal-
Inadequate mate-
rials, dirty scrub-
ber water
pH excursions or
variations 1n system
scaling, Inadequate
materials of con-
struction
As with sprays a-
bove, motor bearings
failure, abrasion
Corrosion, particu-
late carryover
Various
Inadequate planning
Inadequate design or
Instrumentation
Effect on
Process
None
None
None
None
None
None
Causes operating
difficulties
Corrective 1
Action 1 Frequency
Control pH, better Estimate 1-2 per
materials of con- month
struction, filter 1
recycle water I
Control pH through- Estimate 6 times/year
out system, better 1
materials
1
1
As with sprays above JEstimate 6 events/
repair, use better jyear
design, preclasslfieiT
Repair unknown
I
I
1
Repair Not quantified, but
[significant; all
(users had spare
(capacity
Contain the spill One/year
Add Intermediate Unknown
storage to system, I
Improve instrumenta- 1
tlon
Duration
1-3 hours
Unknown
Variable
•
Unknown
Unknown
10 min - 3 hrs.
Unknown
Environmental
Effects
Reduced efficiency
of scrubber
Reduced scrubber
Reduced efficiency
or complete failure
Reduced scrubber
efficiency;
potential Increase
in misting
Can cause Increased
suspended solids In
effluent
Low pH effluent
Overflows to sewer
Reference
4,5,6
4,Est.
4,Est.
5,6
14
4,5,6
tn
-------
TABLE 2. (cont'd)
Abnormal
Operating
Condition
Fans
Draft loss
Fan failure
Cause
Leaks In ducting or
furnace, corroded or
eroded fan blades
Kigh bearing temper-
ature, vibration,
loss of bearing oil,
no tor failure
Effect on
Process
Lower draft capac-
ity, tendency to
puff
Loss of draft
Corrective
Action
Repair
Repair; preventa-
tlve maintenance
and good Inspec-
tion/instrumenta-
tion :
Frequency
Unknown
One/year
Duration
Unknown
4 to 24 hours
Environmental
Effects
Increased fugitive
emissions
Increased fugitive
emissions due to
reduced draft
Reference
•4
4
Ol
-------
6.0 REFERENCES
1. Meant, G. E. and M. R. Overcash, Environmental Assessment of Steelmaking
Furnace Dust Disposal Methods. February 1977, EPA-600/2-77-044.
2. McGannon, H. E., editor, The Making, Shaping, and Treating of Steel, 9th
Edition, United States Steel Corporation, 1971.
3. EPA Reg. 40 CFR 420.82 and 420.85.
4. Trip report, Inland Steel, April 19-20, 1977.
5. Trip Report, Jones and Laughlin Steel, August 2-3, 1977.
6. Based on data supplied by U.S. Steel, Gary Works.
7. Allegheny County Health Department data for Jones and Laughlin
Steel, Pittsburgh Works.
8. Development Document for Effluent Limitations Guidelines and NSPS
for the Steelmaking Segment of the Iron and Steel Manufacturing Point
Source Category. June 1974, EPA-440/l-74-024a.
9. Communication with Interlake Steel.
10.. Weber, E., "Treatment of Waste Gases from the Basic Oxygen Furnace in
West Germany," in J. Szekely, Ed., The Steel Industry and the Environ-
ment, New York, Dekker, 1973.
11 Gleason, T. G., "Halt Corrosion in Particulate Scrubbers," Chemical
Engineering, October 24, 1977, pp. 145-148.
12. Communication with Chemico Air Pollution Control Company.
13. Weeks, D. J., "Water Requirements for Fume Cleaning LD Furnaces," in
Management of Water in the Iron and Steel Industry. Publication No. 128,
Iron and Steel Institute, London, 1970, pp. 72-74.
14. Data from Region III NPDES file for Bethlehem Steel, Sparrow's Point
Plant.
15. Trip Report, East Chicago Department of Air Quality Control, January
27, 1977.
55
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-U8d
2.
3. RECIPIENT'S ACCESSION NO.
4. T.TLE AND SUBTITLE pollutiOn Effects of Abnormal Oper-
ations in Iron and Steel Making - Volume IV. Open
Hearth Furnace, Manual of Practice
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
D.W.VanOsdell, D.W.Coy, B.H.Carpenter, and
R. Jablin
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
1AB604
11. CONTRACT/GRANT NO.
68-02-2186
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 10/76-1/78
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES jERL-RTP project officer is Robert V. Hendriks, Mail Drop 62,
919/541-2733.
is. ABSTRACT
reporj. 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. Suck 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 open hearth 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 in a
specific plant, and to help evaluate efforts to reduce or eliminate the problems. The
report enumerates as many AOCs as possible, with emphasis on those which have
the most severe environmental impact. Descriptions include flow diagrams, material
balances , operating procedures , and conditions representing typical process config-
urations .
17.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Shutdowns
Iron and Steel Industry
Opehhearth Furnaces
Abnormalities
Failure
Starting
Pollution Control
Stationary Sources
Abnormal Operations
13B
11F
13H
8. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
64
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
56
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