S-EPA
United States
Environmental Protection
Agency
Industrial Environmental Research EPA-600/2-78-118c
Laboratory June 1978
Research Triangle Park NC 27711
Research and Development
Pollution Effects of
Abnormal
Operations
in Iron and Steel
Making - Volume III.
Blast Furnace
Ironmaking, Manual
of Practice
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RESEARCH REPORTING SERIES
Research reports of the Off ice of Research and Development, U.S. Environmental Protec-
tion Agency, have been grouped into nine series. These nine broad categories were
established to facilitate further development and application of environmental tech-
nology. Elimination of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECHNOLOGY
series. This series describes research performed to develop and demonstrate instrumen-
tation, equipment, and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the new or improved tech-
nology required for the control and treatment of pollution sources to meet environmental
quality standards.
REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-118C
June 1978
Pollution Effects of Abnormal Operations
in Iron and Steel Making - Volume III.
Blast Furnace Ironmaking,
Manual of Practice
by
R. Jablin, D.W. Coy, B.H. Carpenter, and D.W. VanOsdell
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.
11
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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.
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TABLE OF CONTENTS
LIST OF FIGURES vi
LIST OF TABLES vii
INTERNATIONAL SYSTEM OF UNITS AND ALTERNATIVE (METRIC) UNITS WITH
CONVERSION FACTORS viii
1.0 INTRODUCTION 1
1.1 Purpose and Scope 1
1.2 Definition of AOC 2
2.0 DISCUSSION OF THE BLAST FURNACE IRONMAKING PROCESS, NORMAL OPERATION 3
2.1 Process Flow Sheet 3
2.2 Material Balance 6
2.3 Methods of Operation 7
Charging 8
Emissions 13
Emissions Controls 14
Water Pollution 15
3.0 CONTROL TECHNIQUES AND EQUIPMENT 18
3.1 Type of Control Equipment Used 18
3.1.1 Blast Furnace Gas 18
3.1.2 Blast Furnace Scrubber Water 20
3.1.3 Material Handling Emissions 26
3.1.4 Cast House Emissions 27
4.0 ABNORMAL OPERATING CONDITIONS 30
4.1 Process Related 31
4.1.1 Startup 31
4.1.2 Shut Down 34
4.1.3 Abnormal Operating Conditions 38
Slips 38
Backdrafting 42
Water and Power Failures 45
Breakouts 46
Charging Dusty Material 48
Gas Cleaning System 49
Gas Bleeders 51
Carbon Black Formation 52
Furnace Control 53
iv
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TABLE OF CONTENTS (cont'd)
Page
4.2 Control Equipment Related 55
4.2.1 Startup 55
4.2.2 Shut Down 56
4.2.3 Abnormal Operating Conditions 57
Water Quality 57
Pumps 65
General Operation 69
5.0 GRAY AREAS 74
Emissions from Bells 74
Blast Furnace Top Emissions from Bells 75
Emissions from Casting < 79
Tap Hole Related 79
Casting Emissions 80
Burning of Skull 81
5.1 Methods for Minimizing AOC 81
5.1.1 Process Related 81
5.1.2 Control Equipment Related 82
5.2 General 82
6.0 TABULATED SUMMARY OF AOC 85
7.0 REFERENCES 91
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LIST OF-FIGURES
Figure Page
1 Blast furnace plant with auxiliary equipment 4
2 Blast furnace 5
3 Instrumentation and computer control system of blast furnace 10
4 Inland Steel recirculating water system 23
5 U.S. Environmental Protection Agency BPCTCA Model 24
6 Cast house dust collection system 29
7 Schematic illustration of blast furnace top 37
8 Backdrafting through blast furnace stove 43
9 Tons of iron accumulated on hearth during years of service 47
10 Swirl nozzle with replaceable insert arranged centrally above
the throat of the scrubber 59
11 Disintegration of the scrubbing liquid above the throat without
any gas flow 59
12 Disintegration of the scrubbing liquid with the droplets
exposed to the action of the gas flow 60
13 Swirl nozzles after years of operation 60
14 Inland Steel blast furnace water system 71
15 Gas cleaning system for No. 13 Blast Furnace - U.S. Steel,
Gary Works 73
16 Plot of the data presented in Table 8 77
17 Example of AOC report form 84
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LIST OF TABLES
Table Page
1 Effluent Material Generated in a "Once-Through" System 22
2 BPCTA - Effluent Limitations Guidelines 25
3 Gary Works, #13 Blast Furnace Major Delays 33
4 Effect of Alkali on Production at Geneva Blast Furnaces 40
\
5 Quantities of Cyanide and Phenols from BF and Sinter Plant —
Plant A 61
6 Reports from NPDES Files -- Malfunctions in Scrubber Water System 62
7 Analysis of Flue Dust Particles 75
8 Particle Size of Blast Furnace Dust 76
9 Blast Furnace Abnormal Operating Conditions 86
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INTERNATIONAL SYSTEM OF UNITS AND ALTERNATIVE (METRIC) UNITS
WITH CONVERSION FACTORS
Quantity
mass
volume
concentration or
rate
energy
force
area
SI Unit/Modified SI Unit
kg
Mg (megagram = 10 grams)
Mg
Gg (gigagram = 10 grams)
m (cubic meter)
dscm (dry standard cubic meter)
son (standard cubic meter: 21 °C, 1 atm)
a (liter = 0.001 m3)
o q
g/m (grams/m )
3 3
mg/m (mi 11 i grams/m )
g/kg
J (joule)
kJ/m3 (kilojoules/m3)
MJ (mega joules = 10 joules)
MJ/Mg
kPa (kiloPascal)
1 Pascal = 1 N/m
2
m (square meter)
1 Pascal = 1 N/m2 (Newton/m2)
Equivalent To
2.205 Ib
2205 Ib
1.1025 ton
35.32 cf
0.437 gr/ff3
0.000437 gr/fr
2 Ib/ton
0.000948 Btu
0.02684 Btu/ft"
0.430 Btu/lb
859 Btu/ton
0.146 lb/in2
10.76 fr
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1.0 INTRODUCTION
1.1 PURPOSE AND SCOPE
Air and water pollution standards, generally based upon control of
discharges during normal (steady-state) operation of a control system, are
frequently exceeded during "upsets" in operation. When such upsets
become repetitive and frequent, the regional and local enforcement agencies
undertake, through consent agreements, to work with the plant toward
resolution of the problem, and plans are developed for such equipment and
operating practice changes as will eliminate or alleviate the frequent
violations. Should the planning process fail to resolve abnormally frequent
occurrences of malfunctions, the problem may lead to litigation. Thus,
periods of abnormal operation are becoming recognized as possibly contributing
to the emissions of high concentrations of pollutants. Similarly, upsets
may contribute to spills of increased amounts of effluent-borne pollutants
into waterways.
There is a need for information concerning abnormal operating conditions
(AOC): their identity, cause, resulting discharges, prevention, and minimiza-
tion.
The purpose of the manual is to alert those who deal with environmental
problems on a day-to-day basis to the potential problem areas caused by abnormal
conditions, to assist in determining the extent of the problem created by
abnormal conditions in a specific plant, and to provide help in evaluating
any efforts to reduce or eliminate the problems. The processes considered
are those in the primary section of the integrated iron and steel plant.
Included are the sintering, blast furnace ironmaking, open hearth, electric
arc furnace, and basic oxygen steelmaking. This manual covers the blast
furnace ironmaking process.
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This manual is based on reviews of somewhat limited data, visits to a
few of the many steel plants, interviews with persons intimately involved
in either steelmaking or attendant environmental regulations, and the expertise
of the study team. It is, therefore, a preliminary assessment which concen-
trates on enumerating as many of the conditions as possible, with emphasis on
those which have the most severe environmental impact.
Each process is described separately. Descriptions include flow diagrams
and material balances, operating procedures and conditions. The flow sheets
and material balances presented are representative of the most typical process
configurations.
Within each process are variations, both in the process itself and in the
equipment for control of pollution. Variations in equipment and process are
accompanied by variations in AOC. It is, therefore, of value to identify as
many of the variations as possible. At the same time, it is necessary to
limit consideration of the numerous alternatives to those which are currently
in greatest application and use.
1.2 DEFINITION OF AOC
In general, an abnormal operating condition (AOC) is considered to be
that which departs from normal, characteristic or steady-state operation,
and results in increased emissions or discharges. In addition to abnormal
operations, this study includes the startup and shutdown difficulties of
processes and control equipment. It also includes substantial variations in
operating practice and process variables, and outages for maintenance, either
scheduled or unscheduled.
The use of the term Abnormal Operating Condition (AOC) in characterizing
any specific condition should not be construed to mean that any operator is
not responsible under the Clean Air Act as amended for designing the systems
to account for potential occurrence in order to comply with applicable State
Implementation Plans or New Source Performance Standards.
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2.0 DISCUSSION OF THE BLAST FURNACE IRONMAKING PROCESS, NORMAL OPERATION
The blast furnace converts iron oxide to molten iron. A typical burden
(feed) comprises ore, sinter, limestone, and coke. The coke provides thermal
energy for the process. The limestone becomes calcined, melts, reacts with and
partially removes sulfur from the molten iron.
The burden material is charged into the top of the furnace and descends
slowly. Heated air is injected through tuyeres near the bottom of the furnace.
The air moves countercurrent to the burden, consuming the coke carbon thereby
providing energy for the process. Blast furnace gas leaves through offtakes at
the top of the furnace, is cleaned of particulates and used as a byproduct
fuel. Molten iron and slag are tapped periodically from the bottom of the
furnace.
2.1 PROCESS FLOW SHEET
A flow sheet for the blast furnace ironmaking process is shown in Figure
1.
Burden material is charged through a device which allows the entry of lump
material and restricts the outward flow of blast furnace gas. Blast furnaces
are generally over 100 feet tall and may be 30 feet or more in hearth diameter.
The blast furnace, Figure 2, is roughly pear-shaped, with the hot metal and
slag formed at the hearth. The furnace uses more air than any other raw
material, fay weight. Thermal economy demands that this air be preheated before
it is injected into the hearth through a series of tuyeres (nozzles). The air
consumes coke to provide heat for the process. Coke also is consumed by
reaction with the iron oxide, reducing it to molten iron.
Blast furnace gas, which is mostly carbon monoxide (1/3) and nitrogen
(2/3), leaves the top of the furnace through offtakes. The flow of gas through
the burden entrains dust. The dust is removed by a dust catcher (which is a
low efficiency cyclone) and a high energy wet scrubber. A gas cooler lowers
the temperature of the gas, thereby condensing most of its water vapor and
making it suitable for use as fuel.
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fSTOVE
STACKS
BOILER
STACK
DV-PASS
STACK
HOUSE
^•V
1
-l'-'1
^n
••Hi i ^BM
K/\/\/V
0 . ., . . ... ,.,
•^ — r
I
BLOWER*
CAST HOU'r.P. t:t'UV>'.'-.IQM COHT ROL.
V
CONVEVOR
-y ..-
J
Figure 1. Blast furnace plant with auxiliary equipment,
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Urge Bell
Hopper
Large Charging
Bell
Stotftllne Armor
Offtake
Stack Coolers
iustle Pipe
Blow Pipe
Iron Notch
Figure 2. Blast furnace.
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The clean, cool gas is generally burned in blast furnace stoves and in the
boilers of the power plant. It is also used as an auxiliary fuel in the coke
ovens, the soaking pits and elsewhere in the steelmaking complex.
Molten iron and slag are withdrawn in batches at periodic intervals from
the hearth of the blast furnace. The usual time between taps is 3 to 4 hours.
Tapping is accomplished by drilling out or burning out the tap hole. Iron and
slag flow from the tap hole into a small pool where slag floats to the top.
Separate runner systems in the floor of the cast house carry the iron from-the
pool to iron ladles and the slag from the pool to either slag ladles or to a
slag pit. The ladles of iron are transported by railroad to the steelmaking
facility or, less frequently, to a pig casting machine. The ladles of slag are
transported to a disposal area where the slag is dumped. The solidified slag
may be crushed and then used as aggregate for concrete, roadbeds, etc.
2.2 MATERIAL BALANCE
In order to produce a ton of molten iron in the blast furnace the fol-
lowing burden materials are required:
1. Iron oxide materials, either lump ore, ore pellets, or sinter—
3,000 to 3,400 pounds.
The variation in quantity of iron oxide material is due
primarily to the degree of beneficiation. Oxide
materials may be supplemented by fine scrap such as turnings,
or even by partially reduced ore pellets. The distribution
of the various oxide materials is flexible; for example,
the burden may have all pellets and no ore or sinter.
2. Flux materials—500 to 1200 pounds
The variation is due to the impurities in the burden.
The more sulfur the burden contains, the higher the
flux requirements. Flux is principally limestone/dolo-
mite with some silica added to control fluidity of the
slag. Flux may be used as stone or combined with the
sinter. In the latter case, the flux is calcined by
the sintering process and the thermal requirements
of the blast furnace are reduced.
3- Fuel
The range of fuel for a blast furnace, expressed as
pounds of coke equivalent per ton of iron is 1000-
1500 pounds.
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Factors that decrease the quantity of fuel are de-
creased amounts of ore or flux, increased blast air
temperature, adequate sizing and screening of the
burden and increased efficiency of operating controls.
Although coke is the primary fuel, other fuels may be
substituted for it in equivalent amounts. Anthracite
coal lumps, in moderate quantities, may be charged into
the top of the furnace. Fuel oil or pulverized coal
may be injected through the tuyeres. Finally, oxygen
may be added to the blast air. This latter procedure,
although not a substitution of fuel, decreases the
amount of nitrogen that is heated in the blast furnace
gas and the amount of total fuel required for the process.
4. Other Materials
The amount of slag produced is essentially a function
of the amount of flux charged into the blast furnace.
The amount of dust in the blast furnace gas is a
function of character of the burden and the amount of
fine material contained in it. The less fines there
are in the burden, the less dust is carried out with
the gas.
2.3 METHODS OF OPERATION, PROCEDURES
The blast furnace is a vertical shaft furnace (Figure 1). Raw materials
are charged into the top of the furnace and as they descend in the furnace,
they are heated by a countercurrent flow of gas. Heated air (the hot blast or
wind) is injected through tuyeres which are located near the bottom of the
furnace just above the hearth. Figure 2 shows a diagram of a typical blast
furnace.
The system of introducing raw materials to the blast furnace is usually a
system of two or three pressure sealing bells at the top of the furnace.
Research has shown that blast furnace production can be increased by operating
the furnace under high positive pressures of approximately 100 in. H20 as
measured at the top of the furnace. This high top pressure must be dissipated
before the cleaned blast furnace gas is distributed as plant fuel.
As raw materials are introduced at the top of the blast furnace they fall
to the top of the burden of raw materials already in the furnace. The hottest
temperature zone in the blast furnace is at the hearth level, where the burden
is molten. One operating problem with blast furnaces is maintaining an even
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downward flow of the burden toward the hearth. At times the burden does not
slide downward uniformly because of an arch of partially melted raw material.
If this arch breaks precipitously or "slips", the furnace top pressure in-
creases abruptly. This opens a safety valve to prevent rupturing of furnace
components and results in heavy particulate discharges from the top of the
blast furnace. Improved control of furnace operation and improved raw materials
have reduced the frequency of these slips.
A modern blast furnace is capable of fully automatic or semi-automatic
operati on.
The furnace filling is contolled by the level of the burden in the furnace.
When the level is below a preset (adjustable) point, the stockhouse functions
continuously, filling the skips with predetermined weights of material in
the ordered sequence.
Charging
A typical charging control system consists of the following electrically
independent sub-systems:
1. Coke supply system consisting of:
a. bin vibrating feeder
b. vibrating screen
c. weigh hopper gate
d. interlock with fines handling system
2. Limestone and slag supply system consisting of:
a. limestone bin vibrating feeder
b. slag bin vibrating feeder
3. Ferrous materials supply system consisting of:
a. Sinter, ore, and pellet bin vibrating feeder
b. ferrous materials supply conveyors
c. ferrous materials vibrating screens
d. ferrous materials screen discharge chute gates
e. ferrous materials weigh hopper gates
f. interlock with fines handling system
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4. Water charging and metering system
5. Dual-drive skip hoist
6. Furnace top operating equipment consisting of:
a. gas seal valves
b. gas seal seat steam purging valves
c. gas seal seat steam blowoff valves
d. equalizer valve
e. relief valve
f. revolving chute
g. small bell
h. large bell
i. stock!ine recorder test rods
Control of charging has improved in recent years. An example of a newer
system is found on Figure 3.
Ironmaking in the blast furnace is essentially a continuous process. When
all process conditions, including the nature of the burden, are under control,
smooth operation results and emissions and discharges from abnormal operations
are generally absent. It is obviously to the advantage of the operator to
achieve good control of the process because it provides stable operation which
increases production and decreases operating costs. Good control of the pro-
cess also reduces adverse impact on the environment. Good operating conditions
generally assure an operating reliability of 95 percent, that is, the furnace
is on-line for 95 percent of the time. One company reported 96 1/2 percent
13
reliability over a long period of operation.
Good control of the blast furnace process is of special importance in
minimizing AOC's. Such control acts in two ways. First, a smoothly operating
furnace is conducive to minimizing such environmental factors as slips, con-
tamination in blast furnace scrubber water, and emissions from casting.
Second, a smoothly operating furnace invariably minimizes the consumption of
coke per ton of iron produced. The less coke consumed, the lower are the mass
of emissions from the coke plant.
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Dioqnosllc system of equipmenl
Operation control system
Figure 3. Instrumentation and computer control system of blast furnace.
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In the blast furnace process, the heated raw materials react chemically
with one another. The principal set of reactions are the complex ones between
coke, air, and iron ore. Part of the coke is consumed by the oxygen in the air
to produce heat for the process. Another part of the coke combines with the
oxygen in the iron ore and releases free iron which melts, drips to the bottom
of the furnace, and collects in the hearth. A final portion of the carbon,
approximately 4 percent, dissolves in the iron.
The heat of the blast also serves to calcine the limestone. The resulting
CaO reacts with the impurities in the ore, principally sulfur, and, in molten
form, descends to the hearth. The slag, being about one third the density of
the iron, floats in a separate layer on the iron bath.
The blast furnace gases are reducing in nature. The reactions described
above produce a substantial amount of carbon monoxide, although a small per-
centage of carbon dioxide comes off as well. Carried out of the furnace with
the gases are dusts which are principally a mixture of iron oxides, lime, and
carbon. The gases are low-calorie, usually between 70 and 100 BTU per cubic
foot.
About 30 percent of the blast furnace gas is utilized to preheat the hot
air blast by means of blast furnace stoves. The remainder is used for other
heating purposes through the steel plant: the production of steam in boilers,
the underfiring of coke ovens, heating of steel ingots, etc.
The stoves, generally 3 or 4 per blast furnace, are tall cylinders of
steel plate which are almost completely filled with special refractory shapes.
The arrangement of the shapes in a modern stove provides a large number of gas
passages which are small in diameter. Blast furnace gas, burned with air,
passes downward through the passages to heat the refractories. When the latter
is fully heated, the stoves are switched from the firing mode to one in which
air, moving upward through the passages, extracts heat from the refractories.
The heated air becomes the hot blast for the furnace. This use of refractories
for absorbing and retransmitting heat is termed regenerative heating. It
provides thermal efficiency for the furnace and, at the same time, accelerates
the reactions within the furnace. On modern furnaces, the temperature of the
hot blast may exceed 1093°C (2000°F).
11
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There are two conditions of the blast furnace process which, by them-
selves, contribute to the control of emissions. One is the need to clean the
gas before combustion in the stoves. If the gas contains particulates, even in
moderate concentrations, the gas passage in the stoves quickly fill and become
clogged. The nature of this piece of equipment imposes the need for highly
efficient gas cleaning, 12 mg/dscm (0.005 grains per dscf) or better, being
usually considered good practice in a modern blast furnace.
The other condition is the need to-control the fate of sulfur in the
ironmaking process. Sulfur originates in the raw materials of the burden;
however, the principal source is in the coke. Sulfur is detrimental, even in
very small quantities, to the final steel product. It is, therefore, necessary
to remove as much of the sulfur as is feasible.
In combustion processes, sulfur is released in the form of sulfur dioxide,
thereby causing air pollution. In the ironmaking process sulfur is combined
with slag. Since the slag is generally cooled and crushed for such end uses as
road ballast, the slag provides an environmentally acceptable method for
disposing of the sulfur. A small portion of the sulfur is released from the
cooling slag, causing emissions to the air. These will be described later.
Periodically, usually 6 to 8 times per day, the hearth of the blast fur-
nace becomes full of molten iron and slag. The tap hole (or holes)in the
furnace wall is drilled. First, iron flows from the hole and travels to
receiving ladles via iron runners. Finally, slag flows to slag ladles, to a
cooling pit alongside the furnace, or to a special slag processing machine.
After the flows of iron and slag cease, the tap hole is plugged with a special
clay and the ironmaking process continues.
Certain aspects of the blast furnace operation are not continuous. One is
the periodic tapping just described. The other is the process of filling the
furnace with the burden material. Because the furnace is under pressure, an
arrangement of pressure locks is provided. These locks, operating in sequence,
permit the entry of the raw material and restrict the outward flow of the gas.
Typically, the locks are in the form of two inverted cones called bells, one
above the other, the top bell being considerably the smaller of the two.
Operation consists of placing the material on the top bell, opening it to dump
material to the bottom bell, and repeating the action until the bottom
12
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bell is full of material. When this occurs, the top bell is closed, the bottom
bell is opened and the material passes into the furnace. Gas flow is impeded
by virtue of only one bell being open at a time.
The trend on newer furnaces is toward higher top pressures in the range of
1 to 3 atmospheres above ambient conditions, the purpose being to obtain more
production from a furnace of given physical dimensions. Formerly, it was
common practice to operate with top pressures in the range of 0.2 to 0.33
atmospheres. As a consequence of this trend, leakage of gas and erosion of the
bells has increased, the one effect augmenting the other. To overcome the
problem, a variety of new designs have evolved including nitrogen pressurizing,
the three bell construction, and tops with one or more bells replaced by valves
o
with soft seats. One new top has no bell at all, the function of gas sealing
being achieved by valving and the function of distributing the burden by a
special revolving mechanism.
The blast furnace usually operates continuously for 3 to 5 years, after
which it is shut down for relining with refractory and for effecting major
repairs. All ancillary equipment for the blast furnace must, therefore, be
repairable with the furnace in operation, or at a minimum, in an idling or
banked condition.
Emissions
The only direct source of water pollution in the blast furnace process
itself is the relatively minor one of thermal pollution. In order to contain
the hot gases of the furnace, to resist the pressure of the gases, and to
support the weight of the burden materials, the furnace has a heavy steel outer
shell which is lined with refractory. Water is used to provide additional
cooling for the shell, for special copper cooling plates, for the jacket around
the hearth and for the tuyeres. The heated water, although otherwise uncon-
taminated, constitutes a source of thermal pollution.
13
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A blast furnace is usually on or near a substantial source of water. Its
size is usually great enough to absorb the heat of the cooling water without
the creation of severe environmental problems. In addition, some modern blast
furnaces have evaporative cooling which releases the thermal energy by
evaporating part of the cooling water. Evaporative cooling, therefore, avoids
the discharge of heat to the receiving body of water and avoids thermal pollution.
Emissions Controls
The accepted, proven method of cleaning the particulate from the blast
furnace gas is the dry cyclone followed by the wet, high energy scrubber. The
scrubber has several advantages which make it particularly adaptable to this
service. They are:
1. No fan is required, nor energy required for running the fan.
The pressure within the blast furnace is more than great
enough to force the gases through the scrubber.
2. There is no danger of exploding the combustible blast
furnace gas when using a wet scrubber.
3. Internal components of the wet scrubber are minimal compared
to those in other air pollution control devices such as the
electrostatic precipitator. Such components as are exposed
to the gas scrubbing action may be fabricated of wear
resisting materials or lined with such materials. In con-
sequence of the minimized number of components and the
choice of materials, the scrubber used in blast furnace gas
service is a highly reliable device well suited to an
entirely continuous operation.
4. The modern scrubber is designed with provisions for varying
the area of the gas passage (throat) in which the scrubbing
action takes place. The purpose is to adjust the area to
the variable flow of blast furnace gas from the furnace and
to obtain a constant level of differential pressure across
the scrubber. This, in turn, insures a constant level of
gas cleaning. A well-designed unit has automatic controls
for varying the area.
Blast furnace gas has a low calorific value, usually in the range of
2.6 to 3.7 MJ/m3 (70 to 100 BTU/CF). Large volumes must, therefore, be burned
for a given heat duty and large gas mains are required. The economics of
burning the low BTU, high volume of gas generally dictate its consumption in or
14
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near the blast furnace complex. Typically the gas is used in stoves for
heating the compressed air for the blast furnace (blast or the wind) and in
boilers for producing the large quantities of steam which are needed in iron
and steelmaking. Less common uses include: the coke ovens (all or part of the
heating fuel): the larger furnaces for heating steel; the soaking pits for
heating ingots.
From an environmental standpoint, blast furnace gas is an ideal fuel. As
indicated above, it is quite clean. It also has almost no sulfur. When burned
by itself, or in the proper combination with other fuels, the gas without
special treatment, may meet environmental regulations in respect to parti-
culates and sulfur dioxide.
Water Pollution
Contaminated water comes from three main sources: the venturi scrubbers,
the gas coolers, and from miscellaneous sources like gas main seals, gas main
downlegs, stove seals, etc. Water from the blast furnace gas scrubber is
highly contaminated with suspended solids, dissolved solids, alkalinity, and
thermal energy. Suspended solids are conventionally removed in a clarifier,
the underflow sludge being thickened and otherwise dewatered so that it may be
recycled to the sinter plant or disposed onto a landfill. Thermal energy is
dissipated in a cooling tower. Recycling of the water helps deal with the
problem of dissolved solids, especially those such as phenol, cyanide and heavy
metals which are toxic. A small blowdown is required to avoid scaling and
plugging of pipes and nozzles. If the concentration of toxic solids becomes
high, special treatment of the blowdown water may be required in order to
reduce toxicity to levels that are acceptable for discharge to the receiving
body of water.
Recycling of the water from the blast furnace gas scrubbers causes the
water to increase in alkalinity. Additions of acid serve two functions. One
is to achieve neutral conditions in the water. The other is to reduce the
quantity of cyanide in the water since it has been found that water which is
high in alkalinity tends to be high in cyanide.
15
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Most of the environmental problems from the blast furnace are emissions to
the air. The major water problem is treating and disposing of the scrubber
water as described above. Solid wastes are normally not an environmental
problem, the slag being used for such byproducts as aggregates and road
ballasts, and the dust and sludges from the gas cleaning being usually recycled
to the sinter plant.
The emissions to the air result from a variety of causes, as follows:
1. Cast house emissions. These are particulates of iron oxide and
graphite, called kish, the graphite being emitted from the molten
iron as it leaves the blast furnace and cools upon exposure to
the ambient air. Also emitted from the cast house, but in
lesser quantities than kish, are the gaseous emissions of sulfur
dioxide.
2. Emissions from slag cooling. The cooling of blast furnace
slag with water creates emissions of sulfur dioxide and hydro-
gen sulfide. Various methods to reduce the amount of these
emissions, espcially the hydrogen sulfide which has a noxious
odor even in minute quantities is to add oxidants to the cooling
water, to reduce the rate of cooling and to use a3special tech-
nique which produces lightweight granulated slag.
3. Furnace slips. These result from 'irregularities of the move-
ment of the burden downward in the shaft of the blast furnace.
A part of the burden may hang up for a while, creating a pocket
below it. When the release takes place, it is sudden and causes
a sharp rise in gas pressure. Relief ports at the top of the
furnace open to protect structural integrity. A large volume
of gas then discharges to the atmosphere. This gas is high in
particulate matter and in carbon monoxide.
4. Gas bleeding. In the process of filling the blast furnace with
the burden, there is necessity of bleeding the pressure from
the space between the large and small bells. This action takes
place after each opening and closing of the large bell. In some
furnaces, this gas bleeds to the atmosphere causing a discharge
of particulates and carbon monoxide. In other furnaces, the
gas bleeds to the entry end of the blast furnace gas scrubber,
thereby avoiding the emissions to the atmosphere.
5. Gas leakage. There are numerous sources of gas leaks in the
blast furnace complex. One is at the bells which seat metal -
to-metal and form a less than perfect seal against gas leakage.
Similar leakage although generally smaller in amount, pertains
at the numerous, large goggle valves which direct the flow of
blast furnace gas to the stoves, the boilers, etc. It is also
possible to find gas leaks in the gas mains, the expansion
joints, and the shells of the stoves and blast furnaces. All
such leaks result in the dishcarge of gas which is high in
carbon monoxide.
16
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Gas flaring. On occasion there is an imbalance between the
production of blast furnace gas from the blast furnace and
its consumption in the various combustion units which requires
the release of blast furnace gas to the atmosphere. The gas
which is so released is clean gas; however, it is high in
carbon monoxide. Good practice requires that the gas be
discharged from a stack and that it be ignited.
Material handling. Many of the raw materials which comprise
the burden of the blast furnace are dusty. The dirtiest
are usually sinter, coke, and certain ores. Handling such
materials causes fugitive emissions which may be high in
quantity and relatively uncontrolled. Some sources of
such emissions are the discharge from the railroad car to
the storage bins at the blast furnace trestle, the discharge
from the bins to the scale car or conveyor belt, the filling
of the blast furnace skip car and the discharging of the skip
into the furnace bells. Scrubbers or baghouses may be used
to control emissions from some or all of these sources. Water
sprays, although less effective, may be of environmental value.
17
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3.0 CONTROL TECHNIQUES AND EQUIPMENT
Three areas in the blast furnace process require environmental control
equipment: the cleaning of blast furnace gas, the collection or suppression of
emissions from the handling of raw materials, and the collection of cast house
emissions. In general, all of these emissions are reduced in severity by good
operating and maintenance practice. For example, a well operated furnace using
a screened, beneficiated burden produces less dust in the gas. Likewise, the
improved burden results in minimized emissions to the atmosphere from the raw
material handling system. Finally, a smoothly operating furnace, casting iron
within appropriate metallurgical specifications produces the least amount of
emissions during the casting process. There is usually no environmental
control equipment provided for the capture of emissions from slag processing
and handling, although some reduction in emissions may be obtained by modifi-
cations of process techniques.
3.1 TYPE OF CONTROL EQUIPMENT USED
3-1-1 Blast Furnace Gas
The amount of dust generated and discharged with the blast furnace gas
depends upon the operation of the furnace and the amount of preparation which
had been afforded to the burden. The amount of dust leaving the furnace can
4
range from 14 to 150 g/Mg of molten metal. Dust concentration may be as high
as 30 g/scm of gas.
Most furnaces are equipped with a multistage dust collection system
consisting of a dry cyclone and a wet collection device. The dry cyclone in
this service is commonly called a dust catcher. The wet device is usually a
scrubber either single or dual stage. In some older gas cleaning systems a wet
electrostatic precipitator has provided final cleaning; however, these high
maintenance devices are absent in the later systems. Newer scrubbing systems,
especially the dual stage units operating at high pressure differentials are
capable of cleaning gas to concentrations of 5 to 10 rug/son.
18
-------
The blast furnace gas has a heating value of 2.9 to 3.5 MJ/scm (700 to 850
kcal/scm) of gas. The gas composition will contain 23 to 40 percent of carbon
monoxide and 2 to 6 percent of hydrogen. It is a highly desirable fuel which,
although low in calorific value, is also extremely low in sulfur content. Most
iron and steelmaking plants attempt to make full use of this byproduct fuel in
their operation. Whenever conditions arise in which gas production exceeds
consumption, then the clean gas is flared.
The preferred method of cleaning the gas is the venturi scrubber. In it
gases are accelerated in the convergient section of the venturi throat in order
to impact at high velocity with the injected scrubber water. The wetted parti-
cles of dust are agglomerated to form droplets in the venturi diffuser due to
decreasing velocity and surface tension. The water droplets containing the
pollutants are then separated from the gas in the subsequent gas separator.
Most modern venturi scrubbers are designed with an adjustable throat section to
compensate for varied rates of gas flow from the blast furnace. Wear in the
throat of the venturi is minimized by the provision of a hardened lining and
also by a protecting film of water on the convergent inner wall.
*.
At least two of the major consumers of blast furnace gas require that the
gas be as free of particulate matter as is possible. These consumers are the
blast furnace stoves and the underfiring jets of the coke ovens. Any excess
particulate matter that might remain in the gas would tend to deposit in the
combustion spaces of these units causing premature outages and failures. Since
these units are necessary to the operation of the ironmaking process and since
they require a high investment of capital, even if there were no requirements
for reducing emissions to the atmosphere, the steel maker finds it necessary to
maintain and to operate the gas cleaning equipment at maximum efficiency.
The cleaning of blast furnace gas is thus an essential part of the iron-
making practice over and above its environmental aspects. For this reason, and
because there has been so much attention to the improvement and design and
construction of equipment for the scrubbing of blast furnace gas, there is
comparatively little potential for AOC resulting from malfunctions of this
equipment.
-------
Other wet collection devices include the orifice scrubber, both fixed
and variable, the fixed venturi scrubber and the electrostatic precipitator.
Both forms of fixed scrubber have the disadvantage that the differential
pressure drop across the restriction changes in response to the variation in
the flow of gas from the blast furnace. As the differential pressure varies
so also does the efficiency of cleaning particulates from the gas. The
electrostatic precipitator suffers in respect to the venturi scrubber by
virtue of its increased maintenance, susceptibility to electrical failure,
susceptibility to erosion, etc.
The dry cyclone, or dust catcher, which preceeds the wet collection
device is usually a low energy, low efficiency dust collector. Because the
raw blast furnace gas contains highly abrasive particulate matter the dust
catcher is provided with an abrasion-resistant lining of brick.
Upon leaving the secondary, wet collection device, the blast furnace gas
enters a gas cooler where it is cooled by direct contact with water. Usually
this water is reused, either wholly or in part, by collecting it and pumping
it to the scrubbing device. An efficient gas cooler will provide an outlet
temperature within 10°F of the inlet water temperature. Efficiency of cooling
is especially important in the case of the blast furnace gas because of its
low calorific value. If the gas temperature remains high, there is an increase
in content of evaporated water which lowers the heating value of the gas and
makes it very difficult to burn.
The gas cleaning system also includes goggle valves for isolating the
various portions of the system as well as barometric legs and water seals, at
all discharge points.
3.1.2 Blast Furnace Scrubber Water
In many early systems of cleaning blast furnace gas by use of wet
scrubbing, the contaminated scrubber water was discharged directly to the
waterway. Subsequent environmental measures required the provision of a
clarifier followed by discharge of the cleaned effluent directly to the
receiving body. This effluent was normally combined with the effluent from
the gas coolers and from other miscellaneous discharges. At Inland Steel
20
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Company, it is reported that the total load of parti oil ate matter thus
discharged amounted to 14,782 Ibs/day as given in Table 1. Environmental
regulations required that company to change the once-through water system to a
recirculating water system. This system consists of two loops as shown in
Figure 4. One loop is for the gas cooler water and the other loop is for the
venturi water, seals, disintegrators, and miscellaneous sump water. Each
system has independent pumping, piping, cooling, and treatment facilities. The
systems are linked to one another by the blowdown of one loop supplying the
makeup water for the other loop. As a result of this improved system, the
discharge of particulates was reduced to 575 Ibs/day as seen in Table 1. There
are two thickeners, or clarifiers in the venturi scrubber loop. In case one of
the thickeners is down because of malfunction or need for repairs, the second
thickener may handle the entire flow of water at some reduced level of cleaning
efficiency. Figure 5 and Table 2, obtained from the EPA Document which forms
the basis for BPCTCA Effluent Limitations Guidelines, indicate the level of
f\ »
discharge obtainable by this type of system.
A system for recirculating the scrubber water from blast furnaces has
certain inherent problems that must be overcome. The suspended solids in the
water are principally iron oxide and are highly abrasive. Abrasiveness is
compounded by the fact that a fairly sizeable porportion of the particulate
matter is rather coarse. In consequence, special precautions are required to
prevent deposition in the sumps accompanied by plugging of pump inlets. The
pump application itself is an extremely difficult one and it is not uncommon
for the life of a pump impeller to be rather short. Because of the heavy
nature of the particulates and because of the presence of coarse material, it
is not uncommon for the rakes of the clarifier to stall, thereby taking the
clarifier out of service.
Another problem in blast furnace scrubber service is the high alkalinity
of the water. This results from the carryover of particles of lime in the
blast furnace gas and their subsequent solution in the water. Recycling this
water to achieve effluent guidelines and to minimize the amount of blowdown
leads to a buildup of dissolved solids and, unless special care is taken, to
the plugging of pipelines and spray nozzles. Such plugging becomes particularly
21
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TABLE 1. EFFLUENT MATERIAL GENERATED IN A "ONCE-THROUGH" SYSTEM
Gas Coolers Water Flow
No. 1 Furnace 711 Ibs/day
No. 2 Furnace 459 Ibs/day
No. 3 Furnace 577 Ibs/day
No. 5 Furnace 295 Ibs/day
No. 6 Furnace 322 Ibs/day
TOTAL GAS COOLER WATER FLOW 2,364 Ibs/day
Venturi Scrubbers - Passing Through
Dorr Thickener
12,050 6PM @ 65 mg/liter of suspended solids 9,618 Ibs/day
Miscellaneous Flows Going Directly to Discharge
Miscellaneous Sumps
Miscellaneous Gas Main Seals
Miscellaneous Gas Downlegs
Cast House Drains 2,800 Ibs/day
TOTAL WATER DISCHARGE 14,782 Ibs/day
TOTAL SUSPENDED SOLIDS
A. EFFICIENCY OF A "ONCE-THROUGH" SYSTEM
611,796 Ibs/day generated
14,782 Ibs/day to discharge
97.56% Efficient
WVIBBWWWWHA'BW^WWWVWIVaBBavwMWMWWMWaKMWWWWVIMBMMBWaBWWHBMVB «•»«•««««*•_•..
B. EFFICIENCY OF A RECYCLE SYSTEM
611,796 Ibs/day generated
575 Ibs/day to discharge
99.91% Efficient
22
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GAS COOLERS
VENTURI
T 5-
A '_
VENTURI
Hv
,^J GAS COOLER L J GAS C
"^f SETTLING ^""TH H°
BASIN WE
GAS COOLER LOOP
SERVICE
H20 COOL
• TOW
•I
COLD WELL T
DORR
PUMP __K/" "\/^~^\ JT
TATION BHpr U WiiHH HI
THICKENERS
A
SCRUBBER LOOP SLOWDOWN -^f""
ENTURI A VENTURI A THFI
COLD &•• SETTLING P"""O jZS.
WELL BASIN ^ KUK
1 SLOWDOWN FROM GAS COOLER
OOLER
T
LL
ING
ER
(_.
ENTURI
3T WELL
i
WL
3RS
Figure 4. Inland Steel recirculating water system.
23
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MAIf£-Uf=>
PHENOL.
S&.
SUSR SOUOS
BPCfCA
//•/3'73 (
Figure 5. U.S. Environmental Protection Agency BPCTCA Model
-------
TABLE ;2. BPCTCA - EFFLUENT LIMITATIONS GUIDELINES. SUBCATEGORY BLAST FURNACE CIRQN)
ro
tn
BPCTCA LIMITATIONS
Critical
Parameters
Suspended Solids
*CyanideT
Phenol
Ammonia (as NH.,)
Kg/KKg(1)
(lb/1000 Ib)
0.0260
0.0078
0.0021
0.0651
mg/l(2)
50
15
4
125
(3}
Control & Treatment Techno! ogyv '
Thickening with polymer addition
Vacuum filtration of thickener
sludge
Recycle loop utilizing cooling
tower
ESTIMATED^'
TOTAL COST
$/KKg $/Ton
0.271 0.246
PH
Flow:
6.0 - 9.0
Most probable value for tight system is 522 liters effluent per kkg of
iron produced (125 gal/ton) (excluding all non contact cooling water)
(1) Kilograms per metric ton of iron produced or pounds per 1,000 pounds of iron produced.
(2) Milligrams per liter based on 522 liters effluent per kkg of iron produced (125 gal/ton).
(3) Available technology listed is not necessarily all inclusive nor does it reflect all possible com-
binations or permutations of treatment methods.
(4) Costs may vary some depending on such factors as location, availability of land and chemicals, flow
to be treated, treatment technology selected where competing alternatives exist, and extent of pre-
liminary modifications required to accept the indicated control and treatment devices. Estimated
total costs shown are only incremental costs required above those facilities which are normally
existing within a plant.
*Total cyanide
-------
severe in that portion of the system which follows the cooling tower. The
water, having been reduced in temperature, becomes more susceptible to the
precipitation of scaling compounds.
Finally there are the physical problems that result from retrofit of a
recycle water system to an existing scrubber system for which no provision had
been envisioned for installing the additional equipment. Some blast furnace
complexes, particularly the older ones, were installed in a congested physical
surrounding that did not leave room for the modern technology, including the
recycle system. In such plants, pump houses are often cramped, leading to
difficulty in maintaining and repairing a piece of equipment which is highly
susceptible to outage. Other problems arise due to the necessity of modifying
piping systems without excessive shutdown to the ironmaking process, and so
forth.
3.1.3 Material Handling Emissions
The raw materials which make up the burden of the blast furnace comprise
iron-bearing materials such as iron ore, pellets and sinter, coke, and flux
materials such as limestone and silica. In a modern blast furnace, extensive
attention is paid to the sizing and screening of these materials, both at the
source of the materials and in the stockhouse of the blast furnace. The latter
requres the operation of material screens, accompanied by the generation of
dusts. If the initial burden preparation has been properly done, the amount of
dust is not severe and adequate environmental conditions can often be provided
by the judicial application of water sprays.
In some of the older blast furnace installations, preparation of the
burden is less extensive. The handling of material in the stockhouse becomes a
very dusty operation, especially for coke and sinter. The dusting condition
carries over into the operation of filling the blast furnace skip and of
dumping the skip into the bell at the top of the blast furnace. Dusting also
continues within the furnace itself leading to a high level of particulate
concentration in the raw blast furnace gas. As in the case of the more modern
furnaces having highly beneficiated burdens, usually water sprays will suffice
to provide an acceptable environment in the cast house. The application of
such sprays to the dumping of the skips into the bell is not a current practice
in the United States, thereby leaving this source uncontrolled.
26
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3.1.4 Cast House Emissions
The emissions from the casting of molten iron and slag occur primarily
at the tap hole of the blast furnace and in the pool immediately adjacent to
it. There are also emissions which evolve from the iron and slag runners
following the pool, however, these are considerably reduced in extent.
The mechanism for these emissions results primarily from consideration of
the solubility of carbon in molten iron. As the iron leaves the blast furnace,
it is saturated with carbon and as it cools, the solubility of carbon decreases
and flakes of graphite are emitted from the surface of the molten metal. This
graphite, called kish, as well as other metallic oxide emissions escape to the
atmosphere. In an uncontrolled situation, they rise to the roof of the cast
house and discharge from there through open spaces to the atmosphere. In most
ironmaking facilities in the United States, there is no provision for capturing
and filtering these emissions from the air. Where such control is absent,
there is obviously no associated abnormal operation. There are, however,
abnormal operations concerned with the ironmaking process which cause an
increase in the rate of uncontrolled emissions. These will be discussed in
greater detail in Section 4.0 of this manual.
In October of 1974 tests were conducted at the Sparrows Point Plant of the
Bethlehem Steel Company which yielded an emissions rate of 0.15 gm/kg (0.31
pounds of particulate per ton) of iron. This compares to the results of an
evaluation of the cast house evacuation system at DOFASCO Blast Furnace No. 1
during the period of August 30, 1976 to November 19, 1976 in which the emission
factors ranged from 0.16 to 0.364 gm/kg (0.327 to 0.727 pounds per ton) of
molten iron over 14 samples. The average emission factor was 0.26 gm/kg (0.52
pounds per ton) of molten iron. The range of values given above attest to the
variation in the quantity of emissions from this source. Variability is also
confirmed by numerous visual observations.
The most common method of controlling emissions from the cast house is to
totally enclose the house and evacuate it to a fabric filter. In Japan, where
control of casting emissions is more widely practiced than in the United
States, there are three different control options practiced, often in combina-
tion. These control options involve the method of capturing the fume. Figure
27
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6, which derives from schematics provided by the Nippon Steel Corporation
shows these methods. The features of this control are:
1. A curtain type comprising three wall curtains which are
lowered over the tap hole area when the fume volume
reaches its maximum. At this time suction is commenced.
2. A fixed hood type which is erected over the tap holes and
sinter notches for additional collection.
3. An accumulated type in which fumes are temporarily
accumulated in the roof of the cast house and slowly
vented to the baghouse.
Because of the large air volumes, the concentration of particulates in
the air is low as is the temperature of the air. Both of these factors lead
to long life of bags and minimum maintenance in a well designed baghouse. At
this time, it is not known what sort of maintenance difficulties arise in
respect to the hooding, especially that immediately adjacent to the tap
holes.
28
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Secondary Dust Collection
Blast
Furnace
Primary Dust Collection
Figure 6. Cast house dust collection system.
29
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4.0 ABNORMAL OPERATING CONDITIONS
This section discusses abnormal operating conditions and techniques for
eliminating or minimizing discharges thereunder. Abnormal operating conditions
(AOC) can occur in the blast furnace, in its control equipment, during
startup and shut down. AOC's are addressed relative to resulting increases
in pollution. From this perspective, their causes may be inherent difficiencies
in the design of equipment relative to standards set for pollutant control,
changes in operating practices and feed material, limitations in the applied
technology, equipment or power failure. In assessing AOC's, therefore,
attention is given to the role of and need for preventive maintenance,
redundant capacity, sensing impending upsets, redesign of control equipment,
and alternative strategies for response to AOC's at the plant.
In the following sections, the discussion of AOC as related to the blast
furnace is divided into a section related to the process and a section related
to control equipment. The importance of each individual AOC in terms of its
effect on the environment is not necessarily indicated by the length of dis-
cussion. A simple description of problems that produce serious effects are
possible while less severe problems may require more elaborate explanations.
In the process area of the blast furnace, a well designed furnace that
is equipped with modern techniques and operated according to well established
practices both as to maintenance and operation tends to reduce susceptibility
to AOC. Those factors which tend to produce high quality iron at low operating
cost also tend to reduce the frequency and severity of the AOC. In the
control area, the chief source of AOC is in the recirculated water system
which serves the gas scrubbers.
The description of AOC's given in the following pages, especially those
which are process related are not applicable to all blast furnaces. Procedures
and conditions which occur in one plant would not necessarily occur in another.
Unusual events in operating one blast furnace may not occur in another. Many
accepted conditions of furnace practice, as viewed from the standpoint of
30
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recent and future environmental regulations, may become questionable and
require future consideration.
4.1 PROCESS RELATED AOC
4.1.1 Startup
The startup, or lighting of a blast furnace takes place after the
blast furnace has been relined or after it has been banked for a prolonged
shutdown such as one caused by a strike. Two methods are used to heat the
hearth initially; blowing air into the tuyeres and out the tap holes and
blowing air in through a tap hole by connecting it to an adjacent tuyere
pipe. In either case, the air has been preheated in the stoves and lights up
the furnace by igniting the coke. To prepare for the startup, the furnace
has been previously filled with a special burden which is high in coke.
Right after the furnace lighting begins, the brickwork starts opening up at
the bosh. Until the gas has ignited or until the openings are closed with
blanks, a hazardous gas condition can possibly exist in the cast house.*
The blow-in burden is one that will produce a very limey slag to protect
the bosh brick. Blast furnace slag is also charged so that the initial slag
volume is very high. The ore to coke ratio is slowly increased and the blast
furnace slag decreased until the furnace is eventually put on its full burden.
The rate of increasing the burden ratio and the wind rate is done according
to a predetermined schedule; however, this may be adjusted according to
conditions. With a normal blow-in, the full burden and rate should be reached
after about 70 hours.
During the lighting of the furnace, the large bell may be kept open as
are the dirty-gas bleeders.** With the blowing-in practice, the instant the
wind is blown into the furnace and the coke is ignited, part of the gas will
emerge from the open tap hole. Ignition of the escaping gas which is forced
out in increasing velocity as the wind volume increases is extremely important.
13
*The gas can be lit immediately, however.
**The large bell need not be held open in all systems.
31
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The blast furnace gas, which contains a high percentage of carbon monozide
is very explosive and highly poisonous to the human system. After a good
ignition has taken place, a large quantity of the gas issues from the furnace
top. This gas is also high in carbon monoxide and, because of the water gas
reaction in the furnace, with hydrogen as well.
Gas tests are taken perioidically from the furnace top. After obtaining
a satisfactory sample, i.e., one void of oxygen, the bleeders are closed, the
goggle valve is opened, and the furnace is connected to the gas system of the
plant. The period of bleeding gas may last approximately 27 hours during
which the injection of heated air and the consequent flow of gas has been
gradually increasing.
In an alternative blow-in practice the initial air may be injected
solely through the tap hole pipe assembly. After about 14 hours, the two
tuyeres over the tap hole are opened and the remaining tuyeres are opened at
varying intervals. Practice varies from one plant to another, however, at
the blowing-in of one furnace the average wind rate during the bleed period
was approximately 13 percent of normal wind.
When blowing-in from a bank, upon completion of the first cast, a casting
schedule is established. For the next four to five days, the furnace operating
conditions are watched to spot any variations from the schedule. Some problems
that may arise during this period are:
1. Sustained high silicon content.
2. Drop in slag temperature.
3. Sudden change in slag composition.
When blowing-in a new furnace after a reline, additional problems may
occur. Examples of these are:
1. Mechanical problems.
2. Electrical problems.
3. Charging difficulties.
4. Improper burden control.
32
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Any one of the above mentioned problems may delay and prolong the
startup time. In view of the condition that emissions during startup are
greater than normal, such delays increase the environmental impact.
Reline and the startup accompanying them are infrequent and occur at
intervals of approximately four to five years. The blow-in from a bank,
since it depends upon such external uncontrolled factors such as business
conditions and strikes, may occur at longer or shorter intervals of time.
The startup of a brand new furnace obviously occurs only once and may be a
particularly difficult period through which to go.
During the startup of one new large furnace in 1974 , many minor problems
were encountered and corrected. These included stockhouse logic and computer
inadequacies, hydraulic system failures of various types involving the top,
mud guns, drill machines, and tilting spouts. In addition, tap hole problems
were encountered early and continued until a suitable anhydrous tap hole mix
became available. Some of the delays are shown in Table 3.
TABLE 3. GARY WORKS, 113 BLAST FURNACE MAJOR DELAYS
April 3 and 4
April 4
April 5 and 6
April 18
May 20
May 27
June 2
June 8 and 9
July 11
July 13
August 9
32 hours -
6 hours -
14 hours -
16 hours -
6 hours -
5 hours -
15 hours -
37 hours -
11 hours -
10 hours -
52 hours -
August 23, 24, 25, and 26 83 hours -
Coke mess and iron spill
Hydraulic failure
Mud gun failure
Coke mess
Coke mess
Iron spill
No. 3 hole opened up
No. 1 hole opened up,
burned up hydraulics and
wiring
No. 2 hole opened up
No. 2 mud gun traverse
cylinder broke - missed
stop
No. 2 taphole spill -
expanded into planned stop
for maintenance work
Lost No. 1 taphole
33
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The most persistent problem during the initial operation was with
the tap holes. The furnace was equipeed with rotary drill machines and
hydraulically operated mud guns. Prior to blow-in, the original tap hole
brick work was partially removed and rebricked to change the angle and length.
The rotary drills were not powerful enough to drill to the skull, resulting in
an excessive amount of oxygen lancing. This and other problems made it
difficult to maintain long, strong tap holes. Short holes were a daily occur-
rence and spills were frequent and sizeable.
One of the considerations during startup is to insure that the iron and
slag will flow readily out the tap hole. In order to achieve this, the furnace
is kept hotter than usual. Because of the excessively high temperatures, slips
are more frequent than they are during a normal operating campaign. In
addition, the initial slag should be limey at the start. This type of slag
tends to produce increased emissions from the cast house during the casting
process.
In summary, increased emissions are usually present during the startup of
a blast furnace. These emissions include unburned raw gas, emissions from
increased lancing of the skull, increased emissions during the casting process,
increased slips, and emissions from various spills that may occur. Careful
planning is required to reduce the length of the startup period and in con-
sequence the amount of emissions. The interval between startups is long,
generally in the order of four to five years. The interval between banks is
also long, but variable in frequency.
4.1.2 Shut Down
There are two conditions under which a blast furnace may be shutdown.
One is in anticipation of a prolonged outage such as for a strike. In this
case, the furnace is banked so that it may be restarted upon resumption of
normal operating conditions. The other is in the case of taking a furnace
completely out of service such as for a major reline. In this case, the burden
is quenched.
A typical procedure in banking a blast furnace is to charge it with a
suitably fluxed coke blank approximately 8 hours before the shutdown. This
blank may be equal to approximately 40 percent of the working volume of the
-------
furnace and the remainder of the furnace is filled with a burden in which the
ore to coke ratio is 50 percent of normal. The coke blank at the tuyeres
provides the initial heat requirement when the furnace is blown back in. An
estimate of the number of rounds required to be charged until the coke blank
reaches the tuyere zone is made. The furnace is then shut down coincident with
the first coke blank reaching the tuyeres. The tap hole should be blown hard
and long to drain the furnace of as much iron and slag on the last cast. In
addition, the dust catcher should be blown many times to insure that it is
empty, since any dust remaining could consolidate into a hard mass that is
difficult to remove. Both procedures increase emissions during banking.
After shut down, stringent measures are taken to minimize the ingress of
both water and air into the furnace. Water ingress is prevented by testing
cooling members for leaks, reducing water to coolers to 25 percent of normal,
and turning water off the tuyeres. Air ingress is prevented by removing the
blowpipe and plugging the tuyeres, encasing the furnace shell with a sealing
compound, and making the last top charge to the furnace of uncleaned iron
bearing material to form a top seal. Steam is also used to purge the furnace
and the gas system. The last gas still being produced by the furnace is bled
out of the relief valve until the wind is taken off.
There are several different methods of blowing out a blast furnace. One
method is to blow the furnace down so that most of the stack is empty when
the last cast is finished. Other methods leave the furnace full of materials
that can be raked out.
Blowing the furnace down has the advantage of reducing the time required
for stock removal since the furnace is left partially empty. During blowdown,
it is necessary to install water sprays in the gage rod holes to prevent
excessive temperatures in the furnace top. There must be an ample volume of
water to quench the coke below its kindling temperature. The last cast is
scheduled so that it will be finished when the stock is at the predetermined
level after which the wind is taken off the furnace, the salamander is tapped
and the furnace completely quenched.
35
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The disadvantage of the blowdown method is the danger of an explosion in
the space above the burden. The risk is even greater when the furnace is known
to have a scab or scaffold which may disrupt the distribution of water and
prematurely put out the flame of one or more tuyeres. To reduce the danger of
explosion, coke or silica pebbles are used to fill after the last burden
leaving an empty space only eight to 10 feet below the normal stock line.
Some operators adopt the procedure of quenching the furnace filled with
its regular burden without scrap and other miscellaneous materials. This
requires more time to clear the burden after quenching. It is not wasteful
because the materials may be recharged after cleanout.
A large furnace can be completely quenched in 24 hours if a sufficient
supply of water is available. During this period, the cast house is roped off
and no one is permitted around the furnace or on top. The tuyeres are solidly
plugged and the blowpipes either blanked with steel plate or taken down before
the quench. All furnace bleeders are left open to relieve the steam and the
gas that is formed. At some plants, the bells are also blocked open.
During the quench, the furnace top may get very hot. Due to the water gas
reaction, large quantities of hydrogen may be produced. A gas fire may start
above the furnace in the superstructure. For this reason, it is always advis-
able to clean as much grease off the furnace top as possible before starting
the quench.
The pool of iron in the hearth of the furnace below the tap hole can
either be removed as a liquid by bottom tapping or be allowed to solidify and
removed when the lining is torn out. If the bosh and hearth are not to be
relined, it is left in the furnace. If bottom tapping is employed, a hole is
drilled through the bottom refractory from beneath the hearth plates and the
iron is drained onto the ground.
As in the case of starting up the blast furnace, the process of shutting
it down involves greater than normal emissions. The duration and concentration
of emissions during the latter procedure are much less severe than during the
former. The frequency of both are essentially the same; that is, a shut
down is normally followed by a startup.
36
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4.1.3 Abnormal Operating Conditions
Slips
Slips are due to a bridging of the stock in the furnace. When this occurs,
the material underneath continues to move downward creating a void. The void
increases in size until the bridge collapses, causing a sudden downward move-
ment in the stock above it. In severe cases, this causes a sudden increase in
gas pressure. To relieve this pressure, the raw gas bleeder at the top of the
furnace automatically opens discharging a cloud of particulates and blast
,furnace gas to the atmosphere. The bleeder is shown in Figure 7 which has been
reproduced from Reference 8. This Reference also attributes the cause of
hanging to the following factors:
1. Resolidification of previously fused slag and molten iron.
2. An excessive quantity of fines in the coke. This is
confirmed by common operating experience in the blast g
furnace and is reported as the result of model experiments.
3. Fine carbon formed via the Boudouard reaction may also
fill the spaces in the burden and impede the upward
flow of gases.
4. Alkalis such as the oxides of sodium and potassium,
may contribute to the hanging as well as to the
formation of scabs which adhere to the furnace wall.
5. Overblowing the furnace by excess wind tends to prevent
the smooth downward flow of material. One way of over-
conming this condition is to increase the top pressure
of the furnace.
This same Reference indicates that slip-induced bleeder valve emissions,
based on national production figures, appear to be small relative to the
emissions of other in-plant air pollution sources. Their estimate of emissions
from slips in the United States is 187 to 1842 tons per year. They compare
this to the blast furnace cast house emissions which they estimate to be 4790
to 24,370 tons per year.
Bleeder valve openings which result from slips in the blast furnace are
more serious on an individual basis than on a national basis. Some furnaces
may operate for an entire year without reporting one such opening. Others may
37
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noons AM COUNTER-
WBGMTEO TO AUTOMATICALUr
Oft* WHENEVER (US PRESSURE
THE TOP SYSTEM INCREASES
SUDDENLY we TO sun on OTHER
comers MOT GASES
FROM THE fOM GAS UPTAKIS AND
CARRIES THEM DOWNWARD TO T>C
DUSTCATCHEK.
EQ BEAM CNOS RASED AND
LOWERED BY CABLES (NOT SHOWN)
TO LOWER AND RAISE ««" «
COUNTERWEIGHTS MRTULL7
LOAD TO
auu.ga.LRoo
ISEE ne.K
LOAOS DUMPED BT SKIP
CAMS MTO DISTRIBUTOR.
ROTATES MMT Of A
8 AUTOMATICALLY
TILTEO TO DUMP ITS LOAD
MTO RECEIVING HOPPER.
SECOND SKIP CAR S AT
BOTTOM OF BRIDGE IN
STOCXHOUSE, ANO WILL
RISE AS EMPTT CAR DE-
SCENDS TO SIOCXHOUSE.
SKIP BfllPCg CARRIES TRACKS
ON WHICH SKIP CARS CONVET
<£ ANO LIMESTONE
OF FURNACE.
RAX TURN ATTER EACH SKIP
CM LOAD IS DUMPED TO HELP
DISTRIBUTE ORE, COKE ANO
UUC5TONE EVENUT OH SMAU.
U5C2B, CLOSED 8T LARGE BEU,
RECEIVES MATERIAL FROM THE
RECEIVING HOPPER ABOVE
•MEN SMALL eeu. IS LOWERED.
LOWERING LARGE MU. EMPTIES
HOPPER MTO FURNACE.
FURNACE
"THE VARIOUS PLATFORMS ANO STRUCTURES SUPPORTING THE TOP EQUIPMENT HAVE BEEN OMITTED FROM THIS DRAWING
AS WOO. AS THE CABLES ANO SHEAVES THAT OPERATE THE SKIP ANO THE BEUA ALSO OMITTED ARE THE JS*
BOOM CRANES THAT ASSIST IN HOISTING REPAIR AMD REPLACEMENT MRTS TO THE TOP OF THE FURNACE.
Figure 7. Schematic illustration of blast furnace top.
38
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have 50 a month or more. Older blast furnaces generally have more slips than
younger ones. It is also possible for a bleeder valve to stick in the open
position, thereby increasing the duration of the AOC.
High-alkali burdens are especially important contributors to slipping.
In addition they cause other operating problems in the blast furnace:10
1. Excessive tuyere losses.
2. Coke messes on the cast house floor.
3. Very high blast pressures.
4. Inwall scabbing. The presence of scabs tends to restrict
the area in the stack causing higher gas velocities and
contributing further to the incidence of slips.
5. High coke rates. More coke has to be produced by the
coke ovens leading to increased emissions from that
source.
6. Loss of production for removing scabs. The process of
removing the scabs in itself induces the emissions to the
atmosphere.
One of the most effective ways to decreasing the alkali content of the
burden materials is to determine which materials are the principal sources of
the alkali and to eliminate them from the burden. Alkali may be found most
usually in iron ores, but they are also present in coke and in flux material.
A high slag volume and a lean slag practice (keeping the basicity ratio of
the slag at 1.00 or less) is effective in obtaining reasonably good operation
with a high-alkali input. Analyses show that lean slags remove significantly
more alkali than limey ones. Alkali input not only causes abnormal operating
conditions, but also reduces production and increased coke rates as can be seen
on Table 4.10 The operational problems resulting from high alkali will increase
with a decrease in coke stability.
The factors that induce good performance in respect to meeting metal-
lurgical specifications for iron are also conducive to reducing AOC from slips
and other causes as will be indicated below. In one plant in which the bogey
for casts that are off-analysis is a maximum of 6 percent, the following
29
operating factors contribute to a satisfactory performance record:
39
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TABLE 4. EFFECT OF ALKALI ON PRODUCTION AT GENEVA BLAST FURNACES
Item
Production
Coke Rate
Carbon Wind
Blast Heat
Slag Volume
Ore Usage
Alkali Input
Alkali Input
Unit
NT/day
Ibs/day
C.F.M.
Op
Ibs/NT
T/NTHM
Ibs/NT
T/Fce. Day
Prior to Pellets
100% Utah Ore Burden
35% Sinter 65% C. Ore
1349
1270
62,338
1450
926
1.835
46
31
1964-1975
50% Pellets
30% Sinter 20% C, Ore
1920
1140
79,750
1800-1850
770
1.61
17
13.4
Two Periods in 1975
80% Pellets
10% Sinter 10% C. Ore
2100
1100
78,000
1700-1800
720
1.50
8
8.4
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1. Control of materials
a. Coke stability. Around 55 is excellent. Below 48
is poor. The larger furnaces need better coke for
good performance. These numbers refer to a standard
test of abrasion resistance.
b. Low alkali content of the burden. High alkali contri-
butes to slips.
c. A screened burden.
d. Low ash in the coke.
2. Uniform Operation. Attention to all operating factors that
contribute to the uniformity of operating conditions. In
one plant reliance is placed on thermocouples, located at
the quadrants of the furnace, approximately 6 feet below the
big bell. The thermocouples indicate proper movement of the
burden and proper distribution of the gas. Adjustments in
the burden are based upon the temperature readings.
3. Moisture Control. Moisture is controlled by the addition of
steam into the tuyeres. A desired control level is 11 gms/schi
(5 grains of moisture per scf) of air. In the summertime,
moisture may increase to levels as high as 25 gms/scm (8 grains
for which there is usually no correction provided.
4. Maintenance. A high degree of preventive maintenance will
tend to keep all systems, instruments, and controls operating
as designed. In one plant which is located in a cold cli-
mate, the preparations for winter conditions begin in August.
5. External desulfurization of molten iron in a facility away
from the blast furnace. This permits the blast furnace to
deliver molten iron which is higher in sulfur than required
at the steelmaking facility and results in lower consumption
of flux as well as a leaner slag thatis better able to
deal with removal of alkali. Another benefit is the increased
production of iron from a given furnace up to about 15 percent
and the reduction in coke, up to about 10 percent. By virtue
of the benefits mentioned above, external desulfurization of
iron contributes to the reduction of AOC from the ironmaking
process as well the reduction in normal emissions from this
process and the coke making process.
By carefully monitoring the pressure in the blast furnace, the relief
openings due to slips may be minimized. When the pressure first starts to
build up, a controlled slip can be made to occur by reducing blast pressure.
This procedure called checking helps to break up the bridge which has been
41
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impeding the flow of the burden. By a repeated checking procedure, the gas
channels become more evenly distributed and the stock movement may return to
normal. If this procedure is not successful, another procedure is to increase
the moisture in the blast and to decrease its temperature for a short period of
time.
Backdrafting
The necessity of making certain repairs on the blast furnace requires that
the pressure in the furnace be relieved by taking the wind off the furnace,
backdrafting the bottom of the furnace through the tuyeres and opening the
relief bleeder. Backdrafting refers to the condition in which the furnace
gases are drawn back through the tuyeres to a hot stove where the gas is
burned. As an alternative to the use of a hot stove, some plants deliver the
gas to a special backdraft stack.
Emissions of gas and particulate matter from the opening of the relief
valve and from the backdrafting occurs primarily during the first 15 minutes of
the outage. It is not known how much of these contaminants are emitted; how-
ever, visual observation indicate that it is minor in comparison to other
sources at the blast furnace. Figure 8 diagrams the procedure that occurs
during backdrafting.
Compared to all other blast furnace water-cooled members, tuyere failures
are the single biggest cause for furnace delays and for backdrafting associated
with their repair. Tuyeres are nozzle-like water-cooled copper castings which
project into the hearth of the blast furnace. Their function is to direct the
heated blast from the bustle pipe into the furnace. Some reasons advanced for
their failure are:
1. Inadequate cooling due to poor water circulation, dirty
water, or water stoppage. Newer designs of tuyeres have
been developed which provide higher water velocities at
the tip of the tuyere which is exposed to severe operating
conditions of the blast furnace.
2. Abrasion from the ceaseless swirling of incandescent
coke due to the tremendous activity which occurs at
the nose of the tuyere.
42
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CO
Figure 8. Bsckdrafting through bUst furnace stoye,
-------
3. Iron cutting. The impingement of a large amount of
molten iron on the surface of the tuyere can cause
premature failure. It has been surmised that a sudden
drop of the burden into the molten bath during a slip
may splash an excessive amount of slag and hot metal
onto the tuyere. It is also believed that weak coke
pulverizes excessively and forms a mass of fine particles
which retard the passage of molten globular iron. The
impervious coke collects and forms a pocket at the tuyere
nose for the molten iron.
4. High alkali burdens, as indicated in the previous section
are associated with excessive loss of tuyeres.
On one new blast furnace7 the initial design of tuyeres resulted in a
large number of failures. There were 197 tuyeres changed during the first 9
months of operation and 200 tuyeres in the next year. Since the furnace has 36
tuyeres, this works out to an average life of about 58 days per tuyere.
Continued work on tuyere design and water flow is reported to have favorable
results. In comparison, another furnace reports eight tuyeres out of a total
28 lost in the first 209 days of operation. This works out to 730 days average
life per tuyere.
Other repairs to the blast furnace that require backdrafting include
changing of bleeder valves, changing of furnace large and small bells, etc.,
occur less frequently than do tuyere changes but require longer downtime. A
tuyere may be changed in a comparatively short period of time. To change a
bleeder valve may require about 8 hours of which approximately 3 hours is
required to rig up for the job. A small bell repair may require about 12
hours, whereas the replacement of a large bell may take 7 days.
28
At one plant, normal furnace repairs such as welding on uptakes or down-
comers require 12 to 16 hours. A repair job on both the large and small bells
of the blast furnace has required a total 56 hour downtime. The delays for
repairs have ranged from 25 hours per year to 268 hours. Typically, furnace
downtime is estimated to be 5 percent per year; however, it may be reduced to
as little as 3 to 4 1/2 percent.
When an extended repair is anticipated, in addition to backdrafting, the
tuyeres may be sealed to prevent air from entering the furnace. During alt
such repairs, gas measurements are made to insure safety for the maintenance
44
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crew. After such a repair, when bringing the furnace back on-line, the mains
and dust catchers are purged with steam or an inert gas to avoid the potential
of explosion.
In summary, the amount of time for backdrafting can be reduced by improved
design and maintenance practices as well as by careful attention to water flow
to the water-cooled members and by improved burden which minimizes such AOC's
as slips, tuyere failures, etc. Emissions from backdrafting occur primarily
during the first 15 minutes of the backdraft and, although on some furnaces the
amount of backdrafting may be as frequent as 50 to 60 times per month, the
effect on the environment is small compared to other sources in the blast
furnace.
Hater and Power Failures
A massive power failure is perhaps the most potentially disastrous
occurrence in the blast furnace. The longer the power is off, the longer it
takes to bring the furnace back on-line. If the outage is of short duration
and cooling water pumps are restored during the period, very little damage will
occur to the furnace. However, if the outage is long and there are not supple-
mentary steam driven cooling water pumps, the residual water in the tuyeres,
coolers, bosh plates, and stack plates will boil out and they may become so hot
as to melt. In addition, the hearth cooling plates may become damaged. During
power failures, blast furnace bleeders may be opened, thereby creating a source
of emissions.
If the power outage continues, the gas mains may cool off, the vapors in
gases inside may condense, reduce in volume and create a vacuum. If air is
sucked into the mains, explosions may result. Burned copper coolers may permit
large quantities of water to enter the furnace, chilling it and consuming large
quanitites of coke due to the water-gas reaction. Finally, it may be exceed-
ingly difficult to isolate the blast furnace from the gas system because the
large goggle valves may be difficult to operate manually.
On February 11, 1967, the Aliquippa Works of Jones & Laughlin Steel
Company suffered such a massive power failure. A series of explosions occurred
after the power was restored. The low pressure steam, when turned into the
cold mains, apparently condensed and drew in air creating an explosive mixture.
These explosions wrecked the boiler house gas mains and a furnace gas cooler.
45
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On August 28, 1974 the Gary Works of U.S. Steel Corporation suffered a
complete power failure and their No. 11 Blast Furnace lost all wind, water, and
electrical power. This resulted in filling all the blow stocks, two of them
being burned through with the slag and iron running out. All 35 tuyeres, eight
coolers, and four upper expansion joints had to be replaced. This, as well as
repairing other damage, resulted in the furnace being down for five days.
As a result of the breakouts and explosions as described above, the
emission to the atmosphere from a power failure can be very great. Fortunately,
such occurrences are comparatively rare and may be minimized by building cer-
tain safety features into the plant as follows:
1. Provide a source of power which is separate from the
outside utility company. In addition, provide duplicate
facilities such as power lines and breakers for supplying
electricity to the consuming units.
2. Provide steam driven auxiliary units such as cooling
pumps for the most critical service.
3. Provide an overhead water storage tank to insure an
adequate supply of cooling water to the blast furnace
under emergency conditions.
4. Provide training for operating and maintenance per-
sonnel in respect to dealing with problems which
may arise during power failures.
Breakouts
Breakouts occur in the area of the hearth and the bosh immediately above
it. They are caused by the failure of the walls which, in turn, results in the
uncontrolled flow of liquid slag and/or molten iron out of the furnace. This
can cause considerable damage to the furnace and the auxiliaries. It also
results in a substantial cloud of emissions to the atmosphere.
When a slag breakout occurs it can usually be chilled with water and the
hole plugged by pumping in fireclay grout or by ramming in refractory material.
An iron breakout is much more serious because there is more chance of explosions
if the molten iron comes in contact with water. Also there is usually no prac-
tical way to stop the flow of iron out of the hole until it drains completely.
Most breakouts of iron have occurred in furnaces that are lined with carbon.27
With more experience in the use of carbon, the incidence of these breakouts
has decreased.
46
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Another cause of breakouts, especially in high tonnage carbon hearths may
occur when restarting a furnace after a comparatively short stop in which the
iron salamander is left in the hearth. When this iron solidifies, the sala-
mander shrinks as it cools and draws away from the brick. These shrinkage
cracks then become filled with other material and upon reheating, the reexpan-
sion of the salamander creates enough stress on the hearth jacket as to burst
it. If the cooling water on the jacket is heated to 140°F just prior to blow-
in, the jacket is allowed to expand and the stress is relieved. Heated water
is maintained on the jacket for about 14 days after the blow-in after which
normal cooling water is restored. Typical of such outages which last at least
three days but are not long enough to drain the salamander are for a bell
change, a steel plant oxygen failure, a power failure where a furnace cannot be
restored for several days, major stove repairs, strike threats, etc.
12
Figure 9 illustrates the amount of iron produced and the years of
service
Bethlehem "B" Hearth
10
•g
i s
I
I 6
"Z
•
6 days stopped
Raptured jacket
Blow-in Jan. 1966
13 days stopped
338 days to reline
16 days stopped
200 days stopped due to business decline
27 days stopped
4 6
Years of Service
Figure 9. Tons of iron accumulated on hearth during years of service. Starts
and stops in production and duration of each are shown as well as
point at which hearth jacket ruptured.
47
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An analysis of ten breakouts that occurred in various blast furnace
facilities during the period of 1961 to 1967 reveals one breakout in the bosh
1 9
three feet above the tuyeres. The remaining were breakouts in the hearth.
In only one of these incidents was a man injured being burned by metal and
slag. Damage to equipment, however, was common to all and in some cases,
fairly extensive. One method of guarding against breakouts is to install
thermocouples at strategic places in the hearth of the furnace. These thermo-
couples tend to give early warning of a condition which may lead to breakout
thereby enabling the operating personnel to take the necessary corrective
action before the breakout occurs.
Charging Dusty Material
The most common method of charging material into the top of the blast
furnace is by means of the skip. If the material being charged is weak and
friable and if it has not been beneficiated by crushing to size and screening,
the filling of the skip and its subsequent dumping at the top of the furnace
may give rise to a dust cloud of particulate matter. The dust cloud at filling
is a low level source which tends to remain within the blast furnace area. The
dumping operation is at a high level and prevailing winds tend to entrap the
particulate matter into the atmosphere.
From the standpoint of smooth operating conditions in the blast furnace
leading to high tonnages, low costs, and minimum AOC, a sized and screened
burden is highly desirable. It is desirable in many cases to screen the
burden twice. Typical examples of this are pellets, sinter, and coke. For
each of these materials screening may be performed where the material is
produced and once again in the stockhouse of the blast furnace being charged.
The latter screening serves to remove fine particulate matter with may have
developed in the handling of the raw material from the source of production to
the furnace itself. Where such screening is performed and if it is done in an
efficient manner, the filling and emptying of the skips is relatively dust
free.
48
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All blast furnace operators would prefer to have a screened and sized
burden which is strong and resistant to abrasion. In spite of this, many
furnaces do not have adequate facilities for sizing and screening, either
because of limited space or because of economic considerations. If the burden
is not screened, the filling and emptying of the skip can be quite dusty,
especially in the case of sinter and coke. One way of reducing the amount of
such emissions is by the application of water sprays,23 and preferably in conjunction
with a wetting agent.
A furnace may have up to 600 charges per day from the skip. Each filling
and dumping operation may last five to ten seconds. Thus the aggregate time
for each operation is 3 1/2 to 7 percent of the total operating time. The
amount of emissions from each occurrence is variable depending upon the nature
of the material, the way it was handled, whether or not water was applied, etc.
At the present time there is no information available on the quantity of
emissions.
Gas Cleaning System
This section refers to that portion of the gas cleaning system which
relates to the process itself, i.e., the dust catcher and the scrubber. The
other portion of the system which relates to the recirculation of the water is
covered under control equipment related AOC.
The first element in the gas cleaning system is the dust catcher. Because
this equipment is lined with abrasive resistant refractory and because it is a
low energy device, there is normally little AOC associated with it. The dumping
of the dust catcher should be done at frequent intervals, normally once per
shift. Because the material is hot, dry, and dusty, steam and water sprays are
usually provided for control of emissions. The dust may be discharged directly
from the catcher to a railroad car or it may be preconditioned in a pug mill by
adding water or blast furnace sludge.
At times the flue dust may become hard and lumpy and it may be necessary
to free the dust catcher outlet by means of a small explosive charge. This can
create a minor source of AOC.
49
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If the final cleaning device is a fixed orifice scrubber, the differential
pressure drop across it becomes a function of the rate of flow of gas from the
blast furnace. If the rate of flow is low, the pressure differential becomes
low and the efficiency of gas cleaning suffers. Efficiency may also suffer
because of wear in the lining of the scrubber which damages its internal
configuration. Blockage may also occur in the spray nozzles due to the accumu-
lation and deposits of scale, thereby decreasing the flow of water.
In most blast furnaces, the gas scrubbing equipment operates at high
cleaning efficiency because there is adequate pressure available from within
the blast furnace. An outlet gas loading of 25 mg/scm (0.011 grains/scf) or
better is commonly found; in modern furnaces, the outlet loading may be as low
as 5 to 10 mg/scm (0.002 to 0.004 grains/scf). The blast furnace operators find
it highly desirable and necessary to maintain high cleaning efficiency in order
to protect such costly fuel burning equipment as the blast furnace stoves and
the coke oven underfiring systems. If such units were to burn dirty gas, they
would soon become blocked and inoperative. Therefore, careful attention is
paid to the operation and maintenance of the scrubbing equipment and AOC from
this source is comparatively minor.
The trend in gas scrubbing facilities for the blast furnace is toward
equipment that insures higher efficiency and greater reliability. Constant
pressure differential and, therefore, cleaning efficiency is maintained by the
provision of variable orifices and automatic controls. Wear of the scrubber
internals is minimized by the provision of abrasion resistant linings and by
configurations which establish a water film for additional protection. Scaling
of spray nozzles is minimized by attention to the quality of the water and by
provision of new designs which use a small number of large diameter inlet
nozzles that are less susceptible to the effects of such scaling that does
occur than are small nozzles.
In some gas systems, final cleaning is provided by passing the gas through
a wet electrostatic precipitator. This type of equipment is subject to mal-
function from corrosion of the precipitator internals and from electrical
failures. Corrosion may be minimized by proper attention to water quality and
electrical failures by attention to maintenance practices. In any event,
50
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because the wet precipitator is almost invariably preceded by the dust catcher
and one stage of gas scrubbing, its malfunction causes minimal AOC as far as
the environment is concerned.
Gas Bleeders
In most iron and steelmaking facilities, every effort is made to consume
all of the byproduct gas produced. This is true of blast furnace gas as well
as coke oven gas. There are several conditions under which blast furnace gas
is bled to the atmosphere, as follows:
1. During startup and shut down.
2. From furnace slips.
3. From backdrafts.
4. From bell leakage.
5. From the clean gas bleeders.
The first three items on the list have been covered previously in this
manual. The next item, that of bell leakage, will be covered in Section 5.0 at
the end of this manual.
Whenever blast furnace gas is produced in an amount that exceeds its
useful consumption in various heating processes, it must be bled to the atmosphere.
Normally, the bleeder for blast furnace gas is equipped with an ignition torch
to assure that the gas burns upon entering the atmosphere. The most common
ignition torches burn natural gas or coke oven gas. On occasion, the ignition
flame is extinguished, primarily because of deposits in the coke oven gas
which may in time cause a plugged condition. When this occurs and there is a
sudden opening of the clean gas bleed, the blast furnace gas enters the
atmosphere without being burned. In consequence of the fact that the gas
contains 20 to 30 percent carbon monoxide and of the fact that the amount of
gas bled may be high in quantity, the amount of this contaminant in the
atmosphere becomes substantial. Under certain climatic conditions in which
there are downdrafts from the stack, it is possible that the area around the
base of the stack may contain an atmosphere which is toxic to human beings.
51
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In some plants, the clean blast furnace gas may be bled to the atmosphere
without any ignition. In this case, every time the bleeder opens, there is an
AOC.
The number of times that a clean gas bleeder will open in a particular
steel plant depends upon the operating conditions in that plant. A reasonable
average of frequency for such openings is about once a month and, if there is
failure of ignition, it might take one to four hours to correct the condition.
Carbon Black Formation
Because heavy fuel oil is less expensive per heat unit that is metal-
lurgical coke, the current trend in blast furnace ironmaking is to replace as
much of the coke with heavy oil as is consistent with good operating practices.
Where oil is fired in large quantities, under certain conditions not all of it
is fully combusted by the wind of the blast furnace, forming carbon black which
finds its way into the gas and from there to the scrubber water system. Oil is
normally injected into the blast furnace by means of a pipe located at each
tuyere. The reason for incomplete combustion accompanied by soot formation are
as follows:
1. The distribution of oil is nonuniform from tuyere to
tuyere. Thus, although the total amount of oil injected
in all of the tuyeres may be capable of being burned by
all of the wind which is being injected into the tuyeres,
in one or more of the tuyeres the oil flow may be so
high as to result in incomplete combustion. Some plants
meter the flow of oil at each tuyere and thereby are able
to properly balance the distribution of oil to all the
tuyeres.
2. If the oil lance is not properly centered in the blowpipe,
or if the spray is partially plugged, deflecting the flow
of oil, the oil may not come into proper contact with the
incoming air and may not be completely burned.
When the carbon black gets into the scrubber water, it has a tendency to
float on the surface of the clarifier. The accumulation of carbon black may
become great enough to interfere with the proper operation of the clarifier.
52
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It is obvious that the preferred method of dealing with the problem of
carbon black is to go to the source of its formation and make the correction
there. This not only corrects the environmental AOC but also improves the
utilization of energy in the blast furnace. Failing this, in some plants a
wetting agent injection system has been provided. The operator of the treat-
ment plant manually activates this system whenever carbon black is observed on
the top of the clarifier. Although no actual data are available on the extent
of this problem or the extent of its environmental impact, it does not appear
to be widely spread nor of great severity where it does occur.
Furnace Control
In the preceding sections of this manual there has been discussion of the
importance that smooth furnace operation plays in eliminating AOC. This is a
particularly important subject and deserves special attention.
The first element of good furnace control lies in burden preparation. A
burden that is sized and screened, that contains coke of adequate stability is
conducive to a smooth operation. Screening and careful proportioning of the
burden at the stockhouse is essential. After this, the burden must be placed
in the furnace in such a manner that there is uniform distribution which tends
to insure uniform flow of gas. These are the elements of good furnace operation;
however, not all blast furnaces in the United States have all of these elements.
The next step in assuring smooth operation is to have a full set of appro-
priate and reliable indicators of operation. Some of these are instruments to
measure top pressure, bottom pressure, stock!ine movements, temperature distri-
bution at the top of the furnace, flow meters at the tuyeres for measuring oil
injection and so forth. Once again, not all furnaces in the United States have
these elements.
Finally, having all of the above elements of control, the last element to
be applied may be a computer for the process itself. Such application is
becoming more frequent in the larger high productivity furnaces. Smaller
furnaces of which there are many in the United States may not find economic
justification for computer control.
53
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On the subject of computer control, the following statement has been
made:
"To insure stable operation of large furnaces, it is essential
to detect the condition in the furnace and the equipment main-
tenance condition and to produce such information for subsequent
control. Key points in this operation are:
1. Top sampling and shaft sampling offer information on
the radial gas distribution in the furnace, and provide
guidelines for burdening control by charging sequence
and moveable armors.
2. Venturi meters are provided to measure blast flow at each
tuyere and thermometers mounted around the furnace stove
monitor uniformity of circumferential burden distribution.
If the distribution is not uniform, the oil injection
control corrects for it.
3. The burden surface is monitored by infrared cameras and
thermoviewers to maintain even gas flow.
4. Monitoring of slag extraction and tapping.
5. Information obtained by measurement of temperature,
pressure, etc. is measured by computer to facilitate
preventive maintenance.
6. Computer estimation of the furnace internal condition."
Figure 3 in a previous section of this manual shows an example of the
primary means of instrumentation that is described above.
13
Another author wrote about benefits of computer control for blast
furnaces as follows:
"The overall function intended for the computer has changed
drastically in the last seven years from one of closed loop con-
trol to one of process monitoring. The primary purpose of the
computer, however, is to improve the control and to some extent
this was substantiated in a report prepared by our Research
Department. They analyzed the variations in silicon, sulfur,
manganese, coke rate, and number of off-casts for the No. 5 fur-
naces for two to three month periods; one with computer control
and one without computer control.... The results were incon-
clusive for the coke rate and manganese content but the variations
in silicon and sulfur from cast to cast were considerably better
in the computer period."
54
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4.2 CONTROL EQUIPMENT RELATED
Except for the gas cleaning equipment, which is essentially a part of the
blast furnace process and as such not a pollution control device, there are two
general types of pollution control equipment that may be found. The first is a
fairly common, highly developed system for recirculating the water which serves
the blast furnace gas scrubber and gas cooler. The second, which is more
recent, and less common, is the baghouse which is used for capturing emissions
from the casting of the furnace.
The systems for capturing the emissions from casting are described pre-
viously under Section 3.1. The major portion of the control system is directed
toward the evacuation of fumes from the cast house building. This is
supplemented by local fume hooding in some systems. In other systems, sole
reliance is placed on the building evacuation portion.
Because the cast house emission systems are relatively new in the United
States, there is little information regarding AOC as related to it. Never-
theless, because it is quite similar in nature to the building evacuation
system for the electric arc furnace, it may be reasonably projected that the
AOC associated with the cast house system will be similar to that for the
electric arc furnace building. Therefore, for a discussion of this aspect of
control related AOC, the reader is referred to the process manual on the
electric arc furnace.
The control related AOC for the recirculated water system is given in the
succeeding sections.
4.2.1 Startup
The major startup problems for a blast furnace recirculated water system
occur only once in its life, that is when it is newly commissioned. Subsequent
to that, shutdowns and startups may occur due to such uncontrolled situations
as strikes. The startup and shutdown subsequent to the commissioning occur at
very infrequent intervals and are usually unaccompanied by AOC. Therefore,
this section will deal with a discussion of the practices that should be
followed in achieving a successful initial startup. Assuming that the system
is installed as a retrofit for existing blast furnaces, which is usually the
case, they are:
55
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1. Prior to testing out the system, all water basins and
pipelines should be clean of debris such as wood, rags,
welding rods, etc.
2. Testing of the system should begin well before the actual
system startup, possibly two months in advance. It should
comprise the following steps:
a. Fill all basins and piping systems with service water
from the mi 11.
b. Pump the service water through all of the major pieces
of equipment including the clarifier and the cooling
tower.
c. Run each of the pumps at least two days each to verify
pumping capacity and to check for any vibration at the
base of the pumps.
d. Check all instrumentation for calibration and dependa-
bility.
3. In preparation for activating the system there should be
a meeting of personnel who will be involved with the system
for the purpose of instructing them in its maintenance and
operation. Part of this training session should be the
distribution of a simplified operating manual.
4. In a plant which has a multiplicity of blast furnaces, only
a few of the furnaces should be initially tied into the new
water supply. They should be run for about a month before
tieing in the rest of the furnaces.
In a recirculating water system, one problem which can occur is a system
imbalance caused by starting or stopping of pumps. The result is a rising or
falling water level on clarifiers of sumps. In the case of rising level, the
clarifier or sump may ultimately overflow, spilling onto the ground and potentially
into a storm sewer.
4.2.2 Shut Down
Once a blast furnace recirculating water system has been in successful
operation, it is rarely shut down except as a result of an unscheduled outage.
Such outages will be covered under Abnormal Operating Conditions in Section 4.2.3.
A planned shut down, if it should occur, is always accompanied by a planned
shut down of the blast furnaces associated with the system. In this case, AOC
from the shut down of the water system is essentially non-existant.
56
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4.2.3 Abnormal Operating Conditions
In the recirculated water system which serves the scrubbers and the
coolers of the blast furnace gas system, there is a need for utmost reliability.
The system must operate 24 hours a day, day in and day out, without shut down.
Any malfunctions in the system which might cause a shut down would either
require a shut down of the blast furnace operation or an increased discharge
of effluents'into the receiving waterway. Because blast furnace ironmaking
is a continuous operation which is exceedingly difficult to shut down without
considerable prior planning, the tendency might be to allow an increase
in the discharge of contaminants in the case of failure in the water system.
In order to prevent this, wherever it is possible and feasible all operating
components of the recirculating water system have in-place standby equipment
to take over in the case of equipment failure.
The requirements of service for the water system are severe. Close
attention must be paid to the quality of the recirculating water, otherwise a
scaling tendency arises which may result in plugging of the pipelines and
nozzles. The suspended solids in the system are heavy and abrasive. The
former quality leads to difficulties of sumps being filled with suspended
solids, thereby plugging the pumps and overleaoding the drives for the rake
mechanisms of the clarifiers. The latter quality leads to abrasion and high
wear in the pipelines and especially in the pumps, resulting in a shortened
life, even when special abrasion resistant materials are employed. Finally,
the recirculation systems for blast furnace cooler and scrubber water are
almost invariably retrofits and in consequence, suffer from congested con-
ditions and other design restrictions. These problems are covered in greater
detail below.
Water Quality
In order to minimize the discharge of pollutants to the receiving body
of water, blast furnace scrubber and cooler water is recirculated to the maxi-
mum degree possible. The BPCTCA model for this system as envisioned by EPA
is shown on Figure 5 in Section 3.0. It will be noted by reference to this
figure that the discharge allowances for contaminants are based on restricting
the flow of the blowdown water to 3.2 percent of the recirculated water.
57
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In 1969, Inter!ake, Inc. undertook a project to evaluate the performance
of a blast furnace recirculation system under a grant from the Environmental
Protection Agency. The results of this program are reported in References 14
and 15. Attempts were made to maintain dissolved solids in the system at 1500
to 2500 ppm, resulting in a blowdown of 7 to 10 percent. In about a year and
a half of operation in this mode, scaling problems developed. One section of
pipe showed a buildup of 5/8 inch. In the several succeeding years, acid
additions were made to the water in an effort to control the Ryzner Stability
Index of the water. Detailed discussion of this Index is given on pages 99
to 105 of Reference 14.
This program for controlling scale was only partially successful. In
time, scale began to accumulate again which was caused primarily by precipi-
tation of the dissolved solids in the recycle water. Subsequently, the
addition of a commercial scale inhibitor to the recycle system was started.
This has been successful as evidenced by later examination of the internals
of the piping system during periodic shutdowns of equipment. The inhibitor
itself caused a secondary problem, that of corrosion in the bronze impellers of
the booster pumps. This was corrected by the addition of a copper corrosion"
inhibitor to the scale inhibitor product.
Figures 10 through 13 show one type of water nozzle.which is used in a
commercially available blast furnace scrubber. The manufacturer claims that
its non-clogging feature is chiefly attributable to proper dimensioning of
the large discharge opening. Figure 13 shows that the opening does not clog
after years of operation; however, it is clear that the size of the opening
is severely restricted. There is no information available on the quality of
water that was used in the system.
Table 5 provides information on the quality of water which was discharged
from one recirculation system which combines blast furnace and sinter plant
water. This was tested for simple and complex cyanides.* Another sample
downstream, after additional discharges, was tested for phenol, which in this
case could only have come from the blast furnace scrubber water stream 102.
*Simple = can be chlorinated.
58
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Figure 10. Swirl nozzle with replaceable insert
arranged centrally above the throat
of the scrubber.
Figure 11. Disintegration of the scrubbing
liquid above the throat without
any gas flow.
59
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Figure 12. Disintegration of the scrubbing
liquid with the droplets exposed
to the action of the gas flow.
figure 13. Swirl nozzles after years of operation,
External deposits did not clog up the
discharge opening.
60
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Of particular interest is the high level of pH, the result of the cyanide
treatment system and its relationship to the level of cyanide in the
water.
TABLE 5. QUANTITIES OF CYANIDE AND PHENOLS FROM BF AND SINTER PLANT—
JONES AND LAUGHLIN-ALIQUIPPA PLANT
1/1-1/31
2/1-2/29
3/1-3/31
4/1-4/30
5/1-5/31
6/1-6/30
7/1-7/31
8/1-8/31
9/1-9/30
Flow
mgd
19.6
19.6
19.6
19.6
19.6
19.6
19.6
19.6
19.6
TSS
Ib/day
.*.
3780
9399
*•*
18135
34736
(2283)
364
7519
326
3310
7028
5230
10420
15202
4577
9971
15038
2125
16019
34817
(6538)
13077
54433
1961
7220
11115
STREAM 102
Cyan Ido
(Not)
Ib/day
«•
48.5
97
«.— *
22
40
(7.4)
56
199
(9.6)
1.5
9.5
(20,1)
( 2.5)
8.97
9.31
19.45
27.3
33
277
914
60.8
745
1677
19.1
28.2
37.3
Cyanide
Removable
Ib/day
...
5.25
28
...
2.5'
20
(30)
30
167
0
0.049
17.3
(20.1)
( 3.7)
5.8
3.4
8.2
16.2
15.5
226
846
5.39
158
310
4.25
6.21
8.33
PH
9.4
...
10.3
•BWV
9.8
10.2
9.0
9.2
9.5
8.9
...
9.5
9.1
9.5
9.1
...
9.6
6.8
...
9.8
8.2
...
9.6
8.9
9.8
OUTFALL 002
Flow
mgd
102
102
102
65
65
65.5
66
66
66
Oil
Ib/day
*_«
0
...
...
0
0
(1000)
( 425
( 0 )
( 580)
803
2713
(1632)
( 75)
1090
542
547
1626
50
550
550
(2202)
(1238)
1514
(1376)
( 457)
0
pH
7.9
10.5
9.0
• •»•
9.6
8.8
9.0
9.2
8.8
.„_
8.3
8.7
9.1
9.0
...
9.2
7.3
9.1
...
8.2
...
9.1
8.2
9.1
TSS
Ib/day
• ••
58304
89321
mmm
264400
376668
39131
53167
66695
(9873)
20103
44948
13850
27844
40189
15962
38310
53943
27522
57976
104537
1651
31926
97427
4403
23394
34953
Nl<3
Ib/day.
• ••
170
1106
• »
2180
3318
4683
5452
6924
1547
2811
4455
515
2101
3207
(5812)
661
3249
2293
4350
5994
974
2664
4387
478
1756
2411
Phenol
Ib/day
*««•
49.5
1U2
• ••
236
510
(72)
187
435
124
182
281
0
155
345
195
316
423
261
1355
3606
166
1592
5105
26.9
269
489
NOTES: (1) The Company monitors the blast furnace and sinter plant waste
treatment facility water for cyanides after the alakaline chlorina-
tion treatment unit (stream 102). The phenol in this water is
measured after dilution (002). Quantities found using grab samples
(one each seven days) are shown above. Three values are shown per
month (min., avg., max.).
(2) By permit, the allowable total cyanide from stream 102 is 261
Ibs/day average and 761 Ibs/day maximum.
61
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The above Table was made available from the Pennsylvania Department of
Environmental Resources files. Table 6, available from these files, gives
upsets in five other steel plants. Those upsets relate to excursions in pH,
suspended solids, and phenol. It is of interest that certain types of
contaminants are more of a problem to one plant than to another. In other words,
problems of upsets in the blast furnace scrubber water system appear to be under
control in one plant and susceptible to AOC in another plant. This fact
emphasizes the relationship between AOC in the water system and specific design,
construction, and operating conditions.
TABLE 6. REPORTS FROM NPDES FILES -- UPSETS IN SCRUBBER WATER SYSTEM
Date
Abnormal Operation
Duration
Plant
I. UPSETS IN PH CONTROL
2/6/75
2/7/75
2/27/75
8/12/75
8/19-24/75
3/15-15/76
pH < 6.0 during acid cleaning of blast
Furnace A, B, C, and D. The acid was
sent to a sump that was believed to
drain to a system where neutralization
was available. It drained direct to the
outfall, however. A new piping arrange-
ment will be made.
pH < 6.0 due to acid cleaning of the Blast
Furnace C scrubber. The scrubber sump had
a continuous overflow to the sewer; acid
overflowed because personnel were unaware.
Plant to institute a "field survey" before
all acid cleaning operations.
pH > 9.0 due to excessive addition of
KOH to the No. 1 Blast Furnace thickener.
The sample line for the pH control became
plugged so an improper low pH signal con-
tinued requesting more KOH.
pH > 9.0 High cyanide output from the
blast furnaces necessitated pH increases
to prevent cyanogen chloride discharges
from the cyanide destruct station.
pH > 9.0 due to failure in the pH probe.
Excess KOH entered the system; the
probe has been replaced.
1.5 hrs
A
Intermittent
over 75 min
1.5 hrs
Intermittent
10 mins
62
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TABLE 6.
(cont'd)
Date
3/20/76
pH <
Abnormal Operation
6.0. During acid cleaning of
Duration
10 mins
Plant
A
6/7/76
3/12/76
7/76
the A-3 Blast Furnace precipitator
appraently some acid entered the sewer.
Spent acid is usually pumped to the
No. 1 Blast Furance thickener where it
can be neutralized by the alkali-chlori-
nation unit.
pH > 9.0 due to a faulty signal from
the pH controller of the alkaline
chlorination unit for No. 1 Blast Fur-
nace thickener.
Exceeded allowable cyanide discharge by
279 Ibs. The outfall is from the blast
furnace, however, no further determina-
tion of cause was possible.
pH of cooling water for blast furnace
wind turboblowers outfall down to 5.9.
II. EXCESS SUSPENDED SOLIDS TO OUTFALL
5/26/76
12/29/75
1/2/76
1/13/76
Total suspended solids limit was
exceeded. The No. 5 Blast Furnace
thickener slurry line was out of service
so solids were being removed by truck.
Truck breakdown resulted in reduced re-
moval rate causing more solids in the
thickener overflow.
Total suspended solids exceeded the limit
by 125 kg/day due to valve repair (blast
furnace and sinter plant).
Total suspended solids limit was exceeded
by 16 kg/day due to downtime for valve
repair (blast furnace and sinter plant).
Total suspended solids limit was exceeded
by 77 kg/day due to frozen pipes (blast
furnace and sinter plant).
30 mins
Exceeded daily B
limit
Unknown-condi-
tion present
for one of 3
July samples
Exceeded A
daily limit
Exceeded C
daily
limit
Exceeded C
daily limit
Exceeded C
daily limit
63
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TABLE 6. (cont'd)
Date
Abnormal Operation
Duration
Plant
3/10/76
7/27/76
7/15/75
11/13/75
12/19/75
12/31/75
Total suspended solids limit was
exceeded by 112 kg/day due to excess
blowdown (blast furnace and sinter
plant).
Total suspended solids limit exceeded
due to line blockage causing overflow
from the settling basin (blast furnace
and sinter plant).
Total suspended solids exceeded the limit
by 1287 kg/day due to clarifier shut
down for cleaning and high river TSS
background (blast furnace and sinter
plant).
Suspended solids maximum concentration
exceeded by 10 mg/x, due to excess over-
flow from the recirculation system
(blast furnace and sinter plant).
Total suspended solids exceeded the limit
by 149 kg/day due to an electrical mal-
function (blast furnace and sinter
plant).
Same as above, but by 198 kg/day.
III. EXCESS PHENOL TO OUTFALL
8/18/75
4/19/76
Phenol 8% high in one outfall. Probably
due to discharge from gas drip legs in
the vicinity of the outfall. These
will be incorporated in gas washer
water recirculation system.
Phenol high due to gas drip legs in
Blast Furnace non-contact cooling water
and process water.
Exceeded
daily limit
Exceeded
daily limit
Exceeded
daily limit
Unknown
Exceeded
daily limit
Exceeded
daily limit
Unknown-
found in one
sample
64
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In order to prevent AOC associated with water quality problems in a blast
furnace recirculation system the following measures should be taken:
1. Provide for the control of the scaling index in the system.
This may require the addition of acid and scale inhibitor
compounds. It is necessary to have a scheduled program
for analyzing the quality of water in order to assure
that scaling conditions are avoided.
2. At points in the system that are particularly susceptible
to scaling, it is desirable to provide a bypass section
which will permit inspection for observation of actual
scaling conditions without the necessity of having to
interfere with the operation of the recirculated water
system.
3. Scrubber spray nozzles should be as large as possible
to minimize the effect of any scaling which does occur.
4. The blowdown from the recirculated system should be
carefully monitored in order to assure minimum quantity
of blowdown consistent with permissible levels of dissolved
solids.
5. Components of the system should be selected with attention
to the potential for scaling conditions. In particular,
the cooling tower should have open internals without baffles
to avoid premature failure from the accumulation of scale
deposits.
If all of the above are observed AOC resulting from problems with water
quality will be minimized.
A typical recirculating water system may have 20 to 30 pumps or more and
in addition, perhaps four times as many valves. Because of the heavy abrasive
particulate matter in the water, life expectancy of a pump unit handling the
slurry is usually about one to two years, although reports of four to six
months are not uncommon. The combination of a large quantity of pumps with a
relatively short life results in the necessity of almost constant attention and
maintenance of these units to keep the system operative. It also mandates that
all pumps have standby units in order to avoid AOC.
65
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There are two areas in the pumps which give particular problems. One is
wear in the pump impeller. This may be minimized by the use of hard abrasion
resistant materials or rubber linings and by the selection of as low impeller
speed as is feasible in consideration of pumping requirements. The other
area of high maintenance is the pump seal. The usual method of overcoming
this problem is to use clean pressurized service water on the seals of
horizontal pumps or to avoid seals entirely by the use of vertical pumps. In
the latter case, it is desirable to have the shaft of cantilevered design so
as to avoid any bearings in the water.
One of the special problems in the handling of slurry is that its high
density leads to rapid settling in the sumps and in pipelines. It is impor-
tant when designing the system that any sections of piping or sumps which may
become isolated and, therefore dead, or that any pocket in which the circu-
lation rate becomes substantially reduced must be eliminated or held to the
minimi urn possible.
In most recirculated systems for blast furnace scrubber water, the
system is retrofitted to existing furnaces. If space is limited, the sumps
for collecting water from the coolers and scrubbers may be too small for
smooth pump operation. Because they are small, they are unable to even out
the variations in flow from the system. They are also unable to provide a
reasonable surge capacity without a large variation in head to the suction of
the pump. Any small upset in the system may cause an overflow from the pump
to the plant sewers.
Also, if space is congested at the blast furnace, the pump house for the
slurry pumps is apt to be too small for the condition of the pumps. Bearing
in mind that the pumps must be serviced on a regular basis and repaired at
frequent intervals, it is of great importance that there is adequate space
around the pumps for servicing them, good handling facilities for removing
and replacing pumps and lay down area for working on the pumps that have been
removed. Adequate floor drains should be provided to avoid any messes and
pools of water that may otherwise occur from leaking seals and the like.
Entrance and egress from the building should be convenient so as to facilitate
the movements of the operating and maintenance personnel. Finally, ventilation
should be adequate so as to avoid the potential accumulation of toxic carbon
monoxide gas.
66
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The single most important item in avoiding AOC as a result of pump
failures is to provide an adequate amount of redundant pump capacity. This,
coupled with a good preventive maintenance program and prompt repairs of worn
out pumps can substantially avoid AOC due to pump failures. In one plant,
where pump problems are rather substantial, there is a diversion sump between
the sewer which receives the overflow from the slurry pumps and the receiving
body of water. As the level in this sump raises, it returns contaminated
water via a second sump back to the slurry system. This diversion sump has
an emergency weir which overflows to the sewer. A level recorder on this
diversion sump has indicated that overflows have occurred about once a week.
A clarifier for blast furnace service should have a specially high
capacity rake drive and provision for automatic lifting of the rake mechanism.
Both features are required because of the high density of the sludge. They
are aggravated if very coarse particulate matter (-1/4 inch + 100 mesh) is
permitted to enter the clarifier. Because this material also tends to plug
the piping from the clarifier to the sludge pumps, all pipelines should be
equipped with cleanout plugs and blowout connections in order to facilitate
14
the removal of stoppages. One plant which had experienced difficulties
with stalling of the rake drive and plugging of the underflow piping has
evolved a procedure which tends to overcome the problem. The blast furnace
clarifier in that plant is equipped with two underflow lines and two pumps,
one on-stream and one on standby. The pump on standby is given prompt corrective
and preventative maintenance so that it is always ready for immediate use.
If there is evidence of plugging, both underflow pumps are immediately put
on-stream. This tends to clear the blockage. In addition, this plant has
found it desirable to provide a second clarifier as backup for the first
which may then be shut down for repairs or cleaning without interfering with
the operation of the recirculated water system.
One blast furnace plant27 has provided a coarse wire mesh screen over
the entire clarifier in order to avoid the entrance of large lumps of foreign
matter. There have been occassions where nut coke from the blast furnace has
entered the recirculated water system and eventually plugged some of the
67
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cooling tower sprays. In one plant, rake failures on one clarifier have
been found to occur up to 2 times per year, mostly as a result of heavy grit
material coming over from the blast furnaces. This plant has two clarifiers,
both on continuous operation. When a clarifier fails, all of the dirty water
is diverted to the one still operating. The quality of water leaving the one
still in operation decreases, but increased addition of polymer is used to
improve the rate of sludge settling. Sometimes solids carry over into the
hot well and settle, necessitating the cleaning of the hot well. In this
plant there are two hot wells, permitting one to be down for cleaning.
Occasionally, solids carry over to the cold well of the cooling tower making
it necessary to clean that sump as well.
As discussed previously under process upsets, conditions may occur in
the injection of oil in the blast furnace which result in the formation of
carbon black. The carbon black enters the water systems, finds it way to the
clarifier where it floats on the surface and becomes a mass which interferes
with proper operation of the clarifier and which may be blown into the at
mosphere. A wetting agent may be used to entrain the carbon black with the
water, however, the best procedure is to avoid the formation of the carbon
black.
Filters for dewatering the blast furnace sludge are usually quite reliable,
30
although one plant which initiated operation with only one filter found it
necessary to install a second one subsequent to commissioning the plant.
Originally, when one filter was down for maintenance the sludge was pumped to
a pond in the ore yard. This pond has two to three days holding capacity.
Further filling causes an overflow to the pellet storage area which, after
drying takes place, becomes a source of fugitive emissions. The second
filter helps to overcome the necessity of having to pump to the pond because
it provides redundant capacity. Another plant found it highly desirable to
provide variable capacity sludge pumps in order to insure uniform sludge
loadings to the filters with varying densities of underflow from the clarifier.
The installation of a barometric leg between the vacuum pump inlet and the
filtrate-air separation tank increased the reliability of that unit. This
68
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item prevents the entrance of abrasive slurry into the pump in case the
filtrate-air tank water level gets too high. It is also desirable that all
overflows from the vacuum be run through open drains as opposed to enclosed
pipelines. This facilitates the removal of any blockages which may occur.
As indicated under the heading Water Quality, above, it is necessary to
blowdown a portion of the recirculated water in order to avoid the buildup of
dissolved solids. Common practice is to discharge a portion of the clarified
water to a receiving stream. One plant14 has permission to discharge it to
the sanitary sewer system of the municipality. Another plant17 uses this
water to cool the slag in the slag pits of the blast furnace where it is
evaporated. This last practice increases emissions of dissolved organics
to the atmosphere.
General Operation
One of the problems in retrofitting a recirculating water system to an
existing blast furnace is to prevent hydraulic imbalance. Imbalance may be
the result of unaccounted-for discharges into the system, leakage into various
underground sewers and sumps that are too small. Diligence must be applied
to isolate and remove from the system the unwanted in-flows. Good communica-
tion between the operators of the blast furnace and the pump tenders
associated with the water system should be established in order that changes
in water flow at the furnaces can be made without upsetting the water balance
in the circulation loop. In one plant, the recirculation system incorporated
sealed dump tanks at each blast furnace. When individual furnaces are
periodically shut down, the furnaces are isolated from the clean gas main by
filling the gas cooler with water until a seal is formed between the clean
gas main and the furnace. When the furnace goes back on-line, this water has
to be dumped to permit the flow of gas through the gas cleaning system. The
dump tank is designed to prevent a rapid surge of 15,000 gallons, the volume
of the water seal, through the water system which might cause an imbalance in
the pumping system. A seal dump tank works as a holding tank into which the
water seal can be dumped quickly and then metered back at a much smaller flow
rate.
69
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In one plant, monitoring instruments in the recycle water system that
alerts operators to impending upsets include the following:
HIGH PRESSURE ALARMS
1. Slowdown discharge
2. Hot well discharge
LOW PRESSURE ALARMS
1. Slowdown discharge
2. Hot well pumps
3. Cold well pumps
4. Seal water
5. Instrument air
- Hot well high level
- Hot well low level
- Cold well pumps on hot well level control
- Cold well discharge low temperature
- Cold well discharge high temperature
- fans high vibration (cooling towers)
6. Recorders are maintained on the following
operations:
- Cold well discharge rate
- Slowdown discharge
- Cold well discharge temperature
- pH of diversion chamber
- Hot well discharge pH
- Monitor rake torque
In the above mentioned plant, staffing to operate the recycle system
includes one operator, one pump man, and one filter man assigned on three
shifts per day. Maintenance requires two to four millwrights on the day
shift plus two electricians as required.
Figure 14 shows a simplified diagram of the recirculated water system at
Inland Steel Company. There are several features in this system that con-
tribute to good operaton as follows:
70
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BLAST FURNACES-31 to #6
o
1 T-
Gas Coolers
* * * \ J 4 |
Gas Scrubbers
r I T" --
/Clari
f
lierj
17cnn „,, • Cooling,
12SOO GPM J
10900 G?
Gas Scrubber
Basin
(Dig out
ones per year)
Make up
865 GPM
Gas Cooler
Basin
slow down to ~~
Terminal Treatment
Basin 700/800 GP
Figure 14. Inland Steel blast furnace water system.
71
-------
1. The gas cooler and scrubber systems are separate loops,
with the makeup water being supplied to the cooler loop
which in turn blows down to the scrubber loop. This has
the advantage of reducing the hydraulic load to the
clarifier and in consequence its size. It also assures
a cleaner supply of water to the gas coolers.
2. The blowdown from the system is discharged to a terminal
treatment basin. Thus any upset in the recirculation
system which might result in AOC is prevented by further
treatment of the effluent.
Figure 15 shows the gas cleaning system for No. 13 Blast Furnace at the
Gary Works of U.S. Steel. Some noteworthy features here are as follows:
1. A pug mill at the dust catcher is used to condition the dust
with water so as to avoid emissions from the handling of
the dry dust.
2. A high differential pressure for the gas scrubber provides high
efficiency of gas cleaning.
3. The classifier which preceeds the thickener protects that
unit from coarse particulate matter and reduces the potential
for jamming and plugging.
72
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[SCRUBBER AP: 150-180 INCHES WATER]
GAS
FROM—i
FURNACE
-vl
co
BLAST FURNACE
GAS TO STOVES, ETC.
SLOWDOWN TO SLAG PIT
260 GPM INTERMITTENT
SOLIDS t DISC FILTER (2)
SINTER PLANT
Figure 15. Gas cleaning system for No. 13 Blast Furnace - U, S, Steel, Qary Works,
-------
5.0 GRAY AREAS
There are three locations in the blast furnace operation where emissions
to the atmosphere take place and do so in variable quantities due to certain
factors. These are the emissions from cooling the slag, the emissions from
V1
bell leakage and emissions from casting the furnace. Emissions from handling
the slag may vary due to the method of cooling the slag and the amount of
water used, if any. The emissions which result from the cooling operation
may be considered to be normal with respect to the type of operation in-
volved. There is also no control equipment applied in current technology.
For both of these reasons, any variations in emissions from the cooling of
slag is not considered AOC.
The other two locations in which variable emissions occur require more
extended explanations as is given below.
Emi s s i on s from Be11s
18
An estimate in a Battelle document, of leakage from the bells of blast
furnaces in the United States is given by the expressions:
Gas leakage * 500 + 1500 N cfm = 14.2 + 42.5 N scm
where N equals the number of years in service.
The same document uses the production data of 1973 where N = 6.9 years
to calculate a total leakage of blast furnace gas in the amount of 23.6 x
109 scm (833 x 109 cubic feet) for 1973.
The gas that leaves the furnace contains the following gaseous components:
Typical Range
Carbon Dioxide, C02 = 11.5% 8-15%
Carbon Monoxide, CO = 27.5 23-33
Nitrogen, NZ = 60.0 50-60
Hydrogen, H2 = 1.0 1.0-3.5
TOTAL 100.0
74
-------
The actual amount of each component will vary with the individual blast
furnace and its mode of operation. For example, the amount of hydrogen will
be increased by such factors as high humidity of the hot blast and high rates
of fuel injection in the tuyeres.
Blast Furnace Top Emissions From Bells
Blast furnace gas as it leaves the burden and enters the uptakes has an
average volume of 1800 scm/Mg (63,500 scf/ton) and contains an average of 84
Ibs/ton (42 kg/Mg) particulate matter20 This dust loading equates to 21.2
g/scm (9.26 grains per SCF). A typical analysis of the flue dust particles
is as follows:
TABLE 7. ANALYSIS OF FLUE DUST PARTICLES*
El ement
Iron
Carbon
Silica
Lime
Magnesia
Sulfur
Manganese
Phosphorus
Carbon (as coke fines)
Symbol
Fe
C
Si02
CaO
MgO
S
Mn
P
G
Percent
48.95
12.08
12.08
4.31
1.28
0.59
0.38
0.045
various
*Particles are expected to show considerable variation in
composition.
The typical particle size for blast furnace dust is as follows:
14
75
-------
TABLE 8. PARTICLE SIZE OF BLAST FURNACE DUST
Particle Size + 635
635 -
423 -
317 -
254 -
169 -
127 -
102 -
94 -
<
423
317
254
169
127
102
94
78
78
microns
microns
microns
microns
microns
microns
microns
microns
microns
microns
11 % by wt.
13
8
7
7
6
3
5
2
38
100 %
A new bell on a blast furnace is normally machined so that it fits to its
seat within 50 microns (0.002"). Referring to Figure 16 which is a plot of
the data in Table 8, about 28 percent of the particles in raw blast furnace gas
is less than 50 microns and can pass through the seat of the bells when the
seat is in new condition. This means that there is a potential of emitting
approximately 28 percent of the particulates in the raw gas annually through
the bells.
There are several factors which must be considered in assessing the above
data:
1. Apparently the Battelle formula was based on the graph
which was derived from Japanese blast furnaces operating
in the range of 69 to 148 KPa (10 to 21.5 psig). Since
most blast furnaces in the United States operate in the
range of 31 to 34 KPa (4 1/2 to 5 psig), the correction
factor for the formula and for the corresponding gas
and dust quantities should be
= 0 55 - -t/Av9- Pressure US
" if Avg. pressure Japan
2. The gas leakage was based on a service life of N = 6.9 years
In the U. S., most companies change bells every 5 years and
the average life is N = 2.5 years. The correction factor
- - --, li.-
for bell life is:
2.5
= 0.36
6.9
76
-------
BLAST FURNACK DUST
x -*
4 6 100 2
Particle Slze-Mlcrona,
1000
Figure 16. Plot of the data presented in Table 8,
-------
3. The amount of particulates which leaks from the bells may
be reduced by virtue of the filtering action that takes
place when burden material is on the bells.
4. The amount of particulates (and gas) which leaks from
the bells may be increased substantially through seats
that are worn out and cut by the dust-laden gas.
5. It is assumed that the calculations on gas leakage
relates to a furnace equipped with two bells. Some
new ones have three bells and use nitrogen for
pressurizing. Some use an arrangment which replaces
at least one of the bells with a valve having a soft
seat.
The correction estimate for leakage of blast furnace gas from the bells
is:
(23.6 x 109) x 0.55 x 0.36 = 4.65 x 109 m3 (165 x 1011 ft3) annually
of which
Carbon monoxide is about 27.5 percent or 1,498,000 Mg
(1,650,000 tons)
Hydrogen is about 1 percent or 3,630 Mg (4,000 tons)
Using a gross loading of 21.2 g/scm (9.26 gr/scf) for the raw gas and 28
percent of that amount in the gas leaked, the estimate mass of particulates
is:
g
'28 X 7m x 1610 = 30»000 tons
giving an emission factor of 0.3 g/kg (0.60 Ibs/ton) of iron.
The above estimates are based on data, some of which has not been verified.
Members of the American Iron and Steel Institute task force assisting with this
study and review of the documents produced believe that the above estimates
significantly overstate the case of bell leak emissions. Although they
cannot be accepted as accurate, they indicate that the problem may have
national significance to air quality and may be of particular significance in
certain non -attainment localities. The available data are so few that this
is an area in which further research is a necessity. On any particular blast
furnace, as service life on a particular bell increases, the emissions past
its seal become greater. The question is whether the increase in emissions
78
-------
are "normal" or AOC. The former appears to fit better and thus the problem
is listed as a "gray" area.
Emissions From Casting
At the present time, there are only a few blast furnaces in the United
States which are equipped with environmental control systems to capture the
emissions which result from casting the blast furnace. In such systems as
are installed to date, one of the key elements of control is a building
evacuation system for the cast house itself. For those cast houses where no
control is installed, there are numerous variations in process and operating
conditions which may increase emissions to the atmosphere. These are described
below. For cast houses that are equipped with environmental controls, the
variations in emissions from the process do not have a significant effect on
the atmosphere, but only on the amount of capture in the final control
equipment.
Generally speaking, smooth furnace operation leads to minimal casting
emissions. The blast furnace operator finds it to has advantage in terms of
economic production of iron to aim for as smooth a performance as is possible
consistent with the technical capability of the furnace, its raw materials,
etc. He thus has an incentive to operate in such a manner and to minimize
emissions to the atmosphere from upsets. If the current trend of providing
control for blast furnace cast houses continues, such upsets as do occur will
not produce significant AOC. For these reasons, upsets which cause excess
emissions are not classified under AOC in this report, but are described
below under "gray" areas.
Tap Hole Related
Emissions from casting are particularly heavy at the tap hole of the
furnace. In recent years, the trend toward larger furnaces and higher top
pressure has increased the problems with the tap hole and the potential of
emissions. In the past, a carbonaceous clay tap hole mix with approximatly
16 percent moisture content was used. This wetness caused a cloud of iron
oxide fumes to be released whenever the tap hole was opened. Such a tap
hole eroded quite rapidly and by the end of the cast, it was usually necessary
to pull wind in order to control iron flow. Recent work has been directed
79
-------
toward altering the mixes by using chemical binders and adding calcines. The
resulting mixes are stronger but more difficult to push. To accommodate the
stiffer mix, the mud gun may have to be modified to increase nozzle pressure.
At the same time, it is necessary to insure that the tap hole drill has
adequate capacity to penetrate the new mixes.
Conventional tap hole mixes are particularly deficient when using higher
blast pressures. In the Gary No. 13 Blast Furnace, it was found that when
the blast pressure was increased to between 275 to 345 KPa (40-50 psi) the
tap hole glaze could not withstand erosion during the cast. It was not
uncommon to have the tap hole erode until it was larger than the mud gun
nozzle, 15.5 cm (6"). With their current practice of using anhydrous mixes,
the erosion problem has been overcome. This is important in regard to
emissions because erosion of tap holes increases the flow of iron and slag
thereby causing increased emissions even though the time period has been
shortened. Not only is there improvement in this area, but there is a signi-
ficant decrease in the number of coke messes which are caused by coke being
thrown out of the eroded tap hole.
Casting Emissions
A slow cast, because emissions persist over a longer period of time, can
result in an increased mass of emissions per cast. This is especially true
when the slag is too limey, or there is a restriction of the tap hole. It is
avoided by keeping a reasonable length of tap hole and maintaining proper
slag chemistry. It is reported that slow casts may occur five times a week
on a particular furnace and may last for one to one and a half hours.
Hot limey slags increase the amount of white fume coming from the slag.
These are especially prevalant after the blow-in of the furnace as is discussed
earlier in the manual. After that, it may occur as frequently as once per
day or as long as once in several months. Emissions from limey slag may last
45 minutes per cast. They are avoided by keeping the furnace slag as lean as
is possible yet still meet sulfur specifications, the higher the sulfur
allowed the leaner the permissible slag. Lean slags also are conducive to
smoother furnace operation, lower coke rates, and higher productivity. One
80
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way of permitting a blast furnace to operate with higher sulfur in the iron
is to provide an external desulfurizing facility for the iron.
When the molten iron is low in silica and high in sulfur, it tends to
tap colder than normal and results in increased emissions of reddish fumes
and kish. This may occur twice a week. If the final blow of one cast is
"cold", the ensuing cast could also be cold.
Burning of Skull
If a skull develops inside the tap hole of the furnace, it may be
necessary to lance it with oxygen. This can cause an emission of reddish
fume for a period of five to 10 minutes. The necessity for lancing with
oxygen is more likely to exist in the case of a rotary tap hole drill than in
the case of a percussion type tap hole drill. The latter type drill is
usually more able to penetrate the skull than the former.
5.1 METHODS FOR MINIMIZING AOC
5.1.1 Process Related
In the preceding sections of the manual, various methods of minimizing
process related AOC were described. A summary is given below:
1. Provide a properly screened and sized burden.
2. Provide high stability coke, at least 50, although 55 is
better. This tends to avoid coke messes.
3. Provide adequate furnace instrumentation and control.
4. Use anhydrous tap hole mixes to avoid fast casts and
reduce coke messes.
5. Direct attention to improved construction of the furnace
top such as hard facing of bell seats, provision of bell
sealing rings, nitrogen equalization, etc.
6. Provide computer control of furnace operations, if tech-
nically and economically feasible for the furnace involved.
7. Provide control of moisture in the hot blast. This will
move the furnace better.
8. Provide control for the distribution of fuels which are
injected into the tuyeres. This helps to move the furnace,
avoids formation of carbon black and increases the
efficiency of energy utilization.
81
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9. Provide external desulfurization of iron. This results
in smoother furnace operation and uses less stone and
coke as well as produces more tons of iron.
10. Increase the emphasis on preventative maintenance.
5.1.2 Control Equipment Related
1. Provide all pumps with standby units.
2. Provide adequate space and means for servicing pumps.
3. Provide adequate surge capacity in sumps and retention time
in recycle systems in order to avoid pumping problems
and hydraulic imbalances.
4. Control pH in recycled water to avoid scaling.
5. Install instrumentation for monitoring and alarm.
6. Use scrubbers which have large nozzles which minimize
plugging problems.
7. Use scrubbers which have variable throats to maintain
desired pressure drop. Flooded scrubber walls are
desirable to minimize wear.
8. Provide a discharge tank for gas seal water in order
to permit rapid dumping of the gas seal so as to
avoid system imbalances.
9. Cover clarifier with wire mesh to avoid entrance of
foreign objects.
10. Provide a barometric leg between the filter and the vacuum pump.
11. Collect and monitor discharge water. Routing it to a final
treatment basin provides an increased measure of safety in
avoiding AOC.
12. Maintain good communications between furnace operators and
pump tenders.
5.2 GENERAL
One of the most effective ways of measuring AOC whether process or control
equipment related, is for the responsible environmental control agency to
persue an active and diligent program of monitoring AOC. Monitoring reports
from such agencies are a most valuable record from which to develop normal
operating patterns for the industry. Frequency and duration of specifically
defined AOC's is not at this time clearly defined nor well-known in many cases.
82
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It is recommended, therefore, that the recording of AOC's be continued by
agencies already doing so, and be initiated by those agencies not doing so.
Figure 17 shows an example of a suitable reporting form. This example was
developed by drawing upon the best features of several reproting forms
currently in use.
As stated previously, the factors that avoid emissions from abnormal
process conditions also provide an incentive to the operator in terms of
increased production and reduced costs of operation. All blast furnace
operators would certainly prefer to have the most modern and most well
maintained equipment possible as well as the best burden available so that he
may be assured of smooth operation. Unfortunately, factors of plant age,
existing plant limitations, availability of raw materials, economic factors,
etc., prevent the realization of this ideal. In consequence, operations are
often less smooth than desired and abnormal conditions result which cause
excess emissions.
It is to be expected that abnormal emissions due to process upset will
decrease with time. There are several pressures which will accelerate progress
toward the goal of avoiding upsets. One is the development of new knowledge
and techniques in the control of the blast furnace process. Another is the
economic advantage of implementing such advnaces wherever implementation is
feasible. Finally, there is the pressure imposed to meet environmental
regulations.
83
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POLLUTION CONTROL AGENCY:
ADDRESS:
NOTICE OF MALFUNCTION, STARTUP OR SHUT DOWN
Company, Department:
Date of Report: Time:
»••
Name and Identification of Unit Involved:
Telephone No;
Time Incident Occurred:
Starting time of scheduled corrections:
Cause and Description of Breakdown, Detailed:
Corrective action taken/proposed:
Estimated excess pollutant discharge:
Pollutant Excess Ib/hr
Process Production rate t/hr
If Telephone call:
Person taking call:
Inspector:
Supervisor:
Date Entered in Record:
Figure 17. Example AOC report form.
84
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6.0 TABULATED SUMMARY OF AOC
Table 9 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.).
85
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TABLE 9. BLAST FURNACE ABNORMAL OPERATING CONDITIONS
Abnormal
Operating
Condition
Cause
Effect on
Process
Corrective
Action
Frequency
PROCESS RELATED — STARTUP
Initial slag Is
limey
Dirty gas
bleeders
Blowing out
through tap
hole
Extended start-
up
Excess slips
Needed to coat heart!
& bosh walls to
avoid breakouts
To vent furnaces at
startup
Open tap hole
Electrical & mechani-
cal failures
Hotter than usual
furnace
Reduces openings In
brickwork
Heats furnace hearth
Run w/less basic
slags after 4 days
Close bleeder & put
gas Into mains when
gas conditions war-
rant
Close tap hole when
Iron appears at
hole
Check out equipment
before blowing— keep
mtn. crews available
Use properly screen-
ed burden — don't
overblow. Low blast
temperature
Once In 3-4 yrs/fur-
nace
Once In 3-4 yrs/
furnace
Once In 3-4 yrs/
furnace
I/day during startup
0-2/day during
startup
Duration
2-4 days, Bleeders
open 12-24 hours
12-24 hrs. normally.
Documented up to 336
hrs.
12-48 hrs.
1-4 hrs.
15 sees.
Environmental
Effects
Comments ,
Reference
Heavy white smoke
from limey slag —
generally small casts
)1rty gas discharge
to atmosphere
Sas Ignited, dust
Into cast house
Extended emissions
to atmosphere
Gas & participates to
the atmosphere
Some plants
Dpen large
bell as well,
31
.ess emission
*1th Buffee
Pipe, 2|
PROCESS RELATED — SHUT DOWN
Blow tap hole
hard after last
cast
Blow dust
catcher hard
Bleeder valve
open
Planned
Planned
Planned
Power failure
Removes as much Iror
& slag as possible
from furnace
Completely empty
dust catcher
Releases gas from
furnace after ore
blank or burden
quench
Plug hole after all
liquid removed
Steam & water sprays
to suppress dust
Plug tuyeres & seal
bosh
Once 1n 3-4 yrs/
furnace
6-15 times, 30 sees.
each
Once In 3-4 yrs/
furnace
15-45 mlns.
3-7 1/2 mlns/shut
down
16-24 hrs., Power
failure, 3-4 hrs.
Dirty gas to cast
house
Dirty gas to
atmosphere
Dirty gas to atmos-
phere
Some pliants
use normal
dust catcher
routine!
Emissiqn
reduced
w/tlme,.
26
-------
TABLE 9. (cont'd)
Abnormal
Operating
Condition
Iron flush to
ground
Cause
Planned
Effect on
Process
To empty salamander
Corrective
Action
Frequency
Once 1n 3-4 yrs/
furnace. 6-8 yrs/lf
hearth goes more
than 20 campaigns
Duration
<
Environmental
Effects
Increased emissions
of participates
Comment
Reference
Practice
common to
all fur-
naces
00
PROCESS RELATED — ABNORMAL OPERATING CONDITIONS
Severe burden
slip
Backdraftlng
Water & power
failures
Breakouts
Charging dusty
material
Gases vented to
air ahead of
stove
Loss of igni-
tion on gas
bleeder
Japid movement of
urden
Planned—to make
furnace repairs,
esp. tuyeres
allure of utility
supply
Failure of lining
cooler, tuyere, etc.
Dry, dusty burden
Stove plugged
Plugged flue line,
low gas pressure
ileeder opens to re-
lieve excessive top
pressure
Gas flow to bustle
pipe reversed
Shut down, potential
of breakouts &
explosions
Immediate shut down
Increase participates
in gas
Loss of heat values
None
Reduce wind momen-
tarily to settle
burden (short-term).
Improve burden &
operating practice
(long-term)
Complete repairs
Provide emergency
source of utilities
& steam operated
auxiliaries
Repair Immediately
Improve burden pre-
paration of condi-
tioning sprays for
material
Clean stove
Restor Ignition
1 -50/month
4-50 times/month2
•
Infrequent, 1/6 or
more months
Once In 2 yrs.
Up to 600 charges/
day average
Vyr
Up to one/month
5-30 sees.
J hrs.-7 days for
large repair
Up to several days —
avg. 1-3 days
1-30 mins.
5-10 sees.
hr/day for 21 days
-4 hrs.
28 to 276 Ibs/slip
(solid material)
'articulate emissions
bo atmopshere.
tost emissions occur
1n first 15 mins. 8-
12 g/Mg Iron*
Increased emissions
Emission of gas t>
•articulates
Emissions of partlcu-
ates
ncreased emissions
Clean gas bled to
atmopshere
Based on
30 ft.
diameter
furnace ,
8
Delays
for re-
pairs
25-268
hrs/yr
Variable
emissions
No data
or est.
avail., 24
Amt. of
gas bled
varies
-------
TABLE 9. (cont'd)
Abnormal
Operating
Condition
Formation of
carbon black
Unplugging dust
catcher
Cause
Improper combustion
of oil In tuyeres
Buildup of solids
Effect on
Process
Inefficient use of
oil
Interferes with gas
cleaning
Corrective
Action
Reduce flow of oil
correct distribution
Poke out solids.
Possibly use small
explosive charge
Frequency
Variable
1-8 tlmes/yr.
Duration
Variable, Persistent
till corrected
1-8 hrs.
Environmental
Effects
Floating carbon
black In clarlfler
Emission of dirty gas
Comment
Reference
Dried
carbon
black may
be blown
to atrai,
29, 30
Can be
avoldetj
by regj
dumping &
prevent
conden^a-
tlon
00
CO
PROCESS RELATED — "GRAY AREAS"
Leaky top
CASTING .
EMISSIONS3
Slow cast
Cold metal
Hot, limey
slag
Wet tap hole,
trough, or
runner
Poor seal of small
or large bell, or
holes In bells
Small tap hole,
Hrney slag
Low silica, high
sulfur
Improper slag
chemistry
Improper drying
Loss of gas
Delays cast, lost
production
Incorrect Iron
cheml stry
High coke rate
Possible explosions
Repair or replace
bell. Change de-
sign of furnace top
Proper tap hole
openings & slag
chemistry
Better operating
practice
Lean out slag
Thorough drying
Constant 1f both
bells leak. 80
times/day If small,
600 times If large
1-5/week
1-2/week
2-7/week
Should be rare once
1n 3 months
Constant or 5-10
sees. /occurrence
10-60 mlns. excess
time on cast
15-45 mlns.
5-20 mlns.
Discharge of gas &
participates
Dust - 300 g/Mg
CO - 16.5 kg/Hg
H2 - 40 g/Mg
Increased emissions
proportional to
longer tap time
Increased emissions
of klsh
White fumes from
slag. Excess sul-
fur fumes
Emissions from Iron,
sand, slag
25
-------
TABLE 9. (cont'd)
Abnormal
Operating
Condition
Tap hole en-
larging during
cast
Cause
Erosion of tap hole
Effect on
Process
Iron flow Increases
Corrective
Action
Use of anhydrous
clay will retain
shape of hole better
than water based
clay
Frequency
4 times/day
Duration
20-45 mlns.
Environmental
Effects
Excessive blowing of
dirty gas at tap hole
Comment
Reference
Very long
holes
using an-
hydrous
clay may
extend
cast
causing
Increased
emissions
00
IO
Scrubber pro-
blems
Loss of water
pump
Clarlfler rake
failure
Plugged nozzles &
worn Internals
torn Impeller,
leaky seal, plugged
Inlet
Jammed rake
CONTROL EQUIPMENT RELATED ~ ABNORMAL OPERATING CONDITIONS
Bleeders opened to
allow large bell to
close
Loss of gas cleaning
efficiency
System Imbalance
Shut down of clarl-
fier
Institute repairs
Institute repairs
Provide standby unit
make repairs
Clean out clarlfler
Prevent entrance of
coarse participates
3-4 tlmes/yr
Infrequent In well
designed scrubber
1-6/month
0-2 tlmes/yr
0.2-48 hrs.
Continuous until
repaired
Variable. Depends
on availability of
standby unit
Variable, 1-3 days
Raw dirty gas from
bleeders 5-10 sees.
80 times/day 42 kg/
1g hot metal
-linimal If repairs
Instituted limed.
Increased solids In
blowdown & Increased
ilowdown
Increased sol Ids 1n
blowdown & Increased
>lowdown
Discharge
to ter-
minal
treatment
may avoid
AOC, 31
Discharge
to ter-
minal
treatment
may avoid
Env.
effects',
28, 30,
-------
TABLE 9. (cont'd)
Abnormal
Operating
Condition
WATER QUALITY
PROBLEMS
High or low
pH
High TSS dis-
charge
Cause
Failure of controls
Spills In cleaning
thickener, broken
lines, etc.
Effect on
Process
High pH causes
scaling. Low pH
None
Corrective
Action
Improve pH control
Avoid spills
Frequency
076 times/yr normal .
15 times/yr recorded
Duration
Variable. 1.5 hr 1s
typical
Environmental
Effects
Exceed discharge
limits
Comment
Reference
:requent
samp lino
nay anti-
cipate
iroblem»
32
8
1. Many furnaces on good burdens, especially newer ones with high t6p pressures, rarely have slips. Furnace prone to slipping may slip 5-50 tlmes/mon*.
2. Depends on age and condition of furnace.
3. Installation of control equipment for the cast house will essentially avoid abnormal emissions from casting.
4. Estimated.
-------
7.0 REFERENCES
1. Hasegawa, Akira, "Large Blast Furnace Facilities in Nippon Steel Cor-
poration," Ironmaking Proceedings, 36_, 137 (1977).
2. Legille, E. and K. H. Peters, "Operation of a Blast Furnace Incorporating
a Paul Wurth Bell-Less Top Charging System and its Application to
Large Blast Furnaces," Proceedings of the 32nd Ironmaking Conference.
32_, (1973). a
3. Jablin, R., "Expanding Blast Furnace Slag Without Air Pollution,"
Journal Air Pollution Control Association. 22(3), March 1972.
4. Steiner, B., "Air Pollution Control," International Metal Reviews.
September 1976.
5. White, Douglas, "Blast Furnace Water Recirculation System at Inland
Steel Co.," Ironmaking Proceedings. 36_, 44 (1977).
6. Parle, R. W., "Long-Term Shutdown and Subsequent Recovery of Blast
Furnace Plant," Journal of the Institute of Fuel. June 1972.
7. G. K. Jefferson, "Operating Experience of No. 13 Blast Furnace, Gary
Works, U. S. Steel Corporation," Ironmaking Proceedings, 36, 162
(1977).
8. Mobley, C.E., A. D. Hoffman, and H. W. Lownie, "Blast Furnace Slips
and Accompanying Emissions as an Air Pollution Source," EPA-600/2-76-
268.
9. Wagstaff, J. B., "A Report on Solid Movement on Blast Furnace Models,"
Proceedings Blast Furnace, Coke Oven and Raw Materials Committee.
AIME, 14, 1955.
10. Lambert, C., "Operation of Geneva Works Blast Furnaces with High Alkali-
Bearing Burdens," Ironmaking Proceedings. 35_, 324 (1976).
11. Nanne, S. E., "Operating Experiences on Algoma's #7 Blast Furnace,"
Ironmaking Proceedings, 35, 1976.
12. James, T. E., "Cooling Hazards in High Tonnage Hearths," Ironmaking
Proceedings, 35_, 241 (1976).
13. Ziegert, W. L., "Blast Furnace Control at Inland Steel's Nos. 5 and
6 Blast Furnaces," Ironmaking Proceedings, 36, 298 (1977).
14. Touzalin, R. E., "Pollution Control of Blast Furnace Gas Scrubbers
Through Recirculation," EPA/NTIS PB-250-435, July 1974.
15. Weinberg, W. H., "Blast Furnace Recycle Water System," Ironmaking
Proceedings, 36, 50 (1977).
9,1
-------
16. Bischoff Environmental Systems, "Gas Cleaning with Variable Annular-
Gap Scrubbers," Catalogue.
17. Farrow, T. A., "Gary Works No. 13 Blast Furnace Recycle Water Systems,"
Ironmaking Proceedings, 36, 40 (1977).
18. Battelle Columbus Laboratories, "Potential for Energy Conservation in
the Steel Industry," PB-244-097, pages V-67 and V-68.
19. Marks, L. S., Mechanical Engineer's Handbook, 5th Edition, p. 786.
20. McGannon, The Making. Shaping & Treating of Steel, 9th Edition, p. 457.
21. Greenawald, R. A. and E. L. Auslander, "Burns Harbor High Top Pressure
Operation - Its Problems and Rewards," Ironmaking Proceedings, 33,
167 (1974).
22. Qp. Cit., Reference 7.
23. Lindau, Lars and Lars Hansson, "Fugitive Dust from Steel Works," The
National Swedish Environment Protection Board, Bo Mansson, Stoft Tekniska
Laboratoriet AB, Sweden.
24. EPA, Effluent Guidelines.
25. Communication with Bruce Miller, EPA Region IV, Atlanta, Ga., February 2,
1977.
26. Trip Report, City of Cleveland Division of Air Pollution Control, January
25, 1977.
27. Trip Report, U.S. Steel, April 21-22, 1977.
28. Trip Report, Republic Steel, Gadsden, Alabama, July 6-7, 1977.
29. Trip Report, Inland Steel, East Chicago, Indiana, April 19-20, 1977.
30. Trip Report, Jones and Laugh!in Steel, Cleveland, Ohio, August 2-3, 1977.
31. Trip Report, Erie County Department of Environmental Quality, Buffalo,
N. Y., June 30, 1977.
32. Data supplied by EPA, Region III.
92
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TECHNICAL REPORT DATA
(f lease read Instructions on the reverse before completing)
EPA- 600/2 -78-118c
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Pollution Effects of Abnormal Oper-
ations in Iron and Steel Making - Volume D3. Blast
Furnace Ironmaking, Manual of Practice
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R.Jablin, D.W.Coy, B.H.Carpenter, and
D.W.VanOsdell
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORGANIZATION NAME AND ADDRESS ~~~~ '
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
1AB604
11. CONTRACT/GRANT NO.
68-02-2186
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
13. TYPE OF REPORT AND !
Final; 10/76-1/78
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES ffiRL-RTP project officer is Robert V. Hendriks, Mail Drop 62,
919/541-2733.
is. ABSTRACTTlie repOrt jg one ^ 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 excee-
ded during upsets in operation. Such periods of abnormal operation are becoming
recognized as contributing to excess air emissions and water discharges. In gen-
eral, an AOC includes process and control equipment startup and shutdown, substan-
tial variations in operating practice and process variables, and outages for mainten-
ance. The purpose of this volume, which covers the blast furnace ironmaking pro-
cess , is to alert those who deal with environmental problems on a day-to-day basis
to the potential problems caused by AOCs, to assist in determining the extent of the
problems in a specific plant, and to help evaluate efforts to reduce or eliminate the
problems. The report enumerates as many AOCs as possible, with emphasis on
those which have the most severe environmental impact. Descriptions include flow
diagrams, material balances, operating procedures, and conditions representing
typical process configurations.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
cos AT I Field/Group
Pollution Shutdowns
Iron and Steel Industry
Blast Furnaces
Abnormalities
Failure
Starting
Pollution Control
Stationary Sources
Abnormal Operations
13B
11F
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS {This Report)
Unclassified
101
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
93
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