Timothy W! Devitt
        Division of Process Central Engineering .
       Bureau of Engineering and Physical Sciences
               Public Health Service
     National Air Pollution Control Administration
                 Cincinnati, Ohio

                 December 1968


                           COKE OVENS
     The information presented in the body of this report is summarized be-
     low.   The processes used in the manufacture of iron and steel are sub-
     divided into the normal phases of operation, and the pollutants from each
     are identified.  Emission figures are cited to indicate order of magnitude
     and usually represent the range of values found in the  literature.  Be-
     cause of the significant effect of operating conditions on emissions, this
     range is usually large.  In general, the processes used to manufacture
     coke, pig iron, and steel have been segmented for purposes  of analysis.
     Summary information is given on coke ovens, blast furnaces, steelmaking
     furnaces, agglomerating and miscellaneous operations, their associated            |^_.
     pollution potential, and available pollution control equipment.                     '%•. .
Approximately 25% of the charge is emitted as volatile constituents, I^S,           t_
ammonia salts, phenols, cyanides, etc.; also, dusts are emitted during            v
charging and quenching.  The emission flow rate is approximately                  **'
15,000 scf/ton of coal charged, and the emission stream temperature              •«
is about 1200°F.  Control.  None.                                                I

Charging.  Approximately 0.1% of the charge is emitted as coal dust in             !
sporadic puffs.  The emission stream temperature is about 300°F.
Control.  Control equipment includes telescoping connections between
the charge  car and oven top and double collecting mains.

Coking.  In this closed system, the volatile constituents are usually re-
covered; however, approximately 0. 5 to 0. 8% of the emission stream is emitted
as hydrogen sulfide at the end of the process.  Dusts are emitted during
charging and quenching.  The emission flow rate is approximately
15,000 scf/ton of coal charged, and the emission stream temperature is
about 1200°F. The heating value of the emission stream is approximately
•*-•<-• »••„,

500 to 550 Btu/ft .  ControL  The byproduct plant recovers tars,  ammonia,
and ammonia salts.  The very few plants that have sulfur recovery proc-
esses reduce H0S to approximately 0.05% of the emission stream.

Quenching.  Approximately 6 Ibs of particulates is generated per quench,
"along with phenols.   The emission temperature is 300 to 800°F.  Baffled
towers remove approximately 85 to 90% of the solids.  Although no
attempt is made  to control phenols, they can be removed by extraction
from water in light  oils.

Storage. Coal dust and coke breeze are dispersed by the wind.  Control.
Systems have'been tried; no control practice has proved satisfactory.
                         BLAST FURNACES

Slips are sporadic emission puffs resulting from shifts of the furnace burden.
Control. Better preparation of the furnace burden reduces frequency.

Normal Operation
Approximately 7 to 10 grains of particulates is generated per scf of gas;
or 50 to 200 Ib/ton of product;  2200 to 3000 Ib of CO per ton of product
(i.e. , 25%  of exit gas is CO) is emitted.  The emission flow rate is about          ?
60,000 to 100,000 scf/ton of hot metal, and the emission stream temper-          !
ature is about 3000 to 4000°F.   The top heating value of the emission              j
stream is  80 to 100 Btu/ft^.  Control.  High-energy wet scrubbers (45             i__
to 60 in. w. g.) and electrostatic precipitators  can reduce particulate              f?;''
emissions to 0. 004 to 0.05 grain/scf. Most of the gas is collected for             $&_•>-
use as fuel throughout the plant.                                                p	•
                     OPEN HEARTH FURNACE

Charging and Melting
Approximately 0.05 to 0.25 grain of particulates is generated per scf of
gas.  The emission flow rate is approximately 20,000 to 60,000 scfm,
and the emission stream temperature  is about 1400 to 1800°F.   Com-
ponents  of the emission stream include CO2,  6 to 15%; N2, 72 to 75%;
SO2, 0.0to 0.15%; fluorine, 0 to 300 ppm.  Control.   Furnace checker
work eliminates some of the particulates; high-energy scrubbers , electro-
static precipitators, and fabric filters can reduce emission to 0. 05 grain/

Approximately 0. 5 to 2.0 grains of particulates is emitted per scf of gas
with no oxygen lancing and 1.0 to 6 grains/scf with oxygen lancing.
                        OXYGEN CONVERTER

Approximately 40 Ib of particulates is generated per ton of steel.  The
emission stream is 75 to 90% carbon monoxide.  The emission flow rate
is approximately 50,000 to 450,000 acfm, and the emission stream tem-
perature is about 3000 to 4000°F. Components in the emission stream
include CO2, 5 to 15%; O2, l%;andN2,  5%.   Control.  High-energy wet
scrubbers and electrostatic precipitators can reduce emissions to 0.05
grain/scf; the gas is sometimes used as fuel; this practice is more prev-
alent in Europe.
                          ELECTRIC ARC

Approximately 10 to 30 Ib of particulates is generated per ton of metal
produced, and 0. 7 to 4.1 Ib of NOX per hour per furnace.  The emission
flow rate is approximately 10,000 to 100,000 scfm, and the emission
stream temperature is about 1000 to 3000°F.  Other components in the
emission stream include CO,  1 to 8%. Control.  Fabric filters, high-
energy wet scrubbers, and electrostatic precipitators can reduce partic-
ulateemissions to 0.05 grain/scf; fabric filtration is the most efficient
control method.

Approximately 200 Ib of participates is generated  per ton of sinter; and
about 250 Ib of SC>2 is emitted per day. The emission flow rate is ap-
proximately 150,000 to 500,000 scfm.  Control.  Most plants use cyclones
as primary cleaners; some plants are using electrostatic precipitators for
secondary cleaning.  There is no  control equipment for
                                                                              It '


The iron and steel industry is the backbone of the American economy.
Sales in 1967 amounted to 27.2 billion dollars, and capital expenditures
for new facilities and modernization amounted to 5. 5 billion dollars be-
tween the years 1964 and 1967.  Of the approximately 275 companies
listed in the 1967 American Iron and Steel Institute Directory, the top
ten companies produced over 70 percent of all steel manufactured in the
United States; the top 35 companies accounted for over 93 percent of
the total steel production.

Approximately 130,000,000 net tons of raw steel was produced in the
United States in 1967; of this, 55 per cent was produced in open hearth fur-
naces, 32 per cent in basic oxygen furnaces, and the remainder in electric
furnaces.  The air pollution potential associated with the various proc-
esses used to manufacture coke, pig iron, and steel and the degree of
control practiced vary widely,  depending upon the particular processes
involved.  New steel furnaces and associated installations usually have
adequate control.  On the other hand, there are  several sources of
emissions to which some existing equipment cannot be applied.

The steel industry is  concentrated primarily in about 20 metropolitan
areas.  Six states, Pennsylvania, Ohio, Indiana, Illinois,  Maryland,
and New York,  account for about three-fourths of the Nation's iron and
steel producing capacity. This geographical concentration results from
the availability of coal and iron ore in these regions. Other plants lo-
cated throughout the  country take advantage of regional deposits and

Even though plant steel works located throughout the United States have
controlled emissions from  several of their processes, the  economic
and technical problems of air pollution control have not been sufficiently
established to permit the extension of control devices to all steel works.
The information gap  areas  include operating and  maintenance  costs of
the various control alternatives as well as control efficiencies for dif-
ferent operating conditions.

This report was prepared to provide background for a definitive contract
study of the industry's air pollution control problems.  It is a general

review of the processes, the sources and quantities of emissions, and
effectiveness of emission control equipment.  Because of the scarcity
of cost information, the associated cost of air pollution control could
not be quantified.
                      COKE MANUFACTURE

Coke is the primary fuel used in blast furnaces to reduce iron ore.  Coke
is carbon with relatively few impurities and is manufactured by the de-
structive  distillation of coal in either of two types of ovens: the beehive
or the byproduct oven.  In the byproduct process, the volatile  compo-             i^
nents are recovered and treated in a chemical recovery plant, whereas           ^'?
in the beehive oven process the volatile components are emitted to the              p£—
atmosphere.  Because of the favorable economics of byproduct recovery,
only 2 percent of the coke ovens in the United States are  the beehive type.         ;
However, it has been reported by the Bureau of Mines that there may be
a trend towards increased use of nonrecovery ovens  (i. e. ,  some new
nonrecovery ovens are being built) because of the lower initial capital             ,_„
expenditure for this type of plant and the competition of the petrochemicals        ^
in the byproducts' market.                                                      *.-,.

The byproduct recovery oven consists of a battery of retorts,  each
approximately 40 feet long,  12 feet high, and 10 to 18 inches wide,
alternated with heating chambers of similar size.  Sixteen to twenty tons
of granulated coal is charged to the retorts and heated in the absence of
air.  Gas burned  in the heating chambers provides a temperature of              ^.
2600°F; within  17 to 18 hours the volatile components of  the coal distill           -gv
off as a heavy brown gas. Cooling sprays condense most of the tar,              ^
fixed ammonia salts, and ammonia by cooling the gas from 1200 to  200°F;         ["""
further  refinement produces benzol, toluol, and various  other chemicals.         \
At the end of the cycle, the doors of the oven are  removed.  A hydraulic
ram pushes the incandescent coke into a waiting quenching car, and the
car is pushed to a quenching tower where the coke is rapidly cooled by
a deluge of water.  The coke is then taken to a wharf for  further cooling           ;
prior to screening.

In contrast to the byproduct oven, the beehive oven is a dome-like struc-
ture built of refractory brick with a flat floor sloping towards  an opening
that permits both entry of air during coking operations and  discharge of
the coke upon completion. A typical beehive oven, 12 feet in diameter           j
and 8 feet high, will hold 6. 5 tons of coal.  The coal is charged through           .
a hole in the roof of the oven; this hole also serves as an exit for the pro-         '
ducts of combustion and distillation during the coking operation.

Emissions from Coke Ovens

In the beehive process, all the materials resulting from destructive
distillation of coal are emitted into the atmosphere.   Objectionable odors
and large clouds of smoke are released.  Although no quantitative data
have been found, a material balance would indicate that approximately             &•*"'
25 percent of the coal charged into the oven is emitted as gaseous or
particulate pollutants.   This percentage varies widely,  depending upon
coke composition and carburization temperatures.

In the byproduct recovery process, most of the objectionable odors and
particulates that are emitted to the atmosphere escape during the charg-          ^,.
ing and discharging operations. During the actual coking cycle the vol-            £'(""=
atiles are collected, and only limited amounts escape as a result of               $*"''•
leakage.  Several  controls have been incorporated to reduce particulate
emission from byproduct  coke ovens.  These controls include (1) double
collecting mains; (2) telescoping connections between the oven-top charg-
ing holes and the charging car; (3) proper maintenance of sell-sealing
doors; and (4) aspirating the gases from the oven interior through gas
mains  coupled to the oven during charging and leveling operations.                 !*?•£
Even though a steam jet aspirator is operated during charging, some              '^f
smoke, coincident with the volume of coal charged from the hopper,               r^^
tends to escape.                                    '                            f""

In the byproduct process, any reduction of the time required for  charg-            f
ing the  coke ovens would reduce the air pollution potential.  Several               j
mechanical devices for  reducing air pollution have been proposed, in-             t	
eluding hopper vibrating mechanisms (in conjunction with smooth, stain-          :;;--.
less steel liners),  cylindrical hoppers, bottom turn-table feeders,  and            |C3-
a screw feed mechanism.  1                                                      •»•—-

Recently, coke oven operators in Germany started using a traveling
charging car mounted on tracks on top of the coke  ovens  on which it               '
moves to the appropriate oven for charging.  Air pollution control equip-          }.
ment is mounted on this car to collect the emissions from  the charging            *
operation.  Unfortunately, existing coke ovens do not have the structural
strength to support the added weight of the car.                                   t

At the end of the coking cycle, the incandescent coke  is  transferred from          J
the oven into a quenching car by a hydraulic ram.  The quantity of smoke          >
rising from the mass during the period required to transport the  coke to           j
the quenching station is dependent upon the degree of coking.  Incompletely         j
carbonized coke (green  coke) gives rise to considerable quantities of              ^—
smoke;  conversely, thoroughly carbonized coke gives rise to very little            .'.--•
smoke.                                                                         I •

The violent evaporation of the water as it contacts the hot coke during
quenching gives rise to large volumes of steam that can carry particles
of coke and mist up the stack.  The average solid emissions during a
2 -minute quench is 6 pounds; an average value of 0. 12 grain per scf has
been reported.  Approximately 87 percent of these  emissions occur dur-
ing the first minute of the quench.  The particulates are relatively coarse
and  thus tend to fall out locally.  The following is a typical screen anal-
ysis of solids  collected in a quench
                   Screen Mesh Size       Percent Above Size
                           6                       0
                          16                       1
                          30                      10
                          50                      45
                         100                      84
                         200                      97
                       -200                       3

Louver-type impingement baffles installed in a square quench tower at
U.S.  Steel reduced solid emissions 85 to 90 percent.

In addition to particulate emissions, in the past several years phenol-
contaminated water has been used in coke quenching operations, giving
rise to significant phenol  emissions.  Nothing is presently being done
to control these emissions.

Apart from particulate emissions, the other major contaminant result-
ing from combustion of the coke oven gas is sulfur dioxide. Because it
is advantageous to use low sulfur coke in the blast furnace, the steel in-
dustry attempts to use only low sulfur coal. The average sulfur content
widely quoted is 1.0 percent; however, the U.S. Bureau of Mines suggests
that 1. 6 percent would be  more accurate.  In 1967, 92 million tons  of coal
was used for coking.  It is assumed that if  30 percent of the sulfur con-
tained in 1 percent sulfur  coal was driven off during coking and that all
the coke oven gas was  combusted, the sulfur oxide emissions from  the
92 million tons of coal coked in 1967 amounted to 490,000 tons.  Most of
the sulfur-containing coke-oven gas is used as a fuel at various stations
throughout the integrated  steel plant.   The  sulfur that remains in the
coke is removed by the slag in the blast furnace.

A large percentage of the  coke-oven gas is used to fire the evens.  This
gas contains 300 to 500 grains of sulfur per 100 scf, or 0. 5 to 0. 8 percent
by volume,  mainly in the form of hydrogen sulfide. Various methods are
used to remove this hydrogen sulfide and thus  eliminate sulfur oxides
emissions during combustion of this fuel.  However, in a significant num-
ber of installations the sulfur is not removed,

Control Methods

One control method involves passing coke-oven gas into an absorber
containing a 2 to 3 percent aqueous sodium carbonate solution that re-
moves most of the hydrogen sulfide.  The solution is then passed into
a vacuum tower where it is heated by a waste stream of hot water to               E—-
recover the hydrogen sulfide.  The sulfur content of the gas is reduced
to about 0. 5 grain per scf.  This process works best when the  carbon
dioxide content of the coke-oven gas is  relatively low since the carbon
dioxide tends to reduce the absorption ability of the sodium carbonate                •,
solution.  In the past the stripped hydrogen sulfide was often vented to             >
the stack  or if the quantity was too large for  this, it was flared to form            ^&:
sulfur dioxide. One method for disposing of  the sulfur dioxide is to use            x^
it to produce sulfuric acid.                                                      r—--

In a second treatment method to remove hydrogen sulfide, a sodium
sulfite, thioarsenate scrubbing solution is used.  Hydrogen sulfide is
first removed in an absorber  tower; the rich thioarsenats solution is
then stripped of the hydrogen sulfide in a second tower by regeneration            bu
of the solution with air.  This regeneration liberates the sulfur as el-              f*\
emental sulfur.   The sulfur,  which is recovered by filtration, has an              £*-;'•
arsenic content of less than 0. 5 percent.  Bethlehem Steel, which used            P^M
this hydrogen sulfide recovery system on their plant in Sparrows Point,            f
Maryland, based their decision to use this system not on air pollution              f
abatement considerations, but upon the  necessity of  reducing the sulfur            |
content of the fuels to be used in their open hearth operations.  The               [
company reportedly could not justify installation of such a system on               ^r
the basis of air pollution abatement considerations only,  even with by-
product sulfur recovery. 3                                                      *'*"'

In addition to the direct control methods mentioned above, indirect con-
trol of air pollution can be exercised by reducing the amount of coke
produced.  With increasing technological advances in the blast furnace
process - such as  the use of pelletized  charges, fuel injection through
the tuyere, and oxygen enrichment of the blast - it is expected that the
amount of coke used to produce a ton of pig iron will continue to decline.
In 1948, 1,947 pounds of coke was needed; in 1957, 1,703 pounds was
needed; and in 1959, 1,500 pounds. However,  a lower limit will soon
be reached because there is a minimum amount of coke required for
adequate permeability of the blast furnace burden and for  generation
of the required volume of slag.  The lowest average  is expected to reach
1,200 to 1,300 pounds of coke per ton of hot metal by 1975.  On the other
hand, a revolutionary change such as  direct reduction process  for iron
might completely eliminate the coke-making  stage as part of the steel

                   BLAST FURNACE OPERATION

Process Description

Pig iron, the major raw material for steel manufacture, is made in the
blast furnace by reducing the iron ore to metallic iron.  The combustion
of coke with high pressure  air — called the blast — provides the reducing
atmosphere  and temperatures in excess of 3000°F in the tuyere region
of the furnace.  This generated heat is distributed among the iron-making
reactions, the sensible heat of the hot metal and slag, the sensible  heat
of the top gases, and furnace losses. ^  In addition to the reduction re-
action, calcination of the limestone and  slag formation occur.

The blast furnace is a  large cylindrical steel structure approximately
100 feet high, lined with heat resisting brick to withstand the high tem-
perature.  The air blast for the furnace is preheated in  the stoves,  which
are biick heat regenerators (checkerwork) enclosed in a circular steel
shell.  Modern stoves  are approximately 26 to 28 feet in diameter and
100 feet tall.  The checkerwork consists of a multiplicity of small pas-
sageways with approximately 250,000 to 275,000 square feet of heat
transfer surface.  The gas emitted from the blast furnace is cleaned of
particulates to prevent fouling of the checkerwork and then combusted to
heat the checkerwork in two stoves  while a third stove preheats the  air
used in the blast furnace.   Figures  1 and 2 show typical blast furnace

To produce a ton of pig iron requires approximately 1. 7 tons of iron ore,
0. 8 ton of coke, 0. 5 ton of  limestone, 0. 2 ton  of cinder scale and scrap,
and between 4 to 4-1/2  tons of air.   The iron ore, coke, and limestone
are charged semi-continuously through  the top of the furnace by either
conveyor belts or charging cars.  The charging  maintains the burden level
just a few feet below the double bells of  the furnace. Figure 3 shows the
principal operating parts of the blast furnace top.

Air preheated from 1500 to 2000°F  enters through the tuyere and promotes
combustion of the coke. The iron ore is reduced to molten iron that col-
lects on the hearth where it is periodically withdrawn.  The furnace pro-
duces approximately 0. 5 ton of slag and about  6  tons of gaseous products
from each ton of pig iron produced.  The above quantities depend upon  the
iron and silicon contents of the ore. Figure 4 shows a typical material
balance. ^

Most of the sulfur entering the blast furnace is contained in the coke,
although some sulfur is contained in the iron ore and limestone.  The
sulfur  is released into  the blastfurnace gas stream as H?S or COS when
the coke is burned.  As the gas ascends  through  the stack,  the sulfur

  H^v. -i-*—Tr.'—f« >  'L-J
Blast Furnace
                           Dust       Gas
                         Catcher    Washer
                  Figure 1

                          SECTION OF A BLAST FURNACE
           Bell Section
Hearth and Bosh
                                 Figvire 2

                                                     4 Uptakes Equally Spaced

                           PRINCIPAL OPERATING PARTS OF A

                                 BLAST FURNACE TOP
>mer  collects  hot
;  from  the  four
ip takes
  Beams  and  Counterweights"
.ving Hopper guides
,s dumped by skip
.  into distributor
ributor rotates part of
ull turn after each skip
 load is dumped to help
tribute ore, coke and
estone evenly on small
er, closed by large bell
eives material  from the
eiving hopper above when
11 bell is lowered. Low-
ng large bell empties
per into furnace.
                                                          Pressure Relief Doors
Skip Car is automatically
n - _ J n_ 	L                *
 tilted to dump its load in-
 to receiving hopper. Second
 skip car is at bottom of
 bridge in stockhouse, and
 will rise as empty car de-
 scends to stockhouse.
                                                             _S_kip_Bridge carries tracks
                                                              on which skip cars convey
                                                              ore,  coke> and limestone to
                                                              top of furnace.
                            BLAST FURNACE_MATERIAL BALANCE
                    All Quantities in Amount Per Ton of Hot Metal

iron Ore
Fluxed Sinter
Air      44,280  scf  3277  Ib
Moisture    670  scf    32  II
962 scf   41 Ib
                                                                     OUT PUTS
                                                            Top Gas  63,500 scf  4921 Ib
                                                            Moisture  3,300 scf   165 Ib
                                                            Dust                   44 Ib
                                                                                         •f, '•
                                                                  Slag  418  Ib
Hot Metal     2000 Ib
4.17oC, 0.90%Si,
G.026%S, 0.2967oP
                            Figure 4. Blast-furn&ce material balance.

reacts with the lime in the flux, or the iron.  The sulfur that reacts with
the iron must be removed.  This removal is accomplished in the hearth
where the high temperatures permit the reduction of the iron sulfide by
the basic flux.  This takes place according to the following chemical re-
action:  FeS +  CaO +  C =  CaS +  Fe  +  CO

The extent of sulfur removal depends upon the temperature of the hearth
and the ratio of the basic oxides (lime and magnesia) to acid oxides
(silica and alumina) in the  slag.  As a result of these reactions, little
sulfur, if  any, is released in the blast furnace gas. 6

Emissions and Control Methods

The dust loading to the particulate collection equipment is approximately
7 to 10 grains per scf — approximately 50 to 200 pounds per ton of pro-
duct.   After the gas is cleaned by an electrostatic precipitator or high-
energy scrubber, the typical exit loading is 0.02  to 0. 12 grain per scf —
approximately 1 to  10 pounds per ton of product.  .The recovered dust
is returned to the iron-making process after it has  been agglomerated.
In addition to the  normal dust emissions, slippage of the furnace burden
increases pressure to the point that the relief valves lift, causing further
dust emissions.   Slippage has been minimized by use of pellitized burdens
and improved operating techniques.

Approximately 150,000 cubic feet of gas is generated for each ton of pig
iron produced; about 25 percent of this gas is carbon monoxide —  this
amounts to about  2200 to 3000 pounds of carbon monoxide per ton of pig
iron produced.  Approximately 25 percent of the blast furnace gas  is
sent to the blast furnace stoves to heat the  incoming air.  The remainder
is used to fire boilers,  coke ovens, and soaking pits even chough the
caloric value is only 100 Btu's per cubic foot.
                    STEELMAKING PROCESSES

Charges to steel furnaces contain the following impurities: carbon,
silicon, manganese, sulfur, and phosphorus.  The primary function of
steel furnaces is to reduce these impurities in the charge to specified
limits.  The refining operations consist of (1) oxidation of the carbon
while the materials are in a molten or  gaseous  state, and (2) slag for-
mation that ties up the other impurities.

Complex compounds are formed in the  slag during various stages ot" the
heat. The slag is  composed of oxides formed by the oxidation of metal-
loids from the molten bath, and materials such as limestone, fluorspar,

 and iron ore, whicn are added to obtain the desired steel composition.
 The control of slag composition and the amount of slag formed during
 the reaction depend upon the composition of the charge and the steel-
 making process used.                                                           w^S

-As the composition of the bath changes, the temperature of the bath in-             jj^fe^
 creases because of the exothermic reactions taking place.  In addition
 to  heat caused by the reactions, external heat from sources  such as fuel
 combustion or electrical energy may be necessary.  The amount of heat
 needed and the efficiency of its utilization depend upon the process used.

 Steelmaking furnaces  can be either acidic or basic depending upon the              &$$&•
 refractory lining.  When the refractory material is silica, the furnace             i^w
 is  described as "acid," and when the refractory material is  dolomite or            JyV-
 magnesite, the furnace is described as "basic." Increased use of stain-           f~
 less steel and higher alloy steels has increased the use  of the basic fur-
 nace.   This furnace can use both high- and low-grade alloy scrap and
 plain carbon scrap to  produce  steels that meet  the stringent mechanical
 and purity specifications of both carbon and low- and high-alloy steels. ^
 The following processes are used for steel manufacture.                          *js£v:

 1.   Open Hearth Furnaces - with and without oxygen lancing.                      !>•'' •

 2.   Electric Arc Furnaces - with and without oxygen lancing.                     J

 3.   Oxygen  Converter Process.                                                 ]

                      BESSEMER CONVERTERS                                  jJv'

 Bessemer Converters are included only for historical interest; they are            f
 nearly obsolete.  In 1960 there were only 31 in  operation, producing                I
 3,396,000 tons of steel — or approximately 2. 3 percent of the total.               ;
 Today, even fewer are used and those are used only to melt the charge             *
 to the basic oxygen furnace.
 The converter is a refractory-lined cylindrical vessel with a spout sur-             j
 mounting the top at an angle to the main axis.   The converter is mounted           I
 on  trunions on which it can rotate to a horizontal position to receive a
 charge or to discharge.   One of the trunions is hollow, emitting air from
 a blower to the wind box, which is a chamber  at the bottom of the vessel.
 When the converter is upright, air passes through holes in the refractory
 barrier that separates the wind box from  the molten bath; air pressure             «	
 prevents the metal from trickling down through the holes into the wind              Lf.

Between 25 and 30 tons of molten pig iron is charged to older converters.
The converter can effect complete oxidation in 10 to 15 minutes; however,
its time advantage over the open hearth process is offset by the limited
ability of the converter to melt scrap metal.  Newer converters have
approximately twice the production capacity.

During the operation cycle of the converter, the volume of gas emitted
varies from near zero during the non-blow period to about 2 million
cubic feet (at 2700 to 3500 °F) during the 10- to 15- minute blow period.
The rate of dust emission also varies considerably through the cycle.

The Bessemer flame, which may reach 30 to 40 feet in length,  contains
carbon monoxide, which rapidly burns to carbon dioxide, plus two kinds
of particulate  matter.  Pellets of molten metal and slag are mechanical-
ly ejected by the large volumes of air (this is called spitting), and fine
iron oxide particulates are formed by the volatilization and subsequent
oxidation of the iron.  The mechanically  ejected particles are relatively
coarse — approximately 75 weight percent larger than 100 microns.
The fine particulates are suspended by hot gases, and because of their
buoyancy, rise to great heights, creating a visible orange plume.

Emission rates from a 2 5 -ton converter with a 10- to 14- minute blow
were  estimated to be 10 grains per cubic foot — approximately 15 to 20
pounds per ton of steel produced. A 25-ton converter operating 2 cycles
per hour and emitting 20 pounds  of emissions per ton of steel produced
would emit a total of 12 tons per day.  None of the Bessemer converters
presently used in the United States are equipped with devices to control
these emissions.  The primary difficulty in controlling emissions is the
confinement of the effluent.  Normal operating procedure plus the spit-
ting action of the process preclude the installation of a control device
near the mouth of the converter.
                    OPEN HEARTH FURNACES  '

Process  Description

Most of the steel produced in the United States is produced in open hearth
furnaces. Since a normal heat takes between 8 and 10 hours, to increase
production, many steel manufacturers use two methods:  the oxygen con-
verter process and the open hearth process with oxygen lancing.  Under
normal circumstances, a large open hearth furnace (300 tons) produces
steel at the rate of 25 to  30 tons per hour.  With optimum use of oxygen
                                                                               f •*"

 during the melting and refining stages, the production rate can be increased
 25 to 50 percent.  Consequently, steelmakers who have large investments
 in open hearths and are therefore hesitant  to switch over to the oxygen
 converter furnace are installing oxygen lances to increase production.

'The open hearth furnace consists of a shallow rectangular basin or
 hearth enclosed by walls and roof, all constructed of refractory brick,
 and access doors along one wall adjacent to the operating floor.

 The open hearth furnace is flexible and can take charges  varying from
 100 percent cold metal to high proportions of hot metal.  The  composi-
 tion of the charge does,  however, affect the amount of time required for
 the heat.  The typical charge is a mixture of scrap and hot metal with
 practical ratios of 30 to 70 percent for each.  In practice, a mixture of
 about 60 to 65 percent hot  metal and 35 to 40 percent steel scrap is

 Heat for steelmaking in the open hearth furnace is supplied by the sensi-
 ble heat of the hot metal, ihe exothermic chemical reactions taking  place
 in the bath, and the combustion of fuels with preheated air or with oxygen-
 enriched preheated air.  Fuels used for combustion include fuel oil,
 natural gas, tar pitch, and coke  oven gas.  The overall thermal effi-
 ciency of the  open hearth furnace is in the neighborhood of 20 to 35 per-            ^
 cent, depending upon the charge  to the furnace, the type of fuel used, and
 efficiency of the furnace.  Input heat in the form of fuel to the  open hearth          '
 furnace may vary from 1 million to 6 million Btu's per ingot ton.  Either           •
 of these extremes is encountered only in unusual cases.  Figures 5and6 show       ":
 the typical arrangement of the open hearth furnace.                               *
 A typical heat is composed of 60 percent hot metal and 40 percent scrap
 and usually proceeds in the following manner:  the bottom of the furnace            t
 is  first built up with dolomite and the burners are fired.  The furnace is            ,
 then charged  with limestone and  steel scrap.  The time required for this
 charging and  melt down of the  scrap varies between 2 and 4 hours, de-
 pending upon  the furnace size and the ratio of hot metal to scrap.  The
 hot metal is added when the scrap is partially melted.  Decomposition
 of the limestone begins as  the  temperature of the bath increases.  The
 release of carbon dioxide gas from the limestone increases the activity
 of the bath.  After the lime boil is completed and the lime solution is in            ;
 the slag, the  rate of decarburization increases.  When gaseous oxygen
 is  used for decarburization, the flow of oxygen is started after the addition         \
 of hot metal.   Oxygen flow rates are 20,000 to 100,000 cubic feet per hour           [
 per oxygen lance.                                                               :



          Figure 5


             Figure  6

Emissions and Control Mothers

Fume generation from tho open hearthoccurs duringthe charging and
melting phase and during the refining phase.  During charging and
melting, dust generation is  relatively low — on the average between
0. 05 and 0. 25 grain per scf. In the refining phase,  the temperature
increases, generating fine ferric oxide particles (approximately  50 per-
cent less than 1 micron in diameter).  The dust content may be as high
as 2 grains per scf, but on the  average, it is about 0. 5 grain."  Furnaces
charged with primarily cold metal generate less dust than those charged
with hot metal.

Until recently, open hearth  operators felt little  compulsion to install
control equipment unless they used oxygen lancing; in 1961 no more than
15 percent of all steel produced in open hearths was made in furnaces
with air pollution control equipment.  The fineness of the dust particles,
the variability and low level of  dust content, and the high temperature  of
the exit gas make an economical dust-cleaning operation difficult. Use
of oxygen lances has increased the pollution potential of the furnace
approximately two to five  times, depending upon the volume of oxygen
used.  At the point  of oxygen impingement,  the temperature increases
to between 5000 and 6000°F and causes fume formation, primarily ferric
oxide.  This fume is produced by vaporization of the molten iron and
subsequent oxidation of the iron in the vapor state.  Emission rates
during oxygen lancing are estimated to be between 2 and 6 grains per
scf. On the average an oxygen-lanced open hearth produces fine dust
ranging from 15 to  25 pounds per con of steel produced, with dust con-
centrations varying between 0.2 and 6.0 grains per scf.  Consequently,
most plants that have  installed  oxygen lancing have incorporated some
type of dust control equipment, such as electrostatic precipitators, high-
efficiency wet scrubbers,  or fabric filters.  Research to define the
principles  of fume formation was sponsored by the Technical Committee
for Air and Water Pollution Abatement of the AISI and done by Battelle
Memorial Institute.  Experiments made on eight heats in a six-furnace,
open hearth shop with each furnace  having a nominal capacity of 225  tons
reduced fume generation by 50  percent. 9

In addition to particulates, the  fume gases  contain carbon dioxide, oxy-
gen, sulfur dioxide, sulfur trioxide, nitrogen  oxide, moisture, hydrogen
fluoride, anc silicon tetrafluoride.  If a 1.6 percent sulfur-content fuel
is used, a 200-ton open hearth  furnace emits approximately 130 pounds
of sulfur dioxide per hour.  In the United States, a lower  sulfur-content
fuel is generally used.  Greater use of natural gas and less  use of coke
oven gas decreases sulfur emissions.

Fluoride omissions . both gaseous and participate, are caused by the
fluorspar used in the flux as well as the fluoride in the iron ore  (for
example, from ore mined in southern Utan).  Fluoride emissions are
relatively small; one source indicated emissions of 30 pounds per day
from an  open hearth shop with a capacity of 13,000 tons. ^
         Typical Variation of Average Emission Loadings with
         Stage of Pleat for Oxygen- Lanced Open Hearth Furnace

             Stage of Heat                Emissions, gr/scf

             Scrap Charge                       0.8

             Hot Metal Addition                  1.9

             Lime Boil — Oxygen                2 . 7
             Refine                              0.7

Venturi scrubbers, fabric filters, and electrostatic precipitators have
all been used for controlling particulate emissions.  The stream con-
ditions include dust concentration usually between 0. 2 and 3. 0 grains per
scf,  a gas temperature range of 600 to 1300°F (before cooling), and a
waste gas volume of 170 to 210 cfm per ton of heat.  Venturi scrubbers
have operated very satisfactorily at 99 percent plus efficiencies, result-
ing in exhaust loadings of less than  0. 05 grain per scf.  The venturi
scrubber requires a minimum of 30 inches of pressure drop for efficient
operation and usually 50 to 60 inches of pressure drop to clean the  exit
gas to 0.05 grain per scf.  In particular applications that involved clean-
ing 70,000 scfm, a 500,000-gallon water system was required. Approxi-
mately 600 to 800 gmp evaporated in the venturi throats.  For the eight-
furnace system, approximately 300 pounds of sludge per hour,  contain-
ing 20 percent moisture, was  discharged. ^
                          1 8
Baghouses have been tested   for application to  open hearth furnaces for
fume control. The test baghouse was downstream from the waste heat
boiler at which point the gas temperature averaged 500 °F and the neg-
ative static pressure about 1 inch of water.  Grain loadings up to 15 grains
per scf were reported and mass mean particle diameter estimated be-
tween 0.  8 and 5 microns.   No grain load efficiency tests  \v«'ro made;
however, there was never any visible exit fume  and the outside of the
filter bags remained clean.  Therefore,  it  was assumed in at the collection
efficiency remained high.

The bags tested were glass cloth fiber of the usual fabric weaves.  After
the cleaning cycle,  the pressure drop was in the intermediate, rather
than low, region.  However,  the slow increase in pressure drop with
build-up offset this  disadvantage.  A pressure drop of approximately
6 inches was predicted for a full-size unit.

English application  of electrostatic precipitators to open hearth furnace
fumes resulted in outlet loading concentrations in the range of 0.08 grain
per scf.

Process Description

In 1967, electric furnaces produced 12 percent of all the steel manu-
factured in the United States.  By 1980, approximately 20 percent of all
steel will be produced by electric arc furnaces. The electric furnace is
generally considered a scrap melting and refining process, even though
mixtures of hot metal and scrap are often charged to the furnace.  Fur-
naces range in size from 7 to  30 feet in diameter and produce 2 to 200 tons
of steel per heat.  The typical furnace is 22 to  24 feet in diameter and
produces approximately 125 tons per heat.

Although a  small amount of heat is supplied by  the exothermic reactions
in the bath, the primary heat source is the electrical energy  input.  The
overall thermal  efficiency, which is dependent  upon the size and oper-
ation of the furnace, is usually between 65  to 73 percent.  Power con-
sumption varies  between 450 and 600 kilowatt-hours per net ton.

The process cycle consists of the melt-down, the molten metal period,
the carbon  boil,  the reducing or refining period, and the pour (tap). A
mixture of  light, medium, and heavy scrap and burnt lime is charged
into the furnace.  Some iron ore and/or carbon may be added, depending
upon the carbon  content of the  ore.  After the charging is complete, the
electrodes  are lowered and buried in the charge.  When the first charge
is melted to reduce its bulk, the roof is retracted and additional scrap
is charged. During the melt-down of the scrap, oxidation reactions start
when a pool of liquid metal is  formed.  The refining stage is  an intensi-
fied oxidation period; oxygen is available from ythe iron ore.  Carbon,
manganese, phosphorus, iron, and aluminum are oxidized from the
metallic charge with ore and/or  gaseous oxygen.  Rapid oxidation of
carbon from the  melt causes the carbon boil.  The stages of this cycle
closely approximate those of the cold-metal-charged open hearth except
the electric-arc  furnace is faster and a much greater degree  of control
can be exercised.


 Fume and particulrtes are emitter1 curing two periods: the charging
 operation and the refining- operation.  During the charging operation,
 the top of the furnace is swung open to charge the metal.  When this cold
.charge is exposed to high temperatures within the furnace, massive quan-
 tities of fume are generated.  Therefore, new charging methods may be
                 i1                    7        O  O            */
 necessary to curtail these air pollution emissions. Durin_, ^urefining
 stage, fume generation varies overawide range; on the average, 10 pounds
 of fume per ton of metal processes is  emitted.  The emissions range gen-
 erally from 4. 5 to 3JX 0  pounds per ton;  extremes  of 37. 8 pounds per ton
 have been reported.-^  Participate  size is small  especially when
 oxygen lancing is  used.  Seventy weight percent of  the participates may
 be  less than I micron in diameter.  The large variation in dust concen-
 tration is caused by the  quality of scrap, the cleanness of the scrap, the
 sequence of charge addition,  the refining procedure,  and oxygen lancing.

 Oil and greasy scraps generate considerable amounts  of pollutants. In-
 clusion of large quantities of  low-boiling-point, nonferrous impurities in
 the melt inevitably leads to high  concentrations of these oxides in the
 fume. Inclusion of large portions of galvanized metal generates consid-
 erable amounts of zinc oxide.  In addition to zinc oxide, calcium, man-
 ganese,  and aluminum oxides are often present in the  off-gas.  Metal
 oxide fumes generated by the  melt decrease after  slag formation; the im-
 purities  are trapped in the slag rather than vaporized and emitted to the
 atmosphere.  However,  the vaporization and emission of the added slag
 components partially offsets this reduction of emissions.

 The breaking of the slag layer and the extremely high  surface tempera-
 tures  caused by oxygen lancing create higher emission rates.  The in-
 creased temperatures volatilize the iron, which is then oxidized and
 emitted.  A mill-scale or spontaneous boil also increases volatilization
 and emissions,  but less  than  oxygen lancing.

 The amount of nitrogen oxides formed is dependent upon the amount of
 arcing, ' not on furnace size.  Emissions range from 0. 7 to 4.1 pounds
 per hour  per furnace. *-®

 Control Methods
 The collection system and the treatment system for fume collection pose
 two distinct, problems in the operation of the electric furnace.  The  col-
 lection system is usually one of the following three types:  ;i) canopy-
 type hoods; (2) roof-mounted locri exhaust hoods, or (3; a direct furnace
 evacuation system using either canopy-type or roof-type hoods.  In  the

first two types ,  a largo excess of air is required for exhausi'-.  The air
lowers furnace temperature, thereby increasing electrical energy con-
sumption.  Direct furnace evacuation is more efficient ihan the other
types of collection, but it  creates an effluent scream of higher

Baghouses are the most frequently used collection systems: high-energy
scrubbers  are found in a few installations: and electrostatic precipita-
tors in very few.

Tests at English plants using electrostatic precipitators on electric-arc
furnaces indicate efficiencies in the 98 to 99. 5 percsnt range.  Inlet
loadings varied  between 0.4 and 2.2 grains per scf and outlet concentra-
tions between 0.001 to 0.046 grain per scf. 25
Wet scrubbers are capable of removing 65 to 75 weight percent of the
dust,  but they create a visible stack discharge. *°  Test results on a
venturi scrubber indicate 95 percent plus efficiencies with outlet con-
centrations in the 0. 03 to 0. 04 grain per scf range; there was a 25- inch           i
water pressure drop across the venturi scrubber.                                 **•_-
                                                                                '" ''""
Baghouses are reportedly the most efficient, with 99 percent plus effi-             ••••»•
ciencies.  At one installation  between  14 and 16 pounds of dust per ton             TT
of furnace  output was collected and no emissions were visible.                     \

The control equipment for the electric furnace, in the order of increas-           {
ing capital expenditures, includes the wet orifice scrubber, venturi                »__
scrubber,  cloth filter (baghouse), wet rotary disintegrators,  and electro-          v£ -
static precipitators.  Both the venturi scrubber and electrostatic precip-
itators  can handle effluent streams up to 600°F — a distinct advantage
where oxygen  lancing is used.

In the future,  large-capacity electric furnaces will be in direct compe-
tition with  the oxygen converter process.  A shop with a 1. 5-miilion-ton
annual capacity can be constructed with either four 22-foot-diameter
electric-arc furnaces or with two 180-ton basic oxygen furnace converters.
Estimated  capital expenditure' in both of these cases  is 30 million dollars.
Gas cleaning costs would amount to 6 percent of the total costs for pro-
duction of low carbon steel  in the electric furnace  shop compared to
15 percent of the  total costs in the basic oxygen furnace shop.

Even when the air pollution problems associated with melting, refining,
and tapping are solved, the major air pollution pivblom associated with
furnace charging will remain. All modern furnaces have swing-out roofs
for charging of scrap. The most leaolble solution to the charging problem
                                                 •• r

may be redesign of the electric furnace for ether charging methods.  Also,
there is an increasing trend toward totally enclosing the entire furnace
shop to collect all emissions.

Process Description

In 1955, the oxygen furnace process was used to.produce 0.3 million tons
of steel in the United States out of a total production of 117 million tons.
By 1966, this increased to 34 million tons out of a total  of 134 million
tons that year.  Estimates for  1970 suggest that 75 million tons will be
made by the oxygen furnace process, accounting for approximately 50 per-
cent of the  total production.  This dramatic increase indicates the direc-
tion  of developing steelmaking  technology and suggests that all but the
most modern open hearth furnaces will eventually be replaced  by oxygen
converters and electric furnaces.

Oxygen converter processes for steelmaking are divided into two broad
categories:  (1) processes in which the  converter is in the upright posi-
tion  during the refining operation; and (2) processes in which the convert-
er is horizontal or inclined and rotates during the refining operation. In
both processes, the converter  can be tilted in either direction  in the ver-
tical plane  for purposes of charging metals  and fluxes and discharging
molten steel and slag.   The majority of oxygen converters in steelmaking
plants in operation or under construction in the United States use the up-
right process; only one plant in the United States uses the rotary process.
Figures  7 and 8 show typical configurations of these furnaces.

In the basic oxygen process, high proportions of hot metal are charged.
In the typical upright process,  approximately 70 to 75 percent  of the
charge is hot metal and only 25 to 30 percent scrap steel.  However,
the rotating type of furnace can utilize up to 45 percent scrap in the charge.

Heat for the process is supplied by the sensible heat in the hot metal and
by exothermic reactions in the  bath during the blow.  An external heat
source is not necessary; coolants such as scrap, iron ore, or  limestone
are often necessary to hold the final temperature of the steel at the de-
sired level prior to discharge.  The overall thermal efficiency of the
oxygen converter process is approximately  80 to CO percent.

The  chemical  reactions that take place in each'  of the steelmaking proc-
esses arc essentially the  same, but tho processes cIL'cr greatly in the
speed with which the reactions  lake place.   Ii ihe oxygen process has a

                                                  o i. o.
                                UPRIGHT  OXYGEN CONVERTER

                                          Figure  7
I's^-'-  t " «-s. -V-'
. r-x"-   -•,*
-t •; .,":<';" >• "'-•'"-'' .•*• --^s,' --'•. !;'-'; •'•


         Figure  8


heat size of approximately 200 net tons, the kinetics of the oxygen proc-
ess are approximately eight times faster than those of the open hearth
process and four times faster than those of the electric furnace process.
Consumption of oxygen varies from about 1S50 to 2300 cubic feet per net
ingot ton — approximately 100 scfm per net ton of heat size.

In the normal sequence of operations, the converter is tilted a.nd the
molten pig iron, scrap, fluxes,  and limestone are charged. The con-
verter is then returned to the refining position, the oxygen lance lowered,
the furnace hood positioned,  and the blowing phase begun.


Furnace hoods are inclined,  box-shaped or barrel-shaped enclosures
with water-cooled walls.  The hood is positioned at the mouth  of the oxy-
gen converter prior to the oxygen blowing phase.  Hot fumes and dust
from the furnace are collected by the hood and passed into the duct work
of the gas cleaning system.   The off-gas from a converter has a temper-
ature of about 2500 to 3000°F and a typical composition of 90 percent
carbon monoxide and 10 percent carbon dioxide.  The oxygen cycle con-
stitutes roughly  30 to 40 percent of the total steelmaking time.  Virtually           'fA:-
100 percent of all fumes are  generated during this period.  The dust               fey*'
emitted during the blow varies: an average value  is 40pounds per ton  of            1^^""
steel produced; inlet loadings are about 10 grains per scf.  This flue gas           I
can be cleaned to less  than 0.05 grain per scf, an efficiency in excess of           i
99. 5 percent.                                                                  j

The typical size distribution  of the particles formed during the blowing            ^
period follow:                                                                  !&*••..
                                                                               i > >'

                        Minus 400 mesh     -  74%                            F
                        Minus  140, plus 400 -  10%                            I
                        Minus  40, plus 140  -  15%                            f •
                        Plus   40 mesh          1%                            j  .
Because of the large quantity of fume generated by oxygen converters, gas
cleaning systems are usually considered to be a necessity.  Gas cleaning
systems for rotary oxygen converter shops are only about half the size of          \
those required for upright process shops with the same annual capacity.            '

Problems associated with cleaning oxygen converter gas stem from three          t
facts:  (1) the fineness of the particles  entrained in  the gas - 75 percent            I
may be smaller  than 400 mesh,  (2) the exit gas temperature at the mouth           i«—
of the converter, after combustion, may be as high as 4000°F and (3)  at           •*..>.
the vessel mouth before combustion, the gas may contain an average of            £f.-.
87 percent carbon monoxide, constituting a serious explosion potential.            r


Control Methods

There are two basic ways to treat converter off-gas:
    1.  Open hood method.  Sufficient space is left between the con-
        verter mouth and hood to permit complete combustion of the              ?"*"
        carbon monoxide to  carbon dioxide.  The volume of gas to be
        cooled and cleaned is thereby increased.  In Europe, heat re-
        covery systems are  installed to cool the off-gas because of
        the high  cost of heat and energy generation; for economic rea-
       ^ sons  this practice is not generally employed in the United                *•••-
        States.   •                                                            £fe£
    2.  Closed hood method  (e.g. , KSID-CAFL and Yawata OG Process).        £•——
        A moveable skirt is  placed around the mouth of the basic oxygen
        furnace to prevent air from diluting the gases emitted from the
        vessel.  Consequently, the volume of gas that must be cleaned
        is reduced and the resulting  gas, which is rich in carbon monox-
        ide and has a calorific value of 240 Btu's per scf, can be used            ___
        as fuel.  The heating value of the gas is 2. 5 times greater than           (^7
        that of either blast furnace gas or 50 percent carbon monoxide            %:•
        gas.                                      .                            jp*_

With 35,000 cfm of gas  generated inside the vessel, the closed hood wet
system requires that no more than 100,000 cfm be handled by the fan.             \
With the open  hood system, the amount handled is 500,000 to  600,000              \
cfm for the wet or dry system. ^                                              ^—
                                                                              '.'-i •".'
Gas-cleaning systems for oxygen converter shops may be the dry type             ^-v"
(electrostatic  precipitator) or the wet type (usually ventu.ri scrubbers).
Gases to be handled by an electrostatic precipitator must be cooled to
approximately 550°F.  Water is usually sprayed into the exhaust stream
to provide  cooling,  proper humidity,  and lower pollutant resistivity.
For a 250-ton converter, as  much as  900 gpm of water could  be required.         [
To humidify the gas, during the first  2 minutes of the blow, steam is              ;
added at a  rate up to 50,000 pounds per hour.  This is necessary be-
cause there is little carbon monoxide  available to burn and provide the
heat for evaporating the injected water that normally performs  this
function. *•$ The volume of exhaust gases to be treated is also increased
by addition of  dilution air to prevent explosive mixtures of carbon mon-           i
oxide  and air; the surplus air is added at twice the quantity theoretically
needed to burn all the carbon monoxide.  Outlet loadings from the precip-
itator vary between 0. 035 and 0. 05 grain per scf.  At an inlet dirt loading
of 10 grains per scf, this would correspond to precipitator efficiencies  in
excess of 99. 5 percent.                                                        -

Venturi scrubbers are also used to clean off gases from the basic oxygen
furnace.  A quencher is used in addition to the venturi scrubber.
In the quenchers, the dirty gases at a temperature of approximately
2700°F are contacted with a deluge of water.  The gas is quickly saturated
at about 180°F.  There is approximately 5 inches of water pressure drop
across the quencher. To clean the gases to 0.05 grain per scf would re-
quire 42 inches of water pressure drop across the scrubber.   For a
250-ton basic oxygen furnace, a fan with 50 inches-water pressure cap-
able of handling 605,000 acfm at 180 °F would be required.  This 605,000
acfni is the sum of the following:  172,000 cfm from the products  of com-
bustion, 68,000 cfm surplus air — this is about half the amount of sur-
plus air required to  prevent explosion hazards with the precipitator —
365,000 cfm  of water vapor and about 5 percent for leakage. 20

Capital expenditures for the two types of air cleaning equipment — dry
type or wet type —  are practically the same for oxygen converter shops
that have similar annual capacities. For the electrostatic precipitator
system, operating costs  are appreciably lower,  and most installations
in this country  are the dry type.  However, three shops now in operation
have wet scrubber systems and at least two shops planned or  under con-
struction will have wet systems.  The economics of the two systems are
not based on operating costs  alone.  Such factors as the availability of
water and space, the method of dust disposal, and the existence of set-
tling and filtering facilities also must be considered. The approximate
capital  cost of a gas-cleaning system for a 150-ton basic oxygen furnace
shop is  estimated at 2 million dollars and amounts to between 14 and
19 percent of the total cost of the shop.
                  AGGLOMERATION OPERATION     -                          P—~

Agglomeration processes are used on blast furnace feed to beneficiate              ;
ore and to salvage recovered dust.  The primary purpose  of agglomer-             :
ation is to improve the permeability of the burden and the  gas-solid
contact, thereby reducing the quantity of coke required and increasing
the rate of reaction.   A secondary purpose is to reduce the quantity of              i
fine material blown out the top of the furnace.                                    ;

A good feed to a blast furnace should contain a minimum of 60 percent              >
iron and a minimum  of material smaller than 1/4 or larger than 1/2               ,
inch in diameter.  In addition, the material should be strong enough to              ,
withstand high temperatures in the furnace and  degradation during han-             }
dling and should be reducible at a high rate.                                      L~~
                                                                               ' *v.
The decreasing availability of high-grade ore has made it  necessary to             ^j1'
upgrade, that is, beneficiate low-grade ores.  Beneficiation includes


 crushing, grinding, washing, separating, classifying, and agglomerating
 the ore.  Most of the beneficiating operations are conducted at the mine

 Agglomerating the recovered dust at a steel plant is usually considered
.a solid wastes disposal solution.  The recovered product is often not
 valuable enough to make recovery economically attractive.

 Sintering and pelletizing are the principal types of agglomerating proc-
 esses  used.  Sintering is the burning of a mixture of ore, limestone,
 and coke under controlled conditions to provide a fused mass.  Pelletizing
 differs from sintering in that an unbaked green pellet is formed and hard-
 ened by heat.  Almost all agglomerating plants being built are  pelletizing
 plants.  Consumption figures are given below:

                                               1 fi
                  Sinter and Pellet Consumption
                     (Millions of tons per year)
       Year            Sinter           Pellet
     1950                25            Less than 1
     1960                68                15

     1970 (Projection)    75                40


To prepare excellent sinter, the raw materials, namely, iron ore, lime-
stone and coke, must be crushed.  The mixture, which contains approxi-
mately 5 percent coke for fuel,  is carried  on a traveling grate and ignited
by gas burners near the feed end.  The flame front burns down through
the bed as the traveling grate carries the material through the wind box.
At the exit end of the sintering equipment,  lumps are broken and sieved.

Particulates are emitted from sintering operations primarily in the
sinter strand gases and upon discharge of the sintered material from the
machine.  The particle size of the dust in the sinter strand gases varies
widely, depending upon the feed to the strand (i.e. , whether  or not the
feed has been pelletized).  For each ton of sinter produced, approxi-
mately 20,000 cubic feet of-waste combustion gas  — strand gas  — at
160  to 390°F must be treated.  The particulate concentration in the
strand gases usually varies between 0.1 and 1. 0 grain per scf — approxi-
mately 20 pounds per ton of sinter produced.  Dust in the strand gases is
generated early in the process and  again when the flame front burns  through
the bottom of the bed.


The major source of dust generation in the sintering process is at the
discharge end of the sintering machine where the dust load has been
estimated to be between 4 and 6 grains per scf. Without cleaning equip-
ment,  a plant producing 1,000 tons of  sinter per day would emit approxi-
mately 11 tons of dust to the atmosphere.

In addition to emitting large particulates (50 percent greater than 100
microns in diameter),  the sintering process  emits sulfur by reducing the
sulfur content of the feed mixture by as much as 70 percent.   The amount
of sulfur dioxide emitted to the atmosphere  is dependent upon the sulfur
content of the coke-ore mixture and the fuel gas; approximately  250                im-
pounds of sulfur dioxide is emitted each day by a plant producing 1,000
tons of sinter per day.  Where fluorides are present in the ores —
usually the case in Western ores - gaseous  hydrofluoric acid and silicon
tetrafluoride are generated.

Sinter strand gases are readily cleanable.   Gas temperatures usually
fluctuate between 70 and 400°F with a humidity of approximately 10 per-
cent.  English reports of an electrostatic precipitator installation in-              if_-_
dicate 86. 7 percent efficiency, with an outlet loading of 0. 04 grain per              ^.v.
scf. Depending upon chamber design, settling chamber efficiency is                $"-.-.
approximately 70 percent, which corresponds to an outlet loading of                'w***
approximately 0. 5 grain per scf.                                                 j

The discharge end of the sintering machine  is usually completely hooded.           j
The volume of ventilation air required varies from 30,000 to 150,000 cfm,          *
depending upon unit size.  Electrostatic precipitators are usually used to
control this emission source.  Sulfur oxide  emissions are not treated.

Little  information is available on dust generation from pelletizing oper-
ations. However, conventional dust collection equipment should be cap-
able of cleaning the effluent.


In the  previous sections, emissions from blast furnaces, steelmaking
furnaces, agglomerating, and coke manufacturing  operations have been
noted.   In addition to these sources, there are several other sources  of
particulate and gaseous emissions; all combustion operations  can emit
sulfur  oxides and particulates.   In an integrated steel plant, efficient
utilization of internally generated fuel  is practiced.  For example, sulfur-
containing coke-oven gas is used extensively throughout the plant for
various operations such as firing the coke ovens, the open hearth furnaces,
and the reheat furnaces. In addition to the combustion sources of emissions,

other sources exist, such as scarfing operations and slag-quenching-pit
operations.  Most of these miscellaneous sources of emissions are not
presently controlled.  Some of the operating practices and sources  of
emissions are briefly described below.

Power and Utility Plant Operation

Power plants create both particulate and gaseous contaminants primarily
in the form of fly ash,  carbon monoxide and dioxide, sulfur dioxide and
trioxide, and nitrogen oxide.  Those power plants used within the in-
tegrated steel industry differ somewhat from commercial and municipal
facilities because they are designed to use fuels generated on the plant
site.  Both sulfur and particulate emissions are dependent on the fuel
used.  Often because of the large capital expenditures required for  the
power plant,  power is usually purchased from  local utilities.  Conse-
quently, the number of power plants  within the steel industry is reduced.

Scarfing Operations

Before steel can be rolled, surface defects in the bloom, ingot, and
billets must be removed or they will remain during subsequent rolling
operations.  The scarfing operation removes these  defects.   Jets of
oxygen are directed at the surface of the steel, which is maintained at
high temperature, causing localized  melting and subsequent oxidation
of the steel.  The layer of scarfed steel is approximately  1/8 inch thick
and is removed from all four sides of the red hot ingot, slab, or billet.
                                                                               £• "•
Gas exhausted from the scarfing operation amounts to 20,000 to 150,000
cfm, depending upon the size of the scarfing machine.  Estimates of
emissions vary, but if a loading of 0. 8 grain per scf in an effluent stream          m*v
of 50,000 cfm is assumed, more than 4 tons of dust would be emitted              f
daily.  Usually the dust-laden gas is exhausted without extensive clean-            r
ing; however, many plants use a baffled settling chamber to collect the             •
larger particles.                                                                \
                                                                               f *
Heating and Reheating Furnaces
When continuous casting is not employed following the steel operation,
the molten  steel is poured from the furnace into the ladle and then into
a mold where it solidifies and forms ingots.  The entire  ingot is brought           (
to the same temperature in a reheat furnace prior to the rolling operation.
In the past, ingots were placed in holes in the  ground, covered, and allowed        J
to soak until the temperature for rolling the steel was reached; hence the           **—
term "soaking pit" arose.  The principal pollutants emitted from a  properly        "'-• •
designed reheat furnace are the normal gaseous products of combustion.

    S lag Quenching Pits

    For each ton of pip; iron produced in the blast furnace, approximately
    0. 6 ton of slag is produced.  This  hot slag is quenched with water, re-
    sulting in hydrolysis of the calcium sulfide and formation of hydrogen
    sulfide gas.  Concentrations of hydrogen sulfide as high as 20 ppm have
    been noted at distances up to 100 feet from the  edge of the slag quenching
    pit.  The odor threshold for hydrogen sulfide is approximately 0. 8 ppm.
    At the  present time, Battelle Memorial Institute is conducting research
    on emission control under the sponsorship of the Technical Committee
    for Air and Water Pollution Abatement of the American Iron and Steel
    Institute .
                             HEALTH ASPECTS                                    "

    Little is known about the effects of emissions from the iron and steel in-
    dustry on heal tli. Some studies have indicated that these emissions
    might detrimentally  affect man's health if he is exposed for sufficient
    periods of time to high enough concentrations.  During the  course of the            sp?F
    literature search, which was primarily oriented toward emission and              ^v'
    control technology articles , no definitive data on the health effects of              ^^
    emissions from steel plants were located.                                        ^"

                                CONCLUSION                                      \
    Review of summary  at the beginning of this report shows that the proc-             ["/v
    esses used to refine  steel generally can be controlled.  There are oper-            fe^-
    ations,  however, such as charging of electric arc furnaces, for  which              r* '" '
    no completely satisfactory controls have been developed.  Research to             f.
    develop controls for  steelmaking processes should generally be aimed              <
    at minimizing fume formation,  improving reliability of control devices,            ^
    and controlling emissions from the few operations that are  not now satis-           t  •
    factorily controlled.                                                             '

    Coke ovens are not adequately controlled, and a wholly new approach to
    control may be necessary.   Totally enclosing the  coke oven battery has
    been discussed;  this  would necessitate  careful  research to prevent build
    up of explosive mixtures.                                                       i
    Fluoride emissions are not controlled, and the extent of the problem is
    difficult to define.  Since some western plants have had to pay significant
    damage claims as a result of fluoride emissions, research on economical
    methods for controlling these emissions may be  necessary.
*?*. -*.
' *•*•*&.'•

    The sulfur oxides emission problem is fairly minor.  These emissions
    can be substantially controlled by desulfurizing the coke oven gas.  Ex-
    cept in the few cases of process necessity, however, this is generally
    not done  because it is not economically attractive.

    A thorough engineering analysis of the industry should be performed to
    identify and define air pollution control problems that require research
    and development efforts.
                                                                                    * *•» ;l'X
vo^-'-~ v'^rv

 1.   Schueneman, J.J. , M.D. High, andW.E. Bye.  Air pollution
     aspects of the iron and steel industry.  PHS Publ. No. 999-AP-l.
     p. 39.  June 1963.

 2.   Schueneman, J.J. Ibid, p.  36.

 3.   Mallette, F.S.  Problems and control of air pollution.  Reinhold
     Publishing Co., New York.  p. 216.  1955.

 4.   Kesler,  G. H.  Hydrocarbon fuel injection in the blast furnace.
     Chem. Eng. Progress Symp. Ser. 59(43):124.  1963.

 5.   McGannon,  H. E. , ed.   The making, shaping and treating of steel.
     U.S. Steel Corp.  p. 420.  1964.

 6.   McGannon,  H.E.  Ibid, p.  418.

 7.   Schueneman, J.J. Ibid, p. 23.

 8.   Pring, R. T. Air pollution control equipment for melting operations
     in the foundry industry.  Trans. Amer.  Foundry Soc. 61:468. 1953.

 9.   Suppression of iron oxide fumes in the open hearth furnace.
     Magazine 33.   5:61.  Feb.  1967.

10.   Hosey, A. D. ,  and F. Nevins.  Evaluation of plant effluents.  In:
     Air  pollution in Donora, Pa. —  Preliminary Report.  PHS Bull.
     No.  306, pp. 86-109.  1949.

11.   Schueneman, J.J. Ibid, p.  22.

12.   Schueneman, J.J. Ibid, p.  57.

13.   Edgewater showcases its families furnace.   Magazine 33.  5:124.
     June 1967.

14.   Fuel engineering data.  Section F-2, National Coal Assoc.,
     Washington, B.C. Sept. 1961.

15.   Roedere, C. , F. Mangin, S. Ogawa, I. Hamabe,  and G. DeCervens.
     Gas collection without combustion — IRSID-CAFL process-operating
     data.  J. Metals.  18:852.  July 1966.

16.  McGannon, H.E.  Ibid, p.  188.

17.   Broman, C.U. , and R. R. Ischi.  The control of open hearth stack
     emission with venturi-type scrubbers.   Iron and Steel Engineer.
     45: Jan. 1968.
                                                                             ' *
18.  Herrick, R. A.  A baghouse test program for oxygen lanced open             ^H*
     hearth fume control.  Presented at APCA meeting, Chicago, Illinois.
     May 1962.

19.  Henschen, H. C.  Wet vs. dry gas cleaning in the steel industry.
     JAPCA.  18(5):338-42.  May 1968.

20.   Henschen, H.C.  Ibid.

21.  Fullerton, R.W.  Impingement baffles to reduce emissions from
     coke quenching.  JAPCA.  17(12):807-9. Dec. 1967.

22.  Punch, G.  Elimination of fumes  in the iron and steel industry.
     Steel International.  3(12):8-18.   July/Aug. 1967.

23.  Basse, B.  Gases cleaned by the  use of scrubbers.  Blast Furnace
     and Steel Plant.  44:1307-10.  Nov. 1956.

24.  Punch, G.  Ibid, p.  8.

25.  Punch, G.  Ibid, p.  17.

 1.   Bennet, Robert L. , and Robert D. Lopez.  Agglomeration of iron
     ore concentrates.  Chem.  Eng. Progress Symp. Ser. 59(43):40-52.

 2.   Brandt, Allen D.  Current status and future prospects — steel
     industry air pollution control.  Proceedings; The National Con-
     ference on Air Pollution, Washington, D. C.  PHS Publ. No.  1669,
     pp.236-41.  Dec.  12-14, 1966.

 3.   Browning, Jon E.  Agglomeration.   Chem. Eng.  74:147-70.
     Dec. 4, 1967.

 4.   Anonymous.  Pollution crackdown puts premium on sulfur-free
     fuels.  Chem. Eng. 73:94, 96. July 18, 1966.

 5.   Anonymous.  Dust control methods.   Coal Age.  7.2(8):58-62.
     Aug. 1967.

 6.   Cooper, R. L. ,  and G. W. Lee.  Alleviation of air pollution in the
     coking industry.  Session V, Paper V/l.  United Kingdom,  pp.  117-

 7.   Doherty, J.D. , and J.A. DeCarlo.   Comparison of coking practices
     in the U.S. and western Europe.  Congress International.   1966.

,8.   Hibbard, Walter R. , Manual Gomez, J.G. Walters, and John B.
     Gayle.  Report  of investigations 7093, Bureau of Mines.  March

 9.   Hoak, R. D.  , and H. C. Bramer.  Pollution control  in the steel in-
     dustry.  Chem. Eng. Progress.  62(10):48-52. Oct.  1966.

10.   Jones, James R.  Coal and air pollution control.  Proc. Illinois
     Mining Institute, 74th Annual Meeting, Springfield,  111.  pp. 71-90.
     Oct. 1966.

11.   Khanin, I.M. , V.I. Yakovlev,  and M.B. Kartsynel.  A spray-type
     benzole scrubber with radially-slotted gas distributors.
     Dnepropetrovsk Institute of Chemical Technology.   1965.

..  Ill) j

24.  Walker, F.E. , and F.E. Hartner.  Forms of sulfur in U.S. coals.
     U.S. Bureau of Mines Information Circular 8301, Oct. 1965.
12.  King, D.T.  Dust collection in coal preparation plants.  Mining
     Engineering.  19(8):64-9.  Aug. 1967.

13.  Kropp, E.P. , and R, N. Simonsen.  Scrubbing devices for air
     pollution control.  Paint, Oil and Chemical Review.  115(11):13-16.
     July 3,  1952.

14.  Mcllvaine,  Robert W.  Air pollution equipment for foundry cupolas.
     JAPCA.  17(8):540-44.  Aug.  1967.

15.  Quigley, James M. The cost of clean water.  FWPCA Publ. No.
     I.W.P.-l,  Vol.  HI.  U.S. Dept. of the Interior.  Sept. 28, 1967.

16.  Remirez, Raul.  Japanese process makes blast furnace feed from
     pyrite concentrate. Chem. Eng.  75:114-16.  April 8, 1968.

17.  Rengstorff,  George W. P.  A research approach to the control of
     emissions from steelmaking processes.  JAPCA.  13(4):170-2.
     April 1963.

18.  Silver man, Leslie. Technical aspects of high temperature gas    •          .&?•
     cleaning tor steel making processes.  APCA Meeting, Youngstown,          'P*""""
     Ohio, Sept. 23, 1954.                                                    \

19.  Sollenberger,  C.L.  Current world iron ore beneficiation methods.
     Chem. Eng. Progress Symp.  Ser. 59(43):1-11.  Nov. 1967.                  [_

20.  Stone, J.K.  Worldwide distribution of oxygen converter steel-               ^.^
     making plants. Iron and Steel Engineer.  44:104.  Nov. 1967.

21.  VDI 2109.  Restricting emission of hydrogen sulphide and other
     sulphur-containing compounds, except sulphur dioxide from gas
     generators  in  coke, gas, and coal constituent processing plants.
     May 1960.

22.  VDI 2302.  Restricting emission of dust, tar mist and gas when
     charging coke ovens.  June 1962.

23.  VDI 2290.  Restricting emission from gas generators in coke and
     gas plants.   June 1962.

..rrlfr.ri   j 3 nljv/  ;  T.-< jr:
        • >A it1 in? a A  "<~'N
     •   !0 .£oi'$e:a.',  Ic
      ,-iJuA   3}jjjWarn  '9
                                    •f: ';
                                            ?JJ .'.).•

25.  Willett, H.P.  Cutting air pollution control costs.  Chem.  Eng.
     Progress.  63(3):80-3.  March 1967.

26.  Varshavskii, T.P. , A.M. Denisov, L.E.  Zlatin, and K. V. Zolotarev.
     Smokeless charging of coke ovens.  No. 6. pp. 26-31.  1965.

27.  Holden, C.  Factors affecting fuming in open-hearth furnaces.
     Journal of the Iron and Steel Institute,  pp.93-102.  Oct. 1959.
                                                   - - *- *
                                40          ->. .'. u'_n ,OiS.:-bcm Street
28.  O'Dell, Leonard.  Filtration <5f pa^titulate matter from basic
     open hearth gases using glass1 c^th'ftag collector. ~ Presented at
     AISE Meeting, Berkeley, Calif.  March 29, 1960.

29.  Brief,  R.3. , A. H. Rose, and D. G. Stephan.  'Properties and
     control of electric-arc steel furnace fumes.   JAPCA.  6(4):220-24.
     Feb. 1957.

30.  Richardson, A. L.  Role of the electrical  precipitator in the steel
     industry.  Iron and Steel Engineer.  43:97-100.  Oct. 1953.                   ^.

31.  Anonymous.  Prevention of atmospheric pollution by iron and steel            £
     works,  iron and Coal Trades Review, pp. 157-59.  July 20, 1956.

32.  Wolf, Muhlrad.  Problems of smoke emitted from electric-metal-
     lurgical furnaces.  Staub.  22(2):42-50.  Feb. 1962.

33.  Bishop, C.A.  Metallurgical furnace stacks.  Amer.  Ind. Hyg.
     Assoc. Quart. 11:34-9. March 1950.

34.  Bishop, C.A.  Some  experiences with air pollution abatement in
     the steel industry.  Proc. 45th Annual Meeting, Air Pollution and
     Smoke  Prevention Assoc. of America, Cleveland, Ohio. pp.  32-7.

35.  Iron and Steel  Institute. Fume arrestment: Special Report 83.
     Proc. of the Iron and Steel Institute, Autumn General Meeting,
     Nov. 26-27, 1963.