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-208-
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-209-
-------
While the major source of particulate and sulfur dioxide emissions
is the furnace stack, there are three other sources. Dust can be gener-
ated during loading and unloading of charging equipment. The slag launder
and handling equipment are minor sources of sulfur dioxide. The matte
launder and transfer ladle are another source of sulfur dioxide and
particulates.
23.3 Enforcement Procedure
The objective of copper smelting operation inspection is to es-
tablish compliance with the sulfur dioxide and particulate emission regu-
lations. In order to accomplish the above objective, the enforcement
official needs to determine:
1. Current production levels and operating conditions,
2. Design production levels and operating conditions,
3. Current controlled and uncontrolled particulate and sulfur
dioxide emission levels,
4. Efficiency and adequacy of emission control equipment at
current and design operating levels.
Both furnace and emission control equipment design capacities and
operating conditions can be obtained from design drawings and plans.
These data should be obtained from the company representative prior to
plant inspection. Production levels, roaster feed weight rates, roaster
and roaster emission control equipment operating conditions are monitored
by the plant operator and are either recorded in the operator's daily
log or are displayed on instrument panels.
The furnaces will have a control booth nearby for careful monitor-
ing. The enforcement official should have little difficulty assessing the
-210-
-------
current operating status of the furnace by observing the many recorders,
gauges and log sheets which are normally kept.
Of primary importance for the enforcement of the air pollution emission
regulations is the process weight rate and the sulfur content. With the
mass rate and sulfur content of the feed, slag and matte, a sulfur mass
balance can be calculated. From this, S02 emissions can be computed.
Compare the computed emissions with allowable levels in the regulations.
If required, take appropriate action.
It should be pointed out that many state regulations restrict sulfur
emissions from the entire smelter and not separate processes. For deter-
mining compliance with the regulations, sulfur emissions from each oper-
ation must be summed, then compared.
There is little that can be noted on instrument panels regarding the
amount of particulates emitted to the atmosphere. Some plants will have
a smoke density meter which may be used to determine relative particulate
emissions from one visit to another. The enforcement official should
note the pressure drop, spark rate, and flow rate and operational para-
meters of the air pollution control devices.
The enforcement official should subjectively analyze the appearance
of the roaster and note any leaks, SC>2 odors, condition of the duct, etc.
Finally, some attention should be given to the dust emission from the
material handling of the feed to the furnace. The enforcement official
should inspect the dust handling system below the boilers and the flues
and also trace out and inspect the balloon flues leading to the final dust
collection system.
-211-
-------
Two sources of effluent at the reverberatory furnace occur at the
tap hole and the slag notch. Matte is drawn off intermittently into matte
pots resulting in a rather significant source of smoke and dust which,
if not collected, will be emitted through the roof monitors. Matte pots
generally have ventilating hoods which collect the emissions and vent to
ducting system.
No control is attempted for the slag skimming operation. The launders
usually lead to slag cars outside the building. This and the continuous
nature of the skimming process results in low mass emission rates and
rapid dilution of the effluent.
Visible emissions are the simplest means for estimating particulate
control equipment performance. The enforcement official should estimate
the percent opacity of dust control equipment stack plume and if in ex-
cess of allowable limits, take appropriate action.
Building openings should be observed for evidence of escape of in-
adequately captured process dust. If noted, determine point (s) of origin
and require corrective action.
24. CONVERTING
This' is the principal source of sulfur emissions in the copper smelt-
ing process. Individual plants may have recovery units. It may be a
major source of particulate emissions, depending on the adequacy of the
control equipment.
24.1 Process Description
Converting is the final pyrometallurgical process in the production
of blister copper ready for refining. The process consists essentially in
-212-
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blowing air through the molten matte from the reverberatory furnace. The
ferrous sulfide is oxidized to ferrous oxide and slagged off and the copper
sulfide is oxidized to blister copper. Sulfur from both reactions goes off
in the flue gases as sulfur dioxide.
Two types of converters are used:
1. The upright or Great Falls converter ,
2. The horizontal or Fierce-Smith converter.
The operation is similar with both. The general procedure is directed into
two stages: the slag-forming blow and the copper blow.
About 20 tons* of molten matte at about 1,100°C are charged together
with about 5 tons* of siliceous flux, either relatively pure quartz or a
siliceous ore of copper. The blast is then turned on and the converter
rotated until the tuyeres are covered. During the early stages of the
blow (the slagging period) the ferrous sulfide in the matte is oxidized
preferentially, because of its lower free energy of formation as compared
with cuprous sulfide:
2FeS + 302 - *-2FeO + 2S02
The ferrous oxide produced combines with the siliceous flux to form a slag:
FeO + Si02 - »-FeO + Si02
The reaction furnishes sufficient heat to maintain the desired temperature
and, in fact cold copper bearing material in the form of scrap, or matte
skulls are added to prevent overheating and damage to the converter lining.
At the end of the slagging period, when all the ferrous sulfide has
been oxidized and slagged, the bottom of the bath contains nearly pure
* These approximate figures apply to large horizontal converters. Quanti-
ties are smaller with upright converters which are rare today.
-213-
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cuprous sulf ide (white metal) . In normal practice the charge is blown
almost to white metal (30 to 180 minutes) and the converter is then rotated
and most of the slag poured off. A new charge and fresh flux are then
added and blowing and pouring of slag are repeated until the converter is
filled with white metal. The last of the iron is removed as completely
as possible, and the copper blow started.
The copper blow converts the white metal to blister copper:
Cu2S + 02 - ^2Cu + S02
the sulfur oxidizing preferentially to the copper. If the blow is con-
tinued too long, the copper begins to oxidize; if too short, the sulfur
is not completely oxidized.
The Fierce-Smith converter consists of a cylindrical steel shell
mounted on trunnions at either end which permits rotation of the converter
around the long axis. Figure 24.1 is a picture of a 13 by 30 foot con-
verter, a common size. Figure 24.2 is a sketch of a typical converter
aisle cross section. Air enters through tuyeres connected to the wind
box by air pipe and flexible coupling. The tuyeres are usually 1 to 1-1/2
inches in diameter and 8 to 12 inches apart. They are placed high enough
above the bottom to clear the level of the metal at the finish of the con-
version. Frequent punching of the tuyeres is necessary to keep the air
inlets clear.
Siliceous flux may be added to the converter in three ways:
1. By a steel scoop or boat handled by a crane which pours the
material into the mouth of the converter,
2. By a chute from an overhead bin,
-214-
-------
FIGURE 24,1 ELEVATION OF A FIERCE-SMITH CONVERTER
-215-
-------
LU
GO
GO
CD
cc:
oo
cc:
CM
^r
CNl
LU
ceZ
^D
CD
-216-
-------
3. By a Gar gun which blows finely crushed silica into the con-
verter through a tube inserted at one end.
When the converter cycle is finished the converter is tilted to dis-
charge the copper metal into ladles. It is then transferred to the anode
furnace and casting machines. The products of the converter are blister
copper containing 99 percent copper, slag, and flue dust and gas. Con-
verter slags are essentially iron silicates with some alumina and magnesia,
but contain up to 5 percent copper. To avoid the loss of this copper,
converter slags are used to flux the reverberatory furnaces or are solidi-
fied, broken up, and added to the furnace charge.
Flue gases laden with dust and fumes are captured at the converter
mouth by either air-cooled or water-cooled hoods. Sufficient dilution air
is introduced to cool the gases before entrance into large balloon flues
leading to the primary gas cleaners. The gases consist principally of
N2, C>2> an<^ SO™. The production of SO. varies within the converter cycle
and occurs only during the blowing periods. During the slagging blow,
SO^ concentration may be as high as 12 percent at the converter mouth, and
during the finish blow as high as 18 percent. After dilution, SO. concen-
tration varies from 2 to 10 percent at different stages of the converter
cycle with an average of about 4 to 6 percent.
Fumes present in the flue gases are volitalized oxides of arsenic,
antimony and lead and certain metallic sulfates and sulfuric acid. The
dust from the converter contains as much as 45 percent copper. This copper
and by-product arsenious oxide are collected in the flues and the primary
dust collector. Dust concentration in the converter off gasses may average
as high as 12 gr/scf, which for a large converter would produce 15 tons of
particulates per day.
-217-
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24.2 Process Control Operation
The converter operation is a batch process. The parameters depend
upon the converter size and the matte tenor. For instance, a 13-by-30
foot Fierce-Smith converter holds 200 tons of matte. With 40 percent
matte the capacity is about 120 tons of copper per day with 12-hour oper-
ating cycles. Table 24.1 shows a typical operating schedule. Within mod-
erate limits, the daily capacity increases 5 tons for each 1 percent in-
crease in matte tenor and decreases 5 tons for each 1,000 ft. increase in
altitude.
The theoretical quantity of oxygen per ton of copper produced can be
calculated. However, excess air of around 50 percent at 12 to 15 psi is
supplied to the converter and the volume is approximately 150,000 acf/ton
of blister produced. Both the theoretical and actual amount vary with the
g.'ade of matte used. For' the converter schedule outlined in Table 24.1,
approximately 9,000,000 acf of air are required per cycle with an average
flow rate of 15,000 acfm during the 10.1-hr blow period. The use of oxygen
enriched air results in a substantial decrease in air requirements.
Infiltration of dilution air is permitted at the hood covering the
mouth of the converter in order to cool the hot gases. For air cooled
hoods, dilution air can be as much as four times the actual converter gas
volume. In the case of tight fitting water cooled hoods, the dilution air
may be only half the volume of the converter gas.
Operating temperatures within the converter are closely controlled
in the range from 2,200 to 2,300°F by adding cold material to the oxidizing
material as required. After dilution the flue gas temperatures are in the
range 600 to 700°F with properly adjusted hoods. With excess dilution the
temperatures are lower.
-218-
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TABLE 24.1
TYPICAL OPERATING SCHEDULE FOR A
CONVERTER BATCH USING A 40% MATTE
Work Done
Charge 6 tons matte shells
Charge 6 ladles (72 tons) matte
Charge 12 tons ^^ij-ca flax
Skim 3 pots (27 tons) slag
Charge 2 ladles (24 tons) matte
Charge 4 tons converter cleanup
Charge 8 tons silica flux
Skim 2 pots (18 tons) slag
Charge 2 ladles (24 tons) matte
Charge 6 tons copper slag
Charge 7 tons silica flux
Skim 2 pots (18 tons) slag
Charge 1 ladle. (12 tons) matte
Charge 3 tons matte shells
Charge 6 tons silica flux
Skim 2 pots (18 tons) slag
Charge 1 ladle (12 tons) matte
Charge 5 tons silica flux
Skim 1 ladle (9 tons) slag
Final Blow
Skim 1 ladle (9 tons) slag
Charge 4 tons scrap copper
Blowing to copper
Charge 1 ton 90% silica flux (to remove lead)
Blow to high blister
Skim oxidized slag (6 tons) .
Transfer copper to pouring ladle
Cleaning tuyeres, silica gun and adding new matte
charge
„ v t Cumu-
Converter Not . .
Blowing Blowing Time
Hr.
1
-
1
-
1
-
-
-
1
-
-
-
3
-
-
-
-
Min.
30
-
15
-
05
-
55
-
-
-
20
-
45
15
-
-
-
Hr.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Min.
-
15
-
10
-
10
-
10
-
5
-
10
-
-
5
15
20
Hr.
-
1
3
3
4
4
5
5
6
6
6
7
10
11
11
11
11
Min.
-
45
-
10
15
25
20
30
30
35
55
05
50
05
10
25
45
Total time
Total matte
Total silica flux
Total cold material
Total blister produced
Total slag produced
10
05
11
1 40
144 tons
38 tons
17 tons
60 tons
11 pots or 99 tons
45
-219-
-------
The operating variables for a given converter and gas recovery system
are the quantity and tenor of the matte, the converter charging and blowing
schedule, operating temperature and quantity of dilution air. All but the
last of these are carefully controlled by the metallurgist in charge to
produce the most desirable and economical product. Only the quantity of
dilution air is outside the purview of the metallurgist and subject to
other considerations. With acid plant SO. recoverv systems dilution air
will be reduced to a minimum commensurate with the requirement for cooling,
but without acid plant recovery systems dilution air will increase to a
maximum commensurate with flue and air cleaning capacity.
24.3 Enforcement Procedure
Emissions from the converter consist of sulfur dioxide gas and par-
ticulates. The gas composition is on the order of 4 to 6 percent SO™.
The dust loading is on the order of 3 to 10 gr/scf. Air pollution abatement
i
equipment is used on almost all plants to remove the dust and many plants
have sulfuric acid recovery facilities to remove sulfur dioxide from the
gas stream.
The objective of copper converter operation inspection is to estab-
lish compliance with the sulfur dioxide and particulate emission regulations.
In order to accomplish the above objective, the enforcement official needs
to determine:
1. Current production levels and operating conditions,
2. Design production levels and operating conditions,
3. Current controlled and uncontrolled particulate and sulfur
dioxide emission levels,
4. Efficiency and adequacy of emission control equipment at current
and design levels.
-220-
-------
Converter and converter emission control equipment design capacities
and operating conditions can be obtained from design drawings and plans.
These data should be obtained from the company representative prior to
plant inspection. Production levels, converter feed weight rates and
emission control equipment operating conditions are monitored by the
plant operator and are either recorded in the operator's daily log or are
displayed on the instrument panels.
Converters may have a control booth near the unit for process moni-
toring. The enforcement official should have little difficulty assessing
the current operating status of the converter by observing the many re-
corders, gauges and log sheets which are normally kept.
Of primary importance for the enforcement of air pollution emission
regulations is the process weight. With the mass rate and sulfur content
of the feed, the SC^ emissions can be computed (assume negligible content
in copper and slag).
There is little that can be noted on instrument panels regarding the
amount of particulates emitted to the atmosphere, although some plants
will have a smoke density meter which may be used to determine relative
particulate emissions from one visit to another. The enforcement official
shouls note the operational parameters of the air pollution control devices.
Visible emissions are the simplest means for estimating particulate
control equipment performance. The enforcement official should estimate
the percent opacity of dust control equipment stack plumes and if in ex-
cess of allowable limits, take appropriate action.
-221-
-------
Building openings should be observed for evidence of escape of in-
adequately captured process dust and if noted, determine point(s) or origin
and require corrective action.
The enforcement official should complete the Inspector's Worksheet
for the converter.
-222-
-------
INSPECTORS WORKSHEET
FOR COPPER CONVERTERS
Plant Id.
Date of this Inspection Date of last Inspection
No. of converters
Total capacity tons/hr Feed tons/hr copper
Type of converter
Sulfur content of feed %
ABATEMENT EQUIPMENT - Particulates
Pressure Drop in. 1^0
Flow rate scfm
Inlet Temperature °F
Spark Rate spm
Collection Efficiency 7° Grain loading gr/scf
Year Installed
Opacity reading on stack %
DIAGRAM OF CONVERTER, PARTICIPATE CONTROL EQUIPMENT S02 PLANT AND STACK
(Use separate sh^et if necessary.)
GENERAL OBSERVATIONS:
Is hood volume adequate"?_
S02odor?
LeaksP holes, etc.?_
Time In Time Out
-223-
-------
-------
PART IV. LEAD SMELTING
Lead mining and refining ranks as the fifth largest basic metallur-
gical industry. Lead is one of the most useful metals, its major uses
include automobile storage batteries, gasoline additives, building and
construction, and small arms ammunition. Lead is also considered to be
a strategic and critical material and is one of the stockpiled metals.
Essentially all lead ores are mined underground and are concentrated, or
beneficiated, at the mine site. The common lead minerals are galena
(lead sulfide), cerussite (lead carbonate), and anglesite (lead sulfate).
Galena is the most abundant lead mineral and is usually found associated
with zinc, silver, gold, iron, and other minerals.
The domestic lead supply is derived from domestic mine production,
imported ores and concentrates, imported metal, and secondary domestic
production. The 1968 apparent demand of 1.4 million tons was supplied
as follows: domestically refined primary lead - 35 percent, imports -
24 percent, secondary domestic production - 39 percent, and the remaining
2 percent from government stockpile releases.
Table IV-1 shows the 1968 U. S. lead smelters and refineries and
their salient process identification.
The anticipated annual demand growth rate is about two percent and
the forecast demand for the year 2000 ranges between 2.5 to 4.1 million
tons. Environmental and economic considerations and changing use patterns
could have major impact on the consumption patterns and demand rates.
-225-
-------
D
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-226-
-------
Copper, gold, silver, and zinc are the major co- or by-products of
lead production. The minor by-products consist of antimony, bismuth,
cadmium, arsenic, sulfur, tellurium, gallium, germanium, indium, selenium,
and fluorspar. Concentrator tailings may be used for highways, railroads
and agriculture. Smelter slags are valued as construction material.
There are several terms and grades that define lead in terms of
degree of purity, composition of impurities, and the size and shape of
the product marketed.
Refined lead is 99.85 percent pure and is marketed in seven grades:
corroding lead, chemical lead, acid lead, copper lead, and common de-
silverized lead; also antimony and tin alloys are classified as anti-
monial or hard-lead, white metals, fusible alloys, and copper alloys as
leaded brasses or bronzes. The final product may be 1-ton blocks, 100-
pound lead pigs, 25-pound caulking lead strings, powder form such as
litharge and red lead oxide, or liquid tetraethyl lead.
Primary lead production is a sequence of physical-chemical processes
that involves the mining and concentrating of the naturally occurring
lead mineral, mostly as sulfide, the preparatory steps that are necessary
for reducing lead to the metal form, the pyro-reduction process itself
and the subsequent lead purification or refining.
25. MATERIAL HANDLING
The possible emissions will be particulates. Fugitive dust regula-
tions will govern.
25.1 Process Description
Material handling is an important aspect of lead production in
terms of bulk, diversity of equipment as well as the magnitude of the
-227-
-------
problem associated with airborne particulates and their control. Lead
production is the process of separating 5 to 7 pounds of lead from about
100 pounds of mine ore.
Lead ore is mined underground and then transported to the surface
where the first and most substantial bulk reduction, ore concentration,
normally occurs. The concentrating, or milling operation consists of
ore size reduction by grinding, crushing, and separation. Feeders con-
vey the ore to large bins for blending and storing. Further size reduction
takes place in wet-ball mills. The silt-like ore from the ball mill is
classified and separated from coarse material and is pumped as a water
slurry to flotation cells where the pulp is conditioned by additives.
Large propellers stir the solution and the lead bearing minerals separate
and float to the surface where they are skimmed off. The non-lead portion
of the slurry, called tailings, is treated in cyclone separators to re-
move fines from the sand. The clean sand then may be pumped back into
the mine and the fines to a settling pond.
Once separated, the ore concentrates are thickened in settling tanks
and the slurry is fed to vacuum drum filters which reduce the moisture
content to about seven percent. The concentration is now complete and
the lead content has been upgraded from an average of 5 to 7 percent to
about 65 percent.
The concentrates are transported to the smelter site and are stored
in bins. Proper proportions of concentrates, fluxes, coke breeze, sinter
dust, and crude ore, as necessary, are mixed and pelletized. Conveyor
belts carry the pelletized mixture to the sintering unit, which removes
most of the sulfur by roasting, and agglomerates it into a porous mass
-228-
-------
called sinter. The fused sinter is crushed and the dust recovered and re-
cycled. The sinter, now ready for the blast furnace, is mixed with coke
and is conveyed to the blast furnace.
Blast furnace products consist normally of four liquids that are dis-
charged from the bottom: lead metal, matte, speiss, and slag. The lead
usually goes to refining, and the matte and speiss to the dross furnace.
Slag is removed separately to the fuming furnace for recovery of lead
and zinc. Some slag from the fuming furnace may be recycled, the rest
goes to waste. The dross, matte and sepiss from the lead refinery goes
to the reverberatory furnace where lead is recovered and recycled; matte
and speiss are then shipped to a copper smelter for copper recovery.
Lead metal is further refined in kettles where other metals and trace
materials are recovered. The final product is refined lead.
Some lead smelters operate such other equipment as cadmium roasters,
deleading kilns, and slag fuming furnaces. Some slag from the fuming fur-
nace, where lead and zinc are recovered, may be recycled but the rest goes
to waste.
The material handling equipment may include such primary means of
transportation as rail, truck, ships, barges, and pipelines. The secon-
dary and more highly specialized equipment includes conveyors, overhead
cranes, clamshell loaders, and cars. Modes of material storage include
piles, bins, hoppers, kettles, settling tanks, and ponds. Process equip-
ment includes crushers, grinders, ball mills, vibrating screens, vacuum
filter drums, sinter machines, and furnaces. Figure 25.1 depicts princi-
pal emission points. Tables 25.1 and 25.2 summarize the pertinent lead
-229-
-------
TABLE 25.1
LEAD BLAST FURNACE DATA
Furnace Data
Length and width at
stock line, inside
Length and width at
tuyere line, inside
Height, tuyeres to
feed door
Distance, tuyeres
to slag tap
Depth of hearth
Suiglt; or double
tier of jackets
Height of water
Jacket zone
Number and size
of tuyeres
Type of top
Number of settlers
before stag pot
Operating Data
Volume of blast
per minute
Pressure of blast
Volume of cooling
water
Temperature of
water overflow
Charge Data
Total wt. per 24 hr.
exclusive of coke
Per cent sinter
in charge
Per cent lime rock not
included in sinter
Other constituents of
charge, kind and wt.
Per cent of lead
In charge
exclusive of coke
Per cent of coke
per .cent of charge
Product Data
Slag, wt. per 24 hr.
Method of disposing
of slag
AS.fcR.
No. 1
16 ft. 10 in. x 8ft.
16 ft. 10 in. x 48 in.
27 ft. 10-1/2 in.
13-1/2 In.
6 in. below slag tap
Double
8 ft 6 in.
15 per side, 4 in.
Thimble
Two
7500-9000 cu. ft.
35-50 oz.
1500 gal. per min.
100-110° F.
440 tons
70-80
5-10
Leady siliceous ore
10-12 pet.
Scrap Iron 3.5 pet.
26-28
13
275 metric tons
Dumped hot
AS.&R.
No. 2
16ft. x 6 ft. 9 in.
16ft. x 48 In.
24 ft. 1 in.
11 in.
3 ft. 7 in. (2 furnaces)
3ft.l in (1 furnace)
Single
6ft 4-1/2 in (2furnaces)
6ft. 6 in. (1 furnace)
28 4-1/2 in.(2 furnaces)
24:4-1/2 in (1 furnace)
Open
Two
7200 cu. ft.
40 oz.
250 gal per min.
100° F.
470 tons
86
None
Settler slag 4 pet
Plant byproducts3pct.
Zinc plant residues
7 pet.
24
10 regular
3 scrap
3 10 tons
Zinc fuming furnace
A.S.&R,
No. 3
15 ft. 3 in. x5 ft. 8 in.
15 ft. 3 in. K 5(1.6 in.
27ft.
14 in.
21 in.
Double
9 ft.
24-4 in.
Thimble
Two
7500 cu. ft.
40-45 oz.
850 gal. per mm.
140-160° F.
450 tons
85
None
Foul slag 15 pet.
Scrap iron 3 pet.
30
11
275-300 tons
Zinc fuming furnace
AS &R.
No. 4
16 ft. 10 in.xS ft. 6 in.
16 ft. 10 in. x 4 ft.
28 ft. 3 in.
9 in.
2 ft. 3 in.
Single
6ft. 9 In.
29 - 2-1/2 in.
Thimble
Two
0000 cu ft.
46 oz.
500 gal. per min.
100° F.
457 tons
458
11.9 pet.
Scrap iron 3 8 pet.
Siliceous ores 29 2 pet.
Foul slag 9 3 pet.
17.4
12.5
290 tons
Dumped hot
A.S 4R.
No. 5
15 ft. 3 in x6 ft 2 In.
15 ft. 3 in.x4 ft. 6 in.
24 ft. 6-1/2 in.
15 in.
2 ft. 6 in.
Single
7 ft.
24 - 4 in.
Thimble
Two
7200 cu ft.
45 oz.
"
190° F.
550 tons
95
0.2 pet. of total
lime rock used
Foul slag
16 tons - 24 hr.
Scrap iron
8 tons - 24 hr.
30
9.5
245 tons
Dumped hot
Bullion, total wt.
per 24 hi
Before dross ing
After dressing
Wt. dross per 24 hr.
What additions are
made to dressing
kettle?
Wt. primary matte.
If any
Wt primary speiss,
if any
Dross Furnace Data
Wt dross charged
per 24 hr.
Kind and wt. of
other additions
per24hr.
Wt. matte -speiss
produced per 24 hr.
Wt. slag produced
per 24 hr.
—
110 tons
85 tons
Soda ash, coke,
litharge, sulfur,
for decoppenzing
None
3 tons per day
85 tona
Additions made
In dross ing kettle
45 tons
30 tons
None
115 tons
90 tons
25 tons
300 Ib. S
for decopperlzing
per 60 tons bullion
None
7 tons per day
70 tons
4 pet soda ash
1 pet. coke breeze
45 tons
8 Ions matte
15 tons speiss
None
265-275 tons
175 tons
90-100 tons
Salt cake 5 pet.
crushed coke 3 pet.
None
None
00-100 tons
Additions made
in dressing kettle
60 tons
25 tons matte
23 tons apeiss
None
188 tons
150 tons
38 tons
130 Ib. 3
per 55 tons bullion
Sawdust
None
3 tons per 24 hr.
43 tons
Miscellaneous furnace
speiss 22 tons
siliceous ore 1.5 tons
23 tons
35 tons
6 tons
220 tons
151 tona
68 tons
Petroleum coke
Soda ash
None
10 tons per 24 hr.
77 tons
Additions to dressing
kettle + 1/2 ton
litharge
50 tons
21 tons
None
-230-
-------
Bunker Hill
Ktllon, IiUho
Furnace No. 3
Bunker Hill
Kellogg. Idaho
Furnaces 2 & 4
CM. 8,3.
Trail, B.C.
International
Tooele, Utah
St. Joseph Lead
Herculaneum, Mo.
VS. Smelting
Mldvale, Utah
21 It. X 5 ft. 8-1/2 In.
21 It. x 5 (t. 9-1/2 In.
11 It. 4 In.
10 In.
1 ft. 8 In.
Triple. 2 vertical
1 Inclined
19 R.
SB - 2-1/2 In.
Vertical center gas
take-off charge fed at
sides of take-off
One when slag goes
to fuming furnace.
Two when dumped
15 It. X 3 II. 9 In.
15 ft. X 4 ft.
19 ft. 4 In.
14 In.
1ft. 2 In.
Double tier
boshed out
13ft.
20 - 4 In.
End gas take-off.
Center dump feed.
Splitting rail
Same as No. 3
11,000 cu.lt.
26 - 34 02.
ISO gal. per min.
reclrculated
175° F.
350-650 tons
10-80
1-1/2 - 3 pet.
6000 cu. ft.
18 - 24 oz.
350-450 gal.
per min.
75-175" F.
240-370 tons ' •
70-80
1-1/2 -3 pet..
Foul slag 0 - 1/2 pet. Reverb. dross 0-1 pet.
Misc. 0-5 pet. Zinc plant residue 10 - 25 pet.
Dump slag 5-10 pet.
25-40
10-12
25-40
10-14
400-450 tons (2 furnaces)
To slag fuming or dumped hot
Length, 3 8 15 ft.
2 S 22 ft. 6 In
Width, 29 6ft. 4 In.
2 0 6 ft. 10 In.
1 § 10 ft.
Length, 3815 ft.
2 ft 22 ft. 6 In.
Width, 1 6 4 ft.
2 § Sit. 5 In.
lg 611.8 in.
10 84-96 In.
17 ft.
14 In,
2 ft. below bottom
of tuyeres at lead
well only
4 with 2
1 with 1-1/2
4 8 13 ft.
1 9 9-1/2 ft.
2 with 48 - 2-1/2 In.
2 with 72 - 2-1/2 In.
1 with 59 - 2-1/2 In.
Hooded with
central off-take
One
IS ft. X 7 ft. 9 In.
15 ft. x 4 It. 4 in.
24 ft. 8 In.
13 In.
2 It. 7-3/4 In.
Double
15ft.
24-4 In. on sides
2 - 3 In. at back
1-2 In. at front
Open
Two
2g1000cu.lt.
1 6 8000 cu. ft.
2 S 9000 cu. ft.
34 - 36 oz.
50 gal. per min.
Nesmlth Vaporizer
1760 F.
350-550 tons
depends on furnace size
87
None
Pot shells 6.3 pet.
Settler cleanings 1 .9 pet
Miscellaneous 4.8 pet.
31.2
11.5
675 tons new slag
930 total
Zinc fuming furnace
8500 cu. ft.
45 - 54 oz.
"
150-180° F.
• 550-590 tons
90
0-4 pet.
B.F. cleanings 3 pet.
Bag house fume
1-1/2 pet. Conv.slag
1 pet. Ore 4 pet.
Scrap ironO 5-2.5pct.
20-30
10 - 11-1/2
325-360 tons
Zinc fuming furnace
16 ft. x 6 ft.
16 ft. x 5 ft.
19 ft. 5 In.
14 In.
2 ft. 4-3/4 In.
Single
12ft.
24 - 5 In.
Open
One
7000 cu. ft.
32 - 36 oz.
205 gal. per min.
-
486 tons
71.5'
None
Slag 24 pet.
Wind box lead 20 pet.
Dross 50 pet.
Pore hearth clean ings 5.
49
8.5
195 tons
Granulated
15 ft. 4 In. x 5 ft. 5 In.
13 ft. 4 In. x 4 ft.
24 ft. 7-1/4 in.
11 In.
2 ft. 9 In.
Single
( ft.
20 - 5 In.
Open
Two
8000 cu. ft.
40 oz.
480 gal. per min.
1470 p.
575-625 tons
60-96
1-3 pet.
Scrap iron 4 pet.
Siliceous gold ore
1 - 5 pet.
24-28
9-10
375-425 tons
Granulated
180-265 tons (2 furnaces)
170-240 tons (2 furnaces)
10-25 tons (2 furnaces)
15-25 tons coal per 100 ton kettle
100 Ib. S per 90 tons bullion
None
4-10 tons per 24 hr. (2 furnaces)
60 tons
1-3 pet. silica 1 1 Pet. coke. Add
antimony skim to soften crusts
when necessary
25-95 tons
15-20 tons
5-10 tons
415 tons
400 tons
15 tons
None
None
None
45 tons
Dross furnace operated
3-4 months yearly
None
13 tons
15 Ions
9.5 tons
150-230 tons
110-180 tons
50-85 tons
Salt cake ,coke breeze
Finish with 500 Ibs.
to 120 tons Pb
None
None
50-80 tons
Added in dross
kettle
30-45 tons
4-4-1/2 tons speiss
5-5-1/2 tons matte
Kone
217 tons
168 tons
49 tons
None
19 tons per day
None
No dross furnace
--
<
--
-
130-170 tons
105-134 tons
33-39 tons
Pyritc and sulfur
None
4-8 tons per day
33-39 tons
400 Ib. S + 300 Ib.
pyrlte per 30 tons,
stirred in kettle.
24 Ions
10-12 tons
2 tons
-231-
-------
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-232-
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CO
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-233-
-------
blast furnace and sintering machine equipment data, respectively, by
companies for 1968.
Figure 25.2 shows a typical material flow diagram of the total pro-
cess involved in lead production.
Of primary concern in material handling is the containment and con-
trol of fugitive dusts which are generated when sufficiently fine size
material is exposed to moving air. Such material may be stationary or
in transit. Most dusts become airborne during periods of loading and
unloading at points of transfer.
25.2 Process Control Operation
There are two effective and widespread imethods of dust control:
water sprays and physical capture and confinement by such means as hoods
and other enclosures.
Some of the most important variables affecting dust emission into
the air are particle size and density, the relative velocity between par-
ticle and air, and the surface area exposed to air per unit volume of
dust. Total emission control includes, in the final analysis, the manip-
ulation of all the variables affecting emission rates.
Table 25.3 is a summary of the principal materials involved in lead
production. It is relatively simple to identify the major material
handling process variables, namely mass flow rates, composition, size
distribution, plant physical layout, and material flow paths at an
individual plant.
-234-
-------
Lead - Siliceous Crude Zinc plont
concentrate I ore* I ere* I residue 1 Limerock
r "~
AUTCX
1
L
j 1
Pressure leochinq •
1
1 ^ CuSO^, ZnSOj solution I
I LAVE extraction and electrolytic!
1 ' 1
jPbSO^ residue
|
1 , i
* These products ore all crushed ond
ground in a rod mill to -1/8 in. size
*
Return
sinter
Coke
ITHARGE PBFPARATION |
[PELLETIZING ]
t
Slogshell
Sinter
Refinery drossei
t
Low-grade ZnO
Cool
Leaded
zinc oxide
to market
FUMING PLANT
"Zinc oxide
_L
TT=HDE LEADING KILN!
PbO I—— ...... . - J
Deleoded zinc
oxide to market
Dezinced granulated ^
slog to storage
•J BLAST FURNACE^
-Slag
^ Puff
Bullion
Concentration for cadmium-.
extraction electric furnace
Copper dross
DROSS KETTLES
I
Bullion
Bullion
BY-PRODUCT FURNACE
Slag to
blast furnace
Matte
Speiii
Slag to blast furnace
[SOFTENING FURNACE}
I ^
Bullion Joe
Granulation
-Parkes gold crust-
Parkes silver crusr-
Slog to
blatt furnace
Gold dor< Fine silver
to market to market
1 —
A
Antimony skim
i
rialle and sp
to market
Coke
Ir
Fume
Baghoute
Stock
Fume •
[ELECTRIC FURNACE!
t T~^
Slag to Bullion
blast furnace
PbO
| STORAGE
{.EACH
TANkj
| REFINING KETTLE |
J
Casting
Hard lead
to mart*!
Cadmium sponge to 4
electrolytic refining
FILTER "I
Zinc
J
t«b
furn,
PRECIPITATION
TANK
FIGURE 25,2 LEAD PRODUCTION PROCESS FLOW DIAGRAM
-235-
-------
Table 25.3 PRINCIPAL MATERIALS OF LEAD PRODUCTION AND
THEIR ESTIMATED RELATIVE QUANTITIES
Material Weight
(tons)
Lead ore 100
Ore concentrate 15 to 20
Ore tailings 80 to 85
Lead metal 5 to 7
Blast furnace slag 8 to 15
Slag fuming furnace slag 7 to 14
Fluxes and additives
Coke 1 to 2
Speiss and matte 2 to 3
Other 2 to 3
25.3 Enforcement Procedure
The following enforcement procudure lists general observations which
can be made of materials handling schemes at lead plants. At many integrated
plants, fugitive dust losses may account for more atmospheric emission of
particulate matter than the sintering and blast furnaces which have air
pollution control equipment. Because of the different methods of handling
raw materials, product, and tailings, the following general guides are
suggested:
1. Trace the flow of raw materials from the time they arrive at
the plant until they enter the blast or reverberatory furnaces.
2. From a distance observe the raw material and processed materials
for dust clouds either from roadways, stock piles, transfer
points, crushing and screening operations, slag dumping,
-236-
-------
plant construction activities, etc. These sources are
generally not continuous emitters, but depend on the activity
schedule.
3. Make records of the dusty areas for a close-up inspection.
These observations should be made from beyond the plant peri-
meter on a hillside overlooking the entire complex, if possible.
4. Observe the raw material stock piles when the wind is blowing
and note any entrained dust.
5. Observe the material moving methods at the stockpiles.
6. Note any dust emissions at the bulk unloading stations.
7. If cranes, belts, or bulldozers are used to move the raw ma-
terials, note any major dust clouds.
8. Make notes on the lengths and locations of unpaved roadways.
Ask if, and at what frequency, these roadways receive dust
preventive treatment such as the application of water, oil, or
calcium chloride. Observe the paved, macadamized and gravel
roads for latent dust. Occasionally these roads may become
burdened with dust and result in another source for fugitive
dust.
9. Observe the transfer points along belt haulage ways. If no
dust is noted, no further inspection is required here.
The Inspector's Worksheet which follows may be useful for record
keeping. Interpretation of these observations is dependent upon the per-
tinent regulations governing fugitive dust emissions. Since many of these
plants are located on large plots of land, it is important to discriminate
between in-plant housekeeping problems and emissions which cross the prop-
erty line.
-237-
-------
INSPECTORS WORKSHEET
FOR_RECEIVING. STORING AND HANDLING OF RAW MATERIALS
Plant Id.
Date of this Inspection_
Type of Plant
Date of last Inspection
Capacity of Plant_
Type
Source Location Material
Wind
Direction
Wind Speed Preventive
(mph) Plume Description Measures
Sample
Concentrate belt
loading
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
ore
concentrate
SW/10
slightly visible
dust
none
-238-
-------
26. CONCENTRATE DRYING
The possible emissions will be participates. Likelihood of emissions
is remote.
26.1 Process Description
The concentration operation for these various smelting processes is
employed to separate sulfide minerals from waste rock. The drying mechanisms
used to remove moisture from concentrate ores for lead production are gen-
erally not heated. Thus, the air pollution potential from this source is
minimized. Most of the concentrate drying processes at lead plants use fil-
tration drums to draw as much water from the concentrated ores as possible.
This is done at room temperature and with no heat being added to the drum.
The raw ore arrives at the plant and is stored in various silos and
bins for further processing. The ore may come from barges, shipping ves-
sels, underground mines, or railroad cars. The material handling system
is likely to have the most air pollution emissions at the concentrate
building. Moisture content for the raw material is about 3 percent. The
raw ore is then screened, crushed, and ground and sent through a flotation
process to separate zinc ore and lead ore. Figure 26.1 shows a typical
concentrator at a lead production plant. The final lead concentrate will
assay about 67 percent lead, 5 percent zinc. The average moisture content
of the filtered lead concentrate is 7 percent. Tailings from the lead
concentrate assay will average about 55 percent zinc. The zinc concen-
trate filter cake has an average moisture content of about 10 percent.
26.2 Process Control Operation
Very few air pollution emissions occur from the lead concentrate
operation. The concentrator plant is usually located away from the blast
-239-
-------
CO
CNJ
UJ
-240-
-------
furnace and sintering operations in a separate building. The few emis-
sions that do occur from this operation are the result of the material
handling of the bulk ores. Generally speaking, no air pollution control
devices are installed at the concentrator plant. There are no detrimental
off gases of any concern from the concentrate operation. The concentrate
dewatering takes place on a filter drum at room temperature and emits
nothing to the atmosphere.
26.3 Enforcement Procedure
The enforcement official should make a subjective type evaluation
of the material handling system for the concentrate building. It is un-
likely that any of the ore will be entrained by air and present a fugitive
dust problem. The enforcement official should check the transfer points
and the enclosed system of the storage hoppers.
The enforcement official should make note of the amount of material
processed through the concentrate building for future comparisons. No
atmospheric testing needs to be done at this particular process during the
enforcement official's inspection visit.
If fugitive dust violations are apparent, take appropriate action.
27. CONCENTRATE SINTERING
This is the major point of sulfur emissions in the lead smelting
process; however, individual plants may have sulfur recovery units. It
is also a possible major source of particulate emissions if control equip-
ment is not functioning properly.
27.1 Process Description
Sintering is a chemical and physical process that converts metal
sulfides to metal oxides and fuses the concentrate into a porous mas's,
-241-
-------
called calcine, that is suitable for reduction in a blast furnace. The
main chemical reaction taking place on the sintering machine is the oxi-
dation of lead and other metal sulfides. Heat is generated by these re-
actions and the oxidation is self-sustaining. Fuel, usually natural gas,
is required to initiate the reaction. Process temperatures are kept below
1,400 F to prevent excessive loss of metals by vaporization, fusion of the
clinker, and damage to the grating of the pallets.
The feed to the sintering machine consists of pelletized mixture of
lead sulfide concentrate, high silica lead ores, recycled dust, coke
breeze and fluxes. The flux usually consists of high grade limestone,
silica and some steel scrap. The lead concentrate generally has 55 to
70 percent lead, 13 to 18.5 percent sulfur, up to 6.5 percent zinc, 0.5
to 4.0 percent copper, up to 5.0 percent iron and minor amounts of silica,
lime, silver, gold, arsenic and others, depending on the source.
The pelletized feed is loaded on the continuous conveyor, is ignited
and combustion is sustained by supplying air to the pellets. Combustion
gases are removed, usually through sectionalized wind boxes, and the clinker
cakes drop to a coarse breaker and screen at the discharge end of the ma-
chine. The oversized material is crushed and the fines are recycled to
the feed end of the machine. The product is a fused porous sinter which
contains most of the metals as oxides.
Off gases may contain 0.8 to 1.8 percent sulfur dioxide. This repre-
sents about 85 percent of the total sulfur present in the feed; solid
b,-products account for about 14 percent and the remaining one percent is
distributed between blast and dross furnace effluents. In addition to
sulfur oxides, the gases may contain air, water vapor, carbon dioxide,
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hydrogen fluoride, silicon tetra-fluoride and traces of other gases. Or-
ganic vapors from flotation reagents are also present. Fumes include the
more volatile metal oxides such as arsenic, cadmium, selenium, and tellur-
ium. Elemental sulfur may also be present. Fumes are condensed and col-
lected with the dust. If the cadmium content reaches 12 percent or more,
portions of the dust may be diverted to cadmium furnace. Off gas flow
rates vary from 100 to 220 scfm per square foot of bed area.
Table 27.1 shows some emission rates from lead sintering machines.
Table 27.1 EMISSIONS FROM LEAD SINTERING MACHINES
Emission Rates
Plant No. (a)
326.09
1st stage
2nd stage
326.10
326.17
326.18
326.33
326.34
Estimated
Capacity for
Lead Production
(tons/yr)
76,000
n.a.
n.a.
122,000
198,000
120,000
91,000
42,000
Off Gas
Flow Rate
(scfm)
8,200
n.a.
32,400
34,000
35,500
n.a.
n.a.
Temperature
(°F)
300
n.a.
400
300
350
300
350
Sulfur
Equivalent
of Sulfur
Oxides
(tons/yr)
19,200
36,200
39,100
28,500
33,800
13,500
Dust
Recovered
(tons /day)
--
--
22
—
--
--
(a) From Systems Study of Arthur McGee.
A sectionalized windbox is installed beneath or above the pallet grate
to regulate burning rates. Gases are drawn through the windbox into
ducts leading to dust collection equipment. The reported sinter off gas
temperatures range between 300 and 400 F. The collected sinter gases
may be cooled by air dilution and conditioned by water quenching to pre-
pare for dust collection by filtration or precipitation. After the dust
collector the gases are either vented or fed to a sulfuric acid plant, in
which case the high sulfur dioxide content gas is processed separately.
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Sintering machines range in size from 3.5 by 22 feet to 10 by 103 feet
and in capacities from 1.5 to 2.75 tons of charged material, 12 to 18
inches deep, per square foot of bed area per day. In most of the older
and smaller machines, air is introduced from above and flows through the
ore bed on the conveyor and captured in the windbox and duct system un-
derneath. These are known as down-draft machines. The newer and larger
machines, in which the air flow is the reverse, are known as up-draft
machines„ Figure 27.1 shows the process of a sintering unit.
Following the sinter machine the sinter is crushed to usable size
and transported to storage or to the blast furnace. The fines are re-
turned to the feed-end of the sinter machine where they are blended into
the feed.
27.2 Process Control Operation
The most important process variable in the sinter machine is the
temperature. Temperatures exceeding 1,400 F are to be avoided to prevent
excessive loss of metals by volatilization, fusion of the clinker and
damage to the grating of the pallets. To a limited extent, temperature
control is achieved by limiting the sulfur content between 6 and 12 per-
cent. Once oxidation is started, it becomes self-sustaining because the
process is exothermic. Sulfur content is regulated by mixing with sulfur-
free fluxes, such as silica, limestone, fume furnace slag and sinter.
Excess air flow regulation provides additional control.
Relatively high dust carry-over is expected during the period of ig-
nition and initial stages of the oxidation , especially if high or excess
flow rates occur. Initially, when the feed is relatively cool, sufficient
air (oxygen) is required for optimum reaction and later, when the feed
fuses and reaches the upper temperature limit (1,400 F) , excess air is
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csi
LU
a:
:^
CD
OJ
O
CO
o
-245-
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required to provide cooling. Volatilization of most metals occurs in
the upper temperature ranges which is most likely to occur at low air
flow rates. Sulfur dioxide emission is expected to reach maximum then
tail off toward the end of the process. This process characteristic
may be utilized to isolate high sulfur dioxide gases for acid plant
processing.
Emission rates and concentrations can be expected to vary with feed
composition, type of equipment used and operating skill. Particulate
size distribution is also influenced by these factors.
The sinter crushing and screening operations at the machine-discharge
have enormous particulate emission potential. These operations ill be
hooded and ducted to a control device.
27.3 Enforcement Procedure
The objectives of lead concentrate sintering operation inspection
are to determine sulfur dioxide and particulate emission levels from the
sintering operation and to evaluate the pollutant emission potential of
this operation for varying production rates and operating conditions.
In order to accomplish the above objectives, the enforcement official needs
to determine:
1. Current production levels and operating conditions,
2. Design production levels and operating conditions,
3. Current controlled and uncontrolled particulate and sulfur
oxide emission levels,
4. Efficiency and adequacy of emission control equipment at cur-
rent and design operating levels.
Both sintering machine and emission control equipment design capa-
cities and operating conditions can be obtained from design drawings and
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plans. These data should be obtained from the company representative
prior to physical plant inspection. Production levels, sintering machine,
and emission control equipment operating conditions are monitored by the
plant operator and are either recorded in the operators' daily log or are
displayed on instrument panels.
The enforcement official should obtain specific information regarding
the plant layout and plant capacity prior to his inspection of a sintering
operation. Some of the operating variables of importance are:
1. The total feed rate to the sinter machine - these data are
necessary in comparing process weight rate to allowable par-
ticulate emissions from industrial operations,
2. The percent sulfur content of the feed ore - most sintering
plants will have these data readily available from previous
ore assays, and,
3. The percent sulfur content of the sinter.
t
Many sintering plants will have sulfur oxide monitoring equipment
on the sintering machines at various stages along the bed. This infor-
mation may be used as a check against the sulfur oxide emissions calcu-
lated from the feed concentrate and sinter product sulfur mass balance.
When sulfur recovery systems are used, performance data are needed. If
valid information is not available from the plant operator, the enforce-
ment official may elect to spot test the recovery system efficiency by
means of indicator tubes (Part VII).
Visible emissions are the simplest means for estimating particulate
control equipment performance. The enforcement official should estimate
the percent opacity of the dust control equipment stack plumes and if in
excess of allowable limits, take appropriate action. Building openings
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should be observed for evidence of the escape of inadequately captured
process dust. If noted, determine poin't(s) of origin and require cor-
rective adtion.
The enforcement official should obtain off gas temperatures, tlow
rates, sulfur oxide concentration, particulate concentration, opacity,
and other operating data that he can relate from one visit to another.
Upset renditions at Wintering machines can cause elevated notential
emissions, depending on tht parfclcuiate control eauipmeatrused, this
could result in elevated particulate emissions. For example, a hole may
develop in the sinter bed as a/result of an improper distribution of t-he
ore on the sinter bed. |.tiis hole will prevent complete sulfur ojx-tdation
and result in a small quantity of high sulfur content sinter. Continuous
strip charts which record bed pressure on each wind box are available at
most sintering ptaflts. A sharp decrease in pressure on the strip pftarts
wotrlcf indicate that a hole has occurred. The major potential problem
with frequent holes in the bed, over a** fvfcetided period, is elevated par-
ticulate emission potential. TJie''operating record strip charts can be re-
viewed tc est'ablish^this'otJerating problem/. If a baghouse is used as the
control device there is 1 it-tie likelihood of exceeding allowable emissions.
If an electrostatic precijpitator is the /jontrol device, stack tests may bi
required to ^stablish emission data.
The enforcement official should complete the Inspector's Worksheet
for IjKaJ sinter plants and make the calculations for total sulfur1 emis-
sio'ns rrutn this oper/ation. It should be pointed oflt that although most
of the sulfur from lead smelting is emitted trom the .winter plants,
many state air pollution emissions standards are Rased on total
sulfur emission from the sme^tiijg^eperation. Th& total smelting operation
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INSPECTORS WORKSHEET
FOR LEAD SINTER PLANTS
GENERAL
Plant Id,
Date of this Inspection
_Dat$ of last Inspection_
OPERATING VARIABLES
Sinter Machine Feed Rate, including ore,
concentrate flux cok;e, etc.
Sulfur Content of Feed Ore
Sinter Sulfur Content
Moisture Content of Feed Ore
Temperature of Off Gases
Sinter Machine Bed Speed
Number of Windboxes
Exhaust Gas Flow Rate
ft/hr
, No. Updraft_
scfm
_ton/hr Output Rate_
ton/hr
, No. Downdraft
Pressure Drop at Each Windbox; (in. H.O)
10
Number of "Holes" Recorded in last day
Sulfur Dioxide Concentration: hi SO
gas.
%, remaining gas
Type of SO. Control Device
Percent of Exhaust Gases Treated by S0_ Control Dev'ce_
Particulate Control Device
Control Efficiencies:
dO,
%
Particular
Inlet Temperature of -Exhaust Gases to Control Device
Pressure Drop Across Control Device^
in./H20
VISUAL OBSERVATIONS
Physical condition of equipment:
-249-
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Describe ductwork
Maintenance Program
Develop a diagram indicating gas flow from the sinter machine to atmosphere.
CALCULATIONS
% sulfur in feed x feed rate ^lb/hr) - Ib/hr of sulfur.
hi S02 gas
concentration (!) x flQO - 7, efficiency of acid'plant! x flow rate (scfm) x
L ' ItfO J
Ib/hr sulfur in acid stack.
remaining SO^ gas
concentration (%) x flow rate (scfm) x 5 = | sulfur, Ib/hr.
If concentration is not available, take
(% S feed ore - % S calcine) x feed rate (Ib/hr), = Ib/hr net sulfur
from sinter machine.
[net sulfur, (Ib/hr) ]-[ hi SO concentration x (collection eff. °L ) x
100
flow rate (scfm) x 5] = Ib/hr sulfur from sinter plant.
Time In Time Out
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would include not only the sinter machines but also tl"* blast furnace and
the reverberator furnacesJ_=jCE^4i«s''been estimated that about 90 percent
of all sulfur emitted to the atmosphere will occur as a result of the sin-
tering operation. The remaining 10 percent is divided between the blast
furnace and the reverberatory operations.
On his first visit the enforcement official should develop a dia-
gram indicating the gas flow or sulfur oxide gas streams from the process
equipment to the atmosphere. Many lead manufacturing plants will combine
the exhaust gas streams from the, winter plant, lead blast furnace, rever-
beratory furnaces, and^e-cHer ancillary operations into one large abate-
ment facility". Electrostatic precipitators or baghouses are frequently
used to reduce particulate emissions from these operations.
28. ORE REDUCTION - BLAST FURNAC&
This is a major potential particulate emissions and minor sulfur
emission process. Particulate emissions are mainly a function of the
adequacy ot the control system.
28.1 Process Description
Lead oxide is reduced to metallic lead using carbon monoxide as a
reducing agent. The process heat required is derived from coke combustion.
The major chemical reaction^ that take place are:
C + 0 -> CO + heat
C + CO + heat -+ 2CO
PbO + CO + heat -> Pb -t^eO,
~-£
Some iron, zinc and other oxides are also" reduced. Liquid lead collects
at the bottom of the furnace -wliere it is drawn off. Slag floats on top
of the metal and prevents further oxidation of lead. Other metal oxides
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react with silTca to form slag. The blast furnace charge is a mixture
of sinter, coke and some fluxes. Air is introduced through tuyeres at
low pressure and ambient temperature near the furnace bottom. The air
flow rate is related to furnace capacity and varies between 5,000 and
The products from the blast furnace consist of liquids and gases.
The liquids are drawn off at the bottom and the gases are vented at the
top. There are four distinct liquids that comprise the bottom products:
lead, matte, speiss and slag. Lead may be separated from matte and
speiss and sent directly to the refinery or to the dross furnace with
the matte and speiss. Slag is removed separately and is conveyed to a
fuming furnace for recovery of lead and zinc.
Slag is a siliceous amalgam of many constituents. It contains 10
to 20 percent zinc, up to 2 percent lead and 3 percent sulfur.
Matte (metallic sulfides) contains 44 to 62 percent lead, lo to 20
percent zinc, up to 13 percent sulfur, and lesser amounts of iron, copper
and silica.
Speiss (metallic arsenides) contains 55 to 64 percent copper, 8 to
18 pei-'-p.nt lead, up to 1 percent zinc, 0.5 percent each of iron and sil-
ica and lesser quantities of sulfur and arsenic^
Theoretical flue-gas rates vary with t-he size of the furjiace
6,000 to 14,000 scfm, bu*~ is usually diluted to several times this flow
rate by air entering at the top of the furnace.
The flue gases, before uilution and combustion, maV contain 25 to
50 percent carbon monoxide, significant amounts of carbon dioxide and
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nitrogen. They also contain dusts and fumes from chemical reactions as
they become entrained in the air from the tuyeres as it sweeps through
the charge. The fumes include cadmium, lead, and zinc oxides.
Table 28.1 contains some reported emission rate& ^or lead blast fur-
naces. Gas flow rate and temperature values are ,after air dilution and
cooling.
Table 28.1 LEAD BLAST FURNACES
CAPACITIES, EMISSION RATES AND WASTE GAS TEMPERATURES
Plant
1.
2.
3.
4.
5.
6.
Estimated
Lead Production
Capacity
(tons/year)
76,000
122,000
198,000
120,000
91,000
42,000
Waste Gas
Temperature
(°F)
400
450
350
300
350
300
Flow Rate
(scfia)
8,500
11,100
26,200
23,300
20,400
— —
Dust Recovery
(tons /day)
12
9.7
___
26
Blast furnaces (Figure 28.1) have rectangular horizontal cross-sections.
There are tuyeres in each side, and above these the two long sides slope
outwards for a third of the shaft heights. In the upper two-thirds of the
shaft, the outward slope is less. Shaft sides and ends are water-cooled
steel panels.
The flue gas ducts and charge openings are at the top of the furnace
shaft. Below the hearth is a crucible or, in newer furnaces, a trough,
sloped toward one end where liquids from the furnace flow continuously to
an external settler-separator. Hearth widths range from 4.5 to 6.0 feet
and lengths from 15 to 28 feet. The furnace charge is 600 to 1,200 tons/day
for hearth areas from 80 to 150 sq. ft.
-253-
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5 Ton Charge
Bucket
Gas Offtake
FURNACE DIMENSIONS
Between Tuyeres = 1 meter
Length = 7 meters
Height = 8 meters
Slag
Bullion
Blower
1-5 Ton
Button Mold
FIGURE 28,1 LEAD BLAST FURNACE
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28.1.1 Lead refining is the process of recovery of valuable by-products
from blast furnace lead and the removal of impurities. Molten lead is
first treated in dressing kettles for copper removal. Cooling causes
the copper to separate and rise to the surface as a dross. The dross is
skimmed off and is smelted in the dross reverberatory furnace. A con-
tinuous softening process removes arsenic and antimony through oxidation.
The skim may be treated in an electric furnace to produce an arsenical-
antimonial lead known as hard-lead. Gold and silver are removed by the
addition of zinc metal. The zinc amalgam forms a dross on the surface
which is removed. Gold and silver are extracted from the skim by cupel-
lation and retorting. The residual zinc in lead is removed by vacuum
distillation. Addition of sodium hydroxide, or caustic soda, removes
the last traces of impurities and the final product, corroding lead, is
cast out for marketing.
28.1.2 Other smelter operations include dross reverberatory furnaces,
cadmium roasters, slag fuming-furnaces and deleading kilns.
A natural gas-fired dross reverberatory furnace separates the re-
maining lead in the dross skim, matte and speiss from the blast furnace
at temperatures of 1,400 to 1,800°F. The lead is sent to the refinery, the
matte and speiss to the copper smelter.
The off gases consist mainly of combustion products and average
less than 0.05 percent sulfur dioxide, except for short time periods
when sulfur is added to the furnace charge when it may go as high as 0.2
percent. Off gas flow rates are relatively low, 1,000 to 3,000 scfm;
only sufficient draft is provided to remove the smoke and fumes and still
allow as much heat retention as possible over the hearth. Flue dust re-
covery averages 0.75 tons/day at one plant which is believed to be primarily
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metal oxides. The speiss and matte compositions are not believed to be
altered significantly.
Other lead smelter operations emission data and operating conditions
are presented in Table 28.2
Table 28.2 AUXILIARY LEAD SMELTER OPERATIONS, EMISSIONS
AND OPERATING CONDITIONS
Operation
Plant 1
Dross reverb
Plant 2
Dross reverb
Slag fuming
Plant 3
Slag fuming
Plant 4
Dross reverb
Slag fuming
Deleadihg kiln
Plant 5
Dross reverb
Slag fuming
Deleading kiln
Lead Waste Gas
Production Temperature
Capacity ( F )
(tons /year)
76,000
1,700
122,000
1,400
600
2,200
91,000
1,700
600
2,500
42,000
1,650
2,200
1,500
(scfm)
1,100
8,500
59.3
9,000
19,700
4,000
6,000
50,000
Dust
recovered
(tons /day)
67
100
11
0.75
50
10
These operations are auxiliary to the primary lead smelting process
and even though they constitute a significant portion of lead plant oper-
ations, they are not fully treated here.
28.2 Process Control Operation
The basic chemical reactions define the important process variables
-256-
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and can readily be identified as the coke and lead content of the charge
and the air (oxygen) flow rate. Temperature control plays an important
but less critical part than in sintering. In order to reduce lead oxide,
1,100 to 1,300°F is required but temperatures may go higher in portions of
the furnace and cause some distillation and carry-over of lead and zinc
oxides. Sinter, coke, flux and other dust carry-overs are governed by
size distribution and air flow rates, especially during the initial part
of the blasting cycle. Good air flow rate control is also important for
the production of the reducing agent, carbon monoxide.
The flue gases are collected in a hood and duct system where the
carbon monoxide is burned by excess air to carbon dioxide. The volumes
of dilution air are large enough to also cool the gas. Further cooling is
accomplished by quenching with water. The diluted and conditioned gas is
ready for particulate removal by either filtration or precipitation. The
clear flue gas is vented through a stack.
28.3 Enforcement Procedure
The objectives of lead blast furnace operation inspection are to
determine sulfur dioxide and particulate emission levels from the reduc-
tion operation and to evaluate the pollutant emission potential of this
operation for varying production rates and operating conditions. In
order to accomplish the above objectives, the enforcement official needs
to determine:
1. Current production levels and operating conditions,
2. Design production levels and operating conditions,
3. Current controlled and uncontrolled particulate and sulfur
dioxide emission levels,
4. Efficiency and adequacy of emission control equipment at
current and design operating levels.
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Both blast furnace and blast furnace emission control equipment
design capacities and operating conditions can be obtained from design
drawings and plans. These data should be obtained from the company
representative prior to physical plant inspection. Production levels,
blast furnace feed weight rates, furnace, and furnace emission control
equipment operating conditions are monitored by the plant operator and
are either recorded in the operator's daily log or are displayed on
ins trument panels.
Prior to physical inspection of a lead blast furnace, the enforcement
official should obtain specific information regarding the number of loca-
tion of blast furnaces. The enforcement official should compare the feed
weight rate that is indicated on the operator's log during his visit with
what is considered normal operation for this particular furnace. This will
help establish whether the furnace is being overburdened because of in-
creased production or whether a light load has been charged to the furnace
because of the inspector's visit. The most important process variable
with a lead blast furnace is the process weight rate, which is the sum of
ore, fluxes, concentrates, coke and coke breeze charged to the furnace.
The enforcement official should also record the sulfur content of the sin-
ter and of the furnace products. Calculate sulfur emissions from these data.
The enforcement official should examine the air pollution collection
hood at the blast furnace to see whether the inspiration volume is ade-
quate to encompass the entire plume during the heaviest particulate emis-
sions. Additional particulate matter may emanate during the slagging and
tapping operations. Plants will generally have hoods to capture the par-
ticulate from these operations.
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INSPECTORS WORKSHEET
FOR LEAD BLAST FURNACE
GENERAL
Plant Id.
Date of this Inspection Date of last lnspection_
OPERATING VARIABLES
Blast Furnace Feed Rate, Ib/hr
Sulfur Content of Feed Ore %
No. of Blast Furnaces Capacity of Blast Furnaces, total tons/day
Sulfur Content of Slag %
Exhaust gas Flow Rate scfm, scfm, etc.
(Furnace 1) (Furnace 2)
Type of Control Device
Efficiency of Control Device %
Inlet Temperature ^F
Pressure Drop Across Control Device in. H^O
Spark Rate spm
No. of Dead Sections
EMISSION TESTS
Par t iculate s Ib /hr
S02 Ib/hr, expressed as S Ib/hr
Tested by Dated_
VISUAL OBSERVATIONS
Capture Efficiency
Ducts
-259-
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DIAGRAM OF EXHAUST GAS FLOWS
NOTE: For comparison with regulations, total smelter emissions may include
sinter plant and reverberatory operations as well as the blast furnaces,
Time In Time Out
-260-
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There is little telltale evidence on a lead blast furnace that would
indicate any upset condition has occurred. Occasionally a crust may form
over the hot metal and below the cold ore. A slip may occur when the
crust finally breaks and drops into the hot pool, resulting in a heavy
particulate emission. The enforcement official should observe the air
pollution control system during a slip if possible, and note whether the
abatement facility is capable of handling the heavy emissions.
Compare calculated sulfur emissions to applicable regulations. If
the calculated value exceeds limits, a stack test should be conducted
to verify the calculation estimate.
On the basis of stack opacity and/or visible particulate losses
from the building, due to inadequate process ventilation, there may be
cause for issuing a citation or requiring more definitive tests to deter-
mine compliance.
29. ORE REFINING - REVERBERATORY
This is a major potential particulate emission and minor sulfur
emission process. Particulate emissions are mainly a function of the
adequacy of the control system.
29.1 Process Description
The reverberatory furnace is a high temperature separation process
unit where the high lead content of dross skim is separated as lead bullion
from the copper matte and slag and, on occasion, nickel bearing material.
The reverberatory furnace is a refractory lined vessel that radiates
heat from its burner flame, roof and walls onto the dross charge. Figure
29.1 is a graphical depiction of a representative dross reverberatory
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-------
furnace. Fuel, usually natural gas or fuel oil, and combustion air are
introduced into the furnace where the combustion occurs directly above
the molten bath; the walls and roof receive radiant heat from the hot com-
bustion products and, in turn, reradiate this heat to the surface of the
charge. The process temperature is normally between 1,700 and 1,800°F.
The feed to the furnace may include the following components: dross,
soda ash, coke breeze, coal, sawdust, sulfur, ores, and silica. Lead
bullion from the blast furnace is sometimes included in the charge as an
additional step in the refinery operation. The reverberatory products
consist primarily of lead, copper matte, slag, and possibly nickel matte.
Tables 29.1 and 29.2 contain some typical reverberatory charge and product
weight rates and compositions.
The off gases consist mainly of combustion products and normally
average less than one percent sulfur dioxide which may be higher for short
periods when sulfur is added to the furnace charge. Off gas flow rates
are relatively low, 1,100 to 8,500 scfm, because only sufficient draft is
provided to remove the smoke and fumes and still allow as much heat reten-
tion as possible over the hearth. Table 29.3 is a listing of some dross
reverberatory emission data and operating conditions.
29.2 Process Control Operations
The basic process parameter is temperature, which must be sufficiently
high to permit liquefaction of the charge and phase-separation of the
liquid lead bullion from by-products that float on top of the molten bath.
The method of temperature control is fuel rate adjustment.
The off gases are essentially combustion by-products of either natural
gas or fuel oil, slight quantity of excess air, less than one percent
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Table 29.1
TYPICAL ANALYSES OF DROSS
REVERBERATORY FEED AT
ONE LEAD
PLANT
Material Reverb
(%) Bullion
Pb
Cu 1.4
S
Ni
Insol
FeO
Zn
Co
Cd
Bi
Ag
Copper Ni
Matte Matte
15 35
60 35
20
15
-
-
-
-
-
-
-
Dross
60
13
4.5
3
3
1.5
4.3
0.5
-
-
-
Lead
-
0 .010
-
-
0.004
-
0.001
-
0.0000
0.0000
0.031
Table 29.2
TYPICAL REVERBERATORY FEED AND PRODUCT WEIGHT RATES AND COMPOSITIONS
AT ONE LEAD PLANT
Weekly Summary of Reverberatory Operations
Material Charged
Tons
% of Charge
Dross
Soda Ash
Coke Breeze
Silica sand
835
45
16
10
92
5
2
1
Material Tapped
Lead Bullion
Copper Matte
Slag
Ni bearing material
590
164
81
10
65
18
9
1
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Table 29.3
LEAD
DROSS REVERBERATORY EMISSION DATA AND OPERATING CONDITIONS
Plant ,
1
2
3
4
Lead
Production
Capacity
(tons/yr)
76,000
122,000
91,000
42,000
Waste Gas
Temperature
( F)
1,700
1,400
1,700
1,650
Flow Rate
(scfm)
1,100
8,500
-
6,000
Sulfur Dioxide
(%)
0.99
0.02
neg.
0.52
Dust
Recovered
(tons /day)
-
-
-
0.75
sulfur dioxide, and some entrained dusts and fumes. The fumes are believed
to be primarily metal oxides.
The off gases are collected in a hood and duct system and may be
cooled to about 150 to 300°F by heat exchangers, air dilution, or water
spray, before treatment in baghouses. The reverberatory off gases may be
combined with other process off gases before particulate removal.
29.3 Enforcement Procedure
The objectives of dross reverberatory furnace operation inspection
are to determine sulfur dioxide and particulate emission levels from the
furnace operation and to evaluate the pollutant emission potential of this
operation for varying production rates and operating conditions. In order
to accomplish the above objectives, the enforcement official needs to
determine:
1. Current production levels and operating conditions,
2. Design production levels and operating conditions,
3. Current controlled and uncontrolled particulate and sulfur
dioxide emission levels,
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4. Efficiency and adequacy of emission control equipment at
current and design operating levels.
Both furnace and furnace emission control equipment design capacities
and operating conditions can be obtained from design drawings and plans.
These data should be obtained from the company representative prior to
physical plant inspection. Production levels, furnace feed weight rates,
furnace, and furnace emission control equipment operating conditions are
monitored by the plant operator and are either recorded in the operator's
daily log or are displayed on instrument panels
Obtain sulfur content data on both feed and product. Calculate
possible sulfur emissions. This could be verified using indicator tubes
(Part VII). If these estimates indicate that emissions exceed allowable
limits, definitive stack testing and/or a compliance program are in-
dicated.
On the basis of stack opacity and/or visible particulate losses
from the building, due to inadequate process ventilation, there may be
cause for issuing a citation or requiring more definitive tests to de-
termine compliance.
-266-
-------
BIBLIOGRAPHY
American Bureau of Metal Statistics Yearbook, Maple Press Company,
York, Pennsylvania, 1971
Dennis, W. H., Metallurgy in the Service of Man. Pitman Publishing
Company, New York, 1961.
Smith, B. W., The World's Great Copper Mines, Hutchinson, London, 1967.
Bray, J. L., Non-Ferrous Production Metallurgy, John Wiley & Sons,
New Yorl;, 1947
Liddell, D. M., Handbook of Non-ferrous Metallurgy. McGraw-Hill Book
Company, New York, 1945.
Hayward, C. R., Outline of Metallurgical Practice, D. Van Nostrand Com-
pany, New York, 1952.
Ruddle, R. W., Physical Chemistry of Copper Smelting. Institution of
Mining and Metallurgy, London, 1953.
U. S. Department of the Interior, Bureau of Mines, Copper: A Materials
Survey. 1965.
Newton, J. and Wilson, C. L., Metallurgy of Copper. John Wiley and Sons,
Inc., New York, 1942.
Fluor Utah, Inc., The Impact of Air Pollution Abatement on the Copper
Industry, San Mateo, California, 1971.
U. S. Department of the Interior, Bureau of Mines, Information Circular,
Control of Sulfur Oxide Emissions in Copper, Lead, and Zinc Smelting,
1971.
Engineering-Science, Inc. Exhaust Gases from Combustion and Industrial
Processes, Washington, D. C. 1971.
Davis, W. E., National Inventory of Sources and Emissions Barium. Boron,
Copper, Selenium, and Zinc.(Section III Copper) Environmental
Protection Agency, 1972.
Arthur G. McKee and Company, Systems Study for Control of Emissions
Primary Non-ferrous Smelting Industry, National Air Pollution Control
Administration, 1969.
Semrau, K. T. Control of Sulfur Oxide Emissions from Primary Copper, Lead
and Zinc Smelters. - A Critical Review, Journal of the Air Pollution
Control Association, 21-4, 1971.
U. S. Department of the Interior, Bureau of Mines, Mineral Facts and
Problems, 1970.
-267-
-------
American Smelting and Refining Company, Hayden, 1972.
Smith, P. R., Bailey, D. W. and Soane, R. E., Minerals Processing: Where
We Are - Where We're Going, Engineering and Mining Journal, 173-6,
1972.
-268-
-------
PARTY. ZINC SMELTING
Zinc is a strategic and critical material and, as such, is one of the
government stockpiled metals. The zinc industry is one of the primary
metallurgical industries and ranks fourth in production of tonnage after
steel, aluminum and copper.
The United States is the world leader in both metal production ana
consumption. Consumption patterns, both usage and temporal trends, are
given in Table V-l below.
Table V-l UNITED STATES ZINC CONSUMPTIONS
Total Consumption, percent
Galvanizing
Brass
Castings
Rolled Zinc
Other
1940
40
32
16
8
4
1950
46
14
30
7
3
1960
43
11
39
4
3
1968
36
12
42
4
6
100 100 100 100
Total Consumption,
Short Tons 719,000 967,100 877,900 1,333,700
Table V-2 presents the 1968 United States zinc plants and their sal-
ient process identification.
The United States relies on zinc metal supply from domestic primary
and secondary plants, imporcs of metal and its concentrate, and industry
-269-
-------
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-270-
-------
and government stocks. Of the 1968 consumption, 529,400 tons, or about
40 percent, were produced domestically.
Zinc is a bluish-white metal highly valued for its corrosion resis-
tivity. It is used extensively to galvanize iron and steel products
against corrosion. Zinc produced from newly mined ores is termed primary,
or virgin zinc, and when it is produced from scrap or residue it is termed
secondary, redistilled, or remelt zinc. Primary zinc may be referred to
as electrolytic or distilled zinc according to the reduction process used.
The final product may be in the oxide form as a powder or in the metal
form cast into slabs, usually of 55 pounds. Slab zinc is produced in five
standard grades ranging from 98.3 to more than 99.99 percent zinc with
certain limits on maximum impurity contents.
The most abundant zinc ore is the sulfide, called "blende", but a
composite form of oxides, silicates and other, is also significant.
Zinc ores also contain varying amounts of other valuable and recoverable
materials, including cadmium, copper, fluorspar, gallium, germanium, gold,
indium, lead, manganese, silver, sulfur, and thallium. Other commercially
significant sources of zinc include lead ores where zinc is found as a
by- or co-product. Zinc is recovered from ore by a combination of pyro-
metallurgical processes, such as roasting and distillation, or an electro-
lytic process in lieu of distillation.
Significant industrial uses of zinc include transportation, construc-
tion, electrical equipment and supplies, pigments and compounds and others.
Demand for primary zinc is expected to increase to, and range from
about, a low of two million to a high of four million tons by the year
2000. The corresponding growth rates for the possible zinc demand are
between one and three percent per annum.
-271-
-------
The nonmetallic zinc by-products, such as concentrate tailings, are
valued by such diverse industries as highway, railroad and agriculture.
Primary zinc production is a sequence of physical-chemical processes
that involve the mining and concentrating of the naturally occurring zinc
mineral, mostly as sulfide, the preparatory steps that are necessary for
reducing zinc to the metal form, the reduction process itself (either elec-
trolytic or pyrometallurgical), and the subsequent zinc purification. Figure
V-l is a simplified process flow diagram of a zinc plant and Tables V-3 and
V-4 list plant emissions and products.
Table V-3
DUST-IN OFF GAS RATES FOR SOME PRIMARY ZINC PLANT OPERATIONS
,, „ . Feed Capacity
Process Equipment , , , ,.
H ^ (tons/day)
1. Roasters
Multihearth 50 to 120
Ropp 40 to 50
Fluid Bed (2) 240 to 350
(Door Oliver)
Suspension 120 to 350
Fluid Column 225
2. Sinter Machines
Plant 1 240 to 300
Plant 2 400 to 450
Plant 3 550 to 600
Dust-in Off Gas Dust-in Off Gas
(% of feed) (tons/day)
5 to 15 2.5 to 18
5 2.0 to 2.5
75 to 85 180 to 300
50 60 to 175
17 to 18 38 to 40
5 12 to 15
5 to 7 20 to 32
5 to 10 28 to 60
-272-
-------
H
CD
-------
Table V-4
PRINCIPAL MATERIALS OF ZINC PRODUCTION AND THEIR ESTIMATED
RELATIVE QUANTITIES
Material Weight
Zinc Ore 100
Gangue 60 to 70
Zinc Concentrate 10 to 15
Tailings 15 to 30
Retort Furnace Residue 5 to IQ
Zinc Metal 5 to 6
Coke and Coal 4 to 5
Fluxes and Additives 4 to 5
Other 4 to 5
This section on zinc smelting, is divided into five chapters (Chap-
ters 30 through 34): material handling, concentrate drying, concentrate
roasting, sintering, and zinc metal production. Each chapter is sub-
divided into three parts, namely process description, process control
operation and enforcement procedure. This system of subdivision serves
as a structure that incorporates sic process and emission control de-
scriptions and operating principles that serve as a foundation for ef-
fective monitoring and enforcement.
30. MATERIAL HANDLING
The possible emissions will be particulates. Fugitive dust regula-
tions will govern.
-274-
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30.1 Process Description
Material handling is an important aspect of zinc production in
terms of tonnage of material. Zinc production is the process of separa-
ting mechanically and chemically 4 to 5 pounds of zinc from about 100
pounds of mine ore.
Most ore is mined underground and then transported to the surface.
The first and most substantial bulk reduction, ore concentration, normally
occurs here. Concentrating consists of separating the desirable mineral
constituents in an ore from the unwanted impurities by various mechanical
processes. Ore size is reduced bv crushing and wet grinding. Size separ-
ation is accomplished by vibrating or trommel screens and classifiers to
give properly sized feed. Heavy-medium cones, jigs and tables separate
the zinc minerals from a low specific gravity gangue. Conveyors trans-
port the ore to large bins for blending and storing. The ore is next
pumped as an aqueous slurry to flotation cells where it is conditioned
by additives. Large propellers stir the solution and the zinc-bearing
minerals separate and float to the surface where they are skimmed off.
The unprofitable part of the slurry, called tailings, may be treated in
cyclone type separators to remove fines from the sand.
Once separated, the metal concentrates are thickened in settling
tanks and the slurry is fed to vacuum drum filters which reduce the
moisture content to a small percent. At completion of the concentration
process, the zinc content has been upgraded to about 55 to 60 percent.
Thermal drying may be used to further reduce the moisture content of the
concentrates.
The concentrates are transported to a storage site and stored in
bins. Usually, the first step of zinc smelting is the conversion of zinc
-275-
-------
sulfides to zinc oxide by roasting. The sulfur is converted to sulfur
dioxide and is driven off in the off gases. The reduction of zinc ores
and concentrates to zinc is accomplished either by electrolytic deposition
from a solution or by retorting.
The low sulfur calcine is weighed in hoppers and introduced into
tanks where it is leached with dilute sulfuric acid solution. Most me-
tals, among them zinc, copper, cadmium, arsenic, antimony, cobalt and
nickel, enter the solution as sulfates. Insolubles suspended in this mix-
ture include lead, silver, gold, iron, silica and calcium which are re-
moved by filtration. Most of the soluble metals are removed from solu-
tion by selective precipitation and filtration until the zinc sulfate
solution is ready for electrolysis. Zinc is finally electrodeposited on
aluminum cathodes. The high purity zinc is removed from the cathodes and
the sulfuric acid (generated during electrolysis) leaching solution is
recycled.
Pyrometallurgical extraction employs different processes and reduc-
tion principles. The preparation of calcined zinc oxide for pyro-chemical
reduction involves agglomeration, either by sintering or by nodulizing and
blending with coke, fluxes and additives. The blended feed is ready for
retorting, in some cases, after briquetting. Zinc is finally reduced to
zinc metal in retort furnaces and the distilled metal is recovered from
the effluent by condensation. The liquid zinc may be cast into slabs or
further refined by distillation. The magnetic content of the retort resi-
due may be recovered and further processed, the rest goes to waste.
The material handling equipment may include such primary means of
transportation as rail, trucks, ships, barges and pipelines. The sec-
ondary, or more highly specialized equipment includes conveyors, overhead
-276-
-------
cranes, clamshell loaders and cars. Modes of material storage include:
piles, bins, hoppers, kettles, settling tanks and ponds. Material
handling process equipment include crushers, grinders, vibrating screens,
clarifiers, heavy-medium cones, jigs, tables, flotation cells, vacuum
filters, electrolytic cells, leaching tanks, roasters, sintering machines,
nodulizers, retort furnaces. Table 30.1 summarizes the major process and
material flows involved in primary zinc production. Figure 30.1 depicts
principal retort process emission points.
Of primary concern in material handling is the containment and con-
trol of fugitive dusts which are generated when sufficiently fine size
material is exposed to moving air. Such material may be stationary or
in transit. Most dusts become airborne during periods of loading and un-
loading at points of transfer.
30.2 Process Control Operation
There are two effective and widespread methods of dust control:
«
water or other chemical sprays and physical capture and confinement by
such means as hoods and other enclosures.
Some of the most important variables affecting dust emission into
air are particle size and density, the relative velocity between particle
and air, and the size of the surface area exposed to air per unit volume
of dust. Total emission control includes, in the final analysis, the
manipulation of all the variables affecting emission rates.
It is relatively simple to identify the major material handling
process variables, namely mass flow rates, composition, size distribution,
plant physical layout and material flow paths at an individual plant.
-277-
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30.3 Enforcement Procedure
The enforcement official should make a subjective type evaluation
of the material handling system for the concentrate building. It is un-
likely that any of the ore will be entrained by air and present a fugitive
dust problem. The enforcement official should check the transfer points
and the enclosed system of the storage hoppers.
The enforcement official should make note of the amount of material
processed through the concentrate building for future comparisons. No
atmospheric testing needs to be done at this particular process during the
enforcement official's inspection visit.
If fugitive dust violations are apparent, take appropriate action.
31. CONCENTRATE DRYING
The possible emissions will be particulates. Likelihood of emissions
is remote from the wet part of the system. The dryer can be a major par-
ticulate source if control equipment is not functioning properly.
31.1 Process Description
The preparation of the zinc concentrate is usually done wet by grav-
ity or flotation methods. Flotation is usually used to eliminate as much
of the lead as possible. The concentrated zinc ore usually contains about
sixty percent zinc.
Depending on the type of sintering and/or roasting operation that
may accompany a zinc plant, some of the raw zinc orp may be dried. The
drying process takes place in direct-fired rotary dryers. Concentrate en-
tering the dryer contains about 11 percent moisture and leaves at about
3 percent moisture. Below about 3 percent moisture, the concentrate becomes
quite dusty. It is stored in a concentrate silo for future processing in the
flash roaster or sintering plant.
-281-
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INSPECTORS WORKSHEET
FOR RECEIVING, STORING AND HANDLING OF RAW MATERIALS
Plant Id.
Date of this Inspection_
Type of Plant
Date of last Inspection
Capacity of Plant
Type
Source Location Material
Wind
Direction
Wind Speed
(mph) Plume Description
Preventive
Measures
Sample
Concentrate
belt unloading
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Ore
Concentrate
SW/10
slight visible dust
Water spray
-282-
-------
Dust emissions occur as the hot air passes over the moving bed of
concentrate. Most plants will have some type of particulate abatement
equipment at the dryer as dust caught in the air pollution device can
easily be recirculated into the storage bin for further use. Cyclones
and low-to-medium energy scrubbers are likely to be used to remove the
particulate matter from the exhaust gas stream. Cyclones operate on a
dry principle and could remove much of the large particles for reuse dir-
ectly into the flash roaster with no further processing. Particulates
caught in the scrubbers will need to be dried before reuse in the roasters
or sintering plants. Since the specific purpose of this dryer is to re-
duce the moisture content of the ore, a water plume will be noted at the
stack outlet. Not all zinc plants will have an ore drying operation;
virtually no sulfur dioxide is driven off during this process.
31.2 Process Control Operation
Emission to the atmosphere from this process will depend on the
adequacy of the air pollution control system. There is likely to be a
corporate motivation to include air pollution control systems oi\ this
process since the raw ore can easily be reused at another stage in the
zinc reduction process. Pollution control efficiencies for this type of
system will require about 90 percent removal efficiency. This can be
accomplished with the use of low energy scrubbers and multicyclone de-
vices. Operating factors likely to affect air pollution emissions are
process feed rate and product moisture content.
The concentrate drying operation is a continuous one and will nor-
mally operate 24 hours per day. Very few operating instruments are likely
to be found for this particular process. If any, the gas feed rate and
the ore feed rate would be recorded on a daily basis. Analysis of the
-283-
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moisture that is sent to the sintering plant or the flash roaster is
critical and would be recorded at the control booth.
31.3 Enforcement Procedure
The enforcement official should obtain data on the process feed
rate, moisture contents, and the fuel firing rate for the dryer. This
data would be used for future comparisons to determine whether any change
in production rate has occurred for this particular plant. The enforce-
ment official should record the operating variables for the air pollution
control device. These include the:
1. Gas pressure drop across the scrubber or cyclone,
2. Water flow rate,
3. Air flow rate.
The enforcement official should check the hood capture system used
at the tail end of the dryer. Any dust plumes are an indication of a
poorly designed unit, clogged ducts, or malfunctioning control equipment.
The enforcement official should observe the plume for visible emissions.
A water vapor plume will be noted at the stack outlet. The enforcement
official should check for any visible plume noticeable beyond the vapor
plume. A visible plume would indicate that the control device may not
be operating satisfactorily. Reference to allowable emissions and opacity
regulations must be made. If opacity of plume downwind of the steam plume
is excessive, appropriate action should be taken.
32. CONCENTRATE ROASTING
This is the major point of sulfur emissions in the zinc smelting
process. Individual plants may have sulfur recovery units. It is also
a possible major source of particulate emissions if control equipment is
not functioning properly.
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32.1 Process Description
Roasting zinc concentrate is a preparatory step to zinc extraction.
It consists of a high temperature exothermic process that converts metal
sulfides to metal oxides and fuses the concentrate into a porous mass
called calcined oxide. This oxide may require further processing prior
to zinc extraction, either by electrolytic or pyrometallurgical methods.
If extraction is by pyrometallurgy, further calcining of the oxides is
usually necessary.
Fuel combustion is required to initiate the reaction which, if the
sulfide concentration is high enough, becomes self-sustaining.
Reaction temperatures vary from plant to plant between 1,200 and
1,900°F depending on the type of roaster, concentrate composition and the
specific use of the calcine (see Table 32.1). Roaster calcine size also
depends on the same factors and can vary from fine powder to walnut sized
chunks.
Differing requirements have resulted in a great diversity of roaster
machine forms, the most important of which are the multiple hearth furnace,
flash roaster, and fluid bed roaster.
Multiple hearth roasters are some of the oldest and most popular.
The roaster consists of a brick lined cylindrical steel shell through
which runs a central shaft with two rabble arms attached for each hearth.
There may be from four to sixteen hearths in each roaster. The motor
driven shaft contains cooling pipes and rotates slowly, about one-half
to two revolutions per minute. Seven to nine rakes or rabbles are at-
tached to each arm. Their arrangement is such that the ores introduced
into and dried in the upper chamber are gradually moved from the outer
edge toward the center and fall through a drop hole onto the first hearth.
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Table 32.1 TYPICAL ZINC ROASTING OPERATIONS
Type of Roaster
Multihearth
Multihearth
Ropp
Fluid Bed (4)
(Dorr-Oliver)
Fluid Bed (2)
(Dorr-Oliver
Fluid Bed
(Lurgi)
Suspension
Fluid Column
Operating
1,200-1,350
1,600-1,650
1,200
1,640
1,650
1,700
1,800
1,900
Feed
Capacity
(tons /day)
50-120
250
40-50
140-225
240-350
240
120-350
225
Dust -in
Off Gas
(% of feed)
5-15
5-15
5
70-80
75-85
50
50
17-18
Off Gas
(S02%)
4.5-6.5
4.5-6.5
0.7-1.0
7-8
10-12
9-10
8-12
11-12
(1) Dead roast except where noted otherwise.
(2) First stage is a partial roast in multihearth, second stage
is a dry-feed dead roast in Dorr-Oliver fluid bed.
(3) Partial roast.
(4) Slurry Feed.
The ore then moves across this hearth to a slot near the outer edge
and drops to the second hearth. The ore progresses through the furnace
in this zig-zag fashion until it drops into a car or conveyor beneath the
lowest hearth. There are doors for visual observation, repairs and ad-
mission of air for each hearth. Multihearth roaster feed capacities vary
between 50 and 250 tons per day.
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Suspension, or flash roasting, resembles the burning of powdered coal
in furnaces wherein finely ground concentrates are sprayed into a combustion
chamber in a stream of combustion air. The reaction usually proceeds without
the addition of fuel unless the sulfide content is too low, in which case
fuel addition, normally undesired is required. The roaster itself resembles
multihearth roasters. It is made up of a refractory-lined cylindrical steel
shell. The upper portion contains the combustion chamber and the lower por-
tion two to four hearths, similar to those of the multiple hearth furnace.
The feed concentrate is introduced into the lower one or two hearths to dry
before final grinding in an auxiliary ball mill. The dried and ground con-
centrate is then introduced into the combustion chamber. Rotating rabble
arms move the material on the hearths. Flash roaster feed capacities vary
from 120 to 350 tons per day.
Fluid-bed roasters are continuous operating fluidized concentrate feed
combustion chambers. The closely size-regulated, dry, pelletized or slurry
feed is introduced to the usually rectangular cross-section reactor. Low
pressure air is introduced into a windbox and passes through the perforated
bottom, which acts as an air distribution plate. The feed is lifted and flui-
dized. Additional air may be introduced through inlets on each side of the
bed. The roasted material overflows into a collection system and the gases
go to waste heat boilers for heat recovery and to g£.s cleaning equipment.
Table 32.1 shows some typical roaster capacities and operating conditions.
Agglomeration of the calcined oxide from the roaster is usally re-
quired before retorting which may be done by either sintering or nodu-
lizing. Both of these processes involve high temperature fusion and some
additional sulfide conversion (see Chapter 33).
The roaster feed is zinc concentrate consisting of 52 to 60 percent
zinc, 30 to 33 percent sulfur, 4 to 11 percent iron and lesser quantities
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of lead, cadmium, copper and other. Franklinite ore requires special
processing to recover iron and manganese in addition to zinc. Additional
fuel may be required and therefore it may be included in the process
weight, depending on the type of fuel and applicable regulations.
The roasting process converts 93 to 97 percent of the sulfur in the
concentrate to sulfur dioxide.
The roaster products consist of the calcined oxides and the off gases.
Since the solid products' size distribution includes significant portions
of fines, a substantial portion of the feed is carried over by the off
gases requiring major dust recovery operations. Metal fumes, especially
that of cadmium, constitute an appreciable portion of the waste gas par-
ticulate carry over.
The volumes of off gases produced range from 5,000 to 6,000 scfm
for multiple hearth roasters, 10,000 to 15,000 scfm for suspension
roasters and 6,000 to 10,000 scfm for fluid-bed roasters. Sulfur dioxide
content of off gases ranges from 4.5 to 6.5 percent for multiple hearth
roasters and 7 to 12 percent for suspension and fluid-bed roasters.
Tables 32.1 and 32.2 contain more specific operation information.
32.2 Process Control Operation
The basic chemical reactions define the important process variables,
which are: feed composition, feed mass rate, and air flow rate. Roaster
configuration and concentrate size distribution also affect particulate
emission potential. Operating conditions vary greatly from plant to plant
depending on the feed composition, type of roaster and the specific use
of the roaster calcine. Process temperature plays an important, but not
critical, role in monitoring. It varies between 1,200 and 1,900 F for
all plants although the range for a specific roaster is considerably
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Table 32.2 ZINC ROASTERS
CAPACITIES, EMISSION RATES AND
WASTE GAS TEMPERATURES
Estimated Zinc
Production Capacity
Plant (tons /year)
1 252,000
2 88,000
3 88,000
4 59,000
5 92,000
6 44,000
7 215,000
8 53,000
9 56,000
Waste Gas
Temperature Dust Recovery
(°F) Flowrate (scfm) (tons/day)
1,600
1,600
1,900
2,000
n.a.
1,200
—
700
900
94,500 n.a.
32,000 n.a.
22,200 80
16,000 n.a.
23,000 n.a.
9,500 n.a.
--
123,000 n.a.
166,000 n.a.
Sulfur
Equivalent
of Sulfur
'Oxide
Emission Rate
(tons /year)
159,000
49,900
50,100
33,600
52,100
23,400
124,000
27,000
26,500
narrower. Higher roasting temperatures distill more cadmium and increase
formation of ferrites. Temperature control is usually achieved by air flow
rate control. The combination of air flow rate, particulate size distri-
bution and equipment configuration affect the quantity of dust carry over.
The composition of the distilled metal fumes is determined primarily by the
concentrate composition and the operating temperature.
Roaster off gases require cooling and conditioning before particulate
emission control. Emission control is usually accomplished in two stages.
The first stage is cooling (normally by dilution) and removal of coarse
particulates in cyclones. The secondary stage is a high efficiency control
device, such as a filter or precipitator.
32.3 Enforcement Procedure
The objective of the zinc concentrate roasting operation inspection
is to establish compliance with sulfur dioxide and particulate emission
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regulations. In order to accomplish the above objective, the enforcement
official needs to determine:
1. Current production levels and operating conditions,
2. Design production levels and operating conditions,
3. Current controlled and uncontrolled particulate and sulfur
dioxide emission levels,
4. Efficiency and adequacy of emission control equipment at
current and design operating levels.
Both roaster and roaster emission control equipment design capacities
and operating conditions can be obtained from design drawings and plans.
These data should be obtained from the company representative prior to
physical plant inspection. Production levels, roaster feed weight rates,
roaster, and roaster emission control equipment operating conditions are
monitored by the plant operator and are either recorded in the operator's
daily log or are displayed on instrument panels.
All zinc roasters will have a control booth near the roaster for
careful monitoring. The enforcement official should have little difficulty
assessing the current operating status of the roaster by observing the
many recorders, gauges and logs which are normally kept for the roaster.
Of primary importance for the enforcement of air pollution emission
regulations is the process weight rate and the sulfur content. With the
mass rate and sulfur content of the feed and calcine, a sulfur mass balance
can be calculated. From this, SO emissions can be computed. If an acid
plant is used to treat the gases, acid production data must be obtained.
The calculated SO- mass equivalent scrubbed out by the acid plant must be
subtracted from the computed emissions based on the mass balance. Compare
the net computed emissions with allowable levels in the regulations and
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take appropriate action if necessary. It should be pointed out that many
state regulations restrict sulfur emissions from the entire zinc smelter
and not just the zinc roaster. For determining compliance with the regu-
lations, sulfur emissions from each operation must be summed, then compared.
Almost 90 percent of the sulfur is removed in the roasting process. If an
approximation of compliance is desired, the calculated sulfur emissions
from the zinc roaster may be used. Many zinc roasters will have a sulfuric
acid plant to treat exhaust gases from the roaster. These plants will
monitor SO. gases continuously. The enforcement official should note the
flow and concentration of the acid plant inlet and outlet gases for subse-
quent inspections. There should be little deviation (± 20 percent) from
visit to visit because of the fixed design of acid facilities.
There is little that can be noted on instrument panels regarding the
amount of particulates emitted to the atmosphere. Some plants will have
a smoke density meter which may be used to determine relative particulate
emissions from one visit to another. The enforcement official should note
the operational parameters of the air pollution control devices.
Visible emissions are the simplest means for estimating particulate
control equipment performance. The enforcement official should estimate
the percent opacity of dust control equipment stack plume and if in excess
of allowable limits, take appropriate action. Building openings should also
be observed for evidence of escape of inadequately captured process dust
and if noted, determine point(s) of origin and require corrective action.
The enforcement official should subjectively analyze the appearance
of the zinc roaster and note any leaks, SO odors, and condition of the
duct, etc. Finally, some attention should be given to the dust emission
from the material handling of the feed ores and calcine to and from the
roasting machine.
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INSPECTORS WORKSHEET
FOR ZINC ROASTING
GENERAL
Plant Id.
Date of this Inspection Date of last Inspection
OPERATING VARIABLES
Roaster Feed Rate Ib/hr Calcine Product Rate Ib/hr
Sulfur Content of Feed Ore ?„
No. of Roasters Capacity of Roaster tons/day
Moisture Content of Feed Ore %
Sulfur Content of Calcine %
Exhaust Gas Flow Rate
Type of Control Device
Efficiency of Control Device: Part. %, SO %
Inlet Temperature . F
Pressure Drop Across Control Device in. H.O
Spark Rate spm
No. of Dead Sections
EMISSION TESTS
Location of Test Ports
Particulates Ibs/hr
SO Ib/hr, expressed as S Ib/hr
Tested by Dated
VISUAL OBSERVATIONS
Capture Efficiency
Ducts
SO2 Odor_
Other
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DIAGRAM OF EXHAUST GASES AND PROCESSES
Time In Time Out
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33. CONCENTRATE SINTERING
This is a major potential particulate emission and minor sulfur
emission process. Particulate emissions are mainly a function of the
adequacy of the control system.
33.1 Process Description
Sintering is a process that converts remaining metal sulfides to
metal oxides. It eliminates residual lead and cadmium and densifies or
fuses the roasted calcine to make it suitable for retorting.
The feed to the sintering machine consists of a pelletized mixture of
roasted calcine and coal, or coke, and sinter dust. The pelletized mixture
is fed uniformly across the grates of the sintering machine on top of a
shallow returning sinter layer consisting of coarse particles. The feed
is ignited as it enters the natural gas-fired ignition box and combustion
is sustained by supplying air to the pellets. Combustion gases are re-
moved, usually through sectionalized wind boxes. Just before the discharge
end of the machine, the top layer of the sinter bed is shaved off by a ro-
tating scalper. This top layer, from which about 80 percent of the cadmium
and 40 percent of the lead may have been eliminated, constitutes the sinter
product containing approximately 60 percent zinc, 0.4 percent lead and 0.05
percent cadmium. The lower portion of the bed, not removed by the scalper,
is discharged at the end of the machine to a set of crushing rolls and then
the coarser material may be separated on a vibrating screen. The oversized
particles are returned to the sinter machine while the undersize material
is incorporated with the sinter feed mix.
The off gases contain usually less than 1 to 2 percent sulfur dioxide.
This represents, depending on the roaster sulfur removal efficiency, only
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1 to 5 percent of the sulfur originally present in the feed. In addition
to sulfur oxides, the gases contain air, water vapor, carbon dioxide, and
traces of other gases. The fumes consist primarily of cadmium, lead, zinc,
and arsenic oxides. Other metals and other compounds are also present in
lesser quantities. The fumes condense and are collected with the dust.
Some plant capacities, emission rates, and operating conditions are
shown in Table 33.1. Table 33.2 summarizes some zinc sintering operations.
Table 33.1 ZINC SINTERING MACHINES
CAPACITIES, EMISSION
Estimated
RATES AND WASTE GAS TEMPERATURES
Waste Gas
Zinc Production Temperature (°F) Flowrate (scfm)
Capacity
Plant (tons/year)
1 88,000
2 92,000
3 215,000
4 53,000
5 56,000
Table 33.2
Case
New feed material
400 23,200
200 150,000
400 58,500
200 95,000
300 22,200
ZINC SINTERING OPERATIONS
1 2
calcine calcine
Total charge capacity (tons per day) 240 to 300 400 to 450
Machine size (ft)
Fuel added to feed (%)
Total sulfur in new feed (%)
Recycle (% of new feed)
Dust-in off gas (% of feed)
Off gas S02 content (%)
3.5 x 45 6 x 97
6 to 7 10 to 11
8 2
35 to 75 40 to 70
5 5 to 7
1.5 to 2.0 0.1
Sulfur Equivalent
of Sulfur Oxide
Emission
(tons /year)
200
60,100
4,400
5,800
7,800
3
concentrate
550 to 600
12 x 168
0 to 2
31
80
5 to 10
1.7 to 2.4
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Sintering machines, known as Dwight-Lloyd machines, range in size
from 3.5 ft wide x 45 ft long to 12 ft wide x 168 ft long and from
100 to 2,000 square feet of bed area. The loading capacity variation
is from 0.75 to 1.75 tons per day/square foot of bed area. Figure 33.1
is a graphical depiction of a sintering machine and process flow. In
some machines air is introduced from above and flows through the ore
bed OP the conveyor and captured in the wind box and duct underneath.
These are known as downdraft machines and are most widely used in the
zinc industry. Tn other machines, the air flow is the reverse. These
are known as updraft machines. The temperature of the combined exit
sinter gases vary from 500 to 700°F which may be cooled by air dilution
and water sprays in preparation for gas cleaning. The primary collection
means of particulate removal may be by cyclones and settling chambers
followed by secondary removal in electrostatic precipitators or baghouses.
33.2 Process Control Operation
The most important process variable is temperature. Temperature
control is achieved by limiting the coke and coal content and the sulfur
content of the sinter mix. Once oxidation is started it becomes self-
sustaining. Air flow regulation provides additional temperature control.
Sulfur dioxide emission is dependent on the sulfur content of the
roasted calcine or zinc concentrate. It may be assumed that all of the
1 to 5 percent of the original sulfur content of the zinc concentrate re-
maining in the roasted calcine is driven off as sulfur dioxide in the
sinter off gases.
The sinter crushing and screening operations have enormous particu-
late emission potential. These operations will be hooded and ducted to
a control device.
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LJ
o_
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Table 33.3 shows some feed capacities, dust-in off gas and dust
recovery rates for some zinc plant operations.
Table 33.3 DUST-IN OFF GAS RATES FOR SOME ZINC PLANT OPERATIONS
Sintering Machine
Plant 1
Plant 2
Plant 3
Feed Capacity Dust-in Off Gas
(tons/day) (% of feed)
240 to 300. 5
400 to 450 5 to 7
550 to 600 5 to 10
Dust-in Off Gas
(tons/day)
12 to 15
20 to 32
28 to 60
Emission rates and concentrations are expected to vary with feed compo-
sition, type of equipment used, and operating skill.
33.3 Enforcement Procedure
Sintering plants are traditionally dusty. The enforcement official
is likely to find the sintering operation the dirtiest building at a pri-
mary zinc manufacturing plant.
The wind box fan operates at a high negative pressure in order to
pull combustion air through the bed. Leakage between the bed and the fan
will draw in a substantial amount of dilution air and increase the system
gas volume. If a precipitator is used, its performance will be degraded
when gas volume exceeds the design capacity.
Zinc sinter dust is very abrasive. Ducts can develop holes and the
seals between the wind boxes and the bed can deteriorate causing a major
maintenance problem at older plants.
The enforcement official must take particular note of the stack opacity
for elevated visible dust levels. If noted, one probable cause is dilution
air drawn into the system through leaks. The plant inspection should include
observation of the system of wind boxes and ducts leading to the dust collector.
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INSPECTORS WORKSHEET
FOR ZINC SINTER PLANTS
GENERAL
Plant Id.
Date of this Inspection
«
_Date of last Inspection
OPERATING VARIABLES
Sinter Machine Feed Rate, including ore,
concentrate flux coke, etc. ton/hr
Sulfur Content of Feed Ore_
Calcine Discharge Rate
Calcine Sulfur Content
ton/hr
Moisture Content of Feed Ore_
Temperature of Off Gases
Sinter Machine Bed Speed
Number of Windboxes
ft/hr
Exhaust Gas Flow Rate
scfm
Pressure Drop at Each Windbox; in. H«0
12345678
10
ABATEMENT EQUIPMENT
Type of Unit
Pressure Drop
Spark Rate
spm
Primary Voltage_
Water Flow Rate
kv
gpm
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VISUAL OBSERVATIONS
Note leaks on sinter machine
Is SO odor present? Strong, Detectable, Barely detectable
Describe Ductwork
Maintenance Program_
Develop a diagram indicating gas flow from the sinter machine to atmosphere.
Time In Time Out
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Good maintenance is a major part of plant operation, so records will
likely be available. The precipitator should likewise be inspected
for its general condition. Particular note should be made on the adequacy
of dust control when dust hoppers are emptied.
Compare calculated emissions to applicable regulations. If the cal-
culated value exceeds limits, a stack test should be conducted to verify
the calculation estimate.
On the basis of stack opacity and/or visible particulate losses from
the building due to inadquate process ventilation there may be cause for
issuing a citation or requiring more definitive tests to determine com-
pliance.
There are not likely very many monitoring instruments for the sin-
tering operation, and at best, the control booth will monitor the pressure
drop in each of the wind boxes. Occasionally, a hole may result in the bed
and cause excessive particulate generation. The enforcement official
should ask how many holes occurred in the sinter bed for the preceding
day for subsequent comparisons. The enforcement official should also fill
out the Inspector's Work Sheet for this operation.
34. ZINC METAL PRODUCTION
Emissions from the electrolytic process may contain minor amounts
of sulfuric acid mist. The pyrometallurgical processes emit particulates.
Emission levels are a function of control equipment adequacy.
34.1 Process Description
The reduction of roasted zinc calcine to metallic zinc is accom-
plished either by electrolytic depostion from a solution or by pyrometal-
lurgical reduction.
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34.1.1 Electrolytic extraction - This process consists of dissolving the
calcined metal oxides in a sulfuric acid solution and separating the various
soluble and insoluble metals from this solution by selective precipitation
and filtration until the zinc sulfate solution is ready for electrolytic
reduction of sine. The high purity zinc is removed from the cathodes and
the electrolyte (aqueous solution containing the sulfuric acid generated
during electrolysis) is recycled to the leaching tanks.
The roasted sulfur-free calcine is weighed in hoppers and appor-
tioned into leach tanks. The dilute sulfuric acid electrolyte, returned
from the cell room, is mixed with the calcine in the leaching tank and
the ensuing chemical reaction converts the metal oxides to the respective
metal sulfates. The soluble metal sulfates, among them zinc, copper, cad-
mium, arsenic, antimony, cobalt, and nickel are dissolved and go into so-
lution. The insolubles suspended in this aqueous mixture include lead,
silver, gold, iron, silica, and calcium. The insolubles are first sepa-
rated from the solution by filtration. The dewatered residue from the
settling tank contains the lead, gold and silver which are sent to the
smelter and recovered.
The filtered zinc sulfate solution is piped to an agitator tank and
enough zinc dust is added to precipitate the copper. The copper precipi-
tate is removed from solution by filtration. This same process is repeated
through several stages. Other metals such as cadmium, cobalt, nickel,
antimony, and arsenic are precipitated out of the solution. The residues
from the first two filtrations are put into water to form a slurry which
is leached with electrolyte from the cell room and the copper is filtered
out. Zinc dust is added to the remaining solution and the cadmium is re-
moved by filtration. The spongy cadmium product is refined by dissolving
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it in a cadmium cell electrolyte from which the cadmium metal is recovered
by electrolysis, melted, and cast into various shapes.
The remaining zinc sulfate solution is treated in a cell where the
zinc is removed by electrolysis and deposited on aluminum cathodes. The
spent electrolyte is returned to the leaching tanks for reuse, and the
zinc is stripped from the cathodes and sent to the primary melting fur-
naces. The 99.99+ percent pure zinc metal is tapped from the furnaces
and cast into blocks.
34.1.2 Pyrometallurgical zinc reduction - This process is a high-tem-
perature carbon monoxide reduction process.
The reduction temperature is between 1,800 and 2,AOO°F and the
pyroreduction may be done in horizontal or vertical retorts, or in open
or submerged electrothermal arc furnaces. Horizontal retorts are small
ceramic cylinders that are mounted horizontally in racks that hold several
rows of these retorts in layers. Vertical retorts are large, refractory-
lined vessels with external gas combustion chambers. The retorting process
is continuous and highly mechanized. The feed consists of a briquetted
mixture of the following approximate composition: 60 percent roasted zinc
concentrate, 25 percent bituminous coal, 5 percent anthracite fines, 10
percent plastic refractory clay and 1 percent sulfite liquor. The bri-
quets are charged into the upper unheated extension of the retort, known
as the charge column, and the residue briquets are continuously discharged
at the bottom. Air is introduced at the bottom of the retort at a low
rate, and the oxygen is converted to carbon monoxide. The retort is heated
by combustion in the firing chamber external to each sidewall. Good heat
conduction is essential through both the sidewalls and the briquetted charge.
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The gaseous-reaction products formed in the retort, which rise up
through the charge column, have the approximate composition of 40 percent
zinc vapor, 45 percent carbon monoxide, 8 percent hydrogen, 7 percent
nitrogen and some carbon dioxide. These gases exit near the top of
the charge column through a zinc vapor condenser. In the condensation
process, a back oxidation reaction is responsible for the production of
3 to 5 percent partially oxidized zinc powder. This zinc oxide, known as
blue powder, floats on top of the zinc bath and is periodically skimmed
off. A scrubber system may be used to scrub out the entrained blue powder
from the flue gases and this cleaned gas may be used as supplementary fuel
or flared. The zinc thus produced may be further refined. About one-half
of the zinc produced in vertical retorts is refined to 99.99 percent purity
by means of continuous fractional distillation.
Electrothermic furnaces, such as the one graphically depicted in
Figure 34.1, may be used for either zinc or zinc oxide production. Pre-
heated coke and zinc-bearing sinter are continuously fed to the furnace;
electricity is introduced through graphite electrodes and coke serves as
the principal electrical conductor so the developed electric heat provides
the energy required for smelting. Zinc is recovered through condensation
by bubbling through a molten zinc bath and zinc oxide may be produced by
oxidizing zinc vapors with air. The zinc oxide fume-laden gases are cleaned
by cyclones to remove oversized particles and foreign material, then zinc
oxide is removed either by bag filtration or high energy wet scrubbing.
34.2 Process Control Operation
Atmospheric emission of pollutants from electrolytic zinc reduction
is limited to minor amounts of sulfuric acid mist but disposal of liquid
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Granules
Cone Briquets Sinter
CO Gas Burner
Batch Fed Dross
Gas Washer
Carbon
Monoxide
To Vacuum
Pumps
Liquid
Zinc
Charge Level
Detector
Zinc Vapor
& Carbon
Monoxide,
Cooling
Well
Condenser
Water Ring
Rotary Discharge
Table
Rotary
Preheater
Rotary
Distributor
Gamma Ray
Source
Graphite
Electrodes
Vapor Ring
Water Cooled
Jackets
Graphite
El-ectrodes
Residue
Pan Conveyors
to Recovery
System
FIGURE 34,1 ELECTROTHERMIC ZINC METAL FURNACE
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wastes can create a significant water pollution problem. Emissions from
retort furnaces are of minor significance compared to other operations
like concentrate roasting and sintering. Of the total sulfur in the raw
concentrate, only 0.2 to 0.3 percent is emitted from retort furnace oper-
ations. Particulate emission, which consists primarily of metal and metal
oxide fumes, is minor because economics dictate a high-efficiency metal
recovery. Because the retort off gases are rich in carbon monoxide, they
are used as auxiliary fuel either in the retort furnaces themselves, or
in other smelter operations. Retort off gases are commingled with combus-
tion by-products, thus seldom are they directly vented.
The important process variables are the zinc and coke content of the
feed, the feed, and air flow rates. Proper air flow rate is important for
the production of carbon monoxide, the reducing agent, since too much air
might result in nearly complete combustion of coal.
The most important process parameter is temperature. Process tem-
perature is regulated by fuel rate adjustment for conventional retort fur-
naces and by regulating current flow to the electrodes for electrothermic
furnaces. The normal process temperature range is between 1,800 and 2,400
The gases leaving the furnace at essentially atmospheric pressure
bubble through the molte.n condensed zinc. Gas cleaning consists of par-
ticulate removal which may be cyclone removal of oversized particles fol-
lowed by bag filtration after cooling, or high energy wet scrubbing. The
cleaned gases, rich in carbon monoxide, are recycled and used as auxiliary
fuel.
34.3 Enforcement Procedure
Zinc oxide is a fine, highly-visible white particulate, the major
pollutant emitted from the retort furnaces. The retort furnace is an
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entirely closed system except during charging or when a hole occurs in
the wall of the furnace. There are many retort furnaces at a zinc pro-
duction facility and most of these are older furnaces where leaks can occur
if not maintained properly. The enforcement official should ask about the
maintenance schedule used on the furnaces and specifically the maintenance
schedule for the furnace walls.
The enforcement official should also observe the stack plume. If a
white cloud is present, it is an indication that the air pollution control
equipment may not be operating satisfactorily. Most plants will have an
opacity meter located on the stack to warn of any upsets in the furnace
condition. Opacity meter charts (if available) 5' juld be reviewed, as
well as dust collector maintenance records.
The enforcement official should obtain information from the operator's
daily logs on the process operation. The important variables are listed
on the Inspector's Work Sheet shown on the next page. There is little
telltale evidence that can be collected while standing on the floor of the
plant; therefore, the enforcement official should carry out his inspection
program at the control booth for the retort furnaces and at a distance
from the building so that he can observe the stack plumes for this opera-
tion. Observations of the opacity of the stack plumes should be made and
if opacity exceeds allowable levels, appropriate action should be taken.
-307-
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INSPECTORS WORKSHEET
FOR ZINC RETORT FURNACES
Plant Id.
Date of this Inspection Date of last Inspection_
Type of Retorts
No. of Retorts, entire plant
No. of Stacks for Retort furnaces
No. of Retorts out of service this day
Process feed rate, entire retort plant tons/hr
ABATEMENT EQUIPMENT (fill out for each device)
Pressure drop in. FUO
Spark rate spm
Flow rate scfm
Inlet Temperature °F
Opacity Meter Reading %
DIAGRAM OF RETORTS, ABATEMENT EQUIPMENT AND STACKS
GENERAL OBSERVATIONS:
Time In Time Out
-------
BIBLIOGRAPHY
LITERATURE REFERENCES
Rausch, D. 0. and Mariacher, B. C., AIME World Symposium on Mining and
Metallurgy of Lead and Zinc, The American Institute of Mining,
Metallurgical, and Petroleum Engineers, Inc., 1970.
Hayward, C. R., An Outline of Metallurgical Practice, D. Van Nostrand
Company, New York, 1952.
Arthur G. McKee and Company, Systems Study for Control of Emissions
Primary Nonferrous Industry, National Air Pollution Control
Administration, 1969.
Engineering-Science, Inc., Exhaust Gases from Combustion and Industrial
Processes, Washington, D. C., 1971.
System Development Corporation, Air Pollution Control Field Operations
Manual, Environmental Protection Agency, Office of Air Programs,
Raleigh, N. C., 1972.
Midwest Research Institute, Emissions, Effluents, and Control Practices
for Stationary Particulate Pollution Sources, National Air Pollution
Control Administration, Cincinnati, Ohio, 1970.
U. S. Department of the Interior, Bureau of Mines, Mineral Facts and
Problems, 1970.
Strauss, W., Air Pollution Control, Wiley--Interscience, New York, 1971.
Los Angeles County Air Pollution Control District, Air Pollution Engineer-
ing Manual, U. S. Department of Health, Education and Welfare,
National Center for Air Pollution Control, Cincinnati, Ohio, 1967.
Stern, A. C., Air Pollution, Academic Press, New York, 1968.
Southern Research Institute, Manual of Electrostatic Precipitator
Technology, National Air Pollution Control Administration,
Cincinnati, Ohio, 1970.
GCA Corporation, Handbook of Fabric Filter Technology, National Air
Pollution Control Administration, 1970
-309-
-------
-------
PART VI. AIR POLLUTION CONTROL SYSTEMS
Particulates are the principal pollutant from the five metal indus-
tries covered in this report. The air pollution control devices which
have been used to abate particulate emissions include electrostatic pre-
cipitators, fabric filters, wet scrubbers, and cyclones. In the copper,
lead, and zinc industries, sulfur dioxide emissions are significant.
The most effective method for reducing sulfur dioxide emissions to the
atmosphere has been with sulfuric acid plants. However, this particular
type of "abatement device" is not part of the scope of work for this par-
ticular project and will not be treated in this section. In the aluminum
industry, the major air pollutant is fluoride. Two different types of
controls have been used to reduce fluoride gases from these operations,
low energy wet scrubbers and dry adsorption processes. The low energy
wet scrubbers are discussed as part of this section ind the dry adsorption
process is discussed in Chapter 16. Table VI-1 is a list of the common
particulate control devices used by these major metals industries.
There are several factors which affect the selection of the gas
cleaning unit for a particular operation. These include the volumetric
flow rate, the variability of the gas flow, particulate concentration,
allowable pressure drop, product quality requirements, and the required
collection efficiency. Particle size gradients in the inlet gas stream
are also an important factor in selecting the proper abatement device.
Particles larger than about 15 microns are usually removed effectively
by inertial separators such as cyclones. For those sources which have
particles smaller than 15 microns and with many of them being smaller
than one micron (submicron), medium and high energy scrubbers, fabric
-311-
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Table VI-1. USE OF PARTICULATE COLLECTORS BY INDUSTRY
Industrial classification
Process
EP
MC
FF
ws
Other
Rock products
Steel
Mining and metallurgical
Cement
Phosphate
Gypsum
Alumina
Lime
Bauxite — --------------
Magnesium oxide --
Blast furnace
Open hearth
Basic oxygen furnace
Electric furnace
Sintering '
Coke ovens
Ore roasters----- —
Cupola
Pyrites roaster
Taconite
Hot scarfing
Zinc roaster
Zinc smelter
Copper roaster
Copper reverb
Copper converter
Lead furnace
Aluminum
Elemental phos
Ilmenite
Titanium dioxide
Molybdenum
Sulfuric acid
Phosphoric acid
Nitric acid
Ore benef iciation
0
0
0
0
0
0
+
0
0
0
+
0
0
0
+
0
+
0
0
0
0
0
0
0
0
0
+
+
0
+
0 0
0 0
0 0
0 0
0 +
0
+
0
0
0
+
0
0
0
0
0
0
0
+ +
+
0
0
+
0
+
0
0
+
0
0
+
0
0
0
0
0
+
+
+
+
+
0
0
0
+
Key:
0 = Most common
+ = Not normally used
EP = Electrostatic Precipitator
MC = Mechanical Collector
FF = Fabric Filter
WS = Wet Scrubber
Other = Packed towers
Mist pads
Slag filter
Centrifugal exhausters
Flame incineration
Settling chamber
-312-
-------
filters, or electrostatic precipitators will have to be used to clean
the gas stream. Figure VI-1 indicates the type of control systems that
can be used on various size particles.
Once the technological considerations have been made for selecting
control systems, general operating factors play an important role in final
selection. For example, the disadvantages of wet scrubbers include the
potential water pollution problem, high power costs, and the presence of
a visible plume. Fabric filters and electrostatic precipitators capture
particles without any physical modification and the collected material
can readily be reused in the process. However, fabric filters have a
temperature limitation and are sensitive to process conditions. Electro-
static precipitators have few moving parts and low power requirements
but are sensitive to variable dust loadings and variable flow rates. Be-
cause of the wide variations in process operating conditions, different
types of control devices may be found on the same source at different
plants.
The following discussion on electrostatic precipitators, fabric
filters, wet scrubbers, and cyclones provides some background with respect
to the technological considerations applicable to an abatement system.
Air pollution control systems for a single source may include different
control devices in series and in parallel. Particulates coming from
roasters in a lead smelter will often go through cyclones to remove the
large particulate matter prior to entering electrostatic precipitators.
Non-ferrous sintering machines may have the wind boxes divided into sev-
eral sections with the primary combustion gases going to one kind of
control device, say a sulfuric acid plant, and the secondary combustion
zone ga-ses going to a different kind of collector.
-313-
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Particle Oamcter. microns (p)
,1m,! drum! lleml
00001 0001 001 01 1 10 100 1.000 10.000
Equivalent
Sito*
«.«£
WflVM
Technical
Definition
Common Atmospheric
Dnporeoid*
Typical Particle*
and
Gu Ditporsoidl
M.thodi tor
Pirllcle Sin
Anjlytii
TypMot
Gu Ctoaninc
Equipment
Terminal
Gravitational
Sottimf-
fforiDlwrM.]
I IP fr. 2.0 J
Particla Diffusion
Coefficient.'
cm '/we.
fepnods
Sal
hi AM
•j»-c
latm
In WMrf
X
arc
In Air
ai2vc
lafm
1
) K
IngstrOm Units. '
Merber| or Inlcrrutiorul SW ClHWhuMn S
AdopMd by Internal Soc Sod So S"K< 1934
0, CO,
H, 1 f, \ Cl,
^wi
I N, I CM. j
CO HX) HO
•Molecular darnel
from viscosity dat
Reynolds Number
Setibnc Velocity
cm/we
Reynolds Number
Sefl*«f Velocity,
Cm/SK
J
G*> r
Molecules'
tl
OHi.
ten ukutated
J.tO'C
H Vi
1
10 •'' 10"" 1
1
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10 10 10?
1 , , , I II
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mwttar I . 1 ,
* 10'* 1 10'*
jyc , • ' ' • '.•17 »
' 1 — •— • "•.-•! - — • — .'
0 l.(
9.000 1.2
00 10,000 2,500
< Theoretical Mesh
(Used very intrequen
1
Visible
M,st
yWem
M Solar Ra<
^ Rosm Smoke *
• — - — Tobacco
" — Zinc Chude F
fflto*!
^iiT
Aitken
Nuclei
M-SeaS,
^ Combustion t
Nuclei
T«es M
u 1
uge
Ray Diffraction '-*
^Nuclei Counter
urgical Dusts and
**Artmonurn Chtond
ch »u C*
" ™ Sulfur*
* Paint Pigrr
jme — H M-lrr
i— 1
• Spray Di
• Alkali Fu
-*1
iphenc Dust
alt Nuclei -H
^ung
»'""„
»- U
50 w/JiJ-
«5 I'UP
Tm'i
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Tytef Scrt
100 «i n \
ai-dial.* (0 1 40 K>
Myl | 1 1 1 1 1 U S Sere
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, i in i,i i -i— L
•• F»l In
i Ou
rared •*•
st
Spray
10 1 « 3
«nM«sh
1 > 4 J
1? 1 ( }
en Mesh
/' r
K'
x/ r
',' : r f r
- Microwaves (Radar, etc )
~-— Fine Sand -»— Coaree S^nd -~- Gravel
and Fog — ~iMist"Ofizzle*- —
i
k — Fertilizer, Ground Limestone—*
Dust •
E Rme-«-« Cement Dust *
Sutfunc ' ml .
Concentrator Mist
^ .1, Pt.hn.nT.vH Cnii\
Mist "
»ents H
secticide Dusts-*
Ground Talc
.ed Milk -»
me H
Milled
•*- Nebulizer Dro
Damaging _
- — Flotation Ore
J^nl M
Spores1
- — Pollens — •
Flour H
---«
PS-»1 1* 1
Pneumatic
Beach Sand
, »<
Hydraulic Nozzle
Dust i " Nozzle Drops 1
Red Bkxxl Cell Diameter (Adults) 75/ii03/xl
h« 1^ Bacteria — — 1— n-Human Hairn
- immn ^ c . i .Etectrof wmed.. -
Impingere -I- ^^ -t-
Microscope
Centrifuge—
1 M
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Turbidimetry*1
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>.
Ultrasonics
lv«fy hnuud l«4
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n.«wl <
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10'* 10 ' 10"j
10 ',,'?-;,,
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ugal Separators—
.
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co»n«««T
ti
^iwrono msumi* msiituu
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Drops — *
* Furnishes avertfe panrk
diameter but no nt
d»stnout*on
^ * Sue distribution mav be
obtained by s»oal
raiioraiion
Machine Tools (K
Settling Chan
KMI Air Filters — »i
Mechanical Se
to- ', 10-; 10°
f??!1?''!
io~3J io'j ID- ;
'"i,,10",
, 10" ',s 10"'
. , , w\
. , , io-'°.
jarators — ^
10' , 10' ,
> 10' , , ,
10°, 10' , 10
10°,, , 10
, '°-\>.,
. , , io":
icrometen, Calipe
10' , 10
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1 1 4 S
, 10-.,. ,
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10'
b J B «
,10"
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SiSSl",. 00001 °°°| °01 OI ' to 100 1.000 10.000
""*"'"*""""• Pwticle Diameter, microns (M> '"""' ^«,,,"(T!.-,c
FIGURE VI-1 CHARACTERISTICS OF PARTICLES AND PARTICLE DISPERSIONS
-314-
-------
There are many existing air pollution control regulations which apply
to the maintenance of air pollution control systems. Generally speaking,
the laws will require that all air pollution control devices be maintained
in good operating condition. Thus, unbalanced fans, excessive spark rates,
holes in the ducts and water entrainment are indications that the control
system has not been maintained in good operating condition. Observations
of concern to an enforcement official when inspecting an air pollution
control system are included in the following chapters.
35. ELECTROSTATIC PRECIPITATORS
The theory of the successful operation of the electrostatic precipi-
tator will not be discussed in detail in this chapter, since it has been
carefully documented academically. Interest is in the actual field ap-
plication of the precipitator. Basically, there are two types of precipi-
tators used in these five industries: wire-in-plate and wire-in-cylinder.
Because of the nature of the air contaminants, plate-type precipitators
are predominantly used to reduce particulate emissions. The wire-in-
cylinder type precipitator is best applied to wet gas cleaning, which is
uncommon in these industries. Figures 35.1 and 35.2 are diagrams of the
wire-in-cylinder and wire-in-plate type precipitators.
There are several parameters which are important in selecting the
size of precipitator. These include the volume of gases to be treated,
the resistivity of the particulate, particulate size, and dust loading.
Of these, resistivity and dust loading are the most important. The resis-
tivity is dependent upon the nature of the pollutant. Most of the pollu-
tants associated with these five industries have resistivity values be-
7 9
tween 10 and 10 ohm-cm. Dust loadings may range from several hundreths
to 100 gr/scf depending on the manufacturing process.
-315-
-------
High Voltage
Insulator
Compartment
Support
Insulator
Steam
Collector
High Tension
Support Frame
Collecting
Electrode
Pipes
Shell
High Tension
Electrode
Electrode
Weight
Clean Gas
Main
Gas Deflector
Cone
Collected
Dust Out
FIGURE 35,1 A SINGLE-STAGE VERTICAL WIRE AND PIPE UNIT
-316-
-------
FIGURE 35,2 PARALLEL PLATE PRECIPITATOR
-317-
-------
An equation which relates efficiency with gas flow rate and collec-
tion area of the precipitator is:
E - 1 - e ' <* A/V)
Where: A = Area of collecting surface
V = Gas flow rate
w = Precipitator rate parameter
E « Efficiency percent
e = Base of natural logarithm
This equation can be used to calculate the collecting surface area re-
quired for a specified volume of gases. The critical parameter in that
equation is "w", the precipitation rate. The precipitation rate is an
indication of the speed at which particles will migrate to the collecting
electrode. Precipitation rate varies with respect to each individual ap-
plication. For smelters, the precipitation rate is 0.35 fps. For open
hearth steel making furnaces it is 0.06 fps. For EOF furnaces it ranges
between 0.20 and 0.46 with an average of about 0.36 fps. Other precipi-
tator parameters which are important for the effective removal of particu-
lates from a gas stream include spark rate and corona power. Typical
spark rates for these heavy metal industries will usually range between
50 and 250 sparks/minute. At no time should a precipitator for these
industries be operating with a spark rate in excess of 400 sparks/minute.
To a certain degree, spark rate will depend on the physical condition of
the precipitator. Corrosion, reduced electrical insulation, and particu-
late build-up may cause excessive sparking. On the other hand, a low
spark rate, on the order of 10 to 20 sparks/minute, would indicate a de-
ficiency in precipitator power, therefore, reduced efficiency.
The electrical energy necessary to charge a particle and bring it in
-318-
-------
contact with a collecting surface is unique to each specific application.
Generally speaking, the corona power will range from 200 to 300 watts per
1,000 cfm of gases treated for these metals industries.
Once the particle has been deposited on the collecting surface, it
must be removed. A dust build-up would prevent further ionization and re-
duce the overall efficiency of the precipitator. Particulate is removed
from the plates and the wire by vibrators or rappers. These are mechani-
cal means for removing the dirt from the electrodes. The rappers and vi-
brators will knock the agglomerated particulates to the bottom of the pre-
cipitator where it is collected in hoppers. There is no set rapping rate
or average rapping rate that can be associated for each of these large
metals industries. Each precipitator will have its own rapping or vi-
brating sequence.
Another critical operating parameter of a precipitator is the gas
flow rate. In most cases, the gas is preconditioned to meet the design
specifications of the electrostatic precipitator. Often, the gas comes
from a furnace at extremely high temperatures and is cooled by water
sprays or dilution air to a temperature of 500 F on the inlet side of the
unit. It is very important that the distribution of the gas through the
precipitator be uniform. This is usually accomplished by straightening
vanes and distribution vanes. Figure 35.3 illustrates the poor effici-
encies associated with the irregular flow velocity. At a flow velocity
of 0.5 meters per second (mps) there is an efficiency of 99.4 percent.
While in another section of the precipitator, where the flow velocity is
1.5 mps the efficiency is only 91 percent.
Depending on the specific installation, the precipitator may be
designed to have several sections or several units. A unit connotes par-
allel gas flow and a section connotes gas flow in series; therefore, for
-319-
-------
»*
o
Ul
I—•
o
Weighted
Average
94.5
VELOCITY, meters/sec
FIGURE 35,3 EFFECT OF NON-UNIFORM VELOCITY ON
PRECIPITATOR COLLECTION EFFICIENCY
-320-
-------
a precipitator installation which has two units, 50 percent of the gas
will be treated by one unit, and 50 percent of the gas will be treated
by the other unit. A unit may have several sections and for these heavy
metals industries it is common to find up to four sections for each of
the precipitators. The principal advantage of sectionalizing is with
respect to down-time of the precipitator. For example, if one section
of a four sectional precipitator became inoperative, the remaining three
could control particulate levels, although not as efficiently.
The type of monitoring instruments that are available for an electro-
static precipitator installation will include meters to measure spark rate,
voltage and,current. Typical voltages for these industries will be on the
order of 20 to 100 kv and the average current is about 1000 ma or 1 amp.
35.1 Precipitator Inspection
Manufacturers of electrostatic precipitators have usually designed
precipitators for specific applications. It is unlikely that identical
precipitators would be found, even in the same metals application. Such
things as corona power, precipitation rate, type of plates, and gas tem-
peratures will vary from furnace to furnace and also from plant to plant.
It is the intent of this sub-section of this chapter to identify those
general operating characteristics and inspection points which can be ob-
served when a precipitator is in operation. Observation of marked increase
in plume opacity is one indication that the precipitator may not be oper-
ating properly.
Causes for precipitator malfunction include: electrical, gas flow,
and physical. Most electrostatic precipitator service men have indicated
that it is the electrical system of the precipitator which is most often
the cause of malfunction. If there is any doubt as to the operability of
-321-
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the precipitator the electrical meters should be checked first. Older
precipitators will have problems with the rapping or vibrating scheme
and the physical abrasion caused by the pollutants. If the precipitator
monitoring instruments, spark rate meter, primary voltage meter and pri-
mary ammeter indicate that the precipitator is operating normally, yet
visual observations indicate poor precipitator efficiency, then it is im-
perative that the enforcement official obtain the design specifications
from the plant operator.
The following step-wise procedure should be used to detei-uiine the
effective operability of a precipitator. Many items on this check list
came from "The Manual of Electrostatic Precipitator Technology."
1. Observe the electrical monitoring instruments for the precipi-
tator. If the spark rate is less than 400 sparks/minute this is con-
sidered normal operation; however, a spark rate in excess of 400 sparks
minute is an indication that the precipitator section has shorted out.
Record the primary voltage and primary amperage to each of the sections,
if a precipitator has four sections, this inspection procedure must be
carried out on each individual section. A marked voltage drop in one sec-
tion of a precipitator is an indication of a dead section and the unit
is not operating correctly.
2. Record the gas inlet temperature and gas flow rate. The gas
temperature should be between 250 and 500 F. If the temperature is less
than 250 F, it is likely that condensation will form in the precipitator,
causing malfunction. Temperatures in excess of 500 F cause the plates
and wires to warp within the precipitator. Observe the ducts entering
the precipitator for corrosion. Corrosion at the exterior ducts is an
indication of corrosion on the interior of the precipitator.
-322-
-------
3. Open the hatch on several of the precipitator sections. Observe
dust deposits on collecting plates, and wires before cleaning. A 1/4-
inch deposit is normal, but if the metal plates are clean there is a pos-
sibility that a section is shorting out. If more than 1/4-inch of dust is
on the plates the rappers and vibrators are not working properly. Observe
the amount of corrosion adjacent to the door. Leakage to the interior of
the precipitator through the doors could cause non-uniform gas flow and
reduce efficiency. Check plate alignments for equal spacing between plates,
also check for broken wires at the top of the precipitator.
4. Open the hopper access door for this inspection. Check for leak-
age into the precipitator around the door and for dust build-up in upper
corners of hoppers. Check the high tension weights, if one has dropped
more than 3 inches, it is an indication that the wire has broken. Check
the hopper bottom for broken precipitator parts, like wires, insulators
and plates.
5. Check the electrical distribution center by examining the high
tension lines, insulators, bushing, terminals, and arresters for broken
parts. Some minor sparking should be noted in this area.
6. Listen to the rapper or vibrating mechanism which cleans the dust
from the plates and wires. A uniform, rhythmic tapping, of metal to metal,
should be noted. Any irregular sounds are an indication that the rapper
mechanism is not operating correctly.
7. If necessary, make the calculations, which relate efficiency
collection area, gas flow rate and precipitator rate. Compare the calcu-
lated results to design specifications and ask whether any alterations
have been made to the process which might affect precipitator performance.
8. Ask about the routine maintenance schedule for the precipitators,
and to see logsheets for any repairs.
-323-
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36. FABRIC FILTERS
Fabric filter collectors are commonly referred to as baghouses and
are perhaps the oldest and most reliable methods of removing dry particu-
late matter from an air stream. Baghouses have traditionally been de-
signed with a collection efficiency in excess of 99 percent. As mentioned
in the previous chapters, these five metals industries are commonly as-
sociated with fine particulates (minus 10 microns in diameter). Fabric
filters are effective in collecting particulates as small as 0.1 micron
and some investigators have measured and collected particulates smaller
than 0.01 micron in size. The size of these systems range from one or two
bags to as many as many several thousand bags for one system. Figure 36.1
is an illustration of a typical baghouse.
The operating principle of a baghouse is simple, the filter itself
acts as a collection medium. When air is passed through the fabric, par-
ticles come in direct contact with the fabric and are caught. The air
stream or gas is not affected by the fabric filter and passes without in-
terruption to 'the outlet side of the unit. There are several factors which
are special to the design of a fabric filter system. Different fabrics
will have different permeabilities. Permeability is associated with the
ease at which a gas passes through a fabric. The American Society for
Testing and Materials (ASTM) has developed a standard procedure for meas-
uring permeability through new cloth; by keeping the pressure differential
to 0.5 in. wg, the flow rate is recorded that passes through a square
foot of cloth. Table 36.1 indicates the fabric filter characteristics
including air permeability for selected fibers.
The pressure drop commonly found in baghouses in these metals appli-
cation ranges from 2 to 8 in. of water during normal operation. Average
-324-
-------
CLEAN AIR
OUTLET
DIRTY AIR
INLET
CLEAN AIR
SIDE
CELL PLATE
FIGURE 36,1 TYPICAL SIMPLE FABRIC FILTER BAGHOUSE DESIGN
-325-
-------
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-326-
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flows are between 1.5 and 3.0 cfm/ft2 of cloth. This is known as
the air-to-cloth-ratio. Baghouses traditionally found in these five
metals industries have a maximum filtering ratio, air-to-cloth-ratio,
which ranges between 2.0 and 3.5. However, when the bags are cleaned with
2
a reverse air jet stream, the air-to-cloth-ratio increases to about 9 cfm/ft .
Moisture and gas temperature are the most critical operating variables
for baghouse installation. It is desirable to keep the temperature of the
gas 50 to 75 F above the dew point to prevent condensation within the unit.
Moisture would cause mud cakes to form on the bags and cause high resis-
tance and ultimate rupture. Because of the physical and thermal charac-
teristics of each of these fibers, the bags will fail at elevated tempera-
tures. The long and short term operating exposure of selected fibers is
also shown in Table 36.1. Dacron-^ is the most popular bag used in these
metals industries. Its normal operating temperature is about 270 F. Gases
coming from melting and smelting operations from these industries at high
temperatures must be cooled before entering the baghouses. Heat exchangers
and water spray systems are used to cool the gases. Each of* these gas cool-
ing systems must be well designed to prevent moisture and excess temperature
in the baghouses.
There are three types of baghouse designs commonly used today: open
pressure, closed pressure, and closed suction. Open-pressure baghouses
do not have a stack, instead the gases are exhausted through the walls or
sides of the baghouse installation. Closed-pressure baghouses are con-
structed with the fan supplying a positive pressure and the dirty gas to
the unit. Because the fan is on the inlet side, it is subjected to the
abras,ion and wear caused by the air pollutants. In a closed-suction bag-
house, the fan is located on the outlet side of the unit, thus the gases
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at the fan are cleaned and free of abrasive pollutants. One of the
problems encountered with a closed-suction baghouse is the tight seal
required for the entire installation. Air leaks around access doors,
vibrators, and walls may reduce the efficiency of the unit or cause con-
densation at "cold spots".
There are several types of manual shaking systems used to clean the
bags once they become dirty. The cleaning cycle is based on pressure
drop across the bag or a timed cycle. Figure 36.2 illustrates some of
the schemes used to remove dust from the fabrics. Each cleaning scheme
has its advantages for a specifically designed baghouse. Often bag-
houses are sectionalized, that is, having several compartments so that
one compartment may be cleaned while the others continue to operate.
For those baghouses which clean on a pressure drop response, the clean
cycle may begin when the pressure drop across the compartment reaches
3 and 4 in. wg. On the other hand, time cycles vary widely, from once a
minute to once a day.
Bag life for these metallurgical industries ranges between 18 months
and 2 years. There are few operational adjustments which can be made to
a baghouse once it has been installed and most likely, the only monitoring
instrument for baghouses will be a manometer measuring pressure drop
across the entire system. Bags are changed on a regular schedule, also
when they rupture.
36.1 Enforcement Procedure
The following step-wise procedures should be used to assess the opera-
ability of a baghouse abatement installation:
1. Prior to, or upon entry to the plant, obtain design specifications
of the baghouse installation. Ask what type of bags are being used and
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JET
UNI-BAG
INSIDE OUT
FILTERING
SIDE VIEW
COMPRESSED AIR
OUTSIDE IN
FILTERING
Bubble cleaning of dust collector bags.
SIDE VIEW
Jet pulse dust collector bag cleaning.
X
?;
/
,
*•
^ >
#
rj EXHAUST
3
.,
i
^
REPRESSURING
VALVE
URING\ /
SIDE VIEW
SIDE VIEW
, INLET
Q VALVE
FILTERING COLLAPSING
Reverse air flexing to clean dust collector bags by repressuring
SIDE VIEW
CLEANING
AIR HORN
FILTER BAG
TOP ENTRY
\
HIGH PRESSURE
-»-AIR BLOW
RING
DUST--
" >•_* !•*/.'
• Sonic cleaning of dust collector bags.
INSIDE OUT
"FILTERING
CROSS-SECTION
Reverse jet cleaning of dust collector bags.
FIGURE 36,2 BAGHOUSE CONFIGURATIONS
-323-
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ask for historical records which would indicate fan size, inlet tempera-
ture through the baghouse and pressure drop across the unit. Determine
the number bags and collection area of this installation and compare this
data to the data in Table 36.1.
2. Observe the cleaning cycle for this particular installation.
Determine whether a pressure or time cleaning cycle is used to remove
the dirt from the fabric. For a pressure control system, check the con-
trols and their operability to insure that when the pressure drop is
reached, cleaning is initiated. For time-cycle cleaning schemes, observe
the rhythm for a given period to assure its operability.
3. Check for air leakage into the ducts, fans, access door, bag-
house structure, and hopper. For closed-suction baghouses, check the
seals on doors, hatches, and hoppers for a tight seal.
4. Observe the unit for an entire cleaning cycle. If the light or
dark plume is noted emanating from the stack, it is likely that a rupture
or bag failure has occurred but has not been replaced.
5. Measure the wet bulb and dry bulb temperature of the inlet gas
stream. Use the section in Part VIII of this manual to determine the dew
point of the inlet stream. The dew point should be at least 50 F above
the inlet temperature to prevent moisture build-up on the bags.
6. Observe the manometer or pressure drop across the baghouse sec-
tions. After cleaning, the pressure drop across the fabric should be
less than when dirty.
7. Observe during the hopper clean out operation.
37. WET SCRUBBERS
There are many types of scrubbers in use in these five metals indus-
tries today. The types vary from the most simple design of a water spray
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in stack to high energy venturi scrubbers. Each manufacturer has his
own design on the method for impacting particulate matter in a liquid
film. Basically, there are low, medium and high-energy scrubber systems.
The energy requirement refers to the amount of power needed to obtain se-
lected pressure drops across the scrubbing system. Low energy scrubbers
typically have a pressure drop of up to 12 in. wg pressure. High energy
venturi scrubbers can go up to 100 in. wg pressure. For these five
metals industries, we are primarily interested in the high-energy capa-
city scrubber systems. This is mainly due to the nature of the pollu-
tants from these industries. As we have seen in previous chapters, the
particle diameter of much of the metal fume is less than one micron.
This requires the use of high energy venturi scrubbers on most of these
industrial applications. Neither cyclones nor settling chambers have been
effective in removing the submicron particle inherent in these metals
applications.
The collection principle of wet scrubbing systems is accomplished
by impaction of dust with liquid droplets. The particles come in contact,
enlarge in size and finally settle out. Once the particle is trapped, it
is then washed away. There are no universally accepted equations which
relate scrubbing parameters with collection efficiency. Much of the ex-
isting scrubber technology has been defined and presented in the reference
entitled, "Scrubber Handbook." Basically, the collection efficiency of
a scrubber system will depend on the size of the particle. Of particular
importance is the particle size and inlet dust loading. Figure 37.1
shows a relationship between pressure drop and outlet grain loading.
Several investigators have tried to relate input power to efficiency.
Power refers to the amount of energy necessary to overcome the resistance
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100
o
CM
a.
o
10
a.
»—4
cc
1
I
J I I
0.001 0.01 0.1
CLEAN GAS DUST LOADING GRAINS PER STANDARD CUBIC FOOT
10
FIGURE 37,1 CALIBRATION CURVE FOR A BLAST FURNACE VENTURI SCRUBBER
-332-
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caused by a scrubbing system, such as a contracting throat or high pres-
sure sprays. Figures 37.2 and 37.3 show this relationship of contacting
horsepower and efficiency for selected metallurgical operations. These
curves were developed for specific industrial applications. Generally
speaking, it will require about 7 hp/1000 cf of exhaust gases to obtain
an efficiency of above 99 percent for the particle diameter typically found
in these industries. These relationships were developed for high energy
venturi scrubbing systems. Less efficient systems like the impingement
plate scrubber does not have the high collection efficiency commonly as-
sociated with venturi units; however, a lower efficiency would not require
as much contacting horsepower. It is because of the similarity of the
metal fume generated in each of these metals industries that these curves
supply "ball-park" figures for power requirements for scrubbing systems.
As mentioned in the previous chapters, these fumes are fine and many are
submicron in size. The pressure drop, which corresponds to the contacting
power, will represent the most important scrubber operating variable used
to assess the collection efficiency of a unit.
Another fundamental operating parameter of wet scrubber systems is
the liquid flow rate in the unit. This parameter is usually expressed in
terms of gallons of water per 1000 cf of gas processed. For the high en-
ergy venturi systems on these particular applications the flow rate re-
quirement varies between 3 and 10 gal/1000 cf of gas processed. For
plate or impingement type scrubbers (low energy units) the flow rate is
something less; on the order of 1 to 2 gal/1000 cf of exhaust gases pro-
cessed. Under normal operation, high energy venturi units have been
shown to reduce particulate levels to an exit loading of less than 0.01 gr/
scf. Typical throat velocities for venturi units are on the order of 200
-333-
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OXYGEN IN
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99.9
99.5
99
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0.7
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to 600 ft/sec. Packed bed or impingement type scrubbers typically have
pressure drops less than 5 in. wg pressure. Figures 37.4 and 37.5 are
illustrations of a venturi scrubber and a wet impingement scrubber.
The principal disadvantage of using a venturi unit in lieu of an
electrostatic precipitator, fabric filter, or other collection devices is
its high annual operating cost. Once installed, the cost of water is
much cheaper than that for electrical energy for precipitators, and, in
many cases, much cheaper than replacement of bags for the fabric filter
systems. The immense horsepower requirements soon offset these savings.
Venturi systems in these metals industries typically operate about 60 to
80 in. wg pressure. These systems have a collection efficiency in excess
of 99 percent. Packed bed and plate type scrubber systems have an ef-
ficiency of between 80 and 90 percent.
37.1 Medium Energy Scrubbers
Medium energy scrubbers refer to those control devices which op-
erate with a pressure drop of up to 14 in. H~0. Compared to the other
types of control systems, these scrubbers usually require a minimum of
space. Typical efficiencies for these units will be on the order of up
to 90 percent for large dust. Their major application in these metals
industries is in the material handling segment of production. These type
units are found on transfer points from conveyor systems, and at the end
of crushing, screening and grinding operations. In the aluminum industry,
low energy scrubbers (up to 8 in. H«0 wg) are the primary air pollution
control systems. Hydrogen fluoride gas, which emanates from anode curing
ovens, prebake pot and Soderberg pot operations, is very soluble in water
and can be effectively controlled by passing it through these scrubber
systems. Figures 37.6 and 37.7 are illustrations of a flooded-bed
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B
A
FIGURE 37,4 VENTURI SCRUBBERS MAY FEED LIQUID THROUGH JETS (A),
OVER A WEIR (B), OR SWIRL THEM ON A SHELF (C)
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Gas Outlet
Water
Eliminator
Impingement
Baffle Plate
Drain
CLEAN AIR OUT
-ENTRAPMENT
SEPARATOR
FIGURE 37,5 WET IMPINGEMENT COLLECTORS
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GAS OUTLET
MIST
ELIMINATOR
GLASS SPHERES
SPRAY
WATER INLET
FIGURE 37,6 FLOODED BED SCRUBBER
-339-
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DIRT AND WATER
DISCHARGED AT
BLADE TIPS
DIRTY GAS
INLET
CLEAN GAS
OUTLET
WATER AND
SLUDGE OUTLET
FIGURE 37,7 CENTRIFUGAL FAN SCRUBBER
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scrubber and a centrifugal fan wet scrubber. Flooded-bed scrubbers sim-
ilar to Figure 37.6 are the ones that are used to remove hydrogen fluor-
ide gas. The centrifugal wet scrubber is the type of system that would
be used on many material handling sources. Figure 37.8 will provide some
idea of the fan horsepower required for various sized installations.
37.2 Enforcement Procedure
In this subsection it is impractical to discuss typical operating
parameters for each industrial application because of the numerous scrubber
designs. Certain things are similar for scrubbers applied to these in-
dustries. One of the easiest parameters used in assessing the performance
of a scrubber is the contacting horsepower and corresponding flow rate.
The horsepower rating is available on nearly every motor in the form of a
name plate on the frame of the motor housing. Flow rate can be measured
or obtained from fan curve data. A scrubber installation will contain a
manometer which would indicate the pressure drop across the scrubber.
Amperage of the fan, line voltage and water flow rate in the system are
necessary parameters in assessing the operability of the scrubbing system.
The following step-wise procedure will assist the enforcement offi-
cial in determining whether or not a scrubbing system is working effec-
tively:
1. Obtain the horsepower rating of the motor or motors involved in
moving the gas stream through the scrubbing system. Determine the fan ca-
pacity for each of the fans in the system, in terms of scfm. Compare this
power/flow rate ratio to the above mentioned figures for these type indus-
tries. Ascertain that this unit has been properly sized for this particular
installation.
2. Inspect the fan for vibration. Excessive vibration may cause the
fan, ducts, and scrubber components to rupture.
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O
O.
UJ
CO
o:
o
a:
o
ce
LLJ
CO
OL
O
O
1 23456789 10
SATURATED GAS VOLUME CFM x 1000
900
800
700
600
500
450
400
350
300
250
200
150
125
100
75
50
25
0
10 20 30 40 50
SATURATED GAS VOLUME CFM x 1000
FIGURE 37,8 FAN HORSEPOWER REQUIREMENTS FOR
VARIOUS SIZE SCRUBBERS
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3. Check for the distribution of water at the throat or in the
packed bed system. Some venturi systems will have gauges which indicate
the pressure supply to each nozzle or each section of a particular throat.
Observe and insure that these pressures are nearly the same for each sec-
tion or each nozzle. A deficient pressure indication for a nozzle or
section would indicate that the proper amount of water is not being sup-
plied for the ensuing air stream, thus reducing the overall efficiency
of the collection system.
4. Record the temperature of the inlet gas stream to the scrubber.
Temperatures to the scrubber will be on the order of 250 to 500 F. If
the inlet temperature is less than 250 F, it is likely that condensation
will form in the ducts, causing plugging.
5. Inspect the interior of the scrubber for scaling and particulate
build-up. For venturi systems, inspect the interior of the throat care-
fully for caking and other particulate build-up. Any caking that causes
an uneven distribution of the gas stream across the throat would reduce
the overall collection efficiency of the scrubber. Inspect the mist elim-
inator for mud build-up.
6. Observe the water effluent from the scrubber system. A mud
slurry should be noted. Compare the water flow rate for this scrubber
installation with the values mentioned above.
7. Obtain the pressure drop across the entire scrubbing system.
Compare this pressure drop to those values cited for typical installations.
If possible, obtain design specifications for the scrubber installations
and compare the operating parameters, flow rate, horsepower, pressure drop
and water flow rate, to the design specification.
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38. CYCLONES
Cyclones are the least efficient air pollution collection device that
has been used in these metallurgical industries. Cyclones work on a prin-
ciple of centrifugal force and gravitational settling to remove large par-
ticulate matter from gas streams. Cyclones work well in removing particu-
lates greater than 10 microns in diameter. With that size particle, cy-
clones and multicyclones have shown an excess of 80 percent removal
efficiency.
Figure 38.1 illustrates the conventional reverse-flow cyclone. The
inlet gas stream is tangentially applied to the cyclone. The exhaust gas
is removed through the center of the unit. The centrifugal action in the
cyclone causes large particles to settle to the base of the cyclone where
they are removed periodically. Figure 38.2 indicates the kind of effici-
ency that can be found in various mechanical collectors which may have a
load of 4.6 gr/cf.
Cyclones are still used in modern air pollution abatement systems.
Generally they serve as a preliminary knock-out chamber to remove the very
large particles from many of these metallurgical operations. Precipitators
may encounter operational problems if varying loads of fine and large dusts
are cleaned in these systems. In these systems, cyclones may be only 50
percent effective, yet remove virtually all of the large particles. The
particle size range for these metals operations is normally considered to
be fine particulate. This would include particles down to 0.1 microns.
As can be seen from Figure 38.2, cyclones have little effect on particles
in this size range.
38.1 Cyclone Inspection
The successful operation of a cyclone depends on its physical con-
dition. Power requirements, pressure drop, temperature, and moisture have
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ZONE OF INLET
INTERFERENCE
TOP VIEW
INNER
VORTEX
GAS
INLET
SIDE VIEW
OUTER
VORTEX
INNER
VORTEX
OUTER
VORTEX
GAS OUTLET
INNER
CYLINDER
(TUBULAR
GUARD)
CORE
\-DUSTOUTLET
FIGURE 38,1 CONVENTIONAL REVERSE-FLOW CYCLONE
M> a 70* F
RESISTANCE 30 IN WG
LOAD 4 6 GRAMS PER CU FT.,
SP GR 21
1O Z9
PARTICLE DIAMETER. MICRONS
JS 40
FIGURE 38,2 TYPICAL FRACTIONAL EFFICIENCY CURVE OF A CYCLONE
-345-
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little effect on the operating performance of a cyclone. The major prob-
lem attributed to cyclone deficiency is normal wear and abrasion. Par-
ticles can be abrasive and actually wear through the shell of a cyclone.
The enforcement official should observe the cyclone in its entirety for
rust and leaks in the duct work and cyclone shell.
It is unlikely that cyclones will have air pollution monitoring
instrumentation associated with them. At best, a manometer may indicate
the pressure drop across the unit. If the manometer is available the
enforcement official should record this pressure drop for future com-
parisons. A lower pressure drop noticed from visit to visit may indi-
cate that the cyclone performance is deteriorating. For cyclones which
have outlets to the atmosphere, the enforcement official should note the
plume opacity. Finally, the enforcement official should ask what schedule
is used to remove the collected particulate from the cyclone hopper.
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PART VII. FIELD ENFORCEMENT EQUIPMENT
The enforcement official is expected to be able to perform some
direct and simple field tests and measurements. These tests should indi-
cate gaseous volumetric flow rates and pollutant concentrations. Particu-
lates, sulf - J-'"y?de, --.rlror. r.cr-•-;-:•' . 3nd fluorides are of special in-
terest. It is anticipated that other pollutants may become subjects of
interest from time to time.
The purpose of the enforcement official's field testing is to deter-
mine the need for complete source-emission testing in accordance with
rigorous testing procedures. The simple tests performed by the enforcement
official have inherent limitations and provide only an estimate of emission
rates. Most of the information sought by the enforcement official will be
available from plant operating records and instruments and therefore it is
believed that direct field tests for estimating emission rates seldom will
be required.
Source testing considerations must include the adverse field conditions
under which the field tests are to be performed. These include high temper-
atures, presence of noxious gases and, possibly, poor accessibility.
The enforcement official's field testing equipment inventory needs
to include:
1. A pitot tube, inclined manometer, and high and low temperature
thermometers for gaseous emission volumetric flow rate deter-
mination,
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2. A stack particulate sampling assembly that Is to include a probe,
a particulate filter, a flow meter, and a pump,
3. A kit of direct-reading colorimetric indicators primarily for
the concentration determination of sulfur dioxide, carbon mon-
oxide and hydrogen fluoride.
Gaseous emission volumetric flow rates can be obtained by the direct
measurement of the average flow rate by pitot tube. The product of the
average gas velocity and the cross-sectional area of the stack at the
place of measurement gives the gas flow rate.
The pitot tube is a simple probe that is inserted in the stack. It
permits the direct reading of the velocity head of the flowing gas stream
at the tip of the pitot tube on an inclined manometer (Figure VII-1).
A simple mathematical relationship correlates velocity head to gas
velocity. This relationship is defined for gases of density equal to air
at one atmosphere by:
V_,7 = 2.90 "V Ah T
d V
where: Vav = gas velocity, fps
Ah = velocity head, in. 1^0
T = gas temperature, °R (°F + 460)
A correction factor (normally 0.8) must be introduced into the equa-
tion for a type-S pitot tube because it slightly overstates the velocity,
whereas the standard type pitot tube requires no correction. The average
stack gas velocity is determined by measuring the velocity in the stack
at several places and then obtaining the arithmetical average velocity.
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r
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-349-
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Weight concentration determination of particulate matter in the gas-
eous effluent requires the withdrawal of a known volume of gaseous efflu-
ent from the stack and determining the quantity of particulates in the
effluent sample taken by removing the particulates by filtration and weigh-
ing the collected particulates. The net weight gain of the filter is the
weight of the particulate strained from the effluent sample taken. The
particulate weight concentration of the effluent is obtained by dividing
the weight of the particulates collected by the volume of gas sampled,
corrected to standard temperature and pressure. The usual unit of weight
concentration is grains per standard cubic foot (gr/scf).
The desired goal is to obtain a representative average effluent par-
ticulate concentration. In order to achieve this aim as closely as pos-
sible without conducting rigorous tests under isokinetic conditions, the
sample size should be at least 10 to 15 cf collected at an approximate
rate of 1 scfm.
The sampling train is used for particulate concentration determina-
tion. It consists of a probe, housing the sampling nozzle and particulate
filter, a flow meter and a pump. Figure VII-2 shows a Joy Manufacturing Co.
filter holding assembly,, including the probe. It is desired that the meter
and air mover connected to the probe be lightweight, durable, and compact.
For example, an air moving unit, the RAC Midget Air Sampler, manufactured
by the Research Appliance Company, shown in Figure VII-3, is well suited
for this purpose.
After determining the particulate loading (weight concentration) and
the average velocity, it is possible to determine the mass emission rate
in terms of Ibs/hr or tons/day. Temperature pressure, cross-sectional
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FIGURE VII-2 FILTER HOLDER ASSEMBLY AND PROBE
FIGURE VI1-3 MIDGET AIR SAMPLER
-351-
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area, and the proportion by volume of water vapor in the gas are also
required. The temperature, pressure, and cross-sectional area are easily
obtained by simple methodology. The proportion by volume of water vapor
(Bwo) is more difficult to obtain. Hence, in some cases such as for a
dry gas or where accuracy is not of great importance, the term BWQ can be
taken as zero, thus simplifying the equation.
Mass emission rate equation:
Q = 60 (1 - Bwo) Vav A
where:
Q = Volumetric flow rate, scfm
BWO = Proportion by volume of water vapor in the gas stream
Vav = Velocity Average, fps
A = Cross-sectional area of stack at test point, sq ft
Tstd = StaTldard temperature, 530°R
Tav = Average temperature of stack gases, °R
Pav = Average pressure of stack gases, in. Hg
pstd = Standard pressure, 29.92 in. Hg
All values should be measured at the test port.
Q(scfm) x particulate loading (gr/scf) x 0.0086 / min./lbi
Ur/gr J
Mass emission rate (Ib/hr)
(Ib/hr) x 0.012 /ton/hr J = Mass emission
I -. "-- .-. ~— I • ^ .
Mass emission rate
lib/dayj rate (ton/day)
Effluent gaseous pollutant concentrations, such as carbon monoxide,
sulfur dioxide and hydrogen fluoride, can be conveniently estimated by
-352-
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direct reading colorimetric indicators. The most common indicators are
the solid chemical-in-glass indicator tubes. The underlying principle
of these direct reading indicators is a selective chemical reaction be-
tween the chemical reagent in the tube and the pollutant of interest
(different tubes for different pollutants) that produces a color change.
The resulting color change can be directly correlated to the concentra-
tion of pollutant causing the color change by comparing either the color
shade to standardized color-concentration correlation charts or the length
of the colored tube to a calibration curve. The concentration is read
in parts per million (ppm). The use of detecting tubes is extremely
simple. The tubes are placed, after breaking off the sealed ends, in
holders provided by the manufacturer which are fitted with a calibrated
squeeze bulb or piston pump. The recommended volume of gaseous sample
is then drawn through the tube at a low rate. For a few gases, a variable
volume of sample is drawn through the tube until the first visible dis-
coloration is noted. When sampling hot gases, cooling the sample is
essential because of distortions introduced at high temperatures into
calibration and gas volumes.
Indicator-tube gas analysis is very rapid, convenient, and inexpen-
sive. The best accuracy that can be expected from indicator tubes is on
the order of plus or minus 20 percent.
Various detector tubes are available to measure SC^, CO, I^S, HF,
NC>2, 0.,, etc. Although the detector tubes are not accurate, they are
suitable for making an estimate of the gases by an inspector.
Opacity is an index of particulate emission and it is assumed that
the enforcement official will be a certified smoke reader.
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-------
PART VIII. FIELD ENFORCEMENT PROCEDURE
The type of air pollution, regulation that has been adopted for
these primary metallurgical operations include codes which set a maxi-
mum allowable particulate emission rate based on process weight rate,
codes which restrict total sulfur emission as a function of sulfur (in
ore) feed rate, and codes which regulate the mass emission rate of
fluorides. Other types of air pollution regulations also apply to these
primary metallurgical operations. Almost all agencies will have visible
emission regulations which are applicable to these processes. A few
state agencies also have a concentration type regulation for these
industries independent of process weight rate.
From the types of air pollution codes that have been developed for
these industries, it might be expected that the only measurement for
determining compliance with the codes would be source sampling. The
source sampling results could provide engineers with the exact emission
levels of any pollutant and any operation; however, source testing is
quite expensive, completion time is lengthy, and involves prior
scheduling before testing. Any of these three criteria can become a
deterrent for local air pollution control agencies in their enforcement
of air pollution codes. The field enforcement procedures that have been
developed for each of the metallurgical operations in this manual take
these factors into consideration and attempt to minimize the amount of
source testing needed for determining whether or not a source is in
compliance with the existing codes. In order to meet the objectives of
the Clean Air Act of 1970, many sources need to be controlled all of the
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time, not only when the air pollution official arrives on plant for a
visit. The procedures that have heen developed in each of these
chapters will allow the enforcement official to make periodic checks at
selected sources, and from the process operating parameters and air
pollution control variables, assess whether or not a source is in com-
pliance. It has provided guidelines for the enforcement official to
determine whether or not the process is operating correctly and has
identified what variations in operating circumstances affect air pollu-
tion emissions.
In order to develop a viable field enforcement procedure, a control
official must first establish baseline conditions for each of the opera-
tions in his jurisdiction. The baseline conditions must include the
stack sampling data 'which relates the process operating conditions
during the stack test to air pollution control equipment parameters
(eg., spark rate, pressure drop, flow rate, etc.). An enforcement
official who makes periodic visits to certain plants must know what
relationship exists between the source test results and the operating
circumstances at the time of the test. If the enforcement official
returns to the plant at a later date and finds some deviation in the
operating variables (i.e., a higher production rate or lower pressure
drop on scrubber), he can expect some increase or decrease in atmos-
pheric emissions. For example, if a pressure drop across the venturi
scrubber of 60 in. wg provided an atmospheric emission rate of 2 Ibs/hr
from a process feed rate of 500 tons/hr, a subsequent pressure drop of
35 in. wg would likely result in a several-fold increase in particulate
emissions to the atmosphere. Some operating variables are not
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important at all as far as the air pollution control official is con-
cerned. In these chapters it has been noted which variables affect and
which variables do not affect air pollution emissions.
The enforcement official can use the worksheets for establishing
the baseline conditions. A special worksheet should be identified as
the baseline condition. On subsequent visits to the plant, the enforce-
ment official will take along the worksheets for a particular metal
operation of his concern and fill out the worksheet as he conducts his
tour of a plant. The enforcement official should then compare the
operating variables of his most recent visit with the baseline condi-
tions and identify any changes which have occurred which might affect
air pollution emissions. It should be pointed out that published emis-
sion factors were based on industry-wide surveys and cannot be applied
to one specific source. At best, the emission factors indicate the magni-
tude of selected emission levels for the metallurgical operations.
For establishing baseline conditions of emission levels or any
metallurgical operation, an air pollution control agency must have
certain general information relative to the plant. This will include
the name of the plant operator and specifically the personnel to be
contacted when an inspection is required. The general information would
include these data: plant address, phone number, and visiting procedures
including visitor's passes and security clearances. Many control agencies
will have an air pollution permit system. As part of the permit system,
enforcement officials have requested plant layout and blueprints for all
operations which emit pollutants into the atmosphere. The blueprints and
design specifications for the machinery and air pollution control devices
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are important to the enforcement official in assessing design operating
conditions. If process flow sheets are available, this background data will
also be helpful and should be incorporated in the field enforcement file.
Information on the process equipment or machinery should include a general
description of the unit, design specifications, meter readings, capacity and
the operating time. The description of the process should identify whether
this is a batch or continuous operation.
The information on air pollution abatement equipment would include
a general description of the device, the design specification, meter
readings, and collection efficiency. Design parameters such as the gas
flow rate, temperature, pressure drop, water flow rate, and spark rate
are critical factors that should be identified and kept on record.
At this stage of air pollution control in the United States, plant
officials will have made air pollution emissions tests on nearly every
one of their processes and/or stacks. Some of the testing informa-
tion will have already been submitted to the agency in applying for an
air pollution permit. The stack sampling data is of strategic importance
to the enforcement official and inspector who will routinely visit these
plants. Plant operating data are routinely collected with stack tests.
Ask for them. Parameters like pressure drop, spark rate, inlet tempera-
ture, water flow rate, and opacity will help the enforcement official in
his routine inspection. Many plants will use stack opacity meters as a
means of monitoring air pollution control device performance. Enforce-
ment officials will be able to use the same opacity meters and continuous
records for assessing the operability and emission levels. If stack
tests are made on those operations which have opacity meters, and if
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parallel readings were taken, the enforcement official will have
some idea of emission load when he visits the plant.
Each time an enforcement official visits a plant, he will fill out
the Inspector's Worksheet. That information will be kept as a con-
tinuous record on emissions and operating parameters for given certain
operations of a plant. Also included in the field data file would be
the records of complaints that have been received relative to a specific
source. These complaints might precipitate plant visits. If the
plant visits are successful and there are no complaints, then perhaps
a frequency of once-per-year is adequate. If the plant is frequently
in violation and complaints exist, more frequent inspections would be
necessary.
The U. S. Environmental Protection Agency has developed a computer-
ized system entitled, "Enforcement Management System Users Guide, APPD
1237." The bulk of the information included in the field enforcement
file may be applied to this computerized system for an up-to-dqte and
speedy method to retrieve data on selected sources.
Personnel requirements for air pollution control agencies will
vary depending upon the type of sources in its jurisdiction. To inspect
primary metals installations and maintain records of plant activities
would require an individual with an engineering background. Many of
the calculations that have been included in this manual are relatively
simple and could be completed by an individual with several years of
college engineering. Direct working experience in any of the metals
operations would be a tremendous asset for carrying out the objectives
of an enforcement program.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-73-002
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Field Surveillance and Enforcement Guide for
Primary Metallurgical Industries
5. REPORT DATE
December 1973
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Engineering-Science, Inc.
7903 Westpark Drive
McLean, Virginia 22101
10. PROGRAM ELEMENT NO.
2A5137
11. CONTRACT/GRANT NO.
68-02-0627
12. SPONSORING AGENCY NAME A.ND ADDRESS
Environmental Protection Agency
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This manual covers a step-wise enforcement procedure intended for use by
state and local air pollution control agencies. This manual focuses on the
primary metallurgical industry and includes a process description, a discussion
of emission sources, typical control devices, stack gas and process monitoring
instrumentation, and inspectors worksheets for operations in the iron and steel,
aluminum, copper, lead, and zinc industries. All major operations in each of
those industries were analyzed including an enforcement procedure for the storage
and handling of raw materials. Upset conditions and abnormal operating circumstances
were examined in relation to their role in air pollution.
All major pollutants from these five industrial categories were examined.
Generally the pollutant of most concern was particulate matter. Sulfur oxides
and fluorides are unique to specific metals operations and were discussed
accordingly. The manual includes sections on the inspection of pertinent air
pollution control devices.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
13B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
N/A
21. NO. OF PAGES
380
20. SECURITY CLASS (Thispage)
22. PRICE
ML.
EPA Form 2220-1 (9-73)
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INSTRUCTIONS
1. REPORT NUMBER
Insert the EPA report number as it appears on the cover of the publication.
2. LEAVE BLANK
3. RECIPIENTS ACCESSION NUMBER
Reserved for use by each report recipient.
4. TITLE AND SUBTITLE
Title should indicate clearly and briefly the subject coverage of the report, and be displayed prominently. Set subtitle, if used, in smaller
type or otherwise subordinate it to main title. When a report is prepared in more than one volume, repeat the primary title, add volume
number and include subtitle for the specific title.
5. REPORT DATE
Each report shall carry a date indicating at least month and year. Indicate the basis on which it was selected (e.g., date of issue, date of
approval, date of preparation, etc.),
6. PERFORMING ORGANIZATION CODE
Leave blank.
7. AUTHOR(S)
Give name(s) in conventional order (John R. Doe, J. Robert Doe, etc.). List author's affiliation if it differs from the performing organi-
zation.
8. PERFORMING ORGANIZATION REPORT NUMBER
Insert if performing organization wishes to assign this number.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Give name, street, city, state, and ZIP code. List no more than two levels of an organizational hirearchy.
10. PROGRAM ELEMENT NUMBER
Use the program element number under which the report was prepared. Subordinate numbers may be included in parentheses.
11. CONTRACT/GRANT NUMBER
Insert contract or grant number under which report was prepared.
12. SPONSORING AGENCY NAME AND ADDRESS
Include ZIP code.
13. TYPE OF REPORT AND PERIOD COVERED
Indicate interim final, etc., and if applicable, dates covered.
14. SPONSORING AGENCY CODE
Leave blank.
15. SUPPLEMENTARY NOTES
Enter information not included elsewhere but useful, such as: Prepared in cooperation with, Translation of, Presented at conference of,
To be published in, Supersedes, Supplements, etc.
16. ABSTRACT
Include a brief (200 words or less) factual summary of the most significant information contained in the report. If the report contains a
significant bibliography or literature survey, mention it here.
17. KEY WORDS AND DOCUMENT ANALYSIS
(a) DESCRIPTORS - Select from the Thesaurus of Engineering and Scientific Terms the proper authorized terms that identify the major
concept of the research and are sufficiently specific and precise to be used as index entries for cataloging.
(b) IDENTIFIERS AND OPEN-ENDED TERMS - Use identifiers for project names, code names, equipment designators, etc. Use open-
ended terms written in descriptor form for those subjects for which no descriptor exists.
(c) COSATI FIELD GROUP - Field and group assignments are to be taken from the 1965 COSATI Subject Category List. Since the ma-
jority of documents are multidisciplmary in nature, the Primary Field/Group assignment(s) will be specific discipline, area of human
endeavor, or type of physical object. The application(s) will be cross-referenced with secondary Field/Group assignments that will follow
the primary posting(s).
18. DISTRIBUTION STATEMENT
Denote releasability to the public or limitation for reasons other than security for example "Release Unlimited." Cite any availability to
the public, with address and price.
19. &20. SECURITY CLASSIFICATION
DO NOT submit classified reports to the National Technical Information service.
21. NUMBER OF PAGES
Insert the total number of pages, including this one and unnumbered pages, but exclude distribution list, if any.
22. PRICE
Insert the price set by the National Technical Information Service or the Government Printing Office, if known.
EPA Form 2220-1 (9-73) (Reverse)
362
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