EPA-450/3-80-012
Source Category Survey:
Secondary Zinc Smelting
and Refining Industry
Emission Standards and Engineering Division
Contract No. 68-02-3059
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
May 1980
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This report has been reviewed by the Emission Standards and Engineering
Division, Office of Air Quality Planning and Standards, Office of Air, Noise,
and Radiation, Environmental Protection Agency, and approved for publica-
tion. Mention of company or product names does not constitute endorsement
by EPA. Copies are available free of charge to Federal employees, current
contractors and grantees, and non-profit organizations - as supplies permit
from the Library Services Office, MD-35, Environmental Protection Agency,
Research Triangle Park, NC 27711; or may be obtained, for a fee, from the
National Technical Information Service, 5285 Port Royal Road, Springfield,
VA 22161.
..Publication No. EPA-450/3r£D---flI2.
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PREFACE
This Source Category Survey Draft Report is submitted in partial ful-
fillment of EPA Contract No. 68-02-3059. The purpose of the report is to
determine the need for New Source Performance Standards for air emissions
for selected industries. The source category surveyed by this report is
the Secondary Zinc Smelting and Refining Industry.
This study was performed by Midwest Research Institute for the Emissions
Standards and Engineering Division of the U.S. Environmental Protection Agency
at Research Triangle Park, North Carolina. The EPA lead engineer for this
study was Mr. Reid Iversen. Principal Midwest Research Institute contributors
to this study included: Dr. A. D. McElroy (Project Leader), Senior Advisor;
Mr. Franklin Shobe, Associate Environmental Analyst; and Mr. Tim Arnold,
Junior Analyst. This project was conducted in the Environmental and Materials
Sciences Division under the supervision of Mr. A. R. Trenholm, Head, Environ-
mental Control Section.
Midwest Research Institute expresses its appreciation to the industrial
and governmental personnel who provided technical input and advice.
Approved for:
MIDWEST RESEARCH INSTITU1
M. P. Schrag, Director
Environmental Systems D4partment
April 18, 1980
in
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CONTENTS
Preface iii
1.0 Summary 1
2.0 Introduction - . . . 4
3.0 Conclusions and Recommendations ....... 6
3.1 Conclusions . . 6
3.2 Recommendations 7
4.0 Industry Description • 8
4.1 Source category 8
4.2 Industry production 15
4.3 Secondary zinc processes 26
References: Section 4.0 '. 40
5.0 Air Emissions in the Source Category . 42
5.1 Plant and process emissions . . 43
References: Section 5.0 48
6.0 Emissions Control Systems 49
6.1 Current control technology practices 49
6.2 Alternative control techniques 51
6.3 Best systems of emissions reduction 51
7.0 Emission Data . . . ; 53
7.1 Availability of data 53
7.2 Method for sample collection 53
8.0 State and Local Emission Regulations 55
References: Section 8.0. 61
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FIGURES
Number
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11
Title
Consumption of zinc scrap, 1972
Zinc supply and consumption, 1972 ...
Secondary zinc production
Projected secondary zinc production
Exports of zinc scrap, 1965-1979
Flow diagram for secondary zinc processing
Sweat processing of zinc-scrap materials in reverberatory
melting furnace
Sweat processing of zinc-scrap materials in kettle melting
furnace .
Diagram showing one bank of a Belgian retort furnace. . . .
Zinc: retort distillation furnace
Muffle furnace and condenser.
Page
10
11
17
22
25
27
30
33
35
36
39
Number
TABLES
Title
Page
4-1 Active Secondary Zinc Plant ... 12
4-2 Companies Formerly in the Secondary Zinc Industry 14
4-3 Consumption of Slab Zinc, 1978 18
4-4 Data Base for Secondary Zinc Growth Projection 20
4-5 Index of the Use of Zinc in Motor Vehicles 21
4-6 Emission Points and Effluents of Secondary Zinc-Sweat
Processes 31
4-7 Emission Points and Effluents of Secondary Zinc-Distil-
lation Processes 38
5-1 Uncontrolled Particulate Emission Factors for Secondary
Zinc Smelting 44
5-2 Estimates of National Annual Particulate Emissions by
Process Type 45
5-3 Estimates of Emissions From Representative Plants 45
5-4 Estimated Emissions From Specific Secondary Zinc Plants ... 47
7-1 Emission Information 54
8-1 Summary of Particulate Emission Regulations for New Secondary
Zinc Plants 56
8-2 Model Secondary Zinc Plant Parameters ... 57
8-3 Particulate Emission Regulations for the Whole Model Plant. . 58
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1.0 SUMMARY
The secondary zinc industry is assigned a SIC number of 3341, secondary
refining and smelting of nonferrous metals. In this study, the scope of oper-
ations included in the survey includes those plants which refine scrap zinc
(and which may in addition process other scrap metals) via processes which
range from zinc alloy manufacture in pot furnaces, through sweating operations
to recover zinc in a relatively pure state (90 to 92 percent), to distillation
processes which yield zinc metal as slab or dust, or zinc oxide as products.
Most of the secondary commercial zinc is prepared by distillation, with alloy-
ing from scrap contributing a small percentage of the product output.
The annual production rate, on a zinc basis, in secondary zinc plants is
about 50,000 Mg (55,000 tons). Production is distributed throughout most of
the United States, with the exceptions of the Northern High Plains, the Inter-
mountain States, and the Northwest. Ten plants presently produce distilled
zinc products; two plants produce impure slab zinc from sweating operations;
and four plants have been identified that produce alloys from a combination of
virgin zinc and high quality scrap.
The secondary zinc industry has been typified over the past 20 years by
numerous plant openings and closings and by intermittent operations. Within
the last 5 years, one new plant has been placed in operation, and six plants
have eliminated zinc from their product lines.
Growth in the overall zinc industry has been relatively low, about 2 to 3
percent per year, and forecasts indicate probable continuation of growth at
low rates. Current secondary plants operate at 30 to 70 percent of design
capacity, with 50 to 60 percent being a representative figure. The general
economic picture for zinc is uncertain, due to several factors: pressure from
imports; changes in the automotive industry which affect both the supply of
recycle zinc and the market for zinc; current significant shifts in primary
zinc production; and the impacts of increasing energy costs which tend to favor
secondary zinc, but nevertheless, adversely affect the costs of producing zinc
from scrap.
Current secondary zinc producers indicate no plans for expansion of oper-
ations in the foreseeable future, and in fact, most operate at significantly
less than capacity. The potential for new sources is very small. Industry
history indicates that idle capacity will be reactivated if the market picture
for zinc improves.
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Emissions from the secondary zinc industry consist principally of partic-
ipates plus nitrogen oxides generated by combustion of fuel, which almost ex-
clusively is natural gas. Sweating operations release partially burned organic
matter, but the principal particulate emission is zinc oxide plus small quan-
tities of other metal oxides. Particulate emission factors range from negli-
gible for pot furnaces or sweating operations with clean scrap to 20 to 30 kg/
Mg (40 to 60 Ib/ton) for distillation furnaces or dirty sweating operations.
Total annual uncontrolled particulate emissions estimated for the industry are
about 1,200 Mg/year (1,300 tons/year).
Emissions control systems predominantly consist of baghouses with an asso-
ciated network of hoods and dampered ductwork. Two electrostatic precipitators
were reported to be in use. The baghouse system is augmented with afterburners
to help control particulates and to complete combustion of organics from sweat-
ing operations. Zinc oxide, the principal particulate, is controlled at 97 to
99 percent efficiency by these systems. Particulate control is practiced both
to satisfy environmental regulations and to recover zinc oxide, a valuable prod-
uct, which is sold for agricultural use or recycled into the zinc production
business.
The particulate emission control systems, for an integrated plant with
multiple furnaces of one type or another, are designed and operated on a sched-
uled basis for the separate sources. The effectiveness of overall particulate
control is accordingly determined to a great extent by operator care (e.g., in
opening and closing dampers). Given the necessary care to system operation,
surveyed plants appear to have little difficulty meeting requirements of local
or state regulatory agencies.
Controlled particulate emissions estimated for the entire secondary zinc
industry are about 36 Mg/year (40 tons/year), at a control efficiency of 97
percent. Estimates for individual plants range from 11 to 16 Mg (12 to 18 tons)
for the largest plant surveyed to 2 to 4 Mg (2 to 4 tons) for smaller plants.
The emissions could be reduced to approximately one-third of these values by
consistent operation at an efficiency of 99 percent.
State and local regulations for the secondary zinc industry are based
heavily on visible emission limits. (A limit of no greater than 20 percent
opacity except for 3 min/hr.) With this reliance on visible emissions, mass
emissions data are very limited in quantity. The existing data are, however,
consistent with uncontrolled emission factors used in this analysis. Controlled
particulate concentrations less than 0.02 g/scm (0.01 gr/scf) (standard condi-
tions are a temperature of 294°K (70°F) and an absolute pressure of 101 kPa
(14.7 lb/in2)) are supported by the data, as are controlled particulate emission
rates of about 0.6 to 0.8 kg/Mg (1.2 to 1.6 Ib/ton) of products. Current levels
of control of particulates are significantly better than allowed by state regula-
tions, by a factor of 5 to 10 because the particulates are collected for their
economic value.
The impact of New Source Performance Standards on air quality will be es-
sentially nil if projections of new capacity introductions are based on the
uniform lack of plans for expansion or building new plants, and the amount of
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idle capacity in presently operating and idle plants. However, if modest in-
troductions of new capacity are assumed in response to a modest growth rate in
secondary zinc production and to replace existing facilities, New Source Per-
formance Standards would yield maximum estimated impacts of 19 Mg (21 tons) in
1984, and 39 Mg (43 tons) in 1989.
Development of New Source Performance Standards for the secondary zinc
industry is not recommended. Justification for this recommendation is as fol-
1 ows:
1. No announced plans for additions to capacity for design changes or
new plant construction were uncovered in the survey.
2. The potential for overall growth in production is small, being no
more than 2 to 3 percent per year.
3. A majority of the plants presently in operation are operating at less
than capacity, typically at 50 to 60 percent of capacity. Idle capacity would
be considered for reactivation in the event that either local or national eco-
nomics and demand improve.
4. The environmental impacts of a new source (with a probable production
rate of 4,500 to 9,100 Mg (5,000 to 10,000 tons) annually) with state-of-the-art
control are small. Emissions are only about 4 to 7 Mg (4 to 8 tons) of partic-
ulates annually.
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2.0 INTRODUCTION
The authority to promulgate standards of performance for new sources is
derived from Section 111 of the Clean Air Act. Under the Act, the Administra-
tor of the U.S. Environmental Protection Agency is directed to establish stan-
dards relating to the emission of air pollutants and is accorded the following
powers:
1. Identify those categories of stationary emission sources that contrib-
ute signficantly to air pollution, the emission of which could be reasonably
anticipated to endanger the public health and welfare.
2. Distinguish among classes, types, and sizes within categories of new
sources for the purpose of establishing such standards.
3. Establish standards of performance for stationary sources which re-
flect the degree of emission reduction achievable through application of the
best system of continuous emissipn reduction, taking into consideration the
cost, energy, and environmental impacts associated with such emission reduc-
tion.
The term "stationary source" means any building, structure, facility, or
installation which emits or may emit any air pollutants. A source is consid-
ered new if its construction or modification is commenced after publication of
the proposed regulations. Modifications subjecting an existing source to such
standards are considered to be any physical ct^ange in the source or change in
methods of operation which results in an increase in the amount of any air pol-
lutant emitted.
The Clean Air Act amendments of 1977 require promulgation of the new source
standards on a greatly accelerated schedule. As part of that schedule, a source
category survey was performed to determine if development of New Source Perfor^
mance Standards for the secondary zinc smelting and refining industry was justi-
fied and to identify what processes and pollutants, if any, should be subject
to regulation.
Zinc-bearing wastes are processed by the primary zinc industry as well as
by organizations which manufacture zinc product solely from scrap. This survey
is concerned only with the latter group, i.e., those organizations which manu-
facture zinc, zinc oxide, and zinc alloys from scrap, and do not process zinc
ores. The final products produced by these plants are generally the same as
zinc from primary producers.
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In Atypical processes, low grade scrap is sweated (melted away from major
impurities), or distilled in furnaces using natural gas as fuel. The impure
zinc from sweating operations is further refined by distillation in muffle
furnaces or retorts. Distilled zinc is recovered as zinc dust or as slab or
ingot, or may be oxidized directly to zinc oxide. Slab or ingot products are
utilized in other plants, e.g., for the casting, galvanizing, or alloy produc-
tion.
Emission sources primarily examined during this study were the exhausts
from sweat furnaces, and the intermittent exhausts from pot furnaces or dis-
tillation furnaces. Emissions from pot furnace operations contribute a very
small fraction of total emissions from the industry, however.
Information necessary for development of the secondary zinc smelting and
refining source category survey was gathered through the following activities:
1. Collection of process and emission data from literature searches and
contacts with State and local air pollution control agencies.
2. A visit to a secondary zinc plant to develop an understanding of
smelting and refining processes, and to collect data on operating air pollu-
tion control equipment.
3. Contacting representatives of industry, trade associations, and gov-
ernment agencies to gather information on current secondary zinc smelting and
refining production and projected industry expansion.
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3.0 CONCLUSIONS AND RECOMMENDATIONS
3.1 CONCLUSIONS
1. In 1979-1980, 10 plants were identified which produce the following
secondary zinc products: zinc slab or ingot, zinc dust, and zinc oxide. Two
plants are engaged primarily in production of 90 to 92 percent zinc from scrap;
this product must be further refined by primary or secondary zinc plants. In
addition to these, several plants produce zinc alloys in pot furnace operations;
these use some high grade scrap plus virgin zinc.
2. Annual production of the three products is about 50,000 Mg (55,000
tons). Of this, about 13,000 Mg (15,000 tons) is slab zinc, with the remain-
der being zinc dust and zinc oxide.
3. Six plants have discontinued production of secondary zinc products
within the past 4 to 5 years. Generally, over the past 20 years, secondary
zinc facilities have been operated on an in-and-out or intermittent basis.
Production in existing plants is typically at about 50 to 60 percent of capac-
ity, with the range being 30 to 70 percent.
4. None of the existing plants expressed plans for expansion of produc-
tion either in new facilities or in present facilities. However, one new plant
is coming into production in 1980.
5. Existing capacity is adequate for any growth which may occur. Possi-
bilities for growth are clouded by downward trends in zinc usage by the auto-
motive industry, which affect both the supply of scrap zinc and the market for
zinc.
6. Air emissions consist of relatively large quantities of flue gas from
natural gas combustion, and particulates from the refining and smelting opera-
tions. Particulate matter is principally zinc oxide.
7. Annual particulate emissions on an uncontrolled basis are approximately
1,200 Mg (1,300 tons). Controlled emissions are about 33 Mg (36 tons). Less
optimistic emission factors yield controlled emissions of about 45 Mg/year (50
tons/year).
8. Available emissions estimates are based principally on engineering
judgment, but are supported by limited plant emissions tests.
9. Current state regulations, while requiring tight adherence to stan-
dards for visible emissions, allow mass emission rates significantly higher
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than actual rates. This level of control is a consequence of the fact that
recovered particulates have significant economic value.
3.2 RECOMMENDATIONS
Development of New Source Performance Standards for the secondary zinc
industry is not recommended. Factors that support this recommendation are:
1. One new plant with a capacity of 6,000 Mg/year (7,000 tons/year) could
handle optimistic projections of possible growth for the next 5 years. Idle
capacities in currently operating plants could, however, be used to conserva-
tively increase production by 14,000 Mg/year (15,000 tons/year), and additional
idle capacity exists in plants which have ceased zinc production, but are still
active in related secondary metals.
2. No announced plans for additions to capacity, for design changes or
new plant construction were uncovered in the survey.
3. Pollution control systems presently in use have the capability to ade-
quately control emissions, given proper design and proper operation. Signifi-
cant changes in basic design of pollution control systems for new sources does
not therefore appear to be a requirement, nor are demonstrated economically
viable alternates to present systems available.
4. The impact of New Source Performance Standards on air quality will be
essentially nil if no new source production capacity is added, as indicated by
the survey of the plants in the industry. More optimistic projections for the
industry yield estimates of beneficial impacts of 19 Mg (21 tons) in 1984 and
39 Mg (43 tons) in 1989, assuming that emission levels equal to current state
regulations are reduced to levels prescribed by the more stringent state regu-
lations. However, current emission levels are lower than those allowed by the
states, and a NSPS with an actual beneficial impact would have to be developed
on tighter standards, i.e., on the basis of what can be achieved -by current
control technology. Based on the optimistic projection of new capacity addi-
tion, the maximum particulate emissions reduction is 3 to 4 Mg (3 to 4 tons)
in 1984 and 6 to 8 Mg (7 to 9 tons) in 1989.
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4.0 INDUSTRY DESCRIPTION
4.1 SOURCE CATEGORY
"Secondary zinc" denotes zinc derived from scrap, while primary zinc is
derived from ore. The distinction is based solely on the source of the zinc.
There is no difference in quality, and secondary zinc is made into the full
range of zinc products.
Scrap is classified as old or new according to the stage of processing
and use it reached. New scrap is generated during processing and is recycled
without having been part of an end product. Old scrap is recovered from a prod-
uct which has been used for some time.
Zinc scrap may be classified as metallic or residual. Metallic zinc scrap
consists of zinc castings, which may be coated with another metal or with oil,
or which may have such attachments as gaskets, electric insulation, or other
metals. In addition to relatively pure zinc castings, there are many castings
which are made from a zinc-containing alloy. The four types of alloys which
are significant sources of secondary zinc are zinc-base, copper-base, aluminum-
base, and magnesium-base alloys.
The residual scrap may be classified as skimmings or dross. Skimmings
are primarily zinc oxide from surfaces of galvanizing baths and zinc alloy
baths used for die casting. Skimmings contain metals and other compounds, in
addition to zinc oxide. Dross is also formec! in galvanizing and die casting.
Dross is a molten metal which forms from chemical reactions and either floats
to the top or sinks to the bottom. The molten metal has a high zinc content
and typically includes some iron-aluminum compounds, copper and aluminum, or
an iron-zinc compound. Skimmings and dross may contain some chloride flux.
The recycling of zinc may be quite direct: prompt scrap, which is gener-
ated in metal fabrication or conversion processes, is often recycled within a
given plant. Recycling may be slightly less direct, as is exemplified by ar-
rangements between galvanizers and primary zinc producers in which galvanizing
skimmings and dross are returned to the primary zinc producer as part of the
basic sales agreement. Least direct is the recycling of old scrap, typically
die castings. Old scrap can range in purity from the nearlv pure zinc scrap
from the engraving industry to scrap reclaimed from automobiles which is ap-
proximately 50 percent zinc when it is charged into the sweating furnace. New
scrap from plants which use zinc alloys and highly pure old scrap are suitable
for use directly in alloying, while less pure scrap requires processing before
it is suitable for reentry into the zinc market.
8
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Secondary zinc is made into the full range of zinc products. Figure 4-1
shows the principal products which were made from zinc scrap in 1972, a typical
year for which detailed data are readily available. To give a perspective on
the place of secondary zinc in the zinc industry, Figure 4-2 shows the supply
and consumption of zinc in the United States in 1972. About 21 percent of the
zinc supply was from scrap. This is a relatively low percentage for a nonfer-
rous metal. More than half of the copper and lead supplies are from scrap.
The low recovery rate for zinc, especially zinc from old scrap, results from
the manner in which zinc is used—as an alloying agent, as a coating, or as a
small object or fixture in a larger product. These applications make recycling
difficult.3'4
Processing of the less pure grades of zinc scrap to commercial grade prod-
ucts involves some form of smelting and refining. A number of processes are
available (see Section 4.3 for a description of processes). A common operation
typical of the industry consists of "sweating" the scrap, a process in which
the scrap is subjected to temperatures high enough to melt the zinc and effect
a separation of impure (90 percent) zinc. Major impurities—aluminum, steel,
copper—are recovered from the sweating operation and usually are themselves
routed into their respective recycling industries. The still relatively impure
zinc is then further refined by distillation processes. The distillation is
effected in an oxygen-(or air-)free environment, insofar as possible, to prevent
unwanted combustion of metallic, vaporized zinc to the oxide during the distil-
lation. The distilled zinc vapor may be oxidized to zinc oxide by atmospheric
combustion, condensed in small spherical particles (zinc dust), or condensed
in the liquid state and cast into slabs (redistilled slab zinc).2 With a given
furnace, one may have the option of producing a single product (solid metal,
dust, or oxide) or some combination of these products. Zinc oxide and zinc
dust are common products from a single furnace.
The sweating operation may be carried out in a plant as the only refining
process, in which case the product is shipped to another secondary zinc plant
or to a primary plant, for further refinement.
The sweating operation may also be integral with a distillation operation,
e.g., a muffle furnace, in which case the molten sweated zinc is fed directly
into the muffle furnace. Alternatively, a given secondary zinc plant may cast
sweated zinc in 454-kg (1,000-lb) sows, which in turn are melted down to pro-
vide a continuous feed for a distillation furnace.
With scrap of relatively high purity, the sweat process can be eliminated,
and the scrap can be fed directly to retorts or muffle furnaces.
Sixteen plants in the secondary zinc smelting and refining industry have
been identified. Companies presently engaged in smelting and refining of re-
cycle zinc (excluding primary zinc operations) are listed in Table 4.1. Table
4.2 lists companies which recently eliminated recycle zinc from their operations.
The significant features of these listings are as follows:
1. Two companies produce sweat zinc, principally from automobile scrap,
and sell the product to other companies for further refinement.
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TABLE 4-2. COMPANIES FORMERLY IN THE SECONDARY
ZINC INDUSTRY
Company
Location
Raw materials
Apex
Inland
Imperic
Zinc
il Metals
California
Chicago, IL
Chicago, IL
NA
Galvanizing
NA
and Chemicals
Hugo Neu Proler
Company
Prolerized Schiabo
Neu
Rochester Smelting
and Refining •
Terminal Island, CA
Jersey City, NJ
Rochester, NY
Auto scrap
Auto scrap
NA
2. Three companies manufacture zinc alloys, utilizing virgin zinc plus a
small percentage (5 to 20 percent) of high grade scrap.
3. Eleven companies produce distilled zinc, as slab, dust, or oxide, and
may in addition operate sweat furnaces to provide feedstock for distillation
furnaces.
4. Six companies have recently ceased secondary zinc operations.
•
This list is believed to be reasonably complete, but some smaller operators
may not have been identified. On the basis of the survey, one concludes that
16 to 20 plants are operating now and that at least six plants ceased opera-
tions in the 1970's.
Zinc recycling is also a significant aspect of the primary zinc industry.
The major primary zinc companies in the United States are New Jersey Zinc,
St. Joseph Minerals, ASARCO, National Zinc, and Bunker Hill. The primary zinc
companies generally accept zinc scrap, particularly from their customers.(e.g.,
galvanizers), and feed the zinc scrap into their primary production processes.
The secondary zinc industry, as defined in this study, is responsible for
only a small part of the supply of secondary zinc material, less than 30 per-
cent of it in 1972. Most of the secondary zinc industry's production is in-
cluded within the three product classes: slab zinc from secondary smelters,
14
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oS (1°>700 tons); 2lnc dust, 36,400 Mg (40,100 tons); and zinc oxide,
23,500 Mg (25,900 tons) (Figure 4-1). Some zinc dust and zinc oxide are made
from scrap by other processes. Zinc scrap is recovered in a variety of in-
dustries in a variety of ways.
More than half of the recovered zinc is in an alloy, typically a copper-
base alloy. The zinc is usually not separated from the alloy. The alloy is
recovered, remelted, and reused as an alloy, possibly with some addition of
constituents to bring the composition to specifications.1 Relatively pure zinc
scrap may be remelted and reused in this way also.
Similarly, much of the zinc recovered from chemicals is recovered in chem-
ical plants and reused in the form of a zinc-containing chemical.2
The reduction of zinc oxide from skimmings and other waste materials is
for the most part performed in primary smelting plants in present practice x
Primary zinc smelters and refiners produce more than two-thirds of the redis-
tilled slab zinc from scrap (Figure 4-1).
The limited production data from the listed secondary companies indicate
that 3,500 to 5,500 Mg/year (4,000 to 6,000 tons/year) is an average production
rate for intermediate size plants and that only two or three of the plants pro-
cess more than the average (up to 14,000 to 23,000 Mg/year (15,000 to 25 000
tons/year)), with one of these producing remelt zinc (sows or slabs) which must
be processed further by primary plants or other secondary plants. Production
quantities (of secondary zinc) range downward to 50 to 100 Mg/year (55 to 110
tons/year) in some .of the smaller plants. Total production for the secondary
zinc plants (excluding secondary production by primary plants) is accordinqlv
estimated to be 45,000 to 55,000 Mg/year (50,000 to 60,000 tons per year) with-
out double counting and 65,000 to 75,000 Mg/year (70,000 to 80,000 tons/year)
with double counting. The plants usually report that production is significantly
less than capacity (30 to 70 percent). The average operating rate for the in-
dustry is estimated to be 50 to 60 percent.
4.2 INDUSTRY PRODUCTION
This section contains a description of secondary zinc sales and production
and a description of the markets for secondary zinc products. The demand for
secondary zinc is projected through 1989 and possible industry expansion is
discussed.
4.2.1 Secondary Zinc Sales and Production
The U.S. zinc industry has suffered from uneven demand this century Each
war has reduced the zinc supply from foreign sources and significantly stimu-
lated demand, especially for consumption in brass. In peacetime, the lower
price for zinc will not support full use of the U.S. zinc capacity. Over time,
the use of imports tends to increase.1 The secondary zinc industry shares this
shifting economic base and suffers also from the difficulty of recycling zinc
which is widely dispersed by use. A number of plants have come into service '
and left service as secondary zinc smelters and refiners in the last 20 years.
15
-------
Only three plants which report slab zinc production to the Bureau of Mines have
been in continuous service from 1957 to the present.4
The major products of secondary zinc smelters and refiners are redistilled
slab zinc, zinc dust, and zinc oxide. All of these products are produced by
other processes as well. The most detailed statistical information in a con-
tinuous series on the recovery of zinc from scrap is collected and published
by the -U.S. Bureau of Mines.4 6 The Bureau of Mines data include production
of redistilled slab zinc at secondary smelters and the production of zinc dust
and zinc oxide from scrap. These data are shown for 1965 to 1979 in Figure
4-3. The 1979 results are MRI estimates based on preliminary data for the
first 10 months of 1979.
4.2.2 Markets for Secondary Zinc Products
4 2 2.1 Redistilled Slab Zinc. The markets for redistilled slab zinc
are the same as the markets for slab zinc produced from ore. Table 4-3 shows
the 1978 consumption of slab zinc, which may be compared to the 1972 consump-
tion in Figure 4-2.
The major markets are galvanizing, die casting, and brass and bronze.
The largest single use of zinc is for galvanizing steel to protect it from
corrosion. A major use of galvanized steel is in building and construction
where it is used for roofing, siding, wiring channels, heating, cooling, and
ventilation ducts, studs, joists, trusses, water pipes, fences (tubing and wire),
guard rails, lamp posts, road signs, etc. Another major use is in the auto
industry, where it protects the underparts of many cars. A third major use is
in domestic appliances and office equipment. It .is used for the casings of
washers, refrigerators, etc., and for such steel office equipment as desks and
filing cabinets.7'9
Approximately half of the zinc die castings are used by the automobile^
industry. The other major use is builders' hardware, which accounted for 21
percent in 1976.l6 The use of zinc die castings in automobiles has been de-
creasing. The zinc industry has met competition from aluminum and plastics by
the introduction of thin wall zinc, which has about half the conventional zinc
die casting wall thickness. Nearly all zinc die castings in the auto industry
are thin wall zinc, which contributes to the auto industry's weight reduction
Droqram. The use of zinc in one 1966 model luxury car was 68 kg (150 Ib) per
car! Another full-sized 1966 model used.27- kg (60 Ib).11 The average use per
car in 1966 was less than 27 kg (60 Ib) because smaller cars used less than
the models reported here. The trend toward smaller and lighter cars has re-
duced this to an estimated 14 kg (30 Ib) per car average in the 1980 models.
The future for zinc in automobiles is uncertain. The Zinc Institute quotes
"spokesmen for the automobile industry" as believing that the 1979 models are
the turning point for zinc die casting and that growth lies ahead.1* On the
other hand, Chemical Week reported expected reductions to 9 kg (20 Ib) per car
in 1985 and 7 kg (15 Ib) per car in 1990."
16
-------
99 r-
90 r
88
80 -
Total
77
66
55
§ 44-
N
33-
22 -
11 -
OL_
1965
1967
1969
1971
1973
1975
1977
1979
Year
Figure 4-3. Secondary zinc production.
17
-------
TABLE 4-3. CONSUMPTION OF SLAB ZINC, 1978
Megagrams
Galvanizing
Zinc-base alloy
Die casting alloy
Other
Brass and bronze
Rolled zinc
Zinc oxide
Other3
Total
345,968
8,166
454,014
354,134
141,488
24,869
37,202
38,878
1,050,585
Tons
381,364
9,002
500,465
390,366
155,964
27,413
41,008
42,856
1,158,072
Source: U.S. Bureau of Mines.6
a Includes slab zinc used for zinc dust, wet batteries, desilverizing lead,
lightmetal alloys, and other miscellaneous uses.
The uses of brass and bronze are nearly too varied to be characterized.
Important uses include hardware, plumbing, heat exchangers, automobile radia-
tors (aluminum is competing for this), electrical components, and corrosion-
resistant plates. The consumption of metal in brass mill products in the last
20 years has been cyclic with an annual growth trend of 0.9 percent.14
Redistilled slab zinc from secondary smelters accounted for only 10 per-
cent of the 1978 slab zinc production (compare Figure 4-3 and Table 4-2).
4.2.2.2 Zinc Dust. The primary use of zinc dust is in zinc rich paints
which are used both as primers and as complete protective systems on structural
steel and as primers for the underparts of car bodies. It is also used as a
reducing agent in the chemical industry and for bleaching wood pulp for paper.5'9
The secondary zinc smelters are the principal producers of zinc dust. In
1977, 36,000 Mg (40,000 tons) of zinc dust were produced (Figure 4-3) from scrap
out of a total production of 43,177 Mg (47,594 tons).15
4.2.2.3 Zinc Oxide. The principal markets for zinc oxide are rubber,
photocopy paper, and paints. Approximately half of the zinc oxide consumption
is in rubber.4'7'9 In 1978, as in 1972, 16 percent of the zinc oxide production
in the United States was derived from scrap.4 7
4.2.3 Projected Demand for Secondary Zinc
The principal scrap sources for the secondary zinc industry are new resid-
ual scrap from galvanizing and die casting operations and old metallic scrap
18
-------
(die castings) from automobiles and, to a lesser extent, appliances. The sup-
ply of suitable_ scrap limits the demand for zinc which can be met from second-
ary sources. Since zinc die castings are principally for automobiles and gal-
vanizing is principally for construction and automobiles, the relationships
since 1965 between secondary zinc production and, respectively, construction
activity and automobile production were examined. There was no correlation
r - n o?P w?t^newnconstructl"on> but there was a fai>ly strong correlation
(r - 0.85) with the Federal Reserve Board Index for Motor Vehicles and Parts.
The demand for secondary zinc products follows much the same pattern as
the scrap supply which was considered above, except that the rubber industry
uses approximately half of the zinc oxide. However, there is also little cor-
relation between secondary zinc production and tire production (r = -0.11).
A projection of secondary zinc production to 1989 was made by regression
on time and on a rough index of the use of zinc in motor vehicles. The data
mntn h« h? proJect1on 1s shown ™ Table 4~4. An index of the use of zinc in
motor yehic es was prepared by multiplying the Federal Reserve Board Index of
Motor Vehicles and Parts by the estimated average weight of zinc per car as a
f the PrSSe? 13'6 kg (3° 1b) per car' The ^nde* of "otSr vehicles
uas assumed to 9row according to the Predicasts composite forecast,16
is shown in Table 4-5. Since the forecast is published for 5-year inter-
inn 5Thh6 f oi:ecasts . for the intervening years were made by linear
ion. The projected index of motor vehicles and parts grows at an
average annual rate of 2.2 percent from 1978 to 1989. Theaverage weight of
MM tfi^n f H f STed t0 haVe rema1ned a* about 13.6 kg (30 Ib) per car from
1965 to 1980 and to decrease linearly to 9.1 kb (20 Ib) per car in 1985 and
££ nf'th6956 ]Ta-ly *> 6'8 *9 <15 1b) Per car in 1990." The resulting in-
dex of the use of zinc in motor vehicles is also shown in Table 4-5.
Z -
'
-, f°r the Product1ofl °f secondary zince is
inmPt 345y + 163.028x where Z is secondary zinc production
n metric tons, y is the year (y = 0 in 1965), and x is the index of the
use of zinc in motor vehicles (1967 = 100). The value of r* is 0.736 which
represents a moderately strong correlation for an economic model as simple as
this one. The resulting projection is shown in Figure 4-4. It represents an
average annual growth rate of 2.1 percent for 1978 to 1989. rePresenis an
fmm ^6 re based On the h1story of the secondary zinc industry
from 1965 to 1978. If one covers the 1979 point in Figure 4-4, one can see
nndL? * Pr?f " 'f-1" ]l.ne Wlth the trend through 1978. The assumption
underlying the projections is that 1979 is an anomaly resulting from temporary
economic dislocations If 1979 should prove typical of the next several years
the projections will have been too optimistic. The majority of the industry
executives contacted in the telephone survey were pessimistic, although the
opinion was not unanimous.
19
-------
TABLE 4-4. DATA BASE FOR SECONDARY ZINC GROWTH PROJECTION
Total secondary zinc
tons
Tons
Mg
Federal Reserve Board
Tndex of Motor Vehicles and Parts
(1967=100)
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
65,223
62,014
64,728
69,414
64,236
60,757
63,034
76,704
80,920
83,372
77,763
97,471
94,112
81,076
59,169
56,258
58,720
62,971
58,274
55,118
57,183
.69,585
73,409
75,634
70,545
88,424
85,377
. 73,551
115.9
113.9
100.0
120.3
116.5
92.3
118. 6
135.8
148.8
128.2
111.1
142.0
161.1
170a
a Predicasts composite forecast.
20
-------
TABLE 4-5. INDEX OF THE USE OF ZINC IN MOTOR VEHICLES
Year
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1985
1987
1988
1989
1990
Index of the use
of zinc in motor
vehicles
116
114
100
120
116
92
119
136
149
128
111
142
161
170
162
154
152
148
144
139
131
128
124
120
115
111
Index of Motor
Vehicles and Parts
(1967=100)
115.9
113.9
100.0
120.3
116.5
92.3
118. 6
135.8
148.8
128.2
111.1
142.0
161.1
170
162
154
163
171
180
189
197
202
207
211
216
221
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For comparison, the Department of Commerce Industry and Trade Administra-
tion forecasts a 2.8 percent annual growth in slab zinc consumption for 1977
to 1983,a' the U.S. Bureau of Mines forecasts a 2.0 percent annual growth in
the production of slab zinc from scrap for 1973 to 2000,1S and Predicasts re-
ports forecasts for growth in consumption of old zinc scrap in the 3 2 to 3 9
percent range.19
Generally the consumption of zinc in the United States can be expected to
grow with the using industries in the coming years. There are several competi-
tors with zinc to protect steel; also aluminum and plastics compete with gal-
vanized steel, but zinc can be expected to hold its own in most instances.
Galvanized steel may make inroads against wood, because of the more rapid in- '
crease in wood costs. The weight reduction of automobiles can be expected to
deprive zinc of a significant part of its die casting market, as lighter alumi-
num, magnesium, or plastics materials replace zinc, but an electric automobile
powered by a zinc-chloride battery would require 45 kg (100 lb) of zinc 20 If
zinc-chloride or nickel-zinc batteries are widely used to level electrical loads
another significant new market would develop. '
Zinc dust has an importance to the secondary zinc industry far beyond its
importance to the zinc industry as a whole: it is the one zinc product which
has scrap as its principal source. Zinc dust markets were very weak in 1979
but they were also weak from 1970 to 1971 and in 1974 and they recovered There
are many competitors to zinc-rich paints as protective coatings for steel, but
the effectiveness of zinc-rich paints should enable them to hold this market
as long as their price does not become unreasonable.
The use of zinc oxide in rubber should continue to grow with the rubber
industry. The only threat to this market is the possibility of plastic tires
The use of small, long-lasting radial tires will retard growth in this market
nowever.
In conclusion, the demand for secondary zinc should grow slowly over the
next 10 years. The pace of growth is likely to be uneven.
4.2.4 Estimated Industry Expansion
From the point of view of the U.S. zinc industry, the problem is not the
level of zinc consumption, it is competition from imports. For more than a
decade, more than half of the U.S. slab zinc consumption has come from imports
either of ores or of slab zinc. The imports of ores and concentrates have been
^ lly decreasin9> Wh11e the imports of slab zinc have been increasing. In
iy/1 the zinc content of imported slab zinc equaled the zinc content of imported
ores and concentrates. By 1979 the zinc content of imported ores and concen-
trates were only one-fourth the zinc content of imported slab zinc.4'17'20
With the competition from imports, the U.S. zinc industry is experiencina
decreasing prices and low operating rates. The U.S. producer zinc price de-
creased from 86
-------
electrolytic (primary) zinc plants in the United States operated at 75 Percent
of capacity in 1978 while the 44 electrolytic plants in the ^"."PJ™*^**
76 pfrceitof capacity." The two distillation plants primary in tj i Un ted
cti
In ihe UnHed StSet has Increased from 190,000 to 320,000 Mg, (210,000 to
SSOJOOO tons) while the distillation (primary) capacity has decreased from
465iOOO to 107,300 Mg (500,000 to 118,300 tons). Only one primary distllla
tion plant remains.
Not only must the secondary zinc industry compete against the U.S.
^^^
en-gy intensive than the electrolytic process for ,
(72 57 million Btu per ton) of zinc in comparison to 69.96 kJ/g (60.17 mi I lion
Btu o^r ton) "8 The substitution of scrap for ore is a strategy for an elec:
?rothermic primary plant to attempt to remain competitive with an electrolytic
plant.
Meanwhile, the exports of zinc scrap have been increasing since 1975.
Figure 4-5 shows the exports of zinc scrap for 1965 to 19/3.
The U S secondary zinc smelters and refiners are estimated from the tele
^ ar^^Ta t«
A new secondary zinc plant has been built and is scheduled to begin
S i-^Lp^^^rti^^tS ^
industry.
^^^
s^^^
alone to absorb the closed plant's production without difficulty.
The impact of pollution control on the industry has been substantial in
IQTO's and has been at least a part of the reason for plant closings. At
regions is likely to be an important
24
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Perhaps the most significant factor relative to the future of existing
plants is energy supply and cost. Zinc smelting and refining requires large
expenditures of fuel, principally natural gas, and existing plants are not de-
signed for energy efficiency. One plant engineer, for example, expressed a
desire to reengineer retort operations to increase fuel efficiency from 8 to
24 percent. High energy costs favor production of zinc from scrap rather than
from ore, however. Energy use is approximately 23 kJ/g (20 million Btu per
ton) of product,50 or one-third the energy used by an electrolytic primary plant.
One generally concludes, therefore, that the secondary zinc industry (as
well as primary) is in an area in which a holding pattern exists due to signif-
icant changes or pending changes in the scrap supply and market, the need to
upgrade processes for greater energy efficiencies and reduced costs, and pollu-
tion control requirements. The current situation with respect to raw materials
supply and the weak product demand in 1979 would appear to point to decreased
production in the secondary zinc industry. This factor might well be counter-
balanced, however, by an increase in the percentage of zinc recycled and by
greater response in specific plants to local supply of raw materials and product
demand. This latter philosophy was expressed by one plant executive in general
contrast to the negative attitude taken by numerous executives. If the growth
projection shown in Figure 4-4 is realized and if the current capacity is in
the upper half of its estimated range, there would be no reason to increase
secondary zinc capacity in the 1980's. At the most, a single plant one-half
the size of the model plant (Section 8) would be sufficient.
In addition to the possibility of expansion in the secondary zinc industry,
there is the possibility of replacing part of the present capacity with new
sources. The Bureau of Mines list of secondary plants which reported produc-
tion of redistilled slab zinc4'26 was reviewed for 1957 to 1978 to check for
stability. Three of the plants listed in Table 4-1 have been in continuous
production since 1957 or earlier. These three plants account for approximately
35 percent of the industry's capacity. Within the remainder of the industry s
capacity there has been some turnover. Thirteen new plants opened in 22 years,
while the total slab zinc annual capacity of the reporting plants decreased
from 55,000 to 40,000 Mg (61,000 to 50,000 tons). There were 17 openings and
21 closings, but in some instances, a plant closed and reopened. There were
seven closings in 1973 and four closings in 1978, and there were four openings
in 1961, seven openings in 1975, and four openings in 1977. This replacement
of capacity appears to result from economic conditions in the industry, not
from change in technology. This is indicated by the clustering and by the re-
peated exit and reentry of certain companies.
4.3 SECONDARY ZINC PROCESSES
An overall flow diagram for secondary zinc processing is depicted in Fig-
ure 4-6 As shown in Figure 4-6, the process consists of three distinct stages:
scrap preparation, distillation and remelting; and product finishing. These
major stages are discussed in detail in the following sections.
26
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4.3.1 Scrap Preparation
Zinc scrap consumed in the secondary zinc industry can be grouped into
four broad categories, namely, galvanizers1 scrap, new die-cast scrap, mixed
die-cast scrap, and general zinc scrap.
Galvanizers1 scrap (primarily drosses, skimmings, sal skimmings, and ashes)
are largely shipped from galvanizing operations in drums or solid blocks to
the scrap-consuming plant. In many plants, they are charged to the distillation
furnace either directly or after first being melted in a separate operation.
Some plants dry mill and air classify the zinc skimmings to separate the metal-
lic zinc from zinc oxide. In other plants, skimmings are crushed and then
treated in the following manner. The crushed skimmings are washed with water
to separate nonmetals as a slurry and allow zinc-containing metal particles to
settle out; the slurry is then treated with Na2C03 to convert chlorides (mainly
ZnCl2) to NaCl, forming insoluble Zn(OH)2. Most of the NaCl is separated from
the insoluble residues by filtration and settling; the residue is dried and
calcined in a kiln to convert Zn(OH)2 to ZnO by driving off H20 and vaporizing
any remaining ZnCl2. The calcined product is mostly ZnO and is suitable for
smelting. The kiln fume is collected and recycled.
New die-cast scrap, classified as prompt industrial scrap, consists of
castings discarded as a result of manufacturing defects at the die-casting
plant. There are two types of new die-cast scrap. Clean die-cast scrap is
well segregated and can be melted at the scrap processing plant to produce a
product that meets market specifications. Off-specification die-cast scrap is
not so well segregated as clean die-cast scrap and cannot be melted into a prod-
uct meeting market specifications. It is normally refined and blended to meet
market specifications. General zinc scrap includes such items as clippings
and engravers' plates. This scrap category is a relatively minor element in
the secondary zinc industry. New die-cast scrap and general zinc scrap usually
require no preparation before being consumed by a secondary zinc smelter.
Mixed die-cast scrap, which is classified as obsolete scrap, consists of
such products as auto shredders' scrap, old auto parts, and old appliance parts.
It forms a substantial portion of the total zinc scrap supply. The scrap from
auto shredders is sometimes classifed into a separate category, such as auto
die-cast scrap. Mixed die-cast scrap and auto die-cast scrap contain a large
amount of ferrous and nonferrous material, and they are pretreated in a sweat-
ing process to produce a low purity zinc product.
Sweat processing is accomplished by charging the scrap into a sweating
furnace. In the furnace, heat (usually from natural gas) is applied to the
scrap materials to melt and separate metallic zinc from metal attachments,
having higher melting points, and from nonmetallic residues. Any organic ma-
terials in the scrap are also burned off during sweating. The charge may be
worked by agitation or stirring during melting; and chloride flux may be pres-
ent either as residual flux, in charged residual scrap, or as flux added to
the charge. Working and fluxing of the charge are done to help effect the de-
sired metal.separation.
28
-------
A molten metal bath is formed from the metallic zinc (with dissolved alloy
metals). Nonmetallic residues, along with some plating, form above the molten-
metal bath surface and are skimmed off. Unmeltable attachments settle to the
bottom and are removed. The molten metal may then-be (a) cast directly into
blocks for subsequent further processing, or (b) fed directly to a distillation
furnace, or (c) it may sampled and analyzed, and then alloyed by adding metals
to obtain specification composition, and then cast as ingots.
Several types of furnaces are used for sweating zinc-scrap materials and
they are discussed in the following order:
1. Reverberatory furnaces
2. Rotary furnaces
3. Melting-kettle (or kettle) furnaces
4. Muffle furnaces
5. Electric-resistance furnaces
4..3.1.1 Reverberatory Furnace. The reverberatory furnace has a general
box configuration with a sloped bottom (hearth). It is used to process both
metallic and residual zinc scrap materials, which are charged into the furnace
and rest on the hearth. Natural gas or fuel oil burners are located in the
upper part of the furnace; combustion of fuel above the charge supplies heat
to burn off organic substances, as well as heat to melt the zinc alloys in the
charge. Furnaces are designed and burners are positioned to minimize flame
impingement on the charge and to reduce oxidation and entrainment of metal ox-
ide particles. As zinc alloys melt, they separate from unmeltables and flow
downward over the hearth. Bath temperatures in reverberatory furnaces are usu-
ally around 800K (1000°F). Metal flows from the furnace as it melts; and, at
intervals, unmeltables are raked out and additional process material charged.
Reverberatory furnaces may be independent units or they may be integral
with distillation furnaces. Consideration here is limited to the independent
type of unit where molten metal from the hearth flows through a spout into
ladles or kettles. The metal may then be processed further to obtain a speci-
fication alloy, or it may be fed to a distillation furnace.
Sweat processing in a reverberatory furnace is shown schematically in Fig-
ure 4-7, along with emissions and emission points. These emission points and
effluents from these points are detailed further in Table 4-6.
4.3.1.2 Rotary Furnace. The melting unit of the rotary-type furnace con-
sists of a hollow cylinder mounted with its lengthwise axis sloped at a small
angle from horizontal. During operation, this cylinder is mechanically rotated
on that axis and internally heated by gas or oil burners. Scrap materials are
fed into the high end of the melting cylinder. As the cylinder rotates, zinc
melts and flows out through openings in the low end, usually into a kettle where
residues are skimmed off. Unmeltables are separated from the bath by tumbling
29
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them out of the low end of the cylinder or by manual raking and scraping. Ro-
tary furnace bath temperatures are usually lower than those of reverberatory
furnaces because rotation helps separate molten zinc from unmeltables, maintain
molten zinc and alloy metals in solution, and use heat more efficiently by avoid-
ing localized high temperature zones, thereby allowing lower bath temperatures
to be applied. The collected zinc-containing metal may then be transferred to
a distillation furnace, or its composition may be adjusted to an alloy specifi-
cation.
4.3.1.3 Kettle Furnace. The kettle furnace consists of a melting vessel
(kettle), made of cast iron in most cases, mounted over a combustion chamber.
Scrap materials, which may include metallic and/or residual types, are charged
into the kettle. The metallurgical-process bath is formed as zinciferous metal
is melted and residues form above the molten metal surface. Operating temper-
atures of kettle-process baths range from 700 to 800K (800 to 1000°F). Pro-
duction is on a batch basis, with one process heat requiring around 6 to 8 hr
to process and pour. A molten heel may be retained as finished alloy is removed
from furnaces and additional scrap (process material) charged.
Normally, products of fuel combustion are exhausted separately from emis-
sions of the metallurgical-process bath, through separate venting of the com-
bustion chamber. Natural gas is the generally used fuel (fuel oil being used
in a smaller number of cases).
Sweat processing in a kettle furnace is shown schematically in Figure 4-8,
along with emissions and emission points. Emission points and effluents emitted
from these points are detailed further in Table 4-6.
4.3.1.4 Muffle Furnace. In the muffle furnace, as applied to sweating
processes, combustion gases are separated from charged zinc-scrap materials by
a "muffle." This design permits separation of combustion products from those
emissions derived from charged zinc-scrap materials and flux. In this respect,
the muffle furnace is similar to the kettle furnace.
4.3.1.5 Electric-Resistance Furnace. Electric-resistance furnaces are
used in a small number of plants for processing clean, scrap-derived zinc metal.
4.3.2 Remelting and Distillation
Zinc scrap is processed into the final products by three schemes: pot
melting, retort distillation, and muffle furnace distillation. Each method is
discussed separately in the following subsections.
4.3.2.1 Pot Melting. Pot melting of zinc die-cast scrap involves melting
either well segregated or off-specification zinc die-cast scrap in a steel pot
furnace. Pot melting is a simple melting scheme in which heat is supplied (usu-
ally from natural gas) to the charge by indirect heating. Recovery of more
than 90 percent is achieved with losses occurring principally as zinc fumes
and skimmings. The recovered zinc is cast into zinc slabs or alloyed and cast
into zinc alloy ingots.
32
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4.3.2.2 Retort Distillation. Belgian and bottle retorts are used to dis-
till zinc scrap. Belgian retorts are used to reduce zinc oxide to metallic
zinc. Bottle retorts, used for batch ditillations, reclaim zinc from alloys,
refire zinc, make powdered zinc, and make zinc oxide. Although zinc boils at
1180K (1665°F), most retort furnaces are operated at temperatures ranging from
1250 to 1520K (1800 to 2280°F). Zinc vapor burns spontaneously in air; there-
fore, air must be excluded from the retort and condenser when metallic zinc is
the desired product. Condensers are designed, either for rapid cooling of the
zinc vapors to a temperature below the melting point to produce powdered zinc,
or for slower cooling to a temperature above the melting point to produce liquid
zinc. When the desired product is zinc oxide, the condenser is bypassed and
the vapor is discharged into a stream of air where spontaneous combustion con-
verts the zinc to zinc oxide. Excess air is used, not only to ensure suffi-
cient oxygen for the combustion, but also to cool the products of combustion
and convey the oxide to a suitable collector.
4.3.2.2.1 Belgian retort. The Belgian retort furnace, shown in Figure
4-9, is one of several horizontal retort furnaces that have been for many years
the most common device for the reduction of zinc. (No current usage of Belgian
retorts in the secondary industry was uncovered in the survey.) A typical
Belgian retort is about 20 cm (8 in.) in internal diameter and from 122 to 152
cm (48 to 60 in.) long. One end is closed and a conical shaped clay condenser
from 46 to 61 cm (18 to 24 in.) long is attached to the open end. The retorts
are arranged in banks with rows four to seven high and as many retorts in a
row as are needed to obtain the desired production. The retorts are generally
gas fired.
The retorts are charged with a mixture of zinc oxide and powdered coke.
Since these materials are powdered, water is added to facilitate charging and
allow the mixture to be packed tightly into the retort. Three to four times
more carbon than is needed for the reduction reaction is used.
After the charging, the condensers are replaced and their mouths stuffed
with a porous material. A small hole is left through the stuffing to allow
moisture and unwanted volatile materials to escape.
The air contaminants emitted vary in composition and concentration during
the operating cycle of Belgian retorts. During the charging operation, very
low concentrations are emitted. After zinc begins to form, both carbon monoxide
and zinc vapors are discharged. These emissions burn to form gaseous carbon
dioxide and solid zinc oxide. During the heating cycle, zinc is poured from
the condensers about three times at 6- to 7-hr intervals. The amount of zinc
vapors discharged increases during the tapping operation. Before the spent
charge is removed from the retorts, the temperature of the retorts is lowered,
but zinc fumes and dust from the spent charge are discharged to the atmosphere.
4.3.2.2.2 Bottle retort. The bottle retort furnace (Figure 4-10) consists
of pear-shaped, graphite retort, which may be 1.5 meters (5 ft) long by 0.6 meter
(2 ft) in diameter at the closed end by 0.5 meter (1-1/2 ft) in diameter at
the open end and 0.9 meter (3 ft) in diameter at its widest cross-section.
34
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Group Joint
Condensed Metal
Vapors
Ceramic Cone
Condenser
Porous Loom
Stuffing
l_ Flame from
Combustible Gases
Burner Port
Front Wall
of Furnace
Rear Wall
of Furnace
Metallic Oxide Charge
with Reducing Materials
Figure 4-9. Diagram showing one bank of a Belgian retort furnace.
35
-------
Speise Hole
Ceramic
V Condenser
Mefal Vapors
Ceramic
Retort
Impure
Metal
Charge
Pure
Metal
Taphole
Figure 4-10. Zinc: retort distillation furnace.
36
-------
Normally the retort is encased in a brick furnace with only the open end pro-
truding and it is heated externally with gas- or oil-fired burners. The re-
torts 'are charged with molten, impure zinc through the open end, and a condenser
is attached to the opening to receive and condense the zinc vapors. After the
distillation is completed, the condenser is moved away, the residue is removed
from the retort, and a new batch is started.
The vaporized zinc is either conducted to a condenser or discharged through
an orifice into a stream of air. Two type of condensers are used—a brick-lined
steel condenser operated at from 690 to 818K (780 to 1012°F) to condense the
vapor to liquid zinc, or a larger, unlined steel condenser that cools the vapor
to solid zinc. The latter condenser is used to manufacture powdered zinc.
The condensers must be operated at a slight positive pressure to keep air from
entering them and oxidizing the zinc.
When it is desired to make zinc oxide, the vapor from a retort is dis-
charged through an orifice into a stream of air where zinc oxide is formed
inside a refractory-lined chamber. The combustion gases and air, which bear
the oxide particles, are then carried to a baghouse collector where the pow-
dered oxide is collected.
During the 24-hr cycle of the distillation retorts, zinc vapors escape
from the retort (a) when the residue from the preceding batch is removed from
-the retort and a new batch is charged, and (b) when the second charge is added
to the retort. As the zinc vapors mix with air, they oxidize and form a dense
cloud of zinc oxide fumes. Air contaminants are discharged for about 1 hr each
time the charging hole is open. When zinc is actually being distilled, no fumes
escape from the retort; however, a small amount of zinc oxide escapes from the
speise hole in the condenser. Although the emission rate is low, air contami-
nants are discharged for about 20 hr/day.
Emission points in the retort-furnace system are listed, with emissions
from those points in Table 4-7.
4.3.2.3 Muffle Furnace Distillation. Muffle furnaces (Figure 4-11) are
continuously fed retort furnaces. They generally have a much greater vaporiz-
ing capacity than either Belgian retorts or bottle retorts do, and they are
operated continuously for several days at a time. Heat for vaporization is
supplied by gas-or oil-fired burners by conduction and radiation through a
silicon carbide arch that separates the zinc vapors and the products of com-
bustion. Molten zinc from either a melting pot or sweat furnace is charged
through a feed well that also acts as an air lock. The zinc vapors are con-
ducted to a condenser where purified liquid zinc is collected, or the condenser
is bypassed and the vapors are discharged through an orifice into a stream of
air where zinc oxide is formed. Muffle furnaces can produce zinc of 99.8 per-
cent purity and ZnO of 99.9 percent purity. Recoveries of more than 90 percent
are usually obtained. Losses occur as entrapped zinc in the unmelted scrap
and in the fumes.
Emission points and effluents from the muffle furnace system are detailed
in Table 4-7.
37
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REFERENCES: SECTION 4
1. McMahon, A. D., C. H. Cotterill, J. T. Dunham, and W. L. Rice. The U.S.
Zinc Industry: A Historical Perspective. U.S. Department of the Interior,
Bureau of Mines. Washington, D.C. Information Circular 8629. 1974.
pp. 1-12 and 41-76.
2. Herring, W. 0. Secondary Zinc Industry Emission Control Problem Defini-
tion Study. U.S. Environmental Protection Agency, Air Pollution Control
Office. Durham, North Carolina. Undated, approximately 1970. pp. 1-1
through IV-9.
3. Darnay, A. J., and W. E. Franklin. Salvage Markets for Materials in Solid
Waste. U.S. Environmental Protection Agency. Washington, D.C. SW-29C.
1972. p. 63.
4. McMahon, A. D., J. M. Hague, and H. R. Babitzke. Zinc Chapter in Minerals
Yearbook. U.S. Department of the Interior, Bureau of Mines. Washington,
D.C. 1972. pp. 1306-1308 and 1321-1326. (Also zinc chapter in Minerals
Yearbook for other years.)
5. Telecon. Shobe, F., Midwest Research Institute, with Commarota, A., U.S.
Bureau of Mines, Division of Nonferrous Metals. January 29, 1980. Second-
ary Zinc Industry.
6. U.S. Bureau of Mines. Mineral Industry Surveys: Zinc Industry. Washington,
D.C. October 1979. Tables 2, 5, 6, and 11.
,7. Zinc Institute, Inc. U.S. Zinc Industry: Annual Review 1978, New York,
New York. 23 pp.
8. Charles River Associates, Inc. Economic Analysis of the Lead-Zinc Industry.
April 1969. 267 pp. Distributed by the National Technical Information
Service. PB 183 483. Springfield, Virginia.
9. International Lead and Zinc Study Group. Lead and Zinc: Factors Affecting
Consumption. November 1966. United Nations, New York. 83 pp.
10. U.S. Bureau of Mines. Minerals Yearbook. Washington, D.C. 1976. p.
1415.
11. Reference 8, p. 38.
12. Chemical Week. Big Changes Ahead in Automobiles. 125(6):19. McGraw-Hill,
Inc. New York, New York. August 15, 1979.
13. Reference 7, pp. 1-4.
40
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14. Copper Development Association, Inc. Annual Data 1979. New York,
New York. pp. 30-31. The growth trend is based on the slope of the time
series regression line (r2 = 0.13) for 1959 to 1978.
15. Reference 7, p. 7.
16. Predicasts, Issue No. 77. Cleveland, Ohio. October 29, 1979. p. A-21.
17. U.S. Department of Commerce, Industry and Trade Administration. Copper:
Quarterly Report. Washington, D.C. Winter 1978/1979. pp. 16-18.
18. U.S. Bureau of Mines. Mineral Facts and Problems. Bulletin 667.
Washington, D.C. 1975. pp. 1237-1241.
19. Reference 16, pp. B-109 and B-113.
20. U.S. Department of Commerce, Industry and Trade Administration. 1978.
U.S. Industrial Outlook. Washington, D.C. pp. 68-71.
21. American Bureau of Metal Statistics. Non-Ferrous Metal Data 1978.
New York, New York. 1979. pp. 86-87.
22. U.S. Bureau of Mines. Mineral Industry Surveys: Zinc Production.
Washington, D.C. October 1979. Tables 4 and 5.
23. Reference 21, pp. 77-78.
24. Reference 21, pp. 75, 77, and 80.
25. Reference 21, pp. 80 and 81.
26. Reference 22, p. 1.
27. Reference 21, p. 75.
28. Telecon. McElroy, A. D., Midwest Research Institute, with Derham, A.,
Purity Zinc Metals. December 5, 1979. Telephone Survey of Secondary Zinc
Producers.
29. Reference 21, p. 79.
30. Kusik, C. L., and C. B. Kenahan. Energy Use Patterns for Metal Recycling.
U.S. Bureau of Mines Information Circular 8781. Washington, D.C. 1978.
pp. 146-163.
41
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5.0 AIR EMISSIONS IN THE SOURCE CATEGORY
This chapter identifies types and quantities of air emissions in a repre-
sentative secondary zinc plant. There are three basic types of operations in
secondary zinc plants:
1. Distillation processes in muffle furnaces or retorts. In this type
of equipment, the charge is indirectly heated. Combustion gases are vented
without control of emissions, but since natural gas is the fuel of choice,
particulate emissions are negligible in the flue gas, and nitrogen and sulfur
oxides emissions are those expected of natural gas combustion. The principal
emissions occur when the furnace or retort is broken; a hood system collects
particulates released at this point. These are drawn together with hot gases
and dilution air into baghouses. With multiple sources, as nearly always is
the case, a network of dampered hoods and ductwork is employed, and the opera-
tion (breaking of furnaces) is staggered so the emission control system is not
overloaded at any one time, and so that adequate draft exists at emission
sources.
2. Sweat furnaces (kettle, reverberatory, rotary kiln) operate with di-
rect heating, at 800 to 900K (1000 to 1200°F) furnace temperature, and with
combustion gases vented to baghouses. Emissions generated from sweating oper-
ations are a function of the quality and prior history of the charge. Particu-
larly significant is the quantity of organic matter (grease, coatings, etc.)
which partially burns in the sweating operation to both particulate and gaseous
products of incomplete combustion. An afterburner is needed to take care of
this problem, at the expense of approximately doubling fuel costs and creating
added volumes of hot gases which must be cooled by dilution prior to the bag-
house.
3. Pot furnace operations. These are oriented primarily toward alloy
production, with recycle zinc being usually used as a small percentage (5
to 15 percent) of the total charge, and with scrap being of high quality. Con-
trol of emissions is nearly always effected with hood, vent network and bag-
house systems. Pot furnace operations are restricted to only a few plants,
with alloying being the only zinc operation in the plant and with typically
about 90 Mg (100 tons) of recycle zinc processed. For this reason, such oper-
ations are not included in the representative zinc plant, which accordingly
has two basic operations—sweating and distillation..
Other than the easily identified emission sources, namely combustion gas
streams from sweating operations, and emissions which take place when any of
the basic plant equipment is "broken," emissions may occur when furnaces develop
42
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leaks, when certain operating procedures such as utilization of poke rods re-
lease spot emissions, during product and residue handling/conveying, and during
charging operations. These latter emissions are largely uncontrolled, except
to the extent that the in-building air flows (850 standard cubic meters per
minute (30,000 scfm) or greater to a baghouse complex) provide control. One
plant reports that hot ash is blanketed manually with cool ash to minimize dust
emissions.
The pollution control systems of hoods, ductwork, and baghouses in all
the plants surveyed is designed for cost effective control of total operations,
as opposed to a much more costly system in which each source is controlled in-
dependently of others. All sources are not necessarily directed to a common
baghouse via a universal ductwork system. However, the baghouses, ductwork,
and hoods are designed to provide required airflows, and intermingling of air
streams, on the basis that specified ventilating air streams will suffice to
handle all sources, some on a continuous basis, but many on an intermittent
but scheduled basis. The effectiveness of this mode of operation is to a con-
siderable extent governed by how well the operations are actually scheduled to
prevent temporary overloads or an undue burden on the air moving system, and
on operator diligence in management of dampers. The above considerations were
cited most often by regulatory agencies, and were universally recognized as a
problem by plant management, i.e., regulatory agency staff generally expressed
satisfaction with system design and with its operation, if it and the plant
complex is properly operated.
5.1 PLANT AND PROCESS EMISSIONS
5.1.1 Particulate
Emission data and emission factors were obtained primarily from tradi-
tional sources such as AP-42 and the National Environmental Data System.
Limited measured data were obtained from California regulatory agencies.
These latter data corroborate other data or estimates, but only to a very
limited extent. Engineering judgment is the basis for most of the estimates,
and there is a scarcity of actual information, which permits reliable assess-
ment of uncontrolled and controlled emissions.
Uncontrolled emission factors reported for various types of operations
are given in Table 5.1.
These data indicate that distillation operations (retorts and muffle fur-
naces) exhibit the greatest emissions (22 to 24 kg/Mg, 45 to 47 Ib/ton); that
sweating operations with clean scrap have a negligible potential for particulate
emissions, but about 6 to 16 kg/Mg (11-32 Ib/ton) as the quality of scrap de-
teriorates. No data are pesented for rotary sweat furnaces; one data point
for measured emissions from a rotary furnace1 indicates uncontrolled emissions,
at the afterburner inlet, to be in the range of 25 to 40 kg/Mg (50 to 80 Ib/ton).
The only data point for uncontrolled particulate concentration was obtained
from the same, test--12.77 g/scm (5.58 gr/scf), corresponding to 53 kg/hr (117
Ib/hr). Associated data for baghouse exit gases are 0.011 g/scm (0.005 gr/scf)
and 0.4 kg/hr (0.88 Ib/hr), which corresponds to an overall control efficiency
of 99.24 percent, due in part to the afterburner, and in part to the baghouse.
43
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TABLE 5.1. UNCONTROLLED PARTICIPATE EMISSION FACTORS
FOR SECONDARY ZINC SMELTING
Furnace
Emissions
Ib/ton productkg/Mg product
Retort
Muffle
Pot
Kettle sweat
Clean scrap
General scrap
Residual scrap
Reverberatory sweat
Clean scrap
General scrap
Residual scrap
47
45
0.1
Neg.
11
25
Neg.
13
32
23.5
22.5
0.05
Neg.
5.5
12.5
Neg.
6.5
16
The uncontrolled particulate emission rate for the rotary furnace corresponds
to an emission factor of 25 to 40 kg/Mg (50 to 80 Ib/ton) of product, higher
than the rates of up to 16 kg/Mg (32 Ib/ton) of Table 5-1 reported for sweat-
ing operations.
Annual controlled particulate emissions from retorts, muffle furnaces and
sweating operations calculated and reported in NEDS for individual operations
producing 300 to 2,500 Mg/year (600 to 5,000 tons/year) of product ranged from
a lower value of 0.5 Mg/year to about 5 Mg/year (1 to 10 tons/year); correspond-
ing uncontrolled emissions calculated by factoring in control efficiencies (98
to 99 percent) ranged from about 7 to 90 kg/Mg (15 to 180 Ib/ton).
Efficiencies reported in NEDS for control of particulates were as low as
95 percent, but commonly were 98 to 99 percent. Efficiencies of 98 to 99 per-
cent are commonly accepted as being achievable by industry, given proper main-
tenace of baghouses. Actual efficiencies in the overall control of particu-
lates are a function of effectiveness in entraining particulates in air streams
at the source, and in maintaining overall operations to eliminate periodic sys-
tem overloads.
Estimates of uncontrolled and controlled particulates for the entire in-
dustry are presented in Table 5-2. These data are based on emissions factors
of Table 5-1, and a control efficiency of 97 percent. Total uncontrolled par-
ticulates are about 1,200 Mg (1,300 tons) per year, and controlled emissions,
36 Mg (40 tons), with a majority of emissions coming from distillation furnaces.
Emissions estimated for representative plants are shown in Table 5-3.
These estimates indicate that a larger, integrated plant can be expected to
44
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TABLE 5-2. ESTIMATES OF NATIONAL ANNUAL PARTICULATE
EMISSIONS BY PROCESS TYPE
Production
Mg/year (tons/year) Uncontrolled
Emissions, Mg (ton)
Controlled
(97%)
Zinc produced by sweat
processes
Zinc produced by pot
furnaces
Total zinc
Recycle zinc
Distilled zinca
Muffle furnaces
Retorts
Zinc processed
Total emission
25,400 (28,000)
9,000 (10,000)
900 (1,000)
44,500 (49,000)
23,000 (25,000)
22,000 (24,000)
72,000 (79,000)
190 (210) 5.5 (6)
0.5 (0.5) 0.02 (0.02)
511 (562)
491 (540)
15.5 (17)
14;5 (16)
1,200 (1,320) 36 (40)
? Distilled zinc products: slab/ingots, dust, oxide.
Includes virgin zinc, plus double processing of sweat zinc.
TABLE 5-3. ESTIMATES OF EMISSIONS FROM REPRESENTATIVE PLANTS
Production
Plant type
Mg/year (tons/year)
Mg (tons of
controlled emissions)
97% efficiency
Retorts or muffle
furnaces
Integrating sweating,
distillation
Total
Sweating
Pot furnace
3,600 (4,000)
8,200 (9,000)
sweati ng
13,600 (15,000)
distillation
8,200 (9,000)
1,800 (2,000)
2.7 (3)
1.8 (2)
7.3 (8a)
11 (12) 16.3 (18a)
1.8 (2) 7.3 (8a)
4.5 kg (10 Ib)
Estimates obtained with emission factor of 30 kg/Mg (60 Ib/ton) from
sweating operations.
45
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emit 9 to 18 Mg (10 to 20 tons) annually of participates; that a pot furnace/
alloy production operation should emit negligible particulates; and that repre-
sentative single purpose (sweating or distillation) plants can be expected to
emit 2 to 7 Mg/year (2 to 8 tons/year) depending on plant type and assumptions
regarding emission factors.
Emissions for specific plants surveyed in the study cannot in several cases
be estimated with confidence due to the unavailability of production data and/or
process information. The estimates in Table 5-4 are provided with this quali-
fication. The estimates range from less than 1 Mg/year/plant (1 ton/year/plant)
to about 11 Mg/year (12 tons/year) from a large plant.
5.1.2 NO Emissions
•r\
Data on NO emissions are limited to data recorded in NEDS. These data
indicate that NO emissions are of the order of 1 kg/1,000 kg (1 ton/1,000
tons) of product for distillation furnaces, and 1 kg/2,000 to 3,000 kg (1 ton/
2,000 to 3,000 tons) for sweat furnaces. The lower values for sweat furnaces
reflect both the lower temperatures of the sweating operations (800 to 900K
(1000 to 1200°F)) versus 1375 to 1475K (2000 to 2200°F) and lower fuel usage.
Application of these factors yields N0y emissions for the industry of 54
to 64 Mg/year (60 to 70 tons/year). A sweating operation producing 9,000 Mg/
year (10,000 tons/year) will emit on the order of 4 to 5 Mg/year (4 to 5 tons/
year) of NO .
s\
A large integrated sweating and distillation plant (15,000 Mg/year (16,000
ton/year)) of distilled zinc) will emit about 18 Mg (20 tons) of NO , while
the more average plant sized at 4,000 to 4,000 Mg/year (4,000 to 6,500 tons/year)
will emit 5 to 6 Mg (5 to 7 tons) of NOV annually.
XX
Neither nitrogen oxides or sulfur oxides are controlled by the industry.
Sine natural gas is uniformly used in the industry, sulfur oxide emissions are
minimal.
An adequate data base is not available to estimate hydrocarbon emissions.
These can be expected principally from sweating operations, but are reduced in
quantity and concentration by afterburners.
46
-------
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-------
REFERENCES: SECTION 5
1. Telecon. McElroy, A., Midwest Research Institute with A. Bailey, South
Coast Air Quality Management District. Secondary Zinc Operations in
in California, December 18, 1979.
48
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6.0 EMISSIONS CONTROL SYSTEMS
6.1 CURRENT CONTROL TECHNOLOGY PRACTICES
Sources of information on emissions control systems were primarily tele-
phone contacts with plant personnel and state and local regulatory agencies.
Control systems are in operation in all the plants surveyed for particulate
emissions from the several types of furnaces—pot, kettle, reverberatory and
rotary sweat furnaces, and muffle and retort distillation furnaces. After-
burners in some plants augment baghouse control for sweating operations. Only
very limited use is made of electrostatic precipitators and wet scrubbers.
Standard practice in the industry involves baghouse complexes connected
with a network of ducts which lead either directly to flue gas generation
points in the case of sweating operations, or to hoods mounted over intermit-
tent emission points, i.e., directly above a pot furnace or at the point where
retorts or muffle furnaces are "broken." Baghouses, ductwork, and air flows
(including dilution air required to reduce air temperatures) are designed to
accommodate loads from individual and combined sources on a scheduled basis.
The overall system is accordingly underdesigned from the standpoint of control
of all intermittent sources simultaneously. This approach, taken to reduce
costs, is effective to the extent that intermittent sources are scheduled to
prevent overloads, and system effectiveness is a function of operator atten-
tion to damper positioning. The principal concern expressed by regulatory per-
sonnel relates to control system management, i.e., scheduling and damper posi-
tioning. Another factor which is important in control system effectiveness is
management of the bags and baghouses, i.e., replacement of bags and bag shake-
down. If these operational and maintenance factors are properly taken care of
then the pollution control system is capable of good performance.
Very limited use of electrostatic precipitators apparently persists because
of investments in precipitators, as the ESP has a narrow range of effectiveness
for control of zinc oxide. One plant surveyed expressed satisfaction with ESP
performance for control of emissions from zinc alloying pot furnaces plus brass
and bronze operations, but only after a considerable period required to learn
how to operate and maintain the system. The associated regulatory agency ad-
mitted satisfaction with performance, but the engineer was quite positive in
his conviction that precipitators should not be used in zinc operations.
Baghouse control system efficiencies listed in the NEDS printouts ranged
from 95 to 99 percent, with 98 to 99 percent being usual. The measured effi-
ciency for an .afterburner baghouse system for a rotary furnace was 99.24 per-.
cent (loading to afterburner: 53 kg/hur (117 Ib/hr); baghouse effluent load,
0.4 kg/hr (0.88 Ib/hr), 0.011 g/scm (0.005 gr/scf).
49
-------
Air flows to baghouses ranges from 2.8 standard cubic meters per minute
(100 scfm) to 850 standard cubic meters per minute (30,000 scfm), with tempera-
tures ranging from about 340 to 450K (160 to 350°F). Since most of the emis-
sions points exhibit air temperatures of 800 to 1400K (1,000 to 2,000°F), di-
lution is required to lower temperatures to the baghouses.
In addition to the controlled emission points, certain fugitive emission
sources exist within an operating plant. These include emissions from product
(Zn dust, Zn oxide) conveying systems, and dusts from handling scrap and resi-
dues. These sources are generally not controlled except to the extent that
airborne matter is swept into the ventilating system associated with baghouse
operations. Estimated emissions range from 0.2 kg/1,000 kg (0.2 ton/1,000 tons)
processed for screening systems to 2 tons/1,000 tons processed for dust con-
veyors. Emissions from such sources have not been included in estimates of
particulate emissions nationally or from individual plants. Uncontrolled emis-
sions from such sources have the potential to approximately equal the emissions
estimated from controlled sources. Such a conclusion must be qualified, however,
by the essentially complete lack of documented data on fugitive sources.
6.1.1 Retort Emissions Control Systems
Flue gases from indirect heating are vented without control during most
of the cycle. When the furnace is broken for removal of product and ash, and
recharging, a hooding system captures emissions which are directed to a bag-
house.
6.1.2 Muffle Furnace Emissions Control
Emissions control for muffle furnace is similar to that for retorts, i.e.,
intermittent emissions from charging operations and during furnace breakdown
are swept into a hood/ductwork system and to a baghouse.
In addition, that fraction of the distilled zinc burned to zinc oxide is
directed to a product baghouse system.
6.1.3 Emissions Control From Sweating Operations
Sweat furnaces may be completely independent of other operations, includ-
ing being the only zinc-based operation in a plant. Alternatively, sweating
may be integrated directly with operation of a muffle furnace. In all cases,
emission control consists of directing the gases which have been in contact
with furnace charge, to a baghouse. The flue gases may come from natural gas
used solely to provide sweat furnace heat, or may come in part from the hot
flue gases of an associated muffle furnace. If the charge is sufficiently
"dirty," an afterburner may, or should be, interposed between the furnace and
the baghouse. The afterburner approximately doubles fuel requirements. The
emissions control system accordingly consists of baghouses plus afterburners.
As indicated earlier, the control of such a system has been documented at 99+
percent.
50
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6.1.4 Control of Fugitive Emissions
Specific control of fugitives from general plant operations is not prac-
ticed, within the context of providing collection and filtering of the emis-
sions. Control consists of adoption of handling practices to minimize dust
formation, for example blanketing hot ash with cold ash.
6.2 ALTERNATIVE CONTROL TECHNIQUES
The baghouse system is the method of preference for the industry, from
the standpoint of cost, efficiency, and the built in feature of capturing par-
ti cul ate matter for sale or recycle.
Within the framework of the baghouse system, alternates for consideration
in development of New Source Performance Standards consist of possible extension
of controls to fugitive sources not presently taken care of; more universal
usage of afterburners in sweating operations, and evaluation of possibilities
for reduced dust emissions from general plant operations.
Consideration can be given as well to development of uniform standards
for designing baghouse systems to reduce sensitivity to operator neglect.
Automated damper control is, in principle, an option, but one which plant per-
sonnel view as costly and beyond the present state of the art in commercially
demonstrated systems. Added baghouse capacity is a further option, desirable,
in principle, from the standpoint of providing a better capability to handle
overload or emergency situations; this option would, however, add significantly
to the cost of pollution control, without necessarily decreasing the complexity
of managing and scheduling system operation.
Sulfur oxide and nitrogen oxide emissions are not a control problem within
the framework of present standards with natural gas as the fuel. Only in the
event that new sources are required to use other fuels should NSPS be necessary
for these air pollutants.
6.3 BEST SYSTEMS OF EMISSION REDUCTION
Since essentially all the plants surveyed use the same basic system for
particulate control, it is difficult to identify any one plant or system as
"best." The principal difference between plants appears to consist of differ-
ences in management and operation of systems rather than in basic design fea-
tures. The "best" system accordingly consists of a properly designed and well
operated baghouse system, complemented by afterburners to minimize the load of
particulates and unburned hydrocarbons to the baghouse.
Pacific Smelting, in Torrance, California, was selected as a plant which
exemplifies a majority of the operations which can be used in secondary zinc
plants, controls pollutants with an established complex of baghouses and acces-
sories, and which employs after burners. This plant site was visited during
the survey. The plant is equipped with 14 retort furnaces, four muffle furnaces,
a rotary kiln sweat furnace, and other sweat furnaces which either operate in-
dependently or integrated with muffle furnaces.
51
-------
The pollution control and product collection (zinc oxide) baghouse com-
plex has 21 baghouses sized from 2.8 standard cubic meters per minute (100 scfm)
to 850 standard cubic meters per minute (30,000 scfm). Since the plant is in
the metropolitan Los Angeles area and is now surrounded by urban development,
its control of air pollution is observed closely by the area pollution control
authority. Limited emissions data are available; the measurements of uncon-
trolled and controlled particulates for a rotary sweat furnace described earlier,
i.e., afterburner inlet-53 kg/hr (117 Ib/hr); baghouse outlet-0.4 kg/hr (0.88
Ib/hr), 0.011 g/scm (0.005 gr/scf); overall efficiency-99.24 percent, were ob-
tained at the Pacific'Smelting site.
The Pacific Smelting plant is our present recommendation for testing in
the event that New Source Performance Standards are promulgated, since it has
a well rounded complement of sources which would need to be tested, and has in
place pollution control equipment which represents the current best state of
the art. Final selection of a plant for testing might depend, however, on re-
sults of costs for testing, since the plant is not well set up for emissions
testing.
52
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7.0 EMISSION DATA
7.1 AVAILABILITY OF DATA
Emissions data obtained from state and local agencies and the National
Environmental Data System are summarized in Table 7-1. Data recorded in NEDS
were primarily based on engineering judgment. Limited data from actual emis-
sions tests were obtained. These data generally support emissions factors used
in the study, and in addition corroborate effectiveness of emissions control
systems.
7.2 METHOD FOR SAMPLE COLLECTION
EPA Method 5 is the applicable standard method for sample collection and
analysis of particulates from the secondary zinc industry. Information on spe-
cific methods for emission testing was not obtained in the survey.
Methods for collection and analysis of particulates from fugitive sources
require further development.
53
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TABLE 7.1. EMISSIONS INFORMATION
Company
Pacific Smelting
M. J. Bullock
Aetna Metals
Apex SmeltlngS/
Hugo tteu Pro1er§/
Inland KetalsS/
S-G Metals
Canton Metal Alloys
Federated Metals
Superior Zinc
Gulf Reduction
Corporation
Pacific Smelting
Aetna Metals
Process operation
A. NEDS
1978 Retorts
Muffle furnaces
Rotary sweat furnaces
Reverberatory/kettle sweat furnaces
Oust condensers
Screening equipment
1977 Kettle sweat
1977 Reverberatory sweat
Alloy furnace
Muffle furnace
1974 Reverberatory sweat furnace
1977 Retorts
Sweat furnace
1973 Reverberatory furnace
1978 Pot furnace
1975 Sweat furnace
1977 Retorts
1976 Calcining kiln
Retorts!/
1970 Retorts
B. California - Air
Rotary furnace
Muffle furnace
Retorts
Sweat furnace
Control equipment
FF
FF
FF
FF
FF
None
FF
FF
MC
FF
NC
FF
FF
FF
ESP
NC
FF
Wet scrubber
FF
NC
Quality Unit
FF
Afterburner
FF
FF
FF
Afterburner
Pollutants
Particulates
NOX
HC
Particulates
Particulates, NOX
Particulates, NOX, HC, CO
Particulates, SOX, NOX,
HC, CO
Particulates, NOX
Particulates, NOX
Particulates, NOX
Particulates
Particulates
Particulates
Particulates, NOX, HC, CO
Particulates, SOX, NOX
Particulates
Particulates, NOX
Particulates, CO NOX
Particulates
Particulates
Particulates
Organic acids
a/ Ceased zinc operations
54
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8.0 STATE AND LOCAL EMISSION REGULATIONS
State and local emission regulations that apply to new sources in the sec-
ondary zinc smelting and refining industry are summarized in this section.
Eleven of the 13 states which have plants of this industry (Table 4-1) were
examined. It is believed that the 11 states are representative of all areas
where secondary zinc plants are likely to be built. These regulations were
taken primarily from the Environment Reporter with supplemental information
from contacts with state air pollution control agencies.
The emission regulations are summarized in Table 8-1. The allowable emis-
sions in each state are compared for a hypothetical plant, considered typical
of a new plant which might be built. The annual design capacity for distilla-
tion is 19,900 metric tons (21,900 short tons). The model plant has one rever-
beratory furnace, one rotary furnace, 10 retort furnaces, and three muffle fur-
naces. Each furnace was treated as a source. The parameters of the furnaces
are listed in Table 8-2. The plant emissions are collected in a baghouse and
vented through 80, 20 cm (8-in.) diameter pipes at 6 meters (20 ft) above ground.
This is considered equivalent to a 6 meter (20 ft) stack with a 1.8 meter (6
ft) inside diameter. The distillation furnaces are heated indirectly. The
exhaust stream from the distillation process is separate from the combustion
exhaust stream. The process chambers of the distillation furnaces are enclosed,
except for some small vents, during most of the processing time. Emission con-
trols are applied only when the furnaces are "broken" or opened to insert or
remove material. Plant operations are scheduled to avoid breaking a large num-
ber of distillation furnaces at a time, a practice which reduces the required
emission control capacity. In the model plant the flow through the baghouse
under normal operating procedures is 2,000 mVmin (71,000 acfm) at a tempera-
ture of 380K (684°R). The stack exit velocity under these conditions is 13
meters/sec (43 ft/sec). Part of the year the plant will be operating below
the normal rate as furnaces are out of service for maintenance. The annual
average flow, based on the operating hours for each source in Table 8-1 is
1,687 mVmin (59,587 acfm).
Table 8-3 summarizes the particulate emissions regulations of the 11 states
as applied to the whole plant. It is based on Table 8-1, with the plant operat-
ing under normal conditions.
The calculations for Table 8-3 (except Texas) were made by first finding
the total emissions of the model plant if each source emits what the state al-
lows (Table 8-1) for the number of hours the source operates in the year (Table
8-2). The allowable emissions per hour for the plant under average operating
conditions were the annual emissions divided by (24 x 365) hours per year.
The allowable emissions per hour under normal operating conditions (listed in
55
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TABLE 8-1. SUMMARY OF PARTICULATE EMISSIONS RE6UALTIONS FOR NEW
SECONDARY ZINC PLANTS
State
AltblM
California*
Illinois
Kansas
Kaiiactwselts
Visible
Missions
percent
opacity
20
20
30
20
20
Allowable participate emission for each furnace
General process regulation
E = 3.59 P°'62 if P < 30
Lesser of concentration limit
froa Table 404(a) and
emission rate limit from
Table 40S(a)
E - 2.54 P°'534 if P < 450
E « 4.1 P0-67 if P S 30
Emission rate limit from
Date of
last
revision
9/76
10/5/79
5/3/79
1/1/74
1/1/78
Reverberate ry
furnace
kg/hr
2.7
1.1
1.8
3.2
1.4
Ib/hr
5.9
2.5
3.9
7.1
3.2
Rotary
furnace
kg/hr
3.2
3/0
2.1
3.9
1.7
Ib/hr
7.1
G.6
4.6
8.6
3.7
Retort
furnace
kg/hr.
0.4
0.5
0.4
0.5
0.2
Ib/hr
1.0
1.0
0.8
1.0
0.5
Muffle
furnace
kg/hr
1.2
1.3
0.9
1.4
0.7
Ib/hr
2.7
2.9 ,
2.0
3.0
1.6
Hew Jersey
(few York
Ohio
Table 6 if P S 30
20 0.5 Ib/hr for small sources;c
0.02 gr/scf, but not to re-
quire collection efficiency
> 99X
20 A: 99X cleaning or BACTd
B: 90-91% cleaning
C: 70-75X cleaning
0: No cleaning required
sliding scale cleaning
efficiency5
3/18/77
8/23/79
9/25/78
0.2
0.1
0.8
2.5
1.7
0.5
0.2
1.9
5.6
3.7
1.6
0.3
2.4
6.8
3.7
3.5
0.6
5.4
15.0
8.1
0.2
0.02
9
g
0.5
0.05
9
g
1.0
0.1 0.2
0.9 2.0
2.6 5.6
1.4
CklahoM
Pennsylvania
Texts
20
20
20
E = 4.10 PU'D' if P
Less stringent of Q.
or A = 0.76 (FW)
E * 0.048 q°-62f
S 30
.OJ gr/dscf
4/15/71 3.2 7.1
4/9/79 0.2 0.3
5/7/79
3.9 8.6 0.5 1.0 1.4 3.0
1.6 3.5 0.2 0.5 0.5 1.0
-
* South Coast Air Quality Management District.
b E Allowable emissions (Ib/hr).
f Process weight rate (tons/hr)
Allowable concentration of emissions (grains per dry standard cubic foot).
0.01 for sweating operations.
0.3 for refining (distilling) operations.
Production rate (tons/hr).
Stack effluent flow rate (acfa).
Tables 404(a), 4C5(a), and 6 are tables in the appropriate state regulations.
A saall source is one with uncontrolled emissions less than or equal to 50 Ib/hr and with a gas effluent rate less than or equal to
3,000 scf*.
The envtroncental rating A, B, C, or 0 is assigned on the basis of the nature of the emissions, the location of the plant, the
dispersion of the enissions, and the preexisting air quality situation. For the environmental ratings B and C, the required cleaning
efficiency depends on the uncontrolled emission rate.
Ohio has in ealsslons Unit based on process weight rate and a cleaning efficiency limit with a sliding scale. The more stringent
Unit applies.
The Texas standard applies to the entire plant, not to the individual sources. There is a correction factor if the effective stack height is
less than the standard effective stack height, but this correction factor does not apply to the model plant, which has an effective stack
height of 33 Deters (73 ft) and a standard effective stack height of 24 meters (52 ft). Texas also has a limit on net ground level partic-
ulate concentration.
9 For a saall source (uncontrolled emission rate less than or equal to 10 Ib/hr) with an environmental rating of B or C, the required cleaning
efficiency will be specified by the commissioner.
56
-------
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57
-------
TABLE 8-3. PARTICULATE EMISSION REGULATIONS
FOR THE WHOLE MODEL PLANT
State
Allowable particulate
emissions
kg/hr
Ib/hr
Alabama
California
Illinois
Kansas
Massachusetts
New Jersey
New York3 A
B
C
D
Ohio
Oklahoma
Pennsylvania
Texas
10.9
9.9
7.9
12.1
5.9
4.3
0.7
6.4
18.2
-
10.9
12.1
4.2
22.2
24.0
21.9
17.5
26.7
13.0
9.4
1.5
14.0
40.2
-
24.0
26.7
9.3
48.9
See footnotes d and g to Table 8-1. For
Table 8-3 retort furnaces are assumed to
have a 90% cleaning requirement for envi-
ronmental rating B and a 70% cleaning re-
quirement for environmental rating C.
Table 8-3) are the average hourly allowable emissions times the factor 1.1855
= 2,000 -T 1,687, the ratio of the normal flow rate to the average flow rate.
The major pollutant emitted by the secondary zinc industry is particulate
matter, mainly zinc oxide. The emissions are collected by fabric filters.
Often the zinc content of the material collected on the filter is sufficient
to permit recycling or sale for agricultural use. A rotary furnace is often
equipped with an afterburner, which is used if the scrap charge contains a sig-
nificant quantity of combustible contaminants. The energy consumption of the
afterburner, when it is in use, nearly equals the process energy consumption
in the rotary furnace.*
Although the sweat furnaces are heated directly, the distillation furnaces
are heated indirectly. Since natural gas with standby fuel oil is the usual
fuel, the combustion exhaust is" not a major source of pollutants and no emis-
sions controls are placed on it in current practice.
The flow of gasses from the furnaces to the baghouse is controlled by a
complex set of ducts and dampers. The control efficiency depends to a great
extent on operating practices: how carefully the dampers are adjusted, whether
leaks are permitted in the fabric filters, how often the filters are cleaned,
and how many furnaces are broken at a time.
58
-------
Seven of the 11 states have particulate emission limits based on process
weight rate. Two of them, Ohio and California's South Coast Air Quality Man-
agement District also have another standard. California's other standard is a
concentration limit with a sliding scale based on the volume of gas discharged.
The more stringent of the two applies. Ohio's other standard is based on con-
trol efficiency with a sliding scale. Again the more stringent of the two apr
plies. In Ohio, the cleaning efficiency standard applied to the model plant's
sweat furnaces and the process weight standard applied to the distillation fur-
naces, because the sweat furnaces operate at a lower temperature and have a
lower uncontrolled emissions factor (ratio of emissions to process weight) than
the distillation furnaces.
Pennsylvania has a limit based on production rate and a concentration limit
of 0.046 g/dscm (0.02 gr/dscf), with the less stringent of the two applying.
New Jersey has a concentration limit of 0.046 g/dscm (0.02 gr/dscf) and a col-
lection efficiency requirement of 99 percent with the less stringent of the
two applying. In both states the 0.046 g/dscm (0.02 gr/dscf) concentration
limit was less stringent for each source. New Jersey, however, does not re-
quire a small source (Table 8-1, footnote c) to reduce emissions below 0.23
kg/hr (0.5 Ib/hr). New York's regulation is based on efficiency of control
with a sliding scale (Table 8-1, footnotes d and g). Texas has an.emission
rate limit based on the stack effluent flow rate with a correction factor based
on stack exit velocity, gas exit temperature, stack height, and the inside diam-
eter of the stack opening. The correction factor was 1.0 for the model plant.
Texas also limits the net ground level concentration of particulates at the
property line (Table 8-1, footnote f).
The most stringent particulate emission limit is the 99 percent cleaning
required by New York if the environmental rating is A. The most stringent limit
applicable to a whole state is that of Pennsylvania. The applicable limit is
0.046 g/dscm (0.02 gr/dscf). This requires 90 to 98 percent cleaning effici-
ency for the various sources in the model plant.
Using the information on state regulations a Model IV calculation3 was
made to estimate the impact of new source performance standards in 1984 and
1989. The new source performance standard was assumed to be 0.046 g/dscm (0.02
gr/dscf), which equals the standard of the most stringent state. The emissions
under state regulation were assumed to equal the state emission limits. The
calculation was done for each of the 11 states and the results were added.
Since (Table 4-1) the production capacities of most of the states is not known,
an allocation was necessary.
The allocation of the midpoint (92,000 Mg (101,000 tons)) of the range of
estimates of national production capacity to the 16 plants was performed as
follows. The known capacities were assigned to their respective plants. The
three alloying plants were each assigned 300 Mg (330 tons )based on the infor-
mation in Table 4-1 for the plant in Kansas. The plant in Oklahoma was assigned
11,100 Mg (12,200 tons) since it has 14 retorts and 91 kg/hr (0.1 short tons/hr)
is considered a typical retort capacity. The New Jersey plant was assumed to
be similar to the Oklahoma plant. Huron Valley Steel and Superior Zinc were
assigned 10,000 and 6,000 Mg (11,000 and 7,000 tons), respectively, by rounding
59
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the lower bound (Table 4-1) upwards to the next 1,000 Mg (1,100 tons). The
capacity which was still unallocated was divided equally among the remaining
four plants, which assigned each of them 4,700 Mg (5,200 tons).
The resulting allocation of capacities to states was used in the Model IV
calculation. The 11 states which were reviewed represent 84 percent of the
allocated national capacity. The estimated national impact of new source per-
formance standards is the 11-state impact divided by 0.84.
The fractional utilization of existing capacity was assumed to be 0.75
for each state. The national average in 1979 is believed to be 0.5 to 0.6,
but 0.75 is believed to be more typical of recent years.
If the projection of future production (Figure 4-4) is realized and if
capacity is expanded so that production does not exceed 90 percent of capacity,
then the 1989 capacity would be 102,000 Mg (112,000 tons). If the 1979 capacity
is 92,000 Mg (101,000 tons), this would require an average compound annual growth
in capacity of 1.0 percent.
The construction and modification rate to replace obsolete capacity was
assumed to be 0.018 as a decimal fraction of baseline year capacity. This as-
sumption was based on the following assumptions. The rate (13 plants in 22
years) of replacing present capacity with new capacity will continue (Section
4.2.4). This pattern of entry and exit involves the smaller plants: the aver-
age entrant will have a capacity equal to one-half the average capacity of the
industry.
The results of the Model IV calculation are an estimated national impact
of 19 Mg (21 tons) per year in 1984 and 39 Mg (43 tons) per year in 1989. In
1984 allowable emissions under State Implementation Plans would be 250 Mg (275
tons) while under New Source Performance Standards they wold be 231 Mg (255
tons). In 1989 allowable emissions under State Implementation Plans would be
273 Mg (289 tons) while under New Source Performance Standards they would be
224 Mg (246 tons). In 1979 the allowable emissions under the State Implementa-
tion Plans are 238 Mg (262 tons) per year. The actual impact may be much less
than this because Model IV assumes that a plant will emit all the pollutants
which the applicable regulations allow. There is reason to believe that second-
ary zinc plants are emitting less than the present state regulations allow.
One major plant is emitting approximately 10 percent of its allowable emissions.4
The particulates which are collected by the fabric filters have economic value:
they can usually be recycled or sold. Thus there is an economic incentive to
exceed present state requirements. Only 1 plant which was contacted stated
that they are not selling or reprocessing the material which their air pol-
lution control system collects.
It appeared to project personnel that state enforcement activities are
focused primarily on visible emissions. Only when the visible emissions stan-
dard (usually 20 percent opacity with exceptions for short intervals) is re-
peatedly violated are measurements taken to ascertain compliance with process
weight standards, cleaning efficiency standards, or particulate concentration
standards.
60
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REFERENCES: Section 8.0
1.
2.
3.
4.
Bureau of National Affairs.
Washington, D.C.
Environment Reporter. State Air Laws.
Kusik, C. L., and C. B. Kenahan. Energy Use Patterns for Metal Recycling.
U.S. Bureau of Mines Information Circular 8781. 1978. pp. 146-163.
Monarch, M. R., R. R. Cirillo, B. H. Cho, G. A. Concaildi, A. E. Smith,
E. P. Levine, and K. L. Brubaker. Piriorities for New Source Performance
Standards under the Clean Air Act Amendments of 1977. EPA-450/3-78-019.
Research Triangle Park, North Carolina. April 1978. pp. 9-13.
Telecon. McElroy, A., Midwest Research Institute with A. Bailey, South
Coast Air Quality Management District. Secondary Zinc Operations in
California. December 18, 1979.
61
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
t. RJgQfvr NO.
-450/3-80-12
2.
3. RECIPIENT'S ACCESSION-NO.
I. TITLE AND SUBTITLE
5. REPORT DATE
Source Category Survey: Secondary Zinc Smelting and
Refining Industry
May 1980
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
A. D. McElroy, F. D. Shobe
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND AOORESS
Midwest Research Institute
425 Volker Boulevard
Kansas City, Missouri 64110
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-3059
12. SPONSORING AGENCY NAME AND AOORESS
Emission Standards and Engineering Division
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final (10/79-2/80)
14. SPONSORING AGENCY CODE
EPA 200/04
18. SUPPLEMENTARY NOTES
Project Officer:
lS ABSTRACT
Reid Iversen (919-541-5295)
This report describes the results of a survey of the secondary zinc smelting and
refining industry to determine the probable impact of the development of new source
performance standards under Section 111 of the Clean Air Act. This industry recovers
zinc as metallic zinc, zinc dust, zinc oxide, or zinc alloys from scrap by melting or
distillation processes. However, primary zinc smelters and refiners, who process zinc
from ore, were excluded, even though they also process scrap to recover zinc. Infor-
mation was gathered by collecting process, emission, and economic data from literature
searches; contacting air pollution control agencies, other government agencies, indus-
try representatives, and trade associations; and visiting a secondary zinc plant. The
report describes the industry, projects production and capacity to 1989, and describes
industry processes, actual and allowable air emissions, and emission control systems.
State and local emission regulations are compared and the probable impact of a new
source performance standard is assessed.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Secondary Zinc Industry
Air Pollution
Particulates
New Source Performance Standards
Emission Control Systems
Clean Air Act
Recycling
State Implementation
Plans
Zinc
Sweating
i <;-HI
13 B
8. DISTRIBUTION eiTAT^MGNT
Available from National Technical
Information Service, 5285 Port Royal Road,
Springfield, Virginia 22161
19. SECURITY CLASS /ThisReport!
Unclassified
21. NO. OF PAGES
61
20. SECURITY CLASS iThis page;
Unclassified
22. PRICE
EPA Feim 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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