United States
Environmental Protection
Agency
Industrial Environmental Research EPA-600/7-79-1 61
Laboratory August 1979
Cincinnati OH 45268
Research and Development
&EPA
Environmental
Considerations of
Selected Energy-
Conserving
Manufacturing
Process Options
Volume XIX
Solid Residues
Summary Report
Interagency
Energy/Environment
R&D Program
Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3 Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-79-161
August 1979
ENVIRONMENTAL CONSIDERATIONS OF SELECTED
ENERGY-CONSERVING MANUFACTURING PROCESS OPTIONS
Volume XIX. Solid Residues Summary Report
by
Arthur D. Little, Inc.
Cambridge, Massachusetts 02140
Contract No. 68-03-2198
Project Officer
Herbert S. Skovronek
Power Technology and Conservation Branch
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI. OHIO 45268
For male by the Superintendent of Documents, U.S. Government
Printing Office, Washington, D.C. 20402
-------
DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory-Cincinnati, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, con-
verted, and used, the related pollutional impacts on our environment,
and even on our health, often require that new and increasingly more
efficient pollution control methods be used. The Industrial Environ-
mental Research Laboratory - Cincinnati (lERL-Ci) assists in developing
and demonstrating new and improved methodologies that will meet these
needs both efficiently and economically.
This report summarizes information on solid residues from a study
of 13 energy-intensive industries. If implemented over the coming 10
to 15 years, these processes and practices could result in more effec-
tive utilization of energy resources. The study was carried out to
assess the potential environmental/energy impacts of such changes and
the adequacy of existing control technology in order to identify po-
tential conflicts with environmental regulations and to alert the
Agency to areas where its activities and policies could influence the
future choice of alternatives.
The results will be used by the EPA's Office of Research and De-
velopment to define those areas where existing pollution control tech-
nology suffices, where current and anticipated programs adequately ad-
dress the areas identified by the contractor, and where selected pro-
gram reorientation seems necessary.
Specific data will also be of considerable value to individual
researchers as industry background and in decision-making concerning
project selection and direction.
The Power Technology and Conservation Branch of the Energy Sys-
tems-Environmental Control Division should be contacted for additional
information on the program.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
iii
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ABSTRACT
Under EPA Contract No. 68-03-2198, Arthur D. Little, Inc.
undertook a study of the "Environmental Considerations of
Selected Energy-Conserving Manufacturing Process Options."
Some 80 industrial process options were examined in 13 industrial
sectors. Results were published in 15 volumes, including a
summary, industry prioritization report, and 13 industry
oriented reports (EPA-600/7-76-034 a through o).
This present report summarizes the information regarding
sulfur oxide pollutants in the 13 industry reports. Four
parallel reports treat nitrogen oxides, particulates, solid
residues, and toxics/organics. All of these pollutant-oriented
reports are intended to be closely used with the original 15
reports.
iv
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CONTENTS
Forword iii
Abstract iv
Tables vi
English-Metric (SI) Conversion Factors viii
1. INTRODUCTION 1
BACKGROUND AND PURPOSE 1
APPROACH 1
2. FINDINGS AND R&D OVERVIEW 5
FINDINGS 5
IDENTIFICATION OF CROSS-INDUSTRY TECHNOLOGY 16
R&D AREAS 16
3. PROCESSES AND SOLID-RESIDUE DISCHARGES 20
IRON AND STEEL INDUSTRY 20
PETROLEUM REFINING INDUSTRY 28
PULP AND PAPER INDUSTRY 36
OLEFINS INDUSTRY 40
AMMONIA INDUSTRY 45
ALUMINA/ALUMINUM INDUSTRY 48
TEXTILE INDUSTRY 59
CEMENT INDUSTRY 64
GLASS INDUSTRY 67
CHLOR-ALKALI INDUSTRY 72
PHOSPHORUS/PHOSPHORIC ACID INDUSTRY 77
PRIMARY COPPER INDUSTRY 84
FERTILIZER INDUSTRY 92
REFERENCES 95
TECHNICAL REPORT DATA (includes abstract) 96
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TABLES
Number Page
1 Projected U.S. Production in Industries Studied 4
2 Summary of Estimated Solid-Residue Discharges 7
3 Estimated Increase in Annual Solid-Residue Discharges
(1989-1974) Assuming Industry Expands Using Process
Types Indicated 17
4 Estimated Range in Solid-Residue Discharges in 1989
for New Processes Likely to be Implemented 18
5 Comparison of BOP Dust Compositions 23
6 Solid-Residue Discharge From Iron and Steelmaking 29
7 Typical Composition of Stretford Purge Solution 34
8 Solid-Residue Discharge From Petroleum Refining 37
9 Solid-Residue Discharge From Olefin Plants 44
10 Solid-Residue Discharge From Ammonia Production 49
11 Composition of Waste Stream From Leaching Process 51
12 Composition of Waste Stream 53
13 Estimated Composition of Waste Stream 55
14 Estimated Generation Rates of Solid-Residue Streams 57
15 Solid-Residue Discharge From Alumina/Aluminum Production 60
16 Solid-Residue Discharge From Cement Production 68
17 Solid-Residue Discharge From Glass Furnaces 73
18 Solid Residue Generated in Producing Chlorine Via Graphite
Anode Diaphragm. Cell 75
19 Solid Residue Generated by Chlorine Production Units
Equipped With Dimensionally Stable Anodes 76
20 Solid-Residue Discharge From Chlor-Alkali Production 78
21 Solid-Residue Discharge From Wet-Process Production of
Phosphoric Acid 82
vi
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TABLES (cont.)
Number Page
22 Solid-Residue Discharge From Production of Phosphorus/
Phosphoric Acid 85
23 Solid-Residue Stream Generation Rates (Copper) 87
24 Solid-Residue Discharge From Production of Primary Copper 91
25 Solid-Residue Discharge From Fertilizer Production 94
vii
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ENGLISH-METRIC (SI) CONVERSION FACTORS
To Convert From
1°.
Metre2
Pascal
3
Metre
Joule
Pascal-second
Multiply By
4,046
101,325
0.1589
1,055
0.001
Acre
Atmosphere (normal)
Barrel (42 gal)
British Thermal Unit
Centipoise
Degree Fahrenheit
Degree Rankine
Foot
3
Foot /minute
Foot
Foot
Foot/sec
2
Foot /hr
Gallon (U.S. liquid)
Horsepower (550 ft-lbf/sec)
Horsepower (electric)
Horsepower (metric)
Inch
Kilowatt-hour
Litre
Micron
Mil
Mile (U.S. statute)
Poise
Pound force (avdp)
Pound mass (avdp)
Ton (Assay)
Ton (long)
Ton (metric)
Ton (short)
Tonne
Source: American National Standards Institute, "Standard Metric Practice
Guide," March 15, 1973. (ANS72101-1973) (ASTM Designation E380-72)
Degree Celsius
Degree Kelvin
Metre
Metre /sec
Metre3
2
Metre
Metre/sec
2
Metre /sec
Metre
Watt
Watt
Watt
Metre
Joule
Metre
Metre
Metre
Metre
Pascal-second
Newton
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
t° = (t° -32
c F
0 o / n
tK = tR/1.8
0.3048
0.0004719
0.02831
0.09290
0.3048
0.00002580
0.003785
745.7
746.0
735.5
0.02540
3.60 x 106
1.000 x 10"3
1.000 x 10~6
0.00002540
1,609
0.1000
4.448
0.4536
0.02916
1,016
1,000
907.1
1,000
viii
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SECTION I
INTRODUCTION
BACKGROUND AND PURPOSE
During 1975 and the first half of 1976, under EPA Contract No.
68-03-2198, Arthur D. Little, Inc., undertook a study of the "Environmental
Considerations of Selected Energy-Conserving Manufacturing Process
Options" in 13 energy-intensive industry sectors for the U.S. Environmental
Protection Agency (EPA). The results of these studies were published
in the following reports:
• Volume I -- Industry Summary Report (EPA-600/7-76-034a)
• Volume II — Industry Priority Report (EPA-600/7-76-034b)
• Volume III — Iron and Steel Industry (EPA-600/7-76-034c)
• Volume IV — Petroleum Refining Industry (EPA-600/7-76-034d)
• Volume V — Pulp and Paper Industry (EPA-600/7-76-034e)
• Volume VI — Olefins Industry (EPA-600/7-76-034f)
• Volume VII — Ammonia Industry (EPA-600/7-76-034g)
• Volume VIII — Alumina/Aluminum Industry (EPA-600/7-76-034h)
• Volume IX — Textiles Industry (EPA-600/7-76-034i)
• Volume X — Cement Industry (EPA-600/7-76-034J)
• Volume XI — Glass Industry (EPA-600/7-76-034k)
• Volume XII - Chlor-Alkali Industry (EPA-600/7-76-0341)
• Volume XIII — Phosphorus/Phosphoric Acid Industry (EPA-600/7-76-034m)
• Volume XIV — Copper Industry (EPA-600/7-76-034n)
• Volume XV — Fertilizer Industry (EPA-600/7-76-034o)
In the course of this study, some 80 industrial processes were
examined as potential energy-conserving options, focusing on:
• Identification of any major sources of amounts of pollutants
(air, water, and solid) expected from the processes;
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• Development of estimated capital and operating costs for
both production and pollution control aspects of the
processes;
• Estimation of the types and amounts of energy used in
both production and pollution control for the processes;
• Assessment of the economic viability and likelihood of
implementation of those alternative process options
being studied;
• Identification of areas where EPA's activities and policies
could influence the future choice of alternatives; and
• Identification of research and development areas in both
process and pollution control technology.
Because of the industry orientation of the study, encompassing 15
volumes and some 1,700 pages, we felt that pollutant-specific information
across all the 13 sectors studied should be summarized. Five such
pollutant-specific areas were identified to be of particular interest:
• Nitrogen oxide (NO ) emissions,
X.
• Sulfur oxide (SO ) emissions,
X
• Fine particulate emissions,
• Solid residues, and
• Organic and/or toxic pollutants,
A summary pollutant report in each of these areas has been prepared.
Although some estimates and extrapolations of pollutants have been
attempted where the information was readily available, we have not in
general attempted to go beyond the 15 original reports.
APPROACH
These summary pollutant reports are intended to be used closely with
the original 15 reports. Generally, information such as detailed des-
criptions of the processes which can be found in the previous 15 reports
has not been duplicated in the 5 pollutant reports, but has been exten-
sively referenced by volume number and page number (e.g., Vol. VII,
page 20, refers to page 20 of the Ammonia Industry report).
In Section II of this report (Findings and R&D Overview), summary
information on generic, cross-industry solid residue problems that emerge
and suggestions for research and development work in the areas of both
pollution control technology and process technology are presented. All
-------
emissions are estimated unless specifically referenced, since we believe
that actual data do not exist for the processes described, which are
frequently still under development.
To give the reader a sense of the size of the industries for which
the pollution problems covered in these summary pollutant reports are
considered, Table 1 lists these industries, their total production in
1974 (the base case year for the study) and their projected incremental
production in 1989 — 15 years hence. In the following sections and
tables, solid-residue loads calculated for 1989 are based on the assump-
tion that the individual process option accounts for incremental pro-
duction.
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TABLE 1. PROJECTED U.S. PRODUCTION IN
INDUSTRIES STUDIED
Total U.S.
Production
in 1974
Commodity (106 tons*)
Alumina
Aluminum
Ammonia
Cement
Chlorine
Coke
Copper
Fertilizers (HN03)
Glass (flat)
Iron
Olefins (ethylene)
Petroleum
Pulp (kraft)
Pulp (newsprint)
Phosphoric Acid
(detergent grade)
Phosphoric Acid
(wet acid grade)
Steel
Textiles (knit)
Textiles (woven)
7.7
5.0
9.2
79.0
11.0
62.0
1.6
8.2
29.0
100.0
13.0
740.0**
16.0
3.9
1.4
9.0
133.0
0.32
2.1
Projected
Rate
of Growth
(%/yr)
6.0
6.0
6.0
2.0
5.0
2.5
3.5
4.0
2.5
2.5
8.0
1.5
5.0
2.5
2.5
2.5
2.5
2.2
2.2
Total
Projected
Production
in 1989
(106 tons)
18.5
12.0
22.0
106.3
22.9
89.8
2.7
14.8
42.0
144.8
41.2
925.0***
33.5
5.6
2.03
13.0
193.0
0.44
2.91
Increase in
Annual
Production
in 1989 over
that of 1974
(106 tons)
10.75
7.0
12.8
27.3
11.9
27.8
1.1
6.6
13.0
44.8
28.2
185.0****
17.3
1.7
0.63
4.0
60.0
0.12
0.81
*A11 tons referred to in these reports are net tons, unless otherwise
indicated.
,15
**Approximate equivalent of 30 quads (1 quad is equal to 10
***Approximate equivalent of 37.5 quads.
****Approximate equivalent of 7.5 quads.
Btu).
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SECTION II
FINDINGS AND R&D OVERVIEW
FINDINGS
Of the 13 industries studied, 6 have potentially applicable process
options that would result in a significant change (more than 3 x 10
ton/yr) in the base case solid-residue generation rate. These process
options, if adapted in new plants, would result in the following changes
in estimated solid residues discharged:
• Iron and Steel Industry - direct reduction (increase of
15.5 x 10 ton/yr)
• Cement,Industry - fluidized bed process (decrease of
3 x 10 ton/yr)
• Aluminum Industry - use of domestic clays for alumina
production (increase of 7.5 to 27 x 10 ton/yr)
• Pulp and Paper Industry
• Phosphoric Acid (detergent grade) - wet process acid
with chemical clean-up (increase of 3 x 10 ton/yr)
• Copper-Industry - Arbiter process (increase of
3 x 10 ton/yr)
Process options for the textile, fertilizer and pulp and paper
industries, (excluding the production of newsprint) have very little
impact when compared with the base case solid-residue generation rate.
All of the remaining industries have at least one process option
that would result in a significant increase in the base case solid-
residue generation rate. The most common cause of the increased generation
of solid residues is the conversion from natural gas or fuel oil to coal
as the primary raw material and/or process energy source. The major
solid-residue streams associated with the use of coal ash, flue gas
desulfurization sludge, and related wastewater treatment sludge. In
some of these cases, the bulk of the solid-residue load can be, or is
generated, at an electric utility, such as in electric melting for
glass, while in others, such as coal gasification or hot gas generation
for glass melting, the coal must be used on-site. It should, therefore,
be borne in mind that a shift from gas or oil to coal at the power plant
would generate a comparable increase in the solid-residue load, consisting
of coal ash (0.105 Ib/kWh), and, eventually, SO scrubber sludge
(0.25 Ib/kWh). Solid-residue discharges from electric utility power
plants have not been estimated in this study.
-------
In the alumina industry, process options designed to alleviate U.S.
dependence on imported bauxite by extracting alumina from domestic
kaolin clay would result in both a significant increase in the base
case solid-residue generation rate and a significant change in the
chemical composition of the waste. In the copper industry, the use of
the Arbiter hydrometallurgical process for extracting copper from ore
would result in a substantial increase in the base case generation of
solid waste.
For most of the process options that result in a significant
increase in solid-residue generation, there is very little potential
for decreasing the amount of solid waste by either in-plant controls
or by further processing of the waste streams. This is particularly
true when the solid-residue results from the use of coal. Solid residues
of an organic nature, such as certain waste streams associated with
process options in the petroleum refining, olefins, pulp and paper,
and textile industries, could be greatly reduced in volume by incineration.
Finally, there is another group of process options which do not
appear to have a significant impact on solid-residue generation. For
these, other factors (energy savings, cost, water pollution, etc.) will
determine the extent to which the process is implemented over the coming
years.
A comparison of solid-residue generation rates (and resultant incre-
mental solid-residue quantities based on the growth period from 1974
to 1989) for the base case manufacturing technology and its process
options is presented in Table 2. Although it would be unrealistic to
presume that all incremental production over the next 15 years would
incorporate any one of the specified processes, it would be equally
unrealistic to try to estimate the fraction of the production which
might use an individual process. Therefore, in an effort to present to
the reader the perspective of the changes which might occur, we have
compiled in Table 2 the solid-residue outputs which would be generated,
assuming utilization of the designated process option for all incremental
production in 1989 over that produced in 1974.
It should be recognized that the figures given in Table 2 are
related to incremental production. For example, the 9.0 x 10 tons of
solid waste expected in 1989 from the BOP is derived from the incre-
mental production in that year, 60 x 10 ,tons. The total solid-residue
production from the BOP would be 21 x 10 tons, from 190 x 10 ton of
steel, based on the increment plus 62% discharge factor of 150 lb/1000 Ib.
Use of the proposed option — off-gas recovery — does not reduce solid
residue in this case, but does offer other energy and air pollution
advantages.
Similarly, assuming all iron is obtained by the blast furnace, the
total incremental production of solid waste in 1989 would be 20 x 10
ton of iron. Use of the option process — external desulfurization —
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TABLE 2. SUMMARY OF ESTIMATED SOLID-RESIDUE DISCHARGES
Commodity
Coke
Steel
Process
Base Case:
Wet quenching of
coke
• Dry quenching of
coke
Base Case:
No off-gas recovery
• Off-gas recovery
Solid Residue Dis-
charge from Base
Case Process-1974
(106 ton/yr)
N/A
N/A
12.3
__
Solid-Residue
Discharge-1989*+
(106 ton/yr)
N/A
N/A
9.0
9.0
Change in
Solid Residues
from Base
Case-1989
N/A
N/A
—
0.0
Blast Furnace
Hot Metal
Steel
(integrated)
Petroleum
Base Case:
Blast furnace 14.0
• Blast furnace with
external desulfurization —
Base Case:
Steelmaking coke oven
and blast furnace BOP
route 24.6
• EAF route
Base Case:
East Coast refinery model 1.53
6.3
4.7
18.0
33.5
0.38H
-1.6
+15.5
(continued)
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TABLE 2. (continued)
Commodity
oo
Process
Solid Residue Dis-
charge from Base
Case Process-1974
(1Q6 ton/yr)
Base Case:
Gulf Cost refinery
model
• On-site electric power
by asphalt combustion
Base Case:
West Coast refinery
model
• Hydrocracking of
Heavy Bottoms
• High Purity Hydrogen
by partial oxidation
• Flexicoking
• On-site electric power
by combustion of
vacuum bottoms
1.53
1.53
Solid-Residue
Discharge-1989*+
(1Q6 ton/yr)
0.38"
0.38^
0.38^
0.39^
0.40"*
0.742
0.383
Change in
Solid Residues
from Base
Case-1989
Petroleum
(continued)
• Direct combustion
of asphalt —
• Flexicoking —
I 1
0.38++
0.74"""
0.0
+0.36
0.0
+0.01
+0.02
0.359
0.0
(continued)
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TABLE 2. (continued)
Commodity
Process
Solid Residue Dis-
charge from Base
Case Process-1974
(106 ton/yr)
Solid-Residue
Discharge-1989*+
(1Q6 ton/yr)
Change in
Solid Residues
from Base
Case 1989
Petroleum
(continued)
Pulp & Paper
Olefins
Ammonia
Alumina
• High-Purity hydro-
gen via partial
oxidation of asphalt
(Solid-residue streams
unquantified)
Base Case:
Ethane—propane process
• Naphtha process
• Gas-oil process
Base Case:
Ammonia via natural gas
• Ammonia via coal
gasification
• Ammonia via heavy fuel
oil
Base Case:
Bayer process
• Hydrochloric acid ion
exchange
0.0205
6.160
0.403
small (unquantified)
3.01
0.019
8.600
36.000
0.020
0.0442
0.0764
0.1394
—
-1-0.0322
+0.0952
+3.01
0.019
+27.4
(continued)
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TABLE 2. (continued)
Commodity
Aluminum
Textiles
Process
Solid Residue Dis-
charge from Base
Case Process-1974
(IP6 ton/yr)
• Clay chlorination
(Toth) alumina
Base Case:
Hall-Heroult
(current practice, C.P.)
• Hall-Heroult (new)
• Alcoa Chloride
• Refractory hard-metal
cathode
Base Case:
Bayer with Hall-Heroult
(C.P.)**
• Clay Chlorination (Toth
Alumina) and ALCOA
Chloride
(Minor solid-residue-
unquantified)
0.1125
7.81
Solid Residue
Discharge-1989*+
(1Q6 ton/yr)
16.1
0.158
10.92
22.33
Change in
Solid Residue
from Base
Case 1989
Alumina
(continued)
• Nitric acid
exchange
ion
20.400
+11.8
+7.5
0.158
0.158
2.000
—
0.0
1.842
0.0
11.41
(continued)
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TABLE 2. (continued)
Commodity
Cement
Flat Glass
Solid Residue Dis-
charge from Base
Case Process-1974
Process (10^ ton/yr)
Base Case:
Long dry kiln 11.85
• Suspension preheater —
• Flash calciner —
• Fluidized bed
• Coal as fuel instead of
gas in long dry kiln
Base Case:
Regenerative furnace 0.290
• Coal gasification —
• Direct coal firing
• Coal-fired hot-gas
generation —
• Electric melting —
• Batch preheat with
natural gas firing —
Solid Residue
Discharge-1989*+
(106 ton/yr)
4.1
1.75
1.75
0.820
4.1 - 5.7
0.130
0.650
1.222
0.858
0.611
0.130
Change in
Solid Residue
from Base
Case 1989
—
-2.345
-2.345
-3.275
0.0 - +1.60
—
+0.520
+1.092
+0.728
+0.481
0.0
(continued)
-------
TABLE 2. (continued)
Commodity
Process
Solid Residue Dis-
charge from Base
Case Process-1974
(IP6 ton/yr)
Solid Residue
Discharge-1989*+
(1Q6 ton/yr)
Change in
Solid Residues
from Base
Case 1989
Chlorine, NaOH
ro
Phosphoric Acid
(Detergent Grade)
Base Case:
Graphite-anode
diaphragm cell
• Dimensionally stable
anodes
• Polymer modified
asbestos
• Polymer membrane
• Ion exchange membrane
• Expandable DSA
• Mercury cell
Base Case:
Electric furnace
• Chemical clean-up of
wet-process acid
• Solvent extraction of
wet-process acid
0.736
N/A
0.476
0.796
0.764
0.214
3.219
0.573
-0.032
0.762
0.762
0.762
0.762
N/A
-0.034
-0.034
-0.034
-0.034
N/A
+3.005
+0.359
(continued)
-------
TABLE 2. (continued)
u>
Commodity Process
Copper Base Case:
Conventional smelting
• Outokumpu flash
smelting
• Noranda
• Mitsubishi
• Arbiter
Fertilizers Base Case:
Nitric acid manufacturing
w/o NOX control
• Nitric acid manufacturing
w/NOx control
• Catalytic reduction
• Molecular sieve
• Grand Paroisse
• CDL/Vitak
• Masar
Solid Residue Dis-
charge from Base
Case Process-1974
(106 ton/yr)
4.976
—
—
—
—
negligible
negligible
negligible
negligible
negligible
negligible
Change in
Solid-Residue Solid Residues
Discharge-1989*+ from Base
106 ton/yr) Case 1989
3.420
3.420 0.0
3.420 0.0
3.420 0.0
6.380 +2.96
«—
0.0
0.0
0.0
0.0
0.0
(continued)
-------
TABLE 2. (continued)
Commodity
Process
Solid Residue Dis-
charge from Base
Case Process-1974
(106 ton/yr)
Solid Residue
Discharge-l989*+
(106 ton/yr)
Change in
Solid Residues
from Base
Case 1989
Fertilizers
(continued)
Base Case:
Mixed fertilizer plant
w/natural gas firing
• Better equipment tech-
nique with fuel oil
• Conversion from natural
gas to fuel oil (in-
stalling scrubbers)
negligible
negligible
0.0
0.0
0.0125
+0.0125
*Based on incremental production from the year 1974 to 1989 derived from anticipated growth
rates (Table 1).
+Based on the assumption that all increased production would be from the designated process.
**Based on 1.93 tons alumina per ton aluminum.
-H-Assumes all refinery output on a national basis is by processes indicated.
N/A = Not available.
-------
only for the incremental production volume, would reduce the total solid
residue generated to 19 x 10 ton/yr in 1989.
All of these options which occur in very large-volume industries
having major impact on the nation's industrial energy use, offer the
opportunity to reduce significantly both energy use and solid-residue
generation without creating problems in the air or water environment.
These numbers perhaps become more nt-aningful or significant when
one realizes that a single 100 mw <-.cal-fired power plant now generates
46 x 10 ton/yr of coal ash and fly ash and will, with the addition of
SO control by lime scrubbing, add an additional 110 x 10 ton/yr to
give a total of 156 x 10 :.on/yr.
Further comparisons which can be made are that 4.7 x 10 ton/yr
(1972) of municipal sludge and 125 x 10 /1971 ton/yr of solid residue
are generated in the United States annually.
Examination of the last column in Table 2 shows that compared to
the base case processes, the greatest reduction in tons of solid-residue
discharges per year can be achieved by selective implementation of new
processes in:
• Iron and Steel Industry (external desulfurization 25% decrease)
• Cement Industry (kiln with suspension preheater 57% decrease)
flash calcining (57% decrease) and fluidized bed cement
process (80% decrease), and
• Pulp and Paper Industry — de-inking of old newspaper for
newsprint resulting in a 5.6 x 10 ton reduction as a
potential waste is used as raw material in 1989 (see
Table 1).
Process changes in some of the industries shown in Table 2 may be
implemented because of feedstock shortages (e.g., manufacture of olefins
from naphtha rather than natural gas), and fuel switching (e.g., use of
coal in cement making). In other cases, processes may be developed
for other reasons, such as development of a domestic alumina industry
based on indigenous kaolin clays. Such a process, based on using coal
to the extent possible, would result in significantly higher solid -
residue discharge than a Bayer plant based on natural gas, as described
in the Alumina/Aluminum Industry report. Although the estimated change
in emissions listed in Table 2 was based on incremental capacity from
1974 to 1989 only, in some cases an alternative process, or a process
modification, may replace existing capacity. For example, in the aluminum
industry, refractory hard metal cathodes may be installed in existing
Hall-Heroult cells. The application of alternative processes to existing
plant capacity will increase the potential effect on solidr-residue dis-
-------
charges compared to the estimated effect shown in Table 2. Further per-
spectives in each of these industry sectors with descriptions of the
processes can be obtained from the individual industry sector reports
(Volumes III through XV).
Should U.S. industry expand using current (base case) technology,
Table 3 shows that estimated solid-residue discharges in 1989 would
increase by 35.8 x 10 tons per year compared to discharges of 12.5 x
10 ton per year of solid residue generated in 1971. However, if all
U.S. industry expanded by implementing the technologies considered here
that discharged the largest solid residues, Table 3 shows that the
increases in solid-residue discharges in 1989 would be 91.9 x 10 ton
per year, some 154% higher than using conventional technology. On the
other hand, if industry expanded by implementing the least solid-residue
discharging technology, solid-residue discharges in 1989 are calculated
to decrease by 3.3 x 10 ton/yr, some 9% less than by conventional
technology. If the national production growth rate projections shown
in Table 1 are accurate, then calculated emissions will probably lie
somewhere between these extremes. Thus, implementation of such new
technologies as considered here can significantly impact soldd-residue
discharges in the industrial sector.
Table 4 shows our estimate of the types of processes likely to be
installed in the time period up to 1989 with the related solid-residue
discharges from new plants calculated for the year 1989 assuming no
retirement of existing facilities. For example, a reading of the
industry reports shows that in the cement sector incremental cement
capacity will be effected by preheaters, coal firing, etc. If such
capacity is installed, anticipated annual solid-residue discharges in
1989 would be 0.82 x 10 to 1.75 x 10 ton/yr (Table 4) compared to
the 4.095 x 10 ton/yr if conventional rotary kiln technology were
employed. Similar judgments were made in other sectors to arrive at
total calculated annual solid-residue discharges of 44.75 x 10 to
69.915 ton/yr (Table 4) emitted in 1989 from new plant capacity installed
in the period 1974-1989.
IDENTIFICATION OF CROSS-INDUSTRY TECHNOLOGY
As specifically related to the problem of solid residues, the only
cross-industry energy-conserving technology that has a significant
impact on the nature and quantity of solid residue is the conversion
from natural gas or fuel oil to coal.
R&D AREAS
With regard to solid residues emanating from new technology investi-
gated in this study, the following have been identified as deserving
R&D attention:
16
-------
TABLE 3. ESTIMATED INCREASE IN ANNUAL SOLID RESIDUE DISCHARGES
(1989-1974)
ASSUMING INDUSTRY EXPANDS USING PROCESS TYPES INDICATED
(106 Tons Solid Residue/yr)
Commodity (Vol No)*
Base Case
Process
Using Process
With Largest
Potential
Discharges
Using Process
With Smallest
Potential
Discharges
Steel (III)
Petroleum+(IV)
Kraft Pulp (V)
Newsprint Pulp (V)
Olefins (VI)
Ammonia (VII)
Alumina (VIII)
Aluminum (VIII)
Textiles-Knit (IX)
Textiles-Woven (IX)
Cement (X)
Flat Glass (XI)
Chlorine, NaOH (XII)
Phosphoric Acid (XIII)
Copper (XIV)
Fertilizers (HN03) (XV)
TOTAL
18.0
0.383
small,
5.6
0.0442
small
8.6
0.158
small,
small,
4.095
0.130
0.796
0.214
3.42
small
33.5
0.742
. . • f j j
5.6**
0.1394
3.01
36.0
2.0
. £ m J
. . . f J J
4.095
1.222
0.796
3.219
6.38
0.0125
18.0
0.383
0.0
0.0442
small
8.6
0.158
0.82
0.130
0.762
0.214
3.42
small
35.840
91.111
32.531
* Volume Number of Industry Report
**Estimated newsprint pulp production in 1989 (see Table 1).
+Assumes selected regional refinery model applies nationally.
17
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TABLE 4. ESTIMATED RANGE IN SOLID RESIDUE DISCHARGES IN
1989 FOR NEW PROCESSES LIKELY TO BE IMPLEMENTED
Commodity (Vol No)*
Likely Types of
Processes to be
Implemented in
New Plants
Calculated Range in
Annual Discharges
for Plan Capacity
(1989-1974)
(1Q6 ton/yr)
Steel (III)
Petroleum (IV)
Kraft Pulp (V)
Newsprint Pulp (V)
Olefins (VI)
Ammonia (VII)
Alumina(a> (VIII)
Aluminum(a) (VIII)
Textiles, Knit (IX)
Textiles, Woven (IX)
Cement (X)
Flat Glass (XI)
Chlor-alkali (XII)
Phosphoric Acid:
Detergent grade
(XIII)
Copper (XIV)
Fertilizers-Mixed
Fertilizer Plant
TOTAL
Coke oven, Blast Furnace,
Hydrocracking, flexicoking, etc.
Kraft, Rapson, Alakline-oxygen
RMP, TMP, De-inking
Naphtha, gas oil
Heavy fuel oil, coal 0.019
Bayer, leaching domestic clays 20.4
Hall-Heroult, aluminum
chloride(a)
Advanced aqueous, solvent
Advanced aqueous
Preheaters, coal firing
Regenerative furnaces, preheaters
electric furnaces
Dimensionally stable anodes, new
membranes
18.0 - 18.0
0.38 - 0.74
small
0.0 - 5.6
0.076 - 0.14
- 3.01
Wet acid cleanup
Oxygen or flash processes
Fuel Oil
(b)
- 36.0
0.16 - 2.00
small
small
0.82 - 1.75
0.13 - 0.86
0.76 - 0.76
0.57 - 3.22
3.42 - 3.42
0.013 - 0.013
44.8 - 75.5
*Volume Number of Industry Report.
(a)
(b)
(c)
(d)
A significant fraction of the incremental U.S. demand is expected to
be imported.
In addition, electric furnaces are expected to be installed based at
least partially on scrap.
With collection of CO from BOF's.
Assumes East Coast refinery model applies nationally.
18
-------
• Demonstration of adequate landfill disposal techniques.
Further information on the source of pollutants and nature
of the problems in new technology examined in this study
is found in the industry assessment reports dealing with
aluminum, cement, iron and steel, petroleum refining,
and phosphorus. To a lesser extent, it is also a problem
in the ammonia, chlor-alkali, copper, glass, olefins,
pulp and paper, and textile industry sectors.
• Demonstration of thermal destruction technologies for
organic wastes. Further information on the source of
pollutants and nature of the problems in new technology
examined in this study is found in the industry assess-
ment reports dealing with aluminum, olefins, and
petroleum. To a lesser extent, it is also a problem in
the chlor-alkali, iron and steel, and pulp and paper
industry sectors.
• Additional research into the methods of categorization,
regulation and legal methodologies for controlling the
disposal of solid residues. Further information on the
source of pollutants and nature of the problems in new
technology examined in this study is found in the industry
assessment reports dealing with aluminum, ammonia, cement,
copper, fertilizers, glass, iron and steel, olefins,
petroleum refining, and phosphorus. To a lesser extent,
it is also a problem in the chlor-alkali, pulp and paper,
and textile industry sectors.
Thus in each case, the direction of research programs should be
viewed with the objective of attaining the maximum effectiveness for
removal or controlling pollutants at the minimum economic penalty,
since it is rarely possible to remove or control pollutants to present
and anticipated standards without entailing cost penalties. Consequently,
research programs must be examined within the framework of cost/benefits
to the environment, to health, and to the economy. Unfortunately, it
is not yet possible to determine the impact of the Resource Conservation
and Recovery Act of 1976 on needed research and development programs.
19
-------
SECTION III
PROCESSES AND SOLIDHRESIDUE DISCHARGES
In Volume II (page 19) in which we described the methodology
used in this study, we indicated that selected State air emission
regulations, along with the Federal Government's stationary source
performance standards and effluent limitation guidelines, were surveyed
to:
• establish the most probable limits of air and water
emissions, and
• obtain a perspective of the types of pollution control
systems to be considered.
While there are a large number of different regulations for air-
borne emissions at the State regulatory level, we found that approximately
the same type of air pollution control systems would be required, regard-
less of the State or Federal regulations to be met. Generally, these
air pollution control systems included bag houses, venturi scrubbers,
and electrostatic precipitators for particulates and chemical-based
systems for sulfur removal, such as alkaline-based aqueous scrubbing
for SO .
x
For water effluents we chose the EPA's best available technology
economically achievable (BATEA) guidelines (1983) as the effluent
limitations that would have to be met for both currently practiced and
alternative processes considered. The rationale for this choice was
that any plant employing the technologies evaluated in these reports
should install wastewater treatment systems capable of meeting BATEA
standards, although at the time of construction the new source performance
standards might be applicable. Because regulations for the handling
and disposal of solid residues are either non-specific or non-existent,
we chose various types of controlled landfill disposal methods, where
our judgment suggested potential adverse environmental impacts might
occur from uncontrolled disposal.
Solid residues resulting from dust collection, water pollution
control, and industrial process discharges (e.g., slags, slimes, and
so on) as described in the industry reports (Volumes III through XV)
are summarized in this section.
IRON AND STEEL INDUSTRY
Basic Oxygen Process (BOP) for Steelmaking
20
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Base Case Solid-Residue Disposal—
The base case BOP unit (which is described in detail in Volume
III, pages 18-28) is a complete combustion system in which the gases
issuing from the mouth of the furnace are burned and collected in a
hood with considerable infiltration of air, and then cooled and cleaned
of particulates before being released to the atmosphere. There are
two significant solid-residue streams associated with BOP operations:
(1) slag and (2) wet sludge resulting from dust collection.
Neither the composition nor the quantity of the slag is affected by
the process changes selected for analysis in the original study; there-
fore, its disposal was not a subject of comparison in the study. The
ultimate fate of BOP slag (as well as slag from other steelmaking
processes) proceeds along three routes: (1) some of the slag is recycled
back to the blast furnace; (2) some of it is sold to slag processors
where it is made into aggregate material for construction uses; and (3)
a portion is disposed of in landfills on or near the plant site.
Most BOP units employ wet high-energy scrubbers for dust collection.
About 55 Ib of dust are produced per ton of steel in the BOP. The dust-
laden scrubber water is usually subjected to suspended solids removal
in a sedimentation basin or clarifier. A portion of the water is dis-
charged. The suspended solids, i.e., the BOP dust, are removed from
the clarifier as a wet sludge. This sludge is sometimes subjected to
mechanical dewatering to further reduce its volume prior to reclamation
of iron values and/or disposal.
The ability to reclaim iron values depends upon the composition
of the dust, which is influenced by the nature of the scrap charged to
the BOP. If clean, uncoated home scrap is used, the dust consists
primarily of iron oxides and can be recycled to the sinter strand, If
purchased scrap is used, it may not be possible to control the composition
closely; as a result, the dust and resultant sludges can contain lead,
zinc, tin, and other metals.
When the sludge cannot be recycled, suitable care has to be taken
in its disposal. Because of its heavy metal content (mostly in the
form of oxides and hydroxides), special attention should be given to
preventing acidic leaching conditions from occurring, and appropriate
efforts should be taken to mitigate percolation and run-off from the
disposal site.
Process Option 1 - BOP Off-Gas Recovery Process Alternative—
When off-gas recovery is incorporated into a BOP unit, the carbon
monoxide containing off-gas is either collected for eventual use as an
internal plant fuel as in the conventional BOP, or flared which results
in oxidizing the off-gases at the flare rather than at the mouth of the
vessel.
21
-------
BOP units equipped with off-gas recovery equipment produce lower gas
volumes than convetional BOP units, due to the marked reduction in the
volume of infiltration air. Gas-cleaning equipment in both cases con-
sists of high-energy venturi scrubbers. The quantity of dust is essen-
tially the same for conventional and off-gas-recovery-equipped BOP units.
The composition of the dust, however, is slightly different.
In the conventional BOP operation where the carbon monoxide is
burned with entrained air, the dust particules are largely oxidized.
In BOP units equipped with off-gas recovery, the dust is subjected to
far less oxidation and, therefore, contains a higher fraction of
unoxidized or partiallly oxidized species. A comparison of the composi-
tion of BOP dust from conventional units and units equipped with off-gas
recovery is shown in Table 5 (Volume III, page 25).
The use of off-gas recovery in the basic oxygen process for steel-
making will have virtually no effect on the volume of solid residues
produced (^ 150 Ib/ton of steel). See Volume III, page 72.
No new chemical constituents are introduced into the solid-residue
stream. However, since there is less oxidized iron in the solid residues
from BOP units equipped with off-gas recovery, it is reasonable to
expect that the unoxidized or partially oxidized iron will slowly under-
go oxidation once deposited in a disposal site. The oxidation process
could exert a minor oxygen demand on water percolating through the waste.
However, we do not view this as a significant environmental problem.
The Conventional Blast Furnace for the Production of Iron
Base Case Solid-Residue Disposal—
The base case process is the conventional blast furnace used in
the production of iron. A blast furnace produces two major solid-residue
streams: (1) slag and (2) wastewater treatment sludge. (This process
is described in Volume III, page 29-31.) A large fraction of the slag
generated by blast furnaces is sent to slag processors where it is
converted into construction aggregate material. When the demand for
slag is less than the supply, the excess slag must be disposed of on
land.
Blast furnaces are equipped with air pollution control systems that
employ wet scrubbers for the removal of particulate matter. The scrubber
water is subjected to gravity settling. Part of the effluent from the
gravity settling step is recycled back to the scrubbers, while the
remainder is discharged. Future water pollution regulations may require
that the water thus discharged be subjected to further treatment steps
for the removal of selected pollutants. The particulate matter originally
present in the blast furnace gas is removed from the clarifier as a wet
sludge. The volume of the sludge is often reduced by mechanical de-
watering operations.
22
-------
TABLE 5. COMPARISON OF BOP DUST COMPOSITIONS
(weight percent)
BOP with
Conventional BOP Off-Gas Recovery
Ke Total 59 75
Ke Metal - 10
Ke as FeO 1.6 62
Ke as Fe304, Fe^ 57.4 3
CaO 2 2
SiO_ 1 1
23
-------
While the solid phase of the sludge is relatively innocuous (con-
taining mostly carbon and iron particles), the liquid fraction typically
contains such pollutants of concern as phenol, cyanide, sulfide, ammonia,
fluoride, and certain trace heavy metals. For this reason, care should
be taken to dispose of the sludge in a manner that will preclude ground-
water contamination. A portion of the dewatered wastewater treatment
sludge is usually recycled back into the process for reclamation of
iron values.
Process Option 1 - External Desulfurization Alternative-
Coke, which contains some of the sulfur found in the coal used is
the major contributor to the total amount of sulfur entering the blast
furnace. Other sources of sulfur in the blast furnace include fuel
injections, the scrap mixed with the burden, and the minerals themselves
(ore, limestone).
Only a negligible portion of the sulfur is found in the off-gases;
most of the sulfur leaving the blast furnace appears in the liquid slag
and hot metal. Thus, there is a certain degree of "internal" desul-
furization inherent in the process. The capacity of the slag to retain
sulfur is generally increased as more limestone is added. Limestone,
however, increases coke consumption which, in turn, introduced more
sulfur. Clearly, then, there is a limit to the amount to which this
"internal" desulfurization is viable. It may be advantageous to tap
a hot metal containing more sulfur than specified, and to add to the
process sequence a new step, viz., the injection of desulfurization
agents into the molten iron during its transfer from the blast furnace
to the steelmaking furnace. These agents (usually magnesium or calcium
compounds) react with the dissolved sulfur and form a sulfide slag that
can be disposed of. This additional step is called external desulfuri-
zation.
External desulfurization can provide two energy-related benefits:
(1) it can reduce the coke consumption, and (2) more importantly, it
decreases the dependence on low-sulfur metallurgical coal, which is
becoming increasingly difficult to obtain.
The external desulfurization process reduces the amount of coke and
limestone used in the blast furnace, thereby reducing the amount of slag
generated in the blast furnace proper. While external desulfurization
produces a slag stream of its own, the overall effect is a net reduction
in the amount of slag generated.
The external desulfurization process produces a gaseous effluent which,
when subjected to wet scrubbing, will produce a wastewater and resultant
wastewater treatment sludge stream, not unlike that of the parent blast
furnace. Again, the additional wastewater treatment sludge stream,
from the external desulfurization step must be balanced against the
reduced voluem of blast furnace gas and associated particulate matter
and resultant sludge.
24
-------
The overall effect of external desulfurization on the making of
iron in a blast furnace is a net reduction in the total quantity of
solid residues of approximately 25% (Volume III, page 40). The composi-
tion of the solid residue is expected to be essentially unaltered and,
consequently, disposal procedures also remain the same.
The Quenching Operation in Coke Making
Process Option 1 - Dry Quenching vs. Conventional Wet Coking Alternative—
This energy-saving alternative is designed to reclaim the heat that
is lost during the base case practice of quenching coke with water.
Neither the base case wet quenching nor the alternative of dry quenching
produce a solid-residue stream that is destined for ultimate land dis-
posal. There are, therefore, no solid-residue disposal implications
associated with the implementation of dry quenching of coke.
Conventional Iron and Steelmaking Base Case for Comparison with Direct
Reduction of Iron Ore
Base Case Solid-Residue Disposal—
Direct reduction of iron ore is designed to replace the blast
furnace along with its supporting coke plant. In the version of the
direct reduction process selected for comparison, the reduced product
iron from the direct reduction unit is sent to an electric arc furnace
(rather than a more conventional open-hearth or basic oxygen process
furnace) for Steelmaking. To compare direct reduction with the existing
technology on an equivalent basis, it is necessary to make the comparison
all the way through the Steelmaking process. Thus, the base case process
consists of the following units:
• Byproduct coke plant,
• Blast furnace, and
• Basic oxygen process (BOP) furnace.
The major solid-residue streams from the base case process operations
are described below (Volume III, page 72):
• Byproduct Coke - solid residues includes coke dust and waste-
water treatment sludge generated at a rate of approximately
0.0077 ton/ton of steel.
25
-------
• Blast Furnace - solid residues include furnace slag and
wastewater treatment sludge, generated at a rate of approxi-
mately 0.14 ton/ton of steel;
• Basic Oxygen Furnace - solid residues include furnace slag
and wastewater treatment sludge, generated at a rate of
approximately 0.15 ton/ton of steel.
The total solid-residual generation rate for the base case process
is the sum of the above streams, or approximately 0.30 ton/ton of output.
The composition and ultimate disposal of wastewater treatment sludge
were discussed in the previous section of this report dealing with BOP
off-gas recovery and external desulfurization of blast furnace hot metal.
Byproduct coke plant wastewater treatment sludge deserves mention,
however. The wastewater from byproduct coke plant operations contains
relatively high concentrations of phenol, ammonia, oil and grease, and
other pollutants of concern. It is expected that significant fractions
of these pollutants will also be present in the wastewater treatment
sludge.
Process Option 1 - Direct Reduction Process Alternative—
The direct reduction process produces four types of solid residues
(Volume III, page 76):
• Direct reduction kiln waste,
• Wastewater treatment sludge,
• Electric arc furnace slag, and
• Electric furnace air pollution control dust.
The direct reduction kiln waste consists of the following components:
• Lime - 0.07 ton/ton of output
• Coal ash - 0.063 ton/ton of output
*
• Discarded coal - 0.05 ton/ton of output
• (plus utility solid wastes)
A major part of the larger sized coal particles can be separated from
the ash and recycled. Coal fines that cannot be screened from the ash
are discarded.
26
-------
The wastewater treatment sludge is expected to be similar to blast
furnace sludge in that the liquid fraction of the sludge would probably
contain cyanide, ammonia, phenol, and sulfide. However, there should
be very little fluoride present in the wastewater treatment sludge from
the direct reduction alternative, since the use of fluorspar as a fluxing
agent has been eliminated.
An estimation of the solid-residue generation rate from the direct
reduction process is given below (Volume III, page 77):
• Kiln waste - 0.183 ton/ton of steel product
• Wastewater treatment
sludge - 0.157 ton/ton of steel product
• Electric furnace slag - 0.21 ton/ton of steel product
• Electric furnace dust - 0.0075 ton/ton of steel product
Total solid residue - 0.558 ton/ton of steel product
Thus, in terms of quantity, the direct reduction process increases
the amount of total solid residue generated on site by approximately
86% (0.558 ton/ton of output vs. 0.30 ton for the coke oven/blast
furnace/BOP route). However, it should be recognized that a large
fraction of the total solid residue is slag, which as previously des-
cribed, is often recycled for its commercial value in the form of con-
struction material. In addition, the electric arc furnace in the direct
reduction route is capable of using scrap iron and steel to a larger
extent than the BOP route. With regard to the solid residue actually
destined for land disposal from steelmaking, i.e., the wastewater treat-
ment sludge, direct reduction and conventional technology produce very
nearly the same solid residue in terms of both quantity and composition.
Summary
The basic oxygen process (BOP) for steelmaking produces two major
solid-residue streams; slag and wet sludge from dust collection. The
process option involving the combustion of BOP off-gas is not expected
to significantly alter the quantity of either the slag or the dust col-
lection sludge. The composition of the dust collection sludge, however,
will be slightly altered in that it will be far less oxidized than the
dust produced by the base case process and may present somewhat more of
a leaching problem.
The base case blast furnace method for producing iron generates the
two major solid-residue streams; slag and wastewater treatment sludge.
The process option, equipping a blast furnace with external desulfurization,
will result in a slight decrease in the solid-residue generation rate.
The solid-residue composition in expected to be essentially the same as
the base case process.
27
-------
The conventional method of iron and steelmaking, consisting of a
byproduct coke plant, a blast furnace, and a BOP furnace, produces a
number of solid-residue streams which consist of coke dust, slags, and
wastewater treatment sludges. The process option involving the direct
reduction of iron ore eliminates the coke dust, but also produces a
number of slags and wastewater treatment sludges. The total quantity
of solid residue generated by the direct reduction process is substan-
tially greater than that of the base case; however, much of this is
slag which is normally sold for its commercial value. Nevertheless,
if one were to assume (namely) that all incremental production achieved
in 1989 were obtained by the DR/EAS route, the solid residue would be
increased 86% over that for the Coke/Blast Furnace/BOF. A continued
market for slag would have to be assured to minimize the effect.
A comparison of the solid-residue discharge is presented in Table 6.
Of the steel industry process options studied, only external
desulfurization of hot metal and direct reduction have a significant
impact on solid-residue generation with the former achieving a 25%
reduction in the solid-residue waste load, while that generated by
DR/EAF is, surprisingly, some 86% higher. In both cases, the nature
of the solids is not significantly different from that produced by the
existing process. Further, the much larger solid residue load from
DR/EAF is unimportant as long as slag can be sold for use in construction.
Consequently, it does not appear that solid waste will be a significant
factor to be considered by the industry in making its choices as to
future capital investments.
Of course, the question of electricity generation for the EAF has
been discounted. However, in terms of overall environmental considera-
tions, it is not of major importance. For example, if all incremental
steel production were to be achieved by DR/EAF, 0.4 quads of electrical
energy would be required, compared to 17 quads of purchased fuels used
by the utility section in the year 1971.
PETROLEUM REFINING INDUSTRY
Total Petroleum Refining Process
Base Case Solid-Residue Disposal—
For the purpose of performing economic and energy-utilization com-
parisons, three base case refineries were established in the original
study: an East Coast refinery, a West Coast refinery, and a Gulf Coast
refinery. The three base case refineries reflect differences in feed-
stock, process configuration, and product mix. A description of the
refinery models used for comparison is presented in Volume IV, pages
21-32. Although the nature and quantity of solid-residues emanating
from refineries are highly variable and still the subject of investi-
gation, no difference in solid-residue composition or rate of generation
28
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TABLE 6. SOLID-RESIDUE DISCHARGE FROM IRON AND STEELMAKING
VO
Process
Estimated
Discharge Factor
(ton/ton of product)
Estimated Change in
Discharge Factor
(ton/ton of product)
Solid-Residue
Discharge
(106 ton/yr)
1974 1989-1974
Base Case:
The basic oxygen process
for steelmaking
• BOP off-gas recovery
Base Case:
Production of iron in the
conventional blast furnace
• Blast furnace with external
desulfurization
Base Case:
Wet Quenching of coke
o Dry quenching of coke
Base Case:
Conventional iron and steelmaking:
coke oven and blast furnace and BOP
• Direct reduction
0.15
0.15
0.14
0.105
0.0
0.0
0.30
0.558
0.0 12. 3b 9.0a
0.0 — 9.0a
0.0 14. Ob 6.3a
-0.04 — 4.7a
0.0 0.0 0.0
0.0 0.0 0.0
0.0 24. 6b 18. Oa
+0.258 — 33. 5a
Based on increment in production from 1974 to 1989: 27.8 million tons of coke, 44.8 million tons of
iron, and 60 million tons of steel.
(continued)
-------
TABLE 6. (continued)
Estimated 1974 discharge based on multiplying discharge factor by 1974 production: 62 million tons
of coke, 100 million tons of iron and 82 million tons BOP steel.
£
If all slag is sold as byproduct, the remaining solid residue would be very nearly the same as the
base case.
Product refers to coke, iron or steel.
-------
is implied among the three base case refineries. Values given are
estimates, intended to reflect general refinery solid-residue quantities
and characteristics.
A petroleum refinery generates a wide variety of solid-residue
streams, many of which contain materials on the EPA toxic substances,
or priority pollutants lists. Basically refinery solid-residue streams
fall into two main groups: those intermittently generated and those
continuously generated.
The intermittent wastes are generally those that result from cleaning
within the process areas and off-site facilities of the refinery. The
following are typical intermittent waste streams:
• Process vessel sludges, vessel scale, and other deposits
generally removed during plant turnarounds;
• Storage tank sediments; and
• Product treatment wastes, such as spent filter clay and
spent catalysts from certain processing units.
The annual volume of refinery intermittent wastes is largely a
function of the individual refinery waste management and housekeeping
practices.
Continuous residues (those requiring disposal at less than 2-week
intervals) can be further broken down into two groups: process unit
wastes and waste-water treatment wastes.
Major process unit residues include:
t Coker wastes, such as coke fines from delayed or fluidized
cokers, and spilled coke from unloading facilities;
• Spent catalysts and catalyst fines from the fluid catalytic
cracking units; and
• Spent and spilled grease and wax wastes from lube oil
processing plants.
Wastewater treatment wastes include:
• Waste biological sludges from activated sludge units, and
• Dissolved air flotation float.
Typically such wastes are dewatered by means of sludge thickeners,
coupled with vacuum filters or centrifuges. The dewatered sludge can
then either be land-disposed or incinerated. Low concentrations of
31
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heavy metals, which could affect the level of control required, are
usually present in the sludges.
A summary of major refinery solid-residue streams is presented in
Volume IV, page 160. Estimated quantities of the various solid-residue
streams for the base case refineries are presented in Volume IV, page
29. The total base case refinery solid-residue generation rate is
estimated to be approximately 2.07 lb/1000 Ib oil.
Process Option 1 - Direct Combustion of Asphalt in Process Heaters—
At present, the asphalt fraction of a refinery's output is usually
subjected to several processing steps to make it suitable for sale as
a construction material. Asphalt has characteristically been a very
low value refinery product. As a result, the processing and sale of
asphalt have been more of a least-cost means of disposal rather than an
important source of revenue.
Internal refinery heat energy requirements have been filled by
combusting portions of the refinery output. By introducing asphalt
into the total refinery heat generation system, a greater quantity of
higher value fuels is made available to the consumer. A description
of the process involved is given in Volume IV, pages 32-43. Thus,
while the direct combustion of asphalt does not save energy in an
absolute sense, it does improve the overall form value of the refinery
product mix. Direct combustion of asphalt is considered to be most
potentially applicable to a base case East Coast refinery.
Asphalt contains an appreciable amount of sulfur and ash, The
direct combustion of asphalt will result in a significant increase in
the amount of pollution control required. The appropriate control
technology for asphalt combustion sources is flue gas desulfurization
(FGD). A sulfuric acid product is produced from the FGD system, part
of which might be used to offset acid requirements for alkylation,
depending on acid purity. Alternatively the acid could presumably be
marketed.
Implementation of direct combustion of asphalt will not appreciably
alter the quantity or characteristics of the base case East Coast refinery
total solid-residue stream.
Process Option 2 - Hydrocracking of Heavy Bottoms Alternative—
The purpose of this process (described in detail in Volume IV,
pages 43-52) is to convert heavy ends into lighter, more usable fuels.
As in the case of direct combustion of asphalt, this alternative is
designed to improve the form value of the refinery product mix rather
than to conserve energy in absolute terms. It is most likely applicable
to a West Coast base case refinery.
32
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Implementation of heavy bottoms hydrocracking will increase the
total quantity of refinery solid residue very slightly. This process
will require the disposal of a chrome-moly catalyst. It is estimated
that a chrome-moly catalyst waste stream will increase the total refinery
solid-residue stream by approximately 3% or by 0.0611b /1000 Ib of oil.
The catalyst is different.
Process Option 3 - Flexicoking Alternative—
For a variety of process and economic reasons, the Flexicoking
process is most applicable to East Coast refineries. Flexicoking, a
combination of fluid coking with coke gasification, contributes to
energy conservation in two ways:
(1) It frees high-Btu refinery gas for higher priority uses, and
(2) It converts asphalt feed to naphtha and gas oil intermediates
which then become available for refining. This represents
a portion of crude which otherwise would not be a salable
fuel product.
A detailed description of the Flexicoking process is given in
Volume IV, pages 52-67.
The use of Flexicoking increases the amount of sulfur that must
be removed from gaseous streams. The sulfur in the high-Btu fuel gas
is removed using an amine scrubbing system, and the exhaust from that
scrubbing system is sent to the refinery gas plant. The hydrogen sulfide
in the low-Btu "flexigas" is too low in concentration to be economically
scrubbed out, and, therefore, this process includes an integral Stretford
unit for sulfur removal. The Stretford unit has a liquid purge stream
which contains rather high concentrations of metallic and organic
compounds. A typical composition of a Stretford purge stream is shown
in Table 7.
The disposal of Stretford purge solution presents a problem. The
solution contains compounds"that could disrupt the performance of a
biological wastewater treatment system should it be discharged to the
main refinery wastewater system. It may have to be concentrated first
and then disposed of in a lined disposal site, much in the manner of a
solid-residue stream.
The Flexicoking process will also produce a solid-residue stream
consisting of coke fines. We do not expect that the coke fines will be
particularly objectionable in terms of solid-residue disposal.
Overall, the implementation of the Flexicoking process will result
in a significant increase in total refinery solid-residue generation.
Even excluding the Stretford purge stream (since it is not actually a
33
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TABLE 7. TYPICAL COMPOSITION OF STRETFORD PURGE SOLUTION
Constituent mg/1
Na CO 4,700
Sodium anthraquinone disulfonate 700
NaVO_ (sodium meta vanadate 300
Sodium citrate 300
Na2S203 6,000
Na2SCN 6,000
34
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solid waste), the Flexicoking process will almost double the base case
refinery solid-residue waste generation rate.
Process Option 4 - On-Site Electric Power by Combustion of Vacuum Bottoms—
In this process option (described in detail in Volume IV, pages
67-78), electric power is generated within the refinery rather than
purchased from the local power utility. The internal generation of
electric power within the refinery does not conserve energy overall,
nor does it consume more energy than when power is purchased, assuming
that the internal and external power plants would operate at the same
efficiencies. In effect, the form value of the asphalt product is up-
graded to a higher form of electric power for refinery use.
Overall, the solid-residue stream for on-site power generation by
combustion of vacuum bottoms is essentially of the same volume and com-
position as that of the base case Gulf Coast refinery, to which it
would be most applicable, and at which the bottoms would be disposed
of by.
Process Option 5 - High-Purity Hydrogen Production Via Partial Oxidation
of Asphalt—
This alternative is based on the production of high-purity hydrogen
for hydrotreating from vacuum bottoms, using a partial oxidation process.
The feedstorck freed up by this approach would then be available for
sale outside the refinery in the form of pipeline gas or naphtha. This
alternative is considered most applicable to the West Coast base case
refinery.
Implementation of partial oxidation of asphalt will slightly increase
the total flow rate of refinery wastewater and will therefore slightly
increase the quantity of wastewater treatment sludge. In addition, there
will be a small solid-waste stream resulting from waste catalyst used
in the partial oxidation process. The catalyst would probably contain
nickel or iron compounds. The overall increase in solid-waste volume
over the base case is quite small (2.18 lb per 1000 Ib versus 2.07 Ib
per 1000 lb for the base case refinery).
Summary
A petroleum refinery employing base case technology generates a
number of intermittent and continuous solid-residue streams, most of
which are contaminated with petroleum or petroleum products.
All of the process options proposed for the petroleum refining
industry have the same theme: use of heavy ends either to generate
power or to manufacture more light end, salable product. In both manners
the portion of the crude barrel usable as an energy source would be
increased. Of the process options, neither direct combustion of asphalt
35
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nor on-site power generation will appreciably affect the base case
solid-residue generation.
Hydrocracking of heavy bottoms will result in a slight increase in
solid residue by introducing a chrome-moly catalyst. Flexicoking will
require the disposal of coke fines that will more than double the base
case solid-residue generation rate. Environmentally, the coke fines
are not expected to be particularly objectionable. Partial oxidation
of asphalt will result in a slight increase in the base case solid-residue
generation rate by increasing the amount of wastewater treatment sludge.
A comparison of the solid waste streams is presented in Table 8.
The increase in solid-residue volume is not great, even for
Flexicoking. However, increases in metals (catalysts) and, possibly,
sulfur will require more sophisticated and more costly pollution control.
Nevertheless, it would appear that both load and even undesirable metal
pollution would still be less than that produced by generating an equi-
valent quantity of energy from coal and would seem to offer a desirable
short-range increase in available petroleum fuels (and petrochemical
feedstocks) with minimal environmental impact. It should not be ignored
however, that petroleum refining is a large industry, and even the best
of these options from a residues point of view will generate almost
0.04 x 10 tons of solid residues more in 1989 than in 1974.
Consideration of the incremental solid-residue volume, capital
cost, operation cost, and energy savings, is shown in the original
Petroleum Refinery report (Volume IV),
PULP AND PAPER INDUSTRY
Bleached Kraft Pulping
Base Case Solid-Residue Disposal—
A detailed description of the base case Kraft process is given in
Volume V, pages 54-60. In the manufacture of bleached Kraft pulp, a
variety of in-plant solid-residue streams are generated. Many of these
solid-residue streams are recycled through the manufacturing process
either in the form of recovered chemicals or as auxiliary fuel. The
residuals from many of these operations evenutally leave the plant as a
wet sludge via the wastewater treatment system. The sludge from the
wastewater treatment consists largely of wood fiber, inorganic particulate
matter, and excess microorganisms from the biological wastewater treat-
ment process. The sludge is usually subjected to mechanical dewatering
to reduce its volume prior to land disposal on or near the plant site.
36
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TABLE 8. SOLID-RESIDUE DISCHARGE FROM PETROLEUM REFINING
Petroleum Refining
Estimated
Discharge Factor
(lb/1000 Ib oil)
Estimated
Change in
Discharge Factor
(lb/1000 Ib oil)
Base Case:
Gulf Coast Refinery Model 2.07
• With on-site electrical power
generation 2.07
Base Case:
West Coast Refinery Model 2.07
• With hydrocracking of heavy bottoms 2.13
• With partial oxidation of asphalt
to produce H2 2.18
0.0
+0.06
+0.11
Solid-Residue
Discharge
(106 ton/yr)
1974 1989++-1974
Base Case:
East Coast Refinery Model
• With direct combustion of
asphalt in process heating
• With Flexicoking
2.07
2.07
4.01
1.53+ 0.383
0.0 — 0.383
+1.94 — 0.742
1.53
1.53
1.53
0.383
0.383
0.383
0.394
0.403
Estimated 1974 discharge based on multiplying discharge factor by 1974 production of petroleum:
740.0 million tons. Thus this calculation assumes all petroleum in U.S. was refined by the process
indicated.
i I
Based on increment in national production of petroleum from 1974 to 1989 of 185 million tons.
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Process Option 1 - Alkaline-Oxygen Pulping—
A process description of alkaline-oxygen (A-0) pulping is provided
in Volume V, pages 84-85. In terms of pollution control considerations,
its most significant feature is that it employs a non-sulfur cooking
step which would eliminate the air pollution from malodorous sulfur
compounds and greatly alleviate the bleach plant liquid effluent problem.
It is expected that the wastewater effluent flow rate will not be
significantly changed as a result of implementing A-0 pulping. However,
elimination of two of the standard bleach stages should result in
approximately a 50% reduction in both BOD and color for A-0 compared
with Kraft. Since the quantity of sludge produced by a biological waste-
water treatment system is proportional to the amount of BOD removed,
a reduction in total BOD raw waste load will reduce the quanity of
the biological fraction of the wastewater treatment sludge. Implementation
of A-0 pulping would certainly not adversely affect the overall solid-
residue problem (and very likely, may result in a slight reduction in
the quantity of solid-residue generated), nor would the composition
of the solid waste be adversely affected. However, it would not be
realistic to try to estimate the solid-residue load solely on this
information.
Process Option 2 - The Rapson Effluent-Free Kraft Process—
The Rapson effluent-free Kraft process is described in Volume V,
pages 95-97. It essentially consists of a number of modifications to
the conventional Kraft process which are designed to increase the amount
of chemical recovery and water recycle. As its name implies, the main
environmental advantage of the Rapson process over conventional Kraft
processes is the elimination of water effluent from the bleaching step.
A mill using the rapson process would produce significantly less
wastewater than a conventional bleached Kraft pulp mill. It is, there-
fore, anticipated that the quantity of wastewater treatment sludge
would also be less. There is introduced, however, a small stream of
salt cake (sodium sulfate) leaving the process, which can either be
disposed of or sold.
Mechanical Pulping
Base Case Solid Waste Disposal—
Mechanical pulp (i.e., wood reduced to fiber by grinding) is typically
combined with chemical fiber and used primarily in the manufacture of
newsprint. It is also used in combination with chemical fiber in the
manufacture of catalogue paper, construction paper, and other so-called
groundwood papers. Wood chips, sawdust, and shavings from sawmills can
be used as raw materials.
38
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Solid residue from this process is mostly wastewater treatment
sludge, not unlike that produced by Kraft mills (but usually containing
a higher proportion of wood fiber and less dissolved solids).
Process Option - Thermo-Mechanical Pulping (IMP)—
In the IMP process, the wood feed is preheated to 130°C for a short
period and then reduced to fibers mechanically in a pressurized device.
The incentive to switch to IMP has been the improved fiber properties
and an expansion of the wood source base; i.e. , the ability to use chips
and residual wood. These newer methods of preparing mechanical pulp,
therefore, help to dispose of the solid residue that has historically
created a major problem in lumber manufacture.
The use of the TMP process increases the BOD load in the raw waste-
water stream by an estimated 20%. Since the quantity of wastewater
treatment sludge is proportional to the amount of DOB removed in the
biological wastewater treatment system, one can expect that the quantity
of wastewater treatment sludge will also be slightly increased.
The Manufacture of Newsprint
Base Case Solid-Residue Disposal—
Newsprint is manufactured from blends of mechanical pulp and Kraft
pulp. The solid-residue disposal problems associated with these processes
have been discussed in the preceding sections.
Process Option - The De-Inking of Old News for Newsprint Manufacture—
The de-inking of old news for newsprint manufacture is a well-
established commercial practice. Although the concept of blending
recycled fiber with virgin mechanical fiber is not new, it has only
recently been introduced for the manufacture of newsprint on a large
scale. It was chosen for in-depth technical/economic analysis because
the production of newsprint containing de-inked news now accounts for
less than 5% of the total newsprint consumed in the United States, and
its broader application could significantly reduce both energy usage
and pollution.
De-inking is carried out by washing and pulping the old news in
either a batch or continuous operation using heat, water, and de-inking
chemicals, typically consisting of sodium peroxide, sodium silicate,
and detergents. The de-inking chemicals are largely recoverable.
The raw waste suspended solids in wastewater from de-inking
operations are significantly greater than for virgin pulps. Thus, the
quantity of wastewater treatment sludge generated by de-inking operations
will be greater than that from virgin pulp operations. Nevertheless,
although it is difficult to quantify, it is clear that, overall, the
39
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implementation of de-inking old newsprint will alleviate the national
solid-residue disposal problem by substantially reducing the amount of
old news destined for municipal landfills.
Summary
The base case bleach Kraft pulping process produces solid waste
in the form of wastewater treatment sludge. The two process options,
alkaline-oxygen pulping and the Rapson effluent-free Kraft process,
also produce wastewater treatment sludge, but in somewhat lower but
unquantifiable amounts.
Thermo-mechanical pulping is expected to produce slightly more
wastewater treatment sludge than the base case technology consisting
of mechanical pulping. Thermo-mechanical pulping does, however, allow
for the greater use of low-grade wood sources that, in many cases,
would otherwise become scrap.
While the de-inking of old news for newsprint results in a slight
increase in wastewater treatment sludge, it will result in a very signi-
ficant overall reduction in solid waste by using an existing waste
stream as a raw material.
The several processes considered in the pulp and paper industry
offer primarily environmental benefits at the plant site, coupled with
an expectation of energy savings. While neither energy savings nor
solid-residue volume reductions are very great, the combination does
make processes such as the alkaline oxidation and the Rapson attractive
to the industry.
De-inking of newsprint offers several advantages which also make
it attractive even though the de-inking operation generates a waste-
water sludge of its own. The conservation of virgin wood and the
potential reduction in municipal solid-residue volume are social benefits
that should be considered in broadening the use of this technique.
However, it should be borne in mine that advancement of this option
could have an adverse effect on those municipalities considering energy
from solid-residue systems.
OLEFINS INDUSTRY
Production of Ethylene by Ethane Propane Cracking
Base Case Solid-Residue Disposal—
The production of ethylene by ethane propane cracking is a rather
complex process involving the pyrolysis of ethane and propane, followed
by a series of separation and purification steps. The ultimate products
are ethylene, propylene, pyrolysis gasoline, residue gas, and various
other hydrocarbon products. A detailed description of the process is
presented in Volume VI, pages 16-22.
40
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In the production of ethylene by ethane propane cracking, there
are two major solid-residue streams, which are described below:
• Wastewater Treatment Sludge - There are a number of major
wastewater streams associated with the production of ethylene.
The combined wastewater stream contains a variety of hydro-
carbon pyrolysis products, carbonates, sulfates, sulfides,
inorganic slats, and suspended solids. The wastewater is
typically subjected to suspended solids removal followed by
biological treatment. The sludge produced by these treatment
processes contains large quantities of relatively inert
carbon particulate matter ("coke"), biodegradable solids
from the waste microorganisms in the biological treatment
system, and many of the previously listed pollutants
originally present in the raw wastewater. The sludge
is often dewatered by mechanical means prior to landfill.
It is important to note that ethylene and proylene are the
primary feedstocks for many petrochemical production
operations. Ethylene production units are, therefore, often
integrated into large petrochemical complexes. It is a
common practice to combine most of the wastewater streams
from the various production units within the petrochemical
complex into a single wastewater stream, and then to treat
it in a central wastewater treatment facility. Thus,
both the wastewater and the sludge from the wastewater
treatment facility are a composite of the individual con-
tributions from the various manufacturing operations.
We estimate that the ethylene plant generates wastewater
treatment sludge at a rate of 1.5 Ib of sludge per 1000 Ib
of ethylene produced (calculated from Volume VI, page 107).
• Spent Desiccants - Desiccants are used in certain drying
operations in the production of ethylene. The dessicants
are solid particles, typically composed of silica gel,
alumina, or ceramic molecular sieve materials. The desic-
cants themselves are relative inert; however, they can be
contaminated with hydrocarbons. The dessicant solid-residue
stream is quite small and is estimated to be generated at
a rate of 0.075 Ib per 1000 Ib of ethylene produced. It
is generally landfilled on site with other solid-residue
streams.
Process Option 1 - Ethylene from the Pyrolysis of Naphtha Alternative—
Because of the foreseeable shortage of natural gas and hence the
declining availability of ethane and propane, more and more domestic
ethylene production is being based on heavier petroleum products. One
41
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option is the pyrolysis of naphtha. Conceptually, naphtha cracking is
quite similar to ethylene cracking. A detailed process description is
given in Volume VI, pages 22-26.
While the total energy demand for a naphtha cracker is larger on a
per-unit ethylene basis, so much more co-product material is produced
that the energy consumption per unit of net hydrocarbon product is
smaller than for ethylene-propylene cracking.
The production of ethylene from the pyrolysis of naphtha generates
the following solid-residue streams:
• Wastewater Treatment Sludge - The composition of wastewater
treatment sludge is quite similar to that generated by the
production of ethylene from ethane and propane. Due to the
increased size of certain process operations, the quantity
of wastewater treatment sludge (estimated to be generated
at a rate of approximately 2.65 Ib per 1000 Ib of ethylene
production) is about 70% greater than that resulting from
ethylene production from ethane and propane (calculated
from Volume VI, page 34).
• Spent Desiccant - The composition and quantity of spent
desiccant are almost identical to that produced by ethylene
production from ethane and propane.
• Recovered Sulfur - Naphtha feedstocks generally contain
higher sulfur concentrations than those found in ethane
or propane. The sulfur must, therefore, be removed and
recovered as an amorphous solid. The rate of sulfur
generation is estimated to be 1.16 Ib per 1000 Ib of
ethylene produced (calculated from Volume VI, page 34).
If the sulfur cannot be marketed, it must be disposed
of in a landfill. Due to its inert nature open storage
(disposal) of sulfur is not an uncommon practice.
Process Option 2 - Ethylene from the Gas-Oil Cracking Alternative—
A natural gas-conserving option, ethylene production from gas oil
cracking, is also technically quite similar to that of naphtha cracking.
A detailed process description is presented in Volume VI, pages 27-31.
The production of ethylene from gas-oil cracking produces the same
type of solid-residue streams as the production of ethylene from naphtha;
however, the quantities are significantly greater. The solid-residue
streams are as follows:
• Wastewater Treatment Sludge - Due to an even greater increase
in size of certain process units over the base case, ethylene
production from ethane and propane, the quantity of wastewater
42
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treatment sludge is even greater than that produced by naphtha
cracking. The estimated rate of sludge generation is approxi-
mately 4.9 lb/1000 Ib of ethylene produced - which is over
three times greater than the base case and almost twice as
great as the naphtha-cracking alternative.
• Spent Desiccant - The nature and quantity of the spent
desiccant solid-residue stream is the same as in the base
case and the naphtha-cracking alternative.
• Recovered Sulfur - As in the case of naphtha cracking,
sulfur must be removed during the process, and is recovered
as an amorphous solid. Its generation rate is estimated
to be approximately 2.1 lb/1000 Ib of ethylene produced
which is about 1.8 times as great as that generated by
the naphtha-cracking alternative.
Summary
The base case production of ethylene via ethane propane cracking
generates two major solid-residue streams: wastewater treatment sludge
and spent desiccant.
The production of ethylene by the pyrolysis of naphtha also produces
a wastewater treatment sludge and sppnt desiccant. More wastewater
treatment sludge is produced than by the base case technology. In
addition, a recovered sulfur stream is generated.
The production of ethylene by gas-oil cracking also generates waste-
water treatment sludge, spent desiccant, and recovered sulfur, but in
substantially greater quantities than in the naphtha pyrolysis process
option.
A comparison of the solid-residue streams is presented in Table 9.
Both naphtha and gas-oil processes also generate other potentially
marketable hydrocarbon products, so that the Btu yield per ton of feed
and the solid-residue load per ton of feed can also be presented on
that basis. Although that view is not addressed in this report, it is
considered in the original document (Volume VI, page 10-15).
The use of heavier feedstocks to produce the basic petrochemical
building blocks, ethylene and propylene, is accompanied by both lower
yield of these monomers and increased solid residue. However, additional
hydrocarbon products contribute to reduced energy use based on total
useable/salable hydrocarbon products.
The sulfur byproduct recovered from the heavier feeds does constitute
a new pollutant, but not one which can be considered severe; if all new
capacity of ethylene in 1989 were supplied by the worst case, gas oil,
43
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TABLE 9. SOLID-RESIDUE DISCHARGE FROM OLEFIN PLANTS
Production Process
Estimated
Discharge Factor
(lb/1000 Ib)
Estimated
Change in
Discharge Factor
(lb/1000 Ib)
Solid-Residue
Discharge*
(106 ton/yr)
1974 1989*-1974
Base Case:
Ethylene by ethane-propane
cracking
• Ethylene from pyroysis of naptha
• Ethylene from gas oil cracking
1.58
2.73°
4.98C
0.0
1.15
3.4
V.
0.0205 0.0442
0.07643
0.1394a
Based on increment in production of ethylene from 1974 to 1989: 28.2 million tons.
Estimated 1974 discharge based on multiplying discharge factor by 1974 production of ethylene:
13 million tons.
'Excludes recovered sulfur which will presumably be marketed.
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3
sulfur production (at 2.1 lb/1000 Ib ehtylene) would only be 14.7 x 10
ton/yr, a volume which should be readily salable. For comparison,
approximately 11 x 10 ton of sulfur were produced in the United States
in 1974 (Bureau of Mines).
AMMONIA INDUSTRY
Manufacture of Ammonia from Natural Gas
Base Case Solid-Residue Disposal—
The manufacture of ammonia is an integrated process with sub-
processes of:
• Producing a hydrogen-rich stream from a hydrocarbon or
carbon source via reforming or partial oxidation,
• Gas purification, and
• Ammoniation.
The primary raw material for ammonia is natural gas, and about 95%
of the ammonia manufactured in the United States is so produced. A
detailed process description of the manufacture of ammonia from natural
gas is presented in Volume VIII, pages 25-36.
There are two types of solid residue generated in the manufacture
of ammonia from natural gas:
• Wastewater treatment sludge, and
• Waste catalyst.
Wastewater treatment sludge results from treating the following
wastewater streams associated with ammonia production: raw water treat-
ment plant effluent, cooling tower blowdown, boiler blowdown, compressor
blowdown, and process condensate. The total effluent wastewater flow
rate is relatively small and, therefore, the quantity of sludge is also
expected to be small. The nature and quantity of the sludge depend on
the type of treatment employed.
Although we have no quantitative data on the nature of this sludge,
it is reasonable to expect that it would contain inorganic particulate
matter such as rust, chromium compounds (if chromate corrosion inhibitors
are used in the cooling water system), oil and grease, and small amounts
of ammonia.
The unrecovered catalyst from the ammonia converter is composed of
iron oxide and is generally landfilled.
45
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Due to its small quantity, solid residue is not considered a major
environmental problem in the production of ammonia from natural gas.
Process Option 1 - Manufacture of Ammonia from Coal—
Given the shortage of natural gas, and the need for the United
States to reduce its dependence on foreign petroleum, serious consideration
should be given to basing future ammonia plants on coal. Prior to
World War II, nearly all synthetic ammonia production was based on the
use of coal to produce synthetic gas for the actual ammonia production
step. Since that time, only a small number of ammonia plants based on
coal have been built. A detailed description of the process is presented
in Volume VII, pages 37-45.
The use of coal greatly increases the quantity of solid residue
generated. In addition to the base case solid-residue streams previously
described, the manufacture of ammonia via coal gasification generates
the following solid-residue streams:
• Slag - A waste slag, largely composed of the ash content of
the coal, is produced in the coal gasification step. An
elemental analysis of the slag is presented in Volume VII,
page 54. The slag contains leachable heavy metals and,
therefore, presents a disposal problem. Very large
quantities of slag are produced. The estimated rate of
slag generation is 0.182 ton per ton of ammonia produced
(calculated from Volume VII, page 66).
• Runoff Treatment Plant Sludge - Since large quantities
of coal and .slag must be stored on-site, contaminated
stormwater runoff is a major water pollution problem
associated with the coal gasification alternative. The
primary pollutants of concern in the runoff water are
heavy metals. Therefore the proposed wastewater treat-
ment system consists of precipitation (with lime) and
settling. A waste sludge composed of metal hydroxides
is generated at an estimated rate of 0.052 ton per ton
of ammonia (calculated from Volume VII, page 65).
• Synthesis Gas Purification Wastewater Treatment Plant Sludge-
The wastewater from the synthesis gas purification step
contains biodegradable material (notably methanol) and
hydrogen sulfide. If proper design criteria are followed,
it can be treated in a high-detection-time biological
treatment system. The biological treatment system will
produce a small sludge stream largely composed of waste
microorganisms and a certain amount of methanol and sulfide
in the liquid fraction. The rate at which this waste is
generated is estimated to be approximately 0.0011 ton per
ton of ammonia (calculated from Volume VII, page 66).
46
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• Recovered Sulfur - The sulfur removed from the coal during the
gasification step is recovered as molten sulfur. In our
analysis it was assumed that this byproduct sulfur would be
marketed. If market conditions are such that all of the
sulfur cannot be sold, it will become a solid-residue stream
destined for land disposal. Molten sulfur is expected to
be generated at an estimated rate of 0.066 ton per ton of
ammonia (calculated from Volume VII, page 64).
Process Option 2 - Production of Ammonia from Heavy Fuel Oil—
This process change is also intended to conserve natural gas. In
the early 1950's, industrial processes were developed for producing
a synthesis gas, carbon monoxide and hydrogen, by the partial oxidation
of hydrocarbons. In producing ammonia from heavy fuel oil, the fuel
oil is first converted into synthesis gas which is then processed (in
a manner almost identical to that used in the coal gasification alter-
native) to form a feedstock for the actual ammonia-producing step.
A detailed description of the process is presented in Volume VII,
pages 66-79.
In addition to the base case solid-residue streams, the following
solid-residue streams are generated in the production of ammonia from
fuel oil:
• Wastewater Treatment Sludge - There are a number of waste-
water streams associated with the production of ammonia
from heavy fuel oil. While the exact composition of these
streams has not been determined, they do contain biodegradable
material and can very likely be subjected to biological
treatment in much the same manner as the synthesis gas
purification wastewater from the production of ammonia
from coal. The rate of sludge generation is estimated
to be approximately 0.0015 ton per ton of ammonia pro-
duced (calculated from Volume VII, page 77), which is
a far smaller amount than the rate of sludge generation
for the production of ammonia from coal.
• Recovered Sulfur - As in the case of the production of
ammonia from coal, sulfur is removed from the oil and
presumably sold as byproduct in the form of molten
sulfur. The rate of sulfur generation is significantly
less than that for coal gasification (0.0375 ton per
ton of ammonia for oil gasification, vs. 0.066 ton per
ton of ammonia for coal gasification). If all the sulfur
cannot be marketed, a part of it will become a solid-
residue stream destined for land disposal.
47
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Summary
The base case production of ammonia from natural gas produces a
small quantity of wastewater treatment sludge and unrecovered catalyst.
The production of ammonia from coal produces four solid-residue
streams (slag, runoff treatment sludge, synthesis gas purification
wastewater treatment sludge, and recovered sulfur) that result in
a tremendous increase over the relatively small base case solid-residue
generation rate.
The production of ammonia from heavy oil produces two solid-residue
streams (wastewater treatment sludge and recovered sulfur) that, while
representing a substantial increase over the base case, are considerably
smaller than that produced by the coal gasification option.
The various solid-residue streams are compared in Table 10.
It is clear that ammonia production from coal would have a measurable
impact on solid-residue generation. The nature of the waste will be
that inherent in any coal gasification system. Nevertheless, even if
all the incremental ammonia production anticipated for 1989 (12.8 x 10
ton) were to be manufactured from coal, this,would consume only 3%
of the coal that was mined in 1974 (603 x 10 ton). It cannot be
ignored that significant costs will have to be borne by the industry
to shift to either of these fuels from natural gas and satisfy antici-
pated environmental requirements.
ALUMINA/ALUMINUM INDUSTRY
The aluminum industry is comprised of two basic operations: (1) the
production of alumina (Al 0 ) from aluminum-bearing minerals, and (2) the
reduction of alumina to aluminum metal. The two operations are usually
conducted at entirely separate locations.
Alumina Production
Base Case Solid-Residue Disposal—
At present, the sole technology used to produce alumina in the
United States is the Bayer process. It is applicable only to bauxite
as a raw material, most of which is imported from the Caribbean, northern
South America, and Australia.
In the Bayer process (which is described in detail in Volume VIII,
pages 106-118), finely ground bauxite is digested at elevated temperatures
under pressure. The digesting liquor contains sodium aluminate and free
caustic. After the digestion step, the insoluble components of the
bauxite, primarily the oxides of iron, silica, and titanium, are removed
by thickening and filtration. The aluminum-containing liquor is then
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TABLE 10. SOLID-RESIDUE DISCHARGE FROM AMMONIA PRODUCTION
Production Process
Estimated
Discharge Factor
(ton/ton of ammonia)
Estimated
Change in
Discharge Factor
(ton/ton of ammonia)
Solid-Residue
Discharge 19893
(106 ton/yr)
1974 1989-1974
VO
Base Case:
Ammonia from
• Natural gas
Coal
Heavy fuel oil
small (unquantified)
0.235
0.0015
0.235
0.0015
small small
(unquantified)(unquantified)
3.013
0.0193
Based on increment in production of ammonia from 1974 to 1989: 12.8 million tons.
'Estimated 1974 discharge based on multiplying discharge factor by 1974 production of ammonia:
9.2 million tons.
'Excludes recovered sulfur which is expected to be sold as a byproduct.
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subjected to a series of precipitation, separation, and calcination
steps to yield the final product — alumina.
The separated solids, known as "red mud," are discarded, usually
into large tailing ponds. The quantity of red mud removed from the
caustic slurry following digestion varies with the bauxite used and
can range from 0.33-2.0 ton (dry basis) per ton of alumina produced.
About 0.8 ton per ton of alumina is typical in U.S. plants.
The composition of red mud is presented in Volume VIII, page 121.
The solid fraction, in addition to containing the oxides of iron,
silica, and titanium, also contains undissolved alumina, phosphates,
lime, and manganese oxide. The liquid fraction of the red mud is highly
alkaline (typically having a pH of 12.5) and contains high concentrations
of caustic, soda ash, sodium chloride, and dissolved alumina.
Process Option 1 - Production of Alumina from Domestic Clays via
Hydrochloric Acid Leaching—
The impetus for employing this process is not energy conservation
(it actually uses more energy than the base case Bayer process), but
rather to reduce the dependence on foreign sources of raw material.
The hydrochloric acid and other alternatives to the Bayer process are
based on the extraction of alumina from the large reserves of kaolin
clay in Georgia and South Carolina.
The hydrochloric acid process is described in detail in Volume VIII,
pages 23-30. Briefly, in the hydrochloric acid process, clay is dehydrated,
leached with hydrochloric acid, and then settled to separate the residue
from the aluminum chloride/iron chloride solution. This solution is
then purified with an amine ion exchange system operation to remove the
iron chloride, while leaving the aluminum chloride in solution. The
aluminum chloride in the solution is crystallized from the solution and
decomposed to alumina, and the acid value is recovered.
The primary waste material from this process is the underflow from
the series of thickeners. It consists of the acid-insoluble clay fraction
and a dilute aluminum chloride aqueous solution. The composition of this
waste stream is given in Table 11.
On a dry basis, this waste is generated at a rate of approximately
3.35 ton per ton of alumina (excluding "mine mooth" solid residue) which
is about four times greater than the typical 0.8 ton per ton rate for
conventional bauxite-refining plants. The main reason for this tremendous
increase in solid residue is the low alumina content of kaolin clay as
compared to bauxite. The characteristics of the waste are also quite
different. Instead of the liquid fraction of the waste being highly
alkaline, it is acidic and contains high concentrations of chlorides.
This chemical environment is far more conducive to the dissolution of
many trace heavy metals than the alkaline conditions present in red mud
from bauxite refining.
50
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TABLE 11. COMPOSITION OF WASTE STREAM FROM LEACHING PROCESS
Constituent Weight Percent
Alumina (undissolved) 12.8
Silica 33.5
Aluminum chloride (soluble) 0.6
Other soluble chlorides (mostly iron) 1.5
Other impurities (Mg, Ti, P, V. SO ) 2.7
X
Water 48.9
Total 100.0
51
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Process Option 2 - Production of Alumina from Domestic Clays via Nitric Acid—
Also intended for the extraction of alumina from domestic kaolin
clay, the nitric acid process (described in detail in Volume VIII,
pages 30-38) involves the following basic steps:
• Calcining the kaolin clay to make the contained alumina
selectively available for extraction with nitric acid;
• Leaching the calcined clay with hot nitric acid at
atmospheric pressure to produce a solution of
aluminum nitric and a suspension of clay insolubles.
• Separating the clay-insolubles from the aluminum nitrate
liquor in thickeners;
• Removing the iron and other impurities from the
clarified aluminum nitrate liquor by use of a liquid
ion-exchange medium;
• Removing the remaining impurities from the iron-free
aluminum nitrate liquor by means of vacuum crystal-
lization of aluminum nitrate nonohydrate;
• Recovering the nitric acid and nitrogen oxide values
in the form of nitric acid for recycle; and
• Calcining the product alumina.
The primary waste material from this process is the underflow from
the series of thickeners, which consists of the acid-insoluble clay
fraction and a dilute aluminum nitrate aqueous solution. The composition
of this waste stream is given in Table 12.
On a dry basis, this waste is generated at a rate approximately
1.9 ton/ton of alumina which, although lower than that for the hydro-
chloric acid process, is still about double that of conventional
bauxite refining.
The water is acidic, and the pollutants of major concern are the
soluble nitrates which, in general, pose more of a threat to groundwater
contamination than either the chlorides from the hydrochloric acid process
or the alkaline solutions from the conventional bauxite refining process.
Neutralization would be necessary as a first step, even if the waste is
disposed of by return to the mine or lagooning.
Process Option 3 - Toth Alumina Process Alternative—
The Toth Alumina Corporation (TAC) has been developing a process
for the production of alumina and byproducts from clays and other
52
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TABLE 12. COMPOSITION OF WASTE STREAM
(Nitric Acid Process)
Constituent Weight Percent
Alumina (undissolved) 1.5
Silica 45.0
Aluminum nitrate (soluble) 1.9
Other soluble nitrates 2.2
Water 47.2
Other impurities (Mg, Ti, P, V, 804) 2.2
Total 100.0
53
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alumina-containing minerals. The process involves the chlorination of
alumina-containing raw materials in the presence of carbon to produce
aluminum chloride vapor and other volatile chlorides. These are sub-
sequently purified to remove other metal chlorides and then oxidized
to produce alumina and chlorine for recycle. Based on kaolin clays,
the steps in the process involve: (1) ore drying and calcination;
(2) chlorination in which the aluminum, titanium, and iron present in
the ore are carried overhead as volatile chlorides; (3) separation of
the chlorides from the aluminum chloride by fractional condensation
and distillation; and (4) oxidation of the iron, silicon, and titanium
chlorides to their respective oxides for recovery of chlorine for recycle.
Finally, the alumina chloride, after separation, is also oxidized to
produce alumina and to recover chlorine for recycle. A detailed des-
cription of the process is given in Volume VIII, pages 37-49.
The process produces a dry waste stream which contains the rejected
materials present in the clay. An estimated composition of the waste
stream is given in Table 13.
The rate at which this waste is generated is estimated to be approxi-
mately 1.5 ton (dry basis) per ton of alumina.
Although the solid waste streams are produced in an essentially
dry state, liquid waste control will very likely involve the recycling
of wastewater through the disposal lagoon, so the same type of wet
tailing pond situation will be created. As in the case of the hydro-
chloric acid process, the pollutants of greatest concern are soluble
metal chlorides. If conditions are such that there is a wastewater
discharge to the environment, the wastewater would probably have to
be subjected to neutralization.
Aluminum Production
Base Case Solid-Residue Disposal—
The Hall-Heroult electrolytic reduction process is presently used
to produce all of the primary aluminum throughout the world. A detailed
process description is presented in Volume VIII, pages 112-118.
Basically, the alumina is dissolved in molten cryolite (Na A1F,) in
an electrolytic cell wherein aluminum is liberated at the cathode and
oxygen at the anode. The oxygen liberated at the anode reacts with the
carbon anode to produce CO. and CO. Modern Hall-Heroult electrolytic
cells are typically steel boxes lined with insulating refractory and
carbon. Carbon blocks at the bottom of the cell serve as the cathode
in the electric circuit. The anodes are also carbon-suspended in the
electrolyte from above.
Minor amounts of solid residues originate from the handling, storage,
and feeding of raw and consumable materials (alumina, calcined coke,
cryolite, and aluminum fluoride) brought into the smelter. Emissions
54
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TABLE 13. ESTIMATED COMPOSITION OF WASTE STREAM
(Toth Process)
Constituent Weight Percent
Aluminum (insoluble) 6.0
Silica 73.7
Iron (ferric) oxide 0.8
Soluble chlorides 2.2
Other impurities 6.8
Water 10.5
Total 100.0
55
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of these materials are largely in the form of dust from handling and
feeding to the cells and the anode-making operations.
The rebuilding of cells is another source of solid residues from
an aluminum smelter. When a cell reaches the end of its useful life
and has to be rebuilt, it is removed, dismantled, and rebuilt. This
operation generates a good deal of solid rubble and waste solid materials.
Most of the refractory internals are impregnated with cryolite and
aluminum fluoride. These materials are typically leached to recover
the fluorides for reuse. The quantity of this waste also is generally
small and varies greatly from plant to plant.
The major solid-residue stream from aluminum production is the
result of air pollution control intended for the collection of particulate
matter and fluorides. If wet air pollution devices are used, the
scrubber water must be treated for the removal of suspended solids and
fluorides. Lime treatment is typically used to precipitate the fluorides
as calcium fluoride. The rate of sludge generation is estimated to be
15-30 lb/1000 Ib of aluminum produced (Volume VIII, page 137).
Process Option 1 - Production of Aluminum by the Alcoa Chloride Process—
Precise details concerning this process are not available. Basically
the feed alumina is converted to aluminum chloride by chlorination in
the presence of carbon to form volatile aluminum chloride. This, in
turn, is purified and fed to an electrolytic cell to produce molten
aluminum at the cathode and chlorine at the anode. The chlorine is
recycled to the chlorination step.
Various sludges removed from the electrolyte at times might amount
to about 5 lb/1000 Ib of aluminum. The sludge would be predominantly
sodium aluminate contaminated with NaCl/LiCl and would be quite soluble.
Purges of unchlorinated alumina from the chlorinator might amount to
30 lb/1000 Ib of alumina (Volume VIII, page 66).
Very large amounts of cooling water would be necessary for the Alcoa
process. If chromium corrosion inhibitors are used in the cooling
water circuits, a wastewater treatment system would be required for the
removal of chromium and a waste sludge would be generated at a rate of
approximately 4.7 lb/1000 Ib of aluminum (calculated from Volume VIII,
page 60).
Since the process involves coke making to supply the carbon, it is
quite possible that sulfur dioxide will have to be controlled. If so,
a calcium sulfate/sulfite sludge would be generated at a rate of approxi-
mately 250 lb/1000 Ib of aluminum (calculated from Volume VIII, page 67).
The estimated generation rates of solid-residue streams produced by
the Aloca process are summarized in Table 14.
56
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TABLE 14. ESTIMATED GENERATION RATES OF SOLID-
RESIDUE STREAMS (Alcoa Process)
Estimated Generation Rate
Solid-Residue Stream (lb/1000 Ib of Al)
Sludge removed from electrolyte 5.0
Unchlorinated alumina from chlorinator 30.0
Sludge from treatment of cooling water
blowdown 4.7
Calcium sulfate/sulfite sludge from
sulfur dioxide control system 250.0
Total solid residue 289.7
57
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The rate of solid-residue generation is over 10 times that generated
by the base case Hall-Heroult process. It should be noted, however,
that more than 85% of the sludge generated is related to sulfur dioxide
control. If power plants supplying the conventional Hall-Heroult process
plants are required to install sulfur dioxide controls, it would be
necessary to allocate an additional quantity of sludge to the Hall-
Heroult process. Thus, it is very difficult to compare the solid-residue
generation rates on a truly equivalent basis. One comparison can be
made: If one assumes 200 x 10 Btu/ton, primarily as electricity, used
in Hall-Heroult, and accepts 34 Ib of sludge, ash, etc., produced at a
cola-fired power plant per 10 Btu output as electricity, the difference
becomes much smaller. Of course, this does ignore the fact that much of
the current electricity used in aluminum production is hydroelectric.
Process Option 2 - Refractory Hard Metal Cathodes—
Refractory hard metal cathodes, made from zirconium and titanium
carbides and borides and mixtures thereof, have been considered as
potential replacements for the conventional carbon cathodes. They exhibit
operational and energy conservation advantages.
The use of such cathodes would not appreciably change the base case
solid waste disposal problem since the value of the titanium diboride
scrap cathode is high enough to warrant recovery of the material for
return to the manufacturer.
Summary
The base case technology for the production of alumina, the Bayer
process, produces large quantities of alkaline wet sludge which contains
a variety of inorganic constituents. All of the options to the Bayer
process are based on domestic kaolin clays rather than imported bauxite
as the source of alumina. Due to the lower alumina content of domestic
kaolin, all of the process options inherently produce more solid residue
than the base case technology. The composition of the solid residue from
the process options is radically different. Both the hydrochloric acid
and the Toth process produce an acidic waste stream high in soluble
chlorides, while the nitric acid process produces an acidic waste stream
high in soluble nitrates. Land disposal of one form or another would
be the only practical disposal approach.
It cannot be denied that the use of options such as the hydrochloric
acid or nitric acid leaching of domestic kaolins would have a massive
impact on solid-residue generation, both in volume and in nature.
Nevertheless, the nation may find it advisable to pursue such routes
over the coming years and steps should be taken to assure minimal
environmental impact from such mining and processing operations, both
from the technical and from the legal or regulatory point of view.
Proper restoration and reclamation of mined sites after, presumably,
the exhausted, dewatered, and neutralized clays have been returned to
58
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the mines should be considered an integral part of and an integral cost
of the processes.
The major source of solid residue from the base case Hall-Heroult
process for aluminum production is the sludge produced from treating
the wastewater generated by wet air pollution control devices. The
sludge contains calcium fluoride.
While the use of refractory hard metal cathodes will not signifi-
cantly alter the base case solid-residue generation rate, the production
of aluminum by the new Alcoa process will have a major effect on both
the quantity and nature of the solid residue generated. The Alcoa
process would produce a highly soluble process sludge, a cooling water
blowdown wastewater treatment sludge, and a large quantity of calcium
sulfate/sulfite sludge resulting from sulfur dioxide control. The
quantities of these wastes can only be estimated at this time. The
process must be more extensively evaluated in order to assess the total
environmental impact relative to the conventional process; however,
this will remain elusive since existing Hall-Heroult processing uses
off-site electrical generation, often hydroelectrical. It will be
necessary to assess, on a site-by-site basis, the total environmental
impacts of the two processes including control of SO emissions and
ash at the supplying power plant, particularly if coal is to be the
fuel of choice. On such a basis the difference may become much less
significant and cost and energy savings may be the deciding factors.
The quantities of solid waste discharged from the base case
alumina/aluminum production methods and their process options are
presented in Table 15.
TEXTILE INDUSTRY
Integrated Knit Fabric Mills
Base Case Solid-Residue Disposal—
The base case knit fabric mill produces polyester doubleknit using
purchased texturized yarn. It includes the following sequence of
operations: (1) yarn is first knitted into fabric in the greige mill;
(2) the greige (undyed, unbleached) fabric then goes through a scouring
operation to remove knitting oil, followed by dyeing, washing, and
spin-drying to remove as much water as possible before hot-air drying.
A finish (softener/lubricant) is then applied to the fabric, which
is dried and heat-set. Process water is required for the scouring,
dyeing, and washing operation, and this is combined into one wastewater
effluent.
Solid residue is not a big problem in the textile industry. One
type consists of waste fiber in short lengths which accumulates on and
around the machining or is filtered out in the waste treatment system.
This material is usually stored and periodically disposed of to landfill.
59
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TABLE 15. SOLID-RESIDUE DISCHARGE FROM ALUMINA/ALUMINUM PRODUCTION
Process
Estimated
Discharge Factor
(ton/ton of Alumina)
Estimated Change in
Discharge Factor
(ton/ton of Alumina)
Solid-Residue Discharge
(106 ton/yr)
1974 1989a-1974
Alumina Production
Base Case:
Bauxite refining by the
Bayer process
• Hydrochloride acid—
leaching of domestic clays
• Nitric acid leaching of
domestic clays
• Clay chlorination (Toth)
process
Aluminum Production
Base Case:
Hall-Heroult electrolyte
reduction
• The ALCOA process
• Use of refractory hard
metal cathodes
Base Case: ,
Bayer with Hall-Heroult
0.8
3.35
1.9
1.5
(ton/ton of Aluminum)
0.0225°
0.29
0.0225°
1.56
0.0
+2.55
+1.1
+0.7
(ton/ton of Aluminum)
0.0
0.2675
0.0
0.0
6.16L
0.1125
8.6
36.0
20.4
16.1
0.158**
2.0
0.158**
7.8125 10.92
(continued)
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TABLE 15. (continued)
Estimated Estimated Change in Solid-Residue Discharge
Discharge Factor Discharge Factor (10" ton/yr)
Process (ton/ton of Aluminum) (ton/ton of Aluminum) 1974 1989a-1974
• Clay chlorination (Toth
aluminum) and ALCOA chloride) 3.19 +1.63 — 22.33
a
Based on increment in production from 1974 to 1989: 10.75 million tons alumina and 7.0 million tons
aluminum.
Estimated 1974 discharge based on multiplying discharge factor by 1974 production: 7.7 million tons
alumina and 5.0 million tons aluminum.
rt
Based on average of estimated range of 0.015-0.030 ton/ton of aluminum.
Based on 1.93 tons alumina per ton aluminum.
**
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A second type is the tarry residues that gradually accumulate in
the heat-set tenterframes. These residues consist of degradation
products from finishing chemicals, and periodically the tenterframes
are shut down so that the residues can be removed manually.
There is also very little, if any, biological wastewater treatment
sludge generated by most textile mills. The typical textile mill
wastewater treatment plant employs a multiple-stage biological treatment
system that has a very long detection time. As a result, there is very
little accumulation of excess microorganisms in the biological treatment
process.
Color in the effluent of textile mills has been considered a pol-
lutional problem in localized areas. Processes for the removal of
color employ lime and/or alum precipitation and produce a waste sludge.
Although this is an additional solid-residue stream, it is doubtful
whether a high percentage of mills will have to perform color removal
in the foreseeable future.
Process Option 1 - Advanced Processing—
"Advanced processing," as applied to integrated knit fabric mills,
is a term referring to a collection of process changes, plant modifi-
cations, and general operation improvements which are designed to con-
serve both energy and water. Advanced processing consists of the fol-
lowing measures:
• Aqueous size,
• Water conservation,
• Processing at a low liquor/fabric ratio,
• Vacuum impregnation and extraction, and
• Improved finishing techniques.
These are described in detail in Volume IX, pages 28-31.
While advanced processing will diminish the volume of wastewater
and therefore the cost of wastewater treatment, it will have virtually
no effect on the solid-residue disposal problem.
Process Option 2 - Solvent Systems—
A textile mill based on a solvent system would employ an organic
solvent (typically perchlorethylene) instead of water for the various
scouring, dyeing, and finishing operations. The solvent is collected
and recovered in a central solvent still. The small amount of condensate
from the finishing operation and the still represents the only waste-
water effluent that may contain traces of solvent and other chemicals.
Knitting oils removed in scouring and chemicals from dyeing and finishing
remain as residues in the solvent still and are removed as a solid
residue for disposal. Although we have no data on either the quantity
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or composition of this solid-residue stream, it is quite reasonable to
assume that it will contain a certain amount of organic solvent and
finishing chemicals.
Since chlorinated organic solvents are far more environmentally
objectionable than relatively inert waste textile fibers, the possibility
exists that the implementation of solvent systems will have a negative
effect on the base case solid-residue disposal problem. Since the
residue would be quite combustible, incineration may be the best means
of disposal for this waste stream.
Integrated Woven Fabric Mill
Base Case Solid-Residue Disposal—
Woven fabrics require a much longer sequence of processing operation
than knit fabrics. Although more complex, the major processes include
various combinations of scouring, washing, bleaching, dyeing, and
finishing. The combined wastewater stream from the entire operation
contains natural and processing impurities removed by hot alkaline
detergents, dye material, oil and grease, and inorganic dissolved solids.
The wastewater is basically treated in the same way as wastewater from
knit fabric mills. The solid-residue disposal problems are similar.
Process Option 1 - Advanced Processing—
Advanced processing for woven fabrics is similar to advanced pro-
cessing for knit fabrics in that it consists of a collection of process
changes, plant modifications, and general operation improvements. The
most important process change is the inclusion of a polyvinyl alcohol
(PVA) recovery loop which taken the effluent stream from the desizing
step and (after ultrafiltration) recycles the concentrated PVA solution
back to sizing, and the hot water back to the desizing operation. A
process flow diagram of the advanced processing steps for an integrated
woven fabric mill is presented in Volume IX, page 50. This operation
both conserves energy (in the form of heated water) and reduces the
volume of the effluent wastewater stream. Its implementation is not
expected to have a significant effect (either positive or negative) on
the base case solid-residue disposal problem.
Summary
The base case production of both knit fabrics and woven fabrics
produces relatively small solid-residue streams consisting of waste
fiber and tarry residues from finishing chemicals. Although the textile
industry produces moderate amounts of wastewater requiring treatment,
the type of treatment generally employed produces very little, if any,
wastewater treatment sludge.
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The only process option expected to have an impact on the solid-
residue problem is solvent processing. The presence of additional
quantities or organic solvents and finishing chemicals in the solid-
residue stream may very well render the solid residue more environ-
mentally objectionable and require more sophisticated attention to the
disposal option.
It is unlikely that solid residue will be a significant factor in
the textile industry's future decisions concerning the process options
they plan to pursue. However, in the case of solvent finishing (and
even with some dyes and other finishing chemicals in aqueous finishing),
the nature of these solid residues, even after biological treatment,
may be such as to warrant careful study into the nature of the materials
and the acceptability of the disposal techniques being pursued.
CEMENT INDUSTRY
Manufacture of Portland Cement by the Dry Process, Long Rotary Kiln
Base Case Solid-Residue Disposal—
Hydraulic cement is a powder made by burning lime, silica, alumina,
iron and magnesia together in a kiln and then pulverizing the product.
The processing of raw materials into finished cement follows four steps:
• Crushing,
• Grinding,
• Clinkering, and
• Finishing grinding.
These steps are decribed in detail in Volume X, pages 84-89. The
crushing, grinding, and finishing grinding are merely size reduction
and material-preparation steps. The heart of the process - and the
operation which consumes about 70-80% of the total energy used in cement
manufacturing - is the clinkering step. In the clinkering step, the
accurately controlled mixture of raw materials reacts chemically at
high temperatures in the kiln to produce "clinker," which is subsequently
ground into cement.
Since the changes in Portland cement technology and cement industry
practices examined in this study have an effect only on the clinkering
operation, the analysis of solid-residue implications has also been
restricted to the clinkering operation.
The major type of solid residue is the cement dust collected from
the kiln by the air pollution control system (usually consisting of
fabric filters). The base case plant is a "non-leaching" plant in that
the dust is merely discarded rather than leached with water (a process
that can generate serious water pollution problems) to reclaim reusable
fractions of the cement dust. On the average, cement dust is generated
at a rate of approximately 0.15 Ib of dust per Ib of cement product.
64
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Depending on the mix of raw materials, the dust contains a variety
of soluble and insoluble inorganic constituents, the most prevalent
being carbonates, oxides, calcium, potassium, chlorides, and sulfates.
Usually about 15% of the total dust is soluble in water. Due to the
high fraction of soluble species, care should be taken in the disposal
of cement dust to minimize groundwater contamination resulting from
stormwater runoff and percolation (e.g., disposal into liquid ponds).
Process Option 1 - Equipping the Rotary Kiln with a Suspension Preheater—
A suspension preheater is a modification, or an addition, to a cement
rotary kiln. It is attached to the raw feed inlet end of the kiln,
totally replacing the preheating zone of the rotary kiln. A detailed
process description is given in Volume X, pages 16-34. Essentially,
suspension preheating conserves energy by improving heat and mass trans-
fer and making better use of the waste heat in the combustion gases.
As is the case in the base case cement plant, the suspension pre-
heater alternative will produce a waste dust, which probably will also
be stored in large piles or holidng ponds. The quantity of dust generated
is expected to be substantially less than that of the base case, 0.064 Ib
per Ib of cement versus 0.15 Ib per Ib of cement. The dust, however,
is expected to contain a slightly higher soluble fraction than that
generated by the base case cement plant as described in the Cement
Industry report.
Process Option 2 - Installation of a Flash Calciner—
The flash calciner is a process operation intended for installation
between a rotary kiln and a suspension preheater. Its use has a number
of operational and energy conservation benefits, which are described
in detail in Volume X, pages 34-40. The quantity of dust loading of
the combustion gas stream leaving a flash calciner should be essentially
the same as for a comparable suspension preheater.
Process Option 3 - Fluidized Bed Process—
The difference between the fluidized-bed cement-making process
and conventional processes is in the high-temperature clinkering step.
All of the other steps are essentially identical. The fluidized-bed
process has many mechanical, operational, economic, and energy-related
advantages over the rotary kiln manufacturing process. Of particular
note is that practically any form of carbonaceous fuel can be used in
the fluidized bed reactor. Also, current studies indicate that the
cement process employing the fluidized-bed cement reactor, with proper
heat recovery, requires significantly less total energy than the con-
ventional dry, long rotary kiln. A detailed description of the fluidized
bed process is presented in Volume X, pages 40-54.
65
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Cement plants employment the fluidized bed process will produce a
waste dust that is estimated to be generated at a rate of 0.03 ton per
ton of cement produced (Volume X, page 57) which is about one-fifth of
the amount generated by the base case cement plant,
Unlike the base case cement plant, dust generated by the fluidized
bed process will consist of relatively high-grade potassium and sodium
sulfate, both of which are highly soluble. There are possibilities
for selling this material as a byproduct. However, if the material
cannot be sold as a byproduct, it will have to be stored on-site in a
manner similar to that described for the base case. The high solubility
of the material imposes even a stronger need to dike the storage area
and to collect and treat runoff water, since dissolved salts are a
potential pollution problem.
Process Option 4 - Conversion to Coal Fuel from Oil and Natural Gas—
The energy-conservation potential of the use of coal fuel is pri-
marily one of form rather than quantity of energy. A variety of material-
handling steps and process modifications are required to convert a con-
ventional oil- or natural gas-fired rotary kiln to coal. These measures
are discussed in detail in Volume X, pages 60-66.
The solid-residue implications associated with the use of coal have
to do with the ultimate fate of the ash content of the coal. Typical
bituminous coal contains approximately 10% ash by weight. Between 50
and 100% of all of the coal ash produced by the combustion of coal in
a rotary cement kiln contacts and chemically combines with the clinkering
raw materials, thereby losing its identity as coal ash and becoming
Portland cement clinker. When using coal, however, the composition of
the raw materials must be adjusted to incorporate the coal ash.
A portion of the coal ash escapes the rotary kiln with the cement
dust and is eventually disposed of with the cement dust. It alters the
composition of the combined waste, principally due to the presence of
heavy metals in coal ash. (A composition of West Virginia coal ash is
presented in Volume X, page 73.)
The relative fraction of the coal ash which leaves the plant as
cement versus solid waste is highly dependent on the raw material compo-
sitions, process configuration, and other site-specific factors. It is,
therefore, not possible to quantify, with any degree of confidence, the
overall solid-residue implications of using coal as a fuel in cement
manufacturing. The 5.7 million Btu of coal required per ton of cement
amount to about 0.25 ton of coal containing 250 Ib of ash. Up to a half
of this ash (125 Ib) may be discharged with the flue dust. Thus compared
to oil or gas firing, solid residue discharges with coal firing may
increase from zero (if the flue dust is recycled) to 0.06 ton/ton of
cement.
66
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Summary
The base case dry process, long rotary kiln method of cement
manufacture produces a solid-residue stream consisting of cement dust
collected as the result of air pollution control.
Two of the process options — equipping the kiln with a suspension
preheater and installation of flash calciner — result in a smaller
amount of cement dust; however, the dust in these cases is expected to
contain a higher fraction of soluble inorganic constituents.
The fluidized bed process option is expected to produce a solid-
residue stream that is only one-fifth the size of the base case solid-
residue stream. The solid residue will consist largley of highly
soluble potassium and sodium sulfate.
The process option involving the conversion to coal, while intro-
ducing coal ash into the overall process, will not necessarily increase
the base case solid-residue generation rate because a high fraction of
the coal ash will exit the plant in the product cement. However, the
presence of leachable metals, both in the dust and even in the cement
itself, should be of some concern, and work is needed to determine
whether undesirable metals would, in fact, be removed.
The use of coal to fire cement kilns is a particularly attractive
means of conserving more valuable natural gas. Moreover, the impact
on the overall national solid-residue problem would be minimal. For
example, if all 1989 incremental production of cement were to be
achieved by direct firing of coal, the industry would be only using
1% of the coal that was mined in 1974. Incremental solid-residue
generation would be significantly less than that produced at the utility.
A comparison of the solid-residue discharge for the various
process options is presented in Table 16.
GLASS INDUSTRY
Glass Melting
Base Case Solid-Residue Disposal—
Since glass melting is by far the most energy-intensive portion of
the entire glass manufacturing process, downstream finishing operations
have not been included in the analysis. The conventional glass-melting
furnace is presently fired by natural gas. The major raw materials
which make up a soda-lime glass (the most common type of glass) are
silica sand, feldspar, dolimite, limestone, and soda ash. A description
of the base case glass-melting process is given in Volume XI, pages 17-32.
There are two major solid-residue streams from the conventional
glass-melting process, both of which consist of particulates removed
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TABLE 16. SOLID-RESIDUE DISCHARGE FROM CEMENT PRODUCTION
oo
Process
Base case:
Dry process, long rotary kiln
• Kiln with suspention preheater
Estimated
Estimated change in
discharge factor discharge factor
(ton/ton of cement) (ton/ton of cement)
0.15 0
0,064 - 0,086
• Installation of a flash calciner 0.064 - 0.086
• Fluidized bed cement process
• Conversion to coal fuel
0.03 - 0,12
0.15-0.21 0-0.06
Solid-residue
discharge
(10b ton/vr) A
1974 1989-1974
b a
11.85 4.1
1.753
1.753
0.823
4.1-5.73
* 6
Based on cement production in 1989 being 27.3 x 10 ton greater than in 1974.
g,
Based on increment in production of cement from 1974 to 1989: 27.3 million tons.
Estimated 1974 discharge based on multiplying discharge factor by 1974 production of
cement: 79 million tons.
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from gaseous streams by air pollution control devices. One solid-residue
stream consists of dry particulates which have been removed by bag
filters; the other solid-residue stream consists of particulates in the
form of a wet sludge removed from a gas scrubbing system. The composi-
tion of glass-melting gaseous emissions is presented in Volume XI, page
27. Pollutants of concern in the solid waste (i.e., collected particu-
late matter) are fluorides, lead, borates, antimony, arsenic, selenium,
and other heavy metals. In addition, the liquid fraction of the sludge
contains dissolved sulfites and sulfates.
The rate of solid waste generation for a conventional glass-melting
operation is estimated as follows (calculated from Volume XI, pages 32,33
and assuming baghouse dust amounts to 1 Ib per 1000 Ib of glass as in
the coal gasification case, Volume XI, page 43):
Baghouse dust 1.0 lb/1000 Ib of glass
Wastewater treatment
sludge 8.6 lb/1000 Ib of glass
Total solid waste
generation rate 9.6 lb/1000 Ib of glass
Process Option 1 - Melting Energy Supplied by a Coal Gasification System--
In this process change, an on-site coal gasification system is
designed to supply the entire fuel gas requirements for the melting
operation, thus eliminating the dependence on natural gas. Generally,
coal gasification processes include, in some variation, the following
steps:
Coal handling and storage,
Coal preparation,
Gasification,
Oxidant feeding, and
Gas cleaning.
The details of the process are described in Volume XI, pages 32-45.
The introduction of coal into the system generates two additional
solid-residue streams:
• Sulfur removed from the coal, and
• Coal ash.
Thus, implementation of coal gasification increases the quantity
of solid residue by about a factor of 4. While the nature of the solid
residue will also change, one cannot say that the coal ash exacerbates
the need for sound environmental control.
69
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Process Option 2 - Melting Energy Supplied by Direct Coal-Firing—
Direct coal-firing has the advantage over other coal-firing processes
in that is uses all of the heating value of the coal. To use coal
directly in burners, a coal storage area is needed as well as a live
coal storage bin, a pulverizer, screens, a feeder, and the pulverized
coal burner(s). A coal storage area capable of storing about one
month's supply appears reasonable.
Since coal is a high-sulfur fuel, a direct coal-fired glass melting
facility will require a sulfur dioxide scrubbing system. Alkaline-
based SO scurbbers generate solid residue in the form of calcium
sulfate/sulfite sludge.
Additional solid-residue streams resulting from the direct firing
of coal include coal ash, the dust from fabric filters, and wastewater
treatment sludge.
The quantity of filter dust and coal ash is approximately the same
as that generated by the coal gasification alternative, i.e., 38 lb/1000
Ib of glass. The sulfur dioxide scrubber sludge and the wastewater
treatment sludge are generated at a rate of approximately 56 lb/1000 Ib
of glass melted (calculated from Volume XI, page 44).
Process Option 3 - Coal-Fired Hot Gas Generation (COHOGG)—
In this process (which is described in detail in Volume XI, pages
48-53) coal is pyrolyzed to produce a combustible gas for the glass
melting operation. Sulfur is removed directly within the process by
the addition of limestone. In addition to the ash from the coal (about
37 lb/1000 Ib glass) and the base case solid-residue streams amounting
to 9.6 lb/1000 Ib glass, this alternative generates a solid-residue
stream in the form of calcium-sulfate, at a rate of approximately
20 lb/1000 Ib of glass (Volume XI, page 53) resulting in a total solid
waste stream of 66.6 lb/1000 Ib glass.
Process Option 4 - All-Electric Melting—
Molten glass can be heated by the passage of an electric current.
Both the design and the operation of an all-electric glass-melting
furnace differ greatly from the typical natural gas-fired regeneration
furnace. A detailed description of the design and operational differences
is given in Volume XI, pages 53-55.
All-electric melting is based on the use of purchased electrical
power, and, therefore, there is a shift of some of the environmental
problems from the glass manufacturing plant to the electric power
generating station.
70
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This process change generates solid residue in the form of dust
from the fabric filter and coal ash (at the power plant). The dust
and sludge is about the same amount or possibly slightly less than
that generated in the base case (9.6 lb/1000 Ib glass), and the coal
ash is about the same amount as for the other coal alternatives (371 Ib/
1000 Ib glass). Total estimated solid waste discharges are thus 46.6 Ib/
1000 Ib of glass.
Process Option 5 - Batch Agglomeration Preheating—
This process, still in the developmental stage, is designed mainly
to prereact the batch ingredients, rather than to conserve energy. A
variation of the process proposes to use waste heat for preheating the
materials. The preheating step, in itself, does not generate a solid
residue stream.
If natural gas is the energy source, both the nature and quantity
of the solid residue are estimated to be about the same as the base case.
If one of the coal-based alternatives is used, the previously described
solid-residue streams will be generated if the fuel utilization efficiency
remains constant.
Summary
The base case gas-fired, glass-melting operation produces two solid-
residue streams, baghouse dust and wastewater treatment sludge, which
contain raw materials particulate matter.
When melting energy is supplied by coal gasification, two additional
solid-residue streams are introduced: coal ash and the sulfur removed
from the coal. Implementation of coal gasification increases the quantity
of solid waste by about a factor of 5.
Direct coal-firing results in yet another solid-residue stream con-
sisting of sulfur dioxide scrubber sludge, and thereby increases the
solid-residue generation rate by a factor of 9.
The coal-fired, hot gas generation process option also produces
ash and sulfur dioxide removal wastes, but at a lower rate than direct
coal-firing.
All-electric melting produces approximately the same solid waste
as the base case; however, it does so by shifting some of the environ-
mental problem from the glass plant to the electric power generating
station.
71
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A comparison of the solid waste produced by the various options
is presented in Table 17.
Thus, if shortages of natural gas develop in the glass industry,
use of coal gasification and, possibly, electric melting may be expected
over the coming years. Coal-based processes, e.g., gasification,
direct-firing, hot-gas generation, will introduce all of the problems
inherent in the use of coal, including sulfur or SO removal and coal
ash but will reduce the industry's dependence on natural gas. Electric
melting will transfer the bulk of the solid-residue problem to the
utility, but may be beneficial for its load-levelling effect and may
minimize pollution cost and problems by having it done centrally at the
utility.
Although the glass industry is considered a major energy consumer,
its energy use is only 0.4% of the national total. Thus, the solid-
residue volume would constitute only the same small fraction relative
to that generated by utilities. However, the industry is relatively
concentrated in some geographical areas (e.g., New Jersey) where land
disposal of ash for industry — or for utilities — is rather limited
and the local impact of any coal-based alternative could be more signi-
ficant on a local or regional basis.
CHLOR-ALKALI INDUSTRY
Chlorine Production Via the Graphite Anode Diaphragm Cell
Base Case Solid-Residue Disposal Problem—
A detailed description of the diaphragm cell process is given in
Volume XII, pages 21-28. In this process a nearly saturated solution
of sodium chloride is subjected to electrolysis to yield chlorine, sodium
hydroxide, and hydrogen. Prior to electrolysis, heavy metals, calcium,
and magnesium are removed from the raw brine by adding sodium carbonate
and then precipitating the metals as hydroxides and carbonates. The
precipitates are removed as a wet sludge and usually sent to a lagoon.
It is estimated that brine purification sludge is generated at a rate
of 63 lb/1000 Ib of chlorine (Volume VII, page 23).
During normal processing the graphite anodes are consumed and form
tiny particles which clog the diaphragm cathode. As a result, cells
must be periodically rebuilt. The debris from cell rebuilding, asbestos
diaphragm material, anode stubs, and cell bodies, are disposed of through
landfill dumping. Lead is present in cell bottoms, and thus appears in
the total solid-residue stream. The waste material resulting from the
rebuilding of electrolytic cells is estimated to be generated at a rate
of 3.4 lb/1000 Ib of chlorine.
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TABLE 17. SOLID-RESIDUE DISCHARGE FROM GLASS FURNACES
Melting unit fuel process
Base case:
Natural gas-firing
• Coal gasification
• Direct coal-firing
• Coal-fired hot gas generation
• Electric melting
• Batch preheat with natural gas-firing
Estimated
discharge factor
(ton/ton of glass)
0.010
0,050
0,094
0.066
0.047
0.010
Estimated Solid-residue
change in discharge
discharge factor (10 ton/yr) A
(ton/ton of glass) 1974 1989-1974
0 0.29b 0.1303
0.040 0.6503
0.084 1.2223
0.056 0.8583
0.037 0.611a
0 0.130a
* 6
Based on glass production in 1989 being 13 x 10 ton greater than in 1974.
o
Based on increment in glass production from 1974 to 1989: 13 million tons.
Estimated 1974 discharge based on multiplying discharge factor by 1974 glass
production: 29 million tons.
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The reactions between chlorine and organic material in the graphite
anode lead to the formation of volatile chlorinated organic materials
of rather indefinite composition, which must be removed from the product
chlorine. This waste stream is generated at an estimated rate of 0.45 lb/
1000 lb of chlorine produced, and is usually drummed for disposal by
incineration or landfill.
The total solid residue generated by the production of chlorine
via the graphite anode diaphragm cell is summarized in Table 18.
Although the brine purification sludge constitutes the largest
solid-residue stream, in terms of potential pollution problems it is
relatively innocuous when compared to the cell rebuilding waste and
the product chlorine purification waste.
Process Option 1 - Dimensionally Stable Anodes (DSA)—
To eliminate the problems associated with the graphite anode,
the industry has long worked on developing a non-consumable anode for
use in the diaphragm cell. The dimensionally stable anode consists of
an expanded titanium metal substrate coated with precious metal/rare
earth oxides. The DSA has numerous advantages which result in power
savings and reduced pollution loads.
While the brine purification sludge will remain unchanged, DSA-
equipped production units will reduce the quantity of cell-rebuilding
wastes to approximately 1.2 lb/1000 lb of chlorine (Volume VII, page 62)
and, perhaps more importantly, will virtually eliminate the formation
of chlorinated organics and the need for their removal from the product
chlorine. The total solid residue generated by chlorine production units
equipped with dimensionally stable anodes is in Table 19.
Process Option 2 - Modified Diaphragms—
In addition to the significant changes in anodes, some major improve-
ments on diaphragms are being introduced which have beneficial effects
on both power consumption and pollution control. The three most signi-
ficant modified diaphragms are: (1) polymer-modified asbestos, (2)
polymer membrane, and (3) ion exchange membranes. These are described
in detail in Volume XII, pages 48-52.
Polymer-Modified Asbestos - Use of the polymer-modified asbestos
diaphragm has a minor environmental advantage over use of conventional
asbestos diaphragms in that the discarded material, at the time of cell
rebuilding, is in stablilized pieces instead of loose asbestos fibers.
Thus disposal is easier and safer, because the fibers resist dispersion.
The amount of brine sludge generated would be the same as in the base
case, and the quantity of cell-rebuilding waste would be approximately
the same as in the case of the dimensionally stable anode.
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TABLE 18. SOLID RESIDUE GENERATED IN
PRODUCING CHLORINE VIA GRAPHITE
ANODE DIAPHRAGM CELL
Solid-residue stream lb/1000 Ib of chlorine
Brine purification sludge 63.0
Cell rebuilding waste 3.4
Product chlorine purification
waste 0.45
Total 66.9
75
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TABLE 19. SOLID RESIDUE GENERATED BY CHLORINE
PRODUCTION UNITS EQUIPPED WITH
DIMENSIONALLY STABLE ANODES
Solid waste stream
lb/1000 Ib of chlorine
Brine purification sludge
Cell rebuilding waste
Total
63.0
1.2
64.2
76
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Polymer Membranes and Ion Exchange Membranes - While the quantity
of brine purification sludge would remain the same, the use of polymer
membranes and ion exchange membranes would eliminate the graphite and
asbestos rubble associated with the rebuilding of conventional diaphragm
cells. Also, the generation of chlorinated hydrocarbon wastes would
be virtually eliminated. The estimated solid-residue streams are given
below:
Solid-Residue Stream lb/1000 Ib of Chlorine
Brine purification sludge 63.0
Cell-rebuilding waste 1.0
Total 64,0
Summary
The process options proposed for this industry may be considered
improvements on the basic diaphragm cell electrolysis. As such, they
do not reduce the major volumetric source of solid residue (brine
purification), but they do have a significant beneficial effect on the
smaller, but potentially more serious contributors to the total solid-
residue load: the chlorine purification waste (chlorinated organics)
and the cell-rebuilding waste (asbestos). These effects, coupled with
the energy savings achievable by the use of modified cells, suggest
that, while solid residues will not be a determining factor in advance-
ment and/or selection of process options and are not large in national
impact in spite of the industry's high production, such approaches
should be encouraged, recognizing that the potential beneficial effects
are achieved in a somewhat circuitous manner.
A comparison of the solid-residue streams generated by the base
case technology and its process options is presented in Table 20.
Since the quantity of brine purification sludge is the same in all
cases, it has not been included in the comparison.
PHOSPHORUS/PHOSPHORIC ACID INDUSTRY
Furnace Acid - Electric Furnace Production of Phosphorus and Conversion
of Phosphorus to Phosphoric Acid
Base Case Solid-Residue Disposal—
Phosphate rock is mined in Florida, Tennessee, and North Carolina,
and in the Mountain States of the West. It is converted to commercial
end-products either by digestion with sulfuric acid to produce phos-
phoric acid (the "wet process"), or by reduction to elemental phosphorus
in an electric furnace. Most of the phosphorus from the electric furnace
is burned in air and the oxides absorbed in water to form phosphoric acid.
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TABLE 20. SOLID-RESIDUE DISCHARGE FROM CHLOR-ALKALI PRODUCTION
Process
Estimated discharge factor*
(ton/ton of chlorine)
brine
purification
sludge other
Estimated
change in
discharge factor
Solid-residue
discharge
(10 ton/yr)
total (ton/ton of chlorine) 1974 1989-1974
-**
OD
Graphite anode diaphragm
cell
• Use of dimensionally
stable anodes
• Use of modified diaphragms:
Polymer-modified asbestos
Polymer membrane
Ion exchange membranes
0.063 0.00385 0.0669
0.063 0.0012 0,0642
0.063 0.0012 0.0642
0.063 0.001 0.064
0.063 0.001 0.064
- 0.00265
- 0.00265
- 0.00285
- 0.00285
0.736 0.796
0.764
0.764
0.762
0.762
Estimated 1974 discharge based on multiplying discharge factor by 1974 production of chlorine:
11.0 million tons.
**
Based on increment in production of chlorine from 1974 to 1989: 11.9 million tons.
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Although phosphoric acid is the principal commercial end-product
of each of the two methods, there is an important difference in the
purity of the acid obtained. Phosphoric acid produced via the electric
furnace process is essentially a pure chemical that is suitable for
detergent, food, and fine chemical uses. Wet process phosphoric acid
is not pure; it is suitable for fertilizer manufacture, but not for
most other purposes without cleanup.
The key issue in this whole analysis is the fact that the manufacture
of phosphoric acid via the electric furnace process has an energy con-
sumption per unit of product that is approximately 5 times that of the
wet process. There is, therefore, an incentive to modify the wet process
in order to produce phosphoric acid that has a level of purity equivalent
to that produced by the electric furnace process.
In the electric furnace process (which is described in detail in
Volume XIII, pages 22-34) the phosphate rock is first fed to a direct-
fired rotary kiln where it is heated to a temperature of incipient
fusion. It is then processed through a screening operation to a suitable
size range. The kiln gases must be scrubbed to remove dust and fluorides
present in the phosphate rock. The other raw materials, coke and silica,
are also dried before they are fed, along with the prepared phosphate
rock, into the electric arc furnace. The phosphorus is produced as
gaseous P, and is then condensed as a liquid. The production of phos-
phorus and its conversion to phosphoric acid usually occur at different
locations. The most common practice is to ship the liquid phosphorus
to the point of end-use where it is then converted to phosphoric acid
on site.
There are a number of solid-residue streams produced by the overall
production of phosphoric acid via the electric furnace process:
Slag - Large quantities of slag are produced by the electric furnace
process. Slag is generated at an estimated rate of 7.2 tons per ton of
P . The slag is sold as a construction, material and, therefore, does not
become a waste stream destined for disposal.
Wastewater Treatment Sludge - Both the phosphorus manufacturing
plant and the phosphoric acid conversion plant produce a variety of
wastewater streams which must be treated for the removal of phosphorus,
phosphates, fluorides, acidity, and trace heavy metals. The most likely
form of treatment is lime precipitation which produces a wet sludge con-
taining calcium phosphate, phosphorus, calcium fluoride, calcium sulfate,
and a variety of other constituents. We estimate that wastewater treat-
ment sludge from the production of phosphorus and phosphoric acid is
generated at a rate of approximately 0.34 ton per ton of phosphoric acid
(as P0).
79
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Care should be taken to dispose of the sludge in an environmentally
acceptable manner. The presence of elemental phosphorus and trace
arsenic compounds car result in the low-level occurrence of volatile
species such as the phosphorus oxides and arsine, depending upon the
chemical environment.
Process Option 1 - Wet Process Production of Phosphoric Acid Followed
by Chemical Cleanup—
As previously stated, there are a number of impurities in wet-process
phosphoric acid which make it unsuitable for use as detergent phosphate.
These impurities include calcium chloride, iron and aluminum salts,
carbon and organic matter, and small quantities of a number of heavy
metals, such as magnesium, chromium, titanium, manganese, copper, zinc,
arsenic, vanadium, and uranium. The acid is saturated in calcium
sulfate and has a high content of fine suspended solids. It is dif-
ficult to remove these impurities to the degree necessary to meet
specifications for food grade or fine chemical phosphate use, A major
outlet for phosphoric acid, however, is in the form of sodium tripoly-
phosphate (STPP), which is used in the manufacture of detergents. Wet
process acid can be purified to the degree necessary for this product
by a two-stage neutralization cleanup process (see Volume XIII, page 48).
The overall process produces three major solid residue streams:
(1) the gypsum sludge from the primary leaching of phosphate rock with
sulfuric acid; (2) the wastewater treatment sludge produced in the
treatment of gypsum pond overflow water; and (3) the impurities removed
by the two-stage neutralization cleanup step.
Gypsum Sludge - On a dry basis, approximately 3.5 ton of gypsum
(CaSO.H 0) are produced per ton of phosphoric acid as P«0 (Reference 2).
The gypsum is typically stored in huge impoundments which also serve as
water recirculation reservoirs. A substantial fraction of the fluorine
originally present in the phosphate rock is discharged along with the
gypsum as sodium silicofluoride. This stream also contains free phos-
phoric acid and is slightly acidic.
Wastewater Treatment Sludge - Since most phosphoric acid plants
are located in regions of net precipitation, most gypsum ponds overflow,
thereby producing a wastewater stream that must be treated prior to
discharge. The wastewater must be treated with lime both to neutralize
acidity and precipitate soluble phosphates and fluorides. The rate of
sludge generation is estimated to be 0.91 ton per ton of phosphoric
acid as P20 (calculated from Volume XIII, page 39).
Impurities from the Two-Stage Neutralization Cleanup Step - The
impurities from the two-stage cleanup steps consist of filter cakes
containing sodium silicofluoride in both the liquid and solid phases,
phosphoric acid, calcium sulfate, ferric phosphate, aluminum phosphate,
and trace quantities of heavy metals. We estimate that this total waste
80
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stream will be generated at a rate of approxlmatley 0.70 ton per ton
of product as P^O,. (calculated from Volume XIII, page 55),
The total solid-residue discharge from the wet-process production
of phosphoric acid followed by chemical cleanup is given in Table 21.
Process Option 2 - Wet Process Production of Phosphoric Acid Followed
by Solvent Extraction Cleanup—
In this process (described in detail in Volume XIII, pages 60-71),
phosphate rock is dissolved in hydrochloric acid rather than in sulfuric
acid. The crude phosphoric acid thus produced is subjected to a solvent
extraction step in which the phosphoric acid is transferred from solution
in an aqueous phase to solution in an organic phase, such as normal
butanol, leaving behind undesirable impurities, such as calcium chloride,
in the aqueous phase. The organic phase can then be contacted in a
separate unit with fresh water to yeild a pure solution of phosphoric
acid. The calcium chloride brine initially separated from the extraction
step also contains hydrochloric acid and solvent which must be recovered.
Since the process is still in the developmental stage, some of
the solid-residue streams are not accurately quantified. The most
significant difference with respect to solid waste is that a large
volume concentrated calcium chloride brine stream (generated at an esti-
mated rate of 1.65 ton of CaCl per ton of phosphorus, Volume XIII,
page 65) is substituted for a large fraction of the solid gypsum stream
produced by the conventional sulfuric acid leaching process. Undissolved
inorganic solids separated from the digester liquor would be impounded
in much the same way as in the conventional process. Since much of
the solid residue has been converted to calcium chloride brine, the
size of the impoundments would be considerably smaller.
Impoundment overflow would have to be treated in much the same
way as in the conventional process, i.e., via lime treatment to neutralize
acidity and to precipitate fluorides, phosphates, and other inorganics.
We expect that this sludge will be generated at a rate that is the same
as that for the conventional sulfuric acid leaching process — 0.91 ton
per ton of phosphoric acid as P~0 (calculated from Volume XIII, page 68).
It should be noted that solvent (normal butanol) losses within the
process will eventually appear in the liquid fraction of the sludge.
If solvent losses are severe, the liquid fraction of the sludge could
exert a significant biochemical oxygen demand.
This entire process presents serious water pollution control
problems.
Process Option 3 - The Use of Byproduct Sulfuric Acid—
A conventional wet process plant for phosphoric acid consists of
81
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TABLE 21. SOLID-RESIDUE DISCHARGE FROM WET-PROCESS
PRODUCTION OF PHOSPHORIC ACID
Generation rate
(ton/ton of phosphoric acid)
Solid-residue stream _ §s_P
Gypsum sludge 3.5
Wastewater treatment sludge 0.91
Impurities from cleanup process 0.70
Total 5.11
82
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two distinct process units. In the first, sulfur is converted to sul-
furic acid; in the second, sulfuric acid is used as a reagent to convert
phosphate rock to phosphoric acid. Sulfur is a major element of the
production of phosphoric acid; and at the right price, a phosphoric
acid producer would be tempted to use byproduct sulfuric acid (obtained
largely from electrical power plant sulfur dioxide control systems) in
place of the sulfur.
While the use of byproduct sulfuric acid will eliminate that part
of the pollution problem associated with an on-site sulfuric acid plant,
it will have a negligible effect on both the quantity and characteristics
of the solid residue produced in the manufacture of phosphoric acid.
Process Option 4 - Strong Phosphoric Acid Processes—
Although these processes (described in detail in Volume XIII,
pages 73-75) provide certain operational and economic advantages, it
is not apparent that they influence the solid-residue disposal problems
one way or another.
Summary
Anticipated growth in the detergent industry can be expected to
require significant growth in "clean" high-grade phosphoric acid.
The present manufacture of high-grade phosphoric acid via the electric
furnace process produces two solid-residue streams: slag, which is
sold as a construction material, and wastewater treatment sludge. The
wastewater treatment sludge contains calcium phosphate, phosphorus,
calcium fluoride, calcium sulfate, and a variety of other constituents.
Although the process option involving the chemical cleanup of wet
process phosphoric acid offers significant energy advantages, it produces
a gypsum sludge, a wastewater treatment sludge, and impurities from
the cleanup step. The overall process results in a 13-fold increase
in the base case solid-residue generation rate.
The process option involving wet process production of phosphoric
acid followed by solvent extraction cleanup produces a far smaller
solid-residue stream than the chemical cleanup process option, but does
so partially by producting a large concentrated brine stream. Small
amounts of organic solvents may be present in the solid residue.
Since the base case electric furnace process relies on coal (coke)
rather than on oil or gas, there may be no incentive for developing
or encouraging the alternate, more polluting process. Of course, a
complete analysis must also include the incremental solid residues
generated at the electric power plant.
The use of purchased by-product sulfuric acid instead of on-site
generation of sulfuric acid may come about based on economics alone,
83
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but it does not appear that solid residue or its control will be a
deciding factor. Again, the pollution generated by a power plant to
produce the steam needed for the wet-acid process and now supplied as
a "byproduct" of the sulfuric acid manufacture may, at some future
time, also become a factor.
A comparison of the on-site waste discharges is presented in
Table 22.
PRIMARY COPPER INDUSTRY
Manufacture of Copper by Conventional Smelting and Refining of Concentrates^
Base Case Solid-Residue Disposal—
Copper extraction from sulfide ores is traditionally divided into
four segments:
• Mining - where ore containing 0.6 to 2% copper is mined;
• Beneficiation - where the copper-containing minerals are
separated from the waste rock to produce a concentrate
containing about 25% copper;
• Smelting - where concentrates are melted and reacted to
produce 98% pure "blister" copper or "anode" copper
(copper 98 to 99% pure requiring further refining); and
• Refining - where blister copper is refined electrolytically
to produce 99.9% pure "cathode" copper.
The energy-related process changes considered affect only the
smelting and refining portion of copper extraction; therefore, con-
ventional smelting and refining is the base case against which potential
process alternatives have been compared in order to evaluate pollution
and energy consequences of these process alternatives.
Conventional smelting of sulfide concentrate involves the smelting
of concentrates in a reverberatory furnace either directly (green
charge smelting) or after roasting (calcine smelting). The mixture
of molten sulfides from the reverb is converted to blister copper in
converters.
Conventional electrorefining purifies the smelter output to cathode
quality copper. A detailed description of the conventional smelting
and refining processes is presented in Volume XIV, Appendix A.
There are three major solid-residue streams generated by the
conventional smelting and refining of copper, which are described
below:
84
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TABLE 22. SOLID-RESIDUE DISCHARGE FROM PRODUCTION OF PHOSPHORUS/PHOSPHORIC ACID
oo
Process
Estimated
discharge factor
(ton/ton of phos
phoric acid (as
Base case:
Electric furnace production
of phosphorus and conversion
to phosphoric acid
• Wet process production of
phosphoric acid followed by
chemical cleanup
• Wet process production of
phosphoric acid followed by
solvent extraction cleanup
• Use of byproduct sulfuric
acid
• Strong phosphoric acid
process
Estimated
change in
discharge factor
(ton/ton of phos-)
phoric acid (as P^
Solid-residue
discharge
(10b ton/yr)
1974 1989-1974
0,34
5.11
0.91 (minimum;
could be greater)
Same as conventional
wet process plant
Same as conventional
wet process plant
+ 4.77
+ 0.57
0.476
0.214
3.219
0.573
Based on increment in detergent-grade phosphoric acid from 1974 to 1989: 0.63 million tons.
**
Estimated 1974 discharge based on multiplying discharge factor by 1974 detergent-grade
phosphoric acid: 1.4 million tons.
-------
Slag - Slag is produced in the converter and, after being recycled
back to the reverberatory furnace to recover its copper content, it
is removed from the reverberatory furnace and disposed of as an inert
rock. The slag is mainly an iron silicate, containing about 0.5 to 0.9%
copper and small quantities of heavy metals including arsenic, antimony,
bismuth, mercury, lead, zinc, selenium, and tellurium.
Large quantities of slag are produced. On the average, slag is
generated at a rate of approximately 3 ton per ton of copper produced
(Volume XIV, page 26).
Dust Bleed - Flue dusts result from entrained particles and con-
denses effluents in the gas stream. Typically 3 to 6% of the total
weight of solids entering the smelter is evolved as dust. All flue
dusts contain copper oxides. Most of the dust is collected by air pol-
lution control devices and then recycled to the reverberatory furnace.
Since the dust contains impurities, it is not possible to operate in
a total recycle mode, and, therefore, a portion of the dust must be
bled from the system. At times, it is economical to process these
dusts further in order to recover such metals as zinc, lead, etc.
Depending on the composition of the feed, a fraction of the dust
generated may be diverted and either sold to other specialized smelters
or disposed of as a solid waste. The amount of dust destined for ulti-
mate disposal is estimated to be 0.02 ton per ton of copper (Volume XIV,
page 39).
Wastewater Treatment Sludge - In the smelting of copper three major
wastewater streams are generated, slag granulation water, acid plant
blowdown, and anode casting wastewater. The wastewater is acidic,
contains high amounts of suspended solids, and also contains heavy
metals. The recommended means of treatment for meeting the 1983
effluent guidelines includes neutralization and sedimentation, both of
which produce a waste sludge. The sludge from such a treatment system
would contain calcium sulfate and a variety of other inorganic substances.
The estimated rate of wastewater treatment sludge generation is
0.09 ton per ton of copper (calculated from Volume XIV, page 36).
The total solid-residue streams are given in Table 23.
Process Option 1 - Outokumpu Flash Smelting—
Flash smelting (described in detail in Volume XIV, pages 41-44)
combines the separate roasting and smelting operations of conventional
copper extraction into a combined roasting-smelting process. The heat
generated by the exothermic roasting reactions can be used for smelting
so that little or no extraneous fuel is needed. A characteristic of
this method is that fine-grained concentrates are used and the smelting
takes place in suspension, which allows for rapid reaction rates. The
major advantage of the method is a reduction in fuel used for smelting
and the production of a stream of gas high in SO which is suitable for
86
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TABLE 23. SOLID-RESIDUE STREAM GENERATION RATES (COPPER)
Generation rate
Solid-residue stream (ton/ton of copper)
Slag 3.0
Dust bleed 0.02
Wastewater treatment sludge 0.09
Total 3.11
87
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sulfuric acid manufacture. The Outokumpu flash smelting process produces
the same quantity of slag and bleed dust as the conventional smelting
and refining of copper.
Since the water pollution control problems are similar to those
of a conventional smelter, it is reasonable to assume that if the same
recommended treatment technology is applied to the Outokumpu process,
the same quantity of wastewater treatment sludge would be generated.
Process Option 2 - The Noranda Process—
The Noranda process combines the three operations of roasting,
smelting, and converting of copper concentrates in a single reactor.
The heat losses suffered during the transfer of concentrate from the
roaster to the reverberatory furnace are suppressed, as well as the
heat losses occurring during the transfer of matter from the reverberatory
furnace to the converter. In addition, the net heat of oxidation is
used for smelting. A detailed process description is presented in
Volume XIV, pages 55-70.
The quantity and composition of the solid-residue streams are
expected to be very much the same as for the base case conventional
smelting and refining process.
Process Option 3 - The Mitsubishi Process—
The Mitsubishi process consists of three metallurgical stages,
each of which is carried out in a separate furnace, Thus, there is
a smelting furnace for concentrates, a converting furnace to oxidize
iron in the matte and make blister copper, and a slag-cleaning furnace.
Intermediate products in the molten state move continuously among the
respective furnaces which are thus functionally connected with each
other. A detailed process description is presented in Volume XIV,
pages 71-81. The Mitsubishi process has many of the same energy-
conserving advantages as the Outokumpu and Noranda processes.
The quantity and characteristics of the solid-residue stream from
the Mitsubishi process are expected to be very much the same as for
the base case conventional smelting and refining process.
Process Option 4 - The Use of Oxygen in Smelting—
Copper smelting can be conducted with pure oxygen or by using
oxygen-enriched air. Reasons for using oxygen or oxygen enrichment
include:
• Increasing processing temperatures and process heat rates;
• Decreasing the nitrogen content of the flue gases (when
high SO concentrations are needed) and increasing fuel
88
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efficiency (particularly where waste heat is not recovered);
and
• Increasing the specific capacity of furnaces so that
production of metal is increased for a given size of
reactor.
The quantity and characteristics of the solid-residue streams
from a conventional plant are not changed by the use of oxygen in
smelting.
Process Option 5 - Metal Recovery from Slag—
In conventional copper smelting, converter slag is recycled to
the reverberatory furnace, and all of the slag tapped from the rever-
beratory furnace is discarded. The copper contained in this discarded
slag is lost. The amount of copper lost with the slag is quite signi-
ficant, about 1.5 to 3% or more of the copper in the feed materials.
Slag can be recovered by two methods: (1) flotation, and (2) slag
cleaning in electric furnaces.
Flotation - In flotation the slag is ground in the presence of acid,
and copper is recovered via froth flotation. This process converts the
slag into fine particles which are then disposed of as a wet slurry into
a tailings pond. The water from the tailings pond is recycled.
While the overall quantity of slag is not radically different from
that for the base case conventional smelter, the slag is now in the
form of very fine particles mixed with water rather than large dry
particles. The effect of this change is to make control more complex/
costly.
Slag Cleaning in Electric Furnaces - The mechanism by which slag
can be recovered in electric furnaces is discussed in Volume XIV, pages
93-95. Aside from reducing the copper content of the slag, this practice
does not alter the quantity or the nature of the base case solid-residue
streams. If anything, the removal of the copper is beneficial in that
potential copper leaching is reduced.
Process Option 6 - The Arbiter Process—
The Arbiter process is one of several potentially applicable hydro-
metallurgical copper extraction techniques. The basic process (described
in detail in Volume XIV, pages 95-106) consists of five separate stages
for the treatment of copper concentrates. The copper conrpntraf.e slurry
is first leached with aqueous ammonia and oxygen. The pregnant
solution, after separation of leached solids is sent to a solvent
extraction step where copper is selectively extracted with an organic
reagent to form a copper-loaded electrolytic solution. Copper is
89
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recovered from the solution via conventional electro-winning. The
actual process entails a large number of rather complex material
recycle circuits and purification steps.
The Arbiter process produces two major solid-residue streams:
gypsum sludge and leach residue.
Gypsum Sludge - During this process, ammonia is recovered from
spent ammonium sulfate streams by boiling with lime to yield ammonia
and gypsum (calcium sulfate). The gypsum sludge forms a major solid-
residue stream. It is estimated that gypsum sludge is generated at
rate of 4.5 dry ton per ton of copper produced in the form of a slurry.
a
Leach Residue - The process produces a leach residue containing
iron oxide, silica, pyrites, bismuth, sulfides, lead, arsenic, and
other metals. Its estimated generation rate is 1.3 dry ton per ton of
copper produced.
These two waste streams would require storage in lined ponds with
a wet top surface to prevent dust emissions during the period the pond
is in use and proper cover after the pond is after the pond is abandoned.
Summary
The manufacture of copper by conventional smelting and refining of
concentrates produces three major solid-residue streams: slag, dust
bleed, and wastewater treatment sludge.
The Outokumpu flash smelting process, the Noranda process, the
Mitsubishi process, and the use of pure oxygen do not significantly
alter the quantity or composition of the solid-residue generated by
the base case technology.
Metal recovery from slag will only slightly decrease the base
case solid-residue generation rate.
The Arbiter process produces very large quantities of gypsum
sludge which is generated at a rate almost twice that of the total
base case solid-residue stream, plus a leach residue high in metals
but low in quantity.
A comparison of the solid-residue discharges between the base case
and its process options is presented in Table 24.
The alternate pyrometallurigcal process suggested in this study
(Outokumpu, Noranda, and Mitsubishi) can be expected to play increasingly
large roles in the evolution of the industry but the driving forces will
be energy conservation and SO control benefits rather than solid-residue
aspects, which are not changed significantly. Use of oxygen and copper
recovery from slag will, similarly, advance for reasons other than their
impact on solid waste.
90
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TABLE 24. SOLID-RESIDUE DISCHARGE FROM PRODUCTION OF PRIMARY COPPER
Estimated Solid-residue
Process
Base case:
Conventional smelting and
refining of concentrates
• Outokompu flash smelting
• Noranda process
• Mitsubishi process
• Use of pure oxygen in smelting
• Metal recovery from slag
• Arbiter process
Estimated
discharge factor
(ton/ton of copper)
3.11
3.11
3.11
3.11
3.11
3.11
5.8
change in discharge
discharge factor (10 ton/yr) ^
(ton/ton of copper) 1974
**
0 4.976
0
0
0
0
slight decrease
2.69
1989-1974
3.420
3.420
3.420
3.420
3.420
3.420
6.380
**
Based on increment in production of copper from 1974 to 1989: 1.1 million tons.
Estimated 1974 discharge based on multiplying discharge factor by 1974 copper production:
1.6 million tons.
-------
On the other hand, hydrometallurgical processes, such as the
Arbiter process, have not proven out to offer the expected energy
advantages and do generate large volumes of sludge and leach residue
which will require controlled disposal.
FERTILIZER INDUSTRY
The Manufacture of Nitric Acid
Base Case Solid-Residue Disposal—
Of the major fertilizer production activities (excluding the pro-
duction of ammonia which is covered as a separate industry in Volume
VII), the manufacture of nitric acid poses the greatest number of
possible conflicts between energy conservation and pollution control.
The problem areas are in the control of gaesous nitrogen oxide emissions
rather than in the manufacturing process itself.
Nitric acid is an important material in the manufacture of fertilizer-
grade ammonium nitrate and explosives. The acid is produced by the
oxidation of ammonia, usually under high pressure and temperature,
over a platiunum catalyst, forming nitric oxide (NO). The gaseous pro-
ducts from the reactor and oxygen are cooled to form N09, and are then
sent to an absorption tower to form the acid product.
The only significant pollution problem resulting from the pro-
duction of nitric acid is the discharge of unabsorbed oxides of nitrogen
in the absorption tower tail gas. Other than the usual small quantities
of general industrial trash found in all manufacturing facilities,
no solid residue is generated by the production of nitric acid.
While each of the several processes available for the control of
nitrogen oxide emissions have significant energy and air pollution control
implications, none produce a solid-residue stream.
Mixed Fertilizer Plants
Base Case Solid-Residue Disposal—
The base case plant used in this analysis is an ammoniation granu-
lation plant (ammoniation of normal super phosphate) equipped with a
natural gas-fired dryer and baghouse filter to control particulate
emissions. There are no contaminated process wastewater streams, and
the collected particulates actually consist of product material and
are recycled back into the process. There are no solid-residue streams.
92
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Process Option 1 - Conversion from Natural Gas to Fuel Oil and Installation
of a Wet Scrubber for Air Pollution Control—
Due to the impending shortage of natural gas, there is an incentive
to convert drying operations from natural gas to fuel oil. When using
fuel oil, however, there is a tendency for baghouse filters to become
clogged with products of incomplete combustion. While it may be pos-
sible to alleviate this problem by modifying the combustion process
and achieving essentially complete combustion, in which case solid
waste generation would be the same as the base case. However, it is
likely that many plants would require a wet scrubber.
Even though it is possible to recycle scrubber water to a high
degree, a certain amount must be purged to prevent the excessive
buildup of dissolved solids. The scrubber water would contain ammonia,
chloride, fluoride, phosphate, and suspended solids. It would most
likely have to be treated with lime to precipitate the fluoride and
phosphate as calcium fluoride and calcium phosphate, and to convert
ammonium ions to ammonia gas*so that it could be stripped from the
wastewater by aeration. The wastewater treatment system would produce
a waste sludge, principally composed of calcium phosphate and calcium
fluoride, that would be generated at a rate of approximately 1.9 lb/
1000 lb of product fertilizer. Since it would contain phosphate and
fluoride, as well as some dissolved ammonia, care should be taken
in its disposal to avoid groundwater contamination.
Summary
The processes considered to control NO emissions from nitric acid
manufacture cover varying degrees of economic and energy benefits.
Different firms will undoubtedly select one or the other for instal-
lation over the coming years. However, solid waste is not generated in
any of them and should not be a factor in the decision.
The use of oil in the drying of granular fertilizer will probably
require the use of scrubbers in place of baghouse filters. The resul-
tant generation of lime sludge containing fluoride and other pollutants
and the added cost of the scrubber and lime treatment system may be a
deterrent to such fuel switching by the industry. However, the problem
is not one of major national significance and probably should not have
high priority.
The solid-residue discharge from the selected segments of the
fertilizer industry are presented in Table 25.
* Ammonia in solution.
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TABLE 25. SOLID-RESIDUE DISCHARGE FROM FERTILIZER PRODUCTION
Process
Estimated
change in
discharge factor
ton/ton product
Estimated
change in
discharge factor
ton/ton product
Solid-residue
discharge
(10° ton/yr)
1974
1989-1974
Base case:
Nitric acid manufactur
without NO control negligible
X
• Catalytic reduction negligible
• Molecular sieve negligible
• Grand paroisse negligible
• CDL/Vitak negligible
• Masar negligible
Base case:
Mixed fertilizer plants with
natural gas-fired dryers negligible
• Better equipment with fuel oil
technique negligible
• Conversion from natural gas to
fuel oil (installing scrubbers) 0.0019
0.0019
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0125"
Based on increment in production of fertilizers from 1974 to 1989: 6.6 million tons.
-------
REFERENCES
U.S. Environmental Protection Agency, "Characterization of Sulfur Recovery
from Refinery Fuel Gas," EPA-450/3-74-055, 1974, p. 36.
U.S. Environmental Protection Agency, "Development Document.,.Basic
Fertilizer Chemicals," EPA-440/l-74-011-a, March 1974, p. 33.
Bureau of Mines, U.S. Department of Interior, Commodity Data Summary, 1977.
95
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing/
1. REPORT NO.
EPA-600/7-79-161
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Environmental Considerations of Selected Energy-
Conserving Manufacturing Process Options
Volume XIX Solid Residues Summary Report
5. REPORT DATE
August 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Arthur D. Little, Inc.
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arthur D. Little, Inc.
20 Acorn Park
Cambridge, MA 02140
10. PROGRAM ELEMENT NO.
1NE 624B
11. CONTRACT/GRANT NO.
68-03-2198
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Under EPA Contract No. 68-03-2198, Arthur D. Little, Inc. undertook a study
of the "Environmental Considerations of Selected Energy-Conserving Manufacturing
Process Options." Some 80 industrial process options were examined in 13 industrial
sectors. Results were published in 15 volumes, including a summary, industry
prioritization report and 13 industry oriented reports (EPA-600/7-76-034 a through
o).
This present report summarizes the information regarding solid residues in
the 13 industry reports. Four parallel reports treat sulfur oxides, nitrogen
oxides, particulates, and toxics/organics. All of these pollutant oriented
reports are intended to be closely used with the original 15 reports.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Energy, Pollution, Industrial Wastes
b.lDENTIFIERS/OPEN ENDED TERMS
Manufacturing Processes,
Energy Conservation
c. COSATI I ield/Group
68D
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
104
20. SECURITY CLASS {This page/
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
96
.-,-US GOVERNMfNl PRINTINGOFFICf 1979-667-060/5407
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