EPA'S COAL CLEANING PROGRAM
STATUS AND STRATEGY
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600R77013
EPA'S COAL CLEANING PROGRAM
STATUS AND STRATEGY
James D. Kilgroe
Fuel Process Branch
Energy Assessment and Control Division
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Review Notice
This report has been reviewed by IERL/RTP, and approved for distribution
within EPA. Approval does not signify that the contents necessarily
reflect the views and policies of the Agency, nor does the mention of
trade names or commerical products constitute endorsement or recommendation
for use.
March 1977
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I'S COAL CLEANING PROW: STATUS ANH STRATEGY
INTRODUCTION
Sulfur oxide air pollution emissions from coal combustion exceeded 20.5
million tons in 1974. With the increasing use of coal as an energy source,
improved methods are needed for the control of this pollutant. Major strategies
for the control of SO- emissions include the use of coal cleaning, the combustion
of coal in chemically active fluidized beds, the removal of pollutants by flue
gas scrubbing and the generation of clean synthetic fuels. An economically
attractive control strategy is coal cleaning. This paper presents the current
status of coal cleaning technology, and discusses barriers which must be over-
come before this technology can be widely implemented for S0_ emission control.
TECHNICAL STATUS
Coal Cleanability
The sulfur content of coal normally ranges from less than 1 to more than 7
percent. Sulfur appears in coal in three forms: mineral sulfur in the form of
pyrite (FeS_), organically bound sulfur and trace quantities of "sulfate" sulfur.
Sulfate sulfur occurs in coal as a result of the attack of oxygen on the mineral
pyrite. It is soluble in water and can be removed in wet coal preparation
plants. Organic sulfur occurs as part of the organic coal structure and cannot
be removed by physical coal preparation techniques. Pyrite occurs in coal seams
in sizes ranging from small discrete particles to large lumps. It can be found
intimately dispersed in the coal substance, in bands, in layers or in large
pieces.
Physical preparation or cleaning techniques are capable of removing varying
fractions of the coal pyritic sulfur as determined by the properties of each
coal. Chemical processes are capable of removing over 95 percent pf the pyritic
sulfur and up to about 70 percent of the organic sulfur.
Laboratory float-sink studies have..been performed on over 455 U.S. coals to
determine their physical cleanability. *• * The samples tested were from mines- in
the six major coal producing regions of the U.S., the mines which provide more
than 70 percent of the coal used in U.S. utility boilers.
The results of these float-sink tests indicate that in general pyrite
removal increases with reduced particle size and specific gravity of separation.
This fact is extremely important. It implies that to enhance pyritic sulfur
removal more of the coal must be crushed and and processed at finer particle sizes
than historically practiced in coal preparation. A second important fact
determined by these studies is that the final sulfur levels to which coals can
Superior numbers refer to similarly numbered references at the end of this paper.
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be cleaned vary from coal region to coal region and from one coal bed to another
within the same region (coal cleanability also varies to a lesser extent from
location to location within the same mine). These differences in physical
cleaning potential are the result of variations in the organic and pyritic
sulfur levels and the morphology of the coal-pyrite matrix.
Sulfur removal by chemical methods is dependent upon coal properties and
process conditions—time, pressure, temperature, and., chemical reagents. A number
of experimenters have studied these relationships ^ ^ . In other instances the
availability of information is limited because it is considered to be proprietary.
Process costs will probably limit the amount of sulfur which can be removed to
about 95 percent of the pyritic sulfur and 40 percent of the organic sulfur.
Figure 1 presents parametric relationships between the degree of cleaning
(pyritic and organic sulfur reduction), the sulfur level of the cleaned coal and
the percentage of utility coals which can be cleaned to a specified sulfur content.
Coal Cleaning Costs
The costs of physical and chemical coal cleaning for sulfur removal are
to a large extent undefined. Physical cleaning has traditionally been used to
remove ash and mining residues from coals. There is virtually no data correlating
costs and sulfur removal in commercial coal cleaning equipment. However, sub-
stantial data exists on the costs of cleaning for ash removal. Using this data
one can deduce the costs of sulfur removal from correlations between ash and
sulfur removal in commercial equipment. While these correlations are few and
tenuous they do provide estimates which indicate that in many cases physical coal
cleaning will be a more cost effective emission control technique than flue
gas desulfurization CFGD). However, physical cleaning is not a panacea since
it cannot remove organic sulfur from coal or in some cases sufficient pyritic sulfur.
Chemical coal cleaning is capable of removing nearly all the pyritic sulfur
and a substantial fraction of the organic sulfur. However, chemical cleaning
is more costly than physical cleaning. Costs for its use may range from the
costs of FGD to the costs of producing synthetic fuels from coal. Further
because of its early state of development the stated costs for chemical cleaning
coal are less certain than those for physical cleaning.
Cost estimates for physical coal cleaning, chemical coal cleaning and FGD
are presented in Table 1. The wide range in costs results from different
site specific factors, such as coal cleanability, plant capacity, and sulfur
emission regulation, which must be accounted for. While a detailed dis-
course of costs is beyond the scope of this paper one must conclude that for
.those instances where physical cleaning is applicable it will be more cost
effective than FGD. One cannot currently draw conclusions on the applicability
of chemical coal cleaning as an SCL emission control method based solely upon
economic arguments. These costs must first be placed upon a firmer foundation
by additional research, development and demonstration activities.
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LU
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100
80
FEDERAL EPA STANDARD *(1.2 LB S00/MM Btu)
40
20
DATA SOURCE:
ASSUMING 12.500 Btu/lb.
COAL MUST BE CLEANED TO
0.75% S TO MEET FEDERAL
NEW SOURCE STANDARDS FOR
STEAM GENERATORS.
U.S. BUREAU OF MINES
(REPORT OF INVESTIGATION 7633)
0.75 1.0 2.0 3.0
SULFUR CONTENT, PERCENT
4.0
5.0
POTEWTiAL LEVELS OF DESULFUREATION FOR U.S. UTILITY COALS.
Figure 1
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TABLE 1
COMPARATIVE TECHNOLOGY COSTS
Sulfur
Capital Operating Total Removal Energy
Costs Cost Annualized Costs Efficiency Penalty
($/kW) (mills/kWh) (mills/kWh) (%) (%)
FLUE GAS DESULFURIZATION
Regenerablea 70-85b 2.5-3.6c'e 4.0-5.4° >85 ^5
(Sodium or Magnesium)
' Nonregenerablea 60-70b 2.1-2.2c'e 3.4-3.7C >85 -v3
COAL CLEANING 9.3-22.1 0.15-1.19d 1.2-2.4d 30-50 3-10
a. 500 MW, new plant, using 3.5% sulfur coal, 90% SO- removal.
b. Average cost basis for 1977 dollars, includes sludge disposal pond with clay liner.
c. Average cost basis for 1978 dollars, amortized over 30 years, power unit on stream
7000 hrs/yr, investment and revenue requirements for disposal of fly ash excluded.
d. Assume 3960 operational hours/year, 10,000 BTU's/kWh, and 11,000 BTU/lb for g
Eastern coal, 5% coal cleaning BTU loss, and coal energy cost of $0.6 per 10 BTU.
e. Calculated from annualized cost data assuming a 15 percent rate of return (with
adjustment for depreciation, taxes, replacement, and insurance.)
Status of Coal Cleaning Technology
Coal preparation processes for steam coal are oriented toward the removal of
ash and mining residue. Chemical coal cleaning is in the early stages of develop-
ment and it is estimated that a commercial plant could not be put into operation
for at least 5 to 10 years. Figure 2 summarizes several chemical coal cleaning
processes now under development. The remaining discussions will deal primarily
with the use of physical coal cleaning as an S0? pollution control method.
The physical removal of pyritic sulfur from steam coal has not been commercially
used as a method of S0? emission control. The physical removal of pyrite from
many coals will require crushing to fine particle sizes prior to separation.
Separation at these fine sizes while not impossible represents a shift to a mix
of equipment and operating conditions which is different from those traditionally
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PROCESSES UNDER
DEVELOPMENT
DESCRIPTION
MAX, SULFUR
REDUCTION, PERCENT
PYRITIC
ORGANIC
STATUS
ARCO
BATTELLE
HYDROTHERMAL
ERDA,.BRUCETON,PA
TRW
CATALYTIC DEMETALLIZATION
CAUSTIC LEACHING
[NaOH-Ca(OH)2]
OXI-DESULFURIZATION
(AIR-STEAM)
AQUEOUS FERRIC SULFATE
LEACHING [Fe2(S04)3]
95
95
99
40
40
40
95
NIL
LABORATORY
EXPERIMENTS
0.25 tpd
MINI-PLANT
LABORATORY
EXPERIMENTS; DESIGN
OF CONTINUOUS UNIT
LABORATORY
EXPERIMENTS;
CONSTRUCTION OF A
667LB/HR TEST UNIT
STATUS OF SELECTED CHEMICAL
' TREATMENT PROCESSES
Figure: 2
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used for steam coal preparation. Dewatering and drying of a large percentage of
fine coal may be required for many of the new plants.
The variability of sulfur forms within a coal bed or mine presents a special
problem which will require the development of improved technology if coal cleaning
is to be used for SCL emission control. Methods are needed for controlling the
sulfur variation in the plant feed, and process instrumentation is needed to
control the product sulfur level.
The coal preparation plant performance in removing pyritic sulfur can be
seriously affected by wide variations in feed coal properties. Development of
mining and blending schemes to minimize the pyritic sulfur variations in the feed
coal will be needed to insure a product coal which consistently meets fuel
sulfur requirements. Currently there is little published data on the variability
of fuel sulfur forms in coal beds. The effects of mining, blending and prepa-
ration plant operations in "averaging out" the cleaned coal sulfur level are
unknown. Because of these factors, the cleaning plant must now be designed to
remove sufficient pyritic sulfur so that even at peak raw coal sulfur levels
(both organic and pyritic) the product coal sulfur will be maintained below
that required by the fuel sulfur emission regulation. This approach may not be
practical in some cases as it would require the reject of large quantities of
fuel which do not exceed the emission regulation.
A long term objective would be to develop process instruments and controls
which could be used to adjust plant operating conditions in response to the
changes in the feed coal sulfur content. This method of control would allow
optimization of sulfur removal and BTU recovery. Unfortunately instruments which
can be used for a real time determination of coal sulfur, ash and BTU values are
not commercially available.
Options for Using Coal Cleaning
Physical coal cleaning can be used on a limited number of U.S. coals to meet
federal new source performance standards (NSPS) for steam generators. Moreover a
large number of coals can be physically cleaned and used:
1. To meet less stringent state SCL emission standards.
2. In conjunction with flue gas desulfurization (FGD) to lower
emission control costs.
3. To produce a multiplicity of product coal fractions, each with
a different fuel sulfur value.
Only 14 percent of the 455 U.S. coals tested by..the Bureau of Mines are
capable of meeting NSPS standards without cleaning1- . Physically cleaned at a
top size of 1-1/2 in. and with a BTU recovery of 90 percent (10 percent of the
heat from the mined coal would be lost) a total of 24 percent of these coals
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PRODUCT
SAMPLES MEETING
EPA STANDARD,
PERCENT
A RAW COAL
B 1-1/2 INCHES TOP
SIZE, 90% Btu RE-
COVERY
C 14 MESH TOP
SIZE, 50% Btu RE-
COVERY
14
24
32
III I I J I L L I I I I I I
I I i I I I I
6 8 10 12 14 16 IS 20
. COAL POLLUTANT POTENTIAL, LB S02/106 Btu
22
24
EFFECT OF CLEANING VARIABLE OH
COAL POLLUTION. POTENTIAL FIGURE
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CUMULATIVE ANALYSES OF FLOAT UO PRODUCT FOR 3/8" TOP SIZE
COAL
REGION
NORTHERN-
APPALACHIAN
SOUTHERN
APPALACHIAN
ALABAMA
EASTERN
MIDWEST
WESTERN
MIDWEST
WESTERN
TOTAL U. S.
NO.
SAMPLES
227
35
10
95
44
44
455
PERCENT
Btu
RECOVERY
92.5
96.1
96.4
94.9
91.7
97.8
93.8
ASH
8.0
5.1
5.8
7.5
8.3
6.3
7.5
PYRITIC
SULFUR
0.85
0.19
0.49
1.03
1.80
0.10
0.85
TOTAL
SULFUR
1.96
0.91
1.16
2.74
3.59
0.56
2.00
-
POUNDS
SO /10s
Btu
2.7
1.3
1.7
4.2
5.5
0.9
3.0
CALORIFIC
COt/TEW, Sto ?
•PER POUND \
13,768
14,197
14,284
13,138
13,209
'
12,773
13,530
I
CO
U1V1SV1ARY OF THE PHYSICAL DE!
POTENTIAL OF COALS BY
TABLE'
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could meet NSPS. The percentage of coal which will be cleaned to NSPS levels
could be increased by either a reduction in the particle size of coal being
cleaned or a reduction in the BTU recovery value of the cleaned product. In the
latter case the reject coal could probably be used in a boiler with FGD. It
should be pointed out that the percentages given are based on existing coal
production and not on the quality of reserves. Additionally, the values are
nominal and do not account for the variability of sulfur in coal. Both of these
factors should tend to reduce the percentage of coals capable of meeting the NSPS.
A much larger percentage of coals are capable of meeting widely varying
state standards. Table 2 presents data on the amounts of pyritic sulfur
which can be removed from coal samples from six regions by cleaning at conditions
.typically used in commercial coal preparation plants for ash reduction. As
illustrated the average fuel sulfur values for the cleaned coals from these six
regions range from 0.9 to 5.5 Ib SCL/10 BTU. In all cases the BTU recovery
exceeds 91 percent. Many states have emission regulations which range from 2.0
to 5.0 Ib SCL/10 BTU and a large portion of the tested coals can be cleaned to
meet these regulations. Figure 3 presents the relationship between selected
cleaning conditions and the number of samples which can be cleaned to meet
specific emission standards.
The use of physical coal cleaning in combination with flue gas desulfuri-
zation (FGD) represents an approach where the advantages of each technique can
be used to minimize emission control costs while permitting the most effective
use of U.S. coal resources. A recent study on the use of a combination of
physical coal cleaning and flue gas desulfurization shows significant economic
advantages to this combined pollution control method. ' In 36 case studies
in areas where local regulations for SCL emissions vary from 1.2 to 1.6 Ib
SCL/10 BTU, the cost of using a combination of conventional coal cleaning and
flue gas desulfurization was 2 to 55 percent lower than flue gas desulfurization
alone for new plants and 10 to 60 percent lower for existing plants. The
arithmetic average for the cases cited showed costs which were about 30 percent
lower for new plants and 40 percent lower for existing plants.
An alternative strategy which would make greater utilization of our coal
resources would be to prepare (clean) coal in such a fashion that it is divided
into a number of fractions - each with a different sulfur content. Each coal-
fraction could thus be used in a different boiler to meet different sulfur
emission regulations. The multi-stream coal cleaning strategy being used at
the Pennsylvania Electric Company's (PENELEC) Homer City plant for the physical
desulfurization of coal is an example of this approach to pollution control.
At the Homer City plant, the product coals will include 800 tons per hour (tph)
of coal with an equivalent sulfur emission value of 4,0 Ib S02/10 BTU and 400 tph
'of coal with a sulfur emission value of 1.2 Ib SCL/10 BTU.
The production of multiple coal streams in commercial plants to produce
fuel for several non-utility markets has significant potential. Mine-mouth
preparation plants of advanced design could produce a number of product coals
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with different fuel sulfur levels. The lower sulfur fuels could be sold for
use in commercial or industrial boilers in which the scale of. operation makes
FGD uneconomical. The higher sulfur coals could be used in existing boilers
which are not subjected to stringent standards or they could be burned in large
boilers equipped with FGD systems.
EPA'S COAL CLEANING PROGRAM
IERL-RTP and its predecessor organizations have been involved in the
development of coal cleaning as an emission control technique since 1965.
R§D supported by these organizations has provided the data base for the
assessment of coal cleaning as an air pollution control strategy. The current
IERL-RTP coal cleaning program is structured under three main program headings:
(1) the assessment and development of coal cleaning as an air pollution
control technology; (2) the evaluation of pollution which results from coal
cleaning processes and (3) the development of improved pollution control techniques
for coal cleaning processes.
In addition to the management of contract work, IERL-RTP is responsible
for directing cooperative interagency work with the Department of Interior (U.S.
Bureau of Mines and U.S. Geological Survey) and the Energy Research and Devel-
opment Administration. Total support for these interagency programs from FY 75
to FY 77 has exceeded $3.9 million. These programs have encompassed more than
20 individual projects. Principal contract work now directed by IERL-RTP
includes: a coal cleaning demonstration test and evaluation program at
PENELEC's Homer City Power Complex; the construction and operation of the
TRW chemical coal cleaning reactor at Capistrano, California; a project assessing
pollutant emission from commercial coal cleaning plants; and a project evaluating
the performance of commercial coal cleaning equipment in removing sulfur.
At Homer City tests will be made to determine the performance of the
advanced technology, 1200 tph coal preparation plant in removing pyritic sulfur
from central Pennsylvania coals. Environmental tests will also be made to assess
pollution from the coal cleaning process and determine the effects of using
cleaned coals on power plant operation.
The pilot scale chemical coal cleaning work at TRW will evaluate the
performance and costs of aqueous ferric sulfate in leaching pyritic sulfur
from coal. A 10 month test and evaluation program is scheduled to start this
May at the 1/3-tph test facility.
Two major multi-year contracts with the objectives of evaluating the
environmental impacts from coal cleaning processes and in developing costs
and performance data for these processes are in their first year of operation.
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BARRIERS TO THE
IMPLEMENTATION'OF COAL CLEANING TECHNOLOGY
Technical and Regulatory Uncertainties
There is still considerable economic risk related to technical and regu-
latory uncertainties which act as effective barriers to the implementation of
physical coal cleaning as an SO- emission control strategy. The use of coal
cleaning as a tool for meeting SO emission regulations is based upon engineering
and scientific judgment. This pollution control strategy has been used only
in a few isolated cases, generally with easily cleaned coals. The unknown
economic risks are primarily related to the requirement for meeting consistent
fuel sulfur specifications. In a given plant the mix of equipment or the process
controls may not prove to be adequate to consistently remove pyritic sulfur to
the required degree. Technical solutions to this problem would involve a number
of economically unattractive alternatives:
1. Adjust the preparation plant operating conditions in a
manner which would reduce the fuel recovered from the
plant feed.
2. Make extensive equipment modifications.
3. Add a partial FGD system to the boiler.
A great deal of this economic risk could be reduced by more flexible
regulatory activities. The modification of existing emission regulations to
permit emissions to be averaged over a moderate time period, say 8 hours, would
greatly alleviate this risk. In cases where a mix of emission regulations
applies to a single site, the use of a site average emission regulation could
in some instances reduce control costs and risks.
Other technical or regulatory uncertainties include:
1. The costs of pollution control requirements for advanced
coal preparation plants.
2. Changes in boiler operating and maintenance costs which
result from the firing of cleaned coal.
3. The effects of firing cleaned coal on the performance
of electrostatic precipitators.
Extensive commercialization of physical coal cleaning for S0_ emission
control probably cannot be expected until these uncertainties are resolved.
Institutional and Economic Barriers
A number of institutional and economic barriers block implementation of the
use of coal cleaning for S02 emission control. Among these barriers are existing
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investments and contracts, the dependency of the utility industry upon other
organizations for its fuel supply, a limited supply of personnel familiar with
coal cleaning, and the high cost of capital.
Vertical integration in the utility industry is not common. Few utilities
own their own fuel resources. A large percentage of coal resources are owned by
railroads, steel companies, coal companies, oil companies and private owners.
The common practice is to obtain coal through short or-long term contracts.
Further, the coal supplier has traditionally cleaned his coal primarily to
remove ash and mining residue. In today's coal market there is not a clear
recognition by the supplier of clear cost differentials based upon the coal
sulfur levels. The supplier thus does not have an economic incentive to clean
his coal with the objective of removing sulfur. While the coal industry enjoys
a healthy market with high profits, investment is largely directed to expansion
of capacity through mechanization and to the use of goods and services needed to
meet new mine safety and environmental regulations. Incentives for coal cleaning
in the coal industry must come from the market (utilities), regulatory activities
or tax laws. None of these incentives is now operable.
Utilities can contract with coal suppliers for coal cleaning or they can
clean the coal themselves. However in some instances current investments and
contract commitments are disincentives to this action. An example of these
disincentives is the extensive use of Pittsburgh bed coal by utilities in the
Appalachian region. A number of coal companies have high investments in existing
mines and a number of utilities have long term contracts for this Pittsburgh bed
coal. This coal is high in organic and pyritic sulfur and cannot be easily
cleaned for sulfur removal. There are other coals in the region which can be
used to meet emission standards with little or no cleaning. However, the costs
of breaking existing contracts, developing new mines and constructing coal
preparation plants may be more costly than the use of FGD on either existing or
new generating units.
Another problem in implementing coal cleaning technology is that of identi-
fying coal reserves that are adaptable to physical cleaning. Although cleanability
studies have been performed by the Bureau of Mines, their work has been restricted
to coals available from existing mines. Cleanability data is also needed on coal x
seams and geographic areas not currently developed. In this way promising new
resources can be identified for development.
Difficulties which utilities may experience in raising capital may also
serve as a barrier to implementation. Investors may be reluctant to support the
capitalization of coal cleaning facilities because of the technical and.regula-
tory uncertainties involved. Existing tax credits for equipment depreciation may
also favor FGD over coal cleaning. Low interest rate government loans, positive
environmental regulations and modified tax laws could eliminate this economic
barrier.
The lack of familiarity of the utility industry with coal cleaning as a
pollution control may also serve as barrier to implementation. New technology is
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adopted in an industry only after "it has been adequately demonstrated and
accepted as a viable technology by a majority of the industry members. This barrier
to implementation can best be overcome by joint government-industry research,
development and demonstration activities. Recent events indicate an
increasing acceptance by the utility industry of coal cleaning as a pollution
control strategy. PENELEC is constructing a 1200 tph coal cleaning plant at
Homer City, Pa. for the purpose of removing pyritic sulfur from coal for SCL
emission control. The TVA has announced plans to construct a 2000 tph preparation
plant with the objective of removing sulfur for SCL emission control purposes.
The Electric Power Research Institute (EPRI) is placing increased emphasis on R£D
activities for coal cleaning. The prognosis for overcoming the reluctance of
the energy industry in accepting coal cleaning as a SO emission control strategy
is good.
CONCLUSIONS
Physical coal cleaning can be used to meet a variety of state and federal
SO- emission regulations, singly or in combination with flue gas desulfurization.
There is an increasing awareness by the coal and utility industries of coal
cleaning as a method of SO emission control. For readily cleaned coals, phy-
sical coal cleaning will probably be the most cost effective method for meeting
state and federal standards for SO emission control in power boilers. In other
cases combinations of physical coal cleaning and FGD may be more cost effective
than FGD alone.
The acceptance of coal cleaning as a S02 emission control strategy is
dependent upon additional research, development and demonstration activities.
EPA's program will provide for:
1. The development of improved physical and chemical processes
for the removal of contaminants from coal.
2. The identification of air, water and solid pollutants which
result from coal cleaning.
.3. The development of improved pollution control techniques
for coal cleaning processes.
4. The development of the environmental impacts and economic
costs of coal cleaning.
Economic and regulatory activities are the driving forces which determine
the mix of technologies which we apply to the use of our resources. The results
of EPA's coal cleaning program will provide information upon which we can
make sound technical, economic and regulatory decisions concerning yhe use of
'our coal resources.
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REFERENCES
1. Cavallaro, J. A., M. T. Johnston and A. W. Deurbrouck, Sulfur Reduction
Potential of U. S. Coals: A Revised Report of Investigation, EPA-
600/2-76-091 or Bureau of Mines RI 8118, Washington, B.C., April 1976.
2. Hamersma, J. W. and M. L. Kraft, Applicability of the Meyers Process
for Chemical Desulfurization of Coal: Survey of Thirty-Five Coals,
EPA-650/2-74-025-a, Washington, D. C., September 1975.
3. Reggel, et al., Preparation of Ash-free, Pyrite-free Coal by Mild
Chemical Treatment, presented at American Chemical Society (Division of
Fuel Chemistry) National Meeting, New York City, August 27 - September 1,
1972.
4.- Aresco, S. J., L. Hoffman and E. C. Holt, Jr., Engineering/Economic
Analyses of Coal Preparation with SCL Cleanup Processes for Keeping Higher
Sulfur Coals in the Energy Market, Preliminary Report on U. S. Bureau of
Mines contract J0155171, The Hoffman-Munter Corporation, Silver Spring,
Maryland, June 1976.
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