650/2-74-030
Environmental Protection Technology Series
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EPA-650/2-74-030
AN INTERPRETATIVE COMPILATION
OF EPA STUDIES RELATED
TO COAL QUALITY AND CLEANABILITY
by
L. Hoffman, J.B. Truett, and S.J. Aresco
The Mitre Corporation
Westgate Research Park
McLean, Virginia 22101
Contract No. 68-02-1352
ROAP No. 21AFJ-27
Program Element No. LAB013
EPA Project Officer: T.K. Janes
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, N.C. 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D-C. 20460
May 1974
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
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ABSTRACT
This report provides an interpretative compilation of the overall
EPA coal cleaning effort in the form of indepth analysis, evaluation,
and examination of the interrelationships among elements comprising the
EPA coal program. The report basically addresses coal (1) washability
studies, (2) sulfur reduction by cleaning processes including plant
design and associated economics, and (3) the utilization of reject
sulfur and coal values from the cleaning processes.
iii
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ACKNOWLEDGMENTS
The authors gratefully acknowledge the assistance,
technical support, and consultations provided by Mr. T. K. Janes
of the U. S. Environmental Protection Agency, Mr. A. W. Deurbrouck
of the U. S. Department of Interior, Bureau of Mines and
Dr. J. Burton, Mr. L. Rosenberg and Mrs. B. Stokes,of The MITRE
Corporation, in the preparation of this study.
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TABLE OF CONTENTS
LIST OF ILLUSTRATIONS x
1.0 INTRODUCTION 1
2.0 SUMMARY 12
2.1 Introduction 12
2.2 Washability Studies 13
2.3 Laboratory and Pilot Studies Evaluating Processes For Pyrite
Removal from Fine Coals 25
2.3.1 Principal Findings 26
2.4 Prototype Coal Cleaning Plant 29
2.5 Pyrite Utilization Economic Studies 31
2.5.1 The Bechtel Corporation Study 32
2.5.2 The A. D. Little Study 33
2.5.3 The Chemico Study 38
3.0 CONCLUSIONS ' 42
4.0 WASHABILITY STUDIES 48
4.1 Experimental Procedure - Collection of Coal Mine Samples 49
4.2 Procedure for the Conduct of the Washability Studies 49
4.3 Results of Washability Data - Washability Computer Program 52
4.4 Program Results 53
4.4.1 Northern Appalachian Region 57
4.4.1.1 Sewickley Coal Bed 60
4.4.1.2 Pittsburgh Coal Bed 60
4.4.1.3 Upper Freeport Coal Bed 61
4.4.1.4 Lower Freeport Coal Bed 62
4.4.1.5 Upper Kittanning Coal Bed 63
4.4.1.6 Middle Kittanning Coal Bed 64
4.4.1.7 Lower Kittanning Coal Bed 65
4.4.2 Southern Appalachian Region Coals 65
4.4.3 Alabama Region Coals 68
4.4.4 Midwest Region Coals 68
4.4.4.1 Kentucky No. 9 Coal Bed 70
4.4.4.2 Illinois Coal Beds 70
vii
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TABLE OF CONTENTS (Cont'd)
4.4.5 Illinois Geological Survey Studies 72
4.4.6 Western Coal 73
4.4.7 Extension of Float-Sink Test to Finer Grinds 74
4.4.8 Comparability of Core Samples and Face Samples 76
5.0 LABORATORY AND PILOT STUDIES EVALUATING PROCESSES FOR PYRITE
REMOVAL FROM FINE COALS 8*
5.1 Wet Concentrating Table 85
5.2 Concentrating Spiral 90
5.3 Water Cyclone 98
5.4 Air Classifier 103
5.5 Electrokinetics 103
5.6 Agglomo-Separation (Oil) 107
5.7 Froth Flotation 113
5.8 Concentration of Pyrite from Refuse 117
6.0 PROTOTYPE COAL CLEANING PLANTS 120
6.1 Classification and Selection of Coals 123
6.2 Design of Roberts and Schaefer Prototype Cleaning Plant,
Test Plan, and Costs 125
6.2.1 Roberts and Schaefer Plant Design 125
6.2.2 Roberts and Schaefer Test-Program 130
6.2.3 Roberts and Schaefer Capital and Operating Costs 135
6.3 Design of the McNally Pittsburg Prototype Cleaning Plant,
Test Plan and Costs
6.3.1 McNally Pittsburg Plant Design 139
6.3.2 McNally Pittsburg Test-Program ^43
6.3.3 McNally Pittsburg Capital and Operating Costs 147
\
6.4 Data Evaluation ,10
6.4.1 Details of Presently Available Computer Programs 151
6.4.2 Correlation of Coal Characteristics with Cleaning
Results (Multiple Regression Analysis) i CA
7.0 PYRITE UTILIZATION ECONOMIC STUDY . .,
156
7.1 Purposes of the Study; Overview and Approach , c/-
7.2 Description of Candidate Recovery Processes
7.2.1 Brief Description of Recovery Processes , ._
7.2.2 Preliminary Economic Studies of Selected Processes ice
7.2.3 Processes Selected for Detailed Cost Studies
viii
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TABLE OF CONTENTS (Cont'd)
Page
7.3 Sulfuric Acid Market Analysis 173
7.4 Further Analysis of Two Selected Processes 180
7.4.1 Refuse-Combustion/Sulfur-Oxide-Removal (Technical
Aspects) 182
7.4.2 Refuse-Combustion/Sulfur-Oxide-Removal (Economic
Aspects) 184
7.4.3 Fluidized Bed Roasting of Pyrite, followed by
Catalytic Oxidation of Sulfur Dioxide - (Technical
Aspects) 198
7.4.4 Fluidized Bed Roasting of Pyrite Concentrate (Economic
Aspects) 209
7.5 Findings 219
8.0 THE HIGH SULFUR COMBUSTOR — A STUDY OF SYSTEMS FOR
UTILIZATION OF COAL CLEANING REJECT MATERIAL 223
8.1 Objectives and Approach 223
8.2 Types of Coal and Effects of Coal Cleaning 225
8.3 High Sulfur Fuel Characteristics 226
8.4 Performance Requirements for Recovery Systems—Base Parameters
for Five Case Studies 228
8.5 Selection of Equipment and Fuel Compositions 231
8.5.1 High Sulfur Fuels 231
8.5.2 Furnace Types 233
8.5.3 Boiles, Burners, and Combustion Systems 234
8.5.4 Electric Generating Equipment 235
8.5.5 Processes for Recovery of Sulfur Values 235
8.5.6 Process Description and Fuel Composition for Each
Case Study 238
8.6 Economic Analyses of the Five System Designs 238
8.6.1 Method for Valuation of High-Sulfur Fuels 245
8.6.2 Capital Costs 246
8.6.3 Operating Costs 246
8.6.4 Operating Economics: Cost of High-Sulfur Fuel 249
8.7 Findings 253
REFERENCES 257
ix
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LIST OF ILLUSTRATIONS
Page
FIGURE NUMBER
1 FUEL UTILIZATION 6
2 PYRITE COAL PROGRAM 8
3 WASHABILITY SUMMARY OF ALL COALS 15
4 EFFECT OF CRUSHING ON LIBERATION OF TOTAL SULFUR,
SUMMARY OF ALL COALS 16
5 AVERAGE TOTAL SULFUR CONTENT, + 1 STANDARD
DEVIATION AT 3/8 INCH TOP SIZE, SUMMARY OF
ALL COALS I?
6 AVERAGE PYRITIC SULFUR CONTENT, + 1 STANDARD
DEVIATION AT 3/8 INCH TOP SIZE, SUMMARY OF
ALL COALS 18
7 AVERAGE PERCENT TOTAL SULFUR REDUCTION + 1
STANDARD DEVIATION AT 3/8 INCH TOP SIZE,
SUMMARY OF ALL COALS 19
8 AVERAGE PERCENT PYRITIC SULFUR REDUCTION, + 1
STANDARD DEVIATION AT 3/8 INCH TOP SIZE,
SUMMARY OF ALL COALS 20
9 WASHABILITY OF NORTHERN APPALACHIAN REGION COALS 22
10 WASHABILITY OF SOUTHERN APPALACHIAN REGION COALS 23
11 WASHABILITY OF MIDWEST REGION COALS 24
12 ESTIMATED PHYSICAL DESULFURIZATION POTENTIAL OF
EASTERN BITUMINOUS STEAM COAL PRODUCTION 44
13 FLOW DIAGRAM SHOWING PREPARATION OF GROSS SAMPLE 50
14 WASHABILITY SUMMARY OF ALL COALS 55
15 WASHABILITY OF NORTHERN APPALACHIAN REGION COALS 59
16 WASHABILITY OF SOUTHERN APPALACHIAN REGION COALS 67
17 WASHABILITY OF MIDWEST REGION COALS 71
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LIST OF ILLUSTRATIONS (Cont'd)
FIGURE NUMBER Page
. 18 TOTAL SULFUR REDUCTION AT 1.60 SPECIFIC GRAVITY
AS RELATED TO SIZE FOR 70 W. PENNSYLVANIA,
E. OHIO, AND ILLINOIS COALS 77
19 TOTAL SULFUR REDUCTION AT 1.60 SPECIFIC GRAVITY
AS RELATED TO SIZE FOR 20 SOUTHERN, WESTERN,
AND MID-WESTERN COALS 78
20 WASHABILITY CHARACTERISTICS OF SAMPLE 20 82
21 WASHABILITY CHARACTERISTICS OF SAMPLE 22 83
22 DISTRIBUTION OF CLEAN COAL, MIDDLINGS, AND
REFUSE ON THE WET CONCENTRATING TABLE 86
23 HUMPHREYS SPIRAL CONCENTRATOR CLOSED CIRCUIT
TEST UNIT 93
24 COMPOUND WATER CYCLONE 102
25 REFUSE PROCESSES 160
26 REFUSE-COMBUSTION/SULFUR-OXIDES-REMOVAL FLOW
CHART 183
27 DUAL PLANT SCHEME 185
28 TOTAL REFUSE VALUE-REFUSE POWER PLANT CAPACITY-
REFUSE COMPOSITION 193
29 TOTAL REFUSE VALUE-REFUSE SULFUR CONCENTRATION-
SULFURIC ACID PRICE (REFUSE ASH CONCENTRATION,
34.0%) 194
30 TOTAL REFUSE VALUE-REFUSE SULFUR CONCENTRATION-
REFUSE POWER PLANT CAPITAL COSTS (REFUSE ASH
CONCENTRATION, 34 PERCENT; SULFURIC ACID PRICE,
$12.50/TON) 195
31 TOTAL REFUSE VALUE-REFUSE SULFUR CONCENTRATION-
SULFUR RECOVERY PLANT INVESTMENT (REFUSE ASH
CONCENTRATION, 34 PERCENT; SULFURIC ACID PRICE,
$12.50 TON) 196
xi
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LIST OF ILLUSTRATIONS (Cont'd)
FIGURE NUMBER
32
Page
33
34
35
36
37
TOTAL REFUSE VALUE-REFUSE SULFUR CONCENTRATION-
RATE OF RETURN ON INVESTMENT (REFUSE ASH
CONCENTRATION, 34 PERCENT; SULFURIC ACID PRICE,
$12.50/TON)
197
TOTAL REFUSE VALUE COMPONENTS (300 Mw REFUSE
POWER PLANT; REFUSE ASH CONCENTRATION, 34 PERCENT) 199
TOTAL REFUSE VALUE SENSITIVITY, 300-Mw REFUSE
POWER PLANT
PYRITE-REMOVAL PROCESS
FLOW DIAGRAM OF FLUOSOLIDS PYRITE-ROASTING/
SULFURIC-ACID PLANT PLANT TYPE 1-A
200
203
204
ESTIMATED VALUE OF PYRITE FOR SUPPLYING SULFURIC
ACID TO PHOSPHATE FERTILIZER PLANT AT CAIRO,
ILLINOIS AS A FUNCTION OF- 1. PREVAILING
PRICE OF PRBtSTONE (ELEMENTAL SULFUR); 2. LOCATION
OF BRIMSTONE - BASED PHOSPHATE PLANT - BATON
ROUGE, LA., OR CAIRO, ILL. 218
TABLE NUMBER
I
II
III
IV
V
VI
VII
VALUE OF REFUSE 34
HSC FUEL COMPOSITIONS, PRODUCTS, INVESTMENT, AND
OPERATING COSTS 40
TABLE OF FLOAT SINK TEST SIZES WITH SPECIFIC
GRAVITIES 51
COMPARISON OF WASHABILITIES OF SMALL AND LARGE
SAMPLES 80
PRODUCT ANALYSIS OF A 1/4 INCH BY 0 SIZE COAL
WASHED ON A WET CONCENTRATING TABLE 88
PRODUCT ANALYSIS OF A 35 MESH BY 0 SIZE COAL
WASHED ON A WET CONCENTRATING TABLE 89
ANALYSIS OF COALS SELECTED FOR CONCENTRATING
TABLE LISTS 91
xii
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LIST OF ILLUSTRATIONS (Cont'd)
TABLE NUMBER
VIII
IX
X
XI
XII
XIII
XIV
XV
XVI
XVII
'XVIII
XIX
XX
XXI
XXII
Page
CONCENTRATING TABLE TESTS 92
PRODUCT ANALYSIS OF 35 MESH BY 0 MIDDLE KIT-
TANNING BED COAL WASHED OVER THE COAL SPIRAL 95
CONCENTRATING TABLE AND SPIRAL CONCENTRATOR
TESTS EFFECTS OF TWO-STAGE CLEANING 97
COMPARISON OF CONCENTRATING TABLE RUNS AND
COMPOUND WATER CYCLONE RUN WITH 30 MESH X 0,
R.O.M., OHIO NO. 6-A SEAM 99
CONCENTRATING TABLE AND COMPOUND WATER CYCLONE
TESTS-EFFECTS OF TWO-STAGE CLEANING 100
PYRITIC SULFUR REDUCTION IN MAJOR AIR
CLASSIFICATION TESTS 104
SULFUR REDUCTION IN ALPINE ZIGZAG CLASSIFIER
TESTS 105
FRACTIONATION OF A SAMPLE OF 100 BY 325 MESH
LOWER FREEPORT BED COAL IN AN ELECTROPHORESIS
COLUMN 108
EVALUATION OF THE AGGLOMO-SEPARATION PROCESS
FOR THE LOWER FREEPORT BED COAL USING FOUR
PROCESS VARIABLES 110
EVALUATION OF THE AGGLOMO-SEPARATION PROCESS
FOR THE PITTSBURGH BED COAL USING FOUR
PROCESS VARIABLES 111
TWO-STAGE FLOTATION RESULTS WITH LOWER FREEPORT
BED COAL SLURRY 115
TWO-STAGE FLOTATION RESULTS WITH MIDDLE KITTANNING
BED COAL SLURRY 116
SULFUR RECOVERY IN PYRITE CONCENTRATION TESTS
COST ESTIMATES FOR FIFTY-TWO MONTH PROGRAM
COST ESTIMATES FOR 44 MONTH PROGRAM
119
136
138
xiii
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TABLE NUMBER
XXIII
XXIV
XXV
XXVI
XXVII
XXVIII
XXIX
XXX
XXXI
XXXII
XXXIII
XXXIV
XXXV
XXXVI
XXXVII
XXXVIII
XXXIX
XL
LIST OF ILLUSTRATIONS (Cont'd)
SUMMARY OF PROCESSES FOR UTILIZING COAL REFUSE
COST EVALUATION SUMMARY
ASSUMPTIONS FOR PRELIMINARY ECONOMIC ESTIMATES
ESTIMATED REGIONAL PRODUCTION AND DISPOSITION
OF SULFURIC ACID, 1966
SULFURIC ACID DISTRIBUTION BY END USE
GROWTH IN MAJOR SULFURIC ACID END USES,
UNITED STATES
ESTIMATED SULFURIC ACID END-USE PATTERN IN
SELECTED STATES, 1966
SULFURIC ACID SUPPLY-DEMAND SITUATION IN
SELECTED STATES, 1966
750-MW BASE POWER PLANT SUMMARY
REFUSE POWER PLANT SUMMARY
SULFUR RECOVERY PLANT INVESTMENT
STANDARD CONDITIONS 300-MW REFUSE POWER PLANTS
BATTERY LIMIT COSTS AND TOTAL CAPITAL INVESTMENTS
VS. CAPACITY AND FEED CONSUMPTION
TOTAL PROCESSING COSTS VS. FEED PLANT COMPOSITION
AND PLANT CAPACITY
THE PRICE THAT CAN BE PAID FOR PYRITES TO YIELD
THE SAME SULFURIC ACID MANUFACTURING COST AS WHEN
USING BRIMSTONE AT VARIOUS PRICES
ALLOWABLE PRICES FOR 85 PERCENT PYRITE DELIVERED
TO CAIRO PLANT UNDER VARIOUS RETURN-ON-INVESTMENT
REQUIREMENTS*
SUMMARY OF CASE A
SUMMARY OF CASE B
Page
166
169
170
176
177
178
179
181
188
188
190
201
212
214
216
220
239
240
xiv
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TABLE NUMBER
XLI
XLII
XLIII
XLIV
XLV
XLVI
XLVII
XLVIII
LIST OF ILLUSTRATIONS (Cont'd)
SUMMARY OF CASE C
SUMMARY OF CASE D
SUMMARY OF CASE E
SUMMARY OF INPUTS AND OUTPUTS FOR FIVE CASE
STUDIES
ESTIMATED CAPITAL COST
CASE C SYSTEM ESTIMATED OPERATING COST
INCOME FROM SALES COSTS OF OPERATION AND
PRODUCTS GAIN OR LOSS FROM OPERATION
VALUE OF HSC FUELS, OFFSET TO CLEANING COST,
PAYOUT OF INVESTMENT
Page
241
242
243
244
247
248
250
251
xv
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1.0 INTRODUCTION
The exponential technical and economic growth of the last 25 years
has resulted in serious adverse effects on the quality of the Nation's
air. A concern for preserving the quality of the environment resulted
in the Air Quality Act of 1963 which initiated a concerted effort by
federal, state, and local governments for the preservation of the Na-
tion's air quality. This Act called for an expanded federal research
and development program and placed special emphasis on the problem of
sulfur oxides emissions from the combustion of coal and oil in station-
ary plants.
.Coal provides for 20.5 percent (calendar year 1971) of the total
fossil fuel energy consumed by stationary sources (utility, industrial,
commercial, and residential). In the utility industry, over 53 per-
cent (calendar year 1971) of the fossil fuel energy requirement is
supplied by coal. Of the 33.2 million tons of sulfur oxides emitted
into the atmosphere in 1968, 20.1 million tons were from coal-fired
utility operations. The ever-increasing demand for electrical energy,
the shortage of the available oil-gas reserves, and the delay in the
construction and development of breeder-reactor nuclear power plants
have resulted and will continue to result in increasing use of coal
as a major source of energy for the utility industry. Coal consumption
by utilities could reach 500 million tons in 1980 and could be over
a billion tons in the year 2000- Because pollution from fuel has long
been recognized as a problem, both by EPA and its predecessor organiza-
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tions,* major emphasis has been placed on the development of methods
for controlling sulfur oxides emissions.
Currently available methods for controlling sulfur oxides emissions
from coal-fired stationary combustion sources fall into the following
categories:
1. The use of low sulfur coal either naturally occur ing or
physically cleaned;
2. Chemical treatment to extract sulfur from coal;
3. Removal of sulfur compounds during the combustion process;
4. Removal of sulfur oxides from the combustion flue gas;
5. Conversion of coal to a clean fuel by such processes as
gasification and liquefaction.
Of these methods, physical removal of pyritic sulfur (principally
FeS2) is the lowest cost and has the most developed technology.
Sulfur as coal exists in two principal forms, organic and inorganic.
The organic sulfur is bound chemically to the coal substance and cannot
be physically removed. However, inorganic sulfur (i.e., pyritic) is not
bound chemically with the coal substance and may be removed to varying
extents by crushing and physical cleaning. The degree of removal is
dependent upon pyrite size and distribution, coal size, and other
physical characteristics.
throughout this report, the acronym "EPA" is used to designate the U.S.
Environmental Protection Agency (especially its component organization,
the Office of Air Programs), as well as its predecessor agency, the
National Air Pollution Control Administration of the Department of
Health, Education and Welfare.
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Physical cleaning of coal has been used for many years. Its
principal purpose has been to reduce the so-called ash-forming im-
purities. The process in common use for reducing such impurities is a
combination of stage crushing and specific gravity separation. Shale
and coal having different specific gravities may be separated. Froth
flotation, dependent on differences in surface characteristics of coal
and coal impurities, is used for removing ash from fine size coal.
Existing cleaning processes, while removing impurities from coal, also
reduce the total BTU recovery (i.e., a portion of the heat content of
the feed will be lost with the refuse). As a result, the BTU content
per unit weight of the processed product increases due to removal of
low heat value impurities. In practice an economic balance must be
achieved between the BTU loss and the improvement in coal quality.
This balance may be further influenced by environmental considerations.
In 1965, EPA sponsored a study to quantify the impact that coal
cleaning, optimized for pyrite removal, could have on the control of
sulfur oxide emissions. This study found that it was impossible to
quantify the impact of coal cleaning on sulfur oxide emissions because
Of large gaps in available information. The study identified the fol-
lowing areas where required information was either not available or
was inadequate for appraising this impact:
• Knowledge of the distribution of sulfur forms in (all) major
high-sulfur coalbeds in the United States;
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• Effectiveness of available commercial coal preparation methods
for pyrite separation, together with the development or modi-
fication of these techniques to maximize sulfur reduction;
• Identification and assessment of processes that could econom-
ically utilize coal cleaning reject material for byproduct
recovery, thereby aiding the overall cleaning economics and
reducing potential air, water, and solid pollution.
The findings of the 1965 study led EPA to proceed with implemen-
tation of a comprehensive program designed to define the potential role
of coal cleaning in controlling sulfur oxides emissions from coal-fired
sources. The individual program elements were structured to supply the
basic information required. The program permitted flexibility for tailor-
ing new program elements in accordance with findings of previous or on-
going studies. An important part of the program was to determine the
extent to which the sulfur content of U.S. coals could be reduced by coal
cleaning processes based on differences in physical properties. While
pyritic sulfur is amenable to removal by such processes, the other major
form of sulfur (organic sulfur compounds) is not. A good indicator of
the "cleanability" of pyrites from coal is the float-sink, or washabil-
ity, test in which crushed coal is tested at various gravities to sepa-
rate the different specific gravity fractions. The coal fractions float
and the heavier fractions sink. Such washability tests form an important
element of the total program. The overall study concept included the
following elements:
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• A data base of coal cleanability, containing results of pyrite
(and ash) washability studies, to determine the sulfur-release
potential of coals from principal utility-coal-producing beds
of the United States;
• In-depth studies of existing physical cleaning techniques to
obtain maximum pyrite removal;
• The modification of existing methods and evaluation of new
methods for sulfur reduction;
• Studies covering pyrite utilization and related economics;
• A feasibility study (with costs) of a prototype cleaning
plant to evaluate both economic and technical factors asso-
ciated with maximizing sulfur reduction;
• A feasibility study with costs of a high-sulfur combustor
for utilizing reject material from coal cleaning.
The overall basic program concept (Figure 1) has been to develop
a means for achieving full utilization of all values in the coal. The
deep-cleaning of coal to maximize sulfur reduction could result in reject
material high in coal and sulfur values. This refuse material could be
reprocessed into various products: non-polluting refuse for disposal;
a pyrite concentrate that could be converted into sulfuric acid; and
coal products of various sulfur levels for utilization with flue gas
cleaning systems to generate electrical energy. The full utilization of
these values could result not only in lower cost fuels, but also in the
conservation of the Nation's fossil fuel resources.
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RAW COAL
1
COAL
PREPARATION
CLEAN FUEL
(LOW SULFUR/LOW ASH)
CLEANING REJECT
REJECT
PROCESSING
SHALE, SANDSTONE,
INTERMEDIATE SULFUR FUEL
(SULFUR 1-4%; ASH 5-20%)
CLAYEY SUBSTANCES
CONCENTRATED PYRITE
(SULFUR >35%)
HIGH SULFUR FUEL
(SULFUR 6-15%, HIGH ASH)
FIGURE 1
FUEL UTILIZATION
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A diagram identifying the major elements of the program sponsored
by EPA (in whole or part) to develop the information necessary to quantify
the potential role of coal cleaning in the control of sulfur oxides
emissions and to define the relative attractiveness of cleaning options
is given in Figure 2. This figure indicates the interrelations among
the various program elements, together with the beginning date for each
funded effort and the identification of future efforts required to reach
demonstration of commercial applicabilities of considered techniques.
The initial EPA-sponsored washability study began in 1965. Repre-
sentative samples were collected from mines of major producers of coal
primarily for use by the utilities. The samples were stage crushed to
three top sizes; coarse - 1^ inch; intermediate - 3/8 inch, and fine -
14 mesh. Washability studies were performed on the various sized frac-
tions with organic liquids of standardized specific gravities to de-
termine the effects of top size and specific gravity parameters upon
pyrite liberation and separation.
Because of the the large number of coals to be tested and the need
to accelerate their evaluation, EPA expanded the testing program by sup-
"porting three additional organizations. The first of these concentrated
on regions where preliminary data indicate the presence of coals clean-
able for major sulfur reduction.
In another study, EPA cooperatively supported a two-year investiga-
tion to evaluate all active.ly mined coal beds in the state of Illinois,
which has the largest bituminous coal reserves in the United States.
This effort determined the important physical and chemical properties of
7
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PYRITIC SULFUR
WASHABILITY /
STUDIES
PYRITE
REMOVAL
PROCESSES
PYRITE
UTILIZATION
ECONOMIC STUDY
5/67
COMMERCIAL
TESTING AND
ENGINEERING
COMPANY
5/67
ILLINOIS
GEOLOGICAL
SURVEY
7/65
U.S. BUREAU
OF MINES
6/67
BITUMINOUS
COAL
RESEARCH
6/67
A. D. LITTLE
AND
DORR-OLIVER
6/67
BECHTEL AND
STANFORD
RES. INST.
6/68
PROTOTYPE COAL CLEANING
5/70
1. ROBERTS AND
SCHAEFER
COMPANY
2. McNALLY
PITTSBURG
MFG. CORP.
ROBERTS AND
SCHAEFER CO.
AND U.S. BUREAU
OF MINES
DETAILED DESIGN PROTOTYPE
AND EXPERIMENTAL PLANT
TEST PROGRAM
FEASIBILITY STUDY
HIGH SULFUR COMBUSTOR
7/69
FULL-SCALE
UNITS
FEASIBILITY STUDY
DETAILED
DESIGN
PROTOTYPE
PLANT
FIGURE 2
PYRITE COAL PROGRAM
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Illinois coal, including its washability and distribution of sulfur
forms.
To further develop basic data on the effects of size reduction on
pyrite liberation, selected samples (in a separate effort) were further
reduced in top size to 30 mesh and 60 mesh and evaluated by float-sink
evaluation. Although the cleaning of this size material by specific
gravity methods is not normal commercial practice, this information
would define the maximum effects of size reduction on pyrite liberation
and separation.
The four funded washability studies contributed to the development
of a substantial body of data on the cleanability of U.S. coals. This
information is stored in a computerized data bank to facilitate retrieval,
updating, and analysis.
Concurrent with the washability studies, EPA sponsored two separate
investigations of techniques for separating and concentrating pyrites
from fine coal. One of these evaluated the effectiveness of commercially
available equipment; the wet concentrating table, the compound water
cyclone, and the concentrating spiral. The other evaluated conventional
techniques to define operating parameters, modification of these tech-
niques to maximize sulfur reduction, and the development of new tech-
niques .
In 1967, EPA sponsored two preliminary studies that investigated
the economics of recovering by-products from the reject material result-
ing from coal cleaning. One of these included a review and analysis
9
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of commercially applicable processes for recovering sulfur and the ap
plicability of these processes utilizing coal cleaning refuse. The
second was a detailed feasibility study of fluid bed roasting with con-
version to sulfuric acid, plus a market analysis for its principal
product, commercial grade sulfuric acid. The study findings indicated
that the high-sulfur combustor had the highest economic viability po-
tential.
After the preliminary economic studies were completed, EPA funded
a feasibility study of a high-sulfur combustor capable of burning the
reject.material to recover its energy and sulfur values. This study
produced an engineering design and cost analysis associated with the
utilization of high sulfur reject material to generate power and re-
cover sulfuric acid or elemental sulfur.
In order to determine the scope and cost of conducting investiga-
tions and demonstrations of pyrite removal using commercial equipment
on a scale approximating commercial capacity, EPA in 1968 funded two
independent and competing engineering studies. These efforts, predi-
cated on findings of the washability investigations, were for designing
a prototype coal cleaning plant and for estimating capital and operating
cost for the plant. Two studies were required to identify the most ac-
ceptable design/cost option due to plant and operational complexities.
These various studies are described and their results summarized
in the following chapters of this report. The economics, technologies,
etc., provided in this report are those of the addressed studies. It
10
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should be noted that since the reported studies were performed condi-
tions have changed and the economic findings and conclusions of the var-
ious efforts may not be currently valid.
11
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2.0 SUMMARY
2.1 Introduction
This study provides an interpretative evaluation of the EPA (and
its predecessor organizations) coal cleaning program. The EPA coal clean-
ing effort ostensibly began in 1965 when EPA sponsored a study to quan-
tify the impact that coal cleaning, optimized for pyrite removal, could
(2)
have on the control of sulfur oxide emissions. This study found that
it was impossible to quantify the impact of coal cleaning on sulfur
oxide emissions due to large gaps in available information.
The findings of the 1965 study led to the establishment of a com-
prehensive program designed to define the potential role of coal clean-
ing in controlling sulfur oxide emissions from coal-fired sources. Prin-
cipal elements of the resulting program were:
• A data base of coal cleanability, based on findings of pyrite
washability studies, to determine the sulfur-release potential
of coals from principal utility coal producing beds of the
United States;
• An in-depth study of pyrite removal processes;
• Studies covering pyrite utilization and related economics;
• Feasibility studies of a prototype cleaning plant to evaluate
the economic and technical factors associated with maximizing
sulfur reduction;
• A feasibility study of a high-sulfur combustor for utilizing
reject material from coal cleaning.
12
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In essence, the overall program concept was to develop methods for
achieving utilization of all values in the coal. The deep cleaning of
coal to maximize sulfur reduction could result in a reject material high
in coal and sulfur values. This refuse (reject) material could be pro-
cessed into various products: non-polluting refuse for disposal; a
pyrite concentrate that could be converted into sulfuric acid; and coal
products of various sulfur levels for utilizing with flue gas cleaning
systems to generate electrical energy.
The principal elements that comprized the EPA program are summarized
below.
2.2 Washability Studies
Sulfur is found in raw coal in two major forms: organic and in-
organic (pyritic) sulfur. Organic sulfur is chemically bound to the
organic structure of the coal and cannot be removed by use of conven-
tional washing methods. The pyritic sulfur occurs in particles of
varying size mixed with the coal. By crushing (to liberate the pyritic
sulfur) and washing (to remove the liberated particles), the total
amount of sulfur in the coal may be reduced. The degree of removal of
the pyritic sulfur is dependent on the size of the particles of pyrites;
the finer the particles, the more difficult to remove by washing. The
total sulfur reduction, therefore, is dependent on the amount of organic
sulfur and the effects of crushing to liberate the pyritic sulfur. The
desulfurization process results (as do most beneficiation processes) in
some loss in total heat content of the processed coal.
13
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A summary of 322 washability tests reported by the Bureau of Mines
shows that the organic sulfur and the effects of crushing (Figures 3 and
4) vary widely, as would be expected, when washability data of coals
throughout the United States are combined.
The average total sulfur content of all coal studied in the Bureau
of Mines reported investigation of coal washability is 3,23 percent at
a raw coal top size of 3/8 inch (Figure 5). When washed to a 90 percent
yield, this average was reduced to 1.95 percent; reducing the yield to
60 percent results in a 1.82 percent average value. Figure 6 shows the
average pyritic sulfur content of the raw coal is 2.05 percent. At 90
percent yield this average was reduced to 0.75 percent; at 60 percent
yield it was reduced to 0.51 percent. On the average, regardless of
yield, the organic sulfur content of the coals was 1.2 percent. The
average percent total sulfur reduction and the average percent pyritic
sulfur reduction at the varied yields are shown in Figures 7 and 8. Fig-
ure 3 shows that at a 60 percent yield only 20 to 25 percent of the coals
sampled could produce a one percent or less total sulfur washed coal.
The production of one percent or less total sulfur coal by means of
physical cleaning is governed by the amount of organic sulfur and part-
icle sizes of the pyrite in the coals (the fine, intimately mixed pyrite
particles are impossible to remove by conventional washing processes),
regardless of cost. In general, the lower the level of total sulfur re-
quired in the washed coal, the higher the cost of cleaning due to the
lower recovery of the washed coal (i.e., greater loss of coal values
during washing).
14
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w
w
PJ
CO
H
90 PERCENT YIELD
i i i i
80 PERCENT YIELD
i i i
70 PERCENT YIELD
i i i
60 PERCENT YIELD
i i i i
(a)
(b)
(c)
(d)
56780 12
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS 1% INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURES
WASHABILITY SUMMARY OF ALL COALS
345678
SOURCE: REFERENCE 8
15
-------
100
90
80
70
en
3 60
H
O
H
S 50
H
U
C3
Q
3 40
W
e^ 30
20
10 h-
60
70 80
PERCENT YIELD
90
SOURCE: REFERENCE 8
FIGURE 4
EFFECT OF CRUSHING ON LIBERATION OF TOTAL SULFUR,
SUMMARY OF ALL COALS
16
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1
H
I
W
80
PERCENT YIELD
90
SOURCE: REFERENCE 8
100
FIGURES
AVERAGE TOTAL SULFUR CONTENT, ±1 STANDARD DEVIATION
AT 3/8 INCH TOP SIZE, SUMMARY OF ALL COALS
17
-------
70
80
PERCENT YIELD
90
100
SOURCE: REFERENCE 8
FIGURES
AVERAGE PYRITIC SULFUR CONTENT, ±1 STANDARD DEVIATION
AT 3/8 INCH TOP SIZE, SUMMARY OF ALL COALS
18
-------
70 80
PERCENT YIELD
90
SOURCE: REFERENCE 8
FIGURE?
AVERAGE PERCENT TOTAL SULFUR REDUCTION ±1 STANDARD
DEVIATION AT 3/8 INCH TOP SIZE, SUMMARY OF ALL COALS
19
-------
•100
g
OT
E
§
M
H
O
g
PM
70 80
PERCENT YIELD
90
SOURCE: REFERENCE 8
FIGURES
AVERAGE PERCENT PYRITIC SULFUR REDUCTION, ±1 STANDARD
DEVIATION AT 3/8 INCH TOP SIZE, SUMMARY OF ALL COALS
20
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The three regions indicating a potential for washing to a total
sulfur content of one percent or less are the Northern Appalachian
(Figure 9), the Southern Appalachian (Figure 10), and Eastern Interior
or Midwest Region (Figure 11). The remaining coal producing regions
given less attention or excluded are: the Western Interior (the coals
in this region are characteristically high in sulfur content regardless
of the physical treatment used) and Northern and Southern Rocky Mountain
(these coals are generally of low sulfur content).
As shown by Figures 4 and 5, coal crushed to 3/8-inch top size and
cleaned to yield in the order of 90 percent will provide the predominant
benefit. The figures show that, on the average, sulfur content will de-
crease by less than ten percent with an additional yield sacrifice of
30 percent (i.e., 90 to 60 percent). Even so, it must be emphasized
that individual cases may vary and must be independently assessed.
In addition to the Bureau of Mines reported washability studies,
67 washability tests on Illinois coals were reported by the Illinois
Geological Survey. The test samples were taken from Illinois coal mines
located in significant mining areas in the state. The Illinois Geo-
logical Survey tests indicated that most Illinois coals have 3 to 5
percent total sulfur and only in those coals having a relatively low-
sulfur content as mined could the total sulfur content be reduced to
1.5 percent or less by washing techniques. Of the 67 coal samples
tested, 6 could be washed to a total sulfur level of 1 percent and 10
could be washed to 1.5 percent with an 80 percent minimum recovery.
21
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w
£
w
w
53
90 PERCENT YIELD
i
70 PERCENT YIELD
i i i i
60 PERCENT YIELD
(a)
(b)
(c)
(d)
345678
SOURCE: REFERENCE 8
678012
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS 1% INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURE 9
WASHABILITY OF NORTHERN APPALACHIAN REGION COALS
22
-------
w
w
p-
w
S3
(a)
(b)
(c)
(d)
90 PERCENT YIELD
i i i i i
70 PERCENT YIELD
I
80 PERCENT YIELD
i i i i i
60 PERCENT YIELD
I i i i lit
3 A 5 6 7 8
SOURCE: REFERENCES
12345678012
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS 1% INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURE 10
WASHABILITY OF SOUTHERN APPALACHIAN REGION COALS
23
-------
w
w
PL.
a
M
SB
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
PERCENT YIELD
i i i i
70 PERCENT YIELD
i i i i i
(a)
(b)
(c)
(d)
12345678012,
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS 1% INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURE 11
WASHABILITY OF MIDWEST REGION COALS
345678
SOURCE: REFERENCE 8
24
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2.3 Laboratory and Pilot Studies Evaluating Processes For Pyrite Re-
moval From Fine Coals
The goals of EPA-sponsored laboratory and pilot study projects
conducted by the Bureau of Mines and Bituminous Coal Research, Incor-
porated were:
1) to determine the operating parameters for maximum pyrite sep-
aration,
2) to modify existing techniques and/or develop new techniques
to separate pyrite from fine coal, and
3) to evaluate methods to process coal cleaning rejects so as
to concentrate the pyrite and reclaim clean coal products.
The Bureau of Mines concentrated on equipment operational para-
meters and the development of new techniques while the Bituminous Coal
Research effort concentrated on the applicability of equipment to var-
ious coals. The following equipment or processes were evaluated by the
two contractor organizations.
EQUIPMENT/PROCESS INVESTIGATED BY
BUREAU OF BITUMINOUS COAL
MINES RESEARCH. INC.
Wet Concentrating Table (Deister) X X
Concentrating Spiral (Humphrey) X X
Hydrocyclones X X
25
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EQUIPMENT/PROCESS -53 CQAL
' BUREAU OF BITUMINOUS COAL
MINES __ RESEARCH. INC.
v
Air Classifiers
Electrokinetic Techniques Y
Agglomo-Separation X,Y
Froth Flotation X,Y
X - designates pilot plant tests
Y - designates laboratory-scale tests
2.3.1 Principal Findings
Wet Concentrating Table
In tests, the wet concentrating table proved effective in removing
free pyrite from coal. Coals with a high proportion of pyritic sulfur
relative to organic sulfur are particularly amenable to sulfur reduction
by this process. Two-stage cleaning tests, in which a coarse sample was
tabled and the clean fraction pulverized and retabled, indicated that
pyrite removal can be enhanced by use of the concentrating table in two
stages.
Concentrating Spiral
The concentrating spiral experienced a rapid deterioration of wash-
ing efficiency with feed size below 35 mesh, this being a normal char-
acteristic of specific gravity separators.
Overall, the excellent results the concentrating spiral provided on
fine-size coal suggest that it should be considered as a "rougher" clean-
ing unit to remove pyrite from high sulfur coals prior to flotation.
26
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Double-stage cleaning indicate that for some coals the spiral process
produces similar reductions and yields to those obtained with the wet
concentrating table.
Water-Only Cyclone
Preliminary results of the Bureau of Mines water cyclone perfor-
mance evaluation tests showed excellent pyritic sulfur reductions were
obtainable. The clean coal recoveries were highly dependent on the
size of the material. Clean coal recovery of plus 48 .mesh material was
low while most of the minus 100 mesh material reported to the clean coal
product.
Water cyclone tests were also conducted by Bituminous Coal Research,
Inc. (BCR, Inc.). Feed coals were pulverized to minus 30 mesh prior to
test runs. BCR, Inc., results indicated that in general the compound
water cyclone provided smaller sulfur reductions than were achieved by
the concentrating table. However, BCR, Inc., believes that improved re-
sults in total sulfur reduction could be obtained by using a closer-
sized feed to the water cyclone.
Air Classifier
Air is used to separate relatively coarse grind of pulverized coal
into a fine fraction and a coarse, pyrite rich fraction using the BCR-
Majac and Alpine zigzag air classifiers. Pyrite could then be removed
from coarse fractions by wet-coal preparation techniques.
27
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The reduction of total sulfur through use of the Majac unit ranged
from 20.1 to 51.7 percent for 10 samples. Only one coal was processed
on the Alpine zigzag unit.
Electrokinetics
The electrokinetic process for the physical cleaning of coal uses
the technique of electrophoresis for separating the pyrite from the coal.
The laboratory-scale investigation indicated that pyrite and other im-
purities such as silica could be separated from 'the coal. The technique,
unfortunately, was deemed uneconomical for scaling up to the pilot stage
as a coal cleaning procedure.
Agglomo-Separation (Oil)
An oil agglomeration process for the recovery of clean coal from
slime size material and the sulfur and ash reduction potential of this
process was investigated by the Bureau of Mines. This process provided
negligible reduction in sulfur; however, the reduction in coal ash con-
tent was good.
Froth Flotation
Froth flotation is a process for separating fine-size particles by
selective attachment of air bubbles to coal particles, causing the coal
to be buoyed up into a froth while leaving the refuse particles in the
water. Of the several innovative processes for pyrite separation in-
vestigated under the EPA Clean Coal Program, the froth flotation tech-
nique appears to show the greatest potential for scale-up to commercial
operation.
28
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Concentration of Pyrite from Refuse
Studies were performed to determine the potential of fine-cleaning
techniques for preparing a concentrated grade of pyrite from coal clean-
ing reject material. Coals from six mines were cleaned and the reject
concentrated by staged separation with a wet concentrating table and a
hydraulic classifier. The results indicate that pyrite concentrates with
sufficiently high total sulfur content for conventional acid-making pro-
cesses were achieved for all coals tested, sometimes at the expense of
percentage of sulfur recovered. Total sulfur in the pyrite concentrates
ranged from 35.6 to 48.6 percent.
2.4 Prototype Coal Cleaning Plant
The washability studies and pilot plant investigations indicated
the amenability of a wide range of coals to physical desulfurization
under carefully controlled conditions. Although testing for pyrite re-
moval could be conducted to a limited degree in some existing prepara-
tion plants, the equipment and cleaning circuits of such plants are not
normally arranged to maximize sulfur reduction but to meet ash and BTU
specifications. Ideally, a plant to be used for investigating and demon-
strating desulfurization methods at high through-put capacities would
provide flexibility of equipment configurations, cleaning circuits, and
operating conditions.
In order to determine the scope and cost of conducting investiga-
tions and demonstrations of pyrite removal using commercial cleaning
29
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equipment on a scale approximating commercial capacity, EPA funded two
independent and competitive studies for designing a prototype coal clean-
ing plant of 50-100 tons per hour capacity and for estimating the cap-
ital and operating cost for the plant. The study objectives were to
produce a prototype plant design, together with cost estimates for
building, equipping and operating a plant capable of reducing the sulfur
of coals having widely variable washability characteristics.
The prototype plant design and cost studies were conducted by the
McNally Pittsburg Manufacturing Corporation and the Roberts and Schaefer
Company of Chicago. The major difference in the two studies was plant
design; Roberts and Schaefer's design was the more complex of the two;
however, it offered the most flexibility.
The Roberts and Schaefer cost estimate for a fifty-two month pro-
gram covering plant cost, operating cost, laboratory services, and con-
tractor's fee came to $16,457,965. In addition, a cost estimate was
provided for a modified, alternate, lower price program that would not
unduly sacrifice program objectives. The cost estimate for the alter-
nate forty-four month program (instead of the fifty-two month basic pro-
gram) amounted to $8,923,200.
The McNally Pittsburg cost estimate for a fifty-four month program
covering plant cost and operating cost, which include laboratory services,
amounted to $11,406,775. Even though not specifically stated, it is as-
sumed that the contractor's fee charge is included in the above amount.
30
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2.5 Pyrite Utilization Economic Studies
The purposes of the Pyrite Utilization Economic Study portion of
EPA's overall pyrite coal program are:
1. To investigate the economics of utilizing the pyrites ob-
tained from coal beneficiation;
2. To evaluate the applicability of alternative commercial
processes for recovering energy and chemical values from
coal cleaning reject material; and
3, To design, construct, and operate a plant that would demon-
strate the technical and economic feasibility of the pro-
cesses.
Investigations concerned with the first two purposes were conducted
concurrently. In 1967, EPA contracted with the Bechtel Corporation to
perform a general review and evaluation of costs and technology of other
available processes for pyrite—coal utilization. Also in 1967, a con-
tract was awarded to A. D. Little, Inc. (assisted by Dorr-Oliver) to
determine the costs and benefits associated with the processing of
pyrite removed from coal. This study effort was concentrated on the
technology and economics of fluidized-bed roasting of pyrite-coal
followed by conversion of sulfur dioxide to sulfuric acid by the con-
tact process. On the basis of the resulting technical and economic
data, EPA decided to look more closely at a system for burning the high-
sulfur, high-ash material produced by coal desulfurization. The re-
sulting effort was performed by the Chemical Construction Company
(Chemico); a summary is presented in Section 2.5.3.
31
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2.5.1 The Bechtel Corporation Study
Eight processes were selected by the Bechtel Corporation for invest-
igating the recovery of chemical and energy values from pyrite-coal refuse.
After initial study, two of the eight processes were selected for analy-
sis at a more detailed level. The selected processes were the "Combus-
tion/ Sulfur-Oxides-Removal Process" and the "Fluidized-Bed Pyrite Roast-
ing Process". These two, in the order listed, had the most favorable
economics. The overall economics of the "Combustion/Sulfur-Oxides-Removal
Process" indicated the possibility of an economic benefit while the
"Fluidized-Bed Pyrite Roasting Process" indicated the likelihood of a
small cost penalty. The study was predicated on a maximum sulfur level
of washed coal of 1.0 percent and coal washing refuse containing from
about 4 to 25 percent sulfur and ash levels of 20 to 90 percent.
The Bechtel findings are based on examining two general classes
of processes for utilizing coal refuse. These are:
1. The feed is the entire refuse stream from coal preparation,
and
2. A concentrated feed is used.
The study (at time of performance) indicated that:
1. None of the processes which use the entire refuse stream
has reached commercial status,
2. Processes which feed a pyrite concentrate are commercial
but have not been operated with pyrite-coal mixtures, and
32
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3. The Combustion/Sulfur-Oxides-Removal Process shows the most
favorable economic outlook and its technology appears sound.
The Monsanto process for removing sulfur oxides from flue gas was se-
lected for the economic estimates because of its advanced development
state and simplicity.
For the study, a method was developed to calculate the value of
coal refuse as a function of numerous variables. The method assumes
that coal refuse is bought jointly by the owners of a closely integrated
electric utility and sulfuric acid plant; wherein each of the two in-
vestors would pay for his share of the refuse value (fuel or sulfur).
The owner of the coal preparation plant could use this income to offset
part or all the cost of coal cleaning. Table I shows the results of
an estimate for values of the two refuse compositions for specific assump-
tions.
The study indicated that refuse value depends on many variables, the
most important being refuse power plant capital cost and sulfuric acid
sales price. Other factors affecting refuse values are:
• Refuse ash concentration,
• Refuse power plant operating and maintenance cost,
• Sulfuric acid recovery plant investment, and
• Rate of return on acid recovery plant.
2.5.2 The A. D. Little Study
As previously indicated, the A. D. Little effort was predicated on
33
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TABLE I
VALUE OF REFUSE
REFUSE
SULFUR
CONCENT.
(PERCENT)
6.38
6.38
10.62
10.62
SULFURIC
ACID
PRICE
($/TON)
10.00
15.00
10.00
15.00
NET REFUSE
ENERGY VALUE
(CENTS/
106 BTU)
4.0
4.0
4.0
4.0
NET REFUSE
SULFUR VALUE
($/TON
SULFUR)
-10.24
7.70
7.18
25.10
TOTAL REFUSE
VALUE
($/TON
REFUSE)
-0.06
1.09
1.35
3.25
(CENTS/
106 BTU)
nil
7.3
9.2
22.2
CHANGE IN
COAL PREP,
COST
(PERCENT)
2.5
increase
45.4
decrease
56.2
decrease
135.4
decrease
ASSUMPTIONS
Refuse Power Plant Capacity
Refuse Power Plant Capital Cost*
Return On Book Value
Refuse Ash Concentration
Refuse Moisture
Sulfur Oxides Recovery Plant
Investment (in terms of refuse
power plant capacity)
Discounted Rate of Return
Coal Preparation Plant Yield
Coal Preparation Cost
300 Mw (net)
170 $/kw
8.0 percent
34.0 percent
15.0 percent
42 $/kw
12.5 percent
80 percent
$0.60/ton clean coal
*Does not include cost for SO- recovery plant,
34
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fluid-bed roasting of pyrite-coal followed by conversion of sulfur diox-
ide to sulfuric acid by the contact process. The study found that the
economic feasibility of the process, i.e., the amount that can be paid
for pyrite feed (coal cleaning reject), depends on a number of inter-
related factors including: the price of elemental sulfur and sulfuric
acid, the location of the acid plant relative to pyrite deposits, the
expected return on investment, and the markets for sulfuric acid. Tak-
ing these and other considerations (including an f.o.b. price for ele-
mental sulfur of $38 per long ton) into account, it was estimated that
the net financial benefit to coal operators for producing low-sulfur
(1 percent or less) coal and an acceptable pyrite feed material could
range from $1.16 to $1.57 per ton of coal processed. The results are
based on the following:
• It is reasonable to expect that a premium of $1.10 to $1.20
per ton of coal should be obtained by mines supplying less
than 1 percent sulfur coal to utilities subject to stringent
air pollution abatement restrictions;
• Coal companies should obtain a benefit of approximately $0.15
per ton of coal processes resulting from reduced disposal re-
quirements and reduced air and water pollution.
In order to support a 1500 ton per day sulfuric acid plant (the
minimum size believed suitable for economic manufacture), considerable
tonnages of pyrite-bearing coal must be processed. The amount required
would probably come from more than one mine.
35
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Costs associated with the manufacture of sulfuric acid from a pynte
feed will vary primarily as a function of three major variables: plant
size, plant type, and feed composition. Plant size and type will be de-
termined to a considerable degree by market conditions projected over
plant life. Even so, feed stream characteristics could change in accord-
ance with raw material resources and beneficiation processes.
For the study a broad range of possible pyrite feed compositions
were arbitrarily selected and evaluated. The pyrite feed composition
has a pronounced effect on almost all of the process requirements in
both the pyrite roasting section and the contact acid section. While
the cost of pyrite-coal beneficiation must ultimately be taken into
account, for practical purposes a feed composition of no worse than 70
percent pyrite, 10 percent coal, and 20 percent gangue was assumed for
acid manufacture. For the study a feed of 85 percent pyrite, 10 percent
coal, and 5 percent inerts was used.
On the basis of the three major parameters — plant capacity, feed
composition, and plant type — investment and operating costs were cal-
culated for each possible combination. Manufacturing costs (excluding
cost of pyrite) ranged from $5.51 to $25.40 per ton of 98 percent sul-
furic acid. Plant investment cost ranged from $3.7 million to $35.5
million.
For purposes of the study effort, 1500 tons per day acid produc-
tion capacity and a feed of 85 percent pyrite, 10 percent coal, and 5
percent gangue were chosen. Estimated processing cost (excluding raw
36
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material costs and any by-product credit, i.e. low-pressure steam) for
this type of plant is $7.63 per ton of 98 percent produced, with an
estimated plant investment of $14.54 million.
Because of its comparatively high weight and low price, sulfuric
acid is ordinarily marketed within a radius of 150 to 200 miles. With-
in the eight-state area covered by the investigation, the major outlet
for sulfuric acid today and in the foreseeable future is and will be the
phosphate fertilizer industry, which presently consumes approximately 40
percent of all sulfuric acid in the United States. Of the other uses of
sulfuric acid, ammonium sulfate (also used extensively in fertilizer man-
ufacture), titanium dioxide, petroleum refining, and steel making are
the most significant.
To evaluate the need for a pyrite-based sulfuric acid plant, four
major marketing areas which are reasonably close to the potential pyrite
source areas were investigated. The investigated areas were: Pittsburgh,
Pennsylvania; Cairo, Illinois; St. Louis, Missouri; and Chicago, Illinois,
Pittsburgh is too far away to serve as an economic supply point to the
Midwest fertilizer market. The other three areas offer reasonably attrac-
tive possibilities for a large, new sulfuric acid plant, so long as all
or a major portion of production would be captive and related to ferti-
lizer production.. For an acid plant to be advantageously located with
respect to potential pyrite supply and still be in a position to com-
pete effectively in the,fertilizer industry, the St. Louis and Cairo
areas were judged preferable. Since Cairo is closer to possible pyrite
37
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sources in Pennsylvania and southern Illinois (thereby minimizing po-
tential freight costs) it was selected as the location to consider for
an integrated pyrite-based fertilizer operation.
In order to evaluate the economic effect of a pyrite-based opera-
tion contrasted with a brims tone-based operation, a hypothetical situ-
ation was developed wherein phosphate fertilizer would be produced at
Cairo, using pyrite feed obtained either from southern Illinois or the
Pennsylvania region. To assess the competitive situation, an alterna-
tive was calculated, involving a similar phosphate fertilizer plant
using brimstone (elemental sulfur), and located in Cairo or Baton
Rouge, Louisiana. The price of brimstone was assumed to be $38 per long
ton, f.o.b. Gulf Coast port (December 1967 quoted price). Under the
conditions assumed, the net price payable to a coal company for an 85
percent pyrite feed may range from a negative value of $1.50 per ton
to approximately $3.73 per ton, f.o.b. the fertilizer plant. If an
additional penalty is imposed on the pyrite operation to reflect the
risk associated with the higher capital cost required, the price pay-
able for pyrite becomes lower.
2.5.3 The Chemico Study
The Chemico "High Sulfur Combustor Study" examined preliminary
designs and evaluations of several combustion and flue gas treating
systems for processing high sulfur fuels that may be drawn off from
the rejects of coal washing. These fuels (i.e., washing rejects) will
need to be tailored to specifications that depend first on the require*-
38
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ments of available processes for sulfur value recovery and second on the
limitations of combustion equipment with respect to ash. The High Sulfur
Combustion (HSC) fuel specifications can evidently be satisfied by ap-
propriately re-combining selected portions of reject material from deep
cleaning of coal.
Four sample HSC fuel compositions are tabulated in Table II to-
gether with product and cost data on six processing systems for these
fuels. The operating context in each case is one of a number of typi-
cal site possibilities in the bituminous coal-producing area comprised
of Pennsylvania, Ohio, West Virginia, Indiana, and Illinois.
Forward estimates of selling prices of the four products are:
Steam per M pounds $ 0.65
Electricity per KWH 0.0075
Sulfur per long ton 25.00
Sulfuric acid per net ton 12.75
If these prices prevail, the estimates of economic benefit, if any,
treated as credits to coal cleaning costs, are as shown below:
Gain after Tax
Clean Coal
M Ton /Year
CASE
A
M$
1,760
7,100
CASE
B
M$
(420)
2,300
CASE
C
M$
(1,960)
920
CASE
D
M$
690
7,100
CASE
D3
M$
4,700
7,100
CASE
E
M$
4,230
3,500
Netback per Ton
of Clean Coal $0.25 ($0.18) ($2.13) $0.10 0.66 $1.21
39
-------
CASE
_A
33.1
61.0
1.8
6.0
500
CASE
_B
18.3
42.5
0.4
2.0
500
CASE
C
PROTOTYPE
11.7
33.8
0.2
1.2
500
50
CASE
_D
11.7
33.8
0.2
1.2
3,500
500
CASE
D3
11.7
33.8
0.2
1.2
3,500
500
CASE
_E
7.9
28.8
0.12
0,7
3,500
500
TABLE II
HSC FUEL COMPOSITrONS, PRODUCTS, INVESTMENT, AND OPERATING COSTS
High Sulfur Fuel Composition
% Total Sulfur
% Total Ash
Sulfur to Coal Weight Ratio
Percent S02 in Flue Gas
Products for Sale
Energy as Steam - M Lbs/Hr
Energy as Electric Capacity - Megawatts
Sulfur Value as Sulfuric Acid - M Net Tons per Year 610 208 753 473
Sulfur Value as Sulfur - M Long Tons per year 31 233
Co-Produced Clean Coal
M Tons per year
TOTAL INVESTMENT IN HSC SYSTEMS
ANNUAL COST OF OPERATION BEFORE U.S. INCOME TAX
COST OF ENERGY EXTRACTION
Steam per M Lbs
Electricity per MWH
COST OF SULFUR VALUE EXTRACTION
Sulfuric Acid per Net Ton
Sulfur per Long Ton
NOTE: "Cost" does not include any charge for the HSC Fuels. Unit costs of products reflect an adjustment for "pollution control"
In CASE A and CASE B the cost of sulfuric acid manufacture is less than the cost of pollution control, hence the figures
in () parenthesis.
SOURCE: Reference 25.
7
M$18
6
$
($
,100
,340
,990
3.00
8.20)
2,300
M$18,600
6,060
$ 1
($ 2
920
M$29,270
7,530
.60
S 14.50
.00)
S 57.00
7,100
M$128,520
34,500
5 7.
$ 28.
7,100
M$126,520
29,000
00 S 7
$ 3
00
3,500
M$125,700
27,900
.00 S 5.W
-.50 $ 10.00
-------
Case C is intended for possible construction as a prototype or
demonstration plant. The four other case studies, taken together,
amount to a preliminary exploration of the range of possible operating
conditions. Any specific coal cleaning situation will need to be ex-
amined in detail for applicability to the high sulfur combustor con-
cept. Washability of the coal and proximity to sulfuric acid consumers
were found to be major determinants of the choice of technology and
economic expectations. The manufacture of sulfur for conversion to
sulfuric acid after shipment compares unfavorably with manufacture and
direct shipment of sulfuric acid unless very large tonnages are to be
shipped long distances by rail.
41
-------
3.0 CONCLUSIONS
1. Information was developed on the sulfur forms and distribution
of sulfur in coal samples from mines which were producers of utility
coal. Related washability studies were performed to assess the
effects of specific gravity and size reduction on the liberation and
separation of pyritic sulfur and ash from coals. Data on 322 samples
were reported by the Bureau of Mines and data on 67 samples were re-
ported by the Illinois Geological Survey. This effort is continuing.
2. An evaluation of the data from 322 mines sampled showed that
approximately 30 percent of these mines have coal that washed to a total
sulfur content of 1 percent or less. Both the distribution and release
potential of the sulfur in coals varies between the regions and coals
within the region.
3. The Illinois Geological Survey data indicated that there are
only a few Illinois coals whose sulfur content can be reduced to 1.5 per-
cent or less. Coals capable of this amount of sulfur reduction had only
2 percent or less sulfur in the raw coal samples.
4. An evaluation of data obtained from 195 coal samples from the
Appalachian region coal bed showed that significant total sulfur reduc-
tions are obtainable at yields of 70 to 80 percent.
5. An evaluation of data obtained from 13 coal samples from the
Southern Appalachian region showed percentage reductions in pyritic
sulfur contents (via washing) similar to those for Northern Appalachian
coals. However, due to the low pyritic sulfur content of the southern
coals, the attractiveness for cleaning is not as great.
42
-------
6. The Illinois Geological Survey concluded that, for the (Illinois)
coals tested for washability, two-inch-diameter core sample data correlated
very closely with face sample data.
7. All existing commercial coal cleaning processes with the excep-
tion of froth flotation proved effective in separating liberated pyrite
from coal. Of the several innovative processes for pyrite liberation
investigated, the two-stage flotation technique appears to show the
greatest potential for scale-up to commercial operation. The degree of
sulfur reduction was dependent on equipment, operating characteristics,
and, of course, the characteristics of the coal being tested., The
studies defined how sulfur reduction could be optimized.
8. Based on float-sink test results, an estimate was made of the
(9)
physical desulfurization potential of eastern bituminous steam coal.
The estimate was based on washing at 3/8 inch top size with a 90 per-
cent Btu recovery. The resulting estimates of cumulative availability
by sulfur content for both clean and raw coal are given in Figure 12.
9. The technology exists for utilizing reject and middling pro-
ducts to recover sulfur values and generate energy. The variables are
such (e.g., market for sulfur values, cost of coal, cleaning cost, trans-
portation economics, plant cost) that economic generalizations are not
possible and each case must be individually examined.
10. Physical cleaning, in general, will provide a higher Btu,
lower ash, more uniform product. Monetary benefits will result from
using physically cleaned coal. These benefits are attributable to
43
-------
(ALL COAL WASHED) V
SOURCE: DERIVED FROM DATA IN REFERENCE 2
0
12345
TOTAL SULFUR CONTENT - PERCENT BY WEIGHT
FIGURE 12
ESTIMATED PHYSICAL DESULFURIZATION POTENTIAL OF EASTERN
BITUMINOUS STEAM COAL PRODUCTION
-------
higher Btu content (of cleaned coal), an effective transportation cost
saving, an ash disposal cost saving, a grinding cost saving, and a
plant maintenance cost saving.
11. Physical cleaning the higher sulfur content coals, thereby
providing a higher BTU and lower ash product at high yield and reason-
able cost, could provide fuel for a combustor employing a moderate-
cost/moderate-capability supplemental stack gas cleaning system. This
use of physical cleaning and flue gas cleaning could reduce the overall
SC>2 emission control cost.
12. Physical cleaning of coal is essentially a proven technique
with only degree (levels and amounts) to be quantified. The process is
capable of providing a near-term, even though limited, benefit.
13. Physical cleaning of coal as a means to control sulfur oxides
emissions will have the least impact on the economy. Wide-spread com-
merical application of physical cleaning will help maintain a viable
coal industry and will permit increased use of coal, by far our most
abundant fossil fuel resource.
14- Studies performed by the Bechtel Corporation and A. D. Little,
Incorporated indicate that adequate technology exists, in the form of
several commercially-used and proven processes, for recovery of sulfur
values of pyrite materials as elemental sulfur or sulfuric acid and
energy values as steam or electric power. These processes have been
applied to mined pyrites but have not yet been applied to utilizing
pyrite-bearing refuse from coal preparation plants as feedstock.
45
-------
15. The Bechtel Corporation study indicates that several examined
processes are technically capable of accepting coal cleaning refuse as
feedstock, although certain of these processes require concentration of
the refuse to increase its pyrite content.
16. All the processes considered by A. D. Little, Incorporated and
the Bechtel Corporation for utilizing coal cleaning refuse require some
degree of modification to accommodate the relatively low-pyrite, high-
ash feedstock. Modification can be minimized by enriching the input air
with pure oxygen.
17. There is a large and a relatively stable market for sulfuric
acid. The attractiveness of processes for converting the sulfur content
of coal preparation plant refuse to sulfuric acid is highly dependent on
the market value of elemented sulfur.
18. Under conditions prevailing at the time of the A. D. Little,
Inc. and the Bechtel Corp. studies, the refuse-combustion/sulfur-oxides-
removal process and the fluid-bed roasting process were found to be
economically viable.
19. The Chemico study indicated (i.e., at the time of the study)
that by the use of high-sulfur refuse fuel of tailored composition to
meet the requirements of especially designed combustors and commercially
available boilers, generators and sulfur recovery processes, it appears
possible to extract the energy and sulfur values of high-sulfur fuels
on a commercial basis.
46
-------
20. In view of the shipping costs resulting from the heavy weight
of sulfuric acid, it may be highly advantageous for a sulfur recovery
plant to be capable of producing sulfur as several different compounds
(or in elemental form) especially in cases where the sulfur must be
shipped to different points of consumption.
-------
4.0 WASHABILITY STUDIES
This section outlines the procedures employed, details the number
of samples obtained from various locations, summarizes the results of
the washability studies, and reports on the findings of an effort that
examined the comparability of coal core samples and face samples. The
comparability of core samples and face samples effort was to determine
whether useful washability data could be obtained from 2-inch diameter
core samples. A more detailed description of sampling and washability
procedures and an in-depth discussion of results can be found in
References 3, 4, 5, 6, 7, and 8.
The principal purpose of the effort was to determine the sulfur
forms and distribution of sulfur in coal samples from mines which were
principally utility coal producers. Coal samples were obtained from
the following coal regions:
1. Northern Appalachian region: the states of Maryland, Pennsyl-
vania (bituminous), and Ohio and counties located in central
and northern West Virginia.
2. Southern Appalachian region: the states of Tennessee, Virginia,
and eastern Kentucky and some of the southern West Virginia
counties.
3. Alabama region: the state of Alabama.
4. Midwest region: the states of Illinois, Indiana, and western
Kentucky.
5. Western region: all states west of the Mississippi.
48
-------
Generally, the washability data on the coals indicated that the
total sulfur could be reduced by using some combination of stage crush-
ing and specific gravity separation. The washability data were analyzed
with the use of a specifically designed computer program.
4.1 Experimental Procedure - Collection of Coal Mine Samples
Coal samples were collected either from a fresh face in the mine or
from the tipple (raw R.O.M.). The face samples were obtained by cutting
channels approximately ten inches deep and wide enough to provide a sample
of approximately 600 pounds.^- ' Each channel was selected so as to be
as representative as possible of coal being mined. Tipple samples were
collected by taking increments at fixed time and/or weight intervals so
as to insure that all working faces were represented in the gross sample.
4.2 Procedure for the Conduct of the Washability Studies
The sample preparation procedures by investigator with specific
gravity test points for the washability studies are provided in Figure
13 and Table III. Each gross sample was air-dried and crushed to 1 1/2
inch top size using a single roll tooth crusher. The coal was then
divided into required portions by means of cone and quartering. The pre-
paration of each coal portion for float and sink tests was as indicated
in Figure 13. The 100 mesh x 0 material, separated by screening from the
coal fraction used for float and sink tests, was analyzed for ash,
pyritic sulfur, and total sulfur.
49
-------
tn
o
1,2,3,4
SCREEN-
, 3/8" x
MESH
14
14 x 100
MESH
REFERENCE NUMBER OF INVESTIGATION
1 - BUREAU OF MINES
2 - COMMERCIAL TESTING AND ENGINEERING
3 - BITUMINOUS COAL RESEARCH
4 - ILLINOIS GEOLOGICAL SURVEY
INDICATES FLOAT-SINK TEST
FIGURE 13
FLOW DIAGRAM SHOWING PREPARATION OF GROSS SAMPLE
-------
TABLE III
TABLE OF FLOAT SINK TEST SIZES WITH SPECIFIC GRAVITIES
Investigator
Bureau of Mines
Commercial Testing
and Engineering
Company
Bituminous Coal
Research, Inc.
Illinois State
Geological
Survey
Sizes Washed
1 1/2 in. x 100 mesh
3/8 in. x 100 mesh
14 mesh x 0
1 1/2 in. x 100 mesh
3/8 in. x 100 mesh
14 mesh x 0
30 mesh x 0
60 mesh x 0 (p.c.)
1 1/2 in. x 0
3/8 in. x 14 mesh
14 mesh x 100 mesh
Test Points
(Specific Gravities)
1.25-1.29 1.30 1.30-1.39 1.40
x x
X X
X X
X X
X X
X X
X XX
X XX
X XX
1.60
X
X
X
X
X
X
X
X
X
X
X
1.
X
X
X
-------
The float and sink analyses were conducted on the various fractions
at specific gravities as indicated by Table III. After completing the
float-and-sink analysis, the specific gravity fractions of the samples
were analyzed for ash, pyritic sulfur, and total sulfur content.
Additional details of the float-sink tests are provided in Refer-
ence 8.
4.3 Results of Washability Data - Washability Computer Program
A computer program was used to interpolate the washability data to
find the theoretical specific gravity of separation, yield, ash content,
and pyritic and total sulfur contents for specific levels of yield or
total sulfur. The values of the sulfur and yield interpolants were read
into the computer and stored. In addition, the following data were
entered for each mine sample: "state, county, town, mine, and bed codes;
laboratory number, and laboratory identification code, bed-bench and size
fraction codes; year of sample collection; company name, mine name, and
county name; the specific gravity fractions of separation and their
associated levels with the variables, ash, pyritic and total sulfur."^
Using these data, three tables are printed out for each mine. These
tables are: (1) the original cumulative washability data; (2) values
of specific gravity of separation, yield, ash, and pyritic sulfur for
requested levels of total sulfur; and (3) values of specific gravity of
separation, yield, ash, pyritic sulfur, and total sulfur for the request-
ed levels of yield.
52
-------
A second computer program was written to make a statistical evalua-
tion of the washability data. This program calculated averages and the
standard deviation (sigma) values.
The computer program was used to calculate the percentages of total
recovery of ash, pyritic sulfur, and total sulfur for the desired levels
of interpolation. Next, the program was used to calculate the averages
and standard deviations of the ash, pyritic sulfur, and total sulfur.
These averages and standard deviation values were found for each bed and
the required data accumulated for similar averages for the region. Also,
the averages and standard deviation values were calculated for each set
of interpolated values at the various yield levels.
4.4 Program Results
The average composition of the coals evaluated in the Bureau of
Mines study*was 14.4 percent ash, 2.05 percent pyritic sulfur and 3.23
percent total sulfur.' ' The results generally indicated that the largest
reduction in ash and sulfur through washing was obtained by reducing
coal top size from 1 1/2 inches to 3/8 inch. Crushing from 3/8 inch to 14
mesh showed relatively lower ash and sulfur reduction.
*Data from the Commercial Testing and Engineering Company investigations are
reported by the Bureau of Mines.
53
-------
Summary data covering the 322 coal samples evaluated by the Bureau of
fO\
Mines are as follows:v
Ash, Percent
(Raw Avg.: 14.4,
„ ^ XT * Sigma: 5.8)
Percent No. of °
Yield Samples Average Sigma*
Pyritic Sulfur,
Percent
(Raw Avg.: 2.05,
Sigma: 1.35)
Total Sulfur,
Percent
(Raw Avg.: 3.23,
Sigma: 1.75)
60
70
80
90
60
70
80
90
60
70
80
90
260
290
284
168
25.
287
277
145
270
298
274
136
Average Sigma Average
1 1/2 Inch Top Size
5.8
6.4
7.1
7.2
2.3
2.7
2.8
2.4
0.72
0.79
0.89
1.00
0.57
0.59
0.65
0.68
1.95
2.03
2.13
2.27
1.06
1.07
1.12
1.21
3/8 Inch Top Size
5.1
5.6
6.3
6.5
4.6
5.2
5.9
6.0
2.2
2.4
2.4
2.2
2.1
2.3
2.2
2.0
0.57
0.61
0.68
0.75
14 Mesh
0.46
0.50
0.57
0.59
0.48
0.48
0.49
0.56
Top Size
0.40
0.39
0.42
0.48
1.82
1.83
1.92
1.95
1.70
1.72
1.79
1.79
1.04
1.00
1.04
1.12
0.98
0.96
0.99
1.07
The sulfur reductions of these coals attained by washing are further
summarized in Figure 14. This figure indicates that significant total sulfur
reductions are attainable by removing heavy impurities. At 60 percent
yield, 20 to 25 percent of the mine samples showed a 1 percent or less
total sulfur product.
*Sigma (cr) is the standard deviation value.
54
-------
w
OT
W
90 PERCENT YIELD
i i i i i
80 PERCENT YIELD
70 PERCENT YIELD
60 PERCENT YIELD
i i i i
(a)
(b)
(c)
(d)
678012
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS llj INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURE 14
WASHABILITY SUMMARY OF ALL COALS
345678
SOURCE: REFERENCE 8
55
-------
An evaluation of the data from the 322 mines sampled showed that
approximately 30 percent of these mines have coal that washed to a total
sulfur content of 1 percent or less. On crushing to 1 1/2 inch top size,
significant reductions in sulfur content were attainable by removing 10
or 20 percent of the heaviest material. Furthermore, the total sulfur
content was reduced by approximately 50 percent in more than half of the
samples collected by crushing of the coal prior to removing the heaviest
impurities. Both the distribution and release potential of the sulfur
in coals varies between the regions and the coals within the region.
The Illinois Geological Survey washability studies indicated that
most Illinois coals have a total sulfur content of 3 to 5 percent and
there are only a few Illinois coals whose sulfur content can be reduced
to 1.5 percent or less. The coals capable of this amount of sulfur re-
duction had only 2 percent or less sulfur in the raw coal samples.
With regard to the forms of sulfur in the coals, it was found that
approximately 50 percent of the sulfur in the average Illinois coal was
in the pyritic form. The average pyritic sulfur reduction was approxi-
mately 60 percent with an 80 percent yield and 75 percent with a 40 per-
cent yield.
Usually, the float coal fractions had less sulfur when the coal was
crushed to finer sizes. In many of the coals tested, however, the differ-
ences were not great enough to warrant grinding the coals to finer sizes
for sulfur reduction.
56
-------
4.4.1 Northern Appalachian Region
One hundred and ninety-five coal bed samples were collected from
the following four states of the Appalachian region:
1. Maryland - 32 samples
2. Ohio - 48 samples
3. Pennsylvania - 90 samples
4. Northern West Virginia - 25 samples.
The average composition of the raw coal of the region was 14.7 percent
ash, 2.03 percent pyritic sulfur, and 3.07 percent total sulfur. An
analysis of the data indicated that crushing the raw coal to 1 1/2 inch
top size resulted in an average pyritic sulfur reduction of 0.95 per-
centage points at 90 percent yield and 1.12 percentage points at 80 per-
cent yield. Crushing the coal to 3/8 inch top size resulted in an
average pyritic sulfur reduction compared to raw coal of 1.25 percentage
points at 90 percent yield and 1.4 percentage points at 80 percent yield.
Crushing the coal to 14 mesh top size resulted in an average pyritic
sulfur reduction compared to raw coal of 1.46 percentage points at 90
percent yield and 1.52 percentage points at 80 percent yield.
Summary data covering the 195 Northern Appalachian region coal
/Q\
samples evaluated by the Bureau of Mines are as follows:
57
-------
Percent No. of
Yield Samples
Ash, Percent
(Raw Avg.: 14.7,
Sigma: 6.0)
Pyritic Sulfur,
Percent
(Raw Avg.: 2.03,
Sigma: 1.24)
Total Sulfur,
Percent
(Raw Avg.: 3.07,
Sigma: 1.59)
Average Sigma Average Sigma Average Sigma
1 1/2 Inch TOP Size
60
70
80
90
60
70
80
90
169
180
169
99
159
179
163
86
5.8
6.6
7.4
7.4
5.2
5.8
6.5
6.7
2.6
2.9
3.0
2.4
2.4
2.7
2.6
2.2
0.68
0.79
0.91
1.08
3/8 Inch
0.50
0.57
0.63
0.78
0.54
0.59
0.70
0.67
Top Size
0.45
0.49
0.49
0.57
1.73
1.83
1.96
2.25
1.57
1.62
; 1.68
1.90
0.96
1.00
1.11
1.15
0.93
0.94
0.98
1.11
14 Mesh Top Size
60
70
80
90
163
181
161
81
4.7
5.4
6.0
6.2
2.2
2.6
2.3
2.0
0.39
0.44
0.51
0.57
0.35
0.39
0.40
0.45
1.45
1.49
1.55
1.69
0.86
0.87
0.91
1.01
Figure 15 shows the percentage of mines versus sulfur content re-
lationship derived from analyses of coals collected from the Northern Ap-
palachian region. This figure indicates that 32 percent of the mines
sampled contained coal with less than 2 percent total sulfur. Upon
crushing to 1 1/2 inch top size with 90 percent yield, 43 percent of the
mines sampled contained less than 2 percent total sulfur. At 80 percent
yield the value increased to 68 percent with less than 2 percent sulfur.
In general, significant total sulfur reductions are obtainable at yields
of 70 to 80 percent.
The results of sampling various coal beds of the Northern Appalachian
region are discussed in the following sections.
58
-------
w
W
w
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
90 PERCENT YIELD
i i i i i
70 PERCENT YIELD
i i i i
80 PERCENT YIELD
i i i i i
60 PERCENT YIELD
iii iii
(a)
(b)
(c)
(d)
345678
SOURCE: REFERENCES
56780 12
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS 1% INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURE 15
WASHABILITY OF NORTHERN APPALACHIAN REGION COALS
59
-------
4.4.1.1 Sewickley Coal Bed. Thirteen Sewickley coal bed samples
were collected from the following four Northern Appalachian states:
1. Maryland - 2 samples
2. Ohio - 9 samples
3. Pennsylvania - 1 sample
4. West Virginia - 1 sample
The total sulfur content of this coal is high, averaging over 2.5 percent
(with o- «1.37) at 60 percent yield. In general, this coal was quite
refractory, providing small to only moderate reductions of ash and total
sulfur contents as a result of crushing. However, the pyritic sulfur
reduction was high due to the coarseness of the pyrite which reported to
the high specific gravity material.
The organic sulfur content of coals from the Sewickley bed varied
considerably and was generally over 1.5 percent. The high percentage
reduction in pyritic sulfur was reflected in total sulfur reductions
ranging from 23 percentage points at 90 percent yield to 33 percentage
points at 60 percent yield when the coals were crushed to 3/8 inch top
size. Further crushing did not significantly reduce total sulfur content.
4.4.1.2 Pittsburgh Coal Bed. Thirty-six samples from the Pittsburgh
coal bed were collected from the following four Northern Appalachian
Region states:
1. Maryland - 1 sample
2. Ohio - 16 samples
3. Pennsylvania - 5 samples
4. West Virginia - 14 samples
60
-------
The average characteristics of the raw samples collected from the Pittsburgh
coal bed are 12.4 percent ash (tr = 5.8), 2.16 percent pyritic sulfur (a- = 0.92),
and 3.61 percent total sulfur (cr - 1.21). Crushing these coals to 1 1/2 inch
top size provided 90 percent average yield values of 6.7 percent ash (
-------
The average characteristics of raw samples collected from the Upper Freeport
coal bed are 17.2 percent ash (cr = 5.3), 1.72 percent pyritic sulfur (cr = 0.9;
and 2.42 percent total sulfur (cr = 1.10). Crushing these coals to 1 1/2
inch top size provided 90 percent yield values of 9.1 percent ash (cr = 2.9),
1.05 percent pyritic sulfur (cr = 0.72), and 1.81 percent total sulfur
(
-------
The average characteristics of the raw samples collected from the Lower
Freeport coal bed are 12.9 percent ash (cr = 3.5), 1.72 percent pyritic
sulfur (
-------
sulfur (or= 1.19), and 2.37 percent total sulfur (or = 1.29). Crushing
these coals to 1 1/2 inch top size provided 80 percent yield values of
7.1 percent ash (cr = 0.5), 0.48 percent pyritic sulfur (0-== 0.39), and
1.07 percent total sulfur ( cr= 0.46). Crushing to 3/8 inch top size
provided 80 percent yield values of 6.4 percent ash (cr = 0.5), 0.33 per-
cent pyritic sulfur ( a-= 0.33), and 0.89 percent total sulfur (cr = 0.37).
Further crushing to 14 mesh top size proved to be of no practical value.
The sampled data indicated that Upper Kittanning coal is a good
example of coal that can be significantly desulfurized. The average
sulfur content of these coals decreased from the raw coal value of 2.37
percent to 0.89 percent upon crushing to 3/8 inch top size and processing
to provide an 80 percent yield.
4.4.1.6 Middle Kittanning Coal Bed. Twenty-three coal samples
were collected from the following three states:
1. Ohio - 11 samples
2. Pennsylvania - 10 samples
3. West Virginia - 2 samples.
The average characteristics of the raw coal samples collected from the
Middle Kittanning coal bed are 12.7 percent ash (cr = 5.2), 2.25 percent
pyritic sulfur (cr = 1.52), and 3.35 percent total sulfur (cr = 2.02).
Crushing these coals to 1 1/2 inch top size provided 80 percent yield values
of 6.5 percent ash (cr = 3.2), 0.95 percent pyritic sulfur (cr = 1.09), and
2.02 percent total sulfur (cr = 1.45). Crushing to 3/8 inch top size pro-
vided 80 percent yield values of 5 percent ash (cr = 2.1), 0.52 percent
64
-------
pyritic sulfur (cr = 0.34), and 1.56 percent total sulfur (cr = 0.71).
Further crushing to 14 mesh top size proved to be of very limited values.
4.4.1.7 Lower Kittanning Coal Bed. Thirty-seven coal samples were
collected from the following three states:
1. Maryland - 3 samples
2. Ohio - 5 samples
3. Pennsylvania - 29 samples.
The average characteristics of the raw samples collected from the Lower
Kittanning coal bed are 15.1 percent ash (cr = 6.8), 2.31 percent pyritic
sulfur (
-------
1. Tennessee - 6 samples
2. Southern West Virginia - 3 samples
3. Virginia - 4 samples.
The average raw coal of the region contained 11.2 percent ash, 0.29 percent
pyritic sulfur, and 0.93 percent total sulfur. These are generally low-
sulfur-content coals averaging less than 1 percent total sulfur content.
Because the pyritic sulfur is so low, crushing of these coals to release
sulfur would be of almost no benefit, although the pyritic sulfur reduction
owing to crushing and reduced yield is very good. The sulfur reduction
of these coals attained by washing is summarized below and in Figure 16.
Summary data covering the 13 Southern Appalachian region samples
evaluated by the Bureau of Mines are as follows:
.(8)
Percent No. of
Yield Samples Average
Ash, Percent
(Raw Avg.: 11.2,
Sigma: 5.3)
Pyritic Sulfur,
Percent
(Raw Avg.: 0.29,
Sigma: 0.52)
Total Sulfur,
Percent
(Raw Avg.: 0.93,
Sigma: 0.80)
Sigma Average Sigma
1 1/2 Inch Top Size
Average
Sigma
60
70
80
90
60
70
80
90
60
70
80
90
6
12
12
8
5
10
12
8
9
13
12
8
4.0
4.0
4.3
4.8
4.1
3.9
3.8
3.5
2.8
3.2
3.9
4.5
1.6
1.7
2.2
2.1
0.9
1.7
2.2
2.0
1.3
1.6
1.9
1.9
0.15
0.10
0.10
0.14
3/8 Inch Top
0.14
0.09
0.08
0.12
14 Mesh Top
0.07
0.07
0.08
0.11
0.21
0.17
0.18
0.28
Size
0.19
0.16
0.13
0.25
Size
0.09
0.10
0.14
0.22
0.98
0.81
0.81
0.90
1.01
0.81
0.78
0.87
0.84
0.77
0.78
0.84
0.65
0.49
0.50
0.66
0.68
0.51
0.45
0.63
0.44
0.39
0.44
0.58
66
-------
w
w
PU
W
B
(a)
(b)
(c)
(d)
90 PERCENT YIELD
i i i i i
70 PERCENT YIELD
80 PERCENT YIELD
60 PERCENT YIELD
i i iii
345678
SOURCE: REFERENCE 8
12345678012
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS 1% INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURE 16
WASHABILITY OF SOUTHERN APPALACHIAN REGION COALS
67
-------
4.4.3 Alabama Region Coals
Six samples were collected from the Alabama region. The average
characteristics of the raw samples are 14 percent ash (cr = 3.7), 0.97 percent
pyritic sulfur (o- = 0.99), and 1.66 percent total sulfur (
-------
6.0 percent ash, 0.82 percent pyritic sulfur, and 2.61 percent total
sulfur. Crushing to 3/8 inch top size did not provide significant im-
provements in ash and sulfur values.
Crushing these coals to 14 mesh top size provided 90 percent yield
values of 6.7 percent ash, 0.77 percent pyritic sulfur, and 2.53 per-
cent total sulfur. The 70 percent yield values were 5.1 percent ash,
0.66 percent pyritic sulfur, and 2.38 percent total sulfur. At 60 per-
cent yield the values were 4.4 percent ash, 0.58 percent pyritic sulfur
and 2.29 percent total sulfur.
Summary data covering the 82 Midwest region coal samples evaluated
by the Bureau of Mines are.as follows:
Ash, Percent
(Raw Avg.: 14.1,
Pyritic Sulfur,
Percent
(Raw Avg.: 2.29,
Total Sulfur,
Percent
(Raw Avg.: 3.92,
Percent
Yield
60
70
80
90
60
70
80
90
60
70
80
90
No. of
Samples
61
73
79
42
62
73
79
35
71
78
76
33
Sigma:
Average
5.4
6.0
7.0
7.5
4.7
5.3
6.4
6.9
4.4
5.1
6.2
6.7
4.8)
Sigma
1.2
1.6
1.9
1.6
1.1
1.4
1.7
1.6
1.2
1.5
1.8
1.5
Sigma:
Average
1 1/2 Inch
0.75
0.82
0.97
1.00
3/8 Inch
0.66
0.73
0.86
0.85
14 Mesh
0.58
0.66
0.77
0.77
1.00)
Sigma
Top Size
0.32
0.35
0.45
0.48
Top Size
0.25
0.30
0.37
0.34
Top Size
0.22
0.26
0.33
0.34
Sigma:
Average
2.49
2.61
2.72
2.76
2.42
2.47
2.60
2.59
2.29
2.38
2.48
2.53
1.26)
Sigma
0.70
0.69
0.78
0.97
0.70
0.74
0.78
0.86
0.73
0.73
0.75
0.83
69
-------
Figure 17 shows that 60 percent of the collected samples contained less
than 2 percent organic sulfur. For top size crushing of 1 1/2 inch and
less, over half of the pyritic sulfur is removed with 90 percent yield.
The reasonable range of total sulfur in the final product as indicated in
Figure 17 is 2-3 percent.
The results of sampling the various coal beds of the Midwest region
are as follows:
4.4.4.1 Kentucky No. 9 Coal Bed. Thirteen samples from the Kentucky
No. 9 coal bed were collected from Western Kentucky. The average composition
of the raw samples was 11.4 percent ash (
-------
w
en
H
(a)
(b)
(c)
(d)
90 PERCENT YIELD
70 PERCENT YIELD
12345678012
SULFUR, PERCENT
RAW COAL TOTAL SULFUR CONTENT CURVE;
RAW COAL ORGANIC SULFUR CONTENT CURVE;
WASHED COAL TOTAL SULFUR CONTENT COAL CURVE
WHEN RAW COAL WAS CRUSHED TO MINUS 1>J INCHES;
AND,
WHEN RAW COAL WAS CRUSHED TO MINUS 14 MESH.
FIGURE 17
WASHABILITY OF MIDWEST REGION COALS
345678
SOURCE: REFERENCE 8
71
-------
4.4.5 Illinois Geological Survey Studies
In addition to the Bureau of Mines reported studies, washability
studies in two phases were conducted by the Illinois Geological Survey
on samples taken from Illinois coal mines. During the first phase, 40
samples were taken from 35 Illinois coal mines located in most mining
areas in the state, the number of samples being greater than the number
of mines because several mines produced coal from more than one seam
and the different seams were sampled separately.
During the second phase of the Illinois Geological Survey investi-
gation, washability tests were made on 27 coal samples taken from most
of the Illinois mines not sampled during the first phase. The coal
samples (phases I and II) were obtained from the No. 1, No. 2, No. 4,
No. 5, No. 6, No. 7, DeKoven, and Davis seams.
Float-sink tests indicated that only in those Illinois coals hav-
ing relatively low-sulfur content, as mined, could the total sulfur
content be reduced to 1.5 percent or less by washing techniques. Most
Illinois coals, as mined, contain 3-5 percent sulfur. Float-sink tests
indicate this level could be reduced to about 2.5 to 4 percent total
sulfur.
In Phase I, only two of the 40 tested samples could be reduced to
a total sulfur content of less than 1 percent at an 80 percent recovery.
Five samples could be cleaned to less than 1.5 percent total sulfur
with an 80 percent recovery. These five samples were all naturally-
occurring low-sulfur coals. Of the 40 coals tested during Phase I, 10
72
-------
samples could be cleaned to 2.5 percent sulfur or less than an 80 per-
cent recovery. The above was obtained with top size crushing of 1 1/2
inches. Crushing to finer sizes did not provide additional significant
sulfur reductions.
Due to the similarity of Phase I results between 11/2 inch and
3/8 inch top size testing and since 3/8 inch top size testing would
allow the use of a smaller quantity of coal for washing and chemical
tests, the following Phase II results are based on testing at 3/8 inch
top size.
In Phase II, 4 out of the 27 samples tested had less than one per-
cent total sulfur at recovery levels of 80, 60 or 40 percent. Of these
four, one sample was obtained from a mine in current production and with
appreciable unmined reserves. In addition to the above, one sample
obtained from a large mine had float coal with less than 1.5 percent
total sulfur content with an 80 percent recovery. None of the other
samples could be washed, irrespective of yield, to less than 1.5 percent
total sulfur.
( 8)
4.4.6 Western Coal
The examination of Western coals was initiated at a later date than
for coals of the other regions. This is due to the preponderance of
steam coal traditionally supplied by states east of the Mississippi. As
interest in the vast reserves and the potential availability of Western
coal developed, washability examinations were performed, concentrating on
the higher sulfur coals, i.e., those coals in which a sulfur reduction
(9)
potential would be most desirable.
73
-------
For this effort, twenty-six coal samples from the Western region
were collected from the following six states:
1. Iowa - 6 samples
2. Oklahoma - 4 samples
3. Kansas - 4 samples
4. Arkansas - 3 samples
5. Missouri - 4 samples
6. Colorado - 5 samples.
All of the Western coal samples, with the exception of those from Colo-
rado, are from the Western Interior region. Colorado lies in the Rocky
Mountain region.
The average composition of raw coal from the Western region was
14.5 percent ash, 2.48 percent pyritic sulfur, and 3.72 percent total
sulfur. Coals from the Western Interior region are characteristically
high in sulfur content, regardless of sulfur treatment employed. Coals
from the Rocky Mountain region conversely are characteristically of low
sulfur content, often less than one percent sulfur content, and range
in rank from bituminous coal to lignite, with sub-bituminous predominating.
4.4.7 Extension of Float-Sink Test to Finer Grinds^6>1Q^
Washability studies were extended in a separate effort (ref. Figure
13) to cover finer sizes of coal at a specific gravity of 1.60. The coal
sizes studied were the 30 mesh x 0 size and the "as fired" or pulverized
coal (p.c.) grind. All coal in the p.c. grind is minus 60 mesh with a
minimum of 80 percent of the coal minus 200 mesh. The 30 mesh * 0 size
represented the lower limit in sizing that would contain a size range of
74
-------
pyrite typical of a utility pulverizer's recycle load. The coals "as
fired" (or p.c. grind) were of interest because potentially the maximum
pyrite liberation occurs, based on present utilization, with this de-
gree of pulverization.
The results of the float-sink analysis of the coal samples are
discussed in terms of a first series of 70 samples and an additional
series of 20 samples. The first series of 70 coals came from three geo-
graphical areas: Western Pennsylvania, Eastern Ohio, and Illinois. Max-
imum pyritic sulfur reduction obtained at the 30 x 0 mesh size was 93.7
percent with an Ohio No. 6 coal; the minimum pyritic sulfur reduction
obtained was 51.2 percent with an Illinois No. 6 coal. At the p.c. grind,
95 percent of the pyritic sulfur was removable from a Pennsylvania Lower
Freeport coal while the minimum percentage of pyritic sulfur removal was
54.5 percent with a Pennsylvania Middle Kittanning coal which had a very
low R.O.M. pyritic sulfur content. Total sulfur reductions covered a
much wider range since the percentages of organic sulfur, which was not
removable, quite significantly affected the percent reduction.
The second series of 20 coals came from three geographical areas:
(1) the Southern Appalachian, (2) Western Interior, and (3) Rocky Mount-
ain regions. The total sulfur in raw R.O.M. samples ranged from 0.32
to 6.37 percent by weight. Pyritic sulfur levels ranged from 0.09 to
4.66 percent by weight. The evaluation of the second series of 20 coals
differed markedly from the initial series of 70 coals. The majority of
the 20 coals were low in pyritic sulfur and little improvement could be
75
-------
made in sulfur reduction regardless of top size crushing. The majority
of the group, high in pyritic sulfur, were also high in organic sulfur.
Consequently, total reductions were not overly impressive.
The washability results of the first series of 70 coals and the
second series of 20 coals are provided in Figures 18 and 19, respectively.
These figures show the total sulfur reduction at 1.60 float for R.O.M.
coal crushed to the following sizes: 3/8-inch x 100 mesh, 14 mesh x 0,
30 mesh x 0, and p.c. grind. Figure 18 shows that for the initial 70-
coal series, the maximum total sulfur reduction ranged from 50 to 60
percent for 10 of the coals at the 1 1/2 inch top size to 80 to 90 per-
cent for one coal at the p.c. grind. This figure indicates that the
largest incremental sulfur reduction is obtained when the coal is re-
duced in size from a 1 1/2 inch top size to a 3/8 inch top size.
Figure 19, covering the second series of 20 coals, shows that at
the 1 1/2 inch top size 25 percent of the coals tested (five coals) could
be reduced in total sulfur by 20 to 30 percent when washed at a 1.60
specific gravity. In addition, five percent of the coals (i.e., one
coal) did not change in sulfur content when its top size was reduced
from 14 mesh to 30 mesh. The highest obtained total sulfur reduction
was 69 percent with one coal at its p.c. grind; indicating the fineness
of the pyrite distribution in this coal.
4.4.8 Comparability of Core Samples and Face Samples' '
One of the specific objectives of the (Phase II) Illinois Geologi-
cal Survey effort was to ascertain whether useful washability data could
76
-------
90-
80-
H
8
w
60-
40-
30-
20-
14 MESH x 0
30 MESH x 0
3/8 INCH x 100 MESH
p.c. GRIND
1 1/2 INCH x 100 MESH
I I 1 I 1 I I I I
10-20 30-40 50-60 70-80 90-100
TOTAL SULFUR REDUCTION LEVELS, PERCENT
SOURCE: REFERENCE 6
FIGURE 18
TOTAL SULFUR REDUCTION AT 1.60SPECIFIC GRAVITY AS RELATED TO
SIZE FOR 70 W. PENNSYLVANIA, E. OHIO, AND ILLINOIS COALS
77
-------
100
90
80
70
o
g
W
PH
30-
20-
10-
0
p.c. GRIND
30 MESH x 0
14 MESH x 0
3/8" x 100 MESH
1 1/2" x 100 MESH
I I I I I I
10-20 30-40 50-60
I
70-80 90-100
TOTAL SULFUR REDUCTION LEVELS, PERCENT
SOURCE: REFERENCE 10
FIGURE 19
TOTAL SULFUR REDUCTION AT 1.60 SPECIFIC GRAVITY AS RELATED
TO SIZE FOR 20 SOUTHERN, WESTERN, AND MID-WESTERN COALS
78
-------
be obtained from 2-inch-diameter core samples by examining the correla-
tions between this size sample and the normal size (i.e., large) sample.
Since these core samples usually weighed 10 pounds (approximately 6 foot
seam thickness), washability tests were made on both the 10-pound core
samples and the 100-pound fractions from normal face samples taken in
the same approximate locations.
Table IV lists the percentages of total sulfur, pyritic sulfur, and
ash for 40, 60, and 80 percent recoveries for the 23 normal samples cover-
ing this effort. Also shown are the corresponding values for the tests
made on the small (core) samples (Suffix S). The differences between
the values given for the large and small samples are usually less than
those specified by ASTM for analytical tolerance between laboratories.
Figures. 20 and 21 illustrate the similarity of results with large
and small samples. The curves are considered as .the best fit for the
data obtained with the large samples. The deviation from the curves
of the data points for the small sample are considered minor.
79
-------
TABLE IV
COMPARISON OF WASHABILITIES OF SMALL AND LARGE SAMPLES
40 percent recovery
*
Sample
Sulfur (%)
Total
Pyritic
Ash
%
60 percent recovery
Sulfur (%)
Total
Pyritic
Ash
%
80 percent recovery
Sulfur (%)
Total
Pyritic
Ash
%
I
IS
2
2S
3
3S
4
4S
5
5S
6
6S
7
7S
8
8S
9
9S
10
10S
11
3.21
3.29
2.46
2.50
2.39
2.40
2.81
2.96
1.85
1.88
0.81
0.84
1.62
1.64
2.40
2.42
2.77
2.66
1.99
1.93
1.92
0.44
0.53
0.42
0.51
0.49
0.49
0.55
0.65
0.75
0.89
0.17
0.20
0.36
0.40
0.43
0.42
0.56
0.56
0.44
0.44
0.45
4.2
4.2
2.4
2.9
2.8
2.5
6.1
5.6
3.6
4.2
3.4
3.4
2.9
2.8
2.3
2.4
3.5
3.3
3.0
3.2
2.1
3.32
3.30
2.57
2.56
2.55
2.55
2.91
3.03
2.24
2.02
0.85
0.87
1.74
1.78
2.49
2.51
2.88
2.75
2.06
1.99
2.04
0.56
0.57
0.58
0.58
0.66
0.64
0.65
0.73
1.10
1.09
0.22
0.23
0.48
0.50
0.52
0.53
0.67
0.65
0.55
0.52
0.63
5.4
5.2
3.4
3.4
3.8
3.4
6.5
6.1
5.0
5.1
4.3
4.1
4.1
4.0
3.2
3.3
4.3
4.1
4.1
3.9
3.8
3.51
3.45
2.80
2.77
2.90
2.85
3.22
3.30
2.84
2.51
0.93
0.94
1.91
1.95
2.67
2.66
3.08
2.94
2.21
3.15
2.35
0.81
0.79
0.87
0.84
1.01
0.94
0.96
1.00
1.67
1.64
0.31
0.32
0.65
0.67
0.71
0.70
0.85
0.86
0,73
0.71
0.95
7.3
7.0
5.5
5.5
.6.1
5.4
7.5
7.0
6.9
6.9
5.5
.5.4
6.0
5.9
4.9
5.0
5.7
5.5
6.0
6.0
6.6
* S = test run on small sample
80
-------
TABLE IV (con't)
COMPARISON OF WASHABILITIES OF SMALL AND LARGE SAMPLES
40 percent recovery
*
Sample ,
Sulfur (%)
Total 1 Pyritic
Ash
%
60 percent recovery
Sulfur (%)
Total
Pyritic
Ash
%
80 percent recovery
Sulfur (%)
Total
Pyritic
Ash
%
US
12
12S
13
13S
14
14S
15
15 S
16
16S
17
17S
18
18S
19
19S
20
20S
21
21 S
22
22S
23
23S
Source
2.08
1.76
1.78
2.59
2.75
0.71
0.70
0.53
0.57
2.07
2.20
3.14
3.38
2.49
2.77
2.56
2.66
1.37
1.25
2.21
2.26
3.39
3.30
3.81
3.82
0.47
0.72
0.76
0.33
0.60
0.15
0.12
0.02
0.08
0.45
0.54
0.48
0.46
0.71
0.89
0.51
0.63
0.41
0.33
0.32
0.34
1.57
1.61
0.38
0.43
3.3
4.5
4.8
2.9
3.9
3.5
3.5
3.0
3.2
4.5
4.6
4.1
4.0
3.0
4.1
3.1
4.2
3.1
2.4
6.0
7.0
8.4
8.0
3-7
4.1
2.13
1.86
1.82
2.75
2.80
0.71
0.70
0.53
0.57
2.24
2.34
3.16
3.43
2.68
2.91
2.71
2.71
1.41
1.32
2.23
2.26
3.68
3.57
3.85
3.82
0.56
0.84
0.83
0.48
0.66
0.17
0.12
0.02
0.08
0.67
0.67
0.53
0.52
0.87
1.02
0.69
0.70
0.43
0.38
0.36
0.34
1.87
1.92
0.54
0.52
4.5
5.5
5.6
4.4
4.6
4.1
4.0
3.6
3.8
5.9
6.0 .
4.7
4.7
4.3
5.1
4.5
4.8
3.9
3.3
7.0
7.2
10.2
9.9
4.9
5.1
2.39
2.07
1.97
2.93
3.01
0.72
0.70
0.57
0.58
2.59
2.63
3.36
3.62
2.93
• 3.08
2.95
2.91
1.48
1.39
2.26
2.29
4.07
3.94
4.07
4.02
0.87
1.08
1.04
0.66
0.92
0.19
0.15
0.07
0.08
1.04
1.02
0.79
0.76
1.13
1.22
1.02
0.97
0.50
0.47
0.42
0.41
2.31
2.33
0.90
0.86 '
6.8
6.9
6.9
6-. 8
7.4
4.7
4.6
4.6
4.7
7.6
7.7
6.3
6.2
6.6
7.0
6.8
6.9
5.5
5.3
8.6
8.6
12.6
12.3
6.8
7.0
: Reference 11.
81
-------
H
53
W
W
PM
ffi
CO
6
5
4
3
0
26
24
22
20
18
16
14
12
10
8
6
4
2
0
SAMPLE 20
D LARGE SAMPLE
O SMALL SAMPLE
TOTAL SULFUR
-D 30
cr
PYRITIC SULFUR
-D-
10 20 30 40 50 60 70 80 90 100
RECOVERY, PERCENT
SOURCE: REFERENCE 11
FIGURE 20
WASHABILITY CHARACTERISTICS OF SAMPLE 20
82
-------
w
PL,
ac
SAMPLE 22
LARGE SAMPLE
O SMALL SAMPLE
100
RECOVERY, PERCENT
SOURCE: REFERENCE 11
FIGURE 21 r
WASHABILITY CHARACTERISTICS OF SAMPLE 22
83
-------
5.0 LABORATORY AND PILOT STUDIES EVALUATING PROCESSES FOR PYRITE
REMOVAL FROM FINE COALS
This section describes the EPA-sponsored laboratory and pilot study
projects conducted by the Bureau of Mines and Bituminous Coal Research,
Incorporated. The objectives were (1) to determine the operating para-
meters for maximum pyrite separation, (2) to modify existing techniques
and/or develop new techniques to separate pyrite from fine coals, and
(3) to evaluate methods to process coal cleaning rejects so as to con-
centrate the pyrite and reclaim clean coal products.
The equipment or processes were evaluated by the two contractor
organizations as indicated below. The Bureau of Mines efforts concen-
trated on equipment operational parameters and the development of new
techniques while the Bituminous Coal Research efforts concentrated on
the applicability of equipment to various coals.
Investigated by
Bureau of Bituminous
Equipment/Process Mines Coal Research, Inc.
Wet Concentrating Table (Deister) X X
Concentrating Spiral (Humphry) X X
Hydrocyclones X X
Air Classifiers X
Electrokinetic Techniques Y
Agglomo-Separation X,Y
Froth Flotation X,Y
84
-------
X designates pilot plant tests
Y designates laboratory-scale tests
These processes are described briefly in the following sections and re-
sults of their performance are summarized.
5.1 Wet Concentrating Table
The wet table is a rectangular or rhomboid-shaped normally riffled
deck operated in essentially a horizontal plane. A drive mechanism im-
parts a differential motion to the deck along its long axis while water
flows by gravity along the short axis of the table. The rapid shaking
motion causes particles of different densities to migrate to different
zones on the table's periphery.
Commercial tables have a deck approximately 16 feet long on the
clean coal side and 8 feet long on the refuse side. In these studies,
a quarter-size deck, 8 feet long on the clean coal side and 4 feet long
on the refuse side, was used. The direction of the feed coal mixture
and the reporting of the clean coal, middlings, and refuse to the var-
ious sections of the table are shown in Figure 22. As the specific
gravity of the coarse particles increases, the material deposits further
around the table toward the refuse end.
In tests by the Bureau of Mines and Bituminous Coal Research, In-
corporated, the wet concentrating table proved effective in separating
liberated pyrite and ash from coal. Coals with a high proportion of
pyritic sulfur relative to organic sulfur are particularly amenable to
sulfur reduction by this process.
85
-------
DRESSING WATER
FEED
©
COAL
MIDDLINGS
REFUSE
SOURCE: REFERENCE 12
FIGURE 22
DISTRIBUTION OF CLEAN COAL, MIDDLINGS, AND
REFUSE ON THE WET CONCENTRATING TABLE
86
-------
Two series of wet concentrating table tests were performed by the
Bureau of Mines, one on a normal size table feed and the second on a
rather fine size feed. The results of cleaning minus 1/4 inch coal are
shown in Table V. The pyritic sulfur content was reduced from 3.07
to 0.60 percent and the total sulfur from 3.63 to 1.20 percent at a
clean coal recovery of 86.3 percent.
Further analyses on the coal (first series of tests) were made by
screening the minus 1/4 inch coal into four size fractions as indicated
by Table V. The combined pyritic sulfur reduction for the three larger
size fractions was approximately 84 percent each. Also, the efficiency
of the separation deteriorated in the minus 200 mesh size range where
the pyritic sulfur reduction was only 58 percent.
For the Bureau's second series of tests (Table VI) conducted on 35
mesh x 0 size coal, the 35 by 200 mesh fraction shows the pyritic sulfur
content reduced by 75 percent, from 2.05 percent in the feed to 0.50 per-
cent in the clean coal. The pyritic sulfur in the minus 200 mesh by
0 size fraction was reduced by 23 percent, or from 1.69 percent in the
feed to 1.30 in the clean coal.
The results of the second series of wet concentrating table tests
are shown in Table VI. When the sample was broken down into the plus
and minus 200 mesh size fractions, the results showed that the efficiency
of the table for separating pyrite from coal deteriorated below the 200
mesh size range.
87
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TABLE V
PRODUCT ANALYSIS OF A 1/4 INCH BY 0 SIZE
COAL WASHED ON A WET CONCENTRATING TABLE
Percent
Products
Clean coal
Refuse
Feed
Clean coal
Refuse
Feed
Clean coal
Refuse
Feed
Clean coal
Refuse
Feed
Clean coal
Refuse
Feed
Pyrltic
Sulfur
Total
Sulfur
2.6
36.9
7.0
0.56
19.19
2.92
1.13
19.60
3.47
14 by 48 mesh, 38.9 percent
2.6
40.9
7.9
.45
17.15
2.77
1.08
17.66
3.38
48 by 200 mesh, 15.2 percent
Weight Ash
1/4 inch by 14 mesh, 41.6 percent
87.3
12.7
100.0
86.1
13.9
100.0
83.8
16.2
100.0
86.1
13.9
100.0
86.3
13.7
100.0
5.9
68.0
15.8
.56
17.69
3.32
1.17
17.79
3.85
200 mesh by 0, 4.3 percent
28.4
71.9
34.6
2.51
27.51
6.00
3.08
27.64
6.51
1/4 inch by 0, 100.0 percent
4.2
45.6
9.9
.60
18.49
3.07
1.20
18.86
3.63
Source: Reference 12.
88
-------
TABLE VI
PRODUCT ANALYSIS OF A 35 MESH BY 0 SIZE
COAL WASHED ON A WET CONCENTRATING TABLE
Product
Percent
Weight
Ash
Pyritic
sulfur
Total
sulfur
Clean coal
Refuse
Feed
Clean coal
Refuse
Feed
Clean coal
Refuse
Feed
63.7
36.3
100.0
92.4
7.6
100.0
74.0
26.0
100.0
35 by 200 mesh, 63.9 percent
8,7
53.2
24.8
0.50
4.77
2.05
200 mesh by 0, 36.1 percent
16.1 1.30
27.6
17.0
6.51
1.69
35 mesh by 0. 100.0 percent
12.0 .87
50.5 4.95
22.0 1.92
1.25
5.18
2.67
1.98
7.08
2.36
1.58
5.39
2.56
Source: Reference 12.
89
-------
In addition to the above, two-stage cleaning tests, in which a
coarse sample (3/8 inch x 0) was tabled on a quarter sized unit and the
clean fraction pulverized to a finer size (30 mesh x 0) which was re-
tabled, were performed by Bituminous Coal Research. Equipment for
testing the coarse sample had a capacity of 2-1/2 to 3 tons per hour,
and that for the fine sample of 1 to 1-1/4 tons per hour. These tests
indicated that pyrite removal can be improved by use of the concentra-
tion table in two stages. A total of eight coals, five eastern and
three (mid)western, were subjected to two-stage tabling. These coals
are identified and their sulfur contents are shown in Table VII. The
results are given in Table VIII which also shows feed rate during test-
ing, percent total sulfur in the feed, and percent sulfur in clean coal.
Reductions in total sulfur range from 29 percent to 68 percent.
5.2 Concentrating Spiral
The concentrating spiral, although widely used for ore dressing, has
never been used for coal preparation even though it had been previously
considered for coal cleaning purposes. It was evaluated because of its
low capital and operating costs.
The concentrating spiral (see Figure 23) consists of a spiral
conduit of modified semicircular cross section. In operation, pulp is
fed from the top of the spiral and as it flows downward centrifugal
force causes the heavier particles to concentrate in a band along the
inner side of the spiral. They are removed through adjustable ports
90
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TABLE VII
ANALYSIS OF COALS SELECTED FOR CONCENTRATING TABLE TESTS
Coal Identification
Seam
County, State
Eastern Coals
No. 6-A
Harrison, Ohio
Upper Freeport
Westmoreland, Pa.
No. 8
Jefferson, Ohio
No. 6
Columbiana, Ohio
Lower Kittanning
Indiana, Pa.
Midwestern Coals
Lower Cherokee
Upper Spandra
Tebo Seam
BCR
Lot
No.
1735
1750
1768
1745
1755
2415
2416
2417
Weight
Total
Ash Sulfur
10.4 2.50
22.5 3.74
19.4 4.71
10.4 2.44
20.1 4.66
12.8 5.12
6.5 1.59
29.8 6.92
Percent , Dry
Sulfate
Sulfur
0.01
0.03
0.07
0.05
0.05
0.26
0.08
0.68
Basis
Pyritic
Sulfur
1.86
3.22
3.69
1.79
4.00
4.24
0.77
4.44
Organic
Sulfur
0.63
0.49
0.95
0.60
0.61
0.62
0.74
1.80
Organic Sulfur
as Percent
of Total Sulfur
25.2
13.1
20.2
24.6
13.1
Adapted from References 6 and 10.
-------
TABLE VI11
CONCENTRATING TABLE TESTS
EFFECT OF TWO-STAGE CLEANING
Coal Identification
Seam
County State
Eastern Coals
No. 6-A
Harris on , Ohio
Upper Freeport
Westmoreland, Pa.
No. 8
Jefferson, Ohio
<, No. 6
r
-------
FEED BOX
WASH WATER
MIDDLINGS
CENTRIFUGE
50' LENGTH OF 1" FEED HOSE
INCREASES CIRCULATING TIME
TO 15 SECONDS
PUMP
HOSE SUPPORT
REFUSE COLLECTING PIPE
REFUSE PORT
SPIRAL SECTION
SPLITTER BOX
CLEAN COAL,
REFUSE
MIXER
PUMP SUMP
SOURCE; REFERENCE 12
FIGURE 23
HUMPHREYS SPIRAL CONCENTRATOR CLOSED CIRCUIT TEST UNIT
93
-------
located on each turn of the spiral at the lowest point in the cross sec-
tion of the conduit. As the spiral stream is discharged from the lower
end of the spiral, an adjustable splitter divides the stream into two
products: a clean coal product (outer coal) and a middling product
(inner coal).
The Bureau of Mines evaluated spiraling on coals of top sizes rang-
ing from 4 mesh down to 35 mesh and on double sized fractions. It was
found that the best separation occurred when the top size of the spiral
feed was minus 14 mesh or less. Surprisingly, the capacity of the
spiral remained about constant, regardless of the feed top size. Con-
sequently, the capacity of the spiral for was-hing fine-size coal was
very high.
The results of spiraling 35 mesh by 0 Middle Kittanning bed coal
are shown in Table IX. A feed coal having a total sulfur content of 2.53
percent was reduced to 1.48 percent by spiraling at a clean coal recovery
of 90.7 percent. The final sulfur content of the washed 35 by 200 mesh
coal was 0.92 percent sulfur, while the sulfur content of the washed
minus 200 mesh coal was 2.34 percent sulfur. This rapid deterioration
of the efficiency of the washing technique with size reduction is a nor-
mal characteristic of specific gravity separators. The excellent results
achieved by the Bureau of Mines with the spiral on fine-size coal sug-
gest it should be considered along with hydrocyclones and the wet con-
centrating tables as a "rougher" cleaning unit to remove pyrite from
high sulfur coals prior to flotation.
94
-------
TABLE IX
PRODUCT ANALYSIS OF 35 MESH BY 0 MIDDLE KIT-
TANNING BED COAL WASHED OVER THE COAL SPIRAL
Percent
Product Weight
Pyritic
. , Sulfur
Ash
Total
Sulfur
Clean coal
Refuse
Feed
35 by 200 mesh, 61.2 percent of feed
88.3
11.7
100.0
7.2
42.8
11.4
0.29
13.51
1.85
0.92
13.79
2.43
Clean coal
Refuse
Feed
200 mesh by 0, 37.8 percent of feed
94.7
5.3
100.0
12.0
21.4
12.5
1.71
8.48
2/07
2.34
8.96
2.69
Composite 35 mesh by 0, 100.0 percent of feed
Clean coal
Refuse
Feed
90.7
9.3
100.0
9.1
38.2
11.8
.86
12.43
1.94
1.48
12.75
2.53
Source: Reference 12.
95
-------
Five different coals were used by Bituminous Coal Research, Inc.,
in their evaluation of the concentrating spiral for cleaning coal.
These coals were from the following seams:
1. No. 6-A seam, Harrison County, Ohio
2. Lower Kittanning seam, Indiana County, Pennsylvania
3. No. 6 seam, Columbiana County, Ohio
4. Upper Freeport seam, Westmoreland County, Pennsylvania
5. No. 8 seam, Jefferson County, Ohio.
Their sulfur contents are given in Table VII. Coal from the No. 6^-A
Ohio seam was tested at the 30 mesh x 0 size, while the other four were
precleaned on the wet concentrating table at the 3/8 inch x 0 size and
the clean-coal fraction then crushed to 30 mesh x 0. The fine coal was
then cleaned on the spiral,
A 15.3 percent reduction in total sulfur, 94.8 percent recovery,
was obtained by single stage cleaning of the 30 mesh x 0, Ohio 6-A seam
coal. This result was obtained by combining the screen fractions of the
middling material and the clean coal. For both the single and double-
stage cleaning, it was found that all the clean coal fractions contained
a significant quantity of high-ash, high-sulfur sink material. Results
of the double-stage cleaning appear in Table X. Comparison of these
sulfur reductions with those obtained by cleaning the same coals with
the wet concentrating table (Table VIII) indicate that the spiral pro-
duces similar reductions and yields for two of the coals tested and
somewhat lower reductions for the other two.
96
-------
TABLE X
CONCENTRATING TABLE AND SPIRAL CONCENTRATOR TESTS
EFFECTS OF TWO-STAGE CLEANING
Coal Identification
Lot Seam
Location
County, State
Total Sulfur,
Feed to Table*
Percent
Clean Coal, Total Sulfur Reduction,
Two-stage Cleaning Two-stage Cleaning
Percent Percent
-o
VI
2031 Lower
Kit tanning
2026 No. 6
2012 Upper
Freeport
2013 No. 8
Indiana, 3.66
Pennsylvania
Columbiana, 2.90
Ohio
Westmoreland , 3 . 30
Pennsylvania
Jefferson, 3.98
Ohio
78.3
89.3
77.9
87.0
65.3
48.3
54.5
28.4
* Based on Composite of Table Products, Rough Cleaning
Source: Reference 6.
-------
5.3 Water Cyclone
Water cyclone performance evaluation tjests were conducted by the
Bureau of Mines on five units in commercial plants. Preliminary results
of these tests showed excellent pyritic sulfur reductions were attain-
able. The clean coal recoveries were highly dependent on the size of
the material. Clean coal recovery of the plus 48 mesh material was low,
while most of the minus 100 mesh material reported to the clean coal
product. Final results of this work are planned to be published in a
Bureau of Mines report entitled Performance Characteristics of Coal-
Washing Equipment ; Water-Only Cyclones.
Water cyclone tests were also conducted by Bituminous Coal Research,
Inc. ' Feed coals were pulverized to minus 30 mesh size prior to
test runs. Ohio 6-A seam coal was used in the first set of tests. For
the remaining four tests, feed material was prepared by pulverizing the
minus 3/8 inch clean fraction from the concentrating table to minus 30
mesh. This approach is analogous to the two-stage cleaning with the
concentrating table.
In two-stage cleaning of the minus 30 mesh Ohio 6-A coal, the total
sulfur was reduced from 2.90 to 1.59 percent (ref. Table XI). A com-
parison of the compound water cyclone run with the concentrating table
run is shown in Table XII. This table indicates that the concentrating
table performed better than the compound water cyclone in the cleaning
of this coal. This finding is supported by the results of cyclone-
98
-------
TABLE XI
COMPARISON OF CONCENTRATING TABLE RUNS AND
COMPOUND WATER CYCLONE RUN WITH
30 MESH X 0, R.O.M., OHIO NO. 6-A SEAM
Cleaning Unit
Compound Water Cyclone
(Test No. 3, Run No. 6)
Compound Water Cyclone
(Test No. 2, Run No. 2)
Concentrating Table Run
Total Sulfur
in Feed,
Weight Percent
2.47
2.39
2.44
Recovery,
Weight Percent
91.4
90.9
92.0
Total Sulfur
Reduction,
Weight Percent
21.1
27.6
36.5
Source: Reference 6.
99
-------
o
o
TABLE XII
CONCENTRATING TABLE AND COMPOUND WATER CYCLONE TESTS
EFFECTS OF TWO-STAGE CLEANING
Run Ho. 2 Operating Conditions
Total Sulfur Reduction,
Two—stage Cleaning
Percent
57.9
44.8
62.7
34.7
Based on Composite of Table Products, Rough Cleaning.
Run No. 2 Operating Conditions:
Cone Type "M", Vortex Finder Clearance: 1", Inlet Pressure: 8 psi, Feed Solids Concentration: 8.C
Coal Identification
Lot Seam
2031 '
2026
2012
2013
Lower
Kit tanning
No. 6
Upper
Freeport
No. 8
Total Sulfur
Location Feed to Table*
County, State Percent
Indiana, 0 ,,
™ i * -5 . DO
Pennsylvania
Columbiana, „
Ohio
Westmoreland, _ „.
Pennsylvania
Jefferson, ., qa
Ohio y
Clean Coal
Two-stage Cleaning
Percent
73.2
80.3
69.9
78.8
Source: Reference 6.
-------
cleaning the other four coals (at 30 mesh x 0 size) which had been pre-
cleaned on the concentrating table. Table XI gives results under one
set of test conditions. These tests show smaller sulfur reductions for
three of the four coals tested than were achieved by the wet concen-
trating table (Table VIII). Bituminous Coal Research, Inc. believes
that improved results in total sulfur reduction could have been obtained
by using a closer-sized feed or feeds to the compound water cyclone,
i.e., 30 mesh x 200 mesh and 200 mesh x 0^).
A diagram of a McNally Visman Tricone of the type evaluated by
Bituminous Coal Research, Inc., is shown in Figure 24. It consists of
a cylindrical section, a compound conical section and a vortex finder.
In operation, coal/water tangentially enters near the top of the cylin-
drical section, forming a strong vertical flow. Refuse moves along the
wall of the cyclone and is discharged through the apex. The washed coal
passes through the vortex finder to the overflow chamber. Washed coal
is discharged from this chamber through the tangential outlet. This
particular design of the water-only cyclone has three conical sections.
Particles of different sizes and specific gravities form a hindered
settling bed in the first conical section. Light coarse particles are
removed from the first conical section (A) and light middlings are re-
moved from (B) the second conical section. In the last conical section
(C), the bed is destroyed and the heavy fractions pass through the apex.
The central current of the departing water is weak at this point and
101
-------
OVERFLOW
CHAMBER
VORTEX
FINDER
CONICAL
SECTION
WASHED
COAL
CYLINDRICAL
SECTION
ADAPTED FROM REFERENCE 6.
FIGURE 24
COMPOUND WATER CYCLONE
102
-------
only the fine, light particles are discharged through the vortex
finder.
5.4 Air Classifier
This is a two-stage process. First air is used to separate the
relatively coarse grind of pulverized coal into a fine fraction and a
coarse, pyrite-rich fraction using the BCR-Majac and Alpine zigzag air
classifiers. Pyrite can then be removed from the coarse fraction by
wet-coal preparation techniques.
Float-and-sink analyses at 1.60 specific gravity were conducted on
both the coarse and fine fractions. The composite of the coarse and
fine clean coal fractions were also analyzed.
Ten samples from the group of coals used for float-sink washability
studies were selected for testing. (Note that this group is not from
the same sample lots as used for testing other types of cleaning equip-
ment; e.g., the spiral.) The reduction of total sulfur by use of the
Majac unit ranged from 20.1 to 51.7 percent. The results of the ten
coals are given in Table XIII. One coal was also processed on the Alpine
Zigzag unit (Table XIV).
5.5 Electrokinetics
The electrokinetic process for the physical cleaning of coal use
the technique of electrophoresis for separating the pyrite from the coal.
Electrophoresis is defined as the migration of electrokinetically
charged particles in a liquid toward an electrode of opposite charge in
103
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TABLE XIII
PYRITIC SULFUR REDUCTION IN MAJAC AIR CLASSIFICATION TESTS
BCR
Lot
No.
1752
1750
1771
1745
1770
1735
1730
1747
1757
1733
Seam
Upper
Kittanning
Upper
Freeport
Lower
Freeport
No. 6
Thick
Freeport
No. 6-A
No. 6
Lower
Klttanning
and Lower
Freeport
Freeport
No. 8
Total Sulfur
in Raw Coal
Percent
2.71
3.74
2.54
2.44
2.08
2.50
4.72
2.42
2.52
4.58
Pyritic Sulfur
in Raw Coal,
Percent
2.31
3.22
1.89
1.79
1.68
1.86
3.70
1.84
2.16
2.84
Recovery
Majac Product
Percent
90.4
83.6
92.6
94.3
90.9
93.2
92.2
90.7
77.5
87.6
Total Sulfur
in Majac
Product Percent*
1.31
1.98
1.49
1.46
1.25
1.65
3.16
1.65
1.90
3.66
Total Sulfur
Reduction
Percent
51.7
47.1
41.3
40.2
39.1
34.0
33.1
31.8
24.6
20.1
Pyritic Sulfur
in Majac Product*
Percent
0.94
1.48
0.98
1.01
0.92
0.98
2.17
1.08
1.39
1.95
Pyritic Sulfur
Reduction,
Percent
59.3
54.0
48.1
43.6
45.2
47,3
41,4
41.3
35.6
31.3
* Majac product composed of raw fine coal plus cleaned coarse fraction
(1.60 specific gravity)
Source: Reference 6.
-------
TABLE XIV
SULFUR REDUCTION IN ALPINE ZIGZAG CLASSIFIER TESTS
A—Total Sulfur Reduction
BCR
Lot
No.
1733
Seam Rank
No. 8 HVC
Total Sulfur
in Raw Coal,
Percent
4.58
Zigzag Product,
Percent
84.1
Total Sulfur in
Zigzag Product,*
Percent
3.82
Total Sulfur
Reduction,
Percent
16.6
* Zigzag product composed of raw fine coal plus cleaned
coarse fraction (1.60 specific gravity)
o
in
BCR
Lot
No.
1733
Seam Rank
No. 8
HVC
B—Pyritic Sulfur Reduction
Pyritic Sulfur
in Raw Coal,
Percent
2.84
Zigzag Product,
Percent
84.1
Pyritie Sulfur in
Zigzag Product,**
Percent
1.90
Pyritic Sulfur
Reduction,
Percent
33.1
** Zigzag product composed of raw fine coal plus cleaned
coarse fraction (1.60 specific gravity)
Source: Reference 6.
-------
a d-c electrical field. The speed of migration is directly proportional
to the magnitude of the electrokinetic charge of the particles and the
applied voltage and inversely proportional to the distance between the
electrodes. The electrokinetic process was investigated on a laboratory
scale.
The application of electrophoresis to physically wash coal was
based on earlier studies which showed that, while coal and pyrite were
both negatively charged above a pH of 4, the coal was more negatively
charged than the pyrites. In the use of the electrophoretic technique
for the separation of pyrites from coal, however, it was found that the
electrophoretic mobilities of coal and pyrite were never sufficient to
overcome the effects of the specific gravity and the size variance in
particles. Therefore, a modified cell was built to take into account
not only the electrophoretic mobilities of coal and pyrite, but also
their specific gravities (described in Reference 13).
The electrophoretic cell consisted of a rectangular plastic column
with inside dimensions of 3/8 inch by 3/8 inch by 24 inches. Platinum
electrode wires were used to produce a d-c field. The column was longi-
tudinally inclined at an angle of 45 degrees and laterally inclined at
angles varying from 4 to 11 degrees. The anode was located on the high
side of the laterally inclined column and the cathode was on the lower
side. During operation, the coal slurry was fed into the top of the
column and, as the slurry moved down the length of the column with an
applied d-c field, the heavier and less negatively charged pyrites
106
-------
tended to slide toward the cathodic side and the coal was drawn toward
the anode.
Initial tests were conducted with the electrophoresis column using
synthetic coal-pyrite mixtures. Next, a series of tests were conducted
on a high-pyritic-sulfur coal. Results of three test runs are given in
Table XV.
The laboratory-scale investigation indicated that this was an effec-
tive method to remove pyrite and other impurities such as silica from
coal. Economic assessments, unfortunately, indicated that the technique
would be too costly for commercial application. Therefore further devel-
opment was not pursued. The electrophoresis column could probably best
be used as a laboratory instrument for investigating the physical de-
sulfurization of coal.
5.6 Agglomo-Separation (Oil)
The Agglomeration-Separation process developed by the National Re-
search Council of Canada was investigated by the Bureau of Mines. The
process was reported to recover a product low in ash approaching the
clean coal product. It was felt that a similar sulfur reduction might
be obtained. In addition, the process had the capability to agglomerate
fine size coal to a larger size and eventually to provide for pelleti-
zation.
High energy mixing is employed to disperse kerosine or similar
light oils in a coal-water slurry. The oil selectively coats the coal
particles causing the particles to agglomerate and then, with an assist
107
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TABLE XV
FRACTIONATION OF A SAMPLE OF 100 BY 325 MESH LOWER
FREEPORT BED COAL IN AN ELECTROPHORESIS COLUMN
o
oo
APPLIED
TEST VOLTAGE
VOLTS, DC
1 500
2 400
3 250
500
AVERAGE
CURRENT RECOVERY,
MILLIAMPS RECEPTACLE PERCENT
5.0 Coal
Reject
2.0 Coal
Reject
1.5 Coal 1st pass
5.0 Coal 2nd pass
Reject
94.3
5.7
55.6
44.4
13.8
77.3
8.9
ASH,
PERCENT
13.2
45.0
17.0
14.8
44.5
8.9
44.8
PYRITIC
SULFUR,
PERCENT
1.01
19.73
.34
4.63
.38
.62
21.00
TOTAL
SULFUR,
PERCENT
1.61
19.95
1.07
5.58
.61
1.38
22.65
Source: Reference 12.
-------
from entrained air, rise to the surface, while the impurities remain in
the water. The investigation was conducted on both 35 mesh x 0 and
325 mesh x 0 sized coals using kerosine as the agglomerating oil in
slurries containing 10 percent of coal by weight. Experiments were
conducted on both the laboratory and bench scale. A blender-type mixer
was used in the laboratory experiments, and a 4-gallon cell was used for
bench-scale testing.
Four variables; kerosine dosage, retention time, slurry pH, and
mixer speed were evaluated in the laboratory. Kerosine dosage had the
most significant effect. Generally, a concentration of 8 percent kero-
sine, based on the weight of dry coal in the slurry, produced the best
results. At lower kerosine levels the recovery of clean coal decreased,
while using larger amount of kerosine provided minimal increases in
recovery of clean coal. Increasing the retention time from 1 to 2 min-
utes increased recovery. Beyond 2 minutes, however, there was no in-
crease in recovery. Neither the pH of the slurry nor the speed of mix-
ing had a significant effect on the product recovery.
Tables XVI and XVII show the results of two samples of 325 mesh x.-, 0
size coals evaluated in the laboratory. Reductions in total sulfur range
from about 12 percent to 39 percent while yields of clean coal range
from 18 percent to 85 percent, depending on test conditions and the
type of coal. Under the same conditions ash reduction ranges from
25 percent to 60 percent.
109
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TABLE XVI
EVALUATION OF THE AGGLOMO-SEPARATION PROCESS FOR THE
LOWER FREEPORT BED COAL USING FOUR PROCESS VARIABLES
Coal Size
Total Sulfur, percent
Ash, percent
Agglomerating Oil
Slurry, percent solids
TEST
NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
KEROSINE
DOSAGE,
PERCENT
2
4
8
2
4
8
2
4
3
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
AGITATOR
SPEED,
RPM
10,000
10,000
10,000
10,000
10,000
10,000
10,000
10,000
10,000
10,000
10,000
10,000
14,000
14,000
14,000
14,000
14,000
14,000
14,000
14,000
14,000
14,000
14,000
14,000
RETENTION
TIME,
MIN.
1
1
1
2
2
2
1
1
1
2
2
2
1
1
1
2
2
2
1
1
1
2
2
2
Minus 325 mesh
2.5
19.3
Kerosine
10
SLURRY
PH
6.0
6.0
6.0
6.0
6.0
6.0
10.0
10.0
10.0
10.0
10.0
10.0
6.0
6.0
6.0
6.0
6.0
6.0
10.0
10.0
10.0
10.0
10.0
10.0
CLEAN
YIELD
58.5
70.5
81.8
60.4
75.0
82.5
68.5
78.5
82.1
77 .4
81.5
82.7
62.0
70.1
82.6
70.3
75.4
83.9
68.6
76.3
85.0
74.5
78.5
83.6
COAL PERCENT
SULFUR
1.9
2.2
2.1
2.0
1.9
2.2
1.9
1.9
2.1
1.8
2.0
2.2
1.8
1.9
2.1
1.8
1.9
2.0
1.7
2.0
2.1
1.8
1.9
2.1
ASH
12.8
11.2
11.2
12.8
11.2
10.5
12.1
12.0
10.1
10.0
8.7
9.2
11.6
11.6
10.6
10.6
12.3
9.2
10.7
11.9
9.3
10.2
8.8
8.5
Source: Reference 14.
110
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TABLE XVII
EVALUATION OF THE AGGLOMO-SEPARATION PROCESS FOR THE
PITTSBURGH BED COAL USING FOUR PROCESS VARIABLES
Coal Size
Total Sulfur, percent
Ash, percent
Agglomerating Oil
Slurry, percent solids
Test
no.
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
Kerosine
dosage,
percent
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
Agitator
speed,
rpm
6,000
6,000
6,000
6,000
6,000
6,000
6,000
6,000
6,000
6,000
6,000
6,000
12,000
12,000
12,000
12,000
12,000
12,000
12,000
12 ,000
12,000
12,000
12 , 000
12,000
Retention
time,
min.
1
1
1
2
2
2
1
1
1
2
2
2
1
1
1
2
2
2
1
1
1
2
2
2
Minus 325 mesh
2.3
16.1
Kerosine
10
Slurry
PH
3.0
3.2
2.9
3.1
3.0
3.0
10.0
10.0
10.0
10.0
10.0
10.0
3.2
3.1
3.4
3.0
3.1
3.2
10.0
10.0
10.0
10.0
10.0
10.0
Clean Coal Percent
yield
18.1
54.1
60.4
17.1
49.5
63.5
39.8
54.5
65.8
36.3
53.3
60 , 6
35.9
52.9
68.1
24.4
48.8
64.7
40.1
53.4
62.6
42.3
56.3
67.5
sulfur
1.7
1.6
1.7
1.5
1.7
1.7
1.8
1.6
1.8
1.6
1.8
1.6
1.7
1.7
1.7
1.4
1.6
1.6
1.6
1.6
1.6
1.5
1.7
1.4
ash
10.9
11.7
9.9
8.8
10.5
10.0
12.0
11.0
10.6
10.7
10.5
9.0
9.7
9.8
10.1
8.0
9.7
10.3
10.8
10.2
9-0
10.3
10.7
9.0
Source: Reference 14.
Ill
-------
The agglomo-separation process provided only limited sulfur reduc-
tion but a substantial reduction in ash. The oil coats the pyrite as
well as the coal particles, resulting in agglomerates containing both
the clean coal and the pyrite. There is usually some sulfur reduction
accompanying low recoveries of clean coal due to low concentrations of
agglomerating oil but, as the oil concentration is Increased to obtain
maximum clean coal recovery, the percentage of sulfur in the product is
usually equal to or greater than that of the raw coal.
The laboratory work was scaled up to a 500 pound per hour pilot
plant consisting of two 4-gallon capacity cells equipped with turbine
blade impellers, a Bird dewatering screen bowl centrifuge, and a Dravo
39 inch pelletizing disc. With this arrangement, a 10 percent slurry
of 35 mesh x 0 size coal was agglomerated with 8 percent kerosine. The
agglomerated clean coal was dewatered to about 16 percent moisture con-
tent in the centrifuge and then pelletized on the disc-pelletizer using
an asphalt binder. This step was performed to study pelletization as a
means of overcoming some of the problems encountered in drying and handling
fine-sized coals. Pellets made with approximately 5 percent asphalt
binder averaged 1/2 inch in diameter and contained about 16 percent
moisture. The pellets were firm when wet and had good strength and
water resistance when dried.
The quality of the clean coal produced by the pilot plant was sim-
ilar to that obtained in the laboratory unit. The sulfur reduction was
negligible, but the recovery of low ash coal was good.
112
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5.7 Froth Flotation
"Froth flotation is a process for separating fine-size particles by
selective attachment of air bubbles to coal particles, causing them to
be buoyed up into a froth while leaving the refuse particles in the
water. This process deals with fine particles in a rather turbulent
and foamy aqueous system where specific gravity is not as significant
as the surface properties of the particles; although much heavier than
the coal, due to surface characteristics the pyrite remains with the
coal in the froth product11' .
The process consists of thoroughly mixing the fine raw coal par-
ticles with water. A frothing agent is added, and air is bubbled
through the mixture, causing a froth to be produced at the surface.
This froth, containing primarily the hydrophobic components, is skimmed
away, thereby separating the hydrophobic from the hydrophilic fractions
which remain suspended in the bulk of water. The froth flotation proc-
ess is reasonably new for coal processing, although it has long been
used in the mineral industry to effect separations between various
minerals often of a very complex nature.
The research program to determine the pyrite reduction potential
of the froth flotation process pursued two approaches. These are 1)
the depression of coal, and 2) the depression of pyrite. The depression
of pyrite approach, involving a one-stage process, was not encouraging.
The detailed procedures, results, and conclusions are presented in
Reference 15.
113
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The second approach was concerned with a two-stage flotation process
for separating the pyrite remaining in the "initial" froth flotation
product. This product from a conventional single-stage flotation proc-
ess is repulped in fresh water; treated with a coal flotation depressant,
a pyrite collector, and a frother; and is rewashed in a second bank of
froth flotation cells. The pyrites are removed with the froth, leaving
a depressed fraction of clean coal containing less pyrites. This two-
stage process can be reversed, i.e., the pyrite is floated (and the coal
is depressed) in the first stage and the coal is conventionally floated
in the second stage. The two-stage froth flotation process was developed
because in the one-stage process the fine-sized pyrites reported with
the froth product. Work on the two-stage flotation process in a half
ton per hour capacity pilot plant has been completed.
Detailed results of the froth flotation research are presented in
Tables XVIII and XIX and in References 15 and 16. A more complete
description of the process may be found in References 12 and 17.
Of the innovative processes for pyrite separation investigated by
the Bureau of Mines under the EPA Clean Coal Program, the two-stage froth
flotation technique appears to show the greatest potential" for scale-up
to commercial operation. The importance of this process results from
the fact that no other way has been identified to remove pyrite from
fine coals.
114
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TABLE XVIII
TWO-STAGE FLOTATION RESULTS WITH LOWER FREEPORT BED COAL SLURRY
Analysis, percent Distribution, percent
Weight, Total Pyritic Total Pyritic
Product percent Ash sulfur sulfur Ash sulfur sulfur
Test 1: First stage; 40 g/ton MIBC
250 g/ton Aei
150 g/ton pot
40 g/ton MIBC
First stage; 40 g/ton MIBC
Second stage; 250 g/ton Aero Depressant 633,
150 g/ton potassium amyl xanthate,
Af\ rr /<-r«A MTUr1
64.2
9.1
73.3
26.7
100.0
10.0
15.5
10.7
79.8
28.9
1.11
7.06
1.85
3.57
2.31
0.51
6.54
1.26
3.51
1.60
22.2
4.9
27.1
72.9
100.0
30.8
27.8
58.6
41.4
100.0
20.5
37.2
57.7
42.3
100.0
Clean coal 2
Reject 2
Clean coal 1
Reject 1
Feed
Test 2: First stage; 40 g/ton MIBC
Second stage; 500 g/ton Aero Depressant 633,
200 g/ton potassium amyl xanthate,
40 g/ton MIBC
Clean coal 2
Reject 2
Clean coal 1
Reject 1
Feed
63.5
8.1
71.6
28.4
100.0
9.3
17.0
10.2
76.2
28.9
1.03
7.93
1.81
3.43
2.27
.46
7.35
1.24
3.22
1.80
20.4
4.8
25.2
74.8
100.0
28.8
28.3
57.1
42.9
100.0
16.2
33.1
49.3
50.7
100.0
Test 3: First stage; 40 g/ton MIBC
Second stage; 350 g/ton Aero Depressant 633,
250 g/ton potassium amyl xanthate,
40 g/ton MIBC
Clean coal 2
Reject 2
Clean coal 1
Reject 1
Feed
Source: Reference 14.
59.7
12.7
72.4
27.6
100.0
9.8
13.4
10.4
77.2
28.7
.94
5.84
1.80
3.61
2.31
.32
5.06
1.15
3.60
1.83
20.4
5.9
26.3
73.7
100.0
24.3
32.1
56.4
43.6
100.0
10.4
35.1
45.5
54.5
100.0
115
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TABLE XIX
TWO-STAGE FLOTATION RESULTS WITH MIDDLE KITTANNING BED COAL SLURRY
Analysis, Percent
Product
Weight
Percent
Ash
Total
Sulfur
Pyritic
Sulfur
Distribution, Percent
Total Pyritic
Ash Sulfur Sulfur
Test 1: First stage; 300 g/ton kerosine,
80 g/ton MIBC
Second stage; 250 g/ton Aero Depressant 633,
150 g/ton potassium amyl xanthate,
40 g/ton MIBC
Clean coal 2
Reject 2
Clean coal 1
Reject 1
Feed
74.5
10.1
84.6
15.4
100.0
3.2
5.6
3.5
28.8
7.4
1.22
3.23
1.46
10.65
2.88
0.69
2.68
.93
10.18
2.35
32.2
7.6
39.8
60.2
100.0
31.6
11.3
42.9
57.1
100.0
21.9
11.5
33.4
66.6
100.0
Test 2:
First stage;
Second stage;
Clean coal 2
Reject 2
Clean coal 1
Reject 1
Feed
300 g/ton kerosine,
80 g/ton MIBC
350 g/ton Aero Depressant 633,
250 g/ton potassium amyl xanthate,
40 g/ton MIBC
76.1
9.0
85.1
14.9
100.0
2.7
10.5
3.5
30.1
7.5
.95
6.22
1.51
10.68
2.87
.33
6.22
.95
10.53
2.38
27.4
12.6
40.0
60.0
100.0
25.2
19.5
44.7
55.3
100.0
10.6
23.5
34.1
65.9
100.0
Test 3: First stage;
Second stage;
Clean coal 2
Reject 2
Clean coal 1
Reject 1
Feed
300 g/ton kerosine,
80 g/ton MIBC
500 g/ton Aero Depressant 633,
350 g/ton potassium amyl xanthate,
40 g/ton MIBC
78.8
9-9
88.7
11.3
100.0
2.6
12.2
3.7
31.7
6.8
.89
7.83
1.66
12.30
2.87
.34
7.23
1.11
12.13
2.35
30.1
17.8
47.9
52.1
100.0
24.4
27.0
51.4
48.6
100.0
11.4
30.5
41.9
58.1
100.0
116
Source: Reference 14
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5.8 Concentration of Pyrite from Refuse
The laboratory and pilot studies discussed above have been con-
cerned primarily with removing sulfur, principally in the form of
pyrite, from coal. Similar, though less extensive, studies were per-
formed by Bituminous Coal Research, Inc., to determine the potential
of fine-cleaning techniques for preparing a concentrated grade of py-
rite from the reject material^ . These investigations were undertaken
because most of the major commercial processes for conversion of pyritic
sulfur to sulfuric acid or other usable forms require a pyritic feed-
stock considerably richer in pyrite than the reject material produced
by physically cleaning most U.S. bituminous coals.*
Coals from six mines, with total sulfur content ranging from about
1.1 to 6.9 percent, were cleaned and the reject concentrated by staged
separation with wet concentrating tables and a hydraulic classifier.
For this effort, samples of each coal were crushed to 3/8 inch x 0, and
pre-cleaned on a wet concentrating table of the type normally Used for
coal preparation. The fraction with the highest specific gravity (pre-
sumably containing most of the pyrites) was crushed to 30 mesh x 0 and
cleaned on a metallurgical-type wet concentrating table with slime deck.
Conventional processes that burn pyrites and produce sulfuric acid
require ore with a minimum sulfur content of about 42 percent. Total
sulfur in the refuse from high-sulfur coals varies from about 4 to 25
percent. Therefore, if this refuse is to be a suitable feed for acid
production, it must be concentrated to a higher pyrite grade. Also,
see Section 7.2.
117
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This was considered as concentrated pyrite. The fraction having the
next-to-highest specific gravity was crushed to 60 mesh x 0 and re-
cleaned on the metallurgical deck. In some cases, an intermediate
separation of the 60 mesh x 0 material was made with a hydraulic classi-
fier prior to the second cleaning on the metallurgical deck. The hy-
draulic classifier was not used for all tests because of the high per-
centage of fine pyrite lost during this operation.
Results are summarized in Table XX. These indicate that pyrite
concentrates with sufficiently high total sulfur content for conven-
tional acid-making processes can be achieved for all coals tested, but
sometimes at the expense of percentage of sulfur recovered. Total sul-
fur in the pyrite concentrates range from 35.6 percent (corresponding
to a recovery of 46 percent of total sulfur in the ROM coal) to 48.6
percent (corresponding to a 22.9 percent recovery).
The effort verified that pyrite from refuse can be concentrated
for use as a feedstock for the recovery of sulfur values in either the
form of elemental sulfur or sulfuric acid. The processing of rejects
from various cleaning processes offers the capability to recover coal
values and to adjust the feedstock composition to the requirements of
a specific pyrite utilization process such as the High Sulfur Combustor
(covered in Section 8.0).
118
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TABLE XX
SULFUR RECOVERY IN PURITE CONCENTRATION TESTS
Percent of Sulfur in R.O.M.
Total Sulfur,
R.O.M. Coal,
Coal Identification Percent
2234 Ohio No. 6
2255 Upper Kittanning
2287 Indiana VII
2299 Lower Freeport
2415 Lower Cherokee
2417 Tebo
3.19
2.02
1.06
2.82
5.12
6.92
Pyritic Sulfur, Coal Reclaimed in Pyrite Total Sulfur, Ultimate
R.O.M. Coal, ' Concentrate Pyrite Concentrate Carbon,
Percent
2.56
1.72
0.39
2.07
4.24
4.44
Total Sulfur
22.9
46.0
3.8
18.1
13.1
12.3
Pyritic Sulfur
28.5
54.1
10.3
24.6
15.8
19.1
Percent
48.59
35.64
44.07
45.96
44.70
47.18
Percent
3.63
4.84
2.93
4.45
5.46
3.51
Averages 3.52 2.57 19.4 25.4 44.36
Source: Reference 10.
-------
6.0 PROTOTYPE COAL CLEANING PLANTS
The washability studies and pilot plant investigations previously
discussed indicated the amenability of a wide range of coals to physical
desulfurization under carefully controlled laboratory conditions. Quite
different results could be obtained from the same types of coal clean-
ing equipment when operating in the laboratory than when operating in
commercial-scale plants where conditions may be less carefully con-
trolled and where variability in the feed composition may be greater.
Although testing for pyrite removal could be conducted to a limited
degree in some existing preparation plants, the equipment and cleaning
circuits of such plants are not normally arranged to maximize sulfur
reduction but to meet ash and BTU specifications. Commercial cleaning
plants are usually designed for maximum effectiveness in cleaning a
specific coal and do not have the flexibility of cleaning equipment and
circuits to maximize sulfur reduction of different coals having widely
varying washability characteristics. For this reason, testing in exist-
ing plants would be difficult and generally unsatisfactory without ex-
tensive modification to equipment and circuits.
Ideally, a plant to be used for investigating and demonstrating
desulfurization methods at high through-put capacities would provide
flexibility of equipment configurations, cleaning circuits, and operat-
ing conditions to permit adaptability to the desulfurization require-
ments of the various coals to be processed and to provide for maximum
pyrite recovery from the refuse. The plant must have the proper sampling
120
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and laboratory arrangements so that the coals and equipment can be properly
evaluated. Such a plant would ideally be situated in a location central
to the coals to be tested and the plant site should contain ground space
available for a possible future plant for processing the pyrite recov-
ered from the refuse.
In order to determine the scope and cost of conducting investiga-
tions and demonstrations of pyrite removal using commercial cleaning
equipment on a scale approximating commercial capacity, EPA funded two
independent and competitive studies for designing a prototype coal clean-
Ing plant of 50-100 tons per hour capacity and for estimating the capi-
tal and operating cost for the plant. (Ref. 18, 19, 20, 21). Testing
laboratories were addressed in the cost estimates. Due to plant and re-
lated operational complexities and associated costs, two independent
and competitive studies were needed for EPA to identify the most accept-
able design/cost option.
The study objectives were to produce a prototype plant design cap-
able of reducing the sulfur of various coals having widely variable
washability characteristics and other physical and chemical properties
together with providing cost estimates for building and equipping the
plant and for performing appropriate studies on selected coals. Specific
elements of the task were:
• To review and analyze the coal washability data furnished
by EPA;
• To develop a ranking of the coals and select those most
appropriate for evaluation in the prototype plant;
121
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• To develop a design with circuits that could optimize
sulfur reduction from a variety of coals;
• To select the most appropriate plant location;
• To develop detailed installed cost of the prototype plant;
• To develop a test plan and schedule for evaluating each
selected coal; and
• To develop detailed costs for operating the plant, conduct-
ing the tests, and analyzing the generated data.
The prototype plant design and cost studies were conducted by the
Roberts and Schaefer Company of Chicago and the McNally Pittsburg Manu-
facturing Corporation, Pittsburg, Kansas. Each of these organizations
analyzed the washability data for some 200 coals, classified the coals
relative to amenability to physical desulfurization, designed a proto-
type plant for sulfur removal, and developed the required test plans
and cost estimates.
The major difference in the two studies was plant design; Roberts
and Schaefer's design was the more complex of the two, however, it
offered the maximum flexibility; the McNally design was the less com-
plex and provided reduced flexibility and greater ease of operation.
In view of the wide variation in coals to be tested, the provided maxi-
mum flexibility would more than off-set the probable resulting incre-
mental operating difficulties. Results of the two independent studies
are summarized in the following sections.
122
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6.1 Classification and Selection of Coals
Both study efforts (i.e., McNally Pittsburg and Roberts & Schaefer)
reviewed and analyzed the coal washability data provided by EPA. Each
study effort examined the washability data on approximately 200 coals,
from various parts of the United States, to identify coals that poten-
tially would benefit from cleaning by achieving a significant reduction
in sulfur content. Each study effort developed a coal grouping by size,
sulfur content of the washed coal, coal recovery values, and coal type
with region of origin.
The Robert and Schaefer effort considered as candidates those coals
for which cleaning could yield substantial benefits. The criteria used
for selecting candidate coals were:
• Sulfur content in the raw coal should be relatively high;
• The proportion of pyritic sulfur in the raw coal should be
relatively high;
• Significant reduction in total sulfur should be possible at
commercially feasible yields (i.e., greater than 65 percent);
• Sulfur reduction should be judged in relation to geographic
area or coal field considered;
• Substantial reserves of coal should be available;
• Consideration should be given to coals which appear difficult
to clean;
• Consideration should be given to selecting candidates from
different geographic locations; and
123
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• Candidates should be selected according to the sulfur level
in the clean coal and should cover the following ranges: less
than 1 percent, 1.0-1.5 percent, 1.5-2.0 percent, and 2.0-2.5
percent total sulfur.
Based on the above criteria, 32 coals were initially identified
with the decision to select four additional candidates at a later date.
The McNally Pittsburg effort identified 46 coals considered to have
good or fair washability characteristics. These 46 coals were charac-
terized as being cleanable to less than 1.5 percent total sulfur and
deserving testing in the proposed coal cleaning plant. These were com-
posed of 20 coals in excess of 1 percent sulfur that would wash to less
than 1 percent sulfur with a recovery in excess of 75 percent, 26 coals
that would either wash to less than 1 percent sulfur with a 50 to 75
percent recovery, or those that would wash to 1 to 1.5 percent sulfur
with a 75 to 100 percent recovery.
The differences in the numbers of coals selected by the two con-
tractors, i.e., Roberts and Schaefer and McNally Pittsburg is due to
differences in selection criteria and yields. Roberts and Schaefer
limited their selections to coals providing commercial acceptable yields
of 65 percent or more whereas McNally Pittsburg considered yields down
to 50 percent. In addition, the two contractors had different criteria
for acceptable total sulfur in the clean coal.
124
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6.2 Design of Roberts and Schaefer Prototype Cleaning Plant, Test Plan,
and Cost B CM. «• 20)
6.2.1 Roberts and Schaefer Plant Design
The Roberts and Schaefer plant design concept is flexible with
alternate circuits and equipment choices which can be run in various
combinations so as to handle coals of different sizes and widely vary-
ing washability characteristics. The Roberts and Schaefer proposed
plant design comprises the following:
: 1. Heavy medium cyclone. Two stages of heavy medium cyclones
are provided in the prototype plant. The primary stage is
for low-gravity and is fed by gravity. The second stage is
for higher gravities and is fed by pumping.
2. Hydrocyclones. Two stages of 20-inch-diameter hydrocyclones
are used for cleaning 3/8 inch x 0 coal. The hydrocyclones
are used for their flexibility in varying the specific gravity
(1.40 - 1.80). In addition, fourteen-inch-diameter hydro-
cyclones will be available to clean 1/2 mm x 0 raw coal.
3. Deister table. The Deister table is used for 3/8 inch x 0
and 1/2 mm x 100 mesh sized coal cleaning.
The equipment selection is based not only on the ability of each type to
clean coals at low specific gravities but also the relative efficiency
of each. The following equipment was excluded because of lack of ability
to clean coal at low specific gravities: fine coal jig, air table,
hydrotator, and the rheolaveur.
125
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In addition, the plant would contain a complete complement of equip-
ment for receiving, storing, handling, crushing, sizing, sampling, test-
ing, drying, and transporting of coal and reject material, plus utilities
and instrumentation. The facility would also include office space, a
fully equipped chemical laboratory for analysis work, and data process-
ing equipment needed to interface with a leased computer.
The test plant is designed for a maximum capacity of 75 TPH. This
maximum capacity will be maintained while the heavy medium cyclones and
the 20-inch-diameter hydrocyclones are in use. When the Deister tables
are in use using a raw feed of 1/4 or 3/8 inch top size, the plant capac-
ity is reduced to 50 TPH. The plant capacity is also limited to 50 TPH
when raw coal is pulverized to 14 mesh x 0. For preparing the 14 mesh
x 0 size, the pulverizing and cleaning equipment for treating 1/2 mm x 0
are the limiting factors for plant feed capacity.
Specifics concerning the plant and processes are as follows. Two
heavy medium cyclone circuits are furnished; a primary heavy medium
cyclone circuit and a secondary heavy medium cyclone circuit. Three
products are generated from these two circuits: the low sulfur content
clean coal, the high sulfur content middlings, and the refuse. The pri-
mary heavy medium reject is rinsed out on a reject screen. The discharge
of the screen can be fed into the secondary circuit directly or be crushed,
deslimed, and then fed to the secondary circuit.
The raw coal feed to the heavy medium cyclone circuit will be either
1-1/2 inch or 3/8 inch top size. If the raw coal is 1-1/2 inch x 0 size,
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it will by-pass the raw coal screen and will be delivered with water via
raw coal pump to the desliming sieve bend and screen for removing the
1/2 mm x 0 fines. The plus 1/2 mm raw coal will be fed to the primary
heavy medium cyclone, and the 1/2 mm x 0 will be directed to the 1/2 mm
x 0 sump for subsequent cleaning. When the 1-1/2 inch x 0 raw coal
is to be crushed to 3/8 inch x 0 before desliming and cleaning in the
heavy medium cyclone, the 1-1/2 inch x 0 raw coal will be fed to the
raw coal screen for separating at 3/8 inch. The oversize (from the
screen) will be .crushed in a Cage-Paktor crusher to 3/8 inch x 0 size
which will be recycled to the screen for removing plus 3/8 inch material.
The overall 3/8 inch x 0 material will then be deslimed. Three by-
passes are provided in the heavy medium cyclone circuits. These are:
1. Primary heavy medium reject can report to the refuse if its
ash content is high and no further cleaning in the secondary
heavy medium circuit is warranted;
2. The primary heavy reject—crushed to 1/2 mm x 0—normally
will be cleaned; however, it can be rejected to the refuse
thickener if the ash content is high and no further cleaning
is warranted; and
3. The middling product can be loaded out as clean coal if
warranted.
All dilute medium slurries collected from drain-and-rise screens
used in the heavy medium circuits will be pumped to the Dutch State
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Mines magnetite recovery circuit to reclaim the magnetite for reuse.
The recovery circuit consists of magnetite classifying cyclones, a mag-
netic separator, and a magnetite thickener.
The stages of 20-in-diameter cleaning hydrocyclones are furnished
to clean 3/8 inch x 0 raw coal to produce clean coal, middlings, and
refuse. The maximum top size of raw coal that can be cleaned in a
20-inch-diameter unit is 1 inch. Raw coal and water are pumped to the
two primary cleaning hydrocyclones at a concentration of 150 gms per
liter. The reject from the primary unit is repulped and pumped to the
secondary unit for further cleaning. The 1/2 mm x 0 in the 3/8 inch x 0
size will be cleaned to the degree practical for sulfur removal. The
specific gravity of cleaning can be varied by changing the vortex finder
length in the cyclone.
The Deister table circuit is fed with raw 3/8 inch x 0 coal through
a cyclone classifier. Three products are produced from the Deister
table circuit: the clean coal, the middlings, and the refuse. These
products will be dewatered in the same three vibrating screens provided
for the 20 inch diameter hydrocyclone cleaning circuit. Each product
will be automatically sampled in order to establish the performance of
each stage of the cleaning unit.
Two stages of 14-inch-diameter cleaning hydrocyclones will be em-
ployed to clean 1/2 mm x 100 mesh raw coal down to 250 mesh. The sec-
ond stage will be used to clean the primary reject and thereby will
provide for additional clean coal yield.
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The overflow from the combined two-stage 14-inch-diameter hydro-
cyclone will be pumped to 14-inch-diameter cyclone classifiers for
classification at approximately 100 mesh. The plus 100 mesh clean coal
will be separated on a two-stage rapped sieve bend after repulping.
The underflow (containing the rejected material) will report to the
refuse thickener.
The 100 mesh x 0 raw coal from the 14-inch-diameter cyclone class-
ifiers along with the filtrate from the clean coal vacuum filter will
report to flotation cells. The flotation cells (35 TPH capacity) are
used to reduce ash content of the fine-sized raw coal.
Both Deister tables and 20-inch-diameter cleaning hydrocyclones
are to a degree able to clean 1/2 mm x 100 mesh coal. If desirable, the
1/2 mm x 0 fraction from the above cleaning circuits can be pumped to
the 14-inch-diameter cyclone classifiers for separating at 100 mesh
prior to further processing.
The 1/2 mm x 0 clean coal (includes plus 100 mesh from the rapped
sieve bend and minus 100 mesh from the flotation cells) will be de-
watered in a disc filter. The filter cake (1/2 mm x 0 material) and
plus 1/2 mm clean coal from other cleaning circuits will be combined
and conveyed out to the clean coal storage pile prior to shipping.
The flotation tailings and other rejectable 1/2 mm x 0 slurry will
be combined and fed to a 90-foot-diameter refuse thickener. The under-
flow from the refuse thickener will be pumped to a head tank in the
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preparation plant for re-use. An emergency pond will be provided for
draining the refuse thickener if required.
6.2.2 Roberts and Schaefer Test-Program
The purposes of the test program are:
• To evaluate cleanability of each coal selected for processing
(e.g., best cleaning process, yield, refuse, compositions);
• To determine for each selected'coal the best cleaning plant
configuration from both a technical and economic standpoint;
• To define for each coal tested the cost for one or more levels
of cleaning;
• To evaluate the performance of each major piece of equipment
used in the plant; and
• To recommend additional experimental work as indicated by
the cleaning program.
This effort is composed of three phases: pre-experimental, experi-
mental, and post-experimental. Some elements of the pre-experimental
phase will take place during the construction of the plant. Such ele-
ments will include the detailed formulation of the experimental program
together with implementing arrangements for the purchase, shipment, and
receipt of test coals. One coal should be on hand and in plant storage
prior to plant start-up and equipment debugging. Two more coals should
be on hand before the experimental phase begins. In addition, the pre-
experimental phase will include laboratory set-up, the training of plant
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and laboratory personnel, and plant start-up with initial equipment
adjustments.
The following comments apply to the pre-experimental phase.
1. It is assumed that by the time this phase commences, detailed
washability data to be provided by other contractors will be
available.
2. A schedule for testing the different coals will be developed.
The schedule will be based on coal availabilities with asso-
ciated washability data.
3. Sampling requirements, on-site laboratory capabilities, and
data processing analysis requirements will be characterized
so as to aid in planning overall testing sequences.
4. A determination will be made of the best way to process and
to analyze the voluminous data that will be generated during
the coal testing (experimental) phase of the program.
5. Capital cost data for the various processes that may be used
will be collected. These data will be used to define the
economics of cleaning particular coals.
6. To insure that all process equipment and instrumentation is
optimally maintained, a planned maintenance program will be
established.
7. In order to expedite the laboratory work and to operate the
laboratory at maximum efficiency, standardized routines for
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handling different samples will, insofar as possible, be
developed.
8. A written safety program covering plant operations will be
developed prior to scheduled plant "start-up". During the
plant start-up period, the safety program will be monitored
and reviewed as to effectiveness. Revisions will be made
as warranted.
9. Arrangements will be made to sell processed clean coal and
possible quantities of unprocessed raw coal.
The experimental phase is the major and most important portion of
the entire project. This phase will take about 38 months to complete
during which 36 coals will be tested in the prototype cleaning plant.
Actual testing is estimated to take 36 months, with data processing
and evaluation to continue for an additional two months. In general,
it is planned that each coal will be tested under enough different con-
ditions to insure that sufficient data will be collected to accomplish
test objectives.
In order to insure that each coal (sample) to be tested has accept-
able characteristics, each coal test lot will be examined promptly upon
delivery to the plant and well in advance of actual testing. Accordingly,
the plan is to have each test sample arrive at the plant at least 60
days prior to the start of actual testing. The testing schedule calls
for receipt (on the average) of a new coal test sample each month.
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For testing a particular coal, the first week of testing will most
likely be devoted to insuring the test conditions are proper for a test
run. The second week would be devoted to a test run. For many coals,
test runs with different test conditions would take place during the
third and fourth weeks of a test period.
During the washability studies, samples will be collected at 20 to
25 different locations with an estimated 25 to 30 samples per working-
day shift. Samples may vary in size from 30 pounds to perhaps one ton.
In addition to planned sampling, there will be a need for special
spot samples. It is estimated that 10 to 15 percent of the efforts of
laboratory and sample preparation personnel will be devoted to handling
these special samples.
It is anticipated that automatic samplers will be used to collect
these samples. Plant personnel will collect, prepare, and perform the
required tests on these samples.
For complete characterizations and selected in-process tests of raw
coal, clean coal, and refuse, ASTM or other recognized standard methods
will be used. Total sulfur in-process testing can be provided using
the Leco combustion or equivalent method. For in-process testing pur-
poses, a rapid moisture test is believed acceptable.
For each coal tested, the plant operating data and capital cost
data will be carefully documented and evaluated and an individual report
will be prepared upon completion of each coal investigated. Each report
will include the estimated capital and operating cost associated with
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cleaning the investigated coal to one or more sulfur levels. In addi-
tion, each report will include supporting and analytical data character-
izing the raw coal, clean coal, rejects, and where appropriate, the
middlings. It is estimated that data processing, evaluation, and report
preparation will require two months per tested coal.
The post-experimental phase will commence upon completion of the
final coal washing experiment. The first two months of the post-
experimental phase will overlap the last two months of the experimental
phase due to the fact that two months will be required to prepare a
report covering the final coal tested. The post-experimental phase
will consist of two principal activities. These are:
1. Preparation of the final report, and
2. Closing the plant with auxiliary facilities to make ready
for subsequent disposal by the Government.
Since an individual report will be prepared for each coal tested,
it is visualized that the final report will be an overall summary of
the contractual effort. This report will also contain information on
coal cleanability based on coal characteristics, coal source area, rela-
tive merits of processing various coals, and the performance of differ-
ent processing techniques as applied to various coals.
At this time, the ultimate disposition of the proposed cleaning
plant is not known. It appears prudent that at the end of test program
the plant should be put in shape so as to prevent undue deterioration
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in absence of usage. Therefore a plant shut-down effort including
draining water lines and pumps, disconnecting electric service, apply-
ing appropriate lubricants and protective coatings, inventorying assets,
and providing physical security measures should be applied to the de-
activated plant. It is estimated that four months will be required to
complete the post-experimental phase of this effort.
6.2.3 Roberts and Schaefer Capital and Operating Costs
Capital and operating cost estimates based on the design study
cover the prototype cleaning plant and are predicated on the following:
• The plant contains a fully equipped testing laboratory;
• The plant contains an analytical laboratory;
• Suitable office facilities are contained in the plant;
• Operating costs are based on a pre-experimental period of 12
months, an experimental period of 38 months, and a post-
experimental period of 4 months, there being a two month
overlap of the experimental and post-experimental phases; and
• Test lots of 10,000 tons.
The estimated program cost is $16,457,965. Cost details are pro-
vided in Table XXI. The above total does not include estimated credits
received from the sale of processed coal and credits from disposal of
plant equipment after program completion. Total credits are estimated
to amount to $2,000,000.
The initial Roberts and Schaefer overall program of work was re-
viewed to determine how the overall program might be modified to reduce
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TABLE XXI
COST ESTIMATES FOR FIFTY-TWO MONTH PROGRAM
A. Plant Cost
Design $ 175,000
Equipment (machinery only) 1,500,000
Construction (including 1,525,000
building)
Test facilities for process 698,000
evaluation and quality control
$3,898,000
B. Operating Costs
Direct labor 998,210
Travel, relocating, report 214,700
reproduction, computer
use fees
Overhead and personnel services 569,205
Utilities 323,000
Test Coals 3,600,000
Expendable supplies 724,920
Plant and equipment maintenance 600,000
General administration (e.g., 1,169,962
postage, telephone, office
equipment)
8,199,997
C. Laboratory services (via contract)
Preliminary engineering 20,000
Laboratory work 3,353,200
Personnel service (1st year only) 56,400
3,429,600
D. Fee (8% of B and C) 930,368
Total $16,457,965
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overall cost without unduly sacrificing program objectives. As a result
of this effort, an alternative program to be accomplished in less time
and at lower cost was defined. For the alternate lower cost program, the
overall program of work including the detailed design and construction of
the prototype plant, development of the detailed experimental program and
in-plant testing of 36 coals is estimated to require 44 months. The al-
ternative lower priced program is based on the following:
• The amount of each of the 36 coals to be tested in the proto-
type plant will be 4,000 rather than the initially recommended
10,000 tons;
• The experimental work is programmed for 24 months (rather than
36 months);
• The overall effort of work covering the design and construction
of the prototype coal cleaning plant and the execution of the
experimental work has been programmed for 44 months (rather than
52 months); and
• The amount of on^site laboratory work and, consequently, the
equipment and personnel need have been reduced.
Based on these changes, the cost for the modified program concept
was estimated at $8,923,200; details are provided in Table XXII. The
modified program cost estimate does not include credits received from the
sale of processed coal and credits from the disposal of plant equipment
after program completion. These credits are estimated to amount to
$1,000,000.
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TABLE XXII
COST ESTIMATES FOR FORTY-FOUR MONTH PROGRAM
A. Plant Cost
Design $ 175,000
Equipment (machinery only) 1,500,000
Construction (including 1,410,000
building)
Test facilities for process 323,500
evaluation and quality control
$3,408,500
B. Operating Costs
Direct labor 1,415,690
Travel, relocating, report 179,700
reproduction computer use
fees
Overhead and personnel services 788,550
Test coals 1,440,000
Expendable supplies 316,900
Utilities 201,300
Plant equipment maintenance 400,000
Contract testing 30,000
General administrative 334,055
Fee 408,505
$5,514,700
Total $8,923,200
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6.3 Design of the McNally Pittsburg Prototype Cleaning Plant, Test Plan,
(21)
and Costs
6.3.1 McNally Pittsburg Plant Design
The design of the prototype plant required special considerations to
ensure that it will suitably process a wide variety of coals from which
satisfactory clean coals with acceptable sulfur content could be pro-
duced. The plant design provides for flexibility through alternate
circuits and equipment choices which can be run in any combination to
permit the handling of coals of different sizes and widely varying wash-
ability characteristics. The recovery and concentration of pyrite for
possible future commercial utilization were also considered. In the
absence of established standard methods for the recovery of pyrite from
the washery refuse, alternate circuits as well as alternate equipment
items were deemed necessary to enable the determination of the most
suitable recovery processes. All of these considerations were taken
into account in arriving at the prototype plant design concept.
The recommended plant has a 50 TPH capacity, and contains a coarse
coal circuit with a heavy media cyclone for cleaning the various sizes
of 1-1/2 inch x 3/8 inch, 1-1/2 inch x 14 mesh, 3/4 inch x 3/8 inch,
3/4 inch x 14 mesh, and 3/8 inch x 14 mesh coals, and a fine coal cir-
cuit for treating fractions 3/8 inch and less. Coals which would be
crushed to 3/8 inch x 0 or 14 mesh x 0 would be washed in the fine coal
circuits which has available primary and secondary McNally-Visman Tri-
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cone. The secondary Visman Tricone (unlike the primary Tricone) can be
used to treat high specific gravity material at a high cut point.
Besides the fine and coarse coal circuits, adequate arrangements
have been made for unloading, handling, and crushing the raw coal as
well as handling of clean coal and disposal of refuse. A water clarifi-
cation system is included to provide for cleaning and subsequent reuse
of water, thereby substantially reducing the amount of water required by
the plant. An 8000-ton-capacity raw coal storage facility has been pro-
vided through two 4000-ton silos for storing raw coal sufficient for
one month's operation.
In essence, the recommended prototype plant has been provided with
alternate circuits and equipment choices which can be run in any combin-
ation so that it will be able to handle .coals of different sizes and
widely varying washability characteristics. In the absence of standard
methods for the recovery of pyrite from the washery refuse, alternate
circuits as well as alternate equipment are provided to determine the
most suitable process for pyrite recovery from any given coal.
Although not included in the provided plant design, the installa-
tion of a fluid bed type thermal dryer was recommended for consideration.
The dryer could be used to treat fine coals with high moisture content
and would provide for obtaining valuable operating information. The
collected data could be used to assist coal cleaning plant and dust
collector designers and plant operators to meet air pollution restric-
tions in the supply and operation of full scale plants and equipment.
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Specifics concerning the cleaning plant and processes are as follows:
The cleaning process starts with raw coal crushed in a rotary breaker
and stored in one of two 4000-ton steel silos. The two silos provide the
storage capacity necessary for running the plant for 22 days at one shift
per day with an average feed rate of 50 TPH.
Although the overall plant was designed for an average capacity of
50 TPH, the raw coal crusher with associated conveyor belts, screens,
etc., was designed with excess capacity so as to permit an increase in
load in the heavy media cyclone. The raw coal scalping unit has inter-
changeable screens for 14 mesh or 3/8 inch. The 14 mesh x 0 or 3/8 inch
x 0 size coal from the scalping screen will normally be conveyed to 8-inch
primary McNally Visman Tricones for washing.
A crusher, provided after the heavy media cyclone sink screen, will
crush the refuse to liberate interlocked pyrite particles prior to fur-
ther washing in McNally Visman Tricones. Crushed refuse from the heavy
media cyclone or the coal from the raw coal scalping screen will be proc-
essed in eight 8-inch primary Visman Tricones in order to recover low
sulfur coal.
High sulfur refuse from the primary McNally Visman Tricones can be
washed in 8-inch secondary McNally Visman Tricones or in sequence
through secondary McNally Visman Tricones and the Deister coal tables.
The coal table was specified to provide the means to determine the
feasibility as well as efficiency of recoverying low sulfur coal from
pyrite rich refuse by employing a tricone and/or a coal table. Refuse
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from the secondary McNally Visman Tricones can also be fed to two ore
tables to treat the heavier pyrite/refuse fraction.
Tailings from the magnetite separator and the minus 1/2 mm frac-
tion from the classifying cyclone underflow can be processed in the
flotation cells to recover low sulfur coal. When recovery is not re-
quired, the flotation cells can be by-passed and the tailings pumped
to the waste pond.
The flotation concentrate, or coal, if found low in sulfur, will
be filtered and mixed with the coarse washed coal and conveyed to load-
ing. If the coal concentrate from the flotation cell is found high in
sulfur and not worthy of recovery, it will be diverted to the waste pond.
Proper reagents to selectively float coal and depress pyrite along
with other gangue materials present in the coal slurry feed to the flota-
tion cell have not yet been developed for all the different coals. Work
is continuing in this field and the prototype plant will provide an ex-
cellent test facility to carry out tests with the various types of coals
selected for processing. Hopefully, it may be possible in the operation
of this plant to find a suitable collector for the selective flotation
of coal.
Adequate arrangements for the recovery of the magnetite from the
dilute medium have been provided. The dilute medium will be thickened
in a thickener and the magnetite recovered by a double drum magnetite
separator for system reuse. As the washed coal is expected to have
high surface moisture, the recommendation was made that consideration
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be given to the Installation of a fluid bed type thermal dryer for dry-
ing the fine coal. Installation of such a dryer will enable the col-
lection of valuable information on:
• Dryer fuel consumption versus dust loss as a function of
operating conditions,
• Size distributions of solids and dust fraction within the
processing system and those escaping to the atmosphere, and
• Selection of dust collecting equipment required to meet the
dust emission code of the various states.
6.3.2 McNally Pittsburg Test-Program
The purposes of the testing program are:
• To evaluate performances of each major piece of equipment
used in the plant;
• To evaluate each coal selected for processing;
• To define the proper circuit for a given coal;
• To evaluate overall performance of the plant for cost analysis;
and
• To make comprehensive plant studies including material balances,
ash, total sulfur, and pyritic sulfur content for each coal.
Approximately 8000 tons of coal will be required (i.e., delivered
to the plant) for each coal tested. For each test, a raw coal sample
(1-1/2 inch x 0) will be collected one to two weeks prior to test initia-
tion. This sample will be collected by an automatic sampler and will be
based on sampling lots of 2800 tons in seven hours at a 400 TPH feed.
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The sampler will take nine cuts per hour at 55.6 pounds per cut for a
total sample of 500 pounds per hour. Samples will be sent to two bins,
set to receive alternate cuts, for a total of 250 pounds per hour for
each bin. This procedure will satisfy all conditions for ASTM D2234-65T
on mechanical sampling of coal and D492048 on sampling coals classified
according to ash content. It will also provide the proper gross sample
with which to make the washability study from which plant settings will
be determined.
The primary gross sample will be screened to produce the following
sizes:
1-1/2 inch x 3/5 inch
3/4 inch x 3/8 inch
3/8 inch x 14 mesh
14 mesh x 28 mesh
28 mesh x 48 mesh
48 mesh x 0.
Float and sink separations will be run on each size fraction at the
following specific gravities: 1.30, 1.35, 1.40, 1.50, 1.60, 1.90, 2.20,
2.50, and 2.80. The refuse will be visually examined to see if heavier
gravities are required. Laboratory tests will be performed to define
dry ash, total sulfur, and pyritic sulfur contents of each size gravity
fraction. Related coal compositions will be calculated for each coal
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size which might be used as feed to a piece of equipment in the cleaning
plant. These coal sizes are:
1^1/2 inch j£ 3/8 inch
3/8 inch x 14 mesh
1-1/2 inch x 14 mesh
3/8 inch x 0
14 mesh x 0.
Based on the data, operating personnel will anticipate an optimum
setting for each piece of equipment. As a new coal is first fed to the'
plant, samples will be collected to check the specific gravity of opera-
tion. When the various circuits are set to the operators' satisfaction,
daily runs can be started to determine optimum plant conditions to pro-
vide for the maximum sulfur removal. In some cases it is likely that
it will be necessary to check more than one set of alternative condi-
tions to determine the point of optimum sulfur reduction. After the
equipment and the circuits are set for their best performance in sulfur
reduction, prolonged test runs will be made with all the sampling sta-
tions of all the circuits in use so that a complete plant evaluation can
be made for each coal washed. The total plant is specified to contain
29 sampling points (i.e., 27 automatic plus 2 manual).
The plant feed and final products for each coal will be analyzed
to determine compositions and the burning and slagging characteristics
of the feed as well as the final products. Regular checks will also be
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made on the plant effluent as well as on any pond water or streams which
might be affected by the plant operation.
Cleaning and equipment performance data generated in pursuance of
this effort should be properly cataloged and stored for ready access.
With this in view, microfilming arrangements together with an adequate
storage and retrieval system have been suggested. Closed circuit TV
communication is also specified for confidential transmission of data
to the plant and laboratory operations.
The testing program design intent is to permit comprehensive cov-
erage of all sampling stations or only a few stations as may be dictated
by coals and circuits being tested. Sufficient personnel and equipment
are specified to permit completion of all necessary tests on a day's
run prior to the start of the next day's run. In addition to the daily
tests, a washability test is required prior to each program for each
coal. At the end of each month, one or more comprehensive plant studies
including material balances and ash, sulfur, and pyritic sulfur balances
are specified. This work will require substantial personnel and many
auxiliary tasks will have to be performed at off hours so as to not
interfere with the routine tests.
The laboratory staff, in addition to maintaining the plant testing
program, will regularly collect samples of makeup and effluent water for
analyses. Therefore, all water coming onto the property and leaving the
property will be checked.
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6.3.3 McNally Pittsburg Capital and Operating Costs
Capital and operating cost estimates are based on the prototype
cleaning plant plus the following:
• The plant contains a fully equipped testing laboratory,
• The plant contains an analytical laboratory,
• Suitable office facilities are contained in the plant,
• One year is required for total plant installation time,
• Plant start up time is six months, and
• Plant operating time is three years.
Estimated costs are;
LABORATORY
OFFICE PLANT TOTAL
Estimated capital investment
for equipment & installation $1,078,191 $2,158,000 $3,236,191
Six month start-up costs 911,514 253,335 1,164,849
Operating costs for 3 years 5,430,000 1,520,010 6,950,010
Insurance for 4-1/2 years 11.540 44,185 55,725
Totals $7,431,245 $3,975,530 $11,406.775
Depreciated value of the plant and laboratory equipment at the end
of 4-1/2 years has been assumed to be 10 percent of the capital invest-
ment or $323,619. The cost of 96,000 tons of raw coal (for washing at
half the rated capacity during start-up and at 50 TPH for three years)
was estimated to be $3,276,000. The sale price of the washed coal was
estimated to be $995,163.
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(22)
6.4 Data Evaluation
The Roberts and Schaefer Company prototype plant design study was
judged the most appropriate in addressing the overall EPA program goal.
As a result, Roberts and Schaefer was given the responsibility to develop
a detailed test program for the prototype coal cleaning plant. The re-
sulting program contained inputs from Roberts and Schaefer and the McNally
Pittsburg prototype plant design studies, the Bureau of Mines coal pre-
paration group, EPA technical personnel, and from Commercial Testing
and Engineering, Incorporated.
A basic goal of the EPA coal cleaning program is to develop a cor-
relation of the cleanability of any coal with its raw coal physical
properties. This would involve the identification and quantification
of those physical coal properties which correlate with cleanability in-
cluding the identification of the most appropriate process, process
parameters (e.g., coal size, specific gravity of separation), product
yield, and the sulfur and ash characteristics of the clean coal product.
In general, the cleaning capabilities of operating preparation
plants are ascertained by sampling, analyses, and calculations. The
same applies to the performance testing of an experimental prototype
coal cleaning plant.
Since the calculations involved in predicting cleaning results and
in evaluating the test results are time-consuming, a computer is speci-
fied to perform the required calculations. The design of the prototype
test program is based on the use of computer processing to provide for
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timely and economical reduction of a voluminous amount of data and to
rapidly predict plant settings for subsequent runs on a given coal.
This quick response would be mandatory for completely evaluating a given
coal in a one-week test period.
(0\
Four computer programs are availablev' and will be used to ulti-
mately provide one program which will be used for predicting the attain-
able sulfur and ash levels at selected yields from a given coal. The
final computer program will basically evolve from a continuing examina-
tion and modification of an existing "Predicting Program." The basic
"Predicting Program" and its modifications will be used to define the
plant flow scheme which best fits the cleaning objectives. The other
three referenced computer programs will aid in evaluating the validity
and accuracy of the prediction program and its successors.
The four presently available programs are:
Program No. 1 - The Predicting Program:
The program for predicting the cleaning results of a plant or for
predicting the results of a piece of cleaning equipment in a plant
using (1) performance data that is already known from experience
on the various pieces of cleaning equipment, and (2) the grainsize
distribution and washabilities of the raw coal determined by suit-
able laboratory test work;
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Program No. 2 - The Distribution Program:
The program for establishing the distribution-curve data of
cleaning equipment from data acquired as a result of prototype
plant operations.
Program No. 3 - The Classification Program:
The program for establishing the classification curve of classify-
ing equipment from data acquired as a result of prototype plant
operations.
Program No. 4 - The Solids Balance Program:
The program for balancing the solids flow (tons) or the solids flow
rate (tons per hour) with the ash, pyritic sulfur, and total sul-
fur content of the solids through each line of the flow scheme.
The programs will permit the calculations required to characterize
the sharpness and efficiency of a separation in any cleaning unit in the
plant. As data become increasingly available, a running analysis of
variance will delineate the sensitive variations in operating conditions
or physical characteristics of the coals which affect cleaning perfor-
mance. Factors to compensate for these variations will then be defined
and incorporated in the computer program. Even though the initial pro-
grams do not cover sulfur content of the coal, inclusion of this para-
meter in the program will provide the ability to project the sulfur and
ash contents in the clean coal based on raw coal characteristics.
It is anticipated that the final program will include raw coal data
obtained from the following:
150
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(1) Sample crushed to three top sizes with screen analyses for
each with ash and sulfur determination for each size fraction.
(2) Washability relationships derived from float-sink tests for
each of the three size samples and the ash and sulfur analyses
for each specific gravity fraction.
(3) Hardgrove grindability index, BTU, and ultimate and proximate
analyses of each coal sample.
6.4.1 Details of Presently Available Computer Programs
The following presents information on each of the four presently
available computer programs.
a) Program No. 1 - The Predicting Program:
The inputs for the predicting program are the percent by
weight and the ash content for each specific gravity fraction (i.e., from
the washability), and an ashline relationship (between specific gravity
and percent ash) of the raw coal. The computer will interpolate and
extrapolate the washability, calculate the yield, the specific gravity
composition, and the ash content of the end products for a separation by
employing distribution-curve data of the desired cleaning equipment. The
calculation will be based either on a given specific gravity of separation
or a required ash content for the clean coal.
Three systems of separation are available. The first is a separation
arrangement in which clean coal and refuse are separated and then a
middling product is separated from the clean coal. The second is a re-
verse of this, the middling product being separated from the refuse.
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The third arrangement involves middlings being separated from both clean
coal and refuse after these two have been separated from each other.
The program takes the washability data associated with each size
fraction of the raw coal in the order provided by the data card set until
all size fractions are processed. If more than one separation is to be
performed on any size fraction of the coal, the cleaning equipment for
each separation will be specified. The results of the program cleaning
calculations become data supplied to the program for calculation of the
results of the next separation in the system.
b) Program No. 2 - The Distribution Curve Program
This program will be used to establish washing equipment distribu-
tion-curve data based on results obtained from the prototype plant tests.
For the program, the input is the percent by weight from each specific
gravity fraction in each grain-size range of the feed and end products.
In the case of a cleaning unit making only one separation, three para-
meters are involved: feed, clean coal, and refuse. In the case of two
separations, four parameters are involved: feed, clean coal, middlings,
and refuse.
With this input the computer proceeds to calculate the percent
yield for clean coal, for middlings in the case of a two-separation pro-
cess, and for refuse. Employing the yield calculation result, a recon-
structed feed is determined and the distribution numbers calculated for
each piece of equipment. The reconstructed (or reconstituted) feed, as
opposed to the actual sampled feed, is used as a check on the accuracy
152
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of both the analytical and the sampling procedures. The reconstructed
feed is determined by adding the end products together on a weighted
basis for each size and specific gravity composition, based on the cal-
culated yield percentages.
c) Program No. 3 - The Classification Program
Program No. 3 is for establishing the classification curve data of
classifying cyclones and sieve bends from data obtained from prototype
plant testing.
With the help of classification curves obtained by testing, the
standard"classification curve already known from experience for classi-
fying cyclones and the classification curve known for sieve bends can be
checked and, if necessary, modified. Using the standard classification
curve, the grainsize composition of the end products of the classification
equipment can be predicted for different grainsize compositions of the
feed.
A classifying cyclone or a sieve bend component only is not always
used for classifying a product (water plus solids). A combination of
such components can also be employed. The program is written in such a
way that not only the test results of a single component but also the
test results of a combination can be used as input. In such a case the
computer calculates the classification-curve data for both pieces of equip-
ment with less sampling and analytical test work than would be the case if
both units were treated separately.
153
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d) Program No. 4 - The Solids Balance Program
This program is to be used for balancing the solids flow (tons), or
the solids flow rate (tons per hour), with its ash, pyritic sulfur, and
total sulfur content through each line of the flow scheme. The balancing
provides projections on the overall reduction of ash, pyritic sulfur, and
total sulfur in the clean coal obtainable on a full plant basis, and the
ash and sulfur reduction attributable to each piece of cleaning, sizing,
and classifying equipment.
The computer program will allow the simulation of five major and
thirty-three minor flow schemes. By making use of balancing techniques,
the program usage will reduce the requirements for sampling and analyt-
ical test work.
6.4.2 Correlation of Coal Characteristics with Cleaning Results
(Multiple Regression Analysis)
A continual analysis of the variations in the operating conditions
of the plant and in the physical characteristics of the coal that affect
cleaning equipment performance will be provided. Data on the perfor-
mance of each piece of cleaning equipment will be continuously collected,
through sampling and analysis, and the raw coals processed will be
analyzed with respect to certain major properties. The examined proper-
ties include grindability, pyritic sulfur content, and the electrokinetic
potential. The equipment parameters which will be varied include the size
fraction of coal being cleaned and the tons per hour processed. In the
analysis of variations an attempt will be made to establish whether a
correlation can be made between pairs of observations or groups of ob-
154
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servations. The pairs of observations will be in the form of scattered
data in which an attempt will be made to find functional relationships.
These relationships may be linear or non-linear. If they are linear, a
line of regression will be determined taking each variable in turn as the
independent variable by the method of least squares, as used in a linear
regression analysis. If they are non-linear, an attempt will be made to
determine what sort of function is represented. For instance, two vari-
ables may be parabolically or quadratically related and perhaps an equa-
tion describing the relationship can be determined. In the case of a
correlation attempt on groups of observations, multiple correlations will
be attempted by a multiple regression analysis.
The purposes of the analysis of variations are to determine which
coal properties and/or operating conditions prove to be significant par-
ameters and to determine, if possible, the relationship between these
parameters. Once this is known to any substantial degree, predictions
of greater confidence may be provided.
155
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7.0 PYRITE UTILIZATION ECONOMIC STUDY
7.1 Purposes of the Study; Overview and Approach
Commercial coal cleaning plants are designed to remove non-carbon-
aceous materials from the coal. The composition of the reject material
varies with the type and source of the coal. It consists principally of
shale, sandstone, clayey substances, and pyrites (iron-sulfur compounds)
along with carbonaceous materials unavoidably lost.
Several of the reject constituents have commercial value, but the
low concentration of these materials and their relatively low market
price have in the past rendered their recovery and sale commercially un-
attractive. One apparent exception is pyritic and carbonaceous material,
which can serve as a source of sulfur, sulfur compounds, and energy. Con-
centrations of pyrites in the reject from cleaning certain coals appear
sufficient to make recovery of sulfur values economically feasible. This
would be more likely if the sulfur recovery can be combined with combus-
tion processes so that the energy from the combustion of pyrites, as well
as the coal fraction remaining in the rejects, can be utilized.
The purposes of the Pyrite Utilization Economic Study portion of
EPA's overall pyrite coal program are:
(1) To investigate the economics of utilizing the pyrites obtained
from coal beneficiation by determining (a) the degree to which
it is possible to offset the increased costs involved in maxi-
mizing the reduction of sulfur content and (b) the ability to
recover economic values in reject material;
156
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(2) To evaluate the applicability of alternative commercial pro-
cesses for recovering energy and chemical values from coal
cleaning reject material; and
(3) To design, construct, and operate a plant that would demon-
strate the technical and economic feasibility of the processes.
Investigations concerned with the first two purposes listed above
were conducted concurrently. In 1967, EPA awarded a contract to the
Bechtel'Corporation, assisted by Stanford Research Institute, to perform
a general review and evaluation of the technology and costs of available
commercial processes for utilizing pyrite-coal, and to investigate the
technical and economic feasibility of certain processes in greater de-
tail. Also in 1967, EPA awarded a contract to Arthur D. Little, Inc.,
assisted by Dorr-Oliver, Inc., to determine the costs and benefits of
processing pyrites removed from coal. The A. D. Little study concen-
trated on the technology and economics of fluidized bed roasting of
pyrite-coal, followed by conversion of sulfur dioxide to sulfuric acid
by the contact process. A principal goal of the latter study was to
evaluate the acceptability of such processes to the industries involved
(coal, chemical, utilities, steel, etc.). The results of these two
studies of various recovery processes and the market potential for
recovered products and by-products are presented in the remaining por-
tions of Section 7.
The Bechtel and A. D. Little studies lead to the general conclu-
sion that existing technology can readily be adapted to recovery of
157
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sufficient quantities of energy and sulfur values from the reject mater-
ial from coal cleaning operation to be of commercial interest. However,
the economics of such recovery operations are marginal, and the economic
viability of these operations is closely related to the supply and sell-
ing price of elemental sulfur.
On the basis of technical and economic data developed in these two
studies, EPA decided to look more closely at a system for burning the
high-sulfur, high-ash reject materials produced by coal desulfurization.
This decision was based on the applicability of proven technology and
on economic analyses of various processing systems. A contract was sub"-
sequently awarded (in 1969) to Chemical Construction Company (Chemico)
to (1) select the most appropriate sulfur recovery process and design
a high-sulfur combustor system, (2) investigate combustion character-
istics of high-sulfur fuels, and (3) prepare a conceptual design and
cost estimate of a prototype plant employing the high sulfur combustor.
Chemico was assisted by the Foster Wheeler Corporation in this under-
taking. Results of the design and analysis effort are presented in
Section 8 of this report.
7.2 Description of Candidate Recovery Processes
Chemical and energy values can be recovered from pyrite-coal by a
number of processes. These employ markedly different approaches and
yield different combinations of products. Certain processes accept the
entire stream of reject material from a coal preparation plant while
others require additional concentration of the pyrite.
158
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Eight separate processes were selected for evaluation by Bechtel
Corp. Three of the eight (Fluid Bed, Outokumpu, and Orkla) were identi-
fied as being commercially available for the processing of pyrites for
metallurgical purposes, but all three have technical and economic limita-
tions for utilization of the total refuse streams from coal cleaning op-
erations. Thus, evaluations were made of five processes that had not
reached commercial application. These five additional processes accept
the total refuse stream from a conventional coal preparation plant, while
the presently available commercial processes require additional pyrite
concentration. All of the processes considered and their principal pro-
ducts are identified in Figure 25 with descriptions following. The
marketing of product sulfur and sulfuric acid is discussed in Section
7.3, but it should be mentioned at this point that recovery of sulfur
values in the form of elemental sulfur is sometimes preferable to re-
covery in the form of sulfuric acid because of the high shipping costs
for the acid. This consideration does not apply when there is a market
for sulfuric acid near the reject processing plant.
7.2.1 Brief Description of Recovery Processes
The eight recovery processes evaluated are described briefly in the
following paragraphs.* These descriptions include comments on the appli-
cability of each for processing pyrite-coal. It should be noted that
none of those processes that accept the entire refuse stream was in com-
*More complete descriptions including process flow diagrams are given in
Reference 23.
159
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MINING
RAW COAL
COAL PREPARATION
CLEAN COAL
REFUSE
COMBUSTION-
SULFUR OXIDES
REMOVAL
CARBONIZATION-
DESULFURIZATION '
SOLVENT
EXTRACTION
PREFERENTIAL
OXIDATION
TWO-STAGE
GASIFICATION
USULFURIC ACID
|»ELECTRIC POWER
•ELEMENTAL SULFUR
•CHAR
•PIPELINE GAS
^ELEMENTAL SULFUR
LIGHT OIL
'{«COAL EXTRACT
JBON DIOXIDE
GAS
, KSULFURIC ACID
WCHAR
, •ELEMENTAL SULFUR
•ELECTRIC POWER
PYRITE CONCENTRATION
REJECT
PYRITE-
COAL
>rSULFURIC ACID
^ELEMENTAL SULFUR
ksULFURIC ACID
MRON OXIDES
^ELECTRIC POWER
ELEMENTAL SULFUR
SOURCE: REFERENCE 23 (1968)
FIJGURE 25
REFUSE PROCESSES
160
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mercial operation at the time this study was conducted. Processes that
accept a concentrated pyrlte feed were in commercial use, but were utiliz-
ing mined pyrites, not pyrite-coal reject materials.
Combustion/Sulfur-Oxides-Removal
The reject material is burned in a combustor designed for high-
sulfur, high-ash feed. Heat from the combustion is used to
generate steam which is used in turn to generate electric power.
Sulfur oxides produced in the combustion are recovered from the
combustion gas and used to form sulfuric acid. Several processes
have been proposed for sulfur dioxide recovery; the Monsanto
Catalytic Oxidation process was selected as a basis for costing
and evaluating the overall process. In the Cat-Ox process, sulfur
dioxide in the combustion gas stream is oxidized in contact with a
catalyst to form sulfur trioxide, which is absorbed in water to
form marketable sulfuric acid.
Although the Cat'-Ox process was not in commercial use at the time
of this study, it had been tested in a large-scale pilot plant.
Carbonization-Desulfurization
This approach to material and energy value recovery involves a
relatively complex set of reactions in which coal and pyrites in
the reject stream are decomposed by heat. Sulfur is removed from
the decomposition products to form elemental sulfur; a high-
BTU, low-sulfur combustible gas; low-sulfur char; and other solid
products.
The carbonization-desulfurization approach can be illustrated by
a highly abbreviated (and incomplete) description of a specific
process.* Volatile components are removed from coal in the reject
material by contact with a very hot char (produced by another
step in the process). Volatilized components are de-acidified by
amine stripping, then passed through a methanator where constituent
carbon monoxide and hydrogen react to form methane, which is then
compressed to'form a pipeline gas. The solid components of the
feed stream are desulfurized by reaction with hydrogen to form
hydrogen sulfide and a low-sulfur solid char. Sulfur is removed
from the hydrogen sulfide by reaction with dolomite to form a
*The Consolidated Coal Company C02 Acceptor Process,
161
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solid sulfide, which is oxidized to remove sulfur as sulfur dioxide
and to regenerate the dolomite for reuse. The sulfur dioxide is
reduced by reaction with hydrogen sulfide or carbon monoxide (from
other process steps) to form elemental sulfur, water, and carbon
dioxide. The useful products are high-BTU, low-sulfur pipeline
gas; low-sulfur char; and sulfur.
This technically complex process would be further complicated by
the use of pyrite-coal instead of run-of-mine coal. The effects
of additional ash on the process and on the value of the char are
not well understood. The process requires high capital investment.
Preliminary economic studies are not encouraging.
Solvent Extraction*
In this process, the coal in the refuse stream is dissolved in a ,
solvent. A low sulfur, low ash solid coal extract is recovered
from the solvent. Depending on the specific processes used, other
products may include light oil, fuel gas, and sulfur.
This process is characterized by its technical complexity and re-
quirements for high capital investment. It is still under develop-
ment, using run-of-mine coal. The effects of using pyrite-coal
rejects for the feed material are not well known. Prospects for
processing coal-pyrite rejects, based on preliminary economic
analysis and current developmental status, are not attractive but
may become so through continued research and development.
Preferential Oxidation
The reject stream is allowed to react with a limited quantity of
oxygen at a temperature range that promotes oxidation of pyritic
sulfur in preference to carbon. This temperature (around 800°F)
must be carefully controlled to prevent excessive volatilization
and oxidation of the coal. Temperature control is a major tech-
nical problem. The sulfur dioxide formed by oxidation of pyrite
is converted to sulfuric acid.
The process has been studied on a laboratory scale. Data are not
adequate for useful economic analysis.
*It should be recognized that the process termed "solvent extraction"
here (and in Reference 23) involves dissolution of the carbonaceous com-
ponents of coal, not the ash or pyritic components, and in this respect
is similar to the Pittsburg-Midway "Solvent Refined Coal" process.
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Two Stage Gasification Process
A gasifier, fired with coal refuse, operates in a system that
converts the fuel value to electricity and recovers elemental sul-
fur from the gas. Hot gases which contain most of the sulfur as
I^S leave the top of the gasification furnace, generate steam in
a heat recovery boiler, then preheat air for combustion of these
gases later in the system. Gas, now at 250°F, is scrubbed with
100 F water to remove dust and condense water vapor. Hydrogen
sulfide is removed from the gas by an absorbent solution and then
converted to elemental sulfur by a Glaus kiln or perhaps the
Giammarco-Vetrocoke process. Clean gas from this system would
contain about 1.0 grain of hydrogen sulfide per cubic foot, and
sulfur recovery would be about 98 percent of that absorbed. The
sulfur would probably be contaminated with small amounts of arsenic
from the absorbent solution but purification with limewater would
be practical. The clean gas from the sulfur recovery steps would
be burned with the preheated air from the heat exchange in a boiler
equipped for preheating combustion air for the gasifier. Waste
gas at about 450°F would pass to a stack. Steam from this boiler
and from the heat recovery boiler would be available for electrical
power generation.
Fluid-Bed Pyrite Roasting
Crushed pyrite (about 1/4 inch top size), on a grate or bed through
which an upflow of air keeps the material turbulent, is oxidized
at high temperature to produce sulfur dioxide and iron oxide Cprin-
cipally hematite). The sulfur dioxide in the gas stream is oxidized
catalytically to produce concentrated sulfuric acid. The solid.
residue can be further processed to produce a material similar to a
high grade iron ore. Since the oxidation of pyrite under these
conditions is self sustaining and exothermic, the heat produced can
be used to generate steam which then can be used to generate
electric power. The products of this process are a marketable
grade of sulfuric acid (93 to 98 percent ^504), electric power (or
steam), and a solid calcine material. Iron from the pyrite may re-
.main in the calcine as hematite (£6203), or it may be removed as a
separate product, usually in the form of magnetite (£6304) suitable
for steelmaking.
This process is widely used on a commercial scale for sulfuric acid
manufacture from mined pyrites. In at least one installation it
also produces iron oxide pellets for steelmaking. The process
usually requires pyrite containing 40 to 50 percent sulfur. Since
the pyrite-coal reject stream from a coal preparation plant typically
163
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contains 4 to 25 percent sulfur, a pyrite concentration step is
required.
Preliminary economic analysis shows this process to be one of
the more promising for recovering energy and sulfur values from
coal-pyrite rejects.
Outokumpu Process
In this process, pyrites are flash smelted upon contact with hot
gases from an oil burner. Labile sulfur in the pyrites volatilizes
in the form of elemental sulfur vapor, sulfur dioxide, and hydro-
gen sulfide. The sulfur vapor is condensed and sulfur is recov-
ered from the sulfur dioxide and hydrogen sulfide in the form of
elemental sulfur.
Fixed sulfur in the pyrites remains as ferrous sulfide matte. This
is roasted to produce iron-bearing calcine, from which iron can be
recovered, and sulfur dioxide, which is converted to sulfuric acid.
Heat produced at the smelting step and ferrous sulfide roasting
step of this process can be used to generate steam and electric
power.
This process is in commercial operation in Finland. It appears
suited to a set of conditions existing there, where there is a mar-
ket for all of its principal products—sulfur, acid, iron oxide,
and electric power. The economics of the process are not attrac-
tive for use in the U.S., where different market conditions exist
for its products, particularly for iron oxide. If a pyrite-coal
feed is used, yields would be lower and the economic prospects
even less attractive.
Qrkla Process
This process is used in Norway to recover sulfur and metallic values
from copper-bearing pyrites. It employs a furnace, similar to a
blast furnace, which is charged with lump pyrites, coke, sand, and
limestone. Labile sulfur in the pyrites volatilizes initially with-
out oxidation as elemental sulfur in the upper part of the furnace
where no oxygen is present. Fixed sulfur remains as metallic
sulfides, which sink to the smelting zone of the furnace, where a
portion oxidizes to form sulfur dioxide and iron oxide, while the
remainder forms a matte of cupreous sulfide and iron sulfide, which
is resmelted to obtain copper. The iron oxide reacts with silica
and limestone to form a slag, while a portion of the sulfur dioxide
is reduced by coke to form elemental sulfur. The remaining sulfur
dioxide is reacted catalytically with gaseous sulfur compounds
formed at various processing steps to form elemental sulfur and
164
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by-product gases. Principal products are copper and elemental
sulfur, with a by-product slag of high iron content.
While the Orkla process is the only one of the eight evaluated
processes operating on a commercial scale that recovers most of
the pyritic sulfur in elemental form, it has certain inherent
disadvantages. It requires that the pyrite feed be in lump form,
which would necessitate briquetting of pyrite coal produced by a
coal preparation plant. Process economics, which are somewhat
marginal using a cupriferous pyrite feed, are heavily dependent
on recovery of copper, which, of course, would not be feasible
from most pyrite coal feeds. Although the process appears well
suited to the situation in Norway, it does not appear economically
attractive or readily adaptable technically to the processing of
pyrite coal in the U.S.
The eight processes described above are summarized in Table XXIII.
This table indicates the advantages, limitations, and economic character-
istics of each process, in addition to identifying the type of feedstock,
principal products, and major processing steps.
7.2.2 Preliminary Economic Studies of Selected Processes
To obtain a comparison of the economics of the above processes, five
were analyzed in a given scenario using a consistent set of assumptions
relative to size of operation, logistics, power and labor costs, product
market prices, etc. The following processes were subjected to this type
of analysis:
• Refuse Combustion/Sulfur-Oxides-Removal;
• Fluid Bed Roasting;
• Outokumpu;
• Carbonization-Desulfurization;
• Solvent Extraction.
All of the above are either in commercial operation or reached the pilot
plant stage of development. The remaining three processes were not
165
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TABLE XXIII
SUMMARY OF PROCESSES FOR UTILIZING COAL REFUSE
PROCESS
Combustion- Sulfur
Oxides Removal
Carbonization-
Be s ul f ur i zat ion
Solvent Extraction
Preferential
Oxidation
FEED
Entire refuse
stream
Entire refuse
stream
Entire refuse
stream
Entire refuse
stream
PRODUCTS
Sulfuric Acid
(78%)
Electricity
Sulfur
Pipeline gas
Char
Sulfur
Light oil
Coal extract
Carbon dioxide
Fuel gas
Sulfuric acid
PROCESS DESCRIPTION
Coal refuse is burned in
a stream generator de-
signed for high ash and
sulfur fuel. Sulfur is
oxidized to sulfur diox-
ide which is catalyt-
ically converted to 803
followed by recovery of
sulfuric acid.
Process is in develop-
mental status
Coal refuse is dried,
devolatized, then de-
sulfurized in a fluid
bed with gas containing
about 50% H .
Sulfur forms H.S which
is removed by a dolomite
acceptor. Dolomite is
regenerated. H S is
converted to elemental
sulfur, process gas is
converted to fuel gas by
a methanation reaction.
Coal fraction of the re-
fuse is dissolved in
solvent derived from the
coal itself in the pre-
sence of hydrogen. So-
lution is filtered to
remove ash. Filtrate is
evaporated to recover
solvent, and liquid coal
extract is solidified.
The solvent is distilled
to yield light oil; the
heavier fraction is re-
cycled. Process gas
containing H2S, removed
along with solvent
vapor, is passed through
an amine treatment to
remove the acid gas.
Add gas is processed to
recover elemental sulfur
Process gas is steam re-
formed to give H2& for
recycle and C0« bypro-
duct.
Sulfur is oxidized pre-
ferentially without
burning excessive
amounts of coal. This
is done by carefully re-
gulating the quantity of
air and controlling the
temperature.
ADVANTAGES
Does not require pyrite
concentration
Based on relatively simple,
well-known technical
principles ~ -- -
Products are usually mar-
ketable
Requires no pyrite concen-
tration; uses entire re-
fuse stream
Recovers sulfur in ele-
mental form
Requires no pyrite con-
centration; uses entire
refuse stream
Produces high quality
products
Simple process scheme
with few operational
steps
LIMITATIONS
Sulfuric acid product
is slightly discolored
and limited to about 78
percent concentration
Market radius is limited
by shipping cost of acid
(usually about 200 miles
maximum)
Final solution is required
to select economical
corrosion resistant ma-
terials of construction.
Pilot plant status
Complex, multioperation
process with many tech-
nical problems to solve
High-ash char may not be
marketable; this product
may retain sulfur
Pilot plant status
Complex process; it re-
quires further develop-
ment and solution of
technical problems
Economics favor very
large-scale operation
Pilot plant status
treatment removes only a
small fraction of organic
sulfur and not all pyritic
sulfur.
Status of development is
bench-scale with very
limited data.
Temperature control problem
difficult to solve
ECONOMICS
Most promising
process
High capital and
net operating
costs
Highest capital
and net operating
costs of processes
evaluated
No data because of
process status
er>
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TABLE XXIII
SUMMARY. OF PROCESSES FOR UTILIZING COAL REFUSE (CONT'D)
PROCESS
Two- Stage
Gasification
Fluid Bed
Roasting
Outokumpu
Orkla
FEED
Entire refuse
stream
Pyrlte concen^
t rat ion
Pyrite Concen-
tration
i,
Cupriferous
Pyrite
PRODUCTS
ulfur
lectricity
Sulfur acid
!ron oxides
Electric power
Sulfur
Sulfuric acid
Iron oxide
Electricity
Sulfur
PROCESS DESCRIPTION
The gasifier is a spe-
cially designed vertical
cyclone furnace with two
burner ports, one above
the other. Refuse burns
at the upper port with
limited air to produce
an t^S rich gas and slag
containing FeS. The
slag runs down the walls
into the flame at the
lower port where refuse
is burned with excess
air, converting all sul-
fur compounds to 302-
Gases passing up through
furnace become H2S-rich.
Subsequent treatment
recovers sulfur and
yip.lds an-100 Rtu/cubic
foot fuel gac.
Pyrite concentrate is
roasted in a fluid-bed
furnace to produce S02
and a low-sulfur hemati-
tic calcine. S02 is
co verted o aci in a
plant. Iron ore may or
may not be recovered de-
pending upon quality and
market. Waste heat can
be recovered for process
or generation of electri
city.
Pyrite is flash smelted
by combustion gases
which remove the labile
sulfur for recovery in
elemental form. Other
gaseous compounds are
catalytically converted
to S. Liquid FeS matte
is granulated and
roasted to give an iron
oxide product and SO.
for conversion to acid.
rhe Orkla process smelts
pyrite in a specially
designed blast furnace
to produce elemental
sulfur . Iron , copper ,
and precious metals re-
port in the matte.
ADVANTAGES LIMITATIONS
Simple process with
efficient recovery of
fuel value
Produces valuable ele-
mental sulfur
Relatively simple, well-
developed technology
Recovers about half of
the sulfur in elemental
form
Process developed to
commercial scale.
Produces elemental sulfur
Process developed to com-
mercial scale
The process is in the con-
cept stage only, no devel-
opment work has been done.
Requires pyrite concen-
tration
Requires pilot plant de-
velopment for use with
coal refuse
Dilution of pyrite with
centration of SO- in gas
stream.
Degree of acid discolora-
tion is unknown.
Ash content of coal refuse
would cause technical
problems
Economy would suffer be^-
cause iron sinter would
not be marketable.
Requires very large-scale
operations
Limited to a lump pyrite
feed
Modification of technology
for feeding coal refuse
would be difficult.
ECONOMICS
No data because of
process status
Low capi t al cos t
Net operating cost
is encouraging at
this stage of de-
velopment
Not as favorable
as conventional
fluid-bed process
-
No published data
It is generally be-
lieved to be eco-
nomic only with a
copper product.
Source: Reference 23
-------
Included in the economic comparison because of their development status,
technical factors, or a combination of the two. The two-stage gasifica-
tion process was in the concept stage when this study was conducted. The
preferential oxidation process had been studied in the laboratory, but
exhibited serious technical problems in the control of reaction tempera-
ture. The Orkla process was not analyzed further because of its depend-
ency on recovery of copper for overall economic viability, its require-
ment that finely-divided feed be briquetted, and the technical and eco-
nomic problems associated with the briquetting operation.
Results of the preliminary analysis are summarized in Table XXIV.
This table gives estimated costs and credits which can be presented on a
comparable basis for each process. Of particular interest are the
figures for "Change in Clean Coal Price," which indicate the effects of
these processes on the cost of coal preparation under the assumption
that the total costs and credits for processing the pyrite-coal rejects
are integrated with the costs of coal preparation.* One of the processes
shows a small net credit while four show a net cost ranging from about
12 cents to $1.63 per ton of clean coal.
The annual costs for each process reflect a 20-year depreciation
period. Other assumptions relative to production, logistics, marketing,
etc., are detailed in Table XXV.
*The economic data presented in Table XXIV should be viewed as relative,
not absolute, cost or credit information.
168
-------
TABLE XXIV
COST EVALUATION SUMMARY
•. Capital Investment, $
Total Annual Cost,
$/Year
Credits for Products
(FOB Plant), $/Year
Credits for Fuel Value,
$/Year
Net Annual Cost,
$/Year
,H
0 >
•H O
•P S
W 0)
3 PH
-g
B CM
0 0
U CO
T!
0)
ni
, CO
.2 OT
** d)
"2 o
'S o
3 ^
h *
3
a
p 03
3 co
L^ QJ
O 0
•u o
3 M
O PH
i a
o
a -H
.3 ^
•P N
C8 -H
M H
•H 3
C M-i
O T-l
43 3
H 01
n) a)
0 O
a
o
•H
4J -W
Pi O
^
H -P
O !«!
W W
(figures in thousands except *)
8,300
2,201
1,160
1,230
-189
2,400^
1,077
826
36
215
5,000
1,695
867
60
768
14,000
4,006
2,432
—
1,574
19,500
7,420
4,368
—
3,052
Change in Clean Coal
Price, (2)$/ton* -0.10 +0.12 +0.41 +0',84 +1.63
.Cost of Transporting
Products to Market,
$/Year
Selling Cost of Products,
$/Year
Total Cost of Products
to Customer at Market,
$/Year
1,275
100
2,535
568
58
1,452
418
61
1,346
1,609
160
4,201
1,407
278
6,053
(1) Facilities include waste heat boilers and acid plant.
(2) Positive values indicated that cost of process exceeds credits from
fuel value and products, which results in an increase in clean coal
price. Negative values indicate that credits exceed costs, which
results in a decrease in clean coal price.
Source: Reference 23 (1968).
169
-------
TABLE XXV
ASSUMPTIONS FOR PRELIMINARY ECONOMIC ESTIMATES
• Coal Mine: The coal mine produces 2,500,000 tons per year of ROM
coal. Mining cost is $3.50 per ton.
• Coal Preparation Plant: The coal preparation plant produces
1,870,000 tons per year of clean coal (1.0% sulfur) at $0.50 per
ton. This quality is enough to fuel a 1000 Mw(e) electric power
generator.
• Clean Coal; The clean coal has a heating value of 13,750 Btu
per pound, a total sulfur content of 1 percent, and an ash content
of 4 percent.
• Pyrite-Coal Refuse; A 630,000-ton-per-year stream of pyrite-coal '
refuse is produced containing 33 percent mineral matter and 67 per-
cent coal. The total pyritic and organic sulfur content is 6.2
percent, and the heating value-is 9700 Btu per pound.
• ROM Coal; The ROM coal has a heating value of 13,000 Btu per
pound and contains 0.8 percent organic sulfur, 1.5 percent pyritic
sulfur, and 10 percent ash.
• Pyritic Concentration: For the processes which require it, a
pyritic concentration plant processes 1900 tons per day of pyrite-
coal refuse, and produces 110 tons per day of pyrite containing
90 percent FeS2, 5 percent coal, and 5 percent mineral matter with
a pyrite recovery efficiency of 50 percent and a total operating
cost of $3.00 per ton of concentrate.
• Capital Costs; Capital costs for the pyrite-coal utilization plant
are the installed battery limit costs of the process equipment and
auxiliary facilities. The cost of land is not included in the
estimate. The installed costs are derived from estimates published
in nonproprietary sources using published scale factors to adjust
for plant size.
• Utilities; The unit cost of utilities required for operating these
processes are:
Cooling Water $0.05/1000 gallons
Boiler Feedwater 0.50/1000 gallons
Electric Power 0.008/kwhr
170
-------
TABLE XXV (con't)
ASSUMPTIONS FOR PRELIMINARY ECONOMIC ESTIMATES
• Raw Materials; The unit cost of raw materials required for oper-
ating these processes are:
ROM Coal $3.85/ton-13,000 Btu/lb
3.50/ton mining cost
Clean Coal 5.50/ton-13,750 Btu/lb
75% recovery
Pyrite Concentrate 3.00/ton-90% FeS
Ash Disposal Cost 0.75/ton
• Labor; Operating labor rates are averaged at $4.00/hr.
• Supervision and Overhead; The prorated cost of supervision,
employee benefits, and administrative overhead is equal to oper-
ating labor cost.
• Maintenance, Labor, and Material; An amount equal to six percent
of plant capital cost is assumed for annual maintenance, labor,
and material costs.
• Fixed Capital Charges: The annual fixed charge rate is 15 percent
of the pyrite-coal utilization plant capital cost. This includes
20-year depreciation at 6.5 percent interest, property taxes, in-
surance, and administrative expenses.
• Transporation Costs: The cost of shipping products to a market
200 miles away, based on prevailing railroad point-to-point commod-
ity shipping rates for the various products, is as follows:
Clean Coal (unit train) $1.44/ton
Coal Extract 2.90/ton
Coal Char 2.90/ton
Iron Oxide 6.25/ton
Sulfur 8.25/ton
Sulfuric Acid 11.00/ton
Sulfur Dioxide 12.00/ton
Light Oil 8.00/ton
Carbon Dioxide 8.00/ton
171
-------
TABLE XXV (con't)
ASSUMPTIONS FOR PRELIMINARY ECONOMIC ESTIMATES
• By-product Credits; Credits for by-product sale. FOB plant are
derived from the prevailing market selling prices for each by-
product. The credits are:
Sulfuric Acid (98%)
Sulfuric Acid (77.7%)
Elemental Sulfur
Coal Extract
Char
Fuel Value of
Coal Refuse
Pipeline Gas
Light Oil
Iron Oxide Pellets
Liquid Carbon Dioxide
Steam
$16.'00/ton From 500 T/day plant
using elemental sulfur
at $38.00/ton produc-
ing 98% acid
10.00/ton From 98% acid at
$16.00/ton and dis-
count 20% for quality
36.30/long ton Liquid crude, dark
sulfur, midwest plant
6.40/ton 15,800 Btu/lb based
on clean coal at $5.50/
ton
1.10/ton 8600 Btu/lb based on
ROM coat at $3.50/
ton and discounted 50%
for quality
1.95/ton 9700 Btu/lb
0.26/1000 scf 975 Btu/scf
0.10/gal
13.00/ton
15.00/ton
0.50/1000 Ib
Pittsburgh-Midway
67% Fe
Pittsburgh-Midway
and Air Reduction Co.
Source: Reference 23 (1968).
172
-------
7.2.3 Processes Selected for Detailed Cost Studies
Two of the processes discussed above were selected for further anal-
ysis at a more detailed level. The "Fluidized-Bed Pyrite Roasting Proc-
ess" was examined by A. D. Little, Inc., assisted by Dorr Oliver, and
the "Combustion/Sulfur-Oxides-Removal Process" was examined by Bechtel
Corporation. Although the fluidized-bed process was an obvious candi-
date from the outset of the study by virtue of employing proven tech-
nology and having been in successful commercial use for roasting of
mined pyrites, it was nevertheless included in Bechtel's cost analysis
of candidate processes in order to provide a common point of reference
for economic comparison with other technically attractive processes.
Bechtel's preliminary cost analysis indicated that the Combustion/Sulfur-
Oxides-Removal Process and the Fluidized-Bed Pyrite Roasting Process
have the most favorable economic prospects in terms of their effect on
the price of clean coal. (See Table XXIV.)
These two processes will be discussed separately at greater length
later in this chapter. For both, pyritic sulfur is oxidized initially
to sulfur dioxide, which is then converted to sulfuric acid. Although
both processes produce by-product calcine and can produce a good grade
of iron oxide as well as electric power, the major product of both is
sulfuric acid. Pertinent market characteristics of this commodity will
be discussed in the following section.
7.3 Sulfuric Acid Market Analysis
Sulfuric acid, as an industrial chemical, is a relatively low-cost,
heavy commodity. The principal commercial raw material in its manufacture
173
-------
is elemental sulfur or some sulfur-bearing compound such as pyrite. In
1970, over 85 percent of the sulfur consumed in the United States was
used for making sulfuric acid.
There are two features of the sulfuric acid market that warrant
special note. One is the large percentage of the market that is captive
— that is, the consumer owns the acid production facilities needed to
fulfill his demand. Second is the shipping characteristics of the acid
and its raw materials (elemental sulfur and pyrites). Since a ton of
sulfur will yield about three tons of acid, it is usually advantageous
to ship the sulfur to an acid manufacturing plant near the point of acid
consumption rather than ship the acid a great distance.
A different trade-off exists when the source of raw material is
pyrite (FeS2), which in pure form contains about 58 percent sulfur by
weight. One ton of pyrite could theoretically produce about 1-1/2 tons
of acid, although this theoretical conversion efficiency would probably
not be obtained in commercial operation. However, the total coal reject
stream is not pure pyrite and even pyrite concentrate from the reject
stream may contain significant amounts of other material. This lowers
the weight ratio of acid-to-feed even further, and emphasizes the dis-
economy of shipping either acid or pyrite-coal over any appreciable
distance. In general, shipment of the acid in quantity is limited to
100-200 miles, although there are exceptions to this generality. An-
other consideration in the use of pyrite for acid manufacture is the
174
-------
possibility of shipping the solid by-product (iron-bearing calcines) for
iron recovery or other disposition.
The production and utilization of sulfuric acid were examined from
several points of view. The production and disposition on a regional
basis are displayed in Table XXVI. Deposits of coal with high pyritic
sulfur content lie primarily in the Mid-Atlantic and East North Central
Regions, with additional deposits in Kansas and Missouri (i.e., West
North Central Region).
Nationwide consumption of sulfuric acid by end use is indicated in
Table XXVII. Projected nationwide growth rates for six major uses are
given in Table XXVIII.
In view of the costs of shipping either sulfuric acid or pyrite-
coal, it appears that only a limited area of the U.S. could provide a
market for acid made from pyrite-coal. The sources of acid demand must
be relatively near the sources of high-sulfur coal rejects so that the
rejects can serve economically as a raw material for acid. This condi-
tion exists to a greater or lesser degree in an eight-state area con-
taining the Northern Appalachian and North Central coal fields. The
quantities of acid consumption by end use are given for each of the
eight states in Table XXIX. The estimated change in annual rate of con-
sumption is also shown in this table. From the data presented, it is
apparent that the use of sulfuric acid for fertilizer manufacture in this
geographic area represents the largest end use, about four times as great
175
-------
TABLE XXVI
ESTIMATED REGIONAL PRODUCTION AND DISPOSITION OF SULFURIC ACID, 1966
(thousands of short tons)
New England
Middle Atlantic
South Atlantic
East North Central
West North Central
East South Central
West South Central
Mountain
Pacific1
Total
Production
Disposition
New
205
3770
9030
3372
1103
1877
4792
1834
1523
,506
Refortified
0
260
0
158
32
25
304
57
135
971
Total
205
4030
9030
3530
1135
1902
5096
1891
1658
28,477
In-Plant
95
1487
6791
1414
781
514
1632
1052
581
14,347
Shipments
110
2543
2239
2116
354
1388
3464
839
1077
14,130
Total
205
4030
9030
3530
1135
1902
5096
1891
1658
28,477
Capacity 1/1/67 34,652
% Operating Rate 82%
Includes one plant in Hawaii
Source: Reference 24 (1968)
-------
TABLE XXVII
SULFURIC ACID DISTRIBUTION BY END USE
(thousands of tons, 100% H-SO,)
1963 1964
Phosphate Fertilizers
Ammonium Sulfate
Titanium Dioxide
Petroleum - Alkylate Refining
Petroleum - Other uses
Iron and Steel Pickling
Hydrofluoric Acid
2
Rayon and Cellophane
Alcohols
Aluminum Sulfate
Synthetic Detergents
Copper & Uranium Leaching & Processing 607
Dyes and Intermediates
3
Explosives
Other Chemicals
Exports
Miscellaneous
Total
^Includes sulfonated petroleum lube oil additives and other petroleum products.
Includes other cellulose film, sheets, or products.
Excludes mixed acid, which is included in other chemicals for 1963, 1964, 1965,
Source: Reference 24 0968).
177
1963
6906
1390
1951
1325
1130
1084
603
839
599
536
481
607
294
146
2697
7
1165
1,760
1964
7753
1759
1975
1375
1205
1190
630
885
631
574
500
576
312
118
2951
14
1302
23,750
1965
9275
1967
1900
1400
1260
1075
710
895
665
580
510
567
330
100
3099
7
1360
25,700
1966
11675
1885
1740
1435
1335
1000
785
836
700
592
530
550
350
198
3389
-
1500
28,500
7, of Total
41%
7
6
5
5
3
3
3
2
2
2
2
1
1
12
5
100%
-------
TABLE XXVI11
GROWTH IN MAJOR SULFURIC ACID END USES, UNITED STATES
(THOUSANDS OF TONS, H2SO4)
Phosphate Fertilizers
Titanium Dioxide
Ammonium Sulfate
Iron & Steel Pickling
Rayon & Cellophane
Petroleum Refining
* Actual use declined in last few years
Source: Reference 24 (1968).
J.33O
4825
1375
1325
750
650
n.a.
JLSOU
5575
1500
1200
900
700
n.a.
J.SOJ
6906
1951
1390
1084
839
2455
UQD
9275
1900
1967
1075
895
2660
1? DO
11,675
1740
1885
992
836
2770
Historical
12%
2-3%*
5%
0*
3%
4%
Projected to 1972
4-5%
0
5%
—
—
4%
-------
Fertilizers
Ammonium Sulfate
Synthetic Detergents
Titanium Dioxide
Aluminum Sulfate
Iron & Steel Pick-
ling
Rayon & Cellophane
Refineries
Hydrofluoric Acid
Other Uses
Total
TABLE XXIX
ESTIMATED SULFURIC ACID END-USE PATTERN IN SELECTED STATES, 1966
(THOUSANDS OF SHORT TONS 100% H2SO4)
760
577
1814 416
308
130
338
797
5140
* Future growth will be in SO., sulfonation.
Source: Reference 24 (1968).
Projected
Pa.
18
199
27
—
18
142
107
103
—
146
Ohio
93
69
75
—
28
80
—
50.
30
152
111.
1532
28
30
—
12
9
—
102
38
63
Ind.
47
88
50
—
—
105
—
103
~
23
W. Va. Ky. Tenn.
25 126
110 15
—
—
30
10
150 — 132
—
40 55
8 25 50
Mo.
284
—
39
410
30
—
—
17
—
17
Area
Total
2125
509
221
410
118
346
389
375
163
484
Average Annual
Growth Rate
8-10%
3
0*
0
4
0
0
2
4
5
-------
as the next largest, and also shows one of the largest projected rates of
increase.
The supply-demand situation for sulfuric acid in the states of pri-
mary interest is summarized in Table XXX.
7.4 Further Analysis of Two Selected Processes
Two processes were selected from the eight described in Section 7.2
for additional technical and economic analyses. These are the refuse-
combustion/sulfur-oxide-removal process and the fluidized bed roasting
process. The following discussion will augment the brief description of
these processes given in Section 7.2.1.
In the discussions that follow, the technical aspects are discussed
separately from the economic aspects, with primary attention given the
latter. These discussions present only the economic highlights of each
process. More detailed descriptions and analyses of the refuse-combus-
tion/sulfur-oxides-removal process can be found in Reference 23 and of
the fluidized bed roasting process in Reference 24.
In conducting the economic studies, both contractors utilized com-
puterized models to investigate the complex relationships among the
several variables considered, although somewhat different approaches are
used for the two processes. In modeling the refuse-combustion/sulfur-
oxides-removal process in which the entire reject stream is burned, the
reject stream is considered a source of energy that can be used to meet
a given segment of a total (hypothetical) demand for electric power. Re-
covery of sulfur values in the form of sulfuric acid is an ancillary step
180
-------
TABLE XXX
SULFURIC ACID SUPPLY-DEMAND SITUATION IN SELECTED STATES, 1966
(thousands of tons, 100% ILSO,)
Capacity to Produce
Pennsylvania
Ohio
Indiana
Illinois
West Virginia
Kentucky
Tennessee
Missouri
Sub-total
Other States
U.S. Total
Estimated
Production
966
689
677
1763
155
230
955
550
5,985
22,492
28,477
Estimated
Consumption
760
577
416
1814
308
130
338
797
5,140
23,330
28,470
Surplus
(Deficit)
206
112
261
(51)
(153)
100
617
(247)
845
(838)
7
New Acid
1/1/67
1040
865
695
1835
156
220
194
595
6,320
28,332
34,652
Source: Adapted from Reference 24 (1968)
181
-------
whereby credits accrue to the overall process through the sale of by-
product acid. Additional non-monetary benefit is realized from the
attendent reduction in the sulfur oxide content of the combustion gases.
In modeling the economics of the fluidized bed roasting of pyrite
concentrate, emphasis was placed on improving the economics of acid pro-
duction. Although this process can also yield electric power, this was
considered a subsidiary product and its production was not included in
all of the equipment configurations analyzed.
7.4.1 Refuse-Combustion/Sulfur-Oxide-Removal (Technical Aspects)
The basic steps of this process are: combustion of the refuse
stream, steam generation, fly ash removed by an electrostatic precipita-
tor, catalytic oxidation of sulfur dioxide to sulfur trioxide, absorp-
tion of sulfur trioxide in water to form acid, concentration of acid,
and demisting of stack gas. A flow diagram is given in Figure 26.
Three systems of refuse combustion were considered for use in this
process: pulverized refuse, cyclone furnace, and fluidized bed com-
bustion. In the economic analysis presented in Section 7.4.2, equip-
ment cost estimates were developed for a pulverized refuse combustor
and a cyclone furnace; the fluidized bed approach was not analyzed for
this process since it is treated in detail as a means of roasting pyrite
concentrate (Sections 7.4.3 and 7.4.4).
The following processes were considered for processing the sulfur
dioxide in the combustion gases:
182
-------
STEAM
TO
STEAM TURBINE
GENERATOR <
FEED WATER
COMBUSTION CLEAN GAS TO
AIR
STACK, 250 F
COAL „
REFUSE
00
u>
i
FLUE GAS
900 F
CLEAN GAS
850° F
GAS
250° F
STEAM
GENERATOR
ASH
I
ELECTROSTATIC
PRECIPITATOR
CATALYTIC
CONVERTER
FLYIASH
GAS
850° F
ACID CONDENSER
AIR PREHEATER
PREHEATED AIR
SULFU
MIST
ELIMINATOR
SULFURIC ACID
IIC ACID
1
TO WASTE DISPOSAL
PRODUCT ACID
(77% H2S04)
SOURCE: REFERENCE 23 (1968)
FIGURE 26
REFUSE-COMBUSTION/SULFUR-OXIDES-REMOVAL FLOW CHART
-------
• the Topsoe process;
• the Reinluft process;
• the Wellman-Lord process; and
• the Monsanto catalytic oxidation (Cat-Ox) process.
The Cat-Ox process was selected because of its advanced state of
development.
7.4.2 Refuse-Combustion/Sulfur-Oxide-Removal (Economic Aspects)
The economic analysis of the process was made in terms of a scen-
ario in which a given demand for electric power was satisfied in two
ways. First, the demand is met conventionally by a single power plant
(termed the "base plant") fueled by run-of-mine (ROM) coal. Second, it
is met by two smaller plants: one (the "alternate plant") is a con-
ventional steam/electric plant fueled by ROM coal; the other (the "re-
fuse plant") is a combination plant fueled by reject material from a
coal preparation plant. The combination plant produces both electric
power and sulfuric acid. The nominal total power demand is 750kw.
This dual scheme is depicted in Figure 27.
In this analysis, the energy value and the sulfur value of the re-
ject were determined separately. This was done because electric utility
companies and non-regulated companies handle their accounting differently
and have different views on profitability of investments. These separate
components are not reported separately in this summary presentation but
are combined to determine total value which is reported as a function of
appropriate parameters. For an indication of the distribution of values
between these two components, see Figure 31 on page 196.
184
-------
00
Ul
j ROM COAL AT 22$/MILLION BTU ._ BASE POWER PLANT P°WER AT 4.94 MILLS/Kwh _
1 * 750 Mw
1 SINGLE PLANT BASIS FOR POWER COST
j
*" CLEAN COAL SALES
ROM COAL^ rnAT PRRPA1}ATTnK COAL REFUSE ^
PLANT FUEL VALUE +
SULFUR VALUE
ROM COAL AT 22$ /MILLION BTU^
^DUAL PLANT SCHEME
SULFUR RECOVERY
PLANT
REFUSE-FIRED
POWER PLANT
A*Mw
ALTERNATE
POUFT? PT ANT
(750-A) Mw
l
SULFURIC ACID SALES^
POWER AT B* MILLS/Kwh
POWER AT
4.94
MILLS/Kwh
POWER AT C^MILLsTKwh
T— - , ^ J
Refuse-Fired Plant Generating Capacity (A)
Cost of Poer From Refuae-Fired Plant (B), and
Cost of Power From Alternate Plant (C) are
Variables to be Evaluated.
SOURCE: ADAPTED FROM REFERENCE .23 (1968)
FIGURE 27
DUAL PLANT SCHEME
-------
Interrelations among the following parameters were considered in
determining reject value:
• Capacity of the refuse-fueled plant (in terms of electric
power output)—shown as A Mw in Figure 27;
• Percent sulfur in reject material;
• Percent ash in refuse;
• Price of sulfuric acid Cf.o.b. acid plant);
• Capital cost per kilowatt output capacity.
Using typical ranges of values for the above parameters, Bechtel
worked backward to determine the price that a utility using the dual-
plant scheme could afford to pay for refuse as fuel. The back-calculation
approach was used since it is the most direct, if not the only, method to
reflect the economic relationships for a dual-fuel plant with multiple
products. By comparing the cost of producing refuse having acceptable
energy and sulfur content with the estimated price that a utility could
afford to pay for such material, an indication of the market acceptability
of refuse as fuel is thereby obtained.
The determination of energy value of the reject material involved
(23)
the following steps:
1. Establishing load requirement for electric utility (base plant);
2. Estimating power cost for base plant;
3. Establishing capacity of refuse-fired power plant (refuse plant);
4. Establishing capacity factor of refuse plant;
5. Estimating power cost for power plant necessary to supplement
refuse plant (alternate plant);
186
-------
6. Estimating capital cost for refuse plant;
7. Estimating annual operating and maintenance costs for refuse
plant;
8. Calculating annual fuel cost for refuse plant;
9. Calculating refuse energy value.
The annual fuel cost for the refuse plant was determined by difference.
This procedure involves the premise that the cost of power from the two
smaller plants (the refuse plant and the alternate plant) must equal the
cost from the base plant. The calculation is as follows:
Base plant total annual cost (including amortization) is equal to
the total annual cost of the alternate plant plus the refuse plant.
where:
Refuse plant total annual cost is equal to the annual fixed
charges plus the annual operating, maintenance, and fuel costs.
All the above values except the annual fuel cost are calculated when plant
sizes and raw coal costs are established. Note that total annual cost
includes amortization of capital investment plus all operation and main-
tenance costs.
A summary of estimated costs for the base plant is given in Table
XXXI and for refuse plants of three capacities in Table XXXII. For each
refuse plant capacity, separate cost estimates were made for a cyclone-
fired steam generator and for a pulverized-fuel-fired steam generator.
The estimates for the two types of boilers were essentially the same ex-
cept those costs related to ash handling, where the differences were
187
-------
TABLE XXXI
750-MW BASE POWER PLANT SUMMARY
Capacity factor (percent)
Annual output (billion kwh)
Total capital cost (million $)
($/kw)
Levelized Annual Cost
Fixed charges (millions $)
Operating & Maintenance (millions $)
Fuel (millions $)
Total (millions $)
(mllls/kwh)
75
4.93
92.2
122.9
13.0
1.5
9.8
24.3
4,94
Source: Reference 23 (1968).
TABLE XXXII
REFUSE POWER PLANT SUMMARY
Capacity factor (percent)
Annual output (billion kwh)
Total capital cost (millions $)
($/kw)
Levelized , annual
fixed charges (millions $)
Annual operating and
maintenance costs (millions $)
(percent of total annual cost)
Capacity (Mw)
200 300 500
85
1.49
37.8
188.8
5.3
0.7
11.7
85
2.24
51.1
170.3
7.2
0.9
10.4
85
3.72
74.3
148.8
10.5
1.4
8.9
Source: Reference 23 (1968).
188
-------
minor, ranging between 1 percent and 3 percent. An average figure for
estimated capital costs for each size unit was therefore used for all
economic calculations.
Sulfur value of the refuse was determined by a somewhat different
procedure which involved back-calculating the price an acid manufacturer
could afford to pay for various grades of reject material in order to
achieve a given return on investment for varying levels of manufacturing
expense, production capacity, and product acid price. The steps in this
(23)
procedure are outlined below:
1. Estimate capital cost of the sulfur recovery plant for a
specific refuse plant capacity;
2. Establish method of financing;
3. Establish discounted rate of return on equity investment and
calculate discounted equity investment;
4. Establish refuse type and sulfuric acid price (f.o.b. acid
plant;
5. Calculate annual revenue;
6. Estimate annual operating cost less price paid for refuse;
7. Establish depreciation method and calculate annual income tax,
o.ther taxes, investment tax credit, interest, and debt service
payments;
8. Calculate refuse sulfur value.
Investment costs attributable to sulfur recovery are summarized
in Table XXXIII. These cost estimates were based upon a scaling down of
189
-------
TABLE XXXIII
SULFUR RECOVERY PLANT INVESTMENT
Fixed capital cost (millions $)
Working capital (millions $)
Interest during
construction^ (millions $)
Total investment (millions $)
($/kw)
2
Loan (millions $)
Equity investment (millions $)
Discounted rate
of return (percent)
Discounted equity
investment (millions $)
Refuse power plant
net capacity (Mw)
200 300 500
8.3
0.4
0.5
9.2
45.9
2.6
6.5
12.5
5.1
11.4
0.6
0.7
12.7
42.3
3.6
9.0
12.5
7.1
17.2
0.9
1.0
19.1
38.2
5.4
13.6
12.5
10.6
^•6 percent interest for three years-
period of construction
^ 30 percent of fixed and working capital
Source: Reference 23 (1968).
190
-------
more detailed cost estimates for applying a catalytic oxidation type of
process to a 1000 megawatt conventional coal-fired plant.
The operations of the refuse power plant and the sulfur recovery
plant are, of course, not independent. Certain equipment is shared be-
tween the two operations; other equipment (such as blowers and precipi-
tators) needed for either operation must be larger to meet the needs
of both. Similarly, operational costs are mutually interdependent. For
example, high sulfur concentrations that are advantageous for acid pro-
duction result in increased costs for operating the refuse-fired power
plant (assuming a constant level of power output). The effects of such
interdependences were taken into account in establishing the values of
energy and sulfur in the fuel.
Total refuse value was determined by combining the values attribut-
able to energy content and sulfur content. This combined value is af-
fected by a variety of economic and operating conditions, and is re-
ported as a function of:
• , capacity of refuse power plant;
• sulfur content of refuse;
• ash content;
• sulfuric acid sale price (7-7 percent 112804);
• plant investment per unit of output;
• rate of return on investment.
When total value of the refuse is determined on a unit weight basis, its
effect on the value of cleaned coal can be determined from the percentage
yield of the coal preparation operation.
191
-------
Because of the number of variables affecting refuse value, results
are presented in some 17 separate graphs. These will not be reproduced
in total, but the more important ones are presented here. All dollar
figures shown reflect 1967-1968 costs, expenses, taxes, and dollar values.
It should be noted that the total reject (refuse) values presented here
represent the value of refuse at the refuse-fired power/acid plant, and
thus include any costs for transporting the refuse from the coal pre-
paration plant to the refuse-fired power plant.
Figure 28 shows refuse value as a function of plant capacity for
each of three levels of sulfur content and three levels of ash percentage.
All of these values assume an acid selling price of $12.50 per ton f.o.b.
plant. Refuse values are seen to range from a negative value of $1.00
per ton (meaning that a loss would be incurred in the power generating
and acid producing operations) under conditions of low sulfur content and
a very small (200 mw) refuse plant to a positive $4.50 per ton for a
high sulfur refuse being burned in a large (500 mw) plant. The graph
also indicates that some reduction in coal preparation costs can be
achieved for any refuse (pyritic) sulfur content over 8.5 percent, irre-
spective of ash content in the refuse.
For a 300 mw refuse power plant burning reject material with 34
percent ash, Figures 29, 30, 31, and 32 respectively illustrate the
effects of the following parameters on both the reject (refuse) value
and the concentration of sulfur in the refuse:
• sulfuric acid price;
192
-------
w
to
§
H
•OT-
pa
to
1
H
200 250 300 350 400 450 500
REFUSE POWER PLANT CAPACITY (Mw)
PERCENTAGE OF
ASH CONCENTRATION
NOTES:
1. BASE POWER PLANT CAPACITY = 750 Mw
2. BASE POWER PLANT CAPACITY FACTOR = 85%
3. SULFURIC ACID PRICE = $12.50/TON
4. REFUSE MOISTURE = 15.0%
SOURCE: REFERENCE 23 (1968)
FIGURE 28
TOTAL REFUSE VALUE-REFUSE POWER PLANT
CAPACITY-REFUSE COMPOSITION
193
-------
5.0
O
•
Pn
§
EH
w
1
H
8 9 10 11 12 13 14
-3.0
-4.0
SOURCE: REFERENCE 23 (1968)
FIGURE 29
TOTAL REFUSE VALUE-REFUSE SULFUR CONCENTRATION-
SULFURIC ACID PRICE {REFUSE ASH CONCENTRATION, 34.0%)
194
-------
w
cr>
§
H
W
I
H
53 ($/KW)
70 ($/KW)
187 ($/KW)
7 8 9 10 11 12 13 14
-2
-3.0
-A.O
SOURCE: REFERENCE 23 (1968)
FIGURE 30
TOTAL REFUSE VALUE-REFUSE SULFUR CONCENTRATION-REFUSE
POWER PLANT CAPITAL COSTS (REFUSE ASH CONCENTRATION,
34 PERCENT; SULFURIC ACID PRICE, $12.50/TON)
195
-------
5.0
w
CO
§
H
•CO
W
1
$38/KW
1 2 3 4 5 6 7 8 9 10 11. 12 13 14
SULFUR %, WET
SOURCE: REFERENCE 23 (1968)
FIGURE 31
w VALUE-REFUSE SULFUR CONCENTRATION-SULFUR
RECOVERY PLANT INVESTMENT (REFUSE ASH CONCENTRATION
34 PERCENT; SULFURIC ACID PRICE, $12.50 TON)
196
-------
5.0
w
to
g
H
-co-
W
1
I
H
10% ROI
01 2 34 5 6 7 8 9 10 11 12 13 14
SULFUR PERCENT, WET
.SOURCE: REFERENCE 23 (1968)
FIGURE 32
TOTAL REFUSE VALUE-REFUSE SULFUR CONCENTRATION-RATE
OF RETURN ON INVESTMENT (REFUSE ASH CONCENTRATION,
34 PERCENT; SULFURIC ACID PRICE, $12.50/TON)
197
-------
• refuse power plant capital cost;
• sulfur recovery plant investment;
• rate of return on investment.
The distribution of total refuse value between the energy component
and sulfur component for four levels of sulfur content is shown in
Figure 33 for a 300 mw refuse plant fired with a reject material con-
taining 34 percent ash.
Figure 34 graphically illustrates the relative importance of the
variables that affect total refuse value. The origin (0, 0 coordinates)
of this figure represents the specified standard conditions given in Table
XXXIV, the abscissa represents the percent change in a single independent
variable; and the ordinate is the resulting incremental change in total
refuse value. Although this chart was based on a 300 mw refuse-fired
power plant, the conclusions that may be drawn from this graph are gen-
erally true for other sizes.
The chart shows that refuse value is most sensitive to change in
acid price and capital cost of the refuse-fired power plant. For ex-
ample, a 10% increase in acid price nearly offsets a 10% increase in
refuse plant investment.
7.4.3 Fluidized Bed Roasting of Pyrite, followed by Catalytic
Oxidation of Sulfur Dioxide - (Technical Aspects)
This process requires a feed of considerably higher pyrite content
than the reject stream ordinarily produced by coal preparation. Hence
an additional operation is required to concentrate the pyrite in the
198
-------
+2.50 —
+2.00 - ^
^ SULFUR
^ ENERGY
+1.50-
£ SULFUR SULFU
S CONCENT. CONC
o -n.oo- 4-20% 6-38%
5 VALUE VALUE
£ -$0.364 4$0.51
3 +0.50 - pf
* 1*3
|/O/
-0.50 — 1$^
f^o -\
-1.00— ^^
j
'4w
fay,
t*£
ioi
'&££&
' -' - ^ ^ '
SULFUR
CONCENT.
10.26%
VALUE
+$2.30
SULFUR \
CONCENT.
8.50%
VALUE
+$1.403 |
^
ENT.
O
^v
\XNV-
>rs-.
xS>'
x05;
>NX-;
§^
'///
t$t
tot,
////,
P
I
1
w
lw
R
\//^-
m
¥/ *'*
Y*'-0'/,
I'////,
>* ' » «*
-0.081
SOURCE: REFERENCE 2:
FIGURE 33
TOTAL REFUSE VALUE COMPONENTS (300 M\N REFUSE POWER PLANT;
REFUSE ASH CONCENTRATION, 34 PERCENT)
199
-------
+1.50
-10%
CHANGE IN INDEPENDENT
VARIABLE (PERCENT)
PUNT O&M
COST
SOURCE: REFERENCE 23 (1968)
FIGURE 34
TOTAL REFUSE VALUE SENSITIVITY, 300-MW REFUSE
POWER PLANT
200
-------
TABLE XXXIV
STANDARD CONDITIONS
300-MW REFUSE POWER PLANTS
Base Power Plant
Net capacity
Capacity factor
Annual output
First year fuel cost
Fuel cost escalation
750 Mw
75 percent
4.93 billion/kwh
19-8 cents/million Btu
1.5 percent/yr.
II. Alternate Power Plant
Net capacity
Capacity factor
Annual output
First year fuel cost
Fuel cost escalation
450 Mw
68 percent
2.70 billion/kwh
19.8 cents/million Btu
1.5 percent/yr.
III. Cost Refuse Power Plant
Net capacity
Capacity factor
Annual output
Total capital cost
300 Mw
85 percent
2.24 billion kwh
$51.1 million
170.3 $/kw
IV. Sulfur Recovery Plant
Total investment
Discounted rate of return
Debt financing
$12.7 million
42.3 $/kw
12.5 percent
30 percent
Source: Adapted from Reference 23 (1968).
201
-------
reject component to be roasted. The two cleaning and concentrating op-r
erations are shown schematically in Figure 35. The quantities shown in
this figure indicate the approximate processing rates needed to produce
13,500 tons per day of clean coal and 1000 tons per day of 98 percent
sulfuric acid.
The following comments on the fluidized bed roasting process sup-
plement and expand upon the description of this process presented in
Section 7.2. A flow diagram of the basic process yielding sulfuric acid
is shown in Figure 36. The major processing steps are:
• roasting the pyrite in a fluidized bed (where the crushed
pyrite is "fluidized" by air blown through multiple openings
in the floor of the bed and forced upward through the layer
of crushed pyrite), to yield heat, combustion gases, and
calcine;
• generation of steam, then electric power, from heat produced
in the roasting operation;
• recovery of sulfur oxides from the combustion gases;
• catalytic oxidation of sulfur dioxide to form sulfur trioxide;
• absorption of sulfur trioxide in water to form sulfuric acid;
• concentration of the sulfuric acid to commercial densities.
In some locations, an additional major step is added; the recovery of
iron oxides for use in steelmaking. Preliminary analyses indicate
that recovery of iron values would not be economic in most geographic
areas of the U.S. where sulfuric acid is likely to be manufactured from
202
-------
RAW COAL
15,000 TPD (3.5ZS)
I "
COAL
PREPARATION
PLANT I
1 ___
PYRITE REFUSE
1,500 TPD (26.0%S)
CLEAN COAL TO
UTILITIES
(3/8")
13,500 TPD (1.0%S)
REFUSE
CONCENTRATION
PLANT
'"I
REFUSE TO WASTE
725 TPD (5.4%S)
I J
PYRITE-RICH REFUSE
775 TPD (85% PYRITE)
WILL MAKE 1000 TPD 98%
TPD = TONS PER DAY
SOURCE: REFERENCE 24 (1968)
FIGURE 35
PYRITE-REMOVAL PROCESS
203
-------
N>
O
FIGURE 36
FLOW DIAGRAM OF FLUOSOLIDS PYRITE-ROASTING/
SULFURIC-ACID PLANT
PLANT TYPE I-A
SOURCE: REFERENCE 24 (1968)
-------
pyrites, hence credits for iron are not claimed in the economic analyses
that follow and the recovery of iron is not included in the technical
description of the process.
There are several options as to the type of ancillary equipment
that might be included with the basic fluidized bed plant for pyrite
roasting and acid manufacture. The steam/electric generator is ad-
vantageous in some cases, as when the acid plant is integrated with
other types of chemical works or located in an area with high electric
power costs, but this is not generally the case. Also, cooling towers
can be used to reject waste heat to the atmosphere rather than to a
nearby river, but this additional item of equipment would not be re-
quired in some locations (at least it was not in 1968, when this study
was completed). Consequently, several alternative equipment configura-
tions can be assumed for the basic plant. The following alternatives
were evaluated:
• plant with steam generator and cooling tower (designated
in the following tables as Type I-A plant);
• plant with steam generator but no cooling tower (Type I-B);
• plant with cooling tower but no steam generator (Type II-A);
• plant with neither steam generator nor cooling tower (Type II-B).
Any of the above types of plants could be utilized as a stand-alone
installation producing sulfuric acid and, in some cases, electric power,
as the principal product(s). Alternatively, they could be integrated
with other chemical processes to make quite different products, one of
205
-------
the more commercially attractive being phosphate fertilizer, This rep-
resents another type of option in plant configuration. When integrated
in this manner electric power produced by a steam generator heated
by the roaster can generally be utilized advantageously by various steps
in the overall operation.
One possible additional method is oxygen enrichment. This approach
might be used for roasting low-grade (high coal content) pyrite to pro-
duce high strength S(>2 gas for the manufacture of acid. By virtue of
less nitrogen dilution, oxygen enrichment would make it possible to pro-
duce a gas of higher S02 content.
To evaluate the merits of oxygen enrichment a process and economic
study was performed as follows. Consider a pyrite roasting-contact sul-
furic acid plant designed to process pyrite plant feed of a specified
composition (for example, composition No. 2* which contains 90 percent
pyrite, 5 percent coal, 5 percent inerts) . By adding the appropriate
amount of oxygen to the air, lower-grade pyrite-feeds can be processed
in this plant with no increase in gas volume or no decrease in sulfur
dioxide concentration in the gas. Maintaining this level of sulfur
dioxide concentration would permit utilization of conventional equip-
ment in the subsequent conversion of sulfur dioxide to sulfuric acid.
This is one of the real advantages of the use of pure oxygen.
If the total processing costs for pyrite plant feed composition No.
2 are used as a basic standard and to these costs are added the oxygen
*See Tables XXXV and XXXVI for the ranges of feed compositions examined
in the A.D. Little study.
206
-------
costs, the resultant total should represent a reasonable approximation
of the total processing costs for an oxygen enrichment plant. The re-
sulting cost total indicates that the use of oxygen to enrich the air is
not an economical approach to reducing the processing costs. A possible
reduction in processing cost is indicated only for large tonnage, 1500-
2500 tons of acid per day, and for pyrite plant-feed composition numbers*
10 and 12. However, for these low-grade pyrite feeds, the total pro-
cessing costs (with or without oxygen enrichment) make the whole project
economically questionable. Furthermore, a technical problem with the
roaster heat balance and removal of excess heat for these lower-grade
feeds has not been resolved.
In the roasting or oxidation of any particular pyrite-coal material
a certain amount of heat is generated over and above that required to
maintain the roasting reaction at the desired temperature level. With
oxygen-enriched air, the volume of product gas resulting from oxidation
of the feed is less than with air only. As a result, less heat is re-
moved as sensible heat in the product gas and, therefore, more of the
excess heat must be removed by steam-generating bed coils or by water
injection. As the grade of pyrite feed decreases (less pyrite, more
coal) this generation of excess heat becomes more of a problem. At some
point along the line of decreasing feed grade it becomes no longer poss-
ible to place a steam-generating coil with sufficient heat-absorbing ca-
pacity in the fluid bed. Instead, it becomes necessary to increase
*See Tables XXXV and XXXVI for composition of the various feeds
207
-------
materially the number of lines of roasters required for a given produc-
tion capacity. This increases both capital costs and operating costs.
For a plant that uses water or weak acid for removal of excess heat and
for control of roasting temperature, the amount of additional water or
weak acid required for a plant employing oxygen enrichment substantially
increases the roaster exit-gas volume. This, in turn, requires larger
and more expensive gas cooling and cleaning equipment. For these tech-
nical reasons the possible use of oxygen, even for large tonnages, is not
a solution for reducing processing costs.
The use of oxygen instead of secondary air in the acid plant, to
supply the oxygen required for SC>2 oxidation, might be considered as
an alternative to using oxygen-enriched air for the pyrite roaster. This
approach would have the following effect upon the process: (1) the total
oxygen requirement would be less but this oxygen, because of the lower
demand, would be more expensive per pound; (2) the pyrite roasting plant
would not benefit by reduced equipment size, and (3) the acid plant
would benefit by the use of oxygen in place of secondary air from the
standpoint of the acid-plant water balance and the heat balance. With-
out going into detailed process calculations or plant cost data, it is
believed quite likely that the use of oxygen in place of secondary air
would show less economic benefit than if oxygen were used to enrich the
air to the pyrite roasters.
A more practical approach might be to consider the possibility of
adding both elemental sulfur and oxygen to the roaster as a means of
208
-------
decreasing the processing costs. Additional technical and economic
analysis would be required to determine the possible merits of this
approach.
7.4.4 riuidized Bed Roasting of Pyrite Concentrate (Economic
Aspects)
The economic analysis of this recovery system considered that each
of the following parameters could take on a range of values:
• Composition of the feed (in terms of percent pyrite, percent
coal, and percent gangue);
• Plant capacity (tons of sulfuric acid per day);
• Price of elemental sulfur;
• Market for sulfuric acid;
• Proximity of pyrite source to acid market;
• Rate of return on investment.
The analysis determined values of the following variables for various com-
binations of the above parameters (not all parameters were used in each
economic determination):
• Battery limit costs and total capital investment for various
acid plant types;
• Total processing costs for various plant types;
• Prices that could be paid for pyrites to keep manufacturing
costs of sulfuric acid made from pyrites competitive with acid
made from elemental sulfur;
209
-------
• Prices that could be paid for pyrites (f.o.b. coal preparation
plant) to compete with elemental sulfur for manufacture of sul-
fur Ic acid as part of an integrated operation to produce phos-
phatic fertilizer.
Results from the above cost determinations are presented in the follow-
ing discussion.
Capital costs for the various types and sizes of plants were esti-
mated on the basis of a complete plant being constructed from the ground
up. Battery limit costs include purchase and erection of all processing
equipment including:^
(1) Calcine disposal and neutralized waste acid disposal equipment;*
(2) Liming station for neutralization of waste acid;
(3) Boiler-feed water-treatment equipment (for Plant Type I);
(4) Motor-control center, including switch gear and starters;
(5) Open (on the ground) storage for one month's supply of pyrite
feed;
(6) Storage for seven days' production of acid in two or more tanks;
(7) Operating-control room and such other housing as required
to protect such non-weatherproof equipment as instruments,
motor-control center, etc. that are a part of the process
facilities; and
(8) Water-cooling tower with air-circulation fans and water
pumps (for Plant Type I-A and II-A).
*For the purposes of this report, the investment and operating costs
of calcium disposal facilities were assumed to be the same as would
be required if the calcines were sold as a sinter strandfeed material.
210
-------
Total plant costs were obtained by increasing the battery limit
costs by a given percentage to cover offsite facilities such as land,
power substation, water supply and sewers, roads, fencing, etc. This
percentage increase was 18 percent for plants with steam/electric gen-
erating equipment and 20 percent for plants without this equipment.
Total capital investment was obtained by increasing the total plant
costs by 11 percent to cover construction and startup (interest on con-
struction money, taxes, insurance during construction, starting personnel
training, etc.).
For determining plant costs, the following factors were treated as
parameters:
• plant capacity (.tons per day of product acid);
• plant type (with or without steam generation equipment or
cooling tower);
• pyrite feed composition.
Estimated costs of plants reflecting various values of these parameters
are given in Table XXXV. The range of values considered for each para-
meter is shown in the table. Total capital investments for plants meet-
ing this range of parameter values vary from $3.7 million for a Type II-B
plant of 258 tons/day capacity using No. 2 pyrite feed to $35.5 million
for a Type I-A plant of 2500 tons/day capacity using No. 12 pyrite feed.
Total operating costs were determined for plants covering the same
range of parameter values as used for capital cost determination.
211
-------
TABLE XXXV
BATTERY LIMIT COSTS AND TOTAL CAPITAL INVESTMENT VS. CAPACITY AND FEED CONSUMPTION
(MILLIONS OF DOLLARS)
o
Steam
Plant Type IA Cooling tower
TPD Capacity TPY (982) Acid
250 82500
500 165000
1000 330000
15CO 495000
2500 825000
Steam,
Plant TffiiL-IB So cooiins toBe
TPD Capacitv TPV (98%) Acid
250 82500
500 ' 165000
1000 330000
isno 495000
2510 825000
Cooline tower
Plant Type IIA 1]o t^n
TYP Capacity IPY (98%) Acid
"253 85000
517 170600
1033 340900
1550 511500
2583 852000
No cooling tow*
Plant^ype IIB Ko ^^ f .
TPD Capacity TPV (98SQ Acid
"^58 8500
517 170600
1033 340900
1550 511500
2583 852000
2
1.0
Bat Lim Tot Cao
Cost Invest.
3.16
4.19
6.97
9.21
14. 39
4.14
5.48
9.12
12.10
18.86
1
3.11
4.11
6.85
9.06
14.18
4.07
5.39
8.96
11.89
18.55
2.87
3.76
6.05
7.89
12.12
3.82
5.00
8.05
10.50
16.15
r
2.76
3.60
5.81
7.57
11. 71
3.67
4.80
7.73
10.08
15.65
4
0.897
••'lat L' T t C-
Cost Invest.
3.52
4.67
7.75
-0.26
.6.04
4.60
6.10
10.19
13.50
21.00
3.47
4.59
7.65
.0.10
.5.96
4.54
6.00
10.00
13.24
20.70
3.20
4.18
6.75
8.79
.3.50
4.27
5.58
8.98
11.70
17.98
3.07
4.01
6.48
8.44
.3.03
4.08
5.34
8.63-
11.20
17.37
6
0.833
a . ^ o . ap.
3.80
5.03
8.35
11.04
17.30
4.98
6.59
10.96
14.54
22.65
3.74
4.93
8.22
10.86
17.05
4.88
6.46
10.76
14.27
22.25
3.44
4.50
7.26
9.48
14.55
4.58
6.00
9.68
12.61
19.37
3.30
4. 32
6.95
9.09
14.05
4.39
5.75
9.25
12.10
18.73
oosition numbers
8
0.783
a . m. ^o . ^ap.
4.04
5.35
9.92
11.78
18. 37
5.29
7.00
11.66
15.42
24.10
4.06
5.26
8.75
11.56
14.21
5.20
6.87
11.46
15.18
23.70
3.66
4.78
7.73
10.10
15.49
4.88
6.38
10.30
13.45
20.60
3.52
4.59
7.42
9.66
14.95
4.68
6.10
9.87
12.88
19.90
10
0.673
r 't i
Approx.
4.69
6.21
10.30
13.67
21.40
6.14
8.15
13.53
17.95
28.00
4.61
6.11
10.16
13.46
21.00
6.05
8.00
13.31
17.65
27.55
4.26
5.56
8.98
11.70
18.00
5.67
7.51
11.94
15.60
24.00
4.09
5.35
8.60
11.22
17.35
5.44
7.12
11.45
14.99
23.12
12
0.530
B t LI
Order of Mas.
5.96
7.91
13.17
17.40
27.20
7.83
10.31
17.20
22.80
35.50
5.80
7.78
12.95
17.11
26.80
7.60
10.15
16.91
22.40
35.00
5.44
7.10
11.43
14.88
22.86
7.25
9.45
15.24
19.80
30.40
5.22
6.80
10.98
14.31
22.10
6.93
9.04
14.60
19.10
29.40
I-A Cooling tower and steam generation equipment.
I-B Steam generation equipment but no tower.
II-A Cooling tower, no steam generation equipment.
II-B No cooling tower, no steam generation equipment.
SOURCE: REFERENCE 24 (1968)
Plant Peed Composition
No.
2
. 4
6
8
10
12
%Pyrite
90
80
85
70
70
65
%Coal
5
7
10
10
15
23
5
13
5
20
15
12
-------
Operating costs include direct costs (power, fuel, water, chemicals,
maintenance supplies, operating and maintenance labor, etc., but not
pyrite feedstock) and indirect costs (managerial and administrative
expense, office services and supplies, non-plant maintenance, sales
expense, taxes, insurance, depreciation, etc.)- Total operating cost
are presented in Table XXXVI. The following direct and indirect costs
(and credits) were explicitly excluded:
• Cost of purchasing or processing pyrite feedstock;
• Cost of transporting pyrite to acid plant;
• Cost of shipping product acid;
• Credit for by-product steam, electric power, calcines, or iron
oxide (credits for these by-products were estimated but not
reflected in this table because of uncertain markets for these
items at the probable locations of pyrite-coal acid plants);
• Indirect credit for increased value of beneficiated coal or
decreased disposal cost of cleaning plant reject material.
It should be noted that operating cost estimates for plants using No. 10
and No. 12 feed (with low sulfur content and low sulfur-to-carbon ratios)
are of lower accuracy than the other estimates in the table. Considering
only the range of feedstocks from No. 2 to No. 8 for which firm esti-
mates are available, the plant operating costs vary from $5.51 to $20.81
per ton of product acid. Some of these operating costs for smaller plants
are expressed as costs per ton of product, and exceed the estimated sell-
ing price of acid in the area under study in the 1967-1968 time frame.
213
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TABLE XXXVI
TOTAL PROCESSING COSTS (DIRECT & INDIRECT COSTS) (DOLLAR* PER TON OF 98% PRODUCT ACID)
VS. PYRITE PLANT FEED COMPOSITION AND PLANT CAPACITY
Pyrite riant Feed Composition and Plant Capacity
%Pyrite
%Coal
•^Inerts
S/C Ratio
S/H2 Ratio
Plant Type
O
Plant Type I
250
500
1000
1500
2500
Plant Type
258
517
1033
1550
2583
II
Plant Capacity - IPD (98%) Acid
Plant Type I
250
500
1000
1500
2500
Plant Type II
258
517
1033
1550
2583
Source: Reference 24 (1968).
2
90
5
5
13.8
182
IA
18.11
10.74
7.75
6.60
6.20
IB
18.64
11.33
8.34
7,20
6.80
IIA
15.63
9.47
6.92
5.92
5.51
IIB
16.62
10.44
7.91
6.93
6.56
4
80
7
13
8.7
116
IA
18.92
11.34
8.27
7.07
6.88
IB
19.54
11.97
8.91
7.72
7.54
IIA
16.57
10.08
7.43
6.38
6.20
IIB
17.54
11.14
8.55
7.51
7.36
6
85
10
5
6.5
86
IA
19.59
11.76
8.63
7.63
7.20
IB
20.21
12.47
9.34
8.34
7.92
IIA
17.17
10.52
7.82
7.00
6.53
IIB
18.23
11.67
9.00
8.21
7.78
8
70
10
20
5.36
71
IA
20.11
12.15
9.31
7.90
7.72
IB
20.81
12.88
10.07
8.68
8.49
IIA
17.73
10.90
8.46
7.32
7.03
IIB
18.84
12.11
9.70
8.58
8.34
10
70
15
15
3.58
47,5
IA
Approx
21.61
13.66
10.22
8.97
8.74
IB
Ap-proa
22.42
14.64
11. 1O
9.87
9.64
IIA
19.23
12.62
9.41
8.35
8.02
IIB
20.52
13.96
10.86
9.84
9.52
12
65
23
12
2.2
29
IA
Order c
24.53
15.74
12.29
11.53
11.14
IB
Order
25.40
16.86
13.42
12.65
12.29
IIA
f Mae.
22.21
14.65
11.62
10.76
10.32
IIB
of Mag.
23,80
16.45
13.49
12.70
12.23
Plant Type I-A
I-B
II-A
II-B
Cooling tower and steam generation equipment.'
Steam generation equipment but no tower,.
Cooling tower no steam generation equipment.
No cooling tower, no steam generation equipment.
-------
The determination of the price that a manufacturer could afford to
pay for pyrite-coal reject material was approached in two ways. The
first involves a comparison total manufacturing cost for making 98%
acid from elemental sulfur versus the cost for making it from pyrite,
assuming both raw materials are delivered at the plant site. To do this,
a functional relation was established expressing acid manufacturing costs
as a function of price of elemental sulfur f.o.b. the acid plant, assum-
ing plants of various capacities and 15 percent return on investment.
Acid manufacturing costs were determined for various prices of sulfur.
A second functional relation was developed expressing acid manufacturing
costs for the same type and size of plant and return on investment as a
function of delivered price of pyrite feedstock of various grades. The
prices that could be paid for pyrite to maintain acid manufacturing costs
equal to the costs corresponding to various prices of sulfur was thereby
determined. Results are presented in Table XXXVII.
The second approach to determining pyrite prices considered the case
where pyrite would be used to manufacture acid as part of an integrated
operation to produce high analysis fertilizer (diammonium phosphate). A
brief analysis of the supply and demand for this type of fertilizer
revealed a high demand in the upper midwestern U.S. Production within the
region meets only about half of the demand, the remainder being supplied
primarily by production in the southeastern and Gulf states.
Studies of the logistics of transporting pyrite rejects from coal
producing areas to an integrated fertilizer plant and transporting ferti-
lizer from the plant to upper midwestern market areas indicated that the
215
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TABLE XXXVII
THE PRICE THAT CAN BE PAID FOR PYRITES TO YIELD THE SAME SULFURIC ACID
MANUFACTURING COST AS WHEN USING BRIMSTONE AT VARIOUS PRICES
Acid Plant Capacity
(Short Tons Per Day)
Pyrites Feed Composition
Delivered Pyrites Price ($ Per Short Ton) When the
Delivered Price of Brimston per Long Ton is:
$35 $40 $45
500
1000
1500
2500
500
„ 1000
°" 1500
2500
500
1000
1500
2500
4
4
4
4
6
6
6
6
8
8
8
8
1.49
4.00
5.24
5.50
0.46
3.37
4.48
5.10
-0.46
1.71
3.12
3.36
3.52
6.03
7.26
7.52
2.48
5.54
6.65
7.26
1.57
3.48
4.89
5.14
5.54
8.05
9.29
9.55
4.51
7.70
8.81
9.44
3.49
5.26
6.67
6.91
Feed Composition
Source:
Reference 24 (1968).
Number
4
6
8
—y ro w
So A &
Pyrite Coal Gangue
80 7 13
85 10 5
70 10 20
-------
preferred location of such a plant would be the Cairo, Illinois - Paducah,
Kentucky area. Cost studies to determine pyrite prices were based on a
plant in this location.
The plant using pyrite as a source of sulfur was assumed to compete
with another diammonium phosphate fertilizer plant which could be in
either of two locations. In one case, the competing plant would be lo-
cated in Cairo, and would use elemental sulfur shipped in from the Gulf
coast. In the other case the competing plant would be in Baton Rouge,
Louisiana, a location considered typical of new phosphate plants under
construction at the time of this study. It would use Gulf coast sulfur
and its product fertilizer would be shipped to Cairo. Functional rela-
tions for these two cases (Case A and Case B respectively) are shown in
Figure 37, which indicates that the more severe competition would be
imposed by the Baton Rouge-based plant. The data in the figure are based
on a 10 percent return on fixed investment. It is realistic to assume
that fertilizer production in the Gulf coast area will, in fact, provide
the competition indicated in this example. From the Case A (Baton Rouge)
curve, one sees that when sulfur sells for $38 per ton f.o.b. mine, the
fertilizer manufacturer could afford to pay $1 per ton for 85 percent
pyrite delivered to his plant and remain competitive. If the sulfur price
rose to $48/ton, he could pay about $3.50/ton for pyrite, but if it fell
below $33 the price he could pay for pyrite becomes negative, and the
Cairo manufacturer could not successfully compete, with regard to the
acid-making step in his total operation.
217
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oo
CASE A - PYRITE-BASED PHOSPHATE PLANT AT CAIIO MUST COMPETE WITH
BRIMSTONE-BASED PHOSPHATE PLANT AT BATON ROUG E
CASE B - PYRITE-BASED PHOSPHATE PLANT AT CAI10 MUST COMPETE WITH
BRIMSTONE-BASED PHOSPHATE PLANT AT CAIIO
10
,-1
ACID COSTS INCLUDE 10%
PRE-TAX RETURN ON PLANT
INVESTMENT
MOST LIKELY DOMESTIC PRICE RANGE FOR SULFUR
BETWEEN 1963 - 1975 (f.o.b. MINE)
34 36 38 40 42
PRICE OF BRIMSTONE, DOLLARS (ELEMENTAL
SULFUR) PER LONG TON, f.o.b. MINE IN
SOUTHERN LOUISIANA
FIGURE 37
ESTIMATED VALUE OF PYRITE FOR SUPPLYING SULFURIC ACID TO PHOSPHATE
FERTILIZER PLANT AT CAIRO, ILLINOIS AS A FUNCTION OF-
1. Prevailing Price of Brimstone (Elemental Sulfur)
2. Location of Brimstone—Based Phosphate Plant—Baton Rouge, La., or Cairo, III.
SOURCE: REFERENCE 24 (1968)
-------
A different set of functional relations similar to those of Figure
37 would apply if different rates of return on investment were applied to
the plant using pyrite feed. Table XXXVIII shows the effects of this
parameter on allowable price for pyrite, when the return on investment
for the competing plants utilizing brimstone is held at 10 percent.
It should be emphasized that the pyrite prices cited above and in
Table XXXVIII are as delivered to the acid production plant. When the
cost of transportation from the coal preparation plant to the acid (or
fertilizer) plant is considered, the above prices must be adjusted by
deducting transportation costs. If it is assumed that the cost of trans-
portation of pyrite reject from a preparation plant in western Kentucky or
southern Illinois is 50 cents per ton, then the acid manufacturer could
afford to pay the prices tabulated in Table XXXVIII, less 50 cents, for
pyrite at the preparation plant. If the pyrite source Is the northern
Appalachian coal producing region, then the transportation costs are
grossly estimated as 50 cents per ton from preparation plant to dockside
in Pittsburgh, Pennsylvania, plus $2.00 per ton by barge from Pittsburgh
to Cairo, Illinois. Thus, the prices in Table XXXVIII must be reduced
by $2.50 per ton to arrive at the estimated price allowable for pyrite
reject f.o.b. at a preparation plant in the northern Appalachian region.
7.5 Findings
The following conclusions jnay be drawn from the studies performed
by Bechtel Corporation and Arthur D. Little, Inc., on process costs and
economics of pyrite coal utilization:
219
-------
TABLE XXXVIII
ALLOWABLE PRICES FOR 85 PERCENT PYRITE DELIVERED TO CAIRO PLANT
UNDER VARIOUS RETURN-ON-INVESTMENT REQUIREMENTS*
($ Per Ton)
INVESTMENT CONDITION
COMPETING WITH PLANTS USING
ELEMENTAL SULFUR AT
Baton Rouge, La. Cairo, 111.
Straight Manufacturing Costs with No Cost
For Capital Included
2.42
5.65
10% Return on Fixed Investment (ROI) for
both Pyrite-Fed Plants and Sulfur-Fed Plants
1.00
4.23
15% ROI for Pyrite-Fed Plants and 10% ROI
for Sulfur-Fed Plants
(0.14)
3.09
20% ROI for Pyrite-Fed Plant and 10% ROI
for Sulfur-Fed Plant
(01.28)
1.95
*Assume: Price of Elemental Sulfur is $38 per ton f.o.b. Mine
Source: Reference 24 (1968).
-------
• The reject material from large coal preparation plants that proc-
ess pyrite-bearing coal contains sufficient quantities of
sulfur, sulfur compounds, and coal (in addition to ash) to per-
mit recovery of energy of sulfur values on a commercial scale.
• Adequate technology exists, in the form of several commercially-
used and proven processes, for recovery of sulfur values of py-
rite materials as elemental sulfur or sulfuric acid and energy
values as steam or electric power. These processes have been
applied to mined pyrites but have not yet been applied to ut-
ilizing the pyrite-bearing refuse from coal preparation plants
as feedstock.
• Preliminary studies indicate that several processes are tech-
nically capable of accepting such refuse as feedstock, although
certain of the processes require preliminary concentration of the
refuse to increase its pyrite content.
• All processes considered require some degree of modification to
accommodate the relatively low-pyrite, high-ash feedstock. One
reason is the low concentration of sulfur dioxide in the com-
bustion gases generated by burning reject material rather than
elemental sulfur or pyrites. By enriching the input air with
pure oxygen, a higher concentration of sulfur dioxide in the
combustion products may be obtained, thereby minimizing the re-
quired modifications to existing equipment and process design.
221
-------
• There is a large and relatively stable market for sulfuric acid.
The competitive status of processes for converting the sulfur
content of coal preparation plant refuse to sulfuric acid (for
other salable products), compared with processes using elemental
sulfur as a feedstock, is highly dependent on the availability
and market value of elemental sulfur, which fluctuates greatly
as some sources are exhausted and others are discovered.
• Under conditions of the sulfur market at the time of the ref-
erenced studies, two specific processes for recovering sulfur
value and electric power from coal preparation refuse were found
to be economically viable: the refuse-combustion/sulfur-oxides-
removal process (which accepts the entire refuse stream) and the
fluid-bed roasting process (which require preliminary concentra-
tion of the refuse).
• The use of oxygen to enrich the input combustion air would be
advantageous in permitting higher utilization of conventional
process equipment, but would not be economically advantageous
because of oxygen costs and certain technical considerations re-
lating to heat transfer.
222
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8.0 THE HIGH SULFUR COMBUSTOR — A STUDY OF SYSTEMS FOR UTILIZATION
OF COAL CLEANING REJECT MATERIAL
8.1 Objectives and Approach
A study was performed by the Chemical Construction Company (Chemico)
during 1970 and 1971 to identify a combustor system for utilizing reject
material produced by the physical desulfurization of coal and to integrate
the combustor into a system for recovering the energy and sulfur values
of the reject material. Emphasis was on equipment selection and design.
Specific tasks of the study were;
• To select/design an appropriate combustor;
• To select/design processes for recovery of sulfur values as
sulfur or sulfuric acid, with emphasis on those processes
in commercial use Cor nearly so);
• To determine properties of reject material that influence
combustor design;
• To'establish procedures to characterize reject material for
use as fuel;
• To establish, specifications for reject material for use as
a fuel;
• To perform a conceptual design of a prototype plant;
• To estimate costs of plant and of the overall operation, in-
cluding coal cleaning;
• To extrapolate design to full-scale industrial and utility
plants with energy outputs in the range from 500,000 Ib/hr of
223
-------
industrial-quality steam to 500 megawatts electrical power, with
each design providing for recovery of sulfur values;
• To coordinate this study with other elements of EPA's Clean Coal
Program.
These tasks were approached by first examining the characteristics
of raw coal in the geographic area of interest and capabilities of var-
ious methods of physical desulfurization. This made it possible to de-
fine the ranges of reject characteristics for which recovery systems
would be designed, the characteristic of major interest being the sulfur-
to-carbon ratio (S/C ratio) in the reject material.
Next, five "case studies" were developed consisting of very general
performance specifications of various types of plants to extract both
energy and sulfur values from rejects having sulfur-to-carbon ratios
across the range of interest. Conceptual plant designs were developed
for the five case studies and estimates of capital and operating costs
were developed for each design. More detailed engineering designs,
equipment specifications, and cost estimates were prepared for a proto-
type demonstration plant fitting one of the case studies.
The study concludes that the reject material produced by the re-
moval of iron pyrites and ash from coal by conventional coal cleaning
operations can be blended to form a high sulfur fuel suitable for firing
an appropriately designed plant to generate electric power and recover
sulfur values. The prototype plant design developed in the study would
provide the capability to demonstrate technical feasibility on a reduced
224
-------
scale (output: 50 megawatts electric and 100 tons/day sulfur) and to
further investigate the economics of such an operation, which appears
economically viable in preliminary analysis of a larger-scale plant (out-
put: 500 megawatts electric and 770 tons/day sulfur).
The 50 megawatt plant design selected for more detailed analysis
and possible implementation as a prototype plant employs the same basic
power generating system and technically-advanced sulfur recovery process
as the 500 megawatt plant. Although not of commercial scale, it is of
sufficient size to permit investigation of the effects of variations
in fuel characteristics and operating conditions on power and sulfur
output and to produce good estimates of operating costs. However, it
is not so large that disposal of sulfur and waste products is likely
to present a major problem. The production of sulfur in its elemental
form helps to separate the basic problem of sulfur recovery coupled
with power generation from the more complex problem of conversion to
sulfuric acid. Also, since elemental sulfur is easy to store and costs
less to ship than sulfuric acid, the location of a prototype plant
producing elemental sulfur would be less critical, in terms of proximity
to acid-consuming industry, than a plant producing sulfuric acid.
8.2 Types of Coal and Effects of Coal Cleaning
A review of the effects of various methods of physically cleaning
and desulfurizing coals produced in the six-state area of interest (Pennsyl-
vania, Ohio, West Virginia, Kentucky, Indiana and Illinois) led to the
following conclusion relating directly to the design of combustor systems:
225
-------
If, by size reduction and separation, it is feasible to separate
fractions to recover coal low in pyritic sulfur content and to re-
cover pyritic fractions low in coal content, then, by recombining
these fractions, it is possible to produce high-sulfur fuel hav-
ing a controlled ratio of pyritic sulfur to coal. The character-
istics of such fuels can thus be tailored to the requirements of
specific combustion-systems designed for the economic recovery of
energy and sulfur values.
For the five case studies Foster-Wheeler did considerable work on
determining feed compositions which were suitable. Bituminous Coal
Research, Inc., (BCR) demonstrated that the compositions specified by
Foster-Wheeler could be produced through such means as blending, etc.
BCR also performed work on the utilization of clean coal fractions.
Thus, the assumption is made that almost any run-of-mine coal contain-
int pyrites can, in general, be processed to yield low sulfur coal plus
a high-sulfur fuel.
This conclusion permits establishing ranges of interest for the
parameters characterizing high sulfur fuels, and selecting fuels having
specific characteristics, upon which plant design can be based.
8.3 High Sulfur Fuel Characteristics
Reject material from coal cleaned to reduce sulfur content ordin-
arily contains higher percentages of pyrites and non-pyritic ash and
a lower percentage of carbon than run-of-mine coal. The sulfur content
may range from a minimum of about one percent (assuming this one percent
to be the nominal maximum for "desulfurized" coal) to a theoretical maxi-
mum of about 58 percent (corresponding to pure pyrite).
The combustion in air of a known mixture of sulfur and carbon re-
sults in predictable sulfur dioxide concentration in the combustion gas.
226
-------
For practical purposes this is also true of known sulfur-coal and iron-
pyrite mixtures when the conposition of the coal is also known. Sulfur
dioxide concentrations expected from combustion of sulfur-carbon mixtures
can be plotted according to S/C ratios. The use of the S/C ratio for this
purpose avoids the ambiguity of "percent sulfur in coal" which is deter-
minant of total sulfur but not of flue gas composition. However, coal
is not pure carbon and use of the S/C ratio results in some minor incon-
sistencies. The S/C ratio of high sulfur combustor (HSC) fuel must be
held to narrow limits to stabilize the heating value of the fuel and to
avoid penalizing the sulfur recovery operation.
The iron-pyritic ash content must also be controlled, partially
to maintain a specific heating value, but more importantly to avoid
an unpredictable ash fusion temperature. Failure to control ash
content can adversely affect the yield of cleaning operations and the
capability of the furnace designed to burn the HSC fuel.
For recovery of sulfur values from the reject, the percent sulfur
in the fuel is not of as much concern as the ratio of sulfur to carbon.
This sulfur-to-carbon ratio bears an almost direct relation to the per-
centage of sulfur dioxide in the gaseous products of combustion, from
which the sulfur must be recovered. In general, higher concentrations
of sulfur dioxide promote efficiency of recovery, at least in currently
available technology. The percentage of sulfur dioxide may range from
a small fraction of a percent from burning a relatively clean fuel (say
one or two percent sulfur) to about 13 percent from burning pure pyrite
227
-------
(58 percent sulfur). However, high sulfur fuels made from reject ma-
terials will not fall near the high or low end of the scale for either
percent sulfur or sulfur-to-carbon ratio, but within the mid-range.
The following limits were selected to define the range of interest
for high-sulfur fuel composition:
(25)
HSC V
Lower Upper
Parameter Limit L^nit
Sulfur-to-carbon ratio .08 2
Percent S in fuel, (approximate) 7 42
Equivalent percent pyrite 13 79
in fuel, (approximate)
Percent coal combustible 87 21
(sulfur-free) in fuel, approximate)
Higher heating value 12600 5300.
of fuel, (approximate)
Although fuels of various compositions falling within this range were
selected for the various case-study process designs, the basic approach
is to design the process to fit the market, and to tailor-make the
fuel to suit the process.
8.4 Performance Requirements for Recovery Systems—Base Parameters
for Five Case Studies
Three process systems utilizing currently available technology
appear capable of fully exploiting the full range of opportunities for
recovering energy and sulfur values from high-sulfur coal-pyrites. The
chemical processes selected for recovery of sulfur values or the standard
contact process, the Monsanto Cat-Ox process, and the magnesium sulfite/
228
-------
oxide process. Five case studies involving these systems were defined
as follows (letter designations are arranged to group similar processes
instead of in alphabetical order):*
CASE A; Energy Product: 500,000 Ib/hour industrial steam
Sulfur Product: 1800 tons/day 100% sulfuric acid
Fuel S/C Ratio: 2.0
CASE A is designed for firing a high sulfur fuel having a sulfur-
to-carbon ratio of about 2 to produce 500,000 Ibs/hr of industrial
quality steam and a flue gas of 6 percent S02 concentration which
is directly converted to some 1,800 tons/day of commercial grade
sulfuric acid. These outputs would be secondary coproducts of
clean coal produced at a rate of 7 million tons per year by wash-
ing a run-of-mine coal containing 3 percent pyritic sulfur. The
actual clean coal output would, of course, depend on the actual
run-of-mine composition and washability.
A system of this type is conceived to be of possible value as an
addition to an existing coal-burning utility complex, or existing
chemical or steelmaking industry.
CASE B; Energy Product: 500,000 Ib/hour industrial steam
Sulfur Product: 77% sulfuric acid equivalent to 624
tons/day (100% basis)
Fuel S/C Ratio: 0.4
*Adapted from Reference 25 (1971)
229
-------
CASE B is designed to use the Monsanto Cat-Ox process for recovery
of sulfur as 77-80 percent sulfuric acid. Since a lower sulfur-
carbon ratio fuel is used, a smaller quantity of acid would be pro-
duced, the steam output rate remaining constant.
CASE E; Energy Product: 500 megawatts electric power
Sulfur Product: 77% sulfuric acid, equivalent 1420 tons/
day (100% basis)
Fuel S/C Ratio: 0.12
CASE E employs an 862 recovery technology (Monsanto Cat-Ox) similar
to CASE B but this system is scaled to the 500 MW output level
(more than 10 times the energy capacity of CASE B) so that the
combustion equipment is quite different. The S02 recovery trains
operate on relatively weak gas of 0.7 percent SOo which is gener-
ated by a sulfur/carbon ratio of 0.12.
CASE D; Energy Product: 500 megawatts electric
Sulfur Product: 770 tons/day elemental sulfur
Fuel S/C Ratio: 0.2
CASE D is also scaled to 500 MW energy output but the S02 recovery
technology is quite versatile compared to processes mentioned
above. The acid intermediates—liquid S02, magnesium sulfite, or
230
-------
sulfur—can be produced for storage or shipment, or sulfur value
can be converted directly to sulfuric acid, any of these by avail-
able technology. The main design theme of CASE D in this study is
for output of sulfur at 770 net tons per day from a 1 percent S02
flue gas that requires a sulfur/carbon ratio of 0.2
CASE C: Energy Product: 50 megawatts electric
Sulfur Product: 102 tons/day elemental sulfur
Fuel S/C Ratio: 0.2
CASE C is the reduced-scale prototype or demonstration unit of
CASE D, designed to operate on the same HSC fuel composition but
at 50 MW energy capacity and about 100 tons per day of sulfur.
These cases cover sulfur-to-carbon ratios from 0.12 to 2.0.
Cases A and B are primarily of industrial interest, Cases D and E are
of utility interest with chemical co-products, and Case C is for demon-
stration. The plant design for Case C was carried to much greater de-
tail than for the other case studies.
8.5 Selection of Equipment and Fuel Compositions
8.5.1 High Sulfur Fuels
Reject materials produced by coal cleaning operations were reviewed
with respect to sulfur content, coal content, non-pyritic ash content,
heat value, and other relevant characteristics. Fuel compositions for
each case study were specified, based on the following ground rules:
231
-------
• High sulfur fuel specifications must be compatible with
optimum total yield of fuel value from the coal cleaning
plant.
• Sulfur/carbon ratio must be controlled within narrow limits
to facilitate recovery operations.
• Non-pyritic ash content must be controlled to avoid unpre-
dictable ash fusion temperature.
Fuels for each case study were specified in terms of proximate and ulti-
mate analyses. These will be presented in abbreviated form in later ex-
hibits describing the processes employed in each case study (see Sec-
tion 8.5.6).
Test procedures recommended for defining, preparing, and controll-
ing the quality of high sulfur fuels were:
• Ultimate Analysis;
• Proximate Analysis;
• Heating Value;
• Hardgrove Grindability;
• Reactivity (Ignition Index);
• Chemical Analysis of Ash;
• Ash Fusion, Reducing and Oxidizing Atmosphere;
• Size Analysis;
• Free Swelling Index.
Only one of the nine tests, reactivity, is not commonly accepted
in common practice. It was included because it appears to be the best
232
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indicator of combustion conditions over a wide range of fuel specifica-
tions.(25)
8.5.2 Furnace Types
The following types of furnace were considered:
1. Roasting Equipment
(a) Kiln
(b) Multiple Hearth
(c) Flash Roasters
2. Fluidized Bed Combustors
3. Stoker Furnaces
4. Grate Furnaces
5. Crushed Coal-Fired
(a) Cyclone Furnace
6. Pulverized-Fuel Fired
Ca) Wet bottom furnace
(b) Dry bottom furnace
Horizontally fired
Vertically fired.
Types 1, 3, and 4 were eliminated from consideration because they
cannot be fired at sufficiently high temperatures to meet steam produc-
tion requirements.^ Type 2 (fluidized bed) was dropped because it is
not established commercially for this type of operation and because of
the uncertain behavior of a coal-pyrite-ash mixture in a fluidized bed
233
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containing tubes. Type 5(a) (Cyclone) was eliminated because of high
maintenance costs which could be aggravated by a high-iron, high sulfur
fuel.
Pulverized-fuel fired systems were considered preferable to sus-
pension-fired ones on the basis of fuel characteristics, thus eliminat-
ing Type 4 (grate). Wet bottom furnaces (Type 6(a)) were considered un-
suitable because of the high ash fusion temperatures resulting from high
iron content.
Thus, by elimination, the dry-bottom, pulverized-fuel-fired type
of furnace was considered to be relatively risk-free, reliable, and most
generally suitable for all cases studied.
8.5.3 Boilers, Burners, and Combustion Systems
Specific types of combustion systems were selected for Cases A, C,
and D. Combustor designs for Case B were not developed since funds were
not provided, but cost estimates for Case B equipment were made on the
basis of a modified Case A design. The Case D combustor system is suit-
able for Case E with minor modifications.
For Case A, an individual-type boiler fired by a special burner fir-
ing vertically downward, was selected to produce 500,000 Ib/hour of
steam at a pressure of 900 psig.
For Case C, which requires a rate of steam production similar to
Case A but at a higher pressure for generating electric power, a utility-
type boiler fired horizontally with an intervane burner was selected
to produce some 500,000 Ib/hour of steam at 1450 psig.
234
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For Case D» a utility-type boiler was selected to produce larger
quantities of higher quality steam which are fed to 500 MW turbo-gener-
ators. As in Case C, a larger utility boiler fired horizontally with
intervane burners was selected. It would produce some 3.5 million lb/
hour of steam at 2500 psig.
The Case E equipment would be a modification of the Case D equip-
ment.
8.5.4 Electric Generating Equipment
Electric generators driven by a conventional turbine drive cycle
were selected for both the 50 MW requirement (Case A) and the 500 MW
requirement (Cases D and E).
The 500 MW size was fairly typical of U.S. utility installations
ca. 1960. More recently this capacity (i.e., 500 MW) has been toward
the lower end of the range, with most installations falling between 600
and 850 MW. Capacities around 50 MW are still in use for some munici-
palities, industrial Installations, etc. Generating equipment of much
lower capacities is often considered as "special order" with much
higher cost per unit output. Hence the 50 MW size appeared about right
for a prototype demonstration plant.
8.5.5 Processes for Recovery of Sulfur Values
Sulfur values can be recovered from the gaseous products of pyrite
combustion in several forms, including sulfuric acid, elemental sulfur,
sulfur dioxide (liquid), and metallic sulfites. Sulfuric acid is usu-
ally the salable end-product, and the other forms of recovered sulfur
235
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may be considered intermediate materials for the production of acid.
As discussed in Section 7, there are advantages to shipping sulfur in
forms other than sulfuric acid because of the acid's high specific grav-
ity. Hence, under some logistic situations, one of the intermediate
forms of sulfur may be the more desirable output of a recovery operation.
The following processes for producing sulfuric acid or acid inter-
mediates were considered for use in the plant designs for the various
case studies:
• Processes Yielding Sulfuric Acid:
• the "Standard" contact process;
• the Monsanto Cat-Ox process (a modification of the basic
contact process permitting use of sulfur dioxide concentra-
tions in the range of 2 percent down to a few tenths of a
percent);
• the Lurgi process;
• the Hitachi process;
• Processes for Concentrating Gas Mixtures Low in Sulfur Dioxide
to Intermediate Levels:
• the Reinluft process (using char absorption);
• the Grillo process (using metallic oxide absorption);
• the Magnesium Sulfite/Oxide process;
• Processes for Concentrating Weak Sulfur Dioxide Mixtures to
High Levels (90-100 percent):
236
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• aromatic amine absorption;
• basic aluminum sulfate absorption;
• thermal cycle absorption (using water as solvent);
• alkali-metal sulfite/bisulfite absorption (Wellman-Lord
process);
• Processes Yielding Elementary Sulfur:
• reduction of high-concentration sulfur dioxide by hot coke;
• reduction of dilute sulfur dioxide by produce gas (a mix-
ture of hydrogen and carbon monoxide);
* reduction of dilute sulfur dioxide by reformed natural
gas (methane);
• reduction of sulfur dioxide by methane (non-catalytic);
• reduction of sulfur dioxide by methane (the West process);
• reduction of sulfur dioxide by hydrogen sulfide (the Glaus
process).
Three processes (or combinations) from among the above were se-
lected as adequate to exploit the full range of potentials for sulfur
value recovery presented by the five case studies. These were employed
as follows:
Case A — "Standard" Contact Process;
Case B — Monsanto Cat-Ox Process;
Case C — Magnesium Sulfite/Oxide Process;
Case D — Magnesium Sulfite/Oxide Process;
Case E — Monsanto Cat-Ox Process.
237
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8.5.6 Process Description and Fuel Composition for Each Case Study^
Summary descriptions of the processes, fuels, and products for each
case study are presented in Tables XXXIX, XL, XLI, XLII, and XLIII.
Process flow charts for each case study can be found in Reference 25,
Part VII; additional design detail is presented in Parts XIII through
XVII of this reference. The Case C prototype plant design is accorded
special attention in Part XV.
To facilitate comparison among the five case studies, the fuel in-
put requirements and outputs of each are summarized in Table XLIV. This
table shows the quantities of clean coal produced and the quantity of
high sulfur fuel derived from the coal-cleaning reject material. It
also shows the resulting energy value and sulfur value obtained from
utilizing the high sulfur fuel. Equivalent quantities of sulfur pro-
ducts for each case study are shown for purposes of comparison; how-'
ever, the equipment specified in certain of the case studies is not
adapted to produce all of the sulfur products shown in this Table. Com-
parison of the relative quantities of the various forms of sulfur pro-
ducts suggest that when the product is to be shipped over considerable
distances or when storage space is at a premium it may be highly ad-
vantageous to produce the sulfur in elemental form, or as another sul-
fur compound, instead of sulfuric acid.
8.6 Economic Analyses of the Five System Designs
Capital costs and annual operating costs (less cost of high sulfur
fuels) for the processing system employed in each case study were
238
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TABLE XXXIX
SUMMARY OF CASE A
PRODUCTS
Energy Product: 500,000 Ib/hour at 825°F
Sulfur Product: gg% sulfuric acid, equivalent to 1830 tons/day
C100% basis)
SUMMARY
A run of mines bituminous coal containing 3 to 4.5% sulfur,
washable to 1% sulfur, is assumed. The reject is treated for
maximum yield of a high-sulfur fuel of the CASE A specification.
This fuel is pulverized and fired to raise 500,000 Ibs/hr of
industrial quality steam and a flue gas containing 6% sulfur dioxide
and 4.3% oxygen. The gas is wet cleaned in a packed tower, dried
and converted catalytically to sulfur trioxide which is reacted
with water to make 98% sulfuric acid at the rate of 1,830 net tons
(100% basis) per day, 330 days per year. Sulfur emission equals
0.4% of sulfur charged. Sulfur not emitted equals 93 pounds per
million Btu of heat recovered in the CASE A System, or 2,2 pounds
per million Btu of ROM coal charged to the cleaning plant.
FUEL CHARACTERISTICS
„ n „ . 4,* Run of Clean High-Sulfur
Constituents (Wt. /. Dry Basis*) fflne Coal Coal Fuel
Iron Pyrite 1-0 61.6
Organic Sulfur 1-0 0.2
Total Sulfur 3 to 4.5 (33.1)
Coal Combustibles 18-2
Non-Pyritic Ash 20-°
M Tons/Year 64°'°
Tons/Hr: Iron Pyrite 49.3
Coal Combustibles u-7
Non-Pyritic Ash 16-°
Sulfur/Coal Ratio 1'8
BTU/LB 442°
BTU/HR .
* 6% Moisture assumed in high sulfur fuel as fired
Source: Adpated from
Reference 25 (1971).
239
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TABLE XL
SUMMARY OF CASE B
PRODUCTS
Energy Product: 500,000 Ib/hour at 825°F
Sulfur Product: 77% sulfuric acid equivalent to 624 tons/day
(100% basis)
SUMMARY
A run of mine bituminous coal containing 3 to 4.5% sulfur»
washable to 1% sulfur, is assumed. The reject is treated for
maximum yield of a high sulfur fuel of the CASE B specification.
This fuel is pulverized and fired to raise 500,000 Ibs/hour of
industrial quality steam and a flue gas containing 2% sulfur
dioxide and 4.2% oxygen. The gas is cleaned of particulates in an
electric precipitator at 805° F and is then converted catalytically
to sulfur trioxide which is reacted with water to make 77%-80% sulfuric
acid by the Cat-Ox process of Monsanto at the rate of 624 net tons
(100% basis) per day, 330 days per year. Sulfur emission equals
0.5% of sulfur charged. Sulfur not emitted equals 33 pounds per
million Btu of heat recovered in the CASE B System, or 2.0 pounds
per million Btu of ROM coal charged to the cleaning plant.
FUEL CHARACTERISTICS
Constituents (Wt. % Dry Basis*) *un °f 1 Clean High-Sulfur
Mine Coal Coal Fuel
Iron Pyrite 33.8
Organic Sulfur 0.5
Total Sulfur 3 to 4.5 (18f5)
Coal Combustibles 45.7
Non-Pyritic Ash 20.0
M Tons/Year 406
Tons/Hr: Iron Pyrite 17.1
Coal Combustibles 23.4
Non-Pyritic Ash 10.i
Sulfur/Coal Ratio .-.. 0.4
BTU/LB 7400
BTU/HR 750 x 1Q6
* 6% Moisture assumed in high sulfur fuel as fired
Source: Adapted from
Reference 25 (1971).
240
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TABLE XLI
SUMMARY OF CASE C
PRODUCTS
Energy Product: 50 megawatts electric at 500° F
Sulfur Product: 102 tons/day elemental sulfur
SUMMARY
A run of mine bituminous coal containing 3 to 4.5% sulfur,
washable to 1% sulfur, is assumed. The reject is treated for
maximum yield of a high sulfur fuel of the CASE C and D specification.
This fuel is pulverized and fired to raise 500,000 Ibs/hr of sub-
critical steam which is fed to a turbo-generator of 50 MW capacity.
The flue gas containing about 1% sulfur dioxide and 4.3% oxygen is
wet-cleaned in a venturi scrubber and led to a two-stage-venturi
absorber in which sulfur dioxide is.reacted, essentially with
magnesium oxide, to produce magnesium sulfite. This salt is
separated, dried, and calcined to yield a 15% sulfur dioxide gas
concentrate and magnesium oxide which is recycled. The 15% sulfur
dioxide is converted by catalytic reduction to sulfur at the rate
of about 100 net tons per day, 330 days per year. Sulfur emission
equals 1.3% of sulfur charged. Sulfur not emitted equals 16 pounds
per million Btu of heat recovered in the CASE C Prototype System,
or 2.2 pounds per million Btu of ROM coal charged to the cleaning
plant.
FUEL CHARACTERISTICS
Run of Clean High-Sulfur
Constituents (Wt. % Dry Basis*) Mine Coal Coal Fuel
Iron Pyrite 20.8
Organic Sulfur 1.0 0.6
Total Sulfur 3 to 4.5 (11.7)
Coal Combustibles 58.6
Non-Pyritic Ash 20.0
M Tons/Year 298.0
Tons/Hr: Iron Pyrite 7.7
Coal Combustibles 22-°
Non-Pyritic Ash 7-4
Sulfur/Coal Ratio °-2
BTU/LB 900°
BTU/HR 67° x 10
* 6% Moisture assumed in high sulfur fuel as fired
Source: Adapted from
Reference 25 (1971).
241
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TABLE XLII
SUMMARY OF CASED
PRODUCTS
Ene
Sulfur Product: 770 tons/day elemental sulfur
Energy Product: 500 megawatts electric at 500 F
SUMMARY
A run of mine bituminous coal containing 3 to 4.5% sulfur,
washable to 1% sulfur, is assumed. The reject is treated for
maximum yield of a high sulfur fuel of the CASE C and D specification.
The fuel is pulverized and fired to raise 3.5 million pounds per
hour of subcritical steam which is fed to a turbo-generator of
500 MW capacity. The flue gas composition is identical to that of
CASE C and is treated in an identical manner to yield 770 net tons
per day of sulfur. Sulfur emission equals 0.8% of sulfur charged.
Sulfur not emitted equals 16 pounds per million Btu of heat recovered
in the CASE D System, or 2.3 pounds per million Btu of ROM coal
charged to the cleaning plant.
FUEL CHARACTERISTICS
Constituents (Wt. % Dry Basis*) Run of Clean High-Sulfur
Mine Coal Coal Fuel
Iron Pyrite 20.8
Organic Sulfur 0.6
Total Sulfur 3 to 4.5 (11.7)
Coal Combustibles 58.6
Non-Pyritic Ash 20.0
M Tons/Year 2280
Tons/Hr: Iron Pyrite 59.3
Coal Combustibles 338.0
Non-Pyritic Ash 57.0
Sulfur/Coal Ratio 0.2
BTU/LB 9000
BTU/HR 5,128 x 1Q6
* 6% Moisture assumed in high sulfur fuel as fired
Source: Adapted from
Reference 25 (1971).
242
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TABLE XLIII
SUMMARY OF CASE E
PRODUCTS
Energy Product: 500 megawatts electric power at 850° F
Sulfur Product: 77% sulfuric acid, equivalent to 1420 tons/day
(100% basis)
SUMMARY
A run of mine bituminous coal containing 3 to 4.5% sulfur,
washable to 1% sulfur, is assumed. The reject is treated for
maximum yield of a high sulfur fuel of the CASE E specification.
This fuel is pulverized and fired to raise 3.5 million pounds per
hour of sub-critical steam which is fed to a turbo-generator of
500 MW capacity. The flue gas containing 0.7% sulfur dioxide and
4.2% oxygen is treated by the Monsanto Cat-Ox process in a manner
similar to CASE B, but in multiple trains, to yield 1,420 net tons
(100% basis) of 77%-80% sulfuric acid per day. Sulfur emission
equals 1.5% sulfur charged. Sulfur not emitted equals 10 pounds
per million Btu recovered in the CASE E System, or 2.3 pounds per
million Btu of ROM coal charged to the cleaning plant.
FUEL CHARACTERISTICS
Run of Clean High-Sulfur
Constituents (Wt. % Dry Basis*) Mine Coal Coal Fuel
Iron Pyrite 13.2
Organic Sulfur 0.9
Total Sulfur 3 to 4.5 (7.9)
Coal Combustibles 65-9
Non-Pyritic Ash 20-°
M Tons/Year 2133
Tons/Hr: Iron Pyrite 35.2
Coal Combustibles 178.0
Non-Pyritic Ash 53-3
Sulfur/Coal Ratio °'12
BTU/LB 966° ,
BTU/HR
* 6% Moisture assumed in high sulfur fuel as fired
Source: Adpated from
Reference 25 (1971).
243
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TABLE XLIV
SUMMARY OF INPUTS AMD OUTPUTS FOfl FIVE CASE STUDIES
IO
Case
D
A
E
B
C
Input
(Million Tons/Yr.)
Run-of-Mine
Coal
9.7
8.1
5.8
2.8
1.3
Output of Coal
Processing Operation
(Million Tons/Yr.)
Clean
Coal
7.1
7.1
3.5
2.3
0.9
High-Sulfur
Fuel
2.3
0.6
2.1
0.4
0.3
Output of Power and Sulfur Recovery Operations
Enerey
Electrical
(Hegasatts)
500
500
50
Steam
(Lb./Hour at 825 F)
500,000
500,000
Sulfur Values (Net Tons/Dav. Appro*.
Elenental
Sulfur
770*
640
510
230
102*
Sulfuric
Acid
Equivalent
2300
1830*
1420*
£24*
291
Magnesium
Sulfate
Equivalent
2500
1980
1580
710
310
Liquid
Sulfur Dioxide
Equivalent
1520
1220
970
440
190
Votes: (1) BOB: 1Z organic S, 3Z pyritic S, 13Z non-pyritic ash.
-(2) Clean Coal: 12 organic S, 5Z non-pyritic ash
(3) Clean Coal + HSC fuel - 95Z of ROM weight (dry basis)
(4) Total cleaning losses = 5Z
* Design Basis for this Case Study
Source: Adapted fro. Reference 25 C1971).
-------
determined. Anticipated income from sale of products was then estimated,
and the allowable cost of high sulfur fuels was determined by difference.
8.6.1 Method for Valuation of High-Sulfur Fuels
The various systems used to recover energy and sulfur values from
coal-pyrites may be considered salvage systems to improve the economics
of coal cleaning. Sales income, less all costs for energy and sulfur
value recovery and other expense, is a basis for valuation of high
sulfur fuels. The value of .the high sulfur fuel is determined as
follows:
High Sulfur Fuel Value = Sales Value of Products (Electric power,
sulfuric acid, etc)
less: - Selling and Commercial Expense
- Extraction Costs
- General Expense and Income Tax
- High-sulfur Fuel Preparation, Transport and Handling
Costs ("Precombustion Costs")
plus: Cost of Dumping Refuse (shown as a "plus" to indicate
a credit for avoidance of dumping costs).
The "precombustion cost" term has been estimated to be on the
order of 81 cents per ton of high sulfur fuel delivered to the combustor;
this would increase for longer shipping distances. The dumping cost
has been estimated as lying between $1 and $2 per ton of refuse. (Each
of these estimates is highly ""variable with local conditions (land cost,
shipping distances, etc.)). For the present analysis, the assumption
is made that it is as cheap to prepare and deliver high sulfur fuel as
245
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it is to handle and dump an equal tonnage of refuse; that is, the pre-
combustion costs and dumping costs cancel one another out in the above
formula.
8.6.2 Capital Costs
Capital costs are considered to include the costs of construction
labor, plant equipment, and material in 1971 or 1972. Cost escalations,
It
estimated as 10 percent/year for electrical equipment and 6 to 8 percent
for the chemical plant beyond 1972 are not included in the cost analysis.
Estimated capital costs for the five case-study systems are given in
Table XLV.
8.6.3 Operating Costs
This category includes all costs for extraction of energy and
sulfur values except those for high-sulfur fuel, which will be determined
later by difference. In addition to annual costs for utilities, labor
and supervision, maintenance, and general plant expense, operating costs
also include annualized capital costs to the extent that these are re-
flected by depreciation and interest.
Operating cost estimates were prepared for each of the five case
studies using utilities prevalent in the six-state area of interest
(Pennsylvania, Ohio, West Virginia, Kentucky, Indiana, and Illinois)
during late 1970. Detailed data for Case C (the 50 MW prototype de-
sign) is shown in Table XLVI to illustrate the presentation format.
(Data for the other cases not included in this summary report can be
found in Reference 25, Part VIII.)
246
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TABLE XLV
ESTIMATED CAPITAL COST
Combust or/Bo Her
Electric Equipment
Sulfur Recovery
Off-Sites
Land
Fixed Capital
Working Capital
Total Capital
CASE A
$M
5,110
11,300
1,550
250
18,210
130
CASE B
$M
4,210
12,500
1,550
250
18,510
90
18,340 18,600
CASE C
$M
4,310
11,200
10,900
2,550
250
29,210
60
29.270
CASE D
$M
15,760
56,200
44,000
10,100
1.000
128,060
460
CASE E
$M
11,760
56,200
45,700
10,500
1.000
125,160
410
128.520 125.570
Source: Reference 25 (1971).
247
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TABLE XLVI
CASE C SYSTEM ESTIMATED OPERATING COST
ELECTRICITY
SULFUR
Unit
Unit Value
Production
Energy MWH
Sulfur Value L.T.
Utilities, etc.
Electricity MWH $7.50
Cooling Water MMgal. 8.00
Boiler Feed Water Mgal. 0.60
Process Water Mgal. 0.40
Fuel Gas MMBtu 0.40
Chemicals
Waste Disposal N.T. 2.00
Labojr
Supervision Manhour 8.00
Operators and
Helpers Manhour 5.50
Maintenance
Plant General Expense
Factory
Overhead 80% of Direct
Taxes and
Insurance 2.5% of Total
Total Before Depreciation and Interest
Depreciation
Guideline Life 11 Years 9.1%
Guideline Life 28 Years 3.6%
Interest (Average)
Depreciable Capital 4.5%
Non-Depreciable Capital 9%
Cost Before HSC Fuel Charge (Rounded)
Units Annual
Per Year Cost
400,000
3,360 M$ 25
21,600 173
5 3
110,000 220
8,760 70
44,000 242
280
Labor 194
Capital 403
M$l,610
578
723
153
M$3,060
Units Annual
Per Year Cost
30,910
37,360 M$ 280
268 2
113,000 45
2,100,000 840
81
25,400 51
8,760 70
32,000 176
430
141
329
M$2,445
1,174
581
126
M$4,330
Source: Reference 25 (1971),
248
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In these presentations, separate costs are assigned to the pro-
duction of energy and chemical values. Ground rules used in the in-
itial analysis assign all costs for "pollution control" to the re-
covery of chemical values rather than apportioning it between the
two classes of products. This leads to an apparent low cost of energy
production and a high cost of chemical value recovery. An adjustment
for this effect is indicated in the following section on Operating
Economics.
8.6.4 Operating Economics; Cost of High-Sulfur Fuel
The method for estimating allowable prices for high-sulfur reject
material is shown in Tables XLVTI and XLVIII. Here, the expected in-
come from selling products of the five case study plants is computed
on the basic prices expected to prevail in the six-state area, based
on an analysis of price trends. Unit price assumptions are shown in
Table XLVII. Values of energy products and chemical products are
treated separately.
The various categories of expense—costs of selling, operation,
(
etc.—are then subtracted from the income from sales. The resulting
pre-tax income is adjusted for "pollution control" expense, which is
required because of a computational ground rule which assigned all
pollution control costs to the sulfur recovery portion of the system.
Note that this adjustment does not affect the combined income, but
merely shifts a part of the expense from one product category to an-
other. It should be noted that the pollution control tariff reflected
249
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TABLE XLV1I
INCOME FROM SALES COSTS OF OPERATION AND PRODUCTS
GAIN OR LOSS FROM OPERATION
ANKUAL BASIS
Income From Sales
Steam
Electricity
Sulfur
Sulfuric Acid (100%)
Less: Selling & Commercial
Expense @ 1% of Sales Value
@ 5% of Sales Valm
Operating Cost
General & Administrative
@ 2Z of Sales
Adjustment for "Pollution Control"
Add
Deduct
Adjusted Cost of Energy Extraction
Unit Cost of Energy Products:
Per Net Ton of Steam
Per Hegawatt Hour
Unit Cost of Sulfur Products:
Per Long Ton of Sulfur
Per Set Ton of Sulfuric Acid
Combined Sales Ttelue of Products
All Costs Before U.S. Income Tax
Unit Annual
Unit Value Quantity
Sec Ton $ 1.30 2,000,000
MHH 7.50 400,000
4,000,000
Long Ton 25.0 30,910
233,300
Het Ton 12.75 610,000
208,000
473,300
1
alue
alue
ome Tax (Rounded)
Control"
[traction
ucts:
Value Recovery
ucts:
c Acid
oducts
Income Tax
CASE A
Sulfuric
Steam Acid
M$ 2,600
M$7,780
26
389
2,540 3,820
52 156
H$ 2,620 M$4,370
9,380
9,380
M$12,000
$ 6.00
(H$5,010)
H510.380
6,990
MS 3.390
CASE B
Sulfuric
Steam Acid
M$2,*00
MS2.650
26
132
1,880 3,910
52 53
M$l,960 M$4J100
4,520
4,520
MS6.4BO
$ 3.20
(H$ 420)
( 2.00)
H$ 5,250
6,060
01$ 810)
CASE C
Electricity Sulfur
MS30.000
M$ 770
30
39
3,060 4,330
60 15
MS3.150 M? 4,380
2,630
2,630
M55,780
$ 14.50
MS 1,750
MS 3,770
7,530
(MS 3,760)
CASK D
Electricity Sulfur
H$30.000
MS 5.830
300
292
12,600 20,630
600 117
HS13.500 MS 21, 000
14,450
14,450
MS28.000
$ 7.00
MS 6,550
S 28.00
M$ 35,830
34,500
HS 1,330
CASE E
Sulfuric
Electricity Acid
MS 30, 000
H$ 6.040
300
302
11,630 14,970
600 m
M$12,500 MS15.400
10,620
10.620
H$23,100
$ 5.80
M$ 4,780
MS 36,040
27,908
MS 8,140
Source: Reference 25 U971)
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TABLE XLVIII
VALUE OF HSC FUELS, OFFSET TO CLEANING COST,
PAYOUT OF INVESTMENT
Value of HSC Fuels;
Taxable Gain (or Loss) M$ 3,390 (M$ 810) (M$ 3,760) M$ 1,330 M$ 8,140
Gain (or Loss) After 48% Tax Effect M$ 1,760 (M$ 420) (M$ 1,960) M$ 690 M$ 4,230
HSC Fuel Consumed - M Tons Per Year 640 410 300 2,300 2,100
Value of HSC Fuel - Per Ton $ 2.75 ( $ 1.02 ( $ 6.53) $ 0.30 $ 2.01
Offset to Coal Cleaning:
Clean Coal Yield - M Tons Per Year 7,100 2,300 920 7,100 3,500
to Credit (or Debit) Per Ton of Clean Coal $ 0.25 ( $ 0.18) ( $ 2.13) $ 0.10 $ 1.21
Ol
\->
Payout of Investment:
Gain (or Loss) After 48% Tax Effect M$ 1,760 (M$ 420) (M$ 1,960) M$ 690 M$ 4,230
Depreciation 1,634 1,662 1,752 7,169 7,214
Cash Flow M$ 3,394 M$ 1,242 (M$ 208) M$ 7,859 M$ll,444
Total Investment 18,340 18,600 29,270 128,520 125,570
Payout - Years 5.4 15 — 16 11
Source: Reference 25 (1971).
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by the adjustment costs is much more severe than ordinarily required
in conventional coal-fired generators of comparable capacity. This is
because of the high sulfur content and ash content of the reject ma-
terials used as fuel.
Sales income from energy and chemical values, after adjustment
for pollution costs and other expenses, are then combined to form the
total taxable income for each type of plant. A 48 percent income is
applied to yield the net yearly gain for the plant of each design (Table
XLVIII). Dividing this figure by the weight of high sulfur fuel con-
sumed per year yields an estimate of the cost that the manufacturer
could afford to. pay for these fuels.
Table XLVIII indicates that three of the production plant designs
(Cases A, D, and E) show net gains (sales price less total costs) rang-
ing from $0.30 to $2.75 per ton of high sulfur fuel derived from HSC
fuel utilization. This corresponds to pre-sales credits ranging from
$0.10 to $1.21 per ton of the clean coal. In other words, the HSC fuel
can be used for an economic advantage in addition to any profits gained
from selling the low sulfur coal. Case B shows a net loss and there-
fore appears uneconomical. The prototype plant design, Case C, also
shows a relatively high net loss and appears uneconomical as a production
process. This is not surprising nor is it significant since Case C
is a scaled-down version of Case D (which is economically feasible) and
is intended to serve as a research and demonstration unit.
252
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The economic analysis summarized in Tables XLV, XLVII, and XLVIII.
does not present production costs and income on a strictly comparable
basis, since Cases A, B, and E yield sulfuric acid as an end product,
while Case D (and the scaled down version in Case C) yields elemental
sulfur as an end product. The analysis of Case D was extended to
include the conversion of sulfur to sulfuric acid and the marketing
of the acid, An analysis similar to that of Tables XLVII and XLVIII
shows that, under these conditions, the allowable price for high-
sulfur fuel for the Case D plant would be about $2.00 per ton, which
corresponds to a credit of about $0.97 per ton of clean coal.
This extension of the analysis indicates that the plant design
for Case D is much more competitive with the design for Cases A and
E than is apparent from the figures presented in Table XLVIII. In
addition, the Case D design permits production of elemental sulfur
or.other acid intermediates as well as sulfuric acid, thereby provid-
ing a flexibility for adapting plant output to logistic and market
conditions.
8.7 Findings
The following conclusions may be drawn from the Chemico study,
supported by the research on high-sulfur fuel composition conducted by
Bituminous Coal Research, Inc. (BCR):
• Any run-of-mine coal containing pyritic sulfur that can be
processed to yield coal of lower sulfur content will also
yield a fuel of higher sulfur content. The sulfur-to-coal
253
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ratio of the high sulfur fuel can be controlled to any specifi-
cation within wide limits.
• By using high-sulfur fuels of composition tailored to meet re-
quirements of especially designed combustors and commercially
available boilers, generators and sulfur-recovery processes,
it appears possible to extract the energy and sulfur values
of high-sulfur fuels on a commercially profitable basis.
• By appropriate selection of processing equipment, energy values
may be realized in the form of electric power or industrial-
quality steam and sulfur values may be in the form of sulfuric
acid, elemental sulfur, or other intermediate compounds.
• In view of the high shipping costs resulting from the heavy
weight of sulfuric acid, it is sometimes economically advanta-^
geous to ship sulfur in elemental form or as other compounds
instead of the acid. The capability of a sulfur recovery plant
to produce sulfur as several different compounds (or in elemental
form) is therefore highly advantageous, especially in cases when
the sulfur must be shipped to different points of consumption
• Preliminary design and analysis indicate that construction of a
reduced-scale prototype would be warranted for research and
development efforts required to evaluate the promising, but as
yet undemonstrated, approach typified by the Case D design—
large scale (500 raw) electric power generating capacity, with
254
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versatile equipment for recovering sulfur in several alterna-
tive forms to meet various market and logistic situations. The
need for demonstration of the capability to process high sulfur
fuels in a commercially and environmentally acceptable manner
is underscored by recent (1973) shortages of low-sulfur fossil
fuels.
255
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REFERENCES
1. W. E. Morrison, Disaggregated Energy Consumption by Source, Form,
and Sector, Office of Economics, Federal Power Commission, Feb-
ruary 1973.
2. Paul Weir Company, Inc., "An Economic Feasibility Study of Coal
Desulfurization", Volumes I & II, A Study for the Division of Air
Pollution, Public Health Service, U.S. Department of Health, Edu-
cation and Welfare, Contract No. PH 86-65-29, October 1965.
3. "Report of Results of Washability Tests on Raw Run of Mine Coal
Samples," for U.S. Public Health Service, National Center for Air
Pollution Control, Cincinnati, Ohio, Commercial Testing and Engineer-
ing Company, Contract No. PH27-00079, December 1967.
4. "Report of Results of Washability Tests on Raw Run of Mine Coal
Samples," for U.S. Public Health Service, National Center for Air
Pollution Control, Cincinnati, Ohio, Commercial Testing and Engi-
neering Company, Contract No. CPA-69-645, November 1969.
5. "Report of Results of Washability Tests on Raw Run of Mine Coal
Samples," for U.S. Public Health Service, National Center for Air
Pollution Control, Cincinnati, Ohio, Contract No. CPA-69-530,
April 1969.
6. "An Evaluation of Coal Cleaning Processes and Techniques for Re-
moving Pyritic Sulfur from Fine Coal," Bituminous Coal Research,
Inc., Public Health Service, for U.S. Department of Health. Edu-
cation and Welfare, Contract No. PH-86-67-139, September 1969.
7. R. J. Helfinstine, N. F. Shimp, and J. A. Simon, "Sulfur Varieties
in Illinois Coals, Float-Sink Tests," Report of Study Phase I,
Supported in part by U.S. Public Health Service, Department of
Health, Education and Welfare, Contract No. PH 86-67-206, Illinois
State Geological Survey, Urbana, Illinois, August 10, 1969.
8. A. W. Deurbrouck, "Sulfur Reduction Potential of the Coals of the
United States," Report of Investigation 7633, Bureau of Mines,
U.S. Department of Interior, 1972.
Ibid, Appendix I, "Sulfur Concentration in Coal-A Washability
Study," November 1971, in Press.
Ibid, Appendix II, "A Statistical Evaluation of Ash and Sulfur
Contents of U.S. Coals," November 1971, in Press.
257
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Ibid, Appendix III, "Graphical Summation of Appendices I and II
by Coalbeds and Regions," in Press.
9. Hoffman, L., et al. "Survey of Coal Availabilities by Sulfur
Content," MITRE Corporation Technical Report MTR-6086, May 1972
10. "An Evaluation of Coal Cleaning Processes and Techniques for Re-
moving Pyritic Sulfur from Fine Coal," Bituminous Coal Research,
Inc., Monroeville, Pennsylvania, February 1970.
11. R. J. Helfinstine, N. F. Shimp, J. A. Simon, and M. E. Hopkins,
"Sulfur Reduction in Illinois Coals - Washability Studies," Re-
port of Study Phase II, supported in part by U.S. Public Health
Service, Department of Health, Education and Welfare, Contract
No. PH86-67-206, Illinois State Geological Survey, Urbana,
Illinois, July 28, 1971.
12. J. A. Cavallaro, A. W. Deurbrouck, and A. F. Baker, "Physical
Desulfurization of Coal," Paper D28, Bureau of Mines, United
States Department of the Interior.
13. K. J. Miller and A. F. Baker, "Electrophoretic - Specific Gravity
Separation of Pyrite from Coal," Bureau of Mines Report of
Investigations, October 1970.
14. A. W. Deurbrouck, Private Communication.
15. A. F. Baker and K. J. Miller, "Hydrolyzed Metal Ions as Pyrite
Depressants in Coal Flotation: A Laboratory Study," Report of
Bureau of Mines Investigations 7518, May 1971.
16. K. J. Miller and A. F. Baker, "Flotation of Pyrite from Coal,"
Bureau of Mines, Technical Progress Report«-51, February 1972.
17. J. A. Cavallaro and A. W- Deurbrouck, "Froth Flotation Washability
Data of Various Appalachian Coals Using Timed Release Analysis
Technique," U.S. Bureau of Mines Report No. RI6652, 1965.
18. Roberts and Schaefer Company, "Design and Cost Analysis for a
Prototype Coal Cleaning Plant," Volume 1, July 15, 1969, Revised
August 12, 1969.
19. Roberts and Schaefer Company, "Design and Cost Analysis for a
Prototype Coal Cleaning Plant," Volume 2, July 15, 1969,
Revised August 12, 1969.
20. Roberts and Schaefer Company, "Supplemental Report to Design and
Cost Analysis Study for a Prototype Coal Cleaning Plant," January
7, 1970.
258
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21. 'McNally, Pittsburg Mgf. Corp. "A Study on Design and Cost Analysis
of a Prototype Coal Cleaning Plant," Prepared for National Air
Pollution Control Administration Contract PH22-68-59, Parts I-VI,
November 1969.
Ibid., Part VII, "Coal Cleaning Plant: Prototype Plant Specifi-
cations"
Ibid., Part VIII, "Coal Cleaning Plant: Prototype Plant Design
Drawings"
22. Roberts and Schaefer Company, "Research Program for the Prototype
Coal Cleaning Plant," Contract No. CPA 70-157, Program Element
No. IA2013, January 1973.
23. Bechtel Corporation, "Process Costs and Economics of Pyrite-Coal
Utilization," A Report to National Air Pollution Control Adminis-
tration, Contract No. PH86-27-224, December 1968.
24. Arthur D. Little, Inc., "A Study of Process Costs and Economics
of Pyrite-Coal Utilization, A Report to Consumer Protection and
Environmental Health Service, Contract No. PH86-27-258, March 1968.
25. Chemico, "The High Sulfur Combustor," Final Report to Division of
Process Control Engineering, National Air Pollution Control Adminis-
tration, Contract No. CPA22-69-151, February 1971.
Ibid., Volume II.
ADDITIONAL REFERENCES
A. W. Deurbrouck and E. R. Palowitch, "Performance Characteristics
of Coal-Washing Equipment: Concentrating Tables," Report of In-
vestigations 6239, Bureau of Mines, United States Department of
the Interior, 1963.
Deurbrouck, Albert W., "Performance Characteristics of Coal-Washing
Equipment: Hydrocyclones," Report of Investigations 7891, Bureau of
Mines, United States Department of the Interior, 1974.
Joseph W. Leonard and David R. Mitchell, Eds., "Coal Preparation,"
3rd ed,, The American Institute of Mining, Metallurgical, and
Petroleum Engineers, Inc., New York, N.Y., 1968.
R. J. Helfinstine, N. F. Shrimp, J. A. Simon, and M. E. Hopkins,
"Sulfur Reduction of Illinois Coals - Washability Studies Part 1,"
Circular 462, Illinois State Geological Survey, Urbana, Illinois,
1971.
259
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Miller, Kenneth J., "Flotation of Pyrite from Coal: Pilot Plant Study,"
Report of Investigations 7822, Bureau of Mines, United States Department
of the Interior, 1973.
260
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TECHNICAL REPORT DATA
(Please reaJ iHsiriictiuns on I/it- reverse before coii
1. REPORT NO.
EPA-650/2-74-030
2.
3. RECIPIENT'S ACCESSION-NO.
. TITLE AND SUBTITLE
An Interpretative Compilation of EPA Studies
Related to Coal Quality and Cleanability
G. REPORT DATE
May 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
L.Hoffman, J. B. Truett, and S.J. Aresco
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
The Mitre Corporation
Westgate Research Park
McLean, Virginia 22101
10. PROGRAM ELEMENT NO.
1AB013; ROAP 21AFJ-27
11. CONTRACT/GRANT NO.
68-02-1352
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
NERC-RTP, Control Systems Laboratory
Research Triangle Park, NC 27711
13»TYPJE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The report provides an interpretative compilation of the overall EPA coal cleaning
effort in the form of in-depth analysis, evaluation, and examination of the inter-
relationships among elements comprising the EPA coal program. The report
basically addresses coal washability studies , sulfur reduction by cleaning processes
including plant design and associated economics , and the utilization of reject sulfur
and coal values from the cleaning processes.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATl l-'icld/Group
Air Pollution
Coal
Coal Preparation
Washing
Desulfurization
Sulfur
Design Criteria
Economic Analysis
Reclamation
Air Pollution Control
Stationary Sources
Reject Sulfur
Reject Coal Values
13B, 14A
21D
081
13H, 07A
07D
07B
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
276
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
261
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