DOE
EPA
United Stales
Department of
Energy
Sol id Fuel s Mining
and Preparation Division
Washington DC 20241
United States
Environmental Protection
Agency
Office of Energy, Minerals, and
Industry
Washington DC 20460
EPA-600/7-78-124
July 1978
Research and Development
An Engineering/
Economic Analysis
of Coal Preparation
Plant Operation
and Cost
Interagency
Energy/Environment
R&D Program
Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1 Environmental Health Effects Research
2, Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161
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EPA-600/7-78-124
July 1978
AN ENGINEERING/ECONOMIC ANALYSIS OF
COAL PREPARATION PLANT OPERATION AND COST
UNITED STATES DEPARTMENT OF ENERGY
SOLID FUELS MINING AND PREPARATION DIVISION
WASHINGTON, D.C. 20241
Contract Number ET-75-C-01-9025
OFFICE OF ENERGY, MINERALS, AND INDUSTRY
OFFICE OF RESEARCH AND DEVELOPMENT
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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DISCLAIMER NOTICE
THE VIEWS AND CONCLUSIONS CONTAINED IN THIS DOCUMENT ARE THOSE OF THE
AUTHOR AND SHOULD NOT BE INTERPRETED AS NECESSARILY REPRESENTING THE
OFFICIAL POLICIES OR RECOMMENDATIONS OF THE DEPARTMENT OF ENERGY OR
THE UNITED STATES GOVERNMENT.
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PREFACE
The following report presents the results of a study conducted by
the Hoffman-Muntner Corporation of Silver Spring, Maryland, for the
United States Department of Energy under Contract Number ET-75-C-01-9025.
This effort, funded through the Federal Interagency Energy/Environment
Research and Development Program, was performed under the technical
direction of Mr. W. E. Warnke of the U. S. Department of Energy, Solid
Fuels Mining and Preparation Divison. The purpose of this study was to
identify the costs associated with the various types and levels of physical
coal preparation processes currently available. Although data of this
type have been previously generated in fragmented form, it was the objec-
tive of this study to give a comprehensive presentation having a uniform
time base. A methodology was developed that permits meaningful comparison
of the relative costs of coal cleaning. This technique was applied to
current technology and economics, but can also be utilized in the future
with appropriate index adjustment.
To accomplish this objective, eight existing coal preparation plants
were selected for anaylsis. These plants range in complexity from a rela-
tively simple jig plant to a rather sophisticated preparation circuit
utilizing heavy media, froth flotation, and thermal drying. Each of
these plants is discussed separately with an analysis of the individual
process and the level of cleaning achieved as supported by the specific
washability data. Additionally, the major cost components such as capital,
labor, and materials are summarized to arrive at the total cost of clean-
ing for each plant. These analyses are presented from the perspective
of the preparation plant operator and do not assess the many user oriented
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benefits resulting from coal cleaning. In addition to increased heat
content, these benefits include lower emission control, transportation,
boiler maintenance, and ash disposal costs.
For background, general discussions are provided covering the various
types of coal cleaning processes. These discussions include brief de-
scriptions of the processes and associated equipment with cost data de-
tailing their impacts on the total cost of preparation.
ACKNOWLEDGEMENTS
The author wishes to express sincere appreciation to those many
dedicated individuals in the coal industry who took the time out from
their busy schedules to make available the current preparation plant
operating data, a portion of which is summarized in Section 5.0. With-
out their patience and understanding, this study could never have been
accomplished. Further, the author wishes to extend many thanks to those
knowledgeable members of the preparation equipment manufacturing community
who were so very cooperative in providing the price and technical data in-
cluded throughout this report. Finally, the author wishes to convey a
special expression of appreciation to Messrs. W. E. Warnke, A. W. Deurbrouck,
and R. E. Hucko of the Department of Energy, Solid Fuels Mining and Prepara-
i i
tion Divison, for their valuable counsel and constructive suggestions
during the course of the program. It was indeed an honor and privilege
to work on an important study of this type with so many capable personnel,
too numerous to mention.
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TABLE OF CONTENTS
Page
PREFACE i
ACKNOWLEDGEMENTS , i i
LIST OF FIGURES vi
LIST OF TABLES ix
1.0 INTRODUCTION 1
2.0 PREPARATION PLANT COMPLEX 8
2.1 Coal Handling and Storage 14
2.1.1 Coal Storage 15
2.1.2 Conveyors 18
2.1.3 Tramp Iron Removal 20
2.1.4 Loading Facilities 22
2.2 Cleaning Equipment 25
2.2.1 Size Reduction Equipment 30
2.2.2 Screens 40
2.2.3 Baum Jig 53
2.2.4 Heavy Media Vessels 64
2.2.5 Cycl ones 67
2.2.6 Concentrati ng Tables 77
2.2.7 Froth Flotation .\. 84
2.3 Other Equipment and Facilities 89
2.3.1 Dewatering Equipment 89
2.3.1.1 Centrifugal Dewatering Equipment 90
2.3.1.2 Vacuum Disc Filter 99
2.3.1.3 Vor-Siv 102
2.3.1.4 Thermal Dryer 106
2.2.2 Static Thickener 113
2.2.3 Coal Sampling Equipment 116
3.0 SMALLER SIZE PREPARATION PLANTS 119
4.0 OPERATIONAL AND OTHER FACTORS INFLUENCING COST 128
4.1 Plant Utilization 129
4.2 Coal Quality 133
4.3 Capital Amortization 135
4.3.1 Capital Amortization Defined 135
4.3.2 Capital Amortization Applied 137
4.4 Cost of Btu Loss in Cleaning 143
m
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TABLE OF CONTENTS (Continued)
Page
5.0 PREPARATION PROCESS EXAMPLES I46
5.1 Example 1 - Jig Process - Simple I48
5.1.1 General Description 148
5.1.2 Capital Amortization I59
5.1.3 Operating & Maintenance Costs 159
5.1.4 Discussion of Performance and Cost 161
5.2 Example 2 - Jig Process - Intermediate 164
5.2.1 General Description 164
5.2.2 Capital Amortization 176
5.2.3 Operating & Maintenance Costs 176
5.2.4 Discussion of Performance and Cost 178
5.3 Example 3 - Jig Process - Intermediate 180
5.3.1 General Description 180
5.3.2 Capital Amortization 191
5.3.3 Operating & Maintenance Costs 191
5.3.4 Discussion of Performance and Cost 193
5.4 Example 4 - Jig Process - Complex 196
5.4.1 General Description 196
5.4.2 Capital Amortization 212
5.4.3 Operating & Maintenance Costs 212
5.4.4 Discussion of Performance and Cost 214
5.5 Example 5 - Heavy Media Process - Simple 217
5.5.1 General Description 217
5.5.2 Capital Amortization 228
5.5.3 Operating & Maintenance Costs 228
5.5.4 Discussion of Performance and Cost.. 230
5.6 Example 6 - Heavy Media Process - Complex 232
5.6.1 General Description 232
5.6.2 Capi tal Amorti zati on 246
5.6.3 Operating & Maintenance Costs 246
5.6.4 Discussion of Performance and Cost 248
5.7 Example 7 - Heavy Media Process - Complex 251
5.7.1 General Description 251
5.7.2 Capital Amortization 261
5.7.3 Operating & Maintenance Costs 261
5.7.4 Discussion of Performance and Cost 263
5.8 Example 8 - Heavy Media Process - Complex 265
5.8.1 General Description 265
5.8.2 Capital Amortization 282
5.8.3 Operating & Maintenance Costs 282
5.8.4 Discussion of Performance and Cost 284
IV
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TABLE OF CONTENTS (Continued)
Page
5.9 Summary of Preparation Process Examples 285
6.0 FUTURE PROSPECTS FOR COAL PREPARATION 287
REPORT DOCUMENTATION PAGE With Abstract 297
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LIST OF FIGURES
Figure Number Page
2-1 Typical Coal Preparation Complex 9
2-2 Cleaning Plant Central Control Panel 12
2-3 Coal Storage Silo 17
2-4 Tramp Iron Removal From Raw Coal 20
2-5 Rotary Breaker Installation 30
2-6 Cutaway View of Rotary Breaker. 31
2-7 Primary Size Reduction Equipment 34
2-8 Application of Scalping Screen 42
2-9 Application of Raw Coal Sizing Screen 43
2-10 Pre-Wet Screen i n Operati on 45
2-11 Applicaton of Desliming Screen 46
2-12 Drain and Rinse Screen For Heavy Media Recovery .. 48
2-13 Sieve Bend Mounted Ahead of Vibrating Screen 50
2-14 Cutaway View of Sieve Bend Manufactured by
Heyl & Patterson, Inc 51
2-15 Cutaway Views of Baum Jig 56
2-16 Cutaway Views of Batac Jig 62
2-17 Daniels Heavy Media Precision Washer 66
2-18 Heavy Media Cyclone in Inclined Position 70
2-19 Cutaway View of Operating Cyclone 71
2-20 Water-Only Cyclone Installation 72
2-21 Top View of Concentrating Table with Distribution
of Products by Si ze 78
2-22 Double-Deck Concentrating Table
(Deister Concenco "88") 82
VI
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LIST OF FIGURES (Continued)
Figure Number Page
2-23 Froth Flotation Cells in Operation 85
2-24 Vibrating Screen Basket Centrifugal Dryer-
Horizontal Type (WEMCO Model 1100) 91
2-25 Vibrating Screen Basket Centrifugal Dryer-
Vertical Type (H & P Hurricane Model) 93
2-26 Scroll Type Centrifugal Dryers (CMI Model EB-36).. 95
2-27 Vacuum Disc Filter (10 Feet 6 Inch Diameter 12
Disc Version) 100
2-28 Vor-Siv Conical Sieve 103
2-29 Fluid-Bed Thermal Dryer Installation
(FMC Fluid-Flo Model) 109
2-30 Cutaway View of Fluid-Bed Thermal Dryer
(ENI Coal-Flo Model) 110
2-31 Cross-Section of Static Thickener 114
2-32 Top View of Static Thickener 115
2-33 Three-Stage Coal Sampling System - (Denver
Equipment Division of Joy) 118
3-1 Layout of Unitized Jig 121
3-2 Flow Sheet of Unitized Jig Plant 122
3-3 Two-Cell Diaphragm Jig 123
5-1 Example 1 - Jig Process - Simple
Preparation Plant Flow Sheet 149
5-2 Example 2 - Jig Process - Intermediate
Preparation Plant Flow Sheet 165
5-3 Example 3 - Jig Process - Intermediate
Preparation Plant Flow Sheet 181
5-4 Example 4 - Jig Process - Complex
Preparation Plant Flow Sheet 197
5-5 Example 5 - Heavy Media Process - Simple
Preparation Plant Flow Sheet 218
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LIST OF FIGURES (Continued)
Figure Number Page
5-6 Example 6 - Heavy Media Process - Complex
Preparation Plant Flowsheet 233
5-7 Example 7 - Heavy Media Process - Complex
Preparation Plant Flow Sheet 252
5-8 Example 8 - Heavy Media Process - Complex
Preparation Plant Flow Sheet 266
6-1 Hypothetical Flotation Plant With Fine
Refuse Disposal - Simplified Process Flow Sheet..290
vm
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LIST OF TABLES
Table Number page
2-1 Clean Coal Produced Annually by Major
Mechanical Cleaning Methods 54
2-2 VC-48 and'vC-56 Capacity and Performance 94
2-3 Model EB-36 Capacity and Performance 96
2-4 Coal Thermally Dried In Comparison to
Annual Product! on 107
5-1 Example 1 - Jig Process - Simple
Preparation Plant Performance 152
5-2 Example 1 - Jig Process - Simple
Washability Data of Assumed Plant Feed -
3/4 Inch Fraction 153
5-3 Example 1 - Jig Process - Simple
Washability Data of Assumed Plant Feed -
3/4 Inch X 0 Fraction 154
5-4 Example 1 - Jig Process - Simple
Preparation Plant Operating and Maintenance
Personnel 155
5-5 Example 1 - Jig process - Simple
Preparation Plant Capital Requirements 156
5-6 Example 1 - Jig Process - Simple
Operating and Maintenance Costs 160
5-7 Example 2 - Jig Process - Intermediate
Preparation Plant Performance 168
5-8 Example 2 - Jig Process - Intermediate.
Cumulative Washability Data of Assumed
PI ant Feed 169
5-9 Example 2 - Jig Process - Intermediate
Preparation Plant Operating and
Maintenance Personnel 170
5-10 Example 2 - Jig Process - Intermediate
Preparation Plant Capital Requirements 172
5-11 Example 2 - Jig Process - Intermediate
Operating and Maintenance Costs 177
IX
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LIST OF TABLES (Continued)
Table Number Page
5-12 Example 3 - Jig Process-- Intermediate
Preparation Plant Performance ...................... 184
5-13 Example 3 - Jig Process - Intermediate
Composition of Assumed Plant Feed By
Size Fraction
5-14 Example 3 - Jig Process - Intermediate
Cumulative Washability Data of Assumed
Plant Feed ........................................... 186
5-15 Example 3 - Jig Process - Intermediate
Preparation Plant Operating and
Mai ntenance Personnel ............................... 187
5-16 Example 3 - Jig Process - Intermediate
Preparation Plant Capital Requirements ............. 188
5-17 Example 3 - Jig Process - Intermediate
Operating and Maintenance Costs .................... 192
5-18 Example 4 - Jig Process - Complex
Preparation Plant Performance ....................... 201
5-19 Example 4 - Jig Process - Complex
Composition of Assumed Plant Feed by
Size Fraction ...................................... 202
5-20 Example 4 - Jig Process - Complex
Composition of Assumed Feed to Batac
Jigs by Size Fraction .............................. 203
5-21 Example 4 - Jig Process - Complex
Cumulative Washability Data of Assumed
Feed to Batac Ji gs ................................. 204
5-22 Example 4 - Jig Process - Complex
Preparation Plant Operating and
Maintenance Personnel ............................... 205
5-23 Example 4 - Jig Process - Complex
Preparation Plant Capital Requirements ............. 207
5-24 Example 4 - Jig Process - Complex
Operating and Maintenance Costs .................. ____ 213
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LIST OF TABLES (Continued)
Table Number
5-25 Example 5 - Heavy Media Process - Simple
Preparati on PI ant Performance 222
5-26 Example 5 - Heavy Media Process - Simple
Preparation Plant Operating and Maintenance
Personnel 223
5-27 Example 5 - Heavy Media Process - Simple
Preparation Plant Capital Requirements 224
5-28 Example 5 - Heavy Media Process - Simple
Operating and Maintenance Costs 229
5-29 Example 6 - Heavy Media Process - Complex
Preparation Plant Performance 236
5-30 Example 6 - Heavy Media Process - Complex
Washability Data of Assumed Plant Feed - •>
3/4 X % mm 237
5-31 ^ Example 6 - Heavy Media Process - Complex
Washability Data of Assumed Plant Feed -
7h X 3/4 Inch Fraction 238
5-32 Example 6 - Heavy Media Process - Complex
Preparation Plant Operating and Maintenance
Personnel 239
5-33 Example 6 - Heavy Media Process - Complex
Preparation Plant Capital Requirements 241
5-34 Heavy Media Process - Complex
Operating and Maintenance Costs 247
5-35 Example 7 - Heavy Media Process - Complex
Preparation Plant Performance 255
5-36 Example 7 - Heavy Media Process - Complex
Preparation Plant Operating and Maintenance
Personnel 256
5-37 Example 7 - Heavy Media Process - Complex
Preparation Plant Capital Requirements 257
5-38 Example 7 - Heavy Media Process - Complex
Operating and Maintenance Costs 262
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LIST OF TABLES (Continued)
Table Number Page
5-39 Example 8 - Heavy Media Process - Complex
Preparation Plant Performance 270
5-40 Example 8 - Heavy Media Process - Complex
Washability Data of Assumed Plant Feed -
1% X 3/8 Inch Fraction 271
5-41 Example 8 - Heavy Media Process - Complex
Washability Data of Assumed Plant Feed -
3/8 X 1/8 Inch Fraction 272
5-42 Example 8 - Heavy Media Process - Complex
Washability Data of Assumed Plant Feed -
1/8 X 0 Inch Fraction 273
5-43 Example 8 - Heavy Media Process - Complex
Preparation Plant Operating and Maintenance
Personnel 274
5-44 Example 8 - Heavy Media Process - Complex
Preparation Plant Capital Requirements • 276
5-45 Example 8 - Heavy Media Process - Complex
Operating and Maintenance Costs 283
5-46 Summary of Preparation Process Examples. 286
6-1 Hypothetical Flotation Plant With Fine Refuse
Disposal - Preparation Plant Capital Requirements.. 292
6-2 Hypothetical Flotation Plant With Fine Refuse
Disposal - Operating and Maintenance Costs 295
xii
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SECTION 1,0
INTRODUCTION
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1.0 INTRODUCTION
Unlike the manufacture of certain chemicals and metals where a
specific process will give reasonably constant results, there is no
universal approach to the production of clean coal by physical preparation
techniques. This occurs due to the substantial variability in the physical
and chemical composition of coal from seam to seam and even within the seam
itself. Therefore, a given preparation process that is effective with a
coal from one seam may be inappropriate with a coal from another seam in
achieving a comparable level of cleaning. For this reason, the particular
approach taken to coal cleaning must be designed around the specific coal
and the desired end results within the economic constraints of the situation.
Although there is a myriad of approaches to coal cleaning, the
technology is founded on relatively few basic physical principles.
Nearly all physical cleaning techniques being applied today rely either
upon specific gravity or surface characteristics to effect a separation
of the coal from the undesirable constituents such as ash and pyritic sulfur.
Most of the specific gravity processes and all of those relying upon
surface characteristics are wet in nature. For those wet processes
based upon specific gravity, the medium of separation is water either by
itself or mixed with a substance such as magnetite to give the mixture
a density slightly greater than that of coal. These processes are per-
formed in a variety of vessels and other devices described in Section 2.0
of this study. The major process based upon surface characteristics (or
surface chemistry) is froth flotation. As covered in more detail by
Section 2.2.7, this process creates a condition which encourages the coal
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to adhere to air bubbles and float and the refuse to sink. In a coal
preparation plant, these physical separation techniques are applied by
themselves or in combination to most economically achieve a desirable
end product given the physical and chemical composition of the raw coal.
To determine the physical and chemical properties of the raw coal
around which the preparation process is designed, it is necessary to
obtain a representative sample. The importance of this sample cannot be
overemphasized since it constitutes the root of flow sheet (process)
design and thus equipment selection. A screen analysis is normally made
of this sample showing the size consist of the future plant feed. This
has particular significance by showing the amount of finer material in
the feed which is a critical factor in selecting the cleaning approach
and sizing the equipment. Further, a washability study (float and sink
analysis) is made of these size fractions to show the separation of coal
from the undesirable constituents (ash and sulfur) at various specific
gravities. The combination of this data permits the preparation plant
designer to focus on the critical points of separation and thereby de-
termine the approach best suited to achieve the desired results. In
many situations, the process objective is to maximize the reduction of
ash forming constituents. However, in light of today's increasing en-
vironmental restrictions, the optimization of sulfur removal as well as
ash is of prime importance.
Many times the material on which this detailed analysis is performed
is obtained from core samples which are seldom representative of the raw
coal as mined. This occurs because an insufficient number of samples are
collected and the mininq method directly influences the amount of refuse
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and fines in the mined product. Unfortunately, this situation can be
very costly and necessitate substantial plant redesign in order to
approximate the projected plant performance. For this reason, more ex-
tensive sampling should be conducted and performed in a manner which
closely simulates the effects of the particular recovery (mining) tech-
nique.
Since there is by necessity such a variety of approaches to the
physical preparation of coal, there is no single figure for the "cost
of coal cleaning." Our studies have shown there is a range of costs
from less than $2.00 to over $4.00 per ton of raw plant feed depend-
ing upon the capacity and make-up of the preparation circuit. Each
cost within this range is a composite of the capital and operating
and maintenance costs associated with a specific plant during a given
time frame. Time is a factor due to the inherent variability within
any given coal seam as previously mentioned. Although two preparation
plants may have an identical input capacity and essentially the same
equipment, their individual "cost of cleaning" will more than likely
be different for a variety of reasons. Assuming consistent accounting
methods, these reasons include differences in: 1) raw coal feed;
2) operating procedures; 3) clean coal specification; and 4) local
cost of labor, material, and services. Many times these differences
can be significant due to more or less advantageous conditions for
refuse disposal. In spite of the specificity of coal cleaning costs,
meaningful generalizations can be made concerning the cost of various
processes. At the lower end of the above range ($?..00 to $4.00 per ton
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input), would be an intermediate size plant screening out the finer
material and cleaning only the coarser size fractions with inexpensive
equipment such as the Baum jig. The upper end of the range, approaching
$4.00 per ton input, would be representative of a plant cleaning all
size fractions with thorough treatment of the finer material by
such equipment as heavy media cyclones and froth flotation in addition
to fairly extensive thermal drying.
It should be noted that this range of cleaning costs is that ex-
perienced by the coal preparation plant operators. However, this is
only a portion of the economic equation for coal cleaning. In order to
determine the true (net) cost of preparation from an overall economic
perspective one must also account for the benefits accruing to the user
of clean coal. These benefits which should appropriately be set off
against the operator's cost include:
1. Increased Heat Content of Cleaned Coal
(Greater Btu content per unit weight)
2. Transportation Savings
(Less weight to ship for same Btu content)
3. Pulverizing Cost Savings
(Less cleaned coal needs to be pulverized for same Btu content
required to meet output)
4. Boiler and Related Equipment Maintenance Savings
(Clean coal is less corrosive)
5. Ash Disposal Cost Saving
(Clean coal leaves less bottom and fly ash)
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6. Lower Emission Control Costs
(Less particulate and SCL from clean coal)
This being the case, the complete equation for coal preparation
is:
Net Cost of Cleaning = Operator's Cost - User Benefits
Since these user benefits can only be accurately quantified on a
site specific basis, they are not considered by this study. Only the
range of operator's cost will be addressed.
It is the primary purpose of this study to give better definition
to this wide range of costs. This is accomplished by looking at a
spectrum of actual preparation plants and examining the major elements
in their particular cost of cleaning. These eight plants presented in
Section 5.0 range from a relatively simple jig plant to a variety of
fairly complex preparation circuits utilizing a number of heavy media
techniques, froth flotation, and thermal drying. In each case, a .dis-
cussion is given of the plant performance and cost which identifies
for the reader those factors in the design of the plant and/or the
manner in which it is being operated which are most influential on
cost. Using the cost relationships from these actual preparation plant
examples as a base and one's own washability data, the capital and
operating and maintenance (O&M) cost of almost any contemporary cleaning
process can be estimated with reasonable accuracy. Understandably, the cost
developed in this manner for any given process handling a particular
coal would only be an approximation of what might be experienced. How-
ever, it should be a useful planning tool for the would-be preparation
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plant operator to anticipate capital requirements and O&M costs.
Such information permits an assessment of market conditions in relation-
ship to the minimum price for which the clean coal could be sold to
yield a certain rate of return or otherwise satisfy one's economic
criteria for investment.
In the following section, a brief discussion is presented of each
major element within the preparation plant complex and, as appropriate,
how it generally impacts the capital requirements and O&M cost. This
discussion is also intended to give the reader some broad exposure
to the technical aspects of coal preparation which should aid in
understanding the sensitivity of cleaning cost to approach and
operational variances.
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SECTION 2,0
PREPARATION PLMT COFPLEX
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2.0 PREPARATION PLANT COMPLEX
As addressed by this study, the coal preparation complex consists
of the cleaning plant and any outside facilities and equipment associated
with the cleaning process. These additional items include the raw and
clean coal storage areas, water clarification facilities (ponds or
thickeners), conveyors, coal and refuse vehicles, sampling system, load-
out facility, and thermal drying if applicable. A typical preparation
complex is arranged as shown in Figure 2-1 below.
RAW COAL BELT
CLEANING
PLANT
CLEAN COAL BELT
THERMAL DRYER
STATIC THICKENER
FIGURE 2-1
TYPICAL COAL PREPARATION COMPLEX
9
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Layout -
Normally, it is desirable to locate the preparation complex as close
as possible to both the mining activity and transportation. This elimi-
nates much of the initial expense and long term maintenance of long dis-
tance conveying, trucking, or other means of getting the coal to the plant
and then to a suitable location for final transport to market. However,
this is not always possible due to the unavailability of sufficient land
area, required services, or unsuitable topography. Therefore, the final
selection of the preparation plant site must be made on the basis of the
economic and practical realities of the given situation.
Once a suitable site is selected, the layout of the complex will
be a function of capacity and cleaning approach. Regardless of the approach,
most cleaning plants are multi-level steel frame buildings reaching 100
feet or more in height. This type of sturdy construction is necessary to
support the vibrating and other heavy equipment in addition to the weight
of the material flow. Some cleaning plants have as many as twelve levels
permitting the preparation equipment to be sequentially located on various
floors to make the most efficient use of gravity. In addition to reducing
the initial cost of the plant, this arrangement helps to lower the operating
and maintenance cost by limiting the pumping and piping requirements.
Construction -
Although the actual construction of even a large preparation complex
can be accomplished within a year, a minimum of three years is more reason-
able in view of today's conditions. The major contributor to this extended
period is the governmental requirement that an environmental impact statement
(EIS) be filed and approved before a preparation plant can be built. Assuming
10
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there are no problems with filing the EIS, a minimum of 18 months is re-
quired for compliance. This period further assumes there are no law suits
filed and all paperwork is processed by EPA in a timely fashion. Unfortun-
ately, this situation presents a real problem to the organization behind
the future plant in terms of arranging financing and making other commit-
ments. While this lengthy process goes on, costs rise and previous plans
need to be reevaluated. Another factor to be considered which can in-
fluence the construction period is the equipment lead-time. Many essential
items such as belting have a delivery of one year or more.
It is not uncommon to arrange for construction of the entire coal
preparation complex under one contract. Although the prime contractor
is responsible for "delivering" the complex on a turn-key basis, many
subcontractors are involved due to the diversity of specialities required.
Prior to 1970 such contracts were almost always firm fixed price. How-
ever, since the early 1970's, most construction agreements are carefully
worded to allow for cost escalation as a result of material price in-
creases and sometimes labor.
Operation -
All of the larger cleaning plants being built today are operated
from a central control room with the aid of sophisticated electronics.
This permits a single cleaning plant operator to monitor the functioning
of a facility handling 1500 tons per hour or more of raw coal. By look-
ing at a single control panel of the type shown in Figure 2-2 , the
operator can tell whether or not each major piece of equipment within
the plant is operating. Should a serious problem develop within the
plant, all affected equipment is automatically shut down to avoid damage.
11
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In addition to the plant operator, there are a number of other per-
sonnel required to operate and maintain a preparation complex.
For more detail on the numbers and types of such
personnel, the reader is referred to the
specific plant examples
presented in Section 5.0,
Figure 2-2
Cleaning Plant Central Control Panel
Cost -
As of mid-1977, the total capital cost for the larger coal prepara-
tion complexes examined by this study was in a range from around $7,000
to $23,000 per ton hour input. These eight plants had design input
12
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capacities from as much as 1600 tons per hour (tph) down to 600 tph.
Although capital costs for plants in this range are somewhat sensitive
to capacity, they are influenced most by the sophistication of the
cleaning plant itself and the outside facilities such as thermal dryers.
In this regard, some plants will have complete or partial redundancy of
critical pieces of higher maintenance equipment. Such an arrangement
permits servicing of these items without shutting down the entire plant.
The additional capital cost of this arrangement can many times be justi-
fied on the basis of increased operating efficiency and output. An ex-
pansion of this theory is the implementation of complete parallel clean-
ing circuits which theoretically makes the plant capable of continuous
operation at varying levels of production. Another factor which can have a
significant impact upon the initial cost of a complex is the amount of site
preparation required. The capital cost for each of the preparation plants
examined by the study is presented in detail by Section 5.0 along with a
discussion of which elements have the greatest cost impacts.
The balance of this section is devoted to a brief description of
the major elements comprising the preparation plant complex. For ease
of understanding, these have been separated into three categories,
1) Coal Handling and Storage; 2) Cleaning Equipment; and 3) Other
Facilities. As appropriate, the influence of each major element upon
the total cost of the preparation complex is given.
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2.1 Coal Handling and Storage
Depending upon the layout of the particular preparation plant a
significant portion of the total capital investment will be tied up in
coal handling and storage equipment and facilities. As addressed by
this study, this category of items includes:
1) Raw and Clean Coal Storage;
2) Conveyors Handling Coal & Refuse;
3) , Removal of Tramp Iron; and
4) Clean Coal Loading Facilities.
Certainly, the cost of all of these items will vary with the magnitude
of the plant. However, additionally their cost will be quite sensitive
to geographic, environmental, and other factors based upon the site
specific conditions. In the case of coal storage, closed or silo storage
will cost about five times as much as an open pile of comparable capacity.
Even though this is a severe cost penalty to pay for the advantages of
closed storage, it might possibly be justified on economic grounds and/
or necessary to meet local environmental restrictions. Conveyors are
another major expense which vary mostly with the plant layout. However,
other factors such as the need for secure enclosures or special founda-
tions and supports can radically affect their costs. Loading facilities
also vary significantly from plant to plant depending upon their level
of sophistication. The following subsections describe these coal
handling and storage facilities items in greater detail and some of the
principal factors influencing their cost.
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2.1.1 Coal Storage
The storage of the raw coal prior to entering the preparation plant
as well as the clean product itself is a significant factor in the over-
all plant layout. At the raw coal end, adequate storage must be avail-
able to allow for fluctuations in the mining activities while maintaining
a sufficient backlog of material to be efficiently fed to the preparation
plant. Likewise, at the clean coal end, adequate storage arrangements
must be made consistent with the operation of the plant and shipping
commitments/schedules. Whether the clean coal is transported to the user
via barge, unit train, or truck, the storage arrangement must provide for
the efficient withdrawal of the material to minimize loading time.
The options for storage are either open or closed. In this country
the trend is toward closed storage in the form of large cast-in-place
concrete silos holding as much as 15,000 tons. However, in some situations,
the classic open storage consisting of a stacking tube and reciprocating
feeders is still determined to be appropriate. The shift toward silos
is evidenced by the fact that one large organization engaged in the con-
struction of both forms of storage, indicates it is booking orders for
silos at the rate of better than 10 to 1 over open style arrangements.
Factors influencing the use of silos rather than open storage include:
1. Helps insure consistency of feed to preparation plant. Typically,
a more uniform material in size and moisture content is withdrawn
from a silo.
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2. Environmental. Due to the dust and run-off from open coal
storage,many situations dictate the use of closed storage. In
areas near urban centers, regulatory bodies demand such arrangements,
3. Space Considerations. Since a silo requires less land for the
same volume of storage, the price and availability of such
additional space can sometimes be a determining factor.
4. Protection from Freezing. Frozen coal piles can be not only an
inconvenience but a costly problem. Although silos provide
greater protection from moisture and thus freezing, freeze-up
can occur during extended severe cold periods such as the winter
of 76-77. When this does occur, it requires the top layer to be
broken-up with jack-hammers or other methods.
5. Aesthetics. Either for internal reasons or external pressures,
appearance can influence the selection of closed storage.
Although the cost of maintaining a concrete silo is limited, some
periodic maintenance is required. Patching or replacement of portions of
the lining must be performed from time to time. If coal is permitted to
directly impact the side of the silo at the intake, it will eventually
wear through the wall. To avoid or mitigate this situation, baffle plates
are being installed on many existing silos and most new ones to deflect the
material. These plates must be replaced periodically to avoid costly
damage to the silo.
Today, it is not uncommon to have single coal silos in the range of
10,000 to 15,000 tons. When greater storage capacity is required, multiple-
silo configurations are applied. The cost of silos in this tonnage class
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will range from $50 to $125 per ton of storage. This wide variance
relates to local geologic conditions and the cost and availability of
labor and materials. As an example, in parts of Illinois, concrete can
be purchased for as little as $30 per cubic yard, whereas in certain
West Virginia locations the same volume of mix will cost as much as $75.
These enormous differences in material cost relate to local competitive
conditions and the distance from source to construction site of not
only the mixed concrete but the components of the mix.
For the purpose of approximating the current (mid-1977) capital cost
of the various preparation plants examined under Section 5.0, a cost of
$110 per ton of storage was used for larger cast-in-place concrete silos.
Although in the upper part of the above range, this figure is felt to be
a reasonable estimate of the total cost of such facilities which can be
adjusted by the readers to reflect exceptional conditions in their particular
area. The capital cost determined in this manner is the fully constructed
price of the silo alone and does not include any of the necessary conveyors
to and from the structure. As shown below in Figure 2-3, such conveying
requirements can be extensive.
FIGURE 2-3
COAL STORAGE SILO
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2.1.2 Conveyors
Another element common to all coal preparation plants, regardless
of how simple, is a variety of conveying requirements. These requirements
can be quite extensive depending upon the plant size and layout. For
even medium size operations, it is not uncommon to move material several
hundred feet from raw coal storage into the plant and then a comparable
distance from the plant to the load-out area. Additionally, conveyors
are required to handle the refuse from the plant and if thermal drying
is included a further conveying requirement must be met.
Although vibrating conveyors have some application for moving coal
short distances in and around a preparation plant, their use is limited.
The major conveying requirements are met with belt conveyors which come
in a wide range of sizes and configurations. As applied to a preparation
plant, belt conveyors are selected on the basis of their ability to
deliver given dry and wet tonnages between two points at a specified
rate. Such factors influence the belt width and material, idlers, drive
motors, structural requirements, etc.
Belt Conveyor Costs -
Depending upon the width and type of belt, distance traveled,
elevation, and structural and foundation requirements, the price of belt
conveyors will vary significantly. Therefore, based upon a sampling of
mid-1977 prices for actual installations, we have established general
installed pricing guidelines for various belt widths on a per linear
foot basis. These estimated prices have been observed in determining
the capital requirements for the coal preparation plants examined under
Section 5.0 of this study. They are as follows on the next page:
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36 Inch Width - $480 Per Foot
42 Inch Width - $520 Per Foot
48 Inch Width - $560 Per Foot
54 Inch Width - $600 Per Foot
Although there may be special applications for belt conveyors of
smaller or larger widths than those given above, our experience
indicates their use is limited. These prices are indicative of quality
Installations requiring some "normal" foundation work and include all
labor, materials, and electrical hook-up necessary for construction of
a fully tested conveyor. We feel they are valid for estimating the
cost of lengths between 100 to 500 feet which do not have exceptional
elevation requirements. When this occurs, the price can increase by
as much as a factor of two or more. Conversely, when ground level
conveyors can be installed without extensive foundation work, a signi-
ficant savings over these estimated prices will be realized.
Our purpose in identifying the estimating procedure observed is
to give users of the study the opportunity to make their own adjust-
ments for significant variances brought on by unique site specific
conditions. Since certain conveying requirements would exist whether
there was a coal preparation plant or not, only those belts considered
unique to the plant have been included in the capital costs presented
in Section 5.0. For example, transporting of the material from the
mining area to raw coal storage has not been included.
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2.1.3 Tramp Iron Removal
During the mining process, stray ferrous material is loaded out with
the raw coal and can find its way into the preparation plant. This
material comes from broken tools, continuous mining bits, and other miner
induced sources. Although the amount of such material, known as tramp
iron, is relatively small, it can cause significant damage to the coal
preparation equipment if not removed at an early stage in the process.
Some of this debris is removed by rough screening (scalping) or by the
rotary breaker if such steps are in the pre-preparation coal handling
equipment. However, even if these types of equipment are present, it is
common to place an electromagnet over the conveyor belt feeding the plant
to insure the removal of the tramp iron.
Typically the magnet is suspended by threaded rods and turnbuckles
over the trajectory of the material being discharged from the belt con-
veyor as shown in Figure 2-4.
SELF CLEANING
BELT
ELECTROMAGNET
CAPTURED
FERROUS
MATERIAL
FIGURE 2-4
TRAMP IRON REMOVAL FROM RAW COAL
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When the conveyor speed is 350 feet per minute (FPM) or more, this
arrangement promotes maximum removal efficiency since influence of the
magnetic field is most effective when the material is "opened-up" in
flight. Additionally, the material is moving directly toward the face
of the magnet and the momentum of any tramp iron assists in its capture
by the magnet. Such magnets are available in both manual and self-
cleaning types as well as explosion proof designs.
From a design standpoint, the magnet should normally be at least
as wide as the width of the belt. Other factors influencing the
selection of an appropriate tramp iron magnet are:
1. Depth of Feed
2. Suspension Position
3. Tramp Iron Size (minimum & maximum)
4. Size Consist of Feed
5. Belt Speed
6. Feed Rate
7. Operating Temperature Range
8. Head Pulley Material
9. Head Pulley Diameter
10. Available Current (AC or DC)
11. Degree of Troughing Idlers (if magnet is not
placed over head pulley)
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2.1.4 Loading Facilities
Following the preparation process, the clean coal is normally
conveyed to an open or closed storage area to await transportation
to the user via any number of methods. In some cases, this may be as
simple as a conveyor belt direct to the power plant. Where short
distances are involved, trucks also fill an important role. However,
most prepared coal is transported via railroad or barge. When available,
transportation via water is the least expensive of the two major methods.
Barge loading facilities normally consist of a docking area capable of
handling six to eight barges each having a capacity of 1000 to 1500
tons. Coal is fed into the barges via a telescoping tube at the rate
of 1000 to 1500 tons per hour (tph). The cost of such facilities varies
significantly depending upon the difficulty of placing pilings and
other structural members necessary to secure the docking area. How-
ever, based upon the cost of recently completed facilities of this
type, $1.5 million dollars is a good approximation for a river location
capable of loading at the rate of 1000-1500 tph.
The most common method of coal shipment is the railroad. For
obvious reasons, rate preference is given to train-load shipments.
Therefore, it is advantageous to the plant operator, if delivery com-
mitments allow, to accumulate the clean product until there is a suffi-
cient amount of coal to fill a complete train of 80 to 100 cars, each
holding up to 100 tons. For larger coal preparation plants making
numerous train-load shipments annually, it is usually of economic
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benefit to negotiate a unit-train arrangement. Although there is a
variety of unit-train agreements unique to the given situation, the
normal arrangement is to dedicate the particular train to hauling
coal between two specific points over an extended term.
When appropriate to the particular situation, unit train can pro-
vide a substantial savings over regular railroad shipment. In order
to maximize the savings associated with this method of transportation, a
fast efficient loading system must be available. There are currently
in existence many unit train load-out facilities which have the cap-
ability of loading a 100-car train in less than four hours. For ex-
ample, at the Leahy Plant of Amax Coal, cars are automatically flood
loaded at the rate of 5500 tph from a 200-ton over the track, loading
bin. The bin receives 5500 tph via a 296 foot long 7 foot wide belt
from a 15,000 ton concrete silo with eight 750 tph reciprocating
feeders. This rapid car loading rate is possible with the installation
of a special bin with pneumatic gates which are controlled by an elec-
tronic system actuated by beams of light directed across the railroad
tracks. As the cars pass through the beams of light, the position of
the empty hopper is known and the loading bin gates opened or closed
accordingly. With this system, the average 100-car unit train loading
time is broken down as follows:
Train Loading 110 Minutes
Train Switching 100 Minutes
Delays 20 Minutes
Total 230 Minutes or 3 Hours and
50 Minutes
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Similar success has been achieved with over the track silos where
the train passes through a tunnel at the base and is flood loaded.
Although the costs associated with these facilities are justified by
the resultant savings, they add significantly to the initial capital
requirements. Depending upon the sophistication of the arrangement,
unit-train loading facilities will add from $400,000 to a million
dollars or more to the total cost of the complex. Since there is
such a wide cost range, a figure of $500,000 was applied to those prep-
aration plants covered by Section 5.0 where unit-train facilities were
appropriate. This figure was selected as being representative of an
adequate facility which readers may amend to fit their particular
circumstance. Further, the reader may wish to delete such cost en-
tirely on the grounds that it is not attributable to coal preparation
since even without cleaning some type of loading facility would be
required.
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2.2 Cleaning Equipment
Although the entire preparation plant complex must be considered
as an integrated functioning unit, we have, later in this section,
separated the major items of equipment directly involved in the coal
cleaning process for individual discussion. The majority of these
pieces of equipment are found inside the cleaning plant. However,
certain pieces such as rotary breakers and scalping screens do perform
an important cleaning function outside the plant proper. Each major
category of equipment provides a particular function which takes on
varying degrees of importance depending upon the raw coal and the
preparation process or processes being applied. Before discussing
these individual categories of equipment,a few general comments on the
major coal cleaning processes are in order.
As mentioned in the Introduction, most physical cleaning methods
are wet in nature. The most common of these methods uses water as the
separation medium. Prior to 1940, nearly all wet cleaning was accom-
plished by some method based upon water only. Since that time, heavy
media processes have been gaining in popularity, but, as indicated by
Table 2-1 , are not as widely used as water only cleaning. Some of the
more common equipment utilizing this medium include jigs, concentrating
tables, and hydrocyclones. The water separation technique employed by
the first two pieces of equipment is based upon the phenomenon of hindered
settling. Briefly stated, when a mixture of water and solids is agitated
it responds as a single fluid of high specific gravity, with each
solid particle tending to behave independently of all other particles.
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Therefore, as any given particle begins to settle, it is settling in
a medium which effectively has a higher specific gravity than water.
The objective of physical coal cleaning methods employing this technique
is to simulate a specific gravity close to that necessary to effect the
desired separation of the coal from the accompanying heavy impurities
(refuse).
As with all approaches to coal cleaning, there are relative strengths
and weaknesses which make one process more or less advantageous under
various conditions. The advantages of water only cleaning processes
include:
1. Lower capital and operating cost than heavy
media processes of comparable capacity.
2. When the amount of near-gravity material is 10%
or less, - The efficiency of separation can approach
that achieved with heavy media processes.
3. Can be cost-effective as a primary rough washer
prior to heavy media thus reducing the more expensive
heavy media cleaning capacity.
As would be expected from the above description of hindered settling,
the major limitation of water only processes is their inability to make
a sharp separation between coal and refuse. When there is a significant
amount of near gravity material present care must be exercised in apply-
ing this technique so as to not discard too much coal which could be
economically recovered by another process.
As commonly applied today, separation of coal and refuse by heavy
media processes is accomplished in a suspension of magnetite and water.
By varying the amount of magnetite, a medium can be created which has
a specific gravity close to the desired gravity of separation as
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determined by float-sink analysis. Although expensive (approximately
$70.00 per ton), magnetite has superior properties to any additive
developed for this purpose thus far. In addition to being non-toxic,
magnetite can be effectively recovered by magnetic separators. Further,
because of its high density, the volume concentration of magnetite is
kept low. As an example, when only ten pounds of magnetite is added
to one gallon of water the specific gravity of the mixture is increased
to approximately 1.8 grams per cubic centimeter.
Equipments based upon this separation process include heavy media
vessels and cyclones. As discussed later, these equipments take on
various configurations based upon the size and composition of the
material they are handling. Generally, these equipments are more
costly to install and operate than those using water only as the
separation medium. The higher capital cost is mainly attributed to
the additional equipment and facilities associated with pumping,
monitoring, and recovery of the magnetite. Operating costs are higher
because of the greater equipment capacity to maintain and the loss of
magnetite which can be over a pound per ton of clean coal product. Further,
careful sizing of the feed to heavy media processes is necessary to minimize
undersized material. Such material is separated less effeciently and
tends to increase magnetite consumption by contaminating the circulating
medium. In spite of these higher costs and performance limitations,
equipment based upon the heavy media separation process can provide
a more economic solution to cleaning certain coals. Since the sharpness
of the separation can be controlled more closely than water-only processes,
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such equipments can still work well in the presence of larger amounts
(25% or more) of near-gravity material. This means that when applied
to a closely sized feed, they will be able to approach the theoretical
separation limits of the float-sink analysis.
The final major cleaning process to be covered, before discussing
the individual equipment, is froth flotation. This process relies upon
the surface chemistry of coal to effect a separation of coal and its
accompanying refuse. Its major advantage is the ability of this process
to clean very fine size coal (approaching zero). To effect a separation,
a slurry of coal and water is conditioned with frothing and collecting
reagents. Then, as air is bubbled through the slurry, the coal particles
attach themselves to the bubbles and report to the surface as a froth where
they can be collected. The clay and shale impurities stay in the slurry
and are drawn off separately as refuse. When applied to higher rank
coals (bituminous and anthracite), flotation can be very effective
in reducing the ash content although it is not as effective in re-
moving pyrites as some other processes such as concentrating tables
and hydrocyclones. Besides the difficulty of controlling the accuracy
of the separation, one of the major limitations of this process is that
it is presently only effective when treating non-oxidized bituminous
coals and anthracites. Further, since the response time is slow, the
slurry must be retained for an extended period creating the need for
excessive handling capacity. This weakness is being somewhat overcome
through more e/ficient mechanical designs.
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As currently applied, most preparation plant design centers around
either a water only or heavy media process. In both cases, froth flota-
tion may be used on the finer size (28 mesh X 0 and 100 X 0) fractions
depending upon the economics of the particular cleaning application.
However, this is not to say that water-only and heavy media processes
cannot be effectively applied in the same coal preparation circuit. As
an example, water-only cyclones are commonly used as roughing cleaners
which produce a low gravity overflow product that reports to clean coal.
The underflow product is then retreated in heavy media cyclones at a
somewhat higher specific gravity of separation. Then, finer size fractions
can be handled by additional water-only cyclones, concentrating tables,
and/or froth flotation as appropriate to most economically achieve the
desired end product. By combining these processes, some of the more ex-
pensive heavy media capacity can be eliminated thereby making for a more
cost-effective preparation circuit. In Section 5.0 there are some examples
of combined processes. Specifically, Examples 6 and 7 use heavy media
and froth flotation while Example 8 uses heavy media and concentration
tables.
This very brief exposure to the major cleaning processes should aid
in the reader's understanding of the following sub sections which describe
the equipment used to implement these processes. Where appropriate, an
indication is given as to the sensitivity of cost to capacity or other
measurable factors.
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2.2.1 Size Reduction Equipment
Almost without exception, coal being handled by a preparation
plant will at some point from the mine to load-out be reduced in
size. Typically, in many larger preparation plants cleaning both the
coarse and finer size fractions there will be a sequence of size re-
ductions. The first or primary reduction will normally take place
prior to the coal entering the cleaning plant. One widely used approach
is to feed the raw coal from storage to a rotary breaker which, as
described below, not only performs a size reduction function but also
removes some debris. This arrangement is as shown in Figure 2-5.
BELT FROM
RAW COAL STORAGE
ROTARY BREAKER
FEED BELT
TO CLEANING PLANT
FIGURE 2-5
ROTARY BREAKER INSTALLATION
The rotary breaker is not a positive crushing device, but instead
accomplishes its size reduction function through the gravity impact of
the coal dropping from a height to break it to the desired size. A more
complete understanding of this action can be had by looking at Figure 2-6
which is a cutaway view of a breaker manufactured by the McLanahan Corpor-
ation.
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FEED END
OF.BREAKER
ROTATING DRUM
COVERED WITH
REPLACEABLE
SCREEN PLATES
ROTATING
LIFTING SHELVES
(LIFTERS)
REFUSE-PASSES
THROUGH DISCHARGE
END OF BREAKER
PRODUCT FROM BREAKER
PASSES THROUGH SCREEN
PLATES INTO COLLECTION HOPPER
FIGURE 2-6
CUTAWAY VIEW OF ROTARY BREAKER
Essentially, the breaker consists of a rotating drum lined with
screen plates having openings equivalent to the desired product size.
As the raw feed enters the breaker, it is picked up on lifters attached
to the inside of the rotating drum and then fractures as it drops on
other coal or the screen plates. That material which breaks to within
the size of the screen plate openings passes through and is fed to the
cleaning plant. Rock and other material which do not fracture to the
size of the screen plate openings move along the length of the drum until
they are discharged through the refuse end of the breaker. If properly
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matched to the particular raw feed, this piece of equipment can perform a
valuable and efficient initial cleaning function. Advantages of breakers
include: minimum fines, high capacity-to-horsepower ratios, and ability
to reject coarse refuse. The disadvantages included: operation influenced
by moisture content of feed, not appropriate for finer sizing, and
difficult to adjust product size.
The rotary breaker is the one type of physical cleaning equipment
which performs its function by relying upon the difference in hard-
ness between coal and rock. Coals which are too hard will not
completely fracture over the length of the drum with the result being
a significant portion of coal will be lost through the refuse end of
the breaker. The hardness of a coal is normally expressed as a
Hardgrove Grindability Index number. The higher the number, the softer
the coal. For example, a Hardgrove number of 80 to 100 indicates a
softer coal, whereas a number of 40 to 60 relates to a harder coal.
As a general rule, rotary breakers are not applicable for coals having
a Hardgrove Index much below 50. In these cases, a positive action
crusher would be used for reducing the raw coal to the proper size
consistent with the cleaning process or processes selected.
Depending upon the manufacturer and application, rotary breakers
come in a range of diameters from 7 to 12 feet and lengths up to
20 feet. Maximum feed size is based upon the feed opening of the
breaker. In the case of breakers manufactured by the McLanahan
Corporation, the following relationships exist:
Breaker Diameter: 7 Ft. 9 Ft. 11 Ft. 12 Ft.
Maximum Feed Size: 12 In. 18 In. 24 In. 30 In.
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Although the feed opening can be modified to meet a specific
application, the McLanahan Corporation does not recommend deviating
far from these relationships.
In addition to feed size, moisture content, and hardness, the
selection of a rotary breaker is based upon the required capacity.
The capacity is influenced by the amount of refuse in the feed and
the allowable limits of oversize and undersize product. As stated
above, the product size is determined by the openings in the screen
plates. If oversize is permitted in the product, the capacity of
the breaker may be increased by making the openings 1/4 to 1/2 inch
larger than the desired product.
As would be expected, the F.O.B. factory prices of rotary breakers
vary with size, design, and manufacturer. For example, one manufacturer
has a line of 10 ft. diameter breakers which cost from $100,000 to
$130,000 in 12 and 16 ft. lengths, respectively. These units have
nominal capacities of 500 to 1400 tons per hour depending upon the
specifics of the coal and product requirements as noted above. Another
manufacturer has a 9 ft. diameter, 15 ft. long unit which sells for
$80,000, and an 11 ft. diameter, 18 ft. long breaker at $95,000. Although
all of these units perform the same basic functions, they do have
different design configurations which may show advantages under
varying applications. Another factor to consider is the extent to
which the unit is assembled when it arrives on site. Some breakers
come from the manufacturer nearly fully assembled thus reducing
installation time and cost. However, for the purpose of approximating
the installed cost of outside equipment of this type, including the
necessary structural work as shown in Figure 2-5, an amount equal
to two times the F.O.B. factory price is representative for mid-1977.
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In addition to the rotary breaker, there is a variety of large
scale crushers for making a primary size reduction of run-of-mine
coal. These units are available from a number of manufacturers in
various configurations capable of handling feed sizes up to 60 inches
cube at rates as high as 3,000 tons per hour (tph). Two of the more
popular crusher configurations of this type are the single roll crusher
and the single rotor impact crusher shown in Figure 2-7.
'
SINGLE ROLL CRUSHER SINGLE ROTOR
IMPACT CRUSHER
FIGURE 2-7
PRIMARY SIZE REDUCTION EQUIPMENT
Units of this type are designed to operate at slow speeds so as
to produce a fairly uniform product and limit the generation of fines
which can be detrimental to the efficient functioning of the plant. Of
these two configurations, the single roll crusher has been the standard
primary reduction piece in the coal industry. This popularity relates
to its ability to rapidly reduce slabby feeds of almost any hardness to
cubical products with a limited amount of fines. Roll crushers are
further characterized by low headroom and power consumption as well
as the ability to handle wet, sticky feeds with a high percentage of
clay. The only major operational weakness of a single roll crusher is
relatively low reduction ratios of about 6 to 1. Other configurations
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such as the double roll crusher have even lower ratios (4 to 1). This
limitation is overcome by the impact type crushers which have reduction
ratios of as high as 30 to 1.
However, the final selection of a crusher is based upon the
nature of raw coal, the feed size, the desired product size, and the
required capacity. With regard to the nature of the raw coal, the
following characteristics are important: 1) hardness (Hardgrove index);
2) moisture content; and 3) percent and type of refuse. The feed size
is important to determine the dimensions of the crusher, particularly
the roll diameter in the case of that type crusher. Capacity is a
function of all of the factors thus far considered. For single and
double roll crushers, most manufacturers determine the capacity by
first calculating the theoretical ribbon. The theoretical ribbon
is the solid ribbon of coal and/or rock which would pass through the
crusher without taking into account the crushability of the particular
material. This theoretical ribbon which considers the bulk density of
the feed and the space occupied by the roll elements or teeth is cal-
culated as follows:
THEORETICAL RIBBON CAPACITY (tph) =
Roll Diameter X Roll Width X Roll Speed X Crusher Setting X Bulk Density X Time
Conversion Factors (1728 X 2000)
Where: Roll Diameter & Width is in inches
Roll Speed (RPM X TT) = Peripheral Speed
Crusher Setting = Desired Product Size X 2/3
Bulk Density is in Pounds/Cubic Feet
Conversion Factors: Time = 60 Minutes/Hour
1728 Cubic Inches = 1 Cubic Foot
2000 Pounds = 1 Ton
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Once the theoretical ribbon capacity is known,the actual or practical
capacity is merely a function of the crushability (hardness
factor) of the material. This relationship is as follows:
ACTUAL RIBBON CAPACITY (tph) = THEORETICAL RIBBON X HARDNESS FACTOR
For most coal the actual capacity is approximately 2/3 the theoret-
ical and 1/3 for rock. However, the capacity for coal or rock is the
same in most situations because rock is twice as heavy as the coal but
has twice the hardness. From the above relationships, it is observed that
an adjustment of the roll speed and/or increase or decrease of the
product size will result in a direct change in capacity. Another rule-
of-thumb exercised by the crusher industry is that as the capacity of
the crusher is exceeded by 10-15%, the amount of oversize material in-
creases radically.
As would be expected, the F.O.B. factory price of crushers is
related to feed size and rate (capacity), type of design, and manufacturer.
Further, the price is sensitive to the duty cycle. Manufacturers offer
a range of machine strengths varying from heavy duty crushers applicable
for use on harder coals with abrasive refuse to lighter duty machines
handling clean coal from which the majority of the refuse has been re-
moved. For estimating the cost of heavier duty primary size reduction
equipment as a function of feed size and capacity, the F.O.B. factory
prices of the "Coalbuster" line of single rotor impact crushers gives
a good approximation. A picture of this type of crusher produced by
the Jeffrey Manufacturing Division of Dresser Industries was presented
36
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in Figure 2-7. This piece of equipment sells for from $36,500 to
$161,000 depending upon feed capacity. These machines are externally
adjustable to permit product sizes of from 6 to 2 inches. Although
the final selection and thus price will vary with the particular
application, the following specific pricing may be used as a guide:
Nominal Capacity Based
Nominal Feed Size Upon a 5-6" Product Price
30" 300 tph $36,500
40" 600 tph $65,360
50" 900 tph $73,800
60" 1750 tph $113,700
60" 2600 tph $161,000
The above nominal feed sizes are rarely encountered due to the mechanized
mining methods employed today. However, the crusher feed openings are
kept wide to allow for variations in the raw coal as well as handle
greater volume.
Smaller scale reduction equipment capable of reducing coal to a
size of 2 inches or less is also available from a wide variety of
sources. This category of equipment is typically referred to as secon-
dary, since its normal function is to crush coal which has already been
reduced from its ROM state. A typical application is to further reduce
the larger clean coal product from a coarser cleaning process such as a
Baum jig or heavy media vessel prior to load-out or additional cleaning.
However, depending upon the mining method and other factors, crushers of
this type can be applied in a primary role treating ROM coal.
37
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As stated above, secondary size reduction may take place several
times within the cleaning plant depending upon the sophistication of
the process. Double and multiple roll type crushers are commonly
used for this secondary reduction of coal to smaller sizes. However,
there are configurations which combine the compression crushing concept
of the traditional roll crusher with the inherent high capacity capability
of the impact type crusher. One such unit is the "Flextooth" crusher
produced by Jeffrey Manufacturing. The trade name of this line of
crushers is derived from the design of the crushing elements which per-
mits them to "flex" back away from the crushing area when experiencing
tramp iron or other uncrushables. This unit, as with the roll type
crushers, is characterized by a slower operating speed to promote
uniformity of product and limit the creation of fines.
As would be expected, the cost of secondary crushing equipment is
most sensitive to feed size and capacity. Capacity is greatly influenced
by the desired product size and moisture content. This latter factor
can be extremely significant when crushing clean coal following wet
processes such as a heavy media vessel or Baum jig. When the moisture
content of the crusher feed is high, the smaller particles will tend to
stick to the rollers, thereby degrading performance. To cope with this
problem, wipers are installed to scrape the sticking material from be-
tween the crusher teeth. In the case of some double roll crushers, each
roll may be operated at a different speed to help alleviate this problem.
Normally, these secondary units are not as large as the primary
cursher since they are only handling a portion of the plant feed. Further,
they are lighter duty because much of the hard, abrasive refuse has been
38
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separated from the softer coal. As with primary crushers, the final
selection and thus price of secondary size reduction units will vary
with the specifics of the situation. However, for the purpose of esti-
mating the cost of secondary crushers on the basis of capacity the follow-
ing F.O.B. factory prices give a reasonable approximation as of mid-1977:
Nominal Capacity Based
Nominal Feed Size Upon a 2 Inch or Less Product Size Price
14"
14"
20"
24"
24"
28"
30"
Although the feed to this equipment would rarely reach the nominal sizes
noted above, the feed openings are kept large to accommodate the volume
and variation in feed consistency. The capacities above are based upon
a 2 inch product; as the product size is cut in half, the capacity is
likewise affected. Since this equipment is normally used inside the
cleaning plant, its fully installed cost is between 2 and 3 times the
above prices.
165
245
500
635
1065
1540
2500
$8,800
$12,100
$20,400
$33,100
$48,300
$59,000
$94,100
39
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2.2.2 Screens
There is not a coal preparation plant in existence that does not
utilize a stationary or vibrating screen in some portion of the circuit.
Screens perform a variety of sizing and collection functions critical
to the overall success of the preparation process. These functions
include:
1. Coarse Scalping of Smaller Material Prior To Initial Size
Reduction.
2. Separation of Various Sizes of Material Throughout The Process.
3. Collection of fluids combined with the coal or refuse. This
may take the form of simple dewatering or the draining and
rinsing of the material to remove and collect the expensive
heavy media (eg. magnetite).
As noted elsewhere, the proper selection and maintenance of
screens is essential to the realization of the predicted performance
and life expectancy of the screens themselves as well as other
pieces of equipment within the circuit. For example, if a screen is
passing a coarser material ahead of cyclones, the predicted classification
will not be achieved and wear will be accelerated. Situations of this
type are rapidly reflected in increased operating and maintenance
costs brought on by greater amounts of downtime for repair and replace-
ment with the associated materials and labor. It is for these reasons
40
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that a rigidly enforced screen maintenance procedure should be followed
in all preparation plants. In addition to lubrication and alignment, this
procedure should include a provision for periodically checking the tension
on the screen decks as well as the surface for holes. When the wire cloth
is loose, it results in excessive stress which leads to broken wires, the
major cause of premature cloth failure.
Initially the selection of screens is merely a function of plant
size and cleaning method. Influencing this selection are such factors as:
1) feed rate to screening station; 2) maximum size anticipated; 3) size
analysis of feed; 4) required separation and efficiency; and 5) percent solids
in feed. However, there are other important considerations which will in-
fluence the initial cost as well as the longer term operating and main-
tenance expense. These additional considerations involve such things as
existing regulations regarding safety as well as noise and dust emission.
For this reason, explosion proof motors may be required at dry screening
stations in addition to rubber or polyurethane decking to reduce noise.
Special noise reduction mountings and dust enclosures may also be necessary
on vibrating screens. Since there is such a large set of variables
affecting screen selection and thus cost, we have not as yet developed
a simple formula for determining capital cost without knowing details of
the screening application. Therefore, for the purpose of approximating
the capital cost of the preparation plants examined under Section 5.0,
actual price quotations as of mid-1977 were obtained from various screen
manufacturers and applied accordingly.
41
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SCALPING FUNCTION -
This activity which normally takes place outside of the actual prep-
aration plant is often applied ahead of the primary size reduction equip-
ment such as a rotary breaker or coal crusher. One such application is
shown below in Figure 2-8.
RAW COAL
ROTARY
BREAKER
REFUSE
5 Inch X 0
5 Inch X 0
TO PREPARATION PLANT
Figure 2-8
APPLICATION OF SCALPING SCREEN
The raw coal is conveyed to a feed box located above the scalping
screen. In addition to absorbing the initial impact of the coal drop-
ping off the conveyor belt, the feed box spreads the material over the
screen for more efficient operations. Normally, the scalper is a
rugged single deck vibrating screen mounted at a 20° angle to promote
material flow and separation. In a typical installation as shown above,
the screen will pass 5 inch or less material with the oversize going
to the breaker for further reduction. This is a cost-effective
arrangement by reducing the amount of breaker capacity needed and also
permitting the breaker to function more efficiently.
The material which fractures to the size of the breaker screen
42
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plate openings passes through and joins that which was scalped off
by the scalping screen. Rock and other debris which did not break
down to 5 inches or less passes out the refuse end of the breaker and
is disposed of accordingly.
SIZE SEPARATION FUNCTION -
Following the scalping operation as described above, the coal must
be separated into sizes suitable for load-out as is or further treatment
within the preparation plant. Typically, the coal enters a feed box
ahead of the sizing screen. As with the scalping screen, this feed
box reduces the impact of the coal onto the screening surface and pro-
motes a more even materials flow. Commonly, the sizing screen is a
double deck vibrating type mounted on an angle of approximately 20 degrees
in the manner shown below in Figure 2-9.
5 Inch X 0
1-1/4 Inch
1/4 Inch
RAW COAL SIZING
SCREEN
5X1/4 Inch
TO COARSE
CLEANING
1/4 Inch XOJTQ F|N£
CLEANING
FIGURE 2-9
APPLICATION OF RAW COAL SIZING SCREEN
Depending upon the nature of the coal, the top deck will have openings
in the range of 1 to 1 % inches. Bottom deck openings are determined by
the manner in which the finer material will be handled, but are normally
43
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h inch or less. The inclined vibrating double deck arrangement is
conducive to good separation of the material and thus promotes removal
of the finer particles. This removal is important in that the effective-
ness of such coarser cleaning methods as the jig and heavy media vessel
is improved when less fine material is present. Based upon the level
of preparation, the material passing through the sizing screen may go
either to load-out or into the fine coal cleaning circuit of the plant.
The larger material passing over the screen will move onto an optional
pre-wet screen prior to coarse cleaning.
Pre-Wet Screening Function -
A further extension of the separation process occurs at the pre-wet
screen. This function is described above as optional in that it may be
combined with the sizing operation or omitted entirely depending upon
the make-up of the material to be subjected to additional cleaning.
When there is a significant amount of finer particles still trailing
along with the coarse material, a low pressure spray of water can en-
courage their removal prior to entering the cleaning vessel. Typically,
the pre-wet screen is a horizontally mounted double deck type which
vibrates to encourage the distribution and separation of the material
over the two screening surfaces. This reduces the depth of material on
each deck and thus exposes greater surface area to the washing action of
the water spray as shown Figure 2-10, which is a photograph of a pre-wet
screen in operation.
Typically, the top deck of the pre-wet screen has openings of
approximately one inch with the bottom deck passing material of 1mm or
less. All material passing over these screens is fed to the course
44
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WATER
SPRAY
FIGURE 2-10
PRE-WET SCREEN IN OPERATION
washing vessel (jig or heavy media). The fines passing through are handled
by a number of other methods depending upon the nature of the material itself
and the sophistication of the fine cleaning portion of the preparation plant.
In some cases the material may be dewatered in a centrifugal dryer and con-
sidered clean or refuse based upon its composition relative to the clean
coal specification. Where it has been determined economic, this fine material
may undergo additional cleaning. If a fine coal cleaning circuit is included
in the plant, this and the less than 1/2 inch material will be further sized
on what is referred to as a desliming screen.
Desliming Screen Function -
As mentioned above, the function of the desliming screen is to per-
form a further sizing of the finer material making for more efficient cleaning
45
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in the fine coal portion of the plant. This screen is normally a horizon-
tally mounted single deck type which vibrates while receiving a spray of
water to encourage the separation of the extremely fine materials; i.e.
less than 1/2 mm (28 mesh). The name desliming comes from the function
it performs since it removes very fine material. Depending upon the nature
of the sulfur content in the coal, this very fine material may contain a
high percentage of pyritic sulfur which was released during mining or
earlier in the preparation process by crushing. To improve efficiency and
reduce the size of the desliming screen, the material normally first passes
over a sieve bend as shown Figure 2-11.
1/2 Inch X 0
~ DESLIMING SCREEN
1/2 hich X 28 Mesh
BEND X T0 FURTHER
^ FINE CLEANING
28 MESH X 0
TO ULTRA-FINE
CLEANING OR DISPOSAL
FIGURE 2-11
APPLICATION OF DESLIMING SCREEN
To promote better separation, the depth of material on the deck should
be kept to a minimum. The 1/2 mm or greater material passing over this screen
proceeds to the next portion of the fine cleaning circuit which may include
Deister tables and/or cyclones. The less than 1/2 mm material which was
washed through the screen may be either directed to froth flotation cells
or cyclones for further recovery of clean coal or to a static thickener for
eventual disposal. Obviously, the option elected must be based upon the
economics specific to the situation. However, current technology and
46
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environmental considerations along with the price of coal are increasing
the economic applicability of such finer recovery techniques.
FLUIDS COLLECTION FUNCTION -
Of the functions performed by screens, those involving the collection
of fluids are most influential on plant capital and operating costs. One
such cost saving function occurs in the recovery of dense media by drain
and rinse screens. These screens promote a higher recovery.of expensive
heavy media such as magnetite which helps to keep operating costs down.
Another cost saving function is performed by dewatering screens. By re-
ducing most of the free water mixed with the coal, these screens not only
improve the handling properties of the solid material, but also help to
reduce the capacity of other dewatering equipment in the preparation plant.
Heavy Media Recovery Function -
Drain and rinse screens are positioned in the preparation circuit to
handle the clean product as well as the reject from any prior equipment
in which a dense media such as a magnetite/water slurry was the vehicle of
separation. Since the fluid accompanying the material from heavy media vessels
and cyclones contains a high concentration of an expensive material such as
magnetite, these screens are used to collect as much of this fluid as
possible so that it may be reused. This process is normally accomplished
by a horizontally mounted double or single deck vibrating screen over
which a low pressure spray of water is applied to rinse off the heavy media
clinging to the coal and refuse. To aid the process and reduce the screen
size, the material normally passes first over a sieve bend or cross-flow
screen as shown in Figure 2-12. The vibrating motion promotes better
separation of the material over the screen decks giving greater effective-
ness to the rinsing action of the water spray. For this reason, one of the
47
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FEED!
\
SIEVE
BEND
DRAIN & RINSE SCREEN
_ _A_ j
4
X
TO LOAD-OUT 0
FURTHER DEWATER
HEAVY
MEDIA
t
DILUTE
MEDIA
FIGURE 2-12
DRAIN & RINSE SCREEN FOR HEAVY MEDIA RECOVERY
key design criteria is to size the screen properly so the bed depth is kept
to a minimum. As noted in the figure above, those fluids collected over
the first half of the screen are referred to as heavy media and those
from the second half as dilute media. Under normal operation, most plants
route the heavy media directly back to the vessel or cyclone media feed
circuit and the dilute media to magnetic separators which recover the
magnetite for reuse. Typically, the screen openings of the bottom deck
are kept small, thereby passing the fluid containing the magnetite but
only negligible solids. When a double deck arrangement is used, this
screen can also serve in a sizing capacity.
Dewatering Function -
As the name implies, the primary purpose of dewatering screens is to
remove as much of the free moisture as possible in the material they handle.
The need to perform this function is universal to preparation processes in-
volving both heavy media and water only. In the case of heavy media pro-
cesses, the dewatering screen may be applied immediately following the
48
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drain and rinse process where heavy media was recovered from the clean pro-
duct and the refuse. For water only processes, like the Baum jig, dewater-
ing screens are normally the first piece of equipment treating the "float"
from the jig as well as the refuse.
Typically, the dewatering function is performed by a horizontally
mounted single deck vibrating screen. In many installations, a sieve bend
is placed ahead of the screen. Unlike the drain and rinse screens used
for heavy media recovery, dewatering screens have dams at intervals along
the screening surface. These dams develop greater bed depth by restricting
the flow of material and thus give the vibrating action of the screen a
better chance to beat out the water. Depending upon the particular situa-
tion, these screens may eliminate the necessity for further dewatering
before load out or disposal. However, in all cases, they improve the
handling characteristics of the material and reduce the load on subsequent
dewatering equipment such as centrifuges.
Sieve Bend Functions -
In several of the foregoing screening applications, a sieve bend
played an option role ahead of the screen as shown in Figure 2-13. When
mounted in this way, it not only serves as a feed box to help distribute
the material over the width of the screen but also aids the sizing and
dewatering functions by reducing the load on the screen. A sieve bend can
also be applied in the preparation circuit by itself to accomplish these
latter two functions. To explain this action, the reader is referred to
Figure 2-14 which is a cutaway view of a sieve bend manufactured by Heyl
& Patterson, Inc. As the material enters the feed inlet, a series of
baffles in the sieve bend feed box spread the material so that the slurry
49
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SIEVE BEND
FIGURE 2-13
SIEVE BEND MOUNTED AHEAD OF VIBRATING SCREEN
is fed evenly over the width of the curved screen deck. By the arrange-
ment of the feed spout, the slurry actually drops tangentially onto the
screening surface. As the layer of slurry flows down the curved screen,
the thickness is reduced as it passes over the horizontal screen wires.
In practice, the depth of the slurry decreases by increments of about
one-quarter the slot width each time it passes a slot. As an example,
for a screen opening (slot width) of 1 mm, the thickness of the
slurry layer being shaved off by each wire is about 1/4 mm. This 1/4 mm
thick cut can only transport particles of up to 1/2 mm in size. There-
fore, plus 1/2 mm solids pass over the sieve bend. The result is a
50
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mo BOX
SIEVE UNO
GAKf DISCHARGE
FEED INUT
"UNIViRSAl"
REVERSING
MECHANISM
EFFLUENT
FIGURE 2-14
CUTAWAY VIEW OF SIEVE BEND
MANUFACTURED BY HEYL & PATTERSON, INC.
51
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reasonably efficient separation of the feed solids at a size considerably
smaller than the screen openings. This feature of the sieve bend extends
the practical application of screening to much finer coal sizes by re-
ducing the problem of blinding.
Sieve bends come in a range of widths, curvatures,and screen (slot)
openings depending upon the application. When placed ahead of a screen, the
width is normally selected to be one foot less than the screen. These
simple devices have several advantages which include requiring no operat-
ing power, limited space, minimum supporting structure, and very little
maintenance. By reversing the sieve bend periodically, the thickness of
the slurry layers passing through the screen openings can be controlled
and uniform performance maintained. The sieve bend can be reversed until
the triangular wire becomes worn to the extent that the screening is too
coarse. According to Heyl & Patterson, Inc., records indicate that the
screening size remains nearly constant during the life of the sieve bend.
The cost of sieve bends vary as a function of screen curvature and
width. For example, a Heyl & Patterson Inc. sieve bend with a radius of
2 ft 6 in and 4 ft wide has a mid-1977 F.O.B. factory price of $2,600 or
$650 per foot of width whereas one with a 5 ft radius and 4 ft wide sells
for $3,952 or $988 per foot. For purposes of approximating the current
capital cost of the various preparation plants examined under Section 5.0,
a per foot of width price of $800 was applied uniformly regardless of radius
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2.2.3 Baum Jig
The term jig describes a machine used for classifying materials
of different specific gravities or unit weights by the pulsation of a
stream of water flowing through a bed of the materials. As the water
pulsates or "jigs" up and down, the heavier material is encouraged to
settle to the bottom of the bed and the lighter material to rise to the
top. After this classification is made, the heavier material (sink) and
the lighter material (float) may be drawn off separately. This process
can be particularly effective for the separating of heavier refuse from
run-of-mine coal. Since coal has a specific gravity of 1.3 to 1.5, it
will tend to "float" and the accompanying impurities such as quartz
(specific gravity of 2.6), pyrite (5.0), and slate (2.6 to 3.3)
will tend to "sink." The overwhelming number of jigs in this country
are of the Baum type. A more complete explanation of this important
piece of cleaning equipment is given later in this section.
Although one of the oldest coal cleaning methods, the jig continues
to play a dominant role in the domestic preparation industry. According
to Bureau of Mines data covering the 1964 to 1975 period, the jig has
continued to be the major mechanical cleaning method in the United States.
During 1975, jigs put out over 124 million tons of clean coal which was
46.6% of the total clean coal produced for that year. Following the jig,
magnetite heavy media processes accounted for 27.1% of the total for that
year. The third most utilized method is concentrating tables which
contributed 10.7% of the clean coal in 1975. The relative roles these
methods have played in prior years is summarized in Table 2-1.
53
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TABLE 2-1
CLEAN COAL PRODUCED ANNUALLY BY
MAJOR MECHANICAL CLEANING METHODS
(Thousand Short Tons)
Year
1975
1974
1973
1972
1971
1970
1969
1968
1967
1966
1965
1964
Total
Clean Coal
Produced
266,993
265,150
288,918
292,829
271,401
323,452
334,761
340,923
349,402
340,626
332,256
310,203
Percent Produced By -
Jigs
46.6%
48.8
45.9
44.5
42.5
43.4
46.3
46.6
46.2
46.0
45.6
47.0
Magnetite
Heavy Media
27.1%
25.9
25.8
25.3
25.9
23.7
21.4
20.7
18.9
*
*
*
Concentrating
Tables
10.7%
10.9
12.1
13.1
13.1
13.6
13.5
13.9
14.2
13.3
13.0
13.2
*Magnetite Heavy Media Not Reported Separately from other Heavy Media
processes.
Source: Based Upon U.S. Bureau of Mines, Mineral Industry Surveys,
Coal-Bituminous and Lignite Annual, 1964-75, Prepared in
Division of Fuels Data and Division of Coal.
Jigs are applicable to a wide range of coal sizes. In the past,
they have even been applied to raw feeds having chunks as big as 10 inches.
However, they are most practically used on top sizes of 3 to 6 inches.
The major limitations of the jig are that the amount of near gravity
material should not exceed 10% and they are most efficient at high separating
gravities of 1.5 or more. As a general rule, jigs can effect reasonably
good separations on sizes down to % inch and produce limited results on coal
sizes as small as 48 mesh.
In the foregoing text and for the balance of this section, reference is
made to the ability of a jig to effect a separation at a certain specific
54
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gravity. Although technically incorrect, one common simplification of
this subject is to think of the jig producing a clean coal ("float")
having the same ash and sulfur content as that part of the feed to the
jig which would float on a solution having that particular specific
gravity. In other words, if the specific gravity analysis (float-sink
test) of the feed to the jig shows that the ash and sulfur contents of
the float at 1.6 specific gravity are 10% and 1%, respectively, then the
jig is said to be effecting a separation at 1.6 if its product has
similar ash and sulfur contents. This approach gives a very rough
approximation of the actual specific gravity of separation, since it
does not consider the amount of float 1.6 (misplaced product) in the
sink 1.6 and vice versa.
As stated above, jigging is a process to stratify a bed of particles
according to their density. This is accomplished by alternate expansion
and compaction of the bed of particles in a pulsating fluid flow which
encourages the higher density particles to migrate toward the bottom of
the bed and the lower density particles to move toward the upper portion
of the bed . This density stratification is accomplished in spite of
the great differences in size and shape of the particles. To better
understand the mechanics of this process, the reader is referred to the
cutaway views of a Baum jig presented in Figure 2-15.
This particular jig is a five cell, two compartment model, produced
by the Jeffrey Manufacturing Division of Dresser Industries. In the
front view, the inside of the first compartment is shown which consists of
two cells. Although not visible in the drawing, the second compartment
has three cells which perform the same functions. As the slurry of raw
55
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Air
Chamber
Stratified
Bed of Coal
& Refuse
Particles
Refuse
Elevator
Float
(Clean Coal)
Water
Direction
of Flow
Side View
Front View
FIGURE 2-15
CUTAWAY VIEWS OF BAUM JIG
feed enters the jig, water is forced up through the bed of coal and ac-
companying refuse. This force is sufficient to lift the bed and "open it
up" in suspension in the water. Then, the external force pushing the water
up through the bed is quickly removed and gravity creates the force to pull
the water back through the bed to encourage the stratification of the parti-
cles in the bed according to their density as discussed earlier. Looking at
56
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the side view of Figure 2-15 which is a cross-section of any of the five
cells, one can get a feel for how these upward and downward currents
of water are created. A blast of air in the air chamber forces water
up through the screen plate in that cell. This action is referred to
as the pulsion stroke of the jig. As this air pressure is quickly
released, the water is permitted to return to its natural level just below
the screen plate. This action is referred to as the suction stroke
since as the pressure in the air chamber is released, the water is some-
what pulled back through the bed comparable to the action of a suction
pump. The completion of the pulsion and suction strokes is considered a
cycle. In a Baum jig, the speed may be adjusted to the particular re-
quirement but nominally each cell operates around 22 cycles per minute.
Although the cells in each compartment operate together, they are se-
quenced with the cells in the other compartments to permit the build-up
of adequate pressure before opening the valve into the air chamber.
As the bed of particles moves along the screen plate in each com-
partment, the heavier material will sink to the bottom of the bed. At
the end of each compartment, this bottom layer is drawn off as reject
through a gate and then picked up in a bucket elevator having perforated
baskets for partial dewatering. The material in the upper layer of the
bed passes over ("floats") to the next compartment where a further sep-
aration is effected. That material which "floats" through all jig com-
partments is the product from the jig. Depending upon the sophistication
of the particular cleaning process, the reject from the last compartment,
sometimes referred to as middlings, may be reclaimed for further treatment.
57
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Jigs are sized to the particular coal cleaning requirement on the
basis of tons of feed per hour per square foot of effective jigging area.
Specifically, this is the area of the screen plates over which the bed
moves. This capacity is influenced by three factors relative to the
make-up of the feed. In the following order, these are:
1. Percent of Near Gravity Material
2. Percent of Fine Material (% in. X 0)
3. Refuse Volume
The first two factors are especially critical to the performance of
the jig. When the near gravity material is 10% or less, a relatively
"black and white" separation exists. However, over 10% near-gravity
material presents a more difficult washing situation. A very close
second to the percent of near-gravity material is the amount of fine
material in the feed as determined by screen analysis. When the jig is
fed more than one ton per hour per square foot of jigging area of 1/4 inch XO
material there is not as sharp a separation. If this guideline on fines
is observed and the percent of near gravity material is not over 10%, up
to 5 tons per hour per square foot of jigging area may be fed to a typical
Baum jig. How these factors affect capacity can be observed in the
following example:
Given:
Raw Coal Feed: 400 tph of 5 in. x 0
Near Gravity Material at Washing Gravity: 5-10%
Percentage of % in. x 0: 25%
Refuse Volume: Not sufficient to be a limiting factor
58
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Solution:
Based upon near gravity material percentage of 10% or less, jig
should be able to handle 5 tons per hour per square foot of
jigging area or 80 square feet wodld be sufficient. However,
since 25% of the feed is 1/4 inch XO, or 100 tph, 100 square feet
of jigging area should be available to meet the 1 ton per hour
per square foot test.
Therefore, a jig having a minimum of 100 square feet of jigging
area is sufficient to handle the 400 tph.
Baum jigs are produced by a few major companies in this country and
come in a variety of standard sizes. Some indication of the larger
sizes available and their cost is given by the following list of F.O.B.
factory prices of Jeffrey Manufacturing's Baum jigs:
Width of
Screen Plate
6
7
7
Number of
Compartments
2
2
3
Number
of Cells
4
5
6
Jigging
Area
72 ft2
105 ft2
168 ft2
Nominal
Capacity
350 tph
500 tph
800 tph
Price*
$107-118,000
$125-140,000
$168-185,000
*Based upon mid-1977 price quotations.
For the purpose of estimating the installed price of a piece of equipment
of this type, a number of between 2.5 and 3 times the F.O.B. factory price
gives a reasonable approximation. In those coal preparation circuits
considered under Section 5.0 of this study, the above pricing/capacity
relationships'were observed.
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Batac Jig -
A modified form of the Baum type jig is the Batac jig which is manu-
factured in this country by the Roberts and Schaefer Company under
exclusive license from Humboldt Wedag in Germany. Normally, the Batac
jig is intended for use in cleaning finer size coal having a top size
of around 3/4 inch. These jigs come in various configurations depending
upon the feed rate, washability, density, and grading of the raw coal.
The length of the jig bed and its subdivision depends on the percentage
of heavy product or the number of separation cuts, whereas the feed rate
generally determines the bed width.
The Batac jig is considered a hydropneumatic device which differs in
several ways from the conventional Baum jig. A few of these differences
are:
1. Pulsations are produced directly beneath the bed screen
(instead of in an adjacent chamber), in multiple chambers
distributed uniformly throughout the jig. Air pulses in
each chamber are controlled independently.
2. Instead of moving a large volume of water, with its attendant
slow-surge characteristics, the multiple chambers in the
Batac jig each move a small volume of water, allowing rapid
initial surge, and precisely controlled frequency and shape
of the jig stroke.
According to the manufacturer, the Batac jig can be designed with
wider beds thus providing significantly higher throughput in the same
60
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space required by a conventional Baum jig. This is possible because of
its improved operating efficiency and the elimination of the adjacent air
chamber.
The general configuration of a Batac jig is presented in Figure 2-16
along with an identification of the major components. Using this Figure
as a reference, the raw coal is introduced over the full width of the jig
bed as shown by point A. Pulsations in the first two cells separate the
coal and middlings from the coarse refuse, forming separate layers of these
materials. The layer of heavy refuse is discharged at the end of the second
cell as shown by point B. To ensure relative purity of the product leaving
the first two cells, bed depth is monitored constantly (point H), and
the opening of the discharge gate adjusted automatically to control bed
depth.
Cells 3 and 4 utilize a feldspar bed to carry the coal, middlings and
fine refuse which pass over the bridge plate from cell 2. Because the jig
bed screen in these two cells is large (16 mm), as the feldspar bed lifts
and separates in response to water surges, the fine refuse sifts down
through the bed and screen (point D). By the time the incoming product
reaches the end of cell 4, only coal and middlings remain, and these pass
over a bridge into cell 5.
Cell 5 operates much the same as cell 2, with the coarser middlings
serving as the jig bed, and being discharged through a controlled-size
gate at the end of the cell (point E). Finer middlings, together with coarse
and fine clean coal pass over another bridge into cell 6. In cell 6, with
its feldspar bed, fine middlings are discharged through the bed and screen
(point F), leaving clean coal to flow out of the jig (point I) onto dewatering
equipment.
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End View
Side View
Major Components - A.
C,
D.
E.
Raw coal inlet
Coarse refuse discharge
Refuse Collecting hopper
Fine refuse discharge
Coarse middling product
discharge
Fine middling product
discharge
Middling product
collecting hopper
Bed depth sensors
I. Clean, washed coal outlet
J. Air chambers
K. Water inlets
L. Air distributing pipes
M. Air distribution chamber
N. Exhaust air collecting chamber
0. Exhaust air pipes
P. Valve control
Figure 2-16
CUTAWAY VIEWS OF BATAC JIG
The air inlet and outlet valves for the surge chambers(point J) under
Z'.Y^ oatac jig are operated by air cylinders and quick air releases to get
the necessary rapid actuation. Air cylinders, in turn, are actuated by
solenoid-controlled air valves (point P). Sequencing of these valves, and
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the air releases is controlled by solid-state electronic circuitry mounted
on removable panels in the master control panel. Panels are "programmed"
for the particular material being handled, so that only a substitution
of these panels is ordinarily required to modify operation of the jig
for differing materials.
Based upon a high volatile 3/4 X 0 raw coal having 15% to 20%
28 mesh X 0 material, the following capacities, requirements, and costs
are presented as a function of the three standard Batac jig widths.
Bed Maximum Jigging Water Jigging Approximate Approximate F.O.B.
Width Feed Rate Area Supply Air Total Factory Price 3]
in TPH Sq Meters GPM 1] CFM 2] Horsepower 1st Qtr. 1977
Meters
3
4
5
360
480
600
18
24
30
3,600
4,800
6,000
2,800
3,800
4,800
275
330
340
$560,000
$585,000
$610,000
1] At 11.4 psig pressure measured at the inlet header for raw coal feeds
containing not more than 35% refuse material.
2] At 6.4 psig measured at the jigging air distribution chamber.
3] Includes the Batac, Jigging Air Supply Blower, Control Air Compressor,
and Refuse and Middlings dis-posal elevators.
The maximum feed rates will be less as the top size is reduced and/or the
percentage of minus 28 mesh material in the feed increases.
Under Section 5.0 of this report, a preparation plant (Example 4) is
considered which includes two Batac jigs in its fine cleaning circuit.
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2.2.4 Heavy Media Vessels
As the name implies, heavy media vessels effect a separation of coal
from the accompanying refuse by creating a medium having a specific gravity
equivalent to the desired specific gravity of separation. This establishes
an environment which encourages the coal to float and the heavier refuse
to sink in a manner which closely simulates that predicted by specific
gravity (float-sink) analysis. As mentioned earlier, heavy media vessels
can perform a relatively sharp separation by accurately controlling the
amount of magnetite in the solution. Normally, vessels of this type
are used on coarser size fractions down to % inch. Although more expen-
sive to install and maintain than a Baum jig of comparable capacity,
heavy media vessels can show economic advantage with coals having
a large percentage of near gravity material necessitating a sharper degree
of separation. The initial cost of this category of equipment is higher
since in addition to the vessel itself, it is necessary to have adequate
circuitry to recover for reuse the expensive heavy media (magnetite).
This not only includes magnetic separators and the associated pumping,
piping, etc., but also the equipment used to monitor and maintain the
proper density of magnetite in the vessel's circulating medium. Operating
costs are also higher than comparable capacity Baum jig cleaning circuits
due to the cost of the magnetite lost in the washing process in addition
to the greater amount of equipment requiring power and periodic maintenance.
Heavy media vessels are manufactured by several companies in this
country and come in a variety of sizes and configurations. The major
differences in these equipments relate to the methods used for introducing
the raw feed into the washer as well as recovering and discharging the float
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and sink products. Large scale washers can handle raw feeds approaching
800 tons per hour. One such larger unit is the Daniels Precision Washer.
This has a trough type design utilizing a transverse flow where the
feed to the vessel and the discharge of the product are transverse to
the direction of the flight conveyor which collects and rejects the
refuse. Another unique feature of this equipment is the submergence
baffle which immediately forces the feed to the vessel under the sur-
face of the medium (water and magnetite) where the actual separation
occurs. As the float material rises to the surface it overflows the
side of the tank. Figure 2-17 is a top view of this equipment clearly
showing the rectangular conveyor which collects the refuse off the
bottom of the tank and discharges it at the far end of the vessel.
As would be expected, the cost of heavy media vessels varies with
capacity. However, the price is most sensitive to the particular style.
For example, a drum type separator manufactured by the WEMCO Division
of Envirotech Corporation which is capable of handling a feed of 500 tons
per hour (tph) costs $125,000. A 500 tph capacity Barvoy heavy media
vessel manufactured by the Roberts and Schaefer Company costs less than
$50,000 as of mid-1977. Obviously, each of these units has its own
unique features which make it more or less advantageous under varying
coal preparation requirements and conditions. The point to be made
here is that there is no single price per ton of capacity appropriate
for estimating the cost of this particular category of cleaning equip-
ment. This being the case, the prices used for approximating the capital
cost of the heavy media vessels appearing in the preparation plants con-
sidered under Section 5.0 of this study were based on specific quotes.
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Refuse Flight
Conveyor
en
CTv
FIGURE 2-17
DANIELS HEAVY MEDIA PRECISION WASHER
Refuse Reject
End of
Vessel
Washed Coal
(Float)
Overflow
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2.2.5 Cyclones
Essentially, the cyclone is a hydraulic centrifuge working on the
vortex principle. The slurry of coal may be pumped or fed by gravity
to this device. When properly applied, this versatile piece of equip-
ment can be an efficient part of the coal preparation plant. Cyclones
provide a wide range of functions in a variety of coal preparation
circuits. These functions fall into three major categories:
1) Size Separation - Performed by the classifying cyclone.
2) Dewatering - Performed by the thickening cyclone.
3) Separation of Refuse from Coal - Performed by either a heavy
media or water-only (hydro) cyclone.
The size and number of cyclones in any given preparation circuit
will vary with the specific application. The size of a cyclone is de-
termined by the physical and chemical nature of the coal slurry to be
processed as well as its volume and desired performance. This perform-
ance is influenced by such factors as:
1) Solids concentration of the feed.
2) Size distribution and specific gravity of the solids.
3) Desired classification size.
4) Required concentration of underflow and dilution of
overflow.
Depending upon the application, cyclones come in a range of sizes
i*'.
and shapes up to 30 inches in diameter. The initial cost of any given
type and size cyclone will vary significantly based upon the selection
of the lining. These replaceable linings are selected on the basis of
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their wear resistant qualities. A. proper selection of lining to
meet the conditions of corrosion and abrasion can aid in reducing
maintenance costs. Liners of urethane, ceramic, rubber, Nihard,
and other materials are offered by such cyclone manufacturers as
Heyl & Patterson and Krebs Engineers. For more abrasive applications
all ceramic lining is appropriate. Where less abrasive coal slurry
is being fed to the cyclone, a combination of urethane and ceramic
lining may be all that is necessary. This concept of using a combina-
tion of linings cost-effectively addresses the specifics of the wear
factors actually being experienced in various portions of the cyclone.
As an example, urethane may be employed to line the upper portions of
the cyclone where less wear is experienced, while the extreme abrasion
resistance of ceramic is most .appropriate in the lower portions. The
use of combination linings is made possible by a sectionalized construc-
tion where the metal housings are fitted with replaceable linings.
This sectionalized approach not only permits an effective matching of
lining material to subjected abrasion, but also yields cost savings by
eliminating the need to replace the entire lining when only a portion
is worn.
When cyclones with expensive wear resistant liners were first in-
troduced, there was a reluctance on the part of industry to adopt them
due to high initial cost. This cost can be as much as twice that
of a comparable capacity unit. However, over the past eight years,
their proven record of reducing long term maintenance costs has brought
about acceptance. As a result, the major cyclone manufacturers are
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now employing this concept of using better grade linings and combinations
thereof in spite of their initial higher cost.
Even though significant advances have been made in the construction
and application of cyclones used by the coal cleaning industry, it is
difficult to get accurate maintenance cost data. Such costs are greatly
influenced by the manner in which other portions of the plant are main-
tained. Specifically, if proper care is taken of the equipment "up-
stream" from the cyclones, then the feed is consistent with the design
and lining. However, improper care such as when screens are not properly
maintained, can result in a much coarser feed entering the cyclone and
rapidly accelerating wear on the lining.
Heavy Media Cyclones -
Heavy media cyclones can perform an effective and efficient cleaning
of intermediate size coals. In these cases where there are large amounts
of near gravity material and/or the desired specific gravity of separation
is low, these devices play critical roles. These devices provide a degree
of operational flexibility in that you may readily vary the specific gravity
of separation over a wide range. As the name implies, the separation
achieved by these devices is principally controlled by the specific gravity
of the medium which in practice ranges between 1.35 to 1.80. In almost
all cases this medium is a suspension of magnetite and water. The feed
to this type of cyclone may be pumped or gravity fed. Although a heavy
media cyclone is normally mounted in the inclined position as shown in
Figure 2-18, it is capable of operating in the upright position as well.
(The particular heavy media cyclone shown in Figure 2-18 is manufactured
by Heyl & Patterson, Inc.).
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FIGURE 2-18
HEAVY MEDIA CYCLONE IN INCLINED POSITION
To better understand the workings of heavy media cyclones, the reader
is referred to Figure 2-19, which is a cutaway view of a washing cyclone.
A slurry of water, coal, refuse, and magnetite is fed tangentially into
the conically shaped body of the cyclone. As this slurry is carried around
the feed chamber, specific gravity differentials are set up which vary from
the air core to the cone wall and from the bottom of the vortex finder to
the apex of the cone. These differentials create an environment which en-
courages the lighter particles in the slurry to move toward the core.
Conversely, the heavy materials are encouraged to stay against the cone
wall, or if caught in the central low gravity section of the cone near
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FEED INLET
FEED CHAMBER
CONE WALL
OVERFLOW
OVERFLOW ORFICE
(VORTEX FINDER)
AIR CORE
APEX OF CONE
UNDERFLOW ORFICE
FIGURE 2-19
CUTAWAY VIEW OF OPERATING CYCLONE
the air core to quickly sink away toward the wall. These specific
gravity differences and centrifugal effects within the rotating mass
of magnetite, water, and solids are responsible for a relatively sharp
separation of coal and refuse. Heavy media cyclones come in a variety
of sizes up to thirty inches in diameter and several types of linings
are available with varying degrees of wear resistance. There are slight
design variances among manufacturers, each claiming superior performance
characteristics.
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Water-Only Cyclones -
Commonly referred to as hydrocyclones, water-only cyclones
are gravimetric separators used to sort particles of coal and accompany-
ing refuse according to specific gravity using only water and centri-
fugal force. Although it may be applied as an independent cleaning
unit, this type of cyclone is a particularly valuable processing tool
when used in multiple stages or in conjunction with other washing
equipment. As shown in Figure 2-20, which is a bank of Heyl and
Patterson hydrocyclones, this type of cyclone has a cylindrically
shaped body with a conical bottom. It differs from the typical heavy
FEED
OVERFLOW
MANIFOLD
UNDERFLOW
FIGURE 2-20
WATER-ONLY CYCLONE INSTALLATION
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media washing cyclone in that it is short and stubby as opposed to a
long tapered conical appearance. Additionally, the water-only cyclone
has an adjustable vortex finder which is longer and also has larger
overflow openings for a given diameter than other type cyclones. There
are other design variations depending upon the manufacturer.
From an operational standpoint, the raw feed enters the cyclone
tangential to the feed chamber where separation occurs. As in the
case of the heavy media cyclone, the lighter particles report up
through the vortex finder and exit through the larger overflow opening
at the top of the cyclone. The heavier particles (refuse) exit through
the opening in the center (apex) at the bottom of the cyclone. The
diameter of a water-only cyclone is principally selected on the basis
of the size of the coal and the efficiency required. In general, the
smaller the particle size, the smaller will be the required diameter.
For intermediate size coal, diameters of between 12 and 30 inches are
selected as appropriate. Finer sizes are handled by units of 8 to 14
inches in diameter. One popular application is to use 12 or 14 inch
hydrocyclones on the 28 x 100 mesh size fraction in combination with froth
flotation because of their abililty to remove pyrite particles and the
difficulty in floating this size.
Other design features which influence performance include: 1) verti-
cal clearance between lower edge of the vortex finder and the cyclone
bottom; 2) diameter of the vortex finder; 3)apex diameter; 4) solids
concentration in the feed to the cyclone; and 5) pressure at the feed
inlet. The particular specific gravity at which the water-only cyclone
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effects a separation is determined by varying the dimensions of the
discharge orifices. This specific gravity of separation is decreased
as the diameter of the vortex finder is decreased or the apex diameter
is increased. As would be expected, this same result occurs as the
vertical clearance between the lower edge of the vortex finder and the
cyclone bottom is increased. This latter type of adjustment is made
simpler and more precise by water-only cyclones with hydraulic vortex
finder lift mechanisms.
Also affecting the operating specific gravity of separation is the
solids concentration. This concentration is directly scaled to the hydro-
cyclone diameter; the smaller the diameter, the lower the percent solids.
Normally, this concentration is between 8% and 15% by weight. As the
concentration is increased, the specific gravity of separation also in-
creases. This is a critical operating parameter since if feed concentra-
tions are too high or low, undesirable results occur. Specifically, too
high a percentage of solids results in increased particle interaction
and thus less accurate separation of coal and refuse. At the other end,
too low a percentage of solids will also injure performance because the
hydrocyclone will begin to separate on the basis of particle size like
a classifying cyclone resulting in excessive amounts of misplaced coal.
As long as there is adequate feed pressure to generate a vortex,
changing the inlet pressure apparently has little impact on the perform-
ance of the water-only cyclone. By increasing the pressure, there will
be a slight elevation in the specific gravity of separation as well as the
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processing capacity. However, it is not recommended as an economical
means to achieve this latter objective since such increased pressure
accelerates wear on the cyclone lining. As a general rule, the follow-
ing minimum inlet pressure relations apply:
Cyclone
Diameter
8
10
12
15
20
24
26
Maximum
Feed Size
28 mesh
10 mesh
% inch
% inch
h inch
3/4 inch
3/4 inch
Dry Feed
Rate
3-5 tph
4-8 tph
8-16 tph
15-25 tph
25-45 tph
40-70 tph
50-90 tph
Inlet
Pressure
8 psi
10 psi
12 psi
12 psi
15 psi
15 psi
15 psi
Maximum
% Solids
8-10
10
10-15
12
15
15
20
According to an article by Ellis J. O'Brien of Dravo which appeared
in the January 1976 issue of Coal Age, the pros and cons of water-only
cyclones are summarized as follows:
Advantages
1. Simple design with no moving parts and little maintenance.
2. Once initial adjustments have been made, usually no further
adjustments are necessary.
3. Operate with water only and without a heavy medium or reagent;
therefore, heavy-media or reagent consumption is eliminated
and no magnetite recovery system is needed.
4. Requires limited space for operations
5. Does not require pre-screening.
6. Will clean oxidized raw coal down to 100 mesh while flotation will
not.
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7. Will reduce pyritic sulfur more effectively from 28 mesh x 0
coal than flotation.
Disadvantages
1. Large quantities of water are required for proper operation
of the hydrocyclone circuit, therefore more horsepower.
2. Separations obtained in a hydrocyclone aren't nearly as
sharp as those characteristic of the dense-media cyclone
or Deister table.
3. Not for difficult-to-clean coals.
4. Good refuse and a clean coal cannot be produced simultan-
eously from a single unit.
The prices of all types of cyclones vary with size, lining, and
unique design features mostly influenced by the particular manufacturer.
Since there is a multitude of size/lining/manufacturer combinations, it
was necessary to obtain specific price quotations on those cyclones in
the preparation plants addressed under Section 5.0. However, as a
general rule for estimating the installed price of the cyclone portion
of the coal preparation circuit, a figure of between 2 and 3 times the
FOB factory price gives a reasonable approximation including necessary
piping and manifolding. In the case of all ceramic linings the lower
multiplier would apply and for the same cyclone having a less expensive
lining, the higher figure would be appropriate. For heavy media cyclone
installations, there will be the additional cost of the media control and
recovery circuitry which adds appreciably to the total installed price.
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2.2.6 Concentrating Tables
Commonly referred to just as "tables" or as Deister tables (the
name of the principal domestic manufacturer), the concentrating table
has a proven record of efficiently cleaning certain coals in a size
range of 3/4 inch to zero. Tables cannot be adjusted to provide separa-
tions lower than 1.45 to 1.50 specific gravity. Like jigs, their separa-
tion efficiency is adversely affected when more than 10% near gravity
material is present.
The concentrating table effects a separation of coal from the ac-
companying refuse according to size and specific gravity by flowing
a mixture of coal and water over a vibrating table having a series of
riffles. Basically, the table consists of a pair of steel channels
upon which is mounted a rubber-covered deck and a drive mechanism. The
flat, rhomboid-shaped deck is approximately 17 feet long on the clean-
coal side and 8 feet long on the refuse side. It is supported in an
essentially horizontal plane, but slopes enough (perpendicular to the
motion of the deck) so that water fed along the upper long side will
flow across the table surface and discharge along the lower clean-coal
side. The deck is attached to a differential motion drive which gives
it a quick return conveying motion, moving material lying on the table
surface away from the drive end.
Attached to the rubber covering on the deck is a system of rubber
riffles tapering toward the refuse end of the table and parallel to the
direction of the conveying motion as shown in Figure 2-21. Standard body
riffles are approximately % inch high at the drive end of the table.
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Feed
Box
Dressing
Water
Boxes
Ri ff1es
Table
Dri ve
€
Clean Coal Side
€
Clean Coal
Middlings
Q Refuse
FIGURE 2-21
TOP VIEW OF CONCENTRATING TABLE WITH DISTRIBUTION
OF PRODUCTS BY SIZE
Between each set of three or four body riffles are high (over 1 inch at
the drive end) "pool" riffles. These riffles form dams., behind which
stratification of the bed occurs. Low-density particles ride over the
riffles, reporting to the clean-coal side of the table; high-density
particles are carried behind the riffles by the differential-motion drive
to the refuse end of the table. At one corner of the long diagonal and
above the deck is a feedbox with a slotted bottom to spread the feed onto
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the deck. Beside the feedbox and along that side of the deck is a
trough, having adjustable gates through which the flow of dressing
water is distributed to the deck.
Because of the reciprocating action of the table and the transverse
flow of water, the feed fans out immediately upon contacting the table
surface. The upward slope of the table toward the refuse end, usually
1/8 to % inch per foot, and the retaining effect of the pool riffles
cause the slurry to form a pool near the feedbox. In this pool, the
bed of material is several particles deep and substantially above the
standard riffles. This area becomes the zone of primary stratification.
In this zone, the shaking motion of the deck combined with the cross
current of water stratifies the particles by density, similar to the
action of the jig washer described in Section 2.2.3.
The essence of table performance is the stratification according
to size and specific gravity that occurs behind the riffles. This
results from the differential shaking action of the deck. The particles
that make up the feed become arranged so that the finer and heavier
(more dense) particles are at the bottom and the coarser and lighter
(less dense) particles are at the top. The finer, more dense particles
are carried out by the table movement toward the refuse side at a faster
rate than the coarser, more dense particles. The larger pieces of lower
specific gravity ride on the top layer of particles and flow on down the
slope of the deck reporting to the clean coal side. Such movement is en-
couraged by the cross flow of wash water at right angles to the shaking
movement of the table. Since stratification and separation of particles
are not complete as a result of any one riffle, a series of riffles is
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used, repeating the cycle of stratification and hindered settling from
riffle to riffle, obtaining purer refuse products as the particles spread
out and progress forward and downward over the table. Conversely, the
purer, cleaner coal is discharged at the drive side of the table.
As presented in Figure 2-21, successive samples collected along the
clean and refuse sides of the table, starting at the drive motor side,
show a steady increase in ash content and a steady decrease in the average
particle size for each individual specific gravity fraction.
Concentrating tables are provided with a number of adjustments which
are used to obtain the best possible operation. Among these are: (1) reci'
procating speed, (2) length of stroke, (3) feed rate, (4) amount and
distribution of wash water, (5) water-to-sol ids ratio of the feed pulp,
(6) uniformity of feed, (7) riffle design, (8) side tilt and (9) end
elevation. The reciprocation of the deck usually is 260 to 290 strokes
per minute depending on the characteristics of the raw coal and the feed
rate. If there are high percentages of refuse in the raw coal or if
the feed rate is high, an increase in the frequency is required.
Closely related to the frequency is the amplitude. The amplitude
and frequency are varied to maintain the mobility of the bed necessary
for stratification while retaining the coal on the deck long enough
for proper separation. In order to move large quantities of refuse
material along the deck, an amplitude as long as 1% inches may be re-
quired. Conversely, the stroke may be less than % inch long when coals
containing high percentages of near-gravity material are washed. The
amplitude and frequency of the stroke are decreased as the amount of
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near-gravity material in the feed increases. A nominal 3/8 inch x
0 feed would require a stroke amplitude of about 3/4 inch and frequency
of 275 strokes per minute. Generally, a fine feed will require a higher
speed and shorter stroke than a coarse feed.
The cross slope and amount and distribution of dressing water to
the table can be changed easily and quickly to compensate for minor
variations in feed rate and composition. The cross slope is generally
less than 5 degrees, and the dressing water side of the table is higher
than the clean-coal side. The feed dilution (water to solids ratio)
used on a table washing 3/8 inch x 0 is 2 to 1. As the top size of
the feed increases the water to solids ratio increases.
Perhaps the most important of all table adjustments is the end
elevation or the amount of upward inclination of the deck measured
along the line of motion from the feed end to the discharge end. By
creating a moderate slope which the high specific gravity particles will
climb more readily than will the low specific gravity material, the sep-
aration is greatly improved. The high specific gravity particles are
forced to spread out in a thin, wide band which permits a much sharper
separation to be made between clean coal, middling, and refuse products.
The amount of end elevation increases with feed size and specific gravity.
Typically, a 3/8 inch X 0 feed would require approximately 3 to 4 inches
of end elevation depending upon the specific gravity of the refuse.
The capacity of a concentrating table is a function of the size
consist, the percentage of reject, and the washability of the feed.
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As a general rule, capacity increases directly with the size consist,
limited by the percentage of reject above 20%. However, as the diffi-
culty of cleaning decreases, feed rates can be increased. The
majority of all installations treating bituminous coal are handling
the 3/8 in. x 0 or % in. x 0 size fractions. Most of the tables installed
in recent years have a double-deck configuration.
The two major double-deck design configurations manufactured by
the Deister Concentrator Company are the regular Concenco "88" Diagonal -
Deck Coal Washing Table and the High Capacity Refuse Discharge (HCRD)
version of the same. This latter configuration is designed for washing
coals containing more than 20% reject. As depicted by Figure 2-22, the
"88" series tables are built for suspension mounting via wire
ropes in vertical pairs or in a four-deck stack arrangement. This arrange-
Figure 2-22
DOUBLE-DECK CONCENTRATING TABLE (DEISTER CONCENCO "88")
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merit eliminates to a large extent two of the major disadvantages of con-
centrating tables. Specifically, it reduces the floor space requirements
and the need for shock absorptive mounting to handle the impact of the
drive mechanisms. As a general rule, each twin-deck is capable of
efficiently washing up to 25 tons per hour (tph) of % x 0 or 30 tph of
3/4 x 0 feed containing less than 20% reject. The FOB factory price as
of mid-1977 for the standard model twin-deck table was $18,326. The
HCRD model is approximately $2,000 more per double-deck. Both prices
include the necessary drive motor, mounting hardware, controls, and
up to six days field service for start-up and demonstrating the satis-
factory performance of the tables. In addition to the basic price of the
tables, there is an additional hardware expense associated with the feed
distributors. These devices divide the stream of slurry into prede-
termined amounts consistent with the capacity of the table. The primary
importance of feed distributors is to assure uniform feed to all deck
surfaces so that common table settings will provide consistent separating
results. They come in stationary or revolving configuration., which are
selected on the basis of capacity and the required number of splits. As
an indication of their cost, a stationary 8-way distributor sells for
$2,500 and a comparable capacity revolving type has an F.O.B. factory
price of $6,500. These prices were used for approximating the capital
cost of those preparation plants considered under Section 5.0 where tables
were part of the cleaning circuit.
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2.1.1 Froth Flotation
As mentioned at the beginning of this section, froth flotation relies
upon the surface chemistry of coal to effect a separation of coal from
its accompanying refuse. This is the major process capable of cleaning
particle sizes down to zero. To achieve this separation, frothing and
conditioning reagents are added to a slurry of water and fine feed (coal
and refuse particles). Then, as air is bubbled up through the slurry,
the coal particles attach themselves to the bubbles and are carried to
the surface where they can be collected as a concentrated overflow product.
The refuse particles remain below the surface and are discharged at the
underflow opening at the bottom of the vessel.
As shown in Figure 2-23, the froth flotation process is performed in
large steel tanks having a series of compartments or cells. This picture
clearly shows the coal laden froth floating at the top of each cell and the
skimmers which remove this product. Each cell has its own agitating device
at the bottom of the tank to keep the slurry in suspension and distribute
the air bubbles. These agitating devices vary substantially among the
several domestic manufacturers which include the Daniels Company, Denver
Equipment Divison of Joy, Heyl & Patterson, and WEMCO Division of Enviro-
tech. A slurry of coal, frother, conditioners, and water is fed into one end
of the series or bank of cells. The solids concentration of this slurry will
vary between 4% and 12%. A series of several cells is necessary in order
to assure adequate time for the coal to come in contact with the air bubbles.
The slurry moves from one cell to the other during which time that coal which
c
has been floated to the surface overflows the edge of the cell as a concen-
trate of about 25% solids. This concentrate is normally routed to a vacuum
84
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Figure 2-23
FROTH FLOTATION CELLS IN OPERATION
filter or other dewatering device before going to a thermal dryer for final
moisture reduction. The non-coal particles also move from cell to cell but
below the surface until they reach the far end of the tank. Here they are re-
jected through a discharge box or similar mechanism with the bulk of the
vessels' fluid. In most of the preparation plants today, this high
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moisture reject product is routed to the static thickener where the
solids are settled out prior to ultimate disposal.
In the froth flotation process, one of the significant expenses is
the necessary additives which are essential to performance. These re-
agents fall into three groups which are: 1) frothers; 2) collectors or
promoters; and 3) modifying agents. As the name implies, the frother
or frothing agent makes possible the creation of a stable froth which
will last long enough to support coal particles on the surface and hold
them there until they are removed. MIBC (Methyl Isobutyl Carbinol) is
the most common frother used today. Since these frothing agents are not
recoverable, they must be carefully selected not only on the basis of
their effectiveness with the particular coal but also their price. Also,
as their name implies, the collectors or promoters perform the function
of promoting contact between the coal particles and the air bubbles by
selectively forming a thin coating over only the coal particles to make
them water repellent. The most common substances used as collectors are
fuel oil and keorsene. There are some newer reagents which have both
frothing and collecting properties, thereby reducing the number of additives.
The final group of additives, the modifying reagents, perform a
variety of functions as appropriate to the particular coal being treated.
Within this classification are: depressing agents, activating agents, and
pH regulators. Depressing agents are used to inhibit the flotation of
non-coal particles by coating them so they will not adhere to the air
bubbles picking up the coal. Substances used for this purpose include
sodium and potassium cyanides which have proved effective on iron sulfide
86
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(pyrite) particles. Activating agents alter the surface chemistry of the
coal so that it more readily responds to the filming action of the collector
reagent. The pH regulator controls the degree of acidity or basicity of
the flotation slurry. Establishing the proper pH level is a critical
operating parameter which greatly influences the performance of the flota-
tion process. When the pH is between 6 and 7.5, recovery of most coals is
highest. As a general rule, the ash content of the froth increases with
the pH, and the pyritic sulfur content goes down.
The price of froth flotation installations will vary with the size
and number of cells as well as the manufacturer. Since each set or
bank of cells has only one feed box where the slurry enters and one
discharge chamber through which the refuse is rejected, there is not
a simple per cell price for a given capacity installation. Therefore,
it is necessary to price out the particular configuration. For ex-
ample, one manufacturer offers a bank of three flotation cells, each
having a volume of 300 cubic feet (nominally 15-20 tph of feed per cell)
for $34,000 and a bank of four for $38,000. This latter configuration
is offered by another firm for $35,000. Although the 300 cubic feet
capacity cell seems to be the most popular, smaller cells of 100 cubic
feet each and larger ones at 500 cubic feet are also used for treating
bituminous coal. A four cell installation of 100 cubic feet per cell
sells for $28,000 and the 500 cubic feet version sells for $45,000.
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One manufacturer currently has a cell with 1000 cubic feet which is
supposedly capable of handling up to 40 tons per hour of feed at a
solids concentration of between 5% and 10%. These larger capacity
cells have not been required to any great extent in the past since
only a small percentage of the preparation plant feed normally is
processed to this extent. However, as more larger fine coal plants
are put into operation, there will be an increase in demand.
These mid-1977 F.O.B. factory prices were used to approximate
the capital cost of the froth flotation portions of the coal prepara-
4>
tion plants considered in Section 5.0. These prices are only the
"tip of the iceberg" for a fully installed flotation system. This is
because there are extensive pumping and piping requirements which
add appreciably to the cost as well as the system for controlling
the flow of necessary chemical additives. As a general rule, the
total installed price will be slightly over three times the basic
equipment cost.
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2.3 Other Equipment and Facilities
Besides those major pieces of coal handling and storage equipment
described in Section 2.1 and the cleaning equipment covered in the
preceding section, there are other principal components of the modern
coal preparation complex. Although a limited number of these facilities
and equipment are located within the preparation plant, the majority
are separate structures. Many of these other items play a critical role
in the overall performance of the plant. These functions include de-
watering of the clean coal and refuse products, water clarification, and
accurate sampling of the clean coal at the end of the preparation
process prior to shipment. In the following sub-sections, brief
descriptions of these other items are presented along with their cost as
a function of size and sophistication.
2.3.1 Dewatering Equipment
As covered previously, most physical coal preparation techniques
employed today involve wet cleaning processes. During these processes,
the clean coal and refuse products created pick up substantial moisture
which must normally be reduced to some extent. In the case of the clean
coal, the amount of dewatering required is a function of the purchase
specification as well as the economic and practical realities.of trans-
porting and handling a high moisture commodity. Dewatering of refuse
is a less defined issue since the preparation plant operator need only
reduce the moisture content to the point where the material can be
properly disposed. Since fine solids have a larger surface area per
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unit weight than coarser size fractions, they retain relatively more
water and therefore necessitate the availability of greater dewatering
capacity at the preparation plant. Depending upon the amount of finer
coal and refuse generated by the particular process, the dewatering
function can constitute a significant portion of the capital and opera-
ting cost of a plant. There are several forms of dewatering equipment
which are applied as appropriate to the size consist of the material
and the required final moisture content. These are categorized as
centrifugal, vacuum filter, and thermal. Brief descriptions of these
equipments and their cost is presented in the balance of this sub-
section.
2.3.1.1 Centrifugal Dewatering Equipment
As would be expected, this category of dewatering equipment
performs its moisture reducing function by subjecting the wet material
(coal o.r refuse) to centrifugal forces sufficient to drive out as much
of the unwanted water as possible. The design objective of these
machines is not only to reduce the moisture content of the feed but also
to maximize its recovery with minimum degradation. Centrifugal dewatering
equipment is offered in a range of sizes and configurations by a number
of domestic manufacturers each having their own unique design features.
However, the majority of this equipment can be categorized by the follow-
ing types:
1. Vibrating Screen Basket (Horizontal and Vertical Types)
2. Scroll-Type
3. Screen Bowl Type
4. Solid Bowl Type
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(1) Vibrating Screen Basket Type
Vibratory screen basket type centrifugal dryers are offered
by several firms in horizontal and vertical designs. Figure 2-24 shows
one such unit of the horizontal type manufactured by the WEMCO Division
at Envirotech. As depicted by the cross-sectional view of the centrifuge
BELLEVILLE ECCENTRIC WEIGHT SCREEN BASKET FEED
WASHER
RUBBER BUFFER BACK PLATE ; FEED PIPE
BUFFER PLATE
SHEAVE
BEARING
RUBBER
MOUNT
BUFFER PLATE
MAIN SHAFT
Effluent
Discharge
Dewatered
Solids are
Discharged
Through Opening in Base
MECHANISM HOUSING BUFFER RING DISCHARGE HOUSING
CENTRIFUGE MECHANISM
FIGURE 2-24
VIBRATING SCREEN BASKET CENTRIFUGAL DRYER-HORIZONTAL TYPE (WEMCO MODEL 1100)
mechanism, the material to be dewatered enters the small end of the re-
volving cone-shaped screen basket. The free moisture accompanying this
material passes through the screen and the solids move outward along the
surface of this cone-shaped screen until they are discharged over the
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edge of the basket. The vibratory action of this revolving basket,
aids the dewatering process by breaking up the capillary cavities in
the material. According to the manufacturer's data, this unit is capable
of reducing the surface moisture of finer size coal from 30-35% to 8-9%
and from 6-10% to 3% on coarser size fractions with product recoveries
of 97% or better. In terms of capacity, the smaller version of this
centrifuge (Model 1100) is capable of dewatering up to 200 tons per
hour (tph) of Ik X % inch feed or 120 tph of 3/8 inch X 28 mesh. The
larger model (Model 1300) can handle nearly 300 tph of 1% X % inch or
180 tph of 3/8 inch X 28 mesh. These units, which are not recommended
for material less than 28 mesh, sell for $26,000 to $30,000 F.O.B. factory.
A horizontal type is also available from the Bird Machine Co. (Models
1150 and 1300). Depending upon the consistency of the feed, these units
are capable of handling throughputs of up to 275 tph. These units sell
for approximately $50,000 each.
Vertical designs of the vibrating screen basket type centrifugal
dryer are offered by several firms including the Bird Machine Company,
Centrifugal and Mechanical Industries, Inc. (CMI), and Heyl and Patterson
(H&P). Figure 2-25 is a cutaway view of the H & P Hurricane Model showing
how the slurry enters the feed chute at the top and plows down to a
feed chamber where a rotating distributor deposits it on the rotating
basket. At the same time as vertical vibrations are moving the material
up the basket, centrifugal motion is forcing it outward against the
basket screen. This process forces the free moisture through the screen
where it is discharged. As dewatered solids reach the top of the basket,
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CO
FEED
SLURRY
FIGURE 2-25
VIBRATING SCREEN BASKET CENTRIFUGAL DRYER-VERTICAL TYPE (H & P HURRICANE MODEL)
-------
they are discharged over the lip and fall through an opening in the base
of the machine. As with all centrifugal dryers, the capacity of this
machine varies with the consistency of the feed. According to the man-
ufacturer, the Hurricane Model can reduce the moisture content of 150 tph
of 1/4 inch X 48 mesh coal from over 20% to less than 6%%. Several manufac-
turers offer units of this type in a wide range of prices depending upon
design features and quality of construction.
CMI also has a line of vertical type vibrating screen basket cen-
trifugal dryers. These are the VC-48 and VC-56 models which have F.O.B.
factory prices of $28,200 and $49,800, respectively. According to the
manufacturer, these have the capacity and performance at various size
fractions as presented in Table 2-2. This data is based upon feed
moisture concentrations of 30% or less.
TABLE 2-2
VC-48 AND VC-56 CAPACITY AND PERFORMANCE
Solids Capacity in tph Product
Size Fraction VC-48 VC-56 Surface Moisture %
3 X % inch 200 325 2.0
2 X k inch igo 315 2.0
1% X k inch 180 300 2.0
1 X % inch 160 270 2.5
2 inch X 28 mesh 160 270 2.5
1% inch X 28 mesh 150 255 2.5
h X % inch 140 235 3.0
1 inch X 28 mesh 140 235 3.5
% inch X 28 mesh 125 210 5.0
3/8 inch X 28 mesh 115 195 6.5
% inch X mesh 110 185 7.5
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(2) Scroll Type
One of the most popular scroll type centrifugal dryers is the
Model EB-36 manufacturered by CMI. Figure 2-26 shows two of these
units installed in a coal preparation plant. This type of unit consists
FIGURE 2-26
SCROLL TYPE CENTRIFUGAL DRYERS (CMI MODEL EB-36)
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of two conical drums; one turning inside the other at a slightly differ-
ent speed. The outer drum, or basket, is made of stainless steel wire
with replaceable screens mounted on its inner surface. The inner
(scraper) drum carries the scraper blades or flights which control the
solid material movement across the screen. As the material enters at
the top, these blades move it downward over the screen through which
the moisture is ejected by centrifugal force. Eventually, it is worked
down to the discharge area of the dryer where it falls by gravity through
an opening in the bottom of the machine. The moisture and any fine
particles passing through the screen are gathered in a trough around
the periphery of the machine and discharged through effluent openings.
The capacity of this equipment is dependent upon the feed size, surface
moisture, particle shape, and end product requirements. As a general
rule, as the percentage of fines increases, there will be a decrease
in capacity and an increase in the surface moisture of the product. Ac-
cording to the manufacturer, the Model EB-36 has the capacity and perform-
ance at various size fractions as presented in Table 2-3. This data is
based upon feed moisture concentrations of 40% or less.
TABLE 2-3
MODEL EB-36 CAPACITY AND PERFORMANCE
Size Fraction Solids Capacity in tph Product Surface Moisture %
3/8 inch X 28 mesh 80 6 Q
h inch X 28 mesh 60 6 Q
1/8 inch X 28 mesh 50 6_5
1/16 inch X 28 mesh 35 7_5
This unit sells for just over $23,000 F.O.B. factory.
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(3) Screen Bowl Type
The centrifugal dryers discussed thus far are most effective where
the size consist of the wet feed is above 28 mesh. The screen bowl type
centrifugal dryer manufactured by the Bird Machine Company is designed
to dewater finer size clean coal in the 28 mesh X 0 range. In many applica-
tions, this particular equipment can be used instead of a vacuum filter
to handle the fine coal concentrate from froth flotation or other finer
coal products. According to the manufacturer, this machine can reduce
the moisture content of a 28meshX 0 flotation concentrate containing 15% to
20% 325 mesh size particles to 12% to 14% while achieving a 96% to 98%
solids recovery. This is substantially less than the moisture content
of the filter cake produced by vacuum filters which is normally around
20%.
This machine has a horizontal configuration which utilizes some of
the same centrifugal dewatering techniques found in the rotating screen
basket designs covered earlier. From an operational standpoint, the
screen bowl makes a two-step separation. The initial separation takes
place in the solid section of the bowl where centrifugal force aids
the removal of most of the free moisture in the feed. Following this,
the solids move via a conveyor screw onto the screen section of the
bowl where most of the remaining moisture is forced through the openings
in the rotating screen. At the end of screen section, the dewatered
solids are discharged into a collection chamber and drop by gravity
through an opening in the base of the machine.
This Bird screen bowl centrifuge is available in various sizes
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ranging from capacities of 5 tph to as much as 75 tph, depending upon
the feed particle size. Units having these capacities sell for $50,000
and $235,000, respectively. Although these units are significantly
higher in price than comparable capacity vacuum disc filters, this
higher initial cost should be evaluated in terms of the unit's perform-
ance and the potential for lower operating and maintenance costs. One
readily visible operating cost savings comes from the approximately
30% less power consumption over a disc type filter. Another fertile
area for evaluation is the impact on reducing thermal dryer capacity
which as discussed later adds appreciably to the cost of coal preparation.
(4) Solid Bowl Type
This final type of centrifugal dewatering equipment is also appli-
cable to finer size material. Such machines are mainly used in the
same capacity as refuse vacuum disc filters to handle the underflow
from a static thickener. They clarify the water and produce a solid
material suitable for disposal. This machine has a horizontal configur-
ation which has two principal elements. One is a rotating bowl which
is the settling vessel and the other is a scroll conveyor which ad-
vances the settled solids to the discharge ports. The clarified liquid
and the solids are discharged at opposite ends of the machine. As the
bowl rotates, the centrifugal force causes the slurry to form an annular
pool, the depth of which is determined by adjustable effluent weirs.
A portion of the bowl at the solids discharge end has a smaller diam-
eter to form a drainage deck above the level of the pool.
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According to the Bird Machine Company, which manufactures this type
of centrifuge, it is capable of producing a solids product of 30% to 35%
moisture and clean liquid when dewatering feeds having a large concentra-
tion (75-85%) of particles less than 325 mesh. These units are available
for capacities of 2h tph to 30 tph at a cost of approximately $40,000 to
$220,000, respectively. Although they require substantial horsepower to
accelerate the heavy slurry, this type of equipment still requires approx-
imately 50% less horsepower than comparable capacity vacuum disc filter
installations.
2.3.1.2 Vacuum Disc Filter
The disc type vacuum filter is the principal piece of dewatering
equipment used in the coal preparation industry for handling clean
coal and refuse with large amounts of material below 28 mesh. As
mentioned previously, this equipment is commonly used to reduce the
moisture content of the froth concentrate from flotation prior to
thermal drying, as well as handle the static thickener underfow. This
equipment is offered in a wide range of capacities by such companies
as the Denver Equipment Division of Joy and Peterson Filters Corporation.
As shown in Figure 2-27, the vacuum disc filter consists of a
series of discs mounted over a trough shaped tank so that slightly
less than half of the disc is below the edge. These discs are covered
on both sides with a fine mesh filter cloth or other suitable filter
medium. To be effective, this medium must permit the passage of air
but not become clogged by the material being filtered. The discs are
mounted on a hollow shaft with a complex plumbing arrangement permitting
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FIGURE 2-27
VACUUM DISC FILTER (10 FT 6 INCH DIAMETER 12 DISC VERSION)
the application of suction and pressure to the surface of each disc,
as well as the withdrawal of the fluid collected. The slurry to be
dewatered is fed into the trough at which time suction is applied
pulling the slurry toward the disc surfaces. In order to pull the
fluid through the filter surface, an air flow of about 5 cubic feet
per minute (CFM) per square foot of filter surface is normally applied
when processing froth concentrate and about 3 CFM per square foot of
filtering surface when handling thickener underflow. As a result of
this action, the solids portion of the slurry is deposited on the disc
surface. Then, the discs are rotated approximately 120 degrees carrying
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with them the solids or filter cake retained on their surfaces. At this
point the filter cake is loosened from the disc surface by reversing
the pressure (blower action) and scraped off into a discharge chute.
The moisture content of this cake will vary from 20% up, depending
upon the makeup of the slurry.
The capacity of a vacuum disc filter is influenced by the solids
concentration of the slurry to be dewatered and the amount of material
less than 325 mesh. However, as a very general rule, between 40 and
60 pounds per hour per square foot of filtering area is appropriate
when dewatering clean coal and about 20 pounds per hour per square foot
for refuse. For example, a 12 foot 6 inch diameter disc filter having
12 discs has 2,736 square feet of effective filtering surface. There-
fore, on a load philosophy of 40 pounds of clean coal per hour per
square foot, this size vacuum filter should be able to handle a maximum
of 110,000 pounds or 55 tons per hour. Normally, it is a good idea
to have some excess filtering capacity to allow for variations in the
concentration of the feed.
Although there are some design differences among the various vacuum
disc filters on the market, there is not as much variance in their price
for a given capacity unit as might be expected. A representative sample
of mid-1977 F.O.B. factory prices is as follows:
Disc Diameter Number of Discs Filtering Area Price
10 ft 6 inches 7 1,085 sq.ft. $90,000
11 ft 6 960 sq. ft. $ 70,000
11 ft 8 1,280 sq. ft. $ 85,000
12 ft 6 inches 10 2,280 sq. ft. $120,000
13 ft 12 2,880 sq. ft. $128,000
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Besides capacity, prices will be significantly influenced by the type
of filter medium selected. This is not only an important decision from
the standpoint of initial cost, but also operational performance and
reduced maintenance. For example, stainless steel wire mesh will cost
over three dollars per square foot but last as much as 10 to 15 times
longer than a cheaper filter medium such as saran.
2.3.1.3 Vor-Siv
Although one of the major principles governing the operation
of the Vor-Siv is centrifugal force, a discussion of this stationary
dewatering device was omitted from the earlier section on centrifugal
dewatering equipment to allow separate coverage. The Vor-Siv was de-
veloped by the Polish coal industry and is currently manufactured in
this country by the Perforated Metals Division of the National-
Standard Company under an exclusive licensing agreement. It is designed
to handle high volumes of solids in a water slurry. Some of the ways
this equipment has been applied in coal preparation circuits include
dewatering ahead of centrifuges, desliming ahead of concentrating
tables, and as protection devices ahead of thickeners and flotation
cells. The unit can handle particles less than 3/8 inch size in slurries
of 10% to 30% solids concentration. A single unit can handle such a slurry
at feed rates up to 3200 gallons per minute and thereby produce 150 tph
of dewatered material.
To better understand the operation of this device, the reader is
referred to Figure 2-28 which shows the major components and a simulated
flow pattern. Feed is introduced to the unit through a directional
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CIRCULAR RACEWAY
FEED
SIMULATED FLOW PATTERN
GUIDING TROUGH
INLET NOZZLE
DISCHARGE OUTLET FOR
DEWATERED AND CLASSIFIED
MATERIAL
COLLECTION BOX
FOR EFFLUENT
FIGURE 2-28
VOR-SIV CONICAL SIEVE
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nozzle and onto a circular raceway. A certain minimum head is necessary
to accelerate the feed slurry against the walls of the raceway, causing
partial stratification of solids away from the associated water. Normally
gravity is sufficient to create this necessary feed force. As the semi-
stratified feed stream loses energy, it spills from the raceway into a
conical basket of radially slotted profile wire. The remaining energy
in the feed stream creates a downwardly spiral ing vortex flowing per-
pendicular to the slotted openings in the upper three fourths of the
basket. Free water and, depending upon the slot aperture, undersized
solids are accelerated through the basket, becoming an effluent product.
As water is extracted and the vortex continues to lose energy, the
circular swirl gives away to an axial path downward along the lower one
fourth of the basket. Slotted openings in this section are placed per-
pendicular to those in the upper section. Since feed travel has
changed from the horizontal flow into a downward drop, these slots again
provide a "crossflow" action enhancing the final stages of water removal.
The simulated flow pattern in Figure 2-28, shows how the vortex action
causes the solid particles to change their radial position and flow down-
ward along a steep spiral path on the surface of the screen to the dis-
charge outlet at the point of the vortex.
One of this device's principal advantages is its high capacity.
While most stationary screens and sieves are limited to feed rates of 28
to 30 gpm per square foot of screen surface, Vor-Sivs have been success-
fully applied at rates of 50 to 60 gpm per square foot of screen surface.
Even at these high feed rates, water removal and undersize rejection
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efficiency have been equal to or better than achievable with con-
ventional equipment. Other advantages include: they require no
lubrication, generate no noise or vibration, require essentially no
operator attention or adjustment, and maintain consistent performance
over a wide range of feed variables. Capital cost studies have shown
the devices to be quite desirable when contrasted with conventional
dewatering equipment in new plant design. Retrofit applications have
also been quite popular.
As of mid-1977, the F.O.B. factory price of a Vor-Siv was approxv
mately $15,500 to $17,000 depending upon the size of the two-part re-
placeable screen sections.
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2.3.1.4 Thermal Dryer
The final major piece of dewatering equipment to be discussed is
the thermal dryer. This evaporation process is normally applied to
fine and intermediate (typically less than 1 inch) size clean coal
which has not been sufficiently dried to meet the specified moisture
level by the various centrifugal and vacuum filter dewatering tech-
niques discussed earlier. Thermal drying is an expensive process
from both the standpoint of initial capital requirements as well as
the long term operating and maintenance costs. In this country, the
application of thermal drying to physically cleaned coal has decreased
from 19.8% in 1970, to 13.4% in 1975. Moreover, the actual tons dried
have decreased by nearly 50%, i.e., 64,165 in 1970 and 35,681 in 1975.
Although there are many forms of dryers, the dominant thermal drying
method is fluid-bed which has been growing in acceptance in recent
years as shown by Table 2-4. The drop in tons of physically cleaned
coal and thus those subjected to thermal drying decreased during the
the 1973 to 1975 period due to several factors. The major factor was
the sharp increase in demand for coal and thus there was less of a
necessity to perform these costly processes. Another influence was
the tighter environmental/emission control regulations which have
forced the discontinuance of dryers at some locations rather than in-
stall and/or modify the facilities to comply. In addition, as noted
previously, the operation and maintenance problems and costs are
enough by themselves to encourage detailed investigations of other
options and strategies before initiating thermal drying. Therefore,
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TABLE 2-4
COAL THERMALLY DRIED IN COMPARISON TO ANNUAL PRODUCTION*
(Thousand Short Tons)
Year
1975
1974
1973
1972
1971
1970
Production
648,438
603,406
591,738
595,386
552,192
602,932
Mechanically
Cleaned
266,993
265,150
288,918
292,829
271,401
323,452
Thermally
Dried
35,681
36,045
46,202
53,235
48,105
64,165
% Dried
of Total
Production
5.5%
6.0
7.8
8.9
8.7
10.6
% Dried
of Total
Cleaned
13.4%
13.6
16.0
18.2
17.7
19.8
% Dried By
Fluidized-Bed
72.5%
68.3
66.9
64.1
67.7
66.4
* Bituminous & Lignite
Source: Based Upon U.S. Bureau of Mines, Mineral Industry Surveys, Coal-Bituminous and Lignite Annual 1970-75,
Prepared in Division of Fuels Data and Division of Coal.
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it should be employed only after a careful evaluation of the economies
as they relate to the realities of the marketplace. In other words,
if it does not pay to dry - don't.
Due to the nature of the process, the thermal drying function is
conducted in a separate facility linked only with the main coal prepara-
tion plant by way of a conveyor. A view of such an installation ap-
pears as Figure 2-29, which is an intermediate size unit manufactured
by the FMC Corporation. These are sophisticated installations which can
account for over 25% of the capital cost of the total preparation plant
complex when a substantial portion of the output is dried. A more pre-
cise understanding of this relationship can be obtained from a review
of Examples 2, 3, 4, 6, and 8 in Section 5.0 which have varying thermal
drying requirements. To meet these various requirements, fluid-bed driers
are offered by several companies in a wide range of capacities, each
with its own unique design features. Some appreciation for their
sophistication can be gained from Figure 2-30, showing a cutaway view
of a thermal dryer manufactured by the ENI Division of Lively Manu-
facturing. Being a well defined portion of the overall preparation
process permits a fairly accurate appraisal of the capital and 0 & M
costs associated with thermal drying. The following is an example of
the capital cost as of mid-1977 for a medium size fluid-bed dryer.
Description of Drying Requirementi
Bituminous Coal % inch X 0
Reduce Moisture from 13% to 5% at the rate of 350 tons per hour
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1
FIGURE 2-29
FLUID-BED THERMAL DRYER INSTALLATION (FMC FLUID-FLO MODEL)
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TEST PLATFORM
DUST COLLECTOR
CYCLONES
EXHAUST FAN DUCT
MIST ELIMINATOR STACK
FURNACE BY-PASS STACK
DRYER FEED CONVEYOR
/
DRYER FEED
CONTROL BIN
DRYER ROLL FEEDER
FURNACE
STOKER ROOM
DUST
HOPPERS
EXHAUST FAN
MOTOR
VENTURI SCRUBBER
MOTOR & FAN INSTRUMENT AIR COMPRESSOR
ACCESS PLATFORM
f STO HER FUEL
CONVEYOR
OVERFIREFAN
FORCED DRAFT FAN
DRIED PRODUCT
CONVEYOR
TEMPERING AIR DAMPER
DISCHARGE AIR LOCKS
MIST ELIMINATOR
FIGURE 2-30
CUTAWAY VIEW OF FLUID-BED THERMAL DRYER (ENI COAL-FLO MODEL)
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Description of Drying Facility:
One (1) 10' X 14' FMC Fluid-Flo Dryer with connected horsepower
of 2200 hp. Complete with roll feeder, stoker, furnace, ductwork,
fluidization chamber, hood, cyclone dust collectors, exhaust fan,
scrubber, stack, feed bin, fuel conveyors, fuel bin, ash conveyor,
insulation, dust screws and automatic temperature controls.
Price $ 950,000
Installation of Dryer including foundation, structural steel, motors,
motor controls, wiring, piping, field erection, and start-up service.
Price $1,650,000
TOTAL DRYER CAPITAL COST $2,600,000
In order to generate the heat necessary to achieve the required
moisture reduction, this dryer would be consuming approximately 6 tons
per hour of coal having a nominal heat content of 12,500 Btu/lb. If
we assume that such a coal has a cost of $20 per ton to the preparation
plant operator, then, the fuel cost per ton of dried coal would be:
6 tons/hr X $20/ton = $0.343/ton
350 ton/hr
If this particular plant was producing an additional 550 tons per hour
of clean coal for a total output at 900 tph, then the fuel cost impact
per ton of total product would be:
6 tons/hr X $20/ton
= $0.133/ton
900 tons/hr
In addition to the fuel (coal) necessary to operate the thermal
dryer, electricity is another major operating cost factor. Using the
standard relationship between kilowatts and horsepower of 0.745 kw = 1 hp,
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an estimate of the electric power consumption and cost of operating the
thermal dryer can be made. In the case of a dryer having 2200 hp the
following calculations apply:
0.745 kw/hp X 2200 hp = 1,639 kw
With 80% efficiency, consumption would be:
l^p. = 2,048.75 ^ 2,050 kw
U.o
Assuming an electric rate for a large industrial user of between
$ 0.03 & $ 0.05 per kilowatt hour, electricity cost per hour would
be - $ 0.04/kwh x 2,050 kw = $82.00 per hour.
Therefore, if a dryer of this size (2200 hp) is processing
350 tons of coal per hour, the electric cost on a dried ton is -
$82.00/hour - 350 tons/hour = $ 0.23/ton
•
If the plant was producing an additional 550 tons for a total clean
coal output of 900 tph, then the impact on each ton of clean coal
would be -
$82.00/hr - 900 tons/hr = $ 0.09/ton
This tells us that the impact of thermal drying electric cost
alone is $ 0.09 per ton. Since there is normally a comparable volume of
horsepower in the balance of the preparation plant, the overall
electricity cost will be roughly $ 0.18 to $ 0.20 per ton of clean
coal. If the electric rate was $ 0.05 per kwh, then this cost could
be as high as $ 0.23 per ton.
This is just one example of a fluid-bed thermal drying application.
Each case will not only vary with the volume and size of the feed but also
according to the nature of the coal itself and the specified end product.
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However, when some level of thermal moisture reduction is necessary,
the volume of material fed to the dryer should be kept to an absolute
minimum in order to limit the high capital and 0 & M costs referred to
above. As has been said previously regarding other portions of the
preparation plant, the applicability and/or necessity of thermal dryers
must be determined on a specific case basis where the further reduction
in moisture is weighed against the required end product and how and
where it will be handled and eventually consumed.
2.3.2 Static Thickener
The majority of the coal preparation plants in operation today and
all those built in recent years have a closed water system. What this
means is that the effluent from the cleaning plant must be handled in
such a way that the solids and liquid are separated before being released
into the environment. With the increase in fine coal cleaning and
the use of continuous mining methods, a greater amount of solid material
winds up in the waste water from the preparation plant. Although settling
ponds are still used to a large extent, the most common method of clarify-
ing this waste water is with the use of a static thickener.
As shown in Figure 2-1, the typical static thickener is a circular
tank usually of concrete or steel construction which is located close to
the cleaning plant. To understand the workings of this critical piece
of water clarification equipment, the reader is referred to Figure 2-31
showing a cross-sectional representation of a static thickener. The
liquid effluent from the plant is fed via a trough into the feedwell at
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FEED TROUGH FROM PLANT
WALKWAY DRIVING
MECHANISM FEEDWELL
CLEAR
OVER-
FLOW
SOLIDS UNDERFLOW PUMPED
FROM THIS AREA
ROTATING RAKE
TANK BOTTOM
FIGURE 2-31
CROSS-SECTION OF STATIC THICKENER
the center of the thickener. This can be seen in Figure 2-32 which
shows the slurry moving out to the center of the tank and into the feed-
well -whose rim is about one foot above the liquid level. As this slurry
flows from the feedwell out toward the edge of the tank, the solids tend
to settle. This settling is encouraged by the addition of flocculants
and other chemicals. The settled solids are pushed along the bottom of
the tank by slow moving rakes. These rakes or plows are driven by a
heavy duty, all weather, mechanism located at the center of the tank.
Because of the slope of the tank bottom, these solids are moved toward
the center of the tank from which they are pumped to a vacuum filter or
other dewatering device. Once dewatered, this solid underflow material is
normally disposed of with the coarser refuse from the plant. However, in
some plants, this thickener underflow has desirable enough properties to
warrant blending it back in with the clean coal product. The clarified
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DRIVE MECHANISM
FEEDWELL IN CENTER
OF TANK
DIRECTION OF FEED
FIGURE 2-32
TOP VIEW OF STATIC THICKENER
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liquid overflows the outer edge of the tank into a trough from which it
is pumped back into the plant's water system for reuse in the cleaning process.
Static thickeners are sized according to the anticipated clarifica-
tion requirements of the plant plus a reasonable margin for variations
in the quality of the raw feed. This is necessary since during the
mining of any given seam, substantial variations in composition will be
experienced. Also, in cold weather when the coal is damp and muddy,
greater amounts of clays and other fine material are brought into the
plant and must be handled by the water clarification system. This
problem can be particularly acute in the case of strip mined coal.
Depending upon the requirement, static thickeners are constructed
in a range of sizes up to over 200 feet in diameter. Although the
price will vary with the sophistication and quality of the drive mech-
anism, a very good approximation of the total installed price of a con-
crete type between 90 and 200 feet in diameter is $2,000 oer foot of
diameter. In this size range, the drive mechanism alone will account
for 45-55% of the total installed price. This mid-1977 composite price
will also be subject to the cost and availability of local materials
of construction but to a lesser extent than that for concrete silos
discussed in Section 2.1.1.
2.2.3 Coal Sampling Equipment
A detailed discussion of coal sampling techniques and equipment
is beyond the scope of this report. However, it will suffice to say
that with the trend toward larger and more complex coal preparation
plants, there will be an increasing need for efficient and accurate
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analysis of the clean coal product prior to its leaving the plant.
Such data is particularly important where blending is practiced or coal
is prepared for slurry pipelining. This need may also be accentuated
by the application of pending environmental regulations which might re-
quire precise documentation on the amount of sulfur which was present
in the as-mined coal and was removed by the cleaning process.
Regardless of the cleaning plant's level of complexity, some analysis
of the raw and clean coals is necessary to evaluate performance. Many
times the sampling procedure is not just for the benefit of the
preparation plant operator, but is part of a purchase specification.
Under these circumstances, the coal is sampled before it leaves the plant
and then again at the destination. Depending upon the individual contract
relationship, this data can provide the basis for applying bonuses or
penalties according to variances in the as received product in comparison
with predetermined ash, moisture, sulfur, and Btu limits.
Coal sampling equipment is offered in a wide range of sizes and
sophistications. There are multi-stage sampling systems which are of
such size and complexity that they are constructed as a separate building
(tower) adjacent to the cleaning plant or part of the load-out facility.
Sampling systems of this type can cost over half a million dollars and
are usually found only at very large plants. An indication of this
complexity is given in Figure 2-33, which schematically represents a
coal sampling system manufactured by the Denver Equipment Division of
Joy Manufacturing Co. Since there is such a variance in the application
and need for sampling systems, a figure of $300,000 was used to estimate
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Primary
Sampler
Secondary
Sampler
Collector
Reject
Conveyor
FIGURE 2-33
THREE-STAGE COAL SAMPLING SYSTEM - (DENVER EQUIPMENT DIVISION OF JOY)
this capability for all larger preparation plants considered under Sec-
tion 5.0 rather than the cost of the system actually being used. This way
the total capital cost of any given plant was not biased for comparative
purposes because of its particular system.
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SECTION 3,0
SMALLER SIZE PREPARATION PLANTS
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3.0 SMALLER SIZE PREPARATION PLANTS
Although the major thrust of this study was to more accurately define
the costs associated vith preparation plants of 500 tons per hour raw coal
input or greater, it may be useful to the reader to have some indication of
the costs related to smaller scale operations. As in the case of larger
plants, the final cost of the plant is a function of the many variables unique
to the particular situation. Two of the most important variables are the
washability of the coal and the end product specification. These will dic-
tate the make-up of the cleaning circuit and to what extent the material
must be dried. As indicated elsewhere in this report, the extent to which
the product must be dewatered has a very significant impact upon the initial
capital requirements and the on-going 0 & M costs.
Preparation plants can meet a variety of needs in the smaller scale op-
eration. In some cases, a mine can clean a portion of its production with a
simple "semi-portable" plant and come up with a marketable product. There are
a number of smaller size plants being offered by such firms as Coal Process-
ing Equipment, Inc., Jeffrey Manufacturing Division of Dresser Industries,
and RAPCO, Inc. These plants come in a wide range of sophistications, some
of which are even capable of finer size coal recovery. Although there is
not much interest yet, one application for these smaller plants may be in
the recovery of coal from existing refuse piles. The economics of such an
arrangement can be quite favorable under some circumstances since there is
no mining or mine development cost necessary and therefore more investment
in cleaning equipment can be made while still yielding an acceptable rate
of return.
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Jeffrey Unitized Jig Coal Cleaning Plant
One smaller size coal preparation plant is the Jeffrey unitized jig
plant. This is a packaged coal washing plant utilizing a Jeffrey two-cell dia-
phragm jig as the cleaning unit. The plant which has a nominal capacity of 150
tph of feed is structurally arranged as shown in Figure 3-1 below.
FIGURE 3-1
LAYOUT OF UNITIZED JIG
The plant comes as a package containing all equipment, structural steel,
interconnecting chutes, piping, electrical distribution system, lighting, siding
and roofing and other materials necessary for construction. The purchaser
supplies an appropriate site, foundations, power supply and fresh water supply.
The cost of the raw coal delivery system and the clean coal handling system is
not included and can be supplied either by Jeffrey or the purchaser.
General Process Description -
As shown in Figure 3-2, the raw coal is delivered by belt conveyor to the
jig feed chute where the raw coal is mixed with water.
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•RAW COAL
•CLEAN COAL
REFUSE
-CLEAR WATER
• WASTE WATER
FIGURE 3-2
FLOW SHEET OF UNITIZED JIG PLANT
The raw coal then reports to the two-cell diaphragm jig where the coal
is washed. The refuse material is removed from the jig by bucket elevators for
dewatering. The refuse is dewatered on a double deck screen with the coarse
refuse reporting to a 50 ton refuse bin. The fine refuse (-28 mesh) and water
report to waste.
The clean coal from the jig is dewatered and sized on a double deck
vibrating screen. The 1/2 inch coal passing over the top deck of the dewatering
screen is crushed to the desired product size. The 1/2X1/4 inch coal passing over
the second deck of the screen is further dewatered in a centrifugal dryer. The
1/4 inch X 0 material reports to a sump from which it is pumped to clarification
cyclones. The underflow from these cyclones is partially dewatered and deslimed
by sieve bends before being combined with the 1/2X1/4 inch material for centri-
fugal drying. The overflow from these cyclones reports to a head tank for
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recirculation to the jig. The slimes and water from the sieve bends and the
centrifuge combine with the fine refuse and report to waste. The clean coal
from the crusher and the centrifugal dryer is collected as a final product for
loading or storage.
The fine waste (fine refuse and slimes from the sieve bends and centrifugal
dryer) will generally report to settling ponds for clarification. A closed
circuit using a thickener and vacuum filter could be provided as an option.
Such an option has not been considered in the estimated price of the system
appearing at the end of this section.
The mechanical action bringing about the separation of the raw feed into
clean coal (float) and refuse (sink) is shown by Figure 3-3, which also identifies
the major component of a two-cell jig.
FIGURE 3-3
TWO-CELL DIAPHRAGM JIG
123
AV OPEN i »3 Pl*T€
CONIEC TI I«
Cfl iX « IB*
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Plant Performance -
1. Capacity
The performance of the unitized jig plant is dependent strictly on the
performance of the jig since it is the only piece of washing equipment used.
All other equipment has been sized to handle the maximum tonnages and flows
which the jig is capable of handling. The nominal capacity of the jig is
150 tph. The actual capacity of an individual plant is based on the size
consist of the coal to be washed and its washability characteristics. As
the separation becomes more difficult (i.e., fine coal cleaning or a large
amount of near gravity material), the capacity of the jig is reduced to allow
for proper cleaning. As the separation becomes easier (i.e., coarse coal
washing or little near gravity material), the capacity increases.
2. Coal Quality
The clean coal quality produced by the unitized jig plant is dependent
on the washability characteristics of the raw coal and the limitations of
the jig.
The two-cell diaphragm jig will generally wash the coarser size feed (plus
1/4 inch) at a specific gravity between 1.50 and 1.60. It will wash finer coal
(1/4 inch X 28 mesh) at a somewhat higher specific gravity, generally around
1.80, and its ability to wash very fine coal (minus 28 mesh) is negligible al-
though some cleaning does occur. The minus 100 mesh material is discarded as
refuse. The following example will help to illustrate this performance.
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Given a raw coal with the following washability characteristics;
ANALYSIS OF THE RAW FEED
Size Fraction
+1/4 inch
1/4 inch X 28 mesh
28 mesh X 100 mesh
-100 mesh
Total
% of
Total
57.12
33.17
8.77
0.94
% S
1.05
0.95
1.12
1.84
Btu/lb
11,947
11,602
9,555
7,890
100.00
1.03
11,585
% Ash
14.23
16.07
21.27
30.44
15.61
WASHABILITY DATA - PLUS 1/4 INCH
Specific
Gravity
SINK FLOAT
1.35
1.40
50
60
1.35
1.40
1.50
1.60
1.80
1.80
Specific
Gravity
SINK
_
1.35
1.40
1.50
1.60
1.80
FLOAT
1.35
1.40
1.50
1.60
1.80
_
% REC.
68.8
7.4
9.2
3.0
2.4
9.2
% REC.
66.7
7.8
7.8
3.0
2.7
12.0
57.12% of
Individual
Dry Basis
% ASH % S
4.64 0.72
11.04 1.07
18.52 1.34
25.85 1.81
38.28 2.72
74.21 2.58
WASHABILITY DATA
33.17% of
Individual
Dry Basis
'% ASH %'S
4.15 0.65
10.96 0.89
18.86 1.31
29.56 2.05
42.05 2.56
74.59 1.80
Total Sample
Btu/lb % REC.
13,515 68.8
12,541 76.3
11,350 85.4
10,130 88.4
Cumulative
Dry Basis
% ASH % S
4.64 0.72
5.26 0.75
6.69 0.82
7.34 0.85
7,900 90.8 8.14 0.90
1,982 100.0 14.23 1.05
- 1/4 INCH X 28 MESH
Total Sample
Btu/lb % REC.
13,535 66.7
12,437 74.5
11,091 82.3
9,331 85.3
7,226 88.0
2,203 100.0
Cumulative
Dry Basis
'% ASH % S
4.15 0.65
4.86 0.68
6.19 0.74
7.01 0.78
8.09 0.84
16.07 0.95
Btu/lb
13,515
13,420
13,198
13,094
12,959
11,947
Btu/lb
13,535
13,420
13,199
13,063
12,884
11,602
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If only the coarser size (+1/4") was washed the following clean coal quality
from the plant would be expected on a dry basis:
% WT. % Btu
RECOVERY % MOISTURE % ASH % SULFUR Btu/lb RECOVERY
88.4 <6 7.34 0.85 13,094 96.9
This is the quality of the + 1/4" material only. The quality of the composite
clean coal (+1/4" clean coal and -1/4" raw coal) would be:
% WT. % Btu
RECOVERY % MOISTURE % ASH % SULFUR Btu/lb Recovery
93.4 <6 12.08 0.92 12,259 98.8
If all the raw coal sizes were fed to the plant, the following clean coal
quality would be expected:
% WT. % Btu
RECOVERY % MOISTURE % ASH % SULFUR Btu/lb Recovery
89.3 <6 8.97 0.87 12,673 97.7
The choice between washing only the coarser coal or all raw coal sizes is a
judgement decision, dependent on the desired clean coal quality and the washa-
bility. In some cases the-1/4 inch material needs little if any cleaning and could
bypass the plant with very little detrimental effect on the clean coal quality.
In other cases, as the one above, the washing of the fine coal along with the
coarse coal produces a better overall clean coal.
3. Capital Cost
The initial capital cost of a unitized jig plant excluding raw coal and
clean coal handling facilities, site preparation, foundations, power supply
and fresh water supply, is approximately $650,000. The cost of the excluded
items will vary greatly, depending on site configuration and location. However,
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the average expected cost of these items would be approximately $450,000.
This gives a total average cost of $1.1 million. Placed on the basis of
150 tph raw coal input, this translates to $7,300 per ton hour input. As
would be expected, this is slightly higher than larger simple jig plants of
the type described by Example 1 in Section 5.0.
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SECTION
OPERATIONAL AND OTHER FACTORS INFLUENCING COST
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4.0 OPERATIONAL AND OTHER FACTORS INFLUENCING COST
This section is devoted to a brief discussion of the major factors
which influence the cost of coal preparation irrespective of the type of
cleaning process. Although some of these factors such as plant utiliza-
tion are controllable to some extent, others like diminishing coal
quality are more a reality of the times.
4.1 Plant Utilization
Obviously, there are 8,760 hours in most years (24 hours/day x
365 days/year). Although these can be considered the maximum potential
number of working hours per year, there are some practical considerations
brought on by custom and the nature of the process as well as the legal
and union realities of the environment in which business functions. By
custom, we are referring to the fact that most workers today are geared
to a forty hour or less work week, the observance of certain holidays,
and annual vacations. Also limiting the number of hours a particular
process can be fully functional are the practical/economic limits im-
posed by the necessity to shut down for scheduled and unscheduled
maintenance and the doubtful availability of an unlimited pool of
qualified personnel to fill-in when the regular staff is absent. Addi-
tionally, in some industries, such as coal preparation, there is not a
continuous supply of raw material available. Finally, the legal and
union restrictions on the number of hours and designated days an employee
can work without being paid premium wages influence the total number
of hours a particular operation will be productive during any given
year.
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In a capital intensive industry such as coal preparation, the
greater the plant can be productive, the less will be the capital cost
burden carried by each ton of clean coal. Additionally, the more the
plant can run continuously, the less time will be lost in start-up and
shut down. To try and assess the impact of such "lost" time, the in-
fluence of the union contract imposed work hours is discussed below.
Plant Efficiency - Impact of Union Contract
The most recent National Bituminous Wage Agreement of 1974, which
was effective through 5 December 1977, provided for preparation plant
and supporting personnel (outside employees) to have a 7 hour and 15
minute work day. Included in the 7.25 hours is a 30 minute lunch break.
For this 7.25 hours per day and 36.25 hours per week, the employer must
pay the overtime wage rate of time and one-half for the additional
time worked.
Considering the practical application of this number of hours to
the efficient operation of a preparation plant gives some food for
thought which has encouraged operators to use overtime in spite of the
cost. It is standard practice at plants to conduct three shifts per
day beginning at 8 A.M., 4 P.M. and 12 A.M. Assuming two of these
shifts are operating and no overtime is incurred, it will take 30 minutes
to an hour to start-up and the plant will be shut-down between 30 minutes
and an hour before the shift is over if overlapping scheduling of
workers is not permitted. This means that a minimum of one hour and
45 minutes of potential operating time is lost before the next operating
shift comes on duty; i.e., half an hour starting up, half an hour to shut
down plus 45 minutes between shifts. Then, it will take the second
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operating shift between 30 minutes and an hour to get the plant
functioning at capacity again. Toward the end of this shift, the plant
will again have to be shut down which will mean a loss of another 30
minutes to one hour. Therefore, during the period from 8 A.M. to
12 midnight when there was potentially sixteen hours of operating time,
the plant only produced coal during a maximum of 12.5 hours. This was
calculated as follows:
Total Potential Operating Hours 16.0
Between 8 AM and 12 Midnight
Less:
8 A.M. Shift Start-Up 0.50
8 A.M. Shift Shut-Down 0.50
Break Between Shifts .75
4 P.M. Shift Start-Up 0.50
4 P.M. Shift Shut-Down 0.50
Break Between Shifts .75
Total Lost Operating Time 3.50
Net Operating Time 12.5
Since the half an hour at the beginning of the day and the conclusion
of the second shift is essential, an additional 2.5 operating hours
might be picked up if overtime was incurred.
One way of evaluating the impact of this lost operating time is to
look at the additional expenses and income associated with the extended
period. For the purposes of this analysis, it is assumed the preparation
plant is capable of producing 1000 tons of clean coal per hour and
that a profit of $2.00 per ton is realized. This amount is meant to
Be a conservative estimate of the profit after considering all normal
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mining and preparation costs. Therefore, on the income side, if an
additional 2,500 tons of clean coal were produced, $5,000 would be
available to cover the increased labor costs.
Current Industry Practice
During the initial phase of this study conducted during 1975-1976,
we had determined that preparation plants typically operate approximately
3,380 hours per year out of a possible 8,760 for an annual utilization
of 38.6%. This was based upon data collected from plant operators and
other industry sources. However, data collected during the first half
of 1977 indicate that our previous utilization level was high. Many
instances were recorded where operators ran the plant two shifts and
performed maintenance on a third. Unfortunately, although they were
paying for 14.5 operating hours (two 7.25 hour shifts), the plant would
only function 11 to 13 hours per day. Compounding this problem of
utilization was the fact that with vacations, holidays, special leave,
sick days, and unaccountable absences, the plant might only operate
200 days per year. Variations of these current conditions are reflected
in the operating and maintenance costs of the actual preparation plants
examined in Section 5.0.
Those costs such as capital amortization which are sensitive to output
(plant utilization) have been allocated on the basis of the given plant
functioning at the nominal capacity indicated on its flow sheet for
2600 hours per year. This is equivalent to two 7.25 hour operating
shifts (UMWA) 200 days per year reduced by 1.5 hours per day to allow
for start-up on the first shift and shutdown on the second. This assumes
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overlapping of workers on operating shifts. Although this represents
only a 30% utilization of the plant on an annual basis, it is not
uncommon in recent years due to unscheduled work stoppage, mining
production delays, and other factors. However, it is assumed that
not all operations are plagued by these difficulties and those that
are, will be able to increase their utilization. Therefore, the oper-
ating and maintenance costs presented for each preparation plant example
are summarized on the basis of a raw coal input and clean coal output
under both a 30% and 40% utilization. This latter utilization figure
equates to 13 hours per day for 270 days per year '(3510 hours) and rep-
presents an upper bound on being able to retain a maintenance shift for
every two operating shifts with the plant layout considered. Higher
utilization can obviously be achieved if redundant preparation circuits
were to be included which would permit ongoing maintenance without total
plant shutdown. Although there may be definite economic advantage assoc-
iated with such an approach under certain conditions, only one such plant
was examined and thus no definite conclusions can be drawn.
4.2. Coal Quality
The material withdrawn from the coal seam before being subjected
to any form of preparation is referred to as run-of-mine. In addition to
actual coal, this mined product includes rock and other impurities taken
from the ground as part of the mining operation. Since the introduction
of modern mining machinery and methods, the quality of this material
has diminished. This reduced quality is reflected in lower yields from
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preparation plants due to the greater amounts of refuse in the raw
feed. In order to compensate for this situation, existing plants have
had to be redesigned to provide greater refuse handling capacity so as
not to reduce the desired quality of the clean coal product. Several
years ago, plant yields of 80 - 90 % were not uncommon. However, today,
it is equally not uncommon to observe coal preparation plants having
yields in the range of 50 %. Needless to say, this requirement for greater
refuse handling capacity makes for higher capital and operating and
maintenance costs, not to mention the larger refuse disposal problem.
This latter problem can be particularly acute due to the environmental
regulations governing refuse disposal and the lack of suitable landfill
areas.
Some of the specific factors which contribute to the degradation of
the run-of-mine coal are as follows:
1. Mining Machinery - Increased usage of continuous mining equipment.
Due to the manner in which this equipment functions, greater
amounts of material above and below the coal seam (roof and
floor) are loaded out with the coal than occurs in conventional
mining.
2. Mining Methods -
A) Greater use of water for dust control, In an attempt to
meet dust limitations, an increasing amount of water is
now used in the mining process. This water places into
suspension such undesirable impurities as clay and rock
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dust which are eventually loaded out with the coal and
wind up at the preparation plant.
B) Requirement for continuous clean-up. Federal regulations
direct the removal of excess material from the mining
area to keep passages fully open. Thus, it is more convenient for
the miner to load out all the material in the way at one
time rather than make a separate coal and rock cycle.
3. Quality of Coal Seams - Many of the coal seams being mined today
contain large amounts of impurities which cannot be avoided in
the mining process and are therefore loaded out directly with
the coal.
This diminishing coal quality is reflected in terms of higher capital
cost for the same capacity plant. Additionally, operating and maintenance
costs are affected especially in the areas of refuse disposal and chemical
»
expense associated with water clarification.
4.3 Capital Amortization
4.3.1 Capital Amortization Defined
Whether a plant is bought outright, financed through a third party,
or leased over an extended period, the total capital costs represent an
outlay of funds to someone which must be accounted for in determining
the overall cost of coal cleaning. If the company operating the prepa-
ration plant had sufficient liquidity to purchase the installation with-
out outside assistance, they still must account for these funds invested
135
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which they have elected to withdraw or divert from other income pro-
ducing opportunities. Not only do they want to recover these funds
during the useful life of the plant, but they should also receive a fair
rate of return based upon other investment alternatives. If a plant is
fully leased through an outside source, the operator's total lease payments
consist of both the plant cost and a "fair rate of return" to a third party
in the form of interest. Although the period of recovery and the rate of
return/interest will vary, this same "cost of capital" reasoning applies
regardless of the source of funds; only the mechanics differ. This
mechanical process normally takes the form of spreading the cost of the plant
over its output and is referred to as capital amortization.
Nhere a company has purchased the plant with its own or borrowed
funds, the capital is "recovered" as depreciation and is listed as an
expense attributable to each unit of output. If the preparation plant
is leased, the payments are also allocated as an expense to each ton of
clean coal produced. Therefore, it is obvious that whether any given
plant is financed or leased, the capital cost per unit of output will be
reduced as the plant produces more clean coal. This becomes a significant
factor in the case of larger more sophisticated preparation plants, due
to the increasingly capital intensive nature of their processes. A
general indication of this trend comes from the following summarization
of current capital requirements for a variety of preparation plant sizes
and complexities as covered in Section 5.0.
136
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Input Feed Capital Cost
Example Type Of Plant Rate Per Ton Hr Input
1 Jig - Simple 600 tph $ 6,600
2 Jig - Intermediate 1000 tph 13,700
3 Jig - Intermediate 1000 tph 12,100
4 Jig - Complex 1600 tph 14,300
5 Heavy Media - Simple 1400 tph 13,800
6 Heavy Media - Complex 600 tph 22,400
7 Heavy Media - Complex 600 tph 14,000
8 Heavy Media - Complex 900 tph 23,200
These figures are only intended to show the magnitude of preparation
capital costs and do not imply any general relationship concerning the
capital cost of one process over another. Such a discussion is reserved
for Section 5.0 where the reader has the opportunity to review the make-
up of the individual plant and better understand why its cost differs
from another plant of comparable input capacity.
In the following sub-section, an explanation is given of the factors
influencing capital amortization and the rationale used to develop the
approach applied under Section 5.0. It is noted that the approach dis-
cussed therein is only one of many possible ways of spreading the cost of
the preparation complex over the output of the plant. Should the readers
feel another approach better represents their particular circumstance, it
may be substituted without affecting the accuracy of the other costs of
operation presented for each of the preparation process examples.
4.3.2 Capital Amortization Applied
As indicated earlier, there are a variety of approaches to spreading
the preparation plant capital cost over the material processed. Whether
you are allocating this cost to each ton of raw coal fed to the plant
or each ton of clean product, the figure arrived at under all approaches
137
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is sensitive to the following factors:
1) total capital required
2) plant capacity
3) operating hours per period (utilization)
4) cost of money
5) period over which plant is written-off
Certainly, the first two factors will be directly related to the
magnitude and complexity of the particular preparation plant. For most
operations today, the third factor, that of plant utilization, will vary
within a range of between 30% and 40%. It is acknowledged that some ex-
ceptions do exist at either end of this range. However, in the absence
of redundant preparation equipment, it is uncommon for a plant to actually
operate more than 40% of the time. This is equivalent to a plant opera-
ting 12 to 13 hours per day 270 days per year for a total of approximately
3,500 hours per year out of a possible 8,760.
With regard to the cost of money, a range of values will occur in
practice whether the plant is purchased with borrowed or internal funds.
If the funds are acquired outside the firm, their cost will be a function
of the current prime interest rate, term of loan, and the credit of the
borrower. Even larger firms experience loan rates of 2 to 3 percentage
points over prime for purchases of this type. If the plant is to be
funded directly by the firm, consideration must be given to the rate of
return which might be realized by alternative uses.
138
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The final variable in determining capital amortization is the write-
off period. Although this is influenced by the anticipated life of the
plant and Internal Revenue Service depreciation guidelines, its final
determination is made on the basis of individual company fiscal policy.
Certainly, many elements comprising the total plant when properly main-
tained will last 20 to 30 years whereas others will require replacement
within 5 to 10 years. Therefore in practice, the period over which
the plant is written-off will be a composite of the anticipated re-
placement cycles limited by the IRS and specific company fiscal policy
previously noted.
Realizing the diversity of approach as well as the myriad of values
which could be assigned to the factors influencing capital amortization,
we have,for the purposes of the various preparation plants covered by
this study, taken a straightforward approach which is easily understood
and adaptable to individual circumstances. Under this approach, it is
assumed that the plant is entirely financed by an equal monthly payment
self-liquidating loan granted at an annual interest rate of 9% (7% prime
plus 2%). By considering both the principal and interest portions of this
self-liquidating loan as costs, this approach gives equivalent results to
depreciating the principal over the life of the plant. Further, we are
considering loan repayment periods of both 10 and 15 years to provide a
range indicative of the write-off periods actually being observed for
preparation plants by industry. Finally, we have considered a 30% and 40%
plant utilization which relates to approximately 2600 and 3500 operating
hours per year, respectively.
Based upon the above assumptions, the following relationships are
presented which are applied in Section 5..0 to determine the allocation of
capital cost for each of the preparation plants examined therein.
139
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CCM = Capital Cost Per Month = Capital Cost X Periodic Payment Factor
Periodic Payment Factor = Pr = }-i + -;ui -i
Where: n = period of loan in months
i = interest rate per month
Therefore:
When i = prime rate + 2%
i = 0.07 *z 0.02 = 0.0075 per month
And n = 120 months (10 years)
p = 0.0075 (1 + 0.0075)120
F (1 + 0.0075)120 - 1
PF = 0.012668
When n = 180 months (15 years)
PF = 0.010143
Based upon these periodic payment factors, the monthly capital cost
per million dollars of plant investment would be —
CCM for 10 years = $106 X 0.012668 = $12,668
and
CCM for 15 years = $106 X 0.010143 = $10,143/month
Obviously, the annual capital cost per million dollars of plant in-
vestment would be —
CCy = Capital Cost Per Year = CCfv] X 12
Therefore:
CCy for 10 years = $152,016
And
CCy for 15 years = $121,716
140
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This being the case, plants which operate 30% (2,600 hrs) and 40%
(3,500 hrs) of the time will have hourly capital costs per million
dollars of plant investment of —
CCR = Capital Cost Per Hour = CCy T Utilization
At 30% Utilization
CCR for 10 years = $152,016 7 2,600 = $58.47 and
CCH for 15 years = $121,716 T 2,600 = $46.81
At 40% Utilization
CCH for 10 years = $152,016 7 3,500 = $43.43 and
CCH for 15 years = $121,716 7 3,500 = $34.78
Now, knowing these four factors, they can be applied to any plant given
the total capital required and the input/output capacity. For example,
an 11 million dollar plant which is processing 900 tons per hour (tph)
of raw coal and producing 720 tph of clean coal would have capital costs
as follows:
For 10 Year Amortization - 30%
$58.47 X 11 7 900 = $0.71 per ton of raw coal
$58.47 X 11 7 720 = $0.89 per ton of clean coal
Summarizing the various values based upon either 30% or 40% utilization gives:
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
30%
$0.71
$0.89
$0.57
$0.72
40%
$0.53
$0.66
$0.43
$0.53
141
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As mentioned above, there are many portions of the preparation plant
which, with proper maintenance, will last substantially longer than
the 10 to 15 years write-off period. This being the case, one might
assume that following this write-off period, capital amortization
would no longer be an applicable cost of preparation and the clean
coal produced after that time would be "cheaper" since it would not
be burdened with this expense. However, this is not what occurs.
Industry experience indicates that coal preparation plants are essentially
"replaced" from a capital standpoint every 7 to 10 years. What this
means is the operator will reinvest an amount equivalent to the initial
cost of the plant approximately every ten years. Another way of looking
at this subject is to think of the operator incrementally "rolling
over" his capital during the life of the plant, thus never eliminating
capital amortization but making it a recurring expense. These fresh
capital funds are typically required to handle major equipment replace-
ment and refurbishment as well as periodic modification and/or additions
to the preparation plant. This latter requirement can be brought on
by the availability of more effective equipment, variances in the com-
position of the raw coal, and/or changes to the clean coal specification.
Although these major expenses can be anticipated to some extent, they
are not considered part of the routine operation and maintenance cost
of the preparation plant. This being the case, although a 10 or 15
year write-off period is used, the allowance for capital amortization
will be a recurring expense for the total life of the plant to properly
account for the periodic influx of "fresh" capital into the plant.
142
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4-4 Cost of Btu Loss In Cleaning
During the cleaning process some portion of the heat content of
the raw feed is lost. Since the raw coal had some value before cleaning,
the heat content lost also had a definite value. This amount lost
should be accounted for and allocated as an additional cost of coal
cleaning. The specific cost attributed to this Btu loss is a function of
the raw coal value, the Btu content of the raw coal, and the Btu recovery
of the particular coal cleaning process. For ease of understanding, we
have approached this quantity as the difference between the output cost
and input cost per million Btu. To illustrate how this quantity is de-
termined, the following example is given:
Assume -
Raw Coal Cost of $15.00 per ton
Btu Content of Raw Coal 9,000 Btu per Ib
Btu Recovery of Cleaning Process 94%
This gives an input cost of -
Input Cost = $15.OO/ton '- (9,000 Btu/lb X 2000 Ib/ton)
Input Cost = $0.833/1O6 Btu
Since the Btu recovery of the process is 94%, the output cost will be -
Output Cost = Input Cost '- 0.94
Output Cost = $0.833/106 Btu '- 0.94
Output Cost = $0.886/1O6 Btu
Therefore, the Btu loss will be -
Btu Loss = Output Cost - Input Cost
143
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Btu Loss = $0.886/1O5 Btu - 0.833/106 Btu
Btu Loss = $0.053/106 Btu
This approach is observed in determining the Btu loss for each of the
preparation processes examined under Section 5.0. In all cases a raw
coal value of $15.00 per ton is assumed. Obviously, the other two
variables, raw coal Btu content and Btu recovery, are based upon the
specifics of the example presented.
As covered in Section 5.0 on a plant by plant basis, there is much
discussion on whether or not it is appropriate to apply the "cost" of
these "lost" Btu's to coal preparation. This question arises since the
material discarded in cleaning, which contained these "lost" Btu's,
is essentially large quantities of the undesirable raw coal constituents
such as ash and sulfur whose removal was the very purpose of the prepara-
tion process. It is for this reason that the individual process should
be evaluated to determine whether or not a maximum economic Btu recovery
point has been reached. If the process is performing reasonably close
to well conceived design Btu recovery limits, it might be more appropriate
to not consider these "lost" Btu's as a cost. However, if the process is
either poorly conceived from the standpoint of economic Btu recovery or
the plant is not performing close to its design capabilities, then an
inefficiency "penalty" might be assessed to reflect this discarded heat
content which was lost unnecessarily. This being the case, the "cost" of
this "lost" heat content has been treated as a separate element which the
reader may apply or not as seen fit.
144
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Btu Content of Clean Coal -
In order to make an accurate calculation of the Btu content of the
clean product from the preparation plant, consideration must be given
to the final moisture content. If the Btu content of the clean coal
on a moisture free (MF) basis is known, the true Btu content can be
calculated as follows:
Assume - Btu Content (MF) of Clean Product = 13,056 Btu/lb
Moisture Content of Clean Product = 4.6%
Then - True Btu Content of Clean Product =
(1-.046) BtuMp = .954 (13,056)
True Btu = 12,455 Btu/lb
If the Btu content of the coal on a moisture and ash free (MAF) basis
is known, the true Btu content of the clean product can be calculated
as follows:
Assume - Btu Content (MAF) of Coal = 14,511 Btu/lb
Moisture Content of Clean Product = 4.6%
Ash Content of Clean Coal = 10.03% (Dry Basis)
Then - True Btu of Clean Product =
[(1-.1003) (1--046)] BtuMAF = .8583 (14,511)
True Btu = 12,455 Btu/lb
The above computation was used for determining the final Btu con-
tent of the clean product in Example 3 presented in Section 5.0. A
similar approach was used in the other examples where sufficient data
was available. In the absence of such data, reasonable assumptions
were made.
145
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SECTION 5,0
PREPARATION PROCESS EXAMPLES
146
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5.0 PREPARATION PROCESS EXAMPLES
Presented within this section are summaries of eight actual coal
preparation plants along with their individual capital and operating
and maintenance (O&M) costs as of mid-1977. These plants span a spectrum
of currently applied coal preparation technology from a relatively simple
jig process to rather complex circuits utilizing heavy media, froth flo-
tation, and thermal drying. Each of these plants is discussed separately
with an analysis of the specific process and the level of cleaning achieved
based upon the particular coal being processed.
Through these examples of actual operating plants, the reader is
made aware of the sensitivity of the total cost of coal preparation to
such major elements as plant capital cost and the presence of thermal
drying in the circuit. Further, the influence of plant utilization on
the amortization of fixed costs is noted for each example. Since these
costs are presented on a uniform mid-1977 time base, they may be updated
to subsequent periods with appropriate index adjustment.
All cost data relative to these eight plants are presented from the
perspective of the preparation plant operator and do not assess the many
user oriented benefits resulting from coal cleaning. In addition to in-
creased heat content, these benefits include lower emission control,
transportation, boiler maintenance, and ash disposal costs. These costs
must be quantified on a site specific basis and set-off against the
preparation costs presented herein to arrive at the net cost of coal
cleaning.
147
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5.1 Example 1 - Jig Process - Simple
5.1.1 General Description
Although there are more basic preparation processes utilizing a jig
as the primary separation vessel, this plant is categorized as "simple" to
place it in a range with the other jig processes examined under Examples
2, 3, and 4.
This particular plant is designed to handle a variety of coals from
both surface and underground mines. The separation achieved by the process
as presented in the flow sheet, Figure 5-1, is based upon processing a
deep mined coal using continuous mining equipment.
From the raw coal storage area, the 8 inch X 0 material is conveyed
via a 42 inch wide belt to a 6 X 16 foot single deck vibrating screen. As
a result of the force of being dropped onto this screen and the vibrating
action, the larger pieces of coal are fractured to 6 inches or less. The
small amount of material which does not reduce to 6 inches or less passes
over the screen and reports to the refuse belt. The 600 tph of 6 inch X 0
raw coal is fed to an eight cell three compartment Baum type jig. Of the
material entering the jig, 372 tph "floats" out and 234 tph sink as refuse.
This refuse goes to a 5 X 10 foot double deck vibrating screen with l/2mm
openings in the bottom deck where it is partially dewatered before report-
ing to the refuse belt.
The 372 tph of "float" from the jig goes to two 6 X 16 foot vibrating
double deck screens having 3/4 inch and 1/4 inch openings in the top and
bottom decks, respectively. Approximately 90 tph of 6 X 3/4 inch coal
passes over the top deck and goes to a crusher where it is reduced to
2 inch X 0 before dropping onto the clean coal belt. Passing over the
148
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FIGURE 5-1
EXAMPLE 1 - OIG PROCESS - SIMPLE
PREPARATION PLANT FLOW SHEET
FROM MINING AREAS
30 TPH 48m X 0
1
M SPLITTER
T GATE
1 18 TPH
30 TPH " \ SLUDGE
1^"™^^ HYDROCVCLONES ^
12 TPH
350 GPM
PONDS/'
__/
TPH| DESLIMING SCREENS
X 48 mr
II \ \ \ '
I .
48 X 120 ml
12 TPH I
DEWATERING SCREENS
, DESLIMING SCREEN
12 TPH
48 X 120m
142 TPH
1/4 in X 0
u ,,
- m^^m^^^^m
—^3/4 X 1/4 in
140 TPH
0
i
/^ CRUSHER
21n X 0
90 TPH
230 TPH
CENTRIFUGES
112 TPH
12 TPH
2 in X 0
354 TPH
CLEAN COAL
BELT
-------
lower deck is 140 tph of 3/4 X 1/4 inch material which goes directly to
the clean coal belt. The 1/4 inch X 0 material passing through both decks
reports to a sump from which it is pumped to four 20 inch diameter Nihard
classifying cyclones at the rate of 142 tph. The 112 tph of 1/4 inch X 48
mesh underflow from these cyclones goes to two 6 X 16 foot desliming screens.
All measurable material passes over these screens and is fed to two centri-
fugal dryers which recover essentially all of the feed. From the dryers,
the 1/4 inch X 48 mesh material goes to the clean coal belt.
The 30 tph of 48 mesh X 0 overflow from the 20 inch classifying cyclones
reports to a sump from which it is pumped to five 14 inch diameter rubber
lined hydrocyclones. Of this total cyclone feed, 12 tph of 48 X 120 mesh
material reports as underflow and goes to a 3 X 12 foot single deck de-
sliming screen. Essentially all of this material passes over this screen
and goes to a centrifugal dryer before going to the clean coal belt. There
is 18 tph of 120 mesh X 0 overflow from the hydrocyclones which is split
between the jig feed sump and the sludge ponds. Of the 18 tph, 6 tph re-
ports to the sump from which it is pumped back to the jig and the balance
(12 tph) is sluiced to the sludge ponds along with approximately 350 gallons
per minute of water.
A total of 354 tph of 2 inch X 0 material having a heat content of
13,236 Btu/lb drops onto the 36 inch wide clean coal belt and is conveyed
to a 40,000 ton open storage area awaiting unit-train load-out. Based
upon a plant feed of 600 tph with a heat content of 8,523 Btu/lb, this
plant yields an impressive 91.6% Btu recovery. Other performance figures
are presented in Table 5-1.
150
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The personnel necessary to operate and maintain this plant are listed
under Table 5-4. As indicated in Table 5-5, the turn-key construction cost
of this plant is 3.95 million dollars based upon mid-1977 price quotations.
151
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CJl
ro
Raw Coal Feed To Plant:
Size Fraction
6 X 3/4 inch
3/4 inch X 0
TABLE 5-1
EXAMPLE 1 - JIG PROCESS - SIMPLE
PREPARATION PLANT PERFORMANCE*
Tph
180
420
Surface
Moisture %
Btu/lb
8,120
8,693
Ash %
41.17
35.34
Total
Sulfur %
0.60
0.67
600
Clean Coal Product From Plant:
7.0
8,521
37.09
0.65
2 inch X 0
354
8-9.0
13,236
7.68
0.79
Net Performance:
Weight Yield 59.0% Btu Recovery 91.6% Btu of Clean Coal with 8-9% Moisture 12,111 Btu/lb
* Btu, Ash, & Sulfur Presented on Dry Basis
-------
TABLE 5-2
EXAMPLE 1 - JIG PROCESS - SIMPLE
WASHABILITY DATA OF ASSUMED PLANT FEED - +3/4 INCH FRACTION*
en
CO
Specific Gravity
of Separation
Height % Ash % Sulfur % Btu/.lb
Cumulative Float
Height % Ash % Sujfur % Btu/lb
Float 1.40
1.40- 1.45
1.45- 1.50
1.50- 1.55
1.55- 1.60
SINK- 1.60
46.42
2.67
1.22
1.06
1.55
47.08
4.75
13.33
23.63
29.50
55.96
78.89
0.78
0.76
0.93
0.51
0.42
0.41
14,003
12,352
10,990
9,880
5,263
2,060
46.42
49.09
50.31
51.37
52.92
100.0
4.75
5.23
5.66
6.15
7.61
41.17
0.78
0.78
0.78
0.78
0.77
0.60
'14,003
13,913
13,842
13,760
13,512
8,120
* 29.75% of Total Feed
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TABLE 5-3
EXAMPLE 1 - JIG PROCESS - SIMPLE
WASHABILITY DATA OF ASSUMED PLANT FEED - 3/4 INCH X 0 FRACTION*
tn
Specific Gravity
of Separation
Weight % Ash % Sulfur % Btu/ 1 b
Cumulative Float
Height % Ash % Sulfur_% Btu/lb
Float 1.40
1.40- 1.45
1.45- 1.50
1.50- 1.55
1.55- 1.60
SINK- 1.60
47.23
4.49
3.0
2.04
1.99
41.25
4.69
14.67
16.61
21.69
35.99
74.68
0.78
0.80
0.94
0.87
0.76
0.47
13,810
11,737
10,219
9,712
7,707
2,388
47.23
51.72
54.72
56.76
58.75
100.0
4.69
5.55
6.16
6.72
7.71
35.34
0.78
0.78
0.79
0.79
0.80
0.67
13,810
13,630
13,443
13,309
13,119
8,693
* 70.25% of Total Feed
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TABLE 5-4
EXAMPLE 1 - JIG PROCESS - SIMPLE
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-Union Management
Preparation Manager (1/4 time)
Operating Shift (2 per day)
Title
Foreman
Plant Operator
Electrician/Mechanic
Repairman Helper (Greaser)
Utility Man
Mobile Equipment Operator (Raw and
Clean Coal Handling)
Dozer Operator
Maintenance Shift (1 per day)
Foreman
Mechanic
Utility Man
Personnel Summary
General Management
Operating Shifts
Maintenance Shift
*NU-Non-Union
Union Classification
NU*
4-E
4-A
2-F
1-H
Quantity
1
Quantity
1
1
1
1
2
3-A
Total
NU*
4-C
1-H
Total
_2
8
1
3
_1
5
Total
1
16
22
155
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TABLE 5-5
EXAMPLE 1 - JIG PROCESS - SIMPLE
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Raw Coal Storage Area
20,000 Ton Capacity with Stacking Tube,
Reclaiming Feeders, and Tunnel $300,000
Raw Coal Belt To Plant
42 Inch Wide - 200 Feet @ $520 per foot 104,000
Tramp Iron Magnet
Explosion Proof - Self Cleaning Type 20,000
Total Raw Coal Storage & Handling Cost $424,000
PREPARATION PLANT:
Equipment Cost -
6 X 16 Foot Single Deck Vibrating
Scalping Screen
1 @ $17,500 $ 17,500
Eight Cell Baum Type Jig
1 @ $176,000 176,000
6 X 16 Foot Double Deck Vibrating
Dewatering Screens
2 @ $23,000 each 46,000
5 X 10 Foot Double Deck Vibrating Refuse
Dewatering Screen
1 9 $18,000 18,000
156
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Crusher
1 0 $12,100 $ 12,100
Classifying Cyclones
20 Inch Diameter - NiHard
4 @ $2,400 each 9,600
HydrocycTones
14 Inch Diameter - Rubber Lined
5 @ $1,300 each 6,500
3 X 12 Foot Single Deck Desliming Screen
1 @ $12,000 12,000
Centrifugal Dryer *
1 @ $23,200 23,200
Centrifugal Dryers
2 @ $28,200 each 56,400
6 X 16 Foot Single Deck Desliming Screens
2 @ $16,000 each 32,000
Sumps
3 G $10,000 each 30,000
Pumps 75,000
Total Preparation Plant Equipment Cost $514,300
Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$514,300 X 3.0 $1,542,900
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OTHER FACILITIES & EQUIPMENT:
Clean Coal Belt
36 Inch Wide - 300 Feet @ $480 per foot $ 144,000
Clean Coal Storage Area
40,000 Ton Capacity with Stacking Tube,
Reclaiming Feeders, etc. 350,000
Refuse Belt
36 Inch Wide - 250 Feet @ $480 per foot 120,000
Refuse Bin 50,000
Raw Coal and Refuse Handling Equipment
2 - Dozers @ $150,000 each 300,000
Unit-Train Loading Facility 500,000
Total Other Facilities & Equipment $1,464,000
SUMMARY OF CAPITAL COST:
Raw Coal Storage and Handling $ 424,000
Preparation Plant 1,542,900
Other Facilities and Equipment 1,464,000
Contingency (Interest during construction, etc.) 515,000
Total Capital Requirement $3,945,900
SBASED UPON THE 600 TON PER HOUR INPUT TO THIS PLANT THE CAPITAL
IREQUIREMENT TRANSLATES TO $6,600 PER TON HOUR INPUT
158
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5.1.2 Capital Amortization
Based upon the rationale developed in Section 4.0, the capital
amortization for Example 1 is as follows:
Total Capital Required: $3.95 million
Capacity:
Raw Coal Input - 600 tph
Clean Coal Output - 354 tph
CAPITAL AMORTIZATION
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
% Utilization
30% 40%
$0.38 $0.
$0.65 $0.
$0.31 $0.
$0.52 $0.
29
48
23
39
5.1.3 Operating and Maintenance Costs
The operating and maintenance costs summarized in the following
Table 5-6 are based upon:
o Raw Coal Input of 600 Tons Per Hour
o Clean Coal Output of 354 Tons Per Hour
o Btu Recovery of 91.6%
o 10 Year Amortization Period
o 30% Utilization 2,600 Operating Hours Per Year
out of a Possible 8,760 Hours or 13 Hours Per Day for 200
Days Per Year. (Although this is low, this rate is applied
in order to be more consistent with the actual experience
during the period over which the cost data was collected.)
159
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TABLE 5-6
EXAMPLE 1 - JIG PROCESS - SIMPLE
OPERATING AND MAINTENANCE COSTS
Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non-Union) $0.044 $0.075
Operating & Maintenance (Union) 0.303 0.514
Overhead -
Fringe Benefits - 25% Non-Union 0.011 0.019
- 21% Union 0.064 0.108
Other - Includes Welfare Fund,
Payroll Taxes, Property Taxes,
Insurance, etc. 0.059 0.100
Supplies -
Operating 0.155 0.262
Maintenance 0.148 0.251
Major Maintenance - Scheduled repairs
and plant improvements 0.134 0.228
Electricity - 0.073 0.123
Subcontract Services to Dip Sludge Ponds,
Haul Refuse & Miscellaneous Expenses 0.599 1.016
0 & M Cost -
Not Including Capital Amortization $1.59 $2.70
Capital Amortization -
10 Yrs. - 30% Utilization 0.38 0.65
Total Operating & Maintenance Cost $1.97 $3.35
Cost Per Million Btu (12,111 Btu/lb) $0.138
160
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5.1.4 Discussion of Performance and Cost
As indicated by the performance data summarized in Table 5-1, the
Example 1 plant is capable of significantly reducing the ash content of
this particular coal while still maintaining a reasonable Btu recovery.
Since the majority of the already small sulfur content of this raw coal
is organic in nature, the net effect of the cleaning process is to
slightly increase the overall sulfur percentage in the final product.
Although this result is expected since organic sulfur is not removed
by physical cleaning, it does not imply that this process will
produce comparable results with all coals. When handling coals having
greater pyritic sulfur contents, processes of this type can contribute
favorably to reducing the overall sulfur content of the clean coal pro-
duct.
From the washability data given in Tables 5-2 and 5-3, it can be
observed that the jig is effecting a separation at between 1.50 and 1.60
specific gravity. Looking further at the data, it is clear this point
provides a relatively simple or "black and white" separation due to the
limited amount of near gravity material. Such a clear separation makes
for the efficient application of the Baum jig which loses much of its
effectiveness as the percentage of near gravity material exceeds 10%.
Even though slightly over 40% of the feed to the plant is discarded as
refuse, the process still recovers 91.6% of the feed's Btu content.
This occurs since the composite ash content of the material which sinks
at a specific gravity of 1.60 is 76% and has a heat content of only 2,290
Btu/lb. Although a charge can be applied to the total preparation cost to
161
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cover these lost Btu's, it is debatable whether such a penalty is
appropriate since the tangible value of this discarded material is
questionable. If such a penalty is assessed in the manner covered by
Section 4.4, it would have the effect of increasing the cost per million
Btu by $0.081 to $0.219.
Under normal conditions, this plant functions five days per week,
operating two full shifts a day with one shift devoted to maintenance.
As indicated by Table 5-4, the number of personnel required to operate
and maintain a plant of this size and complexity are quite small. Al-
though greater utilization of this plant is technically possible, mining
difficulties and other unscheduled stoppages have prevented operating
hours from exceeding 2,600 per year. This limited utilization is re-
flected in higher fixed charges such as capital amortization, super-
visory salaries, and some overhead costs. In spite of this less than
optimum utilization, the overall cost of cleaning is quite reasonable
considering the results achieved. The $3.35 per ton is a small price
to pay for taking an 8,500 Btu/lb coal containing nearly 40% ash and pro-
ducing a product having less than 8% ash. This cost could be even lower
if it were not for the large expense ($1.02 per ton) associated with
maintaining the sludge ponds and hauling refuse. A modification to
the plant is currently being considered which would help to alleviate
this expensive problem.
Simpler coarse cleaning plants of this type have a definite place
in the future of coal preparation. With many coals, they can cost-
effectively produce a product which is less expensive to handle and
consume. The savings associated with these benefits such as lower trans-
portation cost, ash disposal, boiler maintenance, etc. have not been deducted
162
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from the bottom-line cost in Table 5-6 since these benefits must be
assessed on a site specific basis to be meaningful. However, it
should be noted that when these benefits are quantified and deducted
from the cleaning cost, the net cost of coal preparation can be signif-
icantly less.
163
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5.2 Example 2 - Jig Process - Intermediate
5.2.1 General Description
This particular plant is processing coal from the Pittsburgh Number 8
Seam which is mined mainly with continuous miners. The plant is located
near the mouth of the mine from which the coal is brought in mine cars to
a rotary dump. After being unloaded, the 10 inch X 0 coal is conveyed to
two 6 X 16 foot single deck inclined screens designed to separate the raw
material"at four inches as shown on the flow sheet, Figure 5-2. On its
way, the raw coal passes under a tramp iron magnet for the removal of
ferrous matter such as broken mining bits. The less than 4 inch material
passes through these screens and is conveyed to a 5,000 ton concrete silo.
The plus 4 inch material passing over the screens goes to a crusher where
it is reduced to four inches or less before being conveyed to the silo.
From the silo, the 4 inch X 0 raw coal is fed into the plant at the
rate of 1,000 tph via a 48 inch belt to two eight cell three compartment
Baum type jigs where the initial separation takes place. Under the manner
in which the plant is operated, the sink from the first compartment is
considered refuse. However, the sink from the second and third compart-
ments is treated as middlings. A portion of these middlings is re-
covered on two double deck 5 X 14 foot combination refuse and middlings
screens. This is accomplished by routing the middlings to the top deck
having 1/2 inch openings and the refuse to the lower deck which has 28
mesh screen. By this arrangement, the 4 X 1/2 inch material passing over
the top screen goes to a crusher where it is reduced to 1 inch or less
before being pumped back to the jigs for further separation. The 4 inch
X 28 mesh material passing over the bottom deck goes directly to the
36 inch wide refuse belt. The fine material passing through both decks
164
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TRAMP IRON
FIGURE 5-2
EXAMPLE 2 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT FLOW SHEET
LEGEND
COAL
REFUSE
CLEAN COAL
CRUSHER
25 TPH I HVDROCYCLONES
80 TPH
1-1/4 in X 0
r
FOR TRUCK REMOVAL
TO DISPOSAL SITE
-------
goes to the 120 foot diameter concrete thickener.
The 4 inch X 0 material "floating" out of the jigs passes to fixed
sieves having screen openings of 1/4 inch. The 4 X 1/4 inch material
passing over these sieves goes to four double deck 8 X 16 foot vibrating
screens. The 1/4 inch X 0 material passing through these sieves goes to
four fixed sieves having 28 mesh screening. The 1/4 inch X 28 mesh
material passing over these 28 mesh sieves goes to four 6 X 12 foot
single deck dewatering screens. The 28 mesh X 0 material passing through
the 28 mesh sieves reports to two sumps along with any fines passing
through the 6 X 12 foot dewatering screens. From these sumps, a slurry
of 28 mesh X 0 material is pumped at the rate of 80 tph to four 24 inch
diameter hydrocyclones. These cyclones are essentially performing a
thickening function since the 25 tph 100 mesh X 0 overflow goes to the
static thickener. The 55 tph of 28 X 100 mesh underflow from these
cyclones is considered clean coal and goes to a vacuum disc filter for
partial dewatering before being conveyed to the fluid-bed thermal dryer.
This filter is 12 feet 6 inches in diameter and has 14 discs, giving an
effective filtering surface area of 3,190 square feet. A load factor of
40 pounds per hour per square foot of filtering space allows for approxi-
mately 10% excess filtering capacity.
Returning to the 8 X 16 foot double deck screens, the top deck has
screen openings of 1-1/4 inches and the bottom has 1/4 inch. The 4 X
1-1/4 inch clean coal passing over the top deck goes directly to two
crushers at the rate of 220 tph where it is reduced to 1-1/4 inch X 0
before going to the 48 inch wide clean coal belt for load-out into a
13,000 ton concrete silo. The 1-1/4 X 1/4 inch material passing over
166
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the second deck goes to two centrifugal dryers at the rate of 220 tph
for further dewatering. These dryers recover 215 tph (97-98%) of the
feed which then goes directly to clean coal storage. The 5 tph of
effluent reports to a sump from which it is pumped to the thickener.
The 1/4 inch X 0 material passing through both decks of the 8 X 16 foot
screens joins the overflow from the 28 mesh sieves and is fed to four
6 X 12 foot single deck vibrating dewatering screens having 28 mesh
openings. The 1/4 inch X 28 mesh material passing over these screens
at the rate of 230 tph is fed to two centrifugal dryers for further
dewatering. The 224 tph (97%) recovered by these centrifuges goes to
the thermal dryer. The 6 tph of effluent from these centrifuges is con-
sidered refuse and is pumped to the thickener. The thermal dryer re-
ceives a total of 279 tph of 1/4 inch X 0 coal having a surface moisture
of around 13%. Following drying, the moisture is between 5% and 6%.
This is roughly the moisture content of the entire 714 tph of 1-1/4 inch
X 0 clean coal produced by this plant.
Underflow from the static thickener is pumped at the rate of 66 tph
as a slurry containing approximately 35% solids to a vacuum disc filter.
From this 12 feet 6 inch diameter filter with 15 discs, the filter cake
goes to the refuse silo where it is combined with larger size material
permitting it to be trucked to a landfill site.
The staff necessary to operate and maintain this plant are presented
in Table 5-9.
167
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TABLE 5-7
EXAMPLE 2 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT PERFORMANCE*
Raw Coal Feed To Plant:
Surface Total
Size Fraction Tph Moisture % Btu/ib Ash % Sulfur
4 inch X 0 1000 4.3 9,610 32.32 3.42
Clean Coal Product From Plant:
™ 1-1/4 inch X 0 714 6.9 12,974 12.24 3.16
Moisture & Ash Free Btu -- 14,784 Btu/lb
Net Performance:
Weight Yield 71.4% Btu Recovery 96.4% Btu of Clean Coal with 6.9% Moisture 12,079 Btu/lb
1] Btu, Ash, & Sulfur Presented on Dry Basis
-------
TABLE 5-8
EXAMPLE 2 - JIG PROCESS - INTERMEDIATE
CUMULATIVE WASHABILITY DATA OF ASSUMED PLANT FEED*
en
Specific Gravity
of Separation
Recovery %
Weight Btu
Cumulative Float
Btu/lb Ash %
Cumulative Sink
Wt. % Ash %
FLOAT 1.40
1.40- 1.50
1.50- 1.60
1.60- 1.70
SINK- 1.70
54.88
59.97
62.90
64.84
100.00
78.2
84.7
88.0
90.0
100.0
13,690
13,570
13,440
13,340
9,610
7.40
8.17
8.98
9.73
32.32
100.0
45.12
40.03
37.10
35.16
32.34
62.64
68.51
71.90
73.99
*Btu & Ash Presented on Dry Basis
-------
TABLE 5-9
EXAMPLE 2 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-Union Management
Preparation Manager
General Foreman
Operating Shift (1st)
Foreman
Plant Operator - Central
Stationary Equipment Operator
(Thermal Dryer)
Electrician
Mechanic
Mobile Equipment Operator
Truck Driver (Refuse)
Dozer Operator
Repairman Helper (Greaser)
Utility. Man
Car Dumper
Operating Shift (2nd)
Foreman
Plant Operator - Central
Stationary Equipment Operator
(Thermal Dryer)
Mechanic
Mobile Equipment Operator
Truck Driver (Refuse)
Dozer Operator
Utility Man
Car Dumper
Union Classification
NU*
4-E
3-C
4-A
4-C
3-A
3-A
2-F
1-H
1-B**
Total
NU*
4-E
3-C
4-C
3-A
3-A
1-H
1-B**
Total
Quantity
1
1
Quantity
1
1
1
2
1
2
1
2
2
14
1
1
1
1
2
1
2
10
170
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Maintenance Shift Union Classification Quantity
Foreman NU* 1
Mechanic 4-C 11
**
Car Dumper 1-B 1
Total 13
Personnel Summary
General Management 2
Operating Shifts 24
Maintenance Shift 13
Total 39
* NU-Non-Union
**Car Dumper Operator is paid at Job Class 3 Rate of Pay when equipment
is being operated to dump the car.
171
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TABLE 5-10
EXAMPLE 2 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Raw Coal Belt To Grizzly
48 Inch Wide - 100 feet @ $560 per foot $ 56,000
Tramp Iron Magnet
Explosion Proof - Self Cleaning Type 20,000
Grizzly (Scalping) Tower
Includes screens and structure 250,000
Raw Coal Crusher 66,000
Raw Coal Belt To Silo
48 Inch Wide - 550 feet @ $560 per foot 308,000
Raw Coal Silo (Concrete)
5,000 ton capacity @ $110 per ton 550,000
Raw Coal Belt To Plant
48 Inch Wide - 300 feet @ $560 per foot 168,000
Total Raw Coal Storage & Handling $1,418,000
PREPARATION PLANT:
Equipment Cost -
Baum Jig - Eight Cell
2 @ $176,000 each $352,000
5 X 14 Foot Double Deck Vibrating Screen
2 @ $26,000 each 52,000
172
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8 X 16 Foot Double Deck Vibrating Screen
4 @ $36,000 each $144,000
Fixed Sieves
8 @ $7,000 each 56,000
6 X 12 Foot Single Deck Dewatering Screen
4 @ $16,000 each 64,000
Hydrocyclones - 24 Inch
4 @ $3,500 each 14,000
Sump - Hydrocyclone Feed
2 @ $10,000 each 20,000
Sump - Centrifuge Effluent
1 @ $10,000 10,000
Sump - Crushed Middlings
2 @ $10,000 each 20,000
Pumps
Centrifugal Dryers - Bird Model 11500
4 @ $48,000 each 192,000
Vacuum Disc Filter - Refuse
12 Feet 6 Inch Diameter - 15 Disc
1 @ $135,000 each 135,000
Vacuum Disc Filter - Clean Coal
12 Feet 6 Inch Diameter - 14 Disc
1 @ $130,000 130,000
Crusher - Middlings
2 6 $12,100 each 24,200
Crusher - Clean Coal
2 @ $20,400 each 40,800
Total Preparation Plant Equipment Cost $1,254,000
173
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Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$1,254,000 X 3.0 $3,762,000
OTHER FACILITIES & EQUIPMENT:
Fluid-Bed Thermal Dryer
Complete with structural steel, motors, motor
controls, wiring, piping, field erection, and
start-up service 2,500,000
Static Thickener (Concrete)
120 feet in diameter @ $2,000 per foot 240,000
Refuse Belt To Refuse Silo
36 Inch Wide - 300 feet @ $480 per foot 144,000
Refuse Silo
250 ton capacity @ $200 per ton 50,000
Refuse Handling Equipment
2-50 Ton Trucks 6 $75,000 each 150,000
1 - Dozer (Spreding & Compacting) 150,000
Coal Sampling System 300,000
Clean Coal Belt To Silo
48 Inch Wide - 450 feet @ $560 per foot 252,000
Clean Coal Silo
13,000 ton capacity @ $110 per ton 1,430,000
River Barge Loadout Facility
1000-1500 tph capacity including loading equip-
ment with telescoping tube and necessary docking
facilities 1,500,000
Total Other Facilities & Equipment $6,716,000
174
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SUMMARY OF CAPITAL COST:
Raw Coal Storage and Handling
Preparation Plant
Other Facilities and Equipment
Contingency (Interest during construction, etc.)
Total Capital Requirement
$ 1,418,000
3,762,000
6,716,000
1,785,000
$13,681,000
BASED UPON THE 1000 TON PER HOUR INPUT TO THIS PLANT THE CAPITAL
REQUIREMENT TRANSLATES TO $13,70.0. PER TON HOUR INPUT
175
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5.2.2 Capital Amortization
Based upon the rationale developed in Section 4.0, the capital
amortization for Example 2 is as follows:
Total Capital Required: $13.7 Million
Capacity:
Raw Coal Input - 1000 tph
Clean Coal Output - 714
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
30%
$0.80
$1.12
$0.64
$0.90
40%
$0.59
$0.83
$0.48
$0.67
5.2.3 Operating and Maintenance Costs
The operating and maintenance costs summarized in the following
Table 5-11 are based upon:
o Raw Coal Input of 1000 Tons Per Hour
o Clean Coal Output of 714 Tons Per Hour
o Btu Recovery of 96,4%
o 10 Year Amortization Period
o 30% Utilization 2,600 Operating Hours Per Year
out of a Possible 8,760 Hours or 13 Hours Per Day for 200
Days Per Year. (Although this is low, this rate is applied
in order to be more consistent with the actual experience
during the period over which the cost data was collected.)
176
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TABLE 5-11
EXAMPLE 2 - JIG PROCESS - INTERMEDIATE
OPERATING AND MAINTENANCE COSTS
Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non-Union) $0.039 $0.054
Operating & Maintenance (Union) 0.464 0.650
Overhead -
Includes Training Wages, Welfare Fund,
Payroll Taxes, Workmen's Compensa-
tion, etc. 0.211 0.296
Supplies -
Operating - Water Conditioners,
Flocculants, Electric Repairs &
Parts, etc. 0.141 0.198
Maintenance - Replacement Parts, etc. 0.183 0.256
Fuel and Power - 0.233 0.326
Refuse Expense -
In house and purchased services
associated with refuse disposal such
as truck parts, maintenance, etc. 0.132 0.185
Thermal Dryer Fuel - Based Upon 4.7
Tons/Hr. Coal Consumption & Cost
of Coal $20/Ton. 0.094 0.132
Miscellaneous Expense - Repair & Main-
tenance Items Not Normally Inventoried
or Requiring Outside Subcontract Svcs. 0.321 0.449
0 & M Cost -
Not Including Capital Amortization $1.82 $2.55
Capital Amortization
10 Yrs. - 30% Utilization 0.80 1.12
Total Operating & Maintenance Cost $2.62 $3.67
Cost Per Million Btu (12,079 Btu/lb) $0.152
177
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5.2.4 Discussion of Performance and Cost
The Example 2 plant is representative of many jig circuits
currently in existence which can achieve a substantial reduction in ash
and some sulfur removal with certain coals. As presented in Table 5-7,
this plant recovers, an almost unbelievable, 96% of the Btu content in
the raw feed. Looking at the washability data in Table 5-8, there
appears to be a fairly clear separation at 1.60 specific gravity which
could theoretically be effected by a jig. However, the reprocessing of
the middlings from the jig seems to be increasing the weight yield and
thus Btu recovery, but degrading the quality of the final product.
Obviously, the manner in which a plant is operated at any given time
is influenced by the economic realities of the clean coal specification
the operator must meet.
As presented in Table 5-11, the total operating and maintenance
cost, including capital amortization, is $3.67 per ton of clean coal.
On the basis of a nearly 7% moisture clean coal having 12,079 Btu/lb,
this equates to $0.152 per million Btu. If a cost penalty is assessed
against the process for the limited Btu loss (3.6%), the total cost
of preparation would increase by $0.029 to $0.181 per million Btu.
Using the performance of this plant with this particular coal
as an example, processes of this general type can produce a fairly good
quality coal at a reasonable cost. This cost is quite sensitive to the
amount of thermal drying required and whether or not the plant can be
kept operating for significant periods of the year. As presently oper-
ating, this plant is drying almost 40% of the total production which
178
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greatly impacts electricity consumption and maintenance expense. Further,
the presence of the dryer adds personnel and increases capital require-
ments by 20%. Currently, the plant is barely operating 30% of the time
which keeps the capital amortization at an artifically high level. If
the plant could be operated an additional 10% of the year, a savings of
$0.30 per clean ton could be realized from capital amortization alone;
not to mention the favorable impact on other fixed charges.
The cost data presented in the foregoing tables is intended to
give the reader insight regarding the capital and 0 & M costs which are
required to establish and run a plant of this general make-up and capacity.
When plants of this type are properly applied, efficient cost-effective
results can be achieved which yield a product having cost saving benefits
at the user level. These benefits include lower transportation, ash
disposal, and maintenance costs, as well as limit the required particulate
and FGD emission control capacity. As mentioned elsewhere, these bene-
fits can be quantified on a site specific basis and go to improve the
overall economics of coal preparation.
179
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5.3 Example 3 - Jig Process - Intermediate
5.3.1 General Description
Preparation plants utilizing the Baum type jig as the major cleaning
vessel can turn out an acceptable product at an attractive price with a
variety of coal seams. Plants employing the jig can be combined with a
myriad of other equipment combinations to make for increasingly complex
cleaning circuits. The particular plant discussed herein is referred to
as "intermediate" since in addition to the jig, several other pieces of
equipment aid the cleaning process, thus further improving the quality
of the clean coal product.
In this plant, 18 inch X 0 raw coal, mined mostly by continuous
mining, is conveyed at the rate of 1,050 tons per hour from the open
raw coal storage area to scalping screens where the 4 inch X 0 material
is separated to by-pass the rotary breaker as shown on the -flow sheet,
Figure 5-3. The plus 4 inch material goes to a rotary breaker with
4 inch openings in the screen plates. That material which does not
fracture to 4 inches or less passes through the refuse end of the breaker
and goes to a rock bin for disposal. Approximately 50 tph of rock and
other debris are removed by the rotary breaker.
The 4 inch X 0 material is fed to two eight cell Baum type jigs at
the rate of 1000 tph. Of this amount, 636. tph "floats" out of the jigs
and passes over fixed screens ahead of 8 X 16 foot double deck clean
coal screens for sizing and dewatering. The 4 X 1-1/4 inch material passing
over the top decks of these screens goes to a crusher where it is reduced to
1-1/4 inch or less before being conveyed to the 10,000 ton capacity con-
crete clean coal silo. Passing over the lower decks is the 1-1/4 X 1/4
180
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FIGURE 5-3
EXAMPLE 3 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT FLOW SHEET
SPIRAL CLASSIFIERS I 30 TPH
-------
inch material which goes to centrifugal dryers where the surface moisture
is reduced from about 16.5% to less than 5% before being conveyed to clean
coal storage. The 1/4 inch X 0 material passing through both decks of
the 8 X 16 foot clean coal screens goes to a primary cyclone sump from
which it is pumped to a bank of classifying cyclones where further sizing
into 150 mesh X 0 and 1/4 inch X 150 mesh is effected. The 1/4 inch X 150
mesh underflow from these cyclones is distributed over double deck Deister
tables to separate some of the refuse which was not removed by the jigs.
The refuse from the tables goes to a spiral classifier where the
material is partially dewatered to aid disposal. The clean coal from the
tables goes to Vor-Sivs for dewatering. The coarser material (1/4 inch X
28 mesh) leaving the Vor-Sivs is centrifugally dried to bring the surface
moisture down to less than 10% before being conveyed to the fluid-bed
thermal dryer. The finer material (28 mesh X 0) leaving the Vor-Sivs
goes to a secondary cyclone sump. This same sump is also fed by the 150
mesh X 0 overflow from the classifying cyclones.
From the secondary cyclone sump, a 28 mesh X 0 coal slurry is fed at
the rate of 94 tph to hydrocyclones where a separation into clean coal and
refuse occurs. The 40 tph of overflow from these cyclones goes to the 180
foot diameter static thickener and the 54 tph of underflow goes to the 10
foot six inch, ten disc vacuum filters for partial dewatering before going
to the thermal dryer. The filters reduce the surface moisture of the 28
mesh X 0 coal to around 20%.
The total feed to the fluid-bed dryer is 202 tph of 1/4 inch X 0
coal having a total surface moisture of approximately 15%. Following
drying, the surface moisture is close to 5%.
182
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Of the 1000 tph being fed to the jigs, 566 tph of 1-1/4 inch X 0
with a surface of moisture of around 5% is considered clean coal. This
equates to a 56.6% weight yield.
The material ejected from all three compartments of the eight cell
jigs is considered refuse and goes to 7 X 16 foot double deck refuse
screens for dewatering. The larger material passing over both decks
goes to the refuse bin for disposal with the finer material going as
a slurry to the spiral classifiers for thickening.
With the aid of modern electronic monitoring and controls, this
plant is operated and maintained by the personnel as presented in Table
5-15. A plant of this general make-up could be constructed at a capital
cost of $12.1 million in terms of mid-1977 dollars. Table 5-16 gives a
breakdown of this cost by major component.
The operating and maintenance costs are summarized in Table 5-17.
183
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Raw Coal Feed To Plant;
Size Fraction Tph
4 Inch X 0 1000
TABLE 5-12
EXAMPLE 3 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT PERFORMANCE*
Surface
Moisture %
4.5
Btu/lb
8,908
Ash %
35.97
Pyritic
Sulfur
3.01
Total
Sulfur
4.30
co" Clean Coal Product From Plant:
1-1/4 Inch X 0
1-1/4 X 1/4 Inch
1/4 Inch X 0
Total
46
318
202
3.7
4.5
5.1
12,745
13,242
12,833
11.06
9.0
11.41
566
4.6
Moisture & Ash Free Btu -- 14,511 Btu/lb
13,056
10.03
2.87
4.64
4.30
3.83
4.16
Net Performance:
Weight Yield 56.6%
Btu Recovery 83.0%
*Btu, Ash & Sulfur Presented on Dry Basis
3ut of Clean Coal with 4.6% Moisture 12,455 Btu/lb
-------
Table 5-13
EXAMPLE 3 - JIG PROCESS INTERMEDIATE
Composition of Assumed Plant Feed By Size Fraction
00
CJ1
Size Fraction
4 Inch X 2 Inch
2 Inch X 1 Inch
1 Inch X 1/2 Inch
1/2 Inch X 1/4 Inch
1/4 Inch X 8 Mesh
8 Mesh X 14 Mesh
14 Mesh X 0
Btu/lb
3,492
7,160
9,821
11,122
10,688
9,992
9,069
Ash %
70.03
46.99
30.59
22.48
24.97
28.04
33.88
Pyritic
Sulfur %
3.89
3.19
2.49
2.51
2.51
5.91
2.98
Total
Sulfur %
4.37
4.24
3.87
4.02
3.97
7.43
4.67
% Weight
11.1
18.0
21.6
19.4
12.2
4.9
12.8
% Cumulative Wt.
11.1
29.1
50.7
70.1
82.3
87.2
100.0
*Btu, Ash, & Sulfur Presented on Dry Basis
-------
TABLE 5-14
EXAMPLE 3 - JIG PROCESS - INTERMEDIATE
CUMULATIVE WASHABILITY DATA OF ASSUMED PLANT FEED'
Composite Of 4 Inch X 14 Mesh Fraction - 87.2% of Feed'
**
CO
cr>
Specific Gravity
of Separation
FLOAT 1.30
1.30- 1.35
1.35- 1.40
1.40- 1.50
1.50- 1.60
1.60- 1.70
1.70- 1.80
SINK- 1.80
Recovery
Weight
19.46
43.91.
53.07
59.43
61.93
63.14
63.94
100.00
%
Btu
30.9
68.7
82.1
90.8
93.8
95.1
95.9
100.0
Btu/lb
14110
13907
13747
13577
13464
13387
13321
8884
Ash %
4.44
5.61
6.57
7.60
8.28
8.75
9.15
36.28
Pyri ti c
Sulfur %
.59
1.07
1.50
1.89
2.08
2.17
2.22
3.01
Total
Sulfur %
2.56
2.99
3.39
3.74
3.91
3.99
4.04
4.25
*Btu, Ash, & Sulfur Presented on Dry Basis
12.8% is 14 Mesh X 0 Containing 9,069 Btu Per Pound, 33.88% Ash, 2.98% Pyritic Sulfur, and 4.67% Total Sulfur
**
-------
TABLE 5-15
EXAMPLE 3 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-Union Management
Preparation Manager (1/4 time) -
General Foreman
Operating Shift (Two per day)
Ti tle Union Classification
NU*
Foreman
Plant Operator
Electri cian
Mechani c
Mobile Equipment Operator
(Dozer,Front End Loader,
and Refuse Truck Driver)
Weider
Stationary Equipment Operator
(Thermal Dryer Operator)
Repairman Helper (Greaser)
Utility Man
Maintenance Shift
Foreman
Electrician
Mechanic
Mobile Equipment Operator
Utility Man
Personnel Summary
General Management
Operating Shifts
Maintenance Shift
*NU-Non-Union
4-E
4-A
4-C
3-A
4-D
3-C
2-F
1-H
Total
NU*
4-A
4-C
3-A
1-H
Total
Quantity
1
1
Quantity
1
1
1
2
4
1
1
1
2
14
1
1
3
1
2
8
2
28
8
Total
38
187
-------
TABLE 5-16
EXAMPLE 3 - JIG PROCESS - INTERMEDIATE
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Raw Coal Storage Area
20,000 ton capacity with reclaiming feeders
and tunnel $300,000
Raw Coal Belt To Scalping Tower
48 Inch Wide - 200 feet at $560 per ft. 112,000
Scalping Tower
Including Single Deck Vibrating Screen,
Rock Bin, and Structural Work for Rotary Breaker 350,000
Rotary Breaker -
10 Ft diameter - 12 ft. long 150,000
Raw Coal Belt To Plant
48 Inch Wide 300 feet at $560 per foot 168.000
Total Raw Coal Storage & Handling Cost $1,080,000
PREPARATION PLANT:
Equipment Cost -
Eight Cell Baum Jigs
2 @ $176,000 each $ 352,000
8 X 16 Foot Double Deck Vibrating Clean Coal
Screens -40 $36,000 each 144,000
188
-------
7 X 16 Foot Double Deck Vibrating Refuse Screens -
2 @ $30,500 each $ 61,000
Clean Coal Crusher - 1 33,000
Centrifugal Dryers - 5 @ $28,200 each 141,000
Classifying Cyclones - Ceramic lined
12 @ $3,800 each 45,600
Deister Tables - 13 Double Deck 0
$21,000 each 273,000
Vor-Siv -40 $17,000 each 68,000
Hydrocyclones - 20 0 $1,700 each 34,000
Clean Coal Vacuum Disc Filter
1 - 10'6" ten disc 120,000
Spiral Classifiers - 36 Inch Diameter
2 0 $18,000 each 36,000
Primary Cyclone Sumps -20 $10,000 each 20,000
Secondary Cyclone Sumps - 2 0 $10,000 each 20,000
Pumps 100,000
Total Preparation Plant Equipment Cost $1,447,600
Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$1,447,600 X 3.0 $4,342,800
OTHER FACILITIES & EQUIPMENT:
Fluid-Bed Thermal Dryer
Complete with structural steel, motors, motor
controls, wiring, piping, field erection, and
start-up service $2,100,000
189
-------
Static Thickener
180 feet @ $2,000 per foot
Refuse Belt
36 Inch Wide - 150 feet @ $480 per foot
Refuse Bin
Fabricated Part
Refuse Handling Equipment
2 - Dozers @ $150,000 each
1 - Front-End Loader @ $50,000
2 - Trucks @ $75,000 each
Coal Sampling System
Clean Coal Silo
10,000 Ton Capacity at $110 per ton
Clean Coal Belt To Silo
42 Inch Wide - 200 feet at $520 per foot
Unit-Train Loading Facility
Total Other Facilities & Equipment
SUMMARY OF CAPITAL COST:
Raw Coal Storage and Handling
Preparation Plant
Other Facilities and Equipment
Contingency (Interest during construction, etc.)
Total Capital Requirement
$ 360,000
72,000
50,000
300,000
50,000
150,000
300,000
1,100,000
104,000
500,000
$ 5,086,000
$ 1,080,000
4,342,000
5,086,000
1,576,000
$12,084,000
BASED UPON THE 1000 TONS PER HOUR INPUT TO THIS PLANT THE CAPITAL
REQUIREMENT TRANSLATES TO $12.100 PER TON HOUR INPUT
190
-------
5.3.2 Capital Amortization
Based upon the rationale developed in Section 4.0, the capital
amortization for Example 3 is as follows:
Total Capital Required: $12.1 Million
Capacity:
Raw Coal Input - 1000 tph
Clean Coal Output - 566 tph
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
\
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
30%
$0.71
$1.25
$0.57
$1.00
40%
$0.53
$0.93
.$0.42
$0.74
5.3.3 Operating and Maintenance Costs
The operating and maintenance costs summarized in the following
Table 5-17 are based upon:
o Raw Coal Input of 1000 Tons Per Hour
o Clean Coal Output of 566 Tons Per Hour
o Btu Recovery of 83%
o 10 Year Amortization Period
o 30% Utilization 2,600 Operating Hours Per Year
out of a Possible 8,760 Hours or 13 Hours Per Day for 200
Days Per Year. (Although this is low, this rate is applied
in order to be more consistent with the actual experience
during the period over which the cost data was collected.)
191
-------
TABLE 5-17
EXAMPLE 3 - JIG PROCESS - INTERMEDIATE
OPERATING AND MAINTENANCE COSTS
Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non-Union) $0.054 $0.095
Operating & Maintenance (Union) 0.428 0.757
Includes miscellaneous salaries for
watchmen, etc.
Overhead -
Fringe Benefits - 26% Non-Union 0.014 0.025
- 22% Union 0.094 0.167
Other - Includes Welfare Fund,
training costs, etc. (15% of
total labor) 0.072 0.128
Supplies -
Includes water conditioners, re-
placement parts, lab supplies,
health & safety expenses, neces-
sary equipment rental, etc. 0.538 0.950
Fuel and Power - 0.170 0.301
Thermal Dryer Fuel -
Based upon 3.4 Tons/Hr Coal Consumption
and Cost of Coal $20/Ton 0.068 0.120
Miscellaneous - Subcontract Services, etc. 0.076 0.127
0 & M Cost -
Not Including Capital Amortization $1.51 $2.67
Capital Amortization -
10 Yrs. - 30% Utilization 0.71 1.25
Total Operating & Maintenance Cost $2.22 $3.92
Cost Per Million Btu (12,455 Btu/lb) $0.157
192
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5.3.4 Discussion of Performance and Cost
This Example 3 plant is essentially a coarse cleaning process de-
signed for the purpose of reducing ash. However, following the initial
separation in the Baum jig, the finer size fractions (less than 1/4 inch)
of "float" from the jig are classified and subjected to additional clean-
ing by Deister tables and cyclones. This secondary cleaning has a
favorable impact on further reducing ash as well as lowering the pyritic
sulfur content which is relatively high in the smaller size fractions.
Although this plant does not effect a dramatic reduction in sulfur, it
is achieving its design objective of significantly reducing the ash in
the particular coal currently being treated. Some consideration is
being given to a plant modification which would increase the capacity of
the finer cleaning portion of the circuit and promote further pyritic
sulfur removal.
With the coal now being treated, this plant recovers approximately
56% of the raw feed by weight and only 83% of the heat content. Greater
Btu recovery from this particular coal could probably be achieved by
crushing the larger size fractions from the jig and further treating
them in an expanded version of the finer cleaning portion of the circuit.
However, this would involve additional capital expenditures not necessarily
appropriate at this time since the company is meeting their contractual
product specification as is. Before taking such a step, careful analysis
would have to be performed to determine whether further upgrading of the
product would show economic advantage to the producer as well as provide
the purchaser with a product still having the required characteristics
critical to the particular combustion application.
193
-------
Under current procedures, this plant is scheduled to function three
shifts per day, five days per week with two shifts operating and one for
maintenance. However, because of unscheduled stoppages and other
recurring problems, this plant has not been running coal more than the
equivalent of 2600 hours per year or roughly 30% of the time. Limited
utilization has a negative cost impact upon overall plant operating cost
since fixed charges such as capital amortization, management, certain
overhead expenses, etc. are still incurred even though the plant is
functioning well below capacity. This point is made by the fact that
if this plant could be utilized an additional 10% of the time, the
capital amortization per ton of clean coal would decrease by $0.32. If
this were true, the 0 & M cost per ton of clean coal would drop from $3.92
to $3.60 before accounting for the Btu loss from cleaning.
Another aspect of this plant which contributes significantly to
its operating and maintenance cost is the thermal dryer. Although it
only dries 36% of the total clean coal product, it nearly doubles the
electricity consumption, adds personnel, and accounts for 20% of the
capital cost of the entire facility. In spite of the high cost of thermal
drying, a good case can manytimes be made for its use on the basis of
lower handling and transportation expenses, not to mention the moisture
specification required by the purchaser.
As summarized in the preceding Table 5-17, the total O&M cost of
$3.92 per ton of clean coal translates to $0.157 per million Btu. To
this, an amount of $0.172 per million Btu can be added to account for the
27% of the heat content in the raw coal "lost" during the cleaning process.
If this were done, it would more than double the cost of preparation,
194
-------
bringing the total to nearly $0.33 per million Btu. This is a stiff
penalty to "pay" for having thrown away a low Btu material high in ash
and sulfur. There is much room for discussion on whether it is approp-
riate to assess such a high price to this refuse and thus more than
double the effective cost of coal preparation to the producer. However,
in this particular case, where the Btu recovery is only 83%, it does
accentuate the need to analyze the process to see if greater recoveries
are not possible through alternate cleaning approaches.
Although the Example 3 process when applied to this coal is quite ex-
pensive considering the results achieved, it is representative of many plants
currently in existence which are profitable since the material produced
is capable of selling for more than the raw coal plus the cost of clean-
ing including a return to the producer. However, the producer's cost is
not the end-of-the-line when evaluating the overall economics of coal
preparation to determine whether or not the process is cost effective.
This is true since the producer's cost as presented in Table 5-17 makes
possible a product which has measureable cost benefits to the user.
When these benefits such as lower transportation, ash disposal, etc. are
quantified, they can be set off against the producer's cost to determine
the net cost of cleaning. These cost benefits are not addressed further
at this point since they can only be accurately quantified on a site
specific basis knowing such things as the distance between the coal source
and the user.
195
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5.4 Example 4 - Jig Process - Complex
5.4.1 General Description
As indicated by the simplified flow sheet presented as Figure 5-4s
this particular coal preparation process is comprised of a coarse
circuit where the major separation is made by a single eight-cell Baum
jig and a fine coal circuit centered around two Batac jigs. Based upon
an input to the plant (following rough scalping) of 1600 tons per hour
(tph), the weight yield is 59.6% and the Btu recovery is over 90%. As
is indicated by these results and the sulfur reduction data given in
Table 5-18,the combination of these two circuits performs an effective
and efficient cleaning job on this Lower Freeport seam coal which is
mined by continuous and longwall mining.
Raw coal is fed from the mining areas via 54 inch wide belts at
the rate of 1650 tph to 6 x 16 foot scalping screens where the plus 4 inch
material is screened off and routed to refuse. The 4 inch x 0 material pass-
ing through the scalping screens goes to surge bins ahead of 8 x 20 foot raw
coal screens. When the plant is not operating, the 4 inch x 0 materiel
goes to a 12,000 ton open coal storage area from which it is reclaimed
as required.
The inclined 8 x 20 foot double deck raw coal screens separate the
1600 tph of material into three size fractions. Material of 2 inches or
more passes over the top deck and goes to refuse at the rate of 112 tph.
The 2 x 3/4 inch material passing over the second deck is fed to the Baum
jig via a 36 inch belt at the rate of 253 tph. The l,235tph of 3/4 inch x 0
passing through both decks drops on a 48 inch wide belt and is fed to
the two Batac jigs.
196
-------
FROM
MIMING AREAS ^-x 1650 TPH
FIGURE 5-4
EXAMPLE 4 - JIG PROCESS - COMPLEX
PREPARATION PLANT FLOW SHEET
CLEAN COAL
[WATERING SCREENS
2.X 3/4 In 16 TPH
-------
Of the 253 tph going to the jig, 63 tph "floats" and 190 tph
passes out the bottom of the three compartments as refuse. The 63
tph of 2 inch and less coal goes to 6 x 16 foot double deck clean coal
screens for sizing and dewatering. The top deck has screen with 3/4 inch
openings and the bottom deck 1/4 inch openings. Therefore, the 2 x 3/4 inch
material with a surface moisture of approximately 2.4% passes over the
top deck and is fed directly to the clean coal collection belt. The
3/4 x 1/4 inch material passing over the second deck goes to centrifuges for
further dewatering before going to the clean coal belt. The 1/4 inch x 0
material passing through both decks goes to a sump from which it is
pumped as a slurry to sieve bends ahead of 7 x 16 foot single deck dewatering
screens. All plus 28 mesh material passing over the screens goes to centri-
fuges and onto the clean coal belt. The 28 mesh x 0 material passing
through the screens goes to a sump from which it is pumped to 10 inch
rubber lined thickening cyclones for further dewatering. The overflow
(all measurable material) from these cyclones goes to the two 150 foot
diameter concrete thickeners.
The 190 tph of refuse from the Baum jig goes to 6 x 16 foot single deck
screens for sizing and partial dewatering. The 2 inch x 28 mesh material
passing over the screens has a surface moisture of around 3% and goes
direct to the refuse belt. The small amount (4 tph) of 28 mesh x 0 material
passing through the screens goes to a sump from which it is pumped to
thickening cyclones and then to solid bowl centrifuges to get the sur-
face moisture down to 18% before going to the refuse belt.
198
-------
Returning to the fine coal cleaning portion of the plant, the two
Batac jigs are fed 3/4 inch x 0 material at the rate of 1235 tph (roughly 600 tph
each). Batac jigs come in 3, 4, and 5 meter widths. As a general sizing
philosophy, each meter of width equates to 100 tph of feed capacity. However,
this may be exceeded to some degree, as is the case of this plant, without
significant degradation in performance. Of the total feed to the Batac
jigs, 890 tph separate out as clean coal and 345 tph are refuse. The clean
coal is fed to fixed sieves ahead of 7 x 16 foot single deck screens
for sizing and partial dewatering. The 685 tph of 3/4 inch x 28 mesh
material passing over the screens goes to fine coal centrifuges where
the surface moisture is brought down from 25% to 6.5% before going to
the fluid-bed thermal dryers. The 205 tph of 28 mesh x 0 material passing
through the screens goes to a sump from which it is pumped to classify-
ing cyclones (14 inch ceramic lined). The 100 mesh x 0 overflow from these
cyclones go to the static thickeners. From the thickeners, it is pumped
to vacuum disc filters for dewatering before going to the thermal dryers.
The 28 mesh X 0 underflow goes directly to the disc filters and then on to
thermal drying. In this circuit there is a total of four 12 disc vacuum
filters. Each disc is 12 feet 6 inches in diameter. The total feed to
these filters is 223 tph. These filters have been sized on the basis of
50 pounds per hour per square foot of disc surface. Therefore, the
following calculation applies:
Weight Being Processed:
223 tons/hour = 446,000 pounds/hour
Surface Required:
446,000 pounds/hour _ g
i)
50 pounds/hour/ft
199
-------
Available Surface:
4 filter x 2736 ft2 = 10.944 ft2
This additional 2,000 ft of available filtering surface allows for
substantial fluctuations in feed without overburdening the equipment.
A total of 894 tph of 3/4 inch x 0 material is fed to the two thermal
dryers each having a capacity of 550 tph. The surface moisture is re-
duced from over 11% to around 6% by the dryers.
The 300 tph of refuse from the Batac jigs goes to inclined single
deck fixed screens which the majority of the material (310 tph) passes
over before being further dewatered by centrifugal dryers. The efflu-
ent from these dryers and the 28 mesh x 0 material passing through the
refuse screens go to a sump from which they are pumped to thickening cy-
clones (14 inch rubber lined) where they are partially dewatered•. All meas-
urable solids report to the underflow of these cyclones and go to solid-bowl
centrifuges for further dewatering before going to the refuse belt.
Overall plant performance is summarized by Table 5-13.
This plant is operated and maintained by the staff set forth in
Table 5-22. In addition to a high degree of semi-automated electronic
controls, smooth operation of the plant is aided by a closed-circuit
television monitoring system.
200
-------
ro
o
TABLE 5-18
EXAMPLE 4 - JIG PROCESS - COMPLEX
PREPARATION PLANT PERFORMANCE*
Raw Coal Feed To Plant:
Size Fraction
4X2 inch
2 X 3/4 inch
3/4 inch x 0
Total
Tph
112
253
1,235
1,600
% of
Feed
7.0
15.8
77.2
100.0
Surface
Moisture %
-
-
5.0
Btu/lb
1,250
4,444
10,700
9,050
Ash %
85.32
66.21
28.98
38.81
Total
Sulfur %
0.27
0.51
1.16
1.0
Clean Coal Product From Plant:
2 X 1/4 inch
3/4 inch x 0
59
894
3.0
6.0
13,401
14,300
13.35
7.9
1.14
0.91
953
5.8
14,244
8.24
0.92
Net Performance:
Weight Yield 59.6% Btu Recovery 93.7% Btu of Clean Coal with 5.8% Moisture 13,418 Btu/lb
*Btu, Ash, and Sulfur Presented On Dry Basis
-------
TABLE 5-19
EXAMPLE 4 - JIG PROCESS - COMPLEX
COMPOSITION OF ASSUMED PLANT FEED BY SIZE FRACTION
Size Fraction Weight % Cumulative Wt.%
+ 3 Inch 4.43 4.43
3X2 Inch 2.66 7.09
2 X \\ Inch 3.49 10.58
1% X 1 Inch 5.72 16.30
1 X 3/4 Inch 6.50 22.80
3/4 X 5/8 Inch 4.48 27.28
5/8 X 1/2 Inch 4.00 31.28
1/2 X 3/8 Inch 9-09 40.37
3/8 Inch X 28 Mesh 49.03 89.40
28 X 100 Mesh 7.02 96.42
100 Mesh X 0 3.58 100.00
202
-------
TABLE 5-20
EXAMPLE 4 - JIG PROCESS - COMPLEX
COMPOSITION OF ASSUMED FEED TO BATAC JIGS BY SIZE FRACTION
ro
o
Size Fraction
3/4 Inch X 1/2 Inch
1/2 Inch X 3/8 Inch
3/8 Inch X 1/4 Inch
1/4 Inch X 8 Mesh
8 Mesh X 14 Mesh
14 Mesh X 28 Mesh
28 Mesh X 48 Mesh
48 Mesh X 100 Mesh
100 Mesh X 200 Mesh
200 Mesh X 0
Btu/lb
6,602
9,809
10,683
11,519
12,159
11,806
12,211
12,736
12,445
10,115
Ash %
52.85
34.69
29.39
24.45
20.65
22.52
19.02
15.73
16.98
31.89
Pyritic
Sulfur %
0.45
0.48
0.78 •
0.82
0.91
1.06
1.04
0.95
1.09
0.72
Total
Sulfur %
0.65
0.88
1.06
1.27
1.37
1.55
1.51
1.43
1.61
1.07
Weight %
13.71
9.36
11.31
31.76
11.15
6.37
4.85
3.52
2.39
5.58
Cumulativ<
13.71
23.07
34.38
66.14
77.29
83.66
88.51
92.03
94.42
100.00
-------
TABLE 5-21
EXAMPLE 4 - JIG PROCESS - COMPLEX
CUMULATIVE WASHABILITY DATA OF ASSUMED FEED TO BATAC JIGS
*
Composite of 3/4 Inch X 200 Mesh Fraction - 94.42% of Feed
ro
G
Specific Gravity
of Separation
FLOAT 1.30
1.30- 1.35
1.35- 1.40
1.40- 1.50
1.50- 1.60
1.60- 1.70
1.70- 1.80
1.80- 2.00
SINK- 2.00
Weight
35.48
60.03
65.34
69.10
71.08
72.37
73.32
74.94
100.00
Recovery %
Btu
49.8
82.6
89.3
93.6
95.6
96.7
97.4
98.3
100.0
Btu/lb
15,068
14,769
14,666
14,539
14,435
14,344
14,262
14,085
10,734
Ash %
3.69
5.42
6.01
6.73
7.34
7.86
8.33
9.35
28.81
Pyri ti c
Sulfur %
0.22
0.31
0.35
0.39
0.41
0.43
0.45
0.48
0.78
Total
Sulfur %
0.68
0.78
0.82
0.86
0.89
0.91
0.93
0.96
1.17
"5.58% is 200 Mesh X 0 Containing 10,115 Btu Per pound, 31.89% Ash, 0.72% Pyritic Sulfur, and 1.07% Total Sulfur
-------
TABLE 5-22
EXAMPLE 4 - JIG PROCESS - COMPLEX
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-Union Management
Preparation Plant Superintendent
Operating Shift (1st)
Title
Shift Foreman
Electrical Maintenance Foreman
Plant Operator
Electrician
Mechanic
Stationary Equipment Operator -
(Includes two thermal dryer operators)
Mobile Equipment Operator
Dozer & Truck Drivers
Utility Man (Screentnan)
Laborer
Operating Shift (2nd)
Shift Foreman
Plant Operator
Electrician
Mechanic
Stationary Equipment Operator
Mobile Equipment Operator
Railroad Car Loader Operator
Utility Man (Screenman)
Laborer
Union Classification
NU*
NU*
4-E
4-A
4-C
3-C
-s)
3-A
1-H
1-J
Total
NU*
4-E
4-A
4-C
3-C
3-A
3-E
1-H
1-J
Total
Quantity
1
Quantity
1
1
1
2
3
4
5
1
_2
20
1
1
2
3
4
4
1
1
_2
19
205
-------
Maintenance Shift
Shift Foreman
Electrician
Mechanic
Electrician Helper
Mechanic Helper
Personnel Summary
General Management
Operating Shifts
Maintenance Shift
NU*
4-A
4-C
2-C
2-E
Total
2
2
6
3
_3
16
Total
1
39
16
56
*NU-Non-Union
206
-------
TABLE 5-23
EXAMPLE 4 - JIG PROCESS - COMPLEX
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Scalping Tower
Including Two 6 X 16 Foot Single Deck
Vibrating Screens having 15 hp each $ 300,000
Raw Coal Storage Area
12,000 Ton Capacity with Stacking Tube,
Reclaiming Feeds, and Tunnel 250,000
Raw Coal Belt To Raw Coal Bins
54 Inch Wide - 300 feet at $600 per foot 180,000
Raw Coal Bins
1,200 Ton Capacity - 5 at $50,000 each 250,000
Raw Coal Screens
8 X 20 Foot Double Deck Vibrating having 30 hp
5 @ $30,000 each plus installation 300,000
Raw Coal Belt To Baum Jig
36 Inch Wide - 250 feet at $480 per foot 120,000
Tramp Iron Magnet Over Baum Jig Belt
Explosion Proof - Self Cleaning Type 20,000
Raw Coal Belt To Batac Jigs
48 Inch Wide - 250 feet at $560 per foot 140,000
Total Raw Coal Storage & Handling Cost $1,560,000
207
-------
PREPARATION PLANT:
Equipment Cost -
Eight Cell Baum Jig
1 @ $176,000 $176,000
6 X 16 Foot Double Deck Vibrating
Clean Coal Dewatering Screens having 20 hp
2 @ $23,000 each 46,000
6 X 16 Foot Single Deck Vibrating Refuse
Dewatering Screens having 15 hp
2 @ $19,000 each 38,000
Sump - 1/4 Inch X 0 Clean Coal
1 @ $10,000 10,000
Sieve Bends
6 Foot Wide - 5 Foot Radius
4 @ $4,800 each 19,200
7 X 16 Foot Single Deck Vibrating Slurry
Dewatering Screens having 15 hp
2 @ $21,500 each 43,000
Centrifugal Dryers
2 @ $28,200 each 56,400
Thickening Cyclones
14 Inch Diameter w/Rubber Liner
12 @ $1,300 each 15,600
Batac Jigs - 5 Meter Width
2 (3 $610,000 each 1,220,000
208
-------
Fixed Sieves
5 Feet Wide - 3/4 mm openings
8 @ $4,000 each $ 32,000
7 X 16 Foot Single Deck Vibrating Clean
Coal Screens having 15 hp
8 @ $21,500 each 172,000
Centrifugal Dryers - Bird 1300
4 @ $50,000 each 200,000
Fixed Single Deck Refuse Screens
2 @ $15,000 each 30,000
Centrifugal Dryers
2 @ $28,200 each 56,400
Sump - 28 mesh X 0 Clean Coal
5 @ $10,000 each 50,000
Classifying Cyclones
14 Inch Diameter w/Ceramic Liners
20 @ $3,000 each 60,000
Sump - 28 mesh X 0 Refuse
2 @ $10,000 each 20,000
Thickening Cyclones
14 Inch Diameter y^/Ceramic Liner
4 (a $3,000 each 12,000
Vacuum Disc Filters
1.2 Feet 6 Inch Diameter - 12 Disc
4 @ $125,000 each 500,000
209
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Centrifugal Dryers
Bird Solid Bowl - 36 X 72 Inch
2 @ $110,000 each $ 220,000
Pumps 200.000
Total Preparation Plant Equipment Cost $3,176,600
Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$3,176,600 X 3.0 $9,530,000
OTHER FACILITIES & EQUIPMENT:
Fluid-Bed Thermal Dryers - 2
Complete with structural steel, motors, motor
controls, wiring, piping, field erection, and
start-up service $6,000,000
Static Thickeners - 2
150 Ft Diameter @ $2,000 per foot 600,000
Refuse Belt
36 Inch Wide - 200 feet @ $480 per foot 96,000
Refuse Bin - 200 Ton Capacity
Fabricated Part 50,000
Refuse Handling Equipment
2 - Dozers @ $150,000 each 300,000
3 - Trucks @ $ 75,000 each 225,000
Clean Coal Belt From Dryer To Storage
48 Inch Wide - 400 feet @ $600 per foot 240,000
210
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Clean Coal Storage Area
100,000 Ton Capacity With Reclaiming Feeders
and Tunnel
Coal Sampling System
Unit-Train Loading Facility
Total Other Facilities & Equipment
SUMMARY OF CAPITAL COST:
Raw Coal Storage and Handling
Preparation Plant
Other Facilities and Equipment
Contingency (Interest during construction, etc.)
Total Capital Requirement
$ 500,000
300,000
500,000
$ 8,811,000
$ 1,560,000
9,530,000
8,811,000
2,985,000
$22.886,000
BASED UPON THE 1600 TONS PER HOUR INPUT TO THIS PLANT THE CAPITAL
REQUIREMENT TRANSLATES TO $14,300 PER TON HOUR INPUT
211
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5.4.2 Capital Amortization
Based upon the rationale developed in Section 4.0 , the capital
amortization for Example 4 is as follows:
Total Capital Required: $22.9 Million
Capacity:
Raw Coal Input - 1600 tph
Clean Coal Output - 953 tph
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
30%
$0.84
$1.40
$0.67
$1.12
40%
$0.62
$1.04
$0.50
$0.84
5.4.3 Operating and Maintenance Costs
The operating and maintenance costs summarized in the following
Table 5-24 are based upon:
o Raw Coal Input of. 1600 Tons Per Hour
o Clean Coal Output of 953 Tons Per Hour
o Btu Recovery of 93.7%
o 10 Year Amortization Period
o 30% Utilization 2,600 Operating Hours Per Year
out of a Possible 8,760 Hours or 13 Hours Per Day for 200
Days Per Year. (Although this is low, this rate is applied
in order to be more consistent with the actual experience
during the period over which the cost data was collected.)
212
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TABLE 5-24
EXAMPLE 4 - JIG PROCESS - COMPLEX
OPERATING AND MAINTENANCE COSTS
Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non-Union) $0.030 $0.050
Operating & Maintenance (Union) 0.387 0.650
Overhead -
Includes Payroll Taxes, Insurance,
Welfare Fund, Vacations, Holidays,
etc. for all Preparation Plant
Employees 0.250 0.420
Supplies
Operating 0.137 0.230
Maintenance - Repair Parts and
Materials Associated with
Routine Maintenance 0.273 0.458
Thermal Dryer Fuel -
Based upon 17 Tons/Hr Coal Consumption
and Cost of Coal $20/Ton 0.213 0.357
Electricity 0.387 0.650
Other Expenses 0.084 0.141
0 & M Cost -
Not Including Capital Amortization $1.76 $2.96
Capital Amortization -
10 Yrs. - 30% Utilization 0.84 1.40
Total Operating & Maintenance Cost $2.60 $4.36
Cost Per Million Btu (13,418 Btu/lb) $0.162
213
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5.4.4 Discussion of Performance and Cost
The Example 4 plant is a good illustration of using coarse and
fine coal jigging to produce a clean coal product low in ash and sulfur
at a reasonable cost. Although when treating this particular coal the
process discards over 40% of the plant feed as refuse, it recovers 93.7%
of the Btu content of the raw coal.
The effectiveness of this process lies in the initial sizing of
the feed to insure its consistency with the individual equipment capabil-
ities. That is to say, the coarser material (2X3/4 inch ) is handled by the
Baum jig and the finer material (3/4 inch X 0) material is fed to the
Batac jigs. By restricting the amount of fines getting into the Baum jig,
a more efficient and accurate separation is accomplished. The Baum jig
effects a separation at approximately 1.60 specific gravity and recovers
less than 25% of the total material it processes. This low recovery is
not unexpected since the feed to the Baum jig is over 66% ash.
As noted, the fine coal portion of this plant centers around two
Batac jigs which treat the 3/4 inch X 0 fraction constituting nearly 80% of
the plant feed. These jigs effect a separation at between 1.70 and 1.80
specific gravity. Although this means rejecting nearly 30% as refuse,
the high Btu product from the Batacs is significantly lower in ash and
sulfur.
The number of personnel required to operate and maintain this
plant is somewhat higher than might be expected. However, the incremen-
tal increase in cost over having a more austere staff is not significant
when put on a per ton basis.
214
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As would be expected, the capital amortization of a larger plant
of this type becomes a sizeable cost factor when it is utilized only
30% of the time. Unfortunately, this plant is operated only two shifts
per day, five days per week with one shift reserved for maintenance. If
the plant could be operated an additional 10% of the time, the capital
amortization per ton of clean coal could be reduced by $0.36. Greater
utilization would also favorably impact other fixed charges such as
supervisory salaries and various overhead items.
Another significant cost in the operation of this plant is the
thermal dryer which handles 94% of the clean coal produced. The cost
of such extensive drying is reflected not only in fuel expense but par-
ticularly in higher electricity consumption due to the large horsepower
requirements of the two fluid-bed thermal dryers. However, these high
drying costs are more than justified by lower transportation and handling
expense.
Looking at the overall performance of the process in terms of the
cost, this plant performs cost effectively when treating this particular
coal. The material discarded as refuse carried with it only 6.3% of the
original heat content of the feed. This is a fair "price" to pay for a
significantly higher Btu product with nearly 80% less ash and reasonable
reduction in pyritic sulfur. If a cost was applied for these lost Btu's
as discussed in Section 4.4, the total cost of preparation would increase
by $0.056 per million Btu to $0.219. Although the total cost of producing
the clean coal is $4.36 per ton without considering any Btu loss, the net cost
215
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would be less if consideration was given to the economic benefits
attributable to preparation such as lower transportation, boiler main-
tenance, particulate and other emission controls, etc. As noted pre-
viously, these are not quantified since their full impact can only be
appreciated on a site specific basis where such things as transportation
distance and emission regulations are known.
216
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5.5 Example 5 - Heavy Media Process - Simple
5.5.1 General Description
As noted previously, the term heavy media is applied to any pro-
cess which uses a medium having a specific gravity approaching the
specific gravity of separation. In coal preparation, the most widely
accepted method for establishing the higher specific gravity medium
is to suspend magnetite in water. The process is based on the theory
that as the crushed material passes through such a medium, the coal
will float and the refuse will sink as predicted by laboratory specific
gravity analysis.
There are many levels of sophistication which a coal preparation
circuit based principally on heavy media can reach. Example 5, dis-
cussed herein, is a relatively simple approach which can be quite
effective with certain coals and end product requirements. A simpli-
fied flow sheet appears as Figure 5-5 on the following page.
In this particular circuit, the 24 inch X 0 run-of-mine coal, mined by
conventional and continuous mining, is conveyed to a grizzly where a
coarse scalping of the SinchXO material takes place. The plus 6 inch
material passes over the grizzly to a rotary breaker with 6 inch open-
ing grid plates. All material which is broken down to 6 inches or
less passes through the grid plates with the oversized material going
out the refuse end of the breaker to a rock bin where it is trucked
away to the disposal site. Now, the GinchXO material from the grizzly
and the breaker passes under a tramp iron magnet as it is conveyed to
a 10,000 ton concrete silo. The magnet is intended to remove scrap
217
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FIGURE 5-5
EXAMPLE 5 - HEAVY MEDIA PROCESS - SIMPLE
PREPARATION PLANT FLOW SHEET
MAGNETIC SEPARATOR
I 4^-*^ I
I HEAVV MEDIA SUMP I I !
• —4-—- \
RINSING SCREENS
350 TPH
REFUSE BELT
-------
steel material such as mining bits, tin cans, and roof bolts which
could be damaging to equipment in other portions of the plant. From
the raw coal storage silo, the 6inchXO coal is fed at the rate of 1400
tons per hour to five bins each feeding an 8 X 20 foot double deck
vibrating screen. The top screen has openings of approximately 1-1/4
inch with the bottom deck 1/2 inch. By subjecting the coal to a double
screening at this point, better definition is given to the desired sizing
function by not overloading the surface of the deck. The 1/2 inch or
less material passing through the bottom deck is considered clean coal
and goes directly to the product collection belts at the rate of 680 tph.
The material passing over the first and second decks of the raw coal
sizing screen is conveyed at the rate of 720 tph into the main portion
of the preparation plant. Here it is put onto five 8 X 20 foot double
deck pre-wet screens. The purpose of this wet screening operation is
to further remove any fines prior to the material entering the two
heavy media drums. The limited amount of additional fines passing
through the bottom deck goes to a fixed sieve bend for partial de-
watering with the overflow of the sieve bend going to the centrifuges
for final moisture reduction before going to the clean coal belt. The
underflow of the sieve bend is considered refuse and goes to the 90 foot
diameter thickener.
Approximately 700 tph pass over the pre-wet screens and enter the
two heavy media drums. The heavy media drums effect approximately a
50-50 separation at around 1.6 specific gravity. Floats, at the rate
of 350 tph, goto two 8 X 16 foot double deck drain and rinse screens.
219
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The major purpose of this screening operation is to rinse off the mag-
netite carried along with the coal from the heavy media drums. The top
decks have a 1-1/4 inch opening and the bottom 1 mm. The 210 tph of
6X1-1/4 inch material passing over the top decks is then reduced to 1-1/4
inch by a flextooth crusher to minimize the fines and is conveyed to the
15,000 ton concrete clean coal silo. The 120 tph of 1-1/4 inch and less
material passing over the lower decks of the 8 X 16 foot rinsing screens
goes to centrigugal dryers before being conveyed to the clean coal silo.
The 350 tph of sinks from the heavy media drums pass over two 8 X 16
foot single deck drain and rinse screens. This not only helps to dewater
the material but also salvages some of the magnetite clinging to the
refuse.
Refuse from the thickener is pumped at the rate of 14 tph to a 10
foot 6 inch diameter 9 disc vacuum filter where it is dewatered and
hauled away for disposal. This filter is sized according to the sizing
philosophy of 20 pounds of refuse per hour per square foot of disc area
(a 10' X 6" diameter unit with 9 discs, has approximately 1,395 square
feet of surface; 14 ton = 28,000 Ib; 28,000 Ib ~ 20 Ib/sq ft = 1,400 sq
ft). As observed in some of the other examples considered under this
section, vacuum filters are sized in a range as high as 50 pounds per
hour per square foot depending upon the nature of the material to be
dewatered. In this particular case, the design was deliberately kept on
the conservative side to produce a filter cake which would be sufficiently
low in moisture to permit immediate disposal.
220
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On a plant wide basis, of the 1400 tph fed from the raw coal
silo, 1,036 tph are considered clean and 364 tph refuse for a weight
yield of 74%. However, this is somewhat misleading in that nearly
50% of the raw coal feed is screened off as clean coal in the initial
preparation operation. Therefore, a more relevant indicator of this
circuit's effectiveness is the Btu recovery which approaches 95%.
Adequate operation and maintenance of the plant is achieved by a
staff of forty union and non-union personnel. A listing of these in-
dividuals by job classification appears as Table 5-26. Based upon
mid-1977 costs, the capital investment required to construct a plant
of this configuration is approximately 10 million dollars. A break-
down of this capital cost by major component appears as Table 5-27.
A summary of the operating and maintenance costs is presented in
Table 5-28. Although these costs will vary somewhat due to site spe-
cific conditions such as operating approach, current quality of the
raw coal, local labor problems/availability, etc., they are representa-
tive of the 0 & M cost level one might anticipate for an operation of
this type.
221
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TABLE 5-25
EXAMPLE 5 - HEAVY MEDIA PROCESS - SIMPLE
PREPARATION PLANT PERFORMANCE11
.2]
Raw Coal Feed To Plant:
Size Fraction Tph
6 Inch X 0 1400
Surface
Moisture 3
8.0
Btu/ib
8,600
Ash %
29.4
Total
Sulfur
4.56
IN3
(NO
no
Clean Coal Product From Plant:
1-1/4 Inch X 0
1036
7.5
10,992
22.13
4.17
Moisture & Ash Free Btu — 14,115 Btu/lb
Net Performance:
Weight Yield 74.0% Btu Recovery 94.6% Btu of Clean Coal with 7.5% Moisture 10.168 Btu/lb
1] Btu, Ash, & Sulfur Presented on Dry Basis
2] This is somewhat of a misnomer since nearly half (680 tph) of the total raw coal being processed
never enters the plant.
-------
TABLE 5-26
EXAMPLE 5 - HEAVY MEDIA PROCESS - SIMPLE
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-Union Management
Preparation Superintendent
General Foreman
Operating Shift (Two per day)
Title
Foreman
Plant Operator
Stationary Equipment Operator -
(Vacuum filter, thickener, media
system)
Electri ci an
Screenman (cleaner)
Utility Man
Repairman (Belt Mechanic)
Mobile Equipment Operator (Refuse
Handling)
Truck Driver
Dozer Operator
Maintenance Shift (One per day)
Foreman
Mechanic
Repai rman
Utility Man
Mobile Equipment Operator
Dozer Operator
Personnel Summary
General Management
Operating Shifts
Maintenance Shift
Union Classification
NU*
4-E
3-C
4-A
1-H
1-H
3-B
3-A
3-A
Total
NU*
4-C
3-B
1-H
3-A
Total
Total
Quantity
1
1
Quantity
1
1
I
1
2
1
1
3
2
13
1
7
1
1
2
12
2
26
12
40
*NU-Non-Union
223
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TABLE 5-27
EXAMPLE 5 - HEAVY MEDIA PROCESS - SIMPLE
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Scalping Tower
Including Single Deck Vibrating Screens,
Rock Bin, and Structural Work for Rotary
Breaker $ 350,000
Rotary Breaker
10 Foot Diameter - 12 Feet Long 150,000
Raw Coal Belt To Silo
48 Inch Wide - 200 Feet @ $560 per foot 112,000
Tramp Iron Magnet
Explosion Proof - Self Cleaning Type 20,000
Raw Coal Silo (Concrete)
10,000 Ton Capacity @ $110 per ton 1,100,000
Raw Coal Belt To Raw Coal Bins
54 Inch Wide - 150 Feet @ $600 per foot 90,000
Raw Coal Bins
100 Ton Capacity w/Feeders
5 @ $30,000 each 150,000
Raw Coal Screens
8 X 20 Foot Double Deck Vibrating having 30 hp
5 @ $30,000 each plus installation 300,000
224
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Raw Coal Belt To Plant
48 Inch Wide - 250 Feet @ $560 per foot $ 140,000
Total Raw Storage & Handling Cost $2,412,000
PREPARATION PLANT:
Equipment Cost -
8 X 20 Foot Double Deck Vibrating
Pre-Wet Screens
4 @ $30,000 each $120,000
Heavy Media Drums
Wemco - 12 Foot Diameter, 21 Feet Long
2
-------
Crusher
2 @ $12,100 each $ 24,200
Centrifugal Dryers
2 @ $28,200 each 56,400
Sump - Dryer Effluent
1 @ $10,000 10,000
Vacuum Disc Filter
10 Foot 6 Inch Diameter - 7 Disc
1 @ $90,000 90,000
Pumps 75,000
Total Preparation Plant Equipment Cost $ 914,800
Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$914,800 X 3.0 $2,744,400
OTHER FACILITIES & EQUIPMENT:
Static Thickener
90 Ft. Diameter @ $2,000 per foot 180,000
Refuse Bin - 450 Ton Capacity
Fabricated Part 75,000
Refuse Belt
36 Inch Wide - 200 feet @ $480 per foot 96,000
Refuse Handling Equipment
3 - Trucks @ $ 75,000 each 225,000
2 - Dozers @ $150,000 each 300,000
226
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Coal Sampling System $ 300,000
Clean Coal Belt
54 Inch Wide - 300 Feet @ $600 per foot 180,000
Clean Coal Silo
15,000 Ton Capacity @ $110 per ton 1,650,000
Unit-Train Load Facility 500,000
Total Other Facilities & Equipment $3,506,000
SUMMARY OF CAPITAL COST:
Raw Coal Storage and Handling $2,412,000
Preparation Plant 2,744,000
Other Facilities and Equipment 3,506,000
Contingency (Interest during construction, etc.) 1,300.000
Total Capital Requirement $9,962,000
BASED UPON THE 1400 TONS PER HOUR OF RAW COAL BEING PROCESSED BY THIS PLANT,
THE CAPITAL COST PER TON HOUR INPUT IS QUITE LOW - $7,116. HOWEVER, SINCE
ONLY 720 TPH IS RECEIVING ANY SIGNIFICANT DEGREE OF CLEANING, THE CAPITAL
COST SHOULD BE BASED UPON THE INPUT TO THE PREPARATION PLANT PROPER WHICH
TRANSLATES TO APPROXIMATELY $13.800 PER TON HOUR INPUT.
227
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5.5.2 Capital Amortization
Based upon the rationale developed in Section 4.0, the capital
amortization for Example 5 is as follows:
Total Capital Required: $10.0 Million
Capacity:
Raw Coal Input - 1400 tph
Clean Coal Output - 1036 tph
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
30%
$0.42
$0.56
$0.33
$0.45
40%
$0.31
$0.42
$0.25
$0.34
5.5.3 Operating and Maintenance Costs
The operating and maintenance costs summarized in the following
Table 5-28 are based upon:
o Raw Coal Input of 1400 Tons Per Hour
o Clean Coal Output of 1036 Tons Per Hour
o Btu Recovery of 94.6%
o 10 Year Amortization Period
o 30% Utilization 2,600 Operating Hours Per Year
out of a Possible 8,760 Hours or 13 Hours Per Day for 200
Days Per Year. (Although this is low, this rate is applied
in order to be more consistent with the actual experience
during the period over which the cost data was collected.)
228
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TABLE 5-28
EXAMPLE 5 - HEAVY MEDIA PROCESS - SIMPLE
OPERATING AND MAINTENANCE COSTS
Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non Union) $0.148 $0.200
Operating (Union) 0.360 0.487
Maintenance (Union) 0.254 0.343
Overhead -
Non-Union Benefits - Includes
Payroll Taxes, Group Life &
Medical Insurance, Pension Fund,
etc. 0.030 0.040
Union Benefits - Includes Payroll
Taxes, Welfare Fund, Vacations,
Holidays, Clothing Allowance, etc. 0.184 0.249
Other 0.112 0.152
Supplies
Operating - Magnetite, Flocculants,
and clay settler accounts for 22%.* 0.610 0.824
Maintenance - Equipment Repair, etc. 0.504 0.681
Electricity 0.165 0.223
0 & M Cost-
Not Including Capital Amortization $2.37 $3.20
Capital Amortization
10 years - 30% Utilization 0.42 0.56
Total Operating & Maintenance Cost $2.79 $3.76
Cost Per Million Btu (10,168 Btu/lb) $0-185
Consumption of these major additives on each ton of clean coal is:
Magnetite 1 to 1.5 Ib; Flocculant 0.015 Ib; and clay settler 0.15 Ib.
When the coal is damp and muddy, consumption is much higher. On an
annual basis, their cost averages $0.18 to $0.20 per ton of product.
229
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5.5.4 Discussion of Performance and Cost
Based upon the performance of the Example 5 plant as summarized on
Table 5-25, one has to search for "Why?" the plant is even in existence.
The answer is found in the fact that the current feed to the plant is
substantially different from that around which the plant was designed.
As originally conceived, approximately one-third of the raw coal was to
be less than 1/2 inch and be fairly low in ash and sulfur. However,
recent feed to the plant has been such that nearly half falls below
1/2 inch and contains a much larger percentage of the undesireable con-
stituents (ash and sulfur). As a result, the total performance of the
plant is far from impressive and cannot be improved by simply reducing
the openings of the sizing screens since the plant equipment selection
was predicated upon coarser material. To cope with these changed con-
ditions, an extensive plant modification is being planned which will
include Deister tables treating the 1/2 inchXO fraction. Although the
anticipated results from this modification will be a reduction in weight
yield to around 63% it will more than be justified by the quality of the
final product.
Obviously, this process is not recommended for treating the particular
coal now being run. However, a process of this type could very well show
merit when handling a coal having a physical consistency similar to that
around which the plant was designed. Therefore, the purpose of including
this example is not only to fill out the spectrum of heavy media processes
currently being utilized, but also show the capital and 0 & M costs of a
potentially successful process of this general make-up and capacity. Since
this plant as currently being operated performs very little actual cleaning,
the costs of preparation per ton of clean product, as presented in the
230
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preceeding Table 5-28, are only appropriate if it is assumed that better
operating results will be achieved at a 74% weight yield with another
coal. However, the costs presented on a raw ton can be used as the basis
for projecting product costs for whatever weight yield the reader feels
is proper for another coal.
231
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EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
5.6 Example 6 - Heavy Media Process - Complex
5.6.1 General Description
As shown on the plant flow sheet, Figure 5-6, the major emphasis of
this preparation process is on the material of less than 3/4 inch top size
which constitutes nearly 80% of the feed to the plant. This high concen-
tration of finer material is the result of the continuous and longwall
mining methods used in combination with the friable nature of the raw coal.
From the open raw coal storage area, the material is conveyed via a
42 inch belt to a fixed screen which passes coal of 8 inches or less.
That material greater than 8 inches passes over the screen and is reduced
to SinchXO by a crusher before going to a rotary breaker. In the rotary
breaker, that material reduced to 2-1/2 inches or less passes through
the screen plates and drops onto the 42 inch wide plant feed belt. Any
larger size material passes through the refuse end of the breaker and
reports to the refuse bin.
Raw coal 2-1/2 inch X 0 is conveyed at the rate of 600 tph to two in-
clined 7 X 16 foot double deck vibrating screens. The 126 tph of 2-1/2 X
3/4 inch material passing over both decks goes to the Barvoy heavy media
vessel. The 474 tph of 3/4 inch X 0 passing through the screens reports to
sumps from where it is pumped to the finer cleaning portion of the circuit.
Of the 126 tph entering the heavy media vessel, 58 tph are recovered as
clean coal. The balance (68 tph) sinks as refuse and goes to a 4 X 16
foot double deck drain and rinse screen for partial dewatering and media
recovery before dropping onto the refuse belt. The 58 tph of 2-1/2 X 3/4
inch "float" from the vessel passes over a 4 X 16 foot double deck drain
and rinse screen whose major purpose is media recovery. From this screen
the material goes to a crusher where the clean coal is reduced to 1-1/4 inch
X 0 before being conveyed to the thermal dryer.
232
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FIGURE 5-6
EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT FLOW SHEET
ro
oo
oo
AS SPYING |
CYCLONES
I «______________i_____________--_^^- i ft T » •
DILUTE MEDIA SUHP
TO HAKE-UP WATER
-------
Returning to the finer portion of the circuit, the 3/4 inch X 0
material is pumped from the raw coal sumps to sieve bend ahead of six 8 X
16 foot single deck desliming screens at the rate of 503 tph. Passing over
these screens is 378 tph of 3/4 inch X 1/2 mm (approximately 28 mesh) material
which goes to heavy media cyclones. The 125 tph of 1/2 mm X 0 material
passing through the desliming screens goes to two banks of four froth
flotation cells. Of this total, all but 26 tph is recovered as clean coal
and is partially dewatered by two vacuum disc filters before being conveyed
to the thermal dryer. The refuse from the froth cells reports to the 100
foot diameter concrete static thickener from which it is pumped at the rate
of 26 tph to a vacuum disc filter for partial dewatering before being con-
veyed to the refuse bin.
The 378 tph of 3/4 inch X 1/2 mm material passing over the desliming
screens is handled by six 24-inch diameter heavy media cyclones having
Nihard liners. These cyclones recover 308 tph as clean coal overflow which
goes to sieve bends ahead of six 8 X 16 foot single deck screens for partial
dewatering and media recovery. All but 18 tph passes over these screens
and goes to centrifugal dryers for further dewatering before being conveyed
to the thermal dryer. The 18 tph passing through these screens reports to
the dilute media sump. The 70 tph of underflow from the heavy media cyclones
goes to sieve bends ahead of two 6 X 16 foot single deck screens. All but
4 tph passes over these screens and goes directly to the refuse bin. The 4
tph passing through these screens reports to the dilute media sump from which
it is pumped along with the 18 tph of material which passed through the 8 X
16 foot single deck screens to six 20 inch diameter classifying cyclones.
234
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All 22 tph report as underflow in these cyclones and go to double drum
magnetic separators from which the solids are pumped to the 3/4 inch X 0
raw coal sumps for reprocessing by the finer coal portion of the circuit.
The single fluid-bed thermal dryer handles 440 tph of 1-1/4 inch X 0
material. Following drying, the clean coal is conveyed via a 42 inch wide
belt to a 10,000 ton concrete silo for storage pending unit-train load-out.
As shown in Table 5-29, this plant recovers approximately 73% by weight
of the plant feed having a heat content of 14,336 Btu/lb. This translates
to a 89.2% Btu recovery.
The staff necessary to operate and maintain this plant is listed
under Table 5-32. As summarized in Table 5-33, a plant of this size and
complexity could be built for around 13.5 million dollars.
235
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ro
TABLE 5-29
EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT PERFORMANCE*
Raw Coal Feed To Plant:
Size Fraction
2-1/2 X 3/4 Inch
3/4 Inch X 1/2 mm
(28 mesh)
1/2 mm X 0
Clean Coal Product
1-1/4 Inch X 0
3/4 Inch X 1/2 mm
1/2 mm X 0
% of
Feed
21.0
58.2
20.8
100.0
From Plant:
Surface
Tph Moisture %
126
349
125
600 5.0
58
283
99
Btu/lb
8,800
12,600
12,544
11,790
14,200
14,555
13,788
Ash %
41.4
17.2
17.7
22.4
7.8
6.4
10.4
Total
Sulfur %
4.88
4.24
4.27
4.38
2.65
2.00
2.55
440 5.0 14,336 7.48 2.21
Net Performance:
Weight Yield 73.3% Btu Recovery 89.2% Btu of Clean Coal with 5.0% Moisture 13,619 Btu/lb
* Btu, Ash, & Sulfur Presented on Dry Basis
-------
TABLE 5-30
EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
WASHABILITY DATA OF ASSUMED PLANT FEED - 3/4 Inch X 1/2 mm*
Direct Float
ro
GO
Specific Gravity
of Separation
Float 1.30
1.30- 1.40
1.40- 1.45
1.45- 1.50
1.50- 1.60
1.60- 1.70
1.70- 1.90
SINK- 1.90
Cumulative Float
Weight %
61.3
14.6
2.3
1.5
1.7
1.6
1.7
15.3
Ash %
4.0
11.4
17.3
20.3
24.2
31.1
42.0
70.1
Sulfur %
1.21
3.45
6.32
6.40
8.36
8.82
9.56
15.07
Weight %
61.3
75.9
78.2
79.7
81.4
83.0
84.7
100.0
Ash %
4.0
5.4
5.8
6.0
6.4
6.9
7.6
17.2
Sulfur %
1.21
1.64
1.78
1.87
2.00
2.13
2.28
4.24
* 58.2% of Total Feed
-------
TABLE 5-31
EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
WASHABILITY DATA OF ASSUMED PLANT FEED - 2-1/2 X 3/4 INCH FRACTION*
Specific Gravity
of Separation
Direct Float
Height % Ash % Sulfur
Cumulative Float
Height % Ash % Sulfur %
ro
OJ
CO
Float 1.30
1.30- 1.40
1.40- 1.45
1.45- 1.50
1.50- 1.60
1.60- 1.70
SINK- 1.70
21.5
20.8
2.2
2.1
2.4
2.6
48.4
3.6
10.1
15.7
19.4
24.5
32.9
75.1
1.35
3.20
5.90
7.19
7.73
7.55
6.74
21.5
42.3
44.5
46.6
49.0
51.6
100.0
3.6
6.8
7.2
7.8
8.6
9.8
41.4
1.35
2.26
2.44
2.65
2.90
3.14
4.88
* 21.0% of Total Feed
-------
TABLE 5-32
EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-union Management
Preparation Superintendent (1/2 time)
General Foreman
Operating Shift (2 per day)
Title
Foreman
Plant Operator
Electrician
Mechanic
Mobile Equipment Operator
(Refuse Hauling & Compacting)
Repairman-Helper (Greaser)
Stationary Equipment Operator
(Thermal Dryer, Media, etc.)
Utility Man
Maintenance Shift (1 per day)
Foreman
Electrician
Mechanic
Repairman
Repairman Helper
Total
Union Classification
NU*
4-E
4-A
4-C
3-A
2-F
3-C
1-H
Total
NU*
4-A
4-C
3-B
2-F
Total
Quantity
1
J^
2
Quantity
1
1
1
2
2
1
2
_2
12
1
1
3
2
_2
9
239
-------
Personnel Summary
General Management 2
Operating Shifts 24
Maintenance Shift -i
Total 35
*NU-Non-Union
240
-------
TABLE 5-33
EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Raw Coal Storage Area
20,000 ton capacity with reclaiming feeders
and tunnel $ 300,000
Raw Coal Belt To Scalping Tower
42 Inch Wide - 200 feet @ $520 per foot 104,000
Tramp Iron Magnet Over Raw Coal Belt
Explosion Proof, Self-Cleaning Type 20,000
Scalping Tower
Including Fixed Screen and Structural Work For
Crusher and Rotary Breaker 250,000
Raw Coal Crusher - 1 65,400
Rotary Breaker
9 Ft. Diameter - 17 Feet Long 150,000
Raw Coal Belt To Plant
42 Inch Wide - 250 feet @ $520 per foot 130,000
Total Raw Coal Storage & Handling Cost $1,019,400
PREPARATION PLANT:
Equipment Cost -
7 X 16 Foot Double Deck Vibrating
Raw Coal Screens
2 @ $21,000 each $ 42,000
Heavy Media Vessel
Barvoy Deep Bath Type 35,000
241
-------
4 X 16 Foot Double Deck Vibrating
Drain & Rinse Screens
2 @ $20,500 $ 41,000
Crusher - 1 9,000
Sump - Raw Coal 3/4 Inch X 0
2 @ $10,000 each 20,000
Sieve Bends
6 Feet Wide - 80 Inch Radius
6 @ $4,800 each 28,800
8 X 16 Foot Single Deck Vibrating
Desliming Screens
6 @ $27,000 each 162,000
Heavy Media Cyclones
24 Inch Diameter w/NiHard Liner
6 @ $3,000 each 18,000
Sump - Heavy and Dilute Media
5 @ $14,000 each 70,000
Froth Flotation Cells
2 Banks of Four Cells 76,000
Sieve Bends
5 Feet Wide - 80 Inch Radius
2 @ $4,000 each 8,000
6 X 16 Foot Single Deck Vibrating
Fine Refuse Screens
2 G> $19,000 each 38,000
242
-------
Sieve Bends
7 Feet Wide - 40 Inch Radius
6 @ $5,600 each 33,600
8 X 16 Foot Single Deck Vibrating
Fine Clean Coal Screens
6 @ $30,000 each 180,000
Centrifugal Dryers
Bird Model 1150 D
2 @ $48,000 each 96,000
Vacuum Disc Filters
2-12 Ft. 6 Inch Diameter 10 Disc
$120,000 each 240,000
1-10 Ft. 6 Inch Diameter 9 Disc 100,000
Classifying Cyclones
20 Inch Diameter
6 @ $2,400 each 14,400
Magnetic Separators
Double Drum - 30 Inch Diameter -
6 Ft. Long
3 6 $17,000 each 51,000
Pumps 150.000
Total Preparation Plant Equipment Cost 1,412,800
Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$1,412,800 X 3.0 $4,238,400
243
-------
OTHER FACILITIES & EQUIPMENT:
Static Thickener
100 Ft. Diameter G> $2,000 per foot $ 200,000
Fluid-Bed Thermal Dryer
Complete with structural steel, motors, motor
controls, wiring, piping, field erection, and
start-up service 3,500,000
Clean Coal Belt To Silo
42 Inch Wide - 300 feet @ $520 per foot 156,000
Clean Coal Silo
10,000 ton capacity @ $110 per ton 1,100,000
Coal Sampling System 300,000
Unit-Train Loading Facility 500,000
Magnetite Thickener
30 Ft. Diameter @ $2,500 per foot 75,000
Refuse Belt
36 Inch Wide - 200 feet @ $480 per foot 96,000
Refuse Bin
300 Ton Capacity - Fabricated Part 60,000
Refuse Handling Equipment
2 - Trucks @ $ 75,000 each 150,000
2 - Dozers @ $150,000 each 300,000
Total Other Facilities & Equipment $6,437,000
244
-------
SUMMARY OF CAPITAL COST:
Raw Coal Storage and Handling $ 1,019,400
Preparation Plant 4,238,400
Other Facilities and Equipment 6,437,000
Contingency (Interest during construction, etc.) 1,754.200
Total Capital Requirement $13.449,000
BASED UPON THE 600 TONS PER HOUR INPUT TO THIS PLANT THE CAPITAL
REQUIREMENT TRANSLATES TO $22.400 PER TON HOUR INPUT
245
-------
5.6.2 Capital Amortization
Based upon the rationale developed in Section 4.0, the capital
amortization for Example 6 is as follows:
Total Capital Required: $13.5. Million
Capacity:
Raw Coal Input - 600 tph
Clean Coal Output - 440 tph
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
30%
$1.31
$1.79
$1.05
$1.43
40%
$0.97
$1,33
$0.78
$1.06
5.6.3 Operating and Maintenance Costs
The operating and maintenance costs summarized tn the following
Table 5-34 are based upon:
o Raw Coal Input of 600 Tons Per Hour
o Clean Coal Output of 440 Tons Per Hour
«
o Btu Recovery of 89.2%
o 10 Year Amortization Period
o 30% Utilization 2,600 Operating Hours Per Year
out of a Possible 8,760 Hours or 13 Hours Per Day for 200
Days Per Year.
246
-------
TABLE 5-34
EXAMPLE 6 - HEAVY MEDIA PROCESS - COMPLEX
OPERATING AND MAINTENANCE COSTS
rATfrrriDv Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non Union) $0.099 $0.135
Operating & Maintenance (Union) 0.638 0.870
Overhead -
Fringe Benefits - 25% Non-Union 0.025 0.034
- 20% Union 0.128 0.174
Other - Includes Workmens1
Compensation Insurance, Payroll
Taxes, Welfare Fund, etc. 0.213 0.291
Supplies -
Operating 0.169 0.23
Maintenance & Other 0.242 0.33
Thermal Dryer Fuel -
Based Upon 7.0 Tons/Hr Coal
Consumption & Cost of Coal
$20/Ton 0.233 0.318
Cleaning Plant Repair Parts 0.147 0.20
Electricity (Large Thermal Dryer) 0.334 0.456
0 & M Cost -
Not Including Capital Amortization $2.23 $3.04
Capital Amortization -
10 years - 30% Utilization 1.31 1.79
Total Operating & Maintenance Cost $3.54 $4.83
Cost Per Million Btu (13,619 Btu/lb) $0-177
247
-------
5.6.4 Discussion of Performance and Cost
The Example 6 plant performs a reasonably good job of reducing
ash and sulfur while recovering nearly 90% of the heat content in the
raw coal feed. This is accomplished by treating the coarser size frac-
tions (+3/4 inch) in a heavy media vessel and the finer sizes with
heavy media cyclones and froth flotation. The heavy media vessel
effects a separation at 1.6 specific gravity giving a clean coal yield
consistent with the washability data from Table 5-31. Due to the high
percentage of 3/4 inch XO material in the raw feed, the majority of the
plant is devoted to finer cleaning equipment. The heavy media cyclones
operate at 1.60 specific gravity treating the 3/4 inch X l/2mm(28 mesh)
material with the l/2mm X 0 handled by flotation cells. These cyclones
recover over 80% of their feed as predicted by the washability data
from Table 5-30. The froth cells also recover nearly 80% of their feed
while significantly reducing the ash and sulfur content of the l/2mm X 0
size fraction.
As presented in Table 5-33, this is an expensive plant to build.
One of the major factors contributing to this high capital cost is the
large thermal dryer necessary to handle all of the 440 tons per hour of
clean coal produced by the plant. This one item accounts for 30% of
the total cost of the preparation facility. In spite of the high cost,
drying is necessary to meet their contract specification and can be
further justified on the basis of lower transportation and handling costs.
Since the capital cost is so high and current utilization is only 30%,
there is substantial room for reducing the effect of capital amortization
248
-------
on total cost. If this plant was operated 40% of the time, the capital
cost would be brought down by $0.46 on each ton of clean coal. Greater
plant utilization would also have a favorable impact on other fixed
expenses such as supervisory salaries and certain overhead items.
Since the Example 6 process when treating this particular coal loses
approximately 10% of the heat content in the raw feed, a cost might be
applied to account for these "lost" Btu's. If applied, the total cost
of preparation would increase by $0.077 to $0.254 per million Btu. The
application of this "cost" is based upon the assumption that the raw coal
was saleable in its original form and therefore had value associated with
its heat content. Even if one accepts this assumption, the validity of
applying this "cost" is subject to question since the material discarded,
which carried with it these "lost" Btu's, also carried large quantities of
the undesireable raw coal constituents such as ash and sulfur whose
removal was the very purpose of the cleaning process. Therefore, an
argument might be made that if the cleaning process was performing its
design function efficiently (i.e. to the Btu recovery limits consistent
with its design objective), no cost should be applied for the "lost"
heat content. However, a cost "penalty" would be assessed if the process
did not function close to the maximum Btu recovery consistent with the
desired sulfur and ash reduction. Since there are differing views on
how this subject should be treated, we have identified this cost item
separately above, to permit the reader complete latitude in it's
application.
Although this is an expensive plant to build, the overall operating
and maintenance costs are quite reasonable considering the results achieved.
249
-------
Even with the low plant utilization noted above, the price per ton is
less than $5.00 for a product having one-third the ash and half the
sulfur of the raw coal. This expense is more than recovered by the
producer in the market place who now has a far more valuable and readily
saleable product. Part of the increased value of the cleaned coal is
related to the benefits derived by the user. These include the obvious
savings in transportation and ash disposal as well as the more subtle
and sometimes greater economic benefits reflected in reduced particulate
and FGD emission control capacity. When these benefits are quantified
based upon the particular user's situation, they can significantly re-
duce the effective cost of coal preparation. In this particular case,
the reduction in sulfur would substantially reduce the S02 emission
control equipment and expense at the combustion location. Since the
purpose of this study is to look at coal preparation cost at the pro-
ducers level, we have not attempted to quantify any of these benefits
which our other studies have shown vary on a case by case basis.
250
-------
5.7 Example 7 - Heavy Media Process - Complex
5.7.1 General Description
This plant was designed to process coal with a large percentage
(40-50%) of finer material in the range of 1/4 inch X 0. The presence of
so much fine material in the raw plant feed is related to the nature of
the coal and the continuous mining methods used. Although such mining
machinery is quite efficient from a production standpoint, the as-mined
product can be more difficult to handle and process. Therefore, such a
condition should be a major consideration in the design of a coal prepara-
tion plant.
From the open raw coal storage area, 8 inch X 0 material is fed via
a 42 inch wide belt to a rotary breaker at just over 600 tons per hour
(tph). That material which reduces to 6 inches or less in the breaker
passes through the screen plates and drops onto the 42 inch wide plant
feed belt. That material which does not fracture to 6 inches or less
passes out the refuse end of the breaker and reports to a rock bin.
As the raw coal moves into the plant, it passes under a tramp iron
magnet to remove any stray ferrous material such as broken mining bits
which may have been carried along with the coal. From the plant feed
belt the 6 inch X 0 coal drops at the rate of 600 tph onto two 8 X 20
foot inclined vibrating double deck screens having 1-1/4 inch top deck and
1/4 inch lower deck openings. The actual feed to these screens is 610 tph
due to an additional 10 tph from the magnetite recovery units which is re-
cycled back through the circuit. Of the total feed to these screens, 330
tph of 6 X 1/4 inch material passes over and goes to two 6 X 16 foot
double deck prewet screens having 1/4 inch lower deck openings. All but
251
-------
FIGURE 5-7
EXAMPLE 7 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT FLOW SHEET
HEAVY
_ MEDIA
HEAVY MEDIA -»-dj_ ASUMP
CYCLONES
-------
10 tph passes over both decks of these screens and goes to the heavy media
vessel. Of the 320 tph of 6 X 1/4 inch material entering the vessel, 190
tph "floats" as clean product and passes to two 6 X 16 foot double deck
drain and rinse screens. These screens provide the multiple functions of
sizing, partial dewatering, and media recovery. Passing over the top decks
is 95 tph of 6 X 2 inch clean coal which goes to a crusher where it is re-
duced to 2 inch X 0 before it drops onto the clean coal belt. The 95 tph of
2 inch X 0 clean coal passing over the bottom deck of the 6 X 16 foot drain
and rinse screens goes to two centrifugal dryers which further dewater the
material before it drops onto the clean coal belt.
Of the total feed to the heavy media washer, 130 tph reports as re-
fuse and goes to one 6 X 16 foot double deck drain and rinse screen for
media recovery and partial dewatering. All 130 tph passes over both decks
of these screens and goes to the refuse belt.
Returning to the 8 X 20 foot raw coal screens, 280 tph of 1/4 inch X
0 material (46% of the total plant feed) passes through these screens and
is fed with the 10 tph underflow from the 6 X 16 foot prewet screens to
sieve bends ahead of four 6 X 16 foot single deck desliming screens. Of
the 290 tph fed to these screens, 220 tph of 1/4 inch X 28 mesh material
passes over and is fed to four 24 inch diameter heavy media cyclones. The
overflow from these cyclones is 130 tph of 1/4 inch X 28 mesh material which
goes to sieve bends ahead of four 6 X 16 foot single deck drain and rinse
screens. All but 10 tph passes over these screens and goes to four centri-
fugal dryers for further dewatering. Of the 120 tph fed to these centri-
fuges, 115 tph is recovered and drops onto the clean coal belt. The 5 tph
of effluent reports to a sump from which it is pumped over a sieve bend
on to the froth flotation cells. The 10 tph passing through the 6 X 16
253
-------
foot clean coal drain and rinse screens reports to the dilute media sump
from which it is pumped to magnetic separators. As mentioned earlier, the
magnetic separators recover the 10 tph and send it back to the beginning
of the circuit.
The underflow from the heavy media cyclones is 90 tph of 1/4 inch X
28 mesh material which is fed to a sieve bend ahead of a 6 X 16 foot single
deck vibrating refuse drain and rinse screen. All 90 tph passes over this
screen and reports to the refuse belt.
Returning to the 6 X 16 foot desliming screens, 70 tph of 28 mesh X
0 material passes through and is fed to froth flotation cells along with
the 5 tph of fine dryer effluent material which was recovered through a
sieve bend as mentioned above. The 75 tph of 28 mesh X 0 material is fed
to two banks of three froth cells which recover over 70% as clean coal.
The 55 tph of clean product from the froth cells goes to a 10 foot six
inch diameter vacuum disc filter having 14 discs for dewatering before
dropping onto the clean coal belt. The 20 tph of refuse from the cells
goes to the 100 foot diameter concrete static thickener. Settled material
is pumped from this thickener at the rate of j>0 tph to a 10 foot 6 inch
diameter vaccum disc filter having 12 discs where it is dewatered suffic-
iently to permit disposal.
Of the 600 tph of 6 inch X 0 raw coal feed to the plant, 360 tph of
2 inch X 0 winds up on the 36 inch wide clean coal belt and is fed to a
15,000 ton capacity concrete silo to await unit-train load-out. This plant
is efficiently operated and maintained by a minimum of personnel as set
forth in Table 5-36. Such a small staff is made possible by the aid of
a sophisticated electronic control center.
As presented in Table 5-37, a plant of this size and general make-up
can currently be constructed for a price of $8.4 million.
254
-------
TABLE 5-35
EXAMPLE 7 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT PERFORMANCE*
Raw Coal Feed To Plant:
Size Fraction
6 Inch X 0
Tph
600
Surface
Moisture
5.0
Btu/lb
8,600
Ash %
40.0
Total
Sulfur
1.0
ro
en
cri
Clean Coal Product From Plant:
2 Inch X 0
360
4.88
13,348
11.67
1.14
Moisture & Ash Free Btu = 15,112 Btu/lb
Net Performance:
Weight Yield 60.0 % Btu Recovery 93.1% Btu of^Clean Coal with 4.9% Moisture 12,697 Btu/lb
* Btu, Ash, and Sulfur Presented on Dry Basis
-------
TABLE 5-36
EXAMPLE 7 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-Union Management
Preparation Manager
Operating Shift (Two per day)
Title
Foreman
Plant Operator
Electrician/Mechanic
Mobile Equipment Operator
(Refuse Spreading & Compacting and
Pushing Raw Coal Into Feeders)
Repairman Helper
General Outside Laborer
Maintenance Shift
Foreman
Electrician/Mechanic
Repairman
Repairman Helper
Personnel Summary
General Management
Operating Shifts
Maintenance Shift
Union Classification
NU*
4-E
4-A
3-A
2-F
1-J
Total
NU*
4-A
3-B
2-F
Total
Quantity
1
Quantity
1
1
1
2
1
1
7
1
1
3
I
6
Total
1
14
_6
21
*NU - Non-Union
256
-------
TABLE 5-37
EXAMPLE 7 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Raw Coal Storage Area
10,000 Ton Capacity with Stacking Tube,
Reclaiming Feeders, and Tunnel $250,000
Raw Coal Belt To Rotary Breaker
42 Inch Wide - 200 Feet @ $520 per foot 104,000
Tramp Iron Magnet
Explosion Proof - Self Cleaning Type 20,000
Rotary Breaker 180,000
Raw Coal Belt To Plant
42 Inch Wide - 250 Feet @ $520 per foot 130,000
Total Raw Coal Storage & Handling Cost $684,000
PREPARATION PLANT:
Equipment Cost -
8 X 20 Foot Double Deck Vibrating
Raw Coal Screens
2 G> $30,000 each $60,000
6 X 16 Foot Double Deck Prewet Screens
2 @ $24,000 each 48,000
Heavy Media Washer 45,000
6 X 16 Foot Double Deck Clean Coal
Drain & Rinse Screens
2 @ $23,000 each 46,000
257
-------
6 X 16 Foot Double Deck Refuse Drain &
Rinse Screen
1 I? $26,000 $26,000
Crusher - Clean Coal 12,100
Centrifugal Dryers
2 @ $28,200 each 56,400
Sieve Bends - 5 Feet Wide
5 Ft. Radius - 1/2 mm openings
4 @ $4,000 each 16,000
6 X 16 Foot Single Deck Desliming Screens
4 @ $16,000 each 64,000
Heavy Media Cyclones
24 Inch Diameter - Ceramic Liners
4 @ $4,000 each 16,000
Sieve Bends - 5 Feet Wide
30 Inch Radius - 1/2 mm openings
6 @ $4,000 each 24,000
6 X 16 Foot Single Deck
Drain & Rinse Screens
5 @ $19,000 each 95,000
Centrifugal Dryer
4 @ $23,200 each 92,800
Froth Flotation Cells
2 Banks of Three Cells 68,000
258
-------
Magnetic Separators - Single Drum
30 Inch Diameter - 6 Feet Long
5 @ $6,500 each $ 32,500
Vacuum Disc Filters
Clean Coal - 10 Ft. 6 Inch Diameter -
14 Disc 128,000
Refuse - 10 Ft. 6 Inch Diameter -
12 Disc 120,000
Sumps - Heavy & Dilute Media
4 I? $14,000 each 56,000
Sump - Dryer Effluent
1 0 $10,000 10,000
Pumps 100,000
Total Preparation Plant Equipment Cost $1,115,800
Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$1,115,800 X 3.0 $3,347,400
OTHER FACILITIES & EQUIPMENT:
Static Thickener
100 Feet 0 $2,000 per foot 200,000
Refuse Belt
36 Inch Wide - 200 Feet @ $480 per foot 96,000
Refuse Bin 50,000
259
-------
Refuse Handling Equipment
2 - Dozers @ $150,000 each $ 300,000
1 - Front-End Loader 50,000
Clean Coal Belt To Silo
36 Inch Wide - 300 Feet @ $480 per foot 144,000
Clean Coal Silo - Concrete
15,000 Ton Capacity @ $110 per ton 1,650,000
Automatic Coal Sampling System 300,000
Unit-Train Loading Facility 500.000
Total Other Facilities & Equipment $3,290,000
SUMMARY OF CAPITAL COST:
Raw Coal Storage and Handling $ 684,000
Preparation Plant 3,347,400
Other Facilities and Equipment 3,290,000
Contingency (Interest during construction, etc.) 1,098,200
Total Capital Requirement $8,419,600
BASED UPON THE 600 TON PER HOUR INPUT TO THIS PLANT THE CAPITAL
REQUIREMENT TRANSLATES TO $14,000 PER TON HOUR INPUT
260
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5.7.2 Capital Amortization
Based upon the rationale developed in Section 4.0, the capital
amortization for Example 7 is as follows:
Total Capital Required: $8.4 million
Capacity:
Raw Coal Input - 600 tph
Clean Coal Output - 360 tph
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis | 30%
10 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
$0.82
$1.36
$0.66
$1.09
40% -
0.61
i
1.01 |
!
0.49
0.81
5.7.3 Operating and Maintenance Costs
The operating and maintenance costs summarized in the following
Table 5-38 are based upon:
o Raw Coal Input of 600 Tons Per Hour
o Clean Coal Output of 360 Tons Per Hour
o Btu Recovery of 93.1%
o 10 Year Amortization Period
o 30% Utilization 2,600 Operating Hours Per Year
out of a Possible 8,760 Hours or 13 Hours Per Day for 200
Days Per Year. (Although this is low, this rate is applied
in order to be more consistent with the actual experience
during the period over which the cost data was collected.)
261
-------
TABLE 5-38
EXAMPLE 7 - HEAVY MEDIA PROCESS - COMPLEX
OPERATING AND MAINTENANCE COSTS
Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non-Union) $0.058 $0.096
Operating & Maintenance (Union) 0.211 0.352
Overhead -
Fringe Benefits - 25% Non-Union 0.014 0.024
- 21% Union 0.044 0.074
Other - Includes Welfare Fund,
Payroll Taxes, Property Taxes,
Insurance, etc. 0.060 0.100
Supplies -
Operating - Magnetite 0.055 0.091
- Other 0.307 0.511
Maintenance 0.092 0.154
Major Maintenance - Scheduled repairs
and plant improvements 0.051 0.085
Electricity - 0.090 0.150
Subcontract Services For Major Equipment
Repairs & Miscellaneous Expenses 0.289 0.482
0 & M Cost -
Not Including Capital Amortization $1.27 $2.12
Capital Amortization - 0.82 1.36
10 Yrs. - 30% Utilization
Total Operating & Maintenance Cost $2.09 $3.48
Cost Per Million Btu (12,697 Btu/lb) $0.137
262
-------
5.7.4 Discussion of Performance and Cost
With the coal currently being handled by the Example 7 plant, the
major thrust of the preparation process is the reduction in ash. As
summarized by Table 5-35, this objective is accomplished at a loss of
only 7% of the total heat content in the raw coal feed. Looking at
the increase in sulfur content in the final product over that of the
raw coal, one might think there was a typographical error. However,
this phenomenon occurs because the sulfur content of the raw coal is
mostly organic in nature and is not affected by physically cleaning.
Therefore, as 40% of the raw feed is discarded as refuse, the organic
sulfur bonded to the clean coal becomes a higher proportionate share of
the final product. Although this result is expected with this particular
coal, it should not be assumed that this process is incapable of removing
sulfur. To the contrary, as demonstrated by Example 6, given a coal
having a higher pyritic sulfur content, processes of this type are
quite successful at effecting significant sulfur reductions.
The capital cost of this plant is quite reasonable considering its
demonstrated ability to reduce over 70% of the raw coal ash. Although
this plant's equipment make-up is much the same as Example 6, its capital
cost is over 35% less. The principal reason for this lower capital cost
over comparable capacity heavy media plants is the elimination of thermal
drying. This also has a significant impact on reducing operating and
maintenance costs. Through centrifugal drying methods and vacuum
filters the moisture is reduced to an acceptable level. Although this is
somewhat difficult to accept, it is supported by actual product data
263
-------
showing less than 16% of the final product is smaller than 28 mesh
which is the most trouble to mechanically dewater. In spite of this
lower capital requirement, the capital amortization per ton of clean
coal is still $1.36 due to only a 30% utilization factor. Certainly,
there is room for improvement as demonstrated by the fact that a
savings of $0.35 per ton could be realized by operating merely an
additional 10% of the time.
Regardless of the low plant utilization, the overall cost of pro-
ducing clean coal is quite low in view of quality of the product and
limited Btu loss. Besides the absence of thermal drying, the 0 & M
cost is kept low by having a minimum staff and closely monitoring the
consumption of magnetite, flocculants, and other expensive materials.
As noted previously, Table 5-38, gives the producer's cost to clean a
given coal by a particular process. Certainly, the clean product re-
sults in savings at the user level which go to reduce the effective cost
of coal cleaning. Since these benefits are most accurately quantified on
a site specific basis, no estimate is given here of their impact on
the total economics of coal preparation.
If a cost is applied to account for the 7% loss in heat content of
the raw feed,the cost of preparation increases by $0.066 to $0.203 per
million Btu. As mentioned at several other points in this study, it is
debatable whether or not it is appropriate to assess such a "penalty"
when the material containing this heat content was essentially composed
of the undesirable material (ash and some sulfur) which the cleaning
process was designed to eliminate. This being the case, the reader is
left with the prerogative to treat this matter as seen fit.
264
-------
5.8 Example 8 - Heavy Media Process - Complex
5.8.1 General Description
Although not shown on the flow sheet (Figure 5-8), the raw coal
is sized and most of the debris removed by a rotary breaker before
being conveyed to the raw coal storage area. The 4 inch X 0 raw coal,
mined by continuous and longwall mining, is fed to the breaker which
has approximately 2 inch screen plate openings thereby permitting
1-1/4-inch X 0 material to pass through.
From the raw coal storage area, the 1-1/4 inch X 0 material is fed to
the plant at the rate of 900 tons per hour (tph). On its way into the
plant, the raw coal passes under a tramp iron magnet to remove any
ferrous matter and passes through two 6 X 16 foot single deck trash screens
having two inch openings to remove any larger foreign material not
previously captured. The 1-1/4 inch X 0 raw coal passes over sieve bends
onto twelve 6 X 16 foot single deck desliming screens. These screens with
1/2 mm openings pass the 28 mesh X 0 material at the rate of 166 tph and the
1-1/4 inch X 28 mesh material flows over at the rate of 740 tph. This 740 tph
goes to twelve 24 inch first stage heavy media cyclones operating at
1.8 specific gravity. The 602 tph of overflow from these cyclones goes
to sieve bends ahead of twelve 6 X 16 foot single deck drain and rinse screens
whose primary function Is the recovery of media. All but 4 tph pass
over these screens on the way to centrifuges for partial dewatering
before going to the thermal dryers. The 4 tph passing through these
screens reports to the dilute media sumps.
The 138 tph of 1-1/4 inch X 28 mesh underflow from the first stage heavy
media cyclones goes to sieve bends ahead of four 5 X 16 foot single deck
265
-------
FIGURE 5-8
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT FLOW SHEET
FE V J_ u I 740 TPH
NDS \C ^pJ 1-1/4 -rn X 28 m
2nd STAGE
HEAVY MEDIA
CYCLONES
30 TPH
10
32 TPH
12 TPH ^x/ /
|20 TPH
IZS X 100 m
J— SOLID BOWL
CENTRIFUGES
2 TPH| I ,8 TPH
-------
drain and rinse screens for the purpose of media recovery. Of the
total feed to these screens, 136 tph passes over and is reduced to 1/2 inch X
0 by two double roll crushers. This material reports to the second
stage feed sumps from which it is pumped to sieve bends ahead of the
four second stage 5 X 16 foot single deck desliming screens. The 2 tph of
28 mesh X 0 passing through the first stage 5X16 foot drain and rinse screens
reports to the first stage dilute media sumps where it is pumped to the
eight first stage magnetic separators and recovered for further pro-
cessing.
Of the 136 tph of 1/2 inch X 0 material fed to the second stage de-
sliming screens, 128 tph of 1/2 inch X 28 mesh passes over and is fed to the
four 24 inch second stage heavy media cyclones operating at 1.8 specific
gravity. Only 8 tph of 28 mesh X 0 material passes through these desliming
screens and reports to the hydrocyclone feed sumps. The second stage
heavy media cyclones recover 18 tph of 1/2 inch X 28 mesh clean coal which
passes over two 5 X 16 foot second stage drain and rinse screens on the way
to centrifuges before going to the thermal dryers. The underflow from the
second stage heavy media cyclones is 110 tph of 1/2 inch X 28 mesh refuse
which goes to sieve bends ahead of two 7 X 16 foot second stage drain and
rinse screens for media recovery. All 110 tph passes over these screens and
goes to two horizontal centrifuges where the surface moisture is reduced
from 20% to around 7% before being conveyed to the refuse bin.
Now, returning to the hydrocyclone feed sumps, which receive
28 mesh X 0 material from the first and second stage desliming screens and
267
-------
the effluent from the clean coal centrifuges, a slurry containing 190
tph is fed to thirty-two hydrocyclones. The overflow from these cyclones
is 160 tph of 28 mesh X 0. The underflow is 30 tph of 28 X 100 mesh
material which reports to sumps from which it is pumped to four Deister
tables for final clean coal and refuse separation. Also feeding the tables
is 2 tph from the refuse centrifuge effluent sumps. The 12 tph of 28 X
100 mesh clean product from the tables joins the 160 tph of 28 mesh X 0
overflow from the hydrocyclones to feed thirty 14 inch thickening
cyclones. The 56 tph of 100 mesh X 0 overflow from these cyclones goes
to the two 135 foot diameter concrete static thickeners. The 116 tph of
28 X 100 mesh underflow from the thickening cyclones is joined by 58 tph
of 100 mesh X 0 material pumped from the thickeners before going to the
vacuum filters.
The total of 174 tph is partially dewatered by four vacuum disc
filters each having ten discs 12 feet 6 inches in diameter. This gives
an effective filtering surface area of 2,280 square feet per filter or
a total of 9,120 square feet. Based upon a load factor of 40 pounds
per hour per square foot of filtering surface gives the following
minimum surface area required:
Weight Being Processed:
174 tons/hour = 348,000 pounds/hour
Surface Area Required (Minimum):
348,000 pounds/hour _ 8 70Q ft;2
40 pounds/hour/ft^
268
-------
2
The 420 ft of excess filtering capacity permits slight fluctuations
in the feed without degrading performance. These filters produce a cake
of approximately 25% surface moisture which goes on to the thermal dryers,
The two fluid-bed thermal dryers receive 774 tph of 1-1/4 inch X 0
material with a surface moisture of around 12%. During the drying
process, the moisture is reduced to 5% or less. The dried product is
conveyed to a 15,000 ton concrete silo for storage pending unit-train
loadout.
Plant Operation -
The equipment in this preparation plant is arranged in two
parallel circuits. This permits the plant to operate at full capacity
for two shifts per day and at half capacity for the third shift while
one circuit is shut down for maintenance. Based upon working five
days per week, the plant can operate on an annual basis 4,160 hours at
full capacity and 2,080 hours at half capacity for a total possible
plant utilization of 5,200 hours per year. This would be equivalent
to over 59% of the time (5,200 Hrs 7 8,760 Mrs). However, this is
under ideal conditions and in practice the actual utilization is
closer to 50%. For the purpose of allocating the capital cost of this
plant, this latter utilization factor was used.
269
-------
TABLE 5-39
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT PERFORMANCE
no
—i
o
Raw Coal Feed To Plant:
Size Fraction
1-1/4 X 3/8 Inch
3/8 X 1/8 Inch
1/8 Inch X 0
Tph
215
281
404
900
Surface
Moisture %
5.0
Btu/lb Ash %
31.2
20.7
13.4
11,970 19.9
Total
Sulfur %
2.75
2.65
2.20
2.45
Clean Coal Product From Plant:
1-1/4 X 28 Mesh
28 Mesh X 0
600
174
774
5.0
13,130
14.7
1.8
Net Performance:
Weight Yield 86.0% Btu Recovery 94.3% Btu of Clean Coal with 5.0% Moisture 12,473 Btu/lb
-------
TABLE 5-40
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
WASHABILITY DATA OF ASSUMED PLANT FEED - 1-1/4 X 3/8 INCH FRACTION*
ro
Specific D1rect Float
Gravity of Height % Ash % Sulfur
Cumulative Float
Cumulative Sink
Weight % Ash % Sulfur
FLOAT 1.40
1.40- 1.50
1.50- 1.60
1.60- 1.70
1.70- 1.80
SINK- 1.80
41.8
11.6
7.4
7.0
6.2
26.0
9.4
19.6
28.4
36.9
44.1
67.5
1.50
2.50
3.30
3.35
3.35
4.40
41.8
53.4
60.8
67.8
74.0
100.0
9.4
11.6
13.7
16.1
18.4
31.2
1.50
1.70
1.90
2.05
2.15
2.75
58.2
46.6
39.2
32.2
26.0
46.8
53.6
58.3
63.0
67.5
3.65
3.95
4.05
4.20
4.40
* 23.9% of Total Feed
-------
TABLE 5-41
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
WASHABILITY DATA OF ASSUMED PLANT FEED - 3/8 X 1/8 INCH FRACTION*
ro
--J
ro
Specific D1rect Float
Gravity of Weight % Ash % Sulfur
Cumulative Float
Weight % Ash % Sulfur
Cumulative Sink
Weight % Ash % Sulfur %
FLOAT 1.40
1.40- 1.50
1.50- 1.60
1.60- 1.70
1.70- 1.80
SINK- 1.80
67.0
5.3
5.3
3.6
3.0
15.8
7.5
20.7
29.7
36.2
43.7
65.7
1.30
2.65
3.50
3.40
3.70
7.85
67.0
72.3
77.6
81.2
84.2
100.0
7.5
8.5
9.9
11.1
12.2
20.7
1.30
1.40
1.55
1.60
1.70
2.65
33.0
27.7
22.4
18.8
15.8
47.5
52.6
58.0
62.2
65.7
5.45
6.00
6.60
7.20
7.85
* 31.2% of Total Feed
-------
TABLE 5-42
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
WASHABILITY DATA OF ASSUMED PLANT FEED - 1/8 X 0 INCH FRACTION*
Specific Direct Float
Gravity of Weight % Ash_l Sulfur
Cumulative Float
Weight % Ash % Sulfur
Cumulative Sink
Weight % Ash %. Sulfur
ro
•^j
CO
FLOAT 1.40
1.40- 1.50
1.50- 1.60
1.60- 1.70
1.70- 1.80
SINK- 1.80
81.2
2.4
3.3
2.2
1.5
9.4
5.7
22.6
28.1
34.2
40.9
63.2
1.00
2.20
2.20
3.50
3.05
12.45
81.2
83.6
86.9
89.1
90.6
100.0
5.7
6.2
7.0
7.7
8.2
13.4
1.00
. 1.05
1.10
1.15
1.15
2.25
18.8
16.4
13.1
10.9
9.4
46.7
50.2
55.8
60.1
63.2
7.55
8.35
9.85
11.15
12.45
* 44.9% of Total Feed
-------
TABLE 5-43
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT OPERATING & MAINTENANCE PERSONNEL
General Non-Union Management
Preparation Manager (1/2 time)
General Foreman
Operating Shift - Full (2 per day)
Title Union
Foreman
Plant Operator
Electrician
Mechanic
Mobile Equipment Operator
(Refuse Hauling & Compacting)
Stationary Equipment Operator
(Thermal Dryer & Media Operators)
Repairman Helper (Greaser)
Utility Man
Operating/Maintenance Shift - Partial
(1 per day)
Foreman
Plant Operator
Electrician
Mechanic
Mobile Equipment Operator
Total
Classification
NU*
4-E
4-A
4-C
3-A
3-C
2-F
1-H
Total
NU*
4-E
4-A
4-C
3-A
Quantity
1
_!
2
Quantity
1
1
1
2
2
2
1
_3
13
1
1
1
4
2
274
-------
Stationary Equipment Operator 3-C 2
Repairman 3-B 1
Repairman Helper (Greaser) 2-F 1
Utility Man 1-H _3
Total 16
Personnel Summary
General Management 2
Operating Shifts - Full 26
Operating/Maintenance Shift - Partial 16.
Total 44
W-Non-Union
275
-------
TABLE 5-44
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Raw Coal Belt to Rotary Breaker
48 Inch Wide 350 feet at $560 per foot $ 196,000
Rotary Breaker
10 Ft diameter - 16 ft. long
Includes structural work and rock bin to
receive debris from breaker 330,000
Raw Coal Belt to Storage Area
48 Inch Wide 300 feet at $560 per foot 168,000
Raw Coal Storage Area
20,000 ton capacity with reclaiming feeders
and tunnel 300,000
Raw Coal Belt to Plant
48 Inch Wide 350 feet at $560 per foot 196.000
Total Raw Coal Storage & Handling Cost $1,190,000
PREPARATION PLANT:
Equipment Cost -
6 X 16 .Foot Single Deck Trash Screens
2 @ $15,000 each $ 30,000
Sieve Bends
6 Ft Wide, 2 Ft 6 Inch Radius
14 @ $4,800 each 67,200
276
-------
7 X 16 Foot Single Deck Vibrating
Uesliming Screens
12 @ $21,500 each $258,000
7 X 16 Foot Single Deck Vibrating
Drain & Rinse Screens
2 @ $21,500 each 43,000
Sieve Bends
4 Ft Wide, 2 Ft 6 Inch Radius
4 - 1st Stage, 6 - 2nd Stage
10 @ $3,200 each 32,000
5 X 16 Foot Single Deck Vibrating
Drain & Rinse Screens
6 @ $18,500 each 111,000
5 X 16 Foot Single Deck Vibrating
Desliming Screens
4 @ $18,500 each 74,000
Sieve Bends
5 Ft Wide, 2 Ft 6 Inch Radius
12 @ $4,000 each 48,000
6 X 16 Foot Single Deck Vibrating
Drain & Rinse Screens
12 @ $19,000 each 228,000
Heavy Media Cyclones
24 Inch Diameter w/Ni-Hard Liner
16 @ $3,000 each *8,QQQ
277
-------
Centrifugal Dryers
6 @ $28,200 each $169,200
Crushers - 2 @ $33,100 each 66,200
Magnetic Separators
30 Inch Diameter - 10 Feet Long
10 @ $8,500 each 85,000
Centrifugal Dryers - Solid Bowl
2 @ $110,000 each 220,000
Centrifugal Dryers - Horizontal Refuse
2 @ $25,000 each 50,000
Hydrocyclones - 14 Inch Diameter w/Ni-Hard
Liner & Refrax Underflow
32 @ $2,000 each 64,000
Deister Tables
2 Double Deck @ $21,000 each 42,000
Thickening Cyclones
14 Inch Diameter w/Rubber Liner
30 @ $1,300 each 39,000
Vacuum Disc Filters
12 Ft 6 Inch Diameter - 10 Disc
4 @ $120,000 each 480,000
Sumps - 1st Stage Heavy Media
8,000 gallon - 1/4 Inch Steel
2 @ $14,000 each 28,000
278
-------
Sumps - 1st Stage Dilute Media
7,000 gallon - 1/4 Inch Steel
2 @ $14,000 each $ 28,000
Sumps - 2nd Stage Feed
4,000 gallon - 1/4 Inch Steel
2 @ $10,000 each 20,000
Sumps - 2nd Stage Heavy Media
4,000 gallon - 1/4 Inch Steel
2 @ $14,000 each 28,000
Sumps - 2nd Stage Dilute Media
3,000 gallon - 1/4 Inch Steel
2 @ $14,000 each 28,000
Sumps - Hydrocyclone Feed Sumps
9,000 gallon - 1/4 Inch Steel
2 @ $10,000 each 20,000
Sumps - Refuse Centrifuge Effluent Sumps
2,500 gallon - 1/4 Inch Steel
2 @ $10,000 each 20,000
Sumps - Table Feed
3,000 gallon - 1/4 Inch Steel
2 @ $10,000 each 20,000
Sumps - Other
7 @ $10,000 each 70,000
Pumps 200,000
Total Preparation Plant Equipment Cost $2,616,600
279
-------
Total Cost of Preparation P"Unt
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc,
$2,616,600 X 3.0 $7,849,800
OTHER FACILITIES & EQUIPMENT:
Fluid-Bed Thermal Dryers - 2
Complete with structural steel, motors, motor
controls, wiring, ptping, field erection, and
start-up service 5,400,000
Static Thickeners - 2
Each 135 feet in diameter 9 $2,000 per foot 540,000
Refuse Belt
36 Inch Wide - 200 feet @ $480 per foot 96,000
Refuse Bins
2 - 100 ton capacity - fabricated part 100,000
Refuse Handling Equipment
2 - Trucks @ $ 75,000 each 150,000
2 - Dozers @ $150,000 each 300,000
Coal Sampling System 300,000
Clean Coal Belt to Silo
48 Inch Wide - 200 feet @ $560 per foot 112,000
Clean Coal Silo
15,000 ton capacity @ $110 per ton 1,650,000
Unit-Train Loading Facility 500,000
Total Other Facilities & Equipment $9,148,000
280
-------
SUMMARY OF CAPITAL COST;
Raw Coal Storage and Handling $ 1,190,QQO
Preparation Plant 7,850,000
Other Facilities and Equipment 9,148,000
Contingency (Interest during construction, etc.) 2,728,000
Total Capital Requirement $20,916,000
BASED UPON THE 900 TONS PER HOUR INPUT TO THIS PLANT THE CAPITAL
REQUIREMENT TRANSLATES TO APPROXIMATELY $23.200 PER TON HOUR INPUT
281
-------
5.8.2 Capital Amortization
Based upon the rationale developed in Section 4.0, the capital
amortization for Example 8 is as follows:
Total Capital Required: $20.9 Million
Capacity:
Raw Coal Input - 900 tph
Clean Coal Output - 774 tph
CAPITAL AMORTIZATION
% Utilization
Amortization Period & Basis
10 Year Period
Per Ton of Raw Coal
t
i Per Ton of Clean Coal
15 Year Period
Per Ton of Raw Coal
Per Ton of Clean Coal
30%
$1.36
$1.58
$1.09
$1.26
40%
$1.01
$1.17
$0.81
$0.94
50%
$0.81
$0.94
$0.65
$0.75
5.8.3 Operating and Maintenance Costs
The operating and maintenance costs summarized in the following
Table 5-45 are based upon:
o Raw Coal Input of 900 Tons Per Hour
o Clean Coal Output of 774 Tons Per Hour
o Btu Recovery of 94.3%
o 10 Year Amortization Period
o 50% Utilization 4,380 Operating Hours Per Year
out of a Possible 8,760 Hours or 17.5 Hours Per Day
for 250 Days Per Year.
282
-------
TABLE 5-45
EXAMPLE 8 - HEAVY MEDIA PROCESS - COMPLEX
OPERATING AND MAINTENANCE COSTS
Per Ton Per Ton
COST CATEGORY Raw Coal Clean Coal
Labor -
Supervisory (Non-Union) $0.035 $0.041
Operating & Maintenance (Union) 0.267 0.310
Overhead -
Includes Payroll Taxes, Vacation
and Holiday Pay, Welfare Fund,
Taxes, Insurance, etc. 0.196 0.228
Supplies -
Operating 0.249 0.290
Maintenance - Includes Scheduled
Major Repair and Replacements 0.529 0.615
Thermal Dryer Fuel -
Based upon 12.5 Tons/Hr Coal Con-
sumption andjCost.of Coal $20/Ton 0.278 0.323
Electricity 0.456 0.53
Other 0.087 0.101
0 & M Cost -
Not Including Capital /Amortization $2.10 $2.44
Capital Amortization -
10 Yrs. - 50% Utilization 0.81 0.94
Total Operating & Maintenance Cost $2.91 $3.38
Cost Per Million Btu (12,473 Btu/lb) $0.135
283
-------
5.8.4 Discussion of Performance and Cost ,
The Example 8 plant is simply a two stage heavy media cyclone
process with limited use of Deister tables. As indicated by the per-
formance data summarized in Table 5-39, it has the potential for high Btu
recovery by crushing the underflow from the first stage cyclones and
subjecting it to another round of cleaning.
Of the heavy media processes presented in this study, others show
more dramatic reductions in ash and sulfur than occurs with the coal
currently being treated by the Example 8 plant. However, as we know,
the results achieved by a given preparation process vary with the feed
to the plant and this raw coal is not particularly high in ash or sulfur.
Therefore, the purpose of presenting this plant is to give further under-
standing of capital and operating and maintenance costs for a larger
heavy media plant which is capable of achieving significant reductions
in both ash and sulfur. A further reason for presenting this plant is
to show the favorable cost impact of increasing utilization to 50%.
This plant is capable of operating over 50% of the time by virtue of
its parallel circuit design. Although this increases the initial capital
requirement, it is justified by the greater output which permits a
lower per unit allocation of fixed charges.
Besides the parallel circuitry, necessitating redundant equipment,
the thermal drying of all clean coal produced increases this plant's
capital cost. However, due to the high percentage of fines, thermal
drying is required.
284
-------
Looking at the total producer's cost of preparation summarized on
the preceding Table, it is clear that, in spite of the high capital
requirement, the cost per ton of clean product is substantially less
than some smaller heavy media plants. This lower cost is directly
attributable to the plant capacity and greater utilization mentioned
above. For example, if this plant was operated only 30% of the time
there would be nearly a 20% increase ($0.64) in the cost of each clean
ton resulting from higher capital amortization alone, not to mention
the impact on other fixed charges.
With the raw coal currently being handled by this plant, the process
yields a 94.3% Btu recovery. Therefore, it would seem inappropriate to
apply an additional cost to cover these "lost" Btu's. However, if such
a charge is applied, the total cost of cleaning increases by $0.039 to
$0.174 per million Btu.
In conclusion, the reader is reminded that the operating and
maintenance costs presented herein are those experienced by the pro-
ducer. As stated earlier, the clean product carries with it various
benefits which are reflected in lower costs to the user which go to
reduce the overall net cost of coal preparation.
5.9 SUMMARY OF PREPARATION PROCESS EXAMPLES
Table 5-46 on the following page gives a tabular summary of the
major performance and cost elements from the eight actual operating
preparation plants examined in Section 5.0.
285
-------
TABLE 5-46
SUMMARY OF PREPARATION PROCESS EXAMPLES
1)
ro
co
en
xam|
1
2
3
4
5
6
•7
/
8
pie Process/Level
Jig/Simple
Jig/ Intermediate
Jig/ Intermediate
Jig/Complex
Heavy Media/Simple
Heavy Media/Complex
Heavy Media/ Complex
Heavy Media/Complex
Input
Capacity
600
1000
1000
1600
1400
600
600
900
tph
tph
tph
tph
tph
tph
tph
tph
Capital Cost Per
Ton Per Hr. Input
$
$
$
$
$
$
$
$
6,600
13,700
12,100
14,300
13,800
22,400
14,000
23,200
Clean Coal
Output
354
714
566
953
1,036
440
360
774
tph
tph
tph
tph
tph
tph
tph
tph
Btu
Recovery
91.6%
96.4%
83.0%
93.7%
94.6%
89.2%
93.1%
94.3%
Per Ton
Raw Coal
$1.97
$2.62
$2.22
$2.60
$2.79
$3.54
$2.09
$2.91
Per Ton
Clean Coal
$3.35
$3.67
$3.92
$4.36
$3.76
$4.83
$3.48
$3.38
Per Million
Btu
$0.138
$0.152
$0.157
$0.162
$0.185
$0.177
$0.137
$0.135
1) All cost figures as of mid-1977
2) Includes capital amortization
3) Does not include allowance for Btu loss of Process
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SECTION 6,0
FUTURE PROSPECTS FOR COAL PREPARATION
287
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6.0 FUTURE PROSPECTS FOR COAL PREPARATION
It is the opinion of the author, that there is a significant
potential for larger centralized preparation plants fed by more than
one mine thereby capable of operating almost continuously. To accomplish
this in some areas would necessitate cooperative agreements between
smaller producers to assure round-the-clock availability of plant
feed. Additionally, the plant would have to be laid out in such a
manner to permit parallel circuits or at least redundancy of higher
maintenance equipment. Due to union restrictions, overtime would
be a recurring cost factor. However, such a cost would more than be
covered by the increased output and efficiency of such an arrangement.
As expressed in a recent EPRI report, "The technological factors
that will contribute to the increasing use of preparation for power
coals are the advance of nonselective and continuous types of mining
equipment; problems associated with the use of high ash, high sulfur,
and alkali content coal in the boilers; and the expensive and uncertain
*
performance of flue gas desulfurizers".
Indications are clear that an increasing percentage of utility coals
will be cleaned. This is being brought about by such factors as:
1) Emission Standards - Getting Tougher
Coal Prep Can Eliminate or Reduce FGD costs and Associated
Operational Problems
2) Economic Pressures -
Greater Heat Content Per Unit Weight
Reduced Boiler Maintenance
Price of Higher Quality Coal
: Physical Coal Preparation, EPRI FP-314, May 1977, page 3-1
288
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In order to cost-effectively meet this increase in demand brought
on by these tougher emission standards and increasing economic pressures,
coal preparation processes will have to be designed around maximizing Btu
recovery while substantially reducing the ash and pyritic sulfur contents.
One approach to meeting this design objective might be an all flotation
process of the general configuration presented in Figure 6-1. In this
hypothetical approach, the 8 inch X 0 run-of-mine coal would be fed to a
rotary breaker where the initial size reduction and removal of harder
refuse would occur. From the rotary breaker, the 6 inch X 0 raw coal
would go to a crusher for reduction to 3/4 inch X 0 before going to a
rod mill for final reduction to 28 mesh or less. To minimize the creation
of fines, the rod mill would be operated in such a manner to avoid over-
grinding. This being the case, a significant portion of the product
from the rod mill would be plus 28 mesh. By using a classifier and re-
circulating the oversize product, as shown in Figure 6-1, only 28 mesh
X 6 would be fed to the first stage froth flotation cells. The froth
collected from the first stage flotation would be fed to second stage
froth flotation cells, where further cleaning would occur. The reject
from both stages of flotation would go to static thickeners. Since the
underflow from the static thickeners would be comprised of a high per-
centage of very fine particles, it would have to be pumped to filter
presses for dewatering before disposal. The product from the second
stage flotation cells would be partially dewatered by vacuum disc
filters and then further dried by a disc or other indirect type thermal
dryer. A fluid-bed thermal dryer could not be used under these conditions
due to the fine nature of the clean coal. Currently, most of the in-
direct type thermal dryers available are constructed on a small scale and
289
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1
FIGURE 6-1
HYPOTHETICAL FLOTATION PLANT WITH FINE REFUSE DISPOSAL
SIMPLIFIED PROCESS FLOW SHEET
770 tph
8 inch X 0
20 tph
+ 6 inch
ro
tn
CD
LEGEND
COAL
REFUSE
ROTARY I 6 inch X
BREAKER
CRUSHER
3A INCHXO • 750 tph
2,500 tph
2500 tph
0 tph
750 tph
CLASSIFIERS !••••••
+ 28 MESH | 28 MESH X 0
1st
STAGE
FROTH
FLOTATION
600 tph
210 tph
2nd
STAGt
FROTH
FLOTATION
tph
hJt
210 tph TO DISPOSAL
VACUUM
FILTERS
THERMAL
DRYERS
tph • TO STORAGE
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use oil as the heat source. However, as high volume drying operations of
the type required by this hypothetical plant become more common, larger
scale units using coal fired boilers should become available. Although
the capital cost will not be .influenced to any significant degree, the
fuel consumption cost should be cut in half.
Based upon late-1977 equipment and construction prices, a plant of
this general make-up and capacity would require an initial capital in-
vestment of approximately $38 million dollars. A rough breakdown of
this estimated capital cost is presented in Table 6-1. The personnel
necessary to operate and maintain a plant of this type would not vary
substantially from that required in a comparable capacity heavy media
facility with thermal drying. Assuming this 750 tph input plant, produc-
ing 540 tph of clean coal, was utilized at least 40% of the time and
achieved a 96% Btu recovery, the operating and maintenance cost including
capital amortization would be just under $8.00 per ton of clean product.
Based upon a clean coal (10-12% moisture) having a thermal content of
13,500 Btu per pound, this equates to approximately $0.30 per million Btu.
The major components of this estimated 0 & M cost are listed in Table 6-2.
This total 0 & M cost is greatly influenced by the high capital and power
costs of the fine clean coal and refuse dewatering equipment. Additionally,
the fine grinding of the entire plant feed contributes significantly to
the overall cost of such a plant.
Since all the clean coal produced by this process would be of a
fine size, transportation and handling would present problems. Therefore,
a fine cleaning plant of this type might be most appropriately located adja-
cent to the using power plant or the clean coal transported pneumatically.
291
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TABLE 6-1
HYPOTHETICAL FLOTATION PLANT
WITH FINE REFUSE DISPOSAL
PREPARATION PLANT CAPITAL REQUIREMENTS
RAW COAL STORAGE AND HANDLING:
Raw Coal Storage Area $ 300,000
Raw Coal Belt To Breaker
42 Inch Wide - 200 Feet @ $520 per foot 104,000
Tramp Iron Magnet 20,000
Rotary Breaker including structural work 250,000
Raw Coal Belt To Plant
42 Inch Wide - 300 Feet @ $520 per foot 156.000
Total Raw Coal Storage & Handling Cost $ 830,000
PREPARATION PLANT:
Crusher - $ 90,000
Rod Mills
4 @ $395,000 1,580,000
Classifiers
4 @ 40,000 160,000
Conditioning Tanks 150,000
1st Stage Froth Flotation Cells
10 Banks of 5 cells
10 @ $65,000 650,000
2nd Stage Froth Flotation Cells
8 Banks of 5 cells
8 @ $65,000 520,000
292
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Vacuum Filters
12 feet 6 inch diameter, 15 discs
7 @ $150,000 $ 1,050,000
Pumps 200,000
Total Preparation Plant Equipment Cost $ 4,400,000
Total Cost of Preparation Plant
Including Site Preparation, Construction of
Building, Electrical Service, Piping, etc.
$4,400,000 X 3.0 $13,200,000
OTHER FACILITIES
Static Thickeners
200 Foot diameter - concrete
2 @ $2,000 per foot of diameter 800,000
Filter Presses
7 @ $275,000 (basic equip. Cost)
7 X 3 X $275,000 5,775,000
Thermal Dryers
Indirect Disc Type
(60 tph $1,200,000 full price)
9 X $1,200,000 10,800,000
Clean Coal Silo
10,000 Ton Capacity @ $110 per ton 1,100,000
Clean Coal Belt To Silo
42 Inch Wide - 200 feet @ $520/ft 104,000
Total Other Facilities & Equipment $18,579,000
293
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SUMMARY OF CAPITAL COST
Raw Coal Storage and Handling $ 830,000
Preparation Plant 13,200,000
Other Facilities and Equipment 18,579,000
Contingency (Interest during construction, etc.) 4,891,000
Total Capital Requirement $37.500,000
BASED UPON THE 750 TONS PER HOUR INPUT TO THIS PLANT THE CAPITAL REQUIREMENT
TRANSLATES TO $50,000 PER TON HOUR INPUT
294
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TABLE 6-2
HYPOTHETICAL FLOTATION PLANT
WITH FINE REFUSE DISPOSAL
OPERATING AND MAINTENANCE COSTS*
COST CATEGORY Raw Coal Clear/cSal
Labor -
Supervisory (Non-Union) $ 0.04 $ 0.06
Operating & Maintenance (Union) 0.27 0.38
Overhead -
Includes Payroll Taxes, Insurance,
Welfare Fund, Vacations, Holidays,
etc. for all Preparation Plant
Employees 0.20 0.28
Supplies
Operating 0.25 0.35
Maintenance - Repair Parts and
Materials Associated with
Routine Maintenance 0.60 0.83
Thermal Dryer Fuel -
Based upon 2600 gal/hr Fuel Oil Con-
sumption and Cost of Oil @ $0.32/gal 1.11 1.54
Electricity 1.00 1.39
Other Expenses 0.10 0-14
0 & M Cost -
Not Including Capital Amortization $3.57 $4.97
Capital Amortization -
10 Yrs. - 40% Utilization 2.18 3.02
Total Operating & Maintenance Cost $5.75 $7.99
Cost Per Million Btu (13,500 Btu/lb) $0^30-
*Extrapolated from comparable capacity heavy media plant allowing for
significantly greater power consumption
295
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Another procedure, which would significantly reduce the capital and
operating costs of the plant by eliminating the expensive drying capacity,
might be to transport the product via slurry pipeline to the utility plant.
If the product was to be transported by conventional means, it would be
necessary to consolidate the coal into pellets or briquettes to improve
its handling properties. Such additional processing capability would
slightly increase the total cost of preparation. However, the selection
of this or any other transportation approach could only be made after a
careful evaluation of the overall economics of the specific situation.
296
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RFPORT nnrilMFNTATTflN PARF
1.
4.
REPORT NO. 2.
TITLE AND SUBTITLE
An Engineering/Economic Analysis
Of Coal Preparation Plant
Operation and Cost
/. AUIHORtb)
Elmer C. Holt, Jr.
9.
12.
PERFORMING ORGANIZATION NAME AND ADDRESS
The Hoffman-Muntner Corporation
8750 Georgia Avenue
Silver Spring, Maryland 20910
SPONSORING ORGANIZATION NAME AND ADDRESS
United States Department of Energy
Solid Fuels Mining and Preparation Division
Washington, D.C. 20545
3.
5.
RECIPIENT'S ACCESSION NO.
REPORT DATE
February 1978
6.
8.
10.
11.
13.
PERFORMING ORGANIZATION
REPORT NO. 5004-2 FR
PROJECT/TASK/WORK UNIT NO.
CONTRACT OR GRANT NO.
ET-75-C-01-9025
TYPE OF REPORT
Final Report
14.
15. SUPPLEMENTARY NOTES
16. ABSTRACT - This report presents a discussion of the major physical coal preparation
processes currently available and the equipment used by each to effect a separation of
the coal from the undesirable constituents such as ash and pyritic sulfur. Further,
eight specific examples of a wide range of actual preparation plants are examined from
the standpoint of capital and operating and maintenance costs to develop a total cost
of coal cleaning for each plant. The preparation plants examined were all operating as
of mid-1977 and span a spectrum of cleaning processes from a relatively simple jig plant
to rather sophisticated circuits utilizing heavy media, froth flotation, and thermal
drying.
For the particular plants considered by this study, there was a range of cleaning costs
from over $3.00 to nearly $5.00 per ton of clean coal produced. These costs are especi-
ally sensitive to the make-up and performance of the cleaning circuit in addition to the
manner in which it is being operated. In this latter regard, plant utilization can be a
significant factor since it influences the output over which the fixed costs are amor-
tized. As evidenced by most of the preparation plants examined, many coal cleaning fac-
ilities operate only 30% of the time, thereby experiencing a relatively high capital
burden per ton of clean product. To alleviate this problem, one of the example prepa-
ration plants was designed to include parallel cleaning circuitry with significant
amounts of redundant equipment. Such plant configuration, permits maintenance without
shutting down the entire facility.
17. ORIGINATOR'S KEY WORDS
Coal Preparation (Cleaning)
Coal Preparation Equipment
Coal Preparation Plant Operating and Maintenance Costs
Coal Preparation Plant Capital Cost
Coal Preparation Plant Utilization
Coal Preparation Plant Capital Amortization
18. AVAILABILITY STATEHEN1
19. U.S. SECURITY CLASSIFICATION OF THE REPORT
UNCLASSIFIED
21. NO. OF PAGES
296
20. U S. SECURITY CLASSIFICATION OF THIS PAGE
UNCLASSIFIED
122. PRICE
*OA GOVERNMENT PRINTING OFFICE: 1978 260-880/84 1-3
297
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