TVA
EPA
Tennessee
Valley
Authority
Energy Demonstrations and
Technology
Chattanooga, TN 37401
TVA/OP/EDT-81/30
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/7-81-013
January 1981
Economic Analysis of
Wet Versus Dry Ash
Disposal Systems
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.
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-81-013
January 1981
Economic Analysis of Wet
Versus Dry Ash
Disposal Systems
by
Michael P. Bahor (GAI Consultants, Inc.)
and Ken L. Ogle
TVA Project Director
Hollis B. Flora II
Tennessee Valley Authority
Division of Energy Demonstrations and Technology
1140 Chestnut Street, Tower II
Chattanooga, Tennessee 37401
Interagency Agreement No. EPA-IAG-D5-E721BI
Program Element No. 1NE624A
EPA Project Officer: Julian W. Jones
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ill
DISCLAIMER
This report was prepared by GAI Consultants, Inc., for the Tennessee
Valley Authority and has been reviewed by the Office of Energy, Minerals,
and Industry of the United States Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Tennessee Valley Authority
or the United States Environmental Protection Agency, nor does the mention
of trade names or commercial products constitute endorsement or recommendation
for use.
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IV
ABSTRACT
The objective of this study was to evaluate the economics of
alternative methods of coal ash disposal for a new, coal-fired
power plant. Specifically, wet versus dry methods were compared by
evaluating the economic impact of each system component. These
system components included in-plant handling systems, transportation
systems, and disposal area design. In addition to the component by
component analysis, various plant sizes were compared. These
include 300 MW, 600 MW, 900 MW, 1300 MW, and 2600 MW powerplants.
To provide for a reasonable economic comparison, each disposal
system alternative was analyzed for each power plant size. Capital
and first year O&M costs were calculated. These costs were then
evaluated over the estimated 35-year life of the plant by both
present worth and total system cost analyses. Present worth anal-
ysis was utilized due to its current use in engineering economic
decisions. Total system cost analysis was utilized to indicate the
effect of borrowed capital over the life of the system.
The result of these analyses was an economic comparison that
indicates trends in disposal costs, but does not provide the level
of detail necessary to select a disposal system for a specific
site. System selection can only be accomplished by a detailed
analysis of site specific parameters.
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V
CONTENTS
Disclaimer - • 1
Figures iv
Tables Y
Acknowledgements vi
Abstract vii
1. Executive Summary 1
2. Introduction 3
3. Decision Parameters 5
Introduction 5
Ash quantities and properties 5
Physical/economic considerations 13
Environmental/regulatory requirements. ... 16
4. Overview of Ash Disposal Alternatives 18
Introduction 18
Fly ash disposal 18
Bottom ash disposal 20
Summary 21
5. Ash Handling Systems 22
Introduction 22
General design criteria 22
Fly ash handling systems ..... 22
Economizer and air heater ash handling
systems 31
Bottom ash handling systems 33
Operational considerations 35
6. Ash Storage and Treatment Systems 37
Introduction 37
Fly ash storage 37
Bottom ash dewatering 39
7. Ash Transport 42
Introduction 42
Truck transport 42
Rail transport 47
Barge transport 47
Pipeline transport 47
Conveyor transport 49
8. Disposal Area Conceptual Design 51
Introduction ....... .... 51
Dry disposal area "51
Wet disposal area 54
Summary 56
9. Economic Analysis 57
Introduction .......... 57
Method of economic analysis 57
Ash disposal costs 62
Cost analysis results 62
10. Conclusions 72
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VI
CONTENTS
(Continued)
References 73
Appendices
A. Design conditions A-1
B. Line item cost estimate for 2600 MW plant: dry
compacted ash disposal in a narrow valley .... B-l
C. Line item cost estimate for 2600 MW plant: wet
ash disposal in a narrow valley C-l
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vii
FIGURES
Figure Description Pag<
3-1 Range of Typical Ash Grain-Size Curves 8
4-1 Variations in Ash Disposal Systems 19
5-1 Fly Ash Hoppers 24
5-2 Fly Ash Hopper and Transfer System 25
5-3 Negative Pressure Pneumatic Conveyor 27
5-4 Positive Pressure Pneumatic Conveyor 30
5-5 Approximate Average Air Velocities in
Dilute Phase 32
5-6 Recirculating Sluice Conveyor 34
6-1 Fly Ash Storage Silos 38
6-2 Bottom Ash Dewatering Bin 41
8-1 Cross-Section: Dry Ash Disposal Area 52
9-1 Specific Ash Disposal Schemes Considered
for Cost Estimating 58
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viii
TABLES
Table Description Page
3-1 Self-Hardening Capacity of Eastern Ashes 12
3-2 Recommended Ash Analyses 14
5-1 Classification of Pneumatic Conveyor Systems 26
5-2 In-Plant Handling System Cost Estimates 36
7-1 Truck Transport Information 45
7-2 Total Cost Comparison (2600 MW Plant) 46
9-1 Ash Disposal System: Present Worth Cost 60
9-2 Ash Disposal System: Total System Cost 61
9-3 Cost Analysis: In-Plant Handling System 63
9-4 Ash Disposal System: Cost Per Dry Ton Disposed
at Present Worth Cost 64
9-5 Ash Disposal System: Cost Per Dry Ton Disposed
at Total System Cost 65
9-6 Ash Disposal System (Transportation and Disposal
Area) at Total System Cost 66
9-7 Cost Review: In-Plant Handling System 69
9-8 Total System Cost Comparison for Alternate
In-Plant Handling System O&M Costs 71
A-l Power Plant Characteristics A-l
A-2 Ash Quantities A-2
A-3 Ash Densities A-3
A-4 Site Preparation Costs A-4
A-5 Machine Operating Costs A-5
A-6 Dry Disposal Site Characteristics A-6
A-7 Ash Hauling and Placement Equipment A-7
A-8 Dry Disposal Yearly Operational Hours A-8
A-9 Wet Disposal Site Characteristics A-9
A-10 Ash Slurry Pumps A-10
A-ll Ash Sluice Lines A-ll
A-12 Slurry Pipeline Characteristics A-12
A-13 Return Water Lines A-13
A-14 Wet Disposal Yearly Maintenance Hours A-14
A-15 Belt Conveyor A-15
A-16 Fly Ash Storage Silo A-16
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ix
ACKNOWLEDGEMENTS
This study was initiated by TVA" as part of the project entitled
"Characterization of Effluents From Coal-Fired Utility Boilers" and is
supported under Federal Interagency Agreement No. EPA-IAG— D5-E721-BB
between TVA and EPA for energy-related environmental research. Thanks are
extended to the EPA Project Officer, Mr. Julian A. Jones, and the TVA
Project Director, Dr. Hollis B. Flora II. Appreciation is also extended
to Dana Burns, Jerry W. Chumley, Hendrik Colijn, Robert J. McLaren,
James E. Niece, Harald C. Pedersen, and Walter J. Wujcik for their
assistance in the project.
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SECTION 1
EXECUTIVE SUMMARY
The purpose of this report is to analyze the economics of both
wet and dry ash disposal systems for new, coal-fired power plants,
under a specific series of assumptions and to provide an indication
of trends in ash disposal costs. Knowledge of these trends in
disposal system costs will ultimately aid in the identification of
a least cost ash disposal system for a specific power station. A
secondary purpose is to provide background information concerning
ash disposal system design and selection. Although a specific
range of power plant sizes and characteristics was analyzed, the
results of these analyses have been reported in terms of cost per
dry ton of ash disposal and will be generally applicable to other
disposal situations.
An economic analysis of wet and dry disposal was performed for
a series of coal-fired power plants (300 MW, 600 MW, 900 MW, 1300 MW,
and 2600 MW) burning subbituminous coal with a 20 percent ash con-
tent. The analyses included in-plant handling systems, transport,
and disposal site alternatives. In-plant ash handling systems
analyses included vacuum and pressure pneumatic systems for fly ash
and hydraulic handling systems for bottom ash. Transportation
analyses, which was only accomplished for a one mile haul distance,
included truck, pipeline, belt conveyor, and pneumatic conveyors.
Disposal site alternatives, in addition to the general classi-
fication of wet and dry, included wide valley, narrow valley, and
flat areas with both high and low height disposal schemes.
The analyses indicate that the economic selection of an ash
disposal system is primarily influenced by site topography. Dry
disposal is always the least cost alternative for a flat site.
Valley disposal sites, on the other hand, may be most amenable to
wet disposal, if suitable site conditions exist. Wet versus dry
disposal economic comparisons for valley disposal sites are sen-
sitive to variations in in-plant handling costs and disposal site
construction phasing. Other interpretations of the data utilized
herein could result in dry systems appearing to be the least cost
alternative for valley sites. This assumes that the valley site
can be developed for wet disposal. The selection of a least cost
disposal system was also affected by other parameters. These
included method of economic analysis, method of transport, degree
of compaction, size of plant, etc. However, these considerations
were typically secondary to site topography.
Although primarily influenced by topography, the other afore-
mentioned parameters can significantly alter the selection of a
disposal system based on site, utility or geographic considera-
tions. These considerations can either negate the use of a system
or provide significant economic incentives or restrictions to a
disposal system. However, for the general ash disposal situations
reviewed, the above conclusions are valid.
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The economics of ash transport are dependent on the mode of
transport, ash quantities, and distance. This interdependence
results in various transport modes providing least cost alterna-
tives under varied conditions. Pipeline transport is only appli-
cable to wet disposal. Where dry ash disposal is practiced and
when ash is produced in small quantities, truck transport is the
most economical. However, as the quantity of dry ash increases,
belt and pneumatic conveyor transport systems become the least cost
alternatives. Although cost effective in some situations, the use
of a conveyor transport system requires a long-term commitment to
justify the large capital investment required.
Ash in-plant handling systems costs are also dependent on the
quantity of ash handled, plant configuration, pollution abatement
equipment design, total number of ash hoppers, transport distance,
and other plant specific criteria. Specific plant information was
unknown at the time of the study, so generalized assumptions were
made. The analysis did show that a vacuum collection system is the
lowest cost option, although it is typically only applicable to wet
disposal. Pressure, in-plant systems were utilized for the dry
disposal options due to the need for longer transport distances.
Dense phase systems were more expensive than vacuum systems and
less expensive than pressure systems. However, the estimates for
the dense phase system were extrapolations from experience with
materials other than ash; therefore, these costs were not included
in the final analysis. Although this report presents generalized
ash handling costs, a detailed analysis of ash handling systems
should be performed for each proposed power plant size and config-
uration.
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SECTION 2
INTRODUCTION
The selection of an economical ash disposal system is a prac-
tical means of reducing the overall cost of electrical generation.
The selection process incorporates a number of pathways and alter-
natives which must be considered in arriving at a least cost dis-
posal alternative. It is the purpose of this report to analyze the
costs associated with these alternatives, under a specific series
of assumptions, in order to provide an indication of trends in ash
disposal costs. This report will aid in the selection of an ash
disposal system for a specific power station. The primary objec-
tive of this study was the selection of a least cost alternative
subject to a lower bound of expenditures defined by good engineer-
ing design, environmental regulations, and other considerations
which must be made to provide an acceptable ash disposal system.
Although ash utilization is an effective method for reducing the
economic impact of ash disposal, its use was not included in this
study.
In this report, an ash disposal system is defined as consist-
ing of the following major components:
o Ash handling system;
o Ash transport system; and
o Ash disposal site.
There are various alternatives within each ash disposal system
component. Economic comparisons for these alternatives are based
upon disposal system conceptual designs. In turn, these designs
reflect a number of design parameters, including plant size and
configuration, ash quantities, and environmental regulations.
Conceptual designs developed for this report are conservative in
nature, thereby providing a "safety factor" in disposal system
operation. Safety factors may include redundancy of equipment,
i.e., three 50 percent capacity pumps, a complete backup system,
and/or the use of emergency procedures, such as hiring additional
transport trucks, to insure uninterrupted ash removal from the
generating station. Where possible, manufacturers and utility
personnel were consulted to verify conceptual designs utilized.
A primary differentiation in an ash disposal system is whether
the system is wet or dry. A wet system typically consists of
hydraulically transporting ash to an ash disposal pond. A dry
system consists of dry ash transport to a landfill. Another major
ash disposal system difference is in the topography of the disposal
area. The topography may be flat or a wide or narrow valley. Each
topographic configuration has different design requirements, and
consequently different costs. This report and cost estimates are
for new ash disposal systems with disposal sites located one mile
from the power station. Longer transport distances would raise the
costs for all the alternatives but are beyond the scope of this
report.
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A number of ash disposal systems were reviewed and cost esti-
mates prepared. These estimates were based on specific assumptions
enumerated in Appendix A. It was the intent of this study to
provide an economic comparison for a typical power plant under
average conditions. The result was an economic comparison that
indicates trends in disposal costs, but does not provide the level
of detail necessary to select a disposal system for a specific
site. System selection can only be accomplished by a detailed
analysis of the site specific parameters described in Sections 3
through 8. System costs were compared utilizing both a total
system cost approach and a present worth method of analysis.
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SECTION 3
DECISION PARAMETERS
INTRODUCTION
The selection of an ash disposal system incorporates a number
of diverse and complex parameters. This section will provide an
overview of these parameters, and briefly indicate how they influ-
ence the selection and design processes.
Decision parameters can be placed in the following major cate-
gories :
o Ash quantities and properties;
o Physical/economic considerations; and
o Environmental/regulatory considerations.
These categories will be explored in the following portions of this
section.
ASH QUANTITIES AND PROPERTIES
Ash quantities and properties, both physical and chemical,
determine the type and size of ash handling, storage, transport,
and disposal systems; provide an indication of the environmental
impact associated with ash disposal; establish overall system
constraints; and influence disposal site design. A number of
factors, including type of coal burned, degree of coal cleaning,
degree of coal pulverization, type of boiler, and method of ash
collection, influence the quantity of ash produced and the ash
characteristics. Although some factors influence ash production
more strongly than others, their combined impact on ash generation
and disposal must be considered. Further, an assessment of pos-
sible changes in ash production, which might result from changes in
the coal type or source, boiler retirement, or changes in ash
collection equipment, should be made in the selection and design of
ash disposal systems.
It should be noted that ash data for a new generating station
is sometimes assumed to be similar to that of an existing plant
burning a similar coal. While this may be true, relatively minor
changes in factors which influence ash production can substantially
change the characteristics and quantities of ash produced. There-
fore, actual plant data, if available, should be used in detailing
the final design of ash disposal systems.
I
Ash Quantities
A determination of the quantities of ash requiring collection,
handling, transport, and disposal is necessary for system design.
The quantity of ash produced can be estimated from the following:
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o Quantity of coal burned, average lifetime and daily
maximum;
o Ash content of the coal;
o Boiler type, and ratio of bottom ash to fly ash; and
o Fly ash collection system efficiency.
Peak ash production rates (tons per day at 100 percent capa-
city factor) are often used to size ash handling and transport
systems. However, the average ash production rate, which considers
the projected plant capacity factor over the operating 1" Te of the
plant, is used to size the disposal site.
Ash Physical Properties
During the design, construction, and operation of ash disposal
systems, there are several physical properties which warrant con-
sideration. These include:
o Specific gravity;
o Grain-size distribution;
o Moisture content;
o Density;
o Shear strength;
o Permeability;
o Capillary rise;
o Abrasion; and
o Temperature.
The testing of these properties is defined by either the
American Society of Testing Materials (ASTM), American National
.Standards Institute (ANSI), or the American Association of State
Highway and Transportation Officials (AASHTO). Specific test
methods relative to ash are described in the EPRI Fly Ash Struc-
tural Fill Manual (1).
Testing of an ash to determine these physical properties pro-
vides basic information necessary for the design of ash transport
and disposal systems. In some cases, conservative design values,
based on previous testing of similar ashes, can be used to expedite
preliminary planning and design of ash disposal schemes. Addi-
tional testing, including a geotechnical evaluation of subsurface
conditions, may be required when ash is to be placed in a landfill
or embankment.
Specific Gravity
Specific gravity is the ratio of the density of solids to the
density of- distilled water at four degrees centigrade. Specific
gravity is commonly used in calculations involving the in-place
density and compaction of ash. In addition, specific gravity of
ash is of particular importance since it is related to the rate of
settling. The rate at which ash settles influences the degree of
solids removal from sluice water passed through an ash disposal
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pond, or from runoff from ash landfills routed through a sedimen-
tation basin. Testing for specific gravity is defined by ASTM
D854-58 and AASHTO T100-74.
Grain-Size Distribution
The proportion of particle sizes for a specific material,
within a series of specific size intervals, is described by the
material's grain or particle size distribution. The determination
of this distribution is helpful in describing some properties of
the material. Subsequently, grain-size distribution is important
in the design of ash handling systems, dry disposal sites, and
utilization schemes. Grain-size distribution may be a primary
design parameter when bottom ash is used as a drainage blanket or
filter, when fly ash is used to "choke" aggregate prior to the
placement of concrete or asphalt, or when utilized in the design of
an ash transport system. This is further described in Section 5.
Testing for grain-size distribution is defined by ASTM D422-73 and
AASHTO T88-57. Typical values for bituminous coal fly ash and
bottom ash are shown in Figure 3-1. At this time, little data
exist to describe the grain-size distributions of sub-bituminous
and lignite ashes.
Moisture Content
/
The moisture content of an ash, expressed as a weight percent-
age of total dry weight, is of interest because it influences both
the weight and behavior of the ash. There are two moisture con-
tents which are important in the design of ash disposal or utiliza-
tion systems: natural or in-place moisture content and optimum
moisture content. The unit weight of ash is affected by moisture
content; increasing the moisture content increases the weight to be
transported and, therefore, increases the cost of transport. The
flowability of ash is also a function of moisture content. If the
actual moisture content of the ash varies appreciably, the ability
to make the ash flow, in either pneumatic transport systems or
gravity transfer operations, may be substantially altered. Mois-
ture content is tested in accordance with ASTM D2216-71.
Density
Density, the weight per unit volume of ash, is important
because it influences the method and cost of ash transport and is
also related to engineering properties of ash. In general, as the
density of a specific ash increases, so does its shear strength.
Alternately, permeability decreases as density increases.
The maximum dry density of an ash can be determined from
laboratory testing. Laboratory tests include proctor tests, both
standard (ASTM D698-70 or AASHTO T99-74) and modified (ASTM 1557-70
or AASHTO T180-74), which are utilized to define the moisture
density relationship, and the relative density test (ASTM D2049-69).
Field tests are also available to determine in-place density.
Field density methods include the sand cone, densometer, and nuclear.
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Clear Square
Openings (In.)
No. U.S.
Standard Series
100
Time (mln.)
60 180 1440
100.0
10.0
1.0 0.1 0.01
Particle Diameter (mm)
0.001
0.0001
cobbles
gravel
course fine
sand
coarse I medium I
fine
silt and clay
I clay
FIGURE 3.1 - RANGE OF TYPICAL ASH GRAIN-SIZE CURVES
Source: J. H. Faber and A. M. DIGIola, Jr. Use of Ash for
Embankment Construction. Presented at the Transportation
Research Board Annual Meeting, January. 1976 (2). and Seals
et.al.. 1972 (3).
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Shear Strength
The shear strength of an ash is a consideration in both the
design of ash fills and ash handling or storage systems. Shear
strength is due to the combined effect of two engineering proper-
ties: cohesion and angle of internal friction. Cohesion is a
measure of the shear strength developed by the attraction between
individual particles. The angle of internal friction is a measure
of the frictional resistance between particles. Standard ash
analyses for soils engineering applications assume that the cohe-
sion of the ash is negligible or zero, such that the shear strength
of the ash is equal to that strength caused by the angle of inter-
nal friction. By comparison, ash analyses for material handling
applications must design for both angle of internal friction and
cohesion. Although many ashes exhibit some degree of cohesion
during analysis, this cohesion is normally referred to as "apparent
cohesion." "Apparent" is used because there is a loss of cohesion
at either very high or very low moisture contents. Therefore, the
shear strength of an ash, based entirely on the internal angle of
friction, will determine the steepness of fill slopes which can be
safely constructed. In the case of ash transport it is the actual
shear strength of the material, a function of angle of internal
friction, and apparent cohesion that must be exceeded in order for
the ash to flow. Although geotechnical engineers may design for
the conservative case, material handling engineers must know the
actual ash operating conditions to provide a workable system.
Specific design parameters relating to shear strength include
moisture content and grain-size distribution. Shear strength may
be analyzed by unconfined compression (ASTM D2166-66), direct shear
(ASTM 3080-72), or triaxial shear (ASTM D2435-70).
Permeability
Ash permeability is an important design parameter in both wet
and dry systems. Permeability is defined as the rate of flow
through a unit area under a hydraulic gradient of one. In dry ash
disposal systems, bottom ash used as a filter or drainage blanket
must have sufficient permeability to conduct water out of the fill
and avoid the build-up of hydrostatic pressures. The permeability
of fly ash governs the rate at which water passes through an ash
fill, and affects the rate of leachate formation. In wet disposal
systems, ash permeability, along with the hydraulic gradient,
determines the dewaterability of the ash. For wet disposal sites,
dewatering is a common means of stabilizing the ash for pond clo-
sure. Ash permeability is also an important consideration in"
wet/dry disposal systems where ash is placed in a dry fill after
dewatering. Permeability may be analyzed by either constant head,
falling head, or pressurized methods. ASTM D2434 describes a
constant head method of permeability testing; however, when the
permeability of the material is low, other methods may be required
to provide sufficient volume of water to calculate a value for
permeability. In this case, the pressurized method provides data
in a relatively short time period, while other test methods may
require a longer testing period.
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10
Capillary Rise
Capillary rise is the physical phenomenon in which a liquid is
drawn upward in a tube due to surface tension forces. The height
of capillary rise is a function of the tube size and material
properties. This same phenomenon will occur in soils and soil-like
materials, such as fly ash. Capillary rise influences the sta-
bility of ash fills, and can influence leachate production.
Abrasion
Abrasion is an important ash property in the design of some
ash handling and transport systems. These systems include vacuum
and pressure handling systems, pressure transport systems, and
slurry pipelines. Other systems affected by the degree of ash
abrasion are ash transfer facilities and auxiliary ash handling
equipment, such as baghouses and precipitator hoppers. Analysis of
ash abrasion must consider the proposed transport mode. Although
no standardized abrasion testing is presently used, slurry pipe-
lines may be analyzed by a water abrasion analysis (ANSI/ASTM
G6-77) and pneumatic systems analyzed by an air/abrasion analysis
(ASTM D658). Since these tests are non-standard relative to their
applicability to transport systems, the results provide information
comparable only to other tested materials. However, this data is
applicable to the selection of ash handling equipment and materials.
One limitation of this testing procedure is that, although it
provides a basis for equipment selection, it provides no indication
of life expectancy. Therefore, the life cycle cost cannot be
estimated.
Temperature
The temperature of ash as it enters the in-plant collection
and handling system plays an important part in the selection of
materials and the design of handling system components. For ex-
ample, it may be necessary to incorporate expansion joints in
pneumatic fly ash handling systems near the particulate removal
equipment hoppers, where fly ash is hot. Ash temperature, parti-
cularly fly ash temperature, also is important because it influ-
ences the air temperature, and thus the viscosity, of air used in
pneumatic transport systems. At higher temperatures, the viscosity
of air decreases. This has the effect of less solids handling
capacity per unit of air.
Ash Chemical Properties
Ash chemical properties, while largely pertaining to the envi-
ronmental aspects of ash disposal, may also affect the design of
ash handling, storage, and transport systems. In addition, various
ash utilization schemes, such as the use of fly ash in concrete,
require that the ash have well defined chemical characteristics.
Of particular interest in the design of ash disposal systems are
the corrosive and self-hardening potentials of the ash produced.
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11
Corrosion Potential
Ash with a high corrosion potential requires the use of cor-
rosion resistant materials in the construction of ash handling and
transport systems. Although the actual rate or degree of corrosion
could be estimated by the potential, or electro-motive force (emf),
of the ash and corrodable material, a common method of corrosion
testing is by coupon testing. In this test, a coupon, or sample,
of the material is imbedded in the ash under the assumed tempera-
ture and water content conditions. The sample weight loss, over a
selected time period, is assumed to be the loss due to corrosion.
The results are expressed as mg/dm /day (MDD), and by assuming a
uniform rate of corrosion, may be expressed in inches per year
(IPY). Microscopic examination of the coupon should also be per-
formed to assure the uniformity of corrosion.
Self-Hardening Potential
Fly ash with a potential for self-hardening, primarily the
result of high free-lime content, requires special consideration of
moisture content and ash transport time. In cases where highly
reactive fly ash, i.e., rapidly self-hardening, is produced, slurry
transport to the disposal area may not be feasible. Unfortunately,
standard tests are not available to ascertain whether a fly ash is
self-hardening or reactive. Various existing test methods may be
utilized to determine these parameters. Since self-hardening ash
involves the hydration of available free-lime with moisture, this
sequence may be duplicated in the laboratory. If a series of
unconfined compression cylinders are prepared with various moisture
contents, both the presence and degree of self-hardening may be
determined. Here, unconfined compressive strength would be uti-
lized as the tested strength parameter. Testing performed on
various ash samples for self-hardening are included in Table 3-1.
Reactivity
Reactive ash is defined as ash which exhibits rapid and uncon-
trolled hydration such that excessive temperatures are generated.
These ashes have also been described as "Rapidly Self-Hardening";
although this describes the general process, it is not known
whether the same reactions cause both effects. If fly ash samples
are prepared with various water contents, and their temperature
monitored, both the presence and degree of ash reactivity may be
determined. These samples may also be tested for their unconfined
compressive strength.
Pozzolanic Activity
Another area of interest is the use of fly ash as a pozzolan.
Possible uses which exist in the concrete industry include the use
of fly ash as a cement replacement and as a grout material. Speci-
fic tests required of the fly ash for use in cement concrete are
defined by ANSI/ASTM C311-77. Specific chemical tests include:
-------
Table 3-1
SELF HARDENING CAPACITY OF EASTERN ASHES (4)
Chemical Composition (weight percent)
Self Hardening (psf)
Pozzolanic Index
Bituminous
Coal Ash
Anthracite
Coal Ash
Fe2°3
4.77
5.65
8.65
7.64
12/70
35.10
39.44
20.51
18.90
16.54
11.07
8.66
CaO
.67
1.00
.92
3.19
1.15
3.08
1.71
4.11
4.94
1.98
1.79
.65
MgO
1.30
1.90
1.58
2.62
1.20
1.33
1.39
2.00
4.50
1.30
1.33
1.41
Ti02
1.81
1.65
1.54
1.42
1.29
.94
.69
1.42
1.15
1.54
1.19
2.09
Si02
57.70
55.24
56.39
54.94
53.40
40.30
43.18
47.72
46.75
48.48
57.40
55.33
A12°3
30.28
30.90
27.69
26.21
26.30
16.91
11.86
20.19
18.35
27.47
23.88
28.13
so3
.23
.29
.22
.31
.39
.33
.29
2.16
4.14
.66
.39
.40
LOI*
1.76
1.09
1.77
1.08
5.59
4.06
4.08
16.66
12.00
4.66
11.72
18.24
0 Day
464
2,134
836
579
1,053
555
372
1,200
2,046
257
402
1,409
854
7 Day
552
1,994
629
1,325
1,172
517
316
1,053
1,707
343
572
1,686
939
28 Day
743
2,287
1,015
3,228
804
718
344
1,430
2,622
256
1,114
2,110
901
Lime 7
(psi)
470
835
820
695
670
325
120
990
850
750
240
605
780
Concrete 28
96
94
84
78
79
72
48
100
57
63
45
56
84
*Loss on Ignition
NJ
-------
13
Moisture Content
Loss on Ignition
Silicon Dioxide (SiO2)
Aluminum Oxide (A1_O»)
Iron Oxide (Fe2O3)
Calcium Oxide (CaO)
Magnesium Oxide (MgO)
Sulfur Trioxide (SO3)
Available Alkalies
Fly ash used in concrete must have chemical characteristics within
limits specified by the American Concrete Institute (ACI).
Testing
Table 3-2 is a suggested list of chemical analyses to be per-
formed on the ash to assess its potential for both environmental
impact and utilization. These analyses are divided into a solids
analysis and a leachate analysis. A solids analysis provides
information pertaining to ash utilization potential, and also
provides an indication of amelioration measures which may be re-
quired during site closure and revegetation. A leachate analysis
of the ash provides information on leachate generation within ash
disposal areas, which, in turn, provides an indication of the
potential for groundwater pollution. Although applicable to esti-
mating leachate strength, existing leachate analysis methods do not
accurately predict leachate generation and must be used with great
care. Presently, the proposed Resource Conservation and Recovery
Act (RCRA) regulation includes a leachate analysis and extraction
procedure that may become the standard method of testing in the
future. Other methods have also been proposed and are described in
the EPRI Coal Ash Disposal Manual (5).
PHYSICAL/ECONOMIC CONSIDERATIONS
Physical and economic considerations are primary factors in
the selection of an ash system. Physical constraints of the site
may preclude the construction of certain systems or subsystems.
Once the appropriate site applicable systems are determined, then
economic factors will determine the ranking of these systems.
Environmental/ regulatory considerations, while important in the
selection of overall ash disposal systems, have a more indirect
effect on costs than do physical considerations. The physical/
economic considerations specifically to be reviewed include:
o Power plant size and configuration;
o Cost and availability of land; and
o Cost of money.
Power Plant Size and Configuration
Power plant size and configuration affect various aspects of
the ash disposal system. The configuration of the power plant will
affect the ash transport and storage systems by defining the layout
and distance the ash must be transported. In addition, the area
available for ash storage, treatment, and handling and transport
facilities may also be defined. Other plant specifics to be con-
sidered are the number of boilers, the number and size of ash
-------
Table 3-2
RECOMMENDED ASH ANALYSES
14
SOLID ANALYSIS
(REPORTED ON A DRY SOLID BASIS)
Water Content
Loss on Ignition (LOI)
Carbon (C)
Sulfur Trioxide (S03)
Phosphorus Pentoxide (P2°5)
Silica Oxide (SiO9)
£*
Iron Oxide (Fe2O3)
Aluminum Oxide (AlO)
Calcium Oxide (CaO)
Magnesium Oxide (MgO)
Sodium Oxide (Na2O)
Potassium Oxide (K2O)
Titanium Oxide (TiO_)
Arsenic (As)
Boron (B)
Selenium (Se)
Cadmium (Cd)
Copper (Cu)
Zinc (Zn)
Chromium (Cr)
Mercury (Hg)
Beryllium (Be)
Tin (Sb)
Nickel (Ni)
Lead (Pb)
LEACHATE ANALYSIS
pH
Alkalinity
Acidity
Specific Conductivity
Oxidation Reduction Potential
Chemical Oxygen Demand
Sulfate (S04)
Phosphate (PO4)
Silica (as Si)
Iron (Fe+2 and Fe+3)
Aluminum (Al)
Calcium (Ca)
Magnesium (Mg)
Sodium (Na)
Potassium (K)
Titanium (Ti)
Arsenic (As)
Boron (B)
Selenium (Se)
Cadmium (Cd)
Copper (Cu)
Zinc (Zn)
Chromium (Cr)
Mercury (Hg)
Beryllium (Be)
Tin (Sb)
Nickel (Ni)
Lead (Pb)
14
-------
15
collection hoppers (both bottom ash and fly ash), the size and type
of air pollution abatement equipment (electrostatic precipitators,
fabric filters, or scrubbers), characteristics of the abatement
equipment (including efficiency and location in the gas stream), and
the distance and geometry from the ash hoppers to the storage,
treatment, or transport area.
Cost and Availability of Land
The cost and availability of land is another consideration in
the selection of an ash disposal system. Land is required for ash
storage and transport systems at the plant, as well as for the ash
disposal site. It is advisable to purchase all the land required
for a power plant, including the ash disposal area, at the outset.
If this is not done, the cost to acquire the land at a future date
may be substantially more expensive. Inflation in land costs,
particularly in the proximity of a power plant, can be greater than
the general inflation rate. Due to current siting regulations,
future power plants will most likely be located in rural areas
where the cost of land should not be a major consideration. In the
eastern portion of the U. S., power plants are often located in
river valleys, due to the availability of cooling water. Many of
these sites are restricted in the amount of land that is readily
available near the plant. In this case, the location of available
land in relationship to the plant has a major impact on ash dis-
posal costs, particularly the cost of ash transport.
The land must be suitable for the use for which it is in-
tended. Land designated for ash storage must be capable of sup-
porting the required structures and truck traffic. Land considered
for use as an ash disposal area should receive careful analysis
since the land requirements for the disposal area are much larger
than the plant facilities and often exceed the land requirements of
the entire power plant. Specific land requirements for the dis-
posal area include:
o Sufficient disposal volume for the life of the power
plant;
o Proximity to the power plant;
o Access;
o Stability;
o Minimal surface and groundwater contact;
o Availability of a natural liner material; and
o Suitable material for embankment construction, if con-
sidered for wet disposal.
Additional siting criteria may also be established by the Resource
Conservation and Recovery Act. These criteria may include:
o Exclusion of wetlands;
o Protection of endangered species; and
o Location above the 100 year floodplain.
-------
16
Cost of Money
The cost of money combined with specific accounting methods
has a significant impact on determining the total life cycle ash
system cost. The magnitude of this economic consideration is
substantial, as will be demonstrated in following chapters.
Another economic consideration in the analysis of ash systems
is the method of accounting for overhead factors and their applica-
tion to the ash system. These accounting procedures, which vary
from utility to utility, may not include any overhead factors of
the system, or may include a proportional share of company over-
head. Although the accounting procedures may vary, each ash dis-
posal system must be analyzed with respect to overhead factors. If
these are ignored, then an operation intensive system may seem more
economical than a comparable capital intensive option, since the
overhead cost has not been included.
ENVIRONMENTAL/REGULATORY REQUIREMENTS
The final set of decision parameters to be reviewed are those per-
taining to regulatory requirements. These regulations may exist on
a local, state or federal level and are primarily concerned with
minimizing environmental effects and maximizing public safety.
Examples of regulations and required permits applicable to an ash
system are:
o Solid waste disposal;
o Water quality;
o Air quality;
o Dam construction;
o Occupational Safety and Health Act (OSHA);
o Stream encroachment;
o Highway access; and
o Zoning.
Environmental regulations, solid waste, air and water, are based on
the impact on the environment created by ash disposal. This impact
can be negative or positive in nature. Major areas of environmental
concern are:
o Water quality/aquatic ecology;
o Terrestrial ecology;
o Land use;
o Aesthetics;
o Public health/safety;
o Noise;
o Air quality; and
o Socio-economics.
Positive environmental impact is created by the reclamation of
mined or devastated lands with ash. Negative environmental impact
occurs through the displacement of terrestrial ecology, changes in
land use, and other environmental changes which can be long-term,
-------
17
after site closure, or short term, during ash placement operations.
Methods are available to reduce the degree of environmental impact
by proper siting of the disposal facility (6).
Regulations influence ash system alternatives in several ways.
The disposal area wastewater discharge is regulated by the National
Pollutant Discharge Elimination System (NPDES), usually adminis-
tered by the state. Other state regulations can control dam con-
struction, stream encroachment, and highway access. Local regula-
tions may pertain to solid waste disposal and land use.
The two federal laws which have the greatest impact on ash
disposal are:
o The Clean Water Act of 1977 (CWA);
o The Resource Conservation and Recovery Act of 1976 (RCRA).
As previously mentioned, these regulations will include either
specific information for the design and operation of ash disposal
sites or provisions which will influence area design by specifying
environmental quality standards such as surface and groundwater
contamination levels.
An important design criteria, to be established for future ash
disposal sites by CWA, is the discharge of suspended solids.
Effluent regulations have been proposed for new power plants,-which
may require closed-loop slurry water systems for wet disposal.
This is due to the regulations which may require a zero discharge
of suspended solids from the ash pond. However, current litigation
might alter this requirement. For the purpose of this report, it
was assumed that a closed-loop slurry water system was required.
The siting and operation of an ash disposal system can have a
major impact on surrounding communities, particularly when the
disposal site is located near a community. These concerns are
primarily health and safety. Aesthetics also enter into discussion
of the impact of an operation or system. In the design of the ash
disposal system, consideration should be given to public acceptance
of the disposal operation. Possible specific areas of public
concern are:
o Land use;
o Traffic;
o Noise;
o Dust; and
o Health and safety.
Should the use of a publicly sensitive disposal site be pro-
posed, it may prove expedient to incorporate public comments into
the selection process prior to the final site selection. Under
certain circumstances, the National Environmental Protection Act
(NEPA) may require that an environmental assessment be performed,
and specific comments obtained from the public through a public
participation program.
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18
SECTION 4
OVERVIEW OF ASH DISPOSAL ALTERNATIVES
INTRODUCTION
Ash disposal systems have several major components including
handling, storage, transport, treatment, and disposal. Within
these major components exist various alternatives, as shown by
Figure 4-1. The purpose of this section is to present an overview
of ash disposal alternatives. Subsequent sections will provide more
detailed descriptions of system components.
FLY ASH DISPOSAL
Fly ash is commonly collected dry from particulate removal
systems and temporarily stored in ash hoppers. Upon filling these
hoppers to a predetermined level, the fly ash is pneumatically
conveyed to either a storage silo prior to dry transport, or to a
mixing area where the ash is slurried for wet transport. Pneumatic
fly ash handling systems can be vacuum, pressure, or a combination
of vacuum and pressure. From storage or sluicing areas, ash is
transported to either a wet or dry disposal area.
Dry Disposal
If the fly ash is to be utilized or disposed of in a dry
system, it is transferred from the storage silo into the transport
system. Transport of the dry fly ash is commonly done by truck,
which may be open or closed, depending upon the destination of the
fly ash. Belt and pneumatic conveyor, rail, or barge transport
systems may also be feasible. Fly ash sent to utilization systems
usually must be kept dry. Fly ash trucked to dry disposal sites is
usually mixed with a small amount of water prior to loading in
order to minimize dusting, and can be transported in open dump
trucks. End-dump trucks are preferred due to the tendency of fly
ash to clog bottom-dump openings.
Dry fly ash disposal sites can be constructed landfills or
located in devastated land areas. Constructed landfills can be
located in the bottom of a valley (valley fill), on the slopes of a
valley (side-hill fill), or on relatively flat areas (mounded
fills).
Wet Disposal
If fly ash is placed into a wet disposal system, it is pneu-
matically conveyed to a sluicing area after collection from the
particulate removal devices. At the sluicing area, fly ash is
mixed with water to form a slurry of 5 to 10 percent solids, by
weight. This slurry is usually pumped directly to the disposal
area, although gravity transport systems have been used for short
distances.
-------
Figure 4-1
VARIATIONS IN ASH DISPOSAL SYSTEMS
Waste Typt:
Ash Collect itin
llandlinq System
Transfer System
Disposal Mi?(hod
Transport
Disposal
Si te
1
•uum
^
Pressure
1
Combination
Truck
Highway Dump
Off Road Dump
Off Road Scraper
Pneumatic Tanker
Conveyor
Pneumatic
Belt
1
Rail
Side Dump
Bottom Dump
Barge
1 1
Constructed
Kxcavated
Embankment
vo
-------
20
Wet disposal areas are usually ponds, although it may also be
possible to use devastated lands in a manner similar to dry dis-
posal. Pond embankment types include diked, excavated, side-hill,
and cross-valley.
Combination Disposal
In combination disposal systems, fly ash can be placed in a
dry storage area and later transported by truck to a wet disposal
site where it is mixed with water. Conversely, fly ash can be
sluiced to a wet sluicing area, where it is pumped to a holding
pond or bin. After dewatering, the fly ash can be removed and
transported to a dry disposal site. However, combination systems
are not often used because of various constraints. For example, it
is often difficult to dewater the ash. Due to these constraints,
combination ash disposal systems have not been included in this
report.
Fly Ash Fixation
Other disposal systems are commercially available which chemi-
cally treat fly ash to form a hardened material, similar to cement.
These systems usually involve transporting fly ash from storage
silos to treatment facilities, where it is mixed with various addi-
tives, and then slurried or trucked to disposal cells. Upon cur-
ing, the fly ash slurry hardens, forming a solid mass. Disposal
cell construction and operation is similar in nature to those of
dry ash disposal sites. These processes are proprietary and are
generally only applicable to "reactive" ashes. These ashes pre-
sently compose only a small percentage of the total ash produced;
therefore fixation processes will not be discussed further. If
reactive ashes are encountered, which will be obvious from the ash
physical testing, they must be handled with caution due to self-
hardening tendencies which can make transport difficult.
BOTTOM ASH DISPOSAL
Bottom ash is commonly fed by gravity from the bottom of the
boiler into a hydraulic handling system. This handling system is
used to pump bottom ash to a dewatering area, or directly to a wet
disposal site. Bottom ash can be placed with fly ash in a wet
disposal site or have its own wet disposal site. Separate wet
disposal facilities have the advantage of facilitating bottom ash
recovery for possible future utilization.
If bottom ash is to be placed in a dry disposal system, it
must be dewatered in bins or ponds. Bottom ash, unlike fly ash, is
easily dewatered, primarily due to its larger particle size (Fig-
ure 3-1). After dewatering, it is transported to the disposal
site. Bottom ash may be used in dry ash disposal as temporary
cover to prevent dusting or as drainage blanket material. If the
potential for utilization is high, bottom ash can be stockpiled for
future salvage.
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21
SUMMARY
Dry and wet transport and disposal of fly ash have been found
to be viable ash disposal systems. Combination systems, i.e., wet
transport and dry disposal or dry transport and wet disposal, are,
in general, not cost effective as is evidenced by their lack of use
within the industry. Also, specific fixation processes are not
applicable to the majority of fly ashes and will not be discussed.
Bottom ash is typically transported hydraulically from the
boiler to either a pond or a dewatering bin. Although transported
wet, bottom ash is amenable to dry disposal or utilization due to
its ease of dewatering. This property can play a significant part
in an ash management program where bottom ash can be used as an
aggregate replacement.
-------
22
SECTION 5
ASH HANDLING SYSTEMS
INTRODUCTION
All coals contain a significant fraction of incombustible
material or ash. The total ash quantity can vary from 6 to 50
percent of the coal on a weight basis. Thus, the quantities of ash
produced are substantial and can approach the volume of coal con-
sumed. This ash must be transported away from the boiler area to
prevent the shutdown of the generating system. For the majority of
utility coal fired power plants, the major sources of ash are:
o Fly ash from particulate removal systems;
o Ash deposited in the economizer and air heater hoppers;
and
o Bottom ash from the boiler bottom.
This section will delineate major system components available
to transport these ashes. General design information will be
provided, but a specific system design is beyond the scope of this
report.
GENERAL DESIGN CRITERIA
In developing preliminary designs for ash handling systems,
there are a number of factors to consider. These include the fol-
lowing:
o Ash quantities, physical and chemical properties;
o Plant layout;
o Boiler design and configuration;
o Distribution of ash between fly ash, bottom ash, econ-
omizer ash,, and air heater ash;
o Plant geographical location; and
o Type, configuration, and location in the exhaust gas
stream of particulate removal devices.
Since ash handling is of critical importance in ensuring
generating system operation, ash handling systems are typically
designed to carry the daily maximum amount of ash produced in a 6
to 8 hour shift. This is to allow adequate time for maintenance on
ash handling systems. The design of ash handling systems for
24-hour operation is also possible. Backup or duplicate systems
can also be installed to provide an additional factor of safety in
operation.
FLY ASH HANDLING SYSTEMS
Fly ash is commonly removed from the flue gas by either elec-
trostatic precipitators or baghouses, and deposited into hoppers
located directly beneath the collection equipment. From these
-------
23
hoppers, dry fly ash is either t
fer silo or to a mixing device,
slurry. An alternative method
scrubbing system. Fly ash is co
absorbed by the water. These sy
ing the use of pneumatic ash
slurry, which can be directly
ever, wet scrubbers have a limit
cost. In addition, scrubbers
the use of a wet disposal system
ransported to an ash storage/trans-
rhere water is added to form a
for fly ash collection is a wet
Llected by a wet scrubber and
terns have the advantages of avoid-
handling equipment and creating a
pumped to the disposal area. How-
2d use due to their high operation
liipit disposal options by requiring
Pneumatic transport systems
negative pressure, or a combinat
sures, are used for dry ash hand
both the collection hoppers and
description of these fly ash
handling
Negative Pressure (Vacuum)
utilizing positive pressure,
Ion of negative and positive pres-
Ling. Figures 5-1 and 5-2 describe
an ash transfer system. A brief
systems follows:
1.
Fly ash is transp
through a hydraul
tion tank. The
disposal area.
rted from ash collection hoppers
ic vacuum producer to an air separa-
ly ash is then sluiced to a wet
Fly ash is transp
dry storage silo.
are used to creat
ash is transported
Positive Pressure
1. Fly ash is transp
dry storage silo
quently transport
2. Fly ash is transp
wetting device an
disposal area.
Combination
rted from collection hoppers to a
Hydraulic or mechanical exhausters
e the vacuum. From the silo, fly
to a dry disposal area.
rted from collection hoppers to a
r transfer station, and subse-
ed to a dry disposal area.
rted from collection hoppers to a
d subsequently sluiced to a wet
>rted from collection hoppers to a
y a vacuum system. From the trans-
ash is transported to a dry storage
system.
arameters for the available ash
1. Fly ash is transp
transfer station
fer station, fly
silo by a pressur
Table 5-1 lists typical design p
handling options.
Negative Pressure Systems
Negative pressure or vacuum ash handling systems, as shown on
Figure 5-3, have the advantage of reduced fugitive emissions and
are capable of accommodating a larger number of fly ash collection
hoppers than positive pressure systems. However, the ash transport
-------
IN-* »
Figure 5-1
FLY ASE HOPPERS
NJ
-------
Figure 5-2
FLY ASH HOPPER AND TRANSFER SYSTEM
NJ
Ln
-------
Table 5-1
CLASSIFICATION OF PNEUMATIC SYSTEMS FOR IN-PLANT ASH HANDLING (7)
Transport Medium
Parameter
System Type
Pressure Range
Saturation Capacity
(ft air/lb. material)
Material Loading
(Ib. material/lb. air)
Air Velocity
(fpm)
Maximum Capacity
(TPH)
Practical Distance
limits (ft)
Dilute Phase
Fan
-20" HO
Vacuum
10 - 30
Pressure
4.5 - 13
Vacuum
1.3 - .45
Pressure
3-1
6000
50
Vacuum 100
Vacuum 200
Dilute Phase
Blower
-7 psi
Vacuum
3-5
Pressure
1 - 3.5
Vacuum
4.5 - 2.5
Pressure
13 - 3.8
4000 - 8000
100
Vacuum 100
Vacuum 1000
Dense Phase Dense Phase
Pump Blow tank
15 - 35 psi 40 - 125 psi
0.35-0.75 0.1-0.35
45 - 18 135 - 45
1500 - 3000 300 - 1000
200 200
3000 8000
Airslide
Closed: 1/2-1 psi
Open: 4-5 psi
3-5 cfm/sq ft
10 thru diaphram
500
100 ft 6 ft drop/
length, 3° - 8° slope
r-o
CTi
-------
PRIMARY RECEIVER WITH
SECONDARY SEPARATOR
PRECIPITATOR
-AIR INTAKE "— FLY ASH INTAKE
-BAG FILTER
FLY ASH
BIN
DISCHARGE
I—
J\
EXHAUSTER
— ASH CONDITIONER
FIGURE 5.3 - NEGATIVE PRESSURE PNEUMATIC CONVEYOR
-------
28
distance is limited to approximately 500 feet and their efficiency
is affected by altitude and fly ash temperature.
Vacuum producers in negative pressure systems can be steam,
water, or mechanical exhausters. Of these types of exhausters,
water and mechanical devices are most commonly used in utility
installations. Ash properties, along with the method of ash dis-
posal, influence the selection of exhausters. Water exhausters can
be used in wet or dry disposal systems, while mechanical exhausters
are commonly used in dry disposal systems. Ash from coal having a
high sulfur content is likely to be corrosive when mixed with
water, and would have a substantial corrosive impact on water
exhausters used in wet disposal systems.
A vacuum transport system operates by fluidizing the ash
particle by a pressure differential. Fly ash passes from the
particulate removal equipment to ash collection or storage hoppers.
The fly ash is then transferred through intake valves into con-
veyance pipes. Intake valves are operated on a sequential basis
directed by an automatic timing system. An alternative system
approach would be to operate the intake valves by level controls in
the ash hoppers. Here, as the ash level in the hopper increases
past a preselected point, the intake valve would open. A control
system would protect the conveyance system from being overloaded
and phase in the appropriate intake valves. The primary main-
tenance point in this system is wear in the intake valves asso-
ciated with the sliding gate mechanism. Conveying pipes are com-
monly manufactured from hard iron alloys which are designed to
withstand abrasion and rapid changes in temperature.
Once the fly ash has entered the conveyance system, its move-
ment is a function of the system size and geometry. In a vacuum
system, the maximum length is approximately 500 feet. However, the
length is a function of system geometry and plant layout. As in
any material conveyance situation, the most efficient system is the
most direct, therefore, bends, elbows, and tees should be used as
infrequently as possible.
The method of discharging the ash is dependent on the final
method of transport and/or disposal. If the disposal system is
dry, the fly ash is carried through an air separator and dumped
into a storage silo. Air separators are usually multistage, in
order to protect the vacuum producer and to prevent fly ash from
leaving the system. For wet disposal systems, fly ash is typically
mixed with the water used to create the negative pressure in the
system. This is accomplished at the exhauster, which ejects an
ash, water, and air mixture into an air separating tank. From this
tank, the fly ash is either pumped or gravity fed to the disposal
area. If a mechanical exhauster system is utilized to provide
vacuum, the fly ash is passed through an air separator and dumped
into a water filled tank, where the ash is slurried.
-------
29
Positive Pressure Systems
While positive pressure systems are limited by the number of
fly ash collection hoppers they can handle, they are capable of
transporting fly ash for longer distances than negative pressure
systems. The positive pressure system, as shown on Figure 5-4,
utilizes a blower which is of a somewhat simpler design than a
negative pressure exhauster.
Fly ash leaving the collection hoppers passes through an air
lock/pressure feeder device, which prevents ash from blowing back
into the collection device. These feeders are operated automati-
cally in a predetermined sequence; however, the throughput of these
feeders are less than a comparable vacuum intake valve. This
reduced throughput is due to the operation of the feeder. The
generalized feeder operation is as follows:
o An intake valve is opened and fly ash enters the feeder
from the precipitator hopper under a slight vacuum.
o As the ash reaches a predetermined level or after a pre-
determined time interval has been exceeded, the upper
intake valve is closed.
o The lower outlet valve is then opened and the feeder
pressurized which results in the ash entering the pres-
surized system.
o After the ash has been exhausted, the lower outlet valve
is closed and the feeder is ready for another ash trans-
fer sequence.
Since the operation time of an air lock/pressure feeder is
longer than a vacuum valve, the overall time for fly ash removal is
longer. This time factor limits the number of ash hoppers that can
be emptied during the ash handling operation period. Although the
number of hoppers per pressurized line is limited, the problem can
be resolved if more pressurized lines are added.
From pressure feeders, fly ash passes into conveying pipes of
the same type as vacuum systems. If fly ash is being sent into dry
disposal systems, it is conveyed to a storage silo. Air forced
from the silo is vented through a fabric filter. If fly ash is
being sent to wet disposal, it is conveyed to a slurry tank. The
resulting slurry is sent to an air separating tank and subsequently
pumped to the disposal area.
Pressure systems may be classified as either dilute or dense
phase transport systems. This classification is based on the
solids density of the transported material. Table 5-1 provides
general design data for the available options. The majority of
utility system fly ash transport systems are dilute phase. The
design of a dilute phase transport system is based on the movement
-------
_A L_TE IR NAT E_ _V E_NT
TO PRECIPITATOR
AIR-LOCK
FEEDERS
INTAKE
BLOWER
ASH CONDITIONER-
ILL
FAN
VENT
FLY ASH
BIN
FIGURE 5.4 - POSITIVE PRESSURE PNEUMATIC CONVEYOR
OJ
o
-------
31
of the largest probable particle and the bulk density of the mater-
ial. This data provides the required average system velocity as
described by Figure 5-5. The typical range of fly ash is shown on
Figure 5-5. Bottom ash has not been included due to its large
particle size, relative to dilute phase transport, and severe
abrasion problems. To reduce abrasion problems and to provide
increased design capabilities, a dense phase transport system may
be utilized. As indicated above, this form of transport is similar
to dilute phase transport except that higher pressures and lower
velocities are used. Advantages of dense phase transport include
the ability to transport denser or larger materials, reduced proba-
bility of plugging, reduced pipe size and reduced abrasion. The
reduced abrasion may be described by the following equation (8):
Abrasion = (velocity)a (density)
where: a and b are constants.
Studies on the abrasive characteristics of sand in pressure
transport systems provided the following numbers for the above
abrasion equation:
a = 2.65
b = -0.37
Due to the magnitude of the a and b constants, the equation
indicates that to minimize abrasion one must minimize velocity and
maximize density. This describes a dense phase transport system.
Combination Systems
In cases where a high rate of ash collection is desired, and
fly ash must be conveyed over relatively long distance, combination
vacuum pressure systems may be used. In these systems, fly ash is
collected by a vacuum system and conveyed to a transfer station.
Usually this transfer station has vacuum, equilizing, and pressure
chambers, so that ash received from the vacuum system leaves the
transfer station under pressure. The transfer station may be com-
pared to a large air lock/pressure feeder device, described above
for positive pressure systems. After passing into the pressurized
conveyance lines, it may be transported to either a storage silo,
ash slurry area, or the disposal area.
ECONOMIZER AND AIR HEATER ASH HANDLING SYSTEMS
Economizer and air heater ash can be handled by systems pre-
viously described for fly ash. It is necessary to either provide
crushers or secondary hoppers, installed under each economizer and
air heater hopper, to facilitate pneumatic transport, due to the
tendency of this ash to sinter.
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10
0
.001
.005
.05 .1
Particle Diameter (Inches)
.5
1.0
FIGURfc 5.5 - APPROXIMATE AVERAGE AIR VELOCITIES IN DILUTE PHASE
U)
to
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33
With wet ash disposal, it is possible to collect economizer
and air heater ash in water filled tanks, from which it is perio-
dically pumped. Once wet, this ash is difficult to dewater.
Therefore, hydraulic of handling economizer and air heater ash
transport precludes the use of dry ash disposal.
BOTTOM ASH HANDLING SYSTEMS
Bottom ash is collected in hoppers located directly beneath
the boilers. The description of a "wet" bottom boiler describes
the physical state of the bottom ash within the boiler. Thus, the
bottom ash from a wet bottom boiler is in a molten state when
removed. Bottom ash from a dry bottom boiler is in a solid state
when removed. In both cases, the bottom ash is typically dropped
into a water filled hopper to shatter molten ash leaving the boiler,
and reduce the ash temperature for future handling. There are a
minimum of two bottom ash hoppers per boiler, depending upon boiler
type and the ash melting temperature. Bottom ash hoppers are
typically arranged in "V" or "W" configurations. Discharge from
bottom ash hoppers is usually automatic, but manual discharge
facilities are incorporated to provide a backup discharge system.
Bottom ash leaving the hoppers is usually passed through a
clinker grinder for size reduction, then pumped to either a dewater-
ing area (dry disposal) or directly to a wet disposal pond. Dry
bottom ash transport is provided by at least one bottom ash equip-
ment supplier. Bottom ash pumps can be jet or centrifugal types.
Jet pumps cannot be air bound, require no sump pit, and are capable
of handling overloads. They are limited by head and are subject to
increased wear in closed-loop sluice water systems, where there is
an increase in suspended solids. Centrifugal pumps can be placed
in series for high head applications, and are relatively unaffected
by the quality of recirculated water. Centrifigal pumps require a
sump pit and must be oversized to account for loss of efficiency
due to wear and to handle overloads.
Bottom ash sluice lines are constructed of durable materials,
since bottom ash is an abrasive material. Commonly used pipes
include hard iron alloy pipe, basalt lined steel pipe, and ceramic
lined fiberglass pipe.
If bottom ash is sent to dry disposal or utilization, it is
sluiced to a dewatering bin or pond. A minimum of two dewatering
bins are required to provide bottom ash storage while one bin is
dewatering. Bottom ash placed in dewatering bins can be loaded
directly into ash transport vehicles. Bottom ash placed in ponds
is excavated and then loaded into transport vehicles. In a closed-
loop system, water from dewatering bins or ponds is passed through
a clarifier prior to return to the sluice pumps. Usually the water
return system also incorporates a surge tank to handle overloads.
Figure 5-6 describes a typical bottom ash handling system.
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BOTTOM ASH HOPPER
(WET)
PUMP
SLUDGE
RETURN
PUMP
TO PUMPS
WATER
RECIRCULATION
PUMP
FIGURE 5.6 - RECIRCULATING SLUICE CONVEYOR
U)
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35
OPERATIONAL CONSIDERATIONS
The primary difficulties in ash handling result from the abra-
sive nature of ash, and thermal expansion and contraction of ash
conveying lines during surges in operation. Slide gates, valves,
and elbows in ash transport lines are subject to wear and require
continual inspection and maintenance. Ash slurry lines are some-
times rotated on a regular basis to increase life. Joints subject
to expansion and contraction in fly ash pneumatic lines require
inspection and maintenance to detect and correct leaks. Additional
routine maintenance, including lubrication of moving parts and
replacement of high wear components in pumps, is usually specified
by equipment manufacturers.
In-Plant Handling System Cost
Table 5-2 is a summary of the in-plant handling system cost
estimates made for this study. As can be seen, the variations in
equipment costs and other considerations are quite broad. This
range of costs is due to the general nature of the study and the
importance of specific plant layouts in the actual types and
amounts of equipment supplied. Due to the nature of these systems
and their reliance on plant specific details, the costs used for
this study could only be generalized. This is further described in
Section 9.
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Table 5-2
IN-PLANT HANDLING SYSTEM COST ESTIMATES
Manufacturer
Flakt A,D
United A,C
conveyor
United A,C
conveyor
United A
conveyor
Allen-Sherman- A
Hoff
Allen-Sherman- A
Hoff
Allen-Sherman- A,E
Hoff
Materials only.
Q
Transport
Phase Units
Dense
(dry)
Liquid 1
Dilute 1
[pressure]
(dry)
Dilute 1
[vacuum]
(dry)
Dilute 1
[vacuum]
(dry)
Dilute 1
[pressure]
(dry)
Liquid 1
300 MW
Fly Ash
Hoppers
16
24
24
24
40
40
40
600 MW
Fly Ash
Cost Units Hoppers
$ 463,000 32
1,120,000 1 48
2,400,000 1 48
1,975,000 2 48
2,386,750 1 40
2,616,250 1 40
934,350 1 40
900 MW
Fly Ash
Cost Units Hoppers Cost
$ 926,000 64 $1,389,000
1,240,000 1 96 1,510,000
2,800,000 1 96 4,510,000
3,450,000 3 72 4,775,000
2,386,750 2 80 4,773,500
2,616,250 2 80 5,232,500
934,350 2 80 1,868,700
1300 MW
Fly Ash
Units Hoppers Cost
80 $1,852,000
2 2,480,000
2 5,600,000
2 80 4,773,500
2 80 5,232,500
2 80 1,868,700
2600 MH
Fly Ash
Unli?___Hop_p_ers Cost
160 $ 3,704,000
3 4,530,000
3 13,530,000
160 9,547,000
160 10,465,000
160 3,737,400
Fly ash system only.
Costs based on a per unit basis.
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37
SECTION 6
ASH STORAGE AND TREATMENT SYSTEMS
INTRODUCTION
Various systems exist for the temporary storage or dewatering
of the ash prior to utilization or disposal. These systems are
dependent on ash properties, ultimate use, and other economic con-
siderations. This section will describe the available systems and
provide background on their relative merits.
FLY ASH STORAGE
Ash storage pertains primarily to dry fly ash. Bottom ash,
although technically stored in dewatering bins or ponds, is covered
in the following section. Wet fly ash is not commonly stored but
is slurried to the disposal pond.
Dry fly ash storage silos, as shown on Figure 6-1, are sit-
uated at the transfer point between in-plant handling systems and
out-of-plant transport. This interface is necessary since the
capacity of the in-plant system is much larger than the out-of-
plant system. Therefore, the ash storage silo must act as a surge
chamber equalizing the plant output of ash with the out-of-plant
transport system. Typically, a 72-hour storage capacity is used as
a design factor, with the actual storage provided by one or more
silos. The number of silos is also based, in part, on the number
of boilers.
Fly ash storage silos are normally metal or concrete bins;
however, other materials such as wood or plastics could also be
utilized. These silos operate by accepting the fly ash from the
in-plant system and exhausting the carrier air. To avoid an emis-
sion source, the carrier air is exhausted through a baghouse which
then deposits the collected fly ash back into the silo. The stored
ash may require agitation to assure a free flowing material during
silo discharge. This is provided by air diffusers located at the
base of the silo. Air is diffused through the ash such that the
material becomes fluidized. This maintains the ash in an unagglom-
erated condition so that it may be easily removed.
Ash is normally removed from the silo by gravity and may be
directed to several ash transport alternatives including trucks,
railroad, conveyors, barges, or sluicing. The transfer from the
silo to the out-of-plant ash transport system may include:
o Mixing fly ash with water to provide a slurry for pumped
transport (5-10 percent solids);
o Mixing fly ash with water (10-20 percent) to reduce fugi-
tive emissions for either truck, belt conveyor, or rail
transport;
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38
Figure 6-1
FLY ASH STORAGE SILOS
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39
o Directly depositing fly ash into the transport vehicle
for dry transport, normally for utilization;
o Direct transfer of fly ash to a pneumatic transport
system.
Many power plants use more than one ash transport/transfer
system since it is quite common to utilize a portion of the ash and
dispose of the rest. This might involve slurrying a portion of the
ash for wet disposal and transport of the rest in a dry state for
utilization. This would require an in-plant ash transport system
with two outlets. One would be to the slurry tanks for transport
to a wet disposal area and the other would be to a storage silo for
transfer to the out-of-plant transport system. This out-of-plant
transport system would most likely be a dry system designed for a
fly ash utilization scheme.
The physical requirements for the location of the ash silo are
controlled by the plant layout, number and size of boilers, and the
ultimate means of transport. Although small compared to the power
plant, ash silos are quite large and, due to the congested situa-
tion at many power plants, may not be located near the boiler.
Although this is not a problem for silo construction and operation,
it may require a pressurized in-plant transport system if the silo
is more than 500 feet from the ash hopper. The final requirement
of silo location is the method of ultimate transport. The availa-
ble options are listed in Section 8, however, each option has
physical requirements. These requirements may dictate that the ash
silo be elevated to provide truck clearance or allow the silo to be
on-grade to facilitate pneumatic unloading.
BOTTOM ASH DEWATERING
Bottom ash is collected from the boiler bottom in either a
liquid or solid state with the physical condition of the bottom ash
supplying the boiler designation of "wet bottom" or "dry bottom".
For either case, the ash is quite hot and, to reduce its temper-
ature, is quenched in a water bath. This permits the rapid cooling
or solidification of the ash so that it may be transported away
from the boiler. After quenching, the bottom ash is typically
sluiced to a disposal pond or dewatered. However, dry bottom ash
transport systems, both belt and pneumatic conveyors, are currently
being marketed. The rapid dewatering of the bottom ash is made
possible by the large particle size of the bottom ash. The dewater-
ing of bottom ash can be performed in either a dewatering pond or a
dewatering bin.
Dewatering Pond
Bottom ash dewatering ponds are constructed so that as the
bottom ash slurry enters the pond, the bottom ash settles out and
the resultant liquid is removed. Once the pond is sufficiently
full, the bottom ash is removed by dragline, backhoe, loader, etc.
This removal operation requires that the pond be constructed such
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40
that the equipment can either reach all areas of the pond or that
the equipment can enter the pond to remove the ash. The ash is
loaded onto transport equipment and hauled to its ultimate desti-
nation.
Dewatering Bins
Bottom ash dewatering bins are large settling basins usually
constructed of steel. A typical dewatering bin is shown in Fig-
ure 6-2. The bottom ash slurry enters the bin where the bottom ash
begins to settle out due to the decreased water velocity. Once the
bottom ash has settled out of solution, it is removed from the
bottom of the bin by gravity, and placed into either trucks, rail
cars, or conveyors for transport.
Depending on the settling velocity of the bottom ash par-
ticles, the available detention time, and the required effluent
quality, dewatering bins operating in series may be required. By
operating these bins in series, the discharge will have fewer
suspended and settleable solids. In cases where the discharge must
meet specific effluent requirements, the use of a series operated
system can help to minimize additional effluent treatment.
If a water recirculation system is utilized for the bottom ash
slurry water, a sluice water surge tank is necessary to accommodate
system fluctuations.
Comparison of Dewatering Methods
The physical properties and principles relative to bottom ash
dewatering are the same for both ponds and bins. However, each
specific method has its own relative merits. Bottom ash ponds are
readily constructed, do not require daily operation and are rela-
tively impervious to breakdowns in the dry bottom ash transport
preclude system. These ponds may require significant land area and
careful design to preclude groundwater contamination, and are labor
and equipment intensive in bottom ash removal. Bottom ash dewater-
ing bins do not require significant land area and are amenable to
the constant bottom ash removal necessary for ash utilization.
Dewatering bins can be adversely affected by breakdowns in the dry
bottom ash transport system if they do not have sufficient storage
capacity.
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41
Figure 6-2
BOTTOM ASH DEWATERING BIN
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42
SECTION 7
ASH TRANSPORT
INTRODUCTION
There are a number of methods available to transport the ash
from the storage silo, dewatering bin, or slurry pump to the dis-
posal area. These ash transport systems require a large capital
expenditure and warrant careful design. The degree of variation in
transport systems is typified by the following list of options:
o Truck
o Rail
o Barge
o Pipeline
o Belt Conveyor
o Pneumatic Conveyor
Each transport option also includes several alternatives.
An important consideration to be made in conjunction with the
method of ash transport is whether the bottom ash and fly ash will
be transported jointly or separately. Most transport systems can
be designed for combined transport. Combined transport of the ash
may preclude the use of the bottom ash. In the case of dry dis-
posal areas, and to some extent wet sites, bottom ash may be used
to provide underdrainage blankets, road bases or surfaces, tem-
porary fly ash cover, or be otherwise used as an aggregate replace-
ment. If bottom ash is transported with the fly ash, other mater-
ials must be obtained to serve the above purposes. However, these
other materials are expensive when compared to the cost of bottom
ash segregation.
TRUCK TRANSPORT
The transport of ash by truck is normally restricted to dry or
lightly wetted ash. Commonly used methods of truck transport are:
o Highway trucks
Triaxle, dump truck, 25-ton capacity
Pneumatic trailers, 15-ton capacity
End dump trailer, 30-ton capacity
o Off-road trucks
Off-road dump truck, 35-ton capacity
Self-powered scraper, 30-ton capacity
This list represents a cross-section of available truck trans-
port methods and commonly used sizes and types of equipment. Many
other types and sizes of equipment are available.
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43
Truck transport has the advantage of utilizing an existing
technology that is capable of quickly reacting to changes in operat-
ing conditions. If breakdowns occur, additional equipment can be
rented, or if the primary transportation route is made unusable,
other routes are usually available. Truck transport places the ash
at the point of active disposal operations and, therefore, does not
require second handling. These advantages provide for flexible
operation and the ability to meet future changes. Disadvantages of
truck transport are primarily labor and operating costs. The
reliability of truck transport is dependent on the truck drivers
and the availability of fuel. In addition, since it is labor and
energy intensive, its cost is directly related to these items.
Unfortunately, the costs of labor and fuel are difficult to predict
since recent increases have exceeded normal inflation rates. Thus,
the future cost of truck transport may be difficult to accurately
estimate.
Economic Comparison of Trucking Alternatives
To assess the most economical method of truck transport for
the disposal system cost estimates, an analysis of truck transport
options was performed. Pneumatic trailers were shown to be a cost
effective means of transport primarily for ash utilization schemes
requiring longer transport distances than these considered for this
study and were not considered in this assessment of trucking costs.
This analysis included:
o On-road 25-ton triaxle truck;
o On-road 39-cubic yard end dump trailer with tractor;
o Off-road 35-ton truck (Caterpillar 769C);
o Off-road 50-ton truck (Caterpillar 773);
o Self-powered scraper, 30-cubic yard (Caterpillar 631D);
and
o Self-powered scraper, 40-cubic yard (Caterpillar 657B).
The on-road vehicles analyzed were a 25-ton triaxle diesel
with heavy duty components and a 39-cubic yard end dump trailer
with diesel tractor. The purchase cost of a 25-ton triaxle truck
is approximately $65,000. A life span of ten years was assumed.
The total purchase cost of the 39-cubic yard end dump trailer and
diesel tractor is $57,600. A ten-year life expectancy for the
tractor-trailer combination was assumed. The off-road vehicles
included in the analysis consisted of two trucks and two scrapers.
The purchase cost of a 35-ton Caterpillar 769C truck is $232,235.
The purchase cost of a 50-ton Caterpillar 773 truck is $329,000.
Both were assumed to have a 12-year life. A 21- to 31-cubic yard
Caterpillar standard scraper 63ID has an approximate purchase cost
of $322,850 and an estimated life span of 8 years. The purchase
cost of a 32- to 44-cubic yard Caterpillar tandem scraper 657B is
$467,761. It also has an 8-year estimated life. All above esti-
mated life expectancies were based on a good maintenance program as
recommended by the manufacturer. All purchase costs were based on
a January 1980 purchase.
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44
In order to determine the most economical means of transport
of the six vehicles compared, an analysis was performed to deter-
mine the total number of vehicles required and when they would need
to be replaced. An inflation rate of 8.5 percent was used and all
costs were expressed in 1980 dollars. The life of the power sta-
tion was assumed to be 35 years and the disposal area was located
one mile from the plant.
A 2600 MW plant was used for the analysis. This plant would
produce an estimated 6,656 tons (8,217 cubic yards assuming a unit
weight of 60 pcf) of ash per day. It was assumed that although ash
would be generated 24 hours per day 7 days per week, it would only
be hauled 8 hours per day 5 days per week. The number of trips
required per day for each vehicle are as follows:
o 25-ton triaxle requires 267 trips;
o 39-cubic yard end dump trailer requires 211 trips;
o 769C requires 191 trips;
o 773 required 134 trips;
o 631D requires 266 trips; and
o 657B requires 187 trips.
It was assumed that one-half hour per shift would be required
for refueling and maintenance. Therefore, 7-1/2 hours of hauling
time would be available. Using the Caterpillar Performance Hand-
book, Edition 9 (9) and other available information, the total time
to load, unload, and make a round trip was estimated for each
vehicle. Table 7-1 describes the estimated round trip time, number
of vehicles and total vehicle cost for the estimated 35-year plant
life. This analysis indicates that the cost of the 39-cubic yard
end dump trailer would be significantly less than the other alter-
nates. The operation and maintenance costs of these vehicles must
also be reviewed. Table 7-2 was developed to assess the economic
impact of fuel, lubrication, personnel, and maintenance. This
analysis indicates that the 25-ton triaxle, 39-cubic yard end dump
trailer, and the 35 and 50-ton off road trucks have similar overall
transportation costs. An important consideration in the selection
of a truck transport method is the estimated fuel consumption. Due
to the comparatively high inflation rate of diesel fuel relative to
the estimated 8.5 percent rate of inflation, disparities in fuel
consumption could alter future transportation economics. Again
referring to Table 7-2, the 25-ton triaxle uses the least fuel. If
the cost of fuel rises from the estimated $1 per gallon to $2 per
gallon, in 1980 dollars, then the following present worth compari-
son is relevant:
25-ton triaxle $16,534,000
39-yard trailer $15,685,000
35-ton off-road $19,741,000
50-ton off-road $17,875,000
Due to the above analysis, the 25-ton triaxle and 39-cubic
yard end dump trailer are the preferred method of transport. For
purpose of this report, the 25-ton triaxle truck was selected due
-------
Table 7-1
TRUCK TRANSPORT INFORMATION
Vehicle
Round Trip*
(minutes)
Number of
Vehicles
Required**
Total Number of
Vehicles Including
Rep1acements * * *
25-ton triaxle
3 9 -cubic yard end
dump
35-ton off-road
truck (Cat. 769C)
50-ton off-road
truck (Cat. 773)
30-yard scraper
(Cat. 631D)
40-yard scraper
(Cat. 657B)
13.5
14.0
14.2
16.8
16.1
14.0
8
7
7
6
10
6
32
28
21
18
50
30
*Based on a round trip distance of 2 miles.
**Based on 6656 tons of ash and an 8-hour work day.
***Based on a 35-year power plant life.
Total Vehicle Costs
(in 1980 dollars)
$1,192,000
$ 924,000
$2,009,000
$2,440,000
$10,136,000
$8,811,000
en
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Table 7-2
TOTAL COST COMPARISON
2600 MW PLANT
Equipment
Capital
Fuel**
Lube
Personnel
Maintenance
Total
Present Worth
Total Cost*
25-ton triaxle
$ 10,364,264
$ 16,412,882
$ 1,969,546
$ 88,767,557
$ 9,847,729
$127,360,000
$ 14,646,000
End Dump
Trailer
$ 8,036,294
$ 19,319,112
$ 2,069,905
$ 76,605,297
$ 11,039,493
$117,070,000
$ 13,463,000
769C
$ 17,469,606
$ 33,228,873
$ 1,931,911
$ 75,033,215
$ 10,767,185
$138,430,000
$ 15,919,000
773
$ 21,213,120
$ 28,267,792
$ 2,718,057
$ 64,443,038
$ 10,524,316
$127,170,000
$ 14,625,000
631D
$ 88,139,870
$ 81,554,252
$ 3,089,176
$119,123,030
$ 48,343,548
$340,250,000
$ 39,129,000
65 7B
$ 76,620,828
$101,101,680
$ 3,663,104
$ 70,257,589
$ 56,438,670
$308,080,000
$ 35,429,000
Note: Assumptions utilized for the above analysis are described in Appendix A.
""Assumes 11 percent discount rate.
**The above estimates assume average fuel consumption and are only for purposes of comparison.
in the final cost estimates was 60 percent higher than average.
Actual fuel usage utilized
cn
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47
to greater availability and present use within the industry.
However, the selection of a truck transport method for a specific
site may determine that another truck transport option may provide
the least cost.
RAIL TRANSPORT
The transport of ash by rail car is not common at present due
to operational constraints, such as unloading facilities and sched-
uling. However, ash transport by rail could be increased using the
unit train concept. Existing rail cars which could be utilized for
dry ash transport include bottom dump, side dump, and pneumatic
tank cars.
Rail transport is advantageous since the rail routes made
necessary by coal transport to power stations already exist. The
cost of new track construction would not be included with ash
transport costs. Applicable rail transport costs would include
fuel consumption on the return trip, additional track and bed
maintenance, and the cost of dumping the ash on the return trip at
the coal mine or disposal site. Train routes are usually not
affected by outside influences and are essentially independent of
weather. Disadvantages of rail transport include increased on-site
ash storage capacity, difficulties in unloading cars, and double
handling to place the ash in the disposal site.
Double handling of ash is required since railroad cars can
only deposit ash at a central location or along a specific rail
line. To place this ash in a disposal area requires that it be
picked up, transported, and finally placed. This operation would
require equipment operation in excess of that required for spread-
ing and grading of ash transported by truck.
BARGE TRANSPORT
Barge transport of coal ash may be practical for a few cases,
but it does not show the possibility of wide applicability. Barg-
ing will be limited to stations located on or very close to navi-
gable waterways, stations which can consider ocean disposal, and/or
stations requiring a long transport distance (greater than 100
miles, 161 kilometers). Barging theoretically can accommodate wet
or dry sludges, and provide high system reliability at very low
unit costs. However, the limited transportation routes and the
special loading and unloading facilities make the overall economics
unfavorable for all but a few selected cases. Disadvantages in-
clude increased plant site ash storage capacity, difficulties in
unloading, and double handling to place the ash in the disposal
site.
PIPELINE TRANSPORT
The transport of ash by pipeline requires the slurrying of ash
(typically ten percent solids by weight) and pumping it to an ash
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48
disposal pond. This method of transport is most commonly used for
wet disposal schemes; however, a well draining ash could be de-
watered and later placed in a dry disposal site. The available
options for pumping the ash have been described in Section 5. Pump
design is consistent with standard pumping system design. The only
specific requirement is that the minimum velocity be sufficient to
maintain the ash in suspension. Conveying velocities range between
4.5 and 12.0 feet per second, depending on a number of factors
including particle size, material density, and pipeline configura-
tion. After the pipeline system has been designed, the type of
pipe may be selected. Pipe selection is based on various para-
meters, including ash properties. However, life cycle cost, in-
cluding pipe life and maintenance requirements, is the primary
consideration for pipe selection (10). The types of pipe available
for ash transport are:
o Steel
o Cast iron
o Hard iron alloy
o Basalt lined steel
o Ceramic lined fiberglass
o Plastic (PVC, ABS, etc.)
o Fiberglass
The requirements of a fly ash transport system are not as
severe as a bottom ash or combined transport system, since fly ash
is less abrasive than bottom ash. Standard utility practice tends
to favor either steel or cast iron pipe with mechanical joints. As
the pipe wears, it is rotated such that the pipe is more evenly
worn. A single pipe can be rotated three times prior to replace-
ment. Other procedures are enjoying increased popularity. These
include the use of high quality abrasion resistant pipe, such as
basalt lined steel pipe and ceramic lined fiberglass pipe. These
pipes provide substantial increases in the life expectancy of the
pipe, and thus may warrant their high initial capital cost. How-
ever, some fly ashes may coat the pipe and in time can reduce its
capacity. In this case, provisions for periodic cleaning of the
lines must be provided. Examples of this are periodic pumping of
bottom ash, designed access points for hydraulic and mechanical
cleaners, and back-up lines and pumps.
An integral part of the pipeline transport system is the over-
flow water return system. Based on currently proposed regulatory
requirements for a new source, an ash pond discharge will be
limited to a small concentration of suspended solids. The easiest
method of compliance may be a water recycle system which would
require a water return line from the ash pond to the plant and, if
there is not sufficient head, a water-return pump. Since the
suspended solids concentration in the recycled water would probably
be low, other conventional pipeline materials, such as plastic and
fiberglass pipe, could be used in the water-return pipeline. The
possible accumulation of corrosive substances in the slurry water
should be investigated prior to final pipe selection. In addition,
the potential for dissolved solids accumulation must be recognized.
-------
49
Mitigation methods can include measures for pipeline cleaning
previously discussed, changes in disposal pond operation to enhance
ash settling, and water treatment. In addition to water treatment
for the closed loop water, water treatment may be required for
periodic discharges due to excessive water accumulation within the
system. This problem would only exist in those areas where preci-
pitation exceeds evaporation. These discharges would require
treatment to at least reduce total suspended solids, total dis-
solved solids, and control pH. Current technology to provide total
dissolved solids concentrations less than 500 ppm include reverse
osmosis, electrodialysis, and distillation techniques. Although
this type of treatment may be required at some sites, it was con-
sidered site specific and not included in the economic analysis.
The advantage of a pipeline ash transport system is that is
relatively independent of labor or energy problems. The primary
disadvantage of a pipeline is continual maintenance, although this
may be reduced by the use of abrasion resistant pipe.
CONVEYOR TRANSPORT
Conveyor transport includes both belt and pneumatic transport
of ash. Although the design basis of these transport alternatives
are not similar, they do share similarities in that they:
o Require a dedicated transport line;
o Have a high initial capital cost; and
o Require a storage silo at the disposal area.
Belt Conveyor Transport
The transport of ash by belt conveyor requires that the ash be
dry, although partial wetting may be used to reduce dusting.
Conveyor systems consist of one or more conveyor flights, each made
up of a continuous belt supported by rollers and powered by a
central motor drive. Each flight is separated by a transfer sta-
tion where the ash is transferred from one flight to another. The
length of a conveyor flight is constrained by both strength of
conveyor belt and required horsepower of the motor drive. Conveyor
flights in excess of ten miles have been constructed. Another
restriction of conveyors is the geometry of the transport system.
The maximum slope of the system is typically restricted to less
than ten percent, and large curves or turns cannot be executed
without a transfer station. The number of transfer stations should
be minimized since both their capital and operation costs are quite
high. A final requirement of ash conveyor systems is that fugitive
emissions be minimized. This can be accomplished by either wetting
the ash or enclosing the conveyor. Reduction of fugitive emissions
by wetting would cause emission violations unless a great deal of
moisture control over the entire length of the conveyor is exer-
cised. Therefore, an enclosed conveyor system would be preferred.
Advantages of a belt conveyor system include a lack of depend-
ence on either labor or energy. Disadvantages include its high
-------
50
capital cost, plant disruption in a case of failure (unless a
back-up system is available), and the requirement of double handl-
ing at the site to place the ash in the fill.
Pneumatic Conveyor
Pneumatic ash transport requires that the ash be completely
dry. Pneumatic ash transport consists of a pressurized pipeline
system in which the ash is transported along a stream of air. The
actual design of the transfer method may be either dense phase or
dilute phase, referring to the concentration of ash particles
within the air stream. Upon reaching the disposal area, the air
velocity is reduced and the ash settles into a storage silo prior
to placement in the landfill. The carrier air is exhausted through
a baghouse with the removed ash redeposited into the silo. Design
of this type of system is restricted by the ability of the carrier
air to transport the ash. Specific transport distance capabilities
are based on the type of phase transport, temperature of the air
and/or ash, piping system resistance, and altitude. If long trans-
fer distances are required, a transfer or booster station may be
necessary.
Advantages of pneumatic transport include unattended opera-
tion, use of an existing technology relative to ash handling, and
ability to conform to existing topography. Disadvantages include
high capital cost and double handling of the ash at the disposal
area.
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51
SECTION 8
DISPOSAL AREA CONCEPTUAL DESIGN
INTRODUCTION
The design of ash disposal areas is an integral part of the
cost estimating process incorporated in the selection of an ash
disposal system. The design of an ash disposal area is influenced
by several site specific factors including:
o Area topography and geometry;
o Area geological and soils characteristics; and
o Ash disposal regulations.
The objective of an ash disposal site design is to create a
permanent, stable site with a minimum of environmental impact and
post-closure maintenance. The following portions of this chapter
discuss the major design features of both wet and dry disposal
sites. These features are of a general nature, and could be sub-
stantially modified by additional ash disposal system criteria,
such as the hazardous or non-hazardous RCRA classification of the
ash produced.
DRY DISPOSAL AREA
Dry disposal areas are commonly designed and constructed with
methods similar to those used for the design and construction of
earth fills. The EPRI Fly Ash Structural Fill Manual (1) contains
detailed information concerning the testing of ash to determine its
physical properties along with design considerations which are
somewhat unique to ash. The major factors in the design of dry
disposal areas are:
o Fill configuration and construction;
o Erosion and sediment control; and
o Surface and ground-water protection.
Fill Configuration and Construction
The overall slope stability of the site is influenced by its
configuration and the manner in which it is constructed. Fig-
ure 8-1 shows a cross-section through a dry ash fill. Although the
stages or zones of the cross-section are not typical, the overall
fill configuration is. This figure is used to indicate the pos-
sible extent of ash zoning which could occur in a difficult geo-
technical situation. The simpliest variation of the ash fill would
be where all the ash was placed in a similar manner irrespective of
any material zoning. The major configuration and construction
features that influence slope stability are:
-------
BENCH
UNCOMPACTED
FLY ASH
TOE OF SLOPE
EXISTING
GROUND SURFACE
UNDERDRAIN,
2' BOTTOM ASH - TYPICAL
COMPACTED ASH TOE
FIGURE 8.1 - CROSS-SECTION : DRY ASH DISPOSAL AREA
Ln
-------
53
o Method of ash placement;
o Fill slopes; and
o Exclusion of water from the fill.
In dry ash disposal, ash is commonly hauled to the active
portion of the fill, dumped, spread, and possibly compacted. The
degree of compaction of the ash will influence the overall sta-
bility of the fill, the permeability of the ash, and also the
volume required for ash disposal. For example, compacted ash will
have a higher in-place density, higher shear strength, lower
volume, and lower permeability than an ash loosely dumped without
compaction.
Depending upon the method of ash placement and degree of
compaction, fill slopes are designed to ensure the stability of the
disposal area. Normally ash fills will be designed with overall
slopes of 3 or 4 horizontal to 1 vertical, and incorporate terraces
at 15 to 25 foot vertical intervals although material strength may
dictate greater or lesser slope ratios. Local terrace slopes may
be as steep as 2 horizontal to 1 vertical. It should be noted that
the length and steepness of local slopes can influence other site
features, such as soil cover and vegetation used in erosion control
measures.
Water should be excluded from the fill in order to minimize
the formation of leachate and ensure the fill integrity. The
primary ways of excluding water are:
o Collection of groundwater with a layer of inert, per-
meable material placed beneath the fill. In some cir-
cumstances, the groundwater may require collection in a
pipe underdrain network for discharge;
o Diversion of surface water away from the disposal area;
o Provision of positive drainage to the ash fill surface
and provision of drainage systems to carry runoff away
from the fill.
o Covering the ash with a soil material capable of support-
ing vegetation and providing minimal infiltration.
Erosion and Sediment Control
In order to satisfy environmental regulations and to prevent
erosion, it is necessary to incorporate measures to control erosion
and subsequent sediment transport from the fill. These design
features commonly include:
o Staged site development in order to minimize the area of
ash exposed without soil and vegetal cover;
o Sedimentation pond to trap sediment carried by site run-
off;
-------
54
o Ditches for channeling and controlling the surface runoff
in the disposal site;
o Manipulation of the slope, length, and gradient in order
to control runoff velocity and sediment transport poten-
tial;
o Berms at the foward edge of benches to keep runoff from
flowing over the bench face;
o Sloped benches to direct runoff into collection ditches;
o Temporary sediment traps, such as straw bale barriers or
sandbags, to trap sediment eroded from exposed ash or
earth stockpiles;
o Soil cover and vegetation, if needed, on all exposed ash
surfaces and soil stockpiles.
Surface and Ground-Water Protection
Increasing concern about the pollution of surface and ground
waters has necessitated the use of water protection measures in the
design of ash disposal areas. The use of these protection measures
is determined by regulatory requirements, the type and permeability
of soils underlying the site, and ash leachate characteristics.
Commonly used site features intended to protect surface and ground-
water are:
o A site liner - either natural or synthetic;
o Surface water diversion ditches and pipes;
o A permeable layer of inert material beneath the site to
collect leachate; and
o Treatment of site leachate, if needed.
Although the above design features are commonly used at an ash
disposal site, the actual selection of specific features must be
performed on a site specific basis. For example, if a liner is
required at a site to protect the groundwater system, a choice
exists between a synthetic or clay liner. If clay is present at
the site, the cost of its placement may be less than the cost of a
synthetic liner. However, if the clay must be imported for any
distance, it may become more expensive than a synthetic liner.
WET DISPOSAL AREA
The design of a wet ash disposal area incorporates the follow-
ing major features:
o Embankment design;
o Surface and ground-water protection; and
o Required settling time.
-------
55
In addition to these design features, consideration should be given
to the post-closure requirements of a wet disposal area. If the
disposal area is filled with ash and the power plant discharge is
stopped, then the site is a landfill which should meet the design
requirements previously discussed for dry disposal sites. If water
continues to enter the site, then continuing maintenance of the
embankment and discharge structures is required in order to ensure
their integrity.
Embankment Design
The design of earth embankments is a detailed topic beyond the
scope of this report. The height and type of embankment are influ-
enced by the soil types and quantities available near the site
along with the site topography and the required disposal volume.
Surface and Ground-Water Protection
The protection of groundwater, if required, entails the use of
a site liner. This liner may be constructed of natural or syn-
thetic materials . Surface water protection is somewhat more com-
plex to analyze. It is possible that effluent restrictions will
preclude pond discharge to surface waters and require the use of a
closed loop water recirculation system. If a closed loop water
recirculation system is to be used, it is necessary to undertake a
water flow mass balance study to compare water entering the dis-
posal area from sluicing operations, precipitation, and upland
runoff with water leaving the area by evaporation and discharge.
This type of study is necessary to determine the net amount of
water returned to the plant, and the need for upland runoff diver-
sion ditches. After closure, diversion structures should be con-
structed to direct runoff away from the site and prevent the ero-
sion of ash surfaces.
Required Area for Settling
One of the primary functions of a wet disposal area is to
provide sufficient detention time of the incoming ash slurry to
allow the settling of ash particles. The settling of solids is
theoretically related to the pond outflow rate, the surface area of
the pond, and the critical settling velocity of the ash particles
in the pond influent. This relationship can be stated as:
Required Settling Area = . . . , Ratf . «. - 7
M ^ critical settling velocity of
the smallest particle to be
retained
Other design features, such as baffles or skimmers, may be required
for cenosphere removal and to prevent short circuiting. It may
also be necessary to incorporate underflow weirs, trash racks, or
anti-vortex plates on discharge structures in order to prevent the
-------
56
outflow of particles and ensure the proper functioning of the
discharge structure.
SUMMARY
Both wet and dry ash disposal systems must be constructed
under a similar set of criteria. These include:
o Geotechnical stability of the fill or embankment;
o Protection of ground-water; and
o Protection of surface water.
The protection of surface and ground-water is typically regulated.
However, various options must be examined to provide a cost effec-
tive system. These options include clay versus synthetic liners,
depth and type of underdrain system, and other water quality con-
trol techniques. Regulations specifically pertaining to fill or
embankment stability are not common and, therefore, provide an even
wider range of design options to provide a cost effective system.
-------
57
SECTION 9
ECONOMIC ANALYSIS
INTRODUCTION
The overall purpose of this report is to compare the relative
costs of wet and dry methods of ash disposal for five power plant
sizes ranging from 300 to 2600 MW generating capacity. The five
power plant sizes, the number of units, and the ash quantities are
as follows:
Plant Power Size Units Ash Quantity (tons/year)
300 MW 1 200,229
600 MW 2 400,457
900 MW 2 600,686
1300 MW 3 867,657
2600 MW 4 1,735,314
Conceptual disposal schemes, shown in Figure 9-1, were developed.
These disposal schemes include a number of options within major
segments of the disposal process in order to allow for variable
conditions such as disposal site topography. Due to the general
nature of the report, costs for construction, operation, and main-
tenance of ash disposal systems were estimated. These costs were
based upon information from TVA, equipment manufacturers and sup-
pliers, and current ash disposal system design practice. Assump-
tions used for these estimates are tabulated in Appendix A. Some
decision parameters which can significantly influence ash disposal
system design, such as local regulatory restrictions and site
specific environmental impacts resulting from ash disosal, are
difficult to assume and were not included in developing cost esti-
mates for this report.
METHOD OF ECONOMIC ANALYSIS
Costs for the different disposal schemes were divided into two
categories: capital costs and operation and maintenance (O&M)
costs. It was assumed that the major facilities such as pond
embankment, dry disposal site development, etc., was completed in
1980 and became part of the capital cost of the facility. This
included the in-plant handling system, transportation system, and
disposal area. Operation and maintenance items of the in-plant
handling system were assumed to be those items necessary to main-
tain the system (based on an O&M factor of 17 percent of the capital
-------
FIGURE 9-1
SPECIFIC ASH DISPOSAL SCHEMES CONSIDERED FOR COST ESTIMATING
Waste Type
Ash Collection
Handling System
Disposal Method
Transport
Disposal Site
Ash Disposal
Operations
Ash Rehandling
as ne'eded
Compacted
1
Uncompacted
Ui
oo
-------
59
cost per year), maintenance and/or operation of the transportation
system including required equipment replacements and the operation
and/or maintenance of the disposal area which included ash place-
ment/regrading or ash redistribution. The 17 percent O&M figure
represents the upper limit on O&M costs, as indicated by Barrier (9)
Lower rates, 5 and 10 percent, may better reflect actual utility
costs and are included to illustrate the effect of O&M costs on the
total system cost. The 5 and 10 percent rates may be more indica-
tive of utilities that perform the minimum of O&M on ash disposal
systems. To provide for the time value of money, an 11 percent
discount rate and an 8.5 percent inflation rate were utilized.
The economic analysis of the disposal system cost was per-
formed using two methods. The first was a present worth analysis
of each alternative. The present worth of each alternative was
determined by adding the capital cost of the project to the present
worth value of operation and maintenance (O&M). Present worth O&M
was determined by calculating the 35-year cost of O&M, utilizing an
8.5 percent inflation rate, and then discounting this amount at 11
percent to its present worth in 1980 dollars. The second method of
analysis was a total system cost approach. This approach utilized
a weighted cost of capital which combined the inflation rate with
the cost of capital. O&M costs were inflated at 8.5 percent over
the 35 year life of the plant to provide a total O&M cost. The
total system cost, thus, becomes the summation of the weighted cost
of capital plus the total O&M cost. The following equation was
utilized in the determination of the weighted cost of capital:
(1 + r) = (1 + x) (1 + i)
or
r = [(1 + x) (1 + i)] - 1
where:
r = discount rate (weighted cost of capital in the presence
of inflation)
x = cost of capital in the absence of inflation
i = Inflation rate (8.5 percent)
This equation results in the following factors for the two
analyses:
-------
Table 9-1
ASH DISPOSAL SYSTEM
PRESENT WORTH COST
(ALL COSTS IN MILLION $)
300 MW
Disposal Method
PIPELINE
Wet
25'
50'
N
W
TRUCK TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
BELT CONVEYOR
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
PNEUMATIC
CONVEYOR
Dry-UC
75'
150'
N
W
Diy-C
75'
150'
N
W
*Least cost option
With
Liner
32.6
39.5
17.7*
20.5-
28.2
27.2
28.9
30.2
26.3
23.6
26.9
28.7
29.3
28.3
30.0
31.2
27.4
27.4
28.0
29.8
27.4
26.4
28.1
29.3
25.5
25.5
26.1
27.9
Without
Liner
21.7
33.7
15.6-
15.3*
25.3
24.5
25.8
26.7
23.9
23.9
24.4
25.7
26.3
25.6
26.9
27.8
25.0
25.0
25.5
26.8
24.4
23.7
25.0
25.9
23.1
23.1
23.6
24.9
600 MW
With
Liner
57.5
59.1
35.2*
36.0-
46.3
42.1
46.9
53.5
42.9
40.2-
43.7
47.5
45.9
41.6
46.4
53.1
42.5
39.8-
43.3
47.1
44.4
40.1-
44.9
51.5
40.9
38.3-
41.8
45.5
Without
Liner
36.3
48.6
28.3-
27.4*
41.3
38.1
41.7
46.5
38.9
36.9
39.5
42.3
40.8
37.7
41.2
46.1
38.4
36.5
39.1
41.8
39.3
36.2
39.7
44.6
36.9
35.0
37.5
40.3
900 MW
With
Liner
81.7
78.0
50.0*
50.5-
68.2
60.4
67.6
73.6
62.9
57.5-
63.0
70.5
66.4
58.6
65.8
71.8
61.1
55.7-
61.2
68.6
65.2
57.5-
64.6
70.6
59.9
54.5-
60.0
67.5
Without
Liner
50.2
62.8
40.6-
39.9*
61.0
55.3
60.5
64.9
57.2
53.2
57.3
62.8
59.2
53.4
58.7
63.1
55.4
51.4
55.5
61.0
58.0
52.3
57.6
62.0
54.2
50.3
54.3
60.8
1300 MW
With
Liner
112.3
101.6
68.0*
68.2-
92.7
80.3
89.5
94.2
84.5
75.7-
83.3
89.3
89.3
76.9-
86.1
90.8
81.1
72.3-
79.9
85.9
88.6
76.2-
85.4
90.1
80.4
71.6-
79.2
85.2
Without
Liner
67.0
80.1
56.1-
55.4*
82.6
73.5
80.3
83.7
76.6
70.2
75.8
80.2
79.2
70.1
76.9
80.3
73.2
66.8
72.4
76.8
78.6
69.4
76.2
79.6
72.6
66.1
71.7
76.1
2600 MW
With
Liner
222.5
189.0
133.2*
138.0'
192.2
164.9
171.9
173.8
176.1
155.9
165.9
168.3
183.5
156.1
163.2
165.1
167.3
147.2-
157.1
159.5
183.8
156.4
163.5
165.4
167.6
147.5-
157.4
159.8
Without
Liner
132.6-
147.1
116.2*
119.9-
172.8
152.7
157.9
159.3
161.2
146.3
153.6
155.4
164.1
143.9
149.1
150.5
152.4
137.6
144.9
146.7
164.4
144.2
149.4
150.8
152.7
137.9
145.2
146.9
per column .
•Less than 15 percent greater than least cost
option.
Key: 25', 50', 75', 150' = Depth of disposal area
N = Narrow valley
W = Wide valley
C = Compacted
UC = Uncompacted
(Ti
O
-------
Table 9-2
ASH DISPOSAL SYSTEM
TOTAL SYSTEM COST
(ALL COSTS IN MILLION $)
300 MW
600 MW
900 MW
1300 MW
2600 MW
Disposal Method
PIPELINE
Wet
25'
50'
N
W
TRUCK TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
BELT CONVEYOR
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
PNEUMATIC
CONVEYOR
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
*Least cost option
With
Liner
286
339
186-
192-
256
248-
261-
271-
242*
242*
247-
261-
289
281
294
304
275-
275-
280
294
260-
252-
265-
275-
246-
246-
251-
265-
Without
Liner
201
294
154-
152*
233
227
237
244
224
223
227
237
266
261
270
278
257
256
260
270
237
232
241
249
228
227
231
241
With
Liner
482
494
310*
315-
413
380-
417
468
387
367
394
423
427
394
431
482
401
381
408
437
404
371
409
460
379
358
385
414
Without
Liner
317
413
255-
248*
373
349
377
414
356
341
361
382
388
363
391
428
370
355
375
396
365
341
368
406
348
332
353
314
With
Liner
677
648
430*
435-
601
541
596
643
581
539
582
640
598
537
593
639
577
535
578
636
581
521
577
623
561
519
562
620
Without
Liner
432
530
358
353*
545
501
542
576
537
506
537
580
542
497
538
572
533
502
534
576
525
481
521
556
517
486
518
560
per column.
• Less than 15 percent greater than
least cost
option.
With
Liner
921
838
577*
578-
827
731
802
838
764
696
755
801
804
708
779
816
741
673
732
778
796
700
771
807
733
664-
723
770
Without
Liner
570
671
485-
480*
749
678
731
757
703
653
696
731
726
655
708
734
680
630
673
708
717
647
699
726
672
622
665-
699
with
Liner
1780
1520
1087*
1124-
1682
1470
1525
1539
1578
1422
1499
1518
1606
1394
1449
1464
1503
1346
1424
1442
1613
1401
1456
1471
1510
1354
1431
1449
Without
Liner
1083-
1195
955*
961-
1531
1375
1417
1426
1463
1348
1404
1417
1456
1300
1340
1351
1387
1272
1329
1342
1463
1307
1347
1358
1394
1279
1336
1350
Key:
25' 50' 75'
150' = Depth of disposal area
N = Narrow valley
W = Wide valley
C = Compacted
UC = Uncompacted
c-v
H
-------
62
Present Worth 11% 2.3% 8.5%
Total System Cost 20.4% 11.0% 8.5%
ASH DISPOSAL COSTS
A summary of disposal system costs are included in Tables 9-1
and 9-2. As detailed in Appendix A, the cost estimates for ash
handling, transport, and disposal include many assumptions. To
obtain transportation and disposal area capital and O&M costs for
the different alternatives, detailed calculations were performed.
Budget estimates of capital costs for the in-plant handling systems
based on 17 percent of the capital cost (11) plus 8.5 percent
inflation. The cost of in-plant handling systems has been sum-
marized in Table 9-3. These costs reflect only the average of
suppliers whose equipment is commonly installed in power plants
within the United States. These costs varied appreciably as shown
on Table 5-2. Appendices B and C are line item cost estimates for
the 2600 MW power plant with a lined disposal area in a narrow
valley. Dry compacted ash disposal is detailed in Appendix B and
wet disposal is detailed in Appendix C. Line item cost estimates
were made for each of the disposal system alternatives for the five
power plants. In addition to the total cost of disposal, the cost
per ton of dry ash disposed was developed to provide a common basis
for comparison of disposal costs. This analysis is included in
Tables 9-4 and 9-5. To illustrate the effect of the in-plant
handling system on overall system economics, Table 9-6 was devel-
oped to indicate the total system cost of the transportation and
disposal area only.
COST ANALYSIS RESULTS
The results of the cost analysis indicated a range of disposal
costs as follows:
RANGE OF ASH DISPOSAL COSTS ($/DRY TON DISPOSED)
Present Worth Total System Cost
Dry Disposal $2.19 - $4.50 $20.65 - $40.00
Wet Disposal $1.86 - $5.68 $15.93 - $42.30
The results of these analyses, as shown in Tables 9-1, 9-3, 9-4,
and 9-5, indicate comparisons of both wet and dry options, trans-
port options, disposal area topography, use of a liner and ash
compaction.
-------
Table 9-3
COST ANALYSIS*
IN-PLANT HANDLING SYSTEM
(ALL COSTS IN MILLION $)
Item
300 MW
600 MW
900MW
1300 MW
2600 MW
CAPITAL COST
Wet
Dry
WEIGHTED CAPITAL COST
Wet
Dry
3 5 -YEAR O&M COST
Wet
Dry
PRESENT WORTH OF
3 5 -YEAR O&M COST
Wet
Dry
SYSTEM PRESENT WORTH
Wet
Dry
SYSTEM TOTAL COST
wet
Dry
0.9
2.8
7.0
21.7
32
100
.8
2.6
1.7
5.4
39.0
121.7
1.9
4.3
14.7
33.4
67
153
1.8
4.0
3.7
8.3
81.7
186.4
2.8
6.5
21.7
50.4
100
231
2.6
6.0
5.4
12.5
121.7
281.4
3.7
8.5
28.7
65.9
132
302
3.4
7.8
7.1
16.3
160.7
367.9
8.5
19.5
65.9
151.2
302
693
7.8
18.0
16.3
37.5
367.9
844.2
*A11 costs in million dollars.
CTi
U)
-------
Table 9-4
ASH DISPOSAL SYSTEM
COST PER DRY TON DISPOSED AT PRESENT WORTH COST
(ALL COST IN $)
300 MW
600 MW
900 MW
1300 MW
2600 MW
Disposal Method
PIPELINE
Wet
25'
50'
N
W
TRUCK TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
BELT CONVEYOR
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
PNEUMATIC
CONVEYOR
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
With
Liner
4.69
5.68
2.83
2.95
4.06
3.92
4.16
4.34
3.79
3.78
3.88
4.13
4.21
4.07
4.31
4.50
3.95
3.94
4.03
4.29
3.94
3.80
4.04
4.22
3.67
3.66
3.76
4.01
Without
Liner
3.12
4.85
2.24
2.20
3.63
3.53
3.71
3.85
3.45
3.44
3.51
3.70
3.79
3.69
3.87
4.00
3.60
3.59
3.67
3.86
3.52
3.41
3.60
3.73
3.33
3.32
3.39
3.58
With
Liner
4.14
4.25
2.53
2.59
3.33
3.03
3.37
3.85
3.09
2.89
3.15
3.42
3.30
2.99
3.34
3.82
3.06
2.86
3.12
3.38
3.19
2.89
3.23
3.71
2.95
2.75
3.01
3.28
Without
Liner
2.61
3.50
2.04
1.97
2.97
2.74
3.00
3.35
2.80
2.65
2.84
3.04
2.94
2.71
2.97
3.32
2.77
2.62
2.81
3.01
2.83
2.60
2.86
3.21
2.66
2.51
2.70
2.90
With
Liner
3.92
3.74
2.40
2.42
3.27
2.90
3.24
3.53
3.02
2.76
3.02
3.38
3.18
2.81
3.15
3.44
2.93
2.67
2.93
3.29
3.13
2.76
3.10
3.39
2.87
2.62
2.88
3.24
Without
Liner
2.41
3.01
1.95
1.91
2.93
2.65
2.90
3.11
2.74
2.55
2.75
3.01
2.84
2.56
2.82
3.03
2.66
2.47
2.66
2.92
2.78
2.51
2.76
2.97
2.60
2.41
2.61
2.92
With
Liner
3.73
3.37
2.26
2.26
3.08
2.67
2.97
3.13
2.80
2.51
2.76
2.96
2.97
2.55
2.86
3.01
2.69
2.40
2.65
2.85
2.94
2.53
2.84
2.99
2.67
2.38
2.63
2.83
Without
Liner
2.22
2.66
1.86
1.84
2.74
2.44
2.66
2.78
2.54
2.33
2.52
2.66
2.63
2.33
2.55
2.67
2.43
2.22
2.40
2.55
2.61
2.30
2.53
2.64
2.41
2.19
2.38
2.53
With
Liner
3.69
3.14
2.21
2.29
3.19
2.74
2.85
2.89
2.92
2.59
2.75
2.79
3.05
2.59
2.71
2.74
2.78
2.44
2.61
2.65
3.05
2.60
2.71
2.74
2.78
2.45
2.61
2.65
Without
Liner
2.20
2.44
1.93
1.99
2.87
2.53
2.62
2.64
2.67
2.43
2.55
2.58
2.72
2.39
2.48
2.50
2.53
2.28
2.40
2.43
2.73
2.39
2.48
2.50
2.53
2.29
2.41
2.44
25', 50', 75', 150' = Depth of disposal area
N = Narrow valley
W = Wide valley
C - Compacted
UC = Uncompacted
-------
Table 9-5
ASH DISPOSAL SYSTEM
COST PER DRY TON AT TOTAL SYSTEM COST
(ALL COSTS IN $)
300 MW
600 MW
900 MW
1300 MW
2600 MW
Disposal Method
PIPELINE
Wet
25'
50'
N
W
TRUCK TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
BELT CONVEYOR
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
PNEUMATIC
CONVEYOR
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
With
Liner
41.15
48.78
26.76
27.63
36.84
35.69
37.56
39.00
34.82
34.82
35.54
36.56
41.59
40.43
42.30
43.74
39.57
39.57
40.29
42.30
37.41
36.26
38.13
39.57
35.40
35.40
36.12
38.13
Without
Liner
28.92
42.30
22.16
21.87
33.53
32.66
34.10
35.11
32.23
32.09
32.66
34.10
38.27
37.56
38.85
40.00
36.98
36.84
37.41
38.85
34.10
33.38
34.68
35.83
32.81
32.66
33.24
34.68
With
Liner
34.68
35.54
22.30
22.68
29.71
27.34
30.00
33.67
27.84
26.40
28.35
30.43
30.72
28.35
31.01
34.89
28.85
27.41
29.35
31.44
29.07
26.69
29.43
33.10
27.27
25.76
27.70
29.79
Without
Liner
22.81
29.71
18.35
17.84
26.84
25.11
27.12
29.79
25.61
24.53
25.97
27.48
27.92
26.12
28.13
30.79
26.62
25.54
26.98
28.49
26.26
24.53
26.48
29.21
25.04
23.89
25.40
22.59
With
Liner
32.47
31.08
20.62
20.86
28.83
25.95
28.54
30.84
27.87
25.85
27.92
30.70
28.68
25.76
28.44
30.65
27.68
25.66
27.72
30.51
27.87
24.99
27.68
29.88
26.91
24.89
26.96
29.74
Without
Liner
20.72
25.42
17.17
16.93
26.14
24.03
26.00
27.63
25.76
24.27
25.76
27.82
26.00
23.84
25.80
27.44
25.57
24.08
25.61
27.63
25.18
23.07
24.99
26.67
24.80
23.31
24.85
26.86
With
Liner
30.57
27.82
19.15
19.19
27.45
24.27
26.62
27.82
25.36
23.10
25.06
26.59
26.69
23.50
25.86
27.09
24.60
22.34
24.30
25.83
26.42
23.24
25.59
26.79
24.33
22.04
24.00
25.56
Without
Liner
18.92
22.28
16.10
15.93
24.86
22.51
24.27
25.13
23.34
21.68
23.10
24.27
24.10
21.74
23.50
24.37
22.57
20.91
22.34
23.50
23.80
21.48
23.20
24.10
22.31
20.65
22.08
23.20
With
Liner
29.55
25.23
18.04
18.66
27.92
24.40
25.31
25.54
26.19
23.60
24.88
25.20
26.66
23.14
24.05
24.30
24.95
22.34
23.64
23.93
26.77
23.25
24.17
24.42
25.06
22.47
23.75
24.05
Without
Liner
17.98
19.84
15.85
15.95
25.41
22.82
23.52
23.67
24.28
22.37
23.30
23.52
24.17
21.58
22.24
22.42
23.02
21.11
22.06
22.28
24.28
21.69
22.36
22.54
23.14
21.23
22.18
22.41
Key: 25', 50', 75', 150' = Depth of disposal area
N = Narrow valley
W = Wide valley
C = Compacted
UC = Uncompacted
-------
Table 9-6
ASH DISPOSAL SYSTEM (TRANSPORTATION + DISPOSAL AREA)
TOTAL SYSTEM COST
(ALL COSTS IN MILLION $)
300 MW 600 MW 900 MW 1300 MW 2600 MW
With Without With Without
Liner Liner Liner Liner
785 434 1469 772
702 535 1209 884
441 349 776 644
442 344 813 650
459 381 838 687
363 310 626 531
434 363 681 573
470 389 695 582
396 335 734 619
328- 285- 578 504
387 328 655 560
433 363 674 573
436 358 762 612
340- 287- 550- 456-
411 340 605 496
448 366 620 507
373 312 659 543
305- 262- 502* 428*
364 305 580 485-
410 340 598 498
428 349 769 619
332- 279- 557- 463-
403 331 612 503
439 358 627 514
365 304 666 550
296* 254* 510- 435-
355 297 587 492-
402 331 605 506
Disposal Method
PIPELINE
Wet
25'
50'
N
W
TRUCK TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
CONVEYOR TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
PNEUMATIC
TRANSPORT
Dry-C
75'
150'
N
W
Dry-C
75'
150'
N
W
*Least cost option
With
Without
Liner Liner
253
306
153-
159-
135-
127-
140
150
121*
121*
126-
140
168
160
173
183
154
154
159
173
139-
131-
144
154
125-
125-
130-
144
per
168
261
121
119
112-
106-
116-
123
103-
102*
106-
116-
145
140
149
157
136
135
139
149
116-
111-
120
128
107-
106-
110-
120
column .
•Less than 15 percent greater than
With
Liner
413
425
241
246
227
194-
231
282
201
181-
208
237
241
208
245
296
215
195-
222
251
218
185-
233
274
193
172*
199
228
least cost
Without
Liner
248
344
186
179
187
163-
191
228
170
155-
175
196
202
177
205
242
184
169
189
210
179
155-
182
220
162-
146*
167-
188
option.
With
Liner
574
545
327
332
320
260
315
362
300
258-
301
359
317
256-
312
358
296
254-
297
355
300
240-
296
342
280
238*
281
339
Without
Liner
329
427
255
250
264
220-
261
295
256
225-
256
299
261
216-
257
291
252
221-
253
295
244
200*
240
275
236
205-
237
279
Key; 25' , 50' , 75' , 150' = Depth of disposal area C = Compacted
N = Narrow valley UC = Uncompacted
W = Wide valley
-------
67
A comparison between Tables 9-1 and 9-2 does not indicate a
significant difference in ash system economics based on the method
of analysis. Present worth analysis, as shown in Table 9-1, indi-
cates that wet disposal is typically the least cost alternative.
However, various dry disposal options are within a 15 percent range
of those costs. The costs are, in fact, sensitive to spreading the
dry disposal area capital costs over the life of the power station
and the in-plant handling system cost. Use of either the lower
dilute phase transport system cost or the dense phase collection
system cost results in the dry disposal system alternative becoming
the least cost alternative. Review of Table 9-1 with respect to
disposal area topographic condition indicates that although wet
disposal may be the least cost option for valley areas, it is not
economical for flat disposal areas. Total system analysis, as
shown in Table 9-2, also indicates that although wet disposal is
the typical least cost alternative, dry disposal is often a rea-
sonable alternative. Again, as in Table 9-1, dry disposal is the
least cost alternative for flat areas.
To provide a cost comparison between this analysis and other
ash disposal cost studies, Table 9-6 has been included. Table 9-6
provides a total system cost analysis for only the transportation
and disposal area. This analysis indicates that dry disposal is
the typical least cost alternative.
In reviewing both the method and results of the economic anal-
ysis, it becomes apparent that the cost differential of the in-
plant handling systems is sufficient to drastically alter the
selection of the least cost option. This is readily apparent in a
comparison of Tables 9-2 and 9-6. In reviewing Table 9-6, which
includes the total system cost of the transportation and disposal
portions of the disposal system, one can conclude that dry disposal
is typically less expensive than wet disposal. In addition, it can
be seen that flat dry sites are always the least cost alternative.
However, when Table 9-2 is reviewed, which includes the total
system cost of the in-plant handling system with the transportation
and disposal area cost, one can conclude that wet disposal provides
a significant number of the least cost alternatives although the
majority of least cost options are dry alternatives. Also, the wet
valley sites are typically the lesser cost of the wet options.
As the above comparison between cost estimates with and with-
out in-plant handling systems indicates, the in-plant system cost
alters the selection of the least cost system. Due to the magni-
tude of this change, a review of in-plant handling economics is in
order.
The capital costs of the in-plant ash handling systems were
obtained by the equipment suppliers based on the assumptions pro-
vided in Appendix A. Due to the similarities of their estimates
and the plant generalities involved, these estimates were averaged
and rounded off. To provide for an annual O&M cost of the in-plant
system, an annual charge of 17 percent of the system capital cost
was assessed to cover operation, maintenance, replacement, etc.
-------
68
This annual cost was then inflated at the 8.5 percent inflation
rate and a total system O&M cost determined. Table 9-3 indicates
the capital and O&M costs involved with the in-plant system. Since
these costs are sufficient to alter the final system selection, and
due to the lack of specificity in the 17 percent O&M cost, a review
of the effects of O&M is in order. Table 9-7 includes a re-
analysis of the in-plant system O&M based on a 5 percent and 10
percent factor. These O&M costs have been used to revise the total
system cost estimates for the 1300 and 2600 MW power plants. This
comparison is shown in Table 9-8 and indicates that as the O&M cost
of the in-plant handling system decreases, the use of dry disposal
becomes more desirable. As previously mentioned, the variations in
budget estimates from the manufacturers is significant. Using
either an average of the most experienced U. S. suppliers or the
higher costs of those suppliers leads to the results reported
herein. However, if the lower estimates are utilized in the cost
estimates, then it can be concluded that the dry systems do provide
the least cost system.
The above analyses were performed on data that would generally
be considered preliminary estimates and as such be accurate within
25 percent. Due to the variance of these estimates, site specific
conditions could alter the ranking of the disposal systems alterna-
tives. Thus, these analyses should only be used for generally
comparative purposes. In addition, site specific conditions could
substantially alter the analyses and, ultimately, the ranking. A
specific example would be a site where a dam or levee would produce
a disproportionate storage volume. Other situations could preclude
the use of a specific system. An example would be a site which was
not amenable to or was unsuitable for other reasons such as exces-
sive leakage, unstable dam abutments, etc.
In addition, the above analyses assumed construction of all
the required facilities upon start-up. In the case of dry dis-
posal, this is a reasonable assumption although site preparation
costs would proceed during the development of the site. In the
case of wet disposal, it may be economically sound to construct the
embankment in stages, even if the amount of material to be placed
or the engineering estimate is higher for staged construction.
This is due to the high cost of the dam or levee and the cost of
money over the life of the project. As an example, the 2600 MW
flat, wet disposal area was analyzed by all construction occurring
in 1980 and by a staged construction sequence (3 stages). In this
case, staged construction provided a 30 percent savings in the
total cost of the system.
-------
Table 9-7
COST REVIEW
IN-PLANT HANDLING SYSTEM
(ALL COSTS IN MILLION $)
Item
CAPITAL COST
Wet
Dry
WEIGHTED CAPITAL COST
Wet
Dry
1ST YEAR O&M COST
@ 10 PERCENT
Wet
Dry
@ 5 PERCENT
Wet
Dry
35-YEAR O&M COST
@ 10 PERCENT
Wet
Dry
@ 5 PERCENT
Wet
Dry
PRESENT WORTH OF
35-YEAR O&M COST
@ 10 PERCENT
Wet
Dry
@ 5 PERCENT
Wet
Dry
300 MW
0.9
2.8
7.0
21.7
.09
.28
.045
.14
18.8
58.5
9.4
29.3
0.5
1.5
0.2
0.8
600 MW
1.9
4.3
14.7
33.4
.19
.43
.095
.215
39.7
89.9
19.9
45.0
1.0
2.3
0.5
1.2
900 MW
2.8
6.5
21.7
50.4
.28
.65
.14
.325
58.5
135.9
29.3
68.0
1.5
3.5
0.8
1.8
1300 MW
3.7
8.5
28.7
65.9
.37
.85
.185
.425
77.4
177.7
38.7
88.9
2600 MW
2.0
4.6
1.0
2.3
8.
19
65.9
151.2
.85
1.95
.425
.975
177.7
407.7
88.9
203.9
4.6
10.6
2.3
5.3
01
-------
Item
Table 9-7
COST REVIEW
IN-PLANT HANDLING SYSTEM
(Continued)
300 MW
600 MW
900 MW
1300 MW
2600 MW
PRESENT SYSTEM WORTH
@ 10 PERCENT
Wet
Dry
@ 5 PERCENT
Wet
Dry
TOTAL SYSTEM COST
@ 10 PERCENT
Wet
Dry
@ 5 PERCENT
Wet
Dry
1.4
4.3
1.1
3.6
25.8
80.2
16.4
51.0
2.9
6.6
2.4
5.5
54.4
123.3
34.6
78.4
4.3
10.0
3.6
8.3
80.2
186.3
51.0
118.4
5.7
13.1
4.7
10.8
106.1
243.6
67.4
154.8
13.1
30.1
10.8
24.8
243.6
558.9
154.8
355.1
-------
Table 9-8
TOTAL SYSTEM COST COMPARISON FOR
ALTERNATE IN-PLANT HANDLING SYSTEM O&M COSTS
(ALL COSTS IN MILLION $)
5 Percent O&M
10 Percent O&M
17 Percent O&M
1300 MW
With Without
Disposal Method
PIPELINE
Wet
25'
50'
N
W
TRUCK TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
Liner Liner
852
794
534
535
614
518-
589
625
551
483
542
588
501
602
416-
411-
536
465-
518
544
490
440-
483
517
2600 MW
With Without
Liner Liner
1623 926
1363 1038
848* 798-
886- 804-
1193 1042
981- 886-
1036 928
1050 937
1089 974
933- 859-
1010 915
1029 929
1300 MW
With
Liner
891
808
547-
548-
703
607-
678
714
640
572-
631
677
Without
Liner
540
641
455-
450*
625
554
607
633
579
529
572
591
2600 MW
With
Liner
1713
1453
1020*
1057-
1397
1185
1240
1254
1852
1137-
1214
1233
Without
Liner
1016-
1128
888*
894-
1246
1090
1132
1141
1178
1063
1119-
1133
1300
With
Liner
921
838
577*
578-
827
731
802
838
764
696
755
801
MW
Without
Liner
570
671
485-
480*
749
678
731
757
703
653
696
731
2600
With
Liner
1780
1520
1087*
1124-
1682
1470
1525
1539
1578
1422
1499
1518
MW
Without
Liner
1083-
1195
955*
961-
1531
1375
1417
1426
1463
1348
1404
1417
CONVEYOR TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
PNEUMATIC
TRANSPORT
Dry-UC
75'
150'
N
W
Dry-C
75'
150'
N
W
*Least cost option
591
495-
566
603
528
460-
519
565
583
487-
558
594
520
451*
510-
557
for
•Less than 15 percent
Key: 25', 50',
75',
513
442-
495
521
467-
417-
460-
495
504
434-
486
513
459-
409*
452-
486
station size
greater than
150' = Depth
1117 967
905- 811
960- 851-
975- 862-
1014 898-
857* 783*
935- 840-
953- 853-
1124 974
912- 818-
967 858-
982 869-
1021 905
865- 790-
942- 847-
960- 861-
.
least cost option.
of disposal area
N = Narrow valley
W = Wide
valley
680
584-
655
692
617-
549-
608-
654
672
576-
647
683
609-
540*
599-
646
C =
UC =
602
531
584
610
556
506-
549
584
593
523
575
602
548
498-
541
575
Compacted
Uncompacted
1321
1109-
1164-
1179
1218
1061
1139-
1157-
1328
1116-
1171-
1186
1225
1069-
1146-
1164-
1171
1015-
1055
1066
1102
987-
1044
1057
1178
1022
1062
1073
1109
994-
1051
1065
804
708
779
816
741
673
732
778
796
700
771
807
733
664-
723
770
726
655
708
734
680
630
673
708
717
647
699
726
672
622
665
699
1606
1394
1449
1464
1503
1346-
1424
1442
1613
1401
1456
1471
1510
1354
1431
1449
1456
1300
1340
1351
1387
1272
1329
1342
1463
1307
1347
1358
1394
1279
1336
1350
-------
72
SECTION 10
CONCLUSIONS
Upon review of the economic comparisons described in Sec-
tion 9, it becomes apparent that the method of economic analysis is
not a primary factor in the selection of an ash disposal system.
The system selection is dependent more on site topography and
in-plant handling system costs. In general, dry ash disposal is
the least cost alternative for flat areas whereas wet ash disposal
is the least cost option for valley disposal. However, this
assumes that the valley is amenable to wet disposal. Although no
overall system selection generalities can be made, certain trends
have been identified for the specific conditions studied. These
include:
o Dry compacted ash disposal costs less than uncompacted
ash disposal;
o The use of a liner significantly increases the cost of
the ash disposal system and could alter the system selec-
tion from dry to wet or vice-versa;
o As the cost of in-plant handling system O&M is decreased,
the use of dry disposal becomes more advantageous;
o As the volume of ash disposed is increased, the cost per
dry ton disposed, typically decreases;
o Comparison of valley disposal sites is sensitive to
in-plant ash handling costs. A higher level of estimate
for the in-plant handling system cost would be required
to make an economic decision for the type of valley sites
considered in this report. However, a higher level
estimate would require plant layout details which were
not a part of this present study;
o Economic comparisons of valley disposal sites can be
sensitive to the method in which site preparation and
embankment construction is phased. Although the analysis
in this report considered all site preparation and con-
struction to occur in the initial year, spreading site
construction costs over the life of the power plant may
alter the economic decision;
o In-plant handling system costs need further documentation
and refinement. This is apparent since the use of the
lower dilute phase system estimate, the dense phase
system estimate, or an average cost utilizing the dense
phase system results in the conclusion that dry disposal
is cheaper in the valley disposal case.
-------
73
REFERENCES
1. Electric Power Research Institute. Fly Ash Structural Fill
Handbook. EPRI RP-1156. Palo Alto, California.
2. Faber, J. H. and A. M. DiGioia, Jr., "Use of Ash for Embank-
ment Construction". Presented at the Transportation Research
Board Annual Meeting, January 1976.
3. Seals, R. K., Moulton, L. K., and Ruth, B. E., "Bottom Ash:
An Engineering Material," Journal of the Soil Mechanics and
Foundations Division, ASCE, pp. 311-325, April 1972.
4. GAI Consultants, Inc., Investigation of the Use of Coal Refuse -
Fly Ash Compositions as Highway Base Course Material, Interim
Report, FHWA-RD-78-208, October 1979.
5. Electric Power Research Institute. Coal Ash Disposal Manual.
EPRI RP-1404. Palo Alto, California.
6. Delwiche, P., DiGioia, A. M., and Niece, J. E., Evaluation of
Ash Storage Sites - A Case History, presented at the Fifth
International Ash Utilization Symposium, February 25-27, 1979,
Atlanta, Georgia.
7. Personal Communication with H. Colijn.
8. Mills, D., and Mason, J. S. The Interaction of Particle Con-
centration and Conveying Velocity on the Erosive Wear of Pipe
Bends in Pneumatic Conveying Lines. International Bulk Solids
Show. Chicago, Illinois. May 1976.
9. Caterpillar Tractor Company. Caterpillar Performance Handbook.
Peoria, Illinois. 1978.
10. Midwest Research Institute, Environmental Systems Section.
St. Louis Demonstration Project Final Report: Power Plant
Equipment Facilities and Environmental Evaluations (Volume II).
Kansas City, Missouri. 1976.
11. Barrier, J. W., Faucett, H. L., and Henson, L. J., Economics of
Disposal of Lime/Limestone Wastes: Untreated and Chemically
Treated Wastes, TVA, Muscle Shoals, Alabama, 1978.
-------
APPENDIX A
DESIGN CONDITIONS
-------
A-l
Table A-l
POWER PLANT CHARACTERISTICS
Boiler Type
Coal Heat Content
Coal Type
Plant Heat Rate
Plant Life
Plant Capacity Factor
Plant Generating Capacity
Plant Location
Plant Altitude
In-Plant Ash Transport
Distance
Fly Ash to Bottom Ash Ratio
Coal Ash Content
Particulate Removal Devices
Fly Ash Collection
Efficiency
Distance to Ash Disposal
Site
Pulverized Coal Dry Bottom
10,500 btu/lb
Subbituminous
10,000 btu/kw hr
35 Years
80 Percent
300 MW, 600 MW, 900 MW, 1300 MW,
2600 MW
Southeastern U. S.
Less than 2,000 feet (msl)
400 Feet
80:20
20 Percent
Cold-Side Electrostatic
Precipitators
99 Percent
1 Mile
-------
A-2
Table A-2
ASH QUANTITIES
Plant Size Bottom Ash Fly Ash
(MW) (tons/day)* (tons/day)*
300 110 434
600 219 869
900 329 1303
1300 475 1883
2600 951 3765
*Daily average based on 80 percent load factor.
-------
A-3
Method of
Ash Placement
Wet (Slurry)
Dry Uncompacted
Dry Compacted
Table A-3
ASH DENSITIES*
Bottom Ash
(lb/ft3)
60
80
100
Fly Ash
(lb/ft3)
40
60
80
*A11 densities are expressed as dry bulk densities.
-------
A-4
Table A-4
SITE PREPARATION COSTS
Land
Drainage Ditch (dry site)
Clearing and Grubbing
Stripping and Stockpiling
Soil
Seeding
Haul Road
Site Liner
Drainage Blanket (dry site)
8-Inch Diameter Drainage Pipe
(dry site)
Embankment Construction
(wet site)
Sedimentation Pond
(dry site)
Appurtenances (wet site)
High embankment (>50')
Low embankment (<50*)
$l,500/acre
$30/linear foot
$l,500/acre
$3/cubic yard
$l,000/acre
$20/linear foot
$5.50/square yard
$1.50/square foot
$10/linear foot
$5/cubic yard
$15,000 each
$100,000
$25,000
-------
A-5
Table A-5
MACHINE OPERATING COSTS
Operator $20.16/hr*
Oiler $12.75/hr*
Fuel $ 1.00/gallon
Maintenance
Front-end loader - Cat 9666 $ 0.50/hr
Dredge - Mud Cat MC-915 $ 0.66/hr
25-ton triaxle truck $ 0.60/hr
*Man-hour costs are twice the hourly pay rate to
include benefits and supervision.
Note: Payrates were estimated from the Tennessee
Valley Authority Schedule of Trades and
Labor Classifications, Minimum hourly rates
of pay and minimum fringe benefits on work
performed under TVA Contract.
-------
A-6
Table A-6
DRY DISPOSAL SITE CHARACTERISTICS
Fill Height
Flat Site
Valley Site
Fill Width
Flat Site
Valley Site
Fill Side Slopes
Maximum
Overall
Terrace Height
Terrace Width
Drainage Blanket Thickness
Drainage Ditch Length
Drainage Pipe Length
Haul Road (on-site)
75 and 150 feet*
As Required
2,500 feet
As Required
3 horizontal to 1 vertical
4 horizontal to 1 vertical
25 feet
25 feet
1 foot
1.5 x site perimeter**
2 x site length**
.5 x site length**
NUMBER OF SEDIMENTATION PONDS (DRY SITE)
300 MW, 600, MW, 900 MW
1300 MW
2600 MW
1
2
4
*Both cases considered to allow for specific site variations
in soils, geology and topography.
**General design conditions based on disposal areas located in
similar topographic areas.
-------
Table A-7
ASH HAULING AND PLACEMENT EQUIPMENT
Equipment
Initial Cost
Estimated Life
Front-end loader (Cat 966C)
Roller (Essex 42 RTE)
25-ton triaxle
$119,000
24,000
65,000
7 yrs
15 yrs
10 yrs
(International Harvester 5,070)
Dredge (Mud Cat MC-915)
103,266**
Fuel Consumption
8.4 gal/hr
8.0 gal/hr***
6.5 gal/hr
Cycle Time"
13.5 rain
*Time required to load, haul one mile, dump, and return to reload.
**Rental cost for one year. Actual site costs were based on utilizing a dredge for redistributing the
ash on an occasional basis based on pond size.
***A1though 5.0 gallons per hour was used in the truck transport comparison (Table 7-2), 8.0 gallons per
hour were utilized in the final estimates to compensate for the effects of haul road grades, idling,
inefficient operation, and other variable factors.
-------
A-8
Table A-8
DRY DISPOSAL YEARLY OPERATIONAL HOURS
Plant Size
Front-end loader
Roller
Oiler
Operator
Front-end loader
Oiler
Operator
300
600
100
300
800
600
COMPACTED
1600
400
800
2000
UNCOMPACTED
500
300
600
1200
600
1400
900
SITE
2400
400
1200
3000
SITE
2000
1000
2400
1300
3400
600
1600
4000
2800
1400
4000
2600
5000
1000
2000
6000
4000
2000
5000
-------
A-9
Table A-9
WET DISPOSAL SITE CHARACTERISTICS
Embankment Heights
Width of Embankment
(Flat Site Only)
Freeboard
Embankment Crest Width
Embankment Side Slopes
25 and 50 feet*
5000 feet
5 feet
25 feet
3 horizontal to 1 vertical
*Both cases considered to allow for specific variations in
soils, geology and topography.
-------
A-10
Table A-10
ASH SLURRY PUMPS
Plant Size Pump Size Pump
(MW) (HP) Cost ($)*
300 50 $3,500
600 60 3,500
900 75 5,200
1,300 100 5,200
2,600 125 5,200
*Purchase price based on manufacturers data.
-------
A-ll
Table A-ll
ASH SLUICE LINES*
Plant Size
(MW)
300
600
900
1300
2600
Slurry Pipe
Diameter (in. )
8
8
10
10
12
Pipe Cost**
($/ft)
$10.46
10.46
13.27
13.27
15.64
Number of
Pipelines***
3
4
4
5
7
Total
Pipeline
Cost
($/ft)
$ 31.38
41.84
53.08
66.35
109.48
*Sluice lines were assumed to have a four-year life.
**Installed cost per linear foot of a single cast iron pipe.
***Number of pipelines includes one additional line to allow
for maintenance and/or breakdowns.
-------
A-12
Table A-12
SLURRY PIPELINE CHARACTERISTICS
Slurry
Slope to Disposal Site
Distance to Disposal Site
Maximum Flow
Pumping TDK
System Operation
10 Percent Solids
10 Percent
1 Mile
2 x Average
100 Feet
7 days/week;
24 hours/day
-------
Table A-13
RETURN WATER LINES*
Plant Size
(MW)
300
600
900
1300
2600
Design
Flow
(cfs)
5.3
10.6
15.9
22.9
45.8
Pipe Diameter
(in.)
10
14
12
14
16
Pipe Cost**
($/ft)
$13.27
18.64
15.64
18.64
24.80
Number of
Pipelines***
2
2
3
3
4
Total
Pipeline
Cost
($/ft)
$26.54
37.28
46.92
55.92
99.20
*Water return lines were assumed to have a 20-year life.
**Installed cost per linear foot of a single cast iron pipe.
***Number of pipelines includes one additional line to allow for maintenance and/or breakdowns.
i
M
U>
-------
A-14
Table A-14
WET DISPOSAL YEARLY MAINTENANCE HOURS
Plant Size (MW)
300
200
200
200
500
600
400
400
400
1000
900
600
600
600
1500
1300
800
800
800
2000
2600
1000
1000
1000
3000
Front-end loader
Dredge
Oiler
Operator
Note: Maintenance hours were based on typical pond
embankment maintenance/repair conditions.
-------
A-15
Table A-15
BELT CONVEYOR**
Plant Size Belt Width Cost*
(MW) (in.) (Million Dollars)
300 18 2.38
600 18 2.38
900 18 2.38
1,300 18 2.38
2,600 36 2.97
*Cost for installed enclosed belt conveyor as supplied by
Can-Belt International.
-------
A-16
Table A-16
FLY ASH STORAGE SILO
Plant Size Silo Capacity Installed Cost*
(MW) (tons) (million dollars)
300 2,310 .35
600 4,620 .70
900 6,930 1.10
1,300 10,011 1.55
2,600 20,022 2.95
*Cost for installed silo as supplied by First Colony Corporation,
-------
APPENDIX B
-------
B-l
APPENDIX B
LINE ITEM COST ESTIMATE
2600 MW POWER PLANT WITH DRY ASH DISPOSAL
NARROW VALLEY WITH LINER
Design Conditions:
Plant:
Size (units) 2600 MW (3 at 867 MW)
Disposal Method Dry Disposal (compacted)
Disposal Area Narrow Valley with Liner
Plant Load Factor 80 Percent
Fly Ash Collection Efficiency 99 Percent
Ash Content 20 Percent
Fly Ash/Bottom Ash Ratio 80/20
CALCULATION OF WASTE QUANTITIES
1. Coal Consumption
a. @ 100 Percent Load Factor
2600 (
b. @ 80 Percent Load Factor
1238 '
10/845,714(t"ggg1)x0.80 = 8, 676, 571 (
2. Ash Produced
a. Total Ash @ 100 Percent Load Factor
1238
10,845,714(^|ffi)x0.20 = 2 , 169, 143
-------
B-2
@ 80 Percent Load Factor
b. Fly Ash - @ 100 Percent Load Factor
248(t"ash)x0.80 = igSf^^
hour hour
@ 80 Percent Load Factor
c. Bottom Ash - @ 100 Percent Load Factor
248 '0'20 = 50(Ho?I)
2,169,143 (|j||^)x0.20 = 433,829(^||)
@ 80 Percent Load Factor
433,829(i)x0.80 = 347,063()
-------
B-3
ESTIMATED COST OF A NARROW VALLEY DRY ASH DISPOSAL AREA
1. Assumptions:
Useful Life 35 yrs
Power Station Load Factor 80 Percent
Depth of Fill 200 ft
Compacted Density 80 Ib/ftf
Dry Density of Fly Ash 60 Ib/ft
Side Slopes 3 horizontal to 1 vertical
Benches 25 ft high
2. Design Parameters:
Site Perimeter = 14,520 fta
Site Length = 6,400 fta
On-Site Haul Road Length = 1/2 x Site Length = 3,200 ft
Drainage Ditch = 1.5 x Perimeter = 21,780 ft
Drainage Pipe = 2 x Site Length = 12,800 ft
Area = Top Surface Area + Bench and Embankment Area*
= 436 +23.5
= 459.5 acres
Stripping and Stockpiling 6" Topsoil
2
459.5(acres) x 43,560( ——) x — ( —) x 6(in) x — (^-) = 370,663 yd3
acre 12 in 27 -.3
Underdrainage Blanket
459.5(acres) x 43,560(——) = 20,015,820 ft2
3.C1T6
Liner
2 2
459.5(acres) x 43,560( ——) x ^(^-) - 2,223,980 yd2
acre y ft^
aAreas planimetered from preliminary design drawings.
-------
B-4
3. Site Preparation Costs:
Land
459.5 acres x $l,500/acre = 689,250
Sedimentation Pond
4 x $15,000 each = 60,000
Drainage Pipe, 8" (j>
12,800 LF x $10/LF = 128,000
Drainage Ditches
21,780 LF x $30/LF = 653,400
Underdrainage Blanket
20,015,820 SF x $1.50/SF = 30,023,730
Clearing and Grubbing
459.5 acres x $l,500/acre = 689,250
Stripping and Stockpiling 6" Topsoil
370,663 CY x $3/CY = 1,111,989
Seeding
459.5 acres x $l,000/acre = 459,500
On-Site Haul Road
3200 LF x $20/LF = 64,000
Liner
2,223,980 SY x $5.50/SY = 12,231,890
Site Preparation Capital Costs = $46,111,009
For present worth analysis, the initial equipment purchase is
included with the capital cost.
[$46,111,000 + $286,000 = $46,397,000] (see Section 4g and 4h).
4. Site Operation Costs:
a. Front End Loader (Caterpillar 966C)
No. Required On-Site 2
Estimated Life 7 years
Present Cost $119,000/unit
Total Capital Cost of Units
-------
B-5
e.
Year
1
7
14
21
28
Total
Capital Cost @ 2 Units Every 7 Years
$ 238,000
421,294
745,750
1,320,084
2,336,730
$5,061,800
Towed Roller (Essex 42RTE, 3-5 ton)
No. Required On-Site
Estimated Life
Present Cost
Total Capital Cost of Units
Year
1
15
Total
Oiler
Hourly Wages
Overhead Rate
Total Wage Cost/Hour
On-Site Hours/Year
Yearly Cost
Operator
Hourly Wages
Overhead Rate
Total Wage Cost/Hour
On-Site Hours/Year
Yearly Cost
Fuel
Fuel Consumption Rate
Fuel Cost
Yearly Operating Hours
Yearly Fuel Cost
Maintenance and Lubrication
Average Cost
Yearly Operating Hours
Yearly Cost
15 years
$24,000/unit
Capital Cost
$ 48,000
200,106
$248,106
$6.375/hr
2.0
$12.75
2,000
$25,500
$10.08/hr
2.0
$20.16/hr
6,000
$120,960
8.4 gal/hr
$1.00/gal
5,000
$42,000
$0.50/operating hour
5,000
$2,500
-------
B-6
g. Site Operation Capital Cost
Front End Loader $5,061,800
Towed Roller 248,000
Total $5,309,800
h. Site Operation Annual Costs0
Oiler $ 25,500
Operator 120,960
Fuel 42,000
Lube & Misc. 2,500
Total $190,960
i. Site Operation 35-Year Total Cost @ 8.5 Percent Inflation
$190,960[<1 + 0>°5 — -1] = $39,926,165*
For present worth analysis, only the initial equipment purchase is
considered a capital expense. Therefore:
O&M Capital = $238,000 + $48,000 = $286,000
35-Year O&M = $39,926,000 + [5,309,800 - 286,000] = $44,950,000
5. Transportation Cost:
a. Capital Cost
Assumes truck transport via 25-ton triaxle diesel trucks
(see Tables 7-1 and 7-2).
No. of Trucks Required 8
Estimated Life 10 years
Present Cost $65,000/unit
Total Capital Cost of Units
Year Capital Cost
1 $ 520,000
10 1,175,712
20 2,658,264
30 6,010,288
Total $10,364,264
-------
B-7
However, only the initial purchase of 8 trucks is con-
sidered to be a capital cost under present worth analysis
Therefore, only $520,000 is considered a capital cost
for the present worth analysis.
b. Operation and Maintenance Cost (O&M)
Oiler
Hourly Wages
Overhead Rate
Total Wage Cost/Hour
Hours/Year
Yearly Cost
Operator
Hourly Wages
Overhead Rate
Total Wage Cost/Hr
Hours/Year
Yearly Cost
Fuel
Fuel Consumption Rate
Fuel Cost
Yearly Operating Hours
Yearly Fuel Costs
Maintenance and Lubrication
Average Cost
Yearly Operating Hours
Yearly Cost
$6.375/hr
2.0
$12.75
8,000
$102,000
$10.08/hr
2.0
$20.16/hr
$16,000
$322,560
8 gal/hr
$1.00/gal
15,700
$125,600
$0.60/operating hour
15,700
$9,420
Annual Operation and Maintenance Cost
Oiler
Operator
Fuel
Lube & Misc.
Total
$102,000
322,560
125,600
9,420
$559,580
Transportation Operation and Maintenance 35-Year Cost @
8.5 Percent Inflation
$559,580[J
0.085)
•ac.fi
JS x
0.085
--1] = 116,996,000'
-------
B-8
For present worth analysis, the future capital cost of the vehicles
may be discounted. Therefore, $10,364,264 - $520,000 or $9,844,264
is added to the O&M Cost for present worth analysis.
[$116,996,000 + $9,844,264 = $126,840,000]
6. In-Plant Handling System:
Capital Cost**
( **Manuf acturers ' data )
$19,500,000
Annual Operation and Maintenance Cost
Percent of Capital Cost $3,315,000
35-Year O&M Cost @ 8.5 Percent Inflation
7. Total System Cost:
Capital Cost
In-Plant
Transportation
Disposal Area
Total
Weighted Cost of Capital
Operation and Maintenance
In-Plant
Transportation
Disposal Area
Total
Total System Cost
= $693,100,000
$ 19,500,000
10,364,000
46,111,000 + 7,841,000
$ 83,816,000
$649,000,000
$693,100,000
116,996,000
39,926,000
$850,022,000
$1,499,000,000
Inflation Rate:
Cost of Capital:
Discount Rate:
PRESENT WORTH ANALYSIS
8.5%
2.3%
11%
-------
B-9
Capital Cost
Disposal area (see pp. B-4) $46,111,009
Front end loader (see pp. B-4,5)
2xll9,OOOx[l+.84+.71+.60+.50] 868,700
Towed roller (see pp. B-5)
2x24,OOOx[l+.69] 81,120
Trucks (see pp. B-6)
8x65,OOOx[1+.78+.61+.48] 1,492,400
In-plant handling system 19,500,000
Total Capital Cost $68,053,229
Note: Numbers in brackets [] are present worth factors based on the
number of years to the expenditure and a 2.3% cost of capital.
Operation and Maintenance (O&M) Cost
Disposal area (see pp. B-5)
Oiler $ 25,500/year
Operator 120,960/year
Fuel 42,000/year
Maint. and lubrication 2,500/year
Total $190,960/year (see pp. B-6)
190,960x24.5f $ 4,678,520
Present worth factor for an annual expenditure over 35 years at a
2.3% cost of capital.
Transportation (see pp. B-7)
Oiler $102,000/year
Operator 322,560/year
Fuel 125,600/year
Maint. and lubrication 9,420/year
$559,580/year (see pp. B-7)
559,580x24.5 $ 81,217,500
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B-10
In-plant handling system (see pp. B-8)
3,315,000x24.5 $ 81,217,500
Total O&M Cost $ 99,605,730
Present Worth $167,658,900
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APPENDIX C
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C-l
APPENDIX C
LINE ITEM COST ESTIMATE
2600 MW POWER PLANT WITH WET ASH DISPOSAL
NARROW VALLEY WITH LINER
Design Conditions
Plant:
Size (units)
Disposal Method
Disposal Area
Plant Load Factor
Fly Ash Collection Efficiency
Ash Content
Fly Ash/Bottom Ash
2600 MW (3 at 867 MW)
Wet Disposal
Narrow Valley
80 Percent
99 Percent
20 Percent
80/20
CALCULATION OF WASTE QUANTITIES
See Appendix B
ESTIMATED COST OF A NARROW VALLEY WET DISPOSAL SITE
1. Assumptions:
Useful Life
Power Station Load Factor
Embankment Height
Freeboard
Side Slopes
Crest Width
35 yrs
80 Percent
255 ft
5 ft
3 horizontal/1 vertical
25 ft
2. Quantity Computations:
3
Capacity = 103,000,000 yd
Embankment Volume3: 6,341,945 yd
Surface Area at Effective Depth:a
28,332,800 ft
Land Area Required3:
Surface area at effective depth + bench and embankment
area
615 acres +23.5 acres = 638.5 acres
aPlanimetered from preliminary design drawings.
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C-2
Clearing and Grubbing
638.5 acres
Liner
2 2
638.5 (acres) x 43,560 (^-) x - (^-) = 3,090,340 yd2
acre 9 2
3. Site Preparation Costs:
Clearing and Grubbing 638.5 ac x $l,500/ac = $ 957,750
Embankment: 6,341,945 yd3 x $5/yd3 = 31,709,725
Liner 3,090,340 yd2 x $5.50/yd2 = 16,996,870
Land 638.5 ac x $l,500/ac = 957,750
Stripping and Stockpiling 6" Topsoil
515,057 yd3 x $3/yd3 = 1,545,171
Seeding 638.5 ac x $l,000/ac = 638,500
Dam Appurtenances - $100,000 lump sum = 100,000
Disposal Area Capital Cost = $52,905,766
4. Site Operation Costs
a. Front End Loader (Catepillar 966C)
No. required on-site 1
Estimated life 7 years
Present cost $119,000/unit
Total Capital Cost of Units:
Year Capital Cost at 1 Unit Every 7 Years
1 $ 119,000
7 210,647
14 372,875
21 660,042
28 1,168,365
TOTAL $2,530,929
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C-3
Dredge (Mud Cat: SP-810)
No. required on-site
Estimated life
Present cost
Total Capital Cost of Units:
10 years
$75,100
Year
1
10
20
30
Oiler
Capital Cost at 1 Unit Every 10 Years
$ 75,100
169,800
383,900
868,000
TOTAL $1,496,800
Hourly wages
Overhead rate
Total wage cost/hour
On-site hours/year
Yearly cost
Operator
Hourly wages
Overhead rate
Total wage cost/hour
On-site hours/year
Yearly cost
Fuel
Fuel consumption rate
Fuel cost
Yearly operating hours
Yearly fuel cost
Maintenance and Lubrication
Cost
Yearly operating hours
Yearly Cost
Site Operation Capital Cost
$6.375/hour
2.0
$12.75
1,000
$12,750
$10.08
2.0
$20.16
2,000
$40,320
14.9 gal/hour [8.4 + 6.5 =
14.9]
$1.00 gallon
1,000
$14,900
$1.16/hr (0.50 + 0.66 = 1.16)
1,000
$1,160
Frt>nt-end loader
Dredge
$2,530,929
1,596,800
TOTAL
$4,028,000
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C-4
h. Site Operation Annual Cost
Oiler
Operator
Fuel
Lube & Misc
TOTAL
$12,750
40,032
14,900
1,160
$69,130
l.
Site operation 35 years, annual cost @ 8.5% inflation
$69,310
-1] = $14,448,000
For present worth analysis, only the initial equipment purchase
is considered a capital expense. Therefore:
O&M Capital: 119,000 + 75,100 = $194,100
35 year O&M: 14,448,000 + [$4,028,000-194,000] = $18,282,000
5. Transportation Costs
Assumptions:
Useful Life
Power Station Load Factor
Pumping Units
Transport (centrifugal slurry)
Return (centrifugal slurry)
35 years
80 Percent
7
4
Transport:
Pump
Velocity
Slurry
24 hours/day
12 feet/sec
10 percent
Pipes designed for maximum flow
Maximum flow = 2 x average flow with 1 out of service.
2600 MW plant has 104,076,020 yds of ash for wet disposal over
35 years.
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C-5
a. Daily Ash Production
104 076 200 . 219,950 (ft3/day)
b. Maximum flow at 10 percent slurry
219,950 <) x 2 x 10 = 4,399,000
c. Transport Lines
Pipe Cross Sectional Area
- I (day)
4 3QQ ooo (-\ .
a - 2 - ' f lday' x 24(hours) 3600 x(sec) _ . OI
V ~ 12 (ft ) ~ 4-2
(sec)
.-. Need six 12 -inch diameter pipes, with 1 spare. Total need is
7 pipes (7x5280 = 36,960 feet x $15.74/foot = $578,000).
d. Return Lines
Assume only water transport back to plant:
0.9 x 4,399,000 () = 3,959,000
Pipe Cross Sectional Area
» 2 3,959,000 (|g) x £ () x 3 (g) _
A = ^ = - •* - ^rr - - 3.80 (It ;
12
f. Need three 16-inch diameter pipes, with 1 spare. Total need is for
4 pipes (4x5280 = 21,120 x $24.80/foot = $523,776).
e. Capital Cost
Transport Pumps
No . required 7
Estimated Life 4 years
Present cost $5,209/unit
Total capital cost of units
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06
Year 1 $ 35,463
4 50,533
8 70,031
12 97,053
16 134,502
20 186,401
24 258,325
28 358,002
32 596,140
TOTAL $1,687,450
However, only the initial purchase of 7 pumps is considered to be
a capital cost under present worth analysis. Therefore, only $36,463
is considered a capital cost for the present worth analysis.
Return pumps
No. required 4
Estimated life 20 years
Present cost $12,834/unit
Total Capital Cost of Units
Year 1 51,336
20 262,432
TOTAL 313,768
However, only initial purchase of 4 pumps is considered to be a
capital cost under present worth analysis.
Transport Lines
No. required 7
Size 12 inch diameter
Estimated life 4 years
Present cost 578,054
Total capital cost of lines
Year 1 $ 578,054
4 801,101
8 1,110,213
12 1,538,598
16 2,132,280
20 2,955,039
24 4,095,266
28 5,675,460
32 7,865,386
TOTAL $26,751,397
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C-7
However, only $578,054 is considered a capital cost for present
worth analysis.
Return lines
No. required 4
Size 16 inch diameter
Estimated life 20 years
Present cost 523,776
Total capital cost of lines
Year 1 $ 523,776
20 2,667,567
TOTAL $3,201,343
However, only $523,776 is considered a capital cost for present worth
analysis.
Ash Transport Capital Cost
Total Capital Present Worth
_ Item _ _ Cost Capital Cost
Transport Pumps $ 1,687,450 $ 36,463
Return Pumps 313,768 51,336
Transport Lines 26,751,397 578,054
Return Lines 3,281,343 523,776
TOTAL $31,951,000 $1,189,629
f . Operation and Maintenance Cost:
Pump Operation Cost
/ hP ) x 04 (QL.) x 365 fday ) x 0 7457 fkw"hr)
(pump} x 24 lday} x 3b5 (year} x °-74b/ (hp-hr)
Transport pumps: 7 @ 125 hp
Return pumps: 4 @ 150 hp
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C-8
Pumping Cost:
Transport : 7xl25x6532x.0208 = $118,800
Return: 4xl50x6532x.0208 = 81,500
Total Annual Pump Cost
Total 35 Year Pumping Cost
Transport: $118,800x209.1
Return: 81,500x209.1
$200,300
$24,800,000
17,000,000
Transport Pumps
Operation
Replacement
TOTAL
Return Pumps
Operation
Replacement
TOTAL
Transport Lines
Return Lines
TOTAL
Total $41,800,00
35 YEAR O&M COST
Present Worth Cost
Total System Cost (includes replacements)
$24,800,000
$24,800,000
$17,000,000
$17,000,000
d
d
$41,800,000
$24,800,000
1,651,000<
$26,451,000
$17,000,000
272,000C
$17,272,000
$26,173,000(
2,678,000
$72,574,000
'Replacement cost, see ash transport capital cost for details.
O&M was considered as replacement and became part of the capital
cost.
sPump O&M was considered well defined by the cost of electricity
for operation. These costs were computed at a rate of $0.208/kw-hr.
Note: Pump maintenance could be included with the cost of pump O&M;
however, its cost is small compared to the cost of electricity.
For example, if annual pump maintenance is taken at 15% of the
pump capital cost, then:
0.15 x (36,463 + 51,336) = $13,169/year
or
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C-9
+ — i
$13,169 P Q Q85 - - -1] = $2,752,321 (total 35 year cost)
Pump maintanance then provides only 6% of the cost of electricity
which is well within the accuracy of this analysis.
Other maintenance items which could be included are the costs
of pipeline maintenance and water treatment for the recycle
water. It was assumed that a replacement period of 4 years
for the transport lines and 20 years for the return lines
would be adequate for the maintenance requirements. However,
although the total dollars are sufficient, they may be
expended in various ways. If the lines become clogged
due to salt buildup, then additional maintenance will be
required but the life expectancy of the pipe will be increased.
Various other options are possible; however, the ultimate
costs are thought to be similar.
6. In-Plant Handling System
Capital cost
$8,500,000
( Manufacturers' data)
Operation and Maintenance Costs^
$1,445,000
35+1
$1,445,000 x [*1+* - ~ ~1] = 302'121'000
g!7% of capital cost.
7. Total System Cost
Capital Cost
In-plant $ 8,500,000
Transportation 31,954,000
Disposal area 52,906,000
TOTAL $ 93,360,000
Weighted Cost of Capital $ 724,100,000
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C-10
Operation and Maintenance
In-plant $ 302,121,000
Transportation 42,140,000
Disposal area 14,448,000
TOTAL $ 358,709,000
TOTAL SYSTEM COST $1,082,800,000
PRESENT WORTH ANALYSIS
Inflation rate: 8.5%
Cost of Capital 2.3%
Discount rate: 11%
Capital Cost
Disposal area (see pp. C-2) $ 52,905,766
Front end loader (see pp. C-2)
119,000 [1+.84+.71+.60+.50] 434,350
Dredge (see pp. C-2)
75,100 [1+.78+.61+.48) 215,537
Transport pumps (see pp. C-5,6)
7x5209x[1+.91+.82+.74+.67+.61+.55+.50+.45] 227,893
Return pumps (see pp. C-6)
4xl2,834x[l+.61] 82,650
Transport lines (see pp. C-6)
7x578,054x[1+.91+.82+.74+.67+.61+.55+.50+.45] 25,289,862
Return lines (see pp. C-7)
4x523,776x[l+.61] 3,373,117
In-plant handling system (see pp. C-8) 8,500,000
Total Capital Cost $ 91,029,175
Note: Numbers in brackets [] are present worth factors based on the
number of years to the expenditure and a 2.3% cost of capital.
Operation and Maintenance (O&M) Cost
Disposal area (see pp. C-3)
Oiler $12,750/year
Operator 40,320/year
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C-ll
Fuel 14,900/year
Maint. and lubrication 1,160/year
Total $69,130/year (see pp. C-4)
69,130 x 24.5f $ 1,694,000
Present worth factor for an annual expenditure over 35 years at
a 2.3% cost of capital.
Transportation
Transport pumps: $118,800/year (see pp. C-7)
Return pumps: 81,500/year (see pp. C-8)
Total $200,300/year
$200,300x24.5 $ 4,907,000
In-plant handling (see pp. C-8)
$l,445,000/year x 24.5 35,402,500
Total O&M Cost $42,003,000
Present Worth $133,032,170
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117
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-81-013
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Economic Analysis of Wet Versus Dry Ash
Disposal Systems
5. REPORT DATE
January 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
M. P. Bahor (GAI Consultants, Inc.) and
K.L. Ogle
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
TVA, Division of Energy Demonstrations and
Technology
1140 Chestnut Street, Tower II
Chattanooga, Tennessee 37401
10. PROGRAM ELEMENT NO.
1NE624A
11. CONTRACT/GRANT NO.
EPAIAG-D5-E721BI
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND I
Final: 1/79-9/80
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES IERL.RTP project officer is Julian W. Jones, Mail Drop 61, 919/
541-2489.
is. ABSTRACT
repOrt gjves results of an analysis of the economics of both wet and
dry methods of coal ash disposal, under a specific series of assumptions. It indi-
cates trends in ash disposal costs and includes an evaluation of system components
including: in-plant handling systems (vacuum, pressure), transportation systems
(pipeline, truck, conveyor, pneumatic systems), disposal area (flat topography,
narrow valley, wide valley), and environmental/engineering considerations (liner
vs. no liner, compaction vs. no compaction). The effect of power plant size (300,
600, 900, 1300, and 2600 MW) was also evaluated. For each case considered, capi-
tal and first year operating and maintenance costs were calculated, then evaluated
over the estimated 35-year plant life, using both present worth and total system
cost analyses. Study conclusions included: of all factors considered, site topography
has the greatest influence on ash disposal costs; dry disposal is the least-cost alter-
native for flat sites and for many valley sites; and for small plants or short hauling
distances, truck transport is the least-cost alternative for dry ash disposal.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Ashes
Coal
Disposal
Economics
Materials Handling
Transportation
Pollution Control
Stationary Sources
Coal Ash Disposal
13B
21B
21D,08G
14G
05C
15E,13H
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
126
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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