&EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
EPA-600/7-80-01 2d
March 1980
Research Triangle, Park NC 2771 1
Waste and Water
Management for
Conventional Coal
Combustion: Assessment
Report-1979
Volume IV.
Utilization of FGC Wastes
Interagency
Energy/Environment
R&D Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide-range of energy-related environ-
mental issues.
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-600/7-80-012d
March 1980
Waste and Water Management
for Conventional Coal Combustion
Assessment Report-1979
Volume IV. Utilization of FGC Wastes
by
C.J. Santhanam, R.R. Lunt, C.B. Cooper,
D.E. Klimschmidt, I. Bodek, and W.A. Tucker (ADL);
and C.R. Ullrich (University of Louisville)
Arthur D. Little, Inc.
20 Acorn Park
Cambridge, Massachusetts 02140
Contract No. 68-02-2654
Program Element No. EHE624A
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
-------
PARTICIPANTS IN THIS STUDY
This First Annual R&D Report is submitted by Arthur D. Little, Inc.
to the U. S. Environmental Protection Agency (EPA) under Contract No.
68-02-2654. The Report reflects the work of many members of the
Arthur D. Little staff, subcontractors and consultants. Those partici-
pating in the study are listed below.
Principal Investigators
Chakra J. Santhanam
Richard R. Lunt
Charles B. Cooper
David E. Kleinschmidt
Itamar Bodek
William A. Tucker
Contributing Staff
Armand A. Balasco Warren J. Lyman
James D. Birkett Shashank S. Nadgauda
Sara E. Bysshe James E. Oberholtzer
Diane E. Gilbert James I. Stevens
Sandra L. Johnson James R. Valentine
Sub contractors
D. Joseph Hagerty University of Louisville
C. Robert Ullrich University of Louisville
We would like to note the helpful views offered by and discussions
with Michael Osborne of EPA-IERL in Research Triangle Park, N. C., and
John Lum of EPA-Effluent Guidelines Division in Washington, D. C.
Above all, we thank Julian W. Jones, the EPA Project Officer, for
his guidance throughout the course of this work and in the preparation
of this report.
ii
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ACKNOWLEDGEMENTS
Many other individuals and organizations helped by discussions with
the principal investigators. In particular, grateful appreciation is
expressed to:
Aerospace Corporation - Paul Leo, Jerome Rossoff
Auburn University - Ray Tarrer and others
Department of Energy - Val E. Weaver
Dravo Corporation - Carl Gilbert, Carl Labovitz, Earl Rothfuss
and others
Electric Power Research Institute (EPRI) - John Maulbetsch,
Thomas Moraski and Dean Golden
•
Environmental Protection Agency, Municipal Environmental Research
Laboratory - Robert Landreth, Michael Roulier, and Don Sanning
Federal Highway Authority - W. Clayton Ormsby
IU Conversion Systems (IUCS) - Ron Bacskai, Hugh Mullen
Beverly Roberts, and others
Louisville Gas and Electric Company - Robert P. Van Ness
National Ash Association - John Faber
National Bureau of Standards - Paul Brown
Southern Services - Reed Edwards, Lament Larrimore, and Randall Rush
Tennessee Valley Authority (TVA) - James Crowe, T-Y. J. Chu,
H. William Elder, Hollis B. Flora, R. Janes Ruane,
Steven K. Seale, and others
iii
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CONVERSION FACTORS
English/American Units
Length:
1 inch
1 foot
1 fathom
1 mile (statute)
1 mile (nautical)
Area:
1 square foot
1 acre
Volume:
1 cubic foot
1 cubic yard
1 gallon
1 barrel (42 gals)
Weight/Mass:
1 pound
1 ton (short)
Pressure:
1 atmosphere (Normal)
1 pound per square inch
1 pound per square inch
Concentration:
1 part per million (weight)
Speed:
1 knot
Energy/Power:
1 British Thermal Unit
1 megawatt
1 kilowatt hour
Temperature:
1 degree Fahrenheit
Metric Equivalent
2.540 centimeters
0.3048 meters
1.829 meters
1.609 kilometers
1.852 kilometers
0.0929 square meters
4,047 square meters
28.316 liters
0.7641 cubic meters
3.785 liters
0.1589 cu. meters
0.4536 kilograms
0.9072 metric tons
101,325 pascal
0.07031 kilograms per square centimeter
6894 pascal
1 milligram per liter
1.853 kilometers per hour
1,054.8 joules
3.600 x 10* joules per hour
3.60 x 106 joules
5/9 degree Centigrade
IV
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Cementitious: A chemically precipitated binding of particles
resulting in the formation of a solid mass.
Fixation; The process of putting into a stable or unalterable
form.
Impoundment: Reservoir, pond, or area used to retain, confine,
or accumulate a fluid material.
Leachate: Soluble constituents removed from a substance by the
action of a percolating liquid.
Leaching Agent: A material used to percolate through something
that results in the leaching of soluble constituents.
Pozzolan: A siliceous or alundnosiliceous material that in
itself possess little or no cementitious value but that in
finely divided form and in the presence of moisture will react
with alkali or alkaline earth hydroxide to form compounds possessing
cementitious properties.
Pozzolanic Reaction: A reaction producing a pozzolanic product.
Stabilization; Making stable by physical or chemical treatment.
v
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ABBREVIATIONS
BOD
Btu
cc
cm
COD
CC
°F
ESP
FGC
FGD
ft
g
gal
gpd
gpn
hp
hr
in.
j
J/B
k
kg
kCal
km
kw
kwh
S, or lit
Ib
M
m2
.3
mg
MGD
MW
MWe
MWH
Ug
mil
min
ppm
psi
psia
scf/m
sec
TDS
TOS
TSS
tpy
yr
biochemical oxygen demand
British thermal unit
cubic centimeter
centimeter
chemical oxygen demand
degrees Centigrade (Celcius)
degrees Fahrenheit
electrostatic precipitator
flue gas cleaning
flue gas desulfurization
feet
gram
gallon
gallons per day
gallons per minute
horsepower
hour
inch
joule
joule per second
thousand
kilogram
kilocalorie
kilometer
kilowatt
kilowatthour
liter
pound
million
square meter
cubic meter
milligram
million gallons per day
megawatt
megawatt electric
megawatt hour
microgram
milliliter
minute
parts per million
pounds per square inch
pounds per square inch absolute
standard cubic feet per minute
second
total dissolved solids
total oxidizable sulfur
total suspended solids
tons per year
year
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TAU [" OF CON'J KN'l S
Page
ACKNOWLEDGEMENTS iii
CONVERSION FACTORS iv
GLOSSARY v
ABBREVIATIONS vi
LIST OF TABLES ix
LIST OF FIGURES ix
1.0 INTRODUCTION 1_1
I.I Purpose and Content: l_i
1.2 Report of Organization ~L-2
2.0 UTILIZATION OF COAL ASh 2-1
2.1 Introduction 2-1
2.2 Current Utilization 2-2
2.2.1 Characteristics of Coal Ash 2-2
2.2.2 Current Utilization 2-5
2.3 Ash Utilization as Fill Material 2-10
2.3.1 Borrow Substitute 2-10
2.3.2 Soil Stabilization 2-14
2.3.3 Market Characteristics and Economics 2-16
2.4 Ash in Cement and Concrete 2-16
2.4.1 Ash in Cement 2-17
2.4.1.1 Cement Production 2-17
2.4.1.2 Ash as Cement Raw Material 2-17
2.4.1.3 Ash as Cement Additive 2-20
2.4.2 Ash in Contrete 2-20
2.4.3 Lime/Fly Ash/Aggregate Basic Courses 2-24
2.4.4 Ash as Aggregate Substitute 2-25
2.4.5 Market Characteristics and Economics 2-25
2.5 Ash in Miscellaneous Use 2-27
2.6 Ash as a Mineral Resource 2-29
2.7 R&D Programs - Ash Utilization 2-30
2.7.1 U. S. Army Corps of Engineers 2-31
2.7.2 Bureau of Reclamation 2-35
2.7.3 Coal Research Bureau - West Virginia U 2-35
2.7.4 Department of Energy - Gordian Associates 2-37
2.7.5 Federal Highway Administration 2-38
2.7.6 National Bureau of Standards 2-39
2.7.7 Tennessee Valley Authority 2-41
2.7.8 GM - Plastic Filler 2-42
2.7.9 Other R&D 2-43
via
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TABLE OF CONTENTS
(Continued)
3.0 UTILIZATION OF FGD WASTES AND BY-PRODUCTS 3-1
3.1 Introduction 3-1
3.2 Utilization of Nonrecovery FGD Wastes 3-1
3.2.1 Description of Wastes 3-1
3.2.1.1 Solid Wastes 3-2
3.2.1.2 Liquid Wastes 3-5
3.2.2 Current Utilization Practices 3-6
3.2.3 Potential Utilization Alternatives 3-6
3.2.3.1 Structural Landfill 3-7
3.2.3.2 Gypsum 3-7
3.2.3.3 Aggregate 3-10
3.2.3.4 Agricultural Uses 3-11
3.2.3.5 Building Brick 3-13
3.2.3.6 Recovery of Chemicals 3-13
3.2.4 R&D Programs - Nonrecovery FGD Wastes 3-13
3.2.4.1 Pullman Kellogg 3-17
3.2.4.2 TVA 3-17
3.2.4.3 TRW 3-20
3.2.4.4 Texas A&M University 3-23
3.3 Utilization of Wastes and By-products
from Recovery FGD Systems 3-25
3.3.1 Introduction 3-25
3.3.2 Waste Streams from Recovery Processes 3-26
3.3.3 Marketability of Sulfur or Sulfuric Acid 3-27
3.3.4 Stockpiling 3-28
3.3.5 Energy Demands 3-29
3.4 FGD Waste and By-product Marketing 3-29
4.0 REGULATORY CONSIDERATIONS 4-1
5.0 ASSESSMENT OF UTILIZATION AND DATA GAPS 5-1
5.1 Assessment of Utilization 5-1
5.1.1 Technical Considerations 5-1
5.1.2 Institutional Barriers 5-2
5.1.3 Other Factors 5-2
5.2 R&D Assessment 5-3
5.3 Future Utilization Considerations and Data Gaps 5-5
5.4 Emerging Technologies 5-8
REFERENCES R-l
INDEX R~7
viii
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LIST OF TABLES
Table No.
2.1 Range of Coal Ash Compositions 2-3
2.2 Commercial Utilization of Coal Ash in the
United States 2-6
2.3 Ash Utilization 2-8
2.4 Total Ash Utilized 2-9
2.5 Ash Utilization as Fill 2-11
2.6 ASTM C 593 Requirements Pertaining to Fly
Ash for Use with Lime/Soil Mixtures 2-15
2.7 Ash Utilization in Cement and Concrete 2-19
2.8 Ash Utilization in Miscellaneous Uses 2-28
2.9 Current Research in Fly Ash Utilization 2-32
3.1 Current Research in FGD Waste Utilization 3-15
3.2 TRW: Sensitivity Analysis 3-24
3.3 Summary of TVA Gypsum Marketing Results 3-32
LIST OF FIGURES
Figure No.
2.1 Coal Ash/Utilization in Concrete Products 2-18
3.1 Process Flowsheet for Producing Solid Granular
Fertilizer Material from Scrubber Waste 3-18
3.2 TRW Process Flowsheet 3-21
5.1 Product Development Logic 5-7
ix
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1.0 INTRODUCTION
1.1 Purpose and Content
With increasing coal utilization in industrial and utility boilers,
generation of coal ash (fly ash and bottom ash) and flue gas desulfuriza-
tion (FGD) wastes, which together comprise flue gas cleaning (FGC) wastes,
is expected to increase dramatically in the next twenty (20) years.
Utilization will constitute a valuable element of an integrated FGC waste
management program. Against the background of developing regulatory
constraints pertaining to air and water pollution control and the rising
cost of disposal, utilization may offer an attractive waste management
alternative to disposal. Furthermore, with a large anticipated mineral
deficit in the United States in the future, FGC wastes may present a
potential source of minerals in the future.
This is the fourth volume in a five-volume report assessing
technology for the control of waste and water pollution from combustion
sources. This volume reports on the status of FGC waste utilization
including both current commercial practice and ongoing resource and
development programs.
The focus of this volume on utilization is the evaluation of the
technical, economic, regulatory, and environmental aspects of ongoing
technology development and commercialization of FGC waste utilization.
FGD wastes considered in this report are primarily those from nonrecovery
systems.
At present, utilization of FGC wastes in the United States is modest
but growing. Many European countries and Japan utilize a higher proportion
of the coal ash and FGD waste produced in these countries than does the
United States. There are, of course, inherent differences in availability
of raw materials and marketability which account for some of the differ-
ences. For some specific end-uses, there may be some technological ad-
vantages favoring higher levels of utilization abroad. However, in gen-
eral, there are significant institutional factors which favor increased
utilization abroad and hinder expansion of domestic utilization.
1-1
-------
The review and assessment has involved two separate efforts as
described below:
(1) Review of the data and information available as of
December 1978 on the utilization of FGC wastes. The
review is based upon published reports and documents
as well as contacts with private companies and other
organizations engaged in FGC utilization technology
development. Much of the information has been drawn
from the FGC waste utilization studies and technology
development/demonstration programs sponsored by various
agencies of the U.S. government including, the Federal
Highway Administration, the Army Corps of Engineers,
the Department of Energy (DOE), the Bureau of Mines, the
Environmental Protection Agency (EPA) and the Electric
Power Research Institute (EPRI) .
(2) An assessment of ongoing work in waste charac-
terization, identification of data and infor-
mation gaps relating to waste utilization, and
development of recommendations for potential
initiatives to assist in closing these gaps.
Throughout this work, emphasis has been placed upon waste utilization
by commercially demonstrated technologies and, where data are available,
by technologies in advanced stages of development that are potentially
capable of achieving commercialization in the United States in the near
future.
1.2 Report Organization
This report:
• Presents an overview on coal ash (.fly ash and bottom ash)
utilization in commercial practice at present,
• Assesses R&D programs for coal ash and FGD waste
utilization,
• Identifies some of the constraints on FGC waste utilization,
and
• Presents an outline of related data and information gaps.
1-2
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2.0 UTILIZATION OF COAL ASH
2.1 Introduction
Coal-fired utility and industrial boilers generate two types of
coal ash—fly ash and bottom ash. (Economizer ash and mill rejects are
lumped into the two major categories here.) Both constitute the non-
combustible (mineral) fraction of the coal and the unburned residuals.
Fly ash, which accounts for the majority of the ash generated, is the
fine ash fraction carried out of the boiler in the flue gas. Bottom
ash is that material which drops to the bottom of the boiler and is
collected either as boiler slag or dry bottom ash, depending upon the
type of boiler.
The total amount of coal ash produced is directly a function of
the ash content of the coal fired. Thus, the total quantity of ash
produced can range from a few percent of the weight of the coal fired
to as much as 35%. The partitioning of ash between fly ash and bottom
ash usually depends upon the type of boiler. Standard pulverized coal-
fired boilers typically produce 80-90% of the ash as fly ash. In cyclone-
fired boilers, the fly ash fraction is usually less. In some cases,
bottom ash constitutes the majority of the total ash.
The technology of ash collection, the characteristics of the ash
produced, and projection of waste generation are discussed in Volume 3.
This volume provides a review of ash utilization, both current practices
as well as potential utilization alternatives that have been or are being
investigated.
Fly ash is the major source of particulate emissions from utilities
and with increasing regulatory stringency has required major collection
systems. Control of particulate emissions from pulverized-coal-fired
steam generators is rapidly becoming a significant factor in the siting
and public acceptability of coal-burning power plants. The particulate
emission limit set by the EPA for large, new coal-fired boilers is 0.043
grams/106 joules (0.1 lb/106 Btu). Some states have requirements more
restrictive than this.
2-1
-------
Fly ash carried in the flue gas stream can be collected in a number
of ways to meet the current particulate emission control limitations as
noted above. Typical methods historically employed include mechanical
collection, electrostatic precipitation, fabric filtration and wet
scrubbing. However, the tightening regulatory requirements support two
criteria for fly ash collection systems:
• The collector must be efficient in removing sub-micron size
particulate matter. This criterion eliminates from con-
sideration all mechanical collectors and many wet scrubber
systems (if they are used alone). Mechanical collectors
may, however, function as a first unit followed by a more
efficient collector.
• The collector must be available commercially and be proven
in a utility boiler application. This constraint eliminates,
for the immediate future, many hybrid wet scrubber systems
and novel collectors that are now under development. In the
long run, however, it is conceivable that such advanced
systems may be used at least in some instances.
Collection of bottom ash (or boiler slag) does not involve systems
outside the boiler. The technology of bottom ash handling is discussed
in Volume 2.
2.2 Current Utilization
2.2.1 Characteristics of Coal Ash
Detailed discussions and data on the physical and chemical charac-
teristics of coal ash are presented in Volume 3. In this section, some
of the salient characteristics affecting ash utilization are outlined.
The chemical composition of coal ash (bottom ash, fly ash, and slag)
varies widely, in concentrations of both major and minor constituents.
Table 2.1 shows a compilation of chemical composition of both fly ash and
bottom ash from the firing of a wide range of different coals. The
principal factor affecting the variation in the composition is the vari-
ability in the mineralogy of the coal. However, differences in compo-
sition can exist between fly ash and bottom ash (or boiler slag) generated
2-2
-------
Table 2.1
Range of Coal Ash Compositions
Major Constituents (wt %)
Silica (as Si02) 25 - 60
Alumina (as A^O-) 10 - 30
Ferric Oxide (as Fe^OO 5-40
Lime (as CaO) 0.5-25
Magnesia (as MgO) 0.2 - 8.0
Potassium Oxide (as K20) 0.1 - 4.0
Sodium Oxide (as No20) 0.1 - 4.0
Titanium Dioxide (as Ti02) 0.5 - 2.5
Sulfur Trioxide (as S03) 0.2-20
Carbon and Volatiles ND - 2
Source: [1, 2]
2-3
-------
from the same coal due to differences in the degree of pulverization of
the coal prior to firing, the type of boiler in which the coal is fired,
and the boiler operating parameters and combustion efficiency. Regard-
less of the type of ash (either fly ash or bottom ash), more than 80%
of the total weight of the ash is usually made up of silica, alumina,
iron oxide, and lime. It should be noted that the compositional break-
down shown in Table 2.1 reflects only the elemental breakdown of the con-
stituents reported as their oxides and not necessarily the actual compounds
present.
The physical properties of fly ash vary with the type of coal fired,
the boiler operating conditions, and the type of fly ash collector em-
ployed. A mechanical collector, which generally removes only the heaviest
fly ash fraction, produces a relatively coarse material with the con-
sistency of a fine sand. In contrast, the ash removed in an electro-
static precipitator is usually finer, with silt-like grading. The range
of specific gravities of fly ash depends upon particle size distribution
and fly ash composition; however, specific gravities typically range from
approximately 1.9 to 2.7. A small portion of the fly ash (<4%) consists
of cenospheres (hollow spheres) which have an apparent density less than
water. Bulk densities of fly ash, because of the variations in specific
gravity and particle size distribution, var> greatly. Bulk densities of
fly ash, therefore, vary greatly, although the typical range for fly ash
3
compacted at optimum bulk density would be 110-135 Ib/ft .
An important property of coal fly ash is its pozzolanic activity.
Pozzolanic activity in fly ash, either due to contained lime or through
the addition of lime, causes the fly ash to aggregate and harden when moist-
ened and compacted. Because of the presence of pozzolanic activity in some
fly ashes, the engineering properties of fly ash vary greatly. In
general, untreated fly ash (that to which lime has not been intentionally
added) exhibits engineering properties similar to soils of equivalent
particle size distributions. Permeabilities of compacted fly ash samples
generally range from 5 x 10 cm/sec to 5 x 10 cm/sec. Treatment
of pozzolanic fly ashes with lime can result in significant increases in
compressive strength and increases in permeability (depending upon the
2-4
-------
amount of lime, the water content, curing time, and degree of compaction).
Bottom ash can be collected either dry or in a molten state, in
which case it is generally referred to as boiler slag. Dry-collected
bottom ash is heavier than fly ash, with a larger particle size dis-
tribution. Since it has a similar chemical composition to that of fly
ash, it behaves similarly, although pozzolanic activity is usually some-
what less in bottom ash.
Boiler slag is a black glassy substance composed chiefly of angular
or rod-like particles, with a particle size distribution ranging from
fine gravel to sand. Boiler slag is porous, although not of so great a
porosity as dry bottom ash. It is generally less reactive in terms of
its pozzolanic properties than either dry bottom ash or fly ash.
2.2.2 Current Utilization
Numerous uses for coal ash have been developed, both here in the
United States and abroad. In 1977, total U.S. generation of coal ash
was 61.6 million metric tons, of which 12.7 million metric tons were
utilized* [3]. Data on utilization of coal ash for some selected years
are presented in Table 2.2 Although the three types of coal ash (fly ash,
bottom ash, and boiler slag) are interchangeable in some circumstances,
they have historically served different markets.
Commercial utilization of coal ash is expected to increase in the
United States, continuing the trend presented in Table 2.2. The increas-
ing reliance on coal as a utility fuel with attendant increases in ash
production may result in the percent of utilization being unchanged or
even decreasing despite efforts to promote ash utilization through in-
creased market visibility and technological development. Preliminary
projections on generation of coal ash and FGD wastes are presented in
Volume 3. Tightening environmental control regulations concerning disposal
*"Utilized" in this sense refers to fly ash which is used as a substitute
for some other material. Particularly in landfill applications (e.g.,
mine subsidence, fill, etc.) the distinction between utilization and
disposal is often unclear. National Ash Association (NAA) statistics
on utilization include material which is removed at no cost (or credit)
to the utility and material which is removed from the utility disposal
site. Federal Power Commission (FPC), on the other hand, includes only
that material which is sold.
2-5
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Table 2.2
Commercial Utilization of Coal Ash in the United States
Millions of Metric Tons (Millions of Short Tons)
19663 1974 1975 1976 1977
Ash Collected
Fly Ash
Bottom Ash
Boiler Slag
Total Ash Collected (Tons
Ash Utilized
£ Fly Ash
Bottom Ash
Boiler Slag
Total Ash Utilized (Tons
Percent of Ash Utilized
% Fly Ash
% Bottom Ash
% Boiler Slag
15.5 (17.
7.4 ( 8.
f.
x 10 )229(25.
1.3 ( 1.
1.5 ( 1.
f.
x 10fc)2.8 ( 3.
7.
21.
Percent of Total Ash Utilized 12.
1)
1)
2)
4)
7)
1)
9
0
1
36.7
13.0
4.4
54.1
3.1
2.6
2.2
7.9
(40.4)
(14.3)
( 4.8)
(59.5)
( 3.4)
( 2.9)
( 2.4)
( 8.7)
8.4
20.3
50.0
14.6
38
11
4
54
4
3
1
8
.5
.9
.2
.5
.1
.2
.6
.9
(42.3)
(13.1)
( 4.6)
(60.0)
( 4.5)
( 3.5)
( 1.8)
( 9.8)
10.6
26.7
40.0
16.4
38.9
13.0
4.4
56.3
5.2
4.1
2.0
11.3
(42.8)
(14.3)
( 4.8)
(61.9)
( 5.7)
( 4.5)
( 2.2)
(12.4)
13.3
31.5
45.8
20,0
44.1
12.8
4.7
61.6
5.7
4.2
2.8
12.7
(48.5)
(14.1)
( 5.2)
(67.8)
( 6.3)
( 4.6)
( 3.1)
(14.0)
13.0
32.6
60.0
20.7
a First year that data were taken.
Source: [3]
-------
of wastes and constraints on land availability in some areas, however,
would continue to impact utilization or disposal of FGC wastes. In
particular, as regulations under the Resource Conservation and Recovery
Act of 1976 (RCRA) become clearer, the impact of this key legislation
on utilization would become better defined. At present, the utility
by-product utilization industry is concerned about potential negative
impact on utilization due to:
• Special waste category, and
• The effect of "use constituting disposal"
issues.
A comparison of utilization data for 1971, 1976, and 1977 is pre-
sented in Table 2.3. Annual total ash utilization is presented in
Table 2.4. Total ash utilization historically has been increasing from
a low of 2.8 million metric tons in 1966 to a high of 12.7 million metric
tons in 1977. However, it is difficult to draw conclusions about the
trends in individual end-use categories; survey coverage has been in-
creasing over the years, the end-use markets listed have been expanded,
and about 35% of total consumption is in poorly defined or unknown
categories.
Based on the available data, the following conclusions can be reached,
Fly ash and bottom ash utilization has been increasing, from 2.8 million
metric tons in 1966 to 4.4 million metric tons in 1971, to 9.9 million
metric tons in 1977. Utilization of boiler slag has fluctuated but has
not shown a discernible trend, staying around 2.7 million metric tons per
year. A possible explanation for some of the variation is that boiler
slag (and sometimes bottom ash) is normally sold out of stockpile; there-
fore, sales in any given year have little relation to production. Fill
usage, the largest single end-use market, has been relatively constant
over the years. Usage in cement and cement products has been increasing
gradually as has the use of slag in blast grit/roofing.
2-7
-------
Table 2.3
Ash Utilization
Millions of Metric Tons (Millions of Short Tons)
Use
A. Commercial Utilization
1. Mixed with raw mat-
erial before forming
cement clinker
2. Mixed with cement
clinker or mixed with
pozzolan cement (I-P)
3. Cement replacement
^ 4. Lightweight aggregate
00 5. Fill material for roads,
construction sites, etc.
6. Stabilizer for road bases
parking areas, etc.
7. Asphalt filler
8. Ice control
9. Blast grit/roofing
10. Miscellaneous
B. Ash Removed from Plant
Site (at no cost to utility
but not covered in catego-
ries listed above)
C. Ash Removed to Disposal
Areas fat company expense)
TOTAL
1971
.09(0.10)
.018(0.02)
.39(0.43)
.16(0.18)
.33(0.36)
.036(0.04)
.14(0.15)
-
-
.09(0.10)
1.70(1.87)
-
2.94(3.25)
Fly Ash
1976
.46(0.51)
.83(0.91)
.10(0,11)
1.34(1.48)
.21(0.23)
.21(0.23)
-
-
.46(0.51)
.26(0.29)
1.29(1.43)
5.17(5.7)
Bottom Ash
1977
.40(0.44)
.29(0.32)
1.43(1.58)
.12(0.13)
1.14(1.26)
.17(0.19)
.12(0.13)
-
-
.17(0.19)
.40(0.44)
1.49(1.64)
5.7(6.3)
1971
-
.036(0.04)
.009(0.01)
.48(0.53)
.007(0.008)
.003(0.003)
-
-
.44(0.48)
.49(0.54)
-
1.46(1.61)
1976
.08(0,
-
-
(0
.62(0
-
.41(0
-
.82(0
.94(1
1.14(1
4.08(4
.09)
.00)
.68)
.45)
.90)
.04)
.26)
.50)
1977
.08(0.09)
-
.13(0.14)
.83(0.92)
.21(0.23)
-
.92(1.01)
-
.37(0.41)
.71(0.78)
.92(1.01)
4.17(4.60)
1971
.08(0.09)
Boiler
Slag
1976
1977
.08(0.09)
.036(0.04)
.07(0.08)
-
2.38(2.63)
0.45(0.05)
.07(0.08)
-
-
.39(0.43)
.34(0.38)
-
3,39(3.74)
-
-
-
.20(0
-
.10(0
1.10(1
.28(0
.16(0
.12(0
2.0(2.
.22)
.11)
.21)
.31)
.18)
.13)
20)
-
-
.23(0.25)
.05(0.06)
-
.36(0.40)
1.35(1.49)
.62(0.68)
.13(0.12)
(O.UO)
2.81(3.1)
Source: [3, 4, 5]
-------
Table 2.4
Total Ash Utilized
Millions of Metric Tons (Millions of Short Tons)
Year
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
Fly Ash
1.3 (1.4)
1.3 (1.4)
1.7 (1.9)
1.7 (1.9)
2.0 (2.2)
3.0 (3.3)
3.3 (3.6)
3.5 (3.9)
3.1 (3.4)
4.1 (4.5)
5.2 (5.7)
5.7 (6.3)
Bottom Ash
1.5 (1.7)
2.1 (2.3)
1.6 (1.8)
1.8 (2.0)
1.6 (1.8)
1.5 (1.6)
2.4 (2.6)
2.1 (2.3)
2.6 (2.9)
3.2 (3.5)
4.1 (4.5)
4.2 (4.6)
Boiler Slag
- (-)
- (-)
1.4 (1.5)
0.9 (1.0)
1.0 (1.1)
3.4 (3.7)
1.2 (1.3)
1.6 (1.8)
2.2 (2.4)
1.6 (1.8)
2.0 (2.2)
2.8 (3.1)
Total
2.8 (3.1)
3.4 (3.7)
4.7 (5.2,)
4.4 (4.9)
4.6 (5.1)
7.9 (8.6?
6.9 (7.5;
7.2 (8.0)
7.9 (8.7)
8.9 (9.8)
11.3 (12.1',)
12.7 (14. (>)
Source: [6]
-------
Important commercial markets for coal ash in the United States in-
clude the manufacture of cement and concrete, use as landfill and soil
stabilizer, use in blasting (abrasion) compound, and for ice control.
For the purposes of this discussion, utilization of coal ash has been
broadly broken down into three end-use categories:
• Fill material,
t Manufacture of cement, concrete, and pavements, and
• Miscellaneous.
Each of these categories is discussed in the following section.
2.3 Ash Utilization as Fill Material
The largest use of coal ash historically has been as fill material
in construction, either as a replacement for common borrow, or to stabi-
lize poor soils in fly ash/soil mixtures or lime/fly ash/soil mixtures.
Ash and ash/soil mixtures can be more economical than common borrow where
the hauling distance is relatively short, if there is a lack of suitable
borrow material near the construction site, or if other material is not
available locally for environmental reasons.
2.3.1 Borrow Substitute
Coal ash can offer distinct technical advantages as a fill material
because of its low density and significant strength (Table 2.5). In
situations where filling is necessary on relatively weak subsoils,
natural materials can produce excessive settlement. Traditional materials
are available for use as a fill in these situations, but because of its
low density, fly ash can represent a more economical solution since it
reduces the overburden weight.
A significant characteristic of fly ash is its strength. Well-
compacted fly ash has been shown to exhibit strengths comparable to those
for soils normally used in earthfill operations. Tests indicate that
most fly ashes have shear strength parameters which would make them stable
and strong construction materials for highway embankments and other light
load-bearing fills [7], In addition, many fly ashes possess self-hardening
properties in the presence of moisture, which can result in the development
of shear strengths in excess of those encountered in many soils. The ad-
dition of lime or cement can induce hardening in fly ashes which may not
self-harden alone. Significant increases in shear strength parameters can
2-10
-------
Ash
Consumer
Table 2.5
Ash Utilization as Fill
Borrow
Material
Contractor
Stabilized
Fill Supplier
Ash
Requirements
a) Particle size dis— a) Particle size distribution
tribution important important
b) Fly, bottom, or b) Must be <10% water soluble
slag c) Fly, bottom, or slag
Technical
Benefits
a) Lighter than
common fill
b) Erosion can be
problem
c) Dusting can be
problem
d) Water slippage
can be problem
a) Can be stronger than
common fill
Direct
Savings
Site specific
Site specific
User
Benefits
Ash fill can be
useful to reduce
load on base
Stabilized fill can
be stronger
Economic
Benefits
Site specific
Site specific
Source: Arthur D. Little, Inc.
2-11
-------
be realized in relatively short periods of time and, if taken into con-
sideration in design, can represent a distinct technical advantage over
other construction fill materials. Addition of lime (or alternatives
allowing the self-hardening process in some fly ashes to proceed) is
called stabilization.
Coal ash, if not properly stabilized, is subject to freeze/thaw
failure, erosion,.and leaching problems (if not properly applied).
• The grain-size distribution of most fly ashes makes them
similar to frost susceptible soils. Frost susceptibility
is influenced by particle size distribution, size, min-
eralogical composition, strength, and permeability [7] but
cannot be satisfactorily correlated with a single parameter
of strength or permeability and no specifications have been
developed for this use. Testing is required for each indi-
vidual fly ash if the ash is to be used in regions where it
is exposed to freezing temperatures.
• Unprotected, compacted slopes of fly ash are subject to
erosion by surface runoff or wind. It is necessary to pro-
tect these surfaces by pavement, topsoil and seeding,
asphalt emulsion, or stabilization with cement.
• Fly ash contains water soluble components in the range of
1-7% by weight [8, 9, 10]. Leaching of these components
can occur by surface runoff or infiltration (percolation).
Leachates from fly ashes are of environmental concern par-
ticularly if the leachate contains trace metals. Potential
pollution of ground and surface water from such leachates
can be minimized by pavement or liners^ topsoil, vegetative
cover, or drains.
Fly ash, bottom ash, and boiler slag can all be utilized as borrow
material. However, fly ash and bottom ash are used in this duty more
frequently; boiler slag often can be used in more valuable ways. When
used by itself, ash can offer an economic advantage in areas where
borrow materials are not easily available. However, except for this
2-12
-------
be realized in relatively short periods of time and, if taken into con-
sideration in design, can represent a distinct technical advantage over
other construction fill materials. Addition of lime (or alternatives
allowing the self-hardening process in some fly ashes to proceed) is
called stabilization.
Coal ash, if not properly stabilized, is subject to freeze/thaw
failure, erosion, and leaching problems (if not properly applied). The
grain-size distribution of most fly ashes makes them similar to frost
susceptible soils. Frost susceptibility is influenced by particle size
distribution, mineralogical composition, strength, and permeability
[7] but cannot be satisfactorily correlated with a single parameter of
strength or permeability, and no specifications have been developed for
this use. Testing is required for each
• individual fly ash if the ash is to be used in
regions where it is exposed to freezing temperatures.
• site where unprotected, compacted slopes of fly ash
are subject to erosion by surface runoff or wind. It
is necessary to protect these surfaces by pavement,
topsoil and seeding, asphalt emulsion, or stabilization
with cement.
• fly ash containing water soluble components in the range
of 1-7% by weight [8, 9, 10]. Leaching of these com-
ponents can occur by surface runoff or infiltration
(percolation), particularly if the leachate contains
trace metals. Leachates from fly ashes are of en-
vironmental concern. Potential pollution of ground
and surface water from such leachates can be mini-
mized by pavement or liners, topsoil, vegetative
cover, or drains.
Fly ash, bottom ash, and boiler slag can all be utilized as borrow
material. However, fly ash and bottom ash are used in this duty more
frequently; boiler slag often can be used in more valuable ways. When
used by itself, ash can offer an economic advantage in areas where
borrow materials are not easily available. However, except for this
2-13
-------
special circumstance, and those instances where it offers a distinct
technical advantage, ash is not generally used for landfill because of
the wide availability of natural fill materials.
2.3.2 Soil Stabilization
Some of the problems associated with unstabilized ash fill can be
overcome (or at least lessened) if the fly ash is used with soil in a
stabilized mixture. These types of mixtures have been used commercially,
especially in England but have not been used extensively in the United
States.
Soil stabilization generally refers to the physical and/or chemical
methods used to improve natural soils or soil-aggregates for use in some
engineering applications. Soil stabilization is used predominantly in
the construction of roadways, parking areas, runways, and foundations.
Soil stabilization can eliminate the need for expensive borrow materials,
expedite construction by improving particularly wet or unstable subgrade,
effect savings in pavement thicknesses by improving subgrade conditions,
and permit the substitution in the pavement cross-section of low-cost
materials for conventional and less economical materials.
The low cost of fly ash and its excellent pozzolanic properties make
lime/fly ash stabilization more advantageous than lime or cement stabiliza-
tion in many cases. Depending on the soil type, lime/fly ash stabilization
can produce greater strengths and improved durability compared with lime
stabilization. In locations where lime is cheaper than cement, lime/fly
ash stabilization can often produce material of comparable long-term
strength and durability at a reduced cost when compared to cement
stabilization.
The suitability of a particular fly ash for stabilization can be
determined by subjecting various mixtures of the fly ash and the soil to
be stabilized to a suitable laboratory testing program. The American
Society for Testing and Materials (ASTM) Specification C 593 places two
constraints on fly ash to be used in lime/soil mixtures. The require-
ments, which pertain to maximum allowable water soluble fraction and to
gradation, are outlined in Table 2.6.
2-14
-------
Table 2.6
ASTM C 593 Requirements Pertaining to Fly Ash
for Use With Lime/Soil Mixtures
Item Criteria %
Water Soluble Fraction Max. 10
Fineness-amount retained
when wet sieved:
No. 30 (595 y) sieve Max. 2.0
No. 200 (74 y) sieve Min. 30.0
Source: [14]
2-15
-------
An important physical indicator of stabilization potential is the
fineness, or specific surface, as determined in accordance with ASTM C
311-68. The finer the fly ash particles, the greater the rate of poz-
zolanic reaction. High carbon content (measured as a loss-on-ignition
in accordance with ASTM C 311-68) tends to inhibit the pozzolanic re-
activity of a fly ash as well as decrease its density. High calcium
oxide (CaO) is usually indicative of the presence of substantial amounts
of free lime, which not only may have a beneficial effect on a soil's
physical properties but which reacts with the siliceous and aluminous
compounds in the fly ash to produce cementation.
Stabilization of soils with fly ash alone is still in the develop-
mental stage. This method is most successful when fly ash with self-
hardening properties is used. In general, fly ash of this type has a high
free lime content and low carbon content, as measured by loss-on-ignition.
2.3.3 Market Characteristics and Economics
The available literature indicates that, to date, there have been
no significant problems with lime/fly ash/soil mixtures when properly
placed [7, 11, 12]. The Federal Highway Administration (FHWA) has done
extensive research in this end-use application and has approved its use
in highway construction in a variety of ways [13].
The market size for fill material is quite large. However, the use
of coal ash in this application is limited. Borrow material usually is
available and costs about $2 to $3 per ton at the borrow site ;
cost of transportation is added to this base cost. The latter usually
is the limiting factor in the cost of borrow material. Since, borrow
sites usually can be developed in reasonable proximity to point of use
(as a fill), the use of coal ash in this application is normally
limited to specific cases where the characteristics of the ash merit such
consideration or where borrow material is not readily available.
2.4 Ash in Cement and Concrete
The use of coal ash in cement and concrete products is the second
largest and one of the more visible uses for ash. Ash can be used in a
variety of ways in this end-use. Some options on using ash in concrete
2-16
-------
products are presented in Figure 2.1. It can be added to the raw mate-
rials and processed with the cement; it can be added to the finished
cement and blended, either at the production facility, at a readymix
plant, or at the construction site; or lime can be added to coal ash to
take advantage of the inherent pozzolanic properties of the ash. Each
use has advantages and disadvantages some of which are summarized in Table
2-7.
2.4.1 Ash in Cement
2.4.1.1 Cement Production
Cement manufacture involves burning lime, silica, alumina, iron, and
magnesia in a kiln and pulverizing the product. The cement reacts with
water to bond rock or sand and gravel into concrete. The key material is
lime (CaO); important sources include cement rock (impure limestone),
limestone, marl, and shell. When alumina and silica are not present with
the lime in sufficient amounts, secondary raw materials are needed to
supply the balance. Natural sources of silica include sand and quartz;
alumina sources include shales, mud, clay, and wastes, such as fly ash,
slag, and red muds from bauxite processing. Iron is sometimes added in
small amounts to adjust the composition of the cement mix. Although
composition varies between different types of cement, the raw material
blend is generally 73-78% CaC03, 12-17% Si02, 2-5% A1203, 1-3% Fe03,
1-5% MgC03, and less than 1% alkalis. For a detailed review of cement
production processes, the reader is referred to [15, 54].
2.4.1.2 Ash As A Cement Raw Material
Ash can substitute for other sources of alumina, silica, or iron in
cement production. Coal ash compares favorably with other raw material
sources for blending with limestone as feed to the kiln. A uniform
quality fly ash is an important chemical requirement in order to avoid
frequent costly and time-consuming checks and adjustments of the raw
mixture to maintain proper kiln feed composition.
The use of fly ash as a raw material eliminates the mining, crushing,
and pulverizing process that is required for use of clay and shale. An
additional advantage of fly ash results from the presence of carbon which
2-17
-------
NJ
(-'
oo
To kiln for i
chemical balance
and fuel content
Raw .
Materials *—
IV.
To concrete plants
as extender
To grinding
as extender
Kiln
To mixing
as extender
Grinding
Mill
Cement Producer
Ready-mix
Plant
Concrete
Blending
&
Distribution
• -ii^ ^ ••^. '
Cement
Distributor
k
F
|
fc
F
Site
Mixed
Pre-Cast
Products
. Concrete
' Products
Source: Arthur D. Little, Inc.
Figure 2.1 Coal Ash Utilization in Concrete Products
-------
Table 2.7
'Ash Utilization in Cement and Concrete
Ash
Consumer
I. Cement
Producer
II. Cement
Producer
III. Cement
Distributor
IV. Readymix Supplier,
Concrete User
Ash
Requirements
Technical
Benefits
Direct
Savings
Benefit
To User
Economic
Benefits
a) High carbon okay
b) Particle size
unimportant
a) Reduces raw
material consump-
tion
Slight—some second-
ary raw material
a) Low carbon required
b) Particle size unim-
portant
c) Fly, bottom, or slag
a) Reduces kiln energy
b) Reduces raw mater-
ials
Portion of kiln
energy
% of cement
manufacturing cost
a) Low carbon required
b) Particle size impor-
tant
c) Must meet ASTM cement
specifications
d) Fly ash only
a) Reduces kiln energy
b) Reduces raw material
c) Reduces grinding
energy
"Portion of kiln and
grinding energy
a) Low carbon required
b) Must meet end-use
(performance)
specifications
c) Particle size importan
d) Fly ash only
Reduces portland
cement consumption
Approximately 45 kg
(100 Ib) of cement
per m concrete
a) Improved workability
b) Decreased heat of hydration
c) Improved surface finish
d) Increased long-term strength
e) Increased resistance to sulfate
attack
% of cement
manufacturing cost
% of concrete
selling price
Source: Arthur D. Little, Inc.
-------
can supply fuel for firing in the kiln, and, since it contains no water
or crystallization which must be driven off as do clay and shale, the
heating requirements are reduced. However, apart from the potential
economic advantage, coal ash has no technical advantage over other raw
materials in this use.
2.4.1.3 Ash As A Cement Additive
Fly ash can be mixed with finished cement or interground with cement
clinker. Fly ash added at either of these two points in the manufacturing
process remains as fly ash and is thoroughly blended into the portland
cement. The resulting material has essentially the same advantages in
use as those obtained by adding fly ash to concrete mix (see- Section
2.2.3.4).
Cement with fly ash additive must be marketed as a separate product
and as such, separate handling, storage, stocking, etc., are involved.
Unless the volume of such fly ash cement is adequate, this utilization
of fly ash would have economic demerits. Also, the blending of the two
materials requires careful control to ensure uniformity of the cement.
It should be noted that the product specifications for the use of
ash in concrete are quite different from that for the use of ash in
cement. It is possible to use different clinkers for these two different
uses.
2.4.2 Ash in Concrete
The ingredients used to produce conventional portland cement concrete
are portland cement, water, gravel or stone, sand, and a variety of chemi-
cals to either increase the air content of the concrete or reduce the
amount of water required for the proportioning of the concrete mixture,
or modify the settling characteristics of the cement. The amounts of
each of the ingredients affect the concrete properties. ASTM Specifica-
tion C 618-77 [19] for the use of fly ash as a pozzolan in concrete manu-
facture classifies fly ash as derived from: 1) anthracite or bituminous coal or
2) lignite or subbituminous coal. The specifications cover combined per-
centages of silica (Si02), alumina (A120,), and ferric oxide (Fe-O-), maxi-
mum SO-, maximum moisture content, maximum loss-on-ignition, maximum
magnesium oxide (MgO) content, maximum sodium oxide (Na^O) content, required
particle fineness, pozzolanic activity index, soundness, and uniformity.
2-20
-------
The use of fly ash as a raw material in the production of concrete
serves two primary purposes:
• To supplement or replace fine aggregate and cement,
and
• To improve properties of the concrete.
Coal ash is useful as aggregate replacement because of its pozzolanic
nature. A pozzolan is a siliceous or alumino-siliceous material which
is not cementitious in itself but which, in finely divided form and in the
presence of moisture, reacts with alkali and alkaline earth products to
produce cementitious products [16]. The pozzolanic reaction between fly
ash and lime (cements) results in a material of substantial strength.
Among the improvements attributed to fly ash/concrete are improved
pumpability, higher compressive strength (and long-term strength), better
workability and finishability, and higher resistance to sulfates and
alkali/aggregate reaction: use of fly ash in concrete decreases the heat
of hydration, drying shrinkage, particle segregation, bleeding, permea-
bility, and leaching [16, 17, 18].
Sulfate Resistance
There is strong evidence that blended cements tend to show higher
resistance to sulfate attack than do portland cements [20]. Sulfate
attack on concrete can lead to expansion of the cement with resultant
catastrophic cracking/crumbling of the concrete. Concrete can be exposed
to sulfate conditions from drainage water, groundwater, and seawater.
While the actual mechanism is not fully understood, attack may result
from reaction of soluble sulfates (e.g., from groundwater) with the cal-
cium hydroxide and hydrated alumina in the cement to form gypsum and
highly hydrated calcium aluminosulfate compounds having large specific
volumes. Susceptibility to these reactions appears to be reduced in
blended cements, possibly because of reactions between the calcium hy-
droxide and fly ash [17, 18, 20].
2-21
-------
Alkali/Aggregate Reaction
The reaction between alkalis present in cement and certain types of
stone aggregate used in concrete sometimes leads to the formation of
highly hydrated alkali silicates [20]. The formation of these com-
pounds can result in disruptive expansion of concrete. The mechanisms
and kinetics of these reactions are not well understood and, depending
on the nature of the aggregate and the exposure conditions, expansion
may manifest itself at an early age or only after several years. Addi-
tions of fly ash to a cement or concrete can reduce the expansion due to
this reaction but low alkali portland cements are more commonly used.
•
Improved Workability
Fly ash improves the workability of concrete by making it more
plastic, decreasing particle segregation, and decreasing bleeding [16].
Normally, more water is required for making concrete when pozzolans have
been added to the mix. Fly ash differs from most pozzolans in this re-
spect. Concrete containing low-carbon (2%) fly ash generally requires
less water than portland cement concrete [21]. However, work by ASTM
Section C09.03.08 suggests that both carbon content and fineness influence
the water requirements [22]; high carbon content does not raise water re-
quirements, per se. Concretes with fly ashes containing an excess of
about 2% carbon require proportionately more water than does standard
concrete.
Heat of Hydration
Concretes containing fly ash have a lower heat of hydration than
portland cement concrete. Consequently, they do not get as warm as
equal amounts of portland cement concrete. For this reason, fly ash is
used in much of the mass concrete construction in dams and spillways
[18, 23]. Specifications exist for this use, and fly ash is proportioned
according to the heat of hydration desired.
Strength
When ash is substituted for portland cement in concrete, the two
products have different rates of strength gain and differences in the
effects of curing temperature on strength gain may be substantial. The
2-22
-------
addition of small amounts (5-10%) of fly ash to Type 1 portland cement
may improve the early strength of the concrete. Concrete containing
greater amounts of fly ash may show less rapid gains in strength but
higher ultimate strengths [20], Mixes in which fly ash is substituted
for cement on a one-for-one basis (to conform to water-cement ratio
specifications) usually produce concrete that is weaker than no-ash
concretes at ages up to 28 days.* Properly proportioned fly ash con-
crete mixes usually will produce concretes with 28-day strengths com-
parable to concrete without fly ash.
Freeze/Thaw Durability
In much of the country, concrete is subject to damage from repeated
freezing/thawing cycles. When fly ash concrete is tested for freeze/
thaw durability, inferior resistance has been observed, probably because
the test is begun after a short curing period (i.e., less than 28 days)
and does not allow for the lower rate of strength development of ash
concrete. Freeze/thaw studies, when initiated after longer curing periods,
have indicated that fly ash concrete develop strengths equivalent or
superior to those of portland cement concrete and develop superior re-
sistance to freezing and thawing [20]. Another factor involved in freeze/
thaw durability is the air content. When fly ash concrete with an air
content equal to that of conventional portland cement concrete is tested,
it appears to have good freeze/thaw durability [24].
Disadvantages
Adequate quality control of the fly ash and proper system design are
essential for effective utilization of ash in concrete. Lack of proper
attention to quality control has been the cause of some problems.
The properties that make ash utilization in concrete desirable can
also make handling difficult; easy flowability may cause problems in
feeding and weighing the fly ash, and the fineness of fly ash can cause
air pollution and other problems. Control of the fineness and other
properties of the fly ash can pose problems. Uniformity of performance
*Much readymixed concrete is required to meet 28-day minimum strength
values.
2-23
-------
of a fly ash/cement depends on both the cement and the fineness and
composition of the fly ash. Determination of the proportions for fly
ash concrete is system-specific due to the variation in the physical and
chemical properties of different ash materials.
Much of the concrete placed in the United States contains chemical
admixtures which are used to regulate set times, entrain air or reduce
water requirements:[20]. Set regulation is used to extend the time
available for finishing; air entrainment (production of small air bubbles
in the cement) is used to improve resistance to freeze/thaw damage;
decreased water requirements lead to a reduction in the porosity of the.
concrete which increases strength and chemical resistance. Cements con-
taining fly ash contain variable amounts of carbon from incomplete com-
bustion of the coal. Carbon adsorbs chemical admixtures and tends to
diminish their effectiveness as well as making them difficult to predict.
2.4.3 Lime/Fly Ash/Aggregate Basic Courses
Lime/fly ash/aggregate (LFA) mixtures are blends of mineral aggregate,
lime, fly ash and water. When combined in proper proportions and com-
pacted to a high relative density with reasonable curing conditions, they
gradually harden to produce high quality paving materials. A wearing
surface is applied to the base course to protect the material from the
abrasive effects of traffic, from weathering, and from water infiltration.
In addition to lime, stabilization (that is, pozzolanic reaction)
of fly ash can be produced in a number of ways. In lime stabilization,
lime is added directly to the fly ash, moisture is introduced, and the
mixture is then compacted to facilitate the pozzolanic reaction. In
cement stabilization, cement is added to the fly ash instead of lime;
the cement hardens as well as releasing certain amounts of lime which
react with the fly ash in a pozzolanic manner. Certain types of fly ash
also contain substantial quantities of free lime which can harden fly
ash without the external addition of lime or cement. This third process
is known as self-hardening of the fly ash.
LFA mixtures have been used extensively abroad. To a lesser extent,
LFA mixtures have been used in the United States. Approximately 500,000
2-24
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to 1,000,000 tons per year are typical quantities placed for the last
10 or more years of lUCS's "Poz-0-Pac" roadbase, and considerable quan-
tities of similar materials have been placed by others [25]. Against
the background of total roadbase construction, these are not large;
however, the potential use is significant.
2.4.A Ash As Aggregate Substitute
Aggregates are the largest single mined commodity in the United
States. However, the supply is decreasing and in certain areas of the
country (particularly some industrial or metropolitan areas) demand for
natural mineral aggregates for construction purposes exceeds locally
available supplies. With increasing energy costs and consequent cost
increase for transportation, there is an economic incentive to find
suitable replacement aggregates in the local area rather than transport
them over large distances. Utilization of fly ash as a lightweight ag-
gregate is feasible, particularly in many parts of the country where there
are shortages and coal-fired generating plants in the same area. There
are few significant technical limitations to the use of fly ash for light-
weight aggrgate.
Bottom ash has also found use as a lightweight aggregate in con-
struction and as aggregate in roadbase construction. Extensive testing
has been done on the physical and structural characteristics of bottom
ash and boiler slag for various purposes in road construction [26].
The increasing acceptance of coal ash as aggregate materials and the
development of appropriate specification for its use may provide an
outlet in those areas of the country where large amounts of coal-fired
wastes will be generated.
2.4.5 Market Characteristics and Economics
While a large body of data has been accumulated on specific uses of
fly ash in cement, concrete, and in roadbase construction, generic eco-
nomic data are not available. Economics of ash utilization in this cate-
gory are very site- and system-specific; a case-by-case evaluation is
required.
2-25
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The profitability of using fly ash depends upon where in the cement
production process it is substituted, its quality, its cost relative to
cement, the transportation distance involved, the value accrued from any
technical advantages, e.g., less pouring time and less finishing time
than for standard concrete, and the expense for additional equipment to
handle fly ash at the cement plant.
Ash can be substituted as a raw material in the cement kiln feed,
as an additive with clinker in the grinder feed, as an additive with
cement at a mixing plant (sold as cement), or as an additive in concrete
at a readymix plant. The profitability of using ash at the cement pro-
ducer is probably minimal except in special cases. As a raw material
additive, ash imparts few technical advantages and has no significant
cost advantages except in cases where other materials are not available.
As an additive to clinker for grinder feed, ash would save a propor-
tional fraction of the kiln energy. Technical advantages may result from
ash use in this application, however the cost savings would probably not
offset the increased capital expenditure for ash-handling equipment.
Ash utilization as an additive to cement or concrete can poten-
tially result in significant cost advantages. Previous work has in-
dicated that the cost advantage to using ash is related to the trans-
portation distance for a given set of conditions (e.g., plant size,
cement cost, transportation cost). This impact will be very site-
specific and vary from location to location. For example, in the west
where there is a lack of natural pozzolans, ash could be transported
great distances and still be an economically usable pozzolan. Conversely,
in the east, transportation costs can offset any cost advantages quite
rapidly. Work just being completed (see R&D-DOE) indicates that ash
utilization usually has an economic advantage but that institutional
factors have hindered further utilization of ash. The latter are dis-
cussed later in Section 5 of this volume.
The profitable marketing of ash in cement/concrete cannot be based
on cost considerations alone. The marketplace is significantly influenced
by a variety of non-economic factors which can easily outweigh any per-
ceived cost advantages.
2-26
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In order to use fly ash in cement economically, it may be necessary
for the cement plant to be located near a coal-burning utility. For
example, clay or shale is stripped to obtain underlying limestone for a
cement plant. That clay or shale will often be used in the raw batch
even if fly ash is available nearby. The fineness and flow characteris-
tics of fly ash require handling, transportation, and dust collection
equipment different from those for the stripped clay or shale. If fly
ash is to be used, considerable capital investment in cement plant de-
sign and equipment must be committed to a fly ash raw material source.
Guarantees as to quantity and quality of fly ash that will be available
for future use will be essential for a cement manufacturer to commit
himself to fly ash. Quality control and long-term guarantees are key
requirements to increase utilization of ash in any premium use.
2.5 Ash in Miscellaneous Uses
Coal ash has been used in a variety of other applications in the
United States, but these are generally on a smaller scale than the uses
described earlier. However, three specialized uses are important and
presented in Table 2.8.
A significant amount of bottom ash (0.92 M tons in 1977) and boiler
slag (0.36 M tons) are used for ice control on winter roads. Such mate-
rials are often provided at no cost or at nominal cost to the user by the
utilities. Little generic information is available on this, but it would
seem to be inherently site-specific. Broadly, there are some environmental
advantages in using ash in preference to salt in this use in addition to
technical and economic benefits. (See Table 2.8.)
Almost half (1.35 K tons in 1977) of all boiler slag is consumed as
blast grit or roofing granules. Again, it would appear to be a site-
specific use depending upon the availability of alternative materials.
A potential end-use for fly ash which could consume significant
quantities of ash in the future, is in production and/or fixation/
stabilization of FGD waste. The amount and type of ash in FGD waste can
influence both the scrubber operation and the disposal operation. In
certain instances, especially with high CaO western coals, the alkalinity
2-27
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Ash
Consumer
Table 2.8
Ash Utilization in Miscellaneous Uses
Blast Grit/
Roofing
Manufacturer
Ice
Control
Highway Department
Ash
Requirements
a) Only boiler slag
b) Size restriction
a) Bottom ash or boiler
slag
Technical
Benefits
Unknown
Low solubility
Direct
Savings
Equal to cost
differential
Equal to cost
differential
User
Benefits
Economic
Benefits
Source: Arthur D. Little, Inc.
2-28
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in the ash can be substituted for some or all of the scrubber reagent.
Fly ash also can aid in disposal because dewaterability is improved, the
fly ash acts as a pozzolan to help "fix" the waste (especially when there
is free lime), and fly ash oxidizes calcium sulfite to sulfate. Proc-
esses are currently being commercially marketed for the fixation of FGD
waste which utilize fly ash; these are discussed in Volumes 3 and 5.
Fixation of FGD wastes by fly ash and lime usually results in a soil-like
material subj ect to less leaching due to lower permeability and occupying
less volume due to increase in final bulk density compared to separate
disposal of these materials.
2.6 Ash As A Mineral Resource
In addition to the uses discussed above, a variety of potential uses
for coal ash have been proposed [6, 11, 16, 71]. These have included:
• Mineral recovery (alumina, iron, magnetite),
• Mineral wool,
• Mineral aggregate, and
• Filler (for plastics, rubber, etc.) and many others.
Some of these uses are currently being commercialized in the United
States; others have been or are being used abroad, and some are still
under development. However, these applications require technical break-
throughs or fundamental institutional or economic changes. An example
of a future potential use requiring technological breakthrough for eco-
nomic competitiveness is mineral recovery from fly ash. Some research
has been done and methods for extracting alumina, magnetite or other min-
erals do exist. However, at present, these processes are either not
capable of competing with more established processes or the market does not
exist because of a readily available alternate supply of the mineral.
To provide some perspective on the potential mineral recovery poten-
tial from coal ash, it may be noted that a 2,600 MW power plant typically
produces 1.1 million tons of coal ash annually containing silicon oxide,
aluminum oxide, iron oxide, and a host of other raw materials [27]. It
is reported that by the year 2000 the minerals deficit in the United States
will exceed the energy deficit; the trade deficit in minerals may be
as high as $100 billion within 25 years [28]. Currently, United States
2-29
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requirements for 22 of the 74 non-energy essential minerals are
met principally from foreign sources. Hence, over the long-term, the use
of coal ash as a mineral resource may be a possibility. For example, ex-
traction of the aluminum content of the fly ash can completely offset
bauxite imports currently [29]. Zinc concentrations in the fly ash are
equivalent to zinc concentrations in commercial ores. It appears that
continuation of R&D on such uses is essential in the light of a potential
mineral crisis in the future.
2.7 R&D Programs - Ash Utilization
Current R&D projects in coal ash utilization are being carried on
both in further refinement/understanding of existing uses, and develop-
ment of new uses.
The manner in which ash is collected can affect its potential
for utilization. Ash can be collected either in dry or wet systems. In
dry collection systems, fly ash is collected in electrostatic precipita-
tors and stored in large silos. Bottom ash is collected from the boilers
in sluice ducts, dewatered, and is stored separately. In wet systems,
fly ash and bottom ash are slurried (either separately or in a common
pipe) and pumped to holding ponds. Water is recycled from the ponds back
into the system when possible.
From a utilization point of view, dry ash or ash slightly wetted
(for dust control) is more advantageous in most situations than wet ash.
Principal advantages are:
• The ash does not need to be dried for certain uses,
saving energy costs.
• If the ash contains CaO and is wet, it may harden
upon standing. Dry ash is easier to recover from stockpile.
• Dry ash may be more uniform than wet ash if leaching,
agglomeration, and cementation have occurred in the latter.
Currently, the split between wet and dry collection is fairly even
[3, 24] although there has been a shift toward dry collection for a variety
of reasons.
2-30
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The U.S. Army Corps of Engineers, the National Bureau of Standards
(NBS), the Department of Energy, and the Bureau of Reclamation all are
carrying on programs on the influence of coal ash on concrete/cement
properties. A particularly active area at present is research in the
increased sulfate resistance developed by fly ash concrete. Strength
gain, alkali-aggregate reaction, and dimensional stability also are being
studied. In addition, numerous small, specific studies are being carried
on both by industry and by universities on various fly ash properties in
specific situations. The Department of Energy is just completing an
evaluation of the use of ash as a cement replacement in concrete. This
work focused on the factors affecting increased utilization of ash. DOE
is also funding research at Iowa State University on recovery of metal
values from fly ash. Programs on development of new uses are being carried
on by the TVA and the Coal Research Bureau (CRB) at West Virginia Univer-
sity (WVU). The TVA currently has a pilot scale development program under-
way using mineral wool technology developed at WVU. Additionally, the
TVA, by itself and with outside contractors and sponsors, is looking at
extraction of alumina, magnetite, iron, etc. The CRB, in addition to
working with TVA on mineral wool, has developed technology for the com-
mercial production of brick from fly ash and bottom ash. The Federal
Highway Administration (FHWA) is completing an extensive program
on the use of coal ash in road construction. Their results favor use and
the Implementation Division is funding projects to demonstrate developed
construction technology [12]. The NBS is not currently looking at new
areas for ash utilization but anticipates reactivating a currently dor-
mant program in this area [30].
Specific R&D programs in these areas are summarized in Table 2.9
and detailed in the following section. In addition, numerous small R&D
projects are being carried on in a variety of organizations.
2.7.1 U.S. Army Corps of Engineers
The Corps of Engineers has been using pozzolans (primarily fly ash)
for over 20 years [31]. Generally, 25-35% by weight fly ash is added
to concrete (about 45 kg per nr or 100 Ib/m^) because it reduces the heat
of hydration of the concrete during setting.
2-31
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Table 2.9
Primary Sponsor
Contractor
Current Research in Fly Ash Utilization
Project Focus/Status
Ref.
U.S. Army Corps of Engineers
Bureau of Reclamation
K3
I
NJ
Coal Research Bureau
West Virginia University
Dept. of Energy - Gordian Associates
Dept. of Energy - Iowa State University
Effect of fly ash on properties of concrete.
Laboratory work on sulfate resistance, strength,
alkali-silicate reaction. Much of the research
work has been completed, reports will be
prepared within next 1-2 years.
(Ongoing)
Effect of fly ash on properties of concrete.
Laboratory work on effect of ash on sulfate
resistance.
(Ongoing)
Development of new and expanded uses for ash.
Laboratory, pilot scale, and demonstration work
in a variety of end-uses. Extensive work has
been/is being done on a process to produce
bricks from fly ahd bottom ash and a process to
produce mineral wool from bottom ash.
(Ongoing)
Overview of use of fly ash for replacement
of cement in concrete. Considered supply
constraints, economics, technical issues,
institutional factors.
(Draft Report - December 1978)
Recovery of metals from fly ash. (ongoing)
18
23
32
33
that this summary specifically excludes research on the use of ash as at soil amendment.
Source: Arthur D. Little, Inc.
-------
Table 2.9 (Continued)
Current Research in Fly Ash Utilization
Primary Sponsor
Contractor
Project Focus/Status
Ref.
Federal Highway Administration
ro
i
u>
National Bureau of Standards
TVA
Use of sulfate waste (including FGD sludge) in
road construction. Laboratory investigations
of lime-fly astv-sulfate waste mixtures for
strength-compositional relationship. Engineering
investigation of most promising mixtures.
(Completed - 1975)
Use of coal ash as a highway construction material.
Assessment of available information, some
laboratory work. Implementation. Division has
sponsored demonstration work.
(Most research is complete-published 1976)
Effects of ash on engineering properties of concrete.
Laboratory work on sulfate resistance, alkali-
aggregate reaction. Sets guidelines for use in
specifications by other agency.
(Ongoing)
Waste Utilization Program currently inactive.
Anticipate reactivation within 1-2 years.
(Currently inactive)
Production of mineral wool from boiler slag. Using
Coal Research Bureau, W. Va. Univ. process, pilot
plant under construction (about 1 tph) will be
started up about December 1979.
(Ongoing)
12, 34
7, 12
35
30
36, 37
37
Several other smaller projects on alumina extraction,
mineral extraction, cenospheres, magnetite. All
projects in preliminary economics - technical feasibility -
process development phase.
(Ongoing)
Source: Arthur D. Little, Inc.
-------
The Corps of Engineers reports good results with the material poured
to date, but control of fly ash quality is important. They suggest a
specification of 6% maximum loss-on-ignition versus the 12% in ASTM
specifications; the higher carbon content causes problems with excess
air entraining agent to obtain desired air content. Tie-form failures
have also occurred due to the slow early strength rise of the fly ash
concrete [31].
The Corps of Engineers is currently conducting a multi-faceted
program on fly ash and its use in concrete at its Waterways Experiment
Station [18]. One area of study is a general analysis of the effect of
fly ash on concrete. They are using various kinds of subbituminous and
lignite fly ashes blended with Type I and Type II cements; specimens are
analyzed for strength. They also have looked at the physical and chemi-
cal tests made in acceptance of the cement and ash in these various uses
and their appropriateness.
A second area of interest to the Corps is sulfate resistance of
concrete. The Corps generally prefers to use Type II* cement in their
work because of the lower heat of hydration, the increased sulfate resis-
tance and the increased long-term strength. Type I-P** cement (inter-
blended with fly ash) is being evaluated as a potential substitute for
Type II in times of shortages. In this laboratory program, fly ash has
been interblended and interground in a Type I-P** cement (22% maximum)
and the effects on sulfate resistance are being analyzed. Indications
are that the ash increases the sulfate resistance sufficiently to make
Type I cement equivalent to Type II* The Corps of Engineers is also
reviewing whether the new type of cement manufacturing equipment will
significantly change cement characteristics.
Type II cement is portland cement for use in general concrete construc-
tion exposed to moderate sulfate action or where moderate sulfate action
or where moderate heat of hydration is required.
kft
Type I cement is portland cement for use in general concrete construc-
tion. Type I-P is the same as Type I with the addition of a pozzolan.
2-34
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A third research topic has been the minimization of alkali-silicate
reaction. Laboratory work has been done with subbituminous and lignite
fly ash, as well as other pozzolans. Test samples were made with high
alkali cement and the ability of the ashes to quench or minimize the
reaction were measured.
Much of the experimental work in all three of these program areas
has been completed. Reports will be prepared within the next year or
two [18]. Preliminary conclusions are that fly ash increases sulfate
resistance, decreases susceptibility to alkali-aggregate reaction, and
increases resistance to sulfate expansion. The Corps also has obtained
substantive data on the fly ash cement chemistry and its behavior. Over
the next five years, much of the research will be aimed at maintenance
and rehabilitation on existing structures. However, some work, on a
smaller scale, may continue on alkali-silica reaction and the mechanisms
involved.
2.7.2 Bureau of Reclamation
The Bureau of Reclamation uses fly ash extensively as a pozzolan
in concrete, primarily in massive structures, dams, canals, etc. Use
is predicated on technical reasons; fly ash decreases the heat of
hydration in setting cement, fly ash increases the ultimate strength
of the cement, and, fly ash is the cheapest pozzolan readily
available.
The Bureau has an ongoing research program providing support to
•»
fly ash use [23]. The primary focus of this program is currently on the
sulfate resistance of fly ash concrete when using "soft" coal ash (i.e.,
sub-bituminous, lignite). Their laboratory program is concentrating
on what causes sulfate resistance in concrete and why some ashes give
good resistance and others not. They also have been looking to a lesser
degree of heat of hydration reduction by fly ash, and the freeze/thaw
durability of fly ash concretes.
2.7.3 CRB-WVU
The Coal Research Bureau of West Virginia University has been
studying new and expanded uses for ash. Although many uses have been
2-35
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studied [32, 38, 39] including use as soil amendment, in concrete, and
for trace metal recovery, major emphasis has been placed in two areas:
a patented process for producing structural materials from fly ash
[40, 41, 42, 43, 44] and a process being developed with the TVA for the
production of mineral wool from boiler slag (see TVA for discussion).
The process for structural materials was developed to produce high-
quality, dry-pressed, fly ash-based brick utilizing most fly ashes;
physical and chemical property variations in the fly ash were not found
to cause serious problems. Bench-scale studies and pilot plant opera-
tions were conducted and process economics were analyzed. A raw mate- -
rials mix consisting of 72.0% fly ash, 25.2% slag, and 2.8% sodium sili-
cate (as a bonding agent) on a dry basis was used. These brick were
much lighter than clay brick and met or surpassed all ASTM standards for
clay brick.
In subsequent work, the sand was replaced with bottom ash and slag
significantly improving product quality. With improved mixing tech-
niques, a product containing over 97% coal-derived ash has been produced.
A pilot plant was designed and constructed at Morgantown, West
Virginia, to produce fly ash-based brick in sufficiently large quantities
to permit projection of technical factors and economic data to a com-
mercial scale. Raw materials used were fly ash, bottom ash, and boiler
slag obtained from eastern, central, and western coal areas. The work
has demonstrated that most, if not all, types of ash produced from
American coals can be made into construction products meeting or exceeding
ASTM standards for superior-grade face brick.
The pilot plant was designed with a productive capacity of up to
3,000 green (unfired) brick per hour and 1,000 fired brick per day and
was successfully operated for several years. It was demonstrated con-
clusively that the process, with slight modifications, could be applied
to virtually any fly ash and that a wide variety of structural products
(brick, block, tile, etc.) could be produced. Economics of the process
were shown to be highly attractive with a high probability of commercial
success. Full-scale design information was developed.
2-36
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Fly ash brick differ from their clay counterparts in three
significant ways:
• Being lighter, they cost less to transport, have
and improved market potential for high-rise con-
struction, and are easier for masons to handle.
• Fly ash structural forms are dimensionally pre-
cise and are therefore replaceable without change
of shape or color.
• Fly ash structural forms can be expanded in size
and shape without warpage, size variation or
surface defects.
Based upon a detailed economic analysis, the WVU-OCR investigation
concluded that fly ash-based brick and other structural materials have
significant potential for economic success. This analysis (1973 costs,
M&S-345) indicated that total production costs for standard 8-inch facing
brick would be $30 to $40 per 1,000 standard brick equivalents [45]. In
some cases, costs as low as $24 to $30 per 1,000 may be attainable de-
pending on local market conditions, labor factors, etc. These figures
represent total cost FOB the plant including equipment write-off and all
overhead costs, such as general and administrative expense.
An attempt to commercialize this process has not been successful
to date.
2.7.4 DOE - Gordian Associates
Gordian Associates has completed a study for the Department of
Energy looking at the use of fly ash and granulated blast furnace slag
as a cement replacement in concrete [33]. This overview study was con-
cerned with supply considerations, availability, cost structure of the
market, other economic considerations, technical considerations, and
institutional issues. The study concluded that although technical con-
cerns may in many cases be valid (e.g., composition variations, carbon
content) they can be handled through proper engineering and still leave
a positive cost advantage to the use of ash. Rather, institutional
factors have created a bias against the use of ash in concrete and thus
2-37
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hinder its use. If this bias can be corrected through a sufficiently
large commercialization program, fly ash use will increase. This report
is currently (January 1979) in a draft form and should be released for
publication soon.
2.7.5 Federal Highway Administration
The FHWA initiated a comprehensive research program in waste uti-
lization in 1972 and focused on utilization of a variety of wastes in
highway construction. Research has been done in two major areas:
Category 4C - Use of Waste as Material for Highways; and Category 4D -
Remedial Treatment of Soil Materials for Earth Structures and Foundations
[46, 47]. Much of this work concerning fly ash and FGD waste has been
completed and has been, or is being, reported in the literature.
Results of the major research work on ash utilization are summarized
in a report on the use of fly ash in highway construction [7]. The tech-
nical information necessary for the use of ash in highway construction
has been developed. These uses include:
• Base and sub-base courses,
• Subgrade modifications,
• Embankments,
• Structural backfill, and
• Grouting.
The FHWA has not put a major emphasis in its research program on
the use of ash in concrete* although some specific studies have been
done in this area [12].
Information has been assembled on production, handling, and physical
and chemical properties of fly ash which influences its use in highway
applications. The FHWA has considered various factors which affect uti-
lization, case histories, design criteria, testing procedures, and con-
struction procedures. The pozzolanic properties of fly ash make it a
good quality base or sub-base course material when used with lime or
cement to stabilize aggregates and soils, or when used alone with lime
or cement. Strength and durability criteria have been established for
this application, and appropriate testing procedures have been developed.
2-38
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Construction procedures utilize standard equipment and techniques for central
mixing or mix in-place operations. Fly ash is used as embankment or struc-
tural backfill material over weak or compressible soils because of the
reduced surcharge that results from its light unit weight. In addition,
it has low compressibility and good stability characteristics, if placed
properly. Economies can be realized in the design of retaining structures
backfilled with lightweight fly ash. Fly ash improves the flow properties
and strength characteristics of grouts. It can be used alone for void-filling
or used in conjunction with portland cement, lime, clay, sand, and gravel to
develop grouts for applications related to highway structures.
Potential application of FGD waste in road construction has been
discussed in a report on sulfate waste use [34], Mixtures of fly ash,
lime, and sulfate waste were evaluated based on fly ash source, form of
calcium sulfate, lime type, mixture consistency, curing temperature, ad-
mixtures, and impurities. Studies of compound development in selected
mixtures were performed. In the second phase of the study, strength-
compositional relationships for samples prepared with actual waste
sulfates were obtained. Results of this phase were used for the selec-
tion of mixtures for engineering evaluation. These mixtures were
examined for compressive and tensile strength, freeze/thaw resistance,
wet/dry stability, California Bearing Ratio, permeability, and leachability.
While the mixtures were found to have acceptable strength properties,
high California Bearing Ratio and low permeability, the durability prop- x
erties were judged to be marginal. This requires that care and proper
precautions be taken in using these mixtures for construction purposes.
Laboratory test procedures for mix design and typical specifications which
might be used were also suggested.
A third area of research was concerned with use of sulfate waste as
a soil conditioner [48, 49]. This work is discussed elsewhere.
2.7.6 National Bureau of Standards
The NBS has been doing research on fly ash for several years. Its
resource recovery program has been dormant for several years but is now
being revitalized and the Bureau plans to look at new uses for coal ash
and FGD waste [30].
2-39
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Most of the NBS work is aimed at establishing tests which can be
referenced by other organizations in establishing standards and speci-
fications for use.
Most of the past and current research has been focused on the effects
of bituminous coal ash addition on the durability of concrete [35],
NBS is just beginning work on lignite ashes; current plans are to look
at the same areas as have been studied with bituminous. Three specific
areas have been looked at and test data are being developed to assess
the effect of fly ash on:
• Alkali-aggregate reaction,
• Sulfate attack, and
• Dimensional stability.
Alkali present in the feed materials to cement kilns tends to volatilize
and is collected as dust. Cement producers would like to recycle
the dust for its lime value. However, as the recycle rate increases,
the alkali content of the cement increases. Reaction of alkali present
in cement with certain types of aggregate can result in disruptive ex-
pansion of the concrete. Fly ash addition tends to quench the reaction.
However, current specification for 'cements to be used with reactive ag-
gregates requires the use of low alkaline cement. If performance speci-
fication for blended fly ash-cement could be developed to account for
the alkali absorptive capacity of the fly ash, the amount of kiln dust
recycled could be increased significantly and higher alkali raw materials
could be used.
Concrete is subject to disruptive expansion when exposed to sulfate
compounds; sulfates can exist in groundwater, seawater, or other sources.
Ash may reduce this susceptibility by quenching the sulfate-cement
reaction. However, ash-cement blends are seldom used at present when
the concrete may be subject to interaction with sulfates because there
are not standard tests for establishing sulfate resistance. The avail-
ability of a test which would simulate sulfate attack under field con-
ditions would allow the selection of an appropriate cement (blended or
otherwise).
2-40
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Hydration of MgO and CaO during setting causes concrete to expand.
Current ASTM specifications (ASTM C595-74) limit MgO to 5% of the cement
clinker. There are indications that the presence of fly ash greatly
diminishes the MgO-hydration expansion. Current work is aimed at
developing necessary data to support or refute these indications and also
to develop more appropriate tests to measure expansion.
The NBS will assist in a potential demonstration project in Mercer
County, North Dakota. Several coal-burning power plants are being built
in the area, and a plant has been proposed to produce bricks from the
fly ash. The NBS will be responsible for developing the necessary standard
tests for durability and strength of the bricks. The project is being
sponsored by the Mercer County Development Board and is at least two to
three years from production.
2.7.7 Tennessee Valley Authority
The TVA is conducting a large-scale feasibility test for the pro-
duction of mineral wool for insulation from boiler slag [36, 37]. The
mineral wool process was developed at the Coal Research Bureau at West
Virginia University under a grant from the Bureau of Mines. Tests will
be run to determine the financial feasibility of the process at the
Thomas Allen Station, Memphis, Tennessee. The TVA prototype will be semi-
commercial size and use four tons per hour of slag on a single eight-hour
shift. The slag is from a single 300-MW unit, with a wet bottom col-
lection system. Slag will be ejected from the boiler at about 1100°C
(2000°F), limestone is added as flux and the temperature will be raised
to 1370°-1540°C (2500°-2800°F); the fibers are spun conventionally. The
;> roc ess i<3 only applicable to wet bottom units. TVA currently is working
on the design for the unit and expects to have the unit operational by
late 1979 [37]. They have run the process in a cupola-type unit. Lime-
stone is added to drop the slag viscosity. Preliminary estimates are that
the process has an approximate payout period of five years.
The TVA staff is currently working in conjunction with an aluminum
company to determine the economic feasibility of extracting alumina from
boiler fly ash. Preliminary economics indicate that extracting alumina
2-41
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from fly ash might well be competitive with conventional technologies
for the extraction of alumina from Georgia clay (kaolin clay). The TVA
is presently considering a 2 ton/hour pilot plant facility to investigate
the feasibility of extracting and recovering certain minerals (alumina,
iron, etc.) from boiler fly ash.
TVA is also working in conjunction with some commercial interests
based in St. Paul, Minnesota, on the development of a process for ex-
tracting magnetite from boiler fly ash. Magnetite is a major constituent
of the heavy medium slurry used in coal cleaning plants, and TVA believes
that the fly ash produced at its 1,700-MW Kingston plant contains suffi-
cient magnetite to feed the TVA Paradise coal cleaning plant.
A TVA program currently is underway by the TVA to study the pos-
sibility of using fluidized bed combustion wastes as soil additives to
stabilize load-bearing fill/sub-base for small airport runways, high-
ways, etc.
One other project in progress, being done with P&W Industries, in-
volves determining the feasibility of separating and collecting ceno-
spheres (hollow glass balls) from dry fly ash and marketing them com-
mercially for application as fillers for plastics, paint extenders, etc.
2.7.8 CM - Plastic Filler
The Polymers Department of General Motors Research Laboratories has
been studying the use of fly ash as a filler in polypropylene [72, 73].
Mineral fillers currently used in plastics consist largely of silica,
alumina, and other oxides in the form of kaolin or talc.
GM obtained fly ash from several sources and in a laboratory program
characterized the particle size, density, and chemical composition. Samples
of filled polypropylene were prepared with appropriate antioxidants on a
roll mill at 190°C (400°F) and by extrusion at 205°C (425°F). The material
was granulated for use in injection molding.
Results indicated that fly ash particle size was important in some
applications. Smaller particles tend to give products with greater impact
strength and better elongation properties than do larger particles.
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However, particle size apparently had no measurable effect on yield
strength or modulus. Tensile strengths were reported to be 2.07 to
2.48 x 107 Pa (3000 to 3600 psi) and tensile moduli were 2.07 x 107
to 2.76 x 109 Pa (300,000 to 400,000 psi) for the filled plastics.
GM postulates that the fly ash-filled material is low in strength
and stiffness because of the particle shape — irregular and jagged
versus platelike talc. The higher length/thickness ratio of talc pro-
vides more reinforcement to the polypropylene matrix.
2.7.9 Other R&D
Some limited information is available on the following:
• The Fossil Energy Division of DOE has funded research at Iowa
State University on the recovery of metals from fly ash. The
objective of the program is to investigate the chlorination
of coal fly ash as a method for recovering the aluminum and to
develop a process for the large-scale recovery of aluminum and
iron from fly ash by this method. Previous work here has achieved
80% recovery of aluminum as aluminum trichloride (A10C1 ).
2. 6
• The Federal Energy Administration has funded research at
Southwest Research Institute for the evaluation of utilization
of slag, fly ash and kiln dust as additions to portland cement
by intergrinding with clinker or blending. Fly ash was added
at 0-15% and blends were tested at ages up to one year for
physical and other characteristics.
• The American Electric Power Service Corp. is funding a field
study of fly ash construction at West Virginia University. The
aim of the research is to study the field behavior of fly ash
embankments and stabilized fly ash base courses to provide
engineering design data. Laboratory and field studies included
(1) placement and compaction techniques; (2) properties of
the in-place material as a function of time and location in the
embankment and/or base; (3) effects of frost action on material
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properties; (4) moisture retention by fly ash and its effect
on strength; (5) effects of traffic on material properties;
(6) corrosion of metals embedded in fly ash: (7) permeability
of fly ash; and (8) immediate and long-term compressibility
of fly ash.
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3.0 UTILIZATION OF FGD WASTES AND BYPRODUCTS
3.1 Introduction
FGD systems are generally categorized into two groups:
• Nonrecovery—or throwaway—systems, which produce a solid or
liquid waste with little market value, and
• Recovery systems, which produce primarily purified, concentrated
S0~ elemental sulfur or sulfuric acid as a byproduct for sale.
At present, the overwhelming majority of FGD systems for controlling
emissions from utility and industrial boilers utilize some form of non-
recovery technology. Over 90% of the more than 50,000 MW of utility
boiler capacity now committed to flue gas desulfurization involve non-
recovery processes. This dominance of nonrecovery systems is expected
to continue for the near future. Except in site-specific cases with
favorable local market conditions for the by-products (sulfur or sulfuric
acid), recovery processes are more expensive.
The technology of recovery and nonrecovery systems, the character-
istics of the wastes produced, and projection of waste generation are
discussed in Volume 3. This chapter provides a review of waste utiliza-
tion, both current practices and potential utilization alternatives
that have been or are being investigated. Emphasis is placed upon wastes
from nonrecovery processes, since nonrecovery technology will be the
principal approach to the desulfurization of flue gases from fossil fuel
combustion, at least over the next 10 to 15 years. Furthermore, the
primary byproduct of recovery systems will be sulfur or sulfuric acid,
conventional products for which markets are already established.
3.2 Utilization of Nonrecovery FGD Wastes
3.2.1 Description of Wastes
Commercially available nonrecovery processes can be conveniently
subdivided into two groups according to the form of the waste material
produced—those which convert the S0~ into a solid waste and those which
produce a liquid waste. Nonrecovery systems can also be classified
according to the manner in which the flue gas is contacted with the S02
sorbent—i.e., wet scrubbing processes versus dry processes.
3-1
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All nonrecovery systems now in commercial operation on utility and
industrial boilers are wet processes involving contact of the gases with
aqueous slurries or solutions of absorbents. Although most nonrecovery
wet systems can withstand relatively high levels of particulate and trace
contaminants and many in the past have been designed for simultaneous SO-
and particulate control, most wet systems being installed today on utility
boilers are downstream from high efficiency electrostatic precipitators
in order to ensure more reliable service. The notable exceptions are
systems designed to utilize alkalinity in the fly ash for all or part of
the SOo removal. These frequently incorporate simultaneous fly ash and
S02 control.
Dry non-recovery processes have not yet been commercially demonstrated
on a utility scale in the United States. However, a number of different
approaches have been investigated, including dry injection of sorbents
into the boiler and flue gas and the use of spray dryers. All of these
involve simultaneous S(>2 and particulate control, and all produce a dry
waste material. The most promising approach at present employs spray
dryers for contacting the flue gas with slurries (or solutions) of
calcium hydroxide or sodium carbonate/bicarbonate. Three such systems
have been contracted for application to utility-scale boilers.
3.2.1.1 Solid Wastes
The four basic types of nonrecovery systems producing solid wastes
are:
• Direct lime scrubbing,
• Direct limestone scrubbing,
• Alkaline fly ash scrubbing, and
• Double (dual) alkali.
The first three of these utilize slurries of lime, limestone, or
ash to contact the flue gases and produce slurries containing 5-20 wt%
solids which are either discharged directly or partially dewatered and
possibly further processed prior to discharge. All three of these are
commercially demonstrated technologies. The fourth, the double alkali
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process, is a second generation technology which has' been applied suc-
cessfully to industrial-scale boilers but is only now reaching commercial
demonstration on utility boilers. Double alkali processes utilize
solutions of sodium salts for S02 removal which are then regenerated
using lime to produce a waste solid that is discharged as a filter cake.
In addition, dry sorbent based FGD systems are also likely to be
in commercial use by the early 1980*s. These will be based on lime,
sodium salts or other sorbents and will produce dry solid wastes. To
date, the extent of focus on utilization of such dry sorbent wastes has
been minimal. EPA is planning some pilot studies on dry sorbent processes
and dry surbent wastes in 1979 [50].
The quantity and composition of ash-free FGD wastes are dependent
upon a number of factors including: coal characteristics (most impor-
tantly, its sulfur content and heating value); S0~ emission regulations;
the type of boiler and its operating conditions; and the type of FGD
system and its operating conditions. In general, the quantity of dry,
ash-free FGD waste produced varies from about 2.0 to about 3.5 times the
quantity of 862 removed from the flue gas. Hence, a typical utility
boiler operating at a 70% load factor could produce anywhere from 50 to
500 tons of dry, ash-free solids annually per megawatt of boiler capacity.
The principal substances making up the solid phase of FGD wastes are
calcium-sulfur salts (calcium sulfite and/or calcium sulfate) along with
varying amounts of calcium carbonate, unreacted lime, inerts and/or fly\
ash. In wet processes the ratio of calcium sulfite to calcium sulfate
is a key design and operating parameter, especially for direct scrubbing
systems since it can affect not only the scale potential of the system
but also the waste solids properties. The relative amounts of calcium
sulfite and sulfate present depend principally upon the extent to which
oxidation occurs within the system. Oxidation is generally highest in
systems installed on boilers burning low sulfur coal or in systems where
oxidation is intentionally promoted. In most medium to high sulfur coal
applications, oxidation of sulfite to sulfate in the scrubber system
amounts to only 10-30%, and calcium sulfite is the predominant material
3-3
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in the waste. When the sulfate content of the waste solids is low, calcium
sulfate can exist with calcium sulfite as a solid solution of the hemi-
hydrate crystals (CaSO • 1/2H70). At higher calcium sulfate levels,
gypsum (CaS04 • 2H20) becomes the predominant form of calcium sulfate.
At very high levels of oxidation (greater than 90% oxidation of the S02
removed) all of the calcium sulfate usually will be present as gypsum.
Because the differences in the crystalline morphology of hemihydrate
and dihydrate solids not only reflect the chemical composition but also
can affect the physical and engineering properties, it is convenient to
classify FGC wastes on the basis of the ratio of calcium sulfate to
total calcium-sulfur salts. The three categories are as follows:
• Sulfate rich (CaSO,/CaSO > 0.90),
*fr X
• Mixed (0.25 < CaSO,/CaSO < 0.90), and
^ •*»
• Sulfite rich (CaSO,/CaSO < 0.25),
™T X
where CaSO is the total calcium-sulfur salts.
X
Calcium sulfite wastes present a problem because of difficulty in
dewatering. However, calcium sulfite wastes can be oxidized to calcium
sulfate, either intentionally in the scrubber or in an external oxidation
reactor. From the viewpoint of utilization, calcium sulfate is the
desirable FGD by-product.
EPA studies at the Industrial Environmental Research Laboratory
(Research Triangle Park, North Carolina) have shown that calcium sulfite
can be readily oxidized to gypsum by simple air/slurry contact in the
hold tank of the scrubber recirculation loop. Although the rate of
oxidation reaches a maximum at a pH of 4.5 and then declines at higher
pH, it was found that oxidation could be accomplished at a practical
rate up to a pH of about 6.0 [69].
In Japan, where natural gypsum is not available, forred oxidation
in scrubber systems has been employed extensively to produce a high-
quality gypsum raw material for the cement and wallboard industries.
Japanese FGD units are primarily used on oil-fired boilers and do not
have to contend with fly ash admixtures with gypsum. In the United States,
FGD systems are mainly on coal-fired boilers and usually supplement fly
3-4
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ash collection units; gypsum admixture with fly ash is possible in poorly
designed or operated systems. Furthermore, scrubber gypsum may be unable
to compete extensively with the widely available natural gypsum except
in some specific areas. Thus, the incentive in the United States has
been to develop simplified forced oxidation procedures and has been
directed only toward improving waste solids handling and disposal prop-
erties and not towards the production of gypsum with minimum fly ash
content; moreover, the oxidation reaction need be carried only to about
95% completion if one is only aiming towards relatively good dewatering
characteris tics.
There is little information currently available on the composition
of wastes from dry scrubbing systems utilizing spray dryers. However,
while all of these wastes would contain fly ash, the fraction of the waste
resulting from SO^ control would be expected to be similar in chemical
composition to those produced by wet processes using the same sorbents.
For lime-based dry scrubbing, the FGD wastes should consist primarily of
a mixture of calcium sulfite, sulfate, and unreacted lime. The quantity
of unreacted lime, however, may be somewhat higher than in wet scrubbing
wastes owing to the higher stoichiometries that would probably be
required. The mix of calcium sulfate and sulfite solids may also be
somewhat different, both in terms of their relative quantities as well
as the crystalline forms present.
For dry systems utilizing alkaline sodium salts (e.g., nahcolite
or sodium bicarbonate) the waste solids would be expected to contain in
addition to fly ash a mixture of principally sodium sulfate, sulfite,
chloride, and unreacted carbonate. These would be similar in
composition to the wastes produced from once-through sodium solution
scrubbing except that the solids would be discharged as a dry material
rathe"r than as a liquid.
3.2.1.2 Liquid Wastes
There are two different liquid waste-producing FGD processes that
are in commercial operation on combustion boilers—(1) once-through-scrubbing
using solutions of alkaline sodium salts and (2) scrubbing using ammonia-laden
water. Of the two, once-through sodium scrubbing has achieved the widest
acceptance, having been applied to many industrial steam plants and a few
utility boilers. Once-through sodium scrubbing produces a waste liquor
containing primarily sodium sulfate, sulfite, and chloride at total
dissolved solids concentrations generally in the range of 15-30 wt%.
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Most of these waste liquors also contain significant levels since the
systems are used for combined participate and SO™ control. Frequently,
the waste liquors are air-sparged to oxidize any residual sulfite to
sulfate, especially where wastes are discharged for disposal.
3.2.2 Current Utilization Practices
The available data on industrial and utility boiler FGD systems
indicate that there is very little commercial utilization of FGD wastes
in the United States. In fact, the only commercial utilization reported
for nonrecovery wastes is the reuse of once-through sodium scrubbing
liquors at pulp and paper plants [51]. There are two such plants where
the scrubber discharge liquor is recycled for use in pulping operations.
3.2.3 Potential Utilization Alternatives
A variety of potential uses for stabilized and unstabilized calcium
sulfite/sulfate wastes from lime- and limestone-based scrubbing have
been proposed including:
• Road construction base,
• Cement and concrete manufacture,
• Filler in glass,
• Fertilizer and fertilizer base,
• Fill material (structural or landfill),
• Brick manufacture,
• Commercial gypsum substitute (in wallboard and cement) either
as a direct waste or converted sulfite-rich material,
• Aggregate,
• Recovery/reuse of chemical values (including beneficiation), and
• Artificial reef constructions (although this is generally con-
sidered to be disposal and is discussed in Volume 5).
Recent studies [7, 43] have indicated the feasibility for use as struc-
tural fill, brick manufacture, and highway construction, although the
current level of development is low at this time. The technical feasi-
bility of most of these product uses has been evaluated on only a limited
scale; and even for those which have been shown to be technically feasible,
the economic viability is still uncertain. Also, for some of the po-
tential uses that have been proposed, coal ash can also be used (as
mentioned earlier), and in many cases, coal ash will be the preferred
material.
3-6
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A brief discussion of some of the more viable options is presented
below prior to the discussion of research and development programs in
waste utilization.
3.2.3.1 Structural Landfill
Unstabilized FGD waste typically has poor structural properties.
Sulfite-rich materials are usually difficult to dewater and can be
structurally unstable (tendency to liquefy and flow). As a result,
unstabilized waste probably will not be useful for fill.
Stabilized waste may provide viable fill materials. On a demonstra-
tion basis, stabilized FGD waste has been used for road base, road fill,
lightweight aggregate, and artificial reefs [52]. Its use also has been
suggested for mine reclamation, subsidence control, acid mine drainage
control, etc. [11]. The stabilization processes are discussed in more
detail in Volume 3.
As more FGD systems begin to utilize stabilization procedures with
landfill of wastes, the modified and stabilized waste might find an
outlet for use in structural fills and enbankments. The stabilized
waste usually contains significant amounts of fly ash as a result of the
stabilization process. The structural properties of stabilized waste
may make it advantageous for landfill or strip mine reclamation.
3.2.3.2 Gypsuro
Forced oxidation of FGD waste can yield gypsum as an end-product.
Gypsum so produced may be useful for wallboard manufacture, cement pro- r-
duction (as a set retarder), and as a soil additive; wallboard has the
potential for being the largest end-use market.
The technical differences between by-product gypsum and natural
gypsum are somewhat uncertain, and conflicting information exists. By-
product gypsum has a smaller particle size and contains more free moisture
(20% versus 3% in natural) than natural gypsum. It is up to 96% pure
calcium sulfate, with the primary impurity calcium carbonate and less
than .05% solubles [67]. Some by-product gypsum is purer than natural
gypsum; in one test, Chiyoda process gypsum was about 90% calcium sulfate
versus 80% purity for natural gypsum being imported from Canada [69].
3-7
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Industry (wallboard) manufacturers have expressed concern over the pos-
sible effect of contaminants (e.g., fly ash, reagents, calcium sulfite,
and soluble salts) on product quality and economics, and the effect of
variations in sludge (gypsum) quality and composition on product quantity
and economics [35]. Wallboard or cement gypsum can contain up to 15%
CaCOo, with the nominal grade containing 8-15% CaCO-j. Sulfuric acid may
be added to convert excess CaC03 to gypsym and also to lower the pH to
enhance oxidation of sulfite to gypsum. The effect of entrained trace
metals and elements on gypsum is unknown.
Wallboard is currently produced from natural gypsum which is either
\
mined domestically or imported. Production is generally from a captive
source, as the industry is vertically integrated and most companies own
or control their own mines either here or abroad. This could make market
entry for by-product gypsum very difficult. The degree and amount of im-
purities that can be tolerated in gypsum depend upon intended use. In
wallboard manufacture, impurities in gypsum reduce the strength of the
product and more pounds of gypsum are required to achieve a given strength
of finished wallboard.
Entrained coal fly ash apparently has little effect on the quality
of the wallboard produced, although it does produce a dark-colored gypsum
which may have some associated sales resistance [35]. Chloride, which
occurs at higher concentrations in scrubbers on coal-fired versus oil-
fired utilities, may cause corrosion problems in wallboard installations
[52]. Chloride also affects calcining temperature, set time, and stucco
slurry consistency. Soluble chlorides are usually limited to 0.02% to
0.03% if the gypsum is used in wallboard. The hydrous sulfate salts affect
moisture pickup and bonding characteristics of the wallboard and are also
limited to 0.02% to 0.03%. Hydrous clays of up to 1.0% to 2.0% may be
tolerated [54]. Gypsum is also used as a soil conditioner; this use is
discussed later in this section.
In Japan, by-product gypsum is widely produced, as most utilities
equipped with lime/limestone scrubbing convert the sludge produced to
gypsum through intentional forced oxidation. However, a distinct set of
3-8
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circumstances exists which tend to encourage this practice:
• Regulatory agencies frown on throwaway or unoxidized waste.
• There is a scarcity of suitable land for waste disposal,
• Since there are no natural sources of gypsum, market demand
is high.
• Boilers are generally oil fired rather than coal fired.
Japan has little or no natural gypsum and, therefore, must depend on
imports and byproduct gypsum from chemical processes (e.g., production
of phosphoric acid). When lime/limestone scrubbing was introduced, this
ready market for gypsum led most system suppliers to develop oxidation
units. Most Japanese power plants burn oil; the ratio of power produced
from oil to that from coal is about 10 to 1 [70]. The gypsum from scrub-
bing coal-fired boilers may be less acceptable becasue of the higher
impurity content from entrained fly ash, chlorides, etc. [52, 70]-
Most of the FGD gypsum made in Japan goes to the wallboard industry
where it commands a higher price than in the cement industry where higher
fly ash content can be tolerated. The market for FGD gypsum in Japan has
held up well, considering the large amounts being produced as a scrubbing
byproduct and as a byproduct of phosphoric acid manufacture. However,
recently supply has exceeded demand, and this may affect the overall
situation.
The potential for utilization of gypsum in the United States is
probably not as favorable as that in Japan. The United States has more
open land available for sludge disposal and hence, disposal costs are less
than in Japan. Moreover, natural gypsum sources are available to satisfy
the market at reasonable cost. Furthermore, FGD systems in the United
States are and will continue to be installed on coal-fired boilers; po-
tential admixture with coal ash would impact quality control requirements.
Market studies by the TVA and others [55,56,67] indicate that the pro-
duction and marketing of abatement gypsum may offer substantial economic
advantages over FGD waste disposal but that abatement gypsum probably can-
not compete with natural gypsum except in specific situations. (See Section
2.3.) Successful entry of abatement gypsum into the wallboard industry as
3-9
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a replacement and competitor of naturally mined gypsum seems uncertain.
The wallboard industry is proceeding with caution in accepting abatement
gypsum as a substitute despite some advantageous properties of abatement
gypsum and several successful demonstrations.
Gypsum could be utilized also in the manufacture of portland cement
[67]. This is practiced in Japan and does not require as high a grade of
gypsum as wallboard manufacture. However, little information exists on
the technical requirements for gypsum in this application. This market
segment is not generally integrated into natural gypsum production and
marketing so that market penetration may be easier here than in the wall-
board industry. Gypsum is used in the cement industry as a set retarder;
it is added to clinker and ground into the final product. The sulfite
content of the by-product gypsum may limit its use. In general, the
specifications for use in cement are not as stringent as those for use in
wallboard.
The use of by-product gypsum in agriculture, although representing
a smaller market than either of the above uses, looks promising. At least
one source indicates current commercial utilization in this capacity [67].
The use of by-product gypsum is discussed more fully in Section 3.2.3.4.
3.2.3.3 Aggregate
Production of aggregate from FGD waste is a potential large volume
market because of increasingly more expensive naturally occurring
aggregate.
A mineral aggregate containing sludge was developed by I.U. Conversion
Systems and has been satisfactorily used in a demonstration project [57].
Mineral aggregate also has been produced using an autoclave process where
pelletized sludge is hydrothermally agglomerated by curing with saturated
steam at 300 psi. This process would be faster than that proposed by the
Corson Company but more expensive because of the energy requirements.
Manufacture of lightweight aggregate has also been proposed as a
potential use for FGD wastes. Lightweight aggregate currently is produced
by expanding shale, slate, or clay. The growth in use of lightweight
aggregates (a doubling of use is expected in the next 20 years) and the
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shortages expected to occur in certain urban areas are likely to favor
such potential utilization of FGD wastes. A number of plants have been
constructed that sinter fly ash into a lightweight aggregate and in some
areas this sintered fly ash has been found to be economically competitive
[58]. Fusion tests indicate that control of the process with FGD waste
might be difficult because of the variability of the sludge and the narrow
softening - fusion temperature band.
Mineral aggregate shows considerable promise for large volume utili-
zation of by-product sludge, but technical and economic problems must be
solved before this use is commercialized.
3.2.3.4 Agricultural Uses
FGD scrubber waste may be useful as a soil amendment, a gypsum
substitute, or in fertilizer. Such use will be possible in some areas,
for example, California and the southeastern states [52], but will probably
be limited to local markets which may coincidentally be available to a
utility.
Research efforts directed toward the use of FGD waste as a fertilizer
base or additive range from simple studies of the effects of directly adding
unstabilized waste to soil to more sophisticated conversion process
technologies related to fertilizer production.
As a direct soil additive, FGD waste has potential benefits including
its neutralization capability and its use as a source of sulfur, calcium,
magnesium, and certain necessary trace metals that may participate in
plant growth. However, FGD waste has little or no nitrogen, phosphorous,
or potassium value, and the presence of high levels of IDS (particularly
sodium and chlorides) as well as some potentially toxic trace metals may
present problems in agricultural uses in any large quantities.
Oxidized FGD waste may be useful as a gypsum substitute. Gypsum is
used in the following ways:
• As a soil amendment on high-alkali soils,
• As a neutral source of calcium, and
• To provide sulfur on sulfur-deficient soils.
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Soil amendments may be of three types: soluble calcium salts (calcium
chloride and gypsum); low solubility calcium salts (limestone); and acid
or acid-forming compounds such as sulfur, sulfuric acid, iron, and
aluminum sulfate [5]. Because of their low cost and suitability, gypsum
and sulfur are the most widely used.
Peanuts require large amounts of soluble calcium in the soil surface
to facilitate pegging and nut formation. Gypsum use is recommended when
soil pH is already satisfactory but additional calcium is needed (gypsum
is a non-alkaline source of calcium).
x Where soils are deficient in sulfur, gypsum can be used as a source
of this nutrient. However, since the requirement per acre is usually
small (VLO Ib/acre), it is usually easier to simply add the sulfur to.
fertilizer and apply both in a single application.
A process to produce granular fertilizer from scrubber waste has
been proposed in the literature and currently is being developed [59].
Research is being conducted by the TVA as part of an Interagency Agreement
involving the use of lime/limestone scrubbing wastes in agricultural
applications. This portion of the work involves use of direct lime and
limestone scrubbing system wastes as a filler material in and as a source
of sulfur for fertilizer. The work includes pilot testing of the fertil-
izer inclusion/production process, testing of field plots using wastes/
fertilizer mixtures, and studies of the costs associated with producing
such a fertilizer and its market potential. To date, initial pilot plant
tests have shown some problems in introducing waste into standard fertil-
izer production units. (See Section 2.3, R&D - TVA.) Waste also may be
useful for its liming value [59]. The liming value will probably vary
with the unreacted lime and the amount and basicity of the fly ash con-
tained in the waste. Gypsum and sulfite have little or no liming value
but provide soluble calcium and sulfur. Fixation additives may affect
the value of sludge as fertilizer. Little information is available on
this end-use, and it probably would be economical within a limited
distance from the waste source.
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3.2.3.5 Building Brick
Brick production by the conventional sintering process as used for
fly ash or clay brick is not technically feasible for FGD waste raw
materials at this time. S(>2 is evolved during the sintering process,
and control of the level of softening during sintering is difficult (see
lightweight aggregate). Calcium silicate brick has been made from FGD
waste [38]. The brick is a mixture of scrubber waste, silica sand, and
lime, which is pressed into shape and then autoclaved. The bricks are
of good quality and meet the ASTM specification for calcium-silicate brick
[38]. Calcium silicate brick is not a common building material in the
United States, and major market changes would have to take place before
this method of utilization would become practical.
3.2.3.6 Recovery of Chemicals
Various investigators have suggested and explored the concept of
the recovery of useful chemicals from scrubber wastes (FGD or FGC).
Furthermore, recovery FGD systems produce sulfur or sulfuric acid as
by-products. At present, two [2] utility plants employ recovery FGD
systems. Thus, the list of possible by-product chemicals from scrubbing
the sulfur contained in flue gases includes calcium oxide, magnesium oxide,
elemental sulfur, sulfuric acid, sodium sulfate, sodium sulfite, and
ammonium sulfate. Some of these chemicals can be obtained from scrubbers
using recovery systems but may not be practicably obtainable from lime/
limestone sludge because of the extensive reprocessing necessary to ex-
tract these materials. The one potential exception is production of ele-
mental sulfur. A variety of processes have been suggested for the pro-
duction of elemental sulfur from FGD waste [56, 60, 61]. None of these
processes have been implemented on a full-scale basis.
3.2.4 R&D Programs - Nonrecovery FGD Wastes
The largest ongoing research program on FGD waste utilization is
that sponsored by the EPA. The EPA is currently sponsoring four projects
connected with utilization of nonrecovery FGD wastes:
1. Converting FGD waste to sulfur (Pullman-Kellogg),
2. Converting FGD waste to fertilizer (TVA),
3-13
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3. Utilizing FGD waste to extract alumina from kaolin clay
(TRW), and
4. Marketing of FGD waste as gypsum (TVA).
A fifth project has been discussed on utilization of FGD waste in
cement manufacture, but no projects are reported. The overall objectives
of the projects are shown in Table 3.1. The current status is as
follows:
• The Pullman-Kellogg sulfur project has proceeded through
pilot plant testing of the critical process units.
Evaluation of process economics is necessary before further
work proceeds.
• Fertilizer production from waste, being studied by TVA,
is currently on hold, partly because of uncertainties over
regulatory requirements in the future. A pilot plant
program has been developed, but further work is unlikely
until resolution of these requirements [37].
• The TRW study of alumina production with FGD has been
completed and a final report published. This economic
study concluded that FGD waste utilization for alumina
production from kaolin clays, coupled with an adjacent
cement plant to utilize by-product dicalcium silicate,
may be feasible in the future depending on alumina prices.
A future series of laboratory projects is suggested in
the report.
• The TVA has recently completed a study of by-product
marketing of sulfuric acid, sulfur, and gypsum [ 67].
A linear programming model was used to determine the
potential marketability (based on low-cost constraints)
of the three by-product wastes. This study is dis-
cussed in more detail in Section 3.4.
Northern States Power Corporation and Texas A&M University have an
ongoing program to demonstrate the technical feasibility of lightweight
aggregate production from FGD waste and clay. Bench-scale work has been
3-14
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Table 3.1
Current Research in FGD Waste Utilization
Primary Sponsor
Contractor
Project Focus/Status
Ref.
Environmental
Protection
Agency
Pullman-Kellogg
TVA
u>
Ui
TVA
TRW
Northern States Power Texas A&M
University
Demonstration of process for conversion of
FGC scrubbing waste to sulfur and calcium
carbonate. Pilot plant work demonstrating
technical feasibility of major units has been
completed. Economics need to be evaluated
before further scale-up.
(Ongoing)
Assessment of FGC waste for conversion
fertilizer. Some pilot plant work has been
completed. Project is currently on hold
awaiting decision vis-a-vis RCRA regulations.
(On Hold)
Marketing of byproducts from FGC waste.
Marketability study of byproduct sulfur,
sulfuric acid, and gypsum using least-cost
linear programming mode. The study has
been completed and reported.
(Completed Final Report, October 1978)
Process design and economic evaluation of proposed
process to use FGC waste was for the extrac-
tion of alumina from kaolin clay with calcium
disilicate byproduct recovery.
(Draft Report)
Assessment of use of FGD waste for production
of lightweight aggregate. Bench scale work
completed. Pilot scale work under development.
60, 61
60, 61
60, 61
60, 61
62
Source: Arthur D. Little, Inc.
-------
completed, and work is proceeding on a pilot level. These projects are
discussed in detail in the following section.
In addition to these programs, several other R&D projects are
ongoing:
a. Southern Services has contracted with the U.S. Gypsum
Company for test runs of wallboard production utilizing
abatement:gypsum generated from the Chiyoda Thoroughbred
101 dilute acid scrubber at the coal-fired Scholz Plant
of Gulf Power. These production runs were conducted in
June and December 1976. The full results of these tests
are not yet available, but indications are that the tests
were reasonably successful [69].
b. Southern California Edison (SCE) has been experimenting
with gypsum production from its Highgrove Station Unit
No. 4. This is a 10-MW oil-fired facility. A 50-ton
full-scale wallboard production run has been completed, but
test results were not available.
c. The Purity Corporation is pursuing the development of
a patented process for using waste as a fertilizer. The
process makes use of the sulfur and calcium in the wastes
with the addition of phosphorous and ammonia to produce
a granulated fertilizer.
d. The University of Florida Agricultural Research Center in
Quincy, Florida, is testing for the Southern Company the
use of two different wastes as soil amendments. The two
wastes being tested are the dual alkali filter cake and
gypsum from the ADL/CEA and Chiyoda prototype systems,
respectively, at the Scholz Steam Plant in Sneads, Florida.
Testing is directed toward determining the effectr of
different concentrations of the wastes on soil pH and the
availability of calcium, magnesium, potassium, and phos-
phorous. Tests are also being conducted to project the
effects of these wastes on the dry matter yield of soybeans
and peanuts.
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3.2.4.1 Pullman Kellogg [61,63]
The M. W. Kellogg Company developed the "KEL-S" process for conver-
sion of lime/limestone scrubbing wastes to elemental sulfur with recovery
of calcium in the waste as calcium carbonate.
As conceived, the process will reduce CaSO- and CaSO/ in FGD waste
to calcium sulfide (CaS) in a rotating kiln with coal. The CaS is
reacted with hydrogen sulfide (H2S) producing calcium hydrosulfide, i.e.,
(Ca(HS)2). The Ca(HS)2 is dissolved in water; the solution is filtered
and reacted with CO^-rich gas from the kiln. The Ca(HS)2 reacts with
the CO- to form ELS gas and calcium carbonate (CaCCO which precipitates.
Some of the H2S is recycled for reaction with the CaS; the remainder is
converted to sulfur in a Glaus unit. The precipitated calcium carbonate
is recycled to the scrubber system.
Pilot-scale work has been conducted to evaluate the technical feasi-
bility of various process steps. The production step (reduction to CaS
and dissolution) has been demonstrated to be technically feasible, and
the calcium regeneration step has been proven satisfactory. The economics
of the process need to be evaluated before any further decision on the
process is made. Design data need to be generated before scaleup to a
larger prototype test unit could be made.
3.2.4.2 TVA [61, 63]
The TVA is assessing the use of lime/limestone FGD waste as a filler
material in and a source of sulfur for fertilizer. The work is being
performed by TVA, Office of Agricultural and Chemical Development, Muscle
Shoals, Alabama, as part of an interagency agreement on the evaluation
of FGD waste utilization.
The process (see Figure 3.1) mixes phosphoric acid (HJPO.) and ammonia
with dewatered FGD waste at approximately 93°C (200°F) in a preneutralizer.
The hot mixture is transferred to an ammoniator-granulator where the slurry
solidifies as it is ammoniated, forming a granular material. This material
is dried, cooled, and screened to obtain a fertilizer product.
3-17
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PHOSPHORIC ACID
I
I-1
oo
TO STACK
1
TO STACK
EXHAUST FAN
r« —i
GAS
SCRUBBER
EXHAUST GAS
CYCLONE
DRYER
COOLER
GAS
TREATMENT
SYSTEM
EXHAUST
FANS
Source: [61]
Figure 3.1 Process Flowsheet for Producing Solid Granular
Fertilizer Material from Scrubber Waste
-------
The tests used waste produced at the 1-MW limestone pilot unit located
at the TVA Colbert Steam Plant. Severe foaming occurred during the intro-
duction of waste, phosphoric acid, and ammonia into the preneutralizer.
A specially designed preneutralizer was constructed to eliminate the
problems encountered. Alternative methods and locations for adding the
waste, acid, and ammonia, improved agitation, foam breaking methods, and
insulation were tested. Initial testing with the modified preneutral-
izer resulted in sulfur losses ranging from 78 to 90 wt% and an ammonia
loss of 34 to 61 wt% based on input quantities.
The losses are suspected to result from a reaction between calcium
sulfite in the waste and phosphoric acid:
3CaS0 + 2HP0 -> Ca
Laboratory tests and past pilot plant experience indicate that these
reactions are possible.
It is expected that these unwanted reactions can be prevented by
either neutralizing the phosphoric acid before it comes into contact with
the waste or by oxidizing the calcium sulfite to calcium sulfate before
feeding to the preneutralizer. Therefore, tests are being planned to
determine the feasibility of using oxidized sludge in the preneutralizer.
Additional tests were conducted to define preneutralizer operating
conditions. These included the effect on ammonia-to-phosphoric acid
ratios and the location of the waste feed and its flow rate. Problems,
including release of SC^, sparger plugging, and temperature and fluidity
control, were encountered under the conditions tested. Indications are
that pH may control the fluidity and SC^ release problem.
Plans and cost estimates for pilot plant development of a cross-
pipe reactor to possibly overcome these problems have been developed.
This program is currently on hold. A key factor that will impact uti-
lization in this and other applications is the emerging regulations under
the Resource Conservation and Recovery Act (RCRA) of 1976. Restarting of
this and possibly other projects depends on future RCRA implications [37].
3-19
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3.2.4.3 TSW [61, 63, 64]
TRW Systems has completed a preliminary process design and economic
evaluation of a process to use lime/limestone FGD waste for the extraction
of alumina from low-grade kaolin clays. Byproduct dicalcium silicate and
elemental sulfur are produced, thereby completely utilizing the waste.
In the conceived process (see Figure 3.2) raw kaolin clay, lime/
limestone scrubber;waste, sodium carbonate solution, and recycled desili-
cation residue are ground and mixed in tube mills. The mixture is dried,
sintered at 780°C (1436°F), and reduced with carbon monoxide (CO) at 1200°C
X(2192°F) to produce soluble sodium aluminate (Na20 • Al20g) and insoluble
dicalcium silicate (2Si02 • 2CaO) plus hydrogen sulfide gas (H2S), sulfur
dioxide (S02), and combustion gases. Most of the H^S and S02 are fed to
a conventional Glaus unit producing elemental sulfur and a Beavon tailgas
plant.
The cooled solids are leached with sodium carbonate (to dissolve the
alumina) and filtered to remove the dicalcium silicate; residual dicalcium
silicate is precipitated from solution with lime. The alumina trihydrate
is precipitated from the pregnant solution by adjusting the pH with
combustion offgases (CO- carbonation), filtered, washed, dried, and
calcined at 1093°C (2000°F) to alumina. The remaining solution is
concentrated and recycled. Dicalcium silicate is washed, filtered, and
sent to an adjacent cement plant where it substitutes for lime and silica
feedstocks.
The process is predicated on several technical assumptions, the
validity of which need to be demonstrated before the process could be
considered technically feasible. These assumptions include:
• One ton of waste requires 0.012 ton of soda ash, 0.30 ton of
clay, and 0.273 ton of coal, and will produce 0.07 ton of alumina
0.156 ton of sulfur, and 0.625 ton of dicalcium silicate.
• The sintering-reduction reactions proceed in the proper sequence
and produce a given offgas composition; otherwise, an absorption
plant may be needed for the Claus unit.
3-20
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Sludge
Tube
Mill
Dryer
H2S/S02
Na C0_
Claus-
Beavon
Heat
Recovery
,
C(
23
Kiln
Grinding
Leach
Tank
Filtration
Dicalcium I
Silicate
Autoclave
Filtration
CO-
>- Stack Gas
>- Sulfur
Dicalcium
Silicate
Product
Carbonation
Classifier
Concentration
Filtration
Dryer
Source: [61, 64]
Alumina
Figure 3.2 TRW Process Flowsheet
-------
• The reactions of soda, alumina, calcium, and silica to form
dicalcium silicate and sodium aluminate will proceed in a
reducing atmosphere to a high percentage completion.
• The reaction rates are sufficiently fast to be practical.
• Side reactions do not occur which inhibit the formation of soluble
sodium aluminate and thus negate the output of alumina.
• Coal can be used to produce a reducing atmosphere in the proper
amounts in this processing scheme. The process may require a
coal gasification reactor for some or all of the coal required.
• The dicalcium silicate byproduct possesses the necessary mechan-
ical properties for compatibility with standard cement manufacture.
TRW noted that an alternative processing scheme in which the principal
product is cement (tricalcium silicate) may have the potential for increased
economic leverage. This latter scheme would use sand and lime/limestone
scrubber waste as primary feedstocks. Physically, the design of such a
process need not extend beyond grinding of the kiln sinter and, hence,
would require significantly less capital than the alumina extraction pro-
cess. Such a process would also be less energy intensive.
The study concluded that the alumina extraction process was commer-
cially feasible based on existing economic conditions, provided that the
process complex includes a cement plant to utilize the dicalcium silicate
byproduct. Investment costs were based on 1975 costs (M&S index * 444.3).
Interest rate during construction was taken as 9% with a two-year con-
struction period. Total investment for a plant capable of handling waste
from a 1000-MW power plant was estimated to be $51.5 million using the
Bureau of Mines "study estimate" method; using a standard estimating method,
capital costs are calculated to be $52.2 million. Standard techniques
were used to ratio purchased equipment costs to installed costs. Major
process equipment was sized and estimated. Raw materials were estimated
as of July 1976. These costs were used with various assumed discounted
cash flow (DCF) rate of return on investment to calculate minimum required
alumina prices, both with and without a combined cement plant.
3-22
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A parametric evaluation of cost sensitivity was done to assess the
affect of raw material costs, by-product credits, energy costs, and DCF
rate on either alumina price or required sludge credit for a given alumina
price. Some of the salient results are presented below. (See Table 3.2.)
For comparison, the current market price of alumina is about $140/ton
[65]. Note that the bulk of the analysis was done without a combined
cement plant, but the results still are generally applicable. A definite
economic advantage exists for the combined alumina/cement plant.
The required price for alumina is sensitive to the rate of return,
sulfur credit, sludge credit, and coal cost. Depending upon what values
are chosen for these variables, the alumina produced may or may not be
economically marketable. TRW used a discounted cash flow rate of return
of 10-15%. This appears low considering the level of risk inherent in
this type of project. A higher rate of return would increase the required
alumina prices even more than the values indicated here.
The study recommended that any further work concentrate on (1) veri-
fying the technical assumptions, and (2) considering production of cement
as the principal product.
3.2.4.4 Texas A&M University [62]
Northern States Power Corporation (NSPC) is sponsoring a study at
Texas A&M which is looking at the feasibility of using FGC waste for the
production of lightweight aggregate. NSPC uses aqueous limestone and fly
ash for scrubbing and produces FGC waste. Texas A&M has produced light-
weight aggregate from this waste in a muffle furnace. Investigations are
cu-rently underway on a pilot plant unit which will utilize a rotary kiln.
The aggregate is produced by mixing clay and sludge, agglomerating, and
firing in the kiln.
This portion of the study is focusing on a technical assessment of
the pilot unit. If the process proves technically feasible, market and
economic studies will be conducted.
3-23
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u>
to
*-
Table 3.2
TRW: Sensitivity Analysis
Combined Cement Coal Clay Capital Sludge Cement Sulfur Estimated Alumina Cost
Case Plant Cost Cost Cost Credit Credit Credit 10% DCF 12% DCF 15% DCF
Sludge No $20 $6 $52M $1 - $10 .. $370 $404 $461
Credit $5 $292 $327 $383
$1-$10 $10 $195 $229 $286
Capital No $20 $6 $52M $5 - $10 $292 $327 $383
Cost xO.5 $193 $210 $237
±50% xl.5 $392 $444 $529 ,
Clay Cost No $20 $1 $52M $5 - $10 $270 $304 $360
$1-$10 $6 $292 $327 $383
Coal Cost $10 $310 $385 $401
@ $40 $40 $6 $468
Sulfur No $20 $6 $52M $5 - $0 $315 $349 $405
Credit $10 $292 $327 $383
$0-$25 $25 $259 $293 $350
With Cement Yes $20 $6 $87M $0 $50 $10 $221 $279 $369
Plant-Sludge $5 $124 $182 $272
Credit $0-$10 $10 $27 $85 $174
Source: [64]
-------
3• 3 Utilization of Wastes and By-products from Recovery FGD Systems
3.3.1 Introduction
As a category, recovery processes differ from nonrecovery processes
in that they are designed to produce a high purity by-product sulfur
compound with an existing, established market. At present, only systems
producing elemental sulfur, concentrated sulfuric acid and/or concentrated
»
SO- are considered to be recovery systems in the United States. In a sense,
processes producing a high quality gypsum by-product could also be con-
sidered recovery systems as they are in Japan; however, in the United
States, there are no commercial FGD systems designed for the production
of relatively high quality gypsum intended for sale. Most processes
now being considered are geared more toward the improvement of system
performance (e.g., minimization of scale prevention, improved limestone
utilization, etc.) and enhancement of waste properties for disposal
operations, rather than manufacturing a product. Present gypsum-producing
processes are therefore thought of in the United States as nonrecovery
systems, and the utilization of FGD gypsum has been discussod along with
other wastes from nonrecovery systems.
Recovery processes (those producing sulfur, sulfuric acid or
concentrated S0?) can offer potential advantages over nonrecovery systems
in that they simultaneously produce a by-product chemical where there
is an existing market and reduce the volume of FGC wastes that may have
to be discarded. However, the total volume of FGC wastes produced will
still be high, since coal ash will still be generated and the recovery
systems themselves also produce a small amount of waste.
There are a number of factors, however, which may tend to offset
the advantages of a saleable by-product and the reduction in waste
volume and which may ultimately impact the viability of producing
sulfuric acid and/or sulfur in many cases. The most important of these
factors are as follows:
• Production of waste streams which require treatment
and disposal,
3-25
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• Immediate and longer-range marketability of by-product
sulfur and sulfuric acid,
• Feasibility of stockpiling by-products such as sulfur
in anticipation of a future market, and
• Increased energy demands of many recovery systems,
especially those producing sulfur. ^
3.3.2 Waste Streams from Recovery Processes
Recovery processes require separate removal of fly ash. Consequently,
fly ash and bottom ash are collected separately and may be maintained
as separate products from the by-product of recovery. Therefore, all
products are potentially marketable on a segregated basis; this may be
an advantage. In addition, since FGD waste essentially is reduced or
eliminated, fly ash which might be needed to stabilize waste can now be
marketed. In the future, nonrecovery processes may require greater and
greater amounts of potentially saleable fly ash to stabilize FGD wastes.
Therefore, one potential advantage of recovery processes would be that
more fly ash could be utilized in a direct fashion rather than being
used to stabilize FGD scrubber waste.
On the other hand, no recovery system is likely to be waste free.
All of the commercially available recovery processes as well as those
now being demonstrated on a utility scale boiler produce some form of
waste in addition to the by-products. The most highly developed
recovery systems (Wellman-Lord process, magnesium oxide scrubbing,
citrate process, and aqueous carbonate scrubbing) are wet processes and
involve contacting the flue gas with absorbent solutions or slurries
analogous to nonrecovery systems. These systems cannot tolerate any sig-
nificant contamination of the absorbent liquors with fly ash, chlorides, or
possibly other trace species present in the flue gas. These impurities can
interfere with the system chemistry and/or contaminate the by-product.
Hence, application of these wet processes to combustion boilers, particularly
coal-fired boilers, would normally require incorporation of a prescrubber
ahead of the SO- absorber, even where a high-efficiency precipitator
is used for particulate control.
3-26
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In addition to removing chlorides, residual fly ash, and some
trace species which would otherwise be trapped in the absorber, such
prescrubbers also can remove significant quantities of S0_. The blow-
down from these prescrubbers is therefore acidic and can contain appre-
ciable levels of suspended solids as well as potentially higher levels
of soluble species than present in many nonrecovery wastes. Treatment
of the blowdown prior to discharge can result in waste quantities equiva-
lent to as much as 15% of that produced by nonrecovery systems.
Some of the processes such as the Wellman-Lord process and
magnesium oxide scrubbing produce secondary waste streams. In the case
of the Wellman-Lord system, it is an impure sodium sulfate waste cake.
Sodium sulfate is formed by oxidation of the sulfite absorbent. Since
it cannot be readily regenerated to an active alkali, it must be purged
from the system. If there is no ready market (e.g., local sodium-based
pulp and paper mill) it must be disposed of.
In the case of magnesium oxide scrubbing, magnesium sulfate may
need to be purged if oxidation levels exceed steady-state levels
consistent with the ability to convert it to magnesium oxide.
3.3.3 Marketability of Sulfur or Sulfuric Acid
A key market-related constraint on recovery FGD systems is the
geographic limitation of the market for elemental sulfur and sulfuric
acid. Transportation costs limit the marketing radius for sulfur or
sulfuric acid. Sulfur or sulfuric acid from recovery FGD systems would x
have to potentially compete against sulfur from other sources including
Frasch sulfur, sulfur from smelters, and sulfur from sour-gas sweetening.
In certain specific locations, a local market may exist with these con-
straints. However, there does not appear to be a sufficient market on the
large scale in the immediate future for the sulfur or sulfuric acid that
would be produced if a significant percentage of power plants produce
by-product sulfur or acid.
3-27
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Furthermore, markets for these products are currently constrained
by oversupply in some areas; and the cost for producing the by-product
with FGD systems is high. Therefore, the market potential for these
types of utilization products is probably limited, except in special
cases. By-products from recovery processes can probably be successfully
marketed:
• In specific locations where a market for the products exists
because of limited supply from other sources (e.g., trans-
portation constraints), or
• In areas where availability of disposal options for
\
nonrecovery processes is so constrained that the
cost of disposal of wastes is higher than the marketing
costs for these by-products.
This potential for utilization of nonrecovery processes will be very
site-specific.
3.3.4 Stockpiling
Since about 80% of sulfuric acid is produced from elemental sulfur,
these chemicals are highly interrelated. Sulfur has a number of other
uses including hydrotreating, fertilizer, insecticides and vulcanization;
and research activities continue to develop new uses for sulfur (e.g.,
road construction). While most current demand is met by the Frasch
(from the Gulf coast) process, at some future date these sources may be
depleted. Further, energy requirements may limit recovery of low-grade
Frasch deposits. TVA [56] concludes that over the long-term a greater
portion of the sulfur will have to come from other than natural sources.
Beyond the year 2000, demand for sulfur is projected to exceed supply
[66]. Then alternative sources could be important. In fact, stockpiling
might be one alternative for utilities which could not find an immediate
market outlet for by-product sulfur. Stockpiling of sulfuric acid is not
practical due to technical difficulties. Stockpiling of elemental sulfur
however, would be feasible if sufficient incentives existed. Stockpiling
could be considered a special type of future utilization. At present, the
full implications—technical, financial and institutional—of stockpiling
are not known.
3-28
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3.3.5 Energy Demands
The production of elemental sulfur from recovery processes requires
the use of some form of reductant such as natural gas, hydrogen, carbon
monoxide or coke. Those processes which produce an intermediate stream
of concentrated S02 for conversion to sulfur (Wellman-Lord, magnesium
oxide) can utilize natural gas directly (the Allied Chemical process)
or lUS (conventional Claus). The citrate process also utilizes H~S
to produce sulfur by reaction with the sulfur-laden absorbent solution.
The hydrogen required can be produced by steam reforming a suitable
feedstock such as naphtha or possibly by coal gasification. However,
coal gasification technology is not as advanced as the recovery systems
and adds another level of complexity to FGD systems. Hence, the principal
source of reductant for conversion to sulfur, at least for the next
few years, would probably be natural gas or naphtha. Aside from the
economics, the uncertainties in supply and the potential constraints
on natural gas and naphtha consumption could be problematic.
In addition to coal gasification, there are other alternatives
now being researched which could avoid the need for natural gas or naphtha.
These include: the Foster Wheeler RESOX process in which S02 is reduced
by passage of the gas through a bed of anthracite coal (a development
program is now being sponsored by EPRI in West Germany); and the aqueous
carbonate FGD process which utilized petroleum coke or coal for direct
reduction of spent scrubbing liquors (a demonstration process is now being
funded by EPA). Allied Chemical also has a coal reduction process.
However, these processes are many years from commercialization and the
current potential shortages of natural gas and oil could impact the im-
plementation of recovery systems.
3.4 FGD Waste and By-product Marketing
Previous work [11, 38] has indicated a variety of potential uses and
markets, but the work devoted to definitive market assessment studies or
utilization economics has been limited. In part, this has been due to
variability in FGC wastes and uncertainties in waste processing and con-
version costs. Unknowns regarding waste properties affecting utilization
coupled with institutional constraints can also act as dissentives to
3-29
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utilization where FGC wastes would be a substitute for existing materials
Examples include the use of FGD gypsum as a substitute for natural gypsum
in the manufacture of construction materials (e.g., use in wallboard and
cement) and the use of stabilized wastes as fill materials. However,
future shortages of chemicals, mineral products and construction mate-
rials may alter the incentives for utilization of FGC wastes (both fly
ash and FGD wastes).
TVA has recently completed a series of studies for the EPA [37, 56,
67] assessing the potential marketability of wastes and by-products for
which conventional markets exist—sulfur, sulfuric acid and gypsum.
Generalized cost models were developed comparing a clean fuel strategy
with nonrecovery scrubbing, and scrubbing systems producing the desired
by-product (gypsum, sulfur, or acid). In all cases, the SO* control
strategy was selected on the basis of minimum cost for compliance where
compliance was based on NSPS regulations for new boilers or the applicable
state implementation plan (SIP) for existing boilers as of 1976. Non-
recovery scrubbing was based on the conventional limestone slurry process
producing sulfite or sulfate-rich material. Sulfuric acid production
utilized the MgO scrubbing process and sulfur production was based on
Wellman-Lord/Allied technology. Production of gypsum was assessed for
three gypsum-producing FGD systems—limestone-gypsum, Chiyoda Thorough-
bred 101 (Japanese technology), and the Dowa process (aluminum sulfate
absorption)—and the limestone-gypsum process was chosen for the market
cost comparison. The analysis was carried out under the assumption that
abatement gypsum would be interchangeable with natural gypsum and the
supply price of natural gypsum would be $3-$6/ton.
For those plants where production of sulfur, gypsum or acid was the
low-cost control strategy, a market simulation model was used to evaluate
the distribution of by-products in competition with existing markets.
A production cost module was used to predict market costs for elemental
sulfur producers, sulfur-burning sulfuric acid producers, by-product
sulfuric acid producers (associated with smelters), and gypsum supplied
to wallboard plants and cement plants. A linear programming costing
model was developed which minimized the total cost to both the acid and
the utility industry subject to acid and gypsum demands being met either
3-30
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from traditional sources or from substitution of abatement by-products^
given production costs for each sulfuric acid plant, each wallboard plant
and cement plant, and the cost of producing and transporting abatement
acid, sulfur, or gypsum at each U.S. utility.
The entire U.S. utility industry was characterized from Federal
Power Commission data with respect to plant age, fuel type capacity,
load factors, and SO emission rates for 1978 (projected). Out of a
X
total 3382 boilers at 800 power stations, 833 boilers at 187 stations
were projected to be out of compliance and were the subject of this
investigation.
In general, the results of the study indicated that taking into
account the credit for sales of the by-products, production of sulfur,
acid, or gypsum can be competitive with conventional direct limestone
scrubbing producing waste for disposal. Gypsum was found to be marketable
in isolated instances and sulfuric acid was marketable in areas near
utilities but remote from traditional sources of supply; however, sulfur
was generally not competitive with other sources of sulfur.
Specific conclusions regarding the marketability of by-product acid
and sulfur, and gypsum that were reached are:
Acid and Sulfur; For the alternatives and technologies
considered, acid production was a less costly alternative
than sulfur production in all cases. At $60 per ton sulfur,
and $.70/MBtu increment for compliance fuel, the amount of
acid produced and marketed would be approximately six million
tons from 29 plants; an additional five million tons would
be available as a low cost alternative but was not competitive
with acid produced from sulfur. The amount of substitution
is very sensitive to the assumed price of sulfur. Generally,
(as could be expected) the by-product acid was competitive in
markets supplied by smaller, older, remotely located conven-
tional acid plants.
Gypsum: Table 3.3 summarizes the results of the study re-
garding gypsum marketability. For the conditions and
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Table 3.3
Summary of TVA Gypsum Marketing Results
Total number of plants out of compliance 187
Lowest-cost strategy
Clean fuel, number of plants 71
Limestone slurry process, number of plants 86
Gypsum production and marketing, number of plants 30
Total gypsum produced, tons 2,400,000
Average production per steam plant, tons 80,000
Smallest gypsum supplier, tons 6,700
•^Largest gypsum supplier, tons 171,000
Total gypsum sold, tons 2,230,000
Total gypsum stockpiled, tons 171,000
No. of plants where part of production was stockpiled 5
Wallboard plants served 1
Cement plants served 92
Sold to wallboard plants, tons 95,000
Sold to cement plants, tons 2,135,000
Total net revenue to utilities, $ 11,076,000
Total savings to gypsum industry, $ 1,900,000
Savings to gypsum industry, % of total cost 1.5
Average savings per ton of gypsum purchased, $ „ 0.86
Total first-year compliance cost for 113 plants using
the limestone slurry process, $ 2,038,000,000
Reduction by marketing gypsum, $ 11,076,000
Cost reduction, % 0.5
Required sulfur removal, tons 4,109,000
Sulfur removed by gypsum process, % 8.7
Reduction in sludge disposal by limestone slurry, % 8.0
Imported gypsum displaced, tons 856,000
Domestic gypsum displaced, tons 1,372,000
1978 calcining market served with abatement gypsum, % 0.8
1978 cement market served with abatement-gypsum, % 67.0
Source: [67]
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alternatives considered, it was found that 15 plants could
produce gypsum from flue gas desulfurization at a lower cost
than that of conventional direct limestone scrubbing generat-
ing waste for disposal. These 15 plants would produce
863,000 tons of gypsum annually. An additional 25 plants
could meet compliance using gypsum producing FGD technology
at an incremental cost over conventional direct limestone
scrubbing of less than $3/ton (the crude gypsum mining cost).
These additional 25 plants could produce another 3.4 million
tons of gypsum annually.
Of these 40 potential plants, 30 plants could produce and
market about 2.4 million tons of gypsum in competition with
the natural material. These 30 plants would serve a total
of 93 demand points. Only one wallboard plant would purchase
abatement gypsum, while 92 cement plants would utilize the
remainder (partly because of the higher price offered by
cement plants).
The utilization of abatement gypsum at 92 cement plants
represents substitution for about 67% of the projected use
of natural gypsum in cement production. Of the total gypsum
used by cement plants, approximately 1.1 million tons were
projected to be imported. Abatement gypsum was estimated to
replace about 74% of this imported gypsum.
Use of gypsum-producing technology at the 30 power plants
would solve only 8.7% of the electric utility sulfur oxides
compliance problem and reduce the required ponding of calcium
solids by 8.0%.
In general, production and marketing of abatement gypsum to
the cement industry appears to offer an opportunity for steam
plants with low annual volumes of sulfur removal to lower their
cost of compliance. There appears to be little opportunity
to lower compliance cost by marketing abatement gypsum to
3-33
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the existing wallboard products industry. The gypsum pro-
duction alternative appears to offer only a limited potential
to solve the utility compliance problems; however, in terms
of a total program of waste utilization, the gypsum production
alternative may fill a specific role in that it appears to
meet the needs of small plants when other by-products may be
better suited to large plants.
Locational considerations were shown to play a major role in
determining the feasibility of marketing of abatement gypsum.
Specific location studies for each plant where gypsum offered
an economic advantage, were recommended. This could also include
the feasibility/marketability of new wallboard producing plants.
This study by TVA as well as most all other studies performed to
date on the utilization of FGC wastes and by-products are generally
based upon conventional uses and existing market structures. A number
of factors could impact the future potential for waste and by-product
utilization, indtrfflng:
• Regulatory incentives or disincentives for utilization,
• Changes in institutional constraints,
• Depletion of existing sources of equivalent raw mate-
rials or chemicals that can be derived from flue gas
desulfurization,
• Development of new, more cost-effective FGD
technologies, and
• Development of new uses for wastes and by-product
values.
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4.0 REGULATORY CONSIDERATIONS
Utilization of FGC wastes is not expected to be significantly en-
couraged or restrained by recent environmental legislation. Implementa-
tion of the Toxic Substances Control Act (TSCA) conceivably could impact
new uses; while the Resource Conservation and Recovery Act (RCRA)
ultimately could have major impact on utilization. The regulations
under these laws are still emerging.
The utility industry is concerned that RCRA, at least in its present
form, may not encourage utilization. The National Ash Association has
expressed this concern [24]. These organizations are concerned that [24]:
• The emphasis of RCRA may be on disposal, at
least over the near-term, and
• The "use constituting disposal" issue may impede
utilization.
Over a long term, RCRA is clearly intended to enhance recycle of
materials.
The TSCA established within the EPA the Office of Toxic Substances
(OTS), with broad authority to regulate the entry of chemicals into the
environment. With an estimated 43,000 chemicals already in commerce,
and new ones coining into use at a rate of about 1,000 per year [68], it
will be necessary for the OTS to set priorities for determining which
chemicals to test and regulate. Because many of these thousands of chemi-
cals are known to be far more important in terms of toxicity than FGC
wastes, it is anticipated that the OTS will not regulate utilization of
these wastes. The necessity of prioritizing chemicals for testing was
recognized in the Act in Section 4(e), which established the Interagency
Toxic Substances Testing Committee which advises the EPA of priority
chemicals for testing. To date, the committee has listed 21 chemicals—
FGC wastes are not listed. Unless important toxic effects from FGC waste
utilization are observed, it is highly unlikely that the OTS will regulate
them in the next 5-10 years.
The OTS has concentrated on two sections of the law to date, those
calling for an inventory of chemicals already in production and use, and
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the development of procedures for premanufacturing notification by in-
dustry of its intent to market a new chemical.
The publication of the inventory has been delayed by over a year
from its mandated deadline [68]. The questionnaire was distributed to
electric utilities, and FGC wastes were reported as existing chemicals
already in use. This would exempt them from the premanufacturing noti-
fication requirements in the future, unless they were being marketed
for a significant new use.
Procedures for premanufacturing notification have not yet been
^established; these rules were only proposed in January 1979. They are -
unlikely to significantly restrain utilization and hence will not be dis-
cussed further here.
The objectives of the RCRA include (Section 1003) the conservation
of valuable material by:
• Providing technical and financial assistance to the states
and local government bodies which will promote new and
improved methods of recovery of solid waste,
• Providing for establishment of guidelines for the recovery of
solid wastes,
• Promoting research and development for recovery and recycling
of solid wastes,
• Promoting the demonstration, construction, and application of
resource recovery systems, and
• Establishing a cooperative effort among federal, state, and
local governments and private enterprise in order to recover
valuable materials from solid wastes.
Based on these objectives the Act would be expected to encourage the
utilization of FGC wastes. However, there are few substantive provisions
of the Act which will encourage use of FGC wastes. The strength of the
Act is in the solid waste and hazardous waste management plans, which
provide for the environmentally sound disposal of wastes.
4-2
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Section 2003 provides for the establishment of "Resource Conserva-
tion & Recovery Panels" - teams of personnel to provide technical assis-
tance to states and local governments on solid waste management, resource
recovery, and conservation. Funding for this program is $7-8 million
per year.
State solid waste management plans established in Subtitle D are
prohibited from hindering resource recovery, but only limited incentives
for resource recovery are provided at present.
In Subtitle E, the Department of Commerce "shall encourage com-
mercialization of proven resource recovery technology by providing:
(1) Accurate specifications for recovered materials, and
(2) Stimulation of development of markets for recovered
materials..."
The specifications pertain to chemical and physical properties of
such materials with regard to their viability in replacing virgin mate-
rials in various uses.
In Subtitle F, federal agencies are required to use recycled materials
to the greatest extent practicable. Government specifications for procure-
ment of materials must not exclude recovered material. EPA is responsible
for setting guidelines for federal procurement of recovered materials.
Section 6002(e) of RCRA focuses on the setting of guidelines for the
federal procurement of recovered materials. Ultimately, this could have a
significant impact on the extent of utilization of FGC wastes. Finally,
Subtitle H provides funding for research into resource recovery.
In addition, another significant support for FGC waste utilization
is the requirement that the Department of Commerce provide adequate
specifications for recovered materials pertaining to their use in replac-
ing virgin materials.
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5.0 ASSESSMENT OF UTILIZATION AND DATA GAPS
5.1 Assessment of Utilization
In 1977 total U.S. production of coal ash (fly ash, bottom ash, and
boiler slag) was 61.6 million tons with 12.7 million tons successfully
recovered and utilized [3]. This is more than three times that used by
any other nation during the same time period. On a percentage basis,
21% of the ash produced was thus utilized. In contrast, Western Europe
uses a much higher percentage of their coal ash and Japan uses a much
greater percentage of their production of FGD wastes. A variety of ex-
planations have been given for this fact, usually in some way related
to the research perspective of the organization doing the assessment.
Specifications, quality control, lack of markets, consumer bias, lack of
technical development, and many other reasons have been put forward and
are hindering increased utilization of ash and sludge in the United
States. All of these reasons are valid in at least some instances, and some
are universally valid. On balance, a combination of three types of
factors constrain FGC waste utilization:
• Technical considerations, particularly in comparison with
alternative materials,
• Institutional barriers related to poor understanding of
the by-products and failure to develop markets by either
the utility industry or user industries, and
• Possible environmental concerns related to some uses.
5.1.1 Technical Considerations
Since coal ash and FGD wastes are by-products, quality control in
the production of these materials is a major factor. Utilities are in
the business of producing power; ash and FGD wastes are simply by-products
of their operation. Since ash and FGD waste characteristics are influenced
by coal properties, system design, and operating conditions, quality
control at the utility can be a problem. Some progress has been made in
setting appropriate standards for quality in FGC wastes for utilization
purposes. In some instances, uncertainty exists as to what waste proper-
ties are important for a particular use. Additional standards and accep-
tance by users are needed to make utilization more attractive.
5-1
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Transportation of the FGC wastes is another constraint. Since most
proposed uses are in low value applications, the economic radius of the
market is often small. Virgin materials may also have a more desirable
transportation rate structure. The economic margin in favor of FGC waste
use in preference to an alternative material is usually not large.
5.1.2 Institutional Barriers
Perhaps the largest institutional barrier has been that the potential
consumer industries for FGC waste utilization are conservative, traditional
industries. Such an industrial sector is reluctant to consider new ap-
proaches that would be required if FGC wastes are to be used. Furthermore,
fVom the utility viewpoint, it is preferable to have all FGC wastes
handled through a single source as opposed to many small consumers buying
from them. Since most users cannot accommodate the entire output of a
large utility, brokers can enter the picture (as well as for other
reasons) which adds another variable. Tax and transportation rate struc-
tures also disfavor by-product use. Basic changes would have to occur
in all of the above factors if FGC by-product utilization is to be
encouraged.
5.1.3 Other Factors
A variety of less obvious issues also plague utilization. The poten-
tial effect of RCRA regulation is of concern vis-a-vis disposal. There
also is concern over whether fly ash could be declared toxic or radioactive.
Product liability concerns may have an effect on utilization. The high
rate of inflation and the rapid rise in energy and raw material costs
make the task of assessing the economic viability of new utilization
schemes in the future somewhat arbitrary. An issue requiring clarification
to enhance FGC waste utilization is that related to short and long-term
liability. There is some hesitancy on the part of some sectors of the in-
dustry to sell FGC wastes for use in otherproducts such as wallboard or
cement. If at a future date a product made with FGC wastes as one of the
5-2
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raw materials is found hazardous or harmful, what will be the liability
to the generator of FGC wastes? All of these concerns, as well as others,
both by themselves and in combination tend to hinder increased utilization
of FGC wastes.
Considering the anticipated growth in the generation of FGC wastes,
removal of, or reduction in, barriers to FGC waste utilization becomes
important. In some cases, technical problems preclude successful large-
scale utilization. The more serious impediments are apparently insti-
tutional in nature but can potentially be overcome by concerted efforts.
Utility companies previously have been concerned primarily with the pro-
duction of electricity: marketing of waste by-products has been secondary.
Wastes have been viewed as a nuisance and liability rather than as a
potential asset to be sold and produced along with electricity. The
utility companies not only need to envision the importance of marketing
their FGC wastes as by-products, but also must aggressively develop mar-
kets with education being a key factor in overcoming the reluctance on the
part of many industries to utilize FGC wastes. Potential users are
concerned about chemical and physical variability of the material, lack
of existing specifications for use in manufacturing processes, and fear
of a lack of constant supply depending upon the vagaries of plant opera-
tion. Furthermore, in those uses where environmental or other regulatory
concerns exist, policy decisions are needed to remove elements of uncertainty.
5.2 R&D Assessment
The use of fly ash in construction (e.g., cement, concrete, aggre-
gate, fill) is a relatively highly developed end-use. These materials are
in widespread full-scale commercial use on a routine basis. Little research
is currently being done on new end-uses within the construction sector
because of this development. However, several organizations either have
been or currently are sponsoring a variety of technical programs aimed
at identifying and quantifying the effect of fly ash on these materials.
Much of this work is aimed at concrete (NBS, Bureau of Reclamation, Corps
of Engineers) although work has been done by the FHWA on use in road con-
struction. It appears that any additional EPA research activity in tech-
nical areas beyond what is currently ongoing is not warranted.
5-3
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Stabilization of FGD waste represents a significant potential for
using fly ash. However, this is probably more appropriately considered
a disposal option. Any additional research sponsored by the EPA on the
utilization aspects of this end-use is probably not warranted.
A variety of new uses for fly ash currently are being investigated,
mostly at the research or bench scale level. Some of these processes may
prove viable in a longer time frame; some (e.g., vanadium recovery) are
currently being practiced on a small scale. It is desirable that this
type of research continue, but additional funding by the EPA is probably
not warranted at present.
The use of bottom ash and boiler slag is quite extensive, about 60%
of the boiler slag is consumed. The markets served are fairly well de-
veloped, and use has been relatively constant over the past several years.
Additional research is probably not required in this area.
FGD wastes currently are being utilized abroad (notably in Japan)
where they are generally oxidized to produce gypsum for sale to the cement
or wallboard industry. There currently is no utilization of FGD wastes
in the United States, principally because FGD wastes have not been pro-
duced in significant quantities until recently (i.e., full-scale lime/
limestone scrubbing is relatively new in the United States). The poten-
tial utilization of FGD wastes is dependent upon successful solutions of
a variety of technical and non-technical problems in addition to those
mentioned earlier.
Gypsum production is the only utilization option which is near full-
scale commercial development in the United States. The EPA is sponsoring
a number of programs which will demonstrate oxidation of FGD waste to
gypsum, but these have been aimed primarily at enhancing the disposal
properties of the waste. (See Volume 5.) If gypsum production does become
a commercial reality, some market penetration can be expected. However,
this will still be only a small fraction of total FGD waste generation,
estimated to be about 38 to 57 million tons per year by 2000 [1J. The
TVA has done some work on the potential market size for abatement gypsum
using a least-cost LP model. A continuation of this work on a more general
market-institutional level may be useful.
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Several other end-uses are being considered by various organizations,
but are not at the same level of development as gypsum. TRW has proposed
a process whereby FGD waste is used as a reagent for the extraction of
alumina from kaolin clay and by-product dicalcium silicate is produced.
A sulfur byproduct is produced. Based on the economic analysis, it is
unclear whether the process is viable at present.
Two projects are being sponsored by EPA on the development of a
sulfur production process, and a fertilizer production process by Pullman-
Kellogg and the TVA, respectively. The economics of both processes are
uncertain at this time and should be investigated further.
5.3 Future Utilization Considerations and Data Gaps
By the year 2000, the U.S. minerals deficit will exceed the energy
deficit, possibly approaching $100 billion dollars [28]. The United
States is currently dependent on foreign sources for 22 of the 74 non-
energy essential minerals. Of the 12 crucial elements, seven are imported
in quantities greater than 50% of consumption [28, 53]. Utilization of FGC
wastes can potentially help offset this deficit and provide an alternative
domestic source for a variety of minerals, thereby reducing dependence on
imports. The presence of these minerals in coal ash and FGD waste, and
the large amounts of FGC wastes available, are incentives for basic R&D
on conversion and/or extraction processes.
Much research has already been done on extracting alumina, magnetite,
and other minerals from ash and FGD. However, these processes are not v.
currently capable of competing generally with more established processes,
and in some cases the market does not exist because of more readily avail-
able alternate sources of minerals. However, utilization R&D is really
just one facet of a long-term product development program with FGC as the
raw material. As such, commercial marketability should be thought of in
a long-term (e.g., 10 years or more) time frame and FGC wastes should
be considered an eventual source of minerals or other raw materials.
This is not to say that some processes might not be viable sooner; only
that R&D should not be discontinued because a process does not appear
to be economic in the near term.
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Additionally, depending upon the current market situation, the
abolishment of disincentives or the establishment of incentives may be
necessary at the state or national level for the effective promotion of
the use of FGC waste as a resource. Ultimately, utilization of FGC waste
should be viewed as an alternative source of minerals, not a disposal
option, although the promotion of utilization may help to alleviate dis-
posal problems.
An overall product development program may be thought of as a
series of steps (see Figure 5.1) which lead to introduction and (hopefully)
acceptance of the product in the marketplace. The steps generally follow
three distinct lines representing the following criteria:
• Technical feasibility,
• Economic attractiveness, and
• Marketability.
The initial step of identifying the potential products may be quite
involved as it ideally looks at all possible products, and considers such
things as technical complexity, commercialization requirements, etc., in
an evaluation of which products have the greatest probability of success
in the largest market. For each product chosen, a technical, economic
and market evaluation must be conducted. If all three yield positive
results, commercialization (implementation) may begin.
Even if the product is technically, economically and marketably
qualified, it may not be accepted in the marketplace for a variety of
reasons beyond the direct control of the market (externalities). It is
desirable to identify all external influences which may affect market
acceptance of the product at the earliest possible date, and to either
correct them or adjust for them in the product.
Three areas could benefit from additional research.
Product Evaluation
From a general point of view, which of many products suggested for
FGC wastes are the most attractive technically, economically, and in the
marketplace, in a 10-20 year time frame?
5-6
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Identify
Potential
Product(s)
t_n
I
T
E
C
H
N
I
C
A
L
Lab
Scale
Demonstration
Pilot-
Scale
Demonstration
E
C
0
N
0
M
I
C
Preliminary
Economic (Cost)
Analysis
Detailed
Economic (Cost)
Analysis
Commercial
Demons t rat ion
M
A
R
K
E
T
Preliminary
Market
Assessment
Detailed
Market
Assessment
Implementation
Externalities
Market
Acceptance
Source: Arthur D. Little, Inc.
Figure 5.1 Product Development Logic
-------
Commercialization Requirements
The issue of quality control is a technical area which is still
cloudy. From the production point of view, the utility has some control
over the carbon content of fly ash, and the characteristics of FGD waste.
Which characteristics are important for utilization? How do various
properties affect, for example, concrete? What effects do storage and
transportation have on utilization? How do ash characteristics vary
across the country? How does this affect utilization? Can blending be
useful for quality control?
Externalities
A better understanding of the various institutional constraints which
affect FGC waste utilization would be very useful. What constraints
exist? How are the constraints interrelated? How can they be overcome?
Which should be overcome? How are institutional factors different abroad?
5.4 Emerging Technologies
This report has been focused on analysis and utilization of FGC wastes
produced by conventional combustion of coal. This will continue to be
the most important method to utilize coal for the next twenty (20) years.
However, a number of other methods of utilization of coal are emerging
and will reach significant commercialization in the next twenty (20)
years. These include:
• FLuidized bed combustion (FBC) of coal,
• Coal preparation processes,
• Coal liquefaction,
• Low Btu gasification and combined cycle
generation of power, and
• Magnetohydrodynamics (MKD).
These have been largely discussed in Volume 1, Section 4.8. All
these technologies will generate wastes; however, the quantity, the
physical and chemical characteristics, and the point of generation (mine
end, utility end or other) of the wastes would be different from those
associated with conventional coal combustion.
5-8
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Additional focus on the waste generated by such technologies and
exploration of potential utilization of such wastes should be an essential
part of the development of these emerging technologies.
5-9
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REFERENCES
1. "Health and Environmental Impacts of Increased Generation of Coal
Ash and FGD Sludges," Office of Research and Development, Environ-
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2. Arthur D. Little, Inc., "An Evaluation of the Disposal of FGD Waste
in Mines and the Ocean — Initial Assessment." EPA-600/7-77-051,
Environmental Protection Agency, Washington, D.C., May 1977.
3. National Ash Association, Ash at Work, Vol. X, No. 4, Washington, D.C.
1978.
4. Browning, J. E., Ash - The Usable Waste, Chemical Engineering,
April 16, 1973, pages 68-70.
5. National Ash Association, Ash at Work, Vol. IX, No. 6, 1977.
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The International Coal Utilization Convention, Houston, Texas,
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7. Mayers, J. F., R. Pichumani, and B. S. Kappies, Fly Ash as a Con-
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Administration. U.S. Department of Transportation, May 1976,
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8. Barber, E.G., The Utilization of Pulverized Fuel Ash, Journal of
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10. Rohrman, F.A., Analyzing the Effect of Fly-ash on Water Pollution,
Power, August 1971.
11. Technical and Economic Factors Associated with Fly Ash Utilization,
Final Report, PB-204 408, Environmental Protection Agency, Washington,
D.C., prepared under EPA Contract No. F04701-70-C-0059 by Aerospace
Corporation, El Segundo, California, July 26, 1971.
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Administration, McLean, Virginia, personal communication with
D. E. Kleinschmidt of Arthur D. Little, Inc. , 1978.
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13. Lindberg, H.A., Use of Fly Ash in Portland Cement Concrete and
Stabilized Base Construction, FHWA Notice N-5080.4, Federal Highway
Administration, Washington, D.C., January 17, 1974.
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Philadelphia, Pennsylvania, 19103.
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Energy Conserving Manufacturing Process Options, Vol. X, Cement
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December, 1976.
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of Applications and Technology, U.S. Bureau of Mines, Washington, D.C.,
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17. Brown, P. W., et al, Limitations to Fly Ash Use in Blended Cements,
National Bureau of Standards, Washington, D. C.
18. Mather, K., U. S. Army Corps of Engineers, Waterways Experiment
Station, Vicksburg, Mississippi, personal communication with
D. E. Kleinschmidt of Arthur D. Little, Inc., 1978.
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Philadelphia, Pennsylvania, 19103.
20. Brown, P.W., eit al, The Utilization of Industrial Byproducts in Blended
Cements, Proceedings of the Fifth Mineral Waste Utilization Symposium,
Chicago, Illinois, April 13-14, 1976, pages 278-284.
21. Davis, R.E., e£ al, Weathering Resistance of Concretes Containing Fly-
ash Cements, Journal of the American Concrete Institute, January 1941.
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for Testing and Materials, Philadelphia, Pennsylvania, 19103.
23. Harboe, E., Department of the Interior, Bureau of Reclamation, Denver,
Colorado, personal communication with D. E. Kleinschmidt of Arthur D.
Little, Inc., 1978.
24. Faber, John, National Ash Association, Washington, D. C., personal
communication with Chakra J. Santhanam of Arthur D. Little, Inc., 1979.
25. Weaver, Val E., Division of Fossil Fuel Utilization, Department of
Energy, Germantown, Maryland, personal communication with Chakra J.
Santhanam of Arthur D. Little, Inc., 1979.
26. Moulton, Lyle, K., Bottom Ash and Boiler Slag, Proceedings, Third
International Ash Utilization Symposium, March 13-14, 1973, pp 148-169.
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27. Morrison, R. E., "Power Plant Ash - A New Mineral Resource,"
Proceedings of the Fourth International Ash Utilization Symposium,
St. Louis, Mo., March 24-25, 1976, pp 204-210.
28. Canon, R. M., et^ al_. , Removal and Recovery of Metals from Fly Ash,
presented at the Conference on Ash Technology and Marketing, London,
October 1978. Oak Ridge National Laboratory, Chemical Technology
Division, Oak Ridge, TN.
29. Murtha, M. J. and G. Burnet, Extraction of Alumina from Bituminous
Coal Fly Ash by the Lime-Soda Sinter Process. Presented at the
Conference on Ash Technology and Marketing, London, 1978.
Ames Laboratory and Department of Chemical Engineering, Iowa State
University, Ames, la.
30. Berke, J. National Bureau of Standards, Washington, D. C.,
personal communications with D. E. Kleinschmidt of Arthur D. Little,
Inc, 1978.
31. Philleo, R. Army Corps of Engineers, Concrete Branch, Washington,
D. C., personal communications with D. E. Kleinschmidt of Arthur D.
Little, Inc., 1978.
32. Humphreys, K., Coal Research Bureau, West Virginia University,
Morgantown, W. Va., personal communication with D. E. Kleinschmidt
of Arthur D. Little, Inc., 1978.
33. Natof, S., Department of Energy, Washington, D. C., personal
communication with D. E. Kleinschmidt of Arthur D. Little, Inc.,
1978.
34. Smith, L. M., et_ al.. , Technology for Using Sulfate Waste in
Highway Construction, PB-254-815/4ST, Federal Highway Administration,
Washington, D. C., December 1975.
35. Brown, P. W., National Bureau of Standards, Washington, D. C.,
personal communication with D. E. Kleinschmidt of Arthur D. Little,
Inc., 1978.
36. Anon, TVA to Produce Mineral Wool from Coal Ash Slag, Skillings
Mining Review. July 15, 1978, page 15.
37. Parker, F., Tennessee Valley Authority, Chattanooga, Tn., personal
communication with D. E. Kleinschmidt of Arthur D. Little, Inc.,
1978.
38. Condry, L. Z., et al: Potential Utilization of Solid Waste from
Lime/Limestone Wet-Scrubbing of Flue Gases, presented at the
Second International Lime/Limestone Wet-Scrubbing Symposium,
New Orleans, November 1971, work performed under EPA contract
CPA 70-66 at West Virginia University, Morgantown, W. Va.
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39. Humphreys, K. K., Fifteen Years of Service to the State of West
Virginia, A Key Word Index of Coal Research Bureau Reports,
Report No. 140, Coal Research Bureau, West Virginia University,
Morgantown, W. Va., January 1977.
40. Humphreys, K. K., Operating and Capital Costs of Producing Fired
Structural Products from Waste Coal Ash, Report No. 98, Coal
Research Bureau, West Virginia University, Morgantown, W. Va.,
July 1974.
41. Slonaker, J. F., The Role of Fly Ash Brick Manufacture in Energy
Conservation, Report No. 149, Coal Research Bureau, West Virginia
University, Morgantown, W. Va., November 1977.
42. Slonaker, J. F., Production of Forty Percent Core Area Fly Ash
Brick using a Southern West Virginia Fly Ash, Report No. Ill,
Coal Research Bureau, West Virginia University, Morgantown, W. Va.,
October 1975.
43. Slonaker, J. F., A New Method for Increasing the Durability of
Fly-ash Structural Products, Report No. 141, Coal Research Bureau,
West Virginia University, Morgantown, W. Va., June 1977.
44. Slonaker, J. F., A Study of the Effect of Firing Conditions Upon
Fly-ash Structural Products, Report No. 128, Coal Research Bureau,
West Virginia University, Morgantown, W. Va., November 1976..
45. Slonaker, J. F., Coal Research Bureau, West Virginia University,
Morgantown, W. Va., personal communication with D. E. Kleinschmidt
of Arthur D. Little, Inc., 1978.
46. 1977 Federally Coordinated Program of Highway Research and Develop-
ment, U.S. Department of Transportation, Federal Highway Administration,
Washington, D. C.
47. FCP Annual Progress Report Year Ending September 30, 1978. Project
No. 4C, "Use of Waste as Material for Highways," U.S. Department of
Transportation, Federal Highway Administration, Washington, D. C.
48. Use of Waste Sulfate for Remedial Treatment of Soils, Vol. II,
Appendices, Final Report No. FHWA-RD-76-144, U.S. Department of
Transportation, Federal Highway Administration, Washington, D. C.,
by Midwest Research, August 1976.
49. Use of Waste Sulfate for Remedial Treatment of Soils, Vol. I,
Discussion of Results, Final Report No. FHWA-RD-143, U.S. Depart-
ment of Transportation, Federal Highway Administration, Washington,
D. C., August 1976.
50. Osborne, M., EPA-IERL, Research Triangle Park, N. C., personal
communication with C. J. Santhanam of Arthur D. Little, Inc., 1979.
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51. Tuttle, J., et al_._, EPA Industrial Boiler FGD Survey: First
Quarter 1979, EPA-600/7-79-067b, IERL, U.S. Environmental
Protection Agency, Washington, D. C., April 1979.
52. Duval, W. A., et^ al^, State of the Art of FGD Sludge Fixation,
Final Report, EPRI-FP-671, EPRI RP 786-1, Michael Baker Associates,
Beaver, Pa., January 1978.
53. Morgan, J. D., "Supply and Demand of Corrosion Resistant Minerals,"
Chem. Eng. Progress, March 1978, pp 25-31.
54. Lefond, S. J., editor, Industrial Minerals and Rocks, 4th edition,
American Institute of Mining, Metallurgical and Petroleum Engineers,
1975, pp 710, ff.
55. Corrigan, P. A., Preliminary Feasibility Study of Calcium Sulfur
Sludge Utilization in the Wallboard Industry, prepared by TVA under
Interagency Agreement No. EPA-IAG-D4-0527 for Control Systems Lab,
Research Triangle Park, N. C., June 21, 1974.
56. Bucy, J. I. and J. M. Ransom, Potential Markets for Sulfur Dioxide
Abatement Products, Paper presented at Flue Gas Desulfurization
Symposium, Hollywood, Florida, November 8-11, 1977.
57. Proceedings, Fourth International Ash Utilization Symposium,
St. Louis, Mo., sponsored by the National Coal Association et al.,
compiled by John H. Faber et^ al., March 24-25, 1976.
58. Taylor, W. C. and J. C. Haas, Potential Uses of the Byproduct from
the Lime/Limestone Scrubbing of S02 from Flue Gases, Paper presented
at the AIME meeting, Dallas, Texas, February 23-28, 1974; Preprint
No. 74-H-47.
59. Terman, G. L., Solid Wastes from Coal-Fired Power Plants: Use or
Disposal on Agricultural Lands, Bulletin Y-129, National Fertilizer
Development Center, Tennessee Valley Authority, Muscle Shoals, Ala.,
June 1978.
60. Leo, P. P. and J. Rossoff, Treatment and Disposal of Flue Gas
Cleaning Wastes from Utility Power Plants: R&D Status, Draft
Aerospace Report No. ATR-76 (72-97-01), Aerospace Corporation,
Los Angeles, Ca., March 1976.
61. Leo, P. P. and J. Rossoff, Control of Waste and Water Pollution
from Coal-Fired Power Plants: Second R&D Report, EPA-600/7-78-224,
U.S. Environmental Protection Agency, Washington, D. C., prepared
under Contract 68-02-1010 by Aerospace Corporation, Los Angeles, Ca.,
November 1978.
62. Leadbetter, W. B., Texas Transportation Institute, Texas A&M University,
College Station, TX, personal communication with D. E. Kleinschmidt of
Arthur D. Little, Inc., 1978.
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63. Jones, J. W., IERL, U.S. Environmental Protection Agency, Washington,
D. C., personal communication with D. E. Kleinschmidt of Arthur D.
Little, Inc., 1978.
64. Cosgrove, T. H. and E. P. Motley, Utilization of Lime/Limestone
Waste in a New Alumina Extraction Process, Draft TRW Report No.
29670-6008-RU-01, U.S. Environmental Protection Agency, Washington,
D. C., EPA Contract No. 68-01-3152, June 1978.
65. Arthur D. Little, Inc., Estimates.
66. Pearse, G. H. K., "Sulfur Economics and New Uses," Presented at
the Canadian Sulfur Symposium, Ottawa, Ontario, Canada, May 30 -
June 1, 1974.
67. Ransom, J. M. et^ al., Feasibility of Producing and Marketing Byproduct
Gypsum from S02 Emission Control at Fossil-Fuel-Fired Power Plants,
EPA Report EPA-600/7-78-192, TVA Bulletin Y-137, U.S. Environmental
Protection Agency, Washington, D. C., October 1978.
68. Science. Vol. 202, November 10, 1978, p 598.
69. Rush, R. E. and R. A. Edwards, Evaluation of Three 20MW Prototype
Flue Gas Desulfurization Processes, EPRI-FD-713, Electric Power
Research Institute, Palo Alto, Ca., March 1978.
70. Maxwell, M. A. et al., Sulfur Oxides Control Technology in Japan,
Interagency Task Force Report to Senate Committee on Energy and
Natural Resources, June 30, 1978.
71. Clifton, J. R., P. W. Brown and G. Frohndorff, Survey of Uses of
Waste Materials in Construction in the United States, NBSIR 77-1244,
National Bureau of Standards, Washington, D. C., July 1977.
72. National Ash Association, Ash at Work, Vol. X, No. 5, Washington,
D. C., 1978.
73. Anon, Fly Ash Shows Promise as Plastics Filler, Chemical and
Engineering News, May 8, 1978, p 29-30,
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INDEX
Army Corps of Engineers, current ash utilization research 2-31
Brick
production from ash, research 2-36
production from FGD wastes 3-13
Boiler slag
physical properties 2-5
utilization - see Utilization of ash
Bottom ash, physical properties 2-5 (see also Vol. Ill)
Bureau of Reclamation, current ash utilization research 2-35
Cenospheres
bulk density 2-4
research on use as plastic filler 2-42
Chemical recovery, from FGD wastes 3-13
Coal ash 2-1
chemical composition 2-2, 2-3 (see also Vol. Ill)
Concrete
research on fly ash in 2-34, 2-35, 2-37, 2-38, 2-40, 2-43
use of fly ash in, See - Utilization of ash
Department of Energy (DOE), ash utilization study, 2-37
Dry scrubbing wastes 3-2
chemical composition 3-5 (see also Vol. Ill)
Environmental Protection Agency (EPA)
FGD waste utilization research 3-17, 3-20
regulation affecting utilization 4-1 to 4-3
Federal Highway Administration (FHA), ash utilization research 2-38
Fertilizer, from FGD wastes 3-12, 3-17
FGD stabilization, with fly ash 2-27
FGD wastes
nonrecovery systems 3-1 to 3-5
recovery systems 3-25 to 3-29
research and development programs 3-14, 3-16
see also - Research and development, FGD
utilization 3-6 see also Utilization of FGD wastes
Fly ash
collection systems 2-2
emission standards 2-1
physical properties 2-4
pozzolanic properties, affect on physical properties 2-4
research and development programs 2-31
(see also research and development, Ash)
utilization 2-5 (see also Utilization of ash)
wet vs. dry collection systems 2-30
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General Motors, research on ash as plastic filler 2-42
Gypsum, from FGD wastes
impurities in 3-8
in Japan 3-8
marketing 3-30
potential use in U. S. 3-9
research on 3-16, 3-30
as soil additive 3-11
wallboard 3-7
Insulation, production from ash 2-41
Lightweight aggregate, production from ash 2-25
Mineral recovery from ash 2-29
research on 2-41, 2-43
National Bureau of Standards (NBS), current ash research 2-39
Nonrecovery FGD systems
chemical composition of waste 3-3, 3-5
classification of wastes 2-1
forced oxidation of 3-4
gypsum production from 3-4, 3-7 to 3-9, 3-11
utilization of wastes from 3-6 to 3-12
Recovery FGD systems 3-25
energy use in 3-29
marketing wastes from 3-29
sulfur and sulfuric acid from 3-27, 3-28
wastes from 3-29
Regulations affecting FGC utilization
Resource Conservation and Recovery Act (RCRA) 4-1
Toxic Substances Control Act (TSCA) 4-2
Research and development, ash utilization related
(see also specific organization)
alkali-silicate reaction in concrete, 2-35, 2-40
brick from ash 2-36
cement additive 2-43
concrete, use of ash in 2-34, 2-35, 2-37
highway construction, use of ash in 2-39
insulation, from boiler slag 2-41
mineral recovery 2-41, 2-43
plastic filler, ash as 2-42
sulfate resistance of concrete 2-34, 2-35, 2-40
Research and development, FGD utilization related,
(see also specific organization)
alumina production from clay, with FGD waste 3-20
fertilizer production 3-17
lightweight aggregate from 3-23
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marketing; sulfur, sulfuric acid, gypsum 3-30
road construction 2-49
sulfur production 3-17
Stabilization of FGD with fly ash 2-27
Tennessee Valley Authority (TVA)
ash related research 2-41
FGD related research 3-17, 3-30
Texas A&M University, FGD related research 3-23
Utilization of ash
as aggregate substitute, 2-25
as blast grit, 2-27
cement
as blending agent 2-20
cement production technology 2-17
as raw material in, 2-17
concrete
advantages of, 2-21
alkali/aggregate reaction, 2-22
disadvantages of, 2-23
freeze/thaw durability, 2-23
heat of hydration effects, 2-22
specifications for use, 2-20
strength effects, 2-22
sulfate resistance, 2-21
workability, 2-22
constraints to increased usage, 5-2
current usage 2-5, 2-6
economic considerations, 2-25 to 2-27
fill material 2-10
limitations 2-12
physical properties 2-10
types of ash used for 2-13
for FGD stabilization 2-27
ice control 2-27
institutional barriers to use 5-2
in lime/fly ash/aggregate mixtures 2-24
market considerations 2-25 to 2-27
mineral recovery 2-29
regulations affecting 4-1
research assessment 5-2
research and development programs 2-31
roofing granules 2-27
soil stabilizer 2-13
economics 2-16
fineness as indicator for usefullness 2-16
suitability of ash 2-13
trends 2-5, 2-6
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Utilization of FGD wastes 2-6
aggregate substitute 3-10
brick production 3-13
chemical recovery 3-13
fertilizer production 3-12
gypsum production, for wallboard 3-7
impurities in 3-8
notential in U. S. 3-9
use in Japan 3-8
research on 3-14, 3-16
soil additive 3-11
structural fill 3-7
West Virginia University, current ash utilization research 2-35
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before cot Dieting)
1. REPORT NO. 2.
EPA-600/7-80-012d
4. TITLE AND SUBTITLE Waste and Water Management for
Conventional Coal Combustion Assessment Report —
1979; Volume IV. Utilization of FGC Wastes
7 AUTHORISE ^ j Santhanam , R. R. Lunt , C. B. Cooper ,
D.E.Klimschmidt.I.Bodek, and W. A. Tucker (ADL);
and C.R.Ullrich (Univ of Louisville)
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arthur D. Little, Inc.
20 Acorn Park
Cambridge, Massachusetts 02140
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
March 1980
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
EHE624A
11. CONTRACT/GRANT NO.
68-02-2654
13. TYPE OF REPORT AND PERIOD COVERED
Final; 9/77-8/79
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES IERL-RTP project officer is Julian W. Jones, Mail Drop 61, 919/
541-2489.
The report, the fourth of five volumes , focuses on utilization of coal ash
- ' 7
and FGD wastes. With increasing utilization of coal, generation of these wastes is
expected to grow, but at a slower rate than generation, thus increasing the volume
of wastes sent to disposal. Many uses for coal ash have been developed in three
categories: as fill material; in the manufacture of cement, concrete, and pave-
ments; and in miscellaneous uses such as ice control and blasting grit. In 1977,
about 21% of the 61. 6 million tons of coal ash generated was utilized. Current R and
D projects on ash focus on understanding existing uses and developing new uses
including mineral recovery. FGD wastes are not presently used in the U.S. Poten-
tial FGD utilization options may include use as gypsum substitutes, as fillers and
soil conditioners, in cement and concrete manufacture, and construction of artifi-
cial reefs. Technical, environmental, and institutional barriers (the last being the
most important) constrain utilization. Data gaps remain in quality requirements
for using coal ash and FGD wastes in specific applications and understanding the
instiutional constraints to utilization.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Pollution
Coal
Combustion
Assessments
Management
Utilization
Water
Flue Gases
Cleaning
18. DISTRIBUTION STATEMENT
Release to Public
b.lDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
Flue Gas Cleaning
Waste Utilization
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COSATI Field/Group |
13B 07B
21D
2 IB 13H
14B
05A
21. NO. OF PAGES
112
22. PRICE
EPA Form 2220-1 <»-73)
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