iesearch EPA-600/7-78-049
Off ice of Research and Development Laboratory *o^o
Research Triangle Park, North Carolina 27711 MdrCll 1978
DISPOSAL OF SOLID RESIDUE
FROM FLUIDIZED-BED
COMBUSTION: ENGINEERING
AND LABORATORY STUDIES
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7 Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
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-600/7-78-049
March 1978
DISPOSAL OF SOLID RESIDUE FROM
FLUIDIZED-BED COMBUSTION:
ENGINEERING AND LABORATORY
STUDIES
by
C. C. Sun, C. H. Peterson, R. A. Newby,
W. G. Vaux, and D. L. Keairns
Westinghouse Research and Development Center
1310 Beulah Road
Pittsburgh, Pennsylvania 15235
Contract No. 68-02-2132
Program Element No. EHE623A
EPA Project Officer: D. Bruce Henschel
Industrial Environmental Research Laboratory
Office of Energy, Minerals and Industry
Research Triangle Park, N.C. 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, D.C. 20460
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PREFACE
The Westinghouse R&D Center is carrying out a program to provide
experimental and engineering support for the development of fluidized-
bed combustion systems under contract to the Industrial Environmental
Research Laboratory, U. S. Environmental Protection Agency (EPA), at
Research Triangle Park, NC. The contract scope includes atmospheric
and pressurized fluidized-bed combustion processes as they may be
applied for steam generation, electric power generation, or process
heat. Specific tasks include work on calcium-based sulfur removal
system studies (e.g., sorption kinetics, regeneration, attrition,
modeling), alternative sulfur sorbents, nitrogen oxide emissions, par-
ticulate emissions and control, trace element emissions and control,
spent sorbent and ash disposal, and system evaluation (e.g., the impact
of new source performance standards on fluidized-bed combustion system
design and cost).
This report contains the results of work defined and completed
under the task on environmental control using calcium-based sorbents.
The work was carried out from December 1975 to January 1977. Results
from work carried out by Westinghouse or reported by other investigators
after January 1977 are not assimilated into this task report. The
work reported represents an extension of prior work completed by
Westinghouse under contract to EPA. Results from this prior work
on fluidized-bed combustion include:
• Assimilation of available data on fluidized-bed combustion,
including sulfur dioxide removal, sorbent regeneration,
sorbent attrition, nitrogen oxide minimization, combustion
efficiency, heat transfer, particle carry-over, boiler tube
corrosion/erosion fouling, and gas-turbine erosion/corrosion
deposition
iii
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• Assessment of markets for industrial boilers and utility power
systems
• Development of designs for fluidized-bed industrial boilers
• Development of designs for fluidized-bed combustion utility
power systems: atmospheric-pressure fluidized-bed combustion
boiler-combined cycle power systems, adiabatic fluidized-bed
combustion-combined cycle power systems—including first- and
second-generation concepts
• Preparation of a preliminary design and cost estimate for a
30 MW (equivalent) pressurized fluidized-bed combustion
boiler development plant
• Assessment of the sensitivity of operating and design parameters
selected for the base power plant design on plant economics
• Collection of experimental data on sulfur removal and sorbent
regeneration using limestone and dolomites
• Preparation of cost and performance estimates for once—through
and regenerative sulfur removal systems
• Evaluation of alternative sulfur sorbents
• Collection and analysis of data on spent sorbent disposal—
utilization and environmental impact of disposal
• Projection and analysis of trace emissions from fluidized-bed
combustion systems
• Analysis of particulate removal requirements and development
of a particulate control system for high-temperature, high-
pressure fluidized-bed combustion systems
• Construction of a high-pressure/temperature particulate
control test facility
• Development of plant operation and control procedures
• Construction of a corrosion/erosion test facility for the
0.63 MW Exxon miniplant
• Continued assessment of fluidized-bed combustion power plant
cycles and component designs to evaluate environmental impact.
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The results of these surveys, designs, evaluations, and exper-
imental programs provide the basis for the work being carried out under
the current contract. Seven reports are available that document the prior
contract work (see references 3, 6, 36). Other reports published under
the current contract include "Alternatives to Calcium-Based Sorbents
for Fluidized-Bed Combustion: Conceptual Evaluation," "Calcium-Based
Sorbent Regeneration for Fluidized-Bed Combustion," and Evaluation
of Trace Element Release from Fluidized-Bed Combustion Systems."
v
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ABSTRACT
An understanding of the environmental impact of the disposal of
spent limestones and dolomites and of fuel ash is critical for the suc-
cess of fluidized-bed combustion (FBC) processes. Land and ocean disposal
of unprocessed and processed effluent solids have been studied. The
quantity and composition of spent sorbents produced from six reference
FBC processes are projected. Effluent solids from atmospheric and pres-
surized fluidized-bed combustion processes, once-through and regenerated
spent sorbent, and bed material and carry-over solids were experimentally
investigated. Laboratory testing procedures were developed to determine
spent sorbent characteristics, leaching behavior, and thermal activity.
Processing the spent sorbent and ash was experimentally investigated to
develop alternatives for reducing the environmental impact and to provide
alternatives for potential utilization. The environmental impact from
the land disposal of unprocessed and processed effluent solids is estim-
ated on the basis of results from an experimental test program and compared
with the behavior of natural gypsum and the drinking water standards. The
potential for ocean disposal is assessed.
vii
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CONTENTS
1. INTRODUCTION 1
2. CONCLUSIONS 3
Spent Sorbent Characteristics 3
Spent Sorbent/Ash Land Disposal 4
Spent Sorbent Utilization 6
Ocean Disposal/Utilization 7
3. RECOMMENDATIONS 8
Spent Sorbent Characteristics 8
Spent Sorbent/Ash Disposal 8
Spent Sorbent/Ash Utilization 9
Ocean Disposal/Utilization 9
4. CHARACTERISTICS OF FBC ASH AND SPENT SORBENT 10
Factors Influencing the Spent Sorbent Characteristics 10
Fresh Sorbent, Coal and Coal Ash Properties 12
Plant Sulfur Balances 17
Projection of Spent Sorbent and Coal Ash Production
Rates 25
Sorbent Utilization for Once-through Operation 26
Sorbent Regenerability 29
Sorbent Attrition and Elutriation 38
Assessment of Spent Sorbent Projections for
Fluidized-Bed Combustion 39
5. LAND DISPOSAL " 46
Regulations/Criteria 46
Related Literature on Disposal 48
Experimental Testing Program 50
Samples 50
Spent Sorbent Characterization 53
Leaching Tests 63
Spent Sorbent 66
Fly Ash and Fines 72
Spent Sorbent/Fly Ash Mixtures 72
Processed Spent Sorbent/Fly Ash Compacts 75
Trace Metal Elements 78
COD/BOD/TOC 81
Activity Tests 82
Conclusions and Assessment 85
ix
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CONTENTS (Cont'd)
Page.
6. OCEAN DISPOSAL 88
Feasibility Study 88
Survey of Current EPA Attitude toward Ocean Dumping 89
Test Program 90
7. UTILIZATION AND REDUCTION OF DISPOSAL IMPACT 91
Options 91
Market Data 92
Primary Markets 92
Special Markets 92
Other Markets 95
Overall Economics 95
Technical Requirements 96
Environmental Considerations 96
Characteristics of Aggregate 99
Characteristics of Cement and Concrete 101
State of the Art - Disposition of Solid Wastes 102
Sulfate Wastes 104
Effect of Water Content on Compressive
Strength 104
Effect of Lime Type 105
Effect of Type of Calcium Compound 105
Effect of Lime/Sulfate Ratio 105
Effect of Fly Ash Content 106
Effect of Sulfate Content 106
Effect of Portland Cement Content 107
Effect of Other Components 107
X-Ray Examination 107
Tests on Industrial Sulfate Wastes 108
Screening Tests for Compressive Strength 108
Engineering Evaluation 109
Aggregate Properties 110
Fly Ash 111
Composition 111
Compressive Strength 112
Linear Expansion 112
State-of-the-Art Specifications and Test Methods 113
Freeze-Thaw Resistance 113
Standard Tests and Specifications 115
Experimental Program 116
Identification of Spent Sorbents to Be Tested 116
Combustor Variables 116
Composition Ranges 118
Sources 120
x
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CONTENTS (Cont'd)
Feasibility Tests 123
Blending Tests 123
Isostatic Pressing 125
Screening Tests - Exxon Stone 125
Screening Tests - PER Stone 127
Assessment of Utilization 138
Preliminary Flow Sheets 138
Preliminary Economics 138
Analysis of Results 142
8. REFERENCES 144
APPENDICES
A THE FEASIBILITY OF OCEAN DUMPING AS AN INTERIM
ALTERNATIVE TO DISPOSAL OF SPENT STONE FROM THE
FLUIDIZED BED COMBUSTION PROCESS 152
Introduction 153
Federal Regulations and Permit Procedures 154
Approved Sites for Ocean Dumping 161
Ocean Dumping Mechanisms 165
Feasibility of Dumping Spent Stone at Sea 169
References 176
B OCEAN DUMPING 177
References 183
C PREDICTED PRODUCTION PROPORTIONS OF SPENT SORBENT
AND FLY ASH FROM FLUIDIZED-BED COMBUSTION 184
xi
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FIGURES
Number "Page
1 Fluidized-Bed Combustion General Sorbent Flow
Diagram 13
2 Size Distribution of Coal Feed 20
3 Required Combustor Sulfur Removal Efficiency 21
4A General Once-through Operation Sulfur Balances 23
4B General Regenerative Operation Sulfur Balances 23
5 Ratio of Ash to Sorbent for Once-through Operation 27
6 Cumulative Distribution of Sorbent Utilization 30
7 Sulfation of Calcined Tymochtee Dolomite 31
8 Basis for Regenerative Sorbent Utilization
Projection 33
9 Distribution of Cycle Number for Regenerative
Spent Sorbent 35
10 Particle Size Distribution for Different Gas
Streams 45
11 Microphotographs of Exxon Run No. 27 (a) Bed Stone
and (b) Fly Ash 59
12 (a) SEM Photomicrograph of Exxon 27 Spent Sorbent
(b) EDAX Spectrum of Spot 1 on SEM
(c) EDAX Spectrum of Spot 2 on SEM 60
13 (a) SEM Photomicrograph of Exxon 19.6 Fly Ash
(b) EDAX Spectrum of Spot 1 on SEM
(c) EDAX Spectrum of Spot 2 on SEM ' 61
XII
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FIGURES (Cont'd)
Number Page
14 SEM and Electron Microprobe Photomicrographs of a
Spent Limestone Particle (Exxon 27)
(a)(b) SEM and Sulfur Scan on a Cross-Sectional
Area Near the Surface
(c)(d) SEM and Sulfur Scan on a Cross-Sectional
Area in the Interior 62
15 Area-Scan Electron Microprobe Photomicrographs on a
Cross Section of a Spent Limestone Particle (Exxon
19.6) Near Its Surface, (a) SEM, (b) Ca, (c) S,
(d) Si, (e) Al, and (f) Fe 64
16 Area-Scan Electron Microprobe Photomicrographs on a
Cross Section of a Completely Sulfated Spent Lime-
stone Particle (Exxon 19.6) Near Its Surface,
(a) SEM, (b) CA, (c) S, (d) Si, (e) Al and (f) Fe 65
17 Leachate Characteristics as a Function of Mixing
Time of Spent Sorbents 68
18 Leachate Characteristics as a Function of Stone
Loading 70
19 Leachate Characteristics of the Argonne Spent Stone
Leachates Induced by the Run-off Tests 71
20 Leachate Characteristics as a Function of Mixing
Time of Fly Ash 73
21 Leachate Characteristics of Bed Material/Fly Ash
Mixtures 74
22 Chemical Characteristics from Consecutive Leachates
for Processed Exxon No. 27 Spent/Fly Ash Compacts 76
23 Specific Conductance of Leachate as a Function of
Total Leaching Time 79
24 Projected Composition Range for Spent Sorbent from
Fluidized-Bed Combustion at 850°C 119
25 Compressive Strength of 5-cm Cubes Cast from Spent
Solids from Exxon Run 27 Using Mix I 132
xiii
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FIGURES (Cont'd)
Number Page
26 Compressive Strength of 5-cm Cubes Cast from Spent
Solids from Exxon Run 27 using Mix II 133
27 Compressive Strength of 5-cm Cubes Cast from Spent
Solids from Exxon Run 27 Using Mix III 134
28 Effect of Water Content on Compressive Strength
of 5-cm Cubes Cast from Spent Solids from Exxon 27 135
29 Spent Sorbent Disposal/Utilization from Atmospheric-
Pressure Fluidized-Bed Combustion 139
xiv
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TABLES
Number Page
1 Chemical and Mineralogical Properties of Limestone 14
2 Accessory Mineral Content of Limestones* 15
3 Analysis of Limestone No. 1359 16
4 SC>2 Sorbent Analysis Used for Preliminary Fluidized-
Bed Boiler Analysis 16
5 Mean Analytical Values for all 101 Coals* 18
6 Ohio Pittsburgh No. 8 Seam Coal 19
7 Plant Sulfur Balance Relationships 24
8 Projections of Once-through Sorbent Utilization 28
9 Projected Regenerative Sorbent Utilizations 34
10 Projected Sorbent Makeup Rates 37
11 Power Plant Basis for Spent Sorbent Projections 40
12 Once-through Sorbent Operation Projections 41
13 One-Step Regeneration Projections 42
14 Two-Step Regeneration Projections 43
15 Turndown Spent Sorbent Projects 44
16 Selected Water Quality Criteria 49
17 Process Conditions of Samples Studied for Their
Environmental Impact on Disposal 52
18 Chemical Compositions of Spent Bed Materials and
Fly Ash from Fluidized-Bed Coal Combustion Units 54
xv
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TABLES (Cont'd)
Number
19 Chemical Compositions of Spent Sorbents from
Fluidized-Bed Coal Combustion
20 Chemical Composition of Spent Sorbent and Fly Ash
By X-ray Diffraction 56
21 Comparison of Chemical Compositions of Actual Spent
Sorbents from Fluidized-Bed Combustion Units with the
Projected Values 58
22 Comparison of Specific Conductance of Leachates from
Spent Bed Materials from Varying FBC Processes 69
23 Leachate Characteristics of Processed and Unprocessed
Spent Sorbent and Fly Ash from Exxon Run 27 77
24 Trace Metal Ion Concentrations in Spent Sorbents and
Fly Ash from the Fluidized-Bed Combustion Process
and Leachates 80
25 Total Inorganic and Organic Carbon in Leachate
from Unprocessed and Processed FBC Solid Waste 82
26 Heat-Release Property of FBC Waste 84
27 Preliminary Indications of Environmental Impact from
the FBC Solid Waste Disposal 88
28 Market Data on Selected Construction Materials 93
29 Definitions of Various Kinds of Cement 103
30 Spent Sorbent Test Compositions 121
31 Chemical Analyses of Pilot Plant Spent Sorbents 122
32 Compressive Strength of Sulfated Dolomite/Fly Ash
Blends 123
33 Compressive Strength on 5-cm Cubes Cast from
Exxon Run 27 Spent Solids 124
34 Matrix for Screening Test Using 2-in Cubes Made
from Spent Sorbent and Fly Ash from Exxon Run 27 128
xvi
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TABLES (Cont'd)
Number Page
35 Compressive Strength of PER Spent Sorbent Mixes 136
36 Estimated Composition of PER Compacts 136
37 Comparison of Composition of PER Compacts with Normal
Portland Cement 137
38 Energy Consumption of the Cement Industry 140
xvii
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ACKNOWLEDGEMENT
We want to express our high regard for and acknowledge the contribu-
tion of Mr. D. B. Henschel who served as the EPA project officer. Mr. P.
P. Turner and Mr. R. P. Hangebrauck, Industrial Environmental Research
Laboratory, EPA, are acknowledged for their continuing contributions
through discussions and support of the program.
We would like to thank Messrs. G. C. Vogel and W. Swift of Argonne
National Laboratories; Mr. Robert Reed of Pope, Evans and Robbins;
Mr. H. B. Lange of Babcock and Wilcox; Mr. H. Stoner of Combustion Power;
and Messrs. J. S. Wilson and R. Rice of Morgantown Research Center for
their cooperation in supplying FBC residues.
The program consultation and continued support of Dr. D. H. Archer,
Manager, Chemical Engineering Research, at Westinghouse, are acknowledged.
xix
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SECTION 1
INTRODUCTION
Fluidized-bed combustion for electric power generation provides the
potential for improved thermal conversion efficiency, reduced costs, and
reduced environmental impact when compared with conventional technology.
The fluidized-bed combustion process, operated at atmospheric or ele-
vated pressure, typically results in the production of spent bed mate-
rial in the form of dry, partially utilized dolomite or limestone
particles from 0 to 6 mm in size. This spent bed material is referred
to in this report as "spent sorbent." In addition, fine particles of
sorbent and ash will be collected in the particulate-removal system.
This material collected in the flue gas particle control equipment is
referred to in this report as "carry-over" or "fly ash," although it
includes some sorbent as well as ash. The spent sorbent bed material
may be either regenerated for recycling to the fluid-bed boiler for
repeated sulfur dioxide removal or disposed of in its partially sulfated
form in a once-through system. The former process has the potential
advantage of producing less solid waste for disposal. The properties
of these spent sorbents (size distribution, composition, etc.) are sen-
sitive to a number of operating and design factors. The major compounds
in the waste stone to be disposed of are calcium sulfate, calcium oxide,
calcium carbonate, and magnesium oxide when dolomite is used; and cal-
cium sulfate and calcium oxide or calcium carbonate when limestone is
used. Trace elements arising from impurities in the coal and sorbent
will also be present.
The quantity of spent sorbent will depend upon the amount of fresh
sorbent fed - that is, upon the sulfur content of the fuel, the emission
standard, the operating conditions, the scrbent characteristics, and
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whether or not sorbent regeneration is employed. The spent sorbent for
disposal will generally range from 0.01 to 0.5 kg sorbent/kg coal. Dis-
posal of the fly ash must also be considered.
An understanding of the environmental impact from the disposal or
use of the spent sorbent and fly ash is critical for the successful
implementation of fluidized-bed combustion processes. The present pro-
gram is designed to provide a basis for:
• Projecting environmental impact from disposal
• Interpreting results from large-scale demonstration sites
• Developing optimal system and design and operating require-
ments, and means for treatment of the residue, to minimize
the environmental impact from the spent sorbent and coal ash
• Screening utilization options in view of the environmental
impact.
The scope of the program conceived to achieve these objectives includes:
identification of fluidized^-bed combustion spent sorbent and coal ash
characteristics and quantities; development of laboratory tests to quan-
tify the environmental impact for land and ocean disposal; conducting
environmental impact tests on actual FBC spent sorbent and ash for land
and ocean disposal; studying methods for reducing the impact of the
material upon disposal; and performing investigations to identify poten-
tial land and ocean utilization options and the resulting potential
environmental impact. The work reported represents results from the
first 12 months of the current program (December 1975 to December 1976).
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SECTION 2
CONCLUSIONS
SPENT SORBENT CHARACTERISTICS
The nominal spent sorbent compositions projected for three basic
fluidized-bed combustion concepts are as follows:
Process
Sorbent
CaSOA
Spent Sorbent Composition,
mole "/, (weight %)
CaS CaO CaCO
Atnospheric Pressure Limestone 25 0 75 0
FBC (43.7) (0) (54) (0)
Once-through
100% load
MgO
oa
(0)
Balance
1.73C
(2.3)
Pressurized Boiler
Once-through
100% load
Adiabatic Conbustor
Once-through
100% load
Pressurized Boiler
Once-through
100% load
Atnospheric FBC
One-step regenera-
tion 100": load
Pressurized Boiler
Once-through
turndown to
r.inimum load
Dolomite
Dolomite
Limestone
Limestone
Dolomite
80
(64.1)
50
(46.7)
40
(60.6)
24d/12.8e
(43.1/26.1)
60
(47.6)
0
(0)
0
(0)
0
(0)
Od/1.2e
(0/1.3)
0
(0)
20
(6.6)
50
(19.2)
60
(37.4)
76d/86e
(54.6/70.1)
0
(0)
0
(0)
0
(0)
0
(0)
0
(0)
40
(23.4)
1.19°
(28.1)
1.19b
(32.7)
Oa
(0)
oa
(0)
1.19b
(27.8)
2.111-
(1.2)
2.11°
(1.4)
1.73C
(2)
1.73C
(2.3/2.5)
2.11C
(1.2)
MgO included vith balance of components
bnoles MgO/-ole Ca
erar.s per ~vle calcium
spent sorber.t from combustor
es3ent sorher.• from regenerator
The size distribution of spent sorbent from the bed will be similar
to the sorbent feed size distribution.
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The spent sorbent fines appearing in the fly ash will depend upon
sorbent attrition rate, bed elutriation rate, and fines recycle (if
applied). The coal ash, in general, will all be elutriated from the
combustor. The quantity of sorbent fines is estimated to range from
0.25 to 1 times the coal ash content of the fly ash for a nominal 10 per-
cent ash coal.
SPENT SORBENT/ASH LAND DISPOSAL
Environmental impact criteria have not yet been established for
the land disposal of spent sorbent. Leaching and activity tests were
developed to permit the projection of environmental impact from land
disposal. Criteria for determining the environmental impact of the
residue, as well as standardized leaching tests, may be developed sepa-
rately by EPA in the near future under the Resource Conservation and
Recovery Act (PL 94-580).
In the absence of other standards for comparison at the present
time, drinking water standards and leachate from a natural gypsum were
selected as reference standards for the leachate tests.
Leaching and activity tests were performed on atmospheric and pres-
surized fluidized-bed combustion systems; once-through and regenerated
spent sorbent; bed and carry-over materials; and processed and unproc-
essed spent sorbent.
Leaching and activity tests show that:
• No water pollution is expected from the leaching of
those trace-metal ions for which drinking water stan-
dards exist, since the leachate meets drinking water
standards.
• An insignificant amount of magnesium is leached out, even
for dolomite sorbent.
• Sulfide may not be a problem for the once-through sorbent,
since the sulfide concentration in the leachate is below
detection limits.
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• The total dissolved organics are below detection limits.
• Residual activity, reflected by heat release upon expo-
sure to water, has not been observed to be significant
with spent sorbent from once-through pressurized oper-
ation. The heat release property of spent sorbent,
however, is a function of the FBC operating conditions -
for example, temperature, stone residence time, degree
of sulfation and calcination, and degree of dead-burning.
• Heat release from the spent sorbent in the atmospheric
FBC system is judged an environmental concern for direct
disposal. This is due to the large amount of calcium
oxide present in the spent sorbent.
• Moderate heat release has occurred with the spent sor-
bent from the regenerative pressurized FBC system.
This, also, may be an environmental concern.
• Potential concerns in the leachates are the high con-
centrations of calcium, sulfate (SO,), pH, and total
dissolved solids (TDS), which are above drinking
water standards.
• The addition of ^20 wt % ash to the spent sorbent
improves leachate quality. Codisposal of spent sor-
bent and ash, thus, can reduce the adverse environ-
mental impact.
• The environmental impact is reduced by room-temperature
processing.
A preliminary comparison of environmental impacts is shown in the
following chart.
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Sample
Sorbent Type
Environmental Farainet_ers_
Heat Release*-
Spontaneous Tenp.
Rise (3g/20 ml)
Trace
Metal
Total
Dissolved
Solids
Total
Organic
Carbon
pH
Sulfide
Bed Material
Pressurized FBC,
once-through
<0.2°C
Bed Material
Pressurized FBC,
once-through
ed material/
fly ash
mixtures
Pressurized FBC,
once-through
Dolomite/
Limestone
<0.2°C
Jypsum
<0.2°C
*Based on results from limited samples available and subject to the procedures specified in the section on "Activity".
on
Pd Do not meet either the drinking water or gypsum leachate criteria
^j Pass gypsum leachate criteria but not drinking water standards
[_J Pass both drinking water and gypsum leachate criteria
SPENT SORBENT UTILIZATION
The construction industry is considered the most attractive market
area for utilization because of the need to market large quantities of
spent sorbent and the potential demand for waste-based products in con-
struction. Utilization options include landfill, road subbase, aggre-
gate, concrete, and cement.
Integration of basic industries (e.g., a cement plant) with the
steam/power plant are potentially attractive for achieving resource and
energy conservation.
Test results show that stable, solid compacts can be produced from
the spent sorbent and coal ash at ambient temperature and pressure.
Compressive strengths meet landfill requirements and may permit sub-
stitution for concrete in low-strength applications.
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Tests results show pressing of spent sorbent and coal ash results
in an axial compressive strength of up to 90 MPa. The compressive
strength of Portland cement is 103 to 172 kPa.
OCEAN DISPOSAL/UTILIZATION
EPA policy is to phase out ocean disposal of industrial waste by
1981. Permits for such disposal are unlikely, although research per-
mits may be issued.
The spent sorbent/ash, however, could potentially be utilized as a
habitat for marine life.
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SECTION 3
RECOMMENDATIONS
SPENT SORBENT CHARACTERISTICS
Obtain spent sorbent from operating test units and demonstration
plants to determine characteristics. Compare results with projections.
Revise models, as needed, to predict spent sorbent characteristics.
SPENT SORBENT/ASH DISPOSAL
Continue leaching and heat-release tests. These tests should
include sorbents generated with the following variations in process
parameters:
• Once-through/regenerative sorbent system
• Atmospheric pressure/pressurized combustor
• Limestone/dolomite sorbent
• One-step/two-step regeneration
• Calcium-based sorbent/alternative sorbent
• Wide range of operating conditions within each process
variation.
Emphasis should be placed on the environmental impact from the disposal
of sorbent produced by a once-through system under atmospheric pressure,
since that is the process considered for the first-generation plants.
Extend leaching tests to include pH, temperature, and salinity of
leachate-inducing liquid. Extend leachate measurements to include other
potential pollutants, according to the EPA comprehensive analysis
concept. '
Perform column-leaching tests to investigate larger amounts of
spent sorbent, its permeability, its possible use as landfill, rate of
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leachate generation, and soil attenuation. A Lysimeter can be designed
to simulate actual disposal geometry, seasonal changes, average natural
precipitation, and soil composition.
Continue investigation of processing spent sorbent to reduce the
residue's environmental impact. Spent sorbent from atmospheric-pressure
operation is of particular interest since the heat release of this mate-
rial may prevent direct disposal.
Perform field tests to monitor ground and surface water and to
generate information for commercial projection. The success of a land
disposal operation depends greatly on the design, construction, and
operation based on the geology, hydrology, topography, and climate of a
particular site.
SPENT SORBENT/ASH UTILIZATION
Perform tests to investigate spent sorbent/ash blending to form a
compact at ambient temperature/pressure. Perform freeze-thaw and sul-
fate resistance tests on the fixed compact.
Investigate the effect of spent sorbent composition (e.g., silica,
alumina, calcium sulfate) on the low-temperature processing option.
Investigate alternative applications, such as agricultural use.
Develop preliminary process design and economics based on screening
tests, for processing options that are attractive.
OCEAN DISPOSAL/UTILIZATION
Implement the marine ecological assessment program to determine
deleterious effects of spent sorbent/ash and to conduct flow-through
tests with a spent sorbent habitat.
-------
SECTION 4
CHARACTERISTICS OF FBC ASH AND SPENT SORBENT
Fluidized-bed combustion power generation systems, operated at
atmospheric pressure and elevated pressures, produce spent sorbent mate-
rials (limestone- or dolomite-based) that may require processing to
generate a material environmentally suitable for disposal, or to con-
vert them into useful by-products. The properties of these spent sor-
bents (size distribution, composition, etc.) are sensitive to a number
of combustor operating and design factors. The purpose of this study
is to project the most probable base characteristics for the spent sor-
bents that will permit sorbent processing and environmental impact
studies to proceed on a meaningful and consistent basis.
Spent sorbent characteristics are projected; and fresh sorbent,
coal, and coal ash properties are also discussed. The assumptions and
data applied to project the spent sorbent properties are summarized to
permit future refinement as new information becomes available. A per-
spective on the sensitivity of the spent sorbent characteristics to the
design and operating conditions and the applied assumptions is also
provided.
FACTORS INFLUENCING THE SPENT SORBENT CHARACTERISTICS
The following factors have a significant influence on the char-
acteristics of the spent sorbent produced by the fluidized-bed combus-
tion system:
• Coal properties - sulfur content, heating value, and ash
content
• Fresh sorbent properties - type of sorbent (limestone or
dolomite), composition, physical structure, and attrition
b ehavior
10
-------
• Fluid-bed combustion system concept - power cycle
(atmospheric-pressure boiler, pressurized boiler, adi-
abatic combustor), once-through or regenerative operation,
and sorbent pretreatment
• Fluid-bed combustor design and operating conditions -
temperature, pressure, excess air, residence times of
sorbent and gas, calcium-to-sulfur feed ratio, superficial
velocity, coal and sorbent feed size, coal and sorbent
feeding, internals design, distributor design, turndown
operating conditions, and so forth.
• Regeneration process concept - once-step (high-temperature)
process or two-step (low-temperature) process, point of
fresh sorbent feeding, and point of spent sorbent
withdrawal
• Regenerator design and operating conditions - temperature,
pressure, reactant-gas (or solid reductant) composition,
residence times of sorbent and gas, multiple stages or
regions, internals design, distributor design, and super-
ficial velocity, and the like
• Other system components design - particulate control, sor-
bent circulation, and so forth.
The list is not exhaustive, but the factors presented appear to be
the most significant. The following spent sorbent characteristics are
considered:
• Composition (major components) - CaO, CaCO_, CaS, CaSO,,
MgO, and other components present in fresh sorbent which
are retained in the spent sorbent
• Size distribution of bed material and overhead fines.
Projections of the relative amounts of coal ash and spent sorbent
are also considered because of their important processing implications.
Trace element content of the spent sorbent has not been projected.
11
-------
Figure 1 is a general sorbent flow diagram for fluidized-bed com-
bustion. A fluid-bed combustor is shown with two stages of particulate
control equipment: the first stage represents recycling of coarse
sorbent and ash (or carbon) to the combustor, and the second stage
represents removal of ash and sorbent fines from the combustor system
to be processed or regenerated. The sorbent material to be processed
or regenerated then consists of the sorbent stream withdrawn from the
combustor, having the bulk bed characteristics, and the sorbent-fines
stream withdrawn from the particulate control system. If the operation
is once-through, these two streams would represent the spent sorbent.
For the regenerative case another processing step with particulate
control is shown in Figure 1, The regenerated sorbent is recycled to
the combustor. The spent sorbent is represented by the fine material
withdrawn from the combustor and regenerator particulate control systems,
plus the sorbent withdrawn either from the combustor or the regenerator
bulk beds. In the regenerative case fresh sorbent may be injected into
the process in either the combustor or the regenerator. The nature of
the spent sorbent may also be sensitive to the exact location within
the bulk beds from which it is withdrawn (e.g., near the distributor in
an oxidizing region or near the top of the bed in a reducing region) .
While all of the factors that can be identified cannot be entirely
accounted for, a reasonable projection of the spent sorbent properties
in terms of the major factors is possible.
Fresh Sorbent, Coal, and Coal-Ash Properties
Sorbent (limestone and dolomite) compositions were studied in some
detail for both fluidized-bed combustion systems and limestone wet-
scrubber systems. A summary of compositions for limestone and dolomite
is shown in Tables 1 and 2. Limestone 1359 and dolomite 1337 were pre-
viously used as bases for fluidized-bed combustion process studies and
have the compositions shown in Tables 3 and 4. ^
Coal compositions were analyzed for a large number of coals from
the eastern U. S. Mean values, standard deviations, and minimum and
maximum values are given for trace elements, minor and major elements,
12
-------
Sorbent
Coal
V
Fluid-Bed
Combustor
Curve 685696-A
Flue
Gas
v
... /To Regenerationx
fines,/ Qr
I Spent Sorbent
v Processing
Utilized
Sorbent
Regenerated
Sorbent
v
General
Regeneration
Process
Alternative Streams
to Spent Sorbent
Processing
i
Acid
Gas
V
Fines,
Sorbent
(and ash)
To Spent
Sorbent Processing
Figure 1. Fluidized-Bed Combustion General Sorbent Flow Diagram
-------
TABLE 1. CHEMICAL AND MINERALOGICAL PROPERTIES OF LIMESTONES
Sorb.
Type
Ign.
loss
Composition wt %
CaO
MgO
Fe2°3
Na20
K20
Mn02
Gan gue
firain
Size,
coded(c)
Unit-cell
Length
a, A
Crystal-
lite
Size, u
Calcites
1336
1343
1350
1355
1359
1363
1368
1369
1377
1379
1677
1679
1681
1685
1687
1691
1692
1693
43.2
42.5
43.6
33.1
43.6
36.1
40.1
43.4
27.3
41.3
26.5
42.7
37.7
43.9
43.2
38.6
42.9
42.7
53.4
54.1
54.7
41.5
54.7
42.2
49.1
54.3
28.4
48.7
31.2
52.1
44.9
48.2
53.4
47.3
54.8
53.3
1.5
0.5
0.5
1.2
0.7
0.9
1.3
0.8
2.8
2.2
1.1
1.4
2.2
4.6
1.2
1.7
0.3
0.6
0.2
0.4
0.2
1.6
0.1
1.6
0.9
0.1
5.1
0.4
0.7
0.3
0.6
0.4
0.1
0.6
0.1
0.2
0.0057
0.0115
0.0056
0.2542
0.0056
0.1406
0.0898
0.0396
0.2326
0.1526
0.0735
0.0917
0.0623
0.0505
0.0284
0.0860
0.0256
0.0573
0.0284
0.0575
0.0282
0.4349
0.0282
0.6518
0.2636
0.0736
3.9985
0.2818
0.2058
0.0802
0.2056
0.0280
0.0363
0.3438
0.0286
0.1031
0.0085
0.0345
0.0451
0.0268
0.0141
0.1278
0.9165
0.0085
0.0872
0.0411
0.0110
0.0086
0.0093
0.0617
0.0284
0.0430
0.0086
0.0086
1.6
0.7
2.6
24.6
0.9
18.0
8.8
0.8
43.8
6.6
45.0
3.6
13.8
3.0
1.5
12.4
0.6
2.8
3.0
1.0
2.0
1.0
1.0
1.0
2.6
1.0
1.0
3.0
1.0
1.0
1.0
2.8
2.6
1.0
3.0
1.0
4.978
4.989
4.986
4.982
4.985
4.989
4.978
4.987
4.975
4.930
4.987
4.975
4.985
4.986
4.986
4.984
4.985
4.985
0.149
0.167
0.177
0.024
0.124
0.124
0.097
0.127
0.162
0.097
0.177
0.048
0.115
0.145
0.177
0.107
0.186
0.160
Dolomites
1337
1340
1341
1367
1380
1678
1680
1686
1688
1690
1695
1701
1702
47.2
46.2
46.7
43.9
46.7
30.8
42.4
46.9
47.1
34.0
42.2
42.5
44.6
29.0
30.7
29.8
32.5
30.4
19.7
28.2
29.7
29.1
22.4
28.9
34.5
33.2
22.7
19.9
22.4
15.8
21.9
14.5
19.3
22.0
22.2
15.5
23.1
13.5
18.0
0.2
1.4
0.3
5.2
0.3
1.3
0.9
0.2
0.5
1.1
0.6
4.3
0.8
0.0053
0.0054
0.0053
0.0224
0.0266
0.0830
0.0346
0.0159
0.0159
0.0396
0.0289
0.0920
0.0277
0.0264
0.0269
0.0266
0.0280
0.0266
0.9826
0.2534
0.0266
0.0265
1.1286
0.0289
0.1553
0.2715
0.0079
0.6890
0.0080
0.5610
0.0080
0.0415
0.0691
0.0080
0.0159
0.0792
0.0087
0.4542
0.0083
1.0
2.0
0.7
7.0
0.6
35.0
9.2
1.0
0.5
24.2
4.8
8.6
4.6
2.0
1.5
3.0
1.0
2.5
1.5
1.0
3.0
1.5
3.0
3.0
1.3
1.3
4.811
4.808
4.806
4.816
4.805
4.808
4.806
4.806
4.807
4.809
4.808
4.822
4.810
0.119
0.141
0.211
0.085
0.189
0.141
0.171
0.189
0.182
0.098
0.189
0.090
0.070
Mixtures
1360
1694
44.5
38,0
45.0
37.2
7.2
12.4
0.7
0.6
0.0277
0.0310
0.0277
0.0310
0.0888
0.0093
3.4
12.6
2.5
3.0
4.910
4.886
0.135
0.159
Magnesites
1375
1376
46. 4
46.8
15.8
7.1
32.2
41.0
0.9
0.8
0.0322
0.0154
0.1340
0.0256
0.0080
0.0154
10.0
28.0
2.5
2.5
4.720
4.720
0.147
0.220
(a) Calculated from composition of calcine.
(b) Accessory minerals.
(c) 1 x fine, <63 u; 2 = medium, 63-250 u; 3 = coarse, >250 u.
*Reproduced from "Investigation of the Reactivities of Limestone to Remove Sulfur Dioxide from
Flue r,as," TVA, 1971, PB 202-407.
14
-------
TABLE 2. ACCESSORY MINERAL CONTENT OF LIMESTONES*
Sorb.
Type
Total
Accessory minerals (wt %)
Quartz
Illite
Montmor-
illonite
Chert
Tremo-
lite
Limo-
nite
Feld-
spar
Musco-
vite
Glass
frit
Calcites
1336
1343
1350
1355
1359
1363
1368
1369
1377
1379
1677
1679
1681
1685
1687
1691
1692
1693
1.6
0.7
2.6
24.6
0.9
18.0
8.8
0.8
43.8
6.6
45.0
3.6
13.8
3.0
1.5
12.4
0.6
2.8
0.0
0.3
1.6
16.0
0.4
6.0
4.2
0.4
13.1
4.6
14.0
1.7
4.6
1.0
0.5
3.8
0.3
1.0
0.0
0.1
0.9
8.6
0.0
6.0
4.2
0.4
13.1
0.0
0.0
1.7
4.6
1.0
0.5
8.0
0.2
- 1.8
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
14.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
4.6
0.9
0.4
0.0
0.0
0.0
1.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.0
0.0
0.0
0.4
0.0
4.5
0.0
3.0
0.2
0.0
0.1
0.0
0.6
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
6.0
0.0
0.0
13.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.4
0.0
0.0
0.0
0.0
0.0
14.0
0.0
0.0
0.0
0.1
0.0
0.0
0.0
Dolomites
1337
1340
1341
1367
1380
1678
1680
1686
1688
1690
1695
1701
1702
1.0
2.0
0.7
7.0
0.6
35.0
9.2
1.0
0.5
24.2
4.8
8.6
4.6
0.7
2.0
0.0
0.3
0.1
15.7
3.1
0.3
0.2
20.6
1.4
3.0
2.3
0.0
0.0
0.0
0.0
0.1
15.7
0.0
0.3
0.2
3.6
0.5
0.0
2.3
0.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.5
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.4
0.0
0.0
0.1
0.0
0.0
6.7
o.o
1.8
0.0
0.0
0.0
0.0
0.0
5.6
0.0
0.0
0.0
0.1
0.0
0.1
1.8
3.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.4
0.0
0.0
0.0
0.0
0.0
0.0
0.3
0.0
3.0
0.0
0.1
0.0
0.0
0.0
0.0
Mixtures
1360
1694
3.4
12.6
0.0
4.0
0.4
0.0
0.0
0.0
1.3
0.0
0.0
4.0
1.3
0.0
0.0
0.0
0.0
0.6
0.4
0.0
Magnesites
1375
1376
10.0
28.0
1.0
0.7
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
*Reproduced from "Investigation of the Reactivities of Limestone to Remove Sulfur Dioxide
from Flue Gas," TVA, 1971, PB 202-407.
15
-------
TABLE 3. ANALYSIS OF LIMESTONE NO. 1359
, (4)
Component As-Received, wt %
S10,
2.
A12°3
Fe2°3
MgO
CaO
Ti02
SrO
Na 0
0.85
0.30
0.17
1.07
97.
<0.05
0.07
<0.02
<0.05
TABLE 4. S02 SORBENT ANALYSIS USED FOR
PRELIMINARY FLUIDIZED-BED BOILER ANALYSES
Component
Si°2
A12°3
MgO
CaO
Ti02
SrO
Na2°
As-Received (4)
Dolomite
1337, wt %
0.78
0.15
0.25
45.0
53.0
0.02
<0.03
<0.02
<0.03
16
-------
total sulfur and ash in Table 5. The variability of coal compositions
is very great for almost all components. An Ohio-Pittsburgh No. 8 Seam
coal was previously used as the basis for fluidized-bed combustion
(3)
process studies. Its composition and the associated ash composition
are shown in Table 6.
Expected coal and fresh sorbent size distributions are presented
(3)
in Figure 2. The size distribution is typical of that obtained from
commercial crushers. Although finer sizes or narrower size distributions
may have possible process advantages, they require pulverization and/or
more extensive size classification.
Plant Sulfur Balances
The required sulfur removal efficiency for the total fluidized-bed
combustion power plant is determined by the existing SO emission stan-
X
dard for coal-fired power plants and is given by the following expression:
SH
1
~
W0 2 x
O
where e is the plant sulfur removal efficiency, S is the SO emission
D «
standard in kg SO«/GJ, W is the coal sulfur content (weight fraction) ,
Z o
and H is the coal heating value. This relationship is illustrated in
Figure 3 for an emission standard of 0.516 kg SO_/GJ which corresponds
to the present U.S. EPA standard for large coal-fired boilers. Two
coal heating values, which span the range of typical values, are
considered.
The sulfur removal efficiency required in the fluidized-bed com-
bustor is dependent upon the sulfur removal or recovery efficiencies of
the individual processing systems comprising the power plant sulfur
removal system (i.e., the regeneration system, the sulfur recovery sys-
tem and the spent sorbent processing system) and the process logic
applied to the sulfur removal system (i.e., once-through versus regen-
erative operation, recycle of tail-gases to the fluid-bed combustor or
the sulfur recovery process, withdrawal of spent sorbent before or
after the regeneration step, etc.).
17
-------
TABLE 5. MEAN ANALYTICAL VALUES FOR ALL 101 COALS*
Constituent
As
B
Be
Br
Cd
Co
Cr
Cu
F
Ga
Ge
Mg
Mn
Mo
Ni
P
Pb
Sb
Se
Sn
V
Zn
Zr
Al
Ca
Cl
Fe
K
Mg
Na
Si
Ti
ORS
PYS
SUS
TOS
SXRF
ADL
Mois.
Vol
FIXC
Ash
Btu/lb
C
H
N
0
HTA
LTA
Mean
14.02 ppm
102.21 ppm
1.61 ppm
15.42 ppm
2.52 ppm
9.57 ppm
13.75 ppm
15.16 ppm
60.94 ppm
3.12 ppm
6.59 ppm
0.20 ppm
49.40 ppm
7.54 ppm
21.07 ppm
71.10 ppm
34.78 ppm
1.26 ppm
2.08 ppm
4.79 ppm
32.71 ppm
272.29 ppm
72.46 ppm
1.29 7.
0.77 %
0.14 %
1.92 %
0.16 7,
0.05 %
0.05 %
2.49 %
0.07 %
1.41 %
1.76 %
0.10 %
3.27 %
2.91 7,
7.70 %
9.05 %
39.70 %
48.82 %
11.44 %
12748.91
70.28 '/.
4.95 %
1.30 7,
8.68 %
11.41 %
15.28 %
Std
17.70
54.65
0.82
5.92
7.60
7.26
7.26
8.12
20.99
1.06
6.71
0.20
40.15
5.96
12.35
72.81
43.69
1.32
1.10
6.15
12.03
694.23
57.78
0.45
0.55
0.14
0.79
0.06
0.04
0.04
0.80
0.02
0.65
0.86
0.19
1.35
1.24
3.47
5.05
4.27
4.95
2.89
464.50
3.87
0.31
0.22
2.44
2.95
4.04
Min.
0.50
5.00
0.20
4.00
0.10
1.00
4.00
5.00
25.00
1.10
1.00
0.02
6.00
1.00
3.00
5.00
4.00
0.20
0.45
1.00
11.00
6.00
8.00
0.43
0.05
0.01
0.34
0.02
0.01
0.00
0.58
0.02
0.31
0.06
0.01
0.42
0.54
1.40
0.01
18.90
34.60
2.20
11562.00
55.23
4.03
0.78
4.15
3.28
3.82
Max.
<>3.00
224.00
4.00
52.00
65.00
43.00
54.00
46.00
143.00
7.50
43.00
1.60
181.00
30.00
80.00
400.00
218.00
8.90
7.70
51.00
76.00
5350.00
133.00
3.04
2.67
0.54
4.32
0.43
0.25
0.20
6.09
0.15
3.09
3.78
1.06
6.47
5.40
16.70
20.70
52.70
65.40
25.80
14362.00
80.14
5.79
1.84
16.03
25.85
31.70
Note: Abbreviations other than standard chemical symbols: organic sulfur
(ORS), pyritic sulfur (PYS), sulfate sulfur (SUS), total sulfur
(TOS), sulfur by X-ray fluorescence (SXRF), air-dry loss (ADI,),
moisture (Mois), volatile matter (Vol), fixed carbon (FIXC), high-
temperature ash (HTA), low-temperature ash (LTA).
*Reproduced from "Occurrence and Distribution of Potentially Volatile
Trace Elements in Coal," R. R. Ruch, H. J. Gluskoter, N. F. Shimp 1974
EPA-650/2-74-054 (Reference 5). ' '
18
-------
TABLE 6. OHIO PITTSBURGH NO. 8 SEAM COAL*
SAMPLE: Run of mine - as
PROXIMATE ANALYSIS (wt %) :
ULTIMATE ANALYSIS (wt %):
(includes moisture)
GROSS HEATING VALUE:
NET HEATING VALUE:
ASH ANALYSIS (wt %):
FUSIBILITY OF ASH:
PARTICLE DENSITY:
GRINDABILITY (Hardgrove)
FREE SWELLING INDEX:
received
Moisture
Volatile matter
Fixed carbon
Ash
C 71.2
H 5.4
0 9.3
N 1.3
S 4.3 (^60% organic & ^40% pyritic)
Ash 8.5
100.0
30,238
29,075
Si02
M2°3
Fe2°3
Ti02
P2°5
CaO
MgO
Na2°
K2°
so3
J/g
J/g
45.3
21.2
27.3
1.0
0.11
1.9
0.6
0.2
1.8
0.7
100.1
Initial deformation temperature 1138°C
Softening temperature 1221°C
Fluid temperature 1327°C
Coal - ^1.4 g/cc
Ash - ^2.8 g/cc
50-60
5-5.5
*(Source of data: USBM, Pittsburgh, PA.)
19
-------
4 Size Distribution for Elutriated
5 Solids from Primary Combustor
& Carbon Burn-up Cell
Range of Size Distribution
— Obtainable from Koppers
Reversible Hammermill
98.5
99
100 1000
Particle Size Microns
10000
Figure 2. Size Distribution of Coal Feed
-------
Curve 684848-^
0.9
0.8
S 0.6
1
^
3
•o
0>
cr
O)
o:
n c
U.!?
0.4
0.3
0.2
0.1
0
Standard =516 ng/J
Coal Heating Value,
MJ/kg(Btu/lb)
23.3 (10,000)
35.0 (15,000)
0.01 0.02 0.03 0.04 0.05
Weight Fraction Sulfur in Coal
0.06
Figure 3. Required Combustor Sulfur Removal Efficiency
21
-------
Figure A shows general process flow diagrams used for sulfur bal-
ances for once-through and regenerative operations. Sulfur recovery or
removal efficiencies are defined for each of the processing systems:
e for the combustor, e for the regenerator, e for the spent sorbent
C R "
processing system, and e for the sulfur recovery process. Sulfur
bK
losses may occur because of gas, liquid, or fines losses, or intentional
tail-gas release. The results of simple material balances for some
alternative process logics are shown in Table 7. The possibility of
the introduction of additional sulfur into the process by means of
reductant-gas generation from sulfur-bearing fuels or other sources has
been neglected, but in come cases it could be a significant factor. A
decrease in the sulfur removal efficiency of any processing step will
increase the required combustor sulfur removal efficiency and also the
required rate of fresh sorbent consumption. Recycling tail-gases to
the combustor also increases the "effective" sulfur content of the coal.
From the relation shown in Table 7, it is evident that, for the
cases with no tail-gas recycle, the sulfur removal efficiencies of the
separate processing steps must be greater than the required plant sul-
fur removal efficiency. For the cases with recycle to the combustor,
the sulfur removal efficiencies of the individual processing steps can
be less than the overall sulfur removal efficiency, but the effective
coal sulfur content will increase greatly as the efficiencies decrease.
For example, the case of once-through operation, with the tail-gas from
the spent sorbent process being recycled to the combustor, is illustrated
below for a 5 wt % sulfur coal (85 percent overall sulfur removal
required):
M/M (E_ - 1)
ep
0.9
0.8
0.7
Required
ec
0.863
0.876
0.890
Vws
1.094
1.21
1.36
1.111
1.247
0.424
22
-------
Sorbent _
Coal
t Stack
| Gas
£c
Combustor
Spent
Sorbent
t Tail
Gas
£P
Spent
Sorbent
Processing
/' To Stack or \
^Recycle to Combustory
Processed
Sorbent
Figure 4A. General Once-through Operation Sulfur Balances
t Stack
| Gas
Sorbent^
£c Sor
Coal *| Combustor CircL
l t Tail
! 1 ^
1 „
Spent
bent £R ^Sorbent
lation Regenerator
Acid
U - Sulfur Removal, Recovery,^ Gas
y Or Retention Efficiency )
t Tail
Gas
£SR
• Sulfur
Recovery
\ Tail
1 Gas
£P
t Spent
Sorbent
Processing
/ To Stack \
\or Recycle/
Sulfur
/'To Stack \
or Recyclej
*
Figure 4B. General Regenerative Operation Sulfur Balances
23
-------
TABLE 7. PLANT SULFUR BALANCE RELATION
S3
Required Conibustor
Sulfur Removal Efficiency
Operation
On ce-through
Tail-gas exhausted
Tail-gas recycled
to combustor
Regenerative
Tail-gas exhausted;
spent sorbent withdrawn
after regeneration step
Tail-gas exhausted;
spent sorbent withdrawn
before regeneration step
Sulfur recovery tail-gas
recycled to combustor;
spent sorbent after
re genera tion
Sorbent processing tail-gas
recycled to sulfur recovery
process; spent sorbent
after regenerator
Effective Sulfur Content
of Combustor Coal
-1
w., u-u-
"^SR"" + ""W^-VsR*1'
SR
e = Sulfur removal, recovery, or retention efficiency; subscript C = combustor, R = regenerator,
P = spent sorbent processing, SR = sulfur recovery process.
M = Sorbent makeup rate, moles calcium per mole of sulfur fed in combustor coal.
U = Sorbent utilization; subscript R = after regeneration, subscript C = after combustor.
W = Wt. fraction of sulfur in coal.
O ___ .. _ . . -
-------
•p
where W is the effective coal sulfur content. If the sulfur removal
efficiency of the spent sorbent processing system drops to 70 percent,
the coal has an effective sulfur content 36 percent greater than its
actual content, and the sorhent consumption rate must increase by about
43 percent, compared to the case of 100 percent sulfur removal effi-
ciency for the spent sorbent processing system.
The purpose of this discussion is only to point out the complex
nature of the system. Projections of sorbent consumption rates based
solely on laboratory performance could easily differ from the ultimate
commercial performance by as much as a factor of two.
PROJECTION OF SPENT SORBENT AND COAL ASH PRODUCTION RATES
A plant material balance shows in general that the mass of coal
ash per unit mass of spent sorbent calcium, A, is given by
where a is the mass fraction of ash in the coal, W is the coal sulfur
o
mass fraction, and M is the molar makeup rate of sorbent, moles of cal-
cium per mole of sulfur fed.
For a once-through operation
M = ^ , (3)
where e_ is the required combustor sulfur removal efficiency and U is
C ^
the sorbent utilization obtained in the combustor. The sorbent utiliza-
tion is a function of the sorbent properties, the combustor operating
conditions, and the combustor design. If it is assumed that the spent
sorbent processing scheme has a high sulfur efficiency, so that sulfur
losses from it can be neglected, then e = e as in equation 1, and
A =
i- SAH 6rx. w)
W 2 x 10
5
25
-------
The quantity A/(aU ) is shown in Figure 5 as a function of the coal sul-
L*
fur content. The value of a may range between 0.02 and 0.30 for eastern
coals. For once-through operation U is expected to range between 0.20
and 0.90. Thus, the ratio A (mass ratio of ash to spent sorbent calcium)
may range between about 0.1 and 200 for once-through operation.
For regenerative operation the sorbent makeup rate is a function
not only of the combustor design and operating conditions, but also of
the regenerator design and operating conditions. It is a function of
the required combustor sulfur removal efficiency and the other process
variables that are not yet well understood. The sorbent attrition
behavior may be the controlling factor in many cases where the rate of
sorbent deactivation is low. For regenerative operation M may range
between 0.2 and 2.0, and the ash/sorbent ratio may range between about
0.15 and 150, a range not much different from the once-through case.
Sorbent Utilization for Once-through Operation
The ranges of sorbent utilization (fraction of calcium as CaSO, or
CaS) to be expected from a once-through fluidized-bed combustor can be
projected from the results of Thermogravimetric (TG) experiments. These
results have generally agreed with batch fluidized-bed and continuous
operation (Exxon miniplant) results. Table 8 lists projections for
500 ym sorbent particle diameters and 90 percent sulfur removal effi-
ciency, based upon the TG results. Three fluidized-bed combustion sys-
tems are considered: the atmospheric-pressure boiler, the pressurized
boiler (at high and low excess air rates), and the adiabatic combustor.
In all three of these systems calcining conditions are expected to pre-
vail (except, possibly, with the pressurized boiler at turndown). Both
limestones and dolomites are considered as general classes of sorbents
though performance will differ within these general classes.
For continuous once-through operation a distribution of sorbent
utilization will exist in the spent sorbent. If the kinetics of desul-
furization are first-order with respect to the S02 concentration and
26
-------
Curve 685679-A
1000
o
CO
O
CD
.0
O
CO
"c
CD
CL
CO
.c
GO
o
o
co
ct:
oo
uo
na
100
10
Weight Fraction Ash in Coal
Average Sorbent Utilization, Fractional
Coal Heating Value
= 35.0MJ/kg (15,000 Btu/lb)
23.3MJ/kg
(10,000 Btu/lb)
1
2345
Weight percent sulfur in coal
Figure 5. Ratio of Ash to Spent Sorbent for Once-through Operation
27
-------
TABLE 8. PROJECTIONS OF ONCE-THROUGH SORBENT UTILIZATION*
System
Conditions
Percent of Available
Calcium Utilized
Limestone
Dolomites
N)
oo
Atmospheric-Pressure
Boiler
Pressurized Boiler
Low excess air (10%)
High excess air (100%)
Adiabatic Combustor
Boiler turndown
100 kPa, 815-870°C
10-25% excess air, 15-13%
CO,
calcining
1000 kPa, 900-1000°C
15% C02, calcining
1000 kPa, 900-1000°C,
8.5% C02, calcining
1000 kPa, 900-1000°C,
300% excess air, 4% CO ,
calcining
Temperature down to ^750°C,
carbonating condition in the
pressurized boiler case,
calcining conditions in the
other cases
25-35
30-40
40-50
40-50
40-50
80-90
80-90
50-80
Same utilization as at full
capacity for all cases except
pressurized boiler. For pres-
surized boiler limestone will
not react under carbonated
conditions; dolomite will be
utilized 50-70% under carbonated
conditions.
*Basis: 500 \im particle diameter, 90% sulfur removal.
-------
the unreacted sorbent concentration, and if the fluidized-bed corabustor
is perfectly mixed, then it can be shown that the sorbent utilization
is distributed as follows:
F(U < X) = 1 - (1 - X) U , (5)
where F(U < X) is the fraction of the spent sorbent having a utilization
less than X, and U is the average spent sorbent utilization. This
result is also independent of the distribution of sulfur releases within
the fluidized-bed combustor. The once-through distribution of sorbent
utilization is plotted in Figure 6 for average utilizations ranging
from 0.1 to 0.9. This distribution should be a reasonable approxima-
tion to be applied in cases where the processing or utilization of the
spent sorbent is sensitive to its composition distribution.
The sorbent particle size also influences the degree to which it
can be utilized in a once-through operation. Figure 7 illustrates this
influence. The projections in Table 8 should be reasonable for
average particle diameters up to about 1000 urn; larger particle sizes
will require a reduction in the projection of the maximum sorbent
utilization.
Sorbent Re gener ability
Two sorbent regeneration schemes have been considered for fluidized-
bed combustion: the one-step, high- temperature regeneration and the
two-step, low-temperature regeneration. Two factors of importance to
the characterization of the spent sorbents from these regenerative
processes are the required makeup rate of fresh sorbent for maintenance
of the combustor desulfurization efficiency, and the level of utiliza-
tion of the sorbent in the combustor and regenerator.
The level of utilization of sorbent in the combustor would be less
than the maximum utilizations projected for once- through operation in
Table 8. For the projection of the sorbent total sulfur content before
29
-------
1.0
to
M
§ 0.8
|s
CD
*^« ^r
o
c:
••§ 0.4
0.2
0
n i i i r
U= Average Bed Sorbent Utilization
O.J 0.2 0.3 0.4 0.5 0.6 0.7
X
Figure 6. Cumulative Distribution of Sorbent Utilization
o
c
-s
O1
CO
c_n
vT>
CD
o
I
.Cs
0.8 0.9 1.0
-------
Curve 695826-A
-5 + 6]
1013 kPa
660 ppm SO,
954°C
11% 0
2
10
100
Time/Minutes
1000
Figure 7. Sulfation of Fully Calcined Tymochtee Dolomite
-------
and after regeneration, the following basis is applied and is illus-
trated in Figure 8: The maximum sorbent utilization for a once-through
desulfurization operation and the maximum extent of regeneration of the
once-through sorbent are averaged to yield the assumed ultimate sorbent
utilization if the process were cycled an infinite number of times. A
typical sorbent utilization differential as found in cyclic experiments
is then applied to project the sorbent utilization before and after
regeneration.
Table 9 summarizes the results of the projections for the one-step
and two-step regeneration processes and lists the specific assumptions
applied.
In a regenerative process the distribution of spent sorbent compo-
sition is expected to be much broader than in the once- through cases.
This statement follows from an examination of the distribution of the
number of spent sorbent cycles. It can be shown that the fraction of
particles in the spent sorbent residing in the system for n cycles is
F(n) =
where M is the feed rate of fresh sorbent (moles calcium per mole sul-
fur fed) and S is the rate of sorbent circulation between the regenera-
tor and combustor (moles calcium per mole sulfur fed to combustor) . The
cumulative distribution is given by
F(n>x) = MT-S . (7)
and the average number of cycles is
+ S\
(8)
Equation 6 is represented in Figure 9 for four average cycle numbers.
The distribution becomes very flat as the average cycle number is
increased or the ratio M/S is decreased.
32
-------
Curve 685692-A
Maximum
Utilization
on First Cycle
Sorbent
Utilization
LO
• Maximum
Regeneration
on First Cycle
Cyclic
Sulfur fAverage -Assumed
Change) Value for Infinite
I Number of Cycles
Sulfur
Change
in
First
Cycle
Time
Figure 8. Basis for Regenerative Sorbent Utilization Projection
-------
TABLE 9. PROJECTED REGENERATIVE SORBENT UTILIZATIONS'
System
One-Step Regeneration
One-Step Regeneration
(at combustor pressure)
Limestone
uc(%)b
UR(%)C
Dolomite
nc(%)
UR(%)
Two-Step Regeneration
Limestone
uc(%) UR(%)
Dolomite
U_(%) R (%)
\j J\
Atmospheric-Pressure
Boiler
24
14
21.5
11.5
UJ
-e-
Pressurized Boiler
Adiabatic Combustor
35
35
25
25
49
32.5
39
22.5
3 9
39
29
29
73
48
63
38
Based on values (lower) given in Table 8.
Assumes 50% regeneration on first cycle for one-step process with limestone and 90% for dolomite
and 30% for the two-step process with limestone or dolomite.
Assumed 10% sorbent utilization differential.
U = utilization of the sorbent in the combustor.
\_»
CU_ = utilization of the sorbent in the regenerator.
R
(7)
-------
Curve 685Snl-/'-
o>
Average _
Curve No. Cycles (n)
0 10 20 30 40 50 60 70 80 90 100
Number of cycles
Figure 9. Distribution of Cycle Number for Regenerative
Spent Sorbent
35
-------
A material balance around the combustor and regenerator results in
the following relationship for the sorbent circulation rate S, moles of
calcium circulated per mole of sulfur fed to the boiler:
s = (EC - MB) (uc - iy"1 , (9)
where £ is the combustor sulfur removal efficiency, U - U is the sor-
C t- K-
bent utilization differential, and U in the numerator is either UG or
TL, depending on whether the spent sorbent is withdrawn before (U ) or
after (U ) the regenerator.
R
For a regenerative system a specific value of the ratio M/S
(H l/(n-l)) is required in order to maintain the combustor sulfur
removal efficiency. Although this ratio is a complex function of the
sulfur removal efficiency, the sorbent properties, the combustor, and
regenerator design and operating conditions, and so on, it is assumed
to have a representative value of 0.1 for the one-step and two-step
regeneration processes.
Solving Equation 9 for the sorbent makeup rate M yields:
Tr/e,
UC - UR +
Table 10 summarizes the projections for the sorbent makeup rate and the
quantity MU/EC> which corresponds to the fraction of the sulfur captured
in the combustor that is handled by the spent sorbent processing system.
The makeup rates range from 0.49 mole calcium per mole of sulfur fed to
0.75 mole of calcium per mole of sulfur fed to the combustor.
There is considerable speculation involved in the projection of the
sorbent makeup rates in Table 10. The assumption of constant value of
the parameters M/S and UC~UR for both regeneration schemes and for both
limestone and dolomite sorbents is certainly an oversimplification. It
was also shown in Table 7 that the required combustor sulfur removal
36
-------
TABLE 10. PROJECTED SORBENT MAKEUP RATES'
System
One-step Regeneration
Limestone
«b „<:
A B
Md MU/e^'f'g M MU/E
C C
Dolomite
A
M
Atmospheric-Pressure 0.69 0.20 0.75 0.12 0.70
Boiler
Pressurized Boiler 0.63 0.26 0.68 0.20 0.57
Adiabatic Combustor 0.63 0.26 0.68 0.20 0.64
MU/EC
0.18
0.33
0.25
B
M
0.76
0.61
0.69
MU/EC
Two-Step Regeneration
Limestone Dolomite
A B A B
M MU/e_ M MU/e., M MtJ/e M MU/E
(j C (_• L.
0.10
0.28 0.61 0.28 0.66 0.23 0.49 0.42 0.52 0.39
0.18 0.61 0.28 0.66 0.23 0.57 0.32 0.62 0.28
aBasis: e = 0.85, M/S = 0.1 (equivalent to n = 11), V -lL = 0.1
O C K
M
sEc
"„ -
A - withdrawal of spent sorbent before regeneration step (U-U )
B - withdrawal of spent sorbent after regeneration step (U-U )
K
M - sorbent make—up rate, moles of calcium per mole of sulfur
U - sorbent utilization, subscript C = after combustor, R = after regenerator; no subscript
means either C or R depending on the point of spent sorbent withdrawal.
£ - combustor sulfur removal efficiency, fractional.
RMU/r represents the fraction of the captured sulfur handled by the spent sorbent process.
-------
efficiency and the effective sulfur content of the coal may vary greatly,
depending upon the sulfur efficiency of the sulfur removal system sub-
systems and the choice of tail-gas recycle or tail-gas cleaning.
Sorbent Attrition and Elutriation
The previous projections in this report have assumed that sorbent
attrition losses are negligible when compared to those of sorbent deac-
tivation. This may not be a valid assumption in all cases, and in some
instances the sorbent makeup rate may be determined by the sorbent
attrition losses rather than by the sorbent activity losses. When sor-
bent attrition is the controlling factor for the sorbent makeup, it is
expected that a substantial stream of spent sorbent will be generated
in the form of fines (probably <100 ym diameter) having compositions
significantly different from those previously projected.
The rate of particle attrition and elutriation in a commercial
fluidized-bed combustion power plant will be very sensitive to the oper-
ating conditions, the sorbent properties, and the hardware design: sor-
bent feeders, distributor plates, bed internals, cyclones, pneumatic
transport systems, and so on. Experimental work conducted to address
attrition has not sufficiently characterized the phenomena to permit a
meaningful projection of the rate of sorbent fines generation, the coal
ash content of the sorbent fines, and the chemical composition of the
sorbent fines.
In general, two stages of particulate control equipment will col-
lect elutriated sorbent and coal ash. Coarse material will be collected
in the first stage and recycled to the combustor. The second-stage
equipment will trap the fine material. This fine material would probably
not be recycled to the combustion because the fines content of the bed
and the resulting elutriation and/or fines recycle rate would increase
to extreme levels. The sulfur content of the sorbent fines depends
upon their residence time in the desulfurizer and the rate of reaction
of the fine particles.
38
-------
While the rate of fines generation and the composition of these
fines cannot be projected with any confidence, it is almost certain that
some significant stream of sorbent fines will be produced and must be
accounted for in the spent sorbent characterization. The following
assumptions are applied to determine the spent sorbent fines properties:
• Fines (<100 ym) are captured in the second-stage particu-
late control equipment at a rate of 10 percent of the sor-
bent makeup rate.
• Most (95 percent) of the coal ash is captured in the second-
stage particulate control equipment.
• Negligible losses of fines occur in the regenerator and in
the combustor due to the regenerated sorbent recycle stream
(i.e., this stream is attrition resistant).
• The fines composition is equal to the bulk bed composition.
ASSESSMENT OF SPENT SORBENT PROJECTIONS FOR FLUIDIZED-BED COMBUSTION
The basis for the fluidized-bed combustion power plant spent sor-
bent characterization is summarized in Table 11. Tables 12 through 14
list the spent sorbent projections for once-through operation and for
the one-step and two-step regeneration processes. Table 15 considers
the spent sorbent produced during plant turndown. Fresh sorbent makeup
rates (calcium-to-sulfur mole ratio), rates of sorbent fines (<100 ym),
capture from the combustor particulate control equipment (calcium-to-
sulfur mole ratio), and the spent sorbent compositions are presented.
The spent sorbent size distribution (coarse bed material) will be
similar to the sorbent feed size distribution given in Figure 2, with
the amount of modification dependent upon the sorbent attrition rate,
the fines recycle rate, and the bed elutriation rate. The sorbent fines
size distribution will be similar to curve 4 in Figure 10, depending
upon the fines recycle rate, the bed attrition behavior, and the cyclone
particle capture performance. Sorbent elutriation from the regenerator
vessel has been neglected.
The projections will be updated as new information is developed.
39
-------
TABLE 11. POWER PLANT BASIS FOR SPENT SORBENT PROJECTIONS
Plant Size = 600 MW
e
Plant Heat Rate - MJ/kWh (Btu/kWh) based on HHV
(3)
Atmospheric-pressure boiler 10.08 (9550) ,^\
Pressurized boiler 9.50 (8967)„,
Adiabatic combustor 9.60 (9096) ^
Coal (Ohio-Pittsburgh No. 8 Seam coal - Table 6)
Sulfur - 4.3 wt %
Ash - 8.5 wt %
Heating value - 29.1 MJ/kg (12,500 Btu/lb) LHV
Coal Rate - Mg/hr
Atmospheric-pressure boiler 200.0 (220.4)
Pressurized boiler 187.7 (206.9)
Adiabatic combustor 190.4 (209.9)
Sulfur Removal Efficiency (%) - no recycle of tail-gases
Power plant - 82.6
Once-through combustor - 87 (assumes e = 0.95 in Table 7)
Regenerative combustor - 92 (assumes, e = e = 1.0,
P R
ecij = 0.90, Table 7)
Ash in Overhead Fines - 95%
Ash in Coarse Spent Sorbent - 5%
Sorbent Fines Rate - 10% of sorbent makeup rate
Limestone Type - 1359 (Table 3)
Dolomite Type - 1337 (Table 4)
-------
TABLE 12. ONCE-THROUGH SORBENT OPERATION PROJECTIONS
Sorbent
Rate
(Ca/S)
Sorbent
Fines Rate
(Ca/S)
Composition of Spent Sorbent on a Molar-Calcium Basis,
Mole % (Total wt fractions in parentheses)
CaS04
CaS
CaO
CaC03
MgO
modes MgO
(per mole Ca)
Other
Components
(gm per
mole Ca
Ratio of
Wt of Ash
to Wt of
Spent Sorbent
Fines
Atmospheric-Pressure
Boiler
Limestone 3.48
(1359)
Dolomite 2.9
(1337)
Pressurized Boiler
Limestone 2.18
(1359)
Dolomite 1.09
(1337)
Adiabatic Combustor
Limestone 2.18
(1359)
Dolomite 1.74
(1337)
0.35 25
(0.437)
0.29 30
(0.315)
0.22 40
(0.606)
0.11 80
(0.641)
0.22 40
(0.606)
0.17 50
(0.467)
0
(0)
0
(0)
0
(0)
0
(0)
0
(0)
0
(0)
75
(0.540)
70
(0.302)
60
(0.374)
20
(0.066)
60
(0.374)
50
(0.192)
0
(0)
0
(0)
0
(0)
0
(0)
0
(0)
0
(0)
oa
(0)
1.19
(0.367)
Oa
(0)
1.19
(0.281)
Oa
(0)
1.19
(0.327)
1.73
(0.023)
2.11
(0.016)
1.73
(0.020)
2.11
(0.012)
1.73
(0.020)
2.11
(0.014)
2.46
1.77
3.41
3.60
3.41
2.62
(a)
MgO is included in other components in the limestone cases.
-------
TABLE 13. ONE-STEP REGENERATION PROJECTIONS
So r bent
Rate
(Ca/S)
Sorbent
Fines Rate
(Ca/S)
Composition of Spent Sorbent, (Mole %)
CaSO^
cas
CaO
CaC03
MgO
(moles MgO
per mole Ca)
Other
Components
(g per mole
calcium)
Atmospheric
Pressure
• Limestone
Combustor
Regenerator
• Dolomite
Combustor
Regenerator
Pressurized
Boiler
• Limestone
Combustor
Regenerator
• Dolomite
Combustor
Regenerator
Adiabatic Combustor
• Limestone
Combustor
Regenerator
• Dolomite
Combustor
Regenerator
0.75
0.81
0.76
0.82
0.68
0.74
0.62
0.66
0.68
0.74
0.69
0.75
0.08
0.08
0.08
0.08
0.07
0.07
0.06
0.07
0.07
0.07
0.07
0.08
24
12.8
21.5
10.4
35
21.5
49
34.1
35
21.5
32.5
19.2
0
1.2
0
1.1
0
3.5
0
4.9
0
3.5
0
3.3
76
86
78.5
88.5
65
75
51
61
65
75
67.5
77.5
0 0
0
0 1.19
0
0 0
0
0 1.19
0
n o
0
0 1.19
0
1.73
2.11
1.73
2.11
1.73
2.11
(a) 5% of the CaSO^ converted to CaS in atmospheric-pressure case, 107 conversion to CaS in
pressurized case.
-------
TABLE 14. TWO-STEP REGENERATION PROJECTIONS
Sorbent
Rate
(Ca/S)
Sorbent
Fines Rate
(Ca/S)
Composition of Spent Sorbent (Mole %)
CaS04(a)
CaS(b)
CaO
CaC03(c)
MgO
(moles MgO
per mole Ca)
Other
Components
(g per mole
calcium)
Pressurized
Boiler
Limestone
.0
OJ
Combustor
Regenerator
• Dolomite
Combustor
Regenerator
Adiabatic
Combustor
• Limestone
Combustor
Regenerator
• Dolomite
Combustor
Regenerator
0.66
0.71
0.53
0.56
0.66
0.71
0.62
0.67
0.07
0.07
0.05
0.06
0.07
0.07
0.06
0.07
18.7
0
73
0
18.7
0
48
0
20.3
29
0
63
20.3
29
0
38
6.1
46.7
27
25.9
61
46.7
52
43.4
0 0
21.3
0 1.19
11.1
0 0
21.3
0 1.19
18.6
1.73
2.11
1.73
2.11
(a) 30% of limestone-based-sorbent CaS resulfated in combustor; 100% of dolomite-based sorbent
resulfated in combustor
(b) 100% conversion of CaSO^ to CaS in first step
(c) 100% calcination in combustor; 30% conversion of CaO to CaC03 in second step.
-------
TABLE 15. TURNDOWN SPENT SORBENT PROJECTS
Sorbent
Rate
(Ca/S)
Composition of Spent Sorbent on a Molar-Calcium Basis
Mole % (Total Weight Fractions in Parentheses)
CaSO,
CaS
CaO
CaC03
MgO
(moles MgO
per mole Ca)
Other
Components
(g per mole
calcium)
Pressurized
Boiler
Dolomite
(1337)
1.45 60
(0.476)
0
(0)
0
(0)
40
(0.234)
1.19
(0.278)
2.11
(0.012)
Assumptions:
• All processes operated once-through during turndown.
• Dolomite-based processes operate at about 750°C during turndown for pressurized operation.
• Limestone-based processes operate at turndown such that calcining conditions always occur
in the combustor.
• All other cases (other than the pressurized boiler with dolomite) result in compositions
identical to those in Table 12 (i.e., the calcium-to-sulfur ratio is fixed during
turndown and the sorbent performance is not affected by turndown conditions).
-------
Curve 6958.17- /'
Type Screen No.
400 200 100 60 40 20
10
Ul
CD
.£i
CO
o>
.1
1
5
15
25
35
45
55
65
75
85
93
96
98
99
1 1 1
-
-
-
-
-
x
X
_x
1 1 1 1
' '/
5/
X
S
f
j/
X/
"XX
X S
1 1 1
1 1 1 1
X
X
.^
>
X
s
i 1 1 1
i i |, |
X
^_y
/
/
sXx
xXx
r^X
X
i i i
^"
s
X
x
X
X
1 1 ' I1 M,
/.
XX
' X X
X /
' X
/
^MII
r^
X
1
X
-
X
Curves 1. 2. & 3 Represent Projected-
Particle Size Distribution
Leaving Fluid-Bed Boiler
System
Curve 4 Represents Projected
Particle Size Distribution -
Leaving Primary Collectors -
Curve 5 Represents Projected ~
Particle Size Distribution
Leaving Secondary Collectors"
1 1 1 1 i i i 1 i 1 1 il
.5
3
10
20
30
40
50
60
70
80
90
95
97
98.5
10 ipo
Particle Size-Microns
1000
Figure 10. Particle Size Distribution for Different Gas Streams
-------
SECTION 5
LAND DISPOSAL
REGULATIONS/CRITERIA
The legislative developments and criteria governing spent sorbent
disposal have been reviewed. The important laws, regulations and cri-
teria are summarized in this section.
With the enactment of the National Environmental Policy Act of
1969 (NEPA), all of us are charged with a "responsibility to contribute
to the preservation and enhancement of the environment." Since the dis-
posal of the solid wastes from the fluidized-bed combustion process must
satisfy the provisions of environmental regulations, the federal legisla-
( 8)
tive developments governing liquid discharges from power plants, dis-
posal of dredged and fill materials, * water discharges from all
sources, * and landfill practices ' have been reviewed.
These include three of the most important environmental laws: The Clean
Air Act Amendments of 1970; the Federal Water Pollution Control Act
(14)
(Public Law 92-500, 1972);v and the Resource Conservation and Recovery
Act (The Solid Waste Disposal Act of 1965, Public Law 89-272, 1965, as
amended by Public Law 91-512, 1970 and by Public Law 94-580, 1976).
Although environmental standards for solid residue disposal from
coal-fired boilers (including the fluidized-bed systems) have not yet
been promulgated, the Resource Conservation and Recovery Act (RCRA)
requires EPA to set criteria by April 1978 for identifying whether a
solid waste is considered "hazardous," and to establish standards cover-
ing generation, handling, treatment, and disposal of such wastes. If
the residue were not "hazardous" — and there is no indication that the
FBC residue would be at this time — it would be subject to any
46
-------
restrictions developed by the individual states under their respective
management plans within the guidelines established by EPA as required
by the RCRA.
In anticipation of forthcoming criteria for solid waste disposal and
the quality of its leachate, the chemical characteristics of leachates
from leaching experiments are compared with the drinking water standards
given by the EPA National Interim Primary Drinking Water Regulations
(NIPDWR)/ The United States Public Health Service (USPHS)(17) Drink-
ing Water Standards, and the World Health Organization (WHO) Potable
C\Q\
Water Standards. This is, of course, extremely conservative; a
leachate dilution/attenuation factor of 10 is currently being considered
in the regulation draft under Section 3001 of the RCRA of 1976 by the
Hazardous Waste Management Division of the Office of Solid Waste, EPA.
It must be pointed out that the drinking water standards are used in
this investigation only in an effort to put data into perspective in
the absence of EPA guidelines and should not be construed as suggesting
that the leachate must necessarily meet drinking water standards.
Although the guidelines for the power plant effluents are not applicable
to the disposal of dry spent sorbent from the fluidized-bed combustion
process, they are used as additional references in this investigation.
Because of the wide variations in the characteristics of solid wastes,
in general, weather, soils, topography, groundwater from site to site,
and nearby stream quality and flow characteristics, permits are currently
being awarded on a site-specific basis. Eventually, as a result of RCRA,
state regulations will apply, but these regulations will not be enacted
until federal standards are enacted. Depending on the actual site
selected for the spent sorbent disposal, the leachates would have to meet
(19)
the water quality criteria for the specific water use. ' The success
of a land disposal application depends, furthermore, above all, on the
design, construction, and operation for a specific disposal site based on
the geology, hydrology, and climate of that particular site.
-------
Related Literature on Disposal
The solid waste research program, under the leadership of EPA, ini-
tially concentrated on programs associated with municipal solid wastes,
but recently has included studies on hazardous and industrial wastes in
anticipation of new regulations and standards for hazardous and non-
(20 21)
hazardous industrial wastes. ' Ahundant literature is available
(20-25)
on sanitary landfill and pollutant migration from municipal wastes.
Recent work includes studies on land disposal of solid wastes from flue
gas cleaning systems with emphasis on flue gas desulfurization
. . (20,26-29)
sludges. '
Literature on disposition of spent sorbent from fluidized-hed coal
combustion is limited but includes BCURA^ and PER, who conducted
bench-scale leaching on small numbers of sorbents x
-------
TABLE 16. SELECTED WATER QUALITY CRITERIA
Substance
Maximum Concentrations (npj £)
National Interim
Primary Drinking
Hater Regulations'-^)
PHS Regulations
on Drinking
Water(15)
World Health
Organization Potable
Water Standards^"'
Proposed
Guidelines
for Power
Plant
Effluent^
VO
pH (pH unit)
Total dissolved solids
AR
As
Ba
Ca
Cd
Cr
Cu
Fe
Mn
Ni
Pb
Se
Sn
SO^
7n
7 - 8.5
6.0 - 9.0
0.05
0.05
1.0
0.01
0.05
0.002
0.05
0.01
500
0.05
0.05
1.0
0.01
1.0(Cr+3)
0.05(Cr+6)
1.0
0.3
0.05
2.0
0.05
0.01
1.0
250
5.0
500
0.2
75
0.05
1.0
0.3
50
0.1
0.1
0.05
200
5.0
0.2
1.0
1.0
1.0
-------
EXPERIMENTAL TESTING PROGRAM
The environmental impact of any disposed material is a function of
its physical and chemical properties as well as of the quantity involved.
Potential water pollution problems can be predicted from the chemical
characteristics of leachates such as pH, specific ion concentrations,
trace element dissolution, and total dissolved solids. Disposal of the
solid wastes from the fluidized-bed coal combustion process may also
create air pollution, odor nuisance, and heat-release problems. To assess
the environmental impact of solid waste disposal and the suitability of
waste material as landfill, leaching and activity tests were performed on
actual spent sorbents and fly ash obtained from the fluidized-bed combus-
(32)
tors operated by Argonne National Laboratory, Exxon Research and
(31)
Engineering CCompany, and Pope, Evans and Robbins (PER), all of
whom are conducting studies on the fluidized-bed coal combustion process
under contracts to EPA or DOE. The spent sorbents available for this
study include spent bed material and fly ash from both the pressurized
and atmospheric-pressure boilers operated with a once-through or regenera-
tive sorbent system.
Samples
Batches of actual spent sorbent and fly ash from pilot-scale fluid-
ized-bed combustors tested for their environmental impact on disposal
are listed below:
• Argonne spent sorbent from run C2/C3 — from Argonne fs 15-cm
(32)
pressurized fluidized-bed combustion unit
• Argonne once- through spent sorbent from run VAR-4
• Argonne once-through spent sorbent from run LST-1
• Argonne once-through spent sorbent from run LST-2
• Argonne once- thro ugh spent sorbent from run LST-3
• Argonne once-through spent sorbent from run LST-4
• Argonne regenerative spent sorbent from run REC-3 — third com-
bustion experiment in 10-cycle combustion/regeneration series
of experiments
50
-------
• Argonne regenerative spent sorbent from run CCS-10 — tenth
regeneration experiment in 10-cycle combustion/regeneration
series of experiments
• Exxon spent sorbent from run 8.4 — from Exxon's 32-cm pressurized
fluidized-bed combustion unit, i.e., Exxon miniplant in Linden,
New Jersey^38^
• Exxon spent sorbent from run27
• Exxon fly ash from run 27
• Exxon spent sorbent from run 19.6
• Exxon fly ash from run 19.6
• Exxon spent sorbent from run 30.2
• Exxon fly ash from run 26
• Exxon fines from run 34
• PER sorbent — from Pope, Evans and Robbins's atmospheric-pressure
fluidized-bed combustor of 0.46 x 1.83 m size
• Gypsum — ground Iowa gypsum 114 was used to represent a refer-
ence for natural CaSO, leachability.
Processed compacts of Exxon No. 27 spent sorbent/fly ash mixture
by room-temperature blending (see Section 7 for Compact Preparation)
include the following:
• I1C and I1D — 35.8 wt % fly ash, 7 day air cure
• I2C and I2D — 35.8 wt % fly ash, 11 day air cure
• I3C and I3D — 35.8 wt % fly ash, 28 day air cure
• II1C and HID — 10 wt % fly ash, 7 day air cure
• II4C and II4D — 10 wt % fly ash, 52 day air cure.
Table 17 summarizes the process conditions under which these sor-
bents are generated. For the purpose of clarification, the term "spent
sorbent" refers to the bed material, "fly ash" to the carry-over material
collected in the primary particulate control device (cvclones), and
"fines" represents the very fine particulates that have passed the
cyclones and are collected on an additional filter or flue gas sampling
device.
51
-------
TABLE 17. PROCESS CONDITIONS OF SAMPLES STUDIED FOR
THEIR ENVIRONMENTAL IMPACT ON DISPOSAL
^"~~ — ,-^_^ Samples Argonne Argcnne Argonne Argom
Conditions^-— ^.^^ C2/C3 VAR-4 REC-3 CCS-
le Argonne Argonne Argonne Argonne
-10 LST-1 LST-2 LST-3 LST-4
Coal Arkwright Arkwright Arkwright Triangle Arkwright Arkwright Arkwright Arkwright
Sorbent Tymochtee Tymochtee Tymoehtee Tymochtee Limestone Dolomite Dolomite Limestone
dolomite dolomite dolomite dolomite 2203 1337 1351 1336
Run Length 23 11 80.6 2.6 34.7 25.5 18.4 17.5
(hr)
Pressure 810 810 810 152 810 810 810 810
(kPa)
Avg Bed Temp 900-955 900 900 1100 870 870 870 870
(°C)
Lower Bed Temp — — — — — — — —
(°C)
Gas Velocity 1.61-1.67 0.7 0.7 1.24 0.76 (1.76 0.76 0.76
Ms)
Expanded Bed Height — 0.91 0.91 0.46 0.91 0.91 0.91 0.91
(m)
Settled Bed Height — — — • — — — — —
(m)
Coal Feed Rate — 7.9 13.5
(kg/hr)
Sorbent Feed Rate — 2.6 2.9
(kg/hr)
Ca/S Molor Ratio 1.1-1.5 1.9 1.5
12.1 11.7 11.7 11.6
1.7 3.6 3.1 1.5
1.5 1.8 1.4 1.4
Excess Air — 17 17 Reducing 17 17 17 17
SO Emission (ppm) 80-375 122 450 67,000 900 160 270 990
NO (ppm) 135 185 120
CO (ppm) — 50 64
C02 (%) — 18 16
02 (%) 3.0 3.0 3.2
150 135 185 95
74 50 30 55
16 15 16 17
3-5 3.1 2.9 3.0
S Retention (%) 82-96 95 79 -.65;: 63 93 Kg 5e
Regeneration
Ib SO-/MBtu — 0.23 O.B5
Ib NO /MBtu — 0.25 0.16
1-5 0.2R 0.47 1.7
0.1R 0.17 0.23 0.12
(a)
(b)
Third combustion experiment in ten-cycle combustion/regeneration series of experiments
Tenth regeneration experiment in ten-cycle combustion/regeneration series of experiments
52
-------
TABLE 17. (Cont'd)
•— ~^_^Samples Exxon Exxon Exxon
Conditions -~~_^ 8.4 27 19. 6
Coal Arkwright Champion Champion
Exxon Exxon Exxon
30.2 26 34 PER
Champion Champion Champion Sewicklev
Sorbent Grove limestone Pfizer Grove limestone Grove limestone Grove limestone Pfizer Grove
1359 dolomite 1337 1359 1359 1350 dolomite 1337 limestone
Run Length 11 240 7.5
(hr)
Pressure 906-907 930 930
(kPa)
Avg Bed Temp — 829-930 880-P88
(°C)
Lower Bed Temp 877-908 840-960 —
(°C)
Gas Velocity 1.77-1.83 1.7-2.2 2.01-:.oi
(m/s)
8.5 15.5 13.25
920 930 932 101.3
929 885-927 900 816°C
945 949 868
2.5 1.9-2.1 1.5 2.7-4.6
Expanded Bed Height — 3-7
(m)
Settled Bed Height 0.66-1.19 — 1.55
(m>
Coal Feed Rate 75-112 112-149 113-1-3
(kg/hr)
Sorbent Feed Rate 10.3-15.2
(kg/hr)
Ca/S Molar Ratio 1.67 0-2.5 2.5
Excess Air 18-72 8-23 15
S02Emission (pmm) — 20-1290 5nn
NO (ppn) 50-200 70-210 10i
CO (ppm) — 30-110
C02 <*) — 1.1-17 11. 7-12. 3
02 (%) — 1.5-3.9 2.5-3."
S Retention (%) 62 41-100 6'
Ib S02/MBtu 1.8 0.03-2.5 1.0
Ib SOj/MBtu — 0.12-0.30 0.14
1.12-2.28 2.29 0.3-0.9
137 130 90 272-363
0-182
3.7 3.7 0.75
17.2 9.5-11.5 20.9
137 140-300 100-300
180-185 52
45 50 61
15.1 13 15.5
3.1 l.B-2.15 3.5 3
80 81-»1
0.29-0.59
0.25-0.28
Spent Sorbent Characterization
Chemical and physical characterization of the spent sorbents and
fly ash was carried out. Methods employed include optical microscopy,
scanning electron microscopy, energy dispersive analyses by X-ray, elec-
tron microprobe analysis, X-ray diffraction, emission and atomic absorp-
tion spectroscopy, and wet chemical methods. Tables 18 and 19 summarize
the chemical composition of the spent sorbent and fly ash as determined
by wet chemical methods. These are in agreement with the chemical
species identified by X-ray diffraction that are listed in Table 20.
53
-------
TABLE 18. CHEMICAL COMPOSITIONS OF SPENT BED MATERIALS AND
FLY ASH FROM FLUIDIZED-BED COAL COMBUSTION UNITS
Sample
Argonne C2/C3
Spent Sorbent
Argonne VAR 4
Spent Sorbent
Argonne REC-3
Spent Sorbent
Argonne LST-1
Spent Sorbent
Argonne LST-2
Spent Sorbent
Argonne LSI- 3
Spent Sorbent
Argonne LST-4
Spent Sorbent
Argonne CCS-10
Spent Sorbent
Exxon 8.4
Spent Sorbent
Exxon 27
Spent Sorbent
Exxon 30.2
Spent Sorbent
Exxon 19.6
Spent Sorbent
PER
Spent Sorbent
Exxon 27
Fly Ash
Exxon 19.6
Fly Ash
Exxon 26
Fly Ash
Exxon 34
Fines*
Process
Pressurized, once-through
Pressurized, once-through
Pressurized, regenerative
(3rd cycle combustor)
Pressurized, once-through
Pressurized, once-through
Pressurized, once-through
Pressurized, once-through
Pressurized, regenerative
(10th cycle regenerator)
Pressurized, once-through
Pressurized, once— through
Pressurized, once- through
Pressurized, once-through
Atmospheric, once-through
Pressurized, once- through
Pressurized, once- through
Pressurized, once-through
Pressurized, once-through
Sorbent
dolomite
dolomite
dolomite
limestone
dolomite
dolomite
limestone
dolomite
limestone
Dolomite/
limestone
Limestone
Limestone
Limestone
Dolomite/
limestone
Limestone
Limestone
Dolomite
Chemical Composition (w/o)
Ca Mg SC^
22.5 11.7 40.
20.6 12.0 27.
18.6 11.7 33.
31.7 1.25 26.
20.0 13.4 31.
21.8 9.1 29.
30.7 1.3 20.
24.5 16.1 9.
36.1 0.5 18.
21.8 6.6 24.
33.4 1.5 17.
40.0 0.5 10.
19.1 0.9 20.
7.9 4.6 14.
7.4 0.8 7.
11.8 1.9 in.
7.7 2.8 14.
s- co3=
0 <0.05 5.1
5 0.04 8.7
5 0.05 0.6
7 0.05
4 0.04
9 0.008 11.3
2 0.05 33.2
8 0.04 0.7 '
3 <0.05 34.8
8 0.002 13.9
3 0 30 . 0
0 0.001 44.0
1 0.04 0.6
fi 0
10
0 0.006
40
*Collected from flue gas sampling filter.
54
-------
TABLE 19. CHEMICAL COMPOSITIONS OF SPENT SORBENTS FROM
FLUIDIZED-BED COAT, COMBUSTION
Sample
Argonne C2/C3
Argonne VAR 4
Argonne REC-3
Argonne LST-1
Argonne LSI- 2
Argonne LSI- 3
Argonne LSI- 4
Argonne CCS-10
Exxon 8.4
Exxon 27
Exxon 30.2
Exxon 19,6
PER
Process
Pressurized, once-through
Pressurized, once-through
Pressurized, regenerative
(3rd cycle combustor material)
Pressurized, once-through
Pressurized, once-through
Pressurized, once- through
Pressurized, once- through
Pressurized, regenerative
(10th cycle regenerator)
Pressurized, once-through
Pressurized, once-through
Pressurized, once-through
Pressurized, once-through
Atmospheric, once-through
Sorbent
Dolomite
Dolomite
Dolomite
Limestone
Dolomite
Dolomite
Limestone
Dolomite
Limestone
Dolomite/
1 imes tone
Limestone
Limestone
Limestone
Molar Fraction (Ca based)
CaSO,
4
0.71
0.55
0.75
0.35
0.65
0.57
0.27
0.16
0.21
0.47
0.22
0.11
0.44
CaC03
0.15
0.28
0.02
0.65
0.35
0.35
0.72
0.02
0.64
0.42
0.60
0.73
0.02
CaO
0.14
0.17
0.23
0
0
0.08
0.01
0.82
0.15
0.1
n.iR
0.16
n.54
CaS
<0.003
<0.003
<0.003
<0.003
CaSO^, and Fe^ but little unsulfated
CaCO or CaO. Exxon spent sorbent No. 27 was separated into dark and
light particles. The light particles were found to contain sulfated and
unsulfated dolomite (CaCO^ CaSO^, and MgO), but the dark particles were
high in impurities consisting mostly of Fe.^ spinel, with some S
CaSO,, MgO, Fe203, and trace CaCOg, CaS, and Al^.
55
-------
TABLE 20. CHEMICAL COMPOSITION OF SPENT SORBENT AND
FLY ASH BY X-RAY DIFFRACTION
Samples CaSO, CaCO CaO
Species Identified
Fe304
MgO SiO aFe-0, Spinel Others
Argonne C2/C3 Major High — Major
minor
Exxon 8.4 Major Major Major
Spent Sorhent
— — — CaS possible
Exxon 27 High Trace — Present High Minor Major CaS present
Spent Sorhent minor minor Al^O, present
(dark particles)
Exxon 27 Major Major — Major Trace
Spent Sorhent
(light particles)
Exxon 19.6 Major Major
Spent Sorbent
Exxon 30.2 Minor Major
Spent Sorbent
PER Major — Minor
Spent Sorbent
Exxon 27 Major
Fly Ash
Exxon 19.6 Major Trace
Fly Ash
Exxon 26 Major Minor
Fly Ash
Trace
Trace
Minor Trace — Ca SiO possible
Major Major
Major High
minor
Major High
minor
Exxon 34 Major — — Present Major High — Ca SiO possible
Fines minor
-------
Table 21 compares the compositions of the actual spent sorbents
with their projected values (Section 4). The most significant differ-
ence exists in the case of the pressurized, once-through system where
the unsulfated sorbent exists as a mixture of CaCO and CaO instead of
CaO alone, as projected.
Spent sorbents from the fluidized-bed combustion process are often
inhomogeneous. Figure 11 shows photomicrographs of the spent sorbents
and fly ash from Exxon run No. 27, showing variations in particle size,
color, shape, and texture.
Trace metal element distribution was investigated by scanning elec-
tron microscopy (SEM) in conjunction with energy dispersive analysis by
X-ray (EDAX) . Figure 12 shows a typical SEM photomicrograph of a spent
sorbent (Exxon No. 27). The EDAX spectra, which plot peak intensity
versus X-ray energy, are shown on Figures 4(b) and (c) for two locations
on the spent sorbent particle as marked on Figure 12(a). The presence
of calcium, silicon, aluminum, sulfur, iron, sodium, potassium, and
titanium is indicated. A similar SEM photomicrograph and EDAX plots are
shown for a fly ash sample (Exxon 19.6) in Figure 13. Much higher silicon
and aluminum and lower calcium peaks are observed for the fly ash sample.
Electron microprobe analysis provided the elemental profiles of
partially sulfated limestone or dolomite particles when polished cross
sections were scanned. One persistent phenomenon was that the partially
sulfated limestone or dolomite always displayed a high concentration of
sulfur at the periphery of the particle and that the sulfur extended into
the particle along the grain boundaries or cracks. Figure 14 shows photo-
micrographs of area scans for sulfur at two locations (edge and center)
on the cross section of a partially sulfated limestone particle illus-
trating this effect. The sulfur concentration is proportional to the
intensity of the white dots on the area scan photos. Another finding
revealed by the electron microprobe was that the highly sulfated periphery
was not only rich in sulfur but also high in silicon, aluminum, and iron.
The high concentrations of silicon, aluminum, and iron at the surface
57
-------
TABLE 21. COMPARISON OF CHEMICAL COMPOSITIONS OF ACTUAL SPENT SORBENTS FROM
FLUIDIZED-BED COMBUSTION UNITS WITH THE PROJECTED VALUES
oo
Process Conditions
Actual Spent Sorbent
(Molar Fraction Ca-Based)
CaSO,
CaO
CaCO
CaS
Projected Composition
(Molar Fraction Ca-Based)
CaS04
CaO
CaCO
CaS
Atmospheric Pressure,*
Limestone Sorbent,
Once-through
0.44 0.54
0.02 <0.003 0.25 0.75
0 0
Pressurized,
Limestone Sorbent,
Once-through
Pressurized,
Dolomite Sorbent,
Once-through
Pressurized,
Dolomite Sorbent,
Regenerative
0.11-0.35 0-0.18 0.60-0.73 <0.003 0.40 0.60 0 0
0.47-0.71 0-0.23 0.15-0.42 <0.003 O.RO 0.20 0 0
0.16 0.82 0.02 <0.003 0.34 0.61 0 0.05
*The only sample available is an unidentified PER sorbent with unknown history and a typical sulfation
level.
-------
(a)
Figure 11. Microphotographs of Exxon Run No. 27 (a) Bed
Stone and (b) Fly Ash.
59
KM-67 07 7
-------
(a)
energy, KeV
(b)
Figure 12. (a) SEM Photomicrograph of Exxon 27 Spent Sorbent
(b) EDAX Spectrum of Spot 1 on SEM
(c) EDAX Spectrum of Spot 2 on SEM
-------
(a)
Figure 13. (a) SEM Photomicrograph of Exxon 19.6 Fly Ash
(b) EDAX Spectrum of Spot 1 on SEM
(c) EDAX Spectrum of Spot 2 on SEM
energy, KeV
(c)
-------
particle
surface
(a)
(b)
particle
interior
(c)
(d)
Figure 14. SEM and Electron Microprobe Photomicrographs of a Spent Limestone Particle (Exxon 21}
(a)(b) SEM and Sulfur Scan on a Cross-Sectional Area Near the Surface
(c)(d) SEM and Sulfur Scan on a Cross-Sectional Area in the Interior.
-------
were also observed for particles that were totally sulfated. TVA recently
reported that a 2 to 5pm thick hematite deposition was found on the
(35)
sorbent particles. Figures 15 and 16 show the photomicrographs of
electron microprobe analysis for a partially and a completely sulfated
limestone particle. The surface coating is suspected to have significant
influence on the reaction mechanism and leaching behavior, but the implica-
tion is not yet fully understood.
Trace metal ion concentrations on spent sorbent and fly ash were
determined by emission and atomic absorption spectroscopy. Results are
summarized in a later section, together with trace elements found in their
leachates.
Leaching Tests
At this time, there is no standard EPA leaching test with which the
potential environmental contamination from a solid waste can be assessed.
Currently, EPA's Office of Solid Waste, Hazardous Waste Management Division
is developing a "standard" leach test method as part of its effort in the
development of national standards for hazardous waste definition to be
promulgated under RCRA Section 3001, planned for April, 1978. Parallel to
the EPA effort, ASTM committee 19.12 (subcommittee 19.1203) is also develop-
ing standard leaching tests for solid waste in general. A shake test is
proposed by both efforts.
In this study leachates are induced by shake tests, except where
otherwise specified. Samples of waste stones were mixed with deionized
water in Erlenmeyer flasks at room temperature. An automatic shaker capable
of 70 excursions per minute was used to agitate the mixtures. Among the
parameters investigated were sorbent/ water loading, sample mixing time,
and aerobic versus anaerobic leaching conditions, with the latter shake
under nitrogen atmosphere. The supernatants resulting from this operation
were filtered, and the filtrate was determined for pH, specific conductance,
calcium, magnesium, sulfide, sulfate trace metal ion concentration, and
total organic carbon content. The solid samples before and after the leach-
ing operation were also analyzed for their chemical and physical
characteristics.
63
-------
particle
surface
(a)
(b)
particle
surface
(c)
(d)
particle
surface
(e)
(f)
Figure 15. Area-Scan Electron Microprobe Photomicrographs on a Cross
Section of a Spent Limestone Particle (Exxon 19.6) Near
Its Surface, (a) SEM, (b) Ca, (c) S, (d) Si, (e) Al, and
(f) Fe
64
RM- 68256
-------
particle
surface
(a)
(b)
particle
surface
(c)
(d)
(e)
particle
urface
(f)
Figure 16.
Area-Scan Electron Microprobe Photomicrographs on a Cross
Section of a Completely Sulfated Spent Limestone Particle
(Exxon 19.6) Near Its Surface, (a) SEM, (b) Ca, (c) S,
(d) Si, (e) Al and (f) Fe.
65
RM-68462
-------
Two shake procedures have been employed. These are described below.
• Continuous shake test. It establishes equilibrium conditions
between the solid and its aqueous surrounding and provides the
worst possible case with respect to contamination release. This
method has been used by Westinghouse since 1975 as one of the
screening tests for determining leaching properties of FBC spent
solids. Typically a 1:10 solid-to-water ratio is used.
• Intermittent shake test. A series of ten to fifteen cycles of
a 72-hour shake test was adopted as part of the leachability
study to provide leaching rate, aging effect, and long-term
leachability of the worst case and to make possible the calcula-
tion of "total fraction leached" for any specific ion or for
TDS as a function of total leach time or total leachate passing
the sample. Leachates are analyzed at the end of each interval
and a fresh charge of deionized water is added for each 72-hour
leach cycle. Typically, a 1:3 solid-to-water ratio is used.
Both shake tests are more severe than conditions anticipated under
actual land disposal; results from the shake tests are expected to pro-
ject the worst.
Spent Sorbent
Leaching properties were investigated for 13 batches of actual spent
bed materials (limestone and dolomite) from a pilot-scale fluidized-bed
combustor and regenerator operated under atmospheric and elevated pres-
sures. The operating conditions and chemical compositions of these
sorbents, which underwent standard shake tests, are presented in
Tables 18 and 19.
Since calcium sulfate is a major constituent of the waste stone
from the fluidized-bed combustion process and leachates contained high
calcium and sulfate concentrations, a naturally occurring gypsum was
tested under similar leaching conditions for comparison.
66
-------
Figure 17 presents the chemical characteristics of leachates as a
function of continuous leaching time and compares them with gypsum leach-
ate. It shows that leachates of the Exxon spent sorbents (all limestone
except Exxon No. 27, which was a mixture of limestone and Pfizer dolomite)
displayed similarly high calcium, sulfate, alkalinity, and total dissolved
solids, independent of operating conditions. Leachates of Argonne's
once-through spent dolomite exhibited noticeably lower TDS and calcium,
approximately in the range of gypsum leachate. Negligible magnesium ion
concentration was found in leachates of spent dolomite sorbent (<20 ppm).
It appears that dolomite sorbent, when generated under similar fluidized-
bed conditions, produces leachate of better quality. Spent dolomite from
either the combustor or the regenerator of the regenerative mode, however,
produced leachate worse than the once-through spent dolomite sorbent.
Further testing employing the 15 x 72 hour intermittent shake method
indicated that the leachate quality of Exxon 19.6 spent limestone improved
much faster than did leachate from Argonne C2/C3 spent dolomite, although
the initial leachate for the spent dolomite was much better.
Leachates or PER spent limestone from the atmospheric fluidized-
bed unit displayed similar chemical properties as did those of Exxon
spent limestones which were generated under elevated pressure. Since
the PER sorbent was the only atmospheric sample tested and it was not
representative due to an unidentified origin, operating conditions, and
storage age, the leaching behavior of spent sorbent generated under
atmospheric pressure should be investigated further.
Specific conductance has been shown to be a good index for leachate
quality, since it represents the total dissolved solids in the system.
Table 22, which compares the specific conductance of various sorbent
systems, shows clearly the results observed in Figure 17 as described
above.
Figure 18 shows leachate characteristics as a function of stone
loading. Again, it shows that the leachate from Argonne's spent dolomite
was of better quality than that of Exxon's spent limestone.
67
-------
Curve 686360-3
t
E"
3
"_G
ru
^^
_
1
oT
5
"5
i/->
CL
E
t/>
o
.c
E
i
a.
o>"
c
(O
-G
3
•g
o
O
o
~
l/J
2000
1500
1000
500
i i i i
-
~° C"^70 ^i - — \
D • D ^
D
r
i i i i i
2000
isnn
J../UU
1000
500
1 1 1 1
-
g (i 0 O
<&0 cm v
-
o
O —
0 1 i 'I
14
1 1 1
i2ks°£ -^' ^° »• -
10
8
* a -
- -
1 1 1 1
10000
8000
6000
4000
"V ' ' i
00% •
. D
o A
o jr--1^ %
A-"^ li*
T
0 1 ii
100 200 300 400 50C
Mixing Time, Mrs.
D Exxon Run 27 * * 1ST -2 pp
• Exxon Run 30. 2^ » LST-3 of
y * Exxon Run 19.6^ o LST-4 *-f
o Exxon Run 8.4 tf
& Argonne Run C2/C3JJP
^ PER Atmospheric Runt/»
« VAR-4 Pf
« LSI -1 ^
• REC-3 OR.P
— Natural Gypsum
Figure 17. Leachate Characteristics as a Function
of Mixing Time of Spent Sorbents
68
-------
TABLE 22. COMPARISON OF SPECIFIC CONDUCTANCE OF LEACHATES
FROM SPENT BED MATERIALS FROM VARYING FBC PROCESSES
Sample
Identification
Argonne C2/C3
Argonne VAR-4
Argonne LST-2
Argonne LST-3
Argonne REC-3
Argonne CCS-10
Argonne LST-1
Argonne LST-4
Exxon 8.4
Exxon 30.2
Exxon 19.6
PER
Process Variation
Dolomite, once-through, pressurized system
Dolomite, once-through, pressurized system
Dolomite, once-through, pressurized system
Dolomite, once-through, pressurized system
Dolomite, regenerative, pressurized system
Dolomite, regenerative, pressurized system
Limestone, once-through, pressurized system
Limestone, once-through, pressurized system
Limestone, once-through, pressurized system
Limestone, once-through, pressurized system
Limestone, once-through, pressurized system
Limestone, once-through, atmospheric system
Specific
Conductance
(p -mhos /cm)
3980
3510
3310
3140
8710
9540
8540
8570
7760
8000-8500
8000-8500
8590
In addition to the shake test, a small column leaching experiment
was conducted on Argonnefs spent dolomite and gypsum at a constant run-off
rate. Solid residues were manually packed into the columns of 11 mm dia.
to 213 mm depth. Successful 250 ml leachates were collected at a flow
rate of 5 ml/min. Results plotted in Figure 19 showed equilihrated cal-
cium and sulfate concentrations but a gradual decrease in total dissolved
solids and leachate alkalinity. It showed that the leachate character-
istics of Argonne's spent dolomite were comparable to or better than the
gypsum leachate except for Argonne's higher pH.
Sulfide was not found in spent bed sorbent or its leachate for the
once-through system. Some sulfide O25 ppm) was found in the anaerobic
leachate from the regenerated sorbent. This may not be a problem because
69
-------
Curve 684735-A
I 1 1 1 1 1 1 1
o>
o
c:
-£S
o
1
o
CD
S
<_>
1500
1000
500
0
13
11
9
7
5
8000
6000
4000
2000
0
D—D-
-O-
5 10 15 20 25 30 35 40 45 50
Stone Loading (gm in 250 ml HJD)
o Exxon Spent Stone Run 8 4
a Argonne Spent Stone C2/C3
° Iowa Ground Gypsum 114
Figure 18. Leachate Characteristics as a Function
of Stone Loading
70
-------
Curve 686%9-A
•g
"c ^5
o en
c E
o —^
o
TO
O
1500
1000
500
0
Gypsum
i i i
CD
- 2000
| 1500
-H 1000
CD
g 500
O
d*
CO
PH
CD
O.
CO
0
12
11
Gypsum
Gypsum
i i i i i i
CD
O
c. —
03 p
T5 S
13
-o o
C JC
o p
0 g
.a b
S 'E
3000
2000
1000
n
_ Gypsum
^ _^ ^
"" CP ° v Q — o — o- — o o
™ ~
II
Figure 19.
u 0 1 2 3 4 5 6 7
Numbers of 250 ml Samples
Leachate Characteristics of the Argonne Spent Stone
C2/C3 Leachates Induced by the Column Tests
71
-------
of the apparent ease of air oxidation of sulfide under aerobic conditions.
Since only limited quantities of regenerative sorbent were available for
testing at this time, further investigation should be conducted in the future.
Flv Ash and Fines
Leaching tests were conducted on four batches of fly ash and fines
from the Exxon miniplant. Results presented in Figure 20 showed that
the leachates of fly ash and fines displayed lower pH, calcium, and TDS
than did those found in the leachates of spent limestone bed materials.
This could be attributed to the greater amount of insoluble silica
present in fly ash and the relatively small amounts of free lime that
might be either partially dead-burned or covered with impermeable CaSO,
because of its smaller particle size or might form insoluble pozzolanic
reaction products (e.g., aluminosilicates) during the aqueous leaching
process. The fines (Exxon No. 34) collected from the flue gas sampling
system produced leachates of quality similar to those of the fly ash
collected from the cyclone. In general, leachates of fly ash and fines
displayed chemical characteristics (Ca, S0~ and TDS) similar to those
of the gypsum leachates except for the higher pH of fly ash. No sulfide
was present in the leachates.
Spent Sorbent/Fly Ash Mixtures
Since both the spent sorbent, which is generated in the bed, and the
fly ash, which is collected in the particulate collection device, are pro-
duced from the fluidized-bed combustion process, it is likely that they
will be disposed of together. Mixtures of various ratios (80/20, 70/30,
50/50, 30/70, 20/80) of the spent sorbent and fly ash from Exxon runs 27
and 19.6 were tested for their combined leaching properties. Results
shown in Figure 21 indicated that the leachates of spent sorbent/fly ash
mixtures displayed lower total dissolved solids, pH, and calciun concen-
tration than did the leachates of the spent sorbent alone. An addition
of >20 x
-------
Curve 686361-B
—
E
E
03
O
oT
03
z:
o.
E.
00
O
"i
t
oT
o
c
ro
"G
13
O
O
o
,w«i-. Dun 10 A Matnral Huncnm
o Exxon Run 26
Figure 20. Leachate Characteristics as a Function of Mixing
Time of Fly Ash
73
-------
Curve 686359-B
^
E"
=3
~c5
1
Q.
E
o
00
O
.c
E
i
a.
oT
c
ro
•c
•C3
0
o
'<3
s.
2000
1500
1000 '
500
0
2000
1500 J
1000
500
0
12 {
10
8
6
10000
8000.
6000
4000
2000
R
I !
^** -^.CL r, * r-, *
1 1
1 1 1
1 ! 1
1 1 1
s. »
D*--* ° °
1- D D -
1 1 1 1
1 I 1
— —
V
\
\
- \*^a ^ Q ^ -
1 1 1 1
H\ X) 4n An sn im
Figure 21.
D Exxon Run 27
A Exxon Run 19.6
Natural Gypsum
Leachate Characteristics of Bed Material/Fly
Ash Mixtures
7A
-------
Processed Spent Sorbent/Fly Ash Compacts
Leaching property was investigated for the processed cubes prepared
by room temperature compacting of sorbent/ash blends, (see identification
of the blends on p. 52). Among the parameters investigated are the
sorbent/ash mixing ratio and the air curing time. These cubes, prepared
in duplicate, were leached by two procedures. One of the cubes was
leached by the continuous shake for 1000 hr. The other underwent the
15 x 72 hr intermittent shake cycles. Figure 22 compares the leaching
rates of four processed sorbent/ash compacts with different mixtures and
air curing time. Several preliminary observations can be made from the
up-to-date data presented in Figure 22.
(1) The leachate quality improves with time. The amounts of solid
leached (e.g., TDS, Ca, SO.) decrease significantly with the total
number of 72-hour consecutive leach periods. The decreasing leach rate
with time is most likely attributable to the formation of the practically
insoluble CaCO, on the sample surface and within the pores, which would
retard the solid dissolution. Indeed, a white CaCO, scale was observed
on the surface of these cubes and on the container wall after leaching.
(2) The leachate pH also decreases gradually with time. This is
also attributed to the neutralization effect of CO- from the air.
(3) Leachates from cubes made from mix II (10 wt % fly ash) had a
lower initial SO, concentration and a higher initial pH than did those
of mix I (36 wt % fly ash) cubes, but they fell within the same range
after approximately 400 hours of leaching. It should be pointed out that
the compacts made from 10 wt % fly ash also had higher compressive strength.
(4) The leaching properties were relatively independent of the air
curing time of the compacts within the experimental range.
Table 23 compares the chemical characteristics of leachates from the
unprocessed Exxon run 27 spent bed material, fly ash, and their mixtures
with those of the processed Exxon run 27 sorbent/ash blends. Note that
75
-------
Curve 687523-B
800
600
400
200
180
t = Total Leach Time =(72) (n) Hour
360 540 720 900
1080
o I ID Mix I, 7 Day Curing
o II ID Mix II, 7 Day Curing
° I2D Mix I, 11 Day Curing
A H4D Mix II, 52 Day Curing
1600
1400
1200
^
I1 1000
sT 80°
600
400
200
0
12
11
10
9
8
7
E
u
o
3000
g 2000
|
1 1000
1
-fi § -n.
O A
I
5 10
n =Total Number of 72 Hr Consecutive Leach
15
Figure 22. Chemical Characteristics from Consecutive Leachates
for Processed Exxon No. 27 Spent Sorhent/Fly Ash
Compacts
76
-------
TABLE 23. LEACHATE CHARACTERISTICS OF PROCESSED AND UNPROCESSED
SPENT SORBENT AND FLY ASH FROM EXXON RUN 27
Sample
Leaching Condition
Leachate Characteristics
PH
Specific
Conductance
( y-mhos-cm"-'-)
Ca
(Mg/O
so4
(Mg/£)
Unprocessed
Exxon
Exxon
27 spent sorb en t
27 fly ash
Exxon 27 sorbent/ash
mixture (80:20)
Processed
Compacts
I1C:
I1D:
I2C:
I2D:
12D:
II1C:
HID:
H4C:
II4D:
36 wt % fly ash,
7 day cure
36 wt % fly ash,
7 day cure
36 wt % fly ash,
11 day cure
36 w/o fly ash,
11 day cure
36 wt % fly ash,
11 day cure
10 wt % fly ash,
7 day cure
10 wt % fly ash,
7 day cure
10 wt % fly ash,
52 day cure
10 wt % fly ash,
52 day cure
10
10
10
g/100 ml/100
g/100 ml/100
g/100 ml/197
hr Cont.
hr Cont.
hr Cont.
174 g/1740 ml/1224 hr
Cont.
182
1st
181
180
180
220
220
216
220
g/546 ml/72
72 hr cycle
hr
.5 g/1815 ml/1080 hr
g/540 ml/72
g/540 ml/72
hr
hr
g/2200 ml/1224 hr
g/660 ml/72
hr
.5 g/2165 ml/1080 hr
g/660 ml/72
hr
12
9
9
8
10
7
10
10
8
11
8
11
.4
.5
.5
.5
.3
.7
.2
.2
.4
.5
.3
.4
6320
2490
2570
2550
2580
2570
2430
2430
2230
2740
2370
2590
1128
684
760
576
572
552
552
552
560
640
544
600
1512
1711
1783
1692
1600
1410
1493
1493
1366
983
1548
1083
-------
the processed sorbent/ash compacts generated leachates of quality superior
to the unprocessed spent sorbent alone. This improved leaching property
was also observed in leachates from mixtures of unprocessed sorbent and
ash mixtures, as reported in the previous section.
Specific conductance is a measurement of total dissolved solids in
a solution and serves as a good index for leachate quality. Figure 23
shows a log-log plot of specific conductance versus total leach time
and total leachate volume passing through the solid for the sorbent/ash
compact, compact crushed to powder, unprocessed sorbent/ash mixtures, and
gypsum; and shows a straight line relation. The data in Figure 23 can be
extrapolated to long-term leachability to indicate that gypsum leached
constantly, independently of the total leach time and the volume of leach-
ate passing the sample. On the other hand, the leachates from the sorbent/
ash compact, the crushed compact powder, and the unprocessed sorbent/ash
mixture displayed improvement with time and total volume and, therefore,
are much less contaminating than are the natural gypsum from their long-
term leachability. Finally, these results clearly demonstrate that the
sorbent/ash compacting process improves the leaching property and reduces
the potential environmental impact through leachate contamination.
Trace Metal Elements
Leachability of trace metal elements was determined by emission
and atomic absorption methods. Table 24 summarizes the heavy metal
concentrations in the spent sorbent and fly ash from the fluidized-bed
coal combustion process and their leachates based on data from all the
available residues. The National Primary Drinking Water Standards
and Public Health Service Regulations and World Health Organiza-
(18)
tion as well as the EPA guidelines and standards for power plant
( 8)
effluent are listed for comparison. It should be noted that the
leachability of the trace metal ions was so low for all the spent sorbent
78
-------
Curve 689564-A
VO
o
I
10.0
8.0
6.0
4.0
2.0
8 1-0
S 0.8
o
I 0.6
o
o
•^ 0.4
o
o>
0.2
Normalized Leachate Quantity, mi per g of Starting Solid
3 6 9 12 18 30 45
r
D
I I
T
Gypsum
Unprxessed Sorbent/Ash Mixture
I 4C1 Crushed Powder
I 4D1 Original Compact
I I
20 40 60 80 100
Total Leach Time, hr
1000
4000
Figure 23. Comparison Specific Conductance of Leachate from Sorbent Compact, Crushed
Compact, Unprocessed Mixture, and Cypsum
-------
TABLE 24. TRACE METAL ION CONCENTRATIONS IN SPENT SORBENTS AND FLY ASH
FROM THE FLUIDIZED BED COMBUSTION PROCESS AND LEACHATES
Substance
Ae
Al
As
B
Ba
Be
Bi
Ca
Cd
Co
Cr
Cu
Ge
Fe
Hg
K
Li
Me
Mn
Mo
Na
Xi
Pb
Sb
Se
Si
Sn
Ti
V
Zn
Zr
Solid wt "
Bed Material fly Ash
'O.ooi 10
'0.03 '0.05
'0.03 o.ni to n.i
'0.02
'0.0005 '0.003
'0.01 <0.01
>10 >1
'0.006 '0.03
'0.01 '0.01
'0.02 '0.1
'0.02 '0.02
'0.01
2 to 5 0 to >in
ND -0.02
0.2
'0.01
o to >in 'O.i
'0.05 '0.05
0.1 '0.01
-0.01
'O.oi 'O.i
'0.01 '0.05
'0.01 '0.05
>:D** NT>
o.i to >in >io
'0.005 '0.01
0.01 to '\ 0.1 to '10
'0.05 '0.05
'0.03 <0.1
'0.02 '0.1
Leachates (mg/1)
Bed Material Fly Ash
'0.01 '0.01
'0.1 '1.0
'0.05 '0.05
<0 '6.0
—
<0.02 <0.02
<0.04 '0.04
>500 >500
'0.04 <0.04
'0.1 <0.1
<0.04 '0.04
<0.04 '0.1
'0.1 '0.1
'0.04 <0.04
'0.001 '0.001
'0.5
'0.2
'30 0 to '300*
'0.04 '0.04
<0.1 '1.0
>10
'0.04 '0.1
<0.04 <0.4
'0.08 '0.08
'0.005 <0.005
'2.0 0 to 30
'0.04 '0.04
'0.04 '0.04
'0.1 '0.1
'0.4 <0.4
'0.05 <0.05
National Primarv
Drinking Water
Standards (mg/1)
0.05
0.05
1.0
1.0
0.01
0.05
1.0
0.3
0.002
0.05
2.0
0.5
0.01
1.0
5.0
Proposed Guidelines
for Power Plant
Effluent (mg/1)
0.2
1.0
1.0
1.0
*High value resulted from leachate of fines collected from the flue gas particulate collection
**ND - Not detected.
80
-------
and fly ash that non,e of the leachates exceeded the drinking water stand-
ards. Leachates from the processed sorbent/ash compacts displayed sim-
ilarly low trace element concentrations. Although the levels of detec-
tion were in some cases limited by the analytical sensitivity achieved
with the small quantity of samples available, the leachability of trace
metal ions from the spent sorbents and fly ash from the fluidized-bed
combustion process will probably not cause water pollution problems, at
least for those trace metals covered by some form of drinking water
standard. This is easily understood since the leachates from a spent
limestone or dolomite system are highly alkaline and suppress the heavy
metal dissolution, since their solubility in an alkaline environment is
governed by their practically insoluble hydroxides and carbonates.
COD/BOD/TOC
Determination of chemical oxygen demand (COD) provides a measure
of the oxygen equivalent of that portion of the organic matter in a
sample that is susceptible to oxidation by a strong chemical oxidant.
The dichromate reflux method is usually employed for the COD determina-
tion because it has advantages over other oxidants in oxidizability.
The biochemical oxygen demand (BOD) determination is an empirical test
in which standardized laboratory procedures are used to determine the
relative oxygen requirements of waste waters, effluents, and polluted
waters. The test is of limited value in measuring the actual oxygen
demands of surface waters; and the extrapolation of test results to
actual situations is highly questionable, since the laboratory environ-
ment does not reproduce actual conditions, particularly as related to
temperature, sunlight, biological population, water movement, and oxygen
concentration. Since both the COD and BOD procedures are time-consuming,
total organic carbon (TOC) determination is often adapted to provide a
speedy and convenient way of estimating the other two parameters that
(45)
express the degree of organic contamination.
Total carbon (TC) and TOC were determined for leachates from
processed and unprocessed spent limestone and dolomite and fly ash from
81
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Argonne and Exxon pressurized fluidized-bed units, along with a control
leachate from a natural gypsum. A model 915 Beckman TOC analyzer was
used. Results summarized in Table 25 verified the assumption that the
organic content is extremely low or nonexistent. The TC and TOC values
were near the limit of detectability for all the leachates and control
analyzed.
Activity Tests
The activity of residual lime in spent sorbents and fly ash was
determined by its heat release property on contact with water, as the
hydration reaction of CaO is extremely exothermic. This was done
TABLE 25. TOTAL INORGANIC AND ORGANIC CARBON IN LEACHATE
FROM UNPROCESSED AND PROCESSED FBC SOLID WASTE
Sample
Exxon No. 19.6
Bed Material
Exxon No. 19.6
Fly Ash
Argonne C2/C3
Bed Material
Argonne LST-1
Bed Material
Argonne CCS- 10,
Regenerator Bed
Material
History
Limestone, pressurized once-
through, unprocessed
Limestone, pressurized once-
through, unprocessed
Dolomite, pressurized once-
through, unprocessed
Limestone, pressurized once-
through, unprocessed
Dolomite, pressurized
regenerative, unprocessed
Total Carbon
Inorganic
<7
<5
<5
<5
<5
(ppm)
Organic
<5
<14
<16
<5
<5
Processed
Compacts:
I2C, I3C, I3D,
I4C, II4C
Processed cubes by room-
temperature blending of
Exxon No. 27 spent
sorbent and fly ash
<5
<5
Natural Gypsum
Control
<7
<8
82
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calorimetrically. In a standard test 3 g of stone were added to 20 ml
of deionized water in a Dewar flask which had been thermally equilibrated.
Chromel-alumel thermocouples were used to monitor the temperature rise
in the stone/water system with an Omega cold junction compensator and a
millivolt recorder. The heat release tests were conducted on the actual
spent sorbent and fly ash from the fluidized-bed combustion units. Cal-
cined and uncalcined limestone and dolomite samples were also tested for
comparison. Table 26 summarizes the maximum temperature rise when 3 g
of a solid sample were added to 20 ml of deionized water. Results showed
that the available batches of spent sorbent and fly ash did not give off
heat spontaneously on contact with water. In cases where there was
residual calcium oxide present, it might have been hydrated in air during
storage, dead-burned during the process, or coated with impermeable
CaSO, so that no spontaneous heat of hydration was detected. These
results seem to indicate that no heat-release problem is to be expected
as a result of the solid waste disposal from the once-through pressurized
FBC process. One must bear in mind, however, that the compositions of
the spent sorbent, and therefore the heat-release properties, differ with
processing variations and operating conditions. The potential heat-release
must be determined from the atmospheric spent sorbent, since the only
sample available in this category was a PER sample from an unknown stor-
age pile that had neither an identified sample history nor a "typical"
sample composition.*
The presently used activity test procedure was established in our
laboratories as a screening test to compare the residual lime activity
of spent sorbent from different processing conditions. The solid/water
f / "7 \
ratio selected in the bulk range as specified by the ASTM C110<- (76 g
in 380 ml water) and work by Murray et al.(48) (lime:water being 1:7) was
found empirically to provide much better repeatability than that from a
*Since the date of the preliminary issuance of this report, several addi-
tional batches of FBC residue (AFBC and regenerative PFBC) have been
made available for testing. The heat release property summarized in
Table 27 reflects the up-to-date results.
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TABLE 26. HEAT-RELEASE PROPERTY OF FBC WASTE
Sample, Solid/Waste (3g/20 ml) AT °(
TtlaX 9
Argonne C2/C3 spent dolomite <0.2
Argonne VAR-4 spent dolomite <0.2
Argonne REC-3 spent dolomite (3rd cycle comibustor) <0.2
Argonne CCS-10 spent dolomite (10th cycle regenerator) <0.2
Argonne LST-1 spent limestone <0.2
Argonne LST-2 spent dolomite <0.2
Argonne LST-3 spent dolomite <0.2
Argonne LST-4 spent limestone <0.2
Exxon No. 8.4 spent limestone <0.2
Exxon No. 27 spent dolomite/limestone <0.2
Exxon No. 27 fly ash <0.2
Exxon No. 19.6 spent limestone <0.2
Exxon No. 19.6 fly ash <0.2
Exxon No. 30.2 spent limestone <0.2
Exxon No. 26 fly ash <0.2
Exxon No. 34 fines <0.2
PER spent limestone (atmospheric) <0.2
Natural gypsum <0.2
Tymochtee dolomite, -16 +18 mesh <0.2
Limestone 1359, -18 +35 mesh <0.2
Calcined limestone 1359, -18 +35 mesh >55
84
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higher solid/water ratio that would give greater magnitude of tempera-
ture rise but lack reproducibility, most likely because of local heat-
ing. The former procedure has been adopted because it is fast, it
requires only a small quantity of stone, and its results reproduce
well. The latter procedure (small quantity of water added to larger
quantity of solid) is also planned, however, because it provides higher
sensitivity and simulates rainfall onto the disposed solid.
CONCLUSIONS AND ASSESSMENT
Results from laboratory testing indicate that the spent sorbent and
fly ash from the fluidized-bed combustion process can be disposed of
directly as landfill. The design and construction of the landfill site
should minimize leachate generation so that potential water contamination
from calcium and sulfate ion dissolution and leachate alkalinity can be
prevented.
Data from the laboratory-scale investigation of direct disposal of
the FBC residues indicated that:
• Trace metal ions are not likely to be water-contaminating.
• The dissolved organic concentration is low and near the limit of
detectability.
• Magnesium is not soluble, even from the spent dolomite sorbent.
• Sulfide will probably not be a problem for the once-through FBC
system.
• Heat-release on contacting water decreases with the following
order: AFBC bed -* AFBC ash -> PFBC bed, regenerative -> PFBC
bed, once-through •> PFBC ash. Heat-release property from the
AFBC residues may be an environmental concern which nay be pre-
vented by careful selection and design of the disposal site.
• Potential environmental concerns are: heat-release, leachate
alkalinity, TDS, calcium and SO^. Calcium and SO^ from most FBC
leachates are similar to those of natural gypsum leachate.
• The potential environmental impact from leaching can be improved
by further processing.
85
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Intermittent leaching results indicated that initial leachate
characteristics were better from the spent dolomite sorbent, but the spent
limestone leachate improved much faster with total leaching time or
leachate volumes. Spent dolomite from the once-through system gave bet-
ter quality leachate than did the regenerated sorbent. Preliminary
results also showed that the spent sorbent from the atmospheric FBC
process displayed leaching properties similar to those of the pressurized
FBC sorbent. This is encouraging but should be confirmed with more
typical spent sorbents from the atmospheric FBC process.
Results also show that the leachate of spent limestone bed material
had higher pH, calcium, and IDS than did the corresponding leachate of
fly ash. The leachate from fly ash is similar to that of natural gypsum,
except for higher pH from the fly ash. The addition of _>20 wt % fly ash
to the spent bed sorbent improved the leachate quality so that it meets
the gypsum criteria except for pH. This suggests codisposal of spent bed
sorbent and fly ash generated from the fluidized-bed combustion process
to minimize the environmental impact from the sorbent's leachability.
The environmental impact from disposal is reduced further by room tem-
perature processing — in other words, spent FBC sorbent/FBC ash blending.
Since there are no criteria for leachates at the present time,
results from the continuous leach test which represents the worst
possible case are compared with drinking water standards and leachate
characteristics for natural gypsum. As an indication of environmental
acceptability, a preliminary comparison is presented in Table 27 for
those categories of spent bed material and fly ash tested. The proc-
essed spent sorbent/fly ash compacts from room-temperature blending
possessed similar and better leachate characteristics than did the unpro-
cessed sorbent/ash mixtures, which in turn displayed better leachate
quality than did the spent bed sorbent alone.
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TABLE 27. PRELIMINARY INDICATIONS OF ENVIRONMENTAL IMPACT FROM THE FBC
SOLID WASTE DISPOSAL
Sample
Process
Sorbent Type
Environmental Parameters
Heat Release*-
Spontaneous Temp. Rise
(3g/20 ml)
Trace
Metal
Total
Dissolved
solids
Total
Organic
Carbon
Calcium
Sulfate
Sulfide
.ed Material
Pressurized FBC,
once-through
Limestone
<0.2°C
Bed Material
Pressurized FBC,
once-through
Dolomite
<0.2°C
Bed Material
Pressurized FBC,
regenerative
Dolomite
To be determined
To be
determined
00
—]
Bed Material
Atmospheric FBC,
once-through
Limestone
To be determined
Fly Ash
Pressurized FBC,
once-through
Limestone
<0.2°C
Mixture of bed
material and
fly ash
(unprocessed)
Pressurized FBC,
once-through
Dolomite/limestone
<0.2"C
Processed
Compacts from
bed material/
fly ash
mixtures
Pressurized FBC,
once-through
Dolomite/limestone
<0.2°C
Gypsum
Natural
<0.2°C
*Based on results from limited samples available and subject to the procedures specified in the section on "Activity".
(§ Do not meet either the drinking water or gypsum leachate criteria
Q Pass gypsum leachate criteria but not drinking water standards
[] Pass both drinking water and gypsum leachate criteria
-------
SECTION 6
OCEAN DISPOSAL
Sorbent, whether regenerated or not, must eventually he disposed
of. Spent sorbent may well be utilized as a product raw material. Some
spent sorbent, particularly from inland plants, will probably be dis-
posed of in landfills. At some sites, however, it is anticipated that,
as an alternative ocean disposal may be preferred or may even be
necessary.
FEASIBILITY STUDY
The first of two studies, an investigation of ocean dumping feasi-
)
bility, was completed in September 1976. This report entitled "The
Feasibility of Ocean Dumping as an Interim Alternative to Disposal of
Spent Stone from the Fluidized-Bed Gasification Process" is included
in its entirety in Appendix A. This report presents the following
information relative to ocean disposal of spent sorbent:
• Federal regulations and permit procedures; summary of EPA
regulations and criteria
• Approved sites for ocean dumping
• Ocean dumping mechanisms; ocean dumping costs
• Feasibility of dumping spent stone at sea
Attitudes toward various disposal methods
Requirements under the established permit system
- Description of the Westinghouse test program for measurement
of solution characteristics, heat release, and chemical
changes associated with ocean dumping of spent stone.
88
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The test results led to the conclusion that because of the high pH
caused by mixing the spent stone and [ocean] water, there may be synergis-
tic effects or the formation of toxic compounds during the immediate
release process. This matter must be clarified further before proceeding
with a permit consideration.
This preliminary study clearly outlined the requirements for obtain-
ing a dumping permit. Before continuing experimental dispersion studies
and biotoxicity testing, a second investigation was conducted to sense
the current attitudes toward issuing dumping permits and to identify
specific testing requirements.
SURVEY OF CURRENT EPA ATTITUDE TOWARD OCEAN DUMPING
This study completed February 1, 1977, is attached as Appendix B.
It is an assessment of today's practice in issuing permits and a projec-
tion of the probability of dumping spent sorbent.
The specific objectives of this assessment were to (1) determine
EPA's attitude toward ocean disposal of sulfated and sulfided limestone
in all contiguous U. S. EPA regions, with emphasis on Regions III and IV,
(2) estimate the probability of EPA issuing an ocean disposal permit
in calendar year 1977 and between 1978 and 1983, and (3) determine what
preliminary bench-scale dispersion and biotoxicity test will satisfy
current EPA requirements.
These three objectives were met by contacting EPA Regional Offices
and research laboratories and reviewing rules and regulations as reported
in the Federal Register. From these contacts and reviews it is con-
cluded that obtaining a permit from EPA to dump waste on a commercial
scale would be extremely difficult in either 1977 or between 1978 and
1983 because of EPA's general policy to phase out all ocean disposal
of industrial waste by 1981. The feasibility of ocean dumping is further
limited by the kinds of constituents associated with the waste and by
the regulatory requirements to perform a detailed environmental assess-
ment of the waste and to monitor the dump site.
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TEST PROGRAM
The resistance to ocean dumping makes issuance of a permit seem
improbable and discourages the appreciable cost of bioassays, chemical
characterization, and dispersion analyses. A revised test program is
being prepared which would permit an initial assessment of the environ-
mental impact of disposal in the ocean and an assessment of ocean utili-
zation as an alternative.
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SECTION 7
UTILIZATION
Whatever the outcome of studies on direct disposal of FBC spent
sorbent, a review of possible commercial uses for the large tonnages
of solids involved was undertaken as an appropriate parallel effort.
This review considered and developed several subjects, including a
detailed look at potential markets, an estimate of the maximum invest-
ment in processing facilities, an examination of work in related areas,
execution of bench-scale tests, and an assessment of utilization.
OPTIONS
An initial appraisal of the problem of spent stone disposition was
(*^fi^
given in Appendix F of the 1975 Westinghouse contract report to EPA.
This included consideration of the effect of variations in the FBC
process itself, the production rate of spent sorbent and its chemical
composition, governmental regulations, possible markets, and stone
processing alternatives. It was apparent that only large markets should
be evaluated. The acceptable final chemical forms for disposal to the
environment would be carbonate, silicate, or sulfate. For dolomitic
sorbents, magnesium would emerge as MgO. Should processing of spent
sorbent prove necessary for either disposal or utilization, twenty-one
alternatives were proposed. Possible end uses identified were:
• Soil stabilization
• Landfill
• Concrete/aggregate
• Gvosum
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• Acid mine drainage treatment
• Municipal waste treatment
o Refractory brick.
These options remain attractive, although the work of the past year has
led to assignment of higher priorities to those requiring a minimum of
processing and, preferably, only low-temperature processing. Low-
temperature fixation of the material is also of interest solely from
the standpoint of reducing the leaching properties of the residue after
disposal.
MARKET DATA
Primary Markets
When considering potential utilization of the spent sorbent, a prime
consideration is the potential quantity of material to be generated.
A 1000 MWe plant operating on a 3 percent sulfur coal will produce per-
haps 570,000 Mg/yr of spent limestone or 450,000 Mg/yr of spent
dolomite. Such quantities can only be utilized in some sector of the
construction industry. This could mean landfill or road construction
and, at upgraded levels of utilization, cement, concrete, and aggregate.
(49)
Some statistics are given in Table 28. The higher prices for aggregate
(sand and gravel) appear to pertain to metropolitan areas that are
exhausting local supplies of acceptable aggregates. Agricultural uses
(liming, soil conditioning) might also be outlets for spent sorbent but
are at a competitive disadvantage with limestone.
Special Markets
On the assumption that a concrete of sufficient compressive strength
could be developed, three specific utilizations, in addition to use in
general heavy construction, were explored. One is in coal mining, a
second in low-cost housing, and the third in radiation shielding. These
are discussed in the following paragraphs.
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TABLE 28. MARKET DATA ON SELECTED CONSTRUCTION MATERIALS
Material Million Mg/year Price level ($/Mg)
Portland Cement
Masonry Cement
Quicklime
Sand
Gravel
67.5
2.8
13.0
333
495
21.10-29.10
22.90-37.50
28.70-70.60
1.75-4.75
, 1.80-4.95
The room-and-pillar method for underground mining of coal has the
disadvantage of leaving about half the coal in the supporting pillars.
On the other hand, mine disposal of solid wastes is economically unat-
tractive in the United States because the transportation costs through
miles of underground tunnels are too high. If recovery of coal frora the
pillars were made possible by the use of pillars made frora spent sorbent,
however, the combined disposal/recovery operation might prove economical.
Assuming square cross-sectional pillars of coal with side W are left
under the present system, and the space between the pillars is aW, then
the fraction of coal recovered is given by:
f (1 + a)2 - 1
2 '
(1 + a)
from which
,1/2
a
= -i + (i/d - f)r
For the typical 50 percent recovery, a = 0.414. Since half the coal is
removed, the compressive load on the remaining coal has been increased
by a factor of 2.
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If the coal has an average sulfur content of 3 percent and an ash
content of 13 percent, and if the gasification or combustion processes
use a limestone/sulfur treat ratio of 3:1, the amount of waste produced
is 37.8 kg/100 kg coal. Adding water at the rate of 0.3 kg/kg of mix
to produce a solid compact, the amount of waste returned to the mine is
0.49 kg/kg coal. If the density and compressive strength of the solid
compact are comparable to those of coal in situ, such an application
would be at least technically feasible.
Another possibility is low-cost modular housing. Assuming a 12
by 15 by 8 ft (inside dimensions) module with 6-in thick walls and
plates, the module would require about 6.8 Mg of material. This
allows for one door and four window cutouts per module. A 1000 MWe
plant on limestone could generate material for about 120,000 such
modules annually. Domestically, assuming a 1 percent population growth,
the demand for dwelling units would be about 1,000,000/yr. At five
modules/unit, the output of forty 1000 MWe power plants would be required.
The potential in other parts of the world is considerably greater.
A further aspect domestically is the potential for radiation shield-
ing either for industrial or residential use. Civil Defense activity
has been at a low level for many years, after an initial flurry of con-
cern. Strategic planning, however, could include the systematic conver-
sion or modification of at least critical plants from conventional
industrial designs to those that offer radiation protection from nuclear
attack. The technology of concrete for such applications involves the
use of such high-density aggregates as iron scrap, iron ores, barium
sulfate, plus a higher water content. With a low-cost concrete, it may
prove feasible to use thicker sections. At present, a concrete reactor
shield for biological protection may be 10 ft thick. Water content is
an important factor for neutron shielding. The presence of calcium
sulfate should not be deleterious per se, since barium sulfate can be
used. Iron oxide from coal ash should be advantageous, but the effect of
trace elements would have to be determined.
94
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Other Markets
Use of spent sorbent as a source of low-cost lime in applications
such as acid mine drainage and municipal sludge treatment was not
examined in detail during this reporting period. It is assumed, a priori,
that this is technicallv feasible; what is needed is a sufficient
quantity of spent sorbent to make a field test.
Tn the high-temperature area both cement and brick remain as pos-
sibilities, although it is expected that these would be at a competitive
disadvantage with respect to low-temperature processes. Nevertheless,
bench-scale tests were planned, at least for limestone-tvpe sorbents,
to explore cement production.
OVERALL ECONOMICS
A rough estimate can be made of the maximum capital investment per-
missible for sorbent processing. A suitable reference case is that of
simple disposal, for which there will be some minimal investment in cool-
ing facilities and, perhaps, storage capacity for a nominal period of 1 to
3 shifts. The major direct operating cost would probably be that of
transporting the spent sorbent to a disposal site. Any alternative
would involve some incremental capital investment over that for the
reference case and either a lower operating cost or some incremental
direct operating cost, plus a product realization.
If P is the selling price of a marketable product per Mg, and
s
AC is the incremental production cost per Mg of spent sorbent, then
P
the gross realization in the case of making a saleable product is
P - AC S/Mg. Since a 1000 MWe plant would produce about 450,000 Mg/yr
s p
of a sulfated dolomite, each $/Mg realization would have the effect of
reducing operating costs by $450,000/vr. Assuming 17 percent capital
charges, 48 percent taxes, and a 20-year life, the allowable incremental
investment then works out to about $890,000 per $/Mg realization in sell-
ing price over incremental direct production cost. The cost includes
utilities, chemicals, direct labor, and certain charges estimated on the
basis of direct labor. This incremental investment would be recovered
95
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in 5 years through the realization. If it is argued that sorbent dis-
posal is not intended to be a profit-making operation, a longer pavout
time can be used. For a 20-year payout time, the incremental investment
would be about $2,060,000.
Since aggregate is selling for about $4.50/Mg, if the flv ash com-
pacts were technically competitive, and therefore could command the same
price, the processing plant obtained for a Si,000,000 incremental
investment over simple disposal would have to have an operating cost
of no more than $3.50/Mg. This would be lower if an economic incentive
had to be provided to permit the compacts to enter the market. If the
usual cost estimating factors apply, each $l/Mg realization would sup-
port a bare equipment investment of about $270,000.
These rough calculations support the viex^ that it is at least mar-
ginally justifiable economically to invest in simple processing facilities
for spent sorbent. It should be noted that all estimates of the economics
of environmental protection are at a disadvantage compared to the do-
nothing or the direct disposal cases since there is as yet no
accepted figure for the cost of the environmental impact.
TECHNICAL REQUIREMENTS
Study of environmental aspects of spent sorbent disposition led to
a recognition of the need to understand the nature of water pollution
control, as well as the nature of aggregates and the characteristics
of cement and concrete.
Environmental Considerations
Water pollution will, of course, be a consideration whether the
final material is used as a landfill, a road bed, or in solid conmacts
exposed to the environment. To put this in an engineering perspective,
such water pollution requires a series of events:
• There must be a source of water.
• The water must contact the solid.
96
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• The substances subject to leaching must be in a chemical and
physical condition such that leaching is possible.
• The contact time, contact temperature, and water/solid ratio
must favor leaching.
• The leachate must be able to migrate to a water stream in
sufficient quantity.
The addition of solutes to ground water supplies can therefore be con-
trolled, or prevented, but perhaps not completely eliminated by appro-
priate action to modify one or -more of these events.
With respect to water sources, omitting man-made sources as sus-
ceptible to control, the question is essentially one of management of
precipitation (rain or snow). Such water either flows to its lowest
level on the surface of the earth or permeates the earth, always flow-
ing downward under the influence of gravity until it reaches an imper-
meable stratum such as rock or dense clay. If an underground aquifer
does not develop, water will collect on the surface, forming a lake
until it is deep enough to overflow the lowest point in its banks.
Thus, if one wishes to avoid water pollution by eliminating the
water source, the site chosen for accumulation of the spent sorbent
must be well above the local water table and must have more annual
evaporation than precipitation. It is likely that neither of these
conditions can be more than partially met for most power plant locations.
Whatever water is available at the site can still be prevented from
contacting the spent sorbent. The site can be designed for maximum
diversion of surface runoff from adjacent areas and for maximum runoff
of surface water from the site itself. Ground water moving vertically
under a hydrostatic head created by its sources can be diverted by
bottom drains and liners. Earth movements and chemical reactions with
the local soil, however, over many vears can change the permeability
of the soil to leachate from the spent solids. In addition, liner life
is probablv no more than about 20 years.
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Even if some water contact cannot he prevented, the potential
pollutants must be in a form that can he leached out hy water. It is
known that exposure to high temperature modifies the pore structure of
solids like lime and gypsum so that they are considerably less reactive
and are hence termed dead-burned. Further, other pollutants like sul-
fide or sulfate sulfur and trace elements may be contained within the
solids and, therefore, may not be leachable except with long contact
times. What this suggests is that a disposal pile might be designed
for maximum porosity to permit any water falling on its surface to drain
off as rapidly as possible. The effluent would, of course, have to be
monitored.
Finally, if some leachate is produced, it can be collected and
treated, since it presumably represents a much smaller amount of pollu-
tant than that in the original solids.
Overall, this brief review indicates that one or more of several
simple design features can be used effectively to control and minimize
water pollution. Leachates must be managed to avoid more expensive cor-
rective measures in subsequent years. Competition for disposal sites
near population centers does exist, but this is a matter of long-term
economics. The trade-off is the cost of mine-mouth power generation
or even population dispersal versus the cost of transporting wastes long
distances. Such a study is outside the scope of the present investiga-
tion but is considered relevant to the total solution.
Some researchers have been investigating the retentive capacity of
clay soils for pollutants. Griffin reported on the ability of mix-
tures of kaolinite, montmorillonite, and illite with sand to remove
heavy metals as well as other substances from leachate from a Chicago
landfill. Anaerobic conditions and long contact times, corresponding
to a flow of less than 2 pore volumes per month, were used. Permeabili-
ties were of the order of 10 cm/s for the pure clays and 10 for
sand. Mercury, lead, zinc, and cadmium were strongly attenuated by the
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clays, with montmorrillonite being the least effective of the three.
The capacity of the clays for heavv metal ions was low, however, as
indicated by the range of 2 to 16 ppm for lead or kaolinite. This means
leachates permeating soils will eventually saturate them, and a further
influx of such ions will result in a breakthrough. Such findings favor
immobilizing potential pollutants as a means of environmental protection
in the event landfill is chosen as the disposal method.
The preceding considerations support the conclusion that a synthetic
aggregate would offer the potential for immobilizing pollutants while
avoiding the question of mass permeability. Some of the spent sorbent
might be usable as fine aggregate, but fines would have to be screened
and disposed of in a suitable manner. By pozzolanic reactions, either
they or the entire spent sorbent might be converted into a coarse
aggregate. A final possibility is to dispose of the spent solids in a
landfill by casting essentially monolithic blocks. If the aggregate
possibility is supported by test data, then the spent sorbents would be
directed to road construction or concrete.
Characteristics of Aggregate
To aid in assessing the potential for synthetic aggregate, the
basic characteristics of natural aggregate were reviewed. By defini-
tion aggregate consists of uncrushed or crushed gravel, crushed
stone or rock, sand, or artificially produced inorganic materials. For
use in concrete, aggregate should be hard, durable, tough, strong, and
clean, with only limited amounts of flaky or elongated particles,
adherent coatings, or harmful materials. The terms gravel, stone, and
rock appear to be used interchangeably, but they may be distinguished by
size; in other words, stones are small rocks or fragments of rock and
gravel consists of small rounded stones or fragments of stones.
Rocks contain one or more minerals, of which the more common are
feldspars, ferromagnesians, micas, clavs, zeolites, silicates, car-
bonates, sulfates, iron sulfides, and iron oxides. Chemically, the first
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five are silicates of aluminum, calcium, iron, or magnesium, with potassium
and/or sodium present in some cases. What is of interest is the chemical
reactivity and the physical structure. Clay minerals and zeolites show
large changes in volume on wetting and drying. Sulfates, as in gypsum
and anhydrite, offer the risk of attack on cement. Porous cherts,
shales, some limestones, and some sandstones are known to be susceptible
to frost damage. Chert is a very fine-grained rock composed of silica
in the form of cryptocrystalline quartz, chalcedony, opal, or com-
binations thereof, and may be alkali reactive. Quartz is anhydrous,
opal is hydrous, and chalcedony is believed to be a mixture of the two.
Other known alkali-reactive constituents are tridymite, cristobalite,
zeolites, heulandite, the glassy-to-cryptocrystalline rhyolites, dacites,
andesites, and certain phyllites. The deleterious expansions sometimes
do not occur until two or more years after the concrete is placed.
Unconsolidated sediments include gravel, sand, silt, and clay,
according to particle size. There is, however, also a trend in composi-
tion. Gravel and coarse sands usually are rock fragments. Fine sands
and silt are predominantly mineral grains. Clay consists exclusively
of mineral grains, largely of the clay minerals group. On consolidation,
sandstones, siltstones, and claystones are formed. The cementing mate-
rial may be quartz, opal, calcite, dolomite, clay, iron oxides, or other
materials. Hard, platy claystones are shales. Some shales cause concrete
to fail because of excessive shrinkage. Dolomite in certain carbonate
rocks is present as large crystals scattered in a finer-grained matrix
of calcite and clay. Such a structure leads to deleterious expansions
in concrete.
Micas are subject to cleavage and also may alter during the hydra-
tion of cement. Iron sulfides form ferrous sulfates that, in turn yield
iron hydroxide and calcium sulfoaluminate. Surface staining is also
possible.
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Characteristics of Cement and Concrete
Concrete has a variety of uses depending on its density, compressive
strength, and durability. These properties depend, in turn, on the
chemical nature of the cement used, the density of the aggregate, the
cement and water content of the mix, the method of preparation of the
concrete and the air content of the mix. Three main types of concrete
may be distinguished.
Structural lightweight concrete aggregate is defined^52^ as con-
crete having a 28-day compressive strength in excess of 17.2 MPa and a
28-day air dry weight not exceeding 1850 kg/m . Compressive strengths
of 41.4 MPa are possible with lightweight aggregate. Low-density con-
cretes from lightweight aggregate have compressive strengths in the
o
range of 0.7 to 7.0 MPa and unit weights of 320 to 800 kg/m . Moderate
strength lightweight aggregate concretes fall in between. Lightweight
aggregate reduces the dead weight of a structure but usually costs more
per cubic yard than ordinary concrete. A lower overall cost can be
obtained through a lower volume of cement and reduced structural and
reinforcing steel and lower forming and handling costs. The low-density
concretes are used for insulation, and moderate strength concretes are
often used as fill. The structural grade is used for high-rise
buildings.
3
High-density concretes, with unit weights to 6010 kg/m are used in
radiation shielding. The high-densitv results from the type of aggre-
gate used, but the water content is also a factor in effectiveness of
neutron deceleration and capture.
3
Normal density concrete 1840 to 3200 kg/m has a wide range of prin-
cipally structural applications. It has compressive strengths in the
range of 17.2 to 27.6 MPa, but strengths are affected bv many factors,
as noted above.
A cement is a material with adhesive and cohesive properties that
render it capable of bonding mineral fragments into a composite whole.
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In construction the bonded materials are stones, sand, bricks, blocks,
and so on. The cements used for this purpose are based on compounds
derived from lime and are mainly silicates and aluminates. Various
(53)
kinds of cements as defined by ASTM " are shown in Table 29.
From these definitions it appears that all of these cements contain
calcium silicates formed at elevated temperatures that in concrete are
hydrated to a silicate gel plus free calcium hydroxide. The current
development effort includes examining the properties of compacts made
by hydrating a blend of coal fly ash and spent sorbent that has not
been exposed to temperatures as high as those in a cement kiln. The
nature of the hydration products has not yet been determined. An alter-
native is to expose such blends to various temperature levels: auto-
claving under moderate steam pressure, processing below the sintering
temperature, processing at the sintering temperature, and processing
above the melting point.
State of the Art - Disposal/Utilization of Solid Wastes
Relatively little has been done on disposal/utilization of FBC
wastes. In contrast, so much has been done in related fields that it
is a major task to summarize the contributions to defining and under-
standing the problem of disposal or utilization of calcium-based wastes.
These fields include flue-gas scrubbing, sulfate wastes, cement, con-
crete, and fly ash. Certain contributions have been singled out to
help answer the following questions:
• What is the impact of a calcium-based waste on the environment?
• Can this impact be lessened by one or more techniques?
• If the waste is utilized, will the product have a potential
impact on the environment?
• What properties can be expected of solid products made from
calcium-based wastes?
• What is the effect of mix composition on field performance?
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TABLE 29. DEFINITIONS OF VARIOUS KINDS 07 CEMENT
Hydraulic Cement -
Natural Cement -
ASTM C10-73
Portland Cement -
ASTM C150-73a
Portland Blast Furnace
Slag Cement -
ASTM C595-73
Portland-Pozzolanic Cement
ASTM C595-73
Slag Cement -
ASTM C595-73
Supersulfated Cement -
Masonry Cement -
ASTM C91-71
A cement capable of setting and hardening
under water
A hydraulic cement produced by calcining
a clay limestone containing up to 25%
by weight of argillaceous material below
the sintering temperature and then
grinding to a fine powder
A hydraulic cement produced by pulveriz-
ing clinker consisting mainly of
hydraulic calcium silicates and usually
containing calcium sulfate as an inter-
ground addition
An interground mixture of Portland cement
clinker and granulated fine blast furnace
slag in which the slag is between 25 and
65 wt % of the blend
A uniform blend of Portland cement or
Portland blast furnace slag cement and
fine pozzolan produced by intergrinding
clinker and pozzolan or blending cement
and finely divided pozzolan, in which
the pozzolan is between 15 and 40 wt % of
the blend
A uniform blend of granulated blast
furnace slag and hydrated lime in which
the slag is at least 60 wt % of the blend
An interground mixture of 80-85 wt %
granulated blast furnace slag with 10-15
wt % dead-burned gypsum or anhydrite and
about 5 wt % Portland cement clinker
A hydraulic cement for masonry construc-
tion containing one or more parts of
Portland cement, natural cement,
Portland-pozzolan cement, slag cement,
or hydraulic lime, and, in addition, one
or more parts of hydrated lime, lime-
stone, chalk, calcareous shale, talc,
slag, or clay
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Such a review is also constructive insofar as it helps identify the kind
of information still needed from an experimental program in order to
formulate recommendations. A practical consideration in the current
work was the delay in receiving adequate supplies of representative
spent sorbents.
Sulfate Wastes
Smith et al., in work sponsored by the Federal Highway Adminis-
tration, reported on the suitability of mixtures of fly ash, lime, and
sulfate wastes for highway construction. This work closely parallels
that planned under the present contract for the examination of the lime-
sulfate waste sorbent from fluid-bed combustion and, therefore, is
reviewed in detail. Following an optimization of the mix composition,
the reaction products were characterized, engineering properties were
determined, and aggregate production was studied. The study differs
from the present one mainly in that fluid-bed combustion waste was not
examined. Conclusions relevant to Westinghouse studies are summarized
in the following paragraphs. First, the effect of calcium sulfate was
explored using simulated wastes. Four hydrated limes from commercial
sources were used, including both calcitic and dolomitic types. Four
calcium compounds were used to simulate wastes: two gypsums, pure
anhydrous calcium sulfate, and a pure calcium sulfite hemihydrate.
Five low-carbon fly ashes were used, low carbon meaning 1 to 6 percent
loss on ignition at 950°C. No rationale was given for why high fly ash
contents were used in the mixes: 80 percent fly ash, 12 percent lime,
and 8 percent gypsum.
Effect of Water Content on Compressive Strength
Three methods were used for adjusting the water content of the
mixes: compaction, extrusion, and slump. The latter involved mixing
in just enough water to produce a consistency comparable to a slump by
a standard AASHTO test on concrete. The water content obtained was
about 18 to 27 percent for the compaction method and 35 to 45 percent
for the slump method. The range of values of compressive strengths for
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test specimens produced by compaction was 16.5 to 35.4 MPa, which was
generally 1.3 to 3.5 times those for specimens produced bv the slump
method. Values for extruded specimens were closer to those for the
slump method than to those for the compaction method. These results
are in line with a commercial technique known as the Schokbeton method
for producing high-density, low water-content, high-strength concrete
by subjecting it to rapid, vertical oscillations without causing segre-
gation of the aggregate.
Effect of Lime Type
The two limes used contained 0.7 and 33.4 percent MgO, respectively.
In two-thirds of the cases, the calcitic lime yielded higher strengths
\
than the dolomitic. Six of the results showed the reverse, and the
remaining four were of about equal strength. Statistical analysis of
the data showed that all main effects (lime type, calcium compound, fly
ash source, and water content) and all interactions were significant at
the 95 percent level. Apparently because a highway construction applica-
tion was in mind, however, the analysis was done only for the 7- and
the 28-day values. It would appear relevant to examine the long-term
(91-day) results since it is probable that the optimum techniques for
utilizing these waste materials have not yet been identified.
Effect of Type of Calcium Compound
For the compactible data only, after 28 days calcium sulfite and
calcium sulfate were equivalent. This finding is of importance to the
present work since it implies that conclusions from the work on FGD
sludges, especially in the fixation work, might be directly applicable
in the processing and disposition of FBC wastes.
Effect of Lime/Sulfate Ratio
Smith found that with the better fly ashes, that is, with the two
which gave the highest early strength in the preceding tests, 28-day
strengths were maximized by using a lime/sulfate weight ratio of 1:1.
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Strengths dropped off sharply on either side of the maximum. Lime/sulfate
ratios in the range of 0.75 to 1.25:1 yielded compressive strengths
within 85 percent of the peak. These results are for the specimens pro-
duced by compaction. No explanation was given for the results. Chemi-
cally, the lime/silica mole ratios for these two sets of data were
nearly identical (0.28 and 0.26). These ratios are very low compared to
Portland cement in which the lime/silica mole ratio is 2:3. On the
other hand, it appears very encouraging that strengths in the normal
concrete range can be obtained with such low lime/silica ratios.
Effect of Fly Ash Content
For the same two fly ashes as above, there was a monotonic and rapid
decrease in strength as this ratio was increased from 4 to over 11,
achieved by increasing the actual fly ash content of the mixes from 83
to 95 percent. It appears unreasonable to expect mixtures containing
as much as 95 percent fly ash to be effective in binding waste sulfates.
These data may be interpreted instead to say that no more than about
85 percent fly ash should be used.
Effect of Sulfate Content
It was found that 10 to 20 percent gypsum in mixtures containing
3 to 5 percent lime would yield maximum compressive strength. In another
study addition of up to 50 percent gypsum on cement showed a linear
increase in compressive strength. Smith found further that substitution
of anhydrous calcium sulfate for gypsuri did not change the strength at
28 days, explaining this on the hypothesis that the calcium sulfate
hydrated to gypsum. Strengths at 7 days were higher with the anhydrous
sulfate, suggesting that this was a more reactive form. In the case of
fluid-bed combustion wastes, any sulfate present should be at least
partially dead-burned and, therefore, less reactive. The question of
longer term effects, however, such as gradual hydration, needs to be
answered.
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Effect of Portland Cement Content
Addition of Portland cement was found to be detrimental to strength.
Fly ash and sulfate levels within each data set, were held constant,
however, so that increasing Portland cement meant decreasing lime. Since
Portland cement depends primarily on hydration of dicalcium and trical-
cium silicates, it would appear that a more meaningful experiment would
keep lime constant or even increase it at the expense of the fly ash.
To be sure, there is a cost factor, but in the case of FBC wastes optimi-
zation of the process design might include a certain minimum amount of
CaO in the spent sorbent before it enters the spent sorbent processing
section.
Effect of Other Components
Other substances tested for their effect on compressive strength
were impurities and accelerators. Aluminum sulfate at the 1 percent
level was concluded to have no effect, but from the data it appears to
have been associated with a decrease in strength both at 7 days and at
28 days. The lime used, however, was dolomitic, and the fly ash used
already included 25 percent alumina. Ferric hydroxide at the level of
2.8 percent also resulted in weak mixes.
The small amount of alumina in normal Portland cement is believed
to have no useful function other than to lower the melting point of the
kiln feed to facilitate the sintering process.
X-Ray Examination
Characterization of the reaction products for selected mixes by
X-ray diffraction showed that for the reference lime-gypsum fly ash mix,
lime disappeared within 7 days of curing, gypsum diminished, mullite
increased over 9 months, and ettringite appeared after 28 days. It was
concluded that a new phase consisting mainly of a calcium sulfoaluminate
was formed, but it was not positively identified as ettringite. New
crystals were observed to grow from the fly ash surface into the pore
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structure and intertwined, which might be an explanation for the strength
increases at early curing times. It was also found that at least 10 wt %
ettringite had to be present before it was visible under X-ray
diffraction.
Tests on Industrial Sulfate Wastes
Having explored the effect of calcium sulfate on the properties of
fly ash compacts, actual industrial sulfate wastes were tested in fly
ash formulations. These included three neutralized acid mine drainage
samples, one titangypsum from extraction of titanium dioxide, one gypsum
from hydrofluoric acid manufacture, one neutralized waste pickling
liquor from steel manufacture and two FGD scrubber sludges. The refer-
ence mix, containing 5 percent lime and 95 percent fly ash, developed
a compressive strength of 2.6 MPa (370 psi) in 28 days. The specimens
were prepared by the compaction technique. In all of the mixes prepared
with waste sulfates, the fly ash content was in the range 72 to 93 per-
cent, while the lime was 1 to 11 percent.
Screening Tests for Compressive Strength
Only two of the acid mine drainage samples were tested, the third
being omitted because its solids content was too low (and apparently
could not be concentrated by mechanical techniques like centrifuging).
Significantly different strengths were demonstrated: 2.6 to 2.8 versus
4.6 to 5.6 MPa (370-405 versus 660-805 psi). No explanation was given
for this difference. The waste with the higher CaO and SO content,
however, gave the higher strengths. Both had about 8 percent alumina
plus iron oxide in the waste. The steel pickling liquor waste had
similarly low values of strength, 2.4 to 3.2 MPa (355-465 psi), at the
level of 5 percent waste. At 10 percent, the strength dropped to
0.34 MPa (50 psi) .
The two waste gypsums yielded strengths in the range 6.6 to 10.1 MPa
(950-1470 psi). It nay be of interest that the total of alumina and
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iron oxide for these wastes was low (2-4 percent). At 3.2 percent lime
increasing the waste sulfate content to 25 percent for the hydrofluoric
acid waste showed a trend of increasing compressive strength for speci-
mens prepared by compaction, 7.9 to 10.1 MPa (1150-1470 psi).
The scrubber sludge from Kansas Power and Light, which had 5 percent
S03 (presumably sulfate sulfur) and 28 percent calcium as CaO, also
showed a trend of increasing strength, with increasing waste content to
13 percent from 6 percent, 12.4 versus 6.3 MPa (1180 versus 920 psi).
The maximum compressive strength obtained was with a sulfite
scrubber sludge from Louisville Gas and Electric, containing 68 percent
solids and 4 percent sulfur as SO and 32 percent calcium as CaO. The
28-day strengths were 10.2 and 12.3 MPa (1480 and 1790 psi). It was
found that, unless mixing was adequate, pockets of unmixed sludge would
be found in the compacted samples. The highest strength corresponded
to the mixing technique in which the lime and fly ash were preblended
and slowly added to the mixer containing the sludge and mixing water.
Engineering Evaluation
Six lime—fly-ash—sulfate formulations were used to make an evalua-
tion of engineering properties like freeze-thaw resistance, wetting and
drying resistance, California bearing ratio, permeability, splitting
tensile strength, and leachability. Again, lime was never more than
5.6 percent of the mix; and the lowest fly ash content used was 62 per-
cent, with four of the six mixes prepared in the range of 80 to 86 per-
cent fly ash. Only calcitic lime was used in these mixes. A gypsum
mix was used as the reference mix.
Effect of Aging on Strength. All of the mixes showed an improve-
ment in strength properties on aging to 91 days. The standard developed
as much as twice the unconfined compressive strength as the other five
test mixes, 15.8 to 7.6 MPa (2295 psi versus 1100) and developed two to
three times the splitting tensile strength, 3.6 MPa versus 1.1 to 1.6 MPa
(520 psi versus 165 to 225 psi). Its CBR was 617 in 28 days versus 335
to 487 for the other mixes.
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These values are all higher than that of the well-graded crushed
stone CBR standard.
Effect of Mix Type on Permeability. In some cases, the permeability
for the test mixes was lower than that for the reference mix, reaching
values as low as 0.8 x 10 cm/s in 28 days. One of the scrubber
sludges, Kansas PEL sludge, had a permeability of 17.0 x 10 cm/s.
To put this in a more direct perspective, a permeability of 1 x 10 cm/s
2
means that at steady state, leachate production would be 0.6 cc/min/m .
It appears that acceptably low values of permeability can be achieved
with fly ash/sulfate sludge mixes.
Samples cured for 28 days had generally much less solute leached
than at 7 days, reaching concentrations in the range of 0 to 50 ppm of
sulfate for some samples. It was concluded that lime and gypsum had
reacted chemically to form insoluble material and that, considering the
low levels of permeability achieved, ground water infiltration by leach-
ates from these mixes would be very small.
Effect of Freeze-Thaw Exposure. In the freeze-thaw tests, it was
found that 7 days curing was insufficient, since only one sample besides
the reference mix survived 12 cycles. Wetting and drying proved to be
less severe than freeze-thaw exposure. Curing for 28 days before freeze-
thaw exposure yielded terminal values of compressive strength of the
order of 2.1 MPa (300 psi).
These results are not favorable, but nor are they considered applic-
able to Westinghouse studies since the mix composition was at a much
higher level of fly ash.
Aggregate Properties
Two formulations were also prepared, using somewhat more lime (7.5-
8.0 percent), which were then cast or extruded to form solid specimens
for testing as aggregate. After 28 days of moist curing, the mixes were
still too soft for use. Curing for 14 days at 40.9°C yielded one usable
material. This was crushed and graded. At least 10 percent fines were
produced, in this step, that would in commercial operation represent
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waste that might not be recyclable or usable in some other way. The
specimens failed the freeze-thaw, the sulfate soundness, and the Los
Angeles abrasion tests. When made into a concrete with Type II Portland
cement and an air-entraining agent, 28-day strengths up to 23.1 MPa were
obtained. Again, all six beam samples tested failed the AASHTO T-161
freeze-thaw test in less than 104 cycles. It was concluded that none of
the mixes yielded aggregates suitable for concrete subject to freeze-thaw
conditions. Lime-fly-ash-waste-sulfate mixtures, however, might be
suitable for road construction as base course, subbase, or embankment
material. Longer curing times, of the order of 6 to 9 months, should
produce stronger and more resistant aggregate particles. The effect of
curing time specifically on freeze-thaw durability should be investigated.
Fly Ash
Dunstan, in work done through the Bureau of Reclamation, con-
cluded that, although lignite and subbituminous fly ashes would make
concrete with satisfactory freeze-thaw durability and adequate compres-
sive strengths, they should not be used where a severe sulfate condition,
as defined by the Bureau's standards, exists. Fly ash characteristics
found are summarized in the following paragraphs.
Composition
None of the five fly ashes tested met all of the requirements for
Federal Class F pozzolans.
Dunstan noted that fly ash from the lower rank coals generally had
lower Fe 0 contents in the glass fraction, which typically is in the
range of 60 to 70 percent. The glass fraction is considered the most
reactive portion of the fly ash. Iron oxide appears to have a moderating
influence on the formation of ettringite which, in turn, is mainly
responsible for deleterious expansions. Fluidized-hed combustion fly
ash, on the other hand, is formed at much lower temperatures than is
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normal fly ash, and the glass content can be expected to be lower. It
is not necessarily less reactive because the lower temperature of
formation may result in less change in pore structure.
Other properties of these low-rank fly ashes also differed from the
requirements of Class F pozzolans. The total of SiO + k1~p~ + Fe2°3
for all three lignite ashes and one of the subbituminous ashes were less
than the 75.0 percent required. These same four ashes also had MgO in
excess of 5.0 percent. Two of the lignites and the other subbituminous
2 3
ash had specific surface areas less than 6500 cm /cm" . It was not
established that these variations were responsible for the differences
in 7-day strength of a standard lime-pozzolan mix and alkali reactivity.
Compressive Strength
When mixed with sand, cement, aggregate, water, and an air-entraining
agent, the 7-day strengths were in the range of 10.A to 18.9 MPa (1510-
2470 psi) versus 17.9 MPa (2600 psi) for a mix containing no fly ash.
Compressive strengths continued to increase on aging for 180 days to
the level of 31.1 to 39.0 MPa (4510-5650 psi) versus 41.0 MPa (5940 psi)
for the mix without fly ash. At 365 days, the corresponding values were
32.3 to 41.5 MPa and 38.6 MPa (4680-6020 and 5560 psi), respectively.
Dunstan pointed out that the fly ash mixes had less total cementitious
material (cement + fly ash) than did the fly ash-free mix. Somewhat
lower compressive strengths for the fly ash mixes were therefore not
unexpected.
Linear Expansion
Mixes with 25 percent replacement of cement by fly ash generally
showed larger expansions due to sulfate attack than did those with only
15 percent replacement. The reference fly ash, a Class F pozzolan
representing a blend of six bituminous coal fly ashes from the Chicago
area, showed about the same linear expansion at 15 and 25 percent fly
ash. Continuous soaking in 10 percent sodium sulfate at room tempera-
ture produced expansions of 0.01 percent in 460 days. In an accelerated
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test consisting of cycles of 16 hours soaking in 2 percent sodium sul-
fate and 8 hours drying at 54.4°C, the expansions in the same length of
time were about double (0.019 percent). In all other cases, including
the no fly ash mix, greater expansions were obtained in less time, some
nearly to the point of failure (0.5 percent).
This indicates a need to identify the cause and whether higher
Fe2°3 content will be effective in reducing these expansions. Until
these expansions can be controlled, the use of lignite and subbituminous
fly ashes in cement-type products will not be possible.
STATE-OF-THE-ART SPECIFICATIONS AND TEST METHODS
Before a new material can become commercially acceptable, it must
be standardized to the extent of meeting specifications on important
characteristics as shown by particular tests. It appears that not only
are there no specifications on FBC solids or products made from them,
but there are also no directly applicable tests. In anticipation of
adapting existing tests, such as ASTM-C666, to the FBC program, work
done by others on freeze-thaw resistance and the more general question
of test methods is presented in the next two sections.
Freeze-Thaw Resistance
BackstronT investigated the effect of water-cement ratio on the
freeze-thaw resistance of non-air- and air-entrained concrete. He con-
cluded that the freeze-thaw resistance varies inversely with the water/
cement ratio of the concrete. For non-air-entrained concrete with a
water/cement ratio less than 0.45, the increased resistance is probably
due to a decreasing amount of freezable water in the cement paste, which
approaches zero at a ratio of 0.40 or less. For air-entrained concrete,
the air void spacing varies directly with the water-cement ratio, and
the freeze-thaw resistance varies inversely with the air-void spacing.
(52)
This parameter is defined in ASTM C457V as the maximum distance of
any point in the cement paste from the periphery of an air void. The
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spacing factor for the specimens used were in the range of 0.10 to
0.23 mm. Air voids reduce the strength of concrete hut increase its
durability. Cordon^ notes that the protective action is obtained
when the spacing factor for the air-void system is 0.20 ran or less.
(59)
There are several kinds of pores and voids in concrete:
• Gel pores - the interstitial cavities between the particles of
tobermorite (CaO-SiO «H 0) and other calcium silicate hydrates,
averaging 0.0015 to 0.0020 urn
• Capillary pores - the unfilled spaces between aggregations of
gel particles formed by uncombined water in excess of that
required for hydration and averaging 0.5 urn in diameter
• Bubbles of entrained air averaging from a few microns to a few
millimeters in diameter.
Water in gel pores in concrete below 0°C is supercooled but not frozen
until, perhaps, -78°C. Water in capillary cavities will freeze since
the cavities are large enough to accommodate a sufficient number of
molecules to make ice crystals. Bubbles of air are ordinarily not
filled with water unless saturation has been brought about by vacuum or
pressure. The basic mechanism of deterioration of concrete, and pre-
sumably of any solid body under freeze-thaw conditions, is the formation
of ice in voids insufficiently large to contain them and insufficiently
connected to the neighboring voids to permit excess water to escape or
the ice to expand into them. Pressures are then developed in excess of
the tensile strength of the cement paste.
In order to cure concrete so that it develops its maximum strength,
sufficient water for hydration must be present within the mix and at the
the boundaries of the mix. This can be provided by moist coverings, fog
cure, or immersion. On the other hand, it appears detrimental to use
conditions leading to saturation of all voids. It is, therefore an
objective in the development of a cementitious material to determine
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optima for particle size distribution, water content, and air content.
Backstrom's work did not cover the effect of air voids on sulfate
resistance.
Standard Tests and Specifications
Another area of investigation is that of test methods and specifica-
tions. Brown, in a paper dealing with energy conservation, con-
cluded that a lack of standard tests and specifications was an important
factor inhibiting the use of blended cements to perhaps 1 percent of
the domestic market, whereas in France it is 60 percent. The indus-
trialized countries use 20 to 30 percent blended cements.
ASTM C595-74, for example, covers three types of blended cements
containing 15 to 40 percent fly ash, or 25 to 65 percent blast furnace
slag or a minimum of 60 percent slag. Other compositions are not
covered, so there is no basis for evaluating their suitability. The
specification, however, includes six chemical tests and ten physical
tests which may be unnecessarily restrictive. The fly ash specifica-
tion C618-73 effectively excludes many western coal ashes on the basis
of their total SiO , AIJ}., and Fe-0 content, even though use of fly
ash not meeting the minimum total of these constituents has not been
shown to produce unsatisfactory cements. This specification also
includes six chemical tests and thirteen physical tests. With regard to
standard tests, Brown believes that new or improved tests are needed,
including soundness, sulfate resistance, and freeze-thaw durability.
The present test for soundness is intended to show whether the hydration
of any dead-burned CaO or MgO in the cement after the cement has hardened
will cause failure through excessive expansion. To get results in a
reasonable time, an autoclave procedure is used in an effort to acceler-
ate the hydration rate. This may be overly severe for Portland cement
and inadequate for blended cements. Another objection is directed at
testing specimens after only one dav of curing. It is argued that this
biases the results against fly ash cements because their one-day strengths
are normally lower than those of Portland cement.
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The only standard sulfate resistance test available is ASTM C452-68,
which deals with the expansion of mortar and is applicable only to Port-
land cement. The description of the method also states that the method
is intended for research on methods of determining sulfate resistance.
Brown points out that the test procedure is not representative of field
conditions. Gypsum is mixed with cement and then water is added. It
is likely that adverse reactions can occur under these conditions before
the mortar has developed its full strength. In the field, sulfate attack
probably occurs by diffusion into the concrete after it has undergone
substantial hydration.
Brown's objection to the ASTM C666-73 freeze-thaw test is similar
to that for the soundness test — namely, testing after a short curing
period. In this case, the curing time specified is 14 days, although
other times are permitted. This may not be an important objection in
the case of FBC sorbents because strengths in the range 6.9 to 13.8 MPa
(1000-2000 psi) within 7 days have already been demonstrated. The test
has not been correlated with field performance quantitatively, however,
so service life cannot be predicted. It would appear that the effect
of curing time before subjecting to freeze-thaw testing should be
included in testing new materials.
EXPERIMENTAL PROGRAM
Actual tests devised reflected the constraint of delay in spent
sorbent supply. Pilot units were operated to yield data on the FBC
process itself; thus, production of spent sorbent and associated fly
ash were generally incidental aspects of the test runs. Within this
constraint, the test program identifies the sorbents to be included,
feasibility tests, and more extensive screening tests.
Identification of Spent Sorbents to Be Tested
Combustor Variables
The spent sorbent from fluid-bed combustion is basically a new
material whose physical and chemical properties must be defined by
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appropriate tests. Examination of the main process as discussed in an
earlier section reveals that at this stage of development there are still
several potential spent sorbents to be characterized. The sorbent may
be a limestone or a dolomite, or a synthetic based on these or on a
different metal atom, such as iron. The spent sorbent is exposed to
elevated temperatures for several hours and has a variable sulfur bur-
den, which for calcium-based sorbents is in the form of calcium sulfate,
possibly with traces of calcium sulfide. The balance of the calcium
is expected to be principally a mix of calcium oxide and calcium car-
bonate, depending on the operating pressure and temperature. It is pos-
sible that some of the calcium may enter into reactions with the coal
fly ash to form calcium silicates or aluminates. Trace elements from
the fossil fuel and from the fresh sorbent will also be present. The
physical structure of the sorbent will be modified by chemical reactions,
pore migration, and pore size changes.
Further variations enter through other process conditions. The
calcium/sulfur molar treat ratio will depend on whether the process is
once-through or regenerative, the sulfur retention required, and the
calcium utilization obtainable. For limestone once-through the ratio
may be in the range of 1 to 5 for 90 percent sulfur retention. For
dolomite the range may be somewhat narrower. For regenerative processes
the range is projected as 0.2 to 2.0. The number of potential calcium-
based sorbents to be characterized is estimated as follows:
• Two sorbent types Limestone or dolomite
• Three molar treat ratios Normal, high extreme, low
extreme
• Three CaO/CaCO ratios Normal, high extreme, low
extreme
• Two coal types Reflects the Si02/Al203/Fe203
content of the coal ash
• One temperature level One is probably representative
117
-------
This leads to 36 different spent sorbents, that must be taken into
account by the spent sorbent test program. It is expected that the
sorbent properties relevant to disposal will not all be critical; thus,
the actual number to be tested should be substantially less than 36.
The manner in which this was handled is tested in the next paragraph.
Composition Ranges
To define the spent sorbent composition range of interest, Fig-
ure 24 was prepared with the aid of information reported in Appendix D
of Reference 35 on sulfur retention in the fluidized-bed combustor ver-
sus calcium/sulfur mole ratio. The temperature selected was 850°C.
The projected percent sulfur retention versus calcium/sulfur mole ratio
of 850°C is:
Percent
Ca/S Sulfur Retention
1.0 50
2.0 80
3.0 95
5.0 98
The sorbent was 1359 limestone. It is not intended to imply that these
values are definitive (since they are based upon laboratory TGA data at
limited conditions), merely that they are representative. Ideally,
90 percent retention will be achieved at Ca/S = 1.0, in which case the
spent sorbent will be mostly CaSO^. Although the graph shows only three
components, the calculations include an allowancexof 5 percent for non-
calcium impurities in the limestone. The parameter reflects the effect
of varying degrees of calcination of the unreacted CaCO
Based on available pilot-plant data, a representative composition,
on an impurity-free basis is 63.3 wt % CaCO 28.4 wt % CaSO and
J 4'
118
-------
I-"
VD
Parameter; Percent of original
CaCCL surviving calcination
98% S Retention @Ca/S = 5.0
90% S Retention @Ca/S= 2.5
50% S Retention @Ca/S = 1.0
90% S Retention
@Ca/S = 1.0
CaStX
Figure 24. Projected Composition Range for Spent Sorbent from Fluidized Bed Combustion at 850°C
-------
8.3 wt % CaO. Table G.I of the same report shows the calcium/sulfur
ratio used was 1.67.
Weight percent CaSO
/OON
ratio used was 1.67. The equations defining the system are:
136.14 a
s x 100
80.06 ag
f /^L^l
+ R[56.08 + 44.01 ^ + 100.09^-^ — )\
56.08 [(l-aL)R-agl
Weight percent CaO = x 100 ,
where D is the same denominator as in equation 1; and
100.09 SL R
Weight percent CaCO = x 100 ,
where
R = molar treat ratio, Ca/S
a = fractional sulfur removal
s
a^ = fraction of CaCO, feed surviving uncalcined
LJ -3
fT = fraction of CaCO, in feed limestone.
LI j
Solving these simultaneously with the above composition, including f
as 0.9218, yields R = 2.2, and a = 50.2 percent and a^ = 60.9 percent.
5 J_i
The latter checks out fairly well, but the other two values do not. As
data are located and processed, they will be used to confirm the area
of interest shown in Figure 24. Obviously, adequate quantities of spent
sorbent of the proper compositions are not yet readily available for
testing.
Sources
Upon review of available information on pilot-plant operations, it
was decided to use the sources shown in Table 30 to represent the vari-
ous FBC options. Chemical analyses of actual material used are in
Table 31; B&W stone is included for comparison in anticipation of
120
-------
TABLE 30. SPENT SOKBENT TEST COMPOSITIONS
Fluidized-Bed Process Type
Once- through
Combustor
Once- through
Boiler
One-Step
Regenerative
Combustor
Pressure
Sorbent
Projected Composition,
wt %
CaSO.
4
CaO
CaS
MgO
Balance
Expected Sorbent Source
Actual Sorbent Composition,
ash-free basis, wt %
CaSO.
4
CaO
MgO
Atmospheric
Limestone
2.3
PER
69.4
30.6
Pressurized Atmospheric
Dolomite Limestone
43.7
54.0
_
64.1
6.6
—
26.1/43.1
70.1/54.6
1.3/0
28.1
1.2
Exxon
61.2
22.6
16.2
2.5/2.3
Not available
aSpent sorbent from regenerator/combustor.
future tests. Table 30 shows the PER stone is more sulfated than
expected while the Exxon stone is close to target. The actual free CaO
content is not known because of its possible chemical combination with
oxides in the ash.
121
-------
TABLE 31. CHEMICAL ANALYSES OF FBC SPENT SORBENTS
Source
Material
Typical
Duquesne
Fly Ash
( Conven tional)
PER Bed
Exxon
Run 43
Bed
Run 43
Fly Ash
B&U
Run 19
Bed
Composition, wt
CaO
MgO
Si02
A12°3
Fe2°3
so3
LOI
Other
Composition,
moles/lOOg
CaO
MgO
Si02
A12°3
Fe2°3
so3
Molar Ratios
S03/CaO
CaO/SiO
CaO/MgO
%
0.40
1.0
44.9
19.1
9.6
—
14.0
11.0
100.00
0.0071
0.0248
0.7472
0.1873
0.0601
—
—
0.0095
—
28.84
2.13
27.20
10.26
5.39
19.90
1.04
5.27
100.00
0.5142
0.0528
0.4526
0.1006
0.0338
0.2486
0.4835
1.1361
—
38.64
13.25
8.60
5.70
3.95
29.00
0.32
0.44
100.00
0.6890
0.3287
0.1631
0.0559
0.0247
0.3635
0.5276
4.8148
2.0951
15.62
7.70
29.40
11.20
8.80
16.38
4.23
6.67
100.00
0.2785
0.1910
0.4893
0.1098
0.0501
0.2046
0.7346
0.5692
1.4581
67.01
1.25
3.90
5.55
2.00
19.09
0.51
0.69
100.00
1.1949
0.0310
0.0649
0.0544
0.0125
0.2384
0.1995
18.4114
—
122
-------
Feasibility Tests
Blending Tests
Experimental work began with bench-scale feasibility tests, making
solid compacts by blending with fly ash. Using available materials,
4.4 by 4.4 by 2 cm blocks were cast from mixes containing Duquesne Light
Company fly ash (from a conventional coal boiler) and oxidized sulfided
Tymochtee dolomite made in the Westinghouse 10-cm laboratory test unit
in Run D-l. The latter contained 28 wt % CaSC^. The spent sorbent
was ground to -125 urn. Compressive strengths given in Table 32 were
normal to the 4.4 x 4.4 faces. These showed that the addition of 10 to
20 percent fly ash with or without Type I Portland cement yields com-
pacts with significant compressive strength within 5 days' curing time.
By way of perspective, a dense clay is perhaps the poorest soil con-
sidered suitable on which to erect buildings. It has an allowable bear-
ing strength of at least 192 kPa. The cubes without Portland cement
had a compressive strength of about 1380 kPa.
TABLE 32. COMPRESSIVE STRENGTH OF SULFATED DOLOMITE/FLY ASH BLENDS
Test
Composition (g)
Sulfated
Dolomite
Fly Ash
Type I
Portland
Cement
Water
Compressive
Strength
(5 days)
MPa
psi
1A
IB
1C
100
100
100
20
10
20
10
76
70
80
1.59
1.17
2.21
230
170
320
123
-------
When Exxon spent sorbent from the miniplant became available, its
pozzolanic activity was tested. Five-centimeter cubes were cast from
mixes of the spent dolomite from miniplant run 27 (refer to EPA-
600/7-77-107) and the associated "fly ash" collected in the miniplant
cyclones. The latter actually is a mixture of dolomite fines and coal
fly ash. The spent sorbent was ground to -125 ym and two cubes of each
of the two mixes prepared as shown in Table 33.
These values were considered very encouraging, especially since the
MgO content was high. Mix 2 can potentially be used for low-grade
structural production, i.e., continuously supported beams. The Mix 2
specimens weakened somewhat at 21 days, but at 28 days were back to the
level of 7-day strength (9.33 MPa or 1352 psi).
TABLE 33. COMPRESSIVE STRENGTH OF 5-CM CUBES CAST
FROM EXXON RUN 27 SPENT SOLIDS
Composition (g)
Pfizer 1337 spent dolomite
Fly ash from miniplant
Fly ash, wt %
Water
Compressive Strength (7 day)
Psi
Average (psi)
(MPa)
Mix 1
765
425
36
530
355, 383
364
2.51
Mix 2
1080
120
10
360
1405, 1325
1365
9.41
Chemical analyses showed that, although the CaSO and CaO contents
of the spent sorbent were approximately as desired, the Ca/Mg ratio was
about 2:1 instead of the expected 1:1. The interpretation was that the
material received from Exxon was probably from an early part of Run 27
and limestone that had served as the start-up bed material had not been
124
-------
completely purged from the bed. The inert content was estimated from
chemical analyses for sulfur, magnesium, C(>2, and H20 as 38 percent, so
the bed apparently retained a substantial amount of fly ash. The fly
ash taken overhead had a Ca/Mg mole ratio of about 1.
Isostatic Pressing
An exploratory experiment was made on another portion of Exxon
run 27 spent sorbent that had been ground to -125 ym. A cylindrical
specimen was prepared dry, with no fly ash, by isostatic compression at
138 MPa (20,000 psi) for 1 to 2 minutes. The specimen was cured in
water for about 2 weeks and then cut into four segments with an L/D
ratio of 1 and the axial compressive strengths determined. Values
obtained were 27.8, 40.1, 30.8, and 4.98 MPa (4040, 5822, 4472, and
7222 psi).
Follow-up data on this technique for three samples cured for about
40 days showed an average compressive strength of 89.3 MPa (12,960 psi).
For comparison, normal Portland cement will yield values in the range
of 103.4 and 172.4 MPa (15,000-25,000 psi).
These feasibility tests showed that:
• Stable solid compacts could be made at ambient temperature
by blending spent sorbent with fly ash and adding water.
• Significantly high values of compressive strength could be
achieved relative to the landfill requirements.
• At least for the curing times tested, MgO did not inter-
fere with the pozzolanic reactions.
• Strengths higher than normal concrete are attainable by
isostatic pressing. The strengths approach those of Port-
land cement cylinders made by isostatic pressing.
Screening Tests - Exxon Stone
It having been demonstrated that stable compacts could be produced
even with a dolomite sorbent, prior to undertaking studies of engineer-
ing properties and durability, a screening test was designed to explore
125
-------
the effect of mix composition, water content, and curing time on com-
pressive strength, response to leaching (which is reported elsewhere in
this document), and compressive strength after leaching. Three mix
compositions were chosen to reflect typical production proportions of
spent bed material and fly ash, a low fly ash content, and an inter-
mediate level of fly ash. The low was chosen arbitrarily at 10 percent,
and the intermediate level was set 50 percent higher. Processing vari-
ables included fly ash/spent sorbent ratio, water/total solids ratio,
particle size range, and free CaO/Si02 ratio. In these tests no CaO
was added, and the spent sorbent was in every case ground to -125 um.
As an incidental aid in planning tests, the predicted spent sorbent/
fly ash weight ratio as a function of the sulfur content of the fuel
and the calcium/sulfur molar treat ratio was developed (Appendix C,
Figure C-l). Projections are based on 10 percent ash in the fuel,
90 percent retention of fuel sulfur, and the impurities in the sorbent.
The ratio varies directly with the sulfur content of the fuel and
inversely with the ash content of the fuel. For dolomite, the calcula-
tions predict 1.8 kg of spent sorbent will be produced per kg of coal
ash from a 2 percent sulfur fuel at a calcium/sulfur treat ratio of 2,
or 0.346 kg ash/kg sorbent + ash. These conditions appeared to be
reasonable estimates applicable to Exxon run 27 material. Chemical
analyses are given in Table 31 for the Exxon residues and for other
residues used in this program.
The three fly ash contents chosen were 10, 35.8, and 15 percent,
corresponding to low, typical production proportions, and intermediate
levels. Two water contents were used, 44.5 and 30.0 percent, with a few
observations at 34.2 percent. A minimum of three curing times was used:
7, 28, and 60 days. Duplicate samples were prepared in most cases. A
parallel set of samples was made to be subjected to leaching for
1040 hours after curing for various lengths of time and then tested for
compressive strength. The data obtained are presented in Table 34 and
Figures 25 through 28, from which the following observations are made:
1. Significant compressive strength (at least 3 MPa or 435 psi)
can be developed with mixes containing 10 to 36 wt % fly ash.
126
-------
2. Most of the mixes developed 75 percent of their apparent
ultimate strength within 7 to 10 days.
3. At 30 days of curing time, Mix III with 15 percent fly ash was
35 percent stronger than Mix II with 10 percent fly ash. Mix II
was 2.5 times stronger than Mix I, which had 35.8 percent fly
ash. All these contained 30 percent water. These trends per-
sisted at 60 days of air curing time.
4. At higher fly ash contents (36 percent as in Mix I), the trend
of the data in Figure 25 suggests the existence of an optimum
water content. This is supported by the crossplot in Fig-
ure 28, where the optimum for 36 percent fly ash mixes is about
35 percent water. Similar optima are postulated for the other
two mixes.
5. Leaching for 1040 hours appears equivalent to water curing.
From Figure 25 strengths equivalent to that for the optimum
water content (34 percent) were obtained by leaching specimens
containing 45 percent water for 1040 hours. This suggests that
it is preferable to have somewhat more water than optimum in
order to have sufficient plasticity in the mix and then achieve
the desired strength by adequate water curing.
Screening Tests - PER Stone
A 55-gallon drum of spent bed material was received from Pope,
Evans and Robbins (PER). This was produced by burning Sewickley coal
with Greer limestone at 815°C. Chemical analyses in Table 31 show that
the calcium was about 48 percent sulfated. This was not a typical sul-
fation level but did offer an opportunity to test a spent sorbent at
the high end of the sulfation range. Free CaO/Si02 works out to 0.6 on
a molar basis. Initial results obtained for 2-in cubes with this mate-
rial are shown in Table 35.
These tests were an exploration of processing PER as received.
PER-1 showed that merely adding water does not result in significant
cementitious reactions. Tables 36 and 37 provide possible explanations
127
-------
TABLE 34. MATRIX FOR SCREENING TEST USING 2-INCH CUBES MADE FROM SPENT
SORBENT AND FLY ASH FROM EXXON RUN 43
NJ
00
Mix Sample
I 1A
IB
1C
ID
2A
2B
2C
2D
2E
2F
2G
2H
3A
3B
3C
3D
3E
3F
3G
3H
4A
4B
Fly Ash/
as % of
Total
Solids
0.358
0.358
0.358
0.358
0.358
0.358
0.358
0.358
0 . 358
0.358
0.358
Water/
as % of
Total
Solids
0.445
0.445
0.445
0.448
0.300
0.342
0.445
0.445
0.300
0.342
0.445
Nominal
Curing
Time (days)
7
7
21
21
21
28
28
28
28
60
Test
CS
CS
L+CS
L+CS
CS
CS
L+CS
L+CS
CS
CS
CS
CS
CS
CS
L+CS
L+CS
CS
CS
CS
CS
CS
CS
Date
Cast
5/28
5/28
5/28
5/28
5/28
5/28
8/9
8/9
6/11
6/11
8/20
8/20
8/9
8/9
8/9
8/9
6/11
6/11
8/20
8/20
11/22
11/22
Compressive
Strength
MPa
2.64
2.45
7.38
8.48
1.74
2.64
6.34
6.20
3.68
3.44
6.88
8.69
5.14
4.45
6.43
6.83
4.03
3.23
6.74
6.58
5.35
5.25
psi
383
353
1070
1230
253
383
920
900
535
500
998
1260
745
645
933
990
585
468
978
955
776
761
Actual
Age at
Test (days)
7
7
7
7
17
17
11
11
14
14
19
19
30
30
28
28
31
31
34
34
64
64
-------
TABLE 34. (Cont'd)
1-0
VO
Mix Sample
4C
4D
4E
4F
5G
5H
II 1A
IB
1C
ID
2A
2B
2C
2D
2E
2F
3A
3B
3C
3D
3E
3F
Fly Ash/
as % of
Total
Solids
0.358
0.358
0.358
0.100
0.100
0.100
0.100
0.100
0.100
0.100
0.100
Water/
as % of
Total
Solids
0.445
0.300
0.342
0.300
0.300
0.300
0.300
0.445
0.300
0.300
0.445
Nominal
Curing
Time (days)
60
60
45
7
7
21
21
21
28
28
28
Test
L+CS
L+CS
CS
CS
CS
CS
CS
CS
L+CS
L+CS
CS
CS
L+CS
L+CS
CS
CS
CS
CS
L+CS
L+CS
CS
CS
Date
Cast
11/22
6/11
6/11
8/20
8/20
6/16
6/16
6/17
6/17
6/17
6/17
«_-
12/3
12/3
6/17
6/17
12/3
12/3
12/3
12/3
Compressive
Strength
MPa
6.55
4.69
4.34
7.77
8.32
9.69
9.14
16.20
14.65
6.89
6.12
—
6.03
7.55
8.65
10.00
14.71
15.24
6.33
6.74
psi
950
680
630
1127
1207
1405
1325
2350
2125
1000
888
—
875
1095
1255
1450
2133
2210
918
978
Actual
Age at
(Test (days)
60
66
66
46
46
7
7
7
7
21
21
—
24
24
29
29
28
28
28
28
-------
TABLE 34. (Cont'd)
u>
o
Fly Ash/ Water/
as % of as % of
Total Total
Mix Sample Solids Solids
4A 0.100 0.300
4B
4C 0.100 0.300
4D
4E 0.100 0.445
4F
III 1A 0.150 0.300
IB
1C
ID
IE 0.150 0.342
IF
2A 0.150 0.300
2B
1C
2D
3A 0.150 0.300
3B
3C
3D
4A 0.150 0.300
4B
Nominal
Curing
Time (days) Test
60 CS
CS
60 L+CS
L+CS
60 CS
CS
7 CS
CS
L+CS
L+CS
7 CS
CS
21 CS
CS
L+CS
L+CS
28 CS
CS
L+CS
L+CS
60 CS
CS
Date
Cast
6/16
6/16
6/16
6/16
12/3
—
11/8
11/8
—
—
1/6
1/6
10/21
10/21
11/8
11/8
10/21
10/21
—
—
—
—
Compressive
Strength
MPa
10.89
10.98
13.79
12.98
7.44
—
9.48
8.57
—
—
10.24
10.47
11.38
11.00
14.65
14.38
11.46
13.53
—
—
—
—
psi
1580
1593
2000
1883
1079
—
1375
1243
—
—
1485
1518
1650
1595
2125
2085
1663
1963
—
—
__
—
Actual
Age at
Test (days)
61
53
52
52
53
—
7
7
—
—
7
7
20
20
21
21
28
28
—
—
__
-------
TABLE 34. (Cont'd)
Mix
Fly Ash/ Water/
as % of as % of
Total Total
Sample+ Solids Solids
AC
4D
5A 0.15 0.300
5B
Nominal
Curing
Time (days) Test
L+CS
L+CS
14 CS
CS
Pate
Cast
__
—
11/8
11/8
Compressive
Strength
MPa psi
__
—
9.96 1445
9.41 1365
Actual
Age at
Test (days)
—
14
14
NOTES: 1. CS = compressive strength
L+CS = specimen was leached as reported elsewhere and then checked for compressive
strength.
2. "Age at test" means age at the end of the initial curing period, when the specimen was
either tested for compressive strength or suhjected to leaching.
-------
Curve 688036-A
oo
co
psi
1600
1400
^ 1200
"c1
£ 1000
00
1 80°
O)
fe. 600
E
o
o
400
*TwU
200
0
i i i
i i i
Symbol Test Water/Total Solids Curve No.
o CS 0.445
V CS 0.341
a CS 0. 300
A L+CS 0.445
Mix I Used Fly ash/Total Solids
~
A V Curve 2
^^^^-^^^^^BB*^
A .—"
/r v § $
/ y\ ^"^
"~ / o
/ o
~ / n ^^— — 0-
/ o • ^r
•***^-r^ p
— / xj o
/ /'^
/ / °
I/
'111
1
2
1
2
Ratio of 0. 358
_
__ v
V
6
Curve 1 D
• u
Portland Cement Concrete
in the Range of
13. 8-^1. 4 M Pa (2000-6000 psi)
i 1 1
MPa
10
c
J
0
10
20 30 40
Curing Time, days
50
60
70
Figure 25. Compressive Strength of 5-cm Cubes Cast from Spent Solids from Exxon
Run 27 Using Mix I
-------
Curve 688035-A
•&
c
o>
i_
CO
$
t
o
o
Symbol Test Water/Total Solids
a CS 0.300
O L+CS 0.300
o CS 0.445
I
Curve No.
1
2
3
Mix III Used Fly ash/Total Solids Ratio of 0.100
psi
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
MPa
15
10
60
Curing Time, days
Flgure
Strength of 5-cm Cubes Cast from Spent
??
133
-------
Curve 688083-A
£
oo
o>
to
to
psi
2000
1800
1600
1400
1200
1000
800
600
400
200
0
I i i i i
Symbol Test Water/Total Solids
n CS 0. 300
O L+CS 0.300
Mix III Used Fly ash/Total Solids Ratio of 0. 150
-
O
D ^-
^^ n
./^U u
jr D
su
TY n
/
~ /
/
-/
/
»
1
1
1
t
\_
1 1 i i i
MPa
15
10
5
10
20 30 40
Curing Time, days
50
60
Figure 27. Compressive Strength of 5-cm Cubes Cast from Spent
Solids from Exxon Run 27 Using >tix III
134
-------
Curve 688082-A
4/0
OJ
ISl
cu
o
o
psi
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0.
1 r I 1 — [—
Symbol Fly ash/Total Solids Curing Time days
XT, ^,-Cr 0.358 7-46
n 0. 100 7 - 61
•n- 0. 150 7 - 28
•D-
s*' '">.. Curve 3
^ ^ X\
_ ^
3 / \ Curve 2
• * ^*w
-' ,_„ ^^
y $%. >s
T?" ^*^
D /p ^\. curve 1X>^
n / V ^urve ^
*
/ ^v ^^ ~
1 X
r >
1 i i i i
2 0. 3 0. 4
MPa
15
10
5
0
Ratio, Water/Total Solids
Figure 28. Effect of Water Content on Compressive Strength
of 5-cn Cubes Cast from Spent Solids from
Exxon Run 27
135
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TABLE 35. COMPRESSIVE STRENGTH OF PER SPENT SORBENT MIXES
Composition (g)
PER spent
sorbent
CaO adder
Water
PER-1
1000
—
300
PER- 2
600
300
200
PER- 3
250
500
1000
PER- 4
600
300
500
Duquesne Fly
Ash
Fused Silica
100
150
Compressive Strength, MPa (psi)
Curing 4 days 0.034(5) 7.5(1090) 0.33(48)
Curing 7 days — — —
Curing 17 days
0.90, 0.83 (130,120)
1.07, 1.19 (155,173)
TABLE 36. ESTIMATED COMPOSITION OF PER COMPACTS
Basis
CaO(C)
Si02(S)
A1203
-------
TABLE 37. COMPARISON OF COMPOSITION OF PER COMPACTS
WITH NORMAL PORTLAND CEMENT
Composition
CaO
Si02
A12°3
Portland
Cement
69.22
27.57
3.21
100.00
PER-1
28.44
51.96
19.60
100.00
PER- 2
63.41
26.57
10.02
100.00
PER- 3
68.80
27.92
3.28
100.00
PER-4
57.45
30.67
11.88
100.00
for the results obtained on PER-1/4. If constituents are allocated into
compounds found in cement, in PER-1 the alumina content is in excess of
that needed to tie up the unsulfated CaO as C«A, or (CaO) -Al 0 . Hence,
no CaO is available for SiO or Fe.O . Since the strength of normal
cement is attributable largely to hydrated calcium silicates, the essen-
tially zero strength of PER-1 is a reasonable expectation. Also, look-
ing at the three main constituents of cement (CaO, Al^, and SiO?), the
as-is composition of the PER stone is definitely outside the Portland
cement area.
PER-2 was intended to test a mix with the CaO/(CaO + Si02 + A1203)
ratio closer to 69.22 percent. This was accomplished by adding fresh
lime to the residue. Although only 63.4 percent was achieved, the com-
pact showed a substantial compressive strength (7.5 MPa or 1090 psi) .
Since alumina in PER-2 was high, relative to that in Portland
cement, mix PER-3 included both extra CaO and SiOr The extra silica
was obtained by adding commercially available fused silica to the
residue. Table 37 shows the composition achieved was very close to
that of Portland cement, but apparently this was not sufficient since
the compressive strength was very low (0.33 MPa or 48 psi). It may be
that pulverized fused silica is not an effective pozzolan.
137
-------
PER-4 used Duquesne fly ash from a conventional coal boiler as the
silica source, limiting it to 10 percent of the total solids. The com-
position was appreciably lower in CaO and higher in Al 0« than is normal
cement. Compressive strength was somewhat higher than in PER-3, sug-
gesting that silica in fly ash is a better pozzolan than ground fused
silica.
A final conclusion on the free lime content needed was deferred,
but the tests were considered to show PER stone must be ground.
ASSESSMENT OF UTILIZATION
Preliminary Flow Sheets
Figure 29 shows a schematic diagram of a flow sheet for spent sor-
bent collection from AFBC. Although industries such as iron and steel
manufacture practice dumping hot slag, the FBC spent sorbent probably
will have to be cooled as the minimum processing step. Since heat
recovery of stack gas to combustion air may be utilized, except in
large plants, as shown in a recent PER report, the heat picked up
from the spent sorbent will probably be discarded. Since contact with
moisture will initiate pozzolanic reactions, the cooled material is sent
to temporary enclosed storage and then sent via rail car to a processor.
The flow sheet also shows secondary particulate removal, which might be
a granular bed filter, to take full advantage of advanced technology.
From this flow sheet other possibilities can be derived. It may be
economical to add on-site grinding facilities to reduce the spent sor-
bent to -125 mm or possibly -44 mm. The next stage would be to add
facilities for making aggregate. Two variations are being examined,
direct casting and isostatic pressing.
Preliminary Economics
In view of the rising cost of energy, attention was given to the
possibility of a closer integration of basic industries. Table 38 shows
figures for the energy consumption in the cement industry. Combining
138
-------
LO
VO
Secondary
Particulate
Removal
Air
Preheater
FBC Cells A,B,C
CBC D
Solids
Cooler
Dv,r 6404A01
Stack
135°C
25°C
Spent Sorbent
& Ash Silo
Figure 29. Spent Sorbent and Fly Ash Collection from Atmospheric-Pressure
Fluidized-Bed Combustion
-------
TABLE 38. ENERGY CONSUMPTION OF THE CEMENT INDUSTRY*
Energy Source
Process
Dry Processes
Total annual usage**
Per bbl cement
Per ton cement
Wet Processes
Total annual usage**
Per bbl cement
Per ton cement
Coal, Mg
3.599
0.02311
0.1229
5.036
0.02102
0.1118
Oil
(bbls)
0.775
0.00499
0.0265
4.987
0.02082
0.1107
Gas
(CF)
62,484
402
2140
140,436
586
3118
Electricity
(kWh)
3,948
25.42
135.2
5,621
23.46
124.8
*Unit quantities based on 155.337 x 10 bbl of cement produced by dry
processes and 239.572 x 10^ bbl by wet processes. One barrel of
cement contains 376 pounds of cement.
**A11 total quantities in millions of indicated units.
Source: Minerals Yearbook, 1968
the different forms of energy input using 27 x 10 Btu/ton of coal,
6.3 x 10 Btu/bbl oil, 1000 Btu/CF gas, and 10,000 Btu/kWh; the energy
requirement works out to 1,376,000 Btu/bbl cement for dry processes and
( 62^
1,423,000 for wet processes. For comparison, the FEAV ' has estimated
the average energy requirement at 1,391,000. The Conference Board^63^
arrived at 1,318,000 for 1967, which has since declined through tech-
nological improvements to 1,218,000 in 1971. The Board did not include
a breakdown, but the kiln itself may consume 700,000 Btu/bbl for the dry
process, of which 95 percent is required for heating from ambient tem-
perature to 900°C and calcining the CaC03 and MgC03 in the limestone.
Additional heat is required to get to the clinkering temperature of about
2600°F, but is largely offset by exothermic clinkering reactions.
Two possibilities for integration with fluid-bed combustion arise.
Close integration would feature transfer of the hot spent sorbent
140
-------
directly to a cement process. The Trief process(64) probably would be
best suited to utilizing this approach, since the charge is fully melted
rather than merely clinkered. Whether the dust problems of a cement
plant are compatible with the air requirements of a large power plant
needs careful review. Alternatively, the spent sorbent would be cooled
and shipped to a cement plant at another location. There it would be
ground to at least Ik ym and used as the CaO source. In this case,
the saving in energy for the cement operation is only the calcination
energy, which is about 54 percent of the kiln energy requirement. If
applied to the entire production of 395 x 10 bbl of cement, the saving
amounts to about 65,000 bbl of fuel oil equivalent (FOE)/day. This
does not have tremendous national significance when compared to the
daily demand of 17 x 10 bbl of petroleum in the United States or even
to the heavy fuel oil demand of 2.4 x 10 bbl/day. Its importance is,
therefore, indirect, since cutting the operating costs of cement manu-
facture would help keep down construction costs. At 378,000 Btu/bbl,
fuel consumption would be reduced from 0.218 bbl FOE/bbl cement to
0.158, a reduction of 27 percent. With cement at $4.50/bbl and fuel
oil at $10/bbl, the fuel cost represents half the cement price, and the
saving is about 14 percent. Equally important factors may be the supply
of limestone of a quality suitable for fluid-bed combustion and the
economics of transportation.
Cement production requires about 0.21 Mg of limestone/bbl of cement
or 33 x 106 Mg of limestone/year, which, by reference to the section in
this report on market data, would correspond to the output of spent
sorbent from about 48-1000 MWe FBC plants using limestone. The minimum-
sized cement plant in 1971 appears to have produced about 1 x 10 bbl/
year, with 16 percent producing over 5 x 10 . A 3 x 10 bbl plant
could take the output from a 1000 MWe power plant. Electrical require-
ment would be 76,000 MWh/yr or about 230 MW, based on a 330-day operating
year. So an interesting possibility is for cement plants to generate
their own electricity via an FBC plant. A larger plant could practice
blending of the FBC spent sorbent with fresh limestone if there were
141
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technical reasons why the spent sorbent could not be used alone. A
further projection is that, by 1980, 60 percent of the energy requirement
of the cement industry will be coal, with another 8 percent from pur-
chased electricity. In 1971, coal provided 35 percent and gas 45 percent
of the energy requirement. Along with the higher consumption of coal
is the higher production of coal ash, a potential source of pozzolan.
A more detailed study of the profitability of the cement business is
needed, however, to clarify the potential FBC market. The long-term
growth rate has been about 2.8 percent/yr from 1909 to about 1967.
Although this growth rate is expected to slow down, partly because
imports will increase to 50 x 10 bbl/yr, there could be 100 x 10 bbl
of domestic capacity required by 1980. Demand for hydraulic cement is
expected to increase in this same period at the rate of 3.0 percent/year.
Analysis of Results
The work described in the foregoing sections has focused on deter-
mining the potential for utilizing FBC spent sorbent and associated fly
ash. Simple tests have shown that stable, solid compacts can be pro-
duced by grinding the spent sorbent to -125 ym, combining it with coal
fly ash, and adding water. Compressive strengths are adequate for land-
fill applications and may permit use of the mixes as replacement for
concrete in low-strength fill applications. The initial work on iso-
static pressing has revealed a potential for use in high-strength
columns and in aggregate. Although a full demonstration of utilization
is considered outside the scope of the present content, certain addi-
tional laboratory tests are under way to confirm further these poten-
tials. Included are an examination of the Trief Process under a
related contract and of resistance to freeze-thaw conditions and to sul-
fate attack.
Process economics will be checked to identify any additional
information that may be needed to support any recommended processing
sequence.
142
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From a broader view, the effect of requiring environmental protec-
tion is expected, in general, to increase the cost of power generation
and probably the cost of most industrial operations. The pressure of
increasing demand on finite resources is also strengthening the case
for conservation. Power generation has grown as a separate entity in
the economy from industrial production. Although plant expansion can
certainly continue in the historical pattern, the work reported here
has shown that potential exists for achieving both environmental protec-
tion and conservation by integrating power generation and cement pro-
duction. Instead of each drawing upon high-quality limestone reserves,
the limestone could be used first in a fluidized-bed combustor and then
used to make either a new type of concrete or a new type of cement.
Even if these new materials were found not to be as strong or as durable
as those they might replace, these deviations might merely require modi-
fication of the design of the application.
143
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SECTION 8
REFERENCES
1. Abelson, H. I., and W. A. Lowenbach, "Procedures Manual for Environ-
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3. Archer, D. H., et al., "Evaluation of the Fluidized Bed Combustion
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4. Coutant, R. W., J. S. McNulty, R. E. Barret, J. J. Carson, R. Fischer,
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7. Zielke, C. W., H. E. Lebowitz, R. T. Struck, E. Gorin, "Sulfur
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9. "Corps Regulation Cover Sanitary Landfill in Navigable Water,"
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12. "Environmental Protection Agency Regulations on Policies and Pro-
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Reporter, April 30, 1976, p. 31.
13. "Environmental Protection Agency-Guidelines for the Thermal Proc-
essing of Solid Wastes and for the Land Disposal of Solid Wastes,"
Federal Register, 39 FR 29328, Aug. 14, 1974; 40 FR 5159,
Feb. 4, 1975, Environmental Reporter, Feb. 28, 1975.
14. "Environmental Protection Agency-Solid Waste Management Guidelines,"
Federal Register, 41 FR 2359, Jan. 15, 1976.
15. "Federal Water Pollution Act," Environmental Reporter, Feb. 28, 1975.
16. "Environmental Protection Agency National Interim Primary Drinking
Water Regulations," Federal Jtegister, *0 FR 59565, Dec. 24, 1975,
Environmental Reporter, Feb. 13, 1976, p. 81.
145
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17. "U.S. Drinking Water Standards 1962," U.S. Public Health Service
Publication No. 956, 1962.
18. Lund, H. F., Industrial Pollution Control Handbook, New York:
McGraw-Hill Book Co., 1971.
19. Water Quality Criteria, Ecological Research Series, EPA-R3/73-033,
March 1973.
20. Schomaker, N. B., "Current EPA Research Activities in Solid Waste
Management," Gas and Leachate from Landfills, March 1976, EPA-600/
9-76-004, NTIS PB 251-161.
21. Schomaker, N. B., "Current Research on Land Disposal of Hazardous
Wastes," paper presented at Hazardous Waste Research Symposium,
Tucson, AR, Feb. 2-4, 1976.
22. "Development of Construction and Use Criteria for Sanitary Landfill,"
County of Los Angeles, 1973, EPA-SW-19D-73, NTIS PB 218-672.
23. Qasim, S. R., "Chemical Characteristics of Seepage Water from
Simulated Landfills," Ph.D. Dissertation, West Virginia University,
Morgantown, WV, 1965.
24. Fungaroli, A. A., "Pollution of Surface Water by Sanitary Landfills,"
1971, NTIS PB 209-001.
25. DeGeare, Jr., T. V., "Current Office of Solid Waste Management
Programs-Landfill Activities," Gas and Leachate from Landfills,
1976, EPA-600/9-76-004, NTIS PB 251-161.
26. Jones, J. W., "Research and Development for Control of Waste and
Water Pollution from Flue Gas Cleaning System," paper presented
at the EPA Symposium on Flue Gas Desulfurization, New Orleans, LA,
March 8-11, 1976.
27. Mahloch, J. L. and D. E. Averett, "Pollutant Potential of Raw and
Chemically Fixed Hazardous Industrial Wastes and Flue Gas Desulfur-
ization Sludges," U.S. Army Engineer, Interim Report to EPA
January 1975, Interagency Agreement EPA-IAG-D4-0569.
146
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in
28. Radian Corporation, "The Environmental Effects of Trace Elements i
the Pond Disposal of Ash and Flue Gas Desulfurization Sludge,"
Final Report to EPRI, EPRI-202, September 1975, NTIS PB 252-090.
29. Fling, R. B., W. M. Graven, F. D. Hess, P. P. Leo, R. C. Rossi,
and R. Rossoff, "Disposal of Flue Gas Cleaning Wastes-EPA Shawnee
Field Evaluation," The Aerospace Corporation, March 1976,
EPA/600/2-76-070.
30. "Pressurized Fluidized Bed Combustion," Report to Office of Coal
Research, National Research and Development Corporation, November
1973, Contract No. 14-32-0001-1511.
31. Pope Evans and Robbins, Inc., "Multicell Fluidized Bed Boiler Design
Construction and Test Program," Interim Report No. 1 to Office of
Coal Research, August 1974, Report PER-570-74, Contract
No. 14-32-0001-1237.
32. Vogel, G. J., Jonke, A. A., et al., "Reduction of Atmospheric Pol-
lution by the Application of Fluidized Bed Combustion and Regenera-
tion of Sulfur-Containing Additives," Report to EPA, Argonne
National Laboratories, Argonne, 111, June 1973, EPA R2-73-253.
33. Henschel, D. B. , "The U.S. Environmental Protection Agency Program
for Environmental Characterization of Fluidized Bed Combustion
Systems," Proceedings of the Fourth International Conference on
Fluidized Bed Combustion, McLean, VA., Dec. 9-11, 1975.
34. Ralph Stone and Company, "Environmental Assesment of Residues from
the Fluidized Bed Combustion of Coal and Gasification of High
Sulfur Fuel Oils," Report to EPA, 1976, EPA Contract No. 68-03-2347.
35. Tennessee Valley Authority, "Processing Sludges From Lime/Limestone
Wet Scrubbing Processes for Disposal or Recycle and Studying
Disposal of Fluidized Bed Combustion Waste Products," 1976, Inter-
agency Agreement TV-41967A, EPA-IAG-D5-0721, Subagreement No. 17,
E-AP No. 77BBA.
147
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36. Keairns, D. L., et al., "Fluldized Bed Combustion Process Evalua-
tion, Phase II-Pressurized Fluidized Bed Coal Combustion Develop-
ment," Report to EPA, Westinghouse Research and Development Center,
September 1975, EPA-650/2-75-027c, NTIS PB 246-116.
37. Keairns, D. L., Peterson, C. H., and Sun, C. C., "Disposition of
Spent Calcium-Based Sorbents Used for Sulfur Removal in Fossil fuel
Sasification," paper presented at the 69th Annual Meeting, AIChE,
Nov. 28-Dec. 2, 1976.
38. Hoke, R. C., et al., "Studies of the Pressurized Fluidized-Bed Coal
Combustion Process," Report to EPA, Exxon Research and Engineering,
Linden, NJ, September 1976, EPA-600/7-76-011.
39. Gruenfeld, M., Private Communication, Industrial Environmental
Research Laboratory, EPA, Edison, NJ, 08817.
40. Henschel, D. B., Private Communication, Industrial Environmental
Laboratory, EPA, Research Triangle Park, NC 27711.
41. Meritt, G. H., Private Communication, Commonwealth of Pennsylvania
Solid Waste Management, Harrisburg, PA.
42. Duritsa, C. A., Private Communication, Commonwealth of Pennsylvania
Department of Environmental Resources, Pittsburgh, PA. 15222.
43. Bern, J., "Probable Environmental Impacts from the Disposal of
Sulfur Removal Sludges Generated by the Slaked Lime-Wet Scrubber
Process," Commonwealth of Pennsylvania Department of Environmental
Resources, Division of Solid Waste Management, Pittsburgh, PA.,
March 1974.
44. Weeter, D. W., J. E. Niece, and A. M. DiGioia, Jr., "Environmental
Management of Residues from Fossil Fuel Fired Power Stations," paper
presented at Annual Water Pollution Control Federation Conference,
Denver, CO, Oct. 8, 1974.
148
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45. Standard Methods for the Examination of Water and Wastewater,
13th Ed., American Public Health Association, 1974.
46. Boynton, B. S., Chemistry and Technolggy of Lime and Limestone,
New York: Interscience Publishers, 1966.
47. "Physical Testing of Quicklime, Hydrated Lime and Limestone,"
ASTMC110-76. 1976 Annual Book of ASTM Standards Part B, p. 68-85.
48. Murray, J. A., et al., "Shrinkage of High-Calcium Limestone during
Burning," J. Am. Ceram. Soc. 37, 7 (1954) p. 323-328.
49. Lewis, J. R. , "Cement," Minerals Yearbook, 1968. Bureau of Mines,
U.S. Department of the Interior.
50. Griffin, R. A., and N. F. Shimp, "Interaction of Clay Minerals and
Pollutants in Municipal Leachate," Illinois Geological Survey,
Urbana, IL, Proceedings of the Second National Conference on Com-
plete Water Reuse, 1975, pp. 801-811.
51. ASTM Annual Book of Standards, Part 10, "Concrete and Mineral
Aggregates," 1973, American Society of Testing and Materials,
Philadelphia, PA.
52. ACI Manual of Concrete Practice, Parts 1 and 2. American Concrete
Institute, Detroit, MI, 1968.
53. ASTM Annual Book of Standards, Part 9, "Cement, Lime, and Gypsum,"
1973, American Society of Testing and Materials, Philadelphia, PA.
54 Smith, L. M., et al.. "Technology for Using Sulfate Waste in High-
way Construction," Federal Highway Administration, Gllette Research
institute, Rockville, MD., December 1975, FHWA-RD-76-31, NTIS
PB 254-815.
55 Peterson, C. H. and H. Gunasekaran, "Utilisation of Spent Limestone
from a Fluidized Bed Oil Gasification/Desulfurization Process in
Concrete," Proceedings of the Fifth Mineral Waste Utilisation
Symposium, IIT Research Institute, Chicago, IL, April 1976.
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56. Dunstan, E. R. Jr, "Performance of Lignite and Subbituminous
Fly Ash in Concrete; A Progress Report," Bureau of Reclamation,
Denver, CO, January 1976, REC-ERC-76-1, NTIS PB 253-010.
57. Backstrom, J. E., "Investigation into the Effect of Water - Cement
Ratio on the Freezing - Thawing Resistance of Non-Air and Air-
Entrained Concrete," Bureau of Reclamation, Denver, CO, Novem-
ber 1955, Concrete Laboratory Report No. C-810.
58. Cordon, W. A., "Freezing and Thawing of Concrete - Mechanisms and
Control, "ACI Monograph No. 3, American Concrete Institute, Detroit,
Michigan, 1966.
59. "Solid Waste Disposal Act," Environmental Reporter, Feb. 28, 1975.
60. Brown, P. W., et al., "Energy Conservation through the Facilitation
of Increased Blended Cement Use," Prepared for ERDA, Institute for
Applied Technology, National Bureau of Standards, Washington, D.C.,
Interim Report July 1-Dec. 1, 1975, NBSIR 76-1008, NTIS PB 251-218.
61. Hoke, R. C., et al., "Studies of the Pressurized Fluidized-Bed Coal
Combustion Process," Report to EPA, Exxon Research and Engineering
Company, Linden, NJ, September 1977, EPA-600/7-77-107.
62. Energy Conservation Potential in the Cement Industry, FEA Conserva-
tion Paper No. 26, 1975.
63. Energy Consumption in Manufacturing, The Conference Board, Cam-
bridge, MA.: Ballinger Publishing Co., 1974.
64. "New Cement Uses Fly Ash, Costs Less to Make," Chemical and
Engineering News, April 5, 1976.
65. Newby, R. A., and D. L. Keairns, "Alternatives to Calcium-Based
S0_ Sorbents for Fluidized-Bed Combustion: Conceptual Evaluation,"
Report to EPA, Westinghouse Research and Development Center,
Pittsburgh, Pa., January 1978, EPA-600/7-78-005.
150
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66. Newby, R. A. S. Katta, and D. L. Keairns, "Calcium-Based Sorbent
Regeneration for Fluidized-Bed Combustion: Engineering Evaluation,"
Report to EPA, Westinghouse Research and Development Center,
Pittsburgh, Pa., March 1978, EPA-600/7-78-039.
67. Alvin, M. A., E. P. O'Neill, L. N. Yannopoulos, and D. L. Keairns,
"Evaluation of Trace Element Release from Fluidized-Bed Combustion
Systems," Report to EPA, Westinghouse Research and Development
Center, March 1978, EPA-600/7-78-050.
151
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76184
APPENDIX A
THE FEASIBILITY OF OCEAN DUMPING
AS AN INTERIM ALTERNATIVE TO
DISPOSAL OF SPENT STONE
FROM THE FLUIDIZED BED
COMBUSTION PROCESS
20 September 1976
Report To: WESTINGHOUSE ELECTRIC CORPORATION
Research and Development Center
Churchill, Pennsylvania *
By: J. M. Forns
WESTINGHOUSE OCEANIC DIVISION
Ocean Research Laboratory
Annapolis, Maryland 21404
152
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INTRODUCTION
The oceans cover more than 70% of the earth's surface, incorporating approximately 140
million square m.les with an average depth of more than 12,000 feet. They are critical in maintaining
the world s environment, contributing to the oxygen-carbon dioxide balances in the atmosphere
affecting global climatology, and providing the base for the world's hydrologic system Oceans are
economically valuable to man in providing necessary food and mineral resources In addition they are
a medium of transportation and recreation to more than 60% of the Nation's population The
continental margins of the world's oceans are the most important individual environmental areas from
the standpoint of gross organic production. According to Odum (1959), estuaries and coastal oceans
contribute more than 58% of the total primary caloric carbon energy for the entire planet. Any serious
detrimental impacts on these marine systems could have far-reaching effects on our global
environment in years ahead.
While our coastal oceans are biologically diverse, extending from tropical to arctic
environments, they are also the ultimate receptacle for many of our wastes. Sewage, chemicals,
construction debris, and many other waste materials are transported to the ocean by riverine systems
or directly by barges, ships, and pipelines. Although the amount of waste presently dumped directly
into the ocean is small compared to the total amount of wastes reaching the oceans, in the future the
impact of ocean dumping, as a means of waste disposal, will increase significantly relative to that of
other sources. Cognizant of this, the Council on Environmental Quality prepared in 1970 a
formulation and recommendation for a national policy concerning ocean dumping. They concluded
that the problem was growing rapidly and that in many cases, feasible and economic alternative
methods were available for disposal of wastes currently being dumped at sea. They also realized that
certain ocean dumping practices did not have immediate or viable alternatives and recognized that
there was no regulatory authority controlling ocean dumping as the jurisdictions of individual State
and the Army Corps of Engineers extended only within the three-mile territorial sea. Their report also
pointed out the international implications of ocean dumping off the U.S. continental margins.
The purpose of the following report is to describe the present national position with regard to
ocean dumping and identify the mechanisms and procedures of ocean disposal as it applies to the spent
stone wastes from the fluidized bed combustion process. In no way is there any intention to predict
future government policy concerning ocean dumping. The material in this report has been gathered
and organized solely to present the established governmental criteria and evaluation process by which
the federally designated ocean dumping permit system operates. The determination of ocean disposal
feasibility is based on presently enacted legislation and existing precedents. Included in this report are
specific sections dealing the the federal regulations, criteria and evaluation process, identification of
approved sites for ocean disposal, the mechanisms to carry out an ocean dumping program, and the
feasibility of dumping spent stone wastes at established ocean dumpsites.
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FEDERAL REGULATIONS AND PERMIT PROCEDURES
Since 1970, two significant pieces of federal legislation have been enacted to establish a
mechanism for evaluation and control of ocean dumping. The first passed in 1972, is known as the
Marine Protection. Research and Sanctuaries Act (M PRSA) (Appendix A). This pulblic law (92-532)
enables Congress to establish a national policy on ocean dumping and to regulate the dumping of all
types of materials into the oceans. It also establishes a system to prevent or strictly limit the ocean
disposal of any materials which would adversely affect human health and the marine environment.
ecological systems, or economic potentialities. This Act became effective April 23, 1973, and since that
time, all ocean dumping of waste materials has been done under a permit from EPA, except for
dredged spoils which are regulated by the Corps of Engineers.
When the ocean dumping program was first initiated, many procedural and technical decisions
were encountered resulting in the development by EPA of Final Regulations and Criteria (Appendix
B) to be included in the MPRSA. These Final Regulations governing ocean dumping were published
in the Federal Register, October 15, 1973, and constitute the legal requirements which must be
followed by anyone using the oceans for waste disposal. The combination of Title I of the MPRSA and
the Final Regulations put out by EPA establish a permit granting procedure to utilize designated
ocean dumpsites for five categories including industrial wastes, sewage sludge, construction and
demolition debris, solid wastes, and explosives. Presently, of the total 281 available disposal areas,
eleven ocean dumping sites in the Atlantic Ocean and Gulf of Mexico are now in active use for disposal
of municipal and industrial wastes. There is no dumping of these wastes in the Pacific Ocean, although
sewage sludge is currently being discharged via several outfalls.
Since the legislation was established ocean dumping activity showed a net increase of about 1.6
million tons from 1973 to 1974, primarily because of a 1.1 million ton increase in construction and
demolition debris. While figures are not yet available, EPA expected to reduce this volume somewhat
because alternative methods of disposal are being developed and implemented. According to EPA
(1975), the major problem in the future with regard to ocean dumping is the anticipation of increased
pressures to dispose of wastes at sea resulting from more and better waste treatment facilities
removing increased amounts of wastes from both municipal and industrial sources. Clearly, the
understanding and technology required to deal with waste disposal has not kept pace with population
growth. EPA's basic approach has been to find and use the least environmentally damaging site and
methodology of waste disposal whether it be via air, land, or water.
The basis for regulation of ocean dumping is given in the form of criteria which reguire EPA to
balance several factors before determining whether or not to issue a dumping permit. These factors,
which are the essence of the federal regulation on ocean dumping, include:
I. The need for the proposed dumping in the ocean, as determined by EPA.
2. The effect of dumping on the marine environment.
3. Social and economic considerations involving the dumping, including effects on human
health and welfare, fishery, and recreational resources.
4. Alternative means of disposal, including alternate methods of treatment, land-based
disposal and recycling.
5. The feasibility of dumping beyond the continental shelf.
154
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Upon consideration of these factors, EPA, through the regional offices, will cons.der
application for a permit for ocean dumping. Schematically, Figures 1 and 2 show the procedural
sequence ,n obtaining dumping permits. In Figure 1 the procedure covers the applicat.on process
where waste d.sposal takes place within a single EPA region's jurisdiction. Figure 2 describes the
application procedure for inter-regional permits.
One important aspect of the Federal Regulations and Criteria is contained in Section 220 3 (d)
(2). This specifies that an "interim permit will reguire the development and active implementation of a
plan to either eliminate...or bring it within limitations of...the ocean dumping criteria". While interim
permits may not be renewed, new interim permits may be granted provided that the permitee
completes the sequence of phases required to meet ocean dumping criteria. By this mechanism EPA
intends to limit the use of ocean dumpsites wherever possible and allow ocean disposal only when
materials dumped fall within the criteria identified.
On Monday, June 28, 1976 EPA published in the federal register a "Proposed Revision of
Regulations and Criteria" on Ocean Dumping (Appendix C). These proposed revisions, if and when
promulgated, would affect both the procedures to be followed in reviewing applications for ocean
dumping and the substantive criteria to be applied in evaluating those applications.
Several aspects of these revisions would directly affect the feasibility of the disposal of spent
stone by ocean dumping. Following is summary of those salient aspects of the proposed revisions.
Section 102 of the Act requires that criteria for the issuance of ocean disposal permits be
promulgated after consideration of the environmental effect of the proposed dumping operation, the
need for ocean dumping, alternatives to ocean dumping, and the effect of the proposed action on
esthetic, recreational and economic values and on other uses of the ocean. Parts 227, 228 of the
proposed revisions constitute the criteria established pursuant to Section 102 of the Act. The decision
of the Administrator, Regional Administrator or the District Engineer, to issue or deny a permit and
to impose specific conditions on any permit issued with be based on an evaluation of the permit
application pursuant to these criteria. Following is a summary of those criteria which apply to the
ocean disposal of spent stone from the fluidized bed combustion process.
Section 227 states that if an applicant can satisfy the following conditions, a permit will be
granted. First, the applicant must satisfy the environmental impact criteria of sub-part B. Several of
these criteria apply to spent stone. Section 227.7 (d) states that in the dumping of wastes of highly
acidic or alkaline nature consideration shall be given to: 1) the effects of any change in acidity or
alkalinity of the water at the disposal site; and 2) the potential for synergistic effects or for the
formation of toxic compounds at or near the disposal site. It further states that allowance may be made
in the permit conditions for the capability of ocean waters to neutralize acid or alkaline wastes;
provided however the dumping conditions must be such that the average total alkalinity or total
acidity of the ocean water after allowance for initial mixing, may be changed, based on stoichiometnc
calculations by no more than 10 percent during all dumping operations at a site. A definition of initial
mixing is given in Section 227.29 of subpart as that dispersion or diffusion of a waste which occurs
within four hours after dumping. In addition, several methods are listed which can be used to estimate
this.
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APPLICATION
SUBMITTED
TO REGIONS
PRELIMINARY
EVALUATION
OF APPLICATION
PUBLIC NOTICE
WITH TENTATIVE
DECISION
TENTATIVE
DECISION
TO DENY
REQUEST FOR
HEARING
PUBLIC HEARING
FINAL EVALUATION
OF APPLICATION
DENIAL OF
PERMIT
COAST GUARD
SURVEILLANCE
ENFORCEMENT
ACTION
MONITORING OF
Figure 1. EPA Regional Permit Application Procedure
156
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APPLICATION SUBMITTED TO
INITIATING REGION
TECHNICAL EVALUATION
OF NEED AND ALTERNATIVES
BY INITIATING REGION
INITIATING REGION FORWARDS
APPLICATION AND TECHNICAL EVALUATIONS
WITH RECOMMENDATIONS FOR
ISSUANCE OR DENIAL OF PERMIT
SITE REGION EVALUATES
IMPACT OF PROPOSED DUMPING
ON SITE
DISPOSAL SITE REGION
FORWARDS APPLICATION WITH
IMPACT EVALUATION WITH
RECOMMENDATIONS FOR
ISSUANCE OR DENIAL OF PERMIT
TO HEADQUARTERS
HEADQUARTERS REVIEWS INFORMATION
FROM BOTH REGIONS AND MAK^S
TENTATIVE DETERMINATIONS
FOR ISSUANCE OR DENIAL OF PERMIT
PUBLIC NOTICE IS GIVEN IN
BOTH REGIONS WITH OPPORTUNITY
FOR HEARING IN BOTH REGIONS
RECOMMENDATIONS FORWARDED
TO ADMINISTRATOR
FINAL ACTION BY ADMINISTRATOR
Figure 2. Permit Procedure for Interregional Application
for Ocean Dumping
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Section 227.7 (c) states that wastes containing biodegradable constituents, or constituents
which consume oxygen in any fashion, may be dumped in the ocean only under conditions in which the
dissolved oxygen after allowance for initial mixing will not be depressed by more than 25 percent
below the normally anticipated ambient conditions in the disposal area at the time of dumping.
Section 227.8 states that no wastes will be deemed acceptable for dumping unless they can be
dumped so as not to exceed the "limiting permissible concentrations." This is defined in Section 227.27
as:
1) "that concentration of a material or chemical constituent in the receiving water
which, after reasonable allowance for initial mixing, will not exceed a toxicity
threshold defined as 0.01 of a concentration shown to be toxic to appropriate sen-
sititve marine organisms in a bioassay carried out in accordance with approved EPA
procedures; or 2) 0.01 of a concentration of a waste material or chemical constituent
otherwise shown to be detrimental to the marine environment."
In section 227.27 (b) a definition of "appropriate sensitive marine organisms", and the necessary
experimental conditions and procedures for an acceptable bioassay are given.
Section 227.9 states that the quantity of the substance dumped at any single time and place
must be controlled to prevent damage to the environment or to amenities.
After satisfying the environmental impact criteria, the applicant must secondly demonstrate a
need for ocean dumping. The specific detailed factors which will be considered in determining if there
is a need for ocean disposal of a material are given insubpart C (sections 227.14 - 227.16). The degree of
treatment feasible for the waste and to what extent this will be carried out will be considered. The
process by which the waste is generated will be examined to see if this process is essential to the
provision of the applicants goods or services or to see if less polluting materials could be used. A
consideration will be made of the relative environmental impact and cost for ocean dumping as
opposed to other feasible alternatives including, but not limited to: land fill; well injection;
incineration; spread of material over open ground; recycling of material for reuse; additional
biological, chemical or physical treatment of intermediate or final waste streams; and storage. At the
same time, a consideration of any irreversible or irretrievable consequences of the use of the
alternatives to ocean disposal will be made. It must be determined after these considerations that there
are no practicable alternative locations and methods of disposal (i.e., which are available at reasonable
incremental cost and energy expenditures, which need not be competitive with the costs of ocean
dumping, taking into account the environmental benefits derived from such activity) or recycling
available which would be less detrimental.
In addition, the administrator may, at his discretion, grant the permit with other terms and
conditions. He may require that the permittee terminate all ocean dumping by a specified date, or
continue research and development of alternative methods of disposal and make periodic reports of
such research and development in order to provide additional information for periodic review of the
need for an alternative to ocean dumping.
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The third major requirement is that there can be no unacceptable adverse effects on esthetic
recreational, or economic values of the ocean. The criteria used for making a judgement of this are
given in subpart D (section 227.17 - 227.19).
In section 227.18 it is stated that the following factors will be considered in making a
determination of this impact: present recreational and commercial use of areas which might be
affected by the proposed dumping; existing water quality and disposal activities in the areas which
might be affected: applicable water quality standards; visible characteristics of the materials which
result in an unacceptable esthetic nuisance in recreational areas; presence in material of toxic chemical
substances released in volumes which might affect humans directly; bioaccumulative or persistent
chemical constituents which may affect humans adversely directly or through food chain interractions;
and constituents in the material which might significantly affect living marine resources of recreational
or commercial value.
A fourth condition upon which being granted a dumping permit is contingent is that the
proposed dumping will not have an unacceptable adverse effect on "other uses" of the ocean. These
uses, listed in section 227.21 of subpart E, are as follows: commercial and recreational fishing;
commercial and recreational navigation; actual oranticipated exploitation of living marine resources
as well as non-living resources such as mineral deposits, oil and gas exploration and development,
future offshore marine terminal or other structure development; and possible scientific research and
study. The assessment of impact on other uses of the ocean will consider both temporary and long-
range effects within the state-of-the-art, but particular emphasis will be placed on any irreversible or
irretrievable commitment of resources that would result from the proposed dumping.
If, in fact, all the criteria presented under the above four broad headings are satisfied, a permit
for ocean disposal can be issued.
Permits are of different kinds. Section 220.3 liss them and describes each. A "general permit"
may be issued for dumping certain materials which will have minimal adverse environmental impact
and are generally disposed of in small quantities, or for specific classes of materials that must be
disposed of in emergency situations. They may be issued with or without application whenever the
Administrator determines that is is necessary or appropriate.
A second kind of permit is a "special permit" which may be issued for materials which satisfy
those criteria discussed above. They are issued with an expiration date no later than three years from
the date of issue.
A third kind of permit, an "interim permit" is described in section 220.3 as one which may be
issued under certain conditions in accordance with subpart A of part 227 to dump materials which are
not in compliance with the environmental impact criteria of subpart B of part 227, or subnarts Dor E
orforwhichan ocean disposal site has not been designated on other than an interim basis. Subpart
A says essentially that interim permits will be granted when it is determined that even though all the
criteria are not satisfied, the need for dumping and unavailability of alternatives are of greater
significance to public interest than the potential for adverse effects on any aspect of the ocean. An
interim permit is not valid for more than one year and requires substantial efforts by the perm.t
5™nuo bring the waste within the limitations required of a special permit or to take the necessary
159
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measures to cease ocean dumping. A limitation, though, found in the description of interim permits in
section 220.3 may make an interim permit unattainable for spent stone. It states that no interim permit
will be granted for the dumping of waste from a facility which has not previously dumped wastes in the
ocean, from a new facility, or from the expansion or modification of an existing facility, after the
effective date of these regulations.
Part 228 is an altogether new addition to the existing regulations with no counterpart in them.
It serves to establish the criteria for the management of ocean disposal sites by EPA, and presents
criteria for the selection of sites, and factors which must be considered with respect to the
determination of the permissible levels of disposal of materials at a particular site. It states the belief
that permit issuance should not be based solely on the testing of waste, but that the specific marine
environment must be considered. In addition, limitations are placed on the times and rates of disposal
of materials (sec. 228.7) and an appropriate monitoring program is made (228.9). It is stated in this
section that EPA will require the full participation of the permittee in the development and
implementation of the monitoring program. Section 228.12 lists sites which will, beginning on the
effective date of these regulations, be approved for dumping certain materials therein indicated on an
interim basis pending completion of baseline or trend assessment surveys and designation for
continuing use or termination of use.
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APPROVED SITES FOR OCEAN DUMPING.
Prior to the enactment of MPRSA in 1973, a total of 281 disposal areas were known to exist
within the estuaries and coastal oceans of the United States. Figure 3 shows these disposal sites in the
Atlantic, Pacific, and Gulf of Mexico. From Table 1 more than half the ocean disposal sites were used
by the Army Corps for dredge spoil disposal. The second largest use of ocean dumping by location was
for industrial wastes constituting 13.7% of the total number of dumpsites available. It is the location of
these dumpsites that is of concern when considering the spent stone wastes from the fluidized bed
combustion process. These industrial disposal areas are located between 15 and 100 miles offshore
depending on the type of waste and established regulatory procedure. For examr/.e, acid wastes from
the New York metropolitan area are dumped in a designated zone 15 miles from New York City while
certain chemically toxic materials must be disposed of at distances more than 125 miles offshore. Most
of the industrial disposal in the Gulf of Mexico is conducted beyond the 400-fathom contour, which in
the case of Galveston, Texas, requires a transport of more than 125 miles one way.
By contrast sewage sludge disposal sites account for a mere 0.6% of the approved dumpsites
and are all within 50 miles of shore. However, when comparing the total tonnage (Table 2) of ocean
dumped municipal and industrial wastes, sewage sludge comprises greater than 50% of the amount of
waste disposed at sea. It is interesting to note that these wastes do not meet the criteria identified in the
Final Regulations and yet additional interim permits have been issued.
It is important to note that only 11 of the 42 municipal and industrial dumpsites from the
Atlantic and Gulf regions are considered active by EPA. This is primarily because most industrial
dumpers have found alternatives to ocean dumping or the costs of disposal and subsequent monitoring
have become uneconomic. While the remaining 31 sites are presently on the inactive list, they could be
utilized once again. For such a case, it would have to be determined by EPA that the proposed ocean
dumping constitutes the least deleterious environmental impact, does not infringe on other socio-
economic potentials and the wastes to be dispossed have no other feasible alternative. If, however, the
wastes meet the criteria specified in the Final Regulations, then an interim permit could be given which
would be subject to review before continuance. The review cycle is presently on an annual basis. At
each review the permitee would have to state the plan and phases for alternatives to ocean disposal,
show the results of monitoring effects and provide quantitative environmental information to
substantiate the case for ocean dumping.
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LEGEND
D DRfDGE SPOILS
I INDUSTRIAL WASTES
S S!WAGE SLUDGE
£ F XPl OSWES
R KOOIOACTIVE WASTES
W ^01 ID WASTE
X INACTIVE SITE
N^—•->*• • — ,j, w i : •
» / ^-^vZ «\—W
^ R r"—:^F~— E' •'
> . ; .^•-.7=v-
\
— i w
X t
Pacific
~t
T EX
VT-" \ : 1
C, 0 )
' "
Atlantic
I < ',1 —-i— , > . .
V. . i •• •*
Gulf
Figure 3. Ocean Disposal Areas Along the U.S. Continental Margins
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Table 1. Ocean Waste Disposal Areas (By Region and Waste Type)"
WASTE TYPE
Dredge spoil
Industrial waste
Sewage sludge***
Refuse
Radioactive waste
Explosive and chemical ammunition
TOTAL
(no duplicates)
DISPOSAL AREAS
PACIFIC
15
9**
0
3**
10**
19**
54
ATLANTIC
83**
15**
2
0
25**
19**
135
GULF
63
16
0
0
2
11
92
TOTAL
161
40
2
3
37
49
281
* Revised and updated by James L Verber, Food and Drug Administration, U.S. Apartment of Health, Education,
and Welfare.
** Areas used for two or more types of wastes.
*** Does not include outfalls
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Table 2. Ocean Disposal: Types and Amounts, 1974* and 1973**
(In Tons, Approx.)
WASTE TYPE
Industrial Waste
Sewage Sludge
Construction &
Demolition
Debris
Solid Waste
Explosives
TOTAL
ATLANTIC
1974
4,767,000
5,676,000
2,242,000
0
0
12,685,000
1973
3,997,100
5,429,400
1,161,000
0
0
10,587,500
GULF
1974
950,000
0
0
0
0
950,000
1973
1,408,000
0
0
0
0
1,408,000
PACIFIC
1974
0
0
0
200
0
200
1973
0
0
0
240
0
240
TOTAL
1974
5,717,000
5,676,000
2,242,000
200
0
13,635,200
1973
5,405,100
5,429,400
1,161,000
240
0
1 1,995,740
*1974 Source EPA Regional Offices. Unpublished Reports, updated information, 1974 (12 months of dumping activity).
**1973 Source - EPA Regional Offices.Unpublished Reports, 1973 (8 months of dumping activity May to December 1973 under
permits issued by Ocean Disposal Program extrapolated for 12 months to provide an annual rate).
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OCEAN DUMPING MECHANISMS
Proceeding with an ocean dumping program requires the establishment of specific ground rules
before planning, organization, estimating, and governmental regulatory permhs can be given For
spent stone wastes from the fluidized bed combustion process, several initial assumptions must be
made including: K
1. Materials will be of sufficient quantity to utilize a standard dumping vessel operating on a
semi-regular schedule.
2. For initial evaluations, the spent stone will be taken unprocessed, directly from the
combustion apparatus in a dry granular form.
3. Disposal will be at established ocean dumpsites designated for industrial wastes.
4. Transport will be from major seaport locations on the Atlantic and Gulf costs by a
commercially established dumping operator.
The vessel type for disposal of granular spent stone will be determined by the magnitude of
initial dispersion desired, ultimate physical fate of the waste and the relative economic advantage. As
this material falls into the category of dry solid waste, similar to crushed rock or constructive debris,
the most probable vessel type to be used is the deck barge with over-the-side dumping. Perhaps the
more modern barges with clamshell bottoms can be used. Deck barges are most frequently used
because disposal time is relatively long. This allows for spreading of the disposed materials over a large
area and minimizes concentrated buildup in a small area of the dumpsite. For spent stone disposal,
deck barge dumping can be accomplished by hydraulic jets flushing the material overboard or by
changing mass to tip down one side of the barge to allow gravity dumping. While dilution and
dispersion over large areas is desirable for liquid wastes, controlled concentration and even spreading
is desired for particulate wastes.
Various types and sizes of dumping craft are used for specific operations. The deck barges
which would be used for spent stone dumping employ different dump actuating mechanisms. It is these
differences which determine the physical characteristics of ocean dumped materials. Older type vessels
have six to eight pockets, each equipped with double gravity dump doors on the bottom. Others have a
hinge type configuration consisting of port and starboard sections hinged topside fore and aft. Large
hydraulically-operated pistons beneath the hinged doors allow controlled gravity forced release of the
materials dumped. Most modern barges are remotely operate from the towing vessel which is equipped
with Loran navigational aid for positive positioning when locating the dumpsite.
Several physical factors influence the disposal of dumped material from the barges. The same
parameters used to control the physical characterist.es and effects of disposed material are the
principal considerations affecting the cost of ocean dumping. Included are such conditions as
discharge rate, water depth, barge capacity, distance to the disposal site and chermcal reactivity of the
dumped materials. Based on existing practices, barging econom.cs have been calculated by EPA
M97H From their data bulk industrial wastes which include spent stone, would in 197! cost
(1971). From their^data^D Atlanticand $2.30alongtheGulf Coast foreach ton of
approximately $ 1 -00 m the Pa< ficjL80 ^ ^ to ^ ^ distances t(j ^
material dumped. The principal reason iui m"
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waters where industrial dumpsites are located. Deep waters can be reached within 20 miles from shore
along the west coast, but one way distances along the eastern Atlantic and Gulf coasts are as much as
100 miles from shore. From Figure 4, 5, and 6 by EPA (1971) one gets a rough order estimate of the
dumping costs for ocean disposal of industrial waster such as spent stone from the fluidized bed
process.
Although ocean dumping has been declining in total tonnage in the past two years, primarily
because of the EPA permit system, there are many dumping operators along the Gulf and Atlantic
coasts. In 1975 EPA reported that 11 private companies were involved in industrial waste ocean
disposal operating under the regulations provided in the permit system. Table 3 includes most of these
operators and their present bases of operation. The primary reason for the observed decline in ocean
dumping has been the reluctance of EPA to issue permits, especially in cases where the wastes to be
disposed do not meet the criteria set forth in the Final Regulations. As a result, many operations which
previously went unchallenged are now being scrutinized by the permit process. More industrial waste
disposers are finding alternative methods to disposal at sea or recycling wastes. However, since the
basic premise of MPRSA and the Final Regulations is to seek out the least environmentally damaging
means of waste disposal, the oceans will undoubtedly continue to be used as a receptacle for man's
waste.
166
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§
SO 100 ' ISOMO " 250
Round Trip Oist«c« In N1lcs
300
Figure 4. Cost Per Trip Mile as a Function
of Round Trip Haul Distance
-is-
100
"~ 150 200 250
»
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Table 3. Ocean Dumping Operators Licensed by EPA
EPA Approved
Ocean Dumpsites
Departure
Points
Number of
Operational
Barges
Safety Projects & Eng. Co.
Pine State By-Products
A & S Trans. Co.
Spentonbush Trans. Service
Sun Trans. Co.
Interstate Ocean Disposal Trans. Co.
Port Arthur Towing Co.
DuPont Lessee
Domar Ocean Trans. Ltd.
Dixie Carriers Inc.
Lockport Chemical Co.
Hingham, Mass.
Portland, Me.
S. Kearny, N.J.
NYC, N. Y.
Marcus Hook, Pa.
Marcus Hook, Pa.
Beaumont, Tx.
La Porte, Tx.
Beaumont, Tx.
La Porte, Tx.
Beaumont, Tx.
La Porte, Tx.
Deer Park, Tx.
Baton Rouge, La.
1
1
2
3
1
1
4
2
1
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FEASIBILITY OF DUMPING SPENT STONE AT SEA
There are two philosophies regarding the dumping of wastes at sea. In the first case certain
ocean areas which are deemed to have limited ecological and sociological significance are designated
ior waste disposal. Dumping is conducted in such a way that any adverse biological effects are
restricted to the dumpsite; the area is "written off and hopefully the surrounding environment not
affected. Generally this philosophy is used to regulate ocean diposal activities in areas off the
continental shelf in deep waters. This rationale of waste disposal has been adopted for most industrial
wastes.
The second philosophy regarding waste disposal in the ocean establishes a classification system
of entire ocean environments within range of the generated wastes. This categorization of the marine
environment is based on the potential or present used of the various areas, taking into consideration
such sociological and ecological values as prime fishing areas, recreational zones or spawning areas.
For each of these designated environments acceptable types and concentrations of wastes can be
computed and dumping proceeds until the area has reached the saturation point for the particular
waste. Upon reaching these specified concentrations dumping must cease until the ecology can absorb
the waste and thereby lower the pollutant concentration. This attitude points toward dispersed
dumping in shallow or surface waters. While segregating wastes to restrict the dumping of particularly
toxic or nondegrading materials in these areas, this philosophy of ocean disposal often finds conflicts
between sociological and ecological values. It would not be suitable for the consideration of industrial
wastes.
Considering ocean dumping of the spent stone from the fluidized bed combustion process, the
first philosophy may be acceptable if controlled disposal at designated sites is demonstrated to have a
minimal impact. As a result, most locations for spent stone disposal would be at offshore areas as
much as 100 miles from the nearest point of embarkment. The feasibility of using the oceans for waste
disposal under the established permit system requires that certain measures be taken. The material to
be disposed must be characterized. Quantities must be estimated. Physical characteristics as well as
chemical constituents must be identified for conditions in a natural state and as the result of seawater
mixing. Such particulars as elemental composition, reactive state, and paniculate sizes of the material
must be quantitated. This characteri/ation must then be checked against the evaluation criteria set
forth in the Final Regulations and any amendments to the regulations. Biological impact assessment
must be performed.
The Westinghouse Ocean Research laboratory has performed some initial impact assessments
of the spent stone likely to the generated from the fluidized bed combustion process. A preliminary
feasibility evaluation was performed with CAFB stone in various mixtures ol seawater taken off the
coast of Maryland in the vicinity of two existing mid-Atlantic dumps.tes. The area from wh.ch the
seawater was taken represents two sites which EPA Region III has .ssued dumping permits for
municipal sewage wastes and industrical liquid wastes (acids with an average PH of 0.1) The m.tial
tests performed included CAFB stone/seawater mixing experiments to identify solution
charactenstics, heat release and chemical changes. Using sample matena prov.ded by the
Wcstinehouse R&D Center, a series of scale experiments were undertaken. Calculations for these
westmgnouse K" capacity of 2,600 cubic yards, average barge area of 15.
^"eared erTi y of ' 2*««/«' for ,he CAFB .one and a, ta« 1,200 ft. depth where
7m mg wTl take piace Oust off the conunental rt.ll). So*ng ,h,s down we «„ ab,e ,„ work w,,h
a .horoughly mixed spent stone concentration of 4.7 x 10 mg I.
169
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The first test undertaken was a simple mixing evaluation to determine the proportions of
material which actually settled out. A series of 50 gram aliquots of CAFB stone were mixed in 1 liter
settling tubes with seawater for 1 and 2 minutes and allowed to settle for 1,3 and 18 hours. Data for this
test are given in Table 4. Two distinct liquid phases were observed, a surfactant layer and a lower
flocculant layer. The surfactant layer was a soapy, thinnly clouded mixture while the flocculant was a
more dense wooly mixture. From the results in Table 4, 7 to 309f of the CAFB stone remained
suspended in the water column over the 18 hour test. As expected, the surfactant layer comprised a
greater percentage of the water column with time and the concentration of suspended particulates
(greater than 0.45/z) decreased from 340 to about 12 mg/1. The lower flocculant layer comprised a
smaller percentage of the water column, but its concentration increased from 2.8 x 10 mg/lto 1.6x
102 mg/1. It is interesting to note that there is not an equilibrium effect where the total suspended solids
remain the same and their proportions in each layer shift. It appeared that the flocculant layer near the
bottom continued to react with the seawater and paniculate material was released throughout the
entire 18 hours. As a result, a continuous dense layer remained just above the sediment mound.
Comparing this test with actual submersible observations of sewage disposal at the Maryland Ocean
Dumpsite there is evidence that a surficial blanket does form near the bottom and breaks up only when
storm-induced mechanical energy causes forced mixing. The result is that ridges of ocean bottom are
clear of this floe and that swails tend to accumulate this material. In all probability this same effect will
be realized from the dumping of spent stone granules.
Another experiment was conducted to measure the heat released as a result of mixing CAFB
stone in seawater. Once again approximately 50 gms of granular spent stone was placed into a 1 liter
settling tube. The ambient seawater temperature was 14.2°C. Thermisters placed in the sediment, at
mid-water and at the water surface were monitored and temperatures plotted from the time the stone
was dumped into the settling tube. Figure 7 shows these results which indicate that the maximum
increase in temperature was 10.4°C over ambient and occurred 19 minutes after the start. Projecting
the curves in Figure 7 equilibrium temperatures would be reached within 1 hour after dumping.
A final experiment was conducted whereby the phases of the spent stone in seawater were
isolated and chemical analysis performed on the solid and liquid fractions. In this test 50 g/1 were
mixed, pH recorded over a 24-hour period and the samples allowed to settle into distinct layers. Heavy
metals analysis was performed on liquid and solid fractions of CAFB stone/sea water mixtures.
Results of the pH data are given in Table 5 and the metals analysis are shown with a comparison to
other ocean dumpsite data in Table 6. From these results it appears that only Vanadium shows any
significant increase over ambient levels expected in seawater.
From the initial assessments made by the Ocean Reasearch Laboratory we believe it may be
possible to secure an interim permit for ocean disposal of spent stone. Our initial judgement is based on
certain precedents which have been set as well as the specific requirements in the Final Regulations.
Some questions have arisen with regard to the amended regulations. Spent stone waste disposal
permits may be secured under the regional permit system in the North and Mid-Atlantic, as well as
Western Gulf states. This includes areas covered by Region 1 in Boston, Region II in New York,
Region III in Philadelphia and Region VI in Dallas as they are the only EPA regional offices with
jurisdiction over active industrial dumpsites. Region IV which includes the Southeastern Atlantic and
Eastern Gulf states does not have any designated industrial dumpsites and would reguire and inter-
regional permit. This would be possible, but more difficult to obtain through the administrator's office
in Washington.
170
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SEDIMENT
8 10 12 14 16 18 20 22 24 26 28 30 32
MINUTES FROM START
34 36
Figure 7. Temperature Changes with CAFB/Seawater Mixture
-------
Table 4. Suspended Particulates From CAFB/Seawater Mixtures
TIME
MINUTES HOURS
MIXED SETTLED
1 - 1
2 - 1
1 - 3
2 3
2 - 18
SURFACTANT FRACTION
% OF TOTAL
LIQUID
8.5
25.1
77.2
83.1
82.8
CONCENTRATION
(mg//)
340
179
37.8
94.6
11.9
FLOCCULANT FRACTION
% OF TOTAL
LIQUID
91.5
74.9
22.8
16.9
17.2
CONCENTRATION
(nig/I)
279 X 101
289 X 101
393 X 101
1 12 X 102
159 X 102
i-o
-------
Tables. Cnanges in pH witii CAFB Mixed in Seawater
TIME (HOURS)
START
0.25
0.50
0.75
1.00
6.00
12.00
18.00
24.00
9.75
11.85
11.95
12.00
12.00
12.25
12.40
12.50
12.80
173
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Table 6 Heavy Metals Evaluation of CAFB Stone
Compared to Other Ocean Dumpsites
Chromium
Copper
Nickel
Lead
Zinc
Silver
Iron
Manganese
Antimony
Titanium
Vanadium
CaCO^
Dump
Control
Dump
Control
Dump
Control
Dump
Control
Dump
Control
Dump
Control
» COMPARABLE DUMPS1TE DATA:
<
a.
UJ
|,
m
5-
Z
43
<34
<53
<32
<15
<12
<88
<75
Mid-Atlantic Bight
Sewage Disposal
Site (EPA)
2
<]
6
8
Mid-Atlantic
Bight-
Shellfish Data
7.52
6.33
4.13
2.11
3.37
3.51
3.73
1.18
o
1(3 s
m^S
> ' § a
Z < u
Range
1 .8-460.0
Mean
60.7
Range
1.5-330.0
Mean
6.32
Range
3.O45.0
Mean
13.9
Range
7.0-700.0
Mean
102.5
Range
9.0-900.0
Mean
141.9
.2 °
~5j -~
£ «
•s g-
c S.<
IQS
il
s <
200
8
16
52
110
1.2
50,000
1,700
10
3,000
220
225,000
(a measure
of acidity
** CAFB SPENT STONE:
Water Mixture
(ppm in solution)
<0.02
0.2
<0.02
<0.02
<2.5
1.3
o.:
<.07
<2.0
-------
in requirements in the EPA Final Regulations which provide the mechanism for ocean
ing are contained m Part 227, SecUons 227.3, 227.4. and 22*.5. Certain classification, -thin
these sections must be made concerning the applicability of spent stone wastes to ocean disposal.
According to Section 227.31 (b). such elements as Nickel and Vanadium mu>t not be available in
the waste atconcentrat.ons greater than 0.01 of the concentration established to be toxic to biota of the
receiving waters. While the evaluation criteria does allow for a mixing zone, special care must bo taken
with elements in the waste which are normally found in sea water at trace concentrations (less than 1
part per million). Section 227.34 of the Final Regulations also identifies the considerations which must
be given to the alkalinity of the waste disposal. Because of the high p H caused by mixing of the spent
stone and water there may be a potential for synergistic effects or the formation of toxic compounds to
be found during the immediate release process. This matter must be clarified further before proceeding
with a permit consideration.
The most important section of the Final Regulations regarding feasibility of spent stone
disposal is contained in Section 227.4 which establishes the implementation plan requirements for
interim permits. This includes the necessary planning and implementation phase for securing ocean
dumping permits. The most critical issue in this section states that for industrial wastes the dumper
must "(a) demonstrate the need for proposed dumping...compared to alternative locations and
methods, (b) demonstrate the need for the proposed dumping outweights the potential harm...and (c)
provide as satisfactory implementation plan...of the best practical technology currently available for
removal of such materials." This also includes the best economically available technology for waste
removal.
175
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REFERENCES
E PA, 1971. The Barged Disposal of Ocean Wastes - A Review of Current Practice and Methods of
Evaluation. B.D. Clark, et. al.. Pacific Northwest Water Laboratory. CorvnlHs. Oregon.
EPA. 1975 Ocean Dumping in the L 'nited States - 797.5. Third Annual Report. Office of Water and
Hazardous Materials, Washington D.C.
Odum, E.P., 1959. Fundamentals of Ecology, 2nd. edition, W.B. Saunders. Philadelphia.
176
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APPENDIX VB
OCEAN DUMPING
177
-------
Environmental Systems Department
236-7146
February 1, 1977
Ocean Dumping
R & D CENTER - BLDG. 501 3E19
W. G. Vaux
The following memorandum describes the results of my assessment of the
Environmental Protection Agency's (EPA) attitude toward ocean dumping
and the kinds of studies required by EPA to obtain a permit for ocean
dumping. The purpose of the assessment as defined in Work Order 34-JP-
CPFF-935644-L-A (WESD Contract #743) was to determine: (1) EPA's atti-
tude toward ocean disposal of sulfated and sulfided limestone in all
contiguous U.S. EPA Regions with emphasis on Regions VI and III,
(2) estimate the probability of EPA issuing an ocean disposal permit in
calendar year 1977 and between 1978 and 1983 inclusive and (3) determine
what preliminary bench-scale dispersion and biotoxicity test will satisfy
current EPA requirements.
These three objectives were met by contacting EPA Regional Offices and
research laboratories and reviewing rules and regulations as reported in
the Federal Register. From these contacts and reviews, it is concluded
that obtaining a permit from EPA to dump waste on a commercial scale
would be extremely difficult in either 1977 or between 1978 and 1983
because of the general policy of EPA to phase out all ocean disposal of
industrial waste by 1981. The feasibility of ocean dumping is further
limited by the kinds of constituents associated with the waste and the
regulatory requirements to perform a detailed environmental assessment of
the waste and monitor the dump site. Reasons leading to these conclusions
are presented in detail in the following paragraphs.
EPA Regions III and VI and the Environmental Research Laboratory in Nar-
rangansett, Rhode Island were contacted regarding EPA policy. Region III
indicated that EPA in all regions is currently attempting to phase out
ocean dumping of industrial waste by 1981.(D Region III summarized the
situation in each region as follows:
Region I (Boston) has at present only two existing ocean dispo-
sal permits. Region II (New York) where most of the ocean
dumping is currently taking place, has currently eliminated
approximately 50 industrial dumping permits and most others are
on a compliance schedule to phase out dumping by 1981. Region III
178
-------
-2-
(Philadelphia) has one ocean dumping permit which will he elimi-
nated by 1980. No ocean dumping of industrial waste, is being
conducted in either Region IV (Atlanta) , Regions IX (San Fran-
cisco) or Region X Seattle) .
Of the _ seven dumping permits issued in Region VI (Dallas) only two are
operational. (2) Region VI is currently being sued by a local" fishing
group for having allowed ocean dumping.
Conversations with personnel at the EPA Environmental Research Laboratory
who are involved in assessing effects of ocean dumping, concurred that
EPA is currently attempting to phase out ocean dumping. (3.4) When the
type of waste being considered was described to one of the staff respons-
ible for research activities, he felt that the vanadium content would pre-
clude it from meeting ocean dumping criteria and that the waste might also
contain higher than allowable mercury levels, particularly if the facility
is to be fitted with scrubbers.
EPA has promulgated regulations and criteria governing ocean dumping
pursuant to Title I of the Marine Protection, Research and Sanctuaries
Act of 1972, Public Law 92-532. Regulations and criteria were published
in the Monday, October 15, 1973 Federal Register. Proposed revisions
of these regulations and criteria were published in the Monday, June 28,
1976 Federal Register, and final revisions of regulations and criteria
were published in the Tuesday, January 11, 1977 Federal Register. The
January 11, 1977 regulations and criteria are the effective regulations
and were reviewed to determine kinds of studies to be conducted in order
to obtain a permit.
The regulations and criteria issued January 11, 1977 identify six basic
types of permits. These are general permits, special permits, emergency
permits, interim permits, research permits and permits for incineration
at sea. General permits may be issued for the dumping of materials
which have a "minimal adverse environmental impact and are generally
disposed of in small quantities, or for specific classes of materials
that must be disposed of in emergency situations." Special permits may
be issued for the dumping of materials which satisfy criteria (refers
to criteria described in January 11, 1977 Federal Register which are
discussed below) and shall expire no later than 3 years from the date
of issue. Emergency permits may be issued to dump such materials where
there is demonstrated to exist: "an emergency requiring the dumping of
such materials, which poses an unacceptable risk relating to human
health and admits of no other feasible solution." Interim permits may
be issued prior to April 23, 1978 to dump materials which are not in
compliance with the environmental impact criteria or which would cause
substantial adverse effects as determined by the criteria or for^which
an ocean disposal site has not been designated on other than an interim
basis. A permittee may continue to dump past the April 23, 1978 dead-
line if the permittee has an implementation schedule to phase out ocean
179
-------
-3-
dumping by December 31, 1981 or if he can meet the requirements of a
special permit. In addition, no interim permit will be granted for the
dumping of waste from a facility which has not previously dumped wastes
in the ocean, from a new facility or for the dumping of an increased
amount of waste from the expansion or modification of an existing facil-
ity. Research permits may be issued for the dumping of materials into
the ocean as part of a research project when it is determined that the
"scientific merit of the proposed project outweighs the potential environ-
mental or other damage that may result from the dumping." Permits for
incineration at sea may be issued in special cases but are not applicable
to disposal of spent stone from fluidized bed combustion.
By considering the types of permits issued, only an interim permit and
special permit are applicable for the disposal of the spent stone on a
commercial scale. However, no interim permits will be issued to new
facilities and existing interim permits will be eliminated by 1981 such
that all ocean dumping of industrial waste must be in compliance with
the rules and regulations of a special permit. Therefore, it is con-
cluded that ocean dumping of spent stone from fluidized bed combustion
process is possible only if provision of a special permit can be met.
Criteria for evaluation of permit applications for ocean dumping and
criteria for management od disposal sites for ocean dumping are pre-
sented in Parts 227 and 228 or the "Final Revision of Regulations and
Criteria" published in the January 11, 1977 Federal Register.
Criteria for the evaluation of permit applications for ocean dumping
require an assessment of the environmental impact, the need for ocean
dumping, impact of the proposed dumping on esthetic, recreational and
economic values and impact of the proposed dumping on other uses of the
ocean. Even if an applicant demonstrates that the material to be dumped
staisfies environmental impact criteria, a permit may be denied if the
other criteria are not met.
Ocean dumping criteria prevent disposal of certain compounds including
mercury and mercury compounds and cadmium and cadmium compounds. Spent
stone could contain significant amount of these substances, depending
on the source of limestone and coal.
To assess the environmental impacts, it is necessary to conduct exten-
sive bioassays. These bioassays must be conducted on the liquid, sus-
pended particulate and solid phases to demonstrate at the 95 percent
confidence level, that when materials are dumped, no significant, unde-
sirable effects will occur. In addition to determination of lethal
effects, the possibility of sub lethal effects due to bioaccumulation
must be considered. Bioassay tests shall be conducted on at least one
species each of phytoplankton or zooplankton, crustacean or mollusk and
fish. Chronic toxicity and bioaccumulation of the solid phase shall be
conducted on benthic organisms, including at least one species each
180
-------
-4-
representing a filter-feeding, deposit feeding and burrowing species.
Therefore, these bioassay and bioaccumulation studies must be conducted
on a total of at least six different test organisms.
The liquid phase of a material is defined as the supernatant remaining
after 1 hour undisturbed settling, after centrifugation and filtration
through a 0.45 micron filter." The suspended particulate phase is the
"supernatant as obtained above prior to centrifugation and filtration"
and the solid phase includes all material settling to the bottom in
1 hour.
It is also necessary to determine if the liquid phase after allowance for
initial mixing (dispersion which occurs within 4 hours after dumping)
meets water quality criteria contained in "Quality Criteria for Water."
A permit may also be denied if "mercury and its compounds are present
in any solid phase in concentrations greater than 0.75 mg/kg or more
than 50 percent greater than the average total mercury of natural sedi-
ments of similar lighographic characteristics as those at the disposal
site" or cadmium and its compounds are present "in amy solid phase of
material in concentrations less than 0.6 mg/kg or less than 50 percent
greater than the average total cadmium content of natural sediments of
similar lithographic characteristics as those at the disposal site."
In disposing of alkaline waste such as the spent stone, dumping condi-
tions must be such that the total alkalinity after allowance for initial
mixing may be changed based on stoichiometric calculations by no more
than 10 percent during all dumping operations. To meet this criterion,
it would involve a thorough analysis of proposed dumping procedures and
dispersion of the waste. Models for predicting disposal of a substance
containing both solid and soluble phases such as spent stone are not
available at this time.(6,7) if no feasible means is available for
estimating dispersion, the liquid and solid phases may be assumed to be
evenly distributed after 4 hours over a column of water bounded on the
surface by an area swept out by the locus of points constantly 100 meters
from the perimeter of the dumping point and extending to the ocean floor,
thermocline or halocline, if one exists, or to a depth of 20 meters
whichever is shallower.
Need for ocean dumping must also be demonstrated. Particular attention
should be given to the relative environmental risks, impact and cost for
ocean dumping as opposed to other feasible alternatives, including but
not limited to: (1) land fill, (2) well injection, (3) incineration,
(4) spread of material over open ground, (5) recycling of material for
reuse (6) additional biological, chemical or physical treatment or
intermediate or final waste streams and (7) storage.
If a potential ocean dumper meets all criteria and regulations and obtains
ermit the EPA Regional Administrator has the authority to require the
permittee to conduct a monitoring program at the dump site. If it is
181
-------
-5-
detennined that the waste to be dumped is not compatible with waste
being dumped at an existing site, the EPA may require the selection of a
new dump site. If a new site is designated, the permittee must conduct
a base line monitoring program at the site.vl)
In summary, EPA is currently attempting to phase out ocean dumping of
industrial waste by 1981. However, if a potential ocean dumper can meet
the stringent criteria of a special permit, a possibility exists for
a permit to be granted. Criteria to be met include not only physical/
chemical characterization and bioassay of the material to be dumped but
also full evaluation of alternatives followed by mointoring of the dump
site if a permit is issued. The possibility that this particular waste
contains constituents such as vanadium, mercury and arsenic from com-
bustion of coal and is highly alkaline suggests that it will not meet
criteria.
The policy of EPA to phase out ocean dumping of industrial waste by 1981,
the stringent criteria which must be meet to obtain a special permit
and the cost associated with demonstrating compliance with the criteria
preclude, in my opinion, consideration of ocean dumping as a means of
disposal of sulfated and sulfided limestone waste from the fluidized bed
combustion process on a commercial scale.
Henry A. Donaldson
Aquatic Biological Sciences
HAD:knw
cc: M. Kirshner
G. A. Valiulis
C-743
182
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APPENDIX B
REFERENCES
1. Muir, W., U.S. Environmental Protection Agency, Region III, personal
communication to H. A..Donaldson, Westinghouse Electric Corporation,
Environmental Systems Department, January 31, 1977.
2. Vickey, R., U.S. Environmental Protection Agency, Region VI, personal
communications to H. A. Donaldson, Westinghouse Electric Corporation,
Environmental^Systems Department, December 20, 1976.
3. Gentile, J. , U.S. Environmental Protection Agency, Environmental
Research Laboratory, Narragansett, RI, personal communication to
H. A. Donaldson, Westinghouse Electric Corporation, Environmental
Systems Department, December 20, 1976.
4. Payne, R. , U.S. Environmental Protection Agency, Environmental
Research Laboratory, Narragansett, RI, personal communicatinn to
H. A., Donaldson, Westinghouse Electric Corporatinn, Environmental
Systems Department, January 27, 1977.
5. Quality Criteria for Water, U.S. Environmental Protection Agency,
prepublication copy, July 26, 1976.
6. Callaway, R., U.S. Environmental Protection Agency, Evnironmental
Research Laboratory, Corvallis, OR, personal communication to
H. A. Donaldson, Westinghouse Electric Corporation, Evnironmental
Systems Department, January 21, 1977.
7. Schmike, G., Arthur D. Little Company, personal communications to
H. A. Donaldson, Westinghouse Electric Corproation, Environmental
Systems Department, January 27, 1977.
183
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APPENDIX C
PREDICTED PRODUCTION PROPORTIONS OF SPENT SORBENT
AND FLY ASH FROM FLUIDIZED BED COMBUSTION
Let
Xc = weight fraction of total sulfur in the fuel
J
X = weight fraction of ash in the fuel
f\
2L. = weight fraction of inerts in the fresh sorbent
R = Ca/S molar treat ratio
Then, on the basis of 100 kg of fuel fed, the fly ash production is
W. = 100 X.
A A
The sorbent feed rate is
100 Xs
W_ = (—— ) R M.. in the case of limestone
L M 1
and
100 Xg
W = (—— ) R M for dolomite
D
where M M and M^ are the molecular weights of sulfur, calcium car-
O i_i JJ
bonate and pure dolomite, respectively.
Let
SR = fraction of feed sulfur retained by the sorbent
The products may contain CaO, CaSO,, CaCO_, fuel ash and limestone
inerts in the case of limestone and CaO-MgO, CaSO -MgO, CaCO «MgO, fuel
184
-------
ash and dolomite inerts in the case of dolomite. The two cases can be
treated as one by writing the sorbent as CaCo~-aMgCO where a = Mg/Ca
molar ratio in the fresh sorbent and is 1 for dolomite and 0 for lime-
stone. The dolomite feed rate is then:
100 X
WD = (-^—> R [ML + a V
where M.. is the molecular weight of magnesium carbonate.
The production rate of spent sorbent is then as follows. (these
calculations assume that magnesium is fully calcined to oxide, and the
calcium is distributed among oxide, sulfate and carbonate):
Let
fraction of feed CaCO surviving calcination
Then
100 X
(CaCO. + a MgO) = a [ (—rj ) R] [H. + a
J L ns
100 Xs
(CaS04 + a MgO) = SR [ (— ) ] [MA + a
100 Xg
(CaO + a MgO) = [ (1 - a ) R - SR] [—g ] [MQ + a
S
where M , M , and M are the molecular weights of magnesia (MgO),
anhydrite (CaSO^) and quick lime (CaO), respectively. The insert con-
tent in the output is
XT 100 X
W, = fc-^r> [C-v-^ R^ IML + aMM]
185
-------
The spent sorbent production rate is then the sum of the above
four expressions which can be reduced to:
100 X M + a M X
WSS = [-lT^] {R [(1-X } + MC K + (1 + a) 1~FT)] + W
O L i-
where Mp and M are the molecular weights of carbon dioxide and sulfur
\s J.
trioxide, respectively.
The sorbent/fly ash ratio, assuming a sharp separation, is
W X M + a M X
- <3r> {R ^-XT ) + Mc
A A S I
Inserting molecular weights and typical values as a = 1.0,
SR = 0.90, aL = 0.0, XA = 0.10, ^ = 0.05, this yields:
for limestone
W
Wqq
r-2- = X_ [19.1353 R + 22.4747]
W . b
A
for dolomite
W
CO
= Xc [33.0929 R + 22.4747]
These equations are plotted in Figure C-l.
186
-------
8
Curve 686999-A
I ' I • I
I Parameter: Ca/S Molar Treat Ratio
Dolomite
L Limestone
Basis:
10% Ash in Fuel
|_90% Retention of Sulfur by
Sorbent
5% Impurities in
I Sorbent
2 3 4
Weight % Sulfur in Fuel
Figure C-l. Spent Sorbent/Fuel Ash Katie in Fluidized-Bed
Combustion
187
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse, before completing)
1 RtPORT NO.
1 TITLE AMD SUBTITLE D^pQg^ of Solid Residue from
Fluidized-bed Combustion: Engineering and
Laboratory Studies
C. C. Sun, C. H. Peterson, R. A. Newby, W. G. Vatvx.
and_p_i_l.i._Ke_airns_
i'. Ki.P.FOHMING ORGANIZATION IMAMIr AND Ar.TJRESS
Westinghouse Researcli and Development Center
1310 Beulah Road
Pittsburgh. Pennsylvania 15235
*'i. SPCNUORING 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 DATS-
March 1978
6. PERFORMING ORGANIZATION CODE
a. p;:r-iFORMiNG ORGANIZATION RFPORT NO
10. PROGRAM E LT M~h:N 1" NO.
_EHE6_23A
11. 'CON?"RACT/cfH ANT "NO".
68-02-2132
13. TYPE OF Ptl'ORT AN.O PERIOD COVERED
SPONSORING
EPA/600/13
is. SUPPLEMENTARY NOTES ffiRL-RTP project officer is D. Bruce Henschel, Mail Drop 61,
919/541-2825. EPA-650/2-75-027c is the previous report relating to this work.
1C.. ABSTRACT
The report gives results of an engineering and laboratory study to evaluate
the environmental impact of disposing of solid residue (spent SO2 sorbent and fuel
ash) from fluidized-bed combustion (FBC) processes. The quantity and composition
of spent sorbents produced by six reference FBC processes were projected. The
experimental investigation considered residue from atmospheric and pressurized
FBC processes, with and without sorbent regeneration, and with and without proces-
sing of the residue. Laboratory tests were conducted to determine residue charac-
teristics, leaching behavior, and thermal activity. The environmental impact from
land disposal of the residue was assessed by comparing the leaching and thermal
activity results with both available drinking water standards and the behavior of
natural gypsum. Processing of the spent sorbent and ash, through fixation of the
residue as a cement-like material, was investigated as away to reduce the envi-
ronmental impact, and to provide alternatives for potential utilization. The poten-
tial for at-sea disposal was also assessed.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
:. COSATl Field/Group
Pollution
Combustion
Fluidizing
Coal
Residues
Waste Disposal
Waste Treatment
Desulfurization
Ashes
Laboratory Tests
Leaching
Properties
Pollution Control
Stationary Sources
Fluidized-bed Combus-
tion
Environmental Impact
At-sea Disposal
13B
2 IB
07A,13H
2 ID
14B
15E
07D
14B
13. DISTRIBUTION STATE1-
Unlimited
19. SECURITY CLASS (This Report}
Unclassified
20. SECURITY CLASS (This page)
Unclassified
21. NO. OF PAGES
208
22. p~mci
EPA Form 2220-1 (9-73)
188
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