CD A U.S. Environmental Protection Agency Industrial Environmental Research EPA~600/7-78~044d
^" • •» Off ice of Research and Development Laboratory -in^O
Research Triangle Park, North Carolina 27711 MaTCh 1978
CONTROLLING SO2 EMISSIONS
FROM COAL-FIRED
STEAM-ELECTRIC GENERATORS:
SOLID WASTE IMPACT
(Volume I. Executive Summary)
Interagency
Energy-Environment
Research and Development
Program Report
-------
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-------
EPA-600/7-78-044a
March 1978
CONTROLLING SO2 EMISSIONS FROM
COAL-FIRED STEAM-ELECTRIC
GENERATORS: SOLID WASTE IMPACT
(Volume I. Executive Summary)
by
P.P Leo and J. Rossoff
The Aerospace Corporation
P.O. Box 92957
Los Angeles, California 90009
Contract No. 68-01-3528
W. A. 6
Program Element No. EHE624A
EPA Project Officer: Julian W. Jones
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
-------
ABSTRACT
The Environmental Protection Agency (EPA) Office of Air Quality
Planning and Standards (OAQPS), Durham, North Carolina, is reviewing the
New Source Performance Standards (NSPS) for sulfur dioxide (SOz) emissions
from coal-fired steam electric generators. A number of control strategies
are defined, e.g., increased scrubbing efficiency and coal washing, for
achieving several levels of SO2 emission control with emphasis on levels
more stringent than the current NSPS. In support of that review, this study
is aimed at providing an assessment of technological, economic, and environ-
mental impacts, projected to 1998, of the increased solid wastes resulting
from the application of the various more-stringent controls as well as the
current NSPS.
The study considers three alternative strategies (1.2 Ib SO2/
10° Btu, 90 percent SOz removal, and 0. 5 Ib SC>2/10D Btu), three plant sizes
(1000, 500, and 25 MW), and five flue gas desulfurization (FGD) systems
(lime, limestone, double alkali, magnesium oxide, and Wellman-Lord).
Typical eastern and western coals containing 3.5 percent and 0.8 per-
cent sulfur, respectively, as well as coal washing are included. The
range of variability of sulfur content in coals, while not considered explicitly,
was assumed to result in the typical values defined when considered in a na-
tional aggregate. Additionally, the ground rules include the following: (a) the
interval for the nationwide survey (19 "78 through 1998), (b) the new plant in-
stalled capacity during that interval (Federal Power Commission projection),
(c) the establishment of 1980 as the effective date for the more stringent
standards for purposes of this study, and (d) the quantity of western coal
burned during the 1980-1998 period to be 45 percent of the total burned on a
nationwide basis.
The application of more stringent standards would possibly affect
the percentage of western coal burned. Because predictions of the impacts of
these standards on western coal usage were not available, the quantities and
volumes of wastes that would be produced nationally as a result of burning dif-
ferent fractions of western coal were computed on a parametric basis.
11
-------
CONTENTS page
Abstract ii
Figures iv
Tables v
Acknowledgments vi
Conversion Table vii
I. Introduction 1
II. Executive Summary 3
2. 1 Quantification of Solid Wastes 14
2. 1. 1 Current Federal standards: 1.2 Ib SO2/106 Btu . 14
2. 1. 2 Effect of a 90-percent SO2 removal requirement . 18
2. 1. 3 Effect of a 0. 5 Ib SO2/106 Btu standard 18
2. 1. 4 Effects of coal washing on quantities of waste
produced 18
2. 1. 5 Effect of plant size on quantities of waste 19
produced 19
2. 1. 6 Effects of coal sulfur on quantities of waste
produced „ 21
2. 1. 7 Effects of the scrubbing process on quantities
of waste produced 23
2. 1. 8 Nationwide projections to 1998 25
2.2 Characterization of Untreated Wastes 25
2. 2. 1 Effect of scrubbing process variables on sludge
chemistry 30
2. 2. 2 Trace element content 30
2. 2. 3 Physical properties 30
2.2.4 Chemical properties 33
111
-------
CONTENTS (Continued)
2. 3 Potential Environmental Impacts of Disposal
Processes and Practices 33
2. 3. 1 Ponding 37
2. 3. 2 Chemical treatment 38
2. 3. 3 Mine disposal 39
2. 3. 4 Ocean disposal 40
2.3.5 Conversion to gypsum 41
2. 3. 6 Conversion to sulfuric acid or sulfur 41
2. 3. 7 Use as a synthetic aggregate 43
2. 4 Waste Disposal 43
2. 5 Utilization 43
2. 6 Economics . . 44
References 46
FIGURES
Number Page
1 Quantities of Waste, Including Ash, Produced by New Plants
for Alternative Standards 17
2 Effect of Power Plant Size and Equivalent Capacities on the
Amount of Solid Wastes Produced (Includes Ash) 20
3 Solid Waste, Including Ash, and Useable By-Products 24
4 Effect of Eastern Coal Use on the Fraction of Waste Quanti-
ties, Including Ash, Produced Nationally by New Plants 27
5 Total Annual Waste Quantities, Including Ash, Produced
Nationwide by All New Plants Coming on Line Beginning
in 1978 28
6 Average Trace Element Content of Sludge Solids 32
IV
-------
TABLES
Number Page
1. Alternative control systems for model plants „ . 2
2 Summary of solid wastes produced 4
3 Cross reference of alternative standards and model plants
with study case numbers 11
4 Coal characteristics used in study 15
5 Basic steam generating plant characteristics used in study ... 16
6 Basic scrubber and FGD process characteristics used in
study 16
7 Effect of high- and low-Btu western coal on waste generated
and disposal area required 22
8 Quantity and volume of nonregenerable SO2 scrubber wastes
produced in 1998 by new coal-burning plants constructed
between 1978 and 1998 26
9 Volume of nonregenerable SC>2 scrubber wastes produced in a
30-year generating plant lifetime 29
10 Range of concentrations of chemical constituents in FGD
sludges from lime, limestone, and double-alkali systems . . 31
11 Status of magnesium-oxide scrubbing plants 42
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ACKNOWLEDGMENTS
Appreciation is acknowledged for the assistance and guidance
of Mr. Julian Jones of the EPA Industrial Environmental Research Lab-
oratory, Research Triangle Park, North Carolina, who served as Technical
Monitor, and Mr. Kenneth Woodard of the EPA Emissions Standards and
Engineering Division.
Messrs. R. B. Fling, W. J. Swartwood, and Dr. W- M. Graven
of The Aerospace Corporation made valuable technical contributions to the
study performed under this contract.
vi
-------
CONVERSION TABLE
British
1 inch
1 foot
1 mile
1 square foot
1 acre
1 cubic foot
1 gallon
1 cubic yard
1 pound
1 ton (short)
1 pound per square inch
1 pound per cubic foot
1 ton per square foot
1 part per million
1 British thermal unit
(Btu)
1 pound per million Btu
1 Btu per pound
Metric
2. 54 centimeters
0.3048 meter
1.609 kilometers
9, 290 square centimeters
4, 047 square meters
28, 316 cubic centimeters
3. 785 liters
0. 7646 cubic meter
0. 454 kilogram
0. 9072 metric ton
0. 0703 kilogram per square
centimeter
0.01602 gram per cubic
. centimeter
9, 765 kilograms per square
meter
1 milligram per liter (equivalent)
252 calories
0.43 grams per million joules;
1.80 grams per million calories
2. 324 joules per gram; 0. 555
calories per gram
vii
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SECTION I
INTRODUCTION
The Environmental Protection Agency (EPA) Office of Air
Quality Planning and Standards (OAQPS), Durham, North Carolina, is
reviewing the New Source Performance Standards (NSPS) for sulfur dioxide
(SO2) emissions from coal-fired steam electric generators. A number of
control strategies have been defined, e.g., increased scrubbing efficiency
and coal washing, for achieving several levels of SO? emission control with
emphasis on levels more stringent than the current NSPS. In support of
that review, this study is aimed at providing an assessment of technological,
economic, and environmental impacts, projected to 1998, of the increased
solid wastes resulting from the application of the various more-stringent
controls as well as the current NSPS.
The study considered three alternative strategies (1.2 Ib
SO2/106 Btu, 90 percent SO2 removal, and 0.5 Ib SO2/10& Btu), three plant
sizes (1000, 500, and 25 MW), and five flue gas desulfurization (FGD) sys-
tems (lime, limestone, double alkali, magnesium, oxide, and Wellman-Lord).
Typical eastern and western coals, as well as coal washing, were included.
Initially, the various study cases totalled 67; they were subsequently increased
to 93 to improve visibility into the impact of the various alternatives. The
study cases are summarized in Table 1. Additional groundrules and guide-
lines were developed in conjunction with the technical monitor during the
course of the study (1, 2). These are also outlined in Table 1 and include
'hs- following: (a) the interval for the nationwide survey (1978 through 1998),
(b) the new plant installed capacity during that interval (Federal Power Com-
mission projection), (c) the establishment of 1980 as the effective date for
the more stringent standards for purposes of this study, and (d) the quantity
of western coal burned during the 1980-1998 period to be 45 percent of the
total burned on a nationwide basis.
The application of more stringent standards would possibly affect
the percentage of western coal burned. Because predictions of the impacts
of these standards on western coal usage were not available, quantities and
volumes of wastes that would be produced nationally as a result of burning dif-
ferent fractions of western coal were computed on a parametric basis.
-------
TABLE 1. ALTERNATIVE CONTROL SYSTEMS FOR MODEL PLANTS
a, b
Plant Sizes To
Be Considered, MW
25; 500; 1000
25; 500; 1000
25; 500
25; 500
500
25; 500; 1000
25; 500
25; 500
25; 500
500
FGD Systems
To Be Considered
5C
Lime /lime stone
Lime /lime stone
5C
Lime /lime stone
Lime -lime stone
Lime /lime stone
Lime /lime stone
Alternative Standards and Model Plant Systems
1. The existing NSPS of 1.2 Ib SO2/106 Btu heat input.
a. 90-percent SC>2 removal on a plant burning a
typical coal of 3 . 5 percent sulfur.
b. A plant burning a typical 7-percent sulfur coal
with 90-percent SC>2 removal by FGD.
c. Low-sulfur coal without FGD for a typical
eastern plant^
d. Low-sulfur coal without FGD for a typical
western plant.
e. 40-percent sulfur removal by coal washing of
a 3. 5-percent- sulfur coal followed by 65-
percent SC>2 removal by FGD.
2. a. 90-percent SC>2 removal by FGD on a typical
coal of 3. 5 percent sulfur and a typical coal of
7 percent sulfur.
b. 90-percent SC>2 removal by FGD on a plant
burning a typical western coal of 0. 8 percent
sulfur ('western plant).
3. 0. 5 Ib SO2 emissions /106 Btu heat input.
a. 70- to 75-percent SO2 removal by FGD on a
0. 8-percent- sulfur western coal (western plant).
b.l 40-percent sulfur removal by coal washing of a
3. 5-percent- sulfur coal and 85-percent removal
by FGD.
b.2 40-percent sulfur removal by coal washing of
a 7-percent-sulfur coal and 95-percent removal
by FGD.
Reference 3.
Per References 1 and 2.
• Study encompasses 1978-1998 period.
• More stringent standards to apply in 1980.
New plant installed capacity per Federal Power Com-
mission projections.
For 1980 and thereafter, 45 percent of the coal burned
nationally is western, low sulfur.
"The five systems to be considered are lime, limestone, magnesium oxide, double alkali, and Wellman-Lord.
-------
SECTION II
EXECUTIVE SUMMARY
Solid wastes resulting from the scrubbing of flue gases from
coal-fired steam-generating utility boilers were quantified for 1000-,
500-, and 25-MW units for nonregenerable (lime, limestone, and double
alkali) and regenerable (magnesium oxide and Wellman-Lord) processes.
Typical eastern and western coals were included in the study (Table 2).
A number of control strategies were included, such as increased scrub-
bing efficiency and coal washing, to achieve several levels of emissions
more stringent than the current New Source Performance Standards
(NSPS). Table 3 is a cross reference of the alternative standards and
model plants (from Table 1) with the study case numbers. The resultant
waste or by-product quantities and volumes are presented in Table 2 for
each case,,
Land requirements and technological, economic, and environ-
mental impacts were projected to 1998, with the application of the more
stringent controls in 1980.
Physical and chemical characteristics of the wastes were identi-
fied with respect to the potential pollution of water supplies, resulting from
disposal of the wastes.
The applicability and effectiveness of the various control strate-
gies in conjunction with existing disposal and utilization techniques to mini-
mize environmental impacts were assessed. The status of the technological
developments for disposal and utilization methods are also discussed.
The findings developed during the study are in the categories of
• Quantification of solid wastes (paragraph 2. 1)
• Characterization of untreated wastes (paragraph 2.2)
• Potential environmental impact (paragraph 2.3)
• Waste disposal (paragraph 2.4)
• Utilization (paragraph 2. 5)
• Economics (paragraph 2. 6)
and are summarized in this report.
3
-------
TABLE 2. SUMMARY OF SOLID WASTES PRODUCED21
Case
No.
1
2
3
4
5
6
7
8
9
10
11
12
Coal
%
S
3. 5
3. 5
3. 5
3. 5
3. 5
3. 5
3. 5
3. 5
3. 5
3. 5
3.5
3. 5
Btu/lb
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
%
Ash
14
14
14
14
14
14
14
14
14
14
14
14
MW
1000
500
25
1000
500
25
1000
500
25
1000
500
25
Absorbent
Lime
Lime
Lime
Limestone
Limestone
Limestone
Na2CO3b
Na2COb
Na2CO3b
MgOd
MgOd
MgOd
Absorbent
Utilized,
%
90
90
90
80
80
80
95C
95C
95c
5f
5f
5f
%c
ij
Removed
by
Wash
0
0
0
0
0
0
0
0
0
0
0
0
% SO2
Removed
by
Scrub
80
80
80
80
80
80
80
80
80
80
80
80
Emis sions,
1 1~ Qrf"! /
Ib oCJ2/
106 Btu
1.2
1. 2
1.2
1.2
1.2
1.2
1.2
1.2
1. 2
1.2
1. 2
1.2
By-Products, Dry,
tons X 103/yr
Ash
222
115
6.4
222
115
6.4
222
115
6.4
222
115
6.4
Sulfur
Sludge
210
108
6. 1
229
118
6.7
206
107
6.0
129e
66. 9e
3. 75e
Total
432
223
12. 5
451
233
13. 1
428
222
12.4
42. 2e
21. 8e
1.22e
Acre-Feet
Required
for
Disposal,
Annual
448
232
13
468
242
14
444
230
13
233
121
7
Based on an average operating load factor of 50% (4380 hr/yr)
Double-alkali process
Q
Regenerant (lime) utilization
Magnesium-oxide process
Q
Sulfuric acid or sulfur produced, respectively
Absorbent make-up
(continued)
-------
TABLE 2. (Continued)
Case
No.
13
14
15
16
17
18
19
20
21
22
23
24
241
Coal
%
S
3. 5
3. 5
3. 5
7. 0
7. 0
7. 0
7. 0
7. 0
7. 0
0, 8
0. 8
0. 6
0.4
Btu/lb
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
13, 500
13, 500
10, 000
8, 000
%
Ash
14
14
14
14
14
14
14
14
14
6
6
8
6
MW
1000
500
25
1000
500
25
1000
500
25
500
25
500
500
Absorbent
Na2SO3a
Na2SO3a
Na2SO3a
Lime
Lime
Lime
Limestone
Limestone
Limestone
None
None
None
None
Absorbent
Utilized,
%
5C
5C
5C
90
90
90
80
80
80
N/A
N/A
N/A
N/A
% S
Removed
by
Wash
0
0
0
0
0
0
0
0
0
0
0
0
0
% S02
Removed
by
Scrub
80
80
80
90
90
90
90
90
90
None
None
None
None
Emissions,
Ib SOz /
lO^ Btu
1.2
1.2
1.2
1.2
1.2
1.2
1. 2
1.2
1. 2
1.2
1.2
1.2
1.0
By-Products, Dry,
tons X 103/yr
Ash
222
115
6.4
222
115
6.4
222
115
6.4
43.8
2.45
78. 8
73. 9
Sulfur
Sludge
129b
66. 9b
3. 75b
472
244
13. 7
515
266
15.0
N/Ad
N/A
N/A
N/A
Total
42. 2b
21.8b
1. 22b
694
359
20. 1
737
381
21.4
43.8
2.45
78.8
73. 9
Acre-Feet
Required
for
Disposal,
Annual
237
122
7
719
372
21
764
395
22
44
3
80
74
Wellman-Lord process
Sulfuric acid or sulfur produced, respectively
cAbsorbent make-up
Not applicable
(continued)
-------
TABLE 2. (Continued)
Case
No.
25
251
26
27
28
29
30
31
32
33
34
35
36
Coal
%
S
0.6
0.4
3. 5
3. 5
3. 5
3. 5
3.5
3. 5
3. 5
3.5
3.5
3. 5
3. 5
Btu/lb
10, 000
8, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
%
Ash
8
6
14
14
14
14
14
14
14
14
14
14
14
MW
25
25
500
500
1000
500
25
1000
500
25
1000
500
25
Absorbent
None
None
Lime
Limestone
Lime
Lime
Lime
Limestone
Limestone
Limestone
Na2CO3c
Na2CO3c
Na2CO3c
Absorbent
Utilized,
%
N/A
N/A
90
80
90
90
90 .
80
80
80
95d
95d
95d
% S
Removed
by
Wash
0
0
40
40
0
0
0
0
0
0
0
0
0
% S02
Removed
by
Scrub
None
None
65
65
90
90
90
90
90
90
90
90
90
Emissions,
lb SOz/
106 Btu
1.2
1.0
1. 1
1. 1
0,6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
By-Products, Dry,
tons X 103/yr
Ash
4.42
4. 14
69
71
222
115
6.4
222
115
6.4
222
115
6.4
Sulfur
Sludge
N/Aa
N/A
48
50
236
122
6. 9
258
133
7. 5
232
120
6.8
Total
4.42
4. 14
117b
121b
458
237
13.3
480
248
13.9
454
235
13.2
Acre-Feet
Required
for
Disposal,
Annual
5
4
121b
126b
475
246
14
497
257
14
470
243
14
Not applicable
Does not include coal-wash tailings: 4. 09 X 10^ tons/yr (dry) and 28 acre-ft
r-
Double-alkali process
Regenerant (lime) utilization
(continued)
-------
TABLE 2. (Continued)
Case
No.
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
Coal
%
S
3.5
3. 5
3. 5
3.5
3.5
3.5
7. 0
7. 0
7.0
7.0
7. 0
7. 0
7.0
7.0
7.0
Btu/lb
12,000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12,000
12, 000
12, 000
12, 000
12, 000
%
Ash
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
MW
1000
500
25
1000
500
25
1000
500
25
1000
500
25
1000
500
25
Absorbent
MgOa
MgOa
MgOa
Na2S03
Na2SO3
Na2S03
Lime
Lime
Lime
Limestone
Limestone
Limestone
Na2C03d
Na2CO3d
Na2CO3d
Absorbent
Utilized,
%
5C
5C
5C
5C
5C
5C
90
90
90
80
80
80
95e
95e
95e
% S
Removed
by
Wash
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
% S02
Removed
by
Scrub
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
Emissions,
Ib SC-2/
106 Btu
0.6
0.6
0.6
0.6
0.6
0.6
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
By-products, Dry,
tons X 103/yr
Ash
222
115
6.4
222
115
6.4
222
115
6.4
222
115
6.4
222
115
6.4
Sulfur
Sludge
146b
75. 3b
4.22b
146b
75. 3b
4. 22b
472
245
13. 7
515
266
15. 0
464
240
13. 5
Total
47. 5b
24. 6b
1.38b
47. 5b
24. 6b
1.38b
694
359
20. 1
737
381
21.4
686
355
19.9
Acre-Feet
Required
for
Disposal,
Annual
11
6
0.3
11
6
0.3
719
372
21
764
395
22
710
367
21
Magnesium-oxide process
Sulfuric acid or sulfur produced, respectively
cAbsorbent make-up
Double-alkali process
"Absorbent (lime) utilization
(continued)
-------
TABLE 2. (Continued)
Case
No.
52
53
54
55
56
57
58
581
59
591
60
601
602
603
6001
Coal
%
S
7.0
7. 0
7.0
7. 0
7.0
7.0
0.8
0.8
0.8
0. 8
0.8
0.8
0.8
0.8
3.5
Btu/lb
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
10, 000
8, 000
10, 000
8, 000
10, 000
8, 000
8, 000
10, 000
12, 000
%
Ash
14
14
14
14
14
14
8
6
8
6
8
6
6
8
14
MW
1000
500
25
1000
500
25
500
500
25
25
500
500
500
500
200
Absorbent
MgOa
MgOa
MgOa
Na2SOJi
Na2S03d
Na2SO3d
Lime
Lime
Lime
Lime
Limestone
Limestone
Limestone
Limestone
Limestone
Absorbent
Utilized,
%
5C
5C
5C
5C
5C
5C
90
90
90
90
80
80
80
80
80
%S
Removed
by
Wash
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
% so2
Removed
by
Scrub
90
90
90
90
90
90
90
90
90
90
90
90
40
25
80
Emissions ,
Ib SOz /
106 Btu
1.2
1.2
1.2
1.2
1.2
1.2
0.2
0.2
0.2
0.2
0.2
0.2
1.2
1.2
1.2
By-Products , Dry,
tons X 103/yr
Ash
222
115
6.4
222
115
6.4
79
74
4.42
4. 14
78
74
74
79
47
Sulfur
Sludge
291b
150b
8.43b
291b
150b
8.43b
33
42
1.87
2.34
37
46
20
10
48
Total
95b
49. 2b
2. 75b
95b
49. 2b
2. 75b
112
116
6.29
6.48
115
120
94. 2
89
95.4
Acre-Feet
Required
for
Disposal,
Annual
22
11
1
22
11
0.6
116
120
7
7
120
124
98
92
99
oo
Magnesium-oxide process
Sulfuric acid or sulfur produced, respectively
Absorbent make-up
Wellman-Lord process
(continued)
-------
TABLE 2. (Continued)
Case
No.
61
611
62
621
63
631
64
641
65
651
66
661
67
68
Coal
%
S
0.8
0.8
0.8
0. 8
0.8
0.8
0.8
0.8
0.8
0.8
3.5
3. 5
3. 5
3. 5
Btu/lb
10, 000
8, 000
10, 000
8, 000
10, 000
8, 000
10, 000
8, 000
10, 000
8, 000
12, 000
12, 000
12, 000
12, 000
%
Ash
8
6
8
6
8
6
8
6
8
6
14
14
14
14
MW
25
25
500
500
25
25
500
500
25
25
500
500
25
500
Absorbent
Limestone
Limestone
Lime
Lime
Lime
Lime
Limestone
Limestone
Limestone
Limestone
Lime
Limestone
Lime
Limestone
Absorbent
Utilized,
%
80
80
90
90
90
90
80
80
80
80
90
80
90
80
%S
Removed
by
Wash
0
0
0
0
0
0
0
0
0
0
40
0
40
40
%S02
Removed
by
Scrub
90
90
70
75
70
75
70
75
70
75
85
91.5
85
85
Emissions,
lb SOz/
106 Btu
0.2
0.2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0. 5
0.5
0.5
0.5
0.5
By-Products, Dry,
tons X 103/yr
Ash
4.41
4. 14
79
74
4.41
4. 14
79
74
4.41
4. 14
69
115
3.87
69
Sulfur
Sludge
2.05
2.56
26
35
1.46
1. 95
28
38
1.59
2. 13
63
135
3. 52
69
Total
6.46
6.70
105
109
5.87
6.09
107
112
6. 00
6.27
132a
250
7. 39b
138a
Acre-Feet
Required
for
Disposal,
Annual
7
7
109
113
6
6
111
116
6
7
137a
260
8^
143a
aDoes not include coal wash tailings: 4. 09 X 104 tons/yr (dry) and 28 acre-ft
Does not include coal wash tailings: 2.29 X 103 tons/yr (dry) and 1.5 acre-ft
(continued)
-------
TABLE 2. (Continued)
Case
No.
69
70
701
702
71
711
712
713
714
715
716
Coal
%
S
3. 5
7.0
7. 0
7. 0
7. 0
7.0
7.0
7. 0
7. 0
7.0
7. 0
Btu/lb
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
12, 000
%
Ash
14
14
14
14
14
14
14
14
14
14
14
MW
25
500
500
500
500
500
500
500
500
500
500
Absorbent
Limestone
Lime
Lime
Limestone
Limestone
Limestone
Limestone
Limestone
Limestone
Limestone
Limestone
Absorbent
Utilized,
%
80
90
90
80
80
80
90
80
80
80
80
% s
Removed
by
Wash
40
40
40
0
40
40
40
30
20
40
40
%S02
Removed
by
Scrub
85
95
92.5
96
95
92.5
92. 5
93.5
94. 5
92.0
92.0
Emissions,
Ib S02/
L
10° Btu
0.5
0.3
0.5
0.5
0.3
0.5
0.5
0. 5
0.5
0.5
0.5
By-Products, Dry,
tons X 103/yr
Ash
3.87
30
30
115
30
30
30
51
72
50
69
Sulfur
Sludge
3. 84
140
136
284
153
149
136
180
214
148
149
Total
7. 71a
170b
166b
399
183b
179b
166b
23ic
286d
198e
218f
Acre-Feet
Required
for
Disposal,
Annual
8a
176°
172b
414
190b
185b
172b
240C
296d
206«
226f
Does not include coal wash tailings: 2. 29 X 10^ tons/yr (dry) and 1. 5 acre-ft
Does not include coal wash tailings: 8. 58 X 10^ tons/yr (dry) and 58 acre-ft
°Does not include coal wash tailings: 6.43 X 10^ tons/yr (dry) and 43 acre-ft
Does not include coal wash tailings: 4. 28 X 10^ tons/yr (dry) and 29 acre-ft
Does not include coal wash tailings: 6.29 X 10"* tons/yr (dry) and 42 acre-ft
Does not include coal wash tailings: 4. 09 X 10^ tons/yr (dry) and 28 acre-ft
-------
TABLE 3. CROSS REFERENCE OF ALTERNATIVE STANDARDS AND MODEL PLANTS
WITH STUDY CASE NUMBERS
Alternative Standards and
Model Plant Systems
1. Meets existing NSPS of 1.2 Ib
SO2/106 Btu heat input
a. 80% SOz removal, plant
burning typical coal with
3. 5% sulfur, 12,000 Btu/lb,
14% ash
b. 90% SO2 removal, plant
burning coal with 7%
sulfur, 12,000 Btu/lb,
14% ash
c. No FGD, low sulfur coal,
typical eastern plant, 0. 8%
sulfur, 13,500 Btu/lb, 6% ash
d. 1 No FGD, low-sulfur coal,
typical western plant, 0.6%
sulfur, 10,000 Btu/lb, 8% ash
d. 2 No FGD, low- sulfur coal,
typical western plant, 0.4%
sulfur, &000 Btu/lb, 6% ash
e. 40% sulfur removal by coal
washing of a 3. 5% sulfur coal,
followed by a 65% SC>2
removal by FGD. Prewash
coal: 12,000 Btu/lb, 14% ash
Plant Sizes,
MW
1000
500
25
1000
500
25
500
25
500
25
500
25
500
FGD
Systems
Lime
Limestone
Double alkali
Magnesium oxide
Wellman-Lord
Lime
Limestone
None
None
None
Lime
Limestone
Case
Numbers
1 - 3
4-6
7-9
10 - 12
13 - 15
16
17
18
19
20
21
22
23
24
25
241
251
26
27
(continued)
-------
TABLE 3. (Continued)
Alternative Standards and
Model Plant Systems
2. 90% SO? removal by FGD
LJ '
a. 1 Plant burning typical 3. 5%
sulfur coal, 12, 000 Btu/lb,
14% ash
a. 2 Plant burning 7% sulfur
coal, 12, 000 Btu/lb,
14% ash
b. 1 Western plant burning
typical 0.8% sulfur
western coal, 10, 000
Btu/lb, 8% ash
b. 2 Western plant burning
typical 0. 8% sulfur western
coal, 8000 Btu/lb, 6% ash
3. Meets more stringent standard
of 0. 5 Ib SO2/106 Btu heat input
a. 1 70% SO2 removal on 0. 8%
sulfur coal, 10, 000 Btu/lb,
8% ash
Plant Sizes,
MW
1000
500
25
1000
500
25
500
25
500
25
500
25
FGD
Systems
Lime
Limestone
Double alkali
Magnesium oxide
Wellman-Lord
Lime
Limestone
Double alkali
Magnesium oxide
Wellman-Lord
Lime
Limestone
Lime
Limestone
Lime
Limestone
Case
Numbers
28 - 30
31-33
34 - 36
37 - 39
40 - 42
43 - 45
46 - 48
49 - 51
52 - 54
55 - 57
58- 59
60 - 61
581 - 591
601 - 611
62 - 63
64 - 65
(continued)
-------
TABLE 3. (Continued)
Alternative Standards and
Model Plant Systems
Plant Sizes,
MW
FGD
Systems
Case
Numbers
3. (continued)
a. 2 75%SC>2 removal on
0.8% sulfur coal,
8000 Btu/lb, 6% ash
b. 1 40% sulfur removal
by coal •washing of a
3. 5% sulfur coal,
followed by a 85%SO2
removal by FGD.
Pre-wash coal: 12,000
Btu/lb, 14% ash
b. 2 40% sulfur removal by
coal washing of a 7%
sulfur coal, followed
by a 95%SO2 removal
by FGD. Pre-wash coal:
12, 000 Btu/lb, 14% ash
500
25
500
25
Lime
Limestone
Lime
Limestone
621-631
641 - 651
66 - 67
68 - 69
500
Lime
Limestone
70
71
-------
2. 1 QUANTIFICATION OF SOLID WASTES
The amount of solid waste or by-products generated by flue
gas desulfurization (FGD) systems is discussed with regard to the following
parameters:
• The present new-source performance standard (1.2 Ib SC>2/10°
Btu)
• Effect of a 0. 5 Ib SO2/106 Btu standard
• Effect of 90-percent SO2 scrubbing
• Coal washing
• Plant size
• Coal sulfur content
• Scrubbing processes
• Nationwide projections to 1998
It should be noted that, for the various study cases, the coal properties
are as summarized in Table 4. Therefore, the results represent typical
values encompassing the range of variations for eastern and western
coals. Assumptions made concerning the basic steam generating plant
characteristics and FGD process characteristics are shown in Tables 5
and 6.
2.1.1 Current Federal Standards: 1. 2 Ib SOz/106 Btu
The current standard of performance limits SO2 emissions to
1.2 lb/l()6 Btu of heat input to the boiler. To achieve this emission limit
with a typical 3. 5-percent-sulfur eastern coal, 80 percent SC>2 removal
by scrubbing is required. The amount of solid waste (ash and sludge)
produced by a. 500-MW power plant with a limestone scrubbing system
(case 5) is 233, 000 dry tons/year or 242 acre-feet by volume. This is
the base case against which other variations in solid waste are considered.
Figure 1 is a graphical presentation of the variations for a 500-MW plant.
14
-------
TABLE 4. COAL CHARACTERISTICS USED IN STUDY
A. Typical Coals
Coal Type
1.
2.
3.
4.
5.
Typical eastern
High sulfur
Typical western low-sulfur
a. High Btu
b. Low Btu
Eastern low -sulfur
Western coal meeting or
bettering current NSPS.
a. High Btu
b. Low Btu
Percent
Sulfur
3.5
7.0
0.8
0.8
0. 8
0.6
0.4
Heating Value,
Btu/lb
12, 000
12, 000
10,000
8, 000
13, 500
10,000
8, 000
Percent
Ash
14
14
8
6
6
8
6
B. Effect of Coal Washing
Coal Type
1. Typical eastern
2. High sulfur
Sulfur
Removed,
Percent
40
40
Percent Sulfur
Unwashed
3.5
7.0
Washed
2. 1
4.2
Heating Value,
Btu/lb
Unwashed
12, 000
12, 000
Washed
13,200
13,200
Percent Ash
Unwashed
14
14
Washed
9.2
4.0
-------
TABLE 5. BASIC STEAM GENERATING PLANT CHARACTERISTICS
USED IN STUDY
1. Energy Conversion Factors
a. 1000 MW 8,700Btu/kWh
b.
c.
500
25
9,000
10,080
2. Average Power Plant Operating Load Factor
a. 50 percent
b. 30-year operating lifetime
TABLE 6. BASIC SCRUBBER AND FGD PROCESS CHARACTERISTICS
USED IN STUDY
1. Absorbent Utilization
a. Non-Regenerable
(1) Lime
(2) Limestone
(3) Lime in double-
alkali process
b. Regenerable
90%
80%
95%, with 3% Na2CO3
make-upa
(1) Magnesium oxide
(a) 3% absorbent make-up (MgO)
(b) 95% separation efficiency
(2) Wellman-Lordb
(a) 3% absorbent make-up (
(b) 95% separation efficiency
Percent (molar basis) of the absorbent lost in the regeneration process.
Percentage based on the fraction of the amount of absorbent required to
scrub the
Percent (molar basis) of the absorbent lost in the absorption, regeneration,
and separation processes, including: 3% (absorbent equivalent) lost in the
absorption-regeneration process due to its inefficiency and an additional
5% (absorbent equivalent) lost in the separation process due to its inef-
ficiency (see Figure 3 for a schematic of the magnesium oxide and
Wellman-Lord processes).
16
-------
4.0
3.0
2.5
LTl
O
X
Cd
LjJ
ce:
Q* 2.0
LjJ
O
Z3-
O
O
1.5
o
LO
1.0
0.5
BASIS: 500
D
PLANT: ALL PROCESSES
LIMESTONE WET SCRUBBING NON
A)80% LIMESTONE UTILIZATION 1 REGENERABLE
O\ MAGNESIUM OXIDE AND WELLMAN LORD
O/PROCESSES: REGENERABLE
COAL WASH (40% S REMOVAL)
TAILINGS DISPOSED AT MINE
REGENERABLE PROCESSES-
-
COAL
% S
7.0
3.5
0.8
Btu/lb
12,000
12, 000
8,000
% ASH
14
14
6
% S02 SCRUBBED
1.2 Ib S02/106Btu
90
80
25
0.5 Ib S02/106Btu
92.5*
85 *
75
Ib S02/106 FOR
90% S02 SCRUBBING
1.2
0.6
0.2
:Coal washed to remove 40% sulfur prior to burning
i i i i i i i
3 4
% SULFUR
COAL
Figure 1. Quantities of waste, including ash, produced by
new plants for alternative standards
17
-------
With a 7-percent-sulfur coal, 90 percent SO2 removal by
scrubbing is required. In this case (case 20) a 500-MW power plant with
a limestone scrubbing system would produce 381, 000 tons/year of ash and
sludge or 395 acre-feet by volume. A coal with 0. 6 percent sulfur and at
a heating value of at least 10, 000 Btu/lb is needed to avoid the necessity
of a FGD system (case 24).
2.1.2 Effect of a 90 Percent SOz Removal Requirement
The quantities of solid waste or by-products resulting from
90-percent removal of SO2 are presented in cases 28-61 and 581-611.
The solid waste from a 500-MW plant burning 3. 5-percent-sulfur coal
with 90 percent SC>2 removal by limestone scrubbing (case 32) is increased
6 percent above the base case (case 5).
2.1.3 Effect of a 0. 5 Ib SO2/106 Btu Standard
A performance standard of 0. 5 Ib 302/10^ Btu heat input
would necessitate the scrubbing of virtually all coal burned.
The quantities of solid waste or by-products resulting from
a standard of 0.5 Ib SO2/106 Btu heat input are presented in cases 62-71
and 621-716. A 500-MW plant burning 3. 5-percent-sulfur coal would
require 91. 5-percent sulfur removal by scrubbing to meet this emission
limit., The solid waste from this system is only slightly greater than for
the 90-percent removal requirement.
20 1.4 Effects of Coal Washing on Quantities of Waste Produced
Only the inorganic fraction, primarily from pyrite (FeS2) of
the sulfur content can be removed by coal washing. Organic sulfur is an
integral part of the coal matrix and cannot be removed by physical separa-
tion. Organic sulfur is 30 to 70 percent of the total sulfur for most coals.
It appears that the maximum sulfur removal that can be achieved by phys-
ically washing the coal is limited to about 40 percent.
Although coal washing would not eliminate the need for flue
gas scrubbing, the required SO2 removal could be reduced from 80 to 60
percent for the current standard (1.2 Ib SO2/10^ Btu) and from 91. 5 to
85 percent for a standard of 0. 5 Ib SO2/106 Btu. Scrubber sludge and
ash at a power plant burning washed coal (40 percent sulfur removed) would
be about 56 percent (and wash tailings would be another 16 percent) of the
amount of sludge, including ash, from a plant burning unwashed coal.
Iron combined with the sulfur and other ash constituents in the
coal are removed by washing, reducing the ash in the washed coal consid-
erably; i.e., 14 percent to 9.2 percent for a 3. 5-percent-sulfur coal
(Table 4). Although a loss in heating value is experienced in coal washing,
18
-------
it is accompanied by a greater proportionate loss in weight (inerts) and,
therefore, the heat content per pound of washed coal increases. Based on
sulfur reduction data, a nominal upgrading of 10 percent was used in the
heat content after washing; i. e. , the removal of 40 percent sulfur by wash-
ing of a 12, 000-Btu/lb coal increased its heating value to 13, 200 Btu/lb.
Although coal washing could apparently reduce solid waste
(sludge plus ash) at the power plant about 44 percent, consideration must
be given to:
a. Disposal of wash tailings (assumed to take place at the mine)
b. Disposal or treatment of the wash process water
c. The increased cost of washed coal over run-of-mine coal
d. The energy required to wash the coal
e. The cost tradeoff of using flue gas desulfurization (FGD) alone
versus coal washing plus FGD.
These aspects of coal washing are covered in this and other reports pre-
pared as part of the EPA review process.
If a 3. 5-percent-sulfur coal is physically washed to remove
40 percent of the pyritic sulfur, sulfur removal by scrubbing could be
reduced to 65 percent to meet the present NSPS (1.2 Ib SO2/106 Btu). The
quantity of scrubber sludge generated in case 27 is 48 percent below case
5, while tailings [pyrites (FeS2) and ash] at the wash site amount to 21
percent of the waste produced in case 5.
If 40 percent of the sulfur is washed from a 3. 5-percent-sulfur
coal, 85-percent-removal by scrubbing is required to meet a standard of
0. 5 Ib SO2/106 Btu. The solid waste (sludge, ash, and tailings) produced
(case 68) would be 77 percent of that in case 5.
2.1.5 Effect of Plant Size on Quantities of Waste Produced
The wastes generated by power plants of different sizes are
not directly proportioned to size (Figure 2). This is the result of higher
operating efficiencies achieved by the larger plants. Therefore, a single
1000-MW plant produces wastes totalling approximately 96. 5 percent of
two 500-MW plants, and two 250-MW units produce about 1.8 percent
more waste than one 500-MW unit. Therefore, in the range of most
utility steam generating plants; i.e., 200 to 1000 MW, the amount of
•waste generated and disposal area required is within +2 to -4 percent
of that produced by equivalent numbers of 500-MW units. This observation
19
-------
1.15 r
00
a:
O
<
LU
C£
00
O
Q_
00
O
O
<
O
G
o
Q_
UJ
oo
1.10
1.05
1.00
0.95
0.90
PLANT SIZE,
MW
1000
500
200
25
HEAT RATE,
Btu/kWh
8700
9000
9200
10080
I I
100 200 300 400 500 600 700 800 900 1000
PLANT SIZE, MW
Figure 2. Effect of power plant size and equivalent capacities
on the amount of solid wastes produced (includes
ash).
20
-------
is important in the nationwide assessment of total quantities of waste
produced because it substantiates the assumption that all the installed
generating capacity can be characterized by an equivalent 500-MW plant
and the study does not require a plant-by-plant summation.
2.1.6 Effects of Coal Sulfur on Quantities of Waste Produced
The coals specified for the study (3) were typical. The eastern
coals contained 3. 5 percent sulfur and high sulfur (7. 0 percent), both con-
taining 14 percent ash and a heat content of 12, 000 Btu/lb. The western
coals contained 0.8 percent sulfurl and included both high- and low-Btu:
10,000 Btu/lb (8-percent ash) and 8, 000 Btu/lb (6-percent ash), respectively.
Since sulfur content is the primary variable, its influence on the
quantities of waste requiring disposal as a function of both current and more-
stringent NSPS federal standards is depicted in Figure 1. Limestone scrubber
•wastes are represented as typical of nonregenerable processes; the quantities
being about 6 percent more than lime or double alkali. Because of the differ-
ences in ash and heat content, boiler heat rates, and SC>2 scrubbing require-
ments, the quantities and disposal area are not directly proportional to the
sulfur content. However, as a first approximation, they may be estimated
as being linearly related.
The waste quantities resulting from the application of regenerable
processes are relatively unaffected for the 3. 5- and 7. 0-percent sulfur cases
studied. The wastes are primarily ash recovered from the combustion of the
coal; both coals containing 14 percent ash. The slightly higher quantity of
wastes for a 7-percent sulfur coal is attributed -to thje slightly higher quanti-
ties of absorbent make-up showing up in the waste because of the larger
quantities of SC>2 being scrubbed (the percent absorbent make-up was held
constant at 3 percent).
The low-Btu western coal (8000 Btu/lb) was used in all calcu-
lations for western coal because it produces only about 5 percent more wastes
than the higher (10, 000 Btu/lb) coal (Table 7). In general, these two coals
represent the high and low extremes expected for western coals. Because of
The coal sulfur values used are base-case averages. Any coals that
may contain these average sulfur contents would meet the NSPS (1.2 lb/
100 Btu) on the average if subjected to appropriate scrubbing conditions,
but may violate it occasionally because of variations in the coal. This
factor does not impact the values for sludge quantities derived herein.
21
-------
TABLE 7. EFFECT OF HIGH- AND LOW-BTU WESTERN COAJL
ON WASTE GENERATED AND DISPOSAL AREA
REQUIRED
A. 90% SO2 Removal, Wet Limestone Scrubbing, 0.8% Sulfur Coal
Case
No.
60
601
Coal
Btu/lb
10, 000
8, 000
% Ash
8
6
Emissions ,
Ib SO2/106 Btu
0. 16
0. ZO
Scrubber
Dry Wastea,
tons x 1 0 /yr
1. 154
1. 196
Disposal
Area
Req'db,
acres
150
155
Quantity and
Volume
Factor
0.965
1. 000
B. Emissions = 1.2 Ib SO2/10b Btu, Wet Limestone Scrubbing, 0.8% Sulfur Coal
Case
No.
603
602
Btu/lb
10, 000
8,000
% Ash
8
6
% SO2 Scrubbed
25
40
Scrubber
Dry Wastea,
tons x. 10^/yr
0. 890
0.942
Disposal
Area
Req'db,
acres
] 15
122
-
Quantity and
Volume
Factor
0.945
1. 000
500-MW plant, 50-percent operating load factor, includes ash.
50-percent solids, 30 years, 50-percent load factor, 30 ft deep.
22
-------
this small difference in quantities produced as a result of burning these
extremes of western coal, no attempt was made in the nationwide compila-
tion to estimate the fraction of each that may be burned in the future, and
the low-Btu coal was used in all of the projections.
In reviewing the effects of the use of western coal, the low-Btu
coal (0.8% sulfur, 8000 Btu/lb, 6% ash) produces scrubber waste quantities
of 40 to 50 percent of the corresponding limestone-scrubbed 3.5-percent
coal.
2.1.7 Effects of the Scrubbing Process on Quantities of Waste
Produced
The basic types of wet scrubbing processes examined were the
nonregenerable and regenerable processes. The nonregenerable produce a
calcium sulfite/sulfate •waste that is discarded, while in the regenerable the
SO2 in the flue gas is absorbed and subsequently released as SC>2 in the
regeneration of absorbent. The SO2 may be processed further to form
sulfuric acid or elemental sulfur.
The types of nonregenerable processes studied were those using
lime and limestone absorbents. The double-alkali process uses a sodium
carbonate (NazCO^) absorbent, -which is then regenerated by lime. The
waste produced is similar to that produced by the direct lime scrubbing
except that it contains Na2CC>3 that is equivalent to the amount of make-up
required (3 percent).
Figure 3 provides the quantities of waste produced from the
five processes as a result of applying the current and alternative federal
NSPS standards with 3. 5-percent coal.
2.1.7.1 Nonregenerable Processes --
Use of the limestone wet scrubbing processes results in approxi-
mately 6 percent more scrubber waste than the lime or double-alkali proc-
esses. The slightly lower quantities are primarily the result of the higher
lime utilization in the latter two processes. An absorbent utilization of 80
percent was considered typical for limestone, whereas 90 percent was used
for the lime process and 95-percent regenerative efficiency for lime in the
double-alkali application.
2.1.7.2 Regenerable Processes --
The wastes produced as a result of applying the regenerable
processes are approximately 50 percent of those from the nonregenerable.
The wastes are primarily ash and are nearly independent of the process.
A regenerative-separation efficiency of 95 percent was assumed. Therefore,
the waste was assumed to include sulfate of magnesium and sodium equiva-
lent to 5 percent of the magnesium sulfite (MgSC^) or sodium bisulfite
(NaHSOs) which was assumed as not being regenerated.
23
-------
90% S02 REMOVAL
1.1
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REFERENCE CASE: LIMESTONE SCRUBBER
"Waste
WASTE FOR 1.2 Ib S02/100 Btu
primarily ash
"Quantities represent H2S04or Sulfur
(not both) from either Magnesium Oxide
or Wellman Lord Processes
#*#
'Tailings from coal washing (40% sulfur
removal) disposed at mine site
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Figure 3. Solid waste, including ash, and useable by-products
(nonregenerable and regenerable systems)
24
-------
2.1.8 Nationwide Projections to 1998
Applying a 90-percent SO2 removal requirement to all new
plants in 1980 will result in the production of approximately 173 million
short tons (dry) of wastes in the year 1998 (Table 8). The actual quantities
of untreated wastes that would require disposal are approximately double
that quantity, assuming that they contain approximately 50-percent moisture.
This results in a volume of 179, 000 acre-feet (wet) produced in those plants
in 1998. The estimate is based on the assumption that eastern (3. 5 percent
sulfur) coal will be burned in 55 percent of the new boiler installations and
45 percent will consume western coal (0.8 percent sulfur (Table 1).
These values were computed on the basis that 45 percent of the
coal burned on a nationwide basis is western coal (4). However, application
of more stringent standards would possibly affect the percentage used. Since
predictions of the impacts of these standards on western coal usage were not
available, the waste quantities resulting from the use of discrete fractions of
eastern coal were computed and are summarized in Figure 4. For example,
if the amount of coal from eastern sources were increased from 55 to 70 per-
cent (western coal use reduced from 45 to 30 percent), the tonnages of eastern
waste v/ould increase from 73 to 83 percent of the nationwide total,for 90 per-
cent SC>2 removal.
The wastes to be disposed of at the generating plants in the year
1998 to meet a 0. 5 Ib SC>2 standard are 118 million short tons (dry) (see Fig-
ure 5). This considers that the eastern coal (3.5 percent sulfur) comprises
55 percent of the total coal used nationally and is washed to remove 40 per-
cent of its sulfur.
Comparable quantities, if the current NSPS were maintained in
1998, are 156 million short tons (dry). Volumes produced are proportional
to those given above.
The volume in acre-feet of nonregenerable scrubber wastes, pri-
marily ash, produced during a 30-year steam generating plant lifetime is shown
in Table 9 for 1000-, 500-, and 25-MW plants burning eastern and western coal,
and assuming that current and two alternative emission standards apply.
2. 2 CHARACTERIZATION OF UNTREATED WASTES
The published data available on the chemical and physical charac-
teristics of untreated sludges produced in eastern and western plants using
lime, limestone, and double-alkali systems are provided in this report. The
waste streams from regenerable systems are primarily fly ash, which is dis-
cussed briefly in Volume II, and purged liquid effluents, the properties of which
are not discussed in this report. Properties discussed are: solids composition
and concentrations in the liquor of major species and trace elements; pH; total
dissolved solids; leaching characteristics; water retention; bulk density; com-
pressive strength; permeability, viscosity; compaction; and porosity. All
properties are widely variant depending on parameters such as types of: coal,
absorbent, scrubber, scrubber operating parameters, and ash collection. The
characteristics included in this report are summarized from various sources.
Key items from that summary are given in the following pages.
25
-------
TABLE 8. QUANTITY AND VOLUME OF NONREGENERABLE SO2
SCRUBBER WASTES PRODUCED IN 1998 BY NEW COAL-
BURNING PLANTS CONSTRUCTED BETWEEN 1978 AND
1998a
NSPS
Alternatives
90% SO2 Removal
0.5 Ib SO2/106 Btuf
1.2 Ib S02/106 Btu
Dry Waste
Quantitiesb'c'd
(short tons)
172. 8 x 106
118.3 x 106
156.2 x 106
Total Wet Volume6
(acre-ft)
For Sludge
Produced in 1998
1.79 X 105
1.22 x io5
1. 62 x IO5
aData derived from Appendix B, Vol II.
Quantities produced, based on:
500-MWe average plant size.
50-percent average operating load factor.
Limestone absorbent, 80% utilization.
Waste includes ash.
Eastern0 coal burned: 55% of total.
Western0* coal burned: 45% of total.
°Eastern coal: 3. 5% S, 12, 000 Btu/lb, 14% ash
dWestern coal: 0.8%S, 8000 Btu/lb, 6% ash
Based on sludge containing 50% solids.
40% of sulfur in eastern coal removed by washing prior to burning,
85% SO2 from eastern plants removed by scrubbing, and 40% SO2 from
western plants removed by scrubbing.
26
-------
o
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90% S02 REMOVAL
0.5-lb S02/106 Btu
THE 0.5 Ib S02/ 10 Btu ALTERNATIVE DOES NOT
INCLUDE COAL WASH TAILINGS
i i i
i i i
i i i
i i i
0 20 40 60 80 100
EASTERN COAL BURNED, % OF ALL COAL
Figure 4. Effect of eastern coal use on the fraction of waste
quantities, including ash, produced nationally
by new plants
27
-------
180 -
170 -
160
150
140
°2 130
X
z 120
o
110
100
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BASIS: NON REGENERABLE SCRUBBING
500 MW PLANTS, 50%
OPERATING LOAD FACTOR
APPLICATION OF
ALTERNATIVE STANDARDS,
YEAR
ALTERNATIVE
STANDARDS
90% S02
REMOVAL
1.2 Ib S02/106 Btu
0.5 Ib S02/10 Btu
(SCRUBBER WASTE)
T—
30 82
— • —
i
84
. — • —
i
86
•
i
88
— — '
i
90
I
92
i
94
((.
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96 98
0.5 Ib S02/10 Btu
(COAL WASH TAILINGS)
Figure 5. Total annual waste quantities, including ash, produced
nationwide by all new plants coming on line be sinning
in 1978
28
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TABLE 9. VOLUME (ACRE-FEET) OF NONREGENERABLE SOz SCRUBBER WASTES
PRODUCED IN A 30-YEARa GENERATING PLANT LIFETIME
Plant
Size,
MW
1000
500
25
Eastern Coalb
Western Coalb
NSPS Alternatives
1.2 Ib S02
per 106 Btuc
14, 030
7,260
405
90% S02
Removal^
14, 920
. 7,720
430
0.5 Ib SO2
per 106 Btue
Sludge
NR
4280
240
Coal wash
Tailings
830
45
1.2 Ib S02
per 106 Btuf
NR
2930
NR
90% S02
Removal^
NR
3720
210
0. 5 Ib SO2
per 106 Btuh
NR
3480
195
ro
o
50-percent average operating load factor; limestone absorbent, 80% utilization; waste includes ash.
bEastern coal: 3. 5% S, 12, 000 Btu/lb, 14% ash; Western coal: 0.8% S, 8000 Btu/lb, 6% ash.
y-»
80% SO2 removal by scrubbing
d0.6 Ib S02/106 Btu
e40% sulfur removal by coal washing, 85% SO2 removal by scrubbing
40% SO2 removal by scrubbing
g0.2 Ib S02/106 Btu
75% SO2 removal by scrubbing
NR - Not required (see Table 3)
-------
2. 2. 1 Effect of Scrubbing Process Variables on
Sludge Chemistry
Process variables affect the concentrations of soluble chemical
species in system liquors through changes in process chemistry:
a. The concentration of major chemical species and trace elements
in flue gas desulfurization (FGD) waste decreases as the sludge
passes from the scrubber to the clarifier underflow for disposal.
Concentrations of sludge constituents for disposal are given in
Table 10.
b. The pH in the scrubber is responsible for trace elements leach-
ing from fly ash; the pH of the system downstream of the scrubber
does not affect the concentration of these trace elements in the
scrubber liquor.
2.2.2 Trace Element Content
The trace element content in FGD sludge is a direct function of the
combustion products of coal:
a. A direct correlation exists between the trace element content
of coal and the trace element content in FGD wastes (see
Figure 6).
b. Fly ash represents the major source of trace elements in all
but the most volatile elemental species (e.g., mercury and
selenium) that are scrubbed from flue gases.
2. 2. 3 Physical Properties
The behavior of FGD wastes in a disposal site is a function of
the unique physical properties of the wastes:
a. The permeability coefficients of untreated FGD wastes are
typically 10"4 cm/sec and of treated wastes are 10"^ cm/sec
or less [based upon sample materials fixed by Chemfix, Dravo,
and IU Conversion Systems (IUCS)].
b. Pumpability (<20 poise) was found for untreated wastes having
a solids content that ranged between 32 and 70 percent.
c. Bulk densities of untreated wastes as a function of dewatering
techniques and material characteristics varied between 1.30
and 1.87 g/cc.
30
-------
TABLE 10.
RANGE OF CONCENTRATIONS OF CHEMICAL
CONSTITUENTS IN FGD SLUDGES FROM LIME,
LIMESTONE, AND DOUBLE-ALKALI SYSTEMS
Scrubber
Constituent
Aluminum
Arsenic
Beryllium
Cadmium
Calcium
Chromium
Copper
Lead
Magnesium
Mercury
Potassium
Selenium
Sodium
Zinc
Chloride
Fluoride
Sulfate
Sulfite
Chemical oxygen
demand
Total dissolved
solids
PH
Sludge Concentration Range3-
Liquor,
(except
0. 03
<0.004 -
<0.002 -
0. 004 -
180
0.015 -
< 0.002 -
0.01
4.0
0.0004 -
5.9
< 0.0006 -
10.0
0.01
420
0.6
600
0.9
< 1
2800
4.3
mg//
pH)b
2.0
1.8
0. 18
0. 11
2600
0.5
0.56
0.52
2750
0.07
100
2.7
29,000
0.59
33,000
58
35,000
3500
390
92, 500
12.7
Solid,
_
0.6
0.05
0.08
105, 000
10
8
0.23
-
0.001
-
2
-
45
-
-
35, 000
1600
-
-
mg/kgc
_
- 52
- 6
- 4
- 268,000
- 250
- 76
- 21
-
- 5
-
-17
- 48, 000
- 430
- 9, 000
-
- 473, 000
- 302, 000
-
-
-
Data derived from Appendix D, Vol II.
Liquor analyses were conducted on 13 samples from seven power plants
burning eastern or western coal and using lime, limestone, or double-
alkali absorbents.
CSolids analyses were conducted on 6 samples from six power plants
burning eastern or western coal and using lime, limestone, or double-
alkali scrubbing processes.
31
-------
oo
tSJ
400 r
100
o
o
10
id
UJ
LU .
o 1
0.1
0.01
LEGEND:
O ARSENIC • MERCURY
D BERYLLIUM 0 COPPER
A CADMIUM ® LEAD
V CHROMIUM H SELENIUM
^ ZINC
I I I
I I I
I I I I
0.1 1 10 100
AVERAGE TRACE ELEMENT CONTENT OF SLUDGE SOLIDS, ppm
1000
Figure 6. Average trace element content of sludge solids.
-------
d. Compaction of untreated sludges dewatered to about 80 percent
solids produced permanent displacement of 1 to 4 percent.
e. Treated wastes have unconfined compression strength greater
than 1.8 tons per square foot (25 psi).
2.2.4 Chemical Properties
Lime and limestone FGD sludge liquors typically have approxi-
mately 10,000 mg/jj total dissolved solids (TDS). Double alkali scrubber
sludge liquors from unwashed filter cake leave a much higher TDS, in excess
of 50, 000 ppm. When the cake is washed with water to remove soluble sodium
salts, the TDS concentration tends to approach that of the lime and limestone
sludge liquors. Trace elements lie typically between 0.01 and 1 mg/j? depend-
ing on coal content and fly ash collection techniques.
The leachate quality of rainwater percolated through untreated
FGD waste attains a nearly constant TDS content of 2000 mg//, primarily
sulfate salts, after passage of five pore volume displacements (PVD).
Initial leachate content is as high as the soluble chemical content and is
dependent upon the type of FGD system.
Chemical treatment has been found to have major benefits which
effectively minimize (and possibly, in some cases, virtually eliminate) the
release of leached sludge constituents to the subsoil through (a) the decreased
permeability of the treated material, and (b) the amenability of the treated
material to compaction and contouring during placement so that standing
water does not occur on the disposal site. The prevention of standing water
avoids having a hydraulic head on the site and, therefore, seepage through
the pores does not occur as a result of hydraulic pressure. This is accom-
plished by managing the site so that a major portion of the rainfall on such a
site runs off and is collected in a peripheral ditch which directs the water to
a settling pond, from which decanted liquor is disposed of in an adjacent
stream, if acceptable, or returned to the power plant water reuse system.
2. 3 POTENTIAL ENVIRONMENTAL IMPACTS OF DISPOSAL,
PROCESSES AND PRACTICES
It has been determined that the chemical and morphological
properties of untreated waste tend to be a function of the coal and, more
importantly, a function of the scrubbing process variables. The morphology
tends to establish the settling and dewatering characteristics of a particular
slurry. Detailed characterization of scrubber solids as a function of scrubber
operating parameters on the properties and work in that area is being con-
ducted (4) under EPA. funding. Furthermore, chemically treated waste
characteristics are also dependent on the treatment process itself.
33
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Prime factors to be considered in the disposal of FGD wastes are as
follows:
a. Structural Strength: Because of the rheological and structural
characteristics of untreated wastes, personnel and equipment
safety cannot be ensured. Treated material, depending on the
treatment process and the solids content, can be expected to
achieve strengths in excess of those considered minimal for
supporting personnel and equipment and, in some cases, build-
ing structures. The long-range effect of weathering on strength,
i. e., wet-dry and freeze-thaw cycling, is yet to be defined.
b. Permeability. Permeability coefficients of untreated materials
range from 2 X 10~4 to 5 X 10~5 cm/sec. Chemical treatment
tends to lower these values over a broad range (from negligible
to several orders of magnitude) depending on the process,
chemical additive, and the solid content of the treated material.
The long-range effect of weathering on permeability is yet to be
determined.
c. Leachate Concentration. Laboratory and field leaching data
show that leachate concentrations of major species in the
leachate from fixed materials are about 25 to 50 percent of the
concentrations of major species in untreated materials.
d. Leachate Mass Release. The mass release of major constit-
uents into the soil from chemically fixed materials is reduced
as a result of lower permeability of the treated wastes, a
reduction of the solubility of major pollutant constituents, and,
in some cases, a minimization of seepage by controlled runoff.
The treatment process and mode of disposal, i. e. , landfill or
lake, determine the mass loading of pollutants into the soil,
which can amount to reductions of one to several orders of
magnitude when compared to untreated materials.
e. Soil Attenuation Effects. The extent that trace elements and
other chemical constituents of FGD wastes may be attenuated in
soils or their mobility to migrate through soils at land disposal
sites is being studied by the U. S. Army under EPA sponsorship
(4). Soil and waste characterization tests are complete. How-
ever, work has not progressed to the point where quantitative
information on the migration and attenuation of FGD waste
constituents has been determined.
34
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f. Liner Evaluation. An experimental program to determine the
compatibility and effectiveness of 18 liner materials with FGD
wastes, liquors, and leachates is under way. Material screen-
ing tests have been conducted. Materials have been selected,
and testing has begun in test cells. Since the exposure of
materials to various wastes has been limited and definitive
information is not available at present, a 2-yr exposure is
planned. The economics of FGD disposal by ponding will also
be assessed.
g. Waste Dewatering Methods. Studies are being conducted to
determine dewatering characteristics of FGD wastes and to
define areas where improvements can be made in dewatering
equipment or techniques. Since the program is in its early
stages, quantitative information is not available. However,
results from this work are expected to be used in assessing
benefits derived from a reduction of: dewatering equipment
size, waste volume handled, disposal acreage, and chemical
additives.
h. Field Disposal Evaluation. A project to evaluate and monitor
the field-site disposal in indigenous soil impoundments of
untreated and treated FGD wastes has been under way for over
3 yr at the TVA Shawnee power plant site (5). Its purpose is
to determine the effects of several scrubbing operations, waste
treatment methods, disposal techniques, soil interactions, and
field operation procedures. Test samples of treated and
untreated wastes, groundwater, surface water, leachate, and
soil cores are being analyzed in order to evaluate the environ-
mental acceptability of current disposal technology.
The analysis of groundwater shows no indications of increases
in concentration levels attributable to the presence of any of
the ponds.
The total dissolved solids (TDS) and the concentration of major
constituents in the supernates of the untreated ponds decreased
with time from initial values corresponding to the values
measured in the input liquor. After the initial decrease, fluctu-
ations were observed in which concentrations increased during
dry weather and decreased again when increased rainfall caused
additional dilution. For the treated ponds the concentrations of
major constituents and TDS in the supernate varied as a function
of dry and wet weather during the monitoring period and did not
exceed values of one-half to two-thirds of the corresponding
concentration of the constituents in the input liquor.
35
-------
Generally, the TDS, SC>4, Ca, and Cl in the leachate from
untreated ponds reached the input concentration and decreased
steadily thereafter to a level approximately one-half the concen-
tration of the input liquor. Minor constituents whose concentra-
tions span a range of six orders of magnitude were relatively
constant over the period monitored. The analyses of leachate
from the ponds containing treated sludge show data trends
similar to the untreated ponds; however, TDS levels consistently
remain at a level approximately one-half of the levels found in the
input liquor. Six minor constituents remained at relatively con-
stant levels throughout the monitoring period, with the exception
of the boron level in one treated site which increased steadily to
a level approaching that of the input liquor.
An evaluation of the environmental effects of settling and the
structural characteristics of disposing of untreated lime wastes
in underdrained field impoundments at the Shawnee site were
initiated in late 1976. Monitoring of underdrained limestone and
gypsum evaluation sites started in early 1977.
Other field evaluations of FGD waste test impoundments and full
scale disposal sites are in early stages of implementation by
Louisville Gas and Electric and the U.S. Army Corps of
Engineers (4).
It is apparent that each disposal site and the material placed in
it have individual characteristics different from most others. These include
waste material properties, weather, topography, soil characteristics, and
nearby stream quality and flow characteristics. Therefore, the disposal
method chosen for any site will generally be selected on site-specific
conditions. Because of this, the establishment of a single criterion for all
cases may be overly conservative in one location and not stringent enough
in another.
Various disposal and waste conversion processes and practices
are capable of minimizing environmental impacts on aquifers and ground-
waters. These are discussed in subsequent sections and include:
a. Ponding of untreated waste, with various alternatives
b. Chemical treatment of waste, and landfill disposal
c. Mine disposal of untreated waste
d. Ocean disposal of treated waste.
36
-------
Processes that produce useable products that minimize or reduce the dis-
posal of wastes include:
a. Conversion to gypsum for wallboard and other uses
b. Production of sulfur or sulfuric acid
c. Use as a synthetic aggregate
2. 3. 1 Ponding
The method that represents the least deviation from state-of-the-
art fly ash disposal is direct ponding of untreated wastes into a disposal
basin. The environmental impact of pond disposal is strongly dependent upon
the ability (a) to contain the components of a sludge so as to prevent environ-
mental pollution, and (b) to retire the disposal site in a manner that does not
create a safety hazard or nuisance in subsequent land use. For pond disposal
the environment can be protected from chemical pollution, principally from
leachate contamination of groundwater, by lining the pond basin with elasto-
meric material or impermeable clay. Some natural clay deposits have suffi-
ciently low permeabilities (effectively impermeable) that sludge disposal
can be safely contained in a natural basin. If an impermeable base is not
used, it is expected that not all trace elements will be attenuated by the sub-
soil. Additionally, soils do not significantly attenuate chloride or sulfate
ions.
The disposal site may be reclaimed either by maintaining the
pond as a lake or by allowing the sludge to dry and covering it with soil
overburden. To maintain the retired disposal basin as a lake, it is neces-
sary to provide a balance between water loss and water input. The water
loss will be by evaporation, and, when no liner is used or when a breach is
developed in the liner, loss also occurs by percolation through the subsoil.
Precipitation in excess of loss requires a means for eliminating excess
water, which must be monitored.
If a pond is reclaimed by air-drying the sludge and covering it
with a soil overburden, certain restrictions may limit reuse of the land.
Proper contouring to control rainfall runoff to minimize percolation of
water through the overburden will be necessary to avoid resaturating the
sludge. Therefore, using site management, it may be possible to dispose
of untreated FGD sludge by ponding in an environmentally acceptable
manner.
Another ponding alternative to dispose of untreated FGD waste
is by including provision for pond underdrainage. This method retains the
advantage of transferring the sludge to the disposal site by liquid transfer.
37
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The leachate from the base of the sludge is returned to the scrubber. The
advantages of this method may be economic and environmental. By elimi-
nating a supernate head above the sludge most of the time, and minimizing
it for short periods after rainfalls, percolation of sludge leachate into the
subsoil can be avoided during the active fill period. Tests have shown
drained sludge to have structural qualities adequate to support lightweight
construction equipment. To retire the disposal site, only several days of
air drying after a rainfall are needed before covering with topsoil. Subse-
quent cover contouring is necessary for the reasons discussed in ponding,
but the underdrainage system provides a means of sampling and elimination
of leachate if required to prevent groundwater contamination. Significant
economic advantages of this method could be its relative reclamation poten-
tial and the elimination of the requirement for a disposal basin liner. Evalu-
ation of this technique is continuing in EPA programs (5, 6).
2. 3. 2 Chemical Treatment
FGD sludge may be treated chemically by several processes,
and can typically be used in landfill applications. Chemical treatments
such as those offered by IU Conversion Systems, Inc. (IUCS), Dravo, Inc. ,
and the Chemfix process vary in terms of the chemical additives used to
physically stabilize the sludge, reduce its permeability, and also reduce
the release of chemical constituents into water permeating through the
treated material.
An evaluation of these three processes (7) indicates thai the
soluble salt content in the leachate from treated sludges is typically one-
half or less than that of the untreated sludge. Additionally, the permeability
of the treated sludge appears to be at least one order of magnitude less than
that of the untreated sludge. Therefore, the dissolved salts that may be
leached from chemically treated sludge and available to the environment
are considerably less in concentration and mass than from untreated sludge.
For every process examined, the structural stability of the
treated sludge exceeded that of the untreated sludge. The treated sludge
texture ranged from soil-like to concrete-like and developed strength equal
to or in excess of natural soils. Restrictions on subsequent land use will
depend upon local conditions and the long-time stability of the treated sludge.
Laboratory data have not been developed by any source from which it -would
be possible to predict the time-dependent stability of treated sludge.
Chemically treated sludges can be used as landfill in submerged
and above-grade conditions. In the submerged condition, the sludge may
serve as a lake bottom; however, the constant hydraulic head requires a
continuing monitoring of local streams to detect any possible leakage from
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the site. In an above-grade condition, the material can be placed and com-
pacted such that rainwater does not penetrate the surface and a leachate is
not produced. However, provisions are generally required to manage run-
off from these sites. The potential environmental impact of treated sludge
is less than that of untreated sludge under most disposal methods, although
the added assurance afforded by the chemical process increases the cost of
disposal.
2. 3. 3 Mine Disposal
In a study (8) assessing the technical, environmental, and eco-
nomic factors associated with mine disposal of FGD wastes, four general
categories of mines were examined: active surface-area coal mines, active
underground coal mines, inactive or mined-out portions of lead or zinc
mines, and inactive or mined-out portions of active underground limestone
mines. In addition to the environmental impacts, each category was
reviewed with regard to: the alternatives for placement, the physical prop-
erties of FGD wastes that would be suitable, the operational impacts, the
capacities, and the availability and accessibility (via transportation sys-
tems) for FGD waste disposal. As a result of this review, the following
mines were determined most promising:
a. Active Interior Region surface-area coal mines
b. Active Eastern and Interior Region room-and-pillar underground
coal mines
In general, Interior region surface-area coal mines appear to
be more promising than western (Rocky Mountain and Pacific Coast) surface-
area coal mines. However, surface-area mines both in the Interior and
the West were considered much more promising than eastern surface con-
tour mines, because of the latter's relatively low capacity for FGD wastes
and, in many cases, the difficulty for waste placement in contour mines.
Individual Interior region surface-area mines have substantial
capacity for receiving FGD wastes, and disposal is considered technically
feasible within existing mine operations. The wastes must be dewatered
to the extent necessary for landfill operations, so that they can be dumped
into a mined-out strip (which can be adjacent to one being mined) and cov-
ered with overburden. Placing FGD waste in the mine void assists in
returning the terrain to its original elevation.
The principal environmental impact anticipated from this dis-
posal method is an increase in total dissolved solids (TDS) in waters that
are recharged by leachate from the disposal site. This impact may be
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lessened by placing part of the overburden in the mined-out strip prior to
placing the FGD waste, thereby elevating the waste above the groundwater
table. In addition, dilution to acceptable TDS levels can be encouraged by
maintaining a suitable distance between the disposal site and the stream, or
by ensuring that the receiving streams have a sufficiently high flowrate.
2. 3. 4 Ocean Disposal
In a study assessing the ocean disposal of FGD wastes (8) vari-
ous methods of transportation and disposal were examined, including surface
craft (e. g. , bottom-dump barge and slurry dispersion) and pipeline (outfall).
Various chemical and physical forms of the FGD wastes were also consid-
ered, i.e., sulfite-rich wastes, sulfate-rich wastes, and chemically treated
wastes in both "soil-like" and "brick-like" forms. Both continental shelf
and deep ocean disposal of the wastes were examined.
Until more definitive data are available, disposal of sulfite-rich
FGD wastes on the Continental Shelf or in the deep ocean was not considered
to be advisable. In addition, the study concluded that all soil-like FGD
wastes, whether sulfite or sulfate and treated or untreated, should not be
disposed of by quick-dumping surface craft or pipeline (outfall) on the Conti-
nental Shelf. Several options using surface craft appeared promising:
a. Dispersed disposal of sulfate-rich FGD wastes 011 the Continental
Shelf
b. Concentrated disposal of chemically treated brick-like FGD
wastes on the Continental Shelf
c. Dispersed disposal of sulfate-rich FGD wastes in the deep ocean
d. Concentrated disposal of both sulfate-rich and chemically treated
FGD wastes in the deep ocean
However, the environmental effects of layering the bottom with wastes
described in a, c, and d above have yet to be defined. In addition, their
environmental effect while traveling down the water column is also unknown.
A more promising method is considered to be item b above.
This is based on the favorable characteristics of treated materials in labora-
tory leaching and permeability tests. Long-term effects on the volumetric
and structural integrity of the material as affected by submergence in sea
water are unknown.
Experiments sponsored by the New York State Energy Research
and Development Authority (NYSERDA) are evaluating the physical, chemical,
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and biologic characteristics of blocks of chemically treated scrubber wastes
(9). Laboratory experiments have been encouraging, and a 10 ft3 reef con-
structed of blocks of chemically treated wastes will be placed in Long Island
Sound. The physical stability of the reef and its effects on the local marine
biology will be studied, and other related assessments will be made.
2. 3. 5 Conversion to Gypsum
Experiments on the forced oxidation of sulfite sludges to form
gypsum for potential use in wallboard were conducted by EPA at Research
Triangle Park and by Southern Services at Plant Scholz using the Chiyoda
process. Wallboard has been fabricated using a 50/50 blend of Chiyoda
gypsum and the natural material (10). However, evaluations of the proper-
ties of FGD gypsum specifically related to manufacturing wallboard and its
application were not available.
Wallboard produced from SC>2 scrubbing processes has had exten-
sive application in Japan, and properties relative to this material have been
reported (11). However, the material has been produced from scrubbing of
flue gases from oil-fired boilers, and the relationship between SC>2 concen-
tration in the flue gas and scrubber operating conditions on the properties
of the gypsum from the oil-fired units in Japan and from the coal-fired
applications in the U. S. are unknown. Estimates for the cost increment
required to adapt to new scrubber systems during construction have been
made (10) and reported. Since no data were available, in that analysis it
was assumed that the resultant properties of the ash-free gypsum would be
satisfactory for wallboard use.
2. 3. 6 Conversion to Sulfuric Acid or Sulfur
Regenerable FGD processes are, in reality, chemical process-
ing plants which, if applied to power plants, add new dimensions to the plant
operating and marketing programs.
Both the magnesium oxide and Wellman-Lord processes require
a complex plant to regenerate the SC>2 from the absorbent, and to reduce the
SC>2 to sulfur or convert it to sulfuric acid. The Wellman-Lord process
uses an evaporator to regenerate the absorbent and form SO2- It then
requires methane and H2S in the plant devoted to the reduction of SO2 to sulfur.
The magnesium oxide process requires a fluidized bed reactor and coke to
regenerate the SO2, which then must be processed further to form the sulfur
or sulfuric acid by-products.
A brief discussion of the technology based on recent surveys and
operational status of existing plants is provided below.
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2. 3. 6. 1 Magnesium Oxide--
Three MgO plants have been tested (Table 11). Two have shut
down completely as SC>2 scrubbers, and a third is in a particulate scrubber
mode only since February 1976 because of the difficulty in locating a chemical
plant to process the spent absorbent (it is scheduled to start up again as an
SC>2 scrubber in mid-1977). The two shut-down plants experienced the same
problem (12). In general, it is considered (13), that the scrubbing process
has been demonstrated; experiencing the usual corrosion and mechanical
problems typical of placing a scrubber system into operation (12). The
major problem has been in the accessibility of a MgSO3 regenerating plant.
To operate effectively, an on-site or central regenerating plant servicing
nearby scrubber operations may be needed.
2.3.6.2 Wellman-Lord--
The Wellman-Lord system has been successfully operated on
tail gas from Glaus and H2SO4 plants and an oil-fired flue gas, but not
coal-fired boiler flue gas (13).
A retrofit system is scheduled to go into operation in mid-1977
on the 115-MW boiler at the Dean Mitchell Station of Northern Indiana Public
Service burning 3- to 3. 5-percent sulfur coal. Elemental sulfur (99. 5 per-
cent purity) is expected.
TABLE 11. STATUS OF MAGNESIUM-OXIDE
SCRUBBING PLANTS
Installation Site, Size, and Fuel
Status
Boston Edison, Mystic No. 6, 150 MW, oil, 2.5%
sulfur
Potomac Electric, Dickerson No. 3, 95 MW, coal,
2% sulfur
Philadelphia Electric, Eddystone No. 1, 120 MW,
coal, 2. 5% sulfur
Start-up 4/72,
shutdown since
6/74
Start-up 9/73,
shutdown since
8/75
Start-up 9/75,
shutdown SO2
scrubber
2/76a
Shutdown—acid plant regeneration facility ceased operations.
Another facility located. Expect to resume SO2 scrubbing and
MgSO3 regeneration in mid-1977.
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Public Service of New Mexico is installing Wellman-Lord
systems at its San Juan No. 1 and 2 stations, which generate in excess of
700 MW. Start-up is expected in November 1977. Low sulfur (0. 8 percent)
coal will be used in the boilers.
2. 3. 7 Use as a Synthetic Aggregate
Chemically treated waste has been used in limited instances
as synthetic aggregate for road base materials.
Poz-o-tec® is a process that is used by IU Conversion Systems
Inc. , to chemically treat wastes capable of being processed as synthetic
aggregate. Its application has been used primarily in road base construc-
tion materials, with some application as dikes and liner material at a
disposal site (14) in the greater Pittsburgh area and in Mohave County,
Arizona. It has also been used to reclaim land in a housing tract. Ross
Township, Pennsylvania, has approved a specification for its use in road
base construction.
The economics of its use appear to be highly site specific rela-
tive to its source and end use; however, no cost data have been published.
2.4 WASTE DISPOSAL
Various forms of disposal are available, and a selection depends
on processing cost in combination with the following factors, which are
generally site specific: characteristics of the waste, climate, geology,
topography, hydrology, and disposal site availability and proximity. Possi-
ble types of disposal are: ponding on indigenous clay soil; ponding with a
flexible liner or a liner of impervious soil; ponding with underdrainage;
mine disposal; ocean disposal; and chemical treatment with landfilling.
There are specific cases where each of these methods is applicable; environ-
mentally and structurally. Although the chemical treatment approach is
universally applicable, it is not necessarily the best choice in all cases if
a ponding or mine disposal approach is environmentally acceptable and less
expensive. All disposal methods require monitoring, and land disposal
sites require management throughout their active life, including special
provisions such as covering the site with soil and the growth of vegetation
to prevent either rewetting the material or runoff problems, as applicable.
2. 5 UTILIZATION
Three major products which can be produced from flue gas scrub-
bing are gypsum from nonregenerable systems and sulfur and sulfuric acid
43
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from regenerable systems. Although the quality of the products produced
may be equivalent to those obtained from current sources, the economics,
however, are generally not favorable when compared with current sources of
supply. Gypsum is not directly cost competitive; however, in consideration
of sludge disposal credits for disposal under certain conditions, it can be
shown to be a cost-effective commercial item. Sulfuric acid would have to
compete in an industry that is currently capable of producing 30 percent
over demand. However, there may be site-specific instances where the
production of sulfur or sulfuric acid from regenerable scrubber systems may
be economically feasible. Attempts are being made to develop other products
from sulfur sludge, such as fertilizer and building materials.
2. 6
ECONOMICS
Cost estimates have been made for disposal of sulfur sludges
by various methods, as well as projected costs on a national basis to 1998
for the same methods considering current NSPS, and the two alternative
revisions, i.e. , 90 percent SO2 removal and 0. 5 Ib SO2/10& Btu. A sum-
mary of disposal costs, including conversion to gypsum and its disposal,
is as follows:
DISPOSAL COSTS (mills/kWh)a> b (1977 DOLLARS)
Untreated Waste
Liner
Added
1.02
Indigenous
Clay
0. 70
Landfill -
Chemical
Treatment
1.33
Mine
0. 37
Ocean
2.38
r- 6
Cry p sum
1.39
*500-MW plant, 3. 5% sulfur coal, 90% SO2 removal. Disposal site within
1 mile from plant, except as noted.
All disposal includes ash.
'Untreated waste, site located 4 miles from power plant.
Treated sludge, on the continental shelf, 25 miles from the eastern seaboard.
a
'Cost of forced oxidation and disposal of gypsum including fly ash in an indige-
nous clay-lined pond.
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An example is given below of the costs for disposal that would be incurred in
1998 if all new plants used nonregenerable scrubbing.
TOTAL COSTS IN 1998 - BILLIONS (1977 DOLLARS)
a, b
Emission Standard
1.2 Ib SO2/106 Btu
90% SO2 removal
0. 5 Ib SO2/106 Btu
Liner
Added
1.41
1. 54
1.06
Indigenous
Clay
0.95
1. 04
0. 72
Landfill -
Chemical
Treatment
1.89
2.07
1.43
Mine
0. 58
0. 64
0.44
Ocean
2. 84
3. 12
2. 15
1500-MW plant, 3.5% sulfur coal, 90% SO2 removal. Disposal site within
1 mile from plant, except as noted.
All disposal includes ash.
"Untreated waste, site located 4 miles from power plant.
Treated sludge, on the continental shelf, 25 miles from the eastern seaboard.
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REFERENCES
1. Meeting of 27 May 1977: J. W. Jones and K. Woodard (U.S. Environ-
mental Protection Agency) and P. Leo and J. Rossoff (The Aerospace
Corp.).
2. Letter from K. Woodard (U.S. Environmental Protection Agency) to
P. Leo (The Aerospace Corp.),15 June 1977.
3, "Assessment of the Effects, on Steam-Electric Plant Solid Wastes, of
More Stringent New Source Performance Standards for Sulfur Dioxide, "
U.S. EPA Contract No. 68-01-3528, Work Assignment No. 6, dated
5 May 1977, with The Aerospace Corp.
4. P. P. Leo and J. Rossoff, Control of Waste and Water Pollution from
Power Plant Flue Gas Cleaning Systems: Second Annual R and D
Report, The Aerospace Corporation, Los Angeles, California (to be
published), prepared for U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina.
5. R. B. Fling, et al. , Disposal of Flue Gas Cleaning Wastes: EPA
Shawnee Field Evaluation - Second Annual Progress Report, The
Aerospace Corporation, Los Angeles, California (to be published),
prepared for U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina.
6. J. Rossoff, et al. , Disposal of By-Products from Nonregenerable Flue
Gas Desulfurization Systems: Final Report, The Aerospace Corpora-
tion, Los Angeles, California (to be published), prepared for U.S.
Environmental Protection Agency, Research Triangle Park, North
Carolina (Contract 68-02-1010).
7. R. B. Fling, et al. , Disposal of Flue Gas Cleaning Wastes: EPA
Shawnee Field Evaluation - Initial Report, EPA-600/2-76-070, U.S.
Environmental Protection Agency, Washington, D. C. (March 1976).
8. R. R. Lunt, et al. , An Evaluation of the Disposal of Flue Gas Desul-
furization Wastes in Mines and the Ocean: Initial Assessment, EPA-
600/7-77-051, U.S. Environmental Protection Agency, Washington,
D. C. (May 1977).
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9. Coal Waste Disposal at Sea, Information pamphlet, New York State
Energy Research and Development Authority.
10. P. P. Leo and J. Rossoff, Control of Waste and Water Pollution from
Power Plant Flue Gas Cleaning Systems: Second Annual Research and
Development Report, The Aerospace Corporation, Los Angeles, Cali-
fornia (to be published), prepared for U. S. Environmental Protection
Agency, Research Triangle Park, North Carolina (Contract No. 68-02-
1010).
11. J. Ando and G. A. Isaacs, SC>2 Abatement for Stationary Sources in
Japan, EPA-600/2-76-013a, U.S. Environmental Protection Agency,
Washington, D. C. (January 1976).
12. Summary Report: Flue Gas Desulfurization Systems, Prepared for
U. S. Environmental Protection Agency, Research Triangle Park,
North Carolina, Contract No. 68-02-1321, by PEDCo Environmental
Specialists, Inc., Cincinnati, Ohio (January-March 1977).
13. K. S. Murthy, et al. , "Status and Problems of Regenerable Flue Gas
Desulfurization Process," J. Air Pollution Control Assoc. 26 (9),
851(1976).
14. Personal communication: R. Basckai, (IU Conversion Systems, Inc.)
with P. P. Leo (The Aerospace Corp. ).
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA-600/7-78-044a
2.
3. RECIPIENT'S ACCESSION NO.
Controlling SO2 Emissions from Coal-
Fired Steam-Electric Generators: Solid Waste Impact
(Volume I. Executive Summary)
5. REPORT DATE
March 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
P. P. Leo and J. Rossoff
8. PERFORMING ORGANIZATION REPORT NO.
ATR-78(7550-06)-1, Vol I
9. PERFORMING ORGANIZATION NAME AND ADDRESS
The Aerospace Corporation
P.O. Box 92957
Los Angeles, California 90009
10. PROGRAM ELEMENT NO.
E HE 62 4 A
11. CONTRACT/GRANT NO.
68-01-3528, W.A. 6
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
IOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTEsiERL-RTP project officer is Julian
2489.
W. Jones, MD-61, 919/541-
16. ABSTRACT
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