AEPA
indn ental Resea EPA 600 7 78 153b
Nov^mti.T 1 978
e P.Hk NC 27/11
Sulfur Retention
in Coal Ash
Interagency
Energy/Environment
R&D Program Report
-------
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EPA-600/7-78-153b
November 1978
Sulfur Retention
in Coal Ash
by
K.L Maloney, P.K. Engel, and S.S. Cherry
KVB, Inc.
17332 Irvine Boulevard
Tustin, California 92680
Contract No. 68-02-1863
Program Element No. EHE624A
EPA Project Officer: David G. Lachapelle
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
-------
ABSTRACT
An analytical study was conducted to assess the potential for sulfur
retention in various types of coal-fired boilers. The results of a field test
of ten industrial coal-fired boilers were used to evaluate the impact on sulfur
retention of the operating variables (load and excess O_).
The effect of ash composition on sulfur retention was also evaluated
with the use of a linear regression analysis. An expression of the form
Percent Sulfur Emitted = a+b (%Na O/%CaO) + C (load/10 )
where a, b and c are constants, gave the best overall fit to the two pulverized
coal-fired boiler data.
The field test results and the regression analysis results were sup-
ported by equilibrium coal ash composition calculations over a range of
temperatures and theoretical air for four coal ash compositions. These cal-
culations show that significant fractions of the sulfur can be tied up as Ca
and Na salts under both reducing and oxidizing conditions at temperatures
below 2500 °F. A minimum in the total condensed phase sulfur species is pre-
dicted at stoichiometric conditions for all temperatures.
-------
CONTENTS
Section Page
Abstract ±±
Figures
IV
Tables .
Conversion Factors viii
1 . 0 INTRODUCTION 1
2.0 SULFUR RETENTION CORRELATIONS WITH BOILER CONDITIONS AND
FUEL ASH COMPOSITION 3
2.1 Sulfur Retention Studies with Boiler Conditions 3
2.2 Sulfur Retention Studies with Fuel Ash Composition 22
2.3 Other Related Sulfur Retention Properties 24
3.0 THERMOCHEMICAL EQUILIBRIUM SULFUR DISTRIBUTIONS 34
3.1 Introduction and Background 34
3.2 Computer Program 34
3.3 Coal Compositions 35
3.4 Computer Results 37
3.5 Discussion of the Equilibrium Results 49
4.0 CONCLUSIONS 57
References 58
iii
-------
FIGURES
Number Page
2
2-1 R vs. number of data points. 10
2-2 Percent sulfur oxides emitted vs. percent rated load 12
(at different percent excess oxygen levels), Alma Unit 3.
2-3 Percent sulfur oxides emitted vs. percent rated load 13
(at different excess oxygen levels), Alma Unit 3.
2-4 Percent sulfur oxides emitted vs. percent rated load 14
(at different percent excess oxygen levels), University
of Wisconsin, Stout.
2-5 Percent sulfur oxides emitted vs. percent rated load 15
(at different percent excess oxygen levels), University
of Wisconsin, Eau Claire.
2-6 Percent sulfur oxides emitted vs. percent rated load 16
(at different excess oxygen levies), University of
Wisconsin, Madison, Unit 2.
2-7 Percent sulfur oxides emitted vs. percent rated load 17
(at different percent excess oxygen levels), Willmar
Unit 3.
2-8 Percent sulfur oxides emitted vs. percent rated load 18
(at different percent excess oxygen levels), Fairmont
Unit 3.
2-9 Percent sulfur oxides emitted vs. percent rated load 19
(at different percent excess oxygen levels), St. John's
Unit 2.
2-10 Percent sulfur oxides emitted vs. percent rated load 20
(at different percent excess oxygen levels), Waupun
Unit 3.
2-11 Percent sulfur oxides emitted vs. percent rated load 21
(at different percent excess oxygen levels), Fremont
Unit 6.
iv
-------
FIGURES (Continued)
Number Page
2-12 Percent sulfur oxides emitted (measured) vs. percent 29
sulfur oxides emitted (calculated), Alma Unit 3,
Sarpy Creek, Montana coal.
2-13 Percent sulfur oxides emitted (measured) vs. percent 30
sulfur oxides emitted (calculated), Fremont Unit 6,
Hanna-Rosebud, Wyoming coal.
2-14 Percent sulfur retention vs. calcium to sulfur (Ca/S) 33
ratio for lignite samples.
-------
TABLES
Number Page
2-1 SO Emission Comparison for Western and Eastern Coals 4
2-2 Operating Conditions and Sulfur Oxide Emissions 5
2-3 Multiple Regression Analysis of All Coals Tested for 8
Excess O , Load, and % Sulfur
2-4 Sulfur Oxide Retention with Boiler Condition Variation 11
2-5 Western Coal Ash Analysis 23
2-6 Multiple Regression Analysis Formulations Assessed for 25
Fuel Ash Composition and Boiler Conditions
2-7a Multiple Regression Analyses for Two Western Coals on 26
Two Pulverized-Coal Boilers
2-7b Multiple Regression Analyses for Two Western Coals on 27
Two Pulverized-Coal Boilers
2-8 Comparison of Measured and Calculated Percent Fuel 28
Sulfur Emitted
2-9 Sulfur Retention by the Ash of the Coals Tested During 31
Laboratory Ashing at 700-750 °C and Subsequent Mineral
Analysis by Commercial Testing
2-10 Variation of Fuel Sulfur Retention with Calcium/Sulfur Ratio 33
3-1 Coal Compositions 36
3-2 Computer Output for Lignite at 50% Theoretical Air 38
3-3 Sulfur Distribution, Montana Coal 40
3-4 Sulfur Distribution, Lignite 42
3-5 Sulfur Distribution, Augmented Lignite 44
3-6 Sulfur Distribution, Pittsburgh #8 46
VI
-------
TABLES (continued)
Number Page
3-7 Sulfur Retention by Condensed Species 48
3-8 Mass Balances for Calcium, Potassium and Sodium at 500 °F 50
3-9 Sulfur Balances on a Laboratory Fuel Bed Simulator 55
VII
-------
CONVERSION FACTORS
SI Units to Metric or English Units
H-
H-
To Obtain
g/Mcal
106 Btu
Btu
lb/106 Btu
ft
in.
ft2
ft3
Ib
Fahrenheit
Fahrenheit
psig
psia
iwg (39.2 °F)
106 Btu/hr
GJ/hr
From
ng/J
GJ
gm cal
ng/J
m
cm
2
m
m3
kg
Celsius
Kelvin
Pa
Pa
Pa
MW
MW
Multiply By
0.004186
0.948
3. 9685x10" 3
0.00233
3.281
0.3937
10.764
35.314
2.205
tp - 9/5
-------
English and Metric Units to SI Units
Multiply*
To Obtain
ng/J
ng/J
GJ
m
cm
m2
m3
kg
Celsius
Kelvin
Pa
Pa
Pa
MW
MW
From
lb/106 Btu
g/Mcal
106 Btu
ft
in.
ft2
ft3
Ib
Fahrenheit
Fahrenheit
psig
psia
iwg (39.2 °F)
fL
10° Btu/hr
GJ/hr
Multiply By
430
239
1.055
0.3048
2.54
0.0929
0.02832
0.4536
tc - 5/9
-------
SECTION 1.0
INTRODUCTION
The objective of this study was to determine the effect of boiler
conditions and coal ash compositions on the sulfur retention characteristics
of different eastern and western coals. To this end the results of field
tests on ten industrial sized coal fired boilers have been evaluated. These
ten industrial boilers represented a variety of firing types ranging from
mass feed stokers to pulverized coal fired boilers. In order to support
the field test results, thennodynamic equilibrium calculations have been
performed on four of the coals tested in the field to predict the sulfur
distribution among the ash constituents at five stoichiometric ratios for
a range of temperatures.
Conditions of temperature, stoichiometry, and ash composition have
been identified where thermodynamic equilibrium predicts large sulfur
retention in the solid ash. Whether these large retentions are attained
in the field depends upon how good the contact is between the sulfur and
the metal compounds within the other constraints. In addition to the contact
problem, the sulfur retention is further governed by the rates of the retention
reactions and the temperature/stoichiometry history of the sulfur and ash
components.
In normal combustion processes, all of the fuel sulfur is converted
to sulfur oxides (SO )—mostly to SO with a small amount being further
Jt A
oxidized to SO_. However, in some instances for the combustion of coal, the
SO emissions have been observed to be less than expected for the complete
x
oxidation of all of the fuel sulfur. These reduced SO emissions were greater
Ji
when the coal ashes were more alkaline.
-------
To explain these reduced SO emissions, the boiler conditions have
3£
been reported by other researchers to have a significant influence. The SO
A
emissions could be related to load and percent excess oxygen by an equation
of the type:
Percent sulfur emitted = a + b (percent excess oxygen)
+ c (load/100, 000) * (1)
Other studies have related sulfur retention to the mineral composition
of the fuels or their ashes. For boilers firing lignite, Gronhovd (Ref. 1) and his
associates found the following relationship that satisfactorily correlated
their data:
Sulfur emitted as % sulfur in coal =
Na 0
For EPA Contract 68-02-1863, comprehensive measurements on ten
industrial boilers were made. Fuel and ash samples were collected for
analysis at recorded load and excess oxygen conditions. The fuel samples
were analyzed for ultimate constituents and the ash samples for chemical
composition including CaO, Na_0, Al O_, MgO, K_0, and SiO .
*In all regression analyses, load was taken in pounds of steam.
-------
SECTION 2.0
SULFUR RETENTION CORRELATIONS WITH BOILER CONDITIONS
AND FUEL ASH COMPOSITION
2.1 SULFUR RETENTION STUDIES WITH BOILER CONDITIONS
Basically, the results of overall study showed that the retention
of sulfur by western coal was significantly greater than the retention of
sulfur by eastern coal. The overall average western coal fuel sulfur content
(of coals tested) was 775 ng/J (1.81 Ib SO /10 Btu fired) with an average
fuel sulfur emitted of 79.8%. For eastern coal, the average fuel sulfur
content was 2021 ng/J (4.7 Ib SO2/10 Btu fired) with an average fuel
sulfur emitted of 90.4%. Table 2-1 shows the SO emission comparison for
western and eastern coals for the industrial-sized boilers.
In order to evaluate the results from sulfur emissions studies of
ten industrial-sized coal-fired boilers, multiple linear regression analyses
using both combustion conditions of the boiler operations and chemical
composition of the fuel ashes were performed. An assumption was made that
effects of load and excess oxygen were independently controllable variables.
Table 2-2 contains the data regarding the combustion conditions
(i.e., percent excess oxygen and load), coal sulfur levels and measurements
of sulfur oxides emitted.
For each boiler and each type of fuel, regression analyses were
performed using the relationship:
Percent sulfur emitted = a + b(percent excess oxygen) + c(load/100,000)
where a is a constant, and b and c are coefficients.
Table 2-3 presents the results of these regression analyses. The
correlations accounted for 16% to 100% of the data for eastern coals and
for 50% to 100% of the data for western coals. Caution must be exercised
in interpreting the data; for example, the Eau Claire site with eastern
coal has only three data points.
-------
TABLE 2-1. 80x EMISSION COMPARISON FOR WESTERN AND EASTERN COALS
Boiler
Test Sit* Type
Alma PC
Stout VG
Madison 55
Willmar SS
Eau Claire TG
St. Johns DG
Fremont PC
Fremont PC
Alma PC
Stout TG
Willmar SS/TG
Eau Claire VG
Madison SS/TG
Fairmont PC
Coal Source (Mine)
Western Coal
Montana (Sarpy Creek)
Wyoming (Bighorn)
Montana (Colstrip)
Montana (Colstrip)
Wyoming (Bighorn)
Wyoming (Bighorn)
Wyoming (Banna-Rosebud)
Colorado (Walden)
Overall Average
Eastern Coal
Kentucky (River King)
Kentucky (Vogue, Seam 2)
So. Illinois (Stone fort)
W. Kentucky (Vogue)
W. Kentucky (Vogue)
So. Illinois (Sahara)
Overall Average
Average Fuel Sulfur
percent
0.96
0.96
0.99
1.15
0.73
0.61
1.38
0.38
3.57
2.94
2.28
2.87
3.04
2.13
ng/J
(Ib B02/106
Btu Fired)
880 (2.05)
822 (1.92)
949 (2.21)
1174 (2.74)
657 (1.53)
498 (1.16)
957 (2.23)
263 (0.61)
775 (1.81)
2800 (6.64)
2043 (4.76)
1567 (3.65)
1803 (4.72)
2167 (5.05)
1471 (3.43)
2021 (4.71)
Average SO. Emissions
pom
791
681
1044
934
695
592
1053
235
3036
2129
1815
2363
2378
1628
ng/J
(Ib S02/106
Btu Fired)
649 (1.51)
559 (1.30)
858 (2.00)
766 (1.79)
570 (1.33)
486 (1.13)
864 (2.01)
193 (0.45)
618 (1.44)
2491 (5.81)
1747 (4.07)
1489 (3.47)
1939 . (4.52)
1952 (4.55)
1336 (3.11)
1826 (4.25)
Fuel
Sulfur
Emitted
percent
73.8
69.6
90.4
65.3
86.8
97.5
90.3
73.4
79.8
87.0
85.5
94.0
95.0
90.0
89.7
90.4
Average SO reduction based on flue gas emission measurements = 1206 ng/J
* 6
Average SO reduction based on fuel analysis = 1244 ng/J (2.90 Ib SO./10
(2.81 Ib S02/10*
Btu) - 61.7%
Btu) » 66.1%
VG - Vibrating Grate
TG/SS - Spreader Stoker with Travel Grate
PC - Pulverized Coal
UR - Underfed stoker
TG - Travel Grate Stoker
-------
TABLE 2-2. OPERATING CONDITIONS AND SULFUR OXIDE EMISSIONS
As Received
Load Excess
Test Factor Oj SOx
Site No. % » ng/J
Ainu (PC
Eastern
Western
, 29 kg/s
6
7
9
11
14
16
21
53
57
63
64
85
49
57
53
89
26
26
57
74
57
74
65*
66
Stout St.
Eastern
western
68
72
73
74
75
76
78
U.
22
19
27
31
3
4
8
11
13
14
IS
36
Eau Claire
Eastern
Western
11
20
30
1
3
4
7
10
75
44
41
39
70
70
48
-------
TABLE 2-2 (Continued).
AB Received
Site
Madison
Eastern
Western
Willnar
Eastern
Western
Painpont
Eastern
Western
Load
Test Factor
No. %
(SS/TG,
11
12
14
IS
17
19
2
5
7
8
9
10
3
(SS/TG
26
28
30
31
32
33
34
8
15
16
(SS/TG
2
4
5
7
8
9
10
11
12
14
15
17
18
19
20
Excess
O2 SOx
% nq/J
12.6 kg/s (lOOxlO3
60
60
90
90
30
30
60
90
30
80
80
30
60
. 20.2
66
78
52
48
55
69
83
68
49
69
, 10.1
61
62
61
74
36
78
76
75
76
57
38
75
57
55
42
10.0
12.0
7.3
9.1
14.7
15.8
6.5
7.2
13.6
9.7
6.2
13.5
10.9
kg/S
8.6
6.5
10.0
8.4
11.9
6.6
5.9
8.6
8.2
6.6
kg/a
9.1
10.1
8.2
8.0
13.5
6.5
9.8
7.0
7.0
8.0
12.9
6.6
9.4
12.4
14.1
1711
1761
1739
1924
2539
2431
862
919
492
1070
1293
1155
1481
Coal Botton
Sulfur Fly Ash Ash
as SO. Sulfur Sulfur
ng/J ng/J ng/J
Ib/hr)
2119
2412
2195
2215
2053
2144
953
719
908
817
937
1224
1767
(160X103 Ib/hr)
1791
1492
1431
1550
1553
1541
1573
1031
899
937
(BOxlO3
1342
1396
1151
1564
1442
1350
1160
1252
1330
1314
1015
1222
1360
1273
1170
1644
1461
1455
1448
1468
1492
1570
1176
1000
703
Ib/hr)
1438
1674
1732
1323
1448
1425
1374
1882
1176
1412
1169
1309
1349
1535
1355
•teas, BCW)
22
25
8
IS
5
7
60
26
37
27
20
48
Heat
Value
J/g
27681
28090
27902
29085
28806
27263
21966
20228
20442
21030
19840
20540
20242
Ash
Content
%
8.79
8.88
9.6
7.98
8.7
9.2
8.26
8.29
7.99
8.12
8.68
8.95
10.22
Measured
Fuel
Sulfur Gronhovd
Emitted Prediction
t %
81
73
79 109
87
124
112
91 99
122
54
131
138
94
84 100
Calculated*
Fuel
Sulfur
Emitted
t
88.1
94.3
73.1
78.7
109.2
112.6
99.6
131.5
69.9
121.7
120.6
69.9
100.9
•team, Detroit Stoker)
steam, Erie City)
15
4
6
11
29182
29133
28978
29257
29275
29341
29022
19540
20179
20467
29050
29248
28930
28640
29255
28860
29190
24316
25400
25185
25510
25900
25020
26686
26549
8.65
8.22
8.25
8.43
7.67
8.34
7.76
9.12
8.82
8.57
8.67
9.24
8.85
8.69
8.74
8.11
8.41
9.14
8.96
8.17
8.97
9.69
8.92
10.00
7.94
109 108
102
98
107
106
103
100
88 100
90
133
93
83
66
118 108
100
95
84
67
113 106
93
87
93
101
83
86
103.5
102.4
104.7
104.7
104.8
103.0
101.9
88.0
90.0
133.0
89.9
92.2
87.9
91.7
90.9
90.0
96.3
91.7
91.5
95.5
89.7
92.7
92.0
84.9
85.0
•Load, Excess O Regression Analysis
(continued)
-------
TABLE 2-2 (Continued).
As Received
Site
Test
No.
Load Excess
Factor O
* r
St. Johns (SS/DG,
Eastern
Western
Fremont
Western
Harms, WY
11
12
13
14
15
16
2
3
4
5
6
8
(PC.
3
4
5
6
7
Western 9
Walden.CO u
Waupan
Western
RDF
Blend
13
14
15
(SS/TC
1
2
3
5
6
0%
20%
RDF
30%
RDF
40%
RDF
63
45
43
43
61
59
62
41
43
42
43
65
20.2
68
41
83
73
68
87
72
70
44
70
, 3.8
54
52
91
91
90
73
75
59
76
SOx
ng/J
1.7 kg/s (13.5x10
14.2 366
15.5
16.3
15.5
15.6
13.40
13.7
16.3
16.5
15.2
17.0
13.4
354
306
413
372
351
392
508
492
608
509
474
Coal
Sulfur Ply Ash
as SO Sulfur
ng/J ng/J
3 Ib/hr) stean,
367
365
321
363
373
380
565
504
515
577
649
498
Bottom
Ash
Sulfur
ng/J
Keeler)
3
3
4
1
1
14
8
IS
8
Heat
Value
J/g
31027
31685
31046
31343
32078
30524
22273
22173
22459
22484
22786
24458
Ash
Content
t
6.63
5.31
7.10
5.92
4.42
5.29
5.52
4.99
5.59
5.66
5.28
5.14
Measured
Fuel
Sulfur
Emitted
100
97
95
114
100
92
63
101
95
105
78
95
Gronhovd
Prediction
109.9
108.6
108.3
108.3
97
Calculated*
Fuel
Sulfur
Emitted
97.0
101. J
102.5
101.5
99.0
96.7
80.1
96.4
89.6
108.4
83.2
79.2
kg/s (160xl03 Ib/hr) steam, BSH)
5.4
5.3
5.4
4.1
3.6
5.5
4.3
5.1
4.2
3.4
987
1014
1151
772
689
251
208
228
184
203
1063 88
1168 75
1072 76
812 52
795 28
221
238 9
-
268 13
258 6
kg/s (30xl03 Ib/hr) steam, Wickes)
13.2 241 747 23
11.8
11.5
11.5
11.0
9.73
9.59
11.53
10.50
469
443
265
204
227
— -
156
255
596
641
799
861
817
822
822
757
10
30
26
23
66
72
83
132
29150
28771
29095
28578
28694
28020
27706
28343
28664
20063
20121
19960
20520
20186
22774
20557
19617
18554
9.85
10.44
9.99
7.76
7.95
8.31
-
7.85
7.91
8.67
7.81
8.21
8.00
8.02
10.55
93
87
107
95
87
113
87
-
68.4
78.7
32
79
69
33
24
28
~~
32
28
106
105
104
106
106
107
99
101.6
93
97.6
85.2
104.6
93.5
88.2
112.3
88.9
68.7
78.1
41.1
69.6
38.6
38.3
49.3
27.6
™~
32.2
28.0
•Load, Excess O. Regression Analysis
-------
TABLE 2-3. MULTIPLE REGRESSION ANALYSIS OF ALL COALS TESTED
FOR EXCESS O , LOAD, AND % SULFUR
Site
Alma (8)
(PC) (11)
(5)
Stout St. U. (4)
(TG) (8)
Eau Claire (3)
(VG) (5)
Madison (6)
(SS) (7)
Willmar (7)
(SS) (3)
Fairmont (7)
(SS) (8)
Waupun (5)
(SS) (4)
St. John's (6)
(SS-DG) (6)
Fremont (5)
(PC) (5)
Coal Type
W. Kentucky
Montana
Montana*
W. Kentucky
Wyoming
W, Kentucky
Wyoming
W. Kentucky
Montana
Illinois
Montana
So. Illinois
Blend
Montana
RDF**
Eastern
Western
Hanna, WY
Walden, CO
a.
88.693
103.065
137.584
107.159
97.143
267.766
169.449
70.038
34.090
106.383
255.141
49.467
136.478
348.850
34.536
88.617
400.946
40.679
- 6.770
b.
(Excess 02
Coefficient)
- 0.275
- 0.282
- 6.221
- 2.642
- 3.686
- 10.524
- 11.018
3.109
0.296
0.174
- 22.318
2.176
- 2.598
- 19.446
0.719
1.243
- 12.769
4.922
9.953
c.
(Load
Coefficient)
7.886
- 11.773
- 14.251
25.035
32.000
- 218.996
55.739
- 21.797
105.896
- 4.115
22.786
42.218
- 43.955
- 317.128
- 61.502
- 107.931
- 1720.779
27.942
45.991
R Fit
Correlation
0.621
0.246
0.913
0.832
0.250
1.000
0.825
0.607
0.688
0.091
1.000
0.027
0.076
0.283
1.000
0.105
0.504
0.875
0.996
*5 high confidence points
**Refuse-derived fuel
( )No. of data points
(SS) - Spreader Stoker
(DG) - Dumping Grate
(TG) - Traveling Grate Stoker
(PC) - Pulverized Coal
(VG) - Vibrating Grate
-------
Figure 2-1 contains the value of R plotted as a function of the number
of data points in Table 2-3 that were used to arrive at the R value. Above
the curve drawn in this figure is the region of 95 percent confidence interval
for that number of data points. It can be seen that when the sample size is
2
small, a large absolute value of R is required to show significant correlation.
Seven values of R fall below the line and twelve values are above the
line.
Specifically for the Alma site for five high confidence points, the
regression analysis yields the relationship:
Percent sulfur emitted = 137.6 - 6.2(percent excess oxygen) - 14.3(load/100,000)
This equation accounts for 95.6% of the variations in the data.
Table 2-4 summarizes the fit correlations for all the coals and units
tested. The entries indicate whether the sulfur retention increases or decreases
when the percent excess oxygen is increased and when the load is increased.
Also at the bottom of Table 2-4, the total number of increases and decreases
for each variable are shown for both eastern and western coals after low confi-
dence data as well as the Waupun Refused-Derived Fuel data were eliminated.
Thirty percent of the data were removed due to low confidence factors. The
conclusions were that, for boilers tested, a greater sulfur retention tendency
was exhibited at higher excess oxygen and a tendency for less sulfur retention
at higher loads. The same overall trends held for both eastern and western coals.
More specifically for the different types of boilers, two pulverized
coal-fired boilers exhibited opposing sulfur retention behavior with respect
to load and excess oxygen. A unit-by-unit analysis of the stoker data did not
reveal an explicit explanation of the different sulfur retention behavior
between units.
Figures 2-2 through 2-11 represent the relationships using the coeffi-
cients developed in the regression analyses as shown in Table 2-3. In these
figures only normal boiler operating conditions are used. The original assump-
tion regarding variation of the boiler conditions must be reassessed. The sul-
fur retention behavior may have been artifically attributed to the boiler con-
ditions as independent variables by the formulation of the terms of the regres-
sion analyses as well as the scarcity of data. In most cases, as the boiler
-------
i.o
0.8
0.6
0.4
0.2
o
Critical Value
Region
5 10
NUMBER OF DATA POINTS
15
Table 2-1. R vs. number of data points.
10
-------
TABLE 2-4. SULFUR OXIDE RETENTION WITH BOILER CONDITION VARIATION
Site
Boiler Type*3
Boiler Capac. (10 Ib/hr)
Alma PC23Q
Eastern
Western
Western
Stout TG/SS
Eastern
Western
Eau Claire VG
Eastern
Western
Madison SS
Eastern
Western
Willmar SS,-..
_ lou
Eastern
Western
Fairmont SS
Eastern
Western
Waupun SS
RDF
Western
St. Johns DG/SS14
Eastern
Western
Fremont PC. __
_ . IbU
Eastern
Western
Totals
Eastern
Western
Conclusion:
Sulfur Retention
Increase Increase R
O^ Load Correlation
1 2
Up
Up
Up
Up
Up*
Up
UP
Down
Down
Down*
Up
Up*
Up*
Down
Up*
Down*
Up
Down
Down
4 Down 7 Up 6
(2 Down) (3 Up) (3
(2 Down) (4 Up) (3
Retention Increases
Retention Decreases
Down 0 . 62
Up 0.91+
Up 0.25*
Down 0.83
Down* 0.25*
Up 1.00
Down 0.83
Up 0.61
Down 0 . 69
Up* 0.09*
Down 1.00
Down* 0.027*
Up* 0.076*
Up 1.000
Up* 0.28*
Up* 0.10*
Up 0.50
Down 0.88
Down 1;00
Down 4 Up
Down) (2 Up)
Down) (2 Up)
With Increased O2
with Increased Load.
•Eliminated from totals
due to blended coal supply
t5 high confidence points
iBoiler Type:
VG - Vibrograte Stoker
TG/SS - Traveling Grate Stoker
SS - Spreader Stoker
PC - Pulverized Coal
DG/SS - Dumping Grate Spreader
11
-------
110
1
H
a
D
CO
3
H
CO
§
H
§
CO
100
90
80
70
2% O
6% O
2% O,
6% O,
Rated load = 29 kg/s
(230,000 Ib/hr) steam
Western
I
Eastern — — — — —
I
25 50
PERCENT RATED LOAD
75
100
Figure 2-2. Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels), Alma Unit 3.
12
-------
110
o
u
2
H
D
to
W
Pk
co
Q
W
H
CO
H
g
§
100
90
80
70
2% O,
2% O.
6% O
Rated load = 29 kg/s
(230,000 Ib/hr) steam
Western
5 High
Confidence
T
25 50 75
PERCENT RATED LOAD
100
Figure 2-3. Percent sulfur oxides emitted vs. percent rated load (at
different excess oxygen levels), Alma Unit 3.
13
-------
1
z
D
a
D
CO
W
g
w
S
H
X
o
Pi
D
CO
100
100
90
80
70
60
50
5% O,
5% O,
10% O.
10% O_ —
Rated load =5.7 kg/s
(45,000 Ib/hr) steam
Western
Eastern —___-—,
I
25 50
. PERCENT RATED LOAD
75
100
Figure 2-4. Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels), University of
Wisconsin, Stout.
14
-------
1
2
H
a,
D
D
CO
w
cu
to
Q
I
CO
w
Q
H
X
o
D
CO
100
80
60
40
20
I
10% O
Rated load = 7.6 kg/s
(60,000 Ib/hr) steam
Western
Eastern __ ._ ^_ ^
25 50
PERCENT RATED LOAD
75
100
Figur.6 2-5.
Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels), University of
Wisconsin, Eau Claire.
15
-------
110
w
8
H
§
OS
D
s
100
90
80
g
u
z
H
D
a
g
w
A 70
60
50
6% 0
Rated load = 12.6 kg/s
(100,000 Ib/hr) steam
Western
Eastern _
» i
25
50
75
100
PERCENT RATED LOAD
Figure 2-6. Percent sulfur oxides emitted vs. percent rated load (at
different excess oxygen levels), University of Wisconsin, Madison,
Unit 2.
16
-------
8
D
CO
W
w
04
CO
Q
E
H
CO
H
§
100
90
80
70
60
50
8% O.
Western
Eastern
Rated load =20.2 kg/s
(160,000 Ib/hr) steam
25 50
10% O —
75
100
PERCENT RATED LOAD
Figure 2-7. Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels) , Willmar Unit 3.
17
-------
110
§
2
H
OS
D
8
CO
Q
W
B
H
C/J
w
Q
H
X
o
100
90
80
70
60
50
O.
Rated load =10.1 kg/s
(80,000 Ib/hr) steam
Blend Western
I
Eastern „ ^ .
i I
25 50 75
PERCENT RATED LOAD
100
Figure 2-8. Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels), Fairmont Unit 3.
18
-------
u
z
H
D
CO
u
8
H
CU
CO
e
H
CO
W
Q
H
D
CO
110
100
90
80
70
60
50
110% O.
12% O.
Rated load =1.7 kg/s
— (13,500 Ib/hr) steam
15% O,
Western
I
Eastern — _ — — —
I I
25 50 75
PERCENT RATED LOAD
100
Figure 2-9. Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels), St. John's Unit 2,
19
-------
140
u
2
H
OS
D
g
Pi
W
Q
EH
M
CO
M
g
PS
D
120
100
80
60
40
20
12% O,
10% O
Rated load = 3.8 lK.g/s
(30,000 Ib/hr) steam
Western
I
Western + RDF Blend
I
I
0 25 50 75 100
PERCENT RATED LOAD
Figure 2-10. Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels), Waupun Unit 3.
20
-------
110
Figure 2-11.
2
H
D
W
w
en
<
Q
I
W
s
g
100
90
80
70
60
50
6%
Rated load =20.2
kg/s
(160,000 Ib/hr) steam
Hanna Western
Walden Western
I
I
2% O,
I
25 50 75
PERCENT RATED LOAD
100
Percent sulfur oxides emitted vs. percent rated load (at
different percent excess oxygen levels), Fremont Unit 6.
21
-------
load increased, the percent excess oxygen decreased. Due to fan capacity
limitations, it was generally impossible to vary the excess oxygen at high
boiler loads. At lower loads changing the excess air could disrupt the fuel
bed in a stoker unit and could lead to smoking in a pulverized-coal boiler.
This meant that the excess oxygen was strongly coupled to the load for most
boilers. The method of formulating the linear multiple regression analysis
relationships, in the manner assumed, may have given undue weighting to the
boiler load. It has been noted that the bulk gas temperature does not change
drastically over the load range of most industrial boilers. The derived
relationships for sulfur retention could be the result of lower operating
excess air at higher load and not the derived dependence of sulfur retention
on boiler load. Additional data would unquestionably increase the confidence
level in the trends and conclusions.
The results of the equilibrium calculations indicate that if kinetic
factors and/or mixing factors are not important, which is doubtful, then the
sulfur retention should increase with decreasing temperature below about
2500 °F for all stoichiometric conditions. Below this temperature there is
significant retention as condensed phase species if the metals are present in
sufficient quantities to combine with the sulfur. Above 2500 °F the sulfur
species are gaseous with SO. the dominant component at 75, 100, 125 and 150
percent theoretical air. At 50 percent air H2S, SO, and SH share the bulk of
the sulfur.
The equilibrium calculations further indicate that increasing the
theoretical air (excess O_) in the oxidizing region at a given temperature
should reduce the sulfur emitted. Therefore, from a thennodynamic equilibrium
viewpoint, the sulfur retention would increase with decreasing temperature
and increase with increasing excess O .
2.2 SULFUR RETENTION STUDIES WITH FUEL ASH COMPOSITION
At two pulverized coal boilers which were fired on western coal,
comprehensive analyses on the fuel ashes were completed for five individual
test conditions as presented in Table 2-5. These sites were Alma with a
maximum load of 29 kg/s (230,000 Ib/hr) which was burning a Montana (Sarpy
Creek) coal and Fremont with a maximum load of 20.2 kg/s (160,000 Ib/hr) which
was burning a Wyoming (Hanna-Rosebud) coal.
22
-------
TABLE 2-5. WESTERN COAL ASH ANALYSIS
to
u>
Site (Coal)/
Test No.
Alma
Creek
(Sarpy
, MO)
72
74
75
76
78
Load
kq/s (103 Ib/h)
12.75
11.36
20.33
20.33
13.89
Fremont (Hanna-
Rosebud, WY)
3 17.55
4
5
6
7
14.52
14.14
8.84
14.14
(101)
(90)
(161)
(161)
(110)
(139)
(115)
(112)
(70)
(112)
Excess
6.7
6.8
5.8
3.8
4.8
5.4
5.3
5.4
4.1
3.6
CaO
11.32
13.50
15.20
13.52
13.50
6.77
7.50
7.72
4.70
4.27
8a2o
2.08
2.71
3.08
2.63
2.57
0.28
0.48
0.41
0.42
0.34
MgO
2.12
2.40
2.84
2.60
2.60
2.16
1.92
2.38
1.90
1.80
A1203
18.21
17.14
19.18
18.07
18.07
20.85
19.24
18.91
15.02
13.37
Meas. In (Meas.%
SiO Sulfur Sulfur
(%) Emitted, % Emitted)
41.96
39.68
37.17
40.13
38.91
48.27
50.08
47.54
61.43
62.90
85
84
76
86
91
93
87
107
95
87
4.443
4.431
4.331
4.454
4.511
4.533
4.466
4.673
4.554
4.466
-------
As shown in Table 2-6, multiple regression analyses were performed
evaluating the dependence of percent sulfur emitted on the fuel ash composi-
tion and boiler conditions. The correlations were shown to account for 17
to 98% of the variation of the percent fuel sulfur emitted for the Alma data
and for 14 to 92% of the variation of the percent fuel sulfur emitted. In
7 out of 14 relationships assessed/ the sign of the coefficients were the
same for both Alma and Fremont indicating that the dependence of sulfur
retention were similar for those particular relationships. Tables 2-7a and
2-7b present the coefficients and R of the various relationships assessed
in this study.
Table 2-8 shows a comparison of measured percent fuel sulfur emitted
and the calculated percent fuel sulfur emitted by Gronhovd's relationship
and the various empirical correlations developed in this study. The plots
comparing the measured and calculated percent fuel sulfur emitted for three
of the fuel ash composition relationships are shown in Figures 2-12 and 2-13
(A, B and C in Table 2-8). The plots show that the relationships developed
from the western coal fuel ash composition data appear to predict more
closely the sulfur emitted than Gronhovd's relationship for lignite burning
boilers.
2.3 OTHER RELATED SULFUR RETENTION PROPERTIES
The effect of Commercial Testing Laboratories' sulfur analysis proce-
dures on sulfur retention in the sample were investigated during the course of
this study. This was done in order to determine the effect of the temperature
history on the sample since the laboratory procedure controls the temperature
as well as provides for a longer residence time at that controlled temperature.
Table 2-9 contains the results of all coal samples tested by this laboratory
during the project. Two points become evident. First, there was significant
sulfur retention under the laboratory ashing condition at 700-750 °C and
secondly, the occurrence of lime increased this retention on the average
by some 45 percentage points from 7.7% retention for eastern coal samples
to 53.1% retention for western coal samples. It is significant that the
calcium content of western coal was higher than the others and that the
western coal showed correspondingly greater sulfur retention.
24
-------
TABLE 2-6. MULTIPLE REGRESSION ANALYSIS FORMULATIONS ASSESSED FOR
FUEL ASH COMPOSITION AND BOILER CONDITIONS
A. RELATIONSHIPS OF TYPE
I Percent Sulfur Emitted
II Percent Sulfur Emitted
III Percent Sulfur Emitted
IV Percent Sulfur Emitted
V Percent Sulfur Emitted
VI Percent Sulfur Emitted
VII Percent Sulfur Emitted
VIII Percent Sulfur Emitted
IX Percent Sulfur Emitted
X Percent Sulfur Emitted
B. RELATIONSHIPS OF TYPE
Y = a + bX + cZ
a + b[% CaO/% Al O ] + c[% Na 0/% SiO ]
a + b[% CaO] + [% Na 0]
a + b[% Na20/% CaO] + c [Load/105]
a + b[% Ma 0/% CaO] + c [Excess Oxygen]
a + b[% CaO] + c [MgO]
a + b[% CaO/% MgO]
a + b[% CaO/% MgO] + c [Excess Oxygen]
a + b[% CaO/% MgO] + c [Load/10 ]
a + b[% CaO/% MgO] + c[ (Excess Oxygen x 10 )/Load]
a + b[% CaO/% MgO] + c[% MgO/% SiO2]
BZ
= AXeorlnY=a + blnX + cZ
tB L°a / ° J
XI Percent Sulfur Emitted = A [% CaO/% MgO] e
XII Percent Sulfur Emitted = A [% CaO/% MgO] e
XIII Percent Sulfur Emitted = A [ (% CaO • % SiO_)/(% Al 0 • % MgO)] e
t
XIV Percent Sulfur Emitted = A [Excess Oxygen] e
[(B EXC6SS <***" X
[B Load/10 1
[B L°a '
25
-------
TABLE 2-7a. MULTIPLE REGRESSION ANALYSES FOR TWO WESTERN COALS ON TWO PULVERIZED-COAL BOILERS
Relationship* for Percent Sulfur Emitted of the Form Y • a + bX + cZ
I II
l»CaO/%Al203], [%CaO],
Site (Coal) l«Ha.O/«SiO.) I%N«,O]
Alma
(Sarpy Creek,
Montana)
a
b
c
R2
Fit Correlation
Fremont
(Hanna-Roiebud,
Wyoming)
a
b
c
R2
Fit Correlation
67.61
39.68
-745.05
0.611
(R) 0.78
48.30
188.95
-2903.68
0.313
(R) 0.56
67.21
11.67
-53.28
0.51
0.72
82.94
2.25
-7.95
0.18
0.43
III
l%Na20/\Ca01 ,
Load/105
177.37
-460.40
-3.06
0.59
0.77
74.61
-121.41
25.55
0.70
0.84
IV
(%Na2O/«CaO) ,
Excess Oxyqen
177.66
-438.58
-1.43
0.51
0.71
121.66
-158.40
-3.17
0.049
0.22
V
(%CaO] ,
IMqOl
111.39
-6.79
25.52
0.41
0.64
23.43
-2.31
41.68
0.84
0.92
VI VII
(%CaO/%Mg01 ,
l»CaO/%HgO) Excess Oxygen
5.2 123.
68.3 -6.
-0.
0.020 0.
0.17 0.
2.37 101.
84.72 -24.
10.
0.032 0.
0.18 0.
47
51
76
13
36
16
59
82
84
92
VIII
|»CaO/»Mg01, |!
Load/105 L
241.65
-26.01
-14.62
0.72
0.85
95.64
1.28
-5.23
0.02
0.14
IX
[% CaO/% MgO),
ixceaa Oxygen x 10
Load
250.
-33.
2.
0.
0.
81.
-3.
4.
0.
0.
81
26
31
45
67
24
86
21
38
62
.- X
' [%CaO/%MgO],
-1 f%HgO/%fiiO.l
92.98
20.16
-360.39
0.38
0.62
68.88
0.91
637.09
0.48
0.69
-------
TABLE 2-7b. MULTIPLE REGRESSION ANALYSES FOR TWO WESTERN COALS ON TWO PULVERIZED-COAL BOILERS
k
Relationships for Percent Sulfur Emitted of the Form
BZ
Y = A X e (or In Y = a •*• b In X + c Z)
to
Site (Coal)
Alma
(Sarpy Creek, Montana)
a
b
c
R2
Fit Correlation (R)
Fremont
(Hanna-Rosebud ,
Wyoming)
a
b
c
R2
Fit Correlation (R)
XI
[% CaO/% MgO] ,
Load/105
7.55
-1.72
-0.18
0.76
0.87
4.53
0.07
-0.07
0.04
0.20
XII
[% CaO/% MgO]
Excess Oxygen x 105
Load
8.28
-2.38
0.03
0.52
0.72
4.39
-0.09
0.04
0.35
0.59
XIII
%CaO ' %SiOp
%AL 0 • %MgO ,
Load/105
3.83
0.25
-0.01
0.31
0.56
5.78
-0.45
-0.22
0.61
0.78
XIV
Excess Oxygen,
Load/105
5.28
-0.29
-0.23
0.96
0.98
4.25
0.29
-0.15
0.32
0.57
-------
TABLE 2-8. COMPARISON OF MEASURED AND CALCULATED PERCENT FUEL SULFUR EMITTED
Fuel Sulfur Emitted
Calculated
Based
on Excess
Calculated
Based on
Gronhovda
Oxygen Coefficient
Site/Coal
Alma
Sarpy Creek,
Montana
Fremont
Hanna-Roaebudi
Wyoming
Test
No.
72
74
75
76
78
3
4
S
6
7
Measured
»
85
84
76
86
91
93
87
107
95
87
and Load
%
89
91
83
83
89
98
85
105
94
88
(%)
(A)
100
97
96
97
97
106
105
104
106
106
I
(B)
86
87
77
86
85
93
94
101
88
83
II
(0
89
80
81
85
88
96
96
97
90
81
Calculated Based on
III
90
82
79
83
86
97
84
102
94
92
IV
87
79
81
87
87
98
94
86
84
97
V
89
81
81
86
86
98
86
105
92
89
VI
96
98
96
95
95
92
94
92
91
90
Relationships in Tables 2-7a 6 b (»)
VII
84
82
84
87
86
97
96
105
91
89
VIII
88
82
79
83
99
92
95
94
95
93
IX
89
81
81
83
88
90
94
98
100
88
X
87
87
79
84
84
98
93
101
89
88
XI
88
82
79
83
91
92
95
94
95
92
XII
89
81
80
83
89
90
94
97
99
88
XIII
87
87
80
83
84
98
88
98
98
86
XIV
84
81
76
86
91
93
96
97
96
86
(A), (B) and (C) indicate correlation coefficients used in Figures 2-12 and 2-13 that follow.
-------
100
95
52 90
B
W
w
Q
H
85
£ so
75
Gronhovd's
New Coeff.
CaO, NaO
o
D
75
(A) from (2)
(B) from Equat. I, Tab. 2-
(C) from Equat. II,
Tab. 2-6
O D
80 85 90 95
SULFUR OXIDES EMITTED CALCULATED, %
100
Figure 2-12. Percent sulfur oxides emitted (measured) vs. percent sulfur
oxides emitted (calculated). Alma Unit 3, Sarpy Creek,
Montana coal.
29
-------
100
I
g
95
90
85
80
75
O D
I
I
OODD
(A) from (2)
(B) from Equat. I,
Tab. 2-6
(C) from Equat. II,
Tab. 2-6
I
Gronhovd's
New Coeff.
CaO, Na_O
\
• (A)
O (B)
D (C)
I
75
80 85 90 95 100
SULFUR OXIDES EMITTED CALCULATED, %
105
110
Figure 2-13.
Percent sulfur oxides emitted (measured) vs. percent sulfur
oxides emitted (calculated), Fremont Unit 6, Hanna-Rosebud,
Wyoming coal.
30
-------
TABLE 2-9. SULFUR RETENTION BY THE ASH OF THE COALS TESTED DURING LABORATORY
ASHING AT 700-750 °C AND SUBSEQUENT MINERAL ANALYSIS BY COMMERCIAL TESTING
Site/Coal Type
Alma/E
Stout/W
Stout/E
Eau Claire/W
Eau Claire/E
Madison/W
Madison/E
Willmar/W
Willmar/E
Fairmont/E
Fairmont/E
Fairmont/Blend
Fairmont/W
St. Johns/W
St. Johns/E
Waupun/Blend RDF
Waupun/W
Waupun/RDF
Fremont/Wyo
Fremont/Wyo
Fremont/Wyo
Fremont/Wyo
Fremont/Wyo
Fremont/Colo
Average
Test No.
9
14
31
7
30
5
14
8
34
3
7
12
—
8
16
2
—
—
3
4
5
6
7
9
Retention
Percent Retention
East West Blend
6.2
1.3
2.6
1.4
2.6
1.1
4.8
15.3
Eastern Coal
(Low CaO+MgO)
7.7
33.0
41.04
65.4
46.2
18.1
54.5
47.9
75.0(W + RDF)
69.2
123.6(RDF)
17.0
10.3
18.8
9.9
8.4
70.8
Western Coal
(High CaO+MgO)
53.1
E = Eastern
W = Western
Wyo = Wymoing (Hanna-Rosebud)
Colo = Colorado (Walden)
RDF = Refuse-Derived Fuel
31
-------
Table 2-10 presents the variations of fuel sulfur retention with cal-
cium to sulfur ratio for a series of lignite samples with and without added
lime that were evaluated in our laboratory. These experiments are of interest
because it allows an experimental and theoretical comparison of the sulfur
retention properties of a fuel with a known added amount of one particular
metal compound. In this case the metal was calcium. Calcium is probably the
most economical metal to be used in the near term to reduce sulfur. Experiments
sponsored by EPA at Battelle Columbus Labs on a stoker fired boiler using lime
augmented coal briquetts are currently underway. This briquetting of lime and
coal technique is also being studied by the Ohio Department of Energy. There-
fore it was of interest to present the results of these laboratory studies
since they are relevant to the topic of sulfur retention. Figure 2-14 is the
graphical representation of these variations. Commercial Testing processed
these lignite samples with various molar calcium to sulfur ratios for sulfur
retention under laboratory conditions. In some cases lime was added to
increase the Ca/S ratio. The natural lignite had about 20% lime in the ash.
The average sulfur retention of the samples with added lime was 86% while the
average retention of the naturally occurring lignite was 66%.
Regression analyses of the data to assess possible relationships with
exponential, logarithmic and power functions lead to the power relationship
resulting in the closest agreement. The power function was of the form
Y =
where Y is the percent sulfur retention,
X is the Ca/S ratio, and
a and b are the coefficients.
2
The R of fit correlation was found to be 0.784. This correlation accounted
for 88.5% of the data.
The data showed that the amount of calcium in the coal does
significantly affect the amount of sulfur retained in the ash under the
proper (residence time and temperature) conditions. The boiler conditions
dictated how close to the optimum retention the boiler would operate.
32
-------
TABLE 2-10. VARIATION OF FUEL SULFUR RETENTION
WITH CALCIUM/SULFUR RATIO
Lignite Samples
Ca/S
0.55
0.64
1.36
1.65
2.63
2.58
1.18
2.80
0.59
% Retention
73.2
69.2
81.3
84.5
92.7
92.9
75.9
88.5
56.0
100 i
90
SO
£70
60
50
40
I
Equation of Curve
% Sulfur Retention
• 74.1 lea/Si0'22
R2 « 0.784
R • 0.885
I
0.5 1.0 1.5 2.0
LIGNITE SAMPLE Ca/S RATIO
2.5
3.0
Figure 2-14. Percent sulfur retention vs. calcium to sulfur (Ca/S) ratio
for lignite samples.
33
-------
SECTION 3.0
THERMOCHEMICAL EQUILIBRIUM SULFUR DISTRIBUTIONS
3.1 INTRODUCTION AND BACKGROUND
The primary objective of this task was to determine, on a thermochemical
equilibrium basis, the gas-phase and condensed-phase distributions of the fuel
sulfur as a function of coal type, temperature and air/fuel ratio (stoichiometry).
These distributions would establish the extent to which the sulfur was associated
with condensed phase (liquid and solid) species which could be electrostatically
precipitated from the flue gas or collected in the bottom ash.
A secondary objective was to evaluate which of the coal types investi-
gated would be amenable to greater sulfur retention by augmentation with
suitable additives. This was only a cursory evaluation and did not identify
sulfur retention sensitivity to augmentation.
All calculations were performed by a generalized computer program
developed by the National Aeronautics and Space Administration (NASA). This
program has received wide industrial acceptance and has recently been extended
specifically for greater flexibility in considering coal analyses.
3.2 COMPUTER PROGRAM
The computer program described in Reference 2 was used to calculate
the thermochemical equilibrium composition of four coal types over ranges in
both temperature and air/fuel weight ratios. This program, which has been
under development for many years, can consider up to 200 distinct species of
which a maximum of 100 may be condensed (liquid or solid).
The coal composition is specified as part of the input and the program
searches an extensive thermochemical file to select those species which can be
formed from the chemical elements present in the coal. The user can specify
that up to 66 species be omitted from those selected if it is known, a priori,
that these species are unimportant.
34
-------
The program then starts an iterative procedure to find product mole
fractions subject to the problem constraints. In this instance the tempera-
ture, pressure (one atmosphere), and elemental composition are the known
constraints. The program then cycles to the next set of constrainst using
the previous solution as an initial estimate of species concentrations.
At low temperature, the solution obtained may be somewhat inaccurate
because of uncertainties in species thermochemical data and the assumptions
that all gases are ideal and interactions among phases may be neglected.
The calculations were performed on an UNIVAC 1108 with certain key
variables expressed in double precision.
3.3 COAL COMPOSITIONS
Table 3-1 contains the coal compositions weight percentages, on a dry
basis, of the four coals investigated in the equilibrium calculations. Chlorine
was omitted from lignite, augmented lignite and Pittsburgh #8,since its
inclusion caused the species count to exceed the 200 limitation. This was
also justifiable since its maximum concentration was 0.02% in the coal.
Phosphorous pentoxide (p~O,.) was not included as an ash constituent because of
its low concentration. The ash metal oxide concentrations shown in Table 3-1
reflect their abundance in the coal and not in the ash.
These coals were selected to cover the range of coal types in terms
of ash composition and as well as to be representative of the coals tested in
the field study. The Montana coal was actually one of the test coals. The
Pittsburgh coal was similar to the eastern coals tested as well as being a
major steam coal. The lignite were investigated since there was laboratory
experimental data available for comparison. The augmented lignite served as
a case where a controlled amount of calcium had been added as well as having
combustion laboratory data on this coal.
•
As shown, there is only a factor of 2 difference in the sulfur content
of the coals, and this factor could increase to 3.5 to 4 for different eastern
coals. Even more pronounced is the difference in calcium (as CaO) content
among the coals, with Pittsburgh #8 being an order of magnitude less than the
next lower value. Further, Pittsburgh #8 has the lowest concentrations of
magnesium (as MgO) and sodium (as Na,0). The impact of these low concentrations
will be discussed later in more detail.
35
-------
TABLE 3-1. COAL COMPOSITIONS
Weight Per
Coal C H N 0 S Ash
Montana 69.78 6.51 0.96 8.70 1.05 13.00
Lignite 66.41 4.45 1.31 17.12 1.00 9.70
Augmented
Lignite 59.27 4.58 1.10 20.99 0.98 13.07
Pittsburgh
#8 77.45 5.19 1.51 6.71 1.84 7.28
cent, Dry
SiO? A12°T Tiop Fe2°T Ca° Mg° K?° Na?°
4.34 4.15 0.13 1.50 1.50 0.33 0.08 0.96
3.72 1.68 0.12 0.73 1.98 0.78 0.04 0.09
3.45 1.47 0.10 0.61 5.39 0.68 0.08 0.07
3.59 1.81 0.08 1.42 0.15 0.05 0.11 0.02
U)
o\
-------
3.4 COMPUTER RESULTS
A total of 160 discrete point calculations were obtained for the
following conditions:
Pressure - 1 atmosphere
Temperature - 3300, 2900, 2500, 2100, 1700, 1300, 900, 500 °F
Stoichiometry - 50, 75, 100, 125, 150% theoretical air (by weight)
The calculations were performed in decreasing temperature steps in order to
minimize computer time, i.e., the solutions were first obtained with the
fewest number of condensed species present. Table 3-2 presents the computer
output for lignite coal at 50% theoretical air. The density and mole fraction
—4
print format is interpreted as follows: 8.4421-4 = 8.4421x10 . The last
part of Table 3-2 lists those species whose concentrations were less than
1x10 (1 ppm) throughout the temperature range.
A sulfur mass balance was established for each of the 160 point
calculations in order to determine which species were combined with sulfur
as a function of temperature and Stoichiometry. The resulting distributions
were then summed by species phase, gas vs. liquid/solid.
The results of the sulfur mass balance for each coal are presented
in Tables 3-3 to 3-6. Only those values greater than, or equal to, 0.1% are
shown in order to improve their readability. The values in Tables 3-3 to
3-6 represent the weight percentage of the total sulfur associated with
each species. For example, in Table 3-3 at 50% theoretical air and 3300 °F,
the sulfur contained in the COS molecule represents 3.6% of the total sulfur
mass in the system. Similarly, H S contains 36.3% of the total sulfur, etc.
Further, all the sulfur is combined with gas-phase species. Conversely, at
500 °F 97.4% (48.0 + 2.5 + 46.9) of the sulfur is associated with condensed
species (L - liquid, S - solid).
Table 3-7 was prepared by summing up the sulfur content of the
condensed species for each of the 160 discrete point calculations. As
anticipated, low temperatures favor sulfur retention by condensed species,
i.e., except for Pittsburgh #8 over 90% of the sulfur is associated with
condensed species for temperatures of 900 °F and less.
37
-------
09/15/78 10152111 COAL
TABLE 3-2. COMPUTER OUTPUT FOR LIGNITE AT 50% THEORETICAL AIR
OI30AA25 000150 9 100 DATE 091578
THERMODYNAMIC EQUILIBRIUM PROPERTIES AT ASSIGNED
TEMPERATURE AND PRESSURE
CASE NO.
CHEMICAL FORMULA
FUEL
FUEL
FUEL
FUEL
FUEL
FUEL
FUEL
FUEL
FUEL
C 1.00000
31 1,00000
AL 2.00000
TI 1.00000
FE 2.00000
CA 1.00000
MG 1.00000
K 2.00000
NA 2.00000
OXIDANT N 1,56180
0/F* a. 2373
H .79670
0 2.00000
0 3.00000
0 2.00000
0 3.00000
0 1.00000
0 1.00000
0 1.00000
0 1.00000
0 .41960
PERCENT F
.01690
.00570
.19350
AR .00930
.• 19.0936
C .00030
EQUIVALENCE RATIO. 1.8211
PAGE
NT FRACTION
(SEE NOTE)
.902982
.037203
.016812
.001154
.008673
.023369
.007790
.000960
.001057
1.000000
ENERGY STATE TEMP
CAL/MOL
.000
.000
,000
.000
.000
.000
.000
.000
.000
,000
DEC K
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
DENSITY
c/cc
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
PHI* 2.0000 REACTANT DENSITY* .0000
w
00
THERMODYNAMIC PROPERTIE8
P, ATM 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000
T, DEC K 2089.0 1667.0 1644.0 1422.0 1200,0 976.0 756.0 533.0
RHO, G/CC 1.5750*4 1.7657-4 2.0060*4 2,3193-4 2,7484*4 3,3729*4 4.9846*4 7.3352-4
H, CAL/G 23.2 *S9.3 -136.1 -210.2 -263.3 -355.7 -596.0 -692.1
8* CAL/C6)(K) 2,3404 2,2967 2,2549 2,2065 2,1506 2.0640 1,6075 1,6603
M, MOL NT
(DLV/DLP)T
(DLV/DLT)P
CP, CAL/(6)(K)
GAMMA (3)
SON VEL.M/8EC
26.996 27.050 27.061
•1.00099 -1.00036 -1.00003
1.0233 1.0069 1.0007
.3645 .3562 .3369
1.2492 1.2652 1.2792
696.5 852.1 803.8
27.062 27.062 27.067 30.923 32.061
•1.00001 -1.00002 -1.00009 -1.01272 -1.00095
1.0001 1.0002 1.0019 1.2567 1.0201
.3313 .3270 .3247 .6526 .2964
1.2648 1.2697 1.2935 1.1665 1.2740
749.2 689.5 623.4 486.9 419.5
(S) = Solid
MOLE FRACTIONS
AL203CS)
AR
C(3)
CO
COS
CQ2
CAO(S) i
CAOH <
CA02H2(S)
CA02H2 '
CA3(S)
FE '
FEO(S)
FEO(L)
FEQ
,4421-4
.9670*3
.0000 0
.4540-1
.4013-5
.7895-2
i. 1209-3
2.942 -6
.0000 0
»,569 -6
.0000 0
S.206 -4
.0000 0
.0000 0
1.007 -5
6.
6.
.
2.
1.
«.
1.
1.
.
1.
3.
4.
•
5.
«.
4514-4
9736-3
0000 0
4265-1
0594-4
0875-2
7976-3
736 -7
0000 0
536 -6
3671-4
560 -5
0000 0
0145-4
659 -7
6.
6.
.
2.
5.
4,
1.
«.
.
1.
1.
1.
5.
.
7.
4543-4
9762-3
0000 0
3852-1
0240*5
5157-2
0292-3
548 .9
0000 0
456 .7
1074-3
770 -6
5293-4
0000 0
919 .9
8.4546-4
6.9765-3
,0000 0
2.3311-1
1.6590-5
5.0615-2
7.2344-4
3.742-11
,0000 0
6,357 -9
1,4134-3
1.674 -8
5.5669-4
.0000 0
2.746-11
6
6
2
4
5
5
4
8
1
3
5
1
.4546-4
.9766-3
,0000 0
.2547-1
.6679*6
,6272*2
.7952-4
,927-14
.0000 0
.131-11
.5573-3
.515-11
.5697-4
.0000 0
.072-14
6.4555-4
6,9772-3
,0000 0
2,1499-1
6,1142*7
6,6758-2
5,2979-4
2.929-18
,0000 0
1.261-13
1.6072-3
3.656-15
5.5702-4
.0000 0
1.052-19
6.4555-4
6.9772-3
1.2359-1
1.6566-2
3.9398*8
1,4361-1
5.7560-4
3.026-25
.0000 0
3.061-17
1.5612-3
6.920-23
5.5702-4
.0000 0
8.592-28
8.4719-4
6.9907-3
1.5369-1
4.6367*5
1.6639*6
1,2962*1
.0000 0
.000 0
6.6600-4
3.757-27
1,4551-3
,000 0
.0000 0
,0000 0
.000 0
-------
TABLE 3-2. (Continued)
vo
09/15/79 10152111 COAL 0130AA25
000130
100
FE02H2
FE304(S)
H
H2
H20
H28
K
KOH
K202H2
K2S04(3)
MG
MCCOJ(S)
HCO(S)
HGOH
MC02M2
N6TI205(S)
MG2TIOa(S)
MC2TI04U)
NO
N2
NA
NACN
NAOH(L)
NAOH
NA2S04(8)
OH
8
SH
80
302
820
SIO
8102(8)
8102(8)
3102(8)
8I02U)
8102
SIS
2.538 .5 9.230 -6 2.243 -6 2.553 -7 1.212 -8 1.272*10 6.426-13 7,121-19
.0000 0 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0 1.8603-4
7.300 -4 1.576 -4 2.250 -5 1.788 -6 5.649 -8 3.778-10 8.290-14 9.273-21
6.4144-2 6,6778-2 7.0555-2 7.5973-2 8.3634-2 9.4147-2 4.5676-2 3,1254-3
4.7897-2 «.5403-2 4.2180-2 3.7023-2 2.9476-2 1.8969-2 6.7465-2 1.0962-1
4.5112-4 8.1685-4 4.3284-4 1,8302-4 5.4036-5 8.5603-6 3,1908-6 2.4160-5
8.634 -5 7..98J -5 6.927 -5 5.345 -5 3.258 -5 1.269 -5 1.329 -9 4.571-22
1.804 -5 2.465 -5 3.525 -5 5,107 -5 7.192 -5 8,874 -5 7.470 -7 2.657-16
2.172-13 1.489-12 1.617-U 3.051-10 1.242 -8 1.552 -6 1.380 -7 6,934-21
.0000 0 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0 5.1754-5 5.2366-5
6.486 -5 2.736 -6 4.692 -8 2.286-10 1.522-13 3,635-18 7.030-27 .000 0
.0000 0 ,0000 0 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0 9.5578-4
7.6560-4 8.3867-4 8.4259-4 8.4273-4 8.4275-4 8.4282-4 8.4282-4 .0000 0
7.094 -6 4.204 -7 1.113 -8 9.348-11 1.276-13 8.088-18 9.417-25 .000 0
3.758 -6 5.729 -7 5.108 -8 2,07l -9 2*411-11 3,292-14 6.621-18 4.442-27
.0000 0 .0000 0 .0000 0 .0000 0 ,0000 0 .0000 0 ,0000 0 3,7109-5
.0000 0 7.4039-5 7.4065-5 7,4068-5 7.4069-5 7.4075-5 7.0075-5 .0000 0
7.3913-5 .0000 0 .0000 0 .0000 0 ,0000 0 ,0000 0 .0000 0 ,0000 0
7.902 -6 6.917 -7 3.074 .8 5.104-10 1.806-12 4.637-16 1.632-20 7.689-29
5.8739-1 5.8797-1 5.8817-1 5.8819-1 5.8821-1 5.8824-1 5.8825-1 5.8939-1
1.631 -4 1.599 .4 1.544 .4 1.449 -4 1.265 -4 2.890 -5 4.128-10 4.242-21
2.315 -9 6.783 -9 2.670 -8 1.635 -7 1.949 -6 2.171 -5 8.306-10 1.973-20
.0000 0 .0000 0 .0000 0 .0000 0 .0000 0 1.0111-4 1.7492-4 .0000 0
1.127 -5 1.463 -5 2.021 -5 2.960 -5 4.632 -5 2.319 -5 1.480 -8 5.338-17
.0000 0 .0000 0 .0000 0 .0000 0 ,0000 0 ,0000 0 ,0000 0 8.7635-5
6.283 -5 8.063 -6 5.839 .7 1,831 -8 1.535-10 1,354-13 2.107-17 7.622-25
6.039 -5 1.6B8 -5 5.715 -7 6.650 -9 1.451-11 1.864-15 2.103-20 3.945-27
2.400 -4 1.330 -4 1.551 -5 9.039 -7 1.772 -8 5.402-11 6.096-14 2.363-17
3.383 -4 7.736 -5 2.898 .6 3.725 -8 8.969-11 1.235-14 2.852-18 9.015-23
4.323 -4 1.264 -4 6.470 -6 1.218 -7 4.825-10 1.296-13 1.635-15 5.627-17
1.737 -6 8.765 -7 2.227 .8 1.666-10 1.852-13 7.819-18 5.261-21 2.284-22
3.534 -4 1.064 -5 1.142 -7 2*992-10 8.419-14 5.511-19 1.264-28 .000 0
.0000 0 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0 3.1753-3 3.1815-3
.0000 0 .0000 0 .0000 0 .0000 0 .0000 0 3.1753-3 .0000 0 .0000 0
.0000 0 3.1628-3 3.1747-3 3.1750-3 3.1751-3 ,0000 0 .0000 0 .0000 0
2.6121-3 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0 .0000 0
1.065 -6 2.050 -6 1.221-10 1.461-13 1.368-17 1.810-23 6.277-33 .000 0
4.106 -6 2.690 -7 1.932 -9 2.978-12 4.032-16 9.099-22 3.868-32 .000 0
DATE 091578
PACE
(S) = Solid
ADDITIONAL PRODUCTS MHICH MERE CONSIDERED BUT WHOSE MOLE FRACTIONS MERE LESS THAN .10000-05 FOR ALL ASSIGNED CONDITIONS
AL
CN
FES(8)
K(8)
MGN
N20
NA2804C8)
SI
TIO(8)
TI305(8)
AL02
CS
FE8(8)
ML)
MGO(L)
NA(S)
NA2804(8)
SIH
TIO(S)
TI305(8)
AL02H
CS2
FES(L)
KO
MGO
NA(L)
NA2804U)
TI(S)
TIO(L)
TI30SCL)
AL20
C2H
FE804O)
K2
HG02H2O)
NAH
NA2S04
TH3)
TIO
TI407(8)
AL202
CA
FES2(S)
K20(8)
M68(8)
NAO
0
TKL)
TI02(8)
TI407U)
AL203U)
CAO
FE203(S)
K2804(8)
HGS
NAOH(S)
02
TI
TI02U)
C
CAS04(S)
FE2S3012O)
K2S04(L>
MGSOU<8)
NA2
8(8)
TIC(S)
TI02
CH
FE02H2(S)
HCN
MG(8)
MCSOflCL)
NA20
8(L)
TIC(L)
TI203O)
CH2
FE03H3(8)
H2S04(L)
HG(L)
MGTI205CL)
NA202(8)
803
TIN(8)
TI203(S)
CH20
FE8(S)
H2804
MGH
N02
NA202O)
8KS)
TIN(L)
TI203U)
NOTE. HEIGHT FRACTION OF FUEL IN TOTAL FUELS AND OF OXIDANT IN TOTAL OXIDANTS
-------
TABLE 3-3. SULFUR DISTRIBUTION, MONTANA COAL
Species
COS
CaS(S)
caso4(S)
FeS(S)
V
"V»4
N.2S04(S,
Na S04 (L)
Na2S04
s
SH
SO
"2
s2o
sis
50» TA
Temperature, 10
33 29 25 21 17
3.6
36.3
4.9
16.8
18.0
20.0
0.2
0.3
5.9
8.7
65.0
1.0
9.2
4.1
5.9
0.1
2.8
60.8
34.8
1.1
0.2
0.3
1.3
80.9
17.7
0.1
1.1
80.9
18.0
2-F
13
0.6
80.9
6.9
11.6
9
0.1
80.9
8.1
8.4
2.5
5
48.0
2.6
2.5
46.9
Woiqht % of Total Sulfur
33
0.1
0.7
0.4
0.7
11.1
87.0
29
0.8
5.0
0.3
1.4
8.7
87.3
75% TA
Temperature, in °F
25 21 17 13 9
4.9
37.0
0.1
2.3
4.1
51.7
3.G
59.0
35.1
0.3
0.1
2.0
1.3
80.9
17.8
0.8
80.9
18.3
0.1
80.9
7.9
8.6
2.5
5
48.8
1.8
2.5
46.9
33
0.6
99.4
29
0.1
99.9
1001 TA
Temperature, 10 *F
25 21 17 13 9 5
0.1
99.9
32.0
0.7
67.4
1.9
46.7
51.4
45.6
0.6
2.5
46.9
4.5
6.6
43.6
0.5
2.5
46.9
12.2
36.9
1.5
2.5
46.9
Note i Only non-zero entries are shown.
(s) = solid
(continued)
-------
TABLE 3-3 (Continued).
Species
COS
CaS(S)
CaS04(S)
FeS(S)
W*
Na2S04(S)
Ha2S04(L)
Na2S04
s
SH
SO
"2
"3
SiS
Weight % of
125* TO
Teoperature, 10 °?
33 29 25 21 17 13 9 5
0.2
99.8
0.1
99.8
0.2
1.3
98.1
0.4
22.7
43.8
0.8
3?. 3
0.4
51.0
2.2
46.8
50.6
2.5
46.9
50.6
2.5
46.9
50.6
2.5
46.9
Total Sulfur
150% TA
Temperature, 10 °F
33 29 25 21 17 13 9 5
99.9
0.1
99.8
0.2
1.4
98.1
0.5
25.5
43.5
1.0
29.6
0.4
51.0
2.2
46.8
50.6
2.5
46.9
50.6
2.5
46.9
50.6
2.5
46.9
Note: Only non-zero entries are shown.
(s) = solid
-------
TABLE 3-4. SULFUR DISTRIBUTION, LIGNITE
Species
COS
CaS(S)
CaS04 (S)
H2S
WS)
Na2S04(S)
Na2S04(L)
Na2S04
S
SH
SO
so2
so3
s2o
SiS
33
4.0
28.0
5.0
14.9
21.0
26.8
0.2
0.3
29
6.6
20.9
50.6
1.1
8.2
4.8
7.8
50» TA
Temperature, 10 T
25 21 17 13
3.1
68.5
26.8
1.0
0.2
0.4
1.2
87.5
11.3
0.1
0.3
96.4
3.3
99.4
0.5
9
96.6
0.2
3.2
5
89.9
1.5
3.2
5.4
Weight % of Total Sulfur
33
0.1
0.4
0.4
0.5
10.1
88.5
29
0.7
3.2
0.3
1.1
8.2
86.6
75* TA
Temperature), 10 °F
25 21 17 13
5.2
27.9
0.1
2.0
4.4
60.3
0.2
3.7
68.2
25.7
0.2
0.1
2.1
0.8
90.6
8.6
0.1
98.2
1.7
9
96.6
0.2
3.2
5
90.3
1.0
3.2
5.4
33
0.6
99.5
100\ TA
Temperature, 10
29 25 21 17
0.1
99.9
100.0
0.3
0.6
99.1
8.7
3.0
5.3
83.0
2 «F
1395
85.3
1.0
3.2
5.4
5.0
12.0
79.0
0.3
3.2
5.4
17.2
73.4
0.8
3.2
5.4
Is)
Hotei Only non-zero entries are shown.
(s) = solid
(Continued)
-------
TABLE 3-4 (Continued).
it*
W
Species
COS
CaS(S)
CaS04(S)
H2S
K2S04(S)
Na2S04(S)
Na2S04(L)
Na2S04
S
SH
SO
so2
so3
s2o
SIS
Weight * of Total Sulfur
125* TA
Temperature, 10 *F
33 29 25 21 17 13 9 5
0.2
99.8
0.1
99.8
0.2
99.6
0.4
67.1
2.9
0.8
29.0
0.3
91.7
3.0
5.3
91.4
3.2
5.4
91.4
3.2
5.4
91.4
3.2
5.4
ISO* TA 2
Temperature, 10 °F
33 29 25 21 17 13 9 5
99.9
0.1
99.8
0.2
90.5
0.5
69 . 6
2.6
0.9
26. f.
0.4
91.7
3.0
5.3
91.4
3.2
5.4
91.4
3.2
5.4
91.4
3.2
5.4
Note: Only non-zero entries are shown.
(s) = solid
-------
TABLE 3-5. SULFUR DISTRIBUTION, AUGMENTED LIGNITE
Species
COS
CaS(S)
CaS04(S)
H2S
K2S04(S)
Ha2S04(S)
Ha2S04(L)
S
SH
SO
"a
"3
s2o
SIS
50» TA
Temperature, 10 *P
33 29 25 21 17 13
25.8
4.3
13.3
21.3
31.7
0.2
0.2
6.1
58.7
1.1
9.3
6.1
11.7
0.2
63.4
31.4
1.1
0.2
0.6
85.3
13.4
0.1
0.3
95.7
4.1
99.3
0.7
9 5
98.1
0.2
1.7
100.0
Weight % of Total Sulfur
33
0.1
0.5
0.3
0.5
9.9
88.7
29
0.7
3.4
0.3
1.1
7.9
86.7
75» TA
Temperature, 10 *P
25 21 17 13 9 S
4.7
28.8
0.1
1.9
4.2
60.0
0.2
3.4
66.5
27.5
0.2
0.1
2.2
0.8
89.9
9.3
0.1
98.1
1.8
98.1
0.2
1.7
92.fi
1.2
1.8
4.5
100* TA
Temperature, 10 *F
33 29 25 21 17 13 9 5
0.6
99.4
0.2
99.9
0.1
99.9
100.0
0.1
1.2
4.3
94.5
0.1
17.4
66.9
3.3
1.8
4.5
6.1
37.7
55.7
0.4
1.8
4.5
42.8
50.0
1.0
1.8
4.5
Note: Only non-sero entries are shown.
(s) - solid \
(Continued)
-------
TABLE 3-5 (Continued).
Species
COS
CaS(S)
CaS04(S)
K.,S04(S)
Na2S04(S)
Na2S04(L)
H.2S04
S
SH
SO
so2
so3
s2o
SiS
Hoiqht \ of Total Sulfur
125% TA
Temperature, 10 *F
33 29 25 21 17 13 9 5
0.2
99.8
0.1
99.8
n.2
99.fi
0.4
69.9
2.0
0.7
?7.P
0.3
94.0
1.5
4.4
93.8
1.8
4.5
93.8
1.8
4.5
91. n
i.a
4.r>
150t TA ,
Temporal uro , 10" °F
33 29 25 21 17 13 0 5
99. 9
.1.1
99. fi
0.2
99. S
n.s
72.4
1.7
n.n
94..
..S
4...
.'4.7
n.4
9 i.n
I.H
4.5
91.11
I.H
4 . S
•>-..„
1 ."
4.'.
i
Note: Only non-zero entries are shown.
(s) = solid
-------
TABLE 3-6. SULFUR DISTRIBUTION, PITTSBURGH #8
Species
COS
CaS(S)
CaS04(S)
FeS(S)
FeS(L)
FeSj(S)
Fe2(S04)3(S)
H2S
£.
HgS04(S)
Na2S04(S)
Ha2S04(U
S
SH
SO
S02
"3
s2o
50% TO
Temperature, 10 °F
33 29 25 21 17 13
4.7
35.5
5.9
18.2
18.3
17.3
0.3
8.0
65.9
1.3
10.4
4.3
5.3
0.2
7.2
19.7
65.2
0.1
2.3
0.3
0.5
5.7
31.9
57.4
0.3
5.0
32.0
58.3
4.5
32.0
58.9
9
0.7
32.0
59.8
2.2
0.7
5
63.9
28.6
2.2
0.7
Weight % of Total Sulfur
33
0.2
0.6
0.4
0.6
11.1
87.2
29
0.9
4.0
0.3
1.3
8.8
84.6
0.1
75% TA
Temperature, 10 °F
25 21 17 13
5.8
31.7
0.2
2.2
4.4
55.4
0.3
11.0
77.8
0.7
0.3
5.4
0.1
5.7
31.9
57.6
3.7
31.9
59.6
9
1.1
31.9
59.4
2.2
0.7
5
63.9
28.6
2.2
0.7
33
0.6
99.5
100% TA
Temperature, 10 "F
29 25 21 17 13 9 5
0.1
99.9
100.0
100.0
2.1
0.6
92.6
2.2
0.7
92.5
1.6
2.2
0.7
90.9
4.6
0.2
2.2
2.1
0.7
85.6
Mote: Only non-zero entries are shown.
(s) = solid
(Continued)
-------
TABLE 3-6 (Continued).
Species
COS
CaS(E)
CaS04(S)
PeS(S)
FeS(L)
PeS2(S)
Fe2(S04)3(S)
H2S
H2S04
KjSC^IS)
KjSO^IL)
HgS04(S)
Ha2S04(s>
Na2S04U>
Ha2S04
S
SH
SO
so2
so3
s2o
Weight t of Total Sulfur
125% TA
Temperature, 10 'f
33 29 25 21 17 13 9 5
0.2
99.8
0.1
99.8
0.2
99.6
0.4
4.7
0.9
0.3
93.1
1.1
4.7
2.2
0.7
87.9
4.6
4.7
2.2
2.1
0.7
61.3
29.1
4.7'
47.9
0.3
2.2
2.1
0.7
2.4
39.8
4.7
47.9
36.7
2.2
2.1
0.7
5.8
150% TA 2
Temperature, 10 *F
33 29 25 21 17 13 9 5
0.1
99.8
0.1
99.8
0.2
99.5
0.5
0.8
0.3
92. B
1.4
2.2
0.7
86.7
5.8
2.2
2.1
0.7
55.9
34.5
47.9
0.3
2.2
2.1
0.7
1.9
40. 3
47.9
35.8
2.2
2.1
0.7
6.7
Notei Only non-zero entries are shown.
(s) = solid
-------
TABLE 3-7. SULFUR RETENTION BY CONDENSED SPECIES
Weight % of Total Sulfur
*>
GO
Coal
Montana
Lignite
Augmented Lignite
Pittsburgh #8
% TA
50
75
100
125
150
50
75
100
125
150
50
75
100
125
150
50
75
100
125
150
3300
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2900
8.7
0
0
0
0
20.9
0
0
0
0
6.1
0
0
0
0
4.7
0
0
0
0
2500
60.8
0
0
0
0
68.5
0
0
0
0
63.4
0
0
0
0
24.3
0
0
0
0
Temperature
2100
80.9
59.0
32.0
66.5
68.9
87.5
68.2
0.3
69.9
72.1
85.3
66.5
0
72.0
74.2
36.6
4.7
0
5.6
5.5
, °F
1700
80.9
80.9
48.6
100.0
100.0
96.4
90.6
17.0
100.0
100.0
95.7
89.9
5.5
100.0
100.0
36.6
36.6
7.4
7.5
7.5
1300
87.8
80.9
95.0
100.0
100.0
99.4
98.2
94.0
100.0
100.0
99.3
98.1
90.5
100.0
100.0
36.6
36.6
7.5
9.6
9.6
900
91.5
91.2
99.5
100.0
100.0
99.8
99.8
99.7
100.0
100.0
99.8
99.8
99.7
100.0
100.0
39.5
39.5
7.5
57.5
57.5
500
97.4
98.2
98.6
100.0
100.0
98.5
99.0
99.2
100.0
100.0
100.0
98.8
99.1
100.0
100.0
71.4
71.4
14.2
57.5
57.5
-------
As previously mentioned, Pittsburgh #8 had a low calcium content in
comparison with the other coals—by at least a factor of 10. An examination
was made of the computer output at 500 °F for all coals in order to perform
calcium, potassium and sodium mass balances with the results shown in
Table 3-8. The results were that all the calcium in Pittsburgh #8 combined
with sulfur to form CaS(s) at 50 and 75% theoretical air, and form CaSO (s)
at the higher air levels. The calcium in the other three coals was present
in sufficient quantities so that it formed Ca(OH) (s) , a non-sulfur containing
compound, in addition to CaS(s) and CaSO.(s). The additional calcium (as
CaO) in augmented lignite appears to be converted directly to additional
Ca(OH)_(s), instead of forming additional condensed sulfur compounds.
Aside from augmented lignite at 50% theoretical air, all the potassium
and sodium was associated with their respective sulfates.
Based on the results of thermochemical equilibrium considerations, it
may be possible to increase the condensed phase sulfur retention of
Pittsburgh #8 coal by augmentation primarily with calcium (as CaO). Augmenta-
tion with potassium and/or sodium does not appear to offer significantly
greater condensed phase sulfur retention.
3.5 DISCUSSION OF THE EQUILIBRIUM RESULTS
The potential performance of sulfur retention by the ash for different
combustion modes can be demonstrated by observing the predicted equilibrium
ash composition at the various theoretical air levels and temperatures for the
Montana coal shown in Table 3-3. The combustion modes considered are:
. pulverized coal combustion
fuel bed coal combustion
cyclone coal combustor
The degree of sulfur retention in each of these combustion systems
is governed by the equilibrium consideration of:
ash composition
temperature
stoichiometry
49
-------
TABLE 3-8. MASS BALANCES FOR CALCIUM, POTASSIUM AND SODIUM AT 500 °F
Weight Percent of Total Element
Coal
Montana
Lignite
Augmented
Lignite
Pittsburgh 18
Element
Calcium
Potassium
Sodium
Calcium
Potassium
Sodium
Calcium
Potassium
Sodium
Calcium
Potassium
Sodium
50
40.6* CalOII). IS),
Si. 4% CaS 1ST
32.0» Ca(OH) IS),
68.3% CaS 1ST
2 4
100% CaS (S)
100% K2(OH)2
100% NaOH (S)
100% CaS (S)
Percent Theoretical Air (by Weight)
T> ion 125 no
39.7% C.I (Oil), IK), 19.2% Ca(OII) (S), 37.4% Ca(OH) IS), 37 .4% r,i (OH) , (S) ,
&0.3\ CaS (St r>.l% CaS 1ST, 62. 6\ CaSO TS) r,2.f>\ CaPO Ts)
4S.7\ CaS04 (S) * 4
31.7% Ca (OH), (S), 31.5% Ca (OH) (S) , 30.9%Ca(OH* (S) , 30.9%Ca(OH) (S) ,
68. 3\ CiS (St 13.0% CaS ISj, 69.1% CaSO TS) 69.1% CaSO TS)
55.5% CaS04 (S) * *
75.6% Ca (OH). (S), 75.5% Ca(OH). (S) , 75.3%Ca(OH) (S) . 75.3%Ca(OH) (S) ,
24.4% CaS (ST 11.3% CaS (ST, 24.7% CaSO TS) 24.7% CaSO TS)
lj.2% CaS04 (S) 4
Ul
o
-------
On top of these considerations must be added
. mixing or contact of sulfur with metals
kinetic limitations of the sulfur reactions
temperature and stoichiometry as a function of time
in the combustor
Each of these factors will be discussed for each combustor type listed above.
The equilibrium calculation show that calcium and sodium are the major
species that combine with sulfur and form liquids or solids at temperatures in
the furnace.
3.5.1 Pulverized Coal
In a pulverized coal flame the reactants are fairly well mixed so that
good contact of the sulfur and metals should occur. However when the coal
particles approach the flame they are heated and begin to devolatilize the
carbon, hydrogen, and sulfur. The metals in the ash are concentrated in the
particle until such time as they are heated to their melting point or vaporize.
In a pulverized coal flame it is very difficult to make the gas phase fuel
rich. The overall bulk stoichiometry may be fuel rich but in the flame the
rate of devolatilization and combustion is not sufficiently rapid to make the
gaseous region surrounding the coal particle fuel rich. Therefore there is
always oxygen available to form sulfur oxides. This along with the equilibrium
constraints are the reasons that large amounts of SO are formed even in sub-
stoichiometric flames.
The temperature and stoichiometry history of the coal particle can
severely affect the sulfur retention. For example, as the particle heats
up it passes through a low temperature fuel rich region where the predicted
equilibrium products are calcium sulfide. However, if these products are
formed in this stage they ultimately pass into a high temperature oxidizing
region where the favored equilibrium products are SO_. Controlling the
temperature of this stage of the flame can shift the favored equilibrium
products to CaSO and Na SO..
It is interesting to note that the same control measures that favor
low NO emissions from P.C. coal flames are also the condition that should
x
favor high sulfur retention by the metals in the coal ash. These conditions
51
-------
are staged combustion with a fuel rich first stage followed by excess air
addition to render the mixture oxidizing. However this excess air addition
stage is critical in terms of both NO and sulfur retention. NO emissions
2C X
are a strong function of excess air in the second stage. The goal in terms
of NO is to supply just enough second stage air to complete carbon burn out.
X
This will be the minimum acceptable NO point. In the case of sulfur reten-
Xt
tion, increasing the excess air in the second stage favors the condensed
sulfate below 2500 °F. Table 3-3 shows that a minimum in the condensed phase
sulfur species occurs at the stoichiometric point, TA = 100, at the optimum
retention temperature, below 2500 °F. Condensed phase sulfides are formed at
low stoichiometric ratios, this shifts to the sulfates at high stoichiometric
ratios. Therefore the conditions for high sulfur retention predicted from
thermodynamic equilibrium are temperatures below 2500 °F and theoretical air
of 125%.
The reactivity of sodium compounds such as sodium bicarbonate with
SO is well known and forms the foundation for the dry SO adsorption
^ ^
processes using nahcolite (mostly NaHCO,) and trona (mostly Na_CO ).
The reaction of sodium with SO_ is thought to proceed via an
adsorption step followed by reaction to form the sulfate. This has been
demonstrated in baghouses by Shah, et al. (Ref. 3) in which a filter cake
containing nahcolite continued to remove SO from the flue gas stream after
the sorbent injection had been stopped. The reactions also occur in suspension
presumably by adsorption onto the sorbent particles.
The reaction of calcium with SO_ is also thought to be a heterogeneous
process. Therefore the contact and mixing processes at the lower temperatures
is important. In pulverized coal flames 80 to 90 percent of the ash is still
suspended in the flue gas in the convective section where the temperatures
for good sulfur capture occur. For the case where sufficient sodium is
present in the ash the only parameter limiting the attainment of the full
thermodynamic equilibrium product would be kinetic considerations. Such
kinetic limitations might be:
insufficient surface area
inactive surface
52
-------
It is well established that sodium can capture sulfur via a
heterogeneous reaction with SO . However the reaction of calcium with
sulfur under reducing conditions can form the sulfide. This reaction is
more than likely heterogeneous, as well as the reaction steps that take the
calcium sulfide to calcium sulfate. Calcium therefore has a fuel rich
reaction mode that the sodium doesn't have. This mode may be important
under the strongly reducing condition exhibited by such combustion systems
as the fuel bed and the cyclone burner.
3.5.2 Fuel Bed Coal Combustion
Combustion systems that operate with the bulk of the combustion
taking place in a thick bed of coal have characteristically low flue gas
particulate loadings. Most of the ash is retained on the bed and discharged
into the ash pit. Combustion takes place within much larger coal particles
and as such, a larger component of the burning is of a diffusion nature.
The bulk temperature of the fuel bed increases from the grate where the
combustion air is supplied to the top of the bed which receives radiant heat
from furnace as well as from exothermic reactions. However, within the fuel
bed surrounding individual coal pirticles, the temperature is not well defined.
The coal particle itself will have a temperature gradient from the coal core
to a hot surface. As the particle heats up, the coal devolatilizes and
thermally cracks. The ash inclusions within the particle can conceivably
experience a temperature stoichiometry history that is conducive to sulfur
retention. Within these inclusions, the calcium could react with sulfur to
form the sulfide under the fuel rich condition. Due to the nature of the
combustion,and the cooling effect of the combustion air, these ash packets may
never experience a temperature emission high enough to decompose the calcium
sulfide compound to SO .
The stoichiometry in the fuel bed varies through the bed and around
the coal particles. The sulfur retention will be lessened to the extent that
the variation from the optimum conditions are great.
53
-------
The fact that sulfur is retained in a fuel bed system, coupled with
the dependence on calcium content of the coal, point to a rather different
reaction mechanism than is found with sodium sulfur capture. The specific
surface area of the coal/ash mixture in the fuel bed is many times less than
the surface area of the fly ash particles from a pulverized coal flame. This
combined with the condition that most of the ash remains in the bed and is not
in intimate contact with the SO in the flue gas indicates that the sulfur
migrates through the bed until contact with the metals occurs.
In a well controlled laboratory fuel bed simulator, sulfur balances
have been made on the gaseous SO emissions and the sulfur retained in the ash.
Table 3-9 contains the data for the solids analysis and gas analysis. Under
the solids analysis three layers of the fuel bed were analyzed separately;
the top unburned coal, the middle partially burned coal, and the ash layer.
The ash was used as a tracer and the pounds of sulfur per pounds of ash are
shown for each layer. Based on the top coal layer and the ash layer, the ash
retained 57% of the available sulfur. Also shown in this table are the gaseous
measurements of SO emitted during the test burn. The theoretical maximum
SO emission at 3% excess O is 783 ppm. The measured value of 364 ppm
represents a 54% retention. This compares very well with the solids analysis.
This test was performed on a coal that had been ground, mixed with additional
lime and reformed into briquettes. The lime addition brought the Ca/S molar
ratio up to 1.65 from the naturally occuring ratio of 0.60 in the coal. This
information implies that only 35% of the available calcium in the fuel bed was
effective in retaining sulfur.
3.5.3 Cyclone Coal Combustor
No test data are available on sulfur retention in cyclone furnaces.
However these systems represent what might be optimal conditions for large
retentions. The cyclone is a relatively well mixed system in which most of
the ash remains in the combustor. This mixing provides good contact of metals
and sulfur. The slag layer temperatures are in the range of 2000 to 2500 °F
since this represents the range of fluid temperatures of most coal ashes under
reducing conditions. The slag layer collects the larger raw incoming coal
particles which devolatilize and burn in the slag. Smaller particles remain
54
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TABLE 3-9. SULFUR BALANCES ON A LABORATORY FUEL BED SIMULATOR
Solids Analysis
Moisture , %
Ash, %
Sulfur, %
Gross Heat of
Combustion
Net Heat of
Combustion
Ib Sulfur/lb Ash
Top Coal - 8-9"
41.89
8.45
0.47
9796*
9366*
0.0556
Middle Coal 20.5-21.5"
2.12
18.78
0.74
10,200*
9923*
0.0394
Ash
0.12
96.68*
Dry Basis
3.06*
—
—
0.0317
(57% retention)
Ca/S (molar) =1.65
Gaseous Analysis
SO,, at 3% 0^, ppro
Theo. max.
Measured
Percent retention
783
364
54
55
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entrained in the gas stream where they burn. Exit gas temperatures from the
cyclone are higher than 2500 °F, however the molten slag layer loses heat to
the water-cooled furnace walls and typically remains just hot enough to flow
out of the furnace. The conditions of rapid mixing, temperatures below 2500 °F,
and containment of most of the ash would presumably favor a high degree of
sulfur retention. The equilibrium calculation predict significant quantities
of liquid sodium sulfate at 2100 °F at 125% theoretical air. The addition of
sodium fluxing compounds to a coal ash usually lowers the fluid temperature of
the slag. Such action would be in the right direction for increased sulfur
retention by both calcium and sodium.
Although it has not been the practice in the past, cyclone combustors
could be run at substoichiometric fuel to air ratios with secondary air addition
to complete burnout. Such a system would be similar to the two stage low
NO combustor developed at B&W (Ref. 4). However by running the cyclone first
stage fuel rich the ash fluid temperatures could be reduced to the 2000 °F
region. Under reducing conditions at these temperatures calcium sulfide is
a favored product which would be removed with the slag.
It would be desirable in order to control sulfur oxides emissions
to investigate the sulfur retention characteristics of cyclone combustors
and to change the process variables in order to optimize the retention of
sulfur in the slag.
56
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SECTION 4.0
CONCLUSIONS
The results of field tests, laboratory tests and equilibrium calcula-
tions show that sulfur can be retained in coal ash by reacting with the calcium,
sodium and potassium components of that ash under reducing as well as oxidizing
conditions. Sodium sulfate is the only condensed phase sulfur compound that
occurs as a liquid.
The field data generally indicated that increasing boiler load and
excess O_ results in increased sulfur retention. This conclusion is supported
by the equilibrium calculation which showed increasing retention with increas-
ing excess O_ up to temperatures of 2100 °F. At this temperature a minimum
sulfur retention was exhibited as the fuel/air mixture passed through the
stoichiometric condition. The retention then increased as the mixture became
increasingly fuel rich.
Although the results do not indicate the mechanism for the sulfur
retention they do point to the condition under which the retention could be
expected. The three major modes of coal combustion, pulverized, fuel bed
and cyclone combustion were analyzed in terms of the potential for sulfur
retention in each. The assessment concluded that the new developing low
NO technology for coal combustion also produces the conditions of stoichiometry
2i
and temperature that are necessary for enhanced sulfur retention.
57
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REFERENCES
1. Gronhovd, G. H., Tufte, P. H. and Selle, S. J., "Some Studies on
Stack Emissions from Lignite-Fired Power Plants," Presented at
1973 Lignite Symposium, Grand Forks, ND, May 9-10, 1973.
2. Gordon, S., and McBride, B. J., "Computer Program for Calculation of
Complex Chemical Equilibrium Compositions, Rocket Performance,
Incident and Reflected Shocks, and Chapman-Jouquet Detonations,"
NASA SP-273, Interim Revision, March 1976.
3. Shah, N. D., Teixeira, D. P. and Muzio, L. J., "Bench-Scale
Evaluation of Dry Alkalis for Removing SO2 from Boiler Flue Gases,"
Presented at Symposium on Transfer and Utilization of Particulate
Control Technology, Denver, CO, July 24-28, 1978.
4. Johnson, S. A., Cioffi, P. L., and McElroy, M. W., "Development of
an Advanced Combustion System to Minimize NOX Emissions from Coal-
Fired Boilers," 1978 Joint Power Conference, Dallas, Texas,
September 11, 1978.
58
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TECHNICAL REPORT DATA
fPleaie read Instructions on the reverie before completing)
1. REPORT NO. ,
EPA-600/7-78-153b
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Sulfur Retention in Coal Ash
5. REPORT DATE
November 1978
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
/. MW I nwni^l
K. L. Maloney, P.K. Engel, and S.S. Cherry
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
KVB, Inc.
17332 Irvine Boulevard
Tustin, California 92680
10. PROGRAM ELEMENT NO.
EHE624A
11. CONTRACT/GRANT NO.
68-02-1863
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVEMED
Final; 2/75 - 2/78
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES T£RL-RTP project officer is David G. Lachapelle, MD-65, 919/
541-2236.
i6. ABSTRACT Tne ygp^ gives results of an analytical study to assess the potential for
sulfur retention in various types of coal-fired boilers. Results of a field test of 10
industrial coal-fired boilers were used to evaluate the impact on sulfur retention of
the operating variables (load and excess O2). The effect of ash composition on sulfur
retention was also evaluated, using a linear regression analysis. The expression
% S Emitted = a+b (% Na2O/% CaO) + c (Load/100,000), where a, b, and c are
constants, gave the best overall fit to the two pulverized coal-fired boiler data. The
field test and regression analysis results were supported by equilibrium coal ash
composition calculations over a range of temperatures and theoretical air for four
coal ash compositions. The calculations show that significant fractions of the sulfur
can be tied up as Ca and Na salts under both reducing and oxidizing conditions at
temperatures below 2500 F. A minimum in the total condensed phase sulfur species
is predicted at stoichiometric conditions for all temperatures.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air PoUution
Coal
Combustion Products
Sulfur Oxides
Sulfur
Stokers
Ashes
Loading
Oxygen
Linear Regression
Air Pollution Control
Stationary Sources
Excess Oxygen
Alkaline Salts
Sulfur Balance
13B
2 ID
21B 12A
07B
13A
IS. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. Or PAGtS
68
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
Form 2220-1 (9-73)
59
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