AUGUST, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
The mean yields of primary oil are recalculated in Table
VI1 as Imperial gallons per short ton, both on the dry and ash-free basis and on the basis of ash as charged and moisture as mined. The latter is probably the better basis for indicating the relative suitability of the coals for commercial use because allowance should be made for the loss incurred in removing ash from the primary product and for the heat consumed in drying the coal. On the dry and ash-free basis all of the coals yielded more than 100 gallons per ton. Two of the Canadian coals (4and 5) gave higher yields than the English standard coal, No. 3. On the basis of capacity moisture (as mined) and ash content as charged, the yields of oil, especially those from the lower ranks, are considerably changed. On this basis only the Nova Scotia coal, No. 4, gave a higher yield than the
1025
standard. The yields from coals lower in rank than high volatile bituminous A decreased progressively to about half that from the standard.
Acknowledgment The writers are indebted to Imperial Chemical Industries, Ltd., Billingham, England, for the sample of coal used as a standard of comparison in this series of tests. The assistance of other members of the staff of the Fuel Research Laboratories is also gratefully acknowledged. PRESENTED befcre the Division of Gas and Fuel Chemistry at the 96th Meeting of the American Chemioal Society, Milwaukee, Wis. Published b y permission of the Director of Mines and Geology Branch, Department of Mines and Resources, Canada.
Effect of Oxidation of Anthracite on Its Heating Value G. S. SCOTT, G. W. JONES, H. M. COOPER
AND
Central Experiment Station, U. S. Bureau of Mines, Pittsburgh, Penna.
D
URING the Bureau of Mines investigation to deter-
mine the causes, behavior, and control of mine fires, consideration was given to the low-temperature oxidation of anthracite as a possible means of determining the tendency of anthracites to heat spontaneously. Oxidation rates a t temperatures of 100-350° C. were reported (1) and also the effect of oxidation for 72-hour periods a t different temperatures on the composition of the coal ( 2 ) . This paper presents a relation observed between the amount (degree) of oxidation and the decrease in heating value of anthracites. It is based on the fact that the calorific value of fresh anthracites increases with increasing volatile content; the opposite is true of oxidized anthracites. This relation not only shows the extent of oxidation of anthracites but also may prove useful in determining the amount of weathering undergone by anthracite. Turner and Scott (3) showed that the ash, volatile, and B. t. u. contents of fresh Pennsylvania anthracites have a fairly close relation; their calculations were based on 322 samples (200 face samples and 122 breaker samples). Since the records of the Bureau of Mines now contain analyses of about a thousand anthracites taken since 1926, the relation was recalculated on the basis of this larger group of samples259 face samples and 749 breaker samples. Face and breaker samples were treated separately, because the former in general represent “fresh” coal; frequently the history of the coal that went into the breaker samples was unknown. As will be shown later, evidence indicates that some of these breaker samples had undergone considerable weathering. The procedure in classifying the anthracite samples was as follows: The analyses were divided into groups having ash contents of 0-8, 8-12, 12-16, and over 16 per cent. Each of these groups was then subdivided into groups having volatile con-
The relation of heating value, volatile matter, and ash content for 1008 samples of anthracite is presented graphically. Tests show that, when anthracite is oxidized with air at elevated temperatures its volatile matter content, oxygen content, and B. t. u. value, as determined by standard methods of coal analysis, change in a manner that indicates a direct relation at the various oxidation temperatures used, and that the relation holds, irrespective of the quality of the coal tested. The tests also show that the actual heating values of the oxidized samples, as determined by standard methods of analysis, deviate from the heating values of average unoxidized anthracite and that the deviation increases with an increase in the amount of oxidation of the samples. These differences are large enough so that all anthracites oxidized at elevated temperatures (350’ C. or less) in the laboratory can be quickly and positively detected by graphs. The relations given may be of value in determining whether different anthracites have oxidized as a result of spontaneous heating, and in determining the amount of weathering undergone by the finer sized anthracite during long storage periods.
tents between given limits. The groups were then averaged arithmetically.
Anthracite Face Samples The results for the face samples are shown in Table I. An equation of the following type was used to depict graphically the data given in Table I:
+
B =a bV - cA where B = heating value, B. t. u./lb. V = volatile matter, per cent by weight A = ash, per cent by weight a, b, c = constants
INDUSTRIAL AND ENGINEERING CHEMISTRY
1026
B, V , and A were on a moisture-free basis. The constants were evaluated by the method of least squares, and the equation for the face samples was found to be: B = 14,767 79.0 B - 166.8 A
+
TABLEI. SUMMARY OF AVERAGES FOR FACE SAMPLES No.
Volatile in Matter," Group % 22 3.31 20 5.02 16 6.57 4 8.50 25 3.53 25 4.52 37 5.48 26 6.82
Ash,a
Heating Value,'
6.05 6.57 6.88 7.28 10.00 10.00 10.04 10.04
14,010 14,078 14,134 14,275 13,377 13,426 13,517 13,647
%
B. t.
U.
Volatile in Matter," Ash,a Group % % 11 8.58 10.57 11 3.62 13.59 20 5.00 13.63 13 6.71 13.85 6 9.02 12.85 10 4.15 19.07 13 7.00 21.97 No.
Heating Value,a B. t. u. 13,685 12,804 12,857 12,957 13,310 11,963 11,653
TABLE11. SUMMARY OF AVERAGES FOR BREAKER SAMPLES
yo. In Group 9 10 19 115 133 74 57 a
-No.
Range 0 1- 25 26- 50 51- 75 76-100 0 Per column
ofCumuDeviations lative Posi- Nega- Agreetive tive menta . . 10 . . 27 25 2319 29 34 48.3 23 16 63.3 16 21 77.6 cent of total number deviating on 8ame line.
-No. ofDeviations B. t. u. Posi- NegaRange tive tive 101-125 11 9 126-150 14 9 151-175 4 2 176-200 1 3 Over200 4 1 less than highest figure in
Cumulative Agreementa 85.3 94.2 96.5 98.0 the first
Ninety-eight per cent of these deviate less than 200 B. t. u. from the formula.
Breaker Samples Table I1 shows the average analyses of the various groups of breaker samples. From the data given in this table and application of the method of least squares, the equation for the breaker samples was found to be: B = 14,840
+ 72.7 V - 168.0A
Ash,'
%
Value,a B. t. u.
3.44 4.70 2.64 3.51 4.44 5.44 6.72
7.37 7.30 9.38 10.04 10.03 10.08 10.26
13,861 13,986 13,420 13,377 13,521 13,572 13,564
%
Heating
No. Volatile In Matter,a Ash,a Group % % 50 3.48 13.67 76 4.43 13.64 53 13.56 5.43 72 6.80 13.77 39 4.37 17.79 43 5.89 18.05 749
Heating Value a B. t. 12,781 12,888 12,972 12,978 12,174 12.250
A.
Deviations of individual groups of analyses from this are as follows :
B. t. u.
B. t. u.
Volatile Matter,a
Dry basis.
Dry basis.
The average deviation of the groups from this formula is * 19.6 B. t. u.; the deviations of the various groups of samples are as follows:
VOL. 31, NO. 8
Range 0 1- 25 26- 50 51- 75 76-100
-No. ofDeviations Posi- Negative tive 29 6g b4 94 86 68 45 71 57
Cumulative Agreement,
yo
20:2 44.2 59.3 76.4
-No. B. t. u.
Range 101-125 126-150 151-175 176-200 Over200
ofDeviations PosiNegative tive 25 30 23 27 15 7 10 23
Cumulative Agreement,
%
83.7 90.4 93.3 96.3
The twenty-three negative deviations greater than 200 B. t. u. are discussed later.
Application of Data Figure 1 is a plot of the equation for the average of face and breaker samples and in general represents the relations of volatile matter, ash, and B. t. u. for the average run of anthracites. The deviations (Table 111) of samples oxidized in the laboratory from these relations is considered below. Columns 5, 6, and 7 give the volatile matter, ash, and B. t. u. values (moisture-free basis) for the various tests in which the laboratory test samples consumed the quantities of oxygen shown in column 4. Column 8 gives the B. t. u. value (from the graphs in Figure 1) that an average normal sample of anthracite should have when the volatile matter and ash content are the same as those of the oxidized samples. The differences between the B. t. u. values for average anthracite and oxidized anthracite of the same volatile and ash content are shown in column 9. Figure 2 shows these differences plotted against quantity of oxygen consumed. Although the fresh anthracite samples in Table I11 show small deviations between actual' determined B. t. u. values and those obtained from Figure 1 (with the exception of sample 40), all tests in which the anthracites were oxidized with air a t the elevated temperatures and for the time periods given in Table I11 show large differences. These may reach 4000 to 5000 B. t. u. a t the higher temperatures of oxidation. Figure 2 also shows that the deviation increases with an increase in the amount of oxygen consumed by the anthracite. It is obvious from the results given that any anthracite which has been heated in contact with air, either
FIGURE 1. RELATIOK BETWEEN ASH, VOLATILEMATTER,AND HEATING VALUEOF ANTHRACITE (MOISTURE-FREE BASIS) Equation of lines; B. t. u. = 14,803 75.8 volatile matter 167.4 ash
+
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
AUGUST, 1939
for a short period of time a t higher temperatures or for longer periods of time a t lower temperatures, will show deviations in excess of 300 to 400 B. t. u. and that the greater the deviation, the greater the amount of oxidation of the coal. The laboratory oxidation tests indicate definitely that oxidized coals may be identified by this method ; however the relationship does not hold when anthracites are oxidized a t temperatures close to or above the carbon monoxide inflection point of the coal (a). The data presented should be useful in determining not only whether anthracite has heated as a result of oxidation processes, but also whether anthracites have oxidized (weathered) a t ordinary prevailing temperatures or slightly elevated temperatures over long periods of time. Here the rate of oxygen absorption is very slow, but if sufficient time elapses, say several years, enough oxygen may be absorbed to show sufficient deviation between the determined heating value and the heating value the coal would have if oxidation did not occur. Some observations along this line were afforded by a review of the history of some of the twenty-three samples that gave negative deviations of over 200 B. t. u., as determined by the graphs in Figure 1. One case involved twelve samples taken from an anthracite breaker: seven samples were newly mined coal and five were bank coal. The bank coal deviated much more than the permissible 300 B. t. u., as follows: COB1 Xewly mined
Bank
Size Egg Stove Chestnut Pea Buckwheat Rice Barley Chestnut Pea Buckwheat Rice Barley
Volatile Matter,
Ash,
5.4 5.6 5.3 5,2 5.2 5.3 5.7
12.1 11.8 11.2 12.6 12.6 13.7 14.4
B. t. u. per Lb. 13,220 13,220 13,400 13,130 13,120 12,920 12,780
7.4 6.4 7,6 8.5 9.2
10.6 10.8 13.6 14.6 14.2
13,110 13,020 12,320 12,020 12,050
%
%
TABLE111. DEVIATION OF ANALYSESOF OXIDIZED SAMPLES FROM B = 14,767 79.0 V - 166.8 A
+
OxidaSample tion No. Temp.
c.
16
9
19 1
32
34 36
40
980
1090
ValuFrom Fig. 1 b B.t. u.
Oxygen Consumed
Volatile Matter'
Asha
Hr.
Grams
%
%
B.t. u.
...
0 2.022 4.307 17.85 4.24 34.48 103.19
4.6 5.7 6.9 12.7 6.6 17.5 26.8
6.0 6.1 6.2 6.0 6.2 6.1 8.3
14,150 13,950 13,730 12,700 13,750 12,080 10,620
0 6.13 63.44
6.8 9.6 20.1
34.1 34.4 40.0
9,530 8,950 6,380
9,610 9,780 9,685
80 830 -3305
+-113080
87 55 186 91 71 71
...
250 350
-Heating Determineda
Time
88 86
...
Deviation 0 -- 270 570 -2080
-
530 -3030 -4880
--
91
11.62
5.4 10.0
25.0 24.6
11,120 10,320
11,040 11,450
350
'94
0 43.94
3.9 16.1
19.0 20.5
11,750 9,780
11,930 12,600
...
, . .
0 9.668 89.22
4.6
8.7 22.9
21.4 22.8 31.9
11,460 10,570 7,140
11,570 11,65C 11,257
110 -1080 -4117
...
0 31.13
6.1 16.7
33.3 31.9
9,710 8,210
9,690 10,767
+-255720
...
250
...
250 350
0
83 92
300
...
92
-
180 -2820
250 300 350
94 92 73 92
0 2.498 6.16 12.47 43.33
4.2 4.8 6.0 8.6 16.7
13.5 13.8 14.1 13.9 14.4
12,650 12,400 12,220 11,900 10,730
12,880 12,850 12,900 13,140 13,685
300
.93 ..
0 28 61
6.7 16.2
25.8 24.9
10,620 9,320
10,990 12,000
200
8,960 120 128.93 38.9 8.0 14,350 0 5.3 5.4 848 202.36 5,490 34.0 300 37.8 5 Moisture-free basis. b Samples having volatile mattes content above 15 per cent were formula given on chart. 16B
300
-
-
230 450 680 -1240 -2955
-
370 -2680
+-7543 10 -4874
16,503 14,340 10,364
figured by means of
Deviationa in B. t. u. 4-30 -30 C 60 +30 20 0 -40
+
-490 -470 -770 -980 1090
-
The deviations of the newly mined coal are normal and within the experimental error allowed in preparing the graph from which the B. t. u. figures are read. However, the bank coal samples showed abnormally high deviations that cannot be considered as a peculiarity of the coal itself. The authors' interpretation of the results is as follows: The five bank samples show unmistakably that the coal has weathered while in storage in the banks because the amount of indicated weathering increased as the size of the coal particles was reduced, as should be expected. On the basis of oxygen consumed by the coal (values taken from Figure 2 ) the following results are obtained: Negative Deviation of Detd. B. t. u: of Samples from Fig. 1 490 470 770
iio
200 250 200 300 350
a Betaeen B. t. u. of samples as obtained from Figure 1 and determined values.
Siie of Coal Chestnut Pea Buckwheat Rice Barley
1027
Grams Oxygen Consumed per 100 Grams Coal 3.5 3.5 6.0 8.0 9.6
A further example of indicated weathering of anthracite is given by samples from another anthracite breaker:
I
0
I
I
10
1
1
20
1
I
I
1
1
1
I
1
1
8
1
I
I
1
30 40 50 M) 70 80 90 OXYGEN CONSUMED, GRAMS PER 100 GRAMS OF COAL
1
1
1OD
,
I
110
FIGURE2. RELATION BETWEEN AMOUNTOF OXYGEN CONDEVIATION FROM FORMULA: B. T. U. = 14,803 7 5 3 VOLATILEMATTER-167.4 ASH
+
SUMED ASD
Volatile Matter, Coal Newly mined
65% bank,,36% newly mined
%
Ash
%'
Size Stove Chestnut Pea
6.6 7.0 6.3
10.3 9.1 9.3
Buckwheat Rice Barley
7.6 7.8 8.0
9.5 10.7 11.1
B. t. u. pes Lb. 13,580 13,820 13,590 13,580 13,260 18,lYO
Deviation of Detd. B. t. u. of Samples from Fig. 1 0 0
-140
-220 -350 -370
Literature Cited (1) Scott, G.S., and Jones, G. W., IND. EKQ.CHEM., 29,822(1937). (2) Scott, G.S., Jones, G. W., and Cooper, H. M., U. S. Bur. Mines, Rept. Investigations 3398 (1938). (3) Turner, H. G., and Scott, G. S., Anthracite Inst., 1934. PRESENTEDbefore the Division of Gas and Fuel Chemistry a t t h e 96th Meeting of the American Chemical Society, Milwaukee, Wis. Published by permission of the Director, U. S. Bureau of Nines. (Not subject t o copyright.)
