Hydrogenation Tests on Canadian Coal Coals Ranging from MediumVolatile Bituminous to Lignite' Hydrogenation tests on nine coals representative of various gtoups in the A. S. T. M. classification between medium-volatile bituminous coal and lignite are described. The method of testing was based on continuous operation in a liquid-phase plant having a capacity of about 9 pounds of coal paste per hour. The vehicle in each case was oil produced previously by the hydrogenation of the coal being tested. The rank of the coal had a fairly consistent influence on the yields although one of the coals was exceptional. The bituminous high-volatile A and B groups gave the highest yields of oil. The effects of composition of ash, geological age, and proportions of nitrogen and sulfur, although largely obscured by the effect of rank, were also studied. The composition of the ash did not appear to have an appreciable influence, and the geological age also had only a minor effect, if any, on the yields. There is an apparent relation, fairly consistent throughout the present series, between the nitrogen content of the coal and the degree of liquefaction. A sample of coal used for commercial hydrogenation in England was included in the series as a standard of comparison. It yielded 71.5 per cent of primary oil on the ash- and moisture-free basis. Two of the Canadian coals gave yields of 77.2 and 73.8 per cent, and the lowest yield of all the coals tested was 53.3 per cent. On the basis of ash as charged and moisture as mined, only one Canadian coal gave a higher yield of primary oil than the standard, and the yields diminished progressively with descending rank to about one half that of the standard.
T. E. WARREN, I i . W. BOWLES, AND R. E. GILMORE Fuel Research Laboratories, Bureau of Mines,
Ottawa, Canada
Description and Preparation of Coals The characteristics of the coals tested'are given in Tables I to V. The coals are numbered in descending order of rank. TABLE I. LOCATION AND GEOLOGICAL PERIOD Coal No.
Province Brit. Columbia Brit. Columbia (England) Nova Scotia Brit. Columbia Alberta Alberta Alberta Saskatchewan
District Crowsnest Vancouver I. (Durham) Sydney Nicola Saunders Drumheller Edmonton Bienfait
Geological Period Lower Cretaceous Upper Cretaceous Carboniferous Carboniferous Tertiary Cretaceous Upper Cretaceous Upper Cretaceous Tertiary
Table I1 gives the ranks of the coals according to the A. S. T. M. classification. The fixed carbon on the dry mineral-matter-free basis, the calorific value on the moist mineral-matter-free basis, and the equilibrium moisture determined a t 86" F. (30" C.) and 100 per cent humidity are also included in Table I1 in order to indicate the relative positions of the coals within the groups of the classification. BY RANK TABLE 11. A. S. T. M. CLASSIFICATION
T
HIS paper describes hydrogenation tests on nine coals, ranging in rank between medium-volatile bituminous coal and lignite in the Classification of the Americaii Society for Testing Materials (A. S. T. M. Designation D388-37). This wide range was studied largely in order t o indicate the types upon which further investigations could most Rrofitably be made. A sample of the coal processed in the commercial hydrogenation plant of Imperial Chemical Industries a t Billingham, England, was included in the series as a standard of comparison. The method of testing was based on continuous liquidphase operation, similar to the primary liquefaction step of the commercial process but with a short duration. The principal liquid product of the tests is a heavy crude oil, the amount of which was taken as an index of the suitability of a coal for the production of motor fuel. I n commercial practice there would be some losses in the subsequent vapor-phase hydrogenation and in refining so that it will be necessary to apply the entire process in order to determine accurately the yields of motor fuel obtainable. 1
The k s t paper in this aeries appeared in Maroh, 1037, page 353.
Coal
No.a 1
2 3 4 5 6
7
8
9
Class Bituminous Bituminous Bituminous Bituminous Bituminous Bituminous Subbituminous Subbituminous Lignitia
Group Med.-volatile High-volatjle High-volatFle Hjgh-volatile High-volatile High-volatile B Lignite
C
A A A B C
Fixed Calorific Carbon, Value, Moisture, % B. t. u. % 72.7 15,350 1.0 63.2 14,950 2.3 64.1 14,680 3.6 60.9 14,660 3.5 58.2 13,210 7.4 62.9 12,350 9.1 58.9 10,410 17.5 59.1 9,090 24.0 57.2 8,300 31.7
a No. 1 to 4 are aaking (i. e.,, coking) coals; No. 5 is weakly asking: Nos. 6 to 9 are nonagglomerating (1. e., noncoking). No. 6 is high-volatile bituminous C because of i t a nonweathering properties, and No. 9 is on the border line between the subbituminous C and lignite groups. The calorifio values on the extrapolated 100 per cent humidity basis are employed rather than the 97 per cent humidity values.
I n commercial practice, ash is removed as completely as possible from the coal before it is mixed with the vehicle; and for this reason it was desirable t o have cleaning data on the coals t o be tested. These data were already available for coals 1 to 4, and float-and-sink tests were made on the others. The samples of coals 1 to 5 were cleaned either a t this laboratory or prior to shipment. The ash in the lower 1021
INDUSTRIAL AND ENGINEERING CHEMISTRY
1022
rank coals (6 to 9) could be reduced only t o a comparatively small extent by flotation, so that these coals were not cleaned. The lower rank coals (7 t o 9) were dried in an oven heated by an open gas flame a t about 230" F. (110" (3.). After drying they were stored in closely covered cans. Finally the samples were crushed and ground in a ball mill. Those which had been dried in the oven and were likely t o reabsorb moisture were ground in small batches for immediate use. The final sizes as used for the tests are given in Table 111; the screen sizes are in accordance with the U. S. Standard Screen Series. TABLE111. SIZEDISTRIBUTION OF COALS Coal No. 1
2 3 4 5 6
7, run 2 7 , run 3 7, sun 4 8, run 2 8 , run 3 9 , run 2 9 , run 3
-16 +30 0 0 0 0 0 0 0 5 3.4 0.2 0 0 0.0 0.0 0.0 0.0 0.0 0.0
-30 +50 0 6
0 3 2 2 3 2 23 6 13.4 0 0 0 0 0.0 0.0 0 0 0 0 0.0
50 +- 100 2 10 21 16 26 30 5 8 7 3 7 6 7
6 5 5 7 4 4 5 5 3 7 0 9 6
- 100
+zoo
16.6
33.1 24.5 26.4 18.8 21.9 30.5 32.6 33,2 30.1 33.1 32.6 32.0
-200 80.2 56 1 51.8 54 2 27.8 34.1 64.0 58.9 59.5 66.2 59.9 60.5 60.4
The analyses of the coals as used in the tests are shown in Table IV. These analyses, reduced to the ash- and moisturefree basis, are given in Table V.
Method of Testing The details of the method of testing were given in a previous publication. Criefly it consists in continuously charging about 9 pounds per h w r of a paste of equal parts of coal and oil to a reaction chamber where it is brought into contact with hydrogen at 3000 pounds per square inch and about 788" F. (420' C.). The products are continuously removed. After operation has been c a r r i e d on for about 7 hours, the accumulated liquid product is distilled with steam, and the fraction: boiling above 446 F. (230' C.) are used as the vehicle for a further quantity of coal.
A material balance is made over the 7-hour run, and from this the yields are calculated. Three or four such runs, all made under the same operating conditions, constitute a test on any given coal. The results of the first run are not taken into consideration because the vehicle and pitch remaining in the reaction chamber are representative of the previous rather tliaa the current test. Thus the test on each coal consists of one preliminary run followed by at least two further runs with a self-generated vehicle. The apparatus has been altered since the previous publication' by making provision for heating the high-pressure receiver and the outlet lines from it with warm water. The water in the cooler is now maintained a t about 140" F. (60" C.). These alterations have been necessary because, under some conditions of,operation, these lines occasionally become obstructed with viscous pitch if they are not warmed. A recording densitometer is used to record the density of the gas recirculated through the reaction chamber, so that the rate of gas recirculation can be more accurately controlled. During the course of this series of tests improvements were made in the measurement of temperature within the reaction chamber. This was previously measured at a point inside the hydrogen-lift pipe, but is now measured a t one or more points in the annular space between the hydrogen lift and the wall of the reaction chamber. In this location the readings are more truly representative of the average temperature of the reacting material. Other minor improvements have been made for the purposes of increasing the safety or convenience of operation of the plant. The catalyst in all the tests was stannous oxide. The amount used was 5 per cent of the coal charged.
Operating Data and Yields The operating conditions and yields of the tests are given in Table VI. The mean values are weighted in proportion t o the duration of the runs. The temperatures indicated were measured as described in the previous paper1 but have been found t o be considerably higher than the average temperature of the reacting material. They are given in Table V I for comparison because the average temperature of the reacting material was not determined throughout the whole series of tests. The average temperature is about 43" F. (24"C.) lower than the temperature given in Table VI. The sum of the quantities in each vertical column under yields is not exactly 100 plus the hydrogen charged. It differs from this value by the difference between the catalyst plus ash as determined in the material charged and the ash as determined in the products. The item on hydrogen charged as per cent of ash- and moisture-free coal is hydrogen measured t o the compressor. It is not corrected for losses by leakage from the compressor and recirculating pump nor for loss by solution in the product. It is, however, corrected for the densitometer sample.
TABLE IV. Coal No.
VOL. 31, NO. 8
1
ANALYSES OF COALS ds USEDIN TESTS 2
3
4
6
5
7
8
9
Proximate analysis, yo: 3.0 2.1 2.3 7.5 2.7 2.1 5.6 1.0 1.1 Moisture 9.8 7.5 9.3 7.3 6.8 2.5 3.0 7.5 Ash 3.6 37.6 36.7 37.9 36.9 32.3 37.3 34.2 34.2 Volatilematter 26.4 51.7 49.3 53.4 52.8 57.6 50.2 Fixed carbon 69.0 57.2 60.6 Ultimate analysis, %: 65.1 65.2 68.6 68.1 79.9 69.8 77.9 81.1 Carbon 84.1 4.9 4.5 4.5 5.8 5.0 5.3 5.5 5.7 Hydrogen 5.0 9.3 9.8 6.8 7.5 2.5 3.0 7.3 3.6 7.5 Ash 0.4 0.7 0.4 0.6 0.3 1.4 1.1 0.7 2.0 Sulfur 1.4 1.8 1.1 1.6 1.7 1.6 Nitrogen 1.5 1.2 1.7 19.3 18.4 18.2 17.6 8.6 14.9 6.1 7.8 Oxygen 5.1 Gross calorific value B. t. u./lb. i4,730 13,880 14,390 14,370 12,400 11,640 11,480 10.760 10,880
TABLEv. ANALYSESOF COALS Coal No.
1
2
ON THE
3
4
Am5
AND
MOISTURE-FREE BASIS 6
7
8
9
Proximate analysis, %: 41.5 43.5 37.6 41.6 39.3 42.4 36.1 27.6 37.4 Volatile matter 58.4 58.5 56.5 57.6 62.4 60.7 62.6 63.9 Fixed carbon 72.4 Ultimate analysis, %: 73.6 74.8 80.1 80.0 75.3 85.6 84.2 85.2 Carbon 88.1 4.8 4.8 5.2 6.0 5.0 5.8 5.6 5.4 Hydrogen 5.2 0.5 0.5 0.6 0.3 0.8 1.4 1.1 0.7 2.2 Sulfur 1.7 1.5 1.5 1.8 1.3 1.9 1.8 1.3 Nitrogen 1.6 19.6 18.0 13.4 17.4 7.1 11.5 5.7 5.7 Oxygen 4.4 Gross calorific value, B . t. u./lb. 15,450 15,180 15,180 15,150 14,240 13,580 12,710 12,170 12,480
REACTION CHAMBER (LOWERP A R T )
.-,_.,
AUGUST, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLEVI.
Coal number R u n number Operating conditions: Temperature, ' F. Temperature, C. Pressure, lb./sq. in. Rate of charging, lb. of paste/hr. Rate of gas recirculation, cu. ft./hr. a t temp, and pressure above Duration of run, hr. Recirculating gas: H2 a t start of charging, H2 a t end of charging, Liquid product: Solids insol. in CClr, Ash in insol. solids, Distillation of liquid products:
2
2
Wlllmv
Oiri&,ion t o 338' F. (170' C.) Oil fraction 338-446' F. (170-230' C.) Oil fraction 446-572' F. 1230-300O C . ) Residue above 572' F. Distillation loss Picoh from reaction chamber: Solids insol. in CCh, % Ash in insol. solids, % Yields in Yo of ash- and moisture-free coal: Oil Combustible solid residue Water Gas Hydrogen charged as % of ash- and moisturefree coal
3
815 435 2940 8.27
5 6.33
6 7.83
2 ..5 3.6 12,s 26.5 53.5 1.1
1.5 3.6 11.3 26.8 56.1 0.7
..
48.27 27 0
38.04 32.5
56.9 16.3 3.3 31.9 5.0
... , . .
Wlter
.
-I-.
Oil fraction to 338' €7. (170' C.) Oil fraction 338-446' F. (170-230° C.) Oil fraction 446-572' F. (230-300° (2.) Residue above 572' F. Distillation loss Pitch from reaction chamber: Solids insol. in CClr, % Ash in insol. solids, % Yields in Yoof ash- and moisture-free coal: n;i
6 7.50
1 4 ,$2 46.0
2.1 4.3 10.5 23.1 59.5 0 5
1 6 3.2 7.1 22.2 65.2 0.7
..
..
38.58 43.6
36 48 42.5
66.2 10.7 0.9 24.4
62.0 13.2 2.0 27.8
67.6 15.4 2.9 17.8
4.5
4.7
4.2
.. .. .. .. , . .. ..
3
4.4 4.0 11.3 27.3 52.4 0.6
3.5 4.7 10.4 23.9 56.9 0.6
..
32.32 37.3
29.52 41.0
30.55 40.0
66.0 18.2 1.8 18.7
66.8 16.8 2.3 18.3
67.0 11.6 3.3 22.4
73.3 5.7 5.6 21.4
74.3 10.1 3.9 16.0
71.5 9.2 4.2 19.9
5.1
4.7
5,6
5.9
5.6
-
.. .. , .
5 7.00
93.4 84.5
..
31.3 50.2
32.6 52.0
76.5 5.0 7.0 19.5
77.7 6.2 7.7 15.7 8.0
8.05
3
3
Mean
.. ..
88.6 75.4
89.6 80.2
9.37 66.9
9.97 66.2
.. , . ..
6 4 8 24 55 0
6 5 8 26 52 0
2 1 8 9 2 8
74.2 4.8 7.3 17.3
73.3 8.0 7.6 16.2
8.0
5.4 Mean
2
3
824 440 3000 8.88
817 436 3000 8.69
. .. , , ..
820 438 3000 9.30
819 437 3000 9 12
5 7.00
5 7.37
5 7.00
., ..
5 6.00
5 6 67
4
,
5 6.50
..
.. ..
5.7
Mean I
.
.. ..
12.62 43.8
8.1 5.7 10.8 22.3 52 6 0.5
8.2 9.6 7.5 20.9 52.9 0.9
..
..
41.74 40.2
48.21 33.1
..
73.8 6.4 7.4 16 8
56.4 19.4 8.8 20.0
50.0 24.6 8.4 23.2
53.3 21.3 8.6 21.5
5.5
4.8
5.2
5.0
3
Mean
,.
813 434 3000 8 60
5 7.00
..
12.78 45.1
,.
-8
817 436 3000 8.62
..
91.3 75.4
..
5.7 7 -
815 435 3000 8.83
..
91 . o 71.9
4 2 7 4 9 4
77.2 5.7 7.4 17.3
.
, .
..
..
22.32 69.0
63
2
..
, .
23.20 71.3
7
r
2
3.2 4.0 9.3 21.2 61.5 0.8
..
..
5 7.17
..
..
8.13 49.6
.. ..
..
6 7.58
6.99 52.1
...
..
5 7.00
10.15
.. ..
E 0.5
5 7.30
.. ..
47.6
813 434 3000 8.88
4.8 4.3 17.0
..
Mean
94.7 74.3
2
4 3 '4.9 22 5
820 438 3000 8.66
87.2 67.2
819 437 3000 8.85
6.36 57.9
..
831 444 3000 8.77
90.5 68 5
..
3.88 59.5
4
828 442 3000 8.98
..
Mean
7.45
3
..
829 443 2940 8.83
..
2
.. ..
12.05 48.5
..
3
7
, .
96.1 78.8
167 5 ) 0 8
2
6 7.10 92.5 78.5
...
2
Coal number R u n number Operating conditkns: Temperature, F. Temperature, O C. Pressure, lb./sq. in. Rate of charging Ib. of paste/hr. Rate of gas recirbulation, cu. ft./hr. at temp. and pressure above Duration of run, hr. Recirculating gas: He a t start of charging, % HZa t end of charging, % Liquid product: Solids insol. in CCL, Yo Ash in insol. solids, % Distillation of liquid product:
.. .. .. ..
10.16 35.5
5 33
808 43 1 3000 8.77
..
8.30 35.7
83 1 444 2940 9.29
817 436 3000 8 58
..
90.7 61.2
2
OiriFactiou to 338" F. (170' C.) Oil fraction 338-4463' F. (170-230° C . ) Oil fraction 446-572" F. (230-300'' C.) Residue above 572' F. Distillation loss Pitch from reaction chamber: Solids insol. in CC14, Ash in insol. solids, Yields in yo of ash- and moisture-free coal: Oil Combustible solid residue Water Gas Hydrogen charged as % of ash- and moisturefree coal
..
89.4 61.3
Pressure, lb./sq. in. Rate of oharging, lb. of paste/hr. Rate of gas recirculation. cu. ft./hr. a t temp. and pressure above Duration of run, hr. Recirculating gas: Hz a t start of charging, HZa t end of charging, Liquid product: Solids insol. in CClr, Ash in insol. solids, Distillation of liquid product:
w. a tar
OPERATING CONDITIONS AND YIELDS 2 4 Mean 2 4 Mean
831 444 2940 9.01
Coal number R u n number
1023
-
Mean , ,
.. .. .. , .
..
2 819 437 3000 8.62
815 435 3000 8.98
5 6 92
5 6.67
..
..
.. ..
,. ..
,. ..
87.2 61.0
87.5 58.2
91.8 60.2
..
..
90 2 63.8
88.0 63 2
.. ..
90.2 60 3
86.8 59.6
6.61 59.5
7 90 62.6
9.46 65.9
..
..
9.93 60.6
11.00 63.1
,.
..
9.77 65.6
10.95 61.8
7.9 6.6 12.2 23.4 49.7 0.2
8.1 5.0 12.7 22.5 51.3 0.4
7.6 6.1 11.0 21.2 53.5 0.6
.. .. .. ..
8.5 4.8 11.0 21.7 53.4 0.6
.. ..
8.6 6.3 10.6 23.7 50.2 0.6
39.64 54.5
40.90 53.8
40.98 56.3
40.67 56.7
.. .. ..
8.3 6.7 12.0 22.4 49.9 0.7
40.50 51.6
.. .. ..
8.1 7.4 10.4 21.9 51.7 0.5
47.36 58.1
43.14 59.0
60.9 6.7 13.4 26.9
57.9 8.3 13.1 27.1
62.5 5.1 13.3 26.3
60.0
4.4 13.0 30.7
55.7 9.9 13.7 27 9
57.7 7.3 13.4 29.2
54.2 8.5 13.4 30.8
59.1 8.5 13.7 28.7
56.6 8.5 13.5 29.8
6.9
6.9
6.9
8.1
7 2
7.6
7.5
7.0
7.3
68 7 Eb'mbustible solid residue 0.3 Water 13.3 Gas 24.8 Hydropen oharged as Yo of ash- and moisturefree coal 6.8 a Hydrogen charged in run 2 assumed the same as in run 3.
..
..
.. t
.
.. ,. .. I
.
.. .. .. ..
..
1024
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 31, NO. 8
fied in the same group. Coal 2 also yielded more solid residue and less oil than the others. However, the conclusion that coals which have been rapidly metamorphosed are not readily liquefied is not generally applicable, for coal 5, although tertiary in origin and high-volatile bituminous B in rank, gave a high yield of oil. Complete analyses of the ash constituents of all the coals were obtained, and the amounts of each constituent calculated in the coals as charged. There is no positive evidence of appreciable catalytic activity of any constituent of the ashes. Coals 2 and 6 might have been expected to have some ash constituent acting so as to hinder liquefaction. Yet each ash constituent, of which both have a high proportion, is also present in a high proportion in one or more of the other coals. On the other hand, there is no evidence that any catalytic action GENERAL VIEW OF APPARATUS,SHOWING) TEMPERATUR~ CONTROLLER AND of the ash assists the liauefaction of the other RECORDER IN FOREGROUND coals. Coal4, which gave the best yield, has less of every ash constituent except manganese oxide than one or the other of coals 2 and 6. Manganese is Discussion of Results present only in small amounts and in about equal amounts The coals were all tested under a single set of operating in coals 5 and 6 which gave, respectively, high and low yields conditions which7 is not necessarily the optimum for any of of oil. them and probably does not favor them equally. Furthermore 21 hours-that is, three 7-hour periods-may be too short a time to ensure a steady state in an operation of this TABLEVII. YIELDSOF PRIMARY OILS Basis of Ash sort. For these reasons a comparison of the results is of as Charced limited value. However, certain trends can be observed in Dry and and C a p a s t y c Designation of Coal Ash-Free Moisture (as the present data. No. Location Rank Basis Mined) The rank of the coal within the range studied has a con-Imp. ga1./8000 1 b . Y siderable influence on the results. The oil yield rises with 1 Crowsnest Med-vol. bituminous 124 118 2 Vancouver I. High-vol. bituminous A 134 121 descending rank t o a maximum with coals 4 and 5 which are 3 Durhamo High-vol. bituminous A 143 134 4 Sydney High-vol. bituminous A 154 144 in the high-volatile A and B groups, respectively, of the 5 Nicols High-vol. bituminous B 148 127 bituminous class, and then declines progressively with de6 Saunders High-vol. bituminous C 107 90 7 Drumheller Subbituminous B 125 95 creasing rank. There is only one exception t o this general 8 Edmonton Subbituminous C 115 79 9 Bienfait Lignite 113 69 trend-namely, coal 6, which gave lower yields than its a Standard of comparison. neighbors of higher and lower rank. The yield of combustible solid is comparatively high in coals 1, 2 , and 6. This was to be expected in the case of coal 1 which is in the medium-volaThere is an apparent relation between the nitrogen content tile bituminous group and has a carbon content on the ashof the coals as shown in Table IV and the yields of combustible and moisture-free basis of 88.1 per cent. However, coals 2 solid; coals with a high nitrogen content gave low yields of and 6 are outstanding in this respect. The yields of water combustible solid. Variation in the proportion of sulfur did roughly parallel the oxygen content of the coal. The yields not affect the yields consistently. of gas are high a t both extremes of rank and are lowest for coals in the high-volatile bituminous A and B groups which gave the best results in other respects. The hydrogen consumption rises as the scale of rank descends to the subbituminous and lignite groups. It is also high in the case of coal 4 which gave the best yields of oil. The effects of other characteristics of the coals such as geological age, the composition of the ash, and the proportion of nitrogen and sulfur are largely obscured by the effects of rank. However, it was thought that the exceptional behavior of coals 2 and 6 might be accounted for by some peculiarity in these other characteristics, and data on them were studied. The coals from western Canada are considerably younger than those from Nova Scotia and England, although some of them were metamorphosed more rapidly and attained the same or higher ranks. Coal 2 originated in a more recent geological period RECIRCULATING PUMP,HIQH-PRESSURE FLOWMETER, AND GAS DENSITY RECORDER than coals 3 and 4, although all three are classi-
.
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 t o 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, AND H. M. COOPER 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:
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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
