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Determination of mineral matter distribution in a coal seam using O2 chemisorption technique
Fuel Processing Technology, 26 (1990) 67-72
67
ElsevierSciencePublishersB.V., Amsterdam-- Printed in The Netherlands
Short Communication
Determination of Mineral Matter Distribution in a Coal Seam U s i n g 02 Chemisorption Technique A.D. PALMER,J.-C. GOULET,J. GRANSDEN,J.T. PRICE and E. FURIMSKY Energy Research Laboratories, Canada Centre for Mineral and Energy Technology (CANMET), Energy, Mines and Resources Canada, 555 Booth Street, Ottawa, Ontario KIA OG1 (Canada)
(ReceivedJune 9th, 1989;acceptedin revisedformApril 2nd, 1990)
ABSTRACT A seriesof samples taken from differentdepths of the seam of a bituminous coal in Western Canada was used to determine the mineral matter distribution.The measurements were carried out using the 02 chemisorption based on a thermogravimetric technique. The 02 chemisorption increasedwith decreasingmineral matter content.The employed technique was found to be suitable for identifyingthe portion of coal seam leastcontaminated with mineral matter.
INTRODUCTION Oxygen chemisorption as determined by a thermogravimetric technique yields useful information on properties, structure and reactivity of carbonaceous solids. For bituminous coals, anthracite and petroleum cokes a linear correlation between the H / C ratio and the amount of chemisorbed 02 was established [ 1 ]. According to these results the amount of chemisorbed 02 expressed on a dry ash-free basis decreased with increased aromaticity of carbonaceous solids. In a series of carbonaceous solids containing similar organic matter this technique may be suitable for determining mineral matter content. This approach was used in the present work to follow the change in mineral matter content in various depths of a coal seam with the aim to identify the boundary separating part of the seam contaminated with overburden from the uncontaminated area. For this purpose the seam of a bituminous coal from Western Canada exploited for the production of metallurgical coke was used. The suitability of the coal seam for the present investigation was confirmed by the study of particle size effect on properties of three Canadian bituminous coals and the reference Illinois 6 coals [ 2 ]. This study indicated patterns which differed among the coals. The difference was evident when low-sulphur coals, represented by W e s t e r n C a n a d i a n B a l m e r a n d Quintette coals were c o m p a r e d with high-sulphur coals represented by Eastern C a n a d i a n Prince coal a n d the
68 reference Illinois No. 6 coal. For the former the particle size had little effect on the H / C ratio and sulphur content indicating a similar structure of organic matter among different particle fractions. The effect of particle size on surface area was predictable compared with some anomalies observed for the highsulphur coals. For the low-sulphur coals the content of mineral matter exhibited a slight but linear increase with mean particle diameter of fractions decreasing from about 1100 to 20 # m whereas for the high-sulphur coals the mineral matter content more than doubled in the same particle size range. These observations suggest that the fraction of particles which is representative of coal properties can be prepared more readily from the low-sulphur coals. EXPERIMENTAL The five coal samples were taken from different depths of the same seam in the coal mine in Western Canada. The samples are identified as A, B, C, D and E from the top to the bottom of the seam. These coals were crushed and sieved to obtain particle size fractions required for chemisorption. The other three coals taken from a different seam are identified as thermal, boundary and metallurgical from the top to the bottom. Details of the Cahn electrobalance technique, used to measure 02 chemisorption, were given previously [ 1 ]. For the experiment about 500 mg of coal particles were used. Prior to the admission of air, the sample was "cleaned" in N2 stream at 200°C until no further weight decrease occurred. T h e n N2 was replaced by air (2 L / m i n ) and the weight increase was monitored for 2 h. Typical time-weight histories are shown in Fig. 1 for a coal sample identified 50
L
Metallurgical Coal
rn rr
o
30
Ld -r ¢J
o /
o~ 20 ,,
/
200°C
I..Z
o
I0
0
~
2
TIME, hours Fig. 1. Weight increase venus time (500 mg of coal, 200°C, 2 L/rain).
69 as metallurgical. Such results were used to estimate the initial rate as the average rate during the first 4 rain, the steady-state rate as the average rate during the last 30 rain and the Rmount of 02 chemisorbed after 2 h of chemisorption. The B.E.T. 1 technique was used to measure N2 and C02 surface areas. The mean particle diameter of the fractions was determined using the Coulter Counter technique.
RESULTSANDDISCUSSION The results shown in Fig. 2 represent the database from the use of the 02 chemisorption technique by this laboratory for the evaluation of all carbonaceous solids except lignites and sub-bituminous coals. The relatively low surface area of these solids suggests that the external surface played a key role during 02 chemisorption [1,3,4]. The Illinois No. 6 coal deviated from the correlation due to combined effect of the presence of pyrite and surface area which was at least three times greater than that of Canadian coals. The results give a correlation coefficient of 0.873 and the empirical equation Y= 50.1 × H / C - 13.1 in which Y is the amount of 02 (mg/g) chemisorbed at 200°C during a 2 h chemisorption run.
35 A
80 D
~O
~25
.
2O
0
15
10
0 0
tQ 0.9
r 0.6
0.4
0.8
H/G
1
Fig. 2. Effectof H/C ratioon 02 chemisorptionat 200°C in air (circularsymbolsare takenfrom [1], triangularsymbolspresentadditionaldata). 1Brunauer-Emmett-Telleradsorptionisotherm.
70
The results in Table I are typical of those obtained when 02 chemisorption is used for characterization of coal samples taken from different depths of a coal seam. Sample A shows a significant contamination from an overburden, which is also evident to a lesser extent for sample B. The coal's homogeneity increases at greater depths in the seam. This is confirmed by the amount of chemisorbed 02 and initial rate (uncorrected for mineral matter content) for TABLE1
Oxidation data of five coal samples taken from different depths of the same seam Parameter
Coals A
H/C Ash, wt.% Total sulphur, wt.%
B
0.71 55.9 0.12
C
0.66 31.9 0.18
D
0.67 21.2 0.30
E
0.64 13.9 0.25
0.67 22.3 0.22
BET surface area, m2/g 80-120, N2 C02 100-200, N2 CO2 325-400, N2 C02
17 81 16 73 23 105
13 93 18 89 21 133
15 96 21 88 22 147
16 98 24 107 17 142
18 90 15 97 18 140
Mean particle diameter, Hm 80-120, fresh oxidized 100-200, fresh oxidized 325-400, fresh oxidized
123.4 111.4 92.4 90.8 26.1 27.9
136.5 142.7 80.7 85.3 26.4 27.6
153.6 146.9 84.1 89.9 26.1 27.0
150.4 151.9 82.9 92.1 29.2 29.2
146.5 147.0 82.6 77.9 28.8 29.5
02 chemisorbed, mg/g 80-120, as received (dafb) 100-200, as received (dafb) 325-400, as received (dafb)
3.0 6.8 2.7 6.1 7.9 6.6
11.0 16.2 13.0 19.1 18.4 27.1
14.9 18.9 20.0 25.3 29.1 36.9
17.1 19.9 20.8 24.2 28.2 32.8
15.7 20.1 22.2 28.5 29.6 38.1
Initial rate, mg/g min 80-120 100-200 325-400
0.20 0.07 0.25
0.27 0.26 0.48
0.26 0.35 0.63
0.26 0.28 0.67
0.29 0.39 0.71
Steady-state rate, mg/g min 80-120 100-200 325-400
0.02 0.02 0.01
0.08 0.09 0.09
0.10 0.14 0.17
0.12 0.16 0.17
0.12 0.15 0.16
71
all three particle size fractions of sRmples C, D and E. The smaller amount of chemisorbed 02 and the initial rate for sample D, in spite of the lowest content of mineral matter, is attributed, to a lower H / C ratio. As expected, the amount of chemisorbed 02 as well as both initial and steady state rates of chemisorption increased with decreasing particle size [2]. The measured mean particle diameters are in the range of that estimated from the mesh range. A 2-h oxidation in air at 200 °C had little effect on the mean particle diameter. Except for sample A the results for the other samples fit the correlation shown in Fig. 2, if similar particle size fractions are considered. The results in Fig. 3 are for other sets of samples taken from different depths of a coal seam. It was anticipated that the contamination with mineral matter would decrease with increasing depth, from thermal to metallurgical coal. However, at 200 °C little difference was observed between thermal and boundary coals. To ascertain this the chemisorption tests were performed at different temperatures. Thus, every point on the curve in Fig. 3 was obtained isothermally at the indicated temperature. For every case the coal sample was "cleaned" at 200 ° C in N2 stream. This was followed by adjusting the temperature to that of the experiment. The lowest content of mineral matter in the metallurgical coal was confirmed at all temperatures. It may be concluded that the difference between the boundary and thermal coals is not significant, although the greater amount of 02 chemisorbed at 250 °C by the boundary coal is indicative of a lower content in mineral matter as compared to that in the thermal coal. It is, 50 A U
-! ~ so
2O
0 50
100
150
200
i 250
Temperature (°C) Fig. 3. Effect of temperature on 02 chemisorption:[] Metallurgical; + boundary; • thermal coal. (data obtained isothermallyat indicated temperatures).
72
however, believed that at 250 ° C the region is approached in which the amount of chemisorbed 02, as measured by this technique, is affected by an increased rat~ of decomposition of oxygenated surface complexes [5 ]. The present results suggest that the 02 chemisorption is a sensitive tool for identifying those parts of the seam with the highest quality of coal. This is confirmed by the results in Table 1 which show that the amount of chemisorbed 02, as well as the initial and steady-state rates of chemisorption, increased until the least contaminated part of the seam was reached in which these parameters exhibited little change. The results in Fig. 3 suggest that the distance between sampling points of boundary and thermal coals was not large enough for a proper distinction of these two parts of the seam. The information on distribution of mineral matter across the coal seam appears to be crucial during commercial production. An accurate identification of boundaries between different parts of a seam may increase yields and efficiency of coal production. © Minister of Supply and Services Canada, 1990.
REFERENCES 1 2 3 4 5
Furimsky, E., Palmer, A.D., Duguay, D.G., McConnell, D.G. and Henson, D.E., 1988. Fuel, 67: 798-802. Palmer, A.D., Cheng, M., Goulet, J. -C. and Furimsky, E. 1990. Fuel, 69: 183-188. Stach, E., 1982. Coal Petrology 3rd edn., Gebruder Barufr~iger, berlin. Gray, R.J., Rhoades, A.H. and King, D.T., 1976. Trans. Soc. Min. Eng., 260: 123. Furimsky, E., Duguay, D.G. and Houle, J., 1988. Fuel, 67: 182.
67
ElsevierSciencePublishersB.V., Amsterdam-- Printed in The Netherlands
Short Communication
Determination of Mineral Matter Distribution in a Coal Seam U s i n g 02 Chemisorption Technique A.D. PALMER,J.-C. GOULET,J. GRANSDEN,J.T. PRICE and E. FURIMSKY Energy Research Laboratories, Canada Centre for Mineral and Energy Technology (CANMET), Energy, Mines and Resources Canada, 555 Booth Street, Ottawa, Ontario KIA OG1 (Canada)
(ReceivedJune 9th, 1989;acceptedin revisedformApril 2nd, 1990)
ABSTRACT A seriesof samples taken from differentdepths of the seam of a bituminous coal in Western Canada was used to determine the mineral matter distribution.The measurements were carried out using the 02 chemisorption based on a thermogravimetric technique. The 02 chemisorption increasedwith decreasingmineral matter content.The employed technique was found to be suitable for identifyingthe portion of coal seam leastcontaminated with mineral matter.
INTRODUCTION Oxygen chemisorption as determined by a thermogravimetric technique yields useful information on properties, structure and reactivity of carbonaceous solids. For bituminous coals, anthracite and petroleum cokes a linear correlation between the H / C ratio and the amount of chemisorbed 02 was established [ 1 ]. According to these results the amount of chemisorbed 02 expressed on a dry ash-free basis decreased with increased aromaticity of carbonaceous solids. In a series of carbonaceous solids containing similar organic matter this technique may be suitable for determining mineral matter content. This approach was used in the present work to follow the change in mineral matter content in various depths of a coal seam with the aim to identify the boundary separating part of the seam contaminated with overburden from the uncontaminated area. For this purpose the seam of a bituminous coal from Western Canada exploited for the production of metallurgical coke was used. The suitability of the coal seam for the present investigation was confirmed by the study of particle size effect on properties of three Canadian bituminous coals and the reference Illinois 6 coals [ 2 ]. This study indicated patterns which differed among the coals. The difference was evident when low-sulphur coals, represented by W e s t e r n C a n a d i a n B a l m e r a n d Quintette coals were c o m p a r e d with high-sulphur coals represented by Eastern C a n a d i a n Prince coal a n d the
68 reference Illinois No. 6 coal. For the former the particle size had little effect on the H / C ratio and sulphur content indicating a similar structure of organic matter among different particle fractions. The effect of particle size on surface area was predictable compared with some anomalies observed for the highsulphur coals. For the low-sulphur coals the content of mineral matter exhibited a slight but linear increase with mean particle diameter of fractions decreasing from about 1100 to 20 # m whereas for the high-sulphur coals the mineral matter content more than doubled in the same particle size range. These observations suggest that the fraction of particles which is representative of coal properties can be prepared more readily from the low-sulphur coals. EXPERIMENTAL The five coal samples were taken from different depths of the same seam in the coal mine in Western Canada. The samples are identified as A, B, C, D and E from the top to the bottom of the seam. These coals were crushed and sieved to obtain particle size fractions required for chemisorption. The other three coals taken from a different seam are identified as thermal, boundary and metallurgical from the top to the bottom. Details of the Cahn electrobalance technique, used to measure 02 chemisorption, were given previously [ 1 ]. For the experiment about 500 mg of coal particles were used. Prior to the admission of air, the sample was "cleaned" in N2 stream at 200°C until no further weight decrease occurred. T h e n N2 was replaced by air (2 L / m i n ) and the weight increase was monitored for 2 h. Typical time-weight histories are shown in Fig. 1 for a coal sample identified 50
L
Metallurgical Coal
rn rr
o
30
Ld -r ¢J
o /
o~ 20 ,,
/
200°C
I..Z
o
I0
0
~
2
TIME, hours Fig. 1. Weight increase venus time (500 mg of coal, 200°C, 2 L/rain).
69 as metallurgical. Such results were used to estimate the initial rate as the average rate during the first 4 rain, the steady-state rate as the average rate during the last 30 rain and the Rmount of 02 chemisorbed after 2 h of chemisorption. The B.E.T. 1 technique was used to measure N2 and C02 surface areas. The mean particle diameter of the fractions was determined using the Coulter Counter technique.
RESULTSANDDISCUSSION The results shown in Fig. 2 represent the database from the use of the 02 chemisorption technique by this laboratory for the evaluation of all carbonaceous solids except lignites and sub-bituminous coals. The relatively low surface area of these solids suggests that the external surface played a key role during 02 chemisorption [1,3,4]. The Illinois No. 6 coal deviated from the correlation due to combined effect of the presence of pyrite and surface area which was at least three times greater than that of Canadian coals. The results give a correlation coefficient of 0.873 and the empirical equation Y= 50.1 × H / C - 13.1 in which Y is the amount of 02 (mg/g) chemisorbed at 200°C during a 2 h chemisorption run.
35 A
80 D
~O
~25
.
2O
0
15
10
0 0
tQ 0.9
r 0.6
0.4
0.8
H/G
1
Fig. 2. Effectof H/C ratioon 02 chemisorptionat 200°C in air (circularsymbolsare takenfrom [1], triangularsymbolspresentadditionaldata). 1Brunauer-Emmett-Telleradsorptionisotherm.
70
The results in Table I are typical of those obtained when 02 chemisorption is used for characterization of coal samples taken from different depths of a coal seam. Sample A shows a significant contamination from an overburden, which is also evident to a lesser extent for sample B. The coal's homogeneity increases at greater depths in the seam. This is confirmed by the amount of chemisorbed 02 and initial rate (uncorrected for mineral matter content) for TABLE1
Oxidation data of five coal samples taken from different depths of the same seam Parameter
Coals A
H/C Ash, wt.% Total sulphur, wt.%
B
0.71 55.9 0.12
C
0.66 31.9 0.18
D
0.67 21.2 0.30
E
0.64 13.9 0.25
0.67 22.3 0.22
BET surface area, m2/g 80-120, N2 C02 100-200, N2 CO2 325-400, N2 C02
17 81 16 73 23 105
13 93 18 89 21 133
15 96 21 88 22 147
16 98 24 107 17 142
18 90 15 97 18 140
Mean particle diameter, Hm 80-120, fresh oxidized 100-200, fresh oxidized 325-400, fresh oxidized
123.4 111.4 92.4 90.8 26.1 27.9
136.5 142.7 80.7 85.3 26.4 27.6
153.6 146.9 84.1 89.9 26.1 27.0
150.4 151.9 82.9 92.1 29.2 29.2
146.5 147.0 82.6 77.9 28.8 29.5
02 chemisorbed, mg/g 80-120, as received (dafb) 100-200, as received (dafb) 325-400, as received (dafb)
3.0 6.8 2.7 6.1 7.9 6.6
11.0 16.2 13.0 19.1 18.4 27.1
14.9 18.9 20.0 25.3 29.1 36.9
17.1 19.9 20.8 24.2 28.2 32.8
15.7 20.1 22.2 28.5 29.6 38.1
Initial rate, mg/g min 80-120 100-200 325-400
0.20 0.07 0.25
0.27 0.26 0.48
0.26 0.35 0.63
0.26 0.28 0.67
0.29 0.39 0.71
Steady-state rate, mg/g min 80-120 100-200 325-400
0.02 0.02 0.01
0.08 0.09 0.09
0.10 0.14 0.17
0.12 0.16 0.17
0.12 0.15 0.16
71
all three particle size fractions of sRmples C, D and E. The smaller amount of chemisorbed 02 and the initial rate for sample D, in spite of the lowest content of mineral matter, is attributed, to a lower H / C ratio. As expected, the amount of chemisorbed 02 as well as both initial and steady state rates of chemisorption increased with decreasing particle size [2]. The measured mean particle diameters are in the range of that estimated from the mesh range. A 2-h oxidation in air at 200 °C had little effect on the mean particle diameter. Except for sample A the results for the other samples fit the correlation shown in Fig. 2, if similar particle size fractions are considered. The results in Fig. 3 are for other sets of samples taken from different depths of a coal seam. It was anticipated that the contamination with mineral matter would decrease with increasing depth, from thermal to metallurgical coal. However, at 200 °C little difference was observed between thermal and boundary coals. To ascertain this the chemisorption tests were performed at different temperatures. Thus, every point on the curve in Fig. 3 was obtained isothermally at the indicated temperature. For every case the coal sample was "cleaned" at 200 ° C in N2 stream. This was followed by adjusting the temperature to that of the experiment. The lowest content of mineral matter in the metallurgical coal was confirmed at all temperatures. It may be concluded that the difference between the boundary and thermal coals is not significant, although the greater amount of 02 chemisorbed at 250 °C by the boundary coal is indicative of a lower content in mineral matter as compared to that in the thermal coal. It is, 50 A U
-! ~ so
2O
0 50
100
150
200
i 250
Temperature (°C) Fig. 3. Effect of temperature on 02 chemisorption:[] Metallurgical; + boundary; • thermal coal. (data obtained isothermallyat indicated temperatures).
72
however, believed that at 250 ° C the region is approached in which the amount of chemisorbed 02, as measured by this technique, is affected by an increased rat~ of decomposition of oxygenated surface complexes [5 ]. The present results suggest that the 02 chemisorption is a sensitive tool for identifying those parts of the seam with the highest quality of coal. This is confirmed by the results in Table 1 which show that the amount of chemisorbed 02, as well as the initial and steady-state rates of chemisorption, increased until the least contaminated part of the seam was reached in which these parameters exhibited little change. The results in Fig. 3 suggest that the distance between sampling points of boundary and thermal coals was not large enough for a proper distinction of these two parts of the seam. The information on distribution of mineral matter across the coal seam appears to be crucial during commercial production. An accurate identification of boundaries between different parts of a seam may increase yields and efficiency of coal production. © Minister of Supply and Services Canada, 1990.
REFERENCES 1 2 3 4 5
Furimsky, E., Palmer, A.D., Duguay, D.G., McConnell, D.G. and Henson, D.E., 1988. Fuel, 67: 798-802. Palmer, A.D., Cheng, M., Goulet, J. -C. and Furimsky, E. 1990. Fuel, 69: 183-188. Stach, E., 1982. Coal Petrology 3rd edn., Gebruder Barufr~iger, berlin. Gray, R.J., Rhoades, A.H. and King, D.T., 1976. Trans. Soc. Min. Eng., 260: 123. Furimsky, E., Duguay, D.G. and Houle, J., 1988. Fuel, 67: 182.