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Mlller. I.; Freund, J. E. “Probablllty for Scientists and Engineers”; Prentice-Hall of India Pvt. Ltd.: New Delhl; 1977; p 117. Ramanujam, T. K.; Venkateswarulu, D. Proceedings of Particle Technology Seminar, Indian Instltute of Technology, Madras, 1971; p 91. Rosin, P.; Rammbr, E. J. Inst. Fuel. 1933. 7 , 29. RUmDf. H.: Ebert, E. Chem. Inc7. Tech. 1964. 36.523. Schuhmann, J. R., “Principles 6f Commlnutlon”; AIME. Technical Paper No. 1189. Mlning Tech., 1940. Subramanian, P.; Arunachalam. V. R., Paper presented at 32rd Annual IIChE Meeting, Bombay, 1979; Paper 111 El.
Viswanathan, K.; Manl, B. P. Indkrn Chem. Ena. 1980, 22(3). . . 44
Department of Chemical Engineering Indian Institute of Technology New Delhi 110016, India
K.Viswanathan P. V. R. Iyer B. P. Mani*
Received f o r review December 31, 1979 Revised manuscript received January 5, 1981 Accepted August 12, 1981
Effects of Drying and Oxidation on Coal Pore Structure Pore volume distributions and surface areas were measured by mercury intrusion porosimetry for seven coals of different rank and source location. Both pore volume and surface area are reduced during drying with little addiinal change during subsequent moderate temperature (300 A
12-300 A
190 197 87 127 4 135 80
HVC bituminous HVB bituminous lignite LV bituminous HVA bituminous MV bituminous anthracite
0.025 0.032 0.023 0.014 0.012 0.012 0.009
0.089 0.041 0.029 0.026 0.023 0.026 0.019
0.040 0.022 0.062 0.014 0.017 0.016 0.009
0.122 0.013 0.000 0.000 0.000 0.000 0.010
Table 11. Determination of Complex Pores from Porosimeter Hysteresis Analyses coal,
pore vol
PSOC
>35 A ,
no.
cm3/g
190 197 87 127 4 135 80
0.114 0.073 0.052 0.040 0.035 0.038 0.028
Hg trapped after de- % of filled vol not pressurization, cm3/g recovered 0.056 0.034 0.024 0.008 0.008 0.008 0.007
49 47 46 20 22 21 25
seven coals exhibited penetration curves similar in form to the one selected for illustration as Figure 1: a relatively small mercury volume was picked up over the pressure range below approximately 1000 psia (equivalent pore diameter of 0.18 pm), but the penetration volume increased rapidly at pressures over 5000 psia (equivalent pore diameter of 0.035 pm), indicating that the coals contain significant microporosity. Toda and Toyoda (1972) have suggested that coal compressibility could be a source of error in mercury intrusion results at elevated pressures. Considerable additional porosity may also be present in pores less than 35 A in diameter, beyond the range of these measurements. The typical results in Figure 1 also show replication and hysteresis effects by means of the dashed line. The duplicate runs are in excellent agreement, but the pressure swing has a considerable influence on the result. The amount of mercury remaining in the pores when the pressure is reduced to atmospheric is a reflection of the irregular pore structure, since the mercury would be retained by small pore constrictions, roughness, or so-called ink-well or inverted pores. The vertical distance between the dashed and solid lines in Figure 1 represents the volume of irregularly shaped pores smaller than the diameter corresponding to the given pressure. The percentage of irregular volume computed in this way for each coal is given in Table 11. The coals with the greatest porosity, PSOC 190,87, and 197, contain a narrow range of 46 to 49% irregularly shaped pores. The four remaining less porous coals contain only 20 to 25% pores of this type. The irregular pores appear to be more common among coals with extensive porosity. Also included for comparison in Table I are earlier results by Gan et al. (1972), who also used mercury intrusion to estimate the pore volumes of the same coals. Several figures are in excellent agreement but the prior results are appreciably higher for two coals (PSOC 1908 PSOC 87), possibly because of differences in the preparation conditions: the earlier work dried each coal for 1 h at 105 "C. Moreover, although the coals were obtained from the same source, aging in storage is known to be a possible cause of changes in characteristics of coals. Surface areas calculated from the mercury intrusion data via eq 3 are presented in Table I11 together with surface areas determined by Gan et al. (1972) by both nitrogen
Table 111. Surface Areas for Several Coals this study
coal,
porosimetr y surface in pores
PSOC
>35 A ,
no. 190 197 87 127 4 135 80
"/g 53 25 19 15 13 15 12
data of Gan et al. (1972) N2
surface area, m'/g 83
COZ
surface area, m2/g 96
.-
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