Gasification of a South Australian low-rank coal with carbon dioxide and steam: kinetics and reactivity studies

Experimental gasification studies are reported for a highly reactive South Australian low-rank coal, Bowmans coal, with steam and with carbon dioxide in a single-particle reactor operating at atmospheric pressure and at temperatures between 714 and 892 degrees C. Gasification rate at a given temperature is found to be independent of particle size, suggesting that the gasification rate follows the homogeneous model. The observed gasification rate constants are as follows. For CO2 gasification: k = 1327 exp(-10945/T) [A = 1327 min(-1), E-a = 91 kJ mol(-1)] For H2O gasification: k = 261276 exp(-15733/T) [A = 261276 min(-1), E-a = 131 kJ mol(-1)] It is found that the reactivity of Bowmans coal is far higher than for other coals reported in the literature, because of to its high inherent content of inorganic matter. Acid-washed Bowmans coal has similar reactivity to other low-inorganic-content low-rank coals. Gasification reactivity follows the order Na > K > Ca > Ni with the same anions. The combined effect of different cations is found to be less than for the sum of the individual cations. Heat treatment of acid-washed coal prior to ion exchange results in greatly reduced reactivity due to loss of carboxylic functional groups. Reactivity can be varied by removing or adding active cations. A reasonably good correlation is found to exist between gasification reactivity and total Na + Ca cation content. (C) 1998 Elsevier Science Ltd. All rights reserved.