INVESTIGATION OF BROWN-COAL GASIFICATION RESIDUES USING LIGHT-MICROSCOPY

In order to determine the effect of calcium on the gasification behavi our of brown coal, raw and calcium-exchanged brown coal particles were subjected to partial steam gasification (55-81%) in a bench-scale flu idized bed reactor operating at selected temperatures in the range 598 to 802 degrees C and at 1.1 MPa. Morphological and reflectance analys es of the collected gasification char residues reveal that calcium inh ibits the development of plasticity during brown coal gasification. Ex amination of gasification residues of raw coal particles shows that pr eferential gasification occurs within the particle interior and the ch ar particles display a wide distribution of reflectance values-a resul t of the broad range of residence times of particles in the fluidized bed reactor. In contrast, the calcium-loaded coal shows no preference for gasification within the particle interior and displays a narrower distribution of reflectance values. These observations stem from the c atalytic effect of calcium, which speeds the gasification reaction, al lowing char particles to quickly attain their ultimate reflectance val ues. Char reflectance appears to be a good indicator of the progress o f the steam gasification and pyrolysis reactions: it increases as pyro lysis proceeds, signifying an increase in aromaticity of the residual char; it decreases as gasification proceeds, signifying a loss of carb on density. Copyright (C) 1996 Elsevier Science Ltd.