High-pressure pyrolysis and CO2-gasification of coal maceral concentrates:: conversions and char combustion reactivities

The gasification behaviour of maceral concentrates was examined in a fixed-bed and a wire-mesh reactor. 'Extents of gasification' were calculated by subtracting sample weight loss during pyrolysis (He) from weight loss in CO2-gasification. The effect of holding time (10 and 200 s) and pressure (1 and 20 bar) on conversions and on combustion reactivities of chars were studied. During short hold-time gasification experiments (10 s), liptinites gave the highest conversions, followed by the vitrinites and the inertinites. Vitrinite conversions decreased sharply above 90% elemental-C content. Extents of gasification were found to be in the order: vitrinites > liptinites > inertinites. However, at 200 s, a marked increase in inertinite conversion translated into a clear change of relative ordering to: inertinites > vitrinites > liptinites. The high gasification reactivities of inertinites at longer times appear to be related to a more rigid and porous structure, but the late surge suggests that an induction period is needed. More detailed time series data are required. Relative combustion reactivities of chars were generally observed to decrease with (i) pressure, (ii) time at temperature and (iii) increasing elemental carbon content. The data indicated that orders of gasification reactivities may be predicted from the order of combustion reactivities of pyrolysis chars. Inertinite concentrate chars were more reactive. However, the difference in reactivity between inertinite chars and other samples was reduced when the inertinites were heated rapidly-possibly owing to melting at the higher heating rates. (C) 1999 Elsevier Science Ltd. All rights reserved.