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 s ubtracting sample weight loss during pyrolysis (He) from weight loss in CO2 -gasification. The effect of holding time (10 and 200 s) and pressure (1 an d 20 bar) on conversions and on combustion reactivities of chars were studi ed. During short hold-time gasification experiments (10 s), liptinites gave the highest conversions, followed by the vitrinites and the inertinites. V itrinite conversions decreased sharply above 90% elemental-C content. Exten ts 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 > vitr inites > liptinites. The high gasification reactivities of inertinites at l onger 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 t ime series data are required. Relative combustion reactivities of chars wer e generally observed to decrease with (i) pressure, (ii) time at temperatur e and (iii) increasing elemental carbon content. The data indicated that or ders of gasification reactivities may be predicted from the order of combus tion reactivities of pyrolysis chars. Inertinite concentrate chars were mor e reactive. However, the difference in reactivity between inertinite chars and other samples was reduced when the inertinites were heated rapidly-poss ibly owing to melting at the higher heating rates. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.