Pyrolysis of coal maceral concentrates under pf-combustion conditions (I): changes in volatile release and char combustibility as a function of rank

The pyrolytic behaviour of sets of maceral concentrates have been examined under conditions similar to those of pf-combustion. Relative combustion reactivities of chars prepared during the pyrolysis experiments have been compared by standard methods. As expected, for samples of similar elemental C-content, total volatile release decreased as: liptinite > vitrinite > inertinite. The data indicates the absence of synergistic effects between vitrinite and inertinite during pyrolysis. The sensitivity of pyrolysis yields to inertinite content was found to diminish with increasing coal sample rank. In marked contrast to the order established for volatile release, combustion reactivities of maceral chars (of similar carbon content) may be ranked in the order: inertinite > vitrinite > liptinite. A direct comparison with maceral concentrates from the same coal was undertaken. Vitrinite/inertinite graded samples of a South African coal were pyrolysed at 1500 degrees C: these chars exhibited increasing reactivity with increasing inertinite concentration, but observed differences in reactivity between samples from the same coal were not large. Furthermore, for a higher rank coal, char reactivities were found to be essentially independent of original inertinite concentration. It is clearly possible for chars from low volatile coals to be relatively reactive. However, there appears to be no reason to suggest that 'reactive inertinites' might release volatile matter in quantities comparable to those of vitrinites from the same coal. (C) 1998 Elsevier Science Ltd. All rights reserved.