Influence of pyrolysis temperature on char optical texture and reactivity

In this study a set of 10 coals varying in rank and maceral composition has been devolatilised in a flat flame burner at 1000 and 1300 degreesC in order to investigate the changes in char reactivity and structure as a function of pyrolysis temperature. The intrinsic reactivity of the chars, measured isothermally in a thermobalance at 500 degreesC, has been related to the petrographic characteristics of the chars and their CO2 surface areas. The temperature of pyrolysis has shown to have a strong effect on char reactivity for certain coals. Overall, the increase of temperature provoked an enhanced plasticity and a more extensive consolidation during the metaplast stage of pyrolysis and reduced the amount of unfused material in the chars. This effect was more pronounced in low volatile bituminous vitrinites and low rank inertinites. The presence of inertinite derived materials in high rank coal chars enhanced their reactivities, whereas the opposite was observed for low rank coal chars. This was attributed to the fact that inertinite macerals yield both isotropic and anisotropic materials: inertinite in low rank coals increases the amount of anisotropic, less reactive char, but reduces it in high rank coals. (C) 2001 Elsevier Science B.V. All rights reserved.