Quantitative heat effects associated with pyrolysis of coals, ranging from anthracite to lignite

Abstract

Differential scanning calorimetry (d.s.c.), in combination with thermogravimetry (TG), was performed up to 1050 K to study the heat effects associated with the pyrolysis of 17 different coals. The coals ranged in rank from anthracite to lignite. The net heat effects found were principally endothermic in nature; only in the case of low rank coals in the temperature range 450–750 K were some exothermic heat effects found. No large net heat effects are associated with the principal devolatilization reactions. The main part of the endothermic heat effects occurred above 750 K, and is associated with dehydrogenation of the coal char matrix. For the overall heat of pyrolysis, calculated from the net d.s.c. curves over the temperature range 450–1050 K, a maximum in endothermicity in the order of 450–550 Jg −1 (daf) was found for coals with a volatile matter content of 10–15 wt% (daf). On the other hand, the overall heats of pyrolysis are smaller than the specific enthalpies (∝ c p . dT) of the coal chars.