Volatile gas release characteristics of three typical Chinese coals under various pyrolysis conditions

In order to reveal the volatile gas release characteristics under various conditions (pyrolysis temperature, particle size, coal rank and pyrolysis time), three different rank coals (Shenhua 2# bituminous coal, Baorixile coal, and Zhaotong lignite coal) were pyrolyzed in a tubular furnace and the pyrolysis gas was analyzed by online balance and gas chromatography. Results suggest that increasing pyrolysis temperature causes increased release volume of volatile compounds and higher calorific value due to substantial increase of H-2, an incremental increase of CH4 and the changes in molecule ingredients of C-2-C-4 structures. Meanwhile, larger particle size can significantly reduce the released volume for its longer diffusion distance and lower specific surface area. Compared with bituminite, lignite yielded more valuable pyrolysis gases and lower primary reaction temperature. The ideal pyrolysis temperature is 700-800 degrees C for low rank lignite and 800-900 degrees C for bituminites. Basically, the productions of CO and CO2 are associated with oxygen element content in coal while CO2 releases early mainly by the decarboxylation reaction. Based on the results in the whole pyrolysis process, the CH4 of higher rank coals is mostly produced by the rupture of aliphatic side chain while the main CH4 source in lignite is the rupture of alkyl side chains in aromatics. (C) 2017 Energy Institute. Published by Elsevier Ltd. All rights reserved.