Pyrolysis Kinetics of Low-Rank Coals Using Three Model-Free Methods

Abstract—Knowledge on pyrolysis of low-rank coals is of vital important since it has significant effect on their thermal conversion such as gasification, liquefaction, and combustion. However, kinetic background on pyrolysis of different low-rank coals is still insufficient. In this work, pyrolysis of three low-rank coals, i.e., Xilinguole lignite (XL), Naomaohu lignite (NL), and Shenmu-Fugu subbituminous coal (SBC), was performed in a thermogravimetric analyzer from room temperature to 1000°C at different heating rates (10, 20, and 30 K/min). Kinetic parameters including activation energy, reaction order, and pre-exponential factor were determined using three different kinetic models, i.e., Kissinger-Akahira-Sunose (KAS) model, Ozawa-Flynn-Wall (OFW) model, and Coats-Redfern (CR) method. The results show that KAS and OFW models are almost equally effective for calculating activation energy, which varies remarkably from 26.4 to 141.7 kJ/mol for different low-rank coals but all firstly increases with the pyrolysis progress and then decreases. Reaction order and pre-exponential factor determined by CR method vary with different low-rank coals and heating rates.