Kinetic Analysis of Pyrolysis Reaction of Hydrogen-Containing Low Rank Coals Based on Thermogravimetric Method

Abstract

Based on the combined technology of thermogravimetric analysis-mass spectrometry (TG-MS), the non isothermal kinetic of two low rank coals with high hydrogen content and the release characteristics of H2 in volatiles were explored. The effect of coal species and coal particle size on pyrolysis was studied. The CR (Coats-Redfern) method and the DAEM (Distributed activation energy model) method were used to construct the pyrolysis kinetic model by dividing temperature stages, and the results showed that the mechanisms of pyrolysis process of lower rank coals were mainly 3-D diffusion (G-B) and Growth of nucleation (Avrami-Erofeev, n = 1/3). The use of the DAEM method made up for the shortcomings of the CR method in calculating the activation energy, and the analysis of coal pyrolysis kinetics was more comprehensive. The higher the volatile content the coal contained, the lower activation energy the pyrolysis process would require. The larger the particle size of the coal was, the higher activation energy the pyrolysis process would need. The release law of H2 in low rank coal during the pyrolysis process was analyzed by mass spectrometry, and results were presented: the first peak occurs at 500 °C and the second at 750 °C, which was mainly generated by the condensation and dehydrogenation reactions of aromatic compounds.