Reignition Behavior Evolution and Microscopic Kinetic Mechanism of Lignite at Various Preoxidation Temperatures

Abstract In order to reveal the evolution characteristics and microdynamic mechanism of the reignition behavior of Shajihai coal at different preoxidation temperatures, this paper systematically studied the differences in the spontaneous-combustion characteristics of Shajihai coal at different preoxidation temperatures (40, 70, 100, 130, 160 °C) by means of temperature-programmed experiments, simultaneous thermal analysis (TG-DSC), in situ Fourier transform infrared spectroscopy (FTIR), and other experimental methods. The results show that the preoxidation temperature has a nonlinear regulation effect on the spontaneous-combustion tendency of Shajihai coal. In the high temperature stage (>160 °C), the release of CO and CO2 increased by 16% and 9.7%, respectively, compared with the raw coal, indicating that its oxidation activity was the strongest. However, the oxidation activity of preoxidized coal at 130–160 °C was inhibited due to the consumption of active groups caused by high-temperature pyrolysis, and the most prominent passivation effect occurs at 160 °C. FTIR analysis showed that the oxygen-containing functional groups (−OH, C═O) of the preoxidized 100 °C coal sample were slightly reduced by 3%–9.6% compared with the raw coal, and the aliphatic hydrocarbon content was increased by 33%–42% compared with the raw coal. The conversion rate of functional groups in the high temperature stage (230–300 °C) was accelerated, which further aggravated the chain reaction. This study realizes the coupling interpretation of macroscopic reignition performance and microscopic molecular evolution by combining programmed-temperature gas test, TG-DSC, and in situ FTIR measurements.