Evolution and mechanisms of low-temperature oxidation and coal-oxygen coupling processes of a specific low-rank bituminous coal with various microscale particle sizes

Coal fires are very typical hazards caused most significantly by uncontrolled spontaneous combustion processes in coal mines, seams, and the like. By thermogravimetry (TG) experiments, evolution behaviors and properties of thermal oxidation processes at low temperature of a bituminous coal with five microscale particle sizes (L1 215.20 mu m; L2 151.90 mu m; L3 80.22 mu m; L4 43.71 mu m; and L5 19.21 mu m) were investigated. A two-step reaction model was developed by using Coats-Redfern method and pyrolysis kinetics parameters were calculated. Results show that in stage 1 (65.0-160.0 degrees C) segments of water evaporation and gas desorption dominate, while in stage 2 (160.0-320.0 degrees C) segments of generation of coal-oxygen complex and structure oxidation contribute most. Five macro-characteristic temperatures (critical temperature T-1, xerochasy temperature T-2, activity temperature T-3, mass peak temperature T-4, and ignition temperature T-5) move to the low temperature direction with decreasing particle sizes except T-4. Reaction processes during coal-oxygen interactions are proposed. Activation energies decrease as particle sizes reduce during both stage 1 (15.01-32.47 kJ center dot mol(-1)) and stage 2 (64.29-96.34 kJ center dot mol(-1)) since specific surface areas are augmented and more active groups are exposed. This work is expected to better monitoring of temperature thresholds for coal spontaneous combustion processes.