Coupled Effects of Water Temperature and Particle Size on Oxidation Characteristics of Coal: An Experimental Study

To elucidate the alterations in the oxidation reaction characteristics of coal under the joint influence of grain size and water temperature (TW), an oxidation experiment with a set of programmed temperatures was carried out to investigate the oxidation behavior of raw coal and coal samples of different sizes that had been soaked in water at various temperatures. The research results indicate that the kinetic model of oxidation O₂ consumption reaction is applicable to the Avrami-Erofee complex multidimensional uniform nucleation model with n = 4. Compared with the same particle size as raw coal, when the TW is lower (15 °C), the activation energy (E _a) of coal particles with a diameter larger than 2.5 mm reduces and increases for those with a smaller value; when the TW is not lower than 30 °C, the E _a of coal samples after water immersion is notably reduced, typically by 12%-15%. Overall, the reduction in E _a is more pronounced with decreasing particle size and increasing TW. The coal sample with mixed particle sizes demonstrates an enhanced low-temperature oxidation capacity after being immersed in low-temperature water (15 °C), the high-temperature oxidation is inhibited; the oxidation and heat-generation capacity of coal after being soaked in water at 30 °C is comparable to that of the raw coal; upon being soaked in water at a temperature of 45 °C, the low-temperature oxidation capacity of the mixed coal sample is inhibited; however, its high-temperature sustained oxidation capacity significantly enhances after attaining a temperature of 130 °C, thereby substantially elevating the risk of spontaneous combustion as the oxidation temperature escalates.