Experimental Study on the Influence of Pore Structure and Group Evolution on Spontaneous Combustion Characteristics of Coal Samples of Different Sizes During Immersion

[Image: see text] To study the influence of water immersion on the evolution of the groups and spontaneous combustion characteristics of coal samples with different sizes, raw coal from the Fengshuigou Coal Mine operated by Pingzhuang Coal Company in Inner Mongolia was studied. The infrared structural parameters, combustion characteristic parameters, and oxidation reaction kinetics parameters of D1–D5 water immersion coal samples were tested, and the mechanism of spontaneous combustion during the oxidation of submerged crushed coal was investigated. The results were as follows. The water immersion process promoted the re-development of coal pore structure, and the micropore volume and average pore diameter were 1.87–2.58 and 1.02–1.13 times those of raw coal, respectively. The smaller the coal sample sizes, the more significant the change. At the same time, the water immersion process increased the contact point between the active group and oxygen in the coal, and the C=O, C–O, and −CH(3)/–CH(2)– groups in coal were further promoted to react with oxygen to generate −OH functional groups and improve the reactivity of coal. The characteristic temperature of water immersion coal was affected by the temperature rise rate, coal sample size, coal voidage, and other factors. Compared with the raw coal, the average activation energy of the water immersion coal with different sizes decreased by 12.4–19.7%, and the apparent activation energy of the coal sample with a size of 60–120 mesh was the lowest on the whole. In addition, the apparent activation energy in the low-temperature oxidation stage was significantly different.