Study Governing the Impact of Long-Term Water Immersion on Coal Spontaneous Ignition

Oxidation of air-dried coal in mined-out areas is one leading factor contributing to coal spontaneous ignition during exploitation. Although some related work has been done, there is still some space for improvement. We screened out three coal samples with different ranks of coal and immersed them in distilled water for 200 days. Afterward, we identified some changes in pore structure and oxygen consumption characteristics of coal samples after water immersion. Additionally, we analyzed the composition of dissolved substance, both organic and inorganic. The results demonstrated that some parameters of three different residual coal samples increased, including average pore size, specific surface area and pore volume. In regard to the composition of dissolved substance, we identified Na+ and Cl-, which accounted for the largest proportion, along with some organic functional groups. We found that higher rank leads to a smaller total amount of dissolved substance. Additionally, we performed some experiments concerning coal oxidation rate and the amount of CO, CO2 and C2H4 generated during oxidation. The results showed that water immersion does play a significant role, along with coal rank. Considering all results and analysis, long-term water immersion is responsible for pore structure development in coal and the degree of reduction in spontaneous-ignition-proof substance, which helps to boost coal spontaneous ignition.