Experimental and Molecular Simulation Research on the Oxidation Behavior of Soaked Coal Spontaneous Combustion

The goaf residual coal is more susceptible to oxidation after long-term soaking that raises the spontaneous combustion risk level. This paper investigates the oxidation thermodynamic mechanism and the active functional group proliferation trend in soaked coal. A coal macromolecular model C₂₁₇H₁₇₁O₄₄N₃S₂ is constructed to evaluate the oxygen adsorption effectiveness via molecular dynamics simulation. The results show that the soaking behavior reduces the coal intramolecular hydrogen bonds and expands the coal pore volume. The soaked coal creates 1.18 times average oxygen adsorption loading higher than the raw coal. The soaking decreases the crossing point temperature from 147.40 °C to 144.15 °C and enlarges the CO production rate by 1.087 times, increasing the potential hazard of coal oxidation. The reactive functional groups -CHO, –CH₂, –CH₃, and –OH exhibit an evident increase of 0.73, 0.01, 0.42, and 0.72 after water soaking. The –CH₂/–CH₃ drops from 1.95 to 1.13, indicating that aliphatic chain consists of shorter and more branched chains. The increase in oxygen adsorption and reactive functional group of soaked coal promotes the coal oxidation chain reaction, which boosts oxidation temperature rise and gas release.