Effect of Oxygen on Radical Reactions During Oxidation of Water-Soaked Coal

The oxidation of residual coal in goafs usually occurs under different oxygen concentration environments. Moreover, residual coal in goafs exhibits heightened susceptibility to spontaneous combustion following prolonged immersion in mine water. Therefore, this study simulated water-soaked coal (WSC) oxidation under varying oxygen concentration using an electron spin resonance (ESR) spectrometer and a gas chromatograph, investigating oxygen’s role in the process from the perspective of radical reactions. Findings suggest that under lower temperature conditions, oxygen has a relatively small impact on WSC oxidation. Conversely, as temperatures rise incrementally, oxygen’s role in the oxidation process becomes increasingly pronounced. As temperatures rise, both the radical concentration and the g factor demonstrate a steady upward trend, whereas ΔH exhibits a gradual reduction. Based on the trends in radical concentration and CO release, the oxidation process of WSC can be categorized into two distinctive phases: the slow oxidation stage from 30°C to 130°C and the rapid oxidation phase from 130°C to 230°C. In an oxygen-free atmosphere, the CO release maintains a slow growth trend, which is inconsistent with the trend of CO release in an oxygen-containing atmosphere where it first increases slowly and then rapidly. Therefore, the mechanism of CO production during oxidation and pyrolysis is explained from the perspective of radicals. Additionally, the oxidation process of WSC at different stages is discussed, offering important theoretical insights for the management and mitigation of spontaneous combustion risks associated with WSC.