Effects of water immersion and pre-oxidation on re-ignition characteristics of non-caking coal

Coal spontaneous combustion (CSC) in waterlogged goafs has become an essential threat to coal mine safety production, so it is necessary to comprehensively and deeply evaluate the re-ignition characteristics of residual coal after water immersion and pre-oxidation. The re-ignition process of non-caking coal under the influence of water immersion and pre-oxidation was tested using a temperature-programmed test system (TPTS), and the spontaneous combustion characteristic parameters and limit characteristic parameters of low-temperature oxidation were calculated. The results show that the spontaneous combustion characteristic parameters such as CO production rate, oxygen consumption rate, and heat release intensity positively correlate with temperature. The minimum float coal thickness and lower limit oxygen concentration show a trend of increasing and then decreasing with the temperature increase, while the maximal air leakage intensity is the opposite. In addition, the expansion of pores and cracks caused by water immersion and pre-oxidation processes and the increase of unstable functional groups promote the oxygen consumption and heat generation of immersed and oxidized coal, which reduces the characteristic temperature, and activation energy, and limit characteristic parameters. Meanwhile, water immersion and pre-oxidation can synergistically accelerate the low-temperature oxidation process of non-caking coal, which significantly increases the CSC risk of coal O₁₄₀I₃₀ and coal O₉₀I₃₀. The results enrich the research on the characteristics of water immersed and oxidation coals re-ignition, which may be applied to prevent CSC in the future.