Characteristics of lean oxygen combustion and dynamic microreaction process of water-soaked coal

[Display omitted] •The characteristics of low temperature oxidation kinetics of water-soaked coal samples were analyzed.•Find out the migration law of functional groups in the oxygen-lean combustion process of water-soaked coal.•The thermal evolution process of water-soaked coal samples in an oxygen-lean environment is proposed.•A micro-reaction mechanism of coal-oxygen-water molecular chemisorption was constructed. Oxidative spontaneous combustion is likely to occur after long-term water immersion in the gob area of coal mines. Mostly, the oxidation process is slowly carried out under different air leakage conditions. This paper summarizes the four stages of the low-temperature oxidation of water-soaked coal samples through temperature-programmed experiments. Using infrared spectroscopy and thermal analysis experiments, the migration laws of the functional groups and the thermal reaction characteristics of the four stages were investigated. The results show that as the oxygen concentration increases, the gas product concentration increases, and the activation energy of the deep oxidation stage decreases. With the progress of the heating stage, when the oxygen concentration is higher than 10%, the change in each functional group is larger, and the conversion of the functional group and the intermediate complex is relatively closer at an oxygen concentration of 21%. The low-temperature oxidation reaction is a parallel process of the pyrolysis and micro-oxygen absorption, and the DTG size is not affected by the oxygen concentration at the critical temperature. The higher the oxygen concentration is, the lower the initial exothermic temperature is, which promotes the exothermic process in the deep oxidation and oxidation-limited stages. The microreaction mechanism among coal, oxygen and water molecular chemisorption is constructed. By controlling the coal oxidation reaction stages under different air leakage conditions, the spontaneous combustion of water-soaked coal in the goaf is avoided.