Effect of multi-component gases competitive adsorption on coal spontaneous combustion characteristics under goaf conditions

Coal spontaneous combustion in the goaf usually occurs in the multi-component gases environment. In this work, the multi-component gases competitive adsorption properties and its effects on the coal oxidations were investigated by gas adsorption analyzer and in-situ FTIR. Results show that the order of gases adsorption selectivity on coal surface based on IAST is that: CO2 > CH4 > O2 > N2. For all the selected gas components, interactions between the gases and the coal surface undergo two main mechanisms: the physical competitive adsorption or desorption under lower temperature condition and the chemical adsorption or reaction under higher temperature conditions. In ambient temperature conditions, coal spontaneous combustion would be hindered due to the stronger adsorption capability of CH4 and CO2 on coal surfaces. At the late oxidation stage, irreversible chemical adsorption of O2 would be gradually strengthened replaces and O2 preferentially reacts with –CH3/–CH2– to generate much more oxygen-containing functional groups. Reactions of CH4 with O2 on the high-temperature coal surface would accelerate the coal spontaneous combustion, which increases the risk of coal spontaneous combustion.