Assessment of coal spontaneous combustion index gas under different oxygen concentration environment: an experimental study

Oxygen plays a crucial role in coal spontaneous combustion (CSC), and the magnitude of oxygen concentration determines the oxidation reaction intensity of CSC. This work is aiming to investigate the contribution of oxygen concentration to CSC and to predict the spontaneous combustion stage of coal at different oxygen concentrations. Firstly, experiments on the spontaneous combustion of coal samples at six oxygen concentrations (6%, 9%, 12%, 15%, 18%, and 21%) were carried out combined with a temperature-programmed system. Then, the gas products at different temperature stages were extracted to provide detailed classification and assessment of the indicator gasses for coal spontaneous combustion at different oxygen concentrations. The results show that the oxygen concentration and the crossing point temperature (CPT) are inversely proportional. The higher the oxygen concentration, the more intense the coal-oxygen complex reaction and the greater the gas product concentration. The critical temperature of some stages in high oxygen concentration environment is lower than that in low oxygen concentration environment. The oxidation process can be slowed down by reducing the oxygen concentration as much as possible. Indicator gasses are different for different oxygen concentration environments and should be selected reasonably and optimally to match the specific environment for judging natural coal fires in order to effectively prevent coal spontaneous combustion fire disasters.