Determination Criteria for Suppressing Water-Immersed Coal Oxidation: Critical Threshold of Oxygen Concentration

To unravel the veil on the phenomenon that water-immersed coal is prone to spontaneous combustion, the paper digitally re-constructed pore structure and quantitatively assessed the effects of water immersion on it. It was discovered that the pore cross-sectional area of water-immersed coal is 1.59 ~ 5.12 times larger than that of raw coal, which provided more opportunities for the coal-oxygen oxidation reaction. It well explained the reason why water-immersed coal is prone to spontaneous combustion. Besides, in order to find effective measures to suppress spontaneous combustion of water-immersed coal, closed isothermal oxidation experiment was conducted. It was found that oxidation reaction that generates CO and CO2 was dominated by different reaction mechanisms, which was completely inhabited when oxygen concentration is below 2% and 1%, respectively. But when the oxygen concentration is below 5%, the oxidation reaction that generates CO and CO2 was both inhabited, accompanied with declined growth rate. Therefore, oxygen concentration of 5% can be set as critical threshold for suppressing water-immersed coal oxidation. These research results provided solid theoretical foundation for preventing endogenous fire.