Study on the effect of low-methane oxidizing atmosphere on pore structure during coal spontaneous combustion process

Abstract

As the depth of coal mining increases, the complex interactions between coal, oxygen, and gas in the goaf significantly affect coal spontaneous combustion behavior. However, the impact of low-gas oxidizing atmospheres on the pore structure during coal spontaneous combustion has not been sufficiently explored. This study systematically analyzes the pore structure evolution of three coal samples with different degrees of metamorphism in a low-gas oxidizing atmosphere based on low-temperature nitrogen adsorption experiments. The study focuses on the independent mechanisms by which oxygen and methane concentrations influence the coal spontaneous combustion process. The experimental results show that the adsorption/desorption isotherms for lignite and anthracite coal are of Type IV with H3-type hysteresis loops, while bituminous coal follows a Type II isotherm. The pore structure response to the oxidizing atmosphere varies significantly across coal samples of different metamorphic degrees. Anthracite is most responsive to the oxidizing atmosphere, followed by bituminous coal, while lignite is the least sensitive. Increasing methane concentration promotes spontaneous combustion for all three coal samples. In contrast, increasing oxygen concentration accelerates spontaneous combustion of lignite and anthracite, but its effect on bituminous coal is temperature-dependent. Oxygen concentration only significantly accelerates spontaneous combustion of bituminous coal when the temperature exceeds 200°C. The results of this study provide a theoretical basis for predicting and preventing coal spontaneous combustion in low-gas environments.