Adsorption Effect of Residual Coal in Goaf on Gases Under High Ground Temperature Environment

To explore the adsorption characteristics and mechanism of residual coal in goaf on multi-component gases under high ground temperature, anthracite from Guizhou Longfeng (LF), bituminous coal from Anhui Yangliu (YL), and lignite from Yunnan Xiaolongtan (XLT) were selected. Single and multi-component (CH4, N2, O2) adsorption experiments were performed at 30, 50, and 70°C using an H-Sorb 2600 high-temperature high-pressure analyzer and a self-built atmospheric adsorption platform. Gray relational analysis (GRA) was applied to investigate adsorption interactions. The results indicate that under atmospheric pressure, the adsorption isotherms exhibit a strong linear relationship (R2 > 0.95). Adsorption capacity increases with coal metamorphic degree (LF > YL > XLT) but decreases with rising temperature. In the multi-component system, CH4 demonstrates significant preferential adsorption. As its volume fraction increases from 0% to 50%, the total adsorption capacity rises by 142.1% to 170.6%, while the adsorption of O2 and N2 is markedly suppressed. GRA confirms that CH4 dominates the total adsorption behavior, with a correlation coefficient R >0.9, substantially higher than that of N2 and O2 (0.45–0.50). Molecular models representing the three distinct coal ranks were constructed using Materials Studio to calculate adsorption energy. The adsorption energy exhibits the order CH4 > O2 > N4, exhibiting a positive correlation with the measured adsorption capacity. The high adsorption energy of CH4 allows it to preferentially occupy adsorption sites, establishing a competitive advantage. Furthermore, high ground temperature weakens the adsorption capacity of coal, with a more pronounced effect observed in low-rank coal. This study demonstrates that methane can inhibit the adsorption of oxygen on coal surfaces through competitive adsorption, thereby reducing the coal’s oxidation activity and providing a theoretical foundation for the prevention and control of coal spontaneous combustion (CSC) in goaf.