Comprehensive analysis-based experimental investigation on the oxidation characteristics of coal spontaneous combustion

This study aims to compare and analyze the coal tendency to undergo coal spontaneous combustion (CSC) oxidation, thereby providing theoretical guidance for predicting and controlling CSC in goafs. Experimental research was conducted to investigate the oxygen absorption characteristics during the pressure-increasing stage of 0–0.1 MPa and to examine the differences in macro- and microcharacteristic parameters during the oxidation process of coal with varying metamorphic degrees at temperatures ranging from 30 to 250 °C. The experimental data were comprehensively analyzed. The results of the experiments and analysis indicate that high-rank anthracite exhibits the highest physical oxygen absorption capacity. At 30 °C, the O 2 adsorption ( Q max ) maximum values of anthracite is 1.186 cm 3 g −1 when the maximum equilibrium pressure ( P max ) is attained. Low-rank lignite, on the other hand, demonstrates high rates of oxygen consumption and gas generation, with the lowest crossing-point temperature (CPT) observed during the CSC oxidation process. The CPTs for lignite, bituminous coal, and anthracite are 138.2 °C, 167.9 °C, and 185.5 °C, respectively. Additionally, the linewidth ( ΔH ) and g -values for lignite surpass those of bituminous coal and anthracite. The free radical concentrations ( N g ) of coal exhibit a significant increase with rising temperature, with high-rank anthracite demonstrating the highest N g throughout the experimental oxidation process. However, the oxygen adsorption per unit specific surface area ( Q BET ) is greatest, and the rate of increase in free radical concentration (Δ N g ) for low-rank lignite is substantially higher than that of bituminous coal and anthracite. The active structure of lignite possesses a strong capacity to convert physiosorbed oxygen into chemisorbed oxygen, indicating that coal samples with a low degree of metamorphism exhibit a pronounced oxidation self-heating ability, which facilitates the initiation and acceleration of the free radical chain reaction. This study conducts a comprehensive analysis comparing the CSC oxidation capabilities of various types of coal. The findings provide relevant methodologies for assessing the spontaneous combustion characteristics of different metamorphic coals, which is significant for elucidating the mechanism of CSC and offering guidance for its prevention and control.