IsothermalOxygen Consumption Characteristics of CoalSpontaneous Combustion Based on Double Loss of Coal and Oxygen: CouplingEffect of Temperature, Oxygen, and Time

Abstract In the goaf environment, the low-temperature oxidation of residual coal exhibits significant time-dependent evolution characteristics, and the slow temperature-rising process can be approximately regarded as a series of continuous isothermal reaction stages. Based on sealed isothermal oxidation experiments conducted on three coal samples with different metamorphic degrees, an isothermal oxygen-consumption rate model for coal spontaneous combustion was established by considering the coupled effects of temperature, oxygen concentration, and reaction time from the perspective of thermodynamic–kinetic interactions within the coal-oxygen system. The results indicate that the synchronous consumption of coal and oxygen during the oxidation process causes the oxygen-consumption rate to decrease exponentially with time (R2 > 0.95), while the ambient oxygen concentration gradually declines to a critical oxygen concentration. Furthermore, the relationship between temperature and the critical oxygen concentration follows the Van’t Hoff equation (average R2 ≈ 0.94). Experimental results demonstrate that the proposed model can effectively characterize the time-decay behavior of oxygen consumption and the dynamic evolution characteristics at different oxidation stages. On this basis, the time-dependent oxygen-consumption behavior was further integrated with air leakage and working face advancing processes in the goaf, and a quantitative criterion for determining the critical hazardous state of residual coal was established, enabling dynamic analysis of the effects of advancing rate and air leakage on coal spontaneous combustion risk. The calculated critical advancing rate was 1.0402 m/d, which agrees well with the measured value of 1.0364 m/d. The results provide a theoretical basis for the time-dependent prediction and precise prevention of coal spontaneous combustion in goafs.