Thermal Generation Behavior, Key Groups and Disaster-Causing Mechanism of Unloaded Bulk Coal Under High Ground Temperature Conditions

A coal mining area is more susceptible to the danger of coal spontaneous combustion due to elevated ground temperature and high stress from deep mining. To investigate the heat generation behavior and the evolution of critical groups of unloaded bulk coal under high primary temperature in a deep mine, the thermogravimetric and heat release characteristics of unloaded bulk coal were measured using simultaneous thermal analyzer, and the migration and shifts in micro-groups of unloaded bulk coal were investigated by in situ diffuse reflectance. The key groups contributing most to the thermal weightlessness and heat release of coal during the oxidation phase at low temperatures were identified by grey correlation analysis. The results indicated that, as the deep thermal action temperature and initial load stress increase, the characteristic temperature, thermal equilibrium temperature, and initial exothermic temperature of coal decrease gradually, the combustion performance and exothermic capacity increase progressively, the aliphatic structure of coal is detached more easily, and the amount of hydroxyl and oxygenated functional group active groups increases. The key reactive groups that affect thermal weightlessness and heat release were determined by grey correlation analysis to be hydroxyl and carbonyl groups. The increase in thermal environment temperature and initial load in deep wells leads to the enhancement of cryogenic oxidative self-heating tendency of deep residual coals and the growth of spontaneous combustion risk. The research results established a theoretical basis for strategies to curb and manage coal fires in the complex milieu of deep-seam coal mining operations.