Study on staged heat transfer law of coal spontaneous combustion in deep mines

The environmental conditions in the mining region were severely impacted by the high temperature and buried depth of residual coal, which considerably enhanced the likelihood of spontaneous coal combustion and worsened the coal's pyrolysis behavior. Therefore, the change laws of mass and heat during coal oxidation were investigated using industrial analysis and synchronous thermal analysis, and reaction models of coal samples at various phases of oxidation were derived using the Bagchi technique. The findings indicated that the activation energy during the stage of water loss and weight loss increased with the coal's water content, while the activation energy of coal in the early stage of oxidation combustion increased with lower ash percentage and higher carbon content. Additionally, the stages of water loss and weight loss and the stage of oxygen absorption and weight increase in the stable exothermic process of coal samples showed a positive correlation between DTG and DSC. The reaction models for the oxidation and combustion stages were both consistent with the number 7 reaction mechanism. The study's findings may serve as a theoretical roadmap for the further investigation and development of flame retardant avoidance strategies for residual coal oxidation in deep mines.