Study on Thermal Behavior Characteristics and Microstructure Evolution Mechanism of Residual Coal Combustion Process in Deep High Initial Temperature Environment

Abstract

ABSTRACT The shallow coal seam resources are gradually reduced, the depth of coal seam mining is increased, and the underground temperature is increased, which makes the risk of residual coal fire increase year by year. In order to explore the transformation path of functional groups during oxidation and the caloric release characteristics of residual coal in deep coal mine, the microcosmic changes of coal oxidation process in deep mine were analyzed by in situ diffuse reflectance (In situ FTIR) and electron spin resonance (EPR) experiments, and macroscopic characteristics such as characteristic temperature of residual coal were tested by synchronous thermal analysis experiment. In FTIR results, it is observed that hydroxyl groups, active aliphatic hydrocarbon structures, and active oxygen-containing groups are key chemical structures involved in the oxidation process of residual coal, displaying a strong correlation transformation phenomenon. This can be described as follows: oxygen absorption led to a negative correlation between aliphatic hydrocarbon structures and hydroxyl groups, while the conversion of aliphatic hydrocarbon structures into carboxyl and aldehyde groups resulted in a negative correlation between aliphatic hydrocarbons, carboxyl groups, and aldehyde groups. Active oxygen-containing functional groups showed a positive correlation. With the increased of free radical concentration, the type of free radicals increased and the linewidth (ΔH) increased. The high-temperature environment intensified thermal behavior tendencies, increased the number of active structures, and raised the risk of spontaneous combustion. The research results provided a theoretical basis for understanding the process of coal spontaneous combustion, and had important reference value for ensuring the safe mining of deep coal seams and implementing effective disaster prevention measures.