Study on the microstructural evolution and spontaneous combustion thermal reaction of coal under photo-thermal synergism

Abstract

In order to investigate the evolution of coal microstructure and the characteristics of spontaneous combustion reaction under photo-thermal synergism, a self-built coal photo-thermal synergistic oxidation device was employed, and the free radicals, functional groups, pore structure and thermal reaction characteristics of the raw coal and the photo-thermal synergistic oxidized coal were tested, and the thermal reaction behaviors of the two were structured using a multi-component superposition model and the kinetic parameters of each independent reaction were calculated. The results demonstrate that the photo or thermal effects on the coal microstructure are of significant influence, with thermal effects predominating and photo exhibiting a promoting and catalytic effect on thermal effects. The pyrolysis of raw coal can be subdivided into five distinct reactions: water evaporation, first volatilization, secondary volatilization, semi-char generation and semi-char polycondensation. Similarly, the combustion process can be categorized into five phases: water evaporation, oxygen adsorption, volatilizations and oxidation, metaplast combustion and semi-char combustion. Photo-thermal synergistic oxidized coal has additional pre-volatilization reactions but lacks oxygen adsorption reactions. Photo-thermal synergism promotes the conversion of aliphatic hydrocarbons to oxygen-containing groups and the conversion of micro- and mesopores to macropores in the coal structure. This effect reduces the activation energy associated with volatile production and combustion and significantly promotes the volatilization and combustion of unstable structures in the coal structure.