Determination and dynamic variations on correlation mechanism between key groups and thermal effect of coal spontaneous combustion

Abstract This study is aimed at exploring the relationship between the variations of micro-groups and the thermal effect during the heating process of coal spontaneous combustion (CSC). To this end, the thermal effect and microstructure variation characteristics of CSC were analyzed by means of differential scanning calorimetry and in-situ infrared spectroscopy. The results reveal that the exothermic reaction of CSC falls into five stages: water evaporation, desorption-induced heat absorption, slow heat release, benzene ring pyrolysis and combustion. Aliphatic hydrocarbons in coal oxidize into carbonyl which further oxidizes into carboxyl. The dynamic variations of key groups during the different stages of CSC were determined through grey correlation analysis. In addition, structural contribution, a new parameter to characterize the contribution of microstructure to thermal effect of CSC, was defined. The results disclose that the correlations between the thermal effect and the microstructure variation in different stages differ, but the key groups follow the change process of hydroxyl → aliphatic hydrocarbons → oxygen-containing functional groups → aromatic hydrocarbons on the whole. The change of key groups is related to the thermal effect and microstructure reaction characteristics of CSC. The contribution of a microstructure to the thermal effect of CSC is determined by the comprehensive product of its initial content, variations in different stages and correlation. Different microstructures correspond to varying contributions in different stages of CSC. The key to preventing CSC is to hinder the oxidative consumption of –OH(f) and the oxidation of aliphatic hydrocarbons with the highest contents into -C = O and –COOH.