Study on Intrinsic Relationship between Coal Mass Change and Heat Evolution during Different Stages of Coal Spontaneous Combustion

Abstract

ABSTRACT A good understanding of the intrinsic relationship between heat evolution and mass change induced by coal–oxygen oxidation reaction is critical for accurately predicting the behaviour of spontaneous combustion. In this study, thermal subtraction method and six sets of characteristic temperatures were introduced to explore the intrinsic reaction between coal and oxygen which provides the main heat source responsible for coal self-heating. The heat evolution and mass change during coal spontaneous combustion were measured in real time using a sensitive differential scanning calorimeter (DSC) and a thermogravimetric analyzer (TG), respectively. The DSC and TG subtraction curves obtained from subtracting the results of nitrogen atmosphere from those of air atmosphere can reveal the heat change and mass change due only to the reaction between coal and oxygen. The term of q/m defined as the amount of heat release by the change of per unit of coal mass was introduced to study the intrinsic relationship between heat evolution and mass change during coal spontaneous combustion. The q/m values of the three coals show different evolution trends as coal temperature increases and are related to the mechanism of coal spontaneous combustion. The kinetics analysis of this intrinsic relationship was also carried out based on experimental data. Moreover, q/m can be used in the evaluation of spontaneous combustion propensity with respect to different coal types.