Thermodynamics of coal oxidation mass gain behavior based on parallel reaction model by TG and DSC

Abstract

Coal spontaneous combustion (CSC) is a persistent problem in the field of coal mine safety and is highly detrimental. Clarifying the parallel reactions involved in the process of coal oxidation and spontaneous combustion could provide a new perspective on CSC. The coal–oxygen composite reaction processes of three bituminous coals were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). By establishing a parallel reaction model through multimodal Gaussian fitting, we conclude that the process of coal oxidation and spontaneous combustion involves water evaporation, oxygen adsorption, thermal decomposition, gas phase combustion and solid-phase combustion. These five parallel reactions collectively control the mass and heat changes of coal. The results demonstrate that the ratio of heat intensity to mass is more sensitive to temperature changes in a lower metamorphic coal, which is more likely to undergo gas phase combustion. In the reaction stage dominated by the oxygen adsorption reaction, the apparent activation energies of coal samples, from low to high metamorphic grade, are 60.8, 46.6 and 42.4 kJ mol⁻¹, respectively. Consequently, a higher metamorphic coal is more prone to undergoing the oxygen adsorption reaction.

Graphical abstract