Combustion Kinetics and Mechanism of Pre-Oxidized Coal with Different Oxygen Concentrations

The phenomenon of spontaneous combustion of "oxidized coal" is common in mining processes of goafs, thick coal seams, and unsealing of closed fire areas. In order to study the reburning characteristics of coal with different oxidation degrees, the oxygen concentration in the pre-oxidation process was selected as the key influencing factor. Thermogravimetric analysis (TGA) and in situ Fourier-transform infrared (FT-IR) spectroscopy were used to study the macro- and microcharacteristics of raw and oxidized coal during the combustion stage. The results showed that the pre-oxidation treatment exhibited a dual effect on promoting and inhibiting the weight loss characteristics of oxidized coal. The apparent activation energy, Ea, of the combustion reaction for the utilized coal samples was calculated using the Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods, and it was found that the average apparent activation energy (Ea̅) values of the oxidized coal samples were less in magnitude than that of the raw coal and that the coal sample with the pre-oxidized oxygen concentration of 15% was more prone to the combustion reaction. Using the correlation determination method of key active groups in the proposed coal combustion reaction, the key active groups affecting the weight change of the tested coal samples during the combustion stage were determined as −CH3 and C–O. The results can be helpful to prevent and control coal spontaneous combustion during re-mining and unsealing of closed fire areas.