Thermal Reaction Process and Thermokinetic Characteristics of Coking Coal Oxidation

The coal–oxygen composite reaction is a complex physicochemical reaction process, and different heating rates have a great influence on this reaction. In order to reveal the influence of different heating rates on the coal–oxygen composite reaction of coking coal, the TG-DSC experimental method was adopted to analyze the hysteresis effect of the characteristic temperature, inflection point temperature, and peak temperature under different heating rates. Furthermore, the KAS method was employed to calculate the apparent activation energy, and the Málek method was utilized to infer the most probable mechanism functions and determine the compensation effects at different stages of the coal oxidation process. The results show that with an increase in heating rate, the temperature values corresponding to each characteristic temperature point increase, the characteristic temperature exhibits a hysteresis phenomenon, and the heat flow rate and heat flux rate also show an increasing trend. The apparent activation energy gradually increases in Stages II and III, with a maximum value of 198.7 kJ/mol near the ignition point T3, which first increases and then gradually decreases in Stage IV, where the maximum value is around the temperature point T4 of the maximum mass loss rate, which is 170.02 kJ/mol. The variation trend in the pre-exponential factor is consistent with the apparent activation energy, and the dynamic compensation effect is greater in Stage IV. The three different oxidation stages have different mechanism functions: a three-dimensional diffusion mode is present in Stages II and III, which is ultimately transformed into an accelerated form α-t curve with E1 and n = 1 in Stage IV.