The reaction mechanism and kinetics of coal oxidation at temperatures prior to 400 ℃ were studied theoretically, with a focus on the phenomenon of mass increase observed by thermo-gravimetric analysis (TGA). In light of the existing understanding on coal oxidation, chemical reactions taking place at moderate temperatures were simplified into three parallel but competitive reaction sequences, including water release, oxygen adsorption and decomposition of the oxygenated compounds, as well as the direct “burn-off” reaction. Using the non-linear least-square fitting technique, the kinetic parameters of all the reactions occurring within the temperature range studied were determined by fitting the sets of TG and DTG data collected at the oxygen concentrations of 10%, 21% and 40% in volume, respectively. The modeling results are in excellent agreement with the experimental data, confirming the reliability of the model established. It is proved that the mass increase during coal oxidation at moderate temperatures is primarily contributed by the oxygen adsorption and the subsequent decomposition reactions, while influence of the direct “burn-off” reaction on this phenomenon is relatively trivial. Since the mass increase phenomenon is a compromised result of the principal reactions involved, and the kinetic parameters of the oxygen adsorption reaction cannot be determined with accuracy based upon this phenomenon with a utilization of a single- reaction assumption. Enrichment of O2 in the reaction medium speeds up the rates of oxygen adsorption reaction and the decomposition reaction. However, we did not observe the significant effect of the oxygen concentration on the direct “burn-off” reaction, solely due to the nature of the experimental data selected and the techniques utilized for retrieving the kinetic data for the reactions involved.

Key words: coal, oxidation at moderate temperatures, phenomenon of mass increase, reaction mechanism, kinetic data