Study on the Differences in Mass and Energy Balance Characteristics during the Constant-Temperature Oxidation of Bituminous Coal

To find an accurate and convenient method for analyzing the characteristics of low-temperature oxidation reactions of coal, providing a theoretical basis for assessing the susceptibility of coal to spontaneous combustion and making precise predictions of spontaneous ignition, this paper selects four types of bituminous coal with similar coalification degrees but significant differences in oxidation characteristics. The extrapolated onset point method of the DSC curve is used to determine the characteristic oxidation temperatures of the coal. A simultaneous thermal analysis/mass spectrometry instrument is employed to carry out isothermal oxidation reactions, while synchronously monitoring changes in the mass of coal samples, reaction heat, and the generation of gaseous products during the oxidation process. Additionally, an in situ infrared spectrometer is used to explore differences in the mass-energy balance characteristics during the isothermal oxidation reaction of coal samples. The results indicate that the spontaneous combustion tendency of coal is influenced by factors such as the content of easily oxidizable components and their heat release capacity, which prevents the oxidation characteristic temperature from directly determining the ease of coal spontaneous combustion. During the low-temperature oxidation stage of coal, the coal samples can reach a level where the maximum heat release intensity is reduced by 50% within 3–8 min, with the proportion of heat release remaining at 5%–6.5%. The dominant reaction is oxidative dehydrogenation, producing water, which can remove approximately 10% of the hydrogen element. In contrast, oxidative decarbonization is relatively minor during this stage, with a carbon element loss of about 1%. The carbon chains in the LJH coal sample are the most easily broken, exhibiting the highest oxidative reaction activity. The XD coal sample has the strongest low-temperature heat release capacity, but its oxidative reaction activity is lower than that of LJH and HQL.