Effect of gas on microstructure and thermal reactivity of coal during low temperature oxidation

In order to investigate the microscopic physicochemical properties and macroscopic coal-oxygen complex thermal effects in the low-temperature oxidation of coal under gas atmosphere, different metamorphic coal and secondary oxidized coal samples as research objects were selected in this paper. Fourier infrared spectrometer and C80 microcalorimeter were employed to study the changes of physicochemical structural properties, kinetic parameters and thermal effects in the low-temperature oxidation of coal under different gas atmospheres. By analysing the microstructure and macroscopic exothermic characteristics of different gas content during coal spontaneous oxidation, the ultimate influence of gas on the oxidation characteristics of coal was clarified. The results show that gas delays the low-temperature oxidation process of coal by inhibiting the relative content of key active groups in the low-temperature oxidation process of coal. 4% gas has the most obvious inhibitory effect. The degree of inhibition on the four active groups is: oxygen-containing functional groups (66.5%) > Aromatic hydrocarbons (47.0%) > Aliphatic hydrocarbons (29.7%) > Hydroxyl (24.7%). In the rapid exothermic stage, due to the large adsorption capacity of coal to gas molecules, gas occupies the adsorption sites in coal molecules, which hinders the process of coal-oxygen recombination reaction, resulting in the exothermic effect being suppressed by gas; at the same time, gas content significantly affects coal oxygen. The amount of activation energy required for the recombination process. For high metamorphic non-stick coal, lean coal and anthracite, gas has a more significant inhibitory effect on its low temperature oxidation reaction; it has less effect on low metamorphic long flame coal. For secondary oxidized coal samples, the inhibitory effect of gas on coal samples increases with the increase of gas content, while the effect of gas on primary oxidized coal samples decreases as the degree of metamorphism decreases, and the degree of inhibition when the gas content is 2% is stronger than 4%. The results of the work have great significance to the theoretical study of the prevention and control of the coupling of gas and coal spontaneous combustion causing accidents.