Multiscale thermal behavioral characterization of spontaneous combustion of pre-oxidized coal with different air exposure time

To comprehensively investigate the multi-scale characteristics of coal spontaneous combustion, in situ infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were utilized. The samples were pre-oxidized at 70 ?C for 2, 4, 6, and 8 h (the raw coal and above samples were named R-0, R-2, R-4, R-6, and R8), then the secondary oxidation experiments were carried out. The results showed that the contents of -OH, -C=O, and -C=C -increased with the pre-oxidation time. The aromatic structure of pre-oxidized coal is more susceptible to oxygen erosion during secondary oxidation. The migration and transformation of -OH, -C=O are the underlying causes of water evaporation and gas desorption during low-temperature oxidation. The spontaneous combustion be-haviors in stage I and stage II have different reaction mechanisms and kinetic characteristics. In light of Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS), the apparent activation energy of stage I is R-0 > R-2 > R-4 > R-6 > R-8, and stage II is R-6 > R-8 > R-2 > R-4 > R-0. Long pre-oxidation time in stage I will inhibit coal spontaneous combustion, while the opposite is true in stage II. By the Pearson correlation analysis, -OH is the key structure affecting the low-temperature endothermic stage of coal, revealing the correlation between the multi -scale thermal behavior of pre-oxidized coal spontaneous combustion.