Micro-characteristics of spontaneous combustion of second oxidation with different rank coals

To study the spontaneous combustion characteristics of second oxidized coal,the proximate and elemental analysis,Fourier transform infrared spectroscopy,and temperature-programmed experiment system were used to inves- tigate the micro-spontaneous combustion characteristics of raw coal samples and oxidized coal samples,which were from three coal samples of different mines. The findings indicate the content of carbon decreases,oxygen increases,and the moisture decreases. Moreover,because the specific surface area,pore volume,and porosity of second oxidized coal increase,the CO concentration of the coal samples with second oxidation become higher than those of the first oxidation in the earlier stage of oxidation. With temperature increase,the number of active functional groups,which are hydroxyl and aliphatic hydrocarbons in the coal molecules,change a lot,have a large amount of consumption and regeneration, and cracked in C2 H4 gas in the later stage of oxidation. Hence,the concentrations of CO and C2 H4 in the coal samples with the second oxidation are lower compared to the first oxidation. In addition,there are advanced characteristic tem- perature points of the second oxidized coal compared to raw samples. That is,the period of spontaneous combustion is getting earlier. In summary,the oxidation ability of the second oxidized coal is stronger than that at the first time and gets oxidized readily.