Study the effect of drying on the oxidation thermogravimetric and functional group composition characteristics of immersed lignite

Abstract The drying process of immersed lignite has a significant influence on the characteristics and progress of spontaneous combustion. To reveal the influence mechanism of the drying process of immersed coal on the spontaneous combustion characteristics and the change rule of the spontaneous combustion process, in this research, we measured the mass change during coal oxidation with thermogravimetry, and the change of the functional groups with Fourier transform infrared spectroscopy. The influence of the drying process on the coal was analyzed by comparing activation energy, functional group of immersed coal with different drying degrees and raw coal. The results showed that, compared with raw coal, the content of Ar–C–O– and antisymmetric stretching vibration of the carboxylate group (–COO–) as well as the stretching vibration in the quinone group (C=O) and the –OH group increased. For the content of $$\delta s.{\text{RCH}}_{{3}}$$ δ s . RCH 3 , $$\delta as.{\text{R}}_{{2}} {\text{CH}}_{2}$$ δ a s . R 2 CH 2 $$\delta as.{\text{RCH}}_{{3}}$$ δ a s . RCH 3 , the value of Asym.CH2/Asym.CH3 decreased. The content of various functional groups changed to be favorable for oxidation and heat release. At different reaction stages, the activation energy was differently affected by the degree of drying. Average values of activation energies at different reaction stages are shown raw coal had the lowest activation energy. After soaking in water and drying, the activation energy of coal is increased to varying degrees, the reactivity is reduced, and the risk of spontaneous combustion is reduced. After soaking in water and drying, the activation energy of coal is increased to varying degrees, the reactivity is reduced, and the risk of spontaneous combustion is reduced. The activation energy of the coal samples dried for 24 h after soaking in water is the lowest among the coal samples dried for different times after soaking in water, and the moisture content is 10.5%