Exploring effect of water immersion on the structure and low-temperature oxidation of coal: A case study of Shendong long flame coal, China

To investigate the effect of water immersion on the structure and low-temperature oxidation of coal, the untreated coal and soaked coal for 90 days and 180 days were prepared and compared. The surface morphology, pore structure, physical oxygen absorption and free radical parameters were characterized by scanning electron microscope (SEM), N-2 adsorption, chromatography oxygen absorption and electron spin resonance spectrometer (ESR). The crossing point temperature (CPT) and oxidation products of coal samples were investigated using oxidation kinetics experiment. Compared with the untreated coal, larger average pore diameter, more free radical species and concentration were found in the soaked coal. Moreover, more pores with diameter > 10 nm were formed due to soaking process, which would improve the transport capacity of O-2 in pores to react with active sites on pore surfaces in the soaked coal. At the same time, the soaking process increased the physical oxygen absorption of coal by opening up more obturator channels. Moreover, the longer the soaking time, the more obvious the effect of the soaking process on the long flame coal. In addition, immersion process increased the indicator gas production rate of the soaked coal, and decreased its crossing point temperature, increased the risk of spontaneous combustion of Shendong long flame coal in general.