Study on pore structure change and lean oxygen re-ignition characteristics of high-temperature oxidized water-immersed coal

Abstract

After coal seam mining is over, the coal left in the goaf is prone to spontaneous combustion accidents due to air leakage. To explore the oxygen-lean re-ignition characteristics of long flame coal after high-temperature oxidation and water immersion. Using scanning electron microscopy (SEM), nitrogen adsorption experiment method, characterize the high-temperature oxidized water-immersed coal sample. Using programmed temperature rise and synchronous thermal analysis experimental methods, the oxidation and re-ignition characteristics of coal samples under oxygen lean conditions were studied. The results show that compared with the untreated coal sample, the surface of the water-immersed coal sample is rougher, with more pores below 10 nm. The high-temperature oxidized water-immersed coal sample has the phenomenon of pore-to-pore, and the proportion of medium-to-large pores increases. The average pore diameter of the oxidized 200℃ water immersion (O200I200) coal sample is the largest, which increases the number of coal oxygen reaction adsorption sites. The crossover temperature of the O200I200 coal samples is lower at various oxygen concentrations, and the 2–10 nm pores affect the maximum exothermic temperature and initial exothermic temperature changes of the low-temperature oxidation process. Mesopores and macropores mainly affect the change in total heat release during high-temperature oxidation. A high oxygen concentration (above 10%) will promote the oxidation and re-ignition process of the pre-oxidized immersed coal sample. This result provides a theoretical basis for preventing the spontaneous combustion of coal in water immersed by high-temperature oxidation in shallow coal seams.