Study on the distribution of O2 concentration field of coal spontaneous combustion in high ground temperature goaf

It is difficult to fully reflect the distribution of O2 concentration field of coal spontaneous combustion in goaf by using theoretical analysis and experimental research methods to study the impact of high ground temperature on coal spontaneous combustion in goaf. Fluent numerical simulation software is used to analyze the distribution law of O2 concentration field in the inlet air side, return air side and the middle section of the high ground temperature goaf. The results are listed as follows. ① When the temperature increases from 24.8 ℃ to 40 ℃ with the same ventilation volume, O2 flows into the whole goaf with the wind, and the O2 concentration decreases with the increase of goaf depth. When the air volume increases from 1 800 m3/min to 2 700 m3/min with the same temperature, the air leakage range in goaf increases significantly, the O2 concentration field in goaf changes obviously, and O2 almost fills the whole goaf. Moreover, the existence range of high concentration O2 increases, then the temperature of goaf increases due to heat accumulation, and the temperature of the residual coal inside goaf also continues to increase, the coal-oxygen reaction accelerates, and the possibility of spontaneous combustion of the residual coal increases. ② As the distance between goaf and the working face increases, the O2 concentration decreases. The O2 concentration on the inlet air side is greater than the O2 concentration on the return air side, indicating that the risk of coal spontaneous combustion on the inlet air side is greater than that on the return air side. ③ As the depth of goaf increases, the volume fraction of O2 on the inlet air side and the middle section of goaf continues to decrease, and the slope of the curve increases first and then decreases. The volume fraction of O2 on the return air side decreases with the increase of goaf depth. A large amount of high concentration O2 exists before 150 m of goaf, and the risks of coal spontaneous combustion in the inlet air side and the middle section of the whole goaf are greater than in the return air side. ④ When the temperature is 40 ℃ and the ventilation volume is 2 700 m3/min, the maximum width of the oxidation zone is 126 m. This maximum width is regarded as the maximum theoretical width of mining. Further calculation of the safe advancing speed can provide a theoretical basis for coal mining.