Effect of gas extraction on mitigating low-oxygen conditions in upper corners and its impact on coal spontaneous combustion in goaf

Gas extraction technology, as an effective measure to mitigate oxygen deficiency in upper corners of shallow coal seam working faces, may lead to an increased risk of coal spontaneous combustion due to elevated air leakage in the goaf during its application. Working face 19112 of No.1 mine at China Coal Pingshuo Group Co., Ltd. was taken as the research object. A coupled fluid-solid-chemical mathematical model of the goaf was constructed based on an analysis of the causes of low-oxygen phenomena in the upper corner of the typical shallow coal seam working face. The Computational Fluid Dynamics (CFD) numerical simulation method was employed to analyze the effectiveness of gas extraction at flow rates of 90, 120, 240, and 360 m3/min in mitigating low-oxygen conditions in the upper corner while assessing associated spontaneous combustion risks in the goaf. The findings indicated that: ① the low-oxygen phenomenon in the upper corner primarily resulted from multiple factors, such as the coal seam location within the CO2-N2 zone with downward migration of inert gases, low-temperature oxidation of residual coal in the goaf, formation of interconnected fracture channels between the goaf and the surface, and the U-shaped negative pressure ventilation method in the working face. ② When the gas extraction flow rate reached 360 m3/min, the O2 volume fraction in the upper corner region significantly rose, effectively controlling the hypoxic conditions. ③ A quadratic function relationship was identified between the width of the low-oxygen zone and gas extraction flow rate. ④ Although installing extraction ventilators in the upper corner for gas extraction may moderately increase the width of the oxidation zone in the goaf, its maximum width (53.8 m) remained far below the theoretical safety threshold (604.8 m), suggesting that gas extraction technology effectively mitigated low-oxygen conditions without significantly increasing coal spontaneous combustion risks.