Study on the influence of ventilation methods on coal spontaneous combustion in gob-side entry retaining goaf areas

Under gob-side entry retaining mining conditions, the gas distribution characteristics in the goaf are easily affected by the ventilation methods, making it difficult to accurately identify the locations of coal spontaneous combustion hazards. To address this issue, the 8521 working face of a mine in Gansu was used as the research background. A physical model of the gob-side entry retaining goaf was constructed using Fluent software. The study analyzed the coal body porosity in the goaf and compared the leakage airflow field and oxygen concentration distribution characteristics under "W"-type ventilation and "Y"-type ventilation (single entry, two returns, and two entries, one return) methods. The results showed that: the coal body porosity in the gob-side entry retaining goaf generally presents a "shovel-shaped" distribution, with higher porosity at the edges, lower in the center, gradually narrowing towards the goaf. When the ventilation volume and rate of the mine are fixed, the leakage airflow rate in the gob-side entry retaining goaf is influenced by the ventilation method and is positively correlated with the number of intake lanes. The key leakage points in the goaf are mainly located at the intersections of the side airflow, and the leakage rate at these points is influenced by the pressure difference. The differences in the leakage airflow field in the goaf lead to different oxygen concentration and oxidation heating zone distribution characteristics under each ventilation method. Under the "W"-type ventilation method, the gas in both the shallow and deep parts of the goaf migrates in a fan-shaped pattern. The oxidation heating zone is closer to the gob-side entry retaining and is distributed in a "√" shape. The area of the oxidation heating zone accounts for 38.1% of the mined area. A comprehensive comparison of the key leakage points in the goaf, oxidation heating zone distribution, and firefighting difficulty indicates that "W"-type ventilation is more beneficial for preventing and controlling coal spontaneous combustion in the goaf.