Coupling Relation between the Location of Cross-Cut Negative Pressure and Injecting Nitrogen into Coal Mine Goaf

Injecting nitrogen into goaf has been widely adopted for preventing fire hazards in coal mines. In this paper, the coupling relation between different locations of negative pressure of cross-cut drainage and nitrogen injection was investigated. The minefield data collection was carried out by an in situ beam tube system on the intake airway and return airway of the mine goaf. The validated Computational Fluid Dynamics (CFD) model that was secondarily modified by on-site collected data was applied for further research. It is demonstrated that the area of the spontaneous combustion zone generally shows a sharp decline first, then tends to stabilize, and finally has a slight drop and rise with the increasing nitrogen injection time. It is obvious that the location of the negative pressure of cross-cut exerts a significant influence on the optimal nitrogen injection location and time. When the cross-cut is located in the center of the air leakage zone, spontaneous combustion zone, and asphyxiation zone of goaf, the optimal nitrogen injection location and time correspond to the P₂ (25 m, 1200 min), P₃ (30 m, 120 min), and P₄ (35m, 1800 min), respectively. According to the simulation result, the specific relation between the optimal nitrogen injection point N(x) and the distance from the working distance of the cross-cut (x) by Newton interpolation polynomial analysis was figured out and verified that N(x) = 24.70808 + 0.293356x - 0.001436x ². It is hoped that the result can provide scientific guidance for coal mine fire prevention and control with nitrogen injection.