Key Parameters of Separated Nitrogen Injection in Goaf Based on Orthogonal Test

Abstract

ABSTRACT Coal spontaneous combustion (CSC) is a common disaster in underground coal mine, and nitrogen injection into goaf is a common means of preventing and extinguishing fire. Conventional single-pipe nitrogen injection in wide working faces has problems, such as narrow inert area, serious nitrogen waste, and poor fire prevention and extinguishment effects. To solve these problems, this study proposes the separated nitrogen injection technology in goaf. Taking Dahaize Coal Mine as an example, a three-dimensional numerical model of multifield coupling in goaf is established. The distribution range of the CSC hazard zone in goaf is determined through field observations and numerical simulations. The validated computational fluid dynamics model is used to determine the optimal nitrogen injection location. Furthermore, the effects of nitrogen injection location in inlet side (NILI), nitrogen injection location in return side (NILR), and nitrogen injection distribution ratio in both sides (NIDR) on goaf inertisation are studied via orthogonal tests and numerical simulations. The optimal technical parameters of the separated nitrogen injection technology are determined by range analysis. The best inertisation effect is obtained when NILI is 30 m, NILR is 30 m, and NIDR is 4/6. Compared to other cases, the CSC hazard zone area and temperature anomaly zone area are significantly smaller, the asphyxiation zone area is significantly greater, and the maximum temperature is slightly lower in this case. This study provides a reference for preventing and controlling CSC in the goaf of underground coal mines.