3-D simulation of gases transport under condition of inert gas injection into goaf

摘要

To prevent coal spontaneous combustion in mines, it is paramount to understand O_2 gas distribution under condition of inert gas injection into goaf. In this study, the goaf was modeled as a 3-D porous medium based on stress distribution. The variation of O_2 distribution influenced by CO_2 or N_2 injection was simulated based on the multi-component gases transport and the Navier-Stokes equations using Fluent. The numerical results without inert gas injection were compared with field measurements to validate the simulation model. Simulations with inert gas injection show that CO_2 gas mainly accumulates at the goaf floor level; however, a notable portion of N_2 gas moves upward. The evolution of the spontaneous combustion risky zone with continuous inert gas injection can be classified into three phases: slow inerting phase, rapid accelerating inerting phase, and stable inerting phase. The asphyxia zone with CO_2 injection is about 1.25-2.4 times larger than that with N_2 injection. The efficacy of preventing and putting out mine fires is strongly related with the inert gas injecting position. Ideal injections are located in the oxidation zone or the transitional zone between oxidation zone and heat dissipation zone.