Study on the optimization of CO₂ inerting parameters in narrow coal pillar compound goaf

In response to the complex gas flow patterns within narrow coal pillar in compound goafs, the challenges in selecting inert gas injection parameters, and the tendency for inert gases to intrude into working spaces, using the 7271 working face and the adjacent 7269 goaf of Yaoqiao Coal Mine as case studies. This study employs a combined approach of theoretical analysis and numerical simulation. Mathematical model for gas transport in narrow coal pillar compound goafs was established to investigate the gas flow characteristics before and after CO₂ injection. The optimal inerting parameters for the compound goaf were determined. The results indicate that after CO₂ injection, the oxidative zone generally shifts towards the 7271 working face, while CO₂ moves deeper into the goaf and towards the return airway. As the gas injection volume increases, the maximum width of the oxidative zone within the coal pillar decreases from 3.77 m to 1.76 m, enhancing the coal pillar's effectiveness in isolating O₂. In the adjacent 7269 goaf, CO₂ exhibits a wide directional diffusion range with a smaller inclination range; as the injection volume increases, the suppression of O₂ diffusion by CO₂ becomes more pronounced. Mathematical model evaluation determines the optimal CO₂ injection rate to be 750 m³/h.