Study On The Movement Rules And Inerting Range Of Liquid CO₂ In Goaf

The loss caused by coal seam spontaneous combustion is difficult to estimate in our country every year,which not only affects the safety of coal mine production,but also poses a threat to the lives of the majority of miners.Liquid CO₂ is widely used in the prevention and control of coal spontaneous combustion because of its good inertia cooling,flame retardant and explosion suppression effects,safety and reliability,and simple operation.Since the injection mode of liquid CO₂ has always been relatively simple,the analysis of the injection effects of multiple injection sites under the mine is not comprehensive enough.Therefore,it is an urgent problem to study the inertization range of liquid CO₂ at different positions in the goaf.Based on the physical and chemical properties of liquid CO₂ inerting and cooling,flame retardant and explosion suppression,and according to the actual conditions of the goaf,a three-dimensional model of the goaf was established.The ANSYS FLUENT19.0 numerical simulation software was used to reasonably determine and optimize the injection rate of liquid CO₂ injection,Pressure injection position,buried pipe depth and other process parameters,while focusing on the study of the inertization range of liquid CO₂ at different positions in the goaf pressure injection.The simulation results show that:（1）The optimized process parameters are:the injection position is 60m-80m away from the working face,the buried pipe depth is 50m,and the injection flow is 800m³/h,the best inertization effect can be obtained,which can be effectively suppressed The occurrence of coal spontaneous combustion;（2）Compared with the pressure injection of liquid CO₂ on the inlet side,at the same pressure injection position,buried depth and pressure injection flow rate,when injected from the inlet tunnel,liquid CO₂ is more likely to go to the goaf along with the natural air leakage of the inlet tunnel Internal diffusion,with wider inerting range and faster diffusion speed,can achieve better fire extinguishing effect than injection from the inlet side;（3）When injected from the buried pipe on the return side,liquid CO₂ can effectively inert the oxidation zone on the return side,and at the same time it can dilute the gas and CO concentration accumulated at the upper corner to ensure the safe mining of the working face.Finally,combined with the numerical simulation results,by monitoring the pressure change of the index gas in the goaf area before and after the injection of liquid CO₂ in the40203 fully mechanized mining face of Xiaozhuang Mine and the temperature change.It shows that the inertization and cooling effect of liquid CO₂ fire extinguishing technology is good,and the expected effect is achieved.By comparing the field data,the reliability and rationality of the numerical simulation results are determined,which provides theory and data support for the field practice process.