Theoretical Analysis And Experimental Study On Dry Ice Fire Prevention In Goaf

Coal is the most important energy source in China,accounting for 56.2% of the total energy consumption in 2022.Spontaneous combustion is one of the main disasters in coal mines,usually occurring in goafs or coal seams that are not easily discovered.Early identification and control are difficult,posing a serious threat to coal mine safety production.Inert gas,with its strong fire extinguishing ability,high efficiency,and environmental friendliness,has quickly become one of the main technologies used for fire prevention and extinguishing in goaf areas.In fact,dry ice has the effects of cooling,covering,isolating oxygen,and adsorbing inerting to suppress the spontaneous combustion of abandoned coal in goaf areas.However,its disadvantage is that the sublimation rate is slow,and sometimes it cannot meet the fire prevention and extinguishing requirements.This article takes dry ice as the research object,and uses a combination of heat transfer theory analysis,indoor experiments,and numerical simulation to study the influence of different stacking methods of dry ice placed in goaf on its sublimation rate.It analyzes the cooling effect of dry ice on goaf residual coal and the diffusion and transport law of carbon dioxide,and clarifies that this technology can effectively prevent and control goaf fires while also meeting the requirements of safety production.This article first takes heat transfer as the foundation,introduces dry ice fire prevention technology,determines different placement methods of dry ice,establishes an infinite cylindrical model and a semi infinite flat plate model,and theoretically derives formulas for calculating the sublimation rate of dry ice.Through the dry ice sublimation experiment,it is obtained that the actual temperature of dry ice after endothermic sublimation is 1.354 ℃ when the room is open and windless.Combining the experimental results with the theoretical calculation,it can be concluded that the actual sublimation rate of dry ice in Standard state is 0.027g/s.Comparing the point stacking placement method with the line stacking placement method,the theoretical sublimation rate range of dry ice is 0.840g/s～0.899g/s when calculated using point stacking placement method.When dry ice is placed in a linear stacking mode for calculation,the theoretical sublimation rate range of dry ice is 0.916g/s～0.925g/s.The feasibility of using dry ice as a linear stacking method for cooling and fire prevention of coal blocks in goaf has been verified through experiments.From the experimental results,it can be concluded that the low-temperature carbon dioxide generated by dry ice sublimation will reduce the cooling effect of covering coal blocks with increasing distance,and the cooling effect of the area directly behind the dry ice is the best.Comparing the temperature data of coal blocks before and after the completion of dry ice sublimation,it can be concluded that the temperature reduction range of coal blocks within a 0.9m space is 0.2 ℃～28.9 ℃.Through corresponding calculations,it can be inferred that the actual sublimation rate of dry ice with wind and covered by coal blocks is 0.035g/s.Finally,Fluent numerical simulation was used to analyze the temperature changes and carbon dioxide migration and diffusion distribution in the goaf after placing dry ice.The influence of the placement position and specifications of dry ice on the gas flow field in the goaf was simulated under different degrees of advancement of the working face.The optimal placement position of dry ice was found to be 30m～50m away from the working face,and the optimal specification was30 m × 1m × 0.5m,the carbon dioxide concentration in the return air flow of the goaf working face is less than 1.5%.This paper has 37 figures,8 tables,and 61 references.