Experimental Study On The Fire-fighting Performance Of Supercritical CO₂ Injected Into Goaf For Spontaneous Combustion Of Residual Coal

Coal is the main energy in our country at the present stage.In order to solve the problem that the spontaneous combustion of coal in goaf restricts the safe and efficient coal mining in China,a new type of fire-fighting technology in goaf using supercritical CO₂ as fire-fighting material is put forward.This paper adopts the method of combining theory and experiment to study the fire-fighting performance of supercritical CO₂ injected into goaf for spontaneous combustion of residual coal.The main research work and achievements are as follows:A supercritical CO₂ produced and stimulating the spontaneous combustion of residual coal in goaf system was developed independently.Supercritical CO₂ generation system has the function of heating and pressurizing liquid CO₂ in autoclave to produce supercritical CO₂ under different temperature and pressure conditions.The stimulating the spontaneous combustion of residual coal in goaf system was developed,that the system can adjust the proportion according to the actual goaf scale and simulate the actual environment of goaf.In fire-fighting experiment of supercritical CO₂ under different temperature and pressure conditions,compared with supercritical CO₂,it is got that the temperature of coal and air show a negative linear decline with time in the goaf.After stopping the injection,the rule of rebound temperature conforms to the feature of the inverse quadratic function in a small range;In same temperature,supercritical CO₂ extinguishing,high pressure than low pressure better for cooling effect.Cooling performance of supercritical CO₂ is 1.5 times that of the supercritical CO₂ under8MPa,39?for residual coal;According to the change law of cooling rate at different monitoring points,the cooling rate of supercritical CO₂ is balanced and stable with slow attenuation.In fire-fighting experiment of liquid CO₂ and N₂,comparing the effect of supercritical CO₂in fire-fighting performance,it is got that the cooling performance of supercritical CO₂ is better than that of liquid CO₂ and N₂.The cooling capacity of supercritical CO₂ under 12MPa,39?on residual coal is 1.7 times than liquid CO₂ under 6MPa,30?,10 times than gaseous nitrogen under 6MPa,39?;The expansion rate is faster than the vaporization of liquid CO₂ and the expansion of N₂.The oxygen-lowering rate of supercritical CO₂ under 12MPa,39?on goaf is12.5%higher than that of liquid CO₂ under 6MPa,30?and gaseous nitrogen under 6MPa,39?.The rates of N₂ in the gaseous phase and CO₂ in the liquid phase are approximate the same.In experiments on spontaneous combustion tendency of coal on effect of CO₂,it is got that the average oxygen consumption rate of coal samples on impact of CO₂ is low,and the spontaneous combustion tendency of coal samples is weak;Oxidation of coal samples and after effect of CO₂ has a relatively stable temperature characteristics,is slower 30%on average heating rate.Between 25?and 165?,the heating characteristics of coal samples after effect of CO₂ was positively linear change,and the temperature condition was positively law of exponential growth between 165?to 200?.Based on the P-R real gas state equation,the heat absorption and injection amount of supercritical CO₂ were calculated by using the engineering thermodynamics theory.This data was obtained that heat absorption capacity of supercritical CO₂ under 12 MPa,39?is 1.5 times than liquid CO₂ under 6MPa,30?,10 times than N₂ under 6MPa,39?,and it is verified that the ratio of cooling performance of supercritical CO₂ is similar to that in the experiment.Based on the mass conservation equation of components,the calculation formula of average oxygen consumption rate of coal samples was deduced.Combined with the experimental data,the change curve of the average oxygen consumption rate of coal samples was obtained before and after the effect of CO₂.There are 60 figures,8 tables and 83 references in the thesis.