Attenuation Characteristics Of CO₂-ultra-fine Water Mist Inhibiting Coal Dust/gas Explosion Of Different Coal Types

During the mining process of the mine,the explosion of coal dust/gas composite system is a complex but unavoidable problem.Once the explosion occurs,the intensity of disaster is far greater than that of gas explosion,resulting in a large number of casualties and property losses.Therefore,the attenuation characteristics,causes and mechanism of CO₂-ultrafine water mist to suppress coal dust/gas explosion are studied in this thesis,which has important scientific significance and application value for coal mine safety production and accident prevention.In this thesis,the explosion attenuation characteristics of coking coal,fat coal and lignite/gas composite system under the combined action of single explosion inhibitor and CO₂-ultrafine water mist are studied comparatively.The explosion overpressure,flame propagation velocity,flame morphology and flame temperature are analyzed.The reasons for the suppression of coal dust participating in gas explosion are explained by means of PIV and infrared spectroscopy,and the mechanism of the suppression is also discussed.It can be concluded that:（1）Ultra-fine water mist or CO₂ alone can inhibit high volatile coal dust,but lignite/gas composite system is more sensitive to ultra-fine water mist;（2）When CO₂-ultrafine water mist inhibits the explosion of coal dust/gas composite system,the explosion suppression effect decreases obviously in overpressure,maximum flame propagation speed and flame temperature,and the explosion suppression effect increases obviously.For example,when the volume fraction of CO₂is 14%and the mass concentration of ultra-fine water mist is 347.2 g·m^-3,the lowering rates of the maximum explosion overpressure are 77.6%,79.89%and 80.3%respectively,and the explosion overpressure curve shows a"trapezoidal"characteristic.When the volume fraction of CO₂ is 18%,the mass concentration of ultra-fine water mist is 694.2 g·m^-33 and 347.2 g·m^-3,respectively,the coke/gas,fat coal and lignite/gas composite system can not be ignited.It shows that when the control parameters of CO₂-ultrafine water mist increase to a specific value,it has a good inhibition effect on the three kinds of coal dust participating in explosion;（3）At the same time,the key parameters of CO₂-ultrafine water mist to inhibit the explosion of coking coal,fertilizer coal and lignite/gas composite system are 14%CO₂+694.4 g·m^-3ultra-fine water mist.Under these parameters,the detonation suppression effect is good and economic;（4）The reason of co-suppression of CO₂-ultrafine water mist was explained by PIV and infrared spectroscopy.On the one hand,the addition of CO₂-ultrafine water mist changes the movement direction and velocity of coal dust particles,at the same time makes coal dust particles form agglomeration zones,reduces the number of coal dust involved in explosion,and obtains the dominant restraint effect of CO₂-ultrafine water mist in different stages of explosion flame development.On the other hand,by comparing the number of key free radicals in the functional groups of coal dust before and after explosion,it is concluded that single explosion inhibitor and CO₂-ultrafine water mist have a certain control effect on it.However,with the increase of the dose of single explosion inhibitor and CO₂-ultrafine water mist,they are not completely not involved in the reaction,but are controlled in a range.Finally,the explosion suppression mechanism of CO₂-ultrafine water mist is discussed.On the one hand,the addition of ultra-fine water mist makes it form a protective capsule,which restricts the volatile matter of coal dust.On the other hand,the cooling and endothermic effect of superfine water mist reduces the heat supplied to the volatile matter of coal dust.On the other hand,CO₂ is encapsulated in a protective capsule,which further limits the volatile matter of coal dust.The dilution of CO₂ makes the initial stage of the composite system.The explosion intensity decreases,which further reduces the heat supplied to the volatilization analysis of coal dust.