Experimental Study On Suppression Of Coal Dust/Methane Explosion By Inert Gas-Two Phase Fluid

In this paper,the effects of chemical and physical inhibitors such as calcium carbonate,moisture and ammonium dihydrogen phosphate on coal dust combustion were studied by differential thermal balance and gas chromatograph.The explosion experiments were proceeded in a large-scale system to study the regulations of coal dust/methane explosions.In combination with the two-phase water mist generator,the effect of different efficiency of water mist were investigated.The system consists of a tube system,water mist system,data acquisition system,high-speed photography system and ignition system.The system can realize data acquisition of coal/methane flame signal,pressure signal and the high-speed camera images.On the basis of water mist explosion suppression technology,an inert gas-additive-water mist explosion suppression technology is used.Additives and inert gas are added at the same time.Sodium bicarbonate,which has a strong inhibitory effect,was selected as an additive and added into water mist to suppress coal dust/methane explosion.Firstly,coal dust-air explosion characteristics were studied in different tubes under varied conditions.Parameters comparation of explosions in open and closed tube were finished,such as:flame propagating distance,explosion overpressure and the flame speed.The study found that in a closed end tube,the effect of explosion reflection wave is bigger.Because of inactivity of the coal dust,the flame propagation in a closed space distance shortened compared with open conditions.However,the maximum explosion pressure increased.Two different ignition energies were used to study the influence of reflected pressure waves on coal dust explosion in closed tubes.The results show that increasing the ignition energy can significantly increase the explosion pressure.Reflecting pressure waves can make flame propagation reverse.While,increasing the concentration of coal dust can increase the amplitude of coal dust shock in tubes.Secondly,single phase water mist,air-two phase water mist,CO₂-two phase water mist were studied on coal dust-air explosion properties.Due to the significantly reduction of the dust cloud floating in the air,the overall characteristics of deflagration dropped to some extent.The flame propagation velocity decreased by 40%.As well as the flame propagation distance changed from 22 m to 16 m.Finally,the coal-methane-air explosion properties were studied.Adding water mist in the process of explosions under different working conditions were operated to analyze the explosion suppression efficiency.At the same time,high speed camera images were used to compare the characteristic of the flame propagation under different conditions.The results showed that the CO₂-two phase water mist has the best explosion suppression effect.