Experimental study of the effectiveness of water-air suspension to prevent an explosion

Abstract

For many countries where mining facilities exist, the importance of the mining sector is steadily increasing. Also, the mining sector is central to the global economy. However, the environment is adversely affected by explosions of finely dispersed coal dust and methane-air mixture in the mine. Dust deposited on the surface of the mine workings is as dangerous as hovering dust. The use of a water suspension system is effective for reducing the concentration of coal dust because dispersion increases. To ensure technological and environmental safety during combustion, release, mixing and distribution of gas impurities in the atmosphere (including in multiply connected areas with complex terrain or in closed spaces), an adequate mathematical description of the processes of creating and maintaining multiphase dispersed structures is required. The creation of such a mathematical model is possible only using the system of unsteady Navier–Stokes equations for compressible gas. For the practical implementation of this mathematical model, experimental studies are needed, which will confirm the possibility to create a water suspension with the necessary dispersion, the area of irrigated surface and at the required distance by the atomizer. The maximum range (in the extreme drops) of the jet was measured from the projection of the atomizer barrel onto the test site using pre-installed beacons. The size of the water droplets was determined by sampling from a stream on small glass slides coated with a thin layer of paraffin. Glass slides were photographed under a microscope and the diameter of the drop was determined using software. It was established experimentally that spraying a liquid with a mass flow rate of 1.0 l/s through square cells measuring 150 μm ensures the formation of a stable water-air dispersed suspension at a distance of 10 m. This is the most effective range where a stable air-dispersed air curtain was formed. By numerical simulation, it was established that the presence of water droplets provides not only complete deposition of coal dust, but also an additional decrease in the overpressure and temperature of the high-temperature cloud of the combustion products of the methane-air mixture. This is due to the transition of the liquid phase to the vapor state. From the analysis of the simulation results it can be seen that the effectiveness of water curtains decreases when extinguishing explosions of only methane-air mixture (that is, without participation in the explosion of coal dust).