Study and application of dynamic microfog dust control technology considering the influence of the induced airflow of coal flow

When transporting coal in underground tunnels, airflow is induced by coal flow, which results in a large amount of diffuse coal dust. A high percentage of diffuse coal dust can seriously pollute the operating environment and jeopardize the health of coal miners. To address this problem, powered micromist vortex dust control technology and a management scheme based on supersonic water siphon atomization technology and the principles of limited-space vortex airflow and dust control are proposed for coal transportation. A three-dimensional numerical simulation model that tracks wind flow–coal dust–droplet transport during the coal transfer process in underground mines was established via the discrete particle model, finite element method, computational fluid dynamics (CFD) and the k‒ε turbulence model while considering the induced influence mechanism of coal flow in the coal transfer process. The phenomenon of coal dust diffusion and pollution caused by induced airflow and ambient wind flow under the action of coal flow during the coal transportation process was studied at a transfer point. The three-dimensional spatial distributions of wind flow, coal dust, and droplets were analysed. To manage this type of coal dust pollution, the No. 85214 transfer point of the Sandaogou coal mine was taken as the research object. A powered micromist vortex dust control system was created at a transfer point, and numerical simulations and onsite experiments were established to study the coal transportation process both inside and outside the coal chute, the airflow induced by falling coal, the ambient ventilation airflow, the supersonic-powered micromist jet stream coupling state and its impact on fog droplets and dust, and the transportation characteristics of the mist droplets and dust. This explains the special distribution phenomenon of dust concentration and dispersion characteristics at different locations in the downwind side roadway of the transfer point in the field and reveals the dust control and reduction mechanism of this technology. The research results revealed that the high-velocity airflow region, large-scale vortex phenomena, and small-scale vortex phenomena in the reprocessing space are the key factors that cause dust to be stripped from coal. The airflow velocity is faster at the lower part of the coal flow hitting the wall, so the external ventilation flow line of the roadway is more affected near the gap than farther away. A large amount of dust is confined to the coal chute, and most of it is concentrated at the bottom of the chute, forming highly concentrated dust clusters that move at variable speeds with the internal vortex airflow. Most of the dust is affected by impact airflow, which accelerates and spreads from the gap between the lower conveyor and the chute to both sides of the roadway and is transported downwind. The transportation distance of dust at the top of the roadway is greater than that at the bottom plate, and the dust concentration and transportation distance near the impact side of the coal flow in the lower roadway are greater than those at other locations in the roadway. Owing to the faster airflow speed at the impact below the coal stream, the surrounding vortex flow of the highly concentrated dust mass is quickly pulled into the lower roadway through the gap between the sidewall and the conveyor. A dust control system is used at the transfer point of the coal chute and the surrounding roadway dust diffusion area to achieve full coverage, and the supersonic-powered mist spray formed by the internal multiscale vortex fog area can effectively prevent the flow of coal to the outside of the airflow induced by the coal chute from internal effective damage to the original aggregation of dust. The diffusion of the trajectory, the formation of a vortex so that the coal dust is wetting, and the aerodynamic characteristics are significantly changed, thus inhibiting dust from travelling outside the chute and escaping. For the fog droplets to capture dust to separate airborne wind flow and reduce the concentration, time and space are needed so that the dust captured by the fog droplets in the drop tank after leaving is transported a certain distance before settling rapidly. The dust control system has an obvious effect on the prevention and control of dust pollution at the transfer point, with an efficiency level reaching 86.78 %, but the inhibition of dust below 5 μm still needs to be improved. This study provides theoretical support and effective management methods for simulating coal transfer point dust pollution mechanisms and managing coal transfer point dust pollution in underground coal mines.