Integrated method of dust and gas hazard reduction in coal mines

Numerous disastrous explosions of methane and coal dust in coal mines in Russia in recent years were accompanied by exogenous fires and had complex nature, i.e. involved a number of hazardous factors, namely, gas, dust, coal and gas outbursts and fires, while the explosion prevention system focuses on methane. Eventually, prevention of hazardous events should be integrated and coordinated. The foundation for the gas and dust hazard combating in mines is the coal and rock mass control by means of hydrodynamic treatment. On the other hand, efficiency of this approach is insufficiently high due to nonuniform distribution of injected fluid in coal seams and owing to low wettability of coal. In order to make coal wetting more uniform and effective, it is proposed to inject gas-filled solutions of surface active substances. This method includes drilling and sealing of holes, dissolving of gas, e.g. nitrogen, in water at a concentration from 0.3 to 1 %, addition of the gas-filled solution (foamer) with a surfactant, e.g. Neolas, at a concentration from 0.05 % to 5 % of the specific fluid flow rate in pre-wetting of coal (from 10 to 30 l/t) and injection of the resultant working fluid under pressure from 1.5 to 30 MPa. After the soak treatment for 24–96 h, coal seam is cut by shearer and sprayed with water (jets); whereupon liberated gas and methane interact with the foamer and make foam which isolates broken coal and reduces gas and dust release in mine air. Higher intensive mining leads to increasing gas liberation from broken coal. The gas-filled surfactant solutions block gas and dust emission both from exposed coal surface and broken coal particles. Thus, with a view to combating gas and dust hazards which are integrated and synergetic (boost each other) in coal mines, the integrated method of coal wetting with gas-filled solutions of surface active substances is experimentally substantiated. The method will ensure considerable mitigation of explosion risk in underground coal mining.