Key techniques of gas injection, water drainage and slag discharge in aerodynamic excavating coal process

Based on the engineering practice of surface well drilling for aerodynamic excavating coal using compressed air to blow water and slag in Xieyi Mine,the key technologies of water drainage and slag discharge by pressurized air were studied by analyzing the mechanism of carrying water and slag by compressed air in the annulus pipe and then deriving the formula to calculate the single drill depth during the blowing water operation. The control technology for blowing water operation in the casing section,such as single drill depth and time to blow water,was determined for the first time. The methods for water and slag discharge in the coal seam with or without water in the cave were also proposed. The key points include making a connection rapidly,flushing cycle with pressurized air before walking down, keeping drill string rotating,slow drilling velocity,and the fixed point blowing method with strong air for the dry pulverized coal consolidated,etc. The plugging mechanisms for annulus “bridging” and drill pipes “reverse inhaling” and the corresponding countermeasures were investigated. The results suggest that the main reason for annulus “bridging” clogging is the missing of flushing cycle with pressurized air before drilling down when there is water in cave,which can be resolved by lifting the bit above the blocked area and then flushing with pressurized air and that the clogging by drill pipe “reverse inhaling” could be prevented by closing or turning down the purge valve because it is caused by the fast venting. In addition,the mechanism and technology for aerodynamic excavating method to discharge slag with highpressure air injection were investigated. The results demonstrat that the large pressure drop within annulus and quick output of solid-gas mixture occurre along injection with high-pressure air and lead to good flow-back result;the larger output of pulverized coal is achieved when drill pipe is set at the middle or bottom of the cave,rather than the top part;and the collapsed coal with large blocks after air injection could be crushed with rotating bit and then be blown out using the fixed point blowing method with strong air.