Development of Waterjet Cutting System for Hard Coal Seam Degasification

摘要

The high pressure waterjet cutting system has been developed for the improvement of in-seam hard coal gas drainage. For the system proposed, there are two basic functions have to be achieved, one, it has a capacity to cut the hardest coal seam to create the artificial discontinuities along the gas drainage borehole; and two, it is able to conduct the cutting performance deep enough into the coal seam from rib, such as, 80m or more, so as to satisfy the requirements of coal mining operation. Thus, the first part of this work is system development and optimization, in which, the numerical modelling has been carried out to determine the nozzle geometry, which is one of the most important parameters for the jet penetration, including nozzle diameter, the degree..the tube length associated with different levels ofwater pressure applied. Then, the underground trail has been conducted in one of the hardest coal seam in northwest of China. The trail includes cutting along the gas drainage borehole with length of 80m into the rib, and monitoring and comparing the effieiencies of gas drainage with and without cutting. The monitoring results indicated that the significant improvement of methane drainage efficiency, up to 3-6 times over the traditional methods, has been obtained.