Experimental study of shaftless underground gasification in thin high-angle coal seams

The purpose of this article is to study the feasibility of shaftless underground gasification in thin high-angle coal seams and the reliability of a new two-stage technique for pushing-through gasification galleries with firepower permeation. This paper first presents the theory, design, and technical details of a field experiment that tests the new process, which consists of blind-hole electric ignition of an underground gasifier, a forward and backward firepower seepage method, and gasification of a small shaftlike gasifier. The results of the experiment are then analyzed. It is concluded that the bigger the blast intensity, the faster the moving speed of the fire source and the higher the average temperature of the gallery; however, if the blast intensity exceeded a critical value, the moving speed of the fire source (pushing-through speed) and the average temperature exhibited the drop tendency. Under the experimental conditions, the average leakage rate for the blasting was 81.89%, with an average volume of discharge of 93.82 m(3)/h and an average gallery diameter of 0.40 m. Along with the progression of the firepower pushing-through process, the air blast leakage rate dramatically declined. In addition, the heating value of coal gas rose with the increase of gas flow and approached stabilization. The experiment showed that the heating value of underground water gas produced by two-phase gasification could reach 12.00 MJ/m(3), in which the content of H-2 exceeded 48% and those of CO and CH4 were 13% and 7%, respectively.