Abstract
Coalbed methane (CBM) is a source of clean energy and has been recovered in past decades all over the world. Gas dynamic disaster is the primary disaster in outburst coal, and methane drainage plays a key role in eliminating this danger. As an efficient technology, a gas jet is widely used in CBM development and methane drainage. In this work, the full impinging process of coal and rock fracturing by a supersonic gas jet was studied. To understand how jet parameters affect coal and rock fracturing results, an elliptical crushing theoretical model was proposed. In addition, a laboratory experiment was designed to examine the proposed model, and four key parameters affecting the fracturing results were studied. The results show that different from the monotonic variation of theoretical values, there is a turning point in the variation of experimental values under some parameters. Considering the influence of the depth and radius of the erosion pit, the rock-breaking effect is better when the nozzle size is 2.75 Ma. The optimal target distance is 30 mm, and the impact pressure of a gas jet should be continuously increased in order to achieve certain rock-breaking effects under the impact of the jet.
Highlights
Coalbed methane (CBM) is a source of clean energy and has been recovered in past decades all over the world [1,2,3,4]
The pressure regulating valve is adjusted to the required experimental pressure, the impact target distance and the nozzle specification of the nozzle are adjusted, the air outlet valve is opened, and the high-pressure gas flows through the nozzle to form a high-pressure supersonic gas jet, causing erosion damage to the sample
Under the condition of a constant nozzle Mach number and impingement distance, the depth of an erosion pit formed by high-pressure gas jet impact and the area of an erosion pit both increases with the increase of nozzle inlet pressure
Summary
Coalbed methane (CBM) is a source of clean energy and has been recovered in past decades all over the world [1,2,3,4]. To enhance CBM recovery or drainage efficiency, water jet technology has been proposed and has been proven effective [8,9,10,11,12]. Ranjith et al [30] studied the effect of mass flow on the abrasive acceleration of gas jets Previous studies mainly focused on optimizing the nozzle structure and jet parameters to improve the efficiency of fracturing coal and rock [25, 28]. The supersonic air jet impinging laboratory experiment was designed to examine the proposed model and four key parameters affecting the fracturing results were tested, including jet pressure, target distance, nozzle size, and strength of coal and rock. This study is intended to enrich the theories of gas jet coal breaking, providing some guidance for the development of CBM and the prevention of mine gas disasters
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