Analysis on the Shape and Impact Pressure of the High-Pressure Water Jet during the Hydraulic Flushing Cavity Technique

Abstract

A large proportion of minable coal seams in China belong to low-permeability soft coal seams. Such coal seams suffer serious coal and gas outburst hazards and endure a high incidence of major disasters in coal mines. The adoption of the high-pressure water jet (HPWJ) hydraulic flushing cavity can effectively promote the gas drainage efficiency and volume and eliminate the hidden danger of gas disasters. Nevertheless, the shape and impact pressure of rotating HPWJ are rarely researched. In this study, on the basis of the numerical simulation, the axial and radial stress distributions of HPWJ and the energy-gathering effect of a conical-cylindrical combined nozzle were analyzed. It is concluded that the submerged condition will accelerate the attenuation of jet velocity and reduce the impact strength of the jet. The jet diffusion angle grows with the increases in the nozzle diameter and water pressure, and 24° is the optimal contraction angle. Finally, the influences of factors such as the rotation speed on the shape and impact pressure of HPWJ were explored, and the results show that the rotation speed should be controlled within 90 r/min. The research findings lay the foundation of the study on the mechanism of coal crushing by HPWJ and provide technical support for the research and development of drilling and flushing integrated equipment.

Effect of Fragmentation on Pore Structures and Fractal Characteristics of Intact Coal and Deformed Coal Based on Experiments

“…The differences in moisture content and ash content between intact coal and deformed coal are not obvious. The ash content of intact coal is obviously lower than that of 2 Geofluids deformed coal, which shows that there are more impurities such as gangue in deformed coal. The V L and ΔP of deformed coal are larger than those of intact coal, indicating that the adsorption and diffusion ability of deformed coal are stronger.…”

“…China is one of the most important coal production and consumption countries in the world [1][2][3]. The large increase in coal demand leads to the depletion of shallow coal resources and continues to extend to deep coal resources [4][5][6].…”

Design and Dynamic Analysis of Pipeline Dredging Devices

“…Although a large fraction of this concrete has already failed, it can still harden on the inner wall of the pipes, which can seriously affect drainage performance during flooding and waterlogging control and, in turn, cause heavy economic losses. Therefore, the pipeline dredging problem needs to be solved urgently [1][2][3].…”

New Technology of Mechanical Cavitation in a Coal Seam to Promote Gas Extraction

“…Among these measures, hydraulic punching, hydraulic slotting, hydraulic fracturing, and other hydraulic measures are commonly used. 13 − 17 These mainly use the impact, disturbance, and jet of high-pressure water to locally relieve the stress of the coal body around the borehole so as to improve the permeability and gas flow conditions of the coal seam. 18 − 22 …”

“…For coal seams with high permeability, a reasonable gas drainage system, reasonable drainage negative pressure, drilling and sealing methods, etc., can significantly improve the coal seam gas recovery rate. , However, due to the influence of coal seam sedimentary environment, geological structure, and other factors, the permeability of coal seams in most mining areas in China is generally low, only 10 –4 –10 –3 mD, which is not conducive to gas drainage. , To achieve the purpose of high-efficiency drainage, some artificial strengthening and antireflection measures must be taken to improve the permeability of coal seam. Among these measures, hydraulic punching, hydraulic slotting, hydraulic fracturing, and other hydraulic measures are commonly used. − These mainly use the impact, disturbance, and jet of high-pressure water to locally relieve the stress of the coal body around the borehole so as to improve the permeability and gas flow conditions of the coal seam. − …”