Optimal Nozzle Structure for an Abrasive Gas Jet for Rock Breakage

Abstract

Abrasive gas jet technologies are efficient and beneficial and are widely used to drill metal and glass substrates. When the inlet pressure is increased, gas jets could be powerful enough to break rock. They have potential uses in coal-bed methane exploration and drilling because of their one-of-a-kind nonliquid jet drilling, which avoids water invasion and borehole collapse. Improving the efficiency of rock breakage using abrasive gas jets is an essential precondition for future coal-bed methane exploration. The nozzle structure is vital to the flow field and erosion rate. Furthermore, optimizing the nozzle structure for improving the efficiency of rock breakage is essential. By combining aerodynamics and by fixing the condition of the nozzle in the drill bit, we design four types of preliminary nozzles. The erosion rates of the four nozzles are calculated by numerical simulation, enabling us to conclude that a nozzle at Mach 3 can induce maximum erosion when the pressure is 25 MPa. Higher pressures cannot improve erosion rates because the shield effect decreases the impact energy. Smaller pressures cannot accelerate erosion rates because of short expansion waves and low velocities of the gas jets. An optimal nozzle structure is promoted with extended expansion waves and less obvious shield effects. To further optimize the nozzle structure, erosion rates at various conditions are calculated using the single-variable method. The optimal nozzle structure is achieved by comparing the erosion rates of different nozzle structures. The experimental results on rock erosion are in good agreement with the numerical simulations. The optimal nozzle thus creates maximum erosion volume and depth.

Wear Mechanism of Abrasive Gas Jet Erosion on a Rock and the Effect of Abrasive Hardness on It

“…An effective approach to achieve a high air inflow is decreasing the pressure of the air compressor. In the research results of Liu et al and Wen et al [7,37,38], the critical pressure for limestone breakage by abrasive gas jet was 15 MPa, which was set as the outlet pressure of the air compressor. The optimal abrasive size and mass flow were 80 meshes and 16 g/s, respectively, when the gas pressure was 15 MPa.…”

Study on Borehole Arrangement Methods for Gas Extraction by Hydraulic Slotting in Long-Distance Through-Coal Seam Tunnel

“…The average thickness of the coal seam is 1.98 m, and the measured gas content and pressure are 11.5 m 3 /t and 1.2 MPa, respectively, which has an extremely high risk of coal and gas outburst. In order to improve the tunneling efficiency and quickly eliminate the danger of coal and gas outburst in the exposed coal seam, the water jet slotting technology was used to achieve permeability enhancement and gas extraction from the coal seam efficiently [23][24][25]. To optimize the slot arrangement in boreholes, a numerical model was established (as shown in Figure 1) to study the gas distribution in the coal seam and along the monitoring line under different slot arrangement modes.…”

Flow Field Simulation of Swirling Abrasive Jet Nozzle for Hard Rock Breaking

“…into high-speed flowing water, is used for a wide range of industrial applications, mainly for cutting and surface treatment [22]. Due to the impact and cutting action of abrasive particles, AWJ has much better rockbreaking performance [23]. AWJ is widely used in petroleum engineering, such as casing cutting, perforating, and hydraulic jet fracturing [24][25][26][27].…”