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Energies 2015, 8(12), 14260-14271; doi:10.3390/en81212426

Research on and Design of a Self-Propelled Nozzle for the Tree-Type Drilling Technique in Underground Coal Mines

1,2
,
1,* , 1,2,* , 1,2
and
1,2
1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
2
National & Local Joint Engineering Laboratory of Gas Drainage in Complex Coal Seam, Chongqing University, Chongqing 400044, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Vasily Novozhilov
Received: 25 October 2015 / Revised: 14 December 2015 / Accepted: 15 December 2015 / Published: 17 December 2015
View Full-Text   |   Download PDF [1909 KB, uploaded 17 December 2015]   |  

Abstract

Due to the increasing depths of coal mines and the low permeability of some coal seams, conventional methods of gas drainage in underground mines are facing many problems. To improve gas extraction, a new technique using water jets to drill tree-type boreholes in coal seams is proposed. A self-propelled water-jet drilling nozzle was designed to drill these boreholes. The configuration of the self-propelled nozzle was optimized by conducting drilling experiments and self-propelling force measurements. Experimental results show that the optimal self-propelled nozzle has a forward orifice axial angle at 25°, a radial angle at 90°, a center distance of 1.5 mm, and backward pointing orifices with an axial angle of 25°. The self-propelling force generated by the jets of the nozzle with 30 MPa pump pressure can reach 29.8 N, enough to pull the hose and the nozzle forward without any external forces. The nozzle can drill at speeds up to 41.5 m/h with pump pressures at 30 MPa. The radial angles of the forward orifices improve the rock breaking performance of the nozzle and, with the correct angle, the rock breaking area of the orifices overlap to produce a connecting hole. The diameter of boreholes drilled by this nozzle can reach 35.2 mm. The nozzle design can be used as the basis for designing other self-propelled nozzles. The drilling experiments demonstrate the feasibility of using the tree-type drilling technique in underground mines. View Full-Text
Keywords: coalbed methane; high-pressure water jet; drilling technique; self-propelled nozzle coalbed methane; high-pressure water jet; drilling technique; self-propelled nozzle
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Lu, Y.; Zhou, Z.; Ge, Z.; Zhang, X.; Li, Q. Research on and Design of a Self-Propelled Nozzle for the Tree-Type Drilling Technique in Underground Coal Mines. Energies 2015, 8, 14260-14271.

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