| The N00 construction method is a long-wall coal mining method that saves resources and reduces mining costs.Rapid and non-injury directional cutting of roof rock to collapse the roof of the goaf is the key to this method.At present,the method of blasting is used to cut the roof.The direction of the explosion energy is difficult to control,and there are many problems and deficiencies such as large damage to the roof rock.It is difficult to meet the needs of the N00 construction method.Based on the water jet theory and technology,a new idea of using abrasive jet directional cutting roof is proposed.Focusing on the problems of fast,low damage and directional slitting,the structural composition and working principle of the abrasive jet directional cutting system were studied,the key components of the system were designed,and the field test was carried out on the basis of the optimal working parameters obtain by experiments.The main research results are as follows:(1)The effects and advantages and disadvantages of the three directional jointing schemes of pure water jet directional slitting,abrasive jet directional slitting and guided hydraulic fracturing are compared.Comparing the effects of various methods of stitching,the technical solution of abrasive water jet as directional cutting was finally determined.(2)The structural composition and working principle of the abrasive jet directional cutting system are studied and the structures and dimensions of key components such as water jet nozzles,cutting nozzles,directional device,conveyor,and abrasive supply system are designed.The FLUENT software was used to simulate the jet beam shape and velocity of different shape nozzles;the cone-straight nozzle was selected and the streamlined dual-jet cutting nozzle was designed.In order to achieve directional slitting,the centralizer and the rotary quick-connect connecting rod are designed separately,collectively called the locator.A high-pressure hose conveyor is designed,which can adjust the left-right displacement,horizontal deflection,and back-and-forth swing to adapt to the change in the number and position of the slits on the top plate.At the same time,it can effectively arrange the high-pressure hose and control the speed of the retractable function.A large-capacity abrasive supply system is designed,which can realize the four-hole cutting of one step of the working surface at one feeding.(3)The working parameters of abrasive jet directional cutting are optimized.A slit experiment was carried out on rock samples taken from the roof of the coal mine site and the optimal working parameters of the directional cutting of the abrasive jet meeting the requirements of the N00 method were determined: jet pressure 25 MPa,nozzle diameter 1.5mm(8),abrasive type yellow sand /Quartz sand,abrasive concentration 3.5%,cutting speed 4.4mm/s.(4)The on-site slit test was carried out at S1201-II working face of a mine in Shaanxi Province.The results show that under the conditions of the optimal working parameters,the system can operate in 1 cycle time(50min)and 1 step(840mm),synchronously directional slitting of 4 holes with a length of 7000-8000 mm,to achieve fast and efficient directional cutting of the remaining roof.The development and application of this system has far-reaching significance for the promotion of N00 and other safe,efficient and economical coal mining methods in China. |
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