| The synergetic multi-windows top coal caving method and the coal-gangue identification technology for top coal caving are the key points to realize automatic or intelligent top coal caving in longwall top coal caving(LTCC)working face.In this paper,by means of laboratory test,theoretical analysis,numerical simulation and on-site measurement,the influence of the method of top coal caving,the total width of multiwindows and the movement characteristics of coal and rock strata on top coal recovery and caving efficiency are studied,and an algorithm model of the initial top coal caving method is also set up under the condition of synergetic multi-windows top coal caving method.The effect of top coal caving under the conditions of synergetic multi-windows and single window top coal caving method is also analyzed.Meanwhile,an active method of microwave irradiation-infrared detection for coal and gangue identification is put forward.Based on the physical and chemical characteristics of coal and gangue,the chemical element composition,mineral composition and specific heat capacity of coal and gangue were obtained by scanning electron microscopy,X-ray diffraction,specific heat and electrical parameters test,besides,the real and imaginary values of the relative dielectric constant are also used to theoretically analyze the scientificity of the identification method and verify the feasibility of the identification method in the laboratory,so as to solve the problems of fast and accurate identification of coal and gangue in the process of multi-windows top coal caving,and provide a guarantee for the implementation of synergetic multi-windows top coal caving.The main research results obtained are as follows:(1)The method of initial top coal caving with "at the same time turn on and the reverse turn off" is put forward,that is to open all the multi-windows(n)at the same time,and then at a certain time interval inversely to turn off the caving windows in the initial top coal caving process.According to the influence range of caving window,the speed equation of top coal caving process and the movement equation of top coal particles,the solution of the initial top coal caving method for multi-windows is given.(2)Due to the unevenness of top coal looseness above the caving window,the morphology of coal-rock interface presents a "hook-back" shape.In addition,the smaller the thickness of top coal,the smaller the number of caving windows required to form a smoothly inclined coal-rock interface at the same time,and the smoother the interface curve between coal and rock,the more top coal is recovered,and the less coal-bearing layers are interlaced,the more uniform coal top coal discharge is,the higher the top coal recovery rate is,and vice versa.(3)Under the condition of multi-windows top coal caving method,the interface of coal and rock during coal caving is relatively smooth.The top coal recovery rate increases with the number of caving windows opened at the same time,and the recovery rate of top coal is 77.9% to 90.5%,most of which can reach 85%.Under the condition of single window top coal caving method,the interfacial shape between coal and gangue formed in caving process is related to the thickness of top coal,when the thickness of top coal is less than 8.0 m,the mutual layer of coal-gangue is not serious,the coal-gangue interface is more regular,and when the top coal thickness is more than 8.0 m less than 24.0 m,the coal-gangue mutual layer is serious,and the top coal recovery rate of single window top coal caving method is 73.2%~84.9%.(4)A large number of chemical components,physical electrical parameters and microwave irradiation test are carried out.The results show that the different temperature changes of coal and gangue before and after microwave irradiation is due to the different amounts polar molecules contained in coal and gangue.Under the same test conditions,the temperature variation of coal and gangue before and after microwave irradiation is quite different,and the difference between coal and gangue can be obtained accurately by infrared thermal imager.Based on this,an active coal-gangue identification method with microwave irradiation-infrared thermal imaging detection is proposed,and the feasibility of this identification method has been verified in the laboratory.(5)The results of the test sample in this paper show that the ability of coal to absorb microwave is 1.3 times that of gangue.When coal and gangue absorb the same microwave energy,the average temperature of coal rising is 1.15 times than that of gangue.Under the same microwave irradiation environment,the average temperature of coal rising is about 1.5 times higher than that of gangue.For the same microwave irradiation time,the temperature increasing of coal samples with particle sizes of 4.75 mm,1.40 mm,0.60 mm and 0.30 mm before and after microwave irradiation are 1.3 times,1.7 times,2.0 times and 2.3 times higher than those of the same size gangue samples. |
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