Study On Cutting Principle And Mining Technology Of Low-Energy-Consumption In Deep Coal

The development of deep energy utilization should be accelerated in hope of making up energy shortage and enhancing energy security and stability in China.This dissertation is aimed at adapting to the complex geological conditions of “five highs and two disturbances”,solving the problems of low cutting efficiency and reliability in deep coal seams,and breaking the bottleneck of power-increase-oriented mechanical design.In this dissertation,the following research work was carried out by integrating a variety of research methods,including mining technology,mechanical design,experimental research,numerical calculation,comprehensive analysis and theoretical calculation.From the perspective of coal properties,an experiment was performed on single pick cutting of coal,and the cutting force model and the cutting energy consumption model were established.Furthermore,the idea of cutting-induced coal wall fracturing was discussed,and the method of local unloading-induced coal self-fracturing was proposed.In this way,the principle and mining technology of low-energy-consumption cutting with induced coal damage as the core was formed.Besides,the adaptive control strategy of coal cutting was put forward.The main achievements are listed as follows:(1)A full-scale single-pick coal cutting experiment was performed for investigating the effects of cutting depth and cutting speed on cutting force and cutting energy consumption and analyzing the characteristics of acoustic emission(AE)generated during cutting.The cutting force is significantly affected by the cutting depth.Specifically,it increases with the cutting depth.The cutting energy consumption falls with the rise of cutting depth and cutting speed.AE can reflect the whole process of cutting.AE waveforms at the peak cutting force share the same main frequency and the same PSD area,and the peak cutting force can be predicted in accordance with the characteristics of AE generated during cutting.(2)The peak cutting force model and the cutting energy consumption model based on the Griffith strength theory were established,and the mechanism of coal cutting failure was revealed.The depth of dense nucleus was researched on by means of 3D scanning technology,and the function of dense nucleus was discussed.On this basis,the formula for calculating the failure depth was obtained.Moreover,the peak cutting force model considering ductile failure of dense nucleus was built,with the average error between the experimentally obtained value and the theoretically calculated value being 12.14%.Meanwhile,the cutting specific energy consumption considering crack-propagation-induced failure was established,with the average error between the experimentally obtained value and the theoretically calculated value being 11.35%.(3)The characteristics of signals produced by coal mining machinery disturbance were analyzed;the dynamic damage mechanism of coal wall was proposed;the effect of coal damage on cutting was studied;and the mechanism of low-energy disturbance on induced coal cutting was revealed.The disturbance of coal wall from coal mining machinery belongs to low-frequency disturbance whose energy is mainly concentrated within the range 7-12 Hz.The dynamic damage theory of coal wall in the deep working face was put forward according to the propagation and action of vibration wave: It is concluded that coal wall damage varies in different zones and layers.Moreover,the effect of force damage degree on the coal cutting failure was explored: With the growth of damage factor,coal gradually starts to undergo brittle failure and be fragmented into larger sizes.In this process,the cutting force and the cutting energy consumption both decrease.(4)The characteristics of energy storage in deep coal seams were probed into;the disturbance effect of local unloading on coal was explored;the effect of central slotting on coal cutting was discussed;and the mechanism of local unloading on induced coal cutting was disclosed.Abundant elastic energy stored in deep coal seams can be excited,released and utilized through related disturbances.The wave equation of deep coal seams under the action of local unloading was constructed to simulate the process of coal self-fracturing: It is found that the unloading coal primarily undergoes shear failure.Additionally,central slotting induced cutting in deep coal seams was researched on: Central slotting induced cutting not only notably reduces the peak cutting force and the cutting energy consumption,but also promotes the proportion of lump coal during coal cutting.(5)The principle of low-energy-consumption cutting in deep coal seams with induced coal damage as the core was proposed;meanwhile,the mining technology of low-energy-consumption cutting achieved by three-drum shearers was investigated;finally,the principle and mining technology were verified and evaluated.To be specific,the abovementioned principle includes four parts,namely the damage of coal caused by high ground stress,the dynamic damage of coal caused by disturbance from mining machinery,the wave damage of coal induced by local unloading,and the relief of stress boundary caused by central slotting.Three-drum shearers are applicable to the abovementioned mining technology,and triangle coal should not be retained in the application process.Low-energy-consumption induced cutting in deep coal seams,which succeeds in effectively reducing the cutting force and the cutting energy consumption,boasts remarkable technical,economic,social,and environmental benefits.(6)A novel temperature-measuring pick that could recognize the mode of coal-rock cutting was developed,and an adaptive cutting strategy was proposed.The developed pick is equipped with multiple functions,including temperature signal sensing and acquisition,anti-vibration,sealing,and explosion-proof.The cutting temperature rises with the increases in cutting depth,cutting speed,and rock strength.The panel data model of cutting temperature was constructed;the characteristic vector of cutting temperature was obtained;and the recognition of coal-rock cutting mode was realized.Ultimately,the adaptive control strategy of “speed regulation followed by height regulation” was presented according to varying coal cutting modes.