Research On Key Technology Of Pneumatic Conveying And Filling For Coal Auger Mining

In order to reduce or eliminate the prearranged pillars in auger drilling working face, control the subsidence and collapse of coal auger mining goaf roof and promote the widely use of coal auger and drilling technology in thin or extremely thin coal seam, based on the project named " Key Technology and Equipment of Almost Thin Seam Auger Miner" had been approved by "National High Technology Research and Development Projects Program of China(863 Program)" to develop a filling system for coal auger mining with little space occupation, high production efficiency and simple equipment structure. This filling system could make up the disadvantages of large volume and heavy equipments which limited the traditional filling system to apply in coal auger mining goaf. The gangue particles were transported and filled into coal auger mining goaf by pneumatic conveying technology in the coal auger mining filling system. The particle and particle interactions and particle and flow field interactions had directly affect the reliability, conveying efficiency and filling economy of pneumatic conveying and filling system. For this purpose, with the gangue particles and pneumatic conveying flow field as the research object, the combination of theoretical analysis, simulation and experiment were adopted in this dissertation to study of the pneumatic conveying performance of gangue particles and flow field conveying characteristics, which provided design guidance for the pneumatic conveying system and filling process and system of coal auger mining.According to the mining geological condition of working face by coal auger mining and the mining technology of five-bits coal auger, the a whole technology of pneumatic conveying and filling for coal auger mining, included the technology of gangue pneumatic conveying from surface to underground, the technology of coal and gangue separation during drivaging and the technology of gangue filling in coal auger mining, was proposed based on the goaf roof condition of coal auger mining and the filling mechanism of gangue. The system of pneumatic conveying and filling for coal auger mining was constructed and the pneumatic conveying system and the pneumatic filling system were designed, which confirmed the structure of feeding device, supercharger, filling nozzle and filling bit.Based on Hertz contact theory and Mindlin-Deresiewicz contact theory, the soft ball contact theory models without adhesion between gangue particles and between gangue particle and pipe wall were established. The shape characteristic parameters of gangue particle under different granularity was obtained by actual measuring the three axle diameters of gangue particles. The shape characteristic mathematical model of the gangue particle was established based on length index, flat index, Zingg index and particle filled degree. The orthogonal experiments were carried out, with bulk density, porosity, repose angle and the error of the actual experiment as evaluation indicators, with interaction coefficients of particle-particle and particle-wall as factors, and acquired the three kinds of exact gangue particle discrete element models and the precise interaction coefficients. the collision experiment and simulation studies of gangue particles were also conducted to verify the authenticity of the gangue particle contact models and the interaction coefficients.The continuity equation, momentum equation and turbulent transport equations of gas phase were obtained by adopting the Euler method to describe the motion state of fluid micro. According to the influence of fluid drag force, Saffman lift force and Magnus lift force of particle in the flow field, the coupling theory model and coupling simulation method of particle phase and gas phase were established by using Eulerian coupling model. The gangue particle suspension velocity theory expression with the flow field area correction and the particle shape correction was obtained based on the particle size method by considering the pipe diameter, particle shape and the relations between Reynolds number and fluid drag coefficient. The gangue particle suspension experiments and simulations in vertical pipe were carried out. The results shown that both of the simulation results and the theoretical results of gangue particle suspension velocity accorded with the same influence law of pipe wall diameter to conveying particles. The simulation results and the experiment results under different gangue particle granularity were similarity and were slightly bigger than the theoretical results, which verified the feasibility and reliability of the coupling theory model and coupling simulation method of particle phase and gas phase, and provided theoretical and experimental basis for the coupling dynamics study of gangue particle and flow field in pneumatic conveying.The basic parameters of pneumatic conveying system were preliminary set according to the actual working condition of pneumatic conveying system in coal auger mining. The gangue particles and flow field coupling simulation study under pure flow field condition and the coupling condition was carried out, with particle average kinetic energy, ratio of fluid mass flow rate and ejector energy consumption as evaluation indicators. The best ejector structure parameters and the recommended total pressures of nozzle inlet under different gangue particle mass flow rates were obtained based on the coupling simulation results. On this basis, the pneumatic conveying simulation of gangue particles in horizontal straight pipe, elbow and swirling flow pipe were conducted and the results shown that the gangue particles mainly distributed in the bottom of the pipe and were symmetrical about the longitudinal section in the pneumatic conveying simulation of horizontal straight pipe. The bigger flow field velocity was, the more conducive to gangue particles conveying in horizontal straight pipe. The gangue particles formed a particle beam with spiral motion in the elbow and the biggest wear rate decreases with the increase of elbow radius. The particle velocity in the swirling flow pipe was higher than that in horizontal straight pipe under the same air mass flow rate. The smaller of included angle between auxiliary pipe and main pipe, the larger particle velocity was.According to the actual working conditions of coal auger mining, the injection experiments for ejector structure factors effecting on the injection performance of pure flow field and gangue particles were carried out with the conveying properties of gangue particles and the static pressure variation characteristics of flow field in pneumatic conveying as reference indicators. The best ejector structural parameters obtained in injection experiment were similar with the simulation results, which verified the authenticity and reliability of the simulation results. The short pneumatic conveying experiments of gangue particles in horizontal straight pipe, elbow and swirling flow pipe were carried out using optimal ejector structure parameters as power source of gangue particles. The gangue particle conveying properties and pressure variation characteristics of flow field in horizontal flow field, elbow flow field and swirling flow field were obtained, which preliminary proved the feasibility of using pneumatic conveying to transport gangue particles and verified the correctness of coupling simulation results in horizontal straight pipe, elbow, swirling flow pipe. The long-distance pneumatic conveying and filling experiment of gangue particles were carried out. The relations between motion state of gangue particles and static pressure variation of conveying flow field, the relations between particle size and particle breakage rate and the influence law between the pipeline installation position of vortex supercharger and particle conveying time were obtained which verified the feasibility of pneumatic conveying and filling system for coal auger mining and laid a solid and reliable experimental and theoretical basis for the industrial test of pneumatic conveying and filling system in coal auger mining.