Study On Key Technology Of High Efficiency Screening System In South Open-pit Coal Mine

Screening is a basic technological means to improve coal quality,reduce transportation costs,reduce energy consumption and pollutant emission from coal combustion.With the increasingly fierce competition in the coal market around the Zhundong mining area in Xinjiang,the coal processing system of the South Open-pit Coal Mine has been unable to cope with the complex and changeable market environment quickly and effectively.The processing capacity,screening efficiency and equipment reliability of the screening equipment in the 304-screening system have become the key and bottleneck problems in the whole processing system.Based on the above situation,the roller screen in the 304-screening system of the South Open-pit Coal Mine was taken as the research object in this thesis.Based on the discrete element method and the finite element method,the numerical simulations of the screening process,the mechanism of choking and crushing process,the dynamic characteristics of the roller and other key parts of the roller screen were carried out,both of which can provide theoretical and technical support for the efficient operation,optimal control,reliability improvement and optimal design of the roller screen.The main research results of the thesis are as follows:In this work,the structure and working principle of roller screen were studied.A three-dimensional model of industrial-scale roller screen based on DGS1815 was established.The force of the vane in choking process was analyzed,and an automatic control scheme to solve the problem of material choking was designed.The basic principle of discrete element method(DEM)was introduced,which provides a theoretical basis for the following study of the mechanism of the roller screening process and the numerical simulations of choking and crushing process.The high-speed dynamic testof the screening process was carried out,and the reliability of the DEM simulation of the screening process was verified.The DEM model of the screening process of industrial-scale roller screen was established and the simulation study was carried out.The effects of feed rate,the rotational speed of rollers,the inclination angle of screen deck and the adhesion force between wet particles on the screening process of roller screen were analyzed,and the working parameters with the best screening performance were obtained.The effects of working parameters on the screening rate and average velocity of particles of each particle size were discussed.The mechanism of the influence of particle shape and adhesion force between wet particles on the screening process of roller screen was also revealed.The mechanism of the choking process of the roller screen and the crushing mechanical characteristics of the choked particles were analyzed.Based on the bonded particle model(BPM),the DEM model of the material choked crushing process on the screen surface of the roller screen was established.Then,the force of the vane was analyzed under the condition of single-particle choked.The theoretical conditions for the stop rotation of the roller in the process of choked coal were obtained.The torque changing rules of the roller and vane under the condition of multiple particles choked were discussed.The effect of rotational speed on the torque of the roller was further analyzed under the condition of single-particle choked.The finite element analysis of the roller,vane,mandrel and other key parts of the roller screen was carried out under the choking condition.The static and dynamic characteristics of the roller were obtained.The frequency response function of the roller under different frequency exciting force was obtained by using the harmonic response analysis method.The mechanical model of torsional vibration of the mandrel was established.The modal test of the mandrel model was carried out to verify the reliability of the finite element method modal analysis.The dynamic response method under the impact of step load was proposed.The natural frequencies and the modes of each order torsional vibration of the mandrel were obtained,which provides a foundation for the optimization of the roller screen structure.The DEM simulation and optimization of the working parameters of the roller screen were carried out by using the response surface method,and an optimized combination of working parameters was obtained.Based on the principle of equal thickness screening,the model of a multi-stage variable screen inclination type equal thickness roller screen was established.The screening process of the equal thickness roller screen was simulated,and the screening performance was compared with that of the ordinary roller screen,which provides reference for the structural optimization design and industrial application of the roller screen.The screening process of roller screens with different screen vanes and arrangements was simulated,which provides a further reference for the optimization of the structure of roller screen.There are 74 pictures,25 tables and 133 references in this thesis.