Simulation Study On Vibration Screening Process Using 3d Discrete Element Method

Screening is an important technology for separation of particles according to their sizes. Screening is also the source technology to realize energy saving and emission reduction, which has been widely used in many granular media industries, such as mineral process and so on. Screening process is a very complicated stochastic process. However, as the limited development level of physical testing techniques, we still lack insight understanding of the fundamental mechanism of particle motion and penetrating in screening process. So, this paper presents a systematic numerical study of the granular material segregation and vibration screening process by means of three-dimensional discrete element method (DEM) to provide theoretical basis for better understanding segregation mechanism, improving screening theory, proposing new screening method and developing new screening equipment. The key findings of this paper are as follows:Experimental studies of single particle free-falling and particles vibration segregating process were carried out using high-speed dynamic analysis system. DEM simulation results with real physical parameters were consistent with experimental results and the validity and reliability of 3D DEM were validated.Thorough numerical simulation studies of spherical and non-spherical particles vibration segregation process were carried out using 3D DEM. The influence of vibration parameters on segregation speed was analyzed. The optimum values of vibration amplitude, vibration intensity and size ratio for achieving fast segregation were obtained. On the basis of the changes of forces and kinetic energy between particles, segregation mechanism of non-spherical particles was explored and the reason that non-spherical particles were more active than spherical particles was also elucidated. Particle segregation theory in different vibration modes was supplemented. The method to explain particle segregation behaviors in different vibration modes was proposed, which is a comprehensive application of three mechanisms: void filling, sidewall-driven transport of particles and non-equipartition of energy, and the distribution of particle velocity vectors.Systematic numerical studies of linear, circular and elliptical vibration screening processes using 3D DEM were conducted. The concept of dynamic screening efficiency was proposed. Regression equations between amplitude, throwing index, vibration direction angel, inclination of screen deck and particle average velocity on the screen deck, screen deck length and the dynamic screening efficiency were obtained. Influence mechanism of vibration parameters on the screening process was elucidated. And the optimum values of vibration parameters for achieving the best screening performance were also obtained. Particulate matter vibration screening theory which can provide theoretical basis for the optimization of conventional screening machine and the development of new screening equipment was enriched.Thorough numerical simulation studies of banana screening process were carried out using 3D DEM. The motion characteristics and penetrating mechanisms of particles on the screen deck were revealed. Effects of geometric and vibrational parameters of screen deck and vibration modes on banana screening process were elucidated. The optimum values of initial angle of screen deck, increment of screen deck inclination, screen deck numbers were obtained when best screening performance was gotten. The following conclusions, such as smaller vibration intensity and amplitude will help improve screening efficiency, but the values are too small, accumulation of particles on the screen deck will occur, screening performance of elliptical vibration mode was better than linear and circular vibration modes were obtained. The relationship between screen deck length and screening efficiency was further confirmed, which can provide theoretical basis for the optimization of banana screen and reasonable operation.This paper presented a thorough numerical study of capsule shaped and bulk particles banana screening process for revealing the influence mechanism of particle shape on screening process. The results show that spherical particles can well embody the size influence on screening process. And non-spherical particles got bad effects of transportation, segregation and penetration due to complicated forces, increased repose and failure angle, increased anti-shear ability, packing and self-locking effect.A new mineral fractal simulation algorithm based on the fractal theory was proposed in this paper in order to achieve simulating real particle materials. The result shows that the algorithm can generate more realistic coal particles which can provide a new method to further improve the accuracy of particulate matter numerical simulation using 3D DEM.