Combined Non-spherical DEM Model And Numerical Simulation Study Of Ball Milling Process

As an important part of mineral processing,ball milling process has high energy consumption and low energy utilization.Improving the energy utilization efficiency in the process of ball milling has become the focus of mineral processing.The research on mathematical modeling and simulation of ball milling process is helpful to explore the interaction between ore and grinding media and the energy conversion mechanism,which can provide an important theoretical basis for optimizing operation,improving milling equipment and increasing the energy utilization efficiency of ball milling process.Aiming at the three difficulties of numerical simulation research in the process of ball milling,such as particle shape modeling,wear prediction of grinding media and wet milling,numerical simulation methods such as combined non-spherical discrete element method(DEM),wear model of grinding media and three-phase coupling model are established respectively to simulate the dry and wet ball milling process.The main contents and achievements are as follows:Firstly,a combined non-spherical discrete element model based on sphere,super-ellipsoid and polyhedron and a wear model of grinding media are established,and the accuracy of the model is verified by experiments.Combined polyhedron-sphere DEM and polyhedron-super-ellipsoid DEM are proposed for the ball milling process of spherical grinding media and non-spherical grinding media.Polyhedron-sphere model and polyhedron-super-ellipsoid model are used to model the ore particle-spherical grinding media system and ore particle-cylindrical grinding media system respectively.Among them,a method with good accuracy which converts the superellipsoid particle in contact with polyhedron particle into polyhedron is proposed,thereby realizing a stable and efficient solution of the contact problem between super-ellipsoid and polyhedron.Via static stacking and dynamic mixing experiments,it is found that combined non-spherical DEM has quite high accuracy.In addition,the efficiency of combined model and the factors that affect the computational efficiency of the model are evaluated systematically by simulation.Based on the shear impact energy when solids collide,a particle wear model is proposed and its accuracy is verified by the ball grinding experiment in a planetary ball mill.Secondly,the numerical simulations of the dry ball milling process are carried out in an industrial semi-automatic grinding(SAG)mill based on the combined non-spherical discrete element model,and the influence of particle shape and filling level on the ball milling process is revealed.The effects of the shape of ore material and grinding media on the motion behavior,power consumption,wear of liner and media are investigated,and the results show that both the shape of the ore material and the grinding medium have a complex influence on the energy utilization efficiency and wear rate of the mill.Besides,the influence of material filling level and media filling level is explored and the results show that an appropriate filling level of ore material grinding media can achieve the balance of system power consumption,energy utilization efficiency and wear cost.In the third part,a kind of coupling model of gas-liquid-solid based on the CFD-DEM-VOF method is established and the wet ball milling process is investigated by numerical simulation,and the complex influence law of fluid on the ball milling process is revealed.In this method,the DEM and CFD is used to calculate the particle phase and the fluid phase,respectively,and the surface between gas and liquid is controlled by the volume of fluid(VOF)model.A semi-resolved CFD method based on the double grid method is proposed to solve the CFD-DEM-VOF coupling under the condition that the size of fluid grid is comparable to the particle.After that,the accuracy of the CFD-DEM-VOF method is verified in some typical cases such as single-ball entry water,multi-ball entry water and flow in a horizontal drum.Among them,the influence of Reynolds number and fluid mesh size are explored in the simulation of the single-ball entry water,and it is found that the accuracy of the CFD-DEM-VOF method increases with the decrease of particle Reynolds number and fluid mesh size;in the simulation of multi-sphere entry water,it is found that the CFD-DEM-VOF method can accurately calculate the rise of the liquid level;while in the simulation of flow in the horizontal drum,the influence of the liquid-solid filling level and rotation speed is explored combining with the experimental results,and it is found that CFD-DEM-VOF method can accurately model the motion behavior of particle bed and liquid phase.After that,the wet ball milling process in an industrial SAG mill is simulated via CFD-DEM-VOF method,and the motion behavior of particle,power consumption and energy utilization,liner and grinding media wear in the wet ball milling process are analyzed from the motion speed,collision energy spectrum and statistical analysis of wear rate.Finally,the applicability of the CFD-DEM-VOF method in the non-spherical particle system is verified during the wet ball milling of the nonspherical particle system.