Middle Speed Ball Mill Flow Field Analysis And Structure Optimization

Middle speed ball mill utilizes the milling parts with relative compression to grinding coal and integrates grinding,drying,transmission,sorting process in one,so its process is simple and high grinding efficiency.It has been widely used in iron and steel industry,thermal power,cement and other industrial fields.However,there are many problems in actual production,such as large pressure loss,the output is not stable,the coal particle size becomes coarse and over crushing phenomenon is serious.It is of great significance to master the distribution of flow field and grinding mechanism in chamber,for which provide theoretical guidance for the structure optimization,which also improve grinding efficiency and reduce energy consumption.This paper based on EM mill as the research object which design and development by Jiangsu mountop company,Solidworks is used to create its simplified three-dimensional model.Based on the CFD technology and engineering fluid dynamics theory,using discrete phase model(DPM)and Realizable k-? turbulence model,simple algorithm to calculate turbulence parameters in the flow field within grinding chamber,which analysis the chamber characteristics of velocity field,pressure field,temperature field,particle trajectory and streamline,etc.The gas-phase flow field is firstly carried in numerical simulation,until its being convergence,then add the discrete particle phase,particle movement is used random trajectory model,one-way coupling solution for the gas solid two-phase to simulation.Finally,optimization the ring,chamber and ash bucket structural according to the simulation results.The comprehensive results show that the flow field of medium-speed ball mill cavity has obvious three-dimensional rotating flow characteristics,which mainly composed by sudden expansion movement,jet,reflux,and around flow coupling.When the gas passes through the air ring,the speed is high,and formed jet-flow,vortex cavity is formed in the ash bucket and the grinding disc.High temperature hot air and coal particles in the air ring start coupling,along with lots of energy exchange,ascending air entrained coal particles with upward movement,larger particles fall back millstone,smaller particles along with the air flow into the separator and separation again,unqualified coal through the ash bucket fall back to the millstone.Airflow influenced by the effect rotation of the grinding disc and the grinding ball,which flow around the grinding ball and form much small vortex around the ball.During the mill working process,the mill energy consumption and the pressure loss is larger.Accordingto study the changer rule of air flow by adding air volume,the results show that as the air flow increases,the wind speed increases significantly at the wind ring.but the pressure loss in the grinding cavity also increase obviously.According to the grinding chamber flow field simulation and combine problems occur in the engineering.In this paper,the medium speed mill structure optimizations mainly focus on the air ring,air chamber,ash bucket and analysis the flow field of improved model.After plugging part of the air ring,flux at the outlet of the air ring is increase,but the pressure loss also increases significantly.For the chamber structure,at the bottom of chamber entrance install guide plate.Analysis showed that the flux distribution at the air ring tends to be uniform,which conducive to gas powder coupling and transmission.For the ash bucket extension,numerical simulation results show that the weak turbulence pulsation and longitudinal vortex decrease obviously.Through analysis the optimized structure of the medium speed mill,we can see that turbulence,powder transport efficiency are improved,the mill pressure loss has different degrees of decline.