Numerical Study On The Effect Of Impeller Speed And Particle Size On Flow Field In Flotation Machine

As the core equipment in the flotation process,the changes of some important hydrodynamic parameters in the slurry system during the working process of the flotation machine will directly affect the flotation effect.However,due to the complex fluid behavior in the flotation process,it is difficult to obtain these parameters.With the development of Computational Fluid Dynamics(CFD),a new way to study the slurry flow field could be provided.In view of the disadvantages that the Euler model cannot obtain the size distribution of bubble groups,the population balance model(PBM)is used to describe the size distribution and changes of flotation bubbles.The gas phase distribution and bubble size distribution in the flotation cell were obtained;in the process of gas-liquidsolid three-phase flow simulation,considering the calculation time and accuracy,only the Euler model was used.To investigate the influence of solid distribution,gas distribution,gas phase velocity and circulation rate of slurry with different particle sizes and different rotational speed conditions;the coal flotation experiment was designed based on the simulation results,and the clean coal yield,recovery and clean coal ash content were investigated under the conditions of different particle sizes and different rotational speeds.From the numerical simulation results and coal flotation test results,it can be seen that in the process of increasing the impeller speed from 1200 rpm to 1800 rpm,the average diameter of the bubbles in the tank becomes smaller with a linear distribution,while the bubbles with different diameters basically show a peak-valley shape in the flotation tank.And the bubble diameter distribution is basically between 0.5～3.5 mm,the maximum diameter of the bubble is smaller when the impeller speed increases,with the bubble burst caused by strong turbulence is more obvious;The upward circulation enables more particles to have more contact opportunities with air bubbles in the area above the impeller,and the concentrate rate of flotation is also improved.However,because there are gangue particles in the solid phase in the slurry environment,the high rotational speed condition will also make the gangue evenly dispersed in the slurry and reduce the concentrate grade.The distribution of air in the tank is mainly based on diffusion under the condition of low rotation speed,while the main effect of stirring is under the condition of high rotation speed.It is also concluded that for coal with particle size of-125 μm,the optimum speed of impeller speed is 1650 rpm;for coal with particle size of-250+125 μm,the optimum speed is 1500 rpm.