Structure Optimization Of Pneumatic Micro-bubble Flotation Machine Based Onnumerical Simulation

Pneumatic microbubble flotation machine,a new flotation facility appeared in recent years,has advantages of large throughput,simple structure and low consumptions of power and flotation reagents,which has been applied in industrial mineral processing of bauxite,molybdenite,nickel and so on.As a new flotation machine,the aeration performance and internal flow field character haven't been studied clearly,leading to the imperfection in its separation mechanism and the lack of guidance in the scaling-up and structural optimization of the machine.Based on the numerical simulation method of computational fluid dynamics(CFD),the flow field characteristics within the microbubble generator and the cell of pneumatic microbubble floatation machine is simulated in this dissertation,and the mechanisms of mineralization and separation are also analysed theoretically.According to the simulation results,a massive turbulent intensity and a high air fraction were found in the chamber and the orifice zone,which led to a high level of turbulent mineralization.After pulp and bubbles being ejected from the cell from the orifice,bubbles are generated from the surface of mineral particles and the mineralization effect was intensified due to a fast drop of pressure.As for pulp,after being discharged into the cell,most of it go up along the zone between the microbubble generator and the wall of the flotation cell,and then drop down after going up to a certain height through the internal zone of the cell due to gravity.At last,some of it are discharged from the middling pipe while the rest from the tailing pipe.Considering the unstable operating condition of the flotation machine during industrial processing,the effects of two important factors,the amount of pulp feedings and the aeration,were explored in the dissertation.The results showed that the increment of pulp feedings has a significant influence on the flow field in microbubble machine,where both the velocity and turbulent intensity are enhanced obviously.However,little influence were observed in the flow field of flotation cell,little change in velocity distribution and a small increment of air fraction were found.As for the factor of aeration,the velocity of air near the cell's wall increases explicitly with aeration increase,and the max velocity ranges from 0.68m/s to 0.83m/s.Besides,with the increase of aeration,the air fraction in flotation machine rises up as a whole,but The effect of aeration increase on bubbles' dispersion is not distinct.Under the different amount of aeration,the heights that bubbles distribute steadily near the wall as well as the internal zone have few changes.Some defects of pneumatic microbubble flotation machine were found after the numerical simulation,such as the upward velocities of pulp and bubbles are too fast,the flow field is not steady enough and the dispersion of pulp and bubbles are poor,some of unseparated pulp and bubbles are found being discharged from tailing's pipe directly as well.In consideration of all disadvantages above,structure optimizations of were conducted via varying the position of micro bubble generator and structure of release mouth of micro bubble generator.Comparing with previous results,the rising velocity of both pulp and bubble in the flow field slow down,dispersion in flotation cell is intensified,gas volume fraction in the flow flied near flotation cell wall get lower,the intervention of flotation cell wall on gaseous phase is weakened,the overflow of vapor-liquid phase in the tailings tubes is under control as well.