Numerical Simulation Of Mechanical Stirring In Seed Precipitation Tank

The seeded precipitation of NaA102solution is one of the key steps in the Bayer process for the production of alumina. It has great influence on alumina product’s outputs and quality and also has indirect effect on other procedures. Hence it is important both in theories and practices to understand influence factors in the seed precipitation and increase the numerical calculation accuracy of the seed precipitation process, which will result in great improvement of the yield and quality, energy saving as well as rapid progress in alumina production technique.Seed precipitation tank with a new-style impeller-Intermig impeller was numerical simulated by using the commercial software FLUNET12.0on parallel computing graphic workstation. First, by comparing the simulation and cold water experimental data, the feasibility of CFD method was verified to simulate the flow and solid-liquid mixing characteristics.On the base of simulation of cold water experimental, suspending of Al(OH)3particles in the alumina seed precipitator, with different conditions of rotate speed, was numerically simulated by using the Reynolds-averaged Navier-Stokes (RANS) approach with Realizable k-ε model, Eulerian Multiphase Model and Multi-Reference Frame (MRF). According to the analysis of the concentration and velocity fields, increasing rotate speed and enlarging the diameter of the impeller(D) are good for the suspending of Al(OH)3particles. Longer or shorter distance between the impeller(C) and the bottom is harmful.The just off-bottom suspension speed and the stirring power are also studied by using the same method. It has a best distance between the impeller and the bottom that can make the minimal just off-bottom suspension speed. The rotate speed and D have bid influence on the stirring power, higher speed and longer diameter of impeller need more power. By comparison, The C has little effect on the stirring power. With the increase of C, the stirring power increased first, and then began to stabilize.The Solid-Liquid flow flied was simulated by the use of CFD. Under the condition of a constant rotate speed, it has a optimum value of D and C white can get better effect of particle suspension with low power consumption. In this study, the best D and C are111mm and255mm. The result has certain reference value on technology innovation and apparatus improvement industially.