Application Of CFD In Primary Sedimentation Tank

The primary sedimentation tank is the pretreatment construction of secondary waste water treatment plant, and the main construction of first waste water treatment process. The main effects are to discard the solid suspend grains, in order to ease the organic loading. The designing of primary sedimentation tank is depended on experience, so it's necessary to simulate the three-dimensional flow type of fluid and the distribution of suspended solid in the primary sedimentation tank. It has great value in supplying effective theoretic basis and guidelines to the practical operations.In this paper, a three-dimensional Euler two-phase flow model combining high Reynolds number k -εequation for a circular primary sedimentation tank was developed. The interaction between liquid and solid in the model is considered, including influence of interactive drag force, transverse lift force, virtual mass force, dispersion phase volume fraction and the density difference between the dispersion phase and continuous phase. The SIMPLE algorithm and the finite volume method is used to simulate the three-dimensional flow patterns of radial flow primary sedimentation tank and the distribution of suspended solid.The flow field predicted by the model indicates a good agreement with the experimental data of Abdel-Gawad. After analyzing the tangential velocity curved surface, the 3-dimension model reflects the water flow and suspended substance variance accordingly.The result of modeling shows that baffle plate length of sedimentation tank and position influence a lot on the removal efficiency. Under the specific inlet condition, we choose the optimal length and location of baffle, which can make the setting tank obtain favorable removal efficiency. With the low concentration of inlet, the size of suspended substances has a little influence on the flow field, but it has effect on the suspended substances distribution. The effluent equipment which may bring in the bottom silt is the main reason for diminishing the water quality.