3-D Numeral Simulation And Optimization Of The High-density Sedimentation Tank In Water Treatment Plants

The study based on Chongqing Yuelai water treatment plant(600,000m3/d) inChongqing Liangjiang New Area of the third national new area.In this study, choose influence factors of high-density sedimentation tank; theappropriate numerical models have been built to simulat the velocity field in theagitator tank of the reaction zone, and velocity field and concentration field of thesettling zone in high-density sedimentation tank by FLUENT; validate the accuracyand reliability in the agitator tank of the reaction zone and the settling zone ofhigh-density sedimentation tank; the influence of different stirring blade radii andrevolving speed on coagulation effect are analyzed; the influence of differentparameters on sedimentation effect are analyzed including inlet water density, inletwater size, mud bucket position and size; the optimal design of high-densitysedimentation tank are set up.The conclusion of this study as follows:①As stirring blade radius of the reaction zone of high-density sedimentation tankincreases, the fluids agitated get more bringing coagulation effect better; but a oversizeblade radius makes operating cost increasing. The optimal stirring blade radius is1.5m.②Unsuitable revolving speed in the agitator tank of high-density sedimentation tankgoes against coagulation effect. Low speed can’t mix sewage with rinsinghomogeneously; high speed with powerful shear force damages flocs formed in theagitator tank, and makes follow-up sedimentation effect worse due to higher outletvelocities. The optimal revolving speed is4rad/s.③All kinds of preparation equipments should be installed because that the increaseof inlet particle density helps outlet sludge concentration raising and sedimentationworse. The optimum of inlet particle density is1050kg/m3.④Decreasing the inlet particle diameter makes the density current andsedimentation effect worse, which is disadvantageous to outlet water effect. Theoptimum of inlet particle diameter is1000μm.⑤When mud bucket move to x positive axis, the bad flow pattern includingbackward flow and the vortex of the settling zone in high-density sedimentation tankwill be alleviated, the velocities distribution of the outlet section and sedimentation effect will be ameliorated, but movement is not more better. The optimum of mudbucket position is18.05m, mud bucket move3m to x positive axis based on primarystructure.⑥The bigger the size of mud bucket of the settling zone in high-densitysedimentation tank is, the greater the perturbation effect of the flow is, and the higherof outlet volume fraction will be, which is bad for oulet effect. The optimum of mudsize is3.3m of top surface.The study has directively meaning to complete infrastructure facilities of the newarea and promote the development of water treatment technology, provide guidance forfuture design of high-density sedimentation tank, and has higher value in theory andengineering practice.