The Numerical Simulation On New Type Inclined Plate Of Vertical Flow Secondary Sedimentation Tank

The secondary sediment,ation tank is the key facility in sewage treatment, its efficiency directly affects the efficiency of sewage treatment plant. At present, the problem of water pollution is serious in our country. For this reason, not only large scale sewage treatment plants should be built, but also small and medium sized urban sewage treatment plants, engineering of sewage treatment facilities and small movable sewage treatment equipment should be developed. So far the research on domestic and foreign scholars about secondary sedimentation tank are mostly focus on with large sewage treatment capacity of horizontal flow and radial flow sedimentation tank, while research on small and medium sized sewage treatment for the vertical flow sedimentation tank is relatively less. In addition, adding the inclined plate can improve operating efficiency of sedimentation tank. So the research on the internal flow in vertical flow sedimentation tank and the influence of adding inclined plate on its internal flow characteristics and working efficiency, to promote the application of the vertical flow sedimentation tank in medium sized and to improve the sewage treatment capacity of vertical flow sedimentation tank has important significance.In this paper, the numerical simulation method is used to study the effect of flow characteristics and the different flow characteristics on the working efficiency of vertical flow sedimentation tank and the tank with inclined plate. In view of the complex solid-liquid two-phase flow in vertical flow sedimentation tank, in the paper, using FLUENT software.selecting the Mixture model and RNG k-? model to simulate the flow field and concentration field of vertical flow sedimentation tank and the tank with different inclined plate mounting height and spacing. The main contents and conclusions are as follows;(1) By comparing and analyzing the flow field, the concentration field and the settling velocity of suspended matter and the concentration of outlet water: adding inclined plate to avoid the early stage high density current flow upstream, reduce rising velocity of suspended matter, increase the area of sediment, reduce 16.1% of the concentration of suspended matter in the outlet of the sedimentation tank, effectively improve the quality of outlet water.(2) Based on the analysis of the mixture velocity and the concentration of suspended solids in different inclined plate installation height: installation height of inclined plate in sedimentation tank is lower, the greater the protection depth of the water, the greater the velocity of thought inclined plate; The higher the inclined plate installation is, the smaller the protection depth of the water, the greater the velocity of the upper part of the inclined plate,suspended solids are discharged without sufficient settling time. For this model, it is suggested that the protection depth of water is not less than 1.1m, and the distance between the bottom of the inclined plate and the outlet of the water inlet is not less than 1.5m.(3) Through the analysis of the sedimentation tank internal flow, the concentration distribution of suspended solids and the quality of water outlet in different inclined plate spacing: Reducing Inclined plate spacing can shorten the stabilization time of sedimentation tank, reduce the rising velocity of suspended matter between inclined plates, increase the area of sediment, reduce the concentration of suspended solids of water outlet.(4) By analyzing the Influence of different inlet flow velocity and inlet flow concentration on the internal flow of sedimentation tank, precipitation condition and outlet concentration: In a certain inlet flow concentration, inlet flow velocity increased to 0.028m/s, the vortex flow under the inclined plate towards outside the walls of the spread segment of the water inlet pipe,sewage can be evenly distributed to the inclined plate, so as to increase the settling efficiency of suspended matter in inclined plate. In a certain inlet flow velocity, increasing the inlet flow concentration can reduce the cavity area of small concentration between the inclined plates.Therefore, adding the inclined plate the inlet flow velocity can be increased by more than 15%,and the inlet flow concentration can be increased by more than 30%.