Study On Optimization Design And Operation Of Inclined-Plate Sedimentation Tank And Water Distribution Channel Based On CFD

The efficiency of the sedimentation tank directly affects the effluent of the whole water treatment process.With the advantages of high efficiency and small land area covering,the inclined-plate sedimentation tank is commonly used as a mud-water separation structure in the water treatment plant.However,in the operation process,the velocity field and concentration field inside the inclined-plate sedimentation tank are complex.Nowadays,the research on inclined-plate sedimentation tank mainly focuses on the theoretical analysis and small-scale experiment.The sedimentation process and mechanisms under different conditions such as the structure and parameters of inclined plate being changed are still unclear.In this context,designers often select parameters with experience while the optimal conditions cannot be guaranteed.As a connecting structure between the flocculation tank and the sedimentation tank,water distribution channel has a direct impact on the uniformity of the current in the sedimentation tank,yet the present research is insufficient and the optimization methods are simple.The research objects were based on the inclined-plate sedimentation tank and the distribution channel in the water treatment plant.The Realizable k-? model and the Mixture model were adopted during the numerical simulation.The single-phase flow was applied to three-dimensional distribution channel under a steady state.The twodimensional inclined-plate sedimentation tank was simulated with two-phase flow by transient method,the results are summarized as follows:(1)The diffusion of the mainstream in the distribution channel is the main factor which affects the uniformity of the effluent.Firstly,7 conditions were simulated for the different inlet widths and tank widths of the distribution channels,the optimal design parameters of the tank length were obtained.Secondly,the influence of the single &double distribution channels on the uniformity of the outflow was analyzed.The optimal position of the middle wall in the double distribution channel was explored.Thirdly,the influence of 3 export types on the effluent uniformity was investigated.(2)The flow pattern along the width dimension has a small change,while the transient characteristics of the internal flow is significant in the inclined-plate sedimentation tank.The suspended particles continuous congest at the bottom of the inclined-plate and instantly slip down to the sludge hopper.This periodic phenomenon disturbs the velocity field and concentration field and finally makes the flow pattern more complex.Thus,the flow pattern in the inclined-plate sedimentation tank is completely different from the relatively stable flow status in the rectangular and circular sedimentation tank.Besides,the hydraulic experiment was carried out.By comparing with the CFD results,NSE=0.76~0.77 was obtained,which proved that the CFD model is highly reliable.(3)As the surface load is 5m/h,the optimal length of the inclined-plate sedimentation tank ranges from 10 to 18 m,with the length of 14 m being the best.Under such conditions,the removal rate of the suspended particles is stable and the value is high(91.24% for 14m).When the average length of the inclined plate is larger than or equal to 1m,the non-equal length arrangement(the front plate in the tank is longer than the backward plate)can improve the effluent removal rate.When the inclined-plate is arranged dense in the front and sparse backward,the removal rate of the precipitate did not increase significantly.It is more effective to increase the shallow sedimentation area by directly increasing the length of the plate than by increasing the length of the tank.The suspended particles removal rate of the former method is 8 times that of the latter,and no additional land area is required.Finally,the optimized sludge discharge pattern is given for the inclined-plate sedimentation tanks with 3 different tank length conditions.The conclusions provide some theoretical guidance for the design and operation work of the inclined-plate sedimentation tank and its distribution channel.By optimizing the length of the tanks,using double distribution channels at appropriate time,changing the export form,adjusting the length of the plate and the sludge discharge time,the effluent water quality can be improved while the cost of construction and operation can be reduced,making the inclined-plate sedimentation tank more efficient and economic.