Study On Structure Optimization And Operation Parameters Of Newly CSO Storage Tank Based On Numerical Simulation

Combined system overflow(CSO)is one of the most important and difficult problems in water environment treatment in China.With the advantage of large space,the storage tank can quickly intercept the combined overflow sewage,which plays a very important role in the treatment of CSO pollution.But at present,most of the storage tanks are only used to regulate the flow,and the efficiency of sewage interception is not high.Based on the principle of density flow and advection sedimentation,a new type of CSO storage tank is constructed,which can improve the efficiency of sediment interception and is easy to empty and discharge sludge.Based on the combination of CFD steady-state simulation and orthogonal experiment,taking SS removal rate as the index,the structure size of the new type of storage tank was optimized,and the mechanism of sediment interception was analyzed.The results showed that the optimal structure parameters of the new type of storage tank were as follows: the length of water inlet was 1.6m,the depth of vertical baffle was 2m,the retention time was 0.7h,The length of horizontal baffle is 0.75 m and the angle of bottom inclined plate is 45 °;Based on a simple calculation method of CSO water flow hydrograph,with the help of the above optimal parameter model and CFD unsteady simulation method,the SS removal rate of the new type and the traditional storage tank in the actual operation conditions is compared.The results show that the interception efficiency of the new type of storage tank is about 2 times of that of the traditional storage tank with the same volume under the condition of rainstorm recurrence period p less than 1.A small physical model of the new type of storage tank was made by using the similarity criterion.The numerical simulation and physical experiment were carried out under two different residence time conditions.The results show that the change trend of SS removal rate obtained by the two methods is basically the same,and the average error is about 10%;With the help of the above physical model,the effects of different residence time and influent concentration on the precipitation effect of the physical model are studied.The results show that increasing the residence time and decreasing the influent concentration are helpful to improve the sediment interception performance of the physical model.With the aid of CFD steady-state simulation,the effects of different residence time,influent concentration and suspended particle size on the sedimentation effect of the new type of storage tank were studied,and the mechanism of their effects was analyzed.The results show that the increase of residence time and the decrease of influent concentration can improve the sediment interception performance of the new type of storage tank,and the suspended particle size changes in the range of 0.01mm-0.15 mm,When the size of suspended particles is larger than 0.15 mm,the increase of particle size will reduce the sedimentation performance of the baffled section of the new type of storage tank.