Study On Sedimentation And Cleansing Technology For Pressurized CSO Deep Chamber

Pressurized combined sewer overflow(CSO) deep chamber is a special overflow chamber adopted in the interceptor sewer system where the buried depth of existing combined pipe is very large. This CSO chamber is adopted to decrease construction cost and difficulty while there are some problems such as worse hydraulic condition and sedimentation. The hydraulic characteristics and sedimentation regulation of pressurized CSO deep chamber were studied in this paper by combining field inspection, model experiment and numerical simulation. Moreover, based on the aforementioned study, a self-siphon sediment cleansing set was designed and its hydraulic characteristics was studied as well as cleansing effect. Detailed research contents are as following:1. In order to obtain the sedimentation conditions of the pressurized CSO deep chamber as well as sedimentation variation, pipe SONAR system was applied for field inspection. Meanwhile, flowmeters were applied to monitor the flow of CSO chamber which was used for the analysis with sedimentation condition. The results show that there are 1-2m thick sedimentation layer generally in the CSO chambers. There is commonly little sedimentation in the main interceptor pipe coterminous with B1-type chambers, while there are 0.1-0.4m thick sedimentation layer in the main interceptor pipe coterminous with B2-type chambers.2. The hydraulic characteristics and sedimentation regulation of pressurized CSO chamber were studied by model experiment and numerical simulation. And the sedimentation reason was analysed for the design of cleansing set. The results show that the flow field of chamber presents a symmetric structure including two spiral uprising eddies. The shear stress and turbulent energy are small at the central zone of eddy where sediment amount is large while the shear stress and turbulent energy are large at the circumjacent zone where sediment amount is small.3. A self-siphon sediment cleansing set was designed according to the hydraulic condition of the CSO chamber, and its hydraulic characteristic was researched by experiment and simulation. The results show that this sediment cleansing set can obviously improve the hydraulic conditon of the CSO chamber which is very beneficial to sediment cleansing and preventing. There is a linear relationship between the bed shear stress(BSS) of chamber bottom and the efficient water head of self-siphon sediment cleansing set, and a exponential relationship between the BSS and the siphon section parameter(1/S) under same efficient water head.4. The cleansing effect of self-siphon sediment cleansing set was investigated by sediment test. The results show that the first cleansing rate is the largest proportion in total cleansing rate. With the increase of operating number, the sediment surface tends to be stable and cleansing rate decreases rapidly. The first cleansing rate and total cleansing rate both increase with the increase of siphon section parameter(1/S), but its increase rate decreases with 1/S. When 1/S increases to a certain value, the cleansing rate do not increase obviously.5. In the numerical simulation of solid-liquid two-phase flow, there is strong relationship between particle settling phenomenon on boundary and local BSS. By applying the probability selection method of genetic algorithm to the boundary condition, the "probability sedimentation" model of particle was established. This model deals with collision behavior between particle and the bottom surface of chamber at viewpoint of settling probability, which makes up the defect of critical BSS model that the model can’t distinguish the settling difficulty degree and predict relative sedimentation amount. The "probability sedimentation" model was applied in the sedimentation simulation of model and actual CSO chamber, and the simulation results were validated by experiment and SONAR images of field measurement.