Research On The Distribution Of The Suspension Of The Presedimentation Tank

The pre-sinking tank is an important part of the water source pumping station.It is the first line of defense for the sedimentation of suspended sediment and suspended solids in the raw water.It can remove the deposits and floating objects in the raw water and reduce the load of the subsequent treatment facilities.This paper takes a water intake project as the background.Raw water enters pre-settler and aeration tank of intake pump house by self-flow through dyke.After sedimentation and aeration,the pressure is increased.Then the water fed to the next pumping station through the pipeline.The deposition of suspended solids in the pumping station greatly reduces the water supply efficiency and the water quality,which has a great impact on the urban water use of the water receiving area.In this paper,CFD technology is used to study the distribution of suspended solids in pre-sinking tanks under various flow conditions,different water level elevations,different sediment concentrations and different suspended solids particle sizes.The research results provide corresponding basic data for the study of subsequent pre-sinking technology and pipeline deposition law.(1)Commercial software ANSYS 14.5 was used to simulate the distribution of suspended particles in precipitation tank.The Mixture model of Euler-Euler model is chosen as the multiphase flow model.The residual curves of the four models of the standard k-? model,the RNG k-? model,the Realizable k-?model and the k-? model are compared,and the standard k-? model is finally used for the simulation calculation.Through the grid-independent analysis,it is determined that the total number of grids calculated is 9.85 million.(2)Study on the settlement law of suspended solids in pre-sinking pool of water pumping station.Because of the existence of submerged weir at the entrance,the movement of the water flow is relatively severe.There are one large and one small recirculation zones around the perforated wall.There is also a recirculation zone end of pool after drowning over the overcurrent.The recirculation zone is easy to drive the suspension to move,and it is not easy to settle.In general,the closer to the bottom of the pool,the more the suspended solids settle in the pre-sinking pool,due to the effect of the tail drowning over the overcurrent,the volume fraction of the sedimentation situation of the entire pre-sinking pool shows a trend of reducing first and then increasing from the inlet to the tail.(3)Study on the sedimentation law of suspended solids in the pre-sinking tank of the water pumping station under different flow rates and water levels.The discharge of water source is different from that of long-term maximum day,long-term average day,long-term minimum day,initial maximum day,initial average day,initial minimum day and bottom-guaranteed operating water level.The settling law of suspended solids in pre-settler under different flow rates is analyzed.The smaller the inlet flow rate is,the higher the suspended matter content behind the perforated wall is,the larger the area of the high sediment content area at the front of the bottom of the pre-settler,and the lower the suspended matter content from the flow to the submerged weir.Distribution of suspended solids in pre-settler under low water level,normal water level and high water level conditions is analyzed.The higher the water level,the greater the amount of suspended solids deposited at the bottom of the pool.However,at the high water level,the volume of the suspended solid entering the pre-sinking tank is the largest,and the height of submerged weir is much smaller than the high water level.The submerged overflow weirs do not block sediment very well,so the removal efficiency of suspended solids is the highest at constant water level.(4)Study on the sedimentation law of suspended solids in the pre-sinking tank of the water pumping station at different suspended solids content and particle size.at the entrance.The sedimentation rate of suspended solids in the pre-sinking tank increases with the increase of the concentration of suspended solids.When the concentration of suspended solids reaches 0.132kg/m3,the sedimentation rate of suspended solids in the pre-sinking tank decreases.As the particle size of the influent suspension increases,the sedimentation rate of the suspended solids in the pre-sinking tank increases.When the particle size of the incoming suspension continues to increase,the sedimentation rate of the suspended solids in the pre-sinking pool continues to increase,but its growth rate begins to decrease.(5)Study on the sedimentation law of suspended solids in the pre-sinking tank of the water pumping station at the different structure of the pre-settling tank.Comparisons were made by changing the bottom slope to 0.017 and 0.035,and the height of submerged weir to 1.5m and 2.35m.When the slope at the bottom of the pond increases,it will promote the deposition of suspended sediment to a certain extent,but at the same time it will greatly reduce the height of the submerged weir,greatly reduce the sedimentable depth,which is not conducive to the deposition of suspended sediment.When the bottom slope of the pre-settler is 0,the sedimentation rate of suspended solids in the pre-settler is the highest.When the height of the submerged overflow weir increases,it has little effect on the velocity along the flow direction of the characteristic section of the pre-settler,but the settlement rate of suspended solids in the pre-settler increases with the height of the submerged overflow weir.