| It is an innovative measure to deal with the safety risk of water source and water quality by building a front-loaded storage tank to delay the time for contaminated water to enter the plant and leave space for emergency response.The first pump station of Zhenjiang Water Supply Company draws water directly from the Yangtze river.When dealing with several sudden water source pollution accidents in the lower reaches of the Yangtze river,the response time is short and the emergency disposal is hasty,which brings certain influence to the water supply safety.In order to solve this problem,the company carried out the water quality security project construction,The project consists of inlet sluice,two-way pump room,front storage pool,emergency disposal system,etc.The time of raw water entering the plant has been extended from 15 minutes to about 12 hours,which ensures sufficient time for testing and emergency response,and enhances the ability to deal with the water quality safety risks of raw water from the Yangtze River.Due to the very slow speed of the water flow in the storage tank,the sediment is easy to be deposited in the front end,so it is necessary to make clear the distribution of the sediment after a period of operation of the project.In this paper,Fluent software was used to conduct numerical simulation of the flow field of the storage tank under different operating conditions,and field measurement was carried out.The results show that the simulation and measurement results are basically consistent.Then apply EFDC hydrodynamics(environment)software within the storage pool on sediment deposition in the simulation calculation,the engineering operation a year later to regulate distribution of sediment deposition in the pool,deposition parameters such as height,provide the basis for desilting,finally analyzed before and after the construction of storage pool sediment subsidence due to effects on water coagulation precipitation effect.The main conclusions are as follows:(1)The average flow velocity in the storage tank is small,about 0.05m/s.The flow velocity at the inlet of the storage tank(0-50m)is large,and the flow velocity decreases rapidly after a 60° turning(50m).The flow rate of the first corridor was stable at 0.05～0.06m/s.After turning at 180°,the flow velocity fluctuated greatly.In the front section of the second corridor,the flow velocity gradually increased and stabilized at 0.04～0.05m/s.At the end of the storage tank(1500-1800m),the flow rate is basically 0,and the simulated and measured results are basically consistent.(2)Under normal water inlet conditions,the sediment deposition range is distributed at the front end of the reservoir,specifically before the 60° turning of the reservoir body.The sedimentary horizontal distance is about 70m,and the sedimentary area is about 200m2.The maximum sediment accumulation height is about 1.4m,located about 20m near the water inlet,and the average sediment accumulation height is about 50cm.If the perforated wall is set at the inlet to make the reservoir uniformly fill with water,the sediment deposition range is significantly reduced,and the sediment is basically evenly distributed near the perforated wall,the horizontal deposition distance is only about 15m,and the deposition area is about 100m2.The maximum accumulated height of sediment is about 2m,located around the perforated flower wall,and the average accumulated height is about 1m.(3)Due to sediment settlement,the turbidity of the raw water from the storage pond decreases,which brings a certain negative impact on the operation process of the water plant and achieves the same sedimentation effect.The dosage of coagulant needs to be increased by about 6%-8%.Therefore,the construction of the front storage pool does not have a great impact on the subsequent process of the water plant. |
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