Multiphase Flow Simulation And Sludge Discharge Optimization Of Horizontal Flow Sedimentation Tank Based On Fluent

With the rapid development of social economy and the improvement of people's quality of life,water environment problems have emerged in recent years.In order to deal with water environmental problems,the 13th Five-Year Plan proposed and deepened the quality improvement and sludge disposal of the water treatment industry.In response to the call of the"Thirteenth Five-Year Plan",this paper studies the main factors,affecting the performance of sludge-water separation and sludge sedimentation distribution of the horizontal flow sedimentation tank,and explores the law of sludge settling funnel discharging sludge by the method of CFD.By comparing and analyzing the operation status of the horizontal flow sedimentation tank,the design values of the main parameters are optimized,and the optimization method of sludge discharge is provided in details.This study aims to improve the performance of the sedimentation tank,optimize the sludge removal process,and reduce the operating cost of the water purification plant.Currently,sedimentation tank design is based on ideal conditions to determine its size with residence time.Regardless the influence of the shape,size,temperature,wind speed,density flow and other factors on the flow field,the water flow in the sedimentation tank moves in a laminar flow state with a uniform flow rate.In order to study the operation of the actual sedimentation tank under different conditions,a mathematical model of turbulent flow and multiphase flow were established for numerical simulation.The main work of this research is mainly divided into four parts:(1)By comparing and analyzing literature experimental results and meshing results,the numerical model selected Euler multiphase flow mathematical model and Realizable k-?turbulence mathematical model,and used the method of mixed mesh cell division.The numerical model of the S.A.Kantoush experiment was established.The comparison found that the simulation results were in good agreement with the experimental values,which verified the accuracy of the numerical simulation.(2)The simulation results determined that the actual residence time of the sedimentation tank was 8000 seconds,and the numerical simulation was performed by changing the slope of the tank bottom and the number of finger grooves respectively.The results of changing the bottom slope of the tank indicate that:within the range of 0-0.02 bottom slope,increasing the bottom slope increases the effective sedimentation volume of the sedimentation tank,which can improve the sedimentation effect of the sedimentation tank and promote the sludge settlement.It is recommended that the bottom slope of the horizonal sedimentation tank with sludge settling funnels and with perforated sludge discharge pipes are set between 0.01-0.015,and the specific value depends on the actual project.It is recommended to set the slope of the horizonal sedimentation tank with machinery to 0.005,which can be fine-tuned according to the actual project.The setting of the finger groove affects the flow velocity and velocity gradient near the outlet,which ultimately affects the sludge settling performance and sludge sedimentation distribution.The number of finger grooves should be set to ensure that the turbulent energy of the advection sedimentation tank is greater than 0.001m~2/s~2,but to avoid the sludge being lifted due to excessive flow velocity.The optimal number of finger grooves is 7.(3)The particle size and the sludge density of the sludge were changed respectively,and the numerical simulation of the horizonal sedimentation tank with sludge settling funnels was carried out,which shows that the particle size and the density of the sludge is positively correlated with the sludge settling.The sludge with a particle size greater than 150?m and the sludge with a density greater than 1200 kg/m~3 are more likely to settle.(4)Carry out the sludge discharge operation of the horizonal sedimentation tank with sludge settling funnels that runs for 12 hours.The results show that reducing the roughness of the inclined wall surface of the bigger sludge settling funnels improves its sludge discharge efficiency.Due to the difference between the bigger sludge settling funnels and the smaller ones,the sludge discharge time should be set separately.The economical discharge time of the smaller sludge settling funnels are 5 minutes,while this time of the bigger ones are 10 minutes.