Numerical Simulation And Optimization Of The Uniform Media Filter Backwashing

The backwashing of the filter material layer is an important link to restore the normal interception capacity of the filter.In this paper,the CFD technology is used to simulate the backwashing and surface sweeping of the filter material layer of the homogeneous filter material at a three-dimensional scale.The simulation results optimize the backwash strength and structural parameters of the filter.The Euler-Eulerian multiphase flow model and the RNG k-εturbulent flow model are used in the numerical simulation of the backwashing of the uniform media filter,and the particle flow theory is introduced into the force between particles.Verified by empirical formulas and experimental devices,the relative errors of the simulated values are within a reasonable range.Through the simulation,the distribution of the axial velocity of the particles and the circulation of the filter material can be obtained.At the same time,the requirements of the expansion rate during backwashing are considered,and the flushing strength of different particle sizes of filter media in single-water flushing and gas-water flushing is optimized respectively.The results show that when the particle size of the filter material is1.0mm,1.2mm and 1.4mm,the appropriate water intensity for single water flushing is the minimum fluidization speed plus 5L/(s·m~2),and the suitable gas intensity for simultaneous gas and water flushing respectively is 12.5～15.0L/(s·m~2),15.0～17.5L/(s·m~2),17.5～20L/(s·m~2);The average kinetic energy of the filter material surface during simultaneous air and water washing is much larger than that of single water washing,which proves that the effect of simultaneous air and water washing is better than that of single water washing.The Euler-Lagrangian multiphase flow model and the Realizable k-εturbulent flow model are selected in the numerical simulation of filter surface cleaning,The Eulerian-Lagrange multiphase flow model adopts the VOF model and the DPM model respectively;The surface sweeping effect was evaluated through the analysis of the particle escape time,the proportion of non-escaped particles and the streamline-velocity diagram,the structural parameters and the surface sweeping intensity were optimized,and the differences between gas sweeping and water sweeping were compared.The results show that the wider the sweeping width,the worse the sweeping effect,When the sweeping width is greater than 3.2m,the proportion of non-escaping particles will be greatly increased.the sweeping width should not be greater than3.2m.Properly increasing the sweeping hole area can eliminate the existence of eddy currents,can improve the cleaning effect,the best effect is when the diameter of the cleaning hole is 32mm-35mm;properly increasing the height of the cleaning hole can eliminate the existence of eddy current and increase the surface water flow velocity,improve the cleaning effect,the cleaning hole is higher than the drainage The best effect is when the top of the weir is 0.1 m;there are suitable sweeping strengths for different levels of sweeping width,sweeping hole area and sweeping hole height.Air scavenging reduces the existence of eddy currents,and the suitable surface gas scavenging intensity is 4L/(m~2·s).Compared with water scavenging,air scavenging reduces particle escape time by 10%.