| With the migration and flow of sewage,a certain amount of muddy sand will inevitably be collected in the process.Due to China's vast territory and complex geological conditions,the corresponding water quality conditions of urban sewage in China are also complicated.The proportion of mud sand in the sewage and the fine sand(particle size<0.2mm)in the mud sand are significantly higher than those in the developed countries.However,according to the current domestic design manual,grit chamber is mainly to remove the objects are particle size of over 0.2 mm,density of about 2.65 t/m~3,ignoring the small inorganic grit removal in wastewater,this makes a lot of fine sand to flow into the subsequent processing unit,which is harmful to the operation of the subsequent processing equipment,and can obstruct or even destroy the biochemical treatment of sewage.To improve the effect of grit chamber pretreatment,avoiding sewage pretreatment to cause adverse effect to the subsequent biochemical treatment,strengthening the removal of fine sand and organic effective separation,In this study,the grille,the vortex grit chamber and the advection grit chamber are connected in series and organically.A new pretreatment process for sewage treatment named Vortex-Advecation grit chamber has been built,which is of great significance to sewage treatment.This study is based on the CFD calculation module of Fluent numerical simulation platform,respectively build the vortex grit chamber,the advection grit chamber,and the Vortex-Advecation grit chamber 3D model,based on the DPM Discrete phase model and the k-?turbulence model under the RANS,The grain size of the simulated influent water is that 10%for more than 0.45mm,15%for 0.3~0.45mm,30%for 0.2~0.3mm,30%for0.125~0.2mm,and 15%for less than 0.125mm.The total concentration of sand in the water is 400mg/L,and the organics in the simulated influent is that the water-soluble organics(specific gravity 1.12,particle size<0.45um)accounts for40%of the ratio,and the poorly soluble organics(specific gravity 1.44,particle size>0.45 um)accounts for 60%of the ratio,the total concentration of organics in the water is 300mg/L,through single factor simulation experiments,the solid liquid two-phase flow and particle trajectory of internal flow field in vortex grit chamber and advecation grit chamber under different boundary conditions are calculated,Then,on the basis of single factor simulation experiments,orthogonal simulation optimization experiments were conducted to study the removal effect of sand particles in different particle size ranges under different boundary conditions,defined the order of priority and the optimal parameters of each boundary condition.Then,under the optimal operating conditions of the grit chamber,the simulation experiment for the separation of sand particles and organic matter was carried out to explain the influence on the removal efficiency of organic matter of the Vortex-Advecation grit chamber.The main conclusions are as follows:1.The simulation results show that the influence for various boundary conditions on the total sand removal efficiency of the Vortex grit chamber is in turn as follows:the inlet velocity,the stirring speed of the blades,the distance between the blades and the bottom of the pool,the water inlet Angle,and the number of the blades.The optimal parameters of each boundary condition are:The inlet velocity is 1.0 m/s,the stirring speed of the blades is 25 r/min,the distance between the blades and the bottom of the pool is 25 cm,the water inlet Angle is 10°,the number of the blades is 4.At this time,The total desander efficiency was 70.95%,among it,the removal rate of sand with a particle size of over 0.45mm is 100%,that of sand with a particle size of 0.3-0.45mm is87.91%,that of sand with a particle size of 0.2-0.3mm is 75.42%,that of sand with a particle size of 0.125-0.2mm is 59.31%,that of sand with a particle size of less than 0.125mm is 48.97%,Organics removal efficiency is 8.73%;2.The simulation results show that the influence for various boundary conditions on the total sand removal efficiency of the Advecation grit chamber is in turn as follows:the pool width,the pool length and the pool depth.The optimal parameters of each boundary condition are:the pool length(L)is 6.7m,the pool width(B)is 1.4m,and the pool depth(H)is 1.6m.Considering the factors of floor space and the fine sand removal,take the pool depth(H)is 1.5m,the pond length(L)is 6.2m.At this time,The total desander efficiency was53.86%,among it,the removal rate of sand with a particle size of 0.3-0.45mm is 100%,that of sand with a particle size of 0.2-0.3mm is 64.17%,that of sand with a particle size of 0.125-0.2mm is 51.03%,that of sand with a particle size of less than 0.125mm is 40.36%,organics removal efficiency is 9.21%;3.Under the optimal operating conditions,the total sand removal rate of the Vortex-Advecation grit chamber is 81.94%,among it,the removal rate of sand with a particle size of over 0.45mm is 100%,that of sand with a particle size of 0.3-0.45mm is 100%,that of sand with a particle size of 0.2-0.3mm is86.01%,that of sand with a particle size of 0.125-0.2mm is 72.94%,that of sand with a particle size of less than 0.125mm is 61.72%,organics removal efficiency is 15.74%. |
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