Research On Flocculation Removal Of Pollutants By Different Flow Structure

Flocculation precipitation is an important process of sewage treatment,and the hydraulic condition provided by the flocculation tank is the decisive factor of the flocculation precipitation effect.In current engineering practice,full mixing and the physicochemical reaction of reagents and water are achieved by mechanical stirring.Among them,flocculating mixer is used in the flocculating stage of sewage treatment to promote the collision between colloidal particles,so that alumen ustum can be formed to precipitate to achieve the removal of pollutants.Therefore,the flow pattern of the working medium produced by the mixer has an important impact on the flocculation effect.The flocculation effect of pollutants was studied with flow structure as the entry point in this paper.To improve the intensity of turbulence and greatly increase the surface roughness of the blade,an innovative step-shaped blade surface structure has been designed,so that computational Fluid Dynamics(CFD)and prototype tests can be done to verify the effect of different flow structures on flocculation precipitation.The main work and findings are as follows:1.Based on the basic theory of velocity loop distribution and the principle of blade design optimization,on the premise of achieving basic flow,the stepped blade was innovatively designed with the changing of the blade surface shape to increase the turbulence intensity of agitation;2.With the help of CFD simulation software and the new simulation research scheme of temperature field distribution and solid-liquid two-phase flow distribution as well as the evaluation index of mixing effect,the flow patterns generated by different types of blade stirring equipment in the efficient sedimentation tank were studied.It is found that the stepped blade would produce a violent turbulent structure in the blade boundary layer,which would affect the overall flow pattern in the working area.The stirring effect of the stepped blade is significantly better than that of the conventional blade under the condition of medium-low speed rotation.3.Designed and manufactured a small integrated high-efficiency sedimentation tank test prototype,and carried out experimental research on different blades.In the case of the same power,the removal effect of pollutants in the incoming and outgoing water samples was analyzed.It is found that the stepped blade has a higher pollutant removal rate in the stirring process,and the high-efficiency sedimentation tank device with the stepped impeller can achieve the pollutant removal rate of the conventional impeller under the condition of low flocculant dosage.4.The simulation results were compared with the test data,and the reliability of CFD numerical calculation was verified based on computational simulation.According to the CFD simulation and test results,the correlation between fluid dynamics analysis,flocculation precipitation,and pollutant removal was established.Changing the hydraulic conditions to change the flow structure in the flocculation area,has positive significance to optimize the wastewater treatment process and also provides a new idea for the design of stirring blades.