Research And Improvement Of Large Continuous Sand Filter

Continuous sand filter is one of the equipment widely used in water treatment,and it has an important position in the filtering field.This thesis mainly studies the history,status and tendency of the development of the sand filter,expounds the structure,principle,types and advantages of continuous sand filter.According to the present 514 ternary sewage treatment station actual problems of the large continuous sand filter,I designed and improved the three-phase washing machine,water distributor device and sand lifting device.On the basis of the original design of the large continuous sand filter,the structure of it's tank,roof and winding staircase components are improved.Meanwhile,it demonstrated the type of filter material,diameter of filter material and filter layer thickness of the large diameter 4m of the continuous sand filter.Finally,0.6?1.2mm quartz sand filter material was selected,and the filter layer thickness is 3.2m.A complete large continuous sand filter was built by modeling the designed and improved parts with 3d software Creo.By setting the standard deviation of the velocity as the basis for evaluating the distribution uniformity,this thesis used the CFD software to numerically analyze the distribution function of the distributor.The simulation results show that the variance of velocity in any plane is the smallest and the distribution of water is the most uniform when the number of holes in the distribution n_kis 21.The optimal range of D_kdiameter of the distribution hole is 10d_l,maxto D_j/3,where d_l,maxis the maximum particle size of the filter material,and D_jis the inner diameter of the branch pipe of the distributor.To some extent,increasing the angle between the axis of the branch pipe and the horizontal plane of the water distributor can improve the uniformity of the water distribution.The optimal angle?between the axis of the branch pipe and the horizontal plane is?_maxminus 3°?5°,where?_maxis the maximum included angle when the branch pipe interfere with the tank.By setting up a small experimental device for orthogonal test,the optimal operating parameters were optimized:the oil removal effect was the highest when the filter particle size is 0.6-1.2mm,the filter speed is 4m/h,the filter thickness is 1.8m,and the circulation rate less than 2 mm/min.The suspension removal effect is the best when the filter particle size is0.6?1.2mm,filtration rate is 4m/h,filter thickness is 1.0m and the circulation rate is 2?4mm/min.The performance test of the sand lifting device shows that,the fluid form in the sand lifting tube is bubbling type when the air intake is 1.8?3.5 L/min.The fluid form in the sand extraction tube is nodal inrush type when the air intake is 5?12L/min.The flow in the sand extraction tube is turbulent type when the air intake is 15?21L/min.The fluid form in the sand extraction tube is fast type when the air intake is less than 25L/min.The first cleaning effect of the filter material in the sand extraction tube is the best in turbulent flow state.The relationship between the air intake and the sand circulation rate at different pressures was studied in this thesis,and the corresponding line chart was drawn.The defects of the original gas box structure were found by observation test.Then,the structure was improved,including adding screen?screen for the cracks in the filter material minimum size of 70%?80%?and changing the direction of air inlet to tangential.The improved gas box effectively avoids the back-flow of the filter material into the air pipe,and the air flow in the gas box is stable and smooth,and there is no fixed accumulation of the filter material.It can ensure the long-term stable operation of the sand lifting pipe and extend the service life of the large continuous sand filter.