Application Of Continuous Sand Filter

Filtration is the key link of wastewater treatment. Traditional filter has many defects. It can't be backwashed completely, it's easy to be blocked, also it has to be stopped when it's time to backwash it. This dissertation developed a continuous sand filter with its filter media moving downwards to the bottom of the filter. Therefore, the layer can't be blocked and the filter can run without shutdown. Also, the media keep clean all the time.Based on the work principle of filtration and the theory of fluid dynamics, one this kind of filter was designed. Then, experiments and simulations were taken about it. By analyzing the data, we get reasonable operating parameters of the filter and some suggestions were put forward to ameliorate the structure of the filter.Many innovations take up in the design of the filter in this dissertation. The holes in the pipe branches of the distributor are distributed equably. It can not only distribute the water equably on the cross section of the filter, but also make the filter layer be used efficiently. Rotating flow sand washer can separate sand from water to the greatest extent. The nozzle is installed horizontally, so it's not easy to be blocked.Through the experiments, we get some conclusions. The optimal diameter of sand extraction pipe is 28mm; the performance of sand extraction system is best when the pressure of compressed air is 0.3MPa; the flow pattern in sand extraction pipe is sluggish flow when the compressed air flow rate is between 0.25～0.80m3/h; the velocity of sand circulation in the filter is 7～9mm/min; the length of sand washer should be longer to get better sand wash efficiency; the turbidity of feed water has large impact to filtration efficiency, the purified water can be reused directly if the feed water is in low turbidity and the results will be opposite if the feed water is in high turbidity. The results of flow field and pressure simulation demonstrate that homogenous flow rate spreads all over the filtration layer while a large gradient shows in the distributor. For these reasons, it's thought that there are still some defects in the design of the filter. The diameter of the filter's inlet should be increased and the holes'diameters in the pipe branches should be enlarged. Furthermore, the length of sand discharge pipe should be extended. In the course of simulation, DPM model is used to track the traces of particles. Obvious traces are displayed in this dissertation. By analyzing the results, ideal filtration efficiency is obtained. It's about 88.5%.