Research and analysis of dynamic filtration technology

outlined

Dynamic filtration is based on liquid pressure and centrifugal force as thesolid-liquid separationThe driving force of the slurry in the filtration process is always parallel to the filtration media flow, filtrate through the filter media, in the filtration media does not accumulate or only a thin layer of cake on the dynamic thin layer of cake or no cake layer of filtration. The thin layer of cake or no cake layer is mainly caused by the high-speed shear flow of the fluid produced by the shear force to inhibit the growth of the cake layer. Adopting the dynamic filtration principle of rotary lobe filter press is a new type of filtration equipment, domestic and foreign on the mechanism of fluid flow within the filter chamber has carried out a lot of research. Because the tangential velocity of fluid flow directly affects the size of the shear force and filtration rate that suppresses the cake, many analyses and studies have been conducted on the tangential velocity of the fluid.

Shirato, a Japanese scholar, first studied the tangential velocity of fluid in a closed filter chamber without a filtration process and without fluid inflow conditions at the time of laminar flow condition in 1986;

In 1991, Yamaznki et al. assumed the expression for the tangential velocity of the fluid in the turbulent state under the same conditions as described above, and carried out an experimental research group using Newtonian-type and non-Newtonian-type fluids conforming to the power function law, respectively. With the deepening of the research on the rotary lobe filter press, attention is paid to the study of the internal dynamic law of the rotary lobe filter press which is similar to the actual working conditions. In 1988, Lu Weiming, a scholar from National Taiwan University in China, studied the relationship between filtration and fluid flow rate, shear stress and filtration rate under the conditions of one-side filtration and flow rate for the fluid inside the filter chamber in laminar flow condition (Reynolds number Re<104).

Tianjin University, since the 1980s, has also been interested in rotary lobefilter pressA large number of experimental studies have been carried out on the fluid flow law inside the filtration chamber, and some experimental conclusions have been obtained by simulating the double-sided filtration under the actual working conditions. However, the research is still in the theory of certain assumptions and simplifications, the experimental and testing methods are relatively simple, and it is difficult to achieve high testing accuracy. Scholars at home and abroad on the dynamic rotary lobe filter press fluid flow within the filter chamber has carried out a lot of research, but due to the complexity of the structure and flow state within the filter chamber, only a preliminary discussion of laminar flow in theory, the simplification and the experimental conditions are mostly with the actual working conditions have a big difference, and can not be a true description of the flow of the fluid condition. The dynamic rotary lobe filter press is different from the main features of the traditional filtration device is that it can make the fluid inside the filter chamber parallel to the flow of the filter medium, high-speed shear flow generated by the shear force to inhibit the growth of the filter cake, thereby reducing the filtration resistance and improving the filtration rate. Therefore, after the actual industrial application experiments, with appropriate methods to analyse the flow conditions within the entire filter chamber, control the thickness of the filter cake, calculate the filtration flow rate, has a great value of engineering applications.

Experimental Procedure and Installation of Filter

This process is designed according to the production process of Huashu Pharmaceutical Factory, the filtration system is able to complete the material filtration and two kinds of low unit liquid washing cake filtration simultaneously in the filter press, which is a comprehensive two-step production process. The core of the system is a dynamic rotary lobe filter press, the structure of the filter section, the impeller and five layers of metal filter surface spacing is 5mm, the impeller diameter is for 500mm, the diameter of the filter plate @ 600mm, fitted with seven impellers and six double-sided filter plate. Through frequency conversion adjustment, the experimental machine works at different rotational speeds, and the valve of the feed pump is controlled to adjust the inlet pressure and the washing liquid inlet pressure, so as to achieve the balance of material pressure and flow rate. The experimental materials were hygromycin dilution solution and crystallization solution, the filtration of dilution solution, the filtration speed is very fast, the average filtration speed in two hours reached 0.27m3/m2~h, for the ordinary plate and frame filter press 7 times; the quality of filtrate is better than the plate and frame filter press, the transmittance is as high as 92, and it can be directly crystallized without decolourization, the transmittance of filtrate of the ordinary plate and frame filter press is only 82~85. The filter press is good at Filtering ultra-viscous bacterial filtrate material can work, but the filtration rate can only reach 0.103m3/m2-h, at this time the plate and frame filter press can not be filtered. Filter in the inlet pressure of 0.2 ~ 0.4MPa work well, too high a pressure will lead to cake compaction, filtration rate drops, and even the filter plate will be crushed. When filtering crystalline liquid, the filter speed of the filter press is stable, and when the inlet pressure is kept between 0.25 and 0.32MPa, the average filter speed is 0.23m3hnh, and the water content of the concentrated crystalline material is stable, and the dryness is 50%, which is lower than that of the hanging bag centrifugal filter. The experimental situation shows that the dynamic filter has a very good filtration performance, which is manifested in the high quality of filtrate, convenient cake control and fast filtration speed.

Theory of Dynamic Filtering Techniques

Dynamic rotary lobe filter press mainly adopts dynamic cake and cross-flow filtration technology. The filtrate passes through the surface of the filter medium to form a thin cake layer, and under the continuous rotation of the impeller, the cake is suppressed and reduced to keep the filtration stable. At the same time, the cake layer does not stay on the surface of the filter medium, but keeps moving to the edge of the filter plate, and then transfers to the final discharge port along the axial direction, which realises the thickness suppression of the dynamic cake layer and the flow of filter residue.

Dynamic filter development prospects

According to the relevant reports on the current development trend of the filtration and separation machinery industry, the domestic research in the field of technology and foreign research is roughly equivalent to the key product performance of the machine has been close to the level of the developed countries in the early 1990s, in recent years, the use of computer-aided analysis and design in the product design, the manufacture of new technology has greatly improved the quality of the product. Dynamic filtration technology in the three major chemical (oil, natural gas, coal), medicine, environmental protection and other industries have a great deal of use, dynamic filtration technology in the development of petrochemical industry, the use of large-scale pressure centrifuges and municipal sewage treatment of urgently needed large-scale filter presses on the application of the big advantage.

reach a verdict

Combining dynamic pressure filtration with centrifugal separation to overcome the unfavourable factors of difficult control of filtration differential pressure, unstable quality of filtrate and high humidity of filter cake discharge that appeared in the experiments, and improving the experimental dynamic filtration machine will promote the application of dynamic technology in the industry. Under the efforts of enterprise researchers, the application of dynamic filtration technology in domestic industry can be realised soon.