Dynamic filter

Washing by successive dilution is used when the soHds are separated into a slurry, such as in filter thickeners. The soHds, thickened into a small amount of mother Hquor, are diluted into a wash Hquid and then separated again, diluted, separated, etc until clean of mother Hquor. The consumption of the wash Hquid can be reduced in countercurrent washing systems, sometimes referred to as countercurrent decantation. Cocurrent dilution washing, however, can be built into some dynamic filter-thickeners such as the Escher-Wyss filter. 

Mechanical Cake Removal. This method is used in the American version of the dynamic filter described under cross-flow filtration with rotating elements, where turbine-type rotors are used to limit the cake thickness at low speeds. The Exxflow filter, introduced in the United Kingdom, is described in more detail under cross-flow filtration in porous pipes. It uses, among other means, a roUer cleaning system which periodically roUs over a curtain of flexible pipes and dislodges any cake on the inside of the pipes. The cake is then flushed out of the curtain by the internal flow. 

Since its conception, the dynamic filter has been widely reported and further developed. Most European designs are comprised of a multistage disk arrangement (Fig. 28) with both the rotating and stationary elements covered with filter cloth, thus utilising the space inside the pressure vessel. Such filters have been found (29) to be from 5 to 25 times more productive in mass of dry cake per unit area and time than filter presses for the same moisture content of the final slurry. In some cases, the moisture content with the dynamic filter was actually lower than with a filter press. The maximum productivity was achieved with peripheral disk speeds from 2.8 to 4.5 m/s. 

The axial filter (Oak Ridge National Laboratory) (30) is remarkably similar to the dynamic filter in that both the rotating filter element and the outer shell are also cylindrical. An ultrafiltration module based on the same principle has also been described (31). Unlike the disk-type European dynamic filters described above, the cylindrical element models are not so suitable for scale-up because they utilize the space inside the pressure vessel poorly. 

The American version of the dynamic filter, known as the Artisan continuous filter (Fig. 30), uses such nonfiltering rotors in the form of turbine-type elements. The cylindrical vessel is divided into a series of disk-type compartments, each housing one rotor, and the stationary surfaces are covered with filter cloth. The feed is pumped in at one end of the vessel, forced to pass through the compartments in series, and discharged as a thick paste at the other end. At low rotor speeds the cake thickness is controlled by the clearance between the scraper and the filter medium on the stationary plate, while at higher speeds part of the cake is swept away and only a thin layer remains and acts as the actual medium. 

It should be noted that research has shown that there may be significant differences between static and dynamic filtering. 

Dynamic filters, 11 383-387 Dynamic flow calibration, 11 651-652 Dynamic gassing-in kLaL measurement method, 15 680-682... 

European dynamic filter, 11 384 European Inventory of Existing Chemical Substances (EINECS), 26 901 European Molecular Biology Laboratory (EMBL) database, 12 512 European patent, 18 198 European Patent Classification (ECLA) scheme, 18 209, 230 European Patent Convention (EPC), 18 189, 191... 

Karl Fischer titrators, 23 477 Karmen-vortex street, 11 668 Karr RPC plate, 10 779-780 Karstedt s catalyst, in silicone network preparation, 22 563 Karstenite, 5 785t Karyoplasts, 12 451, 458 Kashin-Beck disease, selenium and, 22 101 Kaspar s dynamic filter, 11 384 Katapinands, 24 44 Kauri-butanol value, 23 89 Kazakhstan... 

Table 7. Overview of reported perfusion processes employing dynamic filters as cell retention device... 

This system in its linear version (i.e., when e = 0) is a dynamical filter. Suppose that the oscillators interact with each other with the interaction parameter a = 0.9. The frequency 00 of the external driving field varies in the range 0 < < 4.2. The other parameters of the system are A 200, coq 1, c 0.1, and = 0.05. The autonomized spectrum of Lyapunov exponents A-4, >,5 versus the frequency to is presented in Fig. 23. In the range 0 < < 0.2 the system does not exhibit chaotic oscillation. Here, the maximal Lyapunov exponent Xi = 0 and the spectrum is of the type 0, —, —, —, (limit cycles). 

FIGURE 2. Dynamic filtered deformation electron-density distribution of cyclopropane (1). Sections (a) in the ring plane and (b) in the crystallographic mirror plane, perpendicular to the ring plane. Contours are at 0.05 e A 3 intervals, dashed lines represent negative areas. Reproduced by permission of the International Union of Crystallography from Reference 23b... 

Castilho LR, Anspach FB (2003), CFD-aided design of a dynamic filter for mammalian cell, Biotechnol. Bioeng. 83 514-524. 

Castilho LR, Anspach FB, Deckwer W-D (2002), An integrated process for mammalian cell perfusion cultivation and product purification using a novel dynamic filter, Biotechnol. Progr. 18 776-781. 

Castilho LR (2001), Development of a dynamic filter for integrated perfusion cultivation and purification of recombinant proteins from mammalian cells, Fortschritt-Berichte Series - Reihe 17 (Biotechnologie/Medizintechnik), VDI-Verlag, Diissel-dorf. 

Weight of moving object 9—Speed 15—Dynamic Filter can rotate. As it gets heavy with dusf it rotates to a new section... 

In some cases of pilot scale filtration, entire units have been enclosed as a secondary containment precaution (see Chapter 8). A recent commercial development is the MBR-Sultzer dynamic filter which is available in three sizes. Dynamic filtration is the same as cross flow filtration with little or no recirculation. The cross flow effect is derived from the spinning of the inner surface filter. This type of filter is more efficient, has a lower pump rate and a much higher linear velocity across the filter surface, than conventional cross flow filtration units. There is also little or no damaging effect on sensitive cells. The medium size has the same capacity as the Westfalia SA-7 separator. Van Hemert and Tiesjema concluded that the dynamic filter is suitable for work requiring strict aseptic and primary containment conditions. The use of a double mechanical seal on the rotating shaft could offer a higher degree of containment if required. 

This is a method by which the cake is prevented from forming by the mechanical action of brushes, scrapers or liquid jets. Tiller showed theoretically that the capacity of a drum or belt filter can be increased by using brushes to keep the cake off a portion of the available filtration surface, with the remaining portion used for normal filtration of the thickened slurry. The reduction in filter area available for cake formation need not lead to reduction in solids handling capacity because the thicker slurry would give faster cake build-up. This method has not caught on in practice, with the exception of the scraping action of the turbine rotors used in the American version of the dynamic filter (see section 11.6). 

Figure 11.5 European dynamic filter (only two stages shown)...

The so-called axial filter , developed in the Oak Ridge National Laboratory, is remarkably similar to Morton s and Kaspar s dynamic filter in that the filter leaf is in the tubular form and the outer shell is also cylindrical. An ultra-filtration module based on this principle has also been described more recently. Unlike the European dynamic filters referred to in the previous paragraph, however, this filter is not suitable for scale-up because it poorly utilizes the available space. The Escher-Wyss pressure filter described (identical copy of this paper also appeared subsequently in Filtration and Separation ) takes the idea of axial filtration a step further in... 

The American version of the dynamic filter, known as the Artisan continuous filter Figure 11.7), uses turbine-type elements as rotors and... 

Murkes has reported tests with the same American dynamic filter, except that he eliminated cake formation altogether by spinning the discs faster. No visible abrasion of the medium was observed while the filtration velocities could be maintained high even at relatively low pressures, below 5 bar. Murkes showed clearly the effect of speed and number of rotor vanes on filtration velocities and specific energy input. His results show, for any number of rotor vanes, an increase in specific energy input (kWh per m of filtrate) with rotor speed this increase can be minimized by optimization of... 

Malinovskaya, T. A. and Kobrinsky, I. A., The separation of finely divided suspensions in a dynamic filter . Mechanical Liquid Separation (9th Symp.), Magdeburg, Oct., pp. 47-51 (1971)... 

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