Filtration Rotating disc filters

Kempken et al. [113] employed a rotating disc filter to harvest CHO cells, and observed that the filter could be operated at low transmembrane-pressure with high wall shear rates, leading to high filtrate flow rates, high product yields and minimum fouling. They concluded that their system offered a powerful alternative to conventional tangential flow filtration. 

Dynamic filtration modules are basically of two types rotating disc filter (RDF) and vortex flow filter (VFF). In the latter, the filtration module has a cylindrical shape and has a rotating concentric cylindrical mesh in its interior. The rotational movement of the internal cylinder generates a Taylor-Couette flow in the annular gap (Roth et al., 1997), creating Taylor vortices that minimize concentration polarization and mesh fouling. Continuous perfusion processes based on this type of filter and operating continuously for up to 100 days have been reported (Mercille et al., 1994). 

Continuous filtration is discussed by Coulson and Richardson.. It commonly employs rotary vacuum filters. These are usually cylindrical in shape, rotating about a horizontal axis with a filter medium on the curved surface and a vacuum applied from inside. Rotating disc filters are less frequently employed (see Fig. 2.4). These have a number of discs on the same shaft with vacuum applied from inside but the flat surfaces of the discs hold the filter medium. The methods of continuous discharge of the filter cake during operation, and of replacement of the filter medium at intervals, are less elegant than those applicable to rotating cylinders. 

Membrane filters include flat sheet, spiral wound, and hollow fiber (Fig. 23). In addition, there are also rotating discs, annual gap, and vibrating disc systems for membrane cross-flow filtration. 

Horizontal- or vertical-vessel filters with vertical rotating elements in particular have been under rapid development recently with the aim of making truly continuous pressure filters, particularly, but not exclusively, for the filtration of fine coal. There are basically three categories of continuous pressure filters presently available disc filters, drum filters and belt filters, the last category including both the hydraulic and compression varieties. For the purpose of this review, we shall also briefly consider some semi-continuous, indexing cloth filters and other types with intermittent movement of elements. Only those filters which discharge the solids in the... 

The filter discs consist of a number of sectors. Their number is dependent among other things on the diameter of the discs. The individual sectors have a grooved and/or perforated surface, which is covered both sides with the filter cloth. The discs rotate in the disc-filter trough and during one revolution, they go through one complete filtration cycle. Via the filtrate pipe system accommodated... 

Rather than using a continuous rotation of the filter elements or interstitial discs, another variant employs vibration of the elements to enhance filtration. In this case up to 100 double-sided, flat filter elements separated by thin spacers are clamped together within a cylindrical vessel and caused to vibrate by a motor drive assembly close to the resonant/natural frequency of the unit. The oscillatory motion in the plane of the horizontal elements produces a shear rate up to 150000 s which is many times greater than that observed in typical low shear crossflow filters. As the feed flow rate and... 

Assemblies of small discs are rotated in a planetary movement around a central screw conveyor. The discs are mounted on six hollow axles and the axles revolve on overhanging bearings from the gearbox at one end of the vessel where they are driven, via a drive shaft, by an electric motor. The filtrate is collected from the discs via the hollow shafts and a filter valve into a large collecting pipe. The hollow shafts also collect the water and air from the dewatering process, in another part of the rotational cycle. The number of... 

---