Disc stack

Typical uses Clarification and thickening to produce a solids sludge. 

Typical particle size and feed concentration range 0.1-100 pm and 0.05-2% w/w (self-cleaning and manual discharge), 0.5-10% w/w (nozzle discharge). 

Liquid-liquid mixtures can be separated and with more sophisticated units a three (two liquid and one solid) phase separation is achievable. In all cases, a sufficient density difference must exist between the phases present in the feed. 

Although several variants exist, the generic type is characterised by an imperforate bowl surrounding an inverted stack of 30-200 thin conical discs separated by 0.3-3 mm spacers. The disc spacing is dependent on the viscosity and solids content in the feed and needs to be fixed accordingly, lower viscosities and solids concentrations favour spacings below 1 mm. As the discs are spun on a common vertical axis the process suspension, which is fed centrally from the top, travels through the annular spaces between the discs. 

While disc stack centrifuges are able to accept a wide range of feeds they are both mechanically complex and expensive. Moreover, the close stacking of conical discs means that mechanical cleaning can be difficult, and resort is often made to chemical cleaning. 

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The horizontal plate filter requires attention on a regular basis to safety devices and automation features that accompany modern filters. The space above the filter should have a hoisting device and sufficient headroom to lift the entire disc stack and move it horizontally to a location adjacent to the filter tank. It is recommended to have a special rig that will hold the plate stack for maintenance since the bigger ones may reach a length 3 meters or more. Space must also be allocated for the cover which may be either if it is hinged or removed. 

Microbial cell recovery is carried out in a continuous disc-stack centrifuge. The centrifuge is operated at 5000 rpm for separation of baker s yeast. At a feed rate of 601/min, 50% of the cells are recovered. At constant speed, solid recovery is inversely proportional to flow rate. 

A centrifuge is fitted with a conical disc stack with an included angle of 29, and there are n flow passages between the discs. A suspension enters at radius r and leaves at radius r2. Obtain an expression for the separating power E of the centrifuge. It may be assumed that the resistance force acting on the particles is given by Stokes law. 

Figure 4.14. Separation of cell lysates containing pharmaceutical products, employing large-capacity centrifuges that are configured with tubular bowl (A), multi-chamber bowl (B), disc stack bowl (C), or decanter (scroll) bowl (D).

If a large space-time yield is also required in the laboratory application, a capillary gap cell (disc-stack) is a good choice (Fig. 22.11). Only the upper-... 

Decanters are frequently used in conjunction with disc-stack-type centrifuges in the pre-preparation of clear juices and juice concentrates, where the initial decanter treatment results in a partially clarified juice with a low level of suspended solids. This is followed by a clarification stage using a disc-stack whereby the solids are thrown outwards from the through-flow juice stream into a solids-holding space and automatically discharged therefrom as and when an optimum level of solids is reached (see Figure 3.6). 

Figure 3.6 Self-cleaning clarifier (disc-stack centrifuge). Source. Courtesy of Westfalia Separator Ltd.

Turning now to those molecules whose shape can be approximated by oblate spheroids, one arrives at the discotic phase. Here the average of the normals to planes of the molecules corresponds to the director. A fluid phase in which these normals point in roughly the same direction over a macroscopic distance is said to be discotic. If this factor is the only degree of order, the material is said to be in the nematic discotic phase. If, in addition, the discs stack in regular columns, the material is said to be in the columnar discotic phase. Such structures have been discussed in Section 4.5.1. 

Kempken R, Preissmann A, Berthold W (1995), Assessment of a disc stack centrifuge for use in mammalian-cell separation, Biotechnol. Bioeng. 46 132-138. 

Tebe H, Liitkemeyer D, Gudermann F, Heidemann R, Lehmann J (1997), Lysis-free separation of hybridoma cells by continuous disc stack centrifugation, Cytotech-nology 22 119-127. 

Capillary gap cell — The undivided capillary gap (or disc-stack) cell design is frequently used in industrial-scale electroorganic syntheses, but is also applicable for laboratory-scale experiments when a large space-time yield is required. Only the top and bottom electrodes of c.g.c. (see Figure) are electrically connected to - anode and cathode, respectively, whereas the other electrodes are polarized in the electrical field and act as -> bipolar electrodes. This makes c.g.c. s appropriate for dual electrosynthesis, i.e., pro duct-generating on both electrodes. 

Decanter centrifuges are well suited to high solids concentrations at feed rates between 1 and 100 m3/hr. They cannot achieve such high standards of separation as a disc stack machine, and are more difficult to engineer as truly hygienic or contained units. They are suitable for continuous operation and can discharge solids continuously. 

In accordance with the Invention, therefore, the chamber has at Its front end a section of reduced cross-sectional area. Weight, size and cost are reduced without seriously affecting the efficiency of noise reduction. The silencer may be built as an attachment or, preferably, the rear porfion of the chamber may be built around the barrel of the firearm, with communicating holes through the barrel. The heat absorbing material may be metal screen, which may take the form of apertured discs, stacked one upon another and preferably held In compression. Plating the screen with some metal such as tin before punching the discs will increase the stability of performance. ... 

Sheet filter media for depth filtration are typically made from cellulose fibers and diatomaceous earths compressed into a thin mat. These sheets are typically mounted in plate and frame filters. There are also some special filters available that consist of filter sheet discs stacked and sealed in modules, which fit in closed filter vessels. The filter sheets can be regenerated several times until they need to be (manually) replaced. 

FIG. 18-154 Disc stack-centrifuge bowls a) separator, solid wall (b) recycle clarifier, nozzle discharge. 

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