Rotary vacuum disc filters

Figure 1.27 Schematic side view of a rotary disc vacuum filter [left) and photograph, with permission from Ceramec, of a multiple disc filter installation fitted with ceramic elements (right).

Rotary disc vacuum filter, ceramic None 4C 9 0 8 21 1-700 5-20... 

Rotary disc vacuum filters have the advantage, compared with rotary drum filters, of giving a much larger filter area per unit of floor area. They are thus particularly suitable for the processing of bulk products, for example in coal preparation, ore dressing, pulp and paper processing, and so on. 

The principle of construction of a rotary disc vacuum filter is that a number of filter discs are mounted, parallel to one another, on a horizontal shaft. Each disc... 

The most common types of filters used in industrial processing are pressure filters such filter presses, leaf filters, and cartridge filters, as well as vacuum filters like the rotary drum vacuum filter, and the rotary vacuum disc filter. Most filtration units produce a cake, which at long cycles may become reasonably dry at the expense of declining the flow rafes. Keeping consfanf... 

Filtration and washing of filter cake on a flat disc rotary vacuum filter ... 

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. 

Another idea borrowed from vacuum filtration to produce a continuous pressure filter is the rotary-dmm filter. This filter has the disadvantage that it makes relatively poor use of the space available in the pressure vessel and the filtration areas and capacities of such filters cannot possibly match those of the disc pressure filters. In spite of this disadvantage, however, the pressure drum filter has recently been extensively developed. 

Disc filters are similar in principle to rotary filters, but consist of several thin discs mounted on a shaft, in place of the drum. This gives a larger effective filtering area on a given floor area, and vacuum disc filters are used in preference to drum filters where space is restricted. At sizes above approximately 25 m2 filtration area, disc filters are cheaper but their applications are more restricted, as they are not as suitable for the application of wash water, or precoating. 

Several of the eontinuous filtration units discussed below may be operated in pressure and vacuum conditions thus the continuous rotary vacuum drum, disc or hnmimtsjl belt filter can be enclosed in a pressure v seL Separation may then ensue by use of a gas pressure blanket in the vessdL This technique is oflen used in solvent fihrations. Some processes m the simultaaeous use of pressure upstream, with vacuum downstream of tire filter in this maimer, the continuous filtration characteristic can be coiqiled with fairer filtration dif ential pressures. 

Fig. 2.4. Rotary vacuum disc filter (Automatic Coal Cleaning Co. Ltd. and Davey, Paxman and Co. Ltd.).

Fabrics produced from staple spun fibres usually have a weight between about 400 and 700 g m (see Table 2.7), and find applications in conventional filter presses, vacuum leaf, pressure leaf, disc and rotary dmm filters. 

Hydrate product Rotary vacuum disc filter Crystalline/coarse 5, 9, 14 Resists stretch and abrasion. 

Figure 5 Rotary vacuum disc filter (Eimco). (From Osborne, 1990.)...

The capillary disc filter looks like any other standard rotary vacuum disc filter, as can be seen in Figure 3.25, but the filter medium is a finely porous ceramic disc, which draws filtrate through the disc material by capillary action, under the applied vacuum. The filter discs are made of sintered alumina with uniform micropores less than 1 pm in size, which allows only liquid to flow through it. Despite an almost absolute vacuum, no air penetrates the filter material. The disc material is inert,... 

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