Stacked disc filters

Disc Filters Traditional types of large disc filter holders, if used at all for production purposes, are usually about 300 nun in diameter. The direction of fluid flow is from above the filter to below. The membrane is sandwiched between metal inlet and outlet plates equipped with the sanitary connections necessary to operate the filter. Because of the fragility of disc-type membranes, there must always be a support plate directly beneath the membrane. Support plates must be porous, often photoetched, chemically inert, and have minimal effects on flow rate. This often means an uneasy compronuse. Prevention of flow restriction requires extensive void space this acts against the plate s mechanical strength. Usually there is also a loose mesh drain plate beneath the support plate and resting on the outlet plate (Fig. 2). When serially stacked disc filters are used, each membrane requires its own support plate but there will only be one drain plate. 

Similar to the edge filter in appearance, in that it has an array of disc-shaped components held on a central core, the stacked disc filter differs because the discs are actually hollow, with filter media over the faces of the disc. It employs individual discs, porous on both sides - that are stacked over a perforated inner tube - with intermediate spacing washers creating a flow space between each pair of discs. 

The filter elements should remove particles of five microns, must be water-resistant, have a high flow rate capability with low pressure drop, possess high dirt-retention capacity, and be rupture-resistant. The clean pressure drop should not exceed five psig at 100 °F (38 °C). The elements must have a minimum collapse differential pressure of 50 psig. Pleated-paper elements are preferred—provided they meet these requirements. Usually, the pleated-paper element will yield the five psig clean drop when used in a filter that was sized to use depth-type elements. This result is due to the greater surface area of the pleated element, more than twice the area of a conventional stacked disc-type or other depth-type elements. 

Pulp filters. These filters employ one or more packs of filter-masse (cellulose fibers compressed to a compact cylinder) stacked into a pressure case. The packs are sometimes supported in individual trays which provide drainage channels and sometimes rest on one another with a loose spacer plate between each two packs and with a drainage screen buried in the center of each pack. The liquid being clarified flows under a pressure of 345 kPa (50 psig) or less through the pulp packs and into a drainage manifold. Flow rates are somewhat less than for disc filters, on the order of 20 L/(min m ) [0.5 gal/(min ft )]. Pulp filters are used chiefly to polish beverages. The filtermasse may be washed in special washers and re-formed into new cakes. 

Various materials (metal, paper, plastic) Sohd fabrications stacked discs, edge filters, wedge wire, wire wound... 

Edge (i) Stacked discs (h) Helical wound ribbon < Paper media are capable of extremely fine filtering. Metallic media have high strength and rigidity. 

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. 

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. 

BASF in Germany considered the use of the capillary gap cell (see Fig. 2.16 in Chapter 2) for this electrolysis. The cell consists of a stack of carbon discs closely spaced by 0.2 mm thick strips of an insulator. The electrolyte is pumped through the inter-electrode gaps and a voltage is applied to endplates so that a bipolar cell is formed. The cell design is compact, simple and cheap compared with a filter press cell and the tetraalkylammonium concentration could be reduced to below 0.5% without loss of yield and with an energy consumption below 3000 kWh ton . ... 

The edge filter is of a solid fabrication structure wherein the medium consists of the edges of a stack of specially formed washers or thin discs mounted on a central perforated core (shaft), and held under compression so as to form a continuous cylindrical outer surface. Each washer has grooves or scallops cut into it, such that very fine and carefully controlled gaps occur between the adjacent washers. The gaps are usually sized from 5 pm upwards. Filtration takes place by flow of liquid inward through the narrow gaps between adjacent discs. The filter is essentially a strainer in that particles are stopped on the outside surface. The discs are usually metal but they can be nylon, polypropylene or paper. 

Press belt filters, disc stack centrifuges, basket centrifuges. 

Steam vented from a ruptured process tube would be prefiltered to at least a limited extent by the graphite stack and conducted to the Zone 1 exhaust filters via a low pressure rupture disc and normally open butterfly valve in the reactor gas recirculation system. 

Edge filters involve the use of cartridge elements where the element is composed of a stack of discs or washers of paper, felt, plastic or metal, clamped together in compression. Liquid flow takes place from the outer edge inwards between the discs, which may be in intimate contact in the case of non-rigid disc materials, or through the controlled clearance space between individual discs, provided by spacing washers. 

The edge filter is thus mainly made of individual rings or discs stacked together, with spacers between them as required, or with dimples on the face of the disc to provide a flow channel. The same effect can be achieved by the use of a continuous helical ribbon or flat spring compressed together to give the required spacing between consecutive turns. 

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