Precoat rotary drum

1 Precoat rotary drum Typical uses Clarification. 

Typical particle size and feed concentration range 0.5-100 pm and 1% w/w. 

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A precoated rotary drum vacuum filter is the only filtration equipment from which extremely thin filter cakes can be positively and continuously removed in a semi-dry state. 

Horizontai beit Horizontai rotary table Horizontal tilting pan Precoat rotary drum Rotary disc... 

Figure 1.43 Schematic representation of the precoat rotary drum filter.

In precoating, the prime objective is to prevent the filter medium from fouling. The volume of initial precoat normally applied should be 25 to 50 times greater than that necessary to fill the filter and connecting lines. This amounts to about 5-10 lb/100 fF of filter area, which typically results in a 1/16-in. to 1/8-in. precoat layer over the outer surface of the filter medium. An exception to this rule is in the precoating of continuous rotary drum filters where a 2-in. to 4-in. cake is deposited before filtration. The recommended application method is to mix the precoat material with clear liquor (which may consist of a portion of the filtrate). This mixture should be recycled until all the precoat has been deposited onto the filter medium. The... 

Precoated rotary vacuum drum filters (Fig. 6) are used by filtering a slurry of filter aid and water first, then subsequent product filtration. Difficult filtering materials, which have a tendency to blind, are removed with a doctor blade. Precoat is removed along with the slurry to expose a new filtration surface each cycle. 

Although rotary drum filters are normally employed for materials of moderate to low resistance, they can be used as precoat filters for highly resistant slurries. A thick coat of several centimeters of filter aid is deposited on the drum prior... 

Drum, precoat rotary vacuum particle diameter 0.5-80 pm feed solid concentration 0.02-0.1 % w/w. Recover liquid (rank 4). 

Drum, precoat rotary vacuum submerged 35, 55, 85 %. Usually 85 % air required... 

FQtration with Filter Aids. A wide range of pressure and vacuum cake filters can be used with both precoat and body aid fihration. Most of these operate in the batch mode and include the filter press, the vertical and horizontal leaf filters with sluice or centrihigal disduuge and the vertical tubular fih . The rotary drum vacuum fitter works in a semi-batch shion in that the precoat is removed progressively as the fitration proceeds. 

Rotary Drum Vacuum Filters. This filter can accommodate a large thickness of cake and can take a precoat of filter aid which is up to 150 mm in depth. The feed su ension is filtered onto the precoat and the filtered solids together with a thin layer of precoat is scraped off the cake sur ce by a horizontal knife situated just before the surface passes back into the feed suqiension tank, thus e qposing a fi esh surface of precoat. The scraper knife advances automatically until it reaches a mioimum distance fi-om the cloth, usually 5-10 mm. At this point the cycle is finished and the filter is cleaned of used precoat. 

Rotary drum vacuum filters are a widely used piece of equipment for this filtration step, due to its simple operation and low investment costs. The drum is typically precoated (e.g., with diato-maceous earth, sUica, perlite) to improve the process performance [7]. Additional filter aid is often added to improve the filtrate qnality hence, the amount of slndge generated from this unit operation is relatively large. Several other filtration devices such as filter automates and cross-flow filtration devices are also nsed for the filtration. One of the benefits of the latter is that they can be operated withont addition of filter aids and thus, the amount of generated sludge can be reduced. 

Multi-element candle Multi-element leaf Plate frame press Precoat Nutsche and multielement leaf Precoat plate frame press Recessed plate filter press Sheet filter Single leaf Nutsche Bag Cartridge Dead-end membrane Fibre bed Low shear crossflow Sand bed Simplex strainer Belt press Duplex strainer High shear crossflow Rotary disc Rotary drum Sand bed Tower press Diaphragm filter press Expression (screw) press Horizontal element tube press Vertical diaphragm filter press Vertical element tube press... 

Filter aids can improve the permeability and sometimes porosity of a filter cake, improve filtrate clarity and help to prevent filter medium blinding. They comprise relatively porous particles such as diatomite, perlite and activated carbon and are either filtered as a precoat onto the medium or mixed as body feed with the suspension during a pretreatment stage the latter beneficially improves the porosity of a subsequently formed filter cake. Both the cost of filter aid and the need to remove filter aid from the processed solids can present problems however, the use of filter aids on rotary drum filters and in the filtration of dilute feeds (such as those found in the brewing industries) can bring undoubted benefits. More detail on filter aids is provided in Chapter 2. 

In general, filter aid filtration should be used only for systems that meet two key requirements. First, the desired product is the filtrate, not the cake. Second, the filter aid is acceptable in the filter cake or the filter cake can be easily repulped and refiltered to remove the filter aid. In addition, the particle-settling rate should be less than 0.012 m/min and the particle concentration lower than 0.1 wt% (< 0.3% for rotary drum precoat). 

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. 

RVPF (Rotary Vacuum Precoat Filter) A drum filter that is coated with a thick (up to 6 in.) precoat of filter aid, such as CELITE or equivalent. 

Comments vacuum belt, screens, belts, top feed drum tilting pan, vacuum drums or disks continuous filters vacuiun filter, rotary vacuum, pressiue filters batch cartridge, precoat drums, deep bed... 

The precoat drum shown schematically in Figure 1.43 is similar in basic form and operation to the bottom fed rotary vacuum drum filter (see Section 1.4.1.5). Prior to filtration of the feed, a suspension of precoat is filtered under vacuum onto the drum surface to a depth between 4 and 15 cm. The feed is then introduced and filtration proceeds to produce thin, sometimes... 

Rotary-type enclosed continuous filters are used Almost exclusively in solvent dewaxing because the solvents are valuable and because they usually, form explosive mixtures with air. The principle of operation is the same as that outlined on page 321 with regard to the Oliver precoat filter. However, a precoat is not employed in wax filtering, and the rotating drum is enclosed in a shell so that pressure can be applied (Fig. 12-4). Some plants employ vacuum rather than pressure. The wax cake is sprayed or washed with solvent while it is still on the drum. Closed filtering systems are required because the solvents must be... 

A rotary vacuum drum precoat filter is a specially designed version of the vacuum drum designed to use a thick layer of precoat material to clarify liquid flows. Initially a slurry of the precoat material is prepared and filtered to produce a cake of up to 100mm thickness on the filter cloth. Then the feed trough is drained and refilled with the suspension to be filtered, which is now filtered in the normal way through the precoat layer. The filtered cake can be washed if necessary, and is then discharged by means of a full-width scraper blade. The blade removes the whole of the cake, together with a thin slice (about 0.5 mm) of the precoat layer. 

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