Filter plates

The last few parts of this Section (3J to 3M) have been concerned almost entirely with the clarification of a flow of fiuid, usually to remove contaminants from it, and very often in a utility function. Most of the remaining parts are now concerned with process filtration, in which the filtration process is intended to recover valuable sohds from suspension in a liquid. 

Leaf and plate filters are mostly relatively simple pressure-driven filters made up of fiat filtration elements, although they can also be vacuum driven. The overall configuration of the filter may be horizontal or vertical, and the basic choice between them is often made according to the space available in the factory. They are mainly used for batch-operated solids recovery, although in combination with precoat they can also be employed for clarification and decontamination duties. 

The filter medium is usually a sheet of wire mesh, although finer media are also used, supporfed on a coarse wire mesh or similarly strong substrate. The filter cake builds up on the surface of the leaves to its optimum thickness (determined not only by feed pressure differential increase, but also by the spacing between the leaves and by the tendency of formed cake to break away from the leaf). The array of leaves is usually stationary during filtration, but may have the capability of being shaken or vibrated to promote cake release. As the batch of suspension comes to an end, the shell is blown free of liquid before the cake is discharged. 

All versions are normally available with wet (i.e. re-slurried) or dry cake. Wet discharge is achieved by the washing of the cake off the leaves, using sprays or a sluice. The sluice may oscillate to ensure that the cake is washed from the whole of the leaf surface. The washing action resuspends the solids in a slurry (usually thicker than the original feed suspension), which is then drained or pumped out of the containing vessel. 

Dry discharge can only occur after all of the feed suspension has passed through the filter (with the help of a scavenger plate close to the bottom of the shell if necessary). An air blow may be nsed to dewater the cake, and a reverse blow to discharge the cake. The leaves may alternatively be freed of cake by use of scraper blades, or be subject to vibration to shake the solids free. However it is done, the cake falls to a conveyor below the filter (nsnally through doors in the shell) or below the leaf array if it has been removed from the shell as in the filter in Fignre 3.62. 

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If the clear filtrate in the flask is strongly acidified with concentrated hydrochloric acid and then allowed to cool, benzoic acid (a by-proiluct of the reaction) separates in glistening plates. Filter at the pump, and recrystnilise from hot water m.p- 121°. 

An obvious method of increasing the filtration area in the vessel is to stack several plates on top of each other the plates are operated in parallel. One design, known as the plate filter, uses circular plates and a stack that can be removed as one assembly. This allows the stack to be replaced after the filtration period with a clean stack, and the filter can be put back into operation quickly. The filter consists of dimpled plates supporting perforated plates on which filter cloth or paper is placed. The space between the dimpled plates and the cloth is coimected to the filtrate outlet, which is either into the hoUow shaft or into the vessel, the other being used for the feed. When the feed is into the vessel, a scavenger plate may have to be fitted because the vessel will be full of unfiltered slurry at the end of the filtration period. This type of filter is available with filtration areas up to 25 m and cakes up to 50 mm thick. 

Screw-pressed oil is aUowed to stand to settle out suspended soUds, filtered through plate filter presses, and then pumped to storage. The oil-rich solvent (miscella) from the solvent-extraction process is filtered or clarified, and most of the solvent is removed in a long tube evaporator. FinaUy, the concentrated oil passes through a stripping column where sparging steam is injected to remove the residual solvent. A metric ton of cottonseed yields ca 91... 

Recessed-plate filter press. This press is similar to the plate-and-frame press in appearance but consists only of plates (Fig. 18-113). 

FIG. 18-110 Elevation section of a Sparkler horizontal plate filter. (Spa7-kle7- Fil-te7 s, Inc.)... 

Both faces of each plate are hollowed to form a chamber for cake accumulation between adjacent plates. This design has the advantage of about half as many joints as a plate-and-frame press, making a tight closure more certain. Figure 18-114 shows some of the features of one type of recessed-plate filter which has a gasket to further minimize leaks. Air can be introduced behind the moth on both sides of each plate to assist cake removal. 

A single-plate filter consists of a hollow flat plate, one side of which is covered by... 

Agitated/Monoplate Nutsche Filter/Dryer Horizontal Plate Filter/Dryer Continuous Equipment Rotary Drum Filter Centrifugal Filter Horizontal Belt Filter... 

HORIZONTAL PLATE FILTERS ARE BEST SELECTED IN THE FOLLOWING SITUATIONS ... 

The operation of a horizontal plates filter is labor intensive and requires a eomplex manipulation of valves so present day installations are in most eases fully automated. The operational steps are as follows ... 

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. 

Vertical Pressure Leaf Filters are essentially the same as Horizontal Plate Filters except for the orientation of the filter elements which are vertical rather than horizontal. They are applied for the polishing slurries with very lov solids content of 1-5% or for cake filtration with a solids concentration of 20-25%. As with the horizontal plate filter the vertical leaf filters are also well suited for handling flammable, toxic and corrosive materials since they are autoclaved and designed for hazardous environments when high pressure and safe operation are required. Likewise, they may be readily jacketed for applications whenever hot or cold temperatures are to be preserved.The largest leaf filters in horizontal vessels have a filtration area of 300 m and vertical vessels 100 m both designed for an operating pressure of 6 bar. 

Plate filters are suitable for filtration of batch fermentation broth accumulated biomass must be cleaned periodically. A rotary dram vacuum filter is used for a continuous system. 

Concentrated metal hydroxide sludge is pumped from the clarifier to a polypropylene plate filter press [T-102], The plate filter press56 is of sufficient capacity without any buildup in the lamellar portion of the unit. This also prevents any overflow of precipitate to the sewer system. The metal hydroxides form a dense sludge cake suitable for disposal in an approved landfill. The liquid effluent from the plate filter is returned to the surge tank [T-99],... 

This leads to a consideration of extraction apparatus for solid substances. The best known is that of Soxhlet, which is much used, especially for analytical purposes. For preparative work the simplified extractor (Fig. 27) is to be preferred, for it is cheaper and works more quickly. In order to prevent the formation of channels by the drops of solvent in the material to be extracted, a thin porcelain sieve-plate (filter-plate) is laid on top. 

In the plate filter, a cell suspension is filtered through a flat filtering medium by applying a positive pressure, and the cake of deposited cells must be removed batchwise. 

An aqueous suspension is filtered through a plate filter under a constant pressure of 0.2 MPa. After a 10 min filtration, 0.10 m of filtrate is obtained. When the resistance of the filtering medium can be neglected, estimate the volumes of the filtrate after 20 and 30 min. 

Albumin solutions (1, 2, and 5wt%) are continuously ultrafiltered through a flat plate filter with a channel height of 2 mm. Under cross-flow filtration with a transmembrane pressure of 0.5 MPa, steady-state filtrate fluxes (cm min ) are obtained as given in Table P9.2. 

Procedure. The procedure followed with XAD-8 was that of Thurman and Malcolm (8). The Suwannee River (GA) sample was filtered through 0.45-/zm Ag filters in Millipore, stainless steel, 142-mm, plate filter holders. The Laramie-Foxhills ground-water sample did not require filtration. Samples were processed on site within 24 h after collection to prevent alteration. All column eluates were adjusted to pH 2 upon collection and immediately refrigerated. 

PAMPA is generally carried out in the 96 well format using a PAMPA sandwich construction. The sandwich consists of a standard 96 well plate and a filter plate put on top (Microtiter plate filter plates that are commercially available). The bottom standard 96 well plate is filled with buffer so that the liquid surface will be in contact with the filter material of the filter plate put later on top. The filter material was impregnated... 

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