Plate-and-frame arrangement

Configurations used include tubes, plate-and-frame arrangements and spiral wound modules. Spiral wound modules should be treated to remove particles down to 20 to 50. im, while hollow fiber modules require particles down to 5 im to be removed. If necessary, pH should be adjusted to avoid extremes of pH. Also, oxidizing agents such as free chlorine must be removed. Because of these restrictions, reverse osmosis is only useful if the wastewater to be treated is free of heavy contamination. The concentrated waste material produced by membrane processes should be recycled if possible but might require further treatment or disposal. 

Parallel-plate flow cells Most electrochemical flow cells are based on a parallel-plate electrode design with either horizontal or, more commonly, vertical electrodes in a monopolar or bipolar configuration (see Figure 26.12). With vertical electrodes, the cell is usually constructed in a plate-and-frame arrangement and mounted on a filter press. 

Plate and frame units are also used for cross-flow filtration. Some units take sheet stock MF membranes while others work best with a preassembled membrane cassette-a sandwich of two outer layers of membrane sealed to an inner filtrate collection screen (see Figure 2.47). A cross-flow spacer is placed between the filter packets and stacked in a plate and frame arrangement (see Figure 2.48). In some systems, the cross-flow spacer is a screen, but the "flow-channel" spacer shown in Figure 2.47 is less prone to fouling. 

Because a fuel cell functions at a low voltage (/.c., well below 1 V), it is customary to build up the voltage to the desired level by electrically connecting cells in series to form a stack . This is achieved by means of a bipolar plate-and-frame arrangement similar to that employed for electrolysers see Section 4.2, Chapter 4. There are a number of different designs of fuel cell, but in each case the unit cell has certain components in common. These are as follows. 

With vertical electrodes the cell is usually constructed in a plate-and-frame arrangement and mounted on a filter press. The electrodes, electrolyte chambers, insulating plates to separate cells electrically and, where used, membranes or separators are constructed individually and mounted with suitable gasketing materials between each component the filter press is then used to seal the cells with up to 100 cells in each unit (see Fig. 2.14). It is difficult to manufacture the cells with an area greater than 1 m. Again the electrical connection may be bipolar instead of monopolar (effectively by removing the intercell insulation) and in a series of cells the electrolyte feeds to the cells may be connected so that the cells are in series or parallel so far as the electrolyte is concerned. 

Membrane modules for assembly into equipment (a) plate-and-frame arrangement and (b) spiral-wound arrangement. 

Fig. 35. Schematic diagram of a plate-and-frame electro dialysis stack. Alternating cation- and anion-permeable membranes are arranged in a stack of up to...

The earhest reverse osmosis and ultrafiltration units were based on flat membrane sheets ia arrangements similar to that of a plate and frame filter press. Siace then, mote efficient membrane configurations, ie, tubular, spiral wound, and hoUow fiber, have emerged (96—98). 

A plate-and-frame filter press consists of alternate solid plates and hollow frames in a sandwich arrangement. The open frames are covered by the filter medium (e.g., the filter cloth), and the slurry enters through the frames and deposits the cake on the filter medium. The operation is batch, in that the filter must be disassembled when the cake fills the frame space, then cleaned and reassembled, after which the entire process is repeated. A schematic of a plate-and-frame press is shown in Fig. 13-7. In the arrangement shown, all of the frames are in parallel and the total filter area (which appears in the equations) is... 

There are a variety of arrangements that operate in the same manner as the plate- and-frame filter. One is the leaf filter, which may consist of one or more frames that are covered by the filter medium and immersed in the slurry. These filtration devices, are often operated by means of a vacuum that draws the filtrate through the filter, with the cake collecting on the filter medium on the outside of the frame. 

Parallel plate and frame cell — This - electrolysis cell type has been developed since the 1970s, and reliable cells from laboratory up to industrial production scale in divided or undivided form are commercially available. Parallel plate and frame cells comprise interelectrode gaps of 1 to 12 mm. They can be used as monopolar (A) or -> bipolar electrode (B) arrangement, see figure. 

The principle of operation for a cross-flow filtration system is to recirculate a liquid solution or suspension, usually using a positive displacement pump, through the membrane module, which may be arranged as multiple tubes, a spiral wound sheet or in a plate and frame configuration. The use of... 

Various types of leaf filters are used, with the leaves arranged in horizontal or vertical rows. The leaves consist of metal frames over which filter cloths are draped. The cake is removed either mechanically or by sluicing it off with jets of water. Leaf filters are used for similar applications as plate and frame presses, but generally have lower operating costs. 

The following pressure filters, varying in type and arrangement of elements, are those in which the elements are contained in a pressure vessel. They offer the advantages of lower labor costs and less opportunity for leakage, when compared to plate and frame filters. 

Plate and Plate and Frame Presses.— All the usual procedures in filtering can be carried out with these devices. The leaves can be filled with material to be filtered until filtrate ceases to pass through the medium which is ordinarily canvas when the press must be discharged of its cake. Either the filtrate or cake is rejected. After the press is filled or partially filled various washes may be introduced and separately distrained if desired, the openings in the leaves being arranged to that end. 

In plate-and-frame presses the leaves are assembled with the plates and frames alternately placed. Figure 22 shows the feed eye and part of the frame construction. Figure 23 shows the arrangement of plates, frames and filtering media in section. There is a section of cloth between each plate and frame. Simple washing such as has already been described can be employed with plate-and-frame... 

The development work on films has been done primarily with the small cell of Figure 2. The effective area of this cell is 0.012 sq. foot. It is envisioned that a commercial desalinization unit utilizing these membranes would somewhat resemble a plate and frame filter press with a close stacking arrangement of membranes. To test the feasibility of this concept a larger cell (effective film area 0.2 sq. foot), capable of multiple film arrangement, was designed and fabricated. 

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