Membrane cartridge filters

Bruno, C. F. and Szabo, L. A., Fermentation Air Filtration Upgrading by Use of Membrane Cartridge Filters, American Chemical Society Meeting, New York (August 24, 1981)... 

Membrane cartridge filters are extremely flexible and high in tensile strength. The cartridge construction is based on a multi-layer combination of filter media in pleated format. Those polymers that have been used extensively as filtration media in coarser grades are now widely used as membrane filters. A typical format has a cartridge fabricated from a pleated filter pack, which contains a very fine polyolefin fibre prefilter layer, two nylon membranes of the same pore (0.2 pm) size, and a downstream polypropylene support. The layers of nylon microporous membrane and polypropylene prefilter are pleated together and snpported by an inner snpport core. The end-caps and core are melt sealed in polypropylene. 

For smaller boiler plants, various sieves, screens, cyclones, and strainers may sometimes be used for filtering MU and FW. Also, bag, ceramic membrane, cartridge, and candle filters, either with a filter aid (precoat filters) or without (naked filters), all of which are typically available in single- and multiple-filter component vessel configurations. 

B Bottle IM In situ pump/membrane filter (53, 70 p,m) 1C In situ pump/cartridge filter (0.5,1 am) ST sediment trap 5°S-5°Nand25°W-5°E... 

SPEC was essentially able to market their Zr02-based ultrafiltration membranes to an already existing market in the sense that these membranes replaced polymeric UF membranes in a number of applications. They also developed a certain number of new applications. For Ceraver, the situation was different. When the Membralox membranes were first developed, microfiltration was performed exclusively with dead-end polymeric cartridge filters. In parallel to the development of inorganic MF membranes, Ceraver initiated the development of cross-flow MF with backflushing as a new industrial process. 

Both media filters and cartridge filters can be used in a pretreatment process. Granular media filters involve the filtration of large particles through different layers of fine particles, usually coal, pumice, sand or garnet (Bonnelye et al. 2004). Cartridge filters act as the final filtration step before the water passes through the membranes, and remove fine particles as small as 1 pm. 

A simplified flow scheme for a brackish water reverse osmosis plant is shown in Figure 5.24. In this example, it is assumed that the brackish water is heavily contaminated with suspended solids, so flocculation followed by a sand filter and a cartridge filter is used to remove particulates. The pH of the feed solution might be adjusted, followed by chlorination to sterilize the water to prevent bacterial growth on the membranes and addition of an anti-sealant to inhibit precipitation of multivalent salts on the membrane. Finally, if chlorine-sensitive interfacial composite membranes are used, sodium sulfite is added to remove excess chlorine before the water contacts the membrane. Generally, more pretreatment is required in plants using hollow fiber modules than in plants using spiral-wound modules. This is one reason why hollow fiber modules have been displaced by spiral-wound systems for most brackish water installations. 

Bubble point measurements are most useful to characterize sheet stock or small membrane filters. The technique is more difficult to apply to formed membrane cartridges containing several square feet of membrane because diffusive flow of... 

The first major application of microfiltration membranes was for biological testing of water. This remains an important laboratory application in microbiology and biotechnology. For these applications the early cellulose acetate/cellulose nitrate phase separation membranes made by vapor-phase precipitation with water are still widely used. In the early 1960s and 1970s, a number of other membrane materials with improved mechanical properties and chemical stability were developed. These include polyacrylonitrile-poly(vinyl chloride) copolymers, poly(vinylidene fluoride), polysulfone, cellulose triacetate, and various nylons. Most cartridge filters use these membranes. More recently poly(tetrafluo-roethylene) membranes have come into use. 

Figure 7.11 Cut-away view of a simple pleated cartridge filter. By folding the membrane a large surface area can be contacted with the feed solution producing a high particle loading capacity. (From Membrana product literature)...

However, the short lifetime of in-line cartridge filters makes them unsuitable for microfiltration of highly contaminated feed streams. Cross-flow filtration, which overlaps significantly with ultrafiltration technology, described in Chapter 6, is used in such applications. In cross-flow filtration, long filter life is achieved by sweeping the majority of the retained particles from the membrane surface before they enter the membrane. Screen filters are preferred for this application, and an ultrafiltration membrane can be used. The design of such membranes and modules is covered under ultrafiltration (Chapter 6) and will not be repeated here. 

An RO skid includes the pressure vessels in which the membrane modules are contained (see Chapters 43.3 and 6.3 for detailed discussions about pressure vessels). Skids also commonly include cartridge filters in a housing or housings and an RO feed pump, although combinations exist with just pressure vessels or pressure vessels with cartridge filters. Finally, there are included on the skid instrumentation and controls for the system. Figure 6.1 shows an RO skid with these components. 

Check cartridge filters The cartridge prefilters should be checked biweekly for pressure drop across them and to be sure they are seated properly. High pressure drop means it is time to replace the filters. Improper seating of the filters will lead to particulates bypassing the filters and fouling or abrasion (and destruction) of the membranes. 

Particle unloading from cartridge filters due to high pressure drop leading to fouling of the membranes... 

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