Woven Media

Non-woven media in the form of felts and compressed cellulose pulps, are used for clarification by depth filtration. Unless carefully prepared, they have the disadvantage of losing fibrous material from the downstream side of the filter. The application of sheet media has been discussed earlier. High wet strength is conferred on paper sheets by resin impregnation. An alternative technique employs asbestos fibers supported in a cellulose framework. 

Woven media are flexible and comprise metallic or nonmetallic materials formed by weaving. Metallic woven media are called woven wire, and nonmetallic woven media are called woven cloth or woven fabric. Woven wires are generally made with stainless steel, bnt can also be monel, nickel, inconel, or nichrome. They are stronger, better wear resistant, and more dnrable, but are more expensive compared with woven fabric. Selection of woven wire is sometimes solely on the basis of severe operating conditions. 

Figure 43 Retention characteristics of woven media jPurchas, 1967]...

A novel water pmification filter has been in development over the past seven years. The first version is a pleated depth filter cartridge that has high particle retention efficiency at moderate to high flowrates, while also having a high particle retention capacity. The filter media is also sold as non-woven media by Ahlstrom imder the tradename Disrupter . Argonide manufactures the filter cartridge from Disraptor media. 

The filter s active component is a nano alumina monohydrate fiber, only 2 nm in diameter and with an external surface area of 500 m /g. It has been identified as crystalline boehmite (AlOOH) using x-ray diffraction. The isoelectric point of raw fibers is approximately 11.1 (7). Particles with an electronegative charge are attracted and retained by the nano alumina. The nano alumina is bonded by a proprietary process to a microglass fiber that serves as a scaffold in a non-woven media. 

Table 2.11 Liquid filtration applications of non-woven media (adapted from Purchas, 1996 and Sanstedt, 1980). ...

Woven media can be called woven wire, woven fabric, wire mesh, wire cloth etc. Precision woven wire cloth is a versatile, wear-resistant filter medium which has been widely used for many years and is available in a large variety of weaves made from many metals. The most frequently used metal is stainless steel, in either type 304 or type 316. The basic difference between the two types is the addition of molybdenum to the type 316 for increased corrosion resistance. Both are otherwise 18-8 alloys, i.e. 18% chromium and 8% nickel. Acmally type 304 is 18-20% chromium and type 316 is 16-18% chromium. 

The cleaning action of the pulse is so effective that the dust layer may be completely removed From the surface of the fabric. Consequently, the fabric itself must sei ve as the principal filter medium for at least a substantial part of the filtration cycle. Woven fabrics are unsuitable for such service, and felts of various types must be used. The bulk of the dust is still removed in a surface layer, but the felt ensures that an adequate collection efficiency is maintained until the dust layer has formed. 

Filter-medium selection embraces many types of construction fabrics of woven fibers, felts, and nonwoven fibers, porous or sintered solids, polymer membranes, or particulate solids in the form of a permeable bed. Media of all types are available in a wide choice of materials. 

Fabrics of Woven Fibers For cake filtratiou these fabrics are the most common type of medium. A wide variety of materials are available some popular examples are listed in Table 18-10, with ratings for chemical and temperature resistance. In addition to the mate-ri of the fibers, a number of construction characteristics describe the filter cloth (1) weave, (2) style number, (3) weight, (4) count, (5) ply, and (6) yarn number. Of the many types of weaves available, only four are extensively used as filter media plain (square) weave, twill, chain weave, and satin. 

Normally the filter strueture consists of a stack of plates attached to a hollow shaft which are mounted inside a pressure vessel with eaeh plate eovered with a suitable filter medium. The slurry is fed under pressure into the vessel and the eake, which is retained by the filter medium, forms on the top of eaeh plate whilst the filtrate passes through the hollow shaft further to the proeess. Filter sizes may vary but generally the maximum is 60 m area and designed for a 6 bar operating pressure. Each circular plate in the staek is eonstructed with radial ribs that are welded to the bottom and support a horizontal eoarse mesh screen whieh is eovered with a fmer woven metal screen or filter cloth to retain the cake. The bottom of the plate slopes towards the hollow eentral shaft whieh lets the filtrate flow freely through circumferential holes and further down the shaft to the filtrate outlet. The elearanee between the plates is maintained by speeial spacers... 

The filter floor and cloth, woven mesh screen or sintered metal plate medium... 

FUter medium The permeable portion of a filtration system that provides the liquid-solid separation, such as screens, papers, non-wovens, granular beds and other porous media. 

Cotton filter cloths Woven cotton cloth stretched on a frame to produce a filter medium. 

The most commonly used filter medium is woven cloth, but a great variety of other media is also used. The main types are listed in Table 10.2. A comprehensive discussion of the factors to be considered when selecting filter media is given by Purchas (1971) and Mais (1971) see also Purchas and Sutherland (2001). Filter aids are often used to increase the rate of filtration of difficult slurries. They are either applied as a precoat... 

The filters used for gas cleaning separate the solid particles by a combination of impingement and filtration the pore sizes in the filter media used are too large simply to filter out the particles. The separating action relies on the precoating of the filter medium by the first particles separated which are separated by impingement on the filter medium fibres. Woven or felted cloths of cotton and various synthetic fibres are commonly used as the filter media. Glass-fibre mats and paper filter elements are also used. 

Fabric filters include all types of bag filters in which the filter medium is in the form of a woven or felted textile fabric which may be arranged as a tube or supported on a suitable... 

Woven plastic provides medium-term weed control and allows water to penetrate. Cover with loose mulch to extend life. 

Naruse et al. proposed another bioreactor design [22,23], in which porcine hepatocyte spheroids are immobilized on non-woven polyester fabric. This device allows more direct contact between hepatocytes and perfused medium and improves, therefore, the mass transfer capacity. The non-woven fabric module expressed better metabohc and synthetic functions at 24 hours than a hollow fiber module containing spheroids in suspension culture. Longer term results are not yet available and the immunoexclusion properties of this fabric have not been addressed. 

Cellulosic-Acryiic Fibers. Commonly this blend is used in knilgoods. woven fabrics for slacks, drapery, and upholstery fabrics. Since anionic direct dyes are used for the cellulosic fiber and cationic dyes for die acrylics, a one-bath dyeing process is only suitable for light lo medium shades. Auxiliaries arc needed to prevent precipitation of any dye complexes. 

Wood can also be softened for forming by plasticization with water. Wood shows colloid character it is often defined as a gel, predominantly a matrix of microfibrils surrounded by a fluid medium, hydrate water. Wood substance is generated by the living cell in a water-saturated milieu and, therefore, has by nature a certain flexibility, which is altered even by drying and remoistening. If retained in a never-dried state, thin sections are extremely supple and can be bent and woven readily in the cold. Once dried, wood can be resoftened by raising its water content especially with increase in temperature. For... 

The hltration medium may be made of perforated plates, septum of woven materials, or of granular materials such as sand. Thus, according to the medium used, hlters may also be classihed as perforated plate, woven septum, or granular filters. The hltration medium of the microstrainer menhoned above is of perforated plate. The hlter media used in plate-and-frame presses and vacuum hlters are of woven materials. These units are discussed later. 

Woven septum filter—Filter with a filtering medium that is made of woven materials. 

A variety of sieve apertures is currently available, and these are classified as coarse (4 mm to 100 mm), medium (0.2 mm to 4 mm) and fine (less than 0.2 mm). The fine range extends down to 37 pm with woven wire sieves but the tolerances are liberal and this has limited their acceptance. 

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