Nonwoven filter media

The above section has concentrated on the use of woven filter media in pressure filters. It will be realised that a vast interest lies in the application of non woven, random fibre filter media to gas and liquid filtration systems [Fletcher, 1982], Plate and fl ame 

Applications into the traditional wov i cloth area are increasmg in view of the in roved performance (better ga et action around edges/bosses of plate) following surface treatments for pore size and cake release control Skinned felts, for presses, are sometimes supplied with a surface finish on both sides of the cloth. 

Polymeric cloths of the type maotioned above are produced by dry processes, e.g. vriiere extruded, molten polymer filaments are dispersed by hot air streams and deporited on moving belts. Paper is an exanq le of a nonwov produced fiom a w process, in the separation of cellulosic fibres fi-om thdr diversion in water, by impingement on a high eed, moving monofilament belt. 

The trend is towards inqproved nonwoven performance, by way of fibre sdze reduction. Most woven-cloth manufiictnrers also siq pfy a range of non-wovens, for specific press iqiplications. 

Despite the antiquity of filtration processes involving nonwovens, e.g. felts, laps, paper etc. media developmoits continue to appear involving modem fibres prepared from polymers, glass, fluorocarbons, etc. These are used alone, or in mixtures with traditional fibres such as wool, cotton, cellulose, etc., to produce a vast array of media aimed at solid-liquid separation. A detailed listing of the relevant phydcal properties of these fibres is available in the literature jPurchas, 1981]. 

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Nonwoven filter media are mostly used for filter medium filtration with pore clogging. Because of the relatively low cost of this medium, it is often replaced after pore clogging. In some cases, nonwoven media are used for cake filtration. In this case, cake removal is so difficult that it must be removed altogether from the filter medium. Nonwoven filter media can be prepared so that pore sizes decrease in the direction from the surface of the filter media contacting suspension to the surface contacting the supporting device. This decreases the hydraulic resistance of... 

The second stage of AFS consists of intermediate filters to remove dry impurities such as dust and dry salt in the 2-10 pm range that can cause erosion and FOD of GTs and lead to increased pressure loss and filter loading in the final high-efficiency filtration stage. Hydrophobic nonwoven filter media (e.g., spunbond, wet-laid media, and air-laid media) are typically used as intermediate filters to protect the final high-efficiency filter. 

I.M. Hutten, Handbook of Nonwoven Filter Media (Elsevier, 2007)... 

Purdy AT. The structural mechanics of nonwoven filter media. In Second World Filtration Congress. London Filtration Society, Uplands Press 1979. p. 117-32. 

Snow, C., Toward improving standards in nonwoven filter media . Filtration Engineering, Sept./Oct., 23 (1974)... 

This is another powerhouse sector for technical nonwovens. Recent studies by Smithers Apex have estimated that the global nonwoven filter media market could exceed 5 billion by 2018/2019. The CAGR would exceed 5% [11]. 

Nonwoven filter media are becoming increasingly more sophisticated and complex. 

Hutten IM. The handbook of nonwoven filter media. Oxford, UK Elsevier Ltd 2007. Horrocks AR, Anand SC. Handbook of technical textiles. Woodhead Publishing Ltd 2000. The Journal of Engineered Fibers and Fabrics (JEFF) (http //www.JeffJoumal.org). International Nonwovens Journal (http //www.inda.org/INJ/index.html). 

Nonwoven filter media also play an important role in today s vehicles. In total, there are more than 50 filters in an average passenger car, contributing to functions ranging from the performance of the engine and oil and fuel consumption through to the quality of the air in the cabin. 

The application of nonwoven filter media in the fuel and oil filter segment of the transportation industry is affected significantly by governmental regulations related to the environment and the desire for longer intervals between engine filter replacements. 

Nonwoven filter media employed for filtering fuel and oil must demonstrate good chemical and temperature resistance. The filtration system is also constantly subjected to a great deal of vibration and shock, so the media must withstand extreme operating conditions. And since the filter media represent the last line of defence for engines against contaminant-related wear and tear, the performance of the nonwoven must, in addition, be consistent and predictable during the service cycle. 

One of the drawbacks of wet-laid-based nonwoven filter media is shedding. Small fibre particles can become dislodged from the filter and travel downstream wifli the... 

New injection technology, particularly for diesel engines and those for mass transportation systems, is creating an even bigger need for cleaner fuel, and this, in turn, is demanding more of nonwoven filter media. 

Leading nonwoven filter media manufacturers Ahlstrom and Johns ManviUe have both recently introduced new synthetic and glass hybrid nonwoven media. 

So too, does the new nonwoven filter media being manufacmred by Johns ManviUe. 

Nonwoven filter media are usually produced by using one of six major types of nonwoven web formation methods air-laid, wet-laid, spunbonding, melt blowing,... 

Wood pulp fibres are frequently less than 1 pm in fibre size and dominate wet-laid nonwoven filter media they are able to provide higher filtrafion efficiency and are environmentally fiiendly. Synthetic fibres (eg, polyolefin, polyester, and polycarbonate (PC) fibres) could work as electret fibres to provide additional electrostatic filtration mechanism, and also could be made binder-fitee, thermobond nonwoven fabrics if they are made Ifom thermoplastic polymers. 

A significant reason for the majority of oil and fuel system failurcs is the presence of high water levels as dissolved, dispersed, and free water, which degrades the fuels and oils. There are mainly four types of nonwoven filter media fiequently used for the removal of water contaminations contained in a wide range of fuel and oil products, such as aviation fuel, automotive diesel, and hydraulic oils. They include ceUulosic pulp filter, man-made fibre filter, glass fibre media, water adsorption (eg. 

Fedel T. Not all air filters are created equal nonwoven filter Media provides lAQ energy benefits. Nonwovens Industry November 2012. http //www.nonwovens-industry.com/ issues/2012-ll/view features/not-all-air-filters-are-created-equal-nonwoven-filter-media-provides-iaq-energy-benefits sthash.zPWBAX9F.dpuf. 

Fig. 12.7 (a) MPPS as a function of nanofiber packing density, (b) Operation curves (Ug = 5 cm s, Dp = 200 nm) of multilayer filters formed by stacking up constituent units from NIS to N9S. (c) and (d) SEM images of the structural changes in the nanofiber membranes deposited over nonwoven filter media before and after cyclic compression ((a) and (b) Reprinted with permission from [60]. 2010 Elsevier, (c) and (d) Reprinted with permission from [61]. 2010 Elsevier)... 

The idea of using polymer nanofiber as affinity membrane is based on the fact that the polymer nanofibers deposited on the collector during electrospinning assemble into a membranelike nonwoven fiber mesh. This electrospun nonwoven mesh possesses properties such as high porosity, micron-scaled pore size, and high interconnectivity of the interstitial space. Above all, the nanoscaled fiber diameter gives rise to an increased surface area as compared with the conventional nonwoven filter media composed of currently available textile fibers with typical diameters of several microns. A large surface area-to-volume ratio is one of the most important... 

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