Contents Introduction about Filtration What is Filtration Difference between Filtration & Sieving Objectives of Filtration Type of collections Comparative Filtration Efficiencies Fibers used in Filtration Fabrics used for filtration Filter fabric requirement Dust Filtration Manufacturing Methods Classification of filtration Methods of filtration Designing for filtration Application of Textile filter Operating problems Comparison of woven & Non-woven filter fabric Testing of filters conclusion
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Filtration plays a critical role in our day-to-day life by providing healthier and cleaner products and environment. Textile materials are used in the filtration of air, liquids, in food particles and in industrial production. Filtration fabrics are used widely in vacuum cleaners, power stations, petrochemical plants, sewage disposal, etc. Textile materials, particularly woven and nonwoven, are suitable for filtration because of their complicated structure and thickness. Dust particles have to follow a tortuous path around textile fibres. IJFTR,Aug .1992
What is Filtration ? Filtration is a mechanical or physical operation, which is used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass. examples: 1. Filtration, as a physical operation is very important in chemistry for the separation of materials of different chemical composition. 2. Filtration is also important and widely used as one of the unit operations of chemical engineering.
Objective of Filtration To eliminate the contaminant particles so as to recover dispersing fluid. To recover solid particles by eliminating the dispersing fluid
Type of collections There are four main types of equipments like : Cyclones wet scrubbers Fabric filter Electrostatic Precipitators are used to remove solid particles from air or gas stream. Textile Trends Januarary 1989
Comparative Filtration EfficienciesCollector type Efficiency on Particle size of 10 Um 5Um 1UmHigh efficiency 85.0% 67.0% 10.0%cycloneFabric filter 99.9% 99.9% 99.0%Wet scrubber 99.8% 99.6% 94.0%Electrostatic 99.0% 98.0% 92.0%precipitators Textile Trends Januarary 1989
Fibres used in Filtration Many grades of cellulose and most natural and synthetic fibers at one time or another. The most popular fibers used being polyester, polypropylene and glass. Following are acrylics, rayon, nylon, cotton, fluoro polymers and a host of others that fill niche applications because of their special material compatibility for particular applications. Most people associate glass fibers with air and synthetics with liquid filtration, but there are plenty of exceptions, especially with synthetics in the form of melt blown nonwoven fabrics that are increasing popular in air filtration. The Indian Textile Journal
Dust Filtration Filtration efficiency of a filter fabric is greatly influenced by three factors: Type of fibres Yarn characteristic Weave of filter fabric Textile Trends Januarary 1989
Yarn characteristics Yarn characteristics which greatly affects the filtration efficiency are: Thread count Yarn size Twist of yarns Napping Textile Trends Januarary 1989
Type of yarns also affect the filtrationefficiency of filter fabrics : Staple fibre yarn; Efficient particle retention, poor cake release properties,& can be easily blended. Multi-filament yarn; Retaining extremely fine particles & good cake release properties. Mono-filament yarn; poorest retention of solids but higher flow rate. Textile Trends January 1989
Fabrics used for filtration In filtration, nonwoven fabrics can be generally described as a random fibrous web, formed by either mechanical, wet or air laid means and having interconnecting open area throughout the cross- section and able to remove a percentage of particulate from liquid or gaseous fluids streams flowing through it. Needle felt fabrics for bag house filtration represent the heaviest weight and most costly, whereas spun bonded fabrics, especially from polypropylene polymer for use in coolant filtration used in automotive and aircraft machining are the lowest weight and least expensive. The Indian Textile Journal
Air-laid and air bonding are popular because of its high-loft, bulk and large dirt holding capability in air filtration, including pre filters capable of capturing larger particles. Melt blown nonwoven fabric continues to be the rising star with rapid penetration into many liquid and air filtration applications. Resin bonded nonwovens are popular in air filtration and point-bonded fabrics provide an alternative to overall bonded fabrics which commonly are used to fibers consisting dissimilar melt or softening points The Indian Textile Journal
Filter fabric requirement The necessary efficiency to retain the particulate matter & control the emission. A good dust release property to effect a uniform pressure drop throughout the bag life . Physical characteristic to withstand the mechanical stresses for continued performances. The necessary physical & chemical properties to withstand the conditions at the collection point. Man Made Textile in India April 92
Performance of various weaves usedfor filtration fabrics Initial flow rate was excellent with sateen, good with twill & plain woven fabric was poor . Retention efficiency was excellent with plain, satisfactory with twill, was poor with sateen woven fabric. Excellent resistance to blinding was performed by twill & sateen woven fabrics but poor for plain fabrics. Also the sateen weave gives best cake release then plain weave & poor with twill weave.
Classification offiltration filtration 1) Particle Particle filtration is the separation of particles having size above 10 microns. These can be filtered out easily without any usage of micro porous membrane. 2) Microfiltration A typical microfiltration membrane pore size range is 0.1 to 10 microns (µm). The Indian Textile Journa,98l
3) Ultra filtration Ultra filtration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semi permeable membrane. 4) Nano-filtration Nano-filtration is a relatively recent membrane filtration process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening (polyvalent cation removal) and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter.
5) Reverse osmosis Reverse osmosis is similar to the membrane filtration treatment process. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The Indian Textile Journal,98 ,
Methods of filtration There are many different methods of filtration; all aim to attain the separation of substances. Separation is achieved by some form of interaction between the substance or objects to be removed and the filter. The substance that is to pass through the filter must be a fluid, ie, a liquid or gas. Methods vary depending on the location of the targeted material, ie, whether it is in the fluid phase or not. The Indian Textile Journal oct.2011
Solid Gas separationEg, Filters used in cigars, filters used in AC systems. The Indian Textile Journal oct.2011
Solid Liquid separationEg, Filters used in sewage disposal plants, filters inchemical industries, water purifiers, etc.
Designing for filtration While designing a filter for the end use, below factors have to be considered: 1. Flow velocity. 2. Pressure inside filtering system. 3. Size and concentration of particles to be filtered out. 4. Nature and component of the suspension filtered. Selection of the fibres should be according to their nature which can withstand the harsh environmental conditions such as temperature, abrasion chemical conditions etc.
Generally, for filtrations, syntheticfibres are used because: 1) They have reduced fabric weight 2) They are having higher strength 3) Easier handling and replacement 4) Easier separation of filter cakes 5) Resistance to rot 6) Higher filtration rate 7) Higher fatigue resistance 8) Good dimensional stability 9) High temperature resistance 10) Better abrasion, corrosion and chemical resistance The Indian Textile Journal,oct.2011
Advantages of nonwoven filter over thewoven filters are: 1) High permeability 2) High filtration efficiency 3) Less blinding tendency 4) No yarn slippage as in woven media 5) Good gasketing characteristics 6) Good cake discharge As fibre diameter increases, filtration efficiency decreases. Also, void volume, which is required to reduce the pressure drop is more in case of nonwoven (98%) than that of woven or knitted (70%), thus nonwoven are advantageous to use. The Indian Textile Journal,oct .2011
Application of Textile filter Metallurgical industry Foundries Cement industries Chalk & lime plants Brick works Ceramic industries Flour mills Medical Pharmaceutical Acoustics Screen printing Man Made textile in India december1991
Operating problems Cleaning Rupture of cloth Temperature Bleeding Humidity Chemical attack Man Made textile in india december1991
Comparison of woven & Non-woven filterfabricWoven filter fabric Non-woven filter fabric Man-Made Textile in India,May.2003
Testing of filters It is done to measure the filtering capacity of the fabrics, for intended suspension in liquid filtration. Other factors, which need to be considered include the rate of filter choking, service life of the filter cloth, filtrate purity and cake removal. Efficiency of filter is directly related with the particle size. As the particle size is increased, the efficiency of the filter increases, and vice versa. It is also increased by selection of proper size of fibre, orientation and packing. Man-Made Textile in India,May.2003
Conclusion Each filter fabric is intended for a specific use in the specific climate under the specific conditions for its optimum output and enhanced efficiency. For coming decades, filter fabric filtration will play a very critical role in our day-to-day life; there is not a single type of fabric used in all the applications. The usage of the filter fabrics varies according to their end use. Man-Made Textile in India,May.2003