FILTRATIONFiltration is a mechanical or physical operation, which is used for theseparation of solids from fluids (liquids or gases) by interposing a mediumthrough which only the fluid can pass. Oversize solids in the fluid areretained, but the separation is not complete; solids will be contaminatedwith some fluid and filtrate will contain fine particles (depending on thepore size and filter thickness).Filtration is used to separate particles and fluid in a suspension, where thefluid can be a liquid, a gas or a supercritical fluid. Depending on theapplication, either one or both of the components may be isolated.
PRINCIPLES OF FILTRATION Objective of filter medium is to maximize the possibility of collision and thesubsequent retention of the suspended particles with fibrous structures whileminimizing the energy loss of the system. The efficiency of filtration in industrialfabrics are affected by there porosity. Knowledge of air permeability is alsoimportant for suitability for use. Permeability is capacity of porous materials to transmit the fluids. Liquid and gaspermeability increases with the increase in porosity of the fabric. The type of finishalso affects the permeability. When Porosity increases pressure drop tends todecrease. When flow rate increases, pressure drop increases. There are five principles of filtration:InterceptionInertial dispositionRandom diffusion (Brownian motion)Electrostatic dispositionGravitational forces
FILTRATION AND TEXTILESThe separation of solids from liquids or gases by textile filter media is anessential part of countless industrial processes, contributing to purity ofproduct, savings in energy, improvements in process efficiency, recovery ofprecious materials and General improvements in pollution control.In the coming decades, fabric filtration will play a very critical role in day today life, and there is no single type of fabric being used in all the process.Filtration fabrics are used widely in: Vacuum cleaners Medical uses Power stations Petrochemical plants Sewage disposal Water filtration Geotextiles etc.
FABRIC CONSTRUCTIONThree basic types of construction are found in Filter fabrics, viz., wovenfabrics, needlefelts and knitted structures. The first two are produced in flat formand will require (i) slitting to appropriate width and (ii) converting into tubularsleeves, whereas knitted fabrics may be produced directly in tubular form.The technologist has basically four types of yarn to choose from when designing afilter fabric, namely monofilament, multifilament, fibrillated tape and staple-fibreYarns.IMPORTANT CHARECTERISTICS OF FILTER FABRICS: With the fabric warp and weft density increases, the filtration resistance of thefilter cloth increases gradually. With the increase in the fabric warp, weft twist, the filtration resistance of thefilter cloth is reduced gradually. Fabric tissue filtration resistance: resistance of plain weave, twill path of leastresistance. Porosity of the fabrics. Air permeability of the fabrics.
VARIOUS APPLICTIONS OF TEXTILES INFILTRATION In vaccum cleaners - The bag used invaccum cleaners is the typical method tocapture the debris vacuumed up. Itinvolves a paper or fabric bag thatallows air to pass through, but attemptsto trap all dust and debris in the bag.The bag may be disposable, or designedto be cleaned and re-used. In medical uses – Woven filters set thestandard for safe and efficient filtrationsolutions in medical devices. Precisionwoven fabrics is a critical componentfor medical filter devices, bloodfiltration : precision woven fabrics setthe standard for safe and efficientfiltration.
In Power Stations- A baghouse (BH, B/H)or fabric filter (FF) is an air pollution controldevice that removes particulates out of air orgas released from commercial processes orcombustion for electricity generation. Powerplants, steel mills, pharmaceutical producers,food manufacturers, chemical producers andother industrial companies often usebaghouses to control emission of airpollutants. Baghouses came into widespreaduse in the late 1970s after the invention ofhigh-temperature fabrics (for use in the filtermedia) capable of withstanding temperaturesover 350°F. In Sewage disposal-A non-woven fabricfilter was experimentally evaluated for solid-liquid separation in an activated sludgereactor as an alternative membrane. Apolypropylene fabric filter (70, 50 and 35g/m2) was used.
Water filtration- This type of filter is acommon solution to the problem ofobtaining clean water in many parts of theworld, especially rural parts of developingnations. It is a fairly simple process thatinvolves only materials that are available inmost parts of the world. In Geo-textiles- The non-woven geo-textilefabric is a common choice for areas lookingto stabilize, separate or filter materials. Allnon-woven fabrics come with a needle-punched exterior that allows thin waterparticles to filter through the fabric whilekeeping soil from filtering through. Thisgeo-textile filter fabric helps to retain fineparticles when water passes from fine tocoarse-grained soil layers.
CONCLUSIONThe separation of solids from liquids or gases by textile filter media is an essentialpart of countless industrial processes, contributing to purity of product, savings inenergy, improvements in process efficiency, recovery of precious materials andGeneral improvements in pollution control.The final products of processes which involve filtration by textile filter media mayultimately find their way into our everyday lives.In addition to assisting in the refinement of products for our general everyday use,textile filter media are also engaged in the purification of both industrial and domesticeffluents, thereby contributing to a cleaner environment.
REFERENCES: TEXTILES IN FILTRATION BY Edwin HardmanMadison Filters (formerly Scapa Filtration), Haslingden,Rossendale, Lancashire, UK A HANDBOOK OF TECHNICAL TEXTILES edited by A.R. HORROCKS & S.C. ANAND WIKIPEDIA AND GOOGLE SITESTHANK YOU