filter media and filter aids

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FILTER MEDIA AND FILTER AIDS By UMAIR FAREED B1133043 ROLL#33 Submitted to: Sir Shoaib

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FILTER MEDIA AND FILTER AIDS

FILTER MEDIAANDFILTER AIDSBy UMAIR FAREEDB1133043ROLL#33Submitted to:Sir ShoaibFILTER MEDIAThe surface upon which solids are deposited in a filter is called the Filter mediumProperties of ideal filter medium: 1- It must be capable of delivering a clear filtrate at a suitable production rate.2- It must withstand the mechanical stresses without rupturing or being compressed.3- No chemical or physical interactions with the components of the filtrate should occur.4- It must retain the solids without plugging at the start of filtration.

FILTER MEDIAIn clarification processes the filtration medium is usually the only barrier present.At the beginning of a cake filtration process, the role of the filter medium is to act as a barrier.However, once the cake formation commences, the cake becomes the main particle-retaining barrier and the role of the filter medium is mainly as a support for the cake. Classification of FILTER MEDIA1- Woven filters2- Non- woven filters3- Membrane filters4-Porous platesClassification of FILTER MEDIA1- Woven filters: these include: a- wire screening Wire screening e.g. stainless steel is durable, resistance to plugging and easily cleaned.

Classification of FILTER MEDIA1- Woven filters: these also include: b- fabrics of cotton, wool, nylon.Cotton is a common filter ,however, Nylon is superior for pharmaceutical use, since it is unaffected by mold, fungus or bacteria.In a cloth of a given mesh size, smooth synthetic or metal fibers are less effective than the more ragged natural fibers in removing very fine particles.

Classification of FILTER MEDIA2- Non- woven filters: Filter paper is a common filter medium since it offers controlled porosity, limited absorption characteristic, and low cost.Classification of FILTER MEDIA3- Membrane filters: These are basic tools for micro-filtration, useful in the preparation of sterile solutions. These filters are made by casting of various esters of cellulose, or from nylon, Teflon, polyvinyl chloride. The filter is a thin membrane with millions of pores per square centimeter of filter surface.

Classification of FILTER MEDIA

Classification of FILTER MEDIA4-Porous plates: These include perforated metal or rubber plates, natural porous materials such as stone, porcelain or ceramics, and sintered glass.

Summary of Commonly used FILTER MEDIAThese are:1. Filter paper2. Woven material (e.g. cheese cloth, woven polymer fiber, woven glass fiber)3. Non-woven fiber pads4. Sintered and perforated glass5. Sintered and perforated metal6. Ceramics7. Synthetic membranes

The DRIVING FORCEFiltration is driven by applying a pressure drop across the filter medium.The driving force can be applied by pressurizing the feed side (i.e. positive pressure filtration or simply pressure filtration) or by creating a vacuum in the filtrate side (i.e. negative pressure filtration or vacuum filtration). In the industry, both pressure and vacuum filtration are used. The feed can also be pressurized with a suitable pump. Vacuum filtration is preferred from a safety point of view since explosion is more hazardous than implosion.

Improvement of filtration efficiencyThe efficiency of cake filtration depends on the achieving high cake accumulation on the filter medium. However, the filtration rate declines with cake accumulation due to the increase in cake resistance. One way to solve this problem is to alter cake properties such that the specific cake resistance is reduced.

Improvement of filtration efficiency1. Feed pre-treatmentThe feed can be pre-treated by physical methods (e.g. heating) or by addition of chemicals (e.g. coagulants, flocculants) to obtain a porous cake with low specific cake resistance. Improvement of filtration efficiency2. Filter aidsFilter aids are substances that are mixed with the feed for creating very porous cakes. This increases the filtration rate very significantly.The filter aids which are particulate in nature can later be removed from the dried and powdered cake by suitable separation techniques (e.g. sieving). Improvement of filtration efficiency2. Filter aids (contd.)Filter aids may be used in either or both two ways:1-Pre- coating technique: by forming a pre-coat over the filter medium.2-Body- mix technique: A small proportion of the filter aid (0.1-0.5 %) is added to the slurry to be filtered. This slurry is re-circulated through the filter until a clear filtrate is obtained, filtration then proceeds to completion.

Mechanism of filtration with Filter Aids

Material used as FILTER AIDSThe following materials are used to form the precoat bed:Diatomaceous Earth (or Diatomite) consisting of siliceous skeletal remains of tiny aquatic unicellular plants.

Material used as FILTER AIDSPerlite consisting of glassy crushed and heat-expanded rock from volcanic origin.Asbestos and Cellulose consisting of fibrous light weight and ash less paper like medium.Special ground wood is becoming popular in recent years since it is combustible and reduces the high cost of disposal. There are nowadays manufacturers that grind, wash and classify special IMAGE GALLERYAquarium bacterial house:

IMAGE GALLERYCellulose and fiber filter media:

IMAGE GALLERYCellulose and fiber filter media:

IMAGE GALLERYCeramic filter media:

IMAGE GALLERYHousing for filter media:

IMAGE GALLERYElectronic house air-cleaner:

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