filtration by sidra jabeen department of chemical engineering, university of engineering &...
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Filtration
By
Sidra Jabeen
Department of Chemical Engineering,
University of Engineering & Technology Lahore
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What is filtration?Understanding of the basic termsHow filtration is done?Types of filtrationRate of filtrationFilter MediaFilter Aid
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Lecture includes:
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Removal of solid particles from a fluid by passing it through a septum on which the solids are deposited
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Filtration
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Solubility Valuability
ConcentrationSize
Dissolved
Undissolved
Traces to High %
Micro filtration
Nano Filtration
Ultra filtration
Desired Waste
1. Solid Particles
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A continuous substance which can Flow
Gas Liquid
2. Fluids
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Filter Paper Membrane
3. Septum or Filtering Media
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In the form of cake on the septumOr
Trapped inside the pores of the septum
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4. Solid Deposition
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The solid remaining in the filter paper is called the residue.
The residue can be dried by spreading it out on the filter paper and allowing the liquid to evaporate.
The liquid which has passed through the filter paper is called the filtrate.
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Example
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Fluid flows through the filter medium by virtue of pressure difference across the medium.
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Through Feed Side Pump
Blower
Liquid height of column etcThrough Product Side
By generating Vacuum
How filtration is done?
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Two basic types of filtration are1. Cake filtration Solid particles form a
layer of solids on filtering media (called as cake).
2. Deep or Depth bed filtration Solid particles are caught inside the pores of filtering media.
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Types of filtration
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Solid particles are retained on septum as a layer of solids called as “cake”
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1. Cake Filtration
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Further of two typesa) Clarifying filtrationb) Cross flow filtration
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2. Deep Bed Filtration
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Solid particles are trapped inside the septum
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a. Clarifying Filtration
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Some of the liquid passes through the septum leaving behind conc. solution
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b. Cross flow Filtration
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Drop in pressure from the feed to the far side of septum
Area of the filtering surfaceViscosity of the solutionResistance of the filter cake
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Factors affecting Rate of Filtration
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Filter Media
Desired Properties Good Filtration
Should not PlugChemically ResistantPhysically StrongCheap
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Woven Materials (Cotton, Wool, Silk etc)
Perforated Metal Sheeting
Granular Materials (Sand, Asbestos etc)
Porous Solid
Felted-Fiber materials (Porous Paper)
Material of construction of filter media
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•Metal•Cloth
Filter Media Structure
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o Filter aids are granular solids which are used in combination with filtration to enhance rate of filtration. For example, Diatomaceous silica, perlite, purified wood cellulose etc.
o Filter aids are used in two different ways:Added before filtrationAs a pre-coat
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Filter Aids
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Added before filtrationThis increases the porosity of the cake and
reduces resistance of the cake during filtration.
As a pre-coat They can be used as a precoat before the
slurry is filtered. This will prevent solids from plugging the filter medium and also give a clearer filtrate.
Use of filter aids is usually limited to cases where the cake is discarded.
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Filter Aids
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Types of Filters
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Classification of Filters
Filters are classified on following three different basis:
I. Mechanism II.The driving forceIII.Operation
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On the basis of mechanism1. Cake filters
2. Clarifying filters3. Cross flow filters
On the basis of driving force1. Pressure Filters
2. Vacuum filters3. Centrifugal filters
1. Continuous filters2. Batch or discontinuous filters
On the basis of operation
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Pressure filters Pressure applied at feed side Vacuum filters Vacuum applied at product
sideCentrifugal separators Spinning the slurry to
force separationContinuous filters Flow of fluid and
discharge of solids (cake) is continuous or uninterrupted.
Batch filters Flow of fluid is continuous but it has to be interrupted to permit discharging of the accumulated solids.
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Classification of filters
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They can be pressure filters (filter press, shell & leaf filter)
Or they can operate under vacuum (rotary drum filter)
Or cake filtration can be carried in centrifugal filters (suspended batch centrifuges)
Either type can be batch or continuous.
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Cake filters
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Pressure filter operate in batch mode Sets of plates (circular or square) Plate faces covered by septum Slurry enters at one end Solids (cake) collect in chamber and liquid pass
out ‘Jammed’ filter Wash liquid, air or steam used to remove
residual liquid Press opened and cake removed Washing is time consuming and labor intensive
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1.Filter Press
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Pink : PlatesYellow : filter
ClothBlue : Filtrate
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Filter Press
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Filter Press
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2. Shell and leaf filter
Pressure filter operating in batch modeStack of leaves inside the closed tankFeed enters in the side of the tank Pass through leaves covered with filter Liquid leaves into discharge manifoldCake is removed by gravity force and
vibrationCake is effectively removed and economize
labor
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3. Shell and leaf filter
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Shell and leaf filter cake disposal
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Vacuum filter with continuous operationDrum turns at 0.1 – 2 rpm in slurry troughFilter covers the face of the drumRotary drum filter has four zones:
1. Filtering zone2. Washing and drying zone3. Cake removal zone4. Dead zone
Vacuum is applied in first two zonesPermeate and washing liquid discharge into
separate compartmentsDoctor blade is used in third zone
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3. Rotary Drum Filter
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Rotary Drum Filter
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Rotary Drum Filter
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Rotary Drum Filter
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Rotary Drum Filter
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Centrifugal filter operating in batch modePerforated baskets 750 – 1200 mm in dia. and
18 – 30 inch deepBasket rotates at 750 – 1200 rpmFeed taken from inlet is centrifuged Clear liquid pass out leaving behind solid cake
in basketWash liquid sprayed to remove soluble solids
and cake driedFor cake removal, basket is turned at 30 – 50
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4. Suspended Batch Centrifuge
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Suspended Batch Centrifuge
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Clarifying Filtration
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Removal of the Small amounts of solids or liquids droplets from the fluids.
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Clarifying Filtration
Principle of Clarification
• Particles are trapped inside the filter media or on its surfaces
• Caught by the surface forces• Reduce the active dia. of the channel
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Series of thin disks with close clearances in a vertical stack
Disks carried on a vertical hollow shaftLiquid admitted under pressureTrapping of the solids between disksLiquid flows out through the casingComb cleaner pass between the disks and
drop solids to the bottom of casing
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Liquid Clarification: Cartridge Filter
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Cartridge Filter
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For atmospheric dust – Pad filtersFor process dusts – Bag Filters
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Gas Clarification
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Before
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After
Pad Filter
Air passed through pads of filter mediaPad may be dry or coated with viscous oilFor light duty – pads are disposableFor heavy duty – reused by rinsing and
recoating
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Bag Filter or Bag House
Contains one or more large bags of fabric material inside metal casing
Dust laden gas enters the filter at the bottom
Solid particles trap inside the bag and clean gas leave at the top
Solids are discharged by shaking mechanism
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Cross flow Filtration
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Filtration in which flow of the suspension is parallel to the filtering media used to get concentrated slurry
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Definition
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The feed is passed across the filter membrane at positive pressure relative to the permeate side. A proportion of the material which is smaller than the membrane pore size passes through the membrane as permeate or filtrate; everything else is retained on the feed side of the membrane as retentate.
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Cross flow filtration Operation
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Cross Flow Filtration1. Flow of fluid is parallel
to the surface2. Majority of the feed
travels across the surface of the filter
3. Process feed remains in the form of a mobile slurry, suitable for further processing
4. It is possible to fractionate particles by size
Conventional Filtration1. Flow of fluid is
perpendicular to the surface
2. Solids in the feed trap inside the filter or retain on the filter
3. Process feed is transformed into solid cake & filtrate
4. It is simply the separation of solids from liquids, no fractionation
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Difference b/w cross flow & Conventional filtration
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Fouling of the membrane Permeate flux Percent rejection Back flushing Factors for optimizing permeate flux
1. Trans-membrane pressure2. Shear rate
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Performance of cross flow filtration
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Reverse OsmosisMicrofiltrationUltrafiltrationNanofiltration
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Types of cross flow filtration
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The pressure driven transport of solvent from a solution through a membrane is known as reverse osmosis
Applications Separating low-molecular-weight
substances in solutionConcentratingCleaning wastewater Demineralization
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Reverse Osmosis
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OsmosisOsmotic pressureReveres Osmosis
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Points of discussion
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Used for the particles in the size range of 0.1- 5 μm.
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Applications
• Fermentation• Biomass clarification and recovery
Micro filtration
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Used for the particles in the size range from 1μm down to 10-3 μm.
Applications used in the fractionation of milk as well as
protein fractionation
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Ultra filtration
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Used for the particles up to 1nmNanofiltration is the process with the
characteristics b/w those of Ultrafiltration and reverse osmosis.
ApplicationsPharmaceutical processingWater treatment
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Nano filtration
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