Content• Introduction• Principle of filtration• Filtration mechanism• Filter types• Process design parameters• Equipment d...
Introduction• The separation of solids from a suspension in aliquid by means of a porous medium or• which retains the soli...
Introduction• Filter medium: generally to act as a supportfor the filter cake.• The filter medium should be mechanicallyst...
Introduction• In filtration, the cake gradually builds up on themedium, form the true filtering medium and theresistance t...
Introduction• Filtration is adversely affected by slimes, sincethey tend to choke the filter medium.• Flocculants are adde...
Principle of filtration•The volume of filtrate collected per unit time (dV/dt)is termed as the rate of filtration.•As the ...
Principle of filtration• As the thickness of the cake increases:  resistance to flow of filtrate increases  rate of fi...
Principle of filtration• The factors influencing the rate of filtration: the pressure drop from the feed to the far side ...
Principle of filtration• DARCY LAW: [2]fitration rate: dv/dt = KA∆P/ηL10• V: volume of filtrate• T: time of filtration• K:...
Filtration mechanism slurry is pumped into the filter through themanifold located on the stationary head. the liquid com...
Filtration mechanism• Filter Cake Formation:1) suspension flows through the clean filter medium,some solids stay behind2) ...
Filtration mechanism4) solids have built up on the medium until there isso much resistance that filtration has virtuallyst...
Filtration mechanism In case of batch filters this means stopping thefilter, discharging the cake and cleaning themedium ...
Filter types• The most common types of filters are ‘cakefilters15
Filter types161. Discontinuous Pressure Filters:Apply large ∆P across septum to give economically rapidfiltration with vis...
Filter types• Plate and Frame Filter Press• The plates are clamped together, then a pump startsfeeding the slurry into the...
Filter types18
Filter types• Drum Filter:• consists of a 1 to 5 m diameter cylindrical drum thatrotates while remaining partially submerg...
Process design parameters Characterization of the feed• Particle size distribution• Affect cake formation rates and filtr...
Process design parameters Characterization of the feed• -10 micron solids content• If fine particles are dispersed as tru...
Process design parameters Characterization of the feed• Particle shape• Particle shape starts to influence performance wh...
Process design parameters Characterization of the feed• Suspended solids concentration:• High solids concentrations are c...
Process design parameters Characterization of the feed• Dissolved solids concentration:• Impacts solute viscosity and is ...
Process design parameters Characterization of the feed• The pH of the feed stream:• the initial pH of the feed stream and...
Equipment design parameters• Process tonnage: (affect the economics of equipment selection)• For low tonnages and solids c...
Equipment design parameters• Filtration time• Pressure drop• Filter medium (area and material)• Whether the valuable produ...
AcknowledgementThanks to other presentations about filtrationexisting on www.slideshare.net28
Filtration: mechanism and design parameters
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Filtration: mechanism and design parameters

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A dewatering method in mineral processing

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  • This may be an important consideration depending on the degree of solute saturation, and nature of the dissolved solids present in the treated stream .
  • Filtration: mechanism and design parameters

    1. 1. Content• Introduction• Principle of filtration• Filtration mechanism• Filter types• Process design parameters• Equipment design parameters2
    2. 2. Introduction• The separation of solids from a suspension in aliquid by means of a porous medium or• which retains the solids and allows the liquid topass is termed filtration.• Filtrate may contain some fine particles.(depending on the pore size)• Filtration of the thick pulp gives rise to a moistfilter cake of between 80 to 90% solids3
    3. 3. Introduction• Filter medium: generally to act as a supportfor the filter cake.• The filter medium should be mechanicallystrong, resistant to the corrosive action of thefluid, offer as little resistance as possible.• Made up of: Natural (cloth), Synthetic fibers(nylon) or metal wires.4
    4. 4. Introduction• In filtration, the cake gradually builds up on themedium, form the true filtering medium and theresistance to flow progressively increases.• Depending on the nature of the slurry, the drivingforce required for separation may be groupedinto four categories:• gravity• Pressure drop• Centrifugal5
    5. 5. Introduction• Filtration is adversely affected by slimes, sincethey tend to choke the filter medium.• Flocculants are added to aid filtration• Lower molecular weight flocculants are preferredover those with high molecular weights.• This is because the flocs formed with the latterare relatively large, and entrain water within theirstructure. This, in effect, increases the moisturecontent of the filter cake.6
    6. 6. Principle of filtration•The volume of filtrate collected per unit time (dV/dt)is termed as the rate of filtration.•As the filtration proceeds, solid particle accumulateon the filter medium forming a packed bed ofsolids, called filter cake7
    7. 7. Principle of filtration• As the thickness of the cake increases:  resistance to flow of filtrate increases  rate of filtration gradually decreases.• Filtration rate constant pressure drop increase• Pressure drop constant filtration rate decrease8
    8. 8. Principle of filtration• The factors influencing the rate of filtration: the pressure drop from the feed to the far side ofthe filter medium the filtering surface area the filtrate viscosity the resistance offered by the filter cake The resistance of the filter medium.9
    9. 9. Principle of filtration• DARCY LAW: [2]fitration rate: dv/dt = KA∆P/ηL10• V: volume of filtrate• T: time of filtration• K: constant for filter medium & filter cake• A: area of filter medium• ∆P: pressure drop above & below the filter• η: viscosity of filtrate• L: thickness of the filter bed• V: volume of filtrate• T: time of filtration• K: constant for filter medium & filter cake• A: area of filter medium• ∆P: pressure drop above & below the filter• η: viscosity of filtrate• L: thickness of the filter bed
    10. 10. Filtration mechanism slurry is pumped into the filter through themanifold located on the stationary head. the liquid component passes through the clothmedium. the larger particles in the slurry begin togradually bridge the openings in the filter media,reducing the size of the openings, allowing thefilter cake to form.11
    11. 11. Filtration mechanism• Filter Cake Formation:1) suspension flows through the clean filter medium,some solids stay behind2) suspension continues to flow through the partiallycoated medium and at either reduced rate orhigher pressure differential, more solids stick3) suspension now flow through the cake solids.Most solids will now be caught, filtrate is cleaner,flow reduces further and cake starts toconsolidate12
    12. 12. Filtration mechanism4) solids have built up on the medium until there isso much resistance that filtration has virtuallystopped.13
    13. 13. Filtration mechanism In case of batch filters this means stopping thefilter, discharging the cake and cleaning themedium and restarting, whereas in continuousfilters the cake is continuously discharged andthe medium cleaned. finer particles are separated from the incomingslurry, resulting in a filtrate that’s very low inturbidity.14
    14. 14. Filter types• The most common types of filters are ‘cakefilters15
    15. 15. Filter types161. Discontinuous Pressure Filters:Apply large ∆P across septum to give economically rapidfiltration with viscous liquids or fine solids.2. Vacuum Filter:Vacuum filters are simple and reliable machines andtherefore have gained wide acceptance in the chemical,food and pharmaceutical industries.
    16. 16. Filter types• Plate and Frame Filter Press• The plates are clamped together, then a pump startsfeeding the slurry into the filter press to complete afiltering cycle and produce a batch of solid filteredmaterial, called the filter cake.• A filter press uses increased pump pressure tomaximize the rate of filtration17
    17. 17. Filter types18
    18. 18. Filter types• Drum Filter:• consists of a 1 to 5 m diameter cylindrical drum thatrotates while remaining partially submerged in an open-feed slurry tank.• As panel leaves slurry zone, a wash liquid is drawnthrough filter, then cake is sucked dry with air, and finallycake is scraped off.19
    19. 19. Process design parameters Characterization of the feed• Particle size distribution• Affect cake formation rates and filtration equipmentselection.• the finer the solids(below 44µ), the lower the unitscapacity, the poorer its performance and the morerestrictive the equipment choices.• fine particles with a very narrow distribution are mucheasier to handle than a wide distribution range with thesame average particle size.20
    20. 20. Process design parameters Characterization of the feed• -10 micron solids content• If fine particles are dispersed as true colloids, theyexhibit Brownian movement and do not settle.• Therefore, charge neutralization (coagulation), andsometimes polymer addition, are required for theirremoval.• these finer sizes adversely affect settling rate, filtrationcake, and cake moisture content.21
    21. 21. Process design parameters Characterization of the feed• Particle shape• Particle shape starts to influence performance when itvaries greatly from a general spherical form.• Platelets act as multiple flapper valves within a filter cakeand restrict cake formation rate, particularly at highervacuums.• Long needles can cause blinding of filter media byimbedding in the pores of the cloth. In this case,continuous cloth washing on a belt type filter is requiredto maintain cloth porosity.22
    22. 22. Process design parameters Characterization of the feed• Suspended solids concentration:• High solids concentrations are concerned with cakefiltration (removing bulk solids from the liquid).• Low solids concentrations (usually less than 5%) involveclarification (the removal of small amounts of solids fromthe bulk liquid).• Dilute slurries must be concentrated, usually in a gravitythickener, before going to the final dewatering device.23
    23. 23. Process design parameters Characterization of the feed• Dissolved solids concentration:• Impacts solute viscosity and is a function of the degreeof saturation for the component present.• Dissolved solids can cause:o scaling in the internals of the equipment.o Blind the filter cloth due to precipitation (because ofpressure drop or temperature changes).24
    24. 24. Process design parameters Characterization of the feed• The pH of the feed stream:• the initial pH of the feed stream and the flexibility ofmaking changes to the pH in the process has impact onfiltration performance.• Changes in pH can provide some flexibility inpretreatment of the slurry as a result of its affect on thebehavior of particle surface chemistry.• Use of coagulants are affected by pH.25
    25. 25. Equipment design parameters• Process tonnage: (affect the economics of equipment selection)• For low tonnages and solids concentrations, there is adefinite economic advantage in manual or semi-automatedbatch operations (pressure filtration).• Some pressure filters are fully automated and specificallydesigned to handle large tonnages. Pressure filters of thistype approach the economics of continuous vacuumfiltration.• The economics of continuous versus batch filtrationequipment is governed by the filtration rates achieved,tonnage processed and cake moisture attained.26
    26. 26. Equipment design parameters• Filtration time• Pressure drop• Filter medium (area and material)• Whether the valuable product is the solid, thefluid, or both.• Whether it is necessary to wash the filteredsolids.27
    27. 27. AcknowledgementThanks to other presentations about filtrationexisting on www.slideshare.net28

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