This document discusses filtration principles and parameters for process design. It defines filtration as separating solids from liquid using a porous medium, outlines key factors like filter type and cake formation. The document also describes Darcy's law governing filtration rate based on properties like pressure, area and viscosity. Process design parameters discussed include feed characterization like particle size and shape, while equipment design considerations cover throughput, filtration time and whether washing is needed.

2. Content
• Introduction
• Principle of filtration
• Filtration mechanism
• Filter types
• Process design parameters
• Equipment design parameters
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3. Introduction
• The separation of solids from a suspension in a
liquid by means of a porous medium or
• which retains the solids and allows the liquid to
pass is termed filtration.
• Filtrate may contain some fine particles.
(depending on the pore size)
• Filtration of the thick pulp gives rise to a moist
filter cake of between 80 to 90% solids
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4. Introduction
• Filter medium: generally to act as a support
for the filter cake.
• The filter medium should be mechanically
strong, resistant to the corrosive action of the
fluid, offer as little resistance as possible.
• Made up of: Natural (cloth), Synthetic fibers
(nylon) or metal wires.
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5. Introduction
• In filtration, the cake gradually builds up on the
medium, form the true filtering medium and the
resistance to flow progressively increases.
• Depending on the nature of the slurry, the driving
force required for separation may be grouped
into four categories:
• gravity
• Pressure drop
• Centrifugal
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6. Introduction
• Filtration is adversely affected by slimes, since
they tend to choke the filter medium.
• Flocculants are added to aid filtration
• Lower molecular weight flocculants are preferred
over those with high molecular weights.
• This is because the flocs formed with the latter
are relatively large, and entrain water within their
structure. This, in effect, increases the moisture
content of the filter cake.
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7. 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 accumulate
on the filter medium forming a packed bed of
solids, called filter cake
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8. 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 decrease
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9. Principle of filtration
• The factors influencing the rate of filtration:
 the pressure drop from the feed to the far side of
the filter medium
 the filtering surface area
 the filtrate viscosity
 the resistance offered by the filter cake
 The resistance of the filter medium.
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10. Principle of filtration
• DARCY LAW: [2]
fitration rate: dv/dt = KA∆P/ηL
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• 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

11. Filtration mechanism
 slurry is pumped into the filter through the
manifold located on the stationary head.
 the liquid component passes through the cloth
medium.
 the larger particles in the slurry begin to
gradually bridge the openings in the filter media,
reducing the size of the openings, allowing the
filter cake to form.
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12. Filtration mechanism
• Filter Cake Formation:
1) suspension flows through the clean filter medium,
some solids stay behind
2) suspension continues to flow through the partially
coated medium and at either reduced rate or
higher pressure differential, more solids stick
3) suspension now flow through the cake solids.
Most solids will now be caught, filtrate is cleaner,
flow reduces further and cake starts to
consolidate
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13. Filtration mechanism
4) solids have built up on the medium until there is
so much resistance that filtration has virtually
stopped.
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14. Filtration mechanism
 In case of batch filters this means stopping the
filter, discharging the cake and cleaning the
medium and restarting, whereas in continuous
filters the cake is continuously discharged and
the medium cleaned.
 finer particles are separated from the incoming
slurry, resulting in a filtrate that’s very low in
turbidity.
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15. Filter types
• The most common types of filters are ‘cake
filters
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16. Filter types
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1. Discontinuous Pressure Filters:
Apply large ∆P across septum to give economically rapid
filtration with viscous liquids or fine solids.
2. Vacuum Filter:
Vacuum filters are simple and reliable machines and
therefore have gained wide acceptance in the chemical,
food and pharmaceutical industries.

17. Filter types
• Plate and Frame Filter Press
• The plates are clamped together, then a pump starts
feeding the slurry into the filter press to complete a
filtering cycle and produce a batch of solid filtered
material, called the filter cake.
• A filter press uses increased pump pressure to
maximize the rate of filtration
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18. Filter types
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19. Filter types
• Drum Filter:
• consists of a 1 to 5 m diameter cylindrical drum that
rotates while remaining partially submerged in an open-
feed slurry tank.
• As panel leaves slurry zone, a wash liquid is drawn
through filter, then cake is sucked dry with air, and finally
cake is scraped off.
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20. Process design parameters
 Characterization of the feed
• Particle size distribution
• Affect cake formation rates and filtration equipment
selection.
• the finer the solids(below 44µ), the lower the unit's
capacity, the poorer it's performance and the more
restrictive the equipment choices.
• fine particles with a very narrow distribution are much
easier to handle than a wide distribution range with the
same average particle size.
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21. Process design parameters
 Characterization of the feed
• -10 micron solids content
• If fine particles are dispersed as true colloids, they
exhibit Brownian movement and do not settle.
• Therefore, charge neutralization (coagulation), and
sometimes polymer addition, are required for their
removal.
• these finer sizes adversely affect settling rate, filtration
cake, and cake moisture content.
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22. Process design parameters
 Characterization of the feed
• Particle shape
• Particle shape starts to influence performance when it
varies greatly from a general spherical form.
• Platelets act as multiple flapper valves within a filter cake
and restrict cake formation rate, particularly at higher
vacuums.
• Long needles can cause blinding of filter media by
imbedding in the pores of the cloth. In this case,
continuous cloth washing on a belt type filter is required
to maintain cloth porosity.
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23. Process design parameters
 Characterization of the feed
• Suspended solids concentration:
• High solids concentrations are concerned with cake
filtration (removing bulk solids from the liquid).
• Low solids concentrations (usually less than 5%) involve
clarification (the removal of small amounts of solids from
the bulk liquid).
• Dilute slurries must be concentrated, usually in a gravity
thickener, before going to the final dewatering device.
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24. Process design parameters
 Characterization of the feed
• Dissolved solids concentration:
• Impacts solute viscosity and is a function of the degree
of 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 of
pressure drop or temperature changes).
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25. Process design parameters
 Characterization of the feed
• The pH of the feed stream:
• the initial pH of the feed stream and the flexibility of
making changes to the pH in the process has impact on
filtration performance.
• Changes in pH can provide some flexibility in
pretreatment of the slurry as a result of its affect on the
behavior of particle surface chemistry.
• Use of coagulants are affected by pH.
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26. Equipment design parameters
• Process tonnage: (affect the economics of equipment selection)
• For low tonnages and solids concentrations, there is a
definite economic advantage in manual or semi-automated
batch operations (pressure filtration).
• Some pressure filters are fully automated and specifically
designed to handle large tonnages. Pressure filters of this
type approach the economics of continuous vacuum
filtration.
• The economics of continuous versus batch filtration
equipment is governed by the filtration rates achieved,
tonnage processed and cake moisture attained.
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27. Equipment design parameters
• Filtration time
• Pressure drop
• Filter medium (area and material)
• Whether the valuable product is the solid, the
fluid, or both.
• Whether it is necessary to wash the filtered
solids.
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28. Acknowledgement
Thanks to other presentations about filtration
existing on www.slideshare.net
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