Download - CENTRIFUGAL SEPARATION (Unit Operation-2)
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CENTRIFUGAL SEPARATION
(Unit Operation-2)
Prof. Saikat Maitra
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Today Topics :
Centrifugal Separation
Introduction
Application
Equipment: Cyclone Separator
Theory
Centrifugal force
Rate of Settling
Critical Diameter
TODAY’S TOPIC
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Students should be able to
comprehend & discuss concept & theory on
centrifugal separation
determine centrifugal force, critical diameter, rate of
settling
analyze & design an application
LESSON OUTOMES
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Centrifugal Separation
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Centrifugal settling or sedimentation
separation of particles from a fluid by centrifugal forces acting
on the particles
used on particles that cannot be settled easily in gravity
settling – smaller particles
does not change relative settling velocities
overcome
disturbing effect of Brownian motion
free convective currents
gives faster results than gravity settling
Introduction
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Slurry feed Slurry feed
liquid solid heavy
liquid
fraction
light
liquid
fraction
Liquid-liquid feed Slurry feed Slurry feed
liquid solid heavy
liquid
fraction
light
liquid
fraction
Liquid-liquid feed
Slurry feed
Slurry feed
Slurry feed
Slurry Fed Slurry Fed
Liquid Solid
Liquid –Liquid Feed
Heavy Liquid Faction
Light Liquid Fraction
Basic Theory of Centrifugal Separation
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separation of cream from whole milk
separation of cellular materials
beers
vegetable oil
fish-protein-concentration
fruit juice
drying crystals
separation of emulsion into liquids or solid-liquid
remove dust particles from air
vacuum cleaner
Application
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Size classification
vertical
conical
Equipment: Cyclone Separators
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• Centrifugal force
ae= acceleration from a centrifugal force (m/s2)
r = radial distance from centre
= angular velocity (rad/s)
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• Rotational speed, N rev/min
• Gravitational Force,
• Centrifugal force in terms of gravitational force
Basic theory of centrifugal separation
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Force in a centrifuge
A centrifuge having a radius of the bowl of 0.1016 m is
rotating at N = 1000 rev/min.
a) Calculate the centrifugal force developed in terms of
gravity forces.
b) Compare this force to that for a bowl with a radius of
0.2032 m rotating at the same rev/min.
Example
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Force in a centrifuge
A centrifuge having a radius of the bowl of 0.1016 m is
rotating at N = 1000 rev/min.
a) Calculate the centrifugal force developed in terms of
gravity forces.
b) Compare this force to that for a bowl with a radius of
0.2032 m rotating at the same rev/min.
Example
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Given: (a) r = 0.1016 m (a)
(b) r = 0.2032 m
N = 1000 rev/min
Calculate: centrifugal force
Example : Problem Statement
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g
rNF
F
g
c
6.113
001118.0 2
g
rNF
F
g
c
2.227
001118.0 2
Example : Solution
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Rate of settling in centrifuges
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• Settling in Stoke’s law range,
• Integrating between the limits r = r1 at t = 0 and r = r2 at t = tT
Rate of settling in centrifuges
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• Critical diameter, Dpc – diameter of particle that reaches half
the distance between r1 and r2.
Rate of settling in centrifuges
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Settling in a centrifuge
A viscous solution containing particles with a density
1461 kg/m3 is to be clarified by centrifugation. The
solution density is 801 kg/m3 and its viscosity is 100 cp.
The centrifuge has bowl with r2 = 0.02225 m, r1 =
0.00716 m and height b = 0.1970 m. Calculate the
critical particle diameter of the largest particles in the
exit stream if N=23000 rev/min and the flowrate q =
0.002832 m3/h.
Example
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Given: viscous solution containing particles
rp = 1461 kg/m3
r = 801 kg/m3, m = 100 cp
bowl: r2 = 0.02225 m, r1 = 0.00716 m
N = 23000 rev/min
q = 0.002832 m3/h
Calculate: critical diameter
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Convert rotation into rad/s
Bowl volume
Convert flow rate
Use Eqn. to find Dpc
Example : Solution
3600
002832.0
)(
60
2
2
1
2
2
cq
rrbV
N
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comprehend & discuss concept & theory on centrifugal
separation
determine
centrifugal force, FC
critical diameter, DPC
rate of settling, qC
analyze & design an application
RECAP
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References:
[1] Geankoplis C. J., Transport Processes and Unit Operations,
4th Edition, Prentice Hall, 2003.
[2] Perry, R.H. and Green, D. Perry’s Chemical Engineers’
Handbook, 6th ed. New York, McGraw-Hill Book Company,
1984.
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Question & Answers
THANK YOU