2. PRINCIPLE
2
Centrifugation:
The centrifuge involves the principle of
sedimentation, where the acceleration at centripetal
force causes denser substances to separate along the
radial direction at the bottom of the tube and the
lighter objects will tend move up the tube. The
particle having size more than 5 um are separated by
simple filtration process while the particle having size
5 m or less do not sediment under gravity.
7. 7
Principle of Perforated basket
• In perforated basket centrifuge, separation occurs through
perforated wall depends on the difference in the densities of
solid and liquid phases.
8. CONSTRUCTION:
• It consist of stainless steel perforate basket lined
with filter cloth. The basket should be made of
corrosion resistant material. The basket is covered
with copper or lead. The basket is mounted on
shaft.
• If basket is mounted above the driving shaft then
arrangement is known as under-driven. If basket is
suspended from A shaft then it is known as over-
driven. The shaft is driven by motor.
• The basket is surrounded by casing which collect the
filtrate and discharge through outlet.
• The diameter of basket is 0.90 meter.
• The basket require 5 kilowatt power for starting
and after attaining desired speed the power is
reduced to 2 kilowatt.
• The diameter of perforation depends on crystal size.
• The basket operated at speed of 1000 rpm
WORKING
• The material is loaded into the basket. The amount
of loaded material should be optimum.
• The loading of material should provide even
distribution.
• The power is supplied to rotate the basket. But when
fully loaded basket is rotated at high speed then there
are chances of great strain and vibration due to
centrifugal force,
• The basket contains perforated wall. During
centrifugation liquid phase leaves through perforated
wall and collected at outlet while solid phase retains
in the basket. Then turned off the power.
• Centrifuge is stopped by applying brake. The basket
keep to rest and then solid is removed. The solid
cake is cut by blade and unloaded
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ADVANTAGES:
1. This centrifuge are employed when solid concentration in
slurry is high. 2. It occupy very little space 3. Rapid process
DISADVANTAGES:
1. On prolonged operation the centrifugal force put greater
strain on basket which cause wear of equipment.
2. On prolonged operation, solid get converted into hard cake
which is difficult to remove.
3. It is a batch operation
USES:
Perforated basket centrifuge is used to separate crystalline drug
such as aspirin , to separate sugar crystals and to separate
precipitated protein from insulin.
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Non Perforated basket
• Principle: In this centrifuge the basket contains non perforated
side wall. The separation of solid and liquid phase depends on
difference in densities of both phases without porous barrier.
During centrifugation solid deposited at side of basket while
liquid remained at top which is removed by skimming tube
10. CONSTRUCTION:
• It consist of non perforated basket
made of steel.
• The material is loaded into basket
through feed tube.
• The basket is mounted on vertical
shaft which is rotated by motor.
• The liquid is removed with the help of
skimming tube
WORKING
• The suspension is fed into the basket
continuously through feed tube.
• During centrifugation solid deposited
at side of basket while liquid
remained at top which is removed by
skimming tube.
• When sufficient amount of solid get
deposited at the side of basket then it
is removed intermittently by hand and
continuously by scraper blade
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USES:
Non perforated basket centrifuge is employed
when deposited solids provide high resistance
to the flow of liquid.
11. 11
SEMI CONTINUOUS CENTRIFUGE
• Principle: In Semi Continuous centrifuge, separation
occurs through perforated wall depends on the
difference in the densities of solid and liquid phases.
12. CONSTRUCTION:
• It consist of perforated basket
mounted on horizontal shaft and run
continuously by motor.
• The side of the basket is perforated.
Feed or suspension is introduced
through feed pipe.
• There is also provision of wash pipe
which is used to wash the crystals.
• The thickness of feed depends on the
feeler which rides over the feed. The
layer of cake is removed by a chute
fitted with a knife. The knife cuts
down the cake within the basket.
• The knife-chute assembly is raised
with the help of a hydraulic apparatus
WORKING
• The basket is rotated horizontally
with a motor. The suspension is
introduced through the pipe.
• The slurry passes through the
perforated side. The crystals remain
inside the basket. The filtrate is
eliminated from the outlet.
• When the height of the cake is
approximately 2-3 inches, the
suspension inlet is stopped by a
"feeler diaphragm valve assembly".
The basket rotates a predetermined
time and then the cake is washed with
water.
• The basket is rotated for another
predetermined time.
• After that, the hydraulic apparatus
raises the knife-chute assembly to cut
the cake and cake is collected
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DISADVANTAGES:
1 Complicated process
2 Sometime chances of breakage of crystal
during discharge
3. High power consumption
ADVANTAGES:
1. This centrifuge is used to separate
crystals from mother liquor
2. This is used to clarify Liquids by
removing unwanted solids dirt from oils
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SUPER CENTRIFUGE
• Principle: It is a continuous centrifuge used to separate two
immiscible liquid phases. It is a sedimentation type centrifuge.
During centrifugation, the heavier liquid is thrown against the
container wall while the lighter liquid remains as an inner
layer. The two layers are simultaneously separated.
14. CONSTRUCTION:
• It consists of a long, hollow,
cylindrical bowl of small diameter
which is suspended from a
flexible spindle at the top and the
bottom is fitted loosely in a bush.
• It is rotated on its vertical axis.
• Feed is introduced through the
bottom through a nozzle with
pressure.
• Two liquid outlets are provided at
different heights.
WORKING
• The centrifuge rotate on its vertical
axis at approximately 2000 rpm.
• The feed is introduced in the lower
part through a nozzle with pressure.
• During centrifugation, two liquid
phases were separated according to
their densities.
• The heavier liquid moves towards the
periphery and the lighter liquid forms
an inner layer.
• Both liquids ascend to the upper part
of the vertical bowl.
• These two layers are simultaneously
removed separately from different
heights through modified outlets.
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ADVANTAGES:
This type of centrifuge is employed in case
where amount of solid in liquid is small and it
is necessary to remove it only at long intervals
USES:
Supercentrifuge is widely used for
separating liquid phases of emulsions in
food, biochemical and pharmaceuticals
industries.
