Mechanical separation of solid by centrifugal force. . Prepared by Qaisar Yaqoob linledin.com/techqaisar facebook.com/techqaisar gmail.com/techqaisar hotmail.com/techqaisar instgram.com/techqaisar twitter.com/techqaisar

1. Centrifugal Separator
It is a machine which utilized the centrifugal force for the separation of liquid from
solid. Solid that form a porous cake can be separated from liquid in a filtering centrifuge. For this
purpose, centrifugal force is applied to given slurry by which separation is done on the base of
difference in densities. The force is done by centrifugal action given by following equation,
Fc =
𝑊𝑈2
𝑔 𝑐 𝑟
where; Fc = Force developed by centrifuge
𝑊 = Weight of rotating assembly + load
𝑈 = velocity of basket
𝑔𝑐 = Dimensional constant
𝑟 = Radios of basket
Many type of centrifuge separators are installed for industrial level operation. But
main purpose is same in all separator as follow,
Construction:
It is consisting on a
rotating basket which is fixed on
vertical shaft. This shaft is driven by
motor. The basket is perforated on the
sides and covered by a screen. This
basket is protected by casing that
collect the filtrate after passing
through the perforations. This filtrate
is discharge through the outlet which
is provided in the centrifuge. There is
a feed inlet also given in the
centrifuge. Knife is provided for
removal of cake by scraper discharge
method. In discontinuous or batch
separator removable plates are
available to remove the cake.
Washing of septum is available in
centrifuge separator. For this purpose,

2. washing water is introduced. To stop the centrifuge hydraulic breaks are installed. Speciation of
centrifuge is as fallow,
Basket diameter = 30” - 80”
Depth of basket = 18” - 50”
Speed = (800 - 1800) rpm
Thickness of cake = 2” - 6”
Production rate = (100 – 4000) lbs. solid/hr.
Working:
The material which is to be
centrifuge is filled in the basket when the
basket is on rest in batch type but in
continuous separator feed introduced
without of any interruption. Technically it
is called charging of centrifuge. After this
basket allow to rotate at high speed and
centrifugal force is applied. Due to this
filtrate will pass through perforation by
which cake formation start on screen and
filtrate is collected through outlet. After a
definite length of time centrifuge is stopped
by applying breaks and basket bought to
rest position. After that solid cake is
washed through washing water and then
cake leave to dry, after that cake removed
from basket by applying knife.
But in continues centrifugal separators cake
removal process is done by automatic
system.
Classificationofcentrifugal
separator:
a) Suspended batch centrifuge
b) Automatic batch centrifuge
c) Continuous filtering centrifuge

3. Suspended batch separator: A common type of batch centrifuge in industrial processing is the
suspended batch centrifuge. The perforated basket ranges from (750 – 1200) mm in diameter and
(450 - 750) mm deep and rotate with (600 - 1800) rpm. The basket held at lower end of a free
driven vertical shaft. Filter medium of perforated wall is installed. Feed slurry enters to rotating
basket through an inlet pipe. And filtration
done through centrifugal force and a layer of
cake ranges from 2” – 6” is formed on septum
after definite length of time. Then wash water
is applied on cake to dissolved soluble
material. The cake is then spun as dry as
possible. The motor is shut off and basket is
stopped by mean of breaks. And then cake is
removed and drops out through an opening in
basket floor. After all that cycle repeated.
These separators are used in textile
industries and sugar industries in refining
section. Where operation has short cycle of 2
to 3 min per load and produce up to 5 tones/hr.
of crystals.
Suspended batch centrifuge are divided in two
categories on the base of installed motor,
1- Top driven
2- Under driven

4. Automatic batch centrifuge: In this machine the basket rotates at constant speed about
horizontal axis. Feed slurry, wash liquid and screen rinse are successively sprayed into the basket
at appropriate intervals for controlled length of time. The basket unloaded while turning at full
speed by heavy knife that rises periodically and cut the solids.
The basket in these machine is between (500 – 1100) mm diameter. It has very high productive
capacity with free draining crystal. Usually they are not used when the feed contains finer
particles than 150 mesh. It cannot handle slow draining solids.
Continuous filtering centrifuge: A rotating basket with slotted wall is fed through a revolving
feed funnel. The purpose of the funnel is to accelerate the feed slurry smoothly and gently. Feed
enters the small end of the funnel from a stationary pipe. It travels towards the large end of
funnel. Liquid flow through the wall which cover with woven metal. A layer of crystal of
thickness (25 - 75) mm is formed. This layer is moved over by reciprocating pusher. Each stroke
of pusher moves the cake to the lip of basket until it deposit over.
The gentle acceleration of feed slurry and decelerations of discharge solids minimize
breakage of the crystals. Diameter of basket ranges from (300 - 1200) mm.

5. Applications:
Centrifugal separators are used in chemical industries in the purification of
intermediate or final products and even in the recovery of waste products. These centrifugal

6. separators are largely installed in pharmaceutical and bio-technologies industry, in production
processes of minerals, metals and non-conventional fuels e.g. biodiesel, ethanol
 It is used for fuels cleaning and treatment, for lube oils purification, for the conditioning
and recovery of mineral oils, industrial or environmental slop oils, bottom tank residues
and bilge water.
 These are installed for any type of food or beverage. Centrifugal separators are used for
fruit or vegetable juice purification, wine processing, food treatment, edible additives
extraction.
 Take part in the treatment and recovery of process water and industrial fluids, in polymer
recycling and in drilling mud conditioning.
 Centrifugal separators are also used in milk and dairy industries for separation processes,
heat treatments and waste products recovery with the most advanced technologies and
remote control systems.