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CentrifugalCentrifugal
SeparationSeparation
Dr B K KumbharDr B K Kumbhar
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Application of Centrifugal separationApplication of Centrifugal separation Liquid-liquid separationLiquid-liquid separation
Cream-separated milkCream-separated milk
Liquid-solid separationLiquid-solid separation
Whey-caseinWhey-casein Gaseous-solid separationGaseous-solid separation
Air-milk powderAir-milk powder
Gaseous-liquid separationGaseous-liquid separationVapor-concentrated milkVapor-concentrated milk
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StandardizationStandardization
Standardized cow milk 4.5 % fatStandardized cow milk 4.5 % fat
Standardized buffalo milk 6.0 % fatStandardized buffalo milk 6.0 % fat
Toned milk 3.0 % fatToned milk 3.0 % fat Double toned milk 1.5 % fatDouble toned milk 1.5 % fat
Pearsons squarePearsons square
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Pearson's squarePearson's square
= y1
= y2Skim milk
Cream
Y = y1 + y2 Standardized milkwithC %fat
Cream
Skim milk
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CentrifugeCentrifuge
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CentrifugeCentrifuge
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centrifugecentrifuge
Skimmilk
Cream
Whole Milk
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Centrifugal separatorCentrifugal separator
Skim milk
Cream
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StandardizationStandardization
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StandardizationStandardization
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b
R1
R2
dR
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HeavyLiquid
Lightliquid
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Centrifugal force, FCentrifugal force, Fcc
2c F mR=
260
N =
M= mass of theparticle
R= radius
w = Angularvelocity
N = Speed, RPM
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2
2 2
2 2
22
2
2
dF R dm
dm bRdRdF bR dR
Force bR dRdP
Area Rb
=
==
= =
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2
2 1 1
2
1
2
2
22
2 2 2
2 1
( )
2
( )
2
R
R R
R
R
R
dP R dR
P RdR
R
R R
=
=
=
=
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2 2 2
2 2 2
( )( )
2
( )
( ) 2
i A
i B
A i A
R R
B i B
R R
R RP
R R
P
=
=
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2 2( ) A A B Bi
A B
R RR
=
f i i i
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R= radiusR= radius
=density=densitySubscripts A=heavy liquid zoneSubscripts A=heavy liquid zone
B= light liquid zoneB= light liquid zone
i=interfacei=interface
BA
BBAA
i
RR
R
=
22
22
22
Bi
Ai
s
m
RRRR
=
Interface position in cream separator
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EEss=degree of cream separation=degree of cream separation
ffss=fat content of the separated (skim)=fat content of the separated (skim)
milkmilk
ffww= fat content of the whole milk= fat content of the whole milk
w
ss
f
f
milkwholetheofcontentFat
creamtheofcontentFatE == 1
Es=degree of cream separationEs=degree of cream separation
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m
m
ffff
mm
=
1
2
2
1
MM11 =Mass flow rate of skim=Mass flow rate of skimmilkmilk
mm22 = mass flow rate of cream= mass flow rate of cream
ff11 = fat content of skim milk= fat content of skim milkff22 = fat content of cream= fat content of cream
ffmm= fat content of mixture= fat content of mixture
ProportionProportion
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Q= volumetric flow rate, mQ= volumetric flow rate, m33/s/s
z=number of discsz=number of discs
n=speed, rpsn=speed, rpsRRoo=outer radius, m R=outer radius, m Rii=inner=inner
radius, mradius, m =Density difference=Density differencex=correction factorx=correction factor =angle=angletan=tangenttan=tangent
= absolute viscosity, Pa-s= absolute viscosity, Pa-sd=diameter of fat globule, md=diameter of fat globule, m
( ) ( ) xdnRRzQ io
18tan
32
2233
3
=
Volumetric flow rate in centrifugal separator
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z= centrifugal constantz= centrifugal constantR= radius of the bowlR= radius of the bowl
n=rpmn=rpmg= acceleration due tog= acceleration due to
gravitygravity
( )
894
2 22
Rn
g
Rnz ==
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Power=E / tPower=E / t speedspeed
E=energy required during startingE=energy required during starting
L=lengthL=length BowlBowl = Density of bowl= Density of bowlttspeedspeed = time required to reach running speed= time required to reach running speed
( )LRRnE ioBowl4423 =
Power required
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Factors affectingFactors affecting
separationseparation TemperatureTemperature
Bowl speedBowl speed
Disc separation (Spacing)Disc separation (Spacing) Flow rateFlow rate
Control of fat percent in creamControl of fat percent in cream
Raw milkRaw milk
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TemperatureTemperature
Increase in temperature increases separationIncrease in temperature increases separationefficiencyefficiencyDensity difference increasesDensity difference increases
Reduced viscosityReduced viscosity
Disruption of fat globulesDisruption of fat globules
Separation at around 50Separation at around 50 ooCC
Fat loss atFat loss at
7272 ooC slightly higher than at 54.4C slightly higher than at 54.4 ooCC
3232 ooC much higher than at 54.5C much higher than at 54.5 ooCC
B l dBowl speed
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Bowl speedBowl speed
Velocity of fat globule proportional to (speed)Velocity of fat globule proportional to (speed)22
Increase in bowl speedIncrease in bowl speed Increases separation efficiencyIncreases separation efficiency
Increased energy inputIncreased energy input
Robust design to withstand large forces at theRobust design to withstand large forces at thebowl peripherybowl periphery
Generates more noiseGenerates more noise
Skimming efficiency adequate at 4000-5000Skimming efficiency adequate at 4000-5000rpmrpm
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Flow rateFlow rate Flow of incoming milkFlow of incoming milk
Flow of skim milkFlow of skim milk Flow of creamFlow of cream
Low flow rateLow flow rate More separation efficiency due to more residence timeMore separation efficiency due to more residence time
Should not be so low- significant air entrainmentShould not be so low- significant air entrainment
Too high flow rateToo high flow rate
Flooding of separatorFlooding of separator
No separationNo separation
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Control of fat percent inControl of fat percent in
creamcream
Control of fat percent in cream- relativeControl of fat percent in cream- relative
size ofsize of
Skim milk flowSkim milk flow Cream flowCream flow
Adjusted by back pressureAdjusted by back pressure
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Raw milkRaw milk
Velocity of fat globule depends on sizeVelocity of fat globule depends on size
High proportion of small fat globule reducedHigh proportion of small fat globule reduced
efficiencyefficiency
Lower limit for fat separation- 1Lower limit for fat separation- 1 mm
Fat % in skim milk 0.04-0.06% with cream atFat % in skim milk 0.04-0.06% with cream at
40% fat40% fat
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Nature of the problemand probable reason
Actionto be taken
Skimming is poor
Milk is dirty Clean and strain
Milk is cold Heat to 30-35 C
Milk is soured Separate immediately after milking
Slow speed Increase the speed
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Cream is too thin when the screw is adjusted
Slow speed
Bowl too high Adjust as per recommendation
Cream is too thick when the screw is adjusted
Fast speed Adjust the speed
Dirty regulator pipe Clean it
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Separator vibrate
Separator not fixed rigidly Fix it
Conveyor of the bowl is dirty Clean itNeck bearing spring damaged Remove it and replace
Bowl not well tightened Tighten
Bowl may be damaged ReplaceFaulty driving devices Replace
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Separator runs noisily
Bowl grinds against the skim milkcover
Adjust
Separator runs heavily
Oil is very viscous/contaminated Change oil
Bowl too low in a frame Adjust as per recommendation
Centrifugal filtration
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( )
+
=
m
m
a
c
A
R
AA
M
RRQ
1
21
23
2
2
( )
( )( ) ( ) ( )( )
++
=
3232313
21
23
2
2/ln/22/22 bR
R
RRRRbRRb
M
RRQ
mc
Centrifugal filtration
NomenclaturesNomenclatures
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NomenclaturesNomenclaturesQ= Volumetric flow rateQ= Volumetric flow rate
= filtrate density= filtrate density = angular velocity= angular velocity = filtrate viscosity= filtrate viscosity =Specific resistance of the cake=Specific resistance of the cakeb=height of the basketb=height of the basket
Mc=mass of solid cake in basketMc=mass of solid cake in basket
RR11= radius of inner surface of the liquid ring= radius of inner surface of the liquid ring
RR22
=Radius of the inner surface of the cake=Radius of the inner surface of the cake
RR33 = Radius of inner surface of the bowl= Radius of inner surface of the bowl
AAaa=arithmetic mean area of the cake=arithmetic mean area of the cake
AAll= logarithmic mean cake area= logarithmic mean cake area
AAmm= area of filter medium= area of filter medium
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Q = volumetric flow rate,Q = volumetric flow rate,
mm33
/s/sV = operating volume ofV = operating volume of
the bowlthe bowl = 2= 2 N/60N/60N = rpmN = rpmd = diameter of thed = diameter of the
particleparticle
( )2
122 ln18 R
RVdQ ls
=
Centrifugal clarification
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centrifugecentrifuge
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