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Tuesday, March 2, 2010 1

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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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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