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The Scale-Up of Solid/Liquid Separations

The Role of Particle Size

Terry Redmond

James Ward

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Common Definitions

Filtrate Medium

Filter Cake

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Common Definitions

Medium Resistance (Rm)

Pressure (Pi)

Pressure (Pf)

Cake Resistance (Rc)

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Common Definitions

(Rm)

Pressure (Pi)

Pressure (Pf)

(Rc)

Filtrate Velocity (v)

)( mc

fi

RR

PPVelocity

WherePi = Initial PressurePf = Final PressureRc = Cake ResistanceRm = Media Resistance = Filtrate Viscosity

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Common Definitions

Filtrate Medium

Filter Cake

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Common Definitions

Filtrate Medium

Filter Cake

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Common Definitions

FiltrateMedium

Filter Cake AMRC /

WhereRc = Cake ResistancePf = Dry Mass of ParticlesA = Area = Specific Cake Resistance

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Common Definitions

FiltrateMedium

Filter Cake

Whereq = Volumetric FlowrateA = Filter Areav = Filterate VelocityP = Pressure Drop = Specific Cake Resistancec* = dry mass solid / vol filterateV = Volume = Filtrate viscosity

)*(

)(/

RmAVc

PAvAq

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Inverse Filter Leaf Test

VacuumSource

VacuumAdjust

Vacuum Gauge

Slurry

Filter Media

PA

Rm

PA

VcVt

)2(

*/

2

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Inverse Filter Leaf Test

PA

Rm

PA

VcVt

)2(

*/

2

t /

V

V

PA

Rm

)2(

*2 PA

c

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Filter Blinding - The Role of Fines

t /

V

V

Run 1

PA

Rm

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Inverse Filter Leaf Test

t /

V

V

Run 1

PA

Rm

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Inverse Filter Leaf Test

t /

V

V

Run 1

Run 2

PA

Rm

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Inverse Filter Leaf Test

t /

V

V

Run 1

Run 2

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Inverse Filter Leaf Test

t /

V

V

Run 1

Run 2

Run 3

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The Components of Alpha

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The Components of Alpha

p

pp VSK

3

21 1/

Where = Specific Cake ResistanceK = ConstantSp = Mean Particle Surface AreaVp = Mean Particle Volume = Porosity of Filter Cake

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A Focus on Particle Size

p

pp VSK

3

21 1/

524,000 µm3524,000 µm3Total volume

314,000 µm231,400 µm2Surface area

10 µm100 µmDiameter

1000 particles1 particleTotal number

BA

100B

A

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Alpha and the Real World

1.2 x 10^9

1.8 x 10^9

3.8 x 10^9

3.9 x 10^9

Specific Cake Resistance vs Mean Square Wt

y = -6.6689x + 68.984

R2 = 0.9144

0

10

20

30

40

50

60

70

0 1 2 3 4 5

Specific Cake Resistance

Mea

n S

qu

are

Wei

gh

The mean particle size decreases by 32% as the cake resistance increases by 325+%

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Another Example

Chord length distribution comparison

0

2

4

6

8

10

12

14

Chord length

Pop

ula

tion

%

Control

Ostwald, fast stir

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Another Example

Chord length distribution comparison

0

2

4

6

8

10

12

14

Chord length

Pop

ula

tion

%

Control

Ostwald, fast stir

Existing process (plant batches)

D-90 D-50 D-10 26.8m 9.0m 2.1m

Ostwald ripened (plant batches)

D-90 D-50 D-10 59.4m 18.8m 5.2m

No filter bed blindingeven after 16 batches

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Another Example

Chord length distribution comparison

0

2

4

6

8

10

12

14

Chord length

Pop

ula

tion

%

Control

Ostwald, fast stir

Existing process (plant batches)

D-90 D-50 D-10 26.8m 9.0m 2.1m

Ostwald ripened (plant batches)

D-90 D-50 D-10 59.4m 18.8m 5.2m

No filter bed blindingeven after 16 batches

In Summary• Particle attrition in crystallizer and filter dryer.

reduced, no slurry handling problems.

• Mean particle size doubled.

• Eliminated Fuji plate blinding, entirecampaign run without plate wash.

• Reduced process time by 3 hours (10%).

• Reduced labour by 120 operator hours/month.

• Increased monthly throughput from 20 batchesto 24 batches.

• FBRM paid for itself in 2 months.

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A Focus on Particle Size

p

pp VSK

3

21 1/

87.1B

A

37% Increase1,161,800µm3847,800µm2Total Surface Area

Decrease 3.3%96.7 µm100.0 µmVolume

mean diameter

Decrease 87.7%12.3 µm100.0 µmNumber

mean diameter

0%14,140,000 µm314,140,000 µm3Total volume

Increase 3700%1026 particles27 particlesTotal number

Relative changeAfter breakage of one particle

Initial particle system

(An 87% increase in Specific Cake Resistance)

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Conclusions

Building from Filtration Theory we were able to determine why particles are important to filtration scale-up

By developing the idea of Media Resistance and Filter area we were able to investigate how fines increase filter time by blinding

By looking into the components of Specific Cake Resistance we were able to explain why PSD and cake compressibility are important

We confirmed the literature equations to real world data sets

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Acknowledgements

Ron Washburn and Jon Hokinson for IT work

Cheryl Thom for transportation of instrumentation

Everyone at Mettler Toledo Millersville for the use of facilities and equipment