spray dryer modellingcomo.cheng.cam.ac.uk/seminars/csh33_talk_090507.ppt · ppt file · web...

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vapourbubble form ation w aterrem oved by evaporation ‘blow n shell’ modelling drying and particle formation in spray towers Christopher Handscomb Wednesday 9 th May 2007

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Page 1: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

vapour bubble formation

water removed by evaporation

‘blown shell’

modelling drying and particle formation in spray towers

Christopher HandscombWednesday 9th May 2007

Page 2: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

outline

• Introduction to spray drying

• Modelling approach

• Continuous phase gas flow

• Single particle drying

• Conclusions and further work

Page 3: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

• An important technology in industry• Used to produce, for example:

– Pharmaceuticals– Food stuffs (e.g. milk powder and coffee)– Detergents

• Unique drying technology combining moisture removal and particle formation

what is spray drying?

Page 4: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

what is spray drying?

FeedAtomisation

rotary atomizer pressure nozzle

Spray-Air Contact

co-current mixedcounter-current

Spray EvaporationPowderSeparation

product discharge from chamber and

separation unit

total product discharge from separation unit

Page 5: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

motivation

A computational model would…• predict the effect of process conditions on

final product properties• guide the operator towards safe and

efficient operating conditions• facilitate the design of new plant based on

physics, rather than correlations

Page 6: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

modelling approachC

ontin

uous

Pha

se

(CFD

)Sub Models

Particle Drying

Particle-Particle Interaction

Particle-Wall Interaction

• Adopt an Eulerian-Lagrangian framework

Page 7: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

continuous phase

• Commercial CFD package – STAR CD – used to model the continuous phase– Well known in industry– Easy to test different geometries– Relatively simple to incorporate sophisticated

user defined sub models• Test geometry developed representing a

generic spray dryer

• Counter current dryer• Single spray nozzle• Height: 22m• Diameter: 4m• 118,807 cells in CFD mesh

Page 8: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

continuous phase

• Can fairly easily produce plots of the flow field

z=0.5m

z= 4m

• Consider a single droplet

Page 9: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

• Consider the drying sub-model• Modelling assumptions:

– Three component system: A – solvent; B – solute; D – solid

– Spherical particles, 1D model– Small Biot number uniform particle temperature– Allow for a single centrally located bubble

single particle drying

Assumed ideal binary solution

time

drop

let t

empe

ratu

re

Page 10: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

time

drop

let t

empe

ratu

resingle particle drying

wet bulb temperature

boiling temperature

Cheyne, A., Wilson, I., and Bridgewater, J. (2002).

Page 11: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

single particle drying

• Spherical symmetry reduce to 1-D

• Solve for the moments of this equation

internal coordinates external coordinates

advection terms diffusion terms source term

• Population balance for solids

Cheyne, A., Wilson, I., and Bridgewater, J. (2002).

Page 12: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

single particle drying

• Variable of interest is solids volume fraction

• Related to the moments of the population balance equation by:

• Obtained by solving the moment system:

assumed independent of internal coordinate (particle size)

Page 13: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

evolution advection diffusion crystallization

single particle drying

• Volume averaged transport equations for the continuous phase

• Advection velocity calculated from volume conservation considerations

• Diffusion coefficient from measurements

Volume AveragesSuperficial

Intrinsic

Total

R(c)

S

z

Page 14: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

single particle drying

• Population balance boundary conditions

• Solute boundary conditions

Page 15: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

moving boundary

• Moving boundary handled through a standard coordinate transformation r z:

• This adds a ‘virtual flux’ to all equations

virtual flux

Page 16: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

solution method

• Problem is a system of PDEs and coupled ODEs

• Solved using Numerical Algorithms Group (NAG) library routines for convection-diffusion type equations

• Finite Volume approach with user-defined flux function

Page 17: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

new drying model – example

• Model described so far can simulate up to the point of shell formation

• e.g. Consider a system:– Initial 14wt% sodium sulphate solution – no solids– Crystallisation model from Rosenblatt et al. (1984):

‘Kinetics of Phase Transitions in the System Sodium Sulphate-Water’

– Droplet diameter = 1.78mm– Drying air T = 373K– Droplets initially well mixed

Page 18: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

new drying model – example

0 20 40 60 80 100 1200

0.5

1

1.5

2

2.5

3

3.5Simulated vs. Experimental Mass of the Drying Droplet

Time/s

Dro

plet

Mas

s/m

g

ExperimentModel

• Compare with experimental data from Nesic and Vodnik (1990) Kinetics of Droplet Evaporation Chem. Eng. Sci.

Experimental data from Nesic and Vodnik (1990) Kinetics of Droplet Evaporation Chem. Eng. Sci.

Page 19: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

new drying model – example

0 20 40 60 80 100 12020

30

40

50

60

70

80

90

100

110Simulated vs. Experimental Temperature of the Drying Droplet

Time/s

Dro

plet

Tem

pera

ture

/C

ExperimentModel

Experimental data from Nesic and Vodnik (1990) Kinetics of Droplet Evaporation Chem. Eng. Sci.

But the new model can give us much more…

Page 20: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

new drying model – example

0 20 40 60 80 100 1200

0.5

1

1.5

2

2.5

3Simulated Evolution of the Solvent, Solute and Solids Masses

Time/s

Mas

s/m

g

Solvent MassSolute MassSolids Mass

Page 21: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

new drying model – example

0 1 2 3 4 5 6 7 8

x 10-4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Simulated Continuous Phase Solvent Mass Fraction in a Drying Droplet

Radial Position/mm

Sol

ute

Mas

s Fr

actio

n [-]

Page 22: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

new drying model – example

0 1 2 3 4 5 6 7 8

x 10-4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7Simulated Solids Volume Fraction in a Drying Droplet

Radial Position/mm

Sol

ids

Vol

ume

Frac

tion

[-]

Page 23: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

new drying model – example

0 20 40 60 80 100 1200

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2x 10

-5Simulated Evolution of moments integrated over the drying droplet

Time/s

Inte

grat

ed N

orm

alis

ed M

omen

tsZeroth MomentFirst MomentSecond Moment

Page 24: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

conclusions…

• Introduction to spray drying and the associated modelling challenges

• Results of continuous phase simulation• Overview of a new drying model• Comparison with experiments for a ‘simple’

case…

Page 25: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

…work not shown…

• Drying after shell formation• Simulation of detergent droplets drying

with experimental comparison• Simplified drying models implemented in

CFD code

Page 26: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

…and further work

• Obtain data and validate model for high temperature drying

• Couple (simplified) model to CFD simulation

• Compare with existing drying models when used in CFD

Page 27: Spray Dryer Modellingcomo.cheng.cam.ac.uk/seminars/csh33_Talk_090507.ppt · PPT file · Web view2010-04-28 · modelling drying and particle formation in spray ... defined sub models

Christopher Handscomb([email protected])

acknowledgements