Challenges in Spray Dryer Modeling Alfred Jongsma, Tetra Pak CPS - - PowerPoint PPT Presentation

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Challenges in Spray Dryer Modeling Alfred Jongsma, Tetra Pak CPS March 2012 CHALLENGES IN SPRAY DRYER MODELING Content Spray Drying Technology Modeling Motivation Characteristics Droplet Drying Modeling Parametric Study

SLIDE 1

Challenges in Spray Dryer Modeling

Alfred Jongsma, Tetra Pak CPS March 2012

SLIDE 2

March 2012

CHALLENGES IN SPRAY DRYER MODELING

Content

Spray Drying

► Technology

Modeling

► Motivation ► Characteristics

Droplet Drying

► Modeling ► Parametric Study

Validation Conclusions

SLIDE 3

Challenges in Spray Dryer Modeling

Spray Drying

SLIDE 4

March 2012

SPRAY DRYING

Technology

Hot Air Inlet Powder “Fines” Return Cyclone Spray Spray ”Fines” Fluid Bed Chamber

SLIDE 5

March 2012

SPRAY DRYING

Technology

SLIDE 6

March 2012

SPRAY DRYING

Typical numbers

5 Ton/hr Whole Milk Dryer

► Volume 700m3 ► Energy consumption 5 MW ► Efficiency 40-65%

8.5 m 20 m

SLIDE 7

March 2012

SPRAY DRYING

A ‘Small’ Dryer (1000 kg/hr)

SLIDE 8

Challenges in Spray Dryer Modeling

Characteristics of Spray Drying

SLIDE 9

March 2012

MODELING

Characteristic Spray Drying Process

Continuous Phase (Air)

► Confined Jet = Transient! ► Jet Reynolds Number  106

Dispersed Phase (Droplets / Particles)

► Dilute

: no collisions (αp < 10-3)

► p / air >> 1

: only drag and gravity

Lagrangian approach favoured over 2 Fluid model:

► Easier closures ► Easier incorporation of additional Particle Models, e.g. drying

SLIDE 10

Challenges in Spray Dryer Modeling

Incorporation of Droplet Drying

SLIDE 11

March 2012

DROPLET DRYING

Inter-Phase Transfer

MILK DROPLET FILM FILM R R GAS GAS

HEAT MASS

TEMPERATURE CONCENTRATION

SLIDE 12

March 2012

DROPLET DRYING

Heat Transfer

MILK DROPLET FILM R GAS

HEAT

TEMPERATURE

Assumptions

► No internal gradient

Biot << 1

► Schiller Nauman ► Spherical Particles ► Ideal Shrinkage ► At Particle Surface

Tparticle = Tgas

SLIDE 13

March 2012

DROPLET DRYING

Mass Transfer

MILK DROPLET FILM R GAS

MASS

CONCENTRATION

Assumptions

► Internal gradient

Biot > 1

► Transfer limited by internal

gradient  “CDRC”

► Spherical Particles ► Ideal Shrinkage ► At Particle Surface, Sorption

Equilibrium: Xparticle = f(Xgas)

SLIDE 14

March 2012

DROPLET DRYING

CDRC: Critical Drying Rate Curve

1.0 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1.0

Xe

         

* ,

1 1 log

w b w a w p

Y Y M M DSh d f dt dm 

n X X X X f

e c e 

         

Xc

f

Best fit n = 2 Yw,b Xw Yw *

X

SLIDE 15

March 2012

DROPLET DRYING

Implementation

Field functions

► Correction Mass Transfer Coefficient (Xc & n are constants) ► Sorption Isotherm

n X X X X f

e c e 

         

) 1 )( 1 (

w w w w e

Cka ka ka a Ckm X    

) (

2 2

T p p a

Sat O H O H w 

SLIDE 16

CFD Model Spray Drying

Parametric Study

SLIDE 17

March 2012

PARAMETRIC STUDY

Simplified Geometry

Air Inlet

► T

= 200°C

► m

= 2.9 kg/s

► Yw

= 0.01

Skim milk

► T

= 70°C

► m

= 0.34 kg/s

► Xw

= 0.5

► 1 Nozzle: ► v

= 194 m/s

Air Outlet

► T

= 75°C

► Yw

= 0.064

15° 35°

Hollow Cone Base

SLIDE 18

March 2012

Parameter Base Case Variations

Air

► Velocity (Diameter)

d=base small & large

► Velocity profile

Normal Swirl

► Turbulence intensity

Medium High & low Droplets

► Inlet Velocity

v = 194m/s 100 & 250

► Size

PSD 44, 102 & 160 mm Atomisation

► Cone angle

35° 25º & 45º

► Spray pattern

Hollow cone Full cone

► Nozzle Position

Medium High & low

PARAMETRIC STUDY

Parameter Variations

SLIDE 19

March 2012

PARAMETRIC STUDY

Results Base Case

SLIDE 20

March 2012

PARAMETRIC STUDY

Results Base Case

SLIDE 21

March 2012

PARAMETRIC STUDY

Results Base Case

Particle Tracks dp < 60mm & dp > 100mm Observations:

► Small particles concentrate in Jet centre ► Large particles concentrate on Jet edges

SLIDE 22

March 2012

PARAMETRIC STUDY

Results Base Case

Particle Tracks: Temperature Observations

► Initial stage: wet bulb temperature ► Highest temperatures near Jet centre ► Final stage: uniform temperature

SLIDE 23

March 2012

PARAMETRIC STUDY

Results Base Case

Particle Tracks dp < 60mm & dp > 100mm

SLIDE 24

Challenges in Spray Dryer Modeling

Validation

SLIDE 25

March 2012

VALIDATION

Drying in reality

Mechanism Depends on:

► Chemical composition ► Initial concentration ► Air temperature ► Mixing of droplets and air ► Trajectory ► Agglomeration

SLIDE 26

March 2012

VALIDATION

Drying, even more Real

Cone (Product) Cyclone (Fines)

Powder Morphology: External Structure SEM Images “Regular” Whole Milk Powder

SLIDE 27

March 2012

VALIDATION

Drying, even more Real

Powder Morphology: Internal Structure FIB SEM Images “Regular” Whole Milk Powder

Cone (Product) Cyclone (Fines)

SLIDE 28

Challenges in Spray Dryer Modeling

Conclusions

SLIDE 29

March 2012

CHALLENGES IN SPRAY DRYER MODELING

Conclusions

Spray Dryer Modeling

► Prohibitively Expensive to build Pilot

Plants

► CFD Model Development ► Validation & Refinement Needed

Droplet Drying

► Simple approach already reveals

important phenomena

► Real drying much more complicated

Planned refinements

► Account for Morphology ► Influence on Drag / Drying Rate etc. ► Collisions & Agglomeration