Drying kinetics, coalescence and agglomeration of dairy products particles- Validated modelling tools to support the design of spray-drying

processes

LOREDANA MALAFRONTE

SP Food and Bioscience/Chalmers University of Technology

New affiliation R&D Center, Valio Ltd

Spray-drying process

time and cost reduction

process design

operating conditions

quality enhancement of

final product

Energy-intensive operation

Design and scale-up

Final properties of powders

Limitations

Simulation tools

Spray-drying process

time and cost reduction

process design

operating conditions

quality enhancement of

final product

Energy-intensive operation

Design and scale-up

Final properties of powders

Limitations

Simulation tools

ATOMIZATION

FLOW OF THE

AIR AND FEED

PARTICLE-WALL

PARTICLE-PARTICLE

INTERACTION

Shrinkage

PARTICLE

FORMATION

Modelling approach

Heat Transport

Bi << 0.1

Lumped model

Mass Transport

Bi >> 0.1

Distributed model

Simplified approach

CFD model

Lumped drying-kinetics model(Gianfrancesco et al., 2010; Jin and Chen, 2009, 2010)

Less computational resources

Dairy products

Modelling approach

Heat Transport

Bi << 0.1

Lumped model

Mass Transport

Bi >> 0.1

Distributed model

Complex approach

CFD model

Distributed drying-kinetics model

Accurate description

Dairy products

Goal of the research project

To develop a validated distributed model to describe the drying-kinetics of single particles of dairy products

To use the model to understand the coalescence and agglomeration of particles during spray drying

I

II

Outline

Implementation of modelling tools in a real spray-

drying application

Experimental and modelling tools for drying-

kinetics of single particles

Experimental and modelling tools for coalescence,

agglomeration and non-agglomeration of single particles

Conclusions

Drying kinetics

Experimental procedure

Air

system

Balance

Drying chamber

Air

• Temperature• Humidity• Velocity

Sample

• Temperature• Moisture content• Shrinkage

Drying kinetics

Experimental procedure

Air

system

Balance

Drying chamber

Modelling tool

Shrinkage

Evaporation

Convective heating

Deff (T,w)

Effective water diffusion in dairyproducts

Deff (w,T) = f(T) g(w)

NMR

Parameter estimation

method

Modelling tool

Shrinkage

Evaporation

Convective heating

Deff (T,w)

Drying kinetics

Skim milk

Light miilk

Medium milk

Whole milk

Diluted coffee creamer

Coffee creamer

Heavy cream

Fa

t co

nte

nt

Effective water diffusion in dairyproducts

Fat

Proteins Fat

Regions of coalescence and agglomeration

CF

D m

od

el

Tamb,

RHamb

Liquid Feed Hot air

Powder particles

T(z)

Nu(z)

Sh(z)

RH(z)

d(0.1)

d(0.5)

d(0.9)

X0, T0

Coalescence and agglomeration

Drying-kinetics model

(L. Malafronte et al., 2015)

Coalescence and agglomeration

���~viscousforces

inertia · surfacetensionforces

��� < 1

Coalescence

��� > 1

Stickiness

Non - Stickiness

� − �� > ∆�∗

� − �� < ∆�∗

(Verdurmen et al 2004)

Coalescence region

�Oh2 < 1�Oh2 > 1

Surface Average

Coalescence• Physical properties (Oh2)• Kinetic energy• Impact parameters

Analysis of thickness and strength of particle shells

Impact Shell breakage

Leakageinternal material

Coalescence

Agglomeration regions

Case II Case III

Coalescence Non stickinessStickiness

Case I

∆�∗= 20 ÷ 40℃

Case I:

∆�∗> 20℃

Case II:

∆�∗> 30℃

Case III:

∆�∗> 40℃

Sticky point Conditions for coalescence

Oh2average vs Oh2

surface

Shell formation in a drying particle

Conditions for agglomeration

Accurate sticky conditions

Particle contact test

Air

system

Balance

Drying chamber

Suspension

system

Top view

Air

Experimental procedure Modelling tool

Shrinkage

Evaporation

Convective heating

Deff (T,w)

Particle contact test

Coalescence Stickiness Non-stickiness

∆Taverage > 140°C > 140°C > 140°C

∆Tsurface > 140°C > 30°C < 30°C

Glass transition temperature, ΔT=T-Tg

�

Oh2surface < 1

Coalescence

∆Tsurface > 140⁰C

Oh2surface > 1

Stickiness

∆Tsurface > 30⁰C

Ohnesorge number, Oh

Coalescence Non-coalescence

Oh2average < 1 < 1

Oh2surface < 1 > 1 �

Skim milk and Whole milk

Shell formation – skim milk

μlocal > μ*

Wet shell

ulocal > u*

Dry shell

Conclusions

We have developed an experimental set up, a methodology and a mathematical model able to:

• Determine the effect of feed composition on drying time

• Predict surface properties of particles

• Control agglomeration along the spray dryer and wall deposition

• Determine the wet and dry shell formation in a drying particle

Design and scale-up the process

Product stickiness and drying ability

Preliminary size of the chamber

Preliminary positioning of fines returns

Enhancement and control functional properties of

powders

Future Application

Acknowledgements

Supervisors

Pof. Lilia Ahrné, University of Copenhagen

Prof. Anders Rasmuson, Chalmers University of Technology

Dr. Fredrik Innings, TetraPak Processing Systems

Co-authors

Alfred Jongsma, TetraPak Processing Systems

Erich Schuster, SP Food and Bioscience

Erik Kaunisto, SP Food and Bioscience

Vincenzina Robertiello, Universitá degli Studi di Salerno

Thankyou!

Publications

• Malafronte, L., L. Ahrné, et al. (2015). "Prediction of regions of coalescence and agglomeration along a spray dryer—Application to skim milk powder." Chemical Engineering Research and Design 104: 703-712.

• Malafronte, L., L. Ahrné, et al. (2015). "Estimation of the effective diffusion coefficient of water in skim milk during single-drop drying." Journal of Food Engineering 147: 111-119.

• Malafronte, L., L. Ahrné, et al. (2016). "Coalescence and agglomeration of individual particles of skim milk during convective drying." Journal of Food Engineering 175: 15-23.

• Malafronte, L., L. Ahrné, et al. (2015). "Exploring drying kinetics and morphology of commercial dairy powders." Journal of Food Engineering 158: 58-65.