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Drying by desorption: a toolto determine spray-drying parameters

Pierre SCHUCK1*, Eric BLANCHARD2,Evelyne ONILLON2, Anne DOLIVET1, Serge

MJEAN1, Radwan JALAM1 & Romain JEANTET1

1: UMR 1253 Joint Research Unit on Science and Technologyof Milk and Egg (INRA, Agrocampus Rennes),

65 rue de Saint-Brieuc, 35042 Rennes Cedex, France.2: Laiterie de Montaigu, 85600 Montaigu, France.3: Food Technology, AgrocampusRennes, France.

*: pierre.schuck@rennes.inra.fr

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Introduction (1) Spray drying is useful a technique for water evaporation using hot air, butvery black box in nature

The only way to determine a priori& precisely the parameters of spray drying

for food products consists in pilot / plant experiments

expensive, timeconsuming, empirical & sometimes unreliable

?

To date, there are no available method in order to determine precisely theparameters of spray drying for food products before drying

Why ?

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Air in contact with thedroplet T=45C ; p=9 583 Pa

Drying airT=200C ; p=1554 Pa

Introduction (2)

DROPLET

ENERGY TRANSFER

WATER TRANSFER

POWDERAIR

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Introduction (3)

DROPLET

ENERGY TRANSFER

WATER TRANSFER

AIR

2500 kJ.kg-1 DA

Free water

n x 2500 kJ.kg-1 DA

Bound water

Inlet air

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?

Why?

Water availability &drying behavior needsextra energy to overcomebinding of water

Kinetic of mass / heattransfer phenomena determination of boundary /local conditions ( & watercontent)

Introduction (4)

Watertransfer

Boundary

layer

Droplet

Drying hot air = 200C; P e = 1554 Pa

Heattransfer

Surface of the dropleth = 45C; P e = 9853 Pa

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Alternative spray drying modeling, based on drying physics (mass & heattransfer laws / balance). 2 levels :

Overall mass and energy balanceestablished over the entire spraydryer

Running (settings) and control ofthe drying plant for (weatherconditions) Schuck et al. IFCET (2005), Schuck et al. DairySci. &Technol. (2008)

Air inlet, H2O

Air outlet, H2O

Global level INRA

Local mass (drying rate) and energybalance established at the droplet

Management and control of theproduct quality / functionality Chen & Lin AIChEJournal (2005)

dropletd, H2O = (t)

Micro level REA / Monash

One difficulty remaining taking into account water availability = (product)

Introduction (5)

Droplet

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Inlet air

Fluid bed

Chamber

CyclonesConcentrate

Powder

0

AH

RH

210

2

Outlet air

2 AH

Hot air 1

1

AH2 : Dryer capacity / free water evaporation

RH2 aw x 100

?

?

Isenthalpic drying 1 & RH1

No energy losses and only free water

Spray drying water New method

Introduction (6)

0

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PRODUCT

PRODUCT

H2o H2o

9600 Pa

Step: Concentrate desorption

by aw-metry

ZEOLITE

ZEOLITESENSORmRH (%) T (C)

SENSOR

96 Pa96 Pa

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1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

40

0

Time (h)

mRH(%)

Step: Desorption curve vs. time

WATER

CONCENTRATE

Drying

kinetics

Constant rate :

free water

Falling rate :

bounded water

Energy = Lev + E

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1

2

1

0

1 2 3 4 5 6 70

5

10

15

20

25

30

35

40

0

Time (h)

Dryingkinetics

E

Plotting temperature / humidity

pathway considering non

isenthalpic behavior

Step

: Desorptioncurve vs. time

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Step : Calculation by INRA Software

integrating the ratio of bound andunbound water.

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Concentrate

Powder

Step : View of certain

drying parameters onthe Enthalpic MollierDiagram

Inlet air afterheating1

1

Inlet air beforeheating0

0

InletAirOutlet air

after drying

22

Outlet Air

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Step : Spray drying parameterscalculated with INRA Software

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Materials

BB

II

OO

NN

OOVV

Pilot workshop : Researchand development forevaporation / drying

MSD type drying tower80 kg of water evaporated

per hour

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y = 0.9917x

R2

= 0.97

100

140

180

220

260

300

100 120 140 160 180 200 220 240 260 280 300

Measured inlet air temperature (C)

Calculatedinletairtemperature(C

)

Results (1)

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10

100

1000

10000

100000

10 100 1000 10000 100000

Measured parameters

Calculatedparameters

[C] and Powder flow rate

Air TC

Outlet air AH

r2 0.99

r2 0.95

r2 0.93

Results (2)

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Conclusions (1)

? With this method, it is possible to predict

optimal drying air temperatures ( 1 -5%) for food products in relation to theirdesorption behavior

(, TS, , Cp) [C]

kWh

Air (chamber, FB)m

H2OPowder (RH2)

% drying FB

Current weather conditions (0)

Desorptioncurve analysis

(, H, RH) air 1 (chamber, FB)

ESC

Yield

Cost ($ . t-1 water / powder)

Powder, [C]m

OutputsInputs

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Conclusions (2)

Validation tests (> 30 products) indicate that this method could be applied to a largerange of food products & spray dryer types.

For reasons of calculation speed and reliability, the method has been computerizedand can already be used in the determination of parameters of spray drying for foodproducts. Spray Drying Parameters Simulation & Determination Software(SD2P)

NIDDN.FR.001.480002.002.R.P.2005.000.30100

? With this method, it is possible to predict

optimal drying air temperatures ( 1 -5%) for food products in relation to theirdesorption behavior

The experimental device differs from drying installation in term of duration of drying,temperature of drying, ratio surface / volume etc. We have developed somecomputational tool by taking it into account to improve the method.

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0

20

40

60

80

100

120

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160

180

200

220

240

260

280

300

0 0,01 0,02 0,03 0,04 0,05 0,06

0

2

10

1

2

Concentrate

InletAir

Powder

Outlet Air

Inlet air afterheating

Inlet air beforeheating

Outlet airafter drying

Prospects

1

Particletemperature

Glass transitiontemperature

(T-Tg)

Temps / Position

Axe Z

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Demonstration

SD2P

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15 210 24 2Whey

40 230 220 2MPC/I WPC/I

20 215 28 2Skimmilk

Multi stagespray-dryer

Compactspray-dryer

Pilot plantspray-dryer

Powders

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Humid Air Chart of Inlet Air

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Humid Air Chart of Integrated Fluid Bed Inlet Air

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Desorption curves analysis

Kind of bound water

Approaching Tg

Couchman-Karasz equation extended in tertiary mixtures

332211

g333g222g111g

CpWCpWCpW

TCpWTCpWTCpWT

++

++=

Critical outlet air Tg + (40) C

tightly bound to constituents, solvent

Whey, UF/MF permeate, mono & disaccharides,

polyols, hydrolyzed compounds, minerals

Low Tg / stickiness

High Tg / High outlet compatible

trapped in a hydrophobic network, capillary

Micellar casein, maltodextrins

Inlet & flow rate

Outlet air & AH

Droplet & PowderSD2P AH2

Tg DSC

Critical powder Tg + (20) C

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Examples (1)

MDDE 33

MDDE 7

InletC

OutletC

AHg.kg-1DA

[C]kg.h-1

/ton Water

/ton Powder

Powderkg.h-1

215 4,646 74.9 38.789 41 3,146

237 4,646 86.7 44.589 41 3,146

UFPC

UFPNC (1)

213 3,204 88. 3 69.489 41 1,835

237 3,204 94.9 74.589 41 1,835

Bound and free waterSD

2

P

INRA

UFPNC (2) 153 1,751 116.0 91.180 27 1,003

Spray Drying Parameters Simulation & Determination Software

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Standardization

SMP 1

SMP 2

InletC

OutletC

AHg.kg-1DA

[C]kg.h-1

/ton Water

/ton Powder

Powderkg.h-1

209.4 4,083 68.2 65.678.7 50.3 2,547

218.8 4,083 71.2 69.577.3 50.3 2,547

Examples (2)

SD2PINRA

Spray Drying Parameters Simulation & Determination Software

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