1

Working Party on Drying / EFCETechnical and Business Meeting

April 11th-12th, 2002, Magdeburg, Germany

Coupled population, mass and heat balances for liquid sprayed gas/solid

fluidized beds

Peglow, M.* / Henneberg, M. / Ihlow, M. / Heinrich, S. / Mörl, L.

Otto-von-Guericke-Universität MagdeburgInstitut für Apparate- und Umwelttechnik

Lehrstuhl Chemischer ApparatebauUniversitätsplatz 2, 39106 Magdeburg

www.uni-magdeburg.de/iaut/ca/

*mirko.peglow@vst.uni-magdeburg.de

2Overview

1. Motivation

2. Modeling

3. Simulation results

4. Experimental validation

5. Conclusions and further prospects

31. Motivation

• Coupled calculation of particle size distribution, heat and masstransfer for fluidized bed spray granulation

• Combination of different models to describe the subprocessesin a complex model

• Simulation of unsteady processes

• Analysis of influence of different process parameters

• Prediction of pneumatic and thermodynamic stability

42. Modeling: Structure of model

Particle surface

Particle diameter

Injected mass flow

Temperature

COUPLING

Population balance model• Calculation of PSD and essential fluidized bed

parameters for different process designs• „mechanistic“ model• Time domain: hours

Heat and mass transfer model• Calculation of degree of wetting; air,

liquid and particle temperature and air humidity• Monodispers, unchangeable particle system• Time domain: seconds

52. Modeling: population balance

( , ) ( ) ( , ) ( ) ( ) ( ) ( ) ( )P P Pdust P nuclei P ci P r P bed P

P

n d t G d n d t n d n d n d n d n dt d

∂ ∂= − + + + + −

∂ ∂& & & & &

granulator

overspray)x1(m watersuspension −&

overspraywatersuspension m)x1(m && −−

cyclon

overspraym&

abrasionm&

dust,0dust q,n&

in,dustm&

out,dustm& nuclei,0nuclei q,n&

apparatus-geometry

particle-property

bed,0bed q,n&separator

T,0T q,n&

r,0r q,n&

A,0A q,n&

ci,0ci q,n&

62. Modeling: population balance

Selected submodels for the calculation of PSD

• Granulation model (Mörl)

• Pneumatic behavior (Goroschko)

• Attrition (Rangelova, Werther)

• Overspray

• Classifying with turbulence and circulation time model (Molerus, Mörl)

Mörl, L.: Growth of granules in fluidized-bed drying, taking into account the formation of nuclei, International Chemical Engineering, Vol. 26 (1986), Nr. 2 (April 1986), S. 236-242 Goroschko, W.D., Rozenbaum, R.B., & Todes, O.M. (1958): Neft i Gaz, 1, 125.Molerus, O, & Hoffmann, H. (1969): Darstellung von Windsichterkurven durch ein stochastisches Modell,Chem.-Ing.-Tech., 41 (5/6), 340-344.Rangelova, J., Dalichau, J., Heinrich, S., Mörl, L.: Zerfallsverhalten von Partikeln in Wirbelschichten –Anwendung eines konstanten massenbezogenen Abriebskoeffizienten, Chem.-Ing.-Tech. 73 (2001) 9, S. 1124-1131 Mörl, L., Mittelstraß, M., & Sachse, J. (1978): Berechnung der Verteilungsspektren von Feststoffgranulatteilchen in Wirbelschichtapparaten mit klassierendem Abzug. Chem. Techn., 30 (5), 242-245.

72. Modeling: heat and mass transfer

Differential volume element with wetted particle

82. Modeling: heat and mass transfer

Selected parameters for heat and mass transfer

• Heat transfer gas-particle (Tsotsas)

• Heat transfer gas-wall (Baskakov)

• Heat transfer wall-particle (Martin)

• Heat transfer particle-liquid film (Reppmann)

• Mass transfer gas-particle (Tsotsas)

• Degree of wetting (Mörl)

Groenewold, H., Tsotsas, E.: Predicting Apparent Sherwood Numbers For Fluidized Beds, Proceedings of the 11thInternational Drying Symposium (IDS'98), Halkidiki, Greece, august 19-22, 1998, vol. A. pp.192-199Martin, H.: Wärmeübergang in Wirbelschichten.VDI-Wärmeatlas, 7. Auflage 1994, S. Mf1/Mf8Reppmann, D: Experimentelle und theoretische Untersuchungen zur Eindüsung von Flüssigkeiten in eine Wirbelschicht,Dissertation, TU Magdeburg, 1990Heinrich, S., Mörl, L.: Description of the temperature, humidity and concentration distribution in gas-liquid-solid fluidized beds, Chem. Eng. Technol. 22 (1999) 2, pp. 118-122

93. Simulation results

Selected process parameters:

20bedm kg=31500 /bed kg mρ =

20 /susm kg h=&0.3susx =

350 /airm kg h=&

150airT C= °

1 /nucm kg h=&

• Start-up process• Determination of resulting PSD• Determination of values regarding

heat- and mass transfer• Aim: steady state

103. Simulation results: start up 600 minutes

20bedm kg=31500 /bed kg mρ =

1 /nucm kg h=& 20 /susm kg h=&

0.3susx =350 /airm kg h=&

150airT C= °

113. Simulation results: Variation of parameters

• Start up to steady state• Deflection from steady state

• Aim: coarse particle spectrum

• Reduction of nuclei at t = 600 min

• Raising of suspension mass flow at t = 600 min

• Raising of supply air temperature at t = 600 min

1 / 0.5 /nucm kg h kg h= →&

20 / 30 /susm kg h kg h= →&

150 200airT C C= ° → °

123. Simulation results: Variation of parameters

1 / 0.5 /nucm kg h kg h= →& 20 / 30 /susm kg h kg h= →& 150 200airT C C= ° → °

134. Experimental validation: FB DN400

product

inlet air(classifying air) el.

filter dust

exhaust air

el.el. inlet air(fluidizing air)

M

air

external nuclei

hold-up

of atomization

cyclone dust

internal nuclei

bed

144. Experimental validation

430 mint =

0,05 /dism kg s=&

60 /susm kg h=&

0,8 /nucm kg h=&

30bedm kg=120air Cϑ = °0, 43 /airm kg s=&

• Holdup und nuclei material : glass• Suspension: limestone with binder

HoldupGranulate

Granulate with Nuclei

Nuclei

154. Experimental validation: PSD bed material

430 mint =120air Cϑ = °0, 43 /airm kg s=&

0,05 /dism kg s=&

60 /susm kg h=&

0,8 /nucm kg h=&

30bedm kg=

164. Experimental validation: PSD bed material

430 mint =

0,05 /dism kg s=&

60 /susm kg h=&

0,8 /nucm kg h=&

30bedm kg=120air Cϑ = °0, 43 /airm kg s=&

174. Experimental validation: moisture outlet

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000Zeit [s]

Lufta

ustri

ttsfe

ucht

e [k

g/kg

]

Messung

Simulationh/kg64,8mF =&

h/kg6,13mF =&

h/kg5,18mF =&

h/kg4,23mF =&

h/kg6,18mF =&

h/kg8,13mF =&

h/kg76,8mF =&

h/kg0mF =&

0.0058 /inairY kg kg=3,05Pd mm= 32400 /P kg mρ =30bedm kg=

127air Cϑ = ° * 22.2 /airm kg m s=&15sus Cϑ = °

measurement

simulation

moi

stur

e ou

tlet

time

184. Experimental validation: temperature outlet

0.0058 /inairY kg kg=32400 /P kg mρ =3,05Pd mm= 30bedm kg=

* 22.2 /airm kg m s=&127air Cϑ = ° 15sus Cϑ = °

65

75

85

95

105

115

125

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000Zeit [s]

Lufta

ustri

ttste

mpe

ratu

r [°C

] MessungSimulationh/kg64,8mF =&

h/kg6,13mF =&

h/kg5,18mF =&

h/kg4,23mF =&h/kg6,18mF =&

h/kg8,13mF =&

h/kg76,8mF =&

h/kg0mF =&measurement

simulation

time

air t

empe

ratu

reou

tlet

195. Conclusions and further prospects

Conclusions

• First coupling of heat and mass transfer with populationbalance model for fluidized bed spray granulation

• Simulation of unsteady processes

Further prospects

• Coupling of models over the entire diameter range

• Solving of heat and mass transfer model for entirediameter range

• Implementation of agglomeration model

204. Experimental Validation: PSD bed / product

bed bed

productproduct