coupled population, mass and heat balances for liquid
TRANSCRIPT
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/
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