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1
MODULAR METHODS FOR THE DESIGNAND SIMULATION OF FLUIDIZED
BED DRYERS WITH INDIRECT HEATING
Evangelos Tsotsasand
Hans Groenewold
Thermal Process EngineeringOtto-von-Guericke-University
Magdeburg, Germany
New apparatus or debottlenecking
* compact
* with high capacity
* lower thermal exposition of the solids
Thus interesting for
* vendors
* users
While in open literature
* no experimental results
* no validated simulation tools
2
MOTIVATION
3
MODULAR MODELLING
1. Fluidized bed module
* Fluidization → Werther et al.
* Particle – Fluid heat and mass transfer
→ Tsotsas et al.
2. Product module (Single particle)
- Normalization after van Meel
- Normalization / Hygroscopicity
3. Drying module
- Mass transfer + Adiabatic saturation temperature
- Mass transfer + Heat transfer in detail
4. Heat transfer from immersed element
???
Impact of solids moisture on indirect heating?
Impact of indirect heating on drying?
What can we learn from experiment?
How accurately can we calculate?
4
PARTICLE-TO-FLUID MASS TRANSFER
1 10 100 1000Re0 [-]
0.001
0.01
0.1
1
10
100
Sh p
lug [
-]
experimental resultscalculated with new model
ψ=1.0
ψ=0.4
Average error: prediction: 33.6%, original correlations: 35.4%
5
MATERIALSCharge Description Producer, Market name
G1800 γ-Al2O3 with dp ≈ 1800 µm Condea Chemie, Hamburg, Ak-tivtonerde
G1150 γ-Al2O3 with dp ≈ 1500 µm Condea Chemie, Hamburg, Ak-tivtonerde
G0800 γ-Al2O3 with dp ≈ 800 µm Condea Chemie, Hamburg, Ak-tivtonerde
G0260 γ-Al2O3 with dp ≈ 260 µm, produced by narrow sieving from Charge NWA
NWA γ-Al2O3 with dp ≈ 255 µm Condea Chemie, Hamburg, NWA-155
AOS γ-Al2O3 with dp ≈ 100 µm Aluminium Oxid Stade, Stade, Aluminiumoxid
NG100 γ-Al2O3 with dp ≈ 50 µm Nabaltec GmbH, Schwandorf, NG100
NO203 α-Al2O3 with dp ≈ 50 µm Nabaltec GmbH, Schwandorf, NO203
Charge Material dp
µmρp
kg/m³εmf-
Geldart-Group-
G1800 γ-Al2O3 1820 1070 0.40 D
G1150 γ-Al2O3 1140 915 0.40 D
G0800 γ-Al2O3 770 1350 0.39 B, D
G0260 γ-Al2O3 255 1325 0.365 B
NWA γ-Al2O3 255 1325 0.365 B
AOS γ-Al2O3 100 1870 0.47 A
NG100 γ-Al2O3 49 1850 0.40 A
NO203 α-Al2O3 52 2040 0.44 A
6
EXPE
RIM
ENTA
L SE
T-U
P
Air
in
Air
out
7
FLUIDIZED BED
250
mm
50 m
m
Glass
Steel
Pt100Thermo-couple
Distributor
Usu
al b
ed h
eigh
t
Steel
50 m
m30
0 m
m25
0 m
m
150 mm
300 mm
8
HEATING ELEMENT
MEASUREMENTS
( )Xm&• Drying curve,
from (infrared spectroscopy)( )tYout
• Heat transfer coefficient cylinder-bed
during drying,
from
bedw ,α
dtdTQTT HelbedH /,,, &
Teflon Copper TeflonHeating cartridge
Temperature sensor
electric contact
dd
12
dd
21
dd
25
155 562
dd
17
52
10 10
9
PHENOMENOLOGY, DRYING CURVES
0 0,1 0,2 0,3 0,4 0,5 0,6
X [-]
0
0,1
0,2
0,3
0,4
m. [kg/
m2 h]
ohnemit
0 0,1 0,2 0,3 0,4 0,5
X [-]
0,00
0,05
0,10
0,15
0,20
0,25
m. [kg/
m2 h]
ohnemit
0 0,1 0,2 0,3 0,4 0,5
X [-]
0,000
0,005
0,010
0,015
0,020
0,025
0,030
0,035
m. [kg/
m2 h]
ohnemit
0 0,1 0,2 0,3 0,4 0,5
X [-]
0,000
0,005
0,010
0,015
0,020
0,025
m. [kg/
m2 h]
ohnemit
0,00 0,05 0,10 0,15 0,20 0,25
X [-]
0,000
0,005
0,010
0,015
m. [kg/
m2 h]
ohnemit
0 0,1 0,2 0,3 0,4 0,5 0,6
X [-]
0
0,1
0,2
m. [kg/
m2 h]
ohnemit
G0800
AOS
G0260
NWA
withoutwith
withoutwith
G1800withoutwith
G1150
withoutwith
withoutwith
withoutwith
10
Charge indirect heating
Tin °C
TW
°C airM&
kg/h
Re0
- ε
- H
mm
G1800 without with
50 50
- 100
65.2 83.9
102 131
0.495 0.553
90 105
G1150 without with
50 50
- 100
67.3 75.6
65.4 73.3
0.616 0.646
85 98
G0800 without with
50 50
- 100
64.9 79.9
42.2 51.8
0.640 0.688
82 82
G0260 without with
50 50
- 100
16.81 16.37
3.77 3.65
0.617 0.615
104 106
NWA without with
50 50
- 100
17.3 16.6
3.9 3.7
0.619 0.617
87 84
AOS without with
50 50
- 100
10.25 10.19
0.90 0.88
0.691 0.693
89 100
NG100 without with
50 50
- 70
3.38 2.64
0.15 0.12
0.639 0.623
72 78
NO203 without with
50 50
- 70
3.12 3.09
0.14 0.14
0.640 0.645
78 80
0,00 0,05 0,10 0,15 0,20 0,25
X [-]
0,0000
0,0005
0,0010
0,0015
0,0020
0,0025
m. [kg/
m2 h]
ohnemit
0,00 0,05 0,10 0,15 0,20 0,25
X [-]
0,0000
0,0005
0,0010
0,0015
0,0020
0,0025
m. [kg/
m2 h]
ohnemit
NO203withoutwith NG100
withoutwith
11
PHENOMENOLOGY, HEAT TRANSFER COEFFIENTS
Impact of particle moisture partly present, but
- indirect? (material properties, fluidization) or
- direct? (local heat and mass transfer)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
X [-]
0
100
200
300
400
500α
W,b
ed[W
/m2 K
]
G1800G1150G0800G0260NWA
0 0.05 0.1 0.15 0.2 0.25
X [-]
0
200
400
600
800
αW
,bed
[W/m
2 K]
AOSNG100NO203
1. Fluidized bed module* Fluidization → Werther et al.* Particle - Fluid heat and mass transfer → Tsotsas et al.
2. Product module (Single particle)- Normalization after van Meel- Normalization / Hygroscopicity
3. Drying module- Mass transfer + Adiabatic saturation temperature- Mass transfer + Heat transfer in detail
4. Heat transfer from immersed element- Single particle → Martin modified, cp →∞,
transformed into a fictitious overtemperature ofinlet air
- Single particle → Martin original,directly considered
- Packet models- more complex models
WSMOD:- accurate concerning hygroscopicity and energy balances- complicated in normalization - relatively complicated to implement / use
12
MODEL „WSMOD“
13
0exp
exp*expexp ==→=→ X
calc
calcrel
calcrel x
αα
αα
ααα
αα
ISOLATE THE DIRECT INFLUENCE
0 0,1 0,2 0,3 0,4 0,5 0,6
X [-]
0,8
1,0
1,2
1,4
αre
l* [-
]
G1800
AOS NG100
0.00 0.05 0.10 0.15 0.20 0.250.00 0.05 0.10 0.15 0.20 0.25
0 0,1 0,2 0,3 0,4 0,5
X [-]
0,8
1,0
1,2
1,4α
rel*
[-]
0 0.1 0.2 0.3 0.4 0.50 0.1 0.2 0.3 0.4 0.5 0.6
G0260
1.4
1.2
1.0
0.80.00 0.05 0.10 0.15 0.20 0.25
1.4
1.2
1.0
0.8
1.4
1.2
1.0
0.8
1.4
1.2
1.0
0.8
αre
l*[-]
αre
l*[-]
αre
l*[-]
αre
l*[-]
14
CONSEQUENTLY
Large particles → no direct impact ofparticle moisture
Small particles → large directimpact
Very large particles → direct impact+ agglomeration
OVERVIEW EXPERIMENTAL PROGRAMME
Charge Number / Heating element Tin TW Re0 εtotal without verti. horiz. °C °C - -
G1800 23 12 9 2 50.100.120 100.140 96.3-228 0.43-0.74G1150 30 16 11 3 50.100.140 100.140 35.3-158 0.43-0.86G0800 18 7 8 3 50.100.140 100.140 19.4-98.5 0.44-0.85G0260 24 14 8 2 50.100 100.140 2.48-9.75 0.54-0.67NWA 18 8 7 3 50.100 100.140 2.17-8.07 0.54-0.75AOS 18 11 5 2 50 100 0.50-2.18 0.62-0.80NG100 17 8 6 3 50 70 0.04-0.24 0.53-0.69NO203 12 5 5 2 50 70 0.11-0.40 0.61-0.74Sum 160 81 59 20 50-140 70-140 0.04-228 0.43-0.86
15
MODEL „FLUBED“1. Fluidized bed module
* Fluidization → Werther et al.* Particle - Fluid heat and mass transfer → Tsotsas et al.
2. Product module (Single particle)- Normalization after van Meel- Normalization / Hygroscopicity
3. Drying module- Mass transfer + Adiabatic saturation temperature- Mass transfer + Heat transfer in detail
4. Heat transfer from immersed element- Single particle → Martin modified, cp →∞,
transformed into a fictitious overtemperature of inlet air
- Single particle → Martin original,directly considered
- Packet models- more complex models
FLUBED:- approximate conc. hygroscopicity and energy balances- simple in normalization- relatively simple to implement / use
16
COMPARISON HEAT TRANSFER
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
X [-]
0
20
40
60
80
100
120
140
160
180
200
αW
,bed
[W/m
2 K]
ExperimentWSMODFLUBED
G1800
0 0.1 0.2 0.3 0.4 0.5 0.6
X [-]
0
20
40
60
80
100
120
140
160
180
200
αW
,bed
[W/m
2 K]
ExperimentWSMODFLUBED
G1150
0 0.1 0.2 0.3 0.4 0.5
X [-]
0
20
40
60
80
100
120
140
160
180
200
αW
,bed
[W/m
2 K]
ExperimentWSMODFLUBED
G0800
0 0.1 0.2 0.3 0.4 0.5
X [-]
0
50
100
150
200
250
300
350
400
450
500
αW
,bed
[W/m
2 K]
ExperimentWSMODFLUBED
G0260
17
X [-]0 0.1 0.2 0.3 0.4 0.5
X [-]
0
50
100
150
200
250
300
350
400
450
500
αW
,bed
[W/m
2K
]
ExperimentWSMODFLUBED
NWA
0.00 0.05 0.10 0.15 0.20 0.250
100
200
300
400
500
600
700
αW
,bed
[W/m
2 K]
ExperimentWSMODFLUBED
AOS
0.00 0.05 0.10 0.15 0.20 0.25
X [-]
0
250
500
750
1000
1250
αW
,bed
[W/m
2 K]
ExperimentWSMODFLUBED
NG100
0.00 0.05 0.10 0.15 0.20 0.25
X [-]
0
250
500
750
1000
1250
αW
,bed
[W/m
2 K]
ExperimentWSMODFLUBED
NO203
14
COMPARISON DRYING
0 0.1 0.2
X [-]
0.000
0.005
0.010
0.015
m.[k
g/m2 h]
withoutwithWSMODFLUBED
0 0.1 0.2 0.3 0.4 0.5 0.6
X [-]
0
0.1
0.2
0.3
m.[k
g/m2 h]
withoutwithWSMODFLUBED
G1150
0 0.1 0.2 0.3 0.4 0.5 0.6
X [-]
0
0.1
0.2
0.3
0.4
0.5
m.[k
g/m
2h]
withoutwithWSMODFLUBED
G1800
0 0.1 0.2 0.3 0.4 0.5
X [-]
0
0.1
0.2
0.3
m.[k
g/m2 h]
withoutwithWSMODFLUBED
G0800
AOS
0 0.1 0.2 0.3 0.4 0.5
X [-]
0.000
0.005
0.010
0.015
0.020
0.025
m. [kg/
m2 h]
withoutwithWSMODFLUBED
0 0.1 0.2 0.3 0.4 0.5
X [-]
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
m. [kg/
m2 h]
withoutwithWSMODFLUBED
NWA
G0260
19
0,00 0,05 0,10 0,15 0,20 0,25
X [-]
0
250
500
750
1000
1250
αW
,bed
[W
/m2 K]
MessungWSMODFLUBED
0,00 0,05 0,10 0,15 0,20 0,25
X [-]
0
250
500
750
1000
1250
αW
,bed
[W
/m2 K]
MessungWSMODFLUBED
NG100 NO203
SUMMARY OF COMPARISON
Drying rate Heat transfer coeff. vertical
Heat transfer coeff. horizontal
CHARGE FLUBED WSMOD FLUBED WSMOD FLUBED WSMOD G1800 1.01 0.99 1.31 1.18 0.74 0.66 G1150 1.11 1.02 1.01 0.90 0.98 0.90 G0800 1.39 1.33 0.97 0.87 1.11 1.02 G0260 0.78 0.78 0.81 0.72 1.15 1.04 NWA 0.86 0.84 0.88 0.78 1.20 1.08 AOS 0.81 0,72 0.99 0.84 1.51 1.26 NG100 1.48 1.12 2.26 1.55 3.64 2.43 NO203 1.57 1.23 2.71 1.94 2.89 2.05
20
CONCLUSION
* Indirect and direct impact of latent heat sink
* Direct impact:
dp > 800 µm → negligible
dp > 100 µm, → enhancement of heat transfer
255 µm by 25 % - 30 %
dp < 50 µm → enhancement is blurred by
agglomeration
* Large increase of dryer capacity is possible
by indirect heating
* In-situ delivery of heat can be beneficial forproduct quality
* Satisfactory simulation by modular modelling, relation between difficulty and accuracyadjustable,
further sophistication is possible