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Die Ressourcenuniversitt. Seit 1765.
TU Bergakademie Freiberg I Department of Energy Process Engineering and Chemical EngineeringReiche Zeche I 09596 Freiberg I Germany I Phone +49(0)3731/39-4511 I Fax +49(0)3731/39-4555
Email evt@iec.tu-freiberg.de I Web www.iec.tu-freiberg.de
Department of Energy Process Engineeringand Chemical Engineering
Development of a Kinetic Fluidized Bed Gasifier Model for Application in Flowsheet Simulation
Matthias Gootz, Supervision: Prof. Dr.-Ing. Bernd Meyer Lars- Erik Grtner Prof. Dr.-Ing. Christian Hasse
Leipzig, 13.11.2012
2Content I
I. Introduction
II. Model development
III. Model validation
IV. Simulation results
V. Conclusion
3Introduction
Gasification Coal for power generation and chemicals production Commercially available technology
Flowsheet simulation with Aspen Plus Implementation of gasifier model into larger flowsheet
simulation
Coal gasification kinetics Determined by physico- chemical effects Implementation with user- defined subroutine in
FORTRAN77 Kinetic entrained flow gasifier model with subroutine
already developped at TUBAF
I
4Introduction
Main objectives Development of fluidized bed gasifier model using the
continiously stirred tank reactor model (RCSTR) Comparison of two kinetic rate equation types:
Langmuir- Hinshelwood (LH) N- th order
Reasons RCSTR suitable for representation of fluidized bed gasifier Few literature on gasifier simulation with RCSTR and LH
kinetics available LH more suitable than n- th order equations over broad
operating ranges
I
Model development: Kinetics
5
II
Heterogeneous reactions
N- th order Langmuir- Hinshelwood
Homogeneous reactions
Physico- chemical effects Pore diffusion Surface area evolution
C + O2 CO22C + O2 2CO
C + H2O CO+ H2C + CO2 2CO
2CO + O2 2CO22H2 + O2 2H2O
CH4 + 2O2 CO2 + 2H2O CO + H2O CO2 + H2
Model development: Aspen Plus
6
II
High- Temperature-Winkler- GasifierPilot plant Wesseling
Freeboardzone
Fluidized bed
Coal
Air/ O2Steam
Char
Drying, Devolatilization RYield
RCSTRGasification
Volatiles
Char
Products of combustion
SolidsGas
SsplitSeparation
Recycled solids
Unconverted char, fines, ash Rawgas
Combustion of volatiles RGibbs
Char decomposition RStoic
Air/ O2
Generation rate of components
CalculatorProperties, user input
Generation rate of components
SteamAir/ O2
Solids
Gasification RCSTR
Kinetics Subroutine
Separation
Unconverted char,ash
Recycle
Rawgas,fines
Coal
Freeboard zone
Fluidizedbed
Air/ O2Steam
Air/ O2Steam
7Model validation: Case setup and results
LH: T XC
N-th order: T XC
Validation case setup Pressurized air/ steam gasification of Rhenish brown coal [1] Gasifier temperatures and synthesis gas composition given
III
Observation Low XC at high reactor
temperatures for LH simulation
Simulation validation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
300
400
500
600
700
800
900
1000
1100
1200
LH N- th order Literature
X
C
T
i
n
C
Cases
T DensebedT FreeboardXCXC
[1] Hamel et. al. Modeling of pressurized fluidized bed gasification in comparison with experimental data from a commercial scale and pilot scale HTW-gasification plant. Proceedings of 4th International Symposium on Coal Combustion, Beijing(1999), pages 411 420, 1999.
8Model validation: Results III
LH: CH4 CO2 H2O CO H2
N-th order: CH4 CO2 H2O CO H2
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
LH N- th order Literature
S
y
n
g
a
s
c
o
m
p
o
n
e
n
t
s
i
n
m
(
S
T
P
)
/
h
Cases
CH4CO2H2OCOH2
CH4CO2H2OCOH2
Interpretation Energy balance is solved for lower temperatures
(Aspen Plus: Standard Enthalpy of Formation is used)CO HR,0 = -111 kJ/mol [2]CO2 HR,0 = -393 kJ/mol [2]
Simulation results
[2] Chemgapedia: Standardbildungsenthalpien einiger Verbindungen. http://www.chemgapedia.de/vsengine/supplement/Vlu/vsc/de/ch/11/aac/vorlesung/kap_8/vlus/thermodynamik_thermochemie.vlu/Page/vsc/de/ch/11/aac/vorlesung/kap_8/kap8_4/kap8_4a.vscml/Fragment/faed7b2f1d262b91a3e6062626e0d88c-34.html. Accessed 11.10.2012.
9Model validation: Langmuir- Hinshelwood
0
2
4
6
8
10
12
14
0 0.1 0.2 0.3 0.4
R
e
a
c
t
o
r
h
e
i
g
h
t
i
n
m
Concentration in mol/mol
CH4H2OH2COCO2O2
CH4H2OH2COCO2O2
III
Observations: Homogeneous reactions should proceed faster C- CO2 and C- H2O reactions too slow Inhibition by CO
Low conversion due to inhibition, but high temperatures due to fast combustion
0
2
4
6
8
10
12
14
0.00001 0.0001 0.001 0.01 0.1 1Rh in kmol/(ms)
C- O2C- H2OC- CO2H2- O2
Densebed
Freeboard
C- O2C- H2OC- CO2H2- O2
Model validation: N- th order
10
0
2
4
6
8
10
12
14
0 0.1 0.2 0.3 0.4
R
e
a
c
t
o
r
h
e
i
g
h
t
i
n
m
Concentration in mol/mol
CH4H2OH2COCO2O2
CH4H2OH2COCO2O2
III
Observations: Char oxidation slower than with LH kinetics C- CO2 and C- H2O reactions are faster
Faster endothermic reactions cause high conversionat low temperatures
0
2
4
6
8
10
12
14
0.00001 0.0001 0.001 0.01 0.1 1Rh in kmol/(ms)
C- O2C- H2OC- CO2H2- O2 Freeboard
Densebed
Freeboard
Densebed
Freeboard
Densebed
Freeboard
Densebed
Freeboard
C- O2C- H2OC- CO2H2- O2
Simulation results: Variation of air feed stream
11
IV
Observations: Higher air feed stream raises gasifier output results,
but output parameters are still underpredicted
Conclusion: No advantages of LH equations over n- th order
equations in present simulation
N- th orderLH
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
300
400
500
600
700
800
900
1000
-10% -5% 0% 5% 10%
X
C
T
i
n
C
Change from original air feed stream
T DensebedT FreeboardXCXC
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
300
400
500
600
700
800
900
1000
-10% -5% 0% 5% 10%
X
C
T
i
n
C
Change from original air feed stream
T DensebedT FreeboardXCXC
12
Simulation results: Range of application (LH)
Combustion of volatiles in separate Gibbs reactor Less air used for coal gasification than in reality Unrealistic distribution of gasification agents between zones
IV
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-400
-200
0
200
400
600
800
1000
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
X
C
T
i
n
C
Fraction of air fed to combustion xComb
T DensebedT FreeboardXCXC
Conclusion
13
V
Gasifier model Use with different reaction kinetics data and rate
equations possible Failure to satisfyingly predict gasifier output
parameters
LH and n- th order simulation No recommendation can be made for present simulation
Improvements necessary Suitable rate parameters (from orginial coal) for
heterogeneous reaction kinetics Revision of homogeneous reaction equations External volatiles combustion needs to be transferred to
RCSTR
14
Conclusion
Future developments
Adjustment to different fluidization regimes
Combination RCSTRs withPlug Flow Reactor
Extension for use of fuelblends
V
[3] D. Kunii and O. Levenspiel, Fluidization Engineering, second ed., Butterworth-Heinemann, 1991.
[3]
15
Conclusion
Thank you for your attention.
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