Gootz

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 [email protected] 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

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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

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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


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


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

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0.5

0.6

0.7

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0.9

1

300

400

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-10% -5% 0% 5% 10%

X

C

T

i

n

C

Change from original air feed stream


0

0.1

0.2

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0.9

1

300

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1000

-10% -5% 0% 5% 10%

X

C

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n

C

Change from original air feed stream


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

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1

-400

-200

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600

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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


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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