DEVELOPMENT OF A DYNAMIC MODEL OF A PALLADIUM …...CHEMICAL REACTIONS AND SEPARATION ARE CONSIDERED...

DEVELOPMENT OF A DYNAMIC MODEL OF A PALLADIUM MEMBRANE REACTOR FOR WATER GAS SHIFT

Angelo Rossi, Giacomo Lamonaca, STRUTTURA INFORMATICA, Florence (IT),Pietro Pinacci, Francesca Drago, RSE, Milan, (IT)

6th Trondheim Conference on CO2 Capture, Transport and Storage, June 14-16 2011

STRUTTURA INFORMATICA, a Software and ProcessEngineering Solutions provider, focuses on the study anddevelopment of dynamic simulation models of thermalpower plants and related technologies addressing bothrenewable and conventional sources.

RICERCA SISTEMA ENERGETICORSE carries out research into the field of electrical energy withspecial focus on national strategic projects funded through theFund for Research into Electrical Systems. RSE is a totalpublicly-controlled Company: the sole shareholder is GSES.p.A. The activity covers the entire supply system with anapplication-oriented, experimental and system-basedapproach. RSE has a unique heritage of human resources ,experience and innovation, essential to the continuity andrevival of innovation in this important sector for the country.

STRUTTURA INFORMATICA

Action fields:- CC e IGCC plant (Combined Cycle e Integrated Gasifier CC);- Concentrating Solar Power (CSP);- Gasification plant (carbone e biomasse)- Clean Coal Technologies (CCT);- Carbon Capture & Storage (CCS);- Hydrogen separation.

Modelling activities:- process study and their formulation;- mathematical model definition;- model development and validation;- integration of models or tasks by means of dynamic solutors.

The software platform:- ISAAC Dynamics: development system for dynamic simulations (time depending);- Support tools: Stargate (web-based access tool), Alexandria (document system).

Summary

1. Foreword

2. Process description & phenomena

3. Model Description

4. ISAAC DYNAMICS simulation platform

5. Experimental apparatus and results

6. Simulation and comparison with experimental results

7. Conclusions & Developments

1.Foreword

Palladium and palladium alloy membranes have been extensively studied in bench-scale tests at

several R&D institutes throughout the world. Studies are now focusing on specific

applications in a membrane reactor both for the WGS reaction and for steam reforming.

In this paper the basis of a new dynamic model of a palladium membrane reactor for the

Water Gas Shift Reaction are described and their preliminary validation through

experimental data is presented.

In a membrane reactor,CHEMICAL REACTION,MASS TRANSFER andHEAT TRANSFER occursimultaneously

Simplest models

MONO- DIMENSIONALSTEADY STATECONSIDER EQUILIBRIUM CONDITIONSCHEMICAL REACTIONS AND SEPARATION ARE CONSIDERED AS SEQUENTIAL STEPS

Latest models

Consider kinetics of the WGS reaction and include a more detailed description of

the membrane structure.

However dynamic models able tofollow the time evolution of themain process parameters havebeen not yet developed.

2. Process description and phenomena

The water gas shift is an exothermic reaction where the CO is converted into CO2, thus producing H2:

CO + H2O → CO2 + H2ΔH (298 K )= −41.2 kJ mol−1

The temperature affects the reaction kinetics positively

The conversion is promoted by lowering the temperature.

In industrial applications, thewater gas shift reaction iscarried out in several steps:usually, in order to achieve highconversions this process takesplace in two reactors operatingat high and low temperatures.

2. Process description and phenomena

The WGS reaction can take advantagefrom the use of membrane

reactors

The use of a membrane selectivelypermeable to hydrogen permits removalof one of the reaction products, thusmoving the conversion beyond thethermodynamic equilibrium according tothe well-described ‘shift effect’.

Thin dense Pd-based membranes allow both high H2 fluxes and selectivity

Under these conditions

THE SHIFT EFFECT CAN BE MAXIMIZED

http://www.netl.doe.gov/onsite_research/Facilities/hydrogen.html

http://www.aist.go.jp/index_en.html

3. Model description The models developed by Struttura Informatica are: Pd – based membrane:

Extended model of a palladium membrane. This model takes into account:

Chemical/ physical phenomena involved in the H2 permeation through the Pd;

Flux of H2 and other gases through defects in the Pd layer

Flux of H2 and other gases through the porous support

Simplified model of a palladium membrane. The hydrogen flux through themembrane is evaluated considering the Pd layer and the multilayered support asresistances in series . Further this model takes into account the flux of H2 and ofother gases through defects of the Pd layer.

WGS reactor . Its main features are:

The model is fully dynamic (time depending);

Kinetics of the WGS reaction is considered;

WGS reaction and separation occur simultaneously in a single cell;

3. Model description

The membrane reactor model is composed by:

A. Pd – based membrane (simplified model)

B. WSG Reactor

A. Pd – based membrane simplified

This module simulates: Feed flux shell side incoming;

Hydrogen diffusive flux inside the Pd;

Other gaseous component flux through

defects of Pd layer;

Hydrogen and other components flux

through the multilayered support (2 layers)

“permeate” current flux (rich in H2)

flowing in the inner side of the membrane.

….and calculates:The hydrogen amount permeating through

the membrane;

The out going gas flow rates (unp/per side)

and their correlated compositions;

Temperature variations during the

separation process;

Pd temperature variation during the above

mentioned process;

Pressure changes inside the cells.


H2 flux through the membrane is:

15.0)( <<−= nPPLPeJ n

pn

fS

Where:

• Js is the H2 flux through the Pd – layer

and

• JKH2 is the diffusion component (Knudsen);

•JVH2 is the viscous component (Poiseuille)

RTEa

ePePe−

= 0

Sieverts’ Law

Arrhenius

222 VHKHSH JJJJ ++=

)(22 PfKHKH PPFJ −=

)(22 PfavVHVH PPPFJ −=

=KF f (rpores , PM)

=VF f (µ)


B. WSG ReactorModel main features assumption

Fixed bed tubular catalytic reactor

(Plug Flow Reactor);

Fe/Cr catalyst.

Chemical model:

Well stirred reactor;

The reaction takes place on the catalyst surface the

gaseous phase;

Kinetic parameters depend on the catalyst;

The interaction between catalyst and gaseous

mixture is neglected.

Thermal Model :

Kinetic and potential energies are neglected;

Reaction heat is considered;

The thermal exchange catalyst/gas/reactor

wall is taken in account;

The heat exchange between reactor wall and

external atmospheres is considered.

Hydralic Model:

In the mass balance, the diffusion term is neglected.


Reactor kinetic equation:

TD equilibrium constant

Simplified description based on a semi-empirical model

Weakly influenced by pressure and decreases while temperature

increases.


WSG membrane reactor : Modelling techiniques

The model has been realized in two different steps:

Firtst step : The WGS membrane reactor has been built connecting in series theWGS reactor module and the Pd membrane module. To reach a better degree ofaccouracy we have divided the longitudinal axis of the reactor and themembrane in n - axial cells (e.g. five).

Metallic membrane

CO-Shift reactor

FEED GAS INLET

UNP. OUTLET

PERMEATEINLET

PERMEATEOUTLET


WSG membrane reactor : Modelling techiniques

Second step : Combining the equations forming the mathematical models of the two modules we have got a single module able to represent , in detail, the behaviuor of a WSG membrane reactor both from the hydraulic, thermal and chemical point of view.

In this way the WGS reaction and H2 separation occur simultaneously in a single cell.

Also in this case thereactor can be splittedin one or more axialcells

This dynamic model is able to follow the time evolution of the main process parametersuntil steady state is reached.

Catalytic bed

Pd layer

CO2

H2

CO, H2O

4.ISAAC DYNAMICS simulation platform

Isaac Dynamics© 2.1 is a complete instrument designed for the studying, modelling and running dynamic simulations of integrated and compelx systems.

It allows an easy and effective development of accurate, detailed dynamic models by means of its innovative technical features:

modular architecture;

a friendly graphical user interface;

an auto learning component

connection tool;

maximum portability

indipendence from sw platforms;

and functionalities:

sound and effective solver, based on the Newton-Raphson, operates in double precision;

capabiliity of generating external autonomous applications;

wide component library addressing the market sectors of interest: Concentrating Solar Power (CSP), Carbon Capture and Storage (CCS), Combined Cycle (CC) plants.

5.Experimental set - up @ RSE

Laboratory pilot loop

Mass flow controllers;

Electrically heated oven where process gases areheated and the test section is housed;

On-line gas chromatograph for dry gases analysis;

Acquisition and control system of the processparameters, interfaced with a computer.

TEST SECTIONConsisting of a 316 L stainless steelreactor (20mm I.D.) where themembrane is housed; gas tight sealingis insured by welding the non-porousend of the membrane support to thereactor.

Pd - MEMBRANEObtained by electroless plating on SS macroporous supportPd – layer Thickness 12 – 30 µm

Ref. Cat. Today 156 (2010) 165–172

6. Simulation and comparison of results

Membrane module validation

Permeation test with pure gas

C4 membrane thickness 12 µm 310°C no sweep

0

10

20

30

40

50

0.0E+00 1.0E+05 2.0E+05 3.0E+05 4.0E+05

∆P [Pa]

H2 f

lux

[Nl/h

]

experimentalmodel - without defectsmodel - with defects


Membrane module validationPermeation test with pure gas- membrane C4 -no sweep

C4 - no sweep

0

20

40

60

0,0E+00 1,0E+05 2,0E+05 3,0E+05 4,0E+05

Pressure difference [Pa]

H2 F

lux

[Nl/h

]

experimental 400°Cmodel 400°Cexperimental 310°Cmodel 310°C

400°C

310°C


Membrane module Validation

C4 membrane at 400°C

0

10

20

30

40

50

60

70

0.0E+00 1.0E+05 2.0E+05 3.0E+05 4.0E+05 5.0E+05

∆P [Pa]

H2 f

lux

[Nl/h

]

experimentalmodelexperimentalmodel no sweep

sweep



Permeation test with pure gas-T= 400 C –no sweep

0

15

30

45

60

0.0E+00 1.0E+05 2.0E+05 3.0E+05 4.0E+05

∆P [Pa]

H2 f

lux

[Nl/h

] experimental C3model C3experimental C4model C4

C3

C4

Membrane Thickness (mm)

C3 29

C4 12



0

0.2

0.4

0.6

0.8

1

0.0E+00 1.0E+05 2.0E+05 3.0E+05 4.0E+05 5.0E+05 6.0E+05 7.0E+05

∆P [Pa]

Flux

[Nl/h

]

He 400°C

CO2 400°C

C3 membrane



0

2

4

6

8

0.0E+00 2.0E+05 4.0E+05 6.0E+05 8.0E+05

Feed Pressure [Pa]

H2 F

lux

[Nl/h

]

experimentalmodel

C3 - 400°CWGS mixture

CO 7.6%H2O 27.2%H2 41.5%CO2 23.7%

6.Simulation and comparison of the results

Experimental data

Test performed in a pilot loop at 410-14 C

• Pfeed= 1- 6.5 bar• GHSV =1580 h-1

• Sweep gas = N2• Psweep =atmospheric• Counter-current mode

Feed composition [%vol]

FEED 1 FEED2CO 7.6 7.6H2O 27.2 20.3H2 41.5 45.9CO2 23.7 26.2H2O/CO 3.58 2.67

Reactor geometrical dataInternal diameter [mm] 20Length filled with catalyst [mm] 85Membrane external diameter [mm] 10Membrane internal diameter [mm] 6Membrane active surface [cm2] 23

0

20

40

60

80

100

0.0E+00 1.5E+05 3.0E+05 4.5E+05 6.0E+05 7.5E+05Pfeed ( Pa)

CO

con

vers

ion

%

MR feed 1MR feed 2Eq TD feed 1Eq TD feed 2TR feed 1TR feed 2

WGS membrane reactor module validation


Feed 1

0

20

40

60

80

100

0 2 4 6 8 10Feed pressure [bar]

CO

con

vers

ion

[%]

TD equilibriumExperimental MRExperimental TR

Model TRModel MR


Feed 2

0

20

40

60

80

100

0 2 4 6 8 10

Feed Pressure [bar]

CO

Con

vers

ion

[%]

TD EquilibriumExperimental MRExperimental TRModel TRModel MR

7. Conclusions & developments

H2 permeation through a Pd based membrane is well represented by the membrane model.

WGS reaction is also satisfactory described by the model, although not yet totally validated.

The MRWGS model slightly overestimates experimental data: mismatch between calculatedand experimental data increases while increasing feed pressure.

This can be due to the following main factors, not considered in the model:

concentration polarization of the feed, becoming stronger while increasing H2 recovery (feedpressure);

gas distribution at reactor inlet;

uncertainty about some data regarding catalyst kinetic.

Developments model improvement by considering polarization effects; investigate gas distribution and its influence on the reaction by experimental tests

More Info…

Contact:

[email protected]

Phone +39 055 4379027

www.strutturainformatica.it

[email protected]

www.rse-web.it

Acknowledgements

Preliminary validation of the model has been performed in a national projectfinanced by the Research Fund for the Italian Electrical System under theContract Agreement between RSE and the Ministry of Economic Development

DEVELOPMENT OF A DYNAMIC MODEL OF A PALLADIUM …...CHEMICAL REACTIONS AND SEPARATION ARE CONSIDERED...

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