Steam Reforming in a Packed Bed Membrane Reactor Global Conference 2017 Berlin, March 6-8, 2017...

STAR Global Conference 2017

Berlin, March 6-8, 2017

Fachgebiet Verfahrenstechnik

www.vt.tu-berlin.de

Steam Reforming in a Packed Bed Membrane Reactor

Nico Jurtz, Prof. Matthias Kraume

Technische Universität BerlinChair for Chemical and Process Engineering

[email protected]

Folie 2Fachgebiet Verfahrenstechnik

www.vt.tu-berlin.de



Outline

• Motivation

• Modeling

– Basics of modeling packed-bed reactors

– Basics of modeling membranes

• Validation of reaction mechanism

• Case study PBR vs. PBCMR

– Reaction rate coefficients

– Concentration and temperature field

– Reactor performance

• Outlook


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Motivation

• Hydrogen is the most important compound of chemical and petrochemical industries

• Steam Reforming of Methane (SRM) is the most used and economic process for the large scale production of hydrogen and synthesis gas

• 50% of world wide hydrogen production is produced via SRM

• In terms of process intensification fixed-bed membrane reactorsmay increase the yield by shifting the chemical equilibriumtowards the product side - Le Chatelier's Principle

• Computational Fluid Dynamics (CFD) is a valuable tool for theunderstanding and design of that reactor type

0 50 100 150 200

1

2

3

4

5

6

7

World-wide H2 production[109 Nm3]

Source: www.dwv-info.de


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What is needed?

Itoh et al., Handbook of membrane reactors. 2013, 464-495J. Xu, G.F. Froment, AIChE J. 1989, 35, 88–96.

𝑅1 =𝑘1

𝑝𝐻22.5 𝑝𝐶𝐻4𝑝𝐻2𝑂 −

𝑝𝐻23 𝑝𝐶𝑂

𝐾𝑒1×

1

𝐷𝐸𝑁2

𝑅2 =𝑘2𝑝𝐻2

𝑝𝐶𝑂𝑝𝐻2𝑂 −𝑝𝐻2𝑝𝐶𝑂2𝐾𝑒2

×1

𝐷𝐸𝑁2

𝑅3 =𝑘3

𝑝𝐻23.5 𝑝𝐶𝐻4𝑝𝐻2𝑂

2 −𝑝𝐻24 𝑝𝐶𝑂2𝐾𝑒3

×1

𝐷𝐸𝑁2

DEN = 1 + KCO𝑝𝐶𝑂 + 𝐾𝐻2𝑝𝐻2 + 𝐾𝐶𝐻4𝑝𝐶𝐻4 +𝐾𝐻2𝑂𝑝𝐻2𝑂

𝑝𝐻2

𝐑𝟏: CH4 + H2O → CO + 3H2

𝐑𝟐: CO + H2O → CO2 + H2

𝐑𝟑: CH4 + 2H2O → CO2 + 4H2

3-step mechanism (Xu et al.):

𝐽𝐻2 =𝐴 ∙ 𝑒−

𝐸𝑎𝑅𝑇

𝛿𝑝𝑓0.5 − 𝑝𝑝

0.5

𝐸𝑎 = 15.718𝑘𝐽

𝑚𝑜𝑙

𝐴 = 2.44 ∙ 10−7𝑚𝑜𝑙

𝑚 𝑠 𝑃𝑎0.5

𝛿 = 5𝜇𝑚𝐹𝑚𝑒𝑚/𝑔𝑒𝑜𝑚 = 2

𝑁2𝑁2, 𝐻2

𝐶𝐻4, 𝐻2𝑂 𝐶𝑂2, 𝐶𝑂,𝐻2

𝑱𝑯𝟐

𝒓𝒊 =

𝒋

𝒊

𝝂𝒊𝑹𝒋

Membrane flux (Itoh et al.):




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Modeling Packed Bed Reactors


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Modeling Packed Bed Reactors

Workflow:1. Discrete-Element-Methode (DEM) for packing generation2. Create geometry of packing based on DEM results3. Meshing (local flattening at contacts)4. CFD Simulation


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Fundamentals of Chemical Kinetics

Elementary step mechanism

• Detailed insights

• Transferable to other types of reactor

• Very complexe, high calculation times

• All relevant steps has to be taken into account large systems

Brutto equation

• Limited insights

Lumped kinetics

• Some parameters can be studied

• Limited to experimental setup (p,T, composition)

• Fluid dynamic effects (mass transport limitations) are oftenlumped into the kinetics

𝐶𝐻4 + 𝐻2𝑂 → 𝐶𝑂 + 3𝐻2


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Implementation of Chemical Kinetics

Currently no User-defined Reaction Rateavailable for Surface Chemistry Model

• Define reaction rate expressions via field functions• Use of Wall Boundary Species Flux option

Heat of reaction is calculated through enthalpy differenceBUT: Kinetic mechanism is not thermodynamic consistent

• Use constant and equal specific heat for all species• Use Wall Boundary Heat Flux option




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Modeling Membrane Reactors


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Modeling Transmembrane Flux

• Mass transfer through membrane is proportional to some driving force

• Membrane specific characteristics are lumped into one coefficient (permeance or permeability)

• Temperature dependency of permeability can be modeled by Arrhenius-type equation

• A mapping approach on conformal interfaces is used to calculate the driving force

ሶ𝑚𝑖 ~Δ𝜇𝑖ሶ𝑚𝑖 ~Δ𝑐𝑖ሶ𝑚𝑖 ~Δ𝑝𝑖

Reduced concentration at membrane

Permeate

Concentration profile within the membrane

Poroussupport

Active layer

Semi-permeable membrane

cd,bulkcd,m

cf

cf,m


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Examples of membrane modeling – Gas separation membrane

10 bar10 bar

40 bar40 bar

10 bar10 bar


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Examples of membrane modeling – Tubular membrane reactor

0

0.5

1

1.5

2

2.5

3

0 0.05 0.1 0.15

Rel

ativ

e R

eco

very

Dex

tran

[-]

Radial Position of the Pipe [m]


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Examples of membrane modeling – Flat sheet membrane

Incre

asin

g P

ressu

re

Velocity Inlet:u0=0.2m/s

cNaCl=2g/l

Pressure

Outlet

Membrane Baffle

Feed Side

Permeate Side




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PBR + MBR = PBCMR


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SRM in Annulus Packed Bed Reactor - Validation

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CH4 H2O H2 CO CO2

Mole

Fra

ction [

-]

Mole Fractions @ Outlet

Kuroki 2009 Current Study

0.00

0.25

0.50

0.75

1.00

0 0.01 0.02

Mole

Fra

ction

[-]

Axial Position [m]

Axial Concentration Profile

Series1Series2Series3

PPBR: 1.5bar

Tin,PBR: 973K

uin,PBR: 7.75m/s

: 0.8

H2O/CH4 ratio: 3.5

Heated wall 60kW/m2

Catalyst particlesModels:

Turbulence: Realizable k-

Radiation Surface-to-surface

EoS Ideal Gas

Transport properties: Chapmen-Enskog

Heat Transfer: CHT

CH4H2OH2


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Process Intensification – Packed Bed Membrane Reactor

Adiabatic wall

Catalyst particles

Semi-permeable membrane

PPBR: 3.1bar

Tin,PBR: 750K

uin,PBR: 0.12m/s

: 0.8

H2O/CH4 ratio: 3.5

PM: 0.1bar

Sweep ratio: 1.04


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Reaction Rate Coefficients

𝐑𝟐: CO + H2O → CO2 + H2P

BR

𝐑𝟏: CH4 + H2O → CO + 3H2

Rate Coefficient[mol/kg-cat s]P

BC

MR


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Reaction Rate Coefficient and Membrane Flux

𝐑𝟑: CH4 + 2H2O → CO2 + 4H2

Rate Coefficient[mol/kg-cat s]

PB

R

PB

CM

R


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Temperature and Concentration FieldP

BR

P

BC

MR


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Conclusion and Outlook

0

2

4

6

8

10

12C

onvers

ion

[%]

PBR PBCMR

0

2

4

6

8

10

12

Yie

ld[%

]

25.4%25.4%24.9%24.9%

Outlook:

• Use of Detailed Chemistry

• Variation of operating parameters

– Operating temperature

– Operating pressure

– Transmembrane pressure

– Sweep ratio

– Co- vs. Counter-Current

• Extend bed length


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Thanks

Thanks for your attention!

Acknowledgement:This work is part of the Cluster of Excellence “Unifying Concepts in Catalysis”coordinated by the Technische Universität Berlin. Financial support by the DeutscheForschungsgemeinschaft (DFG) within the framework of the German Initiative forExcellence is gratefully acknowledged (EXC 314).

Steam Reforming in a Packed Bed Membrane Reactor Global Conference 2017 Berlin, March 6-8, 2017...

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