Spatially Resolved Simulations of Heterogeneous Dry ...mdx2.plm.automation.siemens.com/sites/default/files...TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global

TU Berlin – Process & Chemical Engineering Gregor D. Wehinger

STAR Global Conference Vienna, March 17-19, 2014

Slide 1

Spatially resolved simulations of heterogeneous

dry reforming of methane in fixed-bed reactors

G. WEHINGER, T. EPPINGER, M. KRAUME

TU Berlin – Process & Chemical Engineering

STAR Global Conference

Vienna, March 17-19, 2014



Slide 2

Fixed-bed reactors

• 80-90% of chemical processes

involve catalysts

• Fixed-bed reactors: most common

device for heterogeneous catalytic

reactions

• Randomly distributed catalytic

particles (A) or monolithic elements

(B)

Interplay between chemical kinetics

and transport of momentum, heat

and mass

Eigenberger & Ruppel (2000), Ullmann‘s Encycl.

(A)

(B)



Slide 3

Modeling fixed-beds on different time/length scales

• Classic description based on plug

flow and pseudo-homogeneous

kinetics

• Inhomogeneous bed structure

• Significant wall effects

• Local backflows

• Large axial and radial gradients

Heat and mass transfer have to be

modeled adequately with full CFD

and detailed chemical models.

Kapteijn & Moulijn (2008) Handbook of Catalysis, Chap. 9.1



Slide 4

Elements of spatially resolved reacting flow

1. Bed generation

2. Meshing

3. Reliable kinetics

4. Pore model

5. CFD



Slide 5


1. Bed generation

2. Meshing


4. Pore model

5. CFD

Eppinger et al. (2011) Chemical Engineering Journal, 166(1), 324-331

• Randomly distributed • With discrete element method (DEM)



Slide 6


1. Bed generation

2. Meshing


4. Pore model

5. CFD

Caps method: flattening of particle-particle contact points



Slide 7


1. Bed generation

2. Meshing


4. Pore model

5. CFD

• Detailed reaction mechanisms • Adsorption, surface reaction,

desorption • Coupling via bodunary condition



Slide 8


1. Bed generation

2. Meshing


4. Pore model

5. CFD

Pore models

1. Reaction-diffusion model 2. 1D reaction-diffusion model 3. Effectiveness factor approach 4. Instantaneous diffusion



Slide 9


1. Bed generation

2. Meshing


4. Pore model

5. CFD

• STAR-CCM+ for hydro dynamics and heat transfer

• DARS-CFD for calculating reaction source terms



Slide 10

Dry reforming of methane (DRM)

• Dry reforming of methane as an

alternative to steam reforming

CH4 + CO2 ↔ 2H2 + 2CO Δ𝐻 ≈ 260 kJ/mol

• Detailed reaction mechanism by

McGuire (2011) on Rhodium

• 42 irreversible reactions

• 12 surface adsorbed species

• 6 gas phase species

• Fcat/geo = Acat/Ageo = 90

1McGuire et al. (2011) Applied Catalysis A: General, 394, 257 - 265

Stagnation flow reactor1



Slide 11

Validation of DRM kinetics

Wehinger et al. (2014) Chemical Engineering Science

Calculation domain



Slide 12

Catalytic fixed-bed for DRM

• DRM kinetics from McGuire et al.

(2011)

• 113 spherical solid particles

• Fcat/geo = Acat/Ageo= 90

• Approx. 3.4 mio cells

• k-ε turbulence model

• Inlet:

• Re𝑃 =𝑣𝑖𝑛∙𝑑𝑃

𝜈= 35, 350, 700

• 𝑇𝑊𝑎𝑙𝑙 = 𝑇𝑖𝑛 = 700 °C

• xCO2/xCH4

/xN2 = 0,2/0,1/0,7



Slide 13

Pressure drop, porosity and velocity distribution

Pressure drop Velocity and porosity

Eisfeld’s Eq.:

Δ𝑝 = 154 ∙ 𝐴𝑤2 ∙

1 − 𝜀 2

𝜀2∙

1

𝑅𝑒𝑃+

𝐴𝑤

𝐵𝑤∙

1 − 𝜀 2

𝜀2∙

𝐻

𝑑𝑃∙ 𝜌 ∙ 𝑣𝑖𝑛

2

Eisfeld & Schnitzlein (2001) Chemical Engineering Science, 56, 4321–4329.



Slide 14

Flow field and hydrogen production



Slide 15

Velocity distribution

𝑅𝑒𝑝 =𝑣 𝑑𝑝

𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =

𝑣 𝑑𝑝

𝜈 = 700, Twall = 700 °C



Slide 16

Back flow regions


𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =

𝑣 𝑑𝑝

𝜈 = 700, Twall = 700 °C



Slide 17

Temperature distribution


𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =

𝑣 𝑑𝑝

𝜈 = 700, Twall = 700 °C



Slide 18

Catalyst deactivation through carbon deposition


𝜈 = 35, Twall = 700 °C


𝜈 = 700, Twall= 700 °C



Slide 19

Hydrogen gas phase concentrations


𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =

𝑣 𝑑𝑝

𝜈 = 700, Twall = 700 °C



Slide 20

Conclusion

• Successful generation of randomized packed beds with DEM

• Validated bed structure, pressure drop, velocities

• Implementation of detailed heterogeneous reaction mechanism

• Strong axial and radial effects

• Inhomogeneous bed structures call for detailed fluid dynamics and kinetics

Resolved simulations contribute to a better understanding of multi-scale

chemical reactors.



Slide 21

Outlook

• Comparison with spatially resolved

experimental data with Prof. Horn,

TU Hamburg-Harburg

• Model validation and modification

• Pore models

• Heat transfer

• Kinetics

Geske et al. (2013) Catalysis Science & Technology, 3(1), 169-175.



Slide 22

Thank you for your attention.

Special thanks go to the Cluster of Excellence “Unifying concepts

in catalysis (Unicat)” for financial support.

Literature:

de Klerk, A. (2003) AIChE journal, 49(8), 2022-2029

Dixon et al. (2013) Computers & Chemical Engineering, 48, 135-153.

Eigenberger & Ruppel (2000), Ullmann‘s Encycl.

Eisfeld & Schnitzlein (2001) Chemical Engineering Science, 56, 4321–4329.

Eppinger et al. (2011) Chemical Engineering Journal, 166(1), 324-331.

Geske et al. (2013).Catalysis Science & Technology, 3(1), 169-175.

Kapteijn & Moulijn (2008) Handbook of Catalysis, Chap. 9.1

McGuire et al. (2011) Applied Catalysis A: General, 394, 257 - 265

Mueller (1992) Powder technology, 72(3), 269-275.

Wehinger et al. (2014) Chemical Engineering Science



Slide 23

BACK UP



Slide 24

Porosity and velocity distribution

de Klerk, A. (2003) AIChE journal, 49(8), 2022-2029

de Klerk:

Porosity Velocity



Slide 25

Void fraction and velocity



Slide 26

Void fraction and radial velocity



Slide 27

Void fraction and temperature distribution



Slide 28

Validation of random beds

D/dP=7,99

DEM Simulation DEM Simulation shaken

Experiments*

*Mueller (1992) Powder technology, 72(3), 269-275.



Slide 29

Validation of fluid dynamics

Pressure drop Velocity

Dixon, A., Can. J. Chem. Eng. (1988), 705-708 De Klerk, A., AIChE J. (2003), 2022-2029

uz/u

0[-

]

Rep=100

Rep=1

Rep=1000

Eppinger et al. (2011) Chemical Engineering Journal, 166(1), 324-331.



Slide 30

Radial velocity distribution


𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =

𝑣 𝑑𝑝

𝜈 = 700, Twall = 700 °C

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Spatially Resolved Simulations of Heterogeneous Dry ...mdx2.plm.automation.siemens.com/sites/default/files...TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global