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Spatially resolved simulations of heterogeneous dry reforming of methane in fixed-bed reactors G. W EHINGER , T. E PPINGER , M. K RAUME TU Berlin Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Slide 1 TU

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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

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger 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)

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 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

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 4

Elements of spatially resolved reacting flow

1. Bed generation 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD

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SLIDE 5

TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 5

Elements of spatially resolved reacting flow

1. Bed generation 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD

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

  • Randomly distributed
  • With discrete element method (DEM)
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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 6

Elements of spatially resolved reacting flow

1. Bed generation 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD

Caps method: flattening of particle- particle contact points

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 7

Elements of spatially resolved reacting flow

1. Bed generation 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD

  • Detailed reaction mechanisms
  • Adsorption, surface reaction,

desorption

  • Coupling via bodunary condition
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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 8

Elements of spatially resolved reacting flow

1. Bed generation 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD

Pore models

  • 1. Reaction-diffusion model
  • 2. 1D reaction-diffusion model
  • 3. Effectiveness factor approach
  • 4. Instantaneous diffusion
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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 9

Elements of spatially resolved reacting flow

1. Bed generation 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD

  • STAR-CCM+ for hydro dynamics and

heat transfer

  • DARS-CFD for calculating reaction

source terms

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 10

Dry reforming of methane (DRM)

  • Dry reforming of methane as an

alternative to steam reforming CH4 + CO2 ↔ 2H2 + 2CO Δ𝐼 ≈ 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

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 11

Validation of DRM kinetics

Wehinger et al. (2014) Chemical Engineering Science

Calculation domain

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 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:
  • Re𝑄 =

𝑤𝑗𝑜∙𝑒𝑄 𝜉

= 35, 350, 700

  • 𝑈

𝑋𝑏𝑚𝑚 = 𝑈 𝑗𝑜 = 700 °C

  • xCO2/xCH4/xN2 = 0,2/0,1/0,7
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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 13

Pressure drop, porosity and velocity distribution

Pressure drop Velocity and porosity

Eisfeld’s Eq.: Δ𝑞 = 154 ∙ 𝐵𝑥

2 ∙ 1 − 𝜁 2

𝜁2 ∙ 1 𝑆𝑓𝑄 + 𝐵𝑥 𝐶𝑥 ∙ 1 − 𝜁 2 𝜁2 ∙ 𝐼 𝑒𝑄 ∙ 𝜍 ∙ 𝑤𝑗𝑜

2

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

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 14

Flow field and hydrogen production

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 15

Velocity distribution

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 35, Twall = 700 °C

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 700, Twall = 700 °C

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 16

Back flow regions

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 35, Twall = 700 °C

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 700, Twall = 700 °C

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 17

Temperature distribution

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 35, Twall = 700 °C

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 700, Twall = 700 °C

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 18

Catalyst deactivation through carbon deposition

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 35, Twall = 700 °C

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 700, Twall= 700 °C

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 19

Hydrogen gas phase concentrations

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 35, Twall = 700 °C

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 700, Twall = 700 °C

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 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.

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 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.

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 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

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 23

BACK UP

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 24

Porosity and velocity distribution

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

Porosity Velocity

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 25

Void fraction and velocity

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 26

Void fraction and radial velocity

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 27

Void fraction and temperature distribution

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 28

Validation of random beds

D/dP=7,99

DEM Simulation DEM Simulation shaken Experiments* *Mueller (1992) Powder technology, 72(3), 269-275.

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 29

Validation of fluid dynamics

Pressure drop Velocity

uz/u0[-]

Rep=100 Rep=1 Rep=1000

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

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TU Berlin – Process & Chemical Engineering Gregor D. Wehinger STAR Global Conference Vienna, March 17-19, 2014 Slide 30

Radial velocity distribution

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 35, Twall = 700 °C

𝑆𝑓𝑞 =

𝑤 𝑒𝑞 𝜉 = 700, Twall = 700 °C