spatially resolved simulations of heterogeneous dry...
TRANSCRIPT
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
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)
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
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
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)
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
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
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
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
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 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
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
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:
• Re𝑃 =𝑣𝑖𝑛∙𝑑𝑃
𝜈= 35, 350, 700
• 𝑇𝑊𝑎𝑙𝑙 = 𝑇𝑖𝑛 = 700 °C
• xCO2/xCH4
/xN2 = 0,2/0,1/0,7
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.:
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.
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 14
Flow field and hydrogen production
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 15
Velocity distribution
𝑅𝑒𝑝 =𝑣 𝑑𝑝
𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =
𝑣 𝑑𝑝
𝜈 = 700, Twall = 700 °C
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 16
Back flow regions
𝑅𝑒𝑝 =𝑣 𝑑𝑝
𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =
𝑣 𝑑𝑝
𝜈 = 700, Twall = 700 °C
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 17
Temperature distribution
𝑅𝑒𝑝 =𝑣 𝑑𝑝
𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =
𝑣 𝑑𝑝
𝜈 = 700, Twall = 700 °C
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 18
Catalyst deactivation through carbon deposition
𝑅𝑒𝑝 =𝑣 𝑑𝑝
𝜈 = 35, Twall = 700 °C
𝑅𝑒𝑝 =𝑣 𝑑𝑝
𝜈 = 700, Twall= 700 °C
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 19
Hydrogen gas phase concentrations
𝑅𝑒𝑝 =𝑣 𝑑𝑝
𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =
𝑣 𝑑𝑝
𝜈 = 700, Twall = 700 °C
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.
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.
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
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 23
BACK UP
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
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 25
Void fraction and velocity
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 26
Void fraction and radial velocity
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 27
Void fraction and temperature distribution
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.
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
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.
TU Berlin – Process & Chemical Engineering Gregor D. Wehinger
STAR Global Conference Vienna, March 17-19, 2014
Slide 30
Radial velocity distribution
𝑅𝑒𝑝 =𝑣 𝑑𝑝
𝜈 = 35, Twall = 700 °C 𝑅𝑒𝑝 =
𝑣 𝑑𝑝
𝜈 = 700, Twall = 700 °C