Spatially resolved simulations of heterogeneous dry reforming of - PowerPoint PPT Presentation

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

Fixed-bed reactors (A) • 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) (B)  Interplay between chemical kinetics and transport of momentum, heat and mass Eigenberger & Ruppel (2000), Ullmann‘s Encycl. Slide 2 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

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

Elements of spatially resolved reacting flow 1. Bed generation 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD Slide 4 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Elements of spatially resolved reacting flow • Randomly distributed • 1. Bed generation With discrete element method (DEM) 2. Meshing 3. Reliable kinetics 4. Pore model 5. CFD Eppinger et al. (2011) Chemical Engineering Journal , 166 (1), 324-331 Slide 5 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Elements of spatially resolved reacting flow 1. Bed generation Caps method: flattening of particle- 2. Meshing particle contact points 3. Reliable kinetics 4. Pore model 5. CFD Slide 6 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Elements of spatially resolved reacting flow • Detailed reaction mechanisms • Adsorption, surface reaction, 1. Bed generation desorption 2. Meshing • Coupling via bodunary condition 3. Reliable kinetics 4. Pore model 5. CFD Slide 7 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Elements of spatially resolved reacting flow Pore models 1. Bed generation 1. Reaction-diffusion model 2. Meshing 2. 1D reaction-diffusion model 3. Effectiveness factor approach 3. Reliable kinetics 4. Instantaneous diffusion 4. Pore model 5. CFD Slide 8 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Elements of spatially resolved reacting flow • STAR-CCM+ for hydro dynamics and 1. Bed generation heat transfer • DARS-CFD for calculating reaction 2. Meshing source terms 3. Reliable kinetics 4. Pore model 5. CFD Slide 9 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Dry reforming of methane (DRM) Stagnation flow reactor 1 • Dry reforming of methane as an alternative to steam reforming CH 4 + CO 2 ↔ 2H 2 + 2CO Δ𝐼 ≈ 260 kJ/mol • Detailed reaction mechanism by McGuire (2011) on Rhodium • 42 irreversible reactions • 12 surface adsorbed species • 6 gas phase species • F cat/geo = A cat /A geo = 90 1 McGuire et al. (2011) Applied Catalysis A: General, 394 , 257 - 265 Slide 10 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Validation of DRM kinetics Calculation domain Wehinger et al. (2014) Chemical Engineering Science Slide 11 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Catalytic fixed-bed for DRM • DRM kinetics from McGuire et al. (2011) • 113 spherical solid particles • F cat/geo = A cat /A geo = 90 • Approx. 3.4 mio cells • k- ε turbulence model • Inlet: 𝑤 𝑗𝑜 ∙𝑒 𝑄 • Re 𝑄 = = 35, 350, 700 𝜉 • 𝑈 𝑋𝑏𝑚𝑚 = 𝑈 𝑗𝑜 = 700 °C • x CO2 /x CH4 /x N2 = 0,2/0,1/0,7 Slide 12 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Pressure drop, porosity and velocity distribution Pressure drop Velocity and porosity Eisfeld’s Eq.: 2 ∙ 1 − 𝜁 2 ∙ 1 − 𝜁 2 ∙ 1 + 𝐵 𝑥 ∙ 𝐼 2 Δ𝑞 = 154 ∙ 𝐵 𝑥 ∙ 𝜍 ∙ 𝑤 𝑗𝑜 𝜁 2 𝑆𝑓 𝑄 𝐶 𝑥 𝜁 2 𝑒 𝑄 Eisfeld & Schnitzlein (2001 ) Chemical Engineering Science , 56, 4321 – 4329. Slide 13 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

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

Velocity distribution 𝑤 𝑒 𝑞 𝑤 𝑒 𝑞 𝑆𝑓 𝑞 = 𝜉 = 35 , T wall = 700 °C 𝑆𝑓 𝑞 = 𝜉 = 700 , T wall = 700 °C Slide 15 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Back flow regions 𝑤 𝑒 𝑞 𝑤 𝑒 𝑞 𝑆𝑓 𝑞 = 𝜉 = 35 , T wall = 700 °C 𝑆𝑓 𝑞 = 𝜉 = 700 , T wall = 700 °C Slide 16 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Temperature distribution 𝑤 𝑒 𝑞 𝑤 𝑒 𝑞 𝑆𝑓 𝑞 = 𝜉 = 35 , T wall = 700 °C 𝑆𝑓 𝑞 = 𝜉 = 700 , T wall = 700 °C Slide 17 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Catalyst deactivation through carbon deposition 𝑤 𝑒 𝑞 𝑆𝑓 𝑞 = 𝜉 = 35 , T wall = 700 °C 𝑤 𝑒 𝑞 𝑆𝑓 𝑞 = 𝜉 = 700 , T wall = 700 °C Slide 18 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

Hydrogen gas phase concentrations 𝑤 𝑒 𝑞 𝑤 𝑒 𝑞 𝑆𝑓 𝑞 = 𝜉 = 35 , T wall = 700 °C 𝑆𝑓 𝑞 = 𝜉 = 700 , T wall = 700 °C Slide 19 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

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

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

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

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

Porosity and velocity distribution Porosity Velocity de Klerk: de Klerk, A. (2003) AIChE journal , 49 (8), 2022-2029 Slide 24 TU Berlin – Process & Chemical Engineering STAR Global Conference Vienna, March 17-19, 2014 Gregor D. Wehinger

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

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