Master’s Dissertation Defense Carlos M. Teixeira Supervisors: Prof. José Carlos Lopes

1. Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Master’s Dissertation Defense Carlos M. Teixeira Supervisors: Prof. José Carlos Lopes Eng. Matthieu Rolland 17th July 2013

2. Outline Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Introduction • Objectives • State of the Art • Methodology • Results and Discussion • Conclusions FEUP/IFPEN

3. Introduction Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Catalysts performance evaluation • Performed in unitsat pilot scale • The trend is to reduce the size of testing units(economic and safety reasons) • Catalyst size remains constant (customer demands) • Consequence Reactors with low tube-to-particle diameter ratio ) FEUP/IFPEN

4. Introduction Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Reactors with low tube-to-particle diameter ratio • Pseudo Homogeneous Models may not be valid • Local Phenomena are dominant • Wall Effect • Packing Effect FEUP/IFPEN

5. Introduction Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Example of Packing Effect • Problem Description • Packing of eight cylinders with different arrangements • Fluid with zero concentration at the inlet flows through the packing • Laminar regime • Cylinders with constant concentration in their surface • Transfer solute to the fluid Normalized outlet concentration for the different arrangements FEUP/IFPEN

6. Outline Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Introduction • Objectives • State of the Art • Methodology • Results and Discussion • Conclusions FEUP/IFPEN

7. Objectives Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Study the phenomena of single phase fluid flow through fixed-bed reactors at low particle Reynolds number • Understand how the packing structure affects the flow FEUP/IFPEN

8. Outline Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Introduction • Objectives • State of the Art • Methodology • Results and Discussion • Conclusions FEUP/IFPEN

9. State of the Art Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing CFD Simulation of Fixed-Bed Reactors • Benchmark Method: Lattice Boltzmann • Finite Volume method has been successfully used by many authors • In most published works, the ratio of tube-to-particle diameter is low FEUP/IFPEN

10. State of the Art Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing CFD Simulation of Fixed-Bed Reactors • Coupling between Hydrodynamics, Heat Transfer and Chemical Reaction: • Less works on the literature • Applied in small size problems (dozens of particles) • Particle shape: mostly spheres FEUP/IFPEN

11. Outline Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Introduction • Objectives • State of the Art • Methodology • Results and Discussion • Conclusions FEUP/IFPEN

12. Methodology Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Coupling between DEM and CFD • GRAINS3D (Packing Simulation) • PeliGRIFF (Fluid Flow Simulation) FEUP/IFPEN

13. Methodology Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Grid Refinement Studies Relative error in the inlet velocity as a function of the grid resolution (ε=0.799, l/dp=1) FEUP/IFPEN

14. Outline Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Introduction • Objectives • State of the Art • Methodology • Results and Discussion • Conclusions FEUP/IFPEN

15. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Structured Packed Beds • Unit cell approach (a) (b) A packed bed of simple cubic arrangement of spheres. a) Unit cell b) Alternative representation of a simple cubic unit cell. FEUP/IFPEN

16. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Structured Packed Beds of Spheres • Validation Case Comparison between the simulated dimensionless pressure drop and results from Hill et al. (2001) for a dilute array of spheres (ε=0.799) FEUP/IFPEN

17. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Structured Packed Beds of Cylinders • Effect of cylinder orientation Effect of cylinders orientation on dimensionless pressure drop (ε=0.799, l/dp=1) FEUP/IFPEN

18. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Structured Packed Beds of Cylinders • Transition from laminar regime to unsteady and chaotic flow Particle Reynolds number as a function of time for 45º orientation (ΔP=10 Pa) FEUP/IFPEN

19. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders Case ID FBR1 FBR2 FBR3 Nº of particles 540 200 100 Porosity, ε 0.451 0.444 0.467 FEUP/IFPEN

20. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders • Simulated Packed Beds Grid parameters and computing times on 128 processors FEUP/IFPEN

21. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders • Pressure Drop Dimensionless pressure drop as a function of porosity. Comparison between simulations and Ergun correlation predictions (Redp=1). FEUP/IFPEN

22. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders • Spatial Velocity Distribution • Three different zones are identified: • Recirculation zones in the packing top and bottom and in the wake of the particles (with negative velocities) • High velocity zones where the void fraction is small and the velocity increases up to a factor of 15 • Low velocity zones near the particles surfaces FEUP/IFPEN

23. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders • Statistical Velocity Distribution Probability density functions of normalized z-velocity in different zones of the fixed-bed. FEUP/IFPEN

24. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders • Statistical Velocity Distribution (link with porosity) Inlet Outlet Axial average porosity profile FEUP/IFPEN

25. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders • Statistical Velocity Distribution (link with porosity) Probability density functions of normalized z-velocity for different porosities FEUP/IFPEN

26. Results and Discussion Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds of Cylinders • Statistical Velocity Distribution Probability density functions of normalized x-velocity for different porosities FEUP/IFPEN

27. Outline Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing • Introduction • Objectives • State of the Art • Methodology • Results and Discussion • Conclusions FEUP/IFPEN

28. Conclusions Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Structured Packed Beds • The methodology was validated with well-established cases from the literature • Dependence of Pressure Drop across Packed Beds of cylinders on its orientation was studied • Transition from steady laminar flow to time oscillatory and chaotic flow was observed at FEUP/IFPEN

29. Conclusions Direct Numerical Simulation of Fixed-Bed Reactors: Effect of Random Packing Flow through Randomly Packed Beds • Good agreement between Ergun’s pressure drop predictions and simulation results were found • Velocity distributions were analyzed and three different zones were identified • Velocity distributions appear to follow the average local porosity: the length to establish the flow is identical to the length to establish the porosity FEUP/IFPEN

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