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Heat and Mass Transfer in Fixed-bed Tubular Reactor

Heat and Mass Transfer in Fixed-bed Tubular Reactor. Junichiro Kugai. 1. Main issue. Continuum plug flow. Uniformity assumption Semi-empirical. Particle-scale. Non-uniform flow Complex. Purpose.

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Heat and Mass Transfer in Fixed-bed Tubular Reactor

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  1. Heat and Mass Transfer in Fixed-bed Tubular Reactor Junichiro Kugai 1

  2. Main issue Continuum plug flow Uniformity assumption Semi-empirical Particle-scale Non-uniform flow Complex

  3. Purpose Simulating velocity, temperature, and mass distributions in a catalytic tubular reactor using COMSOL Investigating the effect of the flow rate at inlet, heat of reaction, permeability, and porosity on catalytic activity Understanding fluid behavior in particle-scale 3

  4. Model and Equations(Axial 2D) Outlet Fluid flow in porous media Fluid 　　　 : Typical syngas Porous media : Catalyst-bed A Axial sym Equations Velocity : Navier-Stokes Temperature: Convection-conduction Mass (CO conc.) : Convection-diffusion Wall Inlet 4

  5. Parameters and Boundary Conditions 1 e5 Pa Convection Reaction rate expression 0.0025m CO + H2O CO2 + H2 rate = A exp(-Ea/RT)[CO]0.1[H2O]0.8[CO2]-0.2[H2]-0.6(1-β) A 1.0 e8 mol/m3-cat/s Ea 70 kJ/mol ⊿H -40 kJ/mol Axial sym Wall 623.2 K 0.01m Other properties Gas ρ 0.258 kg/m3 η 1.0 e-5 Pa s Gas in solid k 0.76 W/m/K (0.1, 1.2) Cp 316 kJ/K/m3 (2, 525) D 1.5 e-5 m2/s (6 e-5) Solid ρ 1500 (apparent) ε 0.4 κ 1.0 e-7 m2 0.085 m/s 620 K 2.542 mol/m3 5 5

  6. Distribution of velocity, temperature, and mass 0.129 m/s 623.34 K 0.6 mol/m3 0 m/s 620 K 2.54mol/m3 Velocity Temperature CO conc. Catalyst-bed temperature is determined by the inlet temperature Reaction reaches equilibrium at ~4 mm from the inlet 6

  7. Effect of U0 (average linear velocity) on z-velocity 0.4 m/s 0.2 m/s 0.1 m/s 0.05 m/s 0.005 m/s 0.01 m/s r [10-3 m] 7

  8. Effect of U0 (average linear velocity) Temperature 0.005 m/s 0.01 m/s 0.05 m/s 0.1 m/s 0.2 m/s 0.4 m/s z [m] Large difference in behavior btw. 0.01 and 0.05 m/s CO conc. 0.4 m/s 0.2 m/s 0.01 m/s 0.1 m/s 0.05 m/s Equilibrium 0.005 m/s 8 z [m]

  9. Effect of ⊿H (heat of reaction) CO conc. Temperature -400 kJ/mol -80 kJ/mol +20 kJ/mol Z [m] ⊿H : Small impact 9

  10. Effect of permeability Verocity 10-6 10-7 10-8 Homogeneity of fluid r [10-3 m] CO conc. Temperature 10-6 10-7 10-8 r [10-3 m] r [10-3 m] 10

  11. Effect of permeability and porosity 100001 Pressure Κ = 10-8 Pressure [Pa] Κ = 10-7 (ε = 0.2-0.5) Κ = 10-6 100000 Z [m] Permeability : Larger impact 11

  12. Fluid behavior in particle-scale (2D) CO conc. (2.54~1.67 mol/m3) Velocity (0~0.22 m/s)

  13. Velocity and mass inside a particle 0.12 Velocity [m/s] 0.05 2.5 CO conc. [mol/m3] 2.2 0.2 0.6 1.0 1.4 1.8 2.2 z [mm] 13

  14. Conclusion An actual WGS reactor was reproduced by the simulation Inlet temperature is crucial to the catalyst-bed temperature in the given condition Permeability has large impact on homogeneity of fluid in the reaction condition Gas diffusion effectively flatten mass distribution from uneven fluid flow 14

  15. Effect of porosity Verocity 0.5 0.2 kporous = kgasε + ksolid (1- ε) Cpporous = Cpgasε + Cpsolid (1- ε) Dporous = (ε / τ) Dgas in J/K/m3 r [10-3 m] Temperature CO conc. 0.5 0.4 0.3 0.2 15 r [10-3 m] r [10-3 m]

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