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

2. Main issue Continuum plug flow Particle-scale 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 kg/m3
η 1.0 e-5 Pa s
Gas in solid
k 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 (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 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 6

7. Effect of U0 (average linear velocity) on z-velocity
r [10-3 m]
0.005 m/s
0.01 m/s
0.05 m/s
0.1 m/s
0.2 m/s
0.4 m/s 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 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
z [m] 8

9. Effect of ⊿H (heat of reaction)
Temperature
CO conc.
-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]
Temperature
CO conc.
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 = )
Κ = 10-6
100000
Z [m]
Permeability : Larger impact 11

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

13. Velocity and mass inside a particle
0.12
Velocity [m/s]
0.05
2.5
CO conc. [mol/m3]
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 Temperature CO conc.
0.5
0.2
kporous = kgas ε + ksolid (1- ε)
Cpporous = Cpgas ε + 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]