5019 allain presentation

8/6/2019 5019 Allain Presentation

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Modeling of Transport and Reaction

in a Catalytic Bed Using a CatalystParticle Model.Florent Allain (speaker), Anthony G. Dixon

Worcester Polytechnic Institute - Chemical

Eng. Dpt. , Worcester, MA, USA

COMSOL Conference 2010 BostonPresented at the
http://www.comsol.com/conf_cd_2011_us


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Packed bed reactors: COconversion, MSR reaction, Benzeneconversion to cyclohexane

Characterized by N=ratio betweenbed and particle diameter,

Usual model: pseudo-

heterogeneous, effectiveness factorHigh N

Our model: pseudo-heterogeneous,diffusion in the solid particles.

Background


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Our model (1)

Fluid equations:

Solid equations:


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Boundary conditions:

Fluid phase:

Convective fluxes for C and T

Axis symmetry for C and T

Our model (2)


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Boundary conditions:

Solid phase:

Axis symmetry

Our model (3)


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Chemical eng. module

Fluid equations: 2D Convection

conduction/diffusion Solid equations: 3D

Conduction/diffusion

Extrusion coupling variablesfrom one geometry to the other.

Implementation in COMSOL 3.5


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First case: CO conversion over copper-chromitecatalyst. N=11.

CO inlet concentration of 0.5 mol/m3,

O2 considered constant (30.6 mol/m3) in the

fluid and solid, Constant wall temperature of 385K.

Test case - Statement


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Temperature profile Fluid (K) Temperature profile Solid (K)

Test case Results (1)


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CO concentration profile Fluid(mol/m3)

CO concentration profile Solid(mol/m3)



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Machac et al. 2006 Present study

Hot spot in the center, at z= 2

Hot spot temperature: 475 K

Temperature differencesolid/fluid, r=0.5: 20K

Effective inlet concentration:

around 0.45mol/m3

Hot spot in the center, at z=

2.5 Hot spot temperature: 440 K

Temperature differencesolid/fluid, r=0.5: 43K

Effective inlet concentration:

0.414 mol/m3

Test case - Comparison

Similar profiles for both concentration and temperature in the fluid phase.

Need to get better coefficient for conduction/diffusion in the solid.


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MSR reactions. N=6

Reaction rates from Hou et Hughes. The kineticsof methane steam reforming over a Ni/[alpha]-

Al2O catalyst. Chemical Engineering Journal(2001)

Data from simulations by Johnson Matthey.

Study case - Statement


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Temperature profile Fluid (K) Temperature profile Solid (K)



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H2 concentration profile Fluid(mol/m3)

H2 concentration profile Solid(mol/m3)



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Good agreement in the test case with literature,

Model applicable to more complex reactions,

Need to reevaluate the heat and mass transfer

coefficient for MSR reaction, for both fluid andsolid phase.

Conclusion


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The Donors of the American Chemical SocietyPetroleum Research Fund

COMSOL

Acknowledgments

5019 allain presentation

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