Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter December 4, 2014

Numerical Analysis of Residence Time Distribution in Packed Bed Reactors with Irregular Particle Arrangements

Theodoros Atmakidis and Eugeny Y. Kenig

Abstract

The computational fluid dynamics approach is applied to packed bed reactors with moderate tube-to-particle diameter ratios. In order to generate irregular particle arrangements within the reactors, a modified ballistic deposition method is used. While our previous studies were focused on pressure drop and mass transfer characteristics, the present paper uses the same framework to investigate the dispersion phenomena occurring in such reactors. Two different methods, namely the tracer and the post-processing method, are applied. The first method imitates the experimental procedure in which a non-diffusive tracer is injected into the packed bed. The residence time can be evaluated from the evolution of the tracer concentration. The second method is purely numerical and allows fast residence time estimation. Simulation results are successfully validated against experimental data from literature. The suggested numerical analysis is a valuable tool toward a deeper understanding of the fundamental transport phenomena in such reactors and, consequently, for the improvement of the packed bed performance.

Nomenclature

A

Specific surface area, m2/m3

c=CC0

Dimensionless tracer concentration, –

C

Local tracer concentration, mol/m3

Cave

Cross-section-averaged tracer concentration, mol/m3

C0

Total injected tracer concentration, mol/m3

Dax

Axial dispersion coefficient, m2/s

Dm

Molecular dispersion coefficient, m2/s

D

Diffusion coefficient, m2/s

E

Residence time distribution, 1/s

dp

Particle diameter, m

L

Packed bed length, m

Pe=U0dpDax

Peclet number, –

Pem=U0dpDm1ε

Molecular Peclet number, –

Re=dpρU0μ

Reynolds number, –

t

Time, s

u

Local velocity, m/s

U0

Superficial velocity, m/s

z=ZL

Dimensionless vertical coordinate, –

Z

Vertical coordinate, m

Greek letters
ε

Porosity of the packed bed, –

θ=tτˉ

Dimensionless time, –

λ

Tube-to-particle diameter ratio, –

µ

Dynamic viscosity, kg/m s

ρ

Density, kg/m3

σt

Second central moment of the RTD, s2

σ

Dimensionless second central moment of the RTD, –

τ

Local residence time, s

τˉ

Mean residence time, s

References

1. EigenbergerG, RuppelW. Catalytic fixed-bed reactors. New York: Wiley, 2000.10.1002/14356007.b04_199Search in Google Scholar

2. CalisHPA, NijenhuisJ, PaikertBC, DautzenbergFM, Van den BleekCM. CFD modelling and experimental validation of pressure drop and flow profile in a novel structured catalytic reactor packing. Chem Eng Sci2001;56:1713.10.1016/S0009-2509(00)00400-0Search in Google Scholar

3. AtmakidisT, KenigEY. CFD-based analysis of the wall effect on the pressure drop in packed beds with moderate tube/particle diameter ratios in the laminar flow regime. Chem Eng J2009;155:404.10.1016/j.cej.2009.07.057Search in Google Scholar

4. AtmakidisT, KenigEY. Numerical analysis of mass transfer in packed-bed reactors with irregular particle arrangements. Chem Eng Sci2012;81:77.10.1016/j.ces.2012.06.048Search in Google Scholar

5. BennekerAH, KronbergAE, PostJW, Van Der HamAGJ, WesterterpKR. Axial dispersion in gases flowing through a packed bed at elevated pressures. Chem Eng Sci1996;51:2099.10.1016/0009-2509(96)00067-XSearch in Google Scholar

6. FromentGF, BischoffKB. Chemical reactor analysis and design. New York: Wiley, 1979.Search in Google Scholar

7. GunnDJ. Axial and radial dispersion in fixed beds. Chem Eng Sci1987;42:363.10.1016/0009-2509(87)85066-2Search in Google Scholar

8. TsotsasE, SchlunderEU. On axial dispersion in packed beds with fluid flow. Chem Eng Process1988;33:107.Search in Google Scholar

9. TangD, JessA, RenX, BluemichD, StapfS. Axial dispersion and wall effects in narrow fixed bed reactors: a comparative study based on RTD and NMR measurements. Chem Eng Technol2004;27:866.10.1002/ceat.200402076Search in Google Scholar

10. InglezakisV, PoulopoulosS. Adsorption, ion exchange and catalysis: design of operations and environmental applications. Amsterdam: Elsevier Science, 2006.Search in Google Scholar

11. ChungSF, WenCY. Longitudinal dispersion of liquid flowing through fixed and fluidized beds. AIChE J1968;14:857.10.1002/aic.690140608Search in Google Scholar

12. DixonAG, NijemeislandM, StittEH. Packed tubular reactor modeling and catalyst design using computational fluid dynamics. Adv Chem Eng2006;31:307.10.1016/S0065-2377(06)31005-8Search in Google Scholar

13. ManzB, GladdenLF, WarrenPB. Flow and dispersion in porous media: lattice-Boltzmann and NMR studies. AIChE J1999;45:1845.10.1002/aic.690450902Search in Google Scholar

14. ZeiserT, LammersP, KlemmE, LiYW, BernsdorfJ, BrennerG. CFD-calculation of flow, dispersion and reaction in a catalyst filled tube by the lattice Boltzmann method. Chem Eng Sci2001;56:1697.10.1016/S0009-2509(00)00398-5Search in Google Scholar

15. FreundH, BauerJ, ZeiserT, EmigG. Detailed simulation of transport processes in fixed-beds. Ind Eng Chem Res2005;44:6423.10.1021/ie0489453Search in Google Scholar

16. MaierR, KrollD, BernardR, HowingtonS, PetersJ, DavisH. Hydrodynamic dispersion in confined packed beds. Phys Fluids2003;15:3795.10.1063/1.1624836Search in Google Scholar

17. AtmakidisT, KenigEY. A numerical study on the residence time distribution in low and moderate tube/particle diameter ratio fixed bed reactors. Chem Eng Trans2009;18:581.Search in Google Scholar

18. KainourgiakisME, KikkinidesES, StubosAK. Diffusion and flow in porous domains constructed using process-based and stochastic techniques. J Porous Mater2002;9:141.Search in Google Scholar

19. TsotsasE, SchluenderE-U. Measurements of mass transfer between particles and gas in packed tubes at very low tube to particle diameter ratios. Heat Mass Transfer1990;2:245.10.1007/BF01785411Search in Google Scholar

20. WinterbergM, TsotsasE. Impact of tube-to-particle-diameter ratio on pressure drop in packed beds. AIChE J2000;46:1084.10.1002/aic.690460519Search in Google Scholar

21. LevenspielO. Chemical reactor engineering, 3rd ed. New York: Wiley, 1999.Search in Google Scholar

22. GhirelliF, LecknerB. Transport equation for the local residence time of a fluid. Chem Eng Sci2004;59:513.10.1016/j.ces.2003.10.013Search in Google Scholar

23. EppingerT, SeidlerK, KraumeM. DEM-CFD simulations of fixed bed reactors with small tube to particle diameter ratios. Chem Eng J2011;166:324.10.1016/j.cej.2010.10.053Search in Google Scholar

24. NijemeislandM, DixonAG. Comparison of CFD simulations to experiment for convective heat transfer in a gas-solid fixed bed. Chem Eng J2001;82:231.10.1016/S1385-8947(00)00360-0Search in Google Scholar

25. van GelderK, WesterterpK. Residence time distribution and hold-up in a cocurrent upflow packed bed reactor at elevated pressure. Chem Eng Technol1990;13:27.10.1002/ceat.270130106Search in Google Scholar

Published Online: 2014-12-4
Published in Print: 2015-3-1

©2015 by De Gruyter