Numerical simulations of single phase reacting flows in randomly packed fixed-bed reactors and experimental validation

Abstract Randomly packed fixed-bed reactors are widely used in the chemical process industries. Their design is usually based on pseudo-homogeneous model equations with averaged semi-empirical parameters. However, this design concept fails for low tube-to-particle diameter ratios (=aspect ratios) where local phenomena dominate. The complete three-dimensional (3D) structure of the packing has therefore to be considered in order to resolve the local inhomogeneities. New numerical methods and the increase of computational power allow us to simulate in detail single phase reacting flows in such reactors, exclusively based on material properties and the 3D description of the geometry, thus without the use of semi-empirical data. The successive simulation steps (packing generation, fluid flow and species calculation) and their validation with experimental data are described in this paper. In order to synthetically generate realistic random packings of spherical particles, we apply a Monte-Carlo method. The subsequent numerical simulation of the 3D flow field and coupled mass transport of reacting species is done by means of lattice Boltzmann methods. The simulation results reveal that not only the local behaviour but also integral quantities like the pressure drop depend remarkably on the local structural properties of the packings, a feature which is neglected when using correlations with averaged values.

[1]  D. Vortmeyer,et al.  Measured and modeled superficial flow profiles in packed beds with liquid flow , 1998 .

[2]  Franz Durst,et al.  The nature of flows through porous media , 1987 .

[3]  R. Jeschar.  Druckverlust in Mehrkornschüttungen aus Kugeln , 1964 .

[4]  Gilbert F. Froment,et al.  Simulation models accounting for radial voidage profiles in fixed-bed reactors , 1995 .

[5]  G. Eigenberger,et al.  Fluid flow through catalyst filled tubes , 1997 .

[6]  Thomas Zeiser,et al.  Analysis of the flow field and pressure drop in fixed-bed reactors with the help of lattice Boltzmann simulations , 2002, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[7]  R. F. Benenati,et al.  Void fraction distribution in beds of spheres , 1962 .

[8]  S. Ergun,et al.  Fluid Flow through Randomly Packed Columns and Fluidized Beds , 1949 .

[9]  Flekkoy.  Lattice Bhatnagar-Gross-Krook models for miscible fluids. , 1993, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[10]  Evangelos Tsotsas,et al.  Impact of tube-to-particle-diameter ratio on pressure drop in packed beds , 2000 .

[11]  Bernhard Eisfeld.  Pseudokontinuierliche Modellierung der Strömung in Schüttschichtreaktoren , 1999 .

[12]  Anthony G. Dixon,et al.  CFD as a Design Tool for Fixed-Bed Reactors , 2001 .

[13]  E. M. Tory,et al.  Computer simulation of isotropic, homogeneous, dense random packing of equal spheres , 1981 .

[14]  Wim J. J. Soppe,et al.  Computer simulation of random packings of hard spheres , 1990 .

[15]  H.P.A. Calis,et al.  CFD modelling and experimental validation of pressure drop and flow profile in a novel structured catalytic reactor packing , 2001 .

[16]  H. Hofmann,et al.  Implementation of radial porosity and velocity distribution in a reactor model for heterogeneous catalytic gasphase reactions (TORUS-Model) , 1990 .

[17]  Y. Qian,et al.  Lattice BGK Models for Navier-Stokes Equation , 1992 .

[18]  G. Eigenberger,et al.  A reevaluation of fluid flow, heat transfer and chemical reaction in catalyst filled tubes , 1992 .

[19]  G. T. Nolan,et al.  Computer simulation of random packing of hard spheres , 1992 .

[20]  Evangelos Tsotsas,et al.  A simple and coherent set of coefficients for modelling of heat and mass transport with and without chemical reaction in tubes filled with spheres , 2000 .

[21]  Shiyi Chen,et al.  LATTICE BOLTZMANN METHOD FOR FLUID FLOWS , 2001 .