Interstitial-Scale Modeling of Catalytic Foam Reactors: Partial Oxidation of Methane

Interstitial-scale modeling of catalytic foam reactors: partial oxidation of methane

Gregor Wehinger, Matthias Kraume

Chemical and Process Engineering, Technische Universität Berlin, Fraunhoferstr. 33-36, 10587 Berlin, Germany

Catalytic foams represent a promising alternative to conventional fixed-bed reactors in many applications in the chemical and process industry. They are characterized by their low specific pressure drop, high mechanical stability at relatively low specific weight, enhanced radial transport, as well as a high geometric surface area. Designing and planning of foam reactors can be supported by computational fluid dynamics (CFD) simulations. However, the actual shape of a catalytic foam is highly complex and therefore difficult to model.

In this work we present a fully automatic workflow (catalytic Foam Modeler: catFM) with which it is possible to model a realistic foam structure ready for CFD simulations without using data from time consuming image analysis. The modeler is based on a random distribution of points in space followed by the Voronoi tessellations. It applies common foam characteristics, i.e., porosity, specific surface area and strut dimensions, as input parameters to generate artificially the foam structure. Typical morphological parameters such as specific surface area, as well as pressure drop predictions can be reproduced with a high accuracy. Finally, the performance of the tool catFM is illustrated by modeling a catalytic partial oxidation reformer of methane in a foam coated with a rhodium catalyst from literature [1]. Two sets of simulations are performed, one with a fixed surface temperature profile obtained from experiment, the other takes heat transfer inside the solid material into account. On the surface a detailed reaction mechanism is implemented [2]. For both cases, the experimental species profiles can be well reproduced. However, only the second set allows a flexible utilization without knowing the temperature profile a priori. With this modeler it is possible to plan and design catalytic foams by predicting temperature and species concentrations without relying on transport correlations.

Fig 1: CFD setup for foam simulations with details of strut geometry and mesh resolution close to surface.

[1] Nogare, D. D.; Degenstein, N.; Horn, R.; Canu, P. & Schmidt, L. Modeling spatially resolved profiles of methane partial oxidation on a Rh foam catalyst with detailed chemistry, Journal of Catalysis , 2008, 258, 131 - 142

[2] Schwiedernoch, R.; Tischer, S.; Correa, C. & Deutschmann, O. Experimental and numerical study on the transient behavior of partial oxidation of methane in a catalytic monolith, Chemical Engineering Science, 2003, 58, 633 - 642