Modeling fixed-bed reactors from metal-foam pellets with detailed CFD

Abstract

Open-cell metal foams are a promising alternative to conventional solid pellets for the application as structured catalyst support. Pellets made from metal foams can be used in fixed-bed reactors instead of ceramic pellets. In this contribution, a comprehensive and detailed computational fluid dynamics (CFD) model is presented for fixed-bed reactors consisting of metal foams. The inner structure of the foams, i.e. pores, struts, and nodes, is not resolved. Instead, a pseudo-homogeneous model is applied to describe pressure drop and heat transfer inside the foam pellets. The fixed-bed structure is particle-resolved. The bed is generated synthetically with the discrete element method (DEM) and the results are in great agreement with µCT data. The experimental pressure drop for two different porous pellet shapes can be reproduced reasonably with CFD simulations. In an illustrative heat-transfer study, the performance of a state-of-technology solid-pellet bed and a porous cube bed is compared. Whereas the heat transfer is similar in both cases, the pressure drop is lower in the bed of porous cubes. A residence-time distribution analysis reveals that the porous pellet shape should be optimized to obtain a better mixing behavior. The presented fixed-bed model can be applied for such tasks, since it is valid for almost any pellet shape.