(395f) CFD Studies of Shaped Steam Reforming Catalyst Particles

Interactions between reaction rates, conduction and diffusion inside catalyst particles can be complex, especially when influenced by non-uniform surface conditions produced by the flow field external to the particle, or by the highly-directional temperature field near a heated tube wall. These non-uniform fields can produce strongly locally-varying rates of reaction, heat transfer and carbon deposition, resulting in local deactivation of the catalyst, over-heating and tube failure. In this work a three-dimensional, realistic flow field is coupled to species and energy simulations in catalyst particles for the highly endothermic methane steam reforming reaction. The simulation domain was a 120-degree segment of a packed tube of tube-to-particle diameter ratio (N) = 4, packed with cylinders. The simulations employed computational fluid dynamics (CFD) and user-defined-codes, to examine packings of shaped particles, including multi-holed cylinders and cylinders with external features. The catalyst geometries modeled were full cylinder, 1-hole, 3-hole, 4-hole, 4-hole with vertical grooves, and 6-hole cylinders. The simulations were carried out under industrial conditions typical of reactor tube inlet and also of mid-reactor tube, at constant pressure drop for each case. The detailed pellet surface and intra-particle temperature, species and reaction rate distributions were obtained for the near-wall particle, along the particle radius and axis. It was concluded that the 4-hole with grooves and 6-hole catalyst particles offered the best temperature distribution and reaction rate. However, the 4-hole with grooves had a significantly larger void fraction, allowing a higher mass flow rate for a set pressure drop.