Cfd Simulations of Flow and Heat Transfer in Steam Reforming in a Fixed Bed of Cylinders

M. Ertan Taskin1, Anthony G. Dixon1, and Hugh Stitt2. (1) Chemical Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, (2) Johnson Matthey, PO Box 1, Billingham, Cleveland, TS23 1LB, United Kingdom

Fixed bed catalytic reactors are characterized as workhorses of process industries, and used in many different chemical processes. Multitubular reactors with low tube-to-particle diameter ratios (N) are especially used for reactions with strong heat effects, such as steam reforming. The design and optimization of the catalyst particle for activity, pressure drop and heat transfer are particularly important for steam reforming and require an understanding of how the flow patterns and temperature field near the tube wall are affected by changes in particle geometry. This information can be provided by CFD simulations in fixed bed packings. Our previous uses of CFD in fixed bed simulations have been for packings of full beds of spheres, bed segments of spheres and bed segments of cylinders. We have verified that 120-degree segments of tubes packed with spheres can represent very well the flow profiles of full tubes packed with spheres. In the present work, we present the corresponding verification for packings of cylinders in terms of flow and heat transfer characteristics of the segment (WS) and full tube (CW) models at industrial steam reforming conditions. Heat sinks in the particles were used to mimic the heat effects of the endothermic steam reforming. Contours of wall temperatures, velocity and static temperatures at different radial positions were investigated for both models. The radial flow and temperature profiles were also compared considering the strong effects of radial voidage and activity profiles. It was observed that, even though the WS model predicts pressure drop as 30% more than the CW model, the average flow and heat transfer features are quite similar to each other. The symmetry side walls of WS model can be considered as the cause of this pressure drop difference, and the small deviations of flow and temperature characteristics near to the side walls. However, our investigations showed that, a good comparison is obtained for the particles which are positioned in the center near wall region of both models. Therefore it can be concluded that, the WS model with cylindrical particles can be used for detailed analysis if the center near wall region particles are directly focused on.