Synthetic Packed Bed Generation and Contact Modifications for CFD Simulations of Industrial-Scale, Fixed-Bed Reactors

Computational fluid dynamic (CFD) simulations, in which the packed catalyst beds are fully geometrically resolved, become the most established detailed modelling approach for fixed-bed reactors (Jurtz et al., 2017). However, this method has only been used for short bed lengths with a small number of catalyst pellets so far. The present work transfers the CFD approach to the scale of industrial fixed-bed reactors for highly exothermic reactions. To this end, long packed catalyst beds (between 3 and 6 m) with small tube-to-particle diameter ratios (3 < D/d_P < 5) and non-spherical catalyst particles have to be simulated.

Due to the investigated large scales, the packed beds for the CFD simulations are generated synthetically with the Rigid Body Approach (RBA), using the open source software Blender. Based on Dixon and Partopour (2017), a computing-efficient and numerical stable algorithm for RBA was developed to generate physically realistic, as proven experimentally, and industrially relevant packed beds of various particle shapes shown in Figure 1.

Apart from the packed bed generation one of the challenges in particle-resolved CFD simulations are the contacts between particles. Due to close or touching surfaces, the calculation cells of the finite volume mesh show bad quality around the contact. Therefore, the geometry of the packed bed close to the contact zones has to be modified slightly (Wehinger et al., 2017). The presented work tests various modification methods for the different types of contacts (point, line and area). Especially for long beds with more than 5000 particles it is important to detect and locally modify the contacts automatically as shown in Figure 2 for the detection of the area contact between two hollow cylinders.