CFD-based model of adsorption columns: Validation

Abstract

The computational research on adsorption is of significant interest for process development and optimization. Despite the existence of unidimensional models that reproduce simple vertical columns, a further level of detail is required to understand the intricacy of transport phenomena within industrial-grade columns across time and space. With that in mind, this research work focuses on developing and validating a higher-dimensional model to reproduce the flow, heat, and mass transfer phenomena inside adsorption columns using Computational Fluid Dynamics (CFD). The mathematics of adsorption are coded into the commercial CFD solver, ANSYS Fluent v19.2, using User-Defined Functions (UDF). The model is implemented using a mathematical adaptation of Fluent's standard transport equations, so that the material and thermal effects of adsorption can be accounted for. The resulting model is validated against published experimental results for the single-component and competitive adsorption of N2 and CO2 on zeolite 13X on a small-scale pilot unit. Good agreement between our modelling results and experimental data is demonstrated. Afterwards, a modified column geometry with an inlet jet is used to explore the impact of gas injection on the unsteady spatial distribution of matter and energy. Radial gradients and 2D contour plots are illustrated in all cases to showcase the enhanced insight that a higher-dimensional model provides. Finally, this model can be used to predict comprehensive characteristics of adsorption columns of any design and size, taking into account different designs of inflow gas distributors in industrial scale columns. It includes a new sort of adsorption devices using monolith instead of packed beds. All model UDFs are open-source and can be found in supplementary materials.