Hydrodynamic modelling of complex fixed bed geometries in simulated moving bed adsorption processes

Abstract

Hydrodynamics inside industrial simulated moving bed (SMB) adsorption columns can be complex due to the presence of internal distribution devices. They have to be taken into account in SMB numerical models to scale-up processes. In the present work, CFD is used as an intermediate step to develop a 1D model simple enough to be used for cyclic SMB simulations while being able to represent realistic hydrodynamics. First, a mock-up representative of an industrial SMB is used to perform residence time distribution (RTD) experiments and to provide validation data. Experiments are well predicted by a CFD model including porous media and turbulent zones, allowing to consider CFD simulations as references to fit simpler models. The moments of internal age distribution are characterized following the calculation method developed by Liu and Tilton, 2010. AIChE J. 56(10), 2561–2572, which allows to estimate the degree of mixing (Liu, 2012. Chem. Eng. Sci. 69(1), 382–393) inside adsorption beds. A major result is that RTD and degree of mixing inside adsorption beds are well described by a 1D multi-exit model, unlike classical dispersed plug flow models (Ruthven and Ching, 1989) that were generally used to simulate SMB processes. Additionally, a numerical method was developed which is able to reproduce the RTD with steady state simulations.