Investigating the performance of different fluidized bed membrane reactor geometries

The hydrodynamics and mass transfer phenomena occurring in different fluidized bed membrane reactors have been studied with a Two Fluid Model (TFM). The present work focuses on the in-situ selective extraction of hydrogen from a fluidized bed membrane reactor, aiming to study and quantify the membrane performance, including possible concentration polarization. Using a hydrogen-nitrogen gas mixture as fluidizing gas, various fluidized bed geometries containing vertically or horizontally immersed membranes were simulated. The hydrodynamics and mass transfer phenomena of a fluidized bed can be strongly affected by the membrane configuration. Previous work by the group of Van Sint Annaland (1) showed the appearance of densified particle zones near the membranes, which could affect their performance. Furthermore, so called gas pockets (solids free non-rising bubbles, attached to the membrane) are formed underneath horizontal membrane tubes, see Medrano et al. (2). These phenomena are identified, their adverse effect on the membrane flux is quantified and possible remedies are discussed. Hydrogen fluxes of a membrane placed vertically in a fluidized bed were obtained from the TFM, experiments and a 1D model that does not take concentration polarization into account. These fluxes are compared in Figure 1. Concentration polarization is clearly very important in fluidized bed reactors with state-of-the-art high-flux membranes. The TFM predicts the fluxes quite accurately, whereas the model that does not account for concentration polarization severely overpredicts them. Please click Additional Files below to see the full abstract