Characterization of mass transfer in a shallow fluidized bed for adsorption processes: Modeling and supporting experiments

This study characterizes mass transfer processes in a multi-stage fluidized bed (MSFB) using shallow fluidized beds. Multi-stage fluidized beds are of interest for sour gas removal using adsorption, examples are H₂S/CO₂ removal from natural gas and CO₂ capture by amine sorbents. A phenomenological model based on the classical two-phase fluidization model is used to study the mass transfer process. Independent measurements and literature data are used to describe mixing, hold-ups, intraparticle mass transfer and adsorption kinetics. The bubble hold-up was experimentally measured. Mixing was investigated with a temperature response measurement. The mixing in the emulsion gas phase varies between plug flow and ideal mixing with increasing superficial gas velocity, while the solid phase is always ideally mixed. The presented fluidized bed model is able to describe the effects of superficial gas velocity, solid flux, bed height and inlet concentration. Mass transfer was further studied using a sensitivity analysis, which showed that the used shallow fluidized bed is already fairly optimized with respect to mass transfer. Shallow fluidized beds benefit from fast gas interchange because bubbles do not have the chance to grow. Optimal mass transfer and gas interchange conditions can be achieved in shallow fluidized beds for application in MSFBs.