Adsorber dynamics and optimal design of layered beds for multicomponent gas adsorption

Abstract

In order to minimize the bed size and to maximize the utilization of sorbents, layered beds containing different sorbents are being increasingly used for multicomponent separation by cyclic adsorption processes. Adsorber dynamics for multicomponent adsorption in layered beds is studied experimentally and also by numerical simulation. Adsorption in beds layered with activated carbon followed by 5A zeolite for hydrogen separation from a typical cracked gas mixture (H 2/CO 2/CH 4/CO) is used as the case study. While a single rollup in each breakthrough curve is common for the pure sorbent beds, double and multiple rollups are common with layered beds. Both equilibrium and kinetic rollups are observed and their origins discussed. Under the conditions of this study, combined thermal and concentration waves prevail for all components. The wave propagation velocity undergoes a step change upon crossing the interface between two sorbents, and such a change can be either increasing or decreasing. For this reason, transverse waves are seen in layered beds, All experimental features have been predicted by the model. It is demonstrated how the model can be used to provide optimal design of layered beds, based on the criterion that simultaneous breakthrough takes place in the layers, i.e. for the strong component (CO 2) in the weaker sorbent (carbon) and the weaker component (CO or CH 4) in the strong sorbent (zeolite). The optimal layering for a given gas–solid system depends on the feed composition and feed velocity.