Effects of bed pressure drop on isothermal and adiabatic adsorber dynamics

A theoretical and experimental study on the effects of pressure drop on the dynamics of an isothermal fixed bed during adsorption is presented. The system of adsorbate-adsorbent used is oxygen in 13X-PSO₂ zeolite. Simple analytic solutions as well as detailed numerical solutions are compred with the experimental breakthrough curves. The theoretical study is further extended to the case of an industrial-size adiabatic fixed-bed adsorber. The complete numerical simulation involves the solution of heat, mass and momentum balances, using the Galerkin finite element method. An approximate analysis is also attempted using the theory of simple and shock waves. The first conclusion is that the presence of pressure drop leads to an early breakthrough for both concentration and thermal waves, as compared to the case with no pressure drop. Moreover, the constant pattern behavior of concentration and temperature that exists in the absence of pressure drop is distorted when sufficiently high pressure drop is present along the bed, because the concentration-temperature-pressure path in the hodograph space is no longer unique, but varies with time. Another significant conclusion is that the presence of pressure drop can either deflate or inflate the plateau zones of both concentration and temperature waves, depending on the values of certain bed parameters, and in all cases will facilitate the formation of a "pure" thermal wave.