Modelling selective H2S absorption and desorption in an aqueous MDEA-solution using a rate-based non-equilibrium approach

A rate-based algorithm was used to yield a predictive tool for MDEA gas scrubbing processes. The model adopts the two-film theory, assuming that thermodynamic equilibrium exists only at the gas-liquid interphase, but not in the boundary layers, where temperature and concentration gradients are present. Correspondingly chemical equilibrium among the reacting species in the liquid phase is assumed for the bulk phase. but not for the liquid boundary layer. Mass transfer is modelled using calculated mass transfer coefficients in combination with an enhancement model to account for the chemical reactions. Correlations for geometric data, like hold-up and interfacial area, and for reaction rates are provided to give reliable results. The latter correlations are also used to describe the desorption process, which is calculated with an equilibrium approach. considering the kinetics of CO, desorption. The so obtained tool is tested against measurements done recently by Lurgi GmbH at a commercially operated selective MDEA plant in Germany. A closed absorption and desorption loop was build up using Aspen RATEFRAC(TM). capable of modelling the whole process with all necessary equipment. (C) 2003 Elsevier B.V. All rights reserved.