Modeling of a cyclic sorption–desorption unit for continuous high temperature CO2 capture from flue gas

Abstract

This study focuses on the modeling of a sorptive unit for CO2 capture at high temperatures, considering as case-study the data obtained from experiments using a conventional post-combustion stream from coal power plants: 15% CO2/85% N2 at 623 K and 134 kPa. A one-dimensional (1D) heterogeneous dynamic fixed-bed model able to predict the CO2 equilibrium and kinetics of adsorption on a K-promoted hydrotalcite was successfully developed and implemented in gPROMS® software. The bi-Langmuir model was chosen to describe the experimental equilibrium data, as it considers the two different adsorption sites on the K-promoted hydrotalcite. A loss of capacity was observed after the first cycle performed in dry conditions. An Elovich-type expression, accounting for the change in activation energy of adsorption and desorption for each site as a function of the surface coverage, was also introduced in the model. The two sites model was used and an excellent fit to the breakthrough curves of CO2 adsorption/desorption and temperature histories was obtained. In order to make the model more robust, it was additionally validated at 573 K, for a total pressure range between 134 and 200 kPa, in wet conditions. The model validation represents an important advance, since it will allow processes optimization, and consequently the industrial design.