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

This study focuses on the modeling of a sorptive unit for CO2 capture at high temperatures, considering as casestudy the data obtained from experiments using a conventional post-combustion stream from coal power plants: 15% CO2/85% N-2 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 (R) 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.

Automated summary

This study developed and implemented a one-dimensional heterogeneous dynamic fixed-bed model for CO2 capture at high temperatures. The model successfully predicted the equilibrium and kinetics of CO2 adsorption on a K-promoted hydrotalcite. The model considered two different adsorption sites and incorporated a change in activation energy to explain the observed capacity loss. The model was validated under wet conditions, making it more robust for process optimization and industrial design.