Dominating dynamics of the post-combustion CO2 absorption process

Abstract

A dynamic model of the post-combustion CO2 capture process based on chemical absorption is used to investigate the transient behavior and dynamic responses of the process and to detect stabilization time when various disturbances are introduced. Plant dimensions and parameter settings are based on the SINTEF CO2 capture pilot plant at Tiller in Norway, and the overall process model is validated using two sets of steady state pilot plant data. A deviation between model and pilot plant results of −0.8% and −4.5% in absorbed CO2 and 2.6% and 1.2% in desorbed CO2 is seen for the two cases used in validation, respectively, which is within the observed pilot plant CO2 mass balance error of ±6%. The simulated absorber and desorber temperature profiles show also adequate agreement to the pilot plant measurements. The process model is further used to simulate set-point changes in flue gas flow rate, reboiler duty and solvent flow rate in order to investigate typical stabilization times at various locations in the process. As expected, mixing models such as the absorber sump and reboiler will introduce time constants that affect the dynamic response profiles, while plug flow models such as the cross heat exchanger and lean cooler causes pure transport delays and no additional settling time. Mass transfer and chemical reaction rates causes some process inertia, but it is relatively small compared to the inertia of larger mixing vessels such as the absorber sump, reboiler and buffer tank and transport delay caused by plug flow. Changes to the solvent flow rate are also seen as a larger disturbance to the process compared to changes in flue gas flow rate and reboiler duty, reflected by longer process stabilization time to reach new steady state conditions. The estimated 90% settling times for the response in CO2 capture rate in the Tiller pilot plant are less than 1h, 3.5–6h and 3.5–4h for step changes in flue gas flow rate, solvent flow rate and reboiler duty, respectively.