Dynamic modeling and control of an intercooled absorber for post-combustion CO2 capture

A medium-order dynamic model was developed in gPROMS® for an intercooled CO2 absorber column with piperazine solvent. This model represents an improvement from previously published rate-based dynamic models because it uses a regressed eNRTL thermodynamic package and a liquid film mass transfer coefficient with an experimentally measured CO2 loading dependence. Off-design simulation results were validated against a high-order steady state model, and the maximum predicted column temperature differed by less than 1.2 °C for 100–85% flue gas load. Operating the absorber at a constant liquid to gas (L/G) ratio results in favorable dynamic behavior with disturbances in flue gas load, but a commercial system will not have a reliable flue gas flow measurement. The medium-order model was used to identify a liquid phase temperature within the top bed of absorber packing as a control variable that is sensitive to changes in L/G ratio. As the flue gas load was ramped from 100% to 80%, a maximum L/G ratio deviation of 0.9% was observed when controlling the column temperature with the solvent flowrate. Feedforward control may be necessary to account for other process disturbances that influence the temperature profile and was shown to be effective at counteracting a step change in intercooling temperature.