Optimal conception of a post-combustion CO2 capture unit with assessment of solvent degradation

Solvent degradation may be a major drawback for the large-scale implementation of post-combustion CO2 capture due to amine consumption and emission of degradation products. A kinetics model describing solvent oxidative and thermal degradation has been developed based on experimental results. This model has been included into a global Aspen Plus model of the CO2 capture process, so that optimal operating conditions can be identified to minimize both energy and environmental impacts of the process. Global process modeling The global model of the CO2 capture with assessment of solvent degradation may be used for the design of CO2 capture plants to consider not only the process energy penalty, but also its environmental penalty which is particularly relevant for large-scale applications. The optimized process configuration results into a MEA consumption of 78 g MEA/ton CO2. This is lower than values reported in pilot plants, probably due to the modeling assumptions made in first approach. The model highlights that the MEA consumption is mainly related to oxidative degradation in the absorber, with ammonia as the major degradation product. The corresponding energy requirement of the CO2 capture process is evaluated to 3.1 GJ/ton CO2. Finally, this model proposes an original approach for assessing solvent degradation within the modeling and design process of CO2 capture plants. Acknowledgements The authors are grateful to the belgian FRIA-FNRS and to the company Laborelec for financial support and industrial partnership. Kinetics of the solvent degradation The kinetics of MEA degradation has been determined by studying the influence of different operating parameters: • Agitation rate • Temperature • Composition of the flue gas feed (N2, O2, CO2) Two different degradation equations have been included in an Aspen Plus model of the CO2 capture process: F.R.I.A.–F.N.R.S A degradation test rig has been designed and built at the University of Liege. Fresh Degraded [1]: Abu Zahra M., 2009. Carbon dioxide capture from flue gas. PhD Thesis, TU Delft, The Netherlands. The degradation of MEA is artificially accelerated in an experimental test rig. The nitrogen mass balance can be closed within the 10% range and repeatability is demonstrated with a deviation lower than 5%. Identified degradation pathways at lab-scale are similar to pathways observed in PCCC pilot plants. MEA oxidative degradation is the main pathway in pilot plants as well as in the degradation test rig. Lean vapor compression and absorber intercooling reduce the MEA loss by 5% and the energy requirement of the process by 12%