Modeling CO2 Capture in Amine Solvents: Prediction of Performance and Insights on Limiting Phenomena
A model of absorption and stripping columns is developed for post-combustion CO2 capture in amine solvents. The model is based on a rigorous thermodynamic framework, the extended UNIQUAC model, for the representation of vapor?liquid equilibria (VLE) in order to characterize different solvents in a wide range of concentration and temperature. A rate-based formulation of chemically enhanced heat and mass transfer is used for the packed column model. Two modeling approaches are used for mass transfer in film: an enhancement factor model and a diffusion-reaction model. The rigorous absorption and stripping models have been successfully validated against experimental results from an industrial and a laboratory pilot plant. A sensitivity analysis is performed in order to emphasize the role of limiting phenomena on the separation performance, which concludes that none of the phenomena can be neglected. The interfacial area is the most sensitive parameter on absorber performance, whereas the heat of desorption is the prevailing parameter in the stripper. The CO2 equilibrium constant is a sensitive parameter in both absorption and stripping units. The two film models are compared and give similar results for the monoethanolamine solvent. However, the comparison must be redone for each implemented solvent since physicochemical properties are modified, e.g., reaction kinetics, diffusion coefficients, and VLE constants. New insights are given on the contribution of CO2 and H2O on heat fluxes between phases for the absorber and the stripper. Especially, water condensation and evaporation along the packing impact directly the CO2 removal efficiency and reboiler heat duty.