CO2 Separation from Power Plant Exhaust Gases using Reactive Absorption

Reactive absorption is a leading option for post-combustion CO₂ capture at power plants, but the standard 30 wt% monoethanolamine (MEA) solvent requires high regeneration energy and reduces plant efficiency. Within the EU CASTOR project, this work builds and operates a mini plant covering the full absorption–desorption cycle to quantify how operating variables affect energy demand and to provide a basis for comparing new solvents against MEA. Mini-plant experiments with MEA clarify how a specified CO₂ removal rate in the absorber translates into desorber energy via lean/rich loadings and absorber mass-transfer driving-force constraints. An energy-balance breakdown shows regeneration duty consists of contributions from CO₂ release (heat of absorption), stripping steam generation, sensible heating of the solvent, and condensate reflux—each linked to CO₂ solubility equilibria and absorption enthalpy. Parameter studies identify solvent flow rate, desorber pressure, and solvent composition as key levers, with solvent flow rate being particularly critical for optimization. A detailed rate-based CHEMASIM model (with film discretization) is validated against the experimental operating points, highlighting the need for accurate phase-equilibrium models, suitable discretization grids, and well-chosen mass-transfer parameters—especially interfacial area, which strongly impacts desorber energy. The validated model is then used to design a capture plant for a 1000 MW lignite-fired unit, confirming very large equipment sizes and substantial efficiency penalties, reinforcing the importance of improved solvents. For solvent pre-screening, a simplified evaluation method is developed using a modified Kremser approach with piecewise-linear equilibrium isotherms to estimate cycle-level energy-reduction potential from limited input data; application to MEA and the amine-based CASTOR1/CASTOR2 solvents indicates potential energy savings for the new solvents. Screening procedures for solvent degradation are also established: MEA shows thermal decomposition only above ~180 °C, while semi-batch oxidative/CO₂-related degradation tests at elevated pressure/temperature reveal that CO₂ can have a stabilizing effect, motivating standardized feeds containing N₂, O₂, and CO₂ for comparisons. Finally, a mini-plant solvent-comparison protocol is presented that holds flue-gas conditions and CO₂ removal rate constant while varying solvent flow and adjusting reboiler duty, emphasizing that operating-line positions relative to equilibrium curves must be considered, especially for slower-kinetics solvents in short absorbers. Using this framework, CASTOR1 and particularly CASTOR2 emerge as promising candidates for reducing regeneration energy.