Energy Performance of CO2 Capture Processes: Interaction Between Process Design and Solvent

Abstract

Implementation of amine-based post-combustion CO2 capture on power plants would lead to large penalties on the electric production. Researches focus either on the improvement of process flow scheme to maximize exergy integration or on characterization of new promising solvents to reduce this energy consumption. However, both aspects are often taken into account separately whereas they should be studied simultaneously since the energy efficiency of process modifications also depends on the considered solvent. In order to highlight this point, several schemes based on modifications proposed in literature are investigated for several classes of amine-based solvents and the total energy consumption is determined by a rigorous phenomenological model coupled with an optimization algorithm. Simulation results confirms that the efficiency of process modifications depends on the considered solvent since process improvements make use of the solvent specific properties, in particular the differences between thermodynamic and kinetic properties. General understandings are given on the relative efficiency of process modifications according to measurable solvent properties. Carbon dioxide capture and geological storage is foreseen to be one of the solutions to reduce the atmospheric emissions of fossil-fired power plants. Among the different technologies, post-combustion chemical absorption in amine-based solvents is the most mature at this stage of development. However, the energy consumption of such processes implies a large penalty on the power plant efficiency. The reference configuration used for chemical absorption of CO2 is a conventional absorption/desorption loop operating with monoethanolamine (MEA) where the CO2 is separated from the flue gas by chemical absorption in the solvent and the solvent is thermally regenerated in a stripper, sensible heat being exchanged in an economizer between the hot lean solvent and the cold rich solvent. The released CO2 is then compressed up to 110 bars at supercritical state for transportation and storage. For this base case, the energy requirement leads to a loss of around 11 %-pts in terms of power plant efficiency. In order to reduce this penalty, researches focus either on the improvement of process flow scheme to maximize heat integration or on characterization of new promising solvents. This work intends to emphasize the interaction between solvent properties and optimal process design and how both solvent characterization and process design should be carried out simultaneously, since the energy performance of a process modification is deeply dependent of the chosen solvent. In order to highlight this point, several schemes based on modifications proposed in literature are investigated for two classes of amine-based solvents. For each process flow scheme associated with each solvent, the operating parameters are optimized with respect to the total energy consumption with a dedicated algorithm using rigorous thermodynamic and rate-based models, which are mandatory for a proper representation of all limiting phenomena. By this means, the potential of each configuration is determined in terms of total energy penalty on the power plant.