Energy savings in CO2 (carbon dioxide) capture using ejectors for waste heat upgrading

The biggest technical barrier to full scale deployment of absorption technology for post-combustion carbon capture in electric power plants is the high energy consumption for solvent regeneration. This paper presents a new application of ejectors to upgrade external waste heat for the purpose of reducing the amount of valuable turbine steam that is required to supply the solvent regeneration process. A shortcut method is proposed to model and optimize a coal fired post-combustion CO2 capture process enhanced with ejector driven waste heat upgrading. Although the method can be used for any solvent, MEA (monoethanolamine) is the reference solvent for this study. The study evaluates the influence of the position of the point of steam injection into the stripper tower, the CO2 loading of the solvent entering the reboiler from the stripper, the stripper pressure, and the source of the secondary ejector steam. By using the proposed method it is found that the optimal ejector integration allows a 10–25% reduction in the amount of valuable steam. The best results occur when the injected steam is sent to the bottom of the stripper tower, partially replacing the valuable steam from the power plant with waste heat derived steam.