(433b) Improved CO2 Capture Process : Rich Vapor Recompression with Split Flow

CO₂ capture process using MEA scrubbing is the most mature technology for reducing the CO₂ emission into the atmosphere. However the MEA scrubbing process requires a lot of heat energy for solvent regeneration in the stripper reboiler. The reboiler heat requirement is a function of preheating duty and stripper reflux ratio. The reboiler heat requirement decreases with preheating duty increases in the lean/rich heat exchanger. When the stripper reflux ratio decreases, the reboiler heat duty is reduced also. In order to reduce the reboiler heat requirement, large number of advanced configurations have been suggested already. The split flow configuration, well known advanced configuration, reduces the stripper reflux ratio by lowering the stripper top temperature. As a part of cold rich solvent is fed to the stripper top without passing through the lean/rich heat exchanger, the cold rich solvent is directly cooling off the stripper top. Although this split flow configuration reduces the stripper reflux ratio, the heat exchanger preheating duty is decreased due to the cold side flow rate reduction. It is hard to reduce the stripper reflux ratio while maintaining the preheating duty. In order to solve this problem, this paper suggests an innovative configuration of MEA scrubbing process; rich vapor recompression with split flow. The rich vapor recompression is a new configuration which is vaporizing the cold rich solvent at the lean/rich heat exchanger. It is similar concept with lean vapor recompression which is vaporizing the hot lean solvent at the flash drum. However the energy reduction effect is different when split flow is combined. In the suggested configuration, rich vapor recompression with split flow process, a part of cold rich solvent is fed to the stripper top without passing through the lean/rich heat exchanger. The other part of cold rich solvent is vaporized at the lean/rich heat exchanger. The generated vapor is fed to the stripper bottom as steam energy source. The remaining liquid is fed to the stripper middle. Although the heat exchanger inlet feed flow rate is reduced, the cold side heat capacity increases through the solvent vaporization. Consequently, the stripper reflux ratio is decreased with maintaining the preheating duty in the lean/rich heat exchanger. As a result, the reboiler heat requirement was 2.91 GJ/tonCO₂, 3.07 GJ/tonCO₂, and 3.38 GJ/tonCO₂ in the rich vapor recompression with split flow, lean vapor recompression with split flow and conventional MEA process, respectively.