Model development of amine scrubbing and CO₂ liquefaction process using waste LNG cold energy

Amine scrubbing and CO₂ liquefaction processes are generally employed in most power plants for CO₂ capture and storage (CCS) because they are suitable for large-scale plants. However, a significant amount of cold energy is required to cool the lean amine solution in the amine scrubbing system and liquefy compressed CO₂. Hence, liquefied natural gas (LNG) cold energy, which is generally wasted in seawater during LNG regasification, should be recovered. In this study, we developed an amine scrubbing and CO₂ liquefaction process using waste LNG cold energy. The proposed process model comprises the following three steps: (1) LNG regasification, (2) CO₂ capture and regeneration, and (3) CO₂ liquefaction. First, in LNG regasification, the boil-off gas (BOG) is compressed, and the LNG with compressed BOG is regasified in an LNG vaporizer. To regasify the LNG, seawater is used as a heat source, and the waste cold energy in the chilled seawater is recovered in steps 2 and 3. Second, the CO₂ capture and regeneration process involves the use of an absorber and a regenerator, and the waste cold energy is recovered at the lean amine cooler to reduce the temperature of the lean amine solution. Finally, to liquefy CO₂, cold energy derived from LNG regasification is recovered to a heat exchanger to cool the compressed CO₂. Consequently, the total cold energy consumption can be decreased by 31% by recovering waste LNG cold energy. This increases the overall energy efficiency of the amine scrubbing and CO₂ liquefaction processes for CCS using waste LNG cold energy, thus resulting in less fuel use. We believe that the proposed approach will afford significant economic improvements and environmental protection effects.