Designing Amine-Based Capture Units Onboard LNG-Run Ships

Abstract

Efficient CO₂ capture onboard ships is a vital step in mitigating maritime emissions. In our previous work, we showed that amine-based absorption is the best prospect for onboard capture, and ships powered by LNG are better suited than those using HFO. Hence, in this work, an extensive design for amine-based absorption onboard LNG-run ships with different flue gas conditions (flow rate, temperature, and composition) as well as maximum CO₂ storage capacity and number of days at sea is presented. The design comprises discussions on the selection of key variables for separation, e.g., the dimensions of the absorber and regenerator column and solvent flow rate, as well as the selection of optimal CO₂ storage conditions. Additionally, the best configuration for cold energy integration to minimize the extra power demand for the CO₂ compression is also assessed. The design is based on 90% recovery of CO₂ from the total flue gas to be processed, including emissions stemming from extra fuel burned to fulfill the energy deficit for solvent regeneration and the power demand for CO₂ compression. To this end, a novel noniterative approach to calculate total flue gas to be processed as a function of the flue gas conditions under optimized design conditions is also developed. Lastly, cargo losses from the installation of the capture unit are also presented. In summary, the study intends to provide ship owners with a comprehensive design guide for the installation of an amine-based absorption unit. To illustrate the utility of the study, case studies are presented using reference ships available in the literature.