Integrated Process Simulation and Economic Evaluation of Onboard CO₂ Capture Using Optimized Amine Blends

This study presents the optimization of various amine-based solvent systems and their blends for onboard carbon capture (OCC) using three single aminesMEA, DEA, and MDEAand four blended solvents. To evaluate the energy efficiency, key performance indicators such as solvent circulation rate, CO₂ loading capacity, and reboiler duty were analyzed. The CO₂ capture rate was set at 2 tons/h with a target efficiency of 85%, reflecting the concentration in typical vessel diesel engine exhausts. A waste heat boiler (WHB) was integrated to recover thermal energy during flue gas cooling and supply steam for use in the process. Optimization was performed on variables including engine load, exhaust gas bypass ratio, WHB steam vapor fraction, absorber feed temperature, solvent flow rate, and absorber/regenerator pressures to minimize reboiler duty while maintaining the target efficiency. Given the space limitations of onboard installation, equipment sizing for the absorber, regenerator, and heat exchanger was also conducted. Economic evaluation incorporated solvent cost, energy demand, and incentives from the reduction of CO₂. Simulation results confirmed that WHB integration reduced reboiler duty by approximately 65.8%. Among the tested solvents, the aqueous blend of 20 wt % MDEA and 10 wt % PZ exhibited the lowest energy consumption, with a liquid-to-gas ratio of 1.57 and a CO₂ loading of 0.55 in the rich amine stream. Required equipment dimensions were calculated, and under a carbon tax scenario, OCC-equipped ships demonstrated economic competitiveness compared to conventional ships.