Integrated energy system design for decarbonization of liquefied natural gas-powered ships: Coupling oxy-fuel combustion with cryogenic CO₂ capture for enhanced heat recovery and cold energy integration

The decarbonization of maritime transport requires integrated energy system solutions capable of efficiently managing both heat and cold energy while reducing carbon emissions. This study proposes an integrated energy system design for liquefied natural gas (LNG)-powered ships by coupling oxy-fuel combustion with a novel turbo-expander-based cryogenic CO2 capture process. The concept targets newbuild ship configurations to enable high CO2 partial pressure, facilitating energy-efficient phase-change separation while avoiding freeze-out limitations associated with dilute exhaust streams. A process model was developed in Aspen HYSYS and combined with pinch-based heat integration and heat exchanger network synthesis to maximize heat recovery and cold energy integration. The system exploits LNG regasification cold energy, internal CO2 refrigeration, and cold energy from a simplified air separation unit, alongside turbo-expander work recovery to minimize external utility demand. System-level optimization was conducted to evaluate the trade-off between oxygen purity and overall energy consumption. Results indicate that an optimal oxygen purity of similar to 80 mol.% reduces total energy demand by up to 35% compared to high-purity operation. The integrated system achieves 92% CO2 capture efficiency with a low energy penalty of 0.07 GJ/tCO(2) and a capture power requirement of 0.53 MW. Techno-economic analysis yields a levelized cost of capture of 4.37 USD/tCO(2). These findings demonstrate that integrated heat recovery and cold energy utilization can significantly reduce the energy penalty of onboard carbon capture, supporting maritime decarbonization.