Simulation and Optimization of A Dual-loop Organic Rankine Cycle-Onboard Carbon Capture System for LNG-powered Ships

Abstract

A dual-loop organic Rankine cycle-onboard carbon capture system (DORC-OCCS) for liquid natural gas (LNG) -powered ships is proposed to satisfy both objectives of carbon emission reduction and efficient energy utilization for ships. In this system, the wasted heat from the ship powers the reboiler and drives the high-temperature ORC to generate electricity. Simultaneously, LNG cold energy is utilized to liquefy the captured CO₂ while also driving the low-temperature ORC. The effects of liquid-to-gas ratios (L/G), exhaust gas flow rates (m_EG), and absorber packing heights (H_abs) on the heat and mass transfer, thermodynamics, and economic performance of the system are investigated. The working conditions to accomplish ideal thermodynamic performance and economic benefits are determined through multi-objective optimization. The results show that: the carbon capture rate tends to be stabilized at the L/G ratio of 1.2, and the total capture cost is the lowest. Increasing m_EG negatively impacts carbon capture rate, net output power, and exergy efficiency. As H_abs increases, both the total capture cost and payback period are reduced. At the optimal working conditions (L/G =0.91, m_EG =35,210 kg/h, H_abs =10 m), DORC-OCCS obtains a carbon capture rate of 90.56% and a net output power of 305 kW. Meanwhile, the energy and exergy efficiencies are 53.71% and 17.88%, respectively, resulting in a total capture cost of 89.62 $/tCO₂ and a payback of 9.30 years. Compared to a conventional OCCS and an OCCS with a single-stage ORC, DORC-OCCS exhibits superior overall performance. The related study provides a framework for future research and industrialized application of carbon capture technology in marine emissions.