Design and Evaluation of LNG-Hydrogen Hybrid Propulsion System for LNG Carrier

摘要

Marine Environment Protection Committee (MEPC) in International Maritime Organization (IMO) is regulating the CO2 emission from vessels by an established index called the Energy Efficiency Design Index (EEDI). The EEDI is applied to every ocean-going vessel and ratified to be stringent with respect to time; the CO2 emission should be reduced by 30 % in 2022 (Phase 3) and by 40 % in 2025 (Phase 4) from the emission level of 2013. Although the LNG-fuelled propulsion system has been developed to reduce the green-house gas emission, it hardly meet the regulation in Phase 4, and consequently some fuel without green-house gas emission should be combined with LNG. This study proposes the LNG-hydrogen hybrid system of a LNG carrier with 154K, 210K, and 267K cargo capacity and discusses some issues including the relative ratio of hydrogen with respect to LNG, the size of hydrogen fuel tanks, and operating complexities to satisfy the step-by-step regulations. An appropriate ratio of hydrogen fuel to satisfy the environmental regulation is estimated to more than 12% and 27% for Phase 4 and 5 respectively. The tank size of liquid hydrogen for the ship is estimated 1,300 ~ 3,300 m3, and the power of a fuel cell is required to be 4.9 ~ 11.8 MW. Optimising the hybrid propulsion system considering the spatial, operational, and economic feasibility for the hybrid propulsion system is identified as a future challenge.