Liquid Natural Gas (LNG) carriers have, as the only type of commercial vessel, maintained the steam turbine as their preferred propulsion system. This has been done despite the fact that all other types of commercial vessels changed to the more efficient diesel engines in the 1970s, as a consequence of the rising fuel prices and environmental awareness. The LNG carrier has maintained the steam turbine as its propulsion system because the natural evaporated boil-off gas from the cargo is available anyway, and because no other solution for the use of the boil-off gas has been available. The reliquefaction of the boil-off gas from the LNG cargo makes it possible to increase the cargo quantity delivered to the customers, instead of using it as fuel, and to install more efficient propulsion systems on LNG carriers. The system is now technically mature and it includes proven components and systems. The construction of a test plant in Ukraine and the completion of an onshore LNG plant in Norway, further demonstrate the feasibility of the reliquefaction technology. The economical advantage of diesel engine propulsion would have been more than USD 3,000,000 per year for a 125,000 m~3 LNG carrier, and it can be foreseen that the steam turbine will also soon be history on LNG carriers.
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