Steam turbine plant, which burns BOG (Boil-Off Gas) as fuel, has been installed for LNG carriers with the necessity of disposing BOG safely. Are other plants unpractical for LNG carriers? To answer to this question, this paper evaluates 1) Dual fuel diesel, 2) Diesel with reliquefaction plant, 3) Diesel with auxiliary boiler and power assist motor, 4) Gas turbine/steam turbine and 5) Steam turbine with CRP (Contra Rotating Propeller) from several aspects, such as safety & reliability, maintainability & operability, economy and effect on environment. Based on the above studies, this paper proposes Steam turbine with CRP plant as a new energy saving system for future LNG carriers.
Commercial marine transportation of LNG was started in 1964. Since then steam turbine plant has been installed for LNG carriers with necessity of disposing BOG safely, in spite of plant switch from steam turbine to diesel in other merchant ships. It is said that one of the reason of long term record of safe and reliable LNG transportation may be the adoption of steam turbine plant. However, are other plants unpractical for LNG carrier? To answer this question, this paper studies new energy saving system, considering unique features of LNG carriers.
Recently natural gas or LNG attracts attention as an energy source from the viewpoints of future energy demand and global environment, and it is predicted that LNG marine transportation will be greatly increased. In order to cope with future demand, however, circumstances are forcing the reliance on the Middle East sources. Since the Middle East is far from both Europe and Japan, it is unavoidable that both the tonnage required and transportation cost will be increased. On the other hand, it is requested that C02 emission to the air has to be reduced to avoid global warming. On the basis of such background, as one of the effective measures to reduce transportation cost and C02 emission, new energy saving system is required to be studied in addition to the investigation of the ship size enlargement (Itoyama, 1993).
