Feasibility study of an integrated COGES-DF engine power plant in LNG propulsion for a cruise-ferry

The feasibility study of an integrated COmbined Gas Electric and Steam-reciprocating engine propulsion plant for a Liquified Natural Gas (LNG) fueled cruise-ferry is assessed in this paper. Specifically, the purpose of this work is to respond to GNV shipowners' need to equip ships with a propulsion system highly efficient in a wide ship speed range. The issue was addressed through the repowering study of the GNV La Suprema ship. Several power plant configurations based on different dual-fuel (DF) engine and gas turbine combinations have been tested in a cogeneration efficiency maximization study performed over a wide ship speed range. Afterwards, the best power plant was identified. Analysis showed that COmbined Gas Electric and Steam (COGES) plants have a great potential for marine propulsion application due to their benefits in cogeneration efficiency, emissions and required volumes. Furthermore, integrating a COmbined Gas Electric and Steam plant with small size dual-fuel engines revealed high cogeneration efficiency over wide ship operating conditions. The propulsion plant comprising a COmbined Gas Electric and Steam plant based on GE25.1 gas turbine and small size dual-fuel engines was proved to guarantee high cogeneration efficiency (47-52%) over a wide ship speed range (16-26 knots). In particular, a 51% cogeneration efficiency is provided for the current operating condition of GNV La Suprema. Moreover, the energy efficiency design index (EEDI) for the different investigated plants has been also evaluated, to verify their compliance with IMO limits. The selected propulsion plant provides an EEDI margin of 1.42-2.89 gCO2/(t*nm) with respect to the 2025 requirements. Finally, economic analysis was performed for four different ship routes and capital/operational costs have been computed. Overall, the proposed COmbined Gas Electric and Steamreciprocating engine power plant revealed to be economically feasible over all of the operating conditions accounted for.