Economic Evaluation of Propulsion Systems for LNG Carriers: A Comparative Life cycle Cost Approach

This study presented the methodology of a comparative life cycle cost to provide impartial assessment of propulsion options for LNG carriers. The comparison set included the commercial available propulsion solutions based on reheating steam turbines, dual-fuel diesel generators, diesel engines with reliquefaction and dual-fuel diesel engines. In order to achieve unbiased comparison, the scope of the system included not only the main engines for propulsion function but also the systems for BOG handling and electricity generation. One voyage was divided into laden, ballast, port maneuvering, loading, unloading, waiting, and canal transit segment, for each of which the propulsion demand, electrical load and BOG generation were estimated. Operational availability of each subsystem was measured on the basis of its failure rate and repair time. The comparative life cycle cost analysis for a transport case indicated that the operating expenditure was much larger than the capital expenditure, implying that the optimization efforts should be paid to minimizing the operating expenditure. Of the operating expenditure, the fuel cost component including the natural boil-off gas took the major share while portions of the delivery loss cost affected by the propulsion availability and the maintenance costs showed a significant variation with propulsion options. When the fuel cost was changed, the diesel mechanical propulsion with reliquefaction remained relatively invariant in comparison with the other options. This observation was attributed to the segregation of the propulsion and BOG treatment functions. Improvement in availability of the propulsion availability had larger impact than that of the BOG treatment function for all the propulsion options except for the reliquefaction-equipped propulsion. This was because the failure of propulsion function resulted in the delivery delay as well as the BOG loss. To the contrary, the failure of the BOG treatment function did not do harm the propulsion function.