Assessment of Steam Cycle Layouts for COGAS Ship Propulsion Systems

The combined gas and steam turbine (COGAS) power plants are estimated currently the most efficient type of power machinery for terrestrial applications. Their use for marine propulsion is so far limited, mainly in consideration of the investment costs. However the possibility of reducing pollutant emissions and fuel consumption (and therefore operating costs) could favor in a near future the diffusion of these systems also in the shipping sector. In this paper, starting from the performance characteristics of a marine gas turbine, four steam plants layouts are considered, optimized and compared by means of a mathematical model developed by authors. Thus it is possible to obtain information regarding the best solutions for a feasible COGAS ship propulsion system. The presented results take into account not only the overall energy conversion efficiency of the installation, but also other important issues typical of marine applications such as: plant dimensions, weights and economic considerations.