Design and Simulation of Combined Gas Turbine-Steam or Diesel-Steam Plants for Marine Applications

The paper aims to present the main results of a research directed to the development of mathematical models for the design and simulation of combined Gas Turbine-Steam or Diesel-Steam plants for marine applications. The goal of this research is to increase energy conversion efficiency of both gas turbines and diesel engines, adopted in ship propulsion systems, by recovering part of the thermal energy contained in the exhaust gases through Waste Heat Recovery (WHR) dedicated installations. The developed models are used to identify the best configuration of the combined plants in order to optimize, for the different applications, the steam plant pattern and the performance of WHR plant components, such as: Heat Recovery Steam Generator (HRSG), steam turbine, condenser, deaerator, pumps and so on. This research activity has allowed to improve the knowledge and obtain significant results not only on the objective of optimizing the overall energy conversion efficiency of the considered propulsion systems, but also on other important issues typical of marine applications, that is: dimensions and weights of the installations, ship load capacity variations, environmental compatibility, investment and operating costs. On the other hand, it must be observed that the ship energetic requirements typically include, in addition to the mechanical power for ship propulsion, also the mechanical power for electric generation and thermal power for the on board services. Taking into account this more comprehensive approach, different plant layouts have been proposed and compared by simulation in order to identify the configuration that meets in the best way the request of propulsive, electric and thermal power of the ship. The presented results are relative to a container ship and an oil tanker, taken as reference units in this study. The comparison has been carried out taking into account the obtainable increase of the overall energy efficiency, the possible reduction of pollutant emissions and the potential advantages from an economic point of view.