Comparison of ship plant layouts for power and propulsion systems with energy recovery

Currently the increase in fuel costs and the need to reduce CO2 emissions have encouraged the search for even more efficient solutions to be adopted in energy conversion systems for ship installations. These systems generally include thermal prime movers consisting mainly of two-stroke or four-stroke diesel engines, a waste heat recovery (WHR) plant, a steam turbine and possibly a gas turbine, as well as electric machinery. These components may be used in various ways and through different plant configurations, whose optimization is under investigation by researchers and diesel engine manufacturers. In this paper four schemes of ship propulsion plants, using a two-stroke diesel engine equipped with waste heat recovery system are presented, analyzed and compared by simulation. Some of the considered layouts can include also an electric motor to support the main engine in providing power to the propeller. On the other hand the electric power can be generated from both the diesel generators and the WHR plant. The considered propulsion plant schemes are compared in order to identify the configuration that meets in the best way the request of propulsive, electrical and thermal power of a 158000 dead weight tonnes DWT crude oil tanker ship, belonging to Premuda company, taken as a reference unit in this study. The comparison is carried out taking into account the payback time of the installation, the annual saving in the fuel outlay and the carbon dioxide (CO2) emissions. This last parameter is considered through the evaluation of the Energy Efficiency Design Index (EEDI).