Comparison of organic Rankine cycle concepts for recovering waste heat in a hybrid powertrain on a fast passenger ferry

The possibilities of recovering waste heat from the exhaust gas and other waste heat sources from a 900 kW fast passenger ferry Diesel engine by means of an organic Rankine cycle (ORC) were investigated. The recovered energy is to be used in a parallel hybrid powertrain, which would allow for electric propulsion and thus low emissions near stopovers while electricity generated by the ORC when the engine is running at cruising speed is stored in a battery. The benefit of such a solution is that there would be no extra load on the engine and increased fuel consumption while the local emissions around the stopovers could be reduced, which is especially desirable in urban environments. Simple organic Rankine-cycles with and without internal energy regeneration and an organic Rankine cycle with two different heat sources have been modelled. Different working fluid candidates have been compared by means of a simple optimization routine with respect to the maximum recoverable amount of work from the cycles' expander. The method is applied to a vessel serving a typical short fast passenger ferry route between the harbour of the Western Norwegian city of Bergen and the neighbouring Askøy municipality.