Techno-Economic Comparison of Dual-Fuel Marine Engine Waste Energy Recovery Systems

Nowadays alternative and innovative energy recovery solutions are adopted on board ships to reduce fuel consumption and harmful emissions. According to this, the present work compares the engine exhaust gas waste heat recovery and hybrid turbocharger technologies, which are used to improve the efficiency of a dual-fuel four-stroke (DF) marine engine. Both solutions aim to satisfy partly or entirely the ship’s electrical and/or thermal loads. For the engine exhaust gas waste heat recovery, two steam plant schemes are considered: the single steam pressure and the variable layout (single or dual steam pressure plant). In both cases, a heat recovery steam generator is used for the electric power energy generation through a steam turbine. The hybrid turbocharger is used to provide a part of the ship’s electric loads as well. The thermodynamic mathematical models of DF engines, integrated with the energy recovery systems, are developed in a Matlab-Simulink environment, allowing the comparison in terms of performance at different engine loads and fuels, which are Natural Gas (NG) and High Fuel Oil (HFO). The use of NG always involves better efficiency of the system for all the engine working conditions. It results that the highest efficiency value achievable is 56 % at 50 % maximum continuous rating (MCR) engine load.