Ammonia-powered ships: Concept design and feasibility assessment of powertrain systems for a sustainable approach in maritime industry

The decarbonization of the shipping industry is pushing towards the introduction of low-carbon fuels such as hydrogen carriers and towards the installation of cleaner propulsion systems. Among different hydrogen carriers, ammonia (NH3) is considered a promising option due to its high volumetric energy density and to its easier storage and transportation in comparison with pure hydrogen. Therefore, this study is focused on the design, modeling, and feasibility assessment of ammonia-based propulsion systems for shipping applications. Two NH3based fuel cell power generation systems are analyzed: i) a NH3-based Proton exchange membrane Fuel Cell (PEMFC) system and ii) a NH3-based Solid Oxide Fuel Cell (SOFC) system. These systems are designed to replace a conventional diesel powertrain installed on board a container ship. The fuel consumption, according to the ship load profile, is calculated and the analysis on the masses and volumes of the fuel storage tanks and of the ammonia powertrain systems is performed. Results highlight that on board installation of the proposed ammonia-based propulsion technologies causes greater masses and volumes with respect to the conventional diesel system. This criticality, in the face of an advantage in terms of avoided CO2 emissions per cruise, could be overcome by accepting a cargo capacity reduction. It is estimated a cargo reduction in the range 3.3% - 4.8% for the proposed fuel cell-based powertrain solutions. However, by valorizing the avoided CO2 emissions, it is possible to recover the economic penalty due the cargo reduction and break-even with the reference diesel scenario.