Solid Oxide Fuel Cell Propulsion System Fueled by Ammonia

Abstract

As a result of the Paris Agreement, energy technologies require to shift from fossil fuel based to carbon neutral. In 2015, the maritime sector was responsible for 2.6 % of the global CO2 emissions. The combination of the solid oxide fuel cell fueled by sustainable synthesized ammonia is seen as a potential solution to
reduce emissions. Ammonia is considered as a balanced solution in terms of ease of storage, volumetric energy density and cost of production. The solid oxide fuel cell is generally regarded to be a promising technology owing to its high eciency and combined heat and power usage. This MSc thesis investigates the technical viability of a sustainable SOFC propulsion system fueled by ammonia. Technical viability is expressed in equipment weight and volume, whereas sustainability is determined by efficiency and emissions. The solid oxide propulsion system is subjected to a case study: A diesel engine powered vessel from the Watertaxi Rotterdam company with an assumed shaft power of 25 kW. A model was compiled to determine the efficiency, weight and volume of the solid oxide fuel cell system. The model covers activation losses, ohmic losses and diffusion losses within the solid oxide fuel cell stack. With the model, a sensitivity study with a selected set of system parameters was performed to gain insight in the solid oxide fuel cell system. The selected system parameters are: Number of cells in the stack, single-pass fuel utilization, cathode off-gas recirculation rate and anode off-gas recirculation rate. The final solid oxide fuel cell system has a signicantly higher efficiency based on the higher heating value than the diesel engine system: 46.0 % versus 35.0 % respectively. Also, no carbon dioxide is emitted, leading to a reduction of 56.9 ton per year. Furthermore, nitrogen oxide emissions are considered to be negligible compared to the diesel engine system. However, the weight and volume of the solid oxide fuel cell system are signicantly larger: 1199 kg versus 278 kg and 1175 L versus 432 L respectively. Mainly caused by the battery module, required for compensating for temporarily imbalances between power demand and power supply. As a result, it is concluded that the solid oxide fuel cell system is unpractical for the small inland vessel selected for the case study. Larger sized vessels have more potential for the application, because large sized vessel sail more continuously, reducing the battery capacity requirement, may allow for more tolerance regarding heavy and bulky equipment and have more benefit of the higher efficiency due to a lower refuel frequency.