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.

Due to climate change, the growth in renewable energy is still accelerating and reaching new records each year. Not everything can be electrified, hence, the production of green hydrogen as an energy vector is gaining momentum. However, lowest cost hydrogen will not always be produced at the demand centres, necessitating transport of hydrogen which is nascent. In this, it has been realised that due to its easy liquefaction, proven transport at scales and matured production process, ammonia can be an excellent energy carrier. Currently, ammonia production accounts for more emissions than any other chemical and to achieve net-zero targets these emissions must be reduced ∼ 25-fold. Therefore, ammonia synthesis with renewable energy will be imperative. Operating with variable hydrogen feed rates will be part of the challenge. In this work, the dynamics of a small-scale ammonia synthesis plant with a capacity of 60 𝑡𝑜𝑛𝑠/𝑑𝑎𝑦 was studied. The application of chemisorption as replacement for the traditional condensation step for ammonia recovery was adopted in the study. In the system, the hydrogen feed was sourced from an electrolyser powered by renewable energy. Hence, it was imperative to study the sensitivity and the response of the synthesis loop to the fluctuations in hydrogen feed. For the dynamics model, different scenarios of ramp-up and ramp-down were tested for two control structures to evaluate the response of various system parameters to these deviations. Therefore, the feasibility of these control structures was assessed and some of their potential limitations were identified. The objective of this work was achieved with three simulation models. A steady-state model was employed to study the equilibrium conditions of the ammonia synthesis loop. A second more extensive model included reaction kinetics, heat integration and a chemisorption operation. The widely applied Temkin-Pyzhev rate equation was modified into LHHW form to fit this application. With the selected ZA-5 iron-based catalyst the operating pressure was established at 130 𝑏𝑎𝑟 to avoid overheating the catalyst. The simulation resulted in the reactor dimensions to attain the maximum possible conversion of 22.1% under these conditions. For the third model, the inputs from the two models were translated into the a dynamic model. The latter was used to study the behavior of the system parameters when subjected to fluctuations in the hydrogen feed flow. Three scenarios were tested with respect to the hydrogen variations: a (step and linear) reduction in the hydrogen feed of 10%, 25% and 50% of the initial value. With the default control system, the pressure varied by 16 bar with only a 10% step reduction of the hydrogen feed. This necessitated the development of control strategies to control the pressure deviations in order to eliminate metal fatigue in the equipment. The first control structure compensated the lack of hydrogen by adding more nitrogen into the system. The second control structure reduced the recycle flow rate to decrease the ammonia production rate in the reactor. Both control philosophies were successfully applied to control the system pressure for the 10% and 25% H2 ramp-down/up scenarios. The greatest pressure range measured during transient state in a linear 25% H2 reduction scenario for control philosophy 1 and 2 were 3.8% and 4.5%, respectively. The effects of the variations and the control strategies have also been studied. In this research the nitrogen supply was assumed to be infinite, therefore a nitrogen buffer must be present. In addition, the use of a hydrogen buffer is required for a gradual decrease and dampens rapid changes in the hydrogen supply in order to minimize pressure variations.