## 2 Materials and Methods: System Description  
A general cargo ship with ammonia as fuel was chosen as the target of the proposed system with a total propulsion power of 3800 kW. The specifications of the modeling ship are listed in Table 1. The target ship utilizes a type of electric propulsion powered by an ammonia supply system. A schematic of the overall configuration of the system is shown in Figure 1. The general idea underlying the concept integrated system is the utilization of waste heat from SOFCs to generate useful work (electricity). As shown, ammonia is supplied to the SOFC before the working temperature is obtained from the regenerative heat exchanger. The steam Rankine cycle (SRC) absorbs waste heat from the SOFC and releases it into the working fluids. These processes generate electric power through their expander devices. Figure 1: Block flow diagram of the overall configuration of the system. The schematic in Figure 2 depicts the proposed combined system using ammonia as fuel, which comprises a fuel gas supply system, SOFC-GT, SRC, ORC and KC. The air and ammonia are supplied to the SOFC through the fuel gas supply system (FGSS). After reaction in the SOFC, the exhaust gas is led to the afterburner for completing combustion. This generates a considerable amount of heat and enlarges the temperature of the exhaust gas. Subsequently, the exhaust gas is utilized in the gas turbine (GT), heat exchangers, and bottom cycles to generate additional power. Thus, the cascade waste heat is utilized. The main components and working principles of the cycles are described below:  
1. SOFC-GT: First, compressed air and ammonia are preheated in turn by the exhaust gas of the SOFC using two heat exchangers. Thus, the ammonia and compressed air can reach the required inlet temperature for the SOFCs. After preheating, the reforming and electrochemical reactions occur in the SOFC. These reactions generate electrical energy (by converting chemical energy to electrical energy) and produce a large amount of heat. Subsequently, the generated electricity (DC) is converted to an alternating current (AC) before being supplied to the ship propulsion system. There are two main exhaust streams from solid oxide fuel cells. There is exhaust of a nitrogen-rich stream from the cathode (stream 4-1) and a mixed water and nitrogen stream from the anode (stream 6-1) and main exhaust stream 6 to provide to the afterburner. 2. SRC: This operates mainly using the heat received from the exhaust gas of the heat exchanger (E-102). Water in the SRC is first pumped by a pump (P-100) to high pressure. Then, it proceeds to the heat exchanger (E-102) to become a superheated fluid. Next, the high-pressure steam (17) is depressurized in the expander (K-102) to drive the reversible heat pump and produce extra electric power. The saturated water mixture (19) is condensed in the heat exchanger (E-104) and releases heat to the fresh cooling water. This cooling water (21) after the heat exchanger (E-104) at 70.98 \({}^{\circ}\)C is used for the seafers aboard ships. 3. KC: The evaporator heats the ammonia--water using the exhaust gas from the SOFC. The gas then powers the expander (K-104), which produces mechanical work. The liquid blends with the gas after the throttling valve. Subsequently, the working fluid is condensed in the condenser (E-106) before being pressurized by the pump (P-102). Finally, the working fluid is cooled to the required temperature before entering the heat exchanger (E-103) to complete the cycle. 4. ORC: The energy required by the ORC subsystem is supplied by heat exchange (E-108). 1,1-Difluoroethane (R152a) was chosen as the working fluid in this subsystem process. In addition, the working fluid is charged by heat transfer in the heat exchanger (E-108) and transferred to the ORC turbine with flow number 35. Power is produced by expanding the working fluid between flows 35 and 36. The working fluid from the ORC turbine is transferred to the heat exchanger (E-105) with a flow number of 37.