## 7 Conclusions  
Ammonia is a promising candidate as a hydrogen carrier, especially in the maritime sector. An integrated SOFC-SRC-ORC-KC system that uses ammonia as fuel to produce electric power to the main propulsion plant and recover waste heat from SOFCs to generate more electricity for auxiliary machinery and accommodation purposes was proposed and investigated. The proposed multigeneration energy system aims to provide alternative environmentally clean options by utilizing sustainable and carbon-free fuels in power plants. Energy and exergy analyses were performed, and a comprehensive parametric study was conducted to assess the working performance and energy harvesting of the proposed system. R152a is selected as the most suitable working fluid for ORC through parametric study with the performance of five candidates. The following significant conclusions can be drawn from this study:  
1. This study presented a novel SOFC-GT system integrated with SRC-KC-ORC. The overall energy and exergy of the integrated system can reach high values of 60.4% and 57.5%, respectively, which are comparatively higher than those of simple ammonia SOFC-GT powering systems. The SRC-KC-ORC generated and provided 1376.46 kW to the system, equivalent to 26.6% of the total power supply of the system. Hot water was also produced for the seafarers aboard ships.
2. The parametric studies demonstrated that increasing the current density from 930 to 1830 A/m\({}^{2}\) reduced the energy and exergy efficiencies of the SOFC-GT subsystem from 71.55% to 50% and 67.8% to 47.38%, respectively. This is mainly because of the effective decrease in cell voltage, and thus the efficiency of the fuel cell was reduced as well.
3. For the ORC system, a parametric study was conducted with five working fluids as candidates--R152a, R600, R601, R134a, and R124--and the efficiency of the system for each working fluid was estimated. R152a showed the highest energy and exergy efficiencies of 22.49% and 42.76%, respectively.  
Those results suggest that direct ammonia fuel cells are promising in the further development of high-efficiency combined SOFC-GT-SRC-KC-ORC marine propulsion plants. Future studies on the assessment of the economic and stainability aspects of the system are to be performed to fully determine the applicability of the combined system. Since this integrated system is proposed for marine vessel applications, the dynamic behavior of the system should also be implemented in future studies.  
Formal analysis, P.A.D.; investigation, B.R.; methodology, P.A.D. and J.J.; supervision, H.K.; writing--original draft, P.A.D.; writing--review and editing, H.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the project \"Development of guidance for prevention of leaks and mitigation of consequences in hydrogen ships\" (Grant No. 20200520), and the project \"Test evaluation for LNG bunkering equipment and development of test technology (Grant No. 20180048)\", which was funded by the Ministry of Oceans and Fisheries (Korea). This research was supported by BB21 plus, funded by Busan Metropolitan City and Busan Institute for Talent & Lifelong Education (BIT).  
Not applicable.  
The authors declare no conflict of interest.