Innovative ship power plants for the energy transition in the maritime field

In the recent years, global awareness on climate change has been promoting energy transition towards sustainable development strategies. In this scenario, in order to limit GHGs and pollutants generated by the shipping field, even more stringent regulations and policies have been introduced. Specifically, two main strategies are receiving major attention in the scientific community to face energy transition in the maritime sector. First, the overall ship power plant efficiency is required to be improved by either further research on existing technologies and operating condition optimization. Second, innovative and greener solutions for the maritime sector appear necessary pathways to complete energy transition and cope with long-term environmental regulations. Optimization of vessel operating conditions and installation of efficient waste heat recovery systems currently appear promising technologies able to lower primary energy utilisation onboard. Instead, among innovative solutions, major research efforts are payed on alternative fuels and hybrid-electric configurations. In this context, the present work aims to investigate innovative power plant configurations enabling both primary energy savings and long-term reduction of GHG and pollutant emissions from the maritime sector. Where the pathway on existing technologies is concerned, the benefits provided by COmbined Gas Electric and Steam (COGES) plants installed onboard are investigated. Specifically, engine room operating conditions and waste heat recovery systems have been numerically optimized focusing on configurations coupling COGES plants with small-size reciprocating engines. Within the second pathway, attention is paid to GHG and pollutant emission reduction enabled by emerging alternative fuels and hybrid-electric power plants. In details, the applicability and pros/cons offered by Liquefied Natural Gas (LNG), methanol, ammonia and hydrogen are investigated under different temporal horizons. Furthermore, performances obtained by hybrid-electric power plants are analysed considering various optimized energy management strategies. Owing to their benefits in terms of energy savings and fuel flexibility enhancement, the second pathway is assessed focusing on engine room configurations based on both COGES plants and reciprocating engines. Either pathways have been investigated focusing on modern cruise-ferries and large-size cruise ships. Since challenging decisions are needed by the ownerships in a dynamically evolving regulation context to remain cost competitive, all the investigations have been indiscriminately carried out under energetic, economic and environmental point of views. Thus, complete insight on the major solutions available in a short-, mid- and long-term energy transition scenario is provided. In order to numerically perform computation, various codes and optimization tools have been developed in Fortran and MATLAB/Simulink languages. Specifically, quasi-static, dynamical and Mixed-Integer Linear Programming (MILP) models have been implemented and gradient-descent, Multi-Objective Genetic Algorithms (MOGA), full-factorial and Linear Programming optimization tools have been set up. In details, optimization algorithms have been repeatedly used to assess component and power plant design, as well as to optimize engine room operating conditions by various objective functions. Overall, results demonstrated that COGES plants can play a significant role in the energy transition in the maritime sector. Specifically, combining COGES plants with small-size reciprocating engines resulted to be a viable solution by energetic, economic and environmental point of views, independently from the time horizon considered for energy transition. Further GHG and pollutant emission reduction can be achieved by alternative fuels and hybrid-electric power plants, mainly due to the mature fuel flexibility and high energy efficiency of COGES plants.