"The work in this project developed in three, main phases.
In the first phase, a set of tools and methods called ""process integration"" was applied to the design of a cruise ship. Process integration techniques are based on an holistic approach to process design and optimization, which exploits the interactions between different units in order to employ resources effectively and minimize costs.
In the first part of the project, these methods were applied to a reference cruise ship powered by Diesel engines. Despite the existing means for waste heat recovery on board, there are large amounts of heat at low temperature that could be better used, mainly for the purpose of ""freeing"" waste heat at high temperature for being used in a more efficient way. The combined use of Rankine cycles, that can be used for converting high-temperature waste heat to electricity, and of heat pumps, that can be used to ""upgrade"" low-temperature heat to become usable for heat demand on board, was estimated to have the potential to contribute to up to 4-7% fuel savings. While these are promising results, they are not high enough to bring emissions from cruise ships down to a sustainable level. This led to the investigation of more radical changes of the ship's energy system.
Fuel cells are considered as a very promising technology for ship propulsion: they can reach high efficiency and o not have emissions of pollutants such as nitrogen oxides and particulate matter. At the current state, solid-oxide fuel cells (SOFC) are considered to be the most promising for application to shipping because can relatively easily run on a number of conventional fuels.
The second part of this study focused on the evaluation of the potential of using SOFCs on cruise ships, and on how to optimally design a system based on this technology. This part of the study led to the conclusion that there is a very significant potential for the use of fuel cells in ships. Firstly, their higher efficiency in converting fuel to electricity makes them better from the perspective of reducing fuel consumption; this was estimated to provide up to approximately 15% savings when compared to a system based on Diesel engines. In addition, SOFCs allow for the use of different fuels: the use of natural gas can lead to reducing emissions by an additional 15%. In addition, SOFCs are suitable to running on other fuels, such as hydrogen or ammonia, that have potentially no direct emissions of CO2. Hence, the conclusion of this phase of the project was that SOFCs have an important potential for use on ships, and that the development and spread of this technology should be pushed if sustainable shipping operations are expected.
Finally, a third part of the study focused on optimal control. Because of their poor dynamics, SOFCs require the installation of storage technologies. More generally, the use of energy storage is gaining ground in the shipping sector, and the appropriate management of the energy flows in systems equipped with energy storage devices is not trivial. The scope of this part of the project was to test whether the assumption of optimal control is valid when applied to ships. The question that was addressed was: can the system be controlled to be as efficient as we could operate it if we knew the future? The results were very promising, and allowed to validate the approach employed in the other phases of the project. A relatively simple control algorithm was proposed, where predictions about future operations are based on what was learned from the previous ones, recorded over time. The results showed that by doing this the system can be operated very close to optimal efficiency (approximately 90-95% of the maximum) even when the operations of the real voyage are remarkably different from the ones that the system had encountered before.
"
