Modelling, analysis and optimisation of ship energy systems

Doktorsavhandling, 2016

Shipping is the backbone of today's economy, as 90% of global trade volumes is transported by sea. Much of our lifestyle today is only made possible by the existence of shipping as a cheap and reliable mean of transportation across the globe. However, the shipping industry has been challenged in the latest years by, among others, fluctuating fuel prices and stricter environmental regulations. Its contribution to global warming, although today relatively small, has been set under scrutiny: for shipping to be part of a sustainable economy, it will need to reduce its emissions of greenhouse gases. Increasing ship energy efficiency allows reducing fuel consumption and, hence, carbon dioxide emissions. The latest years have witnessed a multiplication of the efforts in research and development for increasing ship energy efficiency, ranging from improvements of existing components to the development of new solutions. This has also contributed to ship energy systems to become more complex. The optimisation of the design and operation of complex systems is a challenging process and the risks for sub-optimisation are high. This thesis aims at contributing to the broader field of energy efficiency in shipping by adopting a systems perspective, which puts a special focus on system requirements and on interactions within the system. In this thesis, the energy systems of two case study ships were analysed using energy and exergy analysis to identify energy flows and inefficiencies. Then, solutions for improving the energy efficiency of the existing systems were proposed and evaluated accounting for the ship's observed operating range and for how added elements influenced the existing systems and their performance. The results of this thesis show the importance of modelling the interactions between different parts of the energy systems. This allows not only a more accurate estimation of the benefits from the installation of new technologies, but also the identification of potential for additional energy savings. This is particularly important when the broad range of ship operations is included in the analysis, rather than focusing on the performance of the system in design conditions. In addition, the results of this thesis also show that there is potential for further improving ship energy efficiency by putting additional focus on heat losses from the engines and on how to efficiently recover them.