Integration of a tank storage solution for alternative fuels on a RoRo ship

Abstract

Although maritime shipping is one of the most efficient logistical solutions, this sector of activity generates around 3 % of global CO2 emissions, accentuating the global warming challenges that the world is facing. Therefore, the International Maritime Organisation established a road map to reduce CO2 emissions to half by 2050 compared to the 2008 levels. To reach this goal, alternative fuels are seen as a solution. Utilising carbon-free/carbon-neutral fuels will cut greenhouse gas emissions. Nonetheless, many alternative fuels are proposed, and each presents different environmental, economic, and technical characteristics. Fuels such as liquified natural gas, hydrogen, ammonia, and methanol are brought forward as potential substitutes for fuel oil and diesel oil. To determine which fuel is the most suitable for integration onboard a RoRo ship running on conventional fuels, a multiple-criteria evaluation is done. The selected evaluation criteria are the volume and weight requirements, environmental safety, technology readiness, and fuel prices. To rank these fuels based on their performances, the analytical hierarchy process is a commonly used multicriteria decision-making method that allows the selection of the most suitable fuel solutions. Methanol and ammonia were elected as suitable solutions based on the ranking results. Therefore, the next step was establishing an integration strategy on board the vessel. The integration process is initiated by defining proper locations for the fuel tanks. Tank dimensions are defined in order to reach the required storage capacity while respecting the structural limitation of the ship. Finally, different systems and components related to each fuel technology are defined, including the fuel supply system, the bunkering concept, and the main engine upgrade. Safety equipment and protocols related to fuel storage and handling are defined as per international regulations and class guidelines in order to prevent fires and other hazards. The viability of ammonia or methanol as fuel solutions for the future has been studied by determining first the impact of the retrofitting process on the ship operation range and carrying capacity. Second, an evaluation of the projected CO2 emissions for each fuel solution over one year of navigation is estimated based on different fuel pathways and compared to the recorded emissions over previous years to provide a better view of the reduction potential of each fuel solution. Finally, the economical viability of the fuel solutions is determined by calculating the total cost of ownership constituted of the capital cost of the engine and storage and the operating costs that are, in this work, fuel costs only. It becomes clear that the major driver of any energy transition project is the fuel price, where non-fossil-based fuels are relatively expensive. However, it is hoped that costs will be significantly reduced due to economies of scale in the future.