Pathways to the Decarbonization of Oceangoing Vessels – From Hydrogen Engines to On-board Carbon Capture Concepts: Wege zur Dekarbonisierung der Hochseeschifffahrt – Vom Wasserstoffmotor bis zu On-board CO2-Abscheidekonzepten

International shipping is considered the most efficient form of transportation but is still responsible for approximately 2.5 % of global greenhouse gas emissions (GHG). Recent years saw the introduction of regulations and GHG reduction targets in the maritime sector by the International Maritime Organization (IMO) and the inclusion of the maritime sector in the EU Emissions Trading System in 2024 as part of the Fit for 55 package. Ship operators have to take significant measures to fulfill these targets. Operational and technological efficiency measures to reduce shipping emissions are important but their decarbonization potential is limited to around 20 %. The most promising option for a complete decarbonization is the switch from fossil fuels to renewable fuels such as carbon-based and carbon-free e-fuels as well as bio-fuels. Since the availability of renewable fuels is expected to be limited in the foreseeable future the use of fossil fuels in combination with on-board carbon capture represents a short-term to mid-term solution that can play a considerable role to reduce GHG emissions in the maritime sector. However, on-board carbon capture will also be a viable option if carbon-based e-fuels are being implemented in the future.

This article provides an overview of potential pathways for the decarbonization of maritime transportation including state-of-the-art post-combustion carbon capture technologies, introduction of renewable fuels as well as novel technology concepts to create a closed-loop CO2 cycle, such as pre-combustion carbon capture concepts and oxyfuel-based separation processes. The investigated technological options for on-board carbon capture will be assessed with regard to their CO2 reduction potential and impact on fuel consumption. For the renewable fuels path different combustion concepts for hydrogen, methanol and ammonia will be discussed and challenges highlighted. The article concludes with a final assessment and comparison of the different approaches.