Alternative fuel options for low carbon maritime transportation: Pathways to 2050

Within the context of achieving low carbon shipping by 2050, high hopes are placed on alternative marine fuels in addition to a large number of technological and operational measures. A technological review has been carried out in this paper to determine the most promising alternative marine fuels considering the simultaneous reduction of sulphur oxides, nitrogen oxides and carbon dioxide emissions as well as sustainability. Firstly, potential alternative marine fuel options have been summarized based on a review of published literature. Then, key physicochemical properties, feedstocks, production processes, transportation and storage factors, and end uses of zero carbon or carbon-neutral fuels have been analyzed. Finally, a qualitative ranking of the potential of different marine fuel options is presented based on a multi-dimensional decision-making framework. It was found that zero carbon synthetic fuels including hydrogen and ammonia accompanied by clean production could play a vital role in domestic and short sea shipping, though current costs and infrastructure are not commercially feasible. Methanol (fossil/renewable) appears likely to be the most promising alternative fuel for global shipping instead of other carbon-neutral biofuels such as renewable natural gas, bioethanol, biogenic dimethyl ether and biodiesels, which may be feasible for domestic and short sea shipping depending on local practices. It should be highlighted that marine fuel substitution is a prolonged process. Accordingly, consensus-building and action-adopting in the maritime community as early as possible is important to anchor expectations and achieve the goals of clean maritime transportation.