Options for low or zero carbon maritime fuels

Eveliina Klemola,
Senior Specialist,
Wega Group Oy,
Finland

Reduction of greenhouse gas (GHG) emissions from transport is vital for mitigating the climate change. Replacing existing vessels with newbuilds is an effective method to ensure deployment of latest environmental technologies. It is also possible to significantly decrease emissions without premature scrapping by combining operational and technical efficiency measures, such as slow steaming and switching to low-carbon fuels, with required retrofitting. However, for each fuel, the whole life cycle must be assessed.

There are several alternatives for shipowners, and the fuel choice is always a compromise between the benefits and drawbacks of each fuel. The most significant factors are the price of the required equipment, the expected price and availability of the fuel, as well as safety. The emission reduction objectives of shipowners, their customers, and financers also play a role.

In the short term, emphasis is expected to be on fuels which can be used in existing powertrains and with proven potential to reduce or even eliminate GHG and other emissions. Liquid biofuels, e.g., ethanol and methanol produced from biomass, fatty acid methyl esters (FAME), and hydrotreated vegetable oils (HVO), have so far been used in the maritime sector mostly as a demonstration or blended with conventional fuels. Their future availability for maritime transport is uncertain, as also road transport and aviation have their needs and may be able to pay higher prices.

Liquefied natural gas (LNG) is a widely available option to reduce the local emissions and, to some extent, carbon dioxide (CO₂) emissions. Many of the newbuilds operating in the Baltic and North Seas run on LNG today due to regional regulation on sulphur and nitrogen oxide emissions. Even as LNG, a fossil fuel, cannot be considered a long-term solution, it is building a bridge toward decarbonization. Its clear advantage is that the infrastructure is directly suitable for liquefied biogas (LBG), which is chemically identical but carbon neutral. LBG has been piloted to replace LNG in ships in the Baltic Sea, and its availability is expected to increase in the next few years. Sustainable feedstock and sufficient production volumes are key issues for all biomass-based fuels. LBG is mainly produced from waste streams with relatively large potential production volumes.

In future, the same infrastructure will be suitable for liquefied synthetic methane as well. Synthetic fuels are produced from CO₂ and water, with electricity as the main source of energy. If the CO₂ is biomass-based or captured from the atmosphere, and the electricity is produced from renewable sources, synthetic fuels can be considered renewable as well. The Power-to-X methods can be utilized in the production of methane, diesel, petrol, methanol, and other alcohols. However, these synthetic fuels are not expected to be commercially available in large scale before the next decade.

In addition to new fuels for combustion engines, new propulsion systems are emerging also in the maritime sector. They have a large potential to reduce emissions, and the first applications, such as fully electric or battery-diesel hybrid vessels, already operate in environmentally sensitive sea areas, such as the Baltic Sea. Their wider deployment depends on further technological development and cost-efficiency from scaling-up. Whereas direct electrification has potential for vessels operating on fixed routes and short distances, hydrogen and ammonia fuel cells are potential solutions for international maritime transport. Their emissions consist only of heat and water, and in the case of ammonia fuel cells, also nitrogen. The yield of fuel cells is superior compared with traditional combustion engines.

So far, the challenges have been the price of hydrogen, the energy required to produce hydrogen and the related GHG emissions, and the space requirements of the fuel cells. Both hydrogen and ammonia also require larger storage space onboard, with novel safety architecture, than traditional fuels, due to their lower energy intensity. However, due to fast technological development and decreasing price of renewable electricity, hydrogen could be available for a commercially competitive price as soon as in 2025. Large-scale investments are expected to promote the use of zero-emission hydrogen, produced with solar or wind power, in the transport sector.

In addition, vessels directly powered by solar and wind energy are being developed, each technology with their own drawbacks and limitations. The current spectrum is wide, and it is difficult to predict the option which will prevail. There is no one-solution-fits-all toward low and zero emission maritime transport. Most likely, a mix of fuels and propulsion methods will be utilized, with tailored solutions for the different needs of various fleets. The composition of the mix will depend on the regulation, availability, speed of technology development, and price of the alternatives.

Email: eveliina.klemola@wega.fi

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