Navigating the future of maritime fuels

The maritime industry is undergoing a profound transformation as it seeks pathways to decarbonisation. Among the emerging fuel options, e-ammonia, e-methane, and e-methanol have garnered significant attention, offering promising routes to reducing greenhouse gas (GHG) emissions. These synthetic fuels are produced using renewable energy and, for e-methane and e-methanol, captured carbon. However, each comes with its unique features, benefits, and challenges, particularly concerning their availability and readiness for large-scale adoption.

E-Ammonia: a zero-carbon contender

E-ammonia is a nitrogen-based fuel produced using green hydrogen combined with nitrogen from the air. The pathway to production of renewable hydrogen is clear, relying on cheap renewable electricity, and nitrogen is abundantly available. Free of carbon, e-ammonia is therefore a zero-CO2 fuel at the point of use. However, to ensure overall GHG reductions occur in practice, close control is needed of the potential release of nitrous oxide emissions, a GHG. 

Though lower than traditional fuels, ammonia’s energy density is sufficient for long-haul voyages with proper storage solutions as it does not need to be stored under significant pressure nor with significant refrigeration. These aspects, and its potential to be low cost in the future, mean the expected primary use case of e-ammonia is by the future deep-sea cargo fleet. Ammonia internal combustion engines are today still a rarity, with two-stroke dual fuel solutions still forthcoming. Its low flammability leads to the expected need to pair with non-trivial quantities of a pilot fuel, which must be sustainable in order to provide overall well-to-wake GHG benefits.

A challenge requiring considerable engineering expertise concerns ammonia’s wider properties. Ammonia is highly toxic, posing storage and handling challenges, both on and off the vessel. Retrofitting existing vessels to accommodate its unique storage and combustion requirements is both costly and technically complex.

Today, ammonia is not available for bunkering in ports. Green shipping corridors that are looking at ammonia are likely to lead the way in trialing ammonia bunkering at scale. That said, there is an international storage network of (fossil-derived) ammonia, including at ports, due to its existing use as a globally-traded component of fertiliser. This network and its existing engineering know-how should be utilised to accelerate the deployment of green e-ammonia. As with all new fuels, significant investment is needed in global bunkering networks, alongside innovations in retrofitting technologies and incentives to offset associated costs.

Currently, e-ammonia production remains limited as renewable hydrogen capacity is still developing. The production and scalability of e-ammonia is intrinsically tied to the availability of green hydrogen, which relies on expanding renewable energy capacity, enhancing electrolysis technology, and building robust supply chains. These developments will require coordinated efforts across industries to ensure a steady and cost-effective supply of green hydrogen for large-scale e-ammonia production. However, significant investments are being made in e-ammonia production plants, signalling a potential rise in availability by 2030.

E-Methane: bridging today and tomorrow

E-methane, also known as synthetic methane, is produced by combining green hydrogen with captured carbon dioxide in a methanation process. Its production process can be nearly carbon-neutral when renewable energy and direct air capture are utilised. E-methane, as with bio-methane, is a drop-in replacement for liquefied natural gas (LNG) and because of its compatibility with existing systems, e-methane can be used in LNG-powered dual-fuel engines without requiring modifications, and can utilise the existing global LNG bunkering network to support immediate deployment. This route to deployment with a drop-in solution is likely to be favoured by those operators that already have LNG assets with appreciable capital life remaining.

However, there are also challenges presented by this fuel. The risk of unburned methane escaping during combustion diminishes its overall climate benefits as it is a potent greenhouse gas. Accounting rules for this by the legislators will be important to reflect the true real-world situation. Second, e-methane requires a carbon source, which must also be sustainable. Gaining long-term access to cheap CO2 streams, ideally close to or co-located with the production plant, enables cost reduction. Third, producing e-methane requires significant renewable energy input, which might place it at a disadvantage for a world constrained by roll-out of renewables.

While LNG is widely available, e-methane production is still in its infancy, requiring green hydrogen production and CO₂ capture to be widely adopted to ensure sufficient supply for maritime needs. Furthermore, logistical frameworks for transporting and storing green hydrogen must be established to create a reliable and efficient supply chain. Addressing these challenges will involve collaboration across industries and government support to enable the deployment of these technologies at scale.

E-Methanol: the versatile middle ground

E-methanol is also created using green hydrogen and captured carbon dioxide and when produced renewably, e-methanol offers near-zero lifecycle carbon emissions. It’s a liquid fuel in ambient conditions, meaning it has less complex storage needs and can be handled relatively easily, making it an attractive option for maritime applications despite its lower energy density than conventional fuels. And compared with e-ammonia, it is possible today to order methanol-powered vessels at scale, with dual-fuel methanol engines providing fuel flexibility. Many large shipping companies have already made investments in e-methanol-compatible vessels, driving demand for the fuel.

To match this demand, the supply of e-methanol (or bio-methanol options) must develop significantly. Pilot projects and investments in e-methanol production remain at a nascent stage. The potential for significant scalability exists, with several projects underway globally. However, as with the other e-fuels, its scalability is closely tied to the availability of green hydrogen and thus the expansion of cheap renewable energy capacity, and alongside e-methane, e-methanol also requires a sustainable source of CO2. Bunkering facilities of methanol are at an early stage in a limited number of ports, reflecting the early stage of demand and supply.  

Comparing E-Fuels: Navigating the Choices

A multifaceted pathway to decarbonisation

E-ammonia, e-methane, and e-methanol each offer unique pathways to decarbonising the maritime sector. However, the successful adoption of these fuels extends beyond the maritime industry and is intricately linked to the broader green hydrogen supply chain as well as competition for feedstocks with other sectors. That competition could also be a benefit: further incentivising investments in hydrogen technologies and reducing costs through economies of scale.

As regulatory pressures mount and decarbonisation deadlines loom, collaboration and learning across industries, along with coordinated policy support, will be critical to navigating the regulatory horizon and achieving sustainability goals.

The New Energies Coalition evaluated the environmental performance of hydrogen, e-ammonia, e-methane & e-methanol compared to conventional fossil fuels, as part of a study conducted by the consultancy Ricardo. The full report can be accessed here. 

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