Ammonia – fuel for thought in our deep-dive Q&A

Four Wärtsilä experts discuss the advantages of ammonia as a future fuel for shipping, as well as the issues that need to be considered.

As vessel owners and operators seek to cook up a decarbonisation strategy that checks all the right boxes, there is an extensive menu of options to choose from in terms of future fuels. Ammonia, which releases no CO2 when combusted, has been on Wärtsilä’s radar for several years. We took a deep dive into the benefits and challenges associated with this future fuel in a Q&A with four of Wärtsilä’s leading experts on the topic.


Ammonia has traditionally been produced from hydrocarbons, typically using natural gas or even coal as the energy source, but there is potential for carbon capture to reduce the emission footprint, producing so-called ‘blue ammonia’, or for production of so-called ‘green ammonia’ from renewable, non-carbon sources such as wind or solar energy.

But ammonia is not without its challenges, which include toxicity, corrosiveness, slow ignition and NOx and possible N2O emissions. The volume and weight of the storage infrastructure required also has a significant impact on the operating range of vessels.


Q: What are the pros and cons of adopting ammonia as a future marine fuel?

Kaj Portin, General Manager, Fuel & Operational Flexibility, Wärtsilä Marine Power

“One of ammonia’s biggest advantages is that it doesn’t contain any molecular carbon, so when it’s combusted in an engine it produces no CO2 emissions. It’s also a known quantity and, although there’s currently no infrastructure to support its use as a fuel, it’s widely manufactured and traded, primarily for use in the production of fertilisers. And it certainly possesses the energy potential to be a viable marine fuel, with an energy density of around 3kWh/litre. But, of course, it’s a toxic, corrosive and smelly chemical that needs to be handled with care.

We are collaborating closely with classification societies to identify protocols and technologies that will allow ammonia to be used safely as a maritime fuel. On the regulatory side things are still very much up in the air, particularly because with ammonia there are safety issues related to toxicity, explosion risk and odours.”

Mathias Jansson, Director, Fuel Gas Supply Systems, Wärtsilä Marine Power

“Although it doesn’t emit CO2 when combusted, there does need to be some form of abatement to handle the NOx emissions and possible ammonia gas releases, with the latter potentially being handled by a wet scrubber system. Solutions to both challenges are still being investigated in cooperation with the classification societies. Compared to LNG and hydrogen, ammonia is easier to handle in liquid form as it is stored at around -33C, meaning the fuel storage and delivery systems are less complex and therefore less costly.

On the other hand, ammonia’s lower volumetric efficiency and energy density means much more storage capacity is required on board. Also, because it is still in the early stages of development as a fuel the regulatory frameworks are still being worked out. Our work with the classification societies is an iterative process where we will see things evolve gradually as pilot projects kick off; collaboration with owners and operators is also critical to give them the confidence in the solutions we are developing.

Compared to LNG, ammonia is easier to handle terms of temperature but more challenging in terms of toxicity. With LNG all you need is a material that can withstand cryogenic temperatures, intrinsically safe electrical equipment and a system to vent the evaporated gas. The toxic nature of ammonia adds a new dimension to the handling of leaks because gas can’t simply be vented into the surrounding atmosphere. However, if there is a leakage there are no operational consequences since the vessel can switch to using the other main fuel alone.”

Jarno Salonen, Business Development Manager, Wärtsilä Marine Power

“As Mathias says, the sacrifices in terms of passenger or cargo capacity need to be weighed up against the benefits of adopting ammonia as a fuel. For example, vessels already running on LNG could install extra storage tanks and fuel supply equipment to enable them to use ammonia to further reduce CO2 emissions, and of course ammonia can be used in dual-fuel operation together with diesel. However, the additional space required to store and handle ammonia may mean that it is not a viable retrofit option for smaller vessels like tugs and fishing vessels, for example.”

Q: What are the next development steps and hurdles to overcome for ammonia as a marine fuel?

Kaj Portin: “Our focus is on keeping things safe and simple, because if it’s not simple, it’s not safe. Our engine test cell in Vaasa has been approved by the Finnish authorities, and in Norway this year we will begin the world’s first long-term, full-scale testing of ammonia as a fuel in a marine four-stroke engine, at the Sustainable Energy Catapult Centre’s testing facilities in Stord. These testing programmes will provide important insights into the long-term effects of an ammonia-fuelled engine in relation to other vessel systems and components, including the required safety measures.”

Mathias Jansson: “Today we have engines that can run 100% on LNG, but at the moment no engine can use ammonia alone as a fuel. The future pathway will likely be a fuel mix involving LNG, diesel or even methanol – different blends are being tested – and this of course has implications for the onboard storage and handling systems. From a full-chain emissions point of view, it’s also important to remember that there is not yet any green ammonia being produced, and we will be waiting a long time for this situation to change, at least in terms of the volumes needed. Initially we will see brown ammonia produced from fossil sources and then blue ammonia from carbon capture. Another thing to highlight is that there will be stiff competition for ammonia as a fuel. The shipping industry will be competing with the fertiliser and energy industries for a slice of the pie, and ramping up production takes time since building and commissioning an ammonia plant can take anything from four to six years.”


Q: What progress has been made with emissions abatement technologies to handle NOx?

Jan Torrkulla, General Manager, R&D, Catalyst Systems, Wärtsilä:

“Ammonia is used in traditional selective catalytic reduction (SCR) systems to capture NOx emissions. Today the carrier is urea because it is safe and easy to handle, but in the future we will see ammonia used as the reagent, though probably initially backed up by urea.

How we handle emissions abatement in the future and the reagents we use in SCR will very much depend on the engine combustion concept that emerges as the frontrunner. Catalysts for eliminating ammonia slip originating from the reagent in the SCR process are already used in projects in the US where strict emission limits apply. Projects like this provide a very good starting point for developing catalyst setups that are optimised for maritime applications. One of the biggest unknowns is how to handle potential emissions of nitrous oxide (N2O), which is a powerful greenhouse gas that, if released untreated, would negate the benefits of using ammonia as a fuel.

Catalysts do exist for N2O in other industries, and we need to work together with suppliers to develop new solutions that are fit for maritime applications.”

Q: How does Wärtsilä see its role in the future?

Kaj Portin: “At Wärtsilä we are already ahead of the game because we have all the puzzle pieces ready to slot together. We can supply proven fuel gas systems, dual-fuel engine technology and emissions abatement systems for exhaust gas treatment, and our R&D programmes focused on ammonia are already very advanced. With one OEM designing, integrating and supplying the needed systems and components the end result is naturally much safer and more efficient for the customer compared to engaging multiple vendors.

As with any other potential future fuel, collaboration with all the stakeholders – vessel owners and operations, classification societies and technology providers – will be critical to identify a viable pathway for the future adoption of ammonia as a maritime fuel. Wärtsilä's Smart Technology Hub, currently being built in Vaasa, Finland, will provide a valuable platform for this kind of collaboration.”

Written by

Charlie Bass

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