Ammonia has emerged as a promising alternative as the shipping industry looks for more sustainable fuel options. This article explores the many sides of using ammonia as a marine fuel and provides insights on how to do it smart.
To meet the IMO’s target of net-zero greenhouse gas emissions by 2050, the shipping industry needs to move to cleaner fuels. There is no clear frontrunner among the several potential options, but ammonia offers some unique benefits that make it a leading contender.
But is it the right solution for your vessel? Read on to find out, or use these shortcuts to take you directly to the topics you’re keen to read more about:
Ammonia is a colourless gas with a powerful odour. It is commonly used in cleaning products, refrigeration systems and fertilisers. It has emerged as a promising alternative fuel for the maritime industry because it has significant potential to reduce greenhouse gas emissions.
Although ammonia has many benefits, it also has some drawbacks, such as its toxicity and flammability.
Nitrogen and hydrogen gases are combined under high pressure at a high temperature in the presence of a catalyst. This reaction produces ammonia gas.
Ammonia has traditionally been produced using natural gas or even coal as the energy source. Because this process produces significant carbon emissions, the result is called grey ammonia, or sometimes brown ammonia.
When carbon capture is added to the ammonia production process, it reduces the carbon emissions and results in blue ammonia.
Green ammonia is produced using renewable energy sources, such as wind or solar power. Using ammonia as a fuel will only reduce overall greenhouse gas emissions if it is green ammonia. There is growing interest in producing green ammonia fuel.
Ammonia releases no CO2 when combusted, so it has great potential to be a more sustainable fuel choice. But as far as overall well-to-wake emissions are concerned, only green ammonia will bring significant environmental benefits. In fact, green ammonia is completely carbon-free whether the resulting emissions are considered from tank-to-wake or from well-to-wake.
On the other hand, producing grey ammonia generates one third more carbon emissions from well to wake than heavy fuel oil.
In the future engines will be able to run on 100% ammonia and use biodiesel as pilot fuel, enabling a fully sustainable solution.
Ammonia is used in traditional selective catalytic reduction (SCR) systems to capture NOx emissions. Today the reagent 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 systems will very much depend on the engine combustion concept that emerges as the frontrunner.
Catalysts for eliminating ammonia slip from the reagent in the SCR process are already used in projects in the US where strict emission limits apply. Such projects provide a very good starting point for developing catalyst setups that are optimised for maritime applications.
Ammonia is an attractive alternative to fossil fuels for the shipping industry. It has the potential to significantly reduce greenhouse gas emissions, but there are still challenges to overcome. These include the development of a reliable ammonia fuel bunkering network and the fact that ammonia engines need additional maintenance because of the fuel’s corrosive nature.
Ammonia can be used as a gaseous or liquid fuel. Engines can burn this fuel well with minor adaptations.
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When it comes to ammonia fuel efficiency, the bottom line is it has a lower volumetric efficiency and energy density than diesel. Ammonia engines also have a lower efficiency than traditional fossil fuel engines. In short, a ship that uses ammonia needs much higher fuel storage capacity. The volume and weight of the storage infrastructure required also has a significant impact on the vessel’s operating range.
There are three main challenges when using ammonia to fuel ships:
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. Adopting green ammonia as a maritime fuel is a great way to decarbonise shipping, helping to reduce the reliance on fossil fuels and move towards a more sustainable future.
Ammonia is abundant and can be produced using renewable energy sources such as wind and solar power. It is widely manufactured and traded, primarily for use in the production of fertilisers, and has the energy potential to be a viable marine fuel.
Fuel storage and delivery systems don’t need to be overly complex when ammonia is used in its liquid form. This reduces the operating costs.
Ammonia is already being used as fuel in power generation.
Because ammonia is highly toxic and corrosive it requires careful handling and storage. However, the risks can be mitigated with proper crew training and equipment such as protective gear and ventilation systems.
Ammonia doesn’t produce CO2 when combusted as fuel. The NOx emissions it produces can be handled with an abatement solution, and a wet scrubber system might be needed to manage potential ammonia gas releases. More investigation into these solutions, with the cooperation of classification societies, is needed.
One of the biggest unknowns with ammonia is how to handle potential N2O emissions. Catalysts are being developed for N2O – a potent greenhouse gas – to minimise N2O emissions and make ammonia a sustainable solution. For example, the Wärtsilä 25 ammonia solution with its optimised combustion and integrated aftertreatment has been designed to minimise all greenhouse gas emissions.
For a quick overview of the advantages and disadvantages of ammonia as a marine fuel, you can download a handy one-page cheat sheet:
Ammonia has several safety issues related to toxicity, explosion risk and odours. Regulations are currently being developed to ensure ammonia can be used safely as a maritime fuel.
Three considerations are important to remember when it comes to ammonia fuel safety:
Wärtsilä is collaborating closely with classification societies to identify protocols and technologies to ensure ammonia is safe to use as a maritime fuel.
Ammonia is a toxic gas that can cause serious health problems if inhaled. It can also be flammable and explosive in certain conditions. Handheld or mounted sensors – or even just the smell – are the best forms of leak detection.
Ammonia leaks are not simple to handle because the gas is toxic and cannot be vented into the surrounding atmosphere. However, a leak will not affect the ship’s operation because the engine can switch to using the other main fuel.
Water can react with ammonia and form chloramine, which is a toxic gas. Carbon dioxide (CO2) should be used to extinguish ammonia fires so that no harmful gases are formed.
If you can smell ammonia, it means there is a leak. Depending on the concentration, it can also mean there is a health risk.
At low levels, ammonia can cause eye, nose and throat irritation. At high levels, it can cause more serious health problems. It is important to evacuate the area immediately if there is a leak and seek medical attention if you experience any symptoms.
Ammonia presents an explosion risk when its concentration in air reaches 15–28 vol.%.
The risk of ammonia toxicity has been defined according to acute exposure guideline levels (AEGLs).
The following table shows the ammonia AEGLs for five exposure periods.
Regulatory frameworks for the development of ammonia as a marine fuel are still being developed. Collaboration with ship owners and operators is critical to give them confidence in the solutions being developed.
There isn’t yet much ammonia available for shipping as there is strong competition for ammonia as a fuel. The shipping industry is competing with the fertiliser and energy industries, and ramping up production takes time. Building and commissioning an ammonia plant can take anywhere from four to six years. However, more than 200 low-carbon ammonia facilities are currently being planned globally.
Wärtsilä introduced the marine sector’s first commercially available 4-stroke engine-based solution for ammonia fuel in November 2023. It is now available as part of the Wärtsilä 25 engine platform.
In addition to the Wärtsilä 25 engine platform, Wärtsilä’s solution for ammonia fuel includes the:
The solution also includes:
The Wärtsilä solution for ammonia fuel has been designed to ensure smooth and safe adoption of ammonia as a new fuel.
Working with a single manufacturer to design, integrate and supply the necessary components and systems makes for a safer solution and more efficient process.
To move to ammonia-based operations your vessel needs to be designed to use ammonia. It might also be possible to retrofit an existing vessel, but there may be challenges to find space for equipment such as ammonia tanks. The fuel gas supply system needs to be designed for ammonia, and this includes a lot of different components.
You will also need an ammonia fuel engine, either one specifically developed for ammonia use or a retrofitted engine that can run on ammonia. A fuel-flexible and easily upgradable engine like the Wärtsilä 25 will be beneficial if you are considering running on ammonia in the future.
Your vessel’s aftertreatment system needs to be adapted according to the fuel it is using. Depending on whether your engines will be running on liquid or gaseous ammonia, you may also require some additional equipment such as a high-pressure room for the pumps if a high-pressure system is used to inject the ammonia fuel into the engine.
As the shipping industry moves towards decarbonisation, ammonia is emerging as a promising alternative fuel. To transition, your engine needs to be designed to use ammonia and specific materials need to be used for the components that will be exposed to the fuel. Using ammonia as marine fuel also requires significant changes in the engine room and the fuel-handling system.
When building a new vessel, it is critical to consider what is needed to use ammonia as a fuel during the design phase. From a retrofit perspective, in order to safely bunker, handle and burn ammonia onboard, some of the existing vessel structures will have to be changed. New structures will need to be designed, assembled and built to create the necessary space to store ammonia onboard and transfer it to the converted engines. Auxiliary systems will need to be arranged to guarantee safely levels required by applicable rules and regulations. New auxiliary systems may also be needed, for example a drain system, bilge system, nitrogen system and ventilation system.
To ensure safety and compliance with regulations, it is important to follow best practices and guidelines for handling ammonia. Proper handling of ammonia in an engine room requires careful consideration of the following questions, among others:
Adopting ammonia as marine fuel will require significant changes in the engine room, the fuel handling system and potentially the exhaust gas after-treatment system. However, with proper precautions and safety measures, ammonia can be a safe and sustainable alternative to traditional marine fuels.
When opening the crankcase door after the engine has run on ammonia, make sure to wear appropriate personal protective equipment and follow the engine manufacturer’s service and maintenance instructions.
Because ammonia has the potential to be carbon free from production to combustion, it has a lot of promise as a future fuel, especially for newbuild vessels. 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.
Ammonia has already been trialled in fuel-cell solutions and in four-stroke ammonia engines. Whether ammonia becomes the dominant fuel of the future will depend on numerous factors, including technological advances, regulatory support and fuel supply investments. Zero-carbon fuels such as green ammonia will play a big role in making maritime transportation more sustainable.
The availability of ammonia as marine fuel, especially green ammonia, will be essential for reaching the marine industry’s decarbonisation targets. We are starting to see more discussions and investment decisions about an ammonia fuel bunkering network. This will scale up as the market starts to adopt ammonia.
Today, the demand for ammonia is mainly driven by fertiliser consumption, but the demand from the marine industry will start to increase as more vessels run on ammonia. DNV predicts ammonia use in shipping will be 170 PJ (1% of the shipping fuel mix) in 2030, 1,900 PJ (13% of the fuel mix) in 2040, and 5,000 PJ (36% of the fuel mix) in 2050.
The ammonia bunkering system can be fixed or mobile. Fixed bunkering involves stationary infrastructure at ports or fuelling stations, while mobile systems use transportable tanks. Ammonia can be stored as a liquid or a gas depending on the temperature or pressure.
Safety measures and environmental considerations play a critical role in the deployment of bunkering systems.
As the shipping industry seeks to reduce its carbon footprint, alternative fuels such as ammonia are becoming increasingly important. While there are challenges to be overcome, the potential benefits of using ammonia as marine fuel are significant.
By investing in the development of a reliable ammonia fuel bunkering network and continuing to improve ammonia engine technology, we can work towards a more sustainable future for the shipping industry.
If you’re interested in learning more about how ammonia could be part of your decarbonisation strategy, Wärtsilä offers a simple three-step approach with Wärtsilä Decarbonisation Services.
Wärtsilä Technical Journal, Vol. 2, 2021
International Maritime Organization (IMO) guidelines on the use of ammonia as marine fuel