Momentum is Building for Ammonia as Technology Matures
Strong demand is driving development but emissions issues remain
Demand for ammonia is being transformed by the energy transition. Until recently used as an input for fertilizer and chemical products, new markets for green and blue ammonia are emerging, replacing coal in power generation, in green steel production and as a marine fuel.
Today some 200 million tonnes per annum is produced worldwide, with 20 million transported in LPG carriers. The scale of the emerging and potential demand will see these figures rise; how quickly this can be achieved will determine its take-up within shipping.
The interest in ammonia stems both from its zero emissions when used as fuel and because its production isn’t dependent on biogenic carbon sources. As the global economy transitions away from fossil-based fuels, biogenic carbon – from captured CO2, electrolysis and even waste sources – will be subject to increasing competition from different industries.
Biogenic carbon will increasingly replace fossil-based carbon in many of the products in use today in industry and consumer goods. Competition from the energy and aviation sectors will inevitably lead to increased prices but production capacity will need to come from industrial sources rather than biomass harvested for this purpose.
The rise of ammonia also creates potential for green hydrogen as a fuel. But because ammonia is significantly cheaper to transport over long distances – and considering the loss of energy when hydrogen is turned into ammonia via the Haber-Bosch process – it seems likely that a majority of hydrogen will be produced by cracking green ammonia at the location where the hydrogen will be consumed.
Ammonia Production
To realize large-scale production of green ammonia to serve new markets, its production capacity, along with that of renewable electricity and green hydrogen, will need to grow tremendously. The current global installed capacity of wind and solar farms and especially the electrolyzers needed to produce the necessary green hydrogen for ammonia production, are dwarfed by the required capacity needed.
Renewable electricity for electrolysis will need to be produced at locations around the globe that have favorable conditions for wind and solar energy generation and also have large land areas available. Those locations tend to be in remote areas; locations such as Western Australia, Chile, West Africa, Oman and Saudi Arabia are the areas that are expected to dominate production. Ammonia needs to be shipped from these locations to demand centers, in the first instance North/East Asia and Europe.
Current projections for the growth in global production indicate there will be enough renewable electricity to produce the volumes of green ammonia needed for the maritime fleet alone by 2040. However, because shipping will also be competing with many other industries for both the renewable electricity and green hydrogen necessary to produce ammonia, as well as with other sectors that depend on the consumption of green ammonia such as agriculture and coal-fired power plants, supply is expected to be constrained.
Propulsion Technology
The first tests have been performed using ammonia as fuel in combustion engines by several of the main engine manufacturers. The tests have been very promising and no showstoppers have been discovered for the use of ammonia as a combustion fuel in internal combustion engines.
Though the amount of pilot fuel and levels of NOx, NH3 slip and N2O emissions have yet to be quantified for the commercial marine engines, marine engine makers generally agree that the Diesel cycle is best suited for combustion of ammonia
Research is ongoing for both diesel and Otto cycle combustion concepts. Optimizing emissions reductions is foreseen as a challenge, and control of N2O and ammonia slip requires high-temperature combustion, which also generates high NOx levels. Tests on two-stroke engines have shown that NOx is less of a problem using the Diesel cycle combustion principle when burning ammonia. When ammonia is injected into the combustion chamber, it expands and generates a cooling effect that removes the high peak temperatures in the combustion zones that generated the high NOx.
Pilot fuel is necessary to ignite ammonia and it is also needed to keep combustion stable. For smaller four-stroke engines, 10% pilot fuel is required once engine optimization has been completed and after the engine is in service. For large two-stroke engines using Diesel cycles, just 5% pilot fuel is required, and some engine makers expect that this amount can be further reduced.
Assessing Emissions
The actual amount of NH3 and N2O emissions is therefore still to be accurately assessed, however, emissions are expected to be low, particularly for the diesel combustion cycle. Even so, with N2O having a 20-year global warming potential (GWP) of 264 and a 100-year GWP of 265 according to IPCC 2013-ARS, the emitted levels may negate much of the CO2 benefit of using ammonia as a fuel. This remains a significant potential barrier to adoption.
Two-stroke marine engine designers have, however, found in their tests that N2O level are low - in the same range as we see for other fuels including marine diesel, LNG and methanol. Overall it seems that the diesel combustion principle is ideal for use of ammonia since the temperature in the combustion chamber hits a ‘sweet spot’ where the NOX, N2O and ammonia slip levels are recorded at a very low level. It is therefore expected that those engines will be able to operate to IMO NOx Tier II standards without any need for an abatement system.
As of Q1 2024, the main marine engine makers have the following development plans and lead times for ammonia fuelled engines:
- Two-stroke ammonia dual fuel engines covering power ranges from 5 MW to 31 MW. These engines will be available for delivery starting from Q4 2024/Q1 2025.
- Four-stroke ammonia engines as dual fuel gensets engines are also becoming available. Two engine manufacturers will launch this type of engine at the end of 2024 or beginning of 2025.
Safety and exhaust treatment
Most engine designers expect that exhaust gas after-treatment will be needed to comply with the IMO NOx Tier III standard, and all of them expect to specify selective catalytic reduction (SCR) as the preferred means of cleaning the exhaust gas after it has left the combustion chamber, rather than exhaust gas recirculation (EGR) which changes the combustion conditions thereby limiting NOX formation. The EGR is reducing the amount of oxygen in the intake air, and the fear is that this will have a very negative impact on the performance of ammonia combustion, but this is still to be investigated.
In addition to main engines and gensets operating on ammonia, designs are also emerging for auxiliary engines required to complete the transition to vessels running on ammonia. Boilermakers are preparing dual-fuel boilers for use with ammonia as fuel to be able to generate steam and heat from burning ammonia.
Working with ammonia onboard on a day-to-day basis requires a solution to collect ammonia vapor in a safe manner. This vapor will be released in case of a normal engine stop if the piping system needs to be purged or in case of a malfunction somewhere in the fuel supply system.
Different solutions for vapor handling are under development from several manufacturers, including water scrubber designs that can remove ammonia vapor from the purge air. In this solution, ammonia vapor is stored in dedicated tanks as a water-ammonia solution. However, this approach would require dedicated infrastructure at the port to receive and store it.
All those systems described above are being prepared for newbuilding projects for different ship types and the expectation is that we will see those systems in service by the end of 2025/beginning of 2026. We estimate that approximately 50-70 ships are under order as of April 2024.
René Sejer Laursen is the Director Fuels & Technology at American Bureau of Shipping (ABS).
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.
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