Demand for ammonia is being transformed by the energy transition. Until recently used as an input for fertilizers and chemicals, new markets are emerging for green and blue ammonia, replacing coal in energy production, green steel production and as marine fuel.
Nowadays, around 200 million tons are produced per year around the world, 20 million of which are transported in LPG carriers. The scale of emerging and potential demand will cause these numbers to increase; how quickly this can be achieved will determine its acceptance for transport.
The interest in ammonia arises both from its zero emissions when used as a fuel, and from its production not depending on biogenic carbon sources. As the global economy moves away from fossil fuels, biogenic carbon – coming from captured CO2, electrolysis and even waste sources – will be subject to increasing competition from different industries.
Biogenic carbon will increasingly replace fossil carbon in many of the products currently used in industry and consumer goods. Competition from the energy and aviation sectors will inevitably lead to rising prices, but production capacity will have to come from industrial sources and not biomass harvested for this purpose.
Rising ammonia also creates potential for green hydrogen as a fuel. But as transporting ammonia over long distances is significantly cheaper – and taking into account the loss of energy when hydrogen is transformed into ammonia via the Haber-Bosch process – it seems likely that most of the hydrogen will be produced by cracking the ammonia. green in the place 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 have to grow tremendously. The current global installed capacity of wind and solar farms, and especially the electrolyzers needed to produce the green hydrogen needed for ammonia production, are dwarfed by the capacity required.
Renewable electricity for electrolysis will have to be produced in locations around the world that have favorable conditions for wind and solar power generation and that also have large areas of land available. These locations tend to be in remote areas; Locations such as Western Australia, Chile, West Africa, Oman and Saudi Arabia are the areas expected to dominate production. Ammonia needs to be shipped from these locations to demand centers, primarily in North/East Asia and Europe.
Current projections for global production growth indicate that there will be enough renewable electricity to produce the volumes of green ammonia needed for the shipping fleet alone by 2040. However, as shipping will also be competing with many other industries for both renewable electricity as for the green hydrogen energy required to produce ammonia, as well as in other sectors that depend on the consumption of green ammonia, such as agriculture and coal-fired power plants, supply is expected to be limited.
Propulsion Technology
The first tests were carried out using ammonia as a fuel in combustion engines by several major engine manufacturers. The tests were very promising and no obstacles were discovered for the use of ammonia as a combustion fuel in internal combustion engines.
Although the amount of pilot fuel and the levels of NOx, NH3 and N2O emissions have not yet been quantified for commercial marine engines, marine engine manufacturers generally agree that the Diesel cycle is best suited for ammonia combustion.
Research is ongoing into diesel cycle and Otto cycle combustion concepts. Optimizing emissions reductions is considered a challenge, and controlling N2O and ammonia slip requires high-temperature combustion, which also generates high levels of NOx. Tests on two-stroke engines have shown that NOx is less of an issue 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 temperature spikes in the combustion zones that generated the high NOx.
Pilot fuel is needed to ignite the ammonia and also to maintain stable combustion. For smaller four-stroke engines, 10% pilot fuel is required once engine optimization is completed and after the engine is in service. For large two-stroke engines using diesel cycles, only 5% pilot fuel is required, and some engine manufacturers hope this amount can be reduced further.
Emissions assessment
The actual amount of NH3 and N2O emissions has not yet been accurately assessed; however, emissions are expected to be low, especially in 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 levels emitted could negate much of the CO2 benefit. the use of ammonia as fuel. This remains a significant potential barrier to adoption.
Two-stroke marine engine designers, however, have found in their testing that N2O levels are low – in the same range we see for other fuels, including marine diesel, LNG and methanol. Overall, it appears that the diesel combustion principle is ideal for the use of ammonia, as the temperature in the combustion chamber reaches a “sweet spot” where the levels of NOX, N2O and ammonia slip are recorded at a very low level. It is therefore expected that these engines will be capable of operating in accordance with IMO Tier II NOx standards without any need for an abatement system.
As of the first quarter of 2024, major marine engine manufacturers have the following development plans and delivery times for ammonia-powered engines:
- Two-stroke ammonia dual-fuel engines covering power ranges from 5 MW to 31 MW. These engines will be available for delivery from Q4 2024/Q1 2025.
- Four-stroke ammonia engines as dual-fuel generator set engines are also becoming available. Two engine manufacturers will launch this type of engine in late 2024 or early 2025.
Exhaust safety and treatment
Most engine designers expect that exhaust gas aftertreatment will be necessary to meet the IMO NOx Tier III standard, and all of them expect to specify selective catalytic reduction (SCR) as the preferred means of cleaning exhaust gases afterward. from having left the combustion chamber, instead of exhaust gas recirculation (EGR), which changes the combustion conditions, thus limiting the formation of NOX. EGR is reducing the amount of oxygen in the intake air, and the fear is that this will have a very negative impact on ammonia combustion performance, but this remains to be investigated.
In addition to main engines and generator sets that operate on ammonia, designs are also emerging for auxiliary engines needed to complete the transition to vessels that operate on ammonia. Boiler manufacturers 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 on board daily requires a solution to safely collect ammonia vapor. This vapor will be released in the event of a normal engine stop, if the piping system needs to be purged, or in the event of a malfunction somewhere in the fuel supply system.
Different vapor handling solutions are being developed by several manufacturers, including water scrubber designs that can remove ammonia vapor from purge air. In this solution, ammonia vapor is stored in dedicated tanks as a solution of water and ammonia. However, this approach would require dedicated infrastructure at the port to receive and store it.
All of the systems described above are being prepared for new construction projects for different types of ships and the expectation is that we will see these systems in service by the end of 2025/early 2026. We estimate that approximately 50-70 ships are on order as of April 2024.
René Sejer Laursen is Director of Fuels and Technology at the American Bureau of Shipping (ABS).
The opinions expressed here are those of the author and not necessarily those of the Maritime Executive.
