Uses of Green Ammonia

Green Ammonia for Fertiliser Manufacture

The overwhelming bulk of the world’s nitrate fertiliser production is made from ‘brown’ ammonia, produced by burning fossil fuels. Almost all the 175 million tonnes of ‘brown’ ammonia produced in this way every year are used for fertiliser manufacture, causing approaching 2% of global greenhouse gas emissions. Fortunately this ‘brown’ ammonia can be replaced with Green ammonia, which is chemically identical.

This is important as it means that Green ammonia producers don’t have to wait for new markets for their product to come into being, which could create a ‘chicken or egg’ standoff. Fertiliser producers who are currently buying in ‘brown’ ammonia as a crucial raw material, or making their own, therefore represent an existing source of demand for Green ammonia as it comes on stream, removing a potential blockage to investment.

Fertiliser companies are also keen to produce products with ultra-low carbon footprints. For example Yara reports on its website: “This year, Yara will introduce fossil-free, green fertilizers that are produced using renewable electricity instead of fossil fuels. These fertilizers will be predominantly made from water and air, resulting in an 80-90 percent reduction in carbon emissions compared to fertilizers made with natural gas.“

Fertilizers Europe also states: “By 2050 – under the right conditions – ammonia production could be based on decarbonised sources of energy”, adding that “A combination of policy solutions is needed to enable the transition to a climate-neutral economy by 2050 while keeping fertilizer industry competitive.”

According to the latest Alternative Fuels Insight report from DNV, not a single ammonia-powered vessel has been ordered to date — although it expects the first orders soon.

Green ammonia is rapidly emerging as the shipping industry’s zero-carbon ‘fuel of choice’ that will enable it to meet targets to reduce carbon emissions in line with the 2015 Paris Agreement.

Currently shipping is responsible for some 2.8% of global carbon emissions, well in excess of 1 Gt/y, a figure that’s growing with the sector’s inexorable expansion concomitant to rising volumes of traded goods.

The 2023 IMO Strategy on Reduction of GHG Emissions from Ships specifies the target to achieve net zero emissions from the sector by 2020, with ambitious intermediate targets for 2030 and 2040. These include a 40% reduction in carbon intensity of international shipping by 2030, while striving for 10% of its energy to be emissions-free by 2030. 

At present IMO regulations stipulate that ammonia may not be used as a fuel for ships, under its International Gas Carrier Code (IGC) and International Code of Safety for Ship Using Gases or Other Low-flashpoint Fuels (IGF Code).

Hence, “Taking into account the urgency of providing guidance to Administrations, shipowners and the industry at large on the safe use of hydrogen and ammonia as fuel, and in support of IMO's emission targets“, the IMO’s CCC Sub-committee accelerated the development of the necessary draft interim guidelines at its September 2023 meeting, and these are due to be finalised in September 2024.

Two-stroke marine diesel engines can already be modified to burn ammonia, and a growing number of manufacturers are designing, testing and producing shipping ‘ammonia-ready’ engines. In what’s claimed to be the first commercial order for ammonia powered ships, joint venture Exmar LPG has ordered a pair of 46,000 tonne Gas Carriers from a South Korean shipyard for delivery in 2026.

Azane Fuel Solutions has also announced its plans for an ammonia powered gas tanker in partnership with Amogy, intended to deliver Green ammonia fuel to ships. Azane plans to start building the world’s first ammonia bunkering network in 2024, expected to be ready for its first operations in 2025.

Some 20 million tonnes of ammonia are currently shipped each year, with around 40 vessels dedicated to the task. Many more ships could be used for ammonia including those now employed in transporting LPG, while new gas carriers, including Very Large Gas Carriers, are often built ‘ammonia ready’ in anticipation of the growth in trade.

Ammonia as a cargo is therefore well understood, and IMO regulations govern its safe handling and transportation. The further step of using ammonia as fuel may look like a small one, but it will have global ramifications.

First ammonia-powered jet flight in 2023: A roadmap to clean aviation

The aviation industry is under growing pressure to reduce its carbon footprint, which is growing even faster than that of international shipping. In 2022 the industry’s specialist UN Body, ICAO, adopted an ‘aspirational goal’ to achieve net zero industry emissions by 2050 in line with the Paris Agreement, stating:

“To achieve the global aspirational goals and to promote sustainable growth of international aviation, ICAO is pursuing a basket of measures including aircraft technology improvements, operational improvements, sustainable aviation fuels, and market-based measures (CORSIA)“ - where CORSIA is ICAO’s carbon offsetting scheme.

ICAO presents little detail of how it intends to achieve its net zero target, but either ‘sustainable aviation fuels’ (SAF) will have to do most of the hard work, or the industry must rely substantially on carbon offsetting. At present ICAO (and airlines) are heavily focused on biomass based fuels, from both waste streams and cropped material.

Some consideration is given to hydrogen as an SAF in ICAO documents such as its Report on the feasibility of a long-term aspirational goal (LTAG) for international civil aviation CO2 emission reductions, but envisages only a 1.9% penetration of hydrogen by 2050. No mention at all is made of Green (or any other kind of) ammonia. We believe the omission is seriously mistaken.

None of ICAO’s three emissions scenarios achieve the UN body’s net zero by 2050 aspirational goal.

Why is Green Ammonia the Right Choice ?

While ammonia’s energy density (18.6 MJ/kg | 12.7 MJ/l) is considerably less than that of kerosene (43 MJ/kg | 35 MJ/l), that does not rule it out as an aviation fuel, indeed it was recently proposed (Boretti & Castelleto 2022) as an alternative to both kerosene and hydrogen for jet engines, propeller piston engines, and electric propellers driven by batteries and fuel cells. The latter option offers high thermodynamic efficiency and the avoidance of NOx emissions arising from combustion.

This is the approach taken by the Australian start-up company Aviation H2 which is working towards the conversion of a small passenger aircraft to run using hydrogen fuel supplemented by batteries, using on-board ammonia in wing tanks as the hydrogen source (see photo).

A similar approach is under development by the Raytheon Technologies Research Center in Connecticut, USA, in association with Arpa-e, part of the US Department of Energy. Their ‘Zero-carbon Ammonia-Powered Turboelectric (ZAPTurbo) Propulsion System’ is a “very high efficiency and lightweight turboelectric system that uses green ammonia as a fuel and coolant via regenerative cooling.”

Waste-heat recovery is used to crack the ammonia to H2 and N2 before combustion, raising its fuel value by some 15% with no drag on engine performance. The proposed propulsion system comprises an AC electric powertrain for turboelectric cruise, with battery boost for takeoff and climb flight phases. It’s projected to cruise with a super-high 66% energy conversion efficiency (compared to the 30-37% typical of most aircraft today) - substantially offseting the lower energy density of ammonia relative to kerosene.

Ammonia also emerges as an excellent fuel for rockets, thanks to its double role as a fuel and nozzle coolant, and the fact that, being carbon free, it leaves no coke (carbon rich encrustations) on surfaces to impair rocket operation.

Ammonia Fuel Safety in Aviation

The accidental release of fuel is always a hazard in aviation, and especially in the context of an aircraft crashing. Where that fuel is kerosene, its ignition may cause many deaths among persons - passengers or bystanders - who have survived the crash itself.

In the case of ammonia, the hazard arises more from ammonia’s toxicity than from the risk of fire. And fortunately it appears that this risk may be substantially mitigated by the use of ambient pressure cold ammonia, cooled to well below its temperature of liquefaction, -33.3C.

Most serious ammonia accidents to date have involved the escape of ambient temperature pressurised ammonia. While some of the gas remains liquid, much of the escaped gas remains in gaseous form resulting in high levels of exposure to any bystanders. But if ammonia were to be stored as a cold liquid it could not volatilise without first taking up the necessary heat from the environment.

Liquid ammonia has a high latent heat of vaporisation (1.37 GJ / tonne), making that process a slow one and giving time for any bystanders (or passengers in the case of a crashed aircraft) to clear the affected area. Of course rigorous testing of the behaviour of cold liquid ammonia in the environment is required.

Three further risk mitigation routes could be considered:

• Foam filled or compartmented tanks: tanks with multiple compartments can greatly reduce the free flow of liquids following a breach of containment. This approach is widely used in military aircraft to prevent fire and explosion.

• Frozen ammonia: if ammonia is stored in its frozen state (below -77.7C) that would prevent it from spilling and ponding were containment breached. Further, more heat would be required to gasify the ammonia, due to the higher combined latent heats of fusion and vaporisation. For fuelling the ammonia can be handled as a slush.

• Rheology modifiers: Increase the viscosity of ammonia to create a honey-like consistency

Ammonia Fuel in other Transport Applications

Green ammonia fuel could also be used in many other transport applications. In general, larger vehicles are best suited to the fuel, such as trains, trucks, tractors and other agricultural machinery, mining machinery, heavy construction vehicles, and buses. One reason is that the containment for the ammonia will be either heavy (for pressurised ammonia) or bulky (for cold ammonia due to the insulation required) making its use less readily accommodated in smaller vehicles.

Thus Amogy, a US company dedicated to ammonia power delivery in transport and other uses, recently demonstrated the world’s first ammonia powered semi truck, a 300kW retrofitted 2018 Freightliner Cascadia powered by Amogy’s ammonia-to-power system. This follows similar achievements with a 5kW drone, and a 100kW mid-size John Deere tractor. Their team is currently retrofitting a 1MW tugboat, the NH3 Kraken, which is on track to be the world’s first ammonia-powered vessel.

Deutsche Bahn (DB) and Fortescue Future Industries (FFI) are also collaborating to modify existing diesel engines to run on ammonia / hydrogen fuel with a view to powering railway locomotives and other large traction units, using Ammonigy’s ammonia cracking technology. A prototype converted diesel engine is currently being tested, with results expected later in 2024.

But Toyota and Chinese carmaker GAC are is bucking the big vehicle trend, with their development of a 2.0-litre four-cylinder engine capable of producing 161bhp. At a technology presentation in July 2023, GAC said it had overcome such issues as excess NOx emissions, and an increase in combustion pressure relative to petrol. “We’ve overcome the pain point of ammonia being difficult to burn quickly and put the fuel to use in the passenger car industry,” said Qi Hongzhong, an engineer at the GAC R&D centre in Guangzhou. “Its value to society and for commercial uses are worth anticipating.”

However many observers are sceptical of the move, in particular the difficulties involved in vehicle maintenance, ignition problems and breakdowns, which could involve the release of ammonia gas with deleterious health and environmental consequences. A further difficulty would be in fuelling up, with no retail filling stations offering the gas. However this may change. (And it’s not like recharge stations for electric vehicles are universally abundant.)

Ammonia as an Industrial Fuel

A remarkable 73% of UK industrial energy demand is for heat, and about half of that is for steam to drive industrial processes. Little if any of that demand for heat, currently supplied mainly by natural gas, is incapable of being replaced by a combination of electricity supplied directly from renewable sources, best used to drive heat pumps, and Green ammonia. There are also many opportunities for improving energy efficiency, which could shave as much as 15% from thermal demand.

There has recently been considerable focus on the use of hydrogen for smelting steel as an alternative to coal, and steel producers are already pressing ahead with the technology to satisfy growing demand for low carbon steel. Europe’s first such steel plant is due to begin production in 2025 at Boden in northern Sweden, using locally produced hydrogen powered by nearby hydropower and wind turbines, and production is anticipated to reach five million tonnes by 2030.

H2 Green Steel will use a direct reduction reactor in the place of a conventional coal-fired blast furnace, chemically stripping the oxygen from the iron ore to produce sponge iron and water. Not only is the process carbon-free, but it also reduces the volume of waste slag arising from steel production, which arises from the combination of mineral impurities in the ore, and coal ash.

The company recently completed an agreement with Spain’s Iberdrola to build a 1GW solar-hydrogen powered plant at an undisclosed location on the Iberian peninsula, which will produce two million tones of iron per year. "Green hydrogen will be a key technology in the decarbonisation of heavy industrial processes, such as steel production”, says Aitor Moso of Ibderola. “Innovative projects such as this will help accelerate the commercialisation of larger and more sophisticated electrolysers, making green hydrogen more competitive.”

Iberdrola will own and operate the solar generation plant while H2 Green Steel will own and operate the steel foundry, a cooperation model that appears certain to be reproduced elsewhere. According to H2 Green Steel’s Kajsa Ryttberg-Wallgren, "The project in Boden in northern Sweden has shown that there is a strong demand for green steel from a broad customer base. With two European locations, we will make an even greater impact, be closer to customers and be able to meet the demand of a growing market.”

Other such examples abound. Hybrit, another Swedish company, hopes to open a fossil-free green steel plant by 2026 in a joint venture with mining operator LKAB, Nordic steel company SSAB and energy company Vattenfall. In Japan, Nippon Steel has plans for a green steel plant, while competitor projects in France and Germany are also under way.