Ammonia is portable, storable, energy-dense, and it also possesses certain properties that make it suitable for use as an energy storage medium, a hydrogen carrier and as a fuel. Like fossil fuels, ammonia is both a chemical energy store and a fuel. The crucial difference is that ammonia does not contain any carbon.
Combustion of NH3 produces H2O and N2, whilst combustion of, for instance, natural gas (CH4) releases CO2 and H2O. Ammonia can be directly burned in internal combustion engines (ICE), gas turbines and coal-fired boilers with minor modifications, or be fed into a fuel cell (FC) to produce electricity. Therefore, low- or zero-carbon ammonia, also known as blue or green ammonia, can be used as a clean fuel replacing fossil fuels for power generation, transport and in industrial processes to reduce carbon emissions. However, there are challenges in burning ammonia in existing combustion systems designed for hydrocarbon fuels such as higher ignition energy, slow flame velocity, low radiation intensity and possibly increased N2O and NOx emissions. Studies indicate that these challenges can be overcome by proper engineering design and system optimisation, and using existing De-NOx technologies. Consequently, ammonia can replace hydrocarbon fuels for use in power generation, transport, and industrial processes. Extensive R&D is underway and developments in ammonia combustion technologies are progressing in fast pace.
Significant progress in cofiring ammonia and coal for power generation has been made in Japan. In 2017, Chugoku Electric Power Corporation of Japan successfully demonstrated the cofiring of ammonia and coal, with a 1% share of ammonia (in terms of total heat rate) at one of their 120 MWe commercial coal power generating units. The test results showed the ammonia was completely burnt and no NH3 was detected outside the plant. NOx emissions were not significantly different from those of 100% coal-firing, and the Japanese environmental standards were met. Currently, work is underway for commercial demonstration of 20% ammonia cofiring at a 1000 MWe unit in Japan’s Hekinan coal power plant, which is scheduled for 2024. Japanese companies are also working to develop an ammonia single-fuel burner for coal boilers, and aiming to verify cofiring with at least 50% ammonia at two units with different types of boilers by 2028. Developments in ammonia-coal cofiring technologies have also been made in Korea and China.
When fully developed and commercialised, the technologies can provide an alternative approach to decarbonise coal power generation. This is especially important for countries and regions such as China, India and Vietnam that have a young coal fleet, or have limited available low-carbon dispatchable resources. For power plants that have no easy access to carbon storage sites or have limited remaining life so carbon capture and storage (CCS) is not a viable option, ammonia combustion/co-combustion can provide a means for CO2 reduction. Cofiring ammonia can allow existing assets to continue operating even when climate regulations are tightened, thereby reducing the risk of becoming stranded assets. This is particularly the case in the East and Southeast Asia.
Ammonia-gas cofiring technologies for gas-fired power generation are under development. Although the technologies currently have a lower technology readiness level than hydrogen cofiring, gas turbine manufacturers have announced plans to offer commercial ammonia-fired turbines as early as 2025. Efforts have also been made to explore the use of ammonia fuel in industrial furnaces. The work is preliminary and is being carried out mostly in Japan with some positive results.
Ammonia is a suitable fuel for transport, especially for heavy good vehicles, trains and shipping where large amounts of energy are required for extended periods of time and where batteries or direct electrical connection are not practical or cost effective. Marine vessels and trains may be best positioned to use ammonia fuel because they can accommodate heavier engines and larger fuel tanks more easily, and ammonia fuelling stations can be built at ports and railway stations. In 2018, the International Maritime Organisation (IMO) set the Initial GHG Strategy with the main goals of cutting annual GHG emissions from international shipping by ≥50% from 2008 level by 2050, and working towards phasing out GHG emissions from shipping entirely as soon as possible. Several recent studies have all identified fuel-switching to ammonia as one of the most compelling options to help achieve this goal.
Ammonia can be burnt in both purposely designed and modified ICE, either in pure form or in a blend with other fuels such as petroleum fuel. However, due to the higher ignition energy of ammonia most existing combustion engines that use ammonia as fuel typically require a combustion promoter (known as secondary fuel or ignition fuel) such as hydrogen, gasoline, and diesel for ignition, operation at low engine loads and/or high engine speed. At present, R&D is ongoing to develop and optimise engine and turbine designs for burning pure ammonia or blends of ammonia with, for instance, petroleum fuel or natural gas for road and marine transport. Recent advances in FC technologies are proving that ammonia-fed FC can be a viable option.
Since 2019, MAN Energy Solutions (MAN ES) of Germany has been working to develop a ammonia propelled two-stroke engine. MAN ES is to integrate existing technology in the ammonia-based propulsion system while designing the ammonia fuel injection, combustion components, exhaust gas De-NOx system and engine components. This project is now supported by the Innovation Fund Denmark and scheduled to install the first ammonia engine in a commercial vessel in 2024. In Japan, MAN ES is collaborating with a consortium of five Japanese heavyweights in the shipping industry to develop ships that run on ammonia and go beyond onboard ship technology including ammonia supply and distribution facilities. MAN ES is also working with Shanghai Merchant Ship Design & Research Institute (SDARI) and American Bureau of Shipping (ABS) to development an ammonia dual-fuelled feeder container vessel.
In 2019, the Japan Engine Corporation (J-ENG) and the National Maritime Research Institute (NMRI) launched a R&D program focusing on engine development for the combustion of carbon-free fuels including hydrogen and ammonia. A diesel engine was modified to operate on a dual fuel mix of light oil and 20% ammonia (by energy content). and an exhaust gas aftertreatment device to mitigate emissions of N2O, NOx, and unburned NH3 was developed. Due to the lower energy density, ammonia weighs about twice as much and requires over 2.5 times more space to contain the same amount of energy as heavy fuel oil – a factor to consider in the design phase. Therefore, NMRI also examined ship design from the perspective of fuel storage. In August 2020, NYK Line, Japan Marine United Corporation and Nippon Kaiji Kyokai (ClassNK) signed a joint R&D agreement to commercialise an ammonia-fuelled gas carrier that would use ammonia as the main fuel, in addition to an ammonia floating storage and regasification barge for offshore bunkering and stable supply of ammonia fuel.
In Europe, the Finish technology group Wärtsilä started full scale tests on ammonia-fuelled marine combustion engines in early 2020 with some encouraging results. In one test, the engine performed well when running on a fuel mix containing 70% ammonia at a typical marine load range. As part of DEMO2000 programme supported by the Norwegian Research Council, Wärtsilä is to test ammonia in a marine four-stroke combustion engine in Norway. Wärtsilä is also developing ammonia storage and supply systems as part of the EU’s ShipFC project. The company has already gained significant experience with ammonia from designing cargo handling systems for liquid petroleum gas carrier vessels used to transport ammonia. Norway’s Color Line has plans to pilot ammonia as a marine fuel. A 16-party consortium has been launched to conduct the case study with Color Fantasy, the world’s largest roll-on/roll-off cruise liner, as the object. Color Fantasy currently burns around 25,000 t/y of bunker fuel and, if the vessel is converted, it will require around 60,000 tNH3, which must be stored and distributed locally.
Ammonia-fuelled road vehicles operate in much the same way as gasoline-driven vehicles, which means that they can generally be built and maintained in the same way as the current vehicle fleet. Most vehicles on the road could be modified to run on a mixture of ammonia and petroleum fuel, and several vehicles powered by ammonia have been demonstrated. For example, a NH3-fuelled truck was developed in 2007 which drove across the USA powered by a mix of ammonia and gasoline. In 2013, South Korean researchers successfully road-tested a dual fuel passenger car that runs on a mixture of ammonia and gasoline in a ratio of 70:30, and an ammonia/gasoline hybrid sports car was displayed at the Geneva Motor Show. A US company, Raso Enterprises, is offering conversion kits, NH3CAR, for cars to run on ammonia. The NH3CAR conversions are automotive dual fuel (gasoline and anhydrous ammonia) systems that provide additional NH3 fuel to the engine depending on the engine’s operating conditions.
In 2019, Canadian company TFX International announced a $2 million Canadian dollar ($1.5 million) project to convert two diesel fuelled generators and transport trucks to use ammonia fuel over three years. The multi-fuels engine retrofit systems developed by Ontario-based Hydrofuel Inc. will be used. After the conversion, the trucks will operate on a dual fuel basis in either a ‘low emission’ configuration that uses diesel and ammonia, or a ‘zero emission’ configuration that uses hydrogen/oxygen assisted NH3 fuel. Despite all the developments and advances in ammonia fuelled ICE technologies, the future of ammonia in the car market is uncertain because battery-powered electric vehicles are currently more economical and are already an established technology.
It is clear that ammonia as a low-carbon fuel can be used to address decarbonisation challenges across power generation, transport and industrial processes. It is likely that coal power plants and shipping vessels will be among the first to deploy ammonia combustion technologies to decarbonise.
Several projects are underway with the first commercial demonstrations scheduled to start in 2024-25, and more similar projects can be expected in the following years. A new report The Potential Role of Ammonia in the Clean Energy Transition (to be published soon) by the International Centre of Sustainable Carbon (ICSC) provides a more detailed review of the recent developments in ammonia combustion technologies and ammonia fuel use.
A successful uptake of ammonia as a clean fuel faces several challenges. In my next blog, I will discuss the challenges and opportunities of utilising ammonia as a fuel, the potential carbon emission reductions that can be achieved by substituting fossil fuels with ammonia for power generation including life cycle analysis.