Ammonia is the preferred carrier of hydrogen in the current wave of hydrogen export projects.
Wood Mackenzie’s Hydrogen Project Tracker, which monitors the progress of declared worldwide hydrogen supply projects, indicates that the majority of the Middle East, Australia, Latin America, and Africa’s more than 100 low-carbon hydrogen supply projects announced to date are export-oriented. Over 85% of the proposed capacity integrates ammonia and hydrogen in some way, with the ammonia primarily destined for export markets and the hydrogen primarily destined for domestic markets.
Ammonia is now favoured for hydrogen exports for three reasons: its high energy density; its established synthesis technique and supply chains; and its inherent ability to support decarbonisation.
Possibly the most significant technological impediment to global hydrogen trade is the sheer volume of hydrogen at normal temperatures and pressures. This can be addressed by compressing the hydrogen to a pressure of generally greater than 200 bar and delivering it via pipelines or tanks by ship. Alternatively, hydrogen can be liquefied by lowering the temperature to -253 °C, which reduces its volume to 1/800th of its typical volume.
Utilizing hydrogen carriers such as ammonia (NH3) in liquid form at low pressures has the advantage of having a threefold energy density compared to compressed hydrogen and a 1.5fold energy density compared to liquefied hydrogen. As a result, using ammonia to carry hydrogen across long distances requires significantly fewer ships to deliver the same amount of energy.
Ammonia synthesis, storage, and transportation are all well-established industries. The existing market for ammonia is around 180 million tonnes per year (Mtpa), with the majority of it being integrated with the manufacture of derivatives such as urea or fertilisers such as ammonium nitrate. At the moment, the seaborne trade in ammonia is roughly 20 Mtpa, while a world-scale ammonia factory produces around 2 Mtpa.
By contrast, commercialization of compressed hydrogen ships has not yet occurred, despite the fact that tiny volumes of compressed hydrogen are transported using trailer-cylinders. The largest proposed liquid hydrogen facilities range in capacity from 15 to 30,000 tonnes per annum, while the sole liquid hydrogen ship currently under construction — a proof-of-concept vessel by Kawasaki Heavy Industries – has a storage capacity of approximately 100 tonnes. Although liquid organic hydrogen carriers (LOHC), such as toluene/methylcyclohexane systems for hydrogenation/dehydrogenation processes, have been piloted, the technology is still in its infancy.
Methanol is another hydrogen derivative that has the potential to be utilized as both a carrier and a clean fuel. However, due to its carbon concentration, the latter generates some emissions.
While hydrogen carrier technology in general will continue to advance, a large-scale supply network for ammonia currently exists.
Low-carbon ammonia is also being recognized as a decarbonisation fuel in and of itself. It can be used in place of grey ammonia or other fossil fuels in existing industries and has the potential to grow in new ones as well. Nuclear-averse nations such as Japan and Germany are particularly enthusiastic about the prospect of employing ammonia in power generation, while South Korea has declared intentions to incorporate ammonia into its thermal power plants, thereby replacing 20% of its coal consumption. Ammonia’s function in the heating sector is also expanding, including as a clean heat exchanger in heat pumps.
Ammonia could potentially be involved in transport. This is especially true in the marine bunkering sector, where engine manufacturers are designing internal combustion engines for ships that can operate on dual fuel, including ammonia, in order to satisfy the International Maritime Organization’s decarbonisation requirements. Additionally, some believe that ammonia fuel cells operating at high temperatures and utilizing solid oxide electrolyzers can function similarly to hydrogen fuel cells. And, if hydrogen storage sites become limited, ammonia may emerge as a viable commercial energy storage medium.
Ammonia is not without complications. While it has a higher energy density than liquid hydrogen, it is a fraction of the price of LNG and gasoline, making its manufacturing and transportation expensive. As a hazardous chemical, its manufacturing and handling are controlled in established sectors, and the risk of leakage or spillage will constrain demand in developing end uses.
While ammonia is a hydrogen carrier that may be freed through cracking or reversing the synthesis step, scaling up this technique presents technical and commercial obstacles. Ammonia is unlikely to substitute hydrogen as a fuel in all areas, and hence new commercially viable methods of transporting hydrogen over long distances on a large scale are expected to arise. As a result, ammonia as a hydrogen carrier is unlikely to be the final solution for hydrogen trading.
Low-carbon ammonia, on the other hand, has the potential to play a substantial role in global decarbonisation, both in old and new ammonia markets. Existing technologies and supply networks can simply be used to provide cost-effective long-distance transportation.
As a result, it’s unsurprising that ammonia is a major component of the current generation of hydrogen export projects. However, in order to succeed, the several potential suppliers must gain a clearer understanding of the true size of the future low-carbon ammonia market.