As countries aim to transition to net zero emissions (NZE), demand grows for low-carbon alternatives to fossil fuels. Ammonia has several advantages as a clean fuel over alternatives such as hydrogen. It has a higher energy density in liquid form than hydrogen and can be easily liquefied, transported, and stored using existing and new infrastructure.
Ammonia can be burnt in boilers, gas turbines, internal combustion engines, and furnaces to partially or totally displace fossil fuels without needing major modifications to the process or system. It emits no CO2 when burnt. Emissions of nitrous oxide and NOx from ammonia combustion can be controlled to the levels required using existing technologies, making ammonia a viable clean fuel for decarbonisation.
Current production of ammonia is predominantly based on unabated fossil fuels which is carbon intensive. The carbon footprint of fossil fuel-based ammonia can be reduced substantially by implementing best available technologies and carbon capture. There are several established pathways for the commercial production of clean ammonia including water electrolysis run on renewable power (renewable ammonia), steam methane reforming (SMR) of natural gas and coal gasification both integrated with carbon capture (low-carbon ammonia), all followed by the Haber-Bosch process.
New technologies are emerging that can synthesise ammonia with an even lower carbon footprint. Low-carbon ammonia can have low life cycle emissions, comparable to those of renewable ammonia. Hence, as a clean fuel, both renewable and low-carbon ammonia can play a critical role in decarbonising hard-to-abate sectors.
At present, production costs of renewable ammonia are 2–3 times higher than those for unabated ammonia, which is a big obstacle to its large-scale deployment. Low-carbon ammonia is also more expensive than unabated ammonia but is much cheaper than renewable ammonia. With appropriate supportive policies, low-carbon ammonia could become competitive with unabated ammonia making it a viable clean fuel relatively quickly and cheaply, with a role in bridging the transition towards renewable ammonia use in the longer term.
There is active RD&D in ammonia combustion technologies for applications in coal- and gas-fired power generation, shipping, and industrial processes. Studies show that the combustion characteristics of ammonia do not prohibit its use as a fuel and existing technology can deliver commercial performance within regulatory limits for emissions of NOx and nitrous oxide. Cofiring up to 30% ammonia with coal has been demonstrated at coal power generating units in Japan and China.
There are several initiatives, mostly in Asia, but also in South America and Europe, to implement ammonia firing or cofiring technologies in existing and new coal and gas power plants. Efforts continue to increase the ammonia ratio to 50%, and eventually to 100%. Interest is growing in the direct combustion of ammonia in gas turbines; construction of ammonia-fired gas power plants is planned. It is expected that initial technology demonstrations of ammonia firing and cofiring at various types of commercial power plants will occur around 2025, followed by large-scale implementation nearer 2030.
All clean ammonia technologies will involve additional costs when compared with conventional processes. To overcome the cost barriers to wider and large-scale deployment of clean ammonia fuel utilisation, a technology-neutral approach should be adopted. To realise the potential benefits of clean ammonia fuel to a clean energy transition at the least cost, it is important that the roles of all clean ammonia production routes including renewable ammonia, low-carbon ammonia from fossil fuels with carbon capture and biomass, are considered objectively and on their merits.