Innovations in ‘green’ ammonia production
Ammonia is considered the lowest-cost ‘green fuel’, and the shipping industry sees it as a possible solution for decarbonising its fleet. Green ammonia can be produced using renewable-energy powered Haber–Bosch (HB) plants. The HB process converts atmospheric nitrogen into ammonia by reacting hydrogen with iron metal. The HB process, although energy-efficient, is only cost-effective at very large scales. The process is not suitable at the smaller scale.
Smaller-scale decentralised ammonia production
“In this project, we wanted to transition away from large, centralised ammonia plants with high-energy consumption and CO2 emissions towards smaller-scale decentralised ammonia production facilities,” explains ORACLE project coordinator Emil Drazevic from Aarhus University in Denmark. “To be truly renewable, the electricity used also needs to be produced from renewable sources such as wind turbines and solar photovoltaic cells.” The idea is that a decentralised model of ammonia production could help small-scale users use ammonia as a renewable fuel, perhaps to power equipment and provide heating, all without producing CO2.
Plasma, electrocatalytic and catalytic approaches
To demonstrate the feasibility of producing ‘green’ ammonia, the ORACLE project brought together eight partners, including two research centres from Japan. “This project was also unusually complex because we wanted to test not just one but three different technologies,” says Drazevic. “These were a plasma-based approach, an electrocatalytic approach and a purely catalytic approach.” Small reactor prototypes were built to synthesise ammonia using the three identified approaches. From this, a number of key insights were gained. The catalytic approach for example (the HB process), which produces heat in a similar way to how an induction cooker produces heat, was shown to be highly efficient. Both the plasma and electro-catalytic reactors also surpassed production expectations, but with lower energy efficiency and higher energy consumption. “A key lesson learned is that, apart from the plasma source, the reactor geometry of the plasma-based approach needs to be adapted in order to reduce energy consumption,” adds Drazevic. “We also learned that energy consumption in the electro-catalytic approach is linked to the presence of lithium, which is something that could be changed.”
Viable strategy for greening ammonia production
The ORACLE project was able to demonstrate that the renewable production of ammonia is feasible and has helped to identify potential next steps in refining the technology. “We surpassed all our aims in terms of reaction efficiencies,” notes Drazevic. “We now need to make more progress in terms of lowering energy consumption.” This is likely to be a key area of further research. Another important success has been the demonstration that a decentralised approach could be a viable strategy for greening ammonia production. “Centralised ammonia plants require an immense upfront capital cost,” says Drazevic. “Splitting this into a number of smaller plants can help to share the burden of the cost and speed up the energy transition.” Indeed, if ammonia is to become a fuel of the future, the sector must find ways to decarbonise. Ammonia production consumes around 1.8 % of global energy output each year and produces as a result about 500 million tonnes of CO2. The ORACLE project has shown that technological solutions to addressing these challenges are advancing, and that decentralised approaches could be one cost-effective solution. Synergies between the three approaches have been identified, and exploitation of them is expected in the near future.
Keywords
ORACLE, ammonia, fuel, renewable, carbon, turbines, photovoltaic
