Green Ammonia Production

Illustration of the process steps of making green ammonia

Renewable electricity provides the energy for all processes described here. Depending on regional availability solar, wind, hydro or nuclear power can power the four key processes: desalination, electrolysis, air separation and Haber-Bosch.

Illustration of desalination process
Desalination of sea water

Desalination

Unless sufficient fresh water is available, sea water can be processed to a quality sufficient for electrolysis. For each kg of ammonia approximately 1.6l of water are needed. With Reverse Osmosis, the electrical energy required for 1t of ammonia is less than 1 kWh.




Illustration of and electrolyser
Electrolyser

Electrolysis

Electrolyses split the water into hydrogen and oxygen. The oxygen itself has potential value and could feed into processes not considered here. To produce 1t of hydrogen approximately 50MWh are required. The cost of the electrolyser itself is expected to fall from around $900 to as little as $400 in the next 10-20 years if GW scale is achieved. (Saba, 2018)




Illustration of the process steps of making green ammonia
Air Separation Unit

Air separation

The nitrogen needed for the ammonia generation is readily available from the ambient air, which consists to 78% of nitrogen. A tonne of nitrogen requires 80kWh of electrical energy.




Illustration of Haber Bosch process
Haber-Bosch process

Haber Bosch

The Haber Bosch process converts nitrogen to ammonia by a reaction with hydrogen using a metal catalyst. A tonne of ammonia requires 176kg of hydrogen and 824kg of nitrogen. Electrically driven Haber Bosch processes can produce a tonne of ammonia from 1.16MWh. (Smith, 2020)

References

  • S. M. Saba, M. Müller, M. Robinius, and D. Stolten. The investment costs of electrolysis – a comparison of cost studies from the past 30 years. International Journal of Hydrogen Energy, 43(3):1209–1223, 2018.
  • C. Smith, A. K. Hill, and L. Torrente-Murciano. Current and future role of haber–bosch ammonia in a carbon-free energy landscape. Energy Environ. Sci., 13:331–344, 2020.