How it began
Professor Kristian Birkeland was working on an electric cannon to fund his research on the northern lights when short circuits produced arcs and a smell of nitrogen oxide. On February 13, 1903 he met the engineer Sam Eyde at a dinner. Eyde held hydroelectric power rights and was looking for a way to extract nitrogen from air, and said he wanted the most powerful electrical discharge on earth. Within days they agreed to patent Birkeland's method. On February 20, 1903 Birkeland filed the application regarded as Norsk Hydro's first patent. The process was developed and tested at the university in Christiania, now Oslo.
How it works
Air is passed through an electric arc, a thermal plasma, formed between two water-cooled copper electrodes set between the poles of a strong electromagnet inside a furnace. The heat makes nitrogen and oxygen combine into nitric oxide. The gas is quenched rapidly to stop the reaction reversing, cooled, and oxidized to nitrogen dioxide, which is absorbed in water in towers to give a solution of about 30 percent nitric acid.
Who pushed back
The process was energy-intensive, consuming about 15 MWh per ton of nitric acid, and produced only 1 to 2 percent nitric oxide in the gas. It was outcompeted by the Haber-Bosch and Ostwald processes, which fix nitrogen with less energy, and declined by the 1920s.
What changed first
The process was the first plasma-based nitrogen fixation method to be commercialized and it ran on hydropower. Power supplied to the plant rose from 2.24 kW in 1903 to 238.6 MW in 1928. The patents formed the foundation of Norsk Hydro, and the factory town of Notodden grew to about 10,000 people by 1911.
Where it stands today
Haber-Bosch dominates nitrogen fixation. Cheap renewable electricity has renewed research interest in plasma-based nitrogen fixation for decentralized fertilizer production, with the Birkeland-Eyde process as the historical reference point. Researchers aim to cut the energy use of plasma processes from about 2.4 to below 0.7 MJ per mole of nitrogen in order to compete.
