Brief description

The Birkeland-Eyde Process was one of the earliest industrial processes for fixing atmospheric nitrogen to produce nitrogen-based synthetic fertilizers and nitric acid. Developed by Norwegian scientist Kristian Birkeland and industrialist Sam Eyde in 1903, it utilizes a high-energy electric arc to force atmospheric nitrogen and oxygen to react, bypassing the need for ammonia or fossil fuels.

Use / Function

Nitric Acid Production: Yields dilute nitric acid, an essential chemical for manufacturing industrial explosives and chemicals.
Nitrogen-Based Fertilizer Production: Allowed the manufacture of calcium nitrate (“Norway saltpeter”), the first synthetic nitrogen fertilizer that helped sustain global agricultural yields before Haber-Bosch.
Scale: Heavy industrial chemical processing, requiring highly specialized electrical infrastructure and massive power input.

Operating principle

The process mimics the natural action of lightning to chemically bind atmospheric nitrogen and oxygen in three main chemical reactions:

Nitrogen Fixation (Electric Arc): Air is pumped through an intense, flat electric arc (magnetic plasma flame) maintained at temperatures around 3000°C. Under this extreme heat, nitrogen ($N_2$) and oxygen ($O_2$) combine to produce nitric oxide ($NO$):

$$\text{N}_2 (g) + \text{O}_2 (g) \leftrightarrow 2\text{NO} (g) \quad (\Delta H = +180 \text{ kJ/mol})$$

To prevent the nitric oxide from decomposing back into raw gases, the hot air is rapidly cooled to below 1000°C as it leaves the furnace.

Oxidation: The cooled nitric oxide gas is further cooled to around 50°C and reacted with excess atmospheric oxygen to produce nitrogen dioxide ($NO_2$), a reddish-brown gas:

$$2\text{NO} (g) + \text{O}_2 (g) \rightarrow 2\text{NO}_2 (g)$$

Absorption: The nitrogen dioxide gas is piped into absorption towers where it is absorbed by trickling water to form nitric acid ($HNO_3$):

$$3\text{NO}_2 (g) + \text{H}_2\text{O} (l) \rightarrow 2\text{HNO}_3 (aq) + \text{NO} (g)$$

To produce solid fertilizer, the nitric acid is reacted with limestone (calcium carbonate, $CaCO_3$) to yield calcium nitrate ($Ca(NO_3)_2$).

How to implement

1. Electric Arc Furnace

Construct a furnace with two water-cooled copper electrodes placed close together.
Connect a massive electric generator supplying high-voltage alternating current (AC).
Place the electrodes in the field of a strong electromagnet. The magnetic field flattens the electric arc into a wide, circular disc of plasma (up to 2 meters in diameter), maximizing contact with incoming air.

2. Rapid Cooling Heat Exchangers

Route the hot gases from the furnace through a high-pressure steam Boiler.
This serves a dual purpose: it instantly chills the gases to preserve the nitric oxide yield and generates useful steam power for other plant operations.

3. Acid Absorption Towers

Erect a series of tall granite or acid-proof brick towers packed with acid-resistant quartz.
Use a water-pump system to trickle water down from the top of the towers while gas flows up from the bottom.

Materials needed

Atmospheric Air: Sourced directly from the environment.
Water: Used for cooling the electrodes and absorbing the gases to form acid. Sourced from Water.
Copper: For the water-cooled electrodes. Sourced from Copper.
Nitric Acid ($HNO_3$): The primary chemical output of the process. Sourced from Nitric Acid.
Refractory and Granite Blocks: To build the high-temperature furnace chamber and corrosive gas absorption towers.

Variants and improvements

Haber-Bosch and Ostwald Process: The ultimate improvement. The Birkeland-Eyde process was highly inefficient, consuming about 15 megawatt-hours of electricity per ton of nitric acid produced. It was replaced by combining Haber-Bosch (producing ammonia) with Ostwald’s catalytic oxidation, which consumes only a fraction of the electricity.

Limits and risks

Extreme Energy Consumption: The process is economically viable only where extremely cheap, abundant electricity (such as hydroelectric power) is available.
Electrode Degradation: The intense electric arc slowly vaporizes the copper electrodes, which require regular replacement and maintenance.
Nitrogen Dioxide Hazard: Nitrogen dioxide gas is extremely toxic and corrosive. Any leaks in the absorption or transport piping pose immediate respiratory hazards to operators.