Electrified Steelmaking Could Cut Five Percent of Global CO2 Emissions

How Boston Metal's electrolytic cell processes metal using electricity. (Source: MIT Technology Review.)

A new approach to making steel could cut five percent of global greenhouse gas emissions from the steel production process.

Boston Metal has created a high-strength steel alloy using a process that replaces the blast furnace—used for centuries to forge steel—with an electrolytic cell that uses electricity to process iron ore.

Conventional steelmaking involves a smelting process that combines iron oxide with a coal-based fuel called coke at high temperatures. The coke is turned into carbon monoxide, which pulls oxygen from the iron, forming carbon dioxide. The resulting substance, called pig iron, is then processed into steel.

However, the process pumps about 1.7 gigatons of carbon dioxide into the atmosphere—or about five percent of global carbon dioxide emission, according to a paper in Science Magazine. This makes the steel industry one of the biggest polluters on the planet.

Boston Metal’s molten oxide electrolysis (MOE) process uses an electrolytic cell, which produces an electric current to break down compounds, forcing the oxygen out of the iron ore without the use of coke—and without creating carbon dioxide.

The company’s prototype is a squat metal cylinder with a chimney-like tube. The “chimney” is an anode, and a thin metal layer on the bottom of the cell functions as the cathode. Together they form a pump that pushes electrons through a liquid oxide electrolyte in the chamber. The iron oxide is dissolved by the other oxides, which act as a solvent at high temperatures without decomposing. The freed oxygen from the iron oxide rises to the top as the resulting molten iron sinks to the bottom.

Boston Metal co-founder Donald Sadoway holds a bar of steel made with his company's electrolytic cell. (Source: Boston Metal.)

Traditional smelting uses carbon to make the final steel product stronger. But steel made via MOE wouldn’t be as strong, which is a big concern for the steelmaking industry. The company believes that this shortcoming can be resolved by adding carbon and other ingredients as the metal cools.

The company plans on building a demonstration facility to produce ferroalloys, which are used to make certain grades of steel and will be its initial target market. Boston Metal is also designing a full-scale cell for producing steel within seven years.

Boston Metal acknowledges that a lot of work is still needed. The technology needs further refining and testing. And the company needs to prove that electrified steel is cheaper than using coke, as indicated in its modelling.

Comparison of cost per tonne of steel between "green" premium steel (orange), coke-based smelting (white), and MOE (molten oxide electrolysis; green). (Source: Boston Metal.)

Greenhouse gas emissions would be further reduced if the electrolytic cell were to run on clean electricity sources.

If the MOE process proves viable and affordable at industrial levels, it could have a profound impact on an industry that is one of the heaviest polluters in the world.

Read more about green construction materials at Scientists Create “Green” Concrete.