How green steel made with electricity can clean up a dirty industry


Industrial steelmaking spews out about two tons of carbon dioxide emissions for every ton of steel produced, representing nearly 10% of such emissions worldwide. The global steel market is expected to grow by about 30% by 2050, the date when some of the largest steel producers committed to achieving net-zero emissions. Unless big changes in the industry come, and soon, that goal may be unattainable.

Boston Metal’s new reactor, recently installed at its headquarters just north of Boston, is an important step towards becoming a commercial steel producer. Since its inception in 2013, the startup has developed a process to make green steel, working out the details in smaller vessels. The new reactor, along with an upcoming fundraising round, represents the next leap for the company as it tries to scale.

Indeed, if Boston Metal can scale up its clean manufacturing process and gain access to enough renewable electricity to run it, the company could help solve one of the world’s biggest challenges in controlling carbon emissions.

A new approach

Steel is used in everything from cars to buildings to wind turbines, but decarbonizing the industry isn’t glamorous. “People don’t pay too much attention to the industry,” said Boston Metal CEO Tadeu Carneiro. “It’s a very conservative industry and it’s hard to cut down.”

Fossil fuels are essential for current steel production. Most steel production begins in a blast furnace, where a coal-derived material called coke, which is nearly pure carbon, reacts with iron ore, a mixture of iron oxides and other minerals. The reaction pulls out the oxygen and leaves behind liquid iron. The carbon and oxygen are then released together as carbon dioxide.

Boston Metal’s solution is an entirely new approach called molten oxide electrolysis (MOE). Rather than using carbon to remove oxygen, the process relies on electricity, which runs through a cell filled with a mixture of dissolved iron oxides along with other oxides and materials. The electricity heats the cell to about 1600°C (nearly 3000°F), melting everything into a hot oxide soup.

In addition to heating things up, electricity drives the oxygen-removing chemical reactions. Molten iron collects at the bottom of the reactor and oxygen gas is emitted instead of carbon dioxide.

Because the impurities remain largely out of the reaction, the MOE process can handle low-quality iron ore, which could be a major advantage of the technology, Carneiro says.