The process of making steel is responsible for up to 9% of worldwide carbon emissions and almost a quarter of all industrial emissions. There’s chemistry involved: The blast furnace reduces the iron oxide content of the ore by blasting air and pulverizing coal into the melted ore. The carbon monoxide from the burning coal reacts with the iron oxide, producing iron and carbon dioxide, or: Fe2O3 + 3 CO → 2 Fe + 3 CO2.
Some companies, like Hybrit, are replacing coal with hydrogen, which combines with oxygen to make water. It has been called the first fossil-fuel-free steel because they were using hydrogen produced through the electrolysis of water with Sweden’s clean hydroelectric power.
But there is another way to separate oxygen from iron using electricity: Molten Oxide Electrolysis (MOE), where you melt the iron ore, add an electrolyte, and apply a serious amount of electricity. That’s the approach being taken by Boston Metal, which claims it has “cracked the code to electrifying steel manufacturing.”
I often run when I hear the phrase “cracked the code”—see just about every modular housing company we have shown—and the idea of molten oxide electrolysis has been around for a while to make very high-grade steel. One problem has been similar to that of aluminum: The anode was made of graphite, which was consumed in the process, releasing carbon dioxide.
The other problem is most electricity in the world is made by burning fossil fuels and electrolysis needs a lot of it; that’s why the greenest aluminum production is in Iceland and Quebec, Canada. But the world is changing as we try to electrify everything, and more renewable and clean electricity is coming on line every day.
Adam Rauwerdink, Boston Metal’s vice president of business development, tells Treehugger that “the cleaner grid makes this all possible.” He notes it takes a lot of electricity: 4 megawatt-hours per tonne of steel. For reference, the average house uses 11 megawatt-hours per year. Rauwerdink says this is less energy than is required for the HYBRIT process between the melting of the iron ore and the making of the hydrogen—about 5-6 megawatt-hours. He also says a “core innovation was the development of the metallic chrome and iron anode that isn’t consumed in the process.”
In the Boston Metal cell, “an inert metallic anode is immersed in an electrolyte containing iron ore and then electrified. The cell heats to 1600C, and electrons split the bonds in the iron ore. The result is a clean, high purity liquid metal that can be sent directly to ladle metallurgy — no reheating required.” The output is really pure iron, which can then be turned into steel with the addition of precise amounts of carbon or other alloys.
It’s very similar to the Hall-Heroult process of making aluminum, although the iron melts at a hotter temperature (1,600 degrees Celsius versus 1,000 degrees Celsius for aluminum), and the electrolyte is different (magnesia and silica) but it uses less electricity per tonne than aluminum because the chemical bond in aluminum oxide is stronger than that in iron oxide. Unlike aluminum, carbon has a greater affinity for oxygen than it does for iron, so historically it was easier and cheaper to make steel with coal than with electricity, which has always been expensive and was not emission-free. But now that we are worried about carbon dioxide emissions, the equation changes, and MOE starts to make sense.
Another major advantage of the Boston Metal design is that, as with aluminum production, it is essentially cellular. Unlike a blast furnace, there are no real harvests of scale, so if you want more MOE steel, you add more cells—and you can put them anywhere. But also, like aluminum, it needs a regular supply of baseload electricity; these cannot be run intermittently. That’s why Rauwerdink tells Treehugger they are talking with companies in Quebec, where there is so much hydroelectric base load.
Yet another advantage of Boston Metal’s MOE system compared to HYBRIT is its more flexible appetite for iron ore. Boston Metal tells Treehugger: “Although several steel manufacturers are starting to plan larger scale hydrogen DRI [Direct Reduced Iron] pilot projects, these technologies require iron ore with at least 67% purity, which currently makes up less than 5% of global iron ore supply. Using renewable electricity, Boston Metal’s modular molten oxide electrolysis (MOE) platform works with all iron ore grades to provide more value across the steel supply chain.”
When writing about HYBRIT and noting its projects for growth in the demand for steel between now and 2050, I worried about where they were going to get all the hydrogen they needed, particularly when they are competing with everything from fertilizer production to aviation. The Boston Metal solution uses electricity directly and can tap into the growth of low-carbon sources like hydro, geothermal, and whatever new technologies come down the wire. This looks promising.