Decarbonization often comes down to finding creative uses for electricity. The playbook is simple. You take aprocess that traditionally burns fossil fuels, and then you replace it with an alternative that uses clean electricity instead. For instance, take acar, swap out an internal combustion engine for abattery charged from agrid with alot of wind and solar, and boom, you’ve got an electric vehicle that runs on cleanpower.
Of course, this is much easier said than done, especially for heavy-duty industrial processes like steel production. In these cases, many solutions rely on green hydrogen as asort of middleman. You can use clean electricity to produce hydrogen, and then burn hydrogen to make steel, with only water as abyproduct. Ajoint venture in Sweden is already producing fossil-free steel using this method, though still in relatively small quantities.
One company, MIT spinout Boston Metal, is aiming to streamline the process by eliminating the green-hydrogren step and instead using electricity directly for making steel. Its process is based on technology called molten oxide electrolysis that uses electric current to separate oxygen from iron ore, acritical step in the steel production process.
“The advantage that we have is that it’s aone-step process directly electrifying steel production,” said Adam Rauwerdink, Boston Metal’s vice president of business development.
Boston Metal has already raised $85 million from climatetech heavyweights like Breakthrough Energy Ventures, The Engine, Prelude Ventures and Energy Impact Partners, along with several industry coalitions and corporate venture groups. It aims to build its first commercial steel plant by 2024 or 2025, and then license its technology to major steel producers.
Green steel is abig deal
Decarbonizing the steel industry is amajor hurdle in dealing with climate change. Steel production is responsible for close to 7% of global greenhouse gas emissions, roughly equivalent to the annual emissions of all the cars on the world’s roads. But steel is also used to make cars, so these impacts are overlapping. And that gets to the very heart of why steel is such abig deal when it comes to climate change: It’s everywhere.
“You don’t realize when you look around your landscape how embedded and engrained [steel] is in society,” said Chathurika Gamage, climate intelligence manager at nonprofit research organization RMI. “Everything that we’re making, the buildings that we’re in — it’s providing structural stability, literally, to all of those spaces.” (Canary Media is an independent affiliate ofRMI.)
Producing 1ton of steel with traditional methods releases almost 2tons of CO2 into the atmosphere, and the world uses almost 2billion tons of steel eachyear.
In the short term, existing steel can be melted down with electricity and reused, which can displace the need for new product — but only to apoint. Most of the world’s steel needs can only be met with primary production because recycled steel doesn’t work for certain high-grade applications, and more significantly, there’s just not enough of it to keep pace with demand.
The traditional way to make steel is to melt iron ore at very high heat (over 1,500 degrees Celsius), then refine it from iron oxide into pure iron and fortify it with small amounts of carbon. It’s acomplex process that emits carbon at different stages. Some emissions come from the heating process, which usually involves burning aheat-refined form of coal called co*ke. Abit of the carbon from the co*ke gets dissolved into the iron, turning it into steel. Another chunk of emissions comes from chemical reactions that occur as the iron oxide is purified of its chemically bonded oxygen. That oxygen reacts with dissolved carbon and breaks off as carbon dioxide gas.
Over half of the emissions come from asingle piece of equipment used in the process: the blast furnace, where the iron ore is converted into aform called pigiron.
“Decarbonization of the iron and steel industry basically means decarbonization of the blast furnace,” said Zhiyuan Fan, aresearch associate at the Center on Global Energy Policy at Columbia University. “If you solve the blast furnace [issue], half of your problem isgone.”
Fan’s team at Columbia published a study last year comparing multiple strategies for decarbonizing steel and found that electrification is the key to canceling out emissions. The more the process can take advantage of clean electricity instead of burning coal and other fossil fuels, the easier it will be to reduce emissions. “We know how to decarbonize the grid better than we know how to decarbonize ablast furnace,” Fansaid.
The Columbia study found that green hydrogen appears to be the most promising route to decarbonizing steel, with hydrogen-powered direct reduction of iron as akey step in cutting the emissions from blast furnaces. This process is now being used in green steel projects in Europe, and some of China’s biggest steelmakers are exploring it aswell.
Molten oxide electrolysis — the technology used by Boston Metal — wasn’t considered in the analysis; the authors regarded it as too nascent to merit inclusion.
The need for more options to produce steel using clean electricity is what spurred Boston Metal to commercialize its technology, which had been developed years earlier in alaboratory at the Massachusetts Institute of Technology.
“Ten or 20years ago, the grid wasn’t clean, so it didn’t make any sense, and there was no demand for agreener version of steel, but now both of those are available,” said Rauwerdink of Boston Metal.
How molten oxide electrolysis works
The core principle of using electricity to refine metal has been around for awhile. In fact, electrolysis has been akey part of making aluminum for over 100years. Boston Metal’s molten oxide electrolysis process applies this technique to iron, which requires hotter temperatures. Aluminum electrolysis happens at temperatures just under 1,000 degrees Celsius, while iron electrolysis requires about 1,600°C, atemperature far hotter than molten lava.
To start, the iron ore is melted with heat produced from electricity. Then it’s placed in acell structured almost like agiant battery. At the top, an anode provides electric charge. At the bottom, acathode receives the electric charge. In between, the charge flows through an electrolyte, which in this case is ascalding bath of molten materials. The electrolyte contains avariety of elements bound to oxygen, including aluminum, silicon and calcium.
All of these oxides are more stable than iron oxide, so the iron oxide is the first to separate when exposed to electric charge, breaking down into pure oxygen and iron. The iron, still liquified, sinks to the bottom where it can be tapped out and turned tosteel.
According to Boston Metal, the composition of the electrolyte is acritical advantage of its technology. All of those other elements in the electrolyte are also present in iron ore as impurities, but the impurities stay behind in the electrolyte after the pure iron is removed. That means the process works even with low-grade iron ore, which is cheaper and more plentiful than higher-grade ore that has fewer impurities.
