IN PURSUIT OF
GREEN STEEL
From hydrogen to electrolysis to lasers, innovators are devising new processes to decarbonize the crucial alloy humanity can’t live without.
Written by Lina Zeldovich
Limelight Steel uses the power of laser light to electrify the ironmaking process—with zero emissions and up to 20 percent energy savings. Photo: Limelight Steel
THE 20TH CENTURY WAS THE AGE OF STEEL. Its defining skyscrapers and suspension bridges, its fleets of automobiles and tanks, its household appliances, cargo containers—even components of the machines that took humans to the moon—were made of the material. And crude steel production exploded to meet that demand, increasing from 28 million metric tons in 1900 to 191 million metric tons in 1950 to 850 million metric tons in 2000.
And yet, for all the emphasis of emerging digital technologies with its use of optical fiber, silicon chips, and highly engineered polymers, steel consumption hasn’t slowed. In 2023, the world cumulatively produced about 1,849.7 million metric tons of crude steel.
While the technological aspects of steel production evolved greatly, the basic principle hasn’t changed much since, well, the Iron Age. The first step is to heat iron ore, a material where iron atoms are bound to oxygen or other impurities, in the presence of carbon-rich charcoal. The carbon strips the oxygen from the ore, leaving behind iron metal mixed with a lot of carbon—an alloy called pig iron. Humans later discovered that removing some excess carbon from pig iron could yield an alloy that was both stronger and tougher than iron itself.
“The same tech we were using in the Iron Age is basically what we’re using today,” said Adam Rauwerdink, senior vice president of business development at Boston Metal. “The incumbent process has served humanity quite well for a few thousand years.”
Carbon—in the form of charcoal or coke, a fuel made from heating coal or petroleum in a low-oxygen environment—has been essential for steelmaking from the beginning, but it has only been recently that the emissions from blast furnaces have drawn attention from engineers. According to the International Energy Agency, the production of one ton of steel creates 1.8 tons of carbon dioxide emissions. The steel industry as a whole is responsible for producing anywhere from 7 percent to 11 percent of the world’s carbon emissions. The exact figure depends on what you include, explained Hilary Lewis, steel director at Industrious Labs, an environmental organization that works to develop more sustainable steel production technology. “The 11 percent includes methane emissions to make coke from coal,” Lewis said.
Those carbon emissions were part of the big run-up in steel production from 1900 and today, but they are no longer sustainable. That’s why efforts to “greenify” the industry are underway. Across the world, steelmakers are exploring alternative methods of turning iron into steel with ambitious goals of drastically reducing greenhouse gas emissions—as close to zero as possible.
In March 2024, the U.S. Department of Energy announced $6 billion to decarbonize energy-intensive industries, steelmaking being one of them. The goal is to develop a way to strip oxygen from iron ore without relying on the carbon sources that have sustained the industry for millennia.
Workers transport equipment past a semi-industrial electrolytic cell, behind, a device that uses electric current to produce liquid iron, at Boston Metal’s Woburn, Mass., facility. Photo: Boston Metal
“We’re using the power of the electrons to do what historically would have been done with the carbon atom.”
– Adam Rauwerdink, senior vice president of business development at Boston Metal.
REDUCES
Ancient steelmaking was a small-batch effort. In the Industrial Age, steelmaking advanced through the use of blast furnaces to melt the iron ore, coke, and limestone (to remove impurities from the ore) while blasting in hot air. “Those run on coal, they started running on coal, and they run on coal today,” said Kaitlyn Ramirez at RMI, (formerly Rocky Mountain Institute), a think tank that works to decarbonize the global energy system. “This traditional steelmaking with the blast furnace is very emission-intensive, as well as producing many other pollutants that impact air quality,” Ramirez said.
While blast furnaces start with iron ore, a lot of steel today is recycled and remelted, a process which requires less energy and emits fewer greenhouse gases. The recycled steel, which comes from construction scraps, cars, appliances, and other sources, is melted inside electric arc furnaces, skipping the reduction step. Worldwide, only 30 percent of steel comes from electric arc furnaces, though that fraction rises to 70 percent in the United States. While in theory steel is infinitely recyclable, recycling scrap steel can’t meet a demand that is growing the way current demand is.
One alternative that can cut carbon emissions from ironmaking is direct reduced iron (DRI), in which natural gas or methane is first reformed into hydrogen and carbon monoxide at high temperature, and then blown at the iron ore inside shaft furnaces. The two highly reactive gases split oxygen atoms from the ore, without actually melting the iron. To make steel, the DRI is then melted in electricity-powered arc furnaces. DRIs produce half of the emissions of coal-fired blast furnaces, but they still require fossil fuels and energy inputs to reform methane.
“It is cleaner in comparison, but it’s not near zero,” Ramirez said.
To develop the DRI concept to a fully zero-emissions process, the Department of Energy tapped two steelmakers, Swedish SSAB and American Cleveland-Cliffs, to potentially receive up to $500 million each for “green steel” projects in the United States using clean hydrogen instead of carbon-based fuels. The hydrogen will play a double role—as a fuel and a reduction agent.
A sample of SSAB’s “fossil-free steel.” Photo: SSAB
The Swedish steel manufacturer SSAB has produced “fossil-free steel” using hydrogen. The first customers are the Volvo Group and Mercedes Benz AG. Mercedes wants to build all cars with fossil-free steel by 2039. Video: SSAB
Steelmaker SSAB has already established a joint venture with sustainable iron ore producer LKAB and power company Vattenfall, launching a ironmaking plant in 2020, in Luleå, Sweden, to pilot the new process. Called HYBRIT, which stands for Hydrogen Breakthrough Ironmaking Technology, the system starts by producing hydrogen by way of electrolysis—using green electricity (from hydropower plants or wind farms) to split water into oxygen and hydrogen. The system then channels the hydrogen to a furnace where it’s blasted at the stream of small iron ore pellets—pea-sized beads, about five to eight millimeters in diameter. Hydrogen draws oxygen away from the iron oxides the way carbon monoxide would, but instead of forming carbon dioxide, the result of the chemical reaction is water vapor. The iron pellets left behind are melted into steel in an electric arc furnace run on fossil-free electricity.
Rather than vent the water vapor, the plant reuses it. “We can condense it, because it comes out from the process as vapor,” said Tomas Hirsch, director and head of energy at SSAB. “And then we can recycle it into electrolysis.” There’re some cleaning steps involved in the process, he added, but the water “can be circulated and used again.”
The Luleå plant has been up and running long enough to sell small quantities of its green steel. In October 2021, the Volvo Group unveiled the world’s first vehicle ever made with fossil-free steel—an autonomous electric dumper, which contains more than three metric tons of HYBRIT steel. Demand is surging, and SSAB is selling every ounce of what the little pilot plant produces—and it can’t make it fast enough. An industrial-scale HYBRIT plant in Gällivare, Sweden, which is projected to start operating in 2027, will help meet the demand. With the grant from the U.S. Department of Energy, SSAB will also build a similar HYBRIT plant in Mississippi.
Cleveland-Cliff is in negotiations with the Department of Energy for a grant to add a green steel plant in its current location in Middletown, Ohio, installing a hydrogen-ready, flex-fuel DRI plant and two 120-MW electric melting furnaces. According to a press statement, "The facility will have the flexibility to be fueled by natural gas, which would reduce current ironmaking carbon intensity by over 50 percent; a mix of natural gas and clean hydrogen; or clean hydrogen, which would reduce current ironmaking carbon intensity by over 90 percent.”
DISSOLVED
While hydrogen is made via electrolysis, it’s not the only possible product—or pathway to green steel. A spinoff from MIT called Boston Metal uses molten oxide electrolysis (MOE). The process requires two electrodes. The positively charged anode is built from an inert alloy of chrome and iron that can withstand high temperatures and oxygen without corroding. The negatively charged cathode is the molten metal itself, which accumulates on the bottom of the chamber called the MOE cell.
In between there’s a liquid electrolyte comprised of primarily iron oxide and other oxides that can be present in the iron ore, such as those of magnesium or aluminum.
“We’re doing electrolysis on iron ore,” Rauwerdink of Boston Metal explained. “So, we’re using the power of the electrons to do what historically would have been done with the carbon atom.”
When electricity runs between the anode and cathode, heating the mix to nearly 3,000 °F, the oxygen atoms break off, yielding liquid iron at the bottom, which can be gathered.
“As you add the iron ore, it dissolves into the electrolyte,” Rauwerdink said. “And then at certain intervals, you will do what’s called tapping. You physically drill into the cell, and you’ll pull out a pool of some of the molten metal. Then you plug that hole shut and the process continues.” The only byproduct of the reaction is oxygen; no greenhouse gases are produced.
Boston Metal’s method can work not only for steel, but for other metals, too.
The company, which has already raised over $250 million, is currently building its first plant in Brazil to extract niobium and tantalum from the waste products of tin mining. For steel, Boston Metal plans to license the technology to steelmakers or to iron ore miners.
This candle holder is the first object crafted from “fossil-free steel” produced at SSAB’s HYBRIT steel mill. Photos: SSAB
ILLUMINATED
Electricity isn’t the only carbon-free power source that can break iron and oxygen bonds. Lasers, which emit a coherent beam of energy-carrying photons, can do so too. That’s the concept that Olivia Dippo, co-founder of Limelight Steel, came up with while working on her doctorate in material science and engineering at University of California, San Diego.
“We were using a couple of different types of lasers to heat materials and 3D-print objects with it,” Dippo said. “And I started thinking about what other technologies can we apply this to.”
Her collaborator, also a doctoral student then, thought the steel industry could use some lasers.
It’s an unexpected turn. While lasers have a fearsome reputation in science fiction, for decades, experts viewed lasers as inefficient tools that belonged to academic labs rather than industry. But that has changed as the technology came of age, Dippo said.
“Lasers are powerful, they’re becoming more efficient, and they can operate on a lot of different material systems that I think people haven’t necessarily thought of before.”
Although Limelight Steel has received $2.9 million from the U.S. Department of Energy, the company is still in the research and development stage and is operating at small scale.
“We are in the tens of grams range right now,” Dippo said, but the company has very ambitious goals and is already erecting a facility in Oakland, Calif. “We’re building a pilot which will be in the 100 tons a year range, and then we’ll build a demonstration plant, and then we’ll be at commercial scale, probably by 2030.”
The industrial plant will have a continuous feeding mechanism channeling the iron ore into the reactor and taping the liquid iron out as it melts. Dippo estimated that the method can cut about 70 percent of emissions.
Of course, those emissions reductions depend on a supply of zero-carbon electricity to run the lasers. The electrolysis cells deployed by Boston Metal or the hydrogen used in the HYBRIT plant also rely on solar, wind, hydroelectric, nuclear, or other carbon-free electricity to replace the carbon directly applied to the iron ore. While some industrial sector emissions are more intractable, the challenge in steelmaking might well be met through the decarbonization of the electrical grid and the application of some clever solutions.
Lina Zeldovich is a science and technology writer based in Woodside, N.Y. Her most recent book, The Living Medicine: How a Lifesaving Cure Was Nearly Lost—and Why It Will Rescue Us When Antibiotics Fail, was published in October 2024.
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