Green steel without green hydrogen — can it work?

Boston Metal wants to reduce steelmaking’s emissions by directly powering the process with clean electricity.

This is the alt text
(Boston Metal)
  • Link copied to clipboard

Decarbonization often comes down to finding creative uses for electricity. The playbook is simple. You take a process that traditionally burns fossil fuels, and then you replace it with an alternative that uses clean electricity instead. For instance, take a car, swap out an internal combustion engine for a battery charged from a grid with a lot of wind and solar, and boom, you’ve got an electric vehicle that runs on clean power.

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 a sort of middleman. You can use clean electricity to produce hydrogen, and then burn hydrogen to make steel, with only water as a byproduct. A joint 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, a critical step in the steel production process.

Subscribe to receive Canary's latest news

The advantage that we have is that it’s a one-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 a big deal

Decarbonizing the steel industry is a major 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 a big 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 of RMI.)

Producing 1 ton of steel with traditional methods releases almost 2 tons of CO2 into the atmosphere, and the world uses almost 2 billion tons of steel each year. 

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 a point. 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 a complex process that emits carbon at different stages. Some emissions come from the heating process, which usually involves burning a heat-refined form of coal called coke. A bit of the carbon from the coke 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 a single piece of equipment used in the process: the blast furnace, where the iron ore is converted into a form called pig iron.

Decarbonization of the iron and steel industry basically means decarbonization of the blast furnace,” said Zhiyuan Fan, a research associate at the Center on Global Energy Policy at Columbia University. If you solve the blast furnace [issue], half of your problem is gone.”

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 a blast furnace,” Fan said.

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 a key 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 as well. 

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 a laboratory at the Massachusetts Institute of Technology.

Ten or 20 years ago, the grid wasn’t clean, so it didn’t make any sense, and there was no demand for a greener 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 a while. In fact, electrolysis has been a key part of making aluminum for over 100 years. 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, a temperature far hotter than molten lava.

To start, the iron ore is melted with heat produced from electricity. Then it’s placed in a cell structured almost like a giant battery. At the top, an anode provides electric charge. At the bottom, a cathode receives the electric charge. In between, the charge flows through an electrolyte, which in this case is a scalding bath of molten materials. The electrolyte contains a variety 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 to steel.

According to Boston Metal, the composition of the electrolyte is a critical 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.

Some of the other technologies that are being developed [to manufacture] green steel need the super-premium grades of ores,” said Rauwerdink. We can take advantage of all the much more abundant grades of ores, which is key to growing the technology in the long term.”

Another of molten oxide electrolysis’s advantages compared to direct reduction of iron is its efficiency. The reason is fairly intuitive. By cutting out the hydrogen step, MOE puts energy directly into steel production, removing interim stages where energy can be lost. MOE requires higher temperatures than hydrogen-based production, which eats into the benefits, but even taking that into account, MOE still winds up being more efficient. Fan, the green-steel expert at Columbia, estimates that making green steel using green hydrogen requires at least 30% more energy than MOE — and possibly as much as 50% to 60% more.

By skipping those different processes, you can actually gain a lot of efficiency improvements,” he said.

The road to scale

Still, the technical advantages of MOE don’t mean much until the technology is actually being used to produce steel in meaningful quantities.

A commercial plant can produce several million tons of steel per year. Operating continuously, Boston Metal’s first demonstration cell will produce less than 100 tons of steel per year, so the company has a long way to go.

It’s just about aggregating those cells, and so the proof is in the pudding of how much that can scale,” said Gamage of RMI.

Scale is important in the steel business, but so is being able to use capital-intensive systems that have already been built. Green hydrogen has a leg up on this front because it’s compatible with the direct reduction of iron process, which is already being used at commercial scale with natural gas. It’s relatively easy to swap out the natural gas for hydrogen. That’s why major steel producers such as SSAB and ArcelorMittal have focused on green hydrogen for their near-term plans.

We’re on the clock here,” said Fan. If we want to fully decarbonize by 2050, we need to think about production-unit replacement in the next 10 years or 20. If MOE is not commercially available at that time, it just missed the window.”

Boston Metal is racing to beat the clock. The company is working on a bigger demonstration cell at its headquarters in Woburn, Massachusetts, which will be able to make several hundred tons of steel per year. Once it perfects the design, multiple cells can be built in the same plant and then potentially lined up by the hundreds, a design common at aluminum smelters. 

Because it’s a modular technology, the path to scaling will be quite quick,” said Rauwerdink. It’s like having a wind turbine and demonstrating five turbines, and then once that’s successful, building 100 or 200 for a commercial plant. It’s the same approach for us. We don’t have to then go back and redesign a cell that’s 100 times larger.”

While Boston Metal prepares its technology for large-scale steelmaking applications, the company is exploring the use of its cells to produce high-value alloys like ferroniobium. Partnerships around this application can create shorter-term revenue streams. 

It’s going to take four to five more years to get fully commercial for steel, but there’s [other] revenue from early applications of the technology in advance of the big prize,” said Rauwerdink.

Boston Metal has not yet signed any contracts with major steel producers, but the leadership team has met with many, Rauwerdink said. Over the last few years, he has observed a groundswell of interest from steel companies. He reflected that five years ago, it was mainly research and development departments that wanted to learn about next-generation technology, but now there’s buy-in from top brass as companies feel increasing pressure to act on climate change.

It’s a night-and-day difference in terms of their commitment and their need to decarbonize,” he said.

A supercharged — and low-carbon — grid

It’s important to note that Boston Metal’s technology will need electricity generated from low-carbon sources in order to make a dent in steelmaking’s carbon emissions. 

The future of steelmaking is really dependent on clean electrification,” said Gamage.

Steelmaking equipment tends to be in constant operation for months at a time, and changing the chemical composition of metal inherently requires a lot of energy, so if the process is electrified, it will guzzle an immense amount of power. Boston Metal says that its technology uses 4 megawatt-hours of electricity to produce 1 ton of steel. That’s enough to power the average U.S. home for more than four months.

According to Columbia’s research on decarbonizing steel, replacing all the world’s blast furnaces with MOE manufacturing processes would require an amount of power equivalent to almost 20 percent of global electricity consumption in 2018. That means the steel industry would become one of the biggest users of electricity on the planet. 

But replacing all steel production with hydrogen-powered direct reduction of iron could require even more electricity. That means there’s no way to address steel’s climate impacts without installing a whopping amount of clean power generation, in addition to making sure that the grid is ready to reliably move around all that extra electricity.

You’re going to need to beef up the grid at a rate that the utilities and the grid operators have not planned for,” said Thomas Koch Blank, senior principal in RMI’s Breakthrough Technology Program. And it would need to be done on a 10- to 15-year timeline.”

Sometimes, developing new decarbonization technology is cast as being at odds with deploying established solutions such as renewable energy, but in many circumstances, these challenges are one and the same. Green steel is a prime example.

For us or for green hydrogen, you’re going to need clean power,” said Rauwerdink, so all the work that’s happening on cleaning up the electricity grid enables solutions like ours.”

As the demand for green steel grows, multiple solutions will be needed in order to satisfy the world’s appetite for steel without overburdening the atmosphere or the electric grid. Koch Blank emphasized that both molten oxide electrolysis and hydrogen-powered direct reduction of iron hold promise for decarbonizing the steel industry and are worth pursuing.

Ultimately, I’d be surprised if there’s not room enough in the market for both technologies,” he said.

Ben Soltoff is a freelance writer who specializes in climatetech.