The production of steel is one of the most energy-intensive of all industrial activities, and also responsible for a good portion of the world’s greenhouse gas emissions. The world produces about 1.5 billion tons of steel annually. The enormous, extremely hot cauldrons where this steel is made contribute around 5% of the world’s total greenhouse gas emissions. On average, the production of one ton of steel generates about two tons of CO2 emissions.
But now, a new process developed by researchers at MIT looks like it may be able to address this, greatly reducing the greenhouse gas emissions associated with steel production, while also lowering costs and improving the purity/quality of the steel. A “win, win, win” proposition, as the researchers put it.
As a brief aside, the association between environmental destruction/pollution and metallurgy is nothing new. Much of the deforestation of the world’s old-growth forests was fueled by metallurgy. Whereas fossil fuels are used today, wood was previously, fueling the ever-hot furnaces of the world’s metal-working civilizations.
In modern times, steel is produced primarily by heating iron oxide up with carbon. As a result, carbon dioxide is also produced as a byproduct.
But the newly created process takes a different approach, using a process known as “molten oxide electrolysis” and the clever use of an iron-chromium alloy.
Interestingly, the new process was arrived at thanks to research that NASA commissioned, investigating possible ways to produce oxygen on the Moon. During that research, it was happened upon that, when using molten oxide electrolysis to create oxygen from the iron oxide in lunar soil, steel was created as a byproduct. In order to make the process economical though, something cheaper needed to be found to replace the expensive iridium anode that he was using during the research for NASA. That’s where the chromium-iron alloy comes in. It’s able to take the role of the iridium anode during the molten oxide electrolysis process, while still being relatively cheap and abundant.
The discovery of that material as a replacement took some work though. “It wasn’t an easy problem to solve,” explains Donald Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT and senior author of the new paper. “A vat of molten iron oxide, which must be kept at about 1600 degrees Celsius, is a really challenging environment. The melt is extremely aggressive. Oxygen is quick to attack the metal.”
What was needed was an alloy that “naturally forms a thin film of metallic oxide on its surface: thick enough to prevent further attack by oxygen, but thin enough for electric current to flow freely through it.” And the chromium-iron alloy fulfills those requirements.
As well as greatly limiting carbon emissions, the process is also well suited to smaller-scale factories, something that currently used processes are not. As it stands, in order for a typical steel production plant to be economical, it needs to produce at least a few million tons of steel per year. With this new process, though, plants on a much smaller scale could possibly be economical, producing on the scale of “only” a few hundred thousand tons per year.
Another advantage to note is that the process results in the creation of steel of “exceptional purity.” And the process could be easily adapted to the carbon-free production of a variety of other metals and alloys, including “nickel, titanium and ferromanganese.”
Ken Mills, a professor of materials at Imperial College, London, says that it should be kept in mind, however, that unless legislation is created that requires the industry to account for its greenhouse-gas production, then it remains to be seen if the new process would be cost-competitive with already established/installed systems.
The researchers have formed a company in order to further develop the process/concept, with the aim of producing a commercially viable prototype electrolysis cell themselves. They are expecting that it will take up to three years to design, build, and test such a prototype.
A research paper detailing the new process was just published in the journal Nature.
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