Making iron produces huge amounts of carbon emissions, but a Tufts chemist thinks there is a better way. Instead of using coal-derived coke in the process of smelting iron ore, he proposes substituting hydrogen-rich ammonia, which would drastically reduce the carbon footprint for the widespread industrial process, and finding a way to make it commercially viable.
Now Luke Davis, an assistant professor of chemistry, and his colleagues have received a $2.9 million grant from the U.S. Department of Energy’s Advanced Research Projects Agency-Energy to fund research that could potentially transform iron and steel production. The funding is part of the Revolutionizing Ore to Steel to Impact Emissions program, which aims to advance zero-process-emission ironmaking and ultra-low life cycle emissions steelmaking.
“We have produced iron with the same chemistry for over 3,000 years,” said Davis. “That one industrial reaction now produces 4% of the globe’s carbon dioxide emissions each year. We wondered, despite the long history of iron making, whether there could be a new way to produce iron without releasing so much carbon dioxide.”
About 90% of iron production is done in blast furnaces, structures 10 to 16 stories high and about 50 feet wide. Alternating layers of iron ore, coke, and limestone are fed in from the top. Heated air enriched in oxygen is blasted in at the bottom, reaching temperatures of about 2000 degrees Fahrenheit. The coke reacts with the hot air and generates more heat and carbon monoxide.
The hot carbon monoxide rises through the furnace, converting iron oxides in the ore to molten metallic iron which sinks to the bottom of the furnace, where it is collected. Impurities from the ore combine with the limestone to form “slag,” which floats to the top. During this process huge amounts of carbon dioxide are released into the atmosphere.
Davis and his team want to find a replacement for coke. Its production releases significant amounts of the greenhouse gas methane, and it is responsible for generating carbon dioxide in the smelting process. Hydrogen can be an effective replacement for coke, leaving a byproduct of water rather than carbon dioxide.
But producing hydrogen at scale for the iron industry is difficult, and it is hard to ship. Compressing and liquifying hydrogen takes a lot of energy, especially in the quantities needed for large-scale iron production.
One alternative is to use ammonia, which is composed of one nitrogen and three hydrogen atoms. “If we are trying to completely decarbonize iron production, ammonia makes more sense,” says Davis. It’s probably the densest form of a hydrogen-containing molecule that can be shipped, since it liquefies at -27 degrees Fahrenheit—cold, but manageable. It is also already made in very large quantities from low-grade fossil fuels.
“We did some calculations which suggested that if ammonia could be used in ironmaking, the only by-products would be water and nitrogen. Nitrogen is already 78% of the Earth’s atmosphere, and it’s not a greenhouse gas,” says Davis.
The U.S. currently makes twice as much ammonia as it would need to convert all its ironmaking to an ammonia-based process. Much of that is used currently to produce fertilizer, but Davis estimates that it would only take five to six years to scale up ammonia capacity to add iron production, using the average annual U.S. growth in ammonia production from 2015-2020. Some carbon release occurs in the production of ammonia itself, but not nearly as much as iron coking, and efforts are in the works to produce “green” ammonia.
While ammonia has been used in iron production at very small scales in academic research laboratories, it is not efficient—the reaction is slow. That’s the focus for Davis and his team, who are looking at ways to accelerate the reaction, “and our preliminary results looked compelling enough for the Department of Energy to fund the work,” he said.
Tufts will take the lead on the project, with collaborators Cornell University, which will analyze solid state reactions at the laboratory scale, the University of Minnesota Natural Resources Research Institute, which will provide ore and analyze iron products for utility in steel production, and the National Renewable Energy Laboratory, which will examine the economic lifecycle of the new process and compare it to the current approach.
