Steel production requires a lot of energy, and the various processes used to make it are a major source of greenhouse gas emissions. The global iron and steel industry is the largest energy consuming manufacturing sector, according to Columbia University’s Global Network for Climate Solutions, and produces roughly 5 percent of total world greenhouse gas emissions.
But the steel industry has come a long way in the last two and a half decades. Organizations such as the American Iron and Steel Institute are leading efforts to coordinate research and development of “green” technologies and processes among the nation’s largest steelmakers. “By deploying new steelmaking technologies and through the innovations of the workers on the plant floor, the industry has reduced energy intensity per ton of steel shipped by more than a third and CO2 emissions by a third per ton of steel produced since 1990,” says Jim Woods, senior director of sustainability communications at AISI.
To put that into perspective, an average of 1.9 metric tons of CO2 were emitted for every metric ton of crude steel cast in 2016, requiring approximately 5.3 megawatt hours of energy in the process, according to the World Steel Association.
Government regulations and standards have been a big driver of this ongoing improvement, but so has industry-led innovation. “Reducing the amount of mining, reducing the emissions, reducing energy intensity of the process is smart business, but it’s also significantly improving the environmental benefits of the steelmaking process,” explains Woods.
Because there are so many steps associated with steelmaking, process efficiency has been a major contributor to the overall greening of the steel industry. “The production of steel itself has become very optimized in a lot of ways,” says Mark Thimons, vice president of sustainability at the Steel Market Development Institute – a business unit of AISI. One example of this, according to Thimons, is the elimination of intermediate steps associated with processing molten steel into the final mill product.
“If you go back many years, you would see a lot of reheating involved in going from molten steel to a slab, which would then be reheated and run through a strip mill,” he says. “A lot of those intermediate reheating processes, which use a lot of energy, have been eliminated by the concept of continuous casting and even continuous processing into coil or strip material.”
The recyclability of steel is another important factor in reducing its overall environmental impact. According to GNCS, 75 percent of the steel industry’s total CO2 emissions come from coke and coal in iron making for primary steel production.
The other main steelmaking process, electric arc furnace production, also requires less overall energy compared with integrated production. “When we’re using steel scrap in place of raw materials, you’re saving the energy associated with harvesting those raw materials, as well as reducing the energy needed to melt iron ore versus steel scrap,” Woods says, adding that a single ton of recycled steel conserves about 4,697 kilowatt-hours of energy.
Currently, more than 65 million tons of steel are consumed and shipped for recycling by the North American steel industry each year. Woods adds that nearly all new steel in North America, whether produced in an integrated mill or minimill, is made using steel scrap. On average, domestic steel contains 25 percent recycled steel, with some processes using as much as 95 percent recycled content.
“There’s a whole host of benefits that come from using steel scrap,” Woods says, pointing to the efforts of the Steel Recycling Institute, which focuses its efforts on improving the infrastructure around steel recycling. “Doing this kind of work actually helps the energy intensity and the overall environmental performance of the steelmaking process.”
However, Thimons notes that comparing the energy requirements of the two main steelmaking processes can be misleading if you focus on a single measure, such as recycling. “It is true that integrated production results in higher overall impacts on things like global warming potential, for instance,” he says. “We like to say that each of the production routes has an environmental impact and that impact can only be portrayed credibly in the context of a full life-cycle assessment that looks at all stages of the life cycle.”
Life-cycle assessment is a technique that gives researchers a holistic view of a product’s environmental impact by assessing it from raw material extraction through processing, distribution, use and recycling. In the case of steel, that would include things like the potential environmental impacts of gathering and using steel scrap. “That’s a very complex question that sounds simple at first but, in reality, it is not.”
Steel isn’t the only product of steel manufacturing being recycled. The industry has also made major strides in reusing the various coproducts produced from the steelmaking process, which untreated can be harmful to the environment. The main coproducts associated with steel production are slag, process gases, dust and sludge, and zinc oxides.
“We’ve also been looking at ways to increase the recycling of coproducts and reusing some of the coproducts that are generated as a result of the steelmaking process,” Woods says. “Right now, we’re at about 97 percent of the products that are generated from the steelmaking process being recycled or reused.”
The World Steel Association estimates that more than 400 million metric tons of iron and steel slags are produced each year, with the worldwide average recovery rate varying from more than 80 percent for steelmaking slag to nearly 100 percent for iron-making slag.
Modern steelmakers in North America certainly have come a long way in their efforts to lower the environmental impact of their product. Despite strides in areas such as decreasing energy inputs and emissions, the laws of thermodynamics have placed limits on the amount of additional progress that can be made with current technologies and processes.
According to a recent WSA report, the technology currently used to produce steel will not be able to achieve future carbon emissions targets. “With most major energy savings already achieved, further large reductions in CO2 emissions are not possible with the existing technology,” the report states. “The target set out by governments and international bodies require breakthrough technologies via innovation and exploration of new production processes.”
To that end, AISI is also working with leading steelmakers on a number of research projects looking into new green technologies and processes. One such project is the Novel Flash Ironmaking Project. Its goal is to produce primary iron from iron ore fines using natural gas. Project participants include ArcelorMittal, Berry Metal, TimkenSteel and U.S. Steel. “The project team has proven the technology and is now working on fine tuning the operating parameters, as well as designing a pilot plant,” Woods explains.
Additional upcoming projects include seeking new technologies to reduce, capture and/or sequester the CO2 from the steelmaking process, as well as ongoing work to recycle steel plant coproducts. And while many coproducts are currently reused, there are others that are not.
Overseas, steelmakers are investigating new production processes that could revolutionize the way steel is produced. Austrian steelmaker Voestalpine is investigating a hydrogen-based approach to steelmaking, which would replace coking coal with hydrogen. Other companies, such as Swedish steelmaker SSAB and POSCO of South Korea, are also looking to develop hydrogen-based steelmaking, but the process is likely decades away.