Green steel: How steel production can reduce its emissions

Last year, the 71 World Steel Association (worldsteel.org) member states alone produced a total of 145.5m tonnes of steel. Production is energy-intensive and generates huge quantities of CO2. But is there anything we can do to counteract these problems?

Steel from scrap steel

“Using scrap steel instead of the primary raw material iron ore for steel production delivers a reduction in carbon emissions of up to 75%,” says Harald Ganster. “And it makes production more energy efficient,” adds his DIGITAL Institute colleague Malte Jaschik. The pair are currently working on an innovative approach to the material characterisation of scrap metal as part of the InSpecScrap project, using artificial intelligence (AI) and hyperspectral multisensorics to characterise the composition of the metal – which has a decisive influence on the quality of the steel produced. This technique allows for detection of impurities and the automated assessment of quality specifications. “The findings will lay the foundations for the development of new approaches to AI-based classification methods for the future, which adds another key aspect to the steel industry digitalisation chain,” the researchers point out. The institute is working closely with TU Graz, the K1-MET competence centres and the Know Center. Industrial partners Marienhütte (a steel mill) and Voestalpine Stahl Donawitz are also supporting the project.

Social responsibility

If the transformation of the steel industry is to be truly sustainable, the social dimension also needs to be kept in mind. In cooperation with the University of Graz, Ingrid Kaltenegger and Michael Brenner-Fließer from the LIFE Institute examined the social compatibility of a transition to more environmentally friendly steel production – using waste wood as opposed to coal – in Belgium, China and the USA. They found that the effects on society depend to a large extent on the location and suppliers. Partially replacing coal with waste wood to fire the blast furnaces undoubtedly translates into lower CO2 emissions, but does not necessarily have a positive impact on the community. For example, China imports coal from Australia, where production standards are high. A changeover would mean replacing this coal with local products, where social sustainability is far less of a priority. By contrast, Belgium imports coal which is mined under poor social conditions. In this case, using waste wood from surrounding regions would generate benefits for society. As part of the EU’s Torero project, waste wood from demolished roof frames and offcuts from sawmills are being used to heat the furnaces at a pilot plant in the Belgian city of Ghent. The research team also analysed its impact on people and the environment: “The results could be applied here in Austria, too, and using waste wood instead of coal has the potential to improve environmental and social conditions in this country as well.” However, steps would also need to be taken to avert the negative effects on countries that currently export the raw material. For instance, they could switch from fossil fuel extraction to alternative energy generation in order to create new jobs.

From coke to green hydrogen

The MATERIALS Institute is involved in the RecHycle project, which is also focused on the use of alternative energy forms. Researchers are investigating the use of green hydrogen and recycled steel mill gases in steel manufacturing as substitutes for coke and coal dust. At the ArcelorMittal steel plant in Ghent, the blast furnaces run on a mixture of hydrogen and cycle gas. The corresponding life cycle assessment (LCA) for evaluating the reduction in CO2 emissions has been defined and optimised. “We are analysing the hydrogen embrittlement of the materials used in the furnace, which poses a significant risk for the proper functioning of the furnace system,” explains Vojislav Petrovic Filipovic, who is heading the project at the MATERIALS Institute. And the primary benefit of hydrogen as an energy source for steel production: steam is the only by-product of the combustion process.

Slag for road construction

The Marienhütte steel works in Graz produces gravel for use in the construction industry from slag. A by-product of rebar steel manufacturing, slag was once viewed with suspicion due to environmental concerns, but it actually delivers ecological and financial advantages – as the LIFE Institute has discovered: “In terms of greenhouse gas potential, using rebar steel slag for road construction saves 300 tonnes of carbon dioxide emissions compared with dumping and natural gravel mining,” says Head of Institute Franz Prettenthaler. “The circular economy approach also performs better than natural gravel and dumping as regards other metrics that we investigated, including primary energy use, space requirements, fine particulate emissions and utilisation of wastewater.” Prettenthaler also points out an economic benefit: the costs of this approach are some 88% lower than disposal. The LIFE research team has calculated that using rebar slag produced in the course of a year translates into EUR 9.1m in value added – a difference of EUR 3m compared with dumping. The Marienhütte mill manufactures around 410,000 tonnes of rebar rods and rings each year and generates 72,000 tonnes of metallurgical gravel. Produced when steel is recycled in the electric arc furnace, this slag has stone-like properties.