Entering the future with green steel

Green steel is currently the most popular concept in the steel industry’s push to go net zero. The industry’s objective is to make its product, which has been the backbone of industrial production for decades, green in future, gradually reducing its CO_₂ emissions to zero in the process.

A large number of steel producers with integrated steelworks, including thyssenkrupp Steel, Salzgitter, ArcelorMittal and Tata Steel Europe, have launched programmes to work towards this goal. It is important to note that no consistent or universally applicable definition for what exactly constitutes green steel has been agreed yet, so at what point a steel product really becomes green is still an open question. The meaning of the term may vary depending on the steel company or country.

The three building blocks of the Green Steel label system (Image: Wirtschaftsvereinigung Stahl)

Definitional debate

Creating green priority markets, or Leitmärkte as they are known in Germany, is an important tool for policy-makers to harness green steel in order to support decarbonisation. The aim is to strengthen demand for the green product. Ultimately, this will reduce the burden on the state to provide initial funding and replace it over the long term.

A clear definition of zero-carbon steel is needed in order to create green priority markets. Since this definition is not yet available, no progress is being made in establishing the priority markets. On a positive note, the first foundations have been laid in the form of action plans and a national hydrogen strategy. The debate over a definition is being held at the international level. This poses the risk of different regional standards emerging – a disadvantage for Germany as an export-heavy industrial economy.

The need to agree on a viable, internationally recognised definition is now widely accepted. The definition could be based on the recommendation which the International Energy Agency submitted in the context of the G7. The German Steel Association (Wirtschaftsvereinigung Stahl) is running with this concept and proposing a labelling system for green steel.

Classification levels for green steel are similarly self-explanatory to the energy label (Image: German Steel Federation)

The definition would have to meet certain criteria:

Compatibility with market ramp-ups – ensuring that the gradual transformation process tracks with the availability of green energy.

A high level of ambition – ambitious goals ensuring that investments in net-zero production are rewarded.

Rewarding transformative processes – efforts that further the goal of going net zero must be rewarded.

Internationalist approach – green priority markets must be devised at a pan-European level and become a mainstay for international “climate clubs”.

Circular economy – current manufacturers of 100% scrap-based products cannot be put at a disadvantage. However, just increasing scrap reuse is not enough to achieve net zero.

Credibility – certifiability based on uniform rules and established ISO standards. Overall footprint assessments only when necessary for technical purposes and under clearly defined conditions.

An essential component of the labelling system is transparency regarding specific steel products (the product carbon footprint). This allows the customer to track a given product’s exact CO₂ content all the way along the value creation chain, with a carbon footprint range between scope 1 and scope 3U. This involves setting company-specific system boundaries from cradle to gate.

Another key element is transparently disclosing how green the production process is, again with a scope 1 to 3U footprint range. This transparency is vital in helping policy-makers to keep green priority markets moving in the right direction. The element of transparency ensures that overall footprint assessments are only carried out in technically justified cases and within clearly defined limits. The uniform system boundary extends as far as hot-rolled steel.

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(Bild: T. You, Max-Planck-Institut für Eisenforschung GmbH)

Ammonia could become an important reducing gas for future green steel production (Image: T. You, Max Planck Institute for Iron Research GmbH)

The process

Green steel is made from direct reduced iron (DRI) without fossil fuels. The DRI process uses hydrogen as a reducing agent. This distinguishes the process from the conventional blast furnace method, which uses coke for this purpose. Instead of CO₂, the reaction between iron oxide and hydrogen produces water vapour, which is not environmentally harmful. Electricity is required for the production of hydrogen; for green steel, this electricity has to be obtained from renewable energy sources.

The direct reduction process

In the DRI shaft furnace, iron ore in pellet or lump form is reduced to sponge iron. Iron ore is poured in at the top, then it continuously sinks down into the shaft. At the same time, reducing gas – carbon monoxide (CO) and hydrogen (H₂) – flows up the furnace. The gas deprives the iron of its oxygen atoms. As a result, Fe₂O₃ first becomes Fe₃O₄, then FeO and finally Fe (iron with carbon residue, which is removed at the bottom as solid, hot sponge iron).

Since a huge volume of hydrogen is required for the DRI process, natural gas can be used as a transitional solution. Natural gas also significantly reduces CO₂ emissions when compared with blast furnaces. Ammonia, a hydrogen derivative, can also be used for direct reduction.

The sponge iron produced can then be processed in two different ways. One option is to insert it into a melting unit which produces molten pig iron using green electricity. Next, this is transported to the oxygen converter in a torpedo car. In the oxygen converter, the crude steel is manufactured by feeding in scrap steel and oxygen. Converter gas is formed as a by-product in the oxygen converter. This can be used as a low-calorific gaseous fuel – for example, to generate electricity.

In the electric arc furnace

The second method involves feeding the sponge iron into an electric arc furnace. The electric steelmaking method used here can also be used to process scrap steel or pig iron. As with the melting unit, this furnace is powered by green electricity from renewable sources. The molten steel is poured into a steel ladle and transported on for the secondary metallurgy process.

The melt produced in the electric arc furnace or oxygen converter is refined using secondary metallurgy to subsequently cast crude steel products such as billets, blooms or slabs by way of a continuous casting process, for example.

In summary, in addition to sustainable input materials such as green sponge iron and green hydrogen, using green electricity from renewable sources throughout the entire process chain is an essential criterion for the “green steel” label.

(Author: Lucas Möllers)