Voestalpine : High voltage at greentec steel

In a few decades, megawatt hours rather than coke tonnages will determine the energy supply of steel production. That's because by then, electric arc furnaces will be indispensable for greentec steel.

In the foreseeable future, an electric arc furnace powered by green electricity will form the center of voestalpine's steel production. It will be at the core of greentec steel and ensure the supply of high-quality steel grades. Since "electric arc furnace" is a rather long-winded term, the abbreviation "EAF" has become established in everyday usage.

What happens in the EAF?

Essentially, EAFs melt down feedstocks for further processing and perform basic metallurgical work. As the name suggests, for melting down, an electric arc is generated in the furnace with the aid of electric energy: Once the furnace vessel is loaded ("charged"), the furnace lid is closed and the three approx. 70 cm thick graphite electrodes are lowered. When ignited, a current of approx. 80,000 amperes flows through them, forming an electric arc.

Its temperature of more than 3,000 °C, supported by burners in the furnace vessel, heats the furnace contents and melts them within approx. 48-50 min. Finally, the slag is removed, the steel tapped off - and then recharged in the still hot furnace vessel. The melting of charge materials and other metallurgical tasks (e.g. removal of unwanted by-products) are assisted by injected oxygen; slag formation is improved with the addition of quicklime or dolomite.

The raw materials

To produce crude steel, the EAF uses

• sorted scrap steel,
• briquetted iron sponge (HBI),
• liquid pig iron as iron supplier and
• quicklime or dolomite as slag formers.

Depending on the type of steel to be produced, the three iron-supplying input materials are proportionately charged in the EAF, e.g. 50% scrap and one quarter each HBI and pig iron. voestalpine can obtain high-quality HBI for this purpose from its own plant in Corpus Christi (USA).

As a special structural feature, the voestalpine sites in Donawitz and Linz provide for direct feeds of molten pig iron to the electric arc furnace, since in the hybrid phase of greentec steel, the blast furnace operation is maintained with fewer units.

Safeguarding the operation of the EAF

The tap weight of the Linz EAF, i.e. the weight of one batch of steel, will be approximately 180 t. EAFs, such as those that will go into operation for greentec steel in 2027, therefore have a huge appetite. Almost another 900,000 t of scrap and 400,000 t of HBI will be needed annually at the Linz site. Program managers Kurt Satzinger and Bernhard Kaiser inform us that "in order to be able to implement this, we are reorganizing the material flow from the scrap yard to the consumption points and we're also building a covered warehouse for HBI". "The construction of EAF and associated logistics present a construction challenge for which we are already extensively preparing."

The future operators of the new units will be trained as early as next year: That's when the first apprentices will familiarize themselves with the basics of electric arc furnaces. As the transformation of steel production progresses, experienced specialists will also upskill from blast furnace to electric furnace operators, an indispensable process on the way to greentec steel.