CO2 Emissions in Steel Production: from 100 to 5 %!
Hydrogen-based direct reduction is a key technology for the CO2-free production of crude steel. By 2050, Salzgitter AG plans to have completed a conversion to virtually CO2-free crude steel production within the framework of the SALCOS project (Salzgitter Low CO2 Steelmaking). Until now, the iron oxide in the ore has been reduced with coal, which is associated with high CO2-emissions – steel production accounts for around 7 % of global CO2-emissions. If instead green hydrogen, produced by electrolysis using electricity from renewable energies, is used in place of coal in a so-called direct reduction process, up to 95 % of CO2 can be saved on the way to crude steel production. Of course, this cannot be achieved overnight, as the conversion is not only associated with high investment costs but is also technically demanding.
But how do you assess the transition of steel production to a more climate-friendly process? What exactly does it mean in concrete terms for the integrated steel mill of Salzgitter Flachstahl GmbH? How much renewable energy is required, for example, to save one ton of CO2? These and other questions were clarified by the “Feasibility Study on the Reduction of CO2-Emissions in the Steel Mill Using Renewable Energies”, MACOR for short. The BMBF-sponsored study was carried out by the three Fraunhofer Institutes IKTS, ISI and UMSICHT, as well as the Salzgitter subsidiaries Salzgitter Flachstahl and Salzgitter Mannesmann Forschung. Fraunhofer IKTS focused primarily on process simulation, while Fraunhofer ISI analyzed the economic efficiency of several process variants. The staff of Fraunhofer UMSICHT examined the processes involved in direct reduction as well as the properties of the reduced iron. For the Salzgitter subsidiaries, the emphasis was on the preparation of an implementation plan for SALCOS, technical analyses of the direct-reduced iron and the ecological balance.
An important parameter is the energy required per ton of reduced CO2. This is because energy from renewable sources is limited – their share of the total energy market in Germany is currently a mere 15 %. The question therefore arises: Where does their use bring the greatest benefit? The result of the study: avoiding CO2 in crude steel production is four times more efficient than capturing the CO2 and using it for other purposes, such as the production of chemicals. Hydrogen-based steel production offers the greatest CO2 savings potential of almost 100 % compared to conventional processes, such as hydrogen injection in the blast furnace. Simulated calculations by IKTS also showed that high-temperature electrolysis is a very efficient and economical process for supplying the hydrogen required for direct reduction in the integrated steel mill.
In the follow-up project “Accompanying Research Hydrogen in Steel Production”, in short BeWiSe – also funded by the BMBF – the established consortium now dedicates itself to further research to optimize the hydrogen-based steel production route investigated in MACOR.