Series of articles concerning hydrogen: Steel production

In the course of the last few years, an immense dynamic can be felt in the field of hydrogen. At the same time, great progress has been made in research and development at many points along the hydrogen value chain and important findings have been made. In the first series of articles on hydrogen, the basics of the gas were explained along its value chain from production to transport and storage to application.

In this second series, individual focus topics are dealt with in detail and the current state of knowledge is summarized. This first article deals with the use of hydrogen in steel production.

Large quantities of coke obtained from coal are used for the production of steel from iron oxides. In the blast furnace process, this ensures the reduction of the iron oxides at high temperatures in several reduction steps to pig iron, which is then further processed in the steelworks to produce various steels. In this process, greenhouse gas emissions are released on a relevant scale. The use of hydrogen produced from renewable sources can help to reduce greenhouse gas emissions in a first step by adding it to the blast furnace process. In order to realize climate-neutral steel production, it is necessary to switch to reduction processes that run on 100 % hydrogen and operate without fossil energy sources.

Adding hydrogen to the blast furnace process

A first quickly realizable use of hydrogen in the iron and steel industry is the addition of hydrogen to the blast furnace process. Due to its reduction potential, hydrogen is just as capable as carbon of reducing iron oxides to pig iron. However, it is not possible to operate a blast furnace without carbon in the form of coke and only with hydrogen. This is due to problems with the gas permeability of the reactor and the discharge of gases, slags and metals. Due to its endothermic behavior – in contrast to the exothermic reduction by coke – the addition of hydrogen is also only energetically useful up to a certain point. Higher hydrogen contents increase the total energy demand and thus also the demand for coke [1].

Such an addition of hydrogen to a blast furnace is being tested at the thyssenkrupp Steel site in Duisburg as part of the H2Stahl project, which is one of the “living labs for the energy transition” [2]. The aim is to achieve a possible reduction in process-related CO2 emissions of 20% [2]. FfE is supporting this and other living labs scientifically together with other partners in the Trans4ReaL project.

Sustainable steel from hydrogen-fueled direct reduction plants

To be able to produce steel as sustainably as possible in the future, it is therefore necessary to switch from the currently dominant blast furnace process to other methods of reducing iron ores to pig iron. The process with the highest technological maturity at present is the direct reduced iron (DRI) process for solid pelletized iron ores. In contrast to the blast furnace process, the ores to be reduced are not melted and tapped as liquid pig iron. Due to the significantly lower temperatures of just over 1000°C of the reducing gas introduced into the reactor – in comparison to the up to 2000°C in the blast furnace-, the ores remain in the solid state and are reduced to a solid, porous form of pig iron called sponge iron [2–5]. Subsequently, the sponge iron produced in this way is melted in an electric arc furnace (EAF) under application of high voltage, the alloying elements required for the desired steel grade are added, and the resulting crude steel is then cast. Electric arc furnaces are well established in secondary steelmaking – the production of steel from iron scrap – and are therefore not a technical challenge.

The reduction gas used in today’s direct reduction plants is a gas mixture of carbon monoxide and hydrogen, which is obtained from natural gas. To date, such plants have therefore been built mainly in regions with access to cheap natural gas, such as Russia, the USA or the Arabian Peninsula [3]. In recent years, the proportion of hydrogen in the reduction gas has been successively increased and, with an appropriate heat supply, operation with up to 100 % hydrogen would also technically possible [5]. However, this is not yet an established large-scale process, so that the optimum operating conditions and the optimum process control of the complex reduction process still have to be determined [5]. Switching to 100% renewably generated hydrogen as a reduction gas and supplying heat from likewise climate-neutral sources would thus make climate neutral pig iron production possible. If the subsequent steel production in the electric arc furnace is carried out using electricity from regenerative sources, nearly CO₂-neutral steel production from iron oxides is possible.

Since plants in the iron and steel industry are designed for a long service life, conversion of the relevant operations to the DRI-EAF route will only be possible gradually. Corresponding plans have already been submitted by the German steel companies. One example are the plans recently announced by thyssenkrupp Steel. The plan is to build a DRI plant with a capacity of 2.5 million tons of pig iron per year at their Duisburg steelmaking site by 2025 [6].

Iron and steel industry as a major application area for green hydrogen

In the future, the iron and steel industry will represent a significant end user for green hydrogen and will also play a central role in the market ramp-up phase of the hydrogen economy in the coming years. For example, if German climate targets are met, the iron and steel industry is already expected to use 10-26 TWh of hydrogen per year by 2030 [7–9]. If climate neutrality is achieved, the hydrogen demand would increase to 35-75 TWh/a [7–9]. According to Hübner et al., the demand of the German iron and steel industry would even amount to 92 TWh/a in case of a complete conversion to DRI and EAF [10].

Further information:

• FfE Discussion Paper: European Steel with Hydrogen

Literature

[1]         D. Spreitzer und J. Schenk, „Reduction of Iron Oxides with Hydrogen – A review“, Steel Research International, Nr. 90, 2019, Art. no. 1900108. [Online]. Verfügbar unter: https://onlinelibrary.wiley.com/doi/pdf/10.1002/srin.201900108

[2]        Energiesystemforschung, Projekt H2Stahl. [Online]. Verfügbar unter: https://www.energiesystem-forschung.de/forschen/projekte/reallabor-der-energiewende-h2-stahl (Zugriff am: 9. September 2022).

[3]        I. Hartbrich, „Direktreduktion: Diese Technik wird bei Thyssenkrupp und Co. den Hochofen beerben“, VDI Verlag GmbH, 7. Apr. 2022, 2022. [Online]. Verfügbar unter: https://www.vdi-nachrichten.com/technik/werkstoffe/direktreduktion-diese-technik-wird-den-hochofen-beerben/. Zugriff am: 9. September 2022.

[4]        Y. Ma et al., „Hierarchical nature of hydrogen-based direct reduction of iron oxides“, Scripta Materialia, Jg. 213, S. 114571, 2022, doi: 10.1016/j.scriptamat.2022.114571.

[5]        A. Bhaskar, M. Assadi und H. Nikpey Somehsaraei, „Decarbonization of the Iron and Steel Industry with Direct Reduction of Iron Ore with Green Hydrogen“, Energies, Jg. 13, Nr. 3, S. 758, 2020, doi: 10.3390/en13030758.

[6]        thyssenkrupp, thyssenkrupp beschleunigt grüne Transformation: Bau der größten deutschen Direktreduktionsanlage für CO2-ar. [Online]. Verfügbar unter: https://www.thyssenkrupp-steel.com/de/newsroom/pressemitteilungen/bau-der-groessten-deutschen-direktreduktionsanlage-fuer-co2-armen-stahl-entschieden.html (Zugriff am: 9. September 2022).

[7]        Prognos, Öko-Institut und Wuppertal-Institut, „Klimaneutrales Deutschland 2045“, 2021.

[8]        Deutsche Energie-Agentur GmbH (dena), Hg., „dena-Leitstudie Aufbruch Klimaneutralität“, Berlin, 2021.

[9]        Fraunhofer-Institut für System- und Innovationsforschung ISI und Consentec GmbH, „Langfristszenarien für die Transformation des Energiesystems in Deutschland 3“, Karlsruhe, 2021.

[10]       T. Hübner, A. Guminski, S. Pichlmaier, M. Höchtl und S. von Roon, „European Steel with Hydrogen: FfE Discussion Paper 2020-04“, München, 2020. [Online]. Verfügbar unter: http://ffe.de/veroeffentlichungen/ffe-discussion-paper-european-steel-with-hydrogen/