The steel industry is an important engine for sustainable growth, added value, and high-quality employment within the European Union. It is committed to reducing its CO2 emissions due to production by up to 50% by 2030 compared to 1990′s level by developing and upscaling the technologies required to contribute to European initiatives, such as the Circular Economy Action Plan (CEAP) and the European Green Deal (EGD). The Clean Steel Partnership (CSP, a public–private partnership), which is led by the European Steel Association (EUROFER) and the European Steel Technology Platform (ESTEP), defined technological CO2 mitigation pathways comprising carbon direct avoidance (CDA), smart carbon usage SCU), and a circular economy (CE). CE approaches ensure competitiveness through increased resource efficiency and sustainability and consist of different issues, such as the valorization of steelmaking residues (dusts, slags, sludge) for internal recycling in the steelmaking process, enhanced steel recycling (scrap use), the use of secondary carbon carriers from non-steel sectors as a reducing agent and energy source in the steelmaking process chain, and CE business models (supply chain analyses). The current paper gives an overview of different technological CE approaches as obtained in a dedicated workshop called “Resi4Future—Residue valorization in iron and steel industry: sustainable solutions for a cleaner and more competitive future Europe” that was organized by ESTEP to focus on future challenges toward the final goal of industrial deployment.

To investigate the use of biomass in the novel HIsarna technology, the reduction of FeO in the slag by chars produced from thermal coal (TC), charcoal (CC), and Bana grass char (BGC) was studied. A drop tube furnace coupled with a quadrupole mass spectrometer (DTF-QMS) was employed to study the injection of chars into pre-melted slag in the temperature range between 1450 °C and 1525 °C. The reduction rate was calculated from evolved gases and the extent of FeO reduction was confirmed by wavelength-dispersive X-ray fluorescence (WDXRF). The FeO reduction proceeds through two stages, starting with a rapid reduction, which is dependent on the carbon type, and followed by gradual leveling off. The reduction rate with the charcoal char (CC) was the highest, over 60 pct reduction was achieved in the first 500 seconds at 1500 °C, while ~ 50 and 40 pct achieved with TC and BGC chars, respectively, for the same reaction time. The kinetic analysis suggests that the first and second stages of the reaction can be described by the second-order (F2) and three-dimensional diffusion (D3) models, respectively. The apparent activation energy values for the first stage were 290, 229 and 267 kJ/mol for reactions with TC, CC and BGC chars, while 265, 369, and 282 kJ/mol were obtained for the second stage. Based on the experimental data and kinetic results, it can be concluded that the first stage is controlled by chemical reactions on the carbon surface, and the second stage is influenced by a mixed-controlling mechanism.

The HIsarna process is a new and breakthrough smelting reduction process for hot metal (liquid iron) production from iron ores and coal directly fed into the reactor. The flue gas from the main reactor enters the off-gas system containing small amounts of H 2 , CO and carbon particles which need to be removed before further treatment by post combustion oxygen injection. A three-dimensional Computational Fluid Dynamics (CFD) simulation of the HIsarna off-gas system is performed and validated using a detailed reaction mechanism and kinetic data for post-combustion of a CO-H 2 mixture and carbon particles. Using the validated model, a series of simulations were performed to investigate the effect of water quenching and post combustion oxygen injection. It was found that water quenching can significantly reduce the off-gas temperature. It is also possible to reduce oxygen injection during operations where inlet CO content of the off-gas system is low.

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In this paper a CFD analysis of HIsarna off-gas system for post combustion of CO-H2-carbon particle mixture is presented to evaluate the effect of different sub-models and parameters on the accuracy of predictions and simulation time. The effects of different mesh type, mesh grid size, radiation models, turbulent models, kinetic mechanism, turbulence chemistry interaction models, including and excluding gas-solid reactions, number of reactive solid particles are investigated in detail. Based on the accuracy of the predictions and agreement with counterpart measured values, the best combination is selected and conclusions are derived. It was found that radiation and turbulence chemistry interaction model have a major effect on the temperature and composition profile prediction along the studied off-gas system, compared to the variations in other models. The effect of these two models becomes even more evident when the temperature and fuel content of the flue gas are high.