The argon-oxygen-decarburization (AOD) process is a common metallurgical treatment to decarburize high-chromium steel melts using oxygen and inert gas injection through sidewall tuyeres and a toplance. AOD converters are characterized by a fast and efficient decarburization, whereby the oxidation of chromium is reduced compared to treatments for regular steel grades like the LD process. However, lowfrequency oscillations with large amplitudes can occur during the process and influence the converter's structural integrity. The aim of plant engineering is the development of an AOD converter using a vessel design that provides a fast decarburization rate and effective mixing, whereby the oscillation's amplitude and the chromium losses are as low as possible. The oscillation of the vessel is induced by the fluid flow. In this study a numerical model is presented, where the oscillation model is integrated in the CFD (computational fluid dynamics) solver by subroutines. The numerical models for both, fluid flow and vessel oscillation, are validated by experiments carried out with a 1:4 scale water model. In a further step, the numerical models are transferred to the actual AOD process. The results of the simulations are compared to experimental results obtained in plant trials. The numerical model developed in the present study can be used as a tool to design AOD vessels that fulfill the above mentioned criteria to satisfy an efficient, reliable and stable process.

During the argon-oxygen-decarburization (AOD) process high-chromium steel melts are decarburized by oxygen and inert gas injection through sidewall tuyeres and a toplance. The tap-to-tap time of the AOD process depends mainly on the time which is necessary to produce a homogeneous distribution of all required components in the melt. This mixing time is correlated to the process time. Shorter tapping times lead to a higher productivity, lower energy consumption and lower operating costs. Prior to the reduction stage, the mixing behavior influences the melting of the solid slag layer after the addition of ferro-silicon. Fast and efficient melting of the solid slag compounds is essential to attain sufficient reduction rates. Conventional approaches to experimentally investigate the mixing efficiency in aqueous models (e.g. the 95%-mixing time criterion), yield results which show a large variance concerning the mixing time for a single operating point. In the present study a novel approach for the determination of the mixing time in a water model of an AOD converter is presented and verified. The results show a lower variance and an increased reproducibility as compared to the prior measurement technique. Using these experimental results, the vessel shape and the required volume flow rate of the AOD process gas can be optimized. Furthermore, numerical simulations can be validated using the presented results. The measurement technique can be utilized in water models representing other metallurgical processes.

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Several roadmaps worldwide identify the decarbonization as one of the main pathways to transform the steel industry into a climate-neutral sector by 2050. New technologies and processes based on the massive use of renewable electricity, green hydrogen, and their combination, will play a fundamental role in this transformation. Aside this decarbonization pathway, the steel sector suffers from a strong inertia due to its characteristics of being very capital intensive, operating in a highly competitive global market and being characterized by an investment cycle between 20 and 30 years. In such scenario, the Tenova “Hydrogen Ready” combustion technology (which identifies a burner family able to work with any natural gas/hydrogen mixture up to 100% H2 without hardware modifications) represents a solution able to support the steelmakers through the current energy transition scenario and, at the same time, to ensure their investments for the future. This paper continues a previous work on the Tenova “SmartBurner” technology and shows the application of the “Hydrogen Ready” concept to three additional burner families, covering a wider range of downstream processes: Tenova TRKSX (flameless self-recuperative burner for heat treatment furnaces), Tenova TRGX (regenerative flameless burner for reheating furnaces), and the Tenova THSQ burners (flameless combustion system for batch annealing furnaces, heat treatment furnaces and other special heat treatment application). All these burners show NOx emissions well below the next envisioned limits (80 mg/Nm3 at 5% of O2 with furnace at 1250 °C) with all the NG/H2 mixtures, as well as with 100% H2. These results confirm the viability of the “Hydrogen Ready” approach, and the effectiveness of the flameless technology in controlling the NOx formation. The first industrial applications of these concepts are also presented.