Investigation on the chemical and thermal behavior of recycling agglomerates from EAF by-products

In addition to the blast furnace converter route, electric steel production in the electric arc furnace (EAF) is one of the two main production routes for crude steel. In 2019, the global share of crude steel produced via the electric steel route was 28%, which in numbers is 517 million metric tons of crude steel. The production and processing of steel leads to the output of a variety of by-products, such as dusts, fines, sludges and scales. At the moment, 10–67% of these by-products are landfilled and not recycled. These by-products contain metal oxides and minerals including iron oxide, zinc oxide, magnesia or alumina. Apart from the wasted valuable materials, the restriction of landfill space and stricter environmental laws are additional motivations to avoid landfill. The aim of the Fines2EAF project, funded by the European Research Fund for Coal and Steel, is to develop a low-cost and flexible solution for the recycling of fines, dusts, slags and scales from electric steel production. During this project, an easy, on-site solution for the agglomeration of fine by-products from steel production has to be developed from lab scale to pilot production for industrial tests in steel plants. The solution is based on the stamp press as the central element of the agglomeration process. The stamp press provides the benefit of being easily adapted to different raw materials and different pressing parameters, such as pressing-force and-speed, or mold geometry. Further benefits are that the stamp press process requires less binding material than the pelletizing process, and that no drying process is required as is the case with the pelletizing process. Before advancing the agglomeration of by-products via stamp press to an industrial scale, different material recipes are produced in lab-scale experiments and the finished agglomerates are tested for their use as secondary raw materials in the EAF. Therefore, the tests focus on the chemical and thermal behavior of the agglomerates. Chemical behavior, volatilization and reduction behavior of the agglomerates were investigated by differential thermogravimetric analysis combined with mass spectroscopy (TGA-MS). In addition, two melts with different agglomerates are carried out in a technical-scale electric arc furnace to increase the sample size

Influence of the Recirculation of Various by-products Generated through Electric Arc Furnace Route on EAF Slag Quality

The Fines2EAF project aims to increase the value of Electric Arc Furnace steelmaking residues by their internal recycling and reuse in form of cement-free briquettes. The project sustainability for a profitable fines' recirculation pass through the conservation of steel and slag quality in terms of chemistry, physics and eco friendliness. To do this, industrial trials have been conducted by the charging of self-reducing and slag-former briquettes made by primary and secondary fines materials. Several slag samples supplied from three different European EAF steel shops have been analysed. The specimens have been characterized by XRF, XRD and SEM to thoroughly define their crystallography, morphology and microstructure. The comparison with the corresponding reference samples (i.e., slag produced without the fines recirculation) also allowed to highlight the differences present. Leaching tests have been conducted on reference and briquette- added slag according to EN 12457-4 standard to assess the compliant with the local environmental regulation. The obtained results highlighted that the slag obtained using cement-free briquettes made by steelmaking fines exhibits crystallographic and morphological properties very similar to the reference samples, with limited differences attributed to slag and scrap feedstock intrinsic heterogeneity. No relevant increase in the leachate concentration could be detected when compared to reference samples and the influence of raw-material fines recirculation into the EAF could be considered at worst negligible, if not positive for some elements like Ba ( - 22.86%), V ( - 13.19%) and W ( - 14.83%). Considering all the analyses performed, no adverse effect on slag quality could be detected

Optical emission spectroscopy as a method to improve the process automation of electric arc furnaces and ladle furnaces

Abstract The steel industry is on its way towards more environmentally friendly steelmaking. To achieve the ambitious goals of significant CO₂ emissions reduction, new processes, practices, sources of on-line data, and digitalization together with automation will be required. To address these issues, this paper discusses optical emission spectroscopy (OES) as an on-line data acquisition method for industrial electric arc furnaces and ladle furnaces. The current state of the OES as a measurement method in the steel industry together with prospects of new applications are presented with examples based on the authors’ prior research

On-line analysis of Cr₂O₃ content of the slag in pilot scale EAF by measuring optical emission spectrum of electric arc

Abstract Control of slag Cr₂O₃ content is essential in stainless steelmaking electric arc furnace (EAF). Excessive Cr₂O₃ content of slag lead to high Cr₂O₃ content after the EAF tapping, since the solid precipitates forming in high Cr₂O₃ contents are not reduced significantly during the tapping procedure. In this work the slag Cr₂O3 content during the EAF process was analysed by measuring the optical emission spectrum of the electric arc. The measurements were conducted in a pilot EAF situated in Aachen, Germany. Cr₂O₃ content of the slag was increased with periodical additions of Cr₂O₃ powder. The line ratios calculated from the optical emission spectra were compared to the results of the X-ray fluorescence (XRF) analysis of the slag samples taken from the furnace. The results indicate that best accuracy in a pilot scale can be obtained by using Ca I, Fe I or Mn I lines as reference for Cr I lines. By combining the most accurate line ratios of these three components, the Cr₂O₃ composition of the slag could be measured with an average absolute error of 0.62%-points and a standard deviation of 0.49%-points. The results suggest that Fe I and Mn I lines are the most promising reference lines for analysing Cr₂O₃ content of industrial EAF slag

Pilot-scale AC electric arc furnace plasma characterization

Abstract Fundamental knowledge of the electric arc properties is important for the development of process control of electric arc furnaces. In this work, a pilot-scale AC electric arc has been studied with optical emission spectroscopy together with filtered camera footage. The properties of the arcs were determined with plasma diagnostics and image analysis in order to obtain both the characteristic plasma parameters and the physical form of the arc. The plasma temperatures, ranging from 4500 to 9000 K, were derived individually for three elements. The electron densities of the plasma were between 10¹⁸ and 10²⁰ cm⁻³ and fulfilled the local thermal equilibrium criterion, but the plasma temperatures derived from atomic emission lines for different elements had high and unpredictable differences. The properties of the electric arcs have been studied with respect to the arc length derived from the image analysis. The slag composition, especially the relative FeO content of over 30%, was observed to have a notable effect on the brightness of the arc on slag and thus also on the radiative heat transfer