Timo Fabritius

Splashing mechanism in combined blowing

Abstract In combined BOF blowing, lance parameters and the combination of bottom or side wall tuyeres have an influence on splashing behaviour. The aim of this study was to clarify the interaction of the lance jet cavity with the bottom blowing plume and the side wall blowing jet and to determine its effects on splashing. According to the water model tests, three basic axioms existed in the combined blowing. First, when the bottom tuyere (or side wall tuyere) was located exactly beneath the lance jet, the lowered cavity turned the direction of splashes to lower trajectories. Second, the total amount of splashing was constant and the splashing peak was generated on the wall above the bottom plume. Third, both the plume and the side wall jet formed a so called protected zone beyond it. The model experiments showed clearly that the combination of bottom tuyeres and interaction of cavities and plumes play a very important role in splash generation in real converters.

Vibration of argon-oxygen decarburisation vessel during gas injection

Abstract Vibration of the molten bath surface in steelmaking vessels can enhance wear of the refractory lining, cause problems with the vessel support system and complicate control of the refining processes. The occurrence of vibration of the vessel during gas injection in argon–oxygen decarburisation (AOD) has been studied. The frequency and intensity of vibrations were measured using an accelerometer. According to a model and industrial tests, the intensity of vibration depends on the gas flowrate, gas composition, carbon removal rate, wear of the refractory lining and penetration of the gas jets. In AOD, the intensity of vibration is dominated by the blowing procedure, not by the carbon removal rate. Also, according to both industrial and model tests, there was a clear link between intensity of vibration and penetration of the gas jets in the liquid bath.

A Detailed Single Bubble Reaction Sub‐Model for AOD Process

A new detailed model that describes the chemical reactions, mass transfer and heat transfer taking place on the surface of a single gas bubble in liquid steel is presented in this paper. By using this model, locally occurring small scale physical and chemical mechanisms can be effectively studied. This information is required later in developing a simplified reaction sub-model to be used in CFD simulation of an operating AOD vessel. To demonstrate the capabilities of the new model, the behaviour of a single bubble under two example conditions was simulated. In the case of high carbon content of the steel, here 1%, a contribution analysis showed that the major fraction of the oxygen goes to oxidize dissolved C. When 50% of the carbon in the bath is burned and if the same gas composition (90% O2, N2) is still used, the main product is initially Cr2O3, indicating that the gas composition should have been changed if this had been a real process in question. To verify, a series of O2/N2 ratios 0.1…0.95 were simulated at 50% C conversion to see how more optimal product yield can be obtained. In addition, time dependent profiles of temperature and all species in and around the bubble are presented. The results presented here are applicable only to a local position in the AOD vessel. To be applicable to a whole AOD vessel, the model should be implemented as a source term into CFD software or a corresponding process simulation tool. This will be our future work.

Analysis of Arc Emission Spectra of Stainless Steel Electric Arc Furnace Slag Affected by Fluctuating Arc Voltage

Control of chromium oxidation in the electric arc furnace (EAF) is a significant problem in stainless steel production due to variations of the chemical compositions in the EAF charge. One potential method to control chromium oxidation is to analyze the emission spectrum of the electric arc in order to find indicators of rising chromium content in slag. The purpose of this study was to determine if slag composition can be gained by utilizing electric arc emission spectra in the laboratory environment, despite electric arc voltage fluctuations and varying slag composition. The purpose of inducing voltage fluctuation was to simulate changes in the industrial EAF process. The slag samples were obtained from Outokumpu Stainless Oy Tornio Works, and three different arc currents were used. The correlation analysis showed that the emission spectra offer numerous peak ratios with high correlations to the X-ray fluorescence-measured slag CrO x /FeO x and MnO/SiO2 ratios. These ratios are useful in determining if the reduction agents have been depleted in the EAF. The results suggest that analysis of laboratory-scale electric arc emission spectra is suitable for indicating the high CrO x or MnO content of the slag despite the arc fluctuations. Reliable analysis of other slag components was not successful.

Fe-Si droplets associated with graphite on blast furnace coke

Fe-Si droplets on the surface of blast furnace (BF) coke from 25 to 50 cm at the tuyere level are mostly composed of Fe3Si, which has various shapes (round, elongated, and irregular) and penetration degrees into the BF coke matrix. The shapes and penetration degrees may depend on the saturation of molten iron by silicon during interaction with the coke matrix. The droplets are covered by a tiny shell of carbon. Graphite observed inside the droplets can be divided into two categories: well-formed tabular crystals with relatively large size and flakes with structures similar as those in cast iron. The textures of the droplets reflect composition, interaction with the coke matrix, and cooling conditions.

Determination of Alloying Elements Ti, Nb, Mn, Ni, and Cr in Double-Stabilized Ferritic Stainless Steel Process Sample Using an Electrolytic Extraction Method and Separate Analysis of Inclusions

Chromium, nickel, and manganese are common alloying elements in stainless steels. Additionally, titanium and niobium are added as microalloying elements to certain stainless steel grades. A double-stabilized stainless steel sample was dissolved in electrolyte using an electrolytic extraction method. Inclusions were separated from the electrolyte with vacuum filtration and put through a separate elemental analysis. Steel-soluble alloying elements were determined from the electrolyte after the extraction, and the elemental analysis of inclusions was performed. The results were compared to the ones obtained from the surface analysis commonly used in the steel industry. It was concluded that the alloying elements were distributed between inclusions and the steel matrix. Therefore, optical emission analysis from a solid steel sample can be misleading. The results might not accurately depict the composition of the steel matrix. Electrolytic extraction methods combined with elemental analysis provide accurate information about the real matrix composition of microalloying elements in steel. The method is also a tool for the simultaneous analysis of inclusions in 3D and soluble alloying elements.

Textural changes in metallurgical coke prepared with polyethylene

The effect of high-density polyethylene (HDPE) on the textural features of experimental coke was investigated using polarized-light optical microscopy and wavelet-based image analysis. Metallurgical coke samples were prepared in a laboratory-scale furnace with 2.5%, 5.0%, 7.5%, 10.0%, and 12.5% HDPE by mass, and one sample was prepared by 100% coal. The amounts and distribution of textures (isotropic, mosaic and banded) and pores were obtained. The calculations reveal that the addition of HDPE results in a decrease of mosaic texture and an increase of isotropic texture. Ethylene formed from the decomposition of HDPE is considered as a probable reason for the texture modifications. The approach used in this study can be applied to indirect evaluation for the reactivity and strength of coke.

Effect of Interfacial Tension on the Emulsification of Slag - Considerations on the CFD Modelling of Dispersion

Top slag emulsification is a significant phenomenon in refining metallurgy. During bottom-or side-blowing, the flowing steel detaches small droplets from the top slag. The interfacial energy between liquid slag and steel is one of the most important factors affecting to emulsification. Surface energy, which can be described by interfacial tension, is the dominant property when determining slag emulsification. During chemical reactions, mass transfer between the phases decreases the interfacial tension at the slag-steel interface. The change in the interfacial tension affects the droplet formation.In this paper, the effect of interfacial tension on the emulsification was studied with Computational Fluid Dynamics (CFD) modelling. Three cases were simulated by considering a 3-phase system consisting of slag, steel and gas. A small area, where a 15 mm slag layer lies on top of the liquid steel, was simulated applying three different interfacial tensions, while keeping other properties unaltered. Gas was included to enable a free slag top-surface. The droplet diameter, size distribution and amount of droplets are in the scope of interest. It was found that the Sauter mean diameter of the slag droplets increased as the interfacial tension increased. The emulsification fraction varied between 1.621.95%.

Dielectric properties and carbothermic reduction of zinc oxide and zinc ferrite by microwave heating

This paper aims to study the dielectric properties and carbothermic reduction of zinc oxide (zincite, ZnO) and zinc ferrite (franklinite, ZnFe2O4) by microwave heating. To achieve this aim, the dielectric properties were measured with an open-ended coaxial method to understand the behaviour of the samples under microwave irradiation. The effects of microwave power, duration time and sample mass on the heating rate, and the effects of the stoichiometric amount of graphite on the reduction of ZnO and decomposition of ZnFe2O4 were investigated. The results show that ZnFe2O4 has significantly higher dielectric properties compared to ZnO. Generally, for both samples, the dielectric values at room temperature were quite low, indicating that both ZnO and ZnFe2O4 are poor microwave absorbers. It was found that the temperatures have a more significant effect on the imaginary permittivities than on the real permittivities. The heating rate showed that the sample temperature increased with increase in microwave power and sample mass. Using 700 W of microwave power and two times the stoichiometric amount of graphite, almost complete reduction of ZnO was achieved in 12 min, while ZnFe2O4 completely decomposed to zincite and wustite in 3 min.

A Mathematical Model for Reactions During Top-Blowing in the AOD Process: Derivation of the Model

In an earlier work, a fundamental mathematical model was proposed for side-blowing operation in the argon–oxygen decarburization (AOD) process. The purpose of this work is to present a new model, which focuses on the reactions during top-blowing in the AOD process. The model considers chemical reaction rate phenomena between the gas jet and the metal bath as well as between the gas jet and metal droplets. The rate expressions were formulated according to a law of mass action-based method, which accounts for the mass-transfer resistances in the liquid metal, gas, and slag phases. The generation rate of the metal droplets was related to the blowing number theory. This paper presents the description of the model, while validation and preliminary results are presented in the second part of this work.