CFD Investigations of Bath Dynamics in a Pilot-Scale TSL Furnace

The hydrodynamics of a Top Submerged Lance (TSL) slag bath are investigated here by means of Computational Fluid Dynamics (CFD) simulation. The object of the study is the pilot-scale furnace located at TU Bergakademie Freiberg, where air is injected beneath the slag bath with a top lance. The fluid dynamics system is evaluated at operating conditions, with experimentally measured slag physical properties and real flow rates. The numerical approach is based on the Volume Of Fluid (VOF) model, a front-tracking method that allows the interface to be geometrically reconstructed. Using a fine computational grid, the multiphase interactions are calculated with a high level of detail, revealing the mechanisms of bubble formation and bath dynamics. Two lance configurations are compared, with and without a swirler, and the effect on the hydrodynamics is discussed with regards to key features of the process, such as bubble dynamics, slag splashing, the interface area, rotational sloshing, and bath mixing. The model predicts bubble frequencies in the range of 2.5 to 3 Hz and captures rotational sloshing waves with half the frequencies of the bubble detachment. These results agree with real furnace data from the literature, proving the reliability of the computing model and adding value to the empirical understanding of the process, thanks to the direct observation of the resolved multiphase flow features. The comparative study indicates that the air swirler has an overall positive effect in addition to the proposed enhancement of lance cooling, with an increase in the bath mixing and a reduction in the splashing.

Increasing energy efficiency of electric arc steelmaking furnace by improvement of aspiration system and recycling of melting dust.

Electric arc furnace (EAF) is considered as a basis of promising micrometallurgical complexes of Ukraine with a flexible production program. It is important to increase energy efficiency of the furnace, which depends crucially on heat loss (up to 12-20% of energy input) and iron loss (up to 20-22 kg/t of steel) with off-gas through disadvantages, inherent for EAF aspiration system, in comparison with BOF one. Purpose of the work is to reduce heat and iron loss with off-gas environment and recycling of melting dust. Research methodology consists in numerical modeling of new solutions for EAF aspiration and liquid-phase reduction of iron. The concept and basic solutions of dispersed aspiration system and liquid-phase process of carbon-thermal reduction of iron-containing wastes in heat- generating slag bath of electric resistance furnace with bottom electrodes are developed and substantiated. It has been experimentally established that increasing the aspiration surface, its distribution between the central and peripheral parts of the roof and approaching to area of electrode passage reduces unorganized emissions into electrode gaps by 40 % and air inflow into slag door by 10 %. Simulation of thermal state of a hearth with liquid cast iron under a layer of slag, which emits Joule heat, showed the need for forced mixing of the bath under conditions that multiplier, taking into account the effect of convection on coefficient of stationary thermal conductivity in the slag bath is at least 2.7. Experimentally determined power consumption is 2.12−2.29 kWh/kg of metallized product, which corresponds to the best foreign analogue "ITmk3". Estimation of expected economic effect of developments in the conditions of 120-t EAF only due to reduction of iron loss with melting dust by using of dispersed aspiration system is about 5 million UAH per year.

INFLUENCE OF THE CONSUMABLE ELECTRODE ROTATION DURING ELECTROSLAG REMELTING ON HYDRODYNAMICS OF A SLAG BATH

Slag melt is a current-carrying medium with intense currents induced by gravitational and electromagnetic forces. The remelted electrode rotation leads to a change in hydrodynamic processes proceeding in a slag bath of the ESR installation and associated primarily with the occurrence of a centrifugal force. The flow pattern, which is developed in the slag bath under this force action, is different from that developed at a stationary consumable electrode. A mathematical model is proposed to assess the impact of consumable electrode rotation on hydrodynamics in a slag bath during electroslag melting. A computer program is created to determine the projections of the flow velocities for a liquid flux near a rotating electrode, the moment of its hydraulic resistance, and the renewal time for the slag bath while being stirred. The critical speed of the rotation of the electrode is determined as a function of its diameter at a transitional flow regime for ANF-6 flux. The dependence of the flux flow velocity on the electrode rotation speed is presented. The moment of the rotating electrode resistance in a slag bath is determined at various electrode diameters and various depths of the electrode immersion into the slag. An expression is proposed for estimating the time of the slag bath renewal. It is also shown that at a small depth in the bath due to its intensive mixing under the action of centrifugal forces, the temperature and chemical composition over the slag bath volume during the ESR process can be considered as constant. The ratio of centrifugal and electromagnetic forces is estimated. The results determine a flow pattern of the liquid slag and th

The Sectors Workpieces and Drum Reel’s Die Cubes Electroslag Casting with Exothermic Electrical Conductive Fluxes

It has been established that the developed method of manufacturing workpieces for the sectors of the drums of X20CrMoWV3 steel reel’s and die cubes from X5CrNiMo steel using a solid start and exothermic flux significantly reduces the complexity of their manufacture. The cast reel’s drum sectors workpieces and die cubes, obtained by the electroslag remelting (ESR) method, had a smooth surface without corrugations, sinkers, and slag inclusions. Heat treatment provides the required mechanical properties and the absence of flocs in the cast electroslag metal. An effective way to increase the performance of electroslag processes is using the exothermic flux, which contain scale, ferroalloys, aluminum powder and standard flux (welding flux ISO 14174 – S F AF3, etc.) in quantities sufficient for the exothermic reactions to occur, which ensures the generation of additional heat in the starting period of electroslag processes and contributes to the accelerated induction of the slag bath of the required volume at the “solid” start both monofilar and bifilar schemes of conducting the process instead of the “liquid” start. Electroslag processes using an exothermic alloyed flux on a “hard” start allow to obtain (compared to existing methods of slag bath formation) an increasing in the output of a suitable metal 2...10 %; saving on melting 1 kg of standard flux 1.2...1.4 kW h; reducing of the starting time of the ESR process to 25 %.

Alloying working surface during electroslag surfacing

Parts subject to intense abrasive wear have a short service life. In the manufacture or restoration of such parts by electroslag surfacing, strengthening of the deposited metal is required. The use of ready-made alloying powders in surfacing increases the cost of the finished part, which necessitates the search for cheaper materials for alloying the parts being welded. The study of the efficiency of alloying the deposited metal through the melted insert, as well as by direct introduction of alloying powders into the slag bath has been carried out. Mixtures based on enriched mineral scheelite concentrate and graphite are used as alloying powders

Dynamics of Rising Bubbles in a Quiescent Slag Bath with Varying Thermo-Physical Properties

The motion of bubbles in a liquid slag bath with temperature gradients is investigated by means of 3D fluid dynamic computations. The goal of the work is to describe the dynamics of the rising bubbles, taking into account the temperature dependency of the thermo-physical properties of the slag. Attention is paid to the modeling approach used for the slag properties and how this affects the simulation of the bubble motion. In particular, the usage of constant values is compared to the usage of temperature-dependent data, taken from models available in the literature and from in-house experimental measurements. Although the present study focuses on temperature gradients, the consideration of varying thermo-physical properties is greatly relevant for the fluid dynamic modeling of reactive slag baths, since the same effect is given by heterogeneous species and solid fraction distributions. CFD is applied to evaluate the bubble dynamics in terms of the rising path, terminal bubble shape, and velocity, the gas–liquid interface area, and the appearance of break-up phenomena. It is shown that the presence of a thermal gradient strongly acts on the gas–liquid interaction when the temperature-dependent properties are considered. Furthermore, the use of literature models and experimental data produces different results, demonstrating the importance of correctly modeling the slag’s thermo-physical properties.

Research on the ingot shrinkage in the electroslag remelting withdrawal process for 9Cr3Mo roller

In order to reduce the air gap between ingot and mould in the electroslag remelting withdrawal (ESRW) process, the taper of the mould should be consistent with the ingot shrinkage.Athree-dimensional mathematical model was developed to describe the interaction of multiple-physical fields (Joule heat, electromagnetic field, velocity field, and temperature field) and ingot shrinkage during the ESRW process. The variations of material thermal and mechanical properties, as well as the yield function with temperature, were considered. The shrinkage behavior of 9Cr3Mo roller in the ESRW process was simulated using the sequential coupling method. A good agreement between the calculated value and the measured valuewas obtained in the temperature field and stress field. Numerical results showed that maximum values of current density, Joule heat, and electromagnetic forcewere at the electrode corner of the slag bath. The direction of the magnetic flux density was tangential to the slag bath and had a clockwise rotation. There were two pairs of vortices and two high temperature zones in the slag bath. The shrinkage displacement was obtained through thermal-stress analysis. As the distance from the mould outlet decreases, the shrinkage displacement of ingot increases. As for the electroslag remelting withdrawal process for 9Cr3Mo roller, the variation of the shrinkage displacement from the slag/metal interface to the mould outlet was 0.0028 m. The maximum shrinkage displacement is at the mould outlet, and the value was 0.0089 m.