Direct Current Electric Arc Furnace Research Articles

Melt azimuthal rotation in direct current electric arc furnace without external axial magnetic field

This paper considers the azimuthal rotation of melt about the vertical axis of a DC EAF, which is ensured by an inclined installation of the power supply electrodes, which is a patented solution that is the basis for this article. Near inclined electrodes, the Lorentz force has a pronounced azimuthal component, which is the driver of the melt rotation without an external axial magnetic field – thus, additional energy consumption to create an external magnetic field is not necessary. The main design and technological solutions, formulated in the patent and presented by the authors, were obtained using observations and numerical LES study for a laboratory-scale experimental setup (capacity 4.8 kg of GaInSn), as well as using LES computations for an industrial-scale DC EAF (capacity 3.6 t of molten steel). Basic technological solutions studied: the flow of the melt may be controlled by varying the number of vertical and inclined electrodes of DC EAF, choosing the angle of inclination of the electrodes as well as choosing the sequence of turning on and turning off power supply through the electrodes.

Numerical modelling of heating and melting of metal in a mini industrial direct current electrical arc furnace

Purpose The purpose of this paper is the study of the electro-vortex flow (EVF) as well as heating and melting processes for mini industrial direct current electric arc furnace (DC EAF). Design/methodology/approach A mini DC EAF was designed, manufactured and installed to study the industrial processes of heating and melting a small amount of melt, being 4.6 kg of steel in the case under study. Numerical modelling of metal melting was performed using the enthalpy and porosity approach at equal values and non-equal values of the solidus and liquidus temperatures of the metal. The EVF of the liquid phase of metal was computed using the large eddy simulation model of turbulence. Melt temperature measurements were made using an infrared camera and a probe with a thermocouple sensor. The melt speed was estimated by observing the movement of particles at the top surface of melt. Findings The thermal flux for metal heating and melting, which is supplied through an arc spot at the top surface of metal, is estimated using the thermal balance of the furnace at melting point. The melting time was estimated using numerical modelling of heating and melting of metal. The process started at room temperature and finished once whole volume of metal was molten. The evolution of the solid/melt phase boundary as well as evolution of EVF patterns of the melt was studied. Originality/value Numerical studies of heating and melting processes in metal were performed in the case of intensive liquid phase turbulent circulation due to the Lorentz force in the melt, which results from the interaction of electrical current with a self-magnetic field.

Study on Mechanism of Titanium Slag Smelting in DC electric Arc Furnace

Based on the production practice of a 30MWA large DC electric furnace in Yunnan, this paper discusses the basic reactions in smelting titanium slag, and discusses the thermodynamic and kinetic behaviors of the main elements and impurities. The results show that the reduction reaction in the smelting process is carried out simultaneously in the multi-component system of Al2O3-CaO-MgO-SiO2-TiO2. The titanium slag containing more than 80% TiO2 can be obtained by enrichment smelting of ilmenite in a large high-power enclosed direct current electric arc furnace, and the output includes by-product pig iron. Impurities MgO, CaO and Al2O3 in titanium concentrate will not be reduced during reduction smelting; SiO2, MnO and V2O5 will be reduced in varying degrees, and the reduced products Si, Mn and V will dissolve in the metal Fe phase or be enriched in titanium slag.

Characteristics Analysis of Fluid Flow and Heating Rate of a Molten Bath Utilizing a Unified Model in a DC EAF

Herein, a 2D unified model coupling a plasma arc–molten bath–cavity in a direct current electric arc furnace was developed for a characteristic analysis of the fluid flow and heating rate of the molten bath. The ‘local thermodynamic equilibrium–diffusion approximation’ method was employed for the physical phenomenon at the plasma arc/molten bath interface, and the volume-of-fluid method was used to track the free surface. After ensuring model validation, the formation processes of the cavity and the flow field and heating rate of the molten bath were investigated by utilizing the unified model. The numerical results showed that the formation processes of the cavity contained three stages, namely the expansion, compression, and dynamic equilibrium stages. The arc pressure and plasma shear stress both contributed to the cavity formation, and dominated the expansion of the cavity depth and diameter, respectively. Under plasma arc jet impingement, there were two flow patterns inside the molten bath: (i) a clockwise eddy on the top surface and lateral part of molten bath dominated by plasma shear stress, and (ii) a counter-clockwise eddy in the bottom part of the molten bath dominated by the electromagnetic force. Meanwhile, the main heated region of the molten bath with the plasma arc–molten bath–cavity coupling was in the radial range of 0.2–0.6 m, and a high-temperature region was formed on the top surface of the molten bath caused by plasma shear stress.

Toward a Simplified Arc Impingement Model in a Direct-Current Electric Arc Furnace

A 2D axisymmetric two-phase model was developed to study the effect of an arc impingement on the liquid metal inside an electric arc furnace. In addition to the arc flow dynamics, the model covered the heat transfer and magneto hydrodynamics of the arc and the liquid metal. Through a parametric study, three different parameters were considered to predict the most important factors affecting the arc and overall behaviour of the process: the arc gap, the density of the gas, and the total electric current. Understanding the effect of these parameters can show the key factors altering the arc dynamics. The study showed that the total applied current was the most important parameter that influenced the impingement depth and mixing of the liquid metal. The depth of the impingement and strength of the mixing of the liquid bath were directly proportional to the current applied in the furnace. The initial arc gap distance was found to be crucial for sustaining a continuous and stable arc. The value of the gas density was very important for the velocity profile; however, it had no significant effect on the impingement depth. This showed that a constant density could be used instead of a varying gas density with temperature to increase the computational efficiency. The study assessed the effects of the aforementioned factors on the arc impingement depth, velocity magnitude, and arc stability. The conclusions acquired and challenges are also presented.

Design and Construction of a Laboratory-Scale Direct-Current Electric Arc Furnace for Metallurgical and High-Titanium Slag Smelting Studies

A novel direct-current electric arc furnace (DC-EAF) was designed and constructed in this study for experimentally investigating high-titanium slag smelting, with an emphasis on addressing the issues of incomplete separation of metal and slag as well as poor insulation effects. The mechanical components (crucible, electrode, furnace lining, etc.) were designed and developed, and an embedded crucible design was adopted to promote metal-slag separation. The lining and bottom thicknesses of the furnace were determined via calculation using the heat balance equations, which improved the thermal insulation. To monitor the DC-EAF electrical parameters, suitable software was developed. For evaluating the performance of the furnace, a series of tests were run to determine the optimal coke addition under the conditions of constant temperature (1607 °C) and melting time (90 min). The results demonstrated that for 12 kg of titanium-containing metallized pellets, 4% coke was the most effective for enrichment of TiO2 in the high-titanium slag, with the TiO2 content reaching 93.34%. Moreover, the DC-EAF met the design requirements pertaining to lining thickness and facilitated metal-slag separation, showing satisfactory performance during experiments.

Numerical Analysis of Fluid Flow and Heat Transfer by Means of a Unified Model in a Direct Current Electric Arc Furnace

Herein, a unified 2D axially symmetric model coupling the plasma arc and molten bath in a direct current electric arc furnace is established, with the physical phenomena at the plasma arc/molten bath interface to be confronted by the “local thermodynamic equilibrium diffusion approximation” method. After ensuring model validation and grid independence test, the fluid flow and heat transfer processes are analyzed. The numerical investigation reveals that in terms of the relative importance of driving forces in the molten bath, an anticlockwise eddy is formed at the molten bath center driven by electromagnetic force, whereas a clockwise eddy is formed near the lateral part of the molten bath driven by buoyancy force. Regarding the distribution of heat flux, the convection–conduction and radiation heat govern the rate of heat transfer from the plasma arc to the molten bath. In addition, for larger arc current, higher arc power in the plasma arc region and higher heating rates in the molten bath are obtained when the arc length is held constant; for shorter arc length, lower arc power in the plasma arc region but higher heat transfer efficiency in the molten bath is attained when the arc current is held constant.

Analysis of Economic and Energy Efficiency of Using Electric-Arc Reduction for Iron-Containing Materials

For many years an important task for metallurgical scientists is the search for alternative technologies of iron production from mineral raw materials without using expensive coke, natural gas and with the least pressure on ecology. Technologies are required with maximum extraction of iron from ore, and with the least pollution of the atmosphere using cheap and least scarce reducing agents, for example power generating coal. Recently in OAO VNIIMT a new method has been developed and proven under laboratory conditions for direct preparation of iron by reduction of fine-grained material with solid reducing agent in a direct current electric arc furnace, including ground ore, iron-bearing sludge, etc. This technology makes it possible to prepare cast iron containing 3–4% carbon in a molten condition that may be granulated, cast into pigs, and treated in a ladle-furnace unit with minimum specific yield of gas and slag.

Analysis of electric arc furnaces efficiency via frequency spectrum-based arc coverage detection

We introduce the analysis of variables measured outside a direct current electric arc furnace that are related to the arc coverage and its electric energy efficiency. We derive an on-line reference to the arc coverage suitable for control decisions. In order to do so, we study the furnace shell vibration frequency spectrum as structure-borne sound sensed by a microphone. The data is analysed using real time software tools to obtain the sound signal spectrum associated with arc coverage likewise related to the optimal performance of the furnace. A statistical test is performed to prove the relationship between sound and electric energy efficiency.

Balance of Raw Input and Energy of Titanium Slag Smelting in Closed High Power Direct Current Electric Arc Furnace

There were two controlling factors, which should be kept balance of raw input and energy during titanium slag smelting in closed high power direct current electric arc furnace, DC furnace for short. The first factor contains compositions and ratio of input raw materials. Compositions of the raw could influence the progress and technical indicators of DC furnace smelting, and on the meanwhile, it could determine the compositions of impurity and contents of TiO2 in titanium slag. On the other hand, the ratio of input infected the compositions of the slag, while too much anthracite would disadvantage to produce high quality slag because of impurity being reduced continually. Meanwhile much more low-state titanium would be generated. The second factor was an important one that energy equilibrium, which influence the production safety of DC furnace. It could keep balance of input and output energy, while the heatloss was 4.971 MVA. While the ratio of anthracite remained the same, the energy would effect slag viscosity and equilibrium of freeze lining directly. The energy input higher than smelting need would result in burnthrough of furnace wall and hearth, on the contrary, lower than smelting need would bring about slagging difficulties. Consequently, raw input and energy must be kept dynamic balance in order to achieve high quality titanium slag and protect freeze lining.

Energy Balance and Offgas Utilization of Ilmenite Smelting in a 30 MVA Direct Current Electric Arc Furnace

Energy balance and offgas utilization of ilmenite smelting in 30 MVA direct current electric arc furnace (DC furnace) of a Yunnan company were investigated to make sure safety production, and to save energy and reduce pollution. The total input energy in the DC furnace was 2,000 kWh per ton of ilmenite, in which 1,003.31 kWh per ton of ilmenite was used to carbothermic reduction and other energy was consumed as heatloss. Based on energy conservation, the whole system heatloss in physical production should be controlled at 1,000 kWh per ton of ilmenite. With high combustion heat, the offgas discharged from furnace after treatment could be used to ilmenite drying, anthracite drying, titanium slag drying, and casting ladle baking. The offgas design flow ranged from 5,000 to 8,000 Nm3/h with the mean of 6,500 Nm3/h. The combustion heat quantity of offgas in the plant was 82,160 MJ per hour, which could save 480,276.8 kWh of electrical energy per day, and thus lower carbon emission of the whole production line.

Acoustic Monitoring of Plasma Arcs in Direct Current Electric Arc Furnaces

In this article, the extraction of features from acoustic signals generated by a 60-kW direct current electric arc furnace and the use of these features to infer the arc length of the plasma jets in the furnace were considered. A sensor capable of such measurements would be more robust to the unobservable fluctuations of the arc length and would, in principle, allow better control of smelting operations. The collected data comprised sets of five separate 10-second recordings of the acoustic signal, furnace current, and voltage, each at nominal arc lengths of 5, 15, and 25 mm. In the approach, time-frequency features initially were obtained through filter bank analysis of the signals. Reduction of the dimensionality of these filter bank features was then performed using a nonlinear subspace method called kernel Fisher discriminant analysis. Finally, kernel discriminant features were used to infer the arc length via a nearest neighbor classification model that associated three classes of arc lengths (5, 15, and 25 mm) with their corresponding features. The results of the small number of experiments suggest that a significant statistical relationship exists between the length of a plasma arc and its acoustic signal despite potentially large variations in arc phenomena inside the furnace.

Carbothermic reduction of pirolusite to obtain carbon-bearing ferromanganese and slag suited to the development of welding materials

Summary This article examines the process for obtaining high carbon ferromanganese by means of carbothermic reduction in a direct current electric arc furnace. It establishes the ideal composition of slag oxides to make a flux for use in submerged arc welding (SAW). The charge components (pirolusite, coke, steel wool, lime, rutile and fluorite) are calculated for a flux-free technology to obtain FeMn taking into account the characteristics of welding fluxes under the SiO2–MnO–CaO system. Reduction experiments are applied to the charge materials so as to obtain FeMn and slag, which are then used to develop an SAW flux.

Mathematical modeling of a direct current electric arc: Part II. Dimensionless representation of a direct current arc

A mathematical model presented in Part I of this work is used to describe fluid-flow, heat-transfer, and electromagnetic phenomena in the arc region of a direct current electric arc furnace (DC EAF). From the analysis of the system, the effects of the arc current and the arc length on the arc characteristics and arc bath interactions can be represented analytically in a rather generalized way, based on the finding that the arc shape is unique (defined with the location of the 10,000 K isotherm) when plotted in the appropriate dimensionless form. This dimensionless arc expansion (only restricted to arcs burned between graphite electrodes in air and outside the region where the arc jet impinges on the bath surface) gives the possibility to derive a unique arc description regardless of the values of the arc current and arc length. Dimensionless correlations representing the relationships among important arc characteristics and arc-bath interactions are derived in this work. These expressions may be used to estimate process variables without the need to run complex numerical calculation.

Mathematical modeling of a direct current electric arc: Part I. Analysis of the characteristics of a direct current arc

A mathematical model is used to describe fluid-flow, heat-transfer, and electromagnetic phenomena in the arc region of a direct current electric arc furnace (DC EAF). Based on those model results, a detailed physical analysis of the arc was performed, where the numerical computations help to explain the arc structure, its behavior, and the highly coupled relationship among their main physical variables. This analysis leads to the conclusion that the arc behaves in such a way that all the arc characteristics are controlled by the expansion of the arc, which is the main feature used to physically describe the arc behavior. The arc expansion is evident from the arc shape, which is defined as the region where conduction of electricity takes place. The arc shape is clearly seen in several contour fields presented in this work, such as the current density, the magnetic flux density, the electric conductivity, the electric potential, and the temperature fields. The results of this article focus on process analysis, to provide insight into the inter-relationship among the arc variables, and to establish physical grounds to subsequently explore dimensionless analytical representations to describe the arc behavior.

Mathematical Modeling of a DC Electric Arc-Dimensionless Representation of a DC Arc

A mathematical model presented in previous publications is used to describe fluid flow, heat transfer and electromagnetic phenomena in the arc region of a Direct Current Electric Arc Furnace (DC-EAF). The effects of the arc current and the arc length on the arc characteristics and arc bath interactions are analyzed in a rather generalized way. This analysis leads to the conclusion that the arc behaves in such a way that when the arc shape (defined with the location of the 10000 K isotherm) is plotted in the appropriate dimensionless form a unique arc expansion is achieved. This unique expansion (only restricted to arcs burned between graphite electrodes in air and outside the region where the arc jet impinges on the bath surface) gives the possibility to provide single dimensionless arc characteristics regardless the values of the arc current and arc length. These dimensionless correlations represent the main finding of this work and they allow means to estimate the important characteristics of the arc under different operational conditions without the need to run complex numerical calculation. The dimensionless characteristics of arc expressed in simple algebraic forms can be used for this purpose employing a pocket calculator.

Mathematical Modeling of Iron and Steel Making Processes. Modeling of a DC Electric Arc Furnace. Mixing in the Bath.

A mathematical model was developed to describe fluid flow, heat transfer and electromagnetic phenomena in the bath region of a Direct Current Electric Arc Furnace (DC-EAF). The different effects on the steel bath from the arc, a layer of slag on the top of the steel, and the injection of argon gas from the bottom, are represented using three different numeric approaches and analyzed in terms of fluid flow, heat transfer, and temperature stratification in the steel bath. Additionally, a sensitivity analysis was performed to explore the effect of the main process parameters and design variables of the process, such as furnace dimensions, arc conditions, and anode configurations. It was found that in the absence of gas injection, the electromagnetic body forces dominate the fluid flow in the bath region overcoming the opposite effects of buoyancy and shear from the arc. Injection of gases homogenizes the melt improving mixing, while the effect of the slag is to decrease mixing in the bath. Regarding the process analysis, the model showed that the best mixing and the best energy optimization from the arc are achieved when the geometry of the furnace presents the highest aspect ratio. Similarly, short arc lengths and high arc currents are beneficial for mixing. However, these improvements in mixing could be detrimental for the bottom refractory of the furnace because of the direct exposure of the hot metal coming from the arc attachment zone at the bottom wall. Then, the anode configuration can be designed to avoid excessive damage to the refractory.

Intelligent Compound Control of Direct Current Electric Arc Furnace

Abstract Due to steelmaking process of the Ultra High Power Direct Current Electric Arc Furnace (UHP DC EAF) is a complex process with physicochemical reactions, there exist highly, nonlinearity, uncertainty, time-variant and seriously interconnected (i.e. some of the variables may not be linearly independent) etc. It is impossible to establish a precise model for the steelmaking of the UHP DC EAF. According to the concrete practice of the steelmaking process, a intelligent compound control strategy is presented based on the steelmaking process of UHP DC EAF in this paper. This method was successfully used in the steelmaking process of the UHP DC EAF in a factory.