Behavior of Conducting Liquid within an Arc Furnace in a Vertical Magnetic Field

In a vertical magnetic field, bulk electromagnetic forces arise in conducting melt within the bath of a dc arc furnace. As a result, the melt is set in motion. The flow of slag and metal in the furnace bath may lead to effective mixing but may also have negative consequences, such as increased lining wear in the region of the hearth electrode. There has been little research on conductive mixing in the bath of a dc arc furnace. Theoretical concerns include the character of the flow in the bath under the action of magnetic fields of specific magnitude; practical considerations include the lack of simple and reliable sources of magnetic fields. In the present work, the utility of a transparent physical model in studying the flow of conducting liquid in an external vertical magnetic field is investigated. The applicability of the modeling results to processes in the 5-t bath of an industrial dc arc furnace is analyzed. It proves possible in principle to study the flow of conducting melt in external vertical magnetic fields on models based on transparent nonmetallic conducting liquids. The use of an aqueous solution of table salt permits assessment of the liquid velocity at its free surface and close to the hearth electrode by video recording. By physical modeling of the flow of conducting fluid in the bath under the action of an external vertical magnetic field, with different switching sequences of the hearth electrode and different currents in the bath, it is possible to establish the character of the liquid flow when the hearth electrode is at the center of the bath or somewhat displaced. The mean rate of liquid rotation in the horizontal plane is increased when the hearth electrode is at some distance from the bath axis. The strength of the vertical magnetic field producing conductive motion in the metal bath of a 5-t dc arc furnace is estimated: around 5 kA/m.     

Numerical study of dc arc plasma and molten bath in dc electric arc furnace

Abstract

A numerical study of the arc plasma and molten bath in a dc electric arc furnace (EAF) is useful for understanding and improving the production process of the dc EAF. In the present paper, a mathematical model based on conservation equations of mass, momentum and energy along with Maxwell's equations is developed to describe the flow field and heat transfer in the arc and molten bath regions of a dc EAF simultaneously. The governing equations are solved using the PHOENICS software package. The calculated results show good agreement with those of previous studies, giving a useful insight into the factors of arc heat transfer and bath circulation.     

单电极直流矿热炉的偏弧分析

针对６．３ＭＶＡ直流矿热炉在冶炼硅铁时电弧偏移的现象,通过对三维磁场的计算,指出电弧偏移是由于炉外短网铜排中流过的强大直流所产生的磁场对电弧施加力的作用而造成的,讨论了炉外短网铜排对称布线方式对电弧偏移大小的影响及其抑制偏弧的效果。     

Fluid Flow and Heat Transfer Modeling of AC Arc in Ferrosilicon Submerged Arc Furnace

 arc has been developed and used to predict heat transfer from the arc to the molten bath in ferrosilicon AC submerged-arc furnace. In this model the time-dependent conservation equations for mass, momentum and energy in the specified domain of plasma zone have been solved numerically coupled with the Maxwell and Laplace equations for magnetic filed and electric potential respectively. A control volume based finite difference method was used to solve the governing equations in cylindrical coordinates. The reliability of the developed model was tested by comparison with the data available in the literature. The present model showed a better consistency with the data given in the literature because of solving the Maxwell and Laplace equations simultaneously for calculation of current density. Parametric studies were carried out to evaluate the effect of electrical current and arc length on flow field and temperature distribution within the arc. According to computed results, a lower power input lead to the higher arc efficiency.     

Fluid Flow Modeling of Arc Plasma and Bath Circulation in DC Electric Arc Furnace

 A mathematical model describing the flow field, heat transfer and the electromagnetic phenomenon in a DC electric arc furnace has been developed. First the governing equations in the arc plasma region are solved and the calculated results of heat transfer, current density and shear stresses on the anode surface are used as boundary conditions in a model of molten bath. Then a two dimensional time dependent model is used to describe the flow field and electromagnetic phenomenon in the molten bath. Moreover, the effect of bottom electrode diameter on the circulation of molten bath is studied.     

炼钢短流程工艺国内外现状及发展趋势

全废钢连续加料电弧炉内长电弧作为炉内主要的能量来源,对废钢熔化及钢液升温至关重要。采用磁矢量势的磁流体动力学方法建立了电弧炉内电弧的数值模型,并基于该数值模型对电弧炉内电磁场、温度场和流场进行耦合求解,研究了电流大小、弧长对电弧炉内电弧的温度、速度、压力及气体剪切力特性的影响。结果表明,全废钢连续加料电弧炉内电弧等离子体呈“长钟型”分布,电弧柱较细长;随着电流增大,电弧有效作用范围增大,阳极表面电弧压力和气体剪切力增大;随着弧长增加,电弧有效作用范围减小,阳极表面的电弧压力和气体剪切力减小。短弧操作对熔池冲击剧烈,长弧操作熔池较为平稳,合理控制电流和弧长能有效提高电弧热效率。     

Arc Distribution During the Vacuum Arc Remelting of Ti-6Al-4V

Currently, the temporal distribution of electric arcs across the ingot during vacuum arc remelting (VAR) is not a known or monitored process parameter. Previous studies indicate that the distribution of arcs can be neither diffuse nor axisymmetric about the center of the furnace. Correct accounting for the heat flux, electric current flux, and mass flux into the ingot is critical to achieving realistic solidification models of the VAR process. The National Energy Technology Laboratory has developed an arc position measurement system capable of locating arcs and determining the arc distribution within an industrial VAR furnace. The system is based on noninvasive magnetic field measurements and a VAR specific form of the Biot–Savart law. The system was installed on a coaxial industrial VAR furnace at ATI Albany Operations in Albany, OR. This article reports on the different arc distributions observed during production of Ti-6Al-4V. It is shown that several characteristic arc distribution modes can develop. This behavior is not apparent in the existing signals used to control the furnace, indicating the measurement system is providing new information. It is also shown that the different arc distribution modes observed may impact local solidification times, particularly at the side wall.     

VAR炉熔炼过程中磁场作用的分析

针对VAR炉的结构特点,探讨了真空自耗熔炼过程中磁场产生的原因及其在熔化区域分布的规律;分析了VAR熔炼过程中存在的3种主要磁场,即熔化电流自生的水平磁场、外加的纵向磁场和VAR炉自身及周围铁质结构件产生的杂散磁场,对熔炼过程及铸锭质量的影响。     

A Multiscale 3D Model of the Vacuum Arc Remelting Process

A three-dimensional, transient, multiscale model of the VAR process is presented, allowing novel simulations of the influence of fluctuations in arc behavior on the flow and heat transfer in the molten pool and the effect this has on the microstructure and defects. The transient behavior of the arc was characterized using the external magnetic field and surface current measurements, which were then used as transient boundary conditions in the model. The interactions of the magnetic field, turbulent metal flow, and heat transfer were modeled using CFD techniques and this “macro” model was linked to a microscale solidification model. This allowed the transient fluctuations in the dendritic microstructure to be predicted, allowing the first coupled three-dimensional correlations between macroscopic operational parameters and microstructural defects to be performed. It was found that convection driven by the motion of the arc caused local remelting of the mushy zone, resulting in variations in permeability and solute density. This causes variations in the local Rayleigh number, leading to conditions under which freckle solidification defects will initiate. A three-dimensional transient tracking of particle fall-in was also simulated, enabling predictions of “white spot” defects via quantification of the trajectory and dissolution of inclusions entering the melt.     

Acoustic characteristics of electric arc furnaces

A mathematical model is constructed to describe the appearance and development of the noise characteristics of superpower electric arc furnaces. The noise formation is shown to be related to the pulsation of the axial plasma flows in arc discharges because of the electrodynamic pressure oscillations caused by the interaction of the self-magnetic field with the current passing in an arc. The pressure in the arc axis changes at a frequency of 100 Hz at the maximum operating pressure of 66 kPa for an arc current of 80 kA. The main ac arc sound frequencies are multiples of 100 Hz, which is supported in the practice of operation of electric arc furnaces. The sound intensity in the furnace laboratory reaches 160 dB and is decreased to 115–120 dB in the working furnace area due to shielding by the furnace jacket, the molten metal, and the molten slag. The appropriateness of increasing the hermetic sealing of electric furnaces and creating furnaces operating at low currents and high transformer voltages is corroborated.     

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.     

Electrical Conditions of Foundry Operation of DC and AC Arc Furnaces

The electrical conditions of operation of ac and dc 0.5- to 25-t furnaces, namely, the installed, active and net powers, the maximum electric arc voltage, the electric arc operating current, and the electrical efficiency, are considered and compared. The parameters of a dc twin furnace, where one power supply is used for two furnaces and the periods of melting and finishing of a liquid metal in these furnaces are separated in time, are analyzed.     

Three-phase Fluid Numerical Simulation and Water Modeling Experiment of Supersonic Oxygen Jet Impingement on Molten Bath in EAF

By means of the computational fluid dynamics software Fluent 6.3, a mathematical model of three-dimensional three-phase fluid flow field in the molten bath of electric arc furnace （EAF） with side accessorial oxygen lances was developed to study the transient phenomena of oxygen jet impingement on the molten steel and the molten slag. The water modeling experiment was carried out to verify the simulation results. The impingement of the supersonic oxygen jet caused impact dent on the molten steel surface accordingly. The area of impact dent changed almost in linear relationship to flow rate of oxygen jet, which can be expressed by a deduced mathematical equation. And the relationship between the impact force of oxygen iet and the correspondingly formed apparent static pressure on molten bath was obtained, which was in linear relationship and a direct proportion, and can also be expressed by a deduced mathematical equation.     

强磁处理对高炉循环冷却水的影响研究

高炉长寿技术的开发和实现是促进高炉生产实现高产、优质、低耗、高效益的有效措施。采用不结垢不腐蚀的冷却水或控制冷却水在工作条件下不结垢不腐蚀,是高炉长寿的前提条件之一。为获得磁化冷却水最佳的防垢、抑垢效果,通过正交试验确定了水磁化处理的最佳工艺参数。分析了磁场强度、磁处理时间和冷却水流速对冷却水磁化效果特征参数：PSI、pH值和电导率的影响,试验结果表明防垢效果最佳时的磁场强度34000GS,并用首钢高炉冷却水进行磁处理取得了满意的效果。     

DC-EAF熔池电磁场的数值模拟

建立了30t底电极直流电弧炉熔池电磁场的数学模型,开发研制了通用计算软件,研究了不同工况下磁场强度、电流密度、洛仑兹力的分布规律。     

Modelling of electrovortex and heat flows in dc arc furnaces with bottom electrode

Abstract

The article is devoted to the investigation of interaction between electrovortex and heat flows of liquid metal in dc arc furnaces with a bottom electrode. A mathematical model of liquid steel flows in a dc arc furnace with a bottom electrode was developed, and an algorithm of a three-stage solution was produced based on standard software packages. The results of electromagnetic, heat transfer and hydrodynamic analysis in industrial dc arc furnaces are given. It is shown that the Lorentz force makes up ～30% of the volumetric gravity force and makes the main contribution to vortex flow of liquid metal in a dc arc furnace. The convection flows with the maximum heat power of furnace make a significant contribution to the vortex flow of liquid metal, and the maximum value of the vortex flow velocity is ～1·5 times more than the movement without convection. The verification of results has been carried out by comparing them with general electrovortex flows theory, experimental data and results of similar software packages.     

The trajectories and distribution of particles in a turbulent axisymmetric gas jet injected into a flash furnace shaft

Numerical computations have been performed for the behavior of a vertical turbulent particle-laden gas jet exemplified by the shaft region of a flash-smelting furnace. The two-equation(k-ε) model was used to describe turbulence. Model predictions for the gas and solid flow fields give a satisfactory representation of experimental data taken from the literature. The predictions of flow properties of the two phases under flash-smelting conditions have been obtained for various inlet conditions, particle sizes, particle loading, and oxygen enrichment. Model predictions show that the axial velocity of the particle phase is substantially higher than that of the gas phase. The presence of solid particles causes the axial velocity of the gas phase to be greater near the centerline and lower in the outer region than in a single-phase gas jet. A more uniform distribution of particles was obtained by introducing a strong radial velocity of the distribution air at the inlet. The implications of the behavior of a particle-laden gas jet on flash-smelting processes arc discussed.     

Simulation of Flow Fluid in the BOF Steelmaking Process

The basic oxygen furnace (BOF) smelting process consists of different chemical reactions among oxygen, slag, and molten steel, which engenders a vigorous stirring process to promote slagging, dephosphorization, decarbonization, heating of molten steel, and homogenization of steel composition and temperature. Therefore, the oxygen flow rate, lance height, and slag thickness vary during the smelting process. This simulation demonstrated a three-dimensional mathematical model for a 100 t converter applying four-hole supersonic oxygen lance and simulated the effect of oxygen flow rate, lance height, and slag thickness on the flow of molten bath. It is found that as the oxygen flow rate increases, the impact area and depth increases, which increases the flow speed in the molten bath and decreases the area of dead zone. Low oxygen lance height benefits the increase of impact depth and accelerates the flow speed of liquid steel on the surface of the bath, while high oxygen lance height benefits the increase of impact area, thereafter enhances the uniform distribution of radial velocity in the molten steel and increases the flow velocity of molten steel at the bottom of furnace hearth. As the slag thickness increases, the diameter of impinging cavity on the slag and steel surface decreases. The radial velocity of liquid steel in the molten bath is well distributed when the jet flow impact on the slag layer increases.     

氯化物熔盐电解槽磁场模拟

氯化物熔盐电解槽内部磁场的稳定对电流效率的提升非常重要。以50 kA氯化物熔盐电解槽为研究对象，运用有限元软件COMSOL建立电解槽三维电磁场模型，模拟了50 kA电解槽不同平面x、y、z三个方向的磁场强度和电磁力分布特点，重点研究工艺参数对磁场强度和电磁力分布的影响。结果表明，电流增加，每个平面的磁场强度和电磁力均增加，且增幅相同；降低极距、增加电解质液面高度、增加阳极半径均会使磁场强度最大值和电磁力最大值增加。