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.     

Modeling of fluid flow and heat transfer in the plasma region of the dc electric arc furnace

A mathematical model describing the transport processes in the plasma arc in dc electric arc furnaces has been developed. The equations of conservation of mass, momentum, and energy are solved numerically in conjunction with Maxwell's equations of the electromagnetic field to calculate the velocity and temperature distributions in the plasma region. The heat transfer from the arc to a rigid anode surface is calculated. The model is applied to obtain quantitative results on the relative importance of the various modes of heat transfer from the electric arc to the anode surface. Computational results were obtained for varying arc current magnitudes and anode-cathode distances. The model predicts higher arc jet velocity and a broader arc core at higher arc current. The shorter arc length is more efficient for transferring heat to the anode.     

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.     

Simulation and application of pulsating bottom-blowing in EAF steelmaking

Pulsating bottom-blowing was proposed to strengthen the electric arc furnace (EAF) molten bath stirring. The fluid flow characteristics and stirring effects of different pulsating bottom-blowing modes on EAF molten bath were studied through water model experiments and numerical simulations. The mixing time was measured by water model experiments and the flow field characteristics of EAF molten bath were simulated by numerical simulations. Compared with conventional bottom-blowing, pulsating bottom-blowing can accelerate the fluid flow velocity and improve the stirring of molten bath. With pulsating bottom-blowing, the molten bath fluid flow field is more disorder, the fluid flow velocity increases and the dead zone volume decreases. Compared with EAF steelmaking with conventional bottom-blowing conditions, pulsating bottom-blowing technology can improve the metallurgical effects and the molten steel quality in EAF steelmaking with lower FeO content of final slag, lower phosphorus content and carbon-oxygen equilibrium of final molten steel, and lower temperature deviation.     

The preparation process of nitrogenous ferrovanadium with bottom-blowing nitriding in electrical arc furnace

The flow field characteristics and stirring abilities of five kinds of bottom-blowing arrangements on the molten bath were researched in a 3t electrical arc furnace (EAF) with regular shape. The mixing time was measured by water experiment under different flow rates. Flow field characteristics of three-phase flow were simulated by numerical simulation. The average mixing time decreased with the flow rate and the radius of circle coincide increasing for the EAF with regular shape. Moreover, weakening counteracting force of counter-swirls could efficiently reduce mixing time than weakening impeding forces of sidewall with concentric circle arrangements at the tested conditions. Compared with 6R bottom-blowing arrangement at industrial application research, the 7R bottom-blowing arrangement, which was determined by the water model experiments and the simulations, could stir molten better in nitriding process, which agreed well with the experimental results of the water experiment and the numerical simulation.     

130 t直流电弧炉喷吹过程的优化模拟

在当今经济健康发展的背景下,电弧炉炼钢凭借其污染小、流程短和产品多样的特点,已逐渐成为各大钢铁企业大力发展的对象,在整个钢铁生产的地位比以往的每个时候都要重要,而电弧炉熔池的流动状态会直接影响电弧炉的冶炼效果,这主要与氧枪喷吹强度和布置方式有关.为研究不同工况条件下电弧炉流场的变化,为大型电弧炉选取最合适的工艺参数,以...     

Effect of the geometric parameters of the EAF bath on the main characteristics of furnace operation

The models of melting a semiproduct in an electric arc furnace (EAF) and metal mixing developed earlier are used to study the effect of the proportion of the bath sizes on the following main technicaleconomic characteristics of a heat: the expenditure of electric energy, the heat time, and the operating time under electric current. The range of the optimal values of the proportion of the EAF bath sizes is determined with allowance for bath stirring with CO bubbles during decarburization. It is useful to increase the bath depth of EAFs operating according to single-slag technology and to classify furnaces according to the type of charge and the method of its loading.     

Effect of oxyfuel burner ratio changes on energy efficiency in electric arc furnace at Co-Steel Lasco

Abstract

Trials were conducted on Co-Steel Lasco's electric arc furnace (EAF) to evaluate the effect of oxyfuel burner ratio changes on furnace energy efficiency and productivity. Carefully controlled trials with the collection of numerous process and sample data over 331 heats provided statistically significant results. The oxygen available for post-combustion in the furnace was increased by 19%. As the burners were operating at their maximum oxygen constraint, this was achieved by decreasing the natural gas consumption by 43%. Results of this study indicate that decreases in terms of specific electrical energy consumption (4·0%), power on time (5·0%), and tap to tap time (4·5%) were realised. Slag chemistry, electrode consumption, and yield were not affected. Measurement data support the finding that more heat was transferred into the steel with the post-combustion burners: a flat bath was achieved earlier; high bath temperatures were reached more quickly; power on time was reduced, leading to reduced electrical energy consumption. Analysis suggests that furnace thermal energy losses were reduced by less air inleakage, less incomplete methane combustion, and earlier achievement of foamy slag conditions.     

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.     

Laws of the DC arc in an inert gas during melting in furnaces with a tungsten electrode

The I?CV and voltage-baric characteristics of the dc arc glowing in argon between a tungsten cathode and a molten anode made of titanium, chromium, or manganese are studied at various gas pressures, arc currents, and arc lengths. The arc is probed to establish the relation between the voltage drop across the arc and its regions on the anode material and the melting conditions.     

Effect of oxygen flow rate and temperature on supersonic jet characteristics and fluid flow in an EAF molten bath

A new operation method for the oxygen lance of an electric arc furnace (EAF) was proposed, meeting the simultaneous demand for low oxygen flow rate and high stirring power in a particular smelting stage. When the oxygen flow rate needs to be reduced, the stirring power of the jet can be improved by increasing oxygen temperature properly. Free supersonic jet characteristics at different flow rates and stagnation temperatures were studied by numerical simulation and validated by a jet measurement experiment. The results showed that the designed Mach number can be maintained by coupling adjustment of flow rate and stagnation temperature. Meanwhile, a three-phase, full-scaled numerical model for a commercial 75t EAF with three oxygen lances on the side-wall was established to study the fluid flow in the molten bath. The velocity distribution, cavity profile and total kinetic energy of the EAF bath induced by the impingement of supersonic jets onto the liquid bath were discussed and compared. It was found that the fluid flow characteristics of the EAF molten bath can be improved even if the oxygen flow rate was reduced as long as the oxygen temperature could be increased reasonably.     

电弧炉炼钢成分预报现状与熔池搅拌对其影响

电弧炉炼钢成分预报与控制直接影响冶炼时间、产品质量与生产成本,是电弧炉炼钢智能化的重要环节。对转炉、电弧炉副枪检测技术和炉气分析技术进行了分析,探讨了炼钢过程的选择性氧化机理与智能算法在成分预报中的应用。结合熔池流动慢、反应不均衡的动力学条件,讨论了电弧炉炼钢成分预报的难点。在国内外文献综述的基础上,讨论了电弧炉底吹搅拌、氧气射流及电磁流体对钢液流动的影响,提出将电弧炉熔池钢液流动行为的动力学影响和炼钢反应选择性氧化热力学相结合,实现成分实时预测研究的设想,对开展电弧炉炼钢成分预测研究具有指导意义。     

Physical modelling of fluid flow in electric arc furnace caused by impinging gas jets

Abstract

The interaction of liquid steel and an inclined impinging oxygen jet in an electric arc furnace (EAF) is of interest both commercially and scientifically. The bath activity in the EAF may vary from a surface splash ejected to high elevation to intense subsurface mixing. The system is appropriately modelled using water and nitrogen with scaled flowrates. In previous work, the gas/liquid contact was investigated by use of a geometrically similar 1/3rd scale three-dimensional water model. The cavity formed by the jet contacting the liquid surface was characterised by four modal regimes. These regimes were seen to depend on the lance angle, the height of the lance and the jet flowrate. To investigate the evolutionary mechanisms of the cavity regimes, a two-dimensional water model study was undertaken. The two-dimensional water model was a rectangular viewing tank with an inner movable glass wall that allowed a very thin slice of the system to be obtained. The shape of the cavity formed on the water surface was seen clearly along with the expected cavity oscillations. High speed video footage of the two-dimensional system allowed the cavity oscillation to be directly observed. The gas-liquid interaction produced a wave that travelled along the surface of the cavity until it reached the cavity crest where it was torn from the liquid surface and dispersed in a splash. It is the regular progression of the wave's nodes and antinodes along the cavity surface that makes the cavity appear to oscillate. When the wave reaches the crest of the cavity, it will either fall back into the path of the gas jet or be projected as a splash depending on the verticality of the cavity surface. The two-dimensional work, along with the initial three-dimensional investigation, has shown that the troublesome splash in the EAF is caused by how the lance is positioned directionally or azimuthally. By changing the lance angle or height the deleterious splashing of molten metal may be prevented, ameliorated or controlled. The frequency of the wave production was determined from the high speed video footage. The cavity oscillation was found to be a function of the size of the cavity, the inclined height of the lance and the modal regime being produced. Alterations to the flow through the lance had only a moderate effect on the frequency of oscillation indicating that velocity was not the major influential factor.     

Development and application of electric arc furnace combined blowing technology

A number of electric arc furnace (EAF) plants in China use high proportions of hot metal in the charge because of availability of excess liquid iron at the steelworks and/or because of the high price of scrap relative to hot metal. Liquid steel costs are still higher than the basic oxygen furnace as the EAF is not as efficient when refining liquid iron. EAF combined blowing technology has been modelled and installed in industrial plants with the aim of increasing stirring and hence improving refining. The industrial application of the combined blowing technology in a number of steel plants indicates that the combined blowing technology of EAF can effectively improve the pool stirring strength and reaction dynamics condition of the molten pool, and optimise production.     

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.     

Control of greenhouse gas emissions from electric arc furnace steelmaking: evaluation methodology with case studies

Abstract

The energy intensive nature of electric arc furnace (EAF) steelmaking necessitates that efforts to reduce greenhouse gas (GHG) emissions will affect steelmakers directly and/or through electric power producers. A model of GHG emissions from an EAF meltshop has been developed using the life cycle assessment approach. Direct and indirect sources of GHG gas emissions are estimated and ranked. Furnace combustion optimisation was evaluated in case studies conducted on a Canadian conventional EAF and a British scrap preheating `shaft' furnace. The analysis assumed 32 and 68% fossil fuel electricity generation, respectively. These case studies show that indirect GHG emission sources, in particular electricity generation, are more significant than direct emissions from the EAF. For the conventional EAF, offgas analysis and improved combustion control reduced electricity consumption by 40 kWh t^-1, costs by US$1·05/t, and GHG emissions by 20 kg CO₂-eq./t. For the shaft EAF, real time offgas monitoring and closed loop burner control reduced electricity consumption by 25 kWh t^-1, costs by US$3·6/t, and GHG emissions by 15 kg CO₂-eq./t. The case studies show that combustion optimisation using an EAF offgas analysis and combustion control system provides greater electricity, cost, and GHG reductions than previously reported in the literature.     

Characterisation of electric arc furnace dust generated during plain carbon steel production

Abstract

Electric arc furnace (EAF) dust is a waste generated in the EAF during the steel production process. Among different wastes, EAF dust represents one of the most hazardous, since it contains heavy metals such as Zn, Fe, Cr, Cd and Pb. The goal of the present work is to characterise the waste through chemical analysis, particle size distribution, X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy detection and thermal analysis. The waste sample is composed essentially of spherical particles and has a very small particle size and the majority of the identified elements were Fe, Zn, Ca, Cr, Mn, K and Si. The XRD has presented compounds such as ZnO, ZnFe₂O₄, Fe₂O₃, MnO, SiO₂, FeFe₂O₄ and MnAl₂O₄. According to the thermal analysis results, up to 1000°C the total weight loss was ～5%. The results of waste characterisation are very important to these further investigations.     

Influence of bottom-blowing gas species on the nitrogen content in molten steel during the EAF steelmaking process

In modern EAF steelmaking process, control of the nitrogen content of molten steel has become more and more important and bottom-blowing technique has been widely applied to promote the molten bath fluid flow, accelerate the metallurgical reaction and improve the quality of molten steel. In this study, the influence of bottom-blowing gas species on the nitrogen content in molten steel during EAF steelmaking was systematically investigated and analysed. Combining the induction furnace experiments and theoretical analysis, the kinetic models of nitrogen change in molten steel with bottom blowing N₂, Ar and CO₂ were established theoretically and validated experimentally. Meanwhile, the thermodynamic laws and agitation capacity of different bottom-blowing gases were also clarified. Then, based on the industrial application research, the metallurgical effects, especially nitrogen removal, with different bottom-blowing gases were also studied and finally, a new concept was proposed for cyclic utilisation of CO₂ in the EAF steelmaking process.     

Magnetic field in a dc arc-furnace bath with different current leads at the bottom electrode

In a dc arc furnace, the design of the current lead at the bottom electrode may affect the current-bearing melt in the bath and also the arc behavior. Mathematical models are developed for the magnetic field strength close to a current lead in the form of a three-dimensional helix and a three-dimensional Archimedes helix. As an example, the behavior of the axial and radial components of the magnetic field strength is simulated over the depth and radius of the bath in a dc arc furnace. The influence of the number of turns in the lead on the increment in the magnetic field strength and on the axial symmetry of the field’s radial component is analyzed.