直流电弧炉的偏弧现象及其对策

伴随着直流电弧炉的大型化和高功率化，直流电弧出现了偏弧现象，导致炉料熔化不均，热损失增大及重新出现炉壁热点等缺点，限制了大型直流电弧能力的发挥。针对这种情况，本文从理论上分析了直流电弧炉产生偏弧现象的原因，并提出了改善的措施。     

电弧炉电能需求的生产实践与评价

电耗是电弧炉的重要技术指标之一,在当前发电行业背景下,降低电弧炉电耗具有显著的经济和环境效益。根据典型电弧炉企业生产数据,系统分析各项工艺参数与电耗之间的关系,并进一步评价了各种方法降低电耗的环境效益。结果表明,优化供电制度和强化供氧是具有良好环境效益的节电手段。对于连续加料电弧炉,天然气喷吹对降低电耗的作用被极大减弱,天然气消耗与电耗的相关系数为-1.13 kW·h/m³,其应用不利于CO₂减排。尽管兑加铁水可以显著降低电耗,但是兑加40%(质量分数)铁水的连续加料电弧炉能耗和碳排放量分别是全废钢连续加料电弧炉的2.25和2.50倍,不利于推动钢铁工业节能减排工作。因此,降低电弧炉电耗需要通过增加电弧炉中化学能和物理热的供应及减少能量损失的手段来实现。     

Power Delivery from the Arc in AC Electric Arc Furnaces with Different Gas Atmospheres

The amount of heat supplied to the electric arc furnace affects the melting rate. Power delivery in a three‐phase EAF is influenced not only by the electric parameters such as arc length and voltage but also by thermal properties of the gases that form the plasma in the arc region. Application of the Channel Arc Model (CAM) suggests that power delivery is enhanced with long‐arc, maximum tap operation and plasma gases with high heat capacity. It is also suggested that foaming improves power delivery due to the presence of gases with high heat capacity.     

铁合金矿热炉烟气余热回收及发电工艺系统

对铁合金矿热炉进行了热平衡分析,对比了不同类型矿热炉的烟气特性,开发出3套针对铁合金烟气特性的余热发电工艺系统,并以具体实例进行了经济效益分析。     

电弧光保护装置在电解铝行业硅整流柜中的应用特点

硅整流装置是电解铝供电整流系统中的主体设备。整流柜发生弧光短路事故给企业带来巨大损失,而现有的保护系统不能满足整流机组快速切除弧光故障和保护覆盖范围的要求。包铝股份供电公司结合行业特点和整流供电系统存在的特殊情况,在电弧光保护装置的应用过程中开发出了不同于普通配电系统的电弧光保护装置,在电弧光保护系统应用方面形成了独特的技术,弥补了电解铝整流系统的保护设计缺陷。     

超高功率电弧炉炼钢工艺模型

本文以物料平衡、热量平衡和化学平衡为基础，采用理论与经验相结合的模化方法，建立了超高功率电弧炉炼钢工艺模型，即冶金模型和热模型。冶金模型包括：优化配料模型、石灰加入量模型、钢水熔清成分模型、吹氧量模型、钢水终点成分模型和最优补加合金模型。热模型包括：废钢预热温度模型、能量消耗模型、能量损耗计算模型、能量供应计算模型和钢水温度预报模型。冶金模型中，加入了造渣料的计算。热模型中，考虑了废钢预热、氧燃烧     

Determination of the allowable graphite amount of a composite electrode for an electric arc furnace

Distribution of heat loads along the length and perimeter of electrodes in terms of the nominal power of transformer, optical characteristics of surfaces taking part in heat exchange and geometric dimensions of the furnace and electrodes has been obtained on the basis of mathematical simulation of processes of heat transfer in working volume of an electric arc furnace, the screening of radiation by electrodes being taken into account. The results obtained give an opportunity of determining the minimal permissible length of the composite electrode graphite part for furnaces with various nominal power transformers. The minimal permissible length of electrode-consumed graphite part is in the range of 80–100 cm for an 100-t electric arc furnace with the transformer of nominal power equal to 75 or 90 MVA. Decrease of the length of electrode graphite part will lead to damage of cooled metal part due to water burn-out.     

Computer modeling of heat flow in welds

This paper summarizes progress in the development of methods, models, and software for analyzing or simulating the flow of heat in welds as realistically and accurately as possible. First the fundamental equations for heat transfer are presented and then a formulation for a nonlinear transient finite element analysis (FEA) to solve them is described. Next the magnetohydrodynamics of the arc and the fluid mechanics of the weld pool are approximated by a flux or power density distribution selected to predict the temperature field as accurately as possible. To assess the accuracy of a model, the computed and experimentally determined fusion zone boundaries are compared. For arc welds, accurate results are obtained with a power density distribution in which surfaces of constant power density are ellipsoids and on radial lines the power density obeys a Gaussian distribution. Three dimensional, in-plane and cross-sectional kinematic models for heat flow are defined. Guidelines for spatial and time discretization are discussed. The FEA computed and experimentally measured temperature field,T(x, y, z, t), for several welding situations is used to demonstrate the effect of temperature dependent thermal properties, radiation, convection, and the distribution of energy in the arc.     

Characteristics of electric arc furnaces powered by a low-frequency alternating current

The changes in the parameters of a DSP-100 electric arc furnace that are induced by a decrease in the current frequency are considered. It is shown that the related decrease in the current lead resistances causes an increase in the arc power and voltage, a decrease in the reactive power, and an increase in the electrical efficiency and the power coefficient. The heat indices are expected to be significantly improved.     

硅铁矿热炉余热利用现状及发展趋势

依据国内硅铁矿热炉余热利用实际情况,重点分析该行业余热发电在审批、设计、管理、运行等方面存在的问题,并对余热发电如何规范发展提出切实可行的建议方案。     

矿热炉烟气1×6 MW余热发电工艺与设备选型

铁合金行业烟气余热资源的综合利用是节能减排的主要方向。文章以比较典型的矿热炉冶炼与精炼工艺,即2×25.5 MVA锰硅矿热炉+1×6.3 MVA精炼炉为基础,配置1×6 MW余热发电,对矿热炉烟气余热发电工艺及设备选型进行了介绍并作了简单的技术经济分析,希望能为该技术的推广实施提供参考。     

我国电弧炉炼钢技术的进展讨论

10年来我国电弧炉炼钢技术在产量、装备技术(大型化、高的技术经济指标)、高效化技术(超高功率供电、辅助能源、炉料多元化、减少非通电时间、废钢预热、连续化生产)和洁净化技术方面均取得了显著进展。但是废钢资源短缺、电力不足和能源结构不合理等因素制约了我国电弧炉炼钢的进一步发展。文中讨论了我国电弧炉炼钢发展的重点(炉料多样化、合理供电、能量多样化、余热利用和绿色环保)和前瞻(低碳经济洁净钢生产)。     

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.     

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.     

Observations of melt rate as a function of arc power,CO pressure,and electrode gap during vacuum consumable arc remelting of Inconel 718

Statistically designed experiments were conducted at two different production melt shops to evaluate the influence of arc power, CO pressure, and electrode gap on melt rate. Approximately 11,000 kg of Inconel 718 alloy 0.4 m diameter electrodes were vacuum consumable arc remelted into 0.5 m diameter ingots. Analysis of the experimental results revealed that melting efficiency (melting rate/kW) was maximized when CO pressure and electrode gap were held at low levels. Under these conditions, the heat distribution (created by the vacuum arc) on the electrode tip and the molten pool exhibited macro uniformity. Increased CO pressure and/or electrode gap depressed the melt rate, and at 13.3 Pa (100 microns) and a 0.050 m electrode gap, this depression exceeds 46 pct. Increasing these parameters also changed the arc behavior to that of a constricted arc with a highly localized heat input. It is hypothesized that the change from the usual diffuse arc to this constricted arc results in intense Lorentz pumping in a localized region of the molten pool atop the ingot causing fluid flow transients. These transients could, in turn, create solidification defects.     

Reducing metal losses when smelting steel in high-power arc furnaces

The heat transfer in arc furnaces with high input power is considered, in the case of induced slag foaming. Most of the power is consumed in evaporation of the metal and slag at hot spots under the electrodes and in zones of oxygen injection.     

Nitrogen Removal and Arc Voltage Increase in EAF Steelmaking by Methane Injection into the Arc

Methane injection into the arcs of electric arc furnaces has been shown on pilot scale to lead to a remarkable arc voltage increase at constant arc current and arc length. Recent investigations have been concerned with the associated metallurgical effects making use of a gas‐tight 150‐kg arc furnace operated with two AC plasma torches. A first test with bored graphite electrodes in this furnace confirmed the power increase observed during methane injection. The carburization slowly occurring when 6 % CH₄ were injected into the argon atmosphere of the furnace could be avoided by adding minor amounts of CO₂. A slag layer decreased mass transfer rates without noticeably affecting heat transfer. Manganese loss by evaporation was measured to investigate the influence of power increase and slag layers. From the results, an increase of 200 K was concluded for the melt surface temperature when CH₄ was added to pure argon. Methane injection into the arcs proved to accelerate nitrogen removal considerably. Starting with an intentionally high nitrogen content of about 200 ppm, the nitrogen removal rate was found to be slowest with pure argon plasma arcs, faster with 90 % Ar + 10 % H₂, and fastest with 95 % Ar + 5 % CH₄ reaching final contents of less than 20 ppm of nitrogen. Based on thermodynamic calculations, the denitrogenation reactions appear to take place via atomic nitrogen in pure argon plasma, via NH₃ in Ar + H₂ and via HCN in Ar + CH₄.     

直流矿热炉熔炼硅锰合金温度场-电磁场数值模拟

采用直流供电成为电弧炉熔炼硅锰合金的发展方向.由于直流供热强度增加,炉衬的温度分布及传热规律需要重新考察及设计.建立了炉衬与炉内熔池耦合的三维非稳态传热模型,研究给定不同外加电压时直流矿热炉炉内的温度场和电磁场.研究表明,外加电压由100 V增大到300 V后,电弧区的最高温度增大了 150％.底电极中心与炉壁的温差T...     

现代电炉炼钢技术在莱钢超高功率电炉的应用实践

论述了强化用氧技术、热装铁水技术、电炉终点控制技术、泡沫渣技术、电炉烟气余热回收及净化技术等现代化电炉炼钢技术在莱钢超高功率电炉的应用情况及取得的实际效果。