Study of Open Eye Formation in an Argon Stirred Ladle

Two cold models were employed to simulate the formation of open‐eyes in a gas stirred ladle. In the first model, water and silicon oils were employed to simulate liquid steel and slag respectively. In the second one, liquid Ga‐In‐Sn alloy was used to simulate liquid steel, while 12% hydrochloric acid simulated the top slag. The experimental results indicated that the gas flow rate, height of the lower liquid and height of the top liquid had a strong impact on the open‐eye size. On the other hand, the viscosity of the top liquid and the interfacial tension between the two liquids had only little effect on the open‐eye size. A semi‐empirical model was developed to describe the size of open‐eye as a function of the heights of the two liquids and the gas flow rate. The two sets of parameters obtained for the water and Ga‐In‐Sn models were very different. Industrial trials were also conducted to examine the applicability of the models. The model developed based on the Ga‐In‐Sn model could well predict the formation of an open‐eye during ladle treatment. The model could be adopted by the industry to estimate the real gas flow rate by measuring the size of the open‐eye online. On the other hand, the mathematical model based on water model experiments was unsatisfactory when applied to the industrial ladle process.     

Numerical Simulation of Fluid Flow and Interfacial Behavior in Three‐phase Argon‐Stirred Ladles with One Plug and Dual Plugs

A numerical investigation is performed to describe the quasi‐steady fluid flow and interfacial behavior in a three‐phase argon gas‐stirred ladle with off‐centered bottom Ar injection through a plug and two plugs placed in 180° and 90°configurations, respectively. The flow of the fluid phase is solved in an Eulerian frame of reference together with the motion of every individually injected Ar bubble, tracked in its own Lagrangian frame. Volume of fluid (VOF) model is used to track any interface between two or more immiscible phases, which include slag/metal, slag/gas and metal/gas. The characteristics of fluid flow in a gas‐stirred ladle with one plug or two plugs configuration are described when the slag layer and the top gas are presented. The slag layer deformation and slag open‐eye formation at different Ar gas flow rates for three types of plug arrangements are given. The comparison of the mixing time, the deformation of slag layer and the behavior of slag/steel interface between one‐plug and two‐plug system is made. Several implications for ladle operational issues during a gas‐stirred ladle refining cycle are discussed. It is found that the proper selection of Ar gas flow rate and plug arrangements during a ladle refining cycle is required for different refining purposes considering the mixing and metallurgical reaction in a three‐phase ladle system.     

吹氩精炼钢包内非金属夹杂物去除机理

 通过物理模拟试验,研究分析了底吹氩精炼钢包内夹杂物去除机理以及吹氩量对其的影响规律。结果表明：钢包中夹杂物的上浮主要是通过上升的钢液流携带,底吹氩量对夹杂物在钢包表面的钢-渣界面去除行为存在重要影响。吹氩量较小时,钢-渣界面稳定,夹杂物在浮力、毛细作用力等共同作用下穿过平坦的钢-渣界面而被吸收;吹氩量较大时,钢-渣界面波动大,渣眼周围发生卷渣,夹杂物被卷入的液滴吸收,随液滴进入渣层;吹氩量大,渣眼周围形成渣泡,夹杂物被渣泡吸收,随渣泡进入渣层。吹氩量达到一定时,夹杂物被钢-渣界面的吸收成为其被去除的限制性环节,且吹氩量较大时夹杂物去除效果最差,为实际吹氩精炼过程吹气量的控制提供了指导。     

Theoretical Study of Equilibrium Reactions between Metal Droplets and Slag

The dispersion of metal droplets in slag was investigated through analysis of slag samples taken during ladle refining at Scana Steel in Björneborg, Sweden. The chemical composition of steel droplets found in the ladle slag was determined for five industrial‐scale heats. Possible reactions occurring between the steel droplets and slag were identified, as were differences in steel‐droplet and steel‐bulk composition. Three different slag models were used to calculate the activities of oxide components (Al₂O₃ and SiO₂) in the slag. These results were then used in the dilute‐solution model, whereby oxygen activities in the steel droplets were calculated and compared with measured oxygen activities in the steel bulk. Significant differences were found in the comparison of both the calculated and measured oxygen activities and the steel bulk and droplet compositions.     

Size analysis of slag eye formed by gas blowing in ladle refining

The formation of slag eye in a gas stirred ladle was studied through cold models and industrial trials.In the cold model,water and sodium tungstate solution were employed to simulate liquid steel,and silicon oil was employed to simulate slag.The simulation results revealed that the gas flow rate and bath height had strong effects on the slag eye size.In particular,the thickness of slag layer played a strong role in the slag eye size.In addition,the slag eye could not be formed when the thickness of the top layer was more than 4 cm in water-silicone oil model.Besides,the section area of vessel had a great impact on the slag eye size.Industrial trials results showed a similar trend that the gas flow rate was very significant on the slag eye size.The predictions of the existing models showed larger predictions deviations compared with the experimental data.Moreover,a new model without fitting parameters was developed based on force balance and mathematical derivation,and verified by the experimental data.The new model provides the prediction with small deviations by comparing with the data acquired from cold models and industrial trials.     

Influence of the Stirring Gas in a 170‐t Ladle on Mixing Phenomena – Formation and On‐line Control of Open‐Eye at an Industrial LD Steel Plant

3D calculations with Computational Fluid Dynamics were carried out to evaluate the flow pattern under industrial conditions with different gas flow rates at the steel plant of Saarstahl AG. The generated flow pattern consists of a circulating loop characterised by an upward flow driven by the argon gas and a downward flow close to the wall on the opposite side of the porous plug in the case of a gas flow rate of 27 STP m³/h. When this high gas flow rate is used, the gas bubbles are taking a straight way from the inlet, but further up the momentum from the circulating steel is affecting the path of the gas bubbles followed by a breakthrough zone at the top surface. Intensive experiments with the 170‐t ladle of Saarstahl AG revealed typical open‐eyes. Large open‐eyes coupled with turbulences in the surface were generated in the case of gas flow rates between 20 and 30 STP m³/h. Intensive turbulences and even smoke formation were identified when a gas flow rate of > 30 STP m³/h was applied. For the investigation of the influence of gas stirring processes on the mixing phenomena samples were taken from the melt immediately after alloying. It could be seen that the analyses of Al, C, Mn and Si increased to the target analyses due to alloying and introduction of Ar through the porous plug. The total time for complete alloying depended on the elements within these experiments. It seemed to be that the alloying time increased in the order of Al, C, Mn and Si. For on‐line control and analysis of open‐eyes in the melt surface during ladle stirring, a BFI image processing system was installed at the steel plant of Saarstahl. It consisted of a conventional digital camera equipped with an infrared filter and coupled to an image processing software. Primary tests showed a slight influence of the open‐eye diameter at the end of the ladle treatment on inclusion densities in the liquid steel and oxidic K0 values of the finished wire rod. Additional experiments were performed but only a small correlation existed between the stirring energy at the end of ladle treatment and the inclusion length index of the applied blue brittle tests. But as soon as an open‐eye came into existence, the inclusion length was higher compared to those heats produced under a closed top slag.     

Use of Computational Thermodynamic Calculations in Studying the Slag/Steel Equilibrium during Vacuum Degassing

The effectiveness of a ladle refining process for production of tool steel with focus on the top slag is studied using computational thermodynamic calculations. The theoretical assessment was based on compositional data of steel and slag samples collected during trials in a plant equipped with a 65‐t EAF, a ladle furnace and a vacuum degasser. The calculation of slag‐metal equilibrium during ladle treatment was performed for top slag excluding (Case A) and including (Case B) slag carryover and deoxidation products. The predictions showed that slag carryover and deoxidation products in the ladle significantly affect the composition of the top slag. Thus, these conditions must be taken into consideration when predicting the actual top slag composition. It was also found that it is possible to predict the final aluminium and sulphur content in steel based on the same calculation approach.     

阈值设定法对钢包眼面积的快速影像分析

在钢的二次精炼过程中,通过惰性气体(Ar)底吹法搅拌钢包里的钢水是一种常规手段,其目的是确保钢液的均匀性,并促进炉渣和金属相之间的化学反应。钢包眼区(Ladle eye)的面积大小对于空气(O₂, N₂)的吸收,以及钢渣的形成有着重要的影响,而钢渣的成分及形态决定了钢液及产品的质量。对钢包眼区域的在线分析有助于帮助操作工人掌握添加各种造渣剂的种类和数量以及对通气量(压力或流量)的控制。实验阐述了一种基于钢包顶部数码影像的快速分析技术,通过冷态模型实验和工业钢炉的实际测试,有效地计算出钢包眼区的面积,且计算速度快于0.1 s/frame,能够基本满足实时测量的要求。     

Emulsification of Top Slags during Argon Stirring through a Porous Plug in the Ladle of Si Deoxidised Carbon Steels

Intensive experiments with 170‐t heats of carbon steels in the LD steel plant of Saarstahl AG were performed to study the emulsification of an acid top slag during different stirring conditions in this research project. During ladle treatment samples were taken from steel for the analysis of the composition of the inclusions together with the top slag. Within these investigations gas flow rates and stirring times were systematically varied in order to study their influence on the entrapment of top slag in the steel melt. At the same time a model was developed for the evaluation of the performance of the porous plug with regard to gas flow rate and gas pressure or finally for blockades and leakages. According to the experiments of this project the following results were established. Small top slag particles are discovered nearly in all steel samples together with endogenous SiO₂‐Al₂O₃ deoxidation products. But emulsified phases or parts of the top slag generating larger inclusions with a size of 30 – 60 μm show the low melting eutectic composition. On the other hand, this emulsification process leads simultaneously to CaO depletion and SiO₂ accumulation of the top slag particularly when a longer stirring period is applied as shown during these experimental trials. The whole process requires low melting top slags and low melting emulsified inclusions in combination with a low viscosity level. To meet the emulsification requirements the gas flow is characterised by high gas flow rates in the order of 30 – 40 STP m³/h and high pressures with 8 – 12 bar indicating a blockade of the porous plug and the existence of a gas jet.     

上水口环形吹氩对中间包内渣眼形成的影响

 中间包上水口环形吹氩可以在塞棒周围形成清洗钢液的环形气幕,同时部分氩气泡随钢液进入上水口内,可以减少非金属夹杂物在水口内壁的黏附,起到防止水口堵塞的作用。然而,不合理的吹氩量会导致中间包内液面渣层受过强的气液羽流冲击而形成渣眼,使得钢液裸露并发生二次氧化,严重影响铸坯质量。采用标准 k ε 湍流模型研究中间包内流体流动,采用DPM模型和VOF模型耦合方法,研究上水口环形吹氩条件下渣眼的形成及演化规律。结果表明,上水口环形吹氩在塞棒周围形成较强的上升流,塞棒上部邻近区域存在多个涡流区;在钢液涡流的影响下,中间包液渣下层远离塞棒区域,上层向塞棒区域迁移;随着吹氩量的增大,平均湍动能增大,塞棒附近钢液速度逐渐增大,钢渣界面钢液速度先增大后减小,渣眼边缘钢液速度先增大后减小然后再增大,速度与垂直方向夹角逐渐减小;增大吹氩量,中间包熔池液面形成以塞棒为中心的渣眼,渣眼面积逐渐增大。试验条件下不产生渣眼的临界吹氩量为4.2 L/min,对应的钢渣界面最大速度为0.247 m/s,与垂直方向夹角为70°。     

Slag eye formation in single and dual bottom purged industrial steelmaking ladles

ABSTRACT

Argon gas is often injected from the bottom of the ladle during steel refining operations. The injected gas interacts with the liquid (metal and slag) bath and enhances the momentum, heat, and mass transfer rate in the melt. However, during these gas–liquid interactions, an opening of the slag layer called slag eye is formed, which exposes the molten metal surface to the atmosphere, which is generally undesirable. In the current work, a transient, three-dimensional mathematical model is used to study the turbulent gas–liquid interactions in single as well as dual bottom blown industrial steelmaking ladles. A Coupled Level Set Volume of Fluid (CLSVOF) model is used for tracking the steel-argon, steel-slag, and argon-slag interfaces, from which the slag-eye area has been predicted. It is found that the inlet gas purging rate, melt height, slag layer thickness, angular and radial positions of the gas inlets affect the slag opening area. Non-dimensional empirical correlations are proposed to predict the slag opening area in both single as well as dual purged ladles, using non-linear regression analysis.     

浇注钢包环出钢口四孔透气塞吹氩控制下渣工艺北大核心CSCD

针对浇注钢包环出钢口四孔透气塞吹氩控制下渣工艺,建立了某钢厂130 t钢包三维DPM-VOF耦合数学模型以计算浇注钢包下渣过程,并通过冷态实验验证了该模型的有效性。利用该模型研究了不同偏心率对下渣行为的影响,揭示了该工艺控制下渣的行为规律,并分析了吹氩流量对控制下渣的影响。结果表明,随着偏心率的增大,不同浇注高度下的最大切向速度减小,汇流漩涡临界高度降低。环出钢口四孔透气塞吹入氩气后,气泡流股的汇聚有效地减弱了水口上方钢液的周向旋转速度,大幅降低了汇流漩涡下渣临界高度。4个气泡流股的气液两相流会抑制流向水口钢液的径向流动速度,由排流沉坑引起的下渣也得到明显抑制。随着吹氩流量的增加,下渣临界高度呈降低趋势。就本研究而言,控制下渣的最佳吹氩流量为30 L/min。     

邢钢钢包底吹卷渣模拟研究

根据钢包底吹气量与钢渣界面流速的关系计算出钢水卷渣的临界值,按照相似原理用混合油模拟渣层、水模拟钢水进行水模试验,考察了吹气量、单双孔底吹透气砖对钢水卷渣行为的影响,单孔吹气量小于450L/min、双孔吹气量小于400L/min可避免卷渣。     

Process metallurgical evaluation and application of very fine bubbling technology

The potential of VFB(v ery f ine b ubbling)‐technology in steelmaking, developed for the production of super clean steels, was investigated. Recent R&D work has proven that with very fine argon bubbling through a developed special porous plug (SPP) at low flow rates, the total oxygen content of low carbon steel grades can be lowered to a level of 6 ppm under industrial vacuum conditions [1; 2] and to a level of 10 ppm under argon protective atmosphere [2]. The perspective of industrial application of the VFB technology to a 56‐t ladle furnace of Helliniki Halyvourgia S.A., Greece, in order to improve steel cleanliness, requires additional R&D efforts. It is important to define the limits of VFB technology in respect of alloys dissolution, mixing time and homogenisation of steel and slag/metal reactions. In this work, a gas driven bubble aqueous reactor model simulating the bottom gas stirred ladle by means of gas injection through a SPP and a conventional porous plug was studied. Various operating conditions as well as different positions for the porous plug with and without a top oil layer were simulated. Tests concerning mixing time, solid‐liquid mass transfer and critical gas flow rate, liquid/liquid mass transfer, using the SPP and a conventional porous plug have been performed. The evaluation of experimental results delivered important information for the design and operation of steel ladles, applying VFB‐technology. Experimental results with SPP bubbles’ agitated steel (1600 °C) in laboratory and technical scale experiments in IF and VIF are presented and discussed.     

钢包底吹氩卷渣临界条件的水模型研究

以钢厂70t钢包为原型,建立模型与原型尺寸比为1:2.75的水模型。通过水模型实验对钢包临界卷渣吹氩量进行测量,得到临界卷渣气量是450 L/min。实验测量不同吹气量下钢包液面水平流速,分析水平流速与钢包卷渣的关系,得到钢包临界卷渣的液面流速为0.652m/s、韦伯准数为6.967。讨论了采用临界卷渣韦伯准数计算临界卷渣液面流速,通过测量达到临界卷渣液面流速时的吹氩量,来确定临界卷渣吹氩量的方法。     

钢包卷渣临界底吹流量规律的水力学模拟研究

用水模拟钢水、油模拟钢渣,通过水力模型研究了底吹钢包中的临界卷渣流量.结果表明,临界卷渣流量随渣层厚度的增加而减小,随粘度的增加而增大,通过分析渣-钢界面的速度分布和能量平衡,对以临界流量作为卷渣发生的判定条件的准确性进行了检验.采用因次分析得到了底吹钢包临界卷渣流量的无因次表达式Qcr∝(Δρσ/ρ2s)0.35(μs/μm)0.3(Hs/Hm)-0.42,利用该表达式计算了实际钢包卷渣的临界流量,分析了影响因素,建议110 t钢包进行钢水弱搅拌净化操作时最大底吹流量为QN＝240 L/min.     

Towards Efficient Modelling of Slag Entrainment during Metallurgical Processes

This paper focuses on the numerical modelling of slag entrainment in liquid metal. Due to the complexity of the multi‐phase flow situation and the inherently unsteady nature of the process, feasible simulations are restricted to rather coarse grids. Nevertheless, important flow structures like secondary suction vortices cannot be captured by an insufficiently resolved grid. As a consequence three numerical approaches are proposed in order to focus on local slag entrainment events within a global flow simulation. Firstly, in the course of Volume of Fluid (VOF) simulations the evolving metal‐slag interface is sharpened by a solution dependent adaptive grid refinement. Secondly, possible suction vortices are tested by super‐imposed Chimera grids. In this approach a finely resolved O‐shaped grid is placed around the trajectory of a representative Lagrangian fluid particle that is started from a local depression at the metal‐slag interface. Thirdly, a simplified concept of Lagrangian slag droplets is utilized in order to detect irregularly occurring flow situations that are prone to slag entrainment. These modelling approaches are applied to metallurgical processes like tundish pouring or continuous casting. With help of these slag entrainment modelling approaches a global metallurgical flow simulation can be augmented by the effect of local entrainment events.     

活性石灰在钢水精炼中的应用

介绍了在钢水精炼过程中，添加一定量的活性石灰和萤石，提高精炼钢水顶渣的碱度，降低熔渣的熔点，改善熔渣的流动性。消除钢包内衬结渣挂渣、顶渣结壳的现象，以及AHF浸渍罩、RH上升管和下降管结渣上涨的现象。同时钢水精炼添加活性石灰后，有一定的脱硫和吸附一定量钢中夹杂物的作用。     

Numerical modelling of the transport and removal of inclusions in an industrial gas-stirred ladle

A full-scale, three-dimensional, transient CFD modelling approach capable of predicting the three-phase fluid flow characteristics and the inclusion removal in a gas-stirred ladle was developed. The comparison with experimental data indicates that this model can accurately predict the multiphase fluid flow and slag eye behaviour. The transport and removal of the inclusions in the gas-stirred ladle were predicted by tracing the movement of individual inclusions through computing their particle trajectories and considering a fluctuant top slag layer. The effects of inclusion size, gas flow rates, and injected bubble diameters as well as various removal mechanisms including slag capture, bubble attachment, and ladle wall adhesion on the removal of inclusions were investigated. It is shown that the slag capture is the prevailing mechanism for inclusion removal and the gas flow rate is the most important parameter for enhancing the inclusion removal efficiency.