Flow Control in Six-Straud Billet Continuous Casting Tundish With Different Configurations

 A 1:2.5 scale tundish model was set up in laboratory for a six-strand billet continuous casting tundish with different configurations to investigate fluid flowing characteristics under different operational conditions by measuring residence time distribution curves. It was known from the investigation that minimum residence time, maximum concentration time and average residence time of the three strands in the same side of the tundish with the former configuration under normal operation, that is, 6 strands were open, were small and non-uniform and the tundish had large dead volume fraction. Vortexes easily formed on the liquid surface in the pouring zone of the tundish. The fluid flow characteristics in the tundish with the optimal turbulence inhibitor and baffles were improved and became less non-uniform among the strands. Vortexes were not found on the pouring zone surface in the optimal tundish. Under un-normal operation, that is, one strand was close, it was important to choose which strand should be closed for flowing characteristics of the rest two strands. It was found from this investigation that fluid flowing characteristics in the optimal configuration tundish with closing strand 2 were better than those with closing strand 3 at the same side.     

Modelling performance of four‐strand, 12 t,delta shaped continuous casting tundish fitted with different flow modifying arrangements for better steel quality

Abstract

The performance of a 12?t, delta shaped, four‐strand, billet casting tundish was investigated using a full scale (1∶1) isothermal model using water as the simulating fluid for steel. Three different modelling experiments were carried out. Quantifiable parameters like ‘number of slag beads’ in transient physical modelling of slag entrainment, or ‘residual ratio of inclusions’ (RRI %), in steady state mathematical modelling of inclusion removal and ‘mean residence time’, ‘dead volume fraction’, etc., in steady state mathematical computation of residence time distributions, were used as the performance indicators. Results for three different flow modifying dam arrangements were considered and compared with those of a bare tundish. Computational fluid dynamic analysis showed that different flow modifying dam arrangements significantly alters the flow pattern within the tundish. On the basis of these performance indicators, the best arrangement was identified. The assumption in this paper that similar conclusions can be drawn from experiments carried out either in transient or in steady state conditions was verified. It was shown that both transient physical modelling experiments and the steady state mathematical predictions, point to the same conclusion.     

Fluid flow behaviour in slab continuous casting tundish with different configurations of gas bubbling curtain

Abstract

Fluid flow characteristics in a two strand slab continuous casting tundish with different configurations of argon gas bubbling curtain (GBC) were investigated in physical modelling experiments. It was found from this research that the GBC with a small flow rate acted as a gas dam and could greatly improve the flow characteristics in the tundish. It increased dramatically the peak concentration time and plug flow volume, decreased greatly the dead volume, created surface directed flow and eliminated short circuiting. Therefore, the fluid flow characteristics in a tundish with GBC were favourable to the floatation and separation of inclusions from molten steel. The flow characteristics with low gas flow rate and short distance of the bubbling curtain from the tundish outlet were better than those with high gas flow rate and large distance of the curtain to the outlet. The optimal configuration for the improvement in fluid flow characteristics was turbulence inhibitor (TI)–weir–dam–GBC (TI–W–D–GBC), followed by TI–channel weir (CW)–GBC, TI–W–GBC and TI–GBC.     

Flow Control in Six-Strand Billet Continuous Casting Tundish With Different Configurations

A 1∶2.5 scale tundish model was set up in laboratory for a six-strand billet continuous casting tundish with different configurations to investigate fluid flow characteristics under different operational conditions by measuring residence time distribution curves.It was found that minimum residence time,maximum concentration time and average residence time of the three strands on the same side of the tundish with the former configuration under normal operation,that is,six strands were open,were small and non-uniform and the tundish had large dead volume fraction.Vortexes easily formed on the liquid surface in the pouring zone of the tundish.The fluid flow characteristics in the tundish with the optimal turbulence inhibitor and baffles were improved and became less non-uniform among the strands.Vortexes were not found on the pouring zone surface in the optimal tundish.For non-normal operation,that is,one strand was close,it was important to choose which strand to be closed for maintaining flow characteristics of the rest two strands.It was found from this investigation that fluid flow characteristics in the optimal configuration tundish with closing strand 2 were better than those with closing strand 3 on the same side.     

五流非对称结构中间包流动及传热特征数值模拟

为优化某钢厂非对称结构中间包内流体流动、均匀各流钢液温度、延长近水口平均停留时间,以达到提高铸坯质量的目的,对工厂原方案及两个优化方案进行流场、温度场及停留时间的数值模拟计算.结果表明无控流装置的原中间包流动及温度场分布不合理,优化方案有了明显的改善,并确定了最佳方案.     

通道式感应加热7流中间包流场的物理模拟

 为解决通道式感应加热7流中间包各流一致性差、第2和第6流钢水停留时间短的问题,通过水模拟试验对该中间包流场进行优化。等温试验结果表明,通过改变通道结构以及添加双挡坝可改善流体的流动状况。与原型结构相比,优化后中间包总体平均停留时间延长了277.8 s,死区比例降低了30.16%,各流一致性得到较大改善。非等温试验表明,感应加热引起的包内自然对流不可忽略,流体经加热从通道流出后会形成明显上升流。通道内外温差越大,中间包各流的一致性越好。针对原型方案,通道内外温差为5 ℃时,中间包内流体停留时间即较无温差时明显延长,死区基本消除。     

40t单流中间包控流装置的优化配置

采用水模型和工业验证的方法针对40 t单流中间包的控流装置进行优化配置研究.通过对单独湍流抑制器控流装置、湍流抑制器+下挡墙组合控流装置、湍流抑制器+下挡墙+上挡墙组合控流装置的研究表明,下挡墙在改善钢液流动形态和减少中间包内死区方面所起的作用大于上挡墙.平均停留时间随下挡墙与长水口的距离增加呈先增大后减小的趋势.确定了单流中间包以湍流抑制器+下挡墙的优化组合形式,死区比例由原来的25.9%降低到了13.6%.通过系统取样分析发现优化后中间包内T.O和N含量大幅降低,正常坯中的大型夹杂物质量分数也由原来的8.4×10-7降低到3.2×10-7.      

Transient steel quality under non-isothermal conditions in a multi-strand billet caster tundish: part I. Analysis of fluid flow,thermal behaviour and inclusion behaviour

A numerical model based on computational fluid dynamics was used to simulate the effect of non-isothermal conditions on melt flows in a multi-strand billet caster tundish. To start with, water was used as the operating fluid in a one-third scale tundish to calculate the fluid flow and temperature fields under isothermal and non-isothermal conditions. The model was then extended to the full-scale tundish with molten steel as the operating liquid in order to simulate the conditions in a real plant. It was observed that using step inputs of 10° and 23° for water and steel cases, respectively, changed the fluid flow patterns significantly, more so at locations far from the inlet, due to stronger buoyancy-driven natural convective flows. The temperature distribution and inclusion trajectories within the tundish were also affected due to the presence of non-isothermal conditions.     

Inertial and buoyancy driven water flows under gas bubbling and thermal stratification conditions in a tundish model

Steel flow dominated by inertial and buoyancy flows under gas bubbling and thermal stratification conditions, in a one-strand tundish, was studied using a 2/5 scale water model. The use of a turbulence inhibitor yields plug flow volume fractions well above 40 pct for a casting rate of 3.12 tons/min under isothermal conditions. Small flow rates of gas injection (246 cm³/min), through a gas curtain, improved the fluid flow by enhancing the plug flow volume fraction. Higher flow rates originated an increase of back-mixing flow, thus forming recirculating flows in both sides of this curtain. Step inputs of hot water drove streams of this fluid toward the bath surface due to buoyancy forces. A rise in gas flow rate led to a thermal homogenization in two separated cells of flow located at each side of the gas curtain. Step inputs of cold water drove streams of fluid along the tundish bottom. Use of the gas curtain homogenized the lower part of the tundish as well as the upper part of the bath at the left side of the curtain. However, temperature at the top corner of the tundish, in the outlet box, remained very different than the rest of the temperatures inside this tundish. High gas flow rates (912 cm³/min) were required to homogenize the bath after times as long as twice the mean residence time of the fluid. Particle image velocimetry (PIV) measurements corroborated the formation of recirculating flows at both sides of the gas curtain.     

五流连铸中间包结构优化的水模型实验

以国内某钢厂五流连铸中间包为研究对象,根据相似原理建立了1：3的中间包水模拟系统,考察不同内部结构对中间包流体流动特性的影响．研究结果表明：原型中间包内部结构不合理,各流水口之间的流体流动特性差异很大,存在较大死区．通过内部结构优化设计,使中间包流场得到明显改善,其中方案Ⅵ效果最佳,平均停留时间离散度最小,活塞区体积达23．84％,死区体积为10％,比原型下降了71．70％．     

挡墙结构对46 t中间包钢液流动特性影响的数值和物理模拟

通过采用流动力学软件FLUENT进行的数值模拟和几何相似比1:3的水模型分别研究了导流孔倾角30°的U型挡墙和导流孔倾角分别为20°,25°,30°的V型挡墙4种结构的挡墙对46 t两流T型Φ800 mm圆铸坯中间包钢液流动特性的影响,并采用稳态模拟计算中间包钢液的温度场分布。结果表明,两种模拟结果有良好的一致性;使用导流孔倾角20°的V型挡墙的中间包流动特性最佳,中间包出口流温差仅为4.0 K,整体最大温差为14.2 K,停留时间最长为803.1 s,死区体积分数最小为0.09,更有利去除钢液夹杂物,提高钢的洁净度。     

四流中间包气幕挡墙水模拟研究

采用不同参数的多孔透气砖进行了25 t四流中间包的底部吹气水模拟实验,结合RTD曲线和标准差分析,研究透气砖面积(210～105 mm×56～28 mm) 、4种吹气位置和吹气量(60～120 L/h)对中间包液体流动特性的影响,并与不吹气的情况进行了对比。结果表明,中间包吹气能改善液体的流动特性,均衡其在不同水口间的停留时间,并能延长峰值时间和降低死区体积。透气砖靠近挡墙,采用小气量和小面积更有利于改善现有中间包流场。     

二流T型23 t中间包控流装置的数值模拟和结构优化

通过计算流体力学软件FLUENT建立的数学模型对钢厂200 mm×1 600 mm铸坯二流T型23 t中间包现挡墙和坝、湍流控制器和坝、湍流控制器和现挡墙以及新挡墙4种结构方案进行三维数值模拟,研究原中间包及安装不同控流装置后的钢水流动特性。结果表明,在所有的设计方案中安装有湍流控制器和坝的中间包能够达到最佳优化效果;中间包的死区体积分率由30.18%降到16.51%,活塞流区与死区的体积分率比R_Vp/Vd由55.80%增大到129.44%;中间包内流动稳定,有利于夹杂物的上浮。     

Reduction of Tundish Skull and Yield Improvement in Steel Plants Through Physical Modeling of Steelmaking Tundish Systems

New types of furniture (also termed as flow modifiers or baffles) were incorporated in industrial scale, slab and bloom casting tundish systems with an aim to reduce residual metal loss (i.e., tundish skull) at the end of sequence casting. To this end, water model experiments were carried out in which, slag vortexing phenomena during emptying of tundish was studied embodying different types of furniture into existing tundish designs. These in general indicate that a wedge shaped bottom together with an embedded pouring box applied in conjunction have the potential to reduce tundish skull and improve yield losses significantly. In addition, limited residence time distribution measurement experiments were made to investigate metallurgical performance of modified design tundish systems. These indicate that deployment of new furniture with minor design modifications, despite contributing to a reduction in tundish capacity (10–12%), do not influence metallurgical performance of steelmaking tundish systems to any significant extent. Accordingly, designs of currently employed slab (32 and 37 tonnes capacity respectively) and bloom casting tundish (10 and a 17 tonnes capacity respectively) systems were modified in four different steel mills and plant trials conducted to assess the extent of yield improvement. Significant improvements in yield losses, to the extent of 50–60%, have been confirmed by the industry during sequence casting.     

包钢烧结合理利用巴西高硅混合粉实验

摘要：为解决六流H型通道感应加热中间包原型死区比例大,各流一致性差,第3流和第4流钢水短路流的问题,通过水模拟实验对中间包流场进行优化,同时采用数值模拟对中间包温度场进行了模拟。结果表明,在中间包内添加挡坝或在V形挡墙上开导流孔均可改善流体的流动状况。与原型结构相比,优化后的A4方案（V形挡墙上开2个水平倾角分别为36°、44°,孔径105mm,距包底分别为170和510mm的导流孔）总体平均停留时间延长了165s,死区比例降低了23.95%,各流水口之间的最大温差仅为0-5K,一致性显著提高。     

六流H型通道感应加热中间包的结构优化

摘要：为解决六流H型通道感应加热中间包原型死区比例大,各流一致性差,第3流和第4流钢水短路流的问题,通过水模拟实验对中间包流场进行优化,同时采用数值模拟对中间包温度场进行了模拟。结果表明,在中间包内添加挡坝或在V形挡墙上开导流孔均可改善流体的流动状况。与原型结构相比,优化后的A4方案（V形挡墙上开2个水平倾角分别为36°、44°,孔径105mm,距包底分别为170和510mm的导流孔）总体平均停留时间延长了165s,死区比例降低了23.95%,各流水口之间的最大温差仅为0-5K,一致性显著提高。     

中间包包型优化的数值模拟及生产应用

中间包包型对钢液流动有重要影响,进而影响中间包的冶金效果。利用数学模拟方法,以钢液停留时间分布曲线(RTD曲线)为评判标准,对某钢厂的中间包包型进行了优化改造,优化后出口浓度最大时间延长了200 s,钢液活塞区比例由39.3%增加至69.6%,死区比例由10.11%降至4.77%,且铸余减少3.5 t;包型优化后的大样电解夹杂物含量减少了72.35%。该包型于2008年12月开始在某钢厂稳定使用,提高了铸坯质量,节省了生产成本,为该钢厂创造了显著的效益。     

Physical and mathematical determination of the influence of input temperature changes on the molten steel flow characteristics in slab tundishes

Transient fluid flow behavior in a tundish with two different arrangements, a bare tundish and a tundish using flow control devices, was studied using physical modeling and a mathematical model. The study places special emphasis on buoyancy effects, particularly transient buoyancy effects due to step change in inlet temperature. For the bare tundish case, the inertial forces are strongly dominant, while in the arrangement using flow control devices, tundish with turbulence inhibitor and low dams, the buoyancy forces are dominant. The results were compared to those representing the real behavior, considering temperature variations, for each tundish arrangement. This comparison made possible the determination of the probable implicit error that could be present in the estimation of the fluid flow characteristic behavior used for the design of the tundish geometry and flow control devices when the temperature variations are not considered.     

Effects of tundish size,tundish design and casting flow rate on fluid flow phenomena of liquid steel

Fluid dynamics of liquid steel in continuous casting tundishes is closely related to tundish volume and geometry, existence of flow control devices and steel flow rate. To study this complex interaction physical and mathematical models were used in the present work. The first one was based in a 1/3 scale water model with injection of tracers and the second one on the solution to the steady state-turbulent Navier-Stokes equations using the K-ε [1] approximation for the turbulent viscosity. When the tundish size is increased from 30 t to 50 t the tracer indicates a strong bypassing in the second case. The mathematical predictions indicate very high fluid velocities along the tundish bottom in agreement with the experimental findings. The employment of turbulence inhibitors promotes a counter-flow that surrounds the incoming stream jet of liquid from the inlet nozzle with steel displacing itself, after leaving this zone, along the upper free surface of the liquid. The addition of well designed baffles complements the action of the turbulence inhibitor to obtain a higher volume fraction under a plug flow pattern giving a softer flow of liquid steel. Besides, the positioning of baffles inside a tundish should be performed according to the steel flow rate.     

Design of single element flow control device in twin strand billet tundish for continuous casting of steel using flow simulation model

Abstract

An optimal single element flow control device (SEFCD) is proposed in the present study for a small capacity twin strand tundish, to produce steel billet with the desired cleanliness, designed by means of numerical experimentation. To achieve this goal, a mathematical model based on the SOLA-SURF technique and the k-? (where k is the kinetic energy of the fluid and ? is its dissipation) two equation turbulence model has been developed to simulate the fluid flow phenomena of molten steel, as well as the mass transfer phenomena of tracer during steady state operation in the tundish. The accuracy of the mathematical model has also been verified by water model experiments, which indicate that the mathematical model is sufficiently accurate and suitable as a tool to develop an optimal SEFCD as required in the present study. Several SEFCD designs have then been evaluated using the mathematical model. The simulated results show that a billet tundish with a high, long, trough shaped pouring pad arrangement has the highest residence time, which promotes inclusion removal, and is thus considered the optimal SEFCD design for the billet tundish.