Mathematical Modelling of Molten Steel Flow Process in a Whole RH Degasser during the Vacuum Circulation Refining Process: Application of the Model and Results

A three‐dimensional mathematical model for the molten steel flow during the RH refining process has been applied to the circulatory flow processes in both a practical RH degasser and its water model unit. The model was presented earlier [1] and one of its characteristics is that ladle, snorkels and vacuum vessel are regarded as a whole. Using this model, the fluid flow field and the gas holdups of liquid phases and others have been computed respectively for a 90 t RH degasser and its water model unit with a 1/5 linear scale. The results show that the mathematical model can properly describe the flow pattern of molten steel during the refining process in an RH degasser. Except in the area close to the liquid's free surface and in the zone between the two snorkels in the ladle, a strong mixing of the molten steel occurs, especially in the vacuum vessel. However, there is a boundary layer between the descending liquid stream from the down‐snorkel and its surrounding liquid, which is a typical liquid‐liquid two‐phase flow, and the molten steel in the ladle is not in a perfect mixing state. The lifting gas blown is ascending mostly near the up‐snorkel wall, which is more obvious under the conditions of a practical RH degasser, and the flow pattern of the bubbles and molten steel in the up‐snorkel is closer to an annular flow. The calculated circulation rates for the water model unit at different lifting gas rates are in good agreement with experimentally determined values.     

Mathematical Modelling of Molten Steel Flow Process in a Whole RH Degasser during the Vacuum Circulation Refining Process: Mathematical Model of the Flow

A three‐dimensional mathematical model for the molten steel flow in a degasser during the RH refining process has been proposed and developed. The physical characteristics of the process, particularly the behaviour of gas‐liquid two‐phase flow in the up‐snorkel and the momentum exchange between the two phases are considered. The ladle, snorkels and vacuum vessel are regarded as a whole in the model, and the gas‐liquid two‐phase flow is treated and described on the basis of the two‐fluid model and using the especially modified two‐equation κ‐? model. The details of the model are presented.     

Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Application of the Model and Results (I) ‐ Decarburization Process and Influences of Some Technological Factors

A novel three‐dimensional mathematical model proposed and developed for the non‐equilibrium decarburization process during the vacuum circulation (RH) refining of molten steel has been applied to the refining process of molten steel in a 90‐t multifunction RH degasser. The decarburization processes of molten steel in the degasser under the conditions of RH and RH‐KTB operations have been modelled and analysed, respectively, using the model. The results demonstrate that the changes in the carbon and oxygen contents of liquid steel with the treatment time during the RH and RH‐KTB refining processes can be precisely modelled and predicted by use of the model. The distribution patterns of the carbon and oxygen concentrations in the steel are governed by the flow characteristics of molten steel in the whole degasser. When the initial carbon concentration in the steel is higher than 400 · 10⁻⁴ mass%, the top oxygen blowing (KTB) operation can supply the oxygen lacking for the decarburization process, and accelerate the carbon removal, thus reaching a specified carbon level in a shorter time. Moreover, a lower oxygen content is attained at the decarburization endpoint. The average contributions at the up‐snorkel zone, the bath bulk and the free surface with the droplets in the vacuum vessel in the refining process are about 11, 46 and 42% of the overall amount of decarburization, respectively. The decarburization roles at the gas bubble‐molten steel interface in the up‐snorkel and the droplets in the vacuum vessel should not be ignored for the RH and RH‐KTB refining processes. For the refining process in the 90‐t RH degasser, a better efficiency of decarburization can be obtained using an argon blow rate of 417 I(STP)/min, and a further increase in the argon blowing rate cannot obviously improve the effectiveness in the RH refining process of molten steel under the conditions of the present work.     

单管RH精炼过程钢液流场的水模型实验

采用物理模拟方法对单管 RH 真空精炼过程流场的循环流动、混合特性等进行了研究,建立与 RH 真空精炼装置原型相似比为1∶5的水模型,研究了不同工艺参数对单管 RH 装置内钢液循环流动的影响。对比实验测量数据发现,增大吹氩量和浸渍管插入深度以及浸渍管有效横截面有利于提高循环流量,减小均混时间;在相同的实验条件下,椭圆形浸渍管 RH 比传统浸渍管 RH 的循环流量要大15％以上,单管 RH 的均混时间比传统RH 可以缩短20％;单管 RH 钢包底部吹氩位置位于距钢包中心0.4R(R 是钢包半径)处时,均混时间最短。     

Mathematical Simulation of Flow Field for Molten Steel in an 80–ton Single Snorkel Vacuum Refining Furnace

The three–dimensional flow field of molten steel in an 80–ton single snorkel vacuum refining furnace has been mathematically simulated to attain the optimal configuration and operation parameters, such as the bottom blowing Ar flow rate, the eccentric position of bottom blowing Ar port at ladle bottom, the single snorkel inner diameter, and the single snorkel immersion depth into molten steel. The mathematical simulation results show that a stable flow field of molten steel can be achieved in 70–second; meanwhile, the maximal circulation intensity of molten steel in the 80–ton single snorkel vacuum refining furnace can be found on a cross–section with y as 0 mm based on the middle of ladle bottom as circular point of the Cartesian space coordinate under the condition of injecting Ar gas on x coordinate considering the asymmetry of flow field for molten steel in the single snorkel vacuum refining furnace. The recommended parameters of the 80–ton single snorkel vacuum refining furnace with ideal circulation intensity as 970.1 kg/s are the bottom blowing Ar flow rate as 450–500 Nl/min, the eccentric position of bottom blowing Ar port as 250 mm, the single snorkel inner diameter as 1000 mm, and the single snorkel immersion depth as 500 mm.     

RH真空精炼过程循环流量的水模型研究

建立了钢厂250 t RH真空精炼装置1/4的水模型,研究浸渍管内径(520～750 mm)、驱动气体流量(1 000～3 000 L/min)、浸渍管浸入深度(525～800 mm)和真空室压力(0～25 kPa)等参数对RH循环流量的影响。结果表明,随驱动气体流量、浸渍管浸入深度增加、浸渍管内径增大以及真空室压力减少,RH钢水循环流量增加;为获得较大流量,浸渍管浸入深度应≥560 mm,真空室液面高度应≥200 mm。得出循环流量的回归方程,通过对钢厂250 t RH设备工艺参数作相应调整后,RH装置的生产效率明显提高。     

Study of Argon/Molten Steel Two-Phase Flow in Refining of High Clean Steel Using Two-Fluid Model

RH vacuum degasser is a very important secondary refining device in the production of high quality steels. The flow field of molten steel in RH system plays a significant role in determining productivity of the equipment. The homogeneous model and VOF method were often used to predict the flow field in RH system, but these kinds of models simplified the interaction between gas bubbles and molten steel. In the present work, a numerical model of a whole RH system, including vacuum degasser, immersed legs and ladle,was built based on gas-liquid two-fluid model, and it could be used to analyze the interaction between argon bubbles and molten steel, to understand the effect of the bubble size to the flow field.     

A simulating investigation into the characteristics of the mass transfer between molten steel and particles in the 150 t RH-IJ refining

The characteristics of the mass transfer between powder particles and liquid steel in the Ruhrstahl Heraeus process injection(RH-IJ)refining were simulatively investigated by the use of a 1/4 scale water model of a 150 t Ruhrstahl Heraeus(RH)degasser.The influences of the lifting gas flow rate,the up-snorkel and down-snorkel inner diameters and the size of powder particles on the characteristics of the mass transfer were examined.The results show that under the condition that the inner diameters of both the up-snorkel and the down-snorkel are the same,the mass transfer coefficient in the liquid,k increases with the increase of the inner diameter of the up-snorkel,the particle size and the lifting gas flow rate(Qg).However,the increase of Qg should not result in a saturated circulation rate.Under the current working condition,k ranges from 3.392×10-5 m/s to 2.661×10-4 m/s.On the other hand,with a given lifting gas flow rate and up-snorkel inner diameters,the mass transfer weakens with the increase of the down-snorkel inner diameter.An inherently nonlinear relationship between the circulation rate(Ql)of molten steel in the RH degasser and k,which increases with the increase of Ql,was found.Under the condition of other parameters being the same,k increases with the increase of the powder particle size.In order to enhance the mass transfer,it is better not to use extremely fine powder.     

Effect of snorkel shape on the fluid flow during RH degassing process: mathematical modelling

A mathematical model was developed to investigate the effect of snorkel shape on the recirculation rate and the erosion of the lining refractory during RH degassing process. A particle image velocimetry technique was used to measure the velocity distribution in a water modelling experiment. The calculated results were well validated with the measured ones. In the mathematical model, the interfaces between the molten steel and the gas phase, and the motion of argon bubbles were simulated and tracked using VOF?+?DPM model by which the argon bubbles were treated as the discrete phase in the molten steel and the top gas phase, and the top gas phase was treated as a second continuous phase. It was found that the recirculation rate of the molten steel with oval snorkels was significantly larger than that with round snorkels. For round snorkels, the optimum gas flow rate was 1800?L?min^?1 and it was 2800?L?min^?1 for oval snorkels. Furthermore, the volume distribution of the argon in the radial direction of the up-snorkel with oval snorkels was much more homogeneous than that with round snorkels. Meanwhile, the predicted maximum wall shear stress showed that the bottom and the sidewall of the ladle with round snorkels were more seriously eroded than that with oval snorkels. Therefore, the oval snorkel was beneficial to improve the service life of the RH degasser.     

马钢RH KTB流场的数值模拟

利用CFX数值计算软件建立的数值耦合模型对马钢RH KTB的流场进行了分析,得出了包括钢包、真空室、上升管、下降管的RH全系统的流场状态及其在精炼过程中的变化规律。在RH吹氩气液两相区的处理上,应用了非均相多相流模型。模拟结果表明RH真空室内流场中存在小环流现象。     

Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Application of the Model and Results (II) ‐ Non‐equilibrium Factors and their Influences on the Decarburization Process

The results, which were obtained by applying the novel three‐dimensional mathematical model proposed and developed earlier [1] to model and analyse the decarburization process of molten steel during the RH and RH‐KTB refining in a 90‐t multifunction RH degasser, showed that under the conditions of the present work, the contributions of the flow, mass diffusion and chemical reactions and other non‐equilibrium processes to the Raleigh‐Onsager dissipation function are not large throughout vacuum circulation refining of molten steel. Thus, it is held everywhere in the whole flow field of the system that the value of the non‐linear dissipation factor is approximately equal to one. The entropy generation and energy dissipation in the system rapidly decrease with increasing refining time. Compared to the work done by the drag force while the bubbles passing through the liquid phase as well as by the viscous and turbulent flow and diffusion processes, the carbon‐oxygen reaction itself plays a more governing role to the entropy production and energy dissipation in the system. The RH refining process of low and ultra‐low carbon steels seems to be close to the linear zone of the non‐equilibrium state. The influences of the viscous and turbulent flow dissipation as well as diffusion processes on the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel may almost be neglected. Except in the regions where the chemical C‐O reaction takes place (the up‐snorkel zone and the bath in the vacuum vessel), the non‐equilibrium components of the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel at the other places in the degasser are all tending towards one. The non‐equilibrium effects (mainly, the C‐O reaction itself) give a restraining role on the decarburization of liquid steel in the RH refining process. This model is able to model more reasonably and precisely the non‐equilibrium decarburization process during the vacuum circulation refining of molten steel in comparison to a model without considering the non‐equilibrium effects.     

唐钢RH钢包混匀时间及流场模拟计算与分析

研究了真空度、提升气体量和吹气孔位置对RH钢水混匀时间的影响,模拟了钢包流场情况。试验结果表明:提高RH系统真空度、增加RH提升气体量或增大气体的吹入深度均可减小混匀时间;唐钢RH精炼过程中无死区存在,在相应的混匀时间内可以实现整包钢水成分和温度的均匀;合理控制真空度、提升气体量和浸渍管插入深度有利于稳定出站钢水碳含量,提高Al2O3夹杂物的去除率。     

马钢RH KTB流场的数值模拟

利用CFX数值计算软件建立的数值耦合模型对马钢RH KTB的流场进行了分析，得出了包括钢包、真空室、上升管、下降管的RH全系统的流场状态及其在精炼过程中的变化规律。在RH吹氩气液两相区的处理上，应用了非均相多相流模型。模拟结果表明RH真空室内流场中存在小环流现象。     

150tRH-IJ精炼条件下钢液—颗粒间的传质特性

采用线性尺寸为150tRH装置1/4的水模型研究了RH-PB(IJ)过程中钢液和粉剂颗粒间的传质特性,测定了液体侧的传质系数,考察提升气体流量,上升管、下降管内径和颗粒粉剂对传质系数的影响。结果表明,在上升管径和下降管径相同的情况下,增大气体流量可增大钢液与喷吹粉剂颗粒钢液侧的传质系数,但不宜增大到使环流量达到"饱和"。在现有工作条件下,传质系数为3.392×10-5～2.661×10-4m/s。在给定的增大气体流量和下降管径下,钢液与粉剂颗粒间钢液侧的传质系数随上升管径的增大而增加。当气体流量增大和上升管径给定时,钢液与粉剂颗粒间钢液侧的传质系数随下降管径的增大而减小。钢液与粉剂颗粒间钢液侧的传质系数随环流量的增大而增大。其他参数相同时,在现有工作所取范围内,粉剂颗粒的粒径越大,其与钢液间钢液侧的传质系数越大;为增大传质速率,粉剂不宜过细。     

Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Mathematical Model of the Process

The characteristics of the non‐equilibrium decarburization process during the vacuum circulation (RH) refining of molten steel have been considered and analysed. On the basis of the fundamentals of metallurgical reaction engineering and non‐equilibrium thermodynamics, as well as the two‐fluid model for gas‐liquid two‐phase flow and a modified k‐? model for turbulent flow, a novel three‐dimensional mathematical model for the process has been proposed and developed. The details of the model, including the establishment of the governing equations and the especially modified two‐equation k‐? model, the determination of the appropriate source terms and boundary conditions and others, have been presented. The related parameters of the model have been discussed and determined for the decarburization refining process of molten steel in a 90‐t multifunction RH degasser under RH and RH‐KTB operating conditions.     

RH熔池内弱搅拌区特性的模拟研究

以某钢铁厂170 tRH精炼装置为原型,运用数值模拟的方法对其在不同吹气量、浸渍管内径、插入深度和真空度下的流场进行了模拟,并对熔池内弱搅拌区的分布和变化进行了分析。研究表明:大包熔池上部存在3个弱搅拌区。随着吹气量的增大,1区、3区区域迅速减小;2区先增大后减小,在100 m3/h时达到最大。增大浸渍管内径,1区、2区、3区区域减小,2区在两浸渍管中下方出现了一狭长的弱搅拌区。增大浸渍管插入深度,3个弱搅拌区增大,熔池液面处速度降低,趋于平稳。增大真空度,3个弱搅拌区略有减小。在降低弱搅拌区的几个因素中,吹气量影响最大,浸渍管内径次之,真空度最小。     

RH装置内夹杂物聚合与去除的三维数值模拟

 摘 要：基于RH精炼装置内流场,建立了一个研究夹杂物聚合与去除行为的三维数学模型。数值结果表明,夹杂物在钢包内上升管左侧存在一个侧“V”分布,上升管下方及下降管右侧均存在大的环状分布;夹杂物浓度和数量密度具有相似的空间分布;钢包内夹杂物的平均数量密度及浓度大于真空室内的平均值;夹杂物在气液两相区浓度较低;整个过程前400秒夹杂物去除最快,900秒后可去除大部分夹杂物,在处理后期,夹杂物平均特征尺寸有减小的趋势。     

REDA精炼过程钢液流场及循环流量的数值模拟

基于欧拉多相流模型建立REDA精炼过程钢液流动行为的数学模型,并借助计算流体力学软件PHOE- NICS对钢液流动过程进行仿真模拟,重点分析了底吹喷嘴位置、吹氩流量、浸渍管插入深度及浸渍管内径等工艺 参数对REDA精炼过程流场及循环流量的影响。数值模拟结果表明:对于300 t REDA精炼装置底吹喷嘴位置取 1/2 R处为宜,浸渍管插入深度对循环流量影响不显著,扩大浸渍管内径可显著提高钢水循环流量,吹氩流量为1 200 L/min时,钢液循环流量约可达到210 t/min     

Mathematical modelling of decarburisation and degassing during vacuum circulation refining process of molten steel: application of the model and results

The mathematical model for decarburisation and degassing in the vacuum circulation refining process of molten steel, proposed and presented earlier, has been applied to the refining process of molten steel in a multifunction RH degasser of 90 t capacity. The decarburisation and degassing processes in the degasser under the RH and RH‐KTB operating conditions have been modelled and analysed using this model. It was demonstrated that for the RH and RH‐KTB refining processes, the results predicted by the model are in good agreement with some plant data. The mean contributions of the three refining sites in six circulation cycles to decarburisation are 10.5 – 11.6, 37.4 – 38.0 and 50.5 – 52.1 % of the overall amount of decarburisation, respectively. The KTB operation can markedly accelerate the decarburisation of molten steel. Using the top blowing oxygen of 6 min with the flow rate of (600 ‐ 1000) m³(STP)/h, the initial carbon mass content of the liquid steel for the RH refining process may be increased to (550 ‐ 700) · 10‐⁴ from 400 · 10‐⁴ %. And the treatment time needed for reducing the carbon mass content in the steel to a level of ≤ 20 · 10‐⁴ % may be shortened over 3 ‐ 4 min. The effectiveness of decarburisation and degassing cannot be obviously improved by increasing the lifting argon blow rate to 900 from 600 I(STP)/min under the operating modes examined in the present work.     

145 t RH真空精炼装置内钢液循环流动特性的水模型研究

基于相似原理,建立几何相似比1:7水模型研究了145t RH真空精炼装置内钢液循环流动行为,研究了提升气量(60~140 m³/h) 、浸渍管浸渍深度(400~600 mm) 、真空室液面高度(426~526 mm)对钢水循环流量和混匀时间的影响。结果表明,循环流量随提升气量增加而增大且呈近似线性关系,混匀时间随提升气量增加而呈非线性减小;500 mm的浸渍管浸渍深度和526 mm的真空室液面高度下均出现较理想的循环流量;130 m³/h提升气量、600 mm浸渍管浸渍深度和526 mm真空室液面高度可获得最佳循环流动特性。