Application of refractory coatings to converter linings by swirling technology. 1. Breakup of liquid slag with a swirling lance

The application of refractory coatings to the converter lining may be improved by means of special injectors, such as swirling lances, for most effective spraying of the slag melt. On the basis of the mechanics of gas–liquid systems, the breakup of liquid slag under the action of swirling jets is simulated. The size of the slag particles entrained from the interaction zone is determined by the speed of the gas flux and the gas flow rate. Decrease in slag viscosity tends to reduce the minimum particle size. At breakdown, foaming of the slag melt is possible. That reduces the speed of the slag particles and impairs the formation of a slag coating on the converter lining.     

Mixing of concentric gas jets issuing vertically into a liquid

Mixing of two concentric jets of dissimilar gases blown vertically upward through wafer was investigated experimentally. Air was blown through the inner pipe and carbon dioxide through the annular space between the inner and the outer pipes. The two jets mixed rapidly upon emergence from the nozzle. This made physical shielding of the air jet by CO₂ ineffective. It was caused by the fact that the air bubbles during and upon emergence from the nozzle were large. Moreover, they exhibited oscillations which made them spread over the annulus. Pursuing this argument it has been inferred that physical shielding would be ineffective in OBM/Q-BOP converter process of steelmaking as well. Therefore, protection of tuyere lining by shrouding gas seems to be due to thermal and chemical shielding, primarily. N.B. BALLAL, formerly a Graduate Student at Indian Institute of Technology, Kanpur, is presently     

180 t转炉超音速射流和聚合射流与炼钢熔池作用的水模型实验研究

以鞍钢180 t顶底复吹转炉为原型,设计超音速氧枪喷头进行了复吹转炉传统射流与聚合射流对熔池相互作用的水力学模型实验。超音速射流水模实验确定最佳的均混时间为12.6 s;在保持最佳顶吹气体流量的条件下,以降低枪位模拟聚合射流对熔池的相互作用。结果表明:当氧枪枪位下降到40 mm时,均混时间为11.8 s,这说明聚合射流完全可以达到传统射流对熔池的搅拌效果,可取消底吹系统,简化转炉设备和提高转炉炉龄。     

Turbulent flow of liquid steel and argon bubbles in slide-gate tundish nozzles: Part I. model development and validation

The quality of continuous-cast steel is greatly affected by the flow pattern in the mold, which depends mainly on the jets flowing from the outlet ports in casting with submerged tundish nozzles. An Eulerian multiphase model using the finite-difference program CFX has been applied to study the three-dimensional (3-D) turbulent flow of liquid steel with argon bubbles in slide-gate tundish nozzles. Part I of this two-part article describes the model formulation, grid refinement, convergence strategies, and validation of this model. Equations to quantify average jet properties at the nozzle exit are presented. Most of the gas exits the upper portion of the nozzle port, while the main downward swirling flow contains very little gas. Particle-image velocimetry (PIV) measurements are performed on a 0.4-scale water model to determine the detailed nature of the swirling velocity profile exiting the nozzle. Predictions with the computational model agree well with the PIV measurements. The computational model is suitable for simulating dispersed bubbly flows, which exist for a wide range of practical gas injection rates. The model is used for extensive parametric studies of the effects of casting operation conditions and nozzle design, which are reported in Part II of this two-part article.     

180 t转炉聚合射流流场的水力学模型的实验研究

采用几何相似比1∶10水模型对180 t顶底复吹转炉内射流与熔池相互作用进行模拟试验,研究了在最佳枪位(150 mm)时氧气流量(38~42 m³/h)对均混时间的影响以及最佳顶枪流量(39 m³/h)下聚合射流氧枪枪位(40~150 mm)对均混时间的影响。结果表明,聚合射流氧枪对熔池的搅拌效果完全能达到顶底复吹的搅拌效果,如能在转炉冶炼工艺中应用,可取消底吹系统,简化转炉设备,提高转炉炉龄。     

The physical behavior of a gas jet injected horizontally into liquid metal

The gas fraction and bubble frequency distributions in a submerged air jet, injected horizontally into mercury, have been measured under isothermal, nonreactive conditions for nozzle diameters of 0.325 and 0.476 cm and jet Froude numbers ranging from 20.5 to 288. The measurements reveal that the jets expand extremely rapidly upon discharge from the nozzle with an initial expansion angle of 150 to 155 deg. This value, which is over seven times greater than is found with air jets in water, indicates that the physical properties of the liquid exert considerable influence on the jet behavior. In conjunction with the rapid expansion, the air jets in mercury were also found to penetrate extensively behind the nozzle, and in many respects resembled a vertically injected jet. The extent of backward penetration of the jets was constant for all blowing conditions studied while the forward penetration increased with both increasing jet Froude number and nozzle diameter. The measured jet penetration in both the forward and backward directions were considerably larger than expected from model predictions. The core of the jets consists of a high concentration of gas bubbles. Both the gas volume fraction and bubble frequency in the core increase with increasing jet Froude number and nozzle diameter. The gas concentration and bubble frequency decrease with increasing distance along the jet trajectory due presumably to entrainment of liquid metal and bubble coalescence. On the basis of these findings, it is likely that process jets, such as are injected into copper converters, also expand rapidly and penetrate only a short distance into the bath. Thus rather than reacting in the middle of the bath, the jets may be impinging on the backwall refractory and contributing to the erosion observed there.     

高供氧压力下高马赫数氧枪数值模拟

  以北方某钢厂100 t转炉为原型，建立顶吹转炉炉内流场的三维数学模型，采用Fluent软件研究了不同高马赫数氧气射流与熔池钢液速度流场分布之间的依赖关系。研究发现，高马赫数氧枪在Ma（马赫数）为2.0～2.3时，曲线平稳，为最佳供氧压力。在提高供氧压力的同时，氧气射流的最大速度、熔池钢液面的冲击直径及冲击深度也随之增加。模拟结果显示，氧气射流在设计工况氧压小于1.0 MPa时，射流之间相互干扰作用最弱；氧气射流在设计工况氧压力大于1.0 MPa后，冲击直径与冲击深度增幅较小。基于上述研究，在实际生产中应用了高马赫数氧枪后，并结合变枪变压操作工艺，可以改善熔池底部钢液流动状况、稳定转炉吹炼过程、控制炉渣喷溅。     

Physical and mathematical models of gas‐liquid fluid dynamics in LD converters

Fluid dynamics of gas‐liquid interactions in a LD converter to refine steel was physically and mathematically simulated. Using a water model three cases of gas supply were considered, top blowing, bottom injection and combined process top blowing‐bottom injection. Mixing time in top blowing increases with bath height and the distance between the lance of the gaseous jet and the bath surface. The jet penetration was found to be dependent on the modified Froude number. The unstable and unsteady behaviour of the bath topography, as affected by the gaseous jet, was well simulated through a multiphase momentum transfer model. In top blowing, three zones of liquid splashing were found, penetration with low splash, heavy splash and dimpling with low splash intensity. These zones depend on the gas flow rate and the distance from the lance to the bath surface. During bottom injection mixing times decrease with the number of tuyères, increases of bath height and gas flow rate. In a combined process mixing time decreases considerably due to the recirculating flow formed by the action of the top jet and the submerged jets. When a submerged jet is located just below the top jet the mixing time does not decrease as compared with the separated processes either top blowing or bottom stirring.     

Oxidation of molten impurities in converters by means of combustion flames: Thermodynamic principles. 1. Thermodynamic analysis of processes in natural-gas combustion

In the production of steel, as the productivity rises and the resource and energy consumption declines, improvements in converter design are required to ensure preliminary scrap and batch heating and to intensify redox processes in the liquid bath and exhaust-gas combustion above the bath, without impairing the durability of the injection systems and the converter lining. The use of fuel–oxygen combustion flames in the converter resolves numerous technological problems. The hydrodynamics in the reaction zones and in the liquid bath may be greatly changed by fuel combustion in the converter’s working space with jet formation or by means of submersible combustion flames. In the present work, thermodynamic methods are used to analyze the dynamics of gaseous-fuel combustion and the oxidation of elements in the converter bath on interaction with high-temperature combustion products. The interaction of the combustion flame and chemical elements in the converter bath is calculated for equilibrium conditions. The use of the combustion flames is found to change the composition of the gas phase in the converter’s working space (above the bath), which contains H₂ and H₂O in addition to the traditional components associated with oxygen injection: O₂, CO, CO₂. The presence of H₂ and H₂O changes the thermal conditions and oxidative properties of the gas phase. In the combustion of gas–oxygen fuel, the optimal composition of the initial gas mixture (natural gas + oxygen) must correspond to the ratio 100% CH₄ + 69% O₂. The oxidation product is gaseous phase consisting of 40% CO₂ + 60% H₂O. The total enthalpy of combustion of the gas–oxygen fuel at converter temperatures, with an oxygen excess greater than 1.0 (up to 2.0), is about 200 kJ per mole of the initial reagents. In the oxidation of methane by carbon dioxide, the total enthalpy of combustion is between–7 and–14.5 kJ/mol of initial reagents at 1800 K. The process becomes endothermal at temperatures above 2000 K: ΔH ₂₂₀₀ = 7.7–15.4 kJ/mol. In the oxidation of natural gas by water vapor, ΔH ₁₈₀₀–2200 = 19.5–70 kJ/mol. Thus, flame temperatures above 1800 K may only be attained in the oxidation of methane by oxygen. The use of air, carbon dioxide, or water vapor as the oxidant does not yield the required thermal effect.     

Computational Fluid Dynamics Modeling of Supersonic Coherent Jets for Electric Arc Furnace Steelmaking Process

Supersonic coherent gas jets are now used widely in electric arc furnace steelmaking and many other industrial applications to increase the gas–liquid mixing, reaction rates, and energy efficiency of the process. However, there has been limited research on the basic physics of supersonic coherent jets. In the present study, computational fluid dynamics (CFD) simulation of the supersonic jet with and without a shrouding flame at room ambient temperature was carried out and validated against experimental data. The numerical results show that the potential core length of the supersonic oxygen and nitrogen jet with shrouding flame is more than four times and three times longer, respectively, than that without flame shrouding, which is in good agreement with the experimental data. The spreading rate of the supersonic jet decreased dramatically with the use of the shrouding flame compared with a conventional supersonic jet. The present CFD model was used to investigate the characteristics of the supersonic coherent oxygen jet at steelmaking conditions of around 1700 K (1427 °C). The potential core length of the supersonic coherent oxygen jet at steelmaking conditions was 1.4 times longer than that at room ambient temperature.     

A water model study of the flow asymmetry inside a continuous slab casting mold

The work studies the extent of asymmetric flow in water models of continuous casting molds of two different configurations. In the molds where fluid is discharged through multiple holes at the bottom, the flow pattern in the lower portion depends on the size of the lower two recirculating domains. If they reach the mold bottom, the flow pattern in the lower portion is symmetrical about the central plane; otherwise, it is asymmetrical. On the other hand, in the molds where the fluid is discharged through the entire mold cross section, the flow pattern is always asymmetrical if the aspect ratio is 1:6.25 or more. The fluid jet swirls while emerging through the nozzle. The interaction of the swirling jets with the wide sidewalls of the mold gives rise to asymmetrical flow inside the mold. In the molds with lower aspect ratios, where the jets do not touch the wide side walls, the flow pattern is symmetrical about the central plane.     

Characterization of Mixing in Upflow Solids-Contacting Clarifier

It has been recognized that flocculation performance can be related to the mixing process. This process has traditionally been described by vessel average parameters such as the root-mean square velocity gradient ?, which may not represent local mixing conditions within a vessel, particularly in the impeller vicinity. The analysis of turbulence in the flocculator allows a more refined specification of flow, energy, and dissipation, which have long been known to be important to the flocculation process. Presented is a study to characterize hydrodynamic conditions in the impeller zone of an upflow solids-contacting clarifier using a laser Doppler anemometer. Results were analyzed based on an analogy of the impeller-generated flow to a swirling radial jet. It was found that mean and fluctuating velocities scaled on the tip speed of the impeller. Use of the swirling radial jet analogy also allowed the scaling of local dissipation rates. Results compared favorably to other impeller studies and true radial jets, indicating the applicability of concepts for the assessment of other flocculation impellers. It was found that local dissipation rates near the impeller were significantly higher than the vessel average values. These high values highlight the need for further study of the impact of local mixing conditions on flocculation performance.     

本钢120t转炉单底枪复吹水模研究

通过模拟１２０ｔ复吹转炉水模实验与文献资料，研究单底枪复吹和双底枪复吹熔池搅拌。找出单、双底枪最佳的布置位置，明确单底枪复吹对溶池的搅拌效果比双底枪复吹对溶池的搅拌效果好。     

水口出口形状对高拉速板坯连铸结晶器内流场特征的影响

采用1∶1的水力学模型研究了浸入式水口出口形状(椭圆形、矩形、方形)对结晶器自由液面特征、流股特征与流场的影响。在通钢量为3.20和4.48t/min时,结晶器液面波动与表面流速都遵循椭圆形水口矩形水口方形水口的变化规律。椭圆形水口的流股为"旋转流股",流股扩展角和倾角最大,流股分散,且在出口处流速分布均匀;方形与矩形水口流股为"平滑流股",方形水口流股的扩展角和倾角最小,流股集中在出口偏下半部分处;矩形水口流股扩展角、倾角、流股分散与均匀程度居中。综合考虑:在高拉速条件下(通钢量为4.48t/min),椭圆形水口条件下结晶器液面的平均波高为5.5mm,表面流速为0.32m/s,仍然有提高拉速的空间,且流股速度在出口处分布均匀,所以较优的水口出口形状为椭圆形。     

Flow regimes in submerged gas injection

The behavior of gas discharging into a liquid has been investigated in the labora-tory and in plant. The laboratory work has involved the injection of different gases from a submerged, horizontal tuyere into water, zinc-chloride solution, and a mercury bath. High speed cinematography and pressure measurements in the tuyere have been carried out to characterize the flow regimes. In the case of the mercury bath, a novel “half-tuyere” has been developed to permit visual observation of the gas. In this way, two regimes of flow, bubbling and steady jetting, have been delineated as a function of the modified Froude number and the ratio of gas to liquid densities. Pressure measurements at the tuyere tip have been correlated to the different stages of bubble growth in the bubbling regime, and can be used to distinguish one flow regime from the other. The measured bubble frequency and volume correspond reasonably well to predictions of a simple model of bubble growth under conditions of constant flow. The forward penetration of the jet centerline from the tuyere tip has been measured and found to depend both onN _Fr′ andρg/ρl. In the industrial tests, pressure taps have been installed in the tuyeres of a nickel converter to monitor the pressure wave of the jets under normal, low pressure blowing operations. The measurements show that the converter jets operate in the bubbling mode with a bubble frequency of 10 to 12 s⁻¹, similar to a gas jet in mercury. Tests involving higher pressure injection indicate that the steady jetting, or underexpanded, regime obtains at pressures of about 340 kPa (50 psi). Based on equivalent experiments in the laboratory, it is clear that low pressure blowing has the disadvantage of poor penetration of air into the bath so that the jets rise close to the back wall and locally accelerate refractory wear. Moreover between the formation of successive bubbles, the bath washes against the tuyere mouth and contributes to accretion formation. This necessitates periodic punching of the tuyeres which also contributes to refractory wear at the tuyere line. The use of high pressure injection to achieve steady jetting conditions, as currently practiced in the new bottom blown steelmaking processes, should be considered to solve these prob-lems, and possibly usher in a new generation of nonferrous converters.     

激光测厚仪在120t转炉内衬上的应用研究与实践

对通钢激光测厚仪在120 t转炉内衬上的应用进行了研究。经过几年的实际应用,通钢已经能够根据测厚系统提供的数据指导转炉炉衬的维护工作,防止了炉体穿漏事故的发生,提高了炉衬的热效率,降低了原材料的消耗,取得了一定的经济效益。     

Steelmaking—the jet age

The origins of pneumatic steelmaking are traced from early operating practices based on the beginning concepts of this steelmaking technique put forth by Sir Henry Bessemer. Development of oxygen jet steelmaking in both its top and bottom blown forms is reviewed. The fundamentals of gas jet behavior are emphasized including the importance of physics, mechanics and chemistry and their role in steelmaking reactions involving slag, gas and metal. The vital combination and the continuing interaction of fundamental science and engineering development in the evolution of pneumatic steelmaking technology are emphasized. The frontiers of knowledge and the areas for further study of jet steelmaking processes are outlined. Future evolution of the application of jets in steelmaking are considered from the perspective of past and present.     

漩流氧枪转炉炼钢熔体的喷溅行为

 转炉冶炼过程金属熔体的喷溅对于转炉反应器的性能有重要影响。氧枪作为氧气射流的产生及控制单元,决定了转炉吹炼过程熔体的喷溅行为。通过水模型试验,研究了漩流氧枪转炉冶炼过程熔体的喷溅,考察了氧枪喷孔扭转角设计及操作参数下熔体喷溅速率和喷溅的空间分布规律,基于此,分析了漩流氧枪对转炉反应器性能的影响。结果表明,相比于传统氧枪吹炼,漩流氧枪吹炼时熔体喷溅速率降低,喷溅高度下降,喷溅在径向空间分布趋于均匀,且随着喷孔扭转角的增大,该分布规律变化更为显著,扭转角大于20°时,喷溅到炉口及炉外的熔体降为零。漩流氧枪吹炼时,喷溅速率及喷溅量在不同径向和高度位置处分布随着顶吹气量的增大而增大,受枪位的影响规律与扭转角有关。     

Effect of methane-hydrogen mixtures on flow and combustion of coherent jets

Coherent jets are widely used in electric arc furnace(EAF)steelmaking to increase the oxygen utilization and chemical reaction rates.However,the influence of fuel gas combustion on jet behavior is not fully understood yet.The flow and combustion characteristics of a coherent jet were thus investigated at steelmaking temperature using Fluent software,and a detailed chemical kinetic reaction mechanism was used in the combustion reaction model.The axial velocity and total temperature of the supersonic jet were measured via hot state experiments.The simulation results were compared with the experimental data and the empirical jet model proposed by Ito and Muchi and good consistency was obtained.The research results indicated that the potential core length of the coherent jet can be prolonged by optimizing the combustion effect of the fuel gas.Besides,the behavior of the supersonic jet in the subsonic section was also investigated,as it is an important factor for controlling the position of the oxygen lance.The investigation indicated that the attenuation of the coherent jet is more notable than that of the conventional jet in the subsonic section.     

转炉超音速氧枪喷头磨损后的吹炼特性变化

 转炉氧枪喷头会随枪龄的增加发生不同程度的侵蚀,为了探究氧枪喷头侵蚀程度对超音速气体射流吹炼特性的影响,建立了120 t转炉及超音速氧枪的三维全尺寸几何模型,研究了氧枪喷头不同磨损角度对气体射流特性、熔池速度及壁面侵蚀的影响。发现随着磨损角度增加,射流速度衰减加快,射流核心区长度缩短,同一等速线长度缩短,射流中心最大速度和最大速度点距中心距离增大。射流动压衰减速度随磨损角度增加而加快,磨损角度由0增至20°,距喷头端面1.5 m处最大动压减小了14.84%,14 000 Pa等压线包围面积由0.038 m2减小至0.002 m2。钢液面处高速区面积随着磨损角度增加而减小,死区面积随着磨损角度增加而增大。熔池纵截面高速区域主要分布在冲击凹坑和底吹元件附近,低速区域主要分布在熔池底部,死区主要分布在熔池底部中心和炉壁下部区域。当熔池深度小于0.6 m时,顶吹气流对熔池的搅拌起主要作用,磨损角度增加,熔池搅拌能力变弱,熔池横截面高速区面积减小,低速区和死区面积增大;当熔池深度大于0.6 m时,底吹气流对熔池搅拌起主要作用,高速区面积基本不变。渣-金作用区域和底吹流股附近流体湍动能较大、壁面剪切应力较为集中,该部位耐火材料侵蚀严重。熔池壁面附近流体湍动能和壁面剪切力随磨损角度增加而降低,转炉炉衬侵蚀速度减小。