Behaviours of supersonic oxygen jet with various Laval nozzle structures in steelmaking process

The top-blowing supersonic oxygen jet is now used widely in steelmaking and metal refining processes. However, the ambient temperature and oxygen flow rate is changed during top-blowing process, making the flow field of supersonic oxygen jet unstable. Hence, it is very important to research the behaviour of supersonic oxygen jet in high ambient temperature. In the present study, the supersonic coherent jet flow fields with 2 kinds of Laval nozzle structures were analysed at various ambient temperature conditions. The total temperature and axial velocity were measured by experiment to verify simulation results. Based on the results, the design method of characteristic-line equation could be more effective in the control the velocity vector of oxygen jet, compared with the one-dimension isoentropic flow theory. As a result, the Laval nozzle designed by characteristic-line equation could suppress the forming of shock wave, reduce the radial velocity and increase the stirring ability of oxygen jet under various ambient conditions.     

提钒用旋流氧枪喷头的数值模拟

首先对喷管内流动特性进行了研究,结果表明传统拉瓦尔喷管在喷管内部易形成大量明显的波系结构,抑制了超音速氧气射流的初始冲击效果,而利用特征线设计的曲线拉瓦尔喷管可有效解决该问题。其次,分析了不同供氧流量下,传统拉瓦尔喷管及曲线拉瓦尔喷管在高温条件下的射流马赫数分布、动压及射流卷吸特性。研究结果表明基于特征线法设计的曲线拉瓦尔喷管应用于转炉氧枪喷头时,可延长氧气射流核心段长度,增大氧气射流对熔池的搅拌能力,并提高氧气在熔池内的传质效果。     

Effect of shrouding Mach number and ambient temperature on the flow field of coherent jet with shrouding Laval nozzle structure

The coherent jet technology was widely used to improve the stirring effect of molten bath in steelmaking field, and the key to this technology was to form a low-density zone around the main oxygen jet by a high-temperature shrouding flame. With this revelation, a shrouding nozzle was processed to a Laval nozzle structure fitted with a loop arrangement for increasing the velocity of shrouding jet. For further increasing the area of the low-density zone, the preheating method was also adopted in this new coherent lance structure. In this paper, the effect of Mach number of the shrouding nozzle on the flow field of the coherent jet was investigated at room and high ambient temperature using numerical simulation and experimental studies. The result represented the simulation model used in this research showed good agreement with the experimental data at the texted conditions. Although the shock wave formed by the shrouding jet removed more kinetic energy form the main oxygen jet, the impaction ability of the coherent jet was much bigger than that of conventional supersonic jet, and this phenomenon would be further strengthen if ambient temperature and Mach number of the shrouding nozzle increases.     

炼钢温度下复吹转炉流场的数值模拟研究

以某钢厂的110 t复吹转炉为原型, 建立三维全尺寸几何模型, 通过数值模拟的方法研究了环境温度对多流股超音速氧气射流特性的影响, 并对比分析了常温和炼钢温度下氧气射流对转炉熔池的冲击搅拌效果.研究结果表明:随着环境温度的升高, 氧气射流的速度衰减减慢, 射流流股半径增大, 与此同时, 射流本身的温度升高、密度降低, 导致射流动压的增加幅度低于射流速度的增加幅度;而且, 高温环境中射流的聚合现象被抑制.在多相流研究中发现, 当环境温度由300 K提高至1723K时, 氧气射流的冲击深度由0.11035 m升高至0.14807 m, 冲击深度增大了34.18%, 熔池平均速度有一定提高, 说明在多相流研究中环境温度的影响不容忽略.     

激波在转炉炼钢中的应用

激波是超音速气流中液体属性的不连续面,气流通过激波时速度下降,温度和压强升高。氧气转炉炼钢的氧气是通过拉瓦尔管以超音速射流状态吹入转炉。在氧枪喷头设计和制定供氧制度时要减小激波损失。在转炉的某些特殊吹炼工艺中要把激波控制在适当范围内,以取得良好的冶金效果。     

聚合射流氧枪射流特性的实验研究

利用带有中心主孔的Laval喷管和16个副孔的聚合射流氧枪喷头的氧枪射流检测系统研究氧枪射流中心速度的衰减规律,测试常温氦气代替高温燃烧的保护气体作为伴流而产生的聚合射流,以及高温以主孔通空气,两副孔分别通入氧气和丙烷来产生保护气体模拟的聚合射流。结果表明,聚合射流特性优于传统射流特性,常温下随氦气入口压力增加,中心射流的轴向衰减变缓,获得比传统超音速射流更长的超声速区域;高温下通过调节燃气和氧气流量可改变环状火焰长度,同时可以根据生产实际情况变化主射流长度,满足冶炼工艺要求。     

集束氧枪环流布置模式对射流流场影响规律研究

为进一步提高集束氧枪对熔池的冲击搅拌效果, 重点分析了在两种环境下, 不同环流布置模式对超音速氧气射流流场与冲击能力的作用效果.通过对比在高温喷射试验与数值模拟研究结果, 分析射流轴向速度与射流总温流动状态, 研究不同环流布置模式下集束射流冲击特性.通过分析不同数量网格的可靠性, 选取合适的数值模拟模型, 并采用涡耗散概念模型和多步燃烧反应机理计算超音速状态下氧气与甲烷的混合与燃烧过程.研究结果表明数值模拟结果与高温喷射试验数据吻合程度较好.环流布置对拉瓦尔管出口流速无明显影响, 主氧射流核心段随环流孔径与主氧射流间距的增大, 有先提高后下降的趋势, 且不同环流布置模式对主氧核心段均有延长效果.     

Numerical Simulation of Fluid Flow in Bath during Combined Top and Bottom Blowing VOD Refining Process of Stainless Steel

The fluid flow in a bath in combined top and bottom blowing vacuum‐oxygen decarburization (VOD) refining process of stainless steel has numerically been simulated. The three‐dimensional mathematical model used is essentially based on that proposed in our previous work for the flow in combined side and top blowing argon‐oxygen decarburization (AOD) process, but considering the influence of reduced ambient pressure. Applying it to the flow in the bath of a 120 t VOD vessel under the refining conditions, the results present that the model can fairly well simulate and estimate the flow phenomena. The flow pattern of molten steel in the bath with the combined blowing is a composite result under the common action of the jets from a three‐hole Laval top lance and gas bottom blowing streams. The jets have a leading role on it; the molten steel in the whole bath is in vigorous stirring and circulatory motion during the blowing process. The streams do not alter the basic features of the gas agitation and liquid flow, but can evidently change the local flow pattern of the liquid and increase its turbulent kinetic energy to a certain extent. The flow field and turbulent kinetic energy distribution in the combined blowing with three tuyeres are more uniform than those in the blowing with double tuyeres. Increasing properly the tuyere eccentricities is of advantage for improving the velocity and turbulent kinetic energy distributions, the stirring and mixing result in the practical VOD refining process.     

聚合射流流场的仿真模拟

 为研究有低密度伴随的聚合射流氧枪射流流场,利用氧枪射流检测系统,对常温下(冷态)以空气模拟的射流进行了物理模拟。结合数值模拟结果,分析了传统无伴随流射流以及带有副孔氦气低密度伴随情况下射流流场的流动状态,讨论了在不同的滞止压力和环境温度时有、无伴随射流流场特性。结果表明,修正的k ε双方程模型能较好地预测实验结果,伴随流的存在减缓了中心射流的沿程衰减,环境温度的变化影响射流在径向和轴向的流动状态。     

环孔雾化喷嘴设计参数的研究

根据对雾化气流流动的理论分析及环孔雾化喷嘴设计参数的研究,提出了环孔雾化喷嘴设计参数的定性解析和定量描述;导出了在环孔雾化喷嘴出口处雾化气体流速及质量流量取得极大值时,雾化喷嘴气流出口截面积与空腔截面积及雾化压力的解析表达式;建立了雾化气体流速与环孔雾化喷嘴节圆直径、环孔直径及喷射顶角的函数关系式;探讨了保障环孔雾化喷...     

不同形状拉伐尔喷嘴中气流行为的研究

在考虑不同形状收缩段的基础上，建立描述不同形状拉伐尔喷嘴中沿喷嘴长各部气流行为的数学模型。数值计算表明，气体速度随入口段曲率半径的增大而增大，拉伐尔喷嘴和长度则随曲率半径的增大而减小。本数学模型可为不同形状超音速氧枪的设计提供理论依据。     

传统与聚合射流氧枪冲击炼钢熔池效果的数值模拟

通过90 t转炉的传统氧枪喷孔周围增加环氧孔,通人辅助氧气保护主氧射流形成聚合状态,建立二维两相数值模型,分析传统氧枪和聚合射流氧枪射流轴线上氧气射流速度分布及不同枪位下熔池中钢液的流动特性和冲击深度。结果表明,与传统氧枪相比,枪位相同时,聚合射流氧枪射流衰减慢,冲击力大,冲击凹坑深度深;在30De(De-氧枪出口直径)枪位下的最大冲击深度与20De枪位下的传统氧枪相同,当聚合射流氧枪在40De枪位下喷吹得平均冲击深度与传统氧枪20De枪位喷吹时相当。     

转炉炼钢氧气压力的选择

 转炉的工作氧压由喷头马赫数决定,使氧射流对熔池的穿透深度[(L)]与熔池深度[(L0)]有一个合适的比例[(L/L0)]。据实际调查,国内有1/3转炉钢厂的工作氧压不合理。根据理论分析和生产实践经验,转炉的工作氧压应比氧气喷头马赫数所对应的滞止压力高5%～15%,可以减少射流在超音速范围内的激波损失,使氧射流对熔池有较大的冲击深度,也可防止因喷孔出口处的负压而使喷孔快速熔损。在氧气喷头设计和制定供氧制度中还需了解氧气管道压力损失[Δp],用实测法所得到的[Δp]值较为可靠。     

环境压力对超音速氧气射流特性影响的数值模拟

超音速氧气射流技术是炼钢精炼过程中的重要环节,关于常压条件下超音速氧气射流的特性已进行了大量的研究,但对真空精炼过程中低压环境下的超音速氧气射流特性目前研究较少。通过数值模拟的方法研究了不同环境压力条件下超音速氧气射流的特性,并与试验结果进行了对比分析。研究结果表明：低压环境条件与高压环境条件相比,超音速氧气射流速度的衰减受到抑制,射流核心段的长度得到延长;不同环境压力条件下,射流压力与射流速度分布趋势一致,均沿轴向不断降低,但压力衰减程度大于速度衰减的程度;不同环境压力条件下,氧气射流的温度随着氧气射流的扩散不断升高,最终趋于环境温度。     

氧枪喷头射流的数值模拟

采用可实现k-ε模型对4孔氧枪的一个喷孔进行了二维流场模拟。以O2、N2和CO2射流为例,通过模拟计算确定在实际炼钢转炉环境下3种射流的流场分布,并对比分析了3种不同气源的射流特性,为进一步优化氧枪参数提供了依据;模拟计算也得出了激波和膨胀波的产生形式。结果表明,O2和N2的射流流场分布几乎不存在差别,而CO2射流流场核心区长度比前两射流要短,因此要达到同样的射流流场效果,要提高CO2射流的入口压力;在实际的操作环境下,很难做到完全满足喷孔的设计条件,产生了微弱的斜激波。     

预热温度对超音速氧气射流特性影响的数值模拟研究

超音速氧气射流特性是影响金属冶炼的重要因素之一。相同条件下,超音速氧气射流的特性会受到喷管入口氧气预热温度的影响。通过数值模拟的方法研究了不同预热温度条件下超音速氧气射流的特性,并与文献值进行了对比分析。结果表明：不同预热温度条件下,超音速氧气射流的速度,温度和压力沿轴向分布趋势相同,首先保持稳定,然后不断地衰减,最终趋于环境参数;与低预热温度相比,高预热温度条件下的超音速氧气射流的出口速度,温度和压力较大;随着预热温度的提高,射流的密度变小,导致射流稳定段的长度有所减小。     

超音速氧枪射流特性的数值模拟

利用GAMBIT建立了轴向计算长度2 200 mm和径向计算长度800 mm的超音速氧枪的数学模型,并采用FLUENT软件对氧枪射流特性进行数值仿真研究。分析了单孔氧枪超音速射流特性,以及操作压力(0.6~1.0 MPa)和环境温度(298~1 873 K)对流动特性的影响。结果表明,入口滞止压力在设计压力±25%内对射流轴向衰减及径向扩展影响不大,其与射流的超音速区长度呈二次曲线关系变化,随环境温度升高,射流轴向衰减变缓慢,核心区长度增加,超音速区长度和环境温度呈线性关系,环境温度对射流径向影响很小。     

基于解析法的氧枪喷管设计及模拟

氧枪喷管由收缩和扩张两段组成,其型线的合理与否直接关系到其流动性能的好坏,因此合理设计方法的选择对喷管设计有着重要的意义。基于解析法设计超音速喷管的收缩段和扩张段,运用CFD数值模拟技术对其进行计算。分析了基于解析法的氧枪喷管的射流特性,得出其内部压力降低,速度增加,压力损失小,且各段流体能够稳定的过渡,出口马赫数满足设计要求。     

鞍钢一炼钢90t转炉氧枪喷头射流特性研究

氧枪射流流股特性直接影响转炉冶炼效果 ,针对鞍钢一炼钢 90 t转炉四孔拉瓦尔管氧枪喷头 ,进行实验室冷态实验测试 ,研究氧枪射流特性。     

Nozzle design in impinging jet steelmaking processes

A criterion to determine throat diameter of a supersonic nozzle is determined from conservation equations of flow of gases and applied successfully to nozzles used in impinging jet steelmaking processes. Influence of surroundings on the nozzle design is evaluated in terms of the force coefficient. It is suggested that a supersonic nozzle design delivering gas at exit pressures slightly greater than the surrounding pressure or overdriving a correctly designed nozzle is beneficial under the conditions of impinging jet steelmaking practice.