底吹喷枪出口端生成蘑菇头热态试验研究

通过热态模拟试验,研究了复吹转炉底吹喷枪出口端生成蘑菇头的过程以及底吹喷枪温度、周围耐火材料内的温度与铁水温度、底吹气体流量之间的关系。当底吹喷枪出口端温度低于铁水凝固温度约60℃时,铁水才会在其上结瘤并生成蘑菇头而保护底吹喷枪,提出了控制蘑菇头生成、长大、熔化、消失的喷吹操作特性曲线。     

铜底吹炉氧枪出口端蘑菇头生成过程水模实验研究

氧气底吹熔池熔炼过程中,高温熔体会逐渐在氧枪出口周围形成蘑菇状的疏松多孔介质区,称为蘑菇头。大小合适的蘑菇头,既不妨碍送气量,又可保护氧枪。本文以铜底吹炉为原型,基于相似原理搭建水力模型试验平台,模拟得到蘑菇头的生成过程。蘑菇头的生成需要满足一定热力学条件,主要与低温气体温度和气体流量有关,稳定蘑菇头生成过程可以分为生成-破碎-生成反复阶段和稳定蘑菇头生成阶段,蘑菇头的尺寸、孔隙率以及生成稳定蘑菇头所需时间受气体流量的影响较大,而受氧枪倾角的影响较小。随着气体流量增加,稳定蘑菇头尺寸和孔隙率都会变大,生成稳定蘑菇头所用的时间则缩短。     

蘑菇头对铜底吹炉内气液流动影响数值模拟研究

氧气底吹熔池熔炼过程中,高温熔体会逐渐在氧枪口周围形成蘑菇状的疏松多孔介质区,称为"蘑菇头",合适大小的蘑菇头,既不妨碍送气量,又可保护氧枪,但蘑菇头的存在也会对气体喷吹和气液流动产生影响。本文首先基于水模实验和热平衡理论计算的方法得到蘑菇头尺寸,随后基于VOF模型对存在蘑菇头时底吹炉内的流动状况进行模拟研究,研究蘑菇头存在情况下气泡上升过程形貌变化、上升时间以及蘑菇头的存在对炉内气液流动的影响。     

长寿复吹转炉工艺技术开发

介绍了长寿复吹转炉在武钢二炼钢80t转炉上应用的基本工艺和冶金效果。通过溅渣，控制底吹喷嘴表面生长炉渣－金属蘑菇头的内部结构、生长高度和供气面积，不仅可保证良好的底部供气功能，而且有效地保护底吹喷嘴不受熔蚀，形成永久性蘑菇头。使底吹喷嘴的一次寿命与溅渣后转炉炉龄同步，并创造了22766炉的世界复吹转炉炉龄纪录。复吹比100％，始终保持良好的复吹冶金效果。     

复吹转炉底枪附近温度场及蘑菇头生长的研究

本文在建立复吹转炉底枪附近传热及蘑菇头生成模型的基础上,分析和讨论了喷嘴砖附近温度场的变化。操作因素对温度场的影响,以及喷嘴出口处蘑菇头的生长规律。研究结果表明,在喷嘴出口附近(从工作面到200mm左右深处)的温度梯度最大,而且切换气体时温变速率最大,因此,该区域内最易产生热裂纹。蘑菇头的生成与否及尺寸主要取决于气体的冷却能力。     

底吹供气元件的维护实践

介绍了某国内钢铁集团210 t转炉底吹透气元件的维护实践,分析得出底吹透气元件失效的主要原因是底吹透气砖熔损以及透气元件堵塞。通过采取有效的措施,采用初期形成炉渣—金属蘑菇头、中后期控制炉底波动的手段,使整个炉役过程中复吹效果良好。     

底吹喷枪异常堵塞的复吹转炉熔池内的搅拌研究

根据重钢转炉生产过程中实际结构尺寸和改造没计的特点，设计制作了复吹转炉冷态模拟模型，针对实际生产过程中转炉底吹喷枪可能出现异常堵塞，实验研究了底吹喷枪正常、有部分堵塞或全部堵塞时，复吹转炉熔池内的搅拌混匀时间与底吹供气强度的关系。     

底吹喷枪异常堵塞时复吹转炉的熔池搅拌

根据重庆钢铁股份公司复吹转炉生产过程中实际结构尺寸和改造设计的特点,设计制作了复吹转炉冷态模型.针对实际生产过程中转炉底吹喷枪可能出现的异常堵塞情况,研究了底吹喷枪正常、部分堵塞或全部堵塞等不同工况下,复吹转炉熔池内的搅拌混匀时间与底吹供气强度的关系.     

天钢顶底复吹转炉底吹透气元件维护实践

介绍了天津钢铁集团有限公司120t顶底复吹转炉底吹透气元件的维护方法。分析出底吹透气元件失效的主要原因是透气砖堵塞、透气元件侵蚀。通过采取有效的措施,采用初期形成炉渣一金属蘑菇头、中后期控制炉底波动的手段,使整个炉役过程中复吹效果良好。     

莱钢120t活炉底复吹转炉长寿技术的应用

对影响活炉底复吹转炉使用寿命原因进行分析,通过对炉衬材质及砖型设计优化、复吹转炉砌筑工艺的优化、炉底底吹金属蘑菇头形成及维护、活炉底复吹转炉溅渣护炉及炉衬挂渣喷补维护等工艺措施,提高了120 t活炉底复吹转炉的使用寿命,炉龄达到27 000炉。     

Hydraulic experiment on mushroom head in bottom-blown smelting furnace

There are many bottom-blown smelting furnaces in metallurgical industry.When oxygen or air sprays from the jet nozzle into the bottom of the furnace, the melting phase will be frozen and a hemispherical porous zone with a mushroom head shape will be formed around the nozzle.The mushroom head can pro-tect the jet nozzle and mitigate the liquid spray on the surface of melt.In order to analyze the formation process of a mushroom head in the bottom-blown smelting furnaces, a hydraulic experiment system was designed and the formation of the mushroom head was investigated by hydraulic experiment.The hydrau-lic experiment results show that the formation process is mainly divided into generating crushing genera-ting process and stable mushroom head generation process.The formation of stable mushroom head re-quires certain thermodynamic condition and water splash is more intense without a mushroom head than with a mushroom head.The size, porosity and diameter of the mushroom head are affected by the flow rate, temperature and heat capacity of the bottom-blowing gas and the temperature of the superheat and the physical parameters of the melt.     

Cold Modelling of Slag Splashing in LD Furnace by Oxygen Lance with Twisted Nozzle Tip

The effects of a conventional lance tip with 4 normal nozzles and a lance tip with 4 twisted nozzles on slag splashing were investigated. A cold model for LD converters, Jiuquan Iron & Steel Co., was established and the amount of slag splashed onto the model walls was measured in the cold modelling experiments. The results from the experiments show that at low top gas flow rate the amount of slag splashing for the tip with twisted nozzles is less than that for the conventional tip, whereas at high top gas flow rate the amount of slag splashing for the nozzle twisted lance is greater than that for the conventional lance. For the nozzle twisted lance tip, slag splashing rates increase with increase in slag amount, lance height and top gas flow rate and the maximum amount of slag splashing for the tip with twisted nozzles can be obtained under the process parameters of 47.6 Nm³/h gas flow rate, 12% slag amount and 247 mm lance height. More slag droplets can be directed onto the cone with a nozzle twisted lance tip than with a normal lance tip at high top gas flow rate.     

Prediction of temperature in secondary steelmaking: mathematical modelling of fluid flow and heat transfer in gas purged ladle

As a first step towards prediction of temperatures in secondary steelmaking, mathematical modelling of fluid flow and heat transfer in ladle furnace was undertaken. A two‐dimensional quasi‐single phase model has been developed for turbulent recirculating flow by solving Reynolds averaged Navier‐Stokes equations along with a two‐equation k‐? model. The model was then extended to include thermal transport in a conjugate domain (i.e., molten steel + refractory shell + steel shell). The flow model was validated with water model data reported in literature by different researchers. Good agreement for velocity field and satisfactory agreement for turbulent kinetic energy field were obtained. The thermal model showed good agreement with results predicted in literature. The paper also presents findings of tests for sensitivity of flow on modelling and process parameters. By comparison with water model experiments, it has been demonstrated that the flow field in a ladle with a porous plug can be represented using a gas voidage fraction in the plume obtained from experiments with nozzles for axial gas injection from the bottom. Flow and thermal fields were insensitive to initial turbulence level at nozzle. Maximum temperature inhomogeneity in the melt was 2 °C after 1.5 min and negligible after 3 min of onset of gas purging.     

Study of solid mushroom formation in direct iron ore smelting reduction process using low temperature water model

Abstract

In the direct iron ore smelting reduction process, molten iron near the bottom blowing gas tuyere is cooled by low temperature/endothermic gas and forms a mushroom shaped solid on top of the tuyere. The formation of an appropriate solid mushroom, which covers the tuyere, can protect the tuyere and the surrounding refractory. In the present study, a water model with a low temperature gas system was established to investigate formation of the solid mushroom and the effects of operating conditions on its shape and dimensions. Transparent acrylic was used to construct the water model, which was 40% of the size of the actual furnace. Water was used to simulate the molten iron. Low temperature air, obtained by passing air through a heat exchanger cooled by liquid nitrogen, was blown into the water bath through a bottom tuyere. The air temperature was able to reach-188±1°C. In the water model experiments, water near the tuyere was cooled, and formed an ice mushroom surrounding the tuyere. The effects of operating conditions, mainly gas flowrate and mould material surrounding the tuyere, on the parameters of the solid mushroom were investigated. The parameters of the solid mushroom included whether it could be formed and duration of the solid mushroom, as well as the shape, dimensions, and weight of the solid mushroom. Attempts were also made to relate the temperature-time and pressure-time relationships of the blown gas to the parameters of the solid mushroom. With copper used as mould material surrounding the tuyere, the water model experiments were conducted with flowrate of the bottom blown gas set in the range 30-90 NL min^-1. The results show that as the gas flowrate was increased, the highest water temperature which allowed the solid mushroom to form in the water model was increased. Three different types of pressure-time curve were obtained under different gas flowrates in the present study. They also corresponded to different forms of solid mushroom. As peaks appeared in the pressure-time curve, they revealed ice capsulation and subsequent bursting to release the pressure. A gas flowrate of 80 NL min^-1 and water temperature of 19·2°C with copper plate as the bottom material are considered to be optimal conditions of the water model for growth of the appropriate ice mushroom. These data are rather consistent with the gas flowrate and superheat for the actual direct iron ore smelting reduction unit, which are 2700 NL min^-1 and 120°C (equivalent to 70 NL min^-1 and 22·7°C in the water model).     

Mathematical Modeling of VOD Oxygen Nozzle Jets

This study has focused on numerically exploring the oxygen flow in the convergent‐divergent De Laval nozzle. The De Laval nozzle has been commonly used as oxygen outlet at the lance tip in the vacuum oxygen decarburization (VOD) process. The nozzle geometry used in an active VOD plant was investigated by isentropic nozzle theory as well as by numerical modeling. Since an optimal nozzle design is only valid for a certain ambient pressure, one VOD nozzle will be less efficient for a large part of the pressure cycle. Different ambient pressures were used in the calculations that were based on the De Laval nozzle theory. Flow patterns of the oxygen jet under different ambient pressures were studied and the flow information at different positions from the nozzle was analyzed. In addition, the study compared the effects of different ambient temperatures on jet velocity and dynamic pressure. The predictions revealed that the modeling results obtained with the CFD modeling showed incorrect flow expansion, which agreed well with the results from the De Laval theory. Moreover, a little under‐expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry have also been studied. It has been observed that an altering ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature has a positive effect on the improvement of the jet dynamic pressure.     

焙烧炉燃烧器射流发散的分析与消除

通过将燃烧器喷嘴锥阀模拟为弹簧——质量——阻尼二阶系统,并分析燃烧器脉冲阀关闭时喷嘴锥阀关闭响应,从流体介质重油的稳态和瞬态两方面加以计算求解,通过建立流体介质的动量方程,伯努力方程,运动微分方程,得出喷嘴锥阀关闭响应时间与脉冲时间的关系,从而找出焙烧炉燃烧器射流发散的原因以及相应的措施。     

底吹气中间包内钢液流动及夹杂物去除模拟研究

通过40 t中间包的1:3水模型实验,对小方坯连铸6流中间包内钢液的流场进行了测定,研究了5种不同底吹气方案对中间包内钢液流动特性和夹杂物去除的影响。结果表明,在注流区吹气能延长钢水在中间包内的停留时间,减弱湍流强度,同时注流区内吹气可将气泡击碎成弥散小气泡促进了夹杂物上浮,夹杂物去除效果最佳。在近流与中流水口之间吹气,可改善各流的流动特性,中间包内的流动状况最佳,但近流处夹杂物去除效果略差。在中流和远流水口之间吹气,流场改善效果不理想。     

基于凸轮驱动喷嘴分阶段变速扫描的锭坯喷射均匀沉积研究

喷射成形技术可以制备出高性能、高质量的工业锭坯,对工业的发展具有重要影响。雾化喷嘴系统是喷射成形装置的核心,喷嘴扫描运动方式对锭坯的均匀沉积有着重要的作用。本文以锭坯均匀沉积为目标,提出了基于凸轮驱动的参数可调的喷嘴扫描方式,建立了喷嘴分阶段变速扫描过程,确定了凸轮形状,对锭坯沉积轨迹进行了仿真并做了分析。最后用喷射成形实验对喷嘴分阶段变速扫描进行了验证,表明了其正确性。     

Flow separation and liquid rundown in a gas-atomization process

“Rundown≓ filming mode was studied in a confined design gas-atomization nozzle of converging/ diverging construction. In this mode, liquid metal runs down to a certain distance up to ≈3 mm on the outer surface of the metal delivery tube in the form of a thin film. Atomization then takes place through the disintegration of this film by the oncoming gas. The rundown effect was simulated by water, and the supersonic gas flow outside the nozzle was visualized by Schlieren photography. It was found that rundown is caused by the liquid being drawn into a separated flow region on the wall of the delivery tube. This separation comes about as a result of the action on the boundary layer of adverse pressure gradients associated with the shock waves in the gas flow. Geometric conditions required for observing rundown are discussed, and a method is outlined for assessing whether a given nozzle design is likely to produce the effect. Evidence is also presented for the filming of the liquid on the tip of the nozzle by radial spreading.