【作者】 李琳；

【导师】 邹宗树；

【作者基本信息】 东北大学 ， 钢铁冶金， 2020， 博士

【摘要】 转炉冶炼是洁净钢生产的重要一环,而造渣是转炉控制钢水洁净度的关键操作。近年来钢铁行业上游供应的铁矿石资源日益复杂化劣质化,致使转炉工序输入的铁水质量逐渐恶化,冶炼负荷不断增加,同时下游用户对钢材的品质要求却在日益提高。这些突出矛盾使得常规转炉冶炼方法越来越难以满足过程快速成渣以便高效且深度脱除磷等杂质的工艺需求,进而影响到基于转炉冶炼平台的洁净钢的稳定、高效和低成本生产。在此背景下,本文提出了旋流氧枪吹氧同时喷粉造渣的转炉冶炼工艺,并采用实验研究和数值模拟相结合的方法,对涉及工艺的旋流氧枪超音速旋流射流及其作用下的气粉输送行为规律开展了基础研究。本文的主要研究工作和结果如下。(1)建立了描述氧枪超音速旋流射流流动的数学模型,明确了超音速旋流射流的流动形态、聚并特点、流体力学参数分布等基础特性,揭示了其与传统氧射流流动特性的差异,探明了旋流射流的切线流流动规律,考察了旋流氧枪喷孔扭转角设计对射流旋流流动特性的影响。结果表明:旋流氧枪产生绕枪体轴线流动的旋流射流,射流旋流强度随喷孔扭转角的增大而加强;与传统氧枪射流相比,旋流射流的聚并减弱,聚并程度与射流的旋流强度负相关,而且射流轴向速度和动压力减小,势流核心变短,但切向速度增大,射流流动参数的径向分布较均匀。旋流射流的这些特性随喷孔扭转角的增大而变得愈加显著,喷孔扭转角大于20°时旋流射流形成了明显的水平旋流流场。研究结果完成了对旋流氧枪超音速旋流射流流体力学行为的系统表征。(2)系统开展了转炉旋流射流喷射实验研究,通过综合考察旋流氧枪吹炼时的冲击坑尺寸和形貌、熔池混匀效率、渣金相间传质速率及熔池喷溅的空间分布等冶炼效果评价指标,明确了旋流氧枪的冶炼特性,并引入熔池流场水平流动强度这一指标定量评价了旋流射流切向流的影响效果。针对不同的转炉冶炼需要,提出了最优化的旋流氧枪喷孔扭转角设计。(3)运用两相平衡流理论,建立了拉瓦尔喷管内气粉两相平衡流的等熵流动模型,理论分析了喷管内气粉两相平衡流的流动特性,解明了气粉两相平衡流的流动特征参数在拉瓦尔喷管内的演变规律。(4)综合考察颗粒相体积分率的影响和颗粒-流体、颗粒-颗粒间的四向耦合作用,构建了描述超音速气粉两相非平衡流动的CFD-VDPM-DEM模型,研究了超音速气流场中颗粒运动规律及其对超音速气流流动的影响,定量解析了两相流动过程的动量和热量松弛效应,并揭示了粉剂参数对气粉流动的影响规律。研究结果发现了气粉两相流的非平衡流动特性以及流动过程中颗粒运动与气流流动的“偏析”现象,指出了气粉流流动过程气流速度分布从“∏”形均匀分布到"M"形非均匀分布再到正态分布的演变过程,表明了气粉流流动过程气流在喷管外的膨胀-压缩呈现出(膨胀-压缩)波先较强而后快速衰弱且波序缩短的演变规律。综合颗粒的运动规律及颗粒相对气流流动的影响特点,给出了适宜的粉剂喷吹参数。(5)结合相界面捕捉技术VOF方法及描述颗粒运动的DPM模型,建立了转炉旋流氧枪粉剂喷吹过程气(氧气)、粉(石灰石粉)、液(金属液)三相耦合传输的VOF-DPM模型,研究了旋流气粉流对熔池的冲击作用特性,以及粉剂颗粒冲击到金属熔池液面后的运动迁移规律。结果表明:与单相氧射流相比,传统氧枪气粉流的冲击坑较深,底部会形成尖锐的凸出,而旋流气粉流的冲击坑深度基本无变化,底部并未形成明显的凸起;气粉流冲击到熔池液面后,大部分粉剂颗粒聚集在冲击坑底部表面,一部分穿透铁水表面进入熔池内部,一部分随反射气流运动到熔池上部空间而溢出熔池;传统氧枪气粉流冲击到熔池液面后粉剂颗粒沿轴向向上反射运动,粉剂颗粒在冲击坑底部分布范围较小,而旋流气粉流粉剂颗粒与气流反射时贴近铁水表面沿径向运动,粉剂在转炉内分布范围较大。研究表明旋流氧枪喷粉时最佳喷孔扭转角为10°。更多还原

【Abstract】 In modern clean steel production,BOF steelmaking is one of the main steps in which the slagging is a key operation to control product quality.In recent years,iron ore resources for iron and steel production is becoming more jumbled and poorer in quality,which results in that the quality of hot metal for steelmaking worsens gradually and the refining load of BOF increases.In the meantime,the requirement for the quality of the steel is increasing.These facts make the existing BOF steelmaking method difficult to meet the requirement of making slag rapidly so as to rapidly and effectively remove the impurities in hot metal such as phosphorus.As such,in this study,a new BOF steelmaking technology named powder injection by a nozzles-twisted lance for slagging was proposed.Fundamental study on the supersonic swirling jets generated by the nozzles-twisted lance and the gas-powder transport behaviors was performed.The main contents and results are summarized as follows.(1)A mathematical model for describing the swirling flow of the jets from a nozzles-twisted lance was developed.Base on this model,the features of the swirling jets,such as the flow pattern,coalescence characteristics and dynamic parameter distribution were studied,and the differences of the flow characteristics between the swirling jets and the normal ones were discussed.Furthermore,the tangential flow of the swirling jets was revealed and the effect of nozzle twist angle on the flow was discussed.The results show that the nozzle-twisted lance imparted a circumferential swirling flow around the lance axis to the jets,and the swirling flow intensity increases with the increase of the nozzle twist angle.The coalescence of the swirling jets,the potential flow core and the axial velocity and dynamic pressure of the jets decrease,but the tangential flow velocity increases with the increase of the nozzle twist angle.It is found that a holistic and effective horizontal swirling flow field develops when the nozzle twist angle is larger than 20°.The present results may contribute to the fluid dynamics of the supersonic swirling jets.(2)Extensive experiments regarding the BOF steelmaking using the nozzlestwisted lance were conducted.The refining characteristics of the nozzles-twist lance were revealed by studying the cavity dimension and morphology,mixing efficiency of the bath,mass transfer rate and splashing distribution.Furthermore,the influence of the tangential flow on the refining characteristics of the nozzlestwist lance was assessed by measuring the horizontal flow intensity inside the bath.The optimal design of nozzle twist angle was also proposed for various refining purposes.(3)An isentropy flow mathematical model for a gas-powder equilibrium flow in a Laval nozzle was developed by using gas-solid equilibrium flow theory.On the basis of the model,the gas-powder flow characteristics in the Laval nozzle were studied,and the evolution of gas-pow-der flow parameters inside the Laval nozzle was revealed.(4)A mathematical model called CFD-VDPM-DEM was firstly developed by including the volumetric replacement effect of powder and the four-ways coupling between the particle and fluid and particle and particle.And then the motion of the particles and its effect on the gas flow were studied.The momentum and heat relaxation phenomena in the gas-powder flow were assessed quantificationally,and the effect of the powder feeding parameters on the gas-powder flow was revealed.The segregation phenomenon of the particle motion and the gas flow was found.The study shows that the velocity profile of the gas flow evolves from "∏" to "M"shapes and then the normal distribution.The results also indicate that the expansion-compression of the gas flow outside the nozzle is intensive in front of the nozzle and then weakens along with its axial flow,which results in a short expansion-compression wave sequence.The optimal powder feeding parameters are suggested by considering the flow behaviors of particles and their effect on the gas flow.(5)Combining with the VOF method for interface capture and the DPM model,a mathematical model of coupled VOF-DPM for describing the transport phenomena of oxygen,powder and molten metal was developed.The impinging characteristics of the swirling gas-powder flow,as well as the movement and distribution of the particles after impinging onto the bath surface were studied with this model.The results show that compared with the single-phase oxygen jet,the impinging depth of the normal gas-powder flow increases and a sharp swelling is formed at the bottom of the cavity,but the impinging depth of the swirling gaspowder flow changes little.Most of the particles distribute on the cavity surface,and some of them penetrate into the bath,and the others move outside the bath with the reflecting gas flow after the gas-powder flow impinges on the bath.It is found that,for the normal gas-powder flow,the particles move upward with the gas flow after impinging onto the bath surface and have a small distribution zone at the cavity surface.For the swirling gas-powder flow,however,the particles concentrate at the bath surface after impinging onto the cavity surface and have a large distribution zone at the bath surface.The nozzle twist angle of 10°for the powder blowing of the nozzles-twisted lance is suggested in this work.更多还原