Preliminary Investigation of Mathematical Modeling of Stainless Steelmaking in an AOD Converter: Application of the Model and Results

The changes in the contents of C, Cr, Si, and Mn in molten steel and the bath temperature during the refining of 304‐grade stainless steel, including both the oxidation (decarburization) and reduction processes, in a side and top combined blowing AOD converter of 120 t capacity have been predicted. The calculations were performed using the mathematical model proposed and presented in Part I of the present work [1] and were based on the designed operational mode of the AOD converter. The model predictions were compared to the referenced values given by the technological design. The results demonstrate that the predictions by the model are in good agreement with the reference values. Not only the competition of oxidation among the elements dissolved in the steel during the oxidative refining process and the corresponding distribution ratios of oxygen, but also the competition of reduction among the oxides during the argon stirring and reductive refining process and the relevant supplied oxygen ratios of the oxides, can all be characterized more comprehensively and determined more reasonably by using the Gibbs free energies of the oxidation and reduction reactions. Corresponding to the top, side, and side and top combined (overall) refining processes of 304‐grade stainless steel in a 120 t AOD converter, the carbon concentrations at the critical rates, i.e. the critical carbon concentrations, after which the decarburization changes to be controlled by the mass transfer of carbon in molten steel, are 1.20, 0.37 and 0.53 mass%, respectively, under the given designed operational mode. The model can offer some useful information for determining the technology of the side and top combined blowing AOD refining process of stainless steel.     

Mathematical Modeling of Fluid Flow in Bath during Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Application of the Model and Results

The mathematical model developed for the molten steel flow in the combined side and top blowing AOD refining process of stainless steel has been used to compute and analyze the flow fields of the liquid phases in the baths of the 120 t AOD converter and its water model unit with a 1/4 linear scale. The influence of the side tuyere number and the angle between each tuyere on the flows has been examined. The results demonstrate that the mathematical model can quite reliably and well model and predict the fluid flow in an AOD bath with the combined blowing. The liquid flow in an AOD converter bath with the combined blowing is resulted from the gas side blowing streams under the influence of a gas top blowing jet. The streams play a governing role on it; and the liquid in the whole bath is in active agitation and circulatory motion during the gas blowing process. The gas jet from the top lance does not change the essential features of the gas stirring and liquid flow in the bath, but can make the local flow pattern of the bath liquid obviously vary and its turbulent kinetic energy enhance. The changes in the tuyere position and number have similarly not altered the basic characteristics and patterns of the gas agitation and liquid flow and turbulent kinetic energy distribution in the bath. At a given tuyere number and gas side blowing rate or a given angular separation between each tuyere and gas side blowing rate, however, the variation of the angle between each tuyere or the tuyere number can locally change them. Using 6 tuyeres with 27° can reach the more uniform flow field and turbulent energy distribution of the liquid in the bath than taking 7 tuyeres with 18° or 22.5° and 6 tuyeres with 22.5°.     

Preliminary Investigation of Fluid Mixing Characteristics during Side and Top Combined Blowing AOD Refining Process of Stainless Steel

The fluid mixing characteristics in the bath during the side and top combined blowing AOD (argon‐oxygen decarburization) refining process of stainless steel were preliminarily investigated on a water model unit of a 120 t AOD converter. The geometric similarity ratio between the model and its prototype (including the side tuyeres and the top lances) was 1:4. On the basis of the theoretical calculations for the parameters of the gas streams in the side tuyeres and the top lances, the gas blowing rates used for the model were more reasonably determined. The influence of the tuyere number and position arrangement, and the gas flow rates for side and top blowing on the characteristics was examined. The results demonstrated that the liquid in the bath underwent vigorous circulatory motion during gas blowing, without obvious dead zone in the bath, resulting in a high mixing effectiveness. The gas flow rate of the main tuyere had a governing role on the characteristics, a suitable increase in the gas flow rate of the subtuyere could improve mixing efficiency, and the gas jet from the top lance made the mixing time prolong. Corresponding to the oxygen top blowing rate specified by the technology, a roughly equivalent and good mixing effectiveness could be reached by using six side tuyeres with an angle of 27 degrees between each tuyere, and five side tuyeres with an angular separation of 22.5 or 27 degrees between each tuyere. The relationships of the mixing time with the gas blowing rates of main‐tuyeres and sub‐tuyeres and top lance, the angle between each tuyere, and the tuyere number were evaluated.     

Mathematical Modeling of Fluid Flow in Bath during Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Mathematical Model of the Fluid Flow

Considering that the liquid flow field under the conditions of the combined side and top blowing would be a combined result from the common action of the side blowing gas streams and a gas top blowing jet, as the first attempt, the three‐dimensional mathematical models for the flows of molten steel in an AOD converter bath during the simple side and top blowing processes have been proposed and developed, respectively. And the mathematical model of the flow in the bath during the combined blowing AOD refining process of stainless steel has been given by the composition and superposition of the two models. In the composed model, the gas‐liquid two‐phase flow is described and treated in terms of the two‐fluid (Eulerian‐Eulerian) model. The especially modified two‐equation k?ε model for the turbulence in the liquid phase is employed. And, the surface of the sunken pit formed by impact of the gas jet blown from a top lance at the central location of the bath liquid surface is regarded as a revolution paraboloid. The related details of the composed model are shown.     

Study on Mass Transfer Characteristics in an AOD Converter Bath under Conditions of Combined Side and Top Blowing

The mass transfer characteristics in a steel bath during the AOD refining process with the conditions of combined side and top blowing were investigated. The experiments were conducted on a water model unit of 1/4 linear scale for a 120‐t combined side and top blowing AOD converter. Sodium chloride powder of analytical purity was employed as the flux for blowing, and the mass transfer coefficient of solute (NaCI) in the bath was determined under the conditions of the AOD process. The effects of the gas flow rates of side and top blowing processes, the position arrangement and number of side tuyeres, the powdered flux particle (bubble) size and others on the characteristics were examined. The results indicated that, under the conditions of the present work, the mass transfer coefficient of solute in the bath liquid is in the range of (7.31×10^?5‐3.84×10^?4) m/s. The coefficient increases non‐linearly with increasing angle between each tuyere, for the simple side blowing process at a given side tuyere number and gas side blowing rate. The gas flow rate of the main tuyere has a governing influence on the characteristics, and the gas jet from the top lance decreases the mass transfer rate, the relevant coefficient being smaller than that for a simple side blowing. Also, in the range of particle (bubble) size used in the present work and with all other factors being constant, raising particle (bubble) size increases the coefficient. Excessively fine powder particle (bubble) sizes are not advantageous to strengthening the mass transfer. With the oxygen top blowing rate practiced in the industrial technology, the side tuyere arrangements of 7 and 6 tuyeres with an angular separation of 22.5° and 27° between each tuyere, as well as 5 tuyeres with an angle of 22.5° between each tuyere can provide a larger mass transfer rate in the bath. Considering the relative velocity of the particles to the liquid, the energy dissipation caused by the fluctuation in the velocity of the liquid in turbulent flow and regarding the mass transfer as that between a rigid bubble and molten steel, the related dimensionless relationships for the coefficient were obtained.     

复吹转炉炼钢过程机理模型

在分析复吹转炉冶炼过程机理的基础上，应用冶金热力学、动力学、传输原理和反应工程学理论，建立了描述冶炼过程的动力学模型，确定了模型的有关参数。模型的关键在于正确找出转炉冶炼过程中各氧化反应的限制环节，建立氧化反应速度与限制环节速度的联系，从而得到转炉中各氧化反应的速度方程。     

顶底复合吹炼转炉冶炼不锈钢

降低不锈钢制造成本,是当前发展国内不锈钢生产的关键所在。采用转炉冶炼不锈钢是降低炼钢工序成本的合理选择。国内外已进行了大量的开发,日本川崎公司K—BOP顶底复吹转炉炼不锈钢已投入生产,太钢K—OBM转炉冶炼不锈钢在技术上是可行的。     

沙钢180t转炉自动炼钢控制工艺的建立与实践

以副枪系统和二级冶金模型为基础,通过优化原材料条件,建立转炉加料、底吹搅拌和供氧等吹炼过程自动控制工艺,以及优化系统操作参数和模型参数等措施,实现了180t转炉自动化炼钢,转炉出钢命中率由25%提高到83%以上,且吹炼过程稳定,转炉生产周期缩短了4min,终渣全铁质量分数平均降低了2.4%,提高了转炉炼钢的金属收得率。     

Fundamental Mathematical Model for AOD Process. Part II: Model validation

A fundamental mathematical model for AOD process has been developed and proposed in “Fundamental Mathematical Model for AOD Process. Part I: Derivation of the Model” 1 . Validation of the model with process data, measured from full scale AOD process, is presented in this paper. A broad selection of input data for the model was exported from various types of full scale industrial AOD heats. In this study 6 different types of heats were studied and simulated. Process data was measured from two AOD converters (95 t, 150 t). Validation of the model was then done by comparing simulated and measured values for carbon and chromium content, carbon release rate, melt composition, slag composition and bath temperature during final stages of carbon removal. The validation results showed that the model was in good agreement with the measured process data, and same model parameters were valid in all of the simulated heats.     

AOD精炼不锈钢工艺发展

论述了国外AOD精炼不锈钢技术的发展。总结了太钢AOD精炼不锈钢在品种、质量、工艺研究方面的成果。对AOD炉材质进行了分析。     

马钢大型转炉炼钢工艺正常化的途径

 马鞍山钢铁股份有限公司第4炼轧厂有300t复吹转炉2座,投产初期生产不正常。通过改进氧枪喷头参数,开展转炉炼钢的基础研究,优化吹氧、造渣制度和规范吹炼操作等措施,经过2年多的生产实践,使转炉炼钢操作正常化,能够满足生产低碳优质深冲钢的技术要求。     

转炉炼钢脱氧工艺的优化

针对鞍钢股份有限公司第二炼钢厂脱氧工艺的不足,对不同钢种采取相应的优化措施,包括采用廉价的焦炭、CaC2、SiC等脱氧剂;优化扩散脱氧剂的应用;组合使用沉淀脱氧、扩散脱氧、真空脱氧3种脱氧方法;RH-TB采用Si、Al、Ti三步脱氧工艺等技术措施,降低了脱氧合金的消耗,提高了连铸坯的质量。     

转炉预直炼法脱磷期亚音速顶吹的物理模拟

在1∶6物理模型上,通过水模型实验,对梅钢复吹转炉亚音速喷吹条件下的熔池搅拌情况进行了研究。结果表明,亚音速喷吹条件下的熔池均混时间明显长于超音速的。在亚音速喷吹条件下降低枪位、增加顶底吹气体流量可降低均混时间;A2底吹为本实验最佳布置方式,A6为适合预直炼的布置方式。     

Fundamental Mathematical Model for AOD Process. Part I: Derivation of the Model

This paper presents a new simulation model for the AOD process that takes the local variations into account but is still computationally efficient. The new idea here was to model AOD reactor as a combination of a plug flow reactor for the plume zone and a continuously stirred tank reactor (CSTR) for the bath and surface slag. This approach adopted has many advantages compared with the previous models. At first, it offers an effective method for considering the locally varying conditions as the gas bubbles rise in the plume. The model can be built computationally very effective compared to CFD due to significantly smaller amount of variables. The validation of the model is also easier as it has features that can be experimentally determined. The model is based on the simultaneous solution of conservation equations of mass, species and energy in all the vertical cells of the plug flow reactor, and a single volume in bath and surface slag. A novel method was developed and used for solving the rates in a mass transfer controlled multi‐component reaction system. In this Part I of this paper, the model is presented and its features discussed by few illustrative examples. In the following Part II, the model is broadly validated with new full scale industrial AOD process measurements for carbon release rate, melt composition, slag composition and bath temperature rise during final stages of carbon removal.     

双流体模型在AOD熔池流场数学模拟中的应用

基于气液双流体模型和湍流的修正k-ε模型,考虑了多股气流侧吹操作对熔池流场的影响,以及AOD熔池内气液两相流的行为和两相间的动量传输,建立了AOD多股气流侧吹精炼过程中熔池内流体流动的数学模型,并对宝钢股份不锈钢事业部120 tAOD原型和线尺寸为其1/4的水模型熔池内流体的流动作了模拟,结果表明,确实可以采用双流体模型来模拟AOD精炼过程中熔池内流体的流动;用该模型计算的结果表明,整个熔池流体处于活泼的搅拌和循环运动状态。     

鞍钢转炉工序负能炼钢生产实践

对比分析了国内转炉工序负能炼钢指标,制定了鞍钢股份有限公司炼钢总厂二工区、三工区实现转炉工序负能炼钢的目标。采取了相应的技术措施进行科技攻关,实现了两个工区负能炼钢,促进了转炉生产节能减排。