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).     

Bath mixing behaviour in top–bottom–side blown converter

Abstract

The influence of blowing process parameters on bath stirring was investigated in a model of a top–bottom–side blown converter using physical modelling experiments. It was shown that the side blowing gas flowrate has an important influence on bath mixing time which decreases as side tuyere gas flowrate increases up to a critical flowrate and then plateaus. Bottom gas injection is favourable for bath mixing for top–bottom–side blown converters; however, top lance height, top gas flowrate and bath level have little influence.     

复吹转炉渣金间传质物理模拟及应用

 将200 t复吹转炉按照1：12的比例缩小,用液体石蜡模拟炉渣、水模拟钢水、压缩空气模拟顶吹和底吹气体,在实验室建立模拟复吹转炉吹炼过程熔池渣金间传质的试验模型,在顶吹气体流量为88 m3/h条件下,通过相对集中非对称布置的4、6、8、10、12支底枪吹入不同底吹气体,用苯甲酸作为传输物质,试验测定了复吹转炉熔池渣金间的容量传质系数,考察不同底枪支数和布置以及底吹气体流量对渣金间传质速率的影响,优化复吹转炉底枪布置和底吹气体流量,以增强复吹转炉熔池的搅拌,改善熔池渣金反应动力学条件。研究结果表明,当底吹气体流量为1.14 m3/h时,在4～12支的底枪布置方案中,4、6支底枪布置方案的容量传质系数(分别为1.77×10-4、1.80×10-4 L/s)低于8、10、12支底枪布置方案的容量传质系数(分别为2.41×10-4、2.24×10-4、2.42×10-4 L/s);当底吹气体流量为0.57 m3/h时,在8～12支底枪布置方案中,10、12支底枪布置方案的容量传质系数(分别为1.68×10-4、1.69 ×10-4 L/s)明显大于8支底枪布置方案的容量传质系数(0.95 ×10-4 L/s);在底吹气体流量不小于1.14 m3/h后,8、10、12支底枪布置的容量传质系数相差不大,在2.24×10-4～2.87×10-4 L/s的范围;在气体流量小于1.14 m3/h时,随着底吹气体流量的增加,渣金间的容量传质系数增加显著,底吹气体流量大于1.14 m3/h后,容量传质系数增加变缓。将12支底枪布置方案应用到实际复吹转炉,整个炉役的平均碳氧积为0.001 96×10-4,在不同炉龄阶段,终点钢水平均碳氧积为0.001 88×10-4～0.002 04×10-4,终点钢水碳氧积小于0.002 5×10-4的炉次比例达到90.53%。     

顶底侧吹转炉炼钢新技术开发研究

在顶底复吹转炉熔池侧壁上安装侧吹枪,形成顶底侧吹转炉。通过实验室物理模拟研究了顶底侧吹条件下转炉熔池的混匀行为;在工业试验中,对比了顶底侧吹转炉和顶底复吹转炉炼钢的冶金效果。实验室研究结果表明,顶底侧吹技术可以显著提高转炉熔池的搅拌能力,大幅度降低转炉熔池的混匀时间,存在一个临界侧吹气量,当侧吹气量大于该临界值后,熔池混匀时间变化不大。工业试验结果表明,转炉采用顶底侧吹技术,可以降低钢铁料消耗,吨钢石灰消耗可降低将近3kg,提高了转炉的脱磷能力,降低炉渣和钢水的氧化性,平均出钢碳氧积为0.0025×10-4,钢水氧化性的降低提高了合金收得率。     

Model study on mixing and mass transfer in ferroalloy refining processes

An experimental study has been performed to investigate the bath mixing intensity induced by a high-strength submerged gas injection in a bottom blown air-stirred one-seventh water model of Creusot-Loire Uddeholm (CLU) reactor using three different tuyere configurations. Experimental results have been discussed in terms of the mass transfer rate and mixing time. The air flow rates varied from 0.00599 to 0.01465 m³/s. The mixing time was determined at various gas flow rates, bath heights, and nozzle orientations, both in the presence and absence of a second phase. The mixing time was found to decrease with increasing gas flow rate and decreasing bath height. The influence of bath mixing intensity on mass transfer between metal (water) and slag (paraffin) was studied by measuring the transfer of benzoic acid from the gas-stirred water bath to paraffin as a function of the gas injection parameters. The bath mixing intensity was characterized by the value of the mass transfer rate constant. The rate constant of mass transfer between the metal and slag was found to increase with increasing gas injection rate and decreasing bath height.     

Mathematical model of COREX melter gasifier: Part I. Steady-state model

The COREX melter gasifier is a countercurrent reactor to produce liquid iron. Directly reduced iron (DRI), noncoking coal, and other additives are charged to the melter gasifier at their respective temperatures, and O₂ is blown through the tuyeres. Functionally, a melter gasifier is divided into three zones: a moving bed, fluidized bed, and free board. A model has been developed for the moving bed, where the tuyere region is two-dimensional (2-D) and the rest is one-dimensional (1-D). It is based on multiphase conservation of mass, momentum, and heat. The fluidized bed has been treated as 1-D. Partial equilibrium is calculated for the free board. The calculated temperature of the hot metal, the top gas, and the chemistry of the top gas agree with the reported plant data. The model has been used to study the effects of bed height, injection of impure O₂, coal chemistry, and reactivity on the process performance.     

Model study of mixing and mass transfer rates of slag-metal in top and bottom blown converters

Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and metal in LD and Q-BOP furnaces using six different circular tuyere arrangements. Splashing and ‘spitting’ were also examined with a view to finding a quiet bath with minimum mixing time and maximum mass transfer rate. Froude’s similarity criterion was fulfilled to determine gas flow rate and bath depth. Complete mixing time of water determined by tracer technique had been 0.9 second to 1.8 seconds for Q-BOP as compared to 6 seconds to 13 seconds for LD. This shows that the stirring intensity in Q-BOP is remarkably larger than that of LD. A simple relationship τ = 5.9(Q/N) ^−0.49 was obtained with gas flow rateQ and number of tuyereN. This indicates that flow rate of gas per tuyere should be intensified to realize better mixing. Mass transfer coefficient K_Ba for bottom blowing was found to be almost double that for top blowing. Of all the tuyere configurations studied for Q-BOP’s, a half circular tuyere arrangement was found to be the best considering all aspects of mixing, mass transfer, and bath agitation.     

Physical simulation of converter steelmaking with powder injection

A water model of top and bottom blown converter with top lance powder injection and bottom tuyere powder injection was established to investigate the powder injection. The results show that the powder penetration ratio under the condition of top lance injection is greater than that under the condition of bottom tuyere powder injection. In both cases, the powder penetration ratio increases with the increase of solid/gas ratio and powder particle size. Powder uniform dispersion time with top lance powder injection is longer than that with bottom tuyere powder injection. Top lance powder injection, lance height of 258?mm, bottom blowing rate of 1·96?Nm³?h^?1 and powder particle size of 0·212–0·380?mm are suggested as the optimum powder injection operation under the experimental condition. The corresponding optimum operation for prototype is top lance powder injection with lance height of 1550?mm, powder size of 1–5?mm and bottom blowing rate of 450?Nm³?h^?1.     

Study of optimal Ca-Si injection position in gas stirred ladle based on water model experiment and flow simulation

Abstract

A mathematical model based on a computational fluid dynamics technique named SOLA-SURF and the k-? two equation turbulence model, and a water model that is one-quarter the scale of an actual ladle system, have been developed in the present study to find the optimal Ca-Si injection position for the ladle secondary refining process. Based on experimental measurements and observations from the water model and simulated results of the mathematical model, which has been verified by the experimental measurements, fluid flow phenomena and corresponding diffusion of the injected Ca-Si under various design and operating conditions have been investigated. The water model experiments and simulated results from the mathematical model for actual ladle operation show that, with an injection depth of 0·8 m and argon gas flowrate of 100, 200, and 300 L min^-1, the optimal position for injection is located on the tuyere-circle centre plane, opposite side to the tuyere, and 0·5-0·8R away from the circle centre. For this injection position, the mixing time is shorter and the flow pattern favours transport of the additive to the bottom of the ladle.     

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.     

A water model study of bottom-blown oxygen steelmaking processes

Investigations were carried out in a water model of bottom-blown oxygen steelmaking processes like OBM/Q-BOP to understand certain aspects of the dynamics of these processes. Wall shear stress along the bottom of a cylindrical plexiglass model vessel was measured as a function of process parameters, using the electro-chemical technique. Experiments were conducted with one, three, six and twelve tuyeres in various geometrical configurations. Air was used to simulate the gases blown into the bottom-blown converters. In single-tuyere experiments, two concentric pipes were employed and air was distributed between the inner pipe and the annular region to simulate oxygen and the shrouding gas respectively. It was found that the wall shear stress (τ) decreased drastically with increasing distance from the tuyere. The rms value of the fluctuations (τ′) in shear stress were directly proportional to the time-averaged value (τ). Percentage air in the annulus and the length of tuyere protrusion into the bath had significant effect on t only at points close to the tuyere. Dimensionless correlations have been attempted for these variables at the point closest to the tuyere at which measurements have been made. Results of visual observations and photogaphy are also reported. Multiple-tuyere experiments were conducted with the tuyeres in symmetric and asymmetric arrangements. It was observed that for any tuyere configuration rms value of τ′ was proportional to t. There seem to be an optimum number of tuyeres for minimizing shear stress along the bottom. Asymmetric arrangement of tuyeres resulted in higher level of shear stress. An attempt has been made to relate the observations of the study to the wear of the bottom ref actory lining. N.B. Ballal formerly a graduate student at Indian Institute of Technology, Kanpur     

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.     

210t转炉底吹供气参数优化模拟研究

为优化某厂210t转炉底吹供气效果,利用气-液两相流相互作用数值模拟方法,研究了底吹元件数量、布置方式和供气强度变化对熔池搅拌效果的影响.通过对8支、10支、12支底吹元件数量下的作用效果分析,得出12支底吹元件布置在0.63D(D为熔池直径)的同心圆上时,熔池内钢液流动相对较稳定,"死区"比例最低,混匀时间最短.随着...     

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.     

Industrial Experiment of Steelmaking in a Top‐Bottom‐Side Blown Converter with Slag Splashing Process

A side purging tuyere was applied in the bath side wall in a top and bottom blown converter to form a top‐bottom‐side(TBS) blown converter and side gas was injected into the converter through the side tuyere during steelmaking process with slag splashing. The metallurgical results from the TBS converter were compared with those from another top and bottom blown converter in the same workshop in the industrial experiment. It is found from the results that consumption of ferrous charges can be reduced and lime consumption of a ton of molten steel can be decreased by about 3 kg in the TBS blown converter. It can enhance dephosphorization capability and lower oxidization of slag and liquid steel. The average [%C] × [%O] at tapping is 0.0025 in the TBS converter, which increases yielding rates of alloy elements.     

关于高炉风口面积调节方法的探讨

通过建立高炉送风系统模型,模拟了风口尺寸对风口速度、流量和鼓风动能的影响,纠正了高炉操作认识上的一些错误。研究表明,缩小少数几个风口面积会减小鼓风动能,但却增大了其它风口的鼓风动能;只有减小多个风口的面积,才会增大所有风口的鼓风动能。减小少数几个风口的操作之所以能抑止边缘气流是其风量明显减少所致。     

关于高炉风口面积调节方法的探讨

通过建立高炉送风系统模型,模拟了风口尺寸对风口速度、流量和鼓风动能的影响,纠正了高炉操作认识上的一些错误。研究表明,缩小少数几个风口面积会减小鼓风动能,但却增大了其它风口的鼓风动能;只有减小多个风口的面积,才会增大所有风口的鼓风动能。减小少数几个风口的操作之所以能抑止边缘气流是其风量明显减少所致。     

100t LF底吹工艺优化冷态模拟及应用

通过冷态模拟实验测定混匀时间,优化了100 t LF底吹两个透气砖的位置和底吹工艺参数.在生产中,采用最佳的底吹工艺,脱硫率提高了15.5 %,并且还研究了单个透气砖在包底最佳的安装位置和底吹工艺参数,为现场进一步改造提供依据.     

Experimental study on slag splashing of an 80 t combined blown converter

Physical modelling of slag splashing practice of an 80 t combined blown converter was conducted in this paper. Through measuring the mass flux of splashed slag, the effect of different operating parameters on slag splashing was investigated. By means of variance analysis, the influence significance of different operating parameters on slag splashing was obtained, and the optimal combination of operating parameters were acquired as follows: lance height 600?mm, top gas flowrate 18000?Nm³?h^?1, four nozzles lance, bottom nozzle configuration D4, bottom gas flowrate 100?Nm³?h^?1, and amount of remained slag 10%. In addition, the relation between the agitation energy of top blow and mass flux of splashed slag was discussed, and the estimation model for mass flux of splashed slag during BOF slag splashing practice was proposed through data analysis.     

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°.