Effects of process conditions on mixing between molten iron and slag in smelting reduction vessel via water model study

Abstract

The present study has been conducted to investigate the effects of operating conditions, which include gas flowrate, tuyere size, tuyere number, and height of iron phase, on the extent of mixing between molten iron and molten slag in the direct iron ore smelting reduction process. A transparent acrylic water model, 30% of the size of the actual smelter, was constructed to study the mass transfer phenomena. In the water model, water and spindle oil were used to simulate molten iron and molten slag, respectively, while air was used to replace the bottom blown nitrogen gas. In addition, thymol (C₁₀H₁₄O₆) was used as a tracer material in the water model, added to the water at the beginning of the experiment. As mixing between water and spindle oil proceeded owing to stirring by the bottom blown gas, the concentration of thymol in the water decreased and that in the spindle oil increased. Water samples were taken from the bottom and 12 cm above the bottom of the water model at various operating times. Concentrations of thymol were then measured using a diode array ultraviolet visible spectrophotometer. By analysing the concentration data, the mass transfer rate k_wA, which is a direct index for evaluating the mixing efficiency, could be derived. The process conditions under investigation included 40-500 L min^-1 gas flowrate, 0·3^-1 cm tuyere size, four or five tuyeres, and 20-30 cm height of the water phase. The test results indicate that when the gas flowrate increases, the value of k_wA increases, which indicates better mixing between oil and water phases. However, as the gas flowrate approaches 40 L min^-1, the improvement becomes less obvious. The smaller tuyere gives better mixing, and the design of five tuyeres results in better mixing compared with four tuyeres when they are blown with the same total gas flowrate. However, mixing efficiency decreases with increased height of the water phase. Also, as the gas flowrate of bottom blowing approaches 40 L min^-1, gas blowing from the top has little effect on the mixing behaviour in the liquid bath. For a four tuyere system, the process conditions of height of oil phase 5 cm, height of water phase 25 cm, diameter of tuyere 0·75 cm, and gas flowrate for each tuyere 40 L min^-1, appear to be the optimal design.     

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.     

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.     

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。     

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。     

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.     

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.     

Study on polychlorinated dibenzo-p-dioxin/furan formation in iron ore sintering process

In order to understand and control the formation of dioxins and furans (PCDD/Fs) in iron ore sinter plants, a CFD model of iron ore sintering, combined with the kinetic models of 14 relevant chemical reactions and thermodynamic calculations of dioxin formation, has been developed to simulate the concentrations of the gaseous species, temperatures of the gas and solid, velocity of the gas, temperature zones, and residence time of the gas in each temperature zone. The predicted off-gas compositions, the velocities of the gas, and the trends for the gas temperature at the bottom of the bed have been compared with measured data from a sinter plant, and good agreement has been obtained. From the predicted temperature zones of the gas and solid, the predicted residence time of the gas in each zone, and thermodynamic conditions of PCDD/F formation, the PCDD/F formation in sinter plants has been discussed. The dioxins are formed in the critical temperature region of 250 °C to 450 °C below the combustion zone in the bed, are then carried downward with the gas, and are condensed close to the bottom of the sinter bed. Transported to the discharge end with the solid mixture, they are again released into the gas phase when the flame front approaches the bottom. The dioxins are also formed in the last wind boxes when the hot off-gases cool and reach the critical temperature range. These pathways on PCDD/F formation can explain the industrial observations well. The preceding information may assist in the effective control or elimination of dioxin formation in iron ore sinter plants.     

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%。     

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.     

A novel method to detect the water leakage from tuyere nose cooling circuit in blast furnace

The water cooled tuyere noses, through which hot blast is blown into the furnace, are exposed to very high temperature region of raceway inside the furnace. As a result the chances of rupture of cooling pipes within the tuyere nose are significantly high. The rupture causes water dripping into the furnace and if it continues and unnoticed for a prolonged period it lowers down the local raceway temperature and thus adversely affects the product hot metal and slag quality. Moreover, with heavy water leakage, there is a danger of explosion; monitoring of the cooling water is therefore essential. Despite the availability of water flow metre at each tuyere it is difficult to identify the leaking tuyere at the early stage unless the rupture size grows bigger and so the leakage. In several cases the furnace is forced to shut down to manually inspect the leakage occurring without prior knowledge of the exact tuyere number. Identification of water leakage at an early stage is therefore necessary to prevent process disturbances due to chilling of the furnace and avoid the unscheduled downtime for tuyere replacement. This paper presents a method to identify the water leakage from tuyere nose cooling circuit in blast furnace and the adverse effect of water leakage on the performance of the blast furnace. A system called water leak detection system is developed for different blast furnaces in Tata Steel Jamshedpur to monitor the water leakage through tuyere nose and identify the exact leaking tuyere based on a dimensionless number called leak detection factor.     

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°.     

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     

Making blast-furnace smelting more efficient through the injection of heated natural gas

Subjecting natural gas to multi-stage heating by passing it through the cooled cavities of certain tuyere elements instead of coolant water is technically simple to accomplish and makes it possible to heat the gas to 300°C or more, the exact temperature depending on the amount of gas used. The cost of instituting this technology is an order of magnitude lower than the savings realized by injecting heated natural gas into blast furnaces. The injection of heated natural gas into a blast furnace introduces additional heat into the furnace and makes it possible to use more natural gas in the smelting process without reducing the theoretical combustion temperature. It also increases the value of the coefficient that characterizes the replacement of coke by natural gas, since the gas undergoes more complete combustion in this case. Finally, the injection of heated natural gas results in a more uniform distribution of hydrogen across the furnace and allows fuller use of this element in the smelting operation.     

底吹喷枪出口端蘑菇头形成机理及模拟研究

本文以水力学模型实验研究了底吹喷枪出口端蘑菇头的形成机理及控制模型。直接观察了蘑菇头的形成过程；研究了水在底吹喷枪出口端开始结晶和形成蘑菇头的条件：底吹喷枪出口端温度与水溶池温度、底吹气体温度及流量、底吹喷枪内径之间的关系。还观察到有无蘑菇头时底吻气体冷却特性的差异；最后，提出了与蘑菇头形成及熔化有关的底吻参数的控制模型。     

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.     

Characteristics and analyses of COG injection from tuyere in COREX melter gasifier

Coke oven gas (COG), as an environment-friendly source, is projected to be introduced into the COREX process to reduce solid fuel consumption. In this paper, a static model has been developed based on mass and heat balance, which can calculate characteristics of melter gasifier, such as the raceway adiabatic flame temperature (RAFT), volume and component of bosh gas. The results showed that compared with N2, the COG injection from tuyere is more effective on reducing the RAFT and improving the bosh gas volume. The quantity of COG injected is limited for the RAFT, and without other thermal compensation, the largest injection quantity is about 150 Nm³ t^?1. The quantity of COG injection can be increased by preheating tuyere oxygen, adjustment of fuel structure and addition of tuyere oxygen. COG injection can promote the reduction and hearth permeability, decrease the RAFT and protect the tuyere, which is beneficial to COREX operation.     

复吹转炉底吹氧气和石灰粉水模拟

 为了考察复吹转炉底吹氧气和石灰粉过程中的熔池特性,建立复吹转炉底吹喷石灰粉的水模型,用水模拟铁水,用空心玻璃微珠模拟石灰粉。利用图像处理法研究了底吹氧气和石灰粉时粉剂分布情况及熔池搅拌情况。采用熔池电导率法考察了相同条件下底吹喷粉与不喷粉时的混匀时间。研究结果表明,喷粉能够促进熔池搅拌,且粉剂扩散速度随底吹载气流量增大而增大;未喷粉时,混匀时间随载气流量增大而减小;在相同底吹载气流量条件下,喷粉时熔池的混匀时间明显低于未喷粉时的混匀时间,且在试验范围内,混匀时间在底吹载气流量为2 m3/h(标准态)时出现极小值。     

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.