Modelling of slag foaming

Abstract

In this work, silicone oils of different viscosities were used to simulate slag foaming. The experimental results showed that the variations of foaming height with superficial gas velocity and liquid viscosity do not show simple increasing trends. At a constant viscosity, foaming height increased first and then started decreasing with increasing superficial velocity. Similarly, a maximum foaming height was observed at an optimum viscosity when a constant gas flowrate was applied. The foaming height started decreasing with further increasing viscosity. Based on the experimental data, a semiempirical equation of foaming height was developed. The predictions of the model agreed well with experimental data. The model could also reasonably well explain the industrial pilot trial experiments. The experimental results with paraffin particle additions indicated that a small amount of particle addition moved the onset of foaming to lower superficial velocity. However, the increase in viscosity due to the presence of solid particles was found not the main reason for the increase in foaming height.     

The structure of foaming BOF-converter slag

The structure of foaming synthetic BOF-converter slags was studied by freezing the foam and using ocular examination. The foams were generated by CO gas formed due to the reaction between FeO in the slag and carbon in the hot metal. The character of the foams varied a lot with slag composition. Slag with lower viscosity resulted in foams with small gas bubbles, while slag having high viscosity resulted in very big bubbles.     

Picture analysing method of slag foaming behaviour

Hot tests of foaming behaviour of steelmaking slags were conducted on a laboratory scale up to 1760 °C using a Tammann furnace. The foaming behaviour of the slags was quantified on the basis of a new measuring method. The volume increase and the progress of the foaming process can be continuously observed and calculated by means of picture analysis. The gas content of foaming slags was compared with the results of the measurements performed in steel plants. The influence of the magnesia content on the foaming behaviour is investigated. The chemical composition of the slag is beside the CO evolution the decisive factor influencing slag foaming behaviour. The highest volume increase values observed lie in the region of 2500 % in relation to the initial volume.     

Effect of carbonaceous particles on slag foaming

Use of carbonaceous particles such as coke or coal char in controlling slag foaming is of great practical significance for bath-smelting and other steelmaking processes. The foamability of the liquid slag in terms of the foam index has been determined with the presence of different amounts of coke and coal char particles. Different sized and shaped particles were used in the experiments. It was found that the foam index decreased significantly as the ratio of the total cross-sectional area of the particles to the liquid slag surface area increased. When the foam was generated by argon gas injection through an alumina nozzle (i.d. = 1.5 mm), a liquid slag, CaO-SiO₂-CaF₂-(Al₂O₃), depending on the alumina content, could have an initial foam index of about 2 to 4 seconds at 1500 °C without any carbonaceous particles. When the slag surface was covered only 15 ~20 pct with either coke or coal char particles, the foam was totally suppressed regardless of the initial foam index. In order to understand the mechanism of the antifoam effect of the carbonaceous particles, interactions of a coke sphere, an iron ore pellet, an alumina tube, and a coal char particle with the liquid slag foam were examined by X-ray observation. It was concluded that the antifoam effect of coke or coal char particles is primarily contributed by the nonwetting nature of the carbonaceous materials with the liquid slag. Possible mechanisms of carbonaceous particles rupturing a slag film could be (1) the rapid thinning of the liquid slag film driven by a difference between the instantaneous contact angle and the equilibrium contact angle or (2) the “dewetting” of the liquid slag from the interface when the film is “bridged” by the particle. Formerly Graduate Student and Research Associate, Department of Materials Science and Engineering, Carnegie Mellon University.     

Reduction and foaming of FeO containing slag

Abstract

Smelting reduction processes being developed for producing liquid iron using coal and oxygen are attractive because they allow the use of ore fines directly and do not depend on coke. This paper presents a brief review of some aspects of smelting reduction and some results of an experimental investigation carried out on the reduction of 5–20 wt-% FeO in a synthetically prepared slag by various reductants in a plasma reactor. Some results of a simulation of the smelting reduction process by carrying out post-combustion with oxygen lancing over the slag surface are also presented. It has been possible to achieve a steady state condition, namely, 1–2 wt-% FeO in the slag with a slag height of 4–5 cm during periodic addition of a charge consisting of iron ore, coal, and flux. A kinetic analysis of FeO reduction with various reductants is presented in detail.     

不锈钢熔渣发泡剂起泡性能工业性试验研究

根据实验室对低氟碳酸盐熔渣发泡剂的研究结果,在宝钢100 t冶炼不锈钢电弧炉上进行熔渣发泡性能的工业性试验.得出了所研制的发泡剂在不锈钢冶炼中具有良好的起泡性能,起泡性能与发泡剂加入方式、发泡剂粒度等有关.根据试验结果总结得出最优的加料方式,分析了发泡剂粒度对熔渣起泡性能的影响.     

酸性含钛炉渣泡沫化问题的研究

为解决攀钢熔分深还原电炉冶炼钒钛磁铁矿金属化球团过程中出现的泡沫化严重的问题,采取提高炉渣二元碱度、控制金属化球团w(FeO)和残碳量、减少低温电炉加料量等措施,使炉内泡沫化严重的现象得到控制,保证了冶炼过程的连续进行。同时钒还原率提高了13%,冶炼时间缩短了45min。     

发泡剂对高碱度LF精炼渣泡沫化性能的影响

外加发泡剂对LF实现埋弧加热和提高精炼效率具有重要意义.本文系统研究了发泡剂种类、加入量和粒度对高碱度精炼渣发泡效果的影响.结果表明,在碳酸盐中,CaCO3最为理想.在一定范围内增大碳酸盐粒度,有利于发泡的持续性.在碳化物中,复合碳化物的发泡效果最好,CaC2好于SiC.随碳化物粒度增大,发泡效果变差.以碳酸盐与碳化物按适当比例混合作为发泡剂,较单一发泡剂具有更好的发泡效果,且应根据渣中FeO含量调整二者比例.     

Formation and effects of slag foaming in smelting reduction

Research was carried out on the foaming phenomenon in the bath of the smelting reduction process with a hydrodynamic model and with high-temperature experiments. There are two mechanisms of slag foaming: when foam is generated by injected gas, the height of the slag foaming can be regulated. Contrarily, the production of gas during the reduction of iron oxides causes slag foaming which can hardly be controlled. High temperature as well as low slag basicity reduce the foam stability. In smelting reduction a large slag volume is expected. A rinse-spot in the slag layer, which can prevent slag foaming, disappears under these conditions. Wall-effects play an important role for the foam stability.     

炼钢过程中熔渣泡沫化的研究现状

熔渣泡沫化是冶金过程中普遍存在的现象。通过文献调研前人对熔渣泡沫化的相关研究,总结熔渣的物理性质（黏度、表面张力）、化学组成（CaO、SiO2、FeO、MgO、P2O5等）等特性对熔渣泡沫化指数的影响,并结合转炉实际总结讨论冶炼过程的温度、脱碳速率等控制因素对熔池熔渣泡沫化高度的影响。针对转炉冶炼前期熔渣低温泡沫化的现象,结合调研总结提出相应的转炉冶炼前期熔渣泡沫化的控制措施,并就熔渣泡沫化今后的研究重点提出意见。     

高铝渣物性及发泡性能的试验分析

以Al₂O₃质量分数为30%的高铝渣为原料,研究了该渣系下的液相比例、黏度、表面张力和密度在不同n(CaO)/n(Al₂O₃) (C/A=1.4、1.5、1.6)、MgO质量分数(0%、5%、10%)下与温度变化(1 550、1 600、1 650 ℃)的关系,并分析了不同n(CaO)/n(Al₂O₃)下高铝渣特性对发泡行为的影响及与发泡指数之间的关系。结果表明,不同n(CaO)/n(Al₂O₃)下,MgO质量分数不同,则熔渣成为全液相时的温度均有所差异;渣的黏度和表面张力随温度的升高而减小,并且温度越高,黏度减小的幅度越小,表面张力减小的幅度越大,而渣的密度随温度升高而增加,但幅度较小,因此温度对密度的影响较小。在温度为1 650 ℃、MgO的质量分数分别为0%和5%的渣系中,改变w(CaO)/w(SiO₂)可以影响熔渣的起泡性能,因此确立了该渣系下熔渣特性与发泡指数的关系。综合分析熔渣特性结果发现n(CaO)/n(Al₂O₃)不宜过高,最佳比值为1.4。通过对不同条件下高铝渣物性及发泡性能的试验分析,掌握高铝渣物性参数的变化规律及发泡指数,为高铝渣在冶金过程中的应用提供一定参考。     

Concept of dynamic foaming index and its application to control of slag foaming in electric arc furnace steelmaking

Abstract

To sustain a foam in steelmaking processes, two basic requirements should be fulfilled, i.e. appropriate physical properties of the slag such as high viscosity, low density, and low superficial tension, and the generation of sufficient reaction gas. To date, foaming indexes have been focused on the physical properties of refining slags. In the present paper a dynamic foaming index (DFI) that involves both above requirements is proposed, using a kinetic model of the electric arc furnace process to calculate the generation rate of reaction gas, mainly CO. When the arc distortion, as affected by electrode submergence in the foam, is compared with the DFI, calculated via the kinetic model, it is observed that both parameters follow very similar trends. This finding indicates the feasibility of knowing the foaming conditions of a heat in advance, or of using the kinetic model online to control the foaming phenomena. Furthermore, experimental results relating to dynamic behaviour of the slag chemistry are well simulated using the kinetic model. To take into account the effect of size distribution of carbon particles injected into the slag to reduce FeO, a Monte Carlo simulation has been integrated into the process simulator, allowing a more realistic prediction of the current steelmaking process.     

Effect of the bubble size and chemical reactions on slag foaming

Slag foams have been investigated with smaller bubbles than those used in the previous studies.^[5,6,7] The bubbles were generated by argon gas injection with the nozzle of multiple small orifices and by the slag/metal interfacial reaction of FeO in the slag with carbon in the liquid iron. The foam stability in terms of the foam index for a bath-smelting type of slag (CaO-SiO₂-Al₂O₃-FeO) was determined for different bubble sizes. The average diameter of bubbles in the foam was measured by an X-ray video technique. When the foam was generated by the slag/metal interfacial reaction at 1450 °C, it was found that the average bubble diameter varied from less than 1 to more than 5 mm as a function of the sulfur activity in the carbon-saturated liquid iron. The foam index was found to be inversely proportional to the average bubble diameter. A general correlation is obtained by dimensional analysis in order to predict the foam index from the physical properties of the liquid slag and the average size of the gas bubbles in the foam. Formerly Graduate Student and Research Associate, Department of Materials Science and Engineering, Carnegie Mellon University.     

Role of prereduced pellets in the slag foaming in modern EAFs

The problems of electric arc furnace slags are considered, and the role of prereduced pellets in the slag foaming in electric arc furnaces is studied. The optimum rate of loading of prereduced pellets into a furnace that ensures effective steelmaking slag foaming is determined as a function of the degree of pellet prereduction.     

Effects of additives on the foaming behaviour of the FeO-SiO2 based slag

The slag foaming of FeO-SiO₂ based desiliconized slags was investigated using an X-ray fluoroscopy technique. Foaming phenomena and antifoaming effects of metallic aluminum and carbon based materials were observed. Aluminum based agents with a proper particle size range had a more significant antifoaming effect than the conventional carbon based ones. The major contribution of antifoaming agent might be due to an instantaneous reduction of FeO in the slag, resulting in the sudden decrease of slag viscosity. Although the carbon based agents also had a capability of lowering slag viscosity, suspension of carbon particles tended to increase a bulk viscosity due to its relatively slow reaction with FeO component in slags.     

转炉泡沫渣气泡分布特点及形成过程

在转炉留渣-双渣工艺脱磷阶段结束倒渣时,分别使用样勺获取倒渣开始时上部泡沫渣,倒渣结束时下部泡沫渣以及倒渣结束后炉内剩余底部泡沫渣,使用宏观及微观的方法分别分析泡沫渣各部位气泡分布特点.结果表明:气泡平均当量直径,上部>下部>底部;孔隙率,上部>下部>底部.转炉泡沫渣的形成过程为:随着大量CO/CO₂气泡进入渣中,气泡之间不断碰撞、合并,上部气泡被下部气泡抬挤且由于气泡本身的浮力作用,气泡不断上升,气泡在上升时由于重力作用,气泡之间渣相在重力作用下析液,气泡的拓扑结构不断发生变化,同时气泡之间不断碰撞、合并,最后形成上部气泡直径大且孔隙率高,下部气泡直径小且孔隙率低的泡沫渣.     

转炉吹炼末期泡沫渣高度控制技术

重点介绍了一些先进钢厂在转炉吹炼末期泡沫渣高度的控制技术。温差法?微波法和声学法都被用于测量吹炼过程中的泡沫渣高度,不仅仅能够有效防止喷溅,而且能够降低吹炼终点的钢中氮含量。此外,讨论了首钢迁安钢铁有限责任公司利用温差法测量吹炼末期泡沫渣高度的可行性。     

Influence of the viscosity and melting point of converter slag on its foaming behavior

To reduce the energy consumption in oxygen converters, the efficiency of injection must be maximized. That reduces the consumption of hot metal, slag-forming materials, and refractories and increases steel output. The influence of the viscosity and melting point of converter slag on its foaming behavior is investigated. By means of a polymer model, the regions of slag homogeneity are identified, and the influence of the liquidus temperature and viscosity of converter slag on its foaming behavior is established.