Kinetics of simultaneous reactions between liquid iron-carbon alloys and slags containing MnO

The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction rate of MnO from slag were examined at 1450 °C to 1550 °C by using high carbon iron alloys and CaO-SiO₂-CaF₂ slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface, and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization. The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of experimental results, were found to increase with increasing the (MnO + CaO)/SiO₂ ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the aid of the kinetic model.     

Effect of Silicon on the Desulfurization of Al-Killed Steels: Part II. Experimental Results and Plant Trials

Recent observations suggest that increased silicon levels improve ladle desulfurization of aluminum-killed steel. A kinetic model was developed and presented in part I of this paper, demonstrating that increased silicon levels in steel suppress the consumption of aluminum by parasitic reactions like silica reduction and FeO/MnO reduction, thus making more aluminum available at the interface for desulfurization. The results are increases in the rate and the extent of desulfurization. Predictions were compared with laboratory induction furnace melts using 1 kg of steel and 0.1 kg slag. The experimental results demonstrate the beneficial effect of silicon on the desulfurization reaction and that alumina can be reduced out of the slag and aluminum picked up by the steel, if the silicon content in the steel is high enough. The experimental results are in close agreement with the model predictions. Plant trials also show that with increased silicon content, both the rate and extent of desulfurization increase; incorporating silicon early into the ladle desulfurization process leads to considerable savings in aluminum consumption.     

Effect of Silicon on the Desulfurization of Al-Killed Steels: Part I. Mathematical Model

Recent observations suggest that increased silicon levels improve ladle desulfurization of aluminum-killed steel. While the overall desulfurization reaction of Al-killed steels does not show a direct role of silicon in desulfurization, model calculations are presented which test the idea that silicon suppresses the reduction of silica which can consume aluminum at the slag/metal interface. Consumption of aluminum would increase the oxygen potential at the slag/metal interface and decrease the sulfur partition coefficient between slag and metal. The model considers the coupled reactions of the reduction of silica, iron oxide, and manganese oxide in the slag and desulfurization of the steel by aluminum. The results show that silicon can indeed suppress consumption of aluminum at the slag/metal interface by side reactions other than desulfurization, with silicon affecting both the kinetics and the equilibrium of desulfurization.     

The effect of carbon content on the rate of reduction of FeO in slag relevant to iron smelting

In the iron smelting, or bath smelting, process the tapped metal contains high amounts of sulfur and the slag contains high amounts of FeO, relative to blast furnace slag. After tapping, the FeO can be further reduced by carbon in the metal, which will also lead to better desulfurization. Although there have been many studies of the reaction of carbon in iron with FeO in slag, discrepancies exist with regards to the effect of carbon in iron on the rate of FeO reduction in slag, which is the subject of this study. Experiments were conducted at 1723 K, using a slag with basicity close to one with an FeO mass content of 5 %. The rate of reduction was measured using a pressure increase technique. For moderate and high sulfur contents, as in the case of iron smelting, the rate is primarily controlled by the dissociation of CO₂ on the surface of the molten iron. Furthermore, if the effect of carbon on sulfur is taken into account, for the range of carbon mass contents of 2 to 4.5 %, there is no effect of the carbon level on the rate of FeO reduction. At low sulfur contents it was found that there is considerable slag foaming, which inhibits mass transfer of FeO in the slag, and significantly reduces the rate. Even when there is no slag foaming at low sulfur contents, mass transfer of FeO in the slag can influence the rate of FeO reduction.     

铁水预处理脱硫渣铁回收再利用

 铁水预处理过程中所产生的脱硫渣铁中铁和硫较高,具有较高的再利用价值,目前国内各大钢铁企业都致力于脱硫渣铁回收再利用的研究。介绍了迁钢公司二炼钢转炉回收利用脱硫渣铁工艺,并对生产数据进行了总结,加入8 t脱硫渣后平均增硫为0.013 6%,转炉出钢硫质量分数高,LF精炼需要深脱硫处理,精炼工艺造渣料电耗都有所增加,生产周期延长。从整体分析,转炉回收利用脱硫渣铁能够提高金属铁收得率,降低炼钢成本,提高经济效益。     

转炉炼钢过程渣钢间硫的分配比

采用热力学分析的方法研究了300t转炉渣钢间脱硫反应。发现渣中氧传质控制转炉炼钢脱硫反应,转炉终点渣钢间硫分配比与（FeO）-O-S热力学模型计算结果相符,说明脱硫反应接近平衡。定量分析结果表明,转炉渣钢间硫分配比主要受碱度、FeO含量、MgO含量及温度的影响。根据生产数据回归得到了对生产指导性较强的渣钢间硫分配比计算...     

Reduction kinetics of manganese oxide in basic oxygen furnace type slag

In order to improve manganese yield during the reduction of manganese ore, the reduction kinetics of manganese oxide in BOF type slag has been investigated on an experimental scale. The reduction rate of (MnO) was promoted for the slag of low basicity and high contents of (FeO). The maximum reduction rate of (MnO) has been found for an iron melt with carbon mass contents of 1.9 %. The silicon in metal may accelerate the reduction of manganese oxide in slag. The kinetic model for the reduction rate of (MnO) has been formulated based on the assumption that the reduction of (MnO) was controlled by the mass transfer through the metal and slag boundary layers at the metal/slag interface. The result calculated by the kinetic model showed a good agreement with the experimental one. The reduction behaviour of (MnO) can be described by the present model.     

Improving the Desulphurization in COREX Process by Adjusting the Hot Metal Chemical Composition

The COREX process, which has many advantages, still has high and fluctuating sulfur levels in the hot metal. To overcome the desulfurization problems, several measures were proposed, and the adjustments of chemical compositions of hot metal were explained in the current study. Theoretical calculations and experimental results showed that increments in either of or both silicon and manganese levels were beneficial to the desulfurization from the thermodynamic viewpoint. However, high silicon content would increase the costs of the coal of COREX process and did not meet the requirements of dephosphorization and low slag content in steelmaking. Besides, superfluous manganese was also unnecessary as it would increase the costs of COREX. Therefore, the existing silicon content should be decreased (< 1.5 pct), and the manganese content should be increased in a suitable range (from 0.6 to 0.8 pct) for COREX-3000 in China.     

Effectiveness of fluidized lime in the desulfurization of hot metal in 300-t casting ladles

The desulfurization of hot metal by the injection of fluidized lime in the 300-t casting ladles of the oxygen-converter shop at OAO Alchevskii Metallurgicheskii Kombinat is investigated. Analysis of the results shows that, in the deep desulfurization of hot metal with an initial sulfur content of 0.020–0.030% by a mixture of granulated magnesium and fluidized lime, the lime injected with magnesium into the hot metal has no significant effect. Measures are proposed to reduce the desulfurization costs and the losses of hot metal with the ladle slag.     

Numerical Simulation of Desulfurization Behavior in Gas-Stirred Systems Based on Computation Fluid Dynamics–Simultaneous Reaction Model (CFD–SRM) Coupled Model

A computation fluid dynamics–simultaneous reaction model (CFD–SRM) coupled model has been proposed to describe the desulfurization behavior in a gas-stirred ladle. For the desulfurization thermodynamics, different models were investigated to determine sulfide capacity and oxygen activity. For the desulfurization kinetic, the effect of bubbly plume flow, as well as oxygen absorption and oxidation reactions in slag eyes are considered. The thermodynamic and kinetic modification coefficients are proposed to fit the measured data, respectively. Finally, the effects of slag basicity and gas flow rate on the desulfurization efficiency are investigated. The results show that as the interfacial reactions (Al₂O₃)-(FeO)-(SiO₂)-(MnO)-[S]-[O] simultaneous kinetic equilibrium is adopted to determine the oxygen activity, and the Young’s model with the modification coefficient R _th of 1.5 is adopted to determine slag sulfide capacity, the predicted sulfur distribution ratio LS agrees well with the measured data. With an increase of the gas blowing time, the predicted desulfurization rate gradually decreased, and when the modification parameter R _k is 0.8, the predicted sulfur content changing with time in ladle agrees well with the measured data. If the oxygen absorption and oxidation reactions in slag eyes are not considered in this model, then the sulfur removal rate in the ladle would be overestimated, and this trend would become more obvious with an increase of the gas flow rate and decrease of the slag layer height. With the slag basicity increasing, the total desulfurization ratio increases; however, the total desulfurization ratio changes weakly as the slag basicity exceeds 7. With the increase of the gas flow rate, the desulfurization ratio first increases and then decreases. When the gas flow rate is 200 NL/min, the desulfurization ratio reaches a maximum value in an 80-ton gas-stirred ladle.     

Mathematical Modelling and Experimental Investigation of Coke Reduction of FeO in Slag

Mathematic model development and experimental investigations were carried out for the reduction of FeO in slag by coke. Rate expressions for the reduction limited by the different steps and through different reaction routes were proposed. In the experimental investigation, the FeO reduction was found to be a first order and irreversible reaction; the reduction rate increased with increasing temperature and the FeO content in slag, and decreased with increasing ash content in the coke. Low CO₂/CO ratio in the product gas and preferential reduction of FeO over SiO₂ in slag were observed in the reaction system. The proposed reaction mechanisms were discussed with the observed kinetic phenomena. The reduction of FeO in slag by coke was found most likely to be jointly dominated by the mass transfer of FeO in slag and the chemical reactions at slag‐coke, slag‐gas or slag‐metal interfaces.     

含铌铁水预处理脱硅保铌的研究

 为防止铁水预处理脱硅过程中脱铌,通过中频感应电炉底吹氧气冶炼含铌铁水,研究了铁水预处理吹氧过程中不加渣和加入造渣剂吹炼过程中脱硅保铌的行为及铁水中各元素含量的变化规律。试验结果表明：在铁水温度1623K加入碱度为4的CaO-SiO2-CaF2的造渣剂、供氧强度为0. 5m3/(t·min)时吹氧冶炼,铁水中的硅含量降低到0. 012%(质量分数,下同)时,铌才开始氧化,脱硫率为83%,磷含量不变;在相同的温度和供氧强度,不加造渣剂吹炼时,铁水中的硅降低至0. 16%时,铌开始氧化,硫和磷含量不变;有渣吹炼脱硅保铌终点硅含量是无渣吹炼脱硅保铌终点硅含量的10%,显著脱硫。     

钢中硅质量分数对出钢渣洗脱硫效果影响

 为了提高出钢渣洗脱硫效果,在国内某钢厂300 t转炉进行了21炉出钢渣洗脱硫试验。研究结果表明,当钢中Als和硫质量分数分别为0.025%～0.045%和0.002%～0.004%时,钢中硅质量分数对出钢渣洗脱硫效果影响十分显著,而锰质量分数对出钢渣洗脱硫效果没有直接的影响。通过将出钢过程钢水硅质量分数控制在0.05%以上,并借助渣洗脱硫工艺,可以稳定生产硫质量分数小于0.002%的管线钢。此外,基于耦合反应动力学模型,通过将Al-O反应、Si-O反应、脱硫反应和Fe-O反应进行耦合,得到钢中硅质量分数是通过影响界面氧活度来影响渣洗脱硫效果。在钢水氧活度变化不大的条件下,界面氧活度主要取决于炉渣氧化性,而从炉渣成分中可以看出,硅质量分数小于0.05%的钢种对应的炉渣氧化性要高于硅质量分数大于0.05%的钢种,这与模型计算结果相一致。     

炉渣成分对COREX铁水脱硫效果的影响

 COREX熔融还原炼铁工艺具有污染小、能耗低、对冶金焦的依赖性低等优点,但存在着铁水中硫质量分数高的问题。为了提高COREX 3000工艺的脱硫效果,针对炉渣中w(CaO)/w(SiO2)、w(MgO)及w(MgO)/w(Al2O3)等指标对脱硫效率的影响进行了研究和实践。通过渣铁耦合试验研究了炉渣成分对脱硫效率和渣铁间硫分配比的影响规律,优化调控炉渣成分并得到适宜的炉渣成分范围。比较两种碱性氧化物对脱硫效率的影响程度,应当优先调整炉渣二元碱度至1.20～1.35,随后是炉渣的MgO质量分数,同时还要兼顾w(MgO)/w(Al2O3),适宜的w(MgO)/w(Al2O3) 为0.80～0.90。     

Hot metal pretreatment by powder injection of lime‐based reagents

A mathematical model earlier proposed has been improved to predict the kinetics of multicomponent reactions in the hot metal pretreatment through the injection of reactive fluxes. It is assumed that there are two reaction zones along the flux injection operation: a transitory reaction between the rising particles and the bulk metal, and the permanent reaction between the metal and the top slag. A criterion to estimate the fraction of solids which will react with molten iron in a three‐phase jet (gas‐solid‐liquid) was considered; this fraction of solids carries out the transitory reaction. The model also takes into account the thermodynamic changes produced in the metal and slag due to the chemical reactions. Calculated results of the model are in good agreement with experimental results for the desulfurization of hot metal through the injection of CaO‐SiO₂‐CaF₂‐FeO‐Na₂O reagents at 1400 ‐ 1450 °C. Two kinds of hot metal were tested, one with a low carbon mass content of 3 % and the other with a high carbon mass content of 4.5 %.     

120 t转炉熔池中硫行为的研究

取样测定了120 t转炉在冶炼过程中熔池中硫的变化情况,通过物料平衡计算研究了熔池中硫的来源,并研究了终点温度、炉渣碱度、渣中(FeO)对硫在渣钢间分配比的影响.结果表明,提高终点温度和炉渣碱度有利于硫分配比的提高,在一定范围内提高渣中(FeO)含量有利于硫分配比的提高,w(FeO)≥18%时,随着(FeO)含量的提高硫分配比减小;减少入炉硫负荷是冶炼低硫钢的基础.     

铁水脱硫渣回硫分析及聚渣剂研究

本文主要研究了梅钢150t铁水包复喷吹脱硫后脱硫渣的重量、成分、硫含量,以及铁水在脱硫前后成分的变化关系,在此基础上进一步研究了残留在铁水包表面的脱硫渣对炼钢回硫影响的幅度。研究结果表明,复喷吹脱硫结束后,脱硫渣中硫含量在2%-3.5%之间,扒渣结束后的残渣量在100kg左右,由此渣导致的回硫最高不超过0.003%。因此,梅钢脱硫残渣对钢水回硫影响幅度较小。同时,为了进一步减小残渣回硫幅度,需向脱硫渣中加入一定量的聚渣剂,以达到改善脱硫渣流动性,提高扒渣效果。     

The reaction behavior of Fe-C-S droplets in CaO-SiO2-MgO-FeO slags

The rate of reduction of FeO in the slag by carbon in iron droplets (2.9 wt pct C, 0.01 wt pct S) was studied for CaO-SiO₂-MgO slags containing between 3 and 35 wt pct FeO and temperatures ranging from 1643 to 1763 K. The effects of Fe₂O₃ additions to the slag and sulfur variations in the metal on the reaction rate were also studied. It was found that the behavior of the metal droplets in the slag, as observed by X-ray fluoroscopy, changed significantly with FeO content in the slag. Below 10 wt pct FeO, the droplet remained intact while reacting with the slag; however, above this FeO concentration, the droplet became emulsified within the slag. The large increase in surface area of the metal droplet due to emulsification caused the rate of reaction to be one to two orders of magnitude faster than for droplets that did not become emulsified. It was suggested that when the droplet is emulsified, the surface area and reaction kinetics are greatly increased, and the rate becomes controlled by mass transfer of FeO as Fe²⁺ and O²⁻ ions in the slag to the emulsified droplet. At low FeO contents for which the droplet does not emulsify, the rate is controlled by dissociation of CO₂ on the metal. It was also found that a critical temperature exists for a given FeO content at which point the rate of CO evolution increases dramatically. Additions of Fe₂O₃ to the slag and sulfur to the metal caused significant changes to the rate of reaction possibly by affecting the emulsification behavior of the droplet.     

Rate of reduction of FeO in slag by Fe-C drops

The rate of reduction of FeO in slags by Fe-C drops plays an important role in several metallurgical processes, including iron bath smelting. In this study, the rate of this reaction was determined by measuring the volume of CO generated as a function of time, and the reaction was observed by X-ray fluoroscopy. The drops entered the slag in a nearly spherical shape, remained as single particles, and for the major portion of the reaction remained suspended in the slag surrounded by a gas halo. The rate was found to decrease with carbon content for alloys with low sulfur contents. The rate decreased significantly with increasing the sulfur content. Based on the results and a comparison of the calculated rates, for the possible rate-controlling mechanisms, a kinetic model was developed. The model is a mixed control model including mass transfer in the slag, mass transfer in the gas halo, and chemical kinetics at the metal interface. At high sulfur contents (>0.01 pct), the rate is primarily controlled by the dissociation of CO₂ on the surface of the iron drop. At very low sulfur, the rate is controlled by the two mass-transfer steps and increases as the gas evolution from the particle increases. Formerly with Carnegie Mellon University     

SiO2-TiO2-CaO-MgO-FeO-MnO渣系与脱钛过程铁水中Ti-Si平衡热力学模型

 为降低铁水中钛含量,采用烧结矿或球团矿进行铁水包脱钛预处理。基于共存理论,采用Matlab编程软件,建立了铁水包脱钛典型渣系SiO2-TiO2-CaO-MgO-FeO-MnO中TiO2活度计算模型。结果表明,随着MgO、FeO、MnO摩尔分数和炉渣碱度的增大,脱钛渣中TiO2活度下降;随着TiO2摩尔分数的增大,TiO2活度提高。脱钛终点铁水中的钛含量与硅含量呈线性关系,其斜率受温度、铁水成分以及炉渣中SiO2和TiO2活度的影响。计算结果与试验结果及实际生产数据十分吻合。