A study of the reduction rate of FeO in slag by solid carbon

The reduction reaction of FeO in slag by carbon plays an important role in bath smelting reduction processes. In this study, the rate of this reaction was measured to understand the kinetic behavior of FeO reduction in slag by using the mass spectrometer technique. The present experimental results implied that the rate-determining step would change from the mass transfer of FeO at a low FeO content (<5 wt pct) to the chemical reaction at the gas/carbon interface at a high FeO content (>30 wt pct), while the total reduction rate would increase with an increasing FeO content in the slag. Based on the results of this study and comparisons with thermodynamical data for FeO in slag, the reduction rate of FeO can be expressed by the following equation:

Application of sessile drop technique (SDT) for study of reduction of FeO in slags: reduction by solid carbon as well as solute carbon

Abstract

With growing importance of smelting reduction processes, experimental research to understand reduction of FeO in molten slag and the foaming behaviour associated therein have assumed greater relevance. In a previous paper, experimental data on reduction of FeO in molten slag in a 30 kW capacity induction furnace have been reported. The present study used around 250 g slag in each experiment was concerned with influence of FeO concentration in molten slag and temperature on foaming and kinetics. The present paper describes a study on the same system carried out using the sessile drop technique (SDT) which, although it uses very small (～25 mg) sample size, is extremely versatile. Moreover, SDT allows one to actually see the reaction occur. An attempt has been made to correlate kinetic data obtained using the present set-up with the data where much larger sample sizes were used. Both solid carbon and solute carbon have been employed in reduction studies.     

Reduction of FeO in smelting slags by solid carbon: Experimental results

The reduction of CaO-SiO₂-Al₂O₃-FeO slags containing less than 10 wt pct FeO by solid carbonaceous materials such as graphite, coke, and coal char was investigated at reaction temperatures of 1400 °C to 1450 °C. The carbon monoxide evolution rate from the system was measured using stationary and rotating carbon rods, stationary horizontal carbon surfaces, and pinned stationary spheres as the reductants. The measured reaction rate ranged from 3.25 × 10^?7 mol cm^?2 s^?1 at 2.1 pct FeO under static conditions to 3.6 × 10^?6 mol cm^?2 s^?1 at 9.5 pct FeO for a rotating rod experiment. Visualization of the experiment using X-ray fluoroscopy showed that gas evolution from the reduction reaction caused the slag to foam during the experiment and that a gas film formed between the carbon surface and the slag at all times during experimentation. The reaction rate increased with increased slag FeO contents under all experimental conditions; however, this variation was not linear with FeO content. The reaction rate also increased with the rotation speed of the carbon rod at a given FeO content. A small increase in the reaction rate, at a given FeO content, was found when horizontal coke surfaces and coke spheres were used as the reductant as compared to graphite and coal char. The results of these experiments do not fit the traditional mass transfer correlations due to the evolution of gas during the experiment. The experimental results are consistent, however, with the hypothesis that liquid phase mass transfer of iron oxide is a major factor in the rate of reduction of iron oxide from slags by carbonaceous materials. In a second article, the individual rates of the possible limiting steps will be compared and a mixed control model will be used to explain the measured reaction rates.     

高铅渣还原过程渣性能及其还原特性的热力学分析

液态高铅渣的还原过程中炉渣物理化学性能变化对其还原特性至关重要。本文在分析高铅渣的主要物化性能指标及其研究方法及分析检测手段基础上,对目前铅渣物理化学性能及还原特性的研究现状进行了概述。并运用热力学软件分析计算了高铅渣还原过程的热力学特性,结果表明,在高铅渣还原反应中,从热力学角度,渣系的所有物相中,无论是和C反应还是和C0反应,Pb_8ZnSi_6O_(21)都是最容易被还原的。在温度700℃条件下,Pb_8ZnSi_6O_(21)和Pb_4SiO_6与C直接还原反应比与C0还原反应更容易进行,但是对Pb_2SiO_4和Pb0没有明显的趋势。     

两段碳还原处理铬渣的工艺实践

利用C和CO的还原性，能有效地将Cr^6 还原成Cr^3 或者金属Cr．韶钢利用烧结、炼铁工艺，有效地回收和利用铬渣中的有效成分，同时利用烧结炼铁工艺中的C和CO在高温下的还原反应，达到解毒目的，实现铬渣的资源化和无害化．     

Reaction mechanism of FeO reduction by solid and dissolved carbon

The reduction reactions of FeO by carbon have been studied in order to be able to understand the fundamental phenomena occurring in smelting reduction process. The reduction of pure FeO by solid carbon proceeds mostly according to the same reaction mechanism as that by dissolved carbon in iron, the rate of which was experimentally determined to be controlled by the interfacial chemical reaction between Fe-C melt and intermediate CO₂ gas. Hence, the reduction rate of pure FeO by solid carbon is also chemically controlled by the Boudouard reaction between the dissolved carbon and CO₂ at the interface of by-product Fe droplet/gas phase, the activation energy of which was found to be about 193.2 kJ/mol. In addition, the reduction reaction of FeO in CaO-SiO₂-Al₂O₃-FeO slags by the dissolved carbon in Fe melt was also investigated over the FeO mass content less than 20 %. The reduction rate shows first order dependence with respect to FeO concentration. The surface active sulphur content in iron does not affect the reduction rate, and the temperature dependence of reduction rate gives the activation energy of 24.78 kJ/mol. Therefore, the reduction rate of FeO in slags by the dissolved carbon can be safely mentioned to be controlled by the liquid phase mass transfer of FeO through the slag phase diffusion-resistant boundary layer over the limited FeO concentration range. The empirical expression for the mass transfer controlled reactioe, deren Aktivierungsenergie ca. 193.2 kJ/mol beträgt. Außerdem wurde die Reduktion von FeO in CaO-SiO₂-Al₂O₃-FeO-Schlacken mit dem in der Eisenschmelze gelöstem Kohlenstoff fär FeO-Massengehalte von weniger als 20% untersucht. Die Reduktionsgeschwindigkeit weist hinsichtlich der FeO-Konzentration eine Abhängigkeit 1. Ordnung auf. Der Anteil an oberflächenaktivemn rate was determined as r = 5.94(±0.07).10^?6.exp(-24780/RT).(%FeOP)^0.96 over the reaction conditions employed.     

Kinetics of manganese oxide reduction from basic slags by carbon dissolved in liquid iron

The reduction of manganese oxide from a basic slag by carbon dissolved in liquid iron is a slow reaction, failing to approach equilibrium closely in 20 hr. Furthermore, the rate of stirring has no apparent effect on the reaction rate. This identifies the rate-controlling step as a chemical reaction at the interface. Only the model for the reactionO ²⁻ =O + 2e ⁻ gave a consistent interpretation as the melt geometry, and concentration of manganese oxide and carbon were varied. The rate constant for this reaction was found to be 1.28 × 10⁻⁵ mole per sq cm per min at 155O°C. The effect of temperature is substantial with a calculated energy of activation for the system of 25 kcal per mole. Formerly Graduate Student, The University of Michigan This paper is based on a portion of a thesis submitted by W. L. DAINES in partial fulfillment of the requirements for the degree Doctor of Philosophy at The University of Michigan.     

微波碳热还原转炉渣气化脱磷反应的宏观动力学

在1 100~1 350℃,1 000Pa,3倍碳当量条件下,采用微波加热方法对碳还原转炉钢渣的气化脱磷反应进行了宏观动力学分析。结果表明,微波加热条件下,气化脱磷率为31.0%~35.7%,该气化脱磷反应为二级反应,活化能为55.52kJ/mol,并得到了气化脱磷反应速率常数与温度的关系式,同时界面化学反应为可能的限制性环节。通过提高反应温度、减小钢渣及焦炭粒度、增大反应物料接触面积,可提高气化脱磷反应的速率。研究结果为探明微波碳热还原脱磷反应的机理及速率问题,实现转炉钢渣在钢铁企业内部的循环利用提供了理论依据。     

固体颗粒对转炉炉渣黏度的影响

通过高温试验考察了固体颗粒对转炉炉渣黏度的影响.高温试验采用Ca2SiO4析晶-熔渣和MgO析晶-熔渣两种体系.试验结果表明:体系的黏度随固相体积分数的升高而显著增加.模型检验结果显示:Roscoe、Ruiz和Zholkov模型预测与试验结果相近(相对误差小于5.4％).该研究对含固相转炉炉渣黏度的预测有一定的指导意义.     

A study on the kinetics of iron oxide reduction by solid carbon

Rate of reduction of ferric oxide in the presence of solid carbon was measured in the laboratory using a thermogravimetry setup. Iron oxide in the form of powder and micropellets were used. Coconut char of high reactivity was employed as carbonaceous material. Product gas analysis was carried out to calculate the rate of carbon loss during reduction. Ferric oxide reduction was found to take place in a stage-wise manner. For the powder system, the overall reaction was found to be exclusively controlled by the gasification process. Gasification rates of coconut char in carbon dioxide were utilized to predict the rates of carbon loss during reduction. The predicted and experimental rates of carbon loss during reduction of ferric oxide by carbon were compared and possible explanations were given for the observed trends.     

Reaction mechanism on the smelting reduction of iron ore by solid carbon

The kinetics of the smelting reduction of iron ore by a graphite crucible and carbon-saturated molten iron was investigated between 1400 °C and 1550 °C, and its reaction phenomena were continuously observed in situ by X-ray fluoroscopy. In the smelting reduction by graphite, it was shown from the observation results that the smelting reduction reaction proceeded by the following two stages: an initial quiet reduction without foaming (stage I) and a following highly active reduction with severe foaming (stage II). At 1500 °C, by the graphite crucible, the reduction rate of iron ore was found to be 8.88×10⁻⁵ mol/cm² · s, and by the molten iron, 8.25×10⁻⁵ mol/cm²·s. The activation energies for the reduction by the graphite crucible and the molten iron were 24.1 and 22.9 kcal/mol, respectively. Based on the results of kinetic research and X-ray fluoroscopic observations, it can be concluded that these two types of smelting reduction reactions of iron ore by the graphite crucible and by the molten iron are essentially the same.     

铜渣熔融还原过程中硫的行为特征

对铜渣熔融还原过程中硫的行为特征进行了研究.结果表明,熔渣碱度从0.8增至1.4,渣硫容量增大脱硫作用增强,铁水硫含量由0.6%降至0.13%;铁水脱硫为吸热反应,熔渣温度由1 773 K升至1 823 K渣脱硫能力提升,铁水含硫由0.13%降至0.089%.熔渣-铁水硫理论分配比远大于实验时间条件下硫分配比,保温时间延长铁水脱硫率提高.熔渣碱度1.4、保温温度1 823 K和保温时间40 min时,处理后铁水含硫为0.11%,含量仍较高,需进一步对铁水进行脱硫预处理才可用于炼钢.     

Kinetics of reduction of lead oxide in liquid slag by carbon in iron

The reduction of lead oxide in dilute solution in CaO-Al₂O₂-SiO₃ slag by carbon dissolved in iron was investigated using a composite crucible as a container so as to exclude graphite from the system. The variables studied to elucidate the reaction mechanism were pressure inside the crucible, carbon content of the metal, lead oxide concentration in slag, and slag composition. The experimental results are best explained by postulating the existence of a gas film at the slag metal interface. It is suggested that the rate controlling step for the lead oxide reduction by carbon is a chemical reaction at the gas/slag interface. The rate constant for up to 3 wt pct PbO in the slag and 2.0 to 4.3 pct C in iron at 1400 °C as calculated from the present study is 4.6 x 10^-4 mol/cm²/min/atm.     

Influence of carbon and nitrogen on solid solution decay

“475 °C embrittlement” of high-chromium ferritic steels with Cr content from 15 to 35 wt pct and different commercial impurities (C, N) has been investigated. The influence of preliminary treatment (600 °C to 1250 °C) and chemical composition of the alloy (Cr, C, N, Mo, Ti, Nb) on kinetics has been established. Internal friction (IF) was used to determine the contribution of interstitial atoms to the formation of Cr-modulated structure during different stages of embrit- tlement of high-chromium steels. By use of IF, static and dynamic (impact) mechanical tests with different states of stress, transmission and scanning electron microscopy of structures and fracture surfaces, and the application of diffraction methods, thermodynamic diagrams of the aging of high-chromium steels have been obtained. In the temperature range of 475 °C em- brittlement, the following sequence of processes has been established: (1) decay of solid solution supersaturated with interstitial atoms by dislocation pinning, (2) formation of substitutional- interstitial (s-i) complexes of interstitial (C, N) and substitutional (Cr) atoms, and (3) formation of zones enriched in Cr.     

Aluminum foam stabilization by solid particles

A room temperature water model and a high temperature molten aluminum systemwere designed and constructed to investigate the effect of solid particles on the stabilization offoams. The average foam life was used to evaluate the stability of the foam. The effects of particlesize, wetability, and concentration of the SiO₂ particles were investigated at variousgas flow rates in the room temperature system. The results indicated that only SiO₂particles with suitable wetability can stabilize liquid foam. The foam stability increases withdecreasing particle size and increasing particle concentration. The effects of melt temperature andSiC particle concentration on aluminum foam stabilization were investigated in the hightemperature system. It was found that a critical concentration of SiC particles was necessary forfoaming to occur. The foam height increased with increasing concentration of SiC particles. Thestability of the foam decreases with increasing temperature.On a conçu et construit un modèle aqueux à la température dela pièce ainsi quun systèmedaluminium fondu à haute température afin détudier leffet de particules solides sur la stabilisation décumes. On a utilisé la vie moyennede lécume pour évaluer sa stabilité. On a étudié leffet de la taille de particule, de la mouillabilité et de laconcentration de particules de SiO₂, à divers taux découlement de gaz, sur le système à la température de la pièce. Les résultats indiquent que seules les particulesde SiO₂ ayant une mouillabilitié adéquate peuvent stabiliser lécume liquide. La stabilité de lécume augmente avec unediminution de la taille de particule et avec laugmentation de leur concentration. On a étudié leffet de la température de fonte et de la concentration de particules de SiC sur la stabilisation décume daluminium du système à haute température. On a trouvé quune concentration critique de particules de SiC était nécessaire pour que lécumage se produise. La hauteur de lécume augmentait avec uneaugmentation de la concentration de particules de SiC. La stabilitéde lécume diminue avec une augmentation de la température. © 1999 Canadian Institute of Mining and Metallurgy. Published byElsevier Science Ltd. All rights reserved.     

含磷钢渣碳热还原脱磷及资源化利用的研究现状

摘要：针对脱磷转炉渣中磷资源高效回收及其资源化利用过程中存在的问题,系统总结了含磷钢渣除磷方式及其应用优缺点,并着重总结了不同条件（炉渣温度、炉渣碱度、钢渣中FeO质量分数、碳当量、底吹气体流量、冶炼时间等）对碳热还原气化脱磷的影响规律。同时,以应用前景较好的碳热还原气化脱磷方法为基础,提出了脱磷转炉渣在碳热还原气化脱磷过程磷的流向规律,展望了渣中磷资源回收制备磷铁及其循环利用模式。这为实现渣中磷资源高效回收及处理后残渣资源化利用提供重要研究基础和方向。     

Post-combustion and heat transfer at blowing of oxygen into a carbon monoxide containing slag foam

A combined post-combustion model (CPM) for smelting reduction processes was developed in a multi-national research project supported by the European Coal and Steel Commission. The project partners were CSM, Rome, Hoogovens, Ijmuiden, MPI, Düsseldorf, and TUB, Berlin. This paper reports about a heat transfer model developed by TU Berlin within this project. The batch-type smelting reduction reactor has a two-layered slag: an upper foamy and a lower less foamy slag. A bubble stream of (CO+H₂) gas originating from the iron oxide reduction reaction with coal in the lower slag flows upwards. The rising (CO+H₂) gas is post-combusted by three oxygen jets blown horizontally into the upper part of the slag. A flame zone, and above the flame a mixing and a bubble zone form, in which post-combustion reaction and transfer of the post-combustion heat to the slag take place. The modelling of the flame zone was the subject of a previous paper. The present report describes models of the mixing and the bubble zone and of the occurrences in the gas space above the slag. The macro-kinetics of the overall heat transfer process including slag recirculation and heat transfer from the upper foamy to the lower dense slag are presented further. The model calculations provide information about the distribution of the post-combustion and the heat transfer processes over the single zones as functions of the important internal process parameters. Further, the oxygen utilisation, the heat efficiency and the temperatures at various locations of the process are described as functions of the ratio of post-combustion oxygen flow rate to (CO+H₂) evolution rate. In all the calculations a specific gas through-put of carbon monoxide of 3 mol/t?s is assumed. This value corresponds to 510 mol/s for the assumed melt of 170 t. The model shows that heat transfer efficiencies of more than 90 % and slag temperatures of less than 1700°C are possible, if the slag circulation rate is 300 kg/s. Lower circulation rates lead to higher slag temperatures and worse heat transfer efficiencies. Controlled slag circulation is thus an important process tool.     

Flame formation and post-combustion at blowing of oxygen into a carbon monoxide containing slag foam

A combined post-combustion model (CPM) for smelting reduction was developed in a multi-national research project supported by the European Coal and Steel Community. The project partners were CSM, Rome, Hoogovens, Ijmuiden, MPI, Düsseldorf, and TUB, Berlin. This paper is a report about a flame model developed by TUB, Berlin. An oxygen jet is blown into a carbon monoxide containing slag foam. The jet entrains carbon monoxide and slag droplets. Carbon monoxide is combusted by oxygen to carbon dioxide and the developed heat is transferred by radiation from the gas to the surrounding slag and by radiation and convection to the entrained droplets. The droplets are mixed with the slag at the flame end so that also their heat content is finally transferred to the bulk slag. The model consists of a detailed treatment of the entrainment processes, the combustion reaction taking into account the carbon dioxide dissociation equilibrium, the enthalpy changes, and the heat transfer processes. One obtains two ordinary differential equations describing the temperature and composition of the flame gas as functions of the flame pass-way. They are solved numerically by the Runge-Kutta method. As the results, the main flame properties, namely the flame velocity, the diameter and the upwards angle of the flame, the amount of gas and slag entrained from the surroundings to the flame, the oxygen utilisation, from which the post-combustion degree is calculated, the flame temperature along the flame pass-way, and the total heat transfer from the flame gas to the slag, are described as functions of various internal and external parameters. The presented flame model is part of a general post-combustion and heat transfer model of a smelting reduction process with post-combustion in the slag.     

碳热还原转炉渣脱磷的试验

 对碳热还原转炉渣进行热力学分析,分别在二硅化钼高温电阻炉和500 kg顶底复吹多功能试验炉开展转炉渣碳热还原脱磷的实验室试验。结果表明,反应温度及动力学条件对脱磷率有较大影响,在电阻炉试验条件下,保证反应温度为1 500 ℃、碳当量为3.0、保温时间为30 min的情况下,可以获得30%左右的脱磷率。在顶底复吹多功能试验炉内,焦粉既作为还原剂也作为升温剂,焦粉与氧气反应放热可以保证脱磷反应在较高温度下进行,同时顶吹氧气对熔渣层的良好搅拌有利于脱磷反应速度进一步提高,试验过程脱磷率为84%,其中还原进入钢液的脱磷率为75.85%,气化脱磷率为8.15%。焦粉带入的硫有10.8%进入钢水,有6.25%进入炉渣。