Dissolution of steel scrap in molten iron is studied by using analytical as well as numerical approaches for the case of a heat transfer-controlled process. The approaches used are Green's function approach, quasi-static approach, integral profile method (IPM) (with parabolic profile), and finite difference methods (FDM). Application of FDM explicit and FDM implicit with fixed grid and variable grid is described. Accuracy of all the approaches is compared in terms of total dissolution time evaluated from overall heat balance criterion. The selection rule of time step and deciding the suitable approach for achieving minimum error for different operating conditions, represented by nondimensional Biot number, are described in this paper.

Transient inclusion formation in low carbon silicon killed steel as a result of ferroalloy additions of ferro-silicon (Fe75Si) and ferro-manganese (FeMn) (for de-oxidation and alloying) was studied in the laboratory using a novel experimental technique. Inclusion chemistries and morphologies were analysed using automated scanning electron microscopy (ASPEX). Formation of these inclusions was studied using thermodynamic software (FactSage) and a mechanism was proposed. Effect of solute concentration gradients during alloy dissolution and mixing was observed. Inclusions which formed initially, at low concentrations of ferroalloy, were liquid phase with a high concentration of FeO. Depending on the ferroalloy addition, initial inclusions become richer in SiO2 or MnO. Inclusions also underwent further phase transformations on cooling.

A new integrated CFD-combined reactors approach is proposed for the description of processes in metallurgical vessels. CFD simulations were used to obtain the melt flow pattern in the vessels (ladle, tundish, and continuous caster mold). From these simulations, the characteristic curves were derived: (i) the residence time distribution curves (RTD) for flow-through systems (at tundish exit or at dendrite coherency surface in the mold) and (ii) the mixing curves for closed systems (ladle). In the next step, the melt flow was represented in a "combined reactors" system consisting of a combination of unit reactors (Plug Flow, Mixer, and Recirculated Volume). An inverse simulation was used to define the volumes of the reactor units and the melt flow rates between them by fitting to the characteristic curves from both methods (CFD and combined reactors). The suggested approach is demonstrated for multiple designs of Ar-stirred ladles, tundish, and SEN. This methodology can be used to enhance traditional post-processing CFD analysis and also as a tool for on-line process control.

The production of iron and steel and non-ferrous metals by pyrometallurgical processes will remain a critical element in meeting the demand for materials in both developed and developing nations. Given the important need to reduce and minimise greenhouse gas emissions the technological focus of future pyrometallurgical R&D by universities and industry alike must concentrate on sustainability issues such as improved energy efficiency, recycling and waste minimization. Continued efforts are also needed on process optimization and new process development with a view to reducing capital and operating costs of the new large "mega" plants. Using the academic and industrial backgrounds of the authors, the present paper reviews the current status of R&D in pyrometallurgy in university departments with a particular emphasis on sustainability issues. The role of industry and government laboratories is also reviewed although primarily for developed countries. The paper also includes comments and suggestions on the future requirements for education and R&D in pyrometallurgy in developed countries to maximise sustainability. It is also suggested that future R&D in pyrometallurgy will be even more concentrated in developing countries - most notably China.

The role of the air gap formed between scrap and a solidified metal shell at the beginning of the scrap dissolution process has been investigated. The effect of air gap has been investigated for different Biot numbers (10 to 100) and ratios of air gap to liquid melt heat transfer coefficient (0.1 to 0.9). The predictions of the mathematical model are compared with the experimental results reported elsewhere. The role of air gap is found to be significant only for low Biot numbers (< 50) and for low ratios of air gap to liquid melt heat transfer coefficient (< 0.25).

The scrap dissolution in an actual process like the BOF is affected both by mass transfer and heat transfer. In this paper, the mass transfer of carbon in liquid melt is considered along with heat transfer. The approaches used in this paper to model the scrap dissolution phenomenon include the application of Green’s function, quasi-static, integral profile, and the finite difference approach for different Biot numbers. Mass transfer coefficients are calculated using the Chilton–Colburn’s analogy for the case of forced convection. Since the quasi-static approach requires the least computational time, it is used for a detailed parametric study, including the effect of other parameters like different scrap ratios and heating rates of liquid melt. The region of control of heat transfer vs mass transfer is also identified. The dissolution of mixed scrap (light and heavy scrap) is investigated for different scrap ratios and the autogenous heating rates of liquid melt, with the help of mathematical models. The heat transfer coefficient is estimated as a function of mixing energy and the mass transfer coefficient by invoking the Chilton–Colburn analogy. The permissible limits of light scrap, which can be charged into the BOF, are also suggested from the results of this model. The Artificial Neural Network (ANN) model is trained on the dataset (patterns) generated by the coupled heat and mass transfer model. The accuracy of the results obtained using different ANN topologies is discussed followed by a recommendation for selecting the best approach.

Vacuum Tank Degassing (VTD) is widely used as a secondary steelmaking process to achieve very low concentrations of nitrogen, hydrogen, carbon, sulphur, and other elements in steel. In the present study, a dynamic model for the VTD has been developed. Fluent CFD software was used to calculate the flow and recirculation rates, which vary over time depending on the rate of CO evolution in the melt and the argon flow rate. These have then been combined in process simulator software (METSIM) to build a dynamic model which incorporates all the kinetic aspects of the process. The steel melt was divided into different zones, at different pressures, with mixing represented by flow between the zones. This model includes reactions at the slag-metal interface, argon bubble-metal interface and in the liquid metal due to the reduced pressure while maintaining the circulation of liquid metal in the VTD.

Experimental work and thermodynamic simulations of cast iron refining were carried out using various additions of alkali and rare earth metals. The refining reactions for sulfur and oxygen removal were studied for melts treated with Mg, Ca, and Ce. The measured data and the results of the computer simulations were in agreement. Experimental kinetic data, together with the thermodynamic calculations, were used for optimization of the amount and sequence of the addition of nodulizers for ductile iron production.

Sequestration of carbon dioxide by steelmaking slag was studied in an atmospheric three-phase system containing industrial slag particles, water, and CO2 gas. Batch-type reactors were used to measure the rate of aqueous alkaline leaching and slag particle carbonization independently. Four sizes of slag particles were tested for the Ca leaching rate in deionized water at a constant 7.5 pH in an argon atmosphere and for carbonate conversion with CO2 bubbled through an aqueous suspension. Conversion data (fraction of Ca leached or converted to carbonate) were evaluated to determine the rate-limiting step based on the shrinking core model. For Ca leaching, the chemical reaction is the controlling mechanism during the initial period of time, which then switches to diffusion through the developed porous layer as the rate-limiting step. Carbonate conversion proceeded much slower than leaching conversion and was found to be limited by diffusion through the product calcium carbonate layer. The calculated value of diffusivity was found to be 5 × 10−9 cm2/s, which decreased by an order of magnitude with increasing carbonization conversion as a result of changing density of the product layer. The experimental data fit the shrinking core model well after correction for the particle specific surface area.

Melting processes may be classified into two groups - stationary and dynamic. In stationary processes (e.g. a reverberatory furnace), the pile of solid charge is more or less fixed in position, and any liquid motion is the result of natural convection. In dynamic processes there is active motion of the solid charge and melt inside the furnace caused by mechanical or electromagnetic forces. Each type of process was analyzed from the point of view of metal recovery and energy efficiency when charge materials of different metallurgical quality were used. The stationary processes minimize the oxidation of high quality charge materials (ingots, large size scrap) while dynamic melting processes have the possibility of increased metal recovery from low-quality scrap with high specific and oxidized surface, such as aluminum turnings and dross, with effective separation of melt from slag by the use of special fluxes. The parameters of melting low quality charge materials in a dynamic rotary furnace were experimentally studied and computationally modeled. Technical results will be presented of using 0.5 t rotary furnace for recycling locally-sourced low-quality aluminum charge materials. The furnace has been used over a period of several years.

Hydrous carbonate sequestration of carbon dioxide using steelmaking slag was studied using a METSIM process model to analyze experimental data and estimate the reactor operating results. Several scenarios of a two-stage system with water/slag contact in reactor 1 and leachate/carbon dioxide contact in reactor 2 were investigated. These scenarios included batch vs continuous processing and fresh water input vs water recirculation. The METSIM leaching and carbonation models were verified with results obtained from previous slag sequestration experiments. Fresh water additions to reactor 1 allowed the highest leaching efficiency and resulted in excellent carbonation in reactor 2, but a continuous system has a high water demand. Recirculation of the spent leachate minimizes the fresh water addition required, but inhibits the leaching process by producing a calcium carbonate product layer on the slag particles in reactor 1. Increasing the slag surface area, slag/solution ratio, or reactor residence time partially overcomes product layer "blinding." Optimal residence times were defined for different process parameters and slag particle sizes.

Levitated drops of Fe-18%Cr-2%C were reacted with oxygen-argon mixtures to study the reactions that occur in the AOD process, where the gases are injected into the melt and form bubbles. In the laboratory an argon-oxygen pulse, followed by pure argon, was flowed past the levitated drop to simulate the transient conditions in the gas phase as the bubbles rise in the melt. Oxide layers formed on the drops immediately when they came into contact with gas pulses containing 75% or more oxygen. Once the oxygen flow had ceased, the oxides reacted with the carbon in the drops to form CO gas and eventually disappeared. The de-carburization reaction occurred without oxide formation when the gas contained 50% oxygen or less. Melts that were sampled after EAF tapping, ready to be charged into the AOD, showed a higher tendency to oxide formation and consequent carbon boil than pure ternary Fe-18%Cr-2%C alloys made in the laboratory. The actual steel samples contained significant impurities, such as 0.25% Si and 0.56% Mn. A similar effect of oxide-forming impurities had been observed previously with binary Fe-C alloys. Movies were taken of the oxide formation and decomposition, and the results will be presented, along with data on the experimental conditions, including temperature and oxide compositions. The results are important because they give an insight into the reaction mechanisms in the AOD, which must be understood in order to improve and model the process.

A two-zone furnace arrangement was used to determine the solubility of tellurium vapour in γ-iron foils at 1273 and 1548 K. Liquid tellurium held at a lower temperature generated Te (g) and Te2 (g) at a known partial pressure which was equilibrated with foils held at a higher temperature. Knowledge of the two temperatures allowed the calculation of the activity of tellurium with respect to the solid reference state. Analysis of the equilibrated foils allowed the calculation of the infinite dilution activity coefficient of tellurium which is expressed as a function of temperature.On a utilisé un arrangement à deux zones d’un four pour déterminer la solubilité de la vapeur de tellure dans des feuilles de fer γ à 1273 et à 1548 K. Le tellure liquide, maintenu à une température plus basse, a engendré du Te (g) et du Te2 (g) à une pression partielle connue qui était mise en équilibre avec les feuilles maintenues à une température plus élevée. Le fait de connaître les deux températures nous a permis de calculer l’activité du tellure par rapport à l’état solide de référence. L’analyse des feuilles en équilibre a permis le calcul du coefficient d’activité de dilution infinie du tellure, lequel est exprimé en fonction de la température.

The mass transfer rate during ladle refining was quantified by taking sequential steel and slag samples during the treatment of 20 heats. Each heat was stirred with a different argon flow rate, ranging between 0 and 63 scfm. Heats were treated at two different plants. Al-killed steel was produced at an LMF in 151-t ladles. Si-deoxidized steel was produced at an LMF in 123-t ladles. Mass transfer rate constants were determined for each heat by using process simulation (Metsim) and thermodynamic (FactSage) models. Relationships between mass transfer rate constants and stirring powers as well as ladle geometries were compared between the two plants and published literature. It was found that the reaction kinetics during ladle refining depend on the bulk transport of the steel to the slag/steel interface and on the thermodynamic equilibrium at the slag/steel interface. The necessary refining time decreases if the newly-defined specific steel transport rate is maximized and the slag has a low basicity and FeO concentration before the start of de-S.

This article evaluates historic developments In continuous steelmaking and explores the possibilities of developing a new process for continuous steelmaking that could become commercially acceptable In the near future.

This work summarizes the different activities undertaken at the University of Missouri-Rolla on developing and testing techniques and instrumentations for the glass industry. Current work includes: (1) on-line measurement of NaOH vapor in the combustion chamber, (2) on-line monitoring of wall refractory thicknesses, and (3) analysis of flame images for burner control and optimization. Limitations and advantages are listed and compared to other current techniques.

The thermodynamics and-kinetics of the reactions involved in fuming zinc from oxide slags using coal or coke were first studied in 1955 and have been the subject of many investigations since that time. The key reaction is ZnO(in slag) + CO = Zn(g) + CO(2). This paper will review the some of the recent work, and will add new insights obtained in experiments carried out by the authors. In the first series of experiments it was shown that the reaction2Fe(2+) + ZnO = 2Fe(3+) + Zn(g) or 2FeO + ZnO = Fe(2)O(3) + Zn(g)does not occur at an appreciable rate, as is expected from thermodynamic considerations. In the second series of experiments it was shown that zinc does not fume from the slag at a significant rate unless a reductant has been added. This again is in accord with thermodynamic considerations, but is in contradiction to some of the experimental results reported in the literature. A third series of experiments was carried out with excess coke being present, so that the rate of supply of reductant was not in any way controlling the rate. The kinetics of zinc oxide reaction were then found to be independent of the zinc oxide concentration, but increased with increasing basicity, and temperature. The presence of high concentrations of FeO in the slag also improves the kinetics. At low zinc oxide concentrations iron oxide reduction occurred in parallel with. zinc oxide reduction. We propose that (under the conditions of this work) the kinetics were controlled by a chemical step, namely the rate of desorption of an adsorbed CO(2) species. This is the same mechanism as reported by Belton and co-workers for the kinetics of the reduction of FeO. This explains why the reduction of metal oxides in slags by hydrogen is often faster than by CO.

Slag cleaning furnaces require extensive wall cooling because they involve the use of a superheated slag bath. This is in direct contrast to smelting furnaces, where the wall is usually (but not always) protected by "banks" of solid charge. In order to understand the heat transfer and flow in slag cleaning furnaces a number of model studies have been carried out using molten wax to simulate the slag. Wax is a good model fluid because, like slag, it has a high Prandtl number. Wax models cannot simulate the behavior close to the electrodes (DC are or AC submerged), but they can and do give a good simulation of the flow and heat transfer at the wall. An understanding of these phenomena is of great importance for the design of cooling panels in the walls of the furnace. Since superheated molten slag will eventually wear away any refractory bricks over time, the wall cooling must be designed to form a frozen layer of slag, referred to as a "freeze lining". The heat flux density (Q/A) required to do this is given by Q/A = h*Delta T, where h is the heat transfer coefficient in the slag phase at the wall, and Delta T is the superheat (bulk slag temperature-liquidus temperature). Both Q/A and h vary greatly with position and both are usually a maximum at the slag line. In the experimental work, molten wax baths were heated by block heaters to provide similar energy densities to those encountered in commercial slag cleaning furnaces. This procedure was considered to be valid since most of the electrical energy into a furnace bath is dissipated as heat. Gas stirring was used to simulate the gas evolved at the electrode in real furnaces-the quantity of this gas could be estimated from a knowledge of electrode consumption. The similarity criterion was equal gas flow per unit area of surface, in model and prototype. Heat transfer coefficients were measured in the models as a function of power density, gas stirring, superheat, etc., and could be related to the full-scale operations by the use of dimensional analysis.