Metallurgical Reactor Research Articles

An inverse front tracking method for modeling solidification process in a smelting furnace

An inverse process based on the conjugate gradient and adjoint problem is developed for predicting the time-varying bank thickness during the solidification/melting process in a smelting furnace. The direct problem rest on a single-phase moving boundary model to simulate the solid bank and refractory brick, simultaneously. The time-varying heat flux at solid/liquid interface, initial bank thickness and time-varying heat transfer coefficient at outer surface of the furnace are considered as the unknowns. Unlike the methods developed so far based on the enthalpy model, the current method does not require any prior information regarding the thermophysical properties of the liquid-phase and complex physical phenomena that occur in it. This improves the uniqueness of the solution that is inherent in the ill-posed inverse methods. To avoid the so-called “inverse crime”, a two-phase enthalpy method is used to generate the simulated measurement. These measurements are used in the present single-phase method for reconstruction of bank history. The model has shown good performance for non-intrusive temperature obtained from the outer surface of the furnace. The inverse model has been validated through an experiment conducted in a metallurgical reactor. A reasonable agreement between the estimated and measured molten salt bank indicates the existence and convergence of the inverse solution.

The Importance of Mixing Time in Intensely Stirred Metallurgical Reactors: Applied on Decarburization Reactions

In metallurgical converter processes, numerical modeling is a useful tool for understanding the complexity of the systems. In this paper, we present a practical model that couples fluid dynamics and chemical reactions to explore the impact of mixing time on decarburization. Using computational fluid dynamics (CFD), in this study, we investigate an arbitrary metallurgical reactor with continuous oxygen supply, focusing on the Fe–C–O system. The model employs local equilibrium, a turbulence limiter, and finite volume method for mass, momentum, and energy transfer. Tracer injection points in the gas plume’s rising region exhibit faster mixing, and a comparison of reaction cases reveals distinct decarburization rates based on oxygen injection distribution and the influence of turbulence on reactions. Overall, while mixing time matters, the results show that this system is primarily governed by thermodynamics and oxygen supply, and a 270% increase in mixing time increase had a small impact on the end carbon content.

Dynamic chaos of imaging measurements for characterizing gas–liquid nonlinear flow behaviour in a metallurgical reactor stirred by top‐blown air

AbstractA modern chaos detection strategy for imaging measurements is proposed in this work to quantify the thermal mixing state quality in a metallurgical reactor stirred by top‐blown air. Specifically, the improved C‐C algorithm is proposed to reconstruct the phase space of the nonlinear time series of the bubble characteristics under thermal conditions. Moreover, a chaos decision tree algorithm is introduced to extract the chaotic mixing characteristics of the thermal two‐phase mixing system for the first time. Experimental and calculated results show that all the possible mixing states of the mixing system are visualized by reconstructing the phase space with the help of the visualization technique of the thermal gas–liquid two‐phase flow. It is found that the attractor of the nonlinear time series of bubbles exhibited more serious variations while the chosen working condition was optimal. Furthermore, the obtained parameter represents the chaotic characteristics of the thermal gas–liquid two‐phase mixing system which has chaotic characteristics under various experimental conditions. Hence, the new strategy would be helpful and effective in beneficial exploration for understanding the nonlinear intensification mechanism of metallurgical thermal processes.

New insight into relationship between casting speed and inclusion removal in the tundish

The tundish is the last refractory metallurgical reactor during the continuous casting process, and the fluid flow in the tundish is one of the key factors to control inclusion collision-coalescence and its removal. Thus, numerical method is applied to obtain the flow field, the RTD curve and the inclusion field. Numerical results showed that the predicted RTD curve and the inclusion number density agree well with the experimental data. In the case of different fluid velocity at tundish inlet, the volume fraction of plug zone, dead zone and well-mixed zone keep unchanged, but the dimensionless tundish inclusion volume concentration, the dimensionless tundish inclusion radius and the inclusion removal ratio have the exponential relation to the fluid velocity at tundish inlet. Further, there is maximum inclusion removal rate for the specific tundish. Another interesting phenomenon is about the inclusion behavior and the characteristic time of the RTD curve. The inclusion removal ratio and the dimensionless tundish inclusion radius have the linear relation to the minimum residence time, the peak concentration time and the average residence time.

Laboratory Evaluation of Tundish Covering Powders and Rice Hull Ash on Cleanliness for a SAE 1055 Modified Steel

The continuous casting tundish is the last metallurgical reactor where molten metal flows before solidifying in the continuous casting mold. A tundish covering powder can be used for improving steel cleanliness; in this case it is named ‘active tundish slag’. The objective of this work is to evaluate, in laboratory, the effect of three kinds of tundish covering powders on cleanliness for a SAE 1055 modified steel - a Ca-aluminate, a Ca-Mg-aluminate, and an Al-silicate powder, analysing their interaction with rice hull ash. The forementioned materials were molten on liquid steel, representing different kinds of tundish covering powders which are used in the steel industry: a Ca-Mg-aluminate, an Al-silicate, and a Ca-aluminate. Experiments were performed with and without a top layer of rice hull ash, simulating industrial conditions. Distribution, density, and mean diameter of inclusions were measured through automated inclusion analyses. Through computational thermodynamics it was possible to evaluate deviation from saturation (considering Al2O3 and MgO from refractory) and slag viscosity. It can be stated that the Ca-aluminate tundish covering powder gives better results regarding cleanliness for the SAE 1055 modified steel under laboratory conditions.

Effect of Salt Tracer Dosages on the Mixing Process in the Water Model of a Single Snorkel Refining Furnace

The improvement in mixing conditions in a vacuum refining unit plays an important role in enhancing the purity and decarburization of molten steel. Mixing time is an important index to evaluate the operation efficiency of a metallurgical reactor. However, in water models, the effect of salt tracer dosages on the measured mixing time in a vacuum reactor is not clear. In this study, a water model of a Single Snorkel Refining Furnace (SSRF) was established to study the effect of salt solution tracer dosages on the mixing time of monitor points. The experimental results show that, in some areas at the top of the ladle, the mixing time decreases first and then increases when increasing the tracer dosage. Numerical simulation results show that, when the tracer dosage increases, the tracer flows downwards at a higher pace from the vacuum chamber to the bottom of the ladle. This may compensate for the injection time interval of large dosage cases. However, the mass fraction of the KCl tracer at the right side of the bottom is the highest, which indicates that there may be a dead zone. For the dimensionless concentration time curves and a 99% mixing time, at the top of the vacuum chamber, the curve shifts to the right side and the mixing time decreases gradually with the increase in tracer dosage. At the bottom of the ladle, with the increase in tracer dosage, the peak value of the dimensionless concentration time curve is increased slightly. The mixing time of the bottom of the ladle decreases significantly with the increase in tracer dosage. However, in the dead zone, the mixing time will increase when the tracer dosage is large. At the top of the ladle, the effect of the tracer dosage is not obvious. The mixing time of the top of the ladle decreases first and then increases when increasing the tracer dosage. In addition, the mixing time of the top of the ladle is the shortest, which means that sampling at the top of the ladle in industrial production cannot represent the entire mixing state in the ladle.

An intelligent dynamic setting control framework for a multimode impurity removal process

Abstract The main task of the impurity removal process is to control the oxidation reduction potential (ORP) within the range of the optimized set value. The impurity removal process is essentially an oxidation-reduction process. Oxidation reduction potential (ORP) is an external reflection of reaction state inside the impurity removal reactor. However, actual industry is time-varying, nonlinear and multimode. It is difficult to determine the appropriate dosage of impurity remover in practice. This will lead to large fluctuations in the operation mode, affecting the safety and stability of the process and the final product quality. To solve these problems, an intelligent dynamic setting control framework (IDSCF) for the multimode impurity removal process is proposed in this paper. It includes a preset module of the dosage of impurity remover based on impurity remover utilization (IRU) estimation, an operation mode detection module based on autoencoder, a normal mode adjustment module based on fuzzy logic, and an unsteady mode adjustment module based on case-based reasoning (CBR). The framework can determine the reasonable preset dosage of impurity remover and adjust the dosage according to the current operation mode of the impurity removal process. Because the operation mode is related to the residual dosage of impurity remover added over a period of time, that is, the accumulative effect of the large-scale metallurgical reactor. When calculating the preset dosage of impurity remover, the reactant accumulation ratio (RAR) is calculated, which makes the calculation of the preset value more reasonable. In addition, it can detect the unsteady modes causing large fluctuations in the process and adjust them in time. Experiments are carried out in accordance with the data of an actual cobalt removal process. The results show that this method can effectively improve the stability of the impurity removal process, control the ORP within the set range and cope with complex mode changes.

Residence Time Distribution (RTD) Applications in Continuous Casting Tundish: A Review and New Perspectives

The continuous casting tundish is a very important metallurgical reactor in continuous casting production. The flow characteristics of tundishes are usually evaluated by residence time distribution (RTD) curves. At present, the analysis model of RTD curves still has limitations. In this study, we reviewed RTD curve analysis models of the single flow and multi-flow tundish. We compared the mixing model and modified combination model for RTD curves of single flow tundish. At the same time, multi-strand tundish flow characteristics analysis models for RTD curves were analyzed. Based on the RTD curves obtained from a tundish water experiment, the applicability of various models is discussed, providing a reference for the selection of RTD analysis models. Finally, we proposed a flow characteristics analysis of multi-strand tundish based on a cumulative time distribution curve (F-curve). The F-curve and intensity curve can be used to analyze and compare the flow characteristics of multi-strand tundishes. The modified dead zone calculation method is also more reasonable. This method provides a new perspective for the study of multi-strand tundishes or other reactor flow characteristics analysis models.

Physicochemical properties and structure of titania-containing metallurgical slags: a review

The titanium industry can hardly bypass the titania-containing slags, and the slag physicochemical properties are essential in the metallurgical reactor design and process control. The TiO2–FeO-based slags and TiO2–SiO2–CaO-based slags are the main metallurgical slag systems in the titanium resource utilization processes. To elaborate the role of TiO2 in the physicochemical properties of titania-containing metallurgical slags, the physicochemical properties including titanium redox ratio, liquidus temperature, viscosity, electrical conductivity, density, surface tension, thermal conductivity, and sulfide capacity were critically reviewed. Moreover, the property prediction models were briefly introduced with regards to the limitations of the existing models. The property prediction models are still required to evolve since not all properties of titania-containing slags can be well modeled. As the slag structure has an intimate relationship with slag properties, the structural details of the titania-containing slag were investigated by using a combination of spectroscopic technologies, but the knowledge of the slag structure was not fully ascertained. The potential research fields related to the physicochemical properties and structure of the titania-containing slags were also suggested.

A novel ladle for metal industry

In the present study a novel ladle metallurgy is innovated which will enhance the mixing efficiency of the metallurgical reactor. By applying this technology approximately 41% improvement in mixing time was observed in numerical simulation. The velocity profile and mixing time were compared with normal ladle and this novel ladle. There is a high negative pressure is generated at the plume region for 5 co-centric plugs novel ladle. This cause development of a large swirling flows throughout the ladle fluid. This is not observed for normal ladle purging system. This high rate swirling flows create less mixing time for novel ladle. It is not affected the wear of the ladle so much.

A review of domestic and foreign experience of steel treatment in CCM tundishes

The modern steelmaking facilities melt as a rule a semi product, which is further subjected to various processes of refining in steel ladle. Recently an additional treatment of the metal in CCM tundish became widespread in the domestic and foreign practice. A tendency of transforming tundish into a multifunctional metallurgical reactor was noted, since more and more technological operations are transferred in it, including alloying, stirring, various methods of heating, modifying and removal of nonmetallic inclusions. Examples of comprehensive utilization of a bloom CCM tundish at some Japanese plants of Kobe Steel in Kakagava presnted, at which the metal is filtered when going through holes in the two partitions thus effectively removing nonmetallic inclusions. New variants of metal blowing off in the tundish by inert gas developed by domestic specialists considered, including a technology for metal blowing off by an inert gas and a facility for the inert gas supply through the stopper of the tundish. Supply of inert gas through the stopper results in efficiency increasing of degassing and nonmetallic inclusions removal as well as submerged nuzzles service time increase, which is particularly important at casting of steels with high content of aluminum. Examples of solutions of metal treatment in tundish by cored and aluminum wire given. Schemes of cored wire introduction into tundish and liquid steel treatment in a CCM mold considered. Considerable attention was given to the problem of metal temperature control in tundish, including by an electric arc, induction and plasma heating. List of domestic and foreign plants presented, implemented facilities of steel plasma heating in the CCM tundish. It was noted, that steel chemical heating in tundish can be applied at unforeseen problems arising at casting.

Numerical Modeling of Equal and Differentiated Gas Injection in Ladles: Effect on Mixing Time and Slag Eye

Ladle refining plays a crucial role in the steelmaking process, in which a gas stream is bubbled through molten steel to improve the rate of removal of impurities and enhance the transport phenomena that occur in a metallurgical reactor. In this study, the effect of dual gas injection using equal (50%:50%) and differentiated (75%:25%) flows was studied through numerical modeling, using computational fluid dynamics (CFD). The effect of gas flow rate and slag thickness on mixing time and slag eye area were studied numerically and compared with the physical model. The numerical model agrees with the physical model, showing that for optimal performance the ladle must be operated using differentiated flows. Although the numerical model can predict well the hydrodynamic behavior (velocity and turbulent kinetic energy) of the ladle, there is a deviation from the experimental mixing time when using both equal and differentiated gas injection at a high gas flow rate and a high slag thickness. This is probably due to the insufficient capture of the velocity field near the water–oil (steel–slag) interface and slag emulsification by the numerical model, as well as the complicated nature of correctly simulating the interaction between both gas plumes.

Physical simulation of bubble refinement in bottom blowing process with mechanical agitation

In order to increase the contact area and promote the mass transfer process of gas and liquid, the process of the bubble refinement in a metallurgical reactor with mechanical agitation was studied by physical simulation. Based on the capillary number, a prediction equation for the bubble refinement was established. The effects of the gas flow rate, the stirring speed and the stirring depth on the bubble refinement in the reactor were discussed in detail. The distribution of the bubble diameter in the reactor was obtained under different conditions. The results show that when the stirring speed reaches 300 r/min, the bubble diameter mainly distributes in the range of 1–2 mm. A higher gas flow rate may increase the number of bubbles in the melt and promote the bubble refinement process. The mechanism of bubble refinement under mechanical agitation was analyzed, and the results indicated that the stirring speed, the blade area and the blade inclination are the main influencing factors.

Modeling and computational simulation of fluid flow, heat transfer and inclusions trajectories in a tundish of a steel continuous casting machine

Currently, the continuous casting process is the main route used in the integrated steelmaking process. The tundish is an essential component of the caster machine and plays an important role in the control of inclusion in the production of the clean steels. Thus, viable methodologies and predictive models to evaluate this metallurgical reactor efficiency are important technological allies to improve the clean steel production. The main goal of the present study is to develop a computational tool to analyze the turbulent fluid flow, temperature distribution and inclusions removal during the continuous operation of the tundish of an industrial facility to improve its internal configuration. New configurations using weirs and dams are proposed which improve the steel quality. We used the Ansys CFX® software based on the element-based finite-volume method (EbFVM) to solve the coupled turbulent flow and heat transfer model equations in an Eulerian flame. A random nucleation mechanism for the inclusions generation and a modified Lagrangian model with a random walking model (RWM) to account for the effect of turbulence on the inclusions trajectories were proposed. The flow pattern was successfully validated with experimental data. The results were presented in terms of velocity and temperature fields and residence time distribution (RTD) curves. Then, the model was used to investigate new scenarios and enhanced geometry configurations.

Electromagnetic Conditions in a Tundish with Channel Type Induction Heating

Numerical simulation is one of the effective methods to solve the magneto‐hydrodynamic problems in electromagnetic metallurgical reactor. A mathematical statement about magnetic vector potential and electric potential is developed to describe the three‐dimensional magnetic field, induced current field, Joule heating power field, and electromagnetic force field in a tundish with channel type induction heating. The resultant equations are solved numerically, and the predicted magnetic field agrees well with the experimental data from the previous reference. The research results show that the magnetic field, the induced current field, the electromagnetic force field, and the heating power are the strongest in the channels, and these fields are eccentric in the channel. In the channel, the induced current is along the axis of the channel, the magnetic field is along the circumferential direction of the channel, the electromagnetic force is along the radius of the channel, and Joule heat power density on the side facing the other channel is greater than that on the side facing away from the other channel.

3D Model Studies on the Effect of Bed and Powder Type Upon Radial Static Pressure and Powder Distribution in Metallurgical Shaft Furnaces

AbstractThe flow of gases in metallurgical shaft furnaces has a decisive influence on the course and process efficiency. Radial changes in porosity of the bed cause uneven flow of gas along the radius of the reactor, which sometimes is deliberate and intentional. However, holdup of solid particles in descending packed beds of metallurgical shaft furnaces can lead to unintentional changes in porosity of the bed along the radial reactor. Unintentional changes in porosity often disrupt the flow of gas causing poor performance of the furnace. Such disruptions of flow may occur in the blast furnace due to high level of powder content in gas caused by large amount of coal dust/powder insufflated as fuel substitute. The paper describes the model test results of radial distribution of static pressure and powder hold up within metallurgical reactor. The measurements were carried out with the use of 3D physical model of two-phase flow gas-powder in the moving (descending) packed bed. Sinter or blast furnace pellets were used as packed bed while carbon powder or iron powder were used as the powder. Wide diversity within both static pressure distribution and powder distribution along the radius of the reactor were observed once the change in the type of powder occurred.

Modification of Basic Oxygen Furnace Slag for Cement Manufacturing

The use of steelmaking slag without chemical modification presents a deleterious effect on cement mechanical properties, due to the expansion caused by the presence of free CaO and MgO in the slag. This work deals with the modification of one basic oxygen furnace (BOF) slag with the objective of making it an appropriate additive in blended cement formulations. Two different modified slags were produced in a pilot-scale metallurgical reactor by mixing additives into 300 kg of remelted BOF slag. The liquid slags were cooled under two conditions: naturally (inside the reactor) and in contact with stainless steel balls. Quantitative X-ray diffraction and energy-dispersive spectroscopy, as well as qualitative scanning electron microscopy and Raman spectroscopy analyses of slag samples, revealed the relationship among cooling conditions and crystalline phases. The modified slags had CaO/SiO2 between 1.8 and 2.0, which is lower than the 3.8 for steelmaking slag. This reduced basicity resulted in the presence of dicalcium silicates (C2S) in higher amounts than in the steelmaking slag. β-Ca2SiO4, α′-Ca2SiO4, bredigite, and RO (FeO–MgO–MnO–CaO solid solution) were detected as major crystalline phases by X-ray diffraction and Raman spectroscopy. Cement samples were produced by mixing 25 wt% of modified steelmaking slag with 75 wt% of ordinary Portland cement, resulting in expansion lower than 0.1% in the autoclave tests and compressive strength higher than 40 MPa after 28 days. Cement samples produced by adding modified slags presented expansions 5 times lower than that determined for cement samples produced by adding steelmaking slag without any modification. The process indicates potential to be applied as a steelmaking slag treatment.

Bubble Motion and Gas-Liquid Mixing in Metallurgical Reactor with a Top Submerged Lance

Abstract The multiphase fluid mixing and bubble motion in a scale-down Isa smelting furnace with a top submerged lance were investigated through cold water model experiments. The mixing time in the liquid bath was determined by a novel criterion, and the bubble formation frequency and gas-liquid contact area were also measured by high-speed photographing. The empirical equations of mixing time (Tm) relating to mixing energy (ε) were ${T_{{\rm{m}},s}} = 913{\varepsilon ^{ - 0.5}}$ for solid tracer and ${T_{{\rm{m}},l}} = 624{\varepsilon ^{ - 0.48}}$ for liquid tracer, respectively. The mixing time trended down with the increasing of bubble formation frequency, affected slightly by the bubbles with small size and decreased obviously when increasing the gas-liquid contact area. The optimal conditions of gas flow rate, bath height, lance submerged height and lance diameter to guarantee high-efficiency mixing and low-level surface fluctuation/splashing were obtained.

Vacuum Shroud (VS) for production of clean steel in tundish

Purpose: Ladle to tundish melt transfer is paramount importance over the last three decades to controlling the cleanliness of high value steel. Tundish is an important buffer between ladle and mould where inclusion separation, flotation can be enhanced and exposed slag eye formation can be hindered by applying the knowledge of fluid dynamics as well heat transfer by changing the design of conventional flow modifiers towards production of ultra clean steel. Design/methodology/approach: In current numerical investigation a new conceptual flow control device called ‘vacuum shroud (VS)’ has been proposed to reduce slag eye formation, emulsifications and unwanted inclusions generations. Due to upward suction force from the side of the pouring nozzle the device is quite capable to reduce turbulence and emulsification within the tundish melt. Findings: Approximately 76% improvement in the overall process and 40% enhancement to inclusion floatability are predictable by using current flow control device (FCD). Research limitations/implications: Slag eye formation during pouring of liquid steel to tundish is a barrier to clean steel production on sustained manner. Several efforts have been made over the decades to resolve this phenomenon by suppressing the turbulence within this reactor incorporating many innovative flow control refractory’s like turbo-stop, trumpet shroud, advance pouring box, dissipative shroud, velocity break shroud, swirling flow shroud etc. But ultimate success is not possible to reach. Originality/value: The present investigation is development of an innovative flow control device (FCD) to control the aforementioned problems within this metallurgical reactor.

Digitalizing the Circular Economy

Metallurgy is a key enabler of a circular economy (CE), its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of metallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT. It is the linkage of the global carrier metallurgical processing system infrastructure that maximizes the recovery of all minor and technology elements in its associated refining metallurgical infrastructure. This will be illustrated through the following: (1) System optimization models for multimetal metallurgical processing. These map large-scale m-IoT systems linked to computer-aided design tools of the original equipment manufacturers and then establish a recycling index through the quantification of RE. (2) Reactor optimization and industrial system solutions to realize the “CE (within a) Corporation—CEC,” realizing the CE of society. (3) Real-time measurement of ore and scrap properties in intelligent plant structures, linked to the modeling, simulation, and optimization of industrial extractive process metallurgical reactors and plants for both primary and secondary materials processing. (4) Big-data analysis and process control of industrial metallurgical systems, processes, and reactors by the application of, among others, artificial intelligence techniques and computer-aided engineering. (5) Minerals processing and process metallurgical theory, technology, simulation, and analytical tools, which are all key enablers of the CE. (6) Visualizing the results of all the tools used for estimating the RE of the CE system in a form that the consumer and general public can understand. (7) The smart integration of tools and methods that quantify RE and deliver sustainable solutions, named in this article as circular economy engineering. In view of space limitations, this message will be colored in by various publications also with students and colleagues, referring to (often commercial) software that acts as a conduit to capture and formalize the research of the large body of work in the literature by distinguished metallurgical engineers and researchers and realized in innovative industrial solutions. The author stands humbly on the shoulders of these developments and their distinguished developers. This award lecture article implicitly also refers to work done while working for Ausmelt (Australia), Outotec (Finland and Australia), Mintek (South Africa), and Anglo American Corporation (South Africa), honoring the many colleagues the author has worked with over the years.