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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Extractive Metallurgy".

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 34795

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Prof. Dr. Geoffrey Brooks

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Department of Mechanical and Product Design Engineering, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
Interests: steelmaking; pyrometallurgy; extractive metallurgy; solar thermal energy; waste processing; metals recycling
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Dear Colleagues,

Oxygen Steelmaking is the dominant process for producing steel. The technology around Oxygen Steelmaking has evolved greatly since pioneering work in Europe in the late 1940s. There have significant developments in lance technology, refractories, sensors and control systems over the last twenty years. This has been coupled with improved scientific understanding of the physical chemistry, kinetics, heat transfer and fluid mechanics of the system. There are still significant challenges in optimizing slag foaming, slag chemistry, scrap melting, post-combustion and control systems. The general shift towards lowering the environmental impact of metal production will also drive innovation in the evolution of the process. This issue will be focused on the most recent developments and examining both technological developments and the underlying scientific issues around these technological challenges. Papers from producers, suppliers and researchers would be most welcome.

Prof. Dr. Geoffrey Brooks
Guest Editor

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Keywords

Oxygen Steelmaking
Pyrometallurgy
Supersonic Lances
Slag Chemistry
Heat Transfer
Fluid Mechanics

Published Papers (11 papers)

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Research

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13 pages, 4873 KiB

Open AccessArticle

Effect of Cr₂O₃ on Physicochemical Properties of CaO-SiO₂-Fe_tO Slags during BOF Smelting Process of Chromium-Bearing Iron

by Shannan Li, Jianli Li, Yue Yu and Hangyu Zhu

Metals 2022, 12(7), 1110; https://doi.org/10.3390/met12071110 - 28 Jun 2022

Cited by 2 | Viewed by 1281

Abstract

The productivity of basic-oxygen-furnace (BOF) smelting process is directly affected by the slag-forming speed during the initial stage of converter. Therefore, it is essential to study the effect of different Cr₂O₃ content on the physicochemical properties of the primary slag in the smelting process of chromium-bearing semi-steel. In this work, Factsage8.1 software, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and a high-temperature melting point tester were used to study the effects of different Cr₂O₃ content on the melting temperature, solidification behavior, mineral composition, and other physicochemical properties of the CaO-SiO₂-Fe_tO system. The results showed that the melting temperature of slag samples increased from 1223 °C to 1354 °C as Cr₂O₃ increased from 0 wt% to 9.09 wt%. With the increase of Cr₂O₃, the content of CaFeSi₂O₆ decreased. Moreover, due to the addition of Cr₂O₃, the chromium-bearing spinel solid solution (Fe(Fe,Cr)₂O₄) began to form in the slag. Furthermore, Cr₂O₃ promoted the increase in the volume of free solid particles in the slag, resulting in an increase in slag viscosity. All in all, the increase of Cr₂O₃ content in the CaO-SiO₂-Fe_tO system will adversely affect the semi-steel steelmaking process. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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23 pages, 3878 KiB

Open AccessArticle

Global Droplet Heat Transfer in Oxygen Steelmaking Process

by Nirmal Madhavan, Geoffrey A. Brooks, M. Akbar Rhamdhani, Bapin K. Rout and Aart Overbosch

Metals 2022, 12(6), 992; https://doi.org/10.3390/met12060992 - 10 Jun 2022

Cited by 3 | Viewed by 1637

Abstract

Generated droplets in a basic oxygen furnace (BOF) process create an interfacial area between metal and slag/emulsion that helps in heat transfer during different stages of the blowing period. Previous studies have developed extensive models to understand bloating behavior and overall refining kinetics contributed by the droplets in a BOF process. Except for the recent study on single droplet heat transfer by the current authors, no studies in the open literature have addressed the heat transfer contributed by droplets in a BOF. The present work is an extension of single droplet heat transfer, wherein a global droplet heat transfer model is developed by integrating kinetic and dynamic aspects of generated droplets during the blowing period. The model was developed based on previous chemical kinetic studies and input values from plant trials. The results from the global droplet heat transfer model are integrated into the overall zone heat balance calculations to predict the temperature evolution profile of hot spot, slag, and hot metal zones during the blowing period. The results highlight that the hot spot temperature ranges from 1900 °C to 2090 °C, with a peak value of around 2300 °C observed during the middle of the blow. Furthermore, computing the overall droplet heat transfer efficiency, it was observed that the droplets transfer 90% of the heat to the slag up to the first 10 min of the blow, and then the heat transfer efficiency drops towards the end of the blow. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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21 pages, 3777 KiB

Open AccessArticle

Hybrid Method for Endpoint Prediction in a Basic Oxygen Furnace

by Ruibin Wang, Itishree Mohanty, Amiy Srivastava, Tapas Kumar Roy, Prakash Gupta and Kinnor Chattopadhyay

Metals 2022, 12(5), 801; https://doi.org/10.3390/met12050801 - 5 May 2022

Cited by 9 | Viewed by 1920

Abstract

Strict monitoring and prediction of endpoints in a Basic Oxygen Furnace (BOF) are essential for end-product quality and overall process efficiency. Existing control models are mostly developed based on thermodynamic principles or by deploying advanced sensors. This article aims to propose a novel hybrid algorithm for endpoint temperature, carbon, and phosphorus, based on heat and mass balance and a data-driven technique. Three types of static models were established in this study: firstly, theoretical models, based on user-specified inputs, were formulated based on mass and energy balance; secondly, artificial neural networks (ANN) were developed for endpoints predictions; finally, the proposed hybrid model was established, based upon exchanging outputs among theoretical models and ANNs. Data of steelmaking production details collected from 28,000 heats from Tata Steel India were used for this article. Machine learning model validation was carried out with five-fold cross-validation to ensure generalizations in model predictions. ANNs are found to achieve better predictive accuracies than theoretical models in all three endpoints. However, they cannot be directly applied in any steelmaking plants, due to possible variations in the production setting. After applying the hybrid algorithm, normalized root mean squared errors are reduced for endpoint carbon and phosphorus by 3.7% and 9.77%. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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18 pages, 3345 KiB

Open AccessArticle

Contribution of CO₂ Emissions from Basic Oxygen Steelmaking Process

by Nirmal Madhavan, Geoffrey Brooks, M. Akbar Rhamdhani and Adam Bordignon

Metals 2022, 12(5), 797; https://doi.org/10.3390/met12050797 - 5 May 2022

Cited by 8 | Viewed by 5436

Abstract

The steelmaking process is an energy-intensive multi-stage process, and the step involving the conversion of molten iron to steel, commonly performed in a basic oxygen furnace (BOF), makes an important contribution to greenhouse gas generation. The effective utilization of energy is one of the major challenges in the process, as minor variations of operational parameters can have significant negative effects on the converter in terms of CO₂ emissions. A recent study published by the same authors analyzed the BOF process by developing a general mass and energy balance model. The present study utilizes these models to quantify the contribution of global warming potential (GWP) from the BOF and analyses its sensitivity with the parameters such as hot metal composition, the temperature of hot metal, tapping temperature, scrap quantity, and levels of post-combustion. The term GWP in this study refers to the quantified CO₂ values obtained by summing up the carbon dioxide associated with the production of CaO associated with the mass of flux and carbon dioxide generated from the off-gas (considering C in hot metal is completely oxidized to CO₂). The results from the analysis indicates that for a tapping temperature increase from 1650 °C to 1683 °C, the percentage change in the global warming potential (GWP) was found to be approximately 1%. The study identified that increasing the scrap percentage in the feed would be the most effective approach to effectively utilizing chemical energy from the process and reduce CO₂ emissions. However, increasing scrap above 30% of the total feed is likely to raise issues around: (a) the presence of residual elements in scrap affecting the quality of liquid steel, (b) the effective utilization of post-combustion heat within the furnace, and (c) the recovery of off-gas heat for scrap preheating (assuming no steam recovery from the off-gas system). If these issues could be addressed at the industrial level, a significant reduction in CO₂ emissions from the BOF process could be achieved. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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17 pages, 26463 KiB

Open AccessArticle

Contribution of Hot-Spot Zone in Decarburization of BOF Steel-Making: Fundamental Analysis Based upon the FactSage-Macro Program

by Prasenjit Singha and Ajay Kumar Shukla

Metals 2022, 12(4), 638; https://doi.org/10.3390/met12040638 - 7 Apr 2022

Cited by 7 | Viewed by 2483

Abstract

An improved computational model to describe the decarburization process in basic oxygen furnaces for steel making is presented in this work. A dynamic model was thus developed to calculate the decarburization rate and its breakup as a contribution coming from the hot-spot zone (under jet impact) and emulsion zone (by droplet and slag reactions). In this work, multiple interconnected equilibrium/adiabatic stoichiometric-reactor-based approaches are used to describe the overall basic oxygen steel-making process. The macroprogramming facility of FactSage™ software was used to understand the thermodynamics and kinetics of basic oxygen steel-making processes. The temperature, compositions, and volumes of various phases are estimated with the use of this model. Hot-spot temperatures in the range from 2000 to 3000 °C as a benchmark was considered for calculations. The major contribution of decarburization was established to come from hot-spot reactions in the major part of the blow, except in the last part when emulsion phase reactions govern it. This development represents an original contribution to our understanding of the BOF steel-making process. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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17 pages, 4091 KiB

Open AccessFeature PaperArticle

Green LD (BOF) Steelmaking—Reduced CO₂ Emissions via Increased Scrap Rate

by Bernhard Voraberger, Gerald Wimmer, Uxia Dieguez Salgado, Erich Wimmer, Krzysztof Pastucha and Alexander Fleischanderl

Metals 2022, 12(3), 466; https://doi.org/10.3390/met12030466 - 10 Mar 2022

Cited by 9 | Viewed by 6663

Abstract

The basic oxygen furnace (BOF) is the dominating primary steelmaking process. It is an autothermal process where hot metal and scrap are used as charging materials. The decarbonization and transformation of integrated BOF steelmaking will be the most important challenge in the coming years. Steel scrap is a charge material without new CO₂ emissions, whose availability is expected to grow significantly and will play a key role in this decarbonization process. Several solutions have been developed by Primetals Technologies to provide additional energy for processing higher scrap rates in integrated BOF steelmaking. Such solutions include simple upgrade packages installed on existing converters such as process models for heat optimization, post-combustion, and scrap preheating lances. For higher scrap rates from 30% to 50%, a combination blowing converter and JET converter is required to provide sufficient mixing during scrap melting and the highest heat transfer from the increased post-combustion. Hybrid EAF–BOF operation and limitations regarding scrap quality also need to be considered for the transformation of steelmaking. Scrap sorting and processing can be a solution to reduce residual levels in crude steel for high scrap rates. Based on reference plant data, the CO₂ reduction potential of the presented solution versus the effort and complexity of implementation is compared. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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15 pages, 3777 KiB

Open AccessArticle

Least Squares Twin Support Vector Machines to Classify End-Point Phosphorus Content in BOF Steelmaking

by Heng Li, Sandip Barui, Sankha Mukherjee and Kinnor Chattopadhyay

Metals 2022, 12(2), 268; https://doi.org/10.3390/met12020268 - 31 Jan 2022

Cited by 6 | Viewed by 1863

Abstract

End-point phosphorus content in steel in a basic oxygen furnace (BOF) acts as an indicator of the quality of manufactured steel. An undesirable amount of phosphorus is removed from the steel by the process of dephosphorization. The degree of phosphorus removal is captured numerically by the ‘partition ratio’, given by the ratio of %wt phosphorus in slag and %wt phosphorus in steel. Due to the presence of multitudes of process variables, often, it is challenging to predict the partition ratio based on operating conditions. Herein, a robust data-driven classification technique of least squares twin support vector machines (LSTSVM) is applied to classify the ‘partition ratio’ to two categories (‘High’ and ‘Low’) steels indicating a greater or lesser degree of phosphorus removal, respectively. LSTSVM is a simpler, more robust, and faster alternative to the twin support vector machines (TWSVM) with respect to non-parallel hyperplanes-based binary classifications. The relationship between the ‘partition ratio’ and the chemical composition of slag and tapping temperatures is studied based on approximately 16,000 heats from two BOF plants. In our case, a relatively higher model accuracy is achieved, and LSTSVM performed 1.5–167 times faster than other applied algorithms. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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19 pages, 25234 KiB

Open AccessArticle

Effect of Bottom Blowing Mode on Fluid Flow and Mixing Behavior in Converter

by Jiankun Sun, Jiangshan Zhang, Wenhui Lin, Xiaoming Feng and Qing Liu

Metals 2022, 12(1), 117; https://doi.org/10.3390/met12010117 - 7 Jan 2022

Cited by 14 | Viewed by 2047

Abstract

Bottom blowing agitation plays a crucial role in improving the reaction kinetics condition of molten bath during the steelmaking process. Herein, the influence of bottom blowing mode on the flow and mixing characteristics of molten bath and the abrasion characteristics of refractory lining in a 6:1 scaled-down model of a 100 t converter were investigated using physical and numerical simulations together. Eight bottom blowing modes were designed (uniform, three-point linear co-direction, three-point linear unco-direction, two-point linear, circumferential linear, A-type, V-type, and triangle alternating). The results indicated that bottom blowing mode has a significant effect on the local flow field at the inner ring of bottom tuyeres, the velocity interval distribution, and the turbulent kinetic energy, which in turn determines the tracer diffusion path and rate as well the mixing time of molten bath. Reasonable non-uniform bottom blowing modes promote the interaction between the various stirring sub-zones of the molten bath. Among them, the three-point linear co-direction mode and A-type mode have the highest mixing efficiency under the conditions of bottom blowing and combined blowing, respectively, which is superior to the uniform mode. In addition, the bottom blowing mode changed the location and degree of abrasion of the refractory lining, and the total abrasion of the non-uniform mode was reduced. The average value and fluctuation degree of integral wall shear stress for the A-type mode were minimal. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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14 pages, 2957 KiB

Open AccessFeature PaperArticle

Effect of the Basicity on Mineralogical Phases and Micro-Structure of Dephosphorization Slag in the New Double Slag Converter Steelmaking Process

by Wenkui Yang, Jian Yang, Runhao Zhang, Han Sun and Yunlong Qiu

Metals 2021, 11(9), 1480; https://doi.org/10.3390/met11091480 - 17 Sep 2021

Cited by 4 | Viewed by 1640

Abstract

In the present work, the effect of the basicity at the lower range from 0.98 to 2.13 on dephosphorization of hot metal at 1623 K was studied through high-temperature laboratorial experiments. With the increase of the basicity from 0.98 to 2.13, the P and C contents in hot metal rapidly decrease and increase at first, and then gradually decrease and increase, respectively. From the scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) results, with the increase of the basicity, the phase containing the high P content changes from the matrix phase into the phosphorus (P)-rich phase. Under the present experimental conditions, the P-rich phase can only be precipitated from the liquid slag when the basicity is higher than 1.55, which is a benefit to the dephosphorization. As the Raman intensity of the P-O-Ca structure unit in the P-rich phase is significantly higher than that of the P-O-Si structure unit, most of the phosphorus in the P-rich phase exists in the P-O-Ca structure unit and a small amount of phosphorus exists in the P-O-Si structure unit. With the increase of the basicity of the dephosphorization slag, the activity coefficient of P₂O₅,

γ_{{(P}_{2} O_{5})}

, in the liquid phase decreases, while the basicity in the liquid phase increases. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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Review

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12 pages, 2280 KiB

Open AccessReview

Acoustic Analysis of Slag Foaming in the BOF

by Jason Heenatimulla, Geoffrey A. Brooks, Michelle Dunn, David Sly, Rod Snashall and Wang Leung

Metals 2022, 12(7), 1142; https://doi.org/10.3390/met12071142 - 5 Jul 2022

Cited by 5 | Viewed by 2397

Abstract

The control of slag foam that is produced during the Basic Oxygen Furnace (BOF) process has been the subject of significant research. The behaviour of slag foams is complex. Hence, the control of slag foam in the dynamic process of the BOF is challenging. Acoustic analysis of the BOF is one of the most promising methods for the indirect measurement of slag foam height. This paper reviews different studies on the fundamental behaviour of acoustics in liquid foams and various acoustic studies related to determining the slag foam height during the BOF process. Studies on the BOF have been carried out using both cold water models and plant trials, where acoustic measurements taken directly from the process were analysed. These studies showed that the attenuation of sound through liquid foam was influenced mainly by factors such as viscosity, bubble size, and foam height. Current systems are said to be 70 to 87 per cent accurate in detecting and/or predicting slopping events in the BOF, though there is a lack of systematic data in the literature to fully quantify this accuracy. There have been various attempts to combine sound with vibration and image signals to improve the prediction of slopping events in BOFs. The review substantiates the lack of accuracy of the current systems in determining the slag foam height using acoustic analysis and the need to address fundamental questions about the behaviour of sound in dynamic foam, its reliance on different factors, and the relatability of comparing cold model data to industrial data. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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24 pages, 6216 KiB

Open AccessReview

70 Years of LD-Steelmaking—Quo Vadis?

by Jürgen Cappel, Frank Ahrenhold, Martin W. Egger, Herbert Hiebler and Johannes Schenk

Metals 2022, 12(6), 912; https://doi.org/10.3390/met12060912 - 26 May 2022

Cited by 7 | Viewed by 5156

Abstract

Basic Oxygen Furnace (BOF) steelmaking is, worldwide, the most frequently applied process. According to the world steel organization statistical report, 2021, it saw a total production share of 73.2%, or 1371.2 million tons per year of the world steel production in 2020. The rest is produced in Electric Arc Furnace (EAF)-based steel mills (26.3%), and only a very few open-hearth and induction furnace-based steel mills. The BOF technology remains the leading technology applied based on its undoubted advantages in productivity and liquid steel composition control. The BOF technology started as the LD process 70 years ago, with the first heat applied in November 1952 in a steel mill in Linz, Austria. The name LD was formed from the first letters of the two sites with the first industrial scale plants, Linz and Donawitz, both in Austria. The history and development of the process have been honored in multiple anniversary publications over the last few decades. Nevertheless, the focus of the steel industry worldwide is significantly changing following a social and political trend and the requirement for fossil-free energy generation and industrial production to be in accordance with the world climate targets committed to in relation to the decades leading up to 2050. Iron and steel production is one of the major polluters of climate changing greenhouse gases; it must change to renewable primary energy sources and the use of climate-neutral reduction agents. Because it is very obvious that carbon, as the main component for steel strength properties, cannot be eliminated totally from the steel production process, the question arises of where a “zero carbon” approach can lead? This paper will review the ongoing success story of the LD-process, discuss the recent technology advancements, and give an outlook on the future role of the process in the steel industry. Full article

(This article belongs to the Special Issue Oxygen Steelmaking Process)

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