LD Converter Research Articles

Influence of ladle slag additions on BOF process performance

A plant trial has been performed, with recycling of ladle slag to the LD converter at SSAB EMEA, Luleå, Sweden. The effect of ladle slag addition on the slag and steel composition, together with the slag weight, was investigated with sampling both during the blow and at blow end. The addition of ladle slag resulted in an increase in slag weight between 1 and 2 t throughout the blow and an increase of 3 wt-% in the slag Al2O3 content. This indicated that the ladle slag melted during the initial stages of the blow and enhanced the early slag formation. Lime additions were reduced with 3·5 kg t−1 liquid steel without drawbacks on the phosphorus or sulphur refining. Heats with added ladle slag had an increase in blowing time with ∼4% and an increased tendency for slopping. However, this can be handled by different lance and addition programmes.

On New Refining Control System for Dephosphorization Using LD Converter

This paper proposes a new control system for dephosphorization of steel-making process using a LD converter. The control system is composed of two steps and it stabilizes low phosphorous content in the hot metal after treatment. The first step creates target concentration of iron oxide in slag for the present charge, which is optimal to achieve effective dephosphorization. The target is obtained as a time series through component analysis of results of previous charges. The second step decides the control inputs for the present charge, oxygen blowing rate and lance height, by calculating a weighted summation of previous control inputs. The weight is based on the difference between the target concentration and the concentration of previous charge. The proposed system was applied to an actual process, and the result shows the high performance of the control at the end of this paper.

NEW BOF SLAGS CONTAINING SODIUM AND MANGANESE

The nature and properties of and dust generated during the manufacture of pig iron indicate the two possibilities of their utilization: sintering or cold agglomerating with Portland cement. Both sinter and pellets can be recycled in the LD converter. It was introduced the concept of preformed synthetic slag to use the recycling of waste. If the material contains components forming the eutectic properties similar to sinter or pellet (obtained outside the converter) it stimulates the creation of in the LD converter.The aim of this research is to address the best way to deal with manganese before the molten metal reaches the final stage of temperature and composition for casting. Ideally, the composition of the and dust produced by the BOF-LD can be adjusted so that the molten metal that reaches the secondary metallurgy contains over 1.0% manganese.

Feed forward neural network for prediction of end blow oxygen in LD converter steel making

A multi layered feed forward neural network model is being developed for the prediction of end blow oxygen in the LD converter using a two step process. In the first step intermediate stopping temperature is being predicted and using this as an input the end blow oxygen is predicted. In both the cases two hidden layers had given the best results compared to the single layer neural network. Intermediate and end blow temperatures played a vital role in end blow oxygen and intermediate stopping temperature predictions. The model acts a guide for the operator and thereby enhances the yield of the converter steel making process.

Chemical and mineralogical characterizations of LD converter steel slags: A multi-analytical techniques approach

The use of LD converter steel slags (coming from Linz–Donawitz steelmaking process) as aggregates in road construction can in certain cases lead to dimensional damage due to a macroscopic swelling that is the consequence of chemical reactions. The aim of this study was to couple several analytical techniques in order to carefully undertake chemical and mineralogical characterizations of LD steel slags and identify the phases that are expected to be responsible for their instability. Optical microscopy, scanning electron microscopy and electron probe microanalyses revealed that LD steel slags mainly contain calcium silicates, dicalcium ferrites, iron oxides and lime. However, as a calcium silicate phase is heterogeneous, Raman microspectrometry and transmitted electron microscopy had to be used to characterize it more precisely. Results showed that lime is present under two forms in slag grains: some nodules observed in the matrix whose size ranges from 20 to 100 μm and some micro-inclusions, enclosed in the heterogeneous calcium silicate phase whose size ranges from 1 to 3 μm. It was also established that without the presence of magnesia, lime is expected to be the only phase responsible for LD steel slags instability. Nevertheless, the distribution of lime between nodules and micro-inclusions may play a major role and could explain that similar amounts of lime can induce different instabilities. Thus, it appears that lime content of LD steel slags is not the only parameter to explain their instability.

AVALIAÇÃO DE TÉCNICAS DE REGRESSÃO E DE UMA NOVA ABORDAGEM PARA A OTIMIZAÇÃO DO PROCESSO DE DESFOSFORAÇÃO DE AÇO NO CONVERTEDOR LD DA V&M DO BRASIL

This paper demonstrates a new model to the phosphorus forecasting content to LD converter from V&M do Brasil. The model from the previous work, trough multiple regression, is evaluated with a new regression, in this time, nonlinear, represented by an Artificial Neural Network. It is demonstrated a new methodology to the phosphorus minimization grade from the process variables available at the moment, knowing that the slag chemistral analysis is only executed after the blowing ends. The results were obtained from a set of real operation conditions samples of the LD converter from V&M do Brasil collected in the period of January to October of the year 2003. The results demonstrate that it is possible to establish new methodologies to the optimization of the LD converter steel dephosphorization process.

Demanganisation of high manganese pig iron to produce high manganese slag

Pig iron with a high manganese content makes further processing to steel using converter technology difficult and unprofitable. In the present study, external demanganisation of high manganese pig iron before the oxygen converter process has been investigated. Pilot plant experimental heats were designed and carried out to optimise the demanganisation process, to produce hot metal adequate for the conventional LD converter, and high manganese slag suitable for the production of silicomanganese. Various high manganese pig irons with different [Si]/[Mn] contents were treated by injection of various oxidisers at varying temperatures, slag basicities and injection rates. The optimum conditions for the demanganisation process have been attained by injection of an oxygen gas–manganese ore mixture at the injection rate of 6.8 L min-1kg-1 into molten high manganese pig iron with a [Si]/[Mn] ratio of 0.3 at an initial temperature of 1350°C and slag basicity of 0.3–0.4.

Manganese Distribution between FeO‐MnO‐SiO2–CaO–MgO‐Al2O3 Slags and Molten Iron

Pretreatment of high manganese hot metal is suggested to produce hot metal suitable for further processing to steel in conventional LD converter and rich manganese slags satisfy the requirements for the production of silicomanganese alloys. Manganese distribution between slag and iron represents the efficiency of manganese oxidation from hot metal. The present study has been done to investigate the effect of temperature, slag basicity and composition of oxidizer mixture on the distribution coefficient of manganese between slag and iron. Ferrous oxide activity was determined in molten synthetic slag mixtures of FeO‐MnO‐SiO2–CaO–MgO‐Al2O3. The investigated slags had chemical compositions similar to either oxidizer mixture or slags expected to result from the treatment of high manganese hot metal. The technique used to measure the ferrous oxide activity in the investigated slag systems was the well established one of gas‐slag‐metal equilibration in which molten slags contained in armco iron crucibles are exposed to a flowing gas mixture with a known oxygen potential until equilibrium has been attained. After equilibration, the final chemical analysis of the slags gave compositions having a particular ferrous oxide activity corresponding to the oxygen potential of the gas mixture. The determined values of ferrous oxide activity were used to calculate the equilibrium distribution of manganese between slag and iron. Higher manganese distribution between slag and iron was found to be obtained by using oxidizer containing high active iron oxide under acidic slag and relatively low temperature of about 1350°C.

Foam level control in a water model of the LD converter process

This paper deals with estimation and control of foam level in dynamic foaming. An improved foam level estimation methodology from a microphone signal and its automatic calibration is presented. The dynamical reaction of the foam level on air lance movements is modelled using system identification. Based on the resulting mathematical model, a controller for foam level stabilisation is designed and applied to a water model, representing the LD converter process. It is shown that the foam level can be controlled using a microphone as the measurement device and air lance movement as the actuator.

Improvement of reaction efficiency in hot metal dephosphorisation

In Japan, the hot metal pretreatment process has been developed to refine hot metal under conditions where each impurity can be removed most efficiently. At Nippon Steel, three types of hot metal pretreatment process, using torpedo car, hot metal ladle, or LD converter, are employed, that make a great contribution to the reduction of slag volume. Recently, Nippon Steel has developed a new hot metal pretreatment called the multirefining converter (MURC) process, in which dephosphorisation and decarburisation are carried out continuously in the same converter. Nevertheless, since the dephosphorisation efficiency of CaO is less than 30%, CaO is now being used in far greater quantities than that stoichiometrically required to make 3CaO.P2O5. As hot metal dephosphorisation is a non-equilibrium reaction, in which hot metal is in contact with slag whose oxygen activity differs greatly from that of hot metal, it is important to increase the interfacial oxygen activity. From the results of a fundamental experiment, the 2CaO.SiO solid phase, in which P2O5 can be dissolved, has a great effect on the dephosphorisation reaction.

Physical and mathematical models of gas-liquid fluid dynamics in LD converters

Fluid dynamics of gas-liquid interactions in a LD converter to refine steel was physically and mathematically simulated. Using a water model three cases of gas supply were considered, top blowing, bottom injection and combined process top blowing-bottom injection. Mixing time in top blowing increases with bath height and the distance between the lance of the gaseous jet and the bath surface. The jet penetration was found to be dependent on the modified Froude number. The unstable and unsteady behaviour of the bath topography, as affected by the gaseous jet, was well simulated through a multiphase momentum transfer model. In top blowing, three zones of liquid splashing were found, penetration with low splash, heavy splash and dimpling with low splash intensity. These zones depend on the gas flow rate and the distance from the lance to the bath surface. During bottom injection mixing times decrease with the number of tuyères, increases of bath height and gas flow rate. In a combined process mixing time decreases considerably due to the recirculating flow formed by the action of the top jet and the submerged jets. When a submerged jet is located just below the top jet the mixing time does not decrease as compared with the separated processes either top blowing or bottom stirring. Physikalische und mathematische Modelle zur Strömung von Gas und Schmelze im LD-Konverter. Das Strömungsverhalten in einem LD-Konverter wurde besonders im Hinblick auf die Wechselwirkungen zwischen Gas und Schmelze physikalisch und mathematisch simuliert. Mit einem Wassermodell wurden drei Varianten des Gaseinleitens betrachtet: Aufblasen, Bodenblasen und kombiniertes Blasen. Beim Aufblasen nimmt die Zeit zur Durchmischung mit der Badhöhe als auch mit dem Abstand der Lanze vom Gasstrahl und der Badoberfläche zu. Es zeigte sich, daß die Eindringtiefe des Strahls von der modifizierten Froude-Nummer abhängt. Das instabile und unstetige Verhalten der Badtopographie, soweit vom Gasstrahl betroffen, ließ sich gut mit einem mehrphasigen Momententransfermodell simulieren. Beim Aufblasen läßt sich das Spritzen in drei Zonen unterteilen: geringes Spritzen beim Eindringen des Gasstrahls in die Schmelze, starkes Spritzen und Dimplebildung mit geringer Spritzintensität. Diese Bereiche hängen von den beiden Parametern Strömungsgeschwindigkeit des Gases und Abstand der Lanze von der Badoberfläche ab. Beim Bodenblasen verkürzt sich die Mischzeit mit der Anzahl der Düsen, steigender Badhöhe und Gasströmungsgeschwindigkeit. Beim kombinierten Blasen fällt die Mischzeit infolge der gegenläufigen Strömung, die sich aus den Gasstrahlen der oberen Düse und der Bodendüsen zusammensetzt, beträchtlich. Wenn die Position des aus dem Tauchrohr austretenden Strahls gleich unterhalb des oberen Strahls liegt, nimmt die Mischzeit im Vergleich zum reinen Auf- oder Bodenblasen nicht ab.

Exergy Analysis of Steel Production Processes

Continuous increase of the annual amount of steel scrap generated presents a problem to the sustainability of human society. The effective utilization of scrap is a serious problem to be solved in the near future, and the optimization of the global system of steel production should be considered from various viewpoints, particularly those of environmental load and material efficiency. For the consideration of a global system that contains many different kinds of flow, a criterion for evaluating the efficiency of the system is necessary for optimizing the utilization of materials in the system. The concept of exergy was adopted in this study and the application of exergy analysis to the evaluation of a complicated system was considered. A simulation model was developed for the steel industry in Japan and the exergy analysis of the Blast Furnace-LD converter (BF-LD) process and the Electric Arc Furnace (EF) process was conducted. The exergy loss was expressed as a function of parameters, such as the mixing rate of pig iron in the EF process and the total exergy loss in the system was calculated. The applicability of exergy as a criterion for the analysis of a production process and for evaluating material efficiency was discussed. Environment and recycling become important keywords in the consideration of a new industry structure for optimizing material efficiency and environmental load for production and utilization of materials. In the present study, a methodology for evaluating the degree of optimization in the system includ- ing material recycling was investigated. The Blast Furnace- LD converter (BF-LD) process for the production of high- grade steel and the Electric Arc Furnace (EF) process for the production of low-grade steel are the main steel produc- tion processes used in Japan. This division occurs because of contamination by tramp elements as impurities, which is inevitable in processes using low-grade scrap as feed. The percentage of EF steel in the total production of crude steel in Japan is about 33%, 1) and the total amount of the accumula- tive steel stock in Japan is increasing continuously. Generally, processes that consume large amounts of electric energy for heating and smelting are wasteful from the viewpoints of ef- fective energy use and environmental load. However, the op- timum steel production ratio in BF-LD and EF processes has not been investigated clearly. For the further improvement of steel productivity, it is necessary to optimize the steel pro- duction system from various viewpoints such as the suitable selection of feed materials, the total demand for steel products in society, and the impurities limit in the steel product. The recent state of the steel industry in Japan is that the amount of scrap is increasing annually and its quality is de- creasing. Therefore, the effective use of iron resources orig- inating from iron ore for the dilution of scrap has recently become a principal subject in the EF steel industry, together with the improvement of scrap recovery technology. Recent electric furnaces are operated with a high mixing rate of pig iron, from 20 to 50%, as iron feed, and other furnaces have been combined with a converter to enable the hybrid steel- making process. 2) Since it is very important for the steel in- dustry in Japan to utilize the iron stock effectively as valu- able resource, the optimum ratio of EF product to BF product and that of scrap utilized in the EF process to that utilized in the converter were investigated in this study in terms of the efficiency of the use of iron resources originating from iron ore for the dilution. A model of the iron and steel recycling system including material flow was constructed, and the ther- modynamic property of exergy was applied to estimate the measure of optimization for the steel production system. 2. The Concept of Exergy

Model-based estimation of molten metal analysis in the LD converter: experiments at SSAB Tnnplat AB in Lulea

Experiences from field tests of a model-based molten metal analysis estimation system for the Linz and Donawitz converter process are reported. Experiments have been carried out during a six-month-long period on two converters at SSAB Tunnplat AB, Lulea, Sweden. The achieved results prove viability of the approach taken and indicate its high potential regarding estimation accuracy and robustness. It is also concluded that some further system development is necessary to enable modeling of additives and lance level before the system can be recommended for permanent installation.

Foam Level Control in a Water Model of the LD Converter Process

This paper deals with estimation and control of foam level in dynamic foaming. An improved foam level estimation methodology from a microphone signal and its automatic calibration is presented. The dynamical reaction of the foam level on air lance movements is modelled using system identification. Based on the resulting mathematical model, a controller Put foam level stabilisation is designed and applied to a water model, representing the LD converter process. It is shown that the foam level can be controlled using a microphone as the measurement device and air lance movement as the actuator.

A new tool for process modelling of metallurgical processes

A new modular process modelling tool has been developed to support the design and operation of metallurgical processes. A modelling concept was formulated and a flowsheeting software tool has been developed for the calculation of complex non-equilibrium phenomena. To test both the basic approach and software tool, the modelling and simulation of a LD converter process was undertaken. The validation of the simulation model shows good agreement of reported and calculated values for species concentration and temperature development in time. The aim of this approach is to achieve a high degree of accuracy in modelling and, at the same time, to correspond to the speed requirements of day to day design work. It is intended to extend the current research to obtain a tool not only for the design and simulation of established processes, but also for the computer-aided development of new process routes.

Optical filtering to reduce chirping influence in LD wavelength conversion

The use of an optical filter to reduce chirping influence in LD wavelength conversion is demonstrated. A part of broadened spectrum of wavelength-converted light is eliminated by a narrow-band optical filter, and sensitivity degradation due to frequency chirping is reduced as a result. In an experiment using a fiber Fabry-Perot filter, the sensitivity was improved by about 1.5 dB in 1.55-/spl mu/m transmissions with normal dispersion fibers when an LD converter was biased at two times the threshold current.

転炉におけるステンレス溶鉄中クロムのオンライン分析技術の開発

転炉におけるステンレス溶鉄中クロムのオンライン分析技術の開発

Some Special Considerations on Magnesia-Carbon Refractories

Rotary drum erosion test has been developed which provides information on corrosion, abrasion and oxidation properties of magnesia carbon bricks. Textural properties of magnesia-carbon bricks have also been determined through this test The result obtained is correlated with service performance in LD converter.

Design technique for extending life of LD converter vessel

At Kakogawa works of Kobe Steel, all three LD converter vessels were replaced. At the time the vessels were replaced, a new design technique for the extending vessel life was established and this technique was applied to the new vessels. As a result, it was possible to restrain deformation of the barrel shell, when the consumption ratio of the MgO-C brick with high thermal conductivity is high.

An application of expert system to LD converter processes.

An application of expert system to LD converter processes.