Hot Metal Pretreatment Research Articles

Hot metal pretreatment by powder injection of lime-based reagents

A mathematical model earlier proposed has been improved to predict the kinetics of multicomponent reactions in the hot metal pretreatment through the injection of reactive fluxes. It is assumed that there are two reaction zones along the flux injection operation: a transitory reaction between the rising particles and the bulk metal, and the permanent reaction between the metal and the top slag. A criterion to estimate the fraction of solids which will react with molten iron in a three-phase jet (gas-solid-liquid) was considered; this fraction of solids carries out the transitory reaction. The model also takes into account the thermodynamic changes produced in the metal and slag due to the chemical reactions. Calculated results of the model are in good agreement with experimental results for the desulfurization of hot metal through the injection of CaO-SiO2-CaF2-FeO-Na2O reagents at 1400 - 1450 °C. Two kinds of hot metal were tested, one with a low carbon mass content of 3 % and the other with a high carbon mass content of 4.5 %. Einblasen von Schlackebildnern auf Kalkbasis zur Roheisenvorbehandlung. Ein bereits früher veröffentlichtes mathematisches Modell wurde weiterentwickelt, um die Kinetik von Mehrkomponentenreaktionen beim Einblasen von Schlackebildnern während der Roheisenbehandlung im voraus zu beschreiben. Man nimmt an, daß zwei Reaktionszonen beim Einblasen existieren: eine davon ist die transitorische Reaktion zwischen den aufsteigenden Teilchen und der Metallschmelze; die andere wird durch die permanente Reaktion an der Grenzfläche Metall/Schlacke charakterisiert. Es wurde ein Kriterium zur Abschätzung des Feststoffanteils diskutiert, der mit dem geschmolzenden Roheisen in einem dreiphasigen (gas-fest-flüssig) Strahl reagiert. Dieser Anteil fester Partikel ist an der transitorischen Reaktion beteiligt. Das Modell berücksichtigt auch die thermodynamischen Umwandlungen in Metall und Schlacke, die von den chemischen Reaktionen ausgelöst werden. Die mit diesem Modell berechneten Ergebnisse zeigen eine gute Übereinstimmung mit den experimentell ermittelten Daten, die für die Roheisenentschwefelung durch Einblasen von CaO-SiO2-CaF2-FeO-Na2O-Schlackenbildnern bei 1400 - 1450 °C erhalten wurden. Der Untersuchung lagen zwei Roheisensorten mit unterschiedlichen Kohlenstoffmassengehalten von 3 und 4.5 % zugrunde.

Kawasaki Steel’s steelmaking technologies for mass production of high quality slabs

Kawasaki Steel’s two integrated steel works, Chiba and Mizushima, produce high quality slabs while keeping high productivity. The steelmaking technologies which provide the high quality and competitive slabs are : –hot metal pretreatment for obtaining the cost- minimum phosphorus content in the melt charged to BOFs ; –optimized operation to produce clean steel ; –continuous casting technology for eliminating the origin of surface defects of sheet products, e.g. molten steel flow control in the casting mould and direct rolling without any scarfing.

Thermodynamics of the simultaneous desulfurization and dephosphorization processes of hot metal with CaO- and BaO-based slags bearing MnO

The technical feasibility of the simultaneous desulfurization and dephosphorization process of hot metal with high basicity slags of the BaO-BaF 2 system is discussed from the thermodynamic point of view. The, partition ratios as well as the degrees of removal of sulphur and phosphorus from the hot metal obtained after a single refining step with BaO-saturated slags have been compared to those achieved when typical hot metal pretreatment slags of the system CaO-CaF 2 -SiO 2 (double saturated with CaO and 3CaO.SiO 2 ) were used. The experiments were carried out in graphite crucibles at 1573 K, under CO atmosphere. Considering that both the desulfurization degree and the dephosphorization degree of hot metal achieved with BaO-based slags, around 95 %, were much higher than those obtained when CaO-based slags were used, maximum 45 %, it was concluded that the simultaneous desulfurization and dephosphorization process of hot metal with high basicity BaO-BaF 2 slags is technically feasible. It has been verified also that the high basicity BaO-based slags led to manganese recovery degrees as high as 86 % and prevented at the same time the undesirable oxidation of carbon from the metal phase.

Activity of Phosphorus Oxide in CaO-MnO-SiO2-PO2.5 (-MgO, FetO) Slags.

The CaO–MnO–SiO2–PO2.5(–MgO, FetO) slags were equilibrated with liquid copper alloys in a molybdenum crucible under a flowing CO2/H2 atmosphere in the temperature range of 1573 to 1673 K. The activity coefficient of PO2.5, γPO2.5, and the phosphate capacity, CPO43-=(%PO43-)/PP21/2PO25/4, of the slags were expressed as follows:log γPO2.5 = –2.59 {(%CaO)+0.33(%MnO)+0.55(%MgO)–0.90(%FetO)–0.77(%PO2.5)}/(%SiO2)+1400/T–5.75log CPO43- = 2.60{(%CaO)+0.33(%MnO)+0.55(%MgO)–0.90(%FetO)–0.77(%PO2.5)}/(%SiO2)+40400/T–6.48 The phosphorus distributions between hot metal and the slag were examined, based on the thermodynamic data obtained in the present study. From comparison with the plant data, it was concluded that the thermodynamic data obtained in the present study are satisfactorily applicable to the thermodynamic assessment of hot metal pretreatment with high MnO slag.

Mathematical Model of Simultaneous Slag-Metal Reactions in Multi-components System.

A mathematical model describing the simultaneous reactions in multi components system, such as hot metal pretreatment in which bulk flow from the bulk to the slag metal interface occurs, is proposed in order to exactly evaluate the mass transfer in the boundary films resulting from diffusion and that from bulk flow, respectively. This model, furthermore, allows accurate estimation of interfacial concentrations and of chemical reactions at interface. The model is applied to the experimental data reported in literatures considering the mass transfer in slag phase, that of in metal phase, and chemical reaction at slag metal interface as the rate controlling steps. The determined kinetic parameters in this model lead to the following conclusions; (1) To describe the decarburization rate, it is necessary to take the retarding phenomena at high interfacial oxygen partial pressure into consideration. (2) The chemical reaction resistance of silicon reaction should be considered. (3) The stirring of the bath by bottom blowing gas tends to accelerate the mass transfer in the metal phase more than that of the slag phase, compared with that by mechanically rotated rod.

Thermodynamics of Mn-O Interactions in Liquid Copper Alloys and Activities of MnO in MnO-SiO2 Slag.

As a provision for measuring the thermodynamic data of high MnO slag by equilibrating with liquid copper in the temperature range of hot metal pretreatment, thermodynamics of manganese-oxygen interactions in liquid Cu-Mn alloy were investigated. The liquid alloys containing 0.2-1.0mass% Mn were equilibrated with solid MnO in a molybdenum crucible under an argon atmosphere. The following equations for the interaction coefficient (f O Mn ) were obtained for the range of 0.2-1.0 mass% Mn. log f O Mn = -0.8122-1.27[%Mn] + 0.37[%Mn] 2 at 1 573 K log f O Mn = -0.7536 -1,14[%Mn] + 0.33 [%Mn] 2 at 1 623 K log f O Mn = -0.6189-1.07[%Mn] + 0.37 [%Mn] 2 at 1 673 K Using the above values of log f O Mn , the activities and activity coefficients of MnO in MnO-SiO 2 slag were determined at 1 673 K and examined in comparison with the values reported by other investigators.

Alumina-Silicon Carbide-Carbon Bonded Bricks for Hot Metal Pretreatment Process (Torpedo Ladle) and Steel Ladle Applications

Alumina-silicon carbide-carbon based resin bonded bricks have been finding increasing applications in the field of hot metal pretreatment process in torpedo ladle worldwide. In the pretreatment process in the steel ladles, refractories are subjected to very stringent demand of performance. This process helps in the production of quality steel and is the most preferred process.The alumina-silicon carbide-carbon based refractories are suitable for the torpedo ladle as they have the best slag penetration resistance and are thus suitable for slag zone and bottom impact zone of steel ladle. A complete study of various aspects of properties that affects the brick application has been enumerated in this paper.

Dephosphorization Reaction of Chromium Containing Molten Iron by CaO-based Flux.

Dephosphorization tests of chromium containing molten iron by CaO-based flux have been carried out by an induction furnace. The following results were obtained: (1) When the carbon content in metal was high enough, chromium containing molten iron was able to be dephosphorized by CaO-CaF2-FeO flux. In this case, oxygen partial pressure at the slag and metal inferface was calculated to be about 10-12 Pa. (2) The higher ratio of CaF2/(CaO+CaF2) and of CaO/O in flux were effective for the dephosphorization without the oxidization of chromium. Based on these results, 200 ton scale industrial tests have been carried out by the hot metal pretreatment station at Yawata Works. By the combination of the flux injection method and the oxygen top blowing method, it was clarified that the dephosphorization without chromium oxidation and the suppression of temperature drop were able to be achieved simultaneously.

Thermodynamics of sulfur in BaO-CaO-CO2 system

The sulfide and carbonate capacity were measured for the CaO-BaO-CO2 system in the temperature range from 1000 °C to 1350 °C by equilibrating a BaO-based mixture, silver, and a CO-CO2-Ar gas mixture. The BaO-CO2 mixture melted completely in the temperature range from 480 °C to 700 °C in an Ar-CO2 atmosphere, while the CaO-BaO-CO2 mixture was solid at experimental temperature under the conditions used. TheCs2− concept was extended for solid-state mixture, and the sulfide capacity was measured as a function of composition. The maximum value of this system, logCs2− = −0.3 at 1200 °C, was the highest of all of the fluxes reported to date. Experimental results for mol pct BaCO3 againstPCO2 at 1200 °C indicated that the dissolution of carbon dioxide loweredCs2− markedly when the ratio (BaO + BaCO3 + BaS)/ BaCO3 exceeded unity. TheCs2− of this system increased with increasing temperature from 1050 °C to 1200 °C, and a value of above zero was predicted at hot metal pretreatment temperature, which is roughly 1300 °C. A linear relation between logCs2− and logCCO32− with a unit slope was observed.

Multiphase Flows in Ironmaking and Steelmaking Processes

Multiphase flows are very popular in ironmaking and steelmaking processes and are characterized as follows:(1) The temperature of fluids in metallurgical reactors is higher than about 1500°C, hence measurements of transport phenomena (fluid motion, heat and mass transfer) are very difficult.(2) The flow in the reactors is highly turbulent (turbulence components are usually larger than mean flow values) and chemical reactions take place at the same time. Many “cold model” experiments have been carried out due to the difficulty in doing measurements under realistic conditions. Water, oil (silicone oil, pentane, liquid paraffin, etc.) and metals with low melting temperatures (mercury, Wood's metal, etc.) are Used as working fluids. Transport phenomena encountered in ironmaking and steelmaking processes (hot metal pretreatment, converter, second refining processes, etc.) are covered here and previous experimental and theoretical results on this subject are reviewed

Development of Analysis and Control Method for Hot Metal Dephosphorization Process by Computer Simulation.

In order to apply a coupled reaction model to the simulation of industrial scale hot metal pretreatment process, a new computer program of MACSIM (Mathematical Analysis Codes for Slag-metal Reaction and Injection Metallurgy) has been developed. In this program, the reactions by injected flux, slag on bath surface and top blown oxygen gas can be calculated and most of the parameters were determined based on the experimental results of the previous paper. The following phenomena were clarified by this program and the control of the hot metal dephosphorization process became possible.(1) In the case of hot metal pretreatment by torpedo car, about 50% of top blown oxygen gas had the same effectiveness as Fe oxide for dephosphorization reaction. The remaining oxygen contributed to the heat supply through decarburization and post combustion reactions.(2) When [P] concentration before treatment was high, the efficiency of oxygen and that of lime for dephosphorization were high but a clear dependence on temperature was not found.(3) The efficiency of oxygen and that of lime for dephosphorization mainly depended on CaO/O and hot metal composition ([P], [Si]) although dephosphorization treatment time and flux supply rate differed widely.

Influence of additives on sulfide capacity of CaO-CaF2-SiO2 slags

In most Japanese integrated steelmaking plants, hot metal pretreatment is a common practice, because the combination of the pretreatment with the combined blowing converter minimized the production cost of high-quality steel. The CaO-CaF{sub 2}-SiO{sub 2} system containing low SiO{sub 2} is an excellent slag for desulfurization, as reported elsewhere. In the actual hot metal pretreatment, the oxides, such as alumina, magnesia, and manganese oxide, are inevitable because of the erosion of refractory or residues in previous processes. Sometimes even additions of such oxides are made in the pretreatment. Therefore, it is of practical importance to know how these additives or contaminants affect the desulfurization capacity of slags. In the paper, the influences of Na{sub 2}O, Al{sub 2}O{sub 3}, MgO, and MnO on the sulfide capacity of CaO-CaF{sub 2}-SiO{sub 2} slags were studied. The addition of Na{sub 2}O was also investigated to understand how it enhanced the sulfide capacity. Emphasis was given to slags of CaO-saturated composition, not only because they have the highest sulfide capacity but also because of the presence of excess CaO in the commercial slags.

Development of silicon sensor for hot metal using thermal electromotive force method

In the iron making process, development is being made on rapid measurement technology of the chemical component in hot metal to better control it. With the ongoing progress of hot metal pretreatment, there have been growing needs of the rapid measuring technology of Si content in hot metal. The authors have developed a disposable Si sensor utilizing EMF method, to be directly immersed into hot metal. The Si sensor was applied to measurement at BF runners and a torpedo car, and the results demonstrated its high performance.

2基の複合吹錬転炉を用いる溶銑予備処理,本吹錬による高効率精錬法の開発

2基の複合吹錬転炉を用いる溶銑予備処理,本吹錬による高効率精錬法の開発

底吹き転炉の精錬機能の拡大

Hot metal pretreatment system has recently established applicable to virtually all hot metal produced in Chiba Works. Several developments have been made for establishing an optimum and cost-efficient Q-BOP operations with dephosphorized metal. The main features of the developments are as follows : 1) Final dephosphorization in Q-BOP is possible by non slag-off blowing method with the use of only a slight amount of dolomite used for coating. By this method, reduction of lime consumption in Q-BOP is achieved. 2) By lowering oxygen flow rate at the final stage of blowing, excess oxidation of steel melt is prevented. Figures of ( T. Fe) in slag and [O] in steel at tapping are lowered by 4% and 100 ppm, respectively. 3) Newly introduced post combustion lance is effective for heat compensation and mouth skull melting. 4) Tapping temperature is successfully decreased by 26°C in manufacturing process of ultra low carbon steel with the aid of the development of KTB, the technology of oxygen blowing through top lance in the vacuum vessel. This technology is effective not only for heat compensation during RH treatment but also for enhancing a decarburization rate in higher carbon region.

高級鋼管および薄板における高純度鋼製造技術

Following purification technology for line pipes or cold sheets has been developed and put to practical use in some works of Nippon Steel Corporation. (1) Synthetic refining system of hot metal pretreatment, top and bottom blowing converter and multi-functional secondary refining, namely ladle injection under reduced pressure (V-KIP), flux injection during RH treatment (RH-Injection, RH-PB) are successfully in operation. Consequently final product of [P] ≤ 50 ppm, [S] ≤ 10 ppm and [H] ≤ 1.5 ppm can be stably produced. (2)Ar injection into RH vacuum vessel or DH snorkel and vacuum vessel drastically improved decarburization rate of ultra low carbon level.Technology of nitrogen removal during top and bottom blowing in converter and protection of molten steel from nitrogen adsorption between the end point of converter and casting have been operated. Consequently final product of [C] _??_ 10 ppm, [N] _??_ 10 ppm can be produced.

溶銑予備処理を用いた効率的な量産製鋼プロセスの確立

溶銑予備処理を用いた効率的な量産製鋼プロセスの確立

Industrial studies on hot metal pretreatment in France

Industrial studies on hot metal pretreatment in France

溶銑予備処理と溶融還元を用いた新製鋼プロセスの工業化

溶銑予備処理と溶融還元を用いた新製鋼プロセスの工業化

珪酸ソーダスラグからのNaおよびSの蒸発

In relation to hot metal pretreatment by soda ash, the vaporization of Na and S from sodium silicate slags has been investigated. At temperatures between 1623 and 1773 K, the slag was melted in a graphite crucible under an atmosphere of argon. The amount of Na and S generated was determined by thermogravimetry and chemical analysis.The rate of Na vaporization from Na2O-SiO2 slag is approximately represented by the first-order-type rate equation. The rate constant increases with increasing slag basicity, i.e. the (%Na2O)/(%SiO2) ratio, and the activation energy varies from 230 to 250 kJ/mol. It is considered that the vaporization would be controlled by the chemical process.Both Na and S evaporate from Na2O-SiO2 slags containing Na2S. Particularly in the acid slag, the most of the mass loss measured is due to the vaporization of Na2S. The vaporization of S is retarded by an increase in the slag basicity, but the reduction of Na2O at an early stage is accelerated by the addition of Na2S to the high basic slag.