Hot Metal Desulfurization Research Articles

Strategies for Development of Process Control Models for Hot Metal Desulfurization: Conventional and AI Techniques

Process control models can be developed by using both conventional and AI approaches. The conventional approaches include regression models and process kinetic models, and the artificial intelligence (AI) approaches are based on artificial neural nets (ANN), genetic algorithm (GA), and fuzzy rule-based expert systems FRBES. Plant data on hot metal desulfurization, carried out by injecting calcium carbide, is analyzed to test and tune different types and combinations of models and then evaluate their relative performance. Although the control models based on process fundamentals provide a fillip to the new ideas for technological developments and improvements, the combination of conventional and AI approaches may be a better option for process control on the shop floor. It is advisable to first develop and test all models and then decide about the best strategy of using them.

CaO-Al<SUB>2</SUB>O<SUB>3</SUB>系フラックスによる溶銑脱硫効率に及ぼすフラックス組成の影響

CaO-Al<SUB>2</SUB>O<SUB>3</SUB>系フラックスによる溶銑脱硫効率に及ぼすフラックス組成の影響

Pelletizing steel mill desulfurization slag

Hot metal desulfurization slag is a high-metallic iron content slag produced at a typical steelmaking facility and is currently considered waste. Each year, 50,000 tons of this slag is produced at one particular steelmaking plant. This material can be beneficiated so that it can be utilized as blast furnace feed, but it is necessary to first develop a process for agglomerating it into pellets. A beneficiated slag concentrate was both conventional bentonite binder and a new fly ash-based binder (FBB) that was formulated by the investigators. The FBB used a high-carbon fly ash that is currently landfilled as waste. In addition to fly ash, FBB contained calcium hydroxide as an activator that also acts as flux known to improve the pellet's reducibility characteristics. The desulfurization slag concentrate pellets bonded with the FBB had superior dry compressive strengths compared to the bentonite-bonded pellets.

CFD, a design tool for a new hot metal desulfurization technology

This paper considers CFD modelling of desulfurization carried out in a large vessel containing hot metal covered by a thick synthetic slag layer. During nitrogen stirring sulfur transfers to the slag. Sulfur ions in the slag have to be removed by oxidation (O 2 lance) to restore slag desulfurization capability. The macroscopic metallurgical reactions occurring during hot metal desulfurization and slag regeneration are studied by kinetic laws for permanent and transient phase contact. Mechanical metal–slag interactions are calculated by shear stress considerations for stratified flows. The position of the phase interface and the slag surface is obtained by an adaptive grid algorithm. Flow initiation by rising gas bubbles is simulated by means of an algebraic drift flux model. As a result of these simulations the fully three-dimensional flow- and temperature fields in the slag and metal phase are obtained. Furthermore the variation of the time-dependent concentration fields of the main reactants can be observed.

マグネシウムを用いた溶銑脱硫におよぼす加圧の効果と反応機構

マグネシウムを用いた溶銑脱硫におよぼす加圧の効果と反応機構

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.

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.

Effect of FeO in the slag and silicon in the metal on the desulfurization of hot metal

Work has been conducted to investigate the effects of FeO in the slag and silicon in the metal on hot metal desulfurization. Laboratory experimental results show that FeO decreases and silicon increases the rate of desulfurization. Silicon in the metal is consumed by the reduction of FeO and also by the desulfurization reaction. A mathematical kinetic model was developed to describe both the effects of silicon and FeO on desulfurization for the laboratory scale. The model predicts the sulfur and silicon content in the metal and the FeO and sulfur content in the slag as a function of time. It is based on four-component simultaneous mass transfer: sulfur and silicon in the metal and FeO and sulfur in the slag. Experimental results, the development of the kinetic model, and a comparison of the model and experimental results are presented.

Na<SUB>2</SUB>O-CaO系フラックスによる溶銑の脱硫速度

Na<SUB>2</SUB>O-CaO系フラックスによる溶銑の脱硫速度

On the hot metal desulfurization

Although there is no thermodynamic limitation to the desulfurization of carbon‐saturated iron with CaO, the process is well‐known to be slow. Consequently, the desulfurization of carbon‐saturated Fe‐S, Fe‐S‐Si, Fe‐S‐Si‐Al, Fe‐S‐Zr alloys by CaO, and Fe‐S‐Si alloys by CaO‐10 % CaF2 were investigated to determine the reaction mechanism. For this purpose, dense CaO and CaO‐10 % CaF2 discs were cemented to the bottoms of graphite crucibles containing the carbon saturated alloys. The desulfurization experiments were run at 1450°C in an SiC resistance furnace under argon gas atmosphere. The results indicate that the desulfurization of hot metal by CaO is greatly improved by prior addition of aluminum to the hot metal. The addition of 10 % CaF2 to CaO also increases the rate of desulfurization. Zirconium, which has a stronger affinity for oxygen than aluminum did not increase the rate. SEM and X‐ray diffraction studies on the surfaces of CaO discs used to desulfurize carbon‐saturated Fe‐S, and Fe‐S‐Si alloys showed that solid CaS, and solid CaS plus small amount of solid 2 CaO · SiO2 compounds form on the lime surface, respectively. The slow reaction rate with CaO is attributed to the solid reaction products which block the reaction by preventing the occurrence of interfacial turbulence.

The Kinetics of Desulfurization of Hot Metal by CaO-CaF2 Based Fluxes.

A kinetic model, which considers the effect of transitory reaction and permanent-contact reaction on sulfur removal rate, as in the case of using CaO-CaF2 based fluxes powder injection to desulfurize hot metal containing vanadium of 0.34% and sulfur content of 0.08% is developed in the present work. Some important factors affecting kinetics of desulfurization, such as the transitory reaction parameter E, rate constant for permanent contact reaction K, can be determined by means of experimental and industrial practice results, respectively. The influence of E and K on sulfur content in hot metal is discussed. The model will be available for predicting the variation of sulfur content in hot metal and will contribute to control automatically for the desulfurization process.

Desulfurization of Hot Metal by Lime Impregnated with Carbon

Desulfurization of Hot Metal by Lime Impregnated with Carbon

Dephosphorization and desulfurization of hot metal by CaO based fluxes containing Fe-oxide and Mn-oxide as oxidant.

Experiments on hot metal dephosphorization by using the mixtures of Fe-oxide and Mn-oxide as oxidant were achieved by the use of Tammann furnace. The results were analyzed by the coupled reaction model which consisted of mass transfer equations of each component. Among many unknown parameters in the model, the effective equilibrium constants of P, Mn and S and the mass transfer coefficient in slag phase were changed by the experimental condition and determined by fitting to the experimental result. The observed distribution ratio of P, S and Mn was consistent with the calculated value for each experiment and the applicability of the coupled reaction model was proved.(1) When a mixture of Fe-oxide and Mn-oxide was used as oxidant, as the ratio of FeO to the total content of Fe-oxide and Mn-oxide in flux decreased, the effective equilibrium constants of P and S and the mass transfer coefficient in slag decreased and the effective equilibrium constant of Mn increased. This result indicated that the degree of dephosphorization, desulfurization, Mn recovery and the reaction rate of these reactions increased as the increase of Fe-oxide ratio in flux.(2) The addition of CaF2 and CaCl2 did not significantly change the effective equilibrium constants but modified the mass transfer coefficient in slag. Together with the result of temperature dependence, the necessary amount of CaF2 to obtain the equivalent reaction rate for each temperature was clarified.(3) The activity coefficients of FeO, P2O5 and MnO converted from the effective equilibrium constants were compared with those values calculated by the thermodynamic models. However satisfactory agreements were not obtained especially for γMnO.

CaCO<SUB>3</SUB> 系脱硫剤による極低硫溶銑の製造と脱硫反応機構

Hot metal desulfurization by injecting CaCO3 base flux into a torpedo car has been studied.The desulfurization efficiency for CaCO3 base flux has been found to be higher than that for CaO base flux. This is attributed to the increase of the reaction interface area due to the thermal decomposition of the injected CaCO3 particles. The rate determining step of the desulfurization reaction in this process is liquid-phase mass transfer when the sulfur content is less than 0.013%, and mass transfer in solid particles when the sulfur content is more than 0.013%.It has also been revealed that the endothermic effect of the thermal decomposition of CaCO3 is compensated by the exothermic effect of the desiliconization reaction by CO2 gas, a product of CaCO3 decomposition, and therefore does not result in larger temperature decrease of the hot metal compared with CaO base flux.

石灰系フラックス吹き込みによる溶銑の同時脱りん脱硫処理に及ぼす酸素ポテンシャルの影響

石灰系フラックス吹き込みによる溶銑の同時脱りん脱硫処理に及ぼす酸素ポテンシャルの影響

石灰系フラックスインジェクション・酸素上吹き法による溶銑の脱りん及び脱硫

石灰系フラックスインジェクション・酸素上吹き法による溶銑の脱りん及び脱硫

Sulfur solubility in iron-carbon melts coexistent with solid CaO and CaS.

Experimental data are presented for the solubility of sulfur in liquid Fe-C alloys coexistent with solid calcium oxide, calcium sulfide and carbon monoxide of known pressures at 1 600°C. The equilibrium constant is determined for the sulfur reaction in terms of the activities of sulfur and carbon in iron for composition ranges 0.005 to 0.4% S and up to 3% C. The extrapolation of the data to hot metal compositions predicts for unit activities of calcium oxide, calcium sulfide and carbon monoxide, the equilibrium sulfur content of 4ppm for 1 600°C and 8ppm for 1 400°C. In relation to ladle desulfurization of hot metal, selected data are presented on some slag-metal reaction equilibria.

Dephosphorization and Desulfurization of Molten Pig Iron by Na2CO3

Dephosphorization and desulfurization of hot metal by adding Na2CO3 was studied experimentally. The results obtained are as follows:(1)The dephosphorization ratio was improved with lower temperature of hot metal, lower Si content and greater quantity of Na2CO3 added.(2) The desulfurization ratio was slightly improved with lower temperature of hot metal. No effect on the ratio was observed with variations in the Si content and quantity of Na2CO3 added.(3) Though the dephosphorization was attained in 3-6min after addition of Na2CO3 under high Si content, rephosphorization was observed subsequently.(4) The gas given off after addition of Na2CO3 was CO. The dust mainly consisted of Na2CO3.(5) The main interactions between Na2CO3 and molten pig iron are assumed to be as follows:(a) Volatilization of Na2CO3(Na2CO3)=Na2CO3(g)(b) Reduction by C(Na2CO3)+C=(Na2O)+2CO(g)(c) Desiliconization(Na2CO3)+Si=(Na2O•SiO2)+C(d) Dephosphorization5(Na2CO3)+4P=5(Na2O)+2(P2O5)+5C(e) Rephosphorization5(Na2O)+2(P2O5)+5Si=5(Na2O•SiO2)+4P

Desulfurization of Hot Metal in an Open Ladle Stirred by an Impeller Modified by Gas Injection

Desulfurization of Hot Metal in an Open Ladle Stirred by an Impeller Modified by Gas Injection

Production experiences with Mo-Nb line pipe steels

Steelmakers are melting high-quality line pipe grades in conventional, high-volume production facilities. The basic oxygen furnace has become the mainstay for high-quality pipe production, but electric furnaces and open-hearth facilities are still utilized. To meet the requirements of high toughness at low temperature, oxygen lancing to reduce carbon content below 0.12% is also commonly employed in the electric and open-hearth furnaces. Hot-metal desulfurization (0.010% S or less) and / or inclusion shape control techniques are employed to enhance transverse ductility and notch toughness. The low-carbon Mo-Nb and Mo-Nb (V) steels are compatible with these new steelmaking, deoxidation and casting practices offering an economical approach to higherstrenth, tough steels needed for the production of heavy wall thickness A rctic and offshore submarine pipelines. The Battelle DWTT and Charpy results demonstrate the high toughness capability of these steels at temperatures of -40°C and below. Approximately 0.5 million metric tons of molybdenum-containing line pipe have been supplied, and this quantity is expected to double in 1976. Continuing production in North America, especially in Canada, and in Western Europe, especially in Italy, coupled with the production of several hundred thousand tons of Arcticquality, 1420-mm-diameter pipe by the Japanese mills will account for this high tonnage. The Mo-Nb/Mo-Nb (V) steel technology is playing an important role in Arctic and offshore, submarine pipelining throughout the world.