Modelling of mixing,mass transfer and phase distribution in a Peirce–Smith converter model

Abstract

This study presents a numerical and physical modelling study of flow pattern, mixing, solid–liquid mass transfer and slag matte phase distribution in an industrial Peirce–Smith converter (PSC) slice model. The two-dimensional (2D) and three-dimensional (3D) numerical simulations of the three phase system were carried out using volume of fluid (VOF) and realisable k?? (RKE) turbulence model to account for the multiphase and turbulence nature of the flow respectively. These models were implemented using the commercial computational fluid dynamics (CFD) numerical code FLUENT. In physical simulations, water, kerosene, air and sintered benzoic acid compacts were used to simulate matte, slag, injected gas and solid additions into PSC. Both numerical and physical simulations were able to predict, in agreement, the mixing and dispersion characteristics of the system in relation to different blowing conditions employed in this study. Measurement of dimensionless turbulence characteristic values conclusively indicated that fluid flow in PSC is stratified.

Ce document présente une étude de modélisation numérique et physique de la configuration de l’écoulement, du mélangeage, du transfert de masse solide-liquide et de la distribution de phase scorie-matte dans un modèle en tranches de convertisseur industriel Peirce–Smith (PSC). On a effectué les simulations numériques 2D et 3D du système à trois phases en utilisant le modèle du Volume de Fluide (VOF) et de la turbulence réalisable (RKE) pour tenir compte des phases multiples et de la nature turbulente de l’écoulement, respectivement. On a exécuté ces modèles en utilisant le code numérique commercial de la dynamique numérique des fluides (CFD) FLUENT. Dans les simulations physiques, on a utilisé de l’eau, du kérosène, de l’air et des compacts frittés d’acide benzoïque pour la simulation de la matte, de la scorie, du gaz d’injection et des additions de solide dans le PSC. Les simulations numériques et physiques étaient toutes deux capables de prédire, en accord, les caractéristiques de mélangeage et de dispersion du système en relation avec les différentes conditions de soufflage utilisées dans cette étude. La mesure des valeurs caractéristiques sans dimension de la turbulence indiquait décisivement que l’écoulement du fluide dans le PSC était stratifié.     

Determinants of right–left and top–bottom prevalence for two-dimensional spatial compatibility.

When stimulus and response sets vary along horizontal and vertical dimensions, the horizontal dimension is more dominant than the vertical one, an effect called right–left prevalence. Three accounts have been proposed that attribute the effect to a reduced ability to code vertical locations when horizontal codes are also present, the use of right–left effectors, or a difference in salience of the 2 dimensions. The accounts differ in terms of whether the ability to code and process the 2 dimensions is of limited capacity and whether the prevalence effect is a consequence of the effectors used for responding. The authors report 4 experiments that evaluated these issues. Results indicate that use of right–left effectors is important to the right–left prevalence effect because it increases the salience of the horizontal dimension. However, a top–bottom prevalence effect can be obtained if the vertical dimension is made more salient. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigation of mixing and slag layer behaviours in the RH degasser with bottom gas injection by using the VOF–DPM coupled model

The mixing time of molten steel has a decisive impact on the refining efficiency during the RH (Rheinsahl–Heraeus) degassing process. In the present work, a coupled volume of fluid method?discrete phase model has been developed to investigate the effect of bottom injection on mixing and slag layer behaviours in the RH degasser. The fluid flow, mixing characteristic, and the formation of slag eye in the RH degasser with bottom injection are well revealed. Numerical results show that X?=??0.75?m (under the up-snorkel) is the optimal injection location to obtain a shortest mixing time, as well as avoid the formation of slag eye in the RH degasser. At the same time, the result of industrial trial shows that the decarburisation efficiency can be accelerated remarkably when the bottom injection is located at X?=??0.75?m.     

Modelling inclusion evolution in Al–Ti-killed steels during ladle mixing process

A reaction model was developed to better understand the evolution of inclusions in Al–Ti-killed steels during the ladle mixing process. The fluctuation of steel chemistry gave rise to the transient evolution of inclusions during the mixing process. The formed Al₂O₃ in the steel can be hardly influenced by the addition of FeTi, while adding Al can effectively modify the TiO_x-containing oxides to solid Al₂O₃. The formation of Al₂O₃–TiO_x inclusions can be suppressed by increasing Al and lowering Ti in the steel. The alloying sequence of adding Ti after the Al addition is beneficial to improve the recovery of Ti. The one-point strong air absorption may cause the formation of the unwanted Al₂O₃–TiO_x inclusions in Al–Ti-killed steels. The critical oxygen contents in the molten steel with varying Al and Ti concentrations were predicted to avoid the formation of Al₂O₃–TiO_x inclusions and Ti loss.     

Phase transformation behaviour in two C–Mn–Si based steels under different cooling rates

Abstract

The continuous cooling transformation (CCT) behaviour of two C–Mn–Si based steels was investigated. The effects of chemical composition and cooling rate on γ→α transformation were studied using dilatometric measurements. Quantitative phase analysis was carried out in order to determine the effect of cooling rate on the precise phase distribution after transformation. Presence of Cr and Mo in the experimental steels appears to retard pearlitic transformation and promotes formation of acicular products (combination of acicular ferrite, Widmanstatten ferrite and bainite). Martensitic transformation also starts at a perceptibly lower cooling rate in the Mo containing alloy as compared with the one without any Mo.     

Dissolution behaviour of MgO based refractories in CaO–Al2O3–SiO2 slag

Abstract

Magnesium oxide (MgO) based refractories are widely used in secondary refining processes, and their dissolution into refining slag is the primary cause of their shortened lifespan. The dissolution rate was investigated for sintered MgO and commercial MgO–C and MgO–Cr₂O₃ refractories in a synthesised 50CaO–45Al₂O₃–5SiO₂ liquid (mass-%) slag. The change in slag composition was measured after a refractory sample was placed into the molten slag that was stirred by flowing argon gas at 1773?K. The dissolution rate of the sintered MgO was above those of the MgO–C and MgO–Cr₂O₃ refractories under the same gas flowrate, although the dissolution rate of all samples increased as the gas flowrate was increased from 25 to 75?mL·min^??1. The slag containing 5?mass-% FeO considerably promoted the dissolution of the MgO–C refractory because of the oxidation of carbon by FeO. The dissolution of all the refractories was greatly affected by penetration of the liquid slag, with the mass transfer of MgO in the penetrating slag at lower gas flowrates likely being the rate controlling step. At high gas flowrates, Ar bubbles covered the surface and blocked the contact between the liquid slag and the solid phase, reducing the dissolution rate.     

Smelting reduction reactions by solid carbon using induction furnace: foaming behaviour and kinetics of FeO reduction in CaO–SiO2–FeO slag

Abstract

Smelting reduction process technology is progressing rapidly, and research to understand the reduction of FeO in molten slag and the associated foaming behaviour has gained importance. The present paper reports experimental data on the reduction of FeO in molten slag generated in a 30 kW capacity induction furnace. The influence of FeO content in the slag and temperature on the foaming and kinetics is discussed. The foaming index, a parameter describing the travel time of gas in the reactor, is shown to decrease with an increase in the superficial gas velocity. The quantitative dependence of the foaming index on slag properties viscosity, surface tension and density has been studied. The data have also been analysed to give an estimation of the activation energy for the reduction reaction. The reduction reaction, initiated by direct slag–graphite contact, produces CO gas, which spreads into the molten slag bath causing foaming of the slag; further reduction of FeO proceeds mostly via indirect reduction. The rate of reduction is found to depend directly on the initial FeO content. An increase in temperature increases the rate of reduction, which has an activation energy of 118 kJ mol^?1 of FeO. The results indicate that transport of FeO in the liquid phase is the rate controlling step. The major findings are in agreement with those reported by earlier investigators.     

Effect of CaO on the reduction behaviour of iron ore–coal composite pellets in multi-layer bed rotary hearth furnace

The effect of CaO on the reduction behaviour of iron ore–coal composite pellets has been studied in a laboratory scale multi-layer bed rotary hearth furnace at 1250°C for 20?min. Reduced pellets have been characterised through weight loss, porosity measurement, phase analysis by XRD, and morphology study by SEM. The addition of CaO to the composite pellets showed different effects at different carbon levels. For higher carbon-containing pellets (C/Fe₂O₃ molar ratio at the upper stoichiometric level of 3), the addition of CaO increased the extent of reduction for all three layers significantly up to a certain limit (4?wt-%); and thereafter the degree of reduction is decreased with a further increase in CaO percentage in the pellets. For low carbon-containing pellets (C/Fe₂O₃ molar ratio of 1.66), the addition of CaO to the pellets did not show any beneficial effect.