A. K. Lahiri

Studies on the reduction of hematite by carbon

Single pellet experiments have been carried out in a nitrogen atmosphere to study the reduction of hematite by graphite in the temperature range 925 to 1060°C. The effect of variables such as c/Fe2O3 molar ratio, pellet size, and so forth, has been investigated. Gas analysis data show a continuous decrease in CO2/CO ratio during reduction, the values being far away from Fe/FeO equilibrium for wustite reduction by CO. The activation energies associated with different degrees of reduction appear to be widely different suggesting a possible changeover in reaction mechanism during the progress of reduction. X-ray diffraction studies confirm the stepwise nature of hematite reduction.

A water model study of the flow asymmetry inside a continuous slab casting mold

The work studies the extent of asymmetric flow in water models of continuous casting molds of two different configurations. In the molds where fluid is discharged through multiple holes at the bottom, the flow pattern in the lower portion depends on the size of the lower two recirculating domains. If they reach the mold bottom, the flow pattern in the lower portion is symmetrical about the central plane; otherwise, it is asymmetrical. On the other hand, in the molds where the fluid is discharged through the entire mold cross section, the flow pattern is always asymmetrical if the aspect ratio is 1:6.25 or more. The fluid jet swirls while emerging through the nozzle. The interaction of the swirling jets with the wide sidewalls of the mold gives rise to asymmetrical flow inside the mold. In the molds with lower aspect ratios, where the jets do not touch the wide side walls, the flow pattern is symmetrical about the central plane.

Water-modeling study of the surface disturbances in continuous slab caster

The present work is based on four static molds using nozzles of different port diameter, port angle, and immersion depth. It has been observed that the meniscus is wavy. The wave amplitude shows a parabolic variation with the nozzle exit velocity. The dimensionless amplitude is found to vary linearly with the Froude number. Vortex formation and bubble entrainment by the wave occurs at the meniscus beyond a critical flow rate, depending upon the nozzle configuration, immersion depth, and the mold aspect ratio.

Sulfide capacity of high alumina blast furnace slags

Sulfide capacities of high alumina blast furnace slags were experimentally determined using the gas-slag equilibration technique. Two different slag systems were considered for the current study, namely, CaO-SiO2-MgO-Al2O3 quaternary and CaO-SiO2-MgO-Al2O3-TiO2 quinary system. The liquid slag was equilibrated with the Ar-CO-CO2-SO2 gas mixture. Experiments were conducted in the temperature range of 1773 to 1873 K. The effects of temperature, basicity, and the MgO and TiO2 contents of slags on sulfide capacity were studied. As expected, sulfide capacity was found to increase with the increase in temperature and basicity. At the higher experimental temperature, titania decreases the sulfide capacity of slag. However, at the lower temperature, there was no significant effect of titania on the sulfide capacity of slag. Sulfide capacity increases with the increase in MgO content of slag if the MgO content is more than 5 pct.

Estimation of viscosity for blast furnace type slags

Abstract A viscosity model based on a new definition of basicity has been proposed for blast furnace type slags. Conceptually, this definition of basicity is close to Bells definition of basicity as used for modelling of sulphide capacity of blast furnace type slags. The model developed in the present work is applicable for wide range of alumina, magnesia and titania containing blast furnace slags, while most of the models available in the literature are mainly applicable for a limited range of slag composition. Viscosity estimation by this model is close to the experimental value for all types of blast furnace slags. This model is based on the chemical composition of slag and is applicable for slags above liquidus temperature.

Cold model study of the surface profile in a continuous slab casting mold: Effect of second phase

Most of the water modeling workV-TJ carried out so far has simulated only the flow of liquid steel, without any slag phase. But, in the actual system, a flux layer is used to cover the meniscus. Only a few investigators have made an attempt to simulate the slag phase over the metal. Sobolewski and HurtuktSl used cork pieces in their water model to simulate the slag entrainment in the melt. Tanaka et al. [91 made water modeling studies using oils as the second phase. They studied the vortex depth formed at the oilwater interface. The present work aims to characterize the complete meniscus profile in the presence of a second phase. The dimensional analysis shows that to simulate the flow of slag and metal, the model liquids should satisfy the following conditions:

Cold model study of raceway under mixed particle conditions

Abstract The raceway phenomenon has been studied using mixed particle systems in a two-dimensional cold model. No study is available in the existing literature for the raceway under the mixed particle conditions that prevail in operating blast furnaces. Two types of material, quartz and polypropylene, in different shapes and sizes have been considered. These particles are mixed in various proportions to study the effect of mixed particles on void and raceway formation and raceway breaking. The effects of particle diameter, density, and gas flowrate have been studied. The results obtained from the mixed particles have been compared with the results obtained from particles of uniform size. Experiments have been carried out using models made of glass and Perspex in order to study the effect of fabricating materials on the results. Some interesting results have been obtained in the study and are reported here. Correlations have been proposed to predict void and raceway formation, raceway growth, and raceway breaking under mixed particle conditions.

On the mechanism of iron oxide reduction by carbon

A theoretical analysis has been made to determine the conditions under which the reduction of iron oxide by carbon takes place according to the 2 step mechanism involving the Boudouard reaction. This is based on the concept of minimum temperature of reduction (Tmin) below which the Boudouard reaction does not affect the reduction process. The effect of variables such as carbon reactivity, total pressure and so forth onTmin has been studied. TheTmin can be used to determine if metallization is possible under a given set of conditions.

Contraction and meltdown behaviour of olivine iron ore pellets under simulated blast furnace conditions

In the present study the contraction behaviour of the olivine iron ore pellet MPBO during reduction under load has been investigated. Three different programmes of reducing conditions have been used, corresponding to three different radial positions of the blast furnace. The reducing programmes have included different temperature profiles, reducing atmospheres, and mechanical loads applied to the specimen bed. The results of reduction under load experiments have shown that contraction has roughly three different stages: initial expansion, followed by contraction at a certain rate, and eventually a third stage with contraction at a higher rate. The process of contraction is comprehensively discussed. The influence of the different reducing conditions is outlined.

Applicability of central atoms models to binary silicate and aluminate melts

A central atoms model is presented which reproduces the phase diagram and the activities in silicate and aluminate melts. A four energy parameter model is required for this purpose. An empirical relationship is proposed which reduces the number of energy parameters to three.