Sabita Sarkar

Purging of argon gas in the molten metal bath is a process that is regularly involved in secondary steel making operations. The injected gas imparts momentum to the liquid metal, which induces high turbulence in the molten metal and helps in homogenization of the bath composition and temperature, and facilitates the slag metal interactions. In this study, a computational fluid dynamics (CFD) based numerical investigation is carried out on an argon gas stirred ladle to study the flow and interface behavior in a secondary steel making ladle. A transient, three phase coupled level-set volume of fluid (CLSVOF) model is employed to track the slag-metal, gas-metal and slag-gas interfaces. The transient behavior of slag layer deformation and open eye formation is studied for different slag layer to metal bath height ratios at various argon gas flow rates.

The present work proposes a hybrid drag model by combining homogeneous Ergun correlation and heterogeneous bubble-based drag formulation. The predictions of bubble size, bubble fraction, bed expansion ratio, particulate fluidized area fraction, and solid volume fraction in a 2D gas-solid tapered fluidized bed using the hybrid, Gidaspow, and Energy Minimization Multi-Scale (EMMS) drag models have been compared with the experimental results. The hybrid drag model predicts these parameters closer to the experimental findings. A heterogeneous flow structure has been observed in simulations similar to experiments for the tapered fluidized bed. The bed shows larger solid volume fraction values near its periphery compared to its center. The solid particles show a central-upward and peripheral-downward flow pattern in the tapered fluidized bed.

The hydrodynamics of tapered fluidized beds is significantly different from the columnar beds due to the variation of the cross-sectional area along the height. The hydrodynamic behavior in tapered beds was studied experimentally using an image analysis method. The peripheral unfluidized region was quantified through the overlapping of binary images. Further, the effect of the taper angle and air velocity on the bubble size, shape, fraction, and rise velocity, along with the bed expansion ratio and the unfluidized region, was investigated. A new method is proposed to obtain expanded bed height from an image. The time-averaged bed expansion ratio and bubble fraction increase with the air velocity and decrease with the taper angle, while a reverse trend is observed for the mean unfluidized area fraction. Correlations are proposed for predicting the bubble fraction, bed expansion ratio, and unfluidized area fraction. An operating regime map is also proposed based on the unfluidized region.

The morphological and hydrodynamic behavior of bubbles in air–water plumes was studied by employing Particle Tracking Velocimetry (PTV) techniques. Individual bubbles were identified by analyzing the instantaneous high-speed camera images of the plume. The bubble velocities were then obtained by Lagrangian tracking of each bubble, based on its size and location. The nature of bubble coalescence and breakup was also investigated based on the change in the projected area of the parent and daughter bubbles. The effect of the bubble position and the air inflow rate on the bubble properties like diameter, aspect ratio, velocity, number flux, etc., and on the coalescence and breakup behavior was investigated. A novel correlation is proposed to estimate the bubble aspect ratio as a function of bubble Reynolds number and Eotvos number, for a wide range of flow conditions, and is compared with existing correlation from the literature.

Argon gas is injected into steelmaking ladles during secondary steelmaking operations, which enhances the rate of heat and mass transfer in the melt. The ladle hydrodynamics also leads to slag eye formation and wall shear stresses, which are detrimental to the steel’s quality. In the present study, a mathematical model is formulated to predict the mixing time, slag opening area, and wall shear stress in single and dual bottom purged industrial steelmaking ladles. Dimensionless empirical correlations have also been proposed to estimate the same. Further, a genetic algorithm-based multi-objective optimization problem has been framed to minimize the objective functions, viz., mixing time, slag opening area, and the wall shear stress. A Pareto optimal solution set, comprising simultaneous optimal solutions, was obtained due to the opposing nature of the objective functions. The desirable process conditions for the optimal performance of the ladle were also identified.

This article deals with the concept of scaling -up and scaling -down of industrial processes which is an essential requirement to understand and optimize the process. The concept has been described based on physical modeling of the process at laboratory scale using various techniques. The concept of physical modeling has been followed by two industrial examples where it has been used successfully. First example deals about scaling down of an industrial process to a laboratory scale to understand the raceway formation phenomena in an iron making blast furnace. In second example development of a new process for Mo addition in EAF practice is described. The development starts from theoretical backgrounds for the process of Mo addition improvements and then follows with number of experimental trials starting from 16g laboratory scale furnace to 70 ton industrial EAF. © 2014 Elsevier Ltd. All rights reserved.

Rotary disc atomization is a process in which a liquid jet continuously impinges on a rotating disc, which then spreads over its surface to form a film. This liquid film leaves the disc tangentially and breaks up to form ligaments and/or droplets. Variation of the droplet size with film thickness is very important for droplet size prediction. In the present work, a steady state, three dimensional and two phase CFD model is used to simulate this process and to obtain the liquid film thickness. The effect of different parameters like inlet flow rate, disc rotational speed, etc. on the thickness of the liquid film is studied using dimensional analysis. A correlation is developed for obtaining the liquid film thickness at the disc edge using linear least square analysis. Further correlation is obtained, using which the droplet size is predicted from the film thickness at varying operating parameters.

Blast furnace slag is a high-value by-product of the iron and steel industry. It leaves the plant at a very high temperature and possesses a large quantity of high-grade energy. One of the promising methods to extract this energy is dry slag granulation. In this study, the effectiveness of dry slag granulation was studied using a mixture of rosin and paraffin wax as an analogue for blast furnace slag. The effects of various parameters such as rotational speed of the disc, diameter of the disc and flow rate of the molten liquid have been studied. Different ranges of operating conditions in terms of non-dimensional numbers for fiber formation and particle formation were determined. This helps us determine the operating conditions under which particle formation is ensured. The study shows that with an increase in the rotational speed or disc diameter the average particle diameter decreases whereas with an increase in the flow rate the average particle diameter increases. The design of a granulation unit for a commercial plant utilizing the data from lab scale experiments is discussed.

The rise of particle–laden bubbles is a common phenomenon in many metallurgical refining processes as well as flotation processes. During its rise, it undergoes path oscillation, which is greatly affected by the mass of particles that are attached to the bubble surface. The experimental investigation was carried out to investigate the effect of coated particle fraction on the bubble, which is on the rise in a quiescent liquid medium. During the experiments, low-density polyethylene particles are coated on a bubble surface in water, which is generally used to mimic the steel in a cold model. The images (one mirror and direct image) of the particle–laden bubble were captured for all positions on its rising path. Further, these images were processed in MATLAB®. The effect of the different fraction of particle coatings such as 10% and 50% on the rising bubble was studied. It is found that the coating fraction has a considerable effect on the path of a rising bubble, which has been characterized by the phase shift of the oscillating path of a rising bubble.

Dual gas purging is often done in a ladle to accelerate the refining operations in steel industries. The purged gas, mainly argon imparts momentum to the molten metal and establishes a turbulent recirculating flow in the melt, which generates shear stresses on the ladle walls. These stresses in-turn leads to the erosion of the refractory lining, which is undesirable. A three dimensional, transient, multi-phase turbulent model has been developed to predict the shear stress distribution along the wall in dual plug, bottom purged ladles. A parametric study has been performed to understand the dependence of wall stresses on various operating parameters like argon flow rate, metal bath depth, slag thickness as well as on the configuration of the gas injectors. A dimensionless correlation is proposed using regression analysis that predicts the maximum wall stress in the form of skin friction coefficient in terms of the above parameters.