Gas-stirred Systems Research Articles

Effects of Interphase Forces on Fluid Flow in Gas-Stirred Steel Ladles Using the Eulerian–Lagrangian Multiphase Approach

The multiphase fluid flow in a gas-stirred system for steelmaking ladles is simulated using an Eulerian–Lagrangian approach. The effects of interphase forces and the bubble-induced turbulence on the fluid flow and the bubble behavior are analyzed by comparing with the measured data. It is found that the drag force strongly affects the velocity field and bubble volume fraction in the plume, but hardly influences the bubble plume shape. The lift force is mainly responsible for the spreading of the bubble plume, and the bubble plume becomes wider as the lift coefficient increases. The virtual mass force has a significant effect on the bubble volume fraction and should be considered reasonable. The pressure gradient force is negligible because it hardly affects the bubble plume dynamic. On increasing the bubble-induced turbulence, the bubble plume becomes wider and the liquid velocity and the bubble volume fraction in bubble plume are reduced.

Numerical Simulation of Desulfurization Behavior in Gas-Stirred Systems Based on Computation Fluid Dynamics–Simultaneous Reaction Model (CFD–SRM) Coupled Model

A computation fluid dynamics–simultaneous reaction model (CFD–SRM) coupled model has been proposed to describe the desulfurization behavior in a gas-stirred ladle. For the desulfurization thermodynamics, different models were investigated to determine sulfide capacity and oxygen activity. For the desulfurization kinetic, the effect of bubbly plume flow, as well as oxygen absorption and oxidation reactions in slag eyes are considered. The thermodynamic and kinetic modification coefficients are proposed to fit the measured data, respectively. Finally, the effects of slag basicity and gas flow rate on the desulfurization efficiency are investigated. The results show that as the interfacial reactions (Al2O3)-(FeO)-(SiO2)-(MnO)-[S]-[O] simultaneous kinetic equilibrium is adopted to determine the oxygen activity, and the Young’s model with the modification coefficient R th of 1.5 is adopted to determine slag sulfide capacity, the predicted sulfur distribution ratio LS agrees well with the measured data. With an increase of the gas blowing time, the predicted desulfurization rate gradually decreased, and when the modification parameter R k is 0.8, the predicted sulfur content changing with time in ladle agrees well with the measured data. If the oxygen absorption and oxidation reactions in slag eyes are not considered in this model, then the sulfur removal rate in the ladle would be overestimated, and this trend would become more obvious with an increase of the gas flow rate and decrease of the slag layer height. With the slag basicity increasing, the total desulfurization ratio increases; however, the total desulfurization ratio changes weakly as the slag basicity exceeds 7. With the increase of the gas flow rate, the desulfurization ratio first increases and then decreases. When the gas flow rate is 200 NL/min, the desulfurization ratio reaches a maximum value in an 80-ton gas-stirred ladle.

Numerical Simulation of Gas and Liquid Two-Phase Flow in Gas-Stirred Systems Based on Euler–Euler Approach

Based on the Euler–Euler approach, a mathematical model is established to describe gas and liquid two-phase flow in the gas-stirred system for steelmaking, and the influences of the interphase force including turbulent dispersion force, drag force, and lift force are investigated. The modified k–e model with extra source terms to account for the bubble-induced turbulence is adopted to model the turbulence in the system, and the simulation results of gas volume fraction, liquid velocity, and turbulent kinetic energy are compared with the measured data. The results show that the turbulent dispersion force dominates the bubbly plume shape and is responsible for successful prediction of the gas volume fraction. The bubble-induced turbulence has a significant influence on the liquid turbulence, and the conversion coefficient Cb, which denotes the fraction of bubble-induced energy converted into liquid turbulence, should be in the range of 0.8 and 0.9. The drag force also strongly influences the bubbly plume dynamics, and the coefficient model proposed by Kolev performs the best for determining the drag force; however, the lift force and bubble diameter do not have much effect on the current bubbly plume system. For different gas flow rates, the current Euler–Euler approach predictions are more consistent with the measured data than the Euler–Lagrange approach and the early Euler–Euler model.

Numerical Simulations of Inclusion Behavior in Gas-Stirred Ladles

A computation fluid dynamics–population balance model (CFD–PBM) coupled model has been proposed to investigate the bubbly plume flow and inclusion behavior including growth, size distribution, and removal in gas-stirred ladles, and some new and important phenomena and mechanisms were presented. For the bubbly plume flow, a modified k-e model with extra source terms to account for the bubble-induced turbulence was adopted to model the turbulence, and the bubble turbulent dispersion force was taken into account to predict gas volume fraction distribution in the turbulent gas-stirred system. For inclusion behavior, the phenomena of inclusions turbulent random motion, bubbles wake, and slag eye forming on the molten steel surface were considered. In addition, the multiple mechanisms both that promote inclusion growth due to inclusion–inclusion collision caused by turbulent random motion, shear rate in turbulent eddy, and difference inclusion Stokes velocities, and the mechanisms that promote inclusion removal due to bubble-inclusion turbulence random collision, bubble-inclusion turbulent shear collision, bubble-inclusion buoyancy collision, inclusion own floatation near slag–metal interface, bubble wake capture, and wall adhesion were investigated. The importance of different mechanisms and total inclusion removal ratio under different conditions, and the distribution of inclusion number densities in ladle, were discussed and clarified. The results show that at a low gas flow rate, the inclusion growth is mainly attributed to both turbulent shear collision and Stokes collision, which is notably affected by the Stokes collision efficiency, and the inclusion removal is mainly attributed to the bubble-inclusion buoyancy collision and inclusion own floatation near slag–metal interface. At a higher gas flow rate, the inclusions appear as turbulence random motion in bubbly plume zone, and both the inclusion–inclusion and inclusion-bubble turbulent random collisions become important for inclusion growth and removal. With the increase of the gas flow rate, the total removal ratio increases, but when the gas flow rate exceeds 200 NL/min in 150-ton ladle, the total removal ration almost does not change. For the larger size inclusions, the number density in bubbly plume zone is less than that in the sidewall recirculation zones, but for the small size inclusions, the distribution of number density shows the opposite trend.

A Study of Spouts on Bath Surfaces from Gas Bubbling: Part II. Elucidation of Plume Dynamics

Quantitative information on the spout dimensions from Part I of this series of articles has been used to extract several critical parameters pertinent to gas-stirred ladles, viz. (1) the scaling criterion for the gas flow rate, (2) a unified representation of gas-liquid plumes from a macroscopic analysis, and (3) the volume- and area-averaged gas fractions and area-averaged gas and liquid velocities in the plume. Further, the issue of Froude similarity in gas-stirred systems is discussed and the proper form of the Froude number is justified from a fundamental viewpoint. The present model is simple and accurate enough to be used as a design tool for unconfined plumes, and the present methodology can be extended to the analysis of multiple plumes or those that interact with vessel walls.

A Mathematical Model of Fluid Flow Phenomena for the Liquid Bath in Smelting Reduction Processes

This study established a mathematical model of fluid flow phenomena for the liquid bath in smelting reduction processes by the CFD (Computational Fluid Dynamic) software PHOENICS. The SEM (Scalar Equation Method) model was employed to treat the multi-phase flow, viz. liquid metal and injection gas. The Chen-Kim k-e turbulent model which is suitable for gas-stirred system was imposed. An index named Mixtrg was defined to evaluate the mixing level of the injection gas to the liquid bath. The accuracy of the model was verified by comparing the theoretically predicted vertical velocity with the experimental data for the bubble-stirred air-water ladle. Based on the standard operational condition, the influence of operational variables of simulated vessel was studied for the flow patterns of liquid bath. The calculated flow patterns of bath were helpful for understanding about distribution of injection gas, flow patterns of liquid bath, wave motion of liquid bath surface and the erosion conditions near the wall of furnace.

Mathematical simulation of fluid flow in gas-stirred liquidsystems

In the present paper, based on the two-phase (Eulerian-Eulerian) model, the3D fluid flows in gas-stirred systems, i.e. air-stirred water vessel andargon-stirred liquid steel ladle, are simulated. In the Eulerian-Euleriantwo-phase model, gas and liquid are considered to be two different continuousfields. The phases are assumed to share space in proportion to their volumefractions. The exchange between the phases is represented by source terms inconservation equations. Turbulence simulated by the k-ε modelis assumed to be the property of the liquid phase. The effects of mathematicaltreatments and operational factors, such as the inter-phase drag force, theturbulent model, the size of bubble and the gas-injection mode, on the fluidflow are discussed.Some interesting results are derived. Except the inter-phase dragforce, the inter-phase lift force should be taken into account inorder to exactly simulate the fluid flow in gas-stirred systems.The suitable turbulent model and drag coefficient have an effecton the mathematical simulation. Injecting small bubbles cangenerate a well mixing flow condition. The distance between thetwo gas-injection nozzles has effect on the fluid flow.

The modeling of gas-bubble driven circulations systems.

A mathematical model is presented of the turbulent recirculating two-phase flow in gas-stirred systems. Conservation equations are solved for each phase variables and these are connected through interaction parameters. Allowance is made both for the direct influence of bubble transport on the turbulence field and the additional generation of turbulence energy at the liquid/gas interphase. In addition, the plume shape is a direct result of the computation rather than being prescribed a priori. Computed flowfields are presented for both air-water and nitrogen-steel systems. The air-water results compare well with established measurements of gas fraction and mean velocities. The steel system results seem to suggest that gas plumes in metals may be narrower than in water.

Dispersion of bubbles and gas-liquid mass transfer in a gas-stirred system.

Dispersion of bubbles and gas-liquid mass transfer in a gas-stirred system.