Fundamental Mathematical Modeling of Gas Injection in AOD Converters with Emphasis on the Inlet

Abstract: The overall purpose of the present work has been to developa novel mathematical model of the gas injection in the AODconverter process, based on fundamental transport equations.The model development was divided into two major steps, wherethe first step involved modeling of gas injection through acylindrical nozzle at high gas flow rates (the nozzle model).The second modeling step consisted of the development of a fulltwo-phase AOD model, where the gas and steel phase are solvedseparately and coupled by friction. The aim of the nozzle modelwas to investigate fluid phenomena and heat transfer that occurin nozzles during injection of gas at high flow rates in theAOD converter and to establish the boundary conditions for thefull AOD model. A similar nozzle model was not found in theliterature. The nozzle model is based on theNavier-Stoke?s equations and the thermal-energy balanceequation for variable properties. The gas density variationswere calculated using both the ideal gas law and the equationof state. The effect of considering gas density variation usingthe equation of state on predicted properties such as the axialgas velocity appeared to be minor. Velocity predictions fromthe nozzle model were also compared to velocity measurementsobtained using a Laser Doppler anemometer (LDA). The agreementbetween the measurements and the predicted values was good. Themodel was also employed to investigate the effect of differentproportions of argon and oxygen in the argon-oxygen mixtureinjected through the nozzle on fluid flow and heat transfer.Results showed the temperature and kinematic viscosity at thenozzle outlet to be independent of the gas composition.However, for the same mass flow rate, the velocity, density,turbulent kinetic energy and dissipation of kinetic energyvaried with a change in the fraction of oxygen in the gasmixture. Overall, it was concluded from the investigationresults that the present model could be used to reliablypredict the parameters at the nozzle outlet. It is alsoconcluded that it is necessary to calculate velocity andturbulence parameter data rather than rely on constant valuesin determining the boundary conditions at the inlet region in aCFD model of the AOD process. The full AOD model is a novel CFDmodel, based on fundamental transport equations and includesthe solution of the steel and the gas phases. The inletboundary conditions at the nozzle are predicted using theseparate AOD nozzle model, as mentioned above. The predictedgas plume has been compared to a plume from a scaled down watermodel of an AOD nozzle in a qualitative manner. The plumeshapes are very similar. The AOD model has also been used topredict fluid flow patterns, turbulence characteristics andbubble diametersKey words:AOD; nozzle; modeling; steel; fluid flow; gasinjection.