Dynamic Modeling of LD Converter Steelmaking: Reaction Modeling Using Gibbs’ Free Energy Minimization

Abstract

Slag–metal emulsion plays an important role in the oxidation kinetics of metalloids in oxygen steelmaking. The importance of droplet generation rate, droplet size, and its residence time in the slag–metal emulsion on the overall reaction kinetics has become evident in recent times. Residence times of the droplets are strongly dependent on the decarburization rate, the CO bubbles giving a buoyant force to the droplets. The present work aims at developing a mathematical model for predicting the composition evolutions of the slag and the metal phases as the blow proceeds in an LD converter. The process dynamics are modeled by dividing the LD convertor into three separate continuous stirred tank reactors. Oxidation reactions are assumed to be primarily taking place at the interface between the slag and the metal phases in the emulsion. Among the different mass transfer and reaction steps controlling the kinetics, the mass transfer of FeO in the slag phase and that of the metalloids within the metal droplet are assumed to be rate-controlling. For a Fe-C-X (X = Mn, Si etc.) droplet, simultaneous removal of elements have been modeled by Gibbs’ free energy minimization at the slag–metal interface. Effects of droplet size, mass transfer coefficient, and initial carbon content on the mean residence time of metal droplets in the slag–metal emulsion have also been identified. Mixing in the metal phase is simulated in terms of metal exchange rate and the reactor weight ratio between the upper and the lower parts of the bath.