A MATHEMATICAL-MODEL FOR THE REDUCTION KINETICS OF IRON-OXIDE IN ELECTRIC FURNACE SLAGS BY GRAPHITE INJECTION

A three-phase, solid-gas-liquid, reactive jet is mathematically modele d in time domain for the injecting operation of graphite particles in complex electric furnace steelmaking slags to reduce the iron oxide co ntents. The model takes-into account the jet penetration in the liquid , the physical changes that the slag suffers due to chemical compositi on variations, the surface active effects of silica in molten slags an d the coupling-uncoupling flow characteristics between the carrier gas and the solid particles in the molten phase. The mathematical simulat ions indicate that at small particle sizes (100-150 mu m) the reaction kinetics is controlled by the gas-melt interface, under this regime a cid slags show higher reduction rates than basic ones. At larger sizes this reaction is controlled by the mass transfer of iron oxide from t he bulk phase to the gas-melt interface and basic slags show higher re duction rates than acid ones. to obtain a given reduction rate of iron oxide there is an optimum particle size at which the consumption rate of the reducing agent is minimum. Below this size the particle is con sumed by the reaction without reaching high efficiencies. Above this m inimum the particle size is so large that it exits the molten bath onl y partially reached decreasing also the efficiency of the reaction. Ju st at this minimum the particle is totally consumed by the reaction wi th a minimum consumption rate of the reducing agent.