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 modeled in time domain for the injecting operation of graphite particles in complex electric furnace steelmaking slags to reduce the iron oxide contents. The model takes into account the jet penetration in the liquid, the physical changes that the slag suffers due to chemical composition variations, the surface active effects of silica in molten slags and the coupling-uncoupling flow characteristics between the carrier gas and the solid particles in the molten phase. The mathematical simulations indicate that at small particle sizes (100-150 μm) the reaction kinetics is controlled by the gas-melt interface, under this regime acid slags show higher reduction rates than basic ones. At larger sizes this reaction is controlled by the mass transfer of iron oxide from the bulk phase to the gas-melt interface and basic slags show higher reduction 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 consumed by the reaction without reaching high efficiencies. Above this minimum the particle size is so large that it exits the molten bath only partially reached decreasing also the efficiency of the reaction. Just at this minimum the particle is totally consumed by the reaction with a minimum consumption rate of the reducing agent.