Thermochemical Behaviour of Oxidising Sponge Iron Pellets

Abstract

The effect of the exothermic nature of oxidation on the temperature of oxidising single sponge iron pel-lets has been examined. The sponge iron pellets employed (produced by reduction in hydrogen at 550°C) were oxidised at 100°C to 400°C. A mathematical model employing equations involving heat transfer were used to study the thereto-chemical behaviour of the sponge iron during the oxidation process. It was found from this simulation that the temperature predicted to be attainable by the pellets (arising from heat generation) were considerably higher than the nominal oxidation temperatures (i.e. the temperature of the furnace atmosphere) - an indication that the oxidation process was far from being isothermal. The temperatures were also studied by direct experimental measurements. Comparison of the two sets of results indicated that experimental in-crease in temperature (above the nominal oxidation temperature) was between 60 and 80% of the temperatures predicated by the model. The discrepancies in the result were attributed mainly to heat losses which were not taken into consideration during the experimental measurements. In all the cases investigated overall experimental (or predicted) temperatures during oxidation exceeded 300°C where parabolic oxidation could occur. At higher oxidation temperatures (>250°C), overall temperatures exceeded 450°C where sintering and cavity formation could occur in the sponge iron.