Effect of the Reduction of Calcium Ferrite on Disintegration Behavior of Sinter under High Hydrogen Atmosphere

The utilization of H2 gas as a reducing agent in blast furnaces is one potential method to reduce CO2 emissions from the iron and steel industry. In order to maintain stable operation of the blast furnace under a high H2 concentration, it is necessary to understand the effects of H2 and H2O gases on the disintegration of the iron ore sinter by reduction under various conditions. In this study, the effect of the reduction of calcium ferrite on the disintegration of sinter was examined. Reduction experiments were carried out under N2 – 20% CO – 20% CO2 (CO reduction) and N2 – 12% CO – x% CO2–8% H2 – (20-x)% H2O (CO–H2 reduction) at temperatures from 773 to 973 K. The reduction of hematite to magnetite mainly proceeds at 773 K. However, longer reduction time is necessary for acicular calcium ferrite as 5.4 ks by CO reduction and 3.6 ks for CO–H2 reduction, while columnar calcium ferrite is not reduced at such temperature. The reduction of acicular calcium ferrite begins after 1.8 ks at 873 K and accelerates disintegration of sinter. At 973 K, on the other hand, disintegration is inhibited because the volume expansion of skeletal hematite becomes small and the cracks formed in the sinter seem to be mended.