Reduction of CO₂ emissions is recognized as an urgent issue for the iron and steel industry. One of the feasible methods for the reduction of CO₂ emissions may be the use of H₂ gas as a reducing agent in blast furnaces for ironmaking. In order to keep the conditions of the blast furnace stable under high H₂ concentration, it is necessary to understand the effects of H₂ and H₂O gases on the disintegration of the iron ore sinter in the upper part of the blast furnace. Therefore, the effects of the concentration of the reducing gas and of the reduction time on the reduction and disintegration behavior of actual sinters are examined in the present work.
Reduction experiments were carried out under N₂–20% CO–20% CO₂ (CO gas) and under N₂–12% CO–17.7% CO₂–8% H₂–2.3% H₂O (CO–H₂ gas) at 773 K. The reduction degree of the sinter reduced under CO–H₂ gas increased with time. On the other hand, it was once retarded when reduced under CO gas. For the same value of reduction degree, however, the value of the reduction-disintegration index, RDI, for the sinter reduced under CO gas was higher than that of the sinter processed under CO–H₂ gas. When reducing hematite to magnetite for long time, e.g., 3.6 ks under CO–H₂ gas, the reduction degree calculated from the weight change was larger than that obtained on the basis of the change in the XRD peak intensity.