Reduction disintegration behavior of iron ore sinter under high H ₂ and H ₂O conditions

Reduction of CO ₂ emissions is an important object for the iron and steel industry. One feasible method may be the utilization of H ₂ gas as a reducing agent in the blast furnace (BF). However, for stable BF operation, it is first necessary to understand the effects of high H ₂, and therefore high H ₂O, concentrations in the reducing gas on the disintegration behavior of iron ore sinter, because it significantly affects the gas permeability of the upper part of the BF. In the present study, disintegration behavior of a sinter sample at 773 K for 3.6 ks under gas flow of N2-CO-CO ₂-H ₂-H ₂O system was examined. The results showed a remarkable increase in the reduction degree and reduction-disintegration index (RDI) upon the addition of a small amount of H ₂. However, further increase in the H ₂ concentration caused these values to decrease gradually. Reduction by CO gas led to the formation of magnetite phases with not only thick and long but also fine cracks near the surface. In contrast, H ₂ reduction did not lead to formation of a significant number of fine cracks. Image analysis of samples revealed that the crack length density showed the similar trend to RDI value. CO gas reduction mainly proceeds near the surface of sinter particles, while H ₂ gas reduction tends to proceed inside the particles. Accordingly, reduction of H ₂ gas gave lower RDI than CO gas to the sinter with same reduction degree.