Influence of Reducing Gas Composition on Disintegration Behavior of Blast Furnace Burden

H2 injection through the shaft into blast furnace (BF) is a potential option for further reduction of CO2 emission from BF. Utilization of H2 promotes reduction reaction of burdens, but its influence on their reduction disintegration behavior has not well clarified in detail. In this study, therefore, we have investigated such influence on the iron ore sinter, and self-fluxed and acid pellets and tried to specify dominant factors governing the reduction disintegration behavior. Two series of experiments were conducted: mass ratios of particles under 3mm in size were measured as RDI after the reduction of burden samples at 823K by the gas mixtures of N2-CO and N2-H2, and observation of the reduced samples with an optical-microscope and an electron probe micro-analyzer. Further, using the measurement results, stress, strain energy and crack area generated during reduction were calculated and formation mechanism of cracks was examined. RDI increased for higher H2 condition and reached to 15 mass% when self-fluxed pellet was reduced with gas mixture of 70%N2-30%H2. Such an increase was larger than that expected compared to the standard RDI test condition without H2. Sample observation revealed that the reduction mode governed generation of the under size, that is, disintegration was promoted by the reduction with non-topochemical mode. This can be explained by the influence of crack formation and its propagation. In case of reduction with topochemical mode, cracks generated in a concentric fashion. Meanwhile, reduction with non-topochemical mode tended to generate cracks in radial direction, which causes pellet chipping and further degradation. Calculated crack area with topochemical mode was higher than that with non-topochemical mode. It indicates that disintegration does not much progress when crack area is less than the limit value, but it drastically proceeds when it exceeded a limit value.