RDI—-Reduction Degradation Index.Raw materials (especially sinter ore) in BF production process will be severely broken and Pulverized when reduced in the low-temperature zone in the upper layer of the blast furnace, which will reduce the porosity of the column and deteriorate the gas permeability.

For every 5% increase in the RDI, the blast furnace output will decrease by 1.5% and the CO utilization rate will also decrease. the level of RDI is related to the type of ore powder used in the sinter production. The sintered ore produced from rich ore powder has a high RDI, the sintered ore produced from concentrate powder with high TiO2 content also has a high RDI, while the RDI is low when magnetite concentrate powder is used. The way to reduce RDI is to try to reduce the number of sintered ore RDI caused by the elevation of the skeletal crystalline rhombic hematite, can be appropriate to increase the FeO content or add halide CaF2, CaCl2, etc.. Many enterprises spraying 3% halide solution on the sintered ore surface, so that the RDI reduced 10.8% -20%, blast furnace output increased by about five percent.