Study On Optimization Of Chengde Vanadium-Titanium Magnetite Sintering Process

Chengde District of Hebei Province is an important production base of vanadium-titanium magnetite in northern China. Chengde vanadium-titanium magnetite is the major raw materials of Chengde Iron and Steel Co. Ltd. Due to the special properties of vanadium-titanium magnetite, the sinter size is small, the sinter low temperature reduction degradation index (RDI+3.15, the same below) and tumbler index (7) are low, the sinter recycle rate from blast furnace is high, and so on, it has a negative impact on the blast furnace smelting process and cost.The basic sintering properties of Chengde vanadium-titanium magnetite were determined by using mini-sintering method. The results show:the four iron ores are typical magnetite, all belong to difficult-sintering ores, the iron grade and SiO2content are low, and the TiO2and Al2O3content are high. Sizes of ore particles are large, the melting points are high, the assimilation property, liquid fluidity and consolidation strength are poor, and so, their single-sintering performances are poor.The sintering process and sinter quality of different vanadium-titanium magnetite ratio were studied using orthogonal experimental scheme, the best blending ratio for Chengde vanadium-titanium magnetite sintering process was determined. The results show, the influence of Chengde General Concentrate ratio on T, Reducing Index (RI) of sinter is the greatest; the influence of Heishan Concentrate ratio on RDI+3.15is the greatest; the influence of New Zealand Sea Sand ratio on Initial Softening Temperature (T10%) is the greatest. As the sinter TiO2content increases, the mineral structure becomes uneven, porosity increases, skeletal crystal-like structure proportion increases; calcium ferrite content is reduced, perovskite content increases sharply, which fills the glass phase. When the ratio of Xiaoying Concentrate and Brazil Concentrate are certain, the preferred order for imported ore is PB Ore, Newman Ore, MAC Ore, Rocket Ore and HIY Ore Powder. As Australian Ore Powder ratio is in30%～33%, the yield, T and RDI of vanadium-titanium sinter are the best.The influence of technological parameters on sintering process and vanadium- titanium sinter quality were studied using orthogonal experimental scheme, the optimal technological parameters were determined. The results show:the influence of MgO content on RI and RDI+3.15is the greatest; when the CaO/SiO2is2.0-2.3, RDI+3.15is in the low-lying area; the influence of fuel ratio on T10%is the greatest. As the fuel ratio increases, perovskite and FeO content increases, calcium ferrite content is decreased, the vertical sintering speed, yield, T, RI are decreased, while the RDI+3.15increases; the mixture moisture not only affect sinter quality, but also affect its production.The low temperature reduction degradation mechanism of vanadium-titanium sinter was studied through the mineral structure analysis. The vanadium-titanium sinter contains large amounts of Hematite, perovskite, and its mineral structure is very complex. The perovskite is hard and brittle, weaken the bonding effect. It cannot resist Hematite expansion stress and fall off during the reducing process, while calcium ferrite content decreases; silicate is the main bonding phase. It leads to low temperature reduction degradation of vanadium-titanium sinter is serious. It is very efficient to use low chlorine inhibitors for improving the RDI+3.15of vanadium-titanium sinter, it can reduce40%chlorine go into blast furnace which has benefit to blast furnace production. The T and RDI+3.15of vanadium-titanium sinter have been significantly improved after multi-function additive was added into sintering mixture.