| Sinter,pellets and natural ore are the most basic iron-containing charge in blast furnaces.Throughout the world,high basicity(Ca O/Si O2)sinter is the main material for blast furnace in China,Japan,Russia,and German,while acidic pellets is the main material for blast furnace in United States and Canada.Through scientific and reasonable composition of iron-containing materials,the sintering product performance can be effectively improved,and the production technical index of sintering process can be improved,which lays a good foundation for efficient smelting of blast furnace.In addition,Chongqing Iron and Steel Co.is located in the inland,with poor basic raw material conditions and a large number of iron ore to be purchased.How to rationally mix ore from the economic and technological point of view is also of great significance to reduce the cost of iron-making.In recent years,with the use of a large number of imported mines and diversification of varieties,the problem of ore blending has become increasingly complex.Based on the sinter blending of Chongqing Iron and Steel Co.,Ltd.,this paper focuses on the basic problems of optimizing ore blending,such as chemical composition,phase composition,appearance,particle size distribution,water absorption characteristics of several iron ore powders commonly used in Chongqing Iron and Steel Co.,Ltd.and their high temperature properties such as assimilation,liquid phase fluidity,bonding strength and bonding phase strength.On this basis,the influence of basicity and sintering time on liquid phase formation ability,phase composition and microstructure of single iron ore powder was further studied by micro-sintering method,and the influence of different ore blending conditions on liquid phase formation ability was calculated by using thermodynamic software Factsage.Based on the above research results,the sintering cup experiment was carried out in the laboratory by using the orthogonal experimental method.The effects of different proportions of domestic concentrate powder,Australian powder(PB),Brazilian powder(CVRD)and basicity on sintering yield and quality were investigated.The effects of MgO content on sinter properties and main bonding of sinter with high basicity were also examined.Based on the above theoretical analysis and experimental research,the optimum ore blending scheme based on the raw material conditions of Chongqing Iron and Steel Co.was put forward,and the production practice was tested.The test results of basic physical and chemical properties of iron ore powder shown that except Qijiang powder,the iron grade of other ore powder was above 60%,and the domestic concentrate powder had the highest grade of 65.27%.Hematite and limonite were the main phases of Australian and Brazilian fines,magnetite was the concentrate of South Africa,and hematite and magnetite were both found in Qijiang and domestic concentrate.The particle size of iron ore powder varies greatly,Qijiang powder was the coarsest,followed by Australian powder,and domestic concentrate powder was the finest.The wet capacity of Australian flour was the largest,followed by domestic concentrate and Brazilian flour,and the wet capacity of high silicon bar was the smallest.The study on high temperature properties of iron ore fines shown that the assimilation of Australian and Brazilian fines was good,that of Qijiang fines was poor,and that of domestic concentrate fines was the worst.Brazilian and domestic concentrate fines had better crystalline strength and good liquid phase fluidity,and the liquid phase fluidity index of Australian fines was greater than 5,and that of Australian fines was worse,and that of domestic concentrate fines was less than 3.The study on liquid phase formation ability of single iron ore powder shown that increasing alkalinity was beneficial to liquid phase formation.The liquid phase formation ability of Qijiang powder and high silicon bauxite powder was stronger,while that of Australian powder and domestic concentrate was weaker.Hematite and composite calcium ferrite were the main phases of micro-sintering products.Extending sintering time and increasing basicity were beneficial to the formation of composite calcium ferrite.Using Fact Sage thermodynamic software,the influence of different ore blending conditions on liquid phase formation in sintering process was theoretically calculated.The results shown that the concentrate ratio had little influence on the liquid phase formation ability,and it was not conducive to the liquid phase formation to increase the Australian powder ratio and decrease the Brazilian powder ratio.With the increase of Australian powder ratio,the liquid phase production shown a slow decreasing trend.When the Australian powder ratio was in the range of 45%to 60%,the alkalinity would be greater than 1.80 in order to make the liquid phase content reach40%.The experimental results of laboratory optimized sintering cup shown that with the increase of concentrate ratio,the sintering utilization coefficient increases first and then decreases,while the return rate decreases,and the drum strength increases obviously;when the concentrate ratio was less than 5%,the low temperature reduction pulverization index of sinter increases significantly with the increase of concentrate ratio,but the concentrate ratio was more than 5%.The reduction pulverization index remained unchanged at low temperature.With the increase of the proportion of Australian powder,the proportion of Brazilian powder decreases,and the sintering utilization coefficient shown a pit trend,which indicated that the mixing of Australian powder and Brazilian powder was not conducive to the increase of sintering utilization coefficient.At the same time,with the increase of Australian powder ratio,the average size of sinter decreased and the drum strength decreased significantly.The reduction pulverization index decreased at low temperature.The research on the effect of basicity on sintering process shown that with the increase of basicity,sintering speed,sintering utilization coefficient,drum index and low temperature reduction pulverization index are all improved,but the yield of sinter decreased;furthermore,the initial softening temperature and the final softening temperature of sinter increased with basicity.When the alkalinity was 2.0,both of them reach the highest value.The effect of MgO content on sinter properties was also discussed in this paper.With the increase of MgO content,the metalorganic rate,product yield and sintering utilization coefficient all shown a downward trend.At the same time,sinter strength decreased with the increase of MgO content.The effect of MgO content on the reduction of calcium ferrite was studied.It was found that the reduction ability of calcium ferrite gradually decreased with the increase of MgO content at the same temperature.The main reason was that MgO inhibited the reduction of calcium ferrite.The production practice of sintering in Chongqing Iron and Steel Co.to increase the proportion of Australian powder was also discussed in this paper.With the increase of Australian powder ratio,sinter strength shown a downward trend,solid fuel consumption gradually increased,and the lower the basicity of sinter,the more obvious the strength decline.Therefore,when the proportion of Australian powder was increased,the influence of chemical composition of mixture and composition of mixture on sintering should be considered comprehensively.By optimizing the proportion of Si O2,MgO and lime in the mixture,the negative effect of the increase of Australian powder ratio on sintering could be reduced.The sintering practice of high iron and low silicon shown that the decrease of Si O2 content caused by increasing the ratio of Australian flour was the main reason for the decrease of sinter strength.When the ratio of Australian flour to Chinese flour is increased to about 50%,the sinter strength could be improved by increasing the ratio of Chinese lime to Australian flour(4.04%).At this time,the calcium ferrite production in sinter could be improved,and good micro-structure ensured the strength of sinter.This study provides an important reference basis for optimizing sinter blending in Chongqing Iron and Steel Co.,and has a certain practical significance for guiding sintering and blast furnace production. |
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