In the context of the global financial crisis, the high cost and long-term co-ordination costs remain high and pose a great threat to domestic steel companies. It is an important measure to cope with the crisis by getting rid of the excessive dependence on high-quality mines, trying to use low-cost mines, and reducing the cost of ironmaking. Jinan Iron & Steel Co., Ltd. made great efforts to explore ways to use low-priced high-alumina limonite and achieved gratifying results. By adopting a series of technical measures in sintering and blast furnace production, they achieved substantial reductions in the cost of ironmaking under the conditions of stable sintering and blast furnace production, and no increase in the fuel consumption of blast furnaces.
High aluminum limonite (Al2O3>3%, mainly from India, Indonesia and other countries, many varieties, small quantities, large fluctuations in the composition, cheaper prices; fewer users, previously used mainly for the supply of small steel companies.
The main problems in the use of high-aluminum limonite are: (1) Reduced strength of sinter. With the use of high-aluminum limonite, the strength of the sinter significantly decreased, the sinter drum index decreased from 75.5% to about 74%, and the 120m2 sinter drum index decreased from 79.5% to 77%. There are three main reasons for the decrease of the strength of sinters: First, high-alumina limonite is high-burning and loss of limonite, and the burning loss is above 7%, and the high is 11.5%. After a lot of use, the appearance of sintered ore is loose and porous, which has a great influence on the strength. The second is that the high-alumina lignite is generally coarse in particle size, has too strong sintering air permeability, and has poor heat storage capacity, which is not conducive to liquid phase formation. The third is that the ratio of aluminum to silicon in sinters has broken through the best range of 0.1 to 0.3, reaching a maximum of 0.6. (2) Blast furnace slag has poor fluidity, making slagging difficult. w (Al2O3 increased to more than 18%, the number of blast furnace furnace collapse significantly increased, blast furnace furnace state is seriously affected.
In response to the above problems, Jinan Iron and Steel Company has taken the following measures and achieved remarkable results.
(1) Appropriately increase the proportion of sinter (W) (SiO2). In order to properly reduce the ratio of sinter Alumina to Si, increase the proportion of Indian high Al-limonite by 52% grade to increase the sinter's w (SiO2 from 5% to 5.4% , Improved raw material sintering performance.
(2) Implement thick layer sintering technology. By using the high granularity and high permeability of high-aluminum limonite, and appropriately increasing the thickness of the material layer, the thickness of the 60m2 and 120m2 sintering machine has been increased by 50mm, reaching 600mm and 700mm respectively, and the sintering material is pressed. It creates conditions for liquid phase formation and recrystallization in the high-temperature roasting process and promotes the strength of the sinter.
(3) Increase the proportion of sinter (w) FeO. Appropriate increase of sinter (FeO) can ensure that sufficient liquid phase is generated in the sinter, which helps to increase the strength of sinter and reduce the reduction rate of low-temperature reduction. According to the used Raw material conditions, the sintering ore w (FeO control standards from 7.5% to 8.5% to 8% to 9%.
(4) Adjust the blast furnace operating heat system and slagging system to ensure the slag iron performance. Appropriately increase the furnace temperature to ensure sufficient physical heat, and the furnace operation controls the temperature of the molten iron above 1480°C, w (Si controlled at 0.45%~0.6%, keeping the slag with good fluidity conditions, overcome the high slag w (Al2O3 brings In addition, adjust the types of accessories and implement the use of serpentine, increase the slag w (from about 9.5% to 11% to 12%, so that the slag w (MgO / w (Al2O3 ratio is increased to 0.6, improve slag flow Sex.
Jigang's active exploration has achieved very good technical and economic indicators. Compared with 2008, the comprehensive coke ratio of 350m3 blast furnace in the first five months of 2009 was 7.6kg/t lower than that of 7.2kg per ton of iron return powder. From January to May in 2009, the use of high-alumina limonite-based economic material will reduce the cost of the tonnage iron by more than 80 yuan.
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