Research Of Decreasing Silicon Content Of Hot Metal In Nanjing Steel

With the development of iron and steel industry, the requirement of ironmaking and steelmaking processing for silicon content of hot metal is much more strickly. Decreasing silicon content in hot metal is not only the development of blast furnace processing, but also the inevitable requirement of modern steelmaking processing. The silicon content in hot metal of Nanjing Steel blast furnace was more than 0.6%, which impeded the development of ironmaking as well as the optimization of following converter steelmaking processing. Therefore, in this paper, our attentions are focused on the problems of high silicon content in hot metal of Nanjing Steel blast furnace; try our best to find out the methods of decreasing silicon content in hot metal of Nanjing Steel by experiment and theory calculation and present recommendations for production and operation. Firstly, the origin and the behavior of silicon in the blast furnace were analyzed theoretically, as well as the principles of decreasing silicon content in hot metal of blast furnace were also discussed. Then for the specific situation of Nanjing Steel blast furnace, the properties of slag from Nanjing Steel blast furnace were studied in the lab. By measuring viscosity of local slag of Nanjing Steel blast furnace,the slag of Nanjing Steel blast furnace slag was optimized. By measuring viscosity of simulation slag samples, which were prepared by analytically pure reagents, the factors affecting silicon content of hot metal and properties of slag were analyzed. The model used to predict silicon content in hot metal was programmed. Adopting optimized slag has resulted the decreased silicon content in hot metal. Then, the softening and melting properties of sintered ores from Nanjing Steel were tested. The testing involved Comprehensive thermal analysis loading softening performance. Followed the mentioned tests above, the theoretical coke ratio of Nanjing Steel blast furnace, sulfur burden, alkali metal oxide equalization and the impacting on silicon content of hot metal were analyzed. Finally, the following conclusions and suggestions for decreasing silicon content in hot metal of Nanjing Steel blast furnace are proposed according to the research results: 1)The Al2O3 content in Nanjing Steel blast furnace slag should be less than 19.4%, in this case the good flowability of blast furnace slag can be reached which will results in low silicon content in hot metal; 2)Increasing MgO content in slag can not only reduce viscosity of slag, improve flowability of slag , but also decrease silicon content in hot metal; 3)Adding MnO in blast furnace slag is in favor of reducing slag viscosity and decreasing silicon content in hot metal; 4)The ideal range of binary basicity for Nanjing Steel blast furnace slag is below 1.17. Increasing slag binary basicity below this limit can ensure trouble-free operation of blast furnace, and attain the aim of decreasing silicon content in hot metal; 5)In order to guarantee sintered ores with high smelting temperature and good loading softening performance and decrease silicon content in hot metal, suitable basicity,MgO content and Al2O3 content of sintered ores of Nanjing Steel should be controlled; 6)Most of actual coke ratio of Nanjing Steel blast furnace are higher than theoretical coke ratio, so lower coke ratio operation should be adopted for further decreasing silicon content of hot metal; 7)alkali metal oxide equalization fluctuates largely in Nanjing Steel blast furnace, and this fluctuation will bring about a lot of unfavorable problems to production of blast furnace. Therefore Nanjing Steel should pay much attention to the problem of alkali metal oxides; 8)The lower desulfurizing ability of Nanjing Steel blast furnace slag limits decreasing of sulfur content in hot metal, and results in blast furnace being operated at higher temperature, which is not good for decreasing silicon content in hot metal. The suggestions mentioned above have been adopted in Nanjing Steel blast furnace operation; the good results and improvements in practical operation are obvious. Now the silicon content in hot metal of Nanjing Steel blast furnace has decreased to the range of 0.48%~0.50%, meanwhile, others technical and economic targets have also been achieved.