The ‘Development of Magnesium-titanium and Low-silicon New Pellets and Application in Ultra-large Blast Furnaces of Shougang Jingtang’ Project jointly developed by the Shougang Institute of Technology and Shougang Jingtang United Iron & Steel Co., Ltd. has won the first prize of Metallurgical Technology 2016. Such an achievement is of great significance for iron and steel enterprises to give full play to the advantages of pellets, improve the technical-economic indicators of blast furnaces, reduce the cost of iron-making and realize energy conservation, environmental protection and green development.

Pellets are one of the major furnace burdens of iron-making in blast furnaces. With the increasingly severe situation of energy conservation and environmental protection, as well as the requirements of iron and steel enterprises for cost reduction, it has drawn increasing attention, and improving the quality of pellets and increasing their use ratio in blast furnaces has become the trend of development. In order to realize energy conservation and environmental protection, most blast furnaces in the United States and Europe are mainly used for high-proportion pellet smelting. The process energy consumption and the emission and production of such pollutants as dust, nitric oxide and Dioxin of the pelletizing process are far lower those of the sintering process. Dioxin produced in the pelletizing process is 1% to 18% that of the sintering process, NO_x is about 60% that of the sintering process and process energy consumption is 35% to 50% that of the sintering process. In particular, the iron grade of pellets is high and the impurity content such as matrix is low, which helps to improve the technical-economic indicators of blast furnaces and reduce the cost of molten iron.

In August 2010, Shougang Jingtang launched a large draper-type roasting machine pellet production line of 504m². Since 2011, in order to further reduce the SiO2 content of pellets, optimize the metallurgical properties of composite burdens and solve such problems as the influenced smelting indexes caused by furnace protection of the direct use of titanium ore in blast furnaces, the Shougang Institute of Technology and Shougang Jingtang United Iron & Steel Co., Ltd. put forward such new concepts and technological ideas of furnace protection as transforming the MgO required by slagging from sintering to pelletizing so as to reduce the SiO₂ content of pellets and increase the charging proportion, as well as adding TiO₂ through pelletizing so as to realize long-term furnace protection and centralized fettling in blast furnaces.

Through the experimental investigation and production practice of more than 3 years, many problems have been overcome including the uncontrollable high index of reduction swelling of low-silicon pellets, the difficult application of such resources as titaniferous tailings in pelletizing that can not only satisfy the needs of blast furnace protection and slagging, but can also meet the quality requirements of pellets for the matching relations of the content of MgO, TiO₂ and SiO₂, the high requirements of MgO and TiO₂ for thermal regulation control of pelletizing, and the smelting rules to be explored for large blast furnaces to adapt to the new pellets. Appropriate raw material structures and technical parameters have been worked out for the production of low-silicon pellets with MgO and TiO₂. Magnesian low-silicon pellets and magnesium-titanium low-silicon pellets have been developed successively so as to provide blast furnaces with quality and multi-functional pellets that can stabilize furnace protection and reduce slag quantity and fuel ratio at the same time, which has been successfully applied in the ultra-large blast furnace of 5,500m³.

In November 2012, Shougang Jingtang began to produce magnesian low-silicon pellets, and it started to produce magnesium-titanium low-silicon new pellets in May 2014 with the SiO₂ content dropping from 3.5% to 2.8%, the MgO content rising from its natural content to 1.7%, the TiO₂ content rising from its natural content to 1.1%, the reduction degree increasing from 67% to 73%, the reduction swelling controlled under 19%, the charging proportion rising from 25% to more than 33% and the comprehensive index reaching the international advanced level. After MgO and TiO₂ have been added into pelletizing, natural magnesium sintering has been realized with an increase of 0.4% in the grade of sinter. Meanwhile, titanium ore used in furnace protection has been replaced with an increase of 0.7% in the grade of blast furnace comprehensive charging. The technical-economic indicators of blast furnaces have been improved with a reduction of over 5 kg per ton in the fuel ratio and a reduction of more than 20 kg per ton in the quantity of slag. After the project is implemented, the cumulative economic benefits will reach RMB 136 million.