The sintering process is the second most energy-intensive process in steel companies after blast furnace ironmaking. The cost and quality of sinter directly affect the cost of blast furnace ironmaking, smelting progress, operating system and technical and economic indicators, as well as the benefits of the entire steel enterprise. Under the current situation of general losses in the main business of steel enterprises, how to further tap the potential of sintering process to reduce costs and increase efficiency has become a common concern of steel enterprises. From June 2 to 5, at the "2015 National Sintering Production Technology Seminar" sponsored by the Chinese Society of Metals, the participants focused on the theme of "optimizing the process, fine operation, reducing consumption and increasing efficiency", and conducted in-depth discussions on the main sintering technologies that can further reduce the cost of the sintering process and increase the benefits, among which the optimization of ore blending technology, low negative pressure ignition technology, low MgO sintering production technology, and homogeneous sintering technology of thick material layer attracted great attention from representatives.
Optimized blending technology for fine operations
At present, the development and application of optimized ore blending technology no longer stop at the level of simple requirements such as chemical composition and cost, but combine the high-temperature sintering performance under the sintering conditions of iron ore powder, its role and contribution in the sintering process, the performance difference and performance complementarity between iron ore powder, and the rational use of different types of iron ore powder. The optimization of ore blending technology provides effective support for enterprises to expand iron ore resources and reduce sintering and ironmaking costs.
The correct concept of optimizing ore blending is: according to the sintering characteristics of different ores, reasonable matching, focus on assimilation and liquid phase fluidity index alkalinity is the core of sinter quality, should choose the best alkalinity and suitable chemical composition. The purpose of ore blending is to reduce costs, but not to reduce the quality of incoming charge, and the establishment of the main ore system of the enterprise is the top priority.
The main methods for optimizing ore blending are: ore blending method according to iron ore powder sintering reactivity, ore blending method according to the basic characteristics of iron ore powder sintering, and ore blending method according to the three characteristics of iron ore powder crystal particle size, hydration degree and Al2O3 content.
Energy-saving low negative pressure ignition technology
The air permeability of the sintered material layer is determined by the ignition negative pressure, sintering exhaust negative pressure, sintering machine air leakage rate and carbon distribution. Among other factors, ignition negative pressure is a key operation in creating air permeability throughout the sintered layer. High negative pressure ignition means that the negative pressure of No. 1-3 bellows is the same value as the negative pressure of sintering exhaust, which compacts the sintering mixture layer, resulting in increased air permeability resistance, and the entire sintering process presents a high negative pressure and uneven sintering state, which not only increases power consumption, but also seriously affects the sintering yield and quality. Some experts advocate the use of low negative pressure ignition, ignition temperature control at 1050-1150 °C, ignition time of 45-90s, ignition negative pressure is 50%-60% of the negative pressure of sintering exhaust, forming a normal uniform sintering, reaching the end point of sintering in advance, which is conducive to reducing sintering power consumption, saving energy, and improving sinter output and quality. However, the ignition negative pressure can not be too low, too low will cause the surface of the lit mixture is not easy to lead down, the sintering speed is slow, resulting in the tail can not reach the end point of sintering, seriously affecting the sinter yield and finished ore strength. In general, low negative pressure ignition is the most suitable ignition method, which can reduce the energy consumption of sintering ignition and improve the yield and quality of sinter.
Low MgO sintering for cost reduction and efficiency
The core of ironmaking concentrate technology is the grade of iron ore raw materials, and the purpose of reducing MgO content is to improve the comprehensive furnace grade, reduce flux consumption, and achieve cost reduction and efficiency increase.
MgO in sinter is different from SiO2 and Al2O3, SiO2 and Al2O3 are brought in by the mineral powder itself, while MgO is brought in by dolomite powder or high magnesium powder, serpentine and other MgO-containing fluxes. The addition of too much flux containing MgO can affect the sinter grade, which in turn affects the comprehensive furnace input grade. Low MgO sintering, on the one hand, can reduce flux consumption, reduce the cost of flux procurement, on the other hand, it can also improve the comprehensive grade of ironmaking, reduce the slag-iron ratio, promote ironmaking, reduce fuel consumption, and reduce production costs.
South Korea's POSCO sinter contains very low MgO content, less than 1%. The MgO in the blast furnace slag is stable at about 4.0%, while the Al2O3 in the slag is not low, the ratio of magnesium to aluminum in the slag is very low (less than 0.3%), and the utilization coefficient and fuel consumption index of the blast furnace are relatively good.
Since 2010, Shagang began to advocate low MgO sintering production and low MgO blast furnace smelting, after several years of production exploration, the sinter MgO content gradually decreased and stabilized at about 1.55%, and the quality of iron production was stable. The key to reducing MgO is that the blast furnace foreman must be able to adapt to the operation of the low MgO slag system, and stabilize the furnace temperature and furnace condition, which tests the operation level of the blast furnace foreman and the company's comprehensive management level.
Homogeneous sintering technology for thick material layers
Thick layer sintering technology has the advantages of reducing sintering energy consumption, improving sinter quality, and promoting a virtuous cycle of sintering process, which is the long-term goal of sintering production. The thickness of the sintered material layer in China has been continuously improved, and 900mm thickness has been achieved