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Tracing back to the source, how to correctly understand the quality of sinter?

Release date:2018-12-18 The author:www.xapyyj.com Click on:

Since the 1980s, high alkalinity sinter has been the main raw material for blast furnace ironmaking in China. Regardless of the composition ratio of the charge, the cost of pig iron, waste discharge and environmental protection, sinter production has a significant impact on blast furnace ironmaking. The quality of the sinter plays a key role in the production of blast furnace iron, energy consumption, pig iron quality and blast furnace life. The quality of sinter consists of three parts: chemical properties, physical properties and metallurgical properties. The relationship between them is: chemical properties are the basis, physical properties are guaranteed, and metallurgical properties are the key.

Chemical properties are the basis

The main chemical properties of sinter include the grade, alkalinity and content of SiO2, MgO, Al2O3, FeO, and the content of harmful elements such as S, P, Ka2O, Zn and Cl.

The value of iron grade to the quality of sinter. Iron content is the core of sinter quality. For a long time, a core problem in improving the quality of sinter is to continuously improve the grade of sinter and reduce the SiO2 content of sinter. As the grade is increased, the amount of slag is reduced, the output of blast furnace ironmaking is increased, and the fuel ratio is lowered. In recent years, many steel companies have adopted the practice of low grade and large slag. The subjective desire is to reduce costs, but the reality is counterproductive, resulting in large emissions, high fuel ratio and inefficient results. To sum up the experience of history, we should continue to take the road of fine materials to achieve the goal of low cost, low fuel ratio and efficient iron making.

The value of alkalinity to the quality of sinter. Theoretical studies and years of production practice have proven that high alkalinity is the basis for sinter quality. Since the quality of the sinter depends on its mineral composition, the mineral composition of the sinter depends on the alkalinity. For blast furnace ironmaking, the optimum alkalinity range of sinter is 1.90~2.30. In production practice, the strength and particle size of the sinter, the metallurgical properties of the sinter are directly related to its alkalinity. The quality of the sinter is closely related to the alkalinity, and the sintering production must adhere to the direction of high alkalinity.

The value of SiO2 content on the quality of sintered ore. SiO2 is an important element of the quality of sinter. In the sintering production, SiO2 is the main component of the slag phase formed by sintering, and it is also an important component of the sintering phase of calcium ferrite. In the production of sinter, the SiO2 content can not be too low or too high, the optimum content is 4.6%~5.3%, and 0.1~0.3 Al2O3/SiO2 is an important condition for the formation of composite calcium ferrite. When the SiO2 content is lower than 4.6%, the strength of the sintered ore will be affected by the insufficient slag phase; when the SiO2 is higher than 5.3%, the strength and metallurgical properties of the sintered ore will be affected as the silicate slag phase increases.

The value of Al2O3 content on the quality of sinter. For the quality of sinter, Al2O3 content is also an important factor affecting the quality. Firstly, certain Al2O3/SiO2 is an important condition for sintering acicular composite calcium ferrite. Sinter can not form SFCA without Al2O3, but the content can not be too high, more than 2%, it will affect the cold strength and RDI of sinter. index. The Al2O3 content of the sinter is generally controlled in the range of 1.0% to 2.0%.

The value of MgO content on the quality of sintered ore. The MgO content is a negative energy factor for the quality of the sintered ore. It is beneficial to improve the low-temperature reduction and pulverization performance of the sintered ore, or to reduce the reduction of the sintered ore. MgO easily reacts with Fe3O4 to form magnesia magnetite (MgO·Fe3O4) during sintering, which hinders the oxidation of Fe3O4 to Fe2O3 during sintering, reduces the formation of calcium ferrite phase, and reduces the cold strength and reduction of finished sintered ore. The reason why the sintering production is to be equipped with MgO is to meet the needs of blast furnace iron slag fluidity, desulfurization and de-alkali (K2O+Na2O).

The value of FeO content on the quality of sinter. FeO content is also an important content of sinter. The level of FeO directly affects the strength, grain size and metallurgical properties of sinter. FeO of sinter is closely related to carbon. Sintering production should pursue the goal of high strength and low FeO. At present, the national average level of FeO content is 8.40%~8.50%. In order to pursue high strength, some companies increase the FeO content one-sidedly, which is neither scientific nor reasonable. The strength of the sinter is related to FeO, but depends on the mineral composition of the sinter. The strengths of different mineral compositions of sinter are listed in Table 1. The effect of FeO content on the quality of sinter is listed in Table 2. The strength of the silicate mineral phase with high FeO content is relatively low. The higher the FeO content, the higher the strength of the sinter, taking into account the strength and metallurgical properties of the sinter. The FeO content should be less than 9%, 6.5%~8.5%. The best range.

The content of harmful elements such as S, P, Ka2O, ZnO and Cl is not negligible in the quality of sinter. These harmful elements are to be controlled, and their hazards and limits are listed in Table 3.

Physical performance is guaranteed

Strength and particle size are the main physical properties of the sinter, in addition to bulk density and porosity. Strength and particle size are important quality indicators for sinter, as it is a limiting link in the upper part of the blast furnace.

Different blast furnace volumes have different requirements on the strength and grain size of sinter. The newly revised "Blast Furnace Ironmaking Engineering Design Specification" lists the different requirements of different furnace capacities for sinter strength, FeO and grain size. See Table 4 for details.

Metallurgical performance is the key

The metallurgical properties of sinter include 900 °C reduction (RI), 500 °C low temperature reduction pulverization performance (RDI), load reduction softening performance (TBS, TBE, △ TB) and droplet performance (TS, Td, △ T, △ Pm, S value), these properties reflect the properties of the sinter in the blast furnace smelting process.

The state in which the iron-containing charge in the blast furnace furnace exists can be divided into three types: a block shape, a softening state, and a molten drip shape. The resistance loss of the upper block of the blast furnace accounts for 15% of the total pressure loss of the blast furnace, and the resistance loss of the softening zone at the lower part of the furnace body and the waist of the furnace accounts for 25% of the total pressure loss, and the resistance of the molten drop zone at the abdomen position of the furnace The loss accounts for 60% of the total pressure loss of the blast furnace. Therefore, the main part affecting the blast furnace antegrade is the droplet drop belt in the lower part of the blast furnace. Because of this, the new concept of keeping the blast furnace stable and long-term is: the blast furnace operation is mainly to control the gas volume index of the lower bilge of the blast furnace, supplemented by the upper cloth operation of the blast furnace, and the gas distribution curve of the large platform plus the small funnel is formed.

The deterioration of 900 °C not only affects the gas utilization rate of the upper part of the blast furnace, but also affects its reflow performance, that is, affects the gas permeability of the lower part of the blast furnace. Therefore, it is a basic metallurgical property, and the alkalinity sinter of general alkalinity of 1.9 , its RI value should be greater than 85%.

The low-temperature reduction pulverization performance at 500 °C is the low-temperature reduction strength of sinter in the blast furnace. It is the limiting link of the upper gas permeability of the blast furnace. The blast furnace smelting requires RDI+3.15≥72%. If the chalking index is lower than 60%, it should be sprayed before entering the furnace. In the past, CaCl2 was sprayed, but the harm caused by Cl entering the blast furnace was too great. Therefore, it is now possible to reduce the new environmentally friendly products without Cl to reduce RDI index.

Blast furnace smelting requires that the initial softening temperature (TBS) of the sinter is higher than 1050 ° C. The acid charge below 900 ° C is not conducive to the permeability of the softening zone in the middle of the blast furnace. The softening properties of sinter are often related to the mineral form of the flux. The silicate flux reduces the TBS value, while the carbonate flux helps to increase the TBS value of the sinter.

Droplet performance is one of the most important properties of sinter metallurgical performance, because the gas permeability resistance of the droplet belt accounts for more than 60% of the total resistance loss of the blast furnace. Therefore, attention should be paid to the improvement of the performance of the sinter droplets and the droplet properties of the sinter. It is related to the content of its grade, SiO2, Al2O3, FeO, TiO2 and so on. High-grade, low slag, low Al2O3, low FeO sinter, the droplet performance is better, and vice versa. The blast furnace ironmaking requires the S value of the integrated charge to be ≤ 40 (kPa ° C).

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