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Blast furnace charge requirements and sintering technology status

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Abstract: Blast furnace is a shaft furnace production technology that uses carbon to reduce iron from iron oxides. The main product is to provide molten iron for steelmaking. Blast furnace ironmaking is based on fine materials, and sinter is the main component of the blast furnace charge. Its quality directly determines the quality of the final steel product. Therefore, improving the quality of sinter finished products is the primary task of blast furnace production.

Keywords: blast furnace charge; sinter; quality

Blast furnace is a shaft furnace production technology that uses carbon (mainly in the form of coke) to reduce iron from iron oxides. Its main product is molten iron, and its by-products are slag and gas. There are many factors that affect the technical and economic indicators of blast furnaces, among which the technical level of fine materials accounts for about 70% of the impact on blast furnace ironmaking production. The so-called blast furnace ironmaking concentrate refers to optimizing the quality of raw materials before entering the blast furnace to make them into furnace materials that can meet the requirements of intensive smelting in the blast furnace. Generally, the blast furnace concentrate technology adopted is reflected in the following aspects.

(1) The iron grade of the ore entering the furnace should be high: the main performance is that the drum strength of the sintered pellets should be high and the alkalinity of the sinter should be high (generally between 1.8 and 2.0).

(2) The proportion of clinker in the raw materials entering the blast furnace should be high. Clinker refers to sinter and pellets.

(3) The particle size <5mm in the raw materials entering the furnace must be less than 5% of the total amount.

(4) The particle size of the charge into the furnace should be small. The optimal particle size is 25-40mm for sinter, 20-40mm for coke, and 8-20mm for easily reduced hematite and limonite.

(5) The particle size of the charge into the furnace should be uniform, which can reduce the filling of the charge and improve the air permeability of the charge.

(6) The chemical composition and physical properties of the raw materials entering the furnace must be stable and have a small fluctuation range. At present, ensuring a reasonable storage capacity in the raw material yard (to ensure that the ore blending ratio does not change much), or establishing a neutralizing and homogenizing stock yard are effective means to ensure the stability of the composition of the blast furnace material.

(7) Iron ore and coke contain less harmful impurities. In particular, the contents of S and P need to be strictly controlled.

(8) The metallurgical properties of iron ore should be better. Metallurgical properties refer to the reduction degree of iron ore should be greater than 60%. The reduction powdering rate of iron ore should be low; the load softening point of the ore should be high and the range of reflow temperature should be narrow; the dripping property of the ore should be high in temperature and in a narrow range.

The main forms of blast furnace material structure in my country at present

High alkalinity sinter combined with acidic pellets

This is a main form that has been used in blast furnaces in my country for many years. Following the successful industrial test of Angang Iron and Steel Co., Ltd. in 1990 using 70% high alkalinity sinter and 30% acidic pellet charge structure, some large blast furnaces (2500m3 level) adopted Compared with the furnace charge structure of 75% sinter with an alkalinity of about 1.85 plus 25% acidic pellets and the index of 100% self-melting sinter, the utilization coefficient is increased by 17% to 20%, and the comprehensive coke ratio is 40kg/t lower on average.

The form of high alkalinity sinter combined with acidic pellets and lumps

This form of charge is also common in my country’s ironmaking industry. Baosteel in 1985: 85% sinter, 5.0% pellets, 10.0% lump ore, coefficient 1.764 t/m3·d; in 1999, sinter 76.1%, pellets The pellet ore is 7.9%, the lump ore is 16.0%, and the coefficient is 2.257 t/m3·d. Due to the excessive use of lump minerals, there is still a large gap in its indicator levels.

Current situation of sintering production at home and abroad

At present, our country has put into operation 43 blast furnaces with a volume of more than 3000m3 and 21 blast furnaces with a volume of more than 4000m3. With the large-scale blast furnace smelting equipment, the quality requirements for raw materials are constantly improving. Among the 1.2 billion tons of sinter production in the world, my country produces about 1 billion tons of sinter, accounting for 83.3%. There are more than 1,240 sintering machines of various sizes in the country, with a total sintering machine area of ​11,000 m2, of which more than 500 m2 is not less than 7 Taiwan, the maximum sintering area reaches 660m2.

The quality requirements for sinter production in blast furnace production are shown in Table 1.

Table 1 Sinter drum index (DI>6.3mm) %

Furnace capacity level/m3 Implementation standard GB50427-2008Recommended implementation intensity
1000≥ 71≥ 74
2000≥ 74≥ 76
3000≥ 77≥ 78
4000≥ 78≥ 79
5000≥ 78≥ 80

The particle size requirements of sinter for blast furnace production are shown in Table 2.

The requirements for low-temperature reduction differentiation (RDI) of sinter in blast furnace production are shown in Table 3.

Table 2 Sinter particle size

Particle size range/mmRatio/%
>50<8
40 ~ 1060 ~ 65
10 ~ 5<30
<5<3

Table 3 Low-temperature reduction differentiation (RDI)

RDI/mmRatio/%
RDI+6.3>40
RDI+3.15>60
RDI-0.5<10

The current status of sintering production technology is as follows.

In order to meet the requirements for sinter quality in blast furnace production and combined with the current iron ore market conditions in the international market, sintering technology has also been improved through continuous exploration and exploration. Currently, the sintering production technologies commonly used in China include the following.

(1) Thick material layer sintering. A thick material layer is used, that is, the material layer of the sintering machine exceeds 700mm, and some are even as high as 800mm. Due to the automatic heat storage of the material layer, the material layer temperature increases with the increase of the material layer height, which allows low-temperature sintering, greatly improves the quality of sintered ore, reduces the amount of returned ore, saves energy consumption, and improves environmental protection conditions.

(2) Spray CaCl2 solution. The CaCl2 solution is sprayed on the sintered ore at a certain temperature. After the water evaporates, the solute crystallizes or the crystals are adsorbed on the surface and pores of the sintered ore, thereby forming a protective film, which can effectively inhibit the low-temperature reduction and powdering rate of the sintered ore.

(3) Hot air ignition process. The hot air ignition process is to take out high-temperature exhaust gas (200 ~ 300℃) from the exhaust gas outlet of the high and medium temperature sections of the ring cooler. After a multi-tube dust collector and a high-temperature induced draft fan, the hot air is sent to the ignition and holding furnace as combustion-supporting air and ignition insulation. At the same time, it is sent to the hot air hood at the rear of the ignition and holding furnace for hot air sintering to improve the quality of the surface sinter. . This process recovers the waste heat of sinter in the form of hot air to make up for part of the heat required in the sintering process, thereby reducing the use of solid fuel and saving energy.

(4) Flue gas circulation process. In the face of increasingly serious environmental pollution problems, the national environmental protection department requires that the concentration of SO2 emitted from sintering flue gas be lower than 200mg/m3. For this reason, continuous exploration of the sintering process has found that circulating flue gas can effectively reduce the SO2 emission concentration. The sintering flue gas circulation process is divided into internal circulation process and external circulation process. The internal circulation process takes air directly from the wind box branch pipe, and the external circulation takes air from behind the main exhaust fan. The sintering air is recycled to achieve the purpose of SO2 enrichment, and at the same time, the waste heat of the flue gas is utilized. In order to increase the air temperature and oxygen content of the sintering material layer, the hot waste gas from the low-temperature section of the ring cooler is also mixed into this part of the flue gas to mix. Then it enters the circulating fume hood on the surface of the sintering machine and participates in the sintering process through the material layer again. Sintering flue gas circulation technology can reduce the consumption of solid fuel, make full use of the thermal energy of the ring-cooled exhaust gas, and reduce the amount of external exhaust gas by 30% to 50%. At the same time, the emissions of SO2, NOx, dioxins, dust, carbon oxides, heavy metals and other pollutants have been reduced, which also plays a certain role in the desulfurization process.

Outlook and Conclusion

The low-level and extensive development of my country’s steel industry with the goal of increasing output has serious environmental impacts and high energy consumption, which has brought serious problems to the energy conservation, emission reduction and sustainable development of the steel industry. In order to prevent further deterioration of the ecological environment , it is necessary to vigorously develop a circular economy, eliminate outdated equipment, integrate resources, scale up steel system equipment, minimize unnecessary input and output in the manufacturing process, reduce resource load and energy load, and utilize emissions and emissions during the production process as much as possible. Waste and residual energy can be used for system design between processes.

On June 27, 2012, my country officially issued the “Air Pollutant Emission Standards for the Steel Sintering and Pelletizing Industry” (GB28662-2012), which marks that my country has put forward higher requirements for energy conservation and emission reduction in the steel industry, and sintering production needs to be strictly controlled. PM2.5 and CO2 emissions, desulfurization and denitrification technology and the rapid development of research and development of efficient dust removal systems are conducive to achieving the goal of clean water and blue skies.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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