1. Overview When the sintering process reaches the end point, the red hot sinter is removed from the sintering machine. The average temperature of the sinter is usually 600-800 ° C. This red hot sinter is transported to the blast furnace. It will add a series of difficulties to transportation and plant layout. Moreover, the sinter plant can not carry out the sinter granulation and the separation of the bottoming material. In addition, it will shorten the life of the blast furnace top equipment and bring some difficulties to the blast furnace operation. Therefore, the new sinter plant adopts the cold mining process, and the existing thermal mining plant will also undergo technical transformation before 2002, using the cold mining process.
Sinter cooling solved the problem of existence of thermal mineral, it has important implications for sintering, smelting iron:
(1) For the sinter plant, the cold ore process can complete the sinter granules and separate the slabs. The primer can improve the gas permeability of the sintered layer, reduce the residual carbon content of the returned ore, improve the particle size composition of the sintered ore, reduce the consumption of the purlin of the sintering trolley, and improve the life of the rotor of the fan. The 24m 2 sintering machine of Shijiazhuang Iron and Steel Plant was tested in October 1982 with the production of non-primed materials. It was found that the bottoming material could increase the speed of the sintering machine by 0.2m/min and increase the yield of sintered ore by 3.31t/(å°â€¢h). The content of grain size less than 5mm in sinter decreased from 8.7% to 3.8%. The 24m 2 sintering machine of Guangzhou Iron and Steel Plant measured in 1986. Due to the use of the primer, the dust concentration of the sintering flue gas before dust removal is only 0.5g/m 3 , and dust is used. In the room plus multi-tube dust collector, under normal production conditions, the dust concentration of the sintering flue gas can reach 69mg/m 3 , which has obvious social benefits.
(2) For blast furnace smelting, the use of cold sinter can strengthen smelting, increase blast furnace output, reduce coke ratio, and extend furnace life. The hot sinter is put into the furnace so that the temperature at the top of the furnace reaches 500-600 ° C, and the pressure at the top of the furnace is generally controlled at 0.5-0.8 kg/cm 2 . However, in the blast furnace using cold-sintered ore, the temperature at the top of the furnace is below 350 ° C, and the pressure at the top of the furnace is maintained for a long time. At 1.0~1.3kg/cm 2 , the production practice proves that for every 0.1kg/cm 2 increase of the top pressure, the blast furnace can increase production by 2% to 3% and the coke ratio by 0.5%. WISCO No. 3 blast furnace uses the whole grain in the first quarter of 1985. Compared with the unsintered sinter in the third quarter of 1984, the sinter decreased by 1.3% and the yield increased by 5.5%. It can be seen that the cold ore process provides favorable conditions for the blast furnace to increase the iron coke.
Second, factors affecting the cooling of sinter
There are many factors affecting the cooling efficiency of sinter. The most important factors are: physicochemical properties of cooling materials, cooling air volume, wind pressure, wind speed, layer thickness, layer temperature, cooling time, etc. In addition, the type, size, and capacity of the chiller also have a large effect on the cooling rate.
(I) Influence of physical and chemical properties of cooling materials Sintering raw materials of different chemical properties have different sintering properties, and the obtained sintered ore has a great influence on the cooling process. China's iron ore fines or iron concentrates contain more acidic substances. At present, each sinter plant basically produces high alkalinity or even ultra-high alkalinity sinter, so many fluxes such as limestone or quicklime must be added during the sintering process. It is bound to generate more 2CaO•SiO 2 .2CaO•SiO 2 with three crystal forms of a, β and γ. When cooled to 675 °C, β-2CaO•SiO 2 is converted into γ-2CaO•SiO 2 , and its bulk density is determined by 3.28 g/cm 3 was reduced to 2.97 g/cm 3 and the volume was increased by 10%. The sudden expansion of the volume generates internal stress, causing the sintered ore to self-fragment, which deteriorates the mechanical strength and stability of the obtained sintered ore. However, this sinter produces more macroporous structure during the cooling process, which can make the cooling proceed to some extent. For high-iron low-silicon iron ore fines, CaO•Fe 2 O 3 is formed in an oxidizing atmosphere in a normal carbon-sintered hematite-based fluxing sinter and in a low-carbon sintered magnetite fluxing sinter. good metallurgical performance, but more dense structure, cooling proceeded slowly. From the phase diagram analysis of the main liquid phase formation and condensation process of iron ore fines sintering, it is known that the low melting point compound formed in the liquid phase and the mineral composition of the crystallization process depend on the chemical composition of the sintered material; Different grain growth speeds, different thermal expansion coefficients, and uneven distribution in the sintered ore body, the cooling process may cause thermal stress to remain in the sintered ore and reduce the strength of the sintered ore.
The physical properties of the material to be cooled affect the cooling process mainly by the size, shape and surface condition of the particles. If the upper limit of the particle size of the cooled sinter is large, the bulk center is not easily cooled down. If the content of the powder in the sinter is large, the powder is filled between the particles, which hinders the circulation of the air, so that the airflow is unevenly distributed, causing uneven cooling, prolonging the cooling time or affecting the cooling effect of the sinter. [next]
(II) Influence of gas permeability of the material layer The gas permeability of the cooling material layer is the main process parameter of the cooling process. In the sinter plant with hot sifting, the fine fraction of 5~0mm is screened out from the sinter, so that the cooling layer has good gas permeability, which can reduce the resistance and dust of the cooling layer, with less air volume and Low wind pressure gives good cooling. If the sinter is not cooled by the hot sifting, in addition to the necessary strengthening measures to ensure the burning and burning, the area of ​​the cooling machine, the cooling air volume and the wind pressure should be appropriately increased to obtain a good cooling effect. The test results of sinter ore with and without hot screen are shown in Figure 1 and Figure 2.
It can be seen from Fig. 1 and Fig. 2 that the cooling layer powder after hot screening has less powder, good gas permeability, low resistance, fast cooling air flow rate, easy to take away the heat of the sinter from the surface, and accelerate the cooling of the sinter. The cooling time is shortened. [next]
(III) Influence of cooling air flow rate and wind speed When the sinter is cooled to an average temperature of 100 to 150 ° C, the cooling process can be considered to be over. Because the sinter is cooled below this temperature, the belt conveyor, the sinter car and the blast furnace tank are not burned out.
Figure 3 shows the relationship between the air flow rate and the cooling time (the thickness of the layer in the figure is 432 mm). As can be seen from the figure, the slopes of all the curves are consistent, indicating that the cooling time is inversely proportional to the air flow. Increasing the wind speed can speed up the cooling; if the wind speed is small, the cooling time is extended. However, if the wind speed is too large, it will not accelerate the cooling rate, but increase the resistance loss, because the cooling wind speed is related to the heat conduction speed of the average largest nugget of the sinter. The relationship between the wind speed and the large heat transfer coefficient of the sintered ore is shown in Fig. 4. It can be seen from Figure 4 that when the wind speed reaches a certain value, increasing the wind speed will no longer speed up the cooling. Suitable wind speeds generally do not exceed 2m/s.
The cooling time is usually about 30min, and the cooling air volume (standard) is generally 3500~4800m 3 /(t•s).
The cooling time of the blast is generally about min, and the cooling air volume (standard state) is generally 2000 to 2200 m 3 /(t•s).
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