(A) a thick layer of low-carbon material before the operation 20 years, the production of multiple self-fluxing sintered ore and a fine-grained magnetic powder as main raw iron ore, sintered poor permeability layers, have been used excessively thin layers The operation principle of fast speed is high, and the fuel consumption of the sinter is high, the FeO content is high, the strength is low, and the reducing property is poor. In the late 1970s, the production of high-alkalinity sinter was started. The proportion of limestone in the mixture increased, and the ratio of imported ore-rich powder increased. The permeability of the layer was improved, plus lime, granulation, The technique of preheating the mixture makes the thickness of the layer gradually increase. In 1991, the average thickness of the sinter layer in China's key enterprises has reached 406mm, reaching 470mm in 1998, and some advanced sinter plants have reached 600-700mm. The thick layer has created conditions for low-carbon sintering.
1. The thick material layer fully exerts the function of automatic heat storage to improve the quality of the sintered ore. In the case of normal segregation of the fuel along the material layer, the temperature of the lower layer is higher due to the automatic heat storage in the sintered layer. Sinter workers use this principle to increase the layer of material, which can result in reduced fuel consumption for sintering. According to the calculation of Shougang Sintering Plant, the sinter layer is increased from 300mm to 400mm, and the fuel per ton of sinter is saved by 4.1kg. The automatic heat storage in the sinter layer increases the temperature of the lower layer and reduces the FeO content of the lower sinter. Improved sinter strength. This is fully confirmed by the results of stratified sampling of Shougang and Baosteel sintering trolleys.
It can be seen that the thick material layer can not only save energy, but also enhance the oxidizing atmosphere in the material layer and improve the quality of the sinter.
2. Thick material layer widened high temperature oxidation zone During the sintering experiment, three thermocouples were inserted along the upper, middle and lower layers of the material layer to measure the temperature change of the material layer and the high temperature zone time, as shown in Figure 1.
Figure 1 illustrates that the high temperature oxidation zone along the bottom of the layer continues for a prolonged period of time, so thickening the layer facilitates the formation of acicular calcium ferrite. This is also the reason for the lower FeO in the lower layer.
(2) Strengthening the thick material layer of the mixed material The sintering mixture is required to have good gas permeability. Therefore, it is necessary to strengthen the granulation of the sintered mixture, which is especially important for many sintering plants in China with fine concentrate as raw material. China's sintering workers have many successful experiences in strengthening granulation and improving the permeability of the material layer, such as adding a certain amount of quicklime or slaked lime, maintaining proper moisture, stabilizing the quantity and quality of returning minerals, using hot returning and Steam heats the mixture and the like.
In recent years, in order to further improve granulation, China's sintering workers have done the following three aspects:
(1) Using the simulation experiment, optimize the rotation speed, filling rate and granulation time of the secondary mixer to achieve the best granulation effect. For example, a simulation experiment was carried out on the secondary mixing machine of the third sintering workshop newly built by Angang Sintering Plant. The best conditions were: filling rate was 11%~14%, and mixer speed was 6~7r/min. The granulation time is 4 min.
(2) Reduce the inclination of the mixer, add a baffle plate in the mixer, and implement spray water atomization to increase the granulation time, improve the ball forming conditions, and strengthen the granulation. For example, the effect is very good in the sinter plant of Shougang Mining Company, and the particles less than 1 mm are basically eliminated in the mixture.
(3) For the sintering plant that uses fine concentrates in a large amount, the method of fundamentally solving the gas permeability of the material layer is to implement the "pellet sintering method". This technology was first proposed by Japan Steel Tube Co., Ltd. and put into production at the Fushan Iron and Steel Plant. China's Anyang Iron and Steel Company has built a high-alkalinity pellet sinter production process in Shuiye Iron and Steel Plant, with very good results. [next]
(C) In the conventional sintering process of two fueling , the fuel is added once in the batching. Although the process is simple, it is not reasonable. The fuel is wrapped in mineral powder, which deteriorates the combustion conditions of the fuel. The so-called two-fueling, that is, a part of the fuel is added to the rear end of the secondary mixer, the purpose is to adhere the part of the fuel to the surface of the formed ball, thereby improving the combustion condition of the fuel and accelerating the sintering process. In addition, the particle size of the pellet caused by the secondary mixing is different, the specific surface area of ​​the large ball is small, and the amount of fuel adhered is small. When fabricating on a sintering trolley, the large ball has a large rolling energy and is laid on the lower layer, thus achieving a reasonable segregation of the fuel. Therefore, two fueling (also known as fuel addition) can increase production, reduce sintering energy consumption and improve quality.
Although individual sinter plants in China have achieved fuel addition, they have not yet summed up successful experiences. The author used Qian'an magnetite concentrate powder as raw material, and the alkalinity value was set to 1.80 fuel as coke powder. The fuel addition series experiment was carried out. The results are shown in Fig. 2 and Fig. 3.
Experiments show that as the proportion of external fuel is increased, the sintering productivity is significantly improved and the strength of the sintered ore is improved. Under the experimental conditions, the internal and external fuel ratios are each 50%. The external fuel blending technology can be used. The particle size of the internal and external fuels can be the same, and the fuel particle size is coarse. This experiment is the best with the coarser coke powder particle size of less than 3mm and 82%. [next]
(4) Limestone Granularity High alkalinity Sintering is required to be added with a large amount of limestone, especially for the sintering of high-concentration of fine-grained magnetite concentrate, which has an important influence on the particle size of limestone. To this end, a sintering experiment of limestone particle size was performed. The limestone particle size is 4~0mm, 3~0mm, 2.5mm~0mm and 2~0mm, respectively. The ore blending of Xinsan Sintering Workshop of Angang Sintering Plant and Qian'an Magnetic Concentrate of Shougang are used as raw materials, and the alkalinity value is matched. At 1.8, two series of sintering cup experiments were performed. The rules of the two groups of experiments were consistent.
(1) With the reduction of the limestone particle size, the powder of less than 1 mm in the mixture is significantly increased, and the gas permeability of the material layer is lowered.
(2) The limestone particle size has a significant effect on the yield and quality of the sinter, see Figure 4 and Figure 5.
As the limestone grain size is refined, it is advantageous for the mineralization reaction and the yield is improved. However, the gas permeability of the material layer deteriorates, the vertical velocity of the sintering decreases, the oxidizing property of the atmosphere is weakened, the acicular calcium ferrite in the sintered ore is reduced, and the glass phase is increased. Comprehensive analysis of the influence of limestone particle size on the quality of sintered minerals is also suitable for particle sizes of 3 to 0 mm.
(5) Low-temperature sintering test of magnetite concentrate The low-temperature sintering with hematite powder has been confirmed by domestic and foreign production practices. China's sintering raw materials are mostly magnetite concentrates. Can low-temperature sintering be achieved? Whether the above theoretical research can guide the actual production is a concern of the majority of sintering workers. To this end, the author conducted a low-temperature sintering test using Shougang Qian'an magnetic concentrate as raw material.
The above various low temperature sintering technical measures were adopted in the test.
The sinter has a basicity of 2.0, plus 3.0% quicklime, a limestone particle size of less than 3 mm, a content of 100% coke powder, a particle size of less than 3 mm, and a moisture content of (7.3 ± 0.3%)%. The parameters of the secondary mixer are: diameter 580mm, length 700mm, rotation speed 17r/min, filling rate 10%, granulation time 4min. Sintering fuel 50% externally, sintering cup diameter 200mm, material layer height up to 650mm.
Indicators and sinter mineral composition is very desirable. Most of the calcium ferrite is needle-like, a few are in the form of flakes, forming an interweaving structure with magnetite, forming a good mineral structure, so that the SiO 2 content in the sinter is reduced to 4.36%, and still has good strength. The higher FeO content in the sinter is mainly due to the fact that the iron ore raw material is completely high-grade magnetite.
(6) Conclusion
(1) The meaning of low-temperature sintering is to form a high-quality high-alkalinity sintered ore with acicular calcium ferrite as the main binder phase under certain process conditions. Acicular calcium ferrite is a Fe 2 O 3 -CaO-SiO 2 -Al 2 O 3 quaternary composite calcium ferrite with a chemical formula of 5CaO•2SiO 2 •9(Fe,Al) 2 O 3 , abbreviated as SFCA Its reducibility is comparable to that of hematite, and its strength is significantly better than other binder phase minerals.
(2) the formation of needle-like iron, calcium, and the development needs of low-temperature sintering, high temperature oxidation zone plays a key role in the formation and consolidation of the development of iron ore-forming needle-like calcium, is particularly important for magnetite sintering. Low-carbon high-layer operation is the basic process system for performing low-temperature sintering and fully exerting the role of high-temperature oxidation zone.
(3) Low-temperature sintering technology is easy to achieve. The ideal process conditions are: high alkalinity, low carbon content, thick layer.
(4) In the same fine magnetite concentrate to produce quality needle-like calcium ferrite sintered ore as the main binder phase content than the calcium ferrite acicular hematite with a low number, a number of high FeO content.
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