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questions :Sintering of iron ore
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[Visitor (113.218.*.*)]answers [Chinese ]Time :2024-03-17
One of the main methods of iron ore briquetting. The iron concentrate obtained from the poor iron ore through beneficiation, the fine ore produced by the rich iron ore in the crushing and screening process, the iron-containing powder recovered in the production (blast furnace and converter furnace dust, continuous casting, rolled steel scale, etc.), flux (limestone, quicklime, slaked lime, dolomite and magnesite, etc.) and fuel (coke powder and anthracite), etc., are matched according to the required proportions, mixed with water to make granular sintering mixture, tiled on the sintering trolley, and sintered into blocks by ignition ventilation.
Brief History In 1887, the British Huntington and Heber Rheinland applied for the patent for the first time for the blast sintering method of sulfide ore and the sintering disc equipment used for this method.In 1906, the Americans Dwight and Lloyd obtained the patent of the extraction belt sintering machine in the United States.In 1911, the first continuous belt exhaust sintering machine with an effective area of 8m2 (also known as DL type sintering machine) was completed and put into operation at the Brocken Steel Company in Pennsylvania, USA. With the development of the iron and steel industry, the output of sinter has also increased rapidly, and the output of sinter in the world has reached more than 500 million tons by the 80s.China's earliest belt exhaust sintering machine was completed and put into operation in Anshan in 1926, the effective area of the sintering machine was 21.81m2.1935~1937 and four sets of 50m2 sintering machines were put into operation one after another, in 1943, the highest annual output of sinter reached 247,000 t The annual output of sinter reached 96.54 million tons, and the blast furnace clinker rate of key enterprises reached 90%...
After the advent of belt extraction sintering method, not only the production scale and output of sinter have been greatly improved, but also the production technology has made great progress: (1) the processing of sintered raw materials has been strengthened, such as the mixing of mineral powder, the crushing of fuel and flux, the accurate batching, granulation and preheating of the mixture, etc.; (2) a variety of new processes have been developed to increase production, save energy and improve quality, such as thick layer sintering, low temperature sintering, small ball sintering, double ball sintering, fine concentrate sintering, double layer sintering, hot air sintering, new ignition process, sinter granule, etc.; 3) Large-scale, mechanized and automated sintering equipment, computer for production management and operation control, (4) Environmental protection technologies such as dust removal, desulfurization and nitrogen oxide removal are applied.
Principle Pulverized ore sintering includes many physical and chemical reaction processes.No matter what kind of sintering method is adopted, the sintering process can basically be divided into: drying and dehydration, sintering material preheating, fuel combustion, high temperature consolidation and cooling and other stages.These processes are carried out in layers in the sintered material in sequence.Figure 1 shows the reaction of each layer of the sintering process under the condition of exhaust air.The extracted air is preheated through the sintered hot sinter layer, and the solid fuel is burned in the combustion layer, and the heat is released to obtain high temperature (1250~1500 °C). The high-temperature exhaust gas extracted from the combustion layer preheats and dehydrates the sintered material.According to the temperature and atmospheric conditions, different physical and chemical reactions are carried out in each layer: evaporation and decomposition of free water and crystal water, decomposition of carbonate, decomposition, reduction and oxidation of iron oxides, removal of impurities such as sulfur and arsenic, solid-phase and liquid-phase reactions of some oxides (CaO, SiO2, FeO, Fe2O3, MgO), cooling crystallization and consolidation of liquid phase, etc...
Combustion and heat transfer The combustion of solid carbon can provide more than 80% of the heat in the heat income of the sintering process and a high temperature of 1250~1500 °C (in the combustion layer), which ensures the physical and chemical reactions such as dehydration, limestone decomposition, iron oxide decomposition and reduction, desulfurization, liquid phase generation and consolidation in the sintering process. The combustion reaction also has an impact on the output of the sintering machine.
The combustion reaction of carbon in the sintered layer is more complex, which can generally be expressed as: C O2=CO2;2C O2=2CO;CO2 C=2CO;2CO O2=2CO2 In the area of carbon concentration, the CO concentration in the gas phase is high, the CO2 concentration is low, and the atmosphere is reducible; in the area of less carbon and no carbon, the CO concentration is low, and the atmosphere is reduced The two most important conditions for carbon combustion in the material layer are that the surface of the fuel particles is heated to the ignition temperature and the hot fuel surface needs to be in contact with the gas flow with sufficient oxygen concentration.The commonly used fuels for sintering are coke powder and anthracite, and the coal with high volatile content is not suitable for sintering because a large amount of volatile matter volatilizes before ignition, which is easy to block the pipeline...
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The heat transfer speed in the sintering process is very fast.The sintered material is a small particle material, the heat transfer efficiency is very high, and there is also an endothermic process such as water evaporation and decomposition, so the heat conduction is carried out very quickly in the sintered material.The heat is well utilized in the sintering process, which is mainly manifested in the low exhaust gas temperature and the "automatic heat storage effect" of the sintering process.The latter refers to the preheating to more than 1000 °C when the air is pumped through the hot sinter layer (quite a "regenerator" effect), which increases the heat income in the combustion layer ( It accounts for about 40% to 60% of the total heat income of the combustion layer), which increases the temperature of the combustion layer, and increases with the thickening of the sinter layer, and the temperature of the combustion layer increases, the sintering liquid phase increases, and the sinter strength increases, but the sintering speed decreases.The temperature of the combustion layer is affected by the amount of fuel and automatic heat storage, as well as the thermal effects of various chemical reactions in the combustion layer...
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Air flow movement in the sintered material layer All reactions and changes in the sintering process are carried out under the condition that the air flow continuously passes through the material layer.The air flow movement has a great impact on the output and quality of the sinter. The temperature of the combustion layer is related to the permeability of the material layer, because each layer is constantly changing in the sintering process, the air permeability and gas flow rate of the material layer are also changing.If the ball is broken after drying, the drying layer and the preheating layer will also produce a large resistance...
Pu = Fer / Ah (Ha / Si) En
In the formula, F is the air volume, m3 / min, A is the exhaust area, m2, h is the thickness of the material layer, m; S is the negative pressure of the exhaust, kPa, n is the coefficient related to the properties of the air flow, the characteristics of the raw material and the state of the material in the sintering process, generally n=0.5~1.0. The preheating of the sintered material is related to the sintering temperature, etc., whether the air flow is evenly distributed along the material surface will affect the uniformity of the sintering process, especially for large sintering machines...
Evaporation and condensation of water Adding a certain amount of water to the sintered material is the need for powder granulation. When the temperature of the sintered material reaches 100°C or higher, the water evaporates violently and the humidity of the sintering exhaust gas increases. When the exhaust gas leaves the drying layer and enters the wet material layer, the temperature is reduced below the dew point due to cooling, and the water vapor in the exhaust gas condenses in the wet material layer, so that the humidity of the wet material layer exceeds the original humidity, which is the "overhumidity phenomenon". Over-humidity destroys the ball and reduces the permeability of the bath. The use of preheated sintering material can reduce or eliminate overwetting. The phenomenon of overwetting during sintering of fine concentrate is more serious than that of sintering of rich ore powder. Water in the form of crystalline water is a chemically bound water that can only be decomposed and removed at higher temperatures.
Decomposition, Oxidation and Reduction The main decomposition reactions in the sintering process are the decomposition of carbonates (CaCO3, MgCO3 and FeCO3, etc.) and some oxides. When the decomposition pressure of carbonate is 101.325kPa, its temperature is: CaCO3 910 °C, MgCO3 630 °C, FeCO3 400 °C. Therefore, they are completely decomposable during the sintering process. If the limestone grain size is coarse, not only the decomposition time is prolonged, but also it cannot be completely decomposed and fully mineralized with other oxides, and the residual free CaO in the sinter will lead to the pulverization of the sinter. Therefore, the limestone grain size is required to be less than 3mm. The decomposition of carbonate is an endothermic reaction, and the amount of limestone is generally increased accordingly.
During the sintering process, iron oxides can be decomposed, reduced or oxidized according to their morphology, temperature and gas phase composition. The decomposition pressure of Fe2O3 is 20.6kPa (0.21 atmosphere) at 1383 °C, and the partial pressure of oxygen during the sintering process is low (6.8~18.6kPa), so thermal decomposition can occur at 1300~1350 °C (combustion layer) (6Fe2O3=4Fe3O4 O2). The decomposition pressure of Fe3O4 and FeO is very small, and it is impossible to produce thermal decomposition in the sintering process.The decomposition pressure of Fe2O3 is high, and the sintering waste gas often contains a small amount of CO, which can be reduced at 300~400 °C, so Fe2O3 is reduced in the preheating layer and the combustion layer; the decomposition pressure of Fe3O4 is low, and it can only be reduced in the atmosphere with high CO concentration, so the reduction is only carried out in the area where the temperature and CO concentration near the fuel particles in the combustion layer are high.FeO can only be reduced to partial metallic iron under the condition of high fuel ratio (>10%).Under the condition of low fuel ratio, the thermal decomposition and reduction reaction of Fe2O3 is relatively small.In the sinter layer, Fe3O4 and FeO can be partially oxidized to Fe2O3 due to the absence of carbon...
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Behavior of non-ferrous elements in the sintering process The decomposition pressure of MnO2 and Mn2O3 is very high (the temperature is 460°C and 927°C at 20.6kPa, respectively), so they can be decomposed and reduced in the preheating layer, and the generated Mn3O4 and SiO2 form Mn2SiO4 with low melting point. FeS2 begins thermal decomposition at 565°C (2FeS2 = 2FeS S2), but oxidation can be carried out before decomposition (4FeS2 11O2 = 2Fe2O3 8SO2), at 565~1383°C, oxidation and thermal decomposition are carried out at the same time, and the oxidation product is Fe3O4 at higher temperatures; FeS2 (FeS) can also be oxidized by Fe2O3, and the generated SO3 can be absorbed by CaO to form CaSO4. Reducing the particle size of mineral powder, with the appropriate amount of fuel to maintain sufficient oxidation atmosphere and high temperature, is conducive to desulfurization, and increasing the alkalinity to reduce the desulfurization rate, the general sintering process can remove more than 90% of the sulfur.The decomposition temperature of sulfate (BaSO4, etc.) is high, and the desulfurization rate is 80%~85%. As2O3 is volatile to remove, but As2O5 is very stable.PbS and ZnS can be oxidized to form PbO and ZnO, which are melted in the silicate slag phase.Therefore, As, Pb, and Zn are difficult to remove in the sintering process, and a part of them can be removed under the condition of high fuel ratio.Add a small amount of chloride (CaCl2, etc.) to generate volatile AsCl3, PbCl2 and ZnCl2, and remove 60% As, 90% Pb and 60% Zn.K2O, Na2O and P2O5 are difficult to remove during the sintering process...
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Melting and solidification of mineral powderThere is a solid-phase reaction before the melting of mineral powder.It is a reaction caused by the migration, diffusion and combination of new compounds caused by the increase of ionic kinetic energy on the surface of the mineral when the mineral powder is heated to a certain temperature below its melting point.The solid-phase reaction product 2CaO· The temperature of SiO2 is 500~690°C; The temperature of Fe2O3 is 400~600°C;2CaO· Fe2O3 is 400°C;2FeO· SiO2 is 970°C.These reactions can be carried out in the preheating layer and the combustion layer, but due to the short time, they will not develop very much.2CaO· SiO2 can be stored in all of it in high-temperature melts, and 2FeO· SiO2 partially decomposes, while CaO· Fe2O3 and 2CaO· Fe2O3 is all decomposed, and the solid-phase reaction is an exothermic reaction, and its reaction degree is not only affected by temperature, but also by mutual contact conditions and chemical affinity.In the process of reduction, oxidation and solid-phase reaction, some substances with low melting point will appear in the sinter, such as 2FeO· SiO2 (melting point 1205 °C) and its eutectic mixture (1177~1178 °C), CaO· Fe2O3 (1216℃),FeO-2CaO· SiO2 eutectic mixture (1280°C), CaO· Fe2O3-CaO·2Fe2O3 eutectic mixture (1200°C) and CaO· Fe2O3 - 2CaO· Fe2O3 - Fe3O4 eutectic mixture (1180 °C).These substances melt first, and continuously melt the rest of the materials, change their own composition, and form a new melt.The composition of the melt is affected by the composition of the sinter material and the degree of reduction and oxidation reaction, but the melt can be basically divided into two categories: silicate system and ferrite system.High grade of sinter (i.e., low SiO2 content), high alkalinity and high degree of oxidation are conducive to the formation of ferrite melt; on the contrary, it is conducive to the formation of silicate melt. Fe2O3 and 2CaO· Fe2O3), calcium silicate (2CaO· SiO2 and 3CaO· SiO2, etc.) and calcite-iron olivine (CaO· FeO· In sinter containing TiO2 and CaF2, perovskite (CaO· TiO2 ) and 3CaO·2SiO2 · The last solidification is the glass with a low melting point, the composition of which is mainly a complex silicate.For example, calcium ferrite has better reducing properties than calcium forsterite, and is better than ordivine (2FeO· SiO2 ) is better;2CaO· SiO2 undergoes crystal transformation (β2CaO· SiO2→γ2CaO· SiO2), about 10% of the volume expansion occurs, causing sinter pulverization, the strength of the amorphous glass is worse than that of the crystalline mineral...
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Sintering method and equipment The sintering method is divided into two kinds according to the flow direction of the gas in the material layer: the exhaust sintering method and the blowing sintering method. In the world's total sinter output, more than 99% of the total output of sinter is produced by belt exhaust sintering machine (see belt sintering machine sintering)...
Sintering process The process of sintering iron ore (concentrate, rich ore fine) into sinter. The modern sintering process consists of three parts: raw material preparation, sintering, and sinter processing. Each part consists of a number of processes (see Figure 2). The raw material preparation part includes the storage and mixing of raw materials (see ore mixing), the processing of fluxes and fuels, batching, mixing and granulation, and the distribution of materials. The sintering part includes ignition and exhaust sintering processes. The sinter treatment part includes cooling and crushing, screening, and granulation.
Processing of flux and fuel The main flux of sintering is lime and dolomite, which are carbonates.In the sintering process, not only should be completely decomposed, but also the decomposed CaO and MgO should be able to fully combine with other oxides to form new minerals; otherwise, the sinter will contain free CaO, causing pulverization, which is not conducive to storage.Therefore, the particle size of the flux should be less than 3mm;but the incoming particle size of limestone and dolomite is generally 40~0mm or coarse, so it must be crushed. Most of the crushing operations use hammer crushers or impact crushers, and the screening operations use self-centering vibrating screens.Quicklime and slaked lime generally enter the plant with a fine particle size, and do not need to be crushed, but quicklime has cautery on human skin, so it is advisable to use gas to convey and strengthen the sealing of the operation area...
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