Position of sinter in sintering machine

1. 1. The concept of sintering

a series of physicochemical changes are made on the sintering equipment after mixing and pelletizing all kinds of powdery iron containing raw materials with appropriate amount of fuel and flux and adding appropriate amount of water< At present, the belt type suction sintering machine is widely used to proce sinter. The technological process of sintering proction is shown in Fig. 2-4. It mainly includes the preparation of sintering material, proportioning and mixing, sintering and proct treatment<
process flow of exhaust sintering

> preparation of sintering raw materials

① iron containing raw materials

high iron content, particle size & lt; 5mm ore powder, iron concentrate, blast furnace st, steel sheet, steel slag, etc

it is generally required that the raw material containing iron should have high grade, stable composition and less impurities

② flux

it requires high content of effective Cao, less impurities, stable composition, about 3% water content and more than 90% particle size less than 3mm in flux

adding a certain amount of dolomite into the sinter can make the sinter contain appropriate MgO, which has a good effect on the sintering process and can improve the quality of sinter

③ the fuel

is mainly coke powder and anthracite

the requirements for fuel are high fixed carbon content, low ash content, low volatile matter, low sulfur content, stable composition, water content less than 10%, and more than 95% of the particles with particle size less than 3mm

see table 2-2 for general requirements of raw materials for sintering<

General requirements of raw materials for sintering into the plant

● proportioning and mixing

① proportioning

proportioning purpose: to obtain sinter with stable chemical composition and physical properties to meet the requirements of blast furnace smelting

commonly used batching methods: Volume batching method and mass batching method

Volumetric Batching method is based on the condition that the bulk density of materials is constant and the mass of raw materials is proportional to the volume. The accuracy is poor

the quality batching method is based on the quality of raw materials. The specific volume proct method is accurate and easy to realize automation

② mixing

mixing purpose: to make the composition of sinter uniform, the moisture content appropriate, and easy to pelletize, so as to obtain the sinter mixture with good particle size composition, so as to ensure the quality of sinter and improve the output

mixing operation: wetting with water, blending and pelletizing

according to the different properties of raw materials, one mixing or two mixing processes can be used

the purpose of one-time mixing: wetting and mixing, and preheating the material when heating the return ore

the purpose of secondary mixing is to continue mixing and pelletizing, so as to improve the permeability of sinter layer

when sintering with rich ore powder with particle size of 10-omm, because its particle size has reached the requirement of pelletizing, one-time mixing is adopted, and the mixing time is about 50s

when fine grinding concentrate powder is used for sintering, because the particle size is too fine and the permeability of material bed is poor, in order to improve the permeability, pelletizing must be made in the mixing process, so the secondary mixing is adopted, and the mixing time is generally not less than 2.5 ~ 3min<

most sintering plants in China adopt secondary mixing< Sintering operation is the central link of sintering proction, which includes feeding, ignition, sintering and other main processes

① distribution

the operation of laying the bottom material and mixture on the sintering machine trolley

when the bedding material process is adopted, a layer of small sinter with particle size of 10-25 mm and thickness of 20-25 mm is laid as bedding material before the mixture is laid. The purpose is to protect the grate, rece the st removal load, prolong the service life of the fan rotor, and rece or eliminate the slag on the grate

after the bottom material is laid, the cloth is distributed. The size and chemical composition of the mixture should be evenly distributed along the vertical and horizontal direction of the trolley, with certain looseness and smooth surface

at present, the round roller distributor is widely used

② ignition

ignition operation is to ignite the material layer surface on the trolley and make it burn

sufficient ignition temperature, suitable high temperature holding time and uniform ignition along the trolley width are required for ignition

the ignition temperature depends on the melting temperature of sintering procts. It is usually controlled at 1250 ± 50℃ < The ignition time is usually 40-60s

ignition vacuum is 4-6kpa< The ignition depth is 10-20 mm

③ sintering

accurately control the air volume, vacuum degree, material layer thickness, machine speed and sintering end point

sintering air volume: the average air volume required per ton of sinter is 3200m3, which is (70-90) m3 / (cm2. Min) according to the sintering area

Vacuum Degree: it depends on the capacity of the fan, the resistance of the exhaust system, the permeability of the material layer and the air leakage loss

material layer thickness: appropriate material layer thickness should combine high yield with high quality. The thickness of material layer is 250-500mm

machine speed: the proper machine speed should ensure that the sinter is thoroughly burned at the predetermined sintering end point. In actual proction, the speed of the machine is generally controlled at 1.5 ~ 4 m / min

judgment and control of sintering end point: control the sintering end point, that is, control the position of the trolley when the sintering process is completed. The end point of small and medium sintering machine is generally controlled at the penultimate bellows, while that of large sintering machine is controlled at the penultimate bellows

the sintering process of belt sintering machine is carried out from top to bottom. The temperature change along the height of the material layer can be generally divided into five layers, and the reaction change in each layer is shown in Fig. 2-5. After ignition, sinter layer, combustion layer, preheating layer, drying layer and over wet layer appear successively. Then the last four layers disappear one after another, and finally only the sinter layer is left< After ignition at high temperature, the fuel in the sinter gives off a lot of heat, which makes the minerals in the sinter melt. With the combustion layer moving down and cold air passing through, the molten liquid phase is cooled and recrystallized (1000-1100 ℃) to solidify into sinter with mesh structure

the main change of this layer is the solidification of the melt, accompanied by crystallization and precipitation of new minerals, the cold air inhaled is preheated, and the sinter is cooled at the same time, and the low valent oxides may be reoxidized when contacting with the air

② combustion layer

the fuel burns in this layer, and the temperature is as high as 1350 ~ 1600 ℃, which makes the minerals soften, melt and bond into lumps

in addition to the combustion reaction, the melting, rection and oxidation of solid materials and the decomposition of limestone and sulfide occur in this layer

③ preheating layer

the mixture in the lower part is preheated to the ignition temperature quickly by the high temperature exhaust gas from the combustion layer, which is generally 400 ~ 800 ℃

solid state reaction begins in this layer, crystal water and part of carbonate and sulfate decompose, and magnetite is oxidized locally< (4) the drying layer is heated by the waste gas from the preheating layer, and the temperature of the drying layer quickly rises to above 100 ℃. A large amount of free water in the mixture evaporates, and the thickness of this layer is generally 10-30mm

in fact, it is difficult to separate the drying layer from the preheating layer, which can be collectively referred to as the drying preheating layer

the pellets in this layer are heated rapidly and dried rapidly, which is easy to be damaged and worsen the permeability of the layer

⑤ over wet layer

the hot waste gas from the dry layer contains a lot of water. When the material temperature is lower than the dew point temperature of the water vapor, the water vapor in the waste gas will re condense, which makes the water in the mixture increase greatly and form over wet layer

too much water in this layer will deteriorate the permeability of the material layer and rece the sintering speed

basic chemical reactions in sintering process

① combustion reaction of solid carbon

the combustion reaction of solid carbon is as follows:
after reaction, C0 and C02 are generated, and part of resial oxygen is proced, which provides oxidation-rection gas and heat for other reactions

the composition of the exhaust gas proced by combustion depends on the sintering raw material conditions, fuel consumption, the development of rection and oxidation reactions, and the composition of the gas pumped through the combustion layer

② decomposition and mineralization of carbonates

the carbonates in sinter are CaC03, mgc03, fec03, mnc03, etc., among which CaC03 is the main one. Under sintering conditions, CaC03 begins to decompose at about 720 ℃, and chemical boiling begins at 880 ℃. The decomposition temperature of other carbonates is lower

the decomposition proct Ca0 of calcium carbonate can react with other minerals in the sinter to form new compounds, which is mineralization. The reaction formula is:

CaCO3 + SiO2 = CaSiO3 + CO2

CaCO3 + Fe2O3 = Cao · Fe2O3 + CO2

if the mineralization is not complete, there will be resial free Ca0. During storage, it will digest with the water in the atmosphere:

CaO + H2O = Ca (OH) 2

make the volume of sinter expand and pulverize<

③ decomposition, rection and oxidation of iron and manganese oxides

under sintering conditions, Fe203 can decompose when the temperature is higher than 1300 ℃

Fe304 can decompose when the sintering temperature is lower than 1300 ℃

I don't know if it can meet your needs?

2.

The basicity of sinter is not the best, as long as the basicity is appropriate, it is good, that is, the basicity is suitable for the needs of blast furnace burden structure. In the case of higher basicity, it is beneficial to the strength of sinter, but it will affect the grade of sinter and rece the smelting strength of blast furnace. In the case of lower basicity, the sinter proportioning of blast furnace decreases, the pellet proportioning increases, and the charging grade increases, which is good for blast furnace

in a word, there is no best, just to see the needs of blast furnace proction, all for the high proction and smooth operation of blast furnace

the following is about sinter and basicity:

sinter

also known as basicity. It refers to the molar ratio of hydroxyl group to aluminum in the compound. The symbol B is generally used to represent alkalinity%. It is an important quality index of basic aluminum chloride, which directly determines the chemical structure and many characteristics of the proct, such as polymerization degree, molecular charge number, coagulation capacity, storage stability, pH value, etc