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What are the factors that affect limestone calcination?

The main component of limestone is calcium carbonate. Calcined to produce quicklime can be used to prepare calcium carbide, ash calcium powder, lime paste, light calcium carbonate, nano calcium carbonate and other products. It is an important industrial raw material. Calcination is a key process in limestone production. The quality of calcination has a great impact on the quality of subsequent products. Therefore, studying the influencing factors in the calcination process of limestone is of great significance to improve the quality of products.
Calcination of limestone is generally carried out in a lime kiln. Calcination of limestone is a series of processes involving physical and chemical changes. According to these changes, limestone is calcined in a kiln and divided into preheating zone, calcination zone and cooling zone three sections.
Factors affecting calcination:
The series of physical and chemical changes of limestone in the shaft kiln is complicated. In actual operation, in order to better control the calcination of limestone in the shaft kiln, to achieve high quality, high yield, stable low consumption, it is necessary to strict control.
Limestone calcination temperature
Limestone calcination rate has a great relationship with temperature. At normal pressure, the decomposition temperature of limestone is 898 ° C, and it decomposes rapidly after the temperature is greater than 925 ° C. When the calcination temperature is 900 ° C, the limestone decomposition rate is 3.3 mm / h; 1000 ° C is 6.6 mm / h; 1100 ° C is 14 mm / h. It can be seen that increasing the calcination temperature can accelerate the decomposition of limestone. However, when the calcination temperature is higher than 1100 ° C, over-burning is liable to occur, the lime crystal grains are rapidly increased, the lime activity is deteriorated, the digestion time is increased, and the product quality is lowered. Therefore, the calcination temperature should be controlled at about 1050 ° C in actual production.
2. Limestone grain size
The calcination rate of limestone depends on the particle size of the limestone, and the larger the particle size, the slower the calcination rate. The decomposition of calcium carbonate in limestone is promoted layer by layer. The thermal conductivity of quicklime is smaller than that of limestone. The thicker the lime layer, the worse the thermal conductivity and the longer the heat transfer time. The more difficult it is to decompose CO2. Escapes, causing the generated lime to gradually increase in CaO crystal due to a long period of high temperature, and the decomposition rate is lowered. It can be seen that the large-diameter limestone has a longer decomposition time than the small particle diameter, and calcination is also more difficult.
3. Fuel particle size, ratio
The production of lime kiln for solid fuel is usually fueled by coke and anthracite. The block size of the fuel must be compatible with the block size of the limestone. The rate of decline of the fuel in the kiln must be compatible with its burning rate. If the particle size is too small, the temperature in the preheating zone will increase, the calorie layer heat will decrease, and the calcination amount of lime will increase. If the particle size is too large, the fuel will not be completely burned in the calcination zone, and the calcination zone will move down, which is easy to produce lime burn.
4. Air supply
In general, the control of the amount of air is expressed by the pressure, that is, the supply air pressure. In the case of a suitable fuel ratio, the magnitude of the wind pressure will affect the up or down movement of the calcination zone in the lime kiln, and affect the change of the kiln gas during the calcination process.
5. Kiln method
The kiln method of the lime kiln is a mixed kiln method and a layered kiln method. The mixing method can make the limestone and the fuel mixture relatively uniform, and is suitable for the shaft kiln with small ratio and small fuel addition at one time; the layering method is convenient for adjusting the distribution state of the fuel in the kiln section, and is suitable for the vertical kiln with a large ratio.

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