Discussion on Calcining Calcium Carbonate by Dynamic Calciner


[1] Northeastern University, Shenyang 110031 [2] Shenyang Science and Technology Machinery Industrial Technology Research Institute, Shenyang 110031 Liaoning Dongda Powder Engineering Technology Co., Ltd.

The calcination process of dynamic calcined calcium carbonate and the industrial experiment made by dynamic calcination device are discussed. Through experiments, it is shown that the products made by dynamic calcination have the advantages of large product capacity, fast digestion, high activity, stable calcination temperature, and high product quality. It has the advantages of stable quality and so on, and it is an advanced calcination process.

I. Overview

The use of shaft kiln to calcine calcium carbonate to prepare light calcium is a method commonly used in the production of light calcium. related to product quality. Practice has proved that the smaller the calcination particle size, the lower the calcination temperature, the shorter the calcination time, and the stable calcination temperature, the product quality is stable, the calcined product has large capacity, fast digestion and high activity. At present, the requirements for high-quality light calcium are getting higher and higher. It is very important to provide a calcining kiln that meets the requirements of advanced technology. Dynamic calcination is a new type of advanced calcining equipment currently used in the production of light calcium to improve product quality. 

Second, the technological comparison between dynamic calcination and shaft kiln calcination

The process of dynamic calcination is to first crush calcium carbonate to 120-325 mesh, and spray the ground dry powder into the furnace at the top of the calcining kiln to achieve a rapid heat exchange process in an instant. After several seconds in the flow, the calcination process ends. , the calcined material is discharged from the bottom of the tower and enters the emulsification process. The carbon dioxide gas and combustion gas produced by calcination are discharged from the tower, and after the water washing and dehydration process, it is ready for carbonization. According to the above process flow, the temperature in the calciner, the particle size of limestone and the calcination time are the important factors to be considered first. Theoretically, the decomposition temperature of calcium carbonate is above 500 °C, and the decomposition is most intense when it is above 800 °C. In shaft kiln calcination, limestone lumpiness and calcination time depend on lime lumpiness. This is because the thermal conductivity of lime is smaller than that of limestone, so the larger the limestone lumpiness is, the surface thickness of the lime layer gradually increases with the progress of calcination. When the thermal conductivity increases, the thermal conductivity decreases, and the more difficult it is for the heat to enter the limestone. It must stay in the high temperature area for a period of time. If the residence time is not reached, the sandwich and burning will occur. If the time is exceeded, it is easy to cause overburning. Therefore, the block size, time and temperature must be strictly controlled. Mastering, can burn out qualified products. The calcination rate of limestone is more closely related to the temperature. When the temperature is 900 °C, 3.3 mm of limestone can be burned through per hour, and at 1000 °C, it can be burned through 14 mm per hour. The higher the temperature, the faster the calcination speed. At the same time, because the heat is introduced deeper into the limestone, the resistance of carbon dioxide to escape is also greater, and the reaction speed is slower. Dynamic calcination and shaft kiln calcination have significant differences in the process of limestone particle size, calcination time and temperature. During dynamic calcination, the limestone is ground to 120-325 mesh, and the particle size is 70-40 μm. Under this particle size, the firing rate of the same shaft kiln can be increased by more than 300 times, the particle size becomes smaller, and the specific surface area increases. , the heat exchange area increases, and the calcination time is only a few seconds to ten seconds. It can be seen that reducing the particle size of limestone and increasing the specific surface area is very beneficial to shorten the calcination time and reduce the resistance to carbon dioxide escape.

The relationship between limestone particle size and calcination time

An important factor that should also be considered in dynamic calcination is the influence of carbon dioxide production during calcination on the carbonization process. As dynamic calcining fuels, oil and gas are used. From economic considerations, a hot gas generator is used to make gas, and the heat produced by burning coal is used as calcination. The heat source is more convenient and economical. The production of 1 ton of calcium oxide requires 500m3 to 600m3 of gas (equivalent to 100kg of standard coal). Burning 1m3 of gas requires a standard air volume of 1.1m3 to 1.2m3, then the production of 1 ton of calcium oxide requires a standard air volume of 1200m3 to 1300 m3, and the production of 1 ton of calcium oxide produces 386 m3 of carbon dioxide, so the total pumping volume of 1 ton of calcium oxide produced About 1500m3 ~ 1600m3. After heat exchange and washing, the gas produced by the dynamic calciner has a temperature of about 50°C, and the total exhaust volume is about 2000m3. At this time, the carbon dioxide concentration accounts for about 20-28%, which is equivalent to the concentration of the mechanized shaft kiln.

Dynamic calcination is a continuous operation process. The material is continuously fed and discharged. The heating and calcination time of the material in the calciner are balanced and equal, and the calcination temperature is very easy to control. The calcination process requirements can achieve small crystals, large specific surface area, high porosity, low bulk density, strong reactivity, and high yield of lime milk, which can produce active lime, small fluctuation during lime digestion, and fast digestion speed to produce gray milk Good physical properties, can produce refined ultra-fine, activated calcium carbonate products.

Three. Improvement and improvement of dynamic calcination to existing technology

The application of dynamic calcination technology in the field of calcium carbonate calcination can improve and stabilize limestone calcination quality and lime milk emulsification quality, realize continuous industrial production, and adjust and improve the existing calcination process.

From the production process, the carbon dioxide gas and the entrained dust produced by calcining limestone in the dynamic calciner are separated by the separator and then enter the water washing tower for washing, then enter the gas-water separator, enter the carbonization process through the compression mechanical blower, and the lime continuously discharged from the calciner The powder can directly enter the emulsifier, and the hot water for washing discharged from the washing tower enters the emulsifier, and the hot water and the heated lime powder are used for emulsification operation, so that the emulsification speed is obviously increased, and a stable operating temperature is formed, so that the digestion can be carried out continuously. , In addition, because the calcium oxide particles after calcination are very small, the volume yield of lime milk varies with the size of the particles. When the calcium oxide particles are 10 mm, the volume of the calcium oxide paste per unit is 147 cm3, and when the calcium oxide particles are 10 mm When the particle size is 0.02 mm, the volume of the paste can reach more than 200 cm3. This is because the calcium oxide with small particle size increases the total surface area of calcium oxide with larger particle size during the reaction process.

As mentioned above, the application of dynamic calcination in the field of calcium carbonate production has a continuous and stable operation process, which reflects the reasonable matching of calcination and emulsification processes. More importantly, it can produce refined calcium carbonate products, which will promote the production of calcium carbonate in my country. Technological progress has brought calcium carbonate production technology to a higher level.