Characteristics of white cement clinker:
1. The grinding particle size is small and the fine powder is more: the analysis result of clinker shows that the white cement clinker has finer grain size and more fine powder, and the fine powder content (80m) reaches about 55%;
2. fragile and difficult to grind: the grinding work index is only 6.32kWH / t, but T3000 = 63.7min, 12% higher than the normal clinker 57min, indicating that the clinker is easy to coarse but difficult to fine grinding, and a warehouse The discharge particle size is also finer than the ordinary double-cylinder mill. This is because the white cement clinker forms a dense glass phase after quenching and quenching in the bleacher, and the particles are fine but difficult to grind and have high abrasiveness.
3. Large water content: Since the clinker is cooled by drifting water spray, the water content is much higher than that of gray cement clinker. The water content of clinker is generally 0%-0.5%, and the white cement clinker is about 1%-2%. The hand is caught in a damp, and the production is easy to paste.
White cement clinker production process
1. raw materials ingredients
The general design principle of the white cement production line is: to reduce the pollution of non-ferrous metal elements, to ensure the quenching effect of the kiln clinker, and to obtain the spoiler high whiteness cement clinker.
In order to ensure that the whiteness of the cement reaches the standard, the raw materials must be selected to limit the color of the oxide. Therefore, white cement raw materials generally use pure limestone (calcium raw materials), kaolin (clay raw materials), quartz sand (corrected raw materials), and choose white alabaster or high-quality fiber gypsum as retarder.
2. raw material preparation
The key to the raw meal preparation system is to make the finished raw product meet the calcination requirements of the firing system. For the white cement firing characteristics, the raw material preparation adopts a dry-wet combination process. For the less greasy silicon raw materials, namely quartz sandstone and pyrophyllite, the ball mill is separately pulverized, and the fineness of grinding is much finer than that of common raw materials. Generally, it is 5% of the 45μm sieve, which has reached or exceeded The fineness of the finished product of ordinary cement.
3. raw material grinding
The pyrophyllite was first crushed by a jaw crusher to a particle size of 25 mm and then fed to a roller press for fine crushing. The finely divided pyrophyllite can reach 90% 3mm, and then two people in parallel with a wet mill to grind separately, in order to reduce the environmental pollution of siliceous dust. The water content of the abrasive slurry is generally 45% to 50%, and the fineness is controlled to be 5% of the 45 μm sieve.
The pyrophyllite slurry is mixed and dried in the roller mill with other raw materials, and the raw material of the roller mill is to ensure the composition, fineness and moisture are qualified. The fineness of the roll mill raw material is controlled to 5% of the 90μm sieve and 0.5% of water. Because the raw material preparation process uses the dry and wet lines to grind separately, and the water content of the pyrophyllite slurry exceeds 45%, so that the comprehensive human grinding moisture is as high as 15% or more, so the raw material composition stability and the material drying in the roller mill. It is a big difficulty in design.
4. clinker calcination
In the calcination process of white cement clinker, the iron content in the raw material composition is extremely low, the amount of liquid phase in the calcination process is small, the calcination temperature is high, and the energy consumption is high. Therefore, a reasonable kiln type must be selected to reduce the heat consumption of white cement clinker. According to relevant research, the heat consumption of traditional small-scale hollow kiln clinker producing white cement is as high as 9614~11286kJ/kg. Compared with the hollow kiln, the calcination heat consumption of the precalciner kiln system is reduced by about 40%. From the point of view of consumption, the precalcining kiln process is an important development direction of white cement production.
5. clinker bleaching
Bleaching of white cement clinker is an important step in improving the whiteness of clinker in firing. At present, the white cement clinker bleaching process at home and abroad mainly has the following methods:
5.1 Water bath method: The high temperature kiln clinker is discharged directly into the pool from the kiln mouth. After the water bath is cooled, the clinker and other equipment are used to take out the clinker. The method has high energy consumption, and partial hydration of the clinker after immersion in water reduces the strength of the clinker.
5.2 Spraying water in rotary kiln: The clinker is sprayed with water before the kiln is cooled, and the reducing agent is sprayed to prevent the formation of Fe203. In this method, some steam kiln increases the system energy consumption and affects the normal operation of the rotary kiln.
5.3 bleaching machine method: the single-cylinder cooling machine for the kiln clinker, also known as the single-tube bleaching machine, a certain nozzle is arranged in the single-tube bleaching machine, the cooling water is evenly sprayed onto the clinker, and the vaporized water vapor is extracted by the exhaust pipe. The single-cylinder bleaching clinker is cooled to 50-150 ° C and directly into the clinker bank. The method is the main process for the bleaching and cooling of clinker in the existing white cement production line, and is widely used.