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What do you know about the kiln coating?
  • Time:Oct 27, 2023
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Kiln coating refers to the cement clinker that adheres to the surface of refractory materials in the high-temperature zone inside the kiln. It plays a crucial role in protecting the kiln lining and extending the lifespan of refractory materials.

In large-scale dry-process cement kilns, the flame temperature can exceed 1700°C. Without the protection of kiln coating, the refractory materials would quickly deteriorate due to the effects of high temperature and chemical erosion.

I. Aspects tobe considered when forming kiln coating in a cement kiln

1. Coordination of feed rate and time

Generally, during the first 24 hours of kiln operation, the kiln should maintain 60% to 70% of the normal feed rate. After 24 hours, the feed rate can be increased by 5% to 10% every 8 to 16 hours, depending on the specific condition of the kiln coating. Within 60 to 72 hours, the feed rate can be increased to the normal level.

If a thick layer of kiln coating is formed in a short period of time, it will collapse. Conversely, if the kiln coating is hung for too long, it will have a significant impact on production. The first layer of kiln coating is crucial for the long-term operation of a rotary kiln, but it is also important to protect the kiln coating under normal conditions.

Therefore, reducing the feed rate appropriately can stabilize the thermal system of the kiln, control the particle size of the materials in the burning zone, and ensure tighter bonding of the kiln coating.

2. Raw material composition during kiln coatingforming

Using conventional raw material composition is suitable for smaller diameter kilns or kilns with lower saturation ratio (KH) during regular operation because it is easier to adhere.

For larger kilns or kilns with higher saturation ratio (KH) during regular operation, the fixed value of calcium carbonate in the raw material composition for kiln coating forming can be slightly lower than normal kiln operation. This decision should be based on the specific situation of each plant while ensuring the quality of clinker.

3. Control of firing temperature

The clinker should have fine and uniform grain size, and the bulk density of clinker should be slightly lower than the normal level.

During kiln coating forming, it is necessary to maintain a stable firing temperature with minimal variation, and the distribution of the high-temperature zone should be uniform. Only in this way can the kiln coating be firmly bonded, compact, and smooth. It is strictly prohibited to have large flames or run raw materials during the entire kiln coating forming period.

Currently, there are two different methods for kiln coating forming:

(1)Strictly control the firing temperature when the materials reach the burning zone, maintain fine and uniform particles to prevent the formation of large clumps and running raw materials (the bulk density of clinker at this time is only used as a reference). This approach is beneficial for achieving dense and uniform kiln coating.

(2) Increase the burning zone temperature slightly higher than the temperature for regular kiln coatingforming when the materials reach the burning zone. After forming the first layer of kiln coating tightly to the refractory bricks, reduce the burning zone temperature to the usual level. Then continue operations at normal temperature, gradually forming kiln coating until reaching the specified time and thickness.

4. The coal powder composition should be appropriate

Using coal powder with volatile content controlled between 5% and 17%. It is important to strictly control the moisture content of raw coal entering the plant, which should not be less than 8‰. Such fuel can stabilize the kiln condition, maintain a stable flame position for the burner, form an appropriate and stable melt, and facilitate the adhesion of kiln coating.

 

II. Methods of protecting and patching kiln coating