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Something you don't know about the kiln coating
  • Time:Nov 02, 2023
  • Views: 1

Kiln coating is cement clinker adhering to the surface of refractory material in the high temperature zone of the kiln, which plays a very important role in protecting the kiln lining and prolonging the life of the refractory material.

The flame temperature of new dry-process cement kiln is up to 1700℃ or more. Without the protection of kiln skin, the refractory material will soon be destroyed due to high temperature and erosion.

 

1、Aspects to consider when forming kiln coating

(1) Coordination of feed rate and timing

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, based on the specific condition of the kiln coating. Within 60 to 72 hours, the feed rate can gradually reach the normal level.

If a thick layer of kiln coating forms too quickly, it may collapse. Conversely, if the kiln coating hangs for too long, it will have a significant impact on production. It is important to establish the initial kiln coating for the long-term operation of the rotary kiln, but it is even more crucial to protect the kiln coating under normal conditions.

Therefore, reducing the feed rate appropriately can help stabilize the thermal system of the kiln, control the particle size of materials in the burning zone, and achieve better adhesion of the kiln coating.

(2) Raw material composition during kiln coating:

Conventional raw material composition can be used for smaller diameter kilns or those with lower saturation ratios (KH).

For larger diameter kilns or those with higher saturation ratios (KH), the calcium carbonate content of the raw material composition during kiln coating can be slightly lower than normal, depending on the specific circumstances of each plant, while ensuring the quality of clinker.

(3) Control of firing temperature:

The standard is to achieve fine and uniform clinker granulation, paying attention to the bulk density of the clinker and ensuring it is slightly lower than the normal bulk density. During kiln coating, it is necessary to maintain a stable burning temperature with minimal fluctuations. The distribution in the high-temperature zone should be uniform to ensure a solid, dense, and smooth kiln coating. Throughout the kiln coating process, large flames and material runout should be strictly prohibited.

Currently, there are two different methods for kiln coating:

  • Strictly control the burning temperature when the materials reach the burning zone, focusing on achieving fine and uniform particle size distribution to prevent the formation of large clumps and material runout (the clinker bulk density at this stage is only used as a reference). This approach greatly benefits the compactness and uniformity of the kiln coating.
  • Increase the temperature of the burning zone slightly higher than the usual kiln coating temperature when the materials reach the burning zone. After applying the first layer of kiln coating tightly adhered to the bricks, reduce the temperature back to the normal kiln coating temperature. Subsequent operations can proceed at the normal temperature, gradually applying kiln coating according to the specified time and thickness.

 

(4) Suitable coal powder composition:

The composition of pulverised coal needs to be appropriate, the choice of volatile matter control in 5%-17% of pulverised coal, strict control of incoming raw coal moisture is not less than 8 ‰, such fuel can stabilise the kiln conditions, so that the position of the burner flames to remain stable, in order to form the number and viscosity of the appropriate, stable melt, more conducive to the kiln skin of the sticking hanging.

 

2、Methods for protecting and repairing the kiln coating: