The temperature gradient in the rotary kiln is large and the chemical atmosphere is complex, so the requirements for the refractory lining in different sections vary significantly. Placing clay bricks in the right position can control costs and extend the life of the kiln.
1.Structural division of rotary kiln
The rotary kiln can be divided into several functional areas along the length of the kiln. The temperature, atmosphere and material state of each zone are significantly different.
(1)Kiln tail and preheating section
The temperature here is usually 400-800°C. The material is preheated here and chemical corrosion is weak.
clay brick
(2)Decomposition zone
The temperature of the decomposition zone rises to 800-1200℃. Here the material begins to decompose, but the basic oxide content is still low.
(3)Firing zone
The firing zone temperature can reach up to 1450℃ or above. The material here melts to form a liquid phase, which causes the most severe chemical erosion and thermal shock to the refractory materials.
(4)Cooling zone and kiln head
The temperature here gradually drops to below 1000℃, and it is mainly subjected to material wear and temperature fluctuations.
2.Specific application areas of clay bricks in rotary kilns
Clay bricks use refractory clay as the main raw material. Its characteristics are low cost, good thermal stability and resistance to acidic medium corrosion.
Therefore, it is mainly used in rotary kilns where the temperature is relatively low and the chemical corrosion is mild. Specifically, there are the following points.
(1)Kiln tail preheating section
The kiln tail feeding end and preheating section are the main application areas of clay bricks. The temperature here is mostly below 800℃, and the material is mainly solid powder, which has weak chemical corrosion on refractory materials. Therefore, the compressive strength and wear resistance of clay bricks can meet the needs.
(2)Decomposition zone
This is the transition between clay bricks and high alumina bricks.
clay brick
At this point, although the material begins to decompose, the amount of alkaline oxide volatilized is small, and the alkaline corrosion effect on the material is limited. There are two points to consider at this point.
On the one hand, if high-alumina bricks are used directly, the cost will increase sharply. On the other hand, if all clay bricks are used, there is a fear that the edges may overheat.
Therefore, a circle of clay bricks is usually laid as a skeleton first, and then a layer of anti-stripping high-alumina bricks is superimposed on the hot surface to form a stepped transition through the thickness difference of the bricks. This allows the clay bricks to function as an “alkali erosion buffer zone,” preventing expensive high-alumina bricks from prematurely peeling off due to chemical erosion, making it both economical and durable.
(3)Cooling belt front end
Here, when there is no strong chemical attack, clay bricks are also used as transitional lining to balance cost and performance.
3.Performance requirements and adaptability of clay bricks in different parts
Although clay bricks are applicable to specific parts of rotary kilns, their performance requirements vary under different working conditions. Therefore, we need to make targeted selections.
First of all, due to the material scouring at the kiln tail and preheating section, clay bricks are required to have higher room temperature compressive strength and wear resistance. At the same time, it needs to have good thermal shock stability to cope with temperature fluctuations.
rotary kiln
Secondly, the low temperature zone in the decomposition zone requires the brick to have high refractoriness. And the load softening temperature needs to be controlled to avoid deformation under long-term high temperature.
Furthermore, clay bricks have insufficient alkali resistance. If the content of alkaline oxides in the material is high, it should be used with caution, or high-alumina bricks and other materials with better alkaline resistance should be used instead.
