- Time:Sep 04, 2023
1. Causes of damage to refractory materials in the cooling zone of cement kiln
1.1. Effect of high temperature
In the production of large dry process cement kilns, the kiln lining of the cooling zone is one of the weakest parts in the large rotary kiln. It is close to the kiln mouth under the heat radiation, the temperature at the kiln mouth is still as high as 1400 ℃, and the temperature of the secondary air entering the kiln reaches 1200 ℃.
1.2. Chemical attack
The flue gas circulates in the rotary kiln, and the enrichment is serious. The continuous penetration of alkali, sulfur and chlorine components intensifies the chemical erosion of the refractory materials in the cooling zone.
1.3. Clinker wear
Because the cooling zone is very short and close to the kiln mouth, the amount of clinker passing through the rotary kiln per unit time is large, and the kiln mouth is not protected by a kiln skin. The large-grained, high-strength clinker will seriously wear and wash the kiln lining. The kiln mouth material is easy to wear, so the refractory material in the cooling zone is worn to varying degrees.
1.4. Mechanical force
The cooling zone is located in the first wheel belt area of the rotary kiln, where the mechanical stress and axial stress will also generate a huge extrusion force on the refractory material.
1.5. Complicated working conditions
At the cooling zone, the temperature of the secondary air in the kiln is greatly increased, and the slope and rotation speed of the kiln body are accelerated. As a result, the working conditions here are extremely complicated, and even the phenomenon of brick falling occurs.
1.6. Frequent kiln shutdown
Frequent shutdown of the kiln will cause the refractory material at the kiln mouth to be subjected to rapid cooling and rapid heating, resulting in unstable thermal shock, cracking or even peeling of bricks.
In summary, the kiln lining with cooling zone faces multiple problems and challenges in the production of dry-process rotary kiln, such as high temperature, chemical erosion, material wear, mechanical force, complex working conditions and kiln shutdown failures. Frequent damage to the refractory materials in the cooling zone will inevitably lead to frequent kiln shutdowns, which not only affects the output, but also makes the refractory bricks in the undamaged parts often in a state of rapid cooling and rapid heating, which aggravates the damage of the overall lining. Therefore, the material selection and maintenance of the cooling belt kiln lining are very important. It is necessary to select the appropriate material and maintain it reasonably to ensure its performance and prolong its service life.
2. Solutions to the damage of refractory materials in the cooling zone of cement kiln
2.1. Optimizing the configuration of refractory materials
The alkali-sulfur content in cement clinker is not very high. Usually, silica bricks can meet the requirements. If the peeling phenomenon caused by too high alkali sulfur content often occurs, magnesia-alumina spinel bricks with strong corrosion resistance and excellent thermal shock stability can be used.
In recent years, on the basis of the original magnesia-alumina spinel bricks, Zhenjin Refractory has improved and upgraded its products and successfully developed a new generation of MA-8 high-grade magnesia-alumina spinel bricks. MA-8 introduces high-purity magnesium-aluminum spinel with small expansion to control the heterogeneous microstructure and improve flexibility and peeling resistance. At the same time, active additive components are added to form a network-like in-situ spinel in the brick, which improves the liquid phase permeability. By optimizing the material composition and microstructure, MA-8 has excellent thermal stress and corrosion resistance, and can effectively cope with high temperature and chemical corrosion.
Generally speaking, for large kilns with a production capacity of 5000t/d and above, the cooling zone is more likely to use magnesia-aluminum spinel bricks. For example, the cooling zone of the 10,000t/d ton production line of Huaxin Cement Huangshi Co., Ltd. uses real gold magnesium aluminum spinel bricks, and its operating cycle reaches 330 days.
Of course, the situation of each cement plant is different, and the selection of specific refractory materials can be dialectically selected according to the actual situation.
2.2. Optimal structural design
When the kiln body rotates, it is easy to cause the refractory bricks in the kiln to slide forward, in order to prevent the displacement between the bricklaying circles caused by this. At intervals of 5-10 meters in the kiln, set brick retaining rings with a thickness of 20-30mm and a height of 50-70mm to reduce axial sliding and improve the stability of the structure.
2.3. Strengthen cooling air control
Reasonably adjust the wind speed and pressure of the cooling air. The negative pressure of the kiln hood is 50--100Pa, and the air speed is 6m/s to ensure uniform cooling of the cooling zone and the kiln mouth, which is beneficial to prolong the service life of the refractory bricks.
2.4. Control process parameters
Adjust the process parameters such as the rotational speed, slope and secondary air temperature of the rotary kiln to reduce the heating degree and exposure time of the cooling zone and the kiln mouth, and create a good environment for the lining.
2.5. Optimize the kiln shutdown maintenance plan
Reasonably arrange the kiln shutdown maintenance plan, reduce the feeding amount 4 hours before the kiln shutdown, reduce fuel and front and rear air, when the hot air temperature drops to 160°C, stop the blower, exhaust fan, electric dust collector, close the front and rear dampers, and burn the kiln ash to The kiln tail temperature is lower than 250°C. Do a good job of maintenance at ordinary times, reduce the frequency and time of kiln shutdown due to failure, so as to reduce the impact of rapid cooling and rapid heat on the cooling zone and kiln mouth.
Through the comprehensive application of various measures, the service life of refractory materials in the cooling zone can be effectively extended, and its anti-wear, anti-erosion and thermal shock stability properties can be fully utilized, thereby reducing the maintenance frequency of the kiln and reducing production costs, thereby improving the stable operation of the production line and overall efficiency.
