What are the reasons for the upward movement of the calcination belt in the lime kiln shaft kiln
The position of the calcination zone is a key parameter in the production process of lime kiln shaft kiln. The normal position of the calcination zone is crucial for the quality, yield, and stability of the entire production process of lime. However, in actual production, there may sometimes be a phenomenon of upward movement of the calcination zone.
1、 Reasons related to raw materials
（1） Limestone particle size
Particle size becomes smaller
When the overall particle size of limestone decreases, its specific surface area increases, and the contact area with heat also increases accordingly. In this way, during the calcination process, heat can be transferred more quickly to the interior of limestone, causing limestone to start decomposing at relatively lower positions, resulting in the upward movement of the calcination zone.
For example, if the particle size of the limestone originally fed was mainly between 50-80mm, but due to adjustments in the crushing equipment, it becomes 30-50mm, it may cause the calcination zone to move upward.
Uneven particle size
The particle size distribution of limestone is uneven, and when the content of fine powder is too high, these fine powders accumulate tightly in the kiln, resulting in poor air permeability. During the calcination process, heat is concentrated in the area with more fine powder, leading to an earlier calcination reaction in that area and causing the calcination zone to shift upward.
（2） Limestone composition
Changes in impurity content
The variation of impurity content in limestone will affect its calcination characteristics. If the impurity content increases, especially the content of some low melting point impurities increases, they will form a liquid phase at lower temperatures, promote the calcination reaction, and cause the calcination zone to appear earlier, leading to upward movement.
For example, an increase in impurities such as silica and alumina may alter the calcination temperature range of limestone, causing the calcination zone to shift upward.
2、 Reasons related to fuel
（1） Fuel particle size
The fuel particle size is too fine
When the particle size of the fuel is finer, its combustion rate will accelerate, and the release position of heat in the kiln will move relatively upward. This is because fine particulate fuel is more easily carried by the airflow to higher positions for combustion in the kiln, causing the position of the calcination zone to rise accordingly.
For example, if the proportion of fine powder with a particle size less than 10mm is too high in coal fuel, it is easy to cause the calcination zone to move upward.
（2） Fuel distribution
Uneven fabric
During the fabric process, if the fuel is unevenly distributed in the kiln and concentrated in the upper part of the kiln, the heat in the upper area will be too concentrated. This will cause the limestone in the area to enter the calcination state earlier, resulting in an upward shift of the calcination zone.
For example, a malfunction or improper operation of the fabric equipment may result in excessive fuel accumulation on one side or area of the kiln, leading to the upward movement of the calcination zone.
3、 Reasons for ventilation
（1） Excessive ventilation volume
The overall ventilation volume exceeds the standard
When the ventilation inside the kiln is too high, heat will be quickly carried away by a large amount of airflow. In order to maintain the temperature required for calcination, the fuel will burn at a higher position inside the kiln, causing the calcination zone to move upward.
For example, if the fan power is set too high or the ventilation duct is not adjusted properly, resulting in a ventilation volume far exceeding the normal production requirements, it will cause the calcination belt to move upward.
Uneven local ventilation
Uneven local ventilation inside the kiln can also affect the position of the calcination zone. If the ventilation rate in the upper part of the kiln body is significantly higher than that in the lower part, more heat will be concentrated in the upper part, promoting the upward movement of the calcination zone.
4、 Reasons for operation and process parameters
（1） Improper control of calcination temperature
Temperature setting too high
If the calcination temperature is set too high during the production process, heat will be rapidly transferred inside the kiln. In this case, the limestone in the upper part of the kiln will reach the calcination temperature faster, causing the calcination zone to move upward.
For example, in order to pursue higher production or due to temperature control system failures, raising the calcination temperature beyond the normal range may cause the calcination zone to shift upward.
（2） Unreasonable adjustment of calcination time
The calcination time is too long
When the calcination time is too long, the limestone in the kiln continues to be calcined in a high-temperature environment. As time goes by, the lower limestone has completed the calcination reaction, and heat continues to transfer upwards, causing the upper limestone to start calcination, resulting in the upward movement of the calcination zone.
5、 Reasons for kiln structure
（1） Thermal insulation performance of kiln body
Poor insulation effect on the upper part
If the insulation performance of the upper part of the kiln body is poor, heat will be more easily dissipated. In order to ensure the calcination effect, more fuel will be burned in the upper part of the kiln, causing the calcination belt to move upward. For example, if the insulation material on the upper part of the kiln body ages or is damaged, resulting in rapid heat dissipation, it may cause the calcination zone to move upward.
The upward movement of the calcination zone in the lime kiln shaft kiln is the result of multiple factors working together. The position of the calcination zone may be affected by factors such as the particle size and composition of raw materials, the particle size and distribution of fuel, ventilation rate, operating process parameters, and kiln structure. In the actual production process, it is necessary to closely monitor the changes in these factors and make timely adjustments and optimizations to ensure that the calcination zone is in a reasonable position, guaranteeing the quality of lime and the stability of production.
