Reasons and treatment methods for circle formation in lime rotary kiln
The lime rotary kiln plays a crucial role in the lime production process. However, the phenomenon of ring formation often troubles production enterprises, not only affecting the ventilation and material transportation inside the kiln, but also reducing production efficiency, increasing energy consumption, and even shortening the service life of the kiln body. Therefore, understanding the causes of lime rotary kiln ring formation and mastering effective treatment methods are of great significance.
1、 Reasons for Ring Formation in Lime Rotary Kiln
（1） Raw material factors
High levels of harmful components in raw materials
If limestone raw materials contain a large amount of low melting point substances, such as oxides of potassium, sodium, sulfur, etc., these substances will form a liquid phase at high temperatures, increasing the viscosity of the material. When the material moves inside the kiln, it is easy to adhere to the kiln wall and gradually form a circle.
Unreasonable particle size of raw materials
If the particle size of the raw material is too fine, it will cause the material to form a liquid phase prematurely in the kiln, increasing the possibility of agglomeration. However, if the particle size is too coarse, it will cause uneven heat and mass transfer of the material in the kiln, which can easily lead to high temperature zones in some areas and create conditions for ring formation.
（2） Fuel factor
Unstable fuel quality
High ash content or inappropriate volatile matter in fuel can affect combustion efficiency. Ash may form slag at high temperatures and adhere to the kiln wall. Excessive or insufficient volatile matter can lead to irregular flame shape, uneven temperature distribution inside the kiln, and thus cause ring formation.
Incomplete combustion
If the ventilation inside the kiln is poor or the fuel is not fully mixed with air, the fuel cannot be completely burned, resulting in a large amount of carbon monoxide and unburned coal powder. These substances will react with other substances in the kiln to form viscous substances, promoting the formation of rings.
（3） Operational factors
Improper temperature control inside the kiln
If the temperature inside the kiln is too high or fluctuates too much, it will increase the amount of liquid phase in the material or change the viscosity of the already formed liquid phase. High temperatures make it easier for materials to adhere to the kiln wall, while temperature fluctuations can cause repeated condensation and melting of materials on the kiln wall, accelerating the formation of rings.
Unreasonable kiln speed
If the kiln speed is too fast and the material stays in the kiln for a short time, it may lead to incomplete calcination of the material, and the insufficiently reacted material is prone to adhere to the kiln wall and form rings. If the kiln speed is too slow, the materials will accumulate inside the kiln, increasing the contact time and friction between the materials and the kiln wall, which is also conducive to the formation of rings.
Unstable feed quantity
The fluctuating amount of feed can disrupt the thermal balance within the kiln. When the amount of feed is large, the load inside the kiln increases, the temperature decreases, and the material is prone to accumulate in the low-temperature zone and form circles. When the feed rate is small, the temperature inside the kiln increases, which in turn increases the liquid phase of the material and promotes ring formation.
（4） Structural factors of kiln body
Damaged kiln lining
The wear or detachment of kiln lining will directly expose the kiln wall to high temperature and material erosion. Without the protection of kiln lining, the kiln walls are more susceptible to erosion and adhesion of materials, thereby accelerating the formation of rings.
Unreasonable kiln design
Improper design of parameters such as kiln inclination and diameter can affect the movement speed and residence time of materials inside the kiln, thereby affecting the heat and mass transfer processes inside the kiln and increasing the risk of ring formation.
2、 Treatment method for circle formation in lime rotary kiln
（1） Adjust raw materials and fuels
Optimize the quality of raw materials
Strictly screen limestone raw materials to reduce the content of harmful components. Advanced mineral processing technology can be used to remove impurities such as potassium, sodium, and sulfur from raw materials. At the same time, control the particle size distribution of the raw materials to meet the production requirements of the rotary kiln. Generally speaking, the particle size of the raw materials should be maintained within a certain reasonable range.
Choose the appropriate fuel
Choose fuels with stable quality, low ash content, and moderate volatile matter. Strengthen the detection and management of fuel to ensure the stability of fuel quality. At the same time, optimize the combustion system, improve the combustion efficiency of fuel, ensure full combustion of fuel, and reduce the production of incomplete combustion products.
（2） Optimize operational parameters
Stabilize the temperature inside the kiln
Adopting advanced temperature detection and control system, real-time monitoring of temperature changes inside the kiln. Reasonably set the temperature inside the kiln based on the characteristics of the materials and production requirements, and strictly control the temperature fluctuation range. By adjusting parameters such as fuel and ventilation, the temperature inside the kiln can be maintained stable.
Control the appropriate kiln speed
Determine the appropriate kiln speed based on the specifications of the kiln and the properties of the materials. During the production process, maintain stable kiln speed and avoid frequent adjustments. In general, the kiln speed should be reasonably selected based on the calcination time of the material and the heat transfer inside the kiln to ensure that the material can be fully calcined inside the kiln without accumulation.
Stable feed rate
Using precise measuring equipment to ensure stable feeding volume. Develop a reasonable feeding plan to avoid significant fluctuations in feeding volume. At the same time, strengthen the maintenance and management of the feeding system to ensure the continuity and uniformity of the feeding.
（3） Processing Circles
Hot burning method
When the ring is not too severe, the hot burning method can be used. By appropriately increasing the temperature inside the kiln, the material at the ring is softened or melted, and under the erosion of the material and the rotation of the kiln body, the ring falls off on its own. But when using the hot firing method, attention should be paid to controlling the amplitude and time of temperature rise to avoid damage to the kiln body.
Cold burning method
For more severe knots, cold burning method can be used. Stop feeding first, let the materials in the kiln gradually empty, and then lower the kiln temperature. After the ring is cooled, it should be manually or mechanically broken and removed. The cold burning method is relatively complex to operate, but the cleaning effect is good.
High pressure water gun flushing method
Use a high-pressure water gun to rinse the ring area and remove the ring material. This method is suitable for situations where the ring is not very sturdy and the position is easy to operate. During the flushing process, attention should be paid to safety to prevent high-pressure water guns from causing harm to personnel and equipment.
（4） Strengthen kiln maintenance
Regularly inspect the kiln lining
Establish a regular inspection system for kiln lining to promptly detect any wear or detachment of the lining. For damaged kiln lining, timely repair or replacement is necessary to ensure effective protection of the kiln wall.
Optimize kiln structure
Based on practical production experience, optimize the structure of the kiln body. For example, adjusting the inclination and diameter of the kiln, improving the movement of materials inside the kiln, and reducing the formation of rings. At the same time, strengthen the sealing performance of the kiln body to prevent cold air from entering the kiln and affecting the temperature distribution and combustion effect inside the kiln.
The formation of circles in lime rotary kilns is a complex problem that involves multiple aspects such as raw materials, fuel, operation, and kiln structure. By conducting in-depth analysis of the causes of ring formation and taking corresponding preventive and treatment measures, the occurrence of ring formation can be effectively reduced, the production efficiency and product quality of lime rotary kilns can be improved, and the service life of the kiln body can be extended. In the actual production process, enterprises should strengthen management, strictly control each production link, continuously optimize production processes and operating parameters to ensure the stable operation of rotary kilns and create greater economic benefits for the enterprise. At the same time, attention should also be paid to new technologies and methods in the industry, constantly exploring and innovating to better solve problems such as lime rotary kiln ring formation.
