How to solve the problem of upward movement of the calcination belt in the vertical lime kiln
The stable operation of lime kilns is crucial for product quality and production efficiency in the lime production process. However, the problem of upward movement of the calcination belt often troubles production enterprises and brings many adverse effects to production. In order to ensure the normal operation of the lime kiln, improve the production and quality of lime, it is of great significance to conduct in-depth research and solve the problem of upward movement of the calcination belt.
1、 Analysis of the reasons for the upward movement of the calcination belt
（1） Raw material factors
Uneven particle size of raw materials
The uneven size and distribution of raw material particle size can affect the permeability and heat transfer efficiency of materials in the kiln. If there is a significant difference in the particle size of limestone entering the kiln, small particle materials are prone to fill the gaps between large particles, resulting in a decrease in the permeability of the material layer and an increase in airflow resistance. This will result in uneven ventilation inside the kiln and excessive local air flow, causing the position of the calcination belt to shift upwards.
Excessive moisture content in raw materials
Excessive moisture content in the raw materials can absorb a large amount of heat during the calcination process, resulting in uneven temperature distribution inside the kiln. The water vapor formed after water evaporation will hinder the flow of gas, affect the progress of calcination reaction, and thus promote the upward movement of calcination zone.
（2） Operational factors
Improper air volume control
Air volume is one of the important factors affecting the calcination process of lime kilns. If the air supply volume is too large, it will cause the air flow velocity in the kiln to be too fast, resulting in a shortened residence time of the material in the kiln, and insufficient heat transfer to the material, thereby causing the calcination belt to move upwards. On the contrary, if the air supply is too small, the oxygen supply in the kiln is insufficient, and the combustion is incomplete, it will also affect the normal position of the calcination belt.
Unreasonable feeding speed and method
Excessive or uneven feeding speed can lead to unstable material layer thickness, with local material layers being too thick or too thin. Areas with excessively thick material layers have poor breathability, making it difficult to transfer heat and easily causing the calcination zone to rise; Areas with a thin material layer are prone to ventilation short circuits, which can also affect the position of the calcination zone.
Unreasonable unloading speed
Slow unloading speed can cause excessive accumulation of materials in the kiln, increase material layer pressure, decrease air permeability, and lead to an increase in the calcination zone. If the unloading speed is too fast, it will cause the material layer in the kiln to become thinner, heat is easily lost, and it is also not conducive to the stability of the calcination belt.
（3） Equipment factors
Unreasonable kiln structure
The unreasonable design of the kiln body structure of the lime kiln, such as improper ratio of kiln diameter to kiln height, unreasonable layout of ventilation pipes, etc., can affect the distribution of airflow and material movement inside the kiln, leading to the upward movement of the calcination belt. Damage to refractory materials
The refractory materials inside the kiln may be damaged due to factors such as high temperature and chemical erosion during long-term use. After the damage of refractory materials, the insulation performance of the kiln body decreases, heat loss increases, and the temperature distribution inside the kiln is uneven, which can easily cause the calcination belt to move upwards.
2、 Specific measures to solve the upward movement of calcination belts
（1） Optimize raw material management
Control the particle size of raw materials
Strictly screen and grade the limestone entering the kiln to ensure uniform particle size of the raw materials. Generally speaking, the particle size of limestone should be controlled between 40-80mm, and the particle size distribution curve should be as narrow as possible. By optimizing the particle size of raw materials, the permeability of the material layer can be improved, the heat transfer effect can be improved, and the position of the calcination belt can be stabilized.
Reduce the moisture content of raw materials
Before the raw materials enter the lime kiln, effective drying measures should be taken to reduce the moisture content of the raw materials. Natural drying and drying methods can be used to control the moisture content of the raw materials below 1%. This can reduce the impact of water evaporation on the temperature and airflow inside the kiln, which helps to maintain the stability of the calcination zone. （2） Standardized operating procedures
Reasonably control the air volume
Accurately calculate and adjust the air supply volume based on the specifications, raw material characteristics, and production requirements of the kiln. By installing an air volume monitoring device, the air volume and pressure inside the kiln can be monitored in real time, and adjusted according to the actual situation. Generally speaking, while ensuring full combustion of fuel, the air flow should be reduced as much as possible to prolong the residence time of materials in the kiln and improve heat utilization efficiency.
Optimize the feeding method
Adopting a uniform and continuous feeding method to ensure stable material layer thickness. Automated feeding equipment can be used to automatically adjust the feeding speed based on parameters such as material level and temperature inside the kiln. At the same time, attention should be paid to the position and angle of feeding to avoid uneven distribution of materials in the kiln.
Adjusting the unloading speed
Reasonably adjust the unloading speed based on the calcination of materials in the kiln and the height of the material layer. The unloading speed should match the feeding speed to maintain the balance of materials in the kiln. By installing a discharge control device, precise adjustment of the discharge speed is achieved to stabilize the position of the calcination belt.
（3） Improve equipment structure
Optimize the kiln structure
When designing and constructing a lime kiln, the structural rationality of the kiln body should be fully considered. Reasonably determine the ratio of kiln diameter to kiln height, optimize the layout of ventilation ducts, and ensure even distribution of airflow inside the kiln. At the same time, it is necessary to ensure good sealing of the kiln body, reduce gas leakage, and improve thermal efficiency.
Regular inspection and maintenance of refractory materials
Regularly inspect and maintain the refractory materials inside the kiln, and promptly identify and repair damaged parts. Select high-quality, high-temperature resistant, and corrosion-resistant refractory materials, and install and masonry according to the correct construction methods. Good refractory materials can effectively maintain the temperature inside the kiln, reduce heat loss, and stabilize the position of the calcination zone.
3、 Implementation steps for resolving the upward movement of the calcination belt
（1） Problem diagnosis
Firstly, conduct a comprehensive inspection and analysis of the operation status of the lime kiln, including aspects such as raw material quality, operating parameters, and equipment condition. Determine the specific reasons and severity of the upward movement of the calcination zone through on-site observation, data monitoring, and sampling analysis.
（2） Develop solutions
Based on the diagnostic results and combined with the actual production situation, develop a detailed solution. The plan should include specific improvement measures, implementation steps, division of responsibilities, and timeline. When formulating a plan, full consideration should be given to feasibility and economy to ensure that the plan can be effectively implemented.
（3） Implement improvement measures
Implement improvement measures gradually according to the formulated solution. During the implementation process, it is necessary to strengthen on-site management and supervision to ensure that all measures are strictly implemented in accordance with requirements. At the same time, it is necessary to timely record the data and situation during the implementation process, in order to evaluate and adjust the effectiveness of improvement.
（4） Effect evaluation
After implementing improvement measures for a period of time, evaluate the operational effectiveness of the lime kiln. By comparing production data before and after improvement, such as output, quality, energy consumption, etc., determine whether the improvement measures are effective. If the improvement effect is not ideal, the reasons should be analyzed in a timely manner, the plan should be adjusted and improved, and further improvement should be carried out.
The upward movement of the calcination belt in a vertical lime kiln is a complex problem that requires comprehensive analysis and solution from multiple aspects such as raw materials, operation, and equipment. By optimizing raw material management, standardizing operating procedures, improving equipment structure, and following scientific implementation steps for improvement, the problem of upward movement of the calcination belt can be effectively solved, improving the production efficiency and product quality of the lime kiln, and bringing greater economic and social benefits to the enterprise.
