Analysis of Common Problems in Lime Kiln Calcination of Lime
Lime production is a complex process that generates calcium oxide through the thermal decomposition reaction of calcium carbonate. As the core equipment for lime production, lime kilns often encounter various problems during the calcination process, which not only affect the production efficiency of lime, but also directly affect the quality of lime. Analyze several common problems in the process of calcining lime in a lime kiln and propose corresponding solutions to better maintain the lime kiln and ensure its normal operation.
1、 Burning phenomenon
Raw burning refers to the incomplete decomposition of limestone during the calcination process, resulting in the production of raw lime containing undecomposed calcium carbonate. The main reasons for the occurrence of raw burning phenomenon are as follows:
Excessive particle size: The calcination rate of limestone is closely related to its particle size. The larger the particle size, the more difficult it is for heat to enter the interior of the stone, resulting in a slower calcination rate and a higher risk of sandwich burning. The particle size of limestone in ordinary vertical kilns should be controlled between 40-80mm, and for larger kilns, it can be relaxed to 50-150mm.
Low fuel ratio or low calorific value: Insufficient fuel or low calorific value cannot provide enough heat to completely decompose limestone. The coal used in mixed firing kilns generally requires a calorific value of 5500 kcal or above, and the fuel particle size should be reasonably controlled. When using fine coal, appropriate water should be added to improve combustion efficiency.
Unreasonable air supply: Insufficient or uneven air supply leads to incomplete fuel combustion, uneven heat transfer, and localized burning. Improve the air supply system to ensure sufficient and evenly distributed air volume, and use probabilistic air caps and other devices to evenly distribute air throughout the entire kiln section, promoting uniform combustion of fuel.
2、 Overburning phenomenon
Overheating refers to the excessive decomposition of limestone during the calcination process due to high temperature or prolonged time, resulting in the formation of dense burnt lime or dead burnt lime. Overburnt lime has low activity and is difficult to differentiate in subsequent production. The main causes of overburning phenomenon are:
High combustion temperature: Excessive fuel ratio or strong air supply can lead to high combustion temperature.
Long calcination time: Poor ventilation or delayed ash discharge in the kiln can cause limestone to stay in the kiln for too long.
The solution strategy includes:
Adjust the fuel ratio, reduce fuel consumption, and ensure that the ratio of fuel to limestone is appropriate.
Optimize the air supply, adjust the air supply volume, and avoid excessive air volume causing high combustion temperature.
Strengthen the ventilation inside the kiln to ensure smooth ventilation, timely discharge of exhaust gas, and reduce the residence time of limestone in the kiln.
Use temperature monitoring equipment to monitor the temperature inside the kiln in real time, in order to avoid overheating caused by excessive temperature.
3、 Move the calcination zone up or down
The upward movement of the calcination zone refers to the upward movement of the calcination zone inside the kiln, which causes the fuel to burn earlier in the upper part of the kiln, and when the furnace material drops to the calcination zone, the fuel loses its firepower, resulting in raw combustion. The downward movement of the calcination zone is the opposite situation, where the fuel is not fully burned in the lower part of the kiln, resulting in incomplete decomposition of limestone in the upper part of the kiln.
The main reasons for the upward or downward movement of the calcination zone are:
High or low top temperature control: The temperature at the kiln top is too high or too low, causing fuel to burn ahead or behind schedule.
Excessive or insufficient wind pressure and air volume: The supply air volume is too large or too small, which affects the combustion speed and position of the fuel.
Uneven particle size of limestone: Limestone with larger particle size has smooth ventilation, which can easily cause the calcination zone to move upward; Limestone with small particle size may cause the calcination zone to move downwards.
The solution strategy includes:
Adjust combustion parameters to reduce or increase kiln top temperature.
Reduce or increase the air supply appropriately to keep the fire layer in a reasonable position.
Control the particle size of limestone within a reasonable range, avoiding being too large or too small.
Increase or decrease the amount of ash to be unloaded, and adjust the residence time of limestone in the kiln.
4、 Nodulation phenomenon
Knotting is a common problem in the production process of lime kilns, mainly manifested as the materials in the kiln sticking together into blocks at high temperatures, forming hard lumps that affect the ventilation and material flow inside the kiln.
The main reasons for tumor formation are:
Raw materials contain many impurities: If limestone contains a large amount of impurities such as silicon, aluminum, and iron, it is easy to form low melting point compounds at high temperatures, leading to nodules.
Uneven temperature distribution inside the kiln: Local temperatures that are too high or too low can cause material bonding.
Improper control of kiln atmosphere: Excessive reducing atmosphere can promote the reduction reaction of impurity elements and increase the risk of nodulation.
The solution strategy includes:
Optimize the selection of raw materials and choose high-quality limestone with low impurities as the raw material.
Improve the temperature distribution inside the kiln by adjusting parameters such as fuel ratio and air supply volume to make the temperature distribution more uniform.
Control the oxygen content inside the kiln to avoid excessive reducing atmosphere.
Regularly clean the kiln, remove lumps, and keep the kiln unobstructed.
The common problems in the process of calcining lime in a lime kiln, such as raw burning, overburning, upward or downward movement of the calcination zone, and agglomeration, have complex and diverse causes, and require comprehensive consideration of factors such as raw material quality, fuel ratio, air supply system, and kiln structure. By deeply analyzing the causes of these problems and taking corresponding measures, the efficiency of lime production and product quality can be significantly improved. Meanwhile, strengthening equipment management, optimizing production processes, and improving operational skills are also key to preventing and solving these problems.
