During the production and operation of lime kilns, excessive temperature at the kiln roof is a common but important issue that requires attention. Excessive temperature at the kiln roof not only affects the quality and yield of lime, but may also cause damage to the kiln structure and equipment, increase energy consumption, and even pose safety hazards. Therefore, it is crucial to accurately identify the cause of high kiln top temperature and take effective measures to solve it.
1、 Fuel combustion situation
（1） Excessive fuel
If too much fuel is added to the kiln, exceeding the actual amount required for calcination, it will cause excessive combustion, generate too much heat, and thus increase the temperature at the top of the kiln.
For example, a certain lime kiln factory blindly increased the input of coal in order to increase production, resulting in a sharp rise in kiln top temperature beyond the normal range.
（2） Uneven distribution of fuel
When the fuel is unevenly distributed inside the kiln, there may be concentrated combustion of the fuel in certain areas, resulting in local high temperatures and heat transfer to the kiln roof, leading to an increase in kiln roof temperature.
For example, in a lime kiln that uses a spray gun to inject coal powder as fuel, if the spray gun is blocked or damaged, resulting in uneven injection of coal powder, it will cause excessive local fuel and abnormal kiln top temperature.
2、 Ventilation system issues
（1） Insufficient ventilation
Insufficient ventilation can prevent the timely discharge of exhaust gases generated by combustion in the kiln, and prevent fresh air from fully entering, resulting in incomplete combustion and heat accumulation inside the kiln, which in turn increases the temperature at the kiln roof.
Taking a small lime kiln as an example, due to fan failure, the ventilation volume decreased, and the exhaust gas inside the kiln was blocked, resulting in a rapid increase in kiln top temperature in a short period of time.
（2） Ventilation duct blockage or leakage
If the ventilation duct is blocked, it will affect the normal circulation of air, resulting in uneven pressure inside the kiln, abnormal heat distribution, and an increase in kiln top temperature. Leakage of ventilation ducts can disrupt the airflow balance inside the kiln, allowing some cold air to enter the kiln and interfere with normal combustion and heat transfer processes, and may also cause temperature fluctuations at the kiln roof.
In a lime kiln enterprise, due to long-term failure to clean and maintain the ventilation ducts, there was severe ash accumulation inside the ducts, resulting in blockage and a significant abnormal increase in kiln top temperature.
3、 Kiln structure and insulation performance
（1） Damage to kiln body
If the refractory bricks of the kiln body are damaged or detached, it will affect the insulation performance and heat transfer effect of the kiln body. Heat may be abnormally transferred to the kiln roof through damaged areas, leading to an increase in kiln roof temperature.
For example, after a long period of operation, some refractory bricks of a certain lime kiln developed cracks due to thermal stress and mechanical wear, and the temperature at the kiln roof gradually increased, which also affected the product quality.
（2） Insulation layer failure
When the insulation layer of the kiln body ages, is damaged, or the quality of the insulation material is poor, the insulation effect will be greatly reduced, and the heat loss inside the kiln will accelerate. In order to maintain the temperature inside the kiln, more fuel combustion is needed, which may lead to an increase in the temperature at the top of the kiln.
Due to the insulation layer not being replaced for many years, the insulation performance of an old lime kiln has decreased. In order to ensure the normal calcination of lime, the fuel input has to be increased, resulting in a significantly higher temperature at the top of the kiln than normal.
4、 Improper production operation
（1） Unreasonable feeding speed
If the feeding speed is too fast, it will cause excessive accumulation of materials in the kiln, affecting the normal flow of gas and the uniform distribution of heat, resulting in local overheating and an increase in kiln top temperature. On the contrary, if the feeding speed is too slow, it may cause excessive heat concentration in the kiln and also have adverse effects on the temperature at the top of the kiln.
The operator of a newly put into operation lime kiln had inaccurate control over the feeding speed. At the beginning, the feeding was too fast, causing the temperature at the top of the kiln to rise rapidly. Later, after adjusting the feeding speed, the situation improved.
（2） Improper control of calcination time
If the calcination time is too long, the heat inside the kiln will continue to accumulate, and the temperature at the top of the kiln will increase; If the calcination time is too short, the limestone may not decompose completely, but it may also cause significant temperature fluctuations at the top of the kiln due to heat concentration.
In a lime plant, due to the replacement of the new production process, the calcination time was not adjusted properly, resulting in a consistently high kiln top temperature, which affected the normal production process.
5、 Raw material characteristics
（1） Uneven particle size of limestone
If the particle size difference of limestone is too large, small particles of limestone may burn through prematurely, while the interior of large particles of limestone has not fully decomposed, which can lead to uneven airflow and heat distribution in the kiln, and the temperature at the kiln top may increase.
For example, after changing the limestone supplier, a certain lime kiln factory found that the newly purchased limestone had uneven particle size and significant fluctuations in kiln top temperature.
（2） Limestone contains excessive impurities
When limestone contains excessive impurities such as soil, quartz, etc., these impurities may absorb or hinder heat transfer during the calcination process, affecting the normal calcination reaction and causing abnormal kiln top temperature.
A lime kiln that uses low-quality limestone as raw material. Due to the high impurity content in limestone, the temperature at the top of the kiln is often high, and the quality of lime is also unstable.
The high temperature at the top of the lime kiln is caused by multiple factors working together. In actual production, it is necessary to comprehensively consider the situation of fuel combustion, ventilation system, kiln structure, production operation, and raw material characteristics. By accurately analyzing the specific reasons, targeted measures should be taken, such as adjusting fuel input, optimizing ventilation system, repairing kiln structure, standardizing production operation, and strictly controlling raw material quality, to effectively solve the problem of high kiln top temperature and ensure the stable operation and product quality of lime kiln.
