One common use for rotary kilns is the production of lime (calcium oxide) by calcinating limestone, which requires significant heat to achieve – approximately 900 °C (1,650 °F). Such high-temperature processes must be handled carefully, and there are several problems that may arise if the kiln is not properly configured for this usage.
Rotary kiln manufacturers will have their own recommended methods for utilizing the kiln, but the problems which occur tend to be the same. In this article, we’ll briefly outline common problems that occur when producing lime, and how they may be avoided.
How Refractory Linings Wear Out
Refractory linings in lime kilns deteriorate due to the harsh conditions they endure. High temperatures and the corrosive nature of the lime-making process, combined with mechanical abrasion, cause the material to wear down. The constant heating and cooling cycles also lead to thermal stress, resulting in cracks and spalling.
The most affected areas tend to be near the burners where temperatures are highest and at the lower sections where material build-up exerts extra pressure. If the refractory material is not well matched to the kiln’s conditions or is poorly installed, it can fail prematurely.
How to Maintain and Repair Refractory Linings for Lime Kilns
Effective maintenance and rotary kiln services for refractory linings relies on regular monitoring to catch and fix problems early. Techniques like thermal imaging can help identify areas where the lining is thinning. For small-scale damage, repair compounds that can withstand high temperatures are used to patch up cracks and gaps, often during brief shutdown periods.
More severe damage will require sections of the refractory lining to be replaced entirely, a process that necessitates a complete shutdown of the kiln. Careful selection of refractory materials tailored to the specific conditions of the kiln is crucial to ensure longevity and reduce the frequency of repairs.
Common Problems Rotary Kiln Manufacturers See From Customers Producing Lime
1. Underfiring
This is the most common issue seen when producing lime, and there are a few potential reasons for it:
- The limestone particles are too large. The calcination process requires the limestone particles to be heated uniformly. The larger they are, the harder this is to achieve.
- Insufficient fuel. The fuel used to power the reaction should generally be providing greater than 5500Kcals to produce the proper reaction,
- Restricted air supply. Oxygen is a necessary component in the reaction, so if the air supply is restricted, output will drop.
- Excessive heat. The temperature of the reaction must be maintained at approximately 900 °C. If the reaction runs hotter, especially above 1000 °C, it will harm the final product.
2. Shifting calcination zones
The ideal area for calcination to occur is in the center of your rotary kiln. If the heat zone shifts too far up or down the kiln, it could significantly affect output. The main reason this could happen is improper airflow. If the calcination zone is shifting upwards, too much air is being used. If it’s shifting downwards, there’s too little air.
However, this can also be caused if there is too much ash building up within the kiln, so take care to remove ash properly. Poorly burning fuel can also cause the calcination zone to shift.
3. Extended calcination zone
Finally, there’s the possibility that the calcination zone will extend too far in both directions. This tends to increase the temperature of the reaction, leading to more wasted lime and lowered output. Carefully manage your fuel and airflow to get the zone back into its proper boundaries.
For more than 20 years, Kiln Technology Company Company has been a leader among rotary kiln manufacturers, as well as having extensive repair and maintenance experience. Whether you need a new kiln or need help maintaining your existing equipment with rotary kiln services, contact us!