Reliable maintenance of a rotary kiln requires an understanding of the prerequisites for mechanical stability of the various components. Timely and proper maintenance procedures, consistent with such knowledge, ensure a long service life and trouble-free operation.
Rotary kilns are an important component of various industrial process systems. Good maintenance is very important to maintain process efficiency, extend equipment service life, and avoid costly repairs. Due to the high temperatures and process reaction that occur within a rotary kiln, there are certain failure points that must be monitored. The main points are damage to the refractory, maintenance or upgrade of the burner, wear of the seals, and misalignment of the shell.
A rotary kiln depends on its refractory lining to operate effectively and maintain the desired temperature within. Unfortunately, the refractory lining begins to degrade over time, causing a loss in the efficiency of the kiln. In addition, in some cases, an object, such as a buildup of hard material, can be introduced into the kiln and cause damage to the refractory lining. A distorted shell can cause severe damage to various components that, rather than being repaired, must be replaced. Since refractories play an important role in protecting the kiln, scheduled routine inspections of the refractory lining must be performed.
Another source of failure in refractory bricks can be chemical incompatibility. Refractory is not designed to withstand certain chemicals. One of the main ones is chlorides. Chlorides can aggressively attack the refractory lining, causing excessive wear of the lining due to its corrosive nature. When these chemicals are identified in advance, the refractory lining can be designed to cope with such aggressive corrosion. Likewise, this failure can also occur when a rotary kiln is used for something that the refractory lining has not been designed for.
In addition to regular inspections, an effective way to extend the service life of a rotary kiln is to check for hot spots. To perform this, select a spot on the rotary kiln shell and use a temperature gun. As the kiln rotates, that spot should maintain the same temperature along the entire circumference of the shell. If the temperature readings are 200 degrees C, 200 degrees C, 250 degrees C, and 200 degrees C, this indicates the presence of a hot spot. A hot spot on the kiln shell suggests a failure in the refractory. If not detected in time, it could cause significant damage to the kiln lining. In addition to ensuring that the temperature is uniform at a specific point, there should be a gradual transition of temperatures from one end of the kiln to the other.
Even if a rotary kiln has a reliable, high-quality burner, burner-related problems can still occur. Parts such as the nozzle, cone, and sensors may need to be replaced to keep the kiln operating as designed. For an older rotary kiln, it is beneficial to upgrade the burner given that burner technology is constantly advancing, and a new burner can increase energy efficiency and material throughput, making this a cost-effective upgrade.
The primary function of a rotary kiln’s sealing system, regardless of its style, is to prevent outside air intake in the kiln. Many kilns are specifically designed to channel exhaust air along with dust into a controlled area. Likewise, the design is set up to discharge the maximum amount of process material while maintaining the desired internal temperature. This also means preventing cold ambient air from entering the kiln. Seals prevent outside air from mixing with the controlled combustion air inside the kiln. A worn out or inefficient sealing system can disrupt this system, causing poor dust control and variations in kiln temperature. This can lead to increased plant cleaning, process inconsistencies and increased fuel consumption.
As with all rotary equipment, proper alignment protects all components from premature wear. Major damage to the inlet or outlet sections caused by a misaligned shell can result in extended downtime. Additionally, a misaligned shell can accelerate wear on tires, trunnion wheels, and thrust rollers, all of which are necessary for operation. Misalignment can occur naturally over time or because of improper installation. Regardless of how the misalignment occurred, it must be realigned before continuing operation to prevent further damage.
Because a rotary kiln is, in many ways, like other rotary drum equipment, many of the same preventive maintenance procedures apply, and should be routinely performed by maintenance personnel. These procedures include lubricating bearings, changing gearbox oil, and rechecking/defining backlash. More extensive maintenance tasks such as: grinding tires and wheels, replacing gears, and changing damaged parts should be performed by trained and experienced maintenance personnel.
In conclusion, periodic maintenance of rotary kilns is essential to ensure their efficient operation and prolong their service life. Early identification is crucial to avoid significant and costly damage to the kiln. In addition, an effective sealing system is critical to maintaining the integrity of the kiln, preventing gas and material leakage, and false air intake. Implementing these maintenance practices and paying attention to technical details ensures optimal rotary kiln performance, contributing to the productivity and sustainability of industrial operations.
Source: ispatguru.com
