Causes of caking inside a limonite rotary kiln and corresponding measures

1. Low Silicate Content in Clinker Batching: High Al₂O₃ and Fe₂O₃ content and low SiO₂ content in the batching scheme are prerequisites for the formation of briquettes in the kiln. Therefore, most precalciner kilns, both domestically and internationally, control the content of Al₂O₃ + Fe₂O₃ to 9%, liquid phase to approximately 24%, SiO₂ to 22%, and n to 2.50.

2. Influence of Harmful Components: Analysis results show that the content of harmful components in the crusting or briquette is significantly higher than that in the corresponding raw feed. This is because harmful components can promote the formation of intermediate phase characteristic minerals, which are the characteristic minerals for forming briquettes and crusts, such as calcium alunite (2CaSO₄·K₂SO₄) and siliceous calcite (2C₂S·CaCO₃). The more harmful components there are, the higher their volatility, the higher the enrichment degree in the system, the more opportunities there are for characteristic minerals to form, and the greater the possibility of briquettes appearing in the kiln.

3. The Influence of Fire Control and Coal Powder Fineness on Kiln Formation: In rotary kiln operation, improper air and coal mixing is sometimes difficult to avoid. Poor ventilation in the kiln can lead to incomplete combustion of coal powder, causing it to burn at the back of the kiln. Uneven mixing of coal ash with raw materials, excessively long flames, and excessively high temperatures at the back of the kiln can cause premature liquid phase formation, easily resulting in formation of briquettes within the kiln. Furthermore, the fineness of the coal powder, its ash content, and the melting point of the coal ash also affect the operation of the rotary kiln. Coarse coal powder with high ash content easily leads to uneven mixing of coal ash and raw materials. When the temperature at the kiln tail is too high, uneven local melting occurs in the material at the back of the kiln, becoming the core for briquette formation, which then grows larger and larger within the kiln, forming large briquettes.

4. The more frequently the kiln is started and stopped, the more unstable the feeding and coal supply, the more severe the system collapse, the greater the fluctuation in the kiln’s thermal regime, and the more prone it is to large brittle particles forming inside the kiln. To avoid or reduce this problem, the clinker ratio should be adjusted appropriately, and the quality of harmful components in the raw feed and pulverized coal should be strictly controlled to improve the uniformity of the raw feed. Kiln operators should operate carefully, ensuring a proper match between air, coal, feed, and kiln speed to stabilize the thermal regime of the firing system. This will help prevent the formation of large brittle particles.

While we cannot predict the future, we can still prevent some problems by paying close attention. Regular equipment inspection and maintenance can also prevent rotary kiln malfunctions, thereby significantly improving production efficiency.