What basic characteristics of kaolin should be considered when selecting a rotary dryer?

First is moisture characteristics. Kaolin moisture is typically categorized into external moisture (adhering to particle surfaces) and internal moisture (retained within particle pores); the ratio of these two and the total moisture content directly influence the heat requirements and process parameters for drying. Generally, the total moisture content of kaolin ranges from 15% to 35%. If the proportion of internal moisture is high, indicating difficulty in dewatering, equipment selection should prioritize heat exchange efficiency—for instance, by employing enhanced heat-transfer lifter designs to increase the contact area between the material and hot air, while also utilizing a high-temperature heat source and optimizing the drying path to minimize heat loss. Conversely, if external moisture predominates, the design of the lifters' lifting and showering action should be optimized to enhance convective heat transfer between the hot air and the material, thereby reducing energy consumption for evaporation and ensuring a smooth drying process.

Second is particle size distribution. Kaolin particles are generally fine and prone to agglomerating into irregular clumps due to moisture; the particle size distribution directly affects material flowability and the amount of material entrained by the hot air stream. A high proportion of fines results in a large specific surface area, leading to rapid drying but also a risk of the material being carried away by the airflow; therefore, the dryer design must incorporate appropriate airflow velocity parameters and lifters that ensure uniform material distribution across the drum's cross-section, preventing localized high air velocities from entraining the fines. If coarse agglomerates are present, the inclusion of a breaking mechanism is necessary—ideally selecting a dryer with an integrated internal breaking structure—to prevent clumps from accumulating and causing blockages or disrupting the balance of material residence time.

Third is viscosity characteristics. Kaolin's viscosity varies with moisture content; high-moisture kaolin is highly viscous and tends to adhere to the inner drum walls and lifters, leading to material buildup (crusting) and reduced heat transfer efficiency, or even obstructing the normal forward movement of the material. When selecting equipment, the design must be adjusted based on the material's stickiness; for highly adhesive kaolin, a dryer equipped with self-cleaning lifters—or one featuring smooth, wear-resistant inner drum walls to minimize material adhesion—is suitable. Additionally, the drum's inclination angle should be optimized to ensure smooth material flow toward the discharge end, preventing prolonged retention that could lead to clumping and uneven drying.