The rotary vacuum paddle dryer (RVPD) is a specialized drying equipment used for drying heat-sensitive materials and substances with high moisture content. It operates under vacuum conditions and employs paddles or blades to facilitate efficient drying. The working principle of a rotary vacuum paddle dryer can be described as follows:
1. Loading: The material to be dried is loaded into the cylindrical drying chamber of the RVPD.
2. Vacuum: A vacuum pump is used to create a vacuum inside the drying chamber. The reduced pressure lowers the boiling point of the liquid in the material, enabling faster evaporation.
3. Heating: The heating medium, such as hot water or steam, is circulated through the jacket surrounding the drying chamber. This raises the temperature inside the chamber and facilitates the evaporation of moisture from the material.
4. Rotation and Mixing: Paddles or blades are mounted on a central shaft within the drying chamber. The shaft and paddles rotate at a controlled speed. As they rotate, the paddles lift and tumble the material, ensuring that it comes into direct contact with the heated surfaces. This promotes efficient heat transfer and uniform drying.
5. Evaporation: The combination of vacuum, heating, and mixing promotes the evaporation of moisture from the material. The evaporated moisture is removed by the vacuum pump.
6. Condensation: The evaporated moisture is condensed back into liquid form, usually in a separate condenser unit connected to the vacuum pump.
7. Discharge: Once the desired level of moisture removal is achieved, the dried material can be discharged from the drying chamber.
The rotary vacuum paddle dryer offers several advantages, including gentle and efficient drying, reduced drying time, and the ability to handle heat-sensitive materials. The vacuum reduces the boiling point of the liquid in the material, minimizing the risk of thermal degradation. The rotation and mixing action ensure even drying and prevent material buildup on the heated surfaces.