Hollow Propeller Drying Machine - Function and Working Principle

Operating Principle  

The hollow shaft is densely arranged with trapezoidal hollow vanes, and the heat medium flows through the vanes via the hollow shaft. The heat transfer area per unit effective volume is large, with the temperature of the heat medium ranging from -40℃ to 320℃, which can be steam or liquid types such as hot water, heat transfer oil, etc. Indirect heat conduction heating is used, with no air carrying away heat, ensuring all the heat is used for heating the material. Heat loss is only due to the heat dissipated through the insulating layer of the equipment to the environment. The trapezoidal vanes have an auto-cleaning function. The relative movement of the material particles with the trapezoidal surface generates a cleaning action, which can remove the adhered material from the trapezoidal surface, maintaining a clean heat transfer surface during operation. The shell of the vane dryer is in an Ω shape, and usually contains two to four hollow agitator shafts inside. The shell is equipped with a sealed end cap and an upper cover to prevent the leakage of material dust and to fully utilize its function. The heat transfer medium flows through the rotating joint, the shell jacket, and the hollow agitator shafts, which have different internal structures depending on the type of heat medium to ensure effective heat transfer.

Material compatible  

Propeller dryers have been successfully used in food, chemical, petrochemical, dye, and industrial sludge fields. The equipment's heat transfer, cooling, and mixing capabilities enable it to perform the following unit operations: combustion (low temperature), cooling, drying (solvent recovery), heating (melting), reaction, and sterilization. The propeller blades, which also serve as heat transfer surfaces, increase the heat transfer area per effective volume, shortening processing time. The wedge-shaped propeller blades also feature self-cleaning properties. The compression-expansion mixing function ensures uniform material mixing. Materials move in an "活塞流" (piston flow) along the axial direction, with minimal gradients in temperature, humidity, and mixing degree within the axial zone. Propeller dryers using thermal oil as the heat medium can perform low-temperature combustion, such as the combustion of calcium sulfate dihydrate (Ca2SO4·2H2O) into half-water calcium sulfate (Ca2SO4·1/2H2O). Sodium bicarbonate (NaHCO3) is calcined into soda ash (Na2CO3), etc. By introducing cooling mediums like water or cooling brine, they can be used for cooling purposes. For instance, propeller coolers in the soda ash industry have replaced outdated air-cooled coolers, saving energy and reducing operating costs. The primary function of the drying equipment is to avoid using hot air, making solvent recovery, energy consumption, and environmental control easily manageable. It is particularly suitable for materials that require solvent recovery, are flammable, oxidizable, or heat-sensitive. It is widely used in the fine chemical, petrochemical, and dye industries. The uniformity of temperature, humidity, and mixing degree within the axial zone allows the equipment to be used for heating or melting, or for certain solid material reactions. It has been successfully applied in the compound fertilizer and modified starch industries. Propeller dryers can be used for sterilization of food and flour. The large heating area per effective volume quickly raises the material to sterilization temperature, avoiding quality changes due to prolonged heating.