Self-returning Rotary Dryer

The self-returning rotary dryer adopts an external return screw belt structure to achieve the mixing function. It is a drying equipment specially designed to strengthen the axial conveying and return mixing of materials. The special screw belt structure of the cylinder realizes the directional flow of materials and drying homogenization.

1. Cylinder structure:

   Tilted rotating cylinder (inclination angle 1°–5°, speed 3–8 rpm), built-in steam heating tube bundle or jacket heating, use of shovelling plate and reserved mixing space in the feeding section of the cylinder, so that the materials can be fully mixed and homogenized.

2.  External return screw belt:

   A screw belt guide plate welded to the outer wall of the cylinder. Axial propulsion pushes the material to move toward the feeding end. When the cylinder rotates, the material rolls back in the gap between the screw belts, extending the residence time and improving the drying uniformity.

The inclination angle of the screw belt is 15°–30°. The larger the inclination angle, the stronger the axial propulsion force. The screw pitch is 0.3–0.8 times the cylinder diameter. Small pitch enhances backmixing, and large pitch accelerates discharge. The height of the screw belt is generally 1/8–1/6 of the cylinder diameter. If it is too high, it is easy to get stuck, and if it is too low, the flow conduction capacity is insufficient.

1. Improved drying uniformity: The screw belt allows the material to be repeatedly thrown to avoid local overheating or insufficient drying;

2. Anti-sticking design: The gap between the screw belt promotes the loosening of the material and reduces wall sticking (especially suitable for high-humidity materials such as sludge and filter cake);

3. Controllable residence time: Adjusting the speed and inclination angle can accurately control the time from material feeding to material discharging (usually 20-60 minutes);

4. Energy saving and consumption reduction: Indirect steam heating + material bakcmixing, the thermal efficiency reaches 65-80% (higher than direct hot air drying).

Highly wet and sticky materials: municipal sludge, chemical filter cakes, ointments.

Particles that need to be homogenized and dried: fertilizers, feed, biomass particles.

Heat-sensitive materials: food additives, polymer chips (low-temperature steam heating).

1. Material characteristics: particle size distribution, initial/final moisture content, viscosity index;

2. Screw belt layout: One-way screw belt: suitable for simple conveying and drying;

3. Segmented composite screw : front section shovelling plate (drying) + rear section dense screw (discharging);

4. Power configuration: The screw belt increases the torque by 10-20%, and the drive motor power needs to be increased accordingly.