Classification of rotary dryer:
According to the heat transfer mode between the drying medium and the wet material, it can be divided into two types: direct heat transfer rotary dryer (where the drying medium directly contacts the wet material to transfer heat) and indirect heat transfer rotary dryer (where the heat required for drying is indirectly transferred from the cylinder wall to the wet material). Due to low transfer efficiency and complex structure, indirect heat transfer rotary dryers are rarely selected and will not be introduced here. Direct heat transfer rotary dryer can be divided into two types based on the direction of flow of the drying medium and material: forward flow and reverse flow.
The main body of the direct heat transfer rotary dryer is a rotating cylinder slightly inclined to the horizontal line. The cylinder is driven by gears, with a speed of generally 2-6r/min. The inclination of the cylinder is related to its length, usually between 1 ° and 5 °. The material is fed from the higher end of the rotary drum and comes into contact with hot air. As the cylinder rotates, the material flows towards the lower end under the action of gravity and is dried before being discharged. Due to the negative pressure condition of the dryer, sealing devices are used at both the feeding and discharging ends to prevent air leakage.
The main internal structure of a rotary dryer
In order to increase the uniform distribution of materials on various parts of the rotating drum section and ensure good contact with the drying medium, a lifting plate is installed inside the drum. There are several types of raised boards:
1、 Lift up lifting plate: suitable for large materials or materials that are easily adhered to the cylinder wall.
2、 Four format lifting board: suitable for materials with high density, non brittle or difficult to disperse. The lifting plate divides the cylinder into four compartments, forming a fan-shaped operating room that is not connected to each other. The contact surface between the material and the hot gas is larger than that of the lifting plate, and it can increase the filling rate of the material and reduce the falling height of the material, thereby reducing dust loss and other advantages.
3、 Cross shaped or rack shaped lifting plate: suitable for brittle and easily dispersed small pieces of material, allowing the material to be evenly dispersed throughout the entire cross-section of the cylinder.
4、 Sleeve type lifting plate: It is a lifting plate for a compound heat transfer (or half diameter heating) rotary dryer.
5、 The fan-shaped lifting plate is suitable for materials with very fine particles that are prone to powder flying. As soon as the material is fed in, it accumulates on the grid plate. When the cylinder rotates, the material is flipped and constantly comes into contact with hot gas. At the same time, the possibility of dry material being carried away by gas is reduced due to the decrease in the height of material descent. The various forms of lifting plates mentioned above can be distributed throughout the entire cylinder. In order to ensure that the material can be quickly and evenly delivered to the lifting plate, a spiral guide plate can also be installed at a distance of 1-5 meters from the feeding end to avoid wet material sticking and accumulating on the cylinder wall. At the same time, due to the fact that the dried material is easily lifted up and carried away by exhaust gas, no lifting plate is installed at a distance of 1-2m from the discharge end.
Rotary dryer, also known as drum dryer or cylindrical dryer, is the most common and widely used drying equipment in mining industry. Suitable for drying magnetic, heavy, and floating concentrates of metallic and non-metallic minerals, as well as clay for the cement industry and coal slurry for the coal mining industry. Its characteristics are high productivity and easy operation.
