Direct Heating Type / Indirect Heating Type Rotary Dryer

 Direct Heating Type / Indirect Heating type Rotary Dryer

• Direct heating type rotary dryer
  This is a direct heating type of dryer that brings materials into direct contact with hot air to dry them by lifting them up inside the rotary shell.
• Indirect heating type rotary dryer
  This is an indirect heating type of rotary dryer that brings materials into indirect contact with heating medium to provide heat exchanging.
  The indirect heating type of rotary dryer is classified into external heating rotary dryer and steam tube dryer, which are applied for the following conditions.
   
  • If you use materials that are easily affected by contact with combustion gas.
  • If you need to minimize the amount of exhaust gas from the dryer.
  • If you use materials that are apt to produce dust.
  • If you use materials that are easily affected by oxidation.
  • If you need to recover volatile component.

The main unit of the rotary dryer is an inclined shell supported by four rollers. Materials, which are fed through one end of the shell, move inside the shell along the inclination of the shell and through the rotary movement and are discharged from the other end. Materials, while moving inside the shell, are lifted up by a lifter incorporated in the shell. Then, the materials fall evenly in the shell space and exchange heat with the hot air flowing through the space to dry. Depending on the method of providing hot air for the materials, this dryer is classified into two types, that is, concurrent flow drying type by which the hot air and materials flow in the same direction and countercurrent flow drying type by which they flow in the opposite direction.
Lifter
The lifter is the most critical part having an influence on the performance of the dryer, which provides uniform dispersion of materials in the shell space. Any of the constructions shown below is used according to the physical properties of materials. Furthermore, spiral lifters designed with consideration of forced feeding of materials are used for the material feeding end.