Rotary dryer

The rotary dryer is a type of industrial dryer employed to reduce or minimize the liquid moisture content of the material it is handling by bringing it into direct contact with a heated gas.

Single Shell Rotary Drum Dryer

The dryer is made up of a large, rotating cylindrical tube, usually supported by concrete columns or steel beams. The dryer slopes slightly so that the discharge end is lower than the material feed end in order to convey the material through the dryer under gravity. Material to be dried enters the dryer, and as the dryer rotates, the material is lifted up by a series of internal fins lining the inner wall of the dryer. When the material gets high enough to roll back off the fins, it falls back down to the bottom of the dryer, passing through the hot gas stream as it falls. This gas stream can either be moving toward the discharge end from the feed end (known as co-current flow), or toward the feed end from the discharge end (known as counter-current flow). The gas stream can be made up of a mixture of air and combustion gases from a burner, in which case the dryer is called a direct heated dryer. Alternatively, the gas stream may consist of air or another (sometimes inert) gas that is preheated. When the gas stream is preheated by some means where burner combustion gases do not enter the dryer, the dryer known as an indirect-heated type. Often, indirect heated dryers are used when product contamination is a concern. In some cases, a combination of direct-indirect heated rotary dryers are also available to improve the overall efficiency.

Brief Introduction Rotary dryer is suitable to dry metallic and nonmetallic mineral, clay in cement industrial and coal slime in coal mine,etc. Rotary dryer can be widely used to dry various materials, and it is simple to be operated.

Applications

Rotary Dryers have many applications but are most commonly seen in the mineral industry for drying sands, limestone, stones and soil, ores, fertilizers, wood chips, coal, iron sulphate, filter cakes, sewage sludge, etc.

Drum or Shell Variations

Double Shell Rotary Drum Dryer

Triple Shell Rotary Drum Dryer

A rotary dryer can consist of a single shell or many, though any more than three drums is not usually necessary. Multiple drums can reduce the amount of space that the equipment consumes. Multi-shell dryers consist of several concentric tubes. Multiple shells allow the dryer to be utilized in a more compact space. The drums are often heated directly by oil or gas burners. The addition of a combustion chamber on the entry end helps ensure efficient fuel usage, and that homogenous drying air temperatures. As the material moves through the rotating drum is heated and moisture released. Some dryers also offer the option to cool, clean, shred, and/or separate the dried material.

Combined Processes

Along with drying rotary dryers have the ability to increase their economy by combining other process needs with drying. Other processes that can be combined with drying are:

• Cooling
• Cleaning
• Shredding
• Separating

Working principle of Rotary dryer

When rotary Dryer is operating, it shall be in direct contact with heated gas. The dryer consists of a large rotating cylindrical tube. In order to convey the material through the underside of dryer, the dryer should be slanted slightly to ensure that the discharge end is lower than the end of material feed .

Working Principle of Rotary Dryer: Material shall be dried to enter the dryer. When the dryer is rotating, a series of internal fins will lift the material by lining the inner wall of the dryer. When the material reaches certain height to roll the fins back, it will be fell back to the bottom of the dryer, then passing through the hot gas stream as it falls. This gas stream can either move toward the discharge end from the feed end (known as co-current flow), or toward the feed end from the discharge end (known as counter-current flow). The gas stream can be composed of a mixture of air and combustion gases from a burner, and in which case the dryer is known as a direct heated dryer. Alternatively, the gas stream may be made up of air or another (sometimes inert) gas that is preheated. When the gas stream is preheated by some means where burner combustion gases are not permitted to enter the dryer, the dryer shall be called an indirect-heated type. Indirect heated dryers are commonly used when product contamination becomes a concern.

See also

• Fluidized bed
• Allgaier (company)- Innovator and developer of Rotary Dryer technology for industrial dryers, and coolers.

References

Working principle of rotary dryer.