dryer
A dryer is an apparatus in which the thermal separation process of drying takes place. The basics of drying can be found under this term. Mechanical dehumidification is often switched on before drying, since the mechanical processes are usually much more favorable in terms of energy.
Dryer types
A device known from the household is the tumble dryer . Drying cabinets are mostly used on a laboratory scale. Technically, a distinction is made between batch and continuously operated dryers, and also according to the functionality of contact and convection dryers or according to type and product.
Contact dryer
The material is heated by contact with a heating surface, which drives out the moisture. It can stay in constant contact with it or it is redeployed. No air may be required if the moisture is removed in a vacuum via a condenser, or the amount of air required is small.
Types of contact dryers:
- Lyophilizer or freeze dryer
- See freeze drying !
- Tube dryer
- Inside a large, steam-heated drum, the material trickles through a large number of smaller tubes
- Paddle dryer
- The material is rearranged in a tubular heating surface by shovels.
- Screw dryer
- A screw conveyor transports the material along a tubular heating surface. There are different types for pasty goods, granulates etc. available.
- Tumble dryer
- This is based on a similar principle with a non-rotationally symmetrical container.
- Plate dryer
- It is operated with heated plates on mostly several floors and often as a vacuum dryer.
- Drum dryer
- The material is moved in a heated, rotating rotary tube and the lifting bars on the cylinder walls ensure that it is mixed.
- Drum dryer
- Suspensions and sludges are applied to slowly rotating, heated rollers and peeled off with knives after they have dried.
- Cylinder dryer
- Belt-shaped goods (paper, textiles, etc.) are guided over heated cylinders. Often these are stabilized by tape guides or belt straps that run along with them.
Convection dryer
The dry goods come into contact with the hot drying air with low relative humidity . The air is removed and may have to be cleaned with dust collectors, if necessary with the return of the air after the moisture has condensed.
Types of convection dryers:
- Jet tower dryer
- This works like a spray dryer, but it can produce larger particles (diameter: 0.3 mm). A fluidized bed dryer is often installed downstream to dry the large particles.
- Tray dryer
- The layered material is overflowed.
- (Infrared) tunnel dryer
- The drying takes place by warming up when passing through the drying tunnel.
- Grinding dryer
- This type of construction uses the heat during grinding (e.g. for lignite).
- Shoe dryer
- Spray dryer
- The suspension is sprayed into the hot air stream (medicinal substances, milk and whey, washing powder, etc.). The round particles produced are about 0.1 mm in size.
- Electric dryer
- A material that can be pneumatically conveyed is placed in the lower part of a mostly vertical tube, carried away by the hot drying gas and separated with a centrifugal separator . Electric dryers are characterized by their compact design and short drying times.
- Drum dryer
- This uses a similar procedure - but with air throughput. Is mainly used for thin-layer materials such as paint, flat materials, building material panels, etc.
- Fluid bed dryer
- The material is flowed through from below, held in suspension and mixed. When it dries, it is carried away through the air.
Dry air dryer
A dry air dryer is a dryer with a dry air whose dew point is below −30 ° C.
Compressed air refrigeration dryer
Compressed air refrigeration dryers dry compressed air by cooling it to approx. 2 ° C to 5 ° C. Due to the compression of the air by means of the compressor, the compressed compressed air also contains more water vapor corresponding to the pressure, which does not condense out due to the higher compression temperature of the compressed air. Only when the compressed air cools below the saturation line does the water vapor condense out as "condensate". Without compressed air preparation, the compressed air always remains saturated with water vapor, so that as the compressed air cools down continuously, condensate is always formed, which can be discharged from the compressed air system with separators. By cooling the compressed air in the compressed air refrigeration dryer to approx. 2 ° C to 5 ° C, condensate can only condense out again when the compressed air temperature is below this cooling temperature of the compressed air refrigeration dryer.
literature
- U. Boltendahl, KH Steppuhn, H. Blahwatt: Drying methods and apparatus. In: Bernd Thier (arrangement): Apparatus: Technology - Construction - Application. 2nd edition, Vulkan, Essen 1997, ISBN 3-8027-2172-1 , pp. 414-438 ( online ).
