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Classification and Selection

DOI 10.1615/hedhme.a.000331

3.13.2 Classification and selection

Among the various requirements that determine the design concept of a dryer, the transportation of the product through the dryer may be very important, since it is closely related to the residence time. Second, the initial state of the product (liquid, paste, solid, powder, granular, sheet, etc.) also influences the design concept to a great extent. Therefore a matrix is presented in Table 1 that correlates the residence time and the initial state of the product (liquid to solid).

Table 1 Classification of dryers with respect to the physical state of the product and the residence time of the product in the dryer

Residence TimeWet, moist material
LiquidPasteSolid
PowderyGranularClumpySheet
Short
(< 1 min)


Spray dryerSpray dryerFlash dryerFlash dryerFlash dryerCylindrical dryer
Drum dryerDrum dryerGrinding dryer(Grinding dryer)
(Agitated film dryer)(Agitated film
dryer)
Moderate
(1 min–1 h)
















Screw conveyer dryerContinuous band dryerContinuous band dryer
Paddle dryerRoto louver dryer
Horizontal cylindrical dryerVibrating dryer
(Kneading dryer)Kneading dryer
Vibrating dryerFluidized-bed dryer
Rotating shelf dryerRotating shelf dryerRotating shelf dryerRotating shelf dryer
Pan dryer
Plate dryer
(Paddle dryer)Paddle dryerPaddle dryer
Horizontal cylindrical dryerHorizontal cylindrical dryerHorizontal cylindrical dryer
Steam-tube rotary dryerSteam-tube rotary dryer
Rotary dryer (with lifters)Rotary dryer (with lifters)Rotary dryer (with lifters)
Long
(> 1h)



Tray dryerTray dryerTray dryerTray dryer
Truck dryerTruck dryerTruck dryerTruck dryer
Tunnel dryerTunnel dryerTunnel dryerTunnel dryer
Continuous band dryer

A brief description of various types of dryers, including some indication of the specific energy consumption per kilogram of evaporated water, is also given in Table 2.

Table 2 Capacity and energy consumption for various types of dryers

aFigure 1Figure 15 show more or less schematically the design of the various types of dryers in common use.
Figure aTypeEvaporation rate,
kg H2O/h per m2 or per m3
Energy consumption,
kJ/kg evaporated H2O
1Drying loft20/m25,000–6,000
2Compartment dryer (normal pressure)0.1–15/m25,000–13,000
3Compartment dryer (vacuum)0.1–1/m23,000–5,000
4Tunnel dryer5,500–6,500
5Band dryer4,000–6,000
6Jet impingement dryer50/m25,000–7,000
7Shelf dryer4–8/m23,500–9,000
8Rotary dryer30–80/m34,600–9,200
9Centrifugal dryer90/m33,000–4,000
10Fluidized-bed dryer
11Pneumatic bed dryerParticle diameter
dp = 0.5 mm: 100/m3
dp = 1 mm: 20/m3
dp = 5 mm: 4/m3
4,600–9,200
12Spiral-tube dryer500/m33,500
13Spray dryer1–50/m34,600–11,500
14Drum dryer for pasty materials7–25/m23,200–6,500
15Holoflite dryer5–15/m2 (0.5–2.5 low moisture content)3,700–6,500

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