Index
Classification and Selection
DOI 10.1615/hedhme.a.000331
3.13.2 Classification and selection
Ernst U. Schlünder
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 Time | Wet, moist material | |||||
|---|---|---|---|---|---|---|
| Liquid | Paste | Solid | ||||
| Powdery | Granular | Clumpy | Sheet | |||
| Short (< 1 min) | Spray dryer | Spray dryer | Flash dryer | Flash dryer | Flash dryer | Cylindrical dryer |
| Drum dryer | Drum dryer | Grinding dryer | (Grinding dryer) | |||
| (Agitated film dryer) | (Agitated film dryer) | |||||
| Moderate (1 min–1 h) | Screw conveyer dryer | Continuous band dryer | Continuous band dryer | |||
| Paddle dryer | Roto louver dryer | |||||
| Horizontal cylindrical dryer | Vibrating dryer | |||||
| (Kneading dryer) | Kneading dryer | |||||
| Vibrating dryer | Fluidized-bed dryer | |||||
| Rotating shelf dryer | Rotating shelf dryer | Rotating shelf dryer | Rotating shelf dryer | |||
| Pan dryer | ||||||
| Plate dryer | ||||||
| (Paddle dryer) | Paddle dryer | Paddle dryer | ||||
| Horizontal cylindrical dryer | Horizontal cylindrical dryer | Horizontal cylindrical dryer | ||||
| Steam-tube rotary dryer | Steam-tube rotary dryer | |||||
| Rotary dryer (with lifters) | Rotary dryer (with lifters) | Rotary dryer (with lifters) | ||||
| Long (> 1h) | Tray dryer | Tray dryer | Tray dryer | Tray dryer | ||
| Truck dryer | Truck dryer | Truck dryer | Truck dryer | |||
| Tunnel dryer | Tunnel dryer | Tunnel dryer | Tunnel 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
| a Figure 1 – Figure 15 show more or less schematically the design of the various types of dryers in common use. | |||
| Figure a | Type | Evaporation rate, kg H2O/h per m2 or per m3 | Energy consumption, kJ/kg evaporated H2O |
|---|---|---|---|
| 1 | Drying loft | 20/m2 | 5,000–6,000 |
| 2 | Compartment dryer (normal pressure) | 0.1–15/m2 | 5,000–13,000 |
| 3 | Compartment dryer (vacuum) | 0.1–1/m2 | 3,000–5,000 |
| 4 | Tunnel dryer | 5,500–6,500 | |
| 5 | Band dryer | 4,000–6,000 | |
| 6 | Jet impingement dryer | 50/m2 | 5,000–7,000 |
| 7 | Shelf dryer | 4–8/m2 | 3,500–9,000 |
| 8 | Rotary dryer | 30–80/m3 | 4,600–9,200 |
| 9 | Centrifugal dryer | 90/m3 | 3,000–4,000 |
| 10 | Fluidized-bed dryer | ||
| 11 | Pneumatic bed dryer | Particle diameter dp = 0.5 mm: 100/m3 dp = 1 mm: 20/m3 dp = 5 mm: 4/m3 | 4,600–9,200 |
| 12 | Spiral-tube dryer | 500/m3 | 3,500 |
| 13 | Spray dryer | 1–50/m3 | 4,600–11,500 |
| 14 | Drum dryer for pasty materials | 7–25/m2 | 3,200–6,500 |
| 15 | Holoflite dryer | 5–15/m2 (0.5–2.5 low moisture content) | 3,700–6,500 |
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