Double cone dryer

FIGURE 8 Double cone dryer. Source Courtesy of Patterson-Kelley. 

The shape of the vessel influences the amount of heated surface available and this factor can be a point of choice for selecting a dryer. For example, a typical double cone dryer (Fig. 8) has a surface/volume advantage over a V-shape dryer up to about 3001 of working volume. At working volumes exceeding 3001, the V-shape gains the surface/ volume advantage. 

For the first group the following types of dryers are generally used convective (tray, band, fluid bed, flash dryers, and their modifications) or contact (vacuum dryers such as double-cone dryer-blender, conical dryer with rotating helical mixer, paddle dryer). Pastelike materials are dried in tray dryers, band dryers equipped with extruding devices, and spin-flash dryers. Finally, thin pastes can be dried in spray dryers or on fluid beds or spouted beds of inert particles. Small amounts of solutions and suspensions are generally freeze-dried, especially if the product is thermolabile. 

Conical Dryer with Screw Mixer The conical dryer with screw mixer is similar in principle to the double-cone dryer-blender although the vessel is stationary and solids are mixed by epicyclic screw mixer (Figure 33.13). For pressures from 25 to 150 mbar and wall temperatures from 40°C to 60°C, Simon [6] reports evaporation rates of water up to 10 kg/h m. Units up to 5 m are commercially available. The dryer has no dead spaces and is easy to clean. 

In a double cone dryer ( mixing dryer ) a drying drum with the form of a double cone revolves around an axis of rotation, which is perpendicular to the drum axis. Bulk material with a poorer flow behavior is dried in batches, usually under vacuum conditions. 

FIG. 12-75 Rotating (double-cone) vacuum dryer. (Stokes Vacuum, Inc.)... 

Performance and Cost Data for Batch Vacuum Rotary Dryers Typical performance data for vacuum rotaiy diyers are given in Table 12-26. Size and cost data for rotaiy agitator units are given in Table 12-27. Data for double-cone units are in Table 12-28. 

TABLE 12-28 Standard (Double-Cone) Rotating Vacuum Dryers ... 

TABLE 9.7. Performance of Agitated Batch Dryers (See Fig. 9.7) (a) Double-Cone Tumbler ... 

A typical vacuum rotary dryer is illustrated in Fig. 12-74 and a double-cone vacuum dryer in Fig. 12-75. 

Vessel rotation, e.g., double-cone and rotary dryers. Mixing and heat transfer are better than for static dryers but may be less than for mechanical agitation. Formation of balls and lumps may be a problem. 

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