*3.3.1.3 Atmospheric twin-drum dryers*

The applied of slurry is by direct dip coating of the twin drums in the feed tray at the dryer bottom (**Figure 11**), or by splash, or spray feeders from a feed tank at the

**Figure 10.** *Twin-drum dryer with dip feed.*

**Figure 11.** *Twin-drum dryer with splasher or sprayer feed.*

**Figure 12.**

*Single-drum dryer with splasher or sprayer feed.*

dryer bottommost (**Figure 12**) onto the top of the both steam-heated drums, which are counter-rotating faraway from each other [38–40, 46]. Sheets are made by cohesion onto the drum top and are held up versus gravity by their surface tension, then dry conductively. This kind of dryer is appropriate for mixtures that produce dusty stuffs.

#### *3.3.1.4 Enclosed drum dryers*

If the solvent steam other than humid discharged in the course of the drying by the drum requires to be improved, or if dried foodstuffs produce much powder, the atmospheric twin-drum dryers could be bounded in vapor or in dust-tight enclosure [38–40, 46]. The steam vapor could be retrieved by an appropriate condenser, and the dust could be eliminated using a wet scrubber.

#### *3.3.1.5 Vacuum double-drum dryer*

Heat-sensitive materials can be dried in a vacuum double-drum dryer where the dryer is enclosed in an airtight enclosure under a vacuum (**Figure 13**) [38–40, 46].

*Drying Technology Evolution and Global Concerns Related to Food Security… DOI: http://dx.doi.org/10.5772/intechopen.109196*

**Figure 13.** *Vacuum double drum dryer.*

This dryer type is also attached to a vacuum pump, a scrubber, and a condenser. Dryer operation is like its atmospheric version excluding that there are two product basins: one is for vacuum breaking and the other is for product discharge.
