Other Dryer Types

Steam dryers These provide closely spaced corrugated plates through which steam must pass. Chevron dryers and other dryer types reduce the velocity at which the steam passes, causing the impurities to drop out. 

Pulse combustion drying systans can be used to dry a wide range of materials, including low- and high-viscosity liquids, pumpable pastes, aU noncohesive filter cakes (and most cohesive ones), and many powders and granules. No other dryer type offers such a variety of feedstocks to handle (Table 23.3, Chowdhury, 1984). 

For dispersiou dryers such as flash, fluid-bed, spray, aud some others, the most practical bag filter collector is the jet pulse type [3]. It causes the least fluctuatiou of air flow aud so allows these dryers perform more efficieutly. Collectors that periodically shut dowu oue of the several compartmeuts for cleauiug are uuable to hold a steady pressure drop. But these collectors have other advautages aud are iu commou use iu other dryer types as well. 

The procedure has been suggested as a means for rating the performance of grain dryers, but it may be applied with equal success to other dryer types or drying methods. 

The following list illustrates the evolutionary developments that have occurred over the past five decades in two commonly used industrial dryers rotary and flash dryers. Similar evolutionary development trends can be traced for most other dryer types as well. 

The ambient air dryer appears to be competitive to other dryer types because... 

We have not discussed multistage fluidized bed dryers for laek of space. However, in some applieations they yield major advantages. A dryer may be a part of a multistage FBD operated at diflerent eonditions or as a part of other dryer types, e.g., a flash dryer or spray dryer followed by a FBD. 

Figure 8 Decision tree for selection of fluidized bed dryers for granular feedstock. Note Other dryer types are also suited for several of the above applications. If the feedstock contains a solvent, fluidized bed dryers are not recommended in general indirect or vacuum dryers are preferred instead.

Tables 7 and 8 compare conventional concepts of spouted bed dryers and vibrated bed dryers with some of the novel ideas not all of which have been tested yet. Table 9 shows the advantages of combining fluid bed dryers with fluid bed as well as other dryer types to improve the performance of the combined two-stage drying system. For some large scale drying applications although a single stage fluid dryer can perform the necessary drying, only the two-stage system is cost-effective. See Mujumdar and Suvachittanont (2000) and Mujumdar (2001) for further details.

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