Stage Spraying

Use at 1 1/4-2 oz/gal. in 3 stage spray system, maintain operating pH within 3.2-4.5 for steel, aluminum and galvanized metal phosphating. 

Many different vacuum bleacher designs are available (Figure 25) to the industry, some with single-stage spraying of the premixed clay/oil slurry into the vacuum... 

Figure 354. Flow sheet of a single-stage spray dryer ...

In a single-stage spray dryer the process is finished when most of the moisture in the pore space has dried. The agglomerates accumulate in the lower part of the spray-drying chamber and are removed by the suction of a fan driving a dust-collection system. The agglomerates are collected in a cyclone while dust is collected in a wet scrubber. Material-laden scrubber water may be recirculated and mixed with the liquid feed. 

When the product coming out of the spray dryer is too fine it does not wet readily and so is harder to reconstitute. To make the product more readily soluble, it is agglomerated in a small fluidized or vibrated fluidized bed, as shown in Figure 23.23. This two-stage arrangement is used in the production of instant coffee, milk powder, cocoa, etc. An extension of this basic concept is the so-called spray-fluidizer, which dries the material in two stages. In the first stage (spray dryer). 

FIGURE 23.23 A two-stage spray drying process for milk (1) air filter (2) heater (3) cooler (4) spray dryer (5) cyclone (6) exhaust fan (7) fluidized bed dryer (8) return line of fine powder. 

Fig. 6.4-8 Typical particle from single stage spray drying with small. .satellites" attached...

FIGURE 3.2 Typical setup of a one-stage spray drier (1 drying chamber, 2 atomizer, 3 air heater, 4 main cyclone, 5 fan/filter, and 6 transport system cyclone). (Reproduced with permission from Westergaard, V.,... 

Two-stage spray dryer systems are sometimes called Spray-Fluidizers, since a fluid bed is installed at the cone of the spray dryer chamber. Alternatively, a vibrated fluid bed (VFB) is installed at the bottom of the drying chamber. It can produce instantly soluble products, such as instant coffee, milk, cocoa, etc., by agglomeration of the product. It is ideal to handle heat-sensitive products. 

FIGURE 4.3 A schematic diagram of a typical three-stage spray-drying system. 

Any of the above layouts plus fluid-bed, agglomerators, flash dryers as second stage Spray and fluidizer... 

In the food industry, because the spray dryer is commonly available, economical, fast, and produces good-quality material [16], it becomes the most common means of encapsulation. The encapsulation process is simple and similar to the one-stage spray drying process. The coated material is called the active or core material, and the coating material is called the shell, wall material, carrier, or encapsulant [43]. The active material to be encapsulated, such as an oil or fia-vor in an oil base, is dispersed in a hydrocolloid carrier, e.g., gelatin, modified starch, dextrin or maltodextrin, or gum arabic. After the emulsifier is added, the mixture must be... 

Mounir, S. and K. Allaf (2008). Three-stage spray drying New process involving instant controlled pressure drop. Drying... 

One-stage spray dryer Reference value Nonagglomerated (=0.2 mm) Wide size distribution Significant fraction of fines... 

Two-stage spray dryer 18% Instantized agglomerated powder... 

Three-stage spray dryer 30% Agglomerated and granulated... 

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