Pressure nozzle atomizers

A spray-dryer eonsists of a feed tank, a rotary or nozzle atomizer, an air heater, a drying ehamber, and a eyelone to separate the powder from the air. A rotary atomizer uses eentrifugal energy to form the droplet. Pressure-nozzle atomizers feed solution to a nozzle under pressure, whieh forms the droplet. Two-fluid nozzles feed solutions separately into a nozzle head, whieh produces high-speed atomizing air that breaks the solution into tiny droplets. Both the feed solution and the drying air are fed into the drying ehamber in a standard eoeurrent flow [27]. 

Spray. Direct type, continuous operation Suited for large capacities. Product is usually powdery, spheric, and free-flowing. High temperatures can be used with heat-sensitive materials. Product may have low bulk density See comments under Liquids. Pressure-nozzle atomizers subject to erosion Requires special pumping equipment to feed the atomizer. See comments under Liquids Not applicable Not apphcable Not applicable Not applicable Not applicable... 

Atomization Rotary atomization Pressure nozzle atomization Two-fluid nozzle atomization... 

For spray dryers with pressure nozzle atomization, the mean particle size of the dried product varies in the range from 50 to 250 pm. 

Figure 12-94a shows a cocurrent cone-based tall form chamber with roof gas disperser. This chamber design is used primarily with pressure nozzle atomization to produce powders of large particle sizes with a minimum of agglomeration. The chamber can be equipped with an oversize cone section to maximize powder discharge from the chamber bottom. This type of dryer is used for dyestuffs, baby foods, detergents, and instant coffee powder. 

Figure 12-94 > shows a countercurrent flow chamber with pressure nozzle atomization. This design is in limited use because it cannot produce heat-sensitive products. Detergent powder is the main application. 

The selection of the atomizer usually means the selection between wheel atomizer and pressure nozzle, as the use of the pneumatic nozzle is very limited. The selection may be based on various considerations, such as availability, flexibility, energy consumption, or particle size distribution of the final dry product. The last is the most common case. The sizes of droplets produced by various atomizers are shown in Table 9.3. The advantages and disadvantages of both wheel and pressure nozzle atomizers are summarized below. 

Pressure-nozzle atomization arrangements and in-line homogenization... 

Aside from the general formula, numerous data on dryer cost dependence on evaporation capacity exist in literature for the given dryers and definite operating parameters [20,28,29]. For example, cost of a spray dryer with a pressure nozzle atomizer, residence time of 16 s, inlet- and outlet-air temperature of 538°C and 121°C, respectively, can be calculated as [28] ... 

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