Dryers, pilot plant sizes spray

The main variables in the operation of atomizers are feed pressure, orifice diameter, flow rate and motive pressure for nozzles and geometry and rotation speed of wheels. Enough is known about these factors to enable prediction of size distribution and throw of droplets in specific equipment. Effects of some atomizer characteristics and other operating variables on spray dryer performance are summarized in Table 9.18. A detailed survey of theory, design and performance of atomizers is made by Masters (1976), but the conclusion is that experience and pilot plant work still are essential guides to selection of atomizers. A clear choice between nozzles and spray wheels is rarely possible and may be arbitrary. Milk dryers in the United States, for example, are equipped with nozzles, but those in Europe usually with spray wheels. Pneumatic nozzles may be favored for polymeric solutions, although data for PVC emulsions in Table 9.16(a) show that spray wheels and pressure nozzles also are used. Both pressure nozzles and spray wheels are shown to be in use for several of the applications of Table 9.16(a). 

The design of spray dryers is based on experience and pilot plant determinations of residence time, air conditions, and air flow rate. Example 9.10 utilizes such data for the sizing of a commercial scale spray dryer. 

Sizing a Spray Dryer on the Basis of Pilot Plant Data... 

Both of these alternative separation techniques could be evaluated in a spray dryer MgO pilot plant. If either or both of these tests yield satisfactory solutions to the MgO/ash separation problem, it might be possible to reduce the investment and revenue requirements significantly by eliminating the 95 efficient ESP and replacing it with a mechanical collector. Therefore it may also be necessary to perform some test work in a pilot plant to determine the relative densities and particle sizes of the MgO and the ash in the calciner off-gas. 

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