Spray dryers pilot plant performance

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). 

TABLE 9.19. Product Numbers and Performance of a 30 X 29 in. Pilot Plant Spray Dryer... 

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. 

To investigate the properties of powder, produced via effervescent atomization, three different pilot plant spray dryers have been used. Several trails were performed with a C117A (Industriewerke Karlsruhe (IWK), buUd year 1961) (Eig. 21.19a). For the experiments, various settings such as liquid mass flow (6-12 L/h), drying temperature (180 °C), drying gas mass flow (150-300 m /h), and ALR (0.2-0.4) were varied in an attempt to spray dry PVP K30 solutions with 20 wt%. Not in every experiment, a proper spray drying process was achieved. The fluctuation of the liquid feed during the atomization process with the effervescent... 

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