Spray dryers operating variables

Dryer Operating Parameters Having considered the formulation and preparation of the material to be spray dried, one must now consider the effect of spray drier operating variables on flavor retention. One needs to choose operating temperatures, air flow rates, inlet air dehumidiiication etc. 

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 9.18. Effects of Variables on Operation of Spray Dryers... 

Fletcher et al. (2003) nsed a commercial CFD software to simulate the full-scale spray dryers. Results obtained for the three scales (laboratory, pilot, and industrial) SD in two configurations (tall and short height to diameter chambers) showed the possibility of exploring the effect of the operational variables on flow stability, wall deposition, and product quality. 

A simplified flow diagram for a lime slurry spray dryer system is shown in Figure 7-34. This diagram represents the 100 MW Demonstration Plant on Units 6 and 7 of the Riverside Station of Northern States Power Conqiany. The plant was used for extensive testing of die effects of various operating variables on a large 46-fi diameter spray dryer absorber (Gutslke etal., 1983). 

---