Spray-drying system

FIG. 12-104 Open spray-drying system with direct-fired heater. (NIRO, Inc. )... 

Pulse Combustion Spray Drying Systems http //www.pulsedry.com/... 

Labrude and Rasolomana [1.80] reported an atomizer-spray-drying system for oxyhemoglobin in a 0.25 M sucrose solution at temperatures between +80 and +100 °C, which resulted in an unchanged dry product if the relative humidity was kept below 3%. When this dry product was compared with a freeze-dried product, in both cases a met-oxyhemoglobin (met-HBO) content of-3% was found. By ERP and spectro-... 

Development of metal chelates suitable for employment in a spray drying system (28,29). Spray drying systems have been demonstrated to be more cost-effective than wet systems for control of SO2 emissions from power plants. 

A few additives have been tested in spray drying systems. Calcium chloride has proven effective in increasing the reactivity of limestone and Ca(0H)2 towards SO2 (10, 11). Adipic acid was also tested (12) with mixed results. Sodium sulfite, sodium hydroxide, Fe++ compounds, Ethylene-diamine-tetra-acetic-acetic acid and disodium salt (EDTA) have been used as additives during simultaneous SO2 and N0X removal (Niro Process) (13). The emphasis in the Niro process was to improve the removal of NOx. 

When operating a spray drying plant for flavourings, the explosion hazard should be determined and the correct protective measures should be taken. The before-mentioned low-oxygen spray drying system and the closed-cycle system offer a high level of safety and the additional advantage of low emission. 

FIGURE 3.27 Correlation between the entropy of fusion (AS ) and the ideal entropy of mixing (ASm) f°r griseofulvin-adipic acid spray-dried systems. (Reproduced from Corrigan, O.I., Thermochim. Acta, 248, 245-258, 1995. With permission.)... 

FIGURE 23.22 Self-inertizing spray drying system (1) drying chamber with rotary atomizer (2) cyclone (3) scrubber condenser (4) direct-fired heater (5) heat exchanger for waste-heat recovery (6) exhaust to atmosphere (7) fuel (8) combustion air (9) cooler (10) condensate F, feed P product. 

Eilkova, 1., and Mujumdar, A.S. 1995. Industrial spray drying systems. In Handbook of industrial drying. 2nd ed. Ed. A.S. Mujumdar, 263-307. New York Marcel Dekker. 

Fig. 7.59 is the simplified flow sheet of a co-current spray drying system with recirculation of fines that is another possibility to accomplish agglomeration in a spray dryer. Often, the fines are returned to the liquid feed bin and redissolved or redispersed (see, for example Fig. 7.68b and c). However, if fine particles are returned to the spray zone, as shown in Fig. 7.59, they are captured by the droplets (similar to a wet scrubbing effect) and incorporated in the product. 

In regard to gas handling and flow, the most involved and costly part of any spray drying system, the flow sheet of Fig. 7.59 shows an open system. However, for economical or other reasons, closed, semi-closed or even aseptic plant gas flow schemes may be applied (Fig. 7.60). 

Fig. 7.59 Simplified flow sheet of a co-current spray drying system with rotary atomizer and recirculation of fines.

Fig, 7,60 Schematic representation of different spray drying system designs, (a) Open, (b) closed, (c) semi-dosed, (d) aseptic plant gas flow schemes (courtesy CEA/NJRO, Soeborg, Denmark). 

Fig. 6.3-1 Diagram of a spray-drying system for the production of conventional laundry detergent powder [B.60]...

Figure 5.1 Spray drying system for redispersible polymer powders. 1990, American Concrete Institute, reprinted with permission.)...

Some foodstuffs have to be prepared in organic solvents rather than water to prevent oxidation of one or more of the active ingredients. In these applications, a closed-cycle spray drying system... 

FIGURE 4.2 Layout of a closed-cycle spray-drying system. 

The mixed-flow spray drying system is a combination of the previous two systems. The droplets may contact the drying medium in the same and opposite direction in one drying chamber. It is usually found in spray dryers fitted with pressure nozzle or pneumatic nozzle. It is sometimes used to obtain agglomerated powders in a small drying chamber. It should be noted that the product must be nonheat sensitive. 

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

Indeed, the hot air distribution is one of the crucial points in a spray drying system design. Today, there are three types of hot air distributors which can be found in spray drying systems in the food industry, i.e., rotating air flow distributor, plug air flow distributor, and central pipe air distributor, A schematic representation of each of these systems is shown in Figure 4.4. 

There are two types of air heaters which can be used in a spray-drying system, e.g., direct air heaters and indirect heaters. Direct air heaters, such as direct gas or oil fired furnace, can be used whenever the contact between combustion gas and spray is acceptable. When products of combustion of fossil fuels cannot contact with the spray, an indirect heater, such as indirect steam air heater, indirect gas, or oil-fired heater, is recommended. Interested readers can find more details about it in the literature (Matsers 1991). 

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