Spray Drying Applications

If the initial feasibility evaluation is successful, it is reasonable to commit additional materials for a spray-drying trial. A laboratory dryer at least 500 mm in diameter is recommended for such tests. Bench-scale spray dryers are available but are limited in their ability to provide adequate atomization or sufficient process air flow for the successful production of dried particles. The laboratory unit, however, eom-bined with very fine atomization (two-fluid or rotary) will often produce aceeptable product for further testing. A series of tests can be performed at different inlet-outlet temperature combinations using small quantities of material and these samples ean be tested for chemieal stability to evaluate thermal effects from process air contact. The relationship between outlet temperature and final product moisture can also be established for this seale. While samples produced in a laboratory dryer are suitable for evaluating the effeet of spray drying on the product, they are not suitable for use in downstream proeessing because the fine particle distribution produced as a result of the small drying chamber dimensions may not be representative of the final spray-dried produet. 

Produetion of eoarser particles requires a larger, pilot-scale dryer, which in turn requires larger feed volumes. This pilot-scale work is often conducted at a spray-sdrying development center since many companies have laboratory dryers but few have the sizes and variety of process types needed to fully develop a spray-dried product from pilot scale through 1/lOth of the commercial scale and into final production. These facilities are usually found at spray-drying manufacturers or custom 

Spray Drying to Produce a Specific Type of Particie 

Because of its inherent costs, spray drying is not always considered as a processing option for many conventional formulations. However, when a specialized particle type is required by the active ingredient or dosage form, spray drying can become a feasible alternative to more conventional manufacturing processes. Such particle types include microcapsules, controlled release particles, nanoparticles, and liposomes. The application of spray drying to pharmaceuticals has been extensively discussed in review articles (21,22). 

A variation of this system is the integrated fluid-bed dryer (Fig. 15). This system includes integrated Alter bags, which are suspended from the chamber roof. This roof is perforated and serves a dual purpose as a gas disperser. The chamber above the roof contains clean gas that supplies the inlet process drying air and also has an exhaust point for clean gas, since any remaining lines are entrapped in the filters. 

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Rotating Nozzle (rotary atomizer) fluid is fed at low pressure to the center of a rapidly rotating disk and centrifugal force breaks up the fluid. These types of nozzles are used mainly in a spray drying application. 

Bhandari, B.R., Dumoulin, H.M.J., Richard, H.M.J. (1992). Flavor encapsulation of spray drying application to citral and linalyl acetate. Journal of Food Science, 51, 1301— 1306. 

Wendel, S. Celik, M. An overview of spray-drying applications. Pharm. Technol. 1997, (Oct), 124—156. 

PHARMACEUTICAL SPRAY DRYING APPLICATIONS Spray Dried Powders for Inhalation... 

Although it lacks the flexibility of the rotary atomizer, the pressure nozzle is nevertheless widely used in spray drying applications. For many products the requirement for nondusty appearance calls for large mean particle size and lack of a fines fraction that cannot be met with a rotary atomizer. In the other end of the particle size range, some products require finer particles than are practically achievable with a rotary atomizer. This is the range where two-fluid nozzles are applied. The following guidelines may be used as an indication of the particle sizes obtainable in spray dryers ... 

Bhandari BR, Dumoulin ED, Richard HMl, Noleau I, Lebert AM. 1992. Flavor encapsulation by spray drying Application to citral and linalyl acetate. Journal ofEood Science 57 217-221. 

However, two-fluid nozzles are expensive to operate because of the high cost of compressed air. Two-fluid nozzles are often used in laboratory and pilot plant spray dry applications because of their ability to produce a wide range of flow rates and droplet sizes. The range of operating pressure range for pressure nozzles used in spray drying is from about 250 PSI (17.4 bar) to about 10,000 PSl (690 bar). 

For a given spray-drying application, the selection between rotary and nozzle atomizers involves the following considerations (9) ... 

Products produced using fluidized spray drying have a broader particle size distribution and lower bulk density than the particles produced by conventional spray dryers with a typical mean size particle size range of 150 00 pm. This process is not meant to replace conventional spray drying processes but instead is a feasible alternative for spray drying applications that require larger mean particle sizes. 

Richard, H. M. J., Noleau, I., Lebert, A., 1992. Flavour encapsulation by spray drying application to citral and linalyl acetate./. Food Sci. 57(1) 217-221. 

Flavor encapsulation hy spray drying Application to citral and hrialyl acetate. 

R. Youngs, Spray Drying Applications in Pharmaceutical Production, I Chem E Pharmaceutical Subject Group Symposium II, 1986. 

Another solution to the sound problem is a rotary-valve combustor enveloped by a steel shell, as shown in Fig. 2.5. Because, for spray-drying applications, such a combustor is running out of its resonant frequency, the sound level will be less than 85 dB at a distance of 1 m from the dryer (Relikopf, 2012). 

Sodium Chloride. Sodium chloride (NaCl) still is used by some formulators in detergent manufacture, its main function being as an inert filler or diluent. In spray-drying applications, NaCl is used to control slurry viscosity and the density of the spray-dried bead or graules. Although salt is used to some extent in automatic dishwashing formulations, its use is not recommended" because of potential machine and dishware corrosion. 

Martins, AO Silva, EL Carasek, E. Sulphoxine immobilized onto chitosan microspheres by spray drying application for metal ions preconcentration by flow injection analysis. Talanta, 2004, 63, 397-403. 

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