Spray drying is the process of mixing and drying a slurry (a kind of suspension) to form a homogeneous mixture of powders. The powders are mixed with a liquid (like water), then the mixture is sprayed into hot dry air, so that the liquidevaporates leaving small spherical granuales of the mixed powders. Flour suspended in water In chemistry, a suspension is a colloidal dispersion (mixture) in which a finely-divided species is combined with another species, with the former being so finely divided and mixed that it doesnt rapidly settle out. ... It has been suggested that this article or section be merged with homogeneity (physics). ... Powder is a substance that has been crushed into very fine grains. ... A liquid will assume the shape of its container. ... Water (from the Old English waeter; c. ... A liquid will assume the shape of its container. ... Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ...
Use in the food industry
Spray drying is sometimes used in the food industry, in milk, egg, fruit juice and dairy products, as well as coffee (although it has been mostly displaced by freeze drying in this aspect). Freeze drying (also known as Lyophilization) is a dehydration process typically used to preserve a perishable material, or to make the material more convenient for transport. ...
Usually a liquid or suspension is pressurized and then sprayed into a stream of hot dry air. The small size of the drops (averaging 100 micrometres in diameter) results in a relatively very large surface area which dries quickly. Although the air dry-bulb usually reaches 200 degrees celsius, the air wet-bulb rarely exceeds 55 C and the dried particles are removed from the drier usually within 30 seconds. The temperatures of the particles during drying can range from the wet-bulb temperature of the inlet air to above 100 C as they exit in the dry state. Although these temperatures are high compared to other drying methods available, the moisture near the end is usually near the BET monolayer and the time of exposure is very short, resulting in relatively high nutrient preservation when used in food processing.
Sources
Nutritional evaluation of food processing second edition (1975), Robert S. Harris, Ph.D. and Endel Karmas Ph.D. (eds)
Spraydrying is the process of mixing and drying a slurry (a kind of suspension) to form a homogeneous mixture of powders.
Spraydrying is sometimes used in the food industry, in milk, egg, fruit juice and dairy products, as well as coffee (although it has been mostly displaced by freeze drying in this aspect).
Although the air dry-bulb usually reaches 200 degrees celsius, the air wet-bulb rarely exceeds 55 C and the dried particles are removed from the drier usually within 30 seconds.
The typical surface temperature of a particle during the constant drying zone is 45-50 C. For this reason, it is possible to spraydry some bacterial suspensions without destruction of the organisms.
The atomized liquid droplets are dried while suspended in the chamber and the powder settles to the floor where it is conveyed by a reciprocating scraper (J) to the screw conveyor (K).
The physical properties of spraydriedpowders is related to the characteristics of the matrix of the shells and to the size of the vacuole.
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