Feed liquid, spray drying

The physical properties of spray-dried materials are subject to considerable variation, depending on the direction of flow of the inlet gas and its temperature, the degree and uniformity of atomization, the solids content of the feed, the temperature of the feed, and the degree of aeration of the feed. The properties of the product usually of greatest interest are (1) particle size, (2) bulk density, and (3) dustiness. The particle size is a function of atomizer-operating conditions and also of the solids content, liquid viscosity, liquid density, and feed rate. In general, particle size increases with solids content, viscosity, density, and feed rate. 

Neither flash nor spin-drying produces highly uniform particles and, even though the bulk of the particles remain at or near the wet bulb temperature, small particles are often over-dried and overheated. Particles of uniform size can be formed by spray drying, however, although it is then necessary that the feed should be in the form of a pumpable liquid which can be atomised so that the particles are evenly exposed to the hot air. 

Even though liquid whey has been successfully commercialized in the form of alcoholic and nonalcoholic beverages, these are still a rarity in most countries. Most whey is converted to whey solids as ingredients for human food or animal feeds by traditional processes such as spray drying, roller drying, concentration to semisolid feed blocks, or production of sweetened condensed whey. Jelen (1979) reported other traditionally established processes including lactose crystallization from untreated or modified whey, production of heat-denatured whey protein concentrate, or recovery of milk fat from whey cheese in whey butter. ... 

Spray drying Atomized liquid feed is brought into contact with a sufficient volume of hot air to evaporate liquid and solidify drops Spray dryers... 

Spray onto dispersed powder (cf. powder clustering, agitation methods above) Atomized liquid feed is sprayed into circulating dispersion of already-dried particles. Hot gases maintain dispersion. Spray granulation, spouted and fluidized bed granulation Fluidized and spouted beds, Wurster apparatus... 

Liquid feed is most often dispersed into the bed by a two-fluid spray nozzle which is flexible in operation and less prone to blockage, especially if heated air is used to atomize crystallizing liquors. Liquid feed may be directed onto the bed surface from the space above the upper bed surface or introduced directly beneath the surface of the bed material. The liquid spray is less likely to dry as a spray before contacting the bed particles in this latter arrangement. 

Spray drying involves converting the atomized liquid droplets into dry powders by hot air. This one-step process is capable of making particles of size suitable for inhalation.The particle size and size distribution of the powder can be manipulated by the concentration of the feed solution, the spray temperature, cyclone efficiency, and chemical nature of the feed. ... 

Spray Diyers Spray drying is a drying process for transformation of a pumpable liquid feed in the form of a solution, dispersion, slurry, or paste into a particulate dried product in one single operation. The process comprises atomization of the feed followed by intense contact with hot air. 

Choice of atomizer system The choice of atomizer system for a specific spray drying operation depends upon the particle size distribution required in the final dried product. It also depends upon the physical and chemical properties of the feed liquid. 

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