Spray Drying

Spray DryingSpray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some industrial products. They also turn a solution or slurry into a dried powder in a single step, which can be advantageous for profit maximization and process simplification.

Spray drying begins with the atomization of the feed liquid into a spray of fine droplets. Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.

All spray dryers use some type of atomizer or spray nozzle to disperse the liquid or slurry into a controlled drop size spray. The most common of these are rotary disks and single-fluid high pressure swirl nozzles. Alternatively, for some applications two-fluid or ultrasonic nozzles are used. The atomized liquid is usually sprayed into a drying chamber along with the hot gas stream, either in a co or counter current flow. The co-current flow enables the particles to have a lower residence time within the system and the particle separator (typically a cyclone device) operates more efficiently. The counter-current flow method enables a greater residence time of the particles in the chamber and usually is paired with a fluidized bed system. Consequently, the liquid’s solvent is evaporated, leaving behind the product in a form of spherical powder. The dry powder is separated from the gas stream and collected at the bottom of the drying chamber or outside of it by means of a cyclone. The dry powder is often free-flowing. Thereafter the exhaust gas is treated to meet environmental requirements and is released into the atmosphere, or in case of a closed system, de-humidified, reheated and lead back into the drying chamber.

Spray drying often is used as an encapsulation technique by the food and other industries. A substance to be encapsulated (the load) and anamphipathic carrier (usually some sort of modified starch) are homogenized as a suspension in water (the slurry). The slurry is then fed into a spray drier, usually a tower heated to temperatures well over the boiling point of water. As the slurry enters the tower, it is atomized. Partly because of the high surface tension of water and partly because of the hydrophobic/hydrophilic interactions between the amphipathic carrier, the water, and the load, the atomized slurry forms micelles. The small size of the drops results in a relatively large surface area which dries quickly. As the water dries, the carrier forms a hardened shell around the load.

For additional information, contact us through email at sales@hemrajindia.com OR sdesai@hemrajindia.com

Spary Dryer Spray Drying KB