Spray drying is the continuous transformation of feed from a fluid state into dried particulate form by spraying the feed into a hot drying medium. The feed may be solution, slurry, emulsion, gel or paste, provided it is pumpable and capable of being atomized. It involves bringing together a highly dispersed liquid and a sufficient volume of hot air to produce evaporation and drying of liquid droplets. The air supplies the heat for evaporation and conveys the dried product to the collector; the air is then exhausted with the moisture.
The dried product can be in the form of powders, granules, or agglomerates depending upon the physical and chemical properties of the feed, the dryer design and final powder properties desired.
The atomizing device, which forms the spray, is the ´heart´ of the spray drying process.
Atomizer: Equipment that breaks bulk liquid into small droplets, forming a spray. Prime functions of atomization are:A high surface area to mass ratio resulting in high evaporation rates,
The aim of atomizing the concentrate is to provide a very large surface, from which the evaporation can take place. The smaller droplets, the bigger surface area to mass ratio, the easier evaporation, and a better thermal efficiency of the dryer are obtained. The ideal from a drying point of view would be a spray of drops of same size, which would mean that the drying time for all particles would be the same for obtaining equal moisture content.
Ultrasonic Atomizer spray drying is suitable for a broad spectrum of markets and applications. Compared to pressure nozzle ultrasonic nozzles are having high particle size repeatability with tight distribution, droplets below 50 microns. Ultrasonic Atomizer produces highly spherical shape, and have ability to produce larger size spheres compared to typical air atomizing nozzles. Ultrasonic vibrations virtually eliminate clogging.
Degree of application decides the importance of process. Spray drying technology is widely applied in pharmaceutical fields as well as non-pharmaceutical fields.
Chemical industry, Ceramic materials, Detergents, soaps and surface-active agents, Pesticides, herbicides, fungicides and insecticides, Dyestuffs, pigments, fertilizers, mineral floatation concentrates, inorganic chemicals, organic chemicals, spray concentration (purification), milk products, egg products, food and plant products, fruits, vegetables, carbohydrates and similar products, slaughterhouse products, fish products and many others.
Many pharmaceutical and biochemical products are spray dried, including antibiotics, enzymes, vitamins, yeasts, vaccines, and plasma. The spray drying capacity required for these products ranges from high, in the case of yeasts to low, as in the case of plasma. Spray drying of most pharmaceutical and biochemical products is done using two-fluid or pressure nozzle atomizers. Spray drying systems used for pharmaceutical/biochemical applications include: Open-cycle, aseptic open-cycle and closed-cycle(figure below).