Spray Dryer
Spray drying is transformation of feed from a fluid state into dried
particulate form by spraying the feed into a hot drying medium. It is a
continuous particle-processing drying operation. The feed can be a
solution, suspension, dispersion, emulsion or slip. 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.
Feed is finely atomized and is introduced in the drying chamber along
with hot air. The mixture of atomized feed and hot air moves towards the
air exhaust of drying chamber. The time taken by this mixture to travel
up to air exhaust is called as residence time of drying. During this
residence time, the feed droplets loose its moisture to the hot air and
is converted into dry powder particles. Hot air absorbs this moisture,
so its absolute humidity increases while its temperature is reduced. The
feed droplets while loosing its moisture to hot air, remain at
temperatures much below the hot air temperature and it is exposed to hot
air for a very short time. Hence spray drying is essentially known as "Low
Temperature Drying". The temperature of feed droplet is the wet
bulb temperature at the prevailing relative humidity.




