Spray drying is the transformation of feed from a
fluid state into a dried form by spraying the feed into a hot drying medium.
The feed is pumped from the product feed tank to the atomizing device,
located in the air disperser at the top of the drying chamber. The drying
air is drawn from the atmosphere via a filter by a supply fan and is passed
through the air heater to the air disperser. The atomized droplets meet the
hot air and the evaporation takes place, while cooling of the air happen
simultaneously. In Spray Drier, after the spray is dried in the drying
chamber, the majority of the dried product falls to the bottom of the
chamber and enters to a pneumatic conveying and cooling system.
The fines, which are the particles with a small diameter, will remain in
the air, and it is therefore necessary to pass the air through cyclones to
separate the fines. The fines leave the cyclone at the bottom via a locking
device and enter the pneumatic system, too.
The air passes from the cyclone to the atmosphere
via the exhaust fan. The two fractions of powder are collected in the
pneumatic system for conveying and cooling and are passed through a cyclone
for separation, after which they are bagged off. The instrumentation
comprises indication of the temperature of the inlet and outlet air, as well
as automatic control of the inlet temperature by altering the steam
pressure, amount of oil or gas to the air heater, and automatic control of
the outlet temperature by altering the amount of feed pumped to the
There are two basic types of atomization :
- Nozzle atomizer
- Disc atomizer
Spray Drier Configuration :
- Co-Current Flow
- Counter Current Flow
Advantages Of Using A Spray Dryer For Drying
- Control of particle size. Spray dryers can typically produce between
30 to 500 micron average particle sizes, in a bell shaped distribution.
- The shape of most spray dried particles is spherical, which provides
for fluid-like flow properties.
- Spray drying produces the most homogeneous product.
- Many heat sensitive products can be spray dried easily at relatively
high inlet temperatures.
- Permits drying without thermal degradation.