|
The process involving conversion of fluid into
fine droplets and exposing them to a hot drying media, so as to
achieve defined dry particulate matter is spray drying. It is a
widely used continuous industrial process which involves particle
formation from feed fluid which may be in the form of solution,
emulsion or pumpable suspension into either dry powder or granules.
Spray drying involves following steps.
ATOMIZATION
Conversion of the feed into fine droplets is achieved by either
pumping the feed under high pressure through an orifice or by spraying
through a high speed rotating perforated disc. The former is known
as Nozzle Atomization and is popularly used to produce coarse droplets
resulting in large granular particles of dried products. The latter
is known as Rotary Disc Atomization and produces fine droplets resulting
in fine powder particles of dried products.
HOT AIR MIXING
Air, which is, normally the drying
media used, is heated to a predefined temperature depending upon
the characteristics of the feed fluid and dried product either an
indirect hot air generator or a direct hot air generator. This hot
air is brought in contact with the spray droplets in one of the
following ways through the air distributor:
Co-current-Air and particles move
in the same direction.
Counter-current-air and particles
move in the opposite direction.
Mixed flow - particles are subjected
to co-current and counter-current phase.
The thermal energy of the hot air
is used for evaporation and the cooled air pneumatically conveys
the dried particles in the system. The contact time of the hot air
and the spray droplets is only a few seconds, during which drying
is achieved and the air temperature drops instantaneously. The dried
particle never reaches the drying air temperature. This enables
efficient drying of heat sensitive materials without thermal decomposition.
POWDER SEPARATION
Dried powder is discharged
continuously from the bottom of the drying chamber through rotary
valve and the air containing fines is taken to either a cyclone
separator or passed through a textile fabric in a bag filter to
recover the fines. The air is further scrubbed in a high efficiency
venturi scrubber before being exhausted out to the atmosphere.
Special powder handling systems are
used for industrial applications to either cool the dried powder
or toe pneumatically convey the same to a product silo. These systems
are tailor designed to suit the specific requirements and layouts.
Spray dried is an ideal choice as it offers defined end product
characteristics in terms of particle size, moisture content, bulk
density and particle shape.
Download
Catalogue
|
