Spray
drying is by definition the transformation of feed
(which is in liquid state) into a dried particulate
formed by spraying the feed into a hot drying medium.(In
short, spray drying involves atomization of feed
into a spray, and contact between spray and drying
medium in co-current flow resulting in moisture
evaporation). Evaporation takes place because of
vast surface area of droplets in a spray.It is a
one-step, continuous particle processing operation
involving drying. The feed can either be a solution,
suspension or paste. The resulting dried product
confirms to powder, granules or agglomerates, the
form of which depends upon the physical and chemical
properties of the feed and the dryer design and
operation.
ADVANTAGES
OF SPRAY DRYER
1.
The powder quality remains constant irrespective
of the design of the dryer.
2. It is a continuous and easy process.
3. Energy Efficient.
4. Compact.
5. Require Minimum Maintenance.
6. Saves Labour .
7. It can be used for both, Heat sensitive and Heat
Resistant Products.
8. Custom Designed to suit your product.
SIZE
OF THE DRIED PARTICLE
Basically two types of atomizers:
CENTRIFUGAL and NOZZLE
and three models:
a) CENTRIFUGAL / DISC (low pressure)
b) NOZZLE ( high pressure)
c) VERSATILE (Combination of Centrifugal and
Nozzle) are offered by us.
Typical
diagram of spray dryer equipped with rotary atomizer
(Centrifugal) and Nozzle atomizer are shown in figures.
Powders comprising of small or medium sized particles
are produced by a centrifugal atomizer. Coarser
powder are produced by fountain drying using pressure
Nozzle atomizer.
PROCESS
Spray Drying consists of four process stages :
A) Atomization of feed into the spray.
B) Spray – Air contact (in co- current
flow).
C) Drying of spray (moisture evaporation).
D) Separation of dried product from the air.
Each stage is carried out according to dryer design
and operation and together with the physical and
chemical properties of the feed, determine the characteristics
of the dried product.
The
liquid feed is pumped from the fed tank to the
a) Centrifugal atomizer or
b) pressure Nozzle within a ceiling air disperser
through which the drying air enters the drying chamber.
The indirectly heated air is drown from the atmosphere
by a fan.
Due
to large surface area of contact between droplet
and hot air, drying is a accomplished in few seconds
and the product leaves the drying chamber as a free
flowing powder. The majority of the dried product
falls to the base of the chamber and is collected
from chamber bottom.
The product fines entrained in the air passes to
the cyclone for separation and the remaining product
is collected from the cyclone bottom. Alternatively
you may choose single point collection also to get
different sizes of the particle .
Further
any escaped fines are trapped in scrubbing system
with the help of water spray and the solution can
be remixed with liquid feed.
The
spray dryer thus completely eliminates filtration,
grinding, etc. and the system is pollution free
.
All
processing conditions such as temperature profile,
feed rate, air velocity, atomizer speed are conventionally
monitored and displayed on central instrument panel.
The running systems can be visualized on the MIMIC
diagram. The system is designed with interlocks
and instruments for auto / manual control.
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