The document describes the working of a spray dryer. A spray dryer uses atomization to form fine liquid droplets that are then dried into powder particles by hot gas. The liquid is sprayed into a drying chamber and the droplets move in a helical path as hot air evaporates the moisture, forming dry particles within seconds. The dried particles are then recovered at the bottom while the hot air exits through the top. Spray drying allows rapid, continuous drying of heat-sensitive materials and produces free-flowing particles of uniform size.

1. SPRAY DRYER

2. SPRAY DRYER

3. PRINCIPLE
• The fluids to be dried is atomized in to fine
droplets
• The droplets thrown radially in to a moving
stream of hot gas
• The temperature of the droplet increases
rapidly and get converted in to dried spherical
particles
• This process completes in a few seconds
before the droplet reach the wall of the dryer

4. CONSTRUCTION
• It consists of a large cylindrical drying chamber
with a short conical bottom
 material : stainless steel
Diameter:2.5-9 M
Height :25 m or more
• Air inlet present in the roof of the chamber
• Another inlet- carrying spray disk atomizer –
set in the roof

5. CONSTRUCTION
• Spray disk atomizer :
– Diameter – 300 mm
– Speed - 3000-50,000 rpm
• Bottom of the dryer is connected to a cyclone
separator

6. WORKING
• 3 stages
Atomization of the liquid
Drying of the liquid droplet
Recovery of the dried product

7. WORKING
ATOMIZATION OF THE LIQUID TO FORM DROPLETS
• The feed is introduced through the atomizer
• It form fine droplets
• The selection of the type of atomizer is
important because the properties of the final
product depends on the nature of the droplet
formed

8. WORKING
• Types of atomizer :
Pneumatic atomizer
Pressure nozzle atomizer
Spinning disc atomizer
The feed rate is adjusted in such a way that the
droplets should be completely dried before
reaching the walls of the drying chamber

9. WORKING
• The product should not be overheated
Drying of the liquid droplet :
• Hot air is introduced through the hot air inlet
• The fine droplet introduced in to this air
stream.
• It absorb heat from the hot air and it get
dried in the drying chamber

10. WORKING
• The surface of the liquid droplet is dried
immediately to form a tough shell
• The liquid from inner side of the shell diffuses out
through the shell at a particular rate
• At the same time heat transfer takes place at a
rate greater than the liquid diffusion rate
• As a result heat inside mounts up
• this allows the liquid to be evaporate at a faster
rate .so vapor will be produced inside the shell

11. WORKING
• So the internal pressure increases and that causes
the droplet to swell
• The vapor present in the shell starts to permeate
through the shell.
• So the thickness of the shell decreases and finally
it ruptures and releases the internal pressure
• The feed rate and the temperature of the air is
adjusted in such a way that the droplets should
be completely dried before reaching the wall of
the drying chamber

12. WORKING
• Recovery of the dried product:
• Centrifugal force of atomizer drives the
droplets to follow helical path
• This particles are dried during their journey
and finally falls at the conical bottom
• All these processes are completed in a few
seconds
• The particle size of final product ranges from
2-500mm

13. USES
• The quantity of the material to be dried is
large
• Thermolabile ,hygroscopic materials can be
handled

14. ADVANTAGES
• Spray drying is a continuous process
• Drying is very rapid(completes within 3-30
seconds)
• Labour costs are low
• Fine droplets formed provide large surface
area for heat and mass transfer .so product
shows excellent solubility

15. ADVANTAGES
• It is suitable for drying sterile products
Free flowing products of uniform spheres is
formed .convenient for tabletting process

16. DISADVANTAGE
• Spray drier is bulky(25m –height ,9m diameter
) and expensive
• Not easy to operate
• Thermal efficiency is low ,as much heat is lost
in the discharged gases.