spray drying is technology widely used in milk powder and coffee powder manufacturing industry because of its working principle and technology involved..

1. SPRAY
DRYINGI N F O O D I N D U S T R Y
powder
Liquid/slurry
Pallavi B.S

2. A SPRAY DRYER, as the name implies, is a device
for drying, utilizing a spray.
• Spray drying is a one-step continuous
unit operation that employs liquid
atomization to produce droplets that are
dried to individual particles when moved
in a hot gaseous drying medium. The
three stages that occurs in a spray dryer
before drying is accomplished includes.
• 1.Atomization
• 2.Spray-air mixing and moisture
evaporation.
• 3.Dry product separation from the exit
air.

3. A SPRAY DRYER CONSISTS OF
• Feed pump
• Atomizer
• Air heater
• drying chamber and systems for exhaust air cleaning and
powder recovery/separator.
• Bag filter for fine separation
• Exhaust fans for dust collection
• Vibratory screen for sieving powder

4. 1.ATOMIZATION
The atomizing device, which forms the spray, is the ´heart´ of
the spray drying process.
Atomizer: equipment that breaks bulk liquid into small droplets, forming a
spray.
• Why atomizer ??
a. A high surface to mass ratio resulting in high evaporation rates,
b. Production of particles of the desired shape, size and density.
The smaller droplets, the bigger surface, the easier evaporation, and a better
thermal efficiency of the dryer are obtained. The ideal from a drying point of
view would be a spray of drops of same size, which would mean that the
drying time for all particles would be the same for obtaining equal moisture
content.
based on the liquid jet theory described in 1878 by Lord Rayleigh

5. THREE BASIC TYPES OF ATOMIZERS ARE
USED COMMERCIALLY:
• a. Rotary atomizer (atomization by centrifugal energy)
• b. Pressure nozzle (atomization by pressure energy)
• c. Two-fluid nozzle (atomization by kinetic energy)
• The selection of a specific atomizer is made based on the
• properties of the feed
• desired powder properties,
• the dryer type and
• its capacity and the atomizer capacity.

6. ROTARY ATOMIZER
Rotary atomizer uses the energy of a high speed-rotating wheel to divide bulk liquid
into droplets. Feed/solution is introduced at the center of the wheel, flows over the
surface to the periphery and disintegrates into droplets when it leaves the wheel.
Advantages Disadvantages
 Great flexibility & ease of
operation.
 Low pressure feed system.
 No blockage problems.
 Handling of abrasive feeds.
 Ease of droplet size control
through wheel speed adjustment.
 Produce large quantities of fine
particles
 High capital cost.
 Very expensive to maintain.
 Cannot be used in horizontal
dryers.
 Difficult to use with highly viscous
materials.

7. PRESSURE NOZZLES:
• Pressure nozzle is the most commonly used atomizer for spray drying.
• Nozzles generally produce coarse, free flowing powders than rotary atomizers.
• Pressure nozzles used in spray drying are called “vortex” nozzles because they contain
features that cause the liquid passing through them to rotate.
• The rotating fluid allows the nozzle to convert the potential energy of liquid under pressure
into kinetic energy at the orifice by forming a thin, high-speed film at the exit of the nozzle.
• As the unstable film leaves the nozzle, it disintegrates, forming first ligaments and then
droplets.
ADVANTAGES:
• Pressure nozzles can be used over a large range of flow rates, and can be
• combined in multiple-nozzle installations to give them a great amount of flow rate and
• Particle size flexibility.

8. TWO-FLUID OR PNEUMATIC NOZZLES:
• Liquid feedstock and compressed air (or steam) are combined in a two-fluid nozzle. The
design utilizes the energy of compressed gas to atomize the liquid.
advantage disadvantage
 ability to produce very fine
 particles atomize highly viscous
feeds.
expensive to operate because of the
high cost of compressed air.

9. 2. MIXING OF SPRAY AND DRYING MEDIUM
• The manner in which spray contacts the drying air is an important factor in spray dryer
design, as this has great bearing on dried product properties by influencing droplet
behavior during drying.
• 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.

10. • The largest and most obvious part of a spray-drying
system is the drying chamber.
• This vessel can be taller and slander or have large
diameter with cylinder height. Selecting these
dimensions is based on two process criteria that must be
met.
• First, the vessel must be of adequate volume to provide
enough contact time between the atomized cloud and
the heated glass.
• second criterion is that all droplets must be sufficiently
dried before they contact a surface.
• Centrifugal atomizer requires larger diameter and less
cylinder height. Nozzles are just the opposite.
• Most spray dryer manufacturers can estimate, a given
powder’s mean particle size, what dimensions are
needed to prevent wet deposits on the drying chamber
walls.
• Drying chambers are usually constructed of stainless
steel sheet metal, with stiffeners for structural support
and vessel integrity.
DRYING CHAMBER

11. POWDER SEPARATION
• In almost every case, spray-drying chambers have cone bottoms to
facilitate the collection of the dried powder.
• When the coarse powder is to be collected, they are usually discharged
directly from the bottom of the cone through a suitable airlock, such as a
rotary valve.
• The gas stream, now cool and containing all the evaporate moisture, is
drawn from the center of the cone above the cone bottom and discharge
through a side outlet. In effect, the chamber bottom is acting as a
• cyclone separator. Because of the relatively low efficiently of collection,
some fines are always
• carried with the gas stream. This must be separated in high-efficiency
cyclones, followed by a
• wet scrubber or in a fabric filter (bag collector). Fines are collected in the
dry state (bag
• collector) are often added to the larger powder stream or recycled.

12. TYPES OF SPRAY DRYER SYSTEMS
1. Co-current flow dryer
In the co-current flow dryer the spray is directed
into the hot air entering the dryer and both pass
through the chamber in the same direction. Spray
evaporation is rapid, and the temperature of the
drying air is quickly reduced by the vaporization
of water. The product does not suffer from heat
degradation since once the moisture content
reaches the target level, the temperature of the
particle does not increase greatly because the
surrounding air is now much cooler. Dairy and
other heat-sensitive food products are preferably
dried in co-current dryers.
A. On the basis of the type of flow

13. 2. COUNTER-CURRENT FLOW DRYER
• In this dryer design the spray and the air are
introduced at opposite ends of the dryer, with the
atomizer positioned at the top and the air
entering at the bottom. A counter-current dryer
offers more rapid evaporation and higher energy
efficiency than a co-current design. Because the
driest particles are in contact with hottest air, this
design is not suitable for heat-sensitive products.
Counter-current dryers normally use nozzles for
atomization because the energy of the spray can
be directed against the air movement. Soaps and
detergents are commonly dried in countercurrent
dryers.

14. MIXED FLOW DRYER
• Dryers of this type combine both co-current
and counter current flow. In a mixed flow
dryer
• The air enters at the top and the atomizer is
located at the bottom. Like the counter-current
design
• The mixed flow dryer exposes the driest
particles to the hottest air, so this design is not
used with heat-sensitive products.

15. B. ON THE BASIS OF THE TYPE OF CYCLE
1. OPEN CYCLE DRYER
In an open cycle dryer drying air is drawn from the atmosphere, heated, conveyed
through the chamber and then exhausted to the atmosphere. This is by far the most
commonly used design.

16. 2. CLOSED CYCLE DRYER
A closed cycle dryer recycles the drying gas, which may be air or more commonly, an
inert gas such as nitrogen.
Closed cycle units are the dryers of choice when:
I. Feedstock consists of solids mixed with flammable organic solvents.
ii. Complete recovery of solvent is required.
iii. The products are toxic
iv. Pollution due to vapor, particulate emissions or odor is not permitted.
v. Explosion risks must be eliminated.
vi. The powder will degrade by oxidation during drying.

17. SEMI-CLOSED CYCLE DRYER
This dryer design is a cross between open and closed cycle dryers. A direct-fired
heater is used and the air entering the system is limited to that required for
combustion.
An amount of air equal to the combustion air is bled from the system at the other
end of the process. The gas (mainly products of combustion) is recycled through the
dryer.
The recycled gas has very low oxygen content, making it suitable for materials that
cannot be exposed to oxygen, due to explosive hazard or product degradation.

18. C. ON THE BASIS OF THE TYPE OF STAGE
1. SINGLE STAGE DRYER
• In a single stage dryer, the moisture is reduced to the target (typically
2-5% by weight) in one
• pass through the dryer. The single stage dryer is used in the majority of
designs.

19. 2. TWO STAGE DRYER
• In a two stage dryer , the moisture content of product leaving the
chamber is higher (5-10%) than
• for the final product. After leaving the chamber, the moisture content is
further reduced during a
• second stage. Second stage drying may be done in fluidized bed dryer
or a vibrating bed dryer.
• Two stage dryers allow the use of lower temperatures in the dryer,
making the design a good
• choice for products that are particularly heat sensitive.
1-drying air; 2-feedstock; 3-pneumaticconveyor; 4-drying chamber; 5-powderconveyor;6-filterbags;7-
cyclone;8- dustreturn;9-exhausttoatmosphere;10-driedpowder.

20. D. ON THE BASIS OF THE POSITION
1. VERTICAL DRYER
• Vertical dryer
• The chamber of a vertical (tower) dryer has the form of a tall cylinder
with a cone-shaped bottom.
• Spray nozzles may be located at the top (co-current flow) or bottom
(counter-current or mixed flow) of the chamber.
• Inlets for the drying air may be located at the top, bottom or side of the
chamber.
• Vertical spray dryers are usually large and the residence time of
sprayed particles is relatively long, allowing the use of higher flow
nozzles such as the TD, which produce relatively large particles.

21. HORIZONTAL DRYER
1-drying air; 2-feedstock; 3-pneumaticconveyor; 4-drying chamber; 5-powderconveyor;6-
filterbags;7-cyclone;8- dustreturn;9-exhausttoatmosphere;10-driedpowder.
The chamber of a horizontal dryer has the form of a rectangular box with either a flat or a
“V”
shaped bottom. Nozzles in a box dryer normally spray horizontally, with the dried
particles
falling to the floor, where they are removed to a bagging area by a sweep conveyor or
screw
conveyor. Box dryers are usually small and the particle residence time relatively short,
requiring
the use of low flow nozzles, which produce relatively small particles.
Figure-

22. BAG FILTER WORKING:
• Dust (product’s very fine powder) with air will enter the bag filter with
velocity. Bags inside the filter separate the air and dust particle, reverse pulse
get flow in top of the bags clear the bags at pre-programmed interval. Dust
accumulated on the bags are detached from the bag and they are collected in
hopper.
Jet pulse system for clearing bags
Clean air outlet
Dusty air
Dust collection

23.  Spray Dryers require large quantities of hot air for drying.
 The quality of the final product is affected by the quality of inlet air entering
the dryer.
 Throughput varies with outside environmental conditions
 Extra moisture in the inlet-air increases drying cycle time
 Varying outside conditions result in inconsistent powder quality
 Higher downtime due to sticking of material on Spray Dryer walls
CHALLENGES IN SPRAY DRYING
PROBLEM

24. CONTINUE….
 The Spray Dryer mixes heated air with an atomized (sprayed) liquid stream within a
vessel (drying chamber) which leads to evaporation and produces free-flowing dry
powder with a controlled average particle size. Thus, the inlet air has to be dry, free of
contamination, foreign particles and odorless.
 However, since the ambient changes throughout 24 hours, 365 days a year, the humidity
present in the air, entering the Spray Dryer is not constant. Thus, the drying temperature
and time inside the dryer needs close monitoring to restrict loss due to varying level of
humidity present in the inlet air. These varying inlet conditions need to be monitored by
an experienced operator to adjust the parameters for stable outlet conditions.

25. TO SOVE THE CHALLENGES:
1.INLET AIR DEHUMIDIFICATION
Dehumidification of the air helps slurry to dry fast, and allows smooth and free
flow operations. Bry-Air has developed a range of special high performance
dehumidifiers which enable this to happen. Bry-Air dehumidifiers control precisely
the moisture content of the incoming air. It results in following advantages.
•Stable & consistent Drying Conditions throughout the year with no effect of
outside conditions
•Reduced dependence on operator for constant monitoring and parameter
adjustment
•Increased efficiency– up to 30% in some cases
•Improved rate of solution by avoidance of the lumping caused by fine particles
•Lowest energy consumption

26. • THE APPLICATION OF SPRAY DRYING IN FOOD INDUSTRY;
• MANUFACTURING OF milk powder, coffee, tea, eggs, cereal, spices, flavorings,
starch and starch derivatives, vitamins, enzymes, stevia, nutraceutical,
colorings, animal feed, etc.

27. THANK
YOU