Drying: definition, types, Principle, construction, working, advantages and disadvantages of equipment

1. DRYING PROCESS
Prepared by: SHRUTI TYAGI
M. Pharm Pharmaceutics (Lecturer in Pharmacy B.S.A.I.P)

2. DRYING
Drying is an essential component of product formulation. It
basically involves the transfer of heat to a wet product
for removal of moisture.
Most of the biological products of fermentation are sensitive
to heat, and therefore require gentle drying methods.

3. TYPE OF DRYERS
• Tray dryer
• Drum dryer
• Spray dryer
• Fluidized bed dryer
• Vacuum dryer
• Freeze dryer.

5. TRAY DRYER
(TRAY DRYER / TRUCK DRYER / SHELF
DRYER / CABINET DRYER /
COMPARTMENT DRYER )
Principal:
• Hot air- Circulation.
Construction:
• Small or a large cabinet insulated (to
reduce
heat loss) compartment in which trays.
• Heater- Heating of air
• Fan: Circulate the air
• Inlet & Outlet.

6. Working:
• Material loaded in trays- Fresh air is
introduced.
• The material is heated by hot air circulated.
• The trays containing the load remain in the
dryer until drying is complete,
• After which they are withdrawn, emptied and
recharged for drying the next batch.
Application:
• For drying of sticky material & granular
mass.
• Drying of crude drugs, chemicals, powders,
tablet granules etc.
Advantages :
• Easy to operate.
• Batch process for
different product.
• Can useful for drying of
verity of material.
Disadvantages:
• Require labor.
• Cost increasing
• Time consuming

7. Drum dryer
(Roller dryer/Film drum
dryer)
Principal:
• Material on drum & dried.
Construction:
• Hollow steel Drum
• Feed pan
• Spreader
• Doctor’s knife
• Storage bin (A conveyor)

8. Working:
• Steam in drum is rotated through feed
pan.
• Material adhere to pan in thin layer
form.
• Material dry during rotation.
• Doctor’s knife- Dry material is scraped
and fall in storage bin.
Application:
• For drying- solutions, slurries,
Suspensions,
• milk products, starch products &
antibiotics.
Advantages :
• Suitable for heat sensitive
materials.
• Compact size.
• Complete drying.
Disadvantages:
• High maintenance cost.
• Skilled operator required.
• Not suitable for less
soluble salts solutions.

9. Spray dryer
Principal:
• Material to fine droplets-
moving stream of hot gas.
Construction:
• Large cylindrical drying
chamber.
• Inlet of hot air & atomizer- In
Roof.
• Connected to a cyclone
separator.

10. Working:
1. Atomization of the liquid: Liquid
feed- into chamber through atomizer.
2. Drying of liquid droplets: Due to
hot air drying.
3. Recovery of dried product:
Recovery in last step.
Application:
• For drying of large quantity
material.
• Drying of thermo-labile,
hygroscopic material.
• Drying of medicine like
chloramphenicol.
Advantages :
• Very rapid & continue process.
• Low labor cost.
• Gives product of uniform
sphere form & fine droplet.
• Suitable for sterile products
Disadvantages:
• Very bulky & expensive.
• Huge equipment (not easy to
operate)
• Low thermal efficiency.

11. Fluidized bed dryer
Principal:
• Hot air-trough bed of granules.
• Granules lifted from bottom & suspend in air
(Fluidized state).
Construction:
• Fluidized bed dryer- steel or plastic.
• Detachable bowl- perforated bottom with wire
mesh-support material.
• Fan- upper part- circulate air.
• Fresh air inlet/pre-filter/heat exchanger- to
heat air.
• Bag filters- collect fine

12. Working:
• Material load – detachable bowl.
• Fresh enter – inlet- heater- hot air-
through bed-with optimum velocity.
• Particle suspend- fluidized state-
drying takes place.
Application:
• Drying of tablet granules.
• Suitable for other process to mixing
etc.
• Modified form – use for coating of
granules.
Advantages :
• Fast process.
• Available in different capacity.
• Easy handling, reduce labor
cost.
• High thermal efficiency.
• Suitable for applying high temp.
• Suitable for thermo-labile
substances.
Disadvantages:
• Develops electric charges.
• Attrition may occur.

13. Vacuum Dryer
Principal:
• Drying – by application of
vacuum.
Construction:
• Iron heavy jacketed vessel.
• Hollow shelves.
• Metal trays.
• Oven to vacuum pump.

14. Working:
• Material of trays- placed on
shelves.
• Pressure decreased by vacuum
pump.
• Steam/hot hair- into jacket of
shelves.
• Drying will takes place.
Application:
• Drying of heat sensitive
material, dusty
hygroscopic material,
• Drugs containing toxic solvents.
Advantages :
• Easy operating
• Easy for batch process of different
compounds.
• Various modes can be used for
heating.
Disadvantages:
• Low heat transfer efficiency.
• Limited capacity.
• More expensive.

15. Freeze dryer
(Lyophilization/
cryodesiccation
)
Principal:
• Drying by sublimation-
triple point- temp. &
pressure below triple point.
Construction:
• Drying chamber in trays.
• Heating coils.
• Vapor condensing or
adsorption system with
refrigerator.
• Vacuum pump.

16. Working:
1. Pretreatment: This may include concentrating the product, formulation revision (i.e.,
addition of components to increase stability, preserve appearance, and/or improve
processing), decreasing a high-vapor-pressure solvent, or increasing the surface area.
2. Pre-freezing for solidifying water: (-50°C to -80°C): During the freezing stage, the
material is cooled below its triple point, the lowest temperature at which the solid, liquid
and gas phases of the material can coexist. This ensures that sublimation rather than
melting will occur in the following steps. To facilitate faster and more efficient freeze drying,
larger ice crystals are preferable. The large ice crystals form a network within the product
which promotes faster removal of water vapor during sublimation. To produce larger
crystals, the product should be frozen slowly or can be cycled up and down in temperature
in a process called annealing.
3. Primary drying: During the primary drying phase, the pressure is lowered (to the range
of a few millibars), and enough heat is supplied to the material for the ice to sublime. In
this initial drying phase, about 95% of the water in the material is sublimated. In this
phase, pressure is controlled through the application of partial vacuum. The vacuum
speeds up the sublimation, making it useful as a deliberate drying process. Furthermore, a
cold condenser chamber and/or condenser plates provide a surface(s) for the water vapour
to re-liquify and solidify on.

17. Application:
• For production of dosage forms as injections, solutions, suspensions. • For drying of Blood plasma and its fractionated products,
Bacterial & viral cultures, Human tissue, Antibiotics, Steroids, Food items (Prawns etc).
Advantages :
• Suitable for thermo-labile material. • Loss of volatile is less. • No migration occurs. • Suitable for moisture sensitive material. •
Sterility maintain
Disadvantages:
• High costs. • Time consuming. • Oxidation may occurs.
4. Secondary drying: The secondary drying phase aims to remove unfrozen water
molecules, since the ice was removed in the primary drying phase. In this phase, the
temperature is raised higher than in the primary drying phase, and can even be above 0 °C
(32 °F), to break any physico-chemical interactions that have formed between the water
molecules and the frozen material. Usually the pressure is also lowered in this stage to
encourage desorption (typically in the range of microbars, or fractions of a pascal).
However, there are products that benefit from increased pressure as well.
5. Packing & sealing: After the freeze-drying process is complete, the vacuum is usually
broken with an inert gas, such as nitrogen, before the material is sealed. At the end of the
operation, the final residual water content in the product is extremely low, around 1% to
4%.

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