2. Drying
It is defined as “ the removal of small amounts of
water or other liquid from a material by the
application of heat.”
The final product after drying is dry solid or
powder
Question
Define the term drying and give its importance in
pharmaceutics.
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3. Pharmaceutical application of drying:
• To prepare granules for tablets & capsules.
• To prepare dried aluminum hydroxide, lactose & powder
extracts.
• To reduce the bulk density & weight.
• For easy transport & storage.
• To facilitate grinding of crude drugs.
• To improve the stability & prevent deterioration of the drugs
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5. Types of dryer Mechanism Examples
Static bed dryer Systems in which there is no relative
movement among the solid particles
being dried, although there may be
bulk motion of the entire drying mass.
Tray dryer
Freeze dryer
Moving bed dryer System in which the drying particles
are partially separated so that they
flow each other.
Drum dryer
Fluidized bed
dryer
Systems in which the solid particles
are partially suspended in an upward
moving heated gas system.
Fluidized bed
dryer
Pneumatic dryer System in which drying particles are
entrained and conveyed at a high
velocity gas stream.
Spray dryer
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6. 1.TRAY DRYER
• Tray dryer consists of a cabinet filled with trays & heaters are
placed on the wall of dryer.
• Tray dryers are made up of stainless steel & heated air is
circulated throughout the trays by fans.
• Number of trays are present in the dryer where substance to
be dried are placed over large area.
• It is very effective & popular method of drying
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9. ADVANTAGES
1. Handling of materials can be done without losses
2. It can be operated batch wise, for following reasons:
3.Each batch can be handled as separate entity
4.Equipment is readily adjusted for use in drying of variety of
materials
5.Valuable products can be handled efficiently
DISADVANTAGE
1.It requires more labour to load and unload, time consuming
Question
Explain process and application of tray dryer.
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10. FLUIDIZED BED DRYER
• Fluidized bed dryer consists of removable bowl at the bottom
of the dryer for loading & unloading of the wet granules or
other material to be dried.
• Hot air is passed at high pressure through bottom of the bowl
which suspends granules in the air (fluidized state) & dries
them.
• The temperature of the hot air and exit air are monitored &
filter bags are placed above the drying bowl for the recovery
of the fines.
• It is made up of stainless steel since it directly comes in
contact with the product.
• There are vertical fluidized bed dryers and horizontal
fluidized bed dryers.
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13. ADVANTAGES
1. It requires less time to complete drying i.e. 20 to 40min.
Compared to 24hr of tray dryer.
2. Different sizes with different drying capacity from 5 to 200
kg/hr
3. Handling simple and low labour cost.
4. Thermal efficiency is 2 to 6 times than tray dryer.
5. Mixing efficiency is also high as compared to other dryers.
6. Hot spots are not observed in the dryer.
7. It facilitates the drying of thermolaible substances, as
contact time is short.
8. It can be used for batch type or continuous type.
9. It has high output from a small floor space.
10.The free movement of individual particles eliminates the
risk of soluble material migrating as may occurs in static
bed.
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14. DISADVANTAGES
1. Many organic powders develop electrostatic charge during
drying. To avoid this, efficient earthing of dryer is
essential.
2. The turbulence of the fluidized state of granules may cause
attrition of some materials resulting in the production of
fines. But using a suitable binding agent this problem can
be solved.
3. Fine particles may become entrained and must be collected
by bag filters.
USES
1. It is popularly used for drying of granules in the production
of tablets.
2. It can be used in three operations like mixing, granulation
and drying.
3. It is modified for coating of granules.
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15. Explain fluidized bed dryer(FBD) with its diagram
,advantages and disadvantages.
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