The presentation is about the basics of Sprayer dryer, its design, types of systems, process stages, Schematic representation of spray drying mechanism, and its application.

1. A presentation on
Spray dryer
By
Dr. Ambekar Abdul Wahid
M. Pharm, Ph. D
Assistant Professor,
Department of Pharmaceutics
Dr. Vithalrao Vikhe Patil Foundation’s
College of Pharmacy
Ahmednagar, Maharashtra; India
E-mail: wahidambekar@gmail.com
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2. Introduction
 Spray drying involves the spraying of a liquid feed
formulation (solutions, suspensions, emulsions) into
the hot drying medium (air/nitrogen)
 The droplets formed by the atomization process are
dried through solvent evaporation to form particles
which are collected as dry powder.
 Unique drying process: involves particles formation
& drying
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 Different design: fines, course particles, agglomerates
or granules can be produce
 Drying air is an important factor, affect final product
property by influencing the droplet behavior.
Schematic illustration of spray drying process

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Different types of spray drying systems
 Open cycle systems
 Closed cycle systems
 Semi-closed cycle systems
 Open cycle systems:
 Air for drying is drawn from atmosphere & the exhaust
drying air is discharged to atmosphere.
 Applied to spray dry aqueous feeds.
 Majority of the industry use this system.

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 Closed cycle systems:
 System is based on recycling and reusing the gaseous
drying medium (which is usually gas such as nitrogen).
 Use to handle flammable solvents, high toxic products and
oxygen sensitive products.
 Avoid atmospheric pollution and or complete recovery of
evaporated solvent.

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 Semi-closed cycle systems:
 Sub classified as:
Partial recycle mode: recycle up to 60% of the exhaust air.
Self inserting mode

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Process stages
Spray drying consist of 4 process stages:
o First stage the liquid feed is atomized into a spray of
droplets.
o Second stage involves the spray-air contact, mixing
and droplet/particle flow.
o Third stage combines drying and particle formation.
o Final stage, particle separation from drying air and
dried product discharge.

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First stage
This stage is also called as atomization stage.
Based on the source of energy utilized in the formation
of droplet these are classified as :
1. Rotary atomizer
2. Pneumatic nozzle atomizer
3. Pressure nozzle atomizer

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1. Rotary atomizer
 Consist of rotating wheel or disk
 Source of energy used: centrifugal energy
 Liquid feed is introduced centrally
 Droplet size: 100 – 200 𝛍m

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2. Pneumatic nozzle atomizer
 Uses compressed air to create high frictional forces
over liquid surfaces.
 Causing liquid disintegration to droplets.
 Droplet size: 05 – 100 𝛍m

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3. Pressure nozzle atomizer
• Applies liquid feed under pressure
• Feed is forced to rotate within the nozzle.
• Resulting in the cone-shaped spray pattern emerging from
the orifice of nozzle.
• Droplet size: 30 – 350 𝛍m

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Second stage
 Involves spray-air contact, mixing and droplet
/particles flow
 The three basic flow design are as below
a) Co-current flow
b) Counter current flow
c) Mixed flow

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a) Co-current flow
 The atomized feed is sprayed in the same direction as
the flow of hot air through the drying chamber.
 The droplet come in contact with the hot drying air
when they are most moist resulting in optimal solvent
evaporation.
 Use for heat sensitive
materials such as
protein, enzymes and
peptides.

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b) Counter current flow
 The atomized feed and the heated drying medium moves
in the opposite direction through the drying chamber.
 Combines the heat treatment and particle agglomeration
effect.
 Resulting in increase powder flow-bility and median
particle size.
 Use for thermally stable
products or non-heat-
sensitive products.

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c) Mixed flow
 Combines co-current and counter current flow modes.
 Typical fountain type system yields coarse and free
flowing products
 Drying chamber of relative small dimensions is
sufficient.

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Third stage
 Drying and particle formation takes place.
 Contact between feed droplets and drying air results
in immediate solvent evaporation.
 Diffusion of solvent within the droplet maintains
saturated surface conditions.
 Resulting in constant drying.

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Final stage
 Particle separation from the drying air and dried
product discharge takes place in the drying chamber
and associate particle collection system.
 Cyclone, filter bag and scrubber.

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Relationship between various spray drying parameters

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Schematic representation of spray drying mechanism

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Application
1. Directly compressible powder
a. Excipient and co-excipient processed production
 Better flow ability and compact ability
a. Improved drug compressibility
 Excellent compressibility and absence of capping tendency.
Eg. Acetazolamide
2. Encapsulation
 Matrix microcapsules containing drug substance and a
biodegradable polymer are usually prepare by spray drying
technique to obtained controlled drug release formulations

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2. Increased bioavailability
a. Complex formation: cyclodextrine complex
b. Formation of solid dispersion
4. Dry powder aerosols and heat sensitive materials
 Excellent method for the production of dry powder
formulations.
 Particle size distribution and residual moisture of
the spray dried product can be easily control.
Example: Bovine serum albumin (BSA)

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Advantages
1. Specifications of powder quality remains constant through
out the entire drying operation.
2. Spray drying operations is continuous, easy, automatic
control and one operator can handle more than one spray
dryer at a time.
3. Wide range of dryer designs are available. Product
specifications can be readily met.
4. Applicable to both heat sensitive and heat resistance
materials.
5. Feed stock in solution, slurry, emulsions, paste and melt can
be handle.

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Industrial scale spray dryer

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In August 2013 the world’s largest dairy spray dryer was
put into operation by New Zealand based Fonterra at their
site Darfield. Capacity: 30 tonne/hr milk powder.

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