Particle size reduction and separation
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Transcript Particle size reduction and separation
Particle Size
Reduction & Separation
1
KAUSAR AHMAD
KULLIYYAH OF PHARMACY
http://staff.iium.edu.my/akausar
PHM3133 Dosage Design 1 2011/12
Contents
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Particle size reduction
Particle size separation
Fluid energy mill
Cyclone
or jet mill
Air classifier mill
Others
Crusher
Grinder
PHM3133 Dosage Design 1 2011/12
Others
Sieves
Classifiers
Membrane
filtration
Equipment & mechanism
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Crusher – compression
E.g. crushing rolls (5 mm)
Grinder – impact and attrition
E.g. hammer/ball millls, bowl grinder (100 m)
Ultra-fine grinder – attrition
E.g.
fluid-energy mills (5 m)
Knife - cutting
E.g.
carrot slicer ( 5 mm)
PHM3133 Dosage Design 1 2011/12
Choosing the equipment
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size of feed
particles
size-reduction ratio
• 5 mm & 100 m
• 100 to 5 m
hardness of feed
• Mohr’s scale: talc=1,diamond=10
processing rate
• 600 kg/hr
type of material
• abrasive, soft
PHM3133 Dosage Design 1 2011/12
Step-by-step size reduction
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Feed material 10 cm
Crusher : 10x
Feed 1 cm
HOW MANY TIMES
REDUCTION?
Grinder: 100x
Feed 100 m
Fluid energy mill: 20x
Product ca. 5 m
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Attrition mills - principle
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attrition - the act of wearing or grinding down by
friction
hit the particles with high velocity air to fracture
them
increasing the impact velocity or the energy
(increase temperature), produces smaller particles
generate a greater amount of fines
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Types of attrition mills
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Fluid energy mill
High pressure steam, high T
Compressed air, high T
Air classifier mill
Air
FEED into slightly negative pressure compartment!
Q. But why?
PHM3133 Dosage Design 1 2011/12
Classifier
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Equipment that is used to narrow down the size
distribution of product
Normally built-in design i.e. comes together with the mill
Classifying ability depends on
Design and operation condition
Feed throughput
Air velocity
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Air classifier mill
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Consists of:
Hammer mill
Hammer mill reduces the size
Classifier
Classifier determines the size distribution
Size and distribution depends on
Design of mill and classifier
Operation conditions
Their speed of rotation
Feed throughput
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Air classifier mill (ACM)
PRODUCT ca. 100 m
(to Fluid Energy Mill)
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ROTATE
CLASSIFIER
FEED
ROTATE
ATMOSPHERIC AIR
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Fluid Energy Mill (FEM)
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FEED (from ACM)
Area enlarged
Superheated
compressed
Air/steam
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FEM: Design & Operation
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Size and distribution depends on
Design
1.
Air nozzles
Feed inlets
Grinding chamber
Operation conditions
2.
Air/steam at high pressure and temperature is introduced
into the chamber and reduces the size of particles
Feed throughput
PHM3133 Dosage Design 1 2011/12
FEM
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After size reduction
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Air/steam at high P, T
Size reduction & separation
CYCLONE
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FEED
into
FEM injector
CYCLONE
FEM
PRODUCT
HIGH
VELOCITY
HOT
AIR/STEAM
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PRODUCT
?
Cyclone
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Equipment for separation
To separate product from air and/or fines
Based on centrifugal force
Heavy particles settle down
Fine particles escape
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Cyclone
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FINES
OUTLET
FROM
FEM
INLET
PRODUCT
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Factors affecting extent of separation
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Design of cyclone
Diameter
Height
Operation of cyclone
Feed
throughput
Velocity
at inlet
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Feed properties
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Need to know size distribution of the feed stream.
may lead to significant cost-reduction methods
such as pre-classifying the material to remove fines
before milling.
Thus, use air classifier mill first, followed by fluid
energy mill.
PHM3133 Dosage Design 1 2011/12
Controlling feed/throughput
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feeding the material into a mill, and handling the product
discharging from it, can pose a significant problem e.g.
FEM back-flow
feed at a controlled rate is critical to optimizing the
performance of mills.
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Problems with poor feed-control
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overfilling the milling zone
• waste
retards exit of properly
sized particles &
• Fail QC, waste
subjecting them to further
size reduction and
excessive generation of
fines
• fail QC, waste
accelerate equipment wear
• maintenance
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Example of equipment wear
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Internal piping
CONSTRUCTION MATERIAL + FEED
FEM milling area
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Problems with FINE products
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Highly charged, static
May produce sparks
Possible explosion
Need to earth equipment
Very cohesive
Stick to silos
Form agglomerates
Poor flow
Add (pyrogenic) silica to allow free flow
Health hazard……………..
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De-duster
Dust Filter
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http://www.pharmaceuticalonline.com/nl/347748/1849996
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Exercise
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What do you do with so much air/steam in your
milled products?
What is the difference between a fluid energy mill
and a fluidised bed dryer?
Function?
Operating principle?
PHM3133 Dosage Design 1 2011/12
References
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Levin, M. (2002). Pharmaceutical process scale-up. New
York: Marcel Dekker. p 71, 120, 205, 224, 322, 417, 501,
503
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