1. Particle Size Reduction & Separation
Kausar Ahmad
Kulliyyah of Pharmacy
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2. Contents Particle size reduction Fluid energy mill or jet mill
Air classifier mill
Others
Crusher
Grinder
Particle size separation
Cyclone
Others
Sieves
Classifiers
Membrane filtration
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3. Equipment & mechanism Knife - cutting E.g. carrot slicer ( 5 mm)
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)
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4. Choosing the equipment
5 mm & 100 m
size of feed particles
100 to 5 m
size-reduction ratio
Mohr’s scale: talc=1,diamond=10
hardness of feed
600 kg/hr
processing rate
abrasive, soft
type of material
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5. Step-by-step size reduction
Feed material 10 cm
Crusher : 10x
Feed 1 cm
Grinder: 100x
Feed 100 m
Fluid energy mill: 20x
Product ca. 5 m
HOW MANY TIMES REDUCTION?
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6. Attrition mills - principle
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
What types of materials can be processed using the attrition methods?
….and what types…. cannot…?
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7. Types of attrition mills
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?
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8. Classifier
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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9. Air classifier mill 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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10. Air classifier mill (ACM)
PRODUCT ca. 100 m
(to Fluid Energy Mill)
ROTATE
CLASSIFIER
FEED
ROTATE
If the particle is TOO BIG when it enters the classifier compartment, the particle will fall down into the mill
Further size reduction occurs until the particle can escape the classifier
Thus the maximum size that goes out of classifier is controlled
Minimum size depends on mill design e.g. height of pin
ATMOSPHERIC AIR
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11. Fluid Energy Mill (FEM)
FEED (from ACM)
Area enlarged
Superheated
compressed
Air/steam
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12. FEM: Design & Operation
Size and distribution depends on
Design
Air nozzles
Feed inlets
Grinding chamber
Operation conditions
Air/steam at high pressure and temperature is introduced into the chamber and reduces the size of particles
Feed throughput
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13. FEM After size reduction Air/steam at high P, T
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14. ? Size reduction & separation FEED into FEM injector CYCLONE CYCLONE
PRODUCT
HIGH VELOCITY
HOT AIR/STEAM
PRODUCT
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15. Cyclone 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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16. Cyclone FINES OUTLET FROM FEM INLET PRODUCT
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17. Factors affecting extent of separation
Design of cyclone
Diameter
Height
Operation of cyclone
Feed throughput
Velocity at inlet
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18. Feed properties 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.
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19. Controlling feed/throughput
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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20. Problems with poor feed-control
waste
overfilling the milling zone
Fail QC, waste
retards exit of properly sized particles &
fail QC, waste
subjecting them to further size reduction and excessive generation of fines
maintenance
accelerate equipment wear
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21. Example of equipment wear
Internal piping
CONSTRUCTION MATERIAL + FEED
FEM milling area
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22. Problems with FINE products
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……………..
De-duster
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23. Dust Filter http://www.pharmaceuticalonline.com/nl/347748/1849996
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24. Exercise
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?
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25. References
Levin, M. (2002). Pharmaceutical process scale-up. New York: Marcel Dekker. p 71, 120, 205, 224, 322, 417, 501, 503
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