Equipment & mechanism PHM3133 Dosage Design /12 3 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)
Choosing the equipment PHM3133 Dosage Design /12 4
Step-by-step size reduction PHM3133 Dosage Design /12 5 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?
Attrition mills - principle PHM3133 Dosage Design /12 6 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
Types of attrition mills PHM3133 Dosage Design /12 7 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?
Classifier PHM3133 Dosage Design /12 8 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
Air classifier mill PHM3133 Dosage Design /12 9 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
PHM3133 Dosage Design /12 Air classifier mill (ACM) CLASSIFIER FEED ATMOSPHERIC AIR ROTATE PRODUCT ca. 100 m (to Fluid Energy Mill) 10
Fluid Energy Mill (FEM) PHM3133 Dosage Design /12 11 Superheated compressed Air/steam FEED (from ACM) Area enlarged
FEM: Design & Operation PHM3133 Dosage Design /12 12 Size and distribution depends on 1. Design Air nozzles Feed inlets Grinding chamber 2. Operation conditions Air/steam at high pressure and temperature is introduced into the chamber and reduces the size of particles Feed throughput
FEM PHM3133 Dosage Design /12 13 After size reduction Air/steam at high P, T
PHM3133 Dosage Design /12 14 FEED into FEM injector Size reduction & separation FEM CYCLONE PRODUCT HIGH VELOCITY HOT AIR/STEAM ?
Cyclone PHM3133 Dosage Design /12 15 Equipment for separation To separate product from air and/or fines Based on centrifugal force Heavy particles settle down Fine particles escape
Cyclone PHM3133 Dosage Design /12 16 INLET OUTLET PRODUCT FINES FROM FEM
Factors affecting extent of separation PHM3133 Dosage Design /12 17 Design of cyclone Diameter Height Operation of cyclone Feed throughput Velocity at inlet
Feed properties PHM3133 Dosage Design /12 18 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.
Controlling feed/throughput PHM3133 Dosage Design /12 19 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.
Problems with poor feed-control PHM3133 Dosage Design /12 20
Example of equipment wear PHM3133 Dosage Design /12 21 FEM milling area CONSTRUCTION MATERIAL + FEED Internal piping
Problems with FINE products PHM3133 Dosage Design /12 22 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
Dust Filter PHM3133 Dosage Design /12 23
Exercise PHM3133 Dosage Design /12 24 What do you do with so much air/steam in your milled products? fluid energy mill fluidised bed dryer What is the difference between a fluid energy mill and a fluidised bed dryer? Function? Operating principle?
References PHM3133 Dosage Design /12 25 Levin, M. (2002). Pharmaceutical process scale-up. New York: Marcel Dekker. p 71, 120, 205, 224, 322, 417, 501, 503