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Drying

Drying. We are primarily concerned with drying wet, porous solids (granules). Important to ensure proper moisture content in the granules: low enough to prevent product degradation and ensure good powder flow, but high enough to provide good tablet properties. Definitions. psychrometry

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Drying

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  1. Drying • We are primarily concerned with drying wet, porous solids (granules). • Important to ensure proper moisture content in the granules: • low enough to prevent product degradation and ensure good powder flow, but high enough to provide good tablet properties CHEE 440

  2. Definitions • psychrometry • determination of the vapor concentration and carrying capacity of drying gas • wet bulb T • dry bulb T • relative humidity (RH) • moisture content CHEE 440

  3. Psychrometric Chart • Determine the relative humidity and moisture content in the air if the wet bulb T is 35 ºC and the dry bulb T is 50 ºC. CHEE 440

  4. Types of Dryers CHEE 440

  5. Static Dryers Tray/truck driers CHEE 440

  6. Drying behavior for static bed CHEE 440

  7. Fluidized Bed CHEE 440

  8. Spray Dryer CHEE 440

  9. Drying Equations • Tray/Truck Dryers • constant rate drying stage only • parallel flow over a static bed • perpendicular flow through a bed CHEE 440

  10. Drying Equations • Fluidized beds and spray driers • use correlation for flow past an individual spherical particle CHEE 440

  11. Example Wet granules (density = 1.5 g/cm3) are spread onto a screen at an amount of 10 kg/m2 of screen. The bed porosity is 45% and the wet granules have an average diameter of 300 mm. Air at 60ºC(dry bulb) and a wet bulb temp of 25ºC is passed through the bed at a velocity of 0.15 m/s. How long will it take to dry the granules from 20 to 10 % moisture? The critical moisture content of the granules is 9 %. CHEE 440

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