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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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Presentation Transcript
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

CHEE 440

definitions
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

psychrometric chart
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

static dryers
Static Dryers

Tray/truck driers

CHEE 440

spray dryer
Spray Dryer

CHEE 440

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

CHEE 440

drying equations1
Drying Equations
  • Fluidized beds and spray driers
    • use correlation for flow past an individual spherical particle

CHEE 440

example
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