Rules of Thumb
Drying and Solids
  1. Rotary, cylindrical dryers employ superficial air velocities of 5-10 ft/s, sometimes to 35 ft/s when the material is coarse. Residence times are 5-90 min. Holdup of solids is 7-8%. An 85% free cross section is taken for design purposes. In countercurrent flow, the exit gas is 10-20C above the solid temperature; in parallel flow, the temperature of exit solids is 100C. Rotation speeds of about 4 rpm are used, but the product of speed (rpm) and diameter (ft) is typically between 15 and 25.
  2. Drying times range from a few seconds in spray dryers, to one hour or less in rotary dryers, and up to several hours (or even days) in tunnel shelf or belt units.
  3. Continuous tray or belt dryers for granular materials of natural size or pelleted to 3-15 mm have 10-200 min drying times.

H I N T S  A N D  R U L E S
Drying and Solids Conveyors for Particular Solids Cooling Towers Compressors and Vacuum Pumps Crushing and Grinding
Extraction, Liquid-Liquid Crystallatisation from Solution Filtration Heat Exchangers Mixing and Agitation
Particle Size Enlargement Piping Pumps Reactors Refrigeration
Hints and Rules Size Seperation of Particles Utilities, Common Specifications Vessels (Storage Tanks) Conveyors for Particular Solids
C O N T A C T   G L Y D E