Packed Towers - Few Thumb Rules

Packed Towers

1. Packed towers almost always have lower pressure drop than comparable tray towers.
2. Packing is often retrofitted into existing tray towers, to increase capacity or separation. Thus same size of packed towers can handle more than tray towers.
3. For gas flow rates of 500 ft3/min (14 m3/min) use 1 in (2.5 cm) packing, for gas flows of 2000 ft3/min (57 m3/min) or more, use 2 in (5 cm) packing.
4. Ratio of tower diameter to packing diameter should usually be less than 15.
5. Due to the possibility of deformation, plastic packing should be limited to an unsupported depth of 10-15 ft (3-4 m) while metallic packing can withstand 20-25 ft (6-7.5 m).
6. Liquid distributor should be placed every 5-10 tower diameters along the length for pall rings and every 20 ft (6.5 m) for other types of random packing.
7. Packed columns should operate near 70% flooding.
8. Height Equivalent to theoretical stages (HETS) for vapor liquid contacting is 1.3-1.8 ft for 1in pall rings and 2.5-3 ft for 2.0 in pall rings
9. Design pressure drop should be as follows
   
   System Pressure drop (in water/ft)

• Absorbers & regenerators
  Non foaming systems 0.25 – 0.40
  Moderate foaming systems 0.15 - 0.25
  
  
• Fume scrubbers
  Water absorbent 0.40 - 0.60
  Chemical absorbent 0.25 - 0.40
  
• Atmospheric or pressure distillation 0.40 – 0.80
• Vacuum distillation 0.15 – 0.40
• Maximum for any system 1.0
  

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