Packed Columns

Packed Columns - An Alternative

           Commercial sized packed columns are preferred to tray and bubblecap columns in processes where two process - phases are brought into intimate contact. The phases can be liquid and gas, liquid and liquid, liquid and solid or liquid and vapour.

           Packed columns are widely used in liquid extraction process scrubbers, absorbers and condensers, reaction chambers, rectifying and fractionating columns drying chambers, fumes or dust extraction plants, catalyst carriers, regenerative heat transfermedia and demisting operations.

PACKED COLUMNS are preferred for the following reasons:

LOW PRESSURE DROP
           With a typical range of 0.35 - 2mm Hg per theoretical plate as compared to 3.05m Hg for trays, the benifit accruing from a lowered pressure drop may be listed as:
a. A reduced base pressure / temperature
b. Lower rates of degradation
c. Lower levels of heat source
d. Enhanced relative velocity.

Capacity

           Depending on flow parameters, the capacity of a properly selected and packed columns is greater than tray column. Higher capacities may be obtained when a tray column is revamped by replacing trays with packings. By using small packings, additional theoritical stage can be generated.

Liquid Hold Up
                      The total Hold up in packed tower would be typically 2-3% maximum as compared to about 10-12% of a tray tower. In other words residence of liquid phase in a tray would be 3-4 times that in a packed tower. The Low resdence time leads to rapid response times following any change in a variable. The time required to establish stable on specification conditions is a fraction of that normal for a tray tower.

High Pressure / Foaming Systems

           Packed columns provide good resistance to fouling provided polymerisation / crystallisation does not occur in vessel. However it must be noted here that fouling will be a major problem in closed sided packings like rasching rings and pall rings. But with the advent of open packings this problem has been overcome to a very great extent. It will be more appropriate to say that a tray tower and a packed tower would choke under similar conditions.

Nilgiris Chemical Stoneware Company (P) LTD.

The Tower Packing People