- Tower Packings :
Packings are made of ceramics, metals and plastics and vary in size from 6 to 75 mm.
- Characteristics of a Tower Packing :
1. It should provide a large interfacial area for phase contacting., i.e., it should have a large wetted surface area per unit volume of packed space for high efficiencies.
2. It should provide a large void volume or empty space in the packed bed so that reasonable throughputs of the phases are handled without excessive pressure drop.
3. It should possess good wetting characteristic.
4. It should have a high corrosion resistance.
5. It should be relatively cheap/inexpensive.
6. It should have a low bulk density so that the weight of the entire packed bed is low which thereby reduces serious support problems.
7. It should possess enough structural strength.
8. It should be chemically inert to the fluids handled in the tower.
Types of packings :
In order to obtain the efficient gas-liquid contact, many different types of packings are available ranging from simple to complex geometrical shapes but are generally classified as random packings and regular packings. If the packings are simply dumped into the tower during installation and fall in a random fashion (the individual pieces are not arranged in any particular pattern), they are called random packings. The packings arranged in a particular pattern are called stacked packings.
In case of randomly packed installations for obtaining the high and uniform voidage and
preventing breakage, a tower is first filled with liquid (usually water) and packings are then dumped into it. Most common random packings used in industrial towers are Raschig rings, Pall rings, Hy-pak, Berl saddles, Intalox saddles, Super intalox saddles, etc. As Pall rings, and Intalox saddles permit a more economical tower design they are replacing older Raschig rings and Berl saddles. Pall rings are made out of metal or plastic (poly propylene) and have the same general form as Raschig rings with height equal to diameter, however portions of the original cylinder wall are cut with the projections bent inward leaving holes in the wall. They are generally available in sizes ranging from 16 to 50 mm (5/8 to 2 in).
Berl saddles and Intalox saddles are available in range 6 to 50 mm and are formed out of
plastic or ceramics. They provide more gas-liquid contacting area than the Raschig rings.
Raschig rings are hollow cylinders with their length equal to outside diameter and
usually formed out of ceramic, carbon and metal. They are generally available in a size ranging from 6 to 100 mm (1/4 to 4) in . They are simple in construction and rela
tively cheap
as compared to other packings. When a single web is added to the inside of the Raschig ring, the packing is called Lessing ring and when a cross web is added to the Raschig ring, then the packing formed is called cross partition ring. Added webs provide additional active surface. They are normally available in a size ranging from 75 to 150 mm (3 to 6 in) and usually used as stacked packings. Stacked packings offer lower pressure drops for the gas than random packings for equivalent phase flow rates.