Types of Tower Packing

A wide variety of types of packing have been suggested at one time or another.These may be classified as follows:

1.Wood Slats

These can be used where the solution to be passed over them is neutral or faintly acid or alkaline. The bottom edge of the slats may be notched to aid in liquid distribution. Wood is light and cheapest packing for those cases where it can be used. It can best be used in towers of rectangular cross section. 
There are following shapes of wood slats are used in different sections according to requirement.

• Horizontal wood slats
• Vertical wood slats
• Interior wood slats 
• Dark wood slats
• Joint wood slats
• Weathered wood slats

Samples of pictures are shown below:

Horizontal

Dark

Interior

Joint

Vertical

Weathered

 
2.Broken Rock

This at once suggest itself, since such material is always at hand. It is not always easy to find material that will be inert. This packing has various disadvantages, chief of which are its great weight, its relatively small surface per unit of volume, and its small free cross section. Its is now employed in only two important cases.
First Case: The use of crushed quartz for the packing of Glover towers in sulfuric acid manufacture.
Second Case: In one of the system for making the liquor for use in sulfite pulp manufacture where broken limestone is used. In this latter case it is desired to have the solution produced in the tower react with limestone and the two operations are thus combined in one.

3.Coke

Coke has the advantage of being light in weight and having a large surface per unit weight. Its disadvantages are a small free cross section and a tendency for some slightly soluble constituents of the coke to pass into solution. It is also rather friable. The surface is not so large as might be expected, since many of the pores are so small that they are completely filled or filmed over with liquid and therefore are not effective in furnishing surface at which contact with the gas phase could take place.Coke is usually cheap and generally available, and in many small and simple operations its used is justified.

4.Stoneware Shapes

So many of the operations of gas absorption are carried out with acid liquids as the solvent that chemical stoneware is common material. This has been employed in the most diverse and elaborate forms.
Towers may be packed with ordinary rectangular brick set on edge, but this packing has a large weight and small surface per unit volume, though it may be arranged to give large free volume and large free cross section.
Every conceivable kind of specially shaped brick has been suggested and made at one time or another, but it is not necessary to discuss these forms here.

4(a). Raschig Rings

These are mostly and widely used form of tower packing. They are cylindrical rings, of the same length as the diameter of the cylinder and with the walls as thin as material will permit. Stoneware raschig rings will vary from 2 to 6 inch in diameter and will have a wall from 3/8 to 5/8 inch thick. Where the rings can be made of metal they are correspondingly lighter and give a larger free cross section and a larger free volume. Raschig rings are almost always dumped into the tower at random and not stacked regularly. They offer the best combination of low weight per unit volume, free volume, free cross section and total surface of any type of packing. Stoneware raschig rings are sometimes made with one or two interior webs which increase the surface without greatly decreasing free cross section.

4(b). Berl Saddles

These are saddle shaped porcelain units that are piled at random. The advantage of this type of packing is the comparatively low frictional resistance that it offers to the flow of the gas while maintaining adequate gas liquid surface.

4(c). Spiral Rings

Machines have been devised for making a stoneware packing having the general dimensions of a Raschig ring, but with an internal helix which may partly or completely fill the cross section of the cylinder. Such rings are always stacked and never dumped at random. It is claimed that the helix gives more thorough contact between gas and liquid and that it increases the surface without greatly decreasing either free cross section or free volume. It greatly increases the cost of the packing and especially the labor for installing.

4(d). Grid Blocks

These are rectangular blocks of stoneware, about 4 X 4 X 7 inch, with vertical slots to act as gas passages. They usually stand on short feet (made as part of the block), and the webs between the ribs may be serrated along the bottom edge. They are best used in rectangular towers of relatively large cross section.

5. Miscellaneous Materials

Especially in very small laboratory distillation columns and absorption towers, a wide variety of packing's have been used that have not found application in large scale operations. The list includes glass beads, mats of Fiberglas, rolls of wire gauze, metal turnings, special shapes stamped from sheet metal or wire gauze, wire spirals and many others too.







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