Ferrules
Distillation. Absorption

The shell is the column's envelope. It must resist pressure and expansion forces, as well as the effects of wind and earthquakes [1][2][3] .

The ferrule can be made up of sections of different diameters. If the flow rate and physical properties of the steam stream vary greatly between the bottom and the top of the column, it will be more economical to adjust the column to the operating conditions and use a column with two or even three diameters.