Absorption and stripping - Principles of Chemical Separations with Environmental Applications - page 155

6

Absorption and stripping

Prevention is better than cure.

- ERASMUS

6.1 Objectives

1 Calculate a mass and a mole ratio and be able to convert from mass (or mole) fractions
to mass (or mole) ratios.
2 Calculate a column diameter based upon flooding velocity.
3 Use the McCabe-Thiele graphical method to determine number of equilibrium stages
and outlet concentrations for absorption and stripping processes.
4 Calculate the number of equilibrium stages and/or outlet concentrations using analytical
methods for dilute concentrations.
5 Use the HTU-NTU (height of transfer unit-number of transfer units) method to deter-
mine the height of packing in:
- concentrated solutions in absorption and stripping columns
- dilute solutions in absorption and stripping columns.

6.2 Background

Absorption is the process by which one or more components of a gas phase are removed
by being solubilized (sorbed) into a liquid. The liquid phase is the mass-separating agent
(MSA); it allows separation by absorption to occur. Stripping, or desorption, is the opposite
of absorption. A reasonably volatile contaminant is moved from a liquid to a gas phase.
In either case the contaminant to be removed is called the solute and the MSA which does