# Absorption and Stripping of Dilute Mixtures

Absorption

Absorption and Stripping Equipment

Absorption in a single equilibrium stage

To approach the study of the absorption/stripping operation, a certain number of assumptions are needed in order to simplify the design and easily understand the basics concepts:

The equilibrium correlation

Linear Equilibrium

Typically in an absorption or stripping problem the solute, which has to be removed, is present in the liquid or in gas phase at very

low concentration (<1%). The Henry’s law is therefore used to represent the equilibrium correlation for a solute A between the gas and the liquid phase.

yA = m xA where m = H/Ptotal

In the x-y composition diagram the equilibrium correlation is represented as follows:

Non-linear Equilibrium

Of course in the range of concentration when Henry’s law can not be applied anymore (xA>1%), the relationship in between y and x is not linear but more in general a curve, expressed as:

yA = f(xA)

which in the same mole fraction composition diagram will give a curve:

Single stage

During the absorption operation,

the gas phase and the liquid phase must be in contact. Before considering the different possible configurations, we consider the thermodynamical aspects of this contact between phases.

The solute contained in G transfers to the liquid phase L. The concentration in the gas decreases while the concentration in the liquid increases. The pairs of points (concentration of solute in the gas and liquid phases) at each moment constitute the operating

line.

Staged operations: (a) single stage; (b) co-current; (c) countercurrent; (d) crosscurrent.

Graphical Method for Equilibrium Stage Trayed Towers

Graphical Method for Equilibrium Stage Trayed Towers

Graphical Method for Equilibrium Stage Trayed Towers

Minimum Absorbent Determination of the Equilibrium Number of Stages

Graphical Determination of N for Absorption

Graphical Determination of N for Stripping

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