Absorption and Stripping of Dilute Mixtures ( Dr. Ali Coşkun DALGIÇ )

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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