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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