Page 75 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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reduction of the efficiency after point E is connected with additional axial
mixing of the liquid phase because of the strong friction forces with the gas.
The column can operate actually up to the flooding point F. But it is
easy to see, that the maximal efficient capacity (MEC or C sc) is reached in point
G. That is why the determination of this point is very important. The rate in it
provides perfeetly stable operation because it has been determined from the
separation efficiency. This approach to packed column capacity has been
verified by the investigation of Kunesh et al. [49]. The maximum hydraulic
capacity of the packing is about 20% higher than this in point G [3, p. 145].
The form of the line HETP as a function of C s is not always identical to
that presented in Fig. 11 as it can be seen in [3, p. 145, 43, 44]. It depends not
only on the packing but also on the investigated system. Nevertheless, in all
cases the value of C sc is well determined.
Hauch and Petshauer [45] offer instead of C sc to use Co defined by a
standardizing equation developed by Dolan [46],

r =
OJS / x-fti/
) ()
20000) {200)

1.5.4.3. Diffusion model
In the case when the piston flow model is not applicable for description
of the processes in the packed bed column, the diffusion model can be used.

H d'Y dY K Ga e *
-Y) (250)
Bo G dh 2 dh

3
H d X
Ba h dh 1 dh

The boundary conditions offered by Danckwerts [26] are:

at h=0:

^- = 0, (252)
dh