Page 226 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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0.1 to 1.3 MPa leads to increasing of the effective surfece of the packing cannot
be considered as doubtless. The investigation was carried out with 6.4 mm Berl
saddles in a column with a 62 mm diameter at constant gas and liquid velocities.
The experimentally obtained values of the packing effective area [294] as a
function of the pressure are presented in Fig. 29. It is to be seen that with
increasing of the pressure 13 times, the effective area increases from 60 to 200
2 3
m /m , i.e. over 3.3 times.
In another paper Benadda et al. [295] find that the partial mass transfer
coefficient for the liquid phase is not depending on the pressure in the interval
from 0.1 to 1.3 MPa. The investigation was carried out with the same packing
and the same column. That is, the pressure is not influencing the liquid-side
control processes.

250
w B=0.037 m/s
200 L=1.48x10»m/s

ISO

100
so

0,1 e.2 0.4 0.6 0.8 1.0 IJ 1.4
Pmssum, MPa

Fig. 29. Influence of the pressure on the interfacial area- CO 2 absorption in NaQH water solution
after Benadda et al. [295].

The hydrodynamic study presented in the same paper [295] shows that
an increase of the pressure leads to an increase of the axial dispersion
coefficient of the gas phase, and consequently gives rise to dispersion of the gas
phase as bubbles. The increase of the interfeeial area can be interpreted as
interpenetration of this new formation of bubbles in the liquid film [295]. It is
easy to see that 13 times increasing of the pressure leads to about 3.6 times
increasing of the F G - factor which can lead to an inversion regime. The
increasing of the axial mixing can compensate the positive effect of the bubbles
on the mass transfer coefficient and in this way to explain the observed results
for the liquid-side controlled mass transfer too.