Page 194 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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times the pressure drop even under the loading point. The reason is that the
formed froth occupies a significant part of the column free cross-section, which
leads to significant increasing of the gas velocity and therefore of the pressure
drop. The investigation shows the following:
1. The froth is formed because of the transformation of a part of the
kinetic energy of the liquid flow in energy of foam connected with its larger
surface. That is why the generation of froth increases with increasing of the
liquid velocity, respectively of the liquid superficial velocity. But the increase
of the liquid velocity leads also to destroying of the already existing froth in the
packing.
2. The foam stability, or the froth life, depends not only on the
composition of the liquid, but also on the hydrodynamie regime in the
apparatus. It is found, for example, that when we have two foam forming
liquids and two methods of measurement of their foam stability, if the stability
for the first liquid according to one of these methods is higher, according to the
other it can be measured as lower.
3. The increasing of the gas velocity also acts in direction of forming
and destroying of the foam,
4. A mechanism and a mathematical model for calculating the pressure
drop of foam forming liquids is presented and experimentally proved.
5. It is predicted and experimentally proved that in a packing with long
vertical walls on which the liquid is fed with proper low velocity almost parallel
to the packing surface, froth is not formed.
Nevertheless that it is possible to build a packed bed column able to
operate in presence of from forming substances, it is better to use anti-foaming
agents to prevent foaming than to construct the column so as to operate with
foam forming liquids.
For calculation of the pressure drop under and over the loading point of
irrigated packings Billet and Schultes [316] offered the following equation:

4F (64 1.8 )( -H f(H T
t
t
S

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