Page 265 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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eyetohexana / n-heptana
P= 1.65 bar {= 24 psia)

I
s.
a
as
I
1
05
I Raschig
Super-Ring No. 2;
metal
0.06
0.2 0.4 0.8 1.0 2.0 4.0
Gas capacity factor F s, Pa"- S

Fig. 43. Comparison of the pressure drop for Raschig Super Rings No 2, Nutter Rings No 2, and
50 mm Pall rinp at total reflux. All packings are metal [321,323].

The first of these packings are produced of ceramics and wood.
The very first structured packing is built of arranged ceramic rings [19],
the same as the Raschig Rings, patented some years later. Their great
disadvantage is that the cross-sections of the channels inside the packing rings,
channels 1, Fig. 44, and the channels 2 outside them are not equal. Moreover,
the surface area corresponding to the channels with greater cross-section (inside
the rings) is smaller, and that of the channels with smaller cross-section
(between the rings) is greater. Taking into account that the greater cross-section
corresponds to greater gas flow rate, it is easy to see that at equal initial
concentrations at a given cross-section, the concentrations after the two lypes of
channels are different. It is well-known that mixing of flows with different
concentrations in the apparatus leads to reduction of the average concentration
difference, i.e., reduction of the driving force of the process. That is why the
efficiency of these packings is low and they are not produced any more.