Page 262 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

252

liquid-side controlled mass transfer for the piston flow model for the packings
gathered in Table 21, the following equation is proposed [125]:

42
s
J7
Sh = 0.0115Re v ss G4 S4 (ad r , (160)
p
L
L
The maximal deviation of all experimental data does not exceed
± 20%. The average arithmetic error is 9.2% and the average square error -
15.4%.
The dimensionless numbers in Eq. (160) are determined like those in
Eq. (153). The effective surface area is also calculated using equation (105).
The ratio of the value of the mass transfer coefficient for the diffusion
model to that for the piston flow model, equations (160) and (153), varies
between 1 and 3.

3.2.1.2.2, Performance characteristics of random packings obtained in hot
experimental installations
Some experimental data for the pressure drop and the number of
theoretical stages (NTP) per 1 m height of the apparatus for different effective
packings obtained by Billet [223] are presented in Figs. 40 and 41.
The comparison of the heights of overall gas mass transfer units versus
the gas capacity factor at constant liquid load for metal 50 mm Pall rings and
Raschig Super Rings [321] is presented in Fig. 42. The pressure drop for the
same packings is compared in Fig. 43.

3.2.2. Structured packings

The modern structured packings are designed to ensure equal channels
for moving of the gas phase through them. This leads to more uniform
distribution of the two phases over the cross-section of the apparatus which
leads to increasing of the real driving force. They are produced of metal, plastic,
ceramics, and carbon.
The modem structured packings can be divided into the following
groups:
1. Packings with vertical smooth walls;
2. Packings with vertical walls with boundary layer turbulizers;
3. Structured packings of expanded metal;
4. Structured packings of corrugated metal sheets;
5. Structured packings for extremely low liquid superficial velocity.