The surface renewal rate from Danckwerts' theory and
the effective interfacial area between gas and liquid per
unit packing volume in a packed absorption tower were
evaluated for the absorption of carbon dioxide into
carbonate/bicarbonate buffer solution accompanied by a
pseudo-first order chemical reaction. The rate of chemical
reaction in the liquid phase was controlled by varying the
buffer ratios.
A small absorption tower was constructed, which had a
packing section, 30 cm high with 10.2 cm inside diameter.
Two kinds of packing, ½-inch Rasehig ring for one part of
the experiment and ½-inch Ben saddle for the other part of
the experiment, were used in the investigation. Sodium
carbonate/bicarbonate buffer solutions, with buffer ratios
varying from 0.4 to 3.0, were used.
Glycerine-water solutions were also used to investigate the effect of density and viscosity on the
physical absorption of carbon dioxide; the content of
glycerine varied from 0 to 40 % wt. Pure carbon dioxide was
used to eliminate the gas side resistance in the mass
transfer operation.
The results of this investigation suggested the
following conclusions:
The surface renewal rate, s, and the effective
interfacial area per unit packing volume, a, for each
packing can be expressed as functions of Reynolds Number of
the liquid flow.
The comparison of values from this study with those
of Danckwerts showed discrepancies; these discrepancies
could be due to different flow patterns, packing densities,
and the apparently more uniform distribution of liquid over
the packing.
The mass transfer coefficient for physical
absorption into glycerine solution was expressed as a
function of Reynolds number and Schmidt number.
The mass transfer coefficient calculated from
Danckwerts' model equation, kL*a = [Ds divided by a*] for absorption
of carbon dioxide into water seemed to be larger than those
measured in this experiment