Page 9 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

The gas velocity, or to be precise, the superficial gas velocity wo, in
m/s, is the average value of the gas velocity defined as volumetric gas flow rate
2
related to 1 m of the whole cross-section of the column.
The real gas velocity w in the dry packing is calculated with the real
cross-section for the gas flow equal to e, that is

(4)

Because the cross-section of the irrigated packing is smaller than that of
the dry one with the holdup, the real gas velocity in this case is calculated by:

(5)
1-B-H
k
An important hydrodynamic parameter of the packed bed column is the
packing pressure drop AP equal to the difference between the pressures at inlet
and outlet of the packing. To characterize the packing, the pressure drop related
to a unit of packing height is used.
The concentrations of the phases are given in two principle ways, in
3 3
kg/m (kmol/m ) and kg/kg (mol/mol). In the first, the concentrations are
denoted by CQ (for the gas phase) and by Q (for the liquid). In the second, they
are denoted by Fand Xalso for the gas and for the liquid phase.
The rate of mass transfer is given by the equation:

W A = K G .FAC G = K t .FAC t, (6)

or

W A = K Y .FAY = K x .FAX, (7)

where WA is the quantity of substance transferred through the interface per unit
2
2
of time in kg/(m s) or kmol/(m s);
3
3
AC G in kg/m (or kmol/m ) and AY in mol/mol - driving force of the mass
transfer process calculated as a difference between the concentration of the
transferred component in the bulk of the gas phase and the equilibrium