Page 198 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

188

2
y'+0.2422x -L9461x + 4.6457 = 0 , (44)

2
(L a \
where y'=lg\ —jMi

Eq. (44) gives the possibility to obtain the gas velocity at the flooding
point:

(45)

KH-*'
where igFj = -4.12881$ ^tul 2 1-8.622 OJ

Another possibility to determine the loading point is connected with its
definition and with the employment of equations (259) and (260) from Chapter
1 and (25) and (27). By definition the loading point is the point where the line
of the irrigated packing pressure drop as a function of the gas velocity, in
double logarithmic coordinates, changes its slope and is no more parallel to the
respective line for dry packing. In other words, it is the point in which the
influence of AA on A cannot be neglected any more, that is the point in which
the ratio

(46)

is significantly greater than 1. Investigations carried out with different packings
show that the value of fa can be taken equal to 1.03 for all of them.
As it has been already mentioned the presence of foam building
substrates (surfactants) in the liquid phase leads to increasing of the pressure
drop which causes also reduction of the gas and liquid superficial velocities at
the loading and flooding points [74, 75]. Using foam destroying agents the
harmful effect of such substances can be eliminated.
For calculation of the gas velocity at the loading point Billet [177]
proposed the equations: