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05_chap_wang.qxd 05/05/2004 3:46 pm Page 207
Wet and Dry Scrubbing 207

Fig. 2. Flooding correction in randomly packed towers.

The actual determination of the tower diameter is as follows:
Calculate the abscissa (ABS):
ABS = (L / G)(D / D ) 0.5 (6)
G L
where L is the solvent flow rate (lb/hr) = (MW )(L ), G is the gas flow rate (lb/hr) =
solvent mol
3
(MW )(G ), D is the density of the liquid (lb/ft ), and D is the density of the gas or
e mol L G
3
emission stream (lb/ft ).
D can be approximated as
G
D = PM/RT (6a)
G
where P is the pressure (atm) (note, normally 1), M is the molecular weight of gas (lb/lb-
3
mol), R is the gas constant (0.7302 ft atm/lb-mol ºR), and T is the temperature (ºR).
The values for L and G are determined by multiplying L and G by their respec-
mol mol
tive molecular weights. Next, the flooding line in Fig. 2 is used to read the ordinate
(ORD). Now, the ordinate expression for G at flooding is
area, f
2
3
ORD = [(G ) (a/e )(µ 0.2 )] / [(D D g )] (7)
area, f L G L c
Solving for G , we have
area, f
3
G = {(ORD D D g ) / [(a/e )(µ 0.2 )]} 0.5 (8)
area, f G L c L
where G is the gas stream flow rate based on tower cross-sectional area at the flood-
area,f
2
ing point (lb/ ft -s), µ is the viscosity of the scrubbing (cP) (1 when using water), and
L
2
g is the gravitational constant (32.2 ft/s ). Note that a and e are packing factors (11).
c