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Calculate the value of
mG
m
/
L
m
, where
m
= Henry's law constant.
G
m
= Gas molar flow rate (lb-mol/ft
2
-hr).
L
m
= Liquid molar flow rate (lb-mol/ft
2
-hr).
Even though the individual values of
G
m
and
L
m
are not known, the ratio of the two has been previ-
ously calculated:
mG
m
/
L
m
= 1.2/1.35 = 0.889
Determine the number of overall gas transfer units (
N
OG
) using the values that we calculated pre-
viously (i.e., 9.80 and 0.899):
N
OG
= 6.2
Now calculate the height of packing
Z
:
Z
= (
N
OG
)(
H
OG
)
where
Z
= Height of packing.
H
OG
= Height of an overall gas transfer unit.
N
OG
= Number of transfer units.
Z
= (
N
OG
)(
H
OG
) = 6.2 × 2.5 = 15.5 ft
What is the diameter of the packed column? The actual gas mass velocity must be determined. To
calculate the diameter of the column, we need the flooding gas mass velocity. USEPA's generalized
flooding and pressure drop correction graph (USEPA, 1984b, p. 107) is used to determine the flood-
ing gas mass velocity. The mass velocity is obtained by dividing the mass flow rate by the cross-
sectional area. Calculate flooding gas mass velocity (
G
f
), and calculate the abscissa of USEPA's
generalized flooding and pressure drop correction graph (
L
/
G
)(
p
/
p
L
)
0.5
:
(
L
/
G
)(
p
/
p
L
)
0.5
= (
L
m
/
G
m
)(18/29)(
p
/
p
L
)
0.5
where
L
= Liquid mass velocity (lb/s-ft
2
).
G
= Gas mass velocity, (lb/s-ft
2
).
p
= Gas densit y.
p
L
= Liquid density.
L
m
= Liquid molar flow rate (lb-mol/ft
2
-hr).
G
m
= Gas molar flow rate (lb-mol/ft
2
-hr).
18/29 = Ratio of molecular weight of water to air.
Note that the
L
and
G
terms (in USEPA's generalized flooding and pressure drop correction graph)
are based on mass and not moles.
(
L
/
G
)(
p
/
p
L
)
0.5
= (1.35)(18/29)(0.075/62.4)
0.5
= 0.0291
Determine the value of the ordinate at the flooding line using the calculated value of the abscissa:
Ψµ
.
()
02
2
GF
ppg
L
Lc
Ordinate =
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