Unformatted text preview: 1.5inch Berl Saddles, AE units From the above figure, HOG = 0.85 ft. From Eq. (2), lT = 2.57(0.85) = 2.2 ft
(b) From Eq. (611), (L/S)min = (V/S) K (fraction absorbed) = 240(2.7)(0.98) = 635 lb/hft2
(c) Consider the differences between 1.5inch ceramic Berl saddles (Saddles) and 1.5inch
ceramic Hiflow rings (Rings). In Table 6.8, data are given for the rings, but not for the saddles
of the 1.5inch size. To make the comparison, take the near1 inch size. Then, the following
parameters apply:
Packings
Saddles
Rings FP
110 a
260
261.2 ε
0.68
0.779 Ch
0.62
1.167 Cp
0.628 CL
1.246
1.744 CV
0.387
0.465 Analysis: (c) (continued) Exercise 6.30 (continued) Note that for the NH3airwater system, the above plot shows that HOG is approximately equal to
HG. Therefore, the liquidphase resistance is small and KL a need not be considered.
Consider KGa and HOG:
In the above table, values of a are essentially the same. From Eqs. (6136) and (6140),
1/ 2 a / a for Rings
0.779
=
= 1.07
aPh/a is proportional to ε /a. Therefore, Ph
aPh / a for Saddles
0.68
From Eq. (6133), if we ignore holdup, hL, in the term (ε  hL), and differences in a, then,
14a
H G is proportional to
ε
CV
aPh
1/2 1
(0.779) 4
H G for Rings
Therefore,
= 0.465
(1.07 ) = 1.53
1
H G for Saddles
4
(0.680)
0.387
This ratio should be about the same for HOG .
K G a for Rings
1
From Table 6.7, KG is inversely proportional to HG. Therefore,
=
= 0.653
K G a for Saddles 1.53
Consider pressure drop:
The pressure drop is given by Eq. (6106). If we ignore holdup, hL, in the term (ε  hL), and
differences in a, and combine Eqs. (699) and (6110) to (6115), then,
Cp
∆P is approximately proportional to 3
ε
However, Table 6.8 does not contain Cp for Berl saddles, so no comparison can be made.
Consider Column NOG and height:
The value of NOG is independent on packing material. Therefore, the height is shorter for
the saddle packing because the HOG is smaller.
Consider column diameter:
The column diameter is related to the flooding velocity, as given in Fig. 6.36(a). For a
given value X, the value of Y is fixed and the product (uo)2FP is a constant. The packing factor
for the ceramic Hiflow rings is not given in Table 6.8. However, if a value is extrapolated from
data for larger rings, the packing factor for the Rings is much less than for the Saddles.
Therefore, the flooding velocity for the Rings will be higher and the column diameter smaller.
Consider maximum liquid rate:
For a fixed gas velocity, the value of Y in Fig. 6.36(a) is smaller for the Rings because the
packing factor is less. Therefore, as shown in the same figure, the value of X is greater for
flooding, which gives a larger maximum liquid rate. Exercise 6.31
Subject: Absorption of CO2 from air into a dilute caustic solution with a packed column.
Given: 5,000 ft3/min at 60oF and 1 atm, containing 3 mol% CO2. Recovery of 97% of CO2.
Equilibrium curve is Y = KX = 1.75X (i.e. mole ratios) at column operating conditions.
Assumptions: No stripping of water. No absorption of air. Caustic soluti...
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 Spring '11
 Levicky
 The Land

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