Unformatted text preview: s velocity at 70% of flooding from above = 13 ft/s for Montz
Gas viscosity = 0.012 cP and gas density = 0.0370 lb/ft3.
From Eq. (6114), for NOR PAC, N ReV = uV DP ρV
(20)(0.012)(0.0370)
KW =
(0.957) = 19, 900
(1 − ε ) µV
(1 − 0.947 ) (0.012)(0.000672) For Montz,
(13)(0.00459)(0.0370)
N ReV =
(0.990) = 3,870
(1 − 0.930 ) (0.012)(0.000672)
From Eq. (6113), for NOR PAC,
Ψo = Cp 64
1.8
64
1.8
+ 0.08 = 0.350
+
= 0.287
N ReV N ReV
19,900 19,9000.08 For Montz,
Ψo = 0.295 64
18
.
+
= 0.279
3,870 3,8700.08 Exercise 7.52 (continued)
Analysis: (e) Stripping section (continued)
From Eq. (2), for NOR PAC,
2
∆Po
a uV ρV 1
86.8(0.3048) 202 (0.0370)
1
= Ψo 3
= 0.287
= 2.15 lbf/ft3 or 0.0149 psi/ft
3
lT
ε 2 g c KW
0.947
2(32.2)
0.957
For Montz,
∆Po
300(0.3048) 8.4 2 (0.0370)
1
= 0.279
= 311 lbf/ft3 or 0.0216 psi/ft
.
3
lT
0.930
2(32.2)
0.990
From Eq. (1), for NOR PAC, with hL = 0.0269 m3/m3 and liquid Froude number = 4.28x104 ∆P
0.947 − 0.0269
= 0.0149
lT
0.947 3/ 2 exp 1/ 2
13300
( 4.28 ×10−4 ) = 0.0150 psi/ft
3003/ 2 From Eq. (1), for Montz, with hL = 0.0341 m3/m3 and liquid Froude number = 6.39x104 ∆P
0.930 − 0.0341
= 0.0216
lT
0.930 1.5 exp 1/ 2
13300
6.39 × 10−4 )
= 0.0218 psi/ft
3/ 2 (
300 Summary of Results:
Column diameter, ft:
Rectifying section
Stripping section
Packed height, ft
Rectifying section
Stripping section
Total
Pressure drop, psi NOR PAC Montz 4.3
3.4 5.3
4.2 6.3
20.2
26.5
0.38 2.9
2.1
5.0
0.093 From these results, the column diameter for NOR PAC would be 4.5 ft without swaging.
The column diameter for Montz would be 5.5 ft without swaging.
The column height for NOR PAC, allowing 4 ft for disengagement, 2 ft for feed entry, and 10 ft
for sump at the bottom would be 42.5 ft or say 43 ft.
Similarly, the column height for Montz would be 21 ft. Exercise 7.52 (continued)
Analysis: Summary (continued)
The above may be compared with the existing plate column of Exercise 7.41: Column diameter, ft
Column height, ft
Pressure drop, psi Plate column
6.0
36
0.8 NOR PAC
4.5
43
0.38 Montz
5.5
21
0.093 The packed columns are smaller in diameter, the NOR PAC column significantly smaller. The
Montz structure packing column is shorter in height and has much less pressure drop. The NOR
PAC rings random packing column is taller and has significantly more pressure drop than the
column with Montz packing. The pressure drop is not critical. Because of the much higher cost
for Montz packing and the much smaller diameter for the NOR PAC column, it is probable that
economics would favor the NOR PAC column. Exercise 7.53
Subject: Distillation of a mixture of benzene and toluene in a packed column. Given: Conditions in Example 7.1, but using 50mm Hiflow rings at 70% of flooding.
Assumptions: Constant molar overflow. Partial reboiler is an equilibrium stage.
Find: (a) Liquid holdup.
(b) Column diameter.
(c) HOG.
(d) Packed height.
(e) Pressure drop.
Advantages of packed column over trayed column.
Analysis:
At the top of the column, L = RD =1.59(275) = 43...
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 Spring '11
 Levicky
 The Land

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