Page 187 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10E 5/30/2001 4:33 PM Page 150

150 Applied Process Design for Chemical and Petrochemical Plants

Shell I.D. 25 inches (Table 10-9) Average properties for mixture at average shell
Number of holes in tubesheet 218 temperature:
(including allowance for tie rods)
Approximate surface area:
970 78.8
Effective length of 24 ft U-bent tube 29.5 ft (Figure 10-25). k a 0.0545a b 0.0118a b
2
Effective area (22.6) (0.2618 ft /ft) (109) 645 ft 2 970 78.8 970 78.8
2
Number of tubes 218/2 109 645 ft 2 0.0513 Btu>hr 1ft 21°F>ft2
Triangular spacing was selected in preference to square
197021142 1,420
primarily due to the large amount of simple gas cooling 0.0409 0.0283
in this unit. 197021142 1,420 197021142 1,420
The I.D. of this plain surface duplex tube is determined 0.0397 lbs>hr 1ft2
by deducting the gage thickness from the O.D. 0.804
in. I.D. of cupro-nickel.
197021142 1,420
Use sea water at 7 ft/sec in tubes. c p 0.566a b 0.45a b
Number of tubes for liquid entrance/pass 218/4 197021142 1,420 197021142 1,420
54.5. Use 54. 0.554 Btu>lb 1°F2
Note that for U-bent bundles the reverse end of the
bent tube acts like a head on a normal fixed tubesheet 9. Shell side coefficients
unit. Therefore, the number of tubes and the number a. Gas cooling interval 250°F—135°F.
of tube holes are not to be confused in determining From equation 10-48 for use with Figure 10-54,
velocities. assume 18-in. baffle spacing:

lb/hr water per pass at 7 ft/sec D s 1C¿B2 125210.2521182
(vel.) (C) (sp. gr.) (number of tubes) (Table 10-3) a s 0.624 ft 2
p11442 11.25211442
C 793 for tube I.D. 0.805-in.
lb/hr (7) (793) (1) (54) 299,000 W 197021142 1,420 2
G s 24,000 lb>hr 1ft 2
gpm 299,000/500 598 a s 0.624
D e 0.72>12 0.06 (Table 10-21)
6. Temperature rise in cooling water:
DG 10.062124,0002
Q 2,005,550 R e 36,200
T w 6.7°F 0.0397
c p 1W2 1121299,0002
From Figure 10-54 for 25% baffle cut:
This rise can be increased and gpm decreased if neces-
sary; however, in brackish and sea water, it is preferable
j H 110
to keep velocity as high as possible. Therefore, design this
j H k C 1>3 0.14
unit as shown. h o a b a b
7. Tube-side film coefficient (clean): D e k a w
2
2
h i 1500(0.95) 1420 Btu/hr (ft ) (°F), Figure 10-50A or 10-50B h o 70.8 Btu/hr (ft ) (°F)
0.804 Because no condensation (theoretically) occurs in
2
h io 11,4202a b 1,140 Btu>hr 1ft 21°F2
1.0 this section, no heat is diffused through condensate
film.
8. Shell-side fluid properties. From previous process
h o (t g t c ) h io (t c t w ) U (t g t w )
calculations, the following properties were determined
70.8 (250 t c ) 1140 (t c (90 6.7))
for the dry gas stream:
t c 105.6 °F
2
k a 0.0545 Btu/hr (ft ) (°F/ft)
0.0409 lb/ft (hr) 70.81250 105.62 1,1401105.6 96.72
c p 0.566 Btu/lb (°F) U t
2
10,230 10,150
For water vapor 10,190
2
k a 0.0118 Btu/hr (ft ) (°F/ft) 2
0.0283 lb/ft (hr) 10,190
2
U 66.4 Btu>hr 1ft 21°F2
c p 0.45 Btu/lb (°F) 250 96.7