Page 188 - Applied Process Design For Chemical And Petrochemical Plants Volume III
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66131_Ludwig_CH10E 5/30/2001 4:33 PM Page 151
Heat Transfer 151
b. Cooler-condenser zone, diffusivity: t g 135°F
3>2 1>2 p v 2.537 psia at 135°F
T k 1 1
k d 0.0166 a b p g 32.5 2.537 29.96
1>3 2
1>3
p¿t1V A V b 2 M A M B
V A for water vapor 14.8 938,700
t w 96.7 93.6°F
V B for hydrocarbon mixture: 1299,0002112
Mol Fraction
V A Weighted V B Note that this assumes that water is warmed from the
gas cooling before it enters this section. This is not
37 0.148 05.45
C 2 H 2
rigorously correct.
14.3 0.531 7.6
H 2
29.6 0.098 2.9
CH 4
CO 22.2 0.223 04.95 t 135 93.6 41.4°F
Latent heat at 135°F 1,017.0 Btu/lb
20.90 V B
Assume temperature of condensate, t c 100°F
Use average temperature of (135 104)/2 for k d 322°K
then: p c 0.949 psia (steam tables)
p g 32.5 0.949 31.55 psia
13222 3>2 1 1 1>2
k d 0.0116 a b
32.5 18 14 p g ' p g 31.55 29.96
4
3114.82 1>3 120.92 1>3 2 p gf ' 31.7 psia
14.7 p g ' 31.55
2
k d 0.572 ft >hr 2.3 log 2.3 log 29.96
p g
Average mol weight of mixture: h o (t g t c ) K G M v (p v p c )
h io (t c t w ) 70.81135 1002
114219702 1,420
M 14.33 lb>mol
970 78.8
5.41 2.537 0.949
118211,017.02a b
3
Average lb/ft of mixture in cooler-condenser zone: £ a 31.7 § 14.7
b
14.7
14.33 460 32 32.5
a ba b 0.0766 lb>ft 3 1,1401100.0 93.62
359 460 120 14.7
2,480 4,960 7,300
2>3 0.0397 2>3
a b a b 0.936 7,440 7,300
10.0766210.5722
k d
c p 2>3 10.554210.03972 2>3 (See the preceding note regarding h io ).
a b a b 0.569
k 0.0513 Close enough check.
7,440 7,300
c. Relation between diffusion and heat transfer: U t 7,370
2
2>3
h o 1c >k2
K G (10-102) U t 73.70
2
2>3 U 177 Btu>hr 1ft 21°F2
cp gf M m a b t g t w 135 93.6
k d
h o same as in gas cooling zone 70.8 Interval 130°F—125°F
t g 130°F
170.8210.5692
K G p v 2.223
10.55421p gf 2114.33210.9362
p g 32.5 2.223 30.277 psia
5.41
2
mol>hr 1ft 21atm2
p gf 179,640
t w 93.6 93.0°F
1299,0002112
10. Cooler-condenser interval: 135°F—130°F.
*Note: The value of h io is not correct for the condens- Flow gas-vapor rate (970)(14) (61.8)(18) 14,713
ing coefficient as described in step 6 of this outline. In
this case, the error is small, but that is not necessarily W 14,713
2
G s 23,600 lb>hr 1ft 2
true for other situations. a s 0.624