Page 237 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10G 5/30/2001 4:37 PM Page 200

200 Applied Process Design for Chemical and Petrochemical Plants

0.0308 log 114 0.030812.0572 Friction inside tubes:
0.0633 psi
Flow rate into tubes
Friction resistance to flow inside tubes:
1397,370211442112
flow rate into tubes 384,000 lb>hr 1ft 2
2
1178210.8362
112,70011442112

2
1187 3210.836 in >tube2 11.032 1384,0002
R e c d 10,200
1122 13.242
2
104,700 lb>hr 1ft cross-section2
f 0.00027
11.03 in.21104,7002 54.5 1
R e 2,700 (from Figure 10-137)
112213.242 62.3 0.606162.32
Arith. mean gravity 0.451
2
2
f 0.00038 ft >in. 2
54.5 1 However, for many cases, particularly when the difference
a b
62.3 2.09162.32 in specific volume is large, the log mean average is much
Mean Sp. Gr. for tube 0.441 better.
2
Log mean average specific volume:
Tube pressure drop
v o v i
v lm (10-196)
2
0.000381112,7702 142112 ln1v o >v i 2
p t 0.0134 psi
10
15.2221102 11.03>12210.4412112 1
0.1835
0.606
For the first try, neglect the piping friction into and out of v lm
1>.606
reboiler. This should be designed with a minimum of pres- ln
0.1835
sure drop.
3
0.0655 ft >lb
Total resistance to flow 0.0633 0.0134 0.0767 psi
1
4154.52 0.0655
x 1 L
Driving force 1.51 psi Log mean Sp. Gr. 0.245
144 144 62.3
2
0.000271384,0002 182112
This is not a satisfactory check. p t 10 0.289 psi
Because the resistances are now considerably less than the 5.221102 11.03>12210.245211.02
available driving force, the new estimate for the recircula- Pressure loss in inlet piping (see Figure 10-96D). Assume
tion ratio must be considerably greater than 20:1. piping consists of the following for an inlet pipe:
Final Trial: 24-in. O.D. shell, 6-in. inlet and 10-in.outlet
nozzles. 8-ft, 6-in. pipe
After several trials to obtain a balance, try a recirculation two 6-in. weld ells
ratio of 73:1 and an exchanger with 178, 12 BWG, 8-ft long one 6-in. open gate valve
tubes. Note: If a tee connection to spare reboiler is used, add tee to pipe
list.
Liquid being circulated 73 (5370) 392,000 lb/hr
Liquid flow at reboiler inlet 392,000 5,370 397,370 lb/hr For equivalent feet pipe:
Total volume of mixture out reboiler:
(392,000) (0.01835) 007,200 two 6-in. weld ells 2 (11 eqft see the “Fluid Flow” chapter in
(5,370) (43.5) 233,500 Vol. I.) 22 ft
3
Total 240,700 ft /hr one 6-in. open gate valve 003.5 eqft
3
Specific volume of mixture 240,700/397,370 0.606 ft /lb 8-ft, 6-in. pipe 8
Total eq ft 33.5 ft
Pressure balance:
From the “Fluid Flow” chapter in Vol. I.:
Static pressure of reboiler leg
6
2.3182 0.606 3.36 10 fLW 2
log 0.331 psi p t
5
14410.606 0.018352 0.01835 d