Page 243 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10G 5/30/2001 4:37 PM Page 206

206 Applied Process Design for Chemical and Petrochemical Plants

Determine Overall Coefficient at Maximum Flux Plot these data as shown in Figure 10-123 to get the flux versus
clean surface T.
64.7
0.6 0.6
1P R 21l v 2 a b1911.82 1.20 (10-197)
3,206 Fouled T at Maximum Flux
From Figure 10-121,
1 1
0.00043
U max clean 2,326
1P R 2 1U2 47
1472 47
2
U a b 2,326 Btu>hr 1ft 21°F2 , r i 0.0010 inside fouling;
1P R 2 0.0202 correct to outside surface
clean based on O.D. surface. (10-198) O.D. 1.00
r io 10.00102a b 10.00102a b 0.0012
I.D. 0.834
Determine Overall T at Maximum Flux
r o 0.0005 outside steam fouling resistance
From Figure 10-122,
1
U max dirty a b
1L21 L 2 1 L 2 0.00043 0.0012 0.0005
For P R 0.0202; cP dc d 0.0268 (10-199)
2
144 1 T21P c 2 469 Btu>hr 1ft 21°F2
1U T2 104,000
T dirty a b 220°F (10-201)
162157.42 157.42 U dirty 469
c64.7 dc d 0.0268
11442 13,20621 T2
Plot this point as on Figure 10-123. Because the correlation is
167.1210.01792
T 44.8°F, clean based on 14 BWG Admiralty tubes, no correction was made for
10.02682 tube wall resistance.
Maximum Flux Fouled T To Maintain Flux for 10°F Clean T

U T 12,3262 144.82 104,000 Btu>hr-ft 2 1 1
a b a b 0.000866
Maximum flux is the same for a clean or fouled tube (see U clean for 10°F T 1,154
Figure 10-123) with T increasing as U decreases due to 1
fouling. U dirty a 0.000866 0.0012 0.0005 b
2
390 Btu>hr 1ft 21°F2
Flux at Operating Levels Below Maximum
11,540
T dirty a b 29.6°F for U T 11,540
U T plotted against T on log-log paper gives a straight line. 390
See Figure 10-123.
Determine U T at, say, 10°F clean T to get another point other Plot this point on Figure 10-123 and connect with the 222°F point
than at 44.8°F. to get the fouled flux line.

From Figure 10-124,
Analysis of Data on Figure 10-123
1n21P c 2 1.15 Boiling point of water in tower 298°F
For P R 0.0202; 244 (10-200) Assume the reboiler will have a full shell diameter top outlet
1P2
elbow vapor nozzle. Thus, a flux of (104,000) (0.90) or 93,600
2
Btu/hr (ft ) is possible if steam temperature is adequate. At the
1P c 2 1.15 13,2062 1.15 10,760 latter flux, the fouled T 204°F. This will require a steam tem-
12442164.72 perature of 298 204 or 498°F equivalent to 693 psia steam.
n 1.467 Because only 200 psig steam is available downstream of the con-
110,7602
trol valve at the chest, a lower flux must be used.
10 1.467 Steam at 215 psia has a temperature 388°F
U T for 10°F T 1104,0002a b
44.8 Available T 388 298 90°F fouled
11,540 Btu>hr-ft 2 From Figure 10-123 for the fouled condition at 90°F T, a flux of
2
only 38,600 Btu/hr (ft ) is available. Because this is less than 60%
of maximum flux allowed for water and other inorganics when
111,5402
2
U for 10°F T 1,154 Btu>hr 1ft 21°F2 clean using a tee-type top vapor side outlet, the latter construction will
1102 be used to reduce investment slightly.