Page 186 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10E 5/30/2001 4:33 PM Page 149

Heat Transfer 149

Gas cooling heat load: Interval 125°F—115°F
Vapor pressure water at 115°F 1.4709 psia
c p gas 7.85 Btu/mol (°F) average for gas mixture Enthalpy water vapor at 115°F 1111.6 Btu/lb
Enthalpy vapor at 250°F 1164.0 Btu/lb (steam tables)* Enthalpy water liquid at 115°F 82.93 Btu/lb
Enthalpy saturated vapor at 135°F 1119.9 Btu/lb (steam tables) Pressure of inerts 32.0 1.47 30.53 psia
Gas cooling (970) (7.85) (250 135) 876,000 Btu/hr
Water vapor cooling (Note the pressure at this interval is assumed to be 32.0
(1420) (1164.0 119.9)* 62,700 Btu/hr psia to allow for additional pressure drop.)
Total 938,700 Btu/hr
*Correcting for superheat, enthalpy at 2.55 Mol water vapor in gas phase at 115°F
psia at 250°F 1172.6 Btu/lb
Water vapor cooling would then 970 1.47
1420 (1172.6 1119.9) 75,000 Btu a b 46.8 mol>hr
30.53 32.0
32.0
Cooler-condenser heat load:
Mol water condensed in this section 61.8 46.8
Interval 135°—130°
15.0 mol/hr
Vapor pressure water at 130°F 2.223 psia (steam tables) p v
Heat load of inerts (970) (7.85) (125 115) 76,000 Btu/hr
Pressure of inerts [34.0 1.5] 2.223 30.28 psia p g
Heat load of water vapor (46.8) (18) (1115.8 1111.6)
lb mol water vapor in gas phase at 130°F
3540 Btu/hr
970 2.223 Heat of condensation (15) (18) (1115.8 82.93)
a b 279,000 Btu/hr
334.0 1.52 2.2234 34.0 1.5
Total 358,540 Btu/hr
134.0 1.52
Interval 115°—104°F
(Note that an allowance of 1.5 psi has been made as pres-
Vapor pressure water at 104°F 1.0695 psia
sure drops to this point; this reduces the pressure at the end
Enthalpy water vapor at 104°F 1106.9 Btu/lb
of this interval to 32.5 psia.) Enthalpy water liquid at 104°F 71.96 Btu/lb
Pressure of inerts 31.0 1.069 29.93 psia
71.2 lb mol/hr
Mol water condensed in this section 78.8 71.2 7.6 mol/hr (Note the pressure at the end of this interval is taken at 31
Heat load of inerts (970) (7.85) (135 130) 38,100 Btu/hr psia.)
Enthalpy water vapor at 130°F 1117.9 Btu/lb
Heat load of water vapor [(71.2) (18)] (1119.9 1117.9) Mol water vapor in gas phase at 104°F 34.6 mol/hr
1540 Btu/hr (from calculation, part 2)
Enthalpy of liquid at 130°F 97.9 Btu/lb Mol water condensed in this section 46.8 34.6
Heat of condensation [(7.6) (18)] (1119.9 97.9) 12.2 mol/hr
140,000 Btu/hr Heat load of inerts (970) (7.85) (115 104) 83,800 Btu/hr
Total heat load this section 179,640 Btu/hr Heat load of water vapor (34.6)(18)(111.6 1106.9)
2930 Btu/hr
Interval 130°F—125°F
Heat of condensation 12.2 (18) (111.6 71.96)
Vapor pressure water at 125° 1.942 psia
228,000 Btu/hr
Enthalpy water vapor at 125° 1115.8 Btu/lb
Total 314,730 Btu/lb
Enthalpy water liquid at 125° 92.91 Btu/lb
Pressure of inerts 32.5 1.942 30.56 psia Grand total heat load
Mol water vapor in gas phase at 125°F 938,700 179,640 213,940 358,540 314,730
2,005,550 Btu/hr
970 1.942
a b 61.8 mol>hr See Figure 10-88 for heat load curve.
30.56 32.5
32.5
5. Assume a unit,
If U 100 , and estimate t 30,
Mol water condensed in this section 71.2 61.8 9.4 mol/hr
Heat load of inerts (970) (7.85) (130 125) 38,100 Btu/hr 2,000,000
A 670 ft 2
Heat load of water vapor (61.8) (18) (1117.9 1115.8) 110021302
2,340 Btu/hr Try: U-tube bundle (for large temperature differential)
Heat of condensation (9.4)(18)(1117.9 92.91) 4 tube passes
173,500 Btu/hr 1-in. tubes, duplex 18 BWG cupro-nickel inside, 18 BWG steel
Total 213,940 Btu/hr outside on 1 / 4 -in. triangular spacing, 32 ft overall length
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