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Unformatted text preview: at volume of mixing = 0
Find: Liquid density in various units using Fig. 2.3 for pure component densities.
Analysis: From Eq. (4), Table 2.4, υL = xiυ iL =
i υ iL = M ρL M ρ iL The calculations are summarized as follows using Fig. 2.3 for pure component densities, Comp. MW Flow rate,
lbmol/h C3
iC4
nC4
iC5
nC5 44.09
58.12
58.12
72.15
72.15 2.2
171.1
226.6
28.1
17.5 Mole
fraction,
xi
0.0049
0.3841
0.5086
0.0631
0.0393 xiυ iL = 139.4 cm3/mol υL = Density,
Fig. 2.3,
g/cm3
0.2
0.40
0.43
0.515
0.525 MW = 59.5 i ρL = Molar
volume, υι
cm3/mol
220
145
135
140
130 MW 59.5
=
= 0.427 g/cm 3
υL
139.4
= 427 kg/m3
= 26.6 lb/ft3
= 3.56 lb/gal
= 149 lb/bbl
where 1 bbl = 42 gal xi υ ι
1.1
55.7
68.7
8.8
5.1 Exercise 2.14
Subject: Condenser duty for a distillation column, where the overhead vapor condenses
into two liquid phases.
Given: Temperature, pressure, and component flow rates of overhead vapor and the two
liquid phases.
Assumptions: Ideal gas and ideal liquid solution for each liquid phase.
Find: Condenser duty in Btu/h and kJ/h
Analysis: Take a thermodynamic path of vapor from 76oC to 40oC and condensation at
40oC.
For water, use the steam tables. Change in enthalpy from vapor at 76oC to
40oC and 1.4 bar = 1133.8  71.96 = 1,062 Btu/lb = 2,467,000 J/kg = 2,467
kJ/kg.
For benzene, using data on p. 2221 from Perry's 7th edition, change in
enthalpy from vapor at 76oC to 40oC and 1.4 bar = 874  411 = 463 kJ/kg
For isopropanol, using data on p. 2179 from Perry's 7th edition,
Average CP over the temperature range = 1.569 kJ/kgK
From data of p. 2157 of Perry's 7th edition,
Heat of vaporization at 40OC = 313 K = 770.4 kJ/kg
Therefore, the enthalpy change of isopropanol = 1.569(7640) +770.4 = 827
kJ/kg
Condenser duty, QC = 2,350(2,467) + 24,600(463) + 6,800(827)
= 22,810,000 kJ/h
= 21,640,000 Btu/h Exercise 2.15
Subject: Kvalues and vapor tendency of light gases and hydrocarbons
Given: Temperature of 250oF and pressure of 500 psia.
Find: Kvalues in Fig. 2.8 and vapor tendency.
Analysis: If the Kvalue is < 1.0, tendency is for liquid phase. If the Kvalue > 1.0,
tendency is for vapor phase. Using Fig. 2.8,
Component
N2
H2S
CO2
C1
C2
C3
iC4
nC4
iC5
nC5 Kvalue
17
3.1
5.5
8
3
1.5
0.71
0.35
0.38
0.10 Tendency
vapor
vapor
vapor
vapor
vapor
vapor
liquid
liquid
liquid
liquid Exercise 2.16
Subject: Recovery of acetone from air by absorption in water.
Given: Temperature, pressure, phase condition, and component flow rates of feeds to
and products from the absorber, except for exiting liquid temperature.
Assumptions: Ideal gas and zero heat of mixing.
Find: Temperature of exiting liquid phase. Potential for explosion hazard.
Analysis: From the given component flow rates, water evaporates at the rate of 22
lbmol/h, and 14.9 lbmol/h of acetone is condensed. Take a thermodynamic path that
evaporates water at 90oF and condenses acetone at 78oF.
Energy to heat air from 78oF to 80oF = nCP∆T = 687(7)(8078)=9,620 Btu/h
Energy to heat unabsorbed acetone from 78oF to 80oF is negligible.
Energy to vaporize water at 90oF = n∆Hvap = 22(1,043)(18) = 413,000 Btu/h
Total required energy = 9,620 + 413,000 = 423,000 Btu/h
Energy available...
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 Spring '11
 Levicky
 The Land

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