Page 39 - Applied Process Design For Chemical And Petrochemical Plants Volume II

28 Applied Process Design for Chemical and Petrochemical Plants

vaporized in a flash vaporization process at a temperature 1w -
of 40°F and a pressure of 600 mm Hg abs?
The following vapor pressure data for 40°F are available: 90-

80-
propane 3,800 mm Hg
n-butane 820 mm Hg m-
n-pentane 190 mm Hg

Assume Raoult’s Law is applicable. At a total pressure, TC,
the temperature of flash must be between the dew point 50 -
and bubble point.
40-

30-
20 -
10 -

L
L
Vapor Press. K=- P1 L - 1 +E I I I I I I I I I
M S mmHg=P~ fjooFxvKv- 0 10 20 30 40 so 60 70 BO 90 100
C3Hs 10 3,800 0.158 1.158 ASSUMED MOCS VAPOR
nC$-IIo 65 820
nCgH12 25 190 0.317 25 3.16 4.16 Figure 8-22. Extrapolatlon curve to determine approximate value of
V” for Example 8-7.

~
8.64
37.6
+&&
V = 52.24 NOT a check, reassume V=- Fx
L
1+- * y; mol. fmc.
and recalculate. See Figure 8-22 for plot of results and the Kv
resultant extrapolation. Use this type chart as a guide to 9.38 0.135
reduce the number of “guesses” to reach an acceptable 49.4 0.711
solution. After several assumptions: 10.63 u.53
69.41 0.999
1. Assume feed = 100 mols These values are close enough for most calculations.
2. Assume L - 30 Therefore, after several trial-and error calculations
3. Then: V = 100 - 30 = 70 mols these results indicate that after flashing, there would be
70% vapor (approximately) of above composition and
X = mols of component i in vapor plus mols of component i in
liquid divided by the total mols of feed (liquid + vapor) 30% (mol) liquid.
F = mols of feed
Quick Estimate of Relative Volatility
Following the same headings as previous table it con- Wagle [92] presents an estimate method for the aver-
tinues:
age relative volatility of two components, related to the
normal boiling points and the latent heats of vaporization
L
Vapor L - L of the two components, in the temperature range of their
~01% a Press. Y RV 1 +Kv boiling points:
Cas 10 10 3,800 0.429 0.0677 1.067
nCqHlO 65 65 820 0.429 0.314 1.314
nCgH12 25 25 190 0.429 1.352 2.352