Page 76 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 65

mixtures at the saturation temperature at a constant pres-
sure.
An effort has been made to present the basic under-
standing of the method as it applies to systems involving
unequal molal overflow, open steam distillation and single
flash vaporization in Figures 842 and 843.
To obtain extreme or even necessary accuracy for some
design conditions, the end portions of the graphical rep-
resentation may require enlargement from the usual size
for graphical plotting. In most cases a size of 11 x 1'7 inch-
es is suggested.

Example 8-21: Ponchon Unequal Molal Overflow

An ammonia-water recirculating solution of 62 wt % is
to be stripped of the ammonia for recovery by condensa-

0
Mol or Weight Fraction of One
Component in Liquid or Vapor

Figure 8-43A-C. Graphical solution of unequal molal overflow, binary
systems.
uilibrium Tie Lines

tion at 260 psia with river water cooling. The overhead
ammonia product is to be at least 99.5 wt 5% and the bot-
toms should approach 0.05 wt % ammonia. The feed
Mol or Weight Fraction of One
Component in Liquid or Vapor enters as a liquid at its boiling point, with an enthalpy of
42 Btu/lb.

B Enthalpy Diagram

Prepared by reading the h and H values from the Jen-
nings and Shannon Aqua-Ammonia Tables [35] at 260
psia and various wt $6'~ of ammonia in the liquid. The tie
lines connect the vapor compositions with the equilibrium
liquid values, Figure 8-44.
Vapor-Liquid Equilibrium Diagram

Prepared from corresponding x and y values in Refer-
ence 35 at 260 pia, Figure 8-45.

Number of Trays
IxB !XF XF = 0.62 weight fraction ammonia
0 1.0 XD = 0.995 weight fraction ammonia
Mol or Weight Fraction of One
Component in Liquid or Vopor XB = 0.0005 weight fraction ammonia