Page 102 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 91

- - -- .~ ~. .- . - -.
Relative Volatilities: Light to Heavy key
@255"F @288"F
Component v.p. a v.p. a ai (avg)
-
v.p. Tri
. --
.~
At top :a - - . ~. A .~ 2050 .- 2.00 -. 3030 . -. 1.91 1.955
1280 2.13
=
v.p.PTri 600
B 1025 1.00 1600 1.00 1.00
750
4300 - 1.98
v.p. Tri
-
At bottoms:a = - - C 650 0.732 1180 0.737 0.735
=
D
0.647
1035
0.634
0.641
v.p.p Tri 2273
E 390 0.380 650 0.406 0.393
~. ~ .- -. ..
a (average) = [(2.13) (1.98)]6 = 2.06
To start, assume 8 = 1.113 (it must lie between 1.00 and 1.955).
Minimum Stages at Total Reflux
- ._ - - - -. . . .
-
.
.-
.-
'%xFi/ aid
Component XFi qxFi (ai - 0) (ai - 0) (~ri - el2
.~ ~- . .-
~
A 0.456 0.891 0.842 1.058 1.252
B 0.0555 0.0555 -0.113 -0.491 4.33
- log (0.999/0.001) (0.101/0.01)
- C 0.3625 0.266 -0.378 -0.704 1.86
log 2.06 D 0.0625 0.0401 -0.472 -0.085 0.18
E 0.0625 0.0246 -0.720 -0.0342 0.0472
=-- 4'003 - 12.6 theoretical stages 2 = -0.2562 27.669
0.318 ~. ~ . __ . ~ . . . . -
BC = 1.113 - (-0.2562/7.669) = 1.113 + 0.0334
Minimum Stages Above Feed: BC = 1.146 (this is close enough check to original, to not require
recalculation.)
log (0.999/0.001) (0.0555/ 0.456)
s, =- The correct value of 1.146 should be used.
log 2.13
Check for balance:
=-- 2.082 - 6.35 theoretical stages
0.328
Thermal Ccndition of Feed
1 - 1.298 = -0.298 = -0.256
Feed temperature = 158°F
This could be corrected closer if a greater accuracy were
Calculated bubble point of feed = 266°F at assumed needed. This is not as good a match as ordinarily desired.
feed tray pressure of 15 psig.
Heat to bring feed to boiling point
+ Heat to vaporize feed
=
Latent Heat of one mol of feed
(for all distillate components)
q = 1.298 (C:alculations not shown, but handled in same man-
ner as for example given in binary section, however all feed (1.953) (0.999) + 1.00 (0.001)
components considered, not just keys.) (L'D)min + (1.953 - 1.146) (1.00 - 1.146)
Minimum KeJw-Underwood lMethod, Determination of a Avg. = 2.41 + (-0.00683)
= 2.404
Assume pinch temperatures (usually satisfactory (L/D)min = 2.404 - 1.0 = 1.40
because a does not vary greatly) at H and ?4 of over-all col-
umn temperature differences. Operating Reflux and Theoretical Trays-Gilliland Plot

Lower pinch = 320 - X (320-223) = 288°F Min trays = SM = 12.6

Upper pincn = 320 - ?4 (320-223) = 255°F (L/D),,,in = 1.4