Page 49 - Applied Process Design For Chemical And Petrochemical Plants Volume II

38 Applied Process Design for Chemical and Petrochemical Plants

Vapor Up Stripping Section: Material Balance:

10,0001b/hr = 66.7
Feed rate : mols/ hr =
(150.0)
xlF = xlD + xlB
0.456 (66.7) = 0.999 D + 0.01 B
-V, 250 - 413 30.4 = .999 D + .01 (66.7 - D)
V, = 163 mols vapor
D = 30.05 mols/hr
bottoms: B = F - D
Stripping Section Operating Line:
B = 66.7 - 30.05 = 36.65 mols/hr

v. P.
Bottoms Mol (316°F) V. P.
213 50 Composition: Fraction Mols/hr mmHg Frac.
ym = - xm+1 - (.05)
163 163 ~~~~~~ ~ ~~~~
Trichlor 0.01 0.3665 4,200 42
ym = 1.307 X, + 1 - 0.01535 Perchlor 0.99 36.2835 1,780 1,762
1 .oo 36.65 1,804 mm
Use these equations as described for Part (a) in solving
for theoretical plates. The 1,804 mm compares to the balance value of 1,800 mm I 20
psig.
Example 8-12: Minimum Theoretical Tkays/Plates/Stages
at Total Reflux Overhead Composition Mol Fraction Mols/Hr

A finishing column is required to produce 99.9% (vol.) Trichlor 0.999 30.02
trichlorethylene purity from 10,000 lb/hour of a feed of o.001 0.03
1 .ooo
40% (wt.) trichlorethylene and 60% (wt.) perchlorethyl-
ene. Only 1% (vol.) of the trichlorethylene can be accept-
ed in the bottoms. Relative Volatility: overhead conditions
Because the process system that will receive vents from
-
this condensing system is operating at 5 psig, allow 5 psi a tri/per v.p. (tri) 1,280 mm = 3.32
pressure drop to ensure positive venting and set top of (2230F) = v.p.(per) - 385mm
tower pressure at 10 psig.
Bottom Conditions
(1) (2) (1) (2) Mol atdper v.p.(tri) - 4,200mm
Feed (158°F) WA MolWt Mols Fraction ( 31@F) v.p.(per) - 1,780mm = 2.36
=
Trichlorethylene 40 131.4 0.00304 0.456
Perchlorethylene 60 165.9 0.00362 0.544 mean a .,/- = 2.80
100 0.00666 1.000 top / bottom =
Thal Condition of the Feed at 158°F
Avg mol wt 1.00/.00666 = 150.0
At conditions of feed tray, assume pressure is 15 psig
Overhead 1,533 mm Hg. Determine bubble point:

Overhead temperature for essentially pure products at
10 psig = 223°F from vapor pressure curve. assume t = Partial
266°F
Component x, v.p. nun Hg Press. x (V.P.)
Bottoms
Trichlor 0.456 2,350 1,072
Allow 10 psi tower pressure drop, this makes bottom Perchlor 0.544 880 478
pressure = 20 psig = 1,800 mm Hg. 1.550