Solution The H-x-y diagram has been established in Tutorial 5. 1

CENG 3210 Separation Processes
Tutorial 6 solution
Continuous Distillation – Ponchon-Savarit method
For the same question in Tutorial 5, Use the Ponchon-Savarit method to determine the total number
of theoretical plates required.
A distillation column operating at 1 atm is to be designed for separating an ethanol-water mixture.
The feed is 20 mole% ethanol and the feed flow rate is 1000 kmol/hr of saturated liquid. A distillate
composition of 80 mole% ethanol and a bottoms composition of not more than 2 mole% ethanol are
desired. The reflux ratio is 5/3.
Solution
The H-x-y diagram has been established in Tutorial 5.
1. Locate the feed enthalpy and composition
xF = 0.20, q = 1, HF = 457 kJ/kmol
2. Locate xD and xB
xD = 0.80, xB = 0.02,
3. Locate ΔD by computation of Q’
DH xD  qc 230.77(1.8)  24099780
Q' 

 104430 kJ/kmol
D
230.77
4. The line ΔD, F is extended to x = xB and thus locates
ΔB whose coordinates can be used to calculate qr. or
Q” = HxB – qr/B =1322 -24659287/769.23= -30735 kJ/kmol
5. The number of theoretical plates is then determined by
application of the straight line relationship on the H-xy diagram and the equilibrium data of the y-x diagram,
which is 15.4. The feed plate is 14 from the top.
1
1e+5
H
5e+4
0e+0
-5e+4
0.0
0.2
0.4
0.6
0.8
1.0
0.8
1.0
x, y
1.0
0.8
y
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
x
2