4 Ponchon Savarit Method
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Transcript of 4 Ponchon Savarit Method
For a non-ideal system, where the molar latent heat is no longer constant and where there is a substantial heat of mixing, the calculations become much more tedious.
For binary mixtures of this kind a graphical model has been developed by RUHEMANN, PONCHON, and SAVARIT, based on the use of an enthalpy-composition chart.
It is necessary to construct an enthalpy-composition diagram for particular binary system over a temperature range covering the two-phase vapor-liquid region at the pressure of the distillation.
The following data are needed:
1. Heat capacity as a function of temperature, composition and pressure.
2. Heat of mixing and dilution as a function of temperature and composition.
3. Latent heats of vaporization as a function of composition and pressure or temperature.
4. Bubble-point temperature as a function of composition and pressure.
Enthalpy-composition diagram
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
18,000
20,000
0 0.2 0.4 0.6 0.8 1
x
HVapor
2 Phase
Liquid Saturated liquid
Saturated vapor
L0, Dh0, hD
V1
H1
(hD – QD), xD
hD – QD – H1
H1 – hD
y1, x0, xD
H o
r h
h0, x0
V1
HD, yD
(HD – QD), yD
HD – QD – H1
H1 – h0
y1, x0, yD
H o
r h
D
x or y
H o
r h
V1V2
V3V4
DL1L2L3
(x, h)
PLATE-TO-PLATE GRAPHICAL PROCEDURE FOR DETERMINING THE NUMBER OF EQUILIBRIUM STAGES:
1. Draw a straight line passing through F and .
2. Draw a vertical straight line at xB all the way down until it intersects the extension of line F in
3. Assuming the reboiler to be an equilibrium stage, the vapor VM+1 is in equilibrium with the bottom stream.
4. Use equilibrium data alone to establish the value of ym+1 on the saturated-vapor line.
5. Draw the operating line between Lm(xm, hm) and VM+1. This line intersects the saturated-liquid line at
6. Repeat steps 4 and 5 until the feed plate is reached.
x or y
H o
r h
hB
1MV MV 1MV
Bx,
LM LM-1
H o
r h
F
123456789
xF xDxB
H o
r h
V1
y1
x1
L1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
x
y
F
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
0 0.2 0.4 0.6 0.8 1
H
= 21,700 cal/mole
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
x
y
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
18,000
20,000
0 0.2 0.4 0.6 0.8 1
H
F
D1
1DD0
hHHQh
DL
D1
1
hHHh
117,5723,12723,12700,21
DL
min
0
= 1.18
(b)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
x
y
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
18,000
20,000
0 0.2 0.4 0.6 0.8 1
H
F
1234567
N = 7
(c)
