Ponchon-Savarit

The Enthalpy-Concentration Method

Ponchon-Savarit Graphical Method

1. The Enthalpy-Concentration diagram

The Enthalpy-Concentration Diagram

Bubble point curve Dew point curve Tie lines Superheated vapor Sub cooled liquid Two phase region

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2. Drawing of saturated liquid enthalpy curve

Enthalpies of at their boiling points

Enthalpy of liquid mixture:

3. Drawing of saturated vapor enthalpy curve

Vapour Enthalpies of at their boiling points

Enthalpy of vapour mixture

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4. Drawing of Tie Lines

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RECTIFICATION SECTION

Material balance:

Energy balance:

Combining by equating the reflux ratio expressions:

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The equation represents three relationships for stages and :

, , ,

The point has a constant value.

The equation represents a set (family) of straight lines on the

diagram all out of the point represented by symbol referred

to as the “UPPER OPERATING POINT”.

Ponchon-Savarit Graphical method

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1. Locate , , .

2. Read the enthalpies of distillate and

3. Draw at , notice that lies a distance above

.

4. For a total condenser :

5. Notice that lies a distance above

Construction procedure:

Equilibrium tie-line from locates .

joined to locates ( operating relationship, straight line

fixes position of )

Equilibrium tie-line from locates .

joined to locates ( operating relationship, straight line

fixes position of ).

…and so on ….. locates by equilibrium and the straight line

locates by the operating relationship.

..this continues until a tie-line falls on or passes the feed composition.

.. in this way the equilibrium stages are determined (each tie line represent an equilibrium stage).

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Ponchon-Savarit Graphical method

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STRIPPING SECTION

Material balance:

Energy balance:

Energy added to the reboiler per unit bottoms product

Combining by equating the ratio expressions:

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The equation represents three relationships for all values of and :

, ,

The point has a constant value.

The equation represents a set (family) of straight lines on the

diagram all out of the point represented by the symbol

referred to as the “LOWER OPERATING POINT”.

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Construction procedure:

1. Locate at intersection of and the bubble point curve.

2. The reboiler is an equilibrium stage, hence and are in

equilibrium. The tie lie from locates. .

3. Straight line joining with the lower operating point locates on

the saturated liquid bubble point curve.

4. locates by equilibrium tie line relationship.

5. Straight line joining to the operating point locates .6. …and so on using tie line and operating point relationships for number of

equilibrium stages until is reached or crossed by a tie line.

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Ponchon-Savarit Graphical method

THE FRACTIONATOR

Material balance:

Material balance

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Combining by equating the ratio expressions

Here a relationship between three points:

, ,

is the feed point represented by the symbol .

The equation, thus, represent a straight line joining the operating points

, , . By drawing the line from any two of the three operating points

the third will be located.

The equilibrium stages for the whole fractionator will be determined as shown in the following steps:

1. Locate and extend upwards2. Calculate 3. Locate at a distance above 4. Fix the feed point from knowledge of and5. extend the line to intersect the vertical line at 6. Start construction of equilibrium stages starting from using tie lines and

upper operating point one after the other until the feed point is passed.

7. After that the lower operating point is used with to give , followed by tie line from to give , then with to give and so on …….

8. Construction stops when is reached or passed.

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