Distillation Column-Pohnchon savrit method.pptx

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1. Separation Process-II (ChE-306) 1

2. Ponchon-Savarit Method For non-ideal systems Molar latent heat is no more constant Heat of mixing will be non-zero Enthalpy balance Using an Enthalpy-Composition diagram

3. Phase A quantity of mixture in any physical state. Phase C between the boiling point and dew point curve will be:  

4. Combination of phases Separation of phases Addition of heat Adding the phases A and B with mass m, composition x and H as enthalpy per unit mass to give phase C will result: If heat Q is added to A then increase in enthalpy from A to C will be:  

5. Enthalpy balance for a continuous Distillation Column Feed, F ( x F ) Distillate ( x D ) Bottom Product ( x W ) H V and H L represent enthalpy per unit mass of vapor and liquid Q C = heat removed in condenser Q B = heat added in reboiler

6. Material and Heat Balance Overall Material balance across section I Material balance with respect to MVC Substitute the value of V n and simplify  

7. Heat Balance Putting the above equation will simplify to: Substitute the value of V n from first equation and simplify  

8.     As left hand sides are same so equating right hand sides   Simplification gives:   Equation of top operating line Relation between the compositions of vapor and liquid streams between any two plates The line passes through a common pole N of coordinates ( x d , H d ’)

9. Overall Material balance across section II Material balance with respect to MVC Substitute the value of V m and simplify   9

10. Heat Balance Putting the above equation will simplify to: Substitute the value of V m from first equation and simplify  

11. Equation of operating line below the feed plate Line passes through pole M of coordinates ( x W , H W ’) Overall sum of phases Phases F, M and N lie on a straight line.  

12. Determination of number of plates on H-x diagram Locate x d , x f and x w Locate pole N Join N to F Extend backwards till x w , this will give pole M Starting from pole N, draw the lines to get the vapor and liquid compositions on each plate Switch to pole M, when feed composition x f is crossed Draw the tie lines to count steps Stop when composition reached to x w Feed plate will be the one where the pole has been switched from N to M

13. L1 L2 L3 V1 V2 V3

14. Self Study Example 11.10