Stripping of Dilute Mixtures The balances are written

Stripping of Dilute Mixtures Ø The balances are written around one end of the tower and an arbitrary intermediate equilibrium stage n. (1) Yn Y 0 X 1 Ch. E 334: Separation Processes XN+1 Dr Saad Al-Shahrani

Stripping of Dilute Mixtures Ø Or, solving for Yn: (2) Ø For the stripper, the operating line lies below the equilibrium line for the opposite reason. Ø The operating line is straight line with a slope of L`/V`. Ø For an stripper, the terminal point of the operating line at the bottom of the tower is fixed at Y 0 by the amount of solute. Ch. E 334: Separation Processes Dr Saad Al-Shahrani

Stripping of Dilute Mixtures Ø Solute balance over the entire stripper (3) Ch. E 334: Separation Processes Dr Saad Al-Shahrani

Stripping of Dilute Mixtures Ø For the minimum V` XN in equilibrium with YN (4) Ø Solving (4) for XN and substituting the result into (3) gives: (5) Ch. E 334: Separation Processes Dr Saad Al-Shahrani

Stripping of Dilute Mixtures Ø For dilute-solute conditions, where Y y and X x, (5) approach = x 0 (fraction of solute stripped) y y. N Ø Fraction of solute stripped = ab / ac y 0 c x 0 Ch. E 334: Separation Processes b a x 1 x. N+1 Dr Saad Al-Shahrani x

YN L’ /V ’ YN Y 0 X 1 XN+1

Stripping of Dilute Mixtures Ø NUMBER OF EQUILIBRIUM STAGES operation Ø As shown in Figure (a). the operating line relates the Solute concentration in the vapor passing upward between two stages to the solute concentration in the liquid passing downward between the same two stages. (a) Ø Figure (b) illustrates that the equilibrium curve relates the equilibrium solute concentration in the vapor leaving an equilibrium stage to the salute concentration in the liquid leaving the same stage. Ch. E 334: Separation Processes (b) Dr Saad Al-Shahrani

Stripping of Dilute Mixtures Ø The number of equilibrium stages required for stripping a solute is determined in a manner similar to that for absorption. TOP Y 3 Y 2 O. L (3) X 4 (2) X 3 Y 1 (1) E. L Y 0 X 2 X 1 Bottom Ch. E 334: Separation Processes Dr Saad Al-Shahrani