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PETE 310

PETE 310. Lecture # 26 Chapter 12 Gas-Liquid Equilibrium Non-ideal VLE. Gas-Liquid Equilibrium Non Ideal Behavior. Applications to low & high pressures Use models for the equilibrium ratios (ki-values) Simpler models ki = f (P,T) More complex models ki = f(P,T,compositions)

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PETE 310

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  1. PETE 310 Lecture # 26 Chapter 12 Gas-Liquid Equilibrium Non-ideal VLE

  2. Gas-Liquid Equilibrium Non Ideal Behavior Applications to low & high pressures • Use models for the equilibrium ratios (ki-values) • Simpler models ki = f (P,T) • More complex models ki = f(P,T,compositions) use equations of state EOS, convergence pressure

  3. VLE general (same) • The equilibrium criteria between 2 phases a and b is,

  4. Statement of Equilibrium Most general case is that Ki is a function of P, T, and compositions 1 3 2 P T

  5. Mathematical Relationships with In general

  6. Bubble Point Evaluation (Non-Ideal Behavior Model) • The bubble point pressure at a given T is

  7. Bubble Point T s P 1 zi=xi s P 2 x ,y 1 1

  8. Dew Point Calculation • At the dew point the overall fluid composition coincides with the gas composition. That is.

  9. Dew Point Calculation (Non-Ideal Behavior Model) • Find DP pressure and equilibrium liquid compositions

  10. Dew Point T s P 1 s zi=yi P 2 x ,y 1 1

  11. Flash Calculations • In this type of calculations the objective is to: findfraction of vapor vaporized (fv) and equilibrium gas and liquid compositions given the overall mixture composition, P and T.

  12. Flash Calculations (Non-Ideal Behavior Calculations) • Start with the equilibrium equation • Material balance

  13. Flash Calculations • Now replace either liquid or gas compositions using Ki values (exercise derive the expression)

  14. Flash Calculations • Objective function (flash function) is

  15. Flash Calculations • There are several equivalent expressions for the flash function (a) (b) (c)

  16. One of the Models for Equilibrium Ratios 1. Require critical properties & acentric factors

  17. Example calculations in excel file VLE_310

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