1. CBE 417
“Unit Operations”
Lecture: 3
7 Sep 2012

2. Overview Introduction UO course overview Equilibrium Stage separations
What are “Unit Operations”
Brief thermodynamics review
Binary flash with energy balance
Multicomponent flash

3. Vapor Liquid Equilibrium (VLE)
Vapor phase: good; liquid phase: good for HC or moderate – high pressures (compressible liquid phase)
Typically used for liquid phase fugacity calculations
Used for special cases (like gases dissolving into liquid phase)
Typical simplifications:
Ideal vapor phase
Ideal liquid phase
Raoult’s Law

4. Phase Equilibrium (Alternate Form VLE)
Historically, when estimates were done by hand:
Seader & Henley (2006)

5. Phase Equilibrium (Recommendations)

6. Phase Equilibrium (Alternate Form VLE)
Historically, when estimates were done by hand:
Sometimes the K values are nearly composition independent
“hand” techniques of design/solution have used DePriester Charts (hydrocarbons):

7. DePriester Chart
P = 2 bar
T = 100 oC
Isobutane
others….

8. DePriester (equation fit)

9. Vapor Liquid Equilibrium (VLE)
Vapor phase: good; liquid phase: good for HC or moderate – high pressures (compressible liquid phase)
Typically used for liquid phase fugacity calculations
Used for special cases (like gases dissolving into liquid phase)
Equations of state models
Activity coefficient models

10. Equations of State Models

11. Phase Equilibrium (Recommendations)

12. Activity Coefficient Models

13. Activity Coefficient Models

14. Activity Coefficient Models

15. Activity Coefficient Models

16. CBE 417
“Unit Operations”
Lecture: 4
10 Sep 2012

17. Overview Introduction UO course overview Equilibrium Stage separations
What are “Unit Operations”
Brief thermodynamics review
Binary flash with energy balance
Multicomponent flash

18. Activity Coefficient Models
^ = lambda

19. Phase Equilibrium (Recommendations)
Mixtures to model:
MeOH – water
EtOH – water
propanol – water
n-butanol – water
n-butane – n-pentane
benzene – toluene
acetic acid – propionic acid
CO2 – toluene (high P)

20. Other Equilibrium Diagrams:
P – T diagram

21. PT Equilibrium Diagram:

22. Other Equilibrium Diagrams:
P = bar
T = various oC
Benzene - Toluene
Y vs X diagram
T vs X or Temp vs Composition

23. Other Equilibrium Diagrams:

24. Y vs X Diagram (LLE)

25. Effect of Pressure:

26. Effect of Pressure:
Seader & Henley (2006)

27. Other Equilibrium Diagrams:

28. Overview Brief thermodynamics review Binary Flash with energy balance
Sequential solution
Simultaneous solution
Multicomponent Flash

29. Binary Flash Overall mole balance mole balance on a mole balance on b
equilibrium eqn for a
mole balance on a

30. Binary Flash Flash separation: Specify: Find: a = n-pentane
b = n-hexane
Vfrac
0.471
V/F P
3.000
bar
function
-1.89E-08 Xa
0.394 Xb
0.606 Ya
0.619 Yb
0.381

31. Binary Flash Overall mole balance mole balance on a mole balance on b
equilibrium eqn for a
mole balance on a

32. Binary Flash Flash separation: Specify: Find: a = n-pentane
b = n-hexane

33. Binary Flash Graphical Solution: mole balance on a solve for ya
“Operating Line”

34. Binary Flash Graphical: Solution!
Equilibrium curve
y = x
Solution!
What if f is unknown, but T is known? Za
Limits:
f = 0
f = 1

35. Binary Flash Energy Balance
EB on CV:

36. Other Equilibrium Diagrams:

37. Alternative Thermodynamics
Older (hand methods):
Raoult’s law
Relative Volatility (VLE):
Aside (couple with MB)

38. Separation Factor or Relative Volatility

39. Effect of Pressure:
Seader & Henley (2006)

40. Constant Relative Volatility?

41. Alternative Thermodynamics
Ki with multicomponent flash:
Into MB:
Sequential solution: suggestions p (Rachford-Rice Eqn)
Simultaneous solution technique: suggestions p 40-43

42. Sizing Flash Drums

43. Simulators
Flash input:
Sensitivity Analysis:
Design Spec:

44. Questions?