1. Unit Operations Lecture 22 (continued)
16 Nov 2012

2. Trayed Columns (Diameter)
Chap 6 (10 ,p 314, Wankat) “Fair’s Procedure”
Considers entrainment flooding (most freq.)
Downcomer flooding (sometimes) – need different procedure
Downcomer flooding rare if (1- h) ≥ 10%
Used in AspenPlus
James R. Fair ( )

3. Trayed Columns (Diameter)
Plate spacing (selected for maintenance, performance). Typ:
12 – 16” for Dia < 5’
24” larger columns
Calc Dia & round up to nearest ½ foot (USA)
2.5’ minimum dia.
If < 2.5’ consider packed tower
Figure 6.23

4. In-Class Exercise
Data:
Let:
Estimate the tower diameter in meters.
Pause video and do exercise. When done, resume the video.

5. In-Class Exercise Data: Let: Estimate the tower diameter in meters.
G =
7920
kg/hr
2.2
kg/s
L =
2883
0.801
roe V
1.92
kg/cum
roe L
986
Flv =
0.016
Csb,f =
0.39
ft/s
surf ten 70
dyne/cm
u flood =
11.34
Ad/A =
0.1
f =
0.8
Dt =
0.766 m

6. Tower Diameter

7. AspenPlus In-Class Exercise
Benzene – Toluene Separation
Estimate the tower diameter in meters. (by hand and by AspenPlus)
F = 100 kmole/hr
XBZ = 0.6
saturated liquid
Use sieve trays

8. AspenPlus PFD

9. Column Internals
Base method: NRTL

10. Column Internals Not optimized by DSTWU Nfeed = 15
Pcol = bar (constant)

11. Column Internals

12. Column Internals

13. Column Internals

14. Column Internals

15. Column Internals

16. Column Internals

17. Column Internals

18. Column Internals

19. AspenPlus In-Class Exercise
Benzene – Toluene Separation
Estimate the tower diameter in meters. (by hand and by AspenPlus)
F = 100 kmole/hr
XBZ = 0.6
saturated liquid
Use sieve trays
G =
kg/hr
8.544
kg/s
L =
9.568
roe V
2.92
kg/cum
roe L
780.68
Flv =
Csb,f =
0.375
ft/s
surf ten
18.18
dyne/cm
u flood =
Ad/A =
0.1
f =
0.8
Dt =
1.68 m

20. Column Internals

21. Column Internals

22. Column Internals

23. Column Internals

30. Overview Questions from last week?? Review rigorous methods / RADFRAC
Multicomponent systems:
Residue curves
DSTWU / RADFRAC
Rules of thumb
Complex (Enhanced) distillation
Column internals
Batch distillation

31. Batch (Rayleigh) Distillation
Usually for small capacity systems
1 column handle multi-”campaigns”
Produce sample new products
Batch upstream processes
Feed contains solids/foulants
Material Balance:
leads to Rayleigh Equation
Seader & Henley (2006)
where:

32. Batch (Rayleigh) Distillation
a) P = constant; K = f(T) only
b) Binary with  = constant
c) y = K x ; but K = f(T,x)
Solve graphically or numerically

33. Multistage Batch Distillation
Seader & Henley (2006)
Modes of operation:
Constant reflux rate or ratio
xD varies with time
easily implemented (flow sensors)
Relatively simple and cost effective
Constant distillate composition
R or D varies with time
Requires fast response composition sensors
Sensors might not be available or only justified for larger batch systems
Optimal control mode
xD and R varied with time
Designed to:
Minimize operation time
Maximize amount of distillate
Maximize profit
More complex control scheme

34. Multistage Batch Distillation
Removing volatile impurities.
Flexible, multi-purpose system
Seader & Henley (2006)

35. Questions?