1. Plate efficiencies 1. Types of plate efficiency
(1) Overall efficiency ET
(2)Murphree efficiency EMV, EML
y*n is in equilibrium with xn.
x*n is in equilibrium with yn. 1

2. y* is in equilibrium with x.
(3) Local efficiency Eo
y* is in equilibrium with x. 2

3. 2. Determining the plate efficiencies (pp.175~176)
*Factors influencing plate efficiency:
(1) Physical properties; (2) Types and structures of columns; (3) Operating conditions.
*Calculations:
(1) AIChE approach to local efficiency;
H=Henry’s law constant 3

4. Types of trays
Describe the constructions, operating principles, and characteristics of several frequently used trays, for examples, sieve-trays; bubble-cap trays; valve-trays; etc.
[Comparing the turndown ratio; plate efficiencies; pressure drops; fabricating cost; production capacity of these 3 kinds of trays.] 4

5. 3-1-3 Design of Valve tray columns
Understanding the meanings of symbols in Figure [p.158] 5

6. 6

7. =height of clear liquid over weir, m
=height of weir, m
=height of clear liquid over weir, m
=spacing between downcomer bottom and tray, m
=horizontal distance between downcomer and underflow weir, m 7

8. =height of underflow weir, m =equivalent height of clear liquid, m
=distance between plates, m
=height of aerated liquid, m 8

9. =width of straight segmental weir, m =width of defoaming area, m
=length of weir, m
=width of straight segmental weir, m
=width of defoaming area, m
=width of installation area, m
=column diameter, m
=radius of active area, m
=half the width of active area, m
=distance between centers of openings of valve trays of the same row, m 9

10. Sectional Design:
Usually the column diameter will not change along the direction of column height, in order for the convenience of fabrication, installation, and maintenance/repairs, except for the great changes of vapor and liquid flow rates.
In practice, because of great differences of vapor and liquid flow rates between rectifying section and stripping section, the column is separated into two sections when designing. 10

11. [Sectional Design]
When designing a column, take the average flow rates, average physical properties, and average operating conditions of every section; adjust the capacity performance chart to the optimum turndown ratio; check the cross sections of maximum and minimum flow rates to make sure the two limit operating points fall into the satisfactory operation zone. 11

12. Design and calculation procedures: (1) Calculation of column height;
(2) Calculation of column diameter;
(3) Design of down-comer/overflow area;
(4) Design of active area;
(5) Checking the performance of fluid mechanics;
(6) Adjusting the capacity performance chart. 12

13. Conditions given for the design:
Vapor and liquid flow rates:
Physical properties:
Operating parameters: 13

14. Average density, such as rectifying section:
(1)Liquid density:
Average density, such as rectifying section:
(2) Density of vapor mixture: 14

15. (3)Latent heat of vaporization of liquid mixture:
(4) Surface tension of liquid mixture:
(5)Average temperature and pressure, such as rectifying section: 15

16. 1. Calculation of technological parameters of valve tray columns
(1)Column height
Effective height of the column:
Question: How to determine HT properly? （p.154~155） 16

17. umax is determined by excessive froth entrainment or flooding.
(2)Column diameter
umax is determined by excessive froth entrainment or flooding. 17

18. According to the settling principle, the maximum permissible vapor velocity is derived as follows:
C=capacity factor 18

19. Firstly, estimate the column diameter D, select HT and hL, get C20 from Fig.3-8 and19

20. Single downcomer: lw/D=(0.6~0.8); two downcomers: lw/D=(0.5~0.6)
1)Weir
Function of weir: Making sure there is certain liquid layer on the plate, and making sure the liquid flow uniformly.
Length of weir lw: Decided by liquid flow rate and types of downcomers.
Single downcomer: lw/D=(0.6~0.8); two downcomers: lw/D=(0.5~0.6) 20

21. Height of weir hw：hw = hL – how
Selecting the liquid layer height on plate hL, and calculating hOWhw
(Straight segmental weir: how>6mm；
When how<6mm ，selecting saw-tooth-like segmental weir.) 21

22. 3)Spacing between downcomer bottom and tray: h0
2)Basic design principle of width Wd and cross sectional area Af of straight segmental weir: Making sure that there is enough residence time for liquid in the downcomer to avoid vapor bubble entrainment. After getting Af from lw/D, check:
3)Spacing between downcomer bottom and tray: h0
Design principle: lessening local resistance of liquid flow ; possessing the function of liquid seal, at the same time avoiding the blockage of downcomer. 22

23. 4)Underflow weir and liquid accumulator 进口堰及受液盘
Setting underflow weir for large columns. [p.158,Fig.3-10]
Functions: 1) liquid seal; 2)Uniform flow of liquid on plate.
For column diameter D>800mm, using liquid accumulator. [p.161, Fig.3-14]
Functions: Side-stream drawoff; liquid seal; buffering缓冲. Liquid accumulator does not apply to the easily polymerizing materials and suspending solids. 23

24. Downcomer area Active area
(4)Layout of plate
Four areas.
Purpose of defoaming area: Avoiding weeping in liquid inlet and defoaming.
installation area
Downcomer area
Active area
Defoaming area 24

25. Select Fo (For valve tray, Fo=9~12)
(5)Number of floating valves and their arrangement (Design of vapor paths)
Select Fo (For valve tray, Fo=9~12)
Number of floating valves
Arranging floating valve openings graphically, and counting the actual number of valve openings; then checking Fo . 25

26. 2. Performance examination of fluid mechanics (pp.163~167)
Auxiliary equipment:
Condenser and its heat transfer area Fc (m2)
Reboiler and its heat transfer area Fh (m2)
Flow rate of cooling medium Wc (kg/h)
Flow rate of heating medium Wh (kg/h) 26

27. (2)Phenomena, judging and regulations:
Operation of columns:
(1) Basic requirements: Vapor and liquid counter-flow along the column height direction, and cross-flow on plate. Vapor and liquid mixes well on plate and without detrimental operations.
(2)Phenomena, judging and regulations:
1)Temperature of reboiler decreases, and column pressure decreases too.
Possible reason: Weeping.
Measures for avoiding weeping: Increasing vapor velocity; Setting defoaming area at the inlet of liquid. 27

28. 2)Temperature on the top of column increases
Possible reasons: Excessive froth entrainment.
Measures for avoiding excessive froth entrainment: Decreasing vapor velocity; letting HT, or D  u . 28

29. 3)Column Pressure increases sharply. Possible reason: Flooding.
Several causes of flooding and corresponding measures:
a. Vs is too large and leading too great flow resistance. The measure can be decreasing vapor velocity.
b. Easily bubbling materials: Letting Af  or HT .
d. Af too small: Letting Af  or HT .
e. spacing between downcomer bottom and tray is too small or blockage of downcomer happens: Cleaning downcomer or letting h0. 29