x
Plate efficiencies
y1. Types yofn plate
efficiency
1
(2)Murphree efficiency
x(1) Overall
n efficiency ET
yn 1 N T x n 1
N 
ET 
  o 

N P x n
N actual 
n
y*
y
xyn 与
yn
1 xn 成平衡
x
x
yy
xn
yn 1
yn 1
xx
yn
y
n
n
yynn11
x
xn 1
xn 1
n
yn 1n
xn
x
xxn 1 n
EMV, EML
yn  yn y1n  yn 1
[M ] EMV
 *
*
yn  yn y1n  yn 1
*
y*
is xin成平衡
equilibrium
yn*n与
y
n n与xn 成平衡
with xn.
EML
xn 1  xn

xn 1  xn*
x*n xis* xin成平衡
equilibrium
n n
with yn.
1
(3) Local efficiency Eo
E0V
y  yn 1
 *
y  yn 1
y 与x成平衡
*
y* is in equilibrium with x.
yn 1
xn 1
n
y
xn 1
x
xn
yn 1
yn
n
xn
xn 1
xn
yn
y
yn
y
yy
xx
x
yn 1
n
yynn11
x
xn 1
n
yn 1n
x
xxnn11 n
n
y
n
x
x
x nn
n 1
y
xn ynn
yn
2
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;
(2) ET ~  ,  L Correlation( for distillation tower)
（O' connell approach）
(3) ET ~  L / HP( Absorption tower)
law
[H=Henry’s
H — Henry
' s constant
law constant ]
3
3-1-1 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
3-1-3 Design of Valve tray columns
•Understanding the meanings of symbols in
Figure 3-10. [p.158]
5
HT
HT
Pn 1
Pn 1 H T
HT
Pn Pn 1
hL Pn
Pn 1
P
Hn T
how
1
P
Hh
n 1
TL
HT
2
Pn1P
1
n
Pn1
hL
hL
12
1
2
 1
1
22
2 2
hL
hw1 hH1
ow
2 21 
H2d h2
w
hw H2
T
d
h1
Pn
hL
1
1
2
2
how
hhowow
hw
hhww
Hd
H
hH0dd
hh00
D WS
R x
WC D
t R
t  WC
lW
t
t
Wd
WS
x
D l
W
R W
d
WC W
S
t x
t D
lW
lW
Wd
Wd
WS
WS
x
x
D
R
WC
D
R
WC
D
Wd
R
WS
WC
x
t
D
t
R
WC
t
t  lW
Wd
WS
x
D
R
WC
6
HT
Pn 1
HT
Pn 1 H T
Pn Pn 1
PnT hL
H
how
1
h
HP
L
n

1
T
hL
hw1 hH1
ow
n
2 21 
Pn1 H d h2
hL 2 w
hL
12 hw H2
Pn1P
1
HT
2
1

2

1

1
hhow
ow
hhhww
Pn
T
d
HT
Pn 1
how
h h
howow
h
1
w
1 h
hHww
2
d
2 H
hH0dd
hh00
Pn
L
h1
22
weir,2m
 2
=height of
=height
of
clear
liquid
over
weir,
m
H
H
how
w dd =spacing between downcomer bottom and tray, m
ow
hw0
hh
H
0 d =horizontal
distance between downcomer and
hH1 d underflow weir, m
h0
7
HT
Pn 1
HT
Pn 1 H T
Pn Pn 1
PnT hL
H
how
1
h
HP
L
n

1
T
how
hw
HT
2
Pn
hL
hw1 hH1
ow
n
2 21 
Pn1 H d h2
hL 2 w
hL
12 hw H2
Pn1P
1
1

2

1

1
T
d
HT
Pn 1
how
h h
howow
h
1
w
1 h
hHww
2
d
2 H
hH0dd
hh00
Pn
L
h1
H
howd
22
weir, m
 =height of underflow
hhH
2 2
ww T
=equivalent height of clear liquid, m
HPnd1
=distance between plates, m
hHP0nT
=height of aerated liquid, m
2h
L
1
8
lW
D
R R
W CW C
t t
t t
WS
WC
x
W
llWWd =length of weir, m
t
lW
D
=width
of
straight
W
lW
t
W
W dS d
Wd
R
segmental weir, m
xd
W
WS S =width of defoaming WlW
WC
WS d
lD
W
xW S area, m
t
x =width of installation W
R
x S
W
t  lW
D
lW
xd
D area, m
x
Wd
W
W
W
R
d
DCS =column diameter, m D
l
D l
WS
R
W
tW
W
x C =radius of active area, R
S
W
R
R W
x
ltD
x
d W
W
DW C m
tW
WC W x
D
C
W
D
S
C
W
tttR d =half the width of
R
t x D
R
R
R
=distance
betweenWcenters
t
W
active
area,
m
S

W
t

C
W
D
W
tt CC
W
C
of openings of valve trays
x
t
t  of the
tt
R tsame
t row, m
t
9
t
D

W
t

W
d
S
C
•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
•[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
•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
•Conditions given for the design:
Vapor and liquid 气液负荷：
flow rates: VS , LS ;
气液负荷：VS , LS ;
物性：V ,  L ,  ,  , M ;
气液负荷：
物性：VV, S,LL,S; ,  , M ;
Physical properties:
操作参数：t , P 。
物性：
V ,  L , t ,, P。
,M;
操作参数：
操作参数：t , P 。
Operating parameters:
13
(1)Liquid density:
Average density, such
as rectifying section:
1
a1
(2) Density of vapor

mixture:


1
a1
a2
1  a11  a22
 L   L1   L 2
混
 LL11  LL 22
混
1
1  L进料   L产品）
 La精2  1（
（L进料
 LL精
（
L产品
, rec2
L , feed
L , D）
 L 2 22
L1
混
PM
1
V  PM , V  1 ( V进料  V
Average density, such1 

,


(



RT
2
V
V
V
进料
V


（



）
V
V
V
进料
V
L精
L进料 RT
as rectifying section:
L产品
2
RT
2
2
PM
1
V 
, V  ( V , feed  V , D )
RT
2
14
(3)Latent heat of
vaporization of
liquid mixture:
(4) Surface tension
of liquid mixture:
(5)Average
temperature and
pressure, such as
rectifying section:
n
1
1 (
r混

x
,


 )D )
n
i
i
feed
r
x
,
r

(
r

r

i i
进料
产品
1
2
i

1
2
r  i 1r x ,r  (r  r )
n
混
n
i i
进料
产品
21 1
 D
) 产
混n  ixii,xi , 1( feed
(进料
i 1i 1
混  
 i xi ,  2 (2 进料   产品 )
2
i 1
1
t  1 (t顶  t进料 )
t 12 (t顶  t进料 )
t  2(ttop  t feed )
1
2
P  1 ( P顶  P进料 )
12 ( P顶  P进料 )
P

P  2( Ptop  Pfeed )
2
i n1

15
1. Calculation of technological parameters of valve
tray columns
(1)Column height
Effective height of the column:
NT
Z
 HT  N P  HT ......(3  1)
ET
Question: How to determine HT properly?
（p.154~155）
16
(2)Column diameter
4VS
D
......(3  2)
u
u （0.6 ~ 0.8）umax
umax is determined by excessive froth entrainment
or flooding.
17
According to the settling principle, the maximum
permissible vapor velocity is derived as follows:
 L  V
umax  C
V
C=capacity factor
初估塔径D：选H T , hL ,由
LS
 L
VS  V
 
查图3  8得C20  C  C20  
 20 
 u适宜  D,圆整。
0.2
 um
18
 L  V
 L  Vumax C


L
V
C Firstly,
umax estimate
C
V
the column
diameter D, select HT
V

V
and hL, get C20 from
Fig.3-8 and
LS   L 
初估塔径LD：选
H T , hLL,由  





S
V

L
塔径D初估塔径
：选H T , hD
由 H T ,hL ,由 S  L S   V 
L ,：选
VS  V  VS  V 
0.2
0.2 
0.2
查图3  8得C20  C  
C20   umax
 8得C  C  C
u
20
宜
1
1
2
1
2
 
  umax
查图
20 3  8得C20
20  C  C20 max 
 20 
20 

 u适宜  D,圆整。
 D
,圆整。
u  D(rounded up)
19
2
(3)Downcomer
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
•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
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:

Af H T
LS
,  (3 ~ 5) s ?
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
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
(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
(5)Number of floating valves and their arrangement
(Design of vapor paths)
F0
选F0 (浮阀塔F0  9 ~选
12F) 0
(浮阀塔
u0  F0  9 ~ 12
V
•Select Fo (For valve tray, Fo=9~12)
F0
F0
VS
VS
~
塔12
F0) 9 u~0 12
 )  u0
 阀孔数
N

阀孔数
作图排列，
N 2 
Number
of floating
valves
2
V
V
4 d 0 u0
4 d 0 u0
VS
得实际阀孔数N 实 得实际阀孔数
核算F0
N实  核
N •Arranging
作图排列，
 作图排列，
2
floating valve openings graphically, and
d
u
0
4 0 0
counting the actual number of valve openings; then

孔数
核算
N
0 核算
实F
checking
FoF.0
25
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
•Operation of columns:
(1) Basic requirements: Vapor and liquid counterflow along the column height direction, and crossflow 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
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
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