DESIGN OF THE DEAERATOR

The deaerator is designed for a typical 200 MW unit. The deaerator is designed for
the maximum flow of condensate. The quantity of flow is about 11% more than for
100%load.
The deaerator selected is tray type counter flow direct contact and high!pressure
type. The pressure of the deaerator is " #g.cm
2
$abs%. The pressure is maintained at
" #g.cm
2
$abs% at all loads by means of pressure regulating &al&es. The guaranteed
residual oxygen in the deaerated water is 0.01ppm $' 10 g(litre%. )t is possible to
achie&e in actual operation e&en less than 0.00" ppm $' " g(litre%.
*omenclature+ !
a Thermal diffusi&ity m
2
(h
c ,pecific heat #cal(#g.-
. .iameter m
/ 0rea of heating surfaces m
2
g 0cceleration due to gra&ity m(sec
2
h 1eight of water column m
i 2nthalpy per unit mass #cal(#g
# 3&erall heat transfer coefficient #cal(h.m2.-
4 Total length of heated surface m
5 5ressure #g(cm
2
or atm
6 6uantity of flow #g(sec or #g(hr
q 6uantity of flow M
7
(sec or m
7
(hr
T 0bsolute temperature t8 2"7 9 :
t Temperature 9 -
T; or t; ,aturated temperature of &apour 9: or 9 - respecti&ely.
< <olume m
7
& ,pecific &olume m
7
(#g

<elocity m (sec or m(hr

=
<apour or gas &elocity m (sec or m(hr
xy> -o!ordinates
g ,pecific weights #g (m
7
Thic#ness m
-oefficient of discharge
0ngle degrees
Thermal conducti&ity #cal(m.h.9-
.imensionless temperature
.imensionless co!ordinate
Time sec or hr
-oefficient of contraction
5age 1 of 17
DATA FOR DESIGNING
Condensate
The quantity of condensate to be deaerated t(h ?@A.A
2nthalpy of condensate at inlet #cal (#g 1?".2B
3xygen content of the condensate ent. .eaerator g(litre ?0
3xygen content of deaerated water g(litre 10
Temperature of the condensate - 1?A
Steam to deaerator
Extraction
steam
Spindle
steam
6uantity of steam t(h ?.7B2 2.7
5ressure of the steam #g(cm
2
$a% 17.22 ".?
2nthalpy of steam #cal(#g @02."7 @20.2@
Temperature of the steam - BB" B"@
Steam from deaerator $To sealing C2Dectors%
6uantity t(h ?.7
2nthalpy of steam #cal(#g A?E.@A
Condensate from H.P Heater
6uantity t(h 100."2
2nthalpy #cal(#g 1E0.B"
HEAT A!ANCE
Heat inp"t to t#e "nit
Main condensate heat input
$?@A.A x 10
7
x ?".2B%
10
A
#cal(h E2.1?
15 drains heat input
$100."2 x 10
7
x 1E0.B"%
10
A
#cal(h 1E.2
2xtraction steam heat input
$?.7B2 x 10
7
x @02."7%
10
A
#cal(h B.2E
,pindle steam heat input
$2.7 x 10
7
x @20.2@%
10
A
#cal(h 1.@E
Total heat input 10
A
#cal(h 11".?7
Heat o"tp"t from t#e "nit
1eat ta#en by feed water
$A@E x 10
7
x 1A?.")
10
A
#cal(h 11B
1eat ta#en by eDector and sealing
steam
$?.7x 10
7
x A?E.@A)
10
A
#cal(h 7.BE
1eat ta#en by &ent steam $)nitially the
quantity of the &ent is
assumed as B?0 #g(h%
$0.B? x 10
7
x A?E.@A)
10
A
#cal(h 0.2@"
Total heat output 10
A
#cal(h 11"."@"
-omparing the output it is higher than the input so the extraction steam is
increased by an amount of B00 #g(h.
0dditional heat input
0.B00 x @02."7 x 10
7
10
A
#cal(h 0.721
5age 2 of 17
0dditional heat output
0.B00 x 1A?." x 10
7

10
A
#cal(h 0.0AA
Therefore
1eat input
$11".?7 8 0.721%
10
A
#cal(h 11".@?1
1eat output
$11"."@" 8 0.0.0AA%
10
A
#cal(h 11".@77
*ow the input and output quantities balances.
Total input quantity of steam
1 2xtraction of steam F ?."B7 t(h
2. ,pindle steam F 2.700 t(h
6uantity of flash steam $from 1.5 -ondensate%
4et 6s be the quantity of flash steam then 6s x A?E.E 8 $100."2 ! 6s% x 1A?."
F 100."2 x 1E0.B"
F
1A?."% $A?E.E
1A?."% $1E0.B" x 100."2

F ?.0B t(h
Total input steam to deaerator F ?."B7 8 2.700 8 ?.0B F
17.0@7 t(h
,team ta#en out from deaerator
1. ,ealing and eDector steam
F ?.70 t(h
2. <ent steam
F 0.B? t(h
Total
F ?."? t(h
Therefore
,team for deaerator F 17.0@7 G ?."? F ".777 t(h
The &olume of condensate to be deaerated F ?@A.A x 1.102 x 10
7
litres.

,team for deaeration F
10 x 1.102 x ?@A.A
10 x ".777
7
E
F 11.72 x 10
7
mg(litre.


120T TH0*,/2H -04-I40T)3*
1ere water is being heated on the principle of direct contact between &apour and liquid. This
increases the rate of condensation of the &apour. The water is bro#en to a number of fine Dets to
increase the contact surface between water and steam. The Det is assumed to be continuous and the
effect of pulsations caused by the interaction of the forces of gra&ity inertia and surface tension is
neglected.
The energy equation is written in the cylindrical co!ordinates assuming both molecular conduction and
isotropic turbulalent conduction ta#e place. The radial temperature gradient is considered to be much
greater than the axial gradient. Inder these conditions the energy equation becomes
5age 7 of 17

,
_

R
t
.
R
1
R
t
c.

x
t
.
2
2
T
x
$ E%
The dimensionless co!ordinates are introduced
o
R
x
x

x
R
R


1
x
t t"
t t"

Where
x
and
X
R are the &elocity and radius of the Det at a distance J from the end of the no>>le
respecti&ely.
Ho is the radius of the no>>le $hole in the plate%K and t1 is the initial temperature of the Det.
The solution of the partial differential equation $ E% is written in the form of the product of two functions.
) f(x).(
2
A.e

Where ;0= is an arbitrary constant

)n an isotropic turbulent steam the turbulent diffusion of the heat is proportional to the &elocity and
radius of the Det.
i.e.
x x. T
R . .C. $ 11 %
where is an empirical constant.
,ubstituting the &alue of
T
from equation $ 11 % into the equation $ E % and reducing the equation to
dimension form we ha&e

1
x ) .R . (a R
R
2
2
x x o
2
x x

+

The &alue of f$x% in equation$ 10 % is selected such that
2
x x.
x x o
R
) .R . (a R
f(x)
dx
d +

$ 17 %
The expression for local &elocity and local radius of a free cylindrical Det of the form
2
0
2
0
x

gx 2 1

+
$ 1B %
2
0
2
0
x

gx 2
1 4
R
R

$ 1? %
The surface area of the Det is
1
1
1
]
1

,
_

gx 2
1
g k
R 4!
dx R 2! "
4

2
0
2 x
0

2
0 0
x

$ 1A %
5age B of 17
The &elocity of Det at no>>le outlet is expressed by
2g#
$

Where

-oefficient of discharge.
1 F 1ydraulic head of the liquid before entering the no>>le in m

F -oefficient of contraction of the Det.

,ubstituting the expression for
x
and
x
R into eqn $ 1? % we get
1
1
1
]
1

,
_

+
+

gR 2
1
gR %
2
x
R
a
dx
R
R (a R
f(x)
4
%
2
0
0
2
0
2
%
2
0 x
2
0 0
x
0
2
x x
x x x 0

$ 1@ %
.ifferentiating 2qn $10 % and substituting the corresponding deri&ati&es into 2qn $ 12 % we obtain
The solution is
0 ()
) d(
( d
.

1
) d(
) ( d
2
2
+ +

%
$ 1E %
) ( & C ) ( ' C ()
0 2 0 1
+
$ 20 %
The boundary conditions are
0 () 0( 1(
The initial conditions are 1 0K x
/or xF0 i.e. for the axis of the Det the Lessel function of >ero order of the first #ind M0 has finite
&alue while the Lessel function of >ero order of the second #ind N0 becomes infinite. -onsequently
for a finite &alue of the temperature at the axis of the Det integration constant -2 must be >ero.
Then
) ( .' C ()
0 1

and

i
i
x f
i i
i
e J A
1
0
2
% $
% $


$ 21 %
)t follows from the initial conditions that
1
0
0

i
i
i i
J A % $
)t is well #nown in this case
% $
i i i
i
J
A

2

from tables of Lessel functions we find the &alues of for which

0 % $
i o
J
The a&erage temperature of the liquid in the Det at location x is

1
0
1
2
2
4
2
i
i
x f
i
x
i
e d
% $
.

$ 22 %
/inally
5age ? of 17
% $ . % $ . % $ .
OO
. . .
O
x f x f x f
x
x
e e e
t t
t t
87 74 47 0 78 5
0534 0 1312 0 6915 0

+ +

$ 27 %
When f$x%P "0.0? we can use the simplified equation retaining only the first term of the series $ 27 %.
The error is negligible
f(x) %.)*
0.+)1%e
x

Ta#ing logarithm of 2q $ 2B % we obtain the con&enient expression

2.%2f(x) 0.1+
t t
t t
,og
x
"
1
"
+

$ 2? %
)n more general form the equation $ 2? % may be written as
f(x) C C
t t
t t
,og
2 1
x
"
1
"
+

$ 2A %
-1 F 0.1A0K -2 F 2.?2K
1
1
1
]
1

,
_

+ + 1
2
1
5
2
4
5
2
0
0
2
0
2
5
2
0
2
0 0

gR
gR
R
a
x f
x
% $
/or freely falling cylindrical Det
/rom the gi&en data
The water inlet temperature t1 F 1?A-
The pressure of the deaerator p F " #g(cm
2
$a%
The saturation temperature t= F 1AB.1"-
,elected &alues+
The diameter of the hole $no>>le% do F 0.00A m
The height water column abo&e the entry
of the no>>le $hole% h F 0.0@0 m
The effecti&e heating length of water Det ) F 0.220 m
-oefficient of contraction F 0.@0
-oefficient of discharge F 0."0
We ha&e
% $ log
O
O
x f C C
t t
t t
x
2 1
1
+

and
5age A of 17
1
1
1
]
1

,
_

+ + 1
2
1
5
2
4
5
2
0
2
0
2
5
2
0
2
0 0

gx
R
R
a
x f
x
% $
Where
a F Thermal diffusi&ity F A22 x 10
!A
m
2
(h
x F 0.220 mK Ho F 0.007 mK F ? x 10
!B
K gF E.@1 m(sec
2
1.1m(sec @0 2.E.@1.0.0
0.@
0."
2g#
$

1
1
]
1

,
_

+ +

1
1.21
B 2xE.@1x0.A
1
0.007 x E.E1 x 0.@ x ?
x1.1 x10 ? x 2
0.007 x 1.1
x0.220 x10 A22
f$x%
B
?
2
?
2 B
2
A
F0.007@B 8 0.01B? $7.B2% F .0?7BB

x
t t
t t
O
O
log
1
0.1A0 8 2.?2 x 0.0?7BB F 0.2EB?
N$%ER OF TRA&S
,ince it is not possible to heat the water exactly to its boiling point it is heated to a temperature
0.2? - less than its oiling point while it is falling as a free Det.
t=!tx F 0.2? - F x
47 3
25 0
0 156 17 164
1
.
.
. .
log log
O
O

x
t t
t t
The no.of Trays required F
0.2EB?
7.B"
F 11."or 12 trays
The &alue of high we select @ trays.
356 2 8 2945 0 . . log
O
O

x
t t
t t
x
5 10.
O
O

x
x
t t
t t
i.e. t=!tx F 0."@
i.e. The water is heated to a temperature 0."@- less than its boiling point. The remaining
temperature can be achie&ed by collecting the water in a trough and intensi&ely scrubbed bubbled by
superheated steam. The time required to heat the water to its boiling point tends to infinity as the
water temperature increases.
DIA%ETER OF THE DEAERATOR
The recommended &alue of &olumetric loading of the tray type deaerator is
0.B to 0.@ x 10
A
#cal(m
7
h.
,elected &alue F 0.@ x10A #cal(m
7
.h
The quantity of condensate F ?@A.?AA t(h
The enthalpy of incoming condensate F 1?".2B #cal(#g
2nthalpy of saturated water F 1A?." #cal(#g
-hange in enthalpy F 1A?." G 1?B.2" #cal(#g
4oading of the deaerator F @.BA x 10
7
x ?@A.?AA #cal(h
5age " of 17
4et . be the diameter of the deaerator and the deaerator height $@ x 0.7% 2.B m
<olume of the deaerator F 2.B x . x
B
Q
2
m
7
<olumetric loading F
2.B x . x
B
Q
?@A.?AA x 10 x @.BA
2
7
This should be within the selected &alue of 0.@ x 10A #cal(m
7
h
i.e. F
A
2
7
10 x 0.@
2.B x . x
B
Q
?@A.?AA x 10 x @.BA

A
7
10 x 0.@ x 2.B x Q
?@A.?AA x 10 x B x @.BA
. i.e. . 1.@1? m
The diameter of the deaerator selected as 2.@ m in order to accommodate the holes in the tray.
N$%ER OF HO!ES PER TRA&
Weight of the condensate to be
.eaerated F ?@A.?AA t(h F
7A00
?@A.?AAx10
7
#g(sec
,pecific &olume of water at a mean F 0.0011020 #g(m
7
Temperature of 1A09-
<olume of water passing throR the holes F 1A7 x0.0011020 F 0.1"E? m
7
(sec
The diameter of the hole F 0.00A m
1eight of the water column abo&e
The hole F 0.0@0 m
-oefficient of discharge F 0."
<olume of water flowing throR hole F 1.2? x 0." x
B
x0.00A Q
x 0 2gh Sx
2

F 2B."x10
!A
m
7
(sec
The number of holes required(Tray F
2B."
10 x 0.1"E?
A
F "2A0 holes.
The holes are arranged in staggered position at a pitch of 1@ mm
5ro&ided holes F ""?0 (tray
5ercentage reser&e F A.@% 100 x
"2A0
"2A0% $""?0

CA!C$!ATION FOR DETER%INING THE '$ANTIT& OF STEA% TO E (ENTED

0s mentioned earlier to #eep the partial pressure of the dissol&ed gases in the deaerator at desired
low le&el it is necessary to remo&e the gases from deaerator.
This is done by &enting non!condensable gases along with portion of steam. The residual oxygen
content depends on the amount of &ent sent to atmosphere. )t is calculated as follows.
.
5age @ of 17
4et
.p Weight of the steam for deaerator including the &ent steam in mg(litre of water.
T# Weight of oxygen carried away by the steam in the &ent in mg(litre of steam
52 5artial pressure of oxygen in the &ent mixture.
5p .eaerator pressure atm.
mp Molecular weight of steam
m# Molecular weight of oxygen
$x% Weight of steam to be &ented mg(litre of water.
Then we ha&e
#
p
2
p
#
p
m
m
5
5
T
.

$ 2" %
1ere .p F U11.72 x 10
7
8 $x%V mg(litre
The initial concentration of oxygen F ?0 g(litre
The final concentration of oxygen F 10 g(litre
The weight of oxygen to be remo&ed F B0 g(litre F B0 x 10
!7
mg(litre
The weight of steam to be &ented F $x% mg(litre.
,pecific &olume of steam F 0.2""@ m
7
(#g
F 0.2""@ x10
!7
litre (#g
<olume of steam F $x%x 0.2""@ x10
!7
litre
T# F
. 10 x 0.2""@ x $x%
10 x B0
7 !
7
mg (litre of steam
5artial pressure of steam in the &ent
The residual oxygen in the water F 10 g(litre
i.e.
2
o
m
F
72
10 x 10
A
moles ( litre.
/or this residual oxygen the corresponding equilibrium pressure is calculated using
1enryRs 4aw
C
-
.
2
o
e

Where 5e equilibrium partial pressure
- F 1enryRs -onstant for water at 1AB.1" 9- F 1.02" x 10
!7

2
o
m
F Molality of oxygen
7
A
1.02"x10
1
x
72
10 x 10

e
P F 0.70B? x10
!7
ata
)n practice it has been found that the partial pressure of the oxygen in the &ent should be
2.?
1
times the equilibrium pressure to ha&e better desorption of gas.
1ence 52 F 5e(2.? F 0.70B? x10
!7
(2.? F 0.121@ x 10!7 ata
Mp F 1@K m# F 72K 5p F " ata
,ubstituting the &alues in eqn $ 2" %
5age E of 17

( ) [ ]
72
1@
x
10 x 0.121@
"
10 x B0
10 x 0.2""@ x x 11.72x10
7 7
7 7

+
$x% F0."7 x 10
7
mg(litre
The weight of steam to be &ented F 0."7 x 1.102 F 0.@0? #g ( tonne of water
Weight of steam to be &ented per hour F 0.@0? x ?@A.A F B"7 #g(h
THE DISTRI$TOR
)n order to distribute the condensate uniformly through out the section of the deaerator a distributor is
pro&ided. )t is a trough consisting of ;<= notches and holes to distribute the water. The notch angle is
E09.
The quantity of condensate to be distributed F ?@A.?AA t(h
The &olume of condensate F
7A00
1.0E"B x ?@A.?AA
F 0.1"@? m
7
/or a ;<= with angle E09 the quantity of
.ischarge $6% is gi&en by F
?
h g 2 W
1?
@
Where
6 F .ischarge m
7
(sec
1 F 1ead causing flow m
F /actor gi&en by equation F 0.?A? 8 .0@A@ x 0.0E0
!0.0?

for A notches h F E0.mm F 0.0A0 m
F 0.A?2@
6uantity of flow throR A notches F
?
0.0E x E.@1 x 2 x
1?.
@
x 0.A?2@ x A
F 0.022B m
7
( sec
/or the remaining 2A notches the head
causing flow F
2
110
F "".@ mm F .0""@ m F 0.A?7
Therefore 6 F
?
0.0""@ x 0.A?7 x
1?
@
x 2A
F 2A x2.A" x10!7 F 0.0AEB m
7
The total flow throR notches F 0.022B 8 0.0A7B F 0.0E1 m
7
( sec
The hole diameter F 0.02? m
The head causing flow F 0.BA0 m
.ischarge throR one hole F
2gh x 0 x S
m
7
(sec
-oefficient of discharge F 0.A
0rea of the hole 0 F
4
2
0.02? x Q
F B.E2 x 10!B m
2
5age 10 of 17
.ischarge throR one hole F 0.A x B.E2 x 10!B x B.B7 x 0.BA m
7
(sec.
F @.@? x 10!B m
7
( sec
*o. of holes pro&ided F EB
.ischarge through holes F EB x @.@? x 10!B F @72.? x 10!B m
7
( sec
Total discharge throR notches and holes F 0.0@72? 8 0.0E1@ F 0.1"?0? m
7
( sec
The remaining &olume of condensate F 0.1"@? G 0.1"?0? F 0.002B? m
7
( sec.
This quantity of condensate is allowed to o&erflow.
DIA%ETER OF THE CONDENSATE PIPE
<olume of water flow F 0.1"@? m
7
( sec
4et us select the &elocity as F 2 m ( sec
0rea required F
2
0.1"@?
F 0.@E2? m
2
)nternal diameter of the pipe should be F 0.77A m
The selected pipe si>e F 7A@ x 11 mm
<elocity of water F
2
0.7BA x Q
B x 0.1"@?
F 1.E m (sec
DIA%ETER OF THE (ENT STEA% PIPE
The quantity of the steam to be &ented F B"7 #g(h
,pecific &olume of steam at " ata F 0.2""@ m
7
( #g
0mount of steam escaping throR pipeF
7A00
B"7 x 0.2""@
F 0.07AB m
7
( sec
4et us select a &elocity of 1? m ( sec
/low area required F
1?
0.07AB
F 0.002B m
2
.iameter of the pipe required F
Q
B x 0.002B
F ??.2 mm
,elected pipe diameter F ?0 mm $nominal%
5age 11 of 17
<elocity of steam F
2
0.0?1 x Q
B x 0.07AB
F 1".A m ( sec
DIA%ETER OF THE E)TRACTION STEA% PIPE
The quantity of steam sent to deaerator directly through the bubbling chamber is ?0% of the extraction
steam. This steam is admitted at two points
Maximum quantity of steam flowing
Through one pipe F B.A t (h
<olume of steam F
7A00
1000 x 0.7"00 x B.A
F 0.B"2? m
7
(sec
,elected steam &elocity F 2? m (sec
0rea required F
2?
0.B"2?
F 0.01@E m
2
.iameter of the pipe required F
Q
B x 0.01@E
F 1?B.? mm
0 pipe with nominal bore of 1?0 mm has been selected.
The &elocity for the selected pipe F 2A.@ m ( sec.
CONSTR$CTION OF THE DEAERATOR
The deaerator is made up of carbon steel sheet welded to which the torishperical heads are welded.
0ll the other elements are housed inside. The eight rows of perforated trays are welded to the shell.
The perforated trays are of stainless steel material $0),) 70B%. Lelow the last row of trays a collecting
trough is pro&ided. ,team enters this collecting trough through the chamber. 0 distribution trough is
pro&ided to distribute the water uniformly through out the entire cross section of deaerator o&er the
first row of perforated trough. The condensate enters the deaerator through a pipe and it flows &ia the
notches and the holes in the distributors to the perforated tray. The water is splitted to ""?0 Dets by the
perforated trays. While water cascades the steam that is admitted to the bottom of the deaerator
flows upward and heats the water. Meanwhile the diffusion of the dissol&ed gases ta#es place. The
perforated trays are #ept precisely hori>ontal. When there is o&erloading of the deaerator ta#es place
the water o&erflows through o&er flow plates. )n order to brea# the water into thin films ;<= notches are
pro&ided. When the deaerator is loaded excessi&ely the water will o&er flow in thic# films and proper
deaeration will not ta#e place. This will increase the residual oxygen content in the deaerated water.
When the water flow is less the cascade will get deformed. The water will flows through the
perforated trays are collected at the bottom by a trough where it is intensi&ely bubbled by
superheated steam. 0ny remaining oxygen will be remo&ed here and the water is completely heated
to its boiling point. /rom here the water flows to feed water tan# through the pipe.
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The trays are mounted in the channels which are welded to the shell. The welded type construction is
made anticipating no maDor defects occur during life period. 1owe&er manholes are pro&ided for
periodical maintenance.
The dissol&ed gases that are collected at the top of the deaerator will be sent to atmosphere through
the &ent pipe. The amount of &ent can be controlled by means of &al&e pro&ided. 5ro&isions are made
to connect pressure gauge and thermometer. The deaerator is supported by four= ) ; beams and is
directly mounted on feed water tan#.
5age 17 of 17