Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1086302
'r l-XCl`lANGl'.R CONSTRUCTION
~ACKGROUND OF THE INVENTION
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Mally types of heat excllallger~ are eolllmcrci;llly
available on the market today. One of the primary prob-
lems with such heat exchangers, however, is that the -
tube bundle is normally fixed in the main housing of
the heat exchanger so that it cannot be removed to
; easily repair any of the tubes in the tube bundle that
may deteriorate. This means that, in order to repair
one of these prior art heat exchangers, it is necessary
to either remove the entire heat exchanger including
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'~ ~ the housing from its installation so as to gain access
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~ to the tube bundle in the heat ex~changer to repair same
'~ or for a workman to enter the main housing and repair
~ the defective tube while the heat exchanger is in place.
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; This results in considerable down time of the equipment
on~which the heat exchanger is being used and further
makes the repair of the particular tube that is dete- -
riorated in the tube bundle extremely difficult since
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it cannot be removed from the housing to gain access
thereto. ~f another heat exchanger is actually in~erted
into the installation while the deteriorated heat ex-
changer is belng repaired, the cost of maintaining
thc~c spare colllplete heat exchangers is prohibitiv~
from a maintenance standpoint.
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SUM~RY OF THE INVENTION
These and other problems and disadvantages asso-
ciated with the prior art are overcome by the invention
which contemplates a heat exchanger construction for
attachment between spaced apart duct sections adapted
to carry a gaseous medium which is to be placed in a
heat exchange relationship with a heat exchange fluid. The
exchanger includes a housing adapted to be connected between
the spaced apart duct sections, and defining a main gas pas-
sage therethrough about a gas passage axis in registra-
tion with the duct sections with the gaseous medium
flowing from one duct section to the other through the
housing. A pair of end tube subchambers are on opposite ;
sides of the main gas passage and coaxially located along a
common access axis generally normal to the gas passage -
axis, the end tube subchambers opening onto opposite
sides of the main gas passage and with an access opening
to one or both of the end tube subchambers opposite the
main gas passage. The housing further includes a pair
of spaced apart slide rails mounted in the housing along
opposite sides of the main gas passage between the end
tube subchambers. A tube bundle unit is removably received
in the housing through the access opening and extends
, across the main gas passage between the end tube sub-
chambers. The tube bundle unit includes a tube frame
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and a tube bundle carried by the tube frame where the
tube frame includes a pair of spacedapart tube sheets.- ~`
A plurality of side members connect the tube sheets r
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and slidably engage the slide rails on the housing
to support the tube bundle unit so that the tube sheets
are in registration with the openings between the main
gas passage and the end tube subchambers and substan-
tially fill the openings when the tube bundle unit is in
place in the housing to separate the main gas passage
from the end tube subchambers. The tube bundle includes
heat exchange tubes extending between the tube sheets ~
with fluid headers to the heat exchange tubes located ~-
outboard of the tube sheets and fluid pipes to the
headers projecting through the access opening in the
housing when the tube bundle unit is in place in the
housing. One or more cover panels separate from the -
tube bundle unit removably close the access openings
with the cover panel defining pipe openings therethrough
in registration with the fluid pipes when the cover
panel is closing the access opening so that the fluid
pipes projéct through the pipe openings in sealing en- -
gagement therewith. Thus, the cover panel may be used to
reclose the access opening while the tube bundle unit
is removed for repair so that the gaseous medium can
continue to flow through the housing while the tube bun-
dle unit is removed without loss of the gaseous medium.
This allows the tube bundle in the heat exchanger
to be selectively removed from the housing while the ;
housing remains in place to permit easy access to the tube
, bundle for repair. Further, this permits the housing to be
j used while the tube bundle is removed for repair to mini-
¦ mize the down time of the equipment to which it is attached.
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~0863QZ
Additionally, a spare tubc bundle may be economically
placed in the housing while the defective tube bundle is
being repaired.
The invention disclosed herein further o~ercomes the
problems associated with the prior art economizers by
selectively recirculating a portion of the feedwater
passing through the heat exchanger in the economizer in
reponse to the average temperature of the flue gases after
passage through the heat exchanger to maintain the ave-
; 10 rage temperature of the flue gases on the exit side of
the economizer above the dew point thereof. Alternatively,
the flow of the feed water may pass through the heat ex-
changer in thc cconomizcr or bypass thc heat exchan~er in
the economizer in response to the average temperature of
the flue gases as they exit the economizer.
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The apparatus of the invention as embodied in an
economizer for a steam boiler includes the heat exchanger
positioned in the flue gas duct from a steam boiler with
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a Eeedwater source connected to the Eeedwatcr inlct Or
the steam boiler through the tube bundle in the heat ex-
changer. A three way valve is positioned in this connec-
tion to selectively divert the flow of feed water back
through the tube bundle by a circulating pump in response
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to the average temperature of the flue gases after pas-
' sagc through thc heat cxchanger. Alternatively the three
way valve may divert the feedwater for flow through the
tube bundle in the heat exchanger to the feed water inlet
of the steam boiler or bypass the tube bundle in the
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heat exchanger in response to the average temperature
of the flue gases as they pass from the heat exchanger. -
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These and other features and advantages of the in-
vention will become more clearly understood upon consi- `
deration of the following specification and accompanying
drawings wherein like characters of reference designate
corresponding parts throughout the several views and in
which:
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an exploded perspective view showing the
heat exchanger of the invention;
Fig. 2 is a reduced longitudinal cross-sectional
view of the heat exchanger of Fig. 1 incorporated in
an economizer;
Fig. 3 is a reduced elevational view showing the
heat exchanger being used as an economizer on a steam
boiler; ~`
Fig. 4 is an enlarged transverse cross-sectional
view taken along line 4-4 in Fig. 2; and,
Fig. 5 is a view similar to Fig. 2 showing the heat
exchanger of Fig. 1 incorporated in a different econo-
ZO~ mizer.
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These Ligures and the following detailed descri~tion
disclose specific embodiments of the invention; however,
it is to be understood that the invention may be embodied
in other forms.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Referring to the figures, it will be seen that the
heat exchanger 10 includes a housing 11 and a tube bundle -
unit 12 removably mounted in the housing 11. The heat
exchanger 10 may be used in a number of different appli-
~lO cations but is illustrated in Figs. 2 and 3 being used
in an econo~izer configuration with Fig. 3 illustrating
its use on a steam boiler. :
The housing 11 as seen in Figs. 1 and 2 includes a
pair of generally parallel spaced apart side walls 20,
~ ~ each of which has a longitudinal centerline CLSw. Each
¦ of the side walls 20 has a main central section 21 which
is centered on the centerline CLSw with a length Ll and a
height Hl. Each corner of each side wall 20 is notched
to form an end tube subchamber extension 22 with a length
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L2 and a height H2. The height H2 of each end tube sub-
chamber extension 22 is less than the height Hl of the
~,~ main central section 21 as best seen in Fig. 1 and the
extension 22 is centered with respect to the centerline
` CLSw. Therefore, it will be seen that each end tube sub-
~`~ chamber extension 22 on each side wall 20 will be laterally
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~`; aligned with a corresponding subchamber extension 22 on the
opposite side wall 20. The upper and lower ends of each
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end tube subchamber extension 22 is connected to the
laterally aligned subchamber extension 22 by an end tube
subchamber cross plate 24. Thus, the end tube subchamber
cross plates 24 determine the overall depth of the hou-
sing 11. Each cross plate 24 has a length L3 as best
seen in Fig. 1 so that opposite ends of the cross plate
24 project beyond the end tube subchamber extension 22
in side walls 20. Each pair of laterally aligned exten- ~.
sions 22 in side walls 20 and the cross plates 24 con-
necting the extension 22 define a tube bundle access
opening 25 therethrough with the height H2 and a width
Wl as best seen in Fig. 1 which opens into the end tube
subchamber 30 bounded by extensions 22 and cross pIates
24. The opposed end tube subchambers 30 and their access
openings 25 are centered on a common axis AES normal to
axis AMp and parallel to side wall centerline CLSw. The
inboard end of each end tube subchamber 30 opens into
the main fluid pzssage 28 as seen in Figs. 1 and 2.
The laterally aligned edges of the main central sec-
tions 21 in side walls 20 at the notches are connected by
~ ~ fluid passage cross plates 26, each of which extends from
; the end tube subchamber cross plate 24 out to the top or
bottom of the maincentral section 21 in the side walls 20. ~ ;
Thus, it will be seen that the main central section 21 of
the side walls 20 along with the fluid passage cross plates
26 define thc main -fluid flow passage 28 therethrough about
the central axis AMp which is oriented generally normal to
the centerline CLSw of the side walls 20 and generally
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1()8630Z
parallel to the plane of the side walls 20. The fluid
passage cross plates 26 and the side walls 20 define main
fluid openings 29 at the top and bottom side of the main
central sections 21 of the side walls 20 so that the pri-
mary fluid can flow through the passage 28 in the housing
11 from one of the fluid openings 29, here shown as the ~ -
bottom opening, to the opposite opening, here shown as the
top opening 29 as best seen in Pig. 2. The direction of
fluid flow through the heat exchanger 10 is immaterial.
It will thus be see that the fluid openings 29 and the
main fluid flow passage 28 have the same cross-sectional
shape with the length Ll and width W2 as best seen in
Fig. 1. The particular size of the main fluid flow pas-
sage 28 is set by the duct work which connects the main
fluid flow to the heat exchanger while the size of the
tube bundle access openings 25 and the end tube subchambers
i 30 is set by the size of the tube bundle unit 12 as will
,l become more apparent. While any fluid may be flowed through
the main fluid flow passage 28, it is illustrated as pla-
cing flue gases in a heat exchange relationship with the
fluid in the tube bundle unit 12 as will become more appa-
rent. ~,
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Opposite ends of the main central section 21 in eachof the side walls 20 is reinforced by an upstanding post 31
with reinforcing flanges 32 about all of the edges of the
side walls 20, the subchamber cross plates 24 and the main
fluid passage cross plates 26 to strengthen the housing 11.
Those reinforcing flanges 32 about the main fluid openings
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29 and the tube bundle access openings 25 ser~e as moun-
ting flanges as will become more apparent.
The tube bundle access openings 25 are respectively
removably closed by a front cover panel 40 and a rear
cover panel 4l as seen in Figs. 1 and 2. Each of the
cover panels 40 and 41 is attached to the reinforcing
flanges 32 abou~ the tube bundle access openings 25
using appropriate fasteners 42 as seen in Figs. 1 and 2.
An appropriate gasket 44 is provided between each cover
panel 40 and 41 and the reinforcing flanges 32 to which
they are attached. The front cover panel 40 is provided
with a pair of spaced apart header openings 45 seen in
I Figs. 1 and 2 which permit the fluid passing through the
i tube bundle unit 12 to be introduced to and removed
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~ therefrom as will become more apparent. Each of the
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~ openings 45 is provided with an appropriate seal 46 to
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~! ~ ~ seal these openings as will become more apparent.
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As best seen in Figs. 2 and 4, a tube bundle slide ~ ;
`- angle 50 is mounted on the lower inside of each central
section 21 of the side walls 20 in alignment with the op- f ~-
posed cross plates 24. These slide angles 50 serve to ~
support the tuhe ~undle unit 12 as it slides into or out ~ -
.
; of the housing 11 as will become more apparent.
The tube bundle unit 12 as best seen in Figs. 1, 2
and 4 includes a tube frame 55 which mounts the tube bun-
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dle 56 thereon about a longitudinal axis ATB. The tube
frame 55 includes a pair of spaced apart tube sheets 60
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with a generally rectilinear shape. The tube sheets 60 are
held in position by a pair of upper side members 61 and a
pair of lowcr siclc members 62 which extend between the cor-
ners of sheets 60. The side members 61 and 62 are oriented
generally parallel to each other and define the side cor-
ners of the frame 55. The frame 55 has a width W4 and
height H4 such that the frame 55 will just slidably pass
through thc access openings 25 in housing 11 as seen in
~ig. 1. The tube sheets 60 are spaced apart so that the
opposed inside surfaces 64 thereof are spaced apart a dis- .~.
tance dl substantially equal to the length Ll of the main
fluid passage 28 in housing 11 as seen in Fig. Z. Thus,
when the frame 55 is in position in housing 11, the in- :
side surfaces 64 of the tube sheets 60 are in registra- :
tion with the main fluid cross plates 26 so that the main
fluid passage 28 is about the same size all the way through
the exchanger 10 when the frame 55 is in place. The ends
of the side members 61 and 62 extend outboard of each of
the tube sheets 60 into the tube end subchambers 30 when
frame 55 is in place as seen in ~ig. 2. The lower side
members 62 are supported by the lower end tube subchamber
cross plates 24 and the slide angles 50 extending between
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cross plates 24. Appropriate seals STs may be provided
, along the edges of the tube sheets 60 between side mem-
: bers 61 and 62 to form a seal with cross plates 24 and
side wall extension 22 and thus separate the end tube sub-
chambers 30 from the main gas passage 28. .'
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10863~Z
The tubc bundle 56 is mounted on the tube sheets 60
so that the straigllt heat exchange tube; 65 extend between
the tube sheets 60 while the tube ends 66 connecting
tubes 65 are outboard of tube sheets 60. Thus, when the
tube bundle unit 12 is in position as seen in Fig. 2, the
heat exchange tubes 65 extend across the main fluid pas-
sage 28 while thc tube ends 66 are located in the tube
end subchambers 30. The main fluid flowing through the
passage 28 will be placed in a heat exchange relationship
with the exchanger fluid flowing through the heat ex-
change tubes 65. The first and last row of tubes 65 are
connected to headers 68 so that the heat exchange fluid
can be introduced into and removed from the tube bundle 56.
Each of the headers 68 has an inlet pipe 69 thereto which
extends through the header openings 45 so that the tube
~ ~; bundle 56 can be externally connected when the tube bun-
¦~ dle unit 12 and the front cover panel 40 are in place as
seen in Fig. 2. The seals 46 seal the openings 45 to
-~ pipes 69. Usually, the pipes 69 are provided with screw-
on flanges 70 to connect the pipes 69 to external piping
3~ P. The screw-on flanges 70 are, of course, removed to
permit the front cover panel to be removed when the tube
bundle unit 12 is to be removed. ~ ~
~ ~ It will be seen that the tube bundle unit 12 may be -
l installed along its longitudinal axis as shown or, Wit}l ~:
appropriate relocation of cover panels 40 and 41, installed
along its lateral axis normal to the main fluid flow.
Also, it is necessary that only one cover panel need be
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1086302
provided rather than the two panels 40 an~ 41 as illus-
trated. Further, one of the cover panels 40 and 41 may
be fixed to the tube bundle unit 12 so that when the tube
bundle unit 12 is in place, the cover panel on the trailing
end of the unit 12 will appropriately seal the access open-
ing 25 through which the tube bundle unit 12 is installed.
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1~136302
OPERATION
In operation, it will be seen that the housing 11
is installed in conventional manner in the ductwork D as
best seen in Figs. 2-4. The housing 11, of course, is ;
installed without the tube bundle unit 12 in place in
the housing 11 and without the front and rear~cover panels
40 and 41 in place. This makes the housing 11 relatively
lightweight thereby reducing to a minimum the personnel
and equipment necessary to install the housing 11. ,
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After the housing 11 is installed, the tube bundle
unit 12 is then installed. The tube bundle unit 12 is
placed in the housing 11 by picking same up with appro-
priate equipment usually available at the installation
I; site and placing one end of the tube bundle unit in one
j ~ of the access openings 25 so that the lower side members
62 rest on the lower cross plate 24 at that access opening. -~
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The tube bundle unit 12 is positioned so that its axis ATB
is coaxial with the axis A of the subchambers 30 and
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J;~ ~ then the tube bundle unit 12 is pushed into the housing 11
20~ with the lower side members 62 being supported on the end
tube subchamber cross plates 24 and the tube bundle slide
~; angles 50 therebetween. When the tube bundle unit 12 is
pushed into the housing so that the inside surfaces 64 of
the tube sheets 60 align with the main fluid passage 28
through the housing 11, the tube bundle unit 12 is in
`' place. The seals STs on the tube sheets 60 seal the end
tube subchambers 30 from the main fluid passage 28. If
the screw-on flanges 70 on the inlet pipes 69 to headers
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~8630Z
68 are in place, they are removed and the front and rear
cover panels 40 and 41 are attached using the fasteners
42. If accessory equipment such as a soot blower is to
be mounted, it is usually mounted through an appropriate
hole in one of the tube sheets 60 before the cover panels
40 and 41 are attached. After the cover panels 40 and 41
are attached, the screw-on flanges are re-attached so
that the piping P can be connected to the inlet pipes 69
on headers 68. The heat exchanger 10 is now ready for
operation. To remove or replace the tube bundle unit
12, it will be seen that this process is simply reversed.
If the repair of the tube bundle unit 12 will result
in considerable down time of the equipment with which the
heat exchanger 10 is being used, then the removed cover ~-
panels 40 and/or 41 may be replaced without the tube bundle
unit 12 in housing 11. This will allow the operation of
, the equipment to continue even though the tube bundle unit
12 is not operational. When the tube bundle unit 12 is
repaired, it can then be replaced and its operation con-
tinued.
10863(~2
ECONOMIZER INSTALLATION
The heat exchanger 10 is shown incorporated in a re-
circulating economizer ER in Figs. 2 and 3. As shown in
Fig. 3, the economizer ER is shown mounted on a conven-
tional steam boiler B with the flue gas ductwork D and
a feedwater inlet connection FC so that feedwater can be
supplied to the steam boiler from a feedwater source FS
as is normally required in steam boiler operation. The
feedwater from the feedwater source FS is supplied to the
boiler B under pressure by feedwater pump PF seen in Fig.
3. The heat exchanger 10 is connected to the feedwater
pump PF through the piping P and also to the feedwater
connection FC on the boiler B. The heat exchanger 10 is ~
plumbed in Figs. 2 and 3 in a counterflow configuration so ~ -
that the cooler feedwater from the pump PF enters the tube
bundle unit 12 on the downstream side of the main fluid
passage 28 through the heat exchanger 10. This makes the
upper header 68 in Fig. 2 the inlet header and the lower
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header 68 the outlet header as labelled in Figs. 2 and 3.
Pipe Pl as seen in Fig. 3 connects the feedwater water
pump PF directly to the inlet header 68 in the heat ex-
changer 10 while pipe P2 connects the outlet header 68 to
the inlet I of a three-way flow diversion valve VR. One
outlet l of the diversion valve VR is connected by pipe
P3 to the feedwater connection FC on boiler B. The other
outlet 2 of the flow diversion valve VR is connected to
the inlet side of a recirculating pump PR by pipe P4 as
seen in Fig. 3 while the outlet side of the recirculating
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pump PR is connected back to the inlet header of the
exchanger lO through pipe P5. If it is desirable to con-
tinuously operate the pump PR, a short pipe P6 with an
i orifice OR interposed therein may be used to connect the
' outlet header 68 of the heat exchanger 10 directly to
the inlet side of the recirculating pump PR bypassing
valve VR with a very small flow of heat exchanger fluid
just sufficient to keep pump PR cool.
The flow diversion valve VR has an actuator A which
', 10 selectively divides the flow of the feedwater through the
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valve VR from the inlet I so that the amount of feedwater
~ flowing out the outlet l and the amoùnt of feedwater : -
'. flowing out the outlet 2 is selectively controlled. : -: While any number of flow dividing valve constructions may
be used, the valve VR illustrated is a pneumatically ope- C
rated proportioning valve which proportions the flow be-
tween the outlets l and 2' To supply the pneumatic
control pressure to operate the actuator A on valve VR,
.~ an electrical-to-pneumatic transducer Tcp may be used
: 20 which produces an output pressure-to the actuator A as ~ ~
~ seen in Fig. 2 in response to the electrical signal re- :
- ~ ceived by the transducer Tcp. The control for the trans-
.diucer.~Tc~p..i-s provlded by an ar~rag~ng thermocouple TA~.
i seen in Fig. 2 which is inserted into the ductwork D on
the downstream side of the main fluid passage 28 through
the heat exchanger 10. The thermocouple TAV provides an
electrical output signal that is controlled by the average
temperature of the flue gases passing out of the heat
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1086302
exchanger 10 and is connected to an appropriate thermo-
couple set poin~ controller Csp designed to operate with
the averaging thermocouple TAV. The controller Csp pro-
duces an electrical output which is indicative of the
average flue gas temperature above or below a particular
set range manually set on controller Csp as it passes out
of the heat exchanger 10. The transducer Tcp receives
this electrical signal from the controller Csp and con-
verts this signal into a pneumatic output to the actuator
A on valve VR which is responsive of the average flue gas
temperature passing out of the heat exchanger 10.
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If the temperature of the flue gases passing out of
the heat exchanger 10 drops below the predetermined value
manually set on controller Csp, the transducer Tcp ope-
rates the valve VR so that a certain portion of the feed- ~ `
water flowing in the inlet I of valve VR is diverted out
the outlet 2 through the recirculating pump PR and back
into the inlet header of the heat exchanger 10 so that the
inlet temperature of the feedwater including the recircu-
lation is raised. The remainder o~ the feedwater that :
does not need to be recirculated passes out of the outlet
l to the feedwater connection FC on the boiler B. This
serves to regulate the flow of the feedwater in such a way
that the average outlet temperature of the flue gases from
the heat exchanger 10 will be maintained above a prescribed
value to prevent condensation of the corrosive chemical com-
pounds in the flue gases on the heat exchange tubes 65 in
the tube bundle 12 and the attendant corrosion thereof.
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108630Z
The dew point of the flue gases from the boiler B is
determined primarily by the sulfur content of the fuel
being burned therein, and the sulfur content in the fuel
varies between the different geographical sources of the
fuel. Usually, the user knows the critical dew--point of
the flue gases from information provided by the source
of the fuel and can then adjust the controller Csp each
time the sulfur content in the fuel varies to make sure
that the average outlet flue gas temperature is above its
dew point after passage through the heat exchanger 10.
The heat exchanger 10 is shown incorporated in a by- .
pass economizer EB in Fig. 5. The economizer EB would be
mounted in the flue gas ductwork on a conventional steam
.~oiler.~B s~imilarly to economize~ R~. The :fee-d~ater und~
pressure from the feedwater source FS is supplied directly
to the inlet header 68 on heat e~changer 10. The outlet
: header 68 on heat exchanger 10 is connected to one inlet
Il on a three-way diversion valve VB whose outlet 0 is con-
nected to the feedwater connection FC on boiler B. The
other inlet I2 on valve VB is connected to the feedwater
source FS in parallel with the tube bundle 56 in heat
exchanger 10. The valve VB serves to selectively divide
the flow of the feedwater from source FS between that
flowing through the tube bundle 56 and that bypassing the
tube bundle 56. The valve VB has an actuator A similar to
that of the valve VR.
The economizer EB also uses an average thermocouple
TAV, a set point controller Csp and a transducer Tcp to
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control the actuator A on valve VB. Thus, it will be
seen that the controller Csp can be adjusted so that the
feedwater flowing through the tube bundle 56 and bypassing
the tube bundle 56 can be proportioned by the valve VB in
response to the outlet temperature of the flue gases after
passage about the tube bundle 56 to maintain the flue
gases within a prescribed temperature range. As the load
on the boiler B varies, the temperature of the flue gases
passing through the ductwork D also varies; however, the
output from the thermocouple TAV controls the three-way
valve VB in such a way that the feedwater flow is con-
'; trolled to maintain the flue gas temperature after pas-
i` sing through the tube bundle 56 in heat exchanger 10 at
a prescribed value to prevent cond0nsation of the corro-
sive chemical compounds in the flue gases on ~e heat ex-
change tubes 65 and the attendant corrosion thereof.
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