Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The invention relates generally to the con-
struction of a forced flow fluid heating unit, and more parti-
cularly to improvements in the construction and arrangement
~ of fluid heating circuits especially adapted for use as a
- furnace waIl support.
~ The present invention is directed at improvements
in the construction of forced circulation once-through vapor
generators of the type disclosed in U.S~ Patents No. 3,665,893
and 3,834,358 wherein the upright boundary walls of the fur-
nace are subdivided into upper and lower portions and include
at least one separate continuous upflow fluid heating pass in
each of the wall portions with tube segments of the separate
fluid heating passes forming a common plane wherein they are
interlaced and coextensive, while above and below this common
plane, the tubes are bent outwardly of the plane of the wall -
and connected to suitably arranged headers which allow for
equalization of enthalpies as the fluid flows from one heat-
~` ing pass to the other.
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The construction of walls of the character des- -
cribed is costly and-time consuming in that it requires the
individual bending of relatively short tube lengths and the
; - manual welding of each of these tube lengths above and below
the common plane formed by the interlaced tube segments of
': the fluid heating passes.
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SUMMARY OF THE INVENTION
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The present invention relates to a forced cir-
~- culation fluid heating unit having a furnace chamber bounded
;~ by upright walls formed with upper and lower portions and
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~ 30 including mixing headers receiving fluid from the lower wall
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Case 4078
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portions and discharging the mixed fluid to the upper wall
portions.
In accordance with the invention, the upper and
lower furnace wall portions are formed of panels of upwardly
extending laterally spaced tubes rigidly united throughout
most of their length. Some of the tube panels of the upper
and lower wall portions are bent out of the plane of the wall
at first and second levels, respectively, for connection to
the mixing headers and are interlaced with each other in the
plane of the wall between the first and second levels. The
remaining tube panels of the upper and lower wall portions
are bent out of the plane of the wall at about the second
and first levels, respectively, for connection to the mixing
headers. The interlaced panel segments of the upper and
lower furnace wall portions are rigidly united to transmit
the load of the lower wall portion to the upper wall portion.
The present invention realizes substantial time
and cost savings by providing shop assembled panels of
parallel coplanar tubes with the tubes of each panel being
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rigidly united through machine welding of webs therebetween
and being collectively bent out of the intended plane of the
wall.
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- BR~EF DESCRIPTION OF THE DRAWINGS
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Figure 1 is a sectional side elevation of a once-
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through forced flow vapor generator embodying the invention;
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` Figure 2 is an enlarged front view of a portion
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of the fluid collection, mixing and distribution system
~: shown in Figure l;
Figure 3 is an enlarged side view of that portion
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of the system shown in Figure 2;
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Case 4078
- 1~54467
Figure 4 is an enlarged front view of a portion
of an alternate fluid collection, mixing and distribution
system;
Figure 5 is an enlarged side view of that portion
of the system shown in ~igure 4;
~- Figure 6 is a detail side view of the wall sealing
- arrangement used with the fluid collection, mixing and
- distribution system;
Figure 7 is a view taken along line 7-7 of
figure 6;
Figure 8 is a view taken along line 8-8 of
;- figure 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
.
In the drawings, the invention has been illustrated
as embodied in a top-supported forced flow once-through
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vapor generator intended for central station use. The main
portions of the unit, as illustrated in Figure 1, include
an upright furnace chamber 10 of substantially rectangular
horizontal cross section defined by a front wall 11, rear
wall 13, side walls 1~, a roof 16 and a hopper 17. The
upper end of the furnace chamber 10 is formed with a gas
outlet 18 opening to a horizontally extending gas passageway
19 of rectangular vertical cross section and defined by a
floor 21 and extensions of the furnace roof 16 and side walls14
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and20. megas passageway 19 communicates at its rear end with
the upper end of an upright gas passageway 22 of rectangular
horizontal cross section and defined by a front wall 23, a
rear wall 24, side walls 26, and an extension of the roof of
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;~ gas passageway 19.
The fuel firing section comprises vertically spaced
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C~se 4078
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rows of burners 27 disposed on opposite walls 11 and 13 at
the lower portion of furnace chamber 10.
The gas passageway 19 houses a secondary super-
heater 28 and a reheater 29 disposed ln series wlth respect
to gas flow while gas passageway 22 houses a primary super-
: heater 33 and an economizer 34 disposed in series with respect
to gas flow.
- In the normal operation of the vapor generator,
combustion air and fuel are supplied to the burners 27 and~- 10 the fu-el is burned in the lower portion of furnace chamber 10.
The combustion gases flow upwardly through chamber 10 to the
furnace outlet, thence over and between the tubes of secondary
superheater 28 and reheater 29 in gas passageway 19 and over ~-
and between the tubes of primary superheater 33 and economizer
34 in gas passageway 22, and then to air preheaters, not
shown, before discharge to a stack, not shown. Itshould be
recognized that in accordance with well known practice, each
of the superheated and reheater sections extends across the
full width of its corresponding gas passageway and is formed
for serial flow of steam through multiple looped tubes.
The vapor generator se~ting is top supported by
structural members including upright members 85 and girders
`- 90 from whence hangers 95, of which only a few are illustrated
v. support the walls and convection surfaces.
;. ~eedwater at high pressure is supplied by one or
more pumps, not shown, to the economizer inlet header 25 for
passage through the tubes of economizer 34 to the outlet
- header 30, from whence it is conveyed by one or more down-
comers 35 to the boundary wall fluid heating circuitry of
` 30 the furnace chamber 10.
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The upright boundary walls of passageways 19 and
22 are of gastlght construction and include the front wall
23 having tubes 71 extending between the inlet and outlet
headers 72 and 73. The rear wall 24 has tubes 74 extend-
ing between the inlet and outlet headers 76 and 77. The side-
walls 26 have tubes 78 extending between the inlet and out-
let headers 79 and 81, and the sidewalls 20 have tubes 82
extending between the inlet and outlet headers 83 and 84.
The floor 21 is lined by a row of tubes 86 having their inlet
: 10 ends connected to the header 57 and their outlet ends to the
header 73, with the latter being connected to the header 88
through a row of screen tubes 89.
The headers 72, 76, 79 and 83 are connected for
parallel supply of fluid from roof header 50 through the
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conduit 69, while the headers 77, 81, 84 and 88 are connected
- for discharge to a collector header 91 from whence fluid
passes to the primary superheater 33 via conduit 920 The
superheated vapor passes from the primary superheater 33 to
the secondary superheater 28 wherein it is further super-
heated before passing to a high pressure turbine, not shown.
The partially expanded vapor exiting from the high pressure
turbine passes through the reheater 29, and from there to
a low pressure turbine, not shown, wherein final expansion
takes place.
Each of the upright boundary walls of furnace 10
is formed by upwardly extending parallel tubes arranged to
provide three upflow fluid heating passes and having their
intertube spacing closed by metallic webs welded to adjacent
tubes to provide a gastight construction. The first two
fluid heating passes comprise a first group of tubes and
form the lower portion of each furnace wall and the third
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105~ ;7
fluid heating pass comprises a second group of tubes and
forms the upper portion of each furnace wall. Special
header provisions are made for mixing the heat absorbing
mediu~ intermediate its flow from one pass to another, the
mixing system from each of the fluid heating passes being
specifically directed at keeping the wall tube temperature
differentials across the width of the furnace walls to a
minimum. With differences in furnace cleanliness as well
as in the flow rates through the multiple parallel fluid -
flow paths it is possible to develop temperature differences
between adjacent tubes of a magnitude sufficient to induce
high stresses in the tubes and in the metallic webs there-
between. By limiting the total absorption in a fluid heat-
ing pass, the degree of thermal imbalance within the tubes
comprising the parallel flow paths is also limited. Accord-
ingly, the boundary wall of the furnace is designed so that
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the temperature at a particular level of furnace height or
elevation differs by no more than 100F from the calculated
average fluid temperature of all furnace wall tubes at that
level, thus, calculated maximum temperature differential
between adjacent tubes is below the predetermined critical
limit to minimize the effect of fluid flow imbalances; and so
that the tubes of each fluid heating pass are sufficient in
flow area to provide an adequate circulation rate. Furthermore,
all heated tubes of the furnace boundary walls are arranged for
upflow of fluid, since flow stability within heating passes
having their tubes so arranged is mar~edly improved over
that condition whereflow circuitry has heated downflow as
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well as upflow tubes. In other words flow imbalances for
the same average and upset heat absorption conditions are
considerably less severe with all upflow tubes than with
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. both upflow and downflow circuitry within a heat absorbing
zone.
The front wall 11 includes first pass upflow tubes
37A, 37A', second pass upflow tubes 37B~ 37B', and third
. pass upflow tubes 37C, 37C'. The rear wall 13 includes first
pass upflow tubes 38A, 38A' second pass upflow tubes 38B,
.
.. - 38B', and third pass upflow tubes 38C, 38C'.Some of the latter
tubes form a screen 42 ahead of gas passageway 19 and the
remainder form a furnace nose arch 41. Each sidewall 14 in-
~. 10 cludes first pass upflow tubes 39A, 39A', second pass upflow
.~ tubes 39B, 39B' and third pass upflow tubes 39C, 39C'.
.,
,~ The first pass upflow tubes 37A, 37A', 38A, 38AI
- and 39A, 39A' have the lower ends connected to inlet headers
~ 44 associated with the corresponding walls The tubes 37A,
:;-~ 38A and 39A have their upper ends connected to outlet headers
~:.
-~ 45, whereas the tubes 37AI, 38AI and 39A' have their upper
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;: ends connected to outlet headers 45A located superjacent to
the headers 45.
The second pass upflow tubes 37B, 37B', 38B, 38B'
~` 20 and 39B, 39B' have their lower ends connected to inlet
. headers 52 associated with the corresponding walls. The
tubes 37B, 38B and 39B have their upper ends connected to
outlet headers 53, whereas the tubes 37B', 38B' and 39BI
~: have their upper ends connected to outlet headers 53A located
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;.~ superjacent to the headers 53.
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: The third pass upflow tubes 37C, 38C and 39C have
.` their lower ends connected to inlet headers 57, and the
~- third pass upflow tubes 37CI, 38CI and 39CI have their lower
.~. ends connected to inlet headers 57A located superjacent to
the headers 57. The tubes 37C and 37CI have their upper
ends connected to the furnace roof supply header 58. Some
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Case 4078
10544~;7
of the tubes 38C and 38C ' have upper ends connected to the
tube screen inlet header 73 and the remaining tubes 38C and
38C' have their upper ends connected to the tube screen outlet
header 88. The tubes 39C and 39C ' have their upper ends
connected to outlet headers 63.
A conduit 35 supplies fluid from the economizer 34
to the inlet headers 44, from whence it is conveyed through
the first pass upflow tubes 37A, 37A ', 38A, 38A ' and 39A, 39A '
and is collected at the first pass outlet headers 45 and 45A,
and thence conveyed through conduits 51 and 51A to second pass
- inlet headers 52 associated with the corresponding walls.
Fluid from the headers 52 is conveyed through the second pass
upflow tubes 37B, 37B ', 38B, 38B ' and 39B, 39B ' and is collected
. at the second pass outlet headers 53 and 53A, and thence con-
veyed through conduits 48 and 48A to third pass inlet headers
57 and 57A. The fluid flowing through the conduits 48 and ~ :
48A could be directed to one or more larger headers, not shown,
.~ for further mixing prior to introduction into the corresponding
third pass inlet headers 57 and 57A. Fluid from the headers
57 and 57A, associated with the rear wall 13, is conveyed
through the third pass upflow tubes 38C and 38C', respectively,
and is collected at the tube screen headers 73 and 88.
Fluid from ,he headers 57 and 57A, associated with the front
wall 11, is conveyed through the third pass upflow tubes 37C
and 37C ', respect~vely, and is collected at the roof supply
header 58. Fluid from the headers 57 and 57A, associated with
the side walls 14, is conveyed through the third pass upflow
tubes 39C and 39C ', respectively, and is collected at the out-
let headers 63.
; 30 From the foregoing description, it is evident that
tubes 37A, 37A ', 38A, 38A ' and 39A, 39A ' constitute the first
fluid heating pass, tubes 37B, 37B', 38B, 38B' and 39B,
39B ' constitute the second fluid heating pass, and
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Case 4078
1~544~
- tubes 37C, 37C I 3 3~C, 38C' and 39C, 39C~ constitute the
: third fluid heating pass. The tubes of the first fluid
heating pass are disposed in spaces between tubes of the
second fluid heating pass and have their intertube spaces
j closed by metallic webs, weld-united to the tubes along
-- substantially their entire parallel lengths so that each
web is welded to one of the tubes of the first heating pass
- and to one of the tubes of the second heating pass. Tubes
of the third fluid heating pass, with the exception of the
screen portions, have ~heir intertube spaces closed by
,
; metallic webs weld united to the tubes. The tubes of the
first and second fluid heating passes are coplanar along
- almost their entire length within their respective walls and
are also coplanar with the tubes of the associated third
fluid heating passes of the corresponding wall except for
. portions of the rear wall.
5ince the construction and arrangement of the
fluid collection, mixing and distribution system and their
associated tubes are substantially the same for all of the
furnace walls, it will suffice to describe the system corres-
ponding to the front wall 11.
; Referring to Figures 2 and 3, there are shown frag-
mented sectional views of the front wall 11 including the
-- panels 137AB whose first and second pass tubes 37A and 37B
have their upper end portions bent outwardly from the plane
of the wall at about the first level lOlA and extending down-
wardly for connection to individual corresponding first and
second pass outlet headers 45 and 53, respectively, and the
panels 137A'B' whose first and second pass tubes 37A' and 37B'
have their upper end portions bent outwardly from the plane
- of the wall at the second level 102 and extending downwardly
for connection to individual corresponding first and second
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1~5~467
pass outlet headers 45A and 53A, respectively. The fluids
collected in the first pass outlet headers 45 and 45A are
passed, via conduits 51 and 51A to the second pass inlet
; headers 52. The fluids collected in the second pass outlet
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headers 53 are passed, via conduit 48, to corresponding third
pass inlet headers 57 for distribution to the panels 137C
whose third pass tubes 37C have their lower end portions ex-
~ tending, from individual corresponding inlet headers 57, hori-
- zontally inward and bent upwardly to enter the front wall 11
at the first level 101 from whence they extend upwardly in
:- the plane of the wall. The fluids collected in the second
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pass outlet headers 53A are passed via conduit 48A to corres-
ponding third pass inlet headers 57A for distribution to the
panels 137C' whose third pass tubes 37C'have their lower end
portions extending, from individual corresponding inlet
headers 57A, horizontally inward and bent upwardly to enter
the front wall 11 at about the second level 102A from whence
they extend upwardly in the plane of the wall. Metallic webs
55 close the intertube spaces and are normally seal welded to
the adjoining tubes.
An alternate embodiment of the fluid collection,
mixing and distribution system is illustrated in Figures 4
and 5 and has each of the upright boundary walls of the fur-
.nace formed by upwardly extending parallel tubes arranged to
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provide two upflow fluid heating passes. The first fluid ~
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heating pass comprises a first group of tubes and forms the
~`i lower section of each furnace wall and the second fluid heat-
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ing pass comprises a second group of tubes and forms the
,~ upper portion of each furnace wall.
Since construction and arrangement of the fluid
collection, mixing and distribution systems and their
associated tubes are substantially the same in all walls,
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: Case 4078
54~67
- it will suffice to describe the system corresponding to the
. .
- front wall 11.
Referring to Figures 4 and 5, there are shown frag-
mented sectional views of the front wall 11 including the
panels 140A whose first pass tubes 40A have their upper end
q portions bent outwardly from the plane of the wall at about
the first level lOlA and extending downwardly for connection
to individual corresponding first pass outlet headers 42,
and the panels 140A' whose first pass tubes 40A' have their
upper end portions bent outwardly from the plane of the wall
at the second level 102 and extending downwardly for connection
to individual corresponding first pass outlet headers 42A.
- The fluids collected in the first pass outlet headers 42 are
` passed, via conduit 36, to corresponding second pass inlet
headers 43 for distribution to the panels'140B whose second
pass tubes 40B have their lower end portions extending from
individual corresponding inlet headers 43 horizontally inward
and bent upwardly to enter the front wall 11 at the first
level 101 ~rom whence they extend upwardly in the plane of-the
wall. The fluids collec~ed in the first pass outlet headers
42A, are passed via conduit 36A to corresponding second pass
inlet headers 43A for distribution to the panels 140B' whose
second pass tubes ~OB' have their lower ends extending from
individual corresponding inlet header 43A horizontally inwardly
to enter the front wall 11 at about the second level 102A
from whence they extend upwardly in the plane of the wall.
Metallic webs 55 close the intertube spaces and are normally
seal-welded to the adjoining tubes. The alternative embodi-
ment is shown with second pass tubes 40B and 40B' having a t
' 30 larger diameter and wider intertube spacing as compared to
the first pass 40A and 40A', however, it should be recognized
that other combinations of tube sizing and spacing may be
used with the invention.
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Case 4078
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- Referring to Figures 6, 7 and 8, there are shown
sectional side, plan and front views, respectively, of a
sealing arrangement provided at the crotch formed between
the levels 102 and 102A. It should be recognized that the
sealing arrangement depicted herein is equally applicable
~ to the crotch formed by the tube bends at levels 101 and
; lOlA and those formed at like le~rels for the alternate embodi-
ment. Accordingly, there are shown the panel 137G whose
- tubes 37C extend upwardly in the plane of the front wall 11,
the panel 137AB' whose tubes 37A' and 37B' have their upper
end portions bent outwardly from the plane of the wall at
the second level 102, and the panel 137C' whose tubes 37C'
have their lower end portions bent outwardly from the plane
of the wall at about the second level 102A. The crotch seal-
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- ing arrangement between the levels 102 and 102A includes a
seal box 59 defined by a slotted plate 60 and flat plates
:
61, a side plate 63, and back plates 64, the latter being
curved to follow the contour of the bent portions of tubes 37A ~, ;
37B' and 37C'. The box 59 is packed with refractory material
- 2~ 65 to provide a gastight seal at the juncture of panel 137C
and the bent tube portions of panels 137A'B' and 137C' between
`~ the levels 102 and 102A. Plate inserts 66 are Iitted between
,.- . - .
~- adjacent tubes and are weldably connected thereto and to a
`~ rod 67 which seals the crotch formed by the bent portions of
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~ tubes 37A', 37At and 37ct. Additional inserts 66 and flat
r,`, bars 6l3 are provided to connect the seal box 59 with the
adjoining tube panels.
By way of example and not of limitation, and
- with reference to the main embodiment, each of the panels
~?`; 30 in the upper and lower furnace wall portions is approximately
- 64 inches wide and contains 37 tubes of 1.25 inch outside
; diameter which are spaced on 1.75inch centers. The alterr~ate
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embodiment has panels of the same width as the main embodi-
`~ ment, however, each of the panels in the upper furnace wall
portion contains 28 tubes of 1.5 inch outside diameter which
are spaced on 2.25 inch centers.
While in accordance with provisions of the
statutes there is illustrated and described herein a speci-
fic embodiment of the invention, those skilled in the art
. will understand that changes may be made in the form of the
invention covered by the claims, and that certain features
of the invention may sometimes be used to advantage without
a corresponding use of the other features.
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