U.S. patent number 3,812,907 [Application Number 05/251,238] was granted by the patent office on 1974-05-28 for heat exchangers.
This patent grant is currently assigned to United Kingdom Atomic Energy Authority. Invention is credited to David Lees Linning.
United States Patent |
3,812,907 |
Linning |
May 28, 1974 |
HEAT EXCHANGERS
Abstract
In a tube-in-shell heat exchanger, each tube plate is secured
along its outer edge to the shell of the heat exchanger by an
intermediate annular member extending across a gap between the
outer edge of the tube plate and the shell, the radial
cross-section of the annular member being of arched form. Thermal
insulation for the tube plates consisting of a series of plate
members edge on to the tube plate and arranged parallel one to
another between successive rows of the heat exchanger tubes, is
also described.
Inventors: |
Linning; David Lees
(Warrington, EN) |
Assignee: |
United Kingdom Atomic Energy
Authority (London, EN)
|
Family
ID: |
10092682 |
Appl.
No.: |
05/251,238 |
Filed: |
May 8, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Jun 25, 1971 [GB] |
|
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21315811/71 |
May 26, 1971 [GB] |
|
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17295/71 |
|
Current U.S.
Class: |
165/83; 165/158;
165/DIG.61; 165/134.1 |
Current CPC
Class: |
F28F
9/0219 (20130101); Y10S 165/061 (20130101) |
Current International
Class: |
F28F
9/02 (20060101); F28g 007/00 () |
Field of
Search: |
;165/158,9,83,181,67-69,178 ;122/32L,32T,32S,32F |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Streule, Jr.; Theophil W.
Attorney, Agent or Firm: Larson Taylor & Hinds
Claims
I claim:
1. In a tube-in-shell heat exchanger in which a bundle of parallel
heat exchanger tubes extend between tube plates at either end of
the bundle, said tubes being connected with holes in the tube
plates, and a shell within which said bundle of tubes is disposed
with means for securing said tube plates to said shell, the
improvement wherein said means for securing each tube plate to said
shell comprises an annular member intermediate each said tube plate
and said shell, said member being secured to the outer edge of the
respective tube plate and to said shell to extend across a gap
therebetween, and the radial cross section of said annular member
being of arched form.
2. A heat exchanger according to claim 1, characterised by the
radial cross section of said member being semi-circular.
3. A heat exchanger according to claim 2, characterised in that
said annular member is arranged so that its inner and outer edges
are substantially in the plane in which the respective tube plate
lies and are joined with said tube plate and said shell by
welding.
4. A heat exchanger according to claim 1, characterised by said
annular member being made of laminated form.
5. A heat exchanger according to claim 1, characterised by said
tube plates each having thermal insulation comprising a series of
individual and mutually isolated plate members edge on to the
respective tube plate and arranged parallel to one another between
successive rows of the heat exchanger tubes.
6. A heat exchanger according to claim 5, characterised by said
plate members being plane for extending in straight runs between
said tubes.
7. A heat exchanger according to claim 5, characterised by said
plate members being of convoluted form for extending between said
tubes where these are closely pitched.
8. A heat exchanger according to claim 5, characterised by said
plate members being supported from their ends by a ring mounted on
the face of the respective tube plate and encircling said heat
exchanger tubes.
9. A heat exchanger according to claim 1 wherein the inner
periphery of said annular arched member is secured to the outer
edge of the respective tube plate, and the outer periphery of said
member is secured to said shell.
Description
BACKGROUND OF THE INVENTION
This invention relates to heat exchangers and in particular to that
kind of heat exchanger in which a bundle of parallel heat exchanger
tubes extend between tube plates at either end of the bundle. The
heat exchanger tubes are connected at their ends with holes in the
tube plates, for example by welding. The bundle of heat exchanger
tubes is disposed within an outer shell or container to which the
tube plates are secured.
In one use of such a heat exchanger, for example, as a steam
generator or steam superheater, a liquid metal heat transfer
medium, such as sodium, is passed through the shell over the tubes
and water, for steam generation, or steam for superheating is
passed through the tubes. In this case the heat exchange is between
fluids which will react violently if they come into contact for
example by escape of steam or water into the bulk sodium in the
shell through a faulty tube/tube plate weld. Current designs of
sodium/water heat exchangers rely on the excellence of tube and
tube/tube plate weld production and inspection to provide a high
degree of integrity. However, the possibility of a major sodium
water reaction has to be allowed for and it is therefore necessary
to design the heat exchanger shell to withstand the substantial
internal pressures which would arise on the occurrence of such a
reaction. Thus the heat exchanger shall and the tube plates have to
be made of considerable thickness.
Copending U.S. Pat. application Ser. No. 20,903, now U.S. Pat. No.
3,680,627 relates to a "tube-in-shell" type of heat exchanger in
which the high pressure water/steam is accommodated in the shell
and the sodium within the tubes, so that tube failure cannot
propogate by overheating and corrosion of further tubes adjacent to
the failed tube. In this case as the high pressure medium is
contained within the shell, the shell and tube plates again have to
be of considerable thickness to withstand the high internal
pressure.
Also in "tube in shell" type heat exchangers means have to be
provided to accommodate for differential longitudinal thermal
expansion of the tubes relative to the shell both on rise to the
steady thermal state and under transient conditions. This can be
achieved by making the tubes of U-shaped configuration within the
shell, with both tube plates located at the one end of the shell.
In another arrangement the tubes are of J or hockey stick
configuration within a shell of similar shape, so that the tube
plate at one end of the shell is in a plane at right angles to the
plane of location of the tube plate at the other end of the shell.
Both these solutions add to the cost and complication of
manufacture of such heat exchangers.
SUMMARY OF THE INVENTION
According to the present invention, in a "tube in shell" heat
exchanger, each tube plate is secured along its outer edge to the
shell of the heat exchanger by an intermediate annular member
extending across a gap between the outer edge of the tube plate and
the shell, the radial cross-section of the annular member being of
arched form.
Preferably the radial cross section of the annular member is
semi-circular so that the annular member is in the form of half of
a tubular toroid. The annular member is preferably arranged with
its inner and outer edges substantially in the plane in which the
tube plate lies, the inner and outer edges of the annular member
being joined with the tube plate and the shell by welding. The
arched radial cross section of the annular member makes it of a
high pressure containing capacity so that the annular member can be
made of relatively thin material. Thus the annular member has a
degree of flexibility in the direction normal to the plane of the
tube plate so that the tube plate can move longitudinally with
respect to the heat exchanger shell, to accommodate for relative
longitudinal thermal expansion between the heat exchanger tubes and
the shell. In order to increase the flexibility of the annular
member whilst retaining the pressure retaining capacity, the
annular member can be made of laminated form.
Furthermore, in such sodium/water heat exchangers of the "tube in
shell" type wherein heated sodium is passed through the heat
exchanger tubes and water is passed through the shell over the
tubes for the generation of steam, it is advantageous to also
provide thermal insulation on the faces of the tube plates inside
the shell, since the tube plates are simultaneously in close
thermal contact with sodium and water or steam. The thermal
insulation is effective to minimise steady state thermal stresses
in the tube plates as well as transient stresses due to sudden
changes in operating conditions. In particular the tube plate at
the steam outlet end of the heat exchanger shell, if uninsulated,
would be exposed to particularly severe conditions, since if the
steam were wet liquid droplets would impact on the tube plate
through which sodium is passing at the high inlet temperature.
A known form of thermal insulation structure comprises a number of
baffle plates arranged parallel to the tube plate and parallel to
each other. The baffle plates are drilled for penetration by the
tubes at their ends adjacent the tube plate and are arranged to
ensure that stagnant fluid, ie steam or water, is trapped in spaces
between the baffle plates to provide the required thermal
insulation.
This type of thermal insulation structure has a main disadvantage
of high cost of manufacture, since it is necessary to drill several
thousands of holes in the baffle plate for penetration of the
baffle plates by the ends of the heat exchanger tubes. The economic
penalty is particularly high where a high degree of thermal
insulation is required which is achieved by the provision of such a
thermal insulation structure consisting of a substantial number of
baffle plates. A further possible disadvantage stems from the fact
that the spaces between the tube plates have only limited access to
the main body of the heat exchanger shell. Thus rapid evaporation
of water in the spaces between the baffle plates, on start up of
the heat exchanger, or due to a transient change in the operating
conditions, might lead to a rapid pressure build up in the spaces
which cannot readily be relieved by venting from the spaces between
the baffle plates to the main body of the shell. Thus there could
be danger of local tube failure due to excessive pressure build
up.
According to a further feature of the present invention, the tube
plates of a "tube-in-shell" type heat exchanger as aforesaid have
thermal insulation comprising a series of plate members edge on to
the tube plate and arranged parallel one to another between
successive rows of the heat exchanger tubes. Where straight runs
exist between the rows of tubes the plate members can be of plane
form. In the case of a heat exchanger having closely pitched tubes
where no straight runs exist between the tubes the plate members
may be of convoluted form so as to fit between the rows of tubes.
This arrangement ensures that each heat exchanger tube at its point
of connection with the tube plate is enclosed in stagnant fluid
either steam or water according to the conditions, which is trapped
in the pockets defined between the plate members and the tubes.
Thus a change of conditions leading to rapid evaporation of water
trapped in the pockets cannot produce local excess pressure since
each of the pockets is fully open to the main body of the
shell.
The said thermal insulation also has the advantage of cheapness
since, for instance, it is not necessary to drill large numbers of
holes in a series of plates to produce the necessary baffles. The
degree of thermal insulation achieved is merely dependent on the
depth of the plate members. A high degree of thermal insulation can
be achieved by simply making the plate members of sufficient depth.
Also the thermal insulation of the invention is easy to assembly
with respect to the tube plates it merely being necessary to
interpose the series of plate members edge on to the tube plate
between parallel rows of the heat exchanger tubes. The plate
members forming the insulation may be supported from their ends by
a ring mounted on the face of the tube plate encircling the heat
exchanger tubes. Alternatively a supporting ring for the plate
members may be mounted around the inner wall of the heat exchanger
shell just beneath the level of the tube plate.
DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described by way of
example with reference to the accompanying drawings in which:
FIG. 1 is a longitudinal section of a heat exchanger incorporating
the present invention,
FIG. 2 is an enlarged longitudinal section illustrating a
modification of the tube/tube plate assembly of the heat exchanger
shown in FIG. 1,
FIG. 3 is a section along the line III--III in FIG. 2, and
FIG. 4 corresponds to FIG. 3 and shows, on a larger scale, a detail
of an alternative arrangement.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The heat exchanger shown in the FIG. 1 of the drawings comprises a
cylindrical shell 1 containing a bundle of parallel heat exchanger
tubes 2. The heat exchanger tubes 2 extend longitudinally through
the shell 1 between tube plates 3 located at each end of the shell
1. The heat exchanger tubes 2 are spaced and transversely located
in the shell 1, either by grids at spaced intervals along the
length of the tubes 1, or, alternatively, the tubes 2 may be spaced
by being wire wrapped or by integral fins on the tubes the tubes
being held together in the bundle by an outer wrapper arrangement
such as is disclosed in said copending application Ser. No.
20,903,
The shell 1 has an inlet branch 4 at its lower end and an outlet
branch 5 at its upper end. The tubes 2 extend through holes 6 in
the tube plate 3 at the upper end of the shell 1 and connect at
their upper ends with an inlet header 7. Similarly the tubes 2
extend through holes 6 in the tube plate 3 at the lower end of the
shell 1 and connect at their lower ends with an outlet header 8.
The tubes 2 are brazed in passage through the holes 6 in the tube
plates 3 and are also brazed at their ends in connection with the
inlet and outlet headers 7 and 8.
Each of the tube plates 3 is connected with the shell 1 in a
similar manner. Referring to the tube plate 3 at the upper end of
the shell 1, the tube plate 3 is of smaller outside diameter than
the internal diameter of the upper end of the shell 1 so that an
annular gap 9 exists between the outer edge of the tube plate 1 and
the edge of the shell 1. The gap 9 is bridged by an annular member
10 which is of semi-circular radial cross section. The member 10
may be described as being in the form of half a tubular toroid and
is made up of several nesting laminations 11. The member 10 is
joined at its inner edge 12 with the outer edge of the tube plate 3
by a weld 13. The member 10 is joined at its outer edge 14 with the
edge of the shell 1 by a weld 15.
In use of the heat exchanger, for example as a once through boiler,
water is passed into the shell 1 through the lower inlet branch 4
and steam is generated in the shell 1 by heat exchange with, for
example, heated sodium which is passed through the heat exchanger
tubes 2. The heated sodium is passed into the tubes 2 through the
upper inlet header 7 and after passing downwards through the heat
exchanger tubes 2 passes out through the lower outlet header 8.
Steam generated for example at a pressure of 2,500 psi in the shell
1 passes out of the shell 1 through the upper outlet branch 5.
There will be a high axial pressure force acting on the tube plates
3 but the heat exchanger tubes will carry the main part of this
axial pressure force by being under longitudinal tension. Therefore
the tube plates 3 can be of relatively small thickness, for example
3 inches as compared with a thickness of 12 inches which would be
required for tube plates which carry the whole of the internal
pressure back to the shell 1.
The shape of the annular members 10 makes it possible to contain
the high internal pressure in the shell 1 with a relatively small
thickness of metal in the annular members 10. Due to geometrical
factors and because the annular members 10 are of relatively thin
laminations 11 the annular member 10 have flexibility in the
direction of the longitudinal axis of the shell 1 ie in the
direction normal to the plane of the tube plates 3. This allows the
tube plates 3 to move longitudinally with respect to the heat
exchanger shell 1, by flexing of the annular members 10, to
accommodate for longitudinal thermal expansion of the heat
exchanger tubes 2 relative to the shell 1. Longitudinal thermal
expansion of the heat exchanger tubes 2 relative to the shell 1
occurs due to the temperature differential which arises between the
tubes 2 and the shell 1 on bringing the heat exchanger to its state
of operating temperature.
The heat exchanger of the invention has the advantage of ease of
assembly as the tubes 2 can be assembled with the tube plates 2
outside the heat exchanger shell 1 and the assembly of the tubes 2
and tube plates 3 can then be inserted into the shell 1 and the
tube plates 3 connected with the ends of the shell 1 by welding the
annular members 10 bridging the gap 9 between the tube plates 3 and
the ends of the shell 1. The laminations 11 of the annular members
10 may be welded individually one by one into position or
alternatively the laminations 11 may be welded to separate rings,
the rings being subsequently welded to the tube plates 3 and the
shell 1. This latter procedure eases the inspection and heat
treatment of the lamination welds.
The modified tube/tube plate assembly shown in FIGS. 2 and 3 of the
drawings comprises a tube plate 21 with which there is connected a
series of heat exchanger tubes 22. The heat exchanger tubes 22 are
arranged in a bundle parallel to one another and are welded at
their ends in connection with holes 23 in the tube plate 21. A heat
insulation structure for the under face of the tube plate 21
comprises a series of parallel plates 24 arranged edge on to the
face of the tube plate 21. The plates 24 are interposed between
parallel rows of the heat exchanger tubes 22. A supporting ring 25
for the plates 24 is welded to the face of the tube plate 21
encircling the bundle of heat exchanger tubes 22. The ends of the
plates 24 rest on an internal flange 26 at the bottom of the ring
25. The bundle of heat exchanger tubes 22 is fitted inside the
shell 1 (FIG. 1) to which the tube plates at either end of the
bundle of tubes 22 are secured via the annular members 10 (FIG.
1).
Where the heat exchanger is of sodium/water type, heated sodium is
passed through the heat exchanger tubes 22 and water for the
generation of steam is passed through the shell 1 over the tubes
22.
The thermal insulation structure of the invention provides thermal
insulation for the tube plates 21 by the trapping of stagnant steam
or water in the pockets defined at the face of the tube plates
between the plates 24 and the ends of the heat exchanger tubes
22.
In the arrangement of FIG. 3, straight paths exist between the rows
of heat exchanger tubes 22 so that the plates 24 can be of plane
form. In the alternative arrangement of FIG. 4, the tubes 22 are of
closer pitch so that there are no straight paths between the rows
of tubes. In this case the plates 24' are made of convoluted or
corrugated form to fit between the tubes 22.
* * * * *