Note: Descriptions are shown in the official language in which they were submitted.
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SUPPORT FOR A TUBE BUNDLE
Field of the Invention
The present invention relates to a support for a
bundle of tubes, in particular to such a support
comprising a plurality of transverse support plates known
as segmental baffles, which are spaced apart along the
direction of the tubes to be supported.
Background of the Invention
A major area of application of the tube bundle is in
shell-and-tube heat exchangers. A shell-and-tube heat
exchanger comprises a cylindrical vessel internally
provided with a bundle of tubes that extend in
longitudinal direction of the vessel. The bundle of tubes
can in particular be a bundle of parallel tubes, and is
also referred to as a tube bundle.
As is well known, the shell-and-tube heat exchanger
is an indirect heat exchanger in which heat is
transferred between a fluid passing through the tubes of
the tube bundle (the tube side) and a fluid passing
through the space outside the tubes (the shell side).
Details of the shell-and-tube heat exchangers can for
example be found in Perry's Chemical Engineers' Handbook.
6th edition, 1984, McGraw-Hill Inc., page 11-3 to 11-21.
The tube bundle is the most important part of the heat
exchanger. The ends of the tubes are secured to a tube
sheet. The heat exchanger can include two tube sheets,
one at each end of the cylindrical vessel, or a single
tube sheet at one end of the cylindrical vessel in the
event the heat exchanger is a U-tube exchanger.
It will be understood that the intermediate portions
of the tubes have to be supported as well, for example to
prevent damage to the tubes due to vibrations caused by
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the fluid flow. To support the intermediate portions of
the tubes, a tube support normally comprises axially
spaced apart transverse support plates. A support plate
is sometimes also referred to as a support sheet or a
support baffle.
The present invention relates to heat exchangers
comprising so-called segmental baffles as support plates.
Several kinds of segmental baffles are discussed in
Perry's. Conventional segmental baffles are made of a
circular metal plate from which a circle segment
("window") is cut off, and through the remainder of the
plate a plurality of openings is punched or cut through
which the tubes can pass. Sometimes two circle segments
are cut off at opposite sides, for example for use in so-
called double segmental baffle arrangements, or in no-
tube-in-window arrangements.
Segmental baffles do not only support the tubes, but
also influence the fluid flow through the shell side.
Therefore the design of a baffle is as well determined by
heat-transfer considerations. Segmental baffle tube
supports are used when a certain amount of cross-flow of
fluid in the shell over the tube bundle is desired for
reasons of optimising heat transfer.
The design of segmental baffles can be adapted,
within certain limits, to the specific requirements of a
particular practical application. For example the so-
called baffle cut can be specifically selected, which is
the percentage of the circle diameter which has been cut
off to form the segmental baffle. A large baffle cut in a
single segmental baffle provides relatively low pressure
drop, however the relatively large part of the tubes that
run through the window remains unsupported. Normally one
tries to support a tube by at least every second
segmental baffle, so that the maximum baffle cut that is
normally adopted is 45%.
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When tubes run through the windows, the maximum
unsupported length of a tube ("unsupported tube length")
is at least twice the spacing between segmental baffles.
Therefore it is inherent with the segmental baffle tube
supports that the number of support plates is at least
twice of that which would be required from a mechanical
support point of view alone. Segmental baffles contribute
substantially to the cost of a heat exchanger, so one
tries to maximise the spacing between baffles. When the
unsupported tube length become too large, this can lead
to vibration problems.
In other heat exchanger designs no tubes run through
the windows. For example, in very tall vertical heat
exchangers (such as those which are referred to as "Texas
towers", used e.g. as feed/effluent heat exchangers in
large-scale industrial processes), single segmental
baffles are commonly arranged at a certain spacing, with
the windows alternatingly at opposite sides in order to
achieve a desired cross-flow pattern of the fluid over
the tube bundle along the shell. Since the spacing that
is desired for reasons of optimum fluid flow and optimum
hydraulic performance (in particular minimum pressure
drop) can be much longer than the spacing required for
good mechanical support against vibrations, a number of
additional segmental support baffles, but with two
windows each, are placed in between the single segmental
baffles. These additional elements represent a
considerable cost element of the entire tube support.
Japanese Patent Application with publication
No. 05-296680 describes a support baffle plate wherein a
plurality of co-operating sheet metal strips are arranged
in the window to suppress vibration. Due to the special
shape required for all individual sheet metal strips,
manufacturing costs are high.
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Summary of the Invention
It is an object to of the present invention to
provide a support for a bundle of tubes, which allows a
simpler (cheaper) mechanical support against vibrations
in segmental baffle tube supports.
To this end the present invention provides a support
for a bundle of tubes, which support comprises a
plurality of transverse support plates spaced apart along
the direction of the tubes to be supported, and which
plates are provided with openings for accommodating the
tubes, wherein the plurality of support plates comprises
segmental baffle support elements and expanded metal
support elements.
Applicant has realized that part of the mechanical
support function in a segmental baffle tube support does
not have to be provided by conventional segmental baffle
elements, but can with advantage be provided by expanded
metal elements. Expanded metal can be manufactured
considerably cheaper than segmental baffles, because less
material is used, less cuttings are produced, and less
labour is required. The present invention allows to
design the tube support such that the segmental baffles
are placed there where they are needed for reasons of
fluid flow, where they also provide mechanical support.
Further mechanical support, in particular to prevent
vibrations, can be provided by expanded metal elements.
Expanded metal influences fluid flow far less than a
segmental baffle.
The invention in this way allows far more flexibility
in designing segmental baffle heat exchangers. The basic
design parameters of the heat exchanger like tube size
and arrangement (e.g. triangular or square pitch), shell
diameter, segmental baffle size and spacing, can be
chosen for optimum fluid flow, heat transfer performance
and pressure drop, not compromised by vibration
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considerations. A vibration problem that might be
encountered can according to the invention be solved by
placing expanded metal support elements.
The expression "support element" is used in the
description and in the claims to refer to a part of a
support plate, or to a full support plate.
Expanded metal and segmental baffle support elements
together can form a combined support plate. To this end
expanded metal can be arranged to span the window(s) of
the segmental baffle support element. In this way
mechanical support can be provided over the full cross-
section of the support plate, but fluid can only flow
through the window. Since the expanded metal also imposes
some flow restriction, be it small, it may be desirable
to slightly increase the size of the window compared to a
conventional segmental support baffle.
It is also possible that expanded metal support
elements in the form of expanded metal support plates are
arranged between two segmental baffle support elements,
as an additional mechanical support.
In a further embodiment the expanded metal support
plate can be have segmental shape itself, i.e. one or
more segments can be cut off so that one or more windows
are formed. This can be advantageous in designs where no
tubes run through the windows of segmental baffles, and
where additional mechanical support between segmental
baffle is desired with minimum disturbance of fluid flow.
Tube supports consisting solely of expanded metal
support elements are disclosed in International Patent
Application Publication No. WO 03/067170. However this
publication does not refer to vibration problems in
conventional segmental baffle heat exchangers and does
not disclose or suggest a combination of conventional
segmental baffles and expanded metal support elements.
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Brief description of the Drawings
The invention will now be described in more detail
and with reference to the accompanying drawings, wherein
Figure 1 shows schematically a longitudinal cross-
section through a first embodiment of a heat exchanger
with support according to the present invention;
Figure 2 shows schematically a cross section along
II-II in Figure 1;
Figure 3 shows schematically a cross section along
in Figure 1;
Figure 4 shows schematically a segmental support
baffle;
Figure 5 shows schematically a combined support
baffle formed of a segmental baffle support element and
an expanded metal support element;
Figure 6 shows schematically a longitudinal cross-
section through a second embodiment of a heat exchanger
with support according to the present invention;
Figure 7 shows schematically a cross section along
VII-VII in Figure 6;
Figure 8 shows schematically a cross section along
VIII-VIII in Figure 6;
Figure 9 shows schematically another segmental
support baffle;
Figure 10 shows schematically a conventional
segmental baffle for use as intermediate support plate in
a Texas tower;
Figure 11 shows schematically an intermediate
expanded metal support plate according to the invention;
Figure 12 shows schematically a longitudinal cross-
section through a third embodiment of a heat exchanger
with support according to the present invention; and
Figure 13 shows schematically a further expanded
metal support element according to the invention.
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Like reference are used in the Figures to refer to
the same or similar objects.
Detailed Description of the Invention
Reference is made to Figures 1-5. Figure 1 shows part
of a vertical shell-and tube heat exchanger 1 in
longitudinal cross-section, and Figures 2 and 3 show two
cross-sections along lines II-II and III-III,
respectively. The heat exchanger 1 has a shell 3 and a
bundle of tubes 5, of which the tubes 8,9,10,11,12,13,14
are visible in Figure 1. The support for the tube
bundle 5 comprises the four support plates 18,19,20,21
shown in Figure 1. The plates are spaced by a fixed
distance L1 from each other along the length direction of
the tubes 8-14.
Support plates 18,19 and 21 are conventional
segmental baffles as shown enlarged in Figure 4. These
segmental baffles are manufactured from a circular
plate 25 from which a segment has been cut off so that
windows are formed when mounted in the heat exchanger,
e.g. window 28. Into the remaining plate 25 openings 30
have been cut.
Support plate 20 is a combined support plate as shown
in Figure 5 in more detail. The combined support plate 35
is formed of a segmental baffle support element 38 and an
expanded metal support element 40 which spans the
window 42 left open by the segmental baffle support
element 38. The expanded metal element 40 can for example
be welded to the segmental baffle element 38 and to the
strip 45 around the window 42. The strip 45 itself can
also be welded to the segmental baffle element, but can
also be a remainder from the original circular plate from
which the segmental baffle element 38 was formed by e.g.
milling.
Expanded metal is a well known material, which can be
made by providing sheet metal with a structure of slits
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followed by stretching the slit sheet metal. A structure
of cross-laths, formed of so-called strands and bonds,
with interstices is formed. The arrangement and length of
the slits as well as the extent of stretching determines
the size, shape and relative arrangement of the
interstices, which can therefore be designed such that
the tubes can pass through them and are optimally
supported.
Normally the strands between adjacent bonds are
twisted out of the plane of the original sheet metal,
which results in a lowering of the restriction to fluid
flow normal to the sheet of expanded metal.
The support plate 20 mechanically supports the tubes
over the full cross-section of the shell 3, i.e. also in
the window 42. Therefore the unsupported tube length of
tube 8 for example, between support plates 19 and 21 is
Ll. For comparison, the unsupported tube length of e.g.
tube 14 between support plates 18 and 20 is 2L1. The
invention can in this way serve to decrease the
unsupported tube length in order to suppress vibrations.
If more or all support plates in the heat exchanger 1
would be combined support plates 35, is would be possible
to increase the spacing between support plates from a
mechanical point of view.
Reference is now made to Figures 6-11, and a second
embodiment of the present invention will now be
discussed.
Figure 6 shows part of a Texas tower heat
exchanger 101 in longitudinal cross-section, and
Figures 7 and 8 show two cross-sections along
lines VII-VII and VIII-VIII, respectively. The heat
exchanger 101 has a vertical cylindrical shell 103 and a
bundle of tubes 105 running through the central part of
the shell 103. The tubes 108,109 and 110 are visible in
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Figure 6. The Texas tower can for example have a height
of 24 m and a diameter of 2.5 m.
The support for the tube bundle 105 comprises the
five support plates 117,118,119,120,121 shown in Figure 6
as support elements. The plates are spaced from each
other along the length direction of the tubes 108-110.
Support plates 117 and 121 are conventional segmental
baffles 124 as shown enlarged in Figure 9. These
segmental baffles are manufactured from a circular
plate 125 from which a segment has been cut off along
line 126 so that windows 127, 128 are formed when the
respective plates are mounted in the heat exchanger 101.
The windows are arranged at opposite sides in the heat
exchanger as shown. Into the remaining plate 125
openings 130 have been cut according to the size and
arrangement of the tubes 105. No openings are arranged in
the part 131 opposite to the window, since the design of
the heat exchanger 101 as shown in Figure 6 is a so-
called no-tube-in-windows design.
The spacing L2 between segmental baffles is chosen
such that an optimised fluid flow is obtained, wherein
the flow passes through the windows 127 and 128 thereby
crossing the tube bundle 105. A typical value for L2 is
1.5 m. If the spacing L2 is too large for preventing
vibrations of the tubes, additional intermediate support
plates are mounted in a conventional Texas tower, like
the plate 133 shown in Figure 10. Plate 133 is a
segmental support baffle which has two sections cut off
at opposite sides, and is provided with openings 134 for
the tubes. Such additional intermediate support plates
would be mounted e.g. at the same locations as shown for
plates 118, 119, 120, and such that the windows register
with the windows 127 and 128.
In the embodiment according to the invention as shown
in Figures 6-8, however, the intermediate support
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plates 118, 119 and 120 are expanded metal support
plates, like the plate 135 schematically shown in
Figure 11.
The plate 135 is formed by a double segmental
expanded metal sheet 136, which is welded to a support
ring 138 and support strips 140 so as to form windows 142
and 143. Support plate 135 can be manufactured much
cheaper than a conventional intermediate plate 134 as
shown in Figure 10.
Reference is now made to Figures 12-13, and with
reference to these Figures a third embodiment of the
invention will be discussed.
The horizontal heat exchanger 201 with shell 203
through which the tube bundle 205 runs is an example of
such a design. Figure 12 shows part of a longitudinal .
cross-section, and it will be understood that the heat
exchanger can be much longer, and that more support
plates than shown can be arranged. The tube bundle 205
includes tubes 208, 209, 210, 211, 212, 213, and 214. The
Figure does not show the end parts of the tubes with the
tube sheet.
The tubes are supported by segmental baffles 218,
219, 220. As further support against tube vibrations
expanded metal support plates 221,222 are arranged. The
segmental baffle support elements and the expanded metal
support elements are alternatingly arranged at a fixed
spacing along the length direction of the tubes 205.
The spacing between adjacent segmental baffles, e.g. 218
and 219, is L3.
The segmental baffle support elements 218, 219, 220
are similar to those shown and described with reference
to Figure 4. Halfway in between adjacent segmental
baffles, an expanded metal support plate like the
plate 235 shown in Figure 13 is arranged. The plate 235
can be cheaply manufactured, for example by cutting a
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sheet of expanded metal to circular shape, e.g. by laser
cutting, and welding to a support ring 245.
The expanded metal support plates 221,222 serve to
prevent vibrations between segmental baffles. The maximum
unsupported tube length of e.g. tube 214 is L3, equal to
the spacing between adjacent segmental baffles. Without
the expanded metal support elements the unsupported tube
length would be twice the spacing between adjacent
segmental baffles. In this way the present invention
allows to choose the spacing between adjacent segmental
baffles larger than when the tube support would be made
of segmental baffles only. The segmental baffles can thus
be placed such that optimum fluid flow in the shell side
and heat transfer is achieved, and the overall cost of
the tube support can be minimized.
However, in some applications, it can also happen that
tube vibration considerations pose a limitation on the
minimum spacing between segmental baffles. This can be
the case when it is desired to maximise cross-flow of
fluid in the shell, in order maximizing heat transfer in
a given heat exchanger volume. In this case segmental
baffles of low baffle cut are used, and one desires to
minimize the spacing between the baffles. This results in
high pressure drop, but also can generate tube vibrations
despite the relatively short spacing between segmental
baffles. In such a situation it would previously have
been needed to increase the baffle spacing and possibly
increase the size of the heat exchanger. With the present
invention, however, additional expanded metal support
plates can solve the vibration problem. Although the cost
of the tube support in the heat exchanger slightly
increases by the use of the additional expanded metal
support elements, the total cost of the heat exchanger
can be lower because a smaller shell can be used.
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It shall be clear that the present invention can equally be applied to
horizontal
and vertical heat exchangers.
The support plates can be mounted in any suitable way in the shell. A
conventional method to mount segmental baffles is to use spacer rods arranged
parallel with the tubes, which are welded to the shell and to the segmental
baffles. Such rods can likewise be welded to the support ring of expanded
metal
support elements.
For many applications of the present invention, the expanded metal support
elements suitably have interstices with a size just large enough such that the
tubes can be passed through, so that each tube is supported from four sides
substantially without play. Typically in this case the size would be such that
at
maximum a gauge of 10% larger diameter than the tube could pass through the
interstices. This size of interstices is for example preferred for the
embodiments
discussed with reference to Figures 1 and 12, wherein each expanded metal
support element preferably supports the tubes sufficiently.
It will be clear, however, that it is also possible to use expanded metal with
interstices so large that several tubes can pass through. In this case
suitably
several sheets of expanded metal are arranged to co-operate so that the tubes
are
supported from all sides, for example the intermediate expanded metals support
elements of the embodiment discussed with reference to Figure 6. Suitable such
arrangements of several expanded metal sheets are discussed in WO 03/067170.
Other suitable arrangements, types of expanded metal and arrangement and
shapes of interstices of expanded metal are described in European Patent
1654510 (published 17.02.2005 as W02005/015107).
DOCSMTL: 4434359\1
