Support for a tube bundle

Abstract

A support for a bundle of tubes, which support has more than one transverse support plates spaced apart along the direction of the tubes to be supported, and which support plates are provided with openings for accommodating the tubes, wherein the support plates are segmental baffle support elements and expanded metal support elements.

Description

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 exchanger can, for example, be found in Perry's Chemical Engineers' Handbook, 6^th 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 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.

One type of support plate is a segmental baffle. 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 not only support the tubes, but also influence the fluid flow through the shell side. Therefore, the design of a baffle is also 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 optimizing 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 a 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%.

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 maximize the spacing between baffles. When the unsupported tube length becomes 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.

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.

It would be useful to provide a support for a bundle of tubes, which allows a simpler, cheaper mechanical support against vibrations in segmental baffle tube supports.

SUMMARY OF THE INVENTION

The present invention is directed to 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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a longitudinal cross-section through a first embodiment of a heat exchanger with support according to the present invention.

FIG. 2 shows schematically a cross section along II-II in FIG. 1.

FIG. 3 shows schematically a cross section along III-III in FIG. 1.

FIG. 4 shows schematically a segmental support baffle.

FIG. 5 shows schematically a combined support baffle formed of a segmental baffle support element and an expanded metal support element.

FIG. 6 shows schematically a longitudinal cross-section through a second embodiment of a heat exchanger with support according to the present invention.

FIG. 7 shows schematically a cross section along VII-VII in FIG. 6.

FIG. 8 shows schematically a cross section along VIII-VIII in FIG. 6.

FIG. 9 shows schematically another segmental support baffle.

FIG. 10 shows schematically a conventional segmental baffle for use as intermediate support plate in a Texas tower.

FIG. 11 shows schematically an intermediate expanded metal support plate according to the invention.

FIG. 12 shows schematically a longitudinal cross-section through a third embodiment of a heat exchanger with support according to the present invention.

FIG. 13 shows schematically a further expanded metal support element according to the invention.

Like reference numbers are used in the Figures to refer to the same or similar objects.

DETAILED DESCRIPTION OF THE INVENTION

Part of the mechanical support function in a segmental baffle tube support does not have to be provided by conventional segmental baffle elements, but may with advantage be provided by expanded metal elements. Expanded metal may be manufactured considerably more cheaply than segmental baffles because less material is used, fewer cuttings are produced, and less labor is required. The present invention allows the tube support to be designed such that the segmental baffles are placed where they are needed for reasons of fluid flow, as well as where they also provide mechanical support. Further mechanical support, in particular to prevent vibrations, may be provided by expanded metal elements. Expanded metal influences fluid flow far less than a conventional 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, may be chosen for optimum fluid flow, heat transfer performance and pressure drop, not compromised by vibration considerations. A vibration problem that might be encountered may, 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 may form a combined support plate. To this end expanded metal may be arranged to span the window(s) of the segmental baffle support element. In this way mechanical support may be provided over the full cross-section of the support plate, but fluid may only flow through the window. Since the expanded metal also imposes some small flow restriction, it may be desirable to slightly increase the size of the window compared to a conventional segmental support baffle.

Expanded metal support elements in the form of expanded metal support plates may also be arranged between two segmental baffle support elements, as an additional mechanical support.

In a further embodiment, the expanded metal support plate may have a segmental shape itself, i.e. one or more segments may be cut off so that one or more windows are formed. This may be advantageous in designs where no tubes run through the windows of segmental baffles, and where additional mechanical support between segmental baffles is desired with a minimum disturbance of fluid flow.

Reference is now made to FIGS. 1-5. FIG. 1 shows part of a vertical shell-and tube heat exchanger 1 in longitudinal cross-section, and FIGS. 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 FIG. 1. The support for the tube bundle 5 comprises the four support plates 18,19,20,21 shown in FIG. 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 FIG. 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. Openings 30 have been cut into the remaining plate 25.

Support plate 20 is a combined support plate, as shown in FIG. 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 may for example be welded to the segmental baffle element 38 and to the strip 45 around the window 42. The strip 45 itself may also be welded to the segmental baffle element, but may also be a remainder from the original circular plate from which the segmental baffle element 38 was formed by e.g. milling.

Expanded metal may be made by providing sheet metal with a structure of slits 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 L₁. For comparison, the unsupported tube length of e.g. tube 14 between support plates 18 and 20 is 2L₁. The invention may 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 were combined support plates 35, it would be possible to increase the spacing between support plates from a mechanical point of view.

Reference is now made to FIGS. 6-11, and a second embodiment of the present invention will now be discussed.

FIG. 6 shows part of a Texas tower heat exchanger 101 in longitudinal cross-section, and FIGS. 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 FIG. 6. The Texas tower may 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 FIG. 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 FIG. 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 FIG. 6 is a so-called no-tube-in-windows design.

The spacing L₂ between segmental baffles is chosen such that an optimized 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 FIG. 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 FIGS. 6-8, however, the intermediate support plates 118, 119 and 120 are expanded metal support plates, like the plate 135 schematically shown in FIG. 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 may be manufactured much more cheaply than a conventional intermediate plate 134 as shown in FIG. 10.

Reference is now made to FIGS. 12-13, and with reference to these FIGS. 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. FIG. 12 shows part of a longitudinal cross-section, and it will be understood that the heat exchanger may be much longer, and that more support plates than shown may 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 FIG. 4. Halfway in between adjacent segmental baffles, an expanded metal support plate like the plate 235 shown in FIG. 13 is arranged. The plate 235 may be cheaply manufactured, for example, by cutting a 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 the spacing between adjacent segmental baffles to be larger than if the tube support were made of segmental baffles only. The segmental baffles may 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 may be minimized.

However, in some applications it may also happen that tube vibration considerations pose a limitation on the minimum spacing between segmental baffles. This may be the case when it is desired to maximize cross-flow of fluid in the shell, in order to maximize heat transfer in a given heat exchanger volume. In this case, segmental baffles of low baffle cut are used, and it is desirable to minimize the spacing between the baffles. This results in a large pressure drop, but may also 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 may be lower because a smaller shell may be used.

It shall be clear that the present invention can equally be applied to horizontal and vertical heat exchangers.

The support plates may be mounted in any suitable way in the shell. A conventional method for mounting segmental baffles is to use spacer rods arranged parallel to the tubes, which are welded to the shell and to the segmental baffles. Such rods may 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 may 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 FIGS. 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 FIG. 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 application No. 03077463.2, unpublished at the first filing (priority) date of the present invention.

Claims

1. 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 support 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.

2. The support of claim 1, wherein the plurality of support plates comprises a combined support plate formed of a segmental baffle support element and an expanded metal support element.

3. The support of claim 2, wherein the expanded metal support element is arranged such that it spans a window that is formed between the segmental baffle support element and a circle of the respective diameter.

4. The support of claim 1, wherein at least one of the expanded metal support elements forms a support plate arranged intermediate between two segmental baffle support plates.

5. The support of claim 4, wherein the intermediate expanded metal support element forms a segmental support plate.

6. A heat exchanger comprising a bundle of tubes supported by a support comprising a plurality of transverse support plates spaced apart along the direction of the tubes to be supported, and which support 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.

7. The heat exchanger of claim 6, wherein the plurality of support plates of the support comprises a combined support plate formed of a segmental baffle support element and an expanded metal support element.

8. The heat exchanger of claim 6, wherein the expanded metal support element of the support is arranged such that it spans a window that is formed between the segmental baffle support element and a circle of the respective diameter.

9. The heat exchanger of claim 6, wherein at least one of the expanded metal support elements of the support forms a support plate arranged intermediate between two segmental baffle support plates.

10. The heat exchanger of claim 9, wherein the intermediate expanded metal support element of the support forms a segmental support plate.