EP1709382A1

EP1709382A1 - Support for a tube bundle

Info

Publication number: EP1709382A1
Application number: EP04804943A
Authority: EP
Inventors: Stephen Wayne Johnston; Dominicus Fredericus Mulder
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2003-12-22
Filing date: 2004-12-20
Publication date: 2006-10-11
Anticipated expiration: 2024-12-20
Also published as: US20050161204A1; EA200601213A1; DE602004020679D1; PT1709382E; AU2004304015B2; CA2550688A1; WO2005061982A1; AU2004304015A1; CA2550688C; EA007892B1; CN1906456A; ES2324351T3; JP2007515615A; ATE428900T1; KR20060130131A; US20090200004A1; EP1709382B1

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

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 seg ental 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, 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. 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%. 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. 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 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. 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 III-III 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 cros's 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. 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 L^ 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 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 Li . For comparison, the unsupported tube length of e.g. tube 14 between support plates 18 and 20 is 2Lχ. 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 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 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 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. 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 application No. 03077463.2, unpublished at the first filing (priority) date of the present invention.

Claims

C L A I M S

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 according to claim 1, wherein the plurality of support plates includes a combined support plate formed of a segmental baffle support element and an expanded metal support element.

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

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