EP0117821B1

EP0117821B1 - Compression sealing of tubes within shell and tube heat exchangers

Info

Publication number: EP0117821B1
Application number: EP84400378A
Authority: EP
Inventors: Katherine K. Flamm; Frank T. Morrison
Original assignee: Baltimore Aircoil Co Inc
Current assignee: Baltimore Aircoil Co Inc
Priority date: 1983-02-28
Filing date: 1984-02-24
Publication date: 1987-11-11
Also published as: EP0117821A2; DK104984D0; JPS59164894A; BR8304341A; ATE30768T1; GR79820B; NZ207207A; ZA841420B; EP0117821A3; AU2507484A; DE3467398D1; DK104984A

Abstract

The invention relates to a sealing means for shell and tube heat exchangers which means uses only components which are external to the heat exchanger shell to mechanically compress a series of rubber type gaskets and metal tube sheets and thereby seal the tube to tube sheet joints and the tube sheet to shell joints.

Description

Background of the invention

There have been a number of devices and sealing means used to seal the tubes and the shells in tube and shell heat exchangers so that fluid flowing in either medium would not intermingle.
Typically, brazing, welding or roller-expansion has been used to seal the tube to tube sheet joints and tube sheet to shell joints in a typical shell and tube heat exchanger. The disadvantages of these sealing methods are : 1) that the individual tubes cannot be easily removed, 2) the shell side cannot be cleaned mechanically, and 3) any use of plastic baffles in the shell would melt during brazing, or welding.
Other methods have been used to compression seal the tubes to the tube sheet, joints and the tube sheets to the shell joints in a typical shell and tube heat exchanger. There were several disadvantages to previous methods of compression sealing. One method required the compressing tube sheet to be welded to the shell. This prevented access to the internal shell area for cleaning or replacement of tube support baffles and allowed tubes to be replaced only singly and by very complicated procedures. Several methods required the presence of internal welded lugs or tube sheet end stops which complicated the removal of tube support assemblies and prevented the use of conventional tube support baffles. Another method required the presence of removable pressure-transfer devices in place of welded lugs and these components obstructed flow in and out of shell and tube nozzles causing wasted energy due to excessive pressure losses. Further methods required the use of four tube sealing gaskets and eight tube sheets per heat exchanger assembly, which caused several problems : (a) more costly assemblies due to the larger number of components, (b) the multiple components occupied space which reduced the effective tube length available for heat transfer. A final method required the use of very close tolerance components to effectively seal the cut- ends of the shell component.
More specifically, the present invention relates to a shell and tube heat exchanger comprising an extension shell and inner shell, a plurality of tubes and a sealing means, so that fluid flowing within the tubes and within the shell cannot mix, which comprises flanged gasket sealing means to seal the shell from outside atmosphere, said flanged gasket sealing means being compressed between two shell flanges and two tube sheets by means of bolts inserted through the flanges, and a tube sealing means to seal the tubes from the inner shell of said heat exchanger, said tube sealing means being compressed between said tube sheets, according to the preamble of claim 1.
A shell and tube heat exchanger of this type is disclosed in US-A-2 762 611, as illustrated at figure 6 thereof. In particular, the tube sealing means used as part of this exchanger are a plurality of deformable packing ring elements mounted onto each one of said tubes, these ring elements bearing against an associated annular shoulder. Another embodiment is illustrated at figure 7 of this patent, comprising specific sealing means 85 and 99 :

1) a flanged gasket 99 to seal the shell from outside atmosphere, said flanged gasket being compressed between a shell flange and one of two tube sheets by means of bolts,
2) a series of deformable annuli 85, one for each tube, to seal the tubes from the inner shell, said annuli being compressed between the two tube sheets.

Such sealing means involve a lot of components, and furthermore make difficult to obtain regular compression forces on each of the tubes, mainly due to tolerances of both the deformable annuli and the tapered edge of corresponding aperture of adjacent tube sheets.
The invention intends to solve this technical problem by providing sealing means which involve a small number of components, and ensure that proper compression forces are exerted on the internal tubes.
A similar state of the art is illustrated by two other documents hereafter commented :

1) DE-A-1 064 966 discloses the use of a full-face gasket compressed between two tube sheets, without flanged gasket sealing means; when tightening the bolts disposed around the shell flanges, the full-face gasket is outwardly radially expanded (as shows the curved outer section illustrated at figure 2) : as a consequence, compression forces on the internal tubes cannot be properly exerted due to this expansion, and more specially for the tubes which are near to the bolting zone.
2) GB-A-1 604 180 discloses the use of a retaining sleeve 16 which prevents outward yielding of the elastic material when pressure is applied by the tube sheets 11, 14. This sleeve 16 :
- is not adjustable in peripheral length,
- surrounds the external end surface of the jacket tube and of the extension tube, so that said end tubes have to slide between the sleeve and corresponding tube sheet.

Thus, it is an object of this invention to provide a shell and tube heat exchanger as defined in the preamble of claim 1, having no mechanical components specifically mechanical stops or pressure-transfer devices, internal to the shell, and wherein proper compression forces are still exerted on the internal tubes, without involving a lot of components.
This is achieved by providing a shell and tube exchanger of the above type, wherein the tube sealing means is a full-face gasket and is contained around its periphery by a retaining structure to prevent outward radial expansion of said full-face gasket, said retaining structure including a peripheral ring which is mechanically adjustable in peripheral length and diameter and abuts on the peripheral edge of the two tube sheets, so that proper compression forces are exerted on the plurality of tubes by the expanding full-face gasket, according to the characterizing portion of claim 1.
Other advantageous features can be further provided, as defined in the dependent claims.
To better understand the invention there are shown provided three Figures. Figure 1 is an isometric cut-away view of the sealing means on a typical shell and tube heat exchanger.
Figure 2 shows a cross-sectional view of the sealing means, which also incorporates a clamp ring gasket retaining assembly.
Figure 3 shows an isometric view of the clamp ring gasket retaining assembly of the sealing means.
Referring now to Figure 1, there is shown a typical shell and tube heat exchanger 1 consisting of a shell 2 and a plurality of tubes 3 located within the shell, preferably in a symmetrical or evenly-spaced pattern within the shell 2. Any fluid flowing with the tubes 3 enters the tubes or leaves the tubes through a conduit tube side connection 31. Fluid flowing counter to the fluid within the tubes and outside the tubes but within the shell 2 enters or leaves the shell and tube heat exchanger 1 through the annulus conduit connection 30. Only one side or one end of the typical shell and tube heat exchanger is shown in Figure 1, but our sealing means would similarly apply to the other end of the shell and tube heat exchanger which is not shown.
There is provided a flange portion 4 on the end of the shell 2. This flange portion is usually welded onto the end of the shell and is an annulus type flange having a typical overlap. Adjacent the flange 4 is a flange gasket 5. The flange gasket merely fits around the face of flange 4 and has an annular clear central portion so that the tubes 3 can pass therethrough.
Adjacent the flange gasket 5 is a tube sheet 6. The tube sheet is made of any metal typically steel, brass, or stainless steel or can be made of other non-compressible materials such as plastics or reinforced plastics. The tube sheet 6 is of a preferably circular design and has individual holes 50 therethrough corresponding to and in alignment with the individual tubes 3, which holes are of a slightly larger diameter than the outer diameter of the tubes 3 so that the tube-ends can pass through the holes, and the tube sheets can exert a maximum clamping force to compress the gasket to a maximum to prevent tube seal leaks.
Adjacent the metal tube sheet 6 is a full-face gasket 7. This gasket is circular and is solid- faced except for individual holes 51 and 15 therein, which holes again line up with the tubes 3 and bolt holes for flanges 4 and tube sheets 8. The diameter of these holes 51 is slightly smaller than the outside diameter of the tubes in order to maximize the gasket clamping force when compressing the full-face gasket 7 over the smooth ends of the tubes 3.
Next to the gasket 7 is another metal tube sheet 8 with holes 52 and 15 therein, similar to those described for the metal tube sheet 6.
Located inside shell 2 is the primary tube bundle assembly composed of tubes 53, segmental support baffles 54 and baffle spacer rods 55. It can be readily seen that this entire assembly of 53, 54, and 55 components can be removed from shell 2 after the flanges, gaskets, tube sheets, and outer shell 32 are removed, since there are no lugs internal to shell 2 to prevent removal.
Adjacent the metal tube sheet 8 rests flange gasket 9 which fits against the annular circular flange 10. Flange gasket 9 is similar to flange gasket 5 previously described. The entire series of flange gaskets and metal tube sheets are then adjacent to flange 10 which is located at the end of extension shell 32.
Extension shell 32 is an extension or continuation of shell 2 and is fitted with a tube side connection 31 through which fluid flowing within the tubes enters or leaves. Extension shell 32 is also preferably fitted with flange 33 on its other closure end (when contrasted with flange 10) so that the extension shell 32 of the shell 2 can be sealed off from the outside atmosphere. This is accomplished by having end closure flange 33 part of the extension shell 32 and having adjacent flange 33, an annular flange gasket 34 similar to gaskets 5 and 9 and finally having an end plate or end closure 35 sealing the end of the extension shell 32 of the shell and tube heat exchanger 1.
As can be seen in Figure 1 when one draws flange 10 and flange 4 closer together to thus compress the two flange gaskets 3 and 9 and the center or full-faced gasket 7, the compression will cause gasket 7 to expand radially inward and thus seal each tube from the fluid within the shell 2 but outside the tubes 3. The metal tube sheets 8 and 6 in conjunction with flanges 10 and 4 compress the rubberlike flange gaskets 9, 5 and 7 to form a seal between both the tube and tube sheets, and the inner and outer shells to atmosphere.
The flange gaskets 9 and 5 and the main center gasket 7 in addition to flange gasket 34 can be made of any sealable and flexible material particularly rubber or any type of elastomeric material which would not tend to corrode or decompose in the presence of the fluid used in the shell and tube heat exchangers.
The tube sheets 6, 8 and blind or end flange 35 are made of non-compressible material and preferably of metal such as steel, brass or stainless steel. The entire sealing means is compressed by any means but particularly by the use of bolts 40 which fit through holes 11 in the flange 4 and correspondingly fit through singly aligned holes 12 in flange gasket 5, holes 13 in the tube sheet 6, holes 14 in the center gasket 7, holes 15 in the tube sheet 8, holes 16 in the flange gasket 9 and finally holes 17 in the flange 10. Once the bolt extends through the holes 17 in flange 10, nuts 41 can be screwed onto the threaded portion 42 of bolts 40 and the entire ensemble tightened to thus force the flanges and tube sheets to compress the flange gaskets 5 and 9 and main center gasket 7 and thus effectively seal the shell and tube heat exchanger.
Similarly, the end of the extension shell 32 can be sealed from the atmosphere by means of compressing the end closure 35 to flange 33 to thus compress the flange gasket 34.
This will permit the mechanical cleaning of the interior of tubes without removing or disturbing the tube compression seals or any external piping connections. Typically bolts 43 can be inserted through holes 38 in flange 33 and correspondingly slipped through aligned holes 37 in flange gasket 34 and extend through holes 36 in end closure 35. Also, the bolts can go in reverse order. Typically one would screw nut 44 on the threaded portion of bolt 43 and tighten the entire outer sealing means. The holes through which the bolts pass can be equally spaced around the entire annulus of the flanges which extend above the outer diameter of the shell 2 or shell extension 32. Typically there would be about 20 holes of about 1/2 inch (12,7 mm) diameter on a flange being on an 8 inch (203 mm) diameter shell.
Also there is shown in Figures 2 and 3 a clamping structure to prevent outward expansion of gaskets. Thus, this illustrates the relationship between inner shell 2, extension shell 32, flange bolts 40, ring gaskets 5 and 9, metal tube sheets 6 and 8, gasket 7 and tubes 3. Also there is shown a preferred variation of outer clamp ring 45 with clamp ring flange 46 and clamp ring bolt 47. Thus, Figures 2 and 3 illustrate an arrangement or functional relationship that exists for the outer clamp ring which provides an entrapment to prevent outward radial expansion of gaskets when assembly clamp bolts 40 are tightened. This assures that proper compression forces are exerted on the internal tubes 3 by the expanding full gasket 7 to allow use of the described invention for application to higher internal pressure duties. Indeed, this component can be employed to increase the range of application to higher internal design pressures than that possible with some older designs wherein standard non-clamp ringed versions were limited to lower pressure duty. By tightening bolt 47, the clamp ring flanges 46 move closer together, making the ring tighten to a smaller diameter which then braces the outer edges of the gasket(s) 5, 7 and 9 to prevent their outward expansion when subsequently tightening bolts 40 to perform the heretofore described sealing of tubes and shell.
While the circular flange 45 tube sheets 6 and 8 and gaskets 5, 7 and 9 arrangement described is preferred, an alternate logically-arranged assembly of gaskets, flanges and tube sheets is visualized which are identical in arrangement of assembled components, but having an outer periphery of square, hexagonal or other non-circular configuration, while retaining preferably circular- shaped internal holes, shell and extension shell configuration. Also, somewhat non-circular tubes and gasket holes can be utilized effectively with this design concept. In this optional configuration, one might envision and accomplish certain advantages of reduced manufactureing cost or reduced material scrap ratios when fabricating multiples of components such as flanges, gaskets or tube sheets by conventional high speed manufacturing methods.
While the outer shell end closure 35, gasket 34 and bolts 43 of Figure 1 represent the preferred mechanical arrangement to allow the most ideal accessibility for maintenance and repair or reassembly of all internal components, an alternate variation, potentially lower cost and/or more leak- free concept employing a welded end cap to completely close the outer end of the extension shell 32 may be employed to perform the required closure of the outer end of the extension shell 32, eliminating the need for flange 33, gasket 34, bolts 43, nuts 44 and utilizing an end-plate or end closure without holes, merely welded all around the periphery thereof to the shell 32. However, this will preclude the ability to clean the interior of tubes, unless inlet and piping connections are dismantled and compression seal bolts removed.

Claims

1. A shell and tube heat exchanger comprising an extension shell (32) and inner shell (2), a plurality of tubes (3) and a sealing means, so that fluid flowing within the tubes and within the shell cannot mix, which comprises flanged gasket sealing means (5, 9) to seal the shell from outside atmosphere, said flanged gasket sealing means being compressed between two shell flanges and two tube sheets (6, 8) by means of bolts inserted through the flanges, and a tube sealing means (7) to seal the tubes from the inner shell of said heat exchanger, said tube sealing means being compressed between said tube sheets (6, 8), characterized in that the tube sealing means (7) is a full-face gasket and is contained around its periphery by a retaining structure (45, 46, 47) to prevent outward radial expansion of said full-face gasket, said retaining structure including a peripheral ring (45) which is mechanically adjustable in peripheral length and diameter and abuts on the peripheral edge of the two tube sheets (6, 8), so that proper compression forces are exerted on the plurality of tubes by the expanding full-face gasket.

2. A shell and tube heat exchanger according to claim 1, wherein the peripheral ring (45) has two clamp ring flanges (46) receiving a clamp ring bolt (47), so that the full-face gasket (7) is entrapped by tightening said clamp ring bolt (47) and then radially expanded without outward expansion when subsequently tightening the shell flange bolts (40).

3. A shell and tube heat exchanger according to anyone of claims 1 and 2, wherein the gaskets (5, 7, 9) are made of elastomeric material.

4. A shell and tube heat exchanger according to anyone of claims 1 and 2, wherein the tube sheets (6, 8) are made of a non-compressible metal or rigid synthetic materials.

5. A shell and tube heat exchanger according to anyone of claims 1 to 4, wherein the gaskets (5, 7, 9), flanges (4, 10), tube sheets (6, 8) and peripheral retaining structure (45) are circular.

6. A shell and tube heat exchanger according to anyone of claims 1 to 4, wherein the gaskets (5, 7, 9), flanges (4, 10), tube sheets (6, 8) and peripheral retaining structure (45) are non-circular.

7. A shell and tube heat exchanger according to anyone of claims 1 to 6, wherein the tube ends and tube gasket holes (12, 14, 16) are circular.

8. A shell and tube heat exchanger according to anyone of claims 1 to 6, wherein the tube ends and tube gasket holes (12, 14, 16) are non-circular.