GB2132330A - Spiral heat exchanger - Google Patents

Abstract

In a spiral heat exchanger, two strips 2 and 3 are wound in an interleaved spiral fashion to form flow passages 4 and 5. One side of each flow passage is normally sealed by welding the strip 2 and 3 together, and the other side by means of gaskets 9. Conventionally, these gaskets are mounted on thick flat end covers. In accordance with the present invention, the thick flat or slab like end covers are replaced by facer sheets 11 of comparatively thin material which are sealed to spherical dished plates 13 to form chambers 14 which are pressurised. The chambers 14 may be pressurised either from an external source, or by bleading off working fluids through aligned apertures in the facer sheets and gaskets, or by feeding or discharging the working fluids through the chambers 14. In the latter case, the complex and expensive pockets which are conventionally used may be eliminated, giving a further cost saving. <IMAGE>

Description

SPECIFICATION Spiral heat exchanger This invention relates to spiral heat exchangers.

In a spiral heat exchanger, the heat exchange surfaces are formed by two long and broad strips of metal coiled together to form a spiral element.

There are thus two generally spiral flow channels formed between the strips in an interleaved arrangement. A number of actual configurations may be employed.

In an arrangement, hereinafter referred to as the first type, the fluids in both passages flow in a spiral arrangement, normally in countercurrent, with one fluid fed in at the centre and out at the periphery, with the other being fed in at the periphery and out at the centre. In such an arrangement both edges of all the channels have to be closed.

In another arrangement, one fluid flows in a spiral passage while the other flow axially across the exchanger. In such an arrangement, the passage for the one fluid has both edges closed, while the other has them open.

In a third arrangement or type, one fluid flows in a spiral while the other is distributed evenly into the other channel via one open side of the passage and flows out via the spiral. The third type is used particularly in condensing under vacuum.

The closing of the edges of the spiral passages may be achieved for one passage by forming one strip so that its edge is in juxtaposition with the edge of the other strip and welding the two strips together.

However, when the edges of both passages have to be closed at the same sides as in the spiral heat exchangers of the first and third types, they cannot both be welded up and recourse is therefore had to welding one channel and closing the other by means of a gasketed cover plate.

Such cover plates have to provde a sure seal to prevent bypassing of the fluid and therefore must be reinforced against distortion under the differential pressure across it in order to maintain the flatness of the inner face of the cover plate.

The cover plate has therefore hitherto had to be thick and also may have needed reinforcement welded on.

It is an object of the invention to improve the cover plate construction by avoiding the need for a massive construction.

In accordance with a first aspect of the invention, there is provided an end cover arrangement for a spiral heat exchanger comprising a face sheet having a gasket on one face to cooperate with and seal the adjacent edge of at least one spiral flow passage, a dished outer housing member sealed around the periphery of the facer sheet and forming a chamber with the other face of the facer sheet, and means for pressurising the chamber to provide reinforcement of the facer sheet.

The pressurisation of the chamber may be by admission of pressurised fluid from an external source, but it is preferred to use the working fluids, either via bleed holes from the heat exchanger, or by feeding the working fluids in via the chambers.

In accordance with a second aspect of the invention, there is provided a spiral heat exchanger having one or both end covers in accordance with the invention as set forth above.

The invention will be further described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a sectional view showing a spiral heat exchanger having two end cover arrangements in accordance with one form of the invention; Figure 2 is a view similar to part of figure 1 showing a modified form of end cover arrangement; Figure 3 is a view similar to Figure 2, showing a further modified form of end cover arrangement; Figure 4 is a plan view of the arrangement of Figure 3; Figure 5 is a sectional detail of a heat exchanger having an end cover arrangement of Figure 3; and Figure 6 is a sectional detail, similar to figure 5, and showing a modification.

Turning first to figure 1, there is shown a fairly typical form of spiral heat exchanger of the first type. Apart from the end cover arrangements, the spiral heat exchanger is generally conventional and includes an outer shell 1 attached to and surrounding a pair of spiral wound broad strips 2 and 3 which between them define two spiral flow passages 4 and 5 for different heat exchange media. The passage 4 is shown plain, while the passage 5 is marked with dots. It will be seen that in the cross-section of figure 1 the flow passages are formed as interleaved spirals. A central or generally axial terminal portion 4a of the passage 4 communicates with a first axial duct 6, while a central axial portion 5a of the passage 5 communicates with a second axial duct 7.The outer or peripheral ends of the passages 4 and 5 communicate with generally conventional pockets 4b and 5b respectively which communicate with ducts 4c and 5c. The ducts 4c, 5c, 6 and 7 are provided with respective unions for connection to external pipework. As is conventional, the pockets 4b and 5b communicate with their respective passages through apertures in shell 1, which apertures are reinforced by end bars 8 welded to the shell 1.

It will be seen that in order to close the upperside of the passage 5, the inner edge of the strip 2 is turned back and sealed by welding to the strip 3. Similarly the lower edge of the strip 3 is turned back and welded to the strip 2 to close the lower side of the passages 4. The upper side of passage 4 and the lower side of passage 5 are sealed by gaskets 9 mounted on the end cover arrangements.

The parts of the spiral heat exchanger so far described are generally conventional, and in a conventional spiral heat exchanger the gaskets would be mounted on flat, slab-form end covers of considerable weight and thickness, and these would probably also need to have reinforcements welded to the outer side to stiffen them further to prevent distortion under the internal pressure whereby bypassing would occur.

In accordance with the teachings of the present invention, the gaskets 9 are mounted on comparatively thin facer sheets 11 which are sealed at their peripheries, in the figure 1 arrangement by welding 12, to spherically dished plates 13. The ducts 6 and 7 are also shown as being welded in a sealing manner to both the facer sheet 1 and the plate 1 3 so that between each facer sheet 11 and its respective plate 13 there is formed a sealed chamber 14. The chambers 14 are filled, by means not shown, with a pressurised fluid at a pressure somewhat greater than the maximum operating pressure in either of the passages 4 and 5 so that the facer sheet 11 behaves as a membrane and is pushed, with the gasket 9, into sealing engagement with the ends of the spiral body, thus preventing bypassing.

It will be seen that the plates 13 are provided with flange rings 1 3a with reinforced bolt holes 1 5 cooperating with bolt holes 16 in a flange on the shell 1. This enables the end cover arrangement to be securely but removably attached to the heat exchanger shell 1.

By using dished plates 1 3 to absorb the stresses, through the medium of the pressurised fluid in the chambers 14, the use of the conventional massive end covers is avoided. The arrangement shown in figure 1 is of a conventional first type of spiral heat exchanger and it will be seen that the medium in the flow passage 5 enters at the axis via the duct 7 and exits through the pocket 5b at the periphery, while the medium in the flow passage 4 enters through the pocket 4b and exits at the axis through the duct 6.

However, it will be envisaged that an end cover arrangement in accordance with the invention may also be used in the so-called third type of spiral heat exchanger in which one end cover of this type will be used and the other will be replaced by an inlet dome to enable the fluid to communicate with more than one turn of the spiral.

Figure 2 shows a modified form of end cover arrangement, showing several modifications. The first modification over the figure 1 arrangement is that instead of the chamber 1 4 being pressurised from an external source, the facer sheet 11 and gasket 9 are provided with small aligned apertures 11 a, 9a respectively to enable pressurised working fluid to be bled or wept off from near the high pressure end of one of the flow passages, in the case illustrated the passage 4. It will be appreciated that if te same arrangement is ued for an end cover at che opposite end of the heat exchanger, then the bleed holes will be provided nearer the axis of the heat exchanger so as to bleed off the working fluid from the passage 5 at its high pressure end.By this arrangement, the pressures on opposite sides of the facer sheet 11 are substantially balanced since the same fluid is present on both sides of the facer sheet 11.

A second modification shown in figure 2 is that the facer sheet 11 and the dished plate 13 are not welded together for sealing, but are sealed by a peripheral gasket 21 which is compressed when the dished plate 13 is bolted to the shell 1. In addition to the provision of the peripheral gasket 21, the duct 6 is also shown as passing through a ring 22 welded to the facer sheet 11 and carrying an O-ring or like seal 23 to maintain a seal while accommodating some movement of the duct 6.

It will be appreciated that this use of a gasketed rather than welded seal to close the chamber 14 may be utilised in conjunction with the figure 1 arrangement, or with the arrangement of figures 3 and 4. The advantage of this arrangement is that the dished plate 13 can be readily separated from the facer sheet 11 for cleaning and maintenance purposes.

Turning now to figures 3 and 4, figure 3 shows a number of further modifications. The principal modification shown is that instead of the pressurised fluid being bled from the flow passage into the chamber 14, the chamber 14 is used as a replacement for one of the pockets. For this purpose, a duct 25 is welded to the dished plate 1 3 so that the working fluid may be introduced to discharged via the chamber 14, and a number of flow slots 26 (see also figure 4) are provided to establish communication between the chamber 14 and one of the flow passages. The duct 6 still acts as an external connection to one or other of the passages. In the arrangement illustrated, the ducts 6 and 25 communicate with the same flow passage, but this is not essential.

It will be appreciated that if the figure 3 type of arrangement is used at both sides, then communications will have to be established with the opposite flow passage.

By utilising the end covers as connections to the heat exchanger, the use of the conventional pockets, with their reinforcing end bars, is avoided, and a considerable further saving can be achieved.

Another separate modifications which is shown in figures 3 and 4 is the provision of stiffening plates 27 welded to the dished plate 13 and to the duct 6 to maintain the rigidity of the axial or central portion of the facer sheet 11.

It will be appreciated that the stiffener plates 27 may also be provided in the figure 1 or figure 2 type of end cover arrangement, particularly when of the welded up construction.

Turning now to figure 4, this shows how the ends of the strips 2 and 3 may be attached to the shell. The shell 1 itself is shown as being formed as an effective extension of the strip 3, e.g. by being welded on to it, and the strip 2 is shown as having its end welded at 31 to the strip 3. The opposite end of the metal forming the shell 1 is shown as having welded to it a closing patch 32 which is also welded to the shell 1 near its attachment to the strip 3.

In the arrangement of figure 6, there is shown an alternative which may be used if the shell is of comparatively thin material. In this arrangement, the shell 1 is somewhat longer to overlap itself as illustrated, and the closing patch 32 can therefore be eliminated. However, in order to form the weld 31, the shell has to be sufficiently deformable for access to be obtained before the shell 1 is put into its final position and welded to itself at 33.

Various modifications may be made within the scope of the invention.

Claims (10)

Claims

1. An end cover arrangement for a spiral heat exchanger comprising a facer sheet having a gasket on one face to cooperate with and to seal the adjacent edge of at least one spaced flow passage, a dished outer housing member sealed around the periphery of the facer sheet and forming a chamber with the other face of the facer sheet, and means for pressuring the chamber to provide reinforcement of the facer sheet.

2. An end cover arrangement as claimed in claim 1, in which a feed or discharge duct for a heat exchange medium passes sealingly through the chamber.

3. An end cover arrangement as claimed in claim 1 or 2, in which the outer housing is welded to the facer sheet to provide the peripheral seal.

4. An end cover arrangement as claimed in claim 1 or 2, in which the outer housing is sealed to the periphery of the facer sheet by a gasket.

5. An end cover arrangement as claimed in any of the preceding claims, in which the chamber is pressurised via weep holes admitting one of the working fluids, under pressure to the chamber.

6. An end cover arrangement as claimed in claim 5, in which the working fluid admitted is the one fluid bsing sealed by the gasket on the facer sheet.

7. An end cover arrangement as claimed in any of claims 1 to 4, in which the chamber has an inlet for a working fluid and an outlet to admit the working fluid to the spiral heat exchanger.

8. An end cover arrangement for a spiral heat exchanger substantially as hereinbefore described with reference to the accompanying drawings.

9. A spiral heat exchanger having one or more end cover arrangements as claimed in any of claims 1 to 8.

10. A spiral heat exchanger substantially as hereinbefore described with reference to the accompanying drawings.