WO1999050608A1

WO1999050608A1 - Heat exchanger

Info

Publication number: WO1999050608A1
Application number: PCT/NL1999/000191
Authority: WO
Inventors: Cornelis Jan Dekker
Original assignee: Continental Engineering B.V.
Priority date: 1998-03-30
Filing date: 1999-03-30
Publication date: 1999-10-07
Also published as: CA2326799A1; NL1008748C2; EP1068482A1; AU3173399A

Abstract

A heat exchanger comprises a housing (1) that is closed at two facing ends (2, 3), through which housing a tube bundle extends, which tubes (7) are attached to a tube plate (4, 5) at both ends (2, 3), baffle plates (12) which the tubes (7) are supported spread out at regular intervals between the tube plates (4, 5), a first supply (8) and drain (9) in the housing (1) for a first heat exchange medium, which first medium is lead between that supply (8) and drain (9) according to a prescribed flow pattern by way of the baffle plates (12), as well as a second supply (10) and drain (11) connected to the inside of the tubes (7) for a second heat exchange medium. At least a part of the tube bundle between two successive baffle plates (12) is stabilized with respect to buckling by a supporting means (14) that is located near a baffle plate (12).

Description

Heat exchanger

The invention relates to a heat exchanger, comprising a housing that is closed at two facing ends, through which housing a tube bundle extends, which tubes are always attached to a tube plate at both ends, baffle plates in which the tubes are supported spread out at regular intervals between the tube plates, a first supply and drain in the housing for a first heat exchange medium, which first medium is lead between that supply and drain according to a prescribed flow pattern by way of the baffle plates, as well as a second supply and drain connected to the inside of the tubes for a second heat exchange medium.

In many industry processes, heat exchangers are used for the control of the energy and heat flows within a process installation. An example is in the chemical industry, where heat exchangers are used to achieve a favorable heat balance by supplying heat from one process flow to another. Normally the tubes are attached to the tube plates at both ends by expansion and possibly welding. These tube plates can in turn be welded onto the housing (fixed tube plates). As a consequence, the tubes are so firmly fixed in the housing that considerable tensile and compression stress can occur in the various parts.

In heat exchangers with a floating head, one tube plate is permanently fixed onto the housing and the other tube plate is not fixed to the housing. Using a sliding closure and/or other provisions, both heat exchange media are kept apart. Unequal pressure in both media lead to the bending of both tube plates, whereby the heat exchangers with a floating head can also have considerable compression stress in at least a part of the tube bundle. As a result of compressive force produced by compression stress, the rather long tubes should quickly buckle, whereby the working of the heal exchanger is disturbed and damage can occur. Using the baffle plates, the buckling-length of the tubes is reduced, however, with the positive effect that the buckling does not occur as easily. Nevertheless, in practice it appears that the danger of buckling still exists under certain circumstances. That can be the case, for example, if the baffle plates 2 are placed relatively far apart for certain reasons, for example, with the goal of limiting the pressure drop across the heat exchanger.

An object of the invention is therefore to provide a heat exchanger that offers better support of the tubes, such that, in the cases mentioned, the risk of buckling remains limited. That object is achieved by stabilizing at least a part of the tube bundle, with respect to buckling, between two successive baffle plates using a support means situated near a baffle plate.

By applying such means of support, the support of the tube bundle is so much improved that higher levels of compression stress are permissible, without the construction of the heat exchanger being at risk of buckling due to instability. That advantage can be made use of in various ways.

Firstly, with otherwise equal conditions, the baffle plates can be placed further apart. The advantage of this is that lower pressure drops across the body side of the heat exchanger occur. As an alternative, with the same distances between the baffle plates, stricter design conditions could be allowed for equal tube dimensions, leading to higher levels of compression stress in the tubes.

The means of support must anyway be positioned so that they disturb the normal medium flow through the housing as little as possible. That condition leads to a position in close proximity to a baffle plate. In practice, there are more or less unavoidable 'still' areas in the vicinity of the baffle plates, so that a support means placed there will give little rise to disturbances.

It must be realized that even a small distance between the baffle plate and support means produces a considerable increase in the critical buckling load. With normal baffle plates, the tubes are considered to be hinged in the baffle plate. The thickness of the baffle plates is too small to provide a full rotation-free clamping.

The pairs, consisting of a baffle plate and a support means, although located at a short distance away from each other, do produce such a rotation- free clamping of the tubes, which in principle increases the critical buckling load by a factor of 4.

The combination of a baffle plate with a closely positioned support means or auxiliary plate, stops the tube bundles from buckling in the overstrcss to the next baffle plate (or combination of baffle plate and support means) by making rotation of the tube bundle almost impossible at that point. 3

The support means can be implemented in various ways. The preference is for support means in the form of an auxiliary plate. According to the invention there is, therefore, at least one auxiliary plate nearby a baffle plate.

Such an auxiliary plate, although having a certain obstructive working, will give rise to few disturbances because of its position.

The distance between the baffle plate and neighboring auxiliary plate is preferably an order of magnitude smaller than the distance between two neighboring baffle plates.

The baffle plates and auxiliary plates can be implemented in various ways. According to a first embodiment, the baffle plates and the auxiliary plates can come into contact with the internal wall of the housing over a part of their circumference, and over another part of their circumference can be at a distance from that wall.

Although these auxiliary plates can be used to support all the tubes in the bundle, it can be more advantageous to support only some of the tubes. The tubes on the outside of the bundle, which are relatively stiffly clamped between the tube plates, are in any case candidates for support by the auxiliary plates.

The tubes that lie nearer the center of the bundle, which are less stiffly clamped in the center region of the tube plate, are less susceptible to buckling. As the baffle plates partly overlap each other, these tubes are often supported by all of the baffle plates. This is in contrast to many tubes around the edge which are only supported by every other one of the baffle plates. Due to the now much larger buckling length, they are much more susceptible to buckling.

According to the invention, these circumstances can also be taken into account by choosing the height of the auxiliary plate to be smaller than the height of the nearby baffle plate, such that the centrally placed tubes extend past the auxiliary plate.

The slight disruptive working of the auxiliary plates on the How can be further reduced if a recess, functioning as a flow window, is fitted in the edge of the auxiliary plate that is turned towards the wall of the housing. As a consequence, the total heat exchange surface of the tubes can also be more or less maintained.

Such a flow window can be rather small. The medium can flow via that flow window around the tubes in the space between the baffle plate and the corresponding auxiliary plate. As the distance between the baffle plate and auxiliary plate is much 4 smaller that the distance between the baffle plates themselves, the flow window only has to let through a proportionally smaller flow. The omission of a small number of tubes is, in itself, enough to realize an adequate flow window.

According to a second embodiment, successive ring-shaped baffle plates and disk-shaped baffle plates can be provided, which ring-shaped plates come into contact with the housing around their circumference and which have a central passage, while the auxiliary plates are also ring-shaped and come into contact with the wall of the housing around their circumference.

In this variant, the height of an auxiliary plate can again be smaller than the height of a ring-shaped baffle plate.

In a known manner, the housing can have a mainly circular cross-section.

The invention will be elucidated with reference to the embodiment shown in the figures.

Figure 1 shows an exposed view, in perspective, of the heat exchanger according to the invention.

Figure 2 shows a vertical and radial section through the heat exchanger.

Figures 3 and 4 show a further variant.

The heat exchanger shown in figure 1 comprises a housing 1 that is closed at both ends by end walls 2, 3. At some distance inside with respect to the end walls 2,3, two tube plates 4,5 are fitted, each provided with a number of holes 6. The tubes 7 are connected to the holes.

Between the end wall 2 and the tube plate 4 is an area in which a first heat exchange medium can be supplied via the first supply 8. This first heat exchange medium flows via the holes 6 through the tubes 7, after which it arrives in the area between the other tube plate 5 and the other end wall 3. The first heat exchange medium is then removed via the first drain 9.

A second supply 10, and also a second drain 11, are connected to the area between both baffle plates 5 and 6. The second heat exchange medium can be lead around the tubes 7 via the second supply 10 and second drain 1 1. In this way, an exchange of heat takes place between both heat exchange media.

In the usual way, a number of baffle plates 12 are fitted in the area between the tube plates 5,6, which enable the second heat exchange medium to pass through in a zigzag shaped path in order to promote the heat exchange. 5

The baffle plates 12 can each extend a little above the height of the area concerned and alternately come into contact with the top and the bottom of the wall of the housing 1, as is clear in figures 1 and 2.

Although the tubes 7 are firmly clamped between both the tube plates 5,6 and the baffle plates 12, the problem of buckling can still arise if the temperature difference between the wall of the housing 1 and the tubes 7 is too large. In that case, the tubes 7 can buckle between the tube plates 5,6 and the baffle plates 12, whereby at the position of the baffle plates 12 the tubes can turn a little.

As a solution to that problem, several baffle plates 12 could be placed nearer to each other, but this is often not permissible due to the associated rise in the flow resistance.

To make a safely working heat exchanger possible, with the temperature differences mentioned and with unchanged baffle plates, according to the invention, auxiliary plates 14 are placed near each baffle plate. These auxiliary plates are situated fairly close to the baffle plate concerned 12, so that the flow 13 of the concerned heat exchange medium is not disturbed too much.

Each auxiliary plate 14 comes into contact with the internal wall of the housing 1. They can be cut-away in the central area so that a flow window 15 remains, through which a certain amount of heat exchange medium can still flow. In this way, the total disturbance by the auxiliary plates 14 with respect to the flow of the heat exchange medium becomes almost negligible.

Every pair consisting of a baffle plate 12 and an auxiliary plate 14 forms a stable clamping of the concerned tubes 7, whereby their buckling load is considerably increased. The tubes 7 can no longer turn at the point of clamping, which results, in principle, in an increase in the buckling load by a factor 4.

As shown in figures 1 and 2, not all tubes 7 are supported by an auxiliary plate 14. Tubes 7 which go through all baffle plates 12 have a much shorter buckling length than tubes which are alternately supported by the baffle plates 12. The shorter supported lengths produce a much larger buckling load that does not need further improvement by the auxiliary plates 14. In addition, the central tubes 7 of the bundle which are farthest away from the wall of the housing 1, are less susceptible to buckling. They can compensate for their length differences, to a certain extent, due to the fact that the tube plates 5,6 bulge somewhat in the middle. 6

The tubes 7 closer to the wall of the housing 1 have that possibility to a much lesser extent, and, for this reason, these tubes 7 are supported by the auxiliary plates.

As can be clearly seen in figure 1, the auxiliary plates are made shorter than the baffle plates 12, for the reason given above. In a known manner, all the baffle plates 12 are attached to each other by means of rods 30. The tube plate 4 is fitted to the leftmost end of these rods 30, as shown in figure 1 ; the other end of the rods is free.

According to the invention, the auxiliary plates 14 are also attached to the rods 30. In the embodiment applied in figures 3 and 4, consecutive ring-shaped baffle plates 20 and disk-shaped baffle plates 21 are used. These baffle plates also prescribe a certain flow curve of the heat exchange medium.

The heat exchange tubes 25 situated further inside are all only supported in the ring-shaped baffle plate 21. Since these are under less pressure, as explained earlier, this does not cause a problem. Some heat exchange tubes situated nearer the outside 26 are supported by both sorts of baffle plate 20, 21, so that there are also few problems to fear here.

Other heat exchange tubes 27 are only supported by the disk-shaped baffle plates 20 and for these heat exchange tubes, extra support is desirable. To that end, the ring-shaped auxiliary plates 24 according to the invention are placed near the ring-shaped baffle plates 20.

Analogously to the embodiment of figures 1 and 2, these auxiliary plates 24 offer an almost non-rotating support, together with the nearby baffle plates 20, whereby the risk of buckling is considerably reduced even for the heat exchange tubes 27 situated nearer the outside.

Claims

1. Heat exchanger, comprising a housing (1) that is closed at two facing ends (2,3), through which housing a tube bundle extends, which tubes (7) are attached to a tube plate (5, 6) at both ends, baffle plates (12) in which the tubes are supported spread out at regular intervals between the tube plates (5, 6), a first supply (10) and drain (11) in the housing (1) for a first heat exchange medium, which first medium is lead between that supply (10) and drain (11) according to a prescribed flow pattern (13) by way of the baffle plates (12), as well as a second supply (8) and drain (9) connected to the inside of the tubes (7) for a second heat exchange medium, characterized in that a part of the tube bundle (7) between two successive baffle plates (12) is stabilized with respect to buckling by a supporting means (14) that is located near a baffle plate (12).

2. Heat exchanger according to claim 1, wherein an auxiliary plate (14) is situated near at least one baffle plate (12).

3. Heat exchanger according to claim 2, wherein the distance between a baffle plate (12) and the neighboring auxiliary plate (14) is an order of magnitude smaller than the distance between two neighboring baffle plates (12).

4. Heat exchanger according to claim 2 or 3, wherein the baffle plates (12) and the auxiliary plates (14) come into contact with the internal wall of the housing over a part of their circumference, and over another part of their circumference are at a distance from the walls.

5. Heat exchanger according to claim 4, wherein the height of an auxiliary plate (14) is smaller than the height of the neighboring baffle plate (12) such that the centrally placed tubes (7) extend past the auxiliary plate (14).

6. Heat exchanger according to claim 4 or 5, wherein an auxiliary plate (14) is partially recessed on the edge that is turned towards the wall of the housing, forming a flow window (15). 8

7. Heat exchanger according to claim 2 or 3, wherein successive ring-shaped baffle plates (20) and disk- shaped baffle plates (21) are provided, which ring-shaped plates (20) come into contact with the housing (1) around their circumference and which have a central passage (23), and the auxiliary plates (24) which are also ring- shaped and come into contact with the wall of the housing (1) around their circumference.

8. Heat exchanger according to claim 7, wherein the height of an auxiliary plate (24) is smaller than the height of the neighboring ring-shaped baffle plate (20).

9. Heat exchanger according to one of the preceding claims, wherein the housing (1) has a substantially circular cross-section.