EP0010679A1 - Heat exchanger for high-temperature gases - Google Patents

Abstract

A U-tube heat exchanger for the heat transfer from a primary gas circuit to a secondary gas circuit in a high temperature reactor. At the high temperatures of approximately 950 DEG C., the additionally permissible stresses on the used materials are low. The cold gas collector is therefore flexibly attached at the housing. The arrangement permits complete and also remote-controlled testing from the secondary gas-side of all parts of the primary gas circuit which are stressed by pressure. The flexible elements are neither stressed by the weight of the heat exchanger nor endangered by high temperatures.

Description

The present invention relates to a heat exchanger for gases of high temperature, in particular for the transfer of heat from a high-temperature reactor from a primary gas circuit to a secondary gas circuit. The secondary gas is to be conducted in counterflow to the primary gas in numerous parallel U-pipes.

Heat exchangers, whose heat-transferring surfaces consist of U-tubes, have considerable advantages, particularly as steam generators, compared to heat exchangers with straight tubes, because the U-tubes are firmly clamped at both ends, but with their U-bends against the housing or against them Can extend the suspension freely. Compared to the reversible tube heat exchangers proposed for gases of high temperature, the U tube heat exchangers have several significant advantages. On the one hand, they are easier to manufacture and easier to assemble and are therefore cheaper overall; on the other hand U-pipes are easier to test and repair after assembly and also after a long period of operation, because you can quickly and reliably test the long, straight legs of these U-pipes from the inside with long probes, which is very important for spiral-tube heat exchangers because of their complicated shape is difficult. In addition, a gas heat exchanger operated in countercurrent between the primary and the secondary medium has only a small temperature difference, which is also approximately constant over the length of the pipes, so that there are no significant temperature differences in the pipes themselves, in their suspension or in the duct walls surrounding the pipes can occur that cause impermissible voltages. Regardless of these advantages, however, a U-tube heat exchanger for gases of, for example, 950 C has considerable problems because the supply and discharge lines and the corresponding collectors for the cold or hot gas have to be separated spatially and constructively, on the one hand, to reduce the stresses between components of different types To avoid temperature and on the other hand undesirable heat loss. Since the supply and discharge lines and the corresponding collectors for the cold or hot gas have considerable dimensions and, accordingly, very different expansions can be expected in different operating conditions, in particular in the longitudinal direction, at least one collector must be elastically fastened. The U-tubes themselves cannot accommodate these expansions because at the high temperatures provided here, the stresses that are still permissible for the materials that can be used are low.

The object of the present invention is a heat exchanger according to the preamble of the first claim. This heat exchanger should be suitable for maximum temperatures of around 950 ° C and for temperature differences of around 650 ° C between the gas inlet and the gas outlet and should therefore largely avoid stresses due to different temperatures. In addition, this heat exchanger should be fully testable and, insofar as it is used for nuclear reactor plants, can be tested remotely from the secondary gas side without having to open the primary gas circuit.

The heat exchanger proposed in the first claim avoids stresses because the U-tubes themselves and the cold gas collector attached to them can expand freely with respect to the hot gas collector and with respect to the housing. Since the cold gas collector is not endangered by high temperatures either on the primary or on the secondary side of a gas heat exchanger operated in counterflow, this cold gas collector can be connected to the housing with conventional flexible elements such as corrugated pipes. The components of the cold gas collector can also be protected from the high temperatures of the hot gas collector by spatial separation and appropriate insulation. The flexible elements are not burdened by the weight of the U-tubes.

The partition wall proposed in the second claim has a local temperature in a countercurrently operated heat exchanger, which is only slightly different from the temperature of the adjacent heat exchanger Rohres differs. Since this partition is thin-walled and insulated on one side and a gas stream flows on the other side at high speed, this partition has about the same temperature as the neighboring heat exchanger tube even when the gas temperature changes due to operation, and expands accordingly to the same extent like this.tube out. Therefore, very different expansions cannot occur between the pipes and the partition wall, and this partition wall can be used not only for the gas routing but also as a supporting component between the hot gas collector and the cold gas collector.

The space proposed in the third claim separated from the primary gas circuit is of essential importance in heat exchangers for nuclear power plants, since the primary gas circuit inevitably contains radioactive contaminants. If you fill this space with the pure primary medium and ensure that the pressure in the room is always the same as that in the primary gas circuit, by means of a suitable control or pressure compensation, then this room is not endangered by the high pressure of the primary gas circuit. If, in addition, a slight overpressure is maintained in this room compared to the primary gas circuit, then it is even guaranteed that no radioactive contaminants can penetrate into this room even with small leaks. During tests or repairs on the heat exchanger, the pressure in the primary gas circuit is reduced so that you can safely open this room from the outside and check collectors, U-pipes and the walls of this room from this room without opening the primary gas circuit. This space, which does not serve to limit the primary gas circuit during operation, can therefore consist of flexible elements.

The arrangement proposed in claim 4 is particularly useful for heat exchangers that are to be accommodated in a cylindrical housing. The hot gas collector, which is particularly stressed by high temperatures, has a straight, cylindrical tube with a geometrically simple shape with clear, precisely calculable loads. The insulation can also be easily and reliably attached to such a geometrically simple component. By contrast, the cold gas collector, which is much less stressed by the lower gas temperature, surrounds the hot gas collector in a ring-shaped and concentric manner and is connected to it or the housing by flexible elements. These flexible elements can either be two corrugated tubes arranged concentrically one inside the other, which form an annular space, or several corrugated tubes of smaller diameter distributed over the circumference. Both embodiments can form the separate space described in claim 3, the supply lines from the outside to the cold gas collector being arranged inside or outside of this space.

The holder of the U-tubes proposed in claim 5 transmits the weight of the U-tubes and their forces to the central hot gas collector, so that the U-tubes laid from this clamping to the hot gas collector with an arc only have to absorb the low forces that can result from a different expansion of the hot gas collector and holder.

The conical shape of the central hot gas collector proposed in claim 6 allows the vertical U-pipes arranged at different distances from the center of the collector to be connected to the central hot gas collector with the same bend, so that the stresses in all pipe bends are the same.

The insulating wall proposed in claim 7 between the central hot gas collector and the primary gas inlet separates this collector from the hot primary gas circuit. Therefore, this collector can only have the temperature of the secondary gas, which is about 50 ° below that of the primary gas. At the high temperatures provided here, 50 are less important for the strength of the collector.

and 9. The sheet metal jackets proposed in claim 8 / claim are intended on the one hand to prevent the hot primary gas from flowing past the U-tubes without heat exchange and on the other hand to reduce the heat exchange between two hot gas streams of different temperatures. Therefore, a non-insulated sheet metal jacket is initially provided in the immediate vicinity of the U-tube bundle, which constantly has the same temperature as the tube bundle itself and therefore expands with it in the same sense. Another insulated sheet metal jacket is attached to the housing and can therefore expand completely independently of the tube bundle. The gap between these two sheet metal jackets is only closed at its cold end by a flexible element, such as a corrugated tube, which is quite permissible there, so that no subsets of the primary gas can flow through this gap without heat exchange with the U-tubes. At this point, too, the advantages of an im Counter-current operated gas heat exchanger, in which only low temperatures can actually occur at the cold end and the flexible elements necessary for perfect sealing are certainly not at risk. The corrugated cross section of the sheet metal jacket solves two different problems; on the one hand, the sheet metal jackets become flexible in the circumferential direction, so that they can expand together with the tube bundle; on the other hand, by these waves, if their division corresponds to the neighboring pipe division, it is avoided that channels develop between the U-pipes and the sheet metal jackets, in which the gas finds a lower flow resistance, accordingly flows faster there and is cooled less, so that in the end Different gas temperatures can be expected across the cross-section.

The support proposed in claim 10 is intended to carry the cold gas collector and the components attached to it during inspections and repairs so that the upper part of the hot gas collector can be removed and its lower part can be checked. In addition, this support can serve as a safeguard against the heat exchanger falling and as a limitation of the vibrations during earthquakes.

• Figur 1 zeigt in schematischer Darstellung einen senkrechten Längsschnitt durch einen erfindungsgemäßen Wärmetauscher für einen gasgekühlten Hochtemperaturreaktor.
• Figur 2 zeigt in vergrößerter Darstellung einen waagerechten Teilschnitt A-A durch Figur 1.
• Figur 3 zeigt einen weiteren Teilschnitt B-B durch Fig.1.
• Figur 4 zeigt eine Ansicht der Figur 3.
• Figur 5 zeigt eine Alternative zu Figur 1.

Figures 1 to 5 show possible embodiments of the invention.

• Figure 1 shows a schematic representation of a vertical longitudinal section through a heat exchanger according to the invention for a gas-cooled high-temperature reactor.
• FIG. 2 shows an enlarged partial horizontal section AA through FIG. 1.
• FIG. 3 shows a further partial section BB through FIG. 1.
• FIG. 4 shows a view of FIG. 3.
• FIG. 5 shows an alternative to FIG. 1.

In Figure 1, the completely closed, cylindrical heat exchanger housing 1 is delimited at its upper end by a support plate 2, to which an upper central hot gas pipe is attached, which in turn carries a lower central hot gas collector 4. Both parts are protected on the inside by the insulation 5. In the lower conical part of the central hot gas collector 4, the hot ends of the U-tubes 6, which are clamped at 7 and carried by the central hot gas collector 4 with a special holder 8, open out. In addition, this collector 4 carries a double-walled and also U-shaped partition 9 in longitudinal section, which is filled with insulation 10. The U-tubes 6 form an annular tube bundle, which is delimited both internally and externally initially by a concentric, non-insulated sheet metal jacket 11 of U-shaped longitudinal section and then by two concentric, insulated sheet metal jackets 12 and 13. A gap is provided between these sheet metal shells, which is flexibly sealed at the cold end by a corrugated tube 14. The U-tubes 6 and the double-walled partition 9 carry at their cold end an annular tube plate 15, on the top of which an annular cold gas collector 16 is also releasably attached. In this collector 16 several, distributed over the circumference helically wound cold gas pipes 17 open, which lead the cold secondary gas from the outside to the U-tubes 6. The tube plate 15 forms, together with the upper end of the housing 1, with the support plate 2 and with at least two concentric corrugated tubes 18 and 19, a space 20 which is separate from the primary gas circuit underneath and which also encloses the tubes 17 in FIG. This Room 20 is filled with the pure medium of the primary gas circuit during operation of the system and is kept at the pressure of the primary gas circuit by means of a control system (not shown in more detail) or by means of pressure compensation. In this way, this space 20 is not burdened by pressure differences and can be opened at reduced pressure in the primary gas circuit from the outside and used for inspection and repair of the collector and the U-pipes, without having to open the primary gas circuit itself. Below the hot gas collector 4 there is an insulating wall 21 which is fastened to the holder 8 and separates the hot gas collector 4 from the primary gas circuit.

• Das heiße Primärgas tritt durch den waagerechten Rohrstutzen 22 in den zentralen, isolierten Blechmantel 13 ein, wird unterhalb der isolierenden Wand 21 umgelenkt und fließt zunächst abwärts und dann aufwärts an den U-Rohren 6 entlang durch einen Raum, der einerseits durch den Blechmantel 11 und andererseits durch die Trennwand 10 gebildet wird. Unterhalb der Rohrplatte 15 wird das inzwischen abgekühlte Primärgas nach unten umgelenkt und fließt zwischen dem Blechmantel 12 und dem Gehäuse 1 abwärts. Das kalte Sekundärgas fließt durch mehrere schraubenlinienartig ineinander gewendelte Rohre 17 in den ringförmigen Sammler 16 und von dort aus durch die in der Rohrplatte 15 befestigten U-Rohre 6 zum Heißgassammler 4 und tritt aus dem oberen Heißgasrohr 3 aus.

The flow of the two heat exchanger media is as follows:

• The hot primary gas enters the central, insulated sheet metal jacket 13 through the horizontal pipe socket 22, is deflected below the insulating wall 21 and initially flows downwards and then upwards along the U-tubes 6 through a space which, on the one hand, through the sheet metal jacket 11 and on the other hand is formed by the partition 10. Below the tube plate 15, the primary gas, which has now cooled, is deflected downward and flows downward between the sheet metal jacket 12 and the housing 1. The cold secondary gas flows through a plurality of helically coiled tubes 17 into the annular collector 16 and from there through the U-tubes 6 fastened in the tube plate 15 to the hot gas collector 4 and emerges from the upper hot gas tube 3.

FIG. 2 shows with the same designations as in FIG. 1 how the U-tubes 6 are arranged in cross-section with their cold leg 6b and the warm leg 6a. In the gas heat exchangers proposed here, the primary gas temperature should not have any significant differences in cross-section with regard to the lowest possible thermal stresses. Therefore, the flow resistance and thus also the free cross-sections outside the U-tubes must remain the same in cross-section from outside to inside. It has therefore proven to be expedient to arrange the individual U-tubes with a constant pitch in involute-curved vertical surfaces. These curved surfaces, each consisting of thirteen U-tubes 6 in FIG. 2, can be preassembled in the workshop and then assembled as a whole surface in the concentric sheet metal jacket 11. Viewed from the inside out, the insulated sheet metal wall 13, which serves as a guide for the incoming hot primary gas, is surrounded at a distance by the inner sheet metal jacket 11a, which, together with the inner partition wall 9a, delimits the hot legs 6a of the U-tubes 6, while the outer partition 9b, together with the outer sheet metal jacket 11b, delimits the cold legs 6b of the U-tubes 6. Outside the sheet metal jacket 11b, the insulated sheet metal jacket 12 is arranged at a distance, which in turn, together with the housing 1 (not shown in FIG. 2), represents an annular channel for the cooled primary gas flowing downward. The partitions 9 and sheet metal jackets 11 are shown in FIG. 2 with a corrugated cross section. The advantages of this undulating cross-section were described in the description of the _9th Claim represented. Between the previously mentioned involute curved surfaces of U-tubes 6 are each provided with horizontal spacers 24 which are inserted into corresponding slots in partition 9 and sheet metal jacket 11 during assembly and are welded there in a gastight manner.

FIGS. 3 and 4 show how the hot ends of the U-tubes 6 are fastened between the holder 8 and the partition 9. Two cylindrical sleeves 30 are fastened one above the other on the U-tubes 6, for example by high-temperature soldering. Corresponding sheet metal strips 31 are inserted between these two sleeves 30 during assembly, which are bent in an involute manner and angled at both ends, so that they fit into a corresponding rotation of the holder 8 or on the partition 9.

FIG. 5 shows, as an alternative to FIG. 1, the upper part of the heat exchanger housing 1, which is likewise delimited at its upper end by a support plate 2 to which an upper central hot gas pipe 3 is fastened, which in turn carries a lower central hot gas collector 4. Instead of the annular tube plate 15 shown in FIG. 1 with the annular cold gas collector 16 screwed thereon, a hollow annular cold gas collector 32 is provided here, which, like in FIG. 1, can be supplied with cold gas from the outside with a plurality of cold gas pipes 33 distributed over the circumference. The cold gas collector 32 itself is closed during normal operation with one or more lids 34 which are arranged within a space 20 which is separate from the primary gas circuit and which has the same function as the corresponding space 20 in FIG. 1 but is significantly smaller and only flexible elements 35 from much smaller diameter than connection to the support plate 2 needed. During operation, as in FIG. 1, this space is closed with a cover 36 and is kept at the pressure of the primary gas circuit by means of a regulation (not shown) or a pressure equalization. Part 37 is the support proposed in claim 10 for the cold gas collector 32 or the tube plate 15 from FIG. 1.

Claims (7)

The present invention relates to a heat exchanger for gases of high temperature, in particular for the transfer of heat from a high-temperature reactor from a primary gas circuit to a secondary gas circuit. The secondary gas is to be conducted in counterflow to the primary gas in numerous parallel U-pipes. Heat exchangers, whose heat-transferring surfaces consist of U-tubes, have considerable advantages, particularly as steam generators, compared to heat exchangers with straight tubes, because the U-tubes are firmly clamped at both ends, but with their U-bends against the housing or against them Can extend the suspension freely. Compared to the reversible tubular heat exchangers proposed for gases of high temperature, the U tubular heat exchangers have several significant advantages. On the one hand, they are easier to manufacture and easier to assemble and are therefore cheaper overall: on the other hand U-tubes are easier to test and repair after assembly and also after a long period of operation, because you can quickly and reliably check the long, straight legs of these U-tubes from the inside with long probes, which is very important for spiral tube heat exchangers because of their complicated shape is difficult. In addition, a gas heat exchanger operated in countercurrent between the primary and the secondary medium has only a small temperature difference, which is also approximately constant over the length of the pipes, so that there are no significant temperature differences in the pipes themselves, in their suspension or in the duct walls surrounding the pipes can occur that cause impermissible voltages. Regardless of these advantages, however, a U-tube heat exchanger for gases of, for example, 950 C has considerable problems because the supply and discharge lines and the corresponding collectors for the cold and hot gas have to be separated spatially and constructively; on the one hand to avoid tensions between components of different temperatures and on the other hand to avoid undesirable heat losses. Since the supply and discharge lines and the corresponding collectors for the cold or hot gas have considerable dimensions and, accordingly, very different expansions can be expected in different operating states, in particular in the longitudinal direction, at least one collector must be elastically fastened. The U-tubes themselves cannot accommodate these expansions because at the high temperatures provided here, the stresses that are still permissible for the materials that can be used are low. arranged bracket clamped and lead from there with an elastic pipe bend to the hot gas collector. 6. Heat exchanger according to claim 5 with the following feature: a) The central hot gas collector is designed conically in the area of the pipe openings of the U-pipes. 7. Heat exchanger according to claim 1 with the following features: a) An insulating wall is arranged between the central hot gas collector for the secondary gas and the primary gas circuit. 8. Heat exchanger according to claim 4 with the following features: a) The U-tubes are bounded both externally and internally by two concentric sheet metal shells, b) a gap is provided between these two sheet metal shells, c) this gap is open at the hot end and closed by a flexible element at the cold end, d) the sheet metal jacket not adjacent to the tube bundle is isolated from these two sheet metal jackets. 9. Heat exchanger according to claim 2 or 4 with the following feature: a) The partitions or sheet metal jackets adjoining the bundle of U-tubes have a wavy cross section. 10. Heat exchanger according to claim 1 in a housing with the following features: a) A support for this collector is provided on the housing below the cold gas collector; b) The upper part of the hot gas collector can be removed upwards.

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