EP0010679B1 - 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 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 check 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 the case with spiral tube heat exchangers because of the complicated shape is very difficult. In addition, a gas heat exchanger operated in counterflow between the primary and secondary medium has only a small temperature difference, which is also approximately constant over the length of the pipes, so that no significant temperature differences can occur in the pipes themselves, in their suspension or in the duct walls surrounding the pipes. which cause impermissible tensions. 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 from one another, in order to avoid stresses between components - Avoid different temperatures and, on the other hand, undesirable heat losses. Since the supply and discharge lines and the corresponding collectors for the cold or hot gas have considerable dimensions and accordingly with different. Operating conditions, particularly in the longitudinal direction, very different expansions are to be expected, at least one collector should be elastically fastened. The U-tubes themselves cannot accommodate these expansions because, at the high temperatures provided here, the voltages that are still permissible for the usable. ren active ingredients are low.

DE-OS 2658086 describes a heat exchanger for gas-cooled high-temperature reactors with a U-tube bundle for the coolant, which is arranged in a ring around a central distributor tube for the heating medium, the coolant flowing through the U-tube bundle from an outer distributor chamber into an inner collector and that Heating medium is guided in counterflow along the U-tube bundle. The two legs of the U-tubes are separated by a wall for flow control. The U-tubes are rigidly attached at both ends, so that different expansions and thus undesirable stresses occur in the U-tubes at the different temperatures to be expected in the hot and cold leg.

The object of the present invention is to design a heat exchanger according to the preamble of the first claim in such a way that it is suitable for maximum temperatures of approximately 950 ° C. and for temperature differences of approximately 650 ° C. between the gas inlet and the gas outlet and therefore impermissible voltages in the U. Tubes due to different temperatures of other components can be largely avoided. In addition, this heat exchanger should be fully testable and, insofar as it is used for nuclear reactor plants, it should be possible to test it 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-pipes themselves and the Kait gas collector attached to them can freely expand compared to the hot gas collector and 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 countercurrent, 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 proposed partition wall has a temperature locally in a countercurrently operated heat exchanger that differs only slightly from the temperature of the adjacent heat exchanger tube. Since this partition is thin-walled and insulated on one side and a gas stream flows against it on the other side at high speed, this partition has approximately the same temperature as the neighboring heat exchanger tube even when the gas temperature changes due to operation and accordingly expands to the same extent like this pipe out. Therefore, very different expansions cannot occur between pipes and partition, and this partition can be used not only for gas routing, but also as a load-bearing connection between the hot gas collector and the cold gas collector.

The space proposed in the second claim, which is separate 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 it by means of a suitable regulation or by pressure equalization via a filter; ^- That the pressure in the room is always the same as in the primary gas circuit, then this room is not endangered by the high pressure of the primary gas circuit. If, in addition, a slight excess pressure 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, however, the pressure in the primary gas circuit is reduced, so that one can open this room without worries from the outside and from this room can check collectors, U-pipes and the walls of 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.

These flexible elements can either be two corrugated tubes arranged concentrically one inside the other, which form an annular space, or a plurality of corrugated tubes of smaller diameter distributed over the circumference. Both embodiments can form the separate space described in claim 2, the supply lines from the outside to the cold gas collector being arranged inside or outside this space.

The mounting of the U-tubes proposed in claim 3 transfers 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 4 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 5 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 ° is less important for the strength of the collector.

The sheet metal jackets proposed in claims 6 and 7 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 is constantly at 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 one between these two sheet metal jackets; existing gap is only at its cold end due to a permissible, flexible element there. ment, for example a corrugated tube, closed 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 a gas heat exchanger operated in countercurrent are evident, 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, these waves, if their division corresponds to the neighboring pipe division, avoid that between. Channels are created in the U-tubes and the sheet metal jackets, in which the gas finds a lower flow resistance, accordingly flows there faster and is cooled less, so that different gas temperatures can ultimately be expected across the cross-section.

The support proposed in claim 8 should 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 Figur 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 an inventive heat exchanger for a gas-cooled high-temperature reactor.
• FIG. 2 shows an enlarged partial 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 3 is fastened, 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. 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 first 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 in FIG. 1 also encloses the tubes 17. During operation of the system, this space 20 is filled with the pure medium of the primary gas circuit 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 from outside when the pressure in the primary gas circuit is reduced and can be used for inspection and repair of the collectors 16 and the U-tubes 6 without the primary gas circuit itself having to be opened. 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 exchange 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 first 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 meanwhile 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 the outside to the inside. It has therefore proven to be expedient to arrange the individual U-tubes with 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: the cold legs 6b of the U-tubes 6 are limited. 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 presented in the description of the 7th claim. Between the aforementioned involute curved surfaces of U-tubes 6 horizontal spacer 24 are provided which, when the assembly into corresponding slots in the partition wall 9 _- are inserted and welded sheet metal casing 11 and there gastight.

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. 'Between these two sleeves 30 corresponding sheet metal strips 31 are inserted 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.

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 pipes 33 from the outside with several 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 separate from the primary gas circuit, which has the same function as the corresponding space 20 in FIG. 1, but is significantly smaller and only flexible elements 35 of significantly less Diameter required for connection to the support plate 2. 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 8 for the cold gas collector 32 or the tube plate 15 from FIG. 1.

Claims (8)

1. A heat-exchanger for gases at high temperature, in particular for the transfer of the heat of a hightemperature reactor from a primary gas cycle to a secondary gas cycle; the secondary gas is fed in counter-flow to the primary gas in numerous vertical U-pipes (6) which are connected in parallel; the U-pipes (6) are supported by a hot-gas collector (4), and open into this hot-gas collector at the hot end and into a cold-gas collector (16) at the cold end; the hot-gas collector (4) is rigidly secured to the housing (1) of the heat exchanger in the longitudinal direction; a partition (9) is arranged between the two limbs of the U-pipes (6); said heat exchanger is characterized by the following features:

a) the cold-gas collector (16) is flexibly secured to the housing (1);

b) the partition (9) serves as a supporting connection between the stationary hot gas collector (4) and the cold-gas collector (16) which is flexibly arranged in the axial direction.

2. A heat exchanger as claimed in Claim 1 for nuclear power plants having the following characteristics:

a) a space (20) which is separated from the primary gas cycle by means of flexible members (18 and 19) and is connected to the cold-gas collector (16);

b) said space (20) contains a channel from the exterior passing through a lid (36) to the cold gas collector (16).

3. A heat exchanger as claimed in Claim 1 having the following characteristic:

a) the hot ends of the U-pipes (6) are fixed at their upper straight parts to a holder (8), which is arranged on the central hot-gas collector (7), and from there in each case lead to the hot-gas collector (4) by means of an elastic pipe bend.

4. A heat exchanger as claimed in Claim 4 having the following characteristic:

a) the central hot-gas collector is conically constructed in the region of the inlet openings of the U-pipes.

5. A heat exchanger as claimed in Claim 1 having the following characteristic:

a) an insulating wall is arranged between the central hot-gas collector for the secondary gas and the primary gas cycle.

6. A heat exchanger as claimed in Claim 1 having the following characteristic:

a) the U-pipes are bounded on both the outside and the inside by two concentric sheet-metal casings (11 and 12, or 11 and 13);

b) a gap is provided between these two sheet-metal casings;

c) said gap is open at the hot end and closed by a flexible member (14) at the cold end; and _' d) of these two sheet-metal casings the sheet-metal casing (12 or 13) which does not adjoin the pipe assembly is insulated.

7. A heat exchanger as claimed in Claim 2 having the following characteristic:

a) the partitions or sheet-metal casings (11) which adjoin the assembly of the U-pipes (6) have an undulating cross-section.

8. A heat exchanger as claimed in Claim 1 in a housing, having the following characteristic:

a) below the cold-gas collector (16), there is arranged on the housing (1), a supporting means (37) for said collector;

b) the upper part (3) of the hot-gas collector (4) can be extended upwardly.

Images