EP0011834B1 - Liquid-metal heated steam generator with integrated reheater - Google Patents

Abstract

PCT No. PCT/EP79/00093 Sec. 371 Date Jul. 28, 1980 Sec. 102(e) Date Jul. 28, 1980 PCT Filed Nov. 23, 1979 PCT Pub. No. WO80/01101 PCT Pub. Date May 29, 1980.Steam generator, preferably for use in nuclear energy plants, which comprises several coiled tube bundles (5) which are arranged in series and disposed in a common container (1), in which steam is generated and superheated thereafter. The individual tube bundles are separated from each other by interspaces (16) in which straight connecting tubes are arranged. Points which require inspection, and are possibly in danger of springing leaks, for example, the welded connections between the individual tube lengths, are positioned in these interspaces for easier accessibility. Furthermore in the same container are also tube bundles (21) arranged in which the steam is superheated. In the middle of the container a central tube (4) is arranged, in which the feedwater supply (6) is conducted, and which in operation closed by a blow-out disc (15), and which, if necessary can discharge the products of a liquid metal-water reaction. Special configurations of the feedwater distributors (8-11) are proposed, which enhance the safety of the steam generator in the case of malfunctions, for example, absorb the reaction forces of torn tube lines. Furthermore embodiments of the steam-collectors (27) are proposed which facilitate the inspection of the tube bundles.

Description

The present invention relates to a steam generator according to the preamble of claim 1.

In order to increase the overall efficiency of steam power plants, it is advisable to reheat the steam which has already relaxed and cooled in the high and medium pressure section of a steam turbine by so-called reheating. With liquid metal, e.g. Sodium-cooled nuclear reactors, which have significantly higher requirements with regard to safety and reliability than conventionally heated steam power plants, have so far either avoided this intermediate overheating or have been installed in separate apparatuses which are connected in parallel with the superheaters on the side of the hot liquid metal. Nuclear reactor plants, which often have significantly higher outputs than conventionally heated plants, should not only generate electricity with high availability and high overall efficiency; in the event of a possible accident, the heat emitted by the nuclear reactor should be able to be dissipated without the nuclear reactor substantially exceeding the operating temperatures suitable for it. Therefore, efforts have so far been made to use different types of apparatus, e.g. Separate superheaters and intermediate superheaters so that they do not affect each other in the event of a malfunction and can be operated independently of one another. However, this separate design leads to a considerable outlay for pipelines, insulation and safety devices, especially in the case of liquid metal-cooled nuclear power plants, quite apart from the additional space requirement, which is associated with high costs especially in the case of nuclear power plants.

DE-A 24 48 832 has already described a liquid metal / water heat exchanger as a steam generator for nuclear power plants. Several vertical tube bundles, each of which is surrounded by a jacket that is open at the top and bottom, are interchangeably arranged in a container. Since the hot liquid metal is guided in countercurrent to the water or steam, a compact arrangement is already possible here, in which the individual tube bundles can be replaced quickly and with little effort in the event of damage. An intermediate overheating of the steam with hot liquid metal is not yet provided in this arrangement.

• 1) in bezug auf den thermischen Wirkungsgrad der Dampfanlage durch Zwischenüberhitzung des Dampfes mit heißem Flüssigmetall,
• 2) in bezug auf die Anlagekosten durch Integration des Zwischenüberhitzers in den ohnehin vorhandenen Dampferzeuger-Behälter,
• 3) in bezug auf Betriebskosten durch erleichterte Inspektion und Reparatur, sowie durch redundante Aufhängung der Dampferzeugerbündel.

The object of the present invention is a liquid metal-heated steam generator which is more economical overall than the previous ones. This economy should be achieved:

• 1) in relation to the thermal efficiency of the steam system by reheating the steam with hot liquid metal,
• 2) in terms of plant costs by integrating the reheater in the steam generator tank which is already present,
• 3) in terms of operating costs through easier inspection and repair, as well as through redundant suspension of the steam generator bundle.

• 1) in regelmäßigen Abständen geprüft und überwacht werden müssen,
• 2) die zur Überprüfung der übrigen Bauteile notwendig sind und
• 3) die für die anderen Bauteile eine Gefahr darstellen könnten.

To solve this problem, a dapfer according to claim 1 is proposed. It was previously customary to build the steam generator heated with liquid metal as compactly as possible and without large gaps between heating surfaces of different types, because the volume of these containers initially directly influenced their price and also indirectly, via the increase in the liquid metal volume, also the price of the entire system, including the auxiliary systems elevated. However, the horizontal gaps between individual tube bundles of different and the same type, which deviate from this basic principle, have considerable advantages for operation, inspection and repair of the heat exchangers, although they consume valuable space. Those components are arranged within these gaps

• 1) must be checked and monitored at regular intervals,
• 2) which are necessary to check the other components and
• 3) that could pose a danger to the other components.

In these spaces ₉ ' _R n the weld seams which are necessarily present in the case of long heat exchanger tubes are arranged at a considerable distance from other components. It has been found that the at least possible damage to liquid metal water heat exchangers occurs almost exclusively on the inevitably present weld seams of the heat exchanger tubes. If you deliberately place these weld seams in the spaces between the individual tube bundles, you can check them there better than in a narrow tube bundle and correct them if necessary. In addition, the arrangement of these welds in a free space at a distance from other components has another significant advantage for the operation of the overall system. Experience has shown that even the smallest leaks on a pipe containing water or steam within a liquid metal container lead to greater damage after a short time because the water vapor escaping under high pressure takes on a flame-like shape in the liquid metal and is too high and locally narrow due to the chemical reaction between water and liquid metal limited temperatures. Together with the high speed of the steam escaping under high pressure, neighboring components are very quickly destroyed by these flame-like phenomena.

The inventive arrangement of horizontal gaps between the Pipe bundles and the arrangement of all welds in these spaces can be ensured with a high probability that no damage will occur in the pipe bundles themselves. Under this condition, it is possible to arrange not only evaporator and superheater sensors but also reheater tube bundles in the same container, because no mutual interference can be expected here.

The steam generator according to claim 2 brings two further advantages for operation and monitoring. Compared to the previously known suspension of an entire heat exchanger tube bundle at the upper end of the container, the proposed arrangement of several support structures between the individual tube bundles initially ensures that each individual support structure is significantly less stressed because it only has to carry part of the overall tube bundle. The reliability of the overall construction is increased by the proposed double function of a supporting structure, namely, on the one hand, in the normal case, on the one hand, to hold the tube bundle underneath and, on the other hand, in the event of failure of an overlying supporting structure, also the overlying tube bundle.

The distributor construction proposed in claim 3 avoids inadmissible tensions on the one hand due to different expansion of the downpipe and central tube with the tube sheets, and on the other hand brings about a uniform flow against all spiral tubes distributed over the circumference of the container. In addition, the eccentric arrangement of the single downpipe and the helical shape of the distributor pipes keep the center of the central pipe free for remote-controlled inspection and repair devices.

The arrangement according to claim 4 fulfills two conflicting requirements. On the one hand, the sub-distributors and the space underneath should be accessible for remote-controlled inspection and repair devices; on the other hand, the subdistributors, which are evenly distributed over the circumference, should support one another in the event of one of them tearing off, so that no secondary damage to other components can occur. The support structure according to the invention, which is arranged at a short distance from the floors of the sub-distributors, is open at the top and bottom and is therefore freely accessible for devices. In addition, it can also be removed with a simple device upwards, if necessary also downwards.

The arrangement proposed in claim 5 is also intended to avoid major consequential damage after damage to the downpipe. The proposed double pipe is intended to hold the lower end of this down pipe in case it starts to move due to recoil forces from its bottom or from a completely torn distribution pipe.

The collector proposed in claim 6 is intended to summarize numerous coiled tubes. Since these long spiral tubes have to be checked at regular intervals from the inside with long flexible probes, the spiral tubes should be accessible from above with a manipulator. So that such a manipulator can now reach all pipe ends from one point in the direction of the pipe axis, it is proposed according to the invention not to weld these pipe ends into a flat pipe plate as before, but into part of a spherical surface. In this way, all the pipe ends lying on a circular path can be reached simply by rotating the corresponding manipulator and reaching the respectively adjacent circular path of pipe ends by changing the angle between the manipulator axis and the collector axis.

The arrangement according to claim 7 proposes a construction that avoids inadmissible thermal stresses due to different expansion of the container and central tube, which nevertheless allows the central tube with the spiral tubes attached to it to be easily removed and which protects the lower end of the central tube against impermissible horizontal loads , for example in the event of an earthquake.

The embodiment according to claim 8 allows repair work by subjecting the helical tubes to a low pressure to remove the water completely from them and from the sub-distributors located at the lowest point.

• Fig. 1 den unteren, und
• Fig. 2 den oberen Teil eines Längsschnittes durch den Dampferzeuger,
• Fig. 3 die Aufsicht auf denselben,
• Fig. 4 einen weiteren Längsschnitt in verkleinertem Maßstab,
• Fig. 5 einen Schnitt entsprechend der Linie III-IV der Fig. 1 in vergrößertem Maßstab,
• Fig. 6 in vergrößertem Maßstab die Einzelheit X der Fig. 1.

Figures 1 to 4 show a possible embodiment of the invention, namely

• Fig. 1 the lower, and
• 2 shows the upper part of a longitudinal section through the steam generator,
• 3 is the supervision of the same,
• 4 shows a further longitudinal section on a reduced scale,
• 5 shows a section along the line III-IV of FIG. 1 on an enlarged scale,
• 6 shows the detail X of FIG. 1 on an enlarged scale.

The steam generator is arranged in a container 1, through which liquid secondary sodium flows, which is heated in a sodium / sodium intermediate heat exchanger (not shown here) by the primary sodium used as a coolant for a nuclear reactor and by a nozzle 2 and by a further nozzle 3 emerges. In the interior of the container 1 there is a central tube 4 closed at the bottom, and between them a number of heat exchanger tubes combined into bundles 5, of which the lower ones are used in a known manner for steam generation and the upper ones for overheating and each occupying a sector of the intermediate space. The feed water is fed through a downpipe 6, which is arranged inside the central tube 4 filled with air or an inert gas, thereby eliminating the risk of a reaction between water and sodium in the event of leaks in the downpipe is switched. The downpipe 6 ends in a distributor 7, of which in the example four pipes 8 coiled to compensate for thermal expansion lead to sub-distributors 9 with an approximately hemispherical bottom and a tube plate 10, into which the individual steam generator tubes 11 are welded. The recoil forces occurring when one of the pipes 8 is torn off from the distributor 7 are absorbed by a double pipe 12 surrounding the latter. In the event of similar damage to the sub-distributors 9, these are based on an expandable construction 13 which, in plan view, fills the empty spaces that arise between the sub-distributors approximately in a star shape (left half of FIG. 5) or circularly (right half). Blockable drain lines 30 lead from the sub-distributors 9 to an annular collecting line 31; Via a further line 32 guided in the central tube 4, all tube bundles 5 can be emptied of water. The central tube 4 is slidably supported at its lower end in a centering 14 fastened to the container 1; it also has an inner tube 34 and an opening which is closed during operation by a rupture disk 15, through which the excess pressure which occurs in the steam generator during a sodium-water reaction is reduced and the reaction products can pass through the central tube 4 to a separating device (not shown) . As an alternative to this, a connecting piece 35 (also shown with a rupture disc) (shown in broken lines) can be arranged if it is possible to blow off the reaction products into the inertized space around the steam generator. The individual tube bundles 5 are separated from one another in height by short sections 16 in which the tubes run straight, as a result of which better inspection and repair options are created; the necessary welded connections between individual parts of the tubes 11 are placed in these sections. Between the tube bundles 5 and the wall of the container 1 there is also a jacket 17 with thermal insulation, which serves to protect the former from the flame occurring during a sodium-water reaction and to guide the flow. For repair purposes, the tube bundles 5 with the jacket 17 can be removed from the container upwards (after loosening the connections to the tube plate 10), just as the downpipe 6, distributor 7, pipes 8 and sub-distributor 9 can be removed through the central tube 4.

In the upper part of the container 1 (see FIG. 2), a honeycomb-like structure, which prevents convection, is attached between it and the jacket 17, via which the temperature range between sodium entry and exit is reduced. This can be dispensed with if the sodium inlet and outlet are sufficiently far apart, as indicated in FIG. 4 with the alternative position of the outlet nozzle 3 shown in dashed lines. At the upper end of the heat exchanger, the superheater tubes end in further tube plates 19, from each of which a steam line 20 begins. In the superheater area, the tube bundles 5 are designed by increasing their tubes 11 so that space is created on the outside for further tube bundles 21 which are constructed from additional tubes 22 in which the steam is reheated. Of course, if necessary, the reheater tube bundles 21 can also extend over the entire height of the steam generator. They are designed so that the sodium temperatures in these bundles are as similar as possible to those prevailing in the steam generators / superheater bundles located at the same level. The steam line is designated 23, the steam line 24. Both end in a tube plate 25 in a distributor or collector 27, which is part of a spherical surface, so that a probe (not shown here) which can be pivoted about point 26 is easily inserted into the individual tubes 22 with a minimum of movement can.

The individual tube bundles 5 and 21 are suspended in a known manner on rods 33 from brackets 28 on the jacket 17 (see FIG. 6). The brackets 28 are designed such that when the rods 33 of a tube bundle are torn off, the bundle is supported on the next lower bracket.

Claims (8)

1. A helical tube steam generator which is heated by liquid metal comprising a central pipe (4) in a container (1), said pipe being sealed at its lower end and containing one or more down pipes (6) for feed water, wherein helical tube groups (5) are surrounded by a casing (17) which is arranged between the container (1) and the central pipe (4), characterised in that a plurality of helical tube groups (5) are arranged one above the other with horizontal interspaces (16) in which the tubes (11) run in a straight line, and that the casing (17) contains further tube groups (21) which comprise intermediate superheating tubes (22).

2. A steam generator as claimed in Claim 1 having brackets (28) arranged in the interspaces (16) between the tube groups (5), characterised in that the helical tube groups (5) are suspended from brackets (28) and in the event of failure of a suspension means are supported on the underlying brackets (28).

3. A steam generator as claimed in Claim 1 having the following characteristics :

a) a plurality of distributing pipes (8) are connected one above another at the lower end (7) of the feed water pipe (6) ;

b) these distributing pipes (8) are helically arranged one within the other ;

c) the other ends of these distributing pipes (8) open into peripherally-spaced subsidiary distributors (9), for the helical pipe groups (5) which are distributed.

4. A steam generator as claimed in Claim 3, comprising a plurality of peripherally-spaced cylindrical subsidiary distributors (9), with outwardly-directed tube plates for the helical tubes and inwardly-directed, rounded plates and which exhibits the following characteristics :

a) between the rounded plates of the subsidiary distributors (9), there is arranged a supporting structure (13) ;

b) this supporting structure (13) is spaced at only small intervals from the rounded plates of the subsidiary distributors (9).

5. A steam generator as claimed in Claim 3 which exhibits the following characteristics :

a) the lower end (7) of the feed water down pipe (6) is surrounded by a double pipe (12) which is spaced from the pipe (6) by a small gap and is sealed at ist lower end ;

b) this double pipe (12) is secured to the inner wall of the central pipe (4).

6. A steam generator as claimed in Claim 1, wherein the helical tubes (5) open into tube plates of collectors (27), which exhibits the following characteristics :

a) the collectors (27) are arranged radially symmetrically relative to the adjoining collecting pipeline ;

b) the tube plates (25) are parts of spherical surfaces.

7. A steam generator as claimed in Claim 1 which exhibits the following characteristic :

the central pipe (4) rests at its lower end in a centering means (14) at the base of the container (1) in vertically sliding manner.

8. A steam generator as claimed in Claim 4 and which exhibits the following characteristics :

a) each subsidiary distributor (9) is provided with a discharge pipe (30) ;

b) the discharge pipes are individually or collectively (31) led upwards in the central pipe (4).

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