JPS6020642B2 - steam generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to steam generators, particularly liquid sodium heated steam generators used in fast breeder reactor plants.

In a steam generator that uses liquid sodium as the heating fluid, it is common to use a heat exchanger in which high-pressure water is passed through a large number of parallel heat transfer tubes, and the sodium is passed to the shell side.

In addition, the parallel heat exchanger tube is configured with a U-shaped heat exchanger tube, and the water inlet and steam outlet are located at the upper part of the shell.
A structure that prevents the part where the transfer tube is attached to the tube sheet from being immersed in sodium is often used. Sodium has excellent thermal conductivity and properties and is suitable as a heat medium for nuclear reactors. Since the thermal shock is also large, we placed the weld between the heat transfer tube and the tube sheet, which is most sensitive to thermal shock, in an inert gas atmosphere that is formed above the free liquid level of sodium to increase its reliability. This is because special considerations have been made. In other words, if a welded part were to break, a chemical reaction between sodium and water would occur, resulting in a major accident, so a U-shaped heat exchanger tube is highly practical as it has a low possibility of such an accident. Figure 1 shows the structure of a steam generator using such U-shaped heat exchanger tubes, which consists of a shell 2 and a number of U-shaped heat exchanger tubes 5, and the shell 2 is made up of an upper shell 3 and a lower shell 4. It is configured. The U-shaped heat exchanger tube 5 is constructed by connecting a straight water supply downcomer pipe 6 and a steam riser pipe 7 spirally wound around an inner cylinder 9 at the lower part of the sleeve 2. The upper end of the water supply downcomer pipe 6 is connected to the water supply header 11 provided on the upper shell 3, and the upper end of the steam riser pipe 7 is connected to the steam header blade 2 provided on the upper shell 3. . A cylindrical heat shield 8 is arranged between the water supply downcomer pipe 6 and the steam riser pipe 7 so as to be concentric with the inner cylinder 9 . A sodium inlet nozzle 21 is provided in the upper body 3, and the lower end of the sodium inlet nozzle 21 is connected to a distribution pipe 22.
The nozzle at the lower end of the distribution pipe 22 is inserted into the upper part of a group of steam riser pipes 6 formed between the heat shield 8 and the inner cylinder 9. A sodium outlet nozzle 23 is provided at the lower end of the lower shell 4, and a sodium outlet nozzle 23 is provided at the top of the upper shell 3 so that even if the heat exchanger tube flea is damaged and sodium and water react, the hydrogen gas generated by the reaction can be quickly reacted. A discharge nozzle 24 is provided to prevent pressure from building up in the arm 2 by discharging it into a product storage tank (not shown). High-temperature sodium heated through an intermediate heat exchanger (not shown) flows through the sodium inlet nozzle 21 and flows into the riser pipe 2 through the distributor 22.

The sodium whose temperature has been lowered by heat exchange with the water or steam flowing through the steam riser pipe 7 in the riser pipe 26 flows out of the shell 2 through the sodium outlet nozzle 23.
Water that has been pressurized and heated to an appropriate pressure and temperature by a water supply pump and a water supply heater (none of which are shown) is supplied from the water supply header 1 to the water supply downcomer pipes 6 of each heat transfer tube 5. 6
It flows down inside and reaches its lower end. When the water makes a U-turn at the lower end and enters the steam riser pipe 7, the water is heated by the opposingly flowing sodium and turns into steam, which flows out from the steam header 12.
This steam is used to rotate a turbine and generate noise. However, when U-shaped heat exchanger tubes are used in this way, when the water flows down inside the feedwater downcomer pipe 6, it absorbs heat from the sodium and lowers its temperature. 1, the temperature difference between the steam and sodium decreases, and the overall heat exchange performance decreases.

Furthermore, if the amount of heat flowing into the feed water downcomer pipe 6 is large, water boils in the feed water downcomer pipe 6, and the buoyancy of the bubbles generates a force that obstructs the flow of the liquid, resulting in an unstable flow phenomenon. It can also cause it. Such flow instability phenomenon causes thermal fatigue of the low-temperature tube, so it is necessary to prevent it. The purpose of the present invention is to eliminate the drawbacks of steam generators having such U-shaped heat exchanger tubes, and to provide a steam generator that has excellent heat exchange performance and can provide stable flow. A heat exchanger tube is provided at the bottom of the shell and has a descending pipe section through which the fluid to be heated descends and an ascending pipe section through which the fluid to be heated ascends, which is partitioned by a cylindrical heat shield disposed concentrically with the shell. In a shell-and-tube type steam generator having a heating fluid outflow nozzle, there is a cylindrical guide plate at the bottom of the shell for guiding the heating fluid to the heating fluid outflow nozzle. The first feature is that the guide plate is located at a higher position than the lower end of the heat shield. The second special laxity is to have the following.

In other words, ``In a steam generator using U-shaped heat exchanger tubes, most of the heat absorbed by the feed water downcomer tubes is
Focusing on the fact that the sodium is carried by the natural convection that occurs in the lower part of the downcomer, he says, This makes it possible to suppress the amount of heat exchange in the region to the lowest possible value.

Examples will be described below.

Figure 2 shows an example. ``The same parts as in Figure 1 are given the same reference numerals, and the difference from the structure in Figure 1 is that the lower part of the shell, that is, the lower part of the lower body, has a cylindrical shape. shaped information board 3
1 is provided.

This guide plate 3 is located above the sodium outlet nozzle 23 and is adjusted so that the upper end of the guide plate 31 is located, for example, 10 to 2 degrees higher than the lower end of the heat shield 8. A drain hole 32 having a diameter of about one ship's length is provided at the lower end of the drain hole 31 near the joint with the lower shell 4.
Note that there is a free liquid level of sodium in the upper part of the shell 2, and the upper part is filled with argon gas, so the water supply header 11 and the steam header 12 are located in an argon gas atmosphere. Even under transient conditions where the sodium temperature changes rapidly, no thermal shock is applied to the weld between the tube plate and the tube plate.

In addition, since the sodium in the downcomer region 25 is separated from the nozzle of the sodium distributor 22 by the heat shield 8, even in a stagnation state, the sodium in the riser region 26 is directly heated to the water supply downcomer pipe 6. will not be given. FIG. 3 shows details of section A in FIG. 2, and shows the relationship between the heat shield 8 and the guide plate 31.

The heat shield 8 has a double cylindrical structure consisting of an inner cylinder 33 and an outer cylinder 34, and argon gas 35 with low thermal conductivity is sealed between the inner cylinder 33 and the outer cylinder 34. Heat is prevented from flowing from the sodium in the riser region 26 where the temperature is low to the sodium in the downcomer region 25 where the temperature is low through the heat shield 8. The lower end of the heat shield 8 is positioned at a position lower than the upper end of the guide plate 31, and there is an annular gap formed by the heat shield 8 and the guide plate 31. A steam riser pipe 7 rises from there. Fourth
The figure shows a cross section taken along the line BB in FIG. 3, showing a U-turn of the heat exchanger tube 5, and 36 is a support for the heat exchanger tube 5. Guide plate 31 having such a configuration
Figure 5 shows the analytical results of the temperature distribution in the height direction in the ascending pipe castle 26 and the descending pipe castle 25 when a guide plate is installed. FIG. 6 shows similar results in the case where there is no such thing.

In both figures, the positions of the downcomer region 25 and the ascender region 26 are indicated by dotted lines, and the leftward arrow indicates the sodium temperature in the downcomer region (
00), and the ascending tube sodium temperature (°C) is indicated by an arrow pointing to the right. If the guide plate shown in FIG. 6 is not provided, the downcomer region 25 would open downward into the riser region 26, and at the closed part, the sodium in the riser region 26 below would be removed. Since the temperature is about 9000 times higher than that of the sodium in the downcomer castle 25 located above, a temperature inversion layer is created near the opening □ where the temperature is higher at the lower part and lower at the upper part.

R in FIG. 6 indicates a temperature inversion layer. In the region of this temperature inversion layer R, the lower the sodium, the lower its specific gravity, so it receives a larger buoyant force, and natural convection occurs here. Due to this natural convection, the sodium in the downcomer pipe region 25 is significantly mixed vertically, so that a phenomenon occurs in which heat enters from the lower part and the heat absorbed by the water supply downcomer pipe 6 increases.
As the amount of heat absorbed by the water supply downcomer pipe 6 increases, the flow on the water side tends to become unstable, and the reliability of the equipment will decrease due to thermal shock caused by the occurrence of the instability phenomenon. On the other hand, in the case of the embodiment shown in FIG. 5, since the guide plate 31 is provided, the downcomer pipe area 25 closes upward into the riser pipe area 26, and at the closing part, The sodium in the riser region 26, where the temperature is high at the top, is repositioned,
In the lower part, the sodium in the downcomer zone 25, where the temperature is low, is repositioned, resulting in a temperature distribution like the curve C (indicated by the broken line) in FIG. 5.

Such a temperature distribution not only prevents natural convection, but also causes buoyancy to actively suppress mixing, resulting in an extremely stable thermal Q dust shielding effect. Since the reinstallation of the guide plate 31 has this effect, the amount of heat absorbed by the water supply downcomer pipe 6 can be significantly reduced, so the flow on the water side can always be maintained in a stable state, improving reliability. Commercial steam generators can be provided. Additionally, temperature fluctuations caused by the mixing of high and low temperature sodium in areas where natural convection occurs are also eliminated, which has the effect of protecting the shell from thermal shock. Furthermore, since the guide plate 31 has a hole 4 at its lower part through which sodium can be drained, even if it is necessary to drain all the sodium from the steam generator, the lower arm 4 and the guide plate 31 can Sodium does not accumulate in the upward cup-shaped space that is formed. FIG. 7 shows another embodiment of the present invention.
The same parts as in the figures are given the same reference numerals, and the difference from the structure in FIG. 2 is that the structure of the heat shield and the relative positions of the heat shield and the guide plate in the opposite direction are different.

That is, in this embodiment, the length of the outer cylinder 34 of the heat shield 8 of the embodiment of FIG. 2 is maintained as it is;
By shortening the length of the inner cylinder 33 that constitutes the argon gas sealed part, a steam riser pipe is installed in the space formed below the argon gas sealed part. As a result, the guide plate 31
The inner surface of the heat shield 8 and the inner surface of the inner cylinder 33 of the heat shield 8 are arranged in the same position in the hook direction. Also in this embodiment, since the upper end of the guide plate is located higher than the lower end of the outer cylinder 34 of the heat shield 8, it is possible to obtain a temperature distribution substantially similar to that in the example of FIG. 2.

Moreover, when the inner surface of the guide plate 31 is arranged at a position that coincides with the inner surface of the inner cylinder 33 of the heat shield 8, the flow of the sodium flowing through the riser pipe castle 26 is not disturbed and is stable. Since the overlapping section of the heat shield 8 and the guide plate 31 becomes longer, the heat shielding effect becomes greater. In addition, in this example, the inner diameter of the guide plate and the inner diameter of the heat shield inner cylinder were made equal, but if the inner diameter of the guide plate is larger than the inner diameter of the inner cylinder of the heat shield, an equivalent effect can be obtained. According to the above embodiment, the amount of heat carried by natural convection from the lower end of the downcomer region can be eliminated, and the amount of heat absorbed by the feed water downcomer pipe can be kept low, so that the flow caused by boiling of the feed water in the feed water downcomer pipe can be suppressed. It is possible to eliminate the occurrence of unstable phenomena and provide a highly reliable steam generator. As described above, the steam generator of the present invention has excellent heat exchange performance and can provide a steam generator that can provide stable flow, and has great industrial effects.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional steam generator, FIG. 2 is a sectional view of an embodiment of the steam generator of the present invention, FIG. 3 is a sectional view of section A in FIG. 2, and FIG. A sectional view taken along the line B-B in the figure, and FIGS. 5 and 6 are schematic diagrams showing the principle of the steam generator of the present invention,
FIG. 7 is a sectional view of another embodiment of the steam generator of the present invention. 5... Heat exchanger tube, 6... Water supply downcomer pipe, 7...
Steam rising pipe, 8... Heat shield, 23... Sodium outlet nozzle, 25... Downcomer pipe, 2
6... Ascent pipe castle " 31... Information board, 33... Heat shield inner cylinder, 34... Heat shield outer cylinder. Ax J figure 2 figure 3 Figure 4 Figure 5 Figure 5 Figure 7

Claims (1)

[Scope of Claims] 1. A heat exchanger tube having a descending pipe section in which a heated fluid descends and a rising pipe section in which a heated fluid ascends, which are partitioned by a cylindrical heat shield disposed concentrically with the shell. A shell-and-tube steam generator having a heating fluid outflow nozzle at the bottom of the shell, the shell and tube steam generator having a cylindrical guide plate at the bottom of the shell for guiding the heating fluid to the heating fluid outflow nozzle. A steam generator characterized in that the upper end of the guide plate is located at a higher position than the lower end of the heat shield. 2. A heat exchanger tube is provided, which is divided by a cylindrical heat shield disposed concentrically with the shell, and has a downcomer pipe section through which the fluid to be heated descends and a riser pipe section through which the fluid to be heated ascends. In a shell-and-tube type steam generator having a heated fluid outlet nozzle at the bottom, a cylindrical guide plate is provided at the bottom of the shell for guiding the heated fluid to the heated fluid outlet nozzle, and the guide plate A steam generator characterized in that an upper end is located higher than a lower end of the heat shield, and the guide plate has an inner diameter greater than or equal to the inner diameter of the heat shield.