JPS586390A - Heat transfer pipes of condenser - Google Patents

Abstract

PURPOSE:To protect the titled heat transfer pipes against damages by a method wherein the generation of hydraulic elastic vibrations in the heat transfer pipes due to steam currents flowing through the pipes are prevented. CONSTITUTION:The outer diameter D2 of each of the heat transfer pipes 5a of a pipe section 10a of a pipe nest 10 located on the side where high velocity turbine steam flows in is made larger than the outer diameter D1 of each of the heat transfer pipes 5b of a central section 10b of the pipe next 10 but the inner diameters (d) of all of the pipes are made equal to one another so that the relationship of D2/d>D1/d is established. As a consequence, the rigidity of the heat transfer pipes 5a of the upper pipe section 10a is increaed, the frequency of natural vibrations thereof is increased and the generation of hydraulic elastic vibrations due to the high velocity steam currents flowing through the pipes is prevented so that the heat transfer pipes are protected against damages.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a condenser heat exchanger tube, and in particular to a condenser suitable for preventing damage to the heat exchanger tube due to hydroelastic vibration caused by the exhaust steam flow rate of a large-capacity steam turbine. This relates to heat exchanger tubes.

Condensers for steam turbines are becoming larger as the capacity of the turbine increases. Recently, hydroelastic vibrations caused by the exhaust steam flow rate have caused contact between heat transfer tubes within the tube group, causing water leakage accidents due to wear and tear, and there have been cases where the turbine has to be stopped.

In particular, in the case of boiling water nuclear power turbines, it is necessary to avoid as much as possible the introduction of seawater into the plant system due to broken trees in the heat transfer tubes, so sufficient consideration must be given to preserving the heat transfer tubes.

The condenser shown in FIGS. 1 and 2 will be specifically explained below.

The condenser consists of a cooling water system and a steam system. Cooling water flows into a water chamber 2 from a cooling water inlet 1, passes through a large number of heat transfer tubes 5 connected by tube plates 3 and 4, Enter water chamber 6,
The cooling water exits the system from the lower part.

Note that the heat exchanger tube 5 may be damaged due to scale or the like attached inside the heat exchanger tube 5.
In order to prevent the heat transfer coefficient from decreasing, the inside of the heat exchanger tube 5 is cleaned using a ball cleaning device that circulates sponge balls inside the tube. Therefore, the inner diameter of each heat exchanger tube 5 is substantially uniform.

On the other hand, turbine loss steam 8 is introduced into the vessel from a steam port 9, and a tube bundle 1 consisting of a large number of thin-walled heat transfer tubes 5 is introduced into the vessel from a steam port 9.
The steam is condensed through the
and then remove it from the vessel.

The heat exchanger tubes 5 are supported by tube support plates 12 with one rigid collar, and the intervals between the tube support plates 12 are set so that the vibration modes of each heat exchanger tube 5 are not the same in order to prevent resonance with turbine equipment and fluid vibration. It is irregularly spaced. The tube support plate 12 is provided with ribs 16 and 17 on the lower surface 13 of the condenser body and on the side surfaces 14 and 15 of the condenser body, respectively.

However, in the above configuration, the heat exchanger tubes in the high flow velocity portion of the incoming steam of the tube bundle 10 may cause hydroelastic vibration and be damaged by mutual contact or the like.

The present invention has been made in view of the above, and its purpose is to prevent hydroelastic vibrations from occurring due to the flow rate of incoming steam, and to protect heat transfer tubes from damage. Our goal is to provide heat pipes.

The feature of the present invention is that the thickness of the heat exchanger tubes in the number sequence of steam inflow into the tube nest + 1111 is thicker than the wall thickness of the heat exchanger tubes in the center of the two-part tube nest to increase the natural frequency. It is in.

Hereinafter, the present invention will be explained by the embodiments shown in FIGS.
This will be explained in detail using figures.

FIG. 3 is a sectional view corresponding to FIG. 2 showing an embodiment of the condenser heat exchanger tube of the present invention, and FIG. 4 is an enlarged view of part 13 of FIG. 3. In FIG. 3, the same parts as in FIGS. 1 and 2 are indicated by the same reference numerals, and their explanation will be omitted here. In FIG. 3, as in FIG.
Although it is wrinkled, this is the upper tube nest 10 into which the turbine 47 + air A air 8 flows in, which has a high flow rate.
As shown in FIG. 4, the outer diameter of the heat transfer tube 5a in the number sequence a is as follows:
Outer diameter D1 of the heat exchanger tubes 5b of the central tube bundle 101) of the tube bundle 1o
It has a much larger outer diameter 1]2. Note that the inner diameters are all the same, so if the inner diameter is d, then D2
/d>i), /d. This increases the rigidity of the heat exchanger tubes 5a of the upper tube bundle 10a of the tube bundle 10, increases the natural frequency, and prevents hydroelastic vibrations caused by steam flow velocity.

In the condenser, the turbine exhaust steam 8 that has flowed into the summer water heater flows over the entire circumference of the tube nest 10 and is condensed.
In this case, in the upper anchorage 10a of the tube bundle 10, the velocity energy of the steam is large, so with the conventional heat exchanger tube diameter ratio 1), /d, the rigidity of the heat exchanger tubes 5a is low, and the steam flow rate Hydroelastic vibrations are likely to occur. On the other hand, according to the embodiment of the present invention described above, the wall thickness of the heat exchanger tube 5a is increased and the tube diameter ratio is increased to D2/d, so that the rigidity is increased and the support plate spacing is the same. Also, the natural frequency becomes high, making it difficult for hydroelastic vibrations to occur.

Accordingly, the heat exchanger tubes 5a are no longer in contact with each other, and the heat exchanger tubes 5a can be protected from damage.

According to past condenser accident cases and experiments, hydroelastic vibrations are observed in several sequences on the outer periphery of the tube bundle. Especially Tahif 11F
Since the velocity energy is large on the steam inflow side, large vibrations occur at the top of the tube bundle.

On the other hand, no vibration was observed in the heat transfer tube group in the center of the tube nest. This means that all the steam flows in from the outer periphery of the tube bundle,
At the beginning of the inflow head, the steam has a large velocity energy, but as it flows into the tube bundle, the steam condenses, so the amount of steam decreases, and as it passes through the outer periphery of the heat exchanger tube group in the center of the tube bundle, the velocity energy decreases. This is because the fluid force applied to the heat exchanger tubes decreases.

For this reason, as a vibration prevention measure, the pipe support plate 1
It has been considered to increase the number of tube support plates 12 and narrow the interval between the tube support plates 12 to increase the natural frequency of the heat exchanger tubes 5a, but this would require a large amount of cost to manufacture and install the tube support plates 12. It's dark. On the other hand, according to the embodiment of the present invention, the heat exchanger tube 5a can be easily realized because the thickness of the heat exchanger tube 5a is simply increased.

Furthermore, since the heat exchanger tubes 5a and 5b have the same inner diameter d, there is no problem in cleaning the balls inside the tubes.

Figure 5 is a diagram showing the experimental results of the relationship between the tube support plate spacing and the vibration generation rate, and the 8 curves in the figure represent the characteristics when the tube diameter ratio of the conventional heat transfer tube is /d. , 1) The curve represents the tube diameter ratio of the heat exchanger tubes 5a of the tube nest according to the present invention in two-part series.
This is the characteristic when thickened to 2/d. As can be seen from the figure, when the support plate spacing is 1, the vibration-generating flow velocity V in case 1) is about 1.5 times as high as in case a, making it difficult for vibrations to occur.

In general, the flow rate at which hydroelastic vibrations occur is, where: I(C; vibration generation limit coefficient f; natural frequency D of the heat exchanger tube; outer diameter δ of the heat exchanger tube; damping coefficient M of the heat exchanger tube; unit length of the heat exchanger tube The mass per unit ρ is expressed by the density of steam.In addition, the natural frequency f of the heat exchanger tube is expressed as: E; modulus of longitudinal elasticity; The diameter ratio is 1), /d
)l), /d By changing the values of E and M, the natural frequency f increases, and accordingly, the flow velocity at which hydroelastic vibration occurs increases, and l increases in the high flow velocity region in the upper part of the tube bundle 10. The safety factor of the placed heat exchanger tube 5a increases.

Note that increasing the outer diameter and increasing the wall thickness of the heat exchanger tubes 5a will reduce the heat transmission coefficient, but the wall thickness of the heat exchanger tubes 5b in the part of the tube nest 10 that is difficult to vibrate in the medium heat section can be made smaller than before. Furthermore, since it is possible to eliminate the influence on the condenser performance.

As explained above, according to the present invention, hydroelastic vibrations are prevented from occurring in the heat exchanger tubes due to the incoming steam flow,
This has the effect of protecting the heat exchanger tubes from damage.

[Brief explanation of the drawing]

Fig. 1 is a structural explanatory diagram of a conventional condenser, Fig. 2 is a cross-sectional view taken along the line A-A in Fig. 1, and Fig. 3 is a diagram illustrating an embodiment of the condenser heat exchanger tube of the present invention. FIG. 4 is an enlarged view of part B in FIG. 3, and FIG. 5 is a diagram for explaining the present invention in detail.

Claims (1)

[Scope of Claims] 1. A heat exchanger supporting a large number of heat exchanger tubes between front and rear tube plates, allowing turbine exhaust steam to flow through the outer circle of each of the heat exchanger tubes, and cooling water flowing into each of the heat exchanger tubes. In the water heater, the wall thickness of several rows of heat transfer tubes on the turbine exhaust steam inflow side of the tube bundle constituted by the large number of heat transfer tubes is made thicker than the wall thickness of the heat transfer tubes in the center of the tube bundle, and the natural vibration A condenser heat exchanger tube characterized by a high number of tubes. 2. The condenser heat exchanger tube according to claim 1, wherein the inner diameter of each of the heat exchanger tubes is the same.