JPH08233212A - Heat exchanger - Google Patents

Abstract

PURPOSE: To provide a structure of a heat exchanger having a high efficiency in which the number of heat transfer pipes is substantially reduced, a high reliability is attained, an easy maintenance is also applicable and it is capable of being easily assembled in the prior art system. CONSTITUTION: In a heat exchanger in which a steam flowing hole 10 is arranged between holes 4a for a group of heat transfer pipes at inlet side and holes 5a for a group of heat transfer pipes at outlet side of a heat transfer pipe supporting plate 3, heat transfer pipes 6 with a pipe diameter being of times (t) (1<t<=K) as compared with that of the prior art in respect to a heat transfer rate amplification coefficient K is constructed and further the number of the heat pipes is substantially reduced down to 1/t<2> times of that of the prior art.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger used in nuclear power plants and thermal power plants with improved heat transfer coefficient.

[0002]

2. Description of the Related Art As a conventional heat exchanger technology, a feed water heater, which is a kind of heat exchanger used in a nuclear power plant, will be described as an example.

As a method of improving the heat transmission rate of the feed water heater, (1) a method of providing a steam flow hole in the heat transfer tube support plate (Atomic Energy Society of Japan 1994 Spring Annual Meeting Proceedings p.44)
2) and (2) two methods of using a low fin tube as a heat transfer tube (Proceedings of the Japan Society of Mechanical Engineers No. 427, P. 527 to 534) have been proposed, which will be described with reference to FIGS. 2 to 4. .

FIG. 2 is a feed water heater used in a nuclear power plant, FIG. 3 is a heat transfer tube support plate having a steam passage hole in the center for improving heat transfer efficiency, and FIG. 4 is a cross-sectional view of a low fin tube. Is.

As shown in FIG. 2, the feed water heater 1 has a body 2
The heat transfer tube group 7 and the heat transfer tube support plate 3 are formed inside the. The steam extracted from the turbine flows into the feed water heater 1 through the extraction steam pipe 14. A baffle plate 1 with a hole at the steam inlet in order to absorb the impact at the time of steam inflow.
1 is provided.

On the other hand, the feed water flows in through the feed water inlet 12, is heated by the steam across the heat transfer tube wall while passing through the heat transfer tube group 7, becomes hot feed water, and flows out through the feed water outlet 13. The condensed steam is discharged from the drain water pipe 15a.

FIG. 3 shows a longitudinal sectional view of a heat transfer tube support plate 3 which divides the feed water heater 1 into sections in the axial direction. The heat transfer tube support plate 3 is provided between the body 2 and the upper gap 8 and the peripheral gap 9 between them.
Is provided to allow the steam to flow from the section on the steam inlet side to the other section, and in addition, the steam flows between the heat transfer tube group hole 4b for the water supply inlet side and the heat transfer tube group hole 5b for the water supply outlet side. The holes 10 are provided to allow the steam to uniformly flow into the central portion, thereby improving the heat transmission rate.

Further, the low fin tube 16 shown in FIG. 4 has a large number of fins 17 so that the heat transfer area is 3 to 4 times as large as that of the smooth tube to improve the heat transfer rate.

The improvement of the heat transfer rate is achieved by shortening the length of the heat transfer tube by 1 / K times or by reducing the number of heat transfer tubes by 1 / K times without changing the tube diameter. Has been proposed for use in miniaturization.

[0010]

However, although attention is paid to the use of the improvement in heat transfer rate for downsizing of the heat exchanger, the problem of increased pressure loss and the improvement of reliability are considered. Not not. Further, the miniaturization of the device is effective only for the first power of the improvement of the heat transfer rate, and cannot be said to be a method which makes full use of the improvement of the heat transfer rate.

In the miniaturization method in which the number of heat transfer tubes is reduced without changing the tube diameter, the total flow passage cross-sectional area is reduced. Therefore, in order to secure the same flow rate as in the conventional case, the flow velocity must be increased, resulting in pressure loss. And the load on the heat transfer tubes and pumps increases.

Although there are 3,000 to 4,000 heat transfer tubes in the heat exchanger, considering the soundness of the entire heat transfer tubes, the smaller number of heat transfer tubes is more reliable.

Furthermore, the work of inspecting thousands of heat transfer tubes one by one at the time of regular inspection is time-consuming and patience-intensive work, and a heavy burden is placed on the inspection worker. Need to be reduced and maintainability should be improved.

An object of the present invention is to provide a structure of a heat exchanger in which the improvement of heat exchange rate is fully utilized, the number of heat transfer tubes is greatly reduced to improve reliability, and maintenance is easy. is there.

[0015]

In a heat exchanger having an improved heat exchange rate, the heat transfer rate multiplication coefficient K of the heat exchanger is t times the diameter of the heat transfer tube (1 <t ≦ K). The number of heat transfer tubes is 1 / t of the conventional one so as not to change the total flow passage cross-sectional area.
^Use a structure that has been drastically reduced to twice.

[0016]

In the structure of the heat exchanger of the present invention, the diameter of the heat transfer tube is t times that of the conventional one. Therefore, the heat transfer area of one heat transfer tube becomes t times. The number of heat transfer tubes is reduced to 1 / t ² times under the condition that the total flow passage cross-sectional area is not changed. As a result, the heat transfer area of the entire heat transfer tube is 1 / t times that of the conventional one, but since the heat transfer rate is K (t ≦ K) times, the conventional performance is sufficiently maintained. In this way, the reliability is improved by fully utilizing the improvement of the heat exchange rate and greatly reducing the number of heat transfer tubes.

[0017]

EXAMPLE As a first example, in the present invention, a heat transfer coefficient is 16% (K = 1.16) by providing steam passage holes in a heat transfer tube support plate and allowing steam to uniformly flow into the central portion. The case of application to the improved reactor feedwater heater will be described below. The heat transfer tubes used in the following examples are
The one that conforms to the JIS standard should be used.

FIG. 1 is a schematic view of a heat transfer tube support plate in this embodiment. 1 is different from FIG. 3 in that the heat transfer tube group hole 4 is provided.
That is, the diameters of a and 5a are large, and the number of holes is greatly reduced. In addition, since FIG. 1 is symmetrical, 1 /
A two-symmetry diagram is used (the same applies to FIG. 3).

The conventional feed water heater has an outer diameter of 15.88 mm,
3,600 heat transfer tubes having an inner diameter of 13.08 mm are installed inside the cylindrical body 2 having a total length of about 9 m.

Instead of this heat transfer tube, the outer diameter of 18.0 mm and the inner diameter of 15.2 mm with respect to the heat transfer coefficient multiplication coefficient K = 1.16.
If you use a thick heat transfer tube (t = 1.16 for inner diameter),
The number of heat transfer tubes can be reduced by 926 to 2674, provided that the cross-sectional area of the entire flow path is not changed. As a result, in this embodiment, as shown in FIG. 1, as compared with the heat transfer tube support plate of FIG. 3, the heat transfer tube group holes 4a and 5a of the heat transfer tube support plate 3 also have a large diameter, and the number of holes is greatly reduced. Will be things.

Further, in the present embodiment, the thickened heat transfer tube uses the same thickness as the conventional one. Therefore, the inner diameter was increased by 1.16 times, while the outer diameter was reduced by 1.13 times. As a result, the heat transfer area is reduced by about 3% more than the improvement in thermal efficiency, so in order to maintain the conventional performance, the pipe length is increased by 3% in this embodiment. Therefore, the conventional water heater, which had a total length of about 9 m, is about 9.2.
It will be 7m. According to the present embodiment, the heat transfer tube 6 having a large tube diameter is provided in the heat transfer tube support plate 3 shown in FIG.
FIG. 5 shows a state in which the cylindrical body 2 having a length of about 9.27 m is attached through each of the 5a. The feed water flows into the feed water heater 1 through the feed water inlet 12, passes through the inside of the heat transfer pipe 6, and flows out from the feed water outlet 13 to the feed water heater in the subsequent stage. The feed water is heated by the extraction steam guided from the extraction steam pipe 14 to the feed water heater 1 in the process of passing through the heat transfer pipe 6, and becomes high temperature feed water.

By greatly reducing the number of heat transfer tubes in this way, the reliability of the heat transfer tube as a whole is significantly improved. In addition, at the time of regular inspection, one 3600 heat transfer tubes
By reducing the number of the actual inspections to about 2,700, the inspection time can be significantly shortened and the burden on the inspection operator can be reduced.

Next, as compared with the case where the improvement in heat transfer rate is used for downsizing of the feed water heater, it is possible to reduce about 500 tubes by the method of reducing the heat transfer tubes without changing the tube diameter. Since the cross-sectional area of the entire flow path of the feed water heater changes, it is necessary to increase the flow velocity in order to secure the conventional feed water flow rate, which increases pressure loss and increases the load on the heat transfer tubes and pumps. Also, with the method of shortening the tube length of the heat transfer tube, the total length of about 9 m is only about 7.8 m.

In these two methods, only the first power of the improvement of the heat exchange rate is effective, whereas in the present invention, by setting t to a value close to K, the improvement of the heat exchange rate is almost the same. There is a squared effect, and maintainability is also improved.

Next, as a second embodiment, by replacing the smooth heat transfer tube with the low fin tube 16 shown in FIG. 4,
A case where the present invention is applied to a feedwater heater of a nuclear reactor having a heat transfer rate improved by 30% (K = 1.30) will be described.

A low fin tube having a fin base diameter of 19.05 mm, a fin tube inner diameter of 16.25 mm (t = 1.24 for the inner diameter), and a fin height of 1.42 mm for a heat transfer coefficient multiplication factor K = 1.30. If the above is used, the number of heat transfer tubes can be reduced by 1267 to 2338 because the cross-sectional area of the entire flow path is not changed. Also in the second embodiment, the increment of the outer diameter is smaller than that of the inner diameter as in the first embodiment, but there is a margin of t = 1.24 with respect to K = 1.30. Is substantially equal to the increase in heat transfer rate, and since it is not necessary to change the tube length of the heat transfer tube, it can be stored as it is in the conventional cylindrical body 2 having a total length of about 9 m.

In the second embodiment, as compared with the case where the improvement of the heat transfer rate is used for downsizing of the equipment, the method of reducing the heat transfer tubes without changing the tube diameter can reduce only about 830 tubes. With the method of shortening the tube length of the heat transfer tube, the total length of about 9 m is only about 7 m.

As described above, in the heat exchanger having the structure of the present invention, the maintainability is improved by greatly reducing the number of heat transfer tubes, and the total flow passage cross-sectional area is changed. Since it does not exist, it can be easily incorporated into a conventional system. Further, since the work of mounting the heat transfer tube, which requires the most time in the manufacturing process of the heat exchanger, is greatly reduced, the time required for the manufacturing is significantly shortened, and the cost of the heat exchanger can be reduced.

[0029]

According to the present invention, maintenance is easy and it can be easily incorporated into a conventional system.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a heat transfer tube support plate of a feed water heater according to the present invention.

FIG. 2 is a vertical sectional view of a feed water heater according to a conventional technique.

FIG. 3 is a vertical cross-sectional view of a heat transfer tube support plate of a feed water heater according to a conventional technique.

FIG. 4 is a cross-sectional view of a low fin tube used in the present invention.

FIG. 5 is a vertical cross-sectional view of the feed water heater according to the present invention.

[Explanation of symbols]

1 ... Water heater, 2 ... Body, 3 ... Heat transfer tube support plate, 4a,
4b ... Inlet-side heat transfer tube group hole, 5a, 5b ... Outlet-side heat transfer tube group hole, 6 ... Heat transfer tube or heat transfer tube group with increased tube diameter,
7 ... Conventional heat transfer tube or heat transfer tube group, 8 ... Upper gap, 9
… Ground gaps, 10… Steam circulation holes.

Claims (3)

[Claims] 1. A cylindrical body, a large number of heat transfer tubes existing in the cylindrical body, and inside the cylindrical body, fixed to the cylindrical body and provided with a plurality of through holes, The heat transfer tube support plate has a function of supporting the plurality of heat transfer tubes on the cylindrical body by passing the plurality of heat transfer tubes through the through holes, and the heat transfer tube support plate is provided with a steam flow hole. In a heat exchanger with improved heat transfer rate,
The heat transfer coefficient multiplication coefficient K of the heat exchanger is increased by t times (1 <t ≦ K) the diameters of the plurality of heat transfer tubes, and the number of the heat transfer tubes is changed so as not to change the total flow passage cross-sectional area. 1 / t
Heat exchanger, characterized in that it has reduced significantly up to ^twice. 2. A cylindrical body, a large number of heat transfer tubes existing in the cylindrical body, and inside the cylindrical body, fixed to the cylindrical body and provided with a plurality of through holes. To increase the heat transfer area as the heat transfer tube by having a heat transfer tube support plate having a function of supporting the plurality of heat transfer tubes on the cylindrical body by respectively passing the plurality of heat transfer tubes through the through holes. In a heat exchanger whose heat transfer rate is improved by using a low fin tube having a large number of fins, the tube diameter of the low fin tube is multiplied by t times the heat transfer rate multiplication coefficient K of the heat exchanger. The heat exchanger is characterized in that 1 <t ≦ K) and the number of the low fin tubes is greatly reduced to 1 / t ² times that of the conventional one so as not to change the total flow passage cross-sectional area. 3. The structure of a heat exchanger according to claim 1, wherein a low fin tube provided with a large number of fins for expanding a heat transfer area is used as the heat transfer tube.