US20130152585A1

US20130152585A1 - Heat exchanger

Info

Publication number: US20130152585A1
Application number: US13/706,985
Authority: US
Inventors: Satoshi Hiraoka; Kenji Kirihara; Masahiko Nagai
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2011-12-15
Filing date: 2012-12-06
Publication date: 2013-06-20
Also published as: JP2013124625A; DE102012023987A1

Abstract

Thermal expansion of U-shaped tubes is permitted to prevent damage to it. A heat exchanger includes a casing having a first fluid inlet provided at one end thereof and a first fluid outlet provided at the other end thereof, the first fluid inlet and the first fluid outlet being connected to each other via a first flow path extending in a straight line from the first fluid inlet to the first fluid outlet; and multiple tube sets accommodated inside the casing so that a fluid that flows through the interiors thereof undergoes heat exchange with a fluid that flows via the first flow path. The multiple tube sets are arrayed along the first flow path, and multiple U-shaped tubes constituting the tube sets are fixed only to a tube plate disposed parallel to the first flow path and located at both ends of the U-shaped tubes.

Description

TECHNICAL FIELD

This application is based on Japanese Patent Application No. 2011-274785, the contents of which are incorporated herein by reference.
The present invention relates to heat exchangers. More specifically, the present invention relates to a heat exchanger that is suitable as a repeater of a solar-heat gas turbine driven with a compressible working fluid, such as air, heated by using sunlight.

BACKGROUND ART

Recently, in order to solve environmental problems, such as global warming, there is interest in natural energy, such as sunlight and wind power.
Accordingly, there have been proposals for solar-heat gas turbines that are driven by generating a high-temperature, high-pressure compressible working fluid by means of solar heat by using sunlight, which is a type of natural energy, and solar-heat gas-turbine power generating units that generate power by driving a generator by means of such a solar-heat gas turbine.
Known examples of such a solar-heat gas turbine and a solar-heat gas-turbine power generating unit are disclosed in Patent Document 1.

CITATION LIST

Patent Literature

{PTL 1}

Japanese Unexamined Patent Application, Publication No. 2010-281272

SUMMARY OF INVENTION

Technical Problem

In a solar-heat gas turbine, the temperature of the interior of a reheater that preheats a high-pressure compressible working fluid ejected from a compressor through heat exchange with a high-temperature compressible working fluid discharged from a turbine becomes very high since the high-temperature compressible working fluid discharged from the turbine passes through the interior. Thus, for example, when the heat exchanger disclosed in Japanese Unexamined Patent Application, Publication No. 2001-147093 is adopted as a reheater of a solar-heat gas turbine, thermal expansion of the U-shaped tubes 18 a in the lengthwise direction is restrained by the U-shaped-tube fixing plate 19, possibly damaging the U-shaped tubes 18 a.
The present invention has been made in view of the problem described above, and it is an object thereof to provide a heat exchanger that permits thermal expansion of U-shaped tubes in the lengthwise direction, thus serving to prevent damage to the U-shaped tubes, that causes less heat dissipation, thus serving to improve the heat efficiency, that is easy to inspect and repair, and that can produce compressed air with less pulsation of temperature.

Solution to Problem

In order to solve the problem described above, the present invention employs the following solutions.
A heat exchanger according to a first aspect of the present invention is a heat exchanger including a casing having a first fluid inlet provided at one end thereof and a first fluid outlet provided at the other end thereof opposite the one end, the first fluid inlet and the first fluid outlet being connected to each other via a first flow path extending in a straight line from the first fluid inlet to the first fluid outlet; and multiple tube sets accommodated inside the casing so that a fluid that flows through the interiors thereof undergoes heat exchange with a fluid that flows via the first flow path, wherein the multiple tube sets are arrayed along the first flow path, and multiple U-shaped tubes constituting the tube sets are fixed only to a tube plate disposed parallel to the first flow path and located at both ends of the U-shaped tubes.
In the heat exchanger according to the first aspect of the present invention, the U-shaped tubes are fixed only at a single side thereof to tube holes that are provided in the tube plate and through which both ends of the U-shaped tubes are inserted.
Thus, thermal expansion of the U-shaped tubes in the lengthwise direction is permitted, which serves to prevent damage to the U-shaped tubes.
Furthermore, in the heat exchanger according to the present invention, the first fluid inlet and the first fluid outlet are connected to each other via a single path, namely, the first flow path extending in a straight line from the first fluid inlet to the first fluid outlet.
Thus, pressure loss in the first flow path can be reduced. Furthermore, it is possible to make a large amount of fluid flow via the first flow path, which serves to improve the heat exchange efficiency.
In the above heat exchanger, more preferably, a partition plate separating straight portions and turning portions of the U-shaped tubes is disposed parallel to the first flow path, and gaps are provided between the inner circumferential surfaces of tube holes that are provided in the partition plate and through which the straight portions of the U-shaped tubes are inserted and the outer circumferential surfaces of the U-shaped tubes.
In the heat exchanger constructed as described above, a space is formed outside the first flow path by the partition plate and the casing, causing a portion of the fluid passing via the first flow path to stagnate in that space.
Thus, the fluid present in the space acts as a heat insulating layer. This serves to maintain the temperature of the fluid passing via the first flow path, which serves to improve the heat exchange efficiency even further.
In the above heat exchanger, more preferably, a header that communicates between the outlet end of a tube set located on the upstream side and the inlet end of a tube set located on the downstream side thereof is provided.
In the heat exchanger constructed as described above, the fluid that has undergone heat exchange with the fluid passing via the first flow path while passing through a tube set located on the upstream side is guided to the tube set located on the downstream side thereof so that the fluid then undergoes heat exchange with the fluid passing via the first flow path. This serves to improve the heat exchange efficiency even further.
In the above heat exchanger, more preferably, the U-shaped tubes are fixed to the tube plate by expanding the ends of the U-shaped tubes inserted through the tube holes.
In the heat exchanger constructed as described above, the ends of the U-shaped tubes are fixed to the tube plate just by tube expansion, without employing welding.
Thus, the combination of the material of the tube plate and the material of the U-shaped tubes, which must be taken into account when welding, need not be considered here, allowing free choice of the material of the tube plate and the material of the U-shaped tubes.
A solar-heat gas-turbine power generating system according to a second aspect of the present invention includes any one of the above heat exchangers as a repeater.
In the solar-heat gas-turbine power generating system according to the second aspect of the present invention, since the heat exchanger that permits thermal expansion of the U-shaped tubes in the lengthwise direction, which serves to prevent damage to the U-shaped tubes, is included as the reheater, the reliability of the solar-heat gas-turbine power generating system can be improved.
Furthermore, in the solar-heat gas-turbine power generating system according to the present invention, since the heat exchanger having a high heat exchange efficiency is included as the reheater, it is possible to further boost the temperature of the compressible working fluid introduced into the turbine. This serves to improve the cycle efficiency of the heat cycle.

Advantageous Effects of Invention

According to the present invention, because the partition plates and the tubes are not joined together, thermal expansion of the U-shaped tubes in the lengthwise direction is permitted. Thus, an advantage is afforded in that damage to the U-shaped tubes can be prevented.
Furthermore, the space between the first partition plate and the casing serves as a stagnation region that is separated from the fluid path. Thus, an advantage is afforded in that the stagnation region exhibits a heat insulating effect, serving to reduce heat dissipation.
Furthermore, the header itself is designed to have a size large enough for a person to enter, a hatch for inspection work of the diameter-expanded joints with the tubes is provided at the header, and a ladder is provided inside the header. This structure facilitates inspection, making it easy to seal off a tube with a plug even if the tube is damaged, forming a perforation.
Furthermore, since multiple headers are provided in the middle of the tube path, the air whose temperature has been boosted by compression and the air that has been further heated by the heat exchanger are mixed in the headers, so that the temperature becomes uniform before it is fed to the heat receiver. Thus, the air discharged from the heat receiver becomes free of pulsation of temperature, so that the rotation rate of the turbine directly connected to the generator becomes free of minute fluctuations. Accordingly, an advantage is afforded in that power of good quality with extremely small frequency fluctuations can be obtained.
Furthermore, it is possible to pull out the headers and tube sets without removing the casing, which facilitates replacement of tubes when the tubes become degraded.
Furthermore, since a gap is provided between tube sets, where the first fluid becomes uniform, the temperature efficiency can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a construction diagram (system diagram) showing a specific example of a case where a heat exchanger according to an embodiment of the present invention is used as a reheater for a solar-heat gas turbine and a solar-heat gas-turbine power generating unit.

FIG. 2 is a perspective view of the heat exchanger according to the embodiment of the present invention.

FIG. 3 is a sectional view of the heat exchanger according to the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Now, a heat exchanger according to an embodiment of the present invention, in particular, a heat exchanger that can be suitably used as a reheater of a solar-heat gas turbine that is driven by using a compressible working fluid, such as air, heated by using sunlight, will be described with reference to FIGS. 1 to 3.
FIG. 1 is a construction diagram (system diagram) showing a specific example of a case where the heat exchanger according to this embodiment is used as a reheater for a solar-heat gas turbine and a solar-heat gas-turbine power generating unit. FIG. 2 is a perspective view of the heat exchanger according to the embodiment. FIG. 3 is a sectional view of the heat exchanger according to the embodiment.
As shown in FIG. 1, a solar-heat gas turbine GT includes, as its main components, a compressor 1 that compresses a compressible working fluid to boost its pressure, a heat receiver 2 that heats the compressible working fluid with heat obtained by converting sunlight to boost its temperature, and a turbine 3 that converts thermal energy possessed by the high-temperature, high-pressure compressible working fluid into mechanical energy. That is, the solar-heat gas turbine GT includes the heat receiver 2 that heats the high-pressure compressible working fluid by using the thermal energy of sunlight to boost its temperature instead of a combustor that combusts a fuel such as natural gas to generate high-temperature, high-pressure combustion gas.
The heat receiver 2 in this case is a device for converting sunlight into thermal energy. With the heat receiver 2, it is possible to heat a high-pressure compressible working fluid to boost its temperature by using the heat of light collected by a light concentrator (heliostat), which is not shown.
Furthermore, a solar-heat gas-turbine power generating unit that generates electric power by using sunlight can be constructed by connecting a generator 4 coaxially to the solar-heat gas turbine GT so that the generator 4 is driven by the solar-heat gas turbine GT.
Furthermore, a reheater 5 preheats the high-pressure compressible working fluid whose pressure has been boosted by the compressor 1, by using exhaust heat of the compressible working fluid that is discharged from a chimney 6 into the air after performing work in the turbine 3.
The heat exchanger 10 according to this embodiment is a heat exchanger that can be suitably used as the reheater 5 of the solar-heat gas turbine GT in particular. As shown in FIG. 2 or FIG. 3, the heat exchanger 10 includes a casing 11 and multiple (four in this embodiment) tube sets 12.
The casing 11 has a substantially rectangular parallelepiped or cubic external shape and accommodates the tube sets 12 inside. On the front face of the casing 11, a first fluid inlet 21 is provided, which is an opening having a rectangular shape when viewed from the front and through which a high-temperature fluid (the high-temperature compressible working fluid discharged from the turbine 3) flows in. On the back face, a first fluid outlet 22 is provided, which is an opening having a rectangular shape when viewed from the back and through which the fluid that has undergone heat exchange inside the casing flows out. On a first face, a tube plate 23 is provided. Furthermore, the three faces of the casing other than the front face, the back face, and the first face are closed off with a second face, a third face, and a fourth face surrounding the front and back faces together with the first face.
In the tube plate 23, multiple (672 in this embodiment) tube holes (not shown) are provided, through which both ends of multiple (336 in this embodiment) U-shaped tubes 24 constituting the tube sets 12 are inserted.
The ends of the U-shaped tubes 24 inserted through the tube holes are expanded by using a tool such as a mandrel, so that the U-shaped tubes 24 are fixed to the tube plate 23 only on that single side.
The first fluid inlet 21 and the first fluid outlet 22 are connected to each other via a first flow path 25 extending in a straight line from the first fluid inlet 21 to the first fluid outlet 22. A fluid that flows in from the first fluid inlet 21 undergoes heat exchange with a fluid that passes through the U-shaped tubes 24 (the high-pressure compressible working fluid ejected from the compressor) and then flows out from the first fluid outlet 22. The first flow path 25 is formed by four faces, namely, the tube plate 23, the second face, a first partition plate (support plate) 26 disposed at the inner side of the third face and parallel to the third face, and the fourth face. Furthermore, between the tube plate 23 and the first partition plate 26, a second partition plate (support plate) 27 and a third partition plate (support plate) 28 are disposed parallel to the tube plate 23 and the first partition plate 26, which separate the first flow path 25 into three flow paths along the flow direction. In each of the first partition plate 26, the second partition plate 27, and the third partition plate 28, multiple (672 in this embodiment) tube holes (not shown) are provided, through which the multiple U-shaped tubes 24 constituting the tube sets 12 are inserted. The tube holes provided in the first partition plate 26 and the second partition plate 27 have an inner diameter greater than the outer diameter of the U-shaped tubes 24 so that thermal expansion of the U-shaped tubes 24 in the lengthwise direction (lateral direction in FIG. 3) will not be restrained. The tube holes provided in the third partition plate 28 disposed so as to separate the straight portions and turning portions of the U-shaped tubes 24 have an inner diameter greater than the inner diameter of the tube holes provided in the first partition plate 26 and the second partition plate 27 so that thermal expansion of the U-shaped tubes 24 in the lengthwise direction will not be restrained and so that a slight amount of the fluid that flows via the first flow path 25 flows into a space S formed between the third partition plate 28 and the third face.
The space S is formed by the third partition plate 28, the second face, the third face, the fourth face, the front face except the area where the first fluid inlet 21 is formed, and the back face except the area where the first fluid outlet 22 is formed.
On the outer side of the tube plate 23, multiple headers, namely, three headers 31, 32, and 33 in this embodiment, are provided.
The first header 31 is a housing substantially having an external shape of a cylinder cut into half with both ends closed. The first header 31 guides the fluid that undergoes heat exchange with the fluid passing via the first flow path 25 to the inlet end of the tube set 12 located on the most upstream side via a second fluid inlet 34 and guides the fluid that flows out from the outlet end of the same tube set 12 to the inlet end of the tube set 12 located on the downstream side thereof. In the first header 31, a barrier wall 35 is provided to prevent mixing between the fluid guided from the second fluid inlet 34 to the inlet end of the tube set 12 located on the most upstream side and the fluid that flows out from the outlet end of the same tube set 12.
The second header 32 is a housing substantially having an external shape of a cylinder cut into half with both ends closed. The second header 32 guides the fluid that flows out from the outlet end of the tube set 12 located second from the upstream side to the inlet end of the tube set 12 located on the downstream side thereof.
The third header 33 is a housing substantially having an external shape of a cylinder cut into half with both ends closed. The third header 33 guides the fluid that flows out from the outlet end of the tube set 12 located third from the upstream side to the inlet end of the tube set 12 located on the downstream side thereof and guides the fluid that flows out from the outlet end of the same tube set 12 to the outside via a second fluid outlet 36. In the third header 33, a barrier wall 37 is provided to prevent mixing between the fluid guided to the inlet end of the tube set 12 located fourth from the upstream side and the fluid that flows out from the outlet end of the same tube set 12.
In each of the tube sets 12, multiple (four in this embodiment) U-shaped tubes 24 having straight portions of the same length and turning portions with different radii are laid out within the same plane such that the U-shaped tubes 24 having smaller radii are disposed at the inner side and the U-shaped tubes 24 having greater radii are disposed at the outer side, and multiple (21 in this embodiment) sets of this arrangement are arrayed so as to be stacked in the direction perpendicular to this plane.
A certain gap is provided between the U-shaped tubes 24 laid out within the same plane and between the U-shaped tubes 24 stacked in the direction perpendicular to the plane, so that the fluid that flows from the first fluid inlet 21 toward the first fluid outlet 22 passes through these gaps.
Furthermore, reference sign 38 in FIG. 3 denotes a hatch for inspection work.
In the heat exchanger 10 according to this embodiment, the U-shaped tubes 24 are fixed only at a single side thereof to the tube holes provided in the tube plate 23, through which both ends of the U-shaped tubes 24 are inserted.
This permits thermal expansion of the U-shaped tubes 24 in the lengthwise direction, which serves to prevent damage to the U-shaped tubes 24.
Furthermore, in the heat exchanger 10 according to this embodiment, the first fluid inlet 21 and the first fluid outlet 22 are connected to each other via a single path, namely, the first flow path 25 extending in a straight line from the first fluid inlet 21 to the first fluid outlet 22.
Thus, pressure loss in the first flow path 25 can be reduced. Furthermore, it is possible to make a large amount of fluid flow via the first flow path 25. This serves to improve the heat exchange efficiency.
Furthermore, in the heat exchanger 10 according to this embodiment, the space S is formed by the first partition plate 26 and the casing 11 outside the first flow path 25. The fluid passing via the first flow path 25 flows into this space S via the gaps provided between the inner circumferential surfaces of the tube holes and the outer circumferential surfaces of the U-shaped tubes 24, causing a portion of the fluid that passes via the first flow path 25 to stagnate in the space S.
Thus, the fluid present in the space S acts as a heat insulating layer. This serves to maintain the temperature of the fluid passing via the first flow path 25, which serves to improve the heat exchange efficiency even further.
Furthermore, in the heat exchanger 10 according to this embodiment, the fluid that has undergone heat exchange with the fluid passing via the first flow path 25 while passing through a tube set 12 located on the upstream side is guided to the tube set 12 located on the downstream side thereof so that the fluid then undergoes heat exchange with the fluid passing via the first flow path 25. This serves to improve the heat exchange efficiency even further.
Furthermore, in the heat exchanger 10 according to this embodiment, the ends of the U-shaped tubes 24 are fixed to the tube plate 23 just by tube expansion, without employing welding.
Thus, the combination of the material of the tube plate 23 and the material of the U-shaped tubes 24, which must be taken into account when welding, need not be considered here, allowing free choice of the material of the tube plate 23 and the material of the U-shaped tubes 24.
Since the solar-heat gas turbine GT according to this embodiment includes, as the reheater 5, the heat exchanger 10 that permits thermal expansion of the U-shaped tubes 24 in the lengthwise direction, which serves to prevent damage to the U-shaped tubes 24, the reliability of the solar-heat gas turbine GT can be improved.
Furthermore, since the solar-heat gas turbine GT according to this embodiment includes, as the reheater 5, the heat exchanger 10 having a high heat exchange efficiency, it is possible to further boost the temperature of the compressible working fluid introduced into the turbine 3. This serves to improve the cycle efficiency of the heat cycle.
The present invention is not limited to the embodiment described above, and suitable modifications and alternatives may be introduced as needed.
For example, although the above-described embodiment includes the four tube sets 12 as a specific example, the present invention is not limited to this embodiment, and the number of tube sets included may be two, three, or five or more.
Furthermore, although the second fluid outlet 36 is provided at the first fluid inlet 21 side, and the second fluid inlet 34 is provided at the first fluid outlet 22 side in the above-described embodiment, the present invention is not limited to this embodiment, and the second fluid inlet 34 may be provided at the first fluid inlet 21 side, and the second fluid outlet 36 may be provided at the first fluid outlet 22 side.

REFERENCE SIGNS LIST

1 Compressor
3 Turbine
5 Reheater
10 Heat exchanger
11 Casing
12 Tube sets
21 First fluid inlet
22 First fluid outlet
23 Tube plate
24 U-shaped tubes
25 First flow path
26 First partition plate (partition plate)
31 First header (header)
32 Second header (header)
33 Third header (header)
GT Solar-heat gas turbine

Claims

1. A heat exchanger comprising:

a casing having a first fluid inlet provided at one end thereof and a first fluid outlet provided at the other end thereof opposite the one end, the first fluid inlet and the first fluid outlet being connected to each other via a first flow path extending in a straight line from the first fluid inlet to the first fluid outlet; and

multiple tube sets accommodated inside the casing so that a fluid that flows through the interiors thereof undergoes heat exchange with a fluid that flows via the first flow path,

wherein the multiple tube sets are arrayed along the first flow path, and multiple U-shaped tubes constituting the tube sets are fixed only to a tube plate disposed parallel to the first flow path and located at both ends of the U-shaped tubes.

2. A heat exchanger according to claim 1, wherein a partition plate separating straight portions and turning portions of the U-shaped tubes is disposed parallel to the first flow path, and gaps are provided between the inner circumferential surfaces of tube holes that are provided in the partition plate and through which the straight portions of the U-shaped tubes are inserted and the outer circumferential surfaces of the U-shaped tubes.

3. A heat exchanger according to claim 1, wherein a header that communicates between the outlet end of a tube set located on the upstream side and the inlet end of a tube set located on the downstream side thereof is provided.

4. A heat exchanger according to claim 1, wherein the U-shaped tubes are fixed to the tube plate by expanding the ends of the U-shaped tubes inserted through the tube holes.

5. A solar-heat gas-turbine power generating system comprising a heat exchanger according to claim 1 as a repeater that preheats a high-pressure compressible working fluid ejected from a compressor through heat exchange with a high-temperature compressible working fluid discharged from a turbine.