WO2015170576A1 - Solar heat collection device and method for producing same - Google Patents

Abstract

In the present invention, a solar heat collection device uses a curved mirror to condense sunlight onto a heat collection tube, thereby heating a heat medium flowing through the heat collection tube. The heat collection tube is provided with an inner tube through the interior of which the heat medium flows, an outer tube provided on the outside of the inner tube, a bellows and flange connecting the inner tube and outer tube together, and a heat insulation space formed between the inner tube and the outer tube. An anti-oxidation film comprising an inorganic oxide is formed by being applied to the inside surface of the inner tube. Due to this configuration, oxidation of the inside surface of the inner tube of the heat collection tube can be prevented.

Description

Solar thermal collector and method for manufacturing the same

The present invention relates to a solar heat collector, and more particularly to a trough solar heat collector.

2. Description of the Related Art A trough solar heat collecting apparatus is known that collects sunlight on a heat collecting tube using a heat collecting means having a parabolic surface and heats a heat medium flowing through the heat collecting tube. The heat collecting tube used in this solar heat collecting device has a double tube structure consisting of a glass outer tube and a metal inner tube in order to efficiently convert sunlight into heat and reduce heat loss. Yes. A sealed space in a vacuum state is provided between the outer tube and the inner tube.

Patent Document 1 describes a parabolic trough heat collector having a steel tube (inner tube) whose outer surface is coated with a radiation-selective absorber. The radiation-selective absorber coating has a metal layer, a barrier layer, an absorption layer, an antireflection layer, and the like. Thus, in the collector of patent document 1, various functions, such as oxidation prevention and reflection prevention, work with respect to an inner pipe by giving various coatings to the outer surface of the inner pipe of a heat collector. It is like that.

JP 2010-271033 A

However, as shown in FIG. 2 of Patent Document 1, in the parabolic trough heat collector of this document, no coating is applied to the inner surface of the steel inner tube that contacts the heat medium. Here, the heat medium flowing through the inner pipe is steam, oil or molten salt, but the inner surface of the inner pipe is more oxidized under the influence of the heat of the heat medium due to oxygen or water mixed in these heat medium. It is easy to do. Therefore, oxidation of the inner surface of the inner tube may cause deterioration of the inner tube of the heat collector and decrease strength.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a solar heat collector that can prevent oxidation of the inner surface of the inner tube of the heat collection tube and a method for manufacturing the same.

In order to solve the above-described problems, a solar heat collecting apparatus according to the present invention heats a heat medium flowing through the heat collecting tube by concentrating sunlight on the heat collecting tube using a condensing unit, and collects the sunlight. The heat pipe is formed between an inner pipe through which the heat medium flows, an outer pipe provided outside the inner pipe, a connecting member connecting the inner pipe and the outer pipe, and the inner pipe and the outer pipe. An antioxidant film including an inorganic compound is formed on the inner surface of the inner tube by coating.

Further, the antioxidant film on the inner surface of the inner tube may contain SiO ₂ or Al ₂ O ₃ .
Furthermore, a selective absorption film may be formed on the outer surface of the inner tube.

Further, as a method of manufacturing the solar heat collecting apparatus according to the present invention, by filling the solution of the composition forming the antioxidant film into the inner tube, and then removing the solution from the inner tube, An antioxidant film may be formed on the inner surface of the inner tube.

Furthermore, as another method for manufacturing the solar heat collecting apparatus according to the present invention, the inner tube on which the selective absorption film is formed is immersed in a liquid tank containing a solution of the composition that forms the antioxidant film, and thereafter By removing the solution from the solution tank or removing the inner tube from the solution, an antioxidant film is formed on the inner surface of the inner tube and reflected on the outer surface of the selective absorption film formed on the inner tube. A prevention film may be formed.

According to the solar heat collecting apparatus and the manufacturing method thereof according to the present invention, oxidation of the inner surface of the heat collecting tube can be prevented.

It is sectional drawing perpendicular | vertical to the longitudinal direction of the heat collecting tube of the solar thermal collector which concerns on embodiment of this invention. It is sectional drawing parallel to the longitudinal direction of the heat collecting tube used for the solar heat collecting apparatus shown in FIG. It is a partial expanded sectional view of the inner tube | pipe of the heat collecting tube of the solar heat collecting apparatus shown in FIG. It is a figure which shows the method of forming an antioxidant film | membrane in the inner surface of the inner tube | pipe of the heat collecting tube used for the solar thermal collector shown in FIG. It is a figure which shows another method of forming an antioxidant film | membrane in the inner surface of the inner tube | pipe of the heat collecting tube used for the solar thermal collector shown in FIG. It is a figure which shows another method of forming an antioxidant film | membrane in the inner surface of the inner tube | pipe of the heat collecting tube used for the solar thermal collector shown in FIG.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIGS. 1 and 2, the solar heat collecting apparatus 100 includes a curved mirror 1 as a condensing unit and a heat collecting tube 2 disposed inside the curved mirror 1. The curved mirror 1 has a shape having a parabolic cross section along the longitudinal direction. Further, the inner surface of the curved mirror 1 is a mirror surface, and the heat collecting tube 2 is supported along the longitudinal direction at the focal position.

The heat collecting pipe 2 is a double pipe provided with a stainless steel inner pipe 4 through which oil, steam or molten salt, which is the heat medium M, circulates, and a glass outer pipe 3 provided outside the inner pipe 4. It has a tube structure. The length of the inner tube 4 and the outer tube 3 in the longitudinal direction is about 4 m. The heat collecting pipe 2 has a flange 8 provided near both ends of the inner pipe 4 and a bellows 7 connecting the flange 8 and the outer pipe 3. The bellows 7 expands and contracts corresponding to the difference in thermal expansion between the outer tube 3 and the inner tube 4. A sealed heat insulation space 9 is formed between the outer tube 3 and the inner tube 4 connected to each other by the bellows 7 and the flange 8. The heat insulation space 9 is in a vacuum state in order to improve heat insulation.
Here, the bellows 7 and the flange 8 constitute a connecting member.

In addition, it does not specifically limit as a material of the outer tube | pipe 3, Generally transparent heat resistant glass can be used. Examples of the transparent heat-resistant glass glass tube include a borosilicate glass tube.
Further, the material of the inner tube 4 is not limited to stainless steel, and other heat-resistant metals such as other iron-based materials (for example, heat-resistant steel, alloy steel, carbon steel) and aluminum-based materials can also be used. .

Moreover, as a means to deform | transform corresponding to the thermal expansion difference between the outer tube | pipe 3 and the inner tube | pipe 4, it is not limited to the bellows 7, You may use a diaphragm.
Furthermore, the material of the bellows 7 and the flange 8 is not particularly limited. For example, a metal having heat resistance such as an iron-based material (for example, stainless steel, heat-resistant steel, alloy steel, carbon steel) or an aluminum-based material is used. Can do.

A selective absorption film 14 is formed on the outer surface of the inner tube 4, and an antireflection film 16 is formed on the outer surface of the selective absorption film 14. As shown in FIG. 3, the selective absorption film 14 includes a metal layer 14a that directly covers the outer surface of the inner tube 4, and an absorption layer 14b formed on the metal layer 14a. An antireflection film 16 is formed on the absorption layer 14b. For example, a metal such as molybdenum, tungsten, nickel, copper, or silver is used for the metal layer 14a. Moreover, the cermet which is a mixture of a metal and a ceramic is used for the absorption layer 14b. The antireflection film 16 is made of SiO ₂ or Al ₂ O ₃ (alumina). The selective absorption film 14 having the metal layer 14a and the absorption layer 14b and the antireflection film 16 are formed on the outer surface of the inner tube 4 to absorb visible light and near infrared light of sunlight L. The far infrared rays radiated from the heat medium M can be reflected.
Note that a molybdenum layer or a SiO ₂ layer may be further provided between the outer surface of the inner tube 4 and the metal layer 14a.

Further, an antioxidant film 17 for preventing permeation of oxygen contained in the heat medium M is formed on the inner surface of the inner tube 4. The antioxidant film 17 is made of SiO ₂ that is an inorganic oxide.
The antioxidant film 17 is not limited to SiO _2, and may be another inorganic oxide having an antioxidant function. Specifically, the antioxidant film 17 may be Al ₂ O _3. Or a composite material of Al ₂ O ₃ and SiO ₂ . The antioxidant film 17 is not limited to an inorganic oxide, and may be another inorganic compound having an antioxidant function such as AlN (aluminum nitride).

A method of forming the antioxidant film 17 on the inner surface of the inner tube 4 will be described with reference to FIG.
First, a substantially disc-shaped lid body 12 with an edge standing is fitted into one end of the inner tube 4. The lid 12 is provided with an opening 13 and an opening / closing valve 15 attached to the opening 13. The inner tube 4 is arranged so that one end into which the lid body 12 is fitted is directed downward and the other open end is directed upward. At this time, the opening / closing valve 15 provided in the lid 12 is in a closed state. Then, the SiO ₂ solution S is poured into the inner tube 4 from one end opened upward and filled. Thereafter, after a sufficient time has elapsed, the on-off valve 15 is switched from the closed state to the open state, and the SiO ₂ solution S gradually flows out from the inside of the inner tube 4 through the opening 13 according to gravity and is removed. Go. Thereby, the inner surface of the inner tube 4 is coated with SiO ₂ which is a composition for forming the antioxidant film 17. That is, the antioxidant film 17 is formed on the inner surface of the inner tube 4 by coating that is a wet process.

Here, the incident path of the sunlight L incident on the solar heat collecting apparatus 100 will be described with reference to FIG. 1. The sunlight L is reflected on the curved mirror 1 and condensed on the heat collecting tube 2. First, the sunlight L incident on the outer tube 3 passes through the outer tube 3 and enters the inner tube 4. Next, the sunlight L incident on the inner tube 4 passes through the antireflection film 16, the selective absorption film 14, the inner tube 4 and the antioxidant film 17, and is absorbed by the heat medium M flowing through the inner tube 4. As a result, the heat medium M is heated.

As described above, in the solar heat collecting apparatus 100 according to this embodiment, since the antioxidant film 17 is formed on the inner surface of the inner tube 4 of the heat collecting tube 2, the heat medium M containing high temperature and oxygen or water is used. Oxidation of the inner surface of the inner tube 4 that is in contact is prevented. Therefore, the corrosion resistance and durability of the inner tube 4 are improved. Further, since the antioxidant film 17 is an inorganic oxide, not only can the oxidation of the inner surface of the inner tube 4 be prevented, but also the heat resistance and thermal conductivity of the inner tube 4 can be improved.

In the case of using SiO ₂ to prevent the oxide film 17, also can be used SiO ₂ of the same material on the antireflective film 16, thereby improving the efficiency of production of the solar heat collector 100.

Further, when the antioxidant film 17 includes Al ₂ O ₃ , that is, when the antioxidant film 17 is Al ₂ O ₃ or a composite material of Al ₂ O ₃ and SiO ₂ , similarly to the case of using SiO _2. The same material containing Al ₂ O ₃ can also be used for the antireflection film 16. Further, the antioxidant film 17 containing Al ₂ O ₃ has not only a function of preventing the oxidation of the inner tube 4 but also a function of suppressing the permeation of hydrogen from the heat medium M. That is, when the hydrogen gas generated in the heat medium M is transmitted through the inner tube 4 enters the insulation space 9, but thermal insulation lowers the vacuum degree of the heat insulation space 9 may be decreased, the antioxidant film 17 Al ₂ By containing O ₃ , such permeation of hydrogen gas is prevented.

Here, an experimental example is shown in which an antioxidant film of Al ₂ O ₃ is formed on a stainless steel plate, that is, a SUS plate by the following steps (1) to (6).
(1) After immersing the SUS plate in an Al ₂ O ₃ precursor sol containing aluminum isopropoxide, pure water and nitric acid, the SUS plate is pulled up at a rate of 0.5 mm / second, and the surface of the SUS plate is made of Al ₂ O ₃ . A coating of precursor sol was formed.
(2) The SUS plate obtained in (1) was left to dry at room temperature for 10 minutes.
(3) The SUS plate obtained in (2) was placed in a drying furnace and dried at 80 ° C. for 30 minutes.
(4) The SUS plate obtained in (3) is placed in a firing furnace, heated to 600 ° C. over 3 hours at a rate of 2 ° C./minute, held at 600 ° C. for 1 hour, and then at a rate of 5 ° C./minute. At room temperature.
(5) The SUS plate was taken out from the firing furnace and washed with pure water.
(6) The steps (1) to (5) were repeated twice.
And the SUS board in which the antioxidant film | membrane was formed in such a process and the SUS board in which the antioxidant film | membrane was not formed were each heated at 400 degreeC for 3 days in 1 degree of vacuum. As a result, no change appeared on the surface of the SUS plate on which the antioxidant film was formed, but the surface of the SUS plate on which the antioxidant film was not formed was oxidized black. Therefore, the oxidation of the SUS plate is suppressed by forming the antioxidant film of Al ₂ O _{3 on} the SUS plate.

Moreover, by forming the selective absorption film 14 on the outer surface of the inner tube 4, the heat collecting tube 2 of the solar heat collecting apparatus 100 efficiently absorbs sunlight L and suppresses heat radiation from the heat medium M. Can do.

Furthermore, in the method for manufacturing the solar heat collecting apparatus 100 according to the embodiment of the present invention, the SiO ₂ solution S is removed after filling the inside of the inner tube 4, whereby the inner surface of the inner tube 4 is removed. SiO ₂ is applied to form an antioxidant film 17. Here, the inner tube 4 has a long length in the longitudinal direction, and in order to form the antioxidant film 17 on the inner surface, a film forming technique by a dry process such as sputtering cannot be used. However, if the wet process is a method in which the inner tube 4 is filled with the solution S and the inner surface of the inner tube 4 is coated with SiO ₂ , the antioxidant film 17 can be reliably formed.

In addition, the manufacturing method of the solar thermal collector 100, that is, the method of forming the antioxidant film 17 on the inner surface of the inner tube 4 by a wet process, fills the inner tube 4 with the solution S as in this embodiment. There is no limitation to the removal method.
For example, as shown in FIG. 5, the liquid tank 22 is prepared as a container having a depth deeper than the length of the inner tube 4 in the longitudinal direction and having an internal volume that can accommodate the entire inner tube 4. An opening 23 is formed on the bottom surface of the liquid tank 22. An opening / closing valve 25 is attached to the opening 23. Here, with the on-off valve 25 being closed, the solution S of SiO ₂ is poured into the liquid tank 22 and filled. At this time, the solution S is filled in the liquid tank 22 so that the depth is deeper than the length of the inner tube 4 in the longitudinal direction. Then, the inner tube 4 is submerged and immersed in the liquid tank 22 filled with the solution S in such a direction that the longitudinal direction becomes vertical. In the step before the inner tube 4 is immersed in the liquid tank 22 containing the solution S, the selective absorption film 14 is already formed on the outer surface of the inner tube 4. After a sufficient time has elapsed, the opening / closing valve 25 is switched from the closed state to the open state, and the SiO ₂ solution S gradually flows out from the inside of the liquid tank 22 through the opening 23 according to gravity and is removed. Go. Thus, the inner surface of the inner tube 4 with SiO ₂ is applied, SiO ₂ on the outside surface yet selective absorption film 14 formed on the outer surface of the inner tube 4 is applied. SiO ₂ applied to the inner surface of the inner tube 4 constitutes an antioxidant film 17. The SiO ₂ applied to the outer surface of the selective absorption film 14 formed on the inner tube 4 constitutes an antireflection film 16.

In addition, as shown in FIG. 6, the antioxidant film 17 and the antireflection film 16 may be formed on the inner tube 4 using a liquid tank 32 that does not have an opening or an opening / closing valve. Like the liquid tank 22 in FIG. 5, the liquid tank 32 is a container having a depth that is deeper than the length of the inner tube 4 in the longitudinal direction and can store the entire inner tube 4. . The solution S is poured into the liquid tank 32 and filled so that the depth is deeper than the length of the inner tube 4 in the longitudinal direction. Then, the inner tube 4 in which the selective absorption film 14 has already been formed on the outer surface is immersed and immersed in the liquid tank 32 containing the solution S in a direction in which the longitudinal direction becomes vertical. Thereafter, after a sufficient time has elapsed, as indicated by the arrow in FIG. 6, the inner tube 4 is gradually pulled up from the solution S and taken out upward. As a result, SiO ₂ is applied to the inner surface of the inner tube 4 and an antioxidant film 17 is formed. Similarly, SiO ₂ is applied to the further outer surface of the selective absorption film 14 formed on the outer surface of the inner tube 4 to form an antireflection film 16.

5 and 6, the inner tube 4 on which the selective absorption film 14 is formed is immersed in the liquid tanks 22 and 23 containing the solution S, and then the solution S is removed from the liquid tank 22. Alternatively, by removing the inner tube 4 from the liquid tank 32 containing the solution S, SiO ₂ can be applied to the inner and outer sides of the inner tube 4. Therefore, the antioxidant film 17 and the selective absorption film 14 can be formed in one process, and the solar heat collecting apparatus 100 can be manufactured more efficiently.

1 curved mirror (condensing means), 2 heat collecting tube, 3 outer tube, 4 inner tube, 7 bellows (connection member), 8 flange (connection member), 9 heat insulation space, 14 selective absorption film, 16 antireflection film, 17 Antioxidation film, 100 solar heat collector, L sunlight, M heat medium, S solution.

Claims (6)

A solar heat collector for heating a heat medium flowing through the heat collection tube by concentrating sunlight on a heat collection tube using a light collecting means,
The heat collecting tube is
An inner pipe through which the heat medium circulates;
An outer tube provided outside the inner tube;
A connecting member for connecting the inner tube and the outer tube;
A heat insulating space formed between the inner tube and the outer tube;
A solar heat collecting apparatus in which an antioxidant film containing an inorganic compound is formed on the inner surface of the inner tube by coating. The solar thermal collector according to claim 1, wherein the antioxidant film includes SiO ₂ . The solar thermal collector according to claim 1, wherein the antioxidant film contains Al ₂ O ₃ . The solar heat collecting apparatus according to any one of claims 1 to 3, wherein a selective absorption film is formed on an outer surface of the inner tube. A method for manufacturing the solar heat collecting apparatus according to any one of claims 1 to 4,
Filling the inside of the inner tube with a solution of the composition forming the antioxidant film, and then removing the solution from the inside of the inner tube, the antioxidant film on the inner surface of the inner tube A method for manufacturing a solar heat collecting apparatus. A method for manufacturing the solar heat collecting apparatus according to claim 4,
The inner tube on which the selective absorption film is formed is immersed in a liquid tank containing a solution of the composition that forms the antioxidant film,
Thereafter, the solution is removed from the liquid tank, or the inner tube is removed from the liquid tank,
A method for manufacturing a solar heat collecting apparatus, wherein the antioxidant film is formed on an inner surface of the inner tube and an antireflection film is formed on an outer surface of the selective absorption film formed on the inner tube.

Images