ES2579053T3 - Heat receiving tube, method for manufacturing the heat receiving tube, parabolic trough collector with the receiving tube and use of the parabolic trough collector - Google Patents

Abstract

Heat receiver tube (1) to absorb solar energy and to transfer absorbed solar energy to a heat transfer fluid (2) that can be located inside a central tube (10) of the heat receiver tube (1) , wherein - the central tube (10) comprises at least a first partial central tube surface (101) covered by at least a first solar-absorbing coating (131) to absorb a first absorption radiation of a first given spectrum of sunlight; and at least a second partial central tube surface (102) covered by at least a second solar-absorbing coating (132) to absorb a second absorption radiation of a second specific spectrum of sunlight; - the first solar energy absorbing coating (131) forms a first surface (11) of partial heat receiving tube of the heat receiving tube (1); characterized in that - an emission radiation inhibition coating (14) for inhibiting emissivity for infrared radiation is deposited on the second solar energy absorbing coating (132) so that the second solar energy absorbing coating (132) is disposes between the second surface (102) of partial central tube and the coating (14) for inhibiting emission radiation; and the emission radiation inhibition coating (14) forms a second surface (12) of the partial heat receiving tube of the heat receiving tube (1).

Description

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HEAT RECEIVER TUBE, METHOD FOR MANUFACTURING THE HEAT RECEIVER TUBE, CYLINDER-PARABOLIC CATCH WITH THE RECEIVER TUBE AND USE OF THE CYLINDER-PARABOLIC CATCH

DESCRIPTION

Background of the invention

1. Field of the invention

This invention relates to a heat receiver and a method of manufacturing the heat receptor tube. In addition, a parabolic trough sensor and a parabolic trough sensor are provided.

2. Description of the related technique

A unit for concentrating solar energy from a solar field plant based on concentrated solar energy technology is, for example, a parabolic trough with parabolic mirrors and a heat receiving tube. The heat receiving tube is arranged in the focal line of the mirrors. By means of the reflecting surfaces of sunlight of the mirrors, the sunlight is focused on the heat receiving tube, which is filled with a heat transfer fluid, for example a thermal oil or a molten salt. Through the heat receiving tube, the sunlight energy is coupled into the heat transfer fluid. Solar energy is converted into thermal energy.

To maximize the efficiency, with which the sunlight energy is coupled into the heat transfer fluid, a solar energy absorbing coating is adhered to a surface of the heat receiving tube. An absorbent coating of this type commonly comprises a multilayer stack with thin film layers sequentially deposited having different optical characteristics.

An essential overall optical characteristic of the absorbent coating is a high solar absorbance (low solar reflectivity) for wavelengths of the solar spectrum (absorption radiation). Additionally, low emissivity (high reflectivity) is essential for infrared radiation. Such a coating is called selective solar coating.

US 2010/0258111 A1 focuses on high absorbance. For this, a coating with carbon nanotubes (NTC) is used.

Unlike this, WO 2006/015815 A1 describes a receiver tube with different surfaces. Thus, the optical characteristics of the selective partial surface coatings of the receiving tube go: the selective coating of the receiving tube facing the parabolic mirror comprises a relatively high solar absorbance while the selective coating of the receiving tube that is offset with respect to The parabolic mirror comprises a relatively low emissivity.

For the manufacture of the heat receiving tube, the solar absorbent coating is adhered to the surface of the heat receiving tube by a sequential profile of deposition of thin films on the surface using a method such as cathode spray.

Summary of the invention

It is an object of the invention to provide a heat receiving tube with an energy efficiency that improves in comparison with the state of the art.

It is a further object of the invention to provide a parabolic trough sensor with the heat receiving tube.

A further object of the invention is to provide a use of the parabolic trough sensor.

These objects are achieved by the inventions specified in the independent claims, 1, 10 and 15 and in the dependent claim 14.

A heat receiving tube is provided to absorb solar energy and to transfer the absorbed solar energy to a heat transfer fluid that can be located inside a central tube of the heat receiving tube. The central tube comprises at least a first partial central tube surface covered by at least a first absorbing solar energy coating to absorb a first absorption radiation of a first certain spectrum of sunlight. The central tube additionally comprises at least a second partial central tube surface covered by at least a second absorbing solar energy coating to absorb a second absorption radiation of a second specific spectrum of sunlight. The heat receiving tube is characterized in that an emission radiation inhibition coating to inhibit the emissivity for infrared radiation is deposited on the second solar energy absorbing coating so that the second solar energy absorbing coating is disposed between the second partial central tube surface and

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the emission radiation inhibition coating. The first solar absorbent coating forms a first partial heat receiving tube surface of the heat receiving tube and the emission radiation inhibition coating forms a second partial heat receiving tube surface of the heat receiving tube. The radiation inhibition coating preferably adheres directly to the second solar energy absorbing coating, leading to a stack of layers arranged on the second partial central tube surface of the central tube. This layer stacking consists of the second solar energy absorbing coating and the emission radiation inhibition coating.

For example, the first partial surface is formed by a first segment with a first circumference (segment angle) between 90 and 270 ° while the second partial surface is formed by a second segment with a second circumference between 180 ° and 90 °.

Additionally, a method for manufacturing a suitable heat receptor tube is disclosed. The method comprises the following stages:

a) providing an uncovered central tube for a heat receiving tube of the first partial central tube surface and the second partial central tube surface;

b) adhering a first solar energy absorbent coating on the first partial central tube surface and adhering a second solar energy absorbent coating on the second partial central tube surface; Y

c) adhering an emission radiation inhibition coating on the second solar absorbent coating so that the second selective solar energy coating is disposed between the second partial central tube surface and the emission radiation inhibition coating.

Also provided is a parabolic trough collector comprising at least one parabolic mirror having a reflective surface of sunlight to concentrate the sunlight on the focal line of the parabolic mirror and at least one heat receiving tube that is arranged in the focal line of the parabolic mirror. The heat receiving tube is arranged in the focal line so that the first partial heat receiving tube surface with the first solar absorbent coating is located partially opposite to the reflective surface of sunlight and the second tube surface Partial heat receptor with the emission radiation inhibition coating is at least partially offset from the reflective surface of sunlight.

Finally, a use of the parabolic trough sensor in a plant to convert solar energy into electrical energy is disclosed.

Preferably, the first solar energy absorbing coating and the second solar energy absorbing coating form a common solar energy absorbing coating with common physical and chemical characteristics. There is only one kind of solar energy absorbing coating adhered to the lateral area of the central tube. This common solar energy absorbing coating has entirely identical chemical and physical characteristics. As a consequence, the first absorption radiation of the first determined spectrum of sunlight and the second absorption radiation of the second determined spectrum of sunlight are almost identical. The use of only one kind of solar absorbent coating is advantageous in terms of manufacturing the heat receiving tube. It is easier to deposit only one kind of solar energy absorbent coating on the overall central tube surface of the central tube.

The concept of the invention is to optimize the thermal characteristics of the heat receiving tube by maximizing the coupling of solar energy (concentrated radiation energy) into the heat receiving tube through the first partial heat receiving tube surface and minimizing the loss of thermal energy through the second surface of partial heat receiving tube. The first solar energy absorbing coating that forms the first partial heat receiving tube surface is designed to absorb as much solar radiation as possible (absorbance of more than 97%). Unlike that, the emissivity through the second partial heat receiving tube is reduced. The heat receiving tube can be arranged in the focal line of a parabolic mirror so that the concentrated solar radiation strikes the first solar absorbent coating of the first partial heat receiving tube surface. The part of the heat receiving tube that is not heated by concentrated solar radiation (that is, that part that is normally facing the sun and, therefore, is only subjected to direct solar radiation) is coated by the radiation inhibition coating broadcast. The emission radiation inhibition coating is a non-selective coating.

Preferably, the first partial surface and / or the second partial surface are aligned along a longitudinal alignment of the heat receiving tube. This feature applies to the first central tube surfaces and / or the second central tube surface, as well. The alignment along the longitudinal alignment of the heat receiving tube and the alignment along the longitudinal alignment of the central tube, respectively, is advantageous in terms of an arrangement of the heat receiving tube in the focal line of the parabolic mirror. The coupling of the concentrated radiation energy of the sun in the heat receiving tube is maximized and the loss of thermal energy

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of the heat receiving tube is minimized.

In a preferred embodiment, the first partial heat receiving tube surface comprises a first segment of a lateral area of the heat receiving tube with a first circumference selected from the range between 50 ° and 300 ° and preferably between 60 ° and 210 ° . In a further preferred embodiment, the second partial heat receiving tube surface comprises a second segment of the lateral area of the heat receiving tube with a second circumference that is selected from the range between 210 ° and 60 ° and preferably between 180 ° and 90 ° . These angles are optimized with respect to the sensor geometry (for example, edge angle).

The emission radiation inhibition coating is deposited on the second partial caloric energy absorbing coating. By reducing the emission radiation inhibition, the magnitude of the emissivity of the infrared radiation is reduced. The emissivity for infrared radiation of the radiation inhibition coating is less than 30%. Preferably, the emission radiation inhibition coating comprises an emissivity for infrared radiation that is less than 20%.

In a preferred embodiment, the emission radiation inhibition coating comprises a metal that is selected from the group consisting of aluminum, copper, silver, gold and molybdenum. Other metals or alloys are also possible. The emission radiation inhibition coating may be metallic and therefore substantially consists only of a metal. For example, the emission radiation inhibition coating is a layer consisting of copper. A coating of this type with copper blocks the caloric radiation (emissivity) in the “upper” part of the heat-receiving tube that affects it by direct solar radiation. This greatly reduces the overall heat loss of the heat receiving tube while losing some of the total radiation that falls on it.

In a further preferred embodiment, the emission radiation inhibition coating comprises a layer thickness that is selected from the range between 100 nm and 800 nm and preferably 200 nm and 800 nm. Most preferably, the thickness is selected from the range between 300 nm and 800 nm. For example, the emission radiation inhibition coating comprises a layer thickness of approximately 500 nm.

Preferably, at least one of the partial heat receiving tube surfaces forms a contiguous area. The heat receiving tube is arranged in the focal line parallel to the longitudinal alignment of the mirror. Through this, the absorption of solar energy is very effective. The concentrated solar radiation always affects the solar absorbent coating of the first partial heat receiving tube surface (intensity of approximately 52 soles) while the concentrated solar radiation (intensity of approximately 0.6 soles) does not affect the second surface of partial heat receiver tube. A very small amount of energy could be wasted while obtaining many more benefits in terms of heat loss due to global emissivity.

The overall rate of absorption with respect to emissivity of the heat receiving tube therefore increases even if part of the direct sun's radiation is lost. The areas of the first partial heat receiving tube surface and the second partial heat receiving tube surface should not have the same extension. The extensions of the partial heat receiving tube surfaces are easily optimized as well as its location on the lateral surface of the heat receiving tube (for example due to the edge).

To improve the physical and chemical stability and the thermal characteristics of the heat receiving tube, additional measures are also implemented. For example, the heat receiving tube has an encapsulation comprising at least one encapsulation wall. This encapsulation wall is at least partially transparent for the first absorption radiation and / or for the second absorption radiation. At least partially transparent is given in the case that the transmission for absorption radiation is more than 80% and preferably more than 90%.

The encapsulation is preferably a glass tube and the encapsulation wall is a glass tube wall. Between the heat receiving surface and the encapsulation wall there is a receiving space. This receiving space is evacuated. This means that the gas pressure in the receiving space is less than 10-2 mbar and preferably less than 10-3 mbar. This has the advantage that thermal heat transfer away from the heat receiving tube with convection heat transfer fluid is reduced. The thermal energy does not dissipate and is available substantially completely for heating the heat transfer fluid.

For the adhesion of at least one of the solar energy absorbing coatings and / or for the adhesion of the emission radiation inhibition coating, a thin film deposition technique is used. The thin film deposition technique is preferably selected from the group consisting of atomic layer deposition, chemical deposition in vapor phase and physical deposition in vapor phase. Physical vapor deposition is for example cathode spray.

To obtain structured layers, structured deposition techniques are used. Alternatively, an unstructured layer can be deposited and after deposition a structuring is carried out, for example by removing deposited material. In a preferred embodiment, the adhesion of at least one of the coatings

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Absorbers of solar energy and / or adhesion of the emission radiation inhibition coating are carried out with the aid of a mask method. Preferably, the first solar energy absorbent coating and the second solar energy absorbent coating form a complete, contiguous and common central tube covering layer. In this situation, it is not necessary to use a mask method.

The following advantages are related to the invention:

- A wider range of materials available for the second surface of the partial heat receiving tube of the heat receiving tube can be accessed.

- It results in a greater blockage of the caloric radiation in the non-selective coated part due to more suitable materials.

- This results in a higher overall absorption ratio with respect to the emissivity of the entire heat receiving tube.

Brief description of the drawings

Additional features and advantages of the invention are obtained from the description of exemplary embodiments with reference to the drawing. The drawings are schematic.

Figure 1 shows the cross section of a heat receiving tube and a parabolic trough with the heat receiving tube.

Figure 2 shows the heat receiving tube on one side.

Detailed description of the invention

A heat receiving tube 1 is provided for absorbing solar energy and for transferring the absorbed solar energy to a heat transfer fluid 2 that may be located inside a central tube 10 of the heat receiving tube. The central tube consists of a wall 103 of central tube with steel.

The central tube 10 comprises a first partial central tube surface 101 that is covered by a first solar energy absorbing coating 131 (selective coating) to absorb a first absorption radiation of a first specific spectrum of sunlight. The first solar energy absorbent coating is a multilayer arrangement with different layers with different optical characteristics.

A second partial central tube surface 102 is covered by a second solar energy absorbing coating 132 to absorb a second absorption radiation of a second spectrum of sunlight. The physical and chemical characteristics of the first solar energy absorbing coating and the second solar energy absorbing coating are the same. The first solar energy absorbing coating 131 and the solar energy absorbing coating form a common adjoining solar absorbent coating 13 which is deposited throughout the latent area of the central tube surface of the central tube.

An emission radiation inhibition coating 14 for inhibiting emissivity for infrared radiation is deposited on the second coating 132 for selective solar energy so that the second coating 132 for selective solar energy is disposed between the second surface 102 of the central tube partial and coating 14 of emission radiation inhibition. The emission radiation inhibition coating consists of copper. Alternatively, the material used is aluminum. The emission radiation inhibition coating comprises a layer thickness of approximately 500 nm.

The first solar energy absorbing coating 131 forms a first surface 11 of the partial heat receiving tube of the heat receiving tube 1. The emission radiation inhibition coating 14 forms a second surface 12 of the partial heat receiving tube of the heat receiving tube 1. These partial central tube surfaces are aligned along a longitudinal alignment 15 of the heat receiving tube 1.

The first surface 11 of the partial heat receiving tube forms a first segment of the lateral area 16 of the heat receiving tube 1 with a first circumference 1611 of approximately 180 °. The second surface 12 of the partial heat receiving tube forms a second segment of the lateral area 16 of the heat receiving tube 1 with a second circumference 1612 of approximately 180 °.

The following structural measures are not shown in the figures: the heat receiving tube is wrapped in a glass tube with a glass tube wall. The glass tube wall is transparent for absorption radiation with a transmission of more than 90%. A receiving space is located between the glass tube wall and the receiving surface 16. This receiving space is evacuated. The gas pressure is approximately 10.3 mbar.

The heat receiver tube 1 is part of a 1000 parabolic trough collector. The parabolic trough sensor 1000 comprises at least one parabolic mirror 3 with a surface 31 reflecting the sunlight. Through the reflective surface 31, sunlight is concentrated in the focal line 32 of the parabolic mirror 3.

5 The tube 1 heat sink is located in the focal line 32 of the parabolic mirror 3. Thus, the first surface 11 of the partial heat receiving tube of the heat receiving tube ("bottom" part of the receiving tube 1) is disposed opposite to the sunlight reflecting surface 31 of the mirror 3. The second surface 12 of the "upper" part of the partial heat receiving tube of the heat receiving tube 1) is offset with respect to the sunlight reflecting surface 31 of the mirror 3.

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Inside the heat receiving tube, a heat transfer fluid 2 is located. Through the solar energy absorbing coating, sunlight is absorbed and transferred to heat. This heat is transferred to the heat transfer fluid.

15 The parabolic trough collector is used in a solar power plant to convert solar energy into electrical energy.

Claims (13)

5 10 fifteen twenty 25 2. 30 3. 35 Four. 40 5. Four. Five 6. 50 7. 8. 55 9. 60 10. Heat receiver tube (1) to absorb solar energy and to transfer absorbed solar energy to a heat transfer fluid (2) that can be located inside a central tube (10) of the heat receiver tube (1) , in which - the central tube (10) comprises at least a first surface (101) of partial central tube covered by at least a first solar energy absorbing coating (131) to absorb a first absorption radiation of a first specific spectrum of light from the Sun; and at least a second partial central tube surface (102) covered by at least a second solar energy absorbent coating (132) to absorb a second absorption radiation of a second specific spectrum of sunlight; - the first solar energy absorbing coating (131) forms a first surface (11) of partial heat receiving tube of the heat receiving tube (1); characterized because - a coating (14) for inhibiting emission radiation to inhibit the emissivity for infrared radiation is deposited on the second solar energy absorbing coating (132) so that the second solar energy absorbing coating (132) is disposed between the second surface (102) of partial central tube and the coating (14) for inhibiting emission radiation; Y - the emission radiation inhibition coating (14) forms a second surface (12) of the partial heat receiving tube of the heat receiving tube (1). Heat receiving tube according to claim 1, wherein the first solar energy absorbing coating (131) and the second solar energy absorbing coating (132) form a common solar energy absorbing coating (13) with common physical and chemical characteristics . Heat receiving tube according to claim 1 or claim 2, wherein the first surface (11) of partial heat receiving tube and / or the second surface (12) of partial heat receiving tube are aligned along a longitudinal alignment (15) of the tube (1) heat sink. Heat receiving tube according to one of the preceding claims, wherein the first surface (11) of partial heat receiving tube comprises a first segment of a lateral area (16) of the heat receiving tube (1) with a first circumference ( 1611) which is selected from the range between 50 ° and 300 ° and preferably between 60 ° and 210 °. Heat receiving tube according to one of the preceding claims, wherein the second surface (12) of partial heat receiving tube comprises a second segment of the lateral area (16) of the heat receiving tube (1) with a second circumference (1621 ) which is selected from the range between 210 ° and 60 ° and preferably between 180 ° and 90 °. Heat-receiving tube according to one of the preceding claims, wherein the emission radiation inhibition coating (14) comprises an emissivity for infrared radiation that is less than 20%. Heat receiving tube according to one of the preceding claims, wherein the emission radiation inhibition coating (14) comprises metal that is selected from the group consisting of aluminum, copper, silver, gold and molybdenum. Heat-receiving tube according to one of the preceding claims, wherein the emission radiation inhibition coating (14) comprises a layer thickness that is selected from the range between 100 nm and 800 nm and preferably between 200 nm and 800 nm . Heat receiving tube according to one of the preceding claims, wherein at least one of the partial heat receiving tube surfaces (11, 12) forms a contiguous area. Method for manufacturing a heat receiving tube according to one of claims 1 to 9, the method comprising the following steps: a) providing a central tube (10) not covered for a heat receiving tube (1) of the first surface (101) of the partial central tube and the second surface (102) of the partial central tube; 5 10 11. 12. fifteen 13. twenty 14. 25 30 35 fifteen. 40 b) adhering a first solar ene absorber coating (131) on the first partial central tube surface (11) and adhering a second solar energy absorbent coating (132) on the second partial central tube surface (12); Y c) adhering a coating (14) to inhibit the emission radiation on the second solar absorbent coating (132) so that the second coating (132) for energy Selective solar is disposed between the second surface (102) of partial central tube and the coating (14) of emission radiation inhibition. Method according to claim 10, wherein for the adhesion of at least one of the coatings (13, 131, 132) solar energy absorbers and / or for adhesion of the coating (14) for inhibition of emission radiation a thin film deposition technique is used. Method according to claim 11, wherein the thin film deposition technique is selected from the group consisting of atomic layer deposition, chemical deposition in vapor phase and physical deposition in vapor phase. Method according to one of claims 9 to 12, wherein the adhesion of at least one of the solar energy absorbing coatings (13, 131, 132) and / or the adhesion of the emission radiation inhibition coating (14) They are carried out with the help of a mask method. Sensor (1000) parabolic trough comprising - at least one parabolic mirror (3) having a surface (31) reflecting the sunlight to concentrate the sunlight on the focal line (32) of the parabolic mirror (31); Y - at least one heat receiver tube (1) according to claim 1 to claim 9, which is arranged in the focal line (32) of the parabolic mirror (3); in which - the heat receiving tube (1) is arranged in the focal line (32) so that the first surface (11) of partial heat receiving tube with the first solar absorbent coating (131) is located partially opposite to the surface (31) reflective of sunlight and the second surface (12) of partial heat receiving tube with the emission radiation inhibition coating (14) is at least partially offset with respect to the reflective surface (31) of sunlight. Use of the parabolic trough sensor (1000) according to claim 14 in a plant to convert solar energy into electrical energy.