(19)
(11)EP 2 739 581 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
29.04.2020 Bulletin 2020/18

(21)Application number: 11770395.9

(22)Date of filing:  30.09.2011
(51)International Patent Classification (IPC): 
C03C 17/34(2006.01)
F28F 13/18(2006.01)
F24S 70/20(2018.01)
F28F 21/00(2006.01)
F28B 3/02(2006.01)
F24S 10/40(2018.01)
F22B 1/00(2006.01)
F28F 19/02(2006.01)
F24S 23/70(2018.01)
F28F 21/08(2006.01)
F24S 80/52(2018.01)
(86)International application number:
PCT/EP2011/067120
(87)International publication number:
WO 2013/044975 (04.04.2013 Gazette  2013/14)

(54)

HEAT RECEIVER TUBE WITH A GLASS TUBE WITH INFRARED LIGHT REFLECTIVE COATING, METHOD FOR MANUFACTURING THE GLASS TUBE, PARABOLIC TROUGH COLLECTOR WITH THE HEAT RECEIVER TUBE AND USE OF THE PARABOLIC TROUGH COLLECTOR

WÄRMEEMPFÄNGERRÖHRE MIT EINEM GLASROHR MIT INFRAROTLICHT-REFLEKTIERENDER BESCHICHTUNG, VERFAHREN ZUR HERSTELLUNG DES GLASROHRS, PARABOLRINNENKOLLEKTOR MIT DER WÄRMEEMPFÄNGERRÖHRE UND VERWENDUNG DES PARABOLRINNENKOLLEKTORS

TUBE RECEPTEUR DE CHALEUR AVEC UN TUBE DE VERRE À REVETEMENT REFLECHISSANT LA LUMIERE INFRAROUGE, PROCEDE DE FABRICATION DE CE TUBE DE VERRE, MIROIR CYLINDRO-PARABOLIQUE AVEC TUBE RECEPTEUR DE CHALEUR ET UTILISATION DE CE MIROIR


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(43)Date of publication of application:
11.06.2014 Bulletin 2014/24

(73)Proprietor: Siemens Concentrated Solar Power Ltd.
99107 Beit Shemesh (Industrial Area West) (IL)

(72)Inventor:
  • BARKAI, Menashe
    69440 Tel Aviv (IL)

(74)Representative: Maier, Daniel Oliver 
Siemens AG Postfach 22 16 34
80506 München
80506 München (DE)


(56)References cited: : 
WO-A1-2004/056564
WO-A1-2010/035064
GB-A- 2 031 756
JP-A- 54 056 272
US-A- 4 153 041
US-A1- 2010 205 963
WO-A1-2009/041947
WO-A2-2011/084902
JP-A- 9 035 534
US-A- 3 981 293
US-A- 5 653 222
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND OF THE INVENTION


    1. Field of the invention



    [0001] This invention relates to a heat receiver tube with a glass tube, a method for manufacturing the glass tube and a parabolic trough collector with the heat receiver tube.

    2. Description of the related art



    [0002] A sun energy collecting unit of a sun field power plant based on the concentrated solar power technique is for instance a parabolic trough collector with parabolic mirrors and a heat receiver tube. For instance, such a solar collecting unit is known from WO 2010/035064 A1. The heat receiver tube is arranged in a focal line of the mirrors. By sunlight reflecting surfaces of the mirrors the sunlight is focused to the heat receiver tube, which is filled with a heat transfer fluid, e.g. a thermo-oil or molten salt. With the aid of a solar radiation absorptive coating of a core tube (inner tube) the heat receiver tube absorbs energy from the sun. Energy from the sun is efficiently coupled into the heat transfer fluid. Solar energy is converted to thermal energy.

    [0003] In order to minimize a loss of thermal energy, the heat receiver tube comprises an encapsulation made of glass (glass tube). The glass tube, which is transparent for the sunlight, is arranged coaxially around an inner, central stainless tube of the heat receiver tube. The space between the inner tube and the glass tube is evacuated. Such a heat receiver tube is described in WO 2011/084902 A2.

    [0004] A similar solution is known from US 3 981 293 A. Here, the core tube for absorbing solar absorption radiation of the sunlight is covered by a glass plate or by a glass tube. The glass plate and the glass tube are capable for passing sunlight radiation in a wavelength range of about 0.3 to 2.1 microns. In addition, the glass plate or the glass tube comprises infrared light reflective features.

    [0005] US 5 653 222 A describes a heat receiver tube which is located in an inner space which is formed by a flat plate semicircular housing. The inner space can be evacuated.

    [0006] US 4 153 041 A describes a kind of heat pipe. The envelope is covered by a solar energy absorptive coating for absorbing solar absorption radiation of the sunlight. Absorbed energy is used for evaporation of a heat transfer fluid.

    [0007] From US 2010/205963 A1 a solar power plant with parabolic trough collectors is known. Thereby, in a focal line of a parabolic mirror a heat receiver tube is located. Sunlight radiation is reflected by the parabolic mirror and absorbed by the heat receiver tube. A

    SUMMARY OF THE INVENTION



    [0008] It is an object of the invention to provide an additional reduction of thermal loss of a glass tube which is used as an encapsulation of a heat receiver tube.

    [0009] A further object of the invention is the providing of a parabolic trough collector with the heat receiver tube comprising an encapsulation with such a glass tube.

    [0010] These objects are achieved by the invention specified in the claims.

    [0011] A heat receiver tube for absorbing solar energy and for transferring absorbed solar energy to a heat transfer fluid, which can be located inside a core tube of the heat receiver tube, is provided. The core tube comprises a core tube surface with a solar energy absorptive coating for absorbing solar absorption radiation of the sunlight. The core tube is enveloped by an encapsulation with the glass tube with the infrared light reflective coating. The core tube surface and the encapsulation are arranged in a distance between the core tube surface and the inner surface of the encapsulation wall with the infrared reflective surface such, that the solar absorption radiation can penetrate the encapsulation with the infrared light reflective coating and can impinge the solar energy absorptive coating. The core tube surface and the encapsulation are arranged in a distance between the core tube surface and the inner surface of the glass tube wall with the infrared reflective surface such, that the solar absorption radiation can penetrate the encapsulation with the infrared light reflective coating and can impinge the solar energy absorptive coating. The heat receiver tube is characterized in that the infrared light reflective coating comprises a transparent conducting coating, the transparent conducting coating comprises tin oxide and the tin oxide comprises indium; and an additional layer comprising Al2O3 or SiO2 covers the infrared light reflective coating. The glass tube of the heat receiver tube can be manufactured with following steps: The method comprises following steps: a) providing a glass tube and b) attaching the infrared light reflective coating onto an inner surface of the glass tube. Moreover a parabolic trough collector is provided comprising at least one parabolic mirror having a sunlight reflecting surface for concentrating sunlight in a focal line of the sunlight reflecting surface and at least one heat receiver tube, which is arranged in the focal line of the parabolic mirror. Alternatively, a solar collector with linear Fresnel technology can be realized. So, a linear Fresnel mirror collector with at least one Fresnel mirror having a sunlight reflecting surface for concentrating sunlight in a focal line of the sunlight reflecting surface and at least one heat receiver tube, which is arranged in the focal line of the Fresnel mirror.

    [0012] The glass tube wall is transparent for a wide wavelength range of the rays of the sun. Preferably the glass tube wall of the glass tube comprises glass (SiOx). Other transparent materials are possible, too. The infrared light reflective coating, which is attached to the inner surface of the glass tube, acts as a mirror for infrared light. By this, infrared light, which is radiated by the core tube of a heat receiver tube, is reflected back to the core tube. The overall thermal loss of the heat receiver tube by infrared light radiation of the core tube of the heat receiver tube is reduced.

    [0013] The inner surface can comprise the infrared reflective coating on its complete circumference. But it is also possible, that the inner surface of the glass tube wall comprises the infrared light reflective coating is just on a part the circumference of the inner glass tube surface. For instance the inner surface of the glass tube is half covered by the infrared reflective coating.

    [0014] Using trough technology, the heat receiver tube is arranged in a focal line of parabolic mirrors. Since the sun incident to the trough parabola downwards, rays of the sunlight are collimated onto a lower half of the core tube circumference. An upper half of the core tube circumference is directly hit by rays of the sun (estimated to be about 1.2% from total incident rays) and stray rays, which come from mirror distortion and statistical aberration (estimated to be about 0%-2% (This depends on the two segmental coatings) of the total incident rays). So, it is preferable to divide the inner surface of the glass tube wall into two areas. One area, which is located face to face to the sunlight reflecting surface of the mirror, has got a high transmission for the complete sunlight radiation. In contrast to that, the area, which is face to face to the sun and which is averted to the sunlight reflecting surface of the mirror, has got a high reflectivity for infrared light. There is a minor loss concerning the direct infrared radiation coming from the sun. But the reduction of thermal loss via infrared radiation emission of the core tube multiply compensates the minor loss.
    In an embodiment of the glass tube the infrared light reflective coating comprises a transmission for solar radiation with a wavelength below 1200 nm, which is selected from the range between 0.5 and 0.99 and preferably selected form the range between is 0.8 and 0.95. The infrared light reflective coating is more or less transparent for the sunlight radiation in this wavelength area.
    The infrared light reflective coating comprises a transparent (electrically) conducting coating (transparent conducting coating, TCO). The transparent conducting coating comprises a tin oxide (SnO). The tin oxide comprises indium. The tin oxide is indium tin oxide (InSnO, ITO).

    [0015] An additional layer comprising Al2O3 or SiO2 is attached onto the infrared light reflective coating. The additional layer covers at least partially or completely the infrared light reflective coating. The additional layer is transparent of nearly transparent for the infrared light of the sun. Between the surface of the glass tube wall and the infrared light reflective coating there can be an intermediate layer. This intermediate layer can have different functions. For instance such an intermediate layer strengthens the adhesion of the infrared light reflective coating onto the inner surface of the glass tube.

    [0016] For the attaching the infrared reflective coating there can be applied different technologies. Preferably the attaching of the infrared light reflective coating is carried out with the aid of at least one technology, which is selected form the group consisting of dip coating, spray coating and atomic layer deposition. Whereas dip coating or spray coating fit to a partially attaching the infrared light reflective coating onto the inner surface of the glass tube (the infrared light reflective coating covers partially the inner surface of the glass tube) the atomic layer deposition (ALD) fits to the complete covering of the inner surface of the glass tube. Additional layers beside the TCO (Al2O3 or SiO2) are used in order to optimize anti reflection layers stuck in the solar spectrum while reflectance in IR region is not interrupted (or changed). A final layer with low index material (e.g. SiOx) will be deposited (for instance by dip coating) on both sides of the glass tube

    [0017] Finally a use of the parabolic trough collector in a power plant for converting solar energy into electrical energy is disclosed.

    BIEF DESCRIPTION OF THE DRAWINGS



    [0018] Further features and advantages of the invention are produced from the description of an exemplary embodiment with reference to the drawings. The drawings are schematic.

    Figure 1 shows a cross section of a glass tube from the side.

    Figure 2 shows a cross section of a parabolic trough collector with the heat receiver tube comprising an encapsulation with the glass tube.


    DETAILED DESCRIPTION OF THE INVENTION



    [0019] Given is a glass tube 1 with a glass tube wall 10. The inner surface 11 of the glass tube wall 10 comprises at least partially at least one infrared light reflective coating 12. The glass tube 1 is an encapsulation 20 of a heat receiver tube 2.
    The infrared light reflective coating 12 comprises indium tin oxide. The thickness of the infrared light reflective coating 12 is about 135 nm.
    The infrared light reflective coating 12 is covered by an additional layer 13. This additional layer 13 comprises silicon oxide. In an alternative example the additional layer 13 comprises aluminum oxide. The thickness of this additional layer 13 is about 120 nm.
    An alternatively following sequence is implemented: Inner side of glass tube/Al2O3 (30nm)/TCO (150nm)/Al2O3 (50nm)/SiOx (120nm-Dip coat).

    [0020] Between the infrared light reflective coating 12 and the inner surface 11 of the glass tube wall 10 there is an intermediate layer 14. This intermediate layer comprises aluminum oxide. The thickness of this intermediate layer is about 85 nm.

    [0021] The core tube 21 of the heat receiver tube 2, which is enveloped by the glass tube 1, is made of steel. Additionally the core tube surface of the core tube comprises an absorptive coating for absorbing sunlight (not shown).

    Example 1:



    [0022] By using half coating of the inner surface of the glass tube (dip and spray coating), α (absorptivity for the sunlight) will be reduced only by small fraction (0.2%) due to reduction of glass transmissivity on the upper segment of the glass tube. Heat losses due to radiation will be reduced by 20% -10% (from 1000Watt/tube to 800-900Watt/tube)

    Example 2:



    [0023] The complete inner surface 11 of the glass tube wall 10 is covered by the infrared light reflective coating 12. For the manufacturing an ALD process is carried out. By this α will be reduced by 1%-1.5% due to decrease in solar transmissivity thorough the glass tube. But on the other hand, heat losses due to radiation will be reduced by 40% -60% (from 1000Watt/tube to 600-400Watt/tube. The heat receiver tube 2 is part of a parabolic trough collector 1000. The parabolic trough collector 1000 comprises at least one parabolic mirror 3 with a sunlight reflective surface 31. By the reflective surface 31 sunlight is concentrated in the focal line 32 of the parabolic mirror 3. The concentrated sunlight is absorbed by the heat receiver tube 2.

    [0024] The parabolic trough collector (and the Fresnel mirror collector, respectively) is used in a solar power plant for converting solar energy into electrical energy. The heated heat transfer fluid is used to produce steam via a heat exchanger. The steam is driving a turbine, which is connected to a generator. The generator produces current.


    Claims

    1. Heat receiver tube (2) for absorbing solar energy and for transferring absorbed solar energy to a heat transfer fluid, which can be located inside a core tube (21) of the heat receiver tube (2), wherein

    - the core tube comprises a core tube surface with a solar energy absorptive coating for absorbing solar absorption radiation of the sunlight;

    - the core tube is enveloped by an encapsulation with a glass tube with a glass tube wall;

    - an inner surface of the glass tube wall comprises at least partially at least one infrared light reflective coating;

    - the infrared light reflective coating comprises a transparent conducting coating;

    - the core tube surface and the encapsulation are arranged in a distance between the core tube surface and the inner surface of the glass tube wall with the infrared reflective surface such, that the solar absorption radiation can penetrate the encapsulation with the infrared light reflective coating and can impinge the solar energy absorptive coating;
    characterized in that

    - the infrared light reflective coating comprises a transparent conducting coating;

    - the transparent conducting coating comprises tin oxide;

    - the tin oxide comprises indium; and

    - an additional layer comprising Al2O3 or SiO2 covers the infrared light reflective coating.


     
    2. Heat receiver tube according to claim 1, wherein the infrared light reflective coating comprises a transmission for solar radiation with a wavelength below 1200 nm, which is selected from the range between 0.5 and 0.99 and preferably selected form the range between is 0.8 and 0.95.
     
    3. Heat receiver tube according to claim 1 or claim 2, wherein the inner surface of the glass tube wall comprises the infrared light reflective coating on a part of its circumference.
     
    4. Heat receiver tube according to one of the claims 1 to 3, wherein an intermediate layer is arranged between the inner surface of the glass tube wall and the infrared light reflective coating.
     
    5. Parabolic trough collector (1000) comprising

    - at least one parabolic mirror (3) having a sunlight reflecting surface (31) for concentrating sunlight in a focal line (32) of the sunlight reflecting surface (31); and

    - at least one heat receiver tube (2) according to one of the claims 1 to 4, which is arranged in the focal line (32) of the parabolic mirror (3).


     
    6. Method for manufacturing a glass tube of a heat receiver tube according to one of the claims 1 to 4, the method comprising following steps:

    a) providing a glass tube; and

    b) attaching the infrared light reflective coating onto an inner surface of the glass tube.


     
    7. Method according to claim 6, wherein the attaching the infrared light reflective coating is carried out with the aid of at least one technology, which is selected form the group consisting of dip coating, spray coating and atomic layer deposition.
     
    8. Use of the parabolic trough collector (1000) according to claim 5 in a power plant for converting solar energy into electrical energy.
     


    Ansprüche

    1. Wärmeempfängerröhre (2) zum Absorbieren von Sonnenenergie und zum Übertragen absorbierter Sonnenenergie an ein Wärmeübertragungsfluid, das sich innerhalb eines Kernrohrs (21) der Empfängerröhre (2) befinden kann, wobei

    - das Kernrohr eine Kernrohroberfläche mit einer Sonnenenergie absorbierenden Beschichtung zum Absorbieren der solaren Absorptionsstrahlung des Sonnenlichts umfasst,

    - das Kernrohr von einer Kapselung mit einem Glasrohr mit einer Glasrohrwand umgeben ist,

    - eine innere Oberfläche der Glasrohrwand wenigstens teilweise wenigstens eine Infrarotlicht-reflektierende Beschichtung umfasst,

    - die Infrarotlicht-reflektierende Beschichtung eine transparente, leitfähige Beschichtung umfasst,

    - die Kernrohroberfläche und die Kapselung in einem Abstand zwischen der Kernrohroberfläche und der inneren Oberfläche der Glasrohrwand mit der Infrarotlicht-reflektierenden Oberfläche derart angeordnet sind, dass die solare Absorptionsstrahlung die Kapselung mit der Infrarotlicht-reflektierenden Beschichtung durchdringen kann und auf die Sonnenenergie absorbierende Beschichtung auftreffen kann,
    dadurch gekennzeichnet, dass

    - die Infrarotlicht-reflektierende Beschichtung eine transparente, leitfähige Beschichtung umfasst,

    - die transparente, leitfähige Beschichtung Zinnoxid umfasst,

    - das Zinnoxid Indium umfasst und

    - die zusätzliche Schicht, die Al2O3 oder SiO2 umfasst, die Infrarotlicht-reflektierende Beschichtung überdeckt.


     
    2. Wärmeempfängerröhre nach Anspruch 1, wobei die Infrarotlicht-reflektierende Beschichtung eine Durchlässigkeit für Sonnenstrahlung mit einer Wellenlänge unter 1200 nm aufweist, die aus dem Bereich zwischen 0,5 und 0,99 ausgewählt ist und vorzugsweise aus dem Bereich zwischen 0,8 und 0,95 ausgewählt ist.
     
    3. Wärmeempfängerröhre nach Anspruch 1 oder Anspruch 2, wobei die innere Oberfläche der Glasrohrwand die Infrarotlicht-reflektierende Beschichtung auf einem Teil ihres Umfangs umfasst.
     
    4. Wärmeempfängerröhre nach einem der Ansprüche 1 bis 3, wobei eine Zwischenschicht zwischen der inneren Oberfläche der Glasrohrwand und der Infrarotlicht-reflektierenden Beschichtung angeordnet ist.
     
    5. Parabolinnenkollektor (1000), umfassend

    - wenigstens einen Parabolspiegel (3) mit einer Sonnenlichtreflektierenden Oberfläche (31) zur Konzentrierung von Sonnenlicht in einer Brennlinie (32) der Sonnenlichtreflektierenden Oberfläche (31) und

    - wenigstens eine Wärmeempfängerröhre (2) nach einem der Ansprüche 1 bis 4, die in der Brennlinie (32) des Parabolspiegels (3) angeordnet ist.


     
    6. Verfahren zur Herstellung eines Glasrohrs einer Wärmeempfängerröhre nach einem der Ansprüche 1 bis 4, wobei das Verfahren die folgenden Schritte umfasst:

    a) Bereitstellen eines Glasrohrs und

    b) Aufbringen einer Infrarotlicht-reflektierenden Beschichtung auf eine innere Oberfläche des Glasrohrs.


     
    7. Verfahren nach Anspruch 6, wobei das Aufbringen der Infrarotlicht-reflektierenden Beschichtung mithilfe von wenigstens einer Technologie ausgeführt wird, die aus der Gruppe bestehend aus Tauchbeschichten, Sprühbeschichten und Atomlagenabscheiden ausgewählt ist.
     
    8. Verwendung des Parabolinnenkollektors (1000) nach Anspruch 5 in einem Kraftwerk zur Umwandlung von Sonnenenergie in elektrische Energie.
     


    Revendications

    1. Tube récepteur de chaleur (2) pour absorber de l'énergie solaire et pour transférer l'énergie solaire absorbée vers un fluide de transfert de chaleur, lequel peut être situé à l'intérieur d'un tube central (21) du tube récepteur de chaleur (2), dans lequel

    - le tube central comprend une surface de tube central avec un revêtement absorbant l'énergie solaire pour absorber des rayonnements d'absorption solaire de la lumière du soleil ;

    - le tube central est enveloppé par une encapsulation avec un tube de verre avec une paroi de tube de verre ;

    - une surface interne de la paroi de tube de verre comprend au moins en partie au moins un revêtement réfléchissant la lumière infrarouge ;

    - le revêtement réfléchissant la lumière infrarouge comprend un revêtement conducteur transparent ;

    - la surface de tube central et l'encapsulation sont agencées à une distance entre la surface de tube central et la surface interne de la paroi de tube de verre avec la surface réfléchissant les infrarouges telle que les rayonnements d'absorption solaire puissent pénétrer dans l'encapsulation avec le revêtement réfléchissant la lumière infrarouge et puissent être incidents sur le revêtement absorbant l'énergie solaire ;
    caractérisé en ce que

    - le revêtement réfléchissant la lumière infrarouge comprend un revêtement conducteur transparent ;

    - le revêtement conducteur transparent comprend de l'oxyde d'étain ;

    - l'oxyde d'étain comprend de l'indium ; et

    - une couche supplémentaire comprenant Al2O3 ou SiO2 recouvre le revêtement réfléchissant la lumière infrarouge.


     
    2. Tube récepteur de chaleur selon la revendication 1, dans lequel le revêtement réfléchissant la lumière infrarouge comprend une transmission pour des rayonnements solaires avec une longueur d'onde au-dessous de 1 200 nm, laquelle est sélectionnée dans la gamme comprise entre 0,5 et 0,99 et de préférence sélectionnée dans la gamme comprise entre 0,8 et 0,95.
     
    3. Tube récepteur de chaleur selon la revendication 1 ou la revendication 2, dans lequel la surface interne de la paroi de tube de verre comprend le revêtement réfléchissant la lumière infrarouge sur une partie de sa circonférence.
     
    4. Tube récepteur de chaleur selon l'une des revendications 1 à 3, dans lequel une couche intermédiaire est agencée entre la surface interne de la paroi de tube de verre et le revêtement réfléchissant la lumière infrarouge.
     
    5. Collecteur cylindro-parabolique (1000) comprenant

    - au moins un miroir parabolique (3) ayant une surface réfléchissant la lumière du soleil (31) pour concentrer la lumière du soleil dans une ligne focale (32) de la surface réfléchissant la lumière du soleil (31) ; et

    - au moins un tube récepteur de chaleur (2) selon l'une des revendications 1 à 4, lequel est agencé dans la ligne focale (32) du miroir parabolique (3).


     
    6. Procédé pour fabriquer un tube de verre d'un tube récepteur de chaleur selon l'une des revendications 1 à 4, le procédé comprenant les étapes suivantes :

    a) la fourniture d'un tube de verre ; et

    b) la fixation du revêtement réfléchissant la lumière infrarouge sur une surface interne du tube de verre.


     
    7. Procédé selon la revendication 6, dans lequel la fixation du revêtement réfléchissant la lumière infrarouge est mise en œuvre à l'aide d'au moins une technologie, laquelle est sélectionnée dans le groupe constitué du revêtement par immersion, du revêtement par pulvérisation et du dépôt de couche atomique.
     
    8. Utilisation du collecteur cylindro-parabolique (1000) selon la revendication 5 dans une centrale électrique pour convertir l'énergie solaire en énergie électrique.
     




    Drawing








    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description