DE102013015017B4 - receiver tube - Google Patents

Abstract

Receiver tube (1) for solar thermal applications, in particular for parabolic trough collectors in solar thermal power plants, with an absorber tube (2) and a the absorber tube (2) coaxially to a longitudinal axis (3) surrounding glass tube (4), wherein two ends of the glass tube (4) two, in each case an axially expandable and to the longitudinal axis (3) concentric bellows (6) having expansion compensating heads (7) are gas-tightly connected to the absorber tube (2), so that between the absorber tube (2), the expansion compensating heads (7) and the glass tube (4) an evacuable annular space (8) is formed, characterized in that in the expansion compensating head (7) of the bellows (6) is arranged radially outside of the glass tube (4), wherein the expansion compensating head (7) with the absorber tube (2) gas-tightly connected end plate (12) and with the end (5) of the glass tube gas-tight connected and to the longitudinal axis (3) coaxial front profile (13), wherein the front profile (1 3) is composed of a cylinder jacket-shaped ring and a front disc (14) aligned perpendicular to the longitudinal axis (3) and centered with the ring, and wherein the bellows (6) are axially coaxial with the longitudinal axis (3) axially between the end disc (3). 12) and the front disc (14) and with the front disc (14) and with the end plate (15) is connected in a gastight manner.

Description

The present invention relates to a receiver tube for solar thermal applications, in particular for parabolic trough collectors in solar thermal power plants, with an absorber tube and the absorber tube coaxially surrounding a longitudinal axis glass tube, two ends of the glass tube by two, each having an axially expandable and concentric with the longitudinal axis bellows having Expansion compensation heads are gas-tight connected to the absorber tube, so that between the absorber tube, the expansion compensating heads and the glass tube evacuated annular space is formed.

Receiver tubes of this type mentioned are known from the prior art. The receiver tubes are used, for example, in a parabolic trough power plant in which a trough-shaped mirror with a parabolic cross section concentrates solar radiation in the direction of a line. Along this line, the receiver tubes are arranged. Such receiver tubes are intended to receive the energy contained in solar radiation and to transfer as lossless as possible in a heat transport medium. As a heat transport medium, for example, a heatable at 400 ° C oil is provided, which flows through the absorber tube. The absorber tube absorbs solar radiation with a high efficiency and transmits the absorbed energy mainly by heat conduction to the heat transport medium. In the receiver tube, the absorber tube is surrounded by a glass tube. Two ends of the glass tube are gas-tight connected to the absorber tube. In the annular space between the absorber tube and the glass tube, a vacuum is provided to form a thermal insulation. The thermal insulation largely prevents heat losses from the absorber tube into the atmosphere.

WO 2012/095 886 A2 describes a technical solution for connecting two adjacent with their front sides pipes for solar thermal power plants. The internal metal pipes are equipped with a rigid, but mechanically movable connection, which is preferably designed as a threaded ring. A mutually radially fixed position arrangement of the tubes is achieved by a plurality of pins engages in congruent shaped recesses on the threaded ring.

On off DE 10 2009 045 100 A1 known absorber tube for collectors in solar thermal power plants has a metal tube for passing and heating a heat transfer medium, which is surrounded by a cladding tube to form an evacuable annular space. Between the cladding tube and metal pipe runs a wall for sealing the annular space. On this wall, a holding device for a getter material is arranged.

The usually made of metal absorber tube and the glass tube have different thermal expansion coefficients, which lead to different length expansions with temperature changes. For a receiver tube with a typical length of 4 m, the change in length between 0 ° C and 400 ° C operating temperature is about 1 cm to 4 cm, depending on the metal used. The glass tube has a much smaller coefficient of thermal expansion and heats up only slightly, for example to 100 ° C. Consequently, the glass tube has only a marginal elongation and a nearly constant length. The mechanical connection between the absorber tube and the glass tube is produced by two compensating heads located at each end of the glass tube, in which, for example, deformable vacuum-tight bellows compensate for the temperature-dependent differences in length between the absorber tube and the glass tube.

The expansion compensation heads should remain functional for a minimum of 20 years. Furthermore, these compensating heads should have only small mechanical dimensions in order to use the largest possible part of the length of the receiver tube for the harvest of solar radiation can. In the DE 102 031 467 B4 compact balance heads are described in which the bellows are at least partially disposed in the annular space between the absorber tube and the glass tube.

In DE 10 2012 214 412 B3 Also described is an absorber tube with a central metal tube and glass tube. These components are displaceable relative to each other with a stretch compensation device in the longitudinal direction and connected to each other. In this case, the expansion compensation device is at least partially disposed in the annular space between the metal tube and a glass metal transition element.

Potentials for improvement in the known receiver tubes exist in the further increase of the service life and the further improvement of the thermal insulation in the compensation heads.

It is the object of the present invention to provide an alternative to the known from the prior art receiver tubes, the long life and the good insulating properties should preferably be further increased.

The object is achieved by a receiver tube of the type defined above, in which in the Expansion compensating head of the bellows is arranged radially outside the glass tube.

In the receiver tube according to the invention, the bellows is arranged outside the glass tube. The thermal insulation capacity determining radial width of the formed between the absorber tube and the glass tube annulus is not reduced in this arrangement by the bellows. The receiver tube according to the invention therefore has wider evacuable annular spaces within the expansion compensating heads. This results in a comparison with the prior art improved thermal insulation. The better thermal insulation leads to lower temperatures and lower thermal loads on the components of the expansion compensation heads and thereby to increased reliability of the expansion compensation heads and ultimately to increased reliability of the receiver tubes according to the invention.

An advantage resulting from the outer arrangement is the greater freedom of design in the construction of the bellows, since these are not subject to the restriction of having to have smaller diameter than the glass tube. In typical embodiments of the receiver tube according to the invention, the bellows has an inner diameter between 76 mm and 85 mm, a radial extent between 15 mm and 30 mm and an axial extent between 15 and 50 mm. The exact dimensions are designed taking into account the materials used and their elastic properties.

The larger compared to the prior art radial distances between the coaxially arranged to the absorber tube bellows and the hot absorber tube lead to lower temperatures of the bellows, so that for the production of the bellows materials with lower temperature resistance than in the prior art can be used. In various embodiments of the receiver tube according to the invention, the bellows is formed of a metal or a coated plastic. For plastics, sufficient gas impermeability is achieved, for example, by coatings. Also metallic bellows can be further improved by appropriate coatings. Likewise, it is alternatively possible to use other functionally equivalent expansion compensation elements instead of a bellows.

In a preferred embodiment of the receiver tube according to the invention, the expansion compensating head has a gas-tight connected to the absorber tube end plate and a gas-tight connected to the end of the glass tube and to the longitudinal axis coaxial front profile, wherein the front profile of a cylinder jacket-shaped ring and connected to the ring at an angle is arranged vertically and centered to the longitudinal axis aligned front disc and wherein the bellows is arranged coaxially to the longitudinal axis axially between the end plate and the front plate and connected to the front plate and the end plate each gas-tight.

In this embodiment, the thermal expansion of the absorber tube leads to an expansion of the bellows. The constructed for the extension bellows is characterized by a particularly small minimum length, which also leads to a particularly small length of the expansion compensating head and a correspondingly large usable for the energy recovery length of the receiver tube.

The expansion compensating head is limited to the end of the receiver tube through an end plate. The end plate is in the preferred embodiment, a planar circular disc whose surface normal is aligned in the direction of the longitudinal axis. The end plate has a concentric circular recess, in which the gas-tight connected to the end plate absorber tube is located. The absorber tube and the end plate are preferably welded together and may consist of both different and of the same material, for example of a stainless steel. But there are also other materials, such as other metals or metal-coated ceramics and other types of attachment, such as soldering or bonding, possible.

An end face of the pleat pad is secured in an outer region of the end plate, the bellows being concentric with the longitudinal axis. A bilge-mounted bellows can thus be stretched and compressed by axial movements of the end plate along the longitudinal axis.

The connection between one of the end side opposite the front side of the bellows with the end of the glass tube is in the preferred embodiment of an annular front profile, which in turn is directly or indirectly connected gas-tightly connected to the end of the glass tube. The front profile has sufficient mechanical strength to evenly transmit the mechanical forces occurring as substantially axial forces to the glass tube. In a planar cross section along the longitudinal axis, the front profile has an angular cross section, the angle being about 90 ° and being enclosed by an axial leg and a radial leg. The axial leg is the cross section of a cylinder jacket to the Longitudinal axis coaxial ring, and the radial leg is the cross section of a planar designated as the front disc with a hollow cylindrical central recess. The coaxial ring and the front disk are parts of the one-piece physical front profile, wherein a front end of the coaxial ring and an inner end of the front disk are connected together to form an angle.

In one embodiment, the coaxial ring of the front profile with a Anglasring, which is embedded in the end face of the glass tube, gas-tight welded. In other embodiments, the front profile is otherwise connected to the glass tube, for example cast or glued. By the gas-tight connections, the space between the end plate, the bellows and the front profile, which is spatially connected to the annulus between the absorber tube and the glass tube, evacuated. The bellows forms in a designated evacuated state, a radially outer wall for the vacuum.

As a further wall, the expansion compensating head in the preferred embodiment, an annular outer bellows covering the bellows on. The outer shield causes on the one hand a mechanical protection for the bellows, on the other hand, the outer shield serves as a reflector for solar radiation which prevents an asymmetrical leading to unreasonable tension heating of the bellows. Visually, the expansion compensating head receives the appearance of a flange through the outer shield.

According to an alternative advantageous embodiment of the receiver tube according to the invention, the expansion compensating head has a gas-tightly connected to the absorber tube end plate, which is connected via an external shield with a glass tube axially displaceable front disc gas-tight, and a gas-tight connected to the end of the glass tube rear disc, and the bellows is arranged coaxially to the longitudinal axis axially between the front disk and the rear disk and connected to the front disk and with the rear disk in each case gastight. In this variant, the thermal expansion of the absorber tube leads to a compression of the bellows.

In this embodiment, the end plate, a bellows outer protective shield and a front plate are connected to a mechanically stable and gas-tight ring profile, which gives the expansion compensating head similarity to a flange. The gas-tight connection of the bellows with the absorber tube is realized in this embodiment not only on the end plate but instead in addition to the outer shield and the front panel. The gas-tightly connected to a front side of the bellows front disc is firmly connected to the rear disc and the absorber tube and slidable relative to the glass tube.

The gas-tight connection between the end of the glass tube and one end side of the bellows is implemented via a rear disc. The rear disk is a hollow cylinder which projects radially outwards from the end of the glass tube and whose diameter is much larger than its cylinder length. In one embodiment, the rear pane is gas-tightly connected to the glass tube via a glass-on ring. The rear disk is located in the axial direction between the end disk and the front disk, wherein all the disks are arranged parallel to each other and centered to the longitudinal axis. With a thermal expansion of the absorber tube, the distance between the end plate and the rear plate increases. At the same time the distance between the rear disc and the front disc is reduced and the bellows located between these two discs is compressed. The designed for compression bellows has a sufficiently large axial length to allow even at the highest practical temperatures still a strain compensation. An evacuable space is in this embodiment between the bellows and the outer shield. Between the glass tube and the bellows there is accordingly a room under atmospheric pressure.

In an advantageous development of this receiver tube according to the invention, the expansion compensating head has a vacuum fitting attached to the outer protective shield with a vacuum valve.

The insulating power of a vacuum layer improves with decreasing pressure. In the receiver tubes according to the invention, for example, a pressure below 0.01 Pa is desired. An evacuated space is never absolutely tight, but gases with gas-specific leak rates always occur. Especially problematic is the entry of hydrogen, which is produced for example in the absorber tube by decomposition of the oil used as a heat carrier. One way to remove gases that have diffused into the vacuum is to refill the vacuum during regular maintenance work by means of a vacuum pump. Between maintenance work, hydrogen can be bound by getter materials and then released during maintenance by heating the getter for pumping off. Such work is made possible by a vacuum pipe connected to the annulus with a vacuum valve. Due to the arrangement of the vacuum nozzle on the Exterior protection shield, it is particularly easy to access. The vacuum valve is in various embodiments of the invention, a manually, electrically or pneumatically actuated valve.

The vacuum pipe can be mounted in a different position, for example, on the glass tube in the receiver tubes according to the invention, for example, if the space lying radially inside the bellows is evacuated. In a variant of the receiver tube according to the invention, the expansion compensating head has a vacuum socket fastened to the end plate with a vacuum valve.

In an advantageous embodiment of the receiver tube according to the invention, the expansion compensating head has a cylinder jacket-shaped Anglasring tip on an end face whose diameter at the top is equal to the average diameter of the glass tube, and which is embedded at the end of the glass tube in the glass tube. About the Anglasring be transferred during the manufacture and operation of the receiver tube according to the invention substantially only rotationally symmetric axial forces on the glass tube, so that no local overloads of the glass tube occur. With a non-glazed part of the Anglasringes other components of the expansion compensating head, such as a front rail or a rear window, connected.

The expansion compensating head of the receiver tube according to the invention preferably has a cylindrical shell-shaped inner heat shield located within the glass tube near an inner surface of the glass tube, whose length extending in the direction of the longitudinal axis is approximately equal to the length of the expansion compensating head extending in the direction of the longitudinal axis. The inner heat shield reflects obliquely into the expansion compensating head incident radiation to the absorber tube, so that this radiation does not contribute to the heating of the expansion compensating head. Benefit of the low heating heat-sensitive components, such as a glass-metal transition region in which materials with different thermal expansion coefficients border each other.

For attachment, the inner heat shield is welded to the Anglasring in one embodiment. However, the inner heat shield can also be mounted differently, for example by clamping or gluing. The type of attachment also depends on the material used to form the inner shield. In various embodiments of the receiver tube according to the invention, the inner heat shield is formed of a metal, a ceramic, a plastic or a metal-coated ceramic. According to an advantageous development, the inner heat shield has a reflection coating on its side facing the absorber tube. The reflective coating may be a metallic and / or a dielectric coating.

The length of the inner heat shield in the direction of the longitudinal axis is preferably dimensioned so long that the heat-sensitive components are shielded from the inner heat shield. Regularly, the entire bellows is shielded by the inner heat shield, for example, in order to avoid Rotationsunsymmetrische warming and resulting thermal stresses.

In preferred embodiments of the receiver tube according to the invention, the end plate is formed of a metal or a metal-coated ceramic and welded or soldered to the absorber tube. Metals, such as stainless steels, are characterized by high mechanical strength, high reliability and good processability. For metals, the joining techniques of welding and soldering can be used, which are inexpensive and result in dense and reliable connections. But it can also be used other materials, such as ceramic. Among other things, ceramic materials are characterized by high temperature resistance and low thermal conductivity. The assembly of a ceramic component is realized in one embodiment by soldering a metal coating of the ceramic component.

The expansion compensating head of the receiver tube according to the invention has in an advantageous development of a projection, which is spatially connected to the evacuable annular space and in which a getter material is attached. In the prior art getters are regularly installed in the annulus. This has the disadvantages that the thermal insulation is deteriorated in the getter and that when the getter disintegrates, particles can be introduced into the annulus which permanently reduce the efficiency of the receiver tube. By shifting the getter in the outer projection of the problems mentioned are eliminated or at least reduced.

The present invention will be explained in more detail below with reference to exemplary embodiments, wherein

1 an end portion of an embodiment of a receiver tube according to the invention with a strain compensation head in a cross section along the longitudinal axis, and

2 shows another embodiment of a receiver tube according to the invention with another expansion compensating head in a cross section along the longitudinal axis.

1 schematically shows an end portion of an embodiment of a receiver tube according to the invention 1 in a cross section along the longitudinal axis 3 , The illustrated end region comprises a strain compensation head 7 that provides an elastically deformable connection between an absorber tube 2 and a glass tube 4 produces, with different thermal expansions of the absorber tube 2 and the glass tube 4 to axial stretching or compression of an elastic bellows 6 to lead. An unillustrated second end portion of the receiver tube 1 is identical as the illustrated end area constructed.

The example 4 m long receiver tube 1 is substantially rotationally symmetrical to the longitudinal axis 3 educated. In a solar thermal power plant becomes the receiver tube 1 with other receiver tubes 1 welded to a, for example, 200 m long strand. At the connection points of the receiver tubes, the strand is secured in pivotable tube receptacles to prevent sagging of the strand. The pipe receptacles, not shown, have insulations and veneers.

An absorber tube 2 is formed by an absorber layer for absorbing solar radiation, wherein the absorber tube 2 heated. During normal operation of the receiver tube 1 becomes the of the absorber tube 2 absorbed energy as heat to one in the absorber tube 2 forwarded flowing heat transfer fluid. The absorber tube 2 consists in the illustrated embodiment of a stainless steel and has an outer diameter of, for example, 38 mm.

Coaxial to the longitudinal axis 3 and the absorber tube 2 is the glass tube 4 , which serves as an outer wall of an evacuable annulus 8th serves. An evacuated in an operating condition annulus 8th Insulates the absorber tube 2 thermally from the atmosphere, which is outside the receiver tube 1 located.

The expansion compensating head 7 provides a gas-tight deformable connection between the absorber tube 2 and the glass tube 4 her and thus also provides an outer wall of the evacuated annulus 8th dar. A bellows 6 serves as an elastic evacuated annulus 8th enclosing wall. In the illustrated embodiment, the bellows made of a stainless steel 6 between an end plate 12 and a front disk 14 arranged and welded with them.

The end disc 12 has a central recess in which the with the end plate 12 welded absorber tube 2 located. The front disc 14 turns in the illustrated cross-section as a radial leg of a front profile 13 dar. The front profile 13 Furthermore, in the illustrated cross-section on both sides of the absorber tube 2 each having an axially aligned leg, in a curvature of the front profile 13 is respectively connected to the radial leg. The axial leg of the front profile 13 is the cross section of a cylinder jacket-shaped ring at one end 5 of the glass tube 4 radially outside the glass tube 4 is arranged.

An axial end of the front profile 13 is in the illustrated embodiment with a Anglasring 9 connected by welding. The Anglasring 9 indicates at its one axial center of the glass tube 4 facing a sharp edge, wherein the diameter of the Anglasringes 9 at the sharp edge equal to the mean diameter of the glass tube 4 is. The Anglasring 9 is at the end 5 of the glass tube 4 in the glass tube 4 embedded to form a gas-tight glass-metal compound.

Glass-to-metal joints can fail and become permeable to gas when exposed to frequent high temperature loads. Such damage can be largely avoided if the receiver tube 1 with an inner heat shield 10 equipped, which has a length range at the end 5 of the pipe 4 protects against solar radiation. In the protected length range is the Anglasring 9 embedded in the glass tube. Outwardly, the bellows 6 mechanically and thermally by an external protective shield 11 protected.

The illustrated expansion compensation head 7 of the receiver tube 1 is designed to allow heating of the absorber tube 2 to a stretch of the bellows 6 leads. In this embodiment, the bellows 6 For example, only the three outer folds shown here. The entire expansion compensating head 7 at room temperature has a particularly short length of, for example, only 25 mm.

2 schematically shows an end portion of another receiver tube according to the invention 1' That is due to a slightly different expansion compensating head 7 ' from the on hand of 1 illustrated receiver tube 1 different. The receiver tubes 1 and 1' have many similarities, which are also reflected in common reference numerals, so that in terms of 2 not described components to the description at 1 is referenced.

In the expansion compensating head 7 ' is at an end disk 12 an outer protective shield 11 and on the outside shield 11 one on the glass tube 4 axially displaceable front screen 14 attached. The end disc 12 , the outer shield 11 and the front disk 14 give the strain compensation head 7 ' a flange-like shape.

At the Anglasring 9 is in the expansion compensating head 7 ' a rear window 15 welded. A coaxial bellows 6 ' with example, five outer folds shown here is axially between the rear pane 15 and the front disc 14 arranged. A heating of the absorber tube 2 leads to an axial displacement of the front disk 14 in the direction of the rear window 15 , This will cause the bellows 6 ' compressed. At the compression form the front disk 14 and the rear disc 15 Stops for the bellows 6 ' so that the welds with which the bellows 6 ' on the front screen 14 and on the rear window 15 is fastened, only exposed to low loads. The length of the in 2 shown expansion compensation head 7 ' is at room temperature, for example, 40 mm.

LIST OF REFERENCE NUMBERS

1, 1 '

receiver tube

2

absorber tube

3

longitudinal axis

4

glass tube

5

End of the glass tube

6, 6 '

bellow

7, 7 '

Expansion unit head

8th

evacuable annulus

9

Anglasring

10

Internal heat shield

11

Outer shield

12

end disk

13

front profile

14

front window

15

backplate

Claims (9)

Receiver tube ( 1 ) for solar thermal applications, in particular for parabolic trough collectors in solar thermal power plants, with an absorber tube ( 2 ) and one the absorber tube ( 2 ) coaxial with a longitudinal axis ( 3 ) surrounding glass tube ( 4 ), wherein two ends of the glass tube ( 4 ) by two, in each case an axially extensible and to the longitudinal axis ( 3 ) concentric bellows ( 6 ) having expansion compensation heads ( 7 ) gas-tight with the absorber tube ( 2 ) are connected so that between the absorber tube ( 2 ), the expansion compensation heads ( 7 ) and the glass tube ( 4 ) an evacuable annulus ( 8th ), characterized in that in the expansion compensating head ( 7 ) the bellows ( 6 ) radially outside the glass tube ( 4 ), wherein the expansion compensating head ( 7 ) one with the absorber tube ( 2 ) gastight end plate ( 12 ) and one with the end ( 5 ) of the glass tube gas-tight connected and to the longitudinal axis ( 3 ) coaxial front profile ( 13 ), wherein the front profile ( 13 ) of a cylinder jacket-shaped ring and one connected to the ring at an angle perpendicular and centered to the longitudinal axis ( 3 ) aligned front disc ( 14 ) and wherein the bellows ( 6 ) coaxial with the longitudinal axis ( 3 ) axially between the end plate ( 12 ) and the front disc ( 14 ) and with the front disk ( 14 ) and with the end plate ( 15 ) is connected in a gastight manner. Receiver tube ( 1 ) according to claim 1, characterized in that the expansion compensating head ( 7 ) an annular, the bellows ( 6 ) outer protective shield ( 11 ) having. Receiver tube ( 1' ) for solar thermal applications, in particular for parabolic trough collectors in solar thermal power plants, with an absorber tube ( 2 ) and one the absorber tube ( 2 ) coaxial with a longitudinal axis ( 3 ) surrounding glass tube ( 4 ), wherein two ends of the glass tube ( 4 ) by two, in each case an axially extensible and to the longitudinal axis ( 3 ) concentric bellows ( 6 ' ) having expansion compensation heads ( 7 ' ) gas-tight with the absorber tube ( 2 ) are connected so that between the absorber tube ( 2 ), the expansion compensation heads ( 7 ' ) and the glass tube ( 4 ) an evacuable annulus ( 8th ), characterized in that in the expansion compensating head ( 7 ' ) the bellows ( 6 ' ) radially outside the glass tube ( 4 ), wherein the expansion compensating head ( 7 ' ) one with the absorber tube ( 2 ) gastight end plate ( 12 ), which have an external protective shield ( 11 ) with one on the glass tube ( 4 ) axially displaceable front disk ( 14 ) is connected gas-tight, and one with the end of the glass tube ( 4 ) gas-tightly connected rear pane ( 15 ) and the bellows ( 6 ' ) coaxial with the longitudinal axis ( 3 ) axially between the front disc ( 14 ) and the rear disc ( 15 ) and with the front disk ( 14 ) and with the rear window ( 15 ) is connected in a gastight manner. Receiver tube ( 1 ) according to claim 3, characterized in that the expansion compensating head ( 7 ' ) one on the outer protective shield ( 11 ) fasten has vacuum fitting with a vacuum valve. Receiver tube ( 1 . 1' ) according to claim 1 or 3, characterized in that the expansion compensating head ( 7 . 7 ' ) one at the end plate ( 12 ) has a vacuum fitting with a vacuum valve. Receiver tube ( 1 . 1' ) according to claim 1 or 3, characterized in that the expansion compensating head ( 7 . 7 ' ) a cylinder jacket-shaped Anglasring on a front side ( 9 ) whose diameter at the top is equal to the mean diameter of the glass tube, and which at the end ( 5 ) of the glass tube ( 4 ) in the glass tube ( 4 ) is embedded. Receiver tube ( 1 . 1' ) according to claim 1 or 3, characterized in that the expansion compensating head ( 7 . 7 ' ) a cylinder jacket inside the glass tube ( 4 ) on the inner surface of the glass tube ( 4 ) inner heat shield ( 10 ), which in the direction of the longitudinal axis ( 3 ) extending length approximately equal to in the direction of the longitudinal axis ( 3 ) extending length of the expansion compensating head ( 7 . 7 ' ). Receiver tube ( 1 . 1' ) according to claim 1 or 3, characterized in that the end plate ( 12 ) formed of a metal or a metal-coated ceramic and with the absorber tube ( 2 ) is welded or soldered. Receiver tube ( 1 . 1' ) According to claim 1 or 3, characterized in characterized in that the expansion compensation head ( 7 . 7 ' ) has a projection, which spatially with the evacuable annulus ( 8th ) and in which a getter material is attached.

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