U.S. patent application number 14/344954 was filed with the patent office on 2014-11-27 for absorber tube.
The applicant listed for this patent is Thomas Kuckelkorn, Marc Mollenhoff, Oliver Sohr. Invention is credited to Thomas Kuckelkorn, Marc Mollenhoff, Oliver Sohr.
Application Number | 20140345600 14/344954 |
Document ID | / |
Family ID | 46845774 |
Filed Date | 2014-11-27 |
United States Patent
Application |
20140345600 |
Kind Code |
A1 |
Mollenhoff; Marc ; et
al. |
November 27, 2014 |
ABSORBER TUBE
Abstract
An absorber tube is provided that has a metal tube and a sleeve
tube, which is made of glass and encloses the metal tube such that
an annular space is formed between the metal tube and the sleeve
tube. The annular space is evacuated and has at least one container
filled with protective gas, where the container is a solder-free
pressure container.
Inventors: |
Mollenhoff; Marc; (Bayreuth,
DE) ; Sohr; Oliver; (Weiden, DE) ; Kuckelkorn;
Thomas; (Jena, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mollenhoff; Marc
Sohr; Oliver
Kuckelkorn; Thomas |
Bayreuth
Weiden
Jena |
|
DE
DE
DE |
|
|
Family ID: |
46845774 |
Appl. No.: |
14/344954 |
Filed: |
September 14, 2012 |
PCT Filed: |
September 14, 2012 |
PCT NO: |
PCT/EP2012/068091 |
371 Date: |
March 14, 2014 |
Current U.S.
Class: |
126/651 |
Current CPC
Class: |
F24S 40/46 20180501;
F24S 80/00 20180501; Y02E 10/44 20130101; F24S 23/74 20180501; F24S
2025/6011 20180501; F24S 10/45 20180501; F24S 40/80 20180501; F24S
20/20 20180501; Y02E 10/40 20130101 |
Class at
Publication: |
126/651 |
International
Class: |
F24J 2/46 20060101
F24J002/46 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2011 |
DE |
10 2011 082 767.6 |
Claims
1-20. (canceled)
21. An absorber tube comprising: a metal tube; a sleeve tube that
encloses the metal tube, the sleeve being made of material
transparent to solar radiation; and an annular space formed between
the metal tube and the sleeve tube, the annular space being
evacuated; at least one container filled with protective gas in the
annular space, wherein the at least one container is a solder-free
pressure container.
22. The absorber tube according to claim 21, wherein the
solder-free pressure container has an opening that is sealed with a
sealing part.
23. The absorber tube according to claim 22, wherein the sealing
part and the solder-free pressure container are composed of a
common material.
24. The absorber tube according to claim 23, wherein the sealing
part is welded to the solder-free pressure container.
25. The absorber tube according to claim 24, wherein the sealing
part is friction welded to the solder-free pressure container.
26. The absorber tube according to claim 24, wherein the sealing
part is laser or resistance welded to the solder-free pressure
container.
27. The absorber tube according to claim 21, wherein the
solder-free pressure container is steel.
28. The absorber tube according to claim 21, wherein the
solder-free pressure container has an arched bottom.
29. The absorber tube according to claim 21, wherein the
solder-free pressure container has a wall thickness of 0.5 mm to 1
mm.
30. The absorber tube according to claim 21, wherein the
solder-free pressure container has a wall thickness of 0.2 mm to
less than 0.5 mm.
31. The absorber tube according to claim 21, wherein the
solder-free pressure container is arranged at the metal tube or at
the sleeve tube.
32. The absorber tube according to claim 21, further comprising a
structural component joining the metal tube and the sleeve tube,
wherein the solder-free pressure container is arranged at the
structural component.
33. The absorber tube according to claim 21, further comprising at
least one optical element arranged in the annular space adjacent to
the solder-free pressure container.
34. The absorber tube according to claim 33, wherein the at least
one optical element is arranged at a location selected from the
group consisting of at the sleeve tube, at the metal tube, and at
the solder-free pressure container.
35. The absorber tube according to claim 33, wherein the at least
one optical element is arranged in a region between the solder-free
pressure container and the sleeve tube.
36. The absorber tube according to claim 33, wherein the at least
one optical element is a glass plate.
37. The absorber tube according to claim 33, wherein the at least
one optical element is a glass tube in which the solder-free
pressure container is arranged.
38. The absorber tube according to claim 33, wherein the at least
one optical element is an aperture.
39. The absorber tube according to claim 33, wherein the at least
one optical element is arranged laterally next to the solder-free
pressure container.
40. The absorber tube according to claim 39, wherein the at least
one optical element is a mirror.
Description
[0001] The invention relates to an absorber tube according to the
preamble of claim 1.
[0002] Solar collectors may be equipped with a parabolic mirror,
for example, which is also referred to as a collector mirror, and
used in so-called parabolic trough power plants. In known parabolic
trough power plants, a thermal oil is used as heat-transfer medium,
which, by means of the solar rays that are reflected by the
parabolic mirrors and focused on the absorber tube, can be heated
to approximately 400.degree. C. The heated heat-transfer medium is
passed through the metal tube and supplied to a vaporization
process, by means of which the thermal energy is converted into
electrical energy.
[0003] The absorber tube is generally composed of a metal tube,
which has a radiation-absorbing layer, and a sleeve tube, which
encloses the metal tube. The sleeve tube is made of a material that
is transparent in the spectral region of solar radiation,
preferably being made of glass. The annular space formed between
the metal tube and the sleeve tube is generally evacuated and
serves to minimize the heat losses at the outer surface of the
metal tube and thus to increase the energy input.
[0004] Such absorber tubes are known from DE 102 31 467 B4, for
example.
[0005] As it increasingly ages, the thermal oil used as
heat-transfer medium releases free hydrogen, which is dissolved in
the thermal oil. The amount of dissolved hydrogen depends, on the
one hand, on the thermal oil used and the operating conditions of
oil circulation and, on the other hand, also on the amount of water
that comes into contact with the thermal oil. Contact with water
can occur more frequently particularly due to leakage in heat
exchangers. The released hydrogen enters the evacuated annular
space as a result of permeation through the metal tube, the
permeation rate also increasing with increasing operating
temperature of the metal tube. In consequence, the pressure in the
annular space increases as well, which results in an increase in
thermal conduction through the annular space, which, in turn, leads
to heat losses and to a lower efficiency of the absorber tube or of
the solar collector.
[0006] In order to at least reduce the pressure increase in the
annular space and thereby prolong the service life of the absorber
tube, the hydrogen entering the annular space can be bound by
getter materials. Absorber tubes that are provided with getter
materials in the annular space are known from WO 2004/063640 A1,
for example. The uptake capacity of the getter materials is
limited, however. After the maximum loading capacity has been
reached, the pressure in the annular space increases until it is in
equilibrium with the partial pressure of the free hydrogen that has
entered the annular space from the thermal oil. The hydrogen
results in increased thermal conduction in the annular space with
the aforementioned detrimental consequences for the efficiency of
the solar collector.
[0007] Known from DE 10 2005 057 276 B3 is an absorber tube in
which inert gas is fed into the annular space when the capacity of
the getter material is exhausted.
[0008] The inert gas is present in a container that is sealed with
solder and is opened from the outside at an appropriate time. As a
result, an H.sub.2/inert gas mixture forms in the annular space,
the thermal conductivity of which is only slightly greater in
comparison to the evacuated state. The accommodation of the
container in the vacuum space of the absorber tube necessitates
that it be opened in a contact-free manner from the outside. This
can be accomplished by melting the solder through heat input. The
other possibility consists in opening the container inductively or
by heating an intermediate ring in the vicinity of which the
container is fixed in place. The drawback of these opening methods
is that the heat input cannot be directed specifically onto the
solder seal of the container to a sufficient degree, but instead
heats all components in the vicinity of the container as well. In
particular, when the sleeve tube is made of glass, the juncture of
glass and metallic components (glass-metal juncture) is
jeopardized.
[0009] The position of the container in the sleeve tube has the
fundamental drawback that the container is heated by insolation and
the solder seal can unintentionally open. Further drawbacks are to
be found in the embrittlement of the solder due to hydrogen uptake.
Moreover, the complex geometry of the container makes the
manufacture of the solder-sealed opening as well as the entire
container expensive.
[0010] The problem of the invention is to provide an absorber tube
having a container that does not have the mentioned drawbacks and
can be opened in a simple manner.
[0011] This problem is solved by an absorber tube having the
features of claim 1.
[0012] A pressure container is understood to refer to a closed
container that has, in particular, a spherical or cylindrical
shape. The pressure container can have a tube. The tube can also
have a curved shape depending the available design space.
[0013] The pressure container comprises at least an arched bottom.
Preferred is a hemispherical bottom. The lid, too, can be arched,
in particular also hemispherical in shape.
[0014] A solder-free pressure container is understood to be a
pressure container that has no solder, no seal with solder, and no
sealing material made of solder. A solder-free pressure container
is a pressure container having a solder-free seal. Seal parts are
components of the pressure container and are likewise
solder-free.
[0015] The solder is a heat-sensitive material, the melting point
of which is far below that of the other material of the pressure
container. A solder is understood to refer to a metal alloy that,
depending on the specific application, consists of a specific
mixture ratio of metals, primarily lead, tin, zinc, silver, and
copper. Solder solders together suitable metals and alloys, such
as, for example, copper, bronze, brass, tombac, nickel silver,
silver, gold, hard lead, zinc, aluminum, as well as iron, by
bonding or amalgamating to them on the surface when it is fused and
then solidifying upon cooling. This amalgamation of the solder with
the metallic workpieces, materials, structural elements, wires,
etc. is the prerequisite for a long-lasting, firmly bonded, solid
soldered juncture. This solder has the property that its melting
point is lower than that of the metallic workpieces to be joined
together. Solder-free means that the pressure container has no
solder at any place, particularly not at an opening.
[0016] The pressure container can have a bottle neck, which has an
opening that can be sealed by means of a sealing element in the
shape of a plate, for example. The sealing element is preferably
fastened to the filled pressure container by means of welding.
Preferred welding processes are friction welding, resistance
welding, and laser welding.
[0017] Another preferred embodiment provides that, at both of its
ends, the container has a bottle neck with a sealing element.
[0018] The pressure container is completely closed and does not
have a prepared opening that is sealed with a heat-sensitive
material, such as, for example, is true in the case a solder
seal.
[0019] The pressure container has at least one opening for filling
with protective gas, said opening being sealed with a sealing part.
The sealing part may be the lid or the bottom, for example. A
preferred sealing part may also be a plate, in particular a round
plate.
[0020] Rotationally symmetrical structural components have the
advantage that they can be fastened to the container opening in a
simply sealed manner by means of resistance or friction
welding.
[0021] The pressure container may be designed in a bottle shape,
for example. In this case, the sealing part is fastened to the
opening of the bottle neck.
[0022] Preferably, the pressure container is made of steel.
According to EN 10020, steel is a material whose mass fraction of
iron is greater than that of any other element, whose carbon
content is generally <2%, and which contains other elements.
Steel is resistant to corrosion, impermeable to gas, and
mechanically stable, and hence is particularly suitable as a
protective gas container.
[0023] Preferred types of steel are those that preferably can be
deep-drawn, are vacuum-tight, and/or are heat-resistant up to
approximately 600.degree. C.
[0024] The pressure container can be opened by means of a laser
drilling method. Given an appropriate laser power, the pressure
container can be opened in a very short time. The method has the
advantage that the pressure container can be opened from the
outside without heating the other components of the absorber tube
and thus damaging them. The laser beam is aimed specifically onto
the container, which can be arranged in the annular space below the
sleeve tube at any desired spot that can be reached by the laser
beam passing through the sleeve tube. Laser drilling is a
non-cutting processing method in which sufficient energy is
introduced into the workpiece by means of a laser so as to melt and
vaporize the material.
[0025] The melting point of steel can be adjusted within a wide
range up to approximately 1500.degree. C. Therefore, it is possible
to adjust the melting point of the container material, including
the wall thickness of the pressure container and the laser
parameters, to one another, so as to open the container in an
optimal manner.
[0026] Because of the high melting point of steel, the maximum
allowable temperature of the pressure container is higher than that
of a container sealed with solder. It is not necessary to protect
the pressure container from insolation, for example, which leads to
heating of the pressure container.
[0027] Preferably, the pressure container is made of stainless
steel. Stainless steel refers to alloyed or unalloyed steels having
a special degree of purity, such as, for example, steels whose
sulfur and phosphorus content does not exceed 0.025% (see EN
10020).
[0028] Preferred stainless steels are Material No. 1.4303 (in
particular X4CrNi18-12), Material No. 1.4306 (in particular
X2CrNi19-11), Material No. 1.4541, Material No. 1.4571.
[0029] The pressure container can be arranged at the metal tube or
at the sleeve tube by means of a suitable holding device.
Preferably, the pressure container is arranged at a structural
component joining the metal tube and the sleeve tube. This can be,
in particular, an expansion compensating device.
[0030] The pressure container can be fastened by welding, for
example, preferably by friction welding. Other welding processes,
such as, for example, laser welding or resistance welding, can also
be employed.
[0031] The wall thickness of the pressure container preferably lies
at 0.5-1 mm, in particular at 0.6-0.8 mm. The wall thickness can
also be less than 0.5 mm, preferably 0.2 to <0.5 mm, in
particular 0.45 mm.
[0032] The pressure container is filled with a protective gas, such
as, for example, an inert gas having a low thermal conductivity.
Xenon or krypton is particularly preferred. The pressure in the
container at room temperature is preferably 5-10 bars.
[0033] The pressure container can be arranged at the metal tube, at
the sleeve tube, or at a structural component joining a sleeve tube
and a metal tube. When, for example, an expansion compensating
device is provided between the sleeve tube and the metal tube, the
pressure container is preferably arranged at such an expansion
compensating device. This expansion compensating device can have,
for example, a bellows and an appropriate connecting element.
[0034] The pressure container is fastened to the connecting
element, for example, by means of a holder, one or a plurality of
holding elements, a holding clip, a holding bracket, or else a
mounting plate. Such a mounting plate can also be provided at the
metal tube, for example.
[0035] Preferably, the holder encloses the pressure container on
the side of the pressure container facing the metal tube. The
holder preferably has a trough shape.
[0036] This embodiment of the holder has the advantage that, to a
large extent, the pressure container can be protected from emission
of heat from the absorber tube, from defocused impinging solar
radiation from the collector mirror and direct insolation. Strong
insolation can impair the container material in terms of its
strength under certain conditions. Moreover, the gas pressure in
the pressure container increases due to an increase in temperature.
The two effects can possibly bring about bursting of the pressure
container. This problem is reduced by the shielding afforded by the
holder.
[0037] The material of the pressure container is vaporized or
ejected counter to the impinging beam during laser bombardment and
is deposited in the annular space of the absorber tube. Once the
wall of the pressure container is penetrated, the protective gas
can escape. In this process, the material can also deposit on the
inner side of the sleeve tube under some circumstances. The still
persisting laser bombardment heats the deposit and thus also the
sleeve tube. The effect of this heat is to give rise to mechanical
strains in the sleeve tube, which can damage the sleeve tube.
[0038] Preferably, therefore, an optical element is arranged in the
annular space adjacent to the pressure container, this having the
advantage that the material of the container that is vaporized or
ejected counter to the impinging beam in the direction of the
sleeve tube during laser bombardment deposits on this optical
element. As a result, this deposit is prevented from forming at the
sleeve tube.
[0039] The optical element can be arranged at the sleeve tube, at
the metal tube, or at the pressure container.
[0040] The holders for the optical element can be combined with the
holder for the pressure container, for example, or else arranged at
a holder for the pressure container.
[0041] The optical element is preferably arranged in the region
between the pressure container and the sleeve tube. Such an optical
element can be a glass plate, in particular a planar glass plate.
This glass plate captures the container material and thus protects
the sleeve tube.
[0042] According to another embodiment, this optical element can
also be designed as a lens, in particular as a concave lens, so as
to correct the aberrations of the laser beam caused by the sleeve
tube.
[0043] According to another embodiment, the optical element can be
a section of glass tube in which the pressure container is
arranged. It is also possible for the glass tube to be processed in
one section and provided there, for example, with a planar section
or a lens.
[0044] Another embodiment provides that the optical element is an
aperture. The aperture opening is preferably only slightly greater
than the beam diameter of the laser beam. Preferably, the aperture
has a circular aperture opening, the diameter of which is
preferably 300 .mu.m.
[0045] According to another embodiment, the optical element can
also be arranged laterally next to the container. In this case, the
optical element is preferably a mirror, in particular a deflection
mirror. The laser beam is deflected via the deflection mirror onto
the container. Because the container material created by laser
bombardment disseminates counter to beam direction, it impinges on
the mirror and not on the sleeve tube.
[0046] Exemplary embodiments will be described in detail on the
basis of the drawings.
[0047] Shown are:
[0048] FIG. 1 a side view of a protective gas container,
[0049] FIG. 2 a cross section through an absorber tube according to
a first embodiment,
[0050] FIGS. 3, 4, and 5 cross sections of absorber tubes according
to other embodiments,
[0051] FIG. 6 an embodiment of an absorber tube in lengthwise
section,
[0052] FIGS. 7 to 12 various embodiments with fastening means for
the pressure container and the optical element, and
[0053] FIG. 13 a trough-shape holder with a pressure container.
[0054] Illustrated in FIG. 1 is a pressure container 30 in side
view. The pressure container has a bottle-shaped design with a
cylindrical jacket 36 and an arched bottom 37. The bottom is
illustrated as a hemispherical bottom.
[0055] The cylindrical jacket 36 transitions into a bottle neck 38,
which has an opening 39. The opening 39 is sealed by means of a
sealing element in the form of a round plate 60. The sealing
element is fastened to the filled pressure container 30 by means of
friction welding, so that a weld seam 62 is created.
[0056] Illustrated in FIG. 2 is a cutout of an absorber tube 1. The
absorber tube 1 has a metal tube 10, through which heat-exchanger
fluid flows and, as described in the introduction, has
radiation-absorbing layers.
[0057] The metal tube 10 is arranged concentrically in a sleeve
tube 20 that is transparent to solar radiation and is made of
glass, for example. Formed between the metal tube 10 and the sleeve
tube 20 is an annular space 5, which is evacuated. Arranged inside
of this annular space is a pressure container 30, which can be
fastened to the sleeve tube 20 or to the metal tube 10 by way of a
suitable holder (see FIGS. 6-12).
[0058] Arranged in the region between the pressure container 30 and
the sleeve tube 20 is an optical element in the form of a planar
glass plate 40, 42. A laser beam, which impinges on the sleeve tube
20 perpendicularly from above, passes through the sleeve tube 20
and the planar glass plate 42 and then enters the pressure
container. During the drilling process, the material of the
container is released and deposits on the bottom side of the planar
glass plate 42. In this way, container material is prevented from
depositing on the sleeve tube 20.
[0059] Illustrated in FIG. 3 is another embodiment, in which the
optical element 40 is designed as a concave lens 44. The
aberrations that arise due to the curvature of the sleeve tube 20,
can be compensated for by the lens 44, so that the laser pulse, as
provided for, impinges on the container wall.
[0060] Provided as an optical element in FIG. 4 is an aperture 46,
which has a circular aperture opening 47 that is slightly greater
than the diameter of the laser beam 50.
[0061] Illustrated in FIG. 5 is another embodiment, in which the
optical element is not arranged in the region between the pressure
container 30 and the sleeve tube 20, but rather is adjacent, next
to the pressure container 30. What is involved here is a mirror 48,
which is arranged such that it is employed as a deflection mirror.
The laser beam 50, penetrating from the outside, impinges on the
mirror 48 and is deflected so that a horizontal beam impinges on
the pressure container 30. The ejected material of the container
that is created during laser boring of the pressure container 30
deposits on the mirror 48 and thus does not reach the sleeve tube
20.
[0062] Because the optical elements are employed only one time when
the pressure container is opened, the deposit on the optical
elements does not insofar cause any interference. After laser
drilling, the protective gas enters the annular space 5 from the
container.
[0063] Illustrated in FIG. 6 is one end of an absorber tube 1 in
sectional view.
[0064] Fastened to the free front-side end of the sleeve tube 20 is
a transition element 22, which has a collar 23 that is directed
radially inward. Arranged in the annular space 5 formed between the
sleeve tube 20 and the metal tube 10 is an expansion compensating
device 24 in the form of a bellows 25, which is fastened at its
outer end 26 to the collar 23 of the transition element 22.
[0065] The bellows 25 thus extends below the transition element 22
into the annular space 5 and is fastened at its opposite-lying end
to a connecting element 27, which has an annular disc 28 for this
purpose. Arranged at this annular disc is the pressure container
30, which is filled with protective gas and is curved
correspondingly to the annular disc and extends over a semicircle.
Provided between the pressure container 30 and the sleeve tube 20
is an optical element 40 in the form of a glass plate 42. This
glass plate can be flat in design or it may also be curved.
[0066] Illustrated in FIG. 7 is a perspective drawing of the
absorber tube 1 according to FIG. 6, such that the curved design of
the pressure container can be seen. Two holding elements 32 are
provided at the two ends of the curved pressure container 30, by
means of which the container 30 is fastened to the annular disc 28
of the connecting element 27.
[0067] Another embodiment is illustrated in FIG. 8. Here, too, the
pressure container, which takes the form of a bottle, is fastened
to the annular disc 28 by means of a holding clip 33. The pressure
container extends parallel to the lengthwise axis of the absorber
tube 1.
[0068] Another embodiment is illustrated in FIG. 9. The pressure
container 30 also extends along the lengthwise axis of the absorber
tube 1 and is fastened to the annular disc 28 by a suitable
fastening element (not illustrated). Arranged at annular disc 28 is
another holder 34, which supports a lens 44 at its end.
[0069] Illustrated in FIG. 10 is an embodiment in which the
pressure container 30 is situated inside of a glass tube 45. This
embodiment has the advantage that the entire pressure container 30
is shielded and the laser beam can be deflected to any point on the
pressure container 30.
[0070] Illustrated in FIG. 11 is another embodiment in which a
mounting plate 35 is fastened to the annular disc 28. The pressure
container 30 lies on this mounting plate, which, in addition,
supports another holder 49 for the lens 44.
[0071] Illustrated in FIG. 12 is an embodiment in which the
mounting plate 35 is arranged on the metal tube 10 and accommodates
the pressure container 30.
[0072] Illustrated in FIG. 13 is a trough-shaped holder 70, which
is arranged at the annular disc 28 of the expansion compensating
device 24, which is designed as a bellows 25, by means of a
fastening element 78. The trough-shaped holder 70 has a bottom wall
72 that faces the metal tube 10. The trough-shaped holder 70
further has side walls 42, which have inwardly curved shielding
walls 76 at the upper edge. As a result, the container 30 is nearly
completely enclosed, with only a part of the container wall being
left free so that the laser beam can be applied there.
[0073] The holder 70 serves to accommodate a getter 80.
LIST OF REFERENCE NUMBERS
[0074] 1 absorber tube [0075] 5 annular space [0076] 10 metal tube
[0077] 20 sleeve tube [0078] 22 transition element [0079] 23 collar
[0080] 24 expansion compensating device [0081] 25 bellows [0082] 26
outer end [0083] 27 connecting element [0084] 28 annular disc
[0085] 29 fastening collar [0086] 30 pressure container [0087] 32
holding element [0088] 33 holding clip [0089] 34 holding bracket
[0090] 35 mounting plate [0091] 36 cylindrical jacket [0092] 37
arched bottom [0093] 38 bottle neck [0094] 39 opening [0095] 40
optical element [0096] 42 glass plate [0097] 44 lens [0098] 45
glass tube [0099] 46 aperture [0100] 47 aperture opening [0101] 48
mirror [0102] 49 holder [0103] 50 laser beam [0104] 60 sealing
element [0105] 62 weld seam [0106] 70 trough-shaped holder [0107]
72 bottom wall [0108] 74 side wall [0109] 76 shielding wall [0110]
78 fastening element [0111] 80 getter
* * * * *