AU2012230467B2

AU2012230467B2 - Solar absorber module

Info

Publication number: AU2012230467B2
Application number: AU2012230467A
Authority: AU
Inventors: Udo Hack
Original assignee: Saint Gobain IndustrieKeramik Roedental GmbH
Current assignee: Saint Gobain IndustrieKeramik Roedental GmbH
Priority date: 2011-03-18
Filing date: 2012-03-16
Publication date: 2017-03-30
Anticipated expiration: 2032-03-16
Also published as: EP2686619B1; WO2012126826A2; WO2012126826A3; EP2686619A2; ES2855156T3; DE102011005817A1; DE102011005817B4

Abstract

The invention relates to a solar absorber module that contains an absorber honeycomb (2) comprising channels (8) which connect the air inlet side (2.1) of the adsorber honeycomb (2) to the air outlet side (2.2) of the absorber honeycomb (2). The absorber module also contains an absorber cup (3) comprising a square-shaped section (3.0), comprising a funnel-shaped section (3.1), and comprising a reduced section (3.2). The absorber cup (3) contains a ceramic material with a thermal conductivity of ≤ 3 W/(mK).

Description

1 2012230467 07 Mar 2017

Solar Absorber Module

The invention relates to an absorber cup, a solar absorber module, and a method for producing a solar module.

Ceramic components, such as solar absorber modules, are distinguished by a particularly high resistance to high thermal gradients. This is true over the spatial expanse of the solar absorber module and also in the event of a rapid temperature change, a so-called thermal shock load.

This property is particularly important with the use of ceramic components as elements of solar absorber modules for the operation of solar thermal power towers. Sunlight is directed by means of automatically positioning mirrors to a central high temperature heat exchanger, a so-called solar receiver, in which a large number of solar absorber modules convert the concentrated sunlight into heat. The surface of the solar absorber module can be heated to temperatures of up to 1380 °C, with technically reasonably manageable temperatures being around 1200 °C. The interior of the high temperature heat exchanger is flowed through by a heat transfer medium, such as air, gas, or water vapor. In the case of air and gas, water vapor, which is used to drive a conventional turbine and, consequently, to generate electrical energy, is generated in a second heat exchanger.

From DE 100 07 648 Cl and WO 2010/086443 A2, components and solar absorber modules composed of funnels and honeycombs made of ceramic materials such as silicon carbide and silicon-infiltrated silicon carbide are known.

In operation in solar thermal power plants, the solar absorber modules are exposed to strong and rapid temperature changes. These temperature changes ordinarily amount to up to 200 °C/min and occur, for example, by shadowing of the incident sunlight during the passage of patches of clouds. A service life of at least 20 years is targeted for such solar absorber modules.

Ceramic materials made of silicon carbide or silicon-infiltrated silicon carbide have appropriate material properties with regard to thermal resistance.

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However, large heat losses and, thus, low thermal efficiency occur with solar modules made of silicon carbide or silicon-infiltrated silicon carbide.

The object of the present invention consists in providing an absorber cup and a solar absorber module with low heat losses and improved thermal efficiency along with sufficient stability.

The object of the present invention is accomplished according to the invention by a solar absorber modulecomprising: - an absorber honeycomb with channels (8) that connect the air inlet side of the absorber honeycomb to the air outlet side of the absorber honeycomb and - an absorber cup with a square-shaped section, with a funnel-shaped section, and a reduced section, wherein the absorber cup contains a ceramic material with a thermal conductivity of < 3 W/(mK), and wherein the square-shaped section of the absorber cup has on its exterior at least one spacer per side with a distance d to the front edge of the absorber cup of 15% to 80% of the length c of the square-shaped section. Preferred embodiments emerge from the subclaims.

The invention further includes a method for producing a solar absorber module. A use of the method according to the invention emerges from further claims.

The solar absorber module according to the invention may comprise an absorber honeycomb made from silicon carbide or silicon-infiltrated silicon carbide and an absorber cup, which contains a ceramic material with a thermal conductivity of < 3 W/(mK).

In an advantageous embodiment of the solar absorber module according to the invention, the absorber honeycomb contains a ceramic material with a thermal conductivity of < 2.5 W/(mK), particularly preferably of < 2 W/(mK).

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In an advantageous embodiment of the solar absorber module according to the invention, the absorber cup contains cordierite and/or aluminum titanate.

In another advantageous embodiment of the solar absorber module according to the invention, the absorber cup contains isostatically pressed cordierite or isostatically pressed aluminum titanate.

The absorber honeycomb contains channels that connect the air intake side of the absorber honeycomb to the air outlet side of the absorber honeycomb. The absorber cup may comprise a square-shaped section that serves to accommodate the absorber honeycomb, a funnelshaped section that pools the sucked-in air, and a reduced section that forwards the sucked-in air to a pipe system.

In an advantageous embodiment of the solar absorber module according to the invention, the absorber cup contains cast cordierite or cast aluminum titanate.

In a preferred embodiment of the solar absorber module according to the invention, the square-shaped section of the absorber cup has, on its exterior, two spacers per side. In this context, "side" means each of the four outward sides of the square-shaped section.

In a preferred embodiment of the solar absorber module according to the invention, the spacer has a distance d to the front edge of the absorber cup (3) from 25% to 40% of the length c of the square-shaped section.

The cordierite material according to the invention preferably contains from 30 wt.-% to 60 wt.-% aluminum oxide (Al203), from 30 wt.-% to 60 wt.-% silicon oxide (Si02), and from 1 wt.-% to 10 wt.-% magnesium oxide (MgO), and from 0 wt.-% to 5 wt.-% titanium oxide (Ti02), from 0 wt.-% to 5 wt.-% zirconium oxide (Zr02), and/or von 0 wt.-% to 5 wt.-% zirconium silicate (ZrSi04).

8807168_1 (GHMatters) P94310.AU 4 2012230467 07 Mar 2017

In a preferred embodiment of the invention, the cordierite material contains from 50 wt.-% to 65 wt.-% aluminum oxide (Al203), from 30 wt.-% to 40 wt.-% silicon oxide (Si02), and from 3 wt.-% to 10 wt.-% magnesium oxide (MgO). The composition can also contain further admixtures and production-related impurities, for example, from 0 wt.-% to 5 wt.-% titanium oxide (Ti02), zirconium oxide (Zr02), and/or zirconium silicate (ZrSi04).

In a particularly preferred embodiment of the invention, the cordierite material contains from 52 wt.-% to 62 wt.-% aluminum oxide (Al203), from 30 wt.-% to 40 wt.-% silicon oxide (Si02), and from 5 wt.-% to 7 wt.-% magnesium oxide (MgO).

The composition can also contain further admixtures and production-related impurities, for example, from 0 wt.-% to 5 wt.-% titanium oxide (Ti02), zirconium oxide (ZT02), and/or zirconium silicate (ZrSi04).

In an alternative embodiment of the invention, the cordierite material contains from 30 wt.-% to 40 wt.-% aluminum oxide (Al203), from 50 wt.-% to 65 wt.-% silicon oxide (Si02), and from 3 wt.-% to 10 wt.-% magnesium oxide (MgO). The composition can also contain further admixtures and production-related impurities, for example, from 0 wt.-% to 5 wt.-% titanium oxide (Ti02), zirconium oxide (Zr02), and/or zirconium silicate (ZrSi04).

In a preferred embodiment of the invention, the cordierite material contains from 35 wt.-% to 40 wt.-% aluminum oxide (Al203), from 30 wt.-% to 40 wt.-% silicon oxide (Si02), and from 5 wt.-% to 7 wt.-% magnesium oxide (MgO). The composition can also contain further admixtures and production-related impurities, for example, from 0 wt.-% to 5 wt.-% titanium oxide (Ti02), zirconium oxide (Zr02), and/or zirconium silicate (ZrSi04).

In a preferred embodiment of the invention, the cordierite material contains from 1 wt.-% to 30 wt.-%, preferably from 20 wt.-% to 30 wt.-% silicon carbide.

Solar absorber modules are heated by concentrated solar radiation on the front side to as much as 1200 °C. Air is sucked through the absorber honeycomb. The sucked-in air heated in

8807168_1 (GHMatters) P94310.AU 5 2012230467 07 Mar 2017 the center of the receiver field to as much as 1000 °C is collected in the absorber cup and passed on into the interior of a double-walled connection pipe in a rear steel structure. After the extraction of the thermal energy in a second heat exchanger, the return air cooled to roughly 120 °C is returned in the return air channel of the double-walled pipe and, at the same time, cools the steel structure.

The return air cooled to 120 °C passes the exterior of the funnel-shaped section of the absorber cup and is heated to roughly 180 °C. At the same time, the air heated to roughly 1000° C in the interior of the funnel-shaped section of the absorber cup is cooled by contact with the wall of the absorber cup cooled from the outside.

The reduced section of the absorber cup and the inner pipe of the double-walled pipe are customarily thermally insulated, for example, by a material that contains aluminum silicate fibers. In the region of the square-shaped section and of the funnel-shaped section of the absorber cup, such insulation can be realized only very time-consumingly and cost intensively due to the curvature of the components.

According to the prior art, absorber honeycombs and absorber cups are customarily made of silicon-infiltrated silicon carbide materials. Silicon-infiltrated silicon carbide materials are, due to their high bending strength, well-suited for high-temperature resistant components in which large mechanical stresses often occur because of high temperature differences.

However, silicon-infiltrated silicon carbide materials have high thermal conductivity such that large heat losses occur between the roughly 1000 °C hot sucked-in air and the return air cooled to roughly 120 °C.

The underlying concept of the present invention is to produce the absorber cups and, in particular, the square-shaped section and the funnel-shaped section from a material with low thermal conductivity. This reduces the heat losses and the cooling of the 1000 °C hot air through contact with the walls of the absorber cups.

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The particular advantage of ceramics that contain aluminum titanate consists in the lower thermal conductivity compared to silicon-infiltrated silicon carbide materials. The lower thermal conductivity of cordierite materials and aluminum titanate materials results in smaller heat losses, in particular in the region of the funnel-shaped section of the absorber cup. Higher thermal efficiency of the solar thermal power plant results from the lower heat losses.

The use of cordierite materials or aluminum titanate materials is, however, not obvious to the person skilled in the art since cordierite materials and aluminum titanate materials have a lower bending strength than silicon carbide. This would have kept the person skilled in the art from considering cordierite materials or aluminum titanate materials.

It turned out, surprisingly for the person skilled in the art, that solar absorber modules made of cordierite materials or aluminum titanate materials withstand the conditions of use in solar thermal power plants. Cordierite materials or aluminum titanate materials have a lower thermal expansion than silicon-infiltrated silicon carbide. The lower thermal expansion of cordierite materials or aluminum titanate materials partially compensates for it lower bending strength in comparison with silicon-infiltrated silicon carbide. Moreover, cordierite materials or aluminum titanate materials have excellent thermal shock resistance.

The solar absorber module according to the invention contains an absorber cup made from cast cordierite or aluminum titanate. Investigations have shown that ceramics made of cast cordierite or aluminum titanate have lower thermal conductivity values and higher bending strength values than pressed cordierite ceramics or aluminum titanate ceramics according to the prior art. This is attributable to the finer grain structure of the ceramic slurry in the case of casting compared to the pressed material.

The solar absorber module according to the invention preferably has an absorber cup with a reduced section for forwarding air guided through the absorber honeycomb. The absorber cup according to the invention preferably consists of a square, funnel-shaped section that opens into a circular, reduced section.

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In the solar absorber module according to the invention, the longitudinal axis (L) of the absorber cup is preferably parallel to the surface-normal direction of the absorber honeycomb. This is particularly advantageous as the sucked-in air can flow uniformly into the absorber cups and no nonuniform temperature peaks occur in the edge region of the absorber cup.

The absorber cup according to the invention and the absorber honeycomb according to the invention preferably include openings. In the installed position, the openings of the absorber honeycomb are opposite the openings of the absorber cup. The absorber honeycomb can be loosely connected to the absorber cup by insertion of a ceramic pin into the opening in order to compensate the different thermal expansion between the absorber honeycomb and the absorber cup. Preferably, the ceramic pin does not protrude beyond the edge of the absorber cup and can be secured during the assembly of the absorber modules, for example, by adhesive tape. After installation in a supporting structure, the ceramic pin is, for example, fixed in the opening by adjacent solar absorber modules or boundaries of the supporting structure.

Another aspect of the invention comprises a solar absorber arrangement with a supporting structure for at least one solar absorber module according to the invention. The supporting structure has a plurality of double-walled pipe sockets with return air channels. The return air channel is formed by the intermediate space between the inner pipe and the outer pipe of the double-walled pipe. Each inner pipe serves to accommodate the reduced section of an absorber cup.

The object of the invention is further accomplished through a method for producing an absorber cup from a ceramic material that contains cast cordierite or cast aluminum titanate, wherein at least: a) a hollow mold with the external shape of an absorber cup is created, b) the hollow mold is filled with a ceramic slurry, c) water is extracted from the ceramic slurry and a ceramic body is obtained, d) the ceramic body is removed from the hollow mold, and e) the ceramic body is fired at a temperature of 1300 °C to 1450 °C,

8807168_1 (GHMatters) P94310.AU 8 2012230467 07 Mar 2017 wherein the square-shaped section has, on its exterior, at least one spacer per side with a distance d to the front edge of the absorber cup from 15% to 80% of the length c of the squareshaped section.

The hollow mold is made, for example, from plaster or another hygroscopic material that can extract moisture from the ceramic slurry.

In a preferred embodiment of the method according to the invention, the square-shaped section of the absorber cup has, on its exterior, two spacers per side. In this context, "side" means the four outward sides of the square-shaped section.

In a preferred embodiment of the method according to the invention, the spacer has a distance d to the front edge of the absorber cup from 25% to 40 of the length c of the square-shaped section.

As experiments of the inventors have surprisingly demonstrated, the distance d of the spacers to the front edge of the absorber cup is of vital significance for the method according to the invention: Ceramic bodies of absorber cups in which the spacers were implemented all the way to the front edge of the absorber cups presented, after removal from the hollow mold, deformations and buckling of the walls of the square-shaped section. These deformations had to be finished by milling or grinding in order to enable the use of the absorber honeycomb. Likewise, the ceramic bodies of absorber cups that had no spacers presented, after removal from the hollow mold, deformations and buckling of the walls of the square-shaped section.

With spacers disposed according to the invention that had a certain distance d to the front edge of the absorber cup, no noticeable deformations of the walls of the square-shaped region occurred. A distance d to the front edge of the absorber cup that amounts to from 15% to 80% of the length c of the square-shaped section has proved well suited.

In another embodiment of the method according to the invention, in step (d), openings are introduced into the absorber honeycomb and/or the absorber cup after removal of the hollow

8807168_1 (GHMatters) P94310.AU 9 2012230467 07 Mar 2017 mold. The openings are preferably introduced into the unfired ceramic body by drilling, punching, or waterjet cutting.

The object of the invention is further accomplished by a method for producing an absorber cup from a ceramic material that contains isostatically pressed cordierite or isostatically pressed aluminum titanate. In this case, in a first step a), a ceramic slurry is granulated to form a granulate. Spray methods for producing a granulate are sufficiently well known to the person skilled in the art. The ceramic slurry corresponds in its composition substantially to a ceramic slurry as is also used in the above-described casting method. The water content and the viscosity of the ceramic slurry are optionally adapted to the conditions of the spraying method. The grain size of the granulate is preferably from 0.2 mm to 0.3 mm.

In a second step, a hollow mold with the external shape of an absorber cup (3) and a die is created. The hollow mold is made, for example, of steel or another material that withstands the conditions of the subsequent pressing procedure. The die is disposed in the interior of the hollow mold. The die contains, for example, a plastic or rubber.

In a third step, the granulate is filled into the intermediate space between the hollow mold and the die.

In a fourth step, the granulate is pressed at a pressure from 800 bar to 4000 bar. The pressing procedure takes place, for example, by filling the interior space of the die with a pressure medium, for example, with oil. The interior space of the die is the region of the die facing away from the hollow mold.

Isostatically pressed ceramics of cordierite or aluminum titanate according to the invention that are produced on the basis of a ceramic casting slurry have small grain size distributions and, consequently, high bending strength values similar to cast ceramics of cordierite or aluminum titanate according to the invention.

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In a preferred embodiment of the invention, the ceramic slurry for producing the absorber cup contains an aluminum titanate powder, in which 80 wt.-% of the powder grains have a grain size of roughly 30 pm and 20 wt.-% have a grain size of 1 pm. The thermal conductivity of a ceramic made of aluminum titanate produced according to the invention is roughly 1.5 W/(mK) to 3 W/(mK), the bending strength roughly 15 MPa to 100 MPa. A further aspect of the invention comprises a solar absorber module wherein the absorber cup of the solar absorber module is produced according to the above-described method according to the invention.

The invention further includes the use of a solar absorber module according to the invention in a solar thermal power plant, for example, as a high-temperature heat exchanger.

The invention is explained in detail in the following with reference to drawings and an example. The drawings are not completely true to scale. The invention is in no way restricted by the drawings. They depict:

Fig. 1A a side view of the long side of a solar absorber module,

Fig. IB a cross-sectional view along the cutting line A-A of Fig. 1A,

Fig. 2A a side view of the long side of an absorber honeycomb,

Fig. 2B a cross-sectional view along the cutting line C-C of Fig. 2A,

Fig. 3A a side view of the long side of an absorber cup,

Fig. 3B a cross-sectional view along the cutting line E-E of Fig. 3A,

Fig. 4 a cross-sectional view of two solar absorber modules and double-walled pipe sockets according to the invention,

Fig. 5 a spatial representation of a solar module arrangement with supporting structure, and Fig. 6 a detailed flowchart of the method according to the invention

Fig. 1A depicts a side view of the long side of the solar absorber module 1 and Fig. IB a crosssectional view along the cutting line A-A of Fig. 1A . The solar absorber module 1 comprises an absorber honeycomb 2 and an absorber cup 3.

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Fig. 2A depicts a side view of the long side of an absorber honeycomb 2. The absorber honeycomb 2 comprises channels 8 that run in substantially straight lines through the absorber honeycomb 2. The channels 8 connect the air inlet side 2.1 to the air outlet side 2.2 of the absorber honeycomb 2. Fig. 2B depicts a cross-sectional view along the cutting line C-C of Fig. 2A. The channels 8 are disposed here, for example, in the form of a grid. In an advantageous embodiment of the absorber honeycomb 2 according to the invention, the channels 8 are configured as polygons and disposed in the form of a honeycomb. The absorber honeycomb 2 has, for example, a substantially square cross-section with a side length of 140 mm and a thickness of 60 mm at the thickest point.

Fig. 3A depicts a side view of the long side of an absorber cup 3 and Fig. 3B a cross-sectional view along the cutting line E-E of Fig. 3A . The absorber cup 3 consists of a square-shaped section 3.0 and a square, funnel-shaped section 3.1 that opens into a round, reduced section 3.2. The square-shaped section 3.0 serves to accommodate the absorber honeycomb 2. The funnel-shaped section 3.1 serves to pool the stream of air that is guided through the absorber honeycomb 2. The reduced section 3.2 serves to forward air that is sucked through the absorber honeycomb 2. The absorber cup 3 has, for example, a length of 154 mm. The length c of the square-shaped section 3.0 is, for example, 25 mm; the length b of the funnel-shaped section 3.1 is, for example, 57 mm; and the length a of the reduced section is, for example, 72 mm. In the funnel-shaped section 3.1, the absorber cup 3 has a substantially square crosssection with an outside width of 140 mm and an inside width of 133 mm. The square-shaped section 3.0 of the absorber cup 3 and the absorber honeycomb 2 are coordinated with each other such that a precisely fitting installation with a joint gap from 0.5 mm to 1 mm is possible. The reduced section 3.2 of the absorber cup 3 is cylindrical and has an internal diameter, for example, of 72 mm and an external diameter of 80 mm.

The exterior 3.4 of the absorber cup 3 has, in the region of the square-shaped section 3.0, for example, eight spacers 9, of which two are in each case disposed on each side of the squareshaped section 3.0. The spacers 9 have a distance d to the front edge 3.3 of the absorber cup 3 of 4 mm to 20 mm and, for example, of 8 mm auf. The distance d of the spacer 9 to the front

8807168_1 (GHMatters) P94310.AU 12 2012230467 07 Mar 2017 edge 3.3 of the absorber cup 3 is preferably from 15% to 80% of the length c of the squareshaped section 3.0 of the absorber cup 3 and particularly preferably from 25% to 40%. The spacer 9 extends, for example, all the way to the transition of the square-shaped section 3.0 to the funnel-shaped section 3.1.

The distance d of the spacer 9 to the front edge 3.3 of the absorber cup 3 is, as already stated above, of vital significance for the method according to the invention for producing the absorber cup 3. A spacer 9 with a distance according to the invention to the front edge 3.3 of the absorber cup 3 stabilizes the walls of the square-shaped section 3.0 of the absorber cup 3 during removal from the hollow mold.

The reduced section 3.2 of the absorber cup contains in its interior, for example, pipe-shaped insulation 3.21 made of aluminum silicate wool, for example, made of the material Kerform KVS 154 of the company Rath AG, Vienna, Austria, with a thermal conductivity of 0.23 W/mK at a temperature of 1000 °C.

The absorber cup 3 contains, for example, high-temperature resistant ceramic materials made of cordierite, with a content of 57 wt.-% aluminum oxide (Al203), 35 wt.-% silicon oxide (Si02), and 6 wt.-% magnesium oxide (MgO), as well as production-related admixtures. The casting slurry is, however, more finely grained than pressed cordierite materials in order to enable a smooth runoff of the slurry from the inner surface of the hollow casting mold. The cordierite material is shaped to form the absorber cup 3, for example, by a casting method. The absorber honeycomb 2 contains, for example, silicon-infiltrated silicon carbide.

The absorber cup 3 and the absorber honeycomb 2 have openings 5. In the installed position, the openings 5 of the absorber cup 3 are opposite the openings 5 of the absorber honeycomb 2. The openings 5 have, for example, a diameter of 4.5 mm. The openings 5 in the absorber honeycomb 2 have, for example, a depth of 6 mm. The absorber honeycomb 2 is connected to the absorber cup 3 by ceramic pins that are inserted into the openings 5. The ceramic pins are, for example, rod-shaped, with a diameter of 4 mm and a length of 10 mm. The ceramic pins

8807168_1 (GHMatters) P94310.AU 13 2012230467 07 Mar 2017 preferably do not protrude beyond the absorber cup 3 and are, for example, fixed by adhesive tape during installation.

Fig. 4 depicts a cross-sectional view of two solar absorber modules 1.1,1.2 and double-walled pipe sockets 4 according to the invention. The inner pipe 4.2 of the double-walled pipe 4 has insulation 4.3 made of a ceramic fiber paper, for example, of a plurality of layers of a 3-mm-thick aluminum silicate fiber paper of the type Alistra 1400 from the company Rath AG, Vienna, Austria.

During operation in a solar thermal power plant, the absorber honeycomb 2 is exposed on its air intake side 2.1 to incident sunlight and heated. Then, air I is sucked in via the air intake side 2.1. The sucked-in air I has, after passage through the absorber honeycomb 2, for example, a temperature of up to 1000 °C. In the region of the walls of the funnel-shaped section 3.1 of the absorber cup 3, the air is cooled by contact with the colder outside wall. The sucked-in air I is transferred in the interior of the absorber cup 3 by the funnel-shaped section 3.1 into the reduced section 3.2 and then fed as expelled air II to energy extraction. During energy extraction, the air is cooled, for example, to temperatures of roughly 120 °C. The cooled return air III is returned through a return air channel 6. The return air channel 6 is formed by the intermediate space between the outer pipe 4.1 and the inner pipe 4.2 of a double-walled pipe 4. The return air IV passes through the intermediate space between the funnel-shaped sections 3.1 of the absorber cup 3. Since the absorber cup 3 in the funnel-shaped section 3.1 has no thermal insulation, large heat losses occur with absorber cups 3 made of materials with higher thermal conductivities according to the prior art. With absorber cups 3 according to the invention made of cast cordierite materials, the heat losses are less. The return air IV is heated, in particular in the non-insulated, funnel-shaped section 3.1 of the absorber cup 3, to roughly 180 °C. The square-shaped sections 3.0 of the absorber cups 3 are held at a distance by spacers 9. The distance is retained even if the absorber cups 3 expand thermally from warming. The return air IV exits the arrangement as outgoing air IV via the intermediate spaces created by the spacers 9. According to the invention, a maximum of 60% of the outgoing air IV can be sucked in again as sucked-in air I.

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Fig. 5 depicts the spatial representation of a solar module arrangement 10 with a supporting structure 7. The supporting structure 7 comprises, for example, 15 double-walled pipe sockets 4. Each double-walled pipe socket 4 serves to accommodate the reduced section 3.2 of an cup 3 of a solar absorber module 1.

Fig. 6 depicts a detailed flowchart of the method according to the invention. In a first step (a), a model of the absorber cup 3 according to the invention is created. The dimensions of the model take into account dry additions and firing shrinkage additions determinable in a simple manner for the person skilled in the art. In a second step (b), a hollow plaster mold with the external shape of the absorber cup 3 is created using the model from the first step (a). In a third step (c), the plaster mold is filled with a ceramic slurry.

The ceramic slurry contains, for example, ceramic components of 7 wt.-% blue clay, 10 wt.-% clay, 32 wt.-% Kerphalite (aluminum silicate) of the company Damrec SAS, Paris, France, 16 wt.-% Sierralite 2000 of the company Luzenac Europe SAS, Toulouse, France, and 35 wt.-% sintered mullite, e.g., of the company VAW Vereinigte Aluminiumwerke AG, Grevenbroich, Germany. The data for wt.-% are based in each case on the dry compound. The Kerphalite has, for example, grain sizes from 0 mm to 0.16 mm. The sintered mullite has, for example, grain sizes from 0 mm to 0.1 mm.

The ceramic slurry contains the ceramic components in a suspension with roughly 28 wt.-% water and other customary auxiliary materials such as 0.2 wt.-% liquefier and 0.2 wt.-% binder.

In another example of the method according to the invention, the ceramic components of the ceramic slurry include from 0 wt.-% to 5 wt.-% titanium oxide (Ti02), 0 wt.-% to 5 wt.-% zirconium oxide (Zr02), and/or 0 wt.-% to 5 wt.-% zirconium silicate (ZrSi04) in the dry compound.

In another another example of the method according to the invention, the ceramic components of the ceramic slurry include from 0 wt.-% to 30 wt.-% silicon carbide (SiC).

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In another step (d), water is extracted from the ceramic slurry by the plaster mold, by which means a ceramic body is obtained. In another step (e), the plaster mold is removed. In the last step (f) of the method, the ceramic body is fired at a temperature of 1300 °C to 1450 °C.

The plaster mold has, on the exterior 3.4 of the absorber cup 3 in the region of the squareshaped section 3.0, recesses for, for example, eight spacers 9, of which two are in each case disposed on each side of the square-shaped section 3.0. The recesses for the spacers 9 have a distance d to the front edge 3.3 of the absorber cup 3 of 4 mm to 20 mm and, for example, of 8 mm. The distance d of the spacer 9 to the front edge 3.3 of the absorber cup 3 is preferably from 15% to 80% of the length c of the square-shaped section 3.0 of the absorber cup 3 and particularly preferably from 25% to 40%. The spacer 9 extends, for example, all the way to the transition of the square-shaped section 3.0 to the funnel-shaped section 3.1.

The distance d of the spacer 9 to the front edge 3.3 of the absorber cup 3 is, as already stated above, of vital significance for the method according to the invention for producing the absorber cup 3 . A spacer 9 with a distance according to the invention to the front edge 3.3 of the absorber cup 3 stabilizes the walls of the square-shaped section 3.0 of the absorber cup 3 at time of removal from the hollow mold.

The porosity of the fired ceramic body can be adjusted by the addition of a pore-forming agent to the ceramic slurry.

The density of the fired ceramic body is, for example, from 1.8 g/cm3 to 2.1 g/cm3, preferably 1.9 g/cm3 to 2.0 g/cm3, and, for example, 1.95 g/cm3. The porosity of the fired cordierite is, for example, 25%.

Solar absorber modules according to the prior art are usually made from silicon-infiltrated silicon carbide (SiSiC). In Table 1, the material properties of silicon-infiltrated silicon carbide are compared with material properties of cordierite which had been processed in the casting method according to the invention.

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The thermal conductivity of the cast cordierite material is 1.24 W/(mK) and is thus lower by roughly 96% than the thermal conductivity of silicon-infiltrated silicon carbide. The lower thermal conductivity of absorber cups made of cordierite results in lower heat losses and thus in higher efficiency of solar thermal power plants.

Table 1

Cast Cordierite Material Silicon Infiltrated Silicon Carbide (Prior Art) Bulk density 1.95 kg/dm3 2.8 kg/dm3 Open porosity 25% 0% Thermal expansion 2.9 * 10-6 K1 4.5* 10-6 K1 Thermal 1.24 W/(mK) 35 W/(mK) conductivity

In tests at the test facility of the German Aerospace Center (DLR), solar absorber modules with absorber cups made of cast cordierite presented, with return air, a thermal efficiency roughly 8% better than solar absorber modules with absorber cups made of silicon-infiltrated silicon carbide according to the prior art.

In Table 2, the bending strength of a pressed cordierite material is compared to a cordierite material cast according to the method according to the invention. The cast cordierite material has a cold bending strength at room temperature of 36 MPa. The cold bending strength of the cast cordierite material is thus 176% higher than the cold bending strength of the pressed cordierite material. The cast cordierite material has a hot bending strength at 1300 °C of 20 MPa. The hot bending strength of the cast cordierite material is thus 133% higher than the hot bending strength of the pressed cordierite material.

8807168_1 (GHMatters) P94310.AU 17 2012230467 07 Mar 2017

The comparison between the cast cordierite material and the pressed cordierite material shows a bending strength of the cast cordierite material surprisingly great for the person skilled in the art. Cast cordierite materials are consequently better suited to accommodate the mechanical stresses of solar absorber modules under temperature change conditions, which increases the service life and stability of the solar absorber modules.

Table 2

Cordierite Material, Pressed According to the Prior Art (AnnaCorit 60) Cordierite material, Cast Cold bending strength (room temperature) 13 MPa 36 MPa Hot bending strength (1300°C) 15 MPa 20 MPa A solar absorber module according to the invention was heated in a field test at the solar furnace at Plataforma Solar de Almeria in Spain more than 100 times with roughly 200 K/min1 and cooled again. The solar absorber module presented no damage or adverse effects whatsoever.

Solar absorber modules with absorber cups made of cast cordierite thus presented sufficient mechanical strength with lower heat losses through thermal conduction and higher thermal efficiency compared to materials of the prior art.

This result was unexpected and surprising for the person skilled in the art.

8807168_1 (GHMatters) P94310.AU 2012230467 07 Mar 2017

List of reference characters: 1, 1.1, 1.2 2 2.1 2.2 3 3.0 3.1 3.2 3.21 3.3 3.4 4 4.1 4.2 4.3 5 6 7 8 9 10 I II III, IV IV a b c d

8807168_1 (GHMatters) P94310.AU 18 solar absorber module absorber honeycomb air intake side of the absorber honeycomb 2 air outlet side of the absorber honeycomb 2 absorber cup square-shaped section of the absorber cup 3 funnel-shaped section of the absorber cup 3 reduced section of the absorber cup 3 insulation of the reduced section 3.2 front edge of the absorber cup 3 exterior of the absorber cup 3 double-walled pipe, double-walled pipe socket outer pipe inner pipe insulation of the double-walled pipe 4 opening return air channel supporting structure channel spacer solar module arrangement sucked-in air expelled air return air outgoing air length of the reduced section 3.2 of the absorber cup 3 length of the funnel-shaped section 3.1 of the absorber cup 3 length of the square-shaped section 3.0 of the absorber cup 3 distance of the spacer 9 from the front edge 3.3 of the absorber cup 3 19 2012230467 07 Mar 2017 A-A cross-section through the solar absorber module 1 C-C cross-section through the absorber honeycomb 2 E-E cross-section through the absorber cup 3 L longitudinal axis of the absorber cup 3 N surface-normal direction of the absorber honeycomb 2

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

8807168_1 (GHMatters) P94310.AU

Claims

Claims

1. Solar absorber module, comprising: - an absorber honeycomb with channels (8) that connect the air inlet side of the absorber honeycomb to the air outlet side of the absorber honeycomb and - an absorber cup with a square-shaped section, with a funnel-shaped section, and a reduced section, wherein the absorber cup contains a ceramic material with a thermal conductivity of < 3 W/(mK), and wherein the square-shaped section of the absorber cup has on its exterior at least one spacer per side with a distance d to the front edge of the absorber cup of 15% to 80% of the length c of the square-shaped section.
2. Solar absorber module according to claim 1, wherein the ceramic material contains cordierite and/or aluminum titanate.
3. Solar absorber module according to one of claims 1 or 2, wherein the ceramic material contains isostatically pressed cordierite or aluminum titanate.
4. Solar absorber module according to claim 1 or 2, wherein the ceramic material contains cast cordierite or cast aluminum titanate.
5. Solar absorber module according to claim 4, wherein the square-shaped section of the absorber cup has, on its exterior, two spacers per side.
6. Solar absorber module according to claim 4 or 5, wherein the spacer has a distance d to the front edge of the absorber cup of 25% to 40% of the length c of the square-shaped section.
7. Solar absorber module according to one of claims 2 through 6, wherein the cordierite contains from 30 wt.-% to 60 wt.-% aluminum oxide (Al203), from 30 wt.-% to 60 wt.-% silicon oxide (Si02), from 1 wt.-% to 10 wt.-% magnesium oxide (MgO), and from 0 wt.-% to 5 wt.-% titanium oxide (Ti02), from 0 wt.-% to 5 wt.-% zirconium oxide (Zr02), and/or from 0 wt.-% to 5 wt.-% zirconium silicate (ZrSi04).
8. Solar absorber module according to claim 7, wherein the cordierite contains from 50 wt.-% to 65 wt.-% aluminum oxide (Al203), from 30 wt.-% to 40 wt.-% silicon oxide (Si02), and from 3 wt.-% to 10 wt.-% magnesium oxide (MgO).
9. Solar absorber module according to claim 7, wherein the cordierite contains from 52 wt.-% to 62 wt.-% aluminum oxide (Al203), from 30 wt.-% to 40 wt.-% silicon oxide (Si02), and from 5 wt.-% to 7 wt.-% magnesium oxide (MgO).
10. Solar absorber module according to claim 7, wherein the cordierite contains from 30 wt.-% to 40 wt.-% aluminum oxide (Al203), from 50 wt.-% to 65 wt.-% silicon oxide (Si02), and from 3 wt.-% to 10 wt.-% magnesium oxide (MgO).
11. Solar absorber module according to claim 7, wherein the cordierite contains from 35 wt.-% to 40 wt.-% aluminum oxide (Al203), from 30 wt.-% to 40 wt.-% silicon oxide (Si02), and from 5 wt.-% to 7 wt.-% magnesium oxide (MgO),
12. Solar absorber module according to one of claims 2 through 11, wherein the cordierite contains from 0 wt.-% to 30 wt.-% silicon carbide (SiC).
13. Solar absorber arrangement with a supporting structure for at least one solar absorber module according to one of claims 1 to 12, wherein the supporting structure has double-walled pipe sockets with return air channels, in whose inner pipe the reduced sections of the absorber cups are accommodated.
14. Method for producing the solar absorber module of claim 4, wherein the absorber cup is produced by: a) a model with dry additions and firing shrinkage additions for production of a hollow plaster mold is created, b) a hollow plaster mold with the external shape of an absorber cup is created, c) the hollow mold is filled with a ceramic slurry, d) water is extracted from the ceramic slurry and a ceramic body is obtained, e) the ceramic body is removed from the hollow plaster mold, and f) the ceramic body is fired at a temperature of 1300 °C to 1450 °C.
15. Method for producing the solar absorber module of claim 3, wherein the absorber cup is produced by: a) a ceramic slurry is granulated in a spray process to form a granulate, b) a hollow mold with the external shape of an absorber cup and a die is created, c) the granulate is filled into an intermediate space between the hollow mold and the die, d) the granulate is pressed at a pressure from 800 bar to 4000 bar.
16. Solar absorber module according to one of claims 1 to 10, with an absorber cup obtained according to a method in accordance with claim 14 or 15.
17. Use of a solar absorber module according to one of claims 1 to 12 or 16 in a solar thermal power plant.