DE3146017A1 - Thermal insulation - Google Patents

Abstract

The invention relates to thermal insulation (1), especially for a high-temperature storage battery. The thermal insulation (1) is formed by a double-walled housing (2). A cavity (6) is provided between the two walls (3A and 2B) of the housing (2). This cavity (6) is filled with at least three fine-grained, powdery insulating materials (3, 4 and 5). The insulating materials used comprise, in particular, powdery means which can be mixed with one another and are optically opaque to infrared. The cavity is additionally evacuated and has only a residual gas pressure of 1 to 10 mbar. <IMAGE>

Description

Thermal insulation

The invention relates to thermal insulation according to the Preamble of claim 1.

Such thermal insulation is used in energy technology, especially in facilities where the loss of heat is avoided target.

Thermal insulation is mainly used in high-temperature storage batteries based on alkali metal and chalcogen used with thermal insulation are surrounded to allow the storage cells to cool down, especially during breaks in operation to prevent.

Until now, it has been common for such high-temperature storage batteries To use insulation, for example made of glass wool or mineral wool are.

These insulations must be used to achieve a sufficient effect Considerable wall thicknesses are provided because of the high temperature storage batteries work at temperatures that are around 3500. This thermal insulation must be constructed in such a way that the temperatures specified above during the breaks in operation, the days can be maintained.

As such thick-walled insulation the dimensions and / or the weight Significantly enlarge the high temperature storage battery is the energy storage density i.e. the electrical energy that can be saved per unit of weight or volume, small amount. This is especially true for such high temperature electrochemical storage batteries disadvantageous for the energy supply of electrically operated vehicles should be used.

It is another thermal insulation for high temperature electrochemical storage batteries known. This is essentially formed by an evacuated cavity inside whose metal foils are arranged.

These metal foils consist, for example, of aluminum and are arranged at a predeterminable distance from one another. The cavity is made by metallic Walls limited, which are provided with a small coefficient of thermal expansion. To prevent the boundary walls from sagging due to the existing vacuum to be avoided inside, rod-shaped supports are in the interior of the cavity between arranged parallel to each other extending boundary walls. The support elements however, cause a large flow of heat from the inside of the insulation to the outside there. This results in the low conductivity achieved with the metallic foils the isolation is largely lost again.

The invention is therefore based on the object #, thermal insulation to create that is as light and thin-walled as possible, and its thermal conductivity at operating temperatures of 3500C and more below l <5 ~ 10-3W / (m ~ K) lies. Furthermore, the thermal insulation should be designed so that on rod-shaped Support elements in the cavity of the insulation completely waived will be on.

The solution takes place according to the characterizing part of claim 1.

The cavity forming the thermal insulation is at least 3 powdery, mixed, infrared optical opacifiers full constantly filled out. According to the invention, a first opacifier is used for this purpose, which has at most a primary particle size of 0.01 to 0.03 # m and a large one Has refractive index in the infrared. Furthermore, the filled in the cavity, powdered mixture a second infrared potic opacifier, which has a primary part ohm diameter of at most 0.2 to 0.5 # m. The second opacifier has more advantageous Way a needle-shaped crystal structure. In particular, the longitudinal axes are the needle-shaped crystals arranged perpendicular to the course of the temperature gradient. The second opacifier is advantageously a ferromagnetic one Material. Titanium oxide is preferably used as the first opacifying agent, while magnetite Fe304 is used as the second opacifier. As a third antifouling agent powdered zirconium oxide, thorium oxide, tantalum oxide, hafnium oxide, uranium oxide, Chromium oxide, cerium oxide, yttrium oxide or other rare earth oxides are used. This third opacifier has a primary part diameter of 1 to 5P> m on. The first two infrared optical opacifiers can be used in mixing ratios between 1 ~ 2 to 10: 1 parts by weight of titanium oxide and magnetite as insulating material be filled into the cavity. The third opacifier is used in one concentration from 0.1 to 0.3 g / cm3 the two mixed with other opacifiers. The selection of the third optical opacifier from the metal oxides listed above is temperature-specific.

One of the metal oxides is preferably used as the third optical opacifier selected that has a high refractive index in the infrared and that of all metal oxides Has the lowest solid-state conductivity at the possible operating temperatures. All three opacifiers filled in the cavity have a high porosity. A low porosity of the mixture means a high density, which in turn means a high solid-state conductivity of the mixture means, while with too high a porosity the powder mixture becomes transparent again in the infrared. The three infrared optical Opacifiers can, for example, in a mixing ratio of 1: 1: 1 and one Density of S C 0.75 g / cm3 can be fed into the cavity. A mix ratio of 2 parts by weight of titanium oxide, one part by weight of iron oxide and two parts by weight Zirconium oxide with a density of 2 o 0.65 g / cm3 is also possible. The three Powdery opacifiers can be added when filling or at an earlier time Time to be mixed together. With a residual gas pressure of at most 1 to 10 mbar inside the cavity is achieved when using one of the mixing ratios given above For example, at a temperature of 300ob, a thermal conductivity A c 5 ~ 10-3 W / (m ~ K) reached. By filling the cavity with the three mixed together Infrared optical opacifiers keep the metallic boundary walls of the same a sufficient support in many applications. In any case it is the three infrared optical opacifier comprising powdery mixture with a to fill the cavity with such porosity that the metallic ones Boundary walls even with a very low residual gas pressure p. = 0.1 mbar-don't see bending inward too much. If the circumstances so require, this can be done by the opacifiers comprehensive powdery mixture for better support of the boundary walls at least arranged in areas with a lower porosity within the cavity will. In this case, however, an increase in the solid-state conductivity of the mixture must be achieved be accepted in these areas.

The thermal insulation of the insulation according to the invention is not overall impaired if these areas are chosen as small as possible. Naturally the compressive strength of the insulation can also be increased by the fact that the Mixture comprising opacifying agents, an addition of about 50 to 60% by weight, based on the total weight of the finely divided silica used in the insulation material added and the mixture is highly compressed.

To increase the flexural strength, 5 to 10% total microfibers can be used be added as an addition. The specified weight refers to the Total weight of the insulation material used. In the case of the fibers that make up the infrared optical Opacifiers are added, it is glass or ceramic fibers, in particular Fibers made of zirconium oxide, thorium oxide, tantalum oxide, hafnium oxide, cerium oxide, uranium oxide, Chromium oxide, yttrium oxide or other oxides of the rare earth metals. The fibers must just like the crystal needles of magnetite perpendicular to the course of the temperature gradients be placed within the cavity. The fibers used should have a diameter of at most 15 µm and a length of not more than 5 to 10 mm. Sol the thermal insulation have a particularly high pressure resistance, so can from the above Mixture plates are pressed with which then the cavity is filled.

The thermal insulation can advantageously not only be used for the insulation used by facilities that maintain a temperature between 300 and 600ob have, rather there is the possibility of this thermal insulation can also be used in the high temperature range. In particular, the isolation comes to the Example as thermal insulation for pipeline networks in question for transportation of flowing media are provided.

This thermal insulation is suitable for temperatures of 8000C and more designed. For the thermal insulation of pipe systems that extend over several km extend, this insulation is particularly suitable.

According to the invention, the cavity forming the insulation is at least 3 intermingled opacifiers filled with a high refractive index in the infrared and are therefore particularly suitable for radiation extinction. The addition of magnetite to the titanium oxide increases the radiation absorbance.

This allows the T3 dependence of the radiation conductivity reduce even better than with pure titanium oxide. As mentioned earlier, the second is Opacifiers used in particular magnetite, as this is partly needle-shaped Has crystal structure.

According to the present invention, these needle-shaped crystals become when filled of the powder mixture into the cavity with the aid of an externally applied magnetic field ordered so that their long axes are perpendicular to the direction of the temperature gradient are aligned. The orientation of the crystal needles of the magnetite is then through compacting the powder mixture, for example by Shaking or Presses fixed in such a way that a different orientation of the needles is no longer possible. This measure suppresses the radiation conduction and the solid-state conduction favored. The orientation of the needle-shaped crystals of magnetite in the above indicated direction causes a reduction of the solid state conductivity, since the Heat flow is directed in the direction of the longer axes in the crystal needles.

Furthermore, this increases the radiation conductivity through increased scattering cross-sections reduced. A further reduction in radiation conductivity can be achieved the addition of the somewhat coarser zirconium oxide or one of the above-mentioned metal oxides achieve. The particle diameter of the zirconium oxide or the metal oxides listed above, which come into question as a third optical opacifier is chosen so that it is optimal large scattering cross-sections can be achieved. For this purpose, the particle diameter for a temperature of 300ob be around 2 to 0Alm. So that the somewhat coarser particles the third opacifier does not increase the solid-state conductivity of the mixture, a material with very low thermal conductivity is used. The first Both opacifiers are caused by the much smaller particle diameter in each case only small proportions of solid-state conduction in the mixture. Zirconium oxide is particularly suitable and thorium oxide as the third optical opacifier as they are different from all of the above Metal oxides only have an extremely low thermal conductivity at high temperatures exhibit in the solid state.

According to the invention, the magnetite filled in the cavity is additionally used to create the vacuum in the cavity. In particular, the The fact made use of the fact that the magnetite Je304 is also present in the shape FeO ~ Fe203 is present. When this material is heated, oxygen is absorbed of FeO, this being converted into a higher degree of occlusion, in particular into Fe203 will. By binding the oxygen to the iron oxide, the partial pressure of the oxygen present in the cavity is additionally broken down. The magnetite acts as a 02 getter, especially at high temperaturesi #.

The invention is explained below with reference to drawings.

1 shows a vertical section through an electrochemical one High-temperature storage battery with thermal insulation, FIG. 2 is a horizontal section by the high-temperature storage battery shown in Fig. 1, Fig. 3 one for hot flowing media provided pipeline with the thermal according to the invention Insulation.

Fig. 1 shows the thermal insulation according to the invention, which is around a High temperature storage battery is arranged. The thermal insulation 1 includes essentially a double-walled housing 2. This is cuboid-shaped, hollow inside and made of stainless steel. Between the two metal walls a gas-tight cavity 6 is formed in the housing 2. The dimensions of the cavity 6, especially its width, is to the desired thickness of the according to the invention thermal insulation 1 matched.

The outer metallic boundary surfaces 2A of the housing 2 are connected to one another in a gas-tight manner, in particular welded to one another. The same applies to the inner metallic boundary surfaces 213 of the housing 2 achieves that the cavity 6 lying between the metallic walls is gas-tight is locked. Before the final gas-tight sealing of the cavity 6 is this is filled with a powdery mixture which, according to the invention, consists of at least three infrared optical opacifiers X, 4 and 5. With the one described here In the exemplary embodiment, the first opacifier 3 consists of titanium oxide, as the second Opacifier II, magnetite is used. As a third infrared optical means for example, zirconia can be used. There is also the possibility vhorium oxide, tantalum oxide, hafnium oxide, cerium oxide, uranium oxide, chromium oxide, yttrium oxide or to use another oxide of the rare earth metals. With the one described here Examples are the infrared optical opacifiers 3, 4 and 5 in a mixing ratio 1: 1: 1 is filled into the cavity 6. The powdery mixture has a porosity # t, which is between 0.85 and 0.95. Inside the cavity 6 is a gas pressure aimed at, which has a maximum value of 1 to 10 mbar. A residual gas pressure 0.1 mbar is desirable. To increase mechanical stability, in particular the load-bearing capacity of the thermal insulation according to the invention is the optical one Opacifiers 3, 4 and 5 an addition of highly disperse silicas 7A and fibers 7B mixed in. In the exemplary embodiment described here, the weight proportions are of the highly disperse silicas 7A about 50 to 80% by weight, while the proportions by weight of fibers 7B about 5 to 10 wt.%. The information in% by weight relate to the total weight of the insulating material used. Preferably becomes the powder fiber mixture comprising the infrared optical opacifiers 3, 4 and 5 doped with glass or ceramic fibers 7B. The fibers 7B used here become together filled with the opacifiers 3, 4 and 5 in the cavity 6 in such a way that their The direction of expansion is arranged perpendicular to the course of the temperature gradient. The diameter of the fibers 7B used here is less than 15 m. The fibers 7B are no longer than 5 to 10 mm. The one shown in Fig. 1 and described here At 300ob insulation only has a thermal conductivity of A z 5 x 10-3 W / (m ~ K).

As mentioned above, the thermal insulation is 1 by one High temperature storage battery arranged, which consists of one or more storage cells 8 is based on sodium and sulfur. The memory cells 8 are arranged inside the housing 2, which forms the thermal insulation 1. she are only shown schematically in the embodiment shown in FIG.

The memory cells 8 are electrically conductive with the interposition of Components 9 supported on an inner boundary wall of the cuboid cavity 6. Here, the electrically conductive components 9 are used for electrical connection of the outer walls of the storage cells 8, which form an electrical pole of the storage cells 8 form. The second electrical poles of the memory cells 8, which are connected to the The upper ends of the same are connected to one another via an electrical line 10 tied together. This is electrically insulated (not shown here) to the outside.

As already mentioned above, the second opacifier is powdery Magnetite is filled into the cavity 6. This magnetite has a needle-shaped crystal structure on. According to the invention, these needle-shaped crystals are when filled into the Cavity 6 oriented with the application of an external magnetic field so that the longitudinal axes their needles are oriented perpendicular to the temperature gradient.

FIG. 2 shows a horizontal section through the one shown in FIG High-temperature storage battery 1. This drawing clearly shows the orientation of needle-shaped magnetite crystals perpendicular to the course of the temperature gradient to see. In this example the opacifiers 3, 14 and 5 are in a mixing ratio 1: 1: 1 and a density of 2 t 0.75 g / cm3 is filled into the cavity 6.

Fig. 3 shows a further embodiment of the thermal insulation 1. In the example shown here, this is arranged around a pipeline system 20, within which hot flowing media, such as gases, are transported. Fig. 3 shows only a limited section of this pipeline system 20. The thermal Insulation 1 is in turn closed off to the outside by a gas-tight one Cavity 6 is formed. The two boundary walls of the cavity 6 are through two Tubes 21 and 22 formed which have different diameters. In particular is the smaller diameter tube 21 concentric within the Tube 22 arranged. This creates an even space between the two Tubes 21 and 22 created as a cavity 6 for the thermal insulation 1 serves. At the ends of these two tubes 21 and 22, the cavity is made of metal Ring disks (not shown here) sealed gas-tight. The inside of the cavity 6 is again with three infrared optical opacifiers mixed with one another 3, 14 and 5 filled out. The first infrared opacifier 3 is titanium oxide. Iron oxide, in particular magnetite, is used as the second opacifying agent 14. That third infrared optical opacifier 5 consists for example of zirconium oxide. However, another metal oxide can also be used, and in particular are also the metal oxides mentioned in the description of FIG. 1 are suitable for this purpose. In the The needle-shaped crystals of magnetite are used to produce the thermal insulation also aligned and fixed in this embodiment so that they are perpendicular to Direction of the temperature gradient are arranged permanently. The gas-tight, with the three opacifiers filled cavity 6 is evacuated so far that he still has a residual gas pressure of 1 to 10 mbar.

The invention is not limited to that shown in FIGS 3 illustrated embodiments, rather it includes all thermal insulation, in which at least three infrared optical opacifiers are used as insulating material be filled into an evacuated cavity.

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Claims (17)

Claims 11 thermal insulation with at least one closed Cavity which is filled with a powdery insulating material, characterized in that that the cavity (6) has at most a residual gas pressure of 1 to 10 mbar and with at least three fine-grained powdery insulating materials (3, 4 and 5), the have a high porosity, is completely filled. 2. Thermal insulation according to claim 1, characterized in that that the cavity (6) with three powdery, mixed together, infrared optical Opacifiers (3, 4 and 5) is completely filled out. 3. Thermal insulation according to one of claims 1 or 2, characterized characterized in that the first infrared optical opacifier (3) is at most one Primary particle size from 0.01 to 0.03 m and has a large refractive index exhibits in the infrared. 4. Thermal insulation according to one of claims 1 to 3, characterized characterized in that the second infrared optical opacifier (a) has a primary particle diameter knife from 0.2 to 0.5 m and has a large refractive index in the infrared. 5. Thermal insulation according to one of claims 1 to #, characterized characterized in that the third infrared optical opacifier (5) has a primary particle diameter from 1 to 5 m and has a large refractive index in the infrared. 6. Thermal insulation according to one of claims 1 to 5, characterized characterized in that the third infrared optical opacifier (5) at all operating temperatures has the smallest solid-state thermal conductivity. 7. Thermal insulation according to one of claims 1 to 6, characterized characterized in that the three infrared optical opacifiers (3, 4 and 5) Addition of 50 to 80% by weight, based on the total weight of the insulating material, of highly disperse silicas (7A) is added. 8. Thermal insulation according to one of Claims 1 to 7, thereby characterized in that the infrared optical opacifiers (3, 11 and 5) to increase glass or ceramic fibers (7B) are added to the flexural strength. 9. Thermal insulation according to one of claims 1 to 8, characterized characterized in that the infrared optical opacifiers (3, 4 and 5) 5 to 10 Weight%, based on the total weight of the insulating material of glass or ceramic fibers (7B) are added. 10. Thermal insulation according to one of claims 1 until 9, characterized in that the second opacifying agent (4) is needle-shaped Has crystal structure. 11. Thermal insulation according to claim 1 to 10, characterized in that that the long axes of the needle-shaped crystals of the second opacifier (#) are arranged perpendicular to the course of the temperature gradient. 12. Thermal insulation according to one of claims 1 to 11, characterized characterized in that the second opacifier is ferromagnetic. 13. Thermal insulation according to one of claims 1 to 12, characterized characterized in that the first opacifying agent (3) is titanium oxide. 1#. Thermal insulation according to one of Claims 1 to 13, characterized characterized in that the second opacifier (#) is magnetite (Fe304). 15. Thermal insulation according to claim 1 to 1 #, characterized in that that the third opacifier (5) zirconium oxide, thorium oxide, tantalum oxide, hafnium oxide, Cerium oxide, yttrium oxide, uranium oxide, chromium oxide or another oxide of the rare earth metals is. 16. Thermal insulation according to one of claims 1 to 15, characterized characterized in that the two infrared optical opacifiers (3 and #) in mixing ratios between 1: 2 to 10: 1 parts by weight of titanium oxide (Ti02) to iron oxide (Fe30 #) in the well-being space (6) are filled. 17. Thermal insulation according to one of Claims 1 to 16, thereby characterized in that the third opacifying agent (5) in the concentration of 0.1 to 0.3 g / cm3 is added to the first two opacifiers (3 and 4).