DE2042869A1 - Double-walled cryogenic storage tank - Google Patents

Description

PATENT LAWYERS

DR. PHIL. G. NICKEL ■ DR.-ING. J. DORNER

8 MONKS 15
LANDWEHRSTR. 35 POST BOX TO4

TEL. (OaiiJ 555719

Munich, August 24, 1970 Lawyers' file t 33 - Pat. 2

Cryogenic Engineering Company, 4955 Bannock Otreet, Denver, Colorado 80216, United States of America

JDouble-walled cryogenic oil storage tank

The invention relates to double-walled cryogenic storage containers or Dewar ¹ see bottles.

To limit the flow of heat to cryogenic storage tanks a large number of design proposals have already been made. Various systems of this type involve constructions to recover the cold from the gases that evaporate inside the container. Facilities of this type are for example, in U.S. Patents 3,133,422 and 3,341,052. The constructions described here have several Good heat conducting shields, which are arranged within the vacuum space surrounding the container. The shields are attached to a heat-absorbing fluid line of the container, so that the cold from the evaporating Gases, which pass through the said line, first on this

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Line is transferred and then passes over to the shields in order to jcünien the vacuum space in this way.

A disadvantage of such known designs is that one a relatively large number of shields is required, resulting in a complicated and expensive structure, especially if flags are also arranged in the inner part of the container line.

The use of flags in the inner part of the tank feed line was limited on the one hand to relatively large lines and on the other hand made the manufacture difficult and expensive.

The invention aims to solve the problem, the cold transition to increase or maintain the substances evaporating from the container contents to the vacuum space surrounding the container and at the same time the number of shields required to reduce. A good cold transfer from the evaporating gas to the vacuum space should also be ensured here be when container feed lines or container necks of proportionately small diameter are provided.

With a double-walled low-temperature storage tank with a cold inner wall separated from a warm outer wall by a vacuum space and one made of material ringer thermal diffusivity existing, certain cross-section having container line, which from the container inner wall extends through the vacuum space to the container outer wall, the object is achieved in that the thermal conductivity of the container line in a certain intermediate section between the inner wall of the container and the outer wall of the container is increased and that at least on the length of this intermediate

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section is the effective cross-section of the .container line for the Flow of the substance evaporating from the container contents to increase its flow rate and thus to increase the flow rate. Enlargement of the cold transition to the relevant container pipe section is decreased.

The flushing line and the venting line of the relevant container or vessel are made of material with a low thermal diffusivity. According to a preferred embodiment is a certain section of the pipe or the neck of the container between its ends with a sleeve-like Surrounding ring of high thermal diffusivity, which is so effective that it surrounds the neck or container supply pipe enclosed by it gives a high thermal diffusivity in the mentioned section. The ring should be at least 25 mm long be, so that he has at least an equally long piece of the container supply line in the sense of an increase in thermal diffusivity influenced. In addition, the flow rate of the gas evaporating from the container contents in the said ring Surrounded length of the container supply line enlarged by a packing in the flow path. It turned out that that this increase in the flow rate also leads to an increase in the amount of cold discharged from the container supply line flowing through, evaporating gases passes over to the ring mentioned. It has also been shown that this effect is reinforced if the packing consists of fine fiber material of low thermal conductivity, for example from Terephthalic ester polymer fibers, which are packed within the container neck or the container feed line, at least on the length piece are arranged on which the container neck is surrounded on the outside by the sleeve ring. There is a shield on the latter attached, which extends through the vacuum space surrounding the vessel, so that the in the manner described above

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carried cold can be distributed in the vacuum space.

It should be noted here that in order to achieve good cold transmission in addition to the shields, the ring, which conducts heat well, appropriately surrounds the container neck in an area which is colder than the shield if it were not connected to the ring.

In the following, the description will make the invention more preferred Embodiments with reference to special features and advantages as well as with reference to the attached Drawings explained in more detail. In the drawings, parts that correspond to one another are given the same reference numbers in the individual figures Mistake. Furthermore, the representations are not necessarily to scale, but only show the basic principles Structure of the embodiments according to the invention clearly. They represent:

Figure 1 is a side view of a Dewar · see vessel of a type to which the invention can be applied,

FIG. 2 shows a partial section corresponding to the section line 2-2 and shown in FIG

Figure 5 shows another embodiment of the invention, which is particularly suitable for use on behave-

"nism-moderately small tank lines, for example

wise vent lines, is applicable.

The Dewar ¹ shown in Figure 1, usual see vial 10 has a neck 12 from which an outlet tube protrudes H. The neck 12 is provided with a flanged cover 16 in which a vent valve 18 is provided. In Figure 2

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this construction is shown cut open, so that on the Dewar ¹ see vessel 10 an outer jacket 20 can be seen which encloses an inner container 22 for a low-temperature medium, not shown. .The space between the two walls 20 and 22 is evacuated, so that an insulating vacuum space 24 is created »

The surrounding vacuum space preferably contains an insulation filling, for example of a type known per se. An insulation filling with a certain number of radiation shields 26 which are separated from one another by a fiber material 28 of low thermal conductivity is very suitable for this purpose. For the sake of simplicity of illustration, only a small part of this insulation is shown in the drawings, but in practice the vacuum space 24 is generally completely filled with such a layered insulation. A more detailed description of such a multilayer insulation can be found in the publication "Multiple Layered Insulation for Uryogenic Application ¹¹ by Dr. Richard H. Kropschot, Cryogenics, March 1961, Volume 1, Mr. 3. A specific powder made opaque can also be used as the insulation filling which is placed in the vacuum space, but since these details do not form an essential part of the invention, further description is superfluous.

The inner wall of the container 22 is opposite the outer wall of the container 20 via a neck tube or line 30 of low thermal conductivity supported, this neck tube 30 preferably made of glass fiber reinforced epoxy resin or stainless steel is and a wall has such a small Dioke, as given for the support of the inner container 22 and its content required strength just about permissible is. The neck tube 30 is surrounded by a King 32 of high thermal conductivity, for example made of aluminum, and is attached to the

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The outside of the neck tube 30 is suitably secured to ensure that good thermal contact is achieved between the neck tube and the ring. The ring 32 is effective in the sense of increasing the thermal conductivity of the part of the neck tube 30 which it surrounds. In this regard, it has been found that the height of the ring (namely, the distance between the lower surface 34 and the upper surface 36) must be a minimum of about 25 mm in order to provide an area of desired expansion on the neck tube 30 with increased thermal conductivity to lend. Successful attempts have also been made with rings the length of which was not less than about 100 mm, but it should be noted that the temperature difference ψ between the end faces 34 and 36 of the ring is only a few degrees. The effective thermal length of the neck tube 30 is thus reduced by the ring. The total length of the neck tube must therefore be increased accordingly in order to keep the heat transfer from the surroundings of the vessel via the neck tube 30 to the inner container 22 sufficiently small.

On the ring 32 a very good heat-conducting casing 38 is attached, which runs within the vacuum space 24 and the inner container 22 surrounds. Inside the haler tube 30 is a further conduit tube 40 made of a material of low thermal conductivity arranged so that a t annular space 42 arises between the two tubes. The top of the inner tube 40 is closed by means of a cap 44 in which a pressure relief valve or the like is arranged. From the inner container 22 evaporating gas must therefore rise via the annular space 42 and pass through a ventilation opening 48 in the halo tube 30 so that this gas passes through the outlet tube 14 to the outside.

If the jacket or shield 38 were not with the hanging 32 connected, it would have a temperature which depends on its

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Order between the container outer wall 20 and the container inner wall 22 would be dependent. Therefore, in order to be able to transfer the cold generated by the evaporating gas to the shielding, must the ring 32 in a region of the outer neck tube 30 surrounds it, which is at a lower temperature than that which would take on a shroud not associated with the King.

In the iLonstruktion according to the invention a packing 50 of fine fiber material of low thermal conductivity is also used, which consists of a terephthalate polymer which is commercially available under the trade name "Dacron". Pipes of this type have a diameter of more than 10 × 10 mm and less than approximately 100 × 10 mm and are arranged within the junction space 42 in the region of the ring 32. For the purposes in question here, packing material also includes metal foil, highly conductive screens and close-meshed metal fabrics, but it will be apparent from the following description that the best results are achieved when essentially non-conductive fiber packing material is used . In any case, the packing material acts in such a way that the cross-sectional area of the king space 42 is displaced and thereby the speed of the evaporating gas as it passes through the area defined by the ring 32 is increased. In addition, the fine fibers dampen certain heat-generating vibrations that otherwise occur. The packing material further increases the turbulence in the flow of the evaporating gas and, in the case of a metallic packing means, also creates a path for the transfer of cold from the inner tube 40 to the outer throat tube 30. Regardless of the type of packing material used, it is achieved by increasing the flow rate of the evaporating gas that the cold transition to the ring 32 _;

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to the shield 38 and thus to the vacuum space 24 is improved and enlarged. Of course, you have to restrict the outflow of gas certain .tacking plugs used in the past, bolts However, stoppers have caused considerable difficulties because they prevent the formation of kegs in the painting tube of the vessel in question favored. The invention avoids the undesirable side effects occurring here, since even in the In the event of a failure, the gases vaporizing from the container are still via the inner neck tube 40 and the pressure relief valve 18 can get outdoors.

The construction described above also results in a considerable increase in the surface over which the evaporating Cold generated by gases can be transferred. The vaporizing gases flow over the entire surface of the Packing material as well as the inner and outer surfaces of the neck tubes adjoining this, so that the cold of the evaporated Gas on the King 32 both by forced convection when the gas is forced through the King room and, at least with metallic .Fackungmaterial, by heat conduction in the solid from the inner throat tube 40 over the metallic packing material and over the area surrounded by the ring 32 the neck tube 30 is transmitted. It turns out that the best results are achieved when the packing material at least over a length of the king space, which corresponds to the length of the king 32 surrounded.

Occasionally the vaporizing gas flows from the boiling contents of the container from the Dewar ¹ see vessel at extremely high speed. This occurs, for example, during filling or when the vessel is damaged and the vacuum in the isolation room is lost. For these cases it has

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Proven to be useful, a pressure relief valve on the inner or central üalsröhre 40 to be provided.

It has been shown that the above-described, inventive K. construction on the one hand allows only a minimal heat transfer in the downward direction towards the inner parts of the storage tank, while on the other hand a considerable one Amount of cold of the evaporating gas on the vacuum space of the vessel can pass. This result is proportional by a simple construction, namely by the ring 32, which surrounds the neck tube 30 of low thermal conductivity and reached by the packing, which the space between the inner and the outer throat tube at least over the length of the area surrounded by the neck is filled in such a way that one can be heard {Flow rate of the evaporating gas results. The construction therefore avoids the need for a large one number of heat transfer shields as used up to now. The invention will rust as well as the effort involved in the production of Dewar vessels is reduced. At the same time, the efficiency of the overall insulation of the vessel is improved. Jöine further improvement of the efficiency results when fine fiber material of low conductivity is used as the packing.

The annular space 42 between the inner and outer neck tubes 40 and 30 preferably has a width of about 1.6 mm to 3.2 mm and the height of the ring is preferably between about 25 mm to 100 mm for Dewar ¹ see vessels with a Capacity between 50 1 and 500 1. The height of the ring 32 can deviate from the specified height range, but then the effectiveness of the construction decreases rapidly if the height is less than 25 mm. If the height is greater than about 100 mm, an inconveniently long neck tube sometimes results.

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As already noted, in a preferred embodiment of the invention a packing material was used which had fibers made of terephthalate polymer with diameters between 10 [beta] 10 "^ mm and 100 x 10" ^ m. This fine fiber packing was placed in the low thermal conductivity inlet of a Dewar ¹ vessel of 50 liter capacity in the manner described above, and the vessel was subjected to heat transfer tests to determine the rate of evaporation. It was found that the losses were only 1.2 i * per day, which represents a considerable improvement over the cold losses, as are to be expected with corresponding vessels without the features according to the invention.

fc The figure given is even a significant improvement over the results of another, otherwise similarly designed Dewar ¹ see experimental vessel, in which only a 16 mm copper sieve was arranged in the area of a 25 mm ring. This so-called copper sieve vessel resulted in a loss of cold of 1.6 ^ per day, which is still a significant improvement over corresponding, conventional vessels. In any case, it should be noted that the embodiment with the fine fiber packing represents an improvement of 25 # over the already good results which are achieved with the copper sieve vessel. For the person skilled in the art it is surprising that the results mentioned with the constructions according to the invention by a relatively significantly lower effort than with

"known vessels can be achieved.

It has also been found that additional jackets or shields and rings are used with good results can. In this case, however, the ring 32 assigned to the colder shield is shorter than that assigned to the warmer shield Run ring. In any case, however, for a given amount of cold of the evaporating gas, which in the Vacuum space of the vessel is to be transferred, the required

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Number of shields 38 is not the number that was previously required in corresponding constructions of a known type was in which no elements corresponding to the elements 32 are used in conjunction with an associated flow obstacle as shown by the packing material 50 within the annulus 42 of the invention.

So far, the invention has been described using the example of relatively large neck tubes which serve to support the inner container of the vessel and its contents. Often, however, small ventilation tubes are led from the inner container of the vessel through the vacuum space to the outer wall of the vessel. It may be inexpedient to arrange a special tube within the vent line, but it is advantageous to apply the inventive concept to such small pipelines as well. An example of this is shown in FIG. A vent line 60 extends from the container inner wall 22 to the container outer wall 20. In the present example, the vent line 60 is shown straight, but such tubes are generally bent several times before exiting the container outer wall for a variety of reasons. The vent line 60 is surrounded by a ring 62, which corresponds to the ring 32 of the previously described embodiment of the invention on the container neck. The ring 62 has a lower surface 64 and an upper surface 66 and is connected to a shield 68 which is in the above-described manner extends through the vacuum space.

The vent line 60 is at least one defined by the lower surface 64 and the upper surface 66 of the ring 62 Length over the entire cross-section with one pack 70 made of terephthalic ester polymer fibers. In this way the packing material 70 can control both the flow velocity and the turbulence of the fluid flowing through the tube 60, increase vaporized gas in an effective manner.

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Both the increased flow velocity and the increased turbulence cause an increase in the transition velocity the cold of the evaporated .Behältinhaltes on that part of the wall of the tube 60, which is surrounded by the ring 62. The amount of cold, which can therefore pass from the ring 62 to the shielding • 68, is therefore significant over that amount of cold in addition, which could be transferred in the absence of either the ring or said packing. Here too will just as in the first-described embodiment, the need for the large number of shields required hitherto avoided, while at the same time a vent line made of material of low thermal conductivity are used can, so that the flow of heat into the container is reduced, which from the ambient air through the walls of the vent line 60 can reach the inner container 22

After the invention has been explained above on the basis of preferred exemplary embodiments, the person skilled in the art has a large number of possible modifications in the form and in the details, which, however, are also encompassed by the underlying principle of the invention. For example, while the invention has been described above with reference to the usual Dewar's neck vessels, those skilled in the art will readily recognize that the invention is also ^{applicable to large, horizontally lying Dewar's 1} see containers, such as are sometimes placed on vehicle platforms. In addition, the area to be formed with increased thermal conductivity can also be formed directly as part of the container line instead of a ring and part of the narrowed area of the line can be produced by reducing the diameter in a certain section. However, the person skilled in the art can undertake modifications of this kind on a case-by-case basis without further description.

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Claims (18)

Claims 1 .jjj double-walled cryogenic storage tank with a a warm outer wall separated by a vacuum space, cold inner wall of the container and with a certain cross-section consisting of material of low thermal conductivity having container line, which extends from the inner wall of the container through the vacuum space to the outer wall of the container, characterized in that the thermal conductivity of the Behäi- f pipe (30 or 60) in a certain intermediate section between the inner wall of the container (22) and the outer wall of the container (20) is increased and that at least the length of this intermediate section of the effective cross section of the container line for the Flow of the substance evaporating from the contents of the container for enlargement of its flow rate and thus to increase the cold transfer to the relevant container line section is reduced (50, 70). 2. Storage container according to claim 1, characterized in that the length of said intermediate section of the container line is at least 25 mm. μ 3. Storage container according to claim 1 or 2, characterized by means (50, 70) for increasing the turbulence of the flow of the substance evaporating from the container contents in the area of the reduced flow rate. 4. Storage container according to claim 3, characterized in that the means for increasing the turbulence of the flow of a Pack (50, 70) are formed from fiber material. - 13 - 109820/1277 2047869 ft 5. Storage container according to one of claims 1 to 4, characterized characterized in that to increase the thermal conductivity of the container line (30 or 60) this is surrounded by a ring (32 or 62) made of very good thermal conductivity material, the Length of said intermediate section corresponding length is at least 25 mm. 6. Storage container according to claim 5 _t, characterized in that on the ring (32 or 62) a through the vacuum chamber (24) extending, very good heat conductive shield (36 or 68) is attached, via which the cold of the container contents evaporating substance is transferred to the vacuum space. 7. Storage container according to one of claims 4 to 6, characterized in that in a heat-transferring arrangement with that ! Part of the inner surface of the container line (30 or 60), which on the outside of the very good heat-conducting King (32 or 62) is surrounded, the or a to reduce the flow cross-section serving pack (50 or 70) is provided. 8. Storage container according to one of claims 1 to 7, characterized characterized in that the means for reducing the effective flow cross-section or the convexity made of fiber material (50 or 70) have a thermal conductivity which corresponds approximately to that of terephthalate polymer fibers. 9. Storage container according to one of claims 1 to 8, characterized in that the means for reducing the effective Flow cross-section or the convolution made of fiber material (50 or 70) contain fibers with a diameter of less than 100 x 10 mm. 10. Storage container according to claim 9, characterized in that that the fibers consist of terephthalate polymer. -H- 109820/1277 11. Storage container according to one of claims 6 to 10, characterized in that within said container line (30) a further line (40) of low thermal conductivity is arranged which, with the container line, forms an annular space (42) forms for the flow of the substance evaporating from the container contents that furthermore the means (50) for reducing the effective Flow cross-section are arranged in this annular space and that means (18) are provided which normally allow the escape of the substance evaporating from the container contents Prevent via the second line (40) (Figure 2). 12. Storage container according to claim 11, characterized in that the devices (18) which allow the escape of the container contents Prevent evaporating substance via the second line (40) normally on a certain overpressure in the container are set and when this overpressure occurs, the substance evaporating from the container contents to relieve this Let the pressure escape through the second line. 13. Storage container according to claim 11 or 12, characterized in that that the means for reducing the effective flow cross-section as a pack in a heat-transferring arrangement with the outer surface of the second conduit (40) and the inner surface the first line (30) are provided between these two parts. 14. Storage container according to one of claims 11 to 13, characterized characterized in that the second conduit (40) is no more than 3.2 mm apart from the first conduit (30). 15. Storage container according to one of claims 1 to 10, characterized in that the means for reducing the effective Through flow cross-section or the packing made of fiber material Extend over the entire cross section of the container line (60) (Jigur 3). - 15 - 109820/1277 16. Storage container according to one of claims 7 to 15 and / or claim 6, characterized in that at least one second very good heat-conducting King is provided in the vacuum space, which at least one second wiper section on the outer surface of the container line surrounds it in such a way that it conducts heat well Contact with this outer surface of course, the height of the king, which is closer to the cold inner wall of the container, being less than is the height of the king further removed from the cold inner wall of the container. 17. storage container according to claim 16, characterized in that that with each of the mentioned Kinge good heat-conducting A-shields are firmly connected, which are in each case in the vacuum space ™ extend into it. 18. Storage container according to claim 16 or 17 »characterized in that that the ring closer to the cold inner wall of the container has a height or length of at least 2i? mm seated. - 16 - 109820/1277