US2916179A - Thermally insulated storage vessels - Google Patents

Description

Dec. 8, 1959 A. G. MONROE THERMALLY INSULATED STORAGE VESSELS Filed Dec. 1'7, 1958 Inventor 4041/ 6656018} you f y QM M Attorney United States Patent 2,916,179 THERMALLY INSULATED STORAGE VESSELS Adam Gregory Monroe, Cheam, England, assignor to The British Oxygen Company Limited, a British com- P y Application December 17, 1958, Serial No. 781,158

Claims priority, application Great Britain January 13, 1958 3 Claims. (Cl. 220-15) This invention relates to thermally insulated storage vessels for the storage of liquids at temperatures substantially above or substantially below atmospheric temperature. The invention is particularly applicable to the storage of liquids having a boiling point substantially below atmospheric temperature, for example, liquid methane and liquiefied atmospheric gases such as liquid oxygen and liquid nitrogen, and for the sake of clarity the invention will be described with reference to the storage of such liquids. It will be appreciated, however, that the same considerations will apply to the storage of liquids at temperatures substantially above atmospheric temperature.

In order to reduce the evaporation losses of liquids, the boiling points of which lie substantially below atmospheric temperature, during storage, the liquids are usually stored in thermally insulated vessels col prising an inner container for the liquid and an outer shell surrounding and spaced from the container, the interspace being filled with a thermal insulation material of fibrous or cellular structure.

It has been observed that the insulation properties of the insulating material deteriorate with time for various reasons.- If the inner container for the liquid is subjected to temperature fluctuations, its overalldimensions vary in accordance with the thermal dilation. Thus, when warming up or cooling down to or from ambient temperature, the movements of the inner container, which is usually, of metal, are transmitted to the insulation surrounding it and have a deleterious elfect'thereon.

When fibrous insulation is used to fill the interspace, the insulation, although originally resilient, gradually becomes less so, owing to the thermal movements of the inner container, which cause the individual fibres to become felted together. Further deterioration of the insulation may then be caused by the ingress of moisture to the interspace and in the case of the storage of liquid at temperatures substantially below ambient its subsequent solidification within the interstices of the insulant. The average thermal conductivity of a mixture of fibrous insulant and ice is substantially higher than that of the dry fibrous insulant.

A mixture formed of fibres and ice is quite'rigid and, once compressed by thermal dilation of the inner container, retains its smaller volume. As a result, on subsequent contraction of the inner container, a void space is formed between the insulation and the container which in the extreme case where moist air has fairly free access to the intersticial spaces in the insulant, would be filled with a layer of ice. It is thus essential to maintain the resilient properties of the insulant and to avoid the formation of voids.

When the cellular type of insulation is used, deterioration of insulating properties also takes place for the following reasons. In the first place, the majority of cellular insulating materials are friable and attrition of the insulant takes place as a result of thermal movements of the inner container. The broken-down par- "ice 2 ticles of the insulant agglomerate andform a, porous body, which has a substantially higher bulk density than the original material and a correspondingly higher thermal conductivity. It further has practically no resilience, forming solid plugs when compressed. Again, when ingress of moisture takes place into the interspace, water may be absorbed by the powdered insulant or even chemically combined therewith, as is the case, for example, with basic magnesium carbonate where the resultant mixture is very similar to and behaves like cement;

It will be seen, therefore, that thermal dilation movements of the inner container may not be accommodated within cellular insulating material, either because the latter has reached its final bulk density and is incompressible, or because it has formed a cement. Consequently, the outer shell of the storage vessel, which is as a rule considerably thinner than the inner container, will be subjected to excessive internal pressure and may be perforated.

It is an object of the present invention to provide a thermally insulated vessel for the storage of liquids at temperatures substantially above or below atmospheric temperature, and particularly for the storage of liquefied gases, the boiling points of which are substantiallybelow atmospheric temperature, in which thermal dilation movements of the inner container are accommodated within the insulation space in such a manner that no deterioration of the insulating performance takes place and the outer shell protecting the insulation is not mechanically affected in any way.

According to the present invention, in a storage vessel for the storage of a liquid at a temperature substantially above or substantially below atmospheric temperature comprising an inner container for the liquid, and an outer shell surrounding and spaced from the inner container, theinterspace being filled with thermally insulating material, thermal movements of said inner container are transmitted to and absorbed by a preformed body of resilient material forming a part of said thermally insulating material.

The thermal movements of the inner container may be transmitted to the preformed resilient material by a body of thermally insulating material in the form of substantially spherular particles freely movable with respect to one another and in contact both with a part of the inner container liable to thermal movement and with the resilient material.

It will be appreciated that in any given case, the particular resilient material and the particular spherular material used must be selected with due regard to the temperature of the liquid being stored.

One arrangement in accordance with the invention is illustrated in the accompanying drawing which shows a sectional side view of a storage vessel according to the invention suitable for the storage of liquefied gases of boiling point substantially below atmospheric temperature, for example, liquid oxygen, liquid nitrogen and liquid methane. The storage vessel comprises a substantially cylindrical inner container 1 for the liquefied gas made of a material the mechanical properties of which do not deteriorate at low temperatures, such as, for example, austenitic stainless steel, copper and its alloys, and aluminum and its alloys. The inner container 1 is surrounded by and spaced from an outer shell 2 which is of thinner material and serves merely to contain the insulating material. It does not contribute to the support of the inner container 1. This is suspended within the outer shell 2 by means of supporting members. These are shown in the drawing as chains 3 but may equally be rods or wires. Each of the chains 3 is connected at one end to a supporting element 4 mounted on the outer wall of the container 1 and at the other to a main structural element supporting the storage vessel indicated at 5. The inner container 1 is therefore free to expand and contract in a vertical direction.

The thermal insulation is contained within the interspace between the inner container 1 and the outer shell 2. This insulation is in three layers. The lowest layer 6 filling the bottom of the interspace consists of substantially spherular particles of insulating material, of average diameter not greater than /8 inch. The spherules may be of any substantially non-friable material having a low thermal conductivity, for example, polytetrafluoroethylene,.nylon, polyvinyl chloride, glass, or slag.

I Directly above the layer 6 of spherular material and in contact therewith is a layer 7 of resilient insulating material, such as, for example, expanded polyvinyl chloride, preformed as a hollow cylindrical body of wall thickness equal to the Width of the interspace. This layer acts as a centering device for the inner container 1, as a sealing device for insulating material placed above it, and owing to its resilience, it accommodates any dis placement movements of the insulation above or below it.

The remainder of the interspace above the layer 7 of resilient material is filled with conventional insulation 8 for low temperature equipment, such as slag wool, mineral wool, expanded aluminium-magnesium silicate known as brelite or perlite, silica aerogel, diatomaceous earth, or a micaceous earth such as vermiculite.

In operation, when the inner container 1 is warmed or cooled by the removal from or introduction into it of a liquefied gas, the container will expand or contract respectively. When the container expands, force is exerted on the bottom layer 6 of the insulant. When under stress the -body of spherular particles behaves like a liquid, and the force exerted on the surface of the layer 6 by the expanding container is transmitted and distributed uniformly within the body of spherular particles with very low frictional losses and negligible compressibility. As a result, the spherular particles are forced downwardly by the expansion of the inner container and rise near the circumference of the outer shell and compress the resilient layer 7.

Similarly, contraction of the inner container 1 causes an upwardmovement of its lower end. The resultant free space directly under the container will befilled by the'spherular particles moved by the expansion of the resilient layer 7 when the thrust exerted by the dilated container is released.

Thus in both the expanded and contracted condition of the inner container 1, no voids are present in the insulation, nor is the outer shell 2 stressed. It will be appreciated, of course, that in filling the insulation space, which will normally be carried out with the container 1 empty and consequently at atmospheric temperature, it is necessary that the resilient layer 7 is compressed against the layer 6 of spherular material to an extent sufficient to ensure that when the vessel is cooled to the desired storage temperature, and the inner container 1 is consequently fully contracted, the spherular material completely fills the interspace below the resilient layer 7, while the latter is uncompressed or only slightly compressed.

I claim:

1. A storage vessel for the storage of a liquid at a temperature substantially different from atmospheric temperature comprising an inner container for the liquid, an outer shell surrounding and spaced from said inner container to define therewith an interspace, a body of thermally insulating material in the form of spherular particles freely movable with respect to one another filling the bottom of said interspace, a body of conventional thermal insulation filling the upper part of said interspace, and a preformed body of resilient material within said interspace separating and in contact with said first and second mentioned bodies of thermally insulated material.

2. A storage vessel according to claim 1 wherein said spherular particles are made of a material selected from the group consisting of polytetrafluoroethylene, nylon, polyvinyl chloride, glass and slag.

3. A storage vessel according to claim 1 wherein said resilient material is expanded polyvinyl chloride.

References Cited in the file of this patent UNITED STATES PATENTS 1,463,498 Burgess July 31, 1923 I 1,866,517 Heylandt July 5, 1932 1,979,221 Dano Oct. 30, 1934 2,110,470 Norton Mar. 8, 1938 2,481,664 Hemp Sept. 13, 1949

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