US3267685A

US3267685A - Container for storing liquids at low temperatures

Info

Publication number: US3267685A
Application number: US436876A
Authority: US
Inventors: Carl E Schroeder
Original assignee: Continental Oil Co
Current assignee: ConocoPhillips Co
Priority date: 1965-03-03
Filing date: 1965-03-03
Publication date: 1966-08-23
Anticipated expiration: 1983-08-23

Description

Aug. 23, 1966 c. E. scHRoEDL-:R 3,267,685

CONTAINER FOR STORING LIQUIDS AT LOW TEMPERATURES Filed March 5, 1965 5 Sheets-Sheet l INVENTOR. C21/PL 6 cHPoe-oe-Q WMM Aug. 23, 1966 c. E. scHRoEDER 3,267,685

CONTAINER FOR sToRING LIQUIDs AT Low TEMPERATURES Filed March 3, 1965 5 Sheets-Sheet 5 INVENTOR CA el. cHpoeof-/e ATTORNEY United States Patent O 3,267,685 CONTAINER FOR STORING LIQUIDS AT LOW TEMPERATURES Cari E. Schroeder, Ponca City, kla., assigner to Contineniai @il Company, Ponca City, kla., a corporation of Oklahoma Filed Mar. 3, 1965, Ser. No. 435,876 22 Ciaims. (Ci. 62-45) This invention relates to a container for confining a body of liquid at relatively low temperatures, particularly, at temperatures below the freezing point of water. More specifically, but no by way of limitation, the present invention relates to a strong, relatively lightweight container which can be economically constructed in either portable or stationary form for storing liquids at a temperature below the freezing point of wate-r.

The storage of large volumes of liquied, normally gaseous materials which, in the liquid state possess a relatively high vapor pressure, presents several problems. Two major problems which are encountered in this type of liquid storage are (a) that which arises from the requirement for a yrelatively eiiicient, thermally inesulating environment for the stored liquid so that its relatively low temperature of storage can be economically maintained, and excessive evaporation or boil off of the liquid can be avoided, and (b) the necessity particularly where large volumes of the liquid are to be stored, of providing a storage tank which is exceptionally strong structurally in order to withstand the vapor pressures which may be developed by vaporization of the stored liquid due to heat exchangewith the environment. It will be noted that these two problems are interrelated in that the eiciency of the insulating coating or barrier provided around the storage container will determine to some extent the requirement for heavy, mechanically strong structural members in the construction of the container. The eiciency of the thermal insulation provided also will be a major factor affecting the cost of any equipment, such as compressors and the like, which must be provided for preventing loss of the stored liquid due to vaporization.

As typic-al of liquids which present some storage diculties as a result of the described problems may be cited liquitied petroleum gases, such as liquied methane, ethane and propane, liquifed inert gases such as liquied helium and liquid nitrogen, and, to some extent, anhydrous ammonia. The large current production of liquied petroleum gases, together with the seasonal market for these materials, results in the requirement that substantial quantities of the materials be stored during certain periods of the year. It has previously been proposed to store normally gaseous materials of this type both in artificial above-ground tanks and storage containers, as well as in earthen cavities or pits. One of the primary motivations in employing the latter type of storage has been the economies which are achieved thereby relative to storage in tanks or other above-ground structures. When the latter have been employed, it has been necessary to use heavy structural materials in fabricating the tanks to obtain the necessary strength to withstand the high vapor pressures, and the expense of such construction has been further increased by the necessity to provide relatively heavy insulation to reduce the rate of heat exchange between the stored liquids and the surrounding environment. Moreover, the necessity to provide liquid tight seals and joints in all locations within the tank contacted by the liquid, and vapor tight seals at other points, has further increased the cost of construction of this type of container so that, in many instances, where even relatively small volumes of the liquiied gases require storage,

Patented August 23, 1966 the use `of above-ground tanks of the type described may become economically infeasible.

The present invention provides an improved container which is especially adapted for the containment of liquids which are normally stored at temperatures below the freezing point of water. Broadly described, the present invention comprises a container formed by a rigid outer shell having a side wall and a bottom, and being open at the top with such outer shell preferably being formed of a mechanically strong material, such as steel. The outer shell is lined with a rigid, thermally insulating material which also has a side wall, and includes a oor overlying the bottom of the outer shell. A groove or trough occupies a horizontal plane in the insulating material lining the outer shell, and is positioned at the junction of the side wall of the insulating material with the iloor thereof, and extends completely around the side wall. The trough opens upwardly and is adapted to retain a liquid therein. A rst, liquid impermeable membrane lines the side wall of the insulating material land has a lower edge which extends into the trough. A second, liquid impermeable membrane lines the floor of the insulating material and has an outer peripheral edge which extends into the trough.

In the use of the container, the trough contains a solid material having a melting point below about 25 C. with the solid material increasing the edge portions of the first and second membranes which are extended into the trough so as to form a liquid tight seal around the edges of the membranes. In a preferred embodiment of the invention, the solid material which is ldisposed in the trough is water. The use of ice `as the material forming `the seal around the edges of the membrane which are extended into the trough has many advantages, and is particularly desirable where the liquid to be stored is a normally gaseous material which has been converted to the liquid state and is stored at Ivery low temperatures. When ice is used to entrap or seal the membranes which line the side wall and floor of the insulating material of the container, a strong liquid tight joint is formed between the membranes, and such joint can be very quickly and economically constructed. Moreover, the joint is `of a semipermanent nature since it can be opened or destroyed merely by permitting the ice to be melted so -that the edges of the membranes can be easily withdrawn from the trough.

In a preferred embodiment of the invention, the upper edge of the membrane which lines the side wall of the insulating material is `also retained in place by a frozen liquid seal by extending such upper edge into a trough formed in the upper portion of the side wall of the insulating material, and filling the trough with a liquid which can be converted to the solid state at a temperature which is below 25 C., and above the temperature at which liquids are to be stored in the container.

From the foregoing description of the invention, it will have become apparent that it is a major object of the present invention to provide an improved container for storing liquids at relatively low temperatures, and preferably, below the freezing temperature of water.

Another object of the present invention is to provide a high mechanical strength container capable of containing large volumes of relatively volatile liquids in a thermally insulated environment, which container can be con-structed at substantially less cost than the types of containers which have previously been provided for this purpose.

An additional object of the present invention is to provide a strong lightweight container which is especially well adapted for containing normally gaseous, liquified materials, such as liquitied petroleum gases, and which may be constructed in either stationary or portable form.

A more specic object of the present invention is to acer/ees o o: provide a container for storing liquids at relatively low temperatures, which container is well insulated to prevent an undesirably high rate of heat exchange between the liquid contents of the container and the container environment.

An additional object of the invention is to provide a container for liquified gases which are to be stored at low temperature, which container is constructed with seals formed by a frozen, normally liquid material which is retained in the solid state by contact with liquids stored in the container, or by location in close proximity to such liquids.

In addition to the foregoing described objects and advantages, additional objects and meritorious features of the invention will become apparent as the following detailed description is read in conjunction with the accomanying drawings which illustrate certain embodiments of the invention.

In the drawings:

lFIGURE 4l is a vertical sectional view which is partially schematic, and which is taken through the center of one embodiment of a liquid storage container constructed in accordance with the present invention.

FIGURE 2 is a sectional view of a detail of the construction illustrated in FIGURE l, such detail showing one of the frozen liquid bottom seals used in the container of the invention.

FIGURE 3 is a sectional detail view illustrating a modified construction of the frozen bottom seals which may be used in the invention.

FXGURE 4 is a sectional detail view showing the frozen liquid seal used between the roof stnucture and the side wall of the container.y

FIGURE 5 is a sectional detail view illustrating the manner in which a suction discharge conduit may be connected through the bottom of the container.

FIGURE 6 is a sectional view illustrating a modified construction of the seal between the roof structure and side wall of the container.

FIGURE 7 is a sectional view illustrating another manner of constructing the seal between the roof structure and the side wall of the container.

FIGURE 8 is a sectional view illustrating yet another modified embodiment of the invention.

Referring to the drawings in detail, and particularly to FIGURE 1, the container of the invent-ion is designated generally by reference character 1G and includes a rigid outer shell 12 constructed of a material having a high mechanical strength, such as carbon steel. The outer shell 12 is lined with a relatively thick layer of rigid insulating material which includes a side wall 14, and a tloor 16 which rests upon and lines the bottom of the outer shell 12. The insulation material can be cellular glass, conk, balsa Wood, or any other relatively inexpensive, lightweight, good thermal insulator which can be suitably secured or adhered to the rigid outer shell 12.

ln the illustrated embodiment of the invention, the container is `generally cylindrical in configuration and an annular groove or trough 118 is formed in the insulating material floor 16 around the periphery thereof at its junction with the side wall 14- of the rigid insulating material. Another annular groove or trough 2li is formed in the door 16 of the insulating material, and is disposed radially inwardly from the trough 11S. A -third annular groove or trough 22 is formed in the top of the side wall 14 of the insulating material and extends completely around the container 10. Each of the grooves 18, 2i) and 22 are preferably of generally rectangular cross-sectional configuration.

The specific construction of the frozen liquid seals which are used in the container of the present invention can best be understood by referring to FIGURES 2, 4 and 5 in conjunction -with their schematic illustration in FIG- URE l. Within each of the annular grooves 1-8, 2li and 22 formed in the rigid insulation material which lines the outer shell 12 is positioned an annular, liquid tight channel 24 preferably having a generally U-shaped cross-sectional configuration. The liquid tight channels 24 can suitably be constructed of metal or plastic, and are used to contain a sealant material 26 which is a liquid at ambient temperatures having a freezing point below about 25 C. The normally liquid sealant material 26 which is placed in the liquid tight channels 2d is preferably water and, in the use of the container, is converted to ice in the manner hereinafter explained. Positioned between one side of each of the liquid tight channels 24 and a parallel side of its respective groove is a relatively loose or compressibie `thermally insulating material .28, such as Fiberglas or the like. The -compressible insulation material 25 permits expansion and contraction of the liquid tight container 24 occasioned -by variations in the temperature of the fluid contents of the container 1t?. It will be perceived in referring `to FlGURES 2, 4 and 5 that the seal arrangements associated with each of the grooves 18, 2f) and 22 are substantially identical, each thus including the liquid tight channel 24, the normally liquid material 26 and the compressible insulating material 28.

The internal surface of the `side wall 14 of the rigid ini sulating material is lined with a relatively iiexible, liquid impermeable membrane 3o which can suitably be constructed of thin metal or plastic. .The upper edge of the membrane 3l? is extended over a rim of compressible or relatively loose insulating material 32 positioned over the inner edge of the upper end of the side Wall 14. vrIhe upper edge of the membrane 3i? is further extended into the normally liquid sealant material -26 in the channel 24. yThe bottom edge of the membrane 3G is extended into the normally liquid sealant material 26 which is carried in the channel 24 positioned in the annular `trough 118. It is preferred .to provide a vent pipe 33 extending through the shell 12 and insulation 16.1 at a point located near the top of the container for a purpose hereinafter described. The vent pipe is provided with a check valve or pressure release valve 33a.

A second, liquid impermeable, flexible membrane designated generally by reference character 34 covers the iioor 16 of the rigid insulating material which lines the outer shell 12. The second membrane may, like the first membrane 3i), be constructed of a thin metal or plastic material. The second membrane 34 may consist of a single sheet of material which covers the entire bottom 16 of the rigid insulation material, or it may be formed as shown in FEGURE l for the purpose of better accommodating a suction discharge conduit 36 which is extended into the center of the bottom of the container 1t). Thus, in the illustrated construction, the second, liquid impermeable membrane 34 comprises a segmented or two-part construction which includes an annular, radially outer section 34a and a central section 34h. The annular radially youter section 34u is provided with an outer peripheral edge portion which extends into the normally liquid sealant material 26 in the channel 24 carried by the annular groove 18. The inner peripheral edge of the radially outer section 34a of the membrane 34 extends into the normally liquid sealant 26 carried by the channel 24 in the groove 2t?. In this embodiment, the central section 34!) is preferably a relatively thin metal sheet having an outer peripheral portion which extends into the sealant material 26 in the channel 24 of the trough 2t). The central portion of the metallic central section 34th is secured by a suitable fluid tight seal 38 around the upper end of the discharge conduit 36.

In order to prevent evaporation of the iliquid stored in the container 10, a roof structure 40 is provided and includes a rigid, outer shell di of metal or the like supporting a relatively rigid `thermally insulating material 42. The insulating material 42 is lined with a vapor-impermeable material id on the concave or inner surface thereof. The vapor-impermeable material 44. can suitably take the form of a covering membrane which has a peripheral edge portion 46 which depends downwardly from t-he roof structure. When `the roof structure 40 is positioned as illustrated in FIGURE l, the peripheral edge portion 46 of the vapor-imperrneable membrane 44 is extended into the normally liquid sealant material 26 carried in the channel 24 located in the groove 22 in the side wall 14 of the rigid insulaitng material.

lt should be pointed out that in the construction of the roof structure 4t), the rigid outer shell 41 can be eliminated or omitted from the construction in some instances, such as 'where relatively rigid and structurally strong insulating material 42 is employed, since the weight of the liquid held within the container is carried entirely by the bottom and side Walls of the container and there is less need for structural strength in the roof structure 40.

In the construction of the lcontainer 19, the outer shell 12 is first shaped as desired by conventional and Iwell known vfabrication procedures. rThe insulating material is then positioned on the inside of the outer shell 12 to constitute a side wall and floor for the container, and to provide adequate thermal insulation for the liquid maeria-l which is to be stored -at a low temperature in the container. The roof structure 40 is similarly constructed.

The liquid

impermeable membranes

30 and 34 which line the side wall 14 and iioor 16, respectively, of the rigid insulating material are then placed in posi-tion as illustrated in FIGURE l. This positioning of the membranes involves the extension of the peripheral edges of the membranes into the channels 24 positioned in the

respective groves

18, and 22. It is not necessary, or even desirable, in most instances, to bond or seal the membrane to the contacting surface of the rigid insulating material, since the seals at the edge of the membrane will retain it in the proper position over the lining of rigid insulating material when the container is in use. Moreover, if the membranes `and 34 are not ysealed to their respective contacting surfaces of the insulating material, any slight leakage through pinhole breaks lor apertures in the membranes does not pres-ent a problem when the liquid is removed from the container l0 by suction. This is because any tendency which the resulting reduced pressure within the container might have to vaporize the stored liquid ywill then not cause rupture tof the membranes. In other words, if lany liquid material remaining in the container and perchance having infiltrated under the

membranes

30 and 34 is ashed by an evacuation procedure used in removing the liquid from the container, the vapor evolved under the membranes -will have sufficient room to expand and can be released through the vent pipe 33 land check vadve 33a since the membranes are not bonded to the areas kof the rigid insulating material with which they are in contact.

After the liquid

impermeable membranes

30 and 34 have bee-n located in their proper positions with their peripheral edges extending into their respective :channels 24, the several channels are partially filled with a normally liquid sealant material 26 which can be easily converted to the solid state by a relatively slight reduction in temperature. The materials 26 employed in forming the seals used in the container 14) of the invention are those which are liquid at ambient or room temperatures, and can thus be poured into the channels 24 without requiring high temperatures to melt the material, and special handling equipment. It is further necessary that the normally liquid sealant materials 26 have a freezing point which is higher than the freezing point of the liquids which are to be stored in the container 10. Since the preferred employment of the container is lcontemplated to be in the storage of normally gaseous materials in the liquid state and at cryogenic temperatures, several normally liquid sealant materials will meet this latter requirement. From the standpoint of economy and ease of use, however, fas well -as certai-n operating and technical advantages, it is highly preferred that water be the sealant material employed for forming the seals used in the invention.

In addition to the advantages offered by water of being relatively economical, being easily poured into the channels 24, and being liquid at ambient or room temperatures yet freezin-g at a higher temperature than most of the liquids which Will be stored in the container, several other marked advantages accrue from the use of water as the sealant material. Thus, upon being converted to the solid state, water, unlike practically all other materials, undergoes expansion, and thus bears tightly against the confining walls of the channel 24, and also tightly grips or engages the free edges of the

membranes

30 and 34 which are extended into the ice. A tight liquid and vapor-impermeable barrier or seal is formed around the edges of the membranes to prevent leakage from the container 10 of either the liquid contained therein, or vapors which might otherwise escape between the roof structure 40 and the side Walls of the container.

Water also presents the advantage of being immiscible with hydrocarbon materials, and thus there is less likelihood of contamination of the stored liquids when such liquids are liquified petroleum gases and the like. Lastly, ice demonstrates a self-healing property which permits any fissures or cracks which might otherwise tend to develop in the ice seal to be immediately healed and the integrity ofthe seal to be maintained.

After the

troughs

18, 20 and 22 have been filled with the normally liquid sealant material 26, the roof structure 40 is positioned as illustrated in FIGURE 1 of the drawings with the peripheral edge 46 vof the vapor-impermeable membrane 44 extending into the channel 24 in the groove 22. The liquid to be stored can then be introduced through a suitable opening (not shown) in the roof structure 40, or in some instances, may have been positioned in the container 10 prior to installation of the roof structure 40. When the low temperature of the stored liquid is to be relied upon to convert the normally liquid sealant material 26 to the solid state, rather than the use of extrinsic refrigeration or heat exchange systems, the roof structure 40 is preferably placed in position prior to introducing the low temperature liquid into the container 10.

During storage of liquids at low temperatures within the container 10, it is contemplated that the temperature of storage or containment will be below the melting point of the normally liquid sealant material 26. As previously indicated, one of the preferred usages of the container 10 is for storing at very low or cryogenic temperatures, normally gaseous materials which develop a relatively high vapor pressure even at such low temperatures. Materials of this type include, for example, liquied natural gas, liquified ethane, liquified propane, liquified helium and liquified nitrogen. When these materials are enclosed within the container 10, and Water is employed as the normally liquid sealant material 26, strong, liquid impermeable seals are established by the ice around the edges of the

membranes

30 and 34 so that no leakage or escape of the liquid is possible at these points. Moreover, the ice seal established around the upper edge of the membrane 30 and the peripheral edge 46 of the vaporirnpermeable membrane 44 `of the roof structure 40 is such that no substantial escape of vapor from the container 10 can occur. The low temperatures at which the normally gaseous materials are to be stored will ret-ain the water in a frozen state in the seal zones so that the integrity of the seals continues during the period of storage.

The desirability of not bonding the

membranes

30 and 34 to the surfaces of the rigid insulating material with which they are in Contact has previously been discussed. Where relatively low pressures are created in the container 10 by evacuation of the contents therefrom, it may, in some instances, be desirable to provide an additional space for accommodating gases produced by flashing of liquid which has leaked between one of the membranes 30 or aaezeea 34 and the rigid insulating material. Additional continuous space or increased volume can be provided by using the embodiment of the seal structure illustrated in FIG- URE 3.

In the modified seal structure illustrated in FIGURE 3, a liquid tight channel d8 of U-shaped cross-section is provided for containing the normally liquid sealant material 26. The channel .4l-S is positioned Within, and spaced from, a lar-ger channel t) by suitable spacer blocks 52 so that a iluent material may flow completely around the outside of the channel 48 in the space between the two channels. With this arrangement, the sudden vaporization of a liquid which has leaked through the membrane k34 into the space between this membrane and the floor I6 of rigid insulating material will not result in rupture of the membrane due to insudcient space for volumetric eX- pansion `of the dashed material. Instead, the entire void space existing between the side wall I4 of the rigid insulating material and the membrane 30 is also available to accommodate the gas developed upon flashing, since this space is permitted by the seal structure of FIGURE 3 to communicate with the space between the door le of the insulating material and the membrane 3d. It should be noted that a similar seal structure can be provided in the trough if desired. The vent pipe 33 is provided adjacent the top of the container to permit complete escape of entrapped vapor from beneath the membrane if the pressure becomes excessive so as to open the pressure release valve 33a.

Where relatively high vapor pressures are not characteristic of the liquids stored within the container 16, two alternative types of seal structures for establishing the seal between the roof structure and the side walls of the container may be employed. `These are illustrated in FIGURES 6 and 7. In referring to these ligures, it will be noted that a relatively loose, compressible insulating material 54is again placed between the top edge of the membrane 39 and the top edge of the side wall i4 of the rigid insulating material lining the shell a2. Also, in both structures, the frozen liquid seal employed around the top of the container lil as illustrated in FIGURE l has been eliminated, and instead, in the embodiment illustrated in FIGURE 6, the upper or top edge of the membrane 30 has been welded or otherwise suitably secured to a circumferential flange 55 which is secured around the upper end of the outer shell 12 of the container. The rigid insulation 42 used in the roof structure 4d is then indented or shaped to a conguration which is complementary to the contour of the membrane 30 as it passes across the top edge of the side of the container. In permanent installations where the roof can remain in place, and access other than by removal of the roof is provided to the interior of the container 10 for lling and emptying the container, the metallic shell 4I of the roof structure can also be welded to the ange 56 it desired.

In the modilied embodiment illustrated in FIGURE 7, the upper edge of the membrane 3d is not welded or `otherwise secured to the llange 56, but is instead sealingly retained in position on the flange 56 by a gasket S3 which extends between the upper surface of the membrane 30 land a circumferential ilange 60 formed around the outer peripheral edge of the outer shell 4l of the roof structure 40. In the construction of the seal illustrated in FIG- URE 6, the anges 6d and 56 are drawn toward each other by suitable clamps to place the resilient gasket 58 in compression, and the two ilanges are then welded to each other by suitable welds 62.

As has previously been pointed out, the seal structures illustrated in FIGURES 6 and 7 and employed between the roof structure 40 and the side walls of the container 1t) are suitable for use where the vapor pressures developed by the stored liquid are not large, and the need for a strong vapor seal at this point is accordingly reduced. Commensurate with this condition, the vaporimpermeable membrane 44 can be eliminated from the C LL) inner surface of the insulation 4Z Which-lines the roof structure d@ as is illustrated in FIGURES 6 and 7.

In another embodiment of the present invention, the wall structure of the container It? is modified to provide more effective Athermal insulation in the manner illustrated in FIGURE 8. In this embodiment, instead of employing a single liquid impermeable membrane 3G lining the side wall 14 of the -rigid insulating material, two superimposed vapor

impermeable membranes

70 and 72 are extended along the side wall 7d of a rigid outer shell, designated generally by reference character 76, and are spaced apart by a porous, relatively rigid insulating material 78. The lower edges of the membrane 7G and 72, and or the insulating material 73, are extended into a channel 86 positioned in grooves or troughs Sl formed in the bottom S2 of the rigid outer shell 76. The upperredges of the membranes 7@ and 72 and the insulating material 78 positioned therebetween are extended into a channel 8d supported in a groove 85 which extends around the upper peripheral edge of the rigid outer shell 7e.

A similar double membrane structure is provided for lining the bottom S2 of the rigid outer shell 76. The double membrane structure lining the bottom of the shell thus includes an upper membrane 86, a lower membrane 88 and a porous, relatively rigid insulating material 9d positioned between the two membranes. The peripheral edges of the membranes S6 and 88 and the insulating material 9@ are extended into the channel Sil similarly to the membranes 79 and 72 and insulating material 78 used to line the side wall 7d of the shell 75.

A vacuum conduit 92 extends through the side wall 7d of the shell 76 and through the membrane 76 to facilitate exacuation of the air filling the pores of the porous insulating material 7d. A similar vacuum conduit 94 extends through the upper membrane 86 and along the side wall of the container to a position of accessibility adjacent the top ot the container. Ey means of the vacuum conduits 92 and 9d, the gas lilled interstic'es of the porous insulation between the superimposed membranes can thus be evacuated to provide highly effective thermal insulation for the liquid stored in the container.

In order to prevent sublimation of the ice seals formed around the ends of the superimposed membranes as the space therebetween is evacuated, a relatively non-volatile, non-sublimable liquid which is immiscible with, and less dense than, water is initially placed in the channels 8d and 84 before lling the channels with water preparatory to forming the ice seals. This material can be selected from a number of suitable materials. For example, relatively high boiling, non-volatile hydrocarbons, such kas petroleum waxes and the like, are suitable. As the channels and 8d are filled with water, the non-sublimable liquid is displaced by the water by a difference of density and str-stilles on top of the water. Then as the water is later frozen to provide the ice seals hereinbefore described, the protective layer of non-sublimable material is positioned on top of the ice as indicated by reference character 96 in FIGURE 8. The material thus forms a barrier preventing sublimation of the ice and consequent destruction of the integrity of the ice seals as the air between each of the pairs of superimposed membranes is evacuated.

It should be noted that if additional mechanical strength and thermal insulation is required, the superimposed membrane structure illustrated in FIGURE 8 can be used to line containers which are constructed with a thick layer of rigid insulation as illustrated in FIGURES 4 through 7. In other words, if the embodiments of the invention illustrated in the latter iigures, the lining comprising superimposed or double layered membranes lhaving an evacuated space therebetween can be used in place of the membranes 36 Iand 34 if more eihcient thermal insulation is required. Any suitable type of roof structure can be used in conjunction with the open top container illustrated in FIGURE S, and can include an insulating lining of the evacuated double membrane type described.

The employment of the 4liquid impermeable membranes, the relatively inexpensive, yet rigid, efficient insulating material forming the side wall 14 and fioor 16 of the container, and the outer metallic shell 12 permit the container to be constructed much more economically than conventional fabricated containers of the ytype heretofore in use. Moreover, the container is of relatively light weight and can be made portable when relatively small volumes of liquid are to be stored` The roof structure 4t) and membranes 39 and 34 of the container can be easily removed in disassembling the container, since both are retained in position primarily by the normally liquid seal structures heretofore described which, of course, are rendered inoperative when the temperature within the container rises above the freezing point of sealant material.

Although certain preferred embodiments of the invention have been hereinbefore described as exemplary of its practice and to provide guidelines for those desiring to practice the invention, the described and depicted structures do not constitute the exclusive means of practicing the invention, or the only form which it may take. Thus, the basic principles herein described may be embodied in other structures of different shape, constructed of different materials and used in slightly different ways than those to which specific reference has been made. Insofar as such modications in structure and use are substantial equivalents of the embodiments of the invention described in the foregoing specification, it is intended that they shall be considered as circumscribed by the spirit and scope of this invention and by the appended claims.

What is claimed is:

1. A container for storing liquids at low temperatures comprising:

a rigid outer shell;

thermally insulating material lining said outer shell;

a plurality of liquid impermeable membranes lining ysaid thermally insulating material; and

a frozen seal structure between said liquid impermeable membranes and preventing fiuid fiow between said membranes, said seal structure including a sealant material sealingly engaging portions -of said membranes and having a melting point below about C. and above the temperature at which said liquids are to be stored, and

trough means -for retaining said sealant material in a substantially horizontal plane whereby said sealant material can be positioned for sealing engagement with said portions of the membranes by pouring the sealant material into trough means in liquid form.

2. A container as defined in claim 1 wherein said sealant material is Water.

3. A container -for storing liquids at low temperatures comprising:

a rigid -outer shell having .a side wall and a bottom,

and open at the top;

thermally insulating material lining said outer shell and covering the side wall and bottom thereof;

a liquid impermeable membrane overlying .the portion of said insulating material covering the side wall of said shell and having a lower peripheral edge portion;

liquid impermeable membrane means overlying the portion of said insulating material lining the bottom of said shell and having a peripheral edge portion;

trough means in said insulating material adjacent the intersection of the portion of said insulating material covering the side wall of the shell .and the portion of said insulating material covering Ithe bottom of the shell, said trough means receiving the peripheral edge portions of said liquid impermeable membrane and said liquid impermeable membrane means, and being adapted to retain a liquid in contact with said portions. Y

4. A container as defined in claim 3 and further characterized to include ice in said trough means sealingly engaging said peripheral edge portions.

5. A container as defined in claim 3 'and further characterized to include a roof structure extending across and closing'the top of said rigid outer shell; said roof structure including a rigid, thermally insulating material having an outer peripheral edge extending at least to the insulating material lining said rigid outer shell.

6. A container as claimed in claim 3 and further characterized t-o include a discharge conduit extending through the bottom of said shell and said thermally insulating material and sealingly engaging at its outer periphery said impermeable membrane means.

7. A container as defined in claim 3 wherein said liquid impermeable membrane means includes a plurality of juxtapositioned liquid impermeable membranes overlying, and collectively covering, all of the portion of said insulating material lining the bottom of said shell, and further characterized to include seal means sealingly joining said juxtapositioned membranes :and comprising a normally liquid, frozen sealant material sealingly engaging portions of each adjacent pair of said juxtapositioned membranes; and means for retaining said -frozen sealant material ina fixed position relative to the insulating material lining the bottom 'of said shell.

8. A container as defined in claim 3 wherein said liquid impermeable membrane has an upper edge, .and said container is further characterized as including a channel in the upper portion of the insulating material land receiving the upper edge of said liquid impermeable membrane; and

a normally liquid, frozen material in said channel and engaging the upper edge of said liquid impermeable membrane.

9. A container as defined in claim 3 wherein said trough means comprises:

a trough in the portion of said insulating material lining the bottom of said outer shell; and

a channel in said trough :and receiving said portions of said liquid impermeable membrane and said liquid impermeable membrane means and adapted to retain .a liquid in contact with said peripheral edge portions.

10. A container as defined in claim 5 wherein 'said roof structure comprises:

a rigid outer shell;

-a rigid thermally insulating material lining said outer shell; and

a substantially vapor impermeable material lining said rigid, thermally insulating material.

11. A container as defined in claim 10 wherein said vapor impermeable material comprises a substantially vapor impermeable membrane.

12. A container as defined in claim 11 wherein said liquid impermeable membrane has yan upper edge and said container is further characterized as including means for sealingly interconnecting the upper edge of said liquid impermeable membrane and said vapor impermeable membrane.

13. A container as defined in claim 12 wherein said means for sealingly interconnecting said membranes comprises trough means extending yaround said container in the upper portion of said first mentioned insulating material and receiving the yupper edge of said liquid impermeable membrane and a portion of said vapor impermeable membrane; and

sealant material in said trough means and sealingly engaging a portion of said membranes therein, said sealant material having a melting point below about 25 \C. and above the temperature at which said liquids are to be stored.

14. A container asV defined in claim 9 wherein said channel is of smaller cross-sectional are-a than said trough, and said trough means is further characterized to include means spacing the walls of said channel from the walls of said trough to permit iiuid fiow around said chan-Y nel and between the undersides of said liquid impermeable membrane and said liquid impermeableV membrane means. i

15. A container for storing liquids at relatively low temperatures comprising:

g a rigid outer shell having sides, `a ybottom and an open upper end;

Vrigid, thermally insulating material lining said outer shell and having a sidewall and a oor;

an upwardly opening channel for containing a liquid occupying `a horizontal plane in said insulating material at the junction of said side wall with said ioor and extending completely around the'fside wal-l;

a iirst liquid impermeable membrane lining the side wall of said insulating material and having a lower edge portion extendingV into said channel; and

a secondliquid impermeable membrane lining the floor of said insulating material and having an outer peripheral edge extending into said channel.

16. A container as defined in claim wherein said channel contains a solid material having a melting point below about C., said solid material encasing and forming a seal with the edge portions of said iirst and second membranes which `are extended into said channel.

17. A container as defined in claim 15 and further characterized as including seal means in the side wall of said rigid insulating material and around the open upper end of said outer shell, said seal means engaging said first liquid impermeable membrane and supporting said first membrane in a downwardly hanging relation thereto.

18. A container as defined in claim i6 and further characterized in including means for by-pasing fluid around said channel between spaces existing between said rigid insulating material and each of said membranes.

19. A container for storing liquids at temperatures below about 25 C. comprising:

a rigid outer shell having a side Wall and a bottom;

a first pair of superimposed impermeable members forming a partial interior lining for said container and extending parallel to the side Wall of said shell, said superimposed impermeable members each having an upper edge and a llower edge;

means spacing said first pair of superimposed members from each other;

means for evacuating the space between said first pair superimposed members;

a second pair of superimposed impermeable members forming a partial interior lining for said container and extending parallel to the bottom of said shell, the superimprosed impermeable members in said second pair each having an outer peripheral edge;

l2 means spacing said second pair of impermeable members from each other; means for evacuating the space between said "second pair of superimposed members; and a frozen seal structure ybetween said pair of superimposed impermeable members and preventing fluid iiow between said pairs of superimposed imperme- 'able members, said frozen seal structure including ,a frozen sealant material sealingly engaging the lower edges of said irst pair of superimposed impermeable members and the peripheral edges `of said second pair of superimposed impermeable members, said sealant material having a melting point below about 25`C. and above the temperature at which said liquids are to be stored, and

means for retaining said sealant material in a substantially horizontal plane whereby said sealant material can be positioned `for sealing engagement with said superimposed impermeable members by pouring the sealant material into said retaining means in liquid form.

Z0. A container as defined in claim 19 wherein said frozen sealant material is ice. e

2l. A container as dened in claim 20 and further `characterized to include a channel around the upper portion of the side wall of said shell and receiving the upper edges of Ysaid first pair of superimposed members; and

a normally liquid, frozen material in said channel and engaging the upper edges of said first pair of superimposed members.

22. A container as defined in claim 20 wherein said frozen seal structure is further characterized in including a material less sublimable than ice on the surface of the ice for deterring sublimation or the ice as the spaces between said first land second pairs of superimposed impermeable members are evacuated.

References Cited by the Examiner UNITED STATES PATENTS 2,333,315 11/ 1943 Klingberg 62-45 X 2,413,243 1'2/1946 Nett 62--45 X 3,092,933 6/1963 Closner et al 62-45 X 3,175,370 3/1965 Schlumberger et al 62-45 3,195,310 3/1965 Schroeder 62-45 X 3,205,665 9/1965 Van Horn 62-45 X Reierences Cited by the Applicant UNITED STATES PATENTS 2,378,128 6/1945 Cates. 2,520,883 8/ 1950 Kornemann et al. 2,550,815 5/1951 inwood. 2,780,386 2/1957 Evans. 2,911,125 11/1959 Dosker. 2,952,569 9/1960 Baer et al. 2,954,892 10/1960 Doslier. 2,963,873 1'2/ 1960 Stow-ers. 2,991,905 7/1961 Monson et al,

ROBERT A. OLEARY, Primary Examiner.

L. L. KING, Assistant Examiner.

Claims

1. A CONTAINER FOR STORING LIQUIDS AT LOW TEMPERATURES COMPRISING: A RIGID OUTER SHELL; THERMALLY INSULATING MATERIAL LINING SAID OUTER SHELL; A PLURALITY OF LIQUID IMPERMEABLE MEMBRANES LINING SAID THERMALLY INSULATING MATERIAL; AND A FROZEN SEAL STRUCTURE BETWEEN SAID LIQUID IMPERMEABLE MEMBRANES AND PREVENTING FLUID FLOW BETWEEN SAID MEMBRANES, SAID SEAL STRUCTURE INCLUDING A SEALANT MATERIAL SEALINGLY ENGAGING PORTIONS OF SAID MEMBRANES AND HAVING A MELTING POINT BELOW ABOUT 25* C. AND ABOVE THE TEMPERATURE AT WHICH SAID LIQUIDS ARE TO BE STORED, AND TROUGH MEANS FOR RETAINING SAID SEALANT MATERIAL IN A SUBSTANTIALLY HORIZONTAL PLANE WHEREBY SAID SEALANT MATERIAL CAN BE POSITIONED FOR SEALING ENGAGEMENT WITH SAID PORTIONS OF THE MEMBRANES BY POURING THE SEALANT MATERIAL INTO TROUGH MEANS IN LIQUID FORM.