US3088621A - Insulated tank for the storage and transportation of a cold boiling liquefied gas - Google Patents

Description

3,088,621 TRANSPORTATION ED GAS May 7, 19.63 E. H. BROWN INSULATED TANK FOR THE STORAGE AND OF A com: BOILING LIQUEFI 2 Sheets-Shet 1 Filed July 1, 1958 Era. i

I IINVEILITOR. K fii owm BY .z iz orneqfi I Edwin If M May 7, 1963 E. H. BROWN INSULATED TANK FOR THE STORAGE AND TRANSPORTATION 2 Sheets-Sheet 2 OF A COLD BOILING LIQUEFIED GAS Filed July 1, 1958 INVENTOR.

Edwinj'i. Brow? (0M0, AQ ZZ WYM United States Patent 3,088,621 INSULATED TANK FOR THE STORAGE AND TRANSPORTATION OF A COLD BOILING LIQUE- FIED GAS Edwin H. Brown, Elmgrove, Wis., assignor, by mesne assignments, to Conch International Methane Limited, Nassau, Bahamas, a corporation of the Bahamas Filed July 1, 1958, Ser. No. 745,977 6 Claims. (Cl. 220-9) This invention relates to the storage and transportation of a low boiling liquefied gas, as represented by a liquefied natural gas formed mostly of methane having a boiling point of about -25 8 F. at atmospheric pressure.

In the engineering for the storage and transportation of liquefied natural gas or other low boiling gas, it is desirable to calculate for a container which can be used to house the liquefied gas in large volume. This makes it impractical to design for a container in which the liquefied gas can be housed at high pressures because then the walls of the container would have to be fabricated of thick panels of metal to be able to withstand the tremendous pressures existing. As a practical matter, high pressure storage is limited to containers of small capacity, too

small for economical use in the storage and transportation of a liquefied natural gas.

It is desirable, therefore, in the construction of a container of large storage capacity, to calculate for the storage of the liquefied gas at about atmospheric pressure and preferably only slightly above. For liquefied natural gas, this means the maintenance of the content liquid at a temperature below about 240 F. to 258 F., depending upon the amount of heavier hydrocarbons in the liquid.

Because of the extremely large temperature differential between the content material and the ambient atmosphere, heat will tend naturally to flow from the atmosphere through the walls of the container into the content material. If the heat flow is excessive, the amount of boil-off can so deplete the load or cargo as to render the system for storage and transportation impractical and uneconomical.

Thus the need is for an insulated container of large capacity which can safely house a liquefied natural gas or other low boiling liquefied gas at about atmospheric pressure and without excessive boil-off due to heat loss through the insulated walls of the container.

The desired characteristics are capable of being achieved in a construction which makes use of a pair of housings of similar shape wherein one is located within the other to provide a spaced relation therebetween which can be filled with a material having a low coefficient of thermal conductivity to minimize heat loss between the walls of the container. The two housings are formed of a fluid impervious material, preferably in the form of a metal container. Because of the extremely cold character of the liquefied gas, it is desirable to construct the inner container of a metal such as aluminum, aluminum alloys, stainless steel, or other austenitic or non-ferrous metal which can retain its strength properties under the conditions existing. Iron or the common non-austenitic steels cannot safely be used for the inner container but any such metal having the desired strength properties can safely be employed for the outer housing since, under ordinary conditions, the outer housing will not be exposed to the extremely cold temperatures of the liquefied gas. The inner container formed of metal is adapted to have structural strength and stability sufi'icient to support the load of the liquefied gas exclusive of any external supports. Thus it represents an internal container for the liquefied gas which need not rely on the outer container or other elements for reinforcement or support.

In order to minimize heat loss through the insulation, it is undesirable to make use of metal bracing members for supporting the inner housing in the desired spaced relation within the outer housing. This can be avoided in the construction described by the use of an insulation layer formed of a material that is capable of self-sufficiency to resist excessive deformation under the load conditions existing when the inner housing is filled with the liquefied gas. While many of the packed insulations, such as are formed of glass wool fibers, ground cork, vermiculite and the like, tend to densify under load and in operation to provide imbalance in the construction and loss in the coefficient of thermal conductivity, the desired characteristics can be secured by the use of a cellular wooden insulation of the type balsa wood, quipo and the like when embodied in the form of built-up panels or blocks ha ving structural strength.

It has been found that when use is made of an insulation of the type described which embodies load carrying characteristics as well as the ability to function as a good thermal insulation, the necessity to make use of an inner housing capable of functioning independently to support load diminishes. It would, of course, be desirable to make use of an inner housing which could rely upon the insulation layer for reinforcement and support so as to permit the construction of an inner housing formed of less material, of less weight, of considerably lesser cost, and wherein more space would be available to increase the capacity of the tank. It is conceivable that the inner housing could even be formed of aluminum having thin Wall sections and which would be characterized by some degree of expansibility to enable the walls of the housing to rest continuously upon the insulation layer for support. Under such circumstances, the composite tank would be much easier to fabricate and to install without loss in the ability of the tank to house the liquefied gas and with the expected reductions in heat loss.

There are a number of problems which would have to be faced in the use of an unsupported inner housing formed of a relatively thin and flexible metallic layer. One problem stems from the wide temperature differentials that would exist through the length of the tank when the tank is only partially filled with the liquefied gas. While the portions below the liquid level would correspond to the temperature of the liquid content material, portions of the housing spaced upwardly from the liquid level would be as much as F. higher in temperature. While expansion or contraction of the housing in the lengthwise direction would raise no particular problem since the tank rests on the floor of the insulation, differentials in expansion and contraction in the crosswise direction would raise serious problems because the use of a :film type tank would depend upon the combination of a structurally strong insulation for support and without such support there would be danger of collapse of the tank.

Another serious problem stems from the wide temperature changes to which the housing would be subjected in use. The housing may be installed at room temperature and subsequently cooled down in use to a temperature as low as 258 F. or possibly less than 300 F. After the tank is returned empty, the housing may again rise to room temperature or even above. This sets up a large change in the dimension of the housing especially when constructed to such dimension as about 4860 feet in diameter in a round tank or 30 x 60 feet in a rectangulargly shaped tank. When the inner housing or shell is formed of metallic Walls having strength sufilcientfor selfsupport under load, contraction of the walls of the housing away from the Walls of the insulating layer does not present a serious problem but even then it is desirable to harness the tank for holding it in a centered position. However, when a film type tank is employed, the tank reliesv upon support by the insulation layer and contrac tion to pull the walls away from the support would be most undesirable.

Thus it is an object of this invention to produce a tank for the storage and/or transportation of a cold boiling liquefied gas which makes use of an inner housing or shell incapable of its own support under load.

More specifically, it is an object of this invention to produce a tank of the type described embodying the combination of a structurally strong insulation layer and a met-a1 shell which relies upon the insulation for support under load and it is a related object to produce a tank structure ofthe type described embodying means whichenalbles the inner shell to rest continuously upon the insulation layer for support independently of diiferences in expansion and contraction through the length and width of the tank due to differentials in temperature and independently of the expansionsand contractions of the tank due to temperature change.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, embodiments of the inve11- tion are shown in the accompanying drawings in which:

FIG. 1 is a schematic sectional elevational view through a tank embodying the features of this invention;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a perspective elevational view in section of the tank structure shown in FIGS. 1 and 2; 7

FIG. 4 is a sectional view similar to that of FIG. 2 illustrating a modification in the tank construction;

FIG. 5 is. a schematic sectional elevational view of a modified form of tank structure embodying the features of thisinvention;

FIG. 6 is.a sectional view taken along the line 6% of FIG. 5, and i FIG. 7 is a perspective elevational view in section of the tank structure shown in FIG. 5.

A tank 10 embodying the features of this invention is formed of. an outer shell 12 of a fluid and vapor impervious material; a thick layer 14 of a porous insulating material having sufficientstructur-al strength to resist appreciableamounts of deformation under the load conditions existing when the tank is filled with a liquefied gas 16, and an inner shell 18 formed of a fiuid and vapor imperviousmaterial which is of such narrow wall thickness as to be substantially incapable by itself of resisting deformation under load but which, in accordance with the practice of this invention, is formed to be expansible toallow the sides of the shell to be displaced in response to load so as to remain in substantially continuous contact with the insulation layer 14 for support of the inner shell.

The tank is additionally provided with an insulated cover 20 dimensioned to extend across the top of the tank and the cover is provided with at least one opening to permit a conduit 22 to extend therethrough to the bottom of the tank for the introduction and removal of liquefied gas and it is provided with at least another opening to enable another conduit 24 to extend therethrough into communication with the upper end portion of the tank for the release of vapors. Both of the conduits 22 and 24 are preferably provided with valves 26 and 28 for the control of the flow of fluids.

The outer shell 12 need not be limited in the materials of which it is fabricated since it will not ordinarily be exposed to low temperatures. It is preferably formed of steel or the like fluid and vapor impervious material of high strength. It can also be formed of stainless steel or aluminum, metals of which the inner shell is preferably constructed. The insulation layer can be formed of prefabricated panels of balsa wood, quipo wood or the like material, characterized by a low thermal conductivity and further characterided by a mass integrity and strength sutficient to provide load carrying properties for support of the inner shell when filled with a liquefied gas without break-down or excessive deformation of the insulation. It can also be formed of sections of panels of reinforced foamed glass or other high strength material having a low coefficient of thermal conductivity and which is capable of retaining its strength and resiliency when exposed to the temperatures of the liquefied gas; The insulation layer is usually formed to a thickness of several inches to minimize heat loss and it is preferably joined at its outer surfaces to the inner face of the outer shell to make use of the shell for additional support.

The inner shell 18 is formed of a metal which is vapor and fluid impervious and which is not harmfully affected by the liquefied gas in surface contact therewith or at the low temperatures thereof. When the temperatures of the liquefied gas fall below l00 F., it is desirable to fabricate the inner shell of a non-ferrous metal such as aluminum or an alloy of aluminum. Use can also be made of a shell formed of stainless steel or other austenitic steels.

Expansibility is built into the inner shell by the use of ribs 30 or corrugations periodically formed in the Walls of the shell to extend lengthwise through the side walls of the shell. The ribs are arranged to provide for expansion and contraction chieflyin the crosswise direction because it is only the bottom walls and the side walls of the shell which must remain in substantially continuous contact with the insulation layer for support. Thus change in. dimension of the shell in the vertical direction will merely result ina decrease in the overall height of the shell without displacement of the bottom wall out of contact with the floor of the insulation.

Lateral expansion and contraction in a circular tank, as illustratedin FIGS. 1-4, is achieved by the construction of the side walls of the tank with periodic ribs 13 arranged to extend vertically preferably from the bottom to the top of the shell and preferably spaced uniformly about the circumference of the shell. The ribs 30 are preferably formed to extend inwardly away from the insulation layer, as illustrated in FIGS. 1 and 2. Instead of making use of ribs, the inner tank 18 may be formed of. corrugations 30 in the form of substantially continuous wave patterns in the side walls of the tank (see FIG. 4).

In a tank dimensioned to be 48 feet in diameter, the shell can be fabricated of aluminum having a wall thickness of about inch and with the vertically disposed ribs 30 turned inwardly to a depth of about 2 /2 to 4 inches along sections spaced about 8 feet apart at the pe riphery. This will provide sufiicient expansibility to enable the side walls of the shell to remain in substantially complete and continuous contact throughout the major portions of its area with the insulation layer for support notwithstanding the amount of contraction which takes place when the shell is cooled down from room temperature to as much as -350 F. while located within the insulation layer. In .a corrugated tank of similar dimension formed of aluminum walls having a thickness of about A inch, the corrugations 30 extending in the vertical direction can be formed with a pitch between waves of about 24 inches and with a rise between waves of about 2 /2 inches. This too will enable expansion and contraction by an amount to enable the side walls of the tank to remain continuously in substantial contact with the insulation layer.

It will be understood that the force conditions resulting from the liquefied gas in the shell will be sufiicient to effect the desired deformation of the shell walls to urge them continuously into contact with the supporting surface of the insulating layer. For this purpose, the shell walls may be constructed to a greater or lesser thickness as long as a continuous barrier is provided to block penetration of the liquid. When an insulation having a porous structure of the type of balsa wood is employed, liquid penetration to the outer shell will be blocked even if the inner shell, possibly formed of film material, should fail, since a back pressure principle will develop.

When the tank is formed round, it is desirable also to provide for expansion and contraction in the bottom wall 32 to minimize relative movements between the contacting surfaces of the insulating layer and the floor of the shell to minimize strains which otherwise would exist in the sections adjacent the corner portions of the shell when expansion or contraction differentials exist between the metal in the bottom wall 32 and the metal in the side walls 34 of the shell. When expansibility is built into the bottom Wall of the shell, it is preferable to form the bottom wall with spaced apart, annular corrugations 36 formed to extend upwardly from the bottom wall of the shell. The number of ribs or corrugations in the bottom .and the depth of such ribs will depend greatly upon the amount of expansion and contraction calculated to take place. it will be found to be sufficient if the bottom wall is formed with as few as three ribs spaced upon 8 foot differentials in radius.

While circular tanks are preferred from the standpoint of stress distribution under load, tanks of prismatic shape are more desirable from the standpoint of the maximum utilization of space when such space is available in limited quantities, as in a ship. The construction of the tank to prismatic shape enables the tanks to be interfitted one with the other without the waste of space that occurs when circular tanks are employed.

Lateral expansion and contraction in a prismatic tank, as represented by a rectangular tank 40 (FIG. 6) is achieved by the use of vertically disposed ribs 42 or corrugations in spaced apart relation in side walls 44 of the inner shell 46 with the other corrugations in each wall preferably located closely adjacent the corners extending continuously between adjacent side walls. The spaced relation between the ribs or the pitch of the corrugations and the depth of the ribs or the rise in corrugations can be calculated from the expansion and contraction characteristics of the metal and the temperature variations that will occur. Usually it is desirable to provide for a large excess in the amount of expansion and contraction allowed to take place to avoid stretching the metal. As in the circular tank, the ribs are formed to extend inwardly in a direction away from the insulation layer.

The bottom wall 48 in the rectangular tank can be formed without ribs but it is preferred to provide for movement with the side walls so as to minimize the development of strains and stresses in the corner portions and in the bottom wall of the tank. Such expansibility in the bottom wall 48 of the rectangularly or prismatic shaped tank can be provided by a criss-cross pattern of ribs 50 (see FIG. 7) in the bottom wall. The ribs may extend lengthwise and crosswise throughout the length and width of the bottom wall with the ribs blending to intersect one another or they may be aligned in spaced apart relation with the diagonals to provide for expansion or contraction in multiple directions.

It will be apparent from the foregoing that I have provided a new and novel tank construction adapted for use in the storage and/or transportation of a cold boiling liquefied gas in large volume. It will be apparent that the operation of the tank depends upon a cooperative relationship between the insulation layer and the inner shell whereby the former provides support for the inner shell to enable the latter to be constructed of lesser ma terial having greater flexibility and therefore greater adaptability in use.

It will be understood that changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. In a tank structure for housing a cold boiling liquid including an outer shell and an inner shell of a fluid and vapor-impervious material with a layer of dimensionally stable thermal insulating material inbetween, the improvement which comprises the combination of a relatively thick insulating layer formed of a structurally strong and dimensionally stable material capable by itself of resisting a noticeable amount of deformation under the load conditions existing when the inner shell of a fluid and vapor-impervious material unbonded to the adjacent insulation surface for enabling relative movements therebetween and is filled with said liquid and an inner shell which is incapable of self-sufiiciency under the load conditions existing, said inner shell including throughout laterally spaced apart, vertically disposed, and inwardly extending corrugations and vertically spaced apart, horizontally disposed corrugations, the dimensions of the vertical walls of the inner shell in any vertical or horizontal plane thus exceeding the corresponding dimension of the walls at the interface of the insulating layer by an amount which exceeds the amount of contraction which can take place in the shell when reduced in temperature from ambient temperature to the tempera ture of the liquid thereby to enable the liquid load to effect displacement of the walls of the inner shell for substantially continuous contact with the insulating layer for support.

2. A tank structure as claimed in claim 1 in which the inner shell is formed of a metal having a relatively thin wall thickness.

3. A tank structure as claimed in claim 1 in which the bottom wall of the inner shell is dimensioned to have an area greater than the area of the floor of the insulating layer.

4. A tank structure as claimed in claim 3 in which the excess dimension of the bottom wall of the shell is taken up in the form of embossments which extend upwardly into the shell.

5. A tank structure as claimed in claim 4 in which, in a round tank, the embossments in the bottom wall of the inner shell are annular and arranged concentrically in spaced apart relation.

6. In a tank structure for housing a cold boiling liquid including an outer shell and an inner shell of a fluid and vapor impervious material with a layer of thermal insulating material in between, the improvement which comprises the combination of a relatively thick insulating layer formed of a structurally strong, dimensionally stable insulating material capable by itself of resisting a noticeable amount of deformation under load conditions existing when the inner shell is filled with a liquid, and in which the inner shell is formed of a film of vapor and liquid impervious material unbonded to the adjacent insulation layer for enabling relative movements therebetween and which relies upon the insulating layer for support and wherein the side walls and the bottom walls of the film are formed to provide corrugations extending in the vertical and horizontal directions in the side walls and in the 7 8 crosswise and lengthwise directions in the bottom wall stantially continuous contact withv the insulating layer for to enable free expansion and contraction without separasupport. tion from the supporting lining, the dimensions of said inner shell when expanded being greater than the vertical References Cited in the file of this patent andhorizontal dimensions at the inner face of the lining 5 UNITED STATES PATENTS by an amount which exceeds the amount of contraction 2 1 I that can take place in the shell when reduced in tem- Henderson et a1 Sept 1940 perature from ambient temperature to the temperature Boardman 53 1946 of the liquid thereby to enable the liquid load to effect 2,676,773 Saul et a1 1954 displacement of the walls of the inner shell into sub- 10 2389953 Morrison June 9i 1959

Claims (1)

1. IN A TANK STRUCTURE FOR HOUSING A COLD BOILING LIQUID INCLUDING AN OUTER SHELL AND AN INNER SHELL OF A FLUID AND VAPOR-IMPERVIOUS MATERIAL WITH A LAYER OF DIMENSIONALLY STABLE THERMAL INSULATING MATERIAL INBETWEEN, THE IMPROVEMENT WHICH COMPRISES THE COMBINATION OF A RELATIVELY THICK INSULATING LAYER FORMED OF A STRUCTURALLY STRONG AND DIMENSIONALLY STABLE MATERIAL CAPABLE BY ITSELF OF RESISTING A NOTICEABLE AMOUNT OF DEFORMATION UNDER THE LOAD CONDITIONS EXISTING WHEN THE INNER SHELL OF A FLUID AND VAPOR-IMPERVIOUS MATERIAL UNBONDED TO THE ADJACENT INSULATION SURFACE FOR ENABLING RELATIVE MOVEMENTS THEREBETWEEN AND IS FILLED WITH SAID LIQUID AND AN INNER SHELL WHICH IS INCAPABLE OF SELF-SUFFICIENCY UNDER THE LOAD CONDITIONS EXISTING, SAID INNER SHELL INCLUDING THROUGHOUT LATERALLY SPACED APART, VERTICALLY DISPOSED, AND INWARDLY EXTENDING CORRUGATIONS AND VERTICALLY SPACED APART, HORIZONTALLY DISPOSED CORRUGATIONS, THE DIMENSIONS OF THE VERTICAL WALLS OF THE INNER SHELL IN ANY VERTICAL OF HORIZONTAL PLANE THUS EXCEEDING THE CORRESPONDING DIMENSION OF THE WALLS AT THE INTERFACE OF THE INSULATING LAYER BY AN AMOUNT WHICH EXCEEDS THE AMOUNT OF CONTRACTION WHICH CAN TAKE PLACE IN THE SHELL WHEN REDUCED IN TEMPERATURE FROM AMBIENT TEMPERATURE TO THE TEMPERATURE OF THE LIQUID THEREBY TO ENABLE THE LIQUID LOAD TO EFFECT DISPLACEMENT OF THE WALLS OF THE INNER SHELL FOR SUBSTANTIALLY CONTINUOUS CONTACT WITH THE INSULATING LAYER FOR SUPPORT.

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