US3339784A - Insulated structure for use in transportation of cold liquids - Google Patents

Description

Sept. 5, 1967 c. G. FILSTEAD, JR 3,339,734 INSULATED STRUCTURE FOR USE IN v TRANSPORTATION OF COLD LIQUIDS Original Filed May 27, 1960 2 Sheets-Sheet 1 I G. 1 Charles fieorge a l 'fgg e dJr p 1957 c. G. FILSTEAD, JR 3,339,784

INSULATED STRUCTURE FOR USE IN TRANSPORTATION OF GOLD LIQUIDS Original Filed May 27, 1960 2 Sheets-Sheet 2 IN V EN TOR. Charles George 72' Lslead ,Jr

fliiarizays United States Patent 3,339,784 INSULATED STRUCTURE FOR USE IN TRANS- PORTATION 0F COLD LIQUIDS Charles George Filstead, Jr., Leahurst, Littleworth Common Road, Esher, Surrey, England Continuation of application Ser. No. 32,248, May 27, 1960. This application Mar. 15, 1965, Ser. No. 444,903

' 14 Claims. (Cl. 220-15) This application is a continuation of application Ser. No. 32,248 of Charles George Filstead, Jr., filed May 27, 1960, now abandoned, for Insulated Structure for Use in Transportation of Cold Liquids.

This invention relates to the storage and transportation of a liquid which needs to be maintained at a temperature diifering widely from ambient temperature and, more particularly, to the transportation in large volumes of a liquefied gas maintained at an extremely cold temperature for storage and transportation of the liquefied gas while in a liquefied state.

This invention will be described with reference to the storage and transportation of liquefied natural gas, but it will be understood that the concepts of this invention will have application also to the storage and transportation of other liquefied gases such as liquefied nitrogen, liquefied hydrogen, liquefied oxygen and liquefied air and the like, many of which are subject to usage in large volumes at stations distant from the liquefaction plant. This may be represented by the wide-scale usage which is also being made of oxygen in steel-making processes based upon the use of oxygen converters.

Referring to the problem of natural gas, there are areas of the world wherein natural gas is available in amounts far in excess of the requirements within the immediate vicinity while there are other areas of the world which are starved for fuel and are required to produce gaseous fuel at high cost from such sources as coal or the like. The areas would be benefited greatly if the natural gas could be transported economically from a source of plentiful supply to areas where deficiencies exist.

One such means of transportation which has become rather highly developed resides in the transmission of the gas in a gaseous state by pipeline. Such means can be economically practiced where the source of plentiful supply is connected to the areas where deficiencies exist by land. However, where the source of plentiful supply is separated from the areas where deficiencies exist by one or more large bodies of water, then transmission by pipeline is nolonger practical.

The concepts which have been made the subject of considerable research, engineering'and development reside in the reduction of the natural gas to a liquefied state at the source of plentiful supply. Reduction of the gas to a liquefied state operates to reduce the gas in volume by a factor of about 600, so that a given space within the transportation means will be able to hold 600 times as much gas in the liquefied state by comparison with the same gas in the gaseous state. The concepts further contemplates the transportation of the liquefied natural gas in the liquefied state from the source of supply tothe area where deficiencies exist, where the liquefied gas can be. reconverted to the gaseous state for use with an accompanying release of tremendous amounts of cold or refrigeration and work.

Transportation of natural gas from a source of plentiful supply to areas where deficiencies exist becomes practical if the gas can be transported in the liquefied state in large volume. Liquefied natural gas boils at a temperature of about 240 F. to about -258 F., depending somewhat upon the amount of heavier hydrocarbons which are contained with the methane which constitutes the principal component of natural gas. It is possible that natural gas could be maintained in a liquefied state for storage and tranportation at temperatures above 8 F. if the liquefied natural gas could be housed in pressure vessels but, to build vessels of such large capacity with walls strong enough to maintain pressure, appears to be impractical from an economic as well as from a structural standpoint. Thus, it has been determined that, for transportation of liquefied natural gas in large volume, it is best to calculate for storage and transportation at about atmospheric pressure or at a pressure slightly above atmospheric where it is desired to maintain positive pressure sufiicient to prevent inflow of air from the surrounding atmosphere.

This means that the ships tanks should be designed to handle large volumes of a liquefied gas at temperatures as low as 25 8 F. for natural gas and still lower temperature in the event that the cargo is made up of other liquefied gases. The handling of such extremely cold liquid in large volume presents a number of very serious problems.

Just to mention a few which are pertinent to the concepts of this invention, measures should be taken to protect the ships hull from the cold because the steel plate of which the ships hull is formed becomes embritttled and loses its ductility at temperatures below l00 F. It has been established that if the steel plate is reduced in temperature below 100 F., the steel will crack such that complete failure of the ship is possible.

Because of the extremely low temperature of the liquid, it is important also to provide means for minimizing heat loss, otherwise vapor disposal becomes a problem and an excessive loss of cargo would render the entire project economically unattractive. Vapor disposal presents a problem when excessive amounts of vapor are made available because the hydrocarbon vapors form very combustible mixtures with air. If the boil-01f can be maintained at a desired minimum, then the amount of vapor released by heat loss into the tanks can be used either as a fuel to power the ship or else can be processed through suitable equipment for reliquefaction and return to the storage tan s.

Further, the extremely low temperature of the liquid raises problems from the standpoint of primary containers in which the liquid can be housed in the storage and transportation means, and the means for stabilizing the position of the storage tank therein. The latter problem arises from the need to insulate the cold of the liquid from the ships structure and the concurrent need to stabilize the position of the tanks within the ship, notwithstanding the wide changes in dimension that will take place in the tank due to change in temperature between the time that the tank is installed or empty and the time when the tank will be filled with the liquefied gas and reduced thereby to a temperature of about 258 F.

In tanks of the capacity contemplated, that is, tanks which for a rectangular tank may be 100' x 100 x p the change in dimension may be as much as from 4-15 inches in any direction, depending upon the metal employed and upon the temperature change.

It is an object of this invention to produce and to provide a method for producing a structure for the safe and economical storage and transportation of a cold liquid cargo, and it is a related object to produce such structure within a ship for the overwater transportation of liquefied natural gas or other gas from a source of plentiful supply to an area where a deficiency exists.

Another object is to produce and to provide a method for producing an insulated storage space which is capable of protecting the steel of the ship, or supports therein, from the cold of the liquid while, at the same time, insulating the liquid against excessive heat loss and loss of cargo by vaporization, and it is a related object to provide an insulated storage space of the type described which is constructed of relatively low cost and readily available materials; which can be economically installed to define an insulated space; and which is capable of embodying the functions of a secondary container as a defense against the transmission of the cold of the liquid to the ships steel in the event of failure of the primary container in which the liquid cargo is originally housed.

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

FIGURE 1 is a schematic sectional elevational view of a section of the insulated space in which the cargo tanks are housed;

FIGURE 2 is a schematic sectional elevational view similar to that of FIGURE 1, showing a modification of the insulation structure embodying features of this invention; and

FIGURE 3 is a schematic sectional elevational view of a cross-section of a ship illustrating the practice of this invention.

In FIGURE 3 of the drawings, illustration is made of a tanker for the transportation of a cold liquid cargo wherein the ship is formed with an outer hull 12. Spaced a short distance inwardly from the outer hull and in parallel relationship therewith is an inner hull 14 interconnected to the outer hull to provide a space 16 therebetween through which a fluid may be circulated and which functions as a precautionary means to prevent the inner hull becoming too cold in case of failure of the cargo tanks and/or of the insulation.

The inner hull 14 is lined on its inner surface with a relatively thick layer 18 characterized by low heat conductivity to define an insulated hold space 20 for the cargo tanks 22 containing the cold liquid 24. The cargo tanks are keyed into the structure at the top and at the bottom by keys 26 and 28, respectively, received within sliding relationship within the keyways 30 and 32, respectively, preferably though not necessarily, aligned with the center of the tank to stabilize the position of the tank or tanks within the insulated hold space while permitting movements of the tanks relative to the insulated space in response to expansions and contractions due to temperature change. The basic concept for the described structure of the ship is more fully described in U.S. Patent to Henry, No. 3,021,808. It will be understood that the insulation system embodying the principal features of the invention are capable of use for insulating the space of such ship or ships or other housing to define an insulated space adapted to receive cargo for the storage of a cold liquid.

In the US. Patent to Dosker, No. 3,140,145, description is made of an insulation system wherein pre-formed panels of rectangular shape are mounted in end-to-end and in side-by-side relation on the inner surface of the inner hull substantially completely to line the hold space of the ship with insulation material. Each panel is formed of a central core of balsa wood or other thermal insulating material, and outer and inner sheets of plywood are independently mounted in the desired relationship onto the inner surface of the inner hull by attachments through the outer plywood panel whereby the inner sections of the panels are free to change in dimension in response to temperature change. In order to minimize heat loss and in order to maintain liquid out of contact with the metal wall of the ship, the panels are joined one to the other adjacent thereto across their inner surfaces by means of fluidimpervious expansion joints which maintain the desired sealing relationship between the panels while permitting change in the spaced relationship therebetween due to expansion and contraction. While the insulation system of the aforementioned patent functions quite satisfactorily in the manner intended, considerable cost and labor are involved in the manufacture of the pre-formed panels per se and in their assembly onto the walls of the ship to provide an insulation layer which is also capable of defense to prevent the penetration of cold liquid to the metal walls of the ship in the event of failure of any tank or other primary container.

Thus, it is a further object of this invention to produce an insulation system which is capable of the desired insulation characteristics but which is less expensive from the standpoint of cost of materials and assembly thereof to provide an insulated space which is capable also of protecting the metal walls from the cold of the liquid cargo.

It has been found, in accordance with the practice of this invention, that when the insulation material is characterized by the ability to resist penetration of liquid therethrough, only a thickness of about 3-6 inches is required to maintain a temperature differential of about 200-300 F. As a result, such thickness of insulation is suflicient to protect the metal walls when interposed between the metal and the liquid, thus it becomes possible to reduce the thickness and consequently the cost of the insulation layer designed to maintain a secondary line of defense against the penetration of the liquid to the metal wall while relying upon additional lower-cost insulation in combination therewith to minimize heat loss. The combination thus provides the desired thermal insulating characteristics and, concurrently, protection against destruction of the metal while making use of insulation of lesser total cost and of lower installation costs.

One of the principal concepts of this invention resides in an insulation system of the type described wherein an essential component comprises an insulation layer of minimum thickness which is characterized by the ability to prevent liquid directly in contact with one surface from penetrating through the thickness of the insulation to the opposite surface, thereby to insure the existence of an insulating space separating the liquid from the metal wall. Such insulation layer can be fabricated of a porous material having a longitudinal pore structure if the face opposite the surface directly contacted with the liquid is sealed onto a substantially fluidand vapor-impervious wall, and if the vapor permeability of the pores in the vertical direction is less than the amount of vapor made available in the pores from the liquid in direct contact with the inner surface of the insulation layer. Under such circumstances, the liquid will penetrate a short distance into the inner surfaces of the insulation layer until it reaches a temperature through a cross-section of the insulation which is above the boiling point temperature of the liquid. Under such circumstances, the liquid at the interface will vaporize in amounts greater than the rate of elimination vertically from the insulation layer, thereby to entrap such vapors between the liquid-insulation interface and the substantially fluidand vapor-impervious wall on the opposite side of the insulation layer. The entrapped vapors generate a back pressure which operates to hold back the liquid from further penetration, thereby to maintain an insulated space in between.

Insulation material capable of the development of such back pressure principles comprises insulation layers formed of balsa wood, with its longitudinal pores arranged normal or substantially normal to the face of the layer.

However, while this effect is useful, it is not clear that it operates under all conditions. Nevertheless, by providing next to the steel outer shell a relatively thin layer of impervious high-grade insulating material of sufiicient insulating value so that it retains the liquid and at the same time provides sufficient insulating value to protect the steel, the effect of a leak in the inner tank is kept from being catastrophic. This high-grade insulation, whether it operates on the back-pressure principle or is completely impervious, provides a necessary safety factor. However, to make all of the insulation of this high-grade material would be very expensive, therefore an inner layer of inexpensive porous insulation is utilized to supplement the thermal insulating effect of the expensive liquid-impervious insulation. If a leak in the inner tank occurs, the inner permeable porous insulation will not be able to retain the liquid and will therefore lose its effectiveness, at least locally, but the primary (outer) layer of impervious insulation will usually enable the trip to be completed, albeit at reduced thermal efiiciency, until the cargo is delivered and the leak can be repaired. It should be understood that the primary layer is referred to herein as impermeable both in the case where it is totally impermeable and in the case where it is slightly permeable, since in either case the liquid is prevented from penetrating to, or dangerously close to the steel shell.

Instead of comprising insulation material formed with longitudinal cells, the primary layer may comprise insulation material containing disconnected pores or interconnected pores. When using material with inter-connected pores, such as open-cell foamed plastics, it is necessary to seal off the inner face of the primary insulation,. as will be described in more detail below with reference to FIGURE 2 (see layer 70 and 72). When using material with disconnected pores, such as foamed glass, foamed cementitous material and closed-cell foamed plastics, such as polyurethane and polyvinyl chloride, the liquid will be incapable of any penetration into the insulation layer.

Having described one of the essential features of the invention, description will now be made of a new and improved insulating structure embodied as a lining on the inner surface of the inner hull, it being understood that the described system will be applicable to other structures wherein the features of a secondary container are adapted to be constructed into a thermal insulating system mounted upon the wall of the metal housing.

Referring now to FIGURE 1 of the drawings, the

numeral represents the metal wall which, in the illustrated modification, represents the inner hull of a ship. Secured onto the inner surface of the inner hull in sealing relationship therewith is the primary insulation layer 42. Inthe illustrated modification, the primary insulation layer is formed of a plurality of thin panels of a structurally strong and dimensionally stable highly porous wood, such as balsa wood, quippo and the like. The thin panels of wood are applied in separate, adhesively bonded layers onto the inner surface of the wall 40. The different layers may be so-arranged that in alternate layers the grain of the wood is at right angles to that of the wood in the adjacent layers.

It has been found to be suflicient to protect the inner metal hull from the cold of the liquid when the balsa wood layer 42 is dimensioned to have a thickness in the order of about 3 or more inches. When, as in the preferred construction, the grain of the balsa wood is at least in part arranged to extend in the horizontal direction, liquid which might come directly into contact with the inner surface of. the insulation layer 42 will penetrate but a short distance into the insulation before the entrapped vapors released from the liquid operate to block further penetration, thereby to maintain an insulation space between the liquid and the metal wall 40 to protect the latter from the cold of the liquid. Instead of balsa wood, the insulation layer may be formed of a foamed plastic which may be applied in the form of pre-forrned panels or which may be foamed in place to cover the entire metal wall as a lining. Instead of foamed plastics, it may be formed of foamed glass, attached in sealing relationship at their outer surface to the inner surface of the metal wall 40.

To protect the insulation layer 42 from the forces to which it would otherwise be exposed during placement of the cargo tanks 22 and in the use thereof, there is provided a protective wall 44 in the form of plywood panels preferably mounted in spaced relationship to the inner surface of the insulation layer 42. For this purpose, the plywood 6 panels may be supported on wooden struts 46 fixed at their inner ends to the balsa wood insulation layer 42 or otherwise extending through the insulation layer for at provide a barrier to the penetration of liquid, the insulation can be selected of low-cost and readily available materials which can be introduced into the available space in simple and inexpensive manners. Thus, the insulation 50 introduced into the void space through which the struts 46 extend, can be selected of such particulate substances as diatomaceous earth, pearlite, granulated cork, sawdust, foamed plastic or foamed glass chips and the like which may be poured into the space. Instead, the insulation materials may be selected of glass wool fibers, rock wool fibers and the like which may be blown into the space or otherwise packed therein. When use is made of a particulate substance of the type described, each particulate material may be packed within containers such as bags, for maintaining the desired distribution of the insulation throughout the space. Thus, a minor proportion, such as A of the insulation requirements, may be contributed by the more expensive insulation intended to provide the benefits of a secondary container for defense against penetration of the liquid to the metal Wall of the ship in the event of failure of any one of the tanks. The remainder, which may constitute as much as A or more of the insulation, can thus be made up of inexpensive materials which can be installed at low cost thereby to produce an insulation system embodying the benefits of the more expensive and more difiicult to install insulation of the type previously described, while still providing the desired protection against excessive heat loss.

The foregoing describes the preferred construction for the insulation forming the side walls. The bottom wall upon which the tank rests desirably makes use of an in-' sulation layer 52 embodying the characteristics of structural strength and dimensional stability for support of the tank when loaded or unloaded, while providing minimum heat loss to the liquid. Thus, the flooring also will embody the characteristics which are primarily limited to the layer 42 to prevent penetration of liquid coming into contact with the inner surfaces to the supporting metal wall. The flooring 52 is provided with an upper layer'54 of a hard wood, such as plywood, to accept the forces in use and to stabilize the positions of the tanks when use is made of the described key and keyway constructions.

In the modification representative of a preferred practice of this invention, provisions are made for the fact that it is difficult to construct a structural wall of substantial dimenion having a sufliciently smooth and fiat surface to permit adhesive bonding of pre-formed flat panels of insulation in a manner to effect the desired sealing relationship therebetween. The preferred practice of this invention takes this inherent non-uniformity in the wall 40 into account and provides wooden firring strips 60 which are secured in spaced-apart relation to the inner surface 62 of the metal wall. Mounted, as by means of nails, screws, or other wooden attachment means, onto the inner faces of the firring strips are plywood panels 64 arranged in end-to-end and side-by-side relationship to provide a substantially continuous flat surface onto which the primaryinsulation layer 66 of the type previously described can be secured adhesively for sealing attachment. It is preferred to fabricate the plywood panels 64 of fluid-impervious hard wood strips whereby the panels 64 can function as the barrier to the passage of vapors so as to embody the back pressure principles within the insulation layer 66. The voids 68 between the outer faces of the plywood panels 64 and the metal wall 40 can be filled with low-cost thermal insulating material such as rock wool,

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(f) a panel wall secured to both primary and secondary layers, said wall supporting said layer of secondary insulating material as a layer adjacent the primary layer,

(g) and a primary container of large capacity within said metal housing, said insulation being between said outer metal housing and said primary container, whereby in case of leakage, the primary container vapors released from the cryogenic liquid become en. trapped in the primary insulation layer between the liquid and the secondary wall and so are maintained out of contact with the outer, rigid metal housing.

'6. A structure as claimed in claim in which the primary insulation layer is formed of balsa Wood arranged at least in part with its grain in the horizontal direction and in which the outer surface of the primary insulation layer is mounted in sealing relationship on the secondary wall.

7. A structure as claimed in claim 5 in which the outer rigid metal housing comprises an inner hull of a ship and defines the hold space of the ship.

8. A structure as claimed in claim 5 in which the insulation between the bottom of the primary container and the bottom of the outer metal housing comprises a primary insulation layer solely, without any secondary insulation layer.

9. A structure as claimed in claim 5 in which the secondary wall is mounted in spaced relationship with the metal wall of the housing by said spacers comprising wooden fir-ring strips secured in spaced apart relation onto the inner surfare of the metal wall of the housing.

10. A structure as claimed in claim 5 in which said 16 panel wall comprises panels of structurally strong, fluid and vapor impervious material mounted in side-by-side relation to provide a substantially fluid impervious protective wall on the inner surface of the primary insulation layer.

11. A structure as claimed in claim 10 in which said secondary wall comprises plywood panels and in which said panels are adhesively bonded to the inner surface of the primary insulation layer in sealing relationship therewith.

12. A structure as claimed in claim 10 in which a continuous thin layer of a fluid and vapor impervious material is secured as a lining on the inner surface of the panel wall.

13. A structure as claimed in claim 12 in which the thin layer of a fluid and vapor impervious material comprises a substantially continuous thin layer of a synthetic resin, which is not attacked by the cold liquid.

14. A structure as claimed in claim 10 which includes additional panels of a structurally strong material mounted inwardly in spaced relationship with the panel wall and in substantially parallel relationship therewith to provide a space therebetween substantially filled with the secondary thermal insulating material.

References Cited UNITED STATES PATENTS 1,924,118 8/ 1933 Fritz et al. 2209 X 1,984,261 12/ 1934 Foy 2209 2,859,895 11/1958 -Beckwith 220-83 X 2,928,566 3/1960 Morrison 220-9 3,039,418 6/ 1962 Versluis.

LOUIS G. MANCENE, Primary Examiner.

Claims (1)

1. A TANK FOR THE TRANSPORTATION AND STORAGE OF CRYOGENIC LIQUIDS AT TEMPERATURES FAR BELOW THE FREEZING POINT OF WATER COMPRISING (A) AN OUTER RIGID METAL HOUSING, (B) AN IMPERVIOUS SECONDARY WALL COMPRISING CONTINUOUS NON-METALLIC PANELS OF STRUCTURALLY STRON MATERIAL, (C) A PLURALITY OF INSULATING FIRRING SPACERS SECURED TO SAID SECONDARY WALL AND TO SAID HOUSING, SAID SPACERS MOUNTING SAID SECONDARY WALL ON THE INNER SURFACE OF SAID OUTER METALLIC HOUSING IN SPACED RELATION THERETO, (D) A PRIMARY THERMAL INSULATION BARRIER CONSISTING OF A LAYER OF INSULATING MATERIAL OF LOW THERMAL CONDUCTIVITY MOUNTED ON SAID SECONDARY WALL ON THE OPPOSITE SIDE FROM SAID SPACER MEMBERS AND SUPPORTED THEREBY, SAID PRIMARY LAYER AND SECONDARY WALL TOGETHER AS A UNIT BEING EFFECTIVE TO RESIST PENETRATION BY LIQUID COMING INTO CONTACT WITH THE INNER SURFACE THEREOF SO AS TO MAINTAIN THE LIQUID OUT OF CONTACT WITH THE OUTER METAL HOUSING, (E) A LAYER OF SECONDARY THERMAL POROUS INSULATING MATERIAL INCAPABLE OF RESISTING PENETRATION OF LIQUID COMING INTO CONTACT THEREWITH POSITIONED INWARDLY OF THE PRIMARY INSULATION LAYER AND ADJACENT THERETO, (F) A PANEL WALL SECURED TO BOTH PRIMARY AND SECONDARY LAYERS, SAID WALL SUPPORTING THE SAID LAYER OF SECONDARY INSULATING MATERIAL AS A LAYER ADJACENT THE PRIMARY INSULATION LAYER, (G) AND A PRIMARY CONTAINER OF LARGE CAPACITY WITHIN SAID METAL HOUSING, SAID INSULATION BEING BETWEEN SAID OUTER WALL HOUSING AND SAID PRIMARY CONTAINER.

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