US3411656A - Thermally insulated container for a liquiefied gas - Google Patents

Description

Nov. 19, 1968 R, G, JACKSON 3,411,656

-THERMALLY INSULATED CONTAINER FOR A LIQUEFIED GAS Filed June 21, 1965 2 Sheets-Sheet 1 lvm wird FIG. 2.

FIG. IA. INVENTOR Robert G. Jackson ATTORNEY Nov. 19, 1968 R. c. JACKSON 3,411,656

THERMALLY INSULATED CONTAINER FOR A LIQUEFIED GAS Filed June 21, 1965 v 2 sneetsQsheet 2 9 l FIG. 3.

FIG. 4.

INVETOR Ro bert. G. Jackson ATTORNEY United States Patent O "Ice 3,411,656 THERMALLY INSULATED CONTAINER FOR A LIQUEFIED GAS Robert Glover Jackson, Hornchurch, England, assignor to Conch International Methane Limited, Nassau, Bahamas, a Bahamian company Filed June 21, 1965, Ser. No. 465,321 Claims priority, application Great Britain, .l'uly 24, 1964, 29,753/64 7 Claims. (Cl. 220--9) ABSTRACT F THE DISCLOSURE An insulated large-scale container for cryogenic liquids such as liquefied methane comprising an outer wall of substantially fluid-impermeable heat insulating material, a Huid-permeable insulating inner layer adjacent to the inner surface of said outer wall and a thin non-self-supporting lining or membrane of very low permeability completely covering the inner surface of the inner layer and supported thereby. The permeability of the inner layer is such that any small amount of cryogenic duid leakage or penetration through the inner membrane is vaporized within the permeable layer and is allowed to vent out of the permeable layer so that no build up of cryogenic fluid or its vapor takes place in the permeable layer.

This invention relates to thermally insulated containers which are suitable for the storage of liquefied gases.

Problems have arisen in connection with such containers which rely on the cold liquefied gas being in direct contact with a thin tough skin of a plastic such as a polyethylene terephthalate resin, which skin is cemented onto a thermally insulating backing such as closed cell foamed polyurethanes. This is because in practice these thin skins are never completely impermeable to liquids such as liquefied methane, at the low temperatures to which they are subjected. The skin becomes stretched at low temperatures allowing molecular penetration by the cold liquid, e.g. liquefied methane. This penetration is additional to any penetration which may occur through voids present at installation or appearing in use due to mechanical damage. The liquid which penetrates such skins becomes trapped in the thermally insulated backing, and when the container is emptied, and is temperature rises, the trappedv liquid vaporizes, expanding in volume, thereby causing rupture of the thin skin of plastic.

Such problems are obviated if liqueed gases are housed in the container according to the invention. Such containers have an outer wall of substantially huid-impermeable heat insulating material, adjacent to the inner surface of which is an intermediate layer of completely fluid-permeable material. This intermediate layer is provided with a vent to allow escape of gases from the layer, and completely covering the inner surface of this layer is a lining of a material having a liquid permeability of no more than 10"3 times the gas permeability of the intermediate layer.

The container of this invention is eminently suitable for y the storage of a liquefied gas, that is a liquid which boils at atmospheric pressure at a temperature below ambient temperature. Examples of such liquefied gases are liquefied ethylene, liquefied propane, liquefied methane and liqueed natural gas.

The container may be any shape but is preferably prismatic, although in some cases a cylindrical tank may be preferred. The outer wall is preferably supported within an outer housing, for example a metal shell made of steel. As this outer housing will not come into contact with a very cold liquid, there is no need for it to be constructed of a material which does not become embrittled at low 3,411,656 Patented Nov. 19, 1968 temperatures. Alternatively the outer wall may be supported in an open structure, such as a trellis-like framework, or a cage.

The outer wall of substantially duid-impermeable heat insulating material should be of suliicient thickness so that if its inner surface is at the temperature of a liquefied gas, its outer surface is at a substantially higher temperature, and at a temperature at which the material surrounding the outer surface of the outer wall does not become embrittled.

Suitable materials from which the outer wall may be constructed are structurally strong and dimensionally stable woods such as balsa wood or quippo. Alternatively predominately closed cell rigid or semi-rigid foamed plastics such as polyurethane, polystyrene, polyethylene, polyvinyl chloride or foamed epoxy resin maybe used.

Other materials which may be used are sandwich blocks comprising plywood layers lining the inner and outer faces of porous insulating cores such as cores of balsa wood, cork board, calcium silicate or honeycomb cores.

In forming the outer wall, these materials may extend continuously throughout the whole area of the wall, but very often it will be necessary or desirable to make up the wall of a plurality of panels. Adjacent panels or lengths of materials should be formed together with a duid-tight seal which retains its sealing properties when the inner face of the wall is subjected to the low temperatures of a liquefied gas.

The intermediate layer is permeable to liuids, that is fluids can pass through substantially the whole of the layer without becoming trapped in localized pockets. Such layers can take many different forms, although as explained later, the particular form chosen will often limit the type of skin which may be used. Thus for example the intermediate layer may be a layer of open cell porous flexible polyurethane foam, or rigid phenolic foam.

Another form of intermediate layer includes perlite, or other powders, or glass wool which are held in place between the outer wall and the lining. This may be achieved by mounting blocks or strips preferably of wood, at intervals on the outer wall and mounting the lining on these blocks or strips. The intervening space is then filled with the glass wool or powder, which powder or glass wool is preferably stabilized with a resin such as an epoxy resin.

Another form of intermediate layer is an expanded metal or plastic sheet which does not become embrittled at the temperature of the liquelied gas. If the expanded sheet is of metal, aluminum is preferable as this is cheaper than for example stainless steel. Suitable plastics from which the expanded sheet may be made include polyethylene, or polypropylene or copolymers of ethylene or propylene with fluorine or chlorine, such as polytetrauoroethylene. Instead of expanded sheets other structural forms may be used which allow suliicient permeability to gases and which present a sufficient overall inner surface to support the mounting of a lining thereon. One such example of another intermediate layer is foamed alummum.

The lining may be very thin provided its permeability to liquids is no more than l0-3 times the gas permeability of the intermediate layer and provided the intermediate layer is such that it is capable of supporting a Very thin lining. Thus, for example, thin linings of between 0.3 and 3 mm. may often be used. The lining of course must be of a material which does not embrittle or weaken at the low temperatures of the liquefied gas.

If the intermediate layer has comparatively large areas which are not iirm enough to support t-he lining, as for example with expanded sheets, or loose insulation such as glass wool or powder, the lining will have to be more or less self supporting itself, and can for example be thin metal sheet, e.g. aluminum or stainless steel, having a thickness for example of between 0.5]and 5 mm. Alternatively in such cases plastic sheets, e.g. glass fibre, reinforced epoxy or polyurethane resins may be used. Such self supporting sheets may if desired be used in cases where the intermediate layer is rm and has a substantially inner continuous inner surface.

Whenvv the intermediate layer is firm and has a substantially continuous inner surface without large interruptions in its surface, as for example in the case of opencellA porous exible polyurethane foams or foamed aluminum, the lining maybe in the form of a metal ilm sprayed onto the intermediate layer, the metal being for example aluminum or copper. Alternatively, in such cases plastic films for example polymer films such as very thin polyethylene lm, polyethylene terephthalate resin lm or epoxy fibre glass film may be used as the lining. Such films may be applied to the intermediate layer by spraying or painting and then rolling to compact, When the intermediate layer is foamed aluminum, it is possible that the skin of the foamed aluminum itself can constitute the lining. The blocks of foamed aluminum can be welded together without destroying their overall permeability.

Whatever material is used as lining it must not have a liquid permeability of more than 10-3, and preferably not more than l04 times the gas permeability of the intermediate buyer. For large tanks this ratio should be of the order of 1012 or even less. It would of course be preferable to have a completely impermeable lining where this is possible and where this would not unduly raise the cost of the container. However, in practicey it is diflicult if not impossible to obtain such lining which would not be unduly expensive.

In practice, the lining will usually be thin enough and of suiciently high thermal conductivity so that there will be substantially no thermal gradient across the thickness of the lining. Because of this, when the container is emptied of cold liquid, heat will rapidly pass through the lining, and anypockets of cold liquid entrapped in the intermediate layer will rapidly vaporize and pass out of said layer through the vent.

In order that substantially no relative displacement between the lining and the intermediate layer shall occur when the container is cooled down from ambient to the low temperature of the liquefied gas or cold liquid it is necessary that there be some defined correlation between certain physical characteristics of the lining and intermediate layer. Thus, the coeicients of thermal expansion of the lining and intermediate layer may be sufficiently close to one another so that the lining and intermediate layer both expand and contract by substantially the same amount over the temperature range to which they are subjected. Examples of combinations of lining and intermediate layer meeting these requirements are an aluminum lining, and foamed aluminum or expanded sheets of aluminum as the intermediate layer; a stainless steel lining and an intermediate layer of expanded sheets of stainless steel; and an epoxy fiber glass lining and epoxy stabilized perlite as the intermediate layer.

Alternatively, either the lining or the intermediate layer may be sufiiciently flexible so that substantially no relative displacement occurs between the lining and intermediate layer over the temperature range to which they are subjected. If, desired, both lining and intermediate layer may have the required flexibility. Examples of lining and intermediate layer having the required flexibility are intermediate layers of open cell porous flexible polyurethane or polyvinyl chloride, and linings comprising a series of aluminum or stainless steel trays arranged offset to one another and welded together at their edges for example as described in UK. patent specification No. 981,732 (corresponding to U.S. application Ser. No. 285,279, iiled June 4, 1963), or linings with endless or intersecting corrugations.

The vent for escape of gases from the intermediate layer should preferably be capable of allowing gases to escape rapidly from the intermediate layer so as to prevent build-up of gases in any portion of the layer which might thereby lead to rupture of the insulation structure, particularly when the tank is emptied, Therefore, where the containers are large the gas permeability in the upper region of the intermediate layer should be great enough to cope with vaporizing pockets of liquid already in this region and also to allow gases which have accumulated in the lower regions of the intermediate layer to pass through. In many cases therefore it is preferable if pipes are inserted in the upper region of the intermediate layer so as to increase the gas permeability in this region. such pipes may alternativelybe inserted in the outer wall adjacent to the intermediate layer so that their inlets communicate with the intermediate layer and their outlets communicate with the vent. Alternatively, if desired the intermediate layer may be provided with several vents, each vent for a different portion of the intermediate layer.

If, for example the containerl is a prismatic container mounted in the inner lhull of a double hulled ship, which container has a thermally insulated trunk extending through the deck of the ship, pipes may be inserted in the intermediate layer at the topA of the container extending from the top of the intermediate layer at the side of the container to the base of the thermally insulated trunk. In this manner any gas which has collected inthe intermediate layer on the side of the container may `be conveyed without obstruction to the vent which is at the top of the thermally insulated trunk. Alternatively, if desired and especially in this particular case, pipes may be inserted in the outer Wall of substantially fluid impermeable heat insulating material, said pipes having inlets at the top of the intermediate layer at the sides of the container and outlets at the top of the insulating outer wall.

According to this invention a liquid such as liquefied gas may be housed in the container of the invention so that the liquid is in actual contact with the inner lining. Alternatively, the liquid may be housed in a separate tank, which tank is mounted in the container of this invention, said separate tank being in Contact with the lining. In this latter case the container of this invention acts as a secondary barrier should liquid leak from the tank.

Two embodiments of this invention are n-ow described with reference to the accompanying drawings.

In FIGURE 1 a vertical cross-section through the center of an insulated container in the inner hull of a double hulled ship is shown.

In FIGURE 1A the use of perlite, glass wool, etc. is shown.

In FIGURE 2 a horizontal cross-section of the ship through line A-A in FIGURE l is shown.

In FIGURE 3 a vertical cross-section through the line 3 3 of FIGURE 4 of a double hulled ship having an insulated container in the inner hull but with a different vent system from FIGURE l is shown.

In FIGURE 4 a horizontal cross-section of the ship through line B--B of FIGURE 3 is shown.

Referring to FIGURES l and 2, the ship 1 has an outer hull 2 and an inner hull 3. Lining the inner hull 3 is a layer 4 of mastic or thick adhesive which is smoothed over so as to level olf the plates of the inner hull 3. This layer 4 also acts as an adhesive for sticking on blocks of,

foamed polyvinylchloride forming the outer wall 5 of the insulated container. Within this outer wall 5 is an intermediate layer 6. This consists of open cell flexible polyurethane foam. On the inner surface of this intermediate layer 6 is a lining 7, consisting of glass reinforced epoxy resin and is applied to the intermediate layer by spraying and rolling.

In the upper region of the intermediate layer 6 a series of pipes 8 can be inserted so as to increase the gas permeability of this layer. The escaping gas reaching the top of the intermediate layer passes out of the container through a vent pipe 9.

In practical use, a suitable insulated cover will, of course, be provided for the trunk.

FIGURE 1A shows the use of blocks or strips 6a of Wood, mounted on outer wall 5, and in turn supporting inner wall or lining 7a, shown in this case as of metal; the permeable insulation 6b is supported by the wood strips.

The arrangement of this example copes with any leaking liquid methane as the following figures show.

Suppose that the intermediate layer 6 of polyurethane is faced with a 0.2 mm. thick layer of glass sheet reinforced epoxy resin as lining 7. This lining has a liquid permeability constant K1 for methane of about 2.2 106 cm.3 cm. cm.2 hours*1 atmos.1. The open cell flexible polyurethane foam has been found to have a resistance to ow of the following for various rates of flow of methane gas:

Resistance to flow in cm. water gauge per cm. thickness Rate of flow of methane gas, litres/min./em.2:

The gas permeability constant Kg is the rate of ow x pressure in cm.3 cm. crn.-2 hours-1 atmosl. Thus for polyurethane foam for a back pressure behind the lining of about 16.0 cm. water gauge/ cm. is

=4.65 10S cm.3 cm. em.-2 hours*1 atmos.-1

Therefore the ratio of the liquid permeability K1 of the lining to the gas permeability Kg of the intermediate layer is about 5 X10-15.

If the tank is metres wide and 20 metres deep the leakage of liquid methane having a density of about 0.45 gm./cm.3 over 20 days, that is the longest period which is conceivable for a ship to take to reach port, the flow of liquid through the lining in gnL/cm. of length of tank will be On evaporation this amount of liquid will become 48 585 cc.=28 litres of gas. This means that for each cm. length of the tank 28 litres of gas Will have to be removed.

As it is desirable that the back pressure behind the lining should remain small, say not more than 16 cm. of water gauge, the maximum flow of gas which can be sustained through the intermediate layer of polyurethane (Flow rate (from tab1e)) Xtime litres/hour/cm. (half bottom of tank-I-half top length of tank of tank-l-Whole of one side) 1.8 litres/hour/cm length of tank Thus the gas formed during a 20 day voyage would be able to escape from the insulation system in about 28/1.8=151/2 hours which is less than the time taken for the tank to warm up, i.e. about 24 hours.

When pipes are fitted at the top of the tank this has the effect of reducing the effective distance through which gas has to ow, and so for the same tank 20 metres wide and 20 metres deep, the figure of 28 litres/cm. of tank for the flow of gas through the fluid permeable layer will be reduced to perhaps 20 litres/cm. length of tank. This means that the gas will be able t0 escape from the insulation system in about 11 hours.

Referring to FIGURES 3 and 4, the ship 1 has an outer hull -2 and an inner hull 3. A layer 4 of mastic or thick adhesive lines the inner hull 3 and this layer is smoothed over so as to present a flat surface to the outer Wall 5. The outer wall 5 of heat insulating material consists of foamed polyvinyl chloride. This material is also used to form the heat insulation 12 for the trunk 11. Adjacent to the outer wall is the intermediate layer 6 consisting of phenolic foam. A lining 7 consisting of epoxy reinforced glass mat face with very thin glass sheet is applied to the inner surface of the intermediate layer 6 by first applying a layer of resin to the phenoliofoam; onto this resin is placed glass mat which is then wetted with more resin and rolled so that it is compressed and the resin squeezed into the voids of the mat. Finally a piece of thin glass sheet is attached to this mat by more resin and rolling to produce an even and smooth surface nish.

In the upper region of the side portions of the outer wall 5 are a series of pipes 10. These pipes 10 at one end cornmunicate with the upper region of the intermediate layer 6 and at the other end com-municate with the vent 9. Thus, the escaping gas reaching the top of the intermediate layer 6 escapes through the vent 9.

AS in Example 1, this arrangement copes with any leaking liquid methane as the following figures show:

In this case t-he intermediate layer 6 is faced 'with 2 mlm. t-hiok epoxy resin reinforced wit-h glass mats and 1inished with 0.2 mlm. of glass sheet. This lining has a liquid permeability constant K-1 for methane of about 2 10n om.3 cm. cm2 hours"1 atmosl. The phenolic foam has been found to have a resistance to flow of the following for various rates of flow of methane gas:

Rate of flow of methane, cc./min./cm.2:

Resistance to ilow in om. water gauge per cm. thickness Therefore the ratio ofthe liquid permeability K1 of the lining to the igas permeability Kg of the intermediate layer is about 5 X10-15.

=If the tank is 20 metres wide and 20 metres deep the leakage of liquid methane having -a density of about 0.45 gin/em.3 over 20 days will be 0.45X 40X 102 20X 24X 0 29 gm./cm. length of tank= 3.9)(10-5 gm./em. length of tank rOn evaporation vthis amount of liqruid will become 3.9 105 585=0.023 cc. of gas. This means that for each cm. length of the tank 0.023 of gas -will have to be removed.

:0.0143 cc./hour/crn. length of tank hours.

With pipes iitted at the top of the tank, as explained in Example 1 the figure of 0.023 cc. of gas/cm. would be reduced to perhaps 0.018 cc./cm. and the gas will be able to escape from the insulated system in about 1.25 hours.

I claim:

1. A thermally insulated container for low-temperature uid such as liquefied gas, said container comprising:

(a) an outer wall of substantially fluid-impermeable -heat insulating material,

(b) an inter-mediate uid-and-gas permeable load-bearing layer adjacent to the inner surface of the outer wall, of open cellular material, the cells being of small size,

(c) venting means for conducting vaporized gas, as rapidly as it forms in the intenmediate layer, from the intermediate layer to the exterior of the container,

(d) a thin membrane lining completely covering the inner surface of and fully supportedby the intermediate layer, said lining7 having a liquid permeability for contained liqueed gas of no more than 10-3 times the gas permeability of the intermediate layer,

(e) the outer ywall being supported Within an outer housing.

2. A thermally insulated container for low-temperature fluid such as liqueed gas, said container comprising:

(a) an outer wall of substantially huid-impermeable heat insulating material,

(b) an intermediate fluid-anddgas pexmeable load-bearing layer adjacent to the inner surface of the outer wall, of open cellular material, the cells bein-g of small size,

(c) venting means for conducting vaporized gas, as rapidly as it forms in the intermediate layer, from the intermediate layer to the exterior of the container,

(d) a thin membrane lining completely covering the inner surface of and fully supported by the intermediate layer, said lining having a liquid permeability for contained liquefied gas of no more than 101-3 times the gas permeability of Vthe intermediate layer,

(e) the outer wall being Imade of a predominantly closed cell rigid or semi-rigid foamed plastic.

3. A container as claimed in claim 2, in which the lining is a metal lm sprayed on to the intermediate layer.

4. A thermally insulated container for low-temperature uid such as liquefied gas, said container comprising:

(a) an outer Wall of substantially Vtimid-impermeable heat insulating material,

(-b) an inter-mediate uid--and-gas permeable load-bearing layer adjacent to the inner surface of the outer wall, of open cellular material, the cells being of-small s1ze,

(c) `venting means for conducting vaporized gas, as rapidly as it forms in the intermediate layer, from the intenmediate layer to the exterior of the container,

(d) a thin membrane lining completely covering the inner surface 4of and fully supported by the intermediate layer, said lining having a liquid permeability for contained liquefied gas of no more than 10*3 times the gas permeability of the intermediate layer,

(e) said venting -means comprising at least one pipe inserted in the upper region of the intermediate layer so `as to increase the -gas permeability in this region.

5. The invention as claimed in claim 4, `wherein said venting pipe or pipes are inserted in the outer Wall of theA substantially fluid-impervious 4heat insulating material, said pipes having inlets at the top of the intermediate layer at the side of the container, and outlets communicating with the exterior of the container.

6. A thermally insulated container for low-temperature uid such as liquefied gas, said container comprising:

(a) lan outer wall of substantially uid-impermeable heat insulating material,

(b) an intermediate uid-and-gas permeable layer adjacent to the inner surface of the outer wall, y

(c) venting means for conducting the Igases from the intermediate layer to the exterior of the container,

(d) a lining completely covering the inner surface of the intermediate layer, said lining having a liquid permeability for contained liquid gas of no more than 10-3 times the gas permeability of the intermediate layer,

(e) the intermediate layer comprising relatively movable packed elements, as in powder or glass wool, and being held in place between the outer Wall and the lining by Ameans of wooden retainers mounted at intervals at the outer Wall.

7. A container as claimed in claim 6, in which the powder or glass wool is stabilized 'with a resin.

References Cited UNITED STATES PATENTS 2,106,840 2/1938 Gould 220--9 2,629,698 2/ 1953 Sterling 260--2.5 2,863,797 12/1958 Meyer 220-9 2,952,987 9/1960 Clauson 114-74 3,027,040 3/ 1962 Iodell et al. 220-9 3,059,804 10/ 1962 Wissmiller 220-14 3,093,259 6/ 1963 Morrison 220-9 3,110,156y 11/1963 Niemann 220-14 3,158,383 11/1964 Anderson et al 220-9 THERON E. CONDON, Primary Examiner.

JAMES R. GARRETT, Assistant Examiner.

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