US3502239A - Thermally insulated container for transporting low temperature liquids - Google Patents

Description

March 24, 1970 R, v. WORBOYS ETAL 3,502,239

THERMALLY INSULATED CONTAINER FOR TRANSPORTING LOW TEMPERATURE LIQUIDS Filed Jan 31 1968 gjauul INVENTORS:

ROBERT V. WORBOYS JOSEPH ESTEBAPEZ THHR ATTORNEY United States Patent THERMALLY INSULATED CONTAINER FOR 'I'RANSPORTING LOW TEMPERATURE LIQUIDS Robert V. Worboys, Cheshire, and Joseph Estehanez, Glamorgan, England, assignors to Shell Oil Company,

New York, N.Y., a corporation of Delaware Filed Jan. 31, 1968, Ser. No. 702,039 Int. Cl. B65d 25/18 US. Cl. 2209 3 Claims ABSTRACT OF THE DISCLOSURE A thermally insulated container which is especially suitable for the bulk storage and transportation of low temperature liquid materials comprises a rigid, impactresistant outer shell internally lined with a first layer of a low-density polyurethane foam, a second layer of an impervious resinous material and a third layer of highdensity polyurethane foam being in direct contact with the contained liquid.

Background of the invention There is wide current interest in the storage and transportation of relatively low-boiling materials such the lower molecular weight saturated and unsaturtaed hydrocarbons, such as, for example, butane, butene, propane, butadiene and isoprene, in the liquid state, and preferably at or near atmospheric pressure. Under these conditions, the cold hydrocarbons are stored in thermally insulated containers and allowed to vaporize as heat is absorbed by the cold liquid. These vapors may be vented directly to the atmosphere, utilized as fuel or condensed and returned as a liquid to the insulated container. Accordingly, in order to increase the efliciency and economy of such storage techniques, it is desirable to increase the effectiveness of the thermal insulation applied to the liquid container.

While vaporization loss is an important consideration in the storage and transportation of low-boiling liquids, another important consideration relates to the embrittlement of the metallic structural components of the container. It is known that ordinary ferrous metals such as low carbon steel exhibit measurable loss of impact resistance or strength when exposed to low temperatures, i.e., to temperatures as low as 50 F. Accordingly, in order to reduce the possibility of brittle failure, it has usually been necessary to either beef-up the structural components of the storage container or to resort to the use of more expensive metals or alloys.

In order to reduce the possibility of physical failure of a container holding cold liquid hydrocarbons in bulk, it has been suggested that such containers be constructed so that internal insulation can be utilized. It will be appreciated that by placing the insulation on the interior wall of a container shell instead of on the customary exterior surface, the shell material will remain substantially throughout its entire thickness at a temperature Which approximates the ambient exterior temperature rather than at the much colder interior temperature of the chilled liquid hydrocarbon. When such internal insulation is employed, low-carbon, low-cost steels may be utilized in the tank structure in lieu of the more costly alloy steels or other expensive materials which exhibit high impact resistance properties at low temperatures.

Insulating materials which are most commonly employed are balsa Wood and cork; however, these materials, while not expensive themselves, are expensive because of the labor involved in fitting the insulation blocks and segments to the metal container shell walls. Also, because it is generally undesirable to expose these insulating materials directly to the chilled material, it is customary to 3,502,239 Patented Mar. 24, 1970 provide an inner tank shell of a material which retains significant low-temperature impact resistance, such as aluminum or stainless steel.

A method has now been discovered for manufacturing thermally insulated containers for transporting and storing low-temperature liquids. More particularly, an improved thermally insulated container has been developed wherein only an exterior shell and internal insulation is required, thereby signficantly reducing the costs of storing low-temperature liquids.

Summary of the invention The instant invention provides a thermally insulated container which is especially suitable for the bulk storage and transportation of low temperature materials (liquids) which comprises (1) a rigid, impact-resistant outer shell and (2) an internal lining comprising (a) a first layer of a low-density rigid plastic or resinous material and (b) a second layer of a high-density rigid plastic or resinous material, said second layer being in direct contact with the contained chilled liquid.

Preferably, the improved thermally insulated container comprises (1) a rigid, impact resistant outer shell, preferably of metal, and (2) an internal lining which comprises (a) a first layer of a low density rigid polyurethane foam, i.e., from about 2 to 7 pounds per cubic foot and (b) a second layer of a higher density rigid polyurethane foam than said first layer, i.e., from about 7 to 24 pounds per cubic foot or higher. If desired, a plastic or resinous layer which is impervious to the stored liquid may be included between the first and second layers. For increased strength, reinforcing fibers, mats, meshes, screens, etc. of suitable material may also be incorporated into the foam layers during fabrication.

As noted hereinbefore, both the first and second rigid plastic materials are polyurethane foams. In addition to being efficient thermal insulators, the polyurethane foams are effective as liquid barriers to liquified gases. The first polyurethane foam preferably has a density in the range of 2 to 7 pounds per cubic foot and the second polyurethane has a density in the range of from 5 to 24 pounds per cubic foot.

The first polyurethane foam is the main thermal insulator and one function of the second foam is to protect the former from physical damage as the higher density foam can withstand greater mechanical stresses and loads than the first foam. The thickness of the second foam need not be as great as that of the first foam. The thickness of both foams will be determined by consideration of the operational requirements of the container, but the overall thickness will preferabl lie within the limits of two to six inches. If, for example, the overall thickness of both foams is two inches then this can be made up of a first low density polyurethane foam one and a half inches thick covered by a half-inch thickness of a second higher density polyurethane foam.

Another function of the higher density foam is to protect the first foam from stenching agents present in liquified petroleum gases. Stcnch, for example, ethyl mercaptan, which is present in liquified petroleum gases as a detector may penetrate into the first lowdensity polyurethane foam and soften the latter so reducing its effective thermal insulating properties. On the other hand it has been found that the stench has a negligible effect on a high-density foam and cannot penetrate through this foam to contact the lowdensity polyurethane foam.

By so thermally insulating the cargo compartments on marine tankers it has been found that liquified petroleum gases can be transported over large distances without substantial losses due to evaporation in the volume of cargo.

A layer of an epoxy resin can be applied to the first foam prior to the application of the second foam so that the resin will be sandwiched between the two foams. The resin is impermeable to the stench and forms an additional effective barrier isolating the first polyurethane foam from contact with the stench in the liquified petroleum gases.

Although the invention is described with particular reference to a marine tanker it will readily be appreciated that it is equally applicable to road or rail tanker vehicles and to land storage vessels. Similarly the invention is not limited to use with liquified petroleum gases but can be used for the thermal insulation of other liquified gases, such as liquified natural gases.

Brief description of the drawing The invention, as it relates particularly to the production of thermally insulated bulk storage and transport of liquified petroleum gases in marine tankers, is described in greater detail and the best mode presently contemplated in carrying out the present invention is illustrated in the attached drawing which represents a cross-sectional view of a marine tanker taken through a thermally insulated cargo compartment.

Description of the preferred embodiments The present thermally insulated container construction is particularly suitable for the bulk transport of chilled liquids, especially liquified petroleum gases, in the bulls of marine tankers; however, the instant containers may be equally suitable as stationary storage tanks.

The present invention will be particularly described with reference to marine tanker transport uses.

Accordingly, reference is made to the drawing which represents a simplified cross-sectional view through the thermally insulated cargo compartment of a marine tanker wherein the marine tanker has an outer hull 1 and an inner hull 2. it will be appreciated that hulls l and 2 are interconnected by means of keel plates, bulkheads, and the like; however, since this construction forms no part of the present invention, it has been omitted from the drawing in the interest of simplicity. The spaces so formed between the two hulls can form compartments for water ballast if desired. Ballast may be necessary not only when the tanker has been discharged, but also when the tanker is fully loaded due to the low density of liquified petroleum gas cargo.

The interior of the inner hull 2 may first be shotblasted to provide a clean surface to receive a first foam layer 3 having a density in the range of from 2 to about 7 pounds per cubic foot. This first foam layer 3 may be applied by any suitable means, but is preferably sprayed onto the inner hull 2, layer by layer until a desired thickness of foam has built up. In general, foam layer 3 may range from about one to about six inches in thickness although a greater or lesser thickness may be employed under various circumstances. The first foam layer 3 is then encased within a second foam 4 having a density greater than that of the first foam layer 3. The density of foam layer 4 may range from about 7 to 24 pounds per cubic foot or higher and preferably about 15 pounds per cubic foot. The important consideration is that foam layer 4 having a density greater than foam layer 3. Foam layer 4 likewise is built up layer by layer by spraying to a desired thickness, preferably between about one-half inch and six inches As shown in the drawing, the top of the tanker is closed by a deck 5, the lower surface of which is coated with the first foam layer 3 which is then encased within the second foam layer 4.

If desired, reinforcing material 6 such as mats of Hessian or other mesh material may be optionally incorporated into foams 3 and 4 during application to confer increased strength,

A resinous or plastic layer 7 may be preferably included between rigid foam layers 3 and 4. Such a layer is impermeable to stench and will act, therefore, as an additional barrier to prevent contamination of and damage to the foam plastics layer. Suitable such barrier layers include the plastic sheet films such as polyethylene, polypropylene, polyvinyl chloride and the like. Preferred, however, are the resinous materials, especially the epoxy resins. Suitable epoxy resins are the polyepoxides possessing more than one vicinal epoxy groups, i.e., more than one group. Such polyepoxides may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted with substituents, such as chlorine, hydroxyl groups, alkoxy groups and the like. They may be monomeric or polymeric.

Various examples of suitable polyepoxides are given in US. 2,633,458, particularly those described as Polyether A, Polyether B, etc. Suitable curing agents, such as acids, anhydrides, amines, etc. are also described in US. 2,633,458 and in a multitude of subsequent patents, books and trade brochures. The thickness of the resin layer is preferably in the order of from about 0.005 to 0.05 inch with about 0.01 inch being generally suitable.

Although the present thermally insulated containers comprise two layers of foamed polyurethanes, any other foamed resins and/or plastic compositions may be empolyed, including, but not limited to, foamed polyepoxides, polyesters, polyethers, polycarbonates, polystyrene, polyolefins, and the like, as well as mixtures thereof. All these polymer compositions are well-known in the art and suitable foamed formulations can be readily obtained from text books, journal articles and patents. Preferred however, are the polyurethane foams.

In general, polyurethane foams are prepared by reacting an organic polyisocyanate or polyisothiocyanate with an organic compound containing in the molecule a plurality of active hydrogen atoms (as determined by the Zerewitinoff method, J.A.C.S., vol. 49, page 3181, 1929), such as, for example, an organic polyhydroxy compound.

Suitable polyisocyanates and polyisothiocyanates have the general formula R(NCX),, wherein R represents an organic radical, X represents an oxygen atom or a sulfur atom and n is a positive integer.

Suitable polyisocyanates are those compounds which have on the average more than one isocyanato group per molecule, such as those polyisocyanates which can be obtained by the reaction of polyamines with phosgene, such as, for example, toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, naphthalene diisocyanate, metaphenylene diisocyanate, diphenyl diisocyanate, diphenyl ether diisocyanate, dianisidine diisocyanate, ethylene diisocyanate and diethyl ether diisocyanate. Polyisocyanates of these types may be applied separately or as mixtures, as for example, mixtures of isomers, such as the mixtures of the isomers 2,4-toluene diisocyanate and 2,6-toluene diisocyanate.

Use can also be made of non-volatile polyisocyanates which have been obtained by reaction of polyhydric alcohols, such as ethylene glycol, glycerol and 1,2,6-hexane triol, with an excess of polyisocyanates of the abovementioned type. An example of such a non-volatile polyisocyanate is the addition product of 1 mole of trimethylolpropane with 3 moles of toluene diisocyanate.

Preferred organic compounds containing active hydrogen atoms include the organic compounds containing terminal hydroxyl groups such as, for example, the polyoxyalkylene polyols prepared from one or more alkylene oxides, i.e., ethylene oxide, propylene oxide, epichlorohydrin. A useful polyoxyalkylene polyol is an alkylene oxide/alkylene polyol adduct that has been reacted with an alkylene oxide as, for example, described in copending United States Patent No. 3,336,242, issued Aug. 15, 1967; for example a propylene oxide/glycerol adduct that has been reacted with less than by weight of ethylene oxide, preferably 3 to 8% by weight of ethylene oxide. The polyoxyalkylene polyols are preferably produced according to the processes disclosed in British Patents Nos. 785,229, 785,053, 793,065, and 799,955, among others. Suitable polyoxyalkylene polyols have an average molecular weight between 300 to 6,000; for example, about 500 to about 3,000.

Other suitable polyisocyanates and organic compounds containing active hydrogen atoms are described in US. 3,222,303, US. 3,238,273, and US. 3,244,673. Suitable foaming processes are also described in these patents.

Additives, such as light and heat stabilizers, catalysts, fillers, pigments, cell-size regulators, foaming agents, solvents, viscosity controllers, surface-active agents (silicone oils) and the like may be used as desired. The usual additives are described in the above-mentioned patents.

Suitable polyurethane foams may be prepared by either the one-shot" or pre-polymer" methods. In the case of the one-shot method, the reactants are usually mixed in a so-called mixing head fitted with a stirrer capable of rotation at speeds of the order to 2000 to 5000 rpm. In addition to promoting rapid and thorough mixing of the reactants, the action of the stirrer also aids foam formation.

The polyurethane foams are preferably produced in a single stage by direct reaction between one or more polyols and a diisocyanate. Generally, the ratio of total isocyanato groups to total hydroxyl groups present in the reaction mixture is substantially equal to 1:1, although 1020% excess of either reactant may be employed as desired.

The invention is illustrated by the following example. The reactants, and their proportions, and other specific ingredients of the foam formulations are presented as being typical and various modifications can be made in view of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or of the claims. Unless otherwise specified parts and percentages disclosed in the example are by weight.

EXAMPLE I The following formulation (mixtures A and B) was mixed in a conventional mixing head and applied to the interior surface of the inner hull of a marine tanker at the rate of 150 pounds per minute.

748) 1.0 Component, mixture B:

Toluene-2,4-diisocyanate and toluene 2,6-di1'socyanate (4:1 mixture) 43.3 Water 3.0 1,4-diaza-bicyclo (2,2,2) octane 0.02 Stannous 2-ethyl hexoate 0.2

The resulting polyurethane foam layer (first layer) was 4 inches thick and had a density of 3.1 pounds per cubic foot, a tensile strength of 16.4 p.s.i., an elongaiton of 102% cgmpression strength of 0.87 p.s.i., and a hysteresis of To the interior surface of this first layer, a resinous layer comprising a glycidyl polyether of 2,2-bis(4-hydroxy phenyl) propane having an average molecular weight of 380 and an epoxide equivalent weight of about of approximately 0.01 inch thick was applied.

Then the above formulation was applied to the resinous layer in a manner so that the resulting inner layer was approximately one inch thick and had an average density of about 15 pounds per cubic foot.

The resulting insulated compartment exhibited a heat flux loss of less than 0.05 B.t.u./hr. ft. F. when LPG was stored therein at 50 F.

We claim as our invention:

1. A thermally insulated container for the bulk storage and transportation of low temperature liquids comprising (1) a rigid, impact-resistant outer shell member and (2) an internal lining comprising (a) a first layer of rigid polyurethane foam having a density of from 2 to 7 pounds per cubic foot and being in substantially continuous contact with the inner surface of said shell member,

(b) a second, impervious, resinous polyepoxide layer having a thickness of from 0.005 to 0.05 inch, and

(c) a third layer of rigid polyurethane foam having a density of from 7 to 24 pounds per cubic foot and being in direct contact with the contained chilled liquid, said first and third layers having a woven mesh reinforcing material incorporated therein.

2. A thermally insulated container as in claim 1 wherein said internal lining has a total thickness of from 2 to 6 inches.

3. A thermally insulated container as in claim 1 wherein the polyepoxide resin is a glycidyl polyether of 2,2-bis(4-hydroxyphenyl)propane.

References Cited UNITED STATES PATENTS 2,952,987 9/1960 Clauson.

3,027,040 3/1962 Iodell et al. 2209 3,070,817 1/1963 Kohrn et al. 2209 3,101,861 8/1963 Mearns et al. 11474 X 3,120,319 2/ 1964 Buddrus.

3,158,383 11/1964 Anderson et a1 2209 X 3,163,434 12/1964 Krueger 2209 X 3,174,642 3/1965 Loewenthal et al. 2209 3,294,462 12/1966 Kesling 2209 X 3,332,386 7/1967 Massac 114--74 3,400,849 9/1968 Pottier et al. 2209 FOREIGN PATENTS 1,383,795 9/1965 France.

OTHER REFERENCES Modern Plastics, vol. 42, No. 4, December 1964, page 7.

JOSEPH R. LECLAIR, Primary Examiner J. R. GARRETT, Assistant Examiner US. Cl. X.R. 114--74

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