WO2009133563A2

WO2009133563A2 - Underwater storage system

Info

Publication number: WO2009133563A2
Application number: PCT/IL2009/000460
Authority: WO
Inventors: Ofir Sarid; Alberto Kraier; Nitai Drimer; Tehila Feiglin; Moshe Rakhman
Original assignee: Seagen Systems Ltd.
Priority date: 2008-05-01
Filing date: 2009-05-03
Publication date: 2009-11-05
Also published as: WO2009133563A3

Abstract

A system for communicating between a source of standard gaseous material (SGM) in a liquid state substantially free of SGM in a gaseous state, and a tank designed to contain SGM in gas and liquid states is provided. The system is configured to be in fluid communication with the source for flow therebetween of SGM in a pure liquid state, and with the tank for drawing SGM from the tank in a first state and returning it to the tank in a second state. The system is configured to cause the drawn SGM to undergo a phase change from the first state to the second state before returning it to the tank.

Description

UNDERWATER STORAGE SYSTEM

FIELD OF THE INVENTION

This invention relates to systems for undersea storage systems of fluids.

BACKGROUND OF THE INVENTION

It is well known to store in a liquid state, certain substances which are normally gaseous at standard conditions during use. For example, petroleum gas, which may comprise propane, butane, methane, or a mixture thereof, is typically stored as liquefied petroleum gas (LPG).

When dispensed for use, it is exposed to standard atmospheric temperature and pressure, and converted into a gas. However, storage in a liquefied form reduces the amount of space needed.

SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided a system for communicating between (i.e., facilitating fluid communication between) a source of standard gaseous material (SGM) in a liquid state substantially free of SGM in a gaseous state, and a tank designed to contain SGM in gas and liquid states; the system is configured to be in fluid communication with the source for flow therebetween of SGM in a pure liquid state, and with the tank for drawing SGM from the tank in a first state and returning it to the tank in a second state, the system being configured to cause the drawn SGM to undergo a phase change from the first state to the second state before returning it to the tank.

It will be appreciated that hereafter in the specification and claims, the term "standard gaseous material" ("SGM") is used to refer to a material which is in a gaseous state at standard terrestrial conditions, i.e., about 20°C and 1 arm. The SGM may be natural gas, hydrocarbon- based gas, petroleum gas, ammonia, etc.

The source may comprise an undersea storage vessel, which may be configured to utilize undersea conditions for maintaining the SGM in a liquid state. The system may comprise a supply pipeline, which may be rigid or flexible, adapted to carry the SGM from the storage vessel for supply via the system, the pipeline being thermally insulated along at least a portion of its length.

It will be appreciated that herein the specification and claims, the term "sea", for example when used as a suffix (e.g., undersea, seawater, etc.), is to be understood as referring to any body of water, such as lakes, oceans, sea, river, etc., which provides the necessary conditions for storage of SGM in a liquid state as per the invention.

The system may comprise a supply system configured to facilitate supply of liquid SGM from the source to the tank, the supply system comprising:

• a supply outlet in fluid communication with the source, and configured for attachment to the tank to bring the source and tank into fluid communication with each other to facilitate the supply;

• a supply inlet configured for attachment to the tank to receive vaporized SGM therefrom; and

• a condenser, which may comprise a heat exchanger, in fluid communication with the supply inlet and downstream thereof, configured to receive vaporized SGM and liquefy it; the supply system being further configured to combine liquefied SGM exiting the condenser with SGM provided by the source.

The supply system may further comprise an injector configured to move the SGM received from the source and from the condenser toward the supply outlet. The liquefied SGM exiting the condenser may combine with SGM provided by the source within the injector.

The system may further comprise an acceptance system configured to facilitate acceptance of liquid SGM from the tank to the source, the acceptance system comprising:

• an acceptance inlet in fluid communication with the source, and configured for attachment to the tank to bring the source and tank into fluid communication with each other to facilitate the acceptance;

• an acceptance outlet configured for attachment to the tank to supply vaporized SGM thereto; and

• a vaporizer in fluid communication with the acceptance outlet and upstream thereof, configured to receive liquid SGM and vaporize it; the acceptance system being further configured to divert a portion of liquid SGM exiting the tank toward the vaporizer. The acceptance system may further comprise a control valve configured to selectively divert a predetermined amount of SGM toward the vaporizer.

In addition, the acceptance system may further comprise:

• an acceptance pump configured for selectively moving liquid in an active state thereof or allowing free passage of liquid therethrough in an inactive state thereof, in a direction toward the source; and

• a heat exchanger configured for ensuring that SGM exits the acceptance system at a temperature which is no greater than a predetermined acceptance temperature.

The acceptance system may further comprise a controller designed to operate the acceptance system in one of:

• a hot-weather mode, wherein the acceptance pump is inactive and the heat exchanger is operating to lower the temperature of the liquid below the acceptance temperature; and

• a cold-weather mode, wherein the acceptance pump is active and the heat exchanger is not operating.

The acceptance system may comprise a temperature sensor to measure the temperature of the liquid received from the tank, the controller being configured to select a mode of operation based on the measured temperate. The controller may be configured to select the hot-weather mode if the measured temperature is above the acceptance temperature, and to select the cold- weather mode if the measured temperature is below the acceptance temperature.

The controller may be configured to allow a user to select a mode of operation. The system may be configured to store SGM received by the acceptance system in a storage vessel anchored at a depth undersea, with the acceptance temperate being determined based on the temperature necessary to maintain the SGM in a liquid state subject to hydrostatic pressure associated with the depth.

The acceptance outlet may constitute the supply inlet, with the system further comprising a valve configured to selectively direct flow of SGM to the condenser during supply of SGM to the tank, and from the vaporizer during acceptance of SGM from the tank.

The source may comprise a liquefying system comprising: • a separation tank having an inlet, a liquid outlet, and a gas outlet, the separation tank configured to receive SGM via the inlet, to provide SGM in a substantially pure liquid state via the liquid outlet, and to provide SGM in a substantially pure gaseous state via the liquid outlet; and • a source compressor in fluid communication with and configured to receive fluid from the gas outlet, the source compressor being configured to increase the pressure of the SGM in a gaseous state; the liquefying system being configured such that SGM exiting the source compressor combines with liquid SGM provided via the liquid outlet.

The liquefying system may further comprise a source pump in fluid communication with the liquid outlet, the source pump being configured to move liquid SGM away from the separation tank.

The liquefying system may further comprise a static mixer configured to receive and mix liquid and gas SGM, and to cool, through the mixing, the compressed gaseous SGM. The static mixer may be provided downstream of the source pump. The system may be at least partially located on land or on a marine vessel. According to another aspect of the present invention, there is provided a system for storage of SGM in an undersea environment, the system comprising: • at least one storage vessel, which may be made of a flexible material, in the form of a

(non-permeable, liquid impervious) membrane and being configured to isolate SGM stored therewithin from seawater, and designed to bring the SGM in thermal communication and baric equilibrium with the undersea environment;

• an anchoring system designed to maintain the storage vessel at a predetermined undersea depth, the anchoring system comprising a set of two or more straps attached to a base and contacting the membrane at a common point, each of the straps being anchored to the base at different distances from a reference point; the straps being designed such that the total tension in the straps, at least when the storage vessel is filled with SGM, is substantially equally divided among the straps; and • at least one pipeline configured to bring the interior of the storage vessel in fluid communication with a non-undersea system.

The anchoring system is designed to preserve the structural integrity of the storage vessel in view of hydrostatic buoyancy of the SGM therewith and external hydrodynamic forces.

The storage vessel may be designed to comprise, at least when filled with SGM, at least one substantially circular cross-section.

The total tension in all of the straps when the storage vessel is full of SGM may be less than or equal to, for example at least 95% of, a reference tension being the tension of the membrane at an uppermost point of the cross-section when the storage vessel is full of SGM in the undersea environment.

The reference tension may be given by: τ __ g x (Pse™ater - PsGM )* ^Dl

2 wherein:

• To is the reference tension per unit length of the vessel (i.e., in a direction which is perpendicular to the cross-section;

• g is the acceleration due to gravity;

• Psea_wa_ter and psGM are the densities of seawater and SGM, respectively; and • D is the diameter of the storage vessel at the cross-section, the reference tension being for a unit length of the vessel.

Each of the straps may be secured at both ends thereof below the storage vessel, a middle section of each of the straps passing over the storage vessel.

The anchoring system may comprise three straps. For example: • a first of the straps may be anchored to sides of the storage vessel at a distance therefrom;

• a second of the straps may be anchored on each side of the storage vessel at a point which is directly below the side when the storage vessel is full of SGM; and

• a third of the straps, which may cross below the storage vessel, may be anchored at points below the storage vessel when the storage vessel is full of SGM.

The second and third straps may be bonded to the storage vessel.

The first strap may make, at least in the vicinity of its anchoring, an angle substantially between 30° and 60° with the horizontal, for example about 45°.

The second strap may make, at least in the vicinity of its anchoring, an angle of substantially 90° with the horizontal.

The third strap may make, at least in the vicinity of its anchoring, an angle substantially between 30° and 60° with the horizontal, for example about 40°.

The storage vessel may comprise a plurality of circular cross-sections, the anchoring system comprising a plurality of the sets of straps, each mounted about one of the cross-sections. The storage vessel may be substantially spherical. It may comprise a substantially cylindrical portion, and may further comprise domed ends. The anchoring system may further comprise an auxiliary set of straps, which may be designed in accordance with the above, mounted about a bisecting longitudinal cross-section of the storage vessel.

The storage vessel and anchoring system may be designed to withstand placement at an undersea location at the predetermined depth, the depth being associated with a hydrostatic pressure sufficient to maintain the SGM in a liquid state at a maximum undersea temperature.

At least one of the pipelines may be thermally insulated along at least a portion of its length. The portion may be adjacent to an end of the pipeline designed to be connected to the non-undersea system. At least one of the pipelines mat be of sufficient length so as to allow SGM carried thereby to the storage vessel to be exposed to the undersea temperature for sufficient time to be brought to a temperature substantially the same as the undersea temperature. For example, it may be designed and/or deployed to follow a serpentine path.

The system may comprise a plurality of storage vessels and a manifold connecting each of the storage vessels to a single pipeline.

The manifold may comprise a valve associated with each storage vessel, and arranged such that no more than one storage vessel is in fluid communication with the pipeline at a time.

According to a further aspect of the present invention, there is provided a flexible layered sheet. The sheet of the invention comprises at least one reinforced liquid impervious layer and an anti-fouling composition. The liquid impervious layer may comprise, for example, rubber. For example, a rubber comprising a nitrile rubber copolymer and at least one of a stimulant of vulcanization, a vulcanizer, accelerator, a vulcanization retardant, nano-particles, a softening/plasticizing agent.

According to one embodiment, the liquid impervious layer is reinforced with a polymeric fabric, such as a polymeric fabric comprises fibers of polyester, polyester/nylon and aramid (Kevlar™). The liquid impervious layer may be adhered onto polymeric fabric by means of an adhesive, or may be embedded in the polymeric fabric.

For use in the construction of an underwater storage container, the layered sheet may have a tensile strength of at least 1000 kg/cm, hydrocarbon permeability of less than 5gr/m2/day.This can be achieved by using a polymeric fabric having a tensile strength of at least 200 kg/cm, thickness at least lmm, elongation at least 3%.

The problem of fouling, which may cause damages to the underwater vessel (the customary methods to treat the problem on metal surfaces are not applicable to rubber) will be dealt with by means of creation of a smooth surface (with the aid of materials such as Teflon and fluoro-elastomers) intended to prevent the attachment of organisms.

In the context of the present invention fouling agents may originate from marine environment (aquatic, oceanic, sweet or salty water reservoirs etc.), such as for example barnacles, balanoidae, spirobidae, bryozoa, ascidians, sponges or any other organisms that may reside in marine environment in varying depths. In other types of environments, such as for example

Anti fouling compositions include: self-polishing systems (for example based on copper or zinc acrylates and acrylic resins or copolymers of vinyl chloride), ablative systems (based on resins that are soluble in water which is gradually eroded with time, such as for example vinyl resins, alkyd resins, epoxy resins, acrylic resins, polyurethane resins, polyester resins, vinyl acrylic resins), and leaching systems (porous matrix comprising water-resistant and water- soluble/dispersible resins).

The anti-fouling composition of the invention is capable of forming an antifouling layer or sheet of said reinforced liquid impervious layer, and exhibits resistance to fractures and cracking due to the flexibility of said layered sheet and also is capable of adhering to reinforced liquid impervious layer so as to ensure less peeling tendency. Anti-fouling compositions can be sprayed to provide a uniform thick layer on said reinforced liquid impervious layer.

According to an embodiment, the anti-fouling composition is incorporated into a sheet that is adhered to the liquid impervious sheet. The anti-fouling sheet may further comprise any one or more of a film forming resin, at least one surfactant, at least one biocidal agent, and least one thixotropic agent, at least one filler. The anti-fouling layer may be adhered to the polymeric fabric or to the liquid impervious layer.

According to a still further aspect of the present invention, there is provided a method for producing the flexible layered sheet of the invention. The method of the invention comprises producing a liquid impervious sheet, reinforcing the liquid impervious sheet, and associating an anti-fouling composition with the liquid impervious sheet. The steps of the method can be carried out in any order. The method of the invention may comprise, for example, steps of providing a rubber composition, providing a polymeric fabric, forming a layer of the rubber composition associated with the polymeric fabric; and vulcanizing the rubber composition to produce the liquid impervious sheet.

The step of forming a layer of the rubber composition associated with the polymeric fabric may comprise applying an adhesive to the polymeric fabric prior to associating the polymeric fabric with the rubber composition. Alternatively or additionally, forming a layer of the rubber composition associated with the polymeric fabric may comprise a step selected from:

• calendaring or pressing the rubber composition with the polymeric fabric;

• dipping the polymeric fabric into the rubber composition; and • spreading the rubber composition onto the polymeric fabric.

The method of the invention may further comprise a step of providing an anti-fouling sheet comprising the anti-fouling composition and adhering the anti-fouling sheet to the liquid impervious sheet.

According to a still further aspect of the present invention, there is provided an article of manufacture comprising the flexible layered sheet of the invention such as a vessel or pipe, especially a vessel or pipe adapted for storing or transporting liquefied SGM. The article may be configured to constitute at least a portion of a container (e.g., the vessel, pipe, or a part of an otherwise solid container), and to facilitate baric communication between the interior and the exterior thereof. The article of manufacture may be a storage tank, especially an underwater storage tank.

According to a still further aspect of the present invention, there is provided a system as described above, wherein at least one of the membrane and pipeline (i.e., one or both of them) comprises an article of manufacture as described above.

Generally, at least one of the following properties are required for an underwater storage tank of the invention: high resistance to hydrocarbons permeability (including leaking of hydrocarbons through flexible layered sheet or absorption of hydrocarbons by flexible layered sheet), minimum draining of resins from liquid impervious sheet to surroundings of flexible sheet, elasticity allowing for bending during emptying, resistance to cyclic bending, resistance to marine environment for extended period of time (10-15 years), capable of withstanding wide range of working temperatures without damage or cracking (-10°C-40°C), resistance to tear and prevention of fouling on the surface of the immersed vessel.

The anti-fouling composition reduces or eliminates fouling of the outer surface of the underwater tank or pipe by aquatic organisms. If left unchecked, fouling of the outer surface may cause damage to the underwater tank or pipe. According to an embodiment, the anti-fouling composition is incorporated into a sheet that is adhered to the liquid impervious sheet. The anti- fouling sheet may comprise, for example, any one or more of a film forming resin, at least one surfactant, at least one biocidal agent, and least one thixotropic agent, and a filler, or any other anti-fouling composition as is known in the art. The anti-fouling layer may be adhered to the polymeric fabric or to the liquid impervious layer.

It will be appreciated that herein the specification and claims, the term "flexible layered sheet" is meant to encompass a sheet comprising a polymeric fabric, as will be disclosed herein below, having at least two layers at least one liquid impervious layer and at least one layer of an anti-fouling composition.

In a further embodiment of the invention a layered sheet of the invention comprises a polymeric fabric as will be disclosed herein below, having at least three layers at least two liquid impervious layers and at least one layer of an anti-fouling composition, In one embodiment of the invention a layered sheet of the invention may comprise at least one of liquid impervious and at least one of anti fouling composition layers on opposite faces of polymeric fabric. In another embodiment a layered sheet of the invention may comprise at least one of liquid impervious and at least one of anti fouling composition layers on each face of said polymeric fabric. In a further embodiment a layered sheet of the invention may comprise at least one of liquid impervious layer and at least one of anti fouling composition layer on one face of said polymeric fabric and at least one of liquid impervious layer or at least one anti fouling composition layer on the opposite face.

A polymeric fabric as used herein is meant to encompass a fabric made out of polymeric fibers such as for example polyester, polyester/nylon, aramid (for example Kevlar™). A rubber composition of the invention may be any type of rubber, elastomer capable of preventing the permeability of liquids from either side of flexible sheet of the invention and also capable of endowing flexible properties of a polymeric fabric of the invention without cracking, braking or receiving any type of damage to the liquid impervious layer or the reinforcing polymeric fabric upon any type of forces impacted on said layered sheet or article of manufacture comprising said layered sheet. Non limiting examples of rubber are nitrile rubber

(NBR) composition, NBR-PVC (Polyvinyl Chloride) composition comprising additional components as will be described herebelow.

Nitrile rubber (elastomer) is an elastomeric copolymer of butadiene and acrylonitril

CH₂=CH-CN. The resistance of nitrile rubber to oils and fuels is the main factor dictating the uses of this type of rubber in the flexible layered sheet of the invention. Commercial polymers regularly containing 20-50% acrylonitril, a NBR-PVC combination (Polyvinyl Chloride) enables production of mixtures with low flammability, high resistance to ozone, oils and fuels, as well as good resistance to heat and humidity. The attachment of a rubber composition of said liquid impervious layer to the polymeric fabric surface can be either of a chemical or a physical (mechanical) nature. The chemical composition of the fibers of said fabric and the extent of adequacy of their polarity to the rubber composition of first layer confers the thread its power, or otherwise, its inability to adhere to the rubber. Further to the above, the measure of ruggedness of the fiber surface and/or of the fabric, determines the measure of mechanical attachment of the rubber with the aid of the penetration power of the rubber composition through the fiber pores. The larger and more rugged the inner surface of the fiber, the greater the penetration of the rubber composition thereby achieving strong mechanical attachment between the fibers and the first layer comprising said rubber composition.

Vulcanization is a chemical reaction in the process of which a three dimensional network is formed by cross-linking of the straight elastomer (rubber) chains. Cross-linking is achieved with the introduction of cross-linking group between two elastomer chains. Vulcanization methods include vulcanization by pressing, vulcanization by open steam or hot air or vulcanization by radiation. The rate of vulcanization may be controlled by use of vulcanization stimulants, accelerators and retardants, as is known in the art of vulcanization processes.

It is important to note that the main criterion determining vulcanization reactions is the duration of the process and its temperature. At different vulcanization temperatures and durations it is possible to obtain different properties. Additional additives may be added to the rubber composition of the invention. For example industrial soot or carbon black is a common additive, the addition of which significantly improves the properties of produced layer and particularly its wear and tear qualities. In general terms, it is possible to state that inorganic materials with an average particle size of less than 50 nanometer or a specific area over 50 m²/g are adequate for use as additives. Non limiting examples of additives are silicon and silicates (and in particular silicon produced by means of sedimentation).

The term "nano-particles" as used herein is meant to encompass particulate materials such as for example nano clays made up of aluminium silicate (1 nm thick platelets) and an organic alkyl amine. After mixing with the elastomer (rubber), said nano-particles are dispersed among the elastomer chains.

A "softening/plasticizing agent" as used herein is meant to encompass a compound capable of softening the rubber layer produced. The addition of softening agents contributes to a reciprocal movement of the chains and so the material is softened. Increasing softness of a rubber composition contributes to moisten and disperse the powders in the composition, preventing adhesion to the roller or calender and increasing friction when covering said fabric. The molecular weight of the softening agent is in direct proportion to viscosity it provides the rubber composition. A softening agent with a high molecular weight produces stable rubber compositions, and a softening agent with a low molecular weight produces active elastic mixtures.

The elasticity is well preserved at low temperatures but the weight losses at high temperatures are great. The use of polymeric plasticizers is intended for prevention of draining by means of oils and fuels (known as stable and resistant to draining) and that may pollute the fuel. General Methods to Prepare a Mixture of rubber composition

The manufacturing method of preparing the rubber composition depends on the type of elastomer and the additional components added. In one embodiment of the invention the following mixing methods were used:

• Rolling - Execution in an internal Roll Mill or an open roll mill with two metal rollers.

• Mixing in a Roll Mill.

A mill with two metal rollers is used which operate in opposite directions and at different speeds one from the other with the possibility of increasing or reducing the distance between the rollers. There is also the possibility of inside heating or refrigeration. The materials are added according to a certain order (there are precise rules and standards for the preparation of a mixture) collection and dispersion of the powders and the liquids in the material, and finally a mixture of rubber composition is produced in the shape of a plate. Fabric and rubber system (adhesion of the rubber to the textile)

The purpose of the use of textiles with the rubber products is to confer the product strength and stability. And since most of the products of this kind are intended for dynamic work it is important that when working with them there be no separation of the textile from the rubber covering it. The various forces acting on the product while it works oblige us to consider the product as built as a double system, and we must take into consideration the physical properties of the two components together: rubber and textile. The bonding power between the rubber and the textile is a decisive factor for the quality of the product. Type of pretreatment of polymeric fabrics

For low adhesion polymeric fabrics (such as polyester and aramid (for example Kevlar)), processes were developed to enlarge the inner surface of the fibers and/or enable perfect moistening power of the yarn by the rubber. a. Coating with rubber or adhesive containing poly-functional chemicals of the isocyanate type (Vulcabond, desmodur). b. Dipping The usual dipping liquid (the adhesive) is a watery solution with a triple composition: Resorcinol-formaldehyde-latex, and therefore it is customary to term this kind of dipping as R.F.L dipping. In our case, that involves a nitrile elastomer, it is desirable for the latex in the RFL to also be of the nitrile type. c. Moisture absorption In order to get good bonding between the fibers and the rubber, it is necessary to dry the fabric and keep as low a percentage of moisture as possible (under 3%) all through the various elaboration processes. In the case of use of adhesives based on isocyanates, the moisture content in the fabrics is still more critical, since the isocyanates participate in the chemical reaction with the water and thus lose their bonding power.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic view of a system for storing and supplying a standard gaseous material (SGM);

Fig. 2A is a perspective view of a storage vessel and anchoring system of the system illustrated in Fig. 1 ; Fig. 2B is a cross-sectional view taken along line II-II in Fig. 2A;

Fig. 3 is a perspective view of an alternative embodiment of a base of the anchoring system illustrated in Fig. 2A;

Fig. 4 is a sectional side view of an alternative embodiment of a storage vessel; Fig. 5 A is a schematic view of a shore station of the system illustrated in Fig. 1; and Fig. 5B is a schematic view of a system modification of a facilitating fluid communication, of the shore station illustrated in Fig. 5A. DETAILED DESCRIPTION OF EMBODIMENTS

As illustrated in Fig. 1, there is provided a system, which is generally indicated at 10, for storing and supplying a standard gaseous material (SGM) in a liquid state. The system comprises an undersea storage system 12 at a predetermined undersea depth, at least one of a terrestrial loading/unloading station (hereafter, "shore station") 14a and a marine-surface loading/unloading station (hereafter, "sea station") 14b. The shore and sea stations 14a, 14b are designed for supplying SGM to and from the storage system 12. It will be appreciated that the predetermined undersea depth is one whereat the conditions, including hydrostatic pressure and temperature, are associated with a liquid state of the SGM, that is, any SGM at under those conditions will be in a liquid state. For example, when the SGM is LPG, the depth may be about 30-120 meters, for example 80-100 meters, below the water surface.

The storage system 12 comprises several storage vessels 16 and pipelines 18 designed for carrying SGM to and from the shore and sea stations 14a, 14b in a liquid state. The vessels 16 are designed to subject their contents to the undersea pressure and temperature (i.e., baric and thermal communication), so that SGM stored therewithin can be maintained in a liquid state without the need for any external mechanism for that purpose. In addition, the vessels 16 are designed so as to increase and reduce their volumes in accordance with the amount of liquid SGM stored therein. This ensures that no vacuum is created therein upon unloading SGM therefrom which may lead to vaporization of the SGM therewithin. In addition, the undersea pressure may be utilized to move SGM stored therewithin toward a storage system.

Each storage vessel 16 is supplied with at least one valve 20. In the event that the vessel is connected to two or more pipelines 18 (for example, to be connected to a shore station 14a and a sea station 14b), one valve is provided per pipeline connected thereto. The valve selectively brings the interior of the vessel 16 into fluid communication with or isolation from the pipeline 18. It will be appreciated that while any storage vessel 16 should only have one of its valves 20 open at a time, the storage system 12 may be used, e.g., to have SGM loaded thereto from the sea station 14b to one storage vessel, while at the same time SGM is unloaded therefrom via the shore station 14a from another storage vessel.

In addition, each pipeline 18 may be connected to a manifold 22 in order to be able to be connected to several storage vessels 16. In this case, the valves 20 are connected to the manifold 22. With such an arrangement, a first manifold 22 may be connected to a first pipeline 18 connected to the shore station 14a, and a second manifold to a second pipeline connected to the sea station 14b. In this way, a valve 20 bridging between the first manifold 22 and a first vessel 16 may be open at the same time that a valve bridging between the second manifold and a second vessel is open, which allows, for example, loading of the storage system 12 via the sea station 14b at the same time that unloading is occurring via the shore station 14a.

The shore and sea stations 14a, 14b are designed to supply SGM in a liquid state to a tank 62 (for example, a tanker truck which then supplies the SGM to individual customers), taking advantage of the fact that the storage vessels 16 are designed to avoid the presence of gaseous SGM therewithin, thus eliminating the need for a system designed to compensate for this phenomenon.

Each storage vessel 16 is in the form of a non-permeable, liquid impervious membrane 26 be made of a flexible material, thus allowing baric communication between the contents thereof and its external environment. The material is selected such that is thermally conductive, so that the temperature of the SGM therewithin may reach the temperature of the undersea environment, thus preventing the temperature thereof to increase (for example, due to condensation of SGM) to a level which would cause it, even subject to hydrostatic pressure, to vaporize.

The membrane 26 is made of a flexible liquid impervious layer. An example of a formulation of the flexible liquid impervious layer is summarized in Table 1.

TABLE 1

Table 2 shows various NBR polymers that may be used in the liquid impervious layer of Table 1. TABLE 2

Table 3 shows various fillers that may be used in the liquid impervious layer of Table 1.

TABLE 3

Table 4 shows various polymeric fabrics that may be used in the liquid impervious layer of Table 1.

TABLE 4

Threads - number of threads per cm width

Weave - (thread on thread)

Elongation - elongation of the fabric when tearing it Table 5 shows the components of a rubber composition ("dipping") into which the polymeric fabric may be dipped, and another rubber composition ("cover") that may be used to cover the polymeric fabric.

TABLE 5

Table 6 shows a procedure for mixing the components of the rubber composition.

TABLE 6

The rheological properties of FC-88 were tested at 3 temperatures in the MDR-2000 rheometer. The results are shown in Table 7.

TABLE 7

ML: minimal moment - measure of plasticity of the composition MH: maximum moment - proportional to the modulus of the composition S" minimum viscosity

Ts₂ preliminary vulcanization time - the time necessary for the moment to rise two units above the minimum

T_{90 :} the necessary time to achieve 90% of the maximum moment.

The mechanical properties of FC-88 were determined, and the results are shown in Table

8.

TABLE 8

The hardness of vulcanized rubber is an expression of the elasticity modulus, that is to say, resistance to deformation under the influence of stress or penetration of a hard needle and defined by a scale (Shore A for example).

The rubber layer would have a hardness in the range of 75-85 units in Shore degrees. Since the sheet strength is determined mainly by the polymeric fabric, while the rubber layer prevents permeability and provides liquid imperviousness. A tensile strength at break of a minimum of 10 Mpa and elongation before break of 250% would be adequate for most applications. PREPARING THE RUBBER COMPOSITION FOR APPLICA TION TO THE POL YMERIC FABRIC

• Solvent - MEK : Toluene ratio 70 : 30

• Adhesive: Desmodur RFE (9.3% NCO content, 27% non volatile, Density 1 gr/cm³) MIXING PROCEDURE

Stage I - Mastication process of the mixture (FC-88)

TABLE 9

Rubber cracking Cracker mill to break down large

Stage II - Addition of solvents to the rubber composition FC-88

TABLE 10

*Technical dry grade solvents.

Mixing is performed 5-6 hours, solvent is added gradually.

The rubber composition A is adequate for coating by means of the spreading method. When preparing a rubber composition for dipping, the process indicated above with FC-87 must be repeated in order to obtain Base composition A₁, dilute once again and add Desmodur RFE as indicated in Table 11. TABLE 11

Solution A₁ is diluted with MEK/Toluene, desmodur RFE is incorporated into dough A₁ slowly by strong stirring immediately before adhesive is applied. The composition is stirred to avoid formation of bubbling.

Pot Life: Solution shall be closed from air. Useful life is approximately 8 hours at 24°C. PREPARA TION OFREINFORCED LIQUID IMPERMEABLE SHEETSAMPLES

Spreading was executed with the aid of a "Doctor knife". The rubberized fabric was left exposed to air for 24 hours for evaporation of the solvents. The sheet was then turned over and the process repeated. Between the two layers of the treated fabric a layer of FC-88 was spread and the three layers together were introduced into a press at a temperature of 160°C in accordance with the rheometer graph for a period of t₉o +5 to obtain cross-linking. 2.5 cm strips were cut and the separation strength between the rubber and the fabric was tested by means of the LLOYD tensometer; test speed: 2"/min in accordance with STD. ASTM D-751. The results are shown in Table 12.

TABLE 12

An adhesion of 7.5kg/5 cm of the coating to the fabric was found to be satisfactory. FC-88 with the addition of Desmodur produced a satisfactory bonding to the polymeric fabrics. FC-87 without stimulants and the addition of Desmodur also gives a satisfactory good adhesion to the tested fabrics. The differences in bonding strength between FC-87 and FC-88 containing Desmodur are most likely not significant and are due to variability in the application of the coating since the coating was applied by hand. The conclusion of this test is that the addition of Desmodur improves adhesion quality (5.2-6kg/cm as opposed to 0.6 kg/5 cm). USE OF FILLERS IN RUBBER COMPOSITIONS For composition of FC-88, Mistron Vapor-Talc was used as a white filler in an amount of

45 parts to 100 NBR parts. The effect of the filler structure and the size of the particles on the properties of the rubber were determined by changing the Mistron Vapor with the same amount of Vltrasil VN3 (45 parts). The particle sizes of the fillers used are as follows:

• Mistron Vapor Microtalc - size of particles 0.32 micron • Vltrasil VN₃. (Nodular) - size of particles 16 - 20

• Cloisite 3OB - Layered Nano - clay - size of particles <2.0-13.0 μm

Table 13 shows the effect of Fillers structure on properties of FC-88

TABLE 13

There is an evident effect of the dimension of the particles on the permeability of hydrocarbons (tested with Isoctane). With Mistron Vapor, permeability is low and its value reaches a mere 12 gr/m²day as opposite to Vltrosil VN₃ which, in the same testing conditions, gave a much higher permeability result - 264 gr/m²day. On the other hand, in the latter case, resistance to tear, elongation and adhesion to fabric are higher.

Even though the properties of Isoctane are similar to the properties of LPG, additional permeability tests were conducted with Fuel "C" (50% Toluene + 50% Isoctan), which is more "aggressive", in order to better detect the influence of Cloisite 30B on the two amounts of permeability of Fuel C.

In a comparison test, FC-88 with Mistron Vapor gave a permeability to Isoctane of 12 gr/m² day, whereas the same FC-88 with Mistron Vapor showed a permeability to Fuel "C" of 18.2 gr/m² day (See Table 13-1 below).

TABLE 13-1

Quite unexpectedly, the results showed that the addition of Cloisite 30B at the two levels did not improve permeability in comparison with the same mixture with Mistron Vapor only.

RUBBER COMPOSITIONS FOR CALENDARING

Two basic properties are desired of compounds destined to be calendared:

• Low elasticity ensuring "flow" of the rubber, and enabling penetration into the spaces, between the fibers.

• Smooth surfaces after the calendaring process.

Table 14 shows two rubber compositions suitable for calendaring on a polymeric fabric.

TABLE 14

In both LP-IO and LP-12 the amount of softener Hycar 1312/Struktol WB-300 quite high (20 parts for 100 parts of NBR) in order to obtain a relatively low viscosity.

In the LP-12 as compared to LP-10, there is a higher amount of sulfur and Si-69 additive for the purpose of achieving a higher level of cross-linking.

Tables 15 and 16 show, respectively, the rheological and mechanical properties of the two rubber compositions.

TABLE 15 TABLE 16

LP-12 showed high values for the properties: hardness, Modulus 100%, Tear strength, and a low value for elongation, all the results in comparison with those of LP-10 demonstrate a higher level of cross-linking.

Table 17 shows permeability of Isoctane through LP-10 and LP-12.

TABLE 17

The result of the permeability test (4 gr/m²/day) is below the maximum allowed permeability.

The difference of weight after soaking in isoctane is minimal up to negligible. Table 18 shows the adhesion of the rubber LP- 12 to fabrics impregnated with FC-87 + Desmodur RFE.

TABLE 18:

ANTI-FOULING COMPOSITIONS

Table 19 provides components of anti-fouling compositions of the invention.

TABLE 19

Table 20 provides components of master batches based on NBR and hydrocarbon resin of the anti fouling compositions of the invention from which the anti-fouling layers will be constructed on said reinforced liquid impervious layer of the invention.

TABLE 20

Table 21 provides anti-fouling compositions based on the master batches given in Table 20, wherein additional components are added to the master batch based on NBR.

TABLE 21

In the preparation of the anti-fouling composition there are two main stages:

• In stage 1 Laroflex, Efka 6230, Tricesyl phosphate and additional components are mixed in solvent solution comprising Toluen-MIBK-EtAc in a 1 :1 :1 ratio.

• In stage 2 Desmodure RE is added as an adhesive agent and MEK. The antifouling layer was formed (spreading) on the reinforced liquid impervious layer (2mm thickness). After

10 min another antifouling layer was spread.

Table 22 provides compositions and provides components of master batches based on NBR and hydrocarbon resin of the anti fouling compositions of the invention from which the anti-fouling layers will be constructed on said reinforced liquid impervious layer of the invention. TABLE 22

Tables 23A and 23B provides components of master batch based on NBR and rosin of the anti fouling compositions of the invention from which the anti-fouling layers will be constructed on said reinforced liquid impervious layer of the invention.

TABLE 23A

TABLE 23B

Table 21 provides anti-fouling compositions based on the master batch given in Table 23, wherein additional components are added to the master batch based on NBR and rosin.

TABLE 24

Table 25 provides components of master batches based on CPVC and isobutyl ether of the anti fouling compositions of the invention from which the anti-fouling layers will be constructed on said reinforced liquid impervious layer of the invention. TABLE 25

Table 26 provides anti-fouling compositions based on fluoro-elastomen

TABLE 26

As illustrated in Fig. 2A, the storage vessel 16 is designed so that when full, it has a cylindrical main portion 28, with a substantially uniform circular cross-section along its length, capped with two domed portions 30. Alternatively (not illustrated), the vessel may be designed to have a full- or semi-spherical shape when full. As illustrated in Figs. 2A and 2B, a storage vessel 16 of the storage system 12 is maintained at the predetermined undersea depth by an anchoring system 24 (as will be described below, the anchoring system comprises a plurality of sets of straps; for clarity only two of these sets, along with a set of auxiliary straps, are illustrated in Fig. 2A). Besides maintaining the storage vessels 16 at the predetermined depth, the anchoring system 24 is designed to preserve the structural integrity thereof. Thus, the internal hydrostatic buoyancy of the SGM, as well as undersea hydrodynamic forces (such as undersea currents and forces due to surface waves) is taken into account when designing the storage vessels 16 and the anchoring system 24.

The anchoring system is designed to prevent the storage vessels 16, when filled with liquid SGM having a density less than that of the surrounding seawater, from floating away. In addition, it helps keep the tension in the membrane 26 of the storage vessel 16 close to the design tension and free of areas of concentrated tension, and preserves its shape in the underwater environment. In addition, it is flexible, adapting its shape to the shape of the storage vessel 16 during filling thereof. It further prevents vertical movement of the storage vessel 16, as well as lateral movement in all directions, due to undersea environmental conditions, for example due to currents, surface waves, etc.

As better seen in Fig. 2B, the anchoring system 24 comprises several sets of straps, each set comprising three straps 32a, 32b, 32c, each at least partially encircling a circular cross- section of the storage vessel 16; when all of the straps are in place, the vessel is completely encircled by the straps, even if it does not contact at least one of the straps at all points along its circumference along the cross-section, or if it is not fastened to the straps. (Hereafter, when all straps are referred to together, or when an arbitrary strap is referred to, the reference numeral 32 will be used for convenience, notwithstanding the fact that it does not appear independently in the figures.) The anchoring system 24 is designed such that when the vessel 16 is full, the total static tension in all of the straps 32 is equally divided among all three straps. Load cells (not illustrated) may be provided on each strap, for example for determining the external forces on the storage vessel 16, as well as the amount of SGM therewithin. The anchoring system 24 further comprises a rigid base 34, for example made of concrete, attached to the seabed, to which the straps 32 are secured. For this purpose, any appropriate connection hardware may be provided.

In order to determine the total design tension (i.e., the maximum operating tension when the vessel 16 is full of GSM in the undersea environment) for the straps 32, a reference tension, which is, for example, the static tension at an uppermost point of the cross-section when the storage vessel is full of GSM at its undersea location. This reference tension, which is given per unit length, in a direction perpendicular to the cross-section, of the vessel 16, is given by:

° ^~ 2 ' where To is the reference tension, g is the acceleration due to gravity, p_seawater and P_SGM are the densities of seawater and SGM, respectively, and D is the diameter of the storage vessel at the cross-section. In practice, the total design tension is slightly lower than this figure, for example 95%-99% thereof. Once the design tension is determined, it is multiplied by a length of vessel which is secured by the set of straps, which is typically the distance between straps, or may be the average distance between sets of straps adjacent thereto along the length of the vessel (for example if the straps are not uniformly spaced), multiplied by the width of the straps, then divided by the number of straps in each set to obtain the design tension for each strap.

It will be appreciated that during design of the system, once the design tension for each strap 32 is determined, the length of each strap is designed so that the strap will be subjected to the design tension when the vessel is full of SGM under static conditions.

As the specific density of the SGM is typically lower than 1 (i.e., it is less dense than the surrounding seawater), the storage vessel 16 floats in the water. Thus, the straps 32 may pass over the storage vessel 16 and be secured therebelow, without having to account for potential sinking thereof (i.e, the lower density of the filled storage vessel vis-a-vis the surrounding seawater assures that any vertical displacement thereof due to buoyancy will be restrained by the passing thereover of the straps 32). hi any event one or more of the straps 32 may be bonded or otherwise attached to the storage vessel 16.

A first strap 32a is secured to the base 34 to the sides of the storage vessel 16, at a distance therefrom. Thus, the first strap 32a may make an angle with the base 34, at least in the area of its anchoring, of about 45°. A second strap 32b is anchored on each side of the storage vessel 16 at a point which is directly below the side when the storage vessel is full of SGM. Thus, the second strap 32b descends from the storage vessel 16, when full, substantially vertically, and thus make an angle with the base 34 of approximately 90°. A third strap 32c is secured to the base 34 in an area of the base below the storage vessel 16, and may cross. It may be secured to the base 34 so as to make an angle therewith, at least in the area of its anchoring, of about 40°. Depending on the shape of the storage vessel 16, it may contain several circular cross- sections. Several sets of straps 32 may be provided, each one at a different one of the circular cross-sections of the storage vessel 16. A sheet of flexible material may be provided attached to the top of the storage vessel 16, to which all of the second and third straps 32b, 32c are attached. An additional sheet of flexible material may be provided at the top of the storage vessel 16 and separate therefrom (i.e., not attached thereto), to which all of the first straps 32a are attached.

A set of auxiliary straps 32a', 32b', 32c' may be provided mounted about a cross-section of the storage vessel 16 which bisects it longitudinally. The auxiliary set of straps may be designed as above, or they may have a different design.

An alternative base 34' is illustrated in Fig. 3. The base 34' comprises two support beams, 36, and a plurality of hollow cylindrical tubes 38 extending therebetween. A control system (not illustrated) is provided, which controls whether or not the interiors of the tubes 38 are in fluid isolation or communication with their surroundings. A pump (not illustrated), adapted to empty the tubes 38 and operated by the control system, is also provided. The support beams are designed such that the overall density of the base 34' is greater than that of seawater when the tubes 38 are filled with water, but less than that of seawater when the tubes are filled with air; thus the raising and lowering of the base 34' is controlled by controlling whether to tubes 38 are filled with air or seawater. In addition, a pipeline 40 may be provided to supply air to the base 34' when it is submerged.

An alternative to a vessel made of a flexible material is presented in Fig. 4, wherein the vessel 16 is made of a rigid material, and formed as a piston having a storage area 31 with a constant cross-section along an axis 33. A plunger 35, having a shape of the cross-section, is free to move along the axis, and restrained from being ejected from the storage area 31. Thus, when SGM is supplied thereto, the plunger 35 moves up, but, since it is subject to the undersea pressure and free to move, it at the same time subjects the contents of the vessel to that pressure. During use, the storage vessel 16 is designed to contain SGM in a liquid state. The pressure necessary to supply the SGM is supplied by the undersea hydrostatic pressure. It will be appreciated that when supplying SGM to a non-undersea environment, the pressure acting thereon as it ascends through the water will decrease, which would tend to allow some of the SGM to vaporize. Therefore, the pipelines 18 may be thermally insulated, at least in the portion in which the external pressure is sufficiently low so as to allow vaporization. For example, these portions of the pipelines 18 may include, e.g., a concrete layer, or a high-density polyethylene or other hard plastic or polymeric layer. This will keep the temperature of the SGM low, which will allow for more of the SGM to remain in its liquid state.

As described above, the SGM may be provided via a shore station 14a. (The following description will be specific to a shore station supplying to a tanker truck. However, it will be appreciated that the same arrangement may be provided at a sea station 14b, mutatis mutandis, for example for loading/unloading SGM to/from a tanker ship. To highlight this point, and for simplification, the term "shore station 14a" will be replaced with the term "station 14".)

Although the pipeline 18 is thermally insulated to limit the amount of vaporization of the SGM therein, a relatively small amount of SGM will vaporize. Thus, as illustrated in Fig. 5A, the station 14 is provided with a liquefying system 42 designed to receive SGM from the undersea storage system 12, and ensure that it is provided as a pure liquid. The undersea storage system 12 (not illustrated in Fig. 5A) and liquefying system 42 can together be considered to constitute an SGM source 44, which provides SGM in a liquid state substantially free of SGM in a gaseous state. Due to the flexibility of the storage vessels 16, the overall volume of the source 44 decreases together with the total volume of the liquid SGM therein. Thus, there is no need to compensate for vaporization of liquid SGM during supply therefrom. The liquefying system 42 comprises a separation tank 46 configured to receive SGM from the undersea storage system 12 and provide it as liquid from one outlet thereof and gas from a separate outlet thereof, a compressor 48 configured to increase the pressure of a gas, a pump 50, and a static mixer 52.

The separation tank 46 comprises an inlet 54 for the receipt of SGM from the undersea storage system 12, a liquid outlet 56 for providing SGM in a liquid state, and a gas outlet 58 for providing SGM in a gaseous state. Typically, the liquid outlet 56 is located near the bottom of the separation tank 46, and the gas outlet 58 is located near the top, in order to take advantage of the physical densities of liquid and gas in order to separate them. However, it will be appreciated that any known device and/or method for separating the liquid and gas portions of the SGM from each other may be employed.

SGM in a gaseous state flows from the gas outlet 58 to the compressor 48, which increases the pressure of the gas, without condensing it. At the same time, SGM in a liquid state flows from the liquid outlet 56, impelled by the pump 50. The two fluids mix in the static mixer, which may have internal blades (not illustrated) to aid in mixing. The elevated pressure of the gas causes it to condense once it mixes with the liquid. As a result, the SGM is provided from the source 44 as a pure liquid.

The station 14 further comprises system 60 for facilitating fluid communication in two directions between the source 44 and a tank 62, such as a tanker truck, designed to contain SGM in gas and liquid states, and which is sealed during loading and unloading of, expect for points of connection to an SGM loading or unloading station. As will be seen, the system 60 is designed such that during fluid flow between the source 44 and the tank 62, SGM is drawn from the tank in one fluid state, undergoes a phase within the system 60, and is returned to the tank in a second fluid state.

The system 60 comprises a supply system 64 configured to facilitate the supply of liquid SGM from the source 44 to the tank 62. The supply system 64 comprises a supply outlet 66 and a supply inlet 68. The supply outlet 66 is positioned to be brought into fluid communication with the source 44, and is designed so as to be attached to the tank 62, so as to bring the source and the interior of the tank in fluid communication with each other. In this way, liquid SGM from the source 44 can be supplied directly to the tank 62. The supply inlet 68 is designed so as to be attached to the tank 62 in such a way that vaporized SGM therewithin can be received by the supply system 64.

In addition, the supply system 64 comprises a condenser 70, which may comprise a heat exchanger, which is in fluid communication with the supply inlet 68 and downstream thereof. Thus, it is configured to receive the vaporized SGM from the tank 62 and liquefy it. This liquefied SGM is then combined with the liquid SGM which is provided directly by the source 44, on its way to the tank 62 via the supply outlet 66. In this way, as the tank 62 is filled, as some of the liquid SGM begins to vaporize, the vapor is recaptured, undergoes a phase change into liquid, and is returned to the tank.

Furthermore, the supply system may comprise an injector 72, which is configured to move the SGM received from the source 44 and from the condenser 70 toward the supply outlet 66. The injector may be configured so as to combine the liquid SGM from the source 44 and from the condenser 70. The system 60 further comprises an acceptance system 74 configured to facilitate the supply of liquid SGM from the tank 62 to the source 44 (i.e., acceptance of liquid SGM by the source from the tank). The acceptance system 74 comprises an acceptance inlet 76 and an acceptance outlet 78. The acceptance inlet 76 is positioned to be brought into fluid communication with the source 44, and is designed so as to be attached to the tank 62, so as to bring the source and the interior of the tank in fluid communication with each other. In this way, liquid SGM from the tank 62 can be supplied directly to the source 44. The acceptance outlet 78 is designed so as to be attached to the tank 62 in such a way that vaporized SGM can be provided thereto by the acceptance system 74.

In addition, the acceptance system comprises a vaporizer 80, which is in fluid communication with the acceptance outlet 78 and upstream thereof. Thus, it is configured to provide vaporized SGM from to the tank 62. A control valve 82 is provided to divert a small amount of liquid SGM thereto during supply of SGM from the tank 62 to the source 44. The SGM for the vaporizer 80 is diverted from that supplied by the tank 62, as it is supplied via the acceptance inlet 76. In this way, as the tank 62 is emptied during supply of SGM to the source 44, and some of the liquid SGM therein begins to vaporize, some of the supplied liquid SGM is diverted, undergoes a phase change into gas, and is returned to the tank.

It is important that when SGM is supplied to the undersea storage system 12, it is in a pure liquid state. Therefore, SGM provided by the acceptance system 74 should be at or below a predetermined safe-storage temperature.

During the winter months, the temperature of the liquid SGM in the tank 62 is typically low enough for this not to be a problem (i.e., it is below the safe-storage temperature). However, this low temperature is associated with a lower pressure. Thus, a pump 84 is provided, designed to operate either in an active state, wherein it moves liquid toward the source 44, or in an inactive state, wherein it allows free passage of liquid therethrough.

During the summer months, the temperature of the liquid SGM in the tank 62 is typically high enough to provide enough pressure to obviate the necessity for the pump 84. However, the temperature is too high for safe storage of the SGM in the undersea storage system 12. Thus, a heat exchanger 86 is provided to cool the SGM to a temperature which does not exceed the safe- storage temperature.

The acceptance system may thus comprise a controller 88 configured to operate the pump 84 and heat exchanger 86 in either a hot-weather mode or a cold-weather mode, wherein:

• in the hot-weather mode, the pump 84 is inactive and the heat exchanger 86 is operating to lower the temperature of the liquid below the safe-storage temperature; and

• in the cold-weather mode, the pump 84 is active and the heat exchanger 86 is not operating. It will be appreciated that other modes are possible, for example if the pressure of the liquid SGM in the tank 62 is sufficiently high that operation of the pump 84 is not necessary, but the temperature is below the safe-storage temperature, so operation of the heat exchanger is not necessary either, etc. A temperature sensor 90, such as a thermostat, may be provided to measure the temperature of the liquid SGM received from the tank 62. The controller is configured to select a mode of operation based on the measured temperate.

Alternatively, the controller 88 may be configured to allow a user to manually select a mode of operation. As illustrated in Fig. 5B, the supply inlet 68 and the acceptance outlet 78 may be formed as a single unit. A valve 92 is provided to selectively direct flow of SGM either to the condenser 70 during supply of SGM from the source 44 to the tank 62, or from the vaporizer 80 during supply of SGM from the tank to the source.

The liquid SGM supplied via the acceptance system 74 does not need to be processed by the liquefying system 42 before being stored in the undersea storage system 12. Thus, the SGM may bypass the liquefying system 42. A valve 94 may be provided upstream of the liquefying system 42, which selectively brings the acceptance system 74 into fluid communication with the undersea storage system 12 for direct supply thereto of liquid SGM, or brings the undersea storage system 12 into fluid communication with the liquefying system for direct supply thereto of SGM. This allows for a single pipeline 18 to be used for providing SGM to and from the undersea storage system 12.

It will be appreciated that valves, for example valves 82, 92, and 94, may be embodied by two or more valves, each on a different branch, and configured such that no more than one is open at a given time, thus directing the flow of SGM. In addition to the above, proper electrical, communication (wire or wireless), and other necessary systems, as deemed necessary, are provided to ensure proper and coordinated use of the system 10. Furthermore, additional valves, venting arrangements, etc., may be provided as necessary, without departing from the spirit and scope of the present invention.

Capacity sensors and/or leak detectors may be provided for each storage vessel 16 and/or for the entire undersea storage system 12.

It will be appreciated that the above system facilitates storage of SGM in an undersea environment, in such a way that the hydrostatic pressure and temperature are exploited to maintain the SGM in a liquid state. This arrangement has several advantages: • As the pressures internal and external to the storage vessel 16 are essentially equal, the pressure acting on the membrane 26 (as compared to a terrestrial storage arrangement, or an undersea storage arrangement wherein the stored SGM is isolated from the undersea pressure) is substantially eliminated. Thus, a lighter and cheaper storage vessel may be provided.

• The land necessary for the storage, while not reduced, can be located away from terrestrial locations, which both frees the land for other uses, and mitigates the aesthetic intrusion that terrestrial storage arrangement pose.

• Undersea storage arrangements are thought to be more secure, as they are not easily accessed by terrorists.

• As the undersea environment does not contain oxygen, the risk of explosion is substantially eliminated.

• As the stored SGM is in baric communication with its surroundings, the undersea hydrostatic pressure can be used to unload SGM therefrom. As the volume of the storage vessel 16 decreases under this pressure with the unloading of SMG, there is no vaporization therewithin due to evacuated space within the vessel, and substantially of the stored SGM may be dispensed without the need for auxiliary equipment such as pumps, etc.

• As the pressure of the SGM is substantially constant throughout the process of unloading, the risk of freezing within pipelines is reduced or eliminated.

• When loading SGM into the undersea storage system 12, other normal operations may be carried out at a station 14.

• In the event of a leak, the SGM floats to the top of the water and evaporates.

Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations and modifications can be made without departing from the scope of the invention mutatis mutandis.

Claims

CLAIMS:

1. A system for communicating between a source of standard gaseous material (SGM) in a liquid state substantially free of SGM in a gaseous state, and a tank designed to contain SGM in gas and liquid states; said system being configured to be in fluid communication with said source for flow therebetween of SGM in a pure liquid state, and with said tank for drawing SGM from said tank in a first state and returning it to the tank in a second state, said system being configured to cause the drawn SGM to undergo a phase change from said first state to said second state before returning it to said tank.

2. A system according to Claim 1, wherein said source comprises an undersea storage vessel.

3- A system according to Claim 2, wherein said undersea storage vessel is configured to utilize undersea conditions for maintaining SGM in a liquid state.

4. A system according to any one of Claims 2 and 3, further comprising a supply pipeline adapted to carry the SGM from said storage vessel for supply via the system, said pipeline being thermally insulated along at least a portion of its length.

5. A system according to any one of the preceding claims, comprising a supply system configured to facilitate supply of liquid SGM from said source to said tank, said supply system comprising:

• a supply outlet in fluid communication with said source, and configured for attachment to said tank to bring said source and tank into fluid communication with each other to facilitate the supply;

• a supply inlet configured for attachment to said tank to receive vaporized SGM therefrom; and

• a condenser in fluid communication with said supply inlet and downstream thereof, configured to receive vaporized SGM and liquefy it; said supply system being further configured to combine liquefied SGM exiting said condenser with SGM provided by said source.

6. A system according to Claim 5, wherein said condenser comprises a heat exchanger.

7. A system according to any one of Claims 5 and 6, said supply system further comprising an injector configured to move said SGM received from said source and from the condenser toward said supply outlet.

8. A system according to Claim 7, wherein the liquefied SGM exiting said condenser combines with SGM provided by said source within said injector.

9. A system according to any one of the preceding claims, further comprising an acceptance system configured to facilitate acceptance of liquid SGM from said tank to said source, said acceptance system comprising:

• an acceptance inlet in fluid communication with said source, and configured for attachment to said tank to bring said source and tank into fluid communication with each other to facilitate the acceptance;

• an acceptance outlet configured for attachment to said tank to supply vaporized SGM thereto; and

• a vaporizer in fluid communication with said acceptance outlet and upstream thereof, configured to receive liquid SGM and vaporize it; said acceptance system being further configured to divert a portion of liquid SGM exiting said tank toward said vaporizer.

10. A system according to Claim 9, said acceptance system further comprising a control valve configured to selectively divert a predetermined amount of SGM toward said vaporizer.

11. A system according to any one of Claims 9 and 10, said acceptance system further comprising:

• an acceptance pump configured for selectively moving liquid in an active state thereof or allowing free passage of liquid therethrough in an inactive state thereof, in a direction toward said source; and

12. A system according to Claim 11 , wherein said acceptance system further comprises a controller designed to operate said acceptance system in one of:

• a hot- weather mode, wherein said acceptance pump is inactive and said heat exchanger is operating to lower the temperature of the liquid below said acceptance temperature; and

• a cold-weather mode, wherein said acceptance pump is active and said heat exchanger is not operating.

13. A system according to Claim 12, wherein said acceptance system comprises a temperature sensor to measure the temperature of the liquid received from the tank, said controller being configured to select a mode of operation based on the measured temperate.

14. A system according to Claim 13, wherein said controller is configured to select said hot- weather mode if the measured temperature is above said acceptance temperature, and to select said cold- weather mode if the measured temperature is below said acceptance temperature.

15. A system according to Claim 12, wherein said controller is configured to allow a user to select a mode of operation.

16. A system according to any one of Claims 11 through 15, configured to store SGM received by said acceptance system in a storage vessel anchored at a depth undersea, said acceptance temperate being determined based on the temperature necessary to maintain said SGM in a liquid state subject to hydrostatic pressure associated with the depth.

17. A system according to any one of Claims 5 through 8 and any one of Claims 9 through 15, wherein said acceptance outlet constitutes said supply inlet, said system further comprising a valve configured to selectively direct flow of SGM to said condenser during supply of SGM to the tank, and from said vaporizer during acceptance of SGM from the tank.

18. A system according to any one of the preceding claims, wherein said source comprises a liquefying system comprising:

• a separation tank having an inlet, a liquid outlet, and a gas outlet, said separation tank configured to receive SGM via said inlet, to provide SGM in a substantially pure liquid state via said liquid outlet, and to provide SGM in a substantially pure gaseous state via said liquid outlet; and • a source compressor in fluid communication with and configured to receive fluid from said gas outlet, said source compressor being configured to increase the pressure of the SGM in a gaseous state; said liquefying system being configured such that SGM exiting the source compressor combines with liquid SGM provided via said liquid outlet.

19. A system according to Claim 18, said liquefying system further comprising a source pump in fluid communication with said liquid outlet, said source pump being configured to move liquid SGM away from the separation tank.

20. A system according to any one of Claims 18 and 19, said liquefying system further comprising a static mixer configured to receive and mix liquid and gas SGM, and to cool, through the mixing, the compressed gaseous SGM.

21. A system according to Claims 19 and 20, wherein the static mixer is provided downstream of said source pump.

22. A system according to any one of the preceding claims, being at least partially located on land.

23. A system according to any one of the preceding claims, being at least partially located on a marine vessel.

24. A system according to any one of the preceding claims, comprising the source.

25. A system for storage of SGM in an undersea environment, said system comprising:

• at least one storage vessel in the form of a membrane and being configured to isolate SGM stored therewithin from seawater, and designed to bring said SGM in thermal communication and baric equilibrium with the undersea environment; • an anchoring system designed to maintain said storage vessel at a predetermined undersea depth, said anchoring system comprising a set of two or more straps attached to a base and contacting said membrane at a common point, each of said straps being anchored to said base at different distances from a reference point; said straps being designed such that the total tension in the straps, at least when the storage vessel is filled with SGM, is substantially equally divided among said straps; and

• at least one pipeline configured to bring the interior of the storage vessel in fluid communication with a non-undersea system.

26. A system according to Claim 25, said storage vessel being made of a flexible material.

27. A system according to any one of Claims 25 and 26, said storage vessel comprising, at least when filled with SGM, at least one substantially circular cross-section.

28. A system according to any one of Claims 25 through 27, being designed such that the total tension in all of the straps when the storage vessel is full of SGM is no greater than a reference tension being the tension of the membrane at an uppermost point of the cross-section when the storage vessel is full of SGM in the tindersea environment.

29. A system according to Claim 28, being designed such that the total tension in all of the straps when the storage vessel is full of SGM is at least 95% of the reference tension.

30. A system according to any one of Claims 28 and 29, wherein said reference tension is given by:

wherein:

• To is the reference tension per unit length of the vessel;

• g is the acceleration due to gravity; • P_seawater and P_SGM are the densities of seawater and SGM, respectively; and

• D is the diameter of the storage vessel at the cross-section; said reference tension being for a unit length of the vessel.

31. A system according to any one of Claims 25 through 30, wherein each of said straps is secured at both ends thereof below said storage vessel, a middle section of each of said straps passing over said storage vessel.

32. A system according to any one of Claims 25 through 31 , wherein said anchoring system comprises three straps.

33. A system according to Claim 32, wherein: • a first of said straps is anchored to sides of the storage vessel at a distance therefrom;

• a second of said straps is anchored on each side of the storage vessel at a point which is directly below the side when the storage vessel is full of SGM; and

• a third of said straps is anchored at points below said storage vessel when the storage vessel is full of SGM.

34. A system according to Claim 33, wherein the third strap crosses below the storage vessel.

35. A system according to any one of Claims 33 and 34, wherein the second and third straps are bonded to the storage vessel.

36. A system according to any one of Claims 33 through 35, wherein the first strap makes, at least in the vicinity of its anchoring, an angle substantially between 30° and 60° with the horizontal.

37. A system according to any one of Claims 33 through 36, wherein the second strap makes, at least in the vicinity of its anchoring, an angle of substantially 90° with the horizontal.

38. A system according to any one of Claims 33 through 37, wherein the third strap makes, at least in the vicinity of its anchoring, an angle substantially between 30° and 60° with the horizontal.

39. A system according to any one of Claims 27 through 38, said storage vessel comprising a plurality of said cross-sections, said anchoring system comprising a plurality of said sets of straps, each mounted about one of said cross-sections.

40. A system according to Claim 39, wherein said storage vessel is substantially spherical.

41. A system according to Claim 39, wherein said storage vessel comprises a substantially cylindrical portion.

42. A system according to Claim 41, wherein said cylindrical portion comprises domed ends.

43. A system according Claim 42, wherein the anchoring system further comprising an auxiliary set of straps mounted about a bisecting longitudinal cross-section of the storage vessel.

44. A system according to Claim 43, wherein said auxiliary set of straps is in accordance with any one of Claims 29 through 34.

45. A system according to any one of Claims 25 through 44, said storage vessel and anchoring system being designed to withstand placement at an undersea location at the predetermined depth, said depth being associated with a hydrostatic pressure sufficient to maintain said SGM in a liquid state at a maximum undersea temperature.

46. A system according to any one of Claims 25 through 45, at least one of said pipelines being thermally insulated along at least a portion of its length.

47. A system according to Claim 46, said portion being adjacent to an end of the pipeline designed to be connected to said non-undersea system.

48. A system according to any one of Claims 25 through 47, at least one of said pipelines being of sufficient length so as to allow SGM carried thereby to the storage vessel to be exposed to the undersea temperature for sufficient time to be brought to a temperature substantially the same as said undersea temperature.

49. A system according to Claim 48, said pipeline being arranged to follow a serpentine path.

50. A system according to any one of Claims 25 through 49, said system comprising a plurality of storage vessels and a manifold connecting each of the storage vessels to a single pipeline.

51. A system according to Claim 50, said manifold comprising a valve associated with each storage vessel, and arranged such that no more than one storage vessel is in fluid communication with the pipeline at a time.

52. A flexible layered sheet comprising:

• at least one reinforced liquid impervious layer; and

• an anti-fouling composition.

53. The layered sheet according to Claim 52 wherein the liquid impervious layer comprises a rubber.

54. The layered sheet according to Claim 53 wherein the rubber comprises a nitrile rubber copolymer and at least one of a stimulant of vulcanization, a vulcanizer, accelerator, a vulcanization retardant, nano-particles, a softening/plasticizing agent, antioxidant and coupling agent.

55. The layered sheet according to any one of Claims 52 through 54, wherein the liquid impervious layer is reinforced with a polymeric fabric.

56. The layered sheet according to Claim 55 wherein the polymeric fabric comprises fibers comprising at least one of polyester, polyester/nylon and aramid.

57. The layered sheet according to Claim 55 or 56 wherein the liquid impervious layer is adhered to the polymeric fabric.

58. The layered sheet according to Claim 55 or 56 wherein the liquid impervious layer is embedded in the polymeric fabric.

59. A layered sheet according to any one of claims 55 to 58 wherein said polymeric fabric has a tensile strength of at least 200 kg/cm, thickness of at least lmm and elongation of at least 3%.

60. A layered sheet according to any one of Claims 55 through 59, having a tensile strength of at least 1000 kg/cm and hydrocarbon permeability of less than 5gr/m²/day.

61. The layered sheet according to any one of Claims 55 through 60, further comprising an anti-fouling layer comprising the anti-fouling composition.

62. The layered sheet according to Claim 61 wherein the anti-fouling layer further comprises any one or more of a film forming resin, at least one surfactant, at least one biocidal agent, and least one thixotropic agent, at least one filler.

63. The layered sheet according to Claim 61 or 62 wherein the anti-fouling layer is adhered to the polymeric fabric.

64. The layered sheet according to Claim 61 or 62 wherein the anti-fouling layer is adhered to the liquid impervious layer.

65. A method producing a layered sheet comprising:

• producing a liquid impervious sheet;

• reinforcing the liquid impervious sheet; and

• associating an anti-fouling composition to the liquid impervious sheet; wherein the steps can be carried out in any order.

66. The method according to Claim 65 comprising steps of:

• providing a rubber composition;

• providing a polymeric fabric; and

• forming a layer of the rubber composition associated with the polymeric fabric; • vulcanizing the rubber composition to produce the liquid impervious sheet.

67. The method according to Claim 66 wherein the step of forming a layer of the rubber composition associated with the polymeric fabric comprises applying an adhesive to the polymeric fabric prior to associating the polymeric fabric with the rubber composition.

68. The method according to Claim 66 or 61 wherein the step of forming a layer of the rubber composition associated with the polymeric fabric comprises a step selected from:

• calendaring or pressing the rubber composition with the polymeric fabric;

• dipping the polymeric fabric into the rubber composition; and

• spreading the rubber composition onto the polymeric fabric.

69. The method according to any one of claims 65 to 68 further comprising a step of providing an anti-fouling sheet comprising the anti-fouling composition.

70. The method according to Claim 69 further comprising adhering the anti-fouling sheet to the liquid impervious sheet.

71. An article of manufacture comprising the flexible layered sheet according to any one of claims 52 to 64.

72. The article of manufacture according to Claim 71 being a vessel or pipe.

73. The article of manufacture according to Claim 71 or 72 configured to constitute at least a portion of a container and to facilitate baric communication between the interior and the exterior thereof.

74. The article of manufacture according to any one of claims 71 to 73 being a storage tank.

75. The article of manufacture according to Claim 74 being an underwater storage tank.

76. The article of manufacture according to any one of claims 71 to 75 adapted for storing or transporting liquefied SGM.

77. A system according to any one of Claims 25 through 51, wherein at least one of said membrane and pipeline comprises an article of manufacture according to any one of Claims 71 through 76.