FIELD

This invention is directed to a pressure vessel comprising a determinate- dimensioned liner that can be expanded to permit on-loading and collapsed to assist offloading of a compressed fluid.

BACKGROUND

The detrimental effects of the burning of fossil fuels on the environment are becoming more and more of a concern and have spurred great interest in alternative energy sources. While progress is being made with solar, wind, nuclear, geothermal, and other energy sources, it is quite clear that the widespread availability of economical alternate energy sources, in particular for high energy use applications, remains an elusive target. In the meantime, fossil fuels are forecast to dominate the energy market for the foreseeable future. Among the fossil fuels, natural gas is the cleanest burning and therefore the clear choice for energy production. There is, therefore, a movement afoot to supplement or supplant, as much as possible, other fossil fuels such as coal and petroleum with natural gas as the world becomes more conscious of the

environmental repercussions of burning fossil fuels. Unfortunately, much of world's natural gas deposits exist in remote, difficult to access regions of the planet. Terrain and geopolitical factors render it extremely difficult to reliably and economically extract the natural gas from these regions. The use of pipelines and overland transport has been evaluated, in some instances attempted, and found to be uneconomical.

Interestingly, a large portion of the earth's remote natural gas reserves is located in relatively close proximity to the oceans and other bodies of water having ready access to the oceans. Thus, marine transport of natural gas from the remote locations would appear to be an obvious solution. The problem with marine transport of natural gas lies largely in the economics. Ocean-going vessels can carry just so much laden weight and the cost of shipping by sea reflects this fact, the cost being calculated on the total weight being shipped, that is, the weight of the product plus the weight of the container vessel in which the product is being shipped. If the net weight of the product is low compared to the tare weight of the shipping container, the cost of shipping per unit mass of product becomes prohibitive. This is particularly true of the transport of compressed fluids, which conventionally are transported in steel cylinders that are extremely heavy compared to weight of contained fluid. This problem has been ameliorated somewhat by the advent of Type III and Type IV pressure vessels. Type III pressure vessels are comprised of a relatively thin metal liner that is wound with a filamentous composite wrap, which results in a vessel with the strength of a steel vessel at a substantial saving in overall vessel weight. Type IV pressure vessels comprise a polymeric liner that is likewise wrapped with a composite filamentous material. Type IV pressure vessels are the lightest of all the presently approved pressure vessels. The use of Type III and Type IV vessels coupled with the trend to make these vessels very large - cylindrical vessels 18 meters in length and 2.5 - 3.0 meters in diameter are currently being fabricated and vessel 30 or more meters in length and 6 or more meters in diameter are contemplated - has resulted in a major step forward in optimizing the economics of ocean transport of compressed fluids.

The trend to make Type III and Type IV pressure vessels very large carries with it a unique set of challenges, one of which is the off-loading of compressed fluids from the pressure vessels. When a vessel is first opened to a receiving vessel, the high pressure under which the fluid was maintained in the pressure vessel results in a very rapid self-driven exodus of fluid from the vessel. As the pressure in the vessel decreases and the pressure in the receiving vessel increases the rate of flow of the fluid from one vessel to the other slows dramatically, usually to a point where, although substantial fluid remains in the source pressure vessel, its removal becomes uneconomical in terms of time lost in trying to remove the remaining fluid and the cost of equipment required to remove the fluid.

The problem, then, is to devise a way to increase both the flow of fluid from a pressure vessel during off-loading and the quantity of fluid off-loaded. The present invention provides a solution to this problem.

SUMMARY

Thus, in one aspect, this invention relates to a pressure vessel, comprising an internal volume defined by an inner wall and a determinate-dimensioned liner that can be expanded and collapsed within the internal volume.

In an aspect of this invention, the dimensions of the determinate-dimensioned liner are such that, when the liner is expanded, an outer surface of the liner is

contiguous to an inner wall of the pressure vessel.

In an aspect of this invention, the determinate-dimensioned liner, when in the collapsed state, has a free volume that is less than 10% of its volume when expanded.

In an aspect of this invention, the determinate-dimensioned liner comprises a polymeric material.

In an aspect of this invention, the polymeric material comprises a thermoplastic polymer.

In an aspect of this invention, the polymeric material comprises a thermoset polymer.

In an aspect of this invention, the determinate-dimensioned liner comprises a flexible metal film.

In an aspect of this invention, the determinate-dimensioned liner is inert to a compressed fluid loaded into the pressure vessel. An aspect of this invention is a method of on-loading and off-loading a compressed fluid from a pressure vessel comprising: providing the vessel with an expandable/collapsible determinate-dimensioned liner in the collapsed state; filling the pressure vessel with a compressed fluid until the collapsed liner is expanded such that its outer surface is contiguous with a wall of the pressure vessel; sealing the vessel for transport or storage; opening the vessel; permitting the self-driven exodus of the compressed fluid from the vessel to occur; injecting a fluid between the outer surface of the liner and the wall of the vessel when the self-driven exodus of compressed fluid slows, forcing the liner to collapse and thereby driving the remaining fluid out of the pressure vessel.

In an aspect of this invention, the fluid comprises sea water.

In an aspect of this invention, the fluid is fresh water.

In an aspect of this invention, the fluid comprises air.

DETAILED DESCRIPTION

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows isometric projections of various types of pressure vessels.

Figure 1 A shows a spherical pressure vessel.

Figure 1 B shows and oblate spheroid pressure vessel.

Figure 1 C shows a toroidal pressure vessel.

Figure 1 D shows a pressure vessel with a cylindrical center section and one domed end section. Figure 1 E shows a pressure vessel with a cylindrical center section and two domed end sections.

DISCUSSION

It is understood that, with regard to this description and the appended claims, any reference to any aspect of this invention made in the singular includes the plural and vice versa unless it is expressly stated or unambiguously clear from the context that such is not intended.

As used herein, any term of approximation such as, without limitation, near, about, approximately, substantially, essentially and the like, mean that the word or phrase modified by the term of approximation need not be exactly that which is written but may vary from that written description to some extent. The extent to which the description may vary will depend on how great a change can be instituted and have one of ordinary skill in the art recognize the modified version as still having the properties, characteristics and capabilities of the word or phrase unmodified by the term of approximation. In general, but with the preceding discussion in mind, a numerical value herein that is modified by a word of approximation may vary from the stated value by ±10%, unless expressly stated otherwise.

As used herein, "impermeable" or "impervious" refers to the property of a substance that renders it substantially impossible for a fluid to penetrate to any significant degree into a surface formed of the first substance.

As used herein, "inert" refers to the property of a substance that renders a surface formed of the substance unreactive toward any components of a fluid that may be contacted with the surface.

As used herein, the use of "preferred," "preferably," or "more preferred," and the like refers to preferences as they existed at the time of filing of this patent application.

As used herein, a "fluid" refers to a gas, a liquid or a mixture of gas and liquid. For example, without limitation, natural gas as it is extracted from the ground and transported to a processing center is often a mixture of the gas with liquid contaminants. Such mixture would constitute a fluid for the purposes of this invention.

As used herein, a "pressure vessel" refers to any closed container designed to hold fluids at a pressure substantially different from ambient pressure. In particular at present, it refers to such containers used to hold and transport CNG. Pressure vessels may take a variety of shapes but most often seen in actual use are spherical, oblate spheroidal, toroidal and cylindrical center section vessels with domed end sections at either or both ends. Non-limiting illustrations of such vessel are shown in Fig. 1 .

Pressure vessels for the transport of compressed fluids, such as compressed natural gas, CNG, presently constitute four regulatory agency approved classes, all of which are cylindrical with one or two domed ends:

Class I. Consist of an all metal, usually aluminum or steel, construct. This type of vessel is inexpensive but is very heavy in relation to the other classes of vessels.

Although Type I pressure vessels currently comprise a large portion of the containers used to ship compressed fluids by sea, their use in marine transport incurs very tight economic constraints.

Class II. Consist of a thinner metal cylindrical center section with standard thickness metal end domes in which only the cylindrical portion is reinforced with a composite wrap. The composite wrap generally constitutes glass or carbon filament impregnated with a polymer matrix. The composite is usually "hoop wrapped" around the middle of the vessel. The domes at one or both ends of the vessel are not composite wrapped. In Class II pressure vessels, the metal liner carries about 50% of the stress and the composite carries about 50% of the stress resulting from the internal pressure of the contained compressed fluid. Class II vessels are lighter than Class I vessels but tend to be more expensive.

Class III. Consist of a thin metal liner for the entire structure wherein the liner is reinforced with a filamentous composite wrap around entire vessel. The stress in Type III vessels is shifted virtually entirely to the filamentous material of the composite wrap; the liner need only withstand a small portion of the stress. Type III vessels are much lighter than type I or II vessels.

Class IV. Consist of a polymeric essentially gas-tight liner that is fully wrapped with a filamentous composite. The composite wrap provides the entire strength of the vessel. Type IV vessels are by far the lightest of the four approved classes of pressure vessels.

For the purpose of this disclosure, a pressure vessel comprising a cylindrical center section with one or two domed end sections will be referred to simply as a "cylindrical" pressure vessel. Vessel size may also vary tremendously and the construct and methods of this invention may be applied to a vessel of any size.

This invention will be described with regard to a cylindrical pressure vessel although it is understood that a determinate-dimensioned liner of this invention may be created for use with any shape pressure vessel and, for that matter, any size vessel. In fact, the liner will find its optimal use with extremely large pressure vessels such as those alluded to above where off-loading of a comprised fluid is both time-consuming and generally incomplete.

As used herein, "contiguous" refers to two surfaces that are adjacent and that are in direct contact or that would be in direct contact were it not for an intervening layer of another material.

As used herein, a "determinate-dimensioned liner" refers to a liner the length, width and thickness of which are constant and unchanging. This differentiates such liners from rubber and elastomeric liners that have one surface area and one thickness when deflated and an entirely different, larger, surface area when inflated at the cost of a substantially reduced thickness. A determinate-dimensioned liner can, of course, be expanded and contracted but its shape and volume in the expanded state is totally predetermined and it cannot be expanded to another shape or volume.

The dimensions of a determinate-dimensioned liner of this invention are dictated by the dimensions of the internal volume of a given pressure vessel as defined by the inner wall of that vessel. That is, the determinate-dimensioned liner is created with particular pressure vessel in mind such that, when the liner is placed in the vessel and expanded by a compressed fluid being on-loaded into the vessel, when the liner reaches its maximum dimensions, the other surface of the liner, that is the surface that is not in contact with the fluid, is contiguous with the inner wall of the pressure vessel.

A determinate-dimensioned liner of this invention can be made of any material that sufficiently flexible to withstand repeated expansion and collapse. Such materials include, without limitation, polymers, including both thermoplastic polymers and thermoset polymers, and thin flexible metal films. Examples of such materials include, without limitation, silicone polymers, butyl and other rubbers, which, while they may be capable of being inflated to various dimensions as would a balloon, for the purpose of this invention would be sized such that in its expanded state their outer surfaces comes into contact with the inner surface of a pressure vessel wall without any axial or lateral stress being imposed on the rubber liner, polyesters such as Mylar ^® , fluoropolymers such as Kynar ^® , and Viton ^® , polyimides such as Kapton ^® , polyamides such as Nylon®, polyethylene, polypropylene, polyethylene terephthalate (PET) and hydrogenated nitrile butadiene rubber (HNBR). A metalized plastic film may also be used.

The material of which the determinate-dimensioned liner of this invention is made is preferably inert to whatever fluid is to be contained in the object pressure vessel. This is particularly true where the surface of the pressure vessel that comes in contact with a compressed fluid comprises of metal, e.g., Types I, II and III vessels, which may be subject to corrosion or other detrimental reactions with components of a contained compressed fluid.

When the determinate-dimensioned liner of this invention is used with a Type IV pressure vessel, that is, a composite vessel, then it is also preferred that it be impervious to the contained fluid since composites are, by their very nature, somewhat porous and therefore penetrable by a fluid, in particular a fluid under pressure.

The use of a determinate-dimensioned expandable/collapsible liner of this application is straight forward. As a non-limiting example, a cylindrical pressure vessel with a domed end section at each end of the cylindrical center portion is provided.

Based on the interior dimensions of the pressure vessel, a liner is fabricated such that, when the liner is in an expanded state, its outer surface will be contiguous with the inner surface of the pressure vessel wall and that such occurs without placing any axial or lateral stress on the liner. The collapsed liner is then inserted through one of the polar openings in the pressure vessel. The open end of the liner is coupled to the pressure vessel at the polar opening so as to present the interior of the liner to an on-loading compressed fluid. Paraphernalia required to complete the pressure vessel such as bosses and coupling devices for connecting the pressure vessel to a source of the fluid to be contained are then assembled on the pressure vessel, which is then ready for use.

A fluid is then on-loaded in a compressed state into the pressure vessel such that it fills the liner to the point that the liner outer surface, the surface that is not in contact with the fluid, comes in contact with the inner wall of the pressure vessel at which time the vessel is considered full. The pressure vessel is then closed and the vessel is ready for, without limitation, transport of the compressed fluid or storage of the fluid.

When it is time to off-load the compressed fluid, the pressure vessel is connected to a system that delivers the fluid to a receiving vessel and the vessel is opened. Since the pressure in the pressure vessel is at first substantially greater than the pressure in the receiving vessel, the compressed fluid begins a rapid self-driven exodus from the pressure vessel into the receiving vessel. At some point, as the pressure in the pressure vessel and that in the receiving vessel approach equilibrium, the flow of fluid from the pressure vessel to the receiving vessel slows to the point where it eventually all but ceases. At this point, a substantial amount of fluid may still be retained in the pressure vessel. At some time prior to reaching this point, a fluid is injected between the inner surface of the pressure vessel and the outer surface of the liner, forcing the liner to collapse and thereby eject further fluid from the pressure vessel into the receiving vessel. In this manner virtually all of the fluid can be transferred in a timely manner from the pressure vessel to the receiving vessel. While the pressure vessel and liner of this invention may be used with virtually any manner of contained compressed fluid, it is a present embodiment of this invention that the system be used for the transport of CNG.

CNG may be contained and transported in the vessels of this invention both as a purified gas and as "raw gas." Raw gas refers to natural gas as it comes, unprocessed, directly from the well. It contains, of course, the natural gas (methane) itself but also may contain liquids such as condensate, natural gasoline and liquefied petroleum gas. Water may also be present as may other gases, either in the gaseous state or dissolved in the water, such as nitrogen, carbon dioxide and hydrogen sulfide. Some of these may be reactive in their own right or may be reactive when dissolved in water, such as carbon dioxide and hydrogen sulfide which produce an acid when dissolved in water. Thus, when transporting raw gas, the material of which the determinate-dimensioned liner is made must be inert to the acids and any other corrosive or reactive components of the raw gas. Based on the disclosures herein, those skilled in the art will be able to readily determine which materials have the requisite properties to inert to and, if necessary impervious the contained fluid and also capable of repeated expansion and collapse.

The pressure vessels can therefore carry a variety of gases, such as raw gas straight from a bore well, including raw natural gas, e.g. when compressed - raw CNG or RCNG, or H2, or CO2 or processed natural gas (methane), or raw or part processed natural gas, e.g. with CO2 allowances of up to 14% molar, H2S allowances of up to 1 ,000 ppm, or H2 and CO2 gas impurities, or other impurities or corrosive species. The preferred use, however, is CNG transportation, be that raw CNG, part processed CNG or clean CNG - processed to a standard deliverable to the end user, e.g. commercial, industrial or residential.

Storage/transportation pressures can be anything up to say 400bar, but usually up to 300 bar, and normally in excess of 100 bar.

CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C2H6, C3H8, C4H10, C5H12, C6H14, C7H16, C8H18, C9+ hydrocarbons, CO2 and H2S, plus potentially toluene, diesel and octane in a liquid state, and other impurities/species.

The invention has been described above purely by way of example. Variations in detail with respect to the above-illustrated embodiments are possible within the scope of the present invention as defined in the appended claims.