Natural gas, both CNG and LNG, can be transported great distances by large cargo vessels or freighters. In one embodiment of the present invention, the gas storage system is constructed integral with a new construction marine vessel. The marine vessel can be any size, limited by the usual marine considerations and economies of scale. For purposes of example, the storage system may be sized to carry between 300 and 1,000 million standard cubic feet of gas, i.e., 0.3 and 1.0 billion standard cubic feet (BCF), at standard conditions, 14.7 psi and 60°F. An ocean-going marine vessel sized to carry this exemplary system can include gas containers constructed using 500 foot lengths of pipe. In general, the length of the pipe will be determined by the cargo size and the need to keep proper proportionality between vessel length, depth and beam.

 To determine the interior volume of pipe required on a marine vessel, equation (1) above, is solved using a known mass of the gas, compressibility factor, gas constant, and the selected pressure and temperature. For example at the preferred storage conditions, 1.1 million cubic feet of interior pipe space is required to contain 300 million standard cubic feet of gas. In the case of 20 inch diameter pipe, 100 miles of pipe is required in the vessel. If the pipe had a 36" diameter, the total length of the pipe would be approximately 32 miles. One example of the preferred dimensions for a marine vessel, constructed in accordance with the present invention. is a length of 525 feet, a width of 105 feet and a height of 50 feet.

 Once the pipe parameters have been determined for the particular gas to be transported, the vehicle or vessel for the gas can now be designed and constructed taking into account the considerations heretofore mentioned. The vessel is preferably constructed for a particular gas source or producing area, i.e., pipe and vessel are designed to transport a gas produced in a given geographic area having a particular known gas composition. Thus, each vessel is designed to handle natural gas having a particular gas composition.

 The composition of the natural gas will vary between geographic areas producing the gas. Pure methane has a specific gravity of 0.55. The specific gravity of hydrocarbon gas could be as high as 0.8 or 0.9. The composition of the gas will vary somewhat over time even from a particular geographic area. As mentioned above, the compressibility factor can be considered optimum over a range of pressures to adjust for slight variations in the composition. However, if a field has a variance that falls outside the range of a particular compressibility factor, heavier hydrocarbons may be added to or removed from the gas to bring the composition into the design range of the particular vessel. Thus, a vessel designed to a particular composition gas being produced can be made more commercially flexible by adjusting the hydrocarbon mix of the gas. The specific gravity can be increased by enriching the gas by adding heavier hydrocarbons to the produced gas or decreased by removing heavier hydrocarbon products. Such adjustments may also be made for different gas fields with different compositions.

 For a particular ship to handle gas with different specific gravities, a reservoir of adjusting hydrocarbons may be maintained at the facility to be added to the natural gas thereby adjusting the composition of the natural gas so that it may be optimized for loading on a particular vessel which has been designed for a particular composition gas. Hydrocarbons can be added to raise the specific gravity. The reservoir of hydrocarbons may be located at the particular port where the natural gas is on-loaded or off-loaded.

 For example, suppose natural gas having a specific gravity of 0.6 is to be loaded on a vessel designed for gas having a specific gravity of 0.7. Propane may be acquired and mixed, at approximately 17% by weight, with the 0.6 natural gas, creating an enriched gas that is loaded onto the vessel. Then when offloading, as the enriched gas expands and cools, the propane will drop out because it will liquefy. That propane could then be put back onto the vessel and used again at the original on-loading port. The capacity to transport natural gas is increased by 41% due to adding propane to the 0.6 specific gravity natural gas. Thus, transporting the propane back and forth can be cost effective. Having a reservoir of propane to adjust the specific gravity of the natural gas may well be more cost effective as compared to building a new vessel just to handle 0.6 specific gravity natural gas. It may also prove cost effective to use the vessel at conditions different from the optimum conditions for which the system was designed.

 In one embodiment of the present invention, the pipe for the compressed natural gas is used as a structural member for the marine vessel. The pipe is attached to the bulkheads which in turn are attached to the marine vessel's hull. This produces a very rigid structural design. By using the pipes as a part of the structure the amount of structural steel normally used for the vessel is minimized and reduces capital costs. A bundle of pipes together is very difficult to bend, thus adding stiffness to the vessel. A preliminary design indicates that a marine vessel, built with an integral pipe structure, and having an overall length of over 500 feet, would only deflect about 2 or 3 inches. It is desirable to limit bending deflection because it places wear and tear on the pipe and ship. Bending deflection is defined as deviation from a horizontal straight line.

 Referring now to FIGS. 5, 6 and 7, there is shown a marine vessel 10 built specifically for the preferred pipe 12 designed to transport a particular gas having a known composition to be on-loaded at a particular site. As for example, the pipe may be 36" diameter pipe having a wall thickness of 0.486 inches for transporting natural gas produced in Venezuela and having a specific gravity of 0.7. The pipe 12 forms part of the hull structure of the marine vessel 10 and includes a plurality of lengths of pipe forming a pipe bundle 14 housed within the hull 16 of the vessel 10. It should be appreciated, however, that the pipe may be housed in other types of vehicles or marine vessels without departing from the invention. A ship may be preferred because it will travel at a faster speed than a barge, for example.

 Cross beams 18 are used to support individual rows 20 of pipe 12 and to form part of the structure of the marine vessel 10. Cross beams 18 extend across the beam of the marine vessel 10 to provide the structural support for the hull 16. The perimeter 22 shown in FIG. 7 with the bundle of pipes 14 represents the hull 16 of the marine vessel 10. The plate that forms the hull 16 around the marine vessel 10 is not the expensive part of the marine vessel 10. Thus, marine vessel 10 is built using the cross beams 18 to hold the individual pieces of pipe 12. The bundle of pipes 14 has a cross section which conforms to the cross section of the hull 16 of the marine vessel 10. Therefore, rather than be in a rectangular cross-section, such as on a barge, the bundle of pipes 14 on the marine vessel 10 may have a generally triangular cross section or a cross section forming a trapezoid. The top of the pipe bundle 14 is flat since it is located just underneath the deck 28 of the marine vessel 10.

 FIG. 5 shows that the pipe bundle 14 extends nearly the full length of the marine vessel 10. It should be appreciated that the marine vessel 10 includes the other standard parts of a ship. For example, the stern 30 may include the crews quarters and the engine. Also there is space 32 in the bow of the marine vessel 10. It should also be appreciated that there will be space adjacent the stern end 34 and bow end 36 of the pipes 12 for manifolding and valving hereinafter described, as well as room to manipulate the valving and manifolding. All that is required is that sufficient space is left in the stem for the engines for the marine vessel 10. The deck 28 and pilot house 29 extend above the pipe bundle 14.

 The cross beams 18 not only support the pipe 12 but, together with the pipe bundle 14, can also serve as a bulkhead 40 within the marine vessel 10. In the preferred embodiment, bulkheads 40 are spaced every 60 feet but this may vary depending on pipe weight and marine vessel design. Thus there would be roughly nine bulkheads 40 in a marine vessel 10 using pipe having a length of 500 feet. The number of bulkheads in the present invention is consistent with the regulations of the United States Coast Guard. The bulkheads 40 cannot leak from one compartment 42 to another compartment 42 in the marine vessel 10. For example, if the marine vessel 10 were to be ruptured in one compartment 42 created by a pair of bulkheads 40, water is not allowed to pass from one compartment 42 to another. Thus, the bulkhead 40 seals off adjacent compartments 42 of the marine vessel 10.

 Encapsulating insulation 24 extends around the bundle of pipes 14 in each compartment 42 and extends to the outer wall 26 formed by the hull 16 of the marine vessel 10. There is insulation along the bottom and around the bundle of pipes 14. The entire bundle 14 is wrapped in insulation 24. However, there is no insulation along the wall of the bulkhead 40 formed by the cross beams 18 since there is no reason to insulate one compartment 42 from another because the temperature is to remain constant in all compartments 42. Insulation is required to limit the temperature rise of the gas during transportation. A preferred insulation is a polyurethane foam and is about 12-24 inches thick, depending on planned travel distance. However, the insulation 24 adjacent the ocean will have a greater heat transfer and may require a slightly thicker insulation. When the entire bundle of pipes 14 is wrapped in insulation 24, the temperature rise may be less than 1/2°F. per thousand miles of travel. Thus, the resulting pressure increase in the pipes is far less than the decrease due to the amount of gas used from gas storage in the operation of the marine vessel 10.

 As shown in FIG. 7, the pipes 12 housed between crossbeams 18 form pipe bundles 14. The pipe 12 is laid individually onto cross beam 18 to form pipe rows 20, shown in FIG. 8. FIGS. 8-10 show one embodiment of cross beams 18. Bottom cross beam 18a shown in FIG. 8 is a bottom or top cross beam while FIG. 9 shows the typical intermediate cross beam 18 having alternating arcuate recesses forming upwardly facing saddles 50 and downwardly facing saddles 52 for housing individual lengths of the pipe 12. A coating or gasket 54 lines each saddle 50, 52 to seal the connection between adjacent saddles 50, 52 in order to create the watertight bulkhead walls 40. One embodiment includes a TeflonTM sleeve or coating to serve as the gasketing material. It should also be appreciated that a gasketing material 56 may be used to seal between the flat portions 58 of cross beams 18. The pipes 12 resting in the mated C-shaped saddles 50, 52 create a sealable connection.

 Cross beams 18 are preferably I-beams. An alternative to using an I-beam is a beam in the form of a box cross section formed by sides made of flat steel plate. The box structure has two parallel sides and a parallel top and bottom. Saddles 50, 52 are then cut out of the box structure. The box structure has more strength than the I-beam. However, the box structure is heavier and more difficult to manufacture.

 The individual pipes 12 are received in the upwardly facing saddles 50 and, after a row 20 of pipes 12 is installed, a next cross beam 18 is laid over row 20 with the downwardly facing saddles 52 receiving the upper sides of the pipes 12. Once the pipe 12 is housed in mating C-shaped, arcuate saddles 50, 52 of two adjacent cross beams 18, the cross beams 18 are clamped together and connectcd to each other. FIGS. 7 and 10 shows the beams 18 stacked to form a bulkhead wall 40.

 There are two methods for securing the pipe 12 between the cross beams 18 to form bulkheads 40, one is welding the pipe 12 to the cross beams 18 to make the entire bundle rigid and the other is to bolt the adjacent cross beams and allow the pipe 12 to move through the bulkhead 40. Because the compressed natural gas is to be maintained at a temperature of -20°F., the pipe 12 is installed at a temperature of 30°F. For a pipe length of 500 feet, the strain over that temperature difference is only about an inch from the middle of the pipe 12 to one of the free ends of the pipe 12. Thus, if the temperature of the pipe 12 goes from 30°F. to 80°F., there is a 1 inch expansion from the mid-point to the free end of the pipe 12.

 Due to the relatively small expansion with respect to the length of pipe 12, neither welding or torquing suffer any expansion problems. Therefore in welding the cross beams 18, when the pipe 12 cools down, the strain is taken in the pipe 12 and in the bulkheads 40 formed by the cross beams 18. Alternatively, if the pipe 12 is not welded to the cross beams 18, the pipe 12 is laid in the cross members 18 in compression and then it is torqued down. The cross beams 18 are bolted together, securing the individual pieces of pipe 12. This provides a frictional engagement between the pipe 12 and the cross beams 18, and the pipe 12 is allowed to expand and contract with the temperature. For non-welded connections, it is preferred that some friction reducing material be present in the bulkhead saddles either as a coating or an inserted sleeve to relieve some of the friction. One such example is a Teflon^TM coating.

 Referring now to FIG. 11, another embodiment of a pipe support system is illustrated. This embodiment uses straps 210 formed from steel plate so as to conform to the outside curvature of the pipes 12. The strap 210 is formed in a roughly sinusoidal pattern with a radius of curvature approximately equal to the outside diameter of the pipe 12 forming upwardly and downwardly facing saddles 50, 52 so the pipes 12 lay substantially side by side . The straps 210a are welded at contact points 214 to adjacent straps 210b creating an interlocked structure providing exceptional structural properties. One effect of the interlocked structure is that the Poisson's ratio of the entire structure 216 approaches one, therefore causing the stresses applied to the hull structure 16 to be absorbed laterally as well as vertically. Even though the use of straps 210 allow fewer pipes per tier, the tiers themselves are packed more tightly allowing a greater number of tiers and therefore the system includes more pipes per cross-sectional area of the system.

 The straps 210 are preferably constructed from the same material as the pipes 12 are or from a similar material that is suitable for welding, or otherwise attaching, where the straps come into contact with each other. A preferred embodiment of the strap 210 is constructed from steel plate having a thickness of 0.6" with each strap being approximately 2' wide. In a configuration with 500' long lengths of pipe 210, ten straps 210 per pipe row are used at the lowest level 218 with the number of straps 210 per pipe row decreasing at higher levels to a minimum of six straps beneath the top tier 220. The number of straps 210 per tier decreasing with height is allowed because of the corresponding decrease in weight being supported by the straps. Spacers 239 can also be used where pipe spans become too long.

 In this embodiment the pipes 12 are not welded to the straps 210 and are allowed to move independently. Because of this movement, the interface between the pipe 12 and the strap 210 is fitted with a low-friction or anti-erosion material 211 to prevent abrasion and smooth out any mismatches between the pipe 12 and the strap 210. Because each pipe is a buoyant, scaled compartment, additional watertight bulkheads are not required. A continuous sheet of material may be included between tiers to act as a barrier if a tier develops a leak. This continuous sheet could be integrated into the straps 210, and be constructed from metal or a synthetic material such as Kevlar^TM, or a membrane material.

 The ends of the straps 210 are preferably rigidly connected to the marine vessel or container (not shown) containing the pipe bundle. The plurality of straps 210, and the supported pipes 12, contribute to the overall stiffness of the hull structure 16. The pipes 12 themselves are not welded to the straps 210 and therefore are allowed to bend, expand, and contract as required. It is preferred that each pipe 12 move independently of other pipes in response to the movement of the hull. This allows each pipe to move longitudinally in response to the stretching, bending, and torsion of the hull. Support for the weight of the pipe is provided both by the straps, which form an interlocking honeycomb structure, and the by the compressive strength of the pipe.

　

 Referring now to FIG. 12, each of the ends 64, 66 of the pipes 12 are connected to a manifold system for on-loading and off-loading the gas. Each pipe end 64, 66 includes an end cap 68, 70, respectively. A conduit 72, 74 communicates with a column manifold 76, 78, respectively. In a preferred embodiment, the pipe ends 64, 66 are hemispherical and conduits 72, 74 are connected to caps 68, 70, respectively, which extend to a tier manifold.

 Individual banks or tiers of pipes 12 communicate with a tier manifold 86, 88 at each end thereof. The plurality of pipes 12 which make up the tier may include any particular set of pipes 12. The tiers are principally selected to provide convenience in on-loading and off-loading the gas. For example, one tier manifold may extend across the top row 20 of pipes 12 such that the top row 20 of pipes 12 would form one tier. The outside rows 20 of pipes 12 may be manifolded into a separate tier in case of collision. The bottom rows 20 of pipe 12 may also be in a separate tier manifold. This allows the outside pipes 12 and bottom pipes 12 to be shut off. The other tiers of pipes may include any number of pipes 12 to provide a predetermined amount of gas to be on-loaded or off-loaded at any one time.

 One arrangement of the manifold system may include tier manifold 86. 88 extending across the ends 64, 66, respectively, of the pipe 12 with tier manifolds 86, 88 communicating with horizontal master manifolds 90, 92, respectively, extending across the beam of the marine vessel 10 for on-loading and off-loading. Each tier of pipes has its own tier manifold with all of the column manifolds communicating with the master manifolds 90, 92 for on-loading and off-loading.

 Horizontal manifolds have the advantage of keeping the marine vessel 10 in relative balance. Thus horizontal manifolds are preferred. One of the master manifolds 90, 92 is preferably in the stern and the other is preferably in the bow of the marine vessel 10 for simplicity of piping and conservation of space. To have all manifolds at one end of the marine vessel 10 is more complicated. One master manifold 90, 92 is used for an incoming displacement fluid for off-loading and the other master manifold 90, 92 is used as an outgoing manifold for offloading the compressed gas. The horizontal master manifolds 90, 92 are the main manifolds which extend across the marine vessel 10. The master manifolds 90, 92 are attached to shore system for on-loading and off-loading the gas. Master valves 91, 93 are provided in the ends of master manifolds 90, 92 for controlling flow on and off the marine vessel