SHIP BASED SYSTEM FOR COMPRESSED NATURAL GAS TRANSPORT

Abstract: A ship based system for compressed natural gas transport that utilizes a ship having a plurality of gas cylinders. The invention is characterized by the plurality of gas cylinders configured into a plurality of compressed gas storage cells. Each compressed gas storage cell consists of between 3 and 30 gas cylinders connected by a cell manifold to a single control valve. A high pressure manifold is provided including means for connection to shore terminals. A low pressure manifold is provided including means for connection to shore terminals. A submanifold extends between each control valve to connect each storage cell to both the high pressure manifold and the low pressure manifold. Valves are provided for controlling the flow of gas through the high pressure manifold and the low pressure manifold.

Description: TITLE OF THE INVENTION SHIP BASED SYSTEM FOR COMPRESSED NATURAL GAS TRANSPORT FIELD OF THF INVENTION The present invention relates to natural gas transportation systems and, more specifically, to the transport of compressed natural gas over water by ship. BACKGROUND OF THE INVENTION There are four known methods of transporting natural gas across bodies of water. A first method is by way of subsea pipeline. A second method is by way of ship transport as liquefied natural gas (LNG). A third method is by way of barge, or above deck on a ship, as compressed natural gas (CNG). A fourth method is by way of ship, inside the holds, as refrigerated CNG or as medium conditioned liquefied gas (MLG). Each method has its inherent advantages and disadvantages. Subsea pipeline technology is well known for water depths of less than 1000 feet. However, the cost of deep water subsea pipelines is very high and methods of repairing and mamtøining deep water subsea pipelines are just been pioneered. Transport by subsea pipeline is often not a viable option when crossing bodies of water exceeding 1000 feet in depth. A further disadvantage of subsea pipelines is that, once laid, it is impractical to relocate them. The liquefaction of natural gas greatly increases its density, thereby allowing a relatively few number of ships to transport large volumes of natural gas over long distances. However, an LNG system requires a large investment for liquefaction facilities at the shipping point and for regassification facilities at the delivery point. In many cases, the capital cost of constructing LNG facilities is too high to make LNG a viable option. In other instances, the political risk at the delivery and/or supply point may make expensive LNG facilities unacceptable. A further disadvantage of LNG is that even on short routes, where only one or two LNG ships are required, the transportation economics is still burdened by the high cost of full shore facilities. In the early 1970s Columbia Gas System Service developed a ship transportation method for natural gas as refrigerated CNG and as pressurized MLG. These methods were described by Roger J. Broeker, their Director of Process Engineering, in an article published in 1974 entitled "CNG and MLG - New Natural Gas Transportation Processes." The CNG required the refrigeration ofthe gas to -75 degree fahrenheit and pressurization to 1150 psi before placing into pressure vessels contained within an insulated cargo hold of a ship. No cargo refrigeration facilities were provided aboard ship. The gas was contained in a multiplicity of vertically mounted cylindrical pressure vessels. The MLG process required the liquefaction ofthe gas by cooling to -175 degrees fahrenheit and pressurization to 200 psi. One disadvantage of both of these systems is the required cooling of the gas to temperatures sufficiently below ambient temperature prior to loading on the ship. The refrigeration ofthe gas to these temperatures and the provision of steel alloy and aluminum cylinders with appropriate properties at these temperatures was expensive. Another disadvantage was dealing with the inevitable expansion of gas in a safe manner as the gas warmed during transport. In 1989 United States Patent 4,846,088 issued to Marine Gas Transport Ltd. which described a method of transporting CNG having the storage vessel disposed only on or above the deck of a seagoing barge. This patent reference disclosed a CNG storage system that comprised a plurality of pressure bottles made from pipeline type pipe stored horizontally above the deck ofthe seagoing barge. Due to the low cost ofthe pipe, the storage system had the advantage of low capital cost. Should gas leakage occur, it naturally vented to atmosphere to obviate the possibility of fire or explosion. The gas was transported at ambient temperature, avoiding the problems associated with refrigeration inherent in the Columbia Gas Service Corporation test vessel. One disadvantage of this method of transport of CNG described was the limit to the number of such pressure bottles that could be placed above deck and still maintain acceptable barge stability. This severely limits the amount of gas that a single barge can carry and results in a high cost per unit of gas carried. Another disadvantage is the venting of gas to atmosphere, which is now viewed as unacceptable from an environmental standpoint. -2- In a more recent years the viability of transport by barge of CNG has been studied by Foster Wheeler Petroleum Development. In an article published in the early 1990s by R.H. Buchanan and AN. Drew entitled "Alternative Ways to Develop an Offshore Dry Gas Field," transport of CΝG by ship was reviewed, as well as an LΝG transport options. The proposal of Foster Wheeler Petroleum Development disclosed a CΝG transport method comprised of a plurality of pipeline type pressure bottles oriented horizontally in a series of detachable multiple barge-tug combination shuttles. Each bottle had a control valve and the temperatures were ambient. One disadvantage of this system was the requirement for connecting and disconnecting the barges into the shuttles which takes time and reduces efficiency. A further disadvantage was the limited seaworthiness ofthe multi-barge shuttles. The need to avoid heavy seas would reduce the reliability of the system. A further disadvantage was the complicated mating system which would adversely affect reliability and increase cost. Marine transportation of natural gas has two main components, the over water transportation system and the on shore facilities. The shortcoming of all ofthe above described CΝG transport systems is that the over the water transportation component is too expensive for them to be employed. The shortcoming of LΝG transport systems is the high cost ofthe shore facilities which, on short distance routes, becomes the overwhelming portion ofthe capital cost. None of the above described references addresses problems associated with loading and unloading ofthe gas at shore facilities. SUMMARY OF THE INVENTION What is required is an over water transportation system for natural gas which is capable of utilizing shore facilities which are much less expensive than LNG liquefaction and regassification facilities or CNG refπgeration facilities, and also provides for over water transport of near ambient temperature CNG, that is less expensive that the prior art. According to the present invention there is provided an improvement in over water CNG transport that utilizes a ship having a plurality of gas cylinders. The gas pressure in the cylinders would, preferably, be in the range of 2000 psi to 3500 psi when charged and in the range of 100 to 300 psi when discharged. The invention is characterized by the plurality of gas cylinders configured into a plurality of compressed gas storage cells. Each compressed gas storage cell consists of between 3 and 30 gas cylinders connected by a cell manifold to a single control valve. The gas cylinders will, preferably, be made from steel pipe with domed caps on each end. The steel cylinders may be wrapped with fibreglass, carbon fibre or some other high tensile strength fibre to afford a more cost effective bottle. A submanifold extends between each control valve to connect each storage cell to a high pressure main manifold and a low pressure main manifold. Both the high pressure main manifold and the low pressure main mamfold include means for connection to shore teπninals. Valves are provided for controlling the flow of gas through the high pressure manifold and the low pressure manifold. With the ship based system for compressed natural gas transport, as described above, the on shore facilities mainly consist of efficient compressor stations. The use of both high and low pressure manifolds permits the compressors at the loading terminal to do useful work compressing pipeline gas up to full design pressure in some cells, while the cells are filling from the pipeline; and at the unloading terminal do useful work compressing the gas of cells below pipeline pressure while some high pressure storage cells are simultaneously producing by blowdown. The technique of opening the storage cells in sequence by groups, one after another, so timed that the backpressure on the compressor is at all times close to the optimum pressure, minimizes the required compression horsepower. Although beneficial results may be obtained through the use ofthe shp based system for compressed natural gas transport, as described above, even more beneficial results may be obtained by orienting the gas storage cells in a vertical manner. This vertical orientation will facilitate the replacement and maintenance ofthe storage cells should it be required. Although beneficial results may be obtained through the use ofthe ship based system for compressed natural gas transport, as described above, the safe ocean transport of the CNG, once loaded, must also be addressed. Even more beneficial results may, therefore, be obtained when the hold ofthe ship is covered with air tight hatch covers. This permits the holds containing the gas storage cells to be flooded with an inert atmosphere at near ambient pressure, eliminating fire hazard in the hold. Although beneficial results may be obtained through the use ofthe ship based system for compressed natural gas transport, as described above, adiabatic expansion ofthe CNG during the delivery process results in the steel bottles being cooled to some extent. It is desirable to preserve -4- the coolness of this thermal mass of steel for its value in the next loading phase. Even more beneficial results may, therefore, be obtained when the hold and hatch covers are insulated. Although beneficial results may be obtained through the use ofthe ship based system for compressed natural gas transport, as described above, should a gas leak occur it must be safely dealt with. Even more beneficial results may, therefore, be obtained when each hold is fitted with gas leak detection equipment and leaking bottle identification equipment so that leaking storage cells can be isolated and vented through the high pressure manifold system to a venting/flare boom. The natural gas contaminated hold would be flushed with inert gas. Although beneficial results may be obtained through the use ofthe ship based system for compressed natural gas transport, as described above, in some markets a continuous supply of natural gas is crucial. Even more beneficial results may, therefore, be obtained when sufficient CNG ships of appropriate capacity and speed are used so that there is at all times a ship moored and unloading. Although beneficial effects may be obtained through the use ofthe ship based system for compressed natural gas transport, as described above, there is a considerable pressure energy on the ship that could be used at the discharge terminal to produce refrigeration. Even more beneficial effects may, therefore, be obtained when an appropriate cryogenic unit at the unloading terminal is used to generate a small amount of LNG. This LNG, produced during a number of ship unloadings, will be accumulated in adjacent LNG storage tanks. This supply of LNG can be used in the event of an upset in CNG ship scheduling. Although beneficial effects may be obtained through the use ofthe ship based system for compressed natural gas transport, as described above, some markets will pay a premium for peak-shaving fuel (i.e., fuel delivered during the few hours per day of peak demand). Even more beneficial results may, therefore, be obtained if the main manifold system and unloading compressor station are so sized that the ship can be unloaded in the peak time, which is typically 4 to 8 hours. BRIEF DESCRIPTION OF THE DRAWINGS These and other features ofthe invention will become more apparent from the following description in which reference is made to the appended drawings, wherein: FIGURE 1 is a flow chart setting forth the operation of a ship based system for compressed natural gas transport. FIGURE 2a is a side elevation view in section of a ship equipped in accordance with the teachings ofthe ship based system for compressed natural gas transport. FIGURE 2b is a top plan view in longitudinal section ofthe ship illustrated in FIGURE 2a. FIGURE 2c is an end elevation view in transverse section taken along section lines A-A of FIGURE 2b. FIGURE 3 is a detailed top plan view of a portion ofthe ship illustrated in FIGURE 2b. FIGURE 4a is a schematic diagram of a loading arrangement for the ship based system for compressed natural gas transport. FIGURE 4b is a schematic diagram of an unloading arrangement for the ship based system for compressed natural gas transport. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The prefeπed embodiment, a ship based system for compressed natural gas transport generally identified by reference numeral 10, will now be described with reference to FIGURES 1 through 4b. Referring to FIGURES 2a and 2b, ship based system for compressed natural gas transport 10 includes a ship 12 having a plurality of gas cylinders 14. The gas cylinders are designed to safely accept the pressure of CNG, which may range between 1000 to 5000 psi, to be set by optimization taking into account the cost of pressure vessels, ships, etc. and the physical -6- properties of the gas. It is prefeπed that the values be in the range of 2500 to 3500 psi. Gas cylinders 14 are cylindrical steel pipes in 30 to 100 foot lengths. A prefeπed length is 70 feet long. The pipes will be capped, typically, by the welding of forged steel domes on both ends. The plurality of gas cylinders 14 are configured into a plurality of compressed gas storage cells 16. Referring to FIGURE 3, each of compressed gas storage cells 16 consist of between 3 and 30 gas cylinders 14 connected by a cell manifold 18 to a single control valve 20. Referring to FIGURES 2a and 2c, gas cylinders 14 are mounted vertically oriented, for ease of replacement, within a hold 22 of ship 12. The length of cylinders 14 will typically be set so as to preserve the stability of ship 12. The holds 22 are covered with hatch covers 24 to keep out seawater in heavy weather, but also to facilitate cylinder changeout. Hatch covers 24 will have airtight seals to enable holds 22 to be flooded with an inert atmosphere at near ambient pressure. The holds 22 are serviced by a low pressure manifold system 42, as shown in FIGURE 2a, to provide initial flood and subsequent maintenance ofthe inert gas atmosphere. The present invention contemplates little or no refrigeration ofthe gas during the loading phase. Typically the only cooling involved will be to return the gas to near ambient temperature by means of conventional air or seawater cooling immediately after compression. However, the lower the temperature of the gas, the larger the quantity that can be stored in the cylinders 14. Because of adiabatic expansion ofthe CNG during the delivery process, the steel cylinders 14 will be cooled to some extent. It is desirable to preserve the coolness of this thermal mass of steel for its value in the next unloading phase, in typically 1 to 3 days time. For this reason, referring to FIGURE 2c, both holds 22 and hatch covers 24 are covered with a layer of insulation 26. Referring to FIGURE 3, a high pressure manifold 28 is provided which includes a valve 30 adapted for connection to shore terminals. A low pressure manifold 32 is provided including a valve 34 adapted for connection to shore terminals. A submanifold 36 extends between each control valve 20 to connect each storage cell 16 to both high pressure manifold 28 and low pressure manifold 32. A plurality of valves 38 control the flow of gas from submanifold 36 into high pressure manifold 28. A plurality of valves 40 control the flow of gas from submanifold 36 into low pressure manifold 32. In the event that a storage cell must be rapidly blown down when the ship 12 is at sea, the gas will be carried by high pressure - - manifold 28 to a venting boom 44 and thence to a flare 46, as illustrated in FIGURE 2a. If the engines ofthe ship 10 are designed to burn natural gas, either the high or low pressure manifold will convey it from the cells 16. Ship 12, as described above, must be integrated as part of an overall transportation system with shore facilities. The overall operation of ship based system for compressed natural gas transport 10 will now be described with the aid of FIGURES 1, 4a, and 4b. FIGURE 1 is a flow chart that sets forth the step by step handling ofthe natural gas. Referring to FIGURE 1, natural gas is delivered to the system by a pipeline (1) at typically 500 to 700 psi. A portion of this gas can pass directly through the shipping terminal (3) to the low pressure manifold 32 to raise a small number of the cells 16 to the pipeline pressure from their "empty" pressure of about 200 psi. Those cells are then switched to the high pressure manifold 28 and another small number of empty cells are opened to the low pressure manifold 32. The larger portion of the pipeline gas is compressed to high pressure at the shipping point compression facility (2). Once the gas is compressed it is delivered via a marine terminal and manifold system (3) to the high pressure manifold 28 on the CNG Carrier (4) (which in this case is ship 12), whence it brings those cells 16 connected to it up to close to full design pressure (e.g., 2700 psi). This process of opening and switching groups of cells, one after the other, is refeπed to as a "rolling fill." The beneficial effect is that the compressor (2) is compressing to its full design pressure almost all the time which makes for maximum efficiency . The CNG Carrier (4) carries the compressed gas to the delivery terminal (5). The high pressure gas is then discharged to a decompression facility (6) where the gas pressure is reduced to the pressure required by the receiving pipeline (9). Optionally the decompression energy ofthe high pressure gas can be used to power a cryogenic unit to generate a small portion of LPG, gas liquids and LNG (6) which can be stored and the gas liquids and LNG regassified later (8) as required to maintain gas service to the market. At some point during the delivery ofthe gas, the gas pressure on the CNG Carrier will be insufficient to deliver gas at the rate and pressure required. At this time the gas will be sent to the delivery point compression facility (7) where it will be compressed to the pipeline (9) required pressure. If the above process is carried out with small groups of cells 16 at a time, a "rolling empty" results which will, as above, provide the compressor (7) with the design back pressure most ofthe time and hence use it with maximum efficiency. -8- Whether or not an LNG storage facility has been added, it is prefeπed that there shall be a sufficient number of CNG carrier ships 12 of appropriate capacity and speed so operated that there will be a ship moored and discharging at the delivery point at all times, except under upset conditions. Operated in this manner, the CNG ship system will provide essentially the same level of service as a natural gas pipeline. In an important alternative embodiment, the ship's manifolds and delivery compression station (7) can be so sized that the ship's cargo can be unloaded in a relatively short time, say 2-8 hours, typically 4 hours, versus one-half to three days, typically one day normal unloading time. This alternative would permit a marine CNG project to supply peak-shaving fuel into a market already possessed of sufficient base load capacity. It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope ofthe invention as hereinafter defined in the Claims. - -

Claims: THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS: 1. A system for compressed gas transport: a ship, said ship having at least one cargo hold; a plurality of gas cylinders, said plurality of gas cylinders constructed and arranged to be transportable within one or more of said at least one cargo hold; said plurality of gas cylinders being configured into a plurality of compressed gas storage cells, wherein each of said compressed gas storage cells includes between 3 and 30 gas cylinders a cell manifold constructed and arranged to connect each of said plurality of gas cylinders in a gas storage cell to a single cell control valve; a high pressure manifold, said high pressure manifold including means for connection to shore terminals; a low pressure manifold, said low pressure manifold including means for connection to shore terminals; and a submanifold, said submanifold extending between each of said single cell control valves to connect each of said compressed gas storage cells to both said high pressure manifold and said low pressure manifold; and a plurality of valves for controlling the flow of gas through said high pressure manifold and said low pressure manifold. 2. The system for compressed gas transport as defined in Claim 1, wherein said plurality of gas cylinders are vertically oriented within said at least one cargo hold. 3. The system for compressed gas transport as defined in Claim 2, wherein said at least one cargo hold is covered with at least one air tight hatch cover; thereby enabling said at least one cargo hold to be flooded with an inert atmosphere at near ambient pressure. 4. The system for compressed gas transport as defined in Claim 3, wherein said at least one cargo hold and said at least one air tight hatch cover are thermally insulated. 5. The system for compressed gas transport as defined in Claim 2, wherein each of said at least one cargo hold is fitted with gas leak detection equipment; so that leaking compressed gas storage cells can be isolated and vented through said high pressure manifold to a venting/flare boom. -10- 6. The system for compressed gas transport as defined in Claim 1, wherein a plurality of ships are used to provide a continuous supply of compressed gas. 7. The system for compressed gas transport as defined in Claim 22, wherein a portion of said compressed gas contained in said gas storage cells is directed to a cryogenic unit; whereby said cryogenic unit is constructed and arranged to produce low pressure gas, gas liquids and LNG; said gas liquids and said LNG to be accumulated in at least one storage tank. 8. The system for compressed gas transport as defined in Claim 1 , further including an on shore unloading compressor station; said manifolds and said unloading compressor station constructed and aπanged to unload said ship during the time of peak demand for compressed gas. 9. A system for compressed gas transport comprising: a ship, said ship having at least one cargo hold; a plurality of gas cylinders, said plurality of gas cylinders constructed and aπanged to fit within said at least on cargo hold of said ship; said plurality of gas cylinders being configured into a plurality of compressed gas storage cells, each of said compressed gas storage cells including between 3 and 30 of said plurality of gas cylinders; each of said plurality of gas cylinders within said compressed gas storage cell being connected by a cell manifold to a single cell control valve; said plurality of gas cylinders being vertically oriented within said at least one cargo hold; each of said at least one cargo hold being covered with at least one air tight hatch cover whereby each of said at least one cargo hold can be flooded with an inert atmosphere at near ambient pressure; each of said at least one hatch cover and each of said at least one cargo hold being thermally insulated; a high pressure manifold, said high pressure manifold including means for connection to shore terminals; a low pressure manifold, said low pressure manifold including means for connection to shore terminals; a submanifold extending between each of said single cell control valves to connect each of said compressed gas storage cells to both said high pressure manifold and said low pressure manifold; a plurality of valves for controlling the flow of compressed gas through said high pressure manifold and said low pressure manifold; each of said at least one cargo hold having a manifold to provide an initial flood and subsequent maintenance of said inert gas atmosphere; and each of said at least one cargo hold being fitted with compressed gas leak detectors so that leaking compressed gas storage cells can be isolated and said leaking compressed gas vented through said high pressure manifold system to a venting/flare boom. 10. In combination: a. a shore terminal; and b. a ship based system for compressed gas transport, said ship based system including: a plurality of gas cylinders, said plurality of gas cylinders being configured into a plurality of compressed gas storage cells, each of said compressed gas storage cells including between 3 and 30 gas cylinders, said between 3 and 30 gas cylinders being connected by a cell manifold to a single cell control valve; a high pressure manifold including means for connection to said on shore compressor station; a low pressure manifold including means for connection to said on shore compressor station; and a submanifold extending between each of said single cell control valves to connect each of said compressed gas storage cells to both said high pressure manifold and said low pressure manifold; and a plurality of valves for controlling the flow of compressed gas through said high pressure manifold and said low pressure manifold. Please add the following claims: 11. The transport system for compressed gas as defined in Claim 5 further including means for flushing said cargo hold in which a leak has been detected. 12. The system for compressed gas transport as defined in Claim 1 wherein said plurality of gas cylinders will contain gas at between 1000 and 5000 psi. 13. A method for filling a ship-borne storage system with compressed gas from a supply pipeline, said ship-borne storage system including a plurality of gas cylinders organized into cells, a high pressure manifold, a low pressure manifold, and a submanifold connecting said -12- cells of gas cylinders to said high and low pressure manifolds, the method comprising the steps of: a. receiving compressed gas from the supply pipeline at a supply pipeline pressure; b. conducting a portion of said compressed gas received from the supply pipeline at said supply pipeline pressure to partially fill a first cell of substantially empty gas cylinders through the low pressure manifold; c. compressing a portion of said compressed gas from said supply pipeline to a pressure that is higher than said supply pipeline pressure; d. switching said first cell of gas cylinders at said supply pipeline pressure to said high pressure manifold and thence conducting gas therethrough at said higher pressure to continue to fill said first cell of gas cylinders; e. conducting a portion of said compressed gas received from the supply pipeline at said supply pipeline pressure to a second cell of substantially empty gas cylinders; and continuing steps c, d, and e until all cells of gas cylinders are filled with compressed gas at said second higher pressure. 14. A method for emptying a ship-borne storage system for compressed gas into a first delivery pipeline and at least one second delivery pipeline, said ship-borne storage system including a plurality of gas cylinders organized into cells, a high pressure manifold, at least one other manifold, and a submanifold connecting said gas cylinders to said high pressure manifold and said at least one other manifold, the method comprising the steps of: a. connecting a first cell of gas cylinders to the first delivery pipeline; b. conducting a portion of said compressed gas to partially empty the first cell of gas cylinders through the high pressure manifold at the ship-bome pressure to the first delivery pipeline; c. connecting said first cell of gas cylinders to at least one second delivery pipeline; d. expanding the remainder ofthe compressed gas in the first cell of cylinders to at least one lower pressure for both continuing to empty the first cell of cylinders and supplying the gas to at least one second delivery pipeline; e. connecting the first delivery pipeline to a second cell of gas cylinders; f . conducting a portion of said compressed gas from the second cell of gas cylinders to the first delivery pipeline at said ship-borne pressure; continuing steps c, d, e, and f until all ofthe gas cylinders borne by the ship have emptied their compressed gas into either the first delivery pipeline or at least one second delivery pipeline. 15. The method as defined in Claim 14 wherein said compressed gas is allowed to adiabatically expand during the ship emptying process. 16. The method as defined in Claim 15 wherein the adiabatic expansion of said compressed gas is used to chill said plurality of emptied gas cylinders; and the chill of said empty gas cylinders is maintained until said chilled empty gas cylinders are refilled with compressed gas. 17. The method as defined in Claim 16 wherein said chill is maintained until the ship- borne storage system is returned to a supply pipeline. 18. A method for filling a ship-borne storage system for compressed gas from a supply pipeline and emptying said ship-borne storage system into a first delivery pipeline and at least one second delivery pipeline, said ship-bome storage system including a plurality of gas cylinders organized into cells, a high pressure manifold, at least one other manifold, and a submanifold connecting said gas cylinders to said high and said at least one other manifold, the method comprising the steps of: a. receiving compressed gas from the supply pipeline at a supply pipeline pressure; b. conducting a portion of said compressed gas at the supply pipeline pressure to partially fill a first cell of substantially empty gas cylinders through said low pressure mamfold; c. compressing a portion of said compressed gas from said supply pipeline to a pressure that is higher than said supply pipeline pressure; d. switching said first cell of gas cylinders at said supply pipeline pressure to said high pressure manifold and thence conducting gas therethrough at said higher pressure to continue to fill said first cell of gas cylinders; e. conducting a portion of said compressed gas received from the supply pipeline at said supply pipeline pressure to a second cell of substantially empty gas cylinders; f. continuing steps c, d, and e until all cells of gas cylinders borne by the ship one filled with compressed gas at said second higher pressure; g. transporting the filled cells of gas cylinders; h. connecting a third cell of gas cylinders to the first delivery pipeline; i. conducting a portion of said compressed gas to partially empty the third cell of gas cylinders through the high pressure manifold at the ship-borne pressure to the first delivery pipeline; j . connecting said third cell of gas cylinders to at least one second delivery pipeline; -14- k. expanding the remainder of the compressed gas in the third cell of cylinders to at least one lower pressure for both continuing to empty the third cell of cylinders and supplying the gas to at least one delivery pipeline; 1. connecting the first delivery pipeline to a fourth cell of gas cylinders; m. conducting a portion of said compressed gas from the fourth cell of gas cylinders to the first delivery pipeline at said ship-borne pressure; continuing steps i, j, and k until all ofthe gas cylinders borne by the ship have discharged their compressed gas into either the first delivery pipeline or at least one second delivery pipeline. 19. The method as defined in Claim 18 wherein said compressed gas is allowed adiabatically expand during the ship emptying process. 20. The method as defined in Claim 19 wherein the adiabatic expansion of said compressed gas is used to chill said plurality of empty gas cylinders; and the chill of said empty gas cylinders is maintained until said empty gas cylinders are refilled with compressed gas. 21. The method as defined in Claim 20 wherein said chill is maintained until the ship- bome storage system is returned to said supply pipeline. 22. The system as defined in Claim 1 wherein the gas is natural gas. 23. The system as defined in Claim 9 wherein the gas is natural gas. 24. The system as defined in Claim 10 wherein the gas is natural gas. 25. The method as defined in Claim 13 wherein the gas is natural gas. 26. The method as defined in Claim 14 wherein the gas is natural gas. 27. The method as defined in Claim 18 wherein the gas is natural gas. 28. The system as defined in Claim 1 wherein the gas cylinders are made from welded steel pipe with domed caps welded on each end. 29. The system as defined in Claim 9 wherein the gas cylinders are made from welded steel pipe with domed caps welded on each end. 30. The system as defined in Claim 10 wherein the gas cylinders are made from welded steel pipe with domed caps welded on each end. 31. The method as defined in Claim 27 wherein a sufficient number of ships of appropriate capacity and speed are used so that there is at least one ship loading and one ship discharging compressed gas at all times. 32. The system for compressed gas transport as defined in Claim 1 further including an on shore loading compressor station. 33. The system for compressed gas transport as defined in Claim 1, wherein a plurality of ships are used to enable a continuous loading of compressed gas.

Inventors: CRAN JAMES A, STENNING DAVID G, CRAN, JAMES, A., STENNING, DAVID, G.
Applicants: ENRON LNG DEV CORP, ENRON LNG DEVELOPMENT CORP.
Application year: 1996
Main classification: F17C1
IPC codes: B63B25, F17C1, F17C5, F17C7