AU783543B2 - Natural gas composition transport system and method - Google Patents

Description

P/00/0 1 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention title: Natural gas composition transport system and method The following statement is a full description of this invention, including the best method of performing it known to us: mcmmmM0110136851v1 999995 4.04.2000 NATURAL GAS COMPOSITION TRANSPORT SYSTEM AND METHOD Field of the Invention The present invention relates to gas transportation, and more particularly, the present invention relates to a natural gas composition transport system and method.

Background of the Invention In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date: part of common general knowledge; or (ii) known to be relevant to an attempt to solve any problem with which this specification is concerned.

Currently, there are three basic means to transport natural gas or natural gas oooo liquids (NGL).

S•The first and usually the most practical and feasible means of transporting natural gas and NGL, is a pipeline. Geographic obstacles are generally the only reasons that a pipeline is either not practical or feasible.

The second most common mode of natural gas transportation is liquefied natural gas (LNG). Unfortunately, LNG has a high capital cost associated and requires a cryogenic liquefaction plant proximate the source, and a re-gasification plant at the discharge point.

ooo 20 A liquefaction plant is generally large and therefore, not practical or feasible for offshore gas production.

The third mode of transporting natural gas and liquids is by compressed natural o• gas (CNG) and compressed natural gas liquids. Unfortunately, conventional CNG concepts have only proposed the use of steel or steel lined pressure vessels. These proposed concepts have inherent problems such as excessive weight, corrosion, and serious safely concerns through violent rupture characteristics. In the event of a pressure vessel failure, the likelihood exists for other surrounding vessels to fail. For this reason, certification agencies have never approved of a CNG concept using steel pressure vessels.

Exemplary of the prior art in this regard is United States Patent No. 5,803,005, issued September 8, 1998 to Stenning et al.

In the distant past, several CNG ship-based pilot projects have been attempted.

Unfortunately, it was found that the weight of the steel pressure vessels required to make a potential project feasible was too heavy for the ships to handle. The excessive weight created stability problems and water draft concerns. Servicing such a heavy ship would be impossible in any of the world's existing dry-docks.

To obtain a practical and feasible means of transporting CNG, a safe and relatively lightweight pressure vessel is required. In addition, a pressure vessel that is resistive to corrosion would allow the transportation of raw and unprocessed natural gas and NGL.

Safety is enhanced by orders of magnitude through the rupture characteristics of composite pressure vessels. Rupture characteristics of composite pressure vessels are opposite to that of steel or steel lined pressure vessels. Due to the construction method of the composite pressure vessels, crack propagation (caused by a projectile piercing the wall of the pressure vessel) is eliminated. This eliminates the potential of violent rupture and shrapnel associated with steel pressure vessels. This further eliminates the potential of catastrophic failure through a domino effect. Composite pressure vessels also have a broader temperature range without strength reduction than conventional steel or steel lined pressure vessels.

The use of composite pressure vessels overcomes the weight-related problems associated with using conventional steel or steel lined pressure vessels. Comparable composite pressure vessels are as much as 70 lighter than conventional pressure vessels that are made of steel.

Unlike steel or steel lined pressure vessels, composite pressure vessels will not corrode. The proposed composite pressure vessels have a non-metallic liner. The use of a °Oleo° non-corrosive composite pressure vessel will therefore allow the storage of raw unprocessed S. natural gas and or NGL.

In view of what has been proposed previously, there exists a need for an improved system for transporting natural gas and natural gas liquids discussed herein. The present invention satisfies this need.

SUMMARY OF THE INVENTION One object of the present invention is to provide a system and method, far improved from previous art, for transporting compressed natural Gas (CNG) and natural gas liquid (NGL) by ship, truck, or modular container.

The invention consists of a (CNG) and (NGL) transportation system designed to operate at ambient temperatures. The CNG transportation system may be ship-based, truck-mounted, or modular, whereby composite pressure vessels are used to overcome the safety limitations, weight restrictions and corrosion problems, related with using steel or steel lined pressure vessels proposed in previous CNG concepts.

An object of one embodiment of the present invention is to provide a light-weight, ship-based system for transporting raw unprocessed, CNG and or NGL, said system comprising: a ship; a plurality of composite material pressure vessels for containing raw CNG and or

NGL;

a connection means for the loading and unloading of the pressure vessels; 20 on-board equipment to assist with the loading and unloading of the pressure vessels; a connection means for interconnecting the vessels, the vessels being integrally connected to interchange pressurized gas and liquid from the vessels to user selected other vessels, whereby weight distribution in the ship may be adjusted.

In the ship-based CNG transportation system, composite pressure vessels are S•oriented vertically and aligned in banks. Each bank of cells is encased in a frame that is removable for maintenance. A module is made up of two or more banks of cells. Within each compartment of the ship, several modules may exist.

All cells in a bank are connected to a gas manifold at the top and a liquids manifold at the bottom. At the end of each manifold exists a control valve. Each bank manifold in a module is then connected together by an upper gas module manifold and a lower liquids module manifold respectively. Each module manifold is then connected to the main gas headers and liquids header of the ship through a respective isolation and control valve.

The transportation of gas and liquids together in multiple pressure vessels may incur an unfavorable distribution of weight. Thus a system to transfer the liquids from certain or all composite pressure vessels, to designated pressure vessels, while under pressure, is required. The ship-based CNG transportation system incorporates a ballast control system by the integral connection of the banks and modules to segregate the free NGL. By orienting the composite pressure vessels vertically, free liquids gravitate to the bottom of the cells.

These free liquids are then transferred to one or more designated banks of cells, by a using slight pressure differential between the gas and liquids manifolds. By controlling the liquids distribution, a desired weight distribution of the cargo may be obtained, and a stable and safe voyage conducted.

Upon arriving at the unloading terminal, the gas and liquids may be unloaded separately but concurrently to minimize delivery time.

To increase capacity and efficiency, refrigeration and insulation may be used.

To increase loading and unloading efficiency, on-board equipment such as compressors, pumps, and slug catchers may be used.

20 In order to maintain continuous production, several shuttle tankers may be required.

The construction of composite pressure vessels varies from companies that manufacture them. The preferred known model is constructed by wrapping an adhesive impregnated carbon fiber in a helical path around a (HDPE) liner. The ends of the pressure vessel would have an integral stainless steel boss to weld to external piping.

Having thus described the invention, reference will now be made to the accompanying drawings illustrating preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of shuttle tanker showing compartments and banks of cells; Figure 2 is an elevation view of shuttle tanker; Figure 3 is a schematic illustration of a typical bank of cells; Figure 4 is a schematic illustration of a typical compartment with multiple modules; Figure 5 is an elevation view of a typical frame containing a bank of cells; Figure 6 is a schematic illustration of a general arrangement of modules, equipment and piping on shuttle tanker; Similar numerals in the figures denote similar elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figures 1 through 6, the preferred embodiment is a ship-based CNG transportation system that uses composite pressure vessels to achieve a safe, light-weight, .e ballast controlled, and corrosive resistant storage and transportation system, designed to ooperate at ambient temperatures.

20 As an example, the vehicle may comprise a shuttle tanker 10 divided into two sides 12 and 14, each with an equal number of compartments. Each compartment may contain one or more modules 16. Within each module 16, there would be contained numerous banks of composite pressure vessel cells 18. Each bank of cells 19 is arranged in line, with two or more pressure vessels 18 stacked and connected vertically to efficiently use the available height within a ship's compartment. Each bank of cells 19 is supported in a metal .frame 20 secured within the compartment. The frames 20 are constructed so that they may be installed or removed without disturbing other frames within the compartment. The frames run aft to bow and are offset side by side.

Each bank of cells 19 is equipped with an upper gas manifold 11 that connects the tops of the pressure vessels 18 within each bank, and respectively, a lower liquid manifold 13 that connects the bottoms of the pressure vessels 18 within each bank. At the end of each respective manifold exists a control valve 26,28. Each control valve is connected to a respective module liquid manifold 22 and module gas manifold 24 that connects one or more banks to form a module 16. Each module 16 is then respectively connected to the liquids header 37 and high-pressure loading and discharging gas header 36 for that side of the ship through an isolation valve 32 and control valve 34. The upper gas module manifold 24 of each module 16 is also connected to a low-pressure gas header 38 through a similar isolation valve 32 and control valve 34.

To assist with ballast control, free liquids may be directed or transferred to designated banks of cells. To direct free liquids to designated cells, the gas being loaded is passed through one or more slug catchers 15, positioned on the deck of the ship 10. The free liquids are continuously removed from the bottom of the slug catchers 15 and directed to designated cells through a liquids header 37.

To transfer free liquids from filled or partially filled modules to designated cells within the module, the module is first isolated from the main headers by closing the respective isolation valves. The pressure in the designated bank of cells is then reduced by partially opening the isolation and control valves on the gas manifold 11 and gas module manifold 24 to the low-pressure gas header 38. Liquids are then transferred by partially opening the liquids control valve on the designated bank or banks of cells. By pressure differential, the free liquids will transfer through the liquids module manifold 22 into designated bank of cells.

Once the transfer is complete, all isolation and control valves will be closed. Liquid levels in 20 respective banks of cells would be monitored by remote instrumentation (not shown). The opening and closing of all valves would also be by remote control (not shown).

For more global ballast control, liquids may be transferred from module to module by a similar pressure differential method using the main headers. A crossover line 33 may be used to transfer liquids from one side of the ship 10 to the other side.

During loading, modules would be first pressurized to the source delivery pressure. If the design pressure is not reached using the delivery pressure, on-board compressors 21 may then be used to increase the pressure to the design pressure. On-board compression equipment may also be used to expedite unloading. Liquids pumps 23 may also be used to load, transfer, and unload liquids.

Upon arriving at the discharge location, the liquids may be discharged separately but concurrent to the gas since the liquids header 37 is independent of the gas unloading process.

Refrigeration and insulation may be used to increase the efficiency and capacity of the storage system if deemed feasible and necessary.

Each bank of cells would be equipped with an emergency relief system that would be tied into a flare boom. For additional safety, the shuttle tanker's compartments may be filled with an inert gas, replacing oxygenated air.

It would be beneficial if the shuttle tanker used natural gas or natural gas liquids for power.

In order to maintain continuous production, several shuttle tankers may be required. The number and size of these shuttle tankers, as well as the number and pressure capacity of the pressure vessels, will be determined by optimization considering such criteria as, production requirements, unloading facilities (rate and volume capacity), and cost.

The truck and modular containerization of CNG and NGL would be similar to that o.o of the ship system.

15 Although embodiments of the invention have been described above, it is not 9.* limited thereto and it will be apparent to those skilled in the art that numerous modifications form part of the present invention insofar as they do not depart from the spirit, nature and scope of the claimed and described invention.

The word 'comprising' or forms of the word 'comprising' as used in this 9 go. 20 description and in the claims do not limit the invention claimed to exclude any variants or additions.

*99o 9* *.99.9

Claims (12)

1. A light-weight, corrosive resistant, ship-based system for transporting raw, unprocessed, compressed natural gas and or compressed natural gas liquid, said system comprising: a ship; a plurality of composite material pressure vessels for containing said raw, unprocessed, compressed natural gas and said compressed natural gas liquid; connection means for interconnecting said vessels, said vessels being integrally connected to interchange pressurized gas and liquid from said vessels to user selected other vessels, whereby weight distribution in said ship may be adjusted.

2. A ship-based transportation system as described in claim 1, wherein said composite pressure vessels are aligned vertically in groups coaxial with the length of said ship, each said group comprising: a lower liquids manifold connecting bottom sections of each vessel, said manifold terminating at a liquids isolation valve; and upper gas manifolds connecting top sections of each vessel, terminating at a gas isolation valve.

3. The system as described in claim 2, comprising at least two groups of vessels; a liquids sub-manifold connecting all said liquids manifolds at said isolation valves of each of said groups within a module, and terminating at a module isolation valve; and a gas sub-manifold connecting all gas manifolds at said isolation valves of each o group within a module, and terminating at a module isolation valve.

The system as described in claim 3, said system including a loading/ unloading header, whereby gas loading and unloading is achieved through said header connected to each said module at said gas isolation valve for loading and unloading gas.

5. The system as described in claim 3, said system including a liquids header, whereby liquids loading and unloading is achieved through said header connected to each sd m said module at said liquids isolation valve for loading, unloading, or transferring of liquids.

6. The system as described in claim 3, said system including a low-pressure header, whereby gas loading, unloading, and transferring is achieved through said header connected to each said module at said gas isolation valve for loading and unloading gas.

7. The system as described in claim 3, whereby said ship is divided into two trains.

8. The system as described in claim 1, further including: at least one slug catcher for removing liquids from loading stream for direction to designated pressure vessel cells; at least one compressor for compressing said natural gas to required pressures for loading, unloading, or transferring of said natural gas; at least one liquid pump for pumping said liquid to required pressures for loading, unloading, or transferring of said liquids. oooo

9. A method of loading, unloading and transferring raw, unprocessed, compressed natural gas and compressed natural gas liquid aboard a ship, comprising the steps of: *"providing a plurality of composite material pressure vessels for receiving said gas or liquid within said ship; providing connection means for interconnecting said vessels; introducing said gas or liquid into said vessels; and **selecting vessels for receiving said gas or liquid to adjust weight distribution of said vessels within said ship for transporting said gas or liquid.

10. The method as described in claim 9, wherein stored natural gas may be unloaded separately and concurrently to that of natural gas liquids through a gas header and compressor.

11. The method as described in claim 9, wherein stored liquid may be unloaded separately and concurrently to that of natural gas through a liquid header and liquid pumps.

12. The method as described in claim 8, further including transferring said liquid or gas from one bank of vessels to another by pressure differentials. Steven Campbell 17 October 2000