Ships – Building – Freighters
Reexamination Certificate
2000-04-19
2002-01-22
Sotelo, Jesus D. (Department: 3617)
Ships
Building
Freighters
C220S901000
Reexamination Certificate
active
06339996
ABSTRACT:
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
Currently, there are three basic means to transport natural gas or natural gas liquids (NGL).
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 liquified 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. A liquefaction plant is generally very large and therefore, not practical or feasible for offshore gas production.
The third mode of transporting natural gas and liquids is by compression of the natural gas (CNG) and compressed natural gas liquids (CNGL). Unfortunately, conventional CNG concepts use steel or steel lined pressure vessels. This usually creates a weight problem as pressure vessel wall thickness is proportional to the design pressure. Steel pressure vessels are usually very heavy, especially when the design pressure is high.
At high pressures, the rupture characteristics of steel pressure vessels becomes a safety concern. In the event of a pressure vessel failure, the likelihood exists for other surrounding vessels to fail. Thus, the nesting of steel or steel lined pressure vessels is not a favourable option. As a concomitant disadvantage, without nesting the storage bottles together, economy of space is not maximized.
Further problems encountered by the use of steel or steel lined pressure vessels are corrosion and certification. To ensure that a minimum wall thickness is maintained, steel pressure vessels are typically x-rayed by use of radiography. This testing requires sufficient space to set up the necessary equipment. This, inherently, eliminates nesting as a possibility.
Several CNG ship-based pilot projects have been carried out in the past. 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. The excessive weight created stability problems and water draft concerns. Also, servicing such a heavy ship would be impossible in any of the world's existing dry-docks. Exemplary of the prior art in this regard is U.S. Pat. No. 5,803,005, issued Sep. 8, 1998 to Stenning et al.
Currently, there are truck-mounted CNG projects in operation, but they are subsidized, since they would not be economically feasible on their own. The capacity of steel pressure vessels used for truck-mounted CNG systems is limited by a weight constraint of a truck transportation system. In addition, to store and transport raw gas and liquids, which most likely would be corrosive, requires a corrosion allowance. This further decreases the capacity, since the allowable operating pressure requires commensurate reduction.
There are communities that are currently tied-in to a natural gas pipeline which experience cyclic demands which the pipeline cannot handle. In such areas, there is a requirement to supply natural gas during peak load times. Unfortunately, current means of CNG transportation are not feasible due to highway weight restrictions, which in turn restricts the amount of natural gas that can be carried on a per trip basis.
Ethane would be an ideal hydrocarbon to use as an additive to meet the cyclic requirements of such areas. It can be transported as a liquid under relatively high pressure (700 psi) thus a significant quantity may be transported per trip. Under pipeline distribution pressure, ethane will exist as a vapor and therefore mix with the natural gas. As sales gas normally contains slightly less than 10% ethane, an incremental quantity will not adversely affect the consumers use of the gas. Nozzle tips would not require adjustment to account for the additional proportion of ethane. As a concomitant advantage, ethane has a higher heat value than the main constituent of natural gas, which is methane.
Generally speaking, there are communities that are not currently tied into a natural gas network because the demand that would exist there does not justify the cost of a pipeline to that community, especially during the transition phase, which may last a number of years. In these cases, liquefied ethane by pressurization may allow for the gradual growth of a distribution system to a point where the cost of a pipeline is justified. It may even be feasible to continue trucking ethane in larger quantities. Methane or a mixture of methane and ethane may also be used, if a feasible means of transporting methane can be obtained.
To obtain a practical and feasible means of transporting CNG and or CNGLs, a safe and relatively light-weight pressure vessel is required. This would elevate the excessive weight related problems that make current steel or steel lined pressure vessels inappropriate for CNG transportation over water or land. In addition, a pressure vessel that is resistive to corrosion would allow the transportation of raw natural gas and NGLs. This would enhance the feasibility of a gas production project, by eliminating the requirement to first process the gas and or liquids at the source.
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 an improved system and method for transporting CNG and NGL.
The use of composite pressure vessels will overcome the safety, weight, and corrosion-related problems mentioned above.
Rupture characteristics of composite pressure vessels are much more favorable than that of steel or steel lined pressure vessels. Composite pressure vessels also have a broader temperature range without strength reduction than conventional steel or steel lined pressure vessels. Thus, the use of comparable composite pressure vessels increases the level of safety over conventional steel or steel lined pressure vessels.
Comparable composite pressure vessels are much lighter (as much as 70% less) than conventional pressure vessels that are made of steel or are steel lined. Thus, the use of composite pressure vessels will overcome the weight-related problems associated with using conventional steel or steel lined pressure vessels.
Composite pressure vessels with a non-metallic liner such as high density polyethylene (HDPE) will not corrode. Composite pressure vessels with a HDPE liner will therefore overcome the corrosion-related problems of storing raw natural gas and or raw NGLs in conventional steel or steel lined pressure vessels.
A further object of one embodiment of the present invention is to provide a light-weight, ship-based system for transporting raw, unprocessed, compressed natural gas and or compressed natural gas liquid, the system comprising:
a ship;
a plurality of composite material pressure vessels for containing raw, unprocessed, compressed natural gas and compressed natural gas liquid;
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.
The construction of composite pressure vessels varies from companies that manufacture them. The preferred 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. This particular type of composite pressure vessel is known.
The transportation of gas and liquids together in multiple pressure vessels on a ship incurs a problem of its own as ballast on a ship is of a critical concern. If gas and
(Marks & Clerk)
Mr. Steven Campbell
Sharpe Paul S.
Sotelo Jesus D.
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