U.S. patent application number 11/454882 was filed with the patent office on 2006-12-21 for method for transporting liquified natural gas.
Invention is credited to Steven Campbell.
Application Number | 20060283519 11/454882 |
Document ID | / |
Family ID | 39343610 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060283519 |
Kind Code |
A1 |
Campbell; Steven |
December 21, 2006 |
Method for transporting liquified natural gas
Abstract
A method of transporting natural gas by cooling and pressurizing
retained natural gas to liquefy the retained natural gas within a
fiber reinforced plastic pressure vessel.
Inventors: |
Campbell; Steven; (St.
John's, CA) |
Correspondence
Address: |
OGILVY RENAULT LLP
1981 MCGILL COLLEGE AVENUE
SUITE 1600
MONTREAL
QC
H3A2Y3
CA
|
Family ID: |
39343610 |
Appl. No.: |
11/454882 |
Filed: |
June 19, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60691782 |
Jun 20, 2005 |
|
|
|
Current U.S.
Class: |
141/82 |
Current CPC
Class: |
F17C 2205/0169 20130101;
F17C 2223/043 20130101; F17C 2250/0452 20130101; F17C 2205/0323
20130101; F17C 2203/0639 20130101; F17C 2221/035 20130101; F17C
2203/03 20130101; F17C 2227/0337 20130101; F17C 2201/032 20130101;
F17C 2203/0648 20130101; F17C 2227/0157 20130101; F17C 2270/0171
20130101; F17C 2265/025 20130101; F17C 2205/0142 20130101; F17C
2201/0109 20130101; F17C 2221/032 20130101; F17C 2205/013 20130101;
F17C 2223/035 20130101; F17C 1/002 20130101; F17C 2265/05 20130101;
F17C 2209/221 20130101; F17C 2270/0105 20130101; F17C 2223/0161
20130101; F17C 2270/0136 20130101; F17C 2223/046 20130101; F17C
2201/056 20130101; F17C 2270/0173 20130101; F17C 2203/0673
20130101; F17C 2205/0107 20130101; F17C 2221/033 20130101; F17C
2205/0305 20130101; F17C 2250/0642 20130101; F17C 2203/0643
20130101; F17C 2205/0397 20130101 |
Class at
Publication: |
141/082 |
International
Class: |
B65B 1/28 20060101
B65B001/28 |
Claims
1. A method of transporting natural gas, comprising: providing a
source of natural gas; providing a fiber reinforced plastic
pressure vessel for retaining said natural gas; and cooling and
pressurizing retained natural gas to liquefy said retained gas
within said fiber reinforced plastic pressure vessel.
2. The method as set forth in claim 1, further including adjusting
the concentration of at least one of C2 and C3+ present in said
natural gas during storage of said natural gas to decrease the
vapor pressure thereof.
3. The method as set forth in claim 1, further including
maintaining said C2 and said C3+ in a liquid state during storage
for recycling to said source of natural gas.
4. The method as set forth in claim 1, further including
maintaining said C2 and said C3+ in a liquid state in said source
of said pressurized and liquefied natural gas during discharge of
said fiber reinforced plastic pressure vessel.
5. The method as set forth in claim 4, wherein said natural gas is
discharged/de-pressurized in a controlled manner for controlling
the boil rate of pressurized and liquefied natural gas to increase
the concentration of C2 and C3+ remaining in said vessel during
discharge/de-pressurization.
6. The method as set forth in claim 5, wherein said C2 and said C3+
remaining in said fiber reinforced pressure vessel subsequent to
discharge of said natural gas is further cooled during return
journey to the source of natural gas.
7. The method as set forth in claim 5, wherein chilled C2 and said
C3 are retained in said vessel and mixed with natural gas during
reloading of said natural gas into said pressure vessel to lower
the temperature of reloaded natural gas and the resulting
mixture.
8. The method as set forth in claim 7, wherein retained and
super-chilled C2 and said C3+ collectively lower the vapor pressure
of the mixture of C2 and said C3+ and natural gas.
9. The method as set forth in claim 1, wherein in alternation,
pressurized and liquefied natural gas is discharged from said
vessel through a lower most manifold connected thereto.
10. Use of a fiber reinforced plastic pressure vessel for retaining
pressurized and liquefied natural gas.
11. The use as set forth in claim 10, wherein said vessel includes
valve means for admitting and discharging said gas, said means
composed of a steel selected from duplex, super duplex and/or
precipitation hardened stainless steel.
12. The use as set forth in claim 10, wherein said vessel is
composed of a material selected from the group consisting of glass,
carbon, and aramid filament fiber.
13. The use as set forth in claim 10, wherein said vessel has an
operating temperature below at least -50 C.
14. A system for transporting natural gas having fluid management
apparatus and transport apparatus, said fluid management apparatus
comprising: a plurality of fiber reinforced plastic pressure
vessels for retaining said natural gas; fluid connection means
interconnecting said pressure vessels; valve means in fluid
communication with said fluid connection means for admitting and
discharging said gas exteriorly of said vessels or between said
vessels; support means for supporting said plurality of fiber
reinforced plastic pressure vessels; cooling means for cooling said
natural gas; and pressurizing means for pressurizing said natural
gas.
15. The system as set forth in claim 14, wherein said support means
comprises a cassette frame.
16. The system as set forth in claim 14, wherein said fluid
connection means comprises a manifold network interconnecting
individual vessels.
17. The system as set forth in claim 14, wherein each said vessel
includes at least one set of first and second opposed valves.
18. The system as set forth in claim 14, wherein said vehicle is
selected from the group consisting of a marine vessel, automobile
and train.
19. A system for land based storage of natural gas, comprising: a
plurality of fiber reinforced plastic pressure vessels for
retaining said natural gas; fluid connection means interconnecting
said pressure vessels; valve means in fluid communication with said
fluid connection means for admitting and discharging said gas
exteriorly of said vessels or between said vessels; support means
for supporting said plurality of fiber reinforced plastic pressure
vessels; cooling means for cooling said natural gas; and
pressurizing means for pressurizing said natural gas.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit from U.S. Provisional
Application No. 60/691,782, filed Jun. 20, 2005.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of transporting
natural gas and more particularly, the present invention relates to
a method and system for transporting pressurized and liquefied
natural gas.
BACKGROUND OF THE INVENTION
[0003] Low emissions and the high cost of oil have made natural gas
the global fossil fuel of choice. Currently, there are 6000
trillion cubic feet (TCF) of proven natural gas reserves in the
world. Approximately half of those reserves are considered
stranded; when it is not economical to transport by pipeline or
ship-based liquefied natural gas (LNG). Both pipelines and LNG have
economical limits; pipelines in distance, LNG by project and
reserve size minimums.
[0004] Pipelines transport natural gas as a vapor, whereas LNG is
transported as a liquid. To liquefy natural gas at ambient pressure
requires cryogenic refrigeration to -165.degree. C. This is a
costly and relatively complex process; however, due to the
increased value of natural gas, the global demand for LNG has
skyrocketed. Although this is the case, approximately TCF of proven
reserves remain stranded.
[0005] To economically transport stranded and other natural gas
reserves, various methods of Compressed Natural Gas (CNG)
transportation methods have been proposed and are in various stages
of development. The most technically feasible and cost effective
method of CNG transportation is through the use of fiber reinforced
plastic (FRP) pressure vessels. Unlike steel-based pressure
vessels, FRP pressure vessels or bottles are lightweight, corrosion
resistant, and have safe failure modes if punctured. The composite
structure of FRP pressure vessels are resistant to temperatures as
low as -80.degree. C. or even lower; however, the port boss in the
domes of FRP pressure bottles, used for connecting to manifold
piping systems, are made of metal, and therefore, FRP bottles are
limited by the metallurgy used. Carbon steels loose strength and
become brittle below temperatures near -40.degree. C. Duplex, super
duplex, precipitation hardened and titanium alloys in contrast
maintain strength and integrity in low temperatures; which
therefore would allow the low-temperature range of an FRP pressure
vessel to be reached.
[0006] Lowering the temperature of natural gas while maintaining a
constant pressure results in gas density increase. The
concentrations of C1+ hydrocarbons determine the thermodynamic
characteristics of a particular mixture under varied temperature
and pressure combinations. Higher density allows for higher volumes
of gas that can be stored in the same space, and therefore
transported by ship, modal rail or roadway. Vapor pressure is
somewhat proportionate to the proportions of larger carbon chain
molecules in a gas mixture. A higher concentration of C2+ in a
mixture lowers the vapor pressure and therefore the inverse
pressure temperature combination that determines when a mixture
begins to liquefy. The phase envelope for a particular natural gas
mixture shows the relative vapor/liquid proportion at any given
pressure and temperature combination. When fully liquefied, density
within the phase envelope is maximized; however, a combination of
gas and liquid may be more practical for storing and or
handling.
[0007] It has been found that the use of FRP pressure vessels to
store natural gas at low temperatures to partially or completely
liquefy the said gas is effective and has wide commercial
application. The use of FRP pressure vessels to store pressurized
liquefied natural gas (PLNG) allows significantly large quantities
of natural gas to be transported by ship, tractor trailer, and
modal container, or stored on land. Compared to compressed natural
gas (CNG) stored at ambient temperature, the density and therefore
net amount of natural gas is doubled by lowering the temperature
by, as an example, forty to fifty degrees Celsius, at approximately
half the pressure.
[0008] Using FRP pressure vessels to store PLNG is a safe,
reliable, lightweight, corrosion resistant and cost effective way
to transport natural gas from source to market. It is also
economically effective to store natural gas on land for surge
containment and storage.
[0009] Insulation of the FRP PLNG system will help keep the system
cool and therefore stabilize the liquid from boiling at sub-zero
temperatures.
[0010] In view of the limitations in the art, it would be highly
desirable to have a method and a system for transporting greater
quantities of natural gas.
[0011] The present invention satisfies this need.
SUMMARY OF THE INVENTION
[0012] One object of the present invention is to provide an
improved method and system for transporting higher quantities of
natural gas by pressurization and conventional thermal reduction to
obtain liquefication.
[0013] A further object of one embodiment of the present invention
is to provide a method of transporting natural gas, comprising
providing a source of natural gas, providing a fiber reinforced
pressure vessel for retaining the natural gas, and cooling and
pressurizing retained natural gas to liquefy the retained gas
within the fiber reinforced plastic pressure vessel.
[0014] A further object of the present invention is to provide a
system for transporting natural gas having fluid management
apparatus and transport apparatus, the fluid management apparatus
comprising a plurality of fiber reinforced plastic pressure vessels
for retaining the natural gas, fluid connection means
interconnecting the pressure vessels, valve means in fluid
communication with the fluid connection means for admitting and
discharging the gas exteriorly of the vessels or between the
vessels, support means for supporting the plurality of fiber
reinforced pressure vessels, the fluid transport apparatus,
comprising a vehicle for receiving the fluid management apparatus,
cooling means for cooling the natural gas, and pressurizing means
for pressurizing the natural gas, whereby pressurized and liquefied
natural gas is transportable with the vehicle.
[0015] Yet another object of one embodiment of the present
invention is to provide a system for transporting natural gas
having fluid management apparatus and transport apparatus, the
fluid management apparatus comprising a plurality of fiber
reinforced plastic pressure vessels for retaining the natural gas,
fluid connection means interconnecting the pressure vessels, valve
means in fluid communication with the fluid connection means for
admitting and discharging the gas exteriorly of the vessels or
between the vessels, support means for supporting the plurality of
fiber reinforced plastic pressure vessels, the fluid transport
apparatus, comprising a vehicle for receiving said fluid management
apparatus, cooling means for cooling the natural gas, and
pressurizing means for pressurizing the natural gas, whereby
pressurized and liquefied natural gas is transportable with the
vehicle.
[0016] Having thus generally described the invention reference will
now be made to the accompanying drawings illustrating preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a graphical illustration of the phase envelopes
for natural gas;
[0018] FIG. 2 is an enlarged view of the manifold system and FRP
vessels as connected according to one embodiment;
[0019] FIG. 3 is a top view of the ship hold with the FRP pressure
vessels held in position by a cassette modular framing system;
[0020] FIG. 4 is a side view of FIG. 3;
[0021] FIG. 5 is a perspective view of a cassette support framing
system according to one embodiment of the present invention;
[0022] FIG. 6 is a view of the cassette with an FRP in situ
together with the manifold system;
[0023] FIG. 7 is a side view of a group of individual stacked
cassettes with modules in position;
[0024] FIG. 8 is a view of another vehicle for retaining the FRP
vessels; and
[0025] FIG. 9 is a view of a land based system.
[0026] Similar numerals denote similar elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] For modes of PLNG transportation and storage including a
ship, the combination of low temperature and pressure to increase
density near or to the point of liquefaction can be further
optimized by increasing the C2+ concentration of the gas mixture.
It is known that increased concentrations of C2+ in a gas mixture,
lowers the vapor pressure of the entire mixture. Thus, higher
concentrations of C2+ in the gas mixture will allow for larger net
volumes of natural gas to be stored and transported comparatively.
This is generally depicted in the phase diagram of FIG. 1.
[0028] Using a vertically oriented FRP PLNG gas containment system,
natural gas may be discharged from the containment system as a
vapor or a liquid. Vapor may be discharged through the upper
manifold piping system. Liquid natural gas may be discharged
through the lower manifold system. To counteract Joule-Thompson
effects during de-pressurization and maintain minimum/maximum
temperatures in the system, some heat may have to be applied. In
one possibility, the heat could be applied directly to one or more
manifolds.
[0029] The thermodynamic characteristics of a natural gas/liquids
mixture are determined by the concentrations of C2 and C3+ in the
mixture. The higher the concentration of C2+, the lower the vapor
pressure of the mixture. Therefore, by adding or maintaining a
significant C2 and C3+ concentration, a relatively low vapor
pressure may be obtained. A lower vapor pressure will allow for the
gas being injected into a FRP PLNG storage system to liquefy with
less pressure or different temperature, than with a higher vapor
pressure.
[0030] By making use of the thermodynamic characteristics, control
of the boil rate during discharge permits significant proportions
of C2 and C3+ hydrocarbons to remain as a liquid in the FRP PLNG
system. This obviates the requirement of having to remove C2 and
C3+ hydrocarbons before injecting the gas into a pipeline
distribution network. Most pipeline distribution systems have a
restriction on the thermal content of gas entering into a pipeline
system. In North America, the limit is generally 1050 Btu's
(British thermal units) per scf (standard cubic feet) of gas.
[0031] As the pressure in the FRP PLNG system is reduced at assumed
constant temperature, the vapor pressure of the liquid/gas mixture
is increased. This will induce more gas to boil. Controlling the
rate of pressure drop and temperature change in the storage system
will therefore control the boil rate of liquid gas. When the boil
rate is constricted, the tendency is for the lighter hydrocarbons
to boil first. C2, but moreover, C3+ hydrocarbons tend to stay as a
liquid. Thus, as the liquid/vapor interface lowers toward the
bottom of the FRP bottles at a constrained rate, the concentration
of C2 and C3+ molecules increases. The propensity is for the
heaviest molecules to collect over repeated cycles as they are less
likely to vaporize at a constrained rate of boil. The heavier
hydrocarbon concentration change during discharge of the cargo will
also change the vapor pressure of the liquid gas mixture. The
greater the concentration of C2+ hydrocarbons, the lower the vapor
pressure of the changing mixture.
[0032] Maintaining a low temperature in the FRP PLNG containment
system during discharge, a high concentration of C2 and C3+ will
remain as a liquid at the bottom part of the system. This C2 and
C3+ mixture can then be returned to the source of natural gas and
reused for the next shipment without processing the gas externally
of the containment storage system to remove C2 and C3+.
[0033] As the concentration of C2 and C3+ builds over time, some C2
and C3+ may be used for power generation on board the ship. There
will be an economical crossover point where additional C2 and C3+
hydrocarbons no longer increase the net amount of cargo transported
on a PLNG carrier or modal system. Any C2 and C3+ over this amount
would not be economically advantageous. The most cost effective
system will be at the crossover point.
[0034] Alternatively, PLNG may be discharged through the lower
manifold and re-gasified on deck for offloading. It may even be
offloaded as a liquid if desired for direct injection into a
land-based storage system. If this alternative is chosen, then some
C2 and C3+ liquids used to achieve increased density could be
extracted separately and restored for the return journey.
[0035] C2 and C3+ concentrations in a land based FRP PLNG storage
system would have the same or similar density/capacity increase
effect within an equal space.
[0036] This method of PLNG storage would also be cost effective to
transport ethane (C2) as a commodity of its own. Ethane is the
feedstock for the petrochemical industry. It therefore has a
significant commodity value. Ethane is currently only transported
by pipeline. The feedstock to the petrochemical industry is
therefore limited to sources obtainable by pipeline. PLNG offers
another transportation mode of much larger distances than feasible
via pipeline transport.
[0037] To overcome thermal input to the system during compression
and loading, the residual C2 and C3+ hydrocarbons can be chilled to
the minimum temperature allowed at a specified pressure. During the
return journey, the residual natural gas liquids and captured C4
and C5+ hydrocarbons, may be super-chilled without danger of rapid
depressurization causing a temperature drop. The pressure drop
would be negligible. Therefore, when mixed with new and possibly
hot gas coming into the system, the temperature will equalize and
remain as low as possible and, as required to achieve the affect
desired. If incoming gas into the system is through the lower
manifolds, the incoming gas would have to percolate through the
heavy hydrocarbon residual. This would help to mix the heavy
hydrocarbons stored in the bottoms of the systems to mix with the
incoming gas.
[0038] With reference to FIGS. 2 through 4 shown as a vehicle,
shown in the example as a ship 10 with the FRP pressure vessels
generally denoted by numeral 12. The vessels each have an upper
metal alloy port boss 14 and a lower metal port boss 16 which may
be composed of the metals noted herein previously (duplex, super
duplex, precipitation hardened) and other suitable stainless steels
of similar grade. The individual port bosses are connected by upper
and lower piping manifolds 18, 20, respectively. The piping
manifolds 18 and 20 will be selected of similar materials as the
port bosses and will have the feature of being capable of
withstanding low or ultra low temperatures.
[0039] The FRP vessels 12 may be held in modular cassette frames,
denoted in FIG. 5 by numeral 22. The cassette frames 22 can be
stacked and nested in the hold of a ship as is indicated in FIGS. 3
and 4. The frame is designed to isolate the vessels including the
piping manifolds from ship movement and vibration. It is also
useful to facilitate full visual inspection of the fiber reinforced
plastic pressure vessels while in service. The cassette is composed
of a frame with a bottom grid 24 which is for the purpose of
supporting the vessels (the vessel is not shown in FIG. 4). The
frame has three sides 26, 28 and 30 and an open top. The lack of a
top section is to facilitate ease of installation for the vessels
into frame 22 and also is useful from a mass point of view; the
absence of a top and one or more sides reduces the overall
mass.
[0040] Once installed in the hold of a ship as shown in FIG. 4 the
adjacent cassette frames can be bolted together and include a
bushing 32 (see FIG. 5) to absorb hydrodynamic movement during
traveling. Where the cassettes 22 are stacked in a vertical manner,
it will be evident that the bottom grid 24 of the upper cassette
provides for lateral bracing of the lower cassette frame as is
clear from FIG. 4.
[0041] Each cassette frame 22 is equipped with upper and lower
piping manifolds 18 and 20 respectively, to connect the top and
bottom 14 and 16 port bosses of vertical vessels 12. The bottom
manifold 20 is secured to the grid 24 of the cassette 22. The upper
manifold 18 is also secured however, it is guided by guides 34 to
allow for elongation of the pressure vessels during pressurization.
This is illustrated in FIG. 6. The connection of the vessels 12 to
pipe it through the piping manifolds 18 and 20 may be directly
welded or via high pressure flange connections (not shown) which
are integral with the port bosses 14, 16 of the vessels 12.
[0042] To create a stack or cluster of cassette modules 22, the
upper manifold 18 of a lower cassette may be connected to the lower
manifold 20 of the upper cassette. The lowermost and uppermost
manifolds would then be connected to the respective piping that
would lead to the first isolation valves located on the deck of the
ship 10. The uppermost and lowermost manifolds denoted by numerals
36 and 38 in FIG. 7 would be connected to isolation valves located
in the deck of ship 10, which valves are denoted by numerals 40 and
42, the latter illustrated in FIG. 4.
[0043] As an option, the manifold piping may be insulated with
suitable insulation denoted by numeral 44 in FIG. 2 or the entire
cassette system may be composed of insulated frames. As a further
possibility, the inside of the ship's hold may be insulated.
[0044] On the main deck of the ship 10, there is included
refrigeration and compression equipment, globally denoted by
numeral 46 in FIG. 4.
[0045] Turning to FIG. 8, shown is a further embodiment of the
invention where the individual cassettes 22 have been installed on
a trailer 50. Suitable pressurization and compression equipment may
be included on board the trailer (not shown) or simply extraneous
of the trailer 50.
[0046] FIG. 9 schematically illustrates a land based system 52,
where the same components are incorporated from FIG. 8 with
exception that the trailer 50 (FIG. 8) is deleted and replaced by
frame 52.
[0047] Although embodiments of the invention have been described
above, it is 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.
* * * * *