Boil-off gas handling in LNG terminals

Abstract

A process for collection, storage and transport of boil off-gas from a liquefied natural gas storage tank. An ultra-low temperature, composite gas tank is provided to accept the boil-off gas and saturated vapor at ultra-low-temperatures in a range of about −80° C. to −45° C. (about −112° F. to −229° F.) and at high pressure of about 150 bar (about 2,175.5 psi). Boil off gas collected from liquefied natural gas storage at a pressure in a range of about 15 to 18 bar (217.5 psi to 261 psi) and at a temperature in of about −150° C. (about −238° F.). The ultra-low temperature, composite gas tank can hold the gas as it warms to ambient temperature. The process includes a liner step; a filament step; a wrap step; and a filling step. Optional steps include an insulation step; a fiber step; a layering step; a nozzle step; and a gas step.

Claims

1. A process for gas storage and transport comprising the steps of: providing a single-wall liner for an ultra-low temperature, composite gas tank, the single-wall liner comprising a metal tube, a seamless top metal end cap and a seamless bottom metal end cap, the metal tube is seamless and integrally formed as a single unitary base piece, comprising: a cylindrical sidewall having a substantially constant diameter; a top end comprising: a top transition zone contoured to seamlessly transition between the cylindrical sidewall and an extended cylindrical neck, the extended cylindrical neck with an opening that provides access into the ultra-low temperature, composite gas tank, and a substantially variable diameter narrowing along said top transition zone from the cylindrical sidewall to the extended cylindrical neck; and a bottom end having a bottom transition zone contoured to seamlessly transition from said cylindrical sidewall to a distal end; the seamless top metal end cap integrally formed as a first single unitary overlay piece, said top metal end cap comprising an inner surface and an outer surface with solid metal therebetween, wherein the inner surface in its entirety is in direct contact with the top end, wherein the top metal end cap overlays the top transition zone and a top portion of said cylindrical sidewall; and the seamless bottom metal end cap integrally formed as a second single unitary overlay piece, said bottom metal end cap overlays the bottom end and a bottom portion of said cylindrical sidewall; providing a structural fiber composite for a filament winding of the single-wall liner, the structural fiber composite comprising a resin matrix composite; completing the ultra-low temperature, composite gas tank by wrapping the single-wall liner in a plurality of layers of the structural fiber; moving a boil-off gas from storage for liquefied gas to a first compressor, the boil-off gas having pressure of 18 bar (261 psi) and a temperature of −150° C. (−238° F.); compressing the boil-off gas in the first compressor to produce a first stage compressed gas having a temperature in a range of −120° C. (−184° F.) to −130° C. (−202° F.) and a pressure of 100 bar (1450 psi); moving the boil-off gas from the storage at −150° C. (−238° F.) to mix in with the first stage compressed gas to produce an intermediate stage compressed gas; compressing the intermediate stage compressed gas to a pressure of 150 bar (2175 pounds per square inch) and a temperature of −145° C. (−229° F.) to produce a virtual pipeline gas; adding the virtual pipeline gas to the ultra-low temperature, composite gas tank; and allowing the temperature of the virtual pipeline gas within the ultra-low temperature, composite gas tank to warm to an ambient temperature up to 25° C. (77° F.), without releasing boil-off gas from the ultra-low temperature, composite gas tank.

2. The process of claim 1, further comprising the step of adding an outer layer of foam insulation over the plurality of layers, the outer layer allowed to harden.

3. The process of claim 1, wherein the structural fiber composite is selected from the group consisting of carbon fiber, fiber glass, aramid, KEVLAR and nylon.

4. The process of claim 1, further comprising the step of adding an inner layer thermal insulation between any two of the plurality of layers.

5. The process of claim 1, further comprising the step of adding threaded nozzle openings at the top end and at the bottom end of the single-wall liner.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The drawings illustrate preferred embodiments of the method of boil-off gas and saturated vapor handling in liquefied natural gas terminals and the components used in the method. The reference numbers in the drawings are used consistently throughout. New reference numbers in FIG. 2 are given the 200 series numbers. Similarly, new reference numbers in each succeeding drawing are given a corresponding series number beginning with the figure number.

(2) FIG. 1 is a schematic view of the components in a method of the invention.

(3) FIG. 2 is a schematic view of the delivery of gas from the ultra-low temperature, composite gas tank as a retail storage tank serving an end user.

(4) FIG. 3 is a flow chart showing required steps in a first process.

(5) FIG. 4 is a flow chart identifying optional steps with a dashed line in the first process.

(6) FIG. 5 is a flow chart showing required steps in a second process.

(7) FIG. 6 is a side sectional view of an ultra-low temperature, composite gas tank according to the disclosure.

(8) FIG. 7 is a side sectional view of a single-wall liner used according to the disclosure.

(9) FIG. 8 is a side sectional view of an alternative single-wall liner with end caps used according to the disclosure.

(10) FIG. 9 is an end elevation view of the ultra-low temperature, composite gas tank according to the disclosure.

(11) FIG. 10 is a chart listing compressed natural gas possible time-temperature-quantity combinations storage and transportation in the ultra-low temperature, composite gas tank.

DESCRIPTION OF EMBODIMENTS

(12) In the following description, reference is made to the accompanying drawings, which form a part hereof and which illustrate several embodiments of the method of storing and transporting boil-off gas and saturated vapor. The drawings and the preferred embodiments of the invention are presented with the understanding that the present invention is susceptible of embodiments in many different forms and, therefore, other embodiments may be utilized and structural, and operational changes may be made, without departing from the scope of the present invention.

(13) The Processes

(14) FIGS. 3 and 4 diagram a first process (300) that includes preferred steps and optional steps. FIG. 5 diagrams an alternative process (500) with preferred steps. The solid lines connecting boxes in FIG. 2 and FIG. 5's flow charts represent mandatory steps and dashed lines in FIG. 4 indicate optional steps. FIG. 3 shows all lines connecting the boxes are solid and are thus required steps. All of the boxes below the first process (300) in FIG. 4 are connected with a dashed line, indicating optional steps potentially added to the mandatory steps of FIG. 2.

(15) The processes disclosed herein will have benefits for the storage and transportation of any gaseous and liquefied gas. Table 1 below lists typical gases and their boiling points for which storage and transportation benefits can be obtained from use of the ultra-low temperature, composite gas tank (130) according to this disclosure.

(16) TABLE-US-00001 TABLE 1 Nitrous Carbon Chemical Helium Hydrogen Nitrogen Argon Oxygen LNG Oxide Dioxide Symbol/ He H.sub.2 N.sub.2 Ar O.sub.2 CH.sub.4 N.sub.2O CO.sub.2 Property (Solid) Boiling −269 −253 −196 −186 −183 −161 −88.5 −78.5 Point at 1013 mbar (° C.) Liquid 0.124 0.071 0.808 1.42 1.142 0.42 1.23 11 Density (Kg/Liter) Gas 0.169 0.085 1.18 1.69 1.35 0.68 3.16 1.87 Density at 15° C. (KG/M.sup.3) Gas 748 844 691 835 853 630 662 845 Volume from 1 liter Liquid (Liter)

(17) The first process (300) includes a liner step (305); a filament step (310); a wrap step (315); and a filling step (320). Optional steps, shown in FIG. 4, include an insulation step (405); a fiber step (410); a layering step (415); a nozzle step (420); and a gas step (425).

(18) The alternative process (500) includes the first three steps of the first process, namely the liner step (305); a filament step (310); a wrap step (315). The alternative process (500) includes a first pumping step (505); a first compressing step (510); a second pumping step (515); a second compressing step (520); and a storing step (525).

(19) The Liner Step

(20) The first step in the first process (300) and the alternative process (500) is a liner step (305). The single-wall liner (625) and the alternative single-wall liner (800), shown in FIG. 8 apply to the first process (300) shown in FIG. 3 and the alternative process (500), shown in FIG. 5. Both the first process (300) and the alternative process (500) use the single-wall liner (625) with its various optional components.

(21) The liner step (305) involves the details in providing a single-wall liner (625) for an ultra-low temperature, composite gas tank. The single-wall liner (625) is also known as a “Metallic Liner with Metal End Caps for a Fiber Wrapped Gas Tank,” as was described in U.S. Pat. No. 8,474,647, issued 2 Jul. 2013 and is hereby incorporated by reference herein in its entirety. The single-wall liner (625) is a component in the ultra-low temperature, composite gas tank (130) needed to implement a preferred claimed first process (300) and an alternative preferred claimed process (505), charted in FIG. 5.

(22) FIG. 7 shows a sectional side view of a preferred embodiment of the single-wall liner (625). FIG. 8 shows a second preferred embodiment, that is an alternative single-wall liner (800). FIGS. 7 and 8, replicate FIGS. 1 and 2 of the '647 patent, modified with changed and added reference numbers.

(23) The single-wall liner (625) that is first preferred is shown in FIG. 7 with three elements. The first element is a metal tube that is defined by cylindrical sidewall (703) (703), a top end (702) to the left of the line A-A, and a bottom end (701) to the right of line B-B. The second element of the single-wall liner (625) is a seamless top metal end cap (710). The third element of the single-wall liner (625) is a seamless bottom metal end cap (711).

(24) The metal tube is seamless and integrally formed as a single unitary base piece of uniform thickness and uniform diameter. The top end (702) includes: a top transition zone (704) to the left of the line A-A in FIG. 7; and a bottom end (701) that includes a bottom transition zone (708) to the right of line B-B. These transition zones seamlessly transition between the cylindrical sidewall (703) and an extended cylindrical neck at each end, except as shown in FIG. 8, with a single extended cylindrical neck at the top end (702) and a closed bottom dome (801).

(25) The top end (702) of the single-wall liner (625) is preferably contoured to form a top dome that seamlessly transitions from the cylindrical sidewall (703) beginning at location (730) to form an extended cylindrical neck, which is shown in the dashed oval (740).

(26) The bottom end (701) of the single-wall liner (625) is preferably contoured to form a bottom dome that seamlessly transitions from the cylindrical sidewall (703) beginning at a second location (731) to form an extended cylindrical neck that is open with a hole (706) through a fitting (724) screwed into the extended cylindrical neck.

(27) The top end (702) and the bottom end (701) have a substantially variable diameter (707) narrowing along these transitions zones from the cylindrical sidewall (703) to the extended cylindrical neck. The bottom end (701) has a bottom transition zone (708) contoured to seamlessly transition from said cylindrical sidewall (703) to a distal end (723).

(28) Each extended cylindrical neck defines an opening into and out of the single-wall liner (625). The extended cylindrical neck preferably has internal threads (720), that is, threads within each extended cylindrical neck. Alternatively, any extended cylindrical neck may have external threads (820). The threads, whether internal or external or both, permit attaching an end cap, fitting or appurtenance.

(29) Typical optional fittings for internal or external threads include, a valve, pressure regulator, stub, or end plug to terminate the opening. In addition, an external thread may be used with a lock nut (811) to secure an end cap, or the end cap itself may be threaded to mate with them. Optionally, the cylindrical neck surrounds a boss, that is, an embedded fitting, such as the solid boss.

(30) The extended cylindrical neck of the bottom end shown in FIG. 7 has external threads that mate (722) with threads on a seamless bottom metal end cap (711) shaped with a flange (721). Alternative arrangements are possible such as a two-part flange with the external flat face screwed into the part embedded within the extended cylindrical neck. The flange (721) facilitates connecting multiple cylinders in series, that is, a tandem connection of cylinders to extend volume capacity.

(31) The second element of the single-wall liner (625) is a seamless top metal end cap (710) having a mating shape to the top dome. The seamless top metal end cap (710) is of seamless construction, that is, it is a single integral piece of metal with no welds or seams of any kind. The seamless top metal end cap (710) is integrally formed as a first single unitary overlay piece, as shown in FIG. 7. The seamless top metal end cap (710) has an inner surface (712) and an outer surface (713) with solid metal therebetween. The inner surface is entirely in direct contact with the top end (702), wherein the seamless top metal end cap (710) overlays the top transition zone (704) to the left of the line A-A in FIG. 7, and a top portion (716) of said cylindrical sidewall (703) to the right of the line A-A in FIG. 7. Preferably, the seamless top metal end cap (710) is attachable to the top dome.

(32) Preferably, the seamless top metal end cap (710) has a neck of same length as that of the extended cylindrical neck of the single-wall liner (625). However, it is not required that the end cap rise to the end of the extended cylindrical neck, as shown in the embodiment illustrated in FIG. 7, but may rise partly up the extended cylindrical neck as shown in FIG. 8 for the alternative seamless top metal end cap (810). Preferably, the seamless top metal end cap (710) also covers the start of the seamless transition from the cylindrical sidewall (703), and thus would preferably cover at least the top end (702) in its entirety. Optionally, an alternative seamless top metal end cap (810) has mating with external threads (820) on an extended cylindrical neck.

(33) The third element of the single-wall liner (625) is a seamless bottom metal end cap (711), which is preferably similarly configured to the seamless top metal end cap (710). The seamless bottom metal end cap (711) is seamless and is integrally formed as a second single unitary overlay piece, as shown in FIG. 7. The seamless bottom metal end cap (711) overlays the bottom transition zone (708) to the right of the line B-B in FIG. 7 and a bottom portion (714) of said cylindrical sidewall (703) to the left of the line B-B in FIG. 7.

(34) The fourth element of the liner is a seamless bottom metal end cap (711) having a mating shape of the bottom dome. The preferences and options for the seamless bottom metal end cap (711) parallel those of the seamless top metal end cap (710). FIG. 7 shows an optional fitting embedded within the extended cylindrical neck, which is shown threaded to flange (721). Optional embedded fittings are well known in the art and other examples include a cryogenic valve fitting (630), a nozzle and a plug. A plug is a solid boss.

(35) The seamless bottom metal end cap (711) is of seamless construction, that is, it is a single integral piece of metal with no welds or seams of any kind.

(36) The preferred metal for the metal tube, the seamless top metal end cap (710), and the seamless bottom metal end cap (711) is 6000 series aluminum alloy. Dissimilar metals may be used for each of these three elements, recognizing that dissimilar metals may involve deleterious effects from galvanic action. FIG. 10 is a chart listing temperature and pressure against the gas weight and other features of compressed natural gas (CNG) in a single-wall liner (625) or the ultra-low temperature, composite gas tank (130) according to the disclosure herein.

(37) In sum, the liner step (305) includes providing a single-wall liner (625) for the ultra-low temperature, composite gas tank (130). The single-wall liner (625) includes a metal tube, a seamless top metal end cap (710) and a seamless bottom metal end cap (711). The metal tube is seamless and integrally formed as a single unitary base piece. The metal tube comprises a cylindrical sidewall (703) having a substantially constant diameter. The metal tube further comprises a top end (702). The top end (702) comprises a top transition zone (704) contoured to seamlessly transition between the cylindrical sidewall (703) and an extended cylindrical neck, which is shown in the dashed oval (740). The extended cylindrical neck defines an opening and has a substantially variable diameter narrowing along said top transition zone (704) from the cylindrical sidewall to the extended cylindrical neck. The metal tube has a bottom end (701), which defines a bottom transition zone (708) contoured to seamlessly transition from said cylindrical sidewall (703) to a distal end (723). The seamless top metal end cap (710) is integrally formed as a first single unitary overlay piece, as shown in FIG. 7. The seamless top metal end cap (710) defines an inner surface (712) and an outer surface (713) with solid metal therebetween, wherein the inner surface (712) in its entirety is in direct contact with the top end (702). The seamless top metal end cap (710) overlays the top transition zone (704) and a top portion (716) of said cylindrical sidewall (703). The metal tube further includes the seamless bottom metal end cap (711) integrally formed as a second single unitary overlay piece, as shown in FIG. 7. The seamless bottom metal end cap (711) overlays the bottom end (701) and a bottom portion (714) of the cylindrical sidewall (703).

(38) The following table provides typical size and volume dimensions for a single-wall liner (625).

(39) TABLE-US-00002 CYLNDER WATER VOLUME (NOMINAL) CALCULATIONS CYLINDER OD (Nominal) INCHES 8.75 8.75 8.75 8.75 8.75 CYLINDER ID Nominal) INCHES 7.75 7.75 7.75 7.75 7.75 OVERALL LENGTH INCHES 60 72 84 100 120 WATER VOLUME LTERS 44 54 63 75 91 CYLINDER OD (Nominal) INCHES 11 11 11 11 11 CYLINDER ID Nominal) INCHES 9.75 9.75 9.75 9.75 9.75 OVERALL LENGTH INCHES 60 72 84 100 120 WATER VOLUME LTERS 69 84 99 118 143 CYLINDER OD (Nominal) INCHES 13.5 13.5 13.5 13.5 13.5 CYLINDER ID Nominal) INCHES 11.5 11.5 11.5 11.5 11.5 OVERALL LENGTH INCHES 60 72 84 100 120 WATER VOLUME LTERS 95 116 136 164 198

(40) The Filament Step

(41) The next step in the first process (300) is the filament step (310). The filament step (310) includes providing a structural fiber composite for a filament winding (905) of the single-wall liner, the structural fiber composite comprising a resin matrix composite (910). Structural fibers are well known in the field. Optionally, the first process (300) may include a fiber step (410) wherein the structural fiber composite is selected from the group consisting of carbon fiber, fiber glass, aramid, KEVLAR and nylon. Structural fiber adds strength to the single-wall liner (625). This strength is needed to contain the high gas pressures capable of being experienced within the ultra-low temperature, composite gas tank (130). The ultra-low temperature, composite gas tank (130) is designed to withstand the hydrostatic and thermal in the circumferential (hoop), tangential or helical directions.

(42) The Wrap Step

(43) The next step in the first process (300) is the wrap step (315). The wrap step (315) includes making the ultra-low temperature, composite gas tank (130) by wrapping the single-wall liner (625) in a plurality of layers of the structural fiber (610), as shown in FIG. 6. Two such layers of the structural fiber (610) are shown in FIG. 6. By cross-weaving continuous rovings of carbon fiber, fiberglass and/or aramid fiber, and impregnating them in a thermosetting or thermoplastic resin matrix, the filament winding (905) results in an optimized ultra-low temperature, composite gas tank (130) for both ultra-low temperature and high pressure storage and transportation.

(44) The next step in the first process (300) is the filling step (320). The filling step (320) includes filling the ultra-low temperature, composite gas tank (130) with gas having a temperature in a range of about minus 80° C. (about minus 112° F.) to about minus 145° C. (about minus 229° F.); the gas having a pressure of about 150 bar (2175.5 pounds per square inch) when the temperature is at about minus 145° C. (about minus 229° F.). The temperature range is approximate and may vary depending on the temperature of the boil-off gas (106) and the recompression machinery available. The initial temperature of the gas may be any temperature above the liquefaction temperature for the gas. For methane, the liquefaction temperature is about −162° C. (−259° F.) and so boil-off gas (106) would be above that temperature and likely about −145° C. (about −229° F.) at a pressure of about 18 bar (261 psi). So, for preferred loading conditions prior to storage in the ultra-low temperature, composite gas tank (130), the gas would preferably be compressed to about 150 bar (2175 psi) and a temperature of about −145° C. (about −229° F.).

(45) Insulation Step

(46) Optionally, the first process (300) may include an insulation step (405). The insulation step (405) includes adding an outer layer (605) of foam insulation over the plurality of layers. This is shown in FIG. 9. The outer layer (605) is preferably one that hardens into a solid. The process then allows the outer layer (605) to harden. Use of foam insulation in cryogenic and near cryogenic applications is well known. For example, spray-on foam insulation (SOFI) has been developed for use on the cryogenic tanks of space launch vehicles beginning in the 1960s with the Apollo program. Also, the Space Shuttle External Tank is covered with rigid polymeric closed-cell foam insulation to prevent ice formation, protect the metallic tank from aerodynamic heating, and control the breakup of the tank during re-entry.

(47) Layering Step

(48) Optionally, the first process (300) may include a layering step (415). The layering step (415) that includes adding an inner layer thermal insulation (615) between any two of the plurality of layers of the structural fiber (610), as shown in FIG. 6.

(49) Nozzle Step

(50) Optionally, the first process (300) may include a nozzle step (420). The nozzle step *420) includes adding threaded nozzle openings at the top end and at the bottom end of the single-wall liner (625).

(51) Gas Step

(52) Optionally, the first process (300) may include a gas step (425). The gas step (425) includes removing boil-off gas (106) from a liquefied gas tank; using a multi-stage compressor to compress the boil-off gas (106) initially at a temperature of about −150° C. (−238° F.) and a pressure of about 18 bar (261 psi) to a pressure of about 100 bar (1450 psi) and a temperature in a range of about −120° C. (−184° F.) to −130° C. (−202° F.); and holding the boil-off gas (106) in a temperature in a range of about minus 80 degrees Centigrade (−112° F.) to minus 100 degrees Centigrade (−148° F.).

(53) Alternative Process

(54) The alternative process (500) uses the same first three steps as the first process (300), namely the liner step (305); the filament step (310); and the wrap step (315) as described above.

(55) First Pumping Step

(56) The next step in the alternative process (500) is the first pumping step (505). The first pumping step (505) includes pumping a boil-off gas (106) from a storage tank for liquefied natural gas to a first compressor, the boil-off gas (106) having pressure of about 18 bar (261 psi) and a temperature of about −150° C. (−238° F.)

(57) First Compressing Step

(58) The next step in the alternative process (500) is the first compressing step (510). The first compressing step (510) includes compressing the boil-off gas (106) in the first compressor (120) to produce a first stage compressed gas having a temperature in a range of about −120° C. (−184° F.) to about 130° C. (−202° F.) and a pressure of about 100 bar (1450 psi). The first stage compressed gas is the gas that leaves the first compressor (120) shown in FIG. 1.

(59) Second Pumping Step

(60) The next step in the alternative process (500) is the second pumping step (515). The second pumping step (515) includes pumping the boil-off gas (106) from storage at about −150° C. (−238° F.) to mix in with the first stage compressed gas to produce an intermediate stage compressed gas. The storage source may be any such source, such as a liquefied natural gas transfer storage tank (115), a liquefied natural gas large storage tank (110), or the liquefied natural gas ship (105). The intermediate stage compressed gas is the gas that enters the second compressor (125), shown in FIG. 1.

(61) Second Compressing Step

(62) The next step in the alternative process (500) is the second compressing step (520). The second compressing step (520) includes compressing the intermediate stage compressed gas to a pressure of about 150 bar (2175 pounds per square inch) and a temperature of about −145° C. (−229° F.) to produce a virtual pipeline gas. The virtual pipeline gas is the gas that leaves the second compressor (125), shown in FIG. 1

(63) Storing Step

(64) The next step in the alternative process (500) is the storing step (525). The storing step (525) includes adding the virtual pipeline gas to the ultra-low temperature, composite gas tank (130). Once stored in the ultra-low temperature, composite gas tank (130), the ultra-low temperature, composite gas tank (130) can be used as long-term storage and transportation to an end-user.

(65) The above-described embodiments including the drawings are examples of the invention and merely provide illustrations of the invention. Other embodiments will be obvious to those skilled in the art. Thus, the scope of the invention is determined by the appended claims and their legal equivalents rather than by the examples given.

INDUSTRIAL APPLICABILITY

(66) The invention has application to the liquefied gas industry.