APPARATUS, SYSTEM AND METHOD FOR RELIQUEFACTION OF PREVIOUSLY REGASIFIED LNG

Abstract

An apparatus, system and method for reliquefaction of previously regasified LNG are described. A natural gas reliquefaction method includes regasifying LNG onboard a FSRU to form high pressure regasified LNG (HP RLNG), delivering the HP RLNG to a natural gas pipeline that commingles with a natural gas grid, flowing the HP RLNG through a lateral, wherein the lateral diverts HP RLNG from the natural gas pipeline to an expander prior to commingling with the natural gas grid, expanding the natural gas with the expander to obtain low pressure regasified LNG (LP RLNG), liquefying the LP RLNG in a cold box of a nitrogen expansion loop to produce low pressure LNG, and transmitting the LNG to a cryogenic cargo tank onboard an LNG tanker truck.

Claims

1. A method of reliquefying previously regasified LNG comprising: diverting high pressure regasified LNG (HP RLNG) from a natural gas pipeline, wherein the HP RLNG is diverted through a lateral that connects to the natural gas pipeline prior to the natural gas pipeline converging with a natural gas grid, and wherein the natural gas pipeline receives the HP RLNG from an FSRU; expanding the HP RLNG from the lateral with an expander to obtain low pressure regasified LNG (LP RLNG); liquefying the LP RLNG in a cold box, wherein the cold box places the LP RLNG in heat exchange with nitrogen of a nitrogen expansion loop to produce low pressure LNG; and transmitting the low pressure LNG to a cryogenic cargo tank onboard an LNG tanker truck.

2. The method of claim 1, further comprising regasifying LNG onboard the FSRU to obtain the HP RLNG.

3. The method of claim 1, further comprising using energy extracted by the expander to drive a compressor that operates in the nitrogen expansion loop, the compressor providing compression of nitrogen in the nitrogen expansion loop.

4. The method of claim 1, further comprising compressing the nitrogen in the nitrogen expansion loop using a compressor powered by a generator, the generator at least partially fueled by a portion of the HP RLNG diverted through the lateral.

5. The method of claim 4, wherein the generator is at least partially fueled by a portion of boil-off gas from one of the cryogenic cargo tank, a land-based LNG storage tank fluidly coupled to the cold box, or a combination thereof.

6. The method of claim 5, wherein the portion of the HP RLNG and the portion of the boil-off gas are combined by an eductor, and the combined gas fuels the generator.

7. The method of claim 1, wherein the nitrogen expansion loop comprises a second expander, and further comprising expanding nitrogen in the nitrogen expansion loop over the second expander.

8. The method of claim 7, further comprising using the nitrogen to extract heat from the LP RLNG in the cold box to produce the low pressure LNG.

9. The method of claim 1, further comprising returning boil-off gas from one of the cryogenic cargo tank, an intermediate land-based LNG storage tank, or a combination thereof to the cold box.

10. The method of claim 9, further comprising using the boil-off gas to at least partially extract heat from the LP RLNG in the cold box.

11. The method of claim 1, wherein the LP RLNG is in heat exchange with the nitrogen in the cold box to extract latent heat from the LP RLNG.

12. A regasified LNG reliquefaction apparatus comprising: a natural gas pipeline extending between a FSRU and a natural gas grid; a lateral pipeline fluidly coupled to the natural gas pipeline prior to a commingling of the natural gas pipeline with the natural gas grid; the lateral pipeline fluidly coupled to an inlet of a natural gas expander and delivering LNG-quality natural gas to the inlet; an outlet of the expander fluidly coupled to a cold box; the cold box coupled to a nitrogen expansion loop; and LNG exiting the cold box, the LNG formed from the LNG-quality natural gas.

13. The regasified LNG reliquefaction apparatus of claim 12, further comprising a power generator fluidly coupled to a portion of the LNG-quality natural gas delivered by the lateral pipeline.

14. The regasified LNG reliquefaction apparatus of claim 13, wherein the power generator is energetically coupled to a compressor of the nitrogen expansion loop.

15. The regasified LNG reliquefaction apparatus of claim 12, further comprising a LNG storage tank receiving the LNG exiting the cold box.

16. The regasified LNG reliquefaction apparatus of claim 15, further comprising a boil-off gas (BOG) return line fluidly coupling the LNG storage tank and the cold box.

17. The regasified LNG reliquefaction apparatus of claim 15, further comprising a power generator, and a boil-off gas (BOG) return line fluidly coupling the LNG storage tank and the power generator.

18. The regasified LNG reliquefaction apparatus of claim 17, further comprising a portion of the LNG-quality natural gas delivered by the lateral pipeline and BOG carried by the BOG return line mixedly coupled by an eductor prior to entering the power generator.

19. The regasified LNG reliquefaction apparatus of claim 15, further comprising an LNG tanker truck cryogenically coupled to the LNG storage tank.

20. The regasified LNG reliquefaction apparatus of claim 12, wherein the natural gas expander is drivingly coupled to a compressor of the nitrogen expansion loop.

21. The regasified LNG reliquefaction apparatus of claim 12, wherein LNG-quality natural gas sendout from the FSRU is liquefied in the cold box without pretreatment.

22. A regasified LNG reliquefaction system comprising: a FSRU fluidly coupled to a natural gas pipeline, the natural gas pipeline comprising high pressure regasified LNG (HP RLNG) produced from LNG-quality natural gas regasified by the FSRU; the natural gas pipeline transmitting the HP RLNG at a first pressure of 70-100 barg and a first temperature of 5-20 C.; a lateral pipeline that couples the natural gas pipeline to an expander; the expander comprising an inlet that receives the HP RLNG from the lateral pipeline at the first pressure and the first temperature, wherein the expander converts the HP RLNG having the first pressure and the first temperature to low pressure regasified LNG (LP RLNG) having a second pressure of less than 10 barg and a second temperature of about 100 C.; a cold box fluidly coupled to the LP RLNG and a nitrogen expansion loop; and LNG exiting the cold box at a third pressure of 5-6 barg.

23. The regasified LNG reliquefaction system of claim 22, wherein the expander drives a compressor in the nitrogen expansion loop.

24. The regasified LNG reliquefaction system of claim 22, further comprising a compressor providing compression of nitrogen in the nitrogen expansion loop, the compressor powered by a generator fueled by a portion of the HP RLNG.

25. The regasified LNG reliquefaction system of claim 22, wherein the nitrogen expansion loop further comprises a second expander that expands the nitrogen.

26. The regasified LNG reliquefaction system of claim 22, wherein the nitrogen extracts heat from the LP RLNG in the cold box causing the LP RLNG to condense in the cold box at the second pressure.

27. The regasified LNG reliquefaction system of claim 22, further comprising a storage tank fluidly coupled to the LNG exiting the cold box.

28. The regasified LNG reliquefaction system of claim 27, wherein the storage tank is fluidly coupled between the cold box and an LNG cargo tank onboard a truck.

29. The regasified LNG reliquefaction system of claim 28, wherein a gas return line fluidly couples boil-off gas from the LNG cargo tank to the cold box.

30. The regasified LNG reliquefaction system of claim 29, wherein the boil-off gas cools the LP RLNG in the cold box and recondenses in the cold box.

31. The regasified LNG reliquefaction system of claim 28, wherein a gas return line fluidly couples boil-off gas from the LNG cargo tanks to a power generator.

32. The regasified LNG reliquefaction system of claim 31, further comprising an eductor coupled to a fuel gas inlet of the power generator, wherein the eductor mixes the boil-off gas with a portion of the HP RLNG sent to the power generator.

33. The regasified LNG reliquefaction system of claim 31, wherein the power generator provides make up power to the nitrogen expansion loop.

34. The regasified LNG reliquefaction system of claim 22, wherein the natural gas pipeline transmits the HP RLNG to downstream consumers via existing gas pipeline infrastructure.

35. A regasified LNG reliquefaction method comprising: regasifying LNG onboard a FSRU to form high pressure regasified LNG (HP RLNG); delivering the HP RLNG to a natural gas pipeline that commingles with a natural gas grid; flowing the HP RLNG from the natural gas pipeline through a lateral at a first pressure of 70-100 barg and a first temperature of 5-20 C., wherein the lateral diverts HP RLNG from the natural gas pipeline to an expander prior to commingling with the natural gas grid; expanding the natural gas having the first pressure and the first temperature with the expander to obtain low pressure regasified LNG (LP RLNG) having a second pressure of less than 10 barg and a second temperature of about 100 C.; liquefying the LP RLNG in a cold box of a nitrogen expansion loop to produce LNG at a third pressure of 5-6 barg; and transmitting the LNG to a cryogenic cargo tank onboard an LNG tanker truck.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings in which:

[0019] FIG. 1 is a schematic diagram of a regasified LNG reliquefaction system of an illustrative embodiment.

[0020] FIG. 2 is a schematic diagram of a regasified LNG reliquefaction system of an illustrative embodiment.

[0021] FIG. 3 is a flowchart of a method of reliquefying regasified LNG of an illustrative embodiment.

[0022] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale. It should be understood, however, that the embodiments described herein and shown in the drawings are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION

[0023] An apparatus, system and method for reliquefaction of previously regasified LNG will now be described. In the following exemplary description, numerous specific details are set forth in order to provide a more thorough understanding of embodiments of the invention. It will be apparent, however, to an artisan of ordinary skill that the present invention may be practiced without incorporating all aspects of the specific details described herein. In other instances, specific features, quantities, or measurements well known to those of ordinary skill in the art have not been described in detail so as not to obscure the invention. Readers should note that although examples of the invention are set forth herein, the claims, and the full scope of any equivalents, are what define the metes and bounds of the invention.

[0024] As used in this specification and the appended claims, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a heat exchanger includes one or more heat exchangers.

[0025] Coupled refers to either a direct connection or an indirect connection (e.g., at least one intervening connection) between one or more objects or components. The phrase directly attached means a direct connection between objects or components.

[0026] As used in this specification and the appended claims high pressure means, with respect to gaseous natural gas, a pressure of between 45 barg and 100 barg. With respect to a conduit, pipe, hose and/or transfer member for transferring gaseous natural gas, high pressure means capable of maintaining, transferring and/or accommodating natural gas at one or more pressures falling in the range of between 45 barg and 100 barg.

[0027] As used in this specification and the appended claims low pressure with respect to gaseous natural gas or LNG, means a pressure of 10 barg or less.

[0028] As used in this specification and the appended claims, FSRU is used liberally to refer to any of a regasification vessel, a floating storage regasification unit and/or a floating regasification unit (FRU).

[0029] One or more embodiments of the invention provide a system and method for supplying low-demand off-grid facilities with liquefied natural gas (LNG) for local distribution. Illustrative embodiments may allow LNG tanker trucks to be supplied with LNG from a high pressure gas pipeline without the need for pretreatment of the gas, in a cost-effective and more efficient manner than conventional methods. Illustrative embodiments may provide a self-sufficient system that does not require a power source external from the system, for reliquefaction of LNG-quality, high pressure, warm natural gas that is economical on a low-demand scale.

[0030] Illustrative embodiments may include taking FSRU sendout through a lateral, before the gaseous natural gas comingles with other natural gas sources that may contain impurities. The high pressure, regasified LNG (HP RLNG) taken through the lateral may be at pipeline pressure and temperature of about 70-100 barg and 5-20 C. The lateral may deliver the high pressure regasified LNG (HP RLNG) to a self-sufficient reliquefaction system mounted on a skid. A expander of the reliquefaction system may expand the natural gas to form low pressure regasified LNG (LP RLNG) of less than 10 barg and about 100 C. Power obtained from the gas expansion may be used to power a compressor in a nitrogen expansion loop and/or may be used to power a generator for the nitrogen expansion loop. The generator providing any make up power may be a gas turbine or dual fuel diesel engine. Similarly if grid based electrical power is available a motor may be used. Some of the regasified LNG may be bled prior to the expander inlet and used to power the generator. The LP RLNG exiting the expander will continue to a cold box where the regasified LNG may be reliquefied. The cold box may employ nitrogen from the nitrogen expansion loop in heat exchange with the natural gas to extract latent heat from the LP RLNG. The reliquefied, low pressure LNG may then be sent to a fixed storage tank and/or an LNG truck for transportation to an off-grid, low demand facility (4547 m.sup.3 useable net volume). Boil-off gas (BOG) from the tanks in the LNG trucks may be returned to the cold box to assist in refrigerating the LP RLNG and/or may be sent to power the generator for fuel. Where the BOG is sent to the generator, an eductor may draw the boil-off gas from the storage tank using the high pressure gas supply to the generator as the motive fluid in the eductor. The mixing will increase the pressure of the BOG so that it can be employed by the generator at about 30 barg.

[0031] FIG. 1 illustrates a regasified LNG reliquefaction system of an illustrative embodiment. FSRU 100 may be moored offshore and contain cryogenic tanks 170 transporting and/or storing LNG cargo. FSRU 100 may deliver regasified, high pressure gaseous natural gas (HP RLNG) 175 into high pressure pipeline 105. FSRU 100 may be a regasification vessel, a floating storage regasification unit or an FRU. FSRU 100 may be docked at subsea buoy 110, a sea island and/or a jetty. Subsea buoy 110 or a high pressure gas arm may receive HP RLNG 175 from vaporizer 115 onboard FSRU 100 and transmit HP RLNG 175 into pipeline 105. A portion of pipeline 105 may be subsea, on a jetty and/or onshore. Pipeline 105 may connect into a gas distribution system or grid 180 that may comingle gas from various sources. Gas delivered into pipeline 105 by FSRU 100 may be HP RLNG at about 70-100 barg and 5-20 C. The particular pressure and temperature of delivered gas may depend on the gas composition, delivery method and/or specifications of the local grid 180. FSRU 100 may be docked at a jetty extending from the shoreline, or may be three, four, five or more kilometers offshore and docked at a sea island or buoy. Lateral 120 may be a natural gas pipe that taps into pipeline 105 at a location prior to comingling of HP RLNG 175 with gas from other sources within grid 180. Placement of lateral 120 along pipeline 105 prior to comingling of gas from other sources within grid 180 will prevent contaminants such as water, hydrogen sulfide, carbon dioxide and/or mercury from mixing with the HP RLNG 175 that originates from FSRU 100.

[0032] The absence of contaminants will allow HP RLNG 175 to be reliquefied without the need for pretreatment. Pretreatment facilities and ancillary equipment is prohibitively expensive and/or complicated for supply of tanker trucks 135, since there is no economy of scale. Pipeline gas typically includes sour gases such as sulfides and CO.sub.2, too much water and mercury, none of which can be present during liquefaction and therefore, if present, must be removed prior to liquefaction. Pretreatment facilities typically consist of amine sweetening units, dehydration units and mercury removal units, and their associated powers, pumps, separators, power facilities and other ancillary utilities. By using HP RLNG 175 as an input, illustrative embodiments provide a system and method that eliminates the need for pretreatment and is simple and cost effective.

[0033] Lateral 120 may supply reliquefaction system 125 with HP RLNG 175. Reliquefaction system 125 may provide reliquefaction of HP RLNG 175 taken through lateral 120. Reliquefaction system 125 may be a self-contained skid-mounted system. HP RLNG 175 transported through lateral 120 may enter skid 255 through control and Emergency Shut Down (ESD) valves. Once reliquefied using reliquefaction system 125, LNG 140 may be delivered into storage tank 130 and/or cryogenic mobile tanks 150 onboard LNG tanker truck 135 through cryogenic hoses 160 and/or cryogenic piping. Boil-off gas (BOG) 145 generated by the LNG transfer, generated within fixed cryogenic storage tank 130 and/or generated in mobile cryogenic storage tank 150 may be returned to reliquefaction system 125 via return line 165. Employing BOG 145 as coolant for reliquefaction system 125 may be beneficial to the environment (cleaner and safer) as opposed to the conventional procedure of venting BOG 145 into the atmosphere. Mobile cryogenic storage tanks 150 onboard LNG tanker truck 135 may carry about 45-47 m.sup.3 useable net volume of LNG 140, a volume suitable for low demand, off-grid, locations such as facility 155. LNG tanker truck 135 may then transport LNG 140 to low demand, off-grid facility 155, which may for example be a remotely-located hospital.

[0034] Turning to FIG. 2, lateral 120 may deliver HP RLNG 175 at 70-100 barg and 5-20 C. to gas expander 200. Gas expander 200 may expand HP RLNG 175 to lower the pressure and temperature of the HP RLNG 175. In some embodiments, HP RLNG 175 may first pass through first heat exchanger 205 to lower the temperature of the gas before it enters gas expander 200. First heat exchanger 205 may be a printed circuit heat exchanger (PCHE), a plate fin heat exchanger (PFHE) or another heat exchanger of a kind well-known to those of skill in the art. A portion of HP RLNG 175 travelling through lateral 120 may be routed to power generator 210, for example a portion of HP RLNG 175 may be diverted to power generator 210 after exiting first heat exchanger 205 and prior to entering the inlet of expander 200. Generator 210 may be a gas turbine, or a dual-fuel diesel generator and allow for self-sufficiency of reliquefaction system 125. Stream 215 to generator 210 may be at pipeline pressure of 75-100 barg until mixed in eductor 220, which eductor 220 may lower the pressure of stream 215 to about 30 barg. A second heat exchanger 205 may also be coupled between eductor 220 and generator 210 should it be desirable to increase and/or change the temperature of stream 215 prior to input into generator 210. Piping, pumps, heat exchanger bypass and/or sets of valves may be employed in connection with fluid flow movement and/or control through the reliquefaction system of illustrative embodiments.

[0035] Gas expander 200 may convert HP RLNG 175 to low pressure regasified LNG (LP RLNG) 225 having a pressure of less than 10 barg and a temperature of 100 C. and/or about 100 C. LP RLNG 225 may then flow into cold box 230. Cold box 230 may include a sensible and latent heat exchanger, and cold box drain pot. The sensible/latent heat exchanger of cold box 230 may be a PCHE or PFHE type heat exchanger that places LP RLNG 225 in heat exchange with nitrogen. A control and instrument box for reliquefaction system 125 may be coupled to cold box 230. LP RLNG 225 within cold box 230 may be at least partially cooled by nitrogen in nitrogen expansion loop 235. Nitrogen may be compressed by compressor 240 in loop 235. Compressor 240 may be powered by one of gas expander 200, generator 210 or partially by gas expander 200 and partially by generator 210. Additionally nitrogen loop expander 250 may also provide power to compressor 240. Nitrogen loop heat exchanger 245 may remove heat from nitrogen, and may for example be a compact heat exchanger. Nitrogen loop expander 250, along with nitrogen loop heat exchanger 245, may complete nitrogen loop 235 by lowering the pressure and temperature of nitrogen entering cold box 230.

[0036] Low pressure LNG 140 may exit cold box 230. Low pressure LNG 140 may be formed from LP RLNG 225 that has been reliquefied in cold box 230. LNG 140 may be sent at about 5-6 barg to fixed cryogenic storage tank 130 and/or to mobile cryogenic storage tank 150 onboard LNG tanker truck 135. In some embodiments, the outlet of reliquefaction system 125 may be LNG at 5-6 barg stored in a pressurized Type C tank 130 for direct filling from storage tank 130 into mobile cryogenic tanks 150 onboard LNG tanker truck 135. BOG 145 may be returned to cold box 230 to assist in cooling LP RLNG 225 and/or may be mixed in eductor 220 to provide gas to generator 210. BOG 145 may be at a low pressure, such as less than 5 barg and about 158 C, and when sent to eductor 220, BOG 145 may assist in lowering the pressure of stream 215 of HP RLNG 175 flowing to generator 210. HP RLNG 175 may serve as the motive fluid in eductor 220.

[0037] FIG. 3 illustrates a method of supplying low-demand, offgrid facilities with LNG using a regasified LNG reliquefaction method of illustrative embodiments. At marine transport step 300, LNG may be transported by an LNC carrier (LNGC), regasification vessel or FSRU 100 across the ocean or other body of water to a location of natural gas demand. One or more LNGCs or FSRU 100 may assist in transport and/or regasification of the LNG. Ship-to-ship transfer protocol and equipment may be employed to transfer LNG between marine vessels and/or units if desired. FSRU 100 may be docked offshore proximate natural gas grid 180 and may regasify LNG at regasification step 305 using onboard vaporizers 115. Vaporizes 115 may use seawater, air and/or indirect heat exchange methods to vaporize LNG to form HP RLNG 175, which HP RLNG 175 may be LNG-quality gaseous natural gas. At transmission step 310, HP RLNG 175 may be transported through pipeline 105 towards natural gas grid 180 and/or additional pipelines or other natural gas distribution systems. During transmission step 310, a portion of the HP RLNG 175 may be diverted through lateral 120. Lateral 120 may be connected along pipeline 105 at a location prior to mixing of the HP RLNG 175 with natural gas from other sources within grid 180, such that only LNG-quality natural gas may travel through lateral 120. Limiting the gas feed through lateral 120 may eliminate the need for any gas pretreatment prior to reliquefaction, thereby disposing of the costs associated with pretreatment. HP RLNG 175 from lateral 120 may be expanded in gas expander 200 at expansion step 315. Expansion in gas expander 200 may produce LP RLNG 225 from HP RLNG 175, with gas expander 200 reducing the temperature and/or pressure of the HP RLNG 175. In some embodiments, at generator fueling step 345 a portion of HP RLNG 175 travelling through lateral 120 may be sent as fuel to generator 210, rather than being sent to gas expander 200.

[0038] At reliquefaction step 325, LP RLNG 225 from expander 200 may be reliquefied using cold box 230 cooled by nitrogen and/or nitrogen expansion loop 235. Power generated from expansion step 315 may be used at powering step 320 to power generator 210, compressor 240 in nitrogen expansion loop 235 and/or other make-up power for reliquefaction system 125. Once reliquefied, LNG 140 obtained from cold box 230 may be transferred to LNG tanker truck 135 at storage step 330. Cryogenic transfer hoses 160 may transfer LNG to storage tank 130 and/or LNG cargo tanks 150 and gas return line 165 may transfer inert gas, BOG 145 and/or natural gas vapor to cold box 230 and/or to eductor 220. BOG 145 from LNG tanks 130, 150 may be returned to cold box 230 and/or sent to generator 210 for fuel at BOG handling step 335. BOG 145 may assist in cooling LP RLNG 225 in cold box 230, may be mixed with HP RLNG 175 in eductor 220 to provide fuel for generator 210 and/or may be utilized rather than vented into the atmosphere. At delivery step 340, tanker truck 135 may transport LNG 140 to facility 155 in need of natural gas. Facility 155 may be off-grid and may have a relatively low-demand that does not justify building a dedicated pipeline.

[0039] An apparatus, system and method for reliquefaction of previously regasified LNG has been described. Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the scope and range of equivalents as described in the following claims. In addition, it is to be understood that features described herein independently may, in certain embodiments, be combined.