Compact, modular method and apparatus for liquefying natural gas

• US 20060213222A1
• Filed: 03/23/2006
• Published: 09/28/2006
• Est. Priority Date: 03/28/2005
• Status: Active Grant

• Current Assignee: Cambridge Cryogenics Technologies
• Original Assignee: Cambridge Cryogenics Technologies
• Inventors: Whitesell, Robert
• Granted Patent: US 7,673,476 B2
• Time in Patent Office: Days
• US Class Current: 62/612
• CPC Class Codes: F25J 1/001 Hydrogen
• CPC Class Codes: F25J 1/0017 Oxygen
• CPC Class Codes: F25J 1/002 Argon
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0027 Oxides of carbon, e.g. CO2
• CPC Class Codes: F25J 1/0035 by gas expansion with extraction of work
• CPC Class Codes: F25J 1/004 by flash gas recovery F25J1/0267 takes precedence
• CPC Class Codes: F25J 1/0042 by liquid expansion with extraction of work
• CPC Class Codes: F25J 1/005 by expansion of a gaseous refrigerant stream with extraction of work
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0082 Methane
• CPC Class Codes: F25J 1/0202 in a quasi-closed internal refrigeration loop F25J1/0208, F25J1/0219, F25J1/0224 take precedence
• CPC Class Codes: F25J 1/0232 integration within a pressure letdown station of a high pressure pipeline system
• CPC Class Codes: F25J 1/0254 controlling particular process parameter, e.g. pressure, temperature
• CPC Class Codes: F25J 1/0257 Construction and layout of liquefaction equipments, e.g. valves, machines F25J1/0279 takes precedence
• CPC Class Codes: F25J 1/0258 vertical layout of the equipments within in the cold box
• CPC Class Codes: F25J 1/0259 Modularity and arrangement of parts of the liquefaction unit and in particular of the cold box, e.g. pre-fabrication, assembling and erection, dimensions, horizontal layout "plot"
• CPC Class Codes: F25J 1/0265 comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
• CPC Class Codes: F25J 1/0275 adapted for special use of the liquefaction unit, e.g. portable or transportable devices
• CPC Class Codes: F25J 1/0283 Gas turbine as the prime mechanical driver
• CPC Class Codes: F25J 1/0287 : including an electrical motor
• CPC Class Codes: F25J 1/0288 : using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
• CPC Class Codes: F25J 2205/02 : using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2220/62 : Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2230/20 : Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
• CPC Class Codes: F25J 2230/60 : the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2240/02 : Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• CPC Class Codes: F25J 2240/30 : Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
• CPC Class Codes: F25J 2240/40 : Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval

Abstract

A compact and modular cryogenic method and apparatus for liquefying natural gas. The liquefaction process is highly efficient and requires no external refrigeration system, and the apparatus is small enough to be transportable from one remote site to another. A compressed natural gas feed stream is cooled and then expanded to form a bi-phase stream comprising a first refrigerated vapor component and a first liquid component. The first liquid component is then separated from the bi-phase stream and expanded to form a second bi-phase stream comprising a second refrigerated vapor component and a second liquid component. The second liquid component is then introduced into a means configured for storage and transport. The remaining feed stream can then be recycled, and at least a substantial portion of the original feed stream can be processed into liquefied natural gas (LNG). The first and second vapor components are recycled through the system and comprise at least a portion of the feed stream in the repeated steps.

Claims

1. A method for liquefying a compressed gas feed stream, the method comprising the steps of:

a. providing a compressed gas feed stream at a pressure of between about 1500 psig to about 3500 psig and at near ambient temperature;

b. cooling the feed stream to between about −

10°

F. to about −

100°

F.;

c. expanding the cooled feed stream to form a first bi-phase stream comprising a first refrigerated vapor component and a first liquid component;

d. separating the first refrigerated vapor component and the first liquid component;

e. expanding the separated first liquid component to form a second bi-phase stream comprising a second refrigerated vapor component and a second liquid component;

f. separating the second refrigerated vapor component and the second liquid component; and

g. isolating the separated second liquid component to a means configured for storage and transport.

2. The method of claim 1, wherein at least a portion of cooling step (b) is accomplished by indirect heat exchange with the separated first refrigerated vapor component, the separated second refrigerated vapor component, or both.

3. The method of claim 1, further comprising:

h. combining the separated first and separated second refrigerated vapor components; and

i. recycling them into the feed stream of step (a).

4. The method of claim 1, wherein expanding step (c) comprises expanding in a sliding vane bi-phase turboexpander.

5. The method of claim 1, wherein at least a portion of cooling step (b) comprises cooling by a gas stream which has evaporated from the liquefied gas in the means configured for storage and transport.

6. The method of claim 1, wherein expanding step (e) comprises expanding in a throttle valve.

7. The method of claim 1, wherein expanding steps (c) and (e) comprise expanding in a throttle valve.

8. A compact and modular apparatus for refrigerating and liquefying a gas such as pure methane or a natural gas stream rich in methane, the apparatus comprising:

a. a means for cooling a compressed main feed stream entering at a pressure between about 1500 psig to about 3500 psig and at near ambient temperature to a temperature of between about −

10°

F. to about −

100°

F.;

b. a turboexpander configured to expand the cooled, compressed feed stream to form a first bi-phase stream comprising a first refrigerated vapor component and a first liquid component;

c. a primary separation tank configured to separate the first refrigerated vapor component and the first liquid component;

d. a means configured to expand the separated first liquid component to form a second bi-phase stream comprising a second refrigerated vapor component and a second liquid component;

e. a secondary separation tank configured to separate the second refrigerated vapor component and the second liquid component; and

f. a means configured for storage and transport of the separated second liquid component.

9. The apparatus of claim 8, further comprising a means to place the separated first refrigerated vapor component into fluid communication with the compressed main feed stream.

10. The apparatus of claim 8, further comprising a means to place the separated second refrigerated vapor component into fluid communication with the compressed main feed stream.

11. The apparatus of claim 10, further comprising placing a gas stream which has evaporated from the liquefied gas in the means configured for storage and transport into fluid communication with the main feed stream.

12. The apparatus of claim 8, wherein the turboexpander is a sliding vane bi-phase turboexpander.

13. The apparatus of claim 8, wherein the means for cooling the compressed main feed stream is a multi-flow heat exchanger, and the means configured to expand the separated first liquid component is a throttle valve.

14. The apparatus of claim 8, further comprising a regeneration heat exchanger configured to receive one of the first liquid component or the second liquid component as a cooling component therein.

15. A compact and modular apparatus for refrigerating and liquefying a gas such as pure methane or a natural gas stream rich in methane, the apparatus comprising:

a. a multistage compressor configured for receiving and compressing a main stream gas at a pressure of about 85 psig and at near ambient temperature to a pressure of between about 1500 psig to about 3500 psig;

b. an after-cooler configured to cool the compressed feed stream to near ambient temperature immediately after each compression stage in the multistage compressor;

c. a heat exchanger configured to cool the compressed feed stream to a temperature of between about −

10°

F. to about −

100°

F., typically between about −

20°

F. to about −

60°

F., and more typically about −

30°

F.;

d. a turboexpander configured to expand the compressed and cooled feed stream to a pressure of between about 15 to about 135 psig, typically between about 80 to about 105 psig, and more typically to between about 90 to about 95 psig, to form a first refrigerated vapor component and a first liquid component having a temperature of between about −

155°

F. to about −

240°

F., typically about −

190°

F. to about −

215°

F., and more typically about −

200°

F. to about −

205°

F.;

e. a primary separation tank configured to separate the first refrigerated vapor component and the first liquid component;

f. a throttle valve configured to expand the first liquid component to a pressure of between about 3 psig to about 7 psig, and more typically to about 5 psig to form a second refrigerated vapor component and a second liquid component having a temperature of between about −

250°

F. to −

265°

F., and typically between about −

252°

F. to about −

258°

F.;

g. a secondary separation tank configured to separate the second refrigerated vapor component and the second liquid component;

h. a means configured for storage and transport of the separated second liquid component; and

i. a means to place the separated first refrigerated vapor component and the separated second refrigerated vapor component into fluid communication with the compressed main feed stream.

16. The apparatus of claim 15, further comprising placing a gas stream which has evaporated from the liquefied gas in the means configured for storage and transport into fluid communication with the compressed main feed stream.

17. The apparatus of claim 15, further comprising a regeneration heat exchanger configured to receive the separated second liquid component as a cooling component therein, the regeneration heat exchanger operable to refrigerate an incoming line for a separate apparatus.

18. The apparatus of claim 17, further comprising a means to place the separated second liquid component, the separated first refrigerated vapor component and the separated second refrigerated vapor component into fluid communication with the compressed main feed stream.

19. The apparatus of claim 17, wherein the turboexpander is the only expansion means and the regeneration heat exchanger is configured to refrigerate the incoming line for a separate apparatus.

20. The apparatus of claim 15, wherein the multi-stage compressor includes a drive means selected from the group consisting of a gasoline engine, a natural gas driver, an electric motor, a diesel engine, a gas turbine, a steam turbine, and any other suitable driver.