Process for liquefaction of natural gas

• US 6,023,942 A
• Filed: 06/18/1998
• Issued: 02/15/2000
• Est. Priority Date: 06/20/1997
• Status: Expired due to Term

• Current Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Original Assignee: Exxon Production Research Company (Exxon Mobil Corporation)
• Inventors: Kimble, Edward L., Thomas, Eugene R., Bowen, Ronald R., Cole, Eric T.
• Primary Examiner(s): DOERRLER, WILLIAM CHARLES
• Application Number:
  US09/099,589
• Time in Patent Office: 607 Days
• Field of Search: 62/612, 62/613, 62/619, 62/620, 62/614, 62/618, 62/631
• US Class Current: 62/613
• CPC Class Codes: B23K 35/3066 with Ni as next major constituent
• CPC Class Codes: B23K 9/173 and of a consumable electrode
• CPC Class Codes: B60K 15/03006 Gas tanks B60K15/07 takes precedence
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/08 containing nickel C22C38/105 takes precedence
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/14 containing titanium or zirconium
• CPC Class Codes: C22C 38/16 containing copper
• CPC Class Codes: F17C 1/00 Pressure vessels, e.g. gas cylinder, gas tank, replaceable cartridge pressurised apparatus for purposes other than storage, see the relevant subclasses such as A62C, B05B; associated with vehicles, see the appropriate subclass of classes B60 - B64; pressure vessels in general F16J12/00 ; autoclaves B01J3/04; tank vehicles B60P3/22; railway tank wagons for carrying fluent materials B61D5/00; accumulators for supplying fluid under pressure F15B1/04; liquefied gas stoves F24C3/00
• CPC Class Codes: F17C 1/002 Storage in barges or on ships
• CPC Class Codes: F17C 1/14 constructed of aluminium; constructed of non-magnetic steel
• CPC Class Codes: F17C 13/001 Thermal insulation specially adapted for cryogenic vessels vessels not under pressure with insulation F17C3/02; thermal insulation in general F16L59/00
• CPC Class Codes: F17C 2201/0109 with exteriorly curved end-piece
• CPC Class Codes: F17C 2201/0128 spherical or elliptical
• CPC Class Codes: F17C 2201/035 with substantially horizontal main axis
• CPC Class Codes: F17C 2201/054 medium (>1 m3)
• CPC Class Codes: F17C 2203/0648 Alloys or compositions of metals
• CPC Class Codes: F17C 2205/013 Two or more vessels
• CPC Class Codes: F17C 2205/0134 : characterised by the presence of fluid connection between vessels
• CPC Class Codes: F17C 2205/0302 : Fittings, valves, filters, or components in connection with the gas storage device
• CPC Class Codes: F17C 2205/0323 : Valves
• CPC Class Codes: F17C 2209/221 : Welding
• CPC Class Codes: F17C 2221/033 : Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
• CPC Class Codes: F17C 2223/0153 : Liquefied gas, e.g. LPG, GPL
• CPC Class Codes: F17C 2223/0161 : cryogenic, e.g. LNG, GNL, PLNG
• CPC Class Codes: F17C 2223/035 : High pressure (>10 bar)
• CPC Class Codes: F17C 2227/0135 : Pumps
• CPC Class Codes: F17C 2227/0337 : by cooling
• CPC Class Codes: F17C 2227/0355 : in a closed loop
• CPC Class Codes: F17C 2260/011 : Improving strength
• CPC Class Codes: F17C 2260/012 : Reducing weight
• CPC Class Codes: F17C 2260/032 : Avoiding freezing or defrosting
• CPC Class Codes: F17C 2265/035 : with subcooling the liquid phase
• CPC Class Codes: F17C 2265/05 : Regasification
• CPC Class Codes: F17C 2265/061 : for supply of supplying vehicles
• CPC Class Codes: F17C 2270/0105 : Ships
• CPC Class Codes: F17C 2270/0136 : Terminals
• CPC Class Codes: F17C 3/00 : Vessels not under pressure
• CPC Class Codes: F17C 3/025 : Bulk storage in barges or on ships constructive aspects B63B25/16
• CPC Class Codes: F17C 7/00 : Methods or apparatus for discharging liquefied, solidified, or compressed gases from pressure vessels, not covered by another subclass
• CPC Class Codes: F17C 7/02 : Discharging liquefied gases
• CPC Class Codes: F17D 1/082 : for cold fluids, e.g. liquefied gas F17D1/086 takes precedence
• CPC Class Codes: F25J 1/0022 : Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0035 : by gas expansion with extraction of work
• CPC Class Codes: F25J 1/0037 : of a return stream
• 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 1/0087 : Propane; Propylene
• CPC Class Codes: F25J 1/0095 : Oxides of carbon, e.g. CO2
• 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 1/0205 : as a dual level SCR refrigeration cascade
• CPC Class Codes: F25J 1/0208 : in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop F25J1/021 takes precedence
• CPC Class Codes: F25J 1/0231 : for the working-up of the hydrocarbon feed, e.g. reinjection of heavier hydrocarbons into the liquefied gas
• CPC Class Codes: F25J 1/0237 : integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas details related to rectification F25J3/02; details related to partial condensation F25J3/06; working-up natural gas C10L3/10
• CPC Class Codes: F25J 1/025 : Details related to the refrigerant production or treatment, e.g. make-up supply from feed gas itself
• CPC Class Codes: F25J 1/0254 : controlling particular process parameter, e.g. pressure, temperature
• CPC Class Codes: F25J 2200/02 : in a single pressure main column system
• CPC Class Codes: F25J 2200/70 : Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/72 : Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2200/74 : Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2205/04 : in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/04 : Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/06 : Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/64 : Propane or propylene
• CPC Class Codes: F25J 2215/66 : Butane or mixed butanes
• CPC Class Codes: F25J 2220/62 : Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2230/08 : Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• CPC Class Codes: F25J 2230/30 : Compression of the feed stream
• CPC Class Codes: F25J 2230/32 : Compression of the product stream
• 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 2245/02 : Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2245/90 : the recycled stream being boil-off gas from storage
• CPC Class Codes: F25J 2260/02 : Integration in an installation for exchanging heat, e.g. for waste heat recovery
• CPC Class Codes: F25J 2290/62 : Details of storing a fluid in a tank
• CPC Class Codes: F25J 3/0209 : Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0233 : separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0242 : separation of CnHm with 3 carbon atoms or more
• CPC Class Codes: F25J 3/0247 : separation of CnHm with 4 carbon atoms or more

Abstract

This invention relates to a process for liquefying a gas stream rich in methane and having a pressure above about 3103 kPa (450 psia). The gas stream is expanded to a lower pressure to produce a gas phase and a liquid product having a temperature above about -112° C. (-170° F.) and a pressure sufficient for the liquid product to be at or below its bubble point. The gas phase and the liquid product are then phase separated in a suitable separator, and the liquid product is introduced to a storage means for storage at a temperature above about -112° C. (-170° F.).

Claims

1. A process for liquefying a gas stream rich in methane which comprises the steps of:

(a) providing the gas stream at a pressure above about 3103 kPa (450 psia);

(b) expanding the gas stream to a lower pressure to produce a gas phase and a liquid product having a temperature above about -112°

C. (-170°

F.) and a pressure sufficient for the liquid product to be at or below its bubble point;

(c) phase separating the gas phase and the liquid product; and

(d) introducing the liquid product to a storage means for storage at a temperature above about -112°

C. (-170°

F.).

2. The process of claim 1 further comprises cooling the gas stream prior to step (b).

3. The process of claim 2 further comprises cooling the gas stream in a heat exchanger cooled by a closed-loop refrigeration system.

4. The process of claim 3 wherein the closed-loop refrigeration system has propane as the predominant refrigerant.

5. The process of claim 3 wherein the closed-loop refrigeration system has carbon dioxide as the predominant refrigerant.

6. The process of claim 2 further comprises the step of cooling the gas stream by heat exchange relationship with the gas phase of step (c) of claim 1, thereby warming the gas phase.

7. The process of claim 6 further comprises compressing the warmed gas phase, cooling the compressed gas phase, and returning the cooled compressed gas phase to the gas stream of step (a) of claim 1 for recycling.

8. The process of claim 6 further comprises, prior to the cooling step of claim 6, cooling the gas stream in a heat exchanger cooled by a closed-loop refrigeration system.

9. The process of claim 1 wherein prior to liquefaction of the gas stream further comprises combining with the gas stream a boil-off gas resulting from evaporation of liquefied natural gas.

10. The process of claim 1 wherein the gas stream contains methane and hydrocarbon components heavier than methane, which further comprises removing a predominant portion of the heavier hydrocarbons by fractionation to produce a vapor stream rich in methane and a liquid stream rich in the heavier hydrocarbons, the vapor stream then being liquefied by expansion according to step (b) of claim 1.

11. The process of claim 10 further comprising cooling the gas stream prior to fractionation of the gas stream.

12. The process of claim 1 wherein the liquefaction of the gas stream is performed without a closed-loop refrigeration system.

13. A process for liquefing a gas stream rich in methane and having a pressure above about 3103 kPa (450 psia) which comprises the steps of

(a) phase separating the gas stream into a first gas stream and a first liquid stream;

(b) passing the first liquid stream to a demethanizer column;

(c) compressing and cooling the first gas stream, thereby producing gas and liquid phases;

(d) phase separating the gas and liquid phases of step (c) to produce a second gas stream and a second liquid stream;

(e) expanding at least a portion of the second gas stream to a lower pressure whereby the second gas stream is further cooled;

(f) supplying the second liquid stream and the expanded second gas stream to the demethanizer column;

(g) removing from the upper region of the demethanizer column a third gas stream, the third gas stream comprising predominantly methane, and passing the third gas stream through a heat exchanger to warm the third gas stream;

(h) removing from the demethanizer a third liquid stream and passing the third liquid stream to a fractionation system having at least one fractionation column and having at least one overhead vapor stream;

(i) combining the warmed third gas stream of step (g) and the overhead vapor stream of step (h) and compressing the combined stream;

(j) cooling the compressed combined stream;

(k) dividing the cooled compressed stream of step (j) into a first cooled stream and a second cooled stream and passing the first cooled stream through the heat exchanger of step (g) to further cool the first cooled stream;

(l) expanding the first cooled stream to produce gas and liquid phases;

(m) phase separating the gas and liquid phases of step (l) in a phase separator, thereby producing a methane-rich liquefied natural gas at a temperature above about -112°

C. (-170°

F.) and a pressure sufficient for the methane-rich liquefied natural gas to be at or below its bubble point;

(n) expanding the second cooled stream of step (k) to a lower pressure whereby it is further cooled, producing gas and liquid phases;

(o) phase separating the gas and liquid phases produced in step (n); and

(p) passing the liquid phase of step (o) to the phase separator of step (m).

14. The process of claim 13 further comprises combining the gas phase of step (o) with the third gas stream of step (g) and passing the combined gas stream through the heat exchanger of step (g).

15. The process of claim 13 further comprises combining the gas phase of step (m) with the third gas stream of step (g) and passing the combined gas stream through the heat exchanger of step (g).

16. The process of claim 14 wherein the cooling of step (j) is by indirect heat exchange with refrigerant from a closed-loop refrigeration system.

17. The process of claim 16 wherein the closed-loop refrigeration system has propane as the predominant refrigerant and the fractionation system of step (h) comprises a depropanizer column producing an overhead stream gas rich in propane, further comprising passing to the closed-loop refrigeration system the propane-rich stream gas from the fractionation system as make-up refrigerant.

18. A process according to claim 14 wherein the process further comprises introducing into the third gas stream of step (g) a boil-off gas resulting from the evaporation of a liquefied natural gas and passing the combined third gas stream and the boil-off gas through the heat exchanger of step (g).

19. A process for liquefying a gas stream rich in methane which comprises the steps of:

(a) compressing the gas stream to a pressure greater than 3103 kPa (450 psia);

(b) phase separating the gas stream into a first gas stream and a first liquid stream;

(c) passing the first liquid stream to a demethanizer column;

(d) compressing and cooling the first gas stream without use of a closed-loop refrigeration system, thereby producing gas and liquid phases;

(e) phase separating the gas and liquid phases of step (d) to produce a second gas stream and a second liquid stream;

(f) expanding at least a portion of the second gas stream to a lower pressure whereby it is further cooled;

(g) supplying the second liquid stream and the expanded second gas stream to the demethanizer column;

(h) removing from the upper region of the demethanizer column a vapor stream, the vapor stream comprising predominantly methane, and passing the vapor stream through a heat exchanger to warm the vapor stream;

(i) removing from the demethanizer a liquid stream and passing the liquid stream to a fractionation system having at least one fractionation column and having at least one overhead vapor stream;

(j) combining the warmed vapor stream of step (h) and the overhead vapor stream of step (i) and compressing the combined stream;

(k) cooling the compressed combined stream of step (j) without use of a closed-loop refrigeration system;

(l) dividing the cooled compressed stream of step (k) into a first cooled stream and a second cooled stream and passing the first cooled stream through the heat exchanger of step (h) to further cool the first cooled stream;

(m) expanding the first cooled stream to produce gas and liquid phases;

(n) phase separating the gas and liquid phases of step (m) in a phase separator, thereby producing a methane-rich liquefied natural gas having a temperature above about -112°

C. (-170°

F.) and a pressure sufficient for the methane-rich liquefied natural gas to be at or below its bubble point;

(o) expanding the second cooled stream of step (l) to a lower pressure whereby it is further cooled, producing gas and liquid phases;

(p) phase separating the gas and liquid phases produced in step (o); and

(q) passing the liquid phase of step (o) to the phase separator of step (n).

20. A process according to claim 19 wherein the process further comprises introducing into the vapor stream of step (h) a boil-off gas resulting from the evaporation of a liquefied natural gas and passing the combined vapor stream of step (h) and the boil-off gas through the heat exchanger of step (h).

21. The process of claim 19 wherein the gas phase of step (n) is combined with the vapor residue of step (h) and the combined gas stream is passed through the heat exchanger of step (h).

22. The process of claim 19 wherein the lowering of cooling of the gas stream temperature in step (d) is performed by water or air.

23. The process of claim 19 further comprising before step (o) the additional step of pressurizing the second cooled stream of step (l) to a higher pressure.

24. A process for liquefying a gas stream rich in methane and having a pressure above about 3103 kPa (450 psia) which comprises the steps of:

(a) cooling the gas stream;

(b) passing the cooled gas stream through a heat exchanger to warm the gas stream;

(c) compressing the warmed gas stream and after-cooling the compressed gas stream;

(d) dividing the cooled compressed stream of step (c) into a first cooled stream and a second cooled stream and passing the first cooled stream through the heat exchanger of step (b) to further cool the first cooled stream;

(e) expanding the first cooled stream to produce gas and liquid phases;

(f) phase separating the gas and liquid phases of step (e) in a phase separator, thereby producing a gas phase and a methane-rich liquefied gas at a temperature above about -112°

C. (-170°

F.) and a pressure sufficient for the methane-rich liquefied gas to be at or below its bubble point;

(g) expanding the second cooled stream of step (d) to a lower pressure whereby it is further cooled, producing gas and liquid phases;

(h) phase separating the gas and liquid phases of step (g); and

(i) passing the liquid phase of step (h) to the phase separator of step (f).

25. The process of claim 24 further comprising before step (g) the additional step of pressurizing the second cooled stream to a higher pressure.

26. The process of claim 24 further comprising the steps of introducing into the cooled gas of step (a) a boil-off gas resulting from the evaporation of a liquefied natural gas and passing the combined cooled vapor stream of step (a) and the boil-off gas through the heat exchanger of step (b).

27. The process of claim 24 wherein the gas phase of step (f) is combined with the cooled gas stream of step (a) and the combined stream is passed through the heat exchanger of step (b).

28. The process of claim 24 wherein the gas phase of step (h) is combined with the cooled gas stream of step (a) and the combined stream is passed through the heat exchanger of step (b).

29. The process of claim 24 wherein the gas phase of step (f) and the gas phase of step (h) are combined with the cooled gas stream of step (a) and the combined stream is passed through the heat exchanger of step (b).