Natural gas liquefaction process

• US 20030089125A1
• Filed: 12/23/2002
• Published: 05/15/2003
• Est. Priority Date: 03/15/2000
• Status: Active Grant

• Current Assignee: Statoil Petroleum As (Asa Equinor)
• Original Assignee: Statoilhydro ASA
• Inventors: Fredheim, Arne Olay, Paurola, Pentti
• Granted Patent: US 7,386,996 B2
• Time in Patent Office: Days
• US Class Current: 62/612
• CPC Class Codes: F25B 1/10 with multi-stage compression with cascade operation F25B7/00
• CPC Class Codes: F25B 2309/06 Compression machines, plants or systems characterised by the refrigerant being carbon dioxide
• CPC Class Codes: F25B 9/008 the refrigerant being carbon dioxide
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• 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 1/0055 originating from an incorporated cascade
• CPC Class Codes: F25J 1/0057 after expansion of the liquid refrigerant stream with extraction of work
• CPC Class Codes: F25J 1/0072 Nitrogen
• CPC Class Codes: F25J 1/0095 Oxides of carbon, e.g. CO2
• CPC Class Codes: F25J 1/0097 Others, e.g. F-, Cl-, HF-, HClF-, HCl-hydrocarbons etc. or mixtures thereof
• CPC Class Codes: F25J 1/0215 with one SCR cycle
• CPC Class Codes: F25J 1/0218 with one or more SCR cycles, e.g. with a C3 pre-cooling cycle
• 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 1/025 Details related to the refrigerant production or treatment, e.g. make-up supply from feed gas itself
• CPC Class Codes: F25J 1/0278 Unit being stationary, e.g. on floating barge or fixed platform
• 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 1/0292 Refrigerant compression by cold or cryogenic suction of the refrigerant gas
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2210/04 : Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2220/60 : Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
• CPC Class Codes: F25J 2220/64 : Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: F25J 2220/66 : Separating acid gases, e.g. CO2, SO2, H2S or RSH
• CPC Class Codes: F25J 2245/02 : Recycle of a stream in general, e.g. a by-pass stream

Abstract

The invention relates to a natural gas liquefaction process and particularly to one suited to use offshore. The invention provides a natural gas liquefaction apparatus wherein a carbon dioxide based pre-cooling circuit is provided in a cascade arrangement with a main cooling circuit. The invention also extends to a natural gas liquefaction apparatus wherein a main cooling circuit uses as a refrigerant a gas stream, at least a portion of which is derived from a raw natural gas source.

Claims

1. A natural gas liquefaction apparatus wherein a carbon dioxide based pre-cooling circuit is provided in a cascade arrangement with a main cooling circuit.

2. An apparatus as claimed in claim 1 comprising a plurality of main cooling cycles.

3. An apparatus according to claim 1 or 2, wherein the main cooling cycle(s) comprises nitrogen rich based expansion loop(s).

7. An apparatus according to any of claims 1 to 6, wherein a cycle of the main cooling circuit uses a nitrogen enriched natural gas stream where the make-up of that gas is taken partly from the overhead of a hydrocarbon removal tower and partly from the reflux drum of the heavy hydrocarbon removal tower.

8. An apparatus according to any preceding claim, wherein the suction of the refrigeration compressors receive unheated, cold refrigerant medium directly from the cryogenic heat exchangers.

9. An apparatus according to any preceding claim, wherein the bottoms from the hydrocarbon removal unit are sent to a condensate stabiliser column or the like.

10. An apparatus as claimed in any preceding claim wherein a refrigerant stream used in the main cooling cycle comprises approximately 50 to 100 mol % nitrogen and about 0 to 50 mol % hydrocarbons.

11. An apparatus as claimed in any preceding claim wherein a refrigerant stream used in the main cooling cycle comprising about 0 to 15 mol % nitrogen and 50 to 100 mol % hydrocarbons.

4. A natural gas liquefaction apparatus wherein a main cooling circuit uses as a refrigerant a gas stream, at least a portion of which is derived from the raw natural gas source.

5. An apparatus according to claim 4 wherein a nitrogen-enriched natural gas stream is used.

6. An apparatus according to claim 4 or claim 5 wherein said gas stream has a portion made-up from the light hydrocarbon stream from the reflux drum of a heavy hydrocarbon removal tower.

12. A natural gas liquefaction process wherein the gas is cooled by a carbon dioxide based pre-cooling circuit in a cascade arrangement with a main cooling circuit.

13. A process as claimed in claim 12, comprising the use of a plurality of main cooling cycles.

14. A natural gas liquefaction process as claimed in claim 12 or 13, wherein the main cooling cycle uses a nitrogen rich refrigerant.

15. A process as claimed in any of claims 12 to 14, wherein the main cooling circuit comprises a cycle using a nitrogen enriched natural gas where the make-up is taken partly from the overhead of a hydrocarbon removal tower and partly from the reflux drum of the heavy hydrocarbon removal tower.

16. A process as claimed in any of claims 12 to 15, wherein the suction of the refrigeration compressors receive unheated, cold refrigerant medium directly from the cryogenic heat exchangers.

17. A process as claimed in any of claims 12 to 16, wherein the bottoms from the hydrocarbon removal unit are sent to a unit for stabilising condensate.

18. A method of producing liquefied natural gas (LNG) wherein an unstabilised condensate product stream is produced.

19. A method of transporting natural gas product, comprising the provision of an unstabilised condensate product stream, and the subsequent transportation of said stream.