Natural gas liquefaction process

• US 7,386,996 B2
• Filed: 03/15/2001
• Issued: 06/17/2008
• Est. Priority Date: 03/15/2000
• Status: Expired due to Term

• Current Assignee: Statoil Petroleum As (Asa Equinor)
• Original Assignee: Den Norske Opera & Ballett As (Government of Norway)
• Inventors: Fredheim, Arne Olay, Paurola, Pentti
• Primary Examiner(s): DOERRLER, WILLIAM CHARLES
• Application Number:
  US10/221,885
• Publication Number:
  US 20030089125A1
• Time in Patent Office: 2,651 Days
• Field of Search: 626/06, 626/11, 626/12, 626/13
• 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 process in which the gas is liquefied at a temperature not greater than about −

150°

C. wherein the gas is cooled by a carbon dioxide based pre-cooling circuit in a cascade arrangement with at least one main cooling circuit, wherein the carbon dioxide pre-cooling circuit cools both the natural gas and a refrigerant of a main cooling circuit.

2. A process according to claim 1, wherein the at least one main cooling circuit is comprised of a plurality of refrigeration compressors and a plurality of cryogenic heat exchangers.

3. A process according to claim 1, wherein the at least one main cooling circuit uses a nitrogen rich refrigerant.

5. A process according to claim 2, wherein the suction of the refrigeration compressors receives unheated, cold refrigerant medium directly from the cryogenic heat exchangers.

4. A natural gas liquefaction process in which the gas is liquefied at a temperature not greater than about −

150°

C., wherein the gas is cooled by a carbon dioxide based pre-cooling circuit in a cascade arrangement with at least one main cooling circuit, and wherein the at least one main cooling circuit comprises a circuit using a nitrogen enriched natural gas where the make-up is taken partly from the overhead of a hydrocarbon removal unit and partly from a reflux drum of a heavy hydrocarbon removal unit.

6. The process according to claim 4, wherein the bottoms from the hydrocarbon removal unit are sent to a unit for stabilising condensate.

7. A natural gas liquefaction apparatus in which the gas is liquefied at a temperature not greater than about −

150°

C., and wherein a carbon dioxide based pre-cooling circuit is provided in a cascade arrangement with at least one main cooling circuit, wherein the carbon dioxide pre-cooling circuit cools both the natural gas and a refrigerant of the main cooling circuit.

8. An apparatus according to claim 7, wherein the at least one main cooling circuit comprises a nitrogen rich based expansion loop.

9. An apparatus according to claim 7, wherein the at least one main cooling circuit uses as a refrigerant a gas stream, at least a portion of which is derived from the raw natural gas source.

10. The natural gas liquefaction apparatus of claim 9 wherein at least one main cooling circuit uses as a refrigerant a nitrogen-enriched natural gas stream, at least a portion of which is derived from the raw natural gas source.

15. An apparatus according to claim 7, wherein the at least one main cooling circuit is comprised of a plurality of refrigeration compressors and a plurality of cryogenic heat exchangers, and wherein the suction of the refrigeration compressors receives unheated, cold refrigerant medium directly from the cryogenic heat exchangers.

17. An apparatus according to claim 7 wherein a refrigerant stream used in the at least one main cooling circuit comprises approximately 50 to 100 mol % nitrogen and about 0 to 50 mol % hydrocarbons.

18. An apparatus according to claim 7 wherein a refrigerant stream used in the at least one main cooling circuit comprises about 0 to 15 mol % nitrogen and 50 to 100 mol % hydrocarbons.

11. A natural gas liquefaction process in which the gas is liquefied at a temperature not greater than about −

150°

C., wherein the gas is cooled by a carbon dioxide based pre-cooling circuit in a cascade arrangement with at least one main cooling circuit, and wherein an unstabilized condensate product stream is produced consisting essentially of a combined condensate and liquefied petroleum gas (LPG) stream.

12. A method of transporting a natural gas product, comprising the steps of producing a liquefied natural gas (LNG) stream and an unstabilized condensate product stream, and transporting said LNG stream and said unstabilized condensate product stream, wherein the unstabilized condensate product stream consists essentially of a combined condensate and liquefied petroleum gas (LPG) stream, and wherein the natural gas product is produced by a natural gas liquefaction process in which the gas is liquefied at a temperature not greater than about −

150°

C., wherein the gas is cooled by a carbon dioxide based pre-cooling circuit in a cascade arrangement with at least one main cooling circuit.

13. A natural gas liquefaction apparatus in which the gas is liquefied at a temperature not greater than about −

150°

C., wherein a carbon dioxide based pre-cooling circuit is provided in a cascade arrangement with at least one main cooling circuit, wherein the at least one main cooling circuit uses as a refrigerant a gas stream, at least a portion of which is derived from the raw natural gas source, and wherein said gas stream has a portion made-up from a light hydrocarbon stream from a reflux drum of a heavy hydrocarbon removal unit.

14. The apparatus according to claim 13, wherein a circuit of the at least one 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 unit and partly from the reflux drum of the heavy hydrocarbon removal unit.

16. The apparatus according to claim 13, wherein the bottoms from the hydrocarbon removal unit are sent to a condensate stabilizer column.