SIMPLIFIED METHOD FOR PRODUCING A METHANE-RICH STREAM AND A C2+ HYDROCARBON-RICH FRACTION FROM A FEED NATURAL-GAS STREAM, AND ASSOCIATED FACILITY

• US 20130255311A1
• Filed: 10/19/2011
• Published: 10/03/2013
• Est. Priority Date: 10/20/2010
• Status: Active Grant

• Current Assignee: Technip France (Technip)
• Original Assignee: Loic Pierre Roger Barthe, Vanessa Marie Stephanie Gahier
• Inventors: Thiebault, Sandra Armelle Karen, Gahier, Vanessa Marie Stphanie, GOURIOU, Julie Anne, BARTHE, Loc Pierre Roger
• Granted Patent: US 10,018,411 B2
• Time in Patent Office: Days
• US Class Current: 62/622
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• 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 2230/24 Multiple compressors or compressor stages in parallel
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2235/60 the fluid being (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 2270/04 Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/06 with multiple gas expansion loops
• CPC Class Codes: F25J 2270/88 Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
• CPC Class Codes: F25J 2290/80 Retrofitting, revamping or debottlenecking of existing plant
• 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 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0247 separation of CnHm with 4 carbon atoms or more

Abstract

A method comprising the cooling of the feed natural-gas (15) in a first heat exchanger (16) and the introduction of the cooled feed natural-gas (40) in separator flask (18). The method further comprising dynamic expansion of a turbine input flow (46) in a first expansion turbine (22) and the introduction of the expanded flow (102) into a splitter column (26). This method includes sampling at the head of the splitter column (26) a methane-rich head stream (82) and sampling in the compressed methane-rich head stream (86) a first recirculation stream (88). The method comprises the formation of at least one second recirculation stream (96) obtained from the methane-rich head stream (82) downstream from the splitter column (26) and the formation of a dynamic expansion stream (100) from the second recirculation stream (96).

Claims

1. A method for producing a methane-rich stream and a C₂⁺ hydrocarbon-rich fraction from a dehydrated feed natural-gas stream, consisting of hydrocarbons, nitrogen and of CO₂, advantageously having a C₂⁺ hydrocarbon molar content of more than 10%, the method being of the type comprising the following steps:

cooling the feed natural-gas stream advantageously at a pressure of more than 40 bars in a first heat exchanger, and introducing the cooled feed natural-gas stream into a separator flask;

separating the cooled natural gas stream in the separator flask and recovering an essentially gaseous light fraction and an essentially liquid heavy fraction;

forming a turbine input flow from the light fraction;

dynamically expanding the turbine input flow in a first expansion turbine, and introducing the expanded flow into an intermediate portion of a splitter column;

expanding the heavy fraction and introducing the heavy fraction into the splitter column, the heavy fraction recovered in the separator flask being introduced into the splitter column without passing through the first heat exchanger;

recovering, at the foot of the splitter column, a C₂⁺ hydrocarbon-rich bottom stream intended to form the C₂⁺ hydrocarbon-rich fraction;

sampling at the head of the splitter column a methane-rich head stream;

heating up the methane-rich head stream in a second heat exchanger and in the first heat exchanger and compressing this stream in at least one first compressor coupled with the first expansion turbine and in a second compressor in order to form a methane-rich stream from the compressed methane-rich head stream;

sampling in the methane-rich head stream a first recirculation stream;

passing the first recirculation stream into the first heat exchanger and into the second heat exchanger in order to cool it down, and then introducing at least one first portion of the cooled recirculation stream into the upper portion of the splitter column;

the method comprising the following steps;

forming at least one second recirculation stream obtained from the methane-rich head stream downstream from the splitter column; and

forming a dynamic expansion stream from the second recirculation stream and introducing the dynamic expansion stream into an expansion turbine in order to produce frigories.

2. The method according to claim 1, wherein the formation of the turbine input flow includes the division of the light fraction into the turbine input flow and into a secondary flow, the method comprising the cooling of the secondary flow in the second heat exchanger and introducing the cooled secondary flow into an upper portion of the splitter column.

3. The method according to claim 1, wherein the second recirculation stream is introduced into a stream located downstream from the first heat exchanger and upstream from the first expansion turbine in order to form the dynamic expansion stream.

4. The method according to claim 3, wherein the second recirculation stream is mixed with the turbine input flow obtained from the separator flask in order to form the dynamic expansion stream, the dynamic expansion turbine receiving the dynamic expansion stream being formed by the first expansion turbine.

5. The method according to claim 3, wherein the second recirculation stream is mixed with the cooled natural gas stream before its introduction into the separator flask, the dynamic expansion stream being formed by the turbine input flow formed from the separator flask.

6. The method according to claim 3, wherein the second recirculation stream is sampled in the first recirculation stream.

7. The method according to claim 3, further comprising the following steps:

sampling a sampling stream in the methane-rich head stream, before its passing into the first compressor and into the second compressor;

compressing the sampling stream in a third compressor;

forming the second recirculation stream from the compressed sampling stream stemming from the third compressor, after cooling.

8. The method according to claim 7, further comprising passing of the sampling stream into a third heat exchanger and into a fourth heat exchanger before its introduction into the third compressor, and then the passing of the compressed sampling stream into the fourth heat exchanger, and then into the third heat exchanger in order to feed the head of the splitter column, the second recirculation stream being sampled in the cooled compressed sampling stream, between the fourth heat exchanger and the third heat exchanger.

9. The method according to claim 7, wherein the sampling stream is introduced into a fourth compressor, the method comprising the following steps:

sampling a secondary diversion stream in the cooled compressed sampling stream from the third compressor and from the fourth compressor ;

dynamically expanding the secondary diversion stream in a second expansion turbine coupled with the fourth compressor;

introducing the expanded secondary diversion stream into the sampling stream before its passing into the third compressor and into the fourth compressor.

10. The method according to claim 1, wherein the second recirculation stream is sampled in the compressed methane-rich head stream, the method comprising the following steps:

introducing the second recirculation stream into a third heat exchanger;

separating the feed natural-gas stream into a first feed flow and into a second feed flow;

establishing a heat exchange relationship of the second feed flow with the second recirculation stream in the third heat exchanger;

mixing the second feed flow after cooling in the third heat exchanger with the first feed flow, downstream from the first exchanger and upstream from the separator flask.

11. The method according to claim 10, further comprising the following steps:

sampling a secondary cooling stream in the compressed methane-rich head stream downstream from the first compressor and downstream from the second compressor;

dynamically expanding the secondary cooling stream in a second expansion turbine and passing the expanded secondary cooling stream into the third heat exchanger for establishing a heat exchange relationship with the second feed flow and with the second recirculation stream;

reintroducing the expanded secondary cooling stream into the methane-rich stream, before its passing into the first compressor and into the second compressor;

sampling a recompression fraction in the cooled methane-rich stream, downstream from the introduction of the expanded secondary cooling stream and upstream from the first compressor and from the second compressor;

compressing the recompression fraction in at least one compressor coupled with the second expansion turbine and reintroducing the compressed recompression fraction into the compressed methane-rich stream from the first compressor and from the second compressor.

12. The method according to claim 1, wherein the second recirculation stream is derived from the first recirculation stream, in order to form the dynamic expansion stream, the dynamic expansion stream being introduced into a second expansion turbine distinct from the first expansion turbine, the dynamic expansion stream from the second expansion turbine being reintroduced into the methane-rich stream before its passing into the first heat exchanger.

13. The method according to claim 12, further comprising the following steps:

sampling a recompression fraction in the heated-up methane-rich head stream from the first heat exchanger and from the second heat exchanger;

compressing the recompression fraction in a third compressor coupled with the second expansion turbine;

introducing the compressed recompression fraction into the compressed methane-rich stream from the first compressor.

14. The method according to claim 1, further comprising the diversion of a third recirculation stream, advantageously at room temperature, from the at least partly compressed methane-rich stream, advantageously between two stages of the second compressor, the third recirculation stream being successively cooled in the first heat exchanger and in the second heat exchanger before being mixed with the first recirculation stream in order to be introduced into the splitter column.

15. A facility for producing a methane-rich stream and a C₂⁺ hydrocarbon-rich fraction from a dehydrated feed natural-gas stream, consisting of hydrocarbons, nitrogen and CO₂, and advantageously having a C₂⁺ hydrocarbon molar content of more than 10%, the facility being of the type comprising:

a first heat exchanger for cooling the feed natural-gas stream advantageously circulating at a pressure of more than 40 bars;

a separator flask;

means for introducing the cooled feed natural-gas stream into the separator flask, the cooled natural-gas stream being separated in the separator flask for recovering an essentially gaseous light fraction and an essentially liquid heavy fraction;

means for forming a turbine input flow from the light fraction;

a first dynamic expansion turbine for the turbine input flow;

a splitter column;

means for introducing the expanded flow into the first dynamic expansion turbine in an intermediate portion of the splitter column;

a second heat exchanger;

means for expansion and introducing the heavy fraction into the splitter column laid out so that the heavy fraction recovered in the separator flask is introduced into the splitter column without passing through the first heat exchanger;

means for recovering, at the foot of the splitter column, a C₂⁺ hydrocarbon-rich foot stream, intended to form the C₂⁺ hydrocarbon-rich fraction;

means for sampling at the head of the splitter column a methane-rich head stream;

means for introducing the methane-rich head stream into the second heat exchanger and into the first heat exchanger for heating it up;

means for compressing the methane-rich head stream comprising at least one first compressor coupled with the first turbine and a second compressor for forming the methane-rich stream from the compressed methane-rich head stream;

means for sampling in the methane-rich head stream a first recirculation stream;

means for passing the first recirculation stream into the first heat exchanger and then into the second heat exchanger for cooling it down;

means for introducing at least one portion of the first cooled recirculation stream into the upper portion of the splitter column;

the facility comprising;

means for forming at least one second recirculation stream obtained from the methane-rich head stream downstream from the splitter column;

means for forming a dynamic expansion stream from the second recirculation stream;

means for introducing the dynamic expansion stream into an expansion turbine for producing frigories.

16. The facility according to claim 15, wherein the means for forming the turbine input flow include means for dividing the light fraction into the turbine input flow and into a secondary flow, the facility comprising means for passing the secondary flow into the second heat exchanger for cooling it down and means for introducing the cooled secondary flow into an upper portion of the splitter column.

17. The facility according to claim 15, wherein the means for forming a dynamic expansion stream from the second recirculation stream comprise means for introducing the second recirculation stream into a stream circulating downstream from the first heat exchanger and upstream from the first expansion turbine in order to form the dynamic expansion stream.