Method for producing a methane-rich stream and a C2+ hydrocarbon-rich stream, and associated equipment

• US 10,619,919 B2
• Filed: 12/26/2011
• Issued: 04/14/2020
• Est. Priority Date: 12/27/2010
• Status: Active Grant

• Current Assignee: Technip France (TechnipFMC, plc)
• Original Assignee: Technip France (TechnipFMC, plc)
• Inventors: Gahier, Vanessa, Gouriou, Julie, Thiebault, Sandra, Barthe, Loic
• Primary Examiner(s): Pettitt, III, John F.
• Application Number:
  US13/976,307
• Publication Number:
  US 20140290307A1
• Time in Patent Office: 3,032 Days
• Field of Search: 62630
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/38 using pre-separation or distributed distillation before a main column system, e.g. in a at least a double 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 2200/76 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 2210/06 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 2230/32 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 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

Abstract

This method comprises a separation of a feed stream (16) into a first fraction (41A) and a second fraction (41B). It comprises injecting the first cooled feed fraction (42) into a first separating flask (22) to produce a light head stream (44).

The method comprises expanding a turbine feed fraction (48) resulting from the light head stream (44) in a first turbine (26) up to a first pressure and injecting the first expanded fraction (54) into a distillation column (30).

The method comprises expanding the second fraction of the feed stream (41B) in a second turbine (40) up to a second pressure substantially equal to the first pressure.

The second expanded fraction (91A) from the second dynamic expansion turbine (40) is used to form a cooled reflux stream (91B) injected into the column (30).

Claims

1. A method for producing a methane-rich stream and a C2⁺ hydrocarbon-rich stream from a feed stream containing hydrocarbons, said method comprising the following steps:

separating the feed stream into a first fraction of the feed stream and at least one second fraction of the feed stream;

cooling the first fraction of the feed stream in a first heat exchanger to produce a cooled first fraction, said separating of the feed stream occurs upstream of the cooling of the first fraction of the feed stream;

injecting the cooled first fraction of the feed stream in a first separating flask to produce a light head stream and a heavy bottoms stream;

expanding a turbine feed fraction formed from the light head stream in a first dynamic expansion turbine to a first pressure and injecting at least part of the first expanded fraction coming from the first turbine into a first distillation column;

expanding the whole heavy bottoms stream to form an expanded bottoms stream and injecting the expanded bottoms stream into the first distillation column without going through the first heat exchanger between the first separating flask and the first distillation column;

recovering a bottoms stream at the bottom of the first distillation column, the C2⁺ hydrocarbon-rich stream being formed from the bottoms stream;

recovering and heating a methane-rich overhead stream from the first distillation column;

compressing at least one fraction of the methane-rich overhead stream in at least a first compressor coupled to the first dynamic expansion turbine and in at least one second compressor;

injecting an entirety of the of the second fraction of the feed stream into a second dynamic expansion turbine, separate from the first dynamic expansion turbine, without cooling between the step for separating the feed stream and the step of injecting the second fraction of the feed stream into the second dynamic expansion turbine;

expanding the entirety of the second fraction of the feed stream in the second dynamic expansion turbine to a second pressure, to form a second expanded fraction coming from the second dynamic expansion turbine, the second pressure being substantially equal to the first pressure; and

cooling and at least partially liquefying at least part of the second expanded fraction coming from the second dynamic expansion turbine to form a cooled reflux stream, and injecting the cooled reflux stream into the first distillation column, wherein no stream issuing from the second dynamic expansion turbine enters into heat exchange in a heat exchanger with the first fraction of the feed stream, upstream of the distillation column.

2. The method according to claim 1, wherein said method includes injecting the first expanded fraction from the first dynamic expansion turbine into a second heat exchanger to be cooled and partially liquefied therein, the first cooled expanded fraction forming an additional cooled reflux stream, the method including the injection of the additional cooled reflux stream into the first distillation column.

3. The method according to claim 1, wherein said method further comprises the following steps:

removing a secondary compression fraction in the methane-rich overhead stream, before the passage of a fraction of the methane-rich overhead stream in the first compressor, passage of the secondary fraction in a third compressor coupled to the second dynamic expansion turbine;

injecting the compressed secondary fraction from the third compressor into the fraction of the compressed overhead stream, downstream of the first compressor.

4. The method according to claim 1, wherein at least part of the second expanded fraction from the second dynamic expansion turbine, at least one fraction of the overhead stream, and possibly the first expanded fraction from the first dynamic expansion turbine, are placed in a heat exchange relationship.

5. The method according to claim 1, wherein said method further comprises the following steps:

dividing the light head stream into the turbine feed fraction and a column feed fraction;

cooling and at least partially condensing the column feed fraction in a second heat exchanger to form a cooled feed fraction;

expanding and at least partially injecting the cooled column feed fraction into the first distillation column; and

at least part of the second expanded fraction from the second dynamic expansion turbine and the column feed fraction advantageously being placed in a heat exchange relationship.

6. The method according to claim 1, wherein said method further comprises the following steps:

removing a bleed stream from the overhead stream;

cooling the bleed stream at least in the first heat exchanger and injecting the cooled bleed stream into the first distillation column; and

optionally, heat exchange of the bleed stream with at least part of the second expanded fraction from the second turbine.

7. The method according to claim 1, wherein the heavy bottoms stream issuing from the first separating flask is expanded in an expansion valve to form the expanded bottoms stream, the expanded bottoms stream being injected in the first distillation column without passing through the first heat exchanger between the outlet of the expansion valve and the injection into the first distillation column.