Method for producing a flow which is rich in methane and a cut which is rich in C2+ hydrocarbons from a flow of feed natural gas and an associated installation

• US 9,759,481 B2
• Filed: 05/05/2014
• Issued: 09/12/2017
• Est. Priority Date: 04/21/2009
• Status: Active Grant

• Current Assignee: Technip France (TechnipFMC, plc)
• Original Assignee: Technip France (TechnipFMC, plc)
• Inventors: Paradowski, Henri, Thiebault, Sandra, Barthe, Loic
• Primary Examiner(s): Alosh, Tareq
• Application Number:
  US14/269,656
• Publication Number:
  US 20140238075A1
• Time in Patent Office: 1,226 Days
• 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 2200/76 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

Abstract

This method comprises cooling the feed natural gas in a first heat exchanger and introducing the cooled, feed natural gas into a first separation flask.

It comprises the dynamic expansion of a turbine supply flow in a first expansion turbine and introducing the expanded flow into a separation column. This method comprises removing, at the head of the separation column, a head flow rich in methane and removing a first recirculation flow from the compressed head flow rich in methane.

The method comprises forming at least a second recirculation flow obtained from the head flow rich in methane downstream of the separation column and forming a dynamic expansion flow from the second recirculation flow.

Claims

1. A method for producing a flow which is rich in methane and a cut which is rich in C₂⁺ hydrocarbons from a flow of dehydrated feed natural gas, which is composed of hydrocarbons, nitrogen and CO2 and which advantageously has a molar content of C₂⁺ hydrocarbons greater than 10%, the method comprising the following steps of:

cooling the feed natural gas flow advantageously at a pressure greater than 40 bar in a first heat exchanger and introducing the cooled, feed natural gas flow into a first separation flask;

separating the cooled natural gas flow in the first separation flask and recovering a light fraction which is substantially gaseous and a heavy fraction which is substantially liquid;

dividing the light fraction into a flow for supplying to a turbine and a secondary flow;

dynamic expansion of the turbine supply flow in a first expansion turbine and introducing the expanded flow into an intermediate portion of a separation column;

cooling the secondary flow in a second heat exchanger and introducing the cooled secondary flow into an upper portion of the separation column;

expanding the heavy fraction, vaporization in the first heat exchanger and introduction into a second separation flask in order to form a head fraction and a bottom fraction;

introducing the head fraction, after cooling in the second heat exchanger, in the upper portion of the separation column;

introducing the bottom fraction into an intermediate portion of the separation column;

recovering, at the bottom of the separation column, a bottom flow which is rich in C₂⁺ hydrocarbons and which is intended to form the cut rich in C₂⁺ hydrocarbons;

removing, at the head of the separation column, a head flow rich in methane;

reheating the head flow rich in methane in the second heat exchanger and in the first heat exchanger and compressing the head flow rich in methane in at least a first compressor and in a second compressor in order to form a flow rich in methane from the compressed head flow rich in methane;

removing a first recirculation flow from the head flow rich in methane;

passing the first recirculation flow into the first heat exchanger and into the second heat exchanger in order to cool the first recirculation flow, then introducing at least a first portion of the first cooled recirculation flow into the upper portion of the separation column;

wherein the method comprises the following steps of;

forming a dynamic expansion flow from a second recirculation flow from the head flow rich in methane and introducing the dynamic expansion flow into the first expansion turbine in order to produce a cooling thermal power, said cooling thermal power being introduced into the separation column, the method comprising;

removing a removal flow from the head flow rich in methane, before the head flow rich in methane is introduced into the first compressor and the second compressor;

compressing the removal flow in a third compressor;

forming the second recirculation flow from the compressed removal flow from the third compressor, after cooling.

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

3. The method according to claim 2, wherein the second recirculation flow is mixed with the turbine supply flow from the first separation flask in order to firm the dynamic expansion flow, the dynamic expansion turbine receiving the dynamic expansion flow being formed by the first expansion turbine.

4. Method according to claim 2, wherein the second recirculation flow is mixed with the cooled natural gas flow before the second recirculation flow is introduced into the first separation flask, the dynamic expansion flow being formed by the turbine supply flow from the first separation flask.

5. The method according to claim 1, further comprising passing the removal flow into a third heat exchanger and into a fourth heat exchanger before the removal flow is introduced into the third compressor, then passing the compressed removal flow into the fourth heat exchanger, then into the third heat exchanger in order to supply the head of the separation column, the second recirculation flow being removed from the cooled, compressed removal flow, between the fourth heat exchanger and the third heat exchanger.

6. The method according to claim 1, wherein the removal flow is introduced into a fourth compressor, the method comprising the following steps of:

removing a secondary branch flow from the cooled, compressed removal flow from the third compressor and the fourth compressor;

dynamic expansion of the secondary branch flow in a second expansion turbine which is connected to the fourth compressor;

introducing the expanded secondary branch flow into the removal flow before the removal flow is passed into the third compressor and into the fourth compressor.

7. An installation for producing a flow rich in methane and a cut rich in C₂⁺ hydrocarbons from a dehydrated feed natural gas flow which is composed of hydrocarbons, nitrogen and CO2 and which advantageously has a molar content of C₂⁺ hydrocarbons greater than 10%, the installation comprising:

a first heat exchanger for cooling the feed natural gas flow which advantageously flows at a pressure greater than 40 bar;

a first separation flask;

an apparatus for introducing the cooled feed natural gas flow into the first separation flask, the flow of cooled natural gas being separated in the first separation flask in order to recover a light, substantially gaseous fraction and a heavy, substantially liquid fraction;

an apparatus for dividing the light fraction into a flow for supplying a turbine and a secondary flow;

a first dynamic expansion turbine for the turbine supply flow;

a separation column;

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

a second heat exchanger for cooling the secondary flow and an apparatus for introducing the cooled secondary flow in an upper portion of the separation column;

an apparatus for expanding the heavy fraction and an apparatus for passing the heavy fraction through the first heat exchanger;

a second separation flask;

an apparatus for introducing the heavy fraction from the first heat exchanger into the second separation flask in order to form a head fraction and a bottom fraction;

an apparatus for introducing the head fraction, after it has been introduced into the second exchanger to cool the head fraction, into the upper portion of the separation column;

an apparatus for introducing the bottom fraction into an intermediate portion of the separation column;

an apparatus for recovering, at the bottom of the separation column, a bottom flow which is rich in C₂⁺ hydrocarbons and which is intended to form the cut rich in C₂⁺ hydrocarbons;

an apparatus for removing, at the head of the separation column, a head flow rich in methane;

an apparatus for introducing the head flow rich in methane into the second heat exchanger and into the first heat exchanger in order to reheat the head flow rich in methane;

an apparatus for compressing the head flow rich in methane comprising at least a first compressor and a second compressor in order to form the flow rich in methane from the compressed head flow rich in methane;

an apparatus for removing a first recirculation flow from the head flow rich in methane;

an apparatus for introducing the first recirculation flow into the first heat exchanger then into the second heat exchanger in order to cool the first recirculation flow;

an apparatus for introducing at least a portion of the first cooled recirculation flow into the upper portion of the separation column;

wherein the installation comprises;

an apparatus for forming a dynamic expansion flow from a second recirculation flow from the head flow rich in methane;

an apparatus for passing the dynamic expansion flow through the first dynamic expansion turbine in order to produce a cooling thermal power, said cooling thermal power being introduced into the separation column;

a third compressor that receives a removal flow from the head flow rich in methane before the head flow rich in methane is introduced into the first compressor and the second compressor, and forms the second recirculation flow by compressing the removal flow after cooling.

8. The installation according to claim 7, wherein the apparatus for forming a dynamic expansion flow from the second recirculation flow comprise an apparatus for introducing the second recirculation flow into a flow which flows downstream of the first heat exchanger and upstream of the first expansion turbine in order to form the dynamic expansion flow.