Method for producing a methane-rich stream and a c2+ hydrocarbon-rich stream, and associated equipment

Abstract

This method comprises a separation of a feed stream ( 16 ) into a first fraction ( 41 A) and a second fraction ( 41 B). 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 ( 41 B) in a second turbine ( 40 ) up to a second pressure substantially equal to the first pressure. The second expanded fraction ( 91 A) from the second dynamic expansion turbine ( 40 ) is used to form a cooled reflux stream ( 91 B) injected into the column ( 30 ).

1 . A method for producing a methane-rich stream and a C2 +  hydrocarbon-rich stream from a feed stream containing hydrocarbons, said method comprising:
 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 at least part of the second fraction of the feed stream into a second dynamic expansion turbine, separate from the first dynamic expansion turbine; 
 expanding the at least part 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; 
 injecting the second expanded fraction coming from the second dynamic expansion turbine into a downstream separating flask to form a second gas head stream and a second liquid bottoms stream; 
 cooling the second gas head stream to form a cooled reflux stream; and 
 injecting the cooled reflux stream into the first 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 injecting at least part of the second expanded fraction from the second dynamic expansion turbine into an auxiliary column, and forming a cooled reflux stream from the bottoms stream of the auxiliary column. 
     
     
         4 . The method according to  claim 1 , wherein said method further comprises optionally, partially condensing the second fraction of the feed stream; injecting the second fraction of the feed stream into an upstream separating flask to form a second gas fraction and a second liquid fraction; injecting the second gas fraction into the second dynamic expansion turbine; injecting the second liquid fraction, after expansion, into a lower part of the first distillation column. 
     
     
         5 . The method according to  claim 1 , wherein said method further comprises 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   
     
     
         6 . The method according to  claim 1 , wherein said method further comprises 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. 
     
     
         7 . The method according to  claim 1 , wherein the second compressor comprises a first compression stage, at least one second compression stage, and a refrigerant inserted between the first compression stage and the second compression stage, the method including a step for passage of the compressed overhead stream from the first compressor successively in the first compression stage, the refrigerant, then the second compression stage. 
     
     
         8 . 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 hum the first dynamic expansion turbine, are placed in a heat exchange relationship. 
     
     
         9 . The method according to  claim 1 , wherein said method further comprises 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. 
     
     
         10 . The method according to  claim 9 , wherein at least a fraction of the overhead stream and at least one part of the second expanded fraction from the second dynamic expansion turbine are placed in a heat exchange relationship in a downstream heat exchanger separate from the second heat exchanger. 
     
     
         11 . The method according to  claim 1 , wherein said method further comprises 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. 
     
     
         12 . The method according to  claim 1 , wherein said method further comprises removing a reboiling stream in the first distillation column at a removal level; putting the reboiling stream in a heat exchange relationship with at least part of the second expanded fraction coming from the second dynamic expansion turbine to cool and at least partially liquefy the part of the expanded second fraction coming from the second dynamic expansion turbine; and optionally, placement in a heat exchange relationship with the first expanded fraction from the first turbine; reinjecting the reboiling stream into the first distillation column at a level below the removal level. 
     
     
         13 . The method according to  claim 1 , wherein said method further comprises removing an extra cooling stream from the methane-rich overhead stream or from the stream formed from the methane-rich overhead stream or a stream formed from the methane-rich overhead stream; expanding and injecting the expanded extra cooling stream into a stream circulating upstream of the first expansion turbine, advantageously in the first fraction of the cooled feed stream or in the turbine feed fraction. 
     
     
         14 . The method according to  claim 1 , wherein said method further comprises passage of the methane-rich overhead stream in the first heat exchanger; removal of an auxiliary expansion stream in the methane-rich overhead stream, after its passage in the first heat exchanger; dynamic expansion of the auxiliary expansion stream in an auxiliary dynamic expansion turbine; injecting the expanded stream from the auxiliary dynamic expansion turbine into the methane-rich overhead stream, before its passage in the first heat exchanger. 
     
     
         15 . An equipment for producing a methane-rich stream and a C2 +  hydrocarbon-rich stream from a feed stream containing hydrocarbons in accordance with the method as recited in  claim 1 , the equipment comprising:
 means for separating the feed stream into a first fraction of the feed stream and at least one second fraction of the feed stream; 
 a first heat exchanger to cool the first fraction of the feed stream, said separating of the feed stream occurs upstream of the cooling of the first fraction of the feed stream; 
 means for injecting the first cooled feed fraction into a first separating flask to produce a light head stream and a heavy bottoms stream; 
 a first dynamic expansion turbine and means for injecting a turbine feed fraction formed from the light head stream into the first dynamic expansion turbine so as to expand the turbine feed fraction to a first pressure; 
 a first distillation column; 
 means for injecting at least part of the first expanded fraction into the first turbine in the first distillation column; means for expanding the whole heavy bottoms stream to form an expanded bottoms stream and means for injecting at least part of the expanded bottoms stream into the first distillation column, the means for injecting the expanded bottoms stream being configured so that the bottoms stream does not pass through the first heat exchanger between the first separating flask and the first distillation column; means for recovering a bottoms stream at the bottom of the first distillation column, the C2 +  hydrocarbon-rich stream being formed from the bottoms stream; means for recovering and heating a methane-rich overhead stream from the first distillation column, at least one first compressor coupled to the first dynamic expansion turbine and at least one second compressor to compress at least one fraction of the methane-rich overhead stream; 
 a means for injecting at least part of the of the second fraction of the feed stream into a second dynamic expansion turbine, separate from the first dynamic expansion turbine, and injecting the at least part of the second fraction of the feed stream into the second dynamic expansion turbine to form a second expanded fraction from the second dynamic expansion turbine at a second pressure, the second dynamic expansion turbine being arranged so that the first pressure is substantially equal to the second pressure; and means for injecting the second expanded fraction coming from the second dynamic expansion turbine into a downstream separating flask to form a second gas head stream and a second liquid bottoms stream, means for cooling the second gas head stream to form a cooled reflux stream, and means for injecting the cooled reflux stream into the first distillation column. 
 
     
     
         16 . The equipment according to  claim 15 , wherein said equipment further comprises an auxiliary column; means for injecting at least part of the second expanded fraction from the second dynamic expansion turbine into the auxiliary column; and means for forming the cooled reflux stream from the bottoms stream of the auxiliary column. 
     
     
         17 . 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. 
     
     
         18 . The method according to  claim 1 , 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. 
     
     
         19 . A method for producing a methane-rich stream and a C2 +  hydrocarbon-rich stream from a feed stream containing hydrocarbons, said method comprising:
 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 at least part 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 at least part 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 
 injecting at least part of the second expanded fraction from the second dynamic expansion turbine into an auxiliary column, and forming a cooled reflux stream from the bottoms stream of the auxiliary column and injecting the cooled reflux stream into the first distillation column.