Method for producing a treated natural gas, a cut rich in c3+ hydrocarbons and optionally an ethane-rich stream, and associated facility

Abstract

The method includes the following steps, sampling a recycling stream ( 152 ) in a head stream ( 131, 140, 141 ) stemming from a recovery column ( 35 ), establishing a heat exchange relationship of the recycling stream ( 152 ) with at least one portion of the head stream ( 131 ) stemming from the recovery column ( 35 ), reintroducing, after expansion, the cooled and expanded recycling stream into the recovery column ( 35 ). The method includes sampling in the bottom of the recovery column ( 35 ) of at least one bottom reboiling stream ( 165 ), and establishing a heat exchange relationship of the re-boiling stream with at least one portion of the initial natural gas ( 13 ) or/and with the recycling stream ( 152 ), the bottom reboiling being ensured by the calories taken from the initial natural gas stream ( 13 ) or/and from the recycling stream ( 152 )

1 . A method for simultaneously producing a treated natural gas, a cut rich in C 3   +  hydrocarbons and under at least certain production conditions, an ethane-rich stream, from an initial natural gas stream containing methane, ethane and C 3   +  hydrocarbons, the method comprising the following steps:
 cooling and partly condensing the initial natural gas stream in at least one first upstream heat exchanger in order to form a cooled initial stream; 
 separating the cooled initial gas stream into a liquid flow and a gas flow; 
 expanding the liquid flow, and introducing a stream stemming from the liquid flow into a column for recovering C 2   +  hydrocarbons at a first intermediate level; 
 forming a stream for feeding a turbine from the gas flow; 
 expanding the feed stream in a dynamic expansion turbine and introducing it the expanded feed stream into the recovery column at a second intermediate level; 
 recovering and compressing at least one portion of the head stream of the recovery column in order to form the natural gas and recovering the foot stream of the recovery column in order to form a C 2   + -hydrocarbon-rich liquid stream; 
 introducing the liquid stream at a feed level (P1) of a fractionation column provided with a head condenser, the ethane-rich stream being produced under said production conditions, from a stream stemming from the fractionation column, the fractionation column producing a foot stream intended to at least partly form the C 3   +  hydrocarbon cut; 
 introducing a primary reflux stream produced in the head condenser with reflux into the fractionation column; 
 producing a secondary reflux stream from the head condenser and introducing the secondary reflux stream at the head of the recovery column, 
 sampling a recycling stream in the head stream stemming from the recovery column; 
 establishing a heat exchange relationship of the recycling stream with at least one portion of the head stream stemming from the recovery column, 
 reintroducing, after expansion, the cooled and expanded recycling stream into the recovery column, 
 sampling in the bottom of the recovery column of at least one bottom reboiling stream, 
 establishing a heat exchange relationship of the bottom reboiling stream with at least one portion of the initial natural gas or/and with the recycling stream, 
 ensuring the bottom reboiling by the calories taken from the initial natural gas stream or/and from the recycling stream. 
 
     
     
         2 . The method according to  claim 1 , including placing at least one portion of the head stream of the recovery column and the recycling stream in a heat exchange relationship with the initial natural gas stream and with the bottom reboiling stream. 
     
     
         3 . The method according to  claim 1 , including putting in a heat exchange relationship in a first head heat exchanger the recycling stream stemming from the first upstream heat exchanger, the secondary reflux stream stemming from the head condenser, and the head stream stemming from the recovery column. 
     
     
         4 . The method according to  claim 1 , including sampling at least one side reboiling stream above the bottom reboiling stream, and placing said or each side reboiling stream in a heat exchange relationship with at least one portion of the initial natural gas stream. 
     
     
         5 . The method according to  claim 1 , including drawing off the ethane-rich stream from an intermediate level of the fractionation column located above the feed level of the column, and below the head level of the fractionation column. 
     
     
         6 . The method according to  claim 1 , including the following steps:
 separating the initial natural gas stream into a first initial stream and into a second initial stream;   introducing the first initial stream into the first upstream heat exchanger;   introducing at least one portion of the second initial stream into an auxiliary dynamic expansion turbine in order to form an auxiliary reflux stream from the effluent stemming from the auxiliary turbine;   introducing the auxiliary reflux stream into the recovery column.   
     
     
         7 . The method according to  claim 6 , including at least one portion of the recycling stream in an auxiliary compressor coupled with the auxiliary turbine. 
     
     
         8 . The method according to  claim 1 , including compressing at least one portion of the head stream in an auxiliary compressor coupled with the auxiliary turbine. 
     
     
         9 . The method according to  claim 1 , including sampling, in the recycling stream, bypass stream, and reintroducing the bypass stream into a stream located upstream from the first dynamic expansion turbine ( 29 ). 
     
     
         10 . The method according to  claim 1 , including expanding the liquid flow stemming from the first upstream separator flask and introducing said liquid flow into a second upstream separator flask in order to form a liquid fraction and a gas fraction,
 the liquid fraction being introduced after expansion at the first intermediate level of the recovery column, the gas fraction being introduced at an upper level of the recovery column, located above the intermediate level.   
     
     
         11 . The method according to  claim 1 , including establishing a heat exchange relationship of the foot stream stemming from the recovery column with the initial natural gas stream and with the bottom reboiling stream in the first upstream heat exchanger before its introduction into the fractionation column. 
     
     
         12 . The method according to  claim 1 , including separating the gas flow stemming from the first separator flask into the feed stream and into a reflux stream, the feed stream being intended to feed the dynamic expansion turbine, and introducing the reflux stream being introduced, after cooling, partial or total condensation, and expansion in a valve, with reflux, into the recovery column. 
     
     
         13 . A facility for simultaneously producing a treated natural gas, a cut rich in C 3   +  hydrocarbons, and under certain production conditions, an ethane-rich stream, from an initial natural gas stream containing methane, ethane and C 3   +  hydrocarbons, the facility comprising:
 an assembly for cooling and partly condensing the initial natural gas stream comprising at least a one first upstream heat exchanger in order to form a cooled initial stream; 
 an assembly for separating the cooled initial stream into a liquid flow and into a gas flow; 
 a column for recovering C 2   +  hydrocarbons 
 an assembly for expanding the liquid flow, and for introducing a stream stemming from the liquid flow into the recovery column at a first intermediate level; 
 an assembly for forming a stream for feeding the turbine from the gas flow; 
 an assembly for expanding the feed stream, comprising a dynamic expansion turbine and an assembly for introducing the expanded feed stream into the recovery column at a second intermediate level; 
 an assembly for recovering and compressing at least one portion of the head stream of the recovery column in order to form the natural gas and an assembly for recovering the foot stream of the recovery column in order to form a liquid stream rich in C 2   +  hydrocarbons; 
 a fractionation column provided with a head condenser, 
 an assembly for introducing the liquid stream at a feed level of the fractionation column, the ethane-rich stream being able to be produced under said production conditions, from a stream stemming from the fractionation column, the fractionation column being able to produce a foot stream intended to form at least partly the C 3   +  hydrocarbon cut; 
 an assembly for introducing a primary reflux stream produced in the head condenser with reflux into the fractionation column; 
 an assembly for producing a secondary reflux stream from the head condenser and an assembly for introducing the secondary reflux stream at the head of the recovery column, 
 an assembly for sampling a recycling stream in the head stream of the recovery column; 
 an assembly for establishing a heat exchange relationship of the recycling stream with at least one portion of the head stream stemming from the recovery column, 
 an assembly for reintroducing, after expansion, the recycling stream into the recovery column, 
 an assembly for sampling in the bottom of the recovery column at least one bottom reboiling stream, and 
 an assembly for establishing a heat exchange relationship of the bottom reboiling stream with at least one portion of the initial natural gas or/and with the recycling stream, the reboiling being able to be ensured by the calories taken from the initial natural gas stream or/and from the recycling stream. 
 
     
     
         14 . The facility according to  claim 13 , including a first upstream heat exchanger capable of establishing a heat exchange relationship with at least one portion of the initial natural gas stream, the bottom reboiling stream, at least one portion of the head stream and the recycling stream. 
     
     
         15 . The facility according to  claim 13 , including a first upstream heat exchanger capable of establishing a heat exchange relationship of a first portion of the initial natural gas stream, with at least one portion of the head stream, a second upstream heat exchanger, distinct from the first upstream heat exchanger, capable of establishing a heat exchange relationship of a second portion of the initial gas stream with the bottom reboiling stream stemming from the recovery column, and a third upstream heat exchanger distinct from the first upstream heat exchanger and from the second upstream heat exchanger, the third upstream heat exchanger being capable of establishing a heat exchange relationship of at least one portion of the recycling stream with at least one portion of the head stream, including an auxiliary compressor capable of compressing the portion of the recycling stream intended to be introduced into the third upstream heat exchanger. 
     
     
         16 . The method according to  claim 8 , wherein the auxiliary compressor is coupled with the auxiliary turbine between a first compressor coupled with the first turbine and a second compressor. 
     
     
         17 . The method according to  claim 10 , including placing the liquid flow stemming from the first upstream separator flask in a heat exchange relationship with the initial natural gas stream so as to be heated up before being introduced into the second upstream separator flask. 
     
     
         18 . The facility according to  claim 14 , wherein the first upstream heat exchanger is capable of establishing a heat exchange relationship with side reboiling streams. 
     
     
         19 . The facility according to  claim 15 , including an auxiliary compressor capable of compressing the portion of the recycling stream intended to be introduced into the third upstream heat exchanger.