CA2878125C - Production process of an ethane rich flow of treated natural gas and theassociated installation - Google Patents

Abstract

The process comprises the following steps: - taking a recycling stream (152) from a top stream (131, 140, 141) resulting from a recovery column (35); - causing heat exchange between the recycling stream (152) and at least one part of the top stream (131) resulting from the recovery column (35), - reintroducing, after expansion, the cooled and expanded recycling stream into the recovery column (35). The process comprises taking at least one bottom reboiling stream (165) from the bottom of the recovery column (35), and causing heat exchange between the bottom reboiling stream and at least a part of the starting natural gas (13) and/or the recycling stream (152), wherein the bottom reboiling is provided by the heat taken from the starting natural gas stream (13) and/or from the recycling stream (152).

Description

Process for producing an ethane-rich stream of a treated natural gas and associated installation The present invention relates to a process for the simultaneous production of a gas natural treated, from a cut rich in C3 + hydrocarbons, and in at least some conditions of production, of a stream rich in ethane, from a stream gas natural starting material containing methane, ethane and hydrocarbons in C3 +, the process comprising the following steps:
- cooling and partial condensation of the natural gas stream from departure in at least a first upstream heat exchanger to form a stream of departure cooled ;
- separation of the cooled starting gas stream into a liquid stream and into a flux gaseous;
- expansion of the liquid flow, and introduction of a current from the flow liquid in a first level C2 + hydrocarbon recovery column intermediate;
- forming a turbine feed stream from the gas stream;
- expansion of the supply current in a first expansion turbine dynamics and introduction into the recovery column at a second level intermediate;
- recovery and compression of at least part of an overhead stream of the recovery column to form natural gas and recovery of the stream of foot of the recovery column to form a liquid stream rich in C2 + hydrocarbons;
- introduction of the liquid stream to a supply level of a column of fractionation equipped with an overhead condenser, the ethane-rich stream being product, under the said production conditions, from a current from the column of fractionation, the fractionation column producing a bottom stream intended for at least partially forming a C3 + hydrocarbon cut;
- introduction of a primary reflux current produced in the condenser of head in reflux in the fractionation column;
- production of a secondary reflux current from the overhead condenser and introduction of the secondary reflux stream at the top of the recovery.
Such a method is intended to treat a stream of natural gas in order to extract to less C3 + hydrocarbons, in order to recover liquids from natural gas and an adjustable quantity of C2 hydrocarbons.
The C2 and C3 + hydrocarbons are extracted from the starting natural gas in order to to avoid condensation during transport and / or handling of the gas. This condensation can lead to the production of liquid plugs in the installations transport, which is detrimental to production. In addition, these hydrocarbons can

2 be marketed with a significant market value, which contributes to the profitability of installations.
As a result, methods have been developed to simultaneously extract the almost all the C3 + hydrocarbons present in the starting natural gas, and a high proportion of ethane present in the starting gas.
However, the market demand for ethane is very fluctuating, while that of C3 + hydrocarbon cuts is relatively constant and well valued.
In some cases, it is therefore necessary to reduce the production of ethane in the process, by reducing the rate of extraction of this compound in the column of recovery. In this case, the rate of extraction of C3 + hydrocarbons decreases also, which reduces the profitability of the installation.
To overcome this problem, it is known to provide double installations, that is ie comprising a secondary unit optimized for production of hydrocarbons in C3 + when the ethane extraction is zero. Such a secondary unit is expensive to operate and maintain.
US Patent 7,458,232 discloses a solution to this problem, by providing a process that guarantees optimized extraction of C3 + hydrocarbons, usually greater than 99%, and which nevertheless achieves ethane recoveries flexible, for example between 2% and 85%, depending on the composition of the gas charge.
The process described in US Pat. No. 7,458,232 is therefore particularly effective and rest very flexible. However, as the rate of ethane extraction increases, the consumption energy resulting from the use of compressors also increases. A
improvement of the efficiency of the installation, in particular for recovery high ethane, is therefore always desirable.
An object of the invention is to obtain a process which makes it possible to obtain in a manner flexible ethane extraction rates of up to 85%, while reducing notably the energy consumption of the installation.
To this end, the invention relates to an installation of the aforementioned type, characterized in that the process comprises the following steps:
- withdrawal of a recycling stream from the overhead stream from the column recovery ;
- connection of heat exchange of the recycling stream with at least part of the overhead stream from the recovery column, - reintroduction, after expansion, of the cooled and expanded recycling stream, in the recovery column;

3 the process comprising taking a sample from the bottom of the recovery of at least one bottom reboiling current, and the exchange relation thermal of the bottom reboiling stream with at least part of the natural gas from departure or / and with the recycling stream, the bottom reboiling being provided by Calories taken from the initial natural gas stream or / and from the recycling.
The method according to the invention can comprise one or more of following characteristics, taken individually or in any combination technically possible:
- at least part of the overhead stream of the recovery column and the recycling streams are placed in a heat exchange relationship with the gas stream natural starting and with the bottom reboiling current;
- the recycling stream from the first upstream heat exchanger, the current secondary reflux from the overhead condenser, and the overhead current from the recovery column are placed in a heat exchange relationship in a first head heat exchanger;
- at least one side reboiling stream is taken above the stream of bottom reboil, the or each side reboil stream being placed Related heat exchange with at least part of the natural gas stream of departure ;
- the stream rich in ethane is withdrawn from an intermediate level of the fractionation column located above the feed level of the column, and in below the head level of the fractionation column;
- it includes the following steps:
= separation of the starting natural gas stream into a first stream of departure and in a second starting stream;
= introduction of the first starting current in the first exchanger upstream thermal;
= introduction of at least part of the second starting current into a auxiliary dynamic expansion turbine to form a reflux stream auxiliary from the effluent from the auxiliary turbine;
= introduction of the auxiliary reflux stream into the recovery column ;
- at least part of the recycle stream is compressed in a auxiliary compressor coupled to the auxiliary turbine;
- at least part of the overhead stream is compressed in a compressor auxiliary coupled to the auxiliary turbine, advantageously between a first compressor coupled to the first turbine and a second compressor,

4 - it comprises a step of compressing at least part of the current of head in a first compressor coupled to the first turbine, then a step of compression of the partially compressed head stream in a second compressor, the recycling stream being taken downstream of the second compressor.
- at least one secondary recycling stream is taken from the recycling, the secondary recycling stream being introduced into a turbine of relaxation secondary before being reintroduced into the overhead stream, advantageously upstream a passage of the overhead stream in the first upstream heat exchanger;
- the secondary reflux current consists of a liquid, a gas, or of a mixture of liquid and gas coming from the top condenser of the splitting ;
- it comprises the removal, in the recycling stream, of a stream of shunt, the shunt current being reintroduced into a current located upstream of the first dynamic expansion turbine;
- the liquid flow from the first upstream separator tank is relaxed and is introduced in a second upstream separator flask to form a liquid fraction and a gas fraction, the liquid fraction being introduced after expansion at the first level intermediary of the recovery column, the gas fraction being introduced at a level superior of the recovery column, located above the intermediate level, the liquid flow coming from the first upstream separator tank being advantageously placed in a heat exchange relationship with the starting natural gas stream to be reheated before being introduced into the second upstream separator tank;
- it includes the heat exchange relationship of the foot current from the recovery column with the starting natural gas stream and with the current of bottom reboiling in the first upstream heat exchanger before its introduction in the fractionation column;
- the gas flow from the first separator tank is separated into the current feed and a reflux stream, the feed stream being intended for feed the dynamic expansion turbine, the reflux current being introduced, after cooling, partial or total condensation, and expansion in a valve, ebbing in the recovery column;
- it includes a step of compressing the foot current from the column of recovery in a pump, before its introduction into the column of splitting

5 - the method comprises a step of cooling the reflux stream secondary by heat exchange with at least part of the head stream of the recovery column.
The invention also relates to a simultaneous production installation of a treated natural gas, from a cut rich in C3 + hydrocarbons, and in less certain conditions of production, of a stream rich in ethane, from a stream gas natural starting material containing methane, ethane and C3 + hydrocarbons, the installation comprising:
- a set of cooling and partial condensation of the current of gas natural starting comprising at least a first upstream heat exchanger for forming a cooled starting stream;
- an assembly for separating the cooled starting stream into a liquid stream and in a gas flow;
- a C2 + hydrocarbon recovery column - a set for relaxing the liquid flow, and introducing a current from flow liquid in the recovery column at a first intermediate level;
- an assembly for forming a turbine feed stream from the flux gaseous;
- an assembly for reducing the supply stream comprising a turbine dynamic expansion and a set of feed current introduction relaxed in the recovery column at a second intermediate level;
- a set of recovery and compression of at least part of the overhead stream of the recovery column to form natural gas and a together recovery of the bottom stream of the recovery column to form current liquid rich in hydrocarbons - a fractionation column fitted with an overhead condenser, - a set for introducing the liquid stream to a supply level of the fractionation column, the stream rich in ethane being suitable for product in said production conditions, from a stream issuing from the column of fractionation, the fractionation column being adapted to produce a current of foot intended to form, at least in part, a cut of hydrocarbons in - a set for introducing a primary reflux current produced in the overhead condenser refluxed in the fractionation column;
- a set for producing a secondary reflux current from the head condenser and a reflux current introduction set secondary in mind the recovery column,

6 characterized in that the installation comprises:
- a set for sampling a recycling stream in the overhead stream the recovery column;
- a set of heat exchange relation of the recycling stream with at least part of the overhead stream from the column of recovery, - a set of reintroduction, after expansion, of the recycling current in the recovery column, the installation further comprising a set of sample at the bottom of the recovery column at least one stream of bottom reboiling, and a set of heat exchange relationship of the current of reboiling of melts with at least part of the starting natural gas or / and with the current of recycling, reboiling being able to be provided by the calories taken from the starting natural gas stream or / and in the recycle stream.
The installation according to the invention can comprise one or more of following characteristics, taken individually or in any combination technically possible:
- it comprises a first upstream heat exchanger clean to put in relationship heat exchange at least part of the starting natural gas stream, the flow bottom reboiling, possibly side reboiling currents, at the minus one part of the overhead stream and the recycle stream;
- it comprises a first upstream heat exchanger clean to put in relationship heat exchange a first part of the starting natural gas stream, with at minus part of the overhead stream, a second upstream heat exchanger, separate from first upstream heat exchanger, suitable for establishing an exchange relationship thermal a second part of the starting gas stream with the reboiling stream background from the recovery column, and a third upstream heat exchanger separate from first upstream heat exchanger and the second upstream heat exchanger, the third upstream heat exchanger being suitable for connecting exchange thermal at least part of the recycle stream with at least part of head current, the installation advantageously comprising a compressor extra suitable for compressing the part of the recycling stream intended to be introduced in the third upstream heat exchanger;
- the installation includes a first head heat exchanger, specific to to place in heat exchange relationship at least part of the overhead stream, eventually the reflux current, and the secondary reflux current;

7 - the installation includes a second head heat exchanger, separate from the first head heat exchanger, and suitable for establishing an exchange relationship thermal a second part of the overhead stream and the recycle stream.
The invention will be better understood on reading the description which follows, given by way of example only, and made with reference to the drawings annexed, on which :
- Figure 1 is a functional block diagram of a first installation of implementation of a first method according to the invention, - Figure 2 is a diagram similar to Figure 1 of a second installation for the implementation of a second method according to the invention;
- Figure 3 is a diagram similar to Figure 1 of a third installation for the implementation of a third method according to the invention;
- Figure 4 is a diagram similar to Figure 1 of a fourth installation for the implementation of a fourth method according to the invention;
- Figure 5 is a diagram similar to Figure 1 of a fifth installation for the implementation of a fifth method according to the invention;
- Figure 6 is a diagram similar to Figure 1 of a sixth installation, for the implementation of a sixth method according to the invention, the sixth installation resulting debottlenecking of an existing installation.
The first installation 11 according to the invention, shown in Figure 1, East intended for simultaneous production, from a stream 13 of natural gas starting, desulfurized, dry, and at least partially decarbonated, of a treated natural gas 15 like main product, a cut 17 of C3 + hydrocarbons, and a stream 19 rich in ethane, adjustable flow.
The term at least partially decarbonated means that the content of dioxide of carbon in the starting natural gas stream 13 is advantageously lower or equal to 50 ppm when the treated natural gas is to be liquefied. This content is advantageously less than 3% when the treated natural gas 15 is sent directly to a gas distribution network.
Likewise, the water content is less than 1 ppm, advantageously less than 0.1 ppm.
The installation 11 comprises a unit 21 for recovering hydrocarbons in C2 +, and a unit 23 for fractionating the C2 + hydrocarbons.
In what follows, a single reference will designate a liquid flow and the driving the vehicle, the pressures considered are pressures absolute, and percentages considered are molar percentages.

WO 2014/00617

8 PCT / EP2013 / 064238 The C2 + hydrocarbon recovery unit 21 comprises successively, a first upstream heat exchanger 25, a first upstream separator tank 27, a first upstream turbine 29, coupled to a first compressor 31, a first exchanger thermal head 33, and a recovery column 35 provided with at least one route 37, 39 side reboiling and a bottom reboiling circuit 41.
In this example, column 35 is provided with two reboiling circuits lateral 37, 39.
The unit 21 further comprises a second compressor 43 driven by a external energy source and a first refrigerant 45 placed downstream of the second compressor 43. Unit 21 also includes a pump 47 at the bottom of the column.
The fractionation unit 23 comprises a fractionation column 61. The column 61 comprises, at the top, a top condenser 63, and at the bottom, a reboiler 65.
The head condenser 63 includes a second refrigerant 67 and a first downstream separator tank 69 associated with a reflux pump 71.
A first method according to the invention implemented using the installation 11 goes now be described.
An example of the initial molar composition of the natural gas stream 13 of departure desulfurized, dry, and at least partially decarbonated, is given in the table below below.
Molar fraction in%
Helium 0.0713 CO2 0.0050 Nitrogen 1.2022 Methane 85.7828 Ethane 10.3815 Propane 2.1904 i-butane 0.1426 n-butane 0.1936 i-pentane 0.0204 n-pentane 0.0102 Hexane 0.0000 Total 100.0000 More generally, the molar fraction of methane in the stream 13 of gas natural starting point is between 75% and 90%, the molar fraction in C2 + hydrocarbons

9 is between 5% and 15%, and the molar fraction of C3 + hydrocarbons East between 1% and 8%.
The feed rate to be treated is for example of the order of 38000 kmol / h.
The starting natural gas stream 13 has a temperature close to ambient temperature and in particular substantially equal to 20 C, and a pressure in particular greater than 35 bars.
In a particular example, the natural gas stream 13 exhibits a temperature of 20 C and a pressure of 50 bars absolute.
In the installation shown in Figure 1, the natural gas stream from departure 13 is cooled and at least partially condensed in the first exchanger thermal upstream 25 to form a cooled starting stream 113.
The cooled starting stream 113 is introduced into the first flask separator upstream 27 in which a separation takes place between a gas phase 115 and a liquid phase 117.
The liquid phase 117 forms, after passing through an expansion valve 119, a relaxed mixed phase 120 which is introduced at a first intermediate level Neither of the recovery column 35, located in the upper region of the column, at the above lateral reboiling circuits 37 and 39.
By (intermediate level, we mean a location comprising means of distillation above and below this level.
The gas fraction 115 is separated into a feed stream 121 and a reflux current 123.
Advantageously, the molar flow rate of the feed stream 121 is greater than at molar flow rate of reflux stream 123.
The feed stream 121 is expanded in the turbine 29 to a pressure close to that of column 35 to give an expanded feed stream 125. The stream 125 is introduced into recovery column 35 at a second level intermediate N2, located above the first intermediate level Ni.
The reflux stream 123 is partially or totally condensed in the first head heat exchanger 33, then is expanded in an expansion valve 127, for form a relaxed reflux current 128. This current 128 is introduced into the column of recovery 35 at a third intermediate level N3, located above the level intermediate N2.
The pressure of the recovery column 35 is for example between 12 and 40 bars.

Recovery column 35 produces an overhead stream 131, which is warmed up in the first head heat exchanger 33 by heat exchange with the current reflux 123 to form a partially heated overhead stream 139.
Stream 139 is reheated again in the first heat exchanger 5 upstream 25 by heat exchange with the starting natural gas stream 13 to form a heated head current 140.
The heated head stream 140 is then compressed in the first compressor 31, then in the second compressor 43, to form a current of head compressed 141. The pressure of the stream 141 is greater than 25 bars, for example equal to

10 50 bars. Stream 141 is then cooled in the first refrigerant 45 to form the treated natural gas 15.
According to the invention, a recycle stream 152 is taken from the stream of head from column 35. In the example shown in FIG. 1, the current recycling 152 is taken from the heated compressed overhead stream 141, after its cooling in the first refrigerant 45.
The ratio of the molar flow rate of the recycle stream 152, relative to the flow rate molar of the overhead stream 131 from the recovery column 35 is between 0% and 25%.
The recycle stream 152 is then introduced into the first exchanger thermal upstream 25 to be cooled there by thermal exchange with at least a part of the head current 131. In this example, the current 152 is placed in relation exchange thermal with the partially heated overhead current 139 from the exchanger thermal head 33, to form a recycling stream 154 partially cooled.
The stream 154 is then introduced into the head heat exchanger 33, For be cooled by heat exchange with the overhead stream 131, and form, after relaxation in a valve 156, a cooled recycle stream 155.
The cooled recycle stream 155 is introduced into the column of recovery at a level N5 located above level N3, advantageously corresponding to first floor from the top of column 35.
The treated gas 15 contains in this example 1.36 mol% of nitrogen, 96.80 mol%
of methane and 1.76 mol% of C2 hydrocarbons.
More generally, the treated gas contains more than 99 mol% of the methane contained in the starting natural gas stream 13 and less than 0.1 mol%
of C3 + hydrocarbons contained in the starting natural gas stream.

11 The treated gas 15 contains a molar proportion varying between 2% and 85% of C2 hydrocarbons contained in the starting natural gas stream 13, this proportion being adjustable.
The gas 15 thus comprises a Cd hydrocarbon content of less than 1 ppm, a water content of less than 1 ppm, advantageously less than 0.1 ppm, and a carbon dioxide content less than 50 ppm. The treated gas 15 can therefore be sent directly to a liquefaction train to produce liquefied natural gas.
he can also be sent directly to a gas distribution network.
In the lateral reboiling circuits 37 and 39, reboiling currents lateral 161 and 163 are extracted from column 35 and are reintroduced there after reheating in the first upstream heat exchanger 25, by heat exchange with at least one part of the starting natural gas stream 13 and at least part of the recycling 152.
Thus, an upper side reboil current 163 is taken at a level located under level Ni, for example on the eleventh floor from the top of the column 35, then is brought to the first heat exchanger 25. The stream 163 is so heated in exchanger 25, then returned to column 35 at a level N7 located below level N6.
Likewise, a lower side reboil stream 161 is taken at a level N8 located below level N7, then is brought into heat exchanger 25. The current 161 is then heated in the heat exchanger 25 then is reintroduced to a level N9 located below level N8, for example on the fourteenth floor from the top of the column 35.
In the bottom reboiling circuit 41, a liquid stream 165 of reboiling of bottom is extracted near the foot of column 35, below the currents of lateral reboiling 161, 163.
According to the invention, the stream 165 is brought into the first exchanger thermal upstream 25, where it is heated by heat exchange with at least one part current starting natural gas 13 and at least part of the recycle stream 152. The heated and partially vaporized bottom reboiling stream 165 is then reintroduced in column 35.
A bottom stream 171 rich in C2 + hydrocarbons is extracted from the bottom of the recovery column 35.
Bottom stream 171 contains more than 99 mol% of C3 + hydrocarbons contained in the starting natural gas stream 13. It has a methane between 0% and 5%.

12 The bottom stream 171 is pumped by the bottom tank pump 47 and introduced at an intermediate level P1 of the fractionation column 61.
In the example shown, the fractionation column 61 operates at a pressure between 20 and 42 bars. In this example, the column pressure of fractionation 61 is at least 1 bar higher than the column pressure of recovery 35.
A bottom stream 181 is withdrawn from fractionation column 61 to form the cut 17 of C3 + hydrocarbons.
The extraction rate of C3 + hydrocarbons in the process is greater than 99%. In all cases, the propane extraction rate is greater than 99%.
The ethane-rich stream 19 is withdrawn directly at a level intermediate P2 located in the upper region of fractionation column 61.
In the example shown in the figures, this current comprises 1.21% of methane, 97.77% ethane and 1.00% propane.
More generally, the molar content of ethane in the stream rich in ethane 19 is greater than 95% and in particular between 96% and 100%.
The number of theoretical plates between the head of column 61 and the level higher P2 is for example between 1 and 7. Level P2 is higher at the level power supply P1.
A second overhead stream 183 is extracted from the head of column 61 then East cooled in the second refrigerant 67 to form a second stream of head 185 cooled and condensed at least partially. This second stream 185 is introduced in the second separator flask 69 to produce a liquid fraction 187 and a fraction carbonated 188.
In the example shown in Figure 1, all of the liquid fraction 187 is pumped through pump 71 to form a primary reflux stream 190 before to be reintroduced as reflux into fractionation column 61 at a level of head P3 located above level P2.
In this case, the whole of the gas fraction 188 forms, after cooling in the head heat exchanger 33 and expansion in a valve 193, a current of secondary reflux 192.
In the head exchanger 33, the gas fraction 188 is cooled by exchange thermal with the head current 131.
In a variant shown in dotted lines, the liquid fraction 187 is separated into a fraction 189 primary reflux liquid and a fraction 191 liquid secondary.

13 The secondary liquid fraction 191, when present, is then mixed to the gas fraction 188 to form, after cooling and expansion, the current of secondary reflux 192.
The secondary reflux stream 192 is refluxed at a level of N4 head of the recovery column 35 located between the head level N5 and the level intermediate N3.
The rate of ethane extraction, and consequently the flow rate of ethane produced in installation 11, is controlled by adjusting the flow rate of the recycling current 152, a hand, by adjusting the pressure in the recovery column 35, using the compressors 43 and 31 which are of the variable speed type, on the other hand, and by adjusting finally the flow of secondary reflux current 192 flowing through the expansion valve 193.
As shown in the table below, the flow rate of the ethane-rich stream is adjustable, practically without affecting the rate of extraction of hydrocarbons in C3 +.
The method according to the invention therefore makes it possible, by simple and limited means expensive, to obtain a variable and easily adjustable flow of a rich current in ethane 19 extracts starting natural gas 13, while maintaining the extraction rate of propane greater than 99%. This result is obtained without significant modification of installation in which the method is implemented.
Pressure Current flow Recovery Recovery Power compression Cl (bara) 152 (kmol / h) ethane (% mole) propane (% mole) total (kW) 29.0 0.37 0.66 99.76 16,254 26.2 1900 15.00 99.48 17622 25.4 2600 29.34 99.06 19 072 24.8 4410 43.42 99.87 21389 22.5 5470 58.34 100 25861 20.7 5750 68.89 100 29554 19.1 6000 77.88 100 33 136 17.9 6200 84.63 100 36183 The values of pressures, temperatures and flow rates in the case where the rate of ethane recovery is equal to 84.99% are given in the table below below.
Current Temperature (C) Pressure (bar abs) Flow (kmol / h) 13 20.0 50.0 38000 15 40.0 50.0 33634 17 86.8 33.5 978 19 11.9 33.0 3389 113 -44.0 49.8 38000 115 -44.0 49.8 36412

14 120 -69.5 17.8 1588 125 -81.0 17.8 30858 128 -108.5 17.8 5554 131 -101.6 17.6 38134 152 40.0 50.0 4500 154 -40.0 49.8 4500 155 -111.7 17.8 4500 171 -5.3 17.8 4376 192 -3.4 33.0 10 194 -99.0 17.8 10 When the flow rate of the ethane-rich stream 19 is reduced, the total power of compression is also greatly reduced.
The installation 11 according to the invention also does not require any use.
imperative of multiflux exchangers. It is thus possible to use only tube exchangers and grille.
The treated natural gas 15 has substantially zero contents of C5 + hydrocarbons, for example less than 1 ppm. Therefore, if the content in dioxide of carbon in the treated gas 15 is less than 50 ppm, this gas 15 can be liquefied without further processing or fractionation.
In the first method according to the invention, the bottom reboiling current is placed in a heat exchange relationship in the first heat exchanger 25 with the recycle stream 152, with at least part of the overhead stream 131, with the starting natural gas stream 13 and with reboiling streams lateral 161, 163.
This particular thermal integration of the process is beneficial in terms of yield, and does not affect the recovery of ethane, when this is desired.
Thus, when the recycle stream 152 is placed in an exchange relationship thermal with at least part of the head current 131, and when the current of bottom reboiling 165 is placed in a heat exchange relationship with the gas stream starting point 13, the inventors have surprisingly observed a synergistic increase in plant efficiency 11.
Thus, as shown in the table below, an efficiency gain of 16% is observed in relation to the installation according to the state of the art in maintaining a rate of 85% recovery, all other conditions being maintained. This gain extremely significant is obtained, maintaining an ethane recovery very high.

15 Case Ethane recovery (/ 0 mole) Total power (kW) Gain (/ 0) State of the art 85.01 44756 US 7,458,232 Installation 11 85.00 40566 9.4 without recycling of treated gas Installation 11 85.04 44651 0.2 without reboiler integrated background Installation 11 84.99 37422 16.4 In addition, the combined presence of recycling part of the treated gas and of a bottom reboiling assembly 41 integrated in the first heat exchanger unexpectedly generates a higher yield gain than is observed in the presence of one or other of these provisions taken individually.
Thus, when the first process is carried out without a recycle stream of treated gas 152, the gain obtained is 9.4%, whereas when the first method 11 is implemented without a bottom reboiler integrated in the heat exchanger 25, Gain obtained is 0.2%. The gain observed by pooling characteristics above is therefore significantly greater than the sum of the individual earnings obtained, demonstrating an unexpected synergistic effect, which does not affect recovery ethane.
Alternatively, the treated gas stream from the first compressor 31 can be fed into a two-stage compressor 43 of equivalent power, with a intermediate refrigerant cooling the gas to the same temperature as the refrigerant 45.
A second installation 201 according to the invention is illustrated in FIG. 2.
Installation 201 differs from first installation 11 in that it also includes a auxiliary expansion turbine 203 and an auxiliary compressor 205 coupled to the turbine 203.
In a first embodiment, the auxiliary compressor 205 is interposed between the first compressor 31 and the second compressor 43.
A second method according to the invention is implemented in the second installation 201.
Unlike the first method according to the invention, the gas stream natural of start 13 is separated into a first start current 207 and a second current of start 209.
The molar flow rate of the first starting stream 207 is advantageously superior at the molar flow rate of the second starting stream 209.

16 Then, the first starting stream 207 is introduced into the first exchanger thermal 25 to be cooled and partially condensed and to form the gas stream natural cooled 113 introduced into the first separator tank 27.
The second starting stream 209 is introduced into the expansion turbine auxiliary 203, to be relaxed there to a pressure close to the pressure of operation of column 35 and form an auxiliary reflux stream 211.
The flow of auxiliary reflux 211 is then introduced into the first exchanger thermal head 33 to be cooled and partially condensed there, then in an expansion valve 213 for forming a relaxed auxiliary reflux stream 215.
Stream 215 is then introduced into recovery column 35 at a upper level N10 located between level N3 and level N4.
In the example shown in Figure 2, the head current 217 from the first compressor 31 is introduced at its outlet from the first compressor 31 into the compressor auxiliary 205, to be compressed there to an intermediate pressure, before join the second compressor 43.
The values of pressures, temperatures, and flow rates in the event that the rate ethane recovery is equal to 85.00% are given in the table below.
below.
Current Temperature (C) Pressure (bar abs) Flow (kmol / h) 13 20.0 50.0 38000 15 40.0 50.0 33634

17 87.7 34.0 978 19 12.6 33.5 3389 113 -50.1 49.8 35074 115 -50.1 49.8 31965 120 -79.3 16.5 3109 125 -88.8 16.5 29505 128 -110.9 16.5 2460 131 -102.9 16.3 36 154 152 40.0 50.0 2520 154 -50.0 49.8 2520 155 -113.5 16.5 2520 171 -8.4 16.5 4376 192 -2.0 33.5 10 194 -100.3 16.5 10 207 20.0 50.0 35074 211 -26.3 20.9 2926 215 -107.0 16.5 2926 The implementation of the second method according to the invention produces a result analogous to that of the first process, thanks to the synergy observed between the setting heat exchange relationship of the bottom reboil stream 165 with the current of starting natural gas 13, taken in combination with the presence of a current of recycling 152, placed in a heat exchange relationship with at least part of the current head 131.
Thus, the consumption of the method for implementing the installation 201 led at a consumed power equal to 37,588 KW, i.e. a gain of 16% compared to the one the installation of the state of the art.
In a variant of Figure 2 (visible in dotted lines), the compressor auxiliary 205 is mounted downstream of the compressor 43 to compress the recycle stream 152, before its introduction into the first heat exchanger 25.
The installation and the implementation of the method are moreover similar to that of figure 2.
A third installation 221 according to the invention is illustrated by FIG.
3. At the difference of the installation 11 shown in Figure 1, the installation 221 has a second upstream separator tank 223 disposed downstream of the first tank separator for collect the liquid phase 117 from the first separator flask 27.
A third method according to the invention is implemented using installation 221. This third method differs from the first method according to the invention, in that that the liquid phase 117 is expanded in a static expansion valve 225. This relaxation is carried out up to a pressure higher than the operating pressure of the column 35.
The liquid phase is then relaxed and introduced into the second flask upstream separator 223.
A liquid fraction 227 is collected at the bottom of the flask 223, and is relaxed in a valve 229 to form an expanded fraction 231. The expanded fraction 231 East introduced into the recovery column 35 at level Ni.
A gas fraction 233 is collected at the top of the second separator flask upstream 223. This fraction 233 is sent to the head heat exchanger 33 for y be cooled before being expanded in an expansion valve 135 to form a relaxed fraction 237.
The expanded fraction 237 is introduced into the recovery column 35 at a intermediate level N11 between level N2 and level N3.
The values of pressures, temperatures, and flow rates in the event that the rate ethane recovery is equal to 84.99% are given in the table below.
below:
Current Temperature (C) Pressure (bar abs) Flow (kmol / h) 13 20.0 50.0 38000 15 40.0 50.0 33658

18 17 86.8 33.5 978

19 13.1 33.0 3364 113 -42.7 49.8 38000 115 -42.7 49.8 36709 117 -42.7 49.8 1291 118 -62.3 23.3 1291 125 -79.4 18.0 32325 128 -108.1 18.0 4384 131 -101.4 17.8 39758 152 40.0 50.0 6100 154 -40.0 49.8 6100 155 -111.3 18.0 6100 171 -3.5 18.0 4392 188 7.2 33.0 50 192 -98.8 18.0 50 231 -67.4 18.0 910 233 -62.3 23.3 381 237 -106.2 18.0 381 The method implemented using the third installation 221 according to the invention leads to a total power consumed by the compressors of 35960 KW, either a gain of 19.7% compared to the process of the state of the art.
It also allows an additional gain of 3.9% compared to the first process according to the invention.
In a variant of the third process, the liquid phase 117 obtained at the bottom of first separator tank 27 is introduced into the first exchanger thermal 25 for be heated there, before being brought into the valve 225.
The mixture is relaxed in the valve 225, before being separated in the second upstream separator tank 223.
A fourth installation 241 according to the invention is illustrated by FIG.
4. At the difference from the first installation 11, the current 171 coming from the column recovery 35 is passed through the first heat exchanger 25, to be heated there before being introduced into fractionation column 61.
The fourth method according to the invention therefore implements a reheating of this background current 171, after it has passed through pump 47.
For an ethane recovery rate of 85.00%, the total consumption is then 34201 kW, which provides a gain of 23.6% compared to installing the state of the technique. The gain is also 8.6% compared to the first process according to invention.
The values of pressures, temperatures, and flow rates in the event that the rate ethane recovery is equal to 85.00% are given in the table below.
below:

Current Temperature (C) Pressure (bar abs) Flow (kmol / h) 13 20.0 50.0 38000 15 40.0 50.0 33656 17 86.8 33.5 976 19 12.9 33.0 3368 113 -40.1 49.8 38000 115 -40.1 49.8 37218 120 -65.8 16.2 782 125 -80.1 16.2 27578 128 -110.6 16.2 9640 131 -102.9 16.0 34051 152 40.0 50.0 395 154 -40.0 49.8 395 155 -113.9 16.2 395 171 -7.7 16.2 4354 188 5.4 33.0 10 192 -100.2 16.2 10 243 12.0 33.5 4354 A fifth installation according to the invention 251 is illustrated by FIG.
5. This installation is intended for the implementation of a fifth method according to invention.
Unlike the first method according to the invention, a bypass current is taken from the recycling stream 152, advantageously downstream of the first heat exchanger 25 and upstream of the second heat exchanger 33, for be reintroduced into a stream located upstream of the first expansion turbine dynamic 29.
The flow rate of the bypass current 253 is for example equal to 47% of the flow rate molar total recycle stream 152 taken from the treated stream.
The fifth method according to the invention is moreover implemented way analogous to the fourth method according to the invention.
In the example of Figure 5, the bypass stream 253 is mixed with the current 121 before it is introduced into the turbine 29.
In a variant shown in dotted lines, the fifth installation 251 further comprises a secondary dynamic expansion turbine 255 coupled to a secondary compressor 257. A secondary recycle stream 258 is then taken in the recycle stream 152 before its introduction into the first exchanger thermal 25.
The secondary recycle stream 258 is introduced into the turbine of relaxation secondary 255, to form an expanded secondary recycling stream 261, who is reintroduced into the partially heated overhead stream 139 from the first interchange thermal head 33.
In addition, a secondary overhead current 263 is taken from the current of head heated 140 from the first heat exchanger 25 to be brought to the 5 secondary compressor 257 and form a secondary overhead current tablet 265.
This stream 265 is then reintroduced into the overhead stream compressed to a intermediate pressure from the first compressor 31 upstream of the second compressor 43.
The power gain obtained compared to the method of the state of the art East 10 then of the order of 15.4%, for a total power consumption of 37851 kW.
The values of pressures, temperatures, and flow rates in the event that the rate ethane recovery is equal to 85.00% are given in the table below.
below:
Current Temperature (C) Pressure (bar abs) Flow (kmol / h) 13 20.0 50.0 38000 15 40.0 50.0 33633 17 86.8 33.5 978 19 11.9 33.0 3389 113 -47.4 49.8 38000 115 -47.4 49.8 35524 120 -74.1 17.7 2477 125 -84.8 17.7 31199 128 -108.8 17.7 6463 131 -101.7 17.5 38183 152 40.0 50.0 4550 154 -40.0 49.8 4550 155 -111.8 17.7 2412 171 -5.5 17.7 4377 188 -3.4 33.0 10 192 -99.1 17.7 10 253 -40.0 49.8 2138 A sixth installation 271 according to the invention is shown in figure 6. This installation 271 is intended for debottlenecking an installation such as illustrated in US
7 458 232 and initially comprising a first upstream heat exchanger 25, a first separator flask 27, a recovery column 35, a first exchanger thermal head 33 and a fractionation column 61 provided with a condenser of head

20 63 ..
Unlike the first installation 11 according to the invention, installation 271 further comprises a second upstream heat exchanger 273 and a third

21 upstream heat exchanger 275, intended to be placed in parallel with the first upstream heat exchanger 25.
The installation 271 further comprises an auxiliary compressor 277 intended to compressing the recycle stream 152, and a make-up coolant 279 for to cool the compressed recycle stream.
Furthermore, the sixth installation 271 comprises a second exchanger head heat 281 intended to be placed in parallel with the first exchanger thermal head 33, to place at least part of the head stream 131 in relation exchange thermal with at least part of the recycle stream 152.
A sixth method according to the invention is implemented in the sixth installation 271. In this process, the starting natural gas stream 13 is separated into a first starting current 207 introduced into the first upstream heat exchanger 25 and in one second starting stream 209 introduced into a second heat exchanger upstream 273.
The first starting stream 207 is then cooled in the first exchanger thermal upstream 25 to form a first cooled starting stream 281A. Of even the second starting stream 209 is cooled in the second exchanger thermal upstream 273 to form a second cooled starting stream 283. The currents 281A and 283 are mixed to form the cooled stream 113 intended to be introduced in the first upstream separator tank 27.
The lateral reboiling streams 161, 163 are introduced into the first heat exchanger 25 to be heated there.
Unlike the first method according to the invention, the current of reboiling of bottom 165 is introduced into the second upstream heat exchanger 273 for y be heated by heat exchange with the second starting current 209.
Likewise, unlike the first method according to the invention, the current of head 131 from the recovery column 35 is first separated into a first fraction 285 of overhead current and a second fraction 287 of overhead current head.
The first fraction 285 is introduced into the first heat exchanger of head 33 to be heated there by thermal exchange, on the one hand, with the current of reflux 123, and on the other hand, with the secondary reflux current 192.
The second fraction 287 is introduced into the second heat exchanger of head 281.
The ratio of the molar flow rate of the first fraction 285 to the second fraction is for example between 0 and 20.

22 Then, the fractions recovered at the outlet of the overhead exchangers 33, 281 are remixed, before being again separated into a first part 289 of the current of reheated head and in a second part 291 of the reheated overhead stream.
The first part 289 is introduced into the first heat exchanger upstream 25 to be heated by thermal exchange with the first current of start 207, simultaneously with the side reboiling streams 161 and 163.
The second part 291 is introduced into the third heat exchanger upstream 275 to be reheated.
The heated parts 289 and 291 are then united to form the current of heated head 140, then are brought to the first compressor 31.
Unlike the first process according to the invention, the recycling stream is taken from the heated overhead stream 140 upstream of the first compressor 31.
The ratio of the molar flow rate of recycle stream 152 to the molar flow rate of overhead stream 131 from column 35 is for example between 0% and 25%.
Recycle stream 152 is then compressed in the booster compressor 277, up to a pressure for example greater than 50 bar, then is cooled in the refrigerant 279, to form a cooled compressed recycle stream 293.
The current 293 is then introduced successively into the third exchanger upstream thermal 275, then in the second head heat exchanger 281 For be cooled, before being expanded in an expansion valve 295 and form a current of recirculation relaxed cooled 297.
The stream 297 is then introduced into the recovery column 35, at the same level as the secondary reflux current 194.
Thus, in the first upstream heat exchanger 25 initially present in the installation, part 207 of the starting natural gas stream 13, the currents of side reboil 161, 163 and part 289 of the overhead stream are placed Related heat exchange.
In the second upstream heat exchanger 273, a second part 209 of the starting natural gas stream 13, and the bottom reboiling stream 165 are placed in heat exchange relationship. In the third upstream heat exchanger 275, a second part 291 of the overhead stream 131, and the recycle stream 152 are placed in heat exchange relationship.
The installation 271 according to the invention also does not require of use multi-flow exchangers imperative. It is thus possible to use only of tube and shell exchangers.

23 In addition, at the top of column 35, the reflux stream 123, a first part of head stream 285, and the secondary reflux stream 192 are placed in relationship heat exchange in the first head heat exchanger 33. In the second head heat exchanger 281, a second part 287 of the head stream 131 and the cooled compressed recycle stream 233 are placed in exchange relation thermal.
The installation 271 as shown in FIG. 6 makes it possible to accommodate of feed rate increases from 0% to 15%, and more preferably at less 10%, limiting the increase in compression power to a minimum necessary.
The values of pressures, temperatures, and flow rates in the event that the rate ethane recovery is equal to 85.00% are given in the table below.
below:
Current Temperature (C) Pressure (bar abs) Flow (kmol / h) 13 20.0 50.0 39900 15 40.0 50.0 35336 17 90.1 33.5 956 19 13.4 33.0 3608 113 -44.3 49.8 39900 115 -44.3 49.8 38 154 120 -74.8 13.5 1746 125 -89.1 13.5 29 961 128 -115.6 13.5 8193 131 -106.5 13.3 36016 140 15.9 12.9 36016 141 150.2 50.2 35336 152 15.9 12.9 680 171 -15.0 13.5 4565 192 5.0 33.0 1 194 -103.7 13.5 1 207 20.0 50.0 39900 225 -118.4 13.5 680 285 -106.5 13.3 33 250 287 -106.5 13.3 2766 289 -58.6 13.1 34935 291 -58.6 13.1 1080 293 40.0 50.2 680 In the examples shown in the Figures, the stream rich in ethane 19 East taken directly from fractionation column 61, advantageously at a level upper P2 of column 61 defined above.
The C3 + hydrocarbon cut 17 is also formed directly by the foot stream 181 of column 61.

24 As a variant (not shown), the O 2 hydrocarbons are extracted from the column fractionation 61 by the foot current 181, at the same time as the hydrocarbons in C3 +. The bottom stream 181 is then introduced into a downstream column of splitting.
The cut rich in ethane 19 as the cut of hydrocarbons in C3 + 17 are then produced in the downstream fractionation column.

Claims (19)

25 1.- Process for the simultaneous production of a treated natural gas (15), a cut (17) rich in C3 + hydrocarbons, and under at least certain conditions of production of a stream (19) rich in ethane, from a stream (13) of natural gas of departure containing methane, ethane and C3 + hydrocarbons, the process comprising the steps following:
- cooling and partial condensation of the natural gas stream (13) of departure in at least a first upstream heat exchanger (25) to form a cooled starting stream (113);
- separation of the cooled starting gas stream (113) into a liquid stream (117) and into a gas stream (115);
- expansion of the liquid flow (117), and introduction of a current from the flow liquid (117) in a column (35) for recovering C2 + hydrocarbons to a first level intermediate (N1);
- formation of a turbine feed stream (121) from the stream gaseous (115);
- expansion of the feed stream (121) in a first turbine (29) of dynamic expansion and introduction into the recovery column (35) at a second intermediate level (N2);
- recovery and compression of at least part of an overhead stream (131) of the recovery column (35) to form natural gas (15) and current recovery bottom of the recovery column (35) to form a liquid stream (171) rich in C2 + hydrocarbons;
- introduction of the liquid stream (171) to a supply level (P1) of a fractionation column (61) fitted with an overhead condenser (63), the stream rich in ethane (19) being produced, under the said production conditions, from of a current from the fractionation column (61), the fractionation column (61) producing a foot stream (181) intended to form at least part of a section hydrocarbons in C3 +;
- introduction of a primary reflux current (190) produced in the condenser head (63) refluxed in the fractionation column (61);
- production of a secondary reflux current (192) from the condenser of head (63) and introduction of the secondary reflux current (192) at the head of the column of recovery (35), characterized in that the method comprises the following steps:

- withdrawal of a recycling stream (152) in the overhead stream (131, 140, 141) from the recovery column (35);
- heat exchange relationship of the recycling stream (152) with at minus part of the overhead stream (131) from the recovery column (35), - reintroduction, after expansion, of the cooled recycling stream and relaxed in the recovery column (35);
the process comprising taking a sample from the bottom of the recovery (35) of at least one bottom reboil stream (165), and setting exchange relationship thermal of the bottom reboiling stream with at least part of the gas natural of start (13) or / and with the recycling stream (152), the bottom reboiling being assured by the calories taken from the initial natural gas stream (13) or / and in the recycle stream (152). 2.- Method according to claim 1, characterized in that at least a part of overhead stream (131) of the recovery column (35) and the stream of recycling (152) are placed in a heat exchange relationship with the natural gas stream of departure (13) and with the bottom reboil stream (165). 3.- Method according to claim 1 or 2, characterized in that the current of recycling (154) from the first upstream heat exchanger (25), the stream of reflux secondary (192) from the top condenser (63), and the top current (131) coming from of the recovery column (35) are placed in a heat exchange relationship in one first head heat exchanger (33). 4.- Method according to any one of claims 1 to 3, characterized in that that at least one side reboiling stream (161, 163) is taken from above current bottom reboil (165), the or each side reboil stream (161, 163) being placed in heat exchange relationship with at least part of the current of gas natural starting point (13). 5.- Method according to any one of claims 1 to 4, characterized in that that the stream rich in ethane (19) is withdrawn from a level intermediary of the fractionation column (61) located above the feed level of the column (61), and below the head level of the fractionation column (61). 6. A method according to any one of claims 1 to 5, characterized in that that it includes the following steps:
- separation of the starting natural gas stream (13) into a first stream of start (207) and a second start stream (209);
- introduction of the first starting stream (207) in the first exchanger upstream thermal (25);

- introduction of at least part of the second starting current (209) in an auxiliary dynamic expansion turbine (203) to form a stream of reflux auxiliary (215) from the effluent from the auxiliary turbine (203);
- introduction of the auxiliary reflux stream (215) in the column of recovery (35). 7.- Method according to claim 6, characterized in that at least a part of recycle stream (152) is compressed in an auxiliary compressor (205) coupled to the auxiliary turbine (203). 8. A method according to any one of claims 1 to 6, characterized in that that at least part of the overhead stream is compressed in a compressor auxiliary (205) coupled to the auxiliary turbine (203). 9. ¨ Method according to claim 8, characterized in that the at least one part of the overhead stream is compressed in an auxiliary compressor (205) coupled to the auxiliary turbine (203) between a first compressor (31) coupled to the first turbine (29) and a second compressor (43). 10.- Method according to any one of claims 1 to 9, characterized in this that it involves the removal, in the recycling stream (152), of a current of bypass (253), the bypass current (253) being reintroduced into a current located in upstream of the first turbine (29). 11.- Method according to any one of claims 1 to 10, characterized in this that the liquid flow (117) from a first upstream separator tank (27) is relaxed and is introduced into a second upstream separator tank (223) to form a liquid fraction (227) and a gas fraction (233), the liquid fraction (227) being introduced after expansion at the first level intermediate (N1) of the recovery column (35), the gas fraction (233) being introduced at an upper level (N11) of the recovery column (35), located above intermediate level (N1), and the liquid flow (117) from the first upstream separator tank (27) is warmed up before being introduced into the second upstream separator tank (223). 12. ¨ Method according to claim 11, characterized in that the liquid flow (117) from the first upstream separator tank (27) is placed in an exchange relation thermal with the starting natural gas stream (13) to be reheated before being introduced in the second upstream separator tank (223). 13. A method according to any one of claims 1 to 12, characterized in this that it involves the heat exchange relationship of the base current (171) from the recovery column (35) with the starting natural gas stream (13) and with the bottom reboiling stream (165) in the first upstream heat exchanger (25) before its introduction into the fractionation column (61). 14.- Method according to any one of claims 1 to 13, characterized in this that the gas flow (115) from the first separator drum (27) is separated into the flow supply (121) and in a reflux current (123), the current power supply (121) being intended to supply the dynamic expansion turbine (29), the reflux current (123) being introduced, after cooling, partial or total condensation, and expansion in valve, refluxing in the recovery column (35). 15.- Simultaneous production facility (11; 201; 221, 241; 251; 271) of a gas treated natural (15), from a cut (17) rich in C3 + hydrocarbons, and in at least certain production conditions, of a stream (19) rich in ethane, to from a stream (13) starting natural gas containing methane, ethane and hydrocarbons C3 +, the installation comprising:
- a set of cooling and partial condensation of the current (13) of starting natural gas comprising at least a first upstream heat exchanger (25) to form a cooled starting stream (113);
- an assembly for separating the cooled starting stream (113) into a stream liquid (117) and in a gas stream (115);
- a column (35) for recovering C2 + hydrocarbons - an assembly for reducing the liquid flow (117), and introducing a current issue of the liquid flow (117) in the recovery column (35) at a first level intermediate (N1);
- an assembly for forming a feed stream (121) for a turbine go from gas stream (115);
- an assembly for reducing the supply current (121) comprising a turbine (29) dynamic expansion and a set of current introduction power supply relaxed in the recovery column (35) at a second level intermediate (N2);
- a set of recovery and compression of at least part of the overhead stream (131) of the recovery column (35) to form the gas natural (15) and a recovery assembly for the bottom stream of the recovery column (35) for form a liquid stream (171) rich in hydrocarbons in - a fractionation column (61) provided with an overhead condenser (63), - a set for introducing the liquid stream to a supply level (P1) from the fractionation column (61), the stream rich in ethane (19) being fit to be produced, under the said production conditions, from a current of the column fractionation column (61), the fractionation column (61) being suitable for produce a foot stream (181) intended to form, at least in part, a section of hydrocarbons in C3 + (17);
- a set for introducing a primary reflux current (190) produced in the overhead condenser (63) refluxed in the fractionation column (61);
- an assembly for producing a secondary reflux current (192) from of head condenser (63) and a reflux current introduction assembly secondary (192) at the top of the recovery column (35), characterized in that the installation comprises:
- an assembly for sampling a recycling stream (152) in the stream of head (131, 140, 141) of the recovery column (35);
- a set of heat exchange relation of the recycling stream (152) with at least part of the overhead stream (131) from the column of recovery (35), - a set of reintroduction, after expansion (35), of the recycling stream (152) in the recovery column (35), the installation further comprising a together sampling at the bottom of the recovery column (35) of at least one current of bottom reboiling (165), and a set of exchange linking thermal bottom reboiling stream with at least part of the natural gas from departure (13) or / and with the recycle stream (152), the reboiling being able to be provided by calories taken from the initial natural gas stream (13) or / and from the current of recycling (152). 16.- Installation (11; 201; 221; 241; 251) according to claim 15, characterized in that it comprises the first upstream heat exchanger (25) specific to bring into heat exchange relationship at least part of the natural gas stream of departure (13), the bottom reboil stream (165), and the recycle stream (152). 17. - Installation (11; 201; 221; 241; 251) according to claim 16, characterized in that it comprises the first upstream heat exchanger (25) specific to bring into heat exchange relationship at least part of the natural gas stream of departure (13), bottom reboil current (165), reboil currents lateral (161, 163), at least part of the overhead stream (131) and the recycle stream (152). 18.- Installation (271) according to claim 15, characterized in that it comprises the first upstream heat exchanger (25) suitable for connecting heat exchange a first part of the starting natural gas stream (13), with at least part of the overhead stream (131), a second heat exchanger upstream (273), separate from the first upstream heat exchanger (25), suitable for relationship heat exchange a second part of the starting gas stream (13) with the bottom reboiling stream (165) from the recovery column (35), and one third upstream heat exchanger (275) separate from the first exchanger thermal upstream (25) and the second upstream heat exchanger (273), the third exchanger upstream thermal (275) being able to put in heat exchange relation to the less part of the recycle stream (152) with at least part of the stream of head (131), the installation (271) comprising a clean backup compressor (277). 19. ¨ Installation (271) according to claim 18, characterized in that the auxiliary compressor (277) suitable for compressing the part of the recycling (152) intended to be introduced into the third upstream heat exchanger (275).