Process for treating a natural gas containing carbon dioxide

Abstract

The disclosure includes a process for treating a natural gas containing carbon dioxide wherein the natural gas is separated by a cryogenic process in order to provide, on the one hand, a stream of liquid carbon dioxide, containing hydrocarbons, and, on the other hand, purified natural gas; at least one part of the natural gas is cooled in a first heat exchanger and then in a second heat exchanger before the cryogenic process and/or before a reflux to the cryogenic process; at least one part of the stream of liquid carbon dioxide is recovered in order to provide a stream of recycled carbon dioxide; the stream of recycled carbon dioxide is divided into a first portion and a second portion; the first portion is expanded and then heated in the first heat exchanger, in order to provide a first stream of heated carbon dioxide; the second portion is cooled, then at least one part of the second portion is expanded and then heated in the second heat exchanger, in order to provide a second stream of heated carbon dioxide; at least some of the hydrocarbons contained in the first stream of heated carbon dioxide and in the second stream of heated carbon dioxide are recovered by liquid/gas separation.

Claims

1. A process for treating a natural gas containing carbon dioxide, the process comprising: separating the natural gas by a cryogenic process in order to provide a stream of liquid carbon dioxide containing hydrocarbons and purified natural gas; cooling at least one part of the natural gas: (a) in a first heat exchanger, (b) then in a second heat exchanger before the cryogenic process or before a reflux to the cryogenic process; recovering at least one part of the stream of liquid carbon dioxide in order to provide a stream of recycled carbon dioxide; dividing the stream of recycled carbon dioxide into a first portion and a second portion; expanding and then heating the first portion in the first heat exchanger, in order to provide a first stream of heated carbon dioxide; cooling the second portion, then expanding and then heating at least one part of the second portion in the second heat exchanger, in order to provide a second stream of heated carbon dioxide; and recovering at least some of the hydrocarbons contained in the first stream of heated carbon dioxide and in the second stream of heated carbon dioxide by liquid/gas separation; the first stream of heated carbon dioxide undergoing a liquid/gas separation in a first separation flask in order to provide a first gaseous phase and a first liquid phase; expanding the first liquid phase; and the second stream of heated carbon dioxide and the first expanded liquid phase undergoing a liquid/gas separation in a second separation flask in order to provide a second gaseous phase and a second liquid phase.

2. The process according to claim 1, further comprising: cooling at least one part of the natural gas in a third heat exchanger before the cryogenic process or before a reflux to the cryogenic process; dividing the second portion of the stream of recycled carbon dioxide into a third portion and a fourth portion; expanding then heating the third portion in the second heat exchanger, in order to provide the second stream of heated carbon dioxide; cooling then expanding the fourth portion, then heating the expanded fourth portion in the third heat exchanger, in order to provide a third stream of heated carbon dioxide; and recovering at least some of the hydrocarbons contained in the third stream of heated carbon dioxide by liquid/gas separation.

3. The process according to claim 1, further comprising operating the first heat exchanger and the second heat exchanger at different temperatures.

4. The process according to claim 3, further comprising operating the first heat exchanger at a higher temperature than the second heat exchanger.

5. The process according to claim 1, wherein the cryogenic process is a distillation.

6. The process according to claim 1, wherein: the cooling of the second portion of the stream of recycled carbon dioxide is carried out in the second heat exchanger.

7. The process according to claim 6, further comprising cooling the stream of recycled carbon dioxide in the first heat exchanger before being divided into the first portion and the second portion.

8. The process according to claim 1, wherein the purified natural gas is heated, first in the second heat exchanger, then the first heat exchanger.

9. The process according to claim 1, further comprising: expanding the second liquid phase; and a third stream of heated carbon dioxide and the second expanded liquid phase undergoing a liquid/gas separation in a third separation flask in order to provide a third gaseous phase and a third liquid phase.

10. The process according to claim 1, further comprising stabilizing the condensate of the second liquid phase in order to provide a liquid phase rich in hydrocarbons and a gaseous phase rich in carbon dioxide.

11. The process according to claim 10, wherein the gaseous phase rich in carbon dioxide undergoes a liquid/gas separation in the second separation flask.

12. The process according to claim 1, further comprising compressing and cooling the first gaseous phase and the second gaseous phase in order to provide an outlet stream of carbon dioxide.

13. The process according to one of claim 1 further comprising at least one of: mixing one part of the second liquid phase with the second portion of the stream of recycled carbon dioxide; and mixing one part of an outlet stream of carbon dioxide with the stream of recycled carbon dioxide.

14. A process for treating natural gas implemented in a plant, comprising: using a cryogenic separation unit; using at least one line for natural gas connected at the inlet of the cryogenic separation unit; using a line for liquid carbon dioxide and a line for purified natural gas originating from the cryogenic separation unit; using a first heat exchanger passed through by at least one of the lines for natural gas connected at the inlet of the cryogenic separation unit; using a second heat exchanger passed through by at least one of the lines for natural gas connected at the inlet of the cryogenic separation unit or by a line for natural gas connected at the outlet of the cryogenic separation unit and feeding a reflux system; using a line for recycled carbon dioxide originating from the line for liquid carbon dioxide; using a line for a first portion and a line for a second portion originating from the line for recycled carbon dioxide, (a) the line for the first portion being equipped with an expander and then passing through the first heat exchanger; (b) the line for the second portion being equipped with a cooler; using a line for a third portion originating from the line for the second portion, the line for the third portion being equipped with an expander and then passing through the second heat exchanger; and using a gas/liquid separator fed by the line for the first portion and the line for the third portion; separating the natural gas by a cryogenic process in order to provide a stream of liquid carbon dioxide containing hydrocarbons and purified natural gas; cooling at least one part of the natural gas; (a) in the first heat exchanger, (b) then in the second heat exchanger before the cryogenic process or before the reflux to the cryogenic process; recovering at least one part of the stream of liquid carbon dioxide in order to provide a stream of recycled carbon dioxide; dividing the stream of recycled carbon dioxide into the first portion and the second portion; expanding and then heating the first portion in the first heat exchanger, in order to provide a first stream of heated carbon dioxide; cooling the second portion, then expanding and then heating at least one part of the second portion in the second heat exchanger, in order to provide a second stream of heated carbon dioxide; and recovering at least some of the hydrocarbons contained in the first stream of heated carbon dioxide and in the second stream of heated carbon dioxide by liquid/gas separation; the first stream of heated carbon dioxide undergoing a liquid/gas separation in a first separation flask in order to provide a first gaseous phase and a first liquid phase; expanding the first liquid phase; and the second stream of heated carbon dioxide and the first expanded liquid phase undergoing a liquid/gas separation in a second separation flask in order to provide a second gaseous phase and a second liquid phase.

Description

DRAWINGS

(1) FIG. 1 diagrammatically shows an embodiment of a plant according to the invention.

DETAILED DESCRIPTION

(2) The invention will now be described in greater detail and in a non-limitative fashion in the following description. All pressures are given in absolute values. All percentages are given as molar values, unless otherwise indicated. The terms upstream and downstream refer to the direction of flow of the fluids in the plant.

(3) Plant

(4) With reference to FIG. 1, the plant according to the invention comprises a feed line for natural gas 1. This feed line for natural gas 1 preferably passes through a pretreatment unit 57, which can include pre-cooling means and/or dehydration means and/or gas/liquid separation means and/or fractionation means. It is preferred, for reasons of simplicity, that the plant be without fractionation means and deacidification means in the pretreatment unit 57.

(5) The feed line for natural gas 1 feeds (indirectly) a cryogenic separation unit 35. By cryogenic separation unit is meant a set of means capable of separating carbon dioxide from methane with a supply of cold at an operating temperature below or equal to 40 C.

(6) Preferably, the cryogenic separation unit 35 is a distillation unit and, more precisely, in the embodiment shown, it is a standard distillation column equipped with a reboiler 32 at the foot. Heat exchange means between the feed line for natural gas 1 and the reboiler 32 are provided; the feed line for natural gas 1 opens into a gas/liquid separator 31. Two lines for natural gas 33, 34, namely a line for gaseous fraction 33 and a line for liquid fraction 34, are connected at the outlet of the gas/liquid separator 31.

(7) The line for gaseous fraction 33 and the line for liquid fraction 34 respectively open into the cryogenic separation unit 35, at different stages. Each of these two lines is equipped with expansion means; moreover, the line for gaseous fraction 33 passes successively through a first heat exchanger 36 and a second heat exchanger 37 before passing through the above-mentioned expansion means and opening into the cryogenic separation unit 35.

(8) A line for liquid carbon dioxide 10 is connected at the foot of the cryogenic separation unit 35, and a line for natural gas 39, feeding a reflux system, is connected at the head of the cryogenic separation unit 35. More precisely, the line for natural gas 39 passes through a third heat exchanger 38 then feeds a gas/liquid separator 40. At the outlet of this gas/liquid separator 40, there are connected, at the foot on the one hand, a reflux line 41 equipped with pumping means and returning to the cryogenic separation unit 35 and, at the head on the other hand, a line for purified natural gas 99.

(9) The line for purified natural gas 99 passes successively through the third heat exchanger 38, the second heat exchanger 37 and the first heat exchanger 36. On the diagram, the streams passing through the heat exchangers from left to right give off heat and the streams passing through the heat exchangers from right to left absorb heat. Thus, the cooling of the heat exchangers 36, 37, 38 is ensured by the line for purified natural gas 99 and by the open refrigeration cycle described below and containing a stream rich in carbon dioxide. The line for purified natural gas 99 can be followed by recompression means.

(10) If necessary, additional treatment means (and in particular additional deacidification means) can be provided from the line for purified natural gas 99, if a finishing purification of the gas is necessary. Such additional treatment means (generally situated downstream of fractionation means) can comprise means for treating the carbon dioxide according to any one of the techniques known in the state of the art (for example scrubbing with amine solvent, separation by membrane, etc.). This can prove useful in the case of a gas comprising a very high CO.sub.2 content.

(11) Downstream, this line for purified natural gas 99 can be linked to the gas transport and/or distribution network, or feed a natural gas liquefaction unit. Moreover, the line for liquid carbon dioxide 10 divides into two branches, namely a line for non-recycled carbon dioxide 11 and a line for recycled carbon dioxide 12. The line for recycled carbon dioxide 12 passes through the first heat exchanger 36. Then it divides into two branches, namely a line for the first portion 13 and a line for the second portion 42. The line for the second portion 42 passes through the second heat exchanger 37 then itself divides into two branches, namely a line for the third portion 16 and a line for the fourth portion 19. The line for the fourth portion 19 passes through the third heat exchanger 38 a first time.

(12) Expansion means 43 are provided on the line for the first portion 13, which then passes through the first heat exchanger 36, before feeding a first separation flask 47. Similarly, expansion means 45 are provided on the line for the third portion 16, which then passes through the second heat exchanger 37, before feeding a second separation flask 48. Finally, the line for the fourth portion 19 passes through the third heat exchanger 38 a second time, expansion means 46 being provided on the line for the fourth portion 19 between its two passages through the heat exchanger 38; finally, the line for the fourth portion 19 feeds a third separation flask 49.

(13) The three separation flasks 47, 48, 49 are suitable for carrying out a liquid/gas separation and they are connected in cascade. In other words, at the outlet of the first separation flask 47 there are connected a line for the first gaseous phase 15 (at the head) and a line for the first liquid phase 14 (at the foot), said line for the first liquid phase 14 feeding the second separation flask 48 after having passed through expansion means 58; similarly, at the outlet of the second separation flask 48 there are connected a line for the second gaseous phase 18 (at the head) and a line for the second liquid phase 17 (at the foot), said line for the second liquid phase 17 feeding the third separation flask 49 after passing through expansion means 59. At the outlet of the third separation flask 49 there are connected a line for the third gaseous phase 23 (at the head) and a line for the third liquid phase 20 (at the foot).

(14) The line for the third liquid phase 20 is equipped with pumping means and feeds a condensate stabilization unit 55. This condensate stabilization unit 55 can be a distillation column or, preferably, a distillation half-column, i.e. a column equipped with a reboiler 56 at the foot, but without a cooling and reflux system at the head.

(15) At the outlet of the condensate stabilization unit 55 there are connected, on the one hand, a line for liquid phase rich in hydrocarbons 21 at the foot and a line for gaseous phase rich in carbon dioxide 22 at the head. The line for gaseous phase rich in carbon dioxide 22 returns to the third separation flask 49. The line for liquid phase rich in hydrocarbons 21 can open into treatment means (for example fractionation means) and/or means for storing condensates.

(16) The line for the third gaseous phase 23 feeds a first compressor 50, at the outlet of which a first intermediate line 24 is connected. This first intermediate line 24 is joined by the line for the second gaseous phase 18, at the inlet of a second compressor 51. A second intermediate line 25 is connected at the outlet of the second compressor 51. This second intermediate line 25 is joined by the line for the first gaseous phase 15, at the inlet of a third compressor 52. An outlet line for carbon dioxide 26 is connected at the outlet of the third compressor 52.

(17) The outlet line for carbon dioxide 26 is equipped with cooling means 53 and joins the line for non-recycled carbon dioxide 11 in order to form a line for final carbon dioxide 27. Pumping means can be provided on this. The line for final carbon dioxide 27 can open into downstream treatment means, for example means for injection into an underground formation.

(18) Process

(19) The natural gas which is treated by the process according to the invention is a gaseous mixture (which may contain a minority liquid fraction) comprising at least methane and CO.sub.2. Preferably, this gaseous mixture comprises at least 5% methane, and generally at least 10% or at least 15% or at least 20% methane or at least 25% methane (molar proportions relative to the natural gas). Preferably, this gaseous mixture comprises at least 10% CO.sub.2, and generally at least 20% CO.sub.2 or at least 30% CO.sub.2 or at least 40% CO.sub.2 or at least 50% CO.sub.2 or at least 60% CO.sub.2 or at least 70% CO.sub.2 (molar proportions relative to the natural gas). The natural gas also contains C3+ hydrocarbons (comprising at least 3 carbon atoms), preferably in a proportion by mass greater than or equal to 1% or 2% or 3% or 4% or 5% relative to the methane.

(20) The natural gas optionally undergoes one or more preliminary treatments (in the pretreatment unit 57) with the aim of removing its solid contaminants or its liquid fraction, dehydrating it and/or pre-cooling it and/or reducing its hydrogen sulphide content. According to a preferred embodiment, the natural gas does not undergo any treatment with the specific aim of reducing its CO.sub.2 content prior to the cryogenic separation. In the embodiment shown, the natural gas is first cooled by heat exchange in the reboiler 32 of the cryogenic separation unit 35, then it undergoes a separation into a gaseous phase and a liquid phase in the gas/liquid separator 31. These two phases are introduced at different stages of the cryogenic separation unit 35, after an expansion.

(21) A stream of liquid carbon dioxide is recovered at the foot of the cryogenic separation unit 35 in the line for liquid carbon dioxide 10. By stream of carbon dioxide is meant, within the context of the present description, a mixture comprising mostly CO.sub.2 and comprising a minority proportion of other compounds, in particular C3+ hydrocarbons.

(22) The cooling needed to implement the cryogenic separation is ensured by the multi-stage open refrigeration cycle (at least two heat exchangers) which is fed by at least one part of the liquid carbon dioxide (stream of recycled carbon dioxide). In the embodiment shown, the refrigeration is carried out in the three heat exchangers 36, 37, 38 operating at decreasing temperatures, the heat exchangers 36 and 37 typically functioning at between 40 C. and 0 C., and the heat exchanger 38 typically functioning at between 60 C. and 45 C. (temperature of the refrigeration fluid after expansion). More precisely, the gaseous phase of the natural gas is cooled in the first heat exchanger 36 and the second heat exchanger 37.

(23) The third heat exchanger 38 serves to cool the reflux of the cryogenic separation, i.e. to cool the stream of natural gas leaving the cryogenic separation unit 35 at the head. After this cooling, the stream of natural gas undergoes a separation in the gas/liquid separator 40 producing a stream of liquid phase which is pumped and returned to the cryogenic separation (reflux line 41), and a stream of purified natural gas which is recovered in the line for purified natural gas 99. In the embodiment shown, the stream of purified natural gas is heated in the three heat exchangers 38, 37, 36 successively, which makes it possible to recover the frigories available therein.

(24) With regard to the functioning of the refrigeration cycle, the stream of recycled carbon dioxide undergoes a first cooling in the first heat exchanger 36, then it is divided into two liquid streams, namely a first portion and a second portion. The first portion is cooled by expansion, and it then returns to the first heat exchanger 36, in which it absorbs heat originating from the natural gas upstream of the cryogenic separation (and also heat originating from the stream of recycled carbon dioxide before expansion). The second portion undergoes a second cooling in the second heat exchanger 37, then it is divided into two liquid streams, namely a third portion and a fourth portion. The third portion is cooled by expansion, and it then returns to the second heat exchanger 37, in which it absorbs heat originating from the natural gas upstream of the cryogenic separation (and also heat originating from the stream of recycled carbon dioxide before expansion). The fourth portion undergoes a third cooling in the third heat exchanger 38, then it is cooled by expansion, and it then returns to the third heat exchanger 38, in which it absorbs heat originating from the natural gas at the level of the reflux of the cryogenic separation (and also heat originating from the stream of recycled carbon dioxide before expansion).

(25) A first, second and third stream of heated carbon dioxide are therefore recovered at the outlet of the first, second and third heat exchanger 36, 37, 38 respectively. A significant part of the C3+ hydrocarbons contained in these streams is recovered by liquid/gas separation carried out on these streams. The liquid/gas separation is carried out by means of the first, second and third separation flasks 47, 48, 49, operating at decreasing pressures. The typical operating pressures are 10 bar to 40 bar for the separation flasks 47 and 48, and bar to 10 bar for the separation flask 49.

(26) Each separation flask (respectively the first, second or third) produces a liquid phase (respectively the first, second or third) and a gaseous phase (respectively the first, second or third). The heavy hydrocarbons (essentially C4+) are mostly in the liquid phase. The first liquid phase is expanded and sent to the second separation flask 48 operating at a lower pressure than the first, and similarly the second liquid phase is expanded and sent to the third separation flask 49 operating at a lower pressure than the second. Thus, the heavy hydrocarbons trapped in the stream of CO.sub.2 tend to concentrate in the bottom of the third separation flask 49 functioning at the lowest pressure, where they can easily be recovered in the third liquid phase.

(27) An additional purification step (stabilization of the condensates) can be implemented, as shown, by means of the condensate stabilization column 55. A liquid phase rich in hydrocarbons is recovered at the foot thereof and a gaseous phase rich in carbon dioxide, which is returned to the separation flask at the lowest pressure, is recovered at the head. Each gaseous phase originating from the different separation flasks, depleted of heavy hydrocarbons, is compressed; these different gaseous phases are mixed, then the mixture is cooled and advantageously combined with the part of the liquid CO.sub.2 that is not recycled for refrigeration. The stream of final liquid CO.sub.2 can be pumped and injected into an underground formation, or else be used or otherwise turned to account.

(28) Variants

(29) The plant according to the invention and the process according to the invention can be varied from the embodiment described above in several ways. For example, it is possible to provide an additional line for carbon dioxide 54 equipped with a valve reaching from the outlet line for carbon dioxide 26 (typically downstream of the cooling means 53) to the line for recycled carbon dioxide 12. This characteristic makes it possible to compensate for any lack of refrigerant in the multi-stage refrigeration system, making it possible to recycle part of the CO.sub.2 stream used for the refrigeration.

(30) It is also possible to provide an additional line for hydrocarbons 44 (optionally equipped with a valve) connected at the outlet of the third separation flask 49 at the foot, equipped with pumping means and returning to the line for the fourth portion 19, upstream of the first passage into the third heat exchanger 38. Thus, part of the third liquid phase can be recycled in the CO.sub.2 stream used for the refrigeration. This characteristic makes it possible to avoid any risk of crystallization at the coldest point, while enriching the expanded stream passing through the third heat exchanger 38 with hydrocarbons.

(31) Moreover, the above description was made in relation to an open refrigeration cycle with three stages. This is the variant that makes an optimum functioning of the system possible. However, it is also possible to provide a cycle with two stages or, alternatively, with four or more stages.

(32) In the case of a system with two stages, compared with the above description: the third heat exchanger 38 and the third separation flask 49 are omitted, as are the associated components, namely the line for the fourth portion 19, the line for the third gaseous phase 23, the first compressor 50 and the first intermediate line 24. The line for the second liquid phase 17 then merges with the line for the third liquid phase 20 and therefore directly feeds the condensate stabilization unit 55.

(33) In the case of a system with four or more stages, compared with the above description, at least one additional heat exchanger (suitable for cooling the natural gas upstream of the cryogenic separation unit or in the reflux of the latter) and at least one additional separation flask are added; at least one additional division of the line originating from the line for recycled carbon dioxide 12, equipped with expansion means and feeding the additional separation flask are also added; and, at the outlet of the (or of each) additional separation flask, there are provided an additional line for gaseous phase, associated with an additional compressor, and an additional line for liquid phase, equipped with expansion means and feeding the following separation flask (i.e. operating at lower pressure).

(34) Moreover, in the embodiment shown, the line for natural gas 33 passing into the first heat exchanger 36 and the second heat exchanger 37 originates from the gas/liquid separator 31 and feeds the cryogenic separation unit 35; and the natural gas line 39 passing into the third heat exchanger 38 forms part of the reflux system of the cryogenic separation unit 35, since it originates from the head of the cryogenic separation unit 35 and feeds the gas/liquid separator 40 to which the reflux line 41 is connected at the foot. However, this distribution can be modified according to, on the one hand, the number of heat exchangers and, on the other hand, the operating parameters of the plant.

(35) For example, the line for natural gas 33 originating from the gas/liquid separator 31 and feeding the cryogenic separation unit 35 can pass through a single heat exchanger (in particular if the refrigeration cycle comprises only two heat exchangers, in which case the second heat exchanger can be associated with the reflux system of the cryogenic separation unit 35). Conversely, this line for natural gas 33 can pass through more than two heat exchangers. Another variant is for all of the heat exchangers to be associated with the line for natural gas 33 originating from the gas/liquid separator 31 and feeding the cryogenic separation unit 35, in which case the reflux system of the cryogenic separation unit 35 is equipped with additional cooling means (replacing the third heat exchanger described above).

(36) The cryogenic separation unit 35 can be a standard distillation column, suitable for the cryogenic separation of CO.sub.2, as described above. But it can also be a distillation column suitable for functioning under solids-forming conditions (CFZ-type column, such as described for example in U.S. Pat. No. 4,533,372 or WO 99/01707). The cryogenic separation unit 35 can also comprise liquefaction means suitable for liquefying the gas under pressure, means for expanding the fluid suitable for creating an intense cold and a partial crystallization of the CO.sub.2, and means for recovering a liquid fraction and a solid fraction comprising a flask suitable for maintaining a bottom temperature in the liquid range (cryocell-type distillation unit as described for example in WO 2007/030888, WO 2008/095258 and WO 2009/144275). In this case, it is advantageous to provide a stabilization column on the line for liquid carbon dioxide 10, suitable for recovering the light hydrocarbons (in particular methane) present in the liquid CO.sub.2.

EXAMPLE

(37) The following example illustrates the invention without limiting it. A numerical simulation was carried out in order to characterize the functioning of a plant corresponding to FIG. 1. Tables 1a, 1b, 1c, 1d, 2a, 2b, 2c and 2d below give the composition of the starting natural gas as well as the flow rates obtained and the composition of the stream obtained in different lines of the plant. The conditions in lines 13, 16, 19 were recorded at the outlet of the respective heat exchangers 36, 37, 38. The conditions in lines 14, 17, 20 were recorded at the outlet of the respective separation flasks 47, 48, 49 and before expansion or pumping. The conditions in line 10 were recorded before pumping.

(38) TABLE-US-00001 TABLE 1a general data and molar data Line of the plant 1 99 10 11 12 Liquid (L) or G + L G + L L L L gaseous (G) state Temperature 4.741 9.948 9.948 ( C.) Pressure 40.680 80.000 80.000 (bar) Molecular 35.485 21.904 43.878 43.878 43.878 weight Flow rate 35260.954 12067.202 23168.041 35.100 23132.941 (kmol/h) Composition (mole %) N.sub.2 0.50 1.46 0.00 0.00 0.00 CO.sub.2 71.00 20.00 97.53 97.53 97.53 H.sub.2S 0.50 0.10 0.71 0.71 0.71 Methane 27.00 77.93 0.50 0.50 0.50 Ethane 0.60 0.49 0.66 0.66 0.66 Propane 0.20 0.02 0.29 0.29 0.29 Heptane 0.20 0.00 0.30 0.30 0.30

(39) TABLE-US-00002 TABLE 1b general data and molar data (continued) Line of the plant 13 14 15 16 17 Liquid (L) or G + L L G G + L L gaseous (G) state Temperature 6.891 6.637 6.637 11.001 11.425 ( C.) Pressure 27.626 27.426 27.426 13.723 13.520 (bar) Molecular 43.878 66.018 43.790 43.878 75.424 weight Flow rate 12435.033 49.604 12385.430 8522.613 70.771 (kmol/h) Composition (mole %) N.sub.2 0.00 0.00 0.00 0.00 0.00 CO.sub.2 97.53 57.83 97.69 97.53 41.85 H.sub.2S 0.71 0.77 0.71 0.71 0.61 Methane 0.50 0.08 0.50 0.50 0.05 Ethane 0.66 0.51 0.66 0.66 0.31 Propane 0.29 1.34 0.29 0.29 1.08 Heptane 0.30 39.47 0.15 0.30 56.11

(40) TABLE-US-00003 TABLE 1c general data and molar data (continued) Line of the plant 18 19 20 21 22 Liquid (L) or G G + L L L G gaseous (G) state Temperature 11.425 33.026 32.595 168.547 30.301 ( C.) Pressure 13.520 5.677 5.477 6.000 6.000 (bar) Molecular 43.745 43.878 82.729 99.655 43.780 weight Flow rate 8501.446 2175.294 66.255 46.184 20.071 (kmol/h) Composition (mole %) N.sub.2 0.00 0.00 0.00 0.00 0.00 CO.sub.2 97.77 97.53 29.50 0.00 97.38 H.sub.2S 0.71 0.71 0.46 0.00 1.51 Methane 0.50 0.50 0.02 0.00 0.08 Ethane 0.66 0.66 0.16 0.00 0.53 Propane 0.29 0.29 0.82 0.98 0.47 Heptane 0.07 0.30 69.03 99.02 0.03

(41) TABLE-US-00004 TABLE 1d general data and molar data (continued) Line of the plant 23 24 25 26 27 Liquid (L) or G G G L L gaseous (G) state Temperature 32.595 40.028 61.729 33.000 32.988 ( C.) Pressure 5.477 13.520 27.926 80.000 80.000 (bar) Molecular 43.722 43.722 43.740 43.767 43.767 weight Flow rate 2199.881 2199.881 10701.327 23086.758 23121.857 (kmol/h) Composition (mole %) N.sub.2 0.00 0.00 0.00 0.00 0.00 CO.sub.2 97.79 97.79 97.77 97.73 97.73 H.sub.2S 0.72 0.72 0.71 0.71 0.71 Methane 0.50 0.50 0.50 0.50 0.50 Ethane 0.66 0.66 0.66 0.66 0.66 Propane 0.30 0.30 0.29 0.29 0.29 Heptane 0.03 0.03 0.06 0.11 0.11

(42) TABLE-US-00005 TABLE 2a data by mass Line of the plant 1 99 10 11 12 Flow rate (kg/h) 1282025.1 264320.9 1016579.3 1540.1 1015039.2 Composition (% by mass) N.sub.2 0.39 1.87 0.00 0.00 0.00 CO.sub.2 85.94 40.18 97.83 97.83 97.83 H.sub.2S 0.47 0.16 0.55 0.55 0.55 Methane 11.91 57.08 0.18 0.18 0.18 Ethane 0.50 0.67 0.45 0.45 0.45 Propane 0.24 0.05 0.29 0.29 0.29 Heptane 0.55 0.00 0.70 0.70 0.70

(43) TABLE-US-00006 TABLE 2b data by mass (continued) Line of the plant 13 14 15 16 17 Flow rate (kg/h) 545630.8 3274.8 542356.1 373959.6 5337.8 Composition (% by mass) N.sub.2 0.00 0.00 0.00 0.00 0.00 CO.sub.2 97.83 38.55 98.18 97.83 24.42 H.sub.2S 0.55 0.40 0.55 0.55 0.27 Methane 0.18 0.02 0.18 0.18 0.01 Ethane 0.45 0.23 0.45 0.45 0.12 Propane 0.29 0.89 0.29 0.29 0.63 Heptane 0.70 59.90 0.34 0.70 74.54

(44) TABLE-US-00007 TABLE 2c data by mass (continued) Line of the plant 18 19 20 21 22 Flow rate (kg/h) 371896.6 95448.7 5481.2 4602.5 878.7 Composition (% by mass) N.sub.2 0.00 0.00 0.00 0.00 0.00 CO.sub.2 98.36 97.83 15.69 0.00 97.89 H.sub.2S 0.55 0.55 0.19 0.00 1.17 Methane 0.18 0.18 0.00 0.00 0.03 Ethane 0.46 0.45 0.06 0.00 0.36 Propane 0.29 0.29 0.44 0.43 0.47 Heptane 0.16 0.70 83.62 99.57 0.07

(45) TABLE-US-00008 TABLE 2d data by mass (continued) Line of the plant 23 24 25 26 27 Flow rate (kg/h) 96184.0 96184.0 468080.6 1010436.7 1011976.8 Composition (% by mass) N.sub.2 0.00 0.00 0.00 0.00 0.00 CO.sub.2 98.43 98.43 98.37 98.27 98.27 H.sub.2S 0.56 0.56 0.55 0.55 0.55 Methane 0.18 0.18 0.18 0.18 0.18 Ethane 0.46 0.46 0.46 0.45 0.45 Propane 0.31 0.31 0.30 0.29 0.29 Heptane 0.06 0.06 0.14 0.24 0.25

(46) It is noted in this example that only 10% of the C7 hydrocarbons (representing the heavy paraffins) present in the liquid CO.sub.2 pass through the coldest heat exchanger. This illustrates the impact of the process, compared with the state of the art, where a cascade refrigeration cycle would collect all of the heavy paraffins in the coldest heat exchanger.