EP2659211B1 - Method for producing a methane-rich stream and a c2+ hydrocarbon-rich stream, and associated equipment - Google Patents

Description

The present invention relates to a process for producing a methane-rich stream and a C ₂ ⁺ hydrocarbon-rich stream from a hydrocarbon-containing feed stream, according to the preamble of claim 1.

The "Texas plant retrofit improves throughput, C2 recovery" article describes a separation process comprising two dynamic expansion turbines in parallel.

US 6,526,777 discloses a method according to the preamble of claim 1.

Such a process is intended for extracting C ₂ ⁺ hydrocarbons, such as, in particular, ethylene, ethane, propylene, propane and heavier hydrocarbons, especially from natural gas, refinery gas or synthetic gas. obtained from other hydrocarbon sources such as coal, crude oil, naphtha.

Natural gas generally contains a majority of methane and ethane constituting at least 50 mol% of the gas. It also contains in a more negligible quantity heavier hydrocarbons, such as propane, butane, pentane. In some cases, it also contains helium, hydrogen, nitrogen and carbon dioxide.

It is necessary to separate heavy hydrocarbons from natural gas to meet at least two requirements.

First of all, economically, C ₂ ⁺ hydrocarbons, and in particular ethane, propane and butane, can be recovered. In addition, the demand for natural gas liquids as a burden for the petrochemical industry is growing steadily and is expected to continue to grow in the coming years.

In addition, for process reasons, it is desirable to separate the heavy hydrocarbons to prevent them from condensing during transport and / or handling of the gases. This avoids incidents such as the arrival of liquid plugs in transport or treatment facilities designed for gaseous effluents.

In order to separate the C ₂ ⁺ hydrocarbons from natural gas, it is known to use an oil absorption process which makes it possible to recover up to 90% of the propane and up to approximately 40% of the ethane.

To achieve higher recovery rates, cryogenic expansion methods are used.

In a known cryogenic expansion process, a portion of the hydrocarbon feed stream is used for the secondary reboilers of a methane separation column.

Then, the different effluents, after partial condensation, are combined to feed a gas-liquid separator.

As described in US5,555,748 the light stream obtained at the top of the separator is divided into a first column feed fraction, which is condensed before being sent to the top feed of the distillation column and to a second fraction which is sent to a feed. dynamic expansion turbine before being introduced into the distillation column.

This method has the advantage of being easy to start and offer significant operational flexibility, combined with good efficiency and good safety.

However, the economic constraints require to further increase the efficiency of the process while maintaining a very high ethane extraction yield. It is also necessary to minimize the size of the installations and to reduce or even eliminate the supply of external refrigerants such as propane, especially for the implementation of the process on floating installations or in sensitive areas in terms of security.

An object of the invention is therefore to obtain a production process which makes it possible to separate a feed stream containing hydrocarbons in a stream rich in C ₂ ⁺ hydrocarbons and in a stream rich in methane, very economically, compact and very efficient.

For this purpose, the subject of the invention is a method according to claim 1.

• la température de la partie de la deuxième fraction du courant d'alimentation introduite dans la deuxième turbine de détente dynamique est supérieure à la température de la fraction d'alimentation de turbine introduite dans la première turbine de détente dynamique ;

The method according to the invention may comprise one or more of the features of claims 2 to 13 or the following characteristic:

• the temperature of the portion of the second fraction of the feed stream introduced into the second dynamic expansion turbine is greater than the temperature of the turbine feed fraction introduced into the first dynamic expansion turbine;

The invention further relates to a plant for producing a methane-rich stream and a stream rich in C ₂ ⁺ hydrocarbons from a feed stream containing hydrocarbons according to claim 14.

The plant according to the invention may comprise the feature of claim 15.

• la Figure 1 est un schéma synoptique fonctionnel d'une première installation de production destinée à la mise en oeuvre d'un premier procédé selon l'invention ;
• la Figure 2 est un schéma synoptique fonctionnel d'une deuxième installation de production destinée à la mise en oeuvre d'un deuxième procédé selon l'invention ;
• la Figure 3 est un schéma synoptique fonctionnel d'une troisième installation de production destinée à la mise en oeuvre d'un cinquième procédé selon l'invention ;
• la Figure 4 est un schéma synoptique fonctionnel d'une quatrième installation de production destinée à la mise en oeuvre d'un sixième procédé selon l'invention ;
• la Figure 5 est un schéma synoptique fonctionnel d'une cinquième installation de production destinée à la mise en oeuvre d'un septième procédé selon l'invention ;
• la Figure 6 est un schéma synoptique fonctionnel d'une sixième installation de production destinée à la mise en oeuvre d'un huitième procédé selon l'invention.

The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, in which:

• the Figure 1 is a functional block diagram of a first production facility for carrying out a first method according to the invention;
• the Figure 2 is a functional block diagram of a second production facility for carrying out a second method according to the invention;
• the Figure 3 is a functional block diagram of a third production facility for carrying out a fifth method according to the invention;
• the Figure 4 is a functional block diagram of a fourth production facility for carrying out a sixth method according to the invention;
• the Figure 5 is a functional block diagram of a fifth production facility for carrying out a seventh method according to the invention;
• the Figure 6 is a functional block diagram of a sixth production facility for carrying out an eighth method according to the invention.

In all that follows, we will designate by the same references a current flowing in a pipe and the pipe that carries it.

In addition, unless otherwise indicated, the percentages mentioned are molar percentages and the pressures are given in absolute bar.

In the numerically simulated examples, the efficiency of each compressor is selected to be 82% polytropic and the efficiency of each turbine is 85% adiabatic.

Similarly, the described distillation columns use trays but they can also use loose packing or structured. A combination of trays and packing is also possible. The additional turbines described involve compressors but they can also cause variable frequency electric generators whose electricity produced can be used in the network via a frequency converter. Currents with a temperature above ambient are described as being cooled by aero-refrigerants. Alternatively, it is possible to use water exchangers for example freshwater or seawater.

The Figure 1 illustrates a first plant 10 for producing a stream 12 rich in methane and a section 14 rich in C ₂ ⁺ hydrocarbons according to the invention, from a gas stream 16 supply.

The gaseous stream 16 is a stream of natural gas, a stream of refinery gas, or a stream of synthetic gas obtained from a hydrocarbon source such as coal, crude oil, naphtha. In the example shown in the figures, stream 16 is a stream of dehydrated natural gas.

The method and the installation 10 are advantageously applied to the construction of a new unit for recovering methane and ethane.

The plant 10 comprises, from upstream to downstream, a first heat exchanger 20, a first separator tank 22 and a first dynamic expansion turbine 26, capable of producing work during the expansion of a current passing through the turbine .

According to the invention, the installation 10 further comprises a second heat exchanger 28, a first distillation column 30, a first compressor 32 coupled to the first dynamic expansion turbine 26, a first refrigerant 34, a second compressor 36, a second refrigerant 38, and a bottom pump 39.

According to the invention, the installation 10 further comprises a second dynamic expansion turbine 40 and a third compressor 41 coupled to the second dynamic expansion turbine 40.

A first production method according to the invention, implemented in the installation 10 will now be described.

By way of example, the feed stream 16 is formed of a dehydrated natural gas which comprises, in moles, 2.06% of nitrogen, 83.97% of methane, 6.31% of ethane, 66% propane, 0.70% isobutane, 1.50% n-butane, 0.45% isopentane, 0.83% n-pentane and 0.51% carbon dioxide.

The feed stream 16 has more generally in mol between 5% and 15% of C ₂ ⁺ hydrocarbons to be extracted and between 75% and 90% of methane.

The term "dehydrated gas" means a gas whose water content is as low as possible and is especially less than 1 ppm.

The feed stream 16 has a pressure greater than 35 bar, in particular greater than 50 bar and a temperature close to ambient temperature and in particular substantially equal to 30 ° C. In this example, the flow rate of the feed stream is 15,000 kmol / hour.

The feed stream 16 is first divided into a first feed stream fraction 41A and a second feed stream fraction 41B.

The ratio of the molar flow rate of the first fraction 41A to the second fraction 41B is, for example, greater than 2 and is in particular between 2 and 15.

In the example shown, the first fraction 41A is introduced into the first heat exchanger 20 where it is cooled and partially condensed to form a fraction 42 of cooled feed stream.

The temperature of the fraction 42 is below -10 ° C. and is in particular equal to -26.7 ° C. Then, the cooled fraction 42 is introduced into the first separating flask 22.

The liquid content of the cooled fraction 42 is less than 50 mol%.

A light head stream 44 and a heavy liquid bottom stream 45 are removed from the first separator tank 22.

In this example, the gas stream 44 is divided into a minor column feed fraction 46 and a major turbine feed fraction 48. The ratio of the molar flow rate of the majority fraction 48 to the minor fraction 46 is greater than 2.

The column feed fraction 46 is introduced into the second heat exchanger 28 to be fully liquefied and subcooled. It forms a cooled column feed fraction 49. This fraction 49 is expanded in a first static expansion valve 50 to form a expanded fraction 52 introduced into reflux in the first distillation column 30.

The temperature of the expanded fraction 52 obtained after passing through the valve 50 is below -70 ° C. and is in particular equal to -111 ° C.

The pressure of the expanded fraction 52 is also substantially equal to the operating pressure of the column 30 which is less than 40 bar and in particular between 10 bar and 30 bar, advantageously equal to 17 bar.

The fraction 52 is introduced into an upper part of the column 30 at a level N1, located at the first stage starting from the top of the column 30.

The turbine feed fraction 48 is introduced into the first dynamic expansion turbine 26. It is dynamically expanded to a pressure P1 close to the operating pressure of the column 30 to form a first relaxed feed fraction. 54 which has a temperature below -50 ° C, especially equal to -79 ° C.

The expansion of the feed fraction 48 in the first turbine 26 makes it possible to recover 3574 kW of energy which cool the fraction 48.

The first expanded fraction 54, which is the effluent from the first dynamic expansion turbine 26, constitutes a first cooled reflux stream 56.

The liquid content of the cooled reflux stream 56 is greater than 5 mol%.

The cooled reflux stream 56 is introduced into an average part of the column 30 located under the upper part, at a level N2 below the level N1, and corresponding in this example to the sixth stage starting from the top of the column 30.

The heavy liquid stream 45 recovered at the bottom of the first separator tank 22 is expanded in a second static expansion valve 58 to form a relaxed heavy stream 60.

The pressure of the expanded heavy stream 60 is less than 50 bars and is notably substantially equal to the pressure of the column 30. The temperature of the expanded heavy stream 60 is less than -30 ° C. and is notably substantially equal to -48 ° C.

The heavy liquid stream 45 is introduced entirely into the column 30 after expansion in the valve 58, without passing through the first heat exchanger 20. Thus, the heavy liquid stream 45 before it passes through the valve 58 and the expanded heavy stream 60 do not enter into a heat exchange relationship with the feed stream 16, nor with the fractions 41A, 41B of this feed stream 16.

In particular, the heavy current 45 does not pass into the heat exchanger 20 between the outlet of the balloon 22 and the inlet of the column 30.

A first reboiling stream 74 is taken near the bottom of the column 30 at a temperature greater than -3 ° C. and in particular substantially equal to 9.6 ° C., at a level N6 situated below the level N3, advantageously at the and a first stage starting from the top of the column 30.

The first stream 74 is brought to the first heat exchanger 20 where it is heated to a temperature above 3 ° C and in particular equal to 16.3 ° C before being returned to a level N7 corresponding to the twenty-second floor from the top of column 30.

A second reboil stream 76 is drawn at a level N8 above the N6 level and below the N3 level, advantageously at the seventeenth stage from the top of the column. The second reboiling stream 76 is introduced into the first heat exchanger 20 to be heated to a temperature above -8 ° C and in particular equal to -4.1 ° C. It is then returned to the column 30 at a level N9 located below the level N8 and above the level N6, advantageously at the eighteenth stage from the top of the column 30.

A third reboiling current 78 is taken at a level N10 located below the level N3 and above the level N8, advantageously at the thirteenth stage starting from the top of the column 30. The third reboiling current 78 is then brought to the first heat exchanger 20 where it is heated to a temperature above -30 ° C and in particular equal to -19 ° C before being returned to a level N11 of the column 30 located below the N10 level and located above from level N8, advantageously to the fourteenth stage from the top of column 30.

Thus, the stream 52 is introduced into the upper part of the column 30 which extends from a height greater than 35% of the height of the column 30, whereas the stream 60 is introduced into an average part which is extends under the upper part.

The column 30 produces at the bottom a liquid stream 82 of the bottom of the column. The bottom stream 82 has a temperature above 4 ° C. and in particular equal to 16.3 ° C.

Thus, the bottom stream 82 contains in mol 1.17% carbon dioxide, 0.00% nitrogen, 0.43% methane, 42.89% ethane, 28.40% propane, 51% i-butane, 11.66% n-butane, 3.47% i-pentane, 6.46% n-pentane.

More generally, the stream 82 has a C ₁ / C ₂ ratio of less than 3 mol%, for example equal to 1%.

The stream 82 contains more than 80%, advantageously more than 87 mol% of the ethane contained in the feed stream 16 and contains substantially 100 mol% of the C ₃ ⁺ hydrocarbons contained in the feed stream 16 .

The column bottom stream 82 is pumped into the pump 39 to form the C ₂ ⁺ hydrocarbon rich section 14.

It can be advantageously heated by placing in heat exchange relation with at least a fraction of the feed stream 16 to a temperature below its bubble temperature, to maintain it in liquid form.

The column 30 produces at the top a gaseous stream 84 of column head rich in methane. The stream 84 has a temperature below -70 ° C and in particular substantially equal to -105 ° C. It has a pressure substantially equal to the pressure of the column 30, for example equal to 17.0 bar.

The overhead stream 84 is successively introduced into the second heat exchanger 28, then into the first heat exchanger 20 to be reheated and form a heated head stream 86 rich in methane. Current 86 has a temperature above -10 ° C and in particular equal to 22.9 ° C.

At the outlet of the first exchanger 20, the stream 86 is divided into a first fraction of the heated overhead stream 87A and a second fraction of the heated overhead stream 87B.

The ratio of the molar flow rate of the first fraction 87A to the molar flow rate of the second fraction 87B is greater than 2 and is for example between 2 and 5, for example.

The first fraction 87A is introduced into the first compressor 32 driven by the main turbine 26 to be compressed at a pressure greater than 20 bar.

The second fraction 87B is introduced into the third compressor 41 to be compressed at a pressure greater than 20 bar and substantially equal to the pressure at which the first fraction 87A is compressed in the first compressor 32.

Then, the compressed fractions 87A, 87B respectively from the compressors 32, 41 are combined before being introduced into the first air cooler 34. The combined fractions 87A, 87B are cooled to a temperature below 60 ° C, in particular Room temperature.

The compressed stream 88 thus obtained is introduced into the second compressor 36 and then into the second refrigerant 38 to form a compressed head stream 90.

The current 90 thus has a pressure greater than 40 bars and in particular substantially equal to 63.1 bars.

The compressed overhead stream 90 forms the methane-rich stream 12 produced by the process of the invention.

Its composition is advantageously 96.28 mol% of methane, 2.37 mol% of nitrogen and 0.92 mol% of ethane. It comprises more than 99.93% of the methane contained in the feed stream 16 and less than 5% of the C ₂ ⁺ hydrocarbons contained in the feed stream 16.

The second fraction 41B of the feed stream 16 is introduced into the second dynamic expansion turbine 40 to be expanded at a second pressure P2 substantially equal to the pressure of the column 30 and thus form a second relaxed feed fraction 91A.

The temperature of the second fraction 41B supplying the second dynamic expansion turbine 40 is greater than the temperature of the turbine feed fraction 48 supplying the first dynamic expansion turbine 26, for example at least 30 ° C.

Moreover, the second pressure P2 is substantially equal to the first pressure P1. The difference between the pressure P1 and the pressure P2 is less than 8 bar, advantageously less than 5 bar and in particular less than 2 bar.

The second fraction 91A relaxed thus has a temperature below 0 ° C and in particular of the order of - 25 ° C.

Then, the second fraction 91A is introduced into the second heat exchanger 28 to be cooled to a temperature below -70 ° C and in particular equal to -102.5 ° C and to be partially condensed, by heat exchange with the current 84 and optionally, with the column feed fraction 46, when present.

The second expanded fraction 91B from the second heat exchanger 28 forms a second reflux stream which is conveyed to the column 30 to be introduced into the upper part at a level N12 situated for example between the level N1 and the level N2, fourth floor from the top of the column.

Examples of temperatures, pressures, and molar flow rates of the different streams are given in Table 1 below. <u> TABLE 1 </ u> Current Temperature Pressure Debit (° C) (bara) (kmol / h) 12,90 40.0 63.1 13074 82 16.3 17.2 1926 16 30.0 62.0 15000 41A 30.0 62.0 12500 41B 30.0 62.0 2500 42 -26.7 61.0 12500 44 -26.7 61.0 11195 45 -26.7 61.0 1305 46 -26.7 61.0 2460 48 -26.7 61.0 8735 49 -102.8 60.0 2460 52 -111.2 17.2 2460 54, 56 -78.6 17.2 8735 60 -48.2 17.2 1305 84 -104.8 17.0 13074 86 22.9 16.0 13074 87A 22.9 16.0 9387 87B 22.9 16.0 3687 88 40.0 24.3 13074 91A -25.5 18.2 2500 91B -102.5 17.2 2500

Table 2 below illustrates the power consumed by the compressor 36 as a function of the flow rate of the second fraction 41B sent to the second turbine 40. <u> TABLE 2 </ u> Recovery of ethane (% moles) Flow to turbine 40 (kmol / h) Turbine power 26 (kW) Turbine power 40 (kW) Compressor power 36 (kW) 87,20 0 4381 0 14111 87,20 1600 3974 923 12996 87,20 2500 3574 1405 12244

The energy consumption of the method according to the invention, constituted by the drive energy of the second compressor 36, is 12244 kW, compared with 14111 kW with a method of the state of the art according to the invention. US 4,157,904 or US 4,278,457 wherein the same charge rate to be processed is used and the same recovery is achieved.

Compared with the state of the art, the method according to the invention thus makes it possible to obtain a significant reduction in the power consumed, while maintaining a high selectivity for the extraction of ethane.

A second installation 110 according to the invention is represented on the Figure 2 . This installation 110 is intended for the implementation of a second method according to the invention.

The second method differs from the first method in that a withdrawal stream 92 is taken from the compressed top stream 90.

The withdrawal stream 92 has a non-zero molar flow rate between 0% and 35% of the molar flow rate of the compressed head stream 90 upstream of the sample, the remainder of the compressed head stream 90 forming the stream 12.

The withdrawal stream 92 is successively cooled in the first exchanger 20, then in the second exchanger 28, before being expanded in a third static expansion valve 94.

The current 96, which before expansion in the valve 94, is essentially liquid, has after expansion a liquid fraction greater than 0.8.

The expanded withdrawal stream 96 coming from the third valve 94 is then introduced in reflux in the vicinity of the head of the column 30 at a level N14 located above the level N1 and advantageously corresponding to the first stage of the column 30.

The temperature of the expanded draw stream 96 prior to introduction into the column 30 is below -70 ° C and is preferably -113.5 ° C.

Examples of temperatures, pressures and molar flow rates of the different streams are given in Table 3 below. <u> TABLE 3 </ u> Current Temperature Pressure Debit (° C) (bara) (kmol / h) 12 40.0 63.1 12962 82 15.5 17.7 2038 16 30.0 62.0 15000 41A 30.0 62.0 13000 41B 30.0 62.0 2000 42 -26.0 61.0 13000 44 -26.0 61.0 11676 45 -26.0 61.0 1324 46 -26.0 61.0 1865 48 -26.0 61.0 9811 49 -108.7 60.0 1865 52 -111.2 17.7 1865 54, 56 -76.9 17.7 9811 60 -46.9 17.7 1324 84 -110.7 17.5 14786 86 25.1 16.5 14786 87A 25.1 16.5 11566 87B 25.1 16.5 3220 88 40.0 24.0 14786 90 40.0 63.1 14786 91A -24.4 18.7 2000 91B -105.0 17.7 2000 92 40.0 63.1 1824 96 -113.5 17.7 1824

In a variant (not shown), the second compressor 36 may comprise two compression stages separated by an air cooler.

The power consumed by the compressor 36 (single-stage) as a function of the flow rate of the second fraction of the supply current 41B is given in Table 4 below. <u> TABLE 4 </ u> Ethane recovery Flow to the turbine 40 Power of the turbine 26 Power of the turbine 40 Compressor Power 36 % mole kmol / h kW kW kW 99,00 0 4421 0 15416 99,00 1000 4235 546 14510 99,00 1700 4051 928 14202 99,00 2000 3951 1100 14105 99,00 2500 3738 1415 14121

The second method according to the invention thus makes it possible to obtain extremely high ethane recovery rates, greater than 90%, and especially greater than 99%. This almost total recovery of the ethane contained in the feed stream 16 can be obtained as in the process described in US5,568,737 , but with a saving in terms of power consumption that can be greater than 8%, of the order of 1300 kW.

A third installation 170 according to the invention is represented on the Figure 3 .

The third installation 170 is intended for the implementation of a third method according to the invention.

The third method according to the invention differs from the first method according to the invention in that the relaxed feed fraction 54 intended for the column 30 is introduced at least partially into the second heat exchanger 28 to be placed in an exchange relationship. thermal with the gaseous stream 84 of methane-rich column head, with the second relaxed feed fraction 91A from the second dynamic expansion turbine 40, and advantageously with the column feed fraction 46, when it is present.

The fraction 54 is thus cooled to a temperature below -60 ° C, and in particular substantially equal to -84 ° C. It is at least partially condensed to form the cooled first reflux stream 56.

The cooled reflux stream 56 is then introduced into the middle portion of the column 30 at the N2 level, as previously described.

A bypass may be provided to introduce a portion of the expanded fraction 54 into the column 30 without passing through the exchanger 28.

Examples of temperatures, pressures and molar flow rates of the different streams are given in Table 5 below. <u> TABLE 5 </ u> Current Temperature Pressure Debit (° C) (bara) (kmol / h) 12,90 40.0 63.1 13071 82 17.4 17.7 1929 16 30.0 62.0 15000 41A 30.0 62.0 13340 41B 30.0 62.0 1560 42 -26.5 61.0 13440 44 -26.5 61.0 12049 45 -26.5 61.0 1391 46 -26.5 61.0 2328 48 -26.5 61.0 9721 49 -102.2 60.0 2328 52 -110.5 17.7 2328 54 -77.5 17.7 9721 56 -84.4 17.6 9721 60 -47.5 17.7 1391 84 -104.2 17.5 13071 86 24.3 16.5 13071 87A 24.3 16.5 10714 87B 24.3 16.5 2358 88 40.0 24.6 13071 91A -24.5 18.7 1560 91B -102.2 17.7 1560

A fourth installation 180 according to the invention is represented on the Figure 4 . The fourth installation 180 is intended for the implementation of a fourth method according to the invention.

The fourth method according to the invention differs from the third method according to the invention, represented on the Figure 3 in that a withdrawal stream 92 is taken from the compressed overhead stream 90, then passed successively into the first heat exchanger 20 and then into the second heat exchanger 28, as described in the second method according to the invention.

The fourth method according to the invention is moreover analogous to the third method according to the invention.

A fifth installation 210 according to the invention is represented on the Figure 5 . This fifth installation 210 is intended for the implementation of a fifth method according to the invention.

The fifth installation 210 is intended to advantageously increase the recovery of C ₂ ⁺ in an existing installation including the type described in the patents US 4,157,904 and US 4,278,457 .

The existing plant comprises the first heat exchanger 20, the first separator tank 22, the distillation column 30, the first compressor 32 coupled to the first expansion turbine 26 and the second compressor 36.

The fifth installation 210 according to the invention further comprises a second dynamic expansion turbine 40, a third compressor 41, and a downstream flask 152 for collecting the effluent from the second dynamic expansion turbine 40.

The plant 210 further comprises an upstream heat exchanger 212, a downstream heat exchanger 214, and an auxiliary distillation column 216 provided with a bottom auxiliary pump 218.

The fifth installation 210 also comprises a fourth compressor 220 interposed between two refrigerant 222A, 222B.

The fifth installation 210 further comprises a downstream flask 152, disposed downstream of the second turbine 40.

The fifth method according to the invention differs from the first method according to the invention in that the feed stream 16 is further separated into a third fraction 224 of the feed stream which is introduced into the upstream heat exchanger 212, before to be mixed with the first fraction 41A from the exchanger 20 to form the first fraction 42 cooled.

The ratio of the molar flow rate of the third fraction 224 to the molar flow rate of the feed stream 16 is greater than 5%.

Thus, the fifth method according to the invention differs from the first method according to the invention in that the second cooled and partially liquefied feed fraction 91A is introduced into the downstream flask 152.

This fraction 91A is separated in the downstream flask 152 into a second liquid foot stream 154 and into a second gaseous head stream 156.

The second liquid foot stream 154 is introduced into a fourth static expansion valve 157 to be substantially expanded under the pressure of the column 30 and form a second relaxed foot stream 158.

Unlike the first method according to the invention described above, the second head stream 156 coming from the downstream flask 152 is introduced into the downstream heat exchanger 214 to be cooled to a temperature below -70.degree. second cooled head stream 225.

The second cooled overhead stream 225 is introduced into the auxiliary column 216 at a lower stage E1.

Column 216 has a theoretical number of stages less than the number of theoretical stages of column 30. This number of stages is advantageously understood. between 1 and 7. The auxiliary column 216 operates at a pressure substantially equal to that of the column 30.

The relaxed foot stream 158 obtained after expansion of the second foot stream 154 in the valve 157 is introduced into the column 30 at a level N1 advantageously corresponding to the first stage from the top of the column 30.

A first portion 226 of the fraction 52 expanded in the valve 50 is introduced into the auxiliary column 216 at a stage E3 located above the level E1. A second portion 228 of the fraction 52 is introduced directly into the column 30 at the level N1, after mixing with the stream 158.

Auxiliary column 216 produces a methane-rich head auxiliary stream 230 and a foot auxiliary current 232.

The auxiliary head stream 230 is mixed with the methane-rich head stream 84 produced by the distillation column 30.

Foot stream 232 is pumped by auxiliary pump 218 to form a cooled reflux stream 234 which is introduced into column 30 after mixing with stream 158.

The stream 234 thus constitutes a cooled reflux stream which is obtained from a portion of the expanded fraction 91A resulting from the second dynamic expansion turbine 40, after separation of this effluent.

The mixture 235 of the overhead streams 84 and 230 is separated into a first major fraction 236 of the overhead stream and a second minor fraction 238 of the overhead stream.

The ratio of the molar flow rate of the majority fraction 236 to the minor fraction 238 is greater than 1.5.

The majority fraction 236 is introduced successively into the second heat exchanger 28, then into the first heat exchanger 20, in order to form the heated overhead stream 86.

The second overhead stream fraction 238 is passed through the downstream heat exchanger 214 countercurrently to the second overhead stream 156 to warm to a temperature above -50 ° C and form a second heated fraction 240. .

The second heated fraction 240 is then separated into a return stream 242, and a compression stream 244.

The return current 242 is reintroduced into the first head stream fraction 236, downstream of the second heat exchanger 28 and upstream of the first heat exchanger 20 to partially form the heated head stream 86.

The recompression stream 244 is then introduced into the upstream exchanger 212 to cool the third fraction of the feed stream 224. The stream 244 warms to a temperature above -10 ° C to form a warmed recompression stream 246 .

A first portion 248 of the recompression stream 246 is mixed with the first fraction of the overhead stream 86, downstream of the first heat exchanger 20 to form the heated overhead stream 87A.

A second portion 250 of the recompression stream 246 is introduced into the third compressor 41, then into the refrigerant 222A, before being recompressed in the fourth compressor 220 and introduced into the refrigerant 222B.

The second compressed portion 252 from the refrigerant 222B has a temperature below 60 ° C and in particular substantially equal to 40 ° C and a pressure greater than 35 bar and in particular equal to 63.1 bar.

This first compressed portion 252 is mixed with the compressed overhead stream 90 to form the methane-rich stream 12.

The fifth installation 210 and the fifth method according to the invention therefore make it possible to increase the C ₂ ⁺ hydrocarbon recovery rate in an existing state of the art installation, without having to modify the existing equipment of the plant. installation, and in particular by keeping the heat exchangers 20 and 28, the column 30, the compressors 32, 36 and the turbine 26 identical and using the entries already present on the column 30.

To preserve the existing equipment intact and improve the C ₂ ⁺ recovery, the pressure of the column 30 has been slightly decreased. Without countermeasure, this decrease would have resulted in the increase of the power of the compressor 36.

However, the addition of the compressor 220 overcomes this problem. In addition, the flow through the existing turbine 26 and its power have not been increased compared to the existing unit.

This installation nevertheless makes it possible to obtain, with an excellent yield, a recovery of ethane much higher than that observed in the state of the art.

A sixth installation 270 according to the invention is represented on the Figure 6 . This sixth installation 270 is intended for the implementation of a sixth method according to the invention.

The sixth method according to the invention differs from the fifth process according to the invention in that a withdrawal stream 92 is taken from the compressed methane-rich top stream 90, advantageously upstream of the point of introduction of the second compressed part. 252 in the current 90.

The withdrawal stream 92 is reintroduced into the column 30 at a head level N14. Unlike the fifth method according to the invention, the second portion 228 of the fraction 52 and the relaxed foot stream 158 are introduced into the column at a level N1 located below the N14 head level and above the N2 level.

The implementation of the sixth method according to the invention is moreover analogous to that of the fifth method according to the invention.

To maintain the C ₂ ⁺ recovery of the existing unit, the pressure of the column 30 is slightly decreased. The presence of the new compressor 220 makes it possible to keep the power of the second compressor 36 the same despite the increase in the flow rate of the feed stream 16.

In addition, the capacity of the first dynamic expansion turbine 26 has been kept constant. The second dynamic expansion turbine 40 is used to process the addition of capacity.

The presence of an auxiliary column 216 also prevents clogging of the column 30 during the flow increase.

The sixth installation according to the invention makes it possible to maintain an ethane recovery greater than or equal to 99%, a temperature and a pressure of the feed stream 16 that are substantially identical. Similarly, the losses of charges allocated in the equipment, the efficiency of the trays in the column 30 and the position of the withdrawals, the maximum methane specification of the bottom stream 82 of the column 30, the efficiencies of the turbines and the compressors, the power of the second compressor 36 and the existing turbine 26 and the heat exchange coefficients of the existing exchangers 20 and 28 are kept identical.

In a variant which is not covered by the present invention (shown in dotted lines on the Figure 1 ), which can be applied to each of the embodiments of the Figures 1 to 6 , the second fraction 41B of the feed stream is taken from the first exchanger 20 and not upstream of it. The second fraction 41B is thus partially cooled and is partially liquefied in the first heat exchanger 20.

The second fraction 41B issuing from the first heat exchanger 20 is then optionally introduced into an upstream separator tank 250. It is then separated in the upstream separator tank 250 in a second bottom liquid fraction 252 and in a second top gas fraction 254. The second bottom fraction 252 is expanded in a static expansion valve 256 to a pressure of less than 40 bar and substantially equal to the pressure of the column 30.

The second fraction of relaxed foot 258 is then introduced into the column 30, advantageously between the level N11 and the level N8.

The second head fraction 254 is introduced into the second dynamic expansion turbine 40 to form the second relaxed feed fraction 91A.

This arrangement with an upstream separator tank is also applicable in the case where the feed stream 16 contains a liquid fraction.

In another variant (not shown) of the embodiments of the Figures 2 , 4 and 6 , the installation comprises a bypass valve of a portion of the withdrawal stream 92 to divert this portion upstream of the first dynamic expansion turbine 26.

In this variant of the process, a supplementary cooling stream is taken from the withdrawal stream obtained after passing through the first heat exchanger 20. The additional cooling stream is reintroduced upstream of the turbine 26, ie in the head stream 44, upstream of the balloon 22 in the cooled supply stream 42.

In another variant (not shown) of the embodiments of the Figures 1 to 6 , the installation comprises a plurality of second exchangers 28, each being intended to receive a fraction of the overhead stream 84 and another stream.

The overhead stream 84 is then divided into a plurality of fractions corresponding to the number of second exchangers 28.

Each second heat exchanger 28 can then put in heat exchange only two flows each including a fraction of the overhead stream 84 and respectively, the first relaxed feed fraction 54, the second relaxed feed fraction 91A, and if necessary, the fraction column supply 46 and / or the sampling stream 92.

In another variant (not shown) of the embodiments of the Figures 1 to 6 a reboil stream is withdrawn from the distillation column at a sampling level. The reboiling current is then put in heat exchange relation with at least a part of the second expanded fraction 91A resulting from the dynamic expansion turbine 40 and optionally with the first expanded fraction 54 coming from the first turbine 26.

This heat exchange connection can be performed within the second heat exchanger 28.

In yet another variant (not shown), an auxiliary expansion current is taken from the methane rich column head stream 86 from the first heat exchanger 20. This auxiliary expansion stream is introduced into a dynamic auxiliary expansion turbine, distinct from the first dynamic expansion turbine 26 and the second dynamic expansion turbine 40. The relaxed current from the auxiliary turbine is reintroduced into the methane-rich column head stream, before it passes through the first heat exchanger 20 to constitute a supplementary cooling stream of the first heat exchanger 20.

More generally, the entire head stream 44 from the first flask 22 can form the turbine feed fraction 48. The method according to the invention is then devoid of separation of the overhead stream 44.

Claims (15)

1. A method for producing a methane-rich stream (12) and a C₂ ⁺ hydrocarbon-rich stream (14) from a feed stream (16) containing hydrocarbons, the method comprising the following steps:

   - separating the feed stream (16) into a first fraction (41A) of the feed stream and at least one second fraction (41B) of the feed stream;

   - cooling the first fraction (41A) of the feed stream in a first heat exchanger (20);

   - injecting the first fraction of the cooled feed stream (42) in a first separating flask to produce a light head stream (44) and a heavy bottoms stream (45);

   - expanding a turbine feed fraction (48) formed from the light head stream (44) in a first dynamic expansion turbine (26) up to a first pressure (P1) and injecting at least part (56) of the first expanded fraction (54) coming from the first turbine (26) into a first distillation column (30);

   - expanding at least part of the heavy bottoms stream (45) to form an expanded bottoms stream (60) and injecting the expanded bottoms stream (60) into the first distillation column (30) without going through the first heat exchanger (20) between the first separating flask (22) and the first distillation column (30);

   - recovering a bottoms stream (82) at the bottom of the first distillation column (30), the C₂ ⁺ hydrocarbon-rich stream (14) being formed from the column stream (82);

   - recovering and heating a methane-rich overhead stream (84);

   - compressing at least one fraction of the overhead stream (84) in at least a first compressor (32) coupled to the first dynamic expansion turbine (26) and in at least one second compressor (36);

   - forming a methane-rich stream (12) from the heated and compressed overhead stream (90);

   the method comprising the following steps:

   - expanding at least part of the second fraction of the feed stream (41B) in a second dynamic expansion turbine (40), separate from the first dynamic expansion turbine (26), up to a second pressure, to form a second expanded fraction (91A) coming from the second dynamic expansion turbine (40),

   - cooling and at least partially liquefying at least part of the second expanded fraction (91A) coming from the second dynamic expansion turbine (40) to form a cooled reflux stream (91B; 160; 232) and inject the cooled reflux stream (91B; 160; 232) in the first distillation column (30);

   characterized in that the second pressure (P2) is substantially equal to the first pressure (P1) such that the pressure difference between the first pressure and the second pressure is less than 8 bars;
   and in that the entire second fraction of the feed stream (41B) is injected into the second dynamic expansion turbine (40), without cooling between the step for separating the feed stream (16) and the step for injecting the second fraction of the feed stream (41B) into the second dynamic expansion turbine (40).
2. The method according to claim 1, characterized in that it includes the injection of the first expanded fraction (54) from the first dynamic expansion turbine (26) into a second heat exchanger (28) to be cooled and partially liquefied therein, the first cooled expanded fraction forming an additional cooled reflux stream, the method including the injection of the additional cooled reflux stream (56) into the first distillation column (30).
3. The method according to any one of the preceding claims, characterized in that it comprises the following steps:

   - injecting the second expanded fraction (91A) coming from the second dynamic expansion turbine (40) into a downstream separating flask (152) to form a second gas head stream (156) and a second liquid bottoms stream (154),

   - cooling the second gas head stream (156) to form a cooled reflux stream.
4. The method according to any one of the preceding claims, characterized in that it comprises the following steps:

   - injecting at least part of the second expanded fraction (91A) from the second dynamic expansion turbine (26) into an auxiliary column (216), and

   - forming a cooled reflux stream from the bottoms stream (232) of the auxiliary column (216).
5. The method according to any one of claims 1 to 4, characterized in that it comprises the following steps:

   - removing a secondary compression fraction (87B) in the methane-rich overhead stream (86), before the passage of a fraction (87A) of the methane-rich overhead stream in the first compressor (32),

   - passage of the secondary fraction (87B) in a third compressor (41) coupled to the second dynamic expansion turbine (40);

   - injecting the compressed secondary fraction from the third compressor (41) into the fraction of the compressed overhead stream, downstream of the first compressor (32).
6. The method according to any one of the preceding claims, characterized in that the second compressor (36) comprises a first compression stage, at least one second compression stage, and a refrigerant inserted between the first compression stage and the second compression stage, the method including a step for passage of the compressed overhead stream (88) from the first compressor successively in the first compression stage, the refrigerant, then the second compression stage.
7. The method according to any one of the preceding claims, characterized in that at least part of the second expanded fraction (91A) from the second dynamic expansion turbine (40), at least one fraction of the overhead stream (84), and possibly the first expanded fraction (54) from the first dynamic expansion turbine (26), are placed in a heat exchange relationship.
8. The method according to any one of the preceding claims, characterized in that it comprises the following steps:

   - dividing the light head stream (44) into the turbine feed fraction (48) and a column feed fraction (46);

   - cooling and at least partially condensing the column feed fraction (46) in a second heat exchanger (28),

   - expanding and at least partially injecting the cooled column feed fraction into the first distillation column (30),

   at least part of the second expanded fraction (91A) from the second dynamic expansion turbine (40) and the column feed fraction (46) advantageously being placed in a heat exchange relationship.
9. The method according to claim 8, characterized in that at least a fraction (238) of the overhead stream (84) and at least one part of the second expanded fraction (91A) from the second dynamic expansion turbine are placed in a heat exchange relationship in a downstream heat exchanger (214) separate from the second heat exchanger (28).
10. The method according to any one of the preceding claims, characterized in that it comprises the following steps:

    - removing a bleed stream (92) from the overhead stream (90);

    - cooling the bleed stream at least in the first heat exchanger (20) and injecting the cooled bleed stream (96) into the first distillation column (30); and

    - possibly, heat exchange of the bleed stream with at least part of the second expanded fraction (91A) from the second turbine (40).
11. The method according to any one of the preceding claims, characterized in that it comprises the following steps:

    - removing a reboiling stream (80) in the first distillation column (30) at a removal level;

    - putting the reboiling stream (80) in a heat exchange relationship with at least part of the second expanded fraction (91A) coming from the second dynamic expansion turbine (40) to cool and at least partially liquefy the part of the expanded second fraction (91A) coming from the second dynamic expansion turbine; and

    - possibly, placement in a heat exchange relationship with the first expanded fraction from the first turbine (26);

    - reinjecting the reboiling stream (80) into the first distillation column (30) at a level below the removal level.
12. The method according to any one of the preceding claims, characterized in that it comprises the following steps:

    - removing an extra cooling stream from the methane-rich overhead stream or from the stream formed from the methane-rich overhead stream (84, 86, 88, 90) or a stream (92) formed from the methane-rich overhead stream (84, 86, 88, 90);

    - expanding and injecting the expanded extra cooling stream into a stream (42, 48) circulating upstream of the first expansion turbine (26), advantageously in the first fraction of the cooled feed stream (42) or in the turbine feed fraction (48).
13. The method according to any one of the preceding claims, characterized in that it comprises the following steps:

    - passage of the methane-rich overhead stream (84) in the first heat exchanger (20);

    - removal of an auxiliary expansion stream in the methane-rich overhead stream (84), after its passage in the first heat exchanger (20);

    - dynamic expansion of the auxiliary expansion stream in an auxiliary dynamic expansion turbine;

    - injecting the expanded stream from the auxiliary dynamic expansion turbine into the methane-rich overhead stream, before its passage in the first heat exchanger (20).
14. An equipment for producing a methane-rich stream (12) and a C₂ ⁺ hydrocarbon-rich stream (14) from a feed stream (16) containing hydrocarbons, of the type comprising:

    - means for separating the feed stream (16) into a first fraction (41A) of the feed stream and at least one second fraction (41B) of the feed stream;

    - a first heat exchanger (20) to cool the first fraction (41A) of the feed stream;

    - means for injecting the first cooled feed fraction (42) into a first separating flask (22) to produce a light head stream (44) and a heavy bottoms stream (45);

    - a first dynamic expansion turbine (26) and means for injecting a turbine feed fraction (48) formed from the light head stream into the first dynamic expansion turbine (26) so as to expand the turbine feed fraction (48) up to a first pressure;

    - a first distillation column (30);

    - means for injecting at least part (56) of the first expanded fraction (54) into the first turbine (26) in the first distillation column (30);

    - means for expanding at least part of the heavy bottoms stream (45) to form an expanded bottoms stream and means for injecting at least part of the expanded bottoms stream (60) into the first distillation column (30), the means for injecting the expanded bottoms stream being configured so that the bottoms stream (45) does not pass through the first heat exchanger (20) between the first separating flask and the first distillation column (30);

    - means for recovering a bottoms stream (82) at the bottom of the first distillation column (30), the C₂ ⁺ hydrocarbon-rich stream (14) being formed from the bottoms stream (82);

    - means for recovering and heating a methane-rich overhead stream (84),

    - at least one first compressor (32) coupled to the first dynamic expansion turbine (26) and at least one second compressor (36) to compress at least one fraction of the overhead stream (84);

    - means for forming a methane-rich stream (12) from the heated and compressed overhead stream (90) from the second compressor (36);

    the equipment comprising :

    - a second dynamic expansion turbine (40), separate from the first dynamic expansion turbine (26),

    - means for injecting at least part of the second fraction of the feed stream (41B) into the second dynamic expansion turbine (40) to form a second expanded fraction (91A) from the second dynamic expansion turbine (40) at a second pressure; and

    - means for cooling and at least partially liquefying at least part of the second fraction (91A) from the second dynamic expansion turbine (40) to form a cooled reflux stream (91B; 160; 232) and means for injecting the cooled reflux stream (91B; 160; 232) into the first distillation column (30),

    characterized in that the second dynamic expansion turbine is arranged so that the second pressure is substantially equal to the first pressure such that the pressure difference between the first pressure and the second pressure is less than 8 bars;
    and in that the installation (10) is configured such that the entire second fraction of the feed stream (41B) is injected into the second dynamic expansion turbine (40), without cooling between the step for separating the feed stream (16) and the step for injecting the second fraction of the feed stream (41B) into the second dynamic expansion turbine (40).
15. The equipment according to claim 14, characterized in that it comprises:

    - an auxiliary column (216);

    - means for injecting at least part of the second expanded fraction (91A) from the second dynamic expansion turbine (26) into the auxiliary column (216); and

    - means for forming the cooled reflux stream from the bottoms stream (232) of the auxiliary column (216).

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