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EP0783031B1 - Process for the dewatering, deactification and degasolination of natural gas, using a mixture of solvents - Google Patents

Process for the dewatering, deactification and degasolination of natural gas, using a mixture of solvents Download PDF

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Publication number
EP0783031B1
EP0783031B1 EP96402909A EP96402909A EP0783031B1 EP 0783031 B1 EP0783031 B1 EP 0783031B1 EP 96402909 A EP96402909 A EP 96402909A EP 96402909 A EP96402909 A EP 96402909A EP 0783031 B1 EP0783031 B1 EP 0783031B1
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EP
European Patent Office
Prior art keywords
stage
mixture
methanol
solvents
column
Prior art date
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EP96402909A
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German (de)
French (fr)
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EP0783031A1 (en
Inventor
Alexandre Rojey
Etienne Lebas
Joseph Larue
Ari Minkkinen
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IFP Energies Nouvelles IFPEN
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IFP Energies Nouvelles IFPEN
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C10L3/101—Removal of contaminants
    • C10L3/102—Removal of contaminants of acid contaminants
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas

Definitions

  • the invention relates to a method for dehydration and / or gas degassing natural, using a mixture of solvents.
  • the treatment of a natural gas requires dehydration, degassing, when natural gas contains condensable hydrocarbons and the deacidification of this gas when the proportion of acid gases it contains is too high.
  • the present invention also makes it possible to recover the methanol contained in the gas by a simple and economical way.
  • the heavy solvent can for example be a polar solvent such as dimethylformamide (DMF), N-methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO).
  • the heavy solvent can also be a chemical solvent such as example a secondary or tertiary amine, for example hydroxylated.
  • methanol makes it possible in particular to very significantly reduce the level of solvent for relatively large contents of acid gases in the gas to be treated.
  • the presence of methanol also makes it possible to absorb and separate from the gas to be treated impurities such as, for example, mercaptans, carbonyl sulfide (COS) and carbon disulfide (CS 2 ).
  • the gas to be treated arrives via line 1. It contains for example methane, ethane, propane, butane, as well as heavier hydrocarbons, water and acid gases such as for example H 2 S and CO 2 .
  • a fraction of this gas is sent through line 2 to the contact column C1, in which it is brought into counter-current contact with a solution of methanol in water arriving via line 3.
  • the via line 40 an aqueous phase substantially free of methanol.
  • a gas loaded with methanol is recovered via line 4 which is mixed with the gas which has not passed through column C1.
  • Gas as well obtained is the gas loaded with methanol from step (a).
  • This gas is then sent by line 6 in column C2, in which it is contacted with a mixture of solvents, including methanol, water and a more solvent heavy than methanol, which arrives via line 7.
  • This mixture of solvents emerges by the conduit 8 charged with acid gases, while the gas evacuated at the head of the column through line 9 is at least partially rid of the acid gases it contains at entry in column C2 (step (b)).
  • the mixture of solvents from this step (b) is first expanded to a intermediate pressure through the expansion valve V1 releasing a phase gas which contains at least some of the hydrocarbons that may have been coabsorbed in the solvent mixture.
  • the gas phase and the liquid phase thus obtained are separated in flask B1.
  • the additional flow rate of aqueous phase thus provided can be controlled for example to a level of solvent mixture in a recipe or storage tank located for example at the output of column D1.
  • the gas phase is evacuated at the head of the balloon B1.
  • the residual solvent mixture is evacuated through line 10 and passes into the exchanger E1, in which it is warmed up. It is then expanded through the valve V2 and regenerated in the column distillation D1.
  • This column is cooled at the head, which makes it possible to evacuate by the conduit 11 of the acid gases relatively little loaded with solvent and heated in bottom, which allows a mixture of solvents to be discharged through line 12 substantially free of acid gases.
  • the acid gases evacuated by the conduit 11 undergo additional refrigeration in the exchanger E5, to recover at least partially the residual methanol.
  • the liquid phase thus obtained is collected in the separator flask B20, which also receives back-up from aqueous phase arriving via line 42 and passing through the expansion valve V40.
  • the liquid phase thus collected in the separator flask B20 is recycled by the pump P12 through the conduit 43 at the head of the column C2.
  • the mixture of solvents discharged through line 12 is taken up by pump P1 and sent through exchanger E1, in which it is cooled by heating the mixture of solvents which arrives via the conduit 10. It is then cooled in the exchanger E2 by exchange with water or cooling air and recycled to column C2.
  • step (b) which is evacuated through line 9 receives a top-up methanol arriving via line 13. It is then cooled, first by exchange internally in the E3 exchanger, then by exchange with a refrigeration fluid external from a refrigeration circuit, in the exchanger E4. This refrigeration condenses a methanol solution and a phase liquid hydrocarbon.
  • the gas phase thus obtained constitutes the treated gas which is substantially free of water, acid gases and hydrocarbons heavy it contains at the start.
  • the three-phase mixture obtained is separated in the balloon B2.
  • the treated gas passes through the exchanger E3, in which it is heated in cooling the gas arriving from column C2 and it is evacuated through line 14.
  • the liquid hydrocarbon phase obtained is discharged through line 15 and the fraction of the aqueous phase containing methanol obtained which is not removed by the conduit 42 is recycled by pump P2 through conduit 41 to column C1.
  • the mixture of solvents sent via line 7 comprises methanol, water and a heavier solvent than methanol.
  • the methanol content of the gas discharged through line 9 must be sufficiently high to prevent the formation of ice and / or hydrates during the stage refrigeration, the addition of methanol arriving through line 13 being reduced and intended to compensate for losses. This means that this methanol content is the higher the refrigeration temperature at the outlet of the exchanger E4 is low.
  • the methanol content in the solvent mixture arriving through the conduit 7 is also higher as the temperature at which the gas is refrigerated is low.
  • the methanol content can be easily regulated by the addition of methanol arriving via line 13.
  • the make-up quantity is for example controlled the methanol content in the aqueous phase collected in the separator B2 so as to reach the content required to avoid the formation of hydrates.
  • the methanol content in the solvent mixture can be in this case for example between 5 and 50% in molar fraction.
  • the heavy solvent which enters into the composition of the mixture of solvents can be a polar solvent such as for example DMF, NMP, DMSO, as described upper; it can also be, sulfolane, propylene carbonate, an alcohol heavier than methanol, an ether or a ketone.
  • a polar solvent such as for example DMF, NMP, DMSO, as described upper; it can also be, sulfolane, propylene carbonate, an alcohol heavier than methanol, an ether or a ketone.
  • the main condition to respect is that its boiling point is higher than the temperature methanol boiling point and preferably above the boiling point some water. It is also necessary that this solvent is at least partially miscible with water and methanol.
  • the heavy solvent content in the solvent mixture may be in this case for example between 10 and 60% in molar fraction.
  • the water content forms the complement but it is preferably at least equal at 10% in molar fraction.
  • the heavy solvent which enters into the composition of the mixture of solvents can be also a chemical type solvent such as for example a secondary amine or tertiary, generally hydroxylated, chosen for example from monoethanolamine, diethanolamine, diglycolamine, diisopropanolamine, methyldiethanolamine.
  • a chemical type solvent such as for example a secondary amine or tertiary, generally hydroxylated, chosen for example from monoethanolamine, diethanolamine, diglycolamine, diisopropanolamine, methyldiethanolamine.
  • the amine content in the mixture of solvents can be understood for example between 1 and 10% in molar fraction.
  • the heavy solvent is selected according to the specifications required for the treated gas. If selective deacidification is sought, consisting in eliminating H 2 S much more selectively than CO 2 , a selective amine such as for example methyldiethanolamine will be used.
  • additives known to a person skilled in the art, such as for example additives making it possible to activate the absorption of CO 2 , or additives acting as corrosion inhibitors, or else additives acting as anti-foaming agents. It may also be advantageous to filter the mixture of solvents which is sent to column C2, in order to stop the solid particles which can promote foaming.
  • step (d) allows an aqueous phase to be removed from the bottom of said column substantially free of methanol. This allows you to recover and easily recycle methanol and avoid any pollution linked to the presence of methanol in the released aqueous phase.
  • the contact column used can be of different types known to those skilled in the art. the art: with trays or with filling. In the case of a packed column, it can be advantageous to use structured packing.
  • the other columns used in the process can be of different known types skilled in the art: with trays or with padding and in particular with padding structure.
  • composition of natural gas is for example the following (in kg / h): Water 60.55 Nitrogen 782.37 Carbon dioxide 8770.15 Methane 31,699.87 Ethane 5210.67 Propane 3,088.88 Isobutane 625.43 N-butane 1024.58 Isopentane 330.39 N-pentane 297.37 N-hexane 118.29 N-heptane 343.99 Total 52352.54
  • the gas to be treated arrives through line 1 at a temperature of 30 ° C and at a pressure of 70 bars with a flow rate substantially equal to 52352 kg / h.
  • a fraction of this gas (50%) is injected into the contact column C1 through line 2.
  • a solution containing 65% by mass of methanol in water, at a flow rate of 159 kg / h and at a temperature of 30 ° C, is injected against the current into column C1 by the line 3.
  • a phase is eliminated through line 40 aqueous containing 12 ppm mass of methanol at a flow rate of 60 kg / h.
  • the gas loaded with methanol is evacuated via line 4 and mixed with gas which has not passed through column C1 and which arrives via line 5.
  • the gas thus obtained is sent via line 6 to column C2.
  • a solution containing 20% by mass of methanol and 20% by mass of diethanolamine in water is injected against the current into column C2 through line 7 at temperature 40 ° C with a flow rate of 117409 kg / h.
  • the mixture of solvents loaded with carbon dioxide is recovered through line 8 to the temperature of 46 ° C.
  • the gas evacuated at the head of column C2 via line 9 now contains only 1.8 % mass of carbon dioxide.
  • This gas is cooled in the E3 exchangers and E4 at a temperature of -26 ° C.
  • the three-phase mixture obtained is separated in the balloon B2.
  • the treated gas, discharged through line 14, has a flow rate of 44,889 kg / h.
  • the liquid hydrocarbon phase obtained is discharged through line 15.
  • the phase aqueous containing methanol is partially recycled in column C1 by conduit 41, the other part (75%) being sent to balloon B20.
  • the solvent mixture loaded with carbon dioxide is expanded to a pressure 10 bar via the expansion valve V1, then sent to the separation tank B1.
  • the liquid phase from balloon B1 is sent through line 10 into the exchanger E1, where it is heated to a temperature of 60 ° C.
  • she is expanded to a pressure of 1.5 bar and injected into the distillation column D1.
  • This column is cooled at the head to a temperature of 40 ° C. and heated at the bottom.
  • the mixture of solvents recovered by line 12 at a temperature of approximately 80 ° C is taken up by the pump P1, then is cooled in the exchangers E1 and E2 before being recycled in column C2.
  • the gas evacuated at the head of column D1 via line 11 is cooled to -26 ° C after its passage through the E5 exchanger.
  • Balloon B20 allows a phase to be separated liquid containing mainly methanol and water and a gas phase essentially containing carbon dioxide.
  • the aqueous phase is recycled in column C2 via line 43.
  • the gas phase is evacuated through the conduit 23.
  • step (b) it can be advantageous to optimize the performance of the process, to perform step (b) by putting the gas successively in contact with fractions of mixtures of solvents of compositions different. If a fraction of the mixture is sent at the top and another in a intermediate point, it is advantageous to send a fraction of the mixture of solvents relatively poor in methanol and send to an intermediate point a fraction of the solvent mixture relatively rich in methanol.
  • the gas loaded with methanol arrives via line 6 in column C2. He is everything first brought into contact in a first zone (lower part) of the column C2 with a fraction of solvent mixture relatively rich in methanol introduced through conduit 16.
  • the methanol content in this first fraction of mixture of solvents can be for example between 20 and 70% in fraction molar.
  • the gas is then brought into contact in a second zone (upper part) of column C2 with a fraction of the solvent mixture relatively low in methanol introduced via line 7.
  • the methanol content in this second fraction of the solvent mixture can be for example between 5 and 30% in molar fraction. This methanol content must be all the higher as the methanol content in the gas leaving via line 9 is high, that is to say the higher the lower the temperature at the outlet of the exchanger E4, this to avoid the formation of ice and / or hydrates.
  • step (b) The mixture of solvents from step (b), that is to say in the case of the example described in relation to FIG. 2a leaving column C2 by the line 8, is regenerated by expansion then by heating in a column of counter-current contact D1, the solvent phase taken from the bottom of said column forming the fraction of the solvent mixture relatively poor in methanol which is injected at the head of the contact column used during step (b), that is to say column C2 in the case of the example described in relation to FIG. 2a.
  • the mixture of solvents charged with acid gases exiting through the conduit 8 is first expanded to an intermediate pressure level through the valve V1, releasing a gaseous phase which contains at least part of the hydrocarbons which could be coabsorbed in the solvent mixture.
  • This gas phase can be washed with a fraction of a mixture of solvents relatively poor in methanol, the flow rate of which is controlled by the distribution valve V30 and which is sent via line 17 at the head of a counter-current contact section located in column element C10.
  • the gas which leaves the head of the column element C10 is thus substantially freed from the acid gases which it contained and can for example serve as fuel-gas or else be recompressed and mixed with the treated gas.
  • step (b) it is possible to subject the mixture of solvents from step (b) a first step of expansion at an intermediate pressure to release at least part of the hydrocarbons coabsorbed.
  • step (c) it is also possible to wash the gas fraction from the expansion at an intermediate pressure of the mixture of solvents from step (b), by a fraction of the mixture of solvents relatively poor in methanol collected at the bottom of the regeneration column used during step (c).
  • the mixture of solvents is expanded to again to a low pressure, for example a pressure close to the atmospheric pressure, through the expansion valve V20.
  • the liquid-vapor mixture thus obtained is separated in the separator flask B10.
  • the vapor phase formed essentially of acid gases and methane is evacuated through the conduit 18.
  • the liquid phase thus obtained is split into two fractions.
  • a first fraction, preferably the largest in flow, is taken up by the pump P11 at through conduit 20 and forms most of the mixing fraction of solvents relatively rich in methanol which is sent via line 16 in one intermediate point of column C2.
  • a second fraction of the solvent mixture obtained at the outlet of the flask separator B10 is heated in the exchanger E1, by heat exchange with the mixture of solvents from the bottom of column D1, then sent to the distillation column D1.
  • Steam reflux is generated at the bottom of column D1 by means of reboiler R1 and a liquid reflux is generated at the top of the column D1 by means of the condenser E6.
  • the gas phase resulting from partial condensation in E6 and which is evacuated at the head via line 19 is formed essentially of acid gases and methanol.
  • the gas mixture thus obtained is refrigerated in the exchanger E5.
  • the liquid-vapor mixture thus obtained is separated in the separator flask B20.
  • a make-up of aqueous phase feeds the flask B20 through the conduit 42 and through the expansion valve V40.
  • the gas phase formed essentially separate acid gases are evacuated through line 23.
  • the liquid phase rich in methanol is taken up by pump P12 through line 22 and, after mixing with the fraction arriving via line 20, forms the fraction of solvent mixture which is sent to an intermediate point in column C2.
  • the liquid phase discharged at the bottom of column D1 is taken up by pump P10. It is cooled in the exchanger E1, from which it emerges through the conduit 21. It is then divided into two fractions by means of the distribution valve V30. A first fraction, the largest in flow is cooled in the exchanger E2 by water or cooling air and sent to the top of column C2 by the conduit 7. A second fraction is sent via conduit 17 at the head of column element C10.
  • the gas to be treated contains a large proportion of CO 2 and of H 2 S, it may be desirable to obtain separate fractions of acid gases, respectively rich in CO 2 and in H 2 S.
  • the gaseous fraction relatively rich in CO 2 which is obtained after the expansion of the mixture of solvents through the expansion valve V20 is sent to the column element C11, in which it is brought into contact with a part a mixture of solvents relatively poor in methanol arriving via line 21, to selectively eliminate the H 2 S present in the gas.
  • the mixture of solvents arriving via line 21 is divided into two fractions by passage through the distribution valve V40. A first fraction is sent through the conduit 24 at the head of the column element C11. A second fraction is sent via line 25 to the head of column C2.
  • the mixture of solvents collected at the bottom of the column element C11 and arriving by the pump P11 and the line 20 is mixed with the liquid fraction arriving by the line 22.
  • the resulting mixture of solvents is sent to an intermediate point of the column C2.
  • the gaseous fractions discharged through the conduits 18 and 19 respectively constituting the fractions rich in CO 2 and in H 2 S are not mixed and can undergo separately a complementary treatment, for example by refrigeration, to eliminate at least in part methanol entrained with acid gases.
  • Another arrangement that can be used is, instead of refrigerating directly the acid gases arriving through line 18, through line 19 or after mixture of these two fractions, to send these acid gases into an element of rectification column according to the example of arrangement of FIG. 4.
  • Acid gases containing methanol obtained by mixing the fractions gas arriving through lines 18 and 19 are sent to the column element C20.
  • the gas fraction at the top of the column element C20 is refrigerated in the E5 exchanger.
  • the liquid-vapor mixture thus obtained is separated in the flask BR reflux.
  • the gas phase rich in acid gases is evacuated through the pipe 23.
  • the liquid phase is sent as reflux to the top of the column element C20.
  • a liquid phase rich in methanol which is taken up by pump P12 and sent through line 22.
  • step (a) it is also possible to at least partially remove the methanol entrained in acid gases by washing these acid gases with water from step (a), that is to say in the embodiments described in relation to FIGS. 1 and 2, collected at the bottom of column C1, the aqueous phase containing methanol thus obtained being returned to step (a), that is to say in the examples of embodiment described in relation to Figures 1 and 2 at the top of column C1.
  • a first fraction is expanded through valve V42 and sent to the head of column D1.
  • a second fraction is expanded through the valve V41, then is reheated in the exchanger E12 by heat exchange with the mixture fraction of relatively rich solvents do methanol which is taken from a point in below the feed point and sent by the P20 pump in the exchanger E12 from which it emerges through conduit 20, to form at least partially the fraction solvent mixture which is sent to an intermediate point in the column C2.
  • the third fraction is expanded through the valve V40, then is reheated in the exchanger E11 by heat exchange with the mixture fraction of solvents relatively poor in methanol which is collected at the bottom of the column regeneration D1 and sent by pump P10 in the heat exchanger E11, from which it emerges through conduit 21, to form at least partially the fraction solvent mixture which is sent to the top of column C2.
  • This embodiment of the method is therefore characterized in that the fraction of the solvent mixture relatively rich in methanol which is sent to a point intermediate of the contact column used during step (b) is removed at an intermediate point in the regeneration column used during the step (vs).
  • each of these fractions can be sent to several different levels. Of even it is possible to use more than two fractions of different compositions, said fractions being taken from different points in the column of D1 regeneration used during step (c) and sent to points different from the absorption column C2 used during step (b).
  • the solvent mixture fraction (s) from the column regeneration D1 are cooled down to a temperature close to the temperature at which step (b) is carried out by heat exchange with one or more fractions of the solvent mixture from step (b) and optionally by an exchange additional thermal, with a cooling fluid such as water or air.
  • the absorption step (b) is carried out in column C2 at a temperature by example between +10 and +40 ° C, but it is also possible to reduce the solvent level to operate this step at lower temperatures, with a mixture of solvents selected so as not to become too viscous at these levels of temperature.
  • the pressure at which the absorption step is carried out in column C2 can be between a few bars and more than a hundred bars. It can be for example close to 70 bars.
  • step (c) natural gas can be refrigerated to a temperature for example between 0 and -100 ° C, the methanol content in the fraction of mixture of solvents sent to the top of the contact column used during step (b) being adjusted so as to obtain in the gas issuing from step (b) a methanol content to avoid the formation of hydrates at the temperature lower obtained during step (c).
  • step (c) When the gas contains condensable hydrocarbons, the refrigeration carried out during step (c) allows to degasoline this gas and to adjust the dew point hydrocarbons at the value required for the transport of gas.
  • This refrigeration can also make it possible to fractionate this gas by separating by example the LPG present in the gas. It is possible in this case to use all devices known to those skilled in the art, such as for example columns of distillation or heat exchangers operating with liquid reflux.
  • the regeneration of the mixture of solvents from step (b) can be carried out after expansion at least in part in a device operating in fractionation and in simultaneous heat exchange.
  • the EC1 device can be for example a heat exchanger placed vertically and operating against the current.
  • the mixture of solvents arriving from the separator tank B10 is sent to the head of this exchanger. It is heated gradually going down into the exchanger, which causes the formation a gas phase containing mainly acid gases and methanol which is evacuated at the head by the conduit 19, by circulating in the exchanger EC1 at counter-current of the liquid phase constituted by the mixture of solvents.
  • the solvent mixture thus leaves purified at the bottom of the exchanger EC1. He is taken back by pump P13, heated in the exchanger E10 and cooled by passing through the exchanger EC1 in which it heats the mixture which descends. At the exit of exchanger EC1, the purified solvent mixture is sent via line 21 in head of the absorption column C2 used during step (b).
  • the EC1 exchanger can be, for example, with tubes and shell or even with plates, either brazed aluminum or stainless steel.
  • the regeneration step can be carried out in two or more columns operating under different pressure and temperature conditions. It is thus possible, for example, to obtain fractions of acid gases of different compositions, for example a fraction concentrated in CO 2 and a fraction concentrated in H 2 S.
  • Each of these regeneration operations can be carried out in one or several distillation sections, some of which can be carried out with a simultaneous heat exchange.
  • the regeneration step (c) thus comprises at least two successive regeneration operations, a gaseous fraction rich in CO 2 being obtained at the end of the first operation and a gaseous fraction rich in H 2 S being obtained at the end of the second operation.
  • the process also makes it possible to separate impurities such as mercaptans, COS and CS 2 which can, for example, be eliminated with the gaseous fraction rich in H 2 S.

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Description

L'invention concerne un procédé de déshydratation et/ou de dégazolinage de gaz naturel, utilisant un mélange de solvants.The invention relates to a method for dehydration and / or gas degassing natural, using a mixture of solvents.

Le traitement d'un gaz naturel requiert la déshydratation, le dégazolinage, lorsque le gaz naturel contient des hydrocarbures condensables et la désacidification de ce gaz lorsque la proportion de gaz acides qu'il contient est trop élevée.The treatment of a natural gas requires dehydration, degassing, when natural gas contains condensable hydrocarbons and the deacidification of this gas when the proportion of acid gases it contains is too high.

Il est possible de déshydrater et de dégazoliner un gaz tel qu'un gaz naturel en le réfrigérant en présence de méthanol pour éviter la formation de glace et/ou d'hydrates.It is possible to dehydrate and degasoline a gas such as natural gas by refrigerant in the presence of methanol to prevent ice formation and / or hydrates.

Il a été découvert, et c'est là un des objets de la présente invention, que le gaz étant chargé en méthanol, il est possible de réaliser dans des conditions avantageuses une étape de désacidification préalablement à l'étape de réfrigération en utilisant pour réaliser ladite étape de désacidification un mélange de solvants contenant du méthanol.It has been discovered, and this is one of the objects of the present invention, that gas being loaded with methanol, it is possible to carry out under conditions advantageous a deacidification step prior to the refrigeration using a mixture to carry out said deacidification step solvents containing methanol.

Il a été également découvert qu'il est alors possible de limiter la coabsorption d'hydrocarbures en utilisant un mélange de solvants comprenant de l'eau, du méthanol et un solvant plus lourd que le méthanol.It has also been discovered that it is then possible to limit coabsorption of hydrocarbons using a mixture of solvents comprising water, methanol and a heavier solvent than methanol.

La présente invention permet également de récupérer le méthanol contenu dans le gaz par un moyen simple et économique.The present invention also makes it possible to recover the methanol contained in the gas by a simple and economical way.

Différents solvants lourds peuvent être mis en oeuvre dans le procédé selon l'invention. Le solvant lourd peut être par exemple un solvant polaire tel que le diméthylformamide (DMF), la N-methylpyrrolidone (NMP) ou le diméthylsulfoxyde (DMSO). Le solvant lourd peut être également un solvant chimique tel que par exemple une amine secondaire ou tertiaire par exemple hydroxylée.Different heavy solvents can be used in the process according to the invention. The heavy solvent can for example be a polar solvent such as dimethylformamide (DMF), N-methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO). The heavy solvent can also be a chemical solvent such as example a secondary or tertiary amine, for example hydroxylated.

Il est ainsi possible d'associer les avantages d'une amine comme solvant chimique et du méthanol comme solvant physique. La présence de méthanol permet notamment de réduire très sensiblement le taux de solvant pour des teneurs relativement importantes en gaz acides dans le gaz à traiter. La présence de méthanol permet également d'absorber et de séparer du gaz à traiter des impuretés telles que par exemple des mercaptans, du sulfure de carbonyle (COS) et du disulfure de carbone (CS2).It is thus possible to combine the advantages of an amine as a chemical solvent and methanol as a physical solvent. The presence of methanol makes it possible in particular to very significantly reduce the level of solvent for relatively large contents of acid gases in the gas to be treated. The presence of methanol also makes it possible to absorb and separate from the gas to be treated impurities such as, for example, mercaptans, carbonyl sulfide (COS) and carbon disulfide (CS 2 ).

Il est également possible dans le procédé selon l'invention d'utiliser des fractions de mélange de solvants de compositions différentes pour optimiser les conditions de lavage du gaz par le mélange de solvants.It is also possible in the process according to the invention to use fractions mixing solvents of different compositions to optimize the conditions washing the gas with a mixture of solvents.

Le procédé de l'invention peut être défini d'une manière générale par le fait qu'il comprend les étapes suivantes :

  • (a) au moins une fraction du gaz est mise en contact avec une phase aqueuse contenant du méthanol, le gaz étant ainsi chargé en méthanol à la sortie de l'étape (a);
  • (b) le gaz sortant de l'étape (a) est mis en contact avec un mélange de solvants comprenant du méthanol, de l'eau et un solvant plus lourd que le méthanol, le gaz sortant de l'étape (b) étant ainsi au moins en partie débarrassée des gaz acides qu'il contient à l'entrée dans le procédé;
  • (c) le mélange de solvants provenant de l'étape (b) chargé en gaz acides est au moins en partie régénéré par réduction de la pression et/ou chauffage en libérant au moins en partie les gaz acides, le mélange de solvants au moins partiellement régénéré étant, à l'issue de l'étape (c), recyclé à l'étape (b); et
  • (d) le gaz provenant de l'étape (b) est réfrigéré en produisant une phase aqueuse contenant du méthanol qui est au moins en partie recyclée à l'étape (a).
    • The method of the invention can be defined in general by the fact that it comprises the following steps:
  • (a) at least a fraction of the gas is brought into contact with an aqueous phase containing methanol, the gas being thus charged with methanol at the outlet of step (a);
  • (b) the gas leaving step (a) is brought into contact with a mixture of solvents comprising methanol, water and a solvent heavier than methanol, the gas leaving step (b) being thus at least partially rid of the acid gases which it contains at the entry into the process;
  • (c) the mixture of solvents originating from stage (b) charged with acid gases is at least partly regenerated by reduction of the pressure and / or heating by releasing at least partly the acid gases, the mixture of solvents at least partially regenerated being, at the end of step (c), recycled in step (b); and
  • (d) the gas from step (b) is refrigerated to produce an aqueous phase containing methanol which is at least partly recycled in step (a).

    • Le procédé selon l'invention est décrit plus en détail ci-après en relation avec le schéma de la figure 1. The method according to the invention is described in more detail below in relation to the diagram of figure 1.

    Le gaz à traiter arrive par le conduit 1. Il contient par exemple du méthane, de l'éthane, du propane, du butane, ainsi que des hydrocarbures plus lourds, de l'eau et des gaz acides tels que par exemple H2S et CO2.The gas to be treated arrives via line 1. It contains for example methane, ethane, propane, butane, as well as heavier hydrocarbons, water and acid gases such as for example H 2 S and CO 2 .

    Une fraction de ce gaz est envoyée par le conduit 2 dans la colonne de contact C1, dans laquelle elle est mise en contact à contre-courant avec une solution de méthanol dans l'eau arrivant par le conduit 3. Au fond de la colonne C1, on élimine par le conduit 40 une phase aqueuse substantiellement débarrassée de méthanol. En tête de la colonne C1, on récupère par le conduit 4 un gaz chargé en méthanol qui est mélangé avec le gaz n'ayant pas traversé la colonne C1. Le gaz ainsi obtenu constitue le gaz chargé en méthanol issu de l'étape (a). Ce gaz est alors envoyé par le conduit 6 dans la colonne C2, dans laquelle il est mis en contact avec un mélange de solvants, comprenant du méthanol, de l'eau et un solvant plus lourd que le méthanol, qui arrive par le conduit 7. Ce mélange de solvants ressort par le conduit 8 chargé en gaz acides, tandis que le gaz évacué en tête de la colonne par le conduit 9 est au moins en partie débarrassé des gaz acides qu'il contient à l'entrée dans la colonne C2 (étape (b)).A fraction of this gas is sent through line 2 to the contact column C1, in which it is brought into counter-current contact with a solution of methanol in water arriving via line 3. At the bottom of column C1, the via line 40 an aqueous phase substantially free of methanol. At the head of column C1, a gas loaded with methanol is recovered via line 4 which is mixed with the gas which has not passed through column C1. Gas as well obtained is the gas loaded with methanol from step (a). This gas is then sent by line 6 in column C2, in which it is contacted with a mixture of solvents, including methanol, water and a more solvent heavy than methanol, which arrives via line 7. This mixture of solvents emerges by the conduit 8 charged with acid gases, while the gas evacuated at the head of the column through line 9 is at least partially rid of the acid gases it contains at entry in column C2 (step (b)).

    Le mélange de solvants provenant de cette étape (b) est d'abord détendu à une pression intermédiaire à travers la vanne de détente V1 en libérant une phase gazeuse qui contient au moins une partie des hydrocarbures qui ont pu être coabsorbés dans le mélange de solvants. La phase gazeuse et la phase liquide ainsi obtenues sont séparées dans le ballon B1.The mixture of solvents from this step (b) is first expanded to a intermediate pressure through the expansion valve V1 releasing a phase gas which contains at least some of the hydrocarbons that may have been coabsorbed in the solvent mixture. The gas phase and the liquid phase thus obtained are separated in flask B1.

    Le débit d'appoint de phase aqueuse ainsi fourni peut être asservi par exemple à un niveau de mélange de solvants dans un bac de recette ou de stockage situé par exemple à la sortie de la colonne D1.The additional flow rate of aqueous phase thus provided can be controlled for example to a level of solvent mixture in a recipe or storage tank located for example at the output of column D1.

    La phase gazeuse est évacuée en tête du ballon B1. Le mélange solvant résiduel est évacué par le conduit 10 et passe dans l'échangeur E1, dans lequel il est réchauffé. Il est alors détendu à travers la vanne V2 et régénéré dans la colonne de distillation D1. Cette colonne est refroidie en tête, ce qui permet d'évacuer par le conduit 11 des gaz acides relativement peu chargés en solvant et chauffée en fond, ce qui permet d'évacuer par le conduit 12 un mélange de solvants substantiellement débarrassé de gaz acides. Les gaz acides évacués par le conduit 11 subissent une réfrigération complémentaire dans l'échangeur E5, pour récupérer au moins en partie le méthanol résiduel. La phase liquide ainsi obtenue est recueillie dans le ballon-séparateur B20, qui reçoit également l'appoint de phase aqueuse arrivant par le conduit 42 et passant à travers la vanne de détente V40. La phase liquide ainsi recueillie dans le ballon-séparateur B20 est recyclée par la pompe P12 à travers le conduit 43 en tête de la colonne C2. Le mélange de solvants évacué par le conduit 12 est repris par la pompe P1 et envoyé à travers l'échangeur E1, dans lequel il est refroidi en réchauffant le mélange de solvants qui arrive par le conduit 10. Il est ensuite refroidi dans l'échangeur E2 par échange avec de l'eau ou de l'air de refroidissement et recyclé à la colonne C2.The gas phase is evacuated at the head of the balloon B1. The residual solvent mixture is evacuated through line 10 and passes into the exchanger E1, in which it is warmed up. It is then expanded through the valve V2 and regenerated in the column distillation D1. This column is cooled at the head, which makes it possible to evacuate by the conduit 11 of the acid gases relatively little loaded with solvent and heated in bottom, which allows a mixture of solvents to be discharged through line 12 substantially free of acid gases. The acid gases evacuated by the conduit 11 undergo additional refrigeration in the exchanger E5, to recover at least partially the residual methanol. The liquid phase thus obtained is collected in the separator flask B20, which also receives back-up from aqueous phase arriving via line 42 and passing through the expansion valve V40. The liquid phase thus collected in the separator flask B20 is recycled by the pump P12 through the conduit 43 at the head of the column C2. The mixture of solvents discharged through line 12 is taken up by pump P1 and sent through exchanger E1, in which it is cooled by heating the mixture of solvents which arrives via the conduit 10. It is then cooled in the exchanger E2 by exchange with water or cooling air and recycled to column C2.

    Si la température en tête de la colonne C2 est plus élevée que la température en fond, par suite de la chaleur d'absorption dégagée, le gaz quittant la colonne C2 par le conduit 9 entraíne une quantité d'eau plus importante que celle qui arrive par le conduit 6. De même, une certaine quantité d'eau peut être évacuée avec les gaz acides par le conduit 11. Pour compenser ces pertes en eau du circuit de mélange de solvants, il est nécessaire dans ce cas de fournir un appoint de phase aqueuse. Cet appoint de phase aqueuse peut être obtenu par exemple en refroidissant le gaz à la sortie de la colonne C2 et en renvoyant dans le circuit du mélange de solvants la fraction condensée. Il est également possible, comme cela est représenté sur la figure 1 de prélever une fraction de la phase aqueuse recueillie dans le ballon-séparateur B2 et de la recycler par le conduit 42 et à travers la vanne de détente V40 vers le circuit de mélange de solvants.If the temperature at the top of column C2 is higher than the temperature at melts, due to the heat of absorption released, the gas leaving column C2 through the conduit 9 causes a greater amount of water than that which arrives through line 6. Likewise, a certain amount of water can be evacuated with the acid gases via line 11. To compensate for these losses of water from the mixture of solvents, it is necessary in this case to provide a phase booster aqueous. This additional aqueous phase can be obtained for example by cooling the gas at the outlet of column C2 and returning it to the circuit of the mixture of solvents the condensed fraction. It is also possible, like this is shown in Figure 1 to take a fraction of the aqueous phase collected in the separator flask B2 and to recycle it through the conduit 42 and to through the expansion valve V40 to the solvent mixing circuit.

    La régénération du solvant qui constitue l'étape (c) du procédé peut être réalisée également selon des agencements différents, qui seront décrits plus loin.The regeneration of the solvent which constitutes step (c) of the process can be carried out also according to different arrangements, which will be described later.

    Le gaz provenant de l'étape (b) qui est évacué par le conduit 9 reçoit un appoint de méthanol arrivant par le conduit 13. Il est ensuite refroidi, d'abord par échange interne dans l'échangeur E3, puis par échange avec un fluide de réfrigération externe provenant d'un circuit de réfrigération, dans l'échangeur E4. Cette réfrigération permet de condenser une solution de méthanol et une phase hydrocarbure liquide. La phase gazeuse ainsi obtenue constitue le gaz traité qui est substantiellement débarrassé de l'eau, des gaz acides et des hydrocarbures lourds qu'il contient au départ. Le mélange triphasique obtenu est séparé dans le ballon B2. Le gaz traité passe dans l'échangeur E3, dans lequel il est réchauffé en refroidissant le gaz qui arrive de la colonne C2 et il est évacué par le conduit 14.The gas from step (b) which is evacuated through line 9 receives a top-up methanol arriving via line 13. It is then cooled, first by exchange internally in the E3 exchanger, then by exchange with a refrigeration fluid external from a refrigeration circuit, in the exchanger E4. This refrigeration condenses a methanol solution and a phase liquid hydrocarbon. The gas phase thus obtained constitutes the treated gas which is substantially free of water, acid gases and hydrocarbons heavy it contains at the start. The three-phase mixture obtained is separated in the balloon B2. The treated gas passes through the exchanger E3, in which it is heated in cooling the gas arriving from column C2 and it is evacuated through line 14.

    La phase hydrocarbure liquide obtenue est évacuée par le conduit 15 et la fraction de la phase aqueuse contenant du méthanol obtenue qui n'est pas évacuée par le conduit 42 est recyclée par la pompe P2 à travers le conduit 41 à la colonne C1.The liquid hydrocarbon phase obtained is discharged through line 15 and the fraction of the aqueous phase containing methanol obtained which is not removed by the conduit 42 is recycled by pump P2 through conduit 41 to column C1.

    Le mélange de solvants envoyé par le conduit 7 comprend du méthanol, de l'eau et un solvant plus lourd que le méthanol.The mixture of solvents sent via line 7 comprises methanol, water and a heavier solvent than methanol.

    La teneur en méthanol du gaz évacué par le conduit 9 doit être suffisamment élevée pour empêcher la formation de glace et/ou d'hydrates au cours de l'étape de réfrigération, l'appoint de méthanol arrivant par le conduit 13 étant réduit et destiné à compenser les pertes. Ceci signifie que cette teneur en méthanol est d'autant plus élevée que la température de réfrigération à la sortie de l'échangeur E4 est basse. La teneur en méthanol dans le mélange de solvants arrivant par le conduit 7 est également d'autant plus élevée que la température à laquelle le gaz est réfrigéré est basse.The methanol content of the gas discharged through line 9 must be sufficiently high to prevent the formation of ice and / or hydrates during the stage refrigeration, the addition of methanol arriving through line 13 being reduced and intended to compensate for losses. This means that this methanol content is the higher the refrigeration temperature at the outlet of the exchanger E4 is low. The methanol content in the solvent mixture arriving through the conduit 7 is also higher as the temperature at which the gas is refrigerated is low.

    La teneur en méthanol peut être aisément régulée au moyen de l'appoint de méthanol arrivant par le conduit 13. La quantité d'appoint est par exemple asservie à la teneur en méthanol dans la phase aqueuse recueillie dans le séparateur B2 de manière à atteindre la teneur requise pour éviter la formation d'hydrates.The methanol content can be easily regulated by the addition of methanol arriving via line 13. The make-up quantity is for example controlled the methanol content in the aqueous phase collected in the separator B2 so as to reach the content required to avoid the formation of hydrates.

    La teneur en méthanol dans le mélange de solvants peut être dans ce cas comprise par exemple entre 5 et 50 % en fraction molaire.The methanol content in the solvent mixture can be in this case for example between 5 and 50% in molar fraction.

    Le solvant lourd qui entre dans la composition du mélange de solvants peut être un solvant polaire tel que par exemple le DMF, la NMP, le DMSO, comme décrit plus haut; ce peut être aussi, le sulfolane, le carbonate de propylène, un alcool plus lourd que le méthanol, un éther ou une cétone. La principale condition à respecter est que sa température d'ébullition soit supérieure à la température d'ébullition du méthanol et de préférence supérieure à la température d'ébullition de l'eau. Il est également nécessaire que ce solvant soit au moins partiellement miscible avec l'eau et le méthanol.The heavy solvent which enters into the composition of the mixture of solvents can be a polar solvent such as for example DMF, NMP, DMSO, as described upper; it can also be, sulfolane, propylene carbonate, an alcohol heavier than methanol, an ether or a ketone. The main condition to respect is that its boiling point is higher than the temperature methanol boiling point and preferably above the boiling point some water. It is also necessary that this solvent is at least partially miscible with water and methanol.

    La teneur en solvant lourd dans le mélange de solvants peut être dans ce cas comprise par exemple entre 10 et 60 % en fraction molaire.The heavy solvent content in the solvent mixture may be in this case for example between 10 and 60% in molar fraction.

    La teneur en eau forme le complément mais elle est de préférence au moins égale à 10 % en fraction molaire.The water content forms the complement but it is preferably at least equal at 10% in molar fraction.

    Le solvant lourd qui entre dans la composition du mélange de solvants peut être également un solvant de type chimique tel que par exemple une amine secondaire ou tertiaire, en général hydroxylée, choisie par exemple parmi la monoéthanolamine, la diéthanolamine, la diglycolamine, la diisopropanolamine, la méthyldiéthanolamine.The heavy solvent which enters into the composition of the mixture of solvents can be also a chemical type solvent such as for example a secondary amine or tertiary, generally hydroxylated, chosen for example from monoethanolamine, diethanolamine, diglycolamine, diisopropanolamine, methyldiethanolamine.

    La teneur en amine dans le mélange de solvants peut être comprise par exemple entre 1 et 10 % en fraction molaire.The amine content in the mixture of solvents can be understood for example between 1 and 10% in molar fraction.

    Le solvant lourd est sélectionné en fonction des spécifications requises pour le gaz traité. Si une désacidification sélective est recherchée, consistant à éliminer de manière beaucoup plus sélective l'H2S que le CO2, une amine sélective telle que par exemple la méthyldiéthanolamine sera employée.The heavy solvent is selected according to the specifications required for the treated gas. If selective deacidification is sought, consisting in eliminating H 2 S much more selectively than CO 2 , a selective amine such as for example methyldiethanolamine will be used.

    Il est également possible d'utiliser un mélange de solvants lourds pour optimiser les caractéristiques du mélange de solvants.It is also possible to use a mixture of heavy solvents to optimize the characteristics of the solvent mixture.

    Il est également possible d'ajouter des additifs connus de l'homme de l'art, tels que par exemple des additifs permettant d'activer l'absorption de CO2, ou des additifs jouant le rôle d'inhibiteurs de corrosion, ou encore des additifs jouant le rôle d'agents anti-moussants. Il peut être également avantageux de filtrer le mélange de solvants qui est envoyé à la colonne C2, afin d'arrêter les particules solides qui peuvent favoriser le moussage. It is also possible to add additives known to a person skilled in the art, such as for example additives making it possible to activate the absorption of CO 2 , or additives acting as corrosion inhibitors, or else additives acting as anti-foaming agents. It may also be advantageous to filter the mixture of solvents which is sent to column C2, in order to stop the solid particles which can promote foaming.

    La mise en contact dans la colonne C1 opérant à contre-courant entre au moins une partie du gaz à traiter et la phase aqueuse contenant du méthanol provenant de l'étape (d) permet d'évacuer en fond de ladite colonne une phase aqueuse substantiellement débarrassée de méthanol. Ceci permet de récupérer et de recycler facilement le méthanol et d'éviter toute pollution liée à la présence de méthanol dans la phase aqueuse rejetée.The contacting in the column C1 operating against the current between at least part of the gas to be treated and the aqueous phase containing methanol from from step (d) allows an aqueous phase to be removed from the bottom of said column substantially free of methanol. This allows you to recover and easily recycle methanol and avoid any pollution linked to the presence of methanol in the released aqueous phase.

    La colonne de contact utilisée peut être de différents types connus de l'homme de l'art : à plateaux ou à garnissage. Dans le cas d'une colonne à garnissage, il peut être avantageux d'utiliser un garnissage structuré.The contact column used can be of different types known to those skilled in the art. the art: with trays or with filling. In the case of a packed column, it can be advantageous to use structured packing.

    De même, les autres colonnes utilisées dans le procédé, notamment C2 et D1 utilisées au cours des étapes (b) et (c), peuvent être des différents types connus de l'homme de l'art : à plateaux ou à garnissage et en particulier à garnissage structuré.Likewise, the other columns used in the process, in particular C2 and D1 used during steps (b) and (c), can be of different known types skilled in the art: with trays or with padding and in particular with padding structure.

    L'exemple numérique suivant illustre le fonctionnement du procédé selon l'invention.The following numerical example illustrates the operation of the method according to the invention.

    Cet exemple de mise en oeuvre du procédé selon l'invention est décrit en relation avec la figure 1.This example of implementation of the method according to the invention is described in relation with figure 1.

    La composition du gaz naturel est par exemple la suivante (en kg/h) : Eau 60,55 Azote 782,37 Dioxyde de carbone 8770,15 Méthane 31699,87 Ethane 5210,67 Propane 3088,88 Isobutane 625,43 N-butane 1024,58 Isopentane 330,39 N-pentane 297,37 N-hexane 118,29 N-heptane 343,99 Total 52352,54 The composition of natural gas is for example the following (in kg / h): Water 60.55 Nitrogen 782.37 Carbon dioxide 8770.15 Methane 31,699.87 Ethane 5210.67 Propane 3,088.88 Isobutane 625.43 N-butane 1024.58 Isopentane 330.39 N-pentane 297.37 N-hexane 118.29 N-heptane 343.99 Total 52352.54

    Le gaz à traiter arrive par le conduit 1 à une température de 30°C et à une pression de 70 bars avec un débit sensiblement égal à 52352 kg/h. Une fraction de ce gaz (50%) est injectée dans la colonne de contact C1 par le conduit 2. Une solution contenant 65 % masse de méthanol dans l'eau, au débit de 159 kg/h et à une température de 30°C, est injectée à contre-courant dans la colonne C1 par le conduit 3. Au fond de la colonne C1, on élimine par le conduit 40 une phase aqueuse contenant 12 ppm masse de méthanol au débit de 60 kg/h. En tête de la colonne C1, le gaz chargé en méthanol est évacué par le conduit 4 et mélangé au gaz qui n'a pas traversé la colonne C1 et qui arrive par le conduit 5.The gas to be treated arrives through line 1 at a temperature of 30 ° C and at a pressure of 70 bars with a flow rate substantially equal to 52352 kg / h. A fraction of this gas (50%) is injected into the contact column C1 through line 2. A solution containing 65% by mass of methanol in water, at a flow rate of 159 kg / h and at a temperature of 30 ° C, is injected against the current into column C1 by the line 3. At the bottom of column C1, a phase is eliminated through line 40 aqueous containing 12 ppm mass of methanol at a flow rate of 60 kg / h. At the head of the column C1, the gas loaded with methanol is evacuated via line 4 and mixed with gas which has not passed through column C1 and which arrives via line 5.

    Le gaz ainsi obtenu est envoyé par le conduit 6 dans la colonne C2. Une solution contenant 20 % masse de méthanol et 20 % masse de diéthanolamine dans l'eau est injectée à contre courant dans la colonne C2 par le conduit 7 à la température de 40°C avec un débit de 117409 kg/h. Au fond de la colonne C2, le mélange de solvants chargé en dioxyde de carbone est récupéré par le conduit 8 à la température de 46°C.The gas thus obtained is sent via line 6 to column C2. A solution containing 20% by mass of methanol and 20% by mass of diethanolamine in water is injected against the current into column C2 through line 7 at temperature 40 ° C with a flow rate of 117409 kg / h. At the bottom of column C2, the mixture of solvents loaded with carbon dioxide is recovered through line 8 to the temperature of 46 ° C.

    Le gaz évacué en tête de la colonne C2 par le conduit 9 ne contient plus que 1,8 % masse de dioxyde de carbone. Ce gaz est refroidi dans les échangeurs E3 et E4 à une température de -26°C. Le mélange triphasique obtenu est séparé dans le ballon B2. Le gaz traité, évacué par le conduit 14, a un débit de 44889 kg/h. La phase hydrocarbure liquide obtenue est évacuée par le conduit 15. La phase aqueuse contenant du méthanol est partiellement recyclée dans la colonne C1 par le conduit 41, l'autre partie (75 %) étant envoyée dans le ballon B20.The gas evacuated at the head of column C2 via line 9 now contains only 1.8 % mass of carbon dioxide. This gas is cooled in the E3 exchangers and E4 at a temperature of -26 ° C. The three-phase mixture obtained is separated in the balloon B2. The treated gas, discharged through line 14, has a flow rate of 44,889 kg / h. The liquid hydrocarbon phase obtained is discharged through line 15. The phase aqueous containing methanol is partially recycled in column C1 by conduit 41, the other part (75%) being sent to balloon B20.

    Le mélange de solvants chargé en dioxyde de carbone est détendu à une pression de 10 bars par la vanne de détente V1, puis envoyé dans le ballon de séparation B1. La phase liquide issue du ballon B1 est envoyée par le conduit 10 dans l'échangeur E1, où elle est rechauffée à une température de 60°C. Elle est ensuite détendue à une pression de 1,5 bar et injectée dans la colonne de distillation D1. Cette colonne est refroidie en tête à une température de 40°C et chauffée en fond. Le mélange de solvants récupéré par le conduit 12 à une température d'environ 80°C est repris par la pompe P1, puis est refroidi dans les échangeurs E1 et E2 avant d'être recyclé dans la colonne C2.The solvent mixture loaded with carbon dioxide is expanded to a pressure 10 bar via the expansion valve V1, then sent to the separation tank B1. The liquid phase from balloon B1 is sent through line 10 into the exchanger E1, where it is heated to a temperature of 60 ° C. Then she is expanded to a pressure of 1.5 bar and injected into the distillation column D1. This column is cooled at the head to a temperature of 40 ° C. and heated at the bottom. The mixture of solvents recovered by line 12 at a temperature of approximately 80 ° C is taken up by the pump P1, then is cooled in the exchangers E1 and E2 before being recycled in column C2.

    Le gaz évacué en tête de la colonne D1 par le conduit 11 est refroidi à -26°C après son passage dans l'échangeur E5. Le ballon B20 permet de séparer une phase liquide contenant essentiellement du méthanol et de l'eau et une phase gazeuse contenant essentiellement du dioxyde de carbone. La phase aqueuse est recyclée dans la colonne C2 par le conduit 43. La phase gazeuse est évacuée par le conduit 23.The gas evacuated at the head of column D1 via line 11 is cooled to -26 ° C after its passage through the E5 exchanger. Balloon B20 allows a phase to be separated liquid containing mainly methanol and water and a gas phase essentially containing carbon dioxide. The aqueous phase is recycled in column C2 via line 43. The gas phase is evacuated through the conduit 23.

    Dans le procédé selon l'invention, il peut être avantageux, pour optimiser les performances du procédé, d'effectuer l'étape (b) en mettant le gaz successivement en contact avec des fractions de mélanges de solvants de compositions différentes. Si une fraction de mélange est envoyée en tête et une autre en un point intermédiaire, il est avantageux d'envoyer en tête une fraction du mélange de solvants relativement pauvre en méthanol et d'envoyer en un point intermédiaire une fraction du mélange de solvants relativement riche en méthanol.In the process according to the invention, it can be advantageous to optimize the performance of the process, to perform step (b) by putting the gas successively in contact with fractions of mixtures of solvents of compositions different. If a fraction of the mixture is sent at the top and another in a intermediate point, it is advantageous to send a fraction of the mixture of solvents relatively poor in methanol and send to an intermediate point a fraction of the solvent mixture relatively rich in methanol.

    Un exemple d'un tel mode de réalisation est décrit en relation avec le schéma de la figure 2.An example of such an embodiment is described in relation to the diagram of the figure 2.

    La colonne C1 est opérée comme dans le cas de l'exemple décrit en relation avec la figure 1.Column C1 is operated as in the case of the example described in relation to Figure 1.

    Le gaz chargé en méthanol arrive par le conduit 6 dans la colonne C2. Il est tout d'abord mis en contact dans une première zone (partie inférieure) de la colonne C2 avec une fraction de mélange de solvants relativement riche en méthanol introduite par le conduit 16 . La teneur en méthanol dans cette première fraction de mélange de solvants peut être comprise par exemple entre 20 et 70 % en fraction molaire. The gas loaded with methanol arrives via line 6 in column C2. He is everything first brought into contact in a first zone (lower part) of the column C2 with a fraction of solvent mixture relatively rich in methanol introduced through conduit 16. The methanol content in this first fraction of mixture of solvents can be for example between 20 and 70% in fraction molar.

    Le gaz est mis en contact ensuite dans une deuxième zone (partie supérieure) de la colonne C2 avec une fraction du mélange de solvants relativement pauvre en méthanol introduit par le conduit 7. La teneur en méthanol dans cette deuxième fraction du mélange de solvants peut être comprise par exemple entre 5 et 30 % en fraction molaire. Cette teneur en méthanol doit être d'autant plus élevée que la teneur en méthanol dans le gaz sortant par le conduit 9 est élevée, c'est-à-dire d'autant plus élevée que la température à la sortie de l'échangeur E4 est basse, ce pour éviter la formation de glace et/ou d'hydrates.The gas is then brought into contact in a second zone (upper part) of column C2 with a fraction of the solvent mixture relatively low in methanol introduced via line 7. The methanol content in this second fraction of the solvent mixture can be for example between 5 and 30% in molar fraction. This methanol content must be all the higher as the methanol content in the gas leaving via line 9 is high, that is to say the higher the lower the temperature at the outlet of the exchanger E4, this to avoid the formation of ice and / or hydrates.

    Le mélange de solvants provenant de l'étape (b), c'est-à-dire dans le cas de l'exemple décrit en relation avec la figure 2a sortant de la colonne C2 par le conduit 8, est régénéré par détente puis par chauffage dans une colonne de contact à contre-courant D1, la phase solvant prélevée en fond de ladite colonne formant la fraction du mélange de solvants relativement pauvre en méthanol qui est injectée en tête de la colonne de contact utilisée au cours de l'étape (b), c'est-à-dire la colonne C2 dans le cas de l'exemple décrit en relation avec la figure 2a.The mixture of solvents from step (b), that is to say in the case of the example described in relation to FIG. 2a leaving column C2 by the line 8, is regenerated by expansion then by heating in a column of counter-current contact D1, the solvent phase taken from the bottom of said column forming the fraction of the solvent mixture relatively poor in methanol which is injected at the head of the contact column used during step (b), that is to say column C2 in the case of the example described in relation to FIG. 2a.

    Dans ce mode de réalisation, le mélange de solvants chargé en gaz acides sortant par le conduit 8 est d'abord détendu à un niveau de pression intermédiaire à travers la vanne V1, en libérant une phase gazeuse qui contient au moins une partie des hydrocarbures qui ont pu être coabsorbés dans le mélange de solvants. Cette phase gazeuse peut être lavée par une fraction de mélange de solvants relativement pauvre en méthanol, dont le débit est contrôlé par la vanne de répartition V30 et qui est envoyée par le conduit 17 en tête d'une section de contact à contre-courant située dans l'élément de colonne C10. Le gaz qui sort en tête de l'élément de colonne C10 est ainsi substantiellement débarrassé des gaz acides qu'il contenait et peut par exemple servir de fuel-gas ou encore être recomprimé et mélangé avec le gaz traité.In this embodiment, the mixture of solvents charged with acid gases exiting through the conduit 8 is first expanded to an intermediate pressure level through the valve V1, releasing a gaseous phase which contains at least part of the hydrocarbons which could be coabsorbed in the solvent mixture. This gas phase can be washed with a fraction of a mixture of solvents relatively poor in methanol, the flow rate of which is controlled by the distribution valve V30 and which is sent via line 17 at the head of a counter-current contact section located in column element C10. The gas which leaves the head of the column element C10 is thus substantially freed from the acid gases which it contained and can for example serve as fuel-gas or else be recompressed and mixed with the treated gas.

    Cette disposition ne se limite pas à l'exemple de réalisation décrit en relation avec la figure 2.This provision is not limited to the example of embodiment described in relation to Figure 2.

    Ainsi, même pour d'autres modes de réalisation, il est possible de faire subir au mélange de solvants provenant de l'étape (b) une première étape de détente à une pression intermédiaire pour libérer au moins une partie des hydrocarbures coabsorbés.Thus, even for other embodiments, it is possible to subject the mixture of solvents from step (b) a first step of expansion at an intermediate pressure to release at least part of the hydrocarbons coabsorbed.

    De même pour d'autres modes de réalisation, il est également possible de laver la fraction gazeuse provenant de la détente à une pression intermédiaire du mélange de solvants issu de l'étape (b), par une fraction du mélange de solvants relativement pauvre en méthanol recueilli en fond de la colonne de régénération utilisée au cours de l'étape (c).Similarly for other embodiments, it is also possible to wash the gas fraction from the expansion at an intermediate pressure of the mixture of solvents from step (b), by a fraction of the mixture of solvents relatively poor in methanol collected at the bottom of the regeneration column used during step (c).

    A la sortie de l'élément de colonne C10, le mélange de solvants est détendu à nouveau jusqu'à une pression basse, par exemple une pression proche de la pression atmosphérique, à travers la vanne de détente V20. Le mélange liquide-vapeur ainsi obtenu est séparé dans le ballon séparateur B10. La phase vapeur formée essentiellement de gaz acides et de méthane est évacuée par le conduit 18. La phase liquide ainsi obtenue est scindée en deux fractions. Une première fraction, de préférence la plus importante en débit, est reprise par la pompe P11 à travers le conduit 20 et forme la majeure partie de la fraction de mélange de solvants relativement riche en méthanol qui est envoyée par le conduit 16 en un point intermédiaire de la colonne C2.At the outlet of the column element C10, the mixture of solvents is expanded to again to a low pressure, for example a pressure close to the atmospheric pressure, through the expansion valve V20. The liquid-vapor mixture thus obtained is separated in the separator flask B10. The vapor phase formed essentially of acid gases and methane is evacuated through the conduit 18. The liquid phase thus obtained is split into two fractions. A first fraction, preferably the largest in flow, is taken up by the pump P11 at through conduit 20 and forms most of the mixing fraction of solvents relatively rich in methanol which is sent via line 16 in one intermediate point of column C2.

    Une deuxième fraction du mélange de solvants obtenu à la sortie du ballon séparateur B10 est réchauffée dans l'échangeur E1, par échange de chaleur avec le mélange de solvants provenant du fond de la colonne D1, puis envoyée dans la colonne de distillation D1. Un reflux vapeur est généré en fond de la colonne D1 au moyen du rebouilleur R1 et un reflux liquide est généré en tête de la colonne D1 au moyen du condenseur E6.A second fraction of the solvent mixture obtained at the outlet of the flask separator B10 is heated in the exchanger E1, by heat exchange with the mixture of solvents from the bottom of column D1, then sent to the distillation column D1. Steam reflux is generated at the bottom of column D1 by means of reboiler R1 and a liquid reflux is generated at the top of the column D1 by means of the condenser E6.

    La phase gazeuse résultant de la condensation partielle dans E6 et qui est évacuée en tête par le conduit 19 est formée essentiellement de gaz acides et de méthanol.The gas phase resulting from partial condensation in E6 and which is evacuated at the head via line 19 is formed essentially of acid gases and methanol.

    Dans ce mode de réalisation, elle est mélangée avec la phase gazeuse évacuée par le conduit 18 et le mélange gazeux ainsi obtenu est réfrigéré dans l'échangeur E5. Le mélange liquide-vapeur ainsi obtenu est séparé dans le ballon séparateur B20. Un appoint de phase aqueuse alimente le ballon B20 à travers le conduit 42 et à travers la vanne de détente V40. La phase gazeuse formée essentiellement des gaz acides séparés est évacuée par le conduit 23. La phase liquide riche en méthanol est reprise par la pompe P12 à travers le conduit 22 et, après mélange avec le fraction arrivant par le conduit 20, forme la fraction de mélange de solvants qui est envoyée en un point intermédiaire de la colonne C2.In this embodiment, it is mixed with the evacuated gas phase via line 18 and the gas mixture thus obtained is refrigerated in the exchanger E5. The liquid-vapor mixture thus obtained is separated in the separator flask B20. A make-up of aqueous phase feeds the flask B20 through the conduit 42 and through the expansion valve V40. The gas phase formed essentially separate acid gases are evacuated through line 23. The liquid phase rich in methanol is taken up by pump P12 through line 22 and, after mixing with the fraction arriving via line 20, forms the fraction of solvent mixture which is sent to an intermediate point in column C2.

    La phase liquide qui est évacuée en fond de la colonne D1 est appauvrie en méthanol. Dans la colonne D1 le strippage en fond de colonne est assuré par une vapeur riche en méthanol, ce qui permet d'assurer le rebouillage de la colonne D1 à une température plus basse et en fournissant moins de chaleur qu'en l'absence de méthanol.The liquid phase which is discharged at the bottom of column D1 is depleted in methanol. In column D1 stripping at the bottom of the column is ensured by a vapor rich in methanol, which ensures reboiling of column D1 at a lower temperature and providing less heat than in the absence methanol.

    La phase liquide évacuée en fond de la colonne D1 est reprise par la pompe P10. Elle est refroidie dans l'échangeur E1, d'où elle ressort par le conduit 21. Elle est alors divisée en deux fractions au moyen de la vanne de répartition V30. Une première fraction, la plus importante en débit est refroidie dans l'échangeur E2 par de l'eau ou de l'air de refroidissement et envoyée en tête de la colonne C2 par le conduit 7. Une deuxième fraction est envoyée par le conduit 17 en tête de l'élément de colonne C10.The liquid phase discharged at the bottom of column D1 is taken up by pump P10. It is cooled in the exchanger E1, from which it emerges through the conduit 21. It is then divided into two fractions by means of the distribution valve V30. A first fraction, the largest in flow is cooled in the exchanger E2 by water or cooling air and sent to the top of column C2 by the conduit 7. A second fraction is sent via conduit 17 at the head of column element C10.

    Différents autres agencements peuvent être utilisés sans sortir du cadre de l'invention.Different other arrangements can be used without departing from the scope of the invention.

    Lorsque le gaz à traiter contient une proportion importante de CO2 et de l'H2S, il peut être souhaité d'obtenir des fractions distinctes de gaz acides, respectivement riches en CO2 et en H2S.When the gas to be treated contains a large proportion of CO 2 and of H 2 S, it may be desirable to obtain separate fractions of acid gases, respectively rich in CO 2 and in H 2 S.

    Dans ce cas, il est possible d'opérer par exemple selon l'agencement de la figure 3 sur laquelle figure uniquement une partie du dispositif. La fraction gazeuse relativement riche en CO2, qui est obtenue à l'issue de la détente du mélange de solvants à travers la vanne de détente V20 est envoyée dans l'élément de colonne C11, dans lequel est elle mise en contact avec une partie du mélange de solvants relativement pauvre en méthanol arrivant par le conduit 21, pour éliminer sélectivement l'H2S présent dans le gaz. Le mélange de solvants arrivant par le conduit 21 est partagé en deux fractions par passage à travers la vanne de répartition V40. Une première fraction est envoyée par le conduit 24 en tête de l'élément de colonne C11. Une deuxième fraction est envoyée par le conduit 25 vers la tête de la colonne C2. Le mélange de solvants recueilli en fond de l'élément de colonne C11 et arrivant par la pompe P11 et le conduit 20 est mélangé avec la fraction liquide arrivant par le conduit 22. Le mélange de solvants résultant est envoyé en un point intermédiaire de la colonne C2.In this case, it is possible to operate for example according to the arrangement of FIG. 3 in which only part of the device appears. The gaseous fraction relatively rich in CO 2 , which is obtained after the expansion of the mixture of solvents through the expansion valve V20 is sent to the column element C11, in which it is brought into contact with a part a mixture of solvents relatively poor in methanol arriving via line 21, to selectively eliminate the H 2 S present in the gas. The mixture of solvents arriving via line 21 is divided into two fractions by passage through the distribution valve V40. A first fraction is sent through the conduit 24 at the head of the column element C11. A second fraction is sent via line 25 to the head of column C2. The mixture of solvents collected at the bottom of the column element C11 and arriving by the pump P11 and the line 20 is mixed with the liquid fraction arriving by the line 22. The resulting mixture of solvents is sent to an intermediate point of the column C2.

    Dans ce cas, les fractions gazeuses évacuées par les conduits 18 et 19 constituant respectivement les fractions riches en CO2 et en H2S, ne sont pas mélangées et peuvent subir séparément un traitement complémentaire, par exemple par réfrigération, pour éliminer au moins en partie le méthanol entraíné avec les gaz acides.In this case, the gaseous fractions discharged through the conduits 18 and 19 respectively constituting the fractions rich in CO 2 and in H 2 S, are not mixed and can undergo separately a complementary treatment, for example by refrigeration, to eliminate at least in part methanol entrained with acid gases.

    Une autre disposition qui peut être employée consiste, au lieu de réfrigérer directement les gaz acides arrivant par le conduit 18, par le conduit 19 ou après mélange de ces deux fractions, à envoyer ces gaz acides dans un élément de colonne de rectification selon l'exemple d'agencement de la figure 4.Another arrangement that can be used is, instead of refrigerating directly the acid gases arriving through line 18, through line 19 or after mixture of these two fractions, to send these acid gases into an element of rectification column according to the example of arrangement of FIG. 4.

    Les gaz acides contenant du méthanol obtenus par mélange des fractions gazeuses arrivant par les conduits 18 et 19 sont envoyés à l'élément de colonne C20. La fraction gazeuse en tête de l'élément de colonne C20 est réfrigérée dans l'échangeur E5. Le mélange liquide-vapeur ainsi obtenu est séparé dans le ballon de reflux BR. La phase gazeuse riche en gaz acides est évacuée par le conduit 23. La phase liquide est envoyée comme reflux en tête de l'élément de colonne C20. En fond de l'élément de colonne C20, on obtient une phase liquide riche en méthanol qui est reprise par la pompe P12 et envoyée à travers le conduit 22.Acid gases containing methanol obtained by mixing the fractions gas arriving through lines 18 and 19 are sent to the column element C20. The gas fraction at the top of the column element C20 is refrigerated in the E5 exchanger. The liquid-vapor mixture thus obtained is separated in the flask BR reflux. The gas phase rich in acid gases is evacuated through the pipe 23. The liquid phase is sent as reflux to the top of the column element C20. At the bottom of the column element C20, a liquid phase rich in methanol which is taken up by pump P12 and sent through line 22.

    Il est également possible d'éliminer au moins en partie le méthanol entraíné dans les gaz acides en lavant ces gaz acides avec de l'eau provenant de l'étape (a), c'est-à-dire dans les exemples de réalisation décrits en relation avec les figures 1 et 2, recueillie en fond de la colonne C1, la phase aqueuse contenant du méthanol ainsi obtenue étant renvoyée à l'étape (a), c'est-à-dire dans les exemples de réalisation décrits en relation avec les figures 1 et 2 en tête de la colonne C1.It is also possible to at least partially remove the methanol entrained in acid gases by washing these acid gases with water from step (a), that is to say in the embodiments described in relation to FIGS. 1 and 2, collected at the bottom of column C1, the aqueous phase containing methanol thus obtained being returned to step (a), that is to say in the examples of embodiment described in relation to Figures 1 and 2 at the top of column C1.

    Pour envoyer en un point intermédiaire de la colonne de contact C2 utilisée au cours de l'étape (b) une fraction de mélange de solvants relativement riche en méthanol mieux épurée en gaz acides, il est possible d'envoyer la totalité du mélange de réfrigérants issu de l'étape (b) à la colonne de régénération D1 utilisée au cours de l'étape (c) et de prélever en un point intermédiaire de la colonne de régénération D1 la fraction de mélange de solvants relativement riche en méthanol, qui est envoyée en un point intermédiaire de la colonne de contact C2 utilisée au cours de l'étape (b).To send to an intermediate point of the contact column C2 used at during stage (b) a fraction of mixture of solvents relatively rich in methanol better purified in acid gases, it is possible to send the entire mixture of refrigerants from step (b) to the regeneration column D1 used during step (c) and take an intermediate point from the column of regeneration D1 the fraction of solvent mixture relatively rich in methanol, which is sent to an intermediate point in the contact column C2 used during step (b).

    Un tel mode de réalisation est illustré par le schéma de la figure 5.Such an embodiment is illustrated by the diagram in FIG. 5.

    Le mélange de solvants chargé en gaz acides provenant du fond de l'élément de colonne C10 représenté sur la figure 2 est partagé en trois fractions.The mixture of solvents charged with acid gases coming from the bottom of the element of column C10 shown in Figure 2 is divided into three fractions.

    Une première fraction est détendue à travers la vanne V42 et envoyée en tête de la colonne D1.A first fraction is expanded through valve V42 and sent to the head of column D1.

    Une deuxième fraction est détendue à travers la vanne V41, puis est réchauffée dans l'échangeur E12 par échange de chaleur avec la fraction de mélange de solvants relativement riche ne méthanol qui est prélevée en un point situé en dessous du point d'alimentation et envoyée par la pompe P20 dans l'échangeur E12 d'où elle ressort par le conduit 20, pour former au moins en partie la fraction de mélange de solvants qui est envoyée en un point intermédiaire de la colonne C2.A second fraction is expanded through the valve V41, then is reheated in the exchanger E12 by heat exchange with the mixture fraction of relatively rich solvents do methanol which is taken from a point in below the feed point and sent by the P20 pump in the exchanger E12 from which it emerges through conduit 20, to form at least partially the fraction solvent mixture which is sent to an intermediate point in the column C2.

    La troisième fraction est détendue à travers la vanne V40, puis est réchauffée dans l'échangeur E11 par échange de chaleur avec la fraction de mélange de solvants relativement pauvre en méthanol qui est recueillie en fond de la colonne de régénération D1 et envoyée par la pompe P10 dans l'échangeur de chaleur E11, d'où elle ressort par le conduit 21, pour former au moins en partie la fraction de mélange de solvants qui est envoyée en tête de la colonne C2. The third fraction is expanded through the valve V40, then is reheated in the exchanger E11 by heat exchange with the mixture fraction of solvents relatively poor in methanol which is collected at the bottom of the column regeneration D1 and sent by pump P10 in the heat exchanger E11, from which it emerges through conduit 21, to form at least partially the fraction solvent mixture which is sent to the top of column C2.

    Ce mode de réalisation du procédé est donc caractérisé en ce que la fraction du mélange de solvants relativement riche en méthanol qui est envoyée en un point intermédiaire de la colonne de contact utilisée au cours de l'étape (b) est prélevée en un point intermédiaire de la colonne de régénération utilisée au cours de l'étape (c).This embodiment of the method is therefore characterized in that the fraction of the solvent mixture relatively rich in methanol which is sent to a point intermediate of the contact column used during step (b) is removed at an intermediate point in the regeneration column used during the step (vs).

    Dans les exemples de réalisation décrits en relation avec les figures 2 à 5, on opère avec deux fractions de mélange de solvants de compositions différentes qui sont envoyées à deux niveaux différents de la colonne C2.In the embodiments described in relation to FIGS. 2 to 5, we operates with two solvent mixture fractions of different compositions which are sent to two different levels in column C2.

    Chacune de ces fractions peut être envoyée à plusieurs niveaux différents. De même il est possible d'utiliser plus de deux fractions de compositions différentes, lesdites fractions étant prélevées en des points différents de la colonne de régénération D1 utilisée au cours de l'étape (c) et envoyées en des points différents de la colonne d'absorption C2 utilisée au cours de l'étape (b).Each of these fractions can be sent to several different levels. Of even it is possible to use more than two fractions of different compositions, said fractions being taken from different points in the column of D1 regeneration used during step (c) and sent to points different from the absorption column C2 used during step (b).

    La ou les fractions de mélange de solvants provenant de la colonne de régénération D1 sont refroidies jusqu'à une température voisine de la température à laquelle est réalisée l'étape (b) par échange thermique avec une ou des fractions du mélange de solvants issu de l'étape (b) et éventuellement par un échange thermique complémentaire, avec un fluide de refroidissement tel que l'eau ou l'air.The solvent mixture fraction (s) from the column regeneration D1 are cooled down to a temperature close to the temperature at which step (b) is carried out by heat exchange with one or more fractions of the solvent mixture from step (b) and optionally by an exchange additional thermal, with a cooling fluid such as water or air.

    L'étape d'absorption (b) est réalisée dans la colonne C2 à une température par exemple comprise entre +10 et +40 °C, mais il est également possible pour réduire le taux de solvant d'opérer cette étape à des températures plus basses, avec un mélange de solvants sélectionné pour ne pas devenir trop visqueux à ces niveaux de température.The absorption step (b) is carried out in column C2 at a temperature by example between +10 and +40 ° C, but it is also possible to reduce the solvent level to operate this step at lower temperatures, with a mixture of solvents selected so as not to become too viscous at these levels of temperature.

    La pression à laquelle est réalisée l'étape d'absorption dans la colonne C2 peut être comprise entre quelques bars et plus de cent bars. Elle peut être par exemple proche de 70 bars. The pressure at which the absorption step is carried out in column C2 can be between a few bars and more than a hundred bars. It can be for example close to 70 bars.

    Au cours de l'étape (c), le gaz naturel peut être réfrigéré jusqu'à une température comprise par exemple entre 0 et -100 °C, la teneur en méthanol dans la fraction de mélange de solvants envoyée en tête de la colonne de contact utilisée au cours de l'étape (b) étant ajustée de manière à obtenir dans le gaz issu de l'étape (b) une teneur en méthanol permettant d'éviter la formation d'hydrates à la température la plus basse obtenue au cours de l'étape (c).In step (c), natural gas can be refrigerated to a temperature for example between 0 and -100 ° C, the methanol content in the fraction of mixture of solvents sent to the top of the contact column used during step (b) being adjusted so as to obtain in the gas issuing from step (b) a methanol content to avoid the formation of hydrates at the temperature lower obtained during step (c).

    Lorsque le gaz contient des hydrocarbures condensables, la réfrigération réalisée au cours de l'étape (c) permet de dégazoliner ce gaz et d'ajuster le point de rosée hydrocarbures à la valeur requise pour le transport du gaz.When the gas contains condensable hydrocarbons, the refrigeration carried out during step (c) allows to degasoline this gas and to adjust the dew point hydrocarbons at the value required for the transport of gas.

    Cette réfrigération peut permettre également de fractionner ce gaz en séparant par exemple les GPL présents dans le gaz. Il est possible dans ce cas d'utiliser tous les dispositifs connus de l'homme de l'art, tels que par exemple des colonnes de distillation ou des échangeurs de chaleur opérant avec un reflux liquide.This refrigeration can also make it possible to fractionate this gas by separating by example the LPG present in the gas. It is possible in this case to use all devices known to those skilled in the art, such as for example columns of distillation or heat exchangers operating with liquid reflux.

    La régénération du mélange de solvants provenant de l'étape (b) peut être réalisée après détente au moins en partie dans un dispositif opérant en fractionnement et en échange thermique simultané.The regeneration of the mixture of solvents from step (b) can be carried out after expansion at least in part in a device operating in fractionation and in simultaneous heat exchange.

    Une telle disposition est illustrée par l'exemple de réalisation représenté sur le schéma de la figure 6.Such an arrangement is illustrated by the embodiment shown in the diagram of figure 6.

    Le mélange de solvants issu de l'étape d'absoption (b) étant détendu jusqu'à la pression basse à laquelle est effectuée l'étape de régénération (c), un mélange liquide-vapeur est obtenu qui est séparé dans le ballon séparateur B10. Une fraction liquide de mélange de solvants partiellement régénéré est prélevée par la pompe P11 pour alimenter la colonne d'absorption dans laquelle est effectuée en l'étape (b), en un point intermédiaire. La fraction restante est envoyée dans le dispositif EC1 dans lequel elle est mise en contact avec un reflux gazeux tout en échangeant de la chaleur avec la fraction liquide du mélange de solvants sortant de l'échangeur EC1 et envoyée par la pompe P13 dans l'échangeur E10 dans lequel elle est chauffée par un fluide extérieur. The mixture of solvents resulting from the absorption step (b) being relaxed until the low pressure at which the regeneration step (c) is carried out, a mixture liquid-vapor is obtained which is separated in the separator flask B10. A liquid fraction of partially regenerated solvent mixture is withdrawn by the P11 pump to supply the absorption column in which is carried out step (b), at an intermediate point. The remaining fraction is sent to the EC1 device in which it is brought into contact with a gas reflux while exchanging heat with the liquid fraction of the outgoing solvent mixture of the exchanger EC1 and sent by the pump P13 in the exchanger E10 in which it is heated by an external fluid.

    Le dispositif EC1 peut être par exemple un échangeur de chaleur placé verticalement et opérant à contre-courant. Le mélange de solvants arrivant du ballon séparateur B10 est envoyé en tête de cet échangeur. Il est chauffé progressivement en descendant dans l'échangeur, ce qui provoque la formation d'une phase gazeuse contenant essentiellement des gaz acides et du méthanol qui est évacuée en tête par le conduit 19, en circulant dans l'échangeur EC1 à contre-courant de la phase liquide constituée par le mélange de solvants.The EC1 device can be for example a heat exchanger placed vertically and operating against the current. The mixture of solvents arriving from the separator tank B10 is sent to the head of this exchanger. It is heated gradually going down into the exchanger, which causes the formation a gas phase containing mainly acid gases and methanol which is evacuated at the head by the conduit 19, by circulating in the exchanger EC1 at counter-current of the liquid phase constituted by the mixture of solvents.

    Le mélange de solvants sort ainsi épuré en fond de l'échangeur EC1. II est repris par la pompe P13, chauffé dans l'échangeur E10 et refroidi en passant dans l'échangeur EC1 dans lequel il chauffe le mélange qui descend. A la sortie de l'échangeur EC1, le mélange de solvants épuré est envoyé par le conduit 21 en tête de la colonne d'absorption C2 utilisée au cours de l'étape (b).The solvent mixture thus leaves purified at the bottom of the exchanger EC1. He is taken back by pump P13, heated in the exchanger E10 and cooled by passing through the exchanger EC1 in which it heats the mixture which descends. At the exit of exchanger EC1, the purified solvent mixture is sent via line 21 in head of the absorption column C2 used during step (b).

    L'échangeur EC1 peut être par exemple à tubes et calandre ou encore à plaques, soit en aluminium brasé soit en acier inoxydable.The EC1 exchanger can be, for example, with tubes and shell or even with plates, either brazed aluminum or stainless steel.

    L'étape de régénération peut être réalisée dans deux ou plusieurs colonnes opérant dans des conditions de pression et de température différentes. Il est ainsi possible par exemple d'obtenir des fractions de gaz acides de compositions différentes, par exemple une fraction concentrée en CO2 et une fraction concentrée en H2S.The regeneration step can be carried out in two or more columns operating under different pressure and temperature conditions. It is thus possible, for example, to obtain fractions of acid gases of different compositions, for example a fraction concentrated in CO 2 and a fraction concentrated in H 2 S.

    Comme cela a déjà été indiqué, il est nécessaire dans ce cas d'utiliser comme solvant lourd un solvant sélectif pour l'H2S. On sépare alors, au cours d'une première opération de régénération le CO2 contenu dans le mélange de solvants. Comme cela a déjà été indiqué, si les gaz acides obtenus au cours de cette première opération de régénération contiennent de l'H2S, celui-ci peut être éliminé par lavage à contre-courant avec une fraction du mélange de solvants. L'H2S est alors séparé du mélange de solvants au cours d'une deuxième opération de régénération. As has already been indicated, it is necessary in this case to use as heavy solvent a solvent selective for H 2 S. The CO 2 contained in the mixture of is then separated, during a first regeneration operation. solvents. As already indicated, if the acid gases obtained during this first regeneration operation contain H 2 S, this can be removed by backwashing with a fraction of the solvent mixture. The H2S is then separated from the solvent mixture during a second regeneration operation.

    Chacune de ces opérations de régénération peut être réalisée dans une ou plusieurs sections de distillation dont certaines peuvent être effectuées avec un échange de chaleur simultané.Each of these regeneration operations can be carried out in one or several distillation sections, some of which can be carried out with a simultaneous heat exchange.

    L'étape de régénération (c) comprend ainsi au moins deux opérations de régénération successives, une fraction gazeuse riche en CO2 étant obtenue à l'issue de la première opération et une fraction gazeuse riche en H2S étant obtenue à l'issue de la deuxième opération.The regeneration step (c) thus comprises at least two successive regeneration operations, a gaseous fraction rich in CO 2 being obtained at the end of the first operation and a gaseous fraction rich in H 2 S being obtained at the end of the second operation.

    Comme cela a été indiqué le procédé permet également de séparer des impuretés telles que les mercaptans, COS et CS2 qui peuvent être par exemple éliminées avec la fraction gazeuse riche en H2S.As indicated, the process also makes it possible to separate impurities such as mercaptans, COS and CS 2 which can, for example, be eliminated with the gaseous fraction rich in H 2 S.

    Claims (19)

    1. A process for dehydration and/or deacidification and/or stripping of a gas that is characterized in that:
      (a) at least one fraction of the gas is brought into contact with an aqueous phase that contains methanol, with the gas thus being charged with methanol at the output of stage (a);
      (b) the gas exiting stage (a) is brought into contact with a mixture of solvents that comprises methanol, water, and a higher boiling solvent than methanol, with the gas exiting stage (b) thus being at least partially free of the acid gases that it initially contained in the process;
      (c) at least a portion of the mixture of solvents that is obtained from stage (b) that is charged with acid gases is regenerated by pressure reduction and/or heating by releasing at least a portion of the acid gases, with the mixture of solvents that is at least partially regenerated being, at the end of stage (c), recycled to stage (b); and
      (d) the gas that is obtained from stage (b) is refrigerated while producing at least one aqueous phase that contains methanol which is recycled at least in part to stage (a).
    2. Process according to claim 1, wherein the solvent that boils higher than methanol that is incorporated into the mixture of solvents that is used during stage (b) has a boiling point that is greater than that of methanol and than that of water and is at least partially miscible with water and methanol.
    3. Process according to claim 1, wherein the solvent that is heavier than the methanol that is incorporated into the mixture of solvents that is used during stage (b) is a hydroxylated secondary or tertiary amine or a polar solvent such as DMF, NMP or DMSO.
    4. Process according to one of claims 1 to 3, wherein in stage (a), the contact that is made between at least a portion of the gas to be treated and the aqueous phase that contains the methanol that is obtained from stage (d) is carried out in countercurrent in a column, with the aqueous phase that is evacuated at the bottom of said column being largely free of methanol.
    5. Process according to one of claims 1 to 4, wherein during stage (b), the gas that is obtained from stage (a) is brought into contact in countercurrent with a column, successively with a fraction of the mixture of solvents that is relatively rich in methanol, which is sent to an intermediate point of the contact column, and then with a fraction of the mixture of solvents that is relatively low in methanol, which is sent to the top of the contact column.
    6. Process according to claim 5, wherein the mixture of solvents that is obtained from stage (b) is regenerated by pressure reduction and then by heating in a contact column in countercurrent, with the solvent phase that is removed at the bottom of said column forming the fraction of the mixture of solvents that is relatively low in methanol which is injected at the top of the contact column that is used during stage (b).
    7. Process according to one of claims 1 to 6, wherein the mixture of solvents that is obtained from stage (b) undergoes a first stage of reduction of pressure to an intermediate pressure for releasing at least a portion of the coabsorbed hydrocarbons.
    8. Process according to claim 7, wherein the gas fraction that is obtained from the reduction of pressure to an intermediate pressure of the mixture of solvents coming from stage (b) is washed by a fraction of the mixture of solvents that is relatively low in methanol collected at the bottom of the regeneration column that is used during stage (c).
    9. Process according to one of claims 5 to 8, wherein the fraction of the mixture of solvents that is relatively rich in methanol, which is sent to an intermediate point of the contact column used during stage (b), is obtained by reducing the pressure of at least a fraction of the mixture of solvents coming from stage (b).
    10. Process according to one of claims 5 to 9, wherein the fraction of the mixture of solvents that is relatively rich in methanol which is sent to an intermediate point of the contact column that is used during stage (b) is removed at an intermediate point of the regeneration column that is used during stage (c).
    11. Process according to one of claims 1 to 10, wherein the mixture of solvents that is obtained from stage (b) is, after pressure reduction, sent to several levels of the regeneration column that is used during stage (c).
    12. Process according to one of claims 1 to 11, wherein the fraction or fractions of the mixture of solvents that is (are) obtained from the regeneration column that is used during stage (c) are cooled to a temperature that is close to the temperature at which stage (b) is carried out by heat exchange with the mixture of solvents coming from stage (b) and optionally by an additional heat exchange step, with a cooling fluid such as water or air.
    13. Process according to one of claims 1 to 11, wherein at least a portion of the mixture of solvents that is obtained from stage (b) is regenerated after pressure reduction, at least partially in a column of which at least a portion operates in simultaneous heat exchange with at least a portion of the regenerated mixture of solvents that is recycled to stage (b).
    14. Process according to one of claims 1 to 13, wherein the acid gases that are released by pressure reduction and/or heating of the mixture of solvents that is obtained from stage (b) are washed by a flow of water that is obtained from stage (a) to recover at least a portion of the methanol that they contain, with the aqueous phase that contains the methanol that is thus obtained being recycled to stage (a).
    15. Process according to one of claims 1 to 13, wherein the acid gases that are released by pressure reduction and/or heating of the mixture of solvents that is obtained from stage (b) are rectified at a temperature that is lower than the temperature at which stage (b) is carried out to free them of the methanol and the water that they contain.
    16. Process according to one of claims 1 to 15, wherein stage (b) is carried out at a temperature of between +10 and +40°C.
    17. Process according to one of claims 1 to 15, wherein during stage (d), the natural gas is refrigerated to a temperature of between 0°C and -100°C, with the methanol content in the fraction of the mixture of solvents sent to the top of the contact column that is used during stage (b) being adjusted to obtain a methanol content, in the gas coming from stage (b), that makes it possible to keep hydrates from forming at the lowest temperature obtained during stage (c).
    18. Process according to one of claims 1 to 17, wherein during stage (d), a liquid hydrocarbon fraction is separated from the treated gas, which is then brought by heat exchange to a temperature that is close to its initial temperature.
    19. Process according to one of claims 1 to 18, wherein regeneration stage (c) comprises at least two successive regeneration operations, with a gas fraction that is rich in CO2 being obtained at the end of the first operation and a fraction that is rich in H2S being obtained at the end of the second operation.
    EP96402909A 1995-12-28 1996-12-27 Process for the dewatering, deactification and degasolination of natural gas, using a mixture of solvents Expired - Lifetime EP0783031B1 (en)

    Applications Claiming Priority (2)

    Application Number Priority Date Filing Date Title
    FR9515626A FR2743083B1 (en) 1995-12-28 1995-12-28 METHOD FOR DEHYDRATION, DEACIDIFICATION AND DEGAZOLINATION OF A NATURAL GAS, USING A MIXTURE OF SOLVENTS
    FR9515626 1995-12-28

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    EP0783031A1 EP0783031A1 (en) 1997-07-09
    EP0783031B1 true EP0783031B1 (en) 2001-09-26

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    US (1) US5782958A (en)
    EP (1) EP0783031B1 (en)
    JP (1) JP4264594B2 (en)
    CA (1) CA2194083C (en)
    DE (1) DE69615522T2 (en)
    DK (1) DK0783031T3 (en)
    FR (1) FR2743083B1 (en)
    NO (1) NO314901B1 (en)

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    EP0783031A1 (en) 1997-07-09
    CA2194083A1 (en) 1997-06-29
    US5782958A (en) 1998-07-21
    NO965609L (en) 1997-06-30
    FR2743083A1 (en) 1997-07-04
    CA2194083C (en) 2006-06-06
    NO965609D0 (en) 1996-12-27
    NO314901B1 (en) 2003-06-10
    FR2743083B1 (en) 1998-01-30
    DE69615522D1 (en) 2001-10-31
    DK0783031T3 (en) 2001-11-26
    JP4264594B2 (en) 2009-05-20
    JPH09194851A (en) 1997-07-29
    DE69615522T2 (en) 2002-04-25

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