Separation method

Abstract

Method for producing a gas enriched in carbon dioxide from a feed synthesis gas 16 comprising at least one condensable component and in particular hydrogen, characterized in that the method further comprises: -a step referred to as a desaturation step during which at least a portion of the condensable component contained in the feed synthesis gas 16 is, upstream of said pressure swing adsorption separation unit (1), condensed by cooling to a temperature below 10°C, in particular below or equal to 5°C, and separated, producing said desaturated synthesis gas (17) and at least one condensate (6); - the feed synthesis gas (16) exchanging heat with the desaturated synthesis gas (17) so as to heat said desaturated synthesis gas (17).

Description

Separation process

[0001] The present invention relates to a method for producing a gas enriched in carbon dioxide from a synthesis gas. The invention also relates to an installation for implementing such a method.

[0002] Carbon dioxide capture processes are used in the production of hydrogen from synthesis gas originating from a steam methane reforming reaction and / or partial oxidation of methane, most often combined with a steam carbon monoxide conversion (also called a shift) reaction. To separate and purify (and possibly capture) the carbon dioxide contained in the synthesis gas cryogenically, for example, it is necessary to dry the feed gas to a separation and purification unit to remove condensable components (mainly water, but also possibly methanol or ammonia). This is, for example, to avoid the solidification of water into ice when the separation and purification unit is a cryogenic unit in which the carbon dioxide is separated and purified by partial condensation.A typically used drying unit is a temperature-modulated adsorption drying unit (also called a TSA unit).

[0003] Syngas typically consists of 75% hydrogen. The remaining 25% is split between carbon dioxide and methane, nitrogen, residual carbon monoxide, and condensable components, including water. The syngas is first passed through a pressure swing adsorption separation unit (also known as a PSA unit) to separate the hydrogen from a carbon dioxide-enriched tail gas. Syngas from steam reforming, partial methane oxidation, and / or potentially steam shift is normally cooled to a temperature of around 30°C or 40°C before being sent to the PSA unit. The gas typically arrives at the PSA unit at a pressure between 20 and 60 bara, saturated with water.

[0004] The waste gas must be compressed, cooled to allow it to be dried and ultimately separated and purified from carbon dioxide in the separation and purification unit. Compression is typically carried out up to 50 bara. The other gases in the waste gas are, for example, burned in the furnace where the reforming reaction takes place.

[0005] Cooling the waste gas during compression reduces the energy consumption of the compression stage. A compression and cooling device is therefore used, comprising one or more compression stages and so-called intermediate cooling heat exchangers, located between two compression stages, to cool the compressed waste gas. Intermediate heat exchangers are also called "intercoolers". Cooling exchangers typically use water as a cooling fluid, which can then be cooled in cooling towers. A problem arises during the compression and cooling of the waste gas in these cooling exchangers: the waste gas can reach its dew point and the condensable components are condensed. Condensate(s) composed mainly of water and dissolved carbon dioxide are then generated.They are particularly acidic (pH ~3).

[0006] Different strategies have been implemented in the prior art to minimize the costs associated with the compression of waste gas.

[0007] The use of corrosion-resistant materials, such as stainless steel, for the compression system, particularly for the intermediate exchangers, allows the waste gas to be dried at high pressure without the risk of corrosion of the materials by the condensable components. The drying cost is also reduced thanks to the relatively high pressure, and operating costs accordingly. However, such materials lead to increased capital expenditure.

[0008] Drying the waste gas upstream of compression allows the use of cheaper materials such as carbon steel for the compression device, since the condensable components have been removed. However, the drying cost is higher due to the large amount of condensable components to be removed, the large volume flow rate and the low-pressure adsorption isotherms.

[0009] Drying the waste gas at an intermediate compression stage is a known compromise, allowing the use of carbon steel in the compression stages downstream of the drying unit and reducing the cost of drying, which is done at a higher pressure. The drying unit (or dryer) is typically located at a compression stage of approximately 10 bara. It is also known to use, upstream of the drying unit, a device for condensing condensable components by cooling to treat the waste gas from the PSA unit. Such a device using, for example, iced water maximizes condensation upstream of the dryer. In order to also maintain carbon steel in the compression stages upstream of the drying unit, it is however necessary to maintain the waste gas at a temperature of 7 to 10°C above the dew point temperature of the condensable components.This is a safety margin against potential temperature fluctuations that could lead to accidental condensation of condensable components. Keeping the waste gas at a higher temperature in this way means that compression takes place at a higher temperature, which consumes more energy.

[0010] It is generally difficult to manage the risks of condensation during this compression stage, particularly at the upper compression stages, upstream of the drying unit if applicable. Furthermore, when the temperature drops in winter, the risk of accidental condensation increases further. There is therefore a need for a process for producing a carbon dioxide-enriched gas with fewer condensation-related constraints and lower electricity consumption.

[0011] The subject of the invention is thus a method for producing a gas enriched in carbon dioxide from a feed synthesis gas comprising at least one condensable component, the feed synthesis gas comprising in particular hydrogen, the method comprising the following steps: a) introducing into a pressure swing adsorption separation unit (PSA unit) a so-called desaturated synthesis gas from the feed synthesis gas; b) separating by the pressure swing adsorption separation unit the desaturated synthesis gas into a first fraction and a carbon dioxide-enriched residual gas; c) compressing the residual gas with at least two compression stages and cooling to at least one intermediate compression stage of the compressed residual gas;characterized in that the method further comprises:- a so-called desaturation step, during which at least a portion of the at least one condensable component contained in the feed synthesis gas is, upstream of said pressure swing adsorption separation unit, condensed by cooling below a temperature below 10°C, in particular below or equal to 5°C and separated, producing said desaturated synthesis gas and at least one condensate;- the feed synthesis gas exchanging heat with the desaturated synthesis gas so as to reheat said desaturated synthesis gas upstream of the pressure swing adsorption separation unit.;

[0012] Contrary to what is known from the state of the art in which the device for condensing the condensable components by cooling treats the residual gas to maximize the condensation of said components upstream of a dryer, the invention proposes to treat the feed gas of the PSA unit. It is known from the prior art that extensively cooling the feed gas of a PSA unit does not provide anything from the point of view of this unit, or is even detrimental to its operation.

[0013] Removing at least a portion of the condensable component(s) from the PSA unit feed gas reduces the risk of accidental condensation of said component(s) during step c) from a certain compression stage. Reheating the PSA unit feed gas, thoroughly cooled during the desaturation step, allows it to be brought back into temperature ranges compatible with proper operation of the PSA unit.

[0014] According to one implementation of the method, the feed syngas comprises between 70 and 80% hydrogen and between 20 and 30% other compounds including carbon dioxide, the at least one condensable component, optionally residual methane and carbon monoxide and for example nitrogen. In particular, the first fraction is enriched in hydrogen.

[0015] According to one implementation of the method, the at least one condensable component is chosen from water, ammonia and / or methanol.

[0016] According to one implementation of the process, the desaturated synthesis gas comprises between 150 and 700 ppmv of condensable component, in particular between 150 and 700 ppmv of water.

[0017] According to one implementation of the method, during the desaturation step, the condensation of the at least one condensable component is carried out by cooling the feed synthesis gas using a refrigerant. The refrigerant is in particular chosen from iced water, cold air or a refrigerant.

[0018] According to one implementation of the method, the feed synthesis gas exchanges heat with the desaturated synthesis gas in a so-called economizer exchanger and a minimum temperature difference between the feed synthesis gas and the desaturated synthesis gas, within the economizer exchanger, is between 2 and 10°C, in particular between 5 and 10°C. A temperature of the desaturated synthesis gas is in particular between 20 and 40°C, in particular between 30 and 40°C.

[0019] According to one implementation of the process, the first fraction is enriched with hydrogen.

[0020] According to one implementation, the method comprises a step d) during which the waste gas is dried by adsorption so as to separate the residual condensable component from the waste gas.

[0021] According to one implementation of the method, the waste gas is dried during step d), downstream of compression step c). Alternatively, the waste gas is dried during step d), at an intermediate compression stage during step c).

[0022] According to one implementation of the method, in step d), the waste gas is dried by adsorption in a waste gas drying unit by adsorption and the method comprises a step of regenerating said waste gas drying unit by adsorption.

[0023] According to one implementation, the method comprises, downstream of step c) and optionally downstream of step d) when the latter exists, a step e) during which the carbon dioxide is separated from the waste gas to be captured or sequestered. The carbon dioxide is in particular separated by partial condensation during step e), the carbon dioxide being at least partly condensed. Alternatively, the carbon dioxide is separated from the waste gas using a membrane in a membrane unit. Alternatively, the carbon dioxide is separated by the combination of separation by partial condensation and separation using a membrane.

[0024] According to one implementation, the method comprises, upstream of the desaturation step, a step of cooling the feed synthesis gas, in particular using a cooling fluid, such as cooling water or air. The step of cooling the feed synthesis gas is in particular carried out in at least one so-called feed heat exchanger arranged upstream of the desaturation step.

[0025] According to one implementation, the method comprises the following steps: - measuring a temperature of the desaturated synthesis gas, - comparing the measured temperature of the desaturated synthesis gas with a minimum set temperature of the desaturated synthesis gas entering the pressure swing adsorption separation unit, - if the measured temperature of the desaturated synthesis gas is lower than the minimum set temperature, regulating the temperature of the desaturated synthesis gas by reducing the cooling of the feed synthesis gas in the feed heat exchanger.

[0026] The invention also relates to a plant for producing a gas enriched in carbon dioxide from a feed synthesis gas comprising at least one condensable component, the feed synthesis gas comprising in particular hydrogen, the plant comprising:- a pressure swing adsorption separation unit (PSA unit) configured to separate a so-called desaturated synthesis gas, from the feed synthesis gas, into a first fraction and a residual gas enriched in carbon dioxide;- a compression device arranged downstream of the pressure swing adsorption separation unit, the compression device comprising at least two stages for compressing the residual gas and at least one intermediate exchanger for cooling the compressed residual gas at an intermediate compression stage;characterized in that the installation comprises:- upstream of the pressure swing adsorption separation unit, a cooling and separation condensation device configured to condense and separate at least part of the condensable component contained in the feed synthesis gas and produce the desaturated synthesis gas and at least one condensate;- an economizer exchanger arranged to cause a heat exchange between the feed synthesis gas and the desaturated synthesis gas.;

[0027] According to one embodiment, the pressure swing adsorption separation unit is configured to separate the desaturated synthesis gas into a first hydrogen-enriched fraction and a carbon dioxide-enriched tail gas.

[0028] According to one embodiment, the installation comprises an adsorption waste gas drying unit configured to separate residual condensable component from the waste gas.

[0029] According to one embodiment, the installation comprises, downstream of the compression device, in particular where appropriate downstream of the waste gas drying unit, a separation and purification unit configured to separate the carbon dioxide from the compressed and optionally dried waste gas and to capture or sequester said carbon dioxide. The separation and purification unit comprises in particular a unit configured to separate the carbon dioxide from the waste gas by partial condensation. Alternatively, the separation and purification unit comprises a membrane unit configured to separate the carbon dioxide from the waste gas using a membrane. Alternatively, the separation and purification unit comprises, for the separation of the carbon dioxide from the waste gas, a combination of a unit configured to separate the carbon dioxide by partial condensation and a membrane unit.

[0030] According to one embodiment, the cooling and separation condensation device comprises:- a dual-fluid exchanger comprising a feed synthesis gas circulation section and a refrigerant fluid circulation section, arranged to be in heat exchange with the feed synthesis gas circulation section, cool the feed synthesis gas, condense the condensable compounds and produce the desaturated synthesis gas and the at least one condensate;- a condensate separation device configured to separate the at least one condensate from the desaturated synthesis gas.The dual-fluid exchanger is in particular a shell-tube type exchanger, the refrigerant fluid circulation section being defined by the internal space of at least one tube contained in a shell and the feed synthesis gas circulation section being defined by a space between the shell and the at least one tube.The device for separating the at least one condensate is, for example, a phase separator container. The device for condensation by cooling and separation comprises in particular a refrigeration unit for cooling the refrigerant fluid.

[0031] According to one embodiment, the economizer exchanger comprises:- a first section for circulating the feed synthesis gas;- a second section for circulating the desaturated synthesis gas, arranged to be in heat exchange with the first section.The economizer exchanger is in particular a shell-tube type exchanger, the section for circulating the desaturated synthesis gas being defined by the internal space of at least one tube contained in a shell and the section for circulating the feed synthesis gas being defined by a space between the shell and the at least one tube.

[0032] According to one embodiment, the installation comprises, upstream of the first section of the economizer exchanger, at least one so-called feed heat exchanger, arranged to regulate the temperature of the feed synthesis gas. The feed heat exchanger comprises in particular a channel for circulating the feed synthesis gas and a channel for circulating a cooling fluid, such as cooling water or air, the cooling fluid circulation channel being arranged to be in heat exchange with the channel for circulating the feed synthesis gas.

[0033] According to one embodiment, the compression device is at least partly made of carbon steel alloy, in particular the at least one intermediate exchanger of said compression device.

[0034] According to one embodiment, the adsorption drying unit is arranged downstream of the compression device. Alternatively, the adsorption drying unit is arranged at an intermediate compression stage of the compression device. The adsorption drying unit is in particular a regenerable unit such as a temperature-modulated adsorption drying unit (TSA unit).

[0035] The plant for producing a gas enriched in carbon dioxide can be used to implement the process as described above.

[0036] The invention also relates to a method for redesigning a plant for producing a gas enriched in carbon dioxide from a feed synthesis gas comprising at least one condensable component, the feed synthesis gas comprising in particular hydrogen, the plant comprising:- a pressure swing adsorption separation unit configured to separate a so-called desaturated synthesis gas, from the feed synthesis gas, into a first fraction and a carbon dioxide-enriched residual gas;- a compression device arranged downstream of the pressure swing adsorption separation unit, the compression device comprising at least two stages for compressing the residual gas and at least one intermediate exchanger for cooling the compressed residual gas at an intermediate compression stage;the method comprising the steps:- arranging upstream of the pressure swing adsorption separation unit a cooling and separation condensation device configured to condense and separate at least a portion of the at least one condensable component contained in the feed synthesis gas and produce the desaturated synthesis gas and at least one condensate;- arranging a first circulation section of an economizer exchanger upstream of the cooling and separation condensation device for circulating the feed synthesis gas and arranging a second circulation section of the economizer exchanger downstream of the cooling and separation condensation device and upstream of the pressure swing adsorption separation unit, for circulating the desaturated synthesis gas.;

[0037] It represents a facility for producing a gas enriched in carbon dioxide from a feed synthesis gas 16 (or syngas).

[0038] In the embodiment shown, the feed syngas 16 is produced in a unit for the production of hydrogen and comprises hydrogen. It is typically a syngas comprising between 70 and 80% hydrogen and between 20 and 30% of other compounds including carbon dioxide, at least one condensable component (a plurality in this embodiment: "the condensable components"), unconverted methane, unconverted carbon monoxide and nitrogen. The feed syngas is for example saturated with condensable components or unsaturated.

[0039] The synthesis gas is treated in a pressure swing adsorption separation unit 1 (also called PSA unit) to separate the synthesis gas into a first hydrogen-enriched fraction and a carbon dioxide-enriched tail gas 2. The PSA unit 1 comprises a first outlet for the first hydrogen-enriched fraction (hydrogen PSA) and a second outlet for the produced tail gas 2. A pipeline supplies the PSA unit 1 with synthesis gas. The pressure swing adsorption separation unit 1 will recover up to 90% of the hydrogen initially contained in the synthesis gas.

[0040] Upstream of the pressure swing adsorption separation unit 1, the feed synthesis gas 16 is separated from at least a portion of its condensable components (here essentially water) in a cooling and separation condensation device which produces a desaturated synthesis gas 17 and condensates 6. The desaturated synthesis gas 17 comprises in particular between 150 and 700 ppmv of water. This device comprises a two-fluid exchanger 3 which itself comprises a circulation section 4 for the feed synthesis gas 16, arranged on the supply line 16 of the PSA unit 1 in synthesis gas, and a circulation section 5 for a refrigerant fluid. These two sections are arranged in the two-fluid exchanger 3 to be in heat exchange with each other.The dual-fluid exchanger 3 thus allows a heat exchange between the refrigerant and the feed synthesis gas 16, the refrigerant cooling the feed synthesis gas 16 to a temperature below 10°C, in particular to a temperature below or equal to 5°C. This cooling thus causes the condensation of a portion of the condensable components contained in the feed synthesis gas 16, thus giving the condensates 6. The PSA unit 1 then treats a gas which has been stripped of a portion of its condensable components, which simplifies its regeneration. The risk of accidental condensation during a compression step of the residual gas 2 produced by the PSA unit 1 is thus reduced. The refrigerant is for example iced water, cold air or a refrigerant. The refrigerant is supplied to the dual-fluid exchanger 3 after having been cooled by a refrigeration unit (not shown).The dual-fluid exchanger 3 is typically a shell-and-tube type exchanger, the circulation section of the refrigerant fluid being defined by the internal space of at least one tube contained in a shell and the circulation section of the synthesis gas being defined by a space between the shell and the at least one tube.

[0041] The condensates 6 are then separated in a condensate separation device 6. The condensate separation device 6 and the dual-fluid exchanger 3 may be integrated, in which case the separation of the condensates 6 takes place in the body of the exchanger itself or the heat exchange takes place in the condensate separation device 6. Alternatively, the condensate separation device 6 may constitute a separate unit from the dual-fluid exchanger 3 within the cooling and separation condensation device. The condensate separation device 6 is, for example, a phase separator can.

[0042] The installation comprises an economizer exchanger 7 arranged to cause a heat exchange between the feed synthesis gas 16 and the desaturated synthesis gas 17. For this, the economizer exchanger 7 comprises a first circulation section 8 of the feed synthesis gas 16, arranged on an upstream portion (relative to the cooling and separation condensation device) of the feed pipe of the PSA unit 1. The economizer exchanger 7 further comprises a second circulation section 9 of the desaturated synthesis gas 17, arranged on a portion of the feed pipe of the PSA unit 1, downstream of the cooling and separation condensation device. These two sections are arranged in the economizer exchanger 7 to be in heat exchange with each other. The economizer exchanger 7 thus allows a heat exchange between the feed synthesis gas 16 (not desaturated) and the desaturated synthesis gas 17.The minimum temperature difference between the two circulation sections of the economizer exchanger 7 (approach to minimum temperature) is between 2 and 10°C, in particular between 5 and 10°C. The feed synthesis gas 16 thus heats the desaturated synthesis gas 17 before sending it to the PSA unit 1. The economizer exchanger 7 is typically a shell-and-tube type exchanger, the circulation section of the desaturated synthesis gas 17 being defined by the internal space of at least one tube contained in a shell and the circulation section of the feed synthesis gas 16 being defined by a space between the shell and the at least one tube. The negative impact of the advanced cooling caused by the condensation device by cooling and separation upstream of the unit is thus avoided.

[0043] In a case where the economizer exchanger 7 would not be sufficient to compensate for the impact of the cooling on the PSA unit 1, it is proposed to regulate the temperature of the feed synthesis gas 16, coming from a reforming unit and / or a partial oxidation unit, using a heat exchanger 15 arranged upstream of the economizer exchanger 7 and the cooling and separation condensation device, from the process point of view (feed exchanger 15). A typical regulation comprises a step of measuring a temperature of the desaturated synthesis gas 17 and a step of comparing this temperature with a minimum set temperature of the desaturated synthesis gas 17 entering the pressure swing adsorption separation unit.If the temperature of the feed synthesis gas 16 is too low, i.e. below the minimum set temperature, it is possible to limit the cooling of the feed synthesis gas 16 by reducing the flow rate of a cooling fluid (chosen from cooling water or air) circulating in the feed exchanger 15 and / or by having a portion of the synthesis gas bypass said feed exchanger 15 (a portion of the feed synthesis gas 16 is then no longer cooled and is mixed with the portion which is cooled in the heat exchanger 15). The operation is carried out until the measured temperature of the desaturated synthesis gas 17 is greater than or equal to the minimum set temperature. A calculation and control unit (not shown) makes it possible to carry out the measurements and calculations necessary for such regulation.

[0044] Since the economizer exchanger 7 provides a large part of the cooling, the cooling and separation condensation device only serves to adjust the cooling temperature and its size and energy consumption can be reduced. The bi-fluid exchanger 3 then only needs to provide the condensation energy of the condensable components but not that of cooling the other compounds of the synthesis gas, such as hydrogen.

[0045] The desaturated synthesis gas 17 is therefore brought to the PSA unit 1, at a temperature typically between 30 and 40°C and a pressure between 20 and 60 bara (bar absolute). The PSA unit 1 then produces the residual gas 2. This is then compressed in a compression device 10. The compression device 10 comprises two stages 11a; 11b or compression levels of the residual gas 2. In other embodiments, the compression device 10 may however comprise more than two compression stages. After compression at the first compression level, the residual gas 2 is cooled by an intermediate exchanger 12 for cooling (intercooler in English) the compressed residual gas at an intermediate compression stage 11a. The fact that at least part of the condensates have been eliminated downstream of the PSA unit makes it possible to further cool the residual gas 2 without risk of condensation in the intermediate exchanger 12.The compression device 10 then consumes less energy to compress the waste gas 2. In the intermediate exchanger 12, water cooled in cooling towers (not shown) typically serves as the cooling fluid. The intermediate exchanger 12 is at least partly made of carbon steel alloy, this being made possible by the reduced risks of condensation. Such materials are less expensive than stainless steel. In particular, such an alloy is not designed to withstand compounds whose pH is lower than 4. A compression stage corresponds to a compression level reached in the compression device 10 at the outlet of a compression member, such as a compression wheel. An intermediate compression stage is then located between two compression members of the compression device 10.

[0046] In a non-shown embodiment, the compressed waste gas from the compression device 10 is cooled in a final cooling exchanger. The compressed waste gas from the compression device 10 is sent to a temperature-modulated adsorption drying unit 13 (TSA unit) in which the waste gas is, by adsorption, freed from the residual condensable components it contains. The TSA unit 13 cyclically undergoes production steps during which the waste gas is dried and regeneration steps during which the adsorbent is regenerated. In the embodiment of the, the drying by the TSA unit 13 takes place after the compression step, downstream of the compression device 10, at a pressure of approximately 50 bara.In another embodiment, the drying by the TSA unit 13 can also take place at an intermediate compression stage 11a of said compression device 12, at a pressure of approximately 10 bara.

[0047] Once dried, the carbon dioxide-enriched waste gas is sent to a separation and purification unit 14 in which the carbon dioxide is separated from the other components of the waste gas during partial condensation, producing a liquid phase and a gaseous phase, the carbon dioxide being at least partly condensed in the liquid phase. The separation and purification unit 14 notably comprises a membrane unit (not shown) configured to separate the residual gaseous carbon dioxide from the gaseous phase from the other gaseous components of the gaseous phase. Alternatively, the separation and purification unit comprises a membrane unit which alone ensures the separation of the carbon dioxide from the other components of the waste gas. Thanks to the separation and purification unit, the carbon dioxide can be captured rather than being emitted into the atmosphere, which improves the carbon footprint of hydrogen production.

[0048] A standard carbon dioxide enriched gas production facility can be revamped to incorporate a cooling and separation condensation device and an economizer exchanger 7 as described above and implement a less restrictive process from a condensation point of view.

[0049] The method according to the invention is also applicable to autothermal reforming processes and partial oxidation processes, in addition to steam reforming processes.

[0050] Thanks to the invention, it is possible to use a compression and cooling device partly made of carbon steel. The investment costs for the compression device are reduced. In addition, reducing the content of condensable components in the synthesis gas and therefore that of the residual gas allows the latter to be cooled further during the compression step, which saves a lot of energy. Furthermore, when it is necessary to separate the residual condensable components from the residual gas, it is possible to carry out the drying by the drying unit 13 of the residual gas by adsorption at a higher pressure than that at which it is normally carried out around 10 bara in the state of the art, without having to use a compression and cooling device made of stainless steel. The cost of drying is then reduced and a smaller drying unit can be used.The process start-up phase is also less restrictive in terms of preheating the installation because the risk of condensation due to excessively cold temperatures is reduced. Condensing some of the condensable components contained in the synthesis gas upstream of the PSA 1 unit also allows certain impurities to be eliminated through the condensates, limiting their quantity in the residual gas. Condensates other than water, possibly present in the synthesis gas, such as methanol or ammonia, can be eliminated. These impurities or condensates would otherwise have had to be treated by a catalytic unit or by an adsorption drying unit oversized for this purpose.

Claims

A method for producing a carbon dioxide-enriched gas from a feed synthesis gas (16) comprising at least one condensable component, in particular hydrogen, the method comprising the following steps: a) introducing a so-called desaturated synthesis gas (17) from the feed synthesis gas (16) into a pressure swing adsorption separation unit (1); b) separating the desaturated synthesis gas (17) into a first fraction and a carbon dioxide-enriched waste gas (2) by the pressure swing adsorption separation unit (1); c) compressing the waste gas (2) with at least two compression stages (11a; 11b) and cooling the compressed waste gas to at least one intermediate compression stage;characterized in that the method further comprises:- a so-called desaturation step during which at least a portion of the condensable component contained in the feed synthesis gas (16) is, upstream of said pressure swing adsorption separation unit (1), condensed by cooling to a temperature below 10°C, in particular below or equal to 5°C and separated, producing said desaturated synthesis gas (17) and at least one condensate (6);- the feed synthesis gas (16) exchanging heat with the desaturated synthesis gas (17) so as to reheat said desaturated synthesis gas (17) upstream of the pressure swing adsorption separation unit (1).; A method according to the preceding claim, wherein the feed synthesis gas (16) comprises between 70 and 80% hydrogen and between 20 and 30% other compounds including carbon dioxide and the condensable component. Method according to one of the preceding claims, in which the condensable component is chosen from water, ammonia and / or methanol. Method according to one of the preceding claims, in which during the desaturation step, the condensation of the condensable component is carried out by cooling the feed synthesis gas (16) using a refrigerant fluid. Method according to one of the preceding claims, in which the feed synthesis gas (16) exchanges heat with the desaturated synthesis gas (17) in an exchanger called an economizer (7) and a minimum temperature difference within the economizer exchanger (7) between the feed synthesis gas (16) and the desaturated synthesis gas (17) is between 2 and 10°C, in particular between 5 and 10°C. Method according to one of the preceding claims, comprising a step d) during which the waste gas is dried by adsorption so as to separate the residual condensable component from the waste gas. Process according to the preceding claim, in which the residual gas is dried during step d), downstream of compression step c). Method according to claim 6, wherein the waste gas is dried during step d), at an intermediate compression stage (11a). Method according to one of the preceding claims comprising, downstream of step c), a step e) during which the carbon dioxide is separated from the waste gas to be captured or sequestered. Method according to the preceding claim, wherein said carbon dioxide is, during step e), separated by partial condensation, the carbon dioxide being at least partly condensed and / or the carbon dioxide is separated using a membrane, in a membrane unit. Method according to one of the preceding claims comprising the following steps: - measuring a temperature of the desaturated synthesis gas (17), - comparing the temperature of the desaturated synthesis gas (17) measured with a minimum set temperature of the desaturated synthesis gas (17) introduced into the pressure swing adsorption separation unit, - if the temperature of the desaturated synthesis gas (17) measured is lower than the minimum set temperature, regulating the temperature of the desaturated synthesis gas (17) by reducing the cooling of the feed synthesis gas (16) in at least one so-called feed heat exchanger (15), arranged upstream of the desaturation step. Installation for producing a gas enriched in carbon dioxide from a feed synthesis gas (16) comprising at least one condensable component and in particular hydrogen, the installation comprising:- a pressure swing adsorption separation unit (1) configured to separate a so-called desaturated synthesis gas (17), from the feed synthesis gas (16), into a first fraction and a residual gas (2) enriched in carbon dioxide;- a compression device (10) arranged downstream of the pressure swing adsorption separation unit (1), the compression device (10) comprising at least two stages (11a; 11b) for compressing the residual gas (2) and at least one intermediate exchanger (12) for cooling the compressed residual gas at an intermediate compression stage;characterized in that the installation comprises:- upstream of the pressure swing adsorption separation unit (1), a cooling and separation condensation device configured to condense and separate at least part of the condensable component contained in the feed synthesis gas (16) and produce the desaturated synthesis gas (17) and at least one condensate (6);- an economizer exchanger (7) arranged to cause a heat exchange between the feed synthesis gas (16) and the desaturated synthesis gas (17).; Installation according to the preceding claim, comprising a drying unit (13) by adsorption of the residual gas, configured to separate the residual condensable component from the residual gas (2). Installation according to one of claims 12 or 13, in which the device for condensation by cooling and separation comprises:- a bi-fluid exchanger (3) comprising a circulation section (4) of the feed synthesis gas (16) and a circulation section (5) of a refrigerant fluid, arranged to be in heat exchange with the circulation section (4) of the feed synthesis gas (16), cool the feed synthesis gas (16), condense the condensable compounds and produce the desaturated synthesis gas (17) and the condensate (6);- a condensate separation device configured to separate the condensate (6) from the desaturated synthesis gas (17). Installation according to one of claims 12 to 14, in which the economizer exchanger (7) comprises:- a first circulation section (8) of the feed synthesis gas (16);- a second circulation section (9) of the desaturated synthesis gas (17), arranged to be in heat exchange with the first section (8).

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