Method and apparatus for separating a mixture containing CO2 by partial condensation

Abstract

Title of the invention: Method and apparatus for separating a mixture containing CO2 by partial condensation In a method for separating a mixture containing CO2 by partial condensation, the mixture (G) containing at least one impurity lighter than CO2 as well as at least one SO2 or SO3 impurity, the mixture is washed in a washing column, dried in a drying unit (A) and separated by partial condensation (15), at least a portion (25B) of the regeneration gas (25) from the drying unit being sent to the washing column in gaseous form. Fig. 1

Description

Title of the invention: Method and apparatus for separating a mixture containing CO2 by partial condensation

[0001] Introduction

[0002] Processes for capturing and purifying CO2 from the fumes of fossil fuel electricity production units or cement or lime production units include steps for managing impurities and contaminants. These impurities can be removed at different points in the process to be recycled to another point where they will be removed. The invention provides a solution for removing certain impurities efficiently.

[0003] State of the art

[0004] There are many techniques for reducing and removing impurities in CO2 capture processes. Typically, they are in the following order: 1. Washing the inlet fumes with water to reduce some of the dust and water-soluble impurities such as strong acids (SO3, HCl, HF for example). The impurities are then removed in the liquid condensates generated. 2. Washing with a basic solution (e.g. sodium hydroxide) to break down acid molecules (e.g. strong acids and SO2). The impurities are then removed in the liquid condensates generated. 3. Filtration of residual dust. The dust is evacuated by gravity. 4. Successive compression and cooling of the fumes allowing the partial reduction of soluble molecules in the acid condensates generated during cooling in the intermediate heat exchangers or in the exchangers at the outlet of the compression stage, such as nitric acid for example. The impurities are then evacuated in the generated acid liquid condensates. 5. Adsorption drying of compressed flue gases allowing at least partial stopping of adsorbed molecules such as water but also many other compounds such as SO2, BTEX, PAHs etc. The adsorbed impurities are evacuated with the generation gas which is recycled upstream of the dryer, in the compression and cooling chain. The impurities are then evacuated in the previous acidic liquid condensates.

[0005] Problem solved by the invention

[0006] Certain molecules are stopped by the adsorption dryer but are not necessarily soluble (or only slightly) in the acid condensates generated during the steps of flue gas compression and cooling. In this case, the state-of-the-art scheme, for example, that of WO2014 / 009449, is not suitable. Here the regeneration gas is returned to the flue gas compressor. The impurities in the regeneration gas will then follow a cycle of stopping (adsorption) and recycling (regeneration and return) then concentrating in the loop to high levels which may involve: parasitic chemical reactions generating new impurities harmful to the process. For example, high concentrations of SO2 can be transformed into SO3 by reaction with oxygen and / or NOx. This SO3 is then present downstream of the basic solution washing, therefore in the compression chain, requiring more stringent material selection, a breakthrough of the molecules concerned at the outlet of the dryer, the maximum adsorption capacity being reached. These impurities will therefore spread throughout the rest of the process, generating other potential problems such as blockage of the cryogenic part, for example.

[0007]

[0008] Description of the invention The invention consists of: increase the processing capacity of the water wash or wash stages to the basic solution install a regeneration gas bypass valve at the dryer outlet to send at least part of the regeneration gas upstream of the water or basic solution washing step potentially perform an impurity analysis on the regeneration gas and regulation of the opening of the previous bypass valve based on the measured content.

[0009] In this way, if an impurity tends to concentrate in the regeneration loop (being stopped by the dryer) and this impurity is at least partially removed during the washing step with the basic solution, it will be removed more easily from the overall system by means of the washing condensates and its concentration will then be limited.

[0010] A notable example is the SO2 molecule. Indeed, in the case of a thorough but not absolute reduction during the washing step with the basic solution, contents of several ppmv or even tens of ppmv are possible at the inlet of the compression and cooling steps. The condensate conditions being acidic, the residual SO2 will be very little reduced and will therefore reach the dryer. In the dryer, a very significant portion of this SO2 will be stopped and therefore sent to regeneration. If this regeneration gas is recycled upstream of compression, the SO2 will therefore concentrate to levels leading to a breakthrough through the dryer or even to levels promoting oxidation to SO3. If at least part of the regeneration gas is sent upstream of the washing step with the basic solution, the SO2 will be strongly evacuated, thus limiting their concentration in the loop.

[0011] It is also possible to open the bypass valve only when the concentration of impurity to be removed is high and to close it when it is low. This saves compression energy when the regeneration is recycled intermediate to the compression stage or even at the outlet of the compression stage before the last cooling.

[0012] The invention makes it possible to purify a gas mixture containing at least 10 mol% of carbon dioxide, or even at least 50 mol% of carbon dioxide, or even at least 75 mol% of carbon dioxide to produce a flow enriched in carbon dioxide relative to the mixture. The percentages cited relate to the dry-based gas mixture, which very often contains water.

[0013] All percentages relating to purities in this document are molar percentages.

[0014] The capture and purification of CO2 by cryogenic means uses the partial condensation of CO2 which can be supplemented by one or more distillations and / or solidification to increase the CO2 purity of the final product. To ensure these partial condensations and distillations, the gases to be purified must be compressed, dried and then cooled to form a liquid phase enriched in CO2 and a gas phase enriched in incondensable gases which will be separated in one or more partial condensation pots. Thanks to this type of process, capture efficiencies of between 80 and 95% are achievable. The term "incondensable gases" refers to gases which condense at lower temperatures than that at which CO2 condenses and may include nitrogen, oxygen, methane, carbon monoxide, argon.

[0015] In certain cases, the CO2 content of the gas to be partially condensed is increased by at least one separation step by adsorption or by permeation.

[0016] The non-condensable gases are most often heated against the gases to be purified, which cool before being emitted into the atmosphere. Before being emitted into the ambient air, they can also be used to regenerate the dryers of the capture unit.

[0017] In order to maximize the CO2 capture efficiency, membranes can also be used on the non-condensable gases coming from the partial condensation pot(s). A method of this kind is known from EP-A-2404656.

[0018] Two important parameters allow the sizing of membranes and the quantification of their performance: the efficiency per membrane and the CO2 selectivity. The higher the CO2 efficiency, the less it will be necessary to add membrane modules to increase the overall efficiency of the unit. The initial investment is then reduced. The higher the CO2 selectivity, the less the other gases will pass through the membrane. High CO2 selectivity makes it possible to obtain a purer CO2 permeate and to reduce the energy consumption of the gas compressor to be purified.

[0019] The membrane used can operate at ambient temperature (not shown) or subambient, as shown in [Fig.l]. The preferred solution is to use the membrane separation units to separate a partially heated gas, either at the hot end of the exchanger 12, preferably with a cold bypass circuit, or at the intermediate outlet of the exchanger 12.

[0020] To optimize both the efficiency and the selectivity of the membranes, using them at subambient temperatures (or even at temperatures <-10°C) can nevertheless prove relevant. A method of this type is described in WO-A-2014 / 009449 and in WO-A-2014 / 009643. They will thus be placed directly downstream of the partial condensation pot(s) with or without expansion of the non-condensable gases. If the temperature of the pot is too low to ensure the proper functioning and especially the feasibility of the membranes, the non-condensable gases can be partially heated before sending them to the membranes, up to temperatures between -45 and -10°C. However, when putting these membranes into operation, it is necessary to control the cooling of these membranes progressively: in fact, a direct supply of cold gas to the membranes could induce strong mechanical stresses on this equipment and lead to their degradation.

[0021] Furthermore, it is necessary to ensure good regulation of the operating conditions of these membranes (in particular the temperature) during normal operation to ensure optimal yields and also ensure the integrity of the materials which make up the membranes.

[0022] According to an object of the invention, there is provided a method for separating a mixture containing CO2 by partial condensation, the mixture containing at least one impurity lighter than CO2 as well as at least one impurity chosen from the list: SO2, SO3, the method comprising the following steps: i. washing the mixture in a washing column allowing the partial reduction of at least one impurity chosen from the list: SO2, SO3 ii. compression of the washed mixture iii. cooling of the compressed washed mixture, iv. drying and purification of at least one impurity chosen from the list: SO2, SO3, from the washed, compressed and cooled mixture in a temperature-swing adsorption unit which is regenerated by a regeneration gas v. separation of the dried and purified mixture in the adsorption unit at least by at least one partial condensation step and optionally by distillation and / or adsorption and / or solidification, the partial condensation producing a gas depleted in carbon dioxide compared to the dried and purified mixture as well as a liquid enriched in carbon dioxide compared to the dried and purified mixture and vi. recycling of at least part of the regeneration gas containing water and at least one impurity chosen from the list: SO2, SO3, to the inlet of the washing column to be washed there, the regeneration gas being a. the gas depleted in carbon dioxide compared to the dried and purified mixture produced by partial condensation, or b. formed by separating the carbon dioxide-depleted gas from the dried and purified mixture produced by partial condensation by at least one adsorption and / or permeation step or c. a portion of a carbon dioxide-rich product formed by separating the carbon dioxide-enriched liquid by distillation and / or adsorption and / or solidification, possibly after a vaporization or sublimation step vii. the regeneration gas having carried out the regeneration containing CO2, water and at least one impurity chosen from the list: SO2, SO3, water and at least one impurity coming from the temperature swing adsorption unit.

[0023] According to other optional aspects: • at least one other part of the regeneration gas containing water and at least one impurity chosen from the list: SO2, SO3, is sent to be compressed with the washed mixture in step ii) and / or cooled with the washed mixture compressed in step iii). • the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas downstream of the adsorption unit is measured and at least part of the regeneration gas is sent to the inlet of the washing column if, preferably only if, the content is above a first threshold. • the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas downstream of the adsorption unit is measured and at least part of the regeneration gas is sent to be compressed with the washed mixture in step ii) and / or cooled with the washed mixture compressed in step iii) if the content is below the first threshold or below a second threshold lower than the first threshold. • the washing of step i) is carried out in a gas / liquid contactor with a basic washing liquid containing NaOH and / or Na2CO3 and / or NaHCO3. • the washed, compressed and purified mixture is separated first by adsorption and then by partial condensation, a gas enriched in CO2 being produced in separating the mixture by adsorption and this CO2-enriched gas being partially condensed and separated in at least one phase separator. • the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas downstream of the adsorption unit is measured and at least part of the regeneration gas is sent to the air if, preferably only if, the content is above a third threshold, higher than the first threshold. • the regeneration gas is formed by membrane separation of the carbon dioxide depleted gas from the dried and purified mixture to produce a permeate having a richer carbon dioxide content than the carbon dioxide depleted gas.

[0024] According to another object of the invention, there is provided a separation apparatus

[0025] of a mixture containing CO2 by partial condensation, the mixture containing at least one impurity lighter than CO2 as well as at least one impurity chosen from the list: SO2, SO3 comprising: a washing column, means for sending the mixture to be washed in the washing column allowing the partial reduction of the at least one impurity chosen from the list: SO2, SO3, a compressor connected to the washing column to compress the washed mixture, means for cooling the compressed washed mixture in the compressor, a temperature-swing adsorption unit, means for sending the compressed and cooled mixture to be dried and purified of the at least one impurity chosen from the list: SO2, SO3, to the temperature-swing adsorption unit, means for sending a regeneration gas to the temperature-swing adsorption unit,at least one phase separator for separating the dried and purified mixture in the adsorption unit at least by at least one partial condensation step and optionally means of separation by distillation and / or adsorption and / or solidification, the at least one phase separator being capable of producing by partial condensation a gas depleted in carbon dioxide compared to the dried and purified mixture as well as a liquid enriched in carbon dioxide compared to the dried and purified mixture and a pipe connected to the temperature-swing adsorption unit for recycling at least part of the regeneration gas containing water and at least one impurity chosen from the list: SO2, SO3, to the inlet of the washing column to be washed there, means for withdrawing the regeneration gas a. as the gas depleted in carbon dioxide compared to the dried and purified mixture from the at least one phase separator, or, b. as a gas formed by separating the carbon dioxide-depleted gas from the dried and purified mixture produced by partial condensation by at least one adsorption and / or permeation step or c. as part of a carbon dioxide-rich product formed by separating the liquid enriched with carbon dioxide by distillation and / or adsorption and / or solidification, possibly after a vaporization or sublimation step.

[0026] According to other optional aspects, the apparatus comprises: • means for measuring the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas downstream of the adsorption unit • means for sending at least one portion of the regeneration gas to be compressed with the washed mixture in step ii) and / or cooled with the washed mixture compressed in step iii) depending on the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas downstream of the adsorption unit.

[0027] The invention will be described in more detail with reference to the figures where

[0028] [Fig-1] represents a separation method according to the invention.

[0029] [Fig.2] represents the part of a separation process according to the invention which is carried out at a temperature above 0°C.

[0030] [Fig.3] represents another separation method according to the invention.

[0031] In the variant of [Fig.l], the device comprises a single multi-fluid heat exchanger, called the main exchanger 13.

[0032] A gas mixture 1 containing carbon dioxide (for example containing at least 10 mol% of carbon dioxide, or even at least 50 mol% of carbon dioxide, or even at least 75 mol% of carbon dioxide), moisture and at least one other gas, chosen from the list: hydrogen, nitrogen, oxygen, argon, carbon monoxide is sent to a five-stage compressor 5A, 5B, 5C, 5D, 5E, stage 5A being followed by cooler RI, stages 5B and 5C by cooler R2 and stages 5D and 5E by a cooler R3. After being cooled by the final cooler R3, the mixture 7 is purified of water by the temperature swing adsorption unit A to form the dried flow 9. The mixture is purified in bed 10 during the regeneration of bed 12 and vice versa. The dried flow 9 is compressed in the compressor 5F, cooled by the cooler R4, partially condenses in the plate and fin heat exchanger 13 and is sent to the phase separator 15.

[0033] The first system operating at low temperature here comprises a single phase separator 15, as well as a stripping column 31, also known as a stripping column.

[0034] Alternatively, the gas from a first phase separator may be cooled in a heat exchanger and partially condense to form a two-phase flow. This two-phase flow may be sent to a second phase separator. The liquids from both separators may feed the top of the column 31.

[0035] The overhead gas 33 from column 31 heats up in the heat exchanger 13 and is recompressed in compressor 5F with flow rate 9. The bottom liquid 35 from column 31 is divided into two. One part 37 vaporizes in heat exchanger 13 and is divided into two. The other part 43 of the bottom liquid 35 is expanded in a valve 36, is sent to exchanger 13, vaporized, sent to a compressor C5 to C8, is cooled by cooler R8, is condensed by cooler R9 and then pumped by pump P to form a pressurized liquid product rich in carbon dioxide.

[0036] A portion 41 of the flow 37 is sent between stages C5, C6. The remainder 39 of the flow 37 is heated to the hot end of the exchanger 13 and is returned to the column 31 in the tank, without having been cooled, to provide reboiling heat.

[0037] The overhead gas 19 of the phase separator 15 is enriched with non-condensable gases, for example hydrogen, carbon monoxide, nitrogen, argon or oxygen. This gas may come from a second phase separator as described above, if there is one or both phase separators including the separator 15.

[0038] This gas is sent to a membrane separation unit 21 producing a permeate 25 enriched in CO2 and a non-permeate 23 depleted in CO2. The non-permeate 23 will be strongly heated before being sent to the atmosphere. The non-permeate 23 can be expanded in a turbine after heating in a heater.

[0039] The flow supplying the membrane system M is here at a temperature below -10°C. However, it is not essential that the membrane system M operates at a temperature other than ambient temperature.

[0040] The permeate 25, enriched in carbon dioxide compared to the flow rate 19, is heated in E1, E2 and used to regenerate the beds 10, 12 of adsorbent A, in turn. The permeate 25 leaving the bed of adsorbents is enriched in water but also in SO2 and / or SO3 accumulated in the bed 10, 12 and is sent at least in part to a washing tower Q by the flow rate 25B in gaseous form to be purified there.

[0041] [Fig. 2] shows in more detail the compressor 5A to 5E of [Fig. 1], as well as the adsorbent beds 10, 12 of the adsorption unit A, the compressor being preceded by a washing tower Q with an alkaline liquid. The tower Q in which the washing takes place is a gas / liquid contactor with a basic washing liquid preferably containing NaOH and / or Na2CO3 and / or NaHCO3.

[0042] A gas mixture G containing carbon dioxide, carbon (for example containing at least 10 mol% of carbon dioxide, or even at least 50 mol% of carbon dioxide, or even at least 75 mol% of carbon dioxide), at least one component lighter than carbon dioxide, and SO2 and / or SO3 is sent to the tower Q where it is washed, producing condensates C in the bottom of the tower and a gas 1 at the top of the tower Q, enriched in CO2 compared to the mixture 1 and depleted in SO2 and / or SO3 but still containing it. The gas 1 is filtered by a filter F, compressed by the stages in series 5A to 5E of the compressor 5 and is sent to the adsorption unit A to be dried forming a dried gas 9, knowing that a part of the water W has already been eliminated by the compression stages. In the adsorption unit, a very significant part of this SO2 and / or SO3 will be stopped and therefore sent to the regeneration gas 25.

[0043] The permeate 25, having served to regenerate the beds of unit A, leaves it loaded with water and can be sent as flow 25A to the compressor 5, for example between stages 5A and 5B or between stage 5E and the cooler 7 and / or as flow 25B through the valve V at the inlet of the tower Q while being mixed with the gas G. If this regeneration gas 25 is recycled only upstream of the compression (one of the stages 5A to 5E), the SO2 will therefore concentrate to levels leading to a breakthrough through the adsorption unit A, or even to levels promoting oxidation to SO3. If at least a portion of the regeneration gas 25 is sent upstream of the washing step Q with the basic solution, the SO2 will be strongly evacuated, thus limiting their concentration in the loop.

[0044] It is therefore possible to open valve V only when the concentration of an impurity to be eliminated, for example SO2, is high and to close it when it is low. This makes it possible to save compression energy when the regeneration is recycled as an intermediate part of the compression stage or even at the outlet of the compression stage before the final cooling.

[0045] For example, if the impurity content, for example SO2, of the permeate 25 having regenerated the adsorption unit A is below a threshold, all of the permeate 25 is sent to the compressor 5 at a point between two of the stages or after the last stage and the last cooler. If the content of this impurity, for example SO2, in the permeate having regenerated the adsorption unit A is above a threshold, which may be the threshold mentioned before or a threshold higher than this threshold, at least a part of the permeate 25 is sent as flow 25B in gaseous form to the bottom of the tower Q to be washed there, the remainder (if any) of the permeate 25 being sent to the compressor as for the previous case.

[0046] [Fig. 3] differs from [Fig. 1] in that the gas mixture G contains between 15 and 50 mol% CO2 9 as well as at least one impurity which is nitrogen. The gas 9 dried in the temperature swing adsorption unit A is separated in an adsorption unit 16, of the pressure swing type or a permeation apparatus to form a higher pressure flow 14 depleted in CO2 and enriched in nitrogen and a lower pressure flow 11 enriched in CO2 and depleted in nitrogen. It is this flow 11, preferably compressed, which is partially condensed in the heat exchanger 13 and separated in the phase separator 15, forming a liquid 17 enriched in CO2 to feed the column 21 and a gas depleted in CO2 25 compared to the mixture 1. The gas 25 is used to regenerate the adsorption unit A and comes out loaded with water and SO2 and / or SO3.

[0047] As for [Fig.l], this [Fig.3] presents the risk of accumulation of SO2 and / or SO3 in the adsorption unit A, if at least part of the gas 25 is not sent at least occasionally to the washing tower Q, as explained in relation to [Fig.2], which applies to both [Fig.3] and [Fig.l].

[0048] A fraction of the regeneration gas loaded with water and SO2 and / or SO2 can be sent to the air to avoid accumulating too many impurities.

[0049] In Figures 1 and 3, a portion of the product 35 can serve as regeneration gas after vaporization of the adsorption unit A.

Claims

1. Claims Process for separating a mixture containing CO2 by partial condensation, the mixture (G) containing at least one impurity lighter than CO2 as well as at least one impurity chosen from the list: SO2, SO3, the process comprising the following steps: i. washing the mixture in a washing column (Q) allowing the partial reduction of at least one impurity chosen from the list: SO2, SO3 ii. compression (5A, 5B, 5C, 5D, 5E) of the washed mixture iii. cooling (R2, 53) of the compressed washed mixture, iv. drying and purification of at least one impurity chosen from the list: SO2, SO3, from the washed, compressed and cooled mixture in a temperature-swing adsorption unit (A) which is regenerated by a regeneration gas (25) v. separation of the dried and purified mixture in the adsorption unit at least by at least one partial condensation step (15) and optionally by distillation (31) and / or adsorption and / or solidification, the partial condensation producing a gas depleted in carbon dioxide (19, 25) compared to the dried and purified mixture as well as a liquid (17) enriched in carbon dioxide compared to the dried and purified mixture and vi. recycling of at least a portion (25B) of the regeneration gas containing water and at least one impurity chosen from the list: SO2, SO3, to the inlet of the washing column to be washed there, the regeneration gas being a. the gas (25) depleted in carbon dioxide compared to the dried and purified mixture produced by partial condensation, or b. formed by separating the carbon dioxide-depleted gas (19) from the dried and purified mixture produced by partial condensation by at least one adsorption and / or permeation step or c. a portion of a carbon dioxide-rich product (17, 35) formed by separating the carbon dioxide-enriched liquid by distillation and / or adsorption and / or solidification, optionally after a vaporization or sublimation step vii. the regeneration gas having carried out the regeneration containing CO2, water and at least one impurity chosen from the list: SO2, SO3, water and at least one impurity coming from the temperature swing adsorption unit.

2. A method according to claim 1 wherein at least one further portion (25A) of the regeneration gas containing water and at least one impurity selected from the list: SO2, SO3, is sent to be compressed with the washed mixture in step ii) and / or cooled with the compressed washed mixture in step iii).

3. Method according to one of claims 1 or 2 in which the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas (25) downstream of the adsorption unit (A) is measured and at least part of the regeneration gas (Q) is sent to the inlet of the washing column if, preferably only if, the content is above a first threshold.

4. Method according to one of claims 2 or 3 when dependent on claim 2 in which the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas (25) downstream of the adsorption unit (A) is measured and at least part of the regeneration gas is sent to be compressed with the washed mixture in step ii) and / or cooled with the washed mixture compressed in step iii) if the content is below the first threshold or below a second threshold lower than the first threshold.

5. Method according to one of the preceding claims in which the washing of step i) is carried out in a gas / liquid contactor (Q) with a basic washing liquid (N) containing NaOH and / or Na2CO3 and / or NaHCO3.

6. A method according to any preceding claim wherein the washed, compressed and purified mixture is separated first by adsorption and then by partial condensation, a CO2-enriched gas being produced by separating the mixture by adsorption and this CO2-enriched gas being partially condensed and separated in at least one phase separator.

7. Method according to one of the preceding claims in which the content of at least one impurity chosen from the list: SO2, SO3, in the regeneration gas (25) downstream of the adsorption unit (A) is measured and at least part of the regeneration gas is sent to the air if, preference only if the content is above a third threshold, higher than the first threshold.

8. A method according to any preceding claim wherein the regeneration gas is formed by membrane separation (21) of the carbon dioxide depleted gas (19) from the dried and purified mixture to produce a permeate (25) having a richer carbon dioxide content than the carbon dioxide depleted gas.

9. Apparatus for separating a mixture containing CO2 by partial condensation, the mixture containing at least one impurity lighter than CO2 as well as at least one impurity chosen from the list: SO2, SO3 comprising: a washing column (Q), means for sending the mixture (G) to be washed in the washing column allowing the partial reduction of the at least one impurity chosen from the list: SO2, SO3, a compressor (5A, 5B, 5C, 5D) connected to the washing column to compress the washed mixture, means (RI, R2, R3) for cooling the compressed washed mixture in the compressor, a temperature-swing adsorption unit (A), means for sending the compressed and cooled mixture (7) to be dried and purified of the at least one impurity chosen from the list: SO2, SO3, to the temperature-swing adsorption unit, means for sending a regeneration gas (25) to the temperature-swing adsorption unit,at least one phase separator (15) for separating the dried and purified mixture in the adsorption unit at least by at least one partial condensation step and optionally means for separation by distillation (31) and / or adsorption and / or solidification, the at least one phase separator being capable of producing by partial condensation a gas depleted in carbon dioxide (19) compared to the dried and purified mixture as well as a liquid (17) enriched in carbon dioxide compared to the dried and purified mixture and a pipe connected to the temperature-swing adsorption unit for recycling at least a portion (25B) of the regeneration gas containing water and at least one impurity chosen from the list: SO2, SO3, to the inlet of the washing column to be washed there, means for withdrawing the regeneration gas a. as the gas depleted in carbon dioxide compared to the dried and purified mixture from the at least one phase separator, or, b. as gas (25) formed by separating the carbon dioxide-depleted gas from the dried and purified mixture produced by partial condensation by at least one adsorption and / or permeation step (21) or c. as part of a carbon dioxide-rich product (17, 35) formed by separating the carbon dioxide-enriched liquid by distillation and / or adsorption and / or solidification, optionally after a vaporization or sublimation step.

10. Apparatus according to claim 9 comprising means for measuring the content of the at least one impurity chosen from the list: SO2, SO3, in the regeneration gas (25) downstream of the adsorption unit (A) and means for sending the at least one portion (25A) of the regeneration gas to be compressed with the washed mixture in step ii) and / or cooled with the washed mixture compressed in step iii) depending on the content of the at least one impurity chosen from the list: SO2, SO3, in the regeneration gas downstream of the adsorption unit.

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